Unfortunately, this is not the correct way to test a robot for repeatability. When you test in this fashion you are preloading all axis gear trains in the same direction, every time. I proved this to my Director at FANUC Robotics by testing similarly, receiving readouts of +/- a half mm, and then (just when everyone thought the robot was perfect) I physically moved the wrist 3 1/2" in the opposite direction and +Z. The ONLY TRUE WAY to test robot repeatability (per Axis) is to invert the arm and counterbalance it for neutrality and then record the measurements when on the gauges and watching the Encoder Counts as you come off the gauges. You then calculate the Delta (slop) and this gives you a true indication of the GOOD the BAD and the REALLY UGLY.
Hello Mark, Sorry, I just saw your comment on my lab's channel. I'm afraid, however, that I don't quite understand it. I agree that the Trical device that we use to measure the robot's repeatability does not respect ISO 9283, because we approach and depart from each position along the same (vertical) direction. Only a laser tracker can be used to measured robot repeatability as prescribed in ISO 9283. The problem with laser trackers, of course, is that they are extremely expensive. The Trical device that we developed in my lab is much more affordable. That said, the way you measure robot repeatability depends on your actual needs. From a user point of view, the best way to measure robot repeatability is to do exactly what a user would do in a specific application. Since in most applications where repeatability is needed, a robot would go repeatedly to a desired end-effector pose following the same approach path, I don't see why our approach would be wrong. The main problem with our device is that it involves contact between the three digital indicators and a precision ball. However, the spring forces and the friction involved are negligible for most industrial robots. We've done similar tests with a non-contact 3D probe (Trinity), and the results are the same. The main problem with repeatability is not how you measure it, but how users interpret it. When you teach a pose, your move to it from different directions (jog a bit to the left, jog a bit to the right), at extremely slow speeds, and often while the robot is cold (not warmed up enough). Then, in the actual application, you approach the desired pose from a different direction, at a higher speed, and while the robot is warmed up. We've done tests and showed that there could be a deviation of more than 0.300 mm from the pose that was taught, even though the repeatability as per ISO 9283 is about 0.030 mm. As for the accuracy, our Trical device was actually developed for calibrating robots. I'll soon post another video where we see the calibration procedure.
@@impactodelsurenterprise2440 Yes, we have several units of a newer version that are for sale. These do not include the digital indicators and the ATI tool changer, however, which are off-the-shelf. Please contact me at ilian.bonev@etsmtl.ca for more details.
Maybe while you’re waiting for the robot you can quantize that beat - it’s out of timing calibration. Amazing to see your robotic calibration process though…
