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The ability to position end effector highly accurately is very
important in the applications of robot manipulator. Due to low
structural completeness of a serial robot arm the goal of high
accuracy can not be easily reached. There- fore a 6 d.o.f.
(degree-of-freedom) Stewart-Platform is presented in this
paper. The distinct property of high stiffness of this
mechanism makes it more suitable for the demands of high
accuracy. The Stewart Platform is consists of 3 identical PRPS
sub-chains which stand on a fixed base and collaborately
support an output platform (parameters P,R and S denote the
prismatic, revolute and spherical joints). All the prismatic
joints in this mechanism are actuated joint which dominate the
motion of the output Platform. This paper describes in details
the mechanism and investigates the closed-form solu- tions of
both forward and inverse kinematics. In addition to the
analysis of work space, theory of geometrics is applied to
identify the situations of singularity, where to prevent the
platform from reaching those undesirable position. The whole
system comprises a Stewart-Platform, a PC controller, hardware
interface, actuating motors and their drivers. The PC
controller provides with 3 groups of adjustable parameters
including feedforward, position and velocity. Experiments show
that the proposed Stewort-Platform can track spatial trajectory
with both high accuracy and high speed.
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