Atsushi Hara

A Study on High-Speed and High-Precision Tracking Control of Large-Scale Stage Using Perfect Tracking Control Method Based on Multirate Feedforward Control

In hard-disk-drive control, the perfect tracking control (PTC) method has already obtained high performance. Therefore, the first author and his group study the PTC scheme for improving the performance of large-scale stages. This paper presents an application of the PTC scheme to the tracking control of two different stages. The results from both simulations and experiments show that the PTC method outperforms the conventional rigid-body-mode-based feedforward method.

A study on high-speed and high-precision tracking control of large-scale stage using perfect tracking control method based on multirate feedforward control

In a control of hard disk drive, perfect tracking control (PTC) method has already gained high performance. Therefore, the first author and his group study PTC scheme for improving performance of large-scale stages. This paper presents an application of PTC scheme for two-types tracking stage. We compare performances of PTC method with a conventional method. Finally, the results of simulation and experiment show the advantages of PTC method which provides high performance.

Basic examination on simultaneous optimization of mechanism and control for high precision single axis stage and experimental verification

In this paper, simultaneous optimization of mechanism and control is discussed for a high precision stage. We pay attention to zeros of a continuous-time plant, and the relationship between a sensor and zero positions has been clarified. In addition, it has been shown that similar relations are provided in structural change of a plant. After the zero position desired for a control system is shown, the vibration suppression PTC (Perfect Tracking Control) is applied to the plant with that condition. Finally, the effectiveness of proposed methods are verified by a simulation and an experiment.

Settling time shortening method using final state control for high-precision stage with decouplable structure of fine and coarse parts

High-precision stages require high-speed and high-precision control to improve their production throughput and quality. However, it is expected that their motion speed and accuracy will reach a limit in the near future if the structure of the conventional high-precision stage is used. Therefore, the authors designed and fabricated a stage called the catapult stage which has a decouplable structure consisting of a fine stage and a coarse stage. This stage is different from conventional dual stages in which the fine stage would be disturbed by the coarse stage since they contact with each other. This paper proposes a novel control system design for the catapult stage, and a settling time shortening control method using final-state control (FSC). So far, FSC is mainly applied to the applications such as hard disk drives whose initial states are the zero. However, it is important to consider the initial states for the catapult stage since the initial position, velocity and acceleration of the catapult stage are not equal to zero. Simulations and experimental results demonstrate the effectiveness of the proposed methods.

Application of mode switching control using initial state variables in constraint final-state control to high-precision dual stage

Precise positioning stages with high-speed and high-precision control performance are increasingly required for improving production efficiency and quality. In this paper, a final-state control method considering input limitation is applied to a novel high-precision dual stage during acceleration. In the method, the timing to activate the final-state control is automatically determined by a proposed criterion. The method can significantly reduce the calculation time so that real-time implementation becomes possible. Experimental results illustrate that the method can reduce the maximum thrust of the fine stage without degrading control performance.

Design fabrication and control of 4-DOF high-precision stage

Motion control techniques are employed on nanoscale positioning in precision mechanical equipment, for example, NC machine tools, exposure systems, and so on. In our past paper, we designed and fabricated an experimental 1-DOF precision stage. Then, we achieved a high-speed nanoscale positioning and a master-slave synchronous position control with another 1-DOF stage. However, the stages in actual industrial equipment often have several degrees of freedom. The degrees of freedom have to be controlled simultaneously. In this paper, a new experimental 4-DOF high-precision stage is designed and fabricated. The 4-DOF stage can move to not only one translation but also the height, the pitching, and the rolling directions. Then, a control system for the 4-DOF stage is proposed. Finally, experiments are performed to show the advantages of the proposed method.

Design fabrication of high-precision stage and ultrahigh-speed nanoscale positioning

Motion control techniques are employed on nanoscale positioning in precision mechanical equipment, for example, NC machine tools, exposure systems, and so on. The advanced motion control techniques are based on the precise current control. However, speed-up of the precise current response has a serious limitation because of the carrier period of an inverter. In addition, the positional response has to be slower than the current response. In this paper, an experimental precision stage was designed and fabricated. Then, a novel ultrahigh-speed nanoscale positioning was achieved based on multirate PWM control. The positional error is in 100 nm. The positioning time is 2 ms which is only 20 times as long as the carrier period.

Reduction of impact force by model prediction and final-state control for a high precision catapult stage

The catapult stage is a high-precision dual stage with a new structure which, by allowing contact between fine and coarse parts, is compatible with increasing size and acceleration. Impact force occurs in acceleration and deceleration regions, and may degrade a stage. This paper thus proposes a control method to reduce the impact force that considers the thrust limitation by combining model prediction and final-state control. In the proposed method, the timing to activate the fine stage is automatically determined by solving an optimization problem. Simulation and experimental results demonstrate that the method can significantly reduce the impact force between the fine and coarse parts.

Trajectory tracking control for pneumatic actuated scan stage with time delay compensation

A pneumatic actuator has several advantages such as low heat generation, high weight power ratio, and low cost. However, it has several disadvantages such as time delays and nonlinearities. Because pressure and position feedback band-widths are limited by the time delay problem, it is difficult to implement a pneumatic actuator for a scan stage. Therefore, this paper proposes a modified Smith predictor for it and implements for an experimental scan stage. The effectiveness of the proposed control system is validated by frequency and time domain experiments.