Analysis and design of compliant mechanisms using analytical and graphical techniques

Gregory Allen Mettlach, Purdue University

Abstract

Compliant mechanisms are defined as mechanical systems that derive some or all of their mobility from the flexibility of one or more of their members. Due to the large-deflection nature of compliant members, analysis and synthesis of such mechanisms are made difficult. One difficulty encountered when designing compliant mechanisms is understanding the deformational characteristics of a flexible continuum. Traditionally, this understanding is gained at the expense of cost-prohibitive, repetetive prototyping and testing. Thus, compliant mechanisms have been limited to applications requiring only simple motions. The development of the pseudo-rigid-body model concept for planar compliant segments has greatly simplified analysis and synthesis of compliant mechanisms comprised of beam type flexible members. The purpose herein is to advance the areas of analysis, modeling, and synthesis of compliant mechanisms. The pseudo-rigid-body model concept is utilized in the development of general methodology by which any compliant member may be analyzed to determine unknown forces and moments satisfying specified displacement boundary conditions. This is facilitated by the development of an average pseudo-rigid-body model concept. The concept of a characteristic detection domain is developed which defines all possible deflected beam end positions for a compliant member. This may assist designers when specifying displacement boundary conditions for synthesis problems. If beam end positions are specified to lie within the domain, then solutions to design problems are assured. A planar, multiple-segment pseudo-rigid-body model concept is introduced which allows arbitrary beam type compliant members, regardless of geometry, loading, or boundary conditions, to be modeled as an assemblage of rigid members with torsional springs at characteristic pivots. This methodology enables existing analysis and synthesis methods to be applied in the design of complex compliant mechanisms. Typically, compliant mechanisms have been composed of initially straight beam type members or small-length flexural pivots. An effort is undertaken to explore initially curved and undulating members, to seek members offering greater kinematic mobility and hence, more versatile compliant mechanism designs. A synthesis method is proposed which incorporates pseudo-rigid-body model concepts and rigid-link synthesis methods to yield first-iteration compliant mechanisms. These approximate compliant mechanisms form the basis for optimal compliant mechanism designs using numerical solution methods.

Degree

Ph.D.

Advisors

Midha, Purdue University.

Subject Area

Mechanical engineering

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