Showing papers on "Compliant mechanism published in 1998"

Topology optimization of compliant mechanisms using the homogenization method

Abstract: A procedure to obtain a topology of an optimal structure considering flexibility is presented. The methodology is based on a mutual energy concept for formulation of flexibility and the homogenization method. A multi-objective optimization problem is formulated as an application of compliant mechanism design. Some examples of the design of compliant mechanisms for plane structures are presented. ( 1998 John Wiley & Sons, Ltd.

A Simple and Accurate Method for Determining Large Deflections in Compliant Mechanisms Subjected to End Forces and Moments

Abstract: Compliant members in flexible link mechanisms undergo large deflections when subjected to external loads. Because of this fact, traditional methods of deflection analysis do not apply. Since the nonlinearities introduced by these large deflections make the system comprising such members difficult to solve, parametric deflection approximations are deemed helpful in the analysis and synthesis of compliant mechanisms. This is accomplished by representing the compliant mechanism as a pseudo-rigid-body model. A wealth of analysis and synthesis techniques available for rigid-body mechanisms thus become amenable to the design of compliant mechanisms. In this paper, a pseudo-rigid-body model is developed and solved for the tip deflection of flexible beams for combined end loads. A numerical integration technique using quadrature formulae has been employed to solve the large deflection Bernoulli-Euler beam equation for the tip deflection. Implementation of this scheme is simpler than the elliptic integral formulation and provides very accurate results. An example for the synthesis of a compliant mechanism using the proposed model is also presented.

An investigation into compliant bistable mechanisms

Abstract: This paper proposes a new class of bistable mechanisms: compliant bistable mechanisms. These mechanisms gain their bistable behavior from the energy stored in the flexible segments which deflect to allow mechanism motion. This approach integrates desired mechanism motion and energy storage to create bistable mechanisms with dramatically reduced part count compared to traditional mechanisms incorporating rigid links, joints, and springs. This paper briefly reviews bistable mechanism theory, introduces some additional bistable mechanism characteristics, and integrates this theory with compliant mechanism theory. The resulting theory of bistable compliant mechanisms is validated by measuring the force and motion characteristics of several test mechanisms and comparing them to predicted values.

Topology optimization of geometrically nonlinear structures and compliant mechanisms

Abstract: Topology optimization of structures has become an area of rapidly increasing interest to researchers during the past decade. Most structural topology optimization problems assume a linear elastic response. This assumption is not valid for systems undergoing large deformation. The structural analysis here accommodates geometric and material nonlinearities, and its impact on the topology optimization is investigated. A well-posed regularized topology optimization problem is developed by introducing a Gaussian-weigh ted density measure. Topology results based on the linear and nonlinear elastic formulations are compared. The formulation of the structural design problem is then extended to design compliant mechanisms undergoing large displacements.

An Introduction to Mechanical Advantage in Compliant Mechanisms

Abstract: An energy approach is utilized to determine mechanical advantage in compliant mechanisms by duly accounting for lost work due to deformation. Three mechanical advantage types are then defined which examine the isolated influences of various parameters. Finally, a case study is investigated to exemplify these definitions and demonstrate resulting trends in mechanical advantage.

Cooperative control of multiple mobile manipulators on uneven ground

Abstract: We have proposed a simple method for carrying a large object by cooperation of multiple mobile manipulators with position controllers. Manipulators on mobile platforms are used as free joint mechanisms by locking some joints and making the rest joints free. These free joints play the role of mechanical compliance in order to avoid excessive inner forces due to the mutual positioning errors. We discuss how to determine feedback control laws for cooperation of mobile platforms on uneven ground. First, compliance needed for cooperation among position-controlled robots, the statics and error characteristics of cooperative systems including compliant mechanisms are reviewed. Second, three feedback control laws for platforms moving on uneven ground are proposed and their control performance is investigated. After additional improved control laws are proposed, the proposed control laws are used for a prototype cooperative system consisting of three moving tables driven by ball screws and the effectiveness of the proposed law is verified.

Optimal design of compliant mechanisms for smart structures applications

Abstract: Compliant mechanisms are currently used in conjunction with induced-strain actuators to provide stroke amplification. These compliant or flexure mechanisms are preferred over conventional rigid-link amplifiers because they avoid problems with clearances in mechanical joints. Many of the current compliant amplifiers are designed using ad-hoc or intuitive methods, however. In this paper, a topology optimization algorithm developed for systematic design of compliant mechanisms is applied to the design of compliant stroke amplifiers for induced-strain actuators. The underlying formulation for the optimization method is presented, and is then illustrated by two design examples. The functionality of the optimal solutions are verified by finite element analyses.

Topological synthesis of compliant mechanisms using the optimality criteria method

Abstract: An optimality criteria approach for the synthesis of compliant mechanisms is presented in this paper. Several possible multi-criteria optimization formulations that can accommodate the conflicting flexibility and stiffness requirements of compliant mechanisms are considered using which the optimality property for compliant topologies is deduced. The property states that the ratio of the mutual potential energy density to the strain energy density is uniform throughout the continuum, but for portions otherwise bounded by gage constraints. It is noted that this multi-criteria formulation is non-convex and that the resulting optimal solutions are, in general, not unique. Based on this observation, a synthesis algorithm is developed that combines both the efficiency of optimality criteria methods and reliability of mathematical programming schemes. Examples are included to illustrate the synthesis procedure using linear frame finite elements which are easy for implementation and are capable of appropriately accounting for the bending behavior in the continuum.

Three-degree-of-freedom flexure-based manipulator for high-resolution spatial micromanipulation

Abstract: Flexure-based compliant mechanism design enables the development of revolute joint manipulators without the backlash or Coulomb friction that impede precision position and especially force control. Additionally, due to scaling effects, the adverse consequences of Coulomb friction are exacerbated at small scales. Conventional approaches to compliant mechanism design impose several limitations, however, such as severely limited ranges of motion, poor kinematic behavior, and significant deformation under multi- axis loading. The authors have developed a new type of compliant mechanism that enables the implementation of spatially-loaded revolute joint manipulators with well- behaved kinematic characteristics and without the backlash and stick-slip behavior that would otherwise impede precision control. The primary innovation in the design is the split-tube flexure, a unique small-scale revolute joint that exhibits a considerably larger range of motion and significantly better multi-axis revolute joint characteristics than a conventional flexure. Specifically, the compliant manipulator has an approximately spherical workspace two centimeters in diameter, yet is structurally rigid along non-actuated axes. Data from the small-scale manipulator demonstrates that positioning resolution is limited by digital quantization and sensor noise, and not by more fundamental physical limitations, such as backlash or Coulomb friction.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Eliminating non-smooth nonlinearities with compliant manipulator design

Abstract: Compliant mechanism design enables the development of revolute joint-based manipulators without the backlash and Coulomb friction that impede precision position and especially force control. Conventional approaches to compliant mechanism design entail several limitations, however, such as severely limited ranges of motion, poor kinematic behavior, and significant deformation under multiaxis loading. The authors have developed an approach to compliant mechanism design that enables a considerably larger range of motion and significantly better multiaxis revolute joint characteristics than conventional approaches. The approach is based upon the development of a revolute joint that enables the implementation of high bandwidth spatially-loaded revolute joint-based manipulators with well-behaved kinematic characteristics and without the backlash and stick-slip behavior that would otherwise impede precision control. The approach has been incorporated into the design of a small-scale three degree-of-freedom manipulator with an approximately spherical workspace two centimeters in diameter. Though applied to a small-scale manipulator, the design approach is also suited to conventional scale devices. Data from the small-scale manipulator indicates that positioning resolution is limited by digital quantization and sensor noise, and not by more fundamental physical limitations, such as backlash or Coulomb friction.

Design of adaptive structures using compliant mechanisms

Abstract: Static shape control of adaptive structures is currently an important and active research area in the smart structures field. Numerous actuation schemes using smart materials have been proposed and developed for shape control of structures. While the results of the smart material based technology is promising, it is also, however, showing more serious limitations such as scalability of laboratory-scale prototype models into real-scale models. In addition, the smart material based approach for shape control requires a multitude of actuators distributed throughout the host structure, the hence, complicates the control system. This paper introduces a novel alternative design concept for shape control of flexible adaptive structures using a single actuator which need not necessarily be smart material based. The novelty in this concept is that it employs distributed compliance in design--through compliant mechanisms, a class of mechanisms that transmit motion through inherent flexibility--rather than distributed actuation to accomplish the shape changes. The paper outlines a method for synthesis of such compliant mechanisms. The concept, and the synthesis method are illustrated through an example where a specified shape change in the leading edge of an airfoil structure is accomplished. The new concept has a great potential to not only eliminate the scalability problem, but also reduce the control complexity, the weight, and cost of the entire system as well.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

柔軟性を考慮した構造の最適化 : 第3報, 入力荷重が周期的に変化する場合

Abstract: In structural design, the stiffest structure has been considered optimal. However, if flexibility is implemented in some appropriate portions, a flexible structure provides higher performance than the stiffest structure. Furthermore, since flexible portions can provide a mechanical function to the structure, a new breed of jointless structural mechanisms known as compliant mechanisms can be designed with structural flexibility. In this study, we present a methodology to provide the optimal structure accounting for structural flexibility in the case of periodic input loads. First, dynamic mutual mean compliance is introduced in order to define flexibility using a mutual energy concept. Socond, a new multi-objective function incorporating the maximization of flexibility and stiffness is proposed. Next, an optimization procedure is constructed based on the homogenization method and sequential linear programming (SLP). Finally, some examples are presented to confirm the problem specifications of the optimal configurations.