Touch Test Fails (Poor Robot Positioning Accuracy) after Mild Collision

Problem

After a mild collision, your robot positioning accuracy is compromised. This is observed as offsets in object picking/placement and failed touch tests, where the robot’s tool tip does not land on the expected point.

Before the collision, your hand-eye calibration results were good, and the touch test passed successfully.

Hand-eye matrix	Calibration residuals	Projection verification	Touch test
Reasonable	Good	Good	Good → Collision → Bad

Example of good hand-eye results

Hand-Eye Calibration Matrix

0.999	-0.002	0.0412	-55.598
0.001	0.999	0.0283	-90.654
-0.041	-0.028	0.998	129.044
0	0	0	1

The Hand-Eye Calibration Matrix appears reasonable and is consistent with what one would expect from rough manual measurements (see image below).

Residuals

The calibration residuals are within an acceptable range, indicating that the optimization has converged successfully. For smaller robots, we expect the residuals to in the sub-millimeter range, while for larger robots, the residuals can be in the millimeter range. As for the rotational component of the residuals, we expect them to be in the sub-degree range.

N (Poses)	Rotation avg (deg)	Rotation max (deg)	Translation avg (mm)	Translation max (mm)
10	0.021	0.042	0.109	0.172

Pose	Rotation (deg)	Translation (mm)
1	0.017292	0.163
2	0.008218	0.135
3	0.028	0.172
4	0.009	0.053
5	0.042	0.080
6	0.008	0.098
7	0.022	0.138
8	0.025	0.077
9	0.036	0.125
10	0.013	0.048

Verification using projection also passes, indicating that the hand-eye transformation is correct and accurate.

Potential Cause

Mild collisions can cause slight shifts in the robot’s joints or end-effector, which may not be severe enough to cause visible damage but can still affect the accuracy of the hand-eye calibration. This can result in failed touch tests and inaccurate robot positioning.

Potential Solution

1. Warm-up the camera and perform Infield Correction.

2. Repeat the Hand-Eye Calibration using the initial dataset.

3. Verify the Hand-Eye Calibration results (matrix, residuals, projection).

4. Re-run the touch test.