Biomimetic Spider Leg Joints: A Review from Biomechanical Research to Compliant Robotic Actuators
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paper_title: Biology of Spiders

paper_content:

1. An Introduction to Spiders 2. Functional Anatomy 3. Metabolism 4. Neurobiology 5. Spider Webs 6. Locomotion and Prey Capture 7. Reproduction 8. Development 9. Ecology 10. Phylogeny and Systematics
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paper_title: A neuromechanical model explaining forward and backward stepping in the stick insect

paper_content:

The mechanism underlying the generation of stepping has been the object of intensive studies. Stepping involves the coordinated movement of different leg joints and is, in the case of insects, produced by antagonistic muscle pairs. In the stick insect, the coordinated actions of three such antagonistic muscle pairs produce leg movements and determine the stepping pattern of the limb. The activity of the muscles is controlled by the nervous system as a whole and more specifically by local neuronal networks for each muscle pair. While many basic properties of these control mechanisms have been uncovered, some important details of their interactions in various physiological conditions have so far remained unknown. In this study, we present a neuromechanical model of the coupled protractor-retractor and levator-depressor neuromuscular systems and use it to elucidate details of their coordinated actions during forward and backward walking. The switch from protraction to retraction is evoked at a critical angle of the femur during downward movement. This angle represents a sensory input that integrates load, motion, and ground contact. Using the model, we can make detailed suggestions as to how rhythmic stepping might be generated by the central pattern generators of the local neuronal networks, how this activity might be transmitted to the corresponding motoneurons, and how the latter might control the activity of the related muscles. The entirety of these processes yields the coordinated interaction between neuronal and mechanical parts of the system. Moreover, we put forward a mechanism by which motoneuron activity could be modified by a premotor network and suggest that this mechanism might serve as a basis for fast adaptive behavior, like switches between forward and backward stepping, which occur, for example, during curve walking, and especially sharp turning, of insects.
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paper_title: Soft Robotics: Challenges and Perspectives

paper_content:

There has been an increasing interest in the use of unconventional materials and morphologies in robotic systems because the underlying mechanical properties (such as body shapes, elasticity, viscosity, softness, density and stickiness) are crucial research topics for our in-depth understanding of embodied intelligence. The detailed investigations of physical system-environment interactions are particularly important for systematic development of technologies and theories of emergent adaptive behaviors. Based on the presentations and discussion in the Future Emerging Technology (fet11) conference, this article introduces the recent technological development in the field of soft robotics, and speculates about the implications and challenges in the robotics and embodied intelligence research. (C) Selection and peer-review under responsibility of FET11 conference organizers and published by Elsevier B.V.
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paper_title: On the Technological Instantiation of a Biomimetic Leg Concept for Agile Quadrupedal Locomotion

paper_content:

The legged locomotion system of biological quadrupeds has proven to be the most efficient in natural, complex terrain. Particularly, horses' legs have been evolved to provide speed, endurance, and strength superior to any other animal of equal size. Quadruped robots, emulating their biological counterparts, could become the best choice for field missions in complex or natural environments; however, they should be provided with optimum performance against mobility, payload, and endurance. The design of the leg mechanism is of paramount importance to achieve the targeted performance, and in order to design a leg mechanism able to provide the robot with such agile capabilities nature is the best source for inspiration. In this work, key principles underlying horse legs' power capabilities have been extracted and translated to a biomimetic leg concept. Afterwards, a real prototype has been designed following the biomimetic concept proposed. A key element in the biomimetic concept is the multifunctionality of the natural musculotendinous system, which has been mimicked by combining series elastic actuation and passive elements. This work provides an assessment of the benefits that bio-inspired solutions can provide versus the purely engineering approaches. The experimental evaluation of the bio-inspired prototype shows an improvement on the performance compared to a leg design based on purely engineering principles.
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paper_title: Soft Pneumatic Actuators for Rehabilitation

paper_content:

Pneumatic artificial muscles are pneumatic devices with practical and various applications as common actuators. They, as human muscles, work in agonistic-antagonistic way, giving a traction force only when supplied by compressed air. The state of the art of soft pneumatic actuators is here analyzed: different models of pneumatic muscles are considered and evolution lines are presented. Then, the use of Pneumatic Muscles (PAM) in rehabilitation apparatus is described and the general characteristics required in different applications are considered, analyzing the use of proper soft actuators with various technical properties. Therefore, research activity carried out in the Department of Mechanical and Aerospace Engineering in the field of soft and textile actuators is presented here. In particular, pneumatic textile muscles useful for active suits design are described. These components are made of a tubular structure, with an inner layer of latex coated with a deformable outer fabric sewn along the edge. In order to increase pneumatic muscles forces and contractions Braided Pneumatic Muscles are studied. In this paper, new prototypes are presented, based on a fabric construction and various kinds of geometry. Pressure-force-deformation tests results are carried out and analyzed. These actuators are useful for rehabilitation applications. In order to reproduce the whole upper limb movements, new kind of soft actuators are studied, based on the same principle of planar membranes deformation. As an example, the bellows muscle model and worm muscle model are developed and described. In both cases, wide deformations are expected. Another issue for soft actuators is the pressure therapy. Some textile sleeve prototypes developed for massage therapy on patients suffering of lymph edema are analyzed. Different types of fabric and assembly techniques have been tested. In general, these Pressure Soft Actuators are useful for upper/lower limbs treatments, according to medical requirements. In particular devices useful for arms massage treatments are considered. Finally some applications are considered.
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paper_title: Safe Human-Robot Cooperation in an Industrial Environment

paper_content:

The standard EN ISO10218 is fostering the implementation of hybrid production systems, i.e., production systems characterized by a close relationship among human operators and robots in cooperative tasks. Human-robot hybrid systems could have a big economic benefit in small and medium sized production, even if this new paradigm introduces mandatory, challenging safety aspects. Among various requirements for collaborative workspaces, safety-assurance involves two different application layers; the algorithms enabling safe space-sharing between humans and robots and the enabling technologies allowing acquisition data from sensor fusion and environmental data analysing. This paper addresses both the problems: a collision avoidance strategy allowing on-line re-planning of robot motion and a safe network of unsafe devices as a suggested infrastructure for functional safety achievement.
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paper_title: Soft robotics: a bioinspired evolution in robotics.

paper_content:

Animals exploit soft structures to move effectively in complex natural environments. These capabilities have inspired robotic engineers to incorporate soft technologies into their designs. The goal is to endow robots with new, bioinspired capabilities that permit adaptive, flexible interactions with unpredictable environments. Here, we review emerging soft-bodied robotic systems, and in particular recent developments inspired by soft-bodied animals. Incorporating soft technologies can potentially reduce the mechanical and algorithmic complexity involved in robot design. Incorporating soft technologies will also expedite the evolution of robots that can safely interact with humans and natural environments. Finally, soft robotics technology can be combined with tissue engineering to create hybrid systems for medical applications.
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paper_title: Hunting without a web: How lycosoid spiders subdue their prey

paper_content:

More than half of all spider species hunt prey without a web. To successfully subdue their prey, they use adapted capture behaviour and efficient grasping mechanisms to interrupt the prey's locomotion, and to restrain it from escaping during the subsequent handling for final envenomation. In this study, we investigated how the prey capture behaviour of different lycosoid spider species is related to leg morphology and venom efficiency; using high speed videography, feeding experiments, stereomicroscopy, scanning electron microscopy and LD50 venom bioassays. We found that different species employed different techniques when grasping their prey and these differences strongly correlate with the distribution and size of hairy adhesive leg pads (so-called scopulae on pro- and retrolateral parts of legs) and erectable spines, which act in a complementary way. Our results indicate that the grasping and handling behaviour and leg morphology is crucial in restricting the prey's movements. However, none of these traits is directly related with venom efficiency.
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paper_title: Safe human-robot interaction based on multi-sensor fusion and dexterous manipulation planning

paper_content:

Valencian Government by the research project "Infraestructura 05/053". Spanish Ministry of Education and Science by the pre-doctoral grant AP2005-1458 and the research projects DPI2005-06222 and DPI2008-02647, which constitute the research framework of this thesis.
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paper_title: Towards flexible medical instruments: Review of flexible fluidic actuators

paper_content:

Abstract Flexible instruments, i.e. instruments presenting a great number of degrees of freedom and able to perform snake-like movements when avoiding obstacles, can find a lot of applications in the medical field. On the other hand, flexible fluidic actuators, i.e. actuators having a flexible inflatable structure and actuated by fluid, present interesting features regarding medical applications. Therefore, this paper proposes to use these actuators to develop medical flexible instruments. Firstly, the advantages and drawbacks linked to the use of flexible fluidic actuators are listed and a discussion about the miniaturization of fluidic actuators peripherics (such as valves) is led. Next, a literature review of the existing flexible fluidic actuators is established. It can serve as basis to develop flexible instruments based on these actuators.
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paper_title: Biology of Spiders

paper_content:

1. An Introduction to Spiders 2. Functional Anatomy 3. Metabolism 4. Neurobiology 5. Spider Webs 6. Locomotion and Prey Capture 7. Reproduction 8. Development 9. Ecology 10. Phylogeny and Systematics
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paper_title: Strains in the exoskeleton of spiders

paper_content:

This is a first attempt to measure strain in the exoskeleton of arthropods during locomotion. The selected sites of measurement at the tibia of large spiders allowed a direct estimation of the mechanical input of slit sense organs, which are biological strain receptors. This study includes (I) the development of techniques for measurement, (II) an anatomical and biomechanical investigation of the tibia-metatarsus joint of spiders, (III) the measurement of cuticular strains developed by external and internal forces in tethered theraphosids (Aviculariidae), and (IV) the measurement of strain in the legs of freely moving animals.
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paper_title: On technomorphic modelling and classification of biological joints

paper_content:

SummaryBiological motion systems are of particular interest to engineers in robotics, prosthetics and micromechanics. Since biological motion systems show a high degree of mobility, smooth movements and minimal deployment of material, the analysis of such systems might help to invent or optimize technical motion systems. To enable the transfer of explanatory techniques, biomechanics and engineering need a shared terminology. Generally, a reference limb, muscles, tendons, a joint and a driven limb are forming two closed mechanisms with different transfer functions. The direction of the forces applied to links is influenced by guiding structures. Movable connections can be constructed by form closure, force closure, and compliance of an anisotropic segment between two rigid segments. Eleven different basic variants of rigid-body joint structures can be classified by the possible relative translatory and rotatory movements in orthogonal co-ordinates. If classified by the form of their rigid parts, biological rigid-body joints (diarthroses) show some similarities to technical joints, but occur in fewer basic variants. The functioning of exoskeletal joints can involve hydrostatic forces, depending on the structure of the rigid elements and the type of linkage between them.Structural classification of biological joints should include at least: 1) degree of freedom (d.o.f.), 2) possible relative movements, 3) variability of d.o.f., 4) restrictions of range of motion, 5) stress in reaction to external forces. From an engineer’s viewpoint, additional features are necessary for structural characterization, including the maintenance of closure and guidance, the geometry and behaviour of contact, geometrical parameters and material properties.
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paper_title: The hemolymph vascular system in Cupiennius salei (Araneae: Ctenidae)

paper_content:

Abstract In terms of physiology and behavior, Cupiennius salei is one of the best-investigated spider species. However, parts of its anatomy have only been described superficially to date. In the course of a comparative survey of the hemolymph vascular system in Araneae we therefore investigated C. salei using several injection methods in combination with semi-thin sections and micro computer tomography (MicroCT). Like all other Arthropoda, C. salei possesses an open circulatory system. A tubular heart is suspended dorsally in the opisthosoma via a number of ligaments. It is equipped with three pairs of ostia, and three pairs of cardiac arteries. The heart is surrounded by a pericardial sinus in which we were able for the first time to describe an intra-pericardial membrane. Anteriorly, the heart is extended by an anterior aorta which runs through the pedicel and divides into two branches within the prosoma. Arteries emanating from the branches of the aorta supply the prosomal appendages and the central nervous system. The subesophageal ganglion is supplied by numerous fine vessels which emanate from the transganglionic arteries and form tight loops. A network of capillaries, i.e. interconnections between afferent and efferent vessels, is here demonstrated for the first time to exist in the central nervous system of chelicerates. Data are compared with existing literature on the morphology of the circulatory system in Araneae and discussed with regard to the extension of the respiratory system and the varying lifestyles of different spiders.
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paper_title: Hydraulic leg extension is not necessarily the main drive in large spiders

paper_content:

SUMMARY Unlike most other arthropods, spiders have no extensor muscles in major leg joints. Therefore, hydraulic pressure generated in the prosoma provides leg extension. For decades, this mechanism was held responsible for the generation of the majority of the ground reaction forces, particularly in the hind legs. During propulsion, the front leg pairs must shorten whereas the hind legs have to be extended. Assuming that hind legs are essentially driven by hydraulics, their force vectors must pass the leg joints ventrally. However, at least in accelerated escape manoeuvres, we show here for the large cursorial spider species Ancylometes concolor that these force vectors, when projected into the leg plane, pass all leg joints dorsally. This indicates a reduced impact of the hydraulic mechanism on the generation of ground reaction forces. Although hydraulic leg extension still modulates their direction, the observed steep force vectors at the hind legs indicate a strong activity of flexors in the proximal joint complex that push the legs against the substrate. Consequently, the muscular mechanisms are dominant at least in the hind legs of large spiders.
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paper_title: Strains in the exoskeleton of spiders

paper_content:

This is a first attempt to measure strain in the exoskeleton of arthropods during locomotion. The selected sites of measurement at the tibia of large spiders allowed a direct estimation of the mechanical input of slit sense organs, which are biological strain receptors. This study includes (I) the development of techniques for measurement, (II) an anatomical and biomechanical investigation of the tibia-metatarsus joint of spiders, (III) the measurement of cuticular strains developed by external and internal forces in tethered theraphosids (Aviculariidae), and (IV) the measurement of strain in the legs of freely moving animals.
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paper_title: The Hydraulic Mechanism of the Spider Leg

paper_content:

1. The blood pressure inside the leg of the house spider Tegenaria atrica has been measured. Maintained pressures of about 5 cm. Hg and transient pressures of up to 40 cm. Hg have been found. ::: ::: 2. The relation between the blood pressure in the leg and the extension torque at the hinge joints has been established. ::: ::: 3. Considerable torques can be developed at the hinge joints during extension, for example, when accelerating a mass fixed to the leg. The transient pressures found to arise in the leg are adequate to account for these torques. ::: ::: 4. The hydraulic mechanism is discussed. The available evidence suggests that the pressure found in the legs occurs also in the prosoma but not in the abdomen, in which case the maintained pressure must be due to the heart. This, however, requires further investigation
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paper_title: Contributions to Our Knowledge of the Anatomy and Relationships of Spiders.

paper_content:

Walckenaer may have been right when in 1837 he pointed with pride to the long list of works on spiders already in existence and said that if Pallas could only see it, he would surely no longer reproach naturalists for neglecting this interesting group of animals. Unfortunately the reproach of Pallas may be repeated now more justly than ever before. It is true that a quantity of excellent work has been published since the time of Walckenaer, much more and much better work than before. But the group remains a neglected one especially if compared with such favorites as insects or vertebrates. When two years ago I began to gather material for a manual on spiders I soon became aware that our knowledge of their anatomy and embryology is entirely inadequate. Not only the nervous system and the sense organs, but even the external sexual organs from which the characters for the identification of species are chiefly derived need thorough re-examination. This sad discovery stimulated me to new research and the present series of articles is a result of it. I shall omit all reference to literature which will be extensively treated in the manual I hope to be able to complete and to publish some day. Only such papers will be mentioned as are absolutely necessary to the understanding of the subject. Moreover to avoid loss of time and to make the reading easier I shall describe things as I found them during my investigations, without making constant mention as to what is new and what was already known. Those who know the literature will easily separate the new from the old, while those who are not so well acquainted with it will be glad to have the subject treated in a short and comprehensive manner. I need scarcely add that everything described by me in the present series of articles is based on careful and extensive study.
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paper_title: The fluid pressure pumps of spiders (Chelicerata, Araneae)

paper_content:

The identity of the fluid pressure pumps in spiders was investigated in Filistata hibernalis through measurements of the activity of certain muscle groups, leg movements, and changes in fluid pressure within the leg. Our results indicate the cephalothorax is the site of the pressure pump responsible for leg extension and the musculi laterales are the major muscles involved in the operation of this pump. Fluid pressures in the legs averaged 5 100 N·m−2 in resting spiders, ranged from 4 000 to 6 700 N·m−2 in walking spiders and reached as high as 61000 N·m−2 in startled spiders. Intra-abdominal fluid pressures were also measured and found to be much lower, ranging from 1000 to 4 000 N· m-2. These pressures are the result of activity of at least two sets of abdominal muscles, the sub-cuticular muscle sheet and the paired series of dorso-ventral muscles. We suggest the abdominal fluid pressure and the rigidity of the book-lungs attenuate pooling of the hemolymph in the abdomen when the spider is active. Finally we hypothesize that evolution of the hydrostatic skeleton in spiders has allowed a greater mass of flexor muscles to be incorporated into the legs and this in turn is an adaptation to the spider in prey capture.
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paper_title: Modelling and Application of the Hydraulic Spider Leg Mechanism

paper_content:

The model-based simulations of the spider hydraulic mechanism allow reaching a new knowledge about kinematic and dynamic behaviours of the spiders. According to the moving principles of the spider leg, technical compliant structures with coherent joint can be developed and performed. Because of the elasticity of such structures they need only one actuator, which can be either hydraulic, like a spider leg, or pneumatic. The elasticity assumes a role of muscles and moves the structure in the beginning shape. These technical compliant structures have several advantages. For example, it can be a monolithic structure (i.e. consist of only one part) and therefore predestined for miniaturisation. Compliant mechanisms feature less friction and accordingly they require low maintenance and also they can perform a complicated trajectory. Such mechanisms can be used as gripper finger, robot arms, legs of walking robots and as a sonde in medical technology.
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paper_title: Blood pressure in the tarantula,Dugesiella hentzi

paper_content:

1. ::: ::: Heart rates in intact spiders at rest were 35/min and after 3 min exercise 77/min. Recovery to the initial rate required 1/2 hr. In cannulated animals heart rates ranged from 44/min at rest to 116/min after a struggle. Heart rate was relatively independent of internal pressure. ::: ::: ::: ::: ::: 2. ::: ::: Variations in heart rate and amplitude occurred spontaneously and in response to various stimuli (Fig. 6). ::: ::: ::: ::: ::: 3. ::: ::: Systole averages 68% of total beat duration through a range of heart rates from 21–116 min (Fig. 4). ::: ::: ::: ::: ::: 4. ::: ::: Intraventricular pressures 10 min after cannulating averaged 22/13 mm Hg, but fell to 12/8 mm Hg after 10 min in the dark (Fig. 5). A maximum pressure of 102 mm Hg was measured in one animal. The pressure recorded in the heart is generated in part by the heart and in part reflects abdominal tension. ::: ::: ::: ::: ::: 5. ::: ::: Resting pressures in any 2 legs were always identical and were above that in the prosoma. ::: ::: ::: ::: ::: 6. ::: ::: Resting pressures in the prosoma and lateral sacs are intermediate to heart systolic and diastolic pressures which in a relaxed animal were 12/8 mm Hg (Fig. 11). ::: ::: ::: ::: ::: 7. ::: ::: At rest a gradient of only a few mm Hg propels the blood through the lung books from the lateral sacs to the pulmonary veins; a gradient of 1–2 mm Hg exists between the pulmonary vein and the heart in diastole. ::: ::: ::: ::: ::: 8. ::: ::: General abdominal pressure is above pulmonary vein pressure suggesting a need for a mechanism to maintain patency of these vessels. ::: ::: ::: ::: ::: 9. ::: ::: During a struggle a maximum pressure of 480 mm Hg was measured in the prosoma. ::: ::: ::: ::: ::: 10. ::: ::: High pressures were recorded in the lateral sacs which communicate freely with the prosoma but were not transmitted to the heart. ::: ::: ::: ::: ::: 11. ::: ::: Pressures of 40–60 mm Hg were measured in the prosoma and legs during wialking (Fig. 18) and delivery of blood through the pedal arteries probably continues at this level. ::: ::: ::: ::: ::: 12. ::: ::: Withdrawal of blood causes an immediate decrease in heart pressure. Within min some recovery occurs presumably because of muscular adjustments (Fig. 19).
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paper_title: The fluid pressure pumps of spiders (Chelicerata, Araneae)

paper_content:

The identity of the fluid pressure pumps in spiders was investigated in Filistata hibernalis through measurements of the activity of certain muscle groups, leg movements, and changes in fluid pressure within the leg. Our results indicate the cephalothorax is the site of the pressure pump responsible for leg extension and the musculi laterales are the major muscles involved in the operation of this pump. Fluid pressures in the legs averaged 5 100 N·m−2 in resting spiders, ranged from 4 000 to 6 700 N·m−2 in walking spiders and reached as high as 61000 N·m−2 in startled spiders. Intra-abdominal fluid pressures were also measured and found to be much lower, ranging from 1000 to 4 000 N· m-2. These pressures are the result of activity of at least two sets of abdominal muscles, the sub-cuticular muscle sheet and the paired series of dorso-ventral muscles. We suggest the abdominal fluid pressure and the rigidity of the book-lungs attenuate pooling of the hemolymph in the abdomen when the spider is active. Finally we hypothesize that evolution of the hydrostatic skeleton in spiders has allowed a greater mass of flexor muscles to be incorporated into the legs and this in turn is an adaptation to the spider in prey capture.
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paper_title: Modelling and Application of the Hydraulic Spider Leg Mechanism

paper_content:

The model-based simulations of the spider hydraulic mechanism allow reaching a new knowledge about kinematic and dynamic behaviours of the spiders. According to the moving principles of the spider leg, technical compliant structures with coherent joint can be developed and performed. Because of the elasticity of such structures they need only one actuator, which can be either hydraulic, like a spider leg, or pneumatic. The elasticity assumes a role of muscles and moves the structure in the beginning shape. These technical compliant structures have several advantages. For example, it can be a monolithic structure (i.e. consist of only one part) and therefore predestined for miniaturisation. Compliant mechanisms feature less friction and accordingly they require low maintenance and also they can perform a complicated trajectory. Such mechanisms can be used as gripper finger, robot arms, legs of walking robots and as a sonde in medical technology.
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paper_title: Hydraulic System of Locomotion

paper_content:

Spiders lack extensor muscles in the main joints of their walking legs (femur–patella and tibia–metatarsus joint, respectively). These leg joints are extended by a rise of hemolymph pressure in the prosoma, caused by contraction of prosomal dorsoventrally running muscles. This leads to volume decrease in the prosoma (made possible by soft and flexible pleurae) and to hemolymph flow into the legs. Inside the legs, hemolymph flows in channels (lacunae) whose cross sections are strongly influenced by intrinsic muscle activity. In hydraulic leg joints, only flexor muscles occur that act antagonistically to hemolymph pressure. The articular membranes in leg joints are bellows-like folded, in this way preventing unfavourable torques opposing joint extension. During maximum activity, perfusion of the prosoma stops because prosomal pressure exceeds systolic heart pressure. In the opisthosoma, a subepidermal muscle-sheet (“abdominal sac”) and several other muscles generate hemolymph pressure that is considerably lower than prosomal pressure during high activity, but may be very close to it during rest or moderate activity. Opisthosomal pressures are sometimes linked to prosomal ones, but sometimes not. This implies (contrary to previous opinions) a temporary hydrostatic separation between pro- and opisthosoma, probably due to a muscular valve at the anterior end of the pedicel. In some spiders, the prosoma forms a stiff capsule unable to generate hemolymph pressure. It is suggested that these spiders produce hemolymph pressure for leg extension mainly in the opisthosoma by contraction of a strongly modified abdominal sac.
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paper_title: Strains in the exoskeleton of spiders

paper_content:

This is a first attempt to measure strain in the exoskeleton of arthropods during locomotion. The selected sites of measurement at the tibia of large spiders allowed a direct estimation of the mechanical input of slit sense organs, which are biological strain receptors. This study includes (I) the development of techniques for measurement, (II) an anatomical and biomechanical investigation of the tibia-metatarsus joint of spiders, (III) the measurement of cuticular strains developed by external and internal forces in tethered theraphosids (Aviculariidae), and (IV) the measurement of strain in the legs of freely moving animals.
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paper_title: The Hydraulic Mechanism of the Spider Leg

paper_content:

1. The blood pressure inside the leg of the house spider Tegenaria atrica has been measured. Maintained pressures of about 5 cm. Hg and transient pressures of up to 40 cm. Hg have been found. ::: ::: 2. The relation between the blood pressure in the leg and the extension torque at the hinge joints has been established. ::: ::: 3. Considerable torques can be developed at the hinge joints during extension, for example, when accelerating a mass fixed to the leg. The transient pressures found to arise in the leg are adequate to account for these torques. ::: ::: 4. The hydraulic mechanism is discussed. The available evidence suggests that the pressure found in the legs occurs also in the prosoma but not in the abdomen, in which case the maintained pressure must be due to the heart. This, however, requires further investigation
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paper_title: Mechanics of cuticular elastic energy storage in leg joints lacking extensor muscles in arachnids

paper_content:

Certain leg joints in arachnids lack extensor muscles and have elastically deformable transarticular sclerites spanning their arthrodial membranes, an arrangement consistent with a model in which flexor muscles load transarticular sclerites during flexion and energy from elastic recoil is used for extension. This study quantifies the potential contribution of elastic recoil to extension torque at joints of the fourth leg of representative arachnids. Extension torques of isolated joints with and without transarticular sclerites were measured as the joint was rotated through angles and at angular velocities comparable with those used by walking animals. The procedure was repeated with the joint subjected to different internal fluid pressures in order to assess the potential role of hydraulically induced extension. The efficiency of elastic energy storage (resilience) in the absence of internal fluid pressure was 70-90% for joints with well-developed transarticular sclerites, and the magnitude of torque was similar to those produced by different joint extension mechanisms in other arthropods. Increased internal fluid pressure acted synergistically with transarticular sclerites in some joints but had little or no effect in others. Joints that lacked both extensor muscles and transarticular sclerites appeared to be specialized for hydraulic extension, and joints operated by antagonistic muscles lacked apparent specializations for either elastic or hydraulic extension. It is well known that elastic energy storage is a significant contributor to propulsion in running vertebrates and certain arthropods, where elastic elements are loaded as the center of mass falls during one phase of the locomotor cycle. However, transarticular sclerites are apparently loaded by contraction of flexor muscles when the leg is not in contact with the substratum. Hence the mechanism of a transarticular sclerite is more similar to the flight and jumping mechanisms of other arthropods than to running vertebrates. The evolutionary significance and potential mechanical advantages of the transarticular elastic mechanism are discussed.
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paper_title: The fluid pressure pumps of spiders (Chelicerata, Araneae)

paper_content:

The identity of the fluid pressure pumps in spiders was investigated in Filistata hibernalis through measurements of the activity of certain muscle groups, leg movements, and changes in fluid pressure within the leg. Our results indicate the cephalothorax is the site of the pressure pump responsible for leg extension and the musculi laterales are the major muscles involved in the operation of this pump. Fluid pressures in the legs averaged 5 100 N·m−2 in resting spiders, ranged from 4 000 to 6 700 N·m−2 in walking spiders and reached as high as 61000 N·m−2 in startled spiders. Intra-abdominal fluid pressures were also measured and found to be much lower, ranging from 1000 to 4 000 N· m-2. These pressures are the result of activity of at least two sets of abdominal muscles, the sub-cuticular muscle sheet and the paired series of dorso-ventral muscles. We suggest the abdominal fluid pressure and the rigidity of the book-lungs attenuate pooling of the hemolymph in the abdomen when the spider is active. Finally we hypothesize that evolution of the hydrostatic skeleton in spiders has allowed a greater mass of flexor muscles to be incorporated into the legs and this in turn is an adaptation to the spider in prey capture.
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paper_title: Blood pressure in the tarantula,Dugesiella hentzi

paper_content:

1. ::: ::: Heart rates in intact spiders at rest were 35/min and after 3 min exercise 77/min. Recovery to the initial rate required 1/2 hr. In cannulated animals heart rates ranged from 44/min at rest to 116/min after a struggle. Heart rate was relatively independent of internal pressure. ::: ::: ::: ::: ::: 2. ::: ::: Variations in heart rate and amplitude occurred spontaneously and in response to various stimuli (Fig. 6). ::: ::: ::: ::: ::: 3. ::: ::: Systole averages 68% of total beat duration through a range of heart rates from 21–116 min (Fig. 4). ::: ::: ::: ::: ::: 4. ::: ::: Intraventricular pressures 10 min after cannulating averaged 22/13 mm Hg, but fell to 12/8 mm Hg after 10 min in the dark (Fig. 5). A maximum pressure of 102 mm Hg was measured in one animal. The pressure recorded in the heart is generated in part by the heart and in part reflects abdominal tension. ::: ::: ::: ::: ::: 5. ::: ::: Resting pressures in any 2 legs were always identical and were above that in the prosoma. ::: ::: ::: ::: ::: 6. ::: ::: Resting pressures in the prosoma and lateral sacs are intermediate to heart systolic and diastolic pressures which in a relaxed animal were 12/8 mm Hg (Fig. 11). ::: ::: ::: ::: ::: 7. ::: ::: At rest a gradient of only a few mm Hg propels the blood through the lung books from the lateral sacs to the pulmonary veins; a gradient of 1–2 mm Hg exists between the pulmonary vein and the heart in diastole. ::: ::: ::: ::: ::: 8. ::: ::: General abdominal pressure is above pulmonary vein pressure suggesting a need for a mechanism to maintain patency of these vessels. ::: ::: ::: ::: ::: 9. ::: ::: During a struggle a maximum pressure of 480 mm Hg was measured in the prosoma. ::: ::: ::: ::: ::: 10. ::: ::: High pressures were recorded in the lateral sacs which communicate freely with the prosoma but were not transmitted to the heart. ::: ::: ::: ::: ::: 11. ::: ::: Pressures of 40–60 mm Hg were measured in the prosoma and legs during wialking (Fig. 18) and delivery of blood through the pedal arteries probably continues at this level. ::: ::: ::: ::: ::: 12. ::: ::: Withdrawal of blood causes an immediate decrease in heart pressure. Within min some recovery occurs presumably because of muscular adjustments (Fig. 19).
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paper_title: The constraints on maximal activity in spiders

paper_content:

1. ::: ::: The relationships between fatigue, heart rate, lactate accumulation, and hemolymph pressure during and after maximal activity were investigated in three spider species (Filistata hibernalis, Lycosa lenta, andPhidippus audax), characterized by different life histories and physiologies (Table 1). ::: ::: ::: ::: ::: 2. ::: ::: In the initial 20 s of a forced two min run, spiders cover up to 50% the total distance of the entire run, lose 2/3rds of their initial speed, and change gait. The remainder of the activity bout is marked by a gradual slowing and increased incidence of individuals that refuse to move. ::: ::: ::: ::: ::: 3. ::: ::: Maximal heart rates are reached late in the two min activity bout, or more commonly, early in recovery (Fig. 2). ::: ::: ::: ::: ::: 4. ::: ::: Prosomal lactate accumulations similar to levels associated with fatigue in many terrestrial ectothermic vertebrates are reached after about 1 min of forced activity (Fig. 3). However, lactate accumulations inLycosa during the first 20 sec of activity (Fig. 4) were less than 1/3rd the level found at 2 min and were probably not high enough to explain the rapid fatigue that occurs during early activity (Fig. 1). ::: ::: ::: ::: ::: 5. ::: ::: Hemolymph pressures were measured in maximally activeFilistata that were restrained in a manner designed to reduce the work load on locomotory muscles. Hemolymph pressures increased rapidly to 100–200 mmHg with the onset of activity but peak pressures of 450 mmHg were not reached until after 20 s (Fig. 5). Alternative forms of stimulation did not result in earlier peak pressures. High pressures (>120 mmHg) continued for most of the 2-min activity period. Lactate accumulation during this exercise was much less than in forced running. ::: ::: ::: ::: ::: 6. ::: ::: The ability of restrained spiders to maintain high hemolymph pressures and continue rapid leg extensions mimicking running and jumping for an extended period of time is contrary to the hydraulic insufficiency hypothesis' explanation of rapid fatigue. The cause of the ultimate locomotory collapse (seen after 1–4 min) is probably related to the accumulation of anaerobic by-products.
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paper_title: Design concept and validation of a robotic arm inspired by the octopus

paper_content:

Abstract The octopus is an invertebrate sea animal, considered as an interesting model of inspiration in robotics, due to its high dexterity, variable stiffness, and very complex behaviours, if compared with its position in the evolutionary scale. This paper reports the design of an artificial muscular hydrostat for developing an octopus-like robot. The experimental study consists of the fabrication of a set of mock-ups demonstrating some of the key features and patterns of movement of the octopus arm. The experimental trials performed with the different mock-ups demonstrated the suitability of the silicone materials used and the patterns of actuators activation to replicate the typical octopus movements of elongation, shortening, bending, and reaching. They also confirm that control is simplified by the arrangement of muscles as well as by the mechanical properties of the muscular hydrostat.
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paper_title: Soft Robotics: Challenges and Perspectives

paper_content:

There has been an increasing interest in the use of unconventional materials and morphologies in robotic systems because the underlying mechanical properties (such as body shapes, elasticity, viscosity, softness, density and stickiness) are crucial research topics for our in-depth understanding of embodied intelligence. The detailed investigations of physical system-environment interactions are particularly important for systematic development of technologies and theories of emergent adaptive behaviors. Based on the presentations and discussion in the Future Emerging Technology (fet11) conference, this article introduces the recent technological development in the field of soft robotics, and speculates about the implications and challenges in the robotics and embodied intelligence research. (C) Selection and peer-review under responsibility of FET11 conference organizers and published by Elsevier B.V.
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paper_title: Stretch reflex improves rolling stability during hopping of a decerebrate biped system.

paper_content:

When humans hop, attitude recovery can be observed in both the sagittal and frontal planes. While it is agreed that the brain plays an important role in leg placement, the role of low-level feedback (the stretch reflex) on frontal plane stabilization remains unclear. Seeking to better understand the contribution of the soleus stretch reflex to rolling stability, we performed experiments on a biomimetic humanoid hopping robot. Various reflex responses to touching the floor, ranging from no response to long muscle activations, were examined, and the effect of a delay upon touching the floor was also examined. We found that the stretch reflex brought the system closer to stable, straight hopping. The presence of a delay did not affect the results; both the cases with and without a delay outperformed the case without a reflex response. The results of this study highlight the importance of low-level control in locomotion for which body stabilization does not require higher-level signals.
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paper_title: A Recipe for Soft Fluidic Elastomer Robots

paper_content:

Abstract This work provides approaches to designing and fabricating soft fluidic elastomer robots. That is, three viable actuator morphologies composed entirely from soft silicone rubber are explored, and these morphologies are differentiated by their internal channel structure, namely, ribbed, cylindrical, and pleated. Additionally, three distinct casting-based fabrication processes are explored: lamination-based casting, retractable-pin-based casting, and lost-wax-based casting. Furthermore, two ways of fabricating a multiple DOF robot are explored: casting the complete robot as a whole and casting single degree of freedom (DOF) segments with subsequent concatenation. We experimentally validate each soft actuator morphology and fabrication process by creating multiple physical soft robot prototypes.
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paper_title: Design and development of starfish-like robot: Soft bionic platform with multi-motion using SMA actuators

paper_content:

This paper presents a starfish-like robot with bionic soft body, multi-motion inspired by live starfishes. The structural design principle is based on the biological investigation. The robot prototype is fabricated with help of 3D printing model. By the locomotion principle and control strategy, the soft starfish-like robot is able to fulfill in crawling on flat ground, climbing over viscous soil terrain, free motions in random directions, navigating through a target object, steering as well as grasping an imaginary prey. The results indicate that the starfish-like robot driven by shape memory alloy (SMA) actuators possesses a great robustness against strong impact and patially demonstrate its capacity of mobility and environmental adaption.
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paper_title: Design, fabrication and control of soft robots

paper_content:

Conventionally, engineers have employed rigid materials to fabricate precise, predictable robotic systems, which are easily modelled as rigid members connected at discrete joints. Natural systems, however, often match or exceed the performance of robotic systems with deformable bodies. Cephalopods, for example, achieve amazing feats of manipulation and locomotion without a skeleton; even vertebrates such as humans achieve dynamic gaits by storing elastic energy in their compliant bones and soft tissues. Inspired by nature, engineers have begun to explore the design and control of soft-bodied robots composed of compliant materials. This Review discusses recent developments in the emerging field of soft robotics.
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paper_title: Musculoskeletal Robots and Wearable Devices on the Basis of Cable-driven Actuators

paper_content:

Cable-driven actuators are a promising alternative for future kinematic designs, particularly when the combination of lightweight, high strength, compact designs and dynamic motions are required. Powered exoskeletons or wearable robots are typical candidates of these novel actuators as has been demonstrated by previous research. This chapter focusses on current work in cable-driven actuators, introduces the Myorobotics toolkit for supporting the engineer to build up prototypes from cable-actuates modules and gives an outlook to using cable-driven actuation for advanced wearable robots.
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paper_title: Safe Human-Robot Cooperation in an Industrial Environment

paper_content:

The standard EN ISO10218 is fostering the implementation of hybrid production systems, i.e., production systems characterized by a close relationship among human operators and robots in cooperative tasks. Human-robot hybrid systems could have a big economic benefit in small and medium sized production, even if this new paradigm introduces mandatory, challenging safety aspects. Among various requirements for collaborative workspaces, safety-assurance involves two different application layers; the algorithms enabling safe space-sharing between humans and robots and the enabling technologies allowing acquisition data from sensor fusion and environmental data analysing. This paper addresses both the problems: a collision avoidance strategy allowing on-line re-planning of robot motion and a safe network of unsafe devices as a suggested infrastructure for functional safety achievement.
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paper_title: Soft robotics : Biological inspiration , state of the art , and future research

paper_content:

Traditional robots have rigid underlying structures that limit their ability to interact with their environment. For example, conventional robot manipulators have rigid links and can manipulate objects using only their specialised end effectors. These robots often encounter difficulties operating in unstructured and highly congested environments. A variety of animals and plants exhibit complex movement with soft structures devoid of rigid components. Muscular hydrostats e.g. octopus arms and elephant trunks are almost entirely composed of muscle and connective tissue and plant cells can change shape when pressurised by osmosis. Researchers have been inspired by biology to design and build soft robots. With a soft structure and redundant degrees of freedom, these robots can be used for delicate tasks in cluttered and/or unstructured environments. This paper discusses the novel capabilities of soft robots, describes examples from nature that provide biological inspiration, surveys the state of the art and outlines existing challenges in soft robot design, modelling, fabrication and control.
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paper_title: Safe human-robot interaction based on multi-sensor fusion and dexterous manipulation planning

paper_content:

Valencian Government by the research project "Infraestructura 05/053". Spanish Ministry of Education and Science by the pre-doctoral grant AP2005-1458 and the research projects DPI2005-06222 and DPI2008-02647, which constitute the research framework of this thesis.
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paper_title: Position Control of Soft-Robots with Rotary-Type Pneumatic Actuators

paper_content:

The objective of this work is the development and evaluation of a non-linear control concept for pneumatic soft-robots based on direct acting actuators of rotary-type (REC-actuators). Providing lightweight and inherent compliance, pneumatic soft-actuators are very suitable to construct service and rehabilitation robots, intended to work in direct contact with humans. However, an accurate and robust control of such robots is a challenging task, due to their high non-linear dynamics, especially for robots with a number of rotary joints. In this paper the usability of a decentralized joint position control scheme is experimentally investigated for soft-robots with two different kinematics, containing 4 and 6 REC-actuators respectively. It is shown, that complemented with active gravity compensation, based on the quasi-static robot model as feed-forward signal, the decentralized control scheme can be successfully applied to achieve robust joint space position control of soft-robots.
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paper_title: Safety and handling concept for assistive robotic devices with pneumatic rotary soft-actuators

paper_content:

Compliance and assistive behavior are essential properties for safe physical human-robot interaction (HRI), an illustrative example for which is robot aided motion therapy. These requirements can be easily fulfilled using inherent compliant and back-drivable (i.e. soft) actuators. This paper describes a fully functional prototype for assistive robotic knee MTD with novel inherent compliant (soft) fluidic actuators of rotary type, which has been developed for orthopedic rehabilitation purposes. Assistive acting motion therapy devices (MTD) are mainly used for neurologic treatment until now, but become increasingly important for orthopedic rehabilitation as well. Device capabilities provide human-like treatment and allow individual adjustable assistance to accomplish desired motions. Utilization of pneumatic soft-actuators demands a special safety concept which is merged with control algorithms to provide sufficient safeness and to catch any possible system errors and sudden emergency situations. A self descriptive user interface allows easy intuitive handling and the prototype can be used very comfortable due to several imperceptible working routines in the background. The same safety and handling concept is used for assistive robotic shoulder MTD, which is currently being developed.
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paper_title: Soft fluidic actuators of rotary type for safe physical human-machine interaction

paper_content:

Safe actuators with controllable compliance are indispensable for assistive robots working in human environment and especially for rehabilitation devices physically interacting with patient. The paper introduces new patent pending soft fluidic actuators with rotary elastic chambers (REC), which produces rotational motion without any additional transmission elements. The key actuator features as inherent compliance, high back-driveability and light-weight design build a foundation for safe physical human-machine interaction, although torques of several tens of Newton-meter can be generated. Due to their compact design the REC-actuators demonstrate better integration capabilities into complex kinematic structures than conventional fluidic muscles of linear type. The actuator compliance can be varied by pressure regulation in antagonistic acting chambers, which makes soft fluidic actuators very suitable for making the transition from continuous passive motion to active (assistive) behaviour during the therapy depending on a patient activity. Conceptual design of modular compact assistive motion therapy devices based on new “slim-line” REC-actuators is presented.
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paper_title: Design and control of a novel compliant differential shape memory alloy actuator

paper_content:

Abstract This paper presents the design and control of a novel compliant differential shape memory alloy (SMA) actuator with significantly improved performance compared to traditional bias and differential type SMA actuators. This actuator is composed of two antagonistic SMA wires and a mechanical joint coupled with a torsion spring. The differential SMA wires are utilized to increase the response speed, and the torsion spring is employed to reduce the total stiffness of SMA actuator and improve the output range. Theoretical models that include the stiffness equations of the SMA wire as well as the dynamics of three different SMA actuation systems are introduced and compared. Simulation and experimental results have proved that this new actuator can provide larger output angle compared to conventional SMA actuators under the same conditions. Moreover, regulation and tracking control experiments have demonstrated that this compliant differential SMA actuator achieves higher response speed compared to the bias SMA actuator using compatible PI controller. The tracking performance is further improved by the saturated PI controller.
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paper_title: On technomorphic modelling and classification of biological joints

paper_content:

SummaryBiological motion systems are of particular interest to engineers in robotics, prosthetics and micromechanics. Since biological motion systems show a high degree of mobility, smooth movements and minimal deployment of material, the analysis of such systems might help to invent or optimize technical motion systems. To enable the transfer of explanatory techniques, biomechanics and engineering need a shared terminology. Generally, a reference limb, muscles, tendons, a joint and a driven limb are forming two closed mechanisms with different transfer functions. The direction of the forces applied to links is influenced by guiding structures. Movable connections can be constructed by form closure, force closure, and compliance of an anisotropic segment between two rigid segments. Eleven different basic variants of rigid-body joint structures can be classified by the possible relative translatory and rotatory movements in orthogonal co-ordinates. If classified by the form of their rigid parts, biological rigid-body joints (diarthroses) show some similarities to technical joints, but occur in fewer basic variants. The functioning of exoskeletal joints can involve hydrostatic forces, depending on the structure of the rigid elements and the type of linkage between them.Structural classification of biological joints should include at least: 1) degree of freedom (d.o.f.), 2) possible relative movements, 3) variability of d.o.f., 4) restrictions of range of motion, 5) stress in reaction to external forces. From an engineer’s viewpoint, additional features are necessary for structural characterization, including the maintenance of closure and guidance, the geometry and behaviour of contact, geometrical parameters and material properties.
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paper_title: Pneumatic and hydraulic microactuators: a review

paper_content:

The development of MEMS actuators is rapidly evolving and continuously new progress in terms of efficiency, power and force output is reported. Pneumatic and hydraulic are an interesting class of microactuators that are easily overlooked. Despite the 20 years of research, and hundreds of publications on this topic, these actuators are only popular in microfluidic systems. In other MEMS applications, pneumatic and hydraulic actuators are rare in comparison with electrostatic, thermal or piezo-electric actuators. However, several studies have shown that hydraulic and pneumatic actuators deliver among the highest force and power densities at microscale. It is believed that this asset is particularly important in modern industrial and medical microsystems, and therefore, pneumatic and hydraulic actuators could start playing an increasingly important role. This paper shows an in-depth overview of the developments in this field ranging from the classic inflatable membrane actuators to more complex piston–cylinder and drag-based microdevices.
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paper_title: Shape memory polymers: Past, present and future developments

paper_content:

Abstract Shape memory polymers (SMPs) represent a highly interesting class of materials. As one representative of the intelligent polymeric systems, these materials gained significant interest in recent years. Consequently, the variety of materials investigated virtually exploded and several promising shape memory effects have been developed. The present review will provide a short overview on the history of SMPs as well as the current developments and concepts for shape memory polymers. Additionally, future developments in this field will be discussed.
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paper_title: Design of a flexible fluidic actuation system for a hybrid elbow orthosis

paper_content:

In this article the design of a new upper limb rehabilitation system will be presented. A lightweight, modular, and portable system is achieved by the combination of electromyographic (EMG) control, functional electrical stimulation (FES), and the use of miniaturized flexible fluidic actuators (FFA) integrated in an elbow orthosis. First, the state of the art of upper limb rehabilitation devices will be discussed and requirements extracted. Then, the design concept of the new prototype upper limb training system will be presented. Subsequently, a miniaturized fluidically driven actuation system, including its mechatronical components, will be highlighted. Finally, an overview of the performance and function will be given.
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paper_title: A Survey on applications of Pneumatic Artificial Muscles

paper_content:

The aim of this article is to present a survey on applications of Pneumatic Artificial Muscles (PAMs). PAMs are highly non-linear pneumatic actuators where their elongation is proportional to the interval pressure. During the last decade, there has been a significant increase in the industrial and scientific utilization of PAMs due to their advantages such as high strength and small weight, while various types of PAMs with different technical characteristics have been appeared in the relative scientific literature. This article will summarize the key enabling applications in PAMs that are focusing in the following areas: a) Biorobotic, b) Medical, c) Industrial, and d) Aerospace applications.
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paper_title: Design, fabrication and control of soft robots

paper_content:

Conventionally, engineers have employed rigid materials to fabricate precise, predictable robotic systems, which are easily modelled as rigid members connected at discrete joints. Natural systems, however, often match or exceed the performance of robotic systems with deformable bodies. Cephalopods, for example, achieve amazing feats of manipulation and locomotion without a skeleton; even vertebrates such as humans achieve dynamic gaits by storing elastic energy in their compliant bones and soft tissues. Inspired by nature, engineers have begun to explore the design and control of soft-bodied robots composed of compliant materials. This Review discusses recent developments in the emerging field of soft robotics.
---
paper_title: Musculoskeletal Robots and Wearable Devices on the Basis of Cable-driven Actuators

paper_content:

Cable-driven actuators are a promising alternative for future kinematic designs, particularly when the combination of lightweight, high strength, compact designs and dynamic motions are required. Powered exoskeletons or wearable robots are typical candidates of these novel actuators as has been demonstrated by previous research. This chapter focusses on current work in cable-driven actuators, introduces the Myorobotics toolkit for supporting the engineer to build up prototypes from cable-actuates modules and gives an outlook to using cable-driven actuation for advanced wearable robots.
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paper_title: Dielectric Elastomers for Actuators and Artificial Muscles

paper_content:

A number of electroactive polymers have been explored for their use as artificial muscles. Among these, dielectric elastomers appear to provide the best combination of properties for true muscle-like actuation. Dielectric elastomers behave as compliant capacitors, expanding in area and shrinking in thickness when a voltage is applied. Materials combining very high energy densities, strains and efficiencies have been known for some time. To date, however, the widespread adoption of dielectric elastomers has been hindered by premature breakdown and the requirement for high voltages and bulky support frames. Recent advances seem poised to remove these restrictions and allow for the production of highly reliable, high-performance transducers for artificial muscle applications.
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paper_title: A shape memory alloy–based soft morphing actuator capable of pure twisting motion

paper_content:

This article introduces a novel design for a soft morphing actuator capable of pure twisting motion through a pair of shape memory alloy wires embedded in a polydimethylsiloxane matrix at constant and opposite eccentricity across the cross section in opposite directions. This report introduces the design of the actuator, the manufacturing method, and experimental results for the twisting angle and twisting force when varying the dimensions of the matrix of the actuator. Afterward, a simple model is applied to verify the effect of matrix dimensions on the twisting angle of the actuator. The results show that there is an optimal actuator thickness for both the twisting angle and the twisting force of the actuator, that there is a trade-off between the twisting angle and the twisting force for the actuator’s thickness, and that a longer length is better for both metrics within the tested dimensions.
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paper_title: A Recipe for Soft Fluidic Elastomer Robots

paper_content:

Abstract This work provides approaches to designing and fabricating soft fluidic elastomer robots. That is, three viable actuator morphologies composed entirely from soft silicone rubber are explored, and these morphologies are differentiated by their internal channel structure, namely, ribbed, cylindrical, and pleated. Additionally, three distinct casting-based fabrication processes are explored: lamination-based casting, retractable-pin-based casting, and lost-wax-based casting. Furthermore, two ways of fabricating a multiple DOF robot are explored: casting the complete robot as a whole and casting single degree of freedom (DOF) segments with subsequent concatenation. We experimentally validate each soft actuator morphology and fabrication process by creating multiple physical soft robot prototypes.
---
paper_title: Pneumatic and hydraulic microactuators: a review

paper_content:

The development of MEMS actuators is rapidly evolving and continuously new progress in terms of efficiency, power and force output is reported. Pneumatic and hydraulic are an interesting class of microactuators that are easily overlooked. Despite the 20 years of research, and hundreds of publications on this topic, these actuators are only popular in microfluidic systems. In other MEMS applications, pneumatic and hydraulic actuators are rare in comparison with electrostatic, thermal or piezo-electric actuators. However, several studies have shown that hydraulic and pneumatic actuators deliver among the highest force and power densities at microscale. It is believed that this asset is particularly important in modern industrial and medical microsystems, and therefore, pneumatic and hydraulic actuators could start playing an increasingly important role. This paper shows an in-depth overview of the developments in this field ranging from the classic inflatable membrane actuators to more complex piston–cylinder and drag-based microdevices.
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paper_title: Soft Pneumatic Actuators for Rehabilitation

paper_content:

Pneumatic artificial muscles are pneumatic devices with practical and various applications as common actuators. They, as human muscles, work in agonistic-antagonistic way, giving a traction force only when supplied by compressed air. The state of the art of soft pneumatic actuators is here analyzed: different models of pneumatic muscles are considered and evolution lines are presented. Then, the use of Pneumatic Muscles (PAM) in rehabilitation apparatus is described and the general characteristics required in different applications are considered, analyzing the use of proper soft actuators with various technical properties. Therefore, research activity carried out in the Department of Mechanical and Aerospace Engineering in the field of soft and textile actuators is presented here. In particular, pneumatic textile muscles useful for active suits design are described. These components are made of a tubular structure, with an inner layer of latex coated with a deformable outer fabric sewn along the edge. In order to increase pneumatic muscles forces and contractions Braided Pneumatic Muscles are studied. In this paper, new prototypes are presented, based on a fabric construction and various kinds of geometry. Pressure-force-deformation tests results are carried out and analyzed. These actuators are useful for rehabilitation applications. In order to reproduce the whole upper limb movements, new kind of soft actuators are studied, based on the same principle of planar membranes deformation. As an example, the bellows muscle model and worm muscle model are developed and described. In both cases, wide deformations are expected. Another issue for soft actuators is the pressure therapy. Some textile sleeve prototypes developed for massage therapy on patients suffering of lymph edema are analyzed. Different types of fabric and assembly techniques have been tested. In general, these Pressure Soft Actuators are useful for upper/lower limbs treatments, according to medical requirements. In particular devices useful for arms massage treatments are considered. Finally some applications are considered.
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paper_title: A pneumatically powered knee-ankle-foot orthosis (KAFO) with myoelectric activation and inhibition

paper_content:

BackgroundThe goal of this study was to test the mechanical performance of a prototype knee-ankle-foot orthosis (KAFO) powered by artificial pneumatic muscles during human walking. We had previously built a powered ankle-foot orthosis (AFO) and used it effectively in studies on human motor adaptation, locomotion energetics, and gait rehabilitation. Extending the previous AFO to a KAFO presented additional challenges related to the force-length properties of the artificial pneumatic muscles and the presence of multiple antagonistic artificial pneumatic muscle pairs.MethodsThree healthy males were fitted with custom KAFOs equipped with artificial pneumatic muscles to power ankle plantar flexion/dorsiflexion and knee extension/flexion. Subjects walked over ground at 1.25 m/s under four conditions without extensive practice: 1) without wearing the orthosis, 2) wearing the orthosis with artificial muscles turned off, 3) wearing the orthosis activated under direct proportional myoelectric control, and 4) wearing the orthosis activated under proportional myoelectric control with flexor inhibition produced by leg extensor muscle activation. We collected joint kinematics, ground reaction forces, electromyography, and orthosis kinetics.ResultsThe KAFO produced ~22%–33% of the peak knee flexor moment, ~15%–33% of the peak extensor moment, ~42%–46% of the peak plantar flexor moment, and ~83%–129% of the peak dorsiflexor moment during normal walking. With flexor inhibition produced by leg extensor muscle activation, ankle (Pearson r-value = 0.74 ± 0.04) and knee ( r = 0.95 ± 0.04) joint kinematic profiles were more similar to the without orthosis condition compared to when there was no flexor inhibition (r = 0.49 ± 0.13 for ankle, p = 0.05, and r = 0.90 ± 0.03 for knee, p = 0.17).ConclusionThe proportional myoelectric control with flexor inhibition allowed for a more normal gait than direct proportional myoelectric control. The current orthosis design provided knee torques smaller than the ankle torques due to the trade-off in torque and range of motion that occurs with artificial pneumatic muscles. Future KAFO designs could incorporate cams, gears, or different actuators to transmit greater torque to the knee.
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paper_title: Towards flexible medical instruments: Review of flexible fluidic actuators

paper_content:

Abstract Flexible instruments, i.e. instruments presenting a great number of degrees of freedom and able to perform snake-like movements when avoiding obstacles, can find a lot of applications in the medical field. On the other hand, flexible fluidic actuators, i.e. actuators having a flexible inflatable structure and actuated by fluid, present interesting features regarding medical applications. Therefore, this paper proposes to use these actuators to develop medical flexible instruments. Firstly, the advantages and drawbacks linked to the use of flexible fluidic actuators are listed and a discussion about the miniaturization of fluidic actuators peripherics (such as valves) is led. Next, a literature review of the existing flexible fluidic actuators is established. It can serve as basis to develop flexible instruments based on these actuators.
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paper_title: Novel Additive Manufacturing Pneumatic Actuators and Mechanisms for Food Handling Grippers

paper_content:

Conventional pneumatic grippers are widely used in industrial pick and place robot processes for rigid objects. They are simple, robust and fast, but their design, motion and features are limited, and they do not fulfil the final purpose. Food products have a wide variety of shapes and textures and are susceptible to damaged. Robot grippers for food handling should adapt to this wide range of dimensions and must be fast, cheap, reasonably reliable, and with cheap and reasonable maintenance costs. They should not damage the product and must meet hygienic conditions. The additive manufacturing (AM) process is able to manufacture parts without significant restrictions, and is Polyamide approved as food contact material by FDA. This paper presents that, taking the best of plastic flexibility, AM allows the implementation of novel actuators, original compliant mechanisms and practical grippers that are cheap, light, fast, small and easily adaptable to specific food products. However, if they are not carefully designed, the results can present problems, such as permanent deformations, low deformation limits, and low operation speed. We present possible solutions for the use of AM to design proper robot grippers for food handling. Some successful results, such as AM actuators based on deformable air chambers, AM compliant mechanisms, and grippers developed in a single part will be introduced and discussed.
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paper_title: Position Control of Soft-Robots with Rotary-Type Pneumatic Actuators

paper_content:

The objective of this work is the development and evaluation of a non-linear control concept for pneumatic soft-robots based on direct acting actuators of rotary-type (REC-actuators). Providing lightweight and inherent compliance, pneumatic soft-actuators are very suitable to construct service and rehabilitation robots, intended to work in direct contact with humans. However, an accurate and robust control of such robots is a challenging task, due to their high non-linear dynamics, especially for robots with a number of rotary joints. In this paper the usability of a decentralized joint position control scheme is experimentally investigated for soft-robots with two different kinematics, containing 4 and 6 REC-actuators respectively. It is shown, that complemented with active gravity compensation, based on the quasi-static robot model as feed-forward signal, the decentralized control scheme can be successfully applied to achieve robust joint space position control of soft-robots.
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paper_title: Soft fluidic actuators of rotary type for safe physical human-machine interaction

paper_content:

Safe actuators with controllable compliance are indispensable for assistive robots working in human environment and especially for rehabilitation devices physically interacting with patient. The paper introduces new patent pending soft fluidic actuators with rotary elastic chambers (REC), which produces rotational motion without any additional transmission elements. The key actuator features as inherent compliance, high back-driveability and light-weight design build a foundation for safe physical human-machine interaction, although torques of several tens of Newton-meter can be generated. Due to their compact design the REC-actuators demonstrate better integration capabilities into complex kinematic structures than conventional fluidic muscles of linear type. The actuator compliance can be varied by pressure regulation in antagonistic acting chambers, which makes soft fluidic actuators very suitable for making the transition from continuous passive motion to active (assistive) behaviour during the therapy depending on a patient activity. Conceptual design of modular compact assistive motion therapy devices based on new “slim-line” REC-actuators is presented.
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paper_title: Pleated pneumatic artificial muscles: compliant robotic actuators

paper_content:

Pleated pneumatic artificial muscles (PPAMs), developed at the Vrije Universiteit Brussel, Department of Mechanical Engineering, are used as robotic actuators. Their distinguishing feature is their pleated design, as a result of which their contraction forces and maximum displacement are very high compared to other pneumatic artificial muscles. The PPAM design, operation and characteristics are presented. A rotative joint actuator, made of two antagonistically coupled PPAMs, is discussed to demonstrate their suitability for robotics. It has several properties that are similar to those of skeletal joint actuators. Positioning tasks are seen to be performed very accurately using a simple PI control. Furthermore, the antagonistic actuator can easily be made to have a soft or careful touch, contributing greatly to a safe robot operation. In view of all the characteristics PPAMs are very well suited for automation and robotic applications.
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paper_title: Static and dynamic characteristics of McKibben pneumatic artificial muscles

paper_content:

This paper reports mechanical testing and modeling results for the McKibben artificial muscle pneumatic actuator. This device first developed in the 1950's, contains an expanding tube surrounded by braided cords. The authors report static and dynamic length-tension testing results and derive a linearized model of these properties for three different models. The results are briefly compared with human muscle properties to evaluate the suitability of McKibben actuators for human muscle emulation in biologically based robot arms.<<ETX>>
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paper_title: Development of a miniaturised hydraulic actuation system for artificial hands

paper_content:

This article will present a powerful miniaturised hydraulic system of compact design that is used for the actuation of artificial hands. This system was developed as an alternative to today's commonly used electromechanical prosthetic actuation systems. System components and hand prototypes reflect many years of experience of our laboratory in rehabilitation medicine, CAD design and prototyping, mechanical engineering, electronic construction, and programming. Prototypes of hydraulically actuated hands were tested by patients under support of orthopaedic companies. The latest hydraulic prostheses have advantages in construction, design, and performance, including adaptivity during grasping and holding of objects. The newly developed miniaturised hydraulic system is competitive with standard mechanical systems of electrically driven prosthetic hands. The modular construction of the system developed allows for customising the mechanical construction of each prosthetic hand and its functional abilities. Contributions of patients concerning grasping activities of prostheses may be taken into account when choosing the hand components already. The components of the new hydraulic actuation system and their technical characteristics will be interesting for specialists in automation technology, actuator development, mechanics, prosthetics, and rehabilitation.
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paper_title: Modelling of the McKibben artificial muscle: A review

paper_content:

The so-called McKibben artificial muscle is one of the most efficient and currently one of the most widely used fluidic artificial muscles, due to the simplicity of its design, combining ease of implementation and analogous behaviour with skeletal muscles. Its working principle is very simple: The circumferential stress of a pressurized inner tube is transformed into an axial contraction force by means of a double-helix braided sheath whose geometry corresponds to a network of identical pantographs. However, behind this apparent simplicity lie two phenomena, which must be considered so as to fully understand how the McKibben muscle works. First, the non-linear relationship between stress and strain inside the inner tube elastomer, together with the complex relationship between physical artificial muscle parameters and its effective working pressure range. Second, the behaviour of the braided sheath which acts like a ‘flexible joint structure’ able to adapt itself during contraction to the increasing radiu...
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paper_title: Modeling and control of McKibben artificial muscle robot actuators

paper_content:

The McKibben artificial muscle is a pneumatic device characterized by its high level of functional analogy with human skeletal muscle. While maintaining a globally cylindrical shape, the McKibben muscle produces a contraction force decreasing with its contraction ratio, as does skeletal muscle. The maximum force-to-weight ratio can be surprisingly high for a limited radial dimension and for a conventional pressure range. A 50 g McKibben muscle can easily develop more than 1000 N under 5 bar pressure for an external radius varying from about 1.5 to 3 cm. Thus, robotics specialists are interested in this well-adapted artificial muscle for motorizing powerful yet compact robot arms. The basic McKibben muscle static modeling developed in the paper, which is based on the three main parameters (i.e., initial braid angle, initial muscle length, and initial muscle radius) and includes a three-parameter friction model of the thread against itself, has shown its efficiency in both isometric and isotonic contraction.
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paper_title: A pneumatically powered knee-ankle-foot orthosis (KAFO) with myoelectric activation and inhibition

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BackgroundThe goal of this study was to test the mechanical performance of a prototype knee-ankle-foot orthosis (KAFO) powered by artificial pneumatic muscles during human walking. We had previously built a powered ankle-foot orthosis (AFO) and used it effectively in studies on human motor adaptation, locomotion energetics, and gait rehabilitation. Extending the previous AFO to a KAFO presented additional challenges related to the force-length properties of the artificial pneumatic muscles and the presence of multiple antagonistic artificial pneumatic muscle pairs.MethodsThree healthy males were fitted with custom KAFOs equipped with artificial pneumatic muscles to power ankle plantar flexion/dorsiflexion and knee extension/flexion. Subjects walked over ground at 1.25 m/s under four conditions without extensive practice: 1) without wearing the orthosis, 2) wearing the orthosis with artificial muscles turned off, 3) wearing the orthosis activated under direct proportional myoelectric control, and 4) wearing the orthosis activated under proportional myoelectric control with flexor inhibition produced by leg extensor muscle activation. We collected joint kinematics, ground reaction forces, electromyography, and orthosis kinetics.ResultsThe KAFO produced ~22%–33% of the peak knee flexor moment, ~15%–33% of the peak extensor moment, ~42%–46% of the peak plantar flexor moment, and ~83%–129% of the peak dorsiflexor moment during normal walking. With flexor inhibition produced by leg extensor muscle activation, ankle (Pearson r-value = 0.74 ± 0.04) and knee ( r = 0.95 ± 0.04) joint kinematic profiles were more similar to the without orthosis condition compared to when there was no flexor inhibition (r = 0.49 ± 0.13 for ankle, p = 0.05, and r = 0.90 ± 0.03 for knee, p = 0.17).ConclusionThe proportional myoelectric control with flexor inhibition allowed for a more normal gait than direct proportional myoelectric control. The current orthosis design provided knee torques smaller than the ankle torques due to the trade-off in torque and range of motion that occurs with artificial pneumatic muscles. Future KAFO designs could incorporate cams, gears, or different actuators to transmit greater torque to the knee.
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paper_title: Improved modelling and assessment of pneumatic muscle actuators

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Traditional robotic/mechatronic design has successfully exploited the attributes of heavy mechanical systems engineering, but future scientific trends suggest a need for technology that will emulate natural systems. Among the most pressing of the requirements are actuation systems that can interact in a safer and more natural way. Pneumatic technology has many of the compliance forms needed for this softer interaction and a number of new systems based on McKibben muscles have been developed in recent years. In this paper a new model of operation of pneumatic muscle systems is developed. In particular, the model considers the distortion effects at the termination nodes and the radial pressure loss due to rubber elasticity. The new model is compared experimentation on a very large actuator and shows how this new model improves the assessment of forces and displacement that can be achieved by the actuator. The new model is compared against previous systems models.
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paper_title: Precise position and trajectory control of pneumatic soft-actuators for assistance robots and motion therapy devices

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The goal of this work is the development and performance analysis of control algorithms for new soft fluidic actuators with rotary elastic chambers (REC-actuators). Due to their inherent compliancy these actuators fulfill the requisites for building intrinsically safe mechanisms as assistance robots and motion therapy devices, working in direct physical contact with humans. Besides the difficulties common for control design of pneumatic systems, these actuators itself posses several nonlinear characteristics causing specific problems in their modeling and control. In this work the decentralized joint control scheme is implemented, where the position controller has a cascade structure with a non-linear model based pressure control in the inner loop. Two different position control approaches, which require minimal information on the dynamics of the actuator mechanical subsystem, were investigated and tested: sliding mode control with time delay estimation as well as a fuzzy control with parameter optimization based on genetic algorithms.
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paper_title: Pneumatic Artificial Muscles : actuators for robotics and automation

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This article is intended as an introduction to and an overview of Pneumatic Artificial Muscles (PAMs). These are pneumatic actuators made mainly of a flexible and inflatable membrane. First, their concept and way of operation are explained. Next, the properties of these actuators are given, the most important of which are the compliant behavior and extremely low weight. A classification and review is following this section. Typical applications are dealt with in the last but one section and, finally, some concluding remarks are made.
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paper_title: The SLS-Generated Soft Robotic Hand - An Integrated Approach Using Additive Manufacturing and Reinforcement Learning

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To develop a robotic system for a complex task is a time-consuming process. Merging methods available today, a new approach for a faster realization of a multi-finger soft robotic hand is presented here. This paper introduces a robotic hand with four fingers and 12 Degrees of Freedom (DoFs) using bellow actuators. The hand is generated via Selective Laser Sintering (SLS), an Additive Manufacturing method. The complex task execution of a specific action, i.e. the lifting, rotating and precise positioning of a handling-object with this robotic hand, is used to structure the whole development process. To validate reliable functionality of the hand from the beginning, each development stage is SLS-generated and the targeted task execution is trained via Reinforcement Learning, a machine learning approach. Optimization points are subsequently derived and fed back into the hardware development. With this Concurrent Engineering strategy a fast development of this robotic hand is possible. The paper outlines the relevant key strategies and gives insight into the design process. At the end, the final hand with its capabilities is presented and discussed.
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paper_title: Towards flexible medical instruments: Review of flexible fluidic actuators

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Abstract Flexible instruments, i.e. instruments presenting a great number of degrees of freedom and able to perform snake-like movements when avoiding obstacles, can find a lot of applications in the medical field. On the other hand, flexible fluidic actuators, i.e. actuators having a flexible inflatable structure and actuated by fluid, present interesting features regarding medical applications. Therefore, this paper proposes to use these actuators to develop medical flexible instruments. Firstly, the advantages and drawbacks linked to the use of flexible fluidic actuators are listed and a discussion about the miniaturization of fluidic actuators peripherics (such as valves) is led. Next, a literature review of the existing flexible fluidic actuators is established. It can serve as basis to develop flexible instruments based on these actuators.
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paper_title: On the Mechanical Compliance of Technical Systems

paper_content:

In the safe physical human-machine interaction the compliance of technical systems is an elementary requirement. The physical compliance of technical systems can be provided either by control functions implementation and/or intrinsic by structural configuration and material properties optimization. The latter is advantageous because of higher reliability as well as general simplicity of the design and production technologies. In the paper we focus on mechanical systems with intrinsic mechanical compliance. In general the deformability of structures is primarly characterised by their stiffness. Compliant mechanisms are mechanisms, whose functionality is based on its deformability. The goal of each engineer is by the design of mechanisms the setting of compliance depending upon the purpose of its application. It should be considered, that the compliance is dependent on a variety of parameters. The optimal design of these mechanisms can be realized only with precise knowledge of the influence parameters and possible types of compliance.
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paper_title: Design of a flexible fluidic actuation system for a hybrid elbow orthosis

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In this article the design of a new upper limb rehabilitation system will be presented. A lightweight, modular, and portable system is achieved by the combination of electromyographic (EMG) control, functional electrical stimulation (FES), and the use of miniaturized flexible fluidic actuators (FFA) integrated in an elbow orthosis. First, the state of the art of upper limb rehabilitation devices will be discussed and requirements extracted. Then, the design concept of the new prototype upper limb training system will be presented. Subsequently, a miniaturized fluidically driven actuation system, including its mechatronical components, will be highlighted. Finally, an overview of the performance and function will be given.
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paper_title: Active articulation for future space applications inspired by the hydraulic system of spiders

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This paper presents and discusses a novel mechanism which was conceived taking inspiration from the micro-hydraulic system used by spiders to extend their legs. The mechanism has the potential to be used in future space applications, although the harsh space conditions, and in particular outgassing, should be carefully addressed in the design of a space-qualified model. The new system has one degree of freedom and is actuated by a pressurized fluidic system. The prototype, which has been designed, simulated, built and tested, is of compact size and presents a repeatable behaviour. The relation between pressure and rotation is approximately linear. The mechanism is suitable for a modular configuration in which several elastic joint modules are joined together. This modular configuration allows large rotations and does not increase the complexity of the actuation. A single module bends about 1.8 degrees when the pressure of the working fluid is 1.2 MPa.
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Title: Biomimetic Spider Leg Joints: A Review from Biomechanical Research to Compliant Robotic Actuators
Section 1: Introduction
Description 1: Introduce the significance of Human-Robot-Interaction (HRI) and the advantages of using biomimetic and compliant robotic actuators, specifically inspired by spider leg joints. Discuss the motivation behind investigating the biological principles and their adaptation to robotics.

Section 2: Biological Research
Description 2: Describe the biomechanical functioning of spider legs, including the structure of the leg joints and the role of muscles and hemolymph. Detail the three main acting joints and their mechanical properties.

Section 3: Hydraulic Leg Extension
Description 3: Explore the research findings on hydraulic leg extension in spiders, including the early discoveries and detailed biomechanical studies. Discuss the role of hemolymph pressure and the mechanical design of the articular membrane.

Section 4: Muscular Flexion and Its Biomechanical Aspects
Description 4: Examine the importance of muscular flexion in spider leg movements. Discuss the structural design and biomechanical principles that maximize flexion force and its application in gripping and climbing tasks.

Section 5: Interaction of Hydraulic Extension and Muscular Flexion
Description 5: Analyze the antagonistic counterplay between hydraulic extension and muscular flexion in spider legs. Discuss the complexities of fluid mechanics and how the muscular flexors control joint movements.

Section 6: Technical Applications
Description 6: Classify robotic applications inspired by spider leg joints. Introduce the structural design and actuation principles of bio-inspired actuators. Provide an overview of the technical developments and applications based on spider leg principles.

Section 7: Classification of Biomimetic Spider Leg Actuators
Description 7: Differentiate between conventional robotic actuators and those with inherent compliance. Define the criteria for biomimetic devices and focus on robots with soft actuation inspired by spider joints.

Section 8: Bio-Inspired Robots with Soft Capabilities
Description 8: Evaluate the structural design and actuation principles of soft actuated robots. Discuss the use of naturally flexible materials and the dynamic behavior of bio-inspired actuators.

Section 9: Flexible Fluidic Actuators
Description 9: Review the principles of fluidically actuated robotic devices, with a focus on pressurization methods and structural expansion or contraction. Discuss the applications and development of these actuators in various fields.

Section 10: Bio-Inspired Actuators with Reference to the Spider Principle
Description 10: Identify and discuss biomimetic actuators directly inspired by spider leg mechanisms. Provide an overview of designs and applications, and compare their performance in terms of torque and control mechanisms.

Section 11: Conclusions and Discussion
Description 11: Summarize the key findings on spider leg biomechanics and their application in biomimetic robotics. Highlight the potential for future research and the challenges in understanding and replicating the dynamic behaviors of spider legs for technical applications.