Using Singularities of Parallel Manipulators to Enhance the Rigid-Body Replacement Design Method of Compliant Mechanisms

Abstract

The rigid-body replacement method is often used when designing a compliant mechanism. The stiffness of the compliant mechanism, one of its main properties, is then highly dependent on the initial choice of a rigid-body architecture. In this paper, we propose to enhance the efficiency of the synthesis method by focusing on the architecture selection. This selection is done by considering the required mobilities and parallel manipulators in singularity to achieve them. Kinematic singularities of parallel structures are indeed advantageously used to propose compliant mechanisms with interesting stiffness properties. The approach is first illustrated by an example, the design of a one degree of freedom compliant architecture. Then the method is used to design a medical device where a compliant mechanism with three degrees of freedom is needed. The interest of the approach is outlined after application of the method. IntroductionCompliant mechanisms are monolithic structures taking advantage of elasticity to produce movements. The absence of backlash and friction allows the production of very accurate movements making them suitable for medical devices [1-3], micropositioning [4,5] and space applications [6]. One challenge is to design compliant mechanisms with multiple degrees of freedom that have adequate stiffness performances, i.e. that demonstrate low stiffnesses along the desired degrees of freedom (DOF), high stiffnesses in the other directions, and that fulfill other design criteria such as compactness. There are different ways to design compliant mechanisms. The most common synthesis approaches, described in [7], are the kinematic-based approaches, the building blocks approaches and the structural optimizationbased approaches. Among the kinematic-based approaches, the FACT method does not require knowledge of existing

Steel compliant Cardan universal joint

“…Studies about spatial compliant mechanisms are limited in the literature [19][20][21][22][23]. Trease, et al [24] and Rubbert et al [25] proposed designs for compliant universal joint. Finally, flexible-ring joints should also be mentioned as compliant universal joints [26].…”

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“…While a semi-compliant mechanism requires additional fabrication tasks such as assembly of flexible members, a fully compliant mechanism is more cost effective because no additional tasks are required to complete the compliant mechanism. Even though compliant mechanisms, either semi-compliant or fully compliant, have found numerous engineering applications, a fully compliant mechanism is commonly preferred in milli-and micro-domain applications where the assembly of a mechanism is topologically sophisticated [2][3][4][5][6]. Sreetharan et al demonstrated a MEMS fabrication technique incorporated with origami folding approach to fabricate and assemble a monolithic flapping wing robotic insect [7].…”

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“…Parallel singularity can be an actuation singularity, constraint singularity or a compound singularity as explained in [5][6][7]. Rubbert et al used an actuation singularity to type-synthesize a compliant medical device [8,9]. Another interesting kind of parallel singularity for a parallel manipulator that does not depend on the choice of ac- tuation is a constraint singularity [10].…”