Analysis and optimal design of a new 6 DOF parallel type haptic device

This paper proposes a new haptic device by using a parallel mechanism and a gimbal mechanism. This device has three legs actuated by 2-DOF gimbal mechanisms, which makes the device simple and light by fixing all the actuators to the base. The reference axis of the gimbal mechanism is rotated about the z axis with 45 degrees, which distributes the end-effector load to each actuator uniformly. Three extra sensors are placed at passive joints to obtain a unique solution for the forward kinematics problem. The proposed haptic device is developed for an operator to use it on a desktop in due consideration of the size of an average Korean person. The proposed haptic device has a small workspace for an operator to use it on a desktop and it has more sensitivity than a serial type haptic device. Therefore, the motors of the proposed haptic device are fixed at the base plate so that the proposed haptic device has a better dynamic bandwidth due to a low moving inertia. With this conceptual design, optimization of the design parameters is carried out by using a genetic algorithm. The objective function is defined by the minimum of the global design indices, the global force/moment isotropy index, the global force/moment payload index, and the workspace. Each global index is calculated by a SVD (singular value decomposition) of the force and moment parts of the jacobian matrix. Division of the jacobian matrix assures a consistency of the units in the matrix. Due to the nonlinearity of this objective function, Genetic algorithms are adopted for a global optimization.