Development of a Pellet Rotation System for Automated Visual Inspection

Nuclear power plants use uranium fuel, consisting of solid ceramic pellets of cylindrical shape with 18 mm diameter and 14 mm height, which are manufactured by various metallurgical processes. The pellets are placed on specially designed trays after grinding and pellet washing operations. These pellets are manufactured in large quantities and must confirm very stringent quality requirements usually prevalent in nuclear engineering applications. As part of quality checks on the fuel pellets, the operators manually check defects like fits, cracks, etc. occurring on the cylindrical surface. With the help of a machine vision system, the pellets were inspected by turning each pellet in its location itself while observing its surface for defects. The main equipment involves transferring system of pellets, a pellet rotation system, a vision system, a pellet retrieval system, and a system of rejection and recirculation of defective pellets. This paper mainly deals with the pellet rotation system. The design equipment has the provision to receive 5 pellets at 80 mm pitch, such that the axis of all the pellets is in the horizontal plane. They are rotated in their position in steps of 30 degrees such that in 12 steps the entire cylindrical surface will cover precisely. The cameras of the vision system were placed above each pellet with proper illumination. The programmable logic controller is used to control the pneumatic cylinders with proper intervals of time to accept or rejection of the pellet by the vision system.