Robotics is expected to be applied to human oriented tasks such as in medical and welfare fields as well as in industrial manufacturing. In order to carry out a cooperative task between human and robot smoothly, contact force should be utilized effectively. In this study, we consider the contact force as information on which human's intention is reflected for the accomplishment of the contact tasks. A pneumatic parallel manipulator is available for the human friendly mechanical system due to the feature of multiple d.o.f. for its compact mechanism and that of essential flexibility originated from air compressibility. Moreover this manipulator works as kind of an elastic body even when its position and orientation is under control, which means it works as an omni-directional force sensor itself Utilizing such elastic characteristics positively to detect contact information, we propose a scheme to estimate a contact force vector and contact point which are applied by a human. The validity of the proposed scheme is confirmed through some experiments.

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Unsteady characteristics in cases of elastic deformation of disk-type hydrostatic thrust bearings based on stepwise change in the loads for a constant supply pressure are discussed experimentally and theoretically. The bearing/seal parts examined in this study are made up by combining stainless steel with stainless steel and stainless steel with plastics. The main results are as follows :
1) In the case of slow stepwise change in the loads, the effects of step-load heights and disk materials on the response of fluid films and pocket pressure are negligible.
2) For elastic materials, a stable fluid film shape is obtained more easily but the response is slower than that of rigid materials, The delay in pocket pressure change becomes more obvious with increased stepwise change in the loads. This phenomenon is much more pronounced for elastic materials.
3) The leakage flow losses become very small by using small nozzle, even at larger step-load heights.

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Water hydraulics is applied to molding press machines for chip-size-package technology. Velocity and force control are essential for molding quality. In this paper, fundamental control performance is investigated using an experimental water-hydraulic servo system. A single rod cylinder is controlled by a water-hydraulic servo valve. A spring is used to simulate the reaction force of plastic tablets under compression. Piston velocity and force are detected using an encoder and a load cell. These signals are fed back to a PI controller. Mathematical models that represent velocity and force control systems are derived. In particular, time delay of force response is modeled on the assumption of annular flow and equivalent bulk modulus. With regard to closed loop systems, a non-dimensional transfer function and a condition of no overshoot are obtained.

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The aim of this research is to study the nonlinear rotational speed characteristics of an eccentric-rotor type hydraulic vibro-hammering machine operating on an elastically supported base. The experiments are carried out on a single eccentric-rotor system. The rotational speed characteristics are analyzed by applying the harmonic analysis method on the nondimensional system equation. The results show the mechanism of stagnation, jump and hysteresis of the rotational speed characteristics of the machine. These phenomena are considered to be caused by the resonance vibration of the base which causes the increase of the load pressure and leakage through the bypass valve in the resonance frequency range.

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