# Applications of Cross-Calibration

## Shuttling Camera Calibration

A shuttling camera application is one where one or more cameras are mounted onto motion devices whose purpose is to reposition the cameras, for capturing images of a different regions of a part. The same result can be achieved by having dedicated cameras for each region to be imaged. Shuttling camera systems are used are to reduce the expense of additional vision hardware. An example of a shuttling camera applications is shown below. Here two cameras are shuttled between two positions, Pos0 and Pos1 to image all the corners of the part.

In practice it is possible to hand-eye calibrate the cameras at the four positions, either by capturing the images of the four corners at each pose of the motion device during hand-eye calibration process, or by performing two hand-eye calibrations, one at Pos0 and another at Pos1. However, the hand-eye calibration process takes more time to complete and might not be convenient.

To calibrate the system in our example the following steps can be executed

1. Perform hand-eye calibration at Pos0.
2. Capture an image of the calibration target at Pos0
3. With the calibration target being stationary, shuttle the cameras to Pos1 and capture the image of the target
4. Perform cross-calibration using the images from the previous two steps

The calibration target could be calibration plate or calibration part with features. It can be manually placed in the beginning on stage/platform with vacuum on to keep it flat.

## Lamination Systems

On some systems, it may not be possible to use a robot to assemble two parts due to mechanical or other constraints. These systems typically use a motion device, for example a UVW stage, that holds one of the parts to be assembled. A platform contains the second part. During run-time, the part on the motion device is manipulated so that it accounts for any variation in the positions of the two parts at their respective stations. After alignment, a gripper attached to a gantry, that simply shuttles between the two stations between two fixed positions, transfers one of the parts from its station to the other station to assemble the parts.

The figure below shows such a system. To calibrate the system the following steps can be executed

1. Perform hand-eye calibration at Station1.
2. Capture an image of the calibration target at Station1
3. With the calibration target being stationary, shuttle the calibration target to Station2 using the gripper that is used to assemble the parts and capture the image of the target
4. Perform cross-calibration using the images from the previous two steps.

Note:

Here the station 1 and 2 can have different Z height which is perpendicular to Home2D plane.

The mechanical transfer of calibration target should be between the same positions as the run time part during assembly, using the same mechanical system. Failure to do so will result in invalid calibration data.

## Another example

In the example above, cross calibration is conducted via the following steps:

1. The system is hand-eye calibrated.
2. Images of the calibration target using the cameras that have been hand-eye calibrated are taken.
3. The calibration target is transferred from stage to platform. The images of the calibration target are captured at Pos1
4. The cameras are shuttled to Pos2 using a different mechanical system, and images of the calibration target are acquired at Pos2.
5. Cross calibration results are computed using the images captured in the above three steps. This result will enable mapping of image features in images at Pos0, Pos1 and Pos2 to Home2D