Two robots handling one lamination need a verified relative-motion envelope. Match their position and timing to control twist, contact loads and vacuum-seal stability throughout the shared lift. [1]
Define the shared geometry
Express both tool poses in one validated cell coordinate frame. Define the intended relative separation and orientation at each stage of the path. Include the lamination contact points: an error between tool frames can produce a different sheet deformation if the contacts are close together or widely separated.
Record both measured tool poses on a common time basis. A timestamp offset can make a correctly synchronized pair appear mismatched during motion, or hide an actual phase lag if separately recorded traces are aligned afterwards by convenience.
Build a relative-error envelope
| Path state | Relative observation | Associated part response |
|---|---|---|
| Initial grip | Separation and orientation at engagement | Preload or initial sheet twist |
| Acceleration and turn | Time-aligned deviation from intended relative pose | Sag, twist and seal stability |
| Placement approach | Contact-point alignment and relative velocity | Unequal arrival or loading |
| Release and stop | Relative response during the defined transition | Residual support, displacement or deformation |
Plot translation components and relative orientation separately. A single distance between tool centres cannot detect every rotational mismatch. Compare the envelope with an experimentally justified part-response boundary rather than setting it from the sum of two brochure repeatability numbers.
Include compliance and grip behaviour
The shared lamination is flexible, and the contacts may also be compliant. A relative displacement can be absorbed by sheet bending, contact movement or tool deformation. Observe which response occurs. A small measured load is not proof of correct geometry if a suction contact is slipping.
NIST research emphasizes position-and-orientation measurement, position-dependent errors and uncertainty in robot assessment. Those principles support the metrology here. They do not establish the behaviour of a particular dual-robot controller or its safe stopping function. [1]
Evaluate interruption through the approved procedure
Use the cell’s authorized commissioning method to assess its defined stop and interruption states with suitable test parts and containment. Record whether the two supports remain compatible during deceleration and whether the lamination can be recovered without guessing its loaded condition. Do not bypass synchronization supervision or safety functions to provoke a mismatch.
Use catalogue gauge 0.23 mm [2]. Assume grips 1.0 m apart have 0.50 mm relative normal displacement: differential slope is 0.00050 rad = 0.02865°. A 0.20 m overhang continuing that plane adds 0.10 mm tip motion, or 0.435 nominal gauges, before flexible sag. Against an assumed 0.08 mm temporary tip allocation this geometry already fails. Reduce and validate differential motion before adding flexure and pose uncertainty; two separate robot repeatability figures cannot qualify the combined placement.
Grip separation, sheet support, acceleration synchronisation and release order control the differential shape. Record both robot frames on one time base and verify the released joint, not only their commanded poses.
Accept the coordinated lift on measured relative motion and the sheet’s response through the qualified path. Preserve the part, grip and support conditions that define that envelope.
References
- G. Qiao and B. A. Weiss, Industrial Robot Accuracy Degradation Monitoring and Quick Health Assessment, Journal of Manufacturing Science and Engineering 141, 2019. DOI: 10.1115/1.4043649.
- Nippon Steel Corporation, Grain-Oriented Electrical Steel Sheets, catalogue D004je, April 2020, specification and typical-property tables.