Showing papers on "Compliant mechanism published in 2008"

Micro-motion devices technology: The state of arts review

Abstract: In this paper we review the world-wide study on micro-motion systems both from an academic and an industrial perspective. The objective of the review is to answer the following questions: (1) What are the limitations of technologies to develop a micro-motion device in terms of function, motion range, accuracy, and speed it can achieve? (2) What is any economic implication of these technologies? (3) What are future research directions? The micro-motion systems considered in this paper are classified into four kinds in terms of their motion ranges: (a) 1000 μm. This review concludes that the PZT actuation element integrated with the compliant mechanism is the most promising technology which can achieve high accuracy (sub-nanometer) of all four kinds of motion ranges. This promise is further based on the amplification technology using the compliant mechanism concept. The amplification mechanism is used to com- pensate the problem with a limited stroke of the PZT actuation element. The compliant amplification mecha- nism allows one to achieve a high resolution and high stiffness motion which does not compromise the loss of accuracy due to motion amplification. The PZT actuation element and the compliant mechanism are both econom- ically viable. Future research direction should generally focus on the interface between the PZT actuation element and compliant mechanism and the reliability of the compliant mechanism under cyclic deformation of com- pliant materials.

A Building Block Approach to the Conceptual Synthesis of Compliant Mechanisms Utilizing Compliance and Stiffness Ellipsoids

Abstract: Ellipsoids this paper, we investigate a methodology for the conceptual synthesis of compliant mechanisms based on a building block approach. The building block approach is intuitive and provides key insight into how individual building blocks contribute to the overall function. We investigate the basic kinematic behavior of individual building blocks and relate this to the behavior of a design composed of building blocks. This serves to not only generate viable solutions but also to augment the understanding of the designer. Once a feasible concept is thus generated, known methods for size and geometry optimization may be employed to fine-tune performance. The key enabler of the building block synthesis is the method of capturing kinematic behavior using compliance ellipsoids. The mathematical model of the compliance ellipsoids facilitates the characterization of the building blocks, transformation of problem specifications, decomposition into subproblems, and the ability to search for alternate solutions. The compliance ellipsoids also give insight into how individual building blocks contribute to the overall kinematic function. The effectiveness and generality of the methodology are demonstrated through two synthesis examples. Using only a limited set of building blocks, the methodology is capable of addressing generic kinematic problem specifications for compliance at a single point and for a single-input, single-output compliant mechanism. A rapid prototype of the latter demonstrates the validity of the conceptual solution. DOI: 10.1115/1.2821387

Design of Nonlinear Springs for Prescribed Load-Displacement Functions

Abstract: A nonlinear spring has a defined nonlinear load-displacement function, which is also equivalent to its strain energy absorption rate. Various applications benefit from nonlinear springs, including prosthetics and microelectromechanical system devices. Since each nonlinear spring application requires a unique load-displacement function, spring configurations must be custom designed, and no generalized design methodology exists. In this paper, we present a generalized nonlinear spring synthesis methodology that (i) synthesizes a spring for any prescribed nonlinear load-displacement function and (ii) generates designs having distributed compliance. We introduce a design parametrization that is conducive to geometric nonlinearities, enabling individual beam segments to vary their effective stiffness as the spring deforms. Key features of our method include (i) a branching network of compliant beams used for topology synthesis rather than a ground structure or a continuum model based design parametrization, (ii) curved beams without sudden changes in cross section, offering a more even stress distribution, and (iii) boundary conditions that impose both axial and bending loads on the compliant members and enable large rotations while minimizing bending stresses. To generate nonlinear spring designs, the design parametrization is implemented into a genetic algorithm, and the objective function evaluates spring designs based on the prescribed load-displacement function. The designs are analyzed using nonlinear finite element analysis. Three nonlinear spring examples are presented. Each has a unique prescribed load-displacement function, including a (i) “J-shaped,” (ii) “S-shaped,” and (iii) constant-force function. A fourth example reveals the methodology’s versatility by generating a large displacement linear spring. The results demonstrate the effectiveness of this generalized synthesis methodology for designing nonlinear springs for any given load-displacement function.

Robust Topology Optimization for Compliant Mechanisms Considering Uncertainty of Applied Loads

Abstract: In this study, a robust topology optimization method is proposed for compliant mechanisms, where the effect that variation of the input load direction has on the output displacement is considered. Variations are evaluated through a sensitivity-based robust optimization approach, with the variance evaluated using first-order derivatives. The robust objective function is defined as a combination of maximizing the output deformation under the mean input load and minimizing variation in the output deformation as the input load is varied, where variance due to changes in load can be obtained through mutual compliance and the presence of a pseudo load. For the topology optimization, a modified homogenization design method using the continuous approximation assumption of material distribution is adopted. The validity of the proposed method is confirmed with two compliant mechanism design problems. The effect that varying the input load direction has upon the obtained configurations is investigated by comparing these with deterministic optimum topology design results.

A Compliant Bistable Mechanism Design Incorporating Elastica Buckling Beam Theory and Pseudo-Rigid-Body Model

Abstract: In this work, a new compliant bistable mechanism design is introduced. The combined use of pseudo-rigid-body model (PRBM) and the Elastica buckling theory is presented for the first time to analyze the new design. This mechanism consists of the large deflecting straight beams, buckling beams, and a slider. The kinematic analysis of this new mechanism is studied, using nonlinear Elastica buckling beam theory, the PRBM of a large deflecting cantilever beam, the vector loop closure equations, and numerically solving nonlinear algebraic equations. A design method of the bistable mechanism in microdimensions is investigated by changing the relative stiffness of the flexible beams. The actuation force versus displacement characteristics of several cases is explored and the full simulation results of one of the cases are presented. This paper demonstrates the united application of the PRBM and the buckling Elastica solution for an original compliant mechanism kinematic analysis. New compliant mechanism designs are presented to highlight where such combined kinematic analysis is required.

Design of a Single-Acting Constant-Force Actuator Based on Dielectric Elastomers

Abstract: The interest in actuators based on dielectric elastomer films as a promising technology in robotic and mechatronic applications is increasing. The overall actuator performances are influenced by the design of both the active film and the film supporting frame. This paper presents a single-acting actuator, which is capable of supplying a constant force over a given range of motion. The actuator is obtained by coupling a rectangular film of silicone dielectric elastomer with a monolithic frame designed to suitably modify the force generated by the dielectric elastomer film. The frame is a fully compliant mechanism whose main structural parameters are calculated using a pseudo-rigid-body model and then verified by finite element analysis. Simulations show promising performance of the proposed actuator.

Stiffness Matrix of Compliant Parallel Mehanisms

Abstract: Starting from the definition of a stiffness matrix, the authors present the Cartesian stiffness matrix of parallel compliant mechanisms. The proposed formulation is more general than any other stiffness matrix found in the literature since it can take into account the stiffness of the passive joints and remains valid for large displacements. Then, the conservative property, the validity,and the positive definiteness of this matrix are discussed.

A New Compliant Mechanical Amplifier Based on a Symmetric Five-Bar Topology

Abstract: A mechanical amplifier is an important device, which together with a piezoelectric actuator can achieve motion with high resolution and long range. In this paper, a new topology based on a symmetric five-bar structure for displacement amplification is proposed, and a compliant mechanism is implemented for the amplifier. In short, the new mechanical amplifier is called a compliant mechanical amplifier (CMA). The proposed CMA can achieve large amplification ratio and high natural frequency, as opposed to the existing CMAs, in terms of topology. Detailed analysis with finite element method has further shown that a double symmetric beam five-bar structure using corner-filleted hinges can provide good performances compared with its counterpart, which is based on four-bar topology. Finally, experiments are conducted to give some validation of the theoretical analysis.

A six-DOF prismatic-spherical-spherical parallel compliant nanopositioner

Abstract: A nanopositioner using a 6-prismatic-spherical-spherical parallel (PSS) linked compliant mechanism driven by 6 multilayered piezoelectric actuators (PZT) is presented. Compared with a traditional Gough-Stewart platform in which each actuator was installed between the end effector and the base, this nanopositioner installed the PZT directly on the base to achieve much smaller mechanical loop, higher stiffness, faster response, and compactness. This nanopositioner consists of one fixed plate; three 2-PSS compliant mechanisms; and one end effector. The kinematics characteristics of the nanopositioner were analyzed through the pseudo-rigid-body model. The behavior of the compliant mechanism was intensively simulated by the finite element method (FEM). Tracking a 5 nm radius circle of the 15 times 15 times 5 cm3 prototype was experimentally demonstrated. The measurement results showed the nanopositioner achieved 8 mum travel with 5 nm resolutions and 200 murad rotation with 0.7 murad resolutions. The nanopositioner can be used to manipulate nano scale devices, fabricate nano components, or operate nano machines.

Design Optimization of a Controllable Camber Rotor Airfoil

Abstract: A conformable airfoil is proposed as an alternative to trailing-edge flaps used for active helicopter vibration reduction through high-frequency changes in camber. The design consists of several compliant mechanisms of predetermined topology that are placed serially within the airfoil along the chord, aft of the leading-edge spar. A shape optimization approach is used to design the compliant mechanisms, in which the objective is to maximize trailing-edge deflection while minimizing airfoil deflections due to aerodynamic loads. Solutions were obtained using a sequential linear programming method coupled with a finite element analysis. An optimized shape is predicted to achieve a trailing-edge deflection of ±6.0 mm or a ±4.6- deg equivalent flap deflection angle using the tip deflection objective. Results indicate that the deflection is dependent on the amount of passive material allowed and the objective function used. The aerodynamic loads are found to cause only small deformations in comparison with those caused by the actuation. Prototype fabrication and bench-top tests demonstrated that rotor airfoil camber is controllable using the proposed concept.

Evaluation and Design of Displacement-Amplifying Compliant Mechanisms for Sensor Applications

Abstract: Displacement-amplifying compliant mechanisms (DaCMs) reported in literature are widely used for actuator applications. This paper considers them for sensor applications that rely on displacement measurement, and proposes methods to evaluate and design such mechanisms. The motivation of this work is to increase the sensitivity of a micromachined capacitive accelerometer and a minute mechanical force sensor using DaCMs. A lumped spring-mass-lever (SML) model, which effectively captures the effects of appending a DaCM to a sensor, is introduced. This model is a generalization of the ubiquitously used spring-mass model for the case of an elastic body that has two points of interest—an input and an output. The SML model is shown to be useful in not only evaluating the suitability of an existing DaCM for a new application but also for designing a new DaCM. With the help of this model, we compare a number of DaCMs from literature and identify those that nearly meet the primary problem specifications. To obtain improved designs that also meet the secondary specifications, topology and size-optimization methods are used. For the two applications considered in this paper, we obtain a few new DaCM topologies, which are added to the catalog of DaCMs for future use. The spring-mass-lever model, the evaluation and design methods, and the catalog of DaCMs presented here are useful in other sensor and actuator applications

Robust Control of a Parallel- Kinematic Nanopositioner

Abstract: This paper presents the design, model identification, and control of a parallel-kinematic XYZ nanopositioning stage for general nanomanipulation and nanomanufacturing applications. The stage has a low degree-of-freedom monolithic parallel-kinematic mechanism featuring single-axis flexure hinges. The stage is driven by piezoelectric actuators, and its displacement is detected by capacitance gauges. The control loop is closed at the end effector instead of at each joint, so as to avoid calibration difficulties and guarantee high positioning accuracy. This design has strongly coupled dynamics with each actuator input producing in multiaxis motions. The nanopositioner is modeled as a multiple input and multiple output (MIMO) system, where the control design forms an important constituent in view of the strongly coupled dynamics. The dynamics that model the MIMO plant is identified by frequency domain and time-domain identification methods. The control design based on modem robust control theory that gives a high bandwidth closed loop nanopositioning system, which is robust to physical model uncertainties arising from flexure-based mechanisms, is presented. The bandwidth, resolution, and repeatability are characterized experimentally, which demonstrate the effectiveness of the robust control approach.

Stiffness research on a high-precision, large-workspace parallel mechanism with compliant joints

Abstract: Parallel-structure mechanisms, especially the non-backlash compliant parallel mechanisms, excel serial-structure ones in many indexes. This paper explores a novel six-strut compliant parallel mechanism based on the development of wide-range flexure hinges, and in this system the repeatability and resolution of sub-micron scale can be achieved over cubic centimeter motion range. The system stiffness, as a very important performance for compliant parallel mechanisms, directly influences the workspace, load-carrying capacity and driving-load capacity, etc. The system stiffness depends on the parallel mechanism's geometric dimensions and spatial layout, which is discussed in detail in this paper. The stiffness equation of individual flexure hinge is established firstly, and then the stiffness of the whole mechanism is modeled via assembling stiffness matrices and formulating constraint equations. Finally, the system stiffness influence plots are presented and discussed. The stiffness research on the six-strut compliant parallel mechanism provides further theoretical principles for designing and developing this kind of precision parallel devices.

A Material-Mask Overlay Strategy for Continuum Topology Optimization of Compliant Mechanisms Using Honeycomb Discretization

Abstract: This paper proposes novel honeycomb tessellation and material-mask overlay methods to obtain optimal single-material compliant topologies free from checkerboard and point-flexure pathologies. The presence of strain-free rotation regions in rectangular cell based discretization is identified to be a cardinal cause for appearance of such singularities. With each hexagonal cell sharing an edge with its neighboring cells, strain-free displacements are not permitted anywhere in the continuum. The new material assignment approach manipulates material within a subregion of cells as opposed to a single cell thereby reducing the number of variables making optimization efficient. Cells are allowed to get filled with only the chosen material or they can remain void. Optimal solutions obtained are free from intermediate material states and can be manufactured requiring no material interpretation and less postprocessing. Though the hexagonal cells do not allow strain-free rotations, some subregions undergoing large strain deformations can still be present within the design. The proposed procedure is illustrated using three classical examples in compliant mechanisms solved using genetic algorithm.

Design of Grip-and-Move Manipulators Using Symmetric Path Generating Compliant Mechanisms

Abstract: This paper presents the problem formulation and design of compliant grip-and-move manipulators. Each manipulator is composed of two identical path generating compliant mechanisms such that it can grip an object and convey it from one point to another. The integration of both gripping and moving behaviors within a simple mechanism is accomplished by the use of compliant mechanisms, which generate paths that are symmetric. The automated synthesis of these symmetric path generating mechanisms is by a structural topology optimization approach. The problem of topology optimization of continuum structures is solved using a multiobjective genetic algorithm coupled with a morphological representation of geometry that efficiently defines the variable structural geometry upon a finite element grid. A graph-theoretic chromosome encoding together with compatible crossover and mutation operators are then applied to form an effective evolutionary optimization procedure. Two designs have been created and are presented in this paper, and some concluding remarks and future work are put forward.

The Stiffness Model of Leaf-Type Isosceles-Trapezoidal Flexural Pivots

Abstract: A leaf-type isosceles-trapezoidal flexural pivot can be of great practical use for designing compliant mechanisms The analysis of load-deflection behavior for such a pivot is essential to the study of the mechanisms that are comprised of them Based on the analysis of a single special loaded leaf segment, a pseudo-rigid-body four-bar model is proposed The four-bar model is further simplified to a pin-joint model for some simple applications The accuracy of both models is demonstrated by comparing results to those of nonlinear finite element analysis At last, the two models are applied to analyze the cartwheel hinge as an example

Modal Synthesis of Flexible Mechanisms for Airfoil Shape Control

Abstract: The use of 'compliant' or flexible mechanisms constitutes a very promising option for the successful realization of shape-adaptable airfoil structures. Achieving large deformations by exploiting structural flexibility instead of employing conventional mechanisms with moveable parts offers several advantages: absence of backlash and wear, no need for lubrication, reduced noise, smooth geometry changes, a lighter design, and reduced manufacturing costs. As a counterpart, compliant systems are more complex to analyze and design due to their inherent coupled behavior. Established design procedures, developed in the framework of kinematics design, are of limited use for application to shape-adaptable structures due to differences in requirement priorities. This study presents a novel synthesis procedure for compliant shape-adaptable airfoils. Initially devised for the so-called belt-rib airfoils, the procedure can be extended to the general case of compliant airfoils with an external flexible skin (optionally reinforced by frames) and a system of internal stiffeners. After the description of the core synthesis algorithm, which is based on a modal approach, its integration in a global design procedure is discussed. Application to the case of a belt-rib airfoil is then considered. The compliant structure resulting from the procedure combines the characteristic qualities of a compliant system (smooth deformation pattern, absence of moveable parts, low weight) with the low load-dependence of kinematics which is typical of conventional mechanisms.

Analysis and Design of Linear Parallel Compliant Stage for Ultra-precision Motion Based on 4-PP Flexural joint Mechanism

Abstract: A linear parallel compliant XY-stage for ultra-precision motion is proposed. The prismatic joints of the compliant stage are implemented by three kinds of flexural joints. Among the flexural joints, a modified double compound linear flexural joint has the function of linear motion guide and displacement amplification so that the compliant mechanism has compact structure. The parallel linear compliant mechanism is analyzed, designed, machined by wire electric discharge machining, and then integrated with stack type piezoelectric elements for driving forces and capacitance-type displacement sensors into an ultra-precision stage for 2-DOF linear motions. Experiments demonstrate the characteristics of the ultra-precision stage implemented by the compliant mechanism.

Towards the Design of a Statically Balanced Compliant Laparoscopic Grasper Using Topology Optimization

Abstract: This paper presents the design of a grasping instrument for minimally invasive surgery. Due to its small dimensions a compliant mechanism seems promising. To obtain force feedback, the positive stiffness of the compliant grasper must be statically balanced by a negative-stiffness compensation mechanism. For the design of compliant mechanisms, topology optimization can be used. The goal of this paper is to investigate the applicability of topology optimization to the design of a compliant laparoscopic grasper and particularly a compliant negative-stiffness compensation mechanism. In this study, the problem is subdivided in the grasper part and the compensation part. In the grasper part the deflection at the tip of the grasper is optimized. This results in a design that has a virtually linear force-displacement characteristic that forms the input for the compensation part. In the compensation part the difference between the force-displacement characteristic of the grasper part and the characteristic of the compensation part is minimized. An optimization problem is formulated enabling a pre-stress to be incorporated, which is required to obtain the negative stiffness in the compensation part. We can conclude that topology optimization is a promising approach in the field of statically balanced compliant mechanism design, even though there is great scope improvement of the method.Copyright © 2008 by ASME

Towards generating diverse topologies of path tracing compliant mechanisms using a local search based multi-objective genetic algorithm procedure

Abstract: A new bi-objective optimization problem is formulated for generating the diverse topologies of compliant mechanisms tracing a user-defined path Motivation behind the present study is to generate the compliant mechanisms which perform the same task of tracing a prescribed trajectory near minimum-weight solution Therefore, the constraint are imposed at each precision point representing a prescribed path for accomplishing the tracing task An additional constraint on stress is also included for the feasible designs The study starts with a single objective analysis of minimum-weight of compliant mechanism and the obtained topology is referred as the reference design Thereafter, a bi-objective optimization problem is solved by considering the objectives as minimization of weight of structure and maximization of diversity of structure with respect to the reference design Here, the diversity is evaluated by finding the dissimilarity in the bit value at each gene position of the binary strings of the reference design and a structure evolved from the GA population A local search based multi-objective genetic algorithm (MOGA) optimization procedure is used in which the NSGA-II is used as a global search and optimization algorithm A parallel computing is employed in the study for evaluating nonlinear geometric FE analysis and also for the NSGA-II operations After the NSGA-II run, a few solutions are selected from the non-dominated front and the local search is applied on them With the help of a given optimization procedure, compliant mechanism designs tracing curvilinear and straight line trajectories are evolved and presented in the study In both examples, compliant mechanisms are designed to have any arbitrary support and loading regions

Design, implementation, and control of a six-axis compliant stage.

Abstract: This paper presents the development of a new compact six-axis compliant stage employing piezoelectric actuators to achieve six-axis actuation with nanometer resolution. The integration of direct metrology in the object space, based on real-time visual feedback, enables high-precision motion control. In order to achieve greater motion range, the simple and compact decoupled mechanical structure utilizes two-tap displacement amplifiers for in-plane motion and semibridge amplifiers for out-of-plane motion. The kinematic analysis of the stage is presented. Laterally sampled white light interferometry was implemented to measure the out-of-plane motion of the stage, and a measurement model associated with the designed target patterns is developed to estimate the in-plane motion in real time. Together, they form a visual tracking system and are integrated with the six-axis compliant stage to realize precision six-axis real-time visual servo-control. Experimental results demonstrate that the six-axis compliant stage has the motion range of 77.42 microm, 67.45 microm, 24.56 microm, 0.93 mrad, 0.95 mrad, and 3.10 mrad, and the resolution of +/-5 nm, +/-8 nm, +/-10 nm, +/-10 murad, +/-10 murad, and +/-20 murad for x-axis, y-axis, and z-axis translation and rotation, respectively.

A Study of Joints Suitable for Lamina Emergent Mechanisms

Abstract: One way to save space and reduce cost in a competitive environment is to use ortho-planar compliant mechanisms which can be made from sheets of material, or lamina emergent mechanisms (LEMs) One major challenge associated with LEM design, however, is creating joints with the desired motion characteristics, especially where complex spatial mechanism topologies are required This paper presents some important considerations for designing joints for LEMs A technique commonly used in robotics, using serial chains of revolute and prismatic joints to approximate the motion of complex joints, is presented for use in lamina emergent mechanisms Important considerations such as linkage configuration and simple prototyping are also discussedCopyright © 2008 by ASME