Measuring and Increasing Z-Width with Active Electrical Damping

The "Z-Width" of a haptic display is the dynamic range of impedances that can be passively rendered. Haptic displays with larger Z-width generally render more realistic feeling virtual environments. We present a new method for measuring and displaying the Z- width of a haptic display. Instead of stiffness-damping plots, we believe a more illustrative technique for plotting the Z-width of a haptic interface is the envelope of achievable passive impedances as a function of frequency. Both hardware and analysis software for this new type of Z-width measurement are discussed. As previous research has shown, the maximum passive impedance that a device can render is directly related to the physical damping available in the mechanism. In an effort to maximize the Z-width of the haptic display, we present a new technique for adding physical damping to a haptic display through the use of analog electronics in the motor amplifier. Due to its electrical nature, active electrical damping has the benefit of dynamically variable parameters with no added mechanical complexity or mass. With the addition of active electrical damping, we show a performance improvement via a larger Z-width and larger range of passive virtual environment parameters.