Enhancing the Z-width of Haptics Interfaces through Dual-rate Sampling

Conventional controllers used in haptic devices are sampled data systems in which the position and velocity of the device is required to realize a visco-elastic virtual wall interaction. Increasing the sampling rate of the controller improves the stable range of virtual wall stiffness but simultaneously exacerbates the estimated velocity. This inefficient velocity estimation limits the implementation range of virtual damping at higher sampling rates, thereby reducing the dynamic range of stable impedance or Z-width of the haptics controller. A dual-rate sampling scheme is proposed here for such controllers, whereby the position and velocity loop is sampled at different rates. Implications of the proposed scheme on the Z-width of haptics controller using a 1-DOF (Degree-of-Freedom) custom haptic device is discussed. Experimental results demonstrate the effectiveness of proposed scheme, particularly at higher sampling rates.

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