Passivity control of a haptic device for thesimulation of knobs

Knobs are one of the details from which household appliances are commonly judged by the customers. Although very subjective, the customers’ requirements reflect real needs, such as robustness and easy use; therefore the design of knobs and buttons, that are the most widely used end-user interfaces, is of utmost importance from the commercial point of view and requires careful investigation. A mechatronic device has been designed to simulate the knobs’ behaviour for supporting an extensive campaign of end-users tests. The impedance control approach is applied exploiting a model of the actuator. However, as the acceleration information is extracted through double differentiation of position measurements, the inertia cannot be compensated; this can sometimes compromise the stability. The stability problem is therefore addressed through the time-domain passivity control approach, which guarantees stability and is easy to implement, but produces a slight decrease in performance, namely a mismatch between desired and real torque.