Most Cartesian-based control strategies require the computation of the manipulator inverse Jacobian in real time at every sampling period. In some cases, the Jacobian matrix is not of full column or row rank due to singularity or redundant robot configuration. This requires the computation of the manipulator pseudo-inverse Jacobian in real time. The calculation of the pseudo-inverse Jacobian may become extremely sensitive to small perturbation in the data and numerical instabilities, when the Jacobian matrix is not of full column or row rank. Even if the Jacobian matrix is of full rank, the ill-conditioned problem may still plague the computation of the pseudoinverse Jacobian. This paper presents the use of residue arithmetic for the exact computation of the manipulator pseudo-inverse Jacobian to obviate the roundoff errors normally associated with the computations. A two-level macro-pipelined residue arithmetic array architecture implementing the Decell’s pseudo-inverse algorithm has been developed to overcome the ill-conditioned problem of the pseudo-inverse computation. Furthermore, the Decell algorithm is quite suitable for VLSI array implementation to achieve the real-time computation requirement. The first-level arrays are data-driven, wavefront-like arrays and perform the matrix multiplications, matrix diagonal additions, and trace computations. A pool or sequence of the first-level arrays are then configured into a second-level macro-pipeline with outputs of one array acting as inputs to another array in the pipe. The proposed architecture can calculate the pseudoinverse Jacobian with a pipelined time in the same computational complexity order as evaluating a matrix product in a wavefront array.
Date of this Version