Kyoji Hashimoto

Trajectory control of a one-link arm using pneumatic rubbertuator

This paper deals with the trajectory tracking control of a one-link arm using pneumatic rubbertuator in which the preview learning control method is applied to improve the system response. The tracking performances for the repetitive reference trajectory are examined by computer simulations and experiments. The computer simulation and experimental results show that the tracking errors produced by the conventional PI control can be greatly reduced by using the preview learning control.

Adaptive Force Control of a Pneumatic Cylinder Using a Pressure Control Loop.

The performance of a pneumatic force control system is affected by the characteristics of objects, compressibility of air, friction between cylinder and piston, etc. To suppress the influence of these factors, a combined control method using a P-D pressure controller for the cylinder and an adaptive model reference controller for the total system is presented in this paper. The P-D gains are determined experimentally, and the pressure command signal is produced by the adaptive controller, which is constructed based on the discretization of the third-order continuous-time transfer function with a lag time.Force control experiments were carried out for hard and soft objects using two kinds of controllers, that is, (A) adaptive controller without pressure control and (B) adaptive controller with pressure control. Comparing the experimental results by (A) and (B), the tracking error between the reference force signal and applied force was greatly improved by the proposed controller (B), and especially, steady-state error of (B) was 0.5N for hard object and 0.7N for soft object in the sense of the root mean square of 30 trials. The robustness of (B) to the sudden change in the supplied pressure was also confirmed.

Speed Control of a Pneumatic Motor by Using an Adaptive Control Scheme.

This paper describes an adaptive speed control scheme for a pneumatic servo system which is composed of an axial piston motor and an electro-pneumatic proportional valve. The features of the adaptive control scheme are that it is applicable to non-minimum phase systems and that its structure is as simple as the MRAC.Experiments of the adaptive speed control were carried out for several conditions, and their results were compared with those of the conventional PI-D control. From the experimental results summarized below, the effectiveness of the proposed scheme was confirmed : (1) Three sampling periods (Ts=36, 71, 106msec) were tested, and the stability of the adaptive control system was confirmed for each Ts even through the identified plant model was non-minimum phase. The steady state error was not influenced by Ts, and its maximum value (±1.0rpm) was smaller than that of PI-D control (±2-±2.5rpm) for a reference speed larger than 300rpm.(2) The second order reference model was used to specify the wave-form of the step response, and good tracking performance was obtained for several damping coefficients and natural frequencies. The distortion of the step response for large amplitude inputs was much smaller than that of PI-D control.(3) A sudden change of the load torque or supplied air pressure was applied to the control system as a disturbance. The speed fluctuation was much the same as that of PI-D control.

Simple desingn method for process control system with smith compensator.

むだ時間を有するプロセスをフィードバック制御する場合, むだ時間が大きいと安定性が損なわれる.スミスにより提案されたむだ時間補償法は, むだ時間を見掛け上閉ループから追いだし, 通常の制御を可能とするもので, 簡単に制御系が構成できることから古くよりその応用が検討されてきた.操作部におけるむだ時間を考慮した分離制御への試み, 実用プラントでの応用が報告され, また理論的なむだ時間補償における問題点が論じられている.ところで, このスミスによる補償法の欠点は制御対象のむだ時間の正確な同定を前提としている.非線形な物理現象を多く含む複雑な化学プロセスからむだ時間を正確に推測することは困難である.本研究では, 従来の制御系の設計法でよく行われている制御対象を一次おくれとむだ時間でモデル化し, ディジタルPID制御にスミス補償法を適用した場合, 非常に良好な制御が得られたので, その簡単な設計法を報告する.

Improvement in control performance of digital PID control systems with saturation in a manipulated variable.

When a large chage is introduced in a reference value, saturation in a manipulated variable results. This would often happen for the control system which has rapid response. That gives undesirable effects and the response becomes rather oscillatory. In this case a softening filter works effectively. A first-order softening filter for the digital PID control system is discussed in this paper. A simple desing method for the filter is considered. The proposed method may be considered as a practical and effective one to improve control performance.

The Analysis of Transient Response of Hydraulic Line Systems Including Viscoelastic Pipe

In this paper, analyses of transient responses for hydraulic line systems including viscoelastic pipe are made by using an approximate calculating method due to frequency response.The transfer functions of test lines were first derived by using a transfer matrix of the transmission line.In this transfer matrix, the viscoelastic characteristics of the pipe material and frequency dependent unsteady friction were taken into consideration.The numerical results using the frequency transfer functions are compared with the strict solution obtained by applying the characteristics method or the experimental results. Also, the comparisons of the CPU time between the numerical methods using the frequency transfer function and the characteristics method (high-speed computing method) are made by using a personal computer. These results confirmed that the approximate calculating method due to frequency response is useful for analyzing the transient response of hydraulic line systems including viscoelastic pipe.

Analysis of transient response of a pneumatic line considering the viscoelastic characteristics.

An approach is developedf or analyzingt he transient response of a pneumatic line with a viscoelastic wall. In the algorithm based on the characteristics grid method, the viscoelastic characteristics of pipe material together with the compressibility of air are taken into consideration. The numericalr esultsw erec ompared with the experimental results and the ones obtained by simulation treated as an elastic pipe. Nylon or rubber tubes were used in this study and the following conclusions were drawn: (1) In the case of the tube with negligible distensibility in comparison with the compressibility of air, it was confirmed that the resultst reated as an elastic pipea gree fairly well with those obtained experimentally. (2) By using a tube with unnegligible distensibility in comparison with the compressibility of air, it was confirmed that the approach which considered the viscoelastic characteristics of pipe material is effective for simulating the transient response.

Transient response of oilhydraulic pipelines with viscoelastic walls.

This paper reports the transient response of oilhydraulic pipelines having viscoelastic walls. Two viscoelastic hoses of different material were used in the present research. Numerical results obtained by the characteristics grid method(CGM) or characteristics method (CCM) were compared with the experimental results. The following conclusions were drawn: (1) In the numerical approach based on CGM, variation in viscoelastic parameters due to pressure change in the pipes was taken into consideration. The numerical results agree fairly well with those obtained experimentally. This approach is thus effective for predicting the transient response of very viscoelastic pipes. (2) In the case of slightly viscoelastic pipes, the numerical procedure of including frequency dependent unsteady friction is necessary for an accurate analysis of the transient response. Also, the numerical results by CCM agree fairly well with those obtained experimentally. (3) The numerical results for the elastic pipes were at variance with the experimental results. Thus, the viscoelastic model is necessary for an accurate analysis of transient response.