Isotropy and Actuator Optimization in Haptic Interface Design

A haptic interface controlled in impedance mode should present its user with a uniform force capability matching the human hand. This paper reviews a mechanism design methodology that maximizes a workspace-inclusive isotropy index. Force maximization in coreless or voice-coil motors is also considered in order to maximize haptic interface acceleration. Example designs of a planar 3-DOF haptic mouse, a 5-DOF haptic pen and a MagLev joystick are presented. 1 Introduction Research in haptic interfaces has led to a number of novel devices that have been used in demonstrations, teleoperation and training. Design criteria have included low effective mass [11], low variations in mass [5], [13], [14], kinematic isotropy [10], [24], stability robustness [2] and a large workspace [8]. Iwata [6] built a 9-DOF Compact Master which combines a 6-DOF parallel positioning device in series with three 1-DOF finger actuators. Iwata [7] also used a pair of commercial 3-DOF hybrid manipulators to actuate each end of a 6-DOF haptic pen. In [1], the 6-DOF hybrid SMARTee interface uses a parallel combination of three 2-DOF serial linkages. In [3], a 6-DOF joystick is described which contains three pantograph linkages and Yokoi et. al. [23] presents a 6-DOF serial hand controller with three prismatic actuators for translation and three rotary actuators for orientation. A 5-DOF (3 translation, 2 rotation) haptic stylus is described in [12] which uses 5 linear actuators in parallel. A 4-DOF (3 translation, 1 rotation) hybrid device using rotary actuators is presented in [9] while a 4-DOF Manipulandum that combines a 3-DOF planar parallel robot in series with a linear vertical motion stage is described in [15]. The hybrid PHANToM of [14] has three active translational degrees of freedom and three passive rotational degrees of freedom. A 2-DOF planar pantograph is optimized in [5] and the 2-DOF linear voice coil actuated Magic Mouse is presented in [8]. Finally, Vertut [22] presents a historical survey of earlier hand controllers, articulated arms and exoskeletons. Most of the interfaces described above have been developed as part of demonstration systems to evaluate potential applications of haptic interfaces, control algorithms and human factors, with relatively little attention paid to the optimization of electromechanical characteristics. In this paper we make the argument that force isotropy over a workspace is a useful and computationally tractable performance criterion for haptic interface design. Following a discussion of design criteria, we outline a previously developed design methodology to achieve force …