Type synthesis of 2R-T parallel mechanisms based on the screw theory for haptic applications

Recently haptic devices are increasingly used in industry and research. As their applications become widespread, their design is needed to be more efficient. At design stage, determinant features of haptic devices such as rigidity, force bandwidth, accuracy etc. must be considered and improved. Structurally, parallel mechanisms (PMs) are appropriate candidates for haptic devices. Due to multi legged structure of PMs and their grounded motors, inertia and stiffness feautures of them are desirable and it also made them popular for applications that require high mechanical transparency. Spherical kinematics (two rotational and one translational motion, 2R-T) is a very common type of motion in haptic devices that is also capable of general rendering. In this paper, several 3-DOF 2R-T PMs are synthesized for haptic applications by means of the screw theory. All of these mechanisms have center of motion (CM) which is a key property in variety of applications such as surgery. These mechanisms are compared qualitatively and their applications as haptic devices are discussed.