A New Algorithm for Gravity Compensation of a 3-UPU Parallel Manipulator
This paper presents a new approach for gravity compensation of a 3-UPU parallel manipulator. The conventional method of computing the effect of gravity force on the end-effector works properly for serial manipulators. However, employing Newton-Euler appro
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PERCRO, TeCIP Institute, Scuola Superiore Sant’Anna Abstract This paper presents a new approach for gravity compensation of a 3-UPU parallel manipulator. The conventional method of computing the effect of gravity force on the end-effector works properly for serial manipulators. However, employing Newton-Euler approach for the parallel robots is computationally expensive and it cannot satisfy the requirements in this work. In order to overcome this difficulty, the new algorithm based on Lagrengian method is proposed. This model is established based on total potential energy of the system as a scalar value and, the position of the end-effector. This paper presents this new algorithm which is more efficient in sense of computation and more proper for Real-Time purposes in parallel robots.
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Introduction
In the recent years, parallel robots have attracted the attention of many researchers worldwide. Literatures from Han et al. (2002), Tsai and Joshi (2000), Li and Xu (2006) show that parallel robot is preferred over its serial counterpart, because of presenting high load-carrying capacity, high velocity, structural stiffness, precision and low inertia. The main drawbacks of parallel robots are complexities of mechanical designs, motion generation, direct kinematics and control, and above all, the limited workspace. As an alternative, many researchers design different parallel manipulators with different degrees of freedom. Some examples are the famous translational 3 DOF Delta robot (Siciliano and Khatib, 2008, part. B/12), the SNU 3-UPU mechanism (Walter et al., 2008), Stewart platform and several other 3 DOF and 6 DOF parallel mechanisms (Wang and Xi, 2008). For several decades, gravity compensation has been of great interest to researchers. Gravity compensation is considered as mechanical compensation, which is to design the mechanical components in order to satisfy ∗
This research was carried out with the financial support of BRAVO and VERE projects.
V. Padois, P. Bidaud, O. Khatib (Eds.), Romansy 19 – Robot Design, Dynamics and Control, CISM International Centre for Mechanical Sciences, DOI 10.1007/978-3-7091-1379-0_15, © CISM, Udine 2013
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statically balancing of the robot, and active compensation through actuators. The literatures of Wang and Xi (2008) and Siciliano and Khatib (2008) show that in the effort of mechanical gravity compensation for serial mechanisms mainly springs and counterweights and in a few cases pulley and cams are employed, while for their parallel counterparts usually different types of springs and sometimes counterweights are used (Deepak and Ananthasuresh, 2011, and Siciliano and Khatib, 2008). In the absence of mechanical gravity compensation components, actuators should provides sufficient torques in order to compensate the force imposed by mechanism weight on the end-effector. The gravity compensation of 3-UPU parallel manipulator is of high importance, while its translational movement makes it a suitable robot to be used widely in industry.
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