Vision
Conveyor Tracking
Conveyor tracking, also called line tracking, is a robot function that uses an encoder on the conveyor to follow parts as they move, so the robot can pick or work on them without stopping the line.
What it is
On a tracking cell the conveyor keeps running and the robot matches its motion. An encoder on the conveyor tells the controller how far the belt has moved, and a trigger (a photo eye, or a vision system that also reports where each part sits) tells it when a part came in. From those two inputs the controller knows where each part is as it travels.
Taught points live in a tracking frame that moves with the belt. The robot catches up to a part, works on it while moving in step, and finishes before the part leaves the tracking window.
How it actually works
The conveyor encoder feeds counts to the controller through a line tracking interface. Setup scales those counts to distance, aligns the tracking frame with the direction of travel, and calibrates it with a real part at the trigger and a reference point downstream. The tracking window sets upstream and downstream limits, and a part that reaches the downstream limit unfinished has to be skipped or released cleanly so the robot doesn't chase it out of reach.
Speed has a ceiling. If the conveyor runs faster than the tracking system can handle, the controller posts SRVO-081 EROFL (track encoder overflow). The tracking encoder has its own FANUC alarm family, SRVO-081 through SRVO-096, which mirrors the motor pulsecoder alarms with battery, no-response (DTERR), and corrupt-data (CRCERR) alarms of its own.
How it differs
- Vision offset · A vision offset corrects for where a stationary part sits. Conveyor tracking follows a part that keeps moving. Picking from a running belt usually combines them: vision finds each part's position and rotation at the camera, and tracking carries that position downstream as the belt moves.
- Indexed conveyor · An indexed conveyor stops each part at a fixed station, so the robot can work from ordinary taught points. Tracking lets the line run continuously, at the cost of encoder hardware, calibration, and a tracking window to manage.
Where you meet it in the field
- Setting Up Conveyor Tracking for a Robot · Encoder scaling, frame calibration with a real part, and setting the tracking window.
- SRVO-081 EROFL alarm (track encoder overflow) · The conveyor ran faster than the tracking system can count, or the tracking hardware is faulty.
- SRVO-092 Line tracking encoder STBERR communication fault · A communication error between the tracking encoder and the line tracking interface board.
- Pick and Place · High-rate picking from a moving belt is where tracking earns its setup time.
Common questions
- Why does the robot miss parts at higher conveyor speeds?
- Check whether parts reach the downstream end of the tracking window before the robot gets to them, since higher speed shrinks the time each part spends in the window. Widen the window if the robot's reach allows, slow the belt, or split the picks across more robots. If the belt outruns the tracking system itself, SRVO-081 posts instead.
- Can I track from the conveyor drive's speed instead of an encoder?
- Use an encoder that measures the belt's actual travel. A drive speed setting doesn't capture slip, speed changes, or stops, and tracking accuracy depends on the controller knowing exactly how far the belt has moved.
- Do I need vision for conveyor tracking?
- Only if parts arrive at random positions. Parts that arrive in a fixed place on the belt, in a nest or against a guide, can be tracked from a photo-eye trigger alone.