Control and performance of the rotational-to-linear Cobotic transmission

We examine the motion control bandwidth and stable impedance range of the Cobotic Hand Controller, a novel, six-degree-of-freedom, admittance controlled haptic display. A highly geared admittance architecture is often used to render high impedances with reasonable sized actuators for a haptic display. The Cobotic Hand Controller is perhaps the ultimate realization of an admittance display, since it is capable of obtaining an infinite gear ratio and can render infinite impedances (up to its own structural stiffness). The incorporation of continuously variable transmissions in the Cobotic Hand Controller provides for an extremely wide, stable z-width, since the transmission ratio can be adjusted quickly to vary the backdrivability. However, finite preloads in the transmissions limit the display's acceleration capabilities. We examine the control challenges and performance characteristics of the Cobotic Hand Controller for free motion and unilateral impact virtual environment scenarios.