University of Twente Student Theses


Design of a statistically balanced fully complaint grasper using the rigid body replacement method

Lamers, A.J. (2012) Design of a statistically balanced fully complaint grasper using the rigid body replacement method.

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Abstract:Monolithic and thus fully compliant surgical graspers are promising when they provide equal or better force feedback then conventional graspers. In this work a fully compliant grasper is designed to have zero stiffness and the capability to obtain zero operation force. The design problem is addressed by taking a building block approach, in which a pre-existing positive stiffness compliant grasper is compensated by a negative stiffness balancer. The design of the balancer is conceived from a 4-bar linkage and explores the Rigid-Body-Replacement method as a novel design approach towards static balancing. Design variables and sensitivities are determined through the use of a pseudo rigid body model. Final dimensions are obtained using rough hand calculations. Justification of the pseudo rigid body model as well as the set of final dimensions is done by non linear finite element analysis. Experimental validation is done through a titanium prototype of 40 [mm] size having an unbalanced positive stiffness of 62.3 [N/mm] showing that a force reduction of 98.92 [%] is achievable over a range of 0.6 [mm]. While hysteresis is approximately 1.32 [%]. The behavior can be tuned from monostable to bistable. The Rigid-Body-Replacement method was proved successful in the design of a statically balanced fully compliant grasper, widening the design possibilities for this kind of mechanisms.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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