Is there a way to check for backlash (worn axis gears) on the robot that is not powered up?
Thanks in advance.
Kuka backlash checking
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bmike -
November 13, 2017 at 5:37 PM -
Thread is marked as Resolved.
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Not... really? You could get a rough idea, perhaps, if you could mount a dial indicator close to each axis center and "wiggle" the axis. But trying to separate out how much of the dial reading is caused by backlash, vs simple flex of the links, vs non-rigidity between the axis and the brakes (and then there's gravity effects on A3, and the counterbalance on A2)... you're only going to get a rough idea. And probably only detect really egregious amounts of wear.
I don't know of any spec for taking these measurements and comparing them to a baseline.
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thanks for the reply.
I was wondering if one would try to move the robot manually by putting a wretch on the back of the motor, would that show if there is any backlash? -
no... that is used to move axis in emergencies (if someone is trapped by robot).
also motor side is wrong side to check gearbox backlash (input), you need to check the output side of the gearbox. for that you need to know what torque to apply (it is different for each axis and each robot), how to measure change, what value range is expected etc... -
that makes sense, thank you.
Someone told me that there is a sleeve (connector) between the motor and the gear for axis 1 , 2 and 3 and that is usually what wears out and it is easy to replace, is that true or is that wishful thinking ? -
Each motor has a spline driveshaft, that inserts into a harmonic drive that serves as the "gearbox" of the axis. I doubt the spline shafts will wear over time. The harmonic drive itself... well, it's claimed that harmonic drives, due to their design, wear much more slowly than comparable planetary gear sets, but that's sales-pamphlet stuff. I haven't seen a comparison test dataset.
Frankly, I'd be inclined to believe that the bearings would wear faster than the harmonic drives, but that's just a gut feeling.
As for replacing them... well, the motors are easy to replace, but I can't speak to the actual bearings and/or harmonic drives. There's a series of videos starting here https://youtu.be/6YiPrytt_Ss that covers the process of completely tearing apart a KR-350, and all mainstream KUKAbots are pretty much the same, aside from sizing.
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out of curiosity, what is the proper way to check/test for backlash? does Kuka has a special tool or can that be done just using the robot?
Thanks -
Powering up the robot and using a laser tracker or dial indicators to measure differences between commanded and actual motion, generally. This holds true for all brands. It pretty much has to be this way, b/c the critical factor you're trying to measure is the difference between how much the robot thinks it moved vs how much it really moved. This is complicated by the fact that the backlash isn't consistent -- a tool mounted to the wrist with an off-center CG might provide enough bias to almost eliminate backlash at certain orientation angles, but produce a massive backlash when making the transition between those angles.