Abstract
Using the macro-micro combination positioning system for nanomanipulating can fulfill the requirements of large workspace, high precision and multi-degrees of freedom. As a macro part of the macro-micro combination positioning system, a redundantly actuated three degrees-of-freedom (DOF) parallel kinematic mechanism (4ṞRR) with a directly driven system is studied in this paper. Firstly, the error sensitivity of the 4ṞRR planar parallel mechanism is analyzed with global errors sensitive index (GESI) based on the error model of the positioning system. Then, a novel and practical calibration method combined with an error compensation strategy is proposed for the 4ṞRR positioning system. Finally, in order to verify the proposed method, a series of experiments are conducted with the laser measurement system in creditable conditions, and the data are illustrated for comparisons. The experimental results show that the positioning accuracy of the 4ṞRR positioning system is improved, and the performances of the end-effector are enhanced based on the proposed method.
Highlights
Compared with the series robot, the virtues of the parallel mechanism (PM) are higher speed, stronger load capacity and better precision with small accumulative errors,[1,2,3] which is suitable for the multi-DOF precision positioning system
When the length and angle errors are in the same order of magnitude, though the input errors from the actuated joints are high in global errors sensitive index (GESI), other errors still have an impact on positioning accuracy
It can be inferred that after the calibration the positioning errors generally decrease, and the peak value of errors reduces dramatically. This indicates that the error compensation method is effective, and it can be commonly used in PMs calibrations
Summary
Compared with the series robot, the virtues of the parallel mechanism (PM) are higher speed, stronger load capacity and better precision with small accumulative errors,[1,2,3] which is suitable for the multi-DOF precision positioning system. Liu[21] introduces an approach to self-calibration for a type of redundant PM using measured information of the redundant kinematic chain He only simulates his model and not all kinematic chains of his 4RRR model drive the end-effector, while we run the experiment based on our error model and all kinematic chains in our model are the same. An error model of the directly driven 4RRR positioning system is derived. The conclusions of this paper are drawn in the last section In this kind of 3-DOF redundant plane parallel mechanism, all kinematic chains are in the position control mode, so it is called the directly driven 4RRR positioning system. (x
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