Workspace Improvement of Two-Link Cable-Driven Mechanisms with Spring Cable
The idea of multi-body cable-driven mechanisms is an extension of the original cable robots where the moving platform is replaced by a multi-body. Cables with variable lengths are attached between the fixed base and the links of the multi-body to provide
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Abstract The idea of multi-body cable-driven mechanisms is an extension of the original cable robots where the moving platform is replaced by a multi-body. Cables with variable lengths are attached between the fixed base and the links of the multibody to provide the motion. There are possible applications for such mechanisms where complex motions as well as low moving inertia are required. One of the main challenges with such mechanisms is the high chance of interference between the cables or between the cables and the links of the multi-body mechanism. This can further reduce the usable workspace. In this article, the idea of adding passive cables in series with springs (spring cable) to improve the workspace is investigated. The spring cables can be added between the multi-body and ground or between the links. The idea is applied to a two-link planar multi-body cable-driven mechanism. The wrench feasible workspace (WFW) is found using the interval analysis. The WFW is shown to improve both in shape and volume. Keywords Cable-driven · Multi-body · Spring · Workspace improvement
A. Taghavi (B) · S. Behzadipour · N. Khalilinasab · H. Zohoor Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran e-mail: [email protected] S. Behzadipour e-mail: [email protected] N. Khalilinasab e-mail: [email protected] H. Zohoor e-mail: [email protected] T. Bruckmann and A. Pott (eds.), Cable-Driven Parallel Robots, Mechanisms and Machine Science 12, DOI: 10.1007/978-3-642-31988-4_13, © Springer-Verlag Berlin Heidelberg 2013
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1 Introduction Cable driven robots are mechanisms in which the end-effector is moved by controlling the lengths of the cables connected to it. The cable robots are appealing because of their structural simplicity, high stiffness, and high exerted wrench-to-weight ratio and easiness of reconfiguration. Their main drawback is their small workspace and interference of cables, so one of their key issues is their optimal design for a desired workspace and given constraints [1]. A cable driven parallel manipulator, according to its number of cables (m) and the degrees of freedom of the end-effector (n), are classified as follows [2]: IRPMs: Incompletely Restrained Positioning Mechanisms, in which the number of cables is less than or equal to the number of the DOFs, namely, m≤n IRPMs robots rely on the presence of gravity or another ballast force to determine the resulting pose of the end-effector. CRPMs: Completely Restrained Positioning Mechanisms, in which there is an extra cable, i.e.: m =n+1 RRPMs: Redundantly Restrained Positioning Mechanisms, in which there are more than one extra cable: m >n+1 Since IRPMs use less number of cables and actuators, the probability of cable interference as well as the production cost is lowered. However, in these robots, the volume of workspace and the magnitude of the externally applied wrench of the robot are limited by the ballast force. In contrast with IRPMs, RRPMs have larger workspace but the inter
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