# Cross Calibration

AlignPlus performs alignment of parts using motion devices by manipulating the parts so that the relative location of their features satisfies a desired geometric constraint. This is made possible by defining the features in a common coordinate system. The coordinate system of choice is Home2D.

On some alignment systems, the parts might be in different substations with each part imaged by a unique set of cameras. One would have to hand-eye calibrate all the cameras in order to establish the relationship between Raw2D and Home2D. Due to the way the part handling system is built it might not be possible to run hand-eye calibration in some of the substations. Some of the reasons could be

- There might be insufficient space to move the calibration target during hand-eye calibration process at these substations
- Hand-eye calibration could be time consuming, especially when a customer uses a part to perform hand-eye calibration, where the customer must move the calibration target to many positions for accurate calibration. The customer might not want run multiple hand-eye calibration operations at each substation.
- On some alignment systems, the parts may be transferred by a motion device that is different than the motion device used for alignment. An example would be a bonding system that might use a motion device to align the parts but might use a repeatable gantry that shuttles between two positions to assemble the aligned parts.

There are a few ways in which cameras can be calibrated to map image features to Home2D. A couple of techniques are manual calibration and cross-station calibration. This document describes cross-station calibration, also known sometimes as remote station calibration.

Cross-station calibration uses the result of hand-eye calibration that has been performed on one of the substations to compute the relationship between Raw2D and Home2D for the cameras at the other substations. AlignPlus implements three techniques to perform cross-station calibration. All the techniques compute the relationship between the gripper, Stage2D, and a calibration target used during cross-station calibration and they assume that this relationship does not change when station is cross-station calibrated with the substation that has been hand-eye calibrated.

AlignPlus supports three types of cross-calibration:

- Checkerboard-based Cross Calibration
- Part-based Cross Calibration
- Hybrid Cross Calibration