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 Transform	Hand-Eye Residuals	Projection Verification	Touch Test
Reasonable	Good	Good	Good → Collision → Bad

Example of good hand-eye calibration results

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

Hand-Eye Transformation 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 calibration residuals are within an acceptable range, indicating that the optimization has converged successfully.

Residuals

N (Poses)	Rot. avg (°)	Rot. max (°)	Trans. avg (mm)	Trans. max (mm)
10	0.021	0.042	0.109	0.172

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.

Complete Residuals

Residuals

Pose	Rotation (°)	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 (transform, residuals, projection).

4. Re-run the touch test.