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The paper focuses on faulty actuator problems in an industrial robot using servomotors, and provides an adaptive sliding mode control law to overcome this circumstance. Because of multifarious reasons, robot actuators can undergo a variety of failures, such as locked or stuck joints, free-swinging joints, and partial or total loss of actuation effectiveness. The robot behavior will become worsen if the system controller has not been designed with adequate faulty tolerance. The proportional degradation of actuator torque at unknown degrees of loss, which is one type of partial loss of actuation effectiveness, is considered in this study to design a suitable controller. The robot model is constructed with uncertain parameters and unknown friction, whereas the controller uses only the approximate parameters. Symmetry and skew-symmetry give important contributions in robot modeling and transformation, as well as in the process of proving the system stability. An adjustable coefficient vector of the proposed controller can adaptively reach the upper bounds of an uncertain parametric vector, which guarantees the criterion of Lyapunov stability. In the numerical simulation stage, the selected industrial robot is a Serpent 1 robot with three degrees of freedom. A quasi-physical model based on MATLAB/Simscape Multibody for the robot is built and used in order to increase the reliability of the simulation performance closer to reality. Simulation results illustrate the efficiency of the proposal control methodology in the presence of the mentioned failure. The controller can still deliver satisfactory responses to the robot system under reasonable levels of actuator torque degradation.

Improving ride comfort of earth-moving machinery is important to avoid potential health hazards for machine operator. A vehicle - road coupled interaction model including vehicle body, cab body and driver seat masses is set up under the random excitation of ground surface and a Fuzzy –PID controller is designed for control of the damping coefficient of a semi-active hydraulic cab isolation system (SHCIs) for an earth-moving machinery. The ride performance of SHCIs with a combined controller is evaluated under different movement conditions. The comparison results indicate that the proposed controller for semi-active cab hydraulic isolation system has the significantly improved vehicle ride comfort in compared with passive hydraulic cab isolation system (PHCIs) under large amplitude and low frequency excitations of ground surface.

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