This paper deals with the adaptive position control of a pneumatic cylinder with two electro-pneumatic proportional valves. The adaptive control law consists of the following four parts : (a) stabilization of the plant by output feedback, (b) identification of the stabilized plant by the constant trace gain algorithm, (c) division of the identified model into an AR model and auxiliary system which output converges rapidly to zero when its input becomes constant, and (d) model reference adaptive control (MRAC) for the AR model. This control law is a modification of the conventional MRAC law so as to make it applicable to non-minimum phase systems.
Experiments of the adaptive position control were carried out for the following cases : (1) the third and second order reference models which approximated the step response of the stabilized plant given by (a), (2) five sampling periods (25, 37, 52, 71, 107 msec), and (3) a sudden change in plant dynamics. Although the identified plant was a non-minimum phase for all cases, the behavior of the control input to the electro-pneumatic valves was stable, and the position of the load followed well the output of the reference model.

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Recently, we proposed remote and quasi-remote instantaneous flow rate measurement methods by making use of the dynamic characteristics between pressures and flow rates at two cross-sections (upstream and downstream of the pipeline) distant from the finite length along the hydraulic pipeline. By using these methods, an instantaneous flow rate at the location difficult to insert a flowmeter can be accurately estimated in real time. The remote instantaneous flow rate measurement method has been investigated using the experiment in the previous paper.
This paper describes the quasi-remote instantaneous flow rate measurement method. In the case of the upstream flow rate measurement, flow rate qu (t) is estimated by implementing convolutions of measured upstream pressure pu (t) and downstream flow rate qd (t) with corresponding weighting functions gp (t) and gq (t) , respectively. The high-speed numerical operation of the convolutions is realized in real time by utilizing the preset tables on memories in the microcomputer system.
The weighting functions in the time domain are obtained by the inverse Laplace transform or inverse fast Fourier transform of the transfer functions in the frequency domain which are derived from the transfer matrix. In a similar manner, downstream flow rate qd (t) can be estimated from measured downstream pressure pd (t) and upstream flow rate qu (t) .
The estimated flow rate waveforms by the method are compared with directly measured ones at the same instant by a cylindrical choke-type instantaneous flowmeter which is used for calibration. The results show good agreement between the estimated and measured flow rate waveforms under an unsteady laminar flow.
As a result of improving and scheming the high-speed operation of convolutions, data processing on the system in real time is achieved using only software.

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In the previous reports, the characteristics of a swash plate type variable delivery axial piston pump in the quasi-zero swash plate angle region were experimentally investigated, and a theory was presented to explain the swash plate zero angle restoring moment. Furthermore, a calculation method was developed to predict the pump characteristics in the quasi-zero swash plate angle region, and methods to improve the characteristics were investigated using the above-mentioned prediction method.
In the present report, an experimental investigation of a new pump, which was designed utilizing the model derived in the previous report, is presented. In this pump, a thrust plate, on which piston shoes slide directly, is put on the swash plate, and is supported such that it can rock freely within a small tilt angle relative to the swash plate.
From the test results, the effects of the improvements regarding the designs of the thrust and swash plates were ascertained, and the effects of newly introduced parameters on the pump characteristics in the quasi-zero swash plate angle region were presented.
Furthermore, a new calculation method was developed to predict the operating moment and equivalent swash plate angle (thrust plate angle relative to the cylinder block around the swash plate trunnion axis) of the improved pump, and calculated values showed good agreement with the experimental ones.

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A model reference adaptive control theory is applied to an electrohydraulic servo system and a number of its applications are reported. This theory is very useful and powerful and can control a plant of which parameters are unknown or vary during systems operation. It can also make the plant output coincide with the reference model output. However, some problems exist. One of them is a nonminimal phase problem. The nonminimal phase system has an unstable zero(s). The model reference adaptive control theory cannot control such a nonminimal phase system.
When the sampling period goes to zero, the discrete-time system composed of a zero-order hold, a continuous-time plant and a sampler in series using z-operator becomes a nonminimal phase system if the relative degree of the continuous-time plant is greater than two. When the discrete-time system is controlled rapidly, a short sampling period is required. However, there is a risk that the discrete-time system will become the nonminimal phase system. The discrete-time electrohydraulic servo system also becomes the nonminimal phase system when the sampling period goes to zero.
δ-operator has better characteristics than z-operator in many respects. The δ-operator approaches s-operator when the sampling period goes to zero, where s is Laplace operator. Therefore, if the continuous-time system is the minimal phase system, the discrete-time system using δ-operator also becomes the minimal phase system when the sampling period goes to zero. Hence, the model reference adaptive control theory can be applied to the discrete-time system.
In this paper, the model reference adaptive control theory using the δ-operator is applied to the electrohydraulic servo system. In addition, the behavior for a long sampling period is important for designing the controller, so it is also considered here.

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