Roundoff method for improving position accuracy of parallel manipulators

Actual position and orientation reached by multi-dof mechanisms are discrete locations within their workspace. Although roundoff error is inevitable for individual controlled joints, their combined effect on the resulted positioning accuracy can be reduced during roundoff processes. This paper shows that the traditional roundoff does not always give the best position accuracy, and presents a Jacobian based roundoff procedure for determining the round down or up of each controlled joint in parallel manipulators. This roundoff scheme is demonstrated with a 3-dof planar parallel manipulator. The proposed procedure provides a way to improve position accuracy without change in hardware. It can therefore be used as an alternative to (or, in addition to) the use of better encoder for better accuracy.