High-gain proportional-integral-derivative (PID) position control involves some risk of unsafe behaviors in cases of abnormal events, such as unexpected environment contacts and temporary power failures. This paper proposes a new position-control method that is as accurate as conventional PID control during normal operation, but is capable of slow, overdamped resuming motion without overshoots from large positional errors that result in actuator-force saturation. The proposed method, which we call proxy-based sliding mode control (PSMC), is an alternative approximation of a simplest type of sliding mode control (SMC), and also is an extension of the PID control. The validity of the proposed method is demonstrated through stability analysis and experimental results.

Modeling of friction force is cumbersome because of its discontinuity at zero velocity. This paper presents a set of discrete-time friction models for the purpose of haptic rendering and virtual environment construction. These models allow friction to be treated as an admittance-type or impedance-type element of a virtual environment. They are derived from implicit Euler integration of Coulomb-like discontinuous friction and linear mass-spring-damper dynamics, and have closed-form expressions. They include rate-dependent friction laws, and their extension to multidimensional cases is easy in most practical cases. The validity of the models is demonstrated through numerical examples and implementation experiments

This paper introduces a device for enhancing detection of surface undulation through active touch. This device, which we call a “tactile contact lens,” is composed of a sheet and numerous pins arranged on one side of the sheet. Experimental results show that a small bump on a surface can be detected more accurately through this device than by bare finger and than through a flat sheet. A mathematical analysis of this phenomenon suggests two possible explanations for this phenomenon. One lies in the lever-like behavior of the pins. The pins convert the local inclination of the object surface into the tangential displacement of the skin surface. The second is the spatial aliasing effect resulting from the discrete contact. Due to this effect, the temporal change in the skin surface displacement is efficiently transduced into the temporal change in the skin tissue strain. The results of this analysis are then discussed in relation to other sensitivity-enhancing materials, tactile sensing mechanisms, and tactile/haptic display devices.

This paper proposes new discrete-time algorithms of the super-twisting observer and the twisting controller to be applied to second-order systems. The algorithms are based on the full implicit-Euler discretization, which contributes to the elimination of chattering. Proofs of some stability properties of the discretized twisting controller are also provided. Simulations show that, as compared to traditional explicit-Euler schemes, the proposed scheme avoids the chattering both in trajectory tracking output and control input in the presence of external disturbances.

This paper presents a sliding mode filter for removing noise. It effectively removes impulsive noise and highfrequency noise, producing a smaller phase lag than linear filters. In addition, it is l...

This paper proposes a new position controller that is suitable for the use as the internal position servo of an admittance controller with bounded actuator forces. The new position controller approximately behaves as a proportional-integral-derivative (PID) controller with an acceleration feedforward in normal situations and as a sliding mode controller when the actuator force is saturated. The admittance controller employing the new position controller realizes smooth transitions between saturated periods and unsaturated periods. Moreover, it quickly responds to changes in the applied force even when the actuator force is saturated, leading to better stability and smoothness. The controller was validated through experiments using a robotic manipulator.