Hydraulic power steering systems, which can provide a large steering assist force, are widely used for heavy-duty commercial vehicles. For the research of a stability control system for commercial vehicles, a combined simulation model for the vehicle, including IPS (Integral Power Steering) system and vehicle body, was constructed. Then linearization and order-reduction of the simulation model were performed for model based controller design. Compared with experimental results, it was found that the established simulation model can adequately represent the dynamic behavior of the vehicle.The linear low-order model was also verified by comparison of eigenvalues and frequency domain responses. Finally, a yaw rate control system was designed based on the linear models and tested on the combined simulation model, which shows the validity of the simulation model and linearized low-order model.

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A power assist system is operated by a human operator, so it is very important to consider the human element in the control loop. In order to evaluate the performance of the power assist system in the design process, usage of simulation, which includes the human factor, is quite effective. In this study simulation of a pneumatic hand crane for work support is developed for system design. The mathematical model of the hand crane consists of the pneumatic cylinder model, link model of the crane and controller, which includes the human model, in order that the hand crane is operated passively by operation force. The validity of the simulation was examined by comparison with measurements results of the operation force and acceleration, and thus performance of the hand crane is evaluated.

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A new pneumatic cylinder on which a micro optical encoder chip was mounted was developed. The cylinder has a position detecting function and makes position/force servo systems possible. The structure of the cylinder is very simple and the size is almost the same as that of a conventional cylinder with the same specifications. Cylindrical stripe codes, typically having a 0.169mm pitch, were fabricated on the piston rod surface through a fine oxidization process with a YAG laser and were detected by the optical encoder. Two prototype models were designed and developed for both human machine interfaces and for industrial uses. A compact controller based on a PSoC was also developed for them. Three typical control algorithms, force control, position control, and an adaptive position control are developed and shown in this paper. The results of servo experiments using them show that the servo systems work very well.

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