Kenta Seki

High-Precision Motion Control Techniques: A Promising Approach to Improving Motion Performance

In this article, the state of the art on high-precision motion control techniques is surveyed by referring to recent publications, mainly in the transactions and conferences of the IEEEIndustrial Electronics Society (IES), where a 2-degree-of-freedom (DoF) control framework is considered a practical and promising approach to improving motion performance. The actual issues and relevant solutions for each component in the 2-DoF control structure are clarified. Next, one of the examples, a 2-DoF controller design for robust vibration suppression positioning, is presented as an application to industrial high-precision positioning devices. Precise modeling and identification for the target mechatronic systems should be indispensable from the standpoint of more accurate model-based feedforward compensation and/or more progressive design of feedback controllers.

Adaptive Compensation for Reaction Force With Frequency Variation in Shaking Table Systems

This paper presents an adaptive control methodology of a shaking table system for earthquake simulators. In the system, reaction forces generated by a specimen deteriorate the table motion performance, resulting in lower control accuracy in seismic tests. In particular, in cases of excitation tests for structures (power facilities, large vehicles, etc.) including motors with periodic rotation, the reaction force as a disturbance is excited with a specific frequency during their actual operations. In addition, the variation of the rotational frequency in the motor causes the variation of frequency in the disturbance. In order to compensate for the disturbance, therefore, an adaptive feedback compensator is designed to improve the disturbance suppression capability, by applying an adaptive notch filter to identify the frequency in an online manner. The proposed control approach has been verified by experiments using a prototype of a shaking table system.

Practical Controller Design of Hybrid Experimental System for Seismic Tests

A hybrid experimental system is one of the powerful tools to perform various seismic tests for unknown and/or huge structures, where an actuator-excited experimental vibratory system and a computational response analysis are simultaneously combined and implemented. This paper presents a control methodology for high-performance hybrid experimental systems. A 2-DOF control framework is applied from the viewpoint of control techniques, where a feedback compensator is designed according to the system stabilization analysis, and a feedforward (FF) compensator is designed to achieve the desired servo characteristics. In the FF compensator design, an iterative learning control approach is particularly adopted to eliminate the response delays in the hydraulic actuator. The proposed compensation algorithm has been verified using a laboratory hybrid experimental set up with two-mass structure as a load mechanism.

High-precision positioning considering suppression of resonant vibration modes by strain feedback

This paper presents a control methodology for high-precision positioning system. In order to realize the high-precision in positioning, the expansion of servo bandwidth is one of the promising approaches. However, since most of mechanisms inherently include mechanical vibration modes around the control response frequency, the control bandwidth is restricted by the resonant frequency. In order to provide the precise positioning performance, therefore, it is indispensable to suppress the mechanical vibration modes. In addition, the controller should be designed to achieve the robust properties against the frequency variations in the vibration modes. In this paper, a robust positioning system is designed by a feedback compensator using a direct signal of vibration modes, where a piezoelectric element is used to detect the vibration signal as a strain signal due to the plant deformation. The proposed approach has been verified by experiments using a positioning device for galvano scanners.

Feedforward Compensation by Specified Step Settling With Frequency Shaping of Position Reference

This paper presents a frequency shaping of position reference in a framework of deadbeat feedforward compensation with specified step settling. In the proposed compensation, a control design freedom is additionally expanded to the frequency shaping in the original position reference, while the feedforward compensation ensures the specified step settling performance under the conventional control scheme. As a result, a two-degree-of-freedom positioning controller using the proposed approach can improve the settling performance with residual vibration suppression rather than the conventional approach. The effectiveness of the proposed shaping has been verified by experiments using a prototype of linear-motor-driven table system.

Modeling and compensation for hysteresis properties in piezoelectric actuators

This paper presents a modeling and compensation approach for hysteresis properties in piezoelectric actuators. Nonlinearities due to the hysteresis and creep phenomena inherently exist in the piezoelectric actuator, resulting in the low control performance in positioning and/or tracking accuracy. In this paper, at first, the hysteresis property is mathematically modeled by Prandtl-Ishlinskii model. Based on the mathematical hysteresis model, an inverse model-based compensator combined with linear feedback controller is applied to compensate for the nonlinearities in piezoelectric actuator. The proposed approach has been evaluated by experiments using a piezo-actuated stage.

Improvement of control performance in shaking-tables by feedback compensation for reaction force

This paper presents a practical control methodology of shaking tables for earthquake simulators. Reaction force generated by a nonlinear specimen on the shaking table generally deteriorates the motion performance of the table, resulting in the lower control accuracy of seismic tests. In order to provide the precise table motion, therefore, a compensator for the reaction force is designed by using a force sensor. The compensator can be designed under considerations of the relationship between the reaction force and the compensation signal, to achieve the desired disturbance suppression performance. The proposed approach has been verified by experiments using a laboratory shaking table system.

Fast-response positioning using H ∞ control in machine tools

This paper presents a robust positioning algorithm for the fast-response and high-precision machine tool drives. In the research, a robust compensator designed by the H/sub /spl infin// control framework is applied to the positioning system in machine tools, where the resonant vibration suppression, the robust stability against parameter variations of unknown vibration modes, and the fast servo characteristic are paid particular attention to the robust compensator design. As a result, the desired positioning with the robust performance can be achieved. The effectiveness of the proposed controller has been verified by experimental results using a positioning system of industrial machine tools.

Improvement of vibration suppression performance of galvano mirror using piezoelectric element

This paper presents a vibration suppression approach for galvano mirrors in laser positioning systems. The systems require the fast and high-precision positioning of the mirror and should maintain the flatness of the mirror after positioning to ensure the control performance. However, resonant vibrations of the mirror, which are excited by the moment force during positioning, lead to residual vibrations after positioning, deteriorating the flatness of the mirror and laser manufacturing accuracy. In this paper, therefore, a vibration suppression approach is proposed by mounting a piezoelectric element on the mirror, where a multi-function of the piezoelectric element as an actuator and a sensor are applied to design the vibration suppression controller. The applicability of the proposed approach to industrial galvano scanners has been verified by performing experiments using a prototype.

Application of self-sensing actuation using piezoelectric element for vibration suppression of galvanometric mirror

This paper presents a vibration suppression approach for a galvanometric mirror in laser positioning devices. In the system, it is important to achieve a fast and high-precision positioning of the mirror by a motor. In addition, it is indispensable to maintain flatness of the mirror after position settling. However, since natural vibration frequencies of the mirror are excited by the force of moment generated during positioning, and corresponding residual vibration occurs, it is difficult to maintain the flatness of the mirror. In this paper, therefore, the vibration is directly suppressed by mounting a piezoelectric element on the mirror, where the function of both sensor and actuator of the piezoelectric element is simultaneously used. The proposed approach has been verified by experiments using a positioning device for industrial galvano scanners.