Translational Parallel Robots with Uncoupled Motions

Abstract

The paper presents a structural synthesis approach of translational parallel manipulators (TPMs) with uncoupled motions (UM) and revolute actuators (RA) situated on the fixed base (TPMs-UM-RA). Parallel robotic manipulators (PMs) show, in general, desirable characteristics like a large payload to robot weight ratio, considerable stiffness, low inertia and high dynamic performances. With respect to serial manipulators, disadvantages consist in a smaller workspace, complex command and a lower dexterity due to a high motion coupling and multiplicity of singularities inside their workspace. A TPM is a 3-DOM (degree of mobility) parallel mechanism whose output link, called platform, can achieve three independent orthogonal translational motions with respect to the fixed base. The manipulators presented in this paper have three legs connecting the moving platform and the base (fixed platform). Only one pair per leg is actuated and the motors are situated on the fixed base. Linear and revolute actuators can be used. Due to space limitations, in this paper we consider only rotational actuators (RA). A one-to-one correspondence exists between the actuated joint space and the operational space of the moving platform. The Jacobian matrix of TPM-UM is a 3×3 diagonal matrix throughout the entire workspace. A method is proposed for structural synthesis based on the theory of linear transformations and an evolutionary morphology approach. The method allows us to obtain all structural solutions of TPMs-UM-RA in a systematic manner. Overconstrained/isostatic solutions with elementary/complex and identical/different legs are obtained. TPM-UM have the advantage of simple command and important energy-saving due to the fact that, for a unidirectional translation, only one motor works as in a serial translational manipulator. Only a small number of the solutions of TPMs-UM-RA presented in this paper are actually known in the literature.