Visual robot guidance in conveyor tracking with belt variables

The paper presents a method and related algorithm for visual robot guidance in tracking objects moving on conveyor belts; the instantaneous location of the moving object is evaluated by a vision system consisting from a stationary, down looking monochrome video camera, a controller-integrated image processor and a vision extension of the structured V+ robot programming environment. The algorithm for visual tracking of the conveyor belt for "on-the-fly" object grasping is partitioned in two stages: (i) visual planning of the instantaneous destination of the robot, (ii) dynamic re-planning of the robot's destination while tracking the object moving on the conveyor belt. The control method uses in addition the concept of Conveyor Belt Window - CBW. The paper discusses in detail the motion control algorithm for visually tracking the conveyor belt on which objects are detected, recognised and located by the vision part of the system. Experiments are finally reported in what concerns the statistics of object locating errors and motion planning errors function of the size of the objects and of the belt speed. These tests have been carried out on a 4-d.o.f. SCARA robot with artificial vision and the AVI AdeptVision software extension of the V+ high-level, structured programming environment.

I. Modelling Conveyor Belts By Means of Belt Variables

The principal mechanism which allows specifying robot motions relative to a conveyor belt consists into modelling the belt by a special type of location data, defined as belt variables. A belt variable is considered as a relative transformation (having a component variable in time) which defines the location of a reference frame attached to the moving belt conveyor [1].