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An analogue input shaper (AIS) is proposed as a means for stably increasing the displayable impedance range of haptic interfaces. Usually, high-frequency inputs can occur during collisions with very stiff virtual objects and induce instabilities. The proposed AIS is basically a nonlinear low-pass filter and acts as a frequency-dependent dissipative element, which can eliminate unwanted high-frequency inputs to haptic interfaces. The proposed AIS is not placed in the power stage but in the signal stage, so that the AIS can be designed independent of motor parameters and does not affect transparency in free motion. In addition, two linear half-wave rectifiers are incorporated into the AIS to allow for a fast decrease of impedance and no negative input to the haptic interface when a haptic pointer leaves a virtual object. Through virtual wall experiments using two different haptic interfaces, the effectiveness of the proposed AIS is shown.
Date of Publication: December 2009