Toshinori Fujita

Feedback linearization for pneumatic actuator systems with static friction

Abstract Though pneumatic actuators are widely used in industrial applications, it is not easy to control them because of the nonlinearities in the valve, the compliance variation and the generating force. In this paper, a method of feedback linearization is applied to a pneumatic actuator system to handle the nonlinearities. It is shown that any single-input pneumatic system with a linearizable load and an isothermal pneumatic actuator is linearizable by state feedback. In addition, feedback linearization with step-type disturbance rejection is proposed by measuring disturbances, which is useful for pneumatic systems with static friction. Experiments with a rubber artificial muscle actuator that has hysteresis characteristics caused by static friction are carried out, and verify the effectiveness of the proposed method.

Instantaneous Flow Rate Measurement of Ideal Gases

In this paper, a chamber called an Isothermal Chamber was developed. The isothermal chamber can almost realize isothermal condition due to larger heat transfer area and heat transfer coefficient by stuffing steel wool in it. Using this chamber, a simple method to measure flow rates of ideal gases was developed. As the process during charge or discharge is almost isothermal, instantaneous flow rates charged into or discharged from the chamber can be obtained measuring only pressure in the chamber. The steady and the unsteady flow rate of air were measured by the proposed method, and the effectiveness of the method was demonstrated.

Study on dynamic characteristic analysis of air spring with auxiliary chamber

Abstract The characteristics of air springs, such as the effects of bellows and those of heat transfer on spring constant and damping factor, have been studied. However, auxiliary chambers and pipes are required in addition to air springs, to vary spring constant in the case of spring rate change by electronically controlled air suspension systems of a vehicle. Few reports have dealt with the effects of auxiliary chambers and pipes. In our study, the relation between vibration frequency and spring reaction has been investigated to clarify the effects of pipes on dynamic spring constant. Our proposed model has proved effective in understanding the phenomena.

Influence of Air Temperature Change on Equilibrium Velocity of Pneumatic Cylinders

This paper shows that equilibrium velocity of pneumatic cylinders not only depends on the effective area of the outlet speed control valve but also on the air temperature at the discharge chamber. Different equilibrium velocities were obtained experimentally with the same speed control valves, when load mass or initial pressure at the discharge chamber was changed. The different equilibrium velocities are explained by the air temperature change. Experiments are simulated using a cylinder model considering heat transfer. Experimental and simulation results are in good agreement.

Air consumption of pneumatic servo table system

We have developed a pneumatic servo table system, which is a precise positioning system using air power. In this paper, the energy consumption of the pneumatic servo table system is investigated. To clarify the energy consumption, the air consumption must be clarified. We analyzed the air consumption of the system and became clear theoretically that the air consumption could be separated to the consumption to move the table and that to accelerate. The certainty of the analysis is confirmed with the experimental result using quick response laminar flow meter. Furthermore the best reference trajectory is derived on the point of energy saving.

CHARACTERISTICS MEASUREMENT OF PNEUMATIC ELEMENTS USING ISOTHERMAL CHAMBER

In this study, methods for the characteristics measurement of pneumatic elements using isothermal chamber, the methods for the flow rate and dynamic characteristic measurement of pneumatic control valve, are proposed. An isothermal chamber is a chamber in which the steel wool is stuffed and isothermal condition can almost be realized. Therefore, the instantaneous flow rate could be measured only from the pressure response using the state equation of gas. Effectiveness and simplicity of the proposed method are confirmed by comparing the measured results obtained by proposed methods with the methods defined JIS and the ISO standards.

Precise Position Stages Using Pneumatically Driven Bellows Actuator and Cylinder Equipped with Air Bearings

In this chapter, two precise positioning stages using pneumatic actuators are introduced. One is for coarse movement and utilizes a pneumatic cylinder with air bearings. The other is for fine movement and utilizes an actuator driven by two pneumatic bellows. Novel servo valves, also developed by the authors, control the actuators. A high performance pneumatic servo valve having high dynamics up to 300 Hz is used for the coarse stage, while a slit type nozzle flapper servo valve that can minimize pressure fluctuations is used for the fine stage. As the proposed system is pneumatically driven, both stages have low heat generation and are nonmagnetic, making them suitable for ultra precise positioning. Our investigations determined that, for the coarse stage, the maximum tracking error was less than 20 µm and the steady state error was just 0.4 µm. For the fine stage, the tracking error was less than 50 nm and steady state error was just 10 nm.

Study of Nonlinearity of Pneumatic Servo Table System

Pneumatic servo table system is one of a precise positioning system using air power. We have derived the linearized model of the pneumatic servo table system and have designed the controller and the observer based on the derived linear model. On experimental results, the servo table system shows tracking error on the linear model based control. This tracking error comes from the discrepancy between the actual system and the linear model.

Characteristics Measurements of the Pneumatic Flow Control Valves.

Recently, pneumatic flow control valves having high responses have been developed and are being wide-ly used. It is very important to know the characteristics of the valves for structuring pneumatic servo systems. The method for measuring the dynamic characteristics of the valves has yet to be established, because of the difficulty of the unsteady flow rate measurements of the compressible fluids.In this study, simple methods to measure the input-output characteristics and the frequency characteristic of the flow control valves using an isothermal chamber are proposed. The isothermal chamber is a chamber in which steel wool is stuffed into a normal chamber to make the heat transfer area larger, and could almost simulate an isothermal condition. Therefore, the flow rate could be obtained only by measuring the pressure in the chamber. Two types of servo valves and proportional control valves were tested using the proposed method. At the same time, the spool displacement of the valves were measured. The effectiveness of the proposed method was confirmed by comparing the results obtained from the proposed method and the spool displacement of the valves. In addition, it could be clarified that the frequency response could be measured up to a frequency of 140Hz by this method.