Dual-channel Haptic Synthesis of Viscoelastic Tissue Properties using Programmable Eddy Current Brakes

We describe a novel method for haptic synthesis of viscoelastic responses which employs a dual-channel haptic interface. It has motors that generate torque independently from velocity and brakes that generate viscous torque independently from position. This way, twice as many states are directly accessible, which reduces reliance on observation and feedback. Torquegenerating actuators, e.g. dc motors, are well known. For the viscous actuators, we use eddy current brakes as programmable, linear, non-contact, physical dampers. By decomposing a mechanical impedance to be realized into viscous and elastic components, we can dedicate each actuator to that component it is ideally suited to synthesize, dampers for the viscous component, and motors for the elastic component. The decomposition is in general not unique so it possible to select the option that takes the best advantage of the hardware. Experimental results show that this technique can render a variety of viscoelastic models without the artifacts that can occur when synthesizing viscous components on conventional haptic interfaces. The synthesized mechanical impedances have guaranteed passivity, and can have arbitrarily high or low viscous and elastic components.