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Abstract
Design aspects of a six degree-of-freedom high-accuracy manipulator are presented. The manipulator arm (called the UTI-arm) comprises four revolute and two prismatic joints. The mechanical design of the manipulator is aimed at obtaining high accuracy and a high stiffness-to-weight ratio of the links. Prestressing of mechanical elements is performed to transform strength to stiffness. Design of links under tension load is carried out to enhance bending stiffness. In the past, researchers have reported inefficiency of prismatic joints due to their high compliance. Compared to a uniform thin-walled tube, prismatic joints used in this design provide an isotropic, higher bending stiffness with a relatively low loss in torsional stiffness. Experiments were conducted to verify the theory presented for calculating torsional stiffness of such joints. A finite element model was also used to validate the model. The mechanical design of the arm is presented in detail in view of the proposed prismatic joint cross section and the prestressing effects.
Keywords: Manipulator Design, Structural Stiffness, Robot Design, Robotics
Introduction
Rigid-link manipulators require light, stiff structures to achieve high accuracy and low inertia. While the analysis and synthesis of revolute joints has been addressed in the literature,ls prismatic joints have not had a great deal of attention due to the relative difficulty in their design and manufacture.
General handbooks to aid in the design of manipulators exist in the literature,3-6 and other works that list design criteria are also numerous.7-11 Design of flexible mechanisms has also been addressed.12 Analysis of stiffness of manipulator links can be found in Rivin3 and Leu, Dukovski, and Wang.13 Computer programs using computer-aided design systems14 were employed to aid in the design of manipulator arms as early as 1979. Optimization techniques"5 and calibration techniques16 have been used to correct errors in accuracy. Passive gravitational compensation has also been addressed by Nathan and Kumar.17
More recently, a number of serial manipulators were designed using analytical criteria adopted for robotics technology. The UTAH/MIT arm and hand"6,9 and the WAMS system20 are two such examples. Other robot designers have attempted to systematically develop analytical criteria for the design of critical components. For example, Fresonke, Hernandez, and Tesar21 have set analytical criteria for the deflection prediction of serial manipulators. Henessey et al.22 have demonstrated the...