Four-DOF PPPR= Parallel Mechanisms

Abstract

In many robotic applications, it is required to move objects in all Cartesian directions as well as orient these objects around an axis having a given direction. A typical example of such tasks is the assembly of computer circuit boards on which electronic components must be mounted. Rotations are required only around an axis orthogonal to the board while translations in all directions must be performed to pick up and place the components. Serial SCARA robots were developed specifically for this family of tasks in the 1970s. SCARA robots have become very popular and are widely spread in industry. The motion pattern of SCARA robots can be described using a PPPR virtual chain. In this chapter, the type synthesis of 4-DOF PPPR= PMs (also called 3T1R PMs in the literature) is dealt with using the general approach proposed in Chap. 5. A PPPR= PM is the parallel counterpart of the serial SCARA robot and generates 4-DOF PPPR motion (also called Schönflies motion). As mentioned above, PMs with a PPPR motion pattern cover a wide range of applications. The four steps of the type synthesis of PPPR= PMs are presented in detail.