Model and modeless friction compensation: Application to a defective haptic interface

A preliminary work is described devoted to the design of a control architecture for a defective haptic interface, i.e. an underactuated haptic interface not able to apply forces along arbitrary directions. This interface is intended to be used for grasping tasks, where unilateral constraints are usually present. The main control problems considered in this paper concern the study of friction compensation techniques by means of a force feedback loop and a feedforward controller. This has been implemented with three different methods: two are based on a model of the friction present in the actuation system, while the latter on a momentum observer. These schemes have been experimentally tested on a simplified setup of the haptic interface, composed by a linear motor, a force sensor, and a Kevlar wire. Two sets of experiments have been considered, i.e. free space motions and interaction with a virtual wall.