A robot can follow a moving part or wait for a stationary one. Continuous lines force the first; batch work usually allows the second. The choice affects the controller options, the mechanical accuracy you need, and how a fault behaves.
The comparison
| Tracking a moving conveyor | Stop station | |
|---|---|---|
| Line | Continuous, no stopping | Indexed or manually loaded |
| Extra hardware | Encoder, tracking card, part-present sensing | Indexing mechanism, stopper, position repeatability |
| Accuracy chain | Encoder resolution, chain wear, hanger swing | Fixture and stopper repeatability |
| Fault behaviour | A stopped robot means a part passes uncoated | The line waits; nothing passes uncoated |
| Programming | Paths referenced to the moving frame | Paths in a fixed frame — simpler to teach and adjust |
What makes tracking work
- An encoder with enough resolution — one delivered wheel line uses 2,000 pulses per revolution at 1.4–1.8 m/min with 1,200 mm hanger pitch.
- Hanger stability. A swinging hanger destroys tracking accuracy no matter how good the encoder is; on one project a guide and stabiliser device was designed specifically for it.
- A calibrated origin, re-checked after any mechanical work. A drifting origin shows up as a consistent offset — on one commissioning an encoder fault shifted the path 100 mm in Z.
Where a stop station is the better answer
Low volume with many variants, manual loading, or a part that must be presented precisely to get into a recess. The glass bonding cell is a stop-station design for exactly that reason: the operator loads, a centering table measures the part to ±0.2 mm, the PLC selects the path, and the robot works in a fixed frame — and it still reached 14 to 18 jobs per hour against 7.5 required.
Frequently asked questions
Can a line run both ways?
Yes — a tracked main line with a stop station for special parts is common, and the robot can be programmed for both frames.
Does tracking need a specific controller option?
It needs a tracking or high-speed counter card and the encoder interface. Specify it with the robot; retrofitting it means opening the cabinet again.
What happens on a conveyor stop?
The cell logic must decide: hold position, retreat, or flush if the material has a pot life. That logic is part of the design, not something to settle during commissioning.
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