Achieving accuracy with robot calibration software

Cole Technologies, located in Columbus, Indiana, is a certified Universal Robots system integrator supplying automation systems specializing in pick and place, deburring and plastic part-trimming applications. One recent project involved the de-flashing of moulded parts where a more accurate robot path was deemed necessary.

The company contracted API Services to perform on-site robot calibration using the API RADIAN 6DoF (six degrees of freedom) laser tracker, in conjunction with its proprietary robot measuring software (RMS), to improve programmed robot motion path accuracy.

The RMS system uses a multiple SMR tracker target frame directly mounted onto the robot end-effector, allowing for dynamic robot tracking. Recorded measurements are used to determine tracked robot position points revealing true robot position and orientation.

RMS procedures use ISO 9283 guidelines to check accuracy, repeatability, pose, distance, drift and overshoot by exercising all robot joints. The robot’s working envelope can be defined applicable to the planned robot application function.

“The availability of additional robot accuracy allows us to provide a better outcome for the customer regardless of application,” says Steve Richard, director of engineering at Cole Technologies. “API [was] able to directly interface with our RoboDK robot programming software for robot calibration, making it seamless and efficient to load the new parameters.”

Measuring a free-point cloud consisting of 80 points, the RMS software generated a new DH (Denavit-Hartenberg) frame model parameter set that was used to correct errors in joint angles and link lengths. The revised DH parameter can be directly input into the robot controller or used to update the robot motion path program, as was the case at Cole Technologies, which resulted in significant improvements to the robot’s accuracy.

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This article originally appeared in the November 2019 issue of Robotics Insider, Manufacturing AUTOMATION’s quarterly e-book focused on robotics.