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Kinematic Design of a Translational Parallel Manipulator with Fine Adjustment of Platform Orientation

DOI: 10.1155/2010/485358

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Abstract:

We present a kinematic design of a translational parallel manipulator with fine adjustment capability of platform orientation. In order to clarify possible kinematic structures for it, structural synthesis of fully decoupled mechanism and partially decoupled mechanism both with six degrees of freedom (dof) was carried out based on the synthesis results of translational and rotational parallel mechanisms with three dof. All possible kinematic structures were obtained. Of these, one partially decoupled mechanism was selected and a kinematic design of a prototype manipulator was done. Its characteristics in terms of workspace, singularity, orientation adjustment capability, and coupling characteristics between translational and rotational displacement were discussed with experimental results regarding fine adjustment capability of platform orientation. 1. Introduction A parallel manipulator that has three degrees of freedom (dof) and outputs translational motion without changing its orientation is called a “translational parallel manipulator.” A translational parallel manipulator has potential for use in assembly, machining, and coordinate measurements. The manipulator is composed of a base, platform, and multiple connecting chains arranged in parallel between the base and platform. Many researchers in recent years have shown interest in translational parallel manipulators and mechanisms. The kinematic conditions for the connecting chain to obtain translational motion of the platform have been investigated [1, 2]. Various kinematic structures for translational parallel manipulators have also been investigated [3, 4]. Further, optimization taking into consideration the manipulator’s workspace has been done [5–7]. Translational parallel mechanisms have been applied to medical robots [8] and micromanipulators [9]. The errors in the output pose of a manipulator caused by dimensional errors, such as these in links, can be classified into two groups. The first group contains errors that can be compensated for by calibration or full closed-loop control. Such errors are called “compensatable errors” [10, 11]. The tolerance requirements with respect to these compensatable errors depend on calibration or the performance of the controller, and these are not usually severe. The second group contains errors that cannot be compensated for by any means, either during or prior to manipulation. Such errors are called “uncompensatable errors” [10, 11]. They depend on kinematic structures and parameters and tolerances. In designing and controlling a lower-dof parallel

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