Improved multi-DOF haptics with spring drive amplifiers

Spring drive amplifiers utilize the natural inductive properties of a DC motor to produce stronger position feedback than is achievable with traditional current amplifiers. Impedance-type haptics devices can leverage these amplifiers to render superior contacts with higher contact stiffness. Use of these amplifiers, however, requires the virtual environment to specify motion commands for each motor. This work extends the recently developed 1-DOF integrated approach to multi-DOF applications. It presents a motion controller working with spring drive amplifiers, together producing the maximum achievable isotropic Cartesian stiffness. Isotropy is necessary to guarantee that haptic contact forces are rendered in the correct direction. The system is implemented on a PHANTOM 1.0 haptic device and analytic performance is verified by experiment.