Quick response solenoid valves acting as simple on-off hydraulic control devices are inexpensive and easy to operate. There are several hydraulic cylinder control methods using the quick response solenoid valves, which control the flow rate by varying the number of opened valves. Based on these methods, multiple valves open and close simultaneously so that the flow rate and the corresponding cylinder motion become stepwise. This might cause noise and/or vibration on the hydraulic system or the machinery moved by the cylinder. We have developed a new hydraulic cylinder control method to cope with this problem. Based on the method, in addition to the number of the opened valves, the period of the open time of each valve is appropriately controlled, while shifting the timing of the opening action. This improves the continuity of the cylinder motion in a wide range of flow rate. This paper presents the specification of the method and the result of application to the servo control of heavy machinery.

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In this paper, we propose a two-degree-of-freedom control method with a parallel feedforward compensators (PFC). The PFC plays a most important role in the stability of a proposed control system. Through the experimental results applied to a six-link electro-hydraulic serial manipulator, it is shown that the stability and the robustness against disturbances are improved by using the proposed control method. As the results of our previous papers, it was shown that the control method using disturbance observer designed by making use of H-infinity control theory is the most suitable among robust control methods. Through the comparisons with the results of the disturbance observer, it is ascertained that the proposed control method is also suitable for the control as well as the disturbance observer above mentioned. We examined and established the design criterion of the control system using the proposed method. The optimal parameters of the controller can be easily determined by using the design algorithm proposed here. The effectiveness of this proposed control method is verified through experiments of the six-link electro-hydraulic serial manipulator.

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The piling ability of a hydraulic vibro-hammering machine in construction work depends on the dynamic characteristics of the ground. A simulator which can realize these dynamic characteristics, i.e. the mechanical impedance, of various types of ground is required for the performance test of the machine. An electro-hydraulic servo mechanism is applied in order to construct the simulator to realize the equivalent reaction force of the ground. The amplitude and the phase of sinusoidal input signal of the servo amplifier of the simulator are adjusted iteratively to coincide the mechanical impedance with the desired impedance using a fuzzy reasoning method. The aim of this research is to find the optimal adjustment law of the input signal so that the number of iterations can be reduced. Experimental results show the simulator performs well enough for practical use.

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