What is a Compliant Mechanism?

A compliant mechanism is a single-piece flexible structure where the structural deformation is utilized to transmit force or deliver motion due to an input actuation. It works as a transmission that is designed to have the desirable characteristics between the input actuation and the output to the environment. Due to the its jointless feature, compliant mechanism has many desirable features, such as no assembly, no wear, no backlash, low cost, and low maintenance. Typical compliant mechanism synthesis involves the use of homogenization method or truss/beam ground structures originally seen in structural optimization. These methods can be incorporated with different objective functions to design compliant mechanisms for various purposes, such as compliant grippers for object manipulation, compliant motion amplifier in MEMS, and compliant end-effector for minimally invasive surgery.

Why Shape Morphing?

The performance of many mechanical systems is directly related to the geometric shapes of their components, such as aircraft wings and antenna reflectors. The wing shape affects the obtained lift and drag, while the antenna reflector shape determines the signal radiation pattern. While the shapes of these components are mostly fixed, morphing their shapes in response to the operation condition or task requirements can increase the flexibility and enhance the performance. Although conventional hinged mechanisms can provide a morphing surface, the joints and seams create discontinuities over the surface, leading to undesirable fluid dynamics characteristics. Another approach is to use distributed smart material actuators (piezo and SMA) to provide local shape changes over the structure surface. Despite the advantages of these actuators, the scalability of the solutions they provide is still uncertain. In 1995, Prof. Sridhar Kota introduced the concept of using compliant mechanisms to achieve shape morphing. Due to the distributed compliance throughout the structure, the compliant mechanism provides a smooth structural deformation which has better fluid dynamics characteristics. The effect of structural deformation in compliant mechanisms also provides a more scalable solution to the shape morphing problem (micro- to large scale).

Shape Morphing Compliant Mechanisms have Multiple Output Points!

Although various synthesis approach for compliant mechanisms have been developed in the past decade or so, very little attention has been directed to shape morphing problems. Most of the previous approaches have been designing compliant mechanisms with only a single output point, but a shape morphing compliant mechanism requires matching the deformed structural shape with a desired target shape. Thus, every point along the morphing boundary can be seen as an output point. In other words, a shape morphing compliant mechanism has multiple output points, and the synthesis approaches for single output problems might be inappropriate for shape morphong problems.

Systematic Synthesis Approach for Shape Morphing Compliant Mechanisms

I have developed two systematic approaches to synthesize shape morphing compliant mechanisms. One uses a beam ground structure to parameterize the design domain, while the other uses a load path representation to address the structural connectivity issue. Both parameterization schemes are incorporated with a genetic algorithm to simultaneously find the structural topology and dimensions that minimizes the shape deviation between the deformed morphing boundary shape and the desired target shape. The use of genetic algorithm allows using binary variables to appropriately address the discrete nature of structural topology, while the majority of the previous research has been using continuous variables to approximate the presence or elimination of elements. Details regarding my research can be found from my papers. Please go to the publicaion page to download my papers.