In the 4^th Industrial Revolution, advancements in semiconductor technology demand high performance, efficiency, and precision, highlighting the importance of high-speed and ultra-precise motion stages. To improve positioning performance of a motion stage, robust torque generation by current controllers alongside position control is crucial. This paper explored a custom current control for linear motor motion stages. We built a linear motor motion stage with a 560 mm stroke, 5 m/s speed, and 280 N continuous thrust supported by air bearings and equipped with a passive reaction force compensation. Custom user code for position and current controls of PowerPMAC motion controller was developed for the motion stage. The position control code included frequency domain system identification, disturbance observer, and repetitive learning control while the current control code featured vector or d/q-axis current controllers and disturbance observer. We developed a current control tuning GUI to adjust the current control gain by injecting an excitation signal into the motion controller and measuring the frequency response of the open-loop transfer function. Experimental results confirmed the effectiveness of the custom current controller for evaluating static and dynamic performance.

A magnetic levitation system (MLS) controls the position of a steel ball with the magnetic force of the electromagnetic actuator. A disturbance observer (DOB) could improve the disturbance rejection and command tracking performance of the voltage-controlled MLS. This paper studied control boost of MLS using current and position DOB. The current-controlled MLS had a higher control performance than the voltage-controlled MLS. The combination of PID position and PI current controls provided stable levitation and a wide operation range of MLS. When DOB was applied to PI current control, it could compensate for inductance change according to the position of the steel ball. In addition, when another DOB was introduced to the PID position control, it improved the disturbance removal performance. Finally, we discussed the effectiveness and limitations of the DOB-based current and position control by measuring closed-loop frequency responses.

This paper describes the control method of an electric gripper using a current control system. A current control system was designed and fabricated, and it consisted of a current sensor, an amplifier, and a precision voltage regulator. As a result of calibration by applying the current control system to the electric gripper, the error was less than ±0.34%. The proportional gain for the PI control of the gripper was 0.41, and the integral gain was 0.01. As a result of the control characteristics test, the arrival time was 0.79 s and the steady-state error was ±5 mV (±0.025 N). As a result of the experiment of holding the object, the gripper was able to hold the object safely. Therefore, the electric gripper applied using the current control system performed excellently in current control based on the reference force (grabbing force); thus, it is judged that it can be used to safely grip various objects in various fields.