Precision control of a T-type gantry using sensor/actuator averaging and active vibration damping

This paper presents the modeling and motion controller design for a linear motor driven T-type gantry and worktable. The worktable motion, which is referred to as the x-axis, is considered independently of the gantry and is controlled using a loop shaping filter. The gantry (or y-axis) is actuated by dual direct drive linear motors and is coupled to the worktable position, which determines its inertial characteristics. A 94Hz yaw mode is handled in the gantry control law using sensor and actuator averaging, and active vibration damping. The stability and robustness of the design is considered using multivariable frequency domain techniques. In the x-axis, a bandwidth of 130Hz is achieved. The y-axis crossover frequency is 52Hz, which is twice that of the crossover frequency that can be achieved using independent PID controllers (26Hz). The performance of the proposed control scheme has been verified in step disturbance (i.e., rope snap) tests, as well as tracking and contouring experiments.