US Patent 8716973 Haptic user interface

A haptic arm comprising: a user connection element; a reference; a first linkage connecting the user connection element to the reference, where the first linkage provides at least six independent degrees of freedom, and contains an intermediate link, three force sensors, three angle sensors; a second linkage connecting the intermediate link to the reference; a third linkage connecting the intermediate link to the reference a fourth linkage connecting the intermediate link to the reference; the second, third, and fourth linkages each containing an independent actuator and position sensor.