Fusing Topology Optimization and Pseudo-Rigid-Body Method for the Development of a Finger Exoskeleton

2021 ◽  
pp. 1-1
Author(s):  
Renghao Liang ◽  
Guanghua Xu ◽  
Min Li ◽  
He Bo ◽  
Umair Khalique
Keyword(s):  
Topology Optimization ◽  
Rigid Body ◽  
Body Method

Topology Optimization of Rigid-Body Systems Considering Collision Avoidance

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Fritz Stöckli ◽  
Kristina Shea
Keyword(s):  
Topology Optimization ◽  
Rigid Body ◽  
Collision Avoidance ◽  
Optimization Problems ◽  
Computational Design ◽  
Optimization Method ◽  
The Body ◽  
Graph Grammar ◽  
Automated Synthesis ◽  
Inertia Properties

Abstract Passive dynamic mechanisms can perform simple robotic tasks without requiring actuators and control. In previous research, a computational design method was introduced that integrates dynamic simulation to evaluate and evolve configurations of such mechanisms. It was shown to find multiple solutions of passive dynamic brachiating robots (Stöckli and Shea, 2017, “Automated Synthesis of Passive Dynamic Brachiating Robots Using a Simulation-Driven Graph Grammar Method,” J. Mech. Des. 139(9), p. 092301). However, these solutions are limited, since bodies are modeled only by their inertia properties and thus lack a shape embodiment. This paper presents a method to generate rigid-body topologies based on given inertia properties. The rule-based topology optimization method presented guarantees that the topology is manifold, meaning that it has no disconnected parts, while still connecting all joints that need to be part of the body. Furthermore, collisions with the environment, as well as with other bodies, during their predefined motion trajectories are avoided. A collision matrix enables efficient collision detection as well as the calculation of the swept area of one body in the design space of another body by only one matrix–vector multiplication. The presented collision avoidance method proves to be computationally efficient and can be adopted for other topology optimization problems. The method is shown to solve different tasks, including a reference problem as well as passive dynamic brachiating mechanisms. Combining the presented methods with the simulation-driven method from Stöckli and Shea (2017, “Automated Synthesis of Passive Dynamic Brachiating Robots Using a Simulation-Driven Graph Grammar Method,” J. Mech. Des. 139(9), p. 092301), the computational design-to-fabrication of passive dynamic systems is now possible and solutions are provided as STL files ready to be 3D-printed directly.

Topology Optimization of Large Motion Rigid Body Mechanisms With Nonlinear Kinematics

2009 ◽  
Vol 4 (2) ◽  
Author(s):  
Kai Sedlaczek ◽  
Peter Eberhard
Keyword(s):  
Topology Optimization ◽  
Rigid Body ◽  
Design Process ◽  
Combinatorial Problem ◽  
Optimization Techniques ◽  
Dimensional Synthesis ◽  
Ground Structure ◽  
Geometrical Properties ◽  
Manual Task ◽  
Large Motion

The modern design process of mechanical structures is increasingly influenced by highly sophisticated methods of topology optimization that can automatically synthesize optimal design variants. However, the typically finite-element-based methods are limited to design tasks with comparably small deflections and simple kinematics. They are not directly applicable to the difficult development process of large motion mechanisms, which remains mainly a manual task based on the engineer’s experience, intuition, and ingenuity. There, optimization techniques are only, if at all, used in the process of dimensional synthesis, where the geometrical properties and the orientation of individual links of a fixed mechanism topology are determined. In this work, two different approaches to optimization-based topology synthesis of large motion rigid body mechanisms are presented and investigated. The goal is to automatically synthesize a combination of linkage topology and joint types that represent the most suitable mechanism layout for a particular task. The first approach is based on a trusslike ground structure that represents an overdetermined system of rigid bars from which the most appropriate topology can be extracted from this ground structure by means of gradient-based optimization algorithms. In the second approach, a genetic algorithm is used to solve the intrinsically combinatorial problem of topology synthesis. Along with several examples, both approaches are explained, their functionality is shown, and their advantages, limitations, and their capability to improve the overall design process is discussed.

Compliant Mechanism Design Through Topology Optimization Using Pseudo-Rigid-Body Models

2016 ◽  
Author(s):  
Venkatasubramanian Kalpathy Venkiteswaran ◽  
Omer Anil Turkkan ◽  
Hai-Jun Su
Keyword(s):  
Finite Element ◽  
Topology Optimization ◽  
Rigid Body ◽  
Finite Element Methods ◽  
Compliant Mechanism ◽  
Beam Theory ◽  
Deformation Analysis ◽  
Optimization Approach ◽  
Algebraic Equations ◽  
Kinematic Loops

The initial design of compliant mechanisms for a specific application can be a challenging task. This paper introduces a topology optimization approach for planar mechanisms based on graph theory. It utilizes pseudo-rigid-body models, which allow the kinetostatic equations to be represented as nonlinear algebraic equations. This reduces the complexity of the system compared to beam theory or finite element methods, and has the ability to incorporate large deformations. Integer variables are used for developing the adjacency matrix, which is optimized by a genetic algorithm. Dynamic penalty functions describe the general and case-specific constraints. A symmetric 3R model is used to represent the beams in the mechanism. The design space is divided into rectangular segments while kinematic and static equations are derived using kinematic loops. The effectiveness of the approach is demonstrated with the example of an inverter mechanism. The results are compared against finite element methods to prove the validity of the new model as well as the accuracy of the approach outlined here. Future implementations of this method will include stress and deformation analysis and also introduce multi-material designs using different pseudo-rigid-body models.

Multistability of Compliant Sarrus Mechanisms

2012 ◽  
Author(s):  
Guimin Chen ◽  
Shouyin Zhang
Keyword(s):  
Rigid Body ◽  
Compliant Mechanisms ◽  
Spatial Motion ◽  
Deployable Structures ◽  
Static Balancing ◽  
Compliant Joints ◽  
Body Method

Although there are many examples of multistable compliant mechanisms in the literature, most of them are of planar configurations. Considering that a multistable mechanism providing spatial motion could be useful in numerous applications, this paper explores the multistable behavior of the overconstrained spatial Sarrus mechanisms with compliant joints (CSMs). The kinetostatics of CSMs have been formulated based on the pseudo-rigid-body method. The kinetostatic results show that a CSM is capable of exhibiting bistability, tristability, and quadristability. Possible applications of multistable CSMs include deployable structures, static balancing of human/robot bodies and weight compensators.

scholarly journals Comprehending Optimality of Finger Flexor Tendon Pulley System using Computational Analysis

2021 ◽  
Author(s):  
Vitthal Khatik ◽  
Shyam Sunder Nishad ◽  
Anupam Saxena
Keyword(s):  
Rigid Body ◽  
Parametric Study ◽  
Computational Analysis ◽  
Flexor Tendon ◽  
Pulley System ◽  
Reconstruction Surgery ◽  
Tendon Tension ◽  
Insight Into ◽  
Body Method ◽  
High Range

Abstract It is rare that existing prosthetic/orthotic designs are based on kinetostatics of a biological finger, especially its tendon- pulley system (TPS). Whether a biological TPS is optimal for use as a reference, say for design purposes, and if so in what sense, is also relatively unknown. We expect an optimal TPS to yield high range of flexion while operating with lower tendon tension, bowstringing, and pulley stresses. To gain insight into the TPS designs, we present a parametric study which is then used to determine optimal TPS configurations for the flexor mechanism. A compliant, flexure-based computational model is developed and simulated using the pseudo rigid body method, with various combinations of pulley/tendon attachment point locations, pulley heights, and widths. Results suggest that three distinct types of TPS configurations corresponding to single stiff pulley, or two stiff pulleys, or one stiff and one flexible-inextensible pulley per phalange can be optimal. For a TPS configuration similar to a biological one, the distal pulleys on the proximal and intermediate phalanges need to be like flexible-inextensible string loops that effectively model the behavior of joint and cruciate pulleys. We reckon that a biological flexor TPS may have evolved to maximize flexion range with minimum possible actuation tension, bowstringing and pulley stress. Our findings may be useful in not only developing efficient hand devices, but also in improving TPS reconstruction surgery procedures.

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