The application of a passive-type force display system is desirable for its high safety. However, there are some directions and link positions for which it is difficult to display the force in a passive-type force display system using only passive elements. To solve this problem, a method for improvement of controllability using redundant brakes had been suggested. This method made it possible to display various force directions and various postures of virtual objects. In our study, two novel methods are presented for performance evaluation of a passive-type force display system with redundant brakes. Using these methods, we evaluate the performances of a 2-DOF passive-type force display system without redundant brakes, a passive system with one redundant brake and a passive system with two redundant brakes. In this paper, two novel performance evaluation methods for a passive-type force display system with redundant brakes are presented. The developed system is outlined and basic experiments with it discussed.

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This paper shows that the VSS observer has the possibility to estimate adhesion force using wheel slip simulation and wheel slip experiments. It has been shown that the disturbance observer was effectives in estimation of adhesion force. To apply a strain gauge to the brake caliper in order to measure the braking torque is difficult, because the delicate parts on bogies are to be avoided at the train depot. When all the axles of vehicles slip, the wheel slip prevention cannot work sufficiently. Moreover, the brake systems of railway vehicles possess strong nonlinear characteristics with variable parameters, such as adhesion force and friction coefficient of brake materials. It is important that the estimation method has robustness against such disturbance and parameter changes, and it is known that the Variable Structure System (VSS) observer has robustness against parameter change, disturbance input and so on. However, there have been no research reports about a Variable Structure System (VSS) observer for the brake system or wheel slip preventing methods in a railway vehicle. In order to compare the theoretical value of adhesion force with estimated value by a VSS observer, wheel slip simulation was preformed. Simulation results show that the VSS observer can estimate the adhesion force efficiently. Moreover, estimation experiments of adhesion force using VSS observer were performed, and it has been clarified that the VSS observer can efficiently estimate the tangential force coefficient from the experimental results.

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In position and trajectory tracking controls of hydraulic manipulators, it is difficult to obtain desired performance due to nonlinearity, for instance, variations of moments of inertia, unsymmetrical effects of single rod cylinders, dead zone of hydraulic control valves, time delay of hydraulic systems and mechanical resonance. Therefore, applications of robust control systems for the nonlinearity and disturbance are desired. Sliding mode control has strong robustness to parameter change and disturbance. Moreover a preview control can improve trajectory tracking performance. By feedback of estimated disturbance from a disturbance observer in an inner loop, the responses of the system are improved. Moreover sliding mode control with frequency shaping suppresses spillover of mechanical resonance. Therefore, we designed a discrete time frequency-shaped preview sliding mode controller with pre-filter, which combines the advantages of these control theories. In this paper, it is shown that our control method can improve trajectory tracking performance and robustness of hydraulic manipulators in experiments and simulations.

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