Modeling and Design of a five Degrees-of-Freedom Delta-Like Robot for Fast Pick-and-Place Applications

Delta-like architectures are widely used for fast pick-and-place applications. When rotational degrees of freedom are required to perform a task, one or more UPU kinematic chains are usually added to transmit the torques from motors located on the base to the platform, in order to actuate a wrist. Packaging applications usually require five degrees of freedom, and two UPU chains are then used to actuate two rotational degrees-of-freedom (DOFs) on the end-effector. However, the UPU chain induces significant limitations for industrial use: it significantly constrains the workspace along the vertical direction and implies a backlash in the universal joints degrading the accuracy of the robot. In this paper, we investigate an alternative to the UPU kinematic chain for designing Delta-like robots with five DOFs. Indeed, the actuation of a two-DOFs wrist is performed through the use of a kinematic chain based on a succession of parallelograms associated with a Delta-like leg. After a description of the kinematic models of the modified leg and an analysis of its singularities, a design optimization procedure is presented in order to define suitable geometric parameters for a given industrial application. Finally, a prototype is presented and its performances are evaluated.