Mechanical Design Process for the Zippy Wrist

In this paper, the mechanical design process of a star spherical parallel robot that we call Zippy Wrist is illustrated. The Zippy Wrist is a 3-RRP spherical parallel manipulator and can perfonn many industrial applications such as, orienting a tool or a workpiece in machine tools, solar panels, space antennas and telescopic mechanisms, flight simulator mechanism and camera devices. The forward and inverse kinematics problem, isotropy design, singularity analysis, accuracy analysis, stiffness analysis, inverse and direct dynamic analysis of this manipulator have previously been investigated by Enferadi and Akbarzadeh and reported in four journals. Our goal was to build a laboratory version of the Zippy Wrist to test theoretical results and to perform additional dynamical and control testing. The selected mechanical design is based on the isotropic design because it is the superior design. The design results in a relatively large workspace, good accuracy and high stiffness. The mechanical design process consists of joints design, structural analysis of main components, geometry determination of components, material selection and safety issues. The controller allows PID control as well as running the system in torque mode. This allows us to directly input the calculated torque, from robot dynamic equations to motors. Structural analysis is performed by finite element models considering load capacity and other design goals. Dynamic and motion of the robot is simulated using hypothetical trajectories to obtain desired kinematic parameters such as speed and acceleration. The robot is assumed to carry an average load of 1kg, mostly due to carrying measurement tools such as accelerometer, laser tool or camera. All mechanical components are designed using commercial solid modelling software and manufacturing processes are briefly discussed.