Circumventing the fundamental tradeoff between stability and performance in haptic rendering — successive force augment approach

This paper proposes a new approach to further enlarge the achievable displayed stiffness range of impedance-type haptic interfaces. Most of the stability guaranteed haptic interaction methods result having much lower achieved stiffness than the original desired stiffness at the cost of stability. This paper introduces a new rendering approach, which can display close to the originally intended high stiffness by only using low value of stiffness in the rendering of the state dependent linear force feedback force together with the state independent feedforward force offset. The biggest advantage of using low stiffness for the rendering of the feedback force rendering is that the interaction remains stable because the produced energy during the interaction can be fully dissipated by the intrinsic damping of the device. In order to achieve the desired stiffness meanwhile using only low stiffness in the rendering of the feedback force rendering, a small feedforward force offset is augmented in the following interaction cycles. The small force offset value is added or subtracted from the low stiffness linear force relation depending on the value of the displayed stiffness. If the displayed stiffness is lower than the desired stiffness after finishing each interaction loop, small force offset is accumulated in the next pressing cycle until the displayed stiffness becomes closer to the desired stiffness. Experimental evaluation has been conducted with PHANToM Premium 1.5, and has achieved much higher transparency than other conventional approaches though displaying close to desired stiffness while minimizing the penetration depth.