This paper deals with the chaotic oscillations occurring in a direct-acting poppet valve circuit with a long pipeline. The system is liable to be unstable and various kinds of oscillations are induced. In this study, a distributed parameter model with average friction was used for the system. The governing equations were spatially discretized into ordinary differential equations with respect to time. The chaotic phenomenon was elucidated numerically based on power spectrum, phase plane trajectory, bifurcation diagram, Poincare map and Lyapunov exponent from the results of the simulation. The route of Lorenz type to chaos from the almost periodic oscillation can be found, using the supply pressure as the control parameter.

抄録全体を表示

This paper describes a design method of a position control system using a disturbance observer for a pneumatic robot manipulator. First, to control the dynamic characteristics of a pneumatic actuator, a pressure control system was developed. The two-degrees-of-freedom control system is used to standardize a pressure response of a pneumatic actuator to the desirable reference characteristic model. Second, to improve the control performance, the position control system using a disturbance observer is designed based on the reference characteristic model. The transfer function of the position control system corresponds with the reference characteristic model when the position control system is at its height against the nonlinear forces such as frictional forces and gravity. The position control system can be designed easily based on the reference characteristic model. Finally, the position control system of a pneumatic robot is applied to impedance control to implement flexible contact motions such as when a robot makes contact with a part of the human body. The validity of the proposed design method is confirmed by the experiments and evaluation of the stability using the root locus method.

抄録全体を表示

Element lengths of the optimized finite element model of pipeline dynamics have been adjusted so to reduce the errors in natural angular frequencies of a pipe with simple boundary conditions. The aim of this paper is to check the natural angular frequencies of pipeline systems with more realistic boundary conditions and demonstrate the accuracy of the optimized finite element model. A pipe and chamber system and a pipe and mass-spring system are considered as examples, and modeled by a lumped parameter model and an impedance model. The non-dimensional parameters are derived for the pipeline systems. Finally, it is shown that the natural angular frequencies are accurately approximated by the optimized finite element model.

抄録全体を表示

A hydraulic oil normally contains gas at about 10% in volumetric ratio at atmospheric pressure. When cavitation occurs in an oil flow, diffusion of the dissolved gas is supposed to play a major role in the growth of cavitation bubbles, which can result in unwanted effects such as noise, vibration and response delays in hydraulic oil systems. Consequently if the gas concentration in the working oil can be somehow lowered, it may be possible to suppress cavitation. In the present paper a new method of degassing an oil by positively utilizing cavitation has been developed. To obtain a method which is of practical use at the engineering site, a cylinder having an orifice at the inlet and a piston actuated by hydraulic oil power are used to deaerate the oil. An idea of closing the orifice midway in the suction process proved effective in enlarging cavitation bubbles and accelerating their separation from the oil. Through observation of cavitation initiation in an orifice flow, it is experimentally confirmed that the critical Reynolds number at which cavitation starts increases when the oil is deaerated.

抄録全体を表示