Motohiro Kawafuku

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.

Deadbeat Feedforward Compensation With Frequency Shaping in Fast and Precise Positioning

This paper presents a novel deadbeat feedforward compensation technique for fast and precise positioning control in mechatronic systems. The proposed compensation provides the desired frequency shaping in control input to suppress the residual vibration, under the constraint of a specified step number in position reference. A 2-DOF positioning controller with the deadbeat feedforward compensation can ensure the required settling performance with the specified steps regardless of the positioning amplitude in reference. The effectiveness of the proposed approach has been verified by numerical simulations and experiments using a prototype of a galvano scanner.

Initial Value Compensation Using Additional Input for Semi-Closed Control Systems

This paper presents a novel initial value compensation (IVC) using an additional input for semi-closed control systems. The authors have already proposed the IVC approach using the additional input for residual vibration suppression in the fast and precise positioning control. In the approach, however, an essential subject has remained, i.e., the positioning control in the load side could not satisfy the required performance because the systems have been constructed under the assumption of a semi-closed control system. An improvement of the control performance in load position, therefore, is discussed in this paper, where the appropriate assignments of poles and zeros in IVC are ensured, considering the transfer functions of position in both sensor and load for the control initial values. The effectiveness of the proposed approach has been verified by numerical simulations and experiments using a prototype.

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.

Nonlinear modeling and evaluation of rolling friction

This paper presents a nonlinear friction modeling and its evaluation for rolling friction behaviors in ball screw-driven table systems. The rolling friction behaves as a nonlinear component in the table drive mechanism, especially in the micro-displacement region, deteriorating the control performance in the fine positioning. The friction characteristic, therefore, should be clarified to provide the precise mathematical simulator and to design the effective compensators. In the friction modeling, the characteristics of rolling friction, which are depending on the displacement region, are especially paid attention: In “starting rolling displacement region”, the friction force dynamically varies for the displacement after velocity reversal. In “rolling region”, on the other hand, the friction force statically indicates the Coulomb friction. Based on the nonlinear behaviors, the rolling friction can be mathematically modeled, and the rolling friction model can express both the dynamic and static characteristics of friction after the reversal. The proposed nonlinear modeling of the rolling friction has been evaluated in both frequency and time domains using a prototype for industrial positioning devices.

2DOF Control-Based Fast and Precise Positioning Using Disturbance Observer

The paper presents a practical compensator design approach for the fast-response and high-precision positioning using a two degrees-of-freedom (2DOF) controller. In the controller design for mechatronic positioning devices, effects of resonant vibrations and nonlinear friction on the positioning performance are especially paid attention. A feedforward control based on a coprime factorization description successfully suppresses the mechanical vibrations and provides the fast response. A feedback control with a disturbance observer, on the other hand, allows the plant system to behave a nominal one with robust stability, and compensates for effects of nonlinear friction on the positioning performance. The disturbance observer is especially designed in order to improve the servo characteristic in positioning, where an initial value compensation based on a rolling friction model is adopted at the starting motion. The proposed positioning controller has been verified by experiments using a prototype which simulates the vibratory mechanism with the nonlinear friction and the dead time components

Initial value compensation using additional input for semi-closed control systems

This paper presents a novel initial value compensation (IVC) using an additional input for semi-closed control systems. The authors have already proposed the IVC approach using the additional input for residual vibration suppression in the fast and precise positioning control. In the approach, however, an essential subject has been still remained that the positioning control in load side could not satisfy the required performance because the systems have been constructed under the assumption of a semi-closed control system. An improvement of the control performance in load position, therefore, is being discussed in the paper, where the appropriate assignments of poles and zeros in IVC are ensured, considering the transfer functions of position in both sensor and load for the control initial values. The effectiveness of the proposed approach has been verified by numerical simulations and experiments using a prototype.

2DOF Control-Based Fast and Precise Positioning for Vibratory Mechanism with Nonlinear Friction

The paper presents a practical compensator design approach for the fast-response and high-precision positioning using a two degrees-of-freedom (2DOF) controller. In the controller design for mechatronic positioning devices, effects of resonant vibration, nonlinear friction, and dead time components on the positioning performance are especially paid attention: a feedforward control based on the coprime factorization description successfully suppresses the mechanical vibrations and provides the fast response, where a disturbance observer compensates for effects of nonlinear friction on the positioning performance. The Smith method, on the other hand, is adopted to the designs of both the feedforward compensators and the disturbance observer, in order to compensate for the effects of the dead time. The proposed positioning controller has been verified by experiments using a prototype which simulates the vibratory mechanism with the nonlinear friction and the dead time components

DISTURBANCE OBSERVER-BASED PRACTICAL CONTROL OF SHAKING TABLES WITH NONLINEAR SPECIMEN

Abstract 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 the seismic tests. In order to provide the precise table motion, therefore, a disturbance observer-based control approach is adopted, where the unknown disturbances in the table can be compensated in real time manner. The proposed compensation algorithm has been verified by experiments using an actual shaking table system.

Residual vibration suppression using initial value compensation for repetitive positioning

This paper presents a novel residual vibration suppression methodology for the repetitive fast-response and high-precision positioning in machine tool drives. In sequential positioning motions, as the interval period of position references becomes shorter, the residual vibration in response due to undesired initial values deteriorates the positioning accuracy, since the positioning controller is generally designed on the condition that initial state variables are zero. In this research, an initial value compensation (IVC) approach is proposed under the theoretical study on effects of the initial values on the position transient response. The IVC can appropriately assign poles and zeros of the transfer characteristic of position output for the initial values by applying an additional input corresponding to the initial state variables, enabling the response to be residual vibration free. The desired positioning performance, as a result, can be achieved in repetitive motions with arbitrary interval period. The effectiveness of the proposed compensation has been verified by numerical simulations and experiments using a positioning device of industrial machine tools.