Flexible feeding system schematic
Each feeder consists of three conveyors. The first conveyor is inclined and lifts parts from a bulk hopper. The second conveyor is horizontal, with a translucent belt. It transports the parts to the robot, presenting them at an underlit section near the robot. The third conveyor returns unused or unfavorably oriented parts to the bulk hopper. Proper functioning of the feeders depends on the parts being lifted from the bulk hopper in a quasi-singulated manner. Many factors influence the effectiveness of the inclined conveyor: the angle of the conveyor with respect to the horizontal, the belt properties (e.g. coefficient of friction), the type of belt (cleated, magnetic, vacuum), and the linear speed of the belt, for example.
When different parts are to be fed, the bulk hopper is emptied and filled with the new parts. If the parts are of a-similar geometry, no changes to the feeding system are typically needed. Some parts, such as circular or cylindrical ones (i.e. ones that would roll back down the incline) may need a different belt surface, such as a cleated one, or a different angle of inclination. The feeders were designed to facilitate quick changeovers of this type.
Overhead cameras are used to locate parts on the horizontal conveyors. An array of compact fluorescent lights is installed within each of the horizontal conveyors. These lights together with a translucent conveyor belt provide an underlit area in which parts can be presented to the vision system. Using binary vision tools (currently provided by an Adept vision system) parts on the feeder belts are examined. First, the vision system looks to see if a part is graspable (i.e. the part is in a recognized, stable pose and enough clearance exists between the part and its neighbors to grasp it with a gripper). Second, the pose of the part in the robot's world coordinates is determined. This pose, and the motion associated with acquiring the part, are checked to make sure that they are within the work envelope of the robot.
The following paper provides more information:
Last update: 1 October 1996
E-mail: rdq@po.cwru.edu