Analysis and Experimentation of a 4-DOF Haptic Device

This paper presents a new configuration of a haptic device based on a 4-DOF hybrid spherical geometry. The spherical parallel ball support (SPBS) type device, as it is referred to, consists of a particular design with the intersecting axes of both active and passive spherical joints. The orientation of the device is determined by the mobile platform on the active spherical joint using a special class of spherical 3-DOF parallel geometry. The passive spherical joint (ball and socket configuration) is used to increase the mechanical fidelity of the device. Previously it has been shown that some configurations of this spherical parallel geometry lead to kinematic optimization. We introduce the design consisting of a stylus such as a laparoscopic gripper attached on the mobile platform supporting an additional translational motion. First, the new forward and inverse kinematics analysis is presented. Our work is motivated by deriving a closed-form solution of the kinematics for this proposed device configuration. Then, a closed-loop system framework which can be used for real-time force feedback control is outlined. Finally, preliminary experimental results obtained with the prototype are presented.