Compliant mechanism | EPFL Graph Search

In mechanical engineering, a compliant mechanism is a flexible mechanism that achieves force and motion transmission through elastic body deformation. It gains some or all of its motion from the relative flexibility of its members rather than from rigid-body joints alone. These may be monolithic (single-piece) or jointless structures. Some common devices that use compliant mechanisms are backpack latches and paper clips. One of the oldest examples of using compliant structures is the bow and arrow. Design methods Compliant mechanisms are usually designed using two techniques: Kinematics approach Kinematic analysis can be used to design a compliant mechanism by creating a pseudo-rigid-body model of the mechanism. In this model, flexible segments are modeled as rigid links connected to revolute joints with torsional springs. Other structures can be modeled as a combination of rigid links, springs, and dampers. Structural optimization appro

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

Lennart Rubbert

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.

American Society of Mechanical Engineers2014

Higher-order continuation method for the rigid-body kinematic design of compliant mechanisms

Simon Nessim Henein, Lennart Rubbert

Compliant mechanisms are of great interest in precision engineering. In this paper we propose a higher order continuation method to help their rigid-body kinematic design. The method helps to investigate the choice of a mechanism configuration through the whole exploration of the workspace, and eases the kinematic analysis to avoid, or take advantage of, the vicinity of kinematic singularities. Such approach is relevant for planar and quasi-planar mechanisms that can be obtained with micro-manufacturing processes adapted to precision applications. The higher-order continuation method allows for a direct and accurate plotting of the input-output relationship of any mechanism by considering only its geometrical closed-loop equations, i.e. without the complex derivation of any analytical model. We show that these plots, called bifurcation diagrams, reveal essential information such as the joint velocity profile and the presence of singular configurations. Moreover, the continuous and accurate computation of the mechanism configuration in the vicinity of singularities provides detailed information about the kinematic behavior of the mechanism in its extreme positions. For the design of compliant mechanisms, the designer can advantageously use the bifurcation diagrams to evaluate the relevance of the selected mechanism, then to identify a configuration in order to obtain desired kinematic properties without the derivation of the inverse kinematic model (IKM). or the direct kinematic model (DKM). The method is exemplified with a 3 universal-joint and 3 spherical-joint mechanism (3-US), the IKM and DKM of which cannot be derived analytically. The latter has a large workspace and special kinematic behaviors consisting of a screw-like motion and a platform gyration, which have not been studied before and could lead to novel compliant devices. (C) 2017 Elsevier Inc. All rights reserved.

Elsevier2017

Analytical modeling and experimental validation of rotationally actuated pinned–pinned and fixed–pinned buckled beam bistable mechanisms

Simon Nessim Henein, Hubert Pierre-Marie Benoît Schneegans, Etienne Frédéric Gabriel Thalmann, Loïc Benoît Tissot-Daguette

Buckled beams have become key building blocks in compliant mechanisms to achieve nonlinear behaviors, such as bistability, constant-force and stiffness tuning. However, designing and modeling such components is challenging due to their highly nonlinear characteristics and existing models typically lack accuracy or rely on numerical computations. This paper aims at giving closed-form formulas to efficiently characterize the snap through behavior and facilitate the design process of rotationally actuated pinned–pinned and fixed–pinned bistable buckled beams. A new generic analytical model for precompressed beams based on Euler–Bernoulli beam theory is first established and then applied to these two configurations. Finite element and experimental validations are performed, showing excellent agreement with the model. The results show that the angular input at the pinned beam extremity is significantly decoupled from the angular or moment output at the other extremity, until snap-through. Additionally, we show that the stable output values can be controlled by adjusting the precompression displacement of the buckled beam. Finally, we demonstrate the practicality of the studied building blocks and their modeling on a novel bistable gripper design.

2022

Higher-order continuation method for the rigid-body kinematic design of compliant mechanisms

Simon Nessim Henein, Lennart Rubbert

Elsevier2017