Rotational force-feedback wrist

Force-feedback structures are mechanical structures that can generate forces to restore to the user a tactile feeling corresponding to the world in which he is manipulating an object. This paper presents the mechanical design of a 3-rotational-degrees-of-freedom (DOF) wrist able to produce force feedback. The wrist, plugged on an existing 3-translation-DOF Delta force-feedback structure (called Delta haptic device), yields a 6-DOF force-feedback structure. The wrist comprises a stylus which is the interface with the user. The kinematic chain of the wrist is serial and composed by a Cardan corresponding to the pitch and the yaw, followed by a rotational joint for the roll. The originality of the wrist comes from the parallel actuation of the Cardan. The advantage of such an actuation is to provide a torque with low inertia and low friction less depending on rotations. The direct geometrical model of the wrist has been implemented, as well as the management of torques and currents applied. Several tests performed show the limit of the actuation of the roll compared with the very promising parallel actuation of the Cardan.