The Art of Flexure Mechanism Design

Mechanism constitute the mechanical organs of machines. They are generally composed of rigid segments connected to each other by articulated joints. The function of the joints is to act as bearings, i.e. to constraint the relative motion of the segments it connects, while leaving a freedom of motion in some specific directions. Conventional mechanisms rely on sliding or rolling motions between solid bodies in order to fulfill the bearing function. Consequently, these bearings exhibit friction forcers limiting the motion precision, they require lubrication, they undergo wear, they produce debris and they have a limited lifetime. Flexure mechanisms rely on a radically different physical principle to fulfill the bearing function : the elastic deformation of beams and membranes. This gets around the above-mentioned limitations. The rigid segments of the mechanism are connected to each other via elastically deformable joints called flexures which are springs whose stiffnesses are designed to be very high in the directions where the joint has to constrain relative motion and very flexile in the directions where freedom of motion is required. As a result, mechanisms can be manufactured monolithically and, by proper choice of materials and geometry of the flexures, lead to lifetimes of tens of millions of cycles without any wear or change in the geometry or forces of motion. Thanks to these unique properties flexure mechanisms have become an inescapable technology in all environments where friction, lubrication, wear, debris or mechanical backlash are forbidden : outer space, vacuum, cryogenics, high radiation, ultra-clean environments, etc. This book comes within the scope of this technological evolution. It gathers the knowledge of experts in flexure mechanisms design having worked in the key fields of high precision robotics, aerospace mechanisms, particle accelerators and watch making industry. It is dedicated to engineers, scientists and students working in these fields. The book presents the basic principles underlying flexure mechanism design, the most important flexures and the key formulas for their proper design. It also covers more general aspects of the kinematic design of multi-degrees of freedom mechanism exploiting the state of the art approaches of parallel kinematics. A wide variety of concrete examples of systems designed based on theses approaches are presented in details.