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How to calibrate vision sensor(Servo robot-i cube)

I weld our product with abb robot, welding tool and vision sensor.
Our product have cylindrical fillet joint.
I have a problem with matching welding path and our product.
There are 2~3mm mismatches(x,y,z directions..) at some position.
I thought it was caused by working only with mathematical rapid programming without synchronizing the vision sensor and welding tool.
It seemed there is a problem with transferring coordinate between vision sensor and welding tool.
Is there any way to synchronize or calibrate vision sensor easier?

tool : Fronius welding torch
sensor : Servo robot - i cube