PWM (Pulse width modulated) solenoid valves possess the advantages of low cost, high flow rate gain, and simple structure. However, the use of a PWM solenoid valve causes both discontinuity and nonlinearity of the flow rate; this results in difficulties of modeling and of control. This paper presents our work on modelling a pneumatic PWM solenoid valve for engineering applications. Two models are presented: one is the instantaneous mass flow rate model which can be used in the simulation to study the dynamic behavior of pneumatic PWM control systems; another model is the equivalent mass flow rate model which is developed for facilitating the synthesis of pneumatic PWM servomechanisms. An equation for determining the maximum operating modulation ratio of the PWM solenoid valve is also presented. Simulated results using the established models are compared with the experimental results for both the static characteristics of a PWM solenoid valve and the dynamic behavior of a system composed of a PWM solenoid valve and a constant volume chamber.

SUMMARYIn this paper we develop a compilant system that permits robotic assembly of chamferless pieces. The idea is to absorb the positioning error between parts to be inserted by giving one of them a planar random movement. An actuator consisting of two axes (X and y) operated by an electromagnetic System is fitted to the work table; when its inputs are pseudo-random binary signais (P.R.B.S.) random motion is obtained. The trajectories of the actuator are analysed depending upon the P.R.B.S. parameters and a peg-in-a-hole assembly task is carried out. Experimental results show that large positioning errors can be compensated for chamferless insertions.

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A method is presented for measuring diffusion coefficient in molecular sieves where gas adsorption in the sieve does not appear because the experimental temperature pressure conditions are far from equilibrium liquid-vapour conditions. The method determines the relation which connects the pressure variation of gas in a system formed by a cell, including the sieve, to the volume variation applied to the cell. The value of the diffusion coefficient for the molecular sieve can be obtained by the analysis of the pressure in terms of time. The method of obtaining the diffusion coefficient is related to a problem of process identification, and thereby the authors have naturally been led to make use of the usual inputs of the technique: i.e., unit step response, harmonic and random analysis. The authors consider the study of theoretical problems raised in the measurement of diffusion coefficient by the use of these three experimental techniques; the description of the apparatus, the experimental results and their synthesis.