Absolute accuracy robot info

[pliedas]

Anybody have a manual that describes the Absolute accuracy option of Staubli robots?

Thanks

[Jim C]

Staubli has had several names for Absolute robots over the years. You would need to post the robot model and possibly the serial number before I could give a definite answer. 

In general, the motion planning software uses a generic kinematic model to calculate positions. With an absolute robot, instead of using a generic model, the actual DH parameters are measured. The differences between the generic measurements and the actual measurements of a specific arm are typically very small, 449.98 mm instead of 450 mm for example, but with 6 parameters per joint and a total of 6 joints they can add up to at least a small amount of error.

Details of the implementation has varied depending on the arm and operating system.

[Puma560]

The Body checking of the BMW Z series over there in the USA, they had 4 Staubli's that checks it's own position with laser targets, and then change the links lengths of the DH parameters to improve the accuracy.

[Juggernaut]

There is a brief writeup of the FRAMs implementation that BMW had.  FRAMS stands for Flexible Robotic Absolute Measuring System and was one of the first serious and branded attempts at offering absolute robot calibration capability to a product line.  You could and still can order a Staubli that has been measured, although I am not sure if Staubli does all of this in house anymore.  There are a few companies in Germany that use a CMM reference table or Laser Tracker to do their calibration.  The calibration itself is actually very simple.  You simply need many samples in which you take two measurements:  1.  Where does the robot think it is and 2. Where does the laser tracker or other external measurement device tell you the robot is in reality.  Most algorithms, just take all of this data and generates an array for the DH parameter offsets.  Staubli has made it so easy to do if you have access to the simple and optimized DH parameter functions that are builtin to the OS (paid option, i believe).  Very cool implementation.   

[Juggernaut]

Sorry,  Forgot the FRAMS BMW link

http://findarticles.com/p/articles/mi_m0FWH/is_4_113/ai_74407050/

[Jim C]

Just catch everyone up on the history, the original RX130 used at BMW were donated by BMW to the state of South Carolina Vocational Technical School system. There are still some FRAMS systems running in Europe at other auto manufacturers. For various reasons not related to the robots performance, BMW has ask Staubli to no longer mention this project.

While we no longer market arms under the FRAMS name, Staubli does still offer "measured" arms. The "measurement" can either be done in house by Staubli when the arms are ordered, or you can contract a third party to make the measurement in the field. There are several ways to make the measurements with a laser tracker being the most common.

You do need a license on the controller to enable the modifications to the robot model.

[Juggernaut]

It's not a Staubli in the video, but I have seen Staubli robots do this same application before.  Absolute robot calibration is key in this type of application because of the direct influence the robot's reported position has on the results of scanning. 

http://www.perceptron.com/index.php/en/-industrial/scanning-solutions/robotic-scanning.html

Absolute Robot Calibration is something almost any industrial robot can utilize.  Even if the robot controller doesn't provide the hooks to make small modifications to the geometry data for the robot.  The commanded position can actually be filtered completely outside the robot control environment and the filtered position can be sent down to the robot based on a requested theoretical position.