Synthesis of Adaptive and Controllable Compliant Systems with Embedded Actuators and Sensors

This paper presents a framework for the design of a compliant system; that is, the concurrent design of a compliant mechanism with embedded actuators and embedded sensors. We focus on methods that simultaneously synthesize optimal structural topology and placement of actuators and sensors for maximum energy efficiency and adaptive performance, while satisfying various weight and performance constraints. The goal of this research is to lay a scientific foundation and a mathematical framework for distributed actuation and sensing within a compliant active structure. Key features of the methodology include (1) the simultaneous optimization of the location, orientation, and size of actuators concurrent with the compliant transmission topology and (2) the concepts of controllability and observability that arise from the consideration of control, and their implementation in compliant systems design. The methods used include genetic algorithms, graph searches for connectivity, and multiple load cases implemented with linear finite element analysis. Actuators, modeled as both force generators and structural compliant elements, are included as topology variables in the optimization. Results are provided for several studies, including: (1) concurrent actuator placement and topology design for a compliant amplifier and (2) a shape-morphing aircraft wing demonstration with three controlled output nodes. Central to this method is the concept of structural orthogonality, which refers to the unique system response for each actuator it contains. Finally, the results from the controllability problem are used to motivate and describe the analogous extension to observability for sensing. INTRODUCTION The basic premise of a compliant system is the integration of motion/force transmission via elastic deformation with embedded actuation and sensing. Current electromechanical systems are generally molded in the rigid-and-discrete paradigm where one first designs a rigid structure with mechanical joints and then adds actuators and sensors, with the design of controls only following as an afterthought. In spite of the “mechatronic revolution” of the early 1990s, this paradigm is still prevalent today. The goal of this research is to lay a scientific foundation and a mathematical framework for distributed actuation and sensing within a compliant active structure. In past studies of compliant mechanisms (CMs) and their synthesis, singleactuator mechanisms have been considered, with the determination of the actuator’s type, orientation, size, and location occurring outside of the automated design synthesis, at the designer’s option. The objective of this research can be stated as a systems approach to synthesis of mechanism, actuator, and sensors, thereby advancing the path from traditional mechanical design to systematic compliant-mechatronic design, as graphically depicted in Fig. 1. The steps made include systematic design tools and algorithms. We are developing methods that simultaneously synthesize optimal structural topology and placement of actuators and sensors for maximum energy efficiency and adaptive performance. From these we seek specific insights that will lead to general engineering design guidelines for embedded systems. 1 Copyright © 2006 by ASME Traditional Mechanism Design Compliant Mechanism Design Compliant Mechatronic System Design Figure 1: Transition from “Traditional Mechanical Design” to “Mechatronic Design with Distributed and Embedded Compliant Systems”. Current State-of-the-Art is “Compliant Mechanism Design”. The physical layout of these components is optimized for energy efficiency, controllability, and responsiveness, while satisfying various weight and performance constraints (e.g. for autonomous robots). Figure 3 shows an example of the problem definition and a conceptual solution generated algorithmically based on the proposed synthesis framework. Allowing for multiple inputs in compliant mechanism design also leads to the question of control. A method for incorporating consideration of control during the design synthesis can enhance the controllability and responsiveness of an adaptive system. Central to this method is the concept of structural orthogonality, which refers to the unique system response for each actuator it contains. A