Showing papers on "Compliant mechanism published in 2019"

Design and Fabrication of a 3-D Printed Metallic Flexible Joint for Snake-Like Surgical Robot

Abstract: Snake-like robots have numerous applications in minimally invasive surgery. One important research topic of snake-like robots is the flexible joint mechanism and its actuation. This letter describes the design and fabrication of a new type of flexible joint mechanism that is enabled by metal powder bed additive manufacturing technique. Kinematics and static models of the flexible joint are presented, which can help in designing and controlling the flexible joint. As a compliant mechanism, the fatigue characteristics of the flexible joint is investigated. Finite element analysis (FEA) is performed aiming for optimizing the design process. In the experiment section, model estimation, FEA, and experimental validation are conducted for further understanding the characteristics of the flexible joint. An example design that can survive after 100 000 full loading cycles is demonstrated. Finally, different design variations of the proposed method and a multi-section flexible endoscope using the proposed design are introduced. The proposed flexible joint has the potential not only in reducing the cost of manufacturing and assembling a snake-like surgical robot, but also benefits for developing of more sophisticated three-dimensional snake robotic structure that has an optimized space for embedded sensing and actuation.

Overhang constraint for topology optimization of self-supported compliant mechanisms considering additive manufacturing

Abstract: This work presents a computational procedure for direct integration of Topology Optimization and Additive Manufacturing (AM) technologies for compliant mechanisms design. Many topologically optimized geometries present manufacturing problems derived from the lack of self-supporting capacities and require sacrificial support material for 3D printing. The proposed strategy introduces a novel overhang constraint to control the amount of sacrificial support material required for additive manufacturing of compliant mechanisms. This overhang constraint is defined as the ratio between the value of self supported contours and the total amount of admissible and inadmissible contours, and is computed by an edge detection algorithm known as the Smallest Univalue Segment Assimilating Nucleus, that analyzes the geometry of the model for locating contours and computes their inclination and orientation. The proposed algorithm has been implemented as part of a software for computer aided design and several benchmark examples have been used to demonstrate the capacities of the approach.

Design and Testing of a Novel 2-DOF Compound Constant-Force Parallel Gripper

Abstract: This paper presents the design and testing of a novel flexure-based compliant parallel gripper with compound constant-force mechanism. One uniqueness of the microgripper lies in that it achieves two-degree-of-freedom (2-DOF) independent constant-force parallel grasping operations. In each direction, the grasping is executed along with active and passive constant-force properties. The passive constant-force property eliminates the use of force control while the active constant-force enlarges the grasping range by reducing the required driving force. Besides, the passive constant-force property can protect the grasped object from overloading. The parallel-kinematic flexure mechanism design enables nearly decoupled operations in 2-DOF manipulation. Analytical modeling of the microgripper mechanism is carried out based on pseudo-rigid-body method and elliptic integral approach, which is verified by conducting simulation study with nonlinear finite-element analysis (FEA). Parametric study is conducted to investigate the influence of dominant design variable on the microgripper performance. To demonstrate the performance of the gripper, a prototype is fabricated by 3D printer. Experimental results reveal that the devised microgripper owns a good decoupling performance and constant-force property in parallel grasping operation.

A PZT Actuated 6-DOF Positioning System for Space Optics Alignment

Abstract: Due to limitations in the fabrication technology, the large aperture space optical mirror is always spliced into several small segments rather than fabricated monolithically. To guarantee the imaging quality of the system, each segment needs to be aligned at micron-level precision with millimeter-level range. For this purpose, a PZT actuated six-axis high-precision positioning system, which consists of three serially connected parallel mechanisms is proposed in this article. Compared with previous 6-DOF positioning solutions, such as a Stewart platform, the proposed design features a relatively compact structure and straightforward kinematics. To realize long stroke and fine resolution simultaneously, bridge-type amplifiers are employed to enhance the stroke of the PZT actuation, and the flexure hinges are utilized to eliminate friction and backlash. The performance of the amplifier under two kinds of external loads are analyzed so that the amplifiers could be designed according to the application conditions. Furthermore, it can be found that the displacement sensors must be employed at the output end of the actuation module to eliminate the input coupling that commonly exists in the compliant mechanisms. The feasibility of the design is validated by finite-element analysis and experiment study. The maximum stroke is 2.1 mm in the Z -axis, and the finest resolution is 0.5 μ m in X - and Y -axis.

Kinetostatic and dynamic analyses of planar compliant mechanisms via a two-port dynamic stiffness model

Abstract: Serial-parallel configurations are widely designed in compliant mechanisms. In this paper, the transfer matrix method is combined with D'Alembert's principle to develop a two-port dynamic stiffness model for analyzing the kinetostatics and dynamics of complex compliant mechanisms with serial-parallel configurations. In detail, two kinds of improved transfer matrices for parallel sub-chains are derived in a unified form by summarizing the common serial-parallel substructures in compliant mechanisms. Then, a two-port dynamic stiffness model describing the frequency-dependent input and output force-displacement relationship of compliant mechanisms is established. Based on the two-port dynamic stiffness model, procedures for solving the static and dynamic performances of compliant mechanisms are presented. The proposed approach is demonstrated by calculating the displacement amplification ratio, input/output stiffness, natural frequencies and forced dynamic response of two typical precision flexure manipulators. The advantage of the proposed approach lies in its capability to describe the simultaneous kinetostatics and dynamics for a large class of serial-parallel configurations with very few degrees of freedom (DOFs), differing from the previous Lagrange-based dynamic modeling methods in the context of compliant mechanisms and should be of interest to designers.

A CAD/CAE integration framework for analyzing and designing spatial compliant mechanisms via pseudo-rigid-body methods

Abstract: Compliant Mechanisms (CMs) are currently employed in several engineering applications requiring high precision and reduced number of parts For a given mechanism topology, CM analysis and synthesis may be developed resorting to the Pseudo–Rigid Body (PRB) method, in which the behavior of flexible members is approximated via a series of rigid links connected by spring-loaded kinematic pairs From a CM analysis standpoint, the applicability of a generic PRB model requires the determination of the kinematic pairs’ location and the stiffness of a set of generalized springs In parallel, from a design standpoint, a PRB model representing the kinetostatic behavior of a flexible system should allow to compute the flexures’ characteristics providing the desired compliance In light of these considerations, this paper describes a Computer-Aided Design/Engineering (CAD/CAE) framework for the automatic derivation of accurate PRB model parameters, on one hand, and for the shape optimization of complex-shape flexures comprising out-of-plane displacements and distributed compliance The method leverages on the modelling and simulation capabilities of a parametric CAD (ie PTC Creo) seamlessly connected to a CAE tool (ie RecurDyn), which provides built-in functions for modelling the motion of flexible members The method is initially validated on an elementary case study taken from the literature Then, an industrial case study, which consists of a spatial crank mechanism connected to a fully-compliant four-bar linkage is discussed At first, an initial sub-optimal design is considered and its PRB representation is automatically determined Secondly, on the basis of the PRB model, several improved design alternatives are simulated Finally, the most promising design solution is selected and the dimensions of a flexure with non-trivial shape (ie hybrid flexure) is computed This technique, which combines reliable numerical results to the visual insight of CAD/CAE tools, may be particularly useful for analyzing/designing spatial CMs composed of complex flexure topologies

Computational Synthesis of Large Deformation Compliant Mechanisms Undergoing Self and Mutual Contact

Abstract: Topologies of large deformation Contact-aided Compliant Mechanisms (CCMs), with self and mutual contact, exemplified via path generation applications, are designed using the continuum synthesis approach. Design domains are parameterized using honeycomb tessellation. Assignment of material to each cell, and generation of rigid contact surfaces, are accomplished via suitably sizing and positioning negative circular masks. To facilitate contact analysis, boundary smoothing is implemented. Mean value coordinates are employed to compute shape functions, as many regular hexagonal cells get degenerated into irregular, concave polygons as a consequence of boundary smoothing. Both, geometric and material nonlinearities are considered in the finite element analysis. The augmented Lagrange multiplier method in association with an active set strategy is employed to incorporate both self and mutual contact. CCMs are evolved using the stochastic hill climber search. Synthesized contact-aided compliant continua trace paths with single and importantly, multiple kinks and experience multiple contact interactions pertaining to both self and mutual contact modes.

A stress-based topology optimization method for heterogeneous structures

Abstract: In this work, we introduce a method to incorporate stress considerations in the topology optimization of heterogeneous structures. More specifically, we focus on using functionally graded materials (FGMs) to produce compliant mechanism designs that are not susceptible to failure. Local material properties are achieved through interpolating between material properties of two or more base materials. Taking advantage of this method, we develop relationships between local Young’s modulus and local yield stress, and apply stress criterion within the optimization problem. A solid isotropic material with penalization (SIMP)–based method is applied where topology and local element material properties are optimized simultaneously. Sensitivities are calculated using an adjoint method and derived in detail. Stress formulations implement the von Mises stress criterion, are relaxed in void regions, and are aggregated into a global form using a p-norm function to represent the maximum stress in the structure. For stress-constrained problems, we maintain local stress control by imposing m p-norm constraints on m regions rather than a global constraint. Our method is first verified by solving the stress minimization of an L-bracket problem, and then multiple stress-constrained compliant mechanism problems are presented. Results suggest that good designs can be produced with the proposed method and that heterogeneous designs can outperform their homogeneous counterparts with respect to both mechanical advantage and reduced stress concentrations.

Topology and Size-Shape Optimization of an Adaptive Compliant Gripper with High Mechanical Advantage for Grasping Irregular Objects

Abstract: This study presents an optimal design procedure including topology optimization and size–shape optimization methods to maximize mechanical advantage (which is defined as the ratio of output force to input force) of the synthesized compliant mechanism. The formulation of the topology optimization method to design compliant mechanisms with multiple output ports is presented. The topology-optimized result is used as the initial design domain for subsequent size–shape optimization process. The proposed optimal design procedure is used to synthesize an adaptive compliant gripper with high mechanical advantage. The proposed gripper is a monolithic two-finger design and is prototyped using silicon rubber. Experimental studies including mechanical advantage test, object grasping test, and payload test are carried out to evaluate the design. The results show that the proposed adaptive complaint gripper assembly can effectively grasp irregular objects up to 2.7 kg.

Origami Kaleidocycle-Inspired Symmetric Multistable Compliant Mechanisms

Abstract: Compliant kaleidocycles can be widely used in a variety of applications, including deployable structures, origami structures, and metamorphic robots, due to their unique features of continuous rotatability and multistability. Inspired by origami kaleidocycles, a type of symmetric multistable compliant mechanism with an arbitrary number of units is presented and analyzed in this paper. First, the basic dimension constraints are developed based on mobility analysis using screw theory. Second, the kinematic relationships of the actual rotation angle are obtained. Third, a method to determine the number of stabilities and the position of stable states, including the solution for the parameterized boundaries of stable regions, is developed. Finally, experimental platforms are established, and the validity of the proposed multistable mechanisms is verified.

Design of a Compliant Mechanism Based Four-Stage Amplification Piezoelectric-Driven Asymmetric Microgripper.

Abstract: The existing symmetrical microgrippers have larger output displacements compared with the asymmetrical counterparts. However, the two jaws of a symmetrical microgripper are less unlikely to offer the same forces on the two sides of a grasped micro-object due to the manufacture and assembly errors. Therefore, this paper proposes a new asymmetric microgripper to obtain stable output force of the gripper. Compared with symmetrical microgrippers, asymmetrical microgrippers usually have smaller output displacements. In order to increase the output displacement, a compliant mechanism with four stage amplification is employed to design the asymmetric microgripper. Consequently, the proposed asymmetrical microgripper possesses the advantages of both the stable output force of the gripper and large displacement amplification. To begin with, the mechanical model of the microgripper is established in this paper. The relationship between the driving force and the output displacement of the microgripper is then derived, followed by the static characteristics' analysis of the microgripper. Furthermore, finite element analysis (FEA) of the microgripper is also performed, and the mechanical structure of the microgripper is optimized based on the FEA simulations. Lastly, experimental tests are carried out, with a 5.28% difference from the FEA results and an 8.8% difference from the theoretical results. The results from theoretical calculation, FEA simulations, and experimental tests verify that the displacement amplification ratio and the maximum gripping displacement of the microgripper are up to 31.6 and 632 μm, respectively.

Compliant Mechanisms for Motion/Force Amplifiers for Robotics

Abstract: The force and motion amplifiers are essential mechanical elements used in building small and (micro) robotic devices. This paper brings a short overview of some mechanical structures and their performance characteristics. Three concepts of force amplifiers are analyzed and results from simulations are discussed. The specific design of the linear motion force amplifier/motion reduction for a high-accuracy positioning device with large payload capacity is discussed.

Design of compliant mechanism-based variable camber morphing wing with nonlinear large deformation:

Abstract: The morphing wing with large deformation can benefit its flight performance a lot in different conditions. In this study, a variable camber morphing wing with compliant leading and trailing edges i...

Design of Planar Large-Deflection Compliant Mechanisms With Decoupled Multi-Input-Output Using Topology Optimization

Abstract: This paper presents a method for topology optimization of large-deflection compliant mechanisms with multiple inputs and outputs by considering the coupling issue. First, the objectives of the design problem are posed by modeling the output loads using several springs to enable control of the input–output behavior. Second, a scheme is proposed to obtain a completely decoupled mechanism. Both input coupling and output coupling are considered. Third, with the implementation of an energy interpolation scheme to stabilize the numerical simulations, the geometrical nonlinearity is considered to appropriately capture the large displacements of compliant mechanisms. Finally, several numerical examples are presented to demonstrate the validity of the proposed method. Comparison studies with the obtained results without considering the coupling issues are also presented.

Alternative elliptic integral solution to the beam deflection equations for the design of compliant mechanisms

Abstract: The interactive design for industrial applications is today carried out through methods and tools, with different level of accuracy and simulation times. Consequently, the time necessary for virtual prototyping and analysis phases are often long and may be definitely reduced by means of optimization of tools and methodologies. Compliant mechanisms are increasingly used in the industrial field and the design methods are the subject of several studies, to improve their performance and reliability. This paper provides the reader with reliable numerical expressions to describe flexural beams with large deflections in case of combined end loads and without inflection points. Most of the numerical expressions describing beam deflection already existing in the literature are based on elliptic integrals that take into account strict limitations on the maximum slope angle. Here, we go beyond these limitations at the same time trying to give an order to the most relevant formulations used for determining large deflections of beams subject to combined tip loads. The proposed method provides the same results of the comprehensive elliptic integral solution described in a recent study.

Optimal Design of Soft Pneumatic Bending Actuators Subjected to Design-Dependent Pressure Loads

Abstract: Soft actuators, mainly composed of soft materials, have made a great impact on applications in unstructured or unknown environments due to their high flexibility and customizability. The design methods of soft actuators can be divided into two groups: the bionic design method and the topology optimization method. Compared to the bionic design method that requires numerous experiments, the topology optimization method can generate innovative structures according to the design requirements. However, the existing topology optimization method cannot be applied to soft pneumatic bending actuator (SPBA) designs because SPBAs are usually subjected to design-dependent pressure loads of which the position depends on the structure. In this paper, we propose an optimal design framework of SPBAs to resolve the design-dependent load problem using an adaptive bi-directional evolutionary structural optimization method. Herein, SPBAs are considered as compliant mechanisms and our goal is to achieve maximum bending deformation as well as structural stiffness. In finite element analysis, each element in the design domain is set to solid or void according to sensitivity number, which is approximated by the objective function derivative with respect to the design variables. During the iterative optimization procedure, we explicitly define the movable solid-void boundary surfaces on which the pressure will act. A precision prototype actuator is fabricated, and its performance is evaluated in terms of free travel experiment. Some extensions are supplied to validate the optimality and reliability of the proposed method. This framework paves a way for the diversity of soft actuators.