Vision system calibration when changing robot joint

Sebastien 2016-09-28

Can I use the vision system on a robot with a replaced joint? Do I need to recalibrate the robot after the joint has been replaced?

Annick_Mottard 2016-09-28

@Sebastien you can use the camera on a UR that has a replaced joint. However, there are some guidelines that need to be followed if you want to keep the vision system’s accuracy that you had before joint replacement.

Following the UR joint replacement procedure, you will see at the end of it that you need to calibrate the robot when you change a joint. There are a few ways to do this and the best way being the dual robot calibration procedure. All this information can be found in the service manual that can be downloaded on the UR support website. Once the robot has been calibrated, you should define new Snapshot positions to use within your Camera Locate nodes. Remember to save your installation file after defining a new Snapshot position. And you should be up and running just like you were before joint replacement!

@Stefan_Stubgaard what are your inputs on this?

Stefan_Stubgaard 2016-09-29

There are basically three ways of calibrating a robot after joint replacement:

1. Calibrate one joint individually

This option is less precise, but very fast. For applications where you don't need high accuracy, like simple pick'n'place, I would go for that option. Procedure is described in Service Manual.

2. Calibrate entire robot using the dual-arm calibration method

This option is the most precise and after the calibration you should be able run the vision application as before joint replacement. It takes less than an hour to perform this operation. You need two robots to perform the calibration and a calibration kit as well (can be purchased from Universal Robots distributors). Procedure is described in Calibration Manual.

3. Plate calibration

This option enables you to calibrate the robot in an area defined by a plate. Prior to performing this calibration, you need to use method 1 to calibrate the replaced joint.

The plate contains a matrix of holes where the tool flange fits into, so you basically teach all the positions in that area and it will increase robot accuracy in this specific area. Multiple areas can be calibrated. Accuracy in calibrated area will be similar to accuracy obtained by using dual-arm calibration procedure. Procedure is described in Calibration Manual.

For all methods, you will definitely need to re-define the Snapshot position as described by @Annick_Mottard