Sridhar Kota

Topological Synthesis of Compliant Mechanisms Using Multi-Criteria Optimization

Compliant mechanisms are mechanical devices that achieve motion via elastic deformation. A new method for topological synthesis of single-piece compliant mechanisms is presented, using a “design for required deflection” approach. A simple beam example is used to illustrate this concept and to provide the motivation for a new multi-criteria approach for compliant mechanism design. This new approach handles motion and loading requirements simultaneously for a given set of input force and output deflection specifications. Both a truss ground structure and a two-dimensional continuum are used in the implementation which is illustrated with design examples.

Design of Large-Displacement Compliant Joints

Flexure joints are widely used to approximate the function of traditional mechanical joints, while offering the benefits of high precision, long life, and ease of manufacture. This paper investigates and catalogs the drawbacks of typical flexure connectors and presents several new designs for highlyeffective, kinematically-behaved compliant joints. A revolute and a translational compliant joint are proposed (Figure 1), both of which offer great improvements over existing flexures in the qualities of (1) large range of motion, (2) minimal axis drift, (3) increased off-axis stiffness, and (4) reduced stressconcentrations. Analytic stiffness equations are developed for each joint and parametric computer models are used to verify their superior stiffness properties. A catalog of design charts based on the parametric models is also presented, allowing for rapid sizing of the joints for custom performance. Finally, two multi-degree-of-freedom joints are proposed as modifications to the revolute joint. These include a compliant universal joint and a compliant spherical joint, both designed to provide high degrees of compliance in the desired direction of motion and high stiffness in other directions.

A Metric for Evaluating Design Commonality in Product Families

Many companies develop a market strategy built around a family of products. These companies regularly add new product variations to the family in order to meet changing market needs or to attract a broader customer base. Although the core functionality remains essentially unchanged across the products within a family, new functions, feature combinations and technologies are incorporated into each new product. If allowed to grow unchecked, these component variations, commonly referred to as “complexity”, can result in a loss of productivity or quality. The challenge lies in an effective management of product variations in the design studio and on the manufacturing floor. The key is to minimize non-value added variations across models within a product family without limiting customer choices. In this paper we discuss the factors that contribute to product complexity in general, and present an objective measure, called the Product Line Commonality Index, to capture the level of component commonality in a product family. Through our Walkman case study, we present a simple yet powerful method of benchmarking product families1. This method gauges the family’s ability to share parts effectively (modularity) and to reduce the total number of parts (multi-functionality). [S1050-0472(00)02704-5]

Design of Compliant Mechanisms for Morphing Structural Shapes

Various compliant mechanism synthesis methods have been developed over the past decade; however, very little attention has been directed towards adaptive shape change problems. In this paper, we present a systematic method for synthesizing compliant mechanisms to morph a given curve or profile into a target curve utilizing minimum number of actuators (typically one). Two objective functions are formulated, using Least Square Errors and a modified Fourier Transformation, to capture the shape differences. The topology and dimensions of the optimal compliant mechanism are generated using Genetic Algorithms. Applications of this synthesis approach are demonstrated through two adaptive antenna design examples.

Static shape control of smart structures using compliant mechanisms

A novel approach to static shape control of smart structures is introduced. This approach uses a special class of mechanisms called compliant mechanisms powered by a single input actuator. The key design Issue in this approach is the synthesis of a suitable compliant mechanism for the task. A systematic procedure for synthesis of such compliant mechanisms is presented by combining the first principles of mechanics and kinematics through a structural optimization scheme. The procedure is illustrated by an example wherein a prescribed smooth shape change in the camber of an idealized airfoil structure is accomplished by a specially synthesized compliant mechanism actuated by a single torque input. The scope and benefits of the proposed approach in providing viable simple solutions for real-scale static shape control applications are also discussed.

Optimal Synthesis of Mechanisms for Path Generation Using Fourier Descriptors and Global Search Methods

Generally, success in synthesis of mechanisms for path generation is limited to finding a reasonable local optima at best in spite of verygood initial guess. The most widely used Structural Error objective function is not effective in leading to practical solutions as it misrepresents the nature of the design problem by requiring the shape, size, orientation and position of the coupler curve to be optimized all at once. In this paper, we present an effective objective function based on Fourier descriptors that evaluates only the shape differences between two curves. This function is first minimized using a stochastic global search method derived from simulated annealing followed by Powells method. The size, orientation and position of the desired curve are addressed in a later stage by determining analogous points on the desired and candidate curves. In spite of highly non-linear mechanisms design space, our method discovers near-global and practical solutions consistently without requiring any initial guess.

Design of Compliant Mechanisms: Applications to MEMS

Compliant mechanisms are single-piece flexible structures that deliver the desired motion by undergoing elastic deformation as opposed to jointed rigid body motions of conventional mechanisms. Compliance in design leads to jointless, no-assembly (Fig. 1), monolithic mechanical devices and is particularly suited for applications with small range of motions. The compliant windshield wiper shown in Fig. 1 illustrates this paradigm of no-assembly. Conventional flexural mechanisms employ flexural joints that connect relatively rigid links as depicted in Fig. 2. Reduced fatigue life, high stress concentration and difficulty in fabrication are some of the drawbacks of flexural joints. Our focus is on designing compliant mechanisms with distributed compliance which employs flexural links (see Fig. 3) and have no joints (neither pin nor flexural joints) for improved reliability, performance, and ease of manufacture. Distributed compliant mechanisms derive their flexibility due to topology and shape of the material continuum rather than concentrated flexion at few regions. This paper focuses on the unique methodology employed to design jointless mechanisms with distributed compliance. The paper also illustrates a compliant stroke amplification mechanism that was recently designed, fabricated and tested for MEMS application.

Design and application of compliant mechanisms for morphing aircraft structures

Morphing aircraft structures can significantly enhance air vehicle performance. This paper highlights ongoing work to design novel compliant mechanisms that efficiently morph aircraft structures in order to exploit aerodynamic benefits. Computational tools are being developed to design structures that deform into specified shapes given simple actuator inputs. In addition, these synthesis methods seek to optimize the stiffness of the structure to minimize actuator effort and maximize the stiffness with respect to the environment (external loading). These tools have been used to study two different types of morphing systems: (i) variable geometry wings and (ii) high-frequency vortex generators for active flow control. Several case studies are presented which highlight the design approach and computational and experimental results of these morphing aircraft systems.

Design of Reconfigurable Machine Tools

In this paper, we present a systematic methodology for designing Reconfigurable Machine Tools (RMTs). The synthesis methodology takes as input a set of functional requirements-a set of process plans and generates a set of kinematically viable reconfigurable machine tools that meet the given design specifications. We present a mathematical framework for synthesis of machine tools using a library of building blocks. The framework is rooted in (a) graph theoretic methods of enumeration of alternate structural configurations and (b) screw theory that enables us to manipulate matrix representations of motions to identify appropriate kinematic building blocks.

Design and Application of Compliant Mechanisms for Surgical Tools

This paper introduces the benefits of exploiting elasticity in the engineering design of surgical tools, in general, and of minimally invasive procedures, in particular. Compliant mechanisms are jointless mechanisms that rely on elastic deformation to transmit forces and motion. The lack of traditional joints in these single-piece flexible structures offers many benefits, including the absence of wear debris, pinch points, crevices, and lubrication. Such systems are particularly amenable to embedded sensing for haptic feedback and embedded actuation with active-material actuators. The paper provides an overview of design synthesis methods developed at the Compliant Systems Design Laboratory and focuses specifically on surgical applications. Compliant systems have potential to integrate. well within the constraints of laparoscopic procedures and telerobotic surgery. A load-path representation is used within a genetic algorithm to solve two gripper example problems. In addition, the paper illustrates the design and construction of an organ (kidney) manipulator for use in minimally invasive procedures.