Every surface the robot cannot reach at a workable angle is a defect waiting to happen. There are two ways to solve it: move the robot, or move the part. On welding cells and on many coating cells, moving the part is the cheaper and more accurate answer.
The comparison
| Positioner | Fixed fixture | |
|---|---|---|
| Access | The part is presented at the best angle for every seam or face | The robot works around whatever angle the fixture fixes |
| Cycle time | Index time is added, but paths get shorter and simpler | No index time, but longer and more awkward robot paths |
| Quality | Downhand welding and consistent gun angle | More out-of-position work |
| Cost | A machine with drives, brakes and its own repeatability | Steel and clamps |
| Loading | Can be loaded outside the cell while the robot works the other side | Load and unload in the robot's time |
How a positioner is selected
- By payload and by moment: an off-centre load at a 600 mm rotation radius is a different machine from the same mass on the faceplate.
- By envelope: rotation radius and spindle centre height decide whether the part clears the floor and the robot.
- By axes: one axis for rotational parts, two axes when the part must tilt and turn, three for complex assemblies.
- By accuracy: 0.05 mm repeatability on single-axis machines and 0.1–0.15 mm on two-axis machines, per the manufacturer datasheet.
The case that shows it
On a delivered hardware package for a Russian integrator, rotational parts of Ø200–1,400 mm and 10–500 kg were handled by a self-centering single-axis vertical positioner with a Ø1,400 mm faceplate and synchronised jaws — the part is centred by the machine on every load, which removes the operator from the accuracy chain entirely.
Frequently asked questions
Do I need a positioner for painting?
Sometimes: on rotating hanger lines the hanger already turns the part — 120 rpm on one delivered line. For batch work on a table, a single-axis positioner can replace a second robot.
What information do you need to select one?
Part weight, envelope, centre of gravity relative to the faceplate, and the seam or face positions. Payload alone is not enough.
Can the positioner be synchronised with the robot?
Yes, as an external axis on the robot controller, so the part moves during the weld or the pass instead of only between them.
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