Parallel Kinematic Devices

Actively Compliant Parallel End-Effector Mechanism for Medical Interventions




KEYWORDS: robot, sensors, parallel mechanism, end-effector, stewart platform, remote triage, ultrasound, combat casualty care

OBJECTIVE: Design and develop a six degree-of-freedom parallel end-effector mechanism that can be mounted on the end of a medium-sized robot manipulator for compliance-based medical imaging and surgical interventions.

DESCRIPTION: The military is currently developing several robotic systems for both teleoperated and autonomous interventions for use in the operating room of the future (Cleary et al, 2004). Intuitive Surgical’s da Vinci® surgical robot broke ground in 1998 by performing the first tele-robotic surgery to repair a heart valve (Guthart & Salisbury, 2000), and Accuray’s CyberKnife radiotherapy robot began treating head, neck and upper spine tumors in 1999 by combining image guidance with a robotically-directed radiation beam (Adler et al., 1997). Ultrasound represents one of the most promising new technologies for use both on and off the battlefield. High-resolution ultrasound imaging can be used to detect internal bleeding (Alvarado et al, 2008) and bone fractures (Lo et al, 2008), and an ultrasonic welding device is now being applied as an alternative to manual suturing (Garcia, 2007). During these procedures, it is typically required that a specified level of force be applied on the patient, which is made particularly difficult because of the compliance of soft skin tissue and involuntary movements due to respiration. It is extremely difficult for a serial-link manipulator to respond quickly enough to accommodate this motion due to high inertia and inaccuracies caused by low stiffness at the tool point. Ultrasonic probes have been mounted and demonstrated on parallel manipulator devices (Ding et al, 2008), but the range of motion is very limited. Alternatively, serial-parallel robot architectures can be implemented in which the serial robot moves the probe into close proximity of the patient, while a parallel mechanism end-effector maintains constant force contact of the probe using minute adjustments (Carbone and Ceccarelli, 2005). In addition to providing increased accuracy and bandwidth, a robotic end-effector mechanism will also yield increase the level of safety through active compliance. Several technologies are potential candidates for this research topic, although dc electric motor-based technologies are preferred. Approaches that could potentially be used include using linear joints such as lead-screws or pistons currently employed in Stewart platforms or rotary joints to drive differential gears to cause multi-axis movement of linkages. In addition to novel end-effector design, research challenges inherent in this topic include actuator devices, colocated sensing, mechanical efficiency, miniaturization, ruggedization, local processing, communication, and packaging. For example, colocated sensing represents a particular challenge due to the close proximity of the actuators and rugged environment in which the device must operate which may be inhospitable to optical encoders typically employed in these applications.

PHASE I: Conceptualize and design a prototype parallel end-effector mechanism that meets the following requirements: mass < 5 Kg, force > 50 N, torque > 5 N-m/rad, force resolution < 0.5 N, position accuracy < 2 mm, position repeability < 0.5 mm, stiffness > 10000 N/m, range of motion 5 cm translation and 30 deg rotation, and diameter < 15 cm x height < 15 cm. Develop a research plan for Phase II.

PHASE II: Develop, integrate, and test a prototype parallel end-effector mechanism that meets the Phase I requirements. Design and implement a controller that can achieve active compliance of less than 2 N/cm up to 10 Hz bandwidth. Demonstrate this system on a serial-link manipulator used in a surgical suite such as a Mitsubishi PA-10 manipulator. Develop a commercialization plan for Phase III.

PHASE III: Assist the Army in transitioning and implementing the parallel end-effector mechanism to a commercial robot application in a surgical suite. Develop and market a commercial version of the end-effector for use in hospitals with trauma units.


  1. Kevin Cleary, Ho Young Chung, and Seong Ki Mun, OR2020: "The Operating Room of the Future", Proc. of the 18th Int. Congress and Exhibition, Computer Assisted Radiology and Surgery (CARS), vol. 1268, June 2004, pp. 847-852. (
  2. Guthart, G. & Salisbury, J. K. (2000). The intuitive telesurgery system: Overview and application, Proc. of the IEEE Int. Conf. on Robotics and Automation, pp. 618-622, San Fransisco, Apr. 2000.
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  5. Lo S-C.B, Liu CC, Freedman MT, Lasser ME, Lasser B, Kula J, Wang Y (2008). Projection-Reflection Ultrasound Images using PE-CMOS Sensor: A Preliminary Bone Fracture Study. Proc. of the SPIE, 6920(4).
  6. Garcia P (2007). Robotic Telesurgery Systems. Medicine Meets Virtual Reality. Feb. 6-9, Long Beach, Calif.
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  8. Carbone G and Ceccarelli M (2005). A Serial-parallel robotic architecture for surgical tasks. Robotica (2005) volume 23, pp. 345–354.

Parallel Kinematic Actuator with Reduced Size and Improved Performance
SBIR contract:
DSM designed an "actively compliant" end-effector that uses parallel kinematics and force feedback. The end-effector can be fixed to the end of a conventional articulated robot. Using its high bandwidth in six axes of motion and force feedback, the end-effector is able to correct for compliance and shifts in the position of the patient. Thus, controlled contact can be maintained between the ultrasound device and the patient.