Kazuaki Saiki

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.

Design and control of 6-DOF high-precision scan stage with gravity canceller

High-precision scan stages are used for fabrication of integrated circuits, liquid crystal displays and so on. To fabricate such precise devices, not only stages position but also stages attitude needs to be controlled rapidly and precisely. In this paper, an experimental 6-degree-of-freedom (6-DOF) high-precision stage with a novel 6-DOF air bearing called “gravity canceller” is designed and fabricated. The 6-DOF stage consists of a fine stage and a coarse stage. The gravity canceller compensates for the fine stages gravity and supports the fine stage without friction. This structure enables us to reduce heat which is generated close to the fine stage. For a 6-DOF control problem, attitude control is as important as translational control. Rotational motion, however, has nonlinearity and coupling arising from dynamics and kinematics which could degrade the attitude control performance. Therefore, in our past paper, our research group proposed a multi-input multi-output nonlinear feedforward attitude controller to compensate such problems. Experiments were performed to verify the effectiveness of the attitude controller by using the new experimental 6-DOF stage.

Improvement of Fast and Precise Positioning of Large-Scale High-Precision Step-Stage Based on Vibration Suppression PTC

In the positioning system of the large-scale high-precision step-stage, the primary resonance mode appears in low frequency even in the high stiffness stage. The resonance mode is a major obstacle of fast and precise positioning. In this paper, we apply vibration suppression PTC (perfect tracking control) which can control the resonance mode actively on the large- scale stage. Finally, simulations and experiments are performed to show the advantages of the vibration suppression PTC.

Application of Perfect Tracking Control to Large-Scale High-Precision Stage

Abstract In the positioning system of the large-scale high-precision stage, the primary resonance mode appears in low frequency, though large-scale high-precision stages are used in industrial fields. In recent years, our research group has applied the perfect tracking control (PTC) method which can design the perfect inverse system of the plant to a large-scale high-precision stage to improve the control performance. Moreover, a synchronous position control based on PTC method is proposed as application to several stages. In early sections, the application of the PTC method to a large-scale stage is introduced. In latter sections, the application to synchronous position control is introduced.

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.

Proposal of attitude control for high-precision stage by compensating nonlinearity and coupling of Euler's equation and rotational kinematics

High-precision stages are used for the fabrication of integrated circuits, liquid crystal displays and so on. Since higher integration density and product quality are continuously required for the development of industry and informatics, not only the stage position but also the stage attitude needs to be controlled rapidly and precisely. The attitude is determined by roll, pitch and yaw motions which are affected by nonlinearity and coupling caused by Eulers equation and rotational kinematics. These effects deteriorate the attitude control performance. This paper proposes a MIMO nonlinear feedforward attitude controller which compensates such effect. The effectiveness of the proposed approach is verified by simulations and experiments.

Basic examination of simultaneous optimization of mechanical and control design for gantry-type precision stage modeled as two-mass 4-DOF system

Gantry-type precision stages are generally designed so that its center of mass can be moved using motors. However, it is impossible to set the gap between the center of mass and the drive point to be exactly zero in real processes manufacturing. This gap causes resonance in the pitching direction. In this paper, a two-mass four-degree-of-freedom (4-DOF) model is constructed for the stage with the gap. Then, the design optimization method of particular parameter variations of the stage is proposed. Finally, simulations and experiments with an experimental precision stage are performed to show the advantages of the proposed optimization method.