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

jewoo

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