An inverse-dynamics-based method for discrete-time control of flexible-joint robots is presented. The main drawbacks of continuous-time analysis are its computational burden and the necessity for very high sampling frequencies. These inconveniences can be avoided by the use of numerical methods conceived for the solution of systems of differential-algebraic equations. Such an approach naturally leads to a predictive control scheme. As a consequence, in the control process a basic dynamic model of the flexible-joint robot can be used, which is much less complex than in the classical inverse dynamics solution. At the same time, the simplified inverse dynamics approach discussed here accepts low sampling frequencies. Control algorithms are presented and their properties are discussed. Successful experiments on computer control of a two-link manipulator with one flexible joint are described.>

Nonlinear feedback control for force-controlled robots with constrained end-effector motion is considered. A general method is presented that assures an exact feedback linearization for both rigid and flexible-joint robots, as the joint flexibility can cause instability of robot control. The feedback control linearizes and decouples the original nonlinear system into a number of decoupled linear subsystems. The effect of stiction on the end-effector contact with the environment is inherently incorporated in the formulation, using the same constrained system formalism. A version of the controller with improved robustness characteristics, based on the robust servomechanism theory, is proposed. The derivation of the control algorithm for a two-link planar robot interacting with a rough plane surface is presented as an example. Numerical simulation results confirm the effectiveness of the method. The issues associated with real-time robot control, such as the choice of sampling frequency and the influence of modeling errors, are discussed.>

A nonlinear decoupling and linearizing feedback control for force-controlled robots with constrained end-effector motion is considered. A general method is presented which assures an exact feedback linearization for both rigid and flexible joint robots, as the joint flexibility can cause instability of robot control. The application of the developed control laws produces a set of decoupled linear subsystems, corresponding to the position/velocity constraint space and contact force constraint space. The implementation of this method is demonstrated for the case of a two-link robot with the end-effector constrained to move along a rough plane.>