Research On Motion Control Technology Of An Electromagnetic Linear Actuator

Electromagnetic linear actuators obtain high performance linear motions by eliminating mechanical transmission mechanisms, and they have been widely used in industrial applications such as automation and robotics in recent years. Electromagnetic linear actuators and their motion control are key technology to realize high performance linear motions. In this dissertation, a series of researches were done on motion control of a novel moving-coil electromagnetic linear actuator based on axially-magnetized magnets.The novel electromagnetic linear actuator was made, and its structure, working principle and characteristics were analyzed. Mathematical model was built, and the system simulation model was established based on Matlab/Simulink. Control system of the electromagnetic linear actuator was constructed based on a digital-signal-processor. Simulation and experiments were carried out based on aforementioned systems.To reduce the commutation force ripple in the novel electromagnetic linear actuator, a compensation approach based on predictive current control was proposed. Conditions of the commutation force ripple generation and working principle of the predictive current control were analyzed. Commutation force ripple reduction strategies in high and low speed operation were given respectively. Compared with the existing compensation methods used for brushless DC motors, the presented approach has the advantages of simple system configuration, high precision and easy to implement. Commutation force ripple was reduced effectively with the proposed method, which is good for the novel electromagnetic linear actuator to realize high performance linear motions.One important motion control task of the electromagnetic linear actuator is precision trajectory tracking, and a modified active disturbance rejection controller has been developed to accomplish this task. A reference acceleration feedforward was added to the conventional active disturbance rejection controller, and its control abilities of sinusoidal trajectory tracking, different point-to-point motion trajectories tracking, parameter variations and external disturbance rejection were tested. Compared with the PID controller with reference acceleration feedforward and conventional active disturbance rejection controller, the proposed modified active disturbance rejection controller achieved precision trajectory tracking control besides the original excellent disturbance rejection performance. Consequently, this novel electromagnetic linear actuator along with the modified active disturbance rejection controller provides a new solution for high-performance linear motion applications.The other important motion control task of the electromagnetic linear actuator is precision positioning under high speeds. An extended state observer-based time-optimal control was proposed to achieve fast and precision point-to-point motions. Extended state observer was combined with time-optimal control of the double-integrator system, and on this basis fast and precision point-to-point motion control system of the electromagnetic linear actuator was designed. Closed-loop stability of the control system was analyzed according to the Lyapunov’s second method. Special nonlinear functions were used to eliminate the chattering of the time optimal control. Experimental results indicated that when the desired position was8mm and the maximum velocity was1m/s, the positioning error was2μm. When the desired position was32mm and the maximum velocity was1.6m/s, the positioning error was3μm. The maximum velocity under exsiting conditions was3.1m/s.Finally, a typical application of the novel electromagnetic linear actuator was studied, that is the motion control of a6-DOF platform. Motion control system was constructed based on dSPACE. Trajectory tracking experiments of the6-DOF platform were carried out based on kinematic control methods, predictive current control and modified active disturbance rejection controller. Experimental results indicated that each electromagnetic linear actuator tracked its desired trajectory accurately, and the upper platform realized the given pose well. The proposed control methods are verified effective, and the novel electromagnetic linear actuator exhibits its good potential in6-DOF platform applications.