Adaptive Sliding Mode Control Anticipating Proportional Degradation of Actuator Torque in Uncertain Serial Industrial Robots

Abstract

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.

Designing Digital Twins of Robots Using Simscape Multibody

“…In fact, Simscape Multibody has already been successfully used in the field of robotics to build models of articulated [9][10][11][12][13][14][15][16][17], parallel [18,19], mobile [20,21] and legged robots [22,23]. It has also been used to test a robot dynamic parameter identification method in [24], to test robot control strategies in [25][26][27][28], to model and simulate a multi-fingered robot arm grasping [29] and to design a 5 degrees of freedom manipulator for additive manufacturing in [30]. However, previous studies using Simscape Multibody have mostly focused on the kinematic modeling of robots, neglecting its dynamic modeling and the inclusion of non-idealities, friction, reduction gears, and motor dynamics.…”

Dynamic Event-Triggered Integral Sliding Mode Adaptive Optimal Tracking Control for Uncertain Nonlinear Systems

“…Owing to the distinguished features such as fast dynamic response, robustness, order reduction, and implementation simplicity, sliding mode control (SMC) is widely studied in the fields of transportation, power grid, industrial communication networks, and uncertain serial industrial robots [12][13][14][15][16][17][18][19][20]. Especially, SMC has been recognized as one of the popular and powerful control tools in power converters based on deriving from the variable structure systems theorem.…”