Understanding Conveyors (Belts) Understanding Conveyors (Belts) This section describes some basic conveyor (belt) concepts. NOTE: In the ACE interface, conveyors are referred to as "belts". Indexing versus Tracking Conveyors There are two basic types of conveyor systems: indexing and tracking. In an indexing conveyor system (also referred to as a noncontinuous conveyor system), you specify either control signals or a time interval for the belt to move between stops. When the conveyor stops, the robot removes parts from the belt and the conveyor is signaled to move again. The conveyor must be equipped with a device that can use digital output to turn the conveyor on and off.
Indexing Conveyors Indexing conveyor systems are configured as either nonvision or vision. With a nonvision indexing system, the part must be in the same location each time the belt stops. In a vision-equipped indexing system, a fixed-mount camera takes a picture when the belt stops and the robot accesses any objects found. Tracking Conveyors In a tracking conveyor system, the belt moves continuously and the robot tracks parts until the speed and location of the robot gripper match those of a part on the belt. The robot then accesses the part. Tracking conveyors must be equipped with an encoder, which reports the movement of the belt, and distance moved, to the ACE software.
Tracking conveyor systems are also configured as either nonvision or vision. With a nonvision tracking con- veyor, a sensor signals that a part has passed a known location. The ACE software tracks the progress of the belt and accesses the part when it comes into the robot working area (belt window). Parts must always be in the same location with respect to the center line of the belt. With a vision-equipped tracking conveyor, a fixed-mount camera takes pictures of the belt based on the dis- tance the conveyor travels, and returns the location of parts it locates. These part locations are queued and accessed by the robot.
The vision system allows detection of parts that are randomly positioned and ori- ented on the belt. Conveyor Calibration Belt calibration, a simple procedure performed from within the ACE software, relates belt direction of travel to the robot work space. Calibration establishes the relationship between an encoder tick and the distance moved by the belt. Once a belt is calibrated, it can be used by the application. For more details on belt cal- ibration, see Belt Calibrations on page 848. Conveyor Terminology The following figure shows a typical robot cell equipped with a conveyor belt. ACE User's Guide, 3.6.x 18316-000 Rev A Page 66