Design of the ‘granit’ Parallel Kinematic Manipulator

This work describes the development of the GRANIT parallel-kinematic robot. The robot endorses a multifunctional end effector, a stiff and precise device aimed at the assembly of heating coils for hairdryers. Such assembly task require repeatability and releability, therefore we developed a custom manipulator which has 4 degrees of freedom like a SCARA robot, although offering a superior rigidity and precision thank to a custom parallel-kinematic design. This robot uses a two-drives, four-bar linkage scheme for the horizontal motion, and a custom differential transmission based on a precision ballscrew, both for the vertical motion and for the rotation of the effector. By performing dynamical analyses with our in-house multibody software, we simulated working volumes and motor torques. This helped us in choosing the best compromise for sizing, drives and transmissions. Using electro-discharge machining and aerospace alloys, we built honeycomb structures for the four arms: this approach offers remarkable stiffness and limited mass. Taking advantage of a multi-functional scheme, three different tools are grouped together in a compact end-effector, whose main tasks are: cutting resistive wires, crimping connectors with sturdy pliers, and inserting mica plates. The GRANIT robot has been built and successfully tested, showing high repeatability and stiffness.