Showing papers on "Compliant mechanism published in 2014"

Multiple-Material Topology Optimization of Compliant Mechanisms Created Via PolyJet Three-Dimensional Printing

Abstract: Compliant mechanisms are able to transfer motion, force, and energy using a monolithic structure without discrete hinge elements. The geometric design freedoms and multimaterial capability offered by the PolyJet 3D printing process enables the fabrication of compliant mechanisms with optimized topology. The inclusion of multiple materials in the topology optimization process has the potential to eliminate the narrow, weak, hingelike sections that are often present in single-material compliant mechanisms and also allow for greater magnitude deflections. In this paper, the authors propose a design and fabrication process for the realization of 3-phase, multiple-material compliant mechanisms. The process is tested on a 2D compliant force inverter. Experimental and numerical performance of the resulting 3-phase inverter is compared against a standard 2-phase design.

Dynamic Simulation of Soft Multimaterial 3D-Printed Objects

Abstract: This article describes a 2D and 3D simulation engine that quantitatively models the statics, dynamics, and nonlinear deformation of heterogeneous soft bodies in a computationally efficient manner. There is a large body of work simulating compliant mechanisms. These normally assume small deformations with homogeneous material properties actuated with external forces. There is also a large body of research on physically based deformable objects for applications in computer graphics with the purpose of generating realistic appearances at the expense of accuracy. Here we present a simulation framework in which an object may be composed of any number of interspersed materials with varying properties (stiffness, density, Poisson's ratio, thermal expansion coefficient, and friction coefficients) to enable true heterogeneous multimaterial simulation. Collisions are handled to prevent self-penetration due to large deformation, which also allows multiple bodies to interact. A volumetric actuation method is...

Development and Active Disturbance Rejection Control of a Compliant Micro-/Nanopositioning Piezostage With Dual Mode

Abstract: In the atomic force microscope (AFM) scanning system, the piezoscanner is significant in realizing high-performance tasks. To cater to this demand, a novel compliant two-degrees-of-freedom (2-DOF) micro-/nanopositioning stage with modified lever displacement amplifiers is proposed in this paper, which can be selected to work in dual modes. Moreover, the modified double four-bar P (P denotes prismatic) joints are adopted in designing the flexible limbs. The established models for the mechanical performance evaluation in terms of kinetostatics, dynamics, and workspace are validated by finite-element analysis. After a series of dimension optimizations carried out via particle swarm optimization algorithm, a novel active disturbance rejection controller, including the components of nonlinearity tracking differentiator, extended state observer, and nonlinear state error feedback, is designed for automatically estimating and suppressing the plant uncertainties arising from the hysteresis nonlinearity, creep effect, sensor noises, and other unknown disturbances. The closed-loop control results based on simulation and prototype indicate that the two working natural frequencies of the proposed stage are approximated to be 805.19 and 811.31 Hz, the amplification ratio in two axes is about 4.2, and the workspace is around 120 ×120 μm2, while the cross-coupling between the two axes is kept within 2%. All of the results indicate that the developed micro-/nanopositioning system has a good property for high-performance AFM scanning.

Design and testing of a selectively compliant underactuated hand

Abstract: Motivated by the requirements of mobile manipulation, a compliant underactuated hand, capable of locking individual joints, has been developed. Locking is accomplished with electrostatic brakes in the joints and significantly increases the maximum pullout forces for power grasps. In addition, by locking and unlocking joints, the hand can adopt configurations and grasp sequences that would otherwise require a fully actuated solution. Other features of the hand include an integrated sensing suite that uses a common transduction technology on flexible printed circuits for tactile and proprioceptive sensing. The hand is analyzed using a three-dimensional rigid body analysis package with efficient simulation of compliant mechanisms and contacts with friction. This package allows one to evaluate design tradeoffs among link lengths, required tendon tensions, spring stiffnesses and braking requirements to grasp and hold a wide range of objects. Results of grasping and pullout tests confirm the utility of the simulations.

DNA origami compliant nanostructures with tunable mechanical properties.

Abstract: DNA origami enables fabrication of precise nanostructures by programming the self-assembly of DNA. While this approach has been used to make a variety of complex 2D and 3D objects, the mechanical functionality of these structures is limited due to their rigid nature. We explore the fabrication of deformable, or compliant, objects to establish a framework for mechanically functional nanostructures. This compliant design approach is used in macroscopic engineering to make devices including sensors, actuators, and robots. We build compliant nanostructures by utilizing the entropic elasticity of single-stranded DNA (ssDNA) to locally bend bundles of double-stranded DNA into bent geometries whose curvature and mechanical properties can be tuned by controlling the length of ssDNA strands. We demonstrate an ability to achieve a wide range of geometries by adjusting a few strands in the nanostructure design. We further developed a mechanical model to predict both geometry and mechanical properties of our compliant nanostructures that agrees well with experiments. Our results provide a basis for the design of mechanically functional DNA origami devices and materials.

Topology optimization of fail-safe structures using a simplified local damage model

Abstract: Topology optimization of mechanical structures often leads to efficient designs which resemble statically determinate structures. These economical structures are especially vulnerable to local loss of stiffness due to material failure. This paper therefore addresses local failure of continuum structures in topology optimization in order to design fail-safe structures which remain operable in a damaged state. A simplified model for local failure in continuum structures is adopted in the robust approach. The complex phenomenon of local failure is modeled by removal of material stiffness in patches with a fixed shape. The damage scenarios are taken into account by means of a minimax formulation of the optimization problem which minimizes the worst case performance. The detrimental influence of local failure on the nominal design is demonstrated in two representative examples: a cantilever beam optimized for minimum compliance and a compliant mechanism. The robust approach is applied successfully in the design of fail-safe alternatives for the structures in these examples.

Design and Smooth Position/Force Switching Control of a Miniature Gripper for Automated Microhandling

Abstract: Automated microhandling tasks demand miniature grippers equipped with position and force sensors to execute reliable operations. This paper presents the design, implementation, and control of a piezoelectrically actuated compliant gripper with combined position and force monitoring/control capabilities. The gripper structure is devised based on a compliant rotary bearing mechanism with the displacement amplification lever, which endows a simplified architecture than the existing parallelogram-based ones. Moreover, the challenge of achieving a smooth transition between the position and force switching control is addressed by means of a new incremental control scheme. Precision control under the influence of hysteretic nonlinearity is guaranteed by a discrete sliding-mode control algorithm. The scheme is implemented with an field-programmable gate array (FPGA) platform. Experimental investigations are undertaken to verify the effectiveness of the gripper system by executing grasp-hold-release operations of a micro copper wire. The results confirm that the proposed incremental-based switching control outperforms conventional approach in terms of position/force regulation accuracy and operation time.

Dipteran-Insect-Inspired Thoracic Mechanism With Nonlinear Stiffness to Save Inertial Power of Flapping-Wing Flight

Abstract: This paper presents the design, analysis, and characterization of a compliant thoracic mechanism that saves inertial power for flapping-wing micro air vehicles. Lightweight polyimide film hinges were previously integrated into a compliant flapping-wing mechanism to reduce friction. However, these were not stiff enough to fully recover wing's inertial energy into elastic energy. To store adequate elastic energy using film hinges, we develop a compliant thoracic mechanism with nonlinear stiffness characteristics by mimicking a Dipteran insect's flight thorax. This thoracic mechanism consists of rigid plates and polyimide film hinges connected to form a closed shell structure. It has a nonlinearly increasing stiffness so that it can slow the wings down rapidly toward the end stroke and subsequently help reverse the wings. It demonstrates almost full recovery of inertial power for 10-cm span flapping wings up to 25 Hz. As a result, it only expends 2% of the total mechanical power on inertial power at 25 Hz. In contrast, the rigid-body mechanism with no elastic storage expends 23% of the total mechanical power on inertial power when the same wings beat at the same frequency. With the capability of elastic energy storage, this compliant thoracic mechanism saves power expenditure ranging from 20 up to 30% to produce the same thrust, in comparison with the rigid-body flapping mechanism. This study shows that power saving is effective only if elastic energy storage is well tuned to recover the wing inertial power.

Evaluating Compliant Hinge Geometries for Origami-Inspired Mechanisms

Abstract: Origami-inspired design is an emerging field capable of producing compact and efficient designs. Compliant hinges are proposed as a way to replicate the folding motion of paper when using non-paper materials. Compliant hinges function as surrogate folds and can be defined as localized reduction of stiffness. The purpose of this paper is to organize and evaluate selected surrogate folds for use in compliant mechanisms. These surrogate folds are characterized based on the desired motion as well as motions typically considered parasitic. Additionally the surrogate folds’ ability to rotate through large deflections and their stability of center of rotation are evaluated. Existing surrogate folds are reviewed and closed-form solutions presented. A diagram intended as a straightforward design guide is presented. Areas for potential development in the surrogate fold design space are noted.Copyright © 2014 by ASME

Topological design of compliant smart structures with embedded movable actuators

Abstract: In the optimal configuration design of piezoelectric smart structures, it is favorable to use actuation elements with certain predefined geometries from the viewpoint of manufacturability of fragile piezoelectric ceramics in practical applications. However, preserving the exact shape of these embedded actuators and tracking their dynamic motions presents a more challenging research task than merely allowing them to take arbitrary shapes. This paper proposes an integrated topology optimization method for the systematic design of compliant smart structures with embedded movable PZT (lead zirconate titanate) actuators. Compared with most existing studies, which either optimize positions/sizes of the actuators in a given host structure or design the host structure with pre-determined actuator locations, the proposed method simultaneously optimizes the positions of the movable PZT actuators and the topology of the host structure, typically a compliant mechanism for amplifying the small strain stroke. A combined topological description model is employed in the optimization, where the level set model is used to track the movements of the PZT actuators and the independent point-wise density interpolation (iPDI) approach is utilized to search for the optimal topology of the host structure. Furthermore, we define an integral-type constraint function to prevent overlaps between the PZT actuators and between the actuators and the external boundaries of the design domain. Such a constraint provides a unified and explicit mathematical statement of the non-overlap condition for any number of arbitrarily shaped embedded actuators. Several numerical examples are used to demonstrate the effectiveness of the proposed optimization method.

Compliant Joints Suitable for Use as Surrogate Folds

Abstract: Compliant Joints Suitable for Use as Surrogate Folds Isaac L. Delimont Department of Mechanical Engineering, BYU Master of Science Origami-inspired design is an emerging field capable of producing compact and efficient designs. The object of a surrogate fold is to provide a fold-like motion in a non-paper material without undergoing yielding. Compliant mechanisms provide a means to achieve these objectives as large deflections are achieved. The purpose of this thesis is to present a summary of existing compliant joints suitable for use as surrogate folds. In doing so, motions are characterized which no existing compliant joint provides. A series of compliant joints is proposed which provides many of these motions. The possibility of patterning compliant joints to form an array is discussed. Arrays capable of producing interesting motions are noted.

Material selection for elastic energy absorption in origami-inspired compliant corrugations

Abstract: Elastic absorption of kinetic energy and distribution of impact forces are required in many applications. Recent attention to the potential for using origami in engineering may provide new methods for energy absorption and force distribution. A three-stage strategy is presented for selecting materials for such origami-inspired designs that can deform to achieve a desired motion without yielding, absorb elastic strain energy, and be lightweight or cost effective. Two material indices are derived to meet these requirements based on compliant mechanism theory. Finite element analysis is used to investigate the effects of the material stiffness in the Miura-ori tessellation on its energy absorption and force distribution characteristics compared with a triangular wave corrugation. An example is presented of how the method can be used to select a material for a general energy absorption application of the Miura-ori. Whereas the focus of this study is the Miura-ori tessellation, the methods developed can be applied to other tessellated patterns used in energy absorbing or force distribution applications.

A strain based topology optimization method for compliant mechanism design

Abstract: The Energy based topology optimization method has been used in the design of compliant mechanisms for many years. Although many successful examples from the energy based topology optimization method have been presented, optimized configurations of these designs are often very similar to their rigid linkage counterparts; except using compliant joints in place of rigid links. These complaint joints will endure large strain under the applied forces in order to perform the specified motions which are very undesirable in a compliant mechanism design. In this paper, a strain based topology optimization method is proposed to avoid a localized high strain of the compliant mechanism design, which is one of the drawbacks using strain energy formulation. Therefore, instead of minimizing the strain energy for structural rigidity, a global effective strain function is minimized. This is done in order to distribute the strain within the entire mechanism while maximizing the structural rigidity. Furthermore, the physical programming method is adopted to accommodate both flexibility and rigidity design objectives. Design examples from both the strain energy based topology optimization and the strain based method are presented and discussed.

A novel analytical model for flexure-based proportion compliant mechanisms

Abstract: This paper proposes a novel analytical model for flexure-based proportion compliant mechanisms The displacement and stiffness calculations of such flexure-based compliant mechanisms are formulated based on the principle of virtual work and pseudo rigid body model (PRBM) According to the theory and method, a set of closed-form equations are deduced in this paper, which incorporate the stiffness characteristics of each flexure hinge, together with the other geometric and material properties of the compliant mechanism The rotation center point for a corner-filleted flexure hinge is investigated based on the finite element analysis (FEA) and PRBM An empirical equation for the rotational angle is fitted in this paper in order to calculate accurately the position of the end-point of the flexure hinge The displacement proportion equation for such mechanisms is derived according to the new approach Combining the new proposed design equation and the existed stiffness equation, a new proportion compliant mechanism with corner-filleted flexure hinges is designed by means of the least squares optimization The designed models are verified by finite element analysis

Linear Variable-Stiffness Mechanisms Based on Preloaded Curved Beams

Abstract: A machine with an internal variable-stiffness mechanism can adapt its output force to the working environment. In the literature, linear variable-stiffness mechanisms (LVSMs) are rarer than those producing rotary motion. This paper presents the design of a class of novel LVSMs. The idea is to parallel connect two lateral curved beams with an axial spring. Through preload adjustment of the curved beams, the output force-todisplacement curves can exhibit different stiffness. The merit of the proposed LVSMs is that very large-stiffness variation can be achieved in a compact space. The stiffness can even be tuned to zero by assigning the appropriate stiffness to the axial spring. LVSMs with pinned curved beams and fixed curved beams are investigated. To achieve the largest stiffness variation with sufficient linearity, the effects of various parameters on the force curves are discussed. Techniques to scale an LVSM and change the equilibrium position are introduced to increase the usefulness of the proposed design. Finally, the LVSMs are experimentally verified through prototypes. [DOI: 10.1115/1.4028705]

New Methods for Developing and Manufacturing Compliant Mechanisms Utilizing Bulk Metallic Glass

Abstract: Compliant mechanisms rely on the elastic bending of thin members to generate motion. In the paper by Homer, et al., bulk metallic glasses (BMGs) are shown to have an optimal combination of mechanical properties and processing ability, making them ideal for complex, low-cost compliant mechanisms.

A multi-objective method of hinge-free compliant mechanism optimization

Abstract: A new multi-objective formulation for topology synthesis of hinge-free compliant mechanisms is presented based on the SIMP method. A weighted sum formed objective function is developed by taking into consideration the input and output mean compliances. The weighting factors are set based on the information that is obtained from the previous iteration and automatically updated with each optimization iteration step. Shape sensitivity analysis is addressed. Some numerical examples are presented to illustrate the validity of the proposed method.

Studies about the use of semicircular beams as hinges in large deflection planar compliant mechanisms

Abstract: Conventional hinge designs in planar compliant mechanisms have a limited deformation range because of the high stresses induced during deflection. To improve the range of motion of these mechanisms, hinges that allow for large displacement are highly desirable. This paper explores the use of curved beams as large displacement hinges in planar compliant mechanisms. To facilitate design, analytic expressions that predict deflections under different types of loads are introduced. These expressions are used in pseudo rigid link models of compliant mechanism designs. Predictions made by the analytic expressions are compared with the results of FEA simulations. To validate the proposed models, two planar compliant mechanism designs were prepared and experimental measurements of deflections under loads were made. Overall, results showed that analytic models and FEA predictions lie within 10% of experimental data for the planar mechanism geometry in which pseudo rigid motion models apply. FEA models of the second case, a more complex mechanism, make predictions that lie within 15% of experimental measurements. Results and ways to improve accuracy of models and designs are discussed at the end of the article.

An Engineering Method for Comparing Selectively Compliant Joints in Robotic Structures

Abstract: Large displacement compliant joints can substitute traditional kinematic pairs in robotic articulated structures for increasing ease-of-assembly, robustness, and safety. Nonetheless, besides their limited motion capabilities, compliant joints might be subjected to undesired spatial deformations which can deteriorate the system stability and performance whenever a low number of control inputs is available. In all these cases, it is convenient to select/design joint morphologies which enable a selectively compliant behavior, i.e., a low stiffness along a single desired direction. Within this context, this paper outlines an engineering method for quantifying the joint’s selective compliance by means of local and global performance indices. The approach is validated by comparing two beam-like flexures whose analytic solution is known from the literature. Finally, two joint morphologies, previously employed in the fabrication of robotic/prosthetic hands, are critically compared on the basis of the proposed criteria.

Level Set-Based Topology Optimization of Hinge-Free Compliant Mechanisms Using a Two-Step Elastic Modeling Method

Abstract: This paper presents a two-step elastic modeling (TsEM) method for the topology optimization of compliant mechanisms aimed at eliminating de facto hinges. Based on the TsEM method, an alternative formulation is developed and incorporated with the level set method. An efficient algorithm is developed to solve the level set-based optimization problem for improving the computational efficiency. Two widely studied numerical examples are performed to demonstrate the validity of the proposed method. The proposed formulation can prevent hinges from occurring in the resulting mechanisms. Further, the proposed optimization algorithm can yield fewer design iterations and thus it can improve the overall computational efficiency.

Pseudo-rigid-body model for corrugated cantilever beam used in compliant mechanisms

Abstract: Common compliant joints generally have limited range of motion, reduced fatigue life and high stress concentration. To overcome these shortcomings, periodically corrugated cantilever beam is applied to design compliant joints. Basic corrugated beam unit is modeled by using pseudo-rigid-body method. The trajectory and deformation behavior of periodically corrugated cantilever beam are estimated by the transformation of coordinate and superposition of the deformation of corrugated beam units. Finite element analysis(FEA) is carried out on corrugated cantilever beam to estimate the accuracy of the pseudo-rigid-body model. Results show that the kinetostatic behaviors obtained by this method, which has a relative error less than 6%, has good applicability and corrugated cantilever beam has the characteristics of a large range of motion and high mechanical strength. The corrugated cantilever beam is then applied to design a flexible rotational joint to obtain a larger angle output. The paper proposes a pseudo-rigid-body model for corrugated cantilever beam and designed a flexible rotational joint with large angle output.

Numerical simulation and experimental investigation of a topologically optimized compliant microgripper

Abstract: In this research work, the compliant based microgripper is developed and the performance of the microgripper is studied through numerical simulation and experiential techniques Conceptual design of microgripper is developed through topology optimization which is logical, authenticate and effortless among other mechanism design methods such as Mechanism synthesis, Pseudo Rigid Body Model (PRBM) and inverse method In conceptual design of microgripper, node to node connections were developed and show the hinge locations of the mechanism These locations were replaced by introducing suitable flexure hinges The effect of flexure hinges at the node-to-node contact regions need to be analyzed for its critical geometric parameter The important critical geometric parameter of flexure hinges are varied and analyzed through Finite Element Method (FEM) and experimental studies In experimental technique, Shape Memory Alloy (SMA) wire is employed to actuate the microgripper Equivalent rigid body model of the mechanism using Graphical Position Analysis (GPA) to the compliant mechanism is developed for comparing the output displacement

Adaptive neuro-fuzzy prediction of grasping object weight for passively compliant gripper

Abstract: The development of universal grippers able to pick up unfamiliar objects of widely varying shapes and surfaces is a very challenging task. Passively compliant underactuated mechanisms are one way to obtain the gripper which could accommodate to any irregular and sensitive grasping objects. The purpose of the underactuation is to use the power of one actuator to drive the open and close motion of the gripper. The fully compliant mechanism has multiple degrees of freedom and can be considered as an underactuated mechanism. This paper presents a new design of the adaptive underactuated compliant gripper with distributed compliance. The optimal topology of the gripper structure was obtained by iterative finite element method (FEM) optimization procedure. The main points of this paper are in explanation of a new sensing capability of the gripper for grasping and lifting up the gripping objects. Since the sensor stress depends on weight of the grasping object it is appropriate to establish a prediction model for estimation of the grasping object weight in relation to sensor stress. A soft computing based prediction model was developed. In this study an adaptive neuro-fuzzy inference system (ANFIS) was used as soft computing methodology to conduct prediction of the grasping objects weight. The training and checking data for the ANFIS network were obtained by FEM simulations.

Improving the Sensitivity and Bandwidth of In-Plane Capacitive Microaccelerometers Using Compliant Mechanical Amplifiers

Abstract: This paper presents a method to enhance both the sensitivity and bandwidth of in-plane capacitive micromachined accelerometers by using compliant mechanical amplifiers, and thus obviating the compromise between the sensitivity and bandwidth. Here, we compare one of the most sensitive single-axis capacitive accelerometers and another with large resonant frequency reported in the literature with the modified designs that include displacement-amplifying compliant mechanisms (DaCMs) occupying the same footprint and under identical conditions. We show that 62% improvement in sensitivity and 34% improvement in bandwidth in the former, and 27% and 25% in the latter can be achieved. Also presented here is a dual-axis accelerometer that uses a suspension that decouples and amplifies the displacements along the two in-plane orthogonal axes. The new design was microfabricated, packaged, and tested. The device is 25-mu m thick with the interfinger gap as large as 4 m. Despite the simplicity of the microfabrication process, the measured axial sensitivity (static) of about 0.58 V/g for both the axes was achieved with a cross-axis sensitivity of less than +/- 2%. The measured natural frequency along the two in-plane axes was 920 Hz. Displacement amplification of 6.2 was obtained using the DaCMs in the dual-axis accelerometer. 2013-0083]

ARES, a variable stiffness actuator with embedded force sensor for the ATLAS exoskeleton

Abstract: Purpose – The purpose of this study is to present a variable stiffness actuator, one of whose main features is that the compliant elements simultaneously allow measuring of the torque exerted by the joint. Conceived as a force-controlled actuator, this actuator with Adjustable Rigidity and Embedded Sensor (ARES) is intended to be implemented in the knee of the ATLAS exoskeleton for children to allow the exploitation of the intrinsic dynamic during the locomotion cycle. Design/methodology/approach – A set of simulations were performed to evaluate the behavior of the actuator mechanism and a prototype of the variable impedance actuator was incorporated into the exoskeleton’s knee and evaluations of the torque measurements capabilities along with the rigidity adjustments were made. Findings – Mass and inertia of the actuator are minimized by the compact design and the utilization of the different component for more than one utility. By a proper match of the compliance of the joint and the performed task, goo...