Abstract: This paper presents an automatic system for alignment of workpieces for robotic manipulation operations. The system consists of a sequence of fixed flat fences, suitably oriented across a conveyor belt, so that a workpiece on the belt will slide along each fence and leave the last one finding itself aligned with a desired orientation. In this way there is no need to provide the robotized system with feedback sensors in order to determine position and orientation of the workpiece to be manipulated, but the grasping task can be performed using an open-loop strategy. A prerequisite to the system design is the development of a simple but robust mathematical model which allows to compute the "exit angle", i.e. the orientation of the workpiece when it leaves the last fence, as a function of the number and orientation of the fences. It is thus straightforward to determine the characteristics of the fences (number and orientation) in order to realize a desired alignment of the piece. Several simulation and experimental tests have been carried out, which confirm the effectiveness of the system.