Overview of Microgrippers and Design of a Micromanipulation Station Based on a MMOC Microgripper
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paper_title: Autonomous micromanipulation using a new strategy of accurate release by rolling

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This paper presents our work in developing an autonomous micromanipulation system. The originality of our system is that it takes advantage of adhesion to grip micro-objects by using a single fingered gripper. This is in fact a tipless cantilever previously designed for atomic force microscopy applications. We describe vision techniques employed to process images provided by an optical microscope, allowing to position accurately the end-effector for a gripping task. A theoretical study of the direct force measurement device and an experimental validation show how we can improve the measurement of impact and contact forces. Then we explain the strategy used to bring the gripper into contact with the object, based on force control and kinematic redundancy. Finally, a simplified model of the release task is proposed in order to determine conditions that allow to roll the object, and then to place it with precision.
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paper_title: A laser-powered micro-gripper

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A micro-gripper actuated by laser power has been developed. The laser-powered micro-gripper is designed for handing micro-objects in very narrow space or overly crowded places, consists of a laser-powered linear actuator and a photoformed micro-gripper. This linear actuator's maximum output power was 2.3 mN and the stroke length was 900 /spl mu/m, and the total dimension of the linear actuator is about 25 mm in length and 2 mm in diameter.
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paper_title: Tactile microgripper for application in microrobotics

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As part of a microrobot we present a micromachined gripper system which has both force sensor and actuator integrated. This gripper is used for handling and assembling and allows control of the gap of the gripper and the gripping force continuously. We use a thermal bimorph actuator for the operation of the gripper. For the force sensor we utilize the piezoresistive effect, known to be very strong in silicon. As compared to previous realizations we have optimized the design: the proposed folded bimorph beam delivers a multiple of the actuators stroke as compared to a simple beam structure. This folded bimorph beam design can also be applied to other bimorph actuators (e.g. piezoelectric, SMA). The actuators maximum stroke is 800 micrometers at a finger length of 1600 micrometers and the maximum force generated is in the order of 1 mN. That means an improvement of a factor of five with respect to designs published earlier. The sensitivity of the sensor finger is about 100 mV/VmN which is an improvement by a factor of three and its shows a good linearity.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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paper_title: Monolithic shape memory alloy microgripper for 3D assembly of tissue engineering scaffolds

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This paper describes a microgripper used for the micro-assembly of an artificial scaffold for tissue engineering. The porous sponge-like scaffold is a three dimensional construct built by tiny unit parts of biodegradable polymer. This application requires the assembly of several parts by applying a suitable level of force. In this framework, a monolithic shape memory alloy (SMA) microgripper was developed. It consists of two small fingers for grasping, an active part that changes its shape when heated and a parallel elastic structure used as a bias spring. The main aspect of the design is that all these elements are included within a single piece of material, but have different mechanical properties, and are used for different functions. Using a new technology of Shape Memory Alloy laser annealing developed at EPFL, a local shape memory effect is introduced on the active part while leaving the remaining areas in a state where no shape memory effect occurs, i.e., in a cold-worked state. The parallel elastic structure is used to provide a pullback force on cooling as well as to guide the finger movement. An electrical path is integrated to heat the active part and drive the gripper by Joule effect. This paper focuses on the principle of the micro-gripper, its design and describes the fabrication process. Some first experimental results are also presented.
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paper_title: Design and fabrication of a gripping tool for micromanipulation

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Abstract A tool for micromanipulation is presented in this paper. A titanium gripper is fabricated by a combination of electro-discharge machining and etching, the latter of which is to provide a material less prone to cracking by removing the heat-affected surface. Evaluation of the design has been carried out by finite-element analysis and the performance of the gripper has been qualitatively as well as quantitatively established. The manipulation system to which the tool belongs is also briefly described.
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paper_title: Selective chemical vapor deposition of tungsten for microelectromechanical structures

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Abstract A selective chemical vapor deposition (CVD) tungsten process is used to fabricate three-dimensional micromechanical structures on a silicon substrate. Patterned structures are formed in silicon dioxide trenches by selective nucleation and growth of tungsten from the bottom of the trench. Examples are shown for selective growth of tungsten on single-crystal silicon, on thin films of silicon and on silicon-implanted, silicon dioxide layers. This high deposition-rate selective CVD tungsten process had been used to fabricate tungsten micromechanical structures greater than 4 μm thick. Tungsten patters with features of 0.3 μm × 0.3 μm in 0.6 μm of tungsten are fabricated using electron beam lithography. As an example of an electromechnical structure, cantilever beams have been fabricated to make micromechanical tweezers that move in two dimensions by the application of potential differences between the beams (lateral motion), and between the beams and the silicon substrate (vertical motion). Tungsten microtweezers 200 μm in length with a cross-section of 2.7 μm × 2.5 μm closed with an applied voltage of less than 150 V.
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paper_title: Analysis of closed-loop control of parallel-plate electrostatic microgrippers

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A design of a high-force-output large-deflection parallel-plate electrostatically actuated microgripper is described. This design uses polysilicon as a structural material and may be fabricated using an IC-based surface machining process. This paper shows that by using a position feedback controller, the microgripper can be stabilized in theory, which is supported by computer simulations. Preliminary data from fabricated micro-grippers also supports the mathematical model for the open loop system, although the pull-in voltages (50 V to 100 V for gaps of 80 to 100 /spl mu/m/sup 2/) are generally lower than predicted ones, probably due to the inherent instability of the electrostatic system. Further experiments are in progress to evaluate the open-loop system and the closed-loop system. >
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paper_title: A micromachined thermally-driven gripper: a numerical and experimental study

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This paper presents the development of a microgripper for micro-assembly and micro-operation applications. Two design configurations for a silicon-based microgripper with integrated thermal expansion actuator and microsensor were proposed and studied in this work. The opening distance of the microgripper is up to 120 µm. The microgripper is designed to operate through an integrated thermal or piezoelectric element that is controlled by an electricity supply. Piezoresistive sensors are integrated on the micromachined gripper to detect and feedback the gripping force applied on gripped objects. The two proposed configurations for the microgripper were simulated numerically and compared with one another. The thermal dynamic response of the thermal expansion element was, in particular, studied through finite-element modelling. Finally, a stainless steel prototype of the designed microgripper was fabricated and tested.
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paper_title: Flexible microgripper and its application to micromeasurement of mechanical and thermal properties

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Two novel micro-measurement systems using microfabricated flexible microgrippers (FMG) are presented. One system is a micro-measurement system for mechanical properties of a gripped micro-object under the microscope. In this system, the gripping force can be calculated from the elasticity of the microfinger and the driving voltage of FMG. By using this FMG-measurement system, the surface force of the cell membrane of sea urchin egg under seawater has been determined successfully from the measured deformation of the egg and the calculated gripping force of FMG. The other system is a micro-measurement system for thermal properties of micro-objects. For this system, a new microgripper with an integrated micro-thermocouple (TC-FMG) is proposed. By using micromachining, a new microfinger which has a thin film micro-thermocouple on the finger end has been developed and fabricated. The fabrication process and characterization results are discussed. By using a microfinger of TC-FMG with small heat capacity, the temperature change of a thermally actuated microfinger of standard FMG has been measured successfully. Using the measured temperature and temperature dependency of the resistivity of the microcoil, the in-air performance of the standard FMG could be written in the form of an equation which includes the resistivity change for various driving voltages.
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paper_title: A New Micro Pneumatic Actuator for Micromechanical Systems

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This paper presents a micro pneumatic actuator as a new actuation principle for micromechanical systems. A first application, a micro gripper driven by two bellow-type micro pneumatic actuators, is described. The basic structures of the micro pneumatic actuator and the micro gripper are fabricated by silicon dry etching in a single etching step. The device consists of a pyrex-silicon-pyrex sandwich structure which was assembled by anodic bonding. Alternatively an SU8 depth lithography process was used to realize the pneumatically driven micro gripper.
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paper_title: A new micro-tools exchange principle for micromanipulation

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This paper deals with the design, fabrication and characterization of a new micro-tools changer for a micromanipulation station including three translation stages (X-Y-Z manipulator) and a new piezoelectric microgripper. This system can be implemented in confined workspaces such as a scanning electron microscope (SEM) or more generally in a micro-factory station by the reduction of the manipulator's size and the flexibility gain. The principle of this micro-tools changer is based on the use of a thermal glue whose state (liquid or solid) is controlled by surface mounted device (SMD) electrical resistances. Such system allows hundreds of automatic micro-tools exchanges with a maximum position error between two consecutive tools exchanges of respectively 4.2, 2.8 and 5.4 /spl mu/m on the X, Y and Z axis. To validate the use of the micromanipulation station in a SEM, an experimental comparison of the working principle in low (vacuum) and high (air) pressure has also been established through thermal and degassing studies.
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paper_title: Manipulating biological and mechanical micro-objects using LIGA-microfabricated end-effectors

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We first discuss some general aspects of micromanipulation and possible different approaches. Then, we present new results in the micromanipulation of mechanical and biological objects. The apparatus we use is a purposely developed workstation comprising macro- and micro-manipulators. The most innovative component of the workstation is a micro-gripper fabricated using LIGA technology and actuated by piezoelectric actuators. We describe the design, fabrication and performance of a few prototypes of LIGA micro-grippers. Results are presented which demonstrate the ability of the system to manipulate effectively both micro-mechanical and biological micro-objects.
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paper_title: Silicon microgripper for microassembly realized by photolithography and fast anisotropic silicon etching

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In this paper we present a new silicon microgripper for microassembly realized by photolithography and fast anisotropic silicon etching. Technological and manufacturing problems of the silicon microgripper will be described. The optimized etch process results in a high silicon etch rate of up to 6.2 micrometers /min, a good selectivity silicon/photoresist of up to 100:1, a high anisotropy, a nearly vertical etch profile, and a smooth surface topography. Excellent profile control for trench etching with a depth of about 250 micrometers and an anisotropy of better than 0.98 at a mean etch rate of 4 micrometers /min was obtained. Higher etch rates of up to 6.2 micrometers /min have been achieved resulting, however, in lower anisotropy. The developed microgripper is driven by a differential-type shape memory alloy (SMA) actuator. SMA actuators exhibit the best power- to-volume ratio of all actuators, do not release any particles, and can perform various movements like bending, elongation or twisting. Heating can easily be achieved by direct electrical current. Therefore SMA actuators are well suited for microgripper applications.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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paper_title: Microgrippers created in microstructurable glass

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In this paper a new microgripper will be presented. The specific feature is the microfabrication based on a UV-lithographic process in microstructurable, photosensitive glass. Technological and manufacturing problems of the gripper will be described. The developed microgripper is actuated by a piezoelectric ceramic (monomorph). Glass microstructures are used as solid state hinges. With the special design of the gripper it is possible to realise a high distance ratio. The deflection of the gripping arms is some hundred micrometers. The gripping forces are a few mN up to 50 mN. The new grippers were fabricated and tested successfully.
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paper_title: A practical microgripper by fine alignment, eutectic bonding and SMA actuation

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Abstract A microgripper with a large gripping force, a relatively rigid structural body, and flexibility in functional design is presented. The actuation is generated by NiTiCu shape memory alloy (SMA) films and the stress induced can deflect each side of the microgripper up to 55 μm for a total gripping motion of 110 μm. When fully open, the force exerted by the film corresponds to a 13 mN gripping force on the tip of the gripper.
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Title: Overview of Microgrippers and Design of a Micromanipulation Station Based on a MMOC Microgripper

Section 1: INTRODUCTION
Description 1: Provide context and background on pick-and-place tasks in the industrial world, the challenges of handling micro-scale objects, and the significance of microgrippers in various fields.

Section 2: TWO-FINGERED MICROGRIPPER OVERVIEW
Description 2: Discuss different types and the actuation principles of two-fingered microgrippers, including the various prototypes developed by research institutes and commercial microgrippers.

Section 3: A MICROMANIPULATION SYSTEM
Description 3: Describe the micromanipulation system based on a MMOC Microgripper, including its components and functionalities.

Section 4: CONCLUSION
Description 4: Summarize the importance of two-fingered microgrippers in solving micromanipulation problems and the success of the semi-automatic micromanipulation station. Discuss future enhancements for fully automatic systems.