Yusaku Shinohara

High precision force control of pneumatic cylinders considering disturbance suppression with specific frequency

This paper presents a practical control methodology of force control systems using a pneumatic cylinder for polishing machines. The typical machine is composed of the pneumatic cylinder as an actuator, a motor to rotate a whetstone, and a force sensor to detect the force value, where the high precision force control is required to achieve the high precision polish for objects. Vibration generated by the motor with periodic rotation, however, deteriorates the trajectory performance in target press force, resulting in the lower control accuracy of the system. In order to provide the precise force performance, therefore, a simple feedback compensator is designed to improve the disturbance suppression characteristic at specific frequency, where a resonant filter is adopted by paying attention to vector locus of the open-loop characteristic The proposed control approach has been verified by experiments using an actual pneumatic cylinder system.

Force controller design based on PQ method for dual-stage actuators in polishing machines

This paper presents a controller design approach to realize a precise force control of load devices in polishing machines. In the load device, a pneumatic actuator and a voice coil motor are combined as dual-stage actuators to expand the servo bandwidth. However, the interference between the dual actuators may deteriorate the servo performance, especially at around the cross-over frequency. In this paper, therefore, PQ method is adopted to achieve the high precision force control by the expansion of servo bandwidth, where the compensators are especially designed to suppress the interference. The proposed approach has been verified by experiments using an actual load device of the polishing machine.

Robust vibration suppression control for resonant frequency variations in dual-stage actuator-driven load devices

This paper presents a controller design approach considering robustness against resonant frequency variations in load devices. In the target load device, a pneumatic actuator and a voice coil motor are combined as a dual-stage actuator to expand the servo bandwidth. In order to provide the precise control performance, not only interference between actuators but also resonant vibrations should be compensated. In addition, the controller should be designed to achieve the robust frequency variations. In this paper, PQ method is applied to compensate for the basis of H∞ control framework. The proposed approach has been verified by experiments using a prototype of load device.

Controller design for dual-stage actuator-driven load devices considering suppression of vibration due to input saturation

This paper presents a controller design approach considering vibration suppression due to input saturation for load devices. In the target load device, a pneumatic actuator and a voice coil motor are combined as a dual-stage actuator to expand the control servo bandwidth. However, vibrations due to the input saturation of the voice coil motor deteriorate the force tracking performance for the desired load reference. In this research, therefore, a loop-shaping approach is adopted to suppress the vibration, where a compensator is designed to improve the disturbance suppression at the plant resonant frequency. The proposed approach has been verified by experiments using a prototype of load device.