Posts by M3WIN

    I wanted to share some updates on my robot "drift" issue, after 2 more months of running parts in the cell the robot in fact moved again, this time 1.5mm in X+ and Y+ when compated to a programmed point in the cell that was being used to check for this. Also the robots joints, J1, J2 and it appears J3 have moved away from the original pre-calibrated whitness mark locations.

    So I re-masterd the robot the the quick master ref position fixture we created, as recomended by tech support, however, that did not work. I believe it was becuase in order for quick master to work the encoders need to be outside of 0.2* degrees, so it was not accurate enough for our applications. After re-calling tech support the do not think that re-master is the way becuase it does not address the root cuase, it was simply something to try that could maybe work as a bandaid untill the real issue is fixed.

    With that being said tech support also did not think using iRvision to re-teach frames or to re-master is a good fix (not sure if iRvision re-masters, only calibrates?) . They said if we were to re-master the robot to the Fanuc fixture every 2 months that would probalby work by resetting all the points, however, it would not be easy and makes almost no sense to do. They believe there is a mechanicle issue, as you guys were thinking.

    They instructed me to check the crash logs and do some other things to look for damage. I was not able to feel vibrations or notice backlash, however, each one of our robots logged on average 625 crashes since they were installed about 2 years ago. Also only one payload schedule when we should have more, and our robot sensitivity is at 100% when they recommend trying to get it to 150-200% to reduce damage when a crash occurs.

    I am planning on having a service engineer come out ot do PM on these robots, they have not been done in 3 years. While they are here, I will ask them to check if there are mechanicle issues, I was told they may see metal chips when re-greasing the joints.

    With all this being said, I am working on touching up all of our robot programs (8 Cells). If Fanuc does deem a gearbox reducer issue or something like that and we do have then change out the components, will I have to re-program all of the cells or would they simply copy and re-load the encoder values.

    Thanks again this forum has such a great help, you guys are wonderful

    The virus I like that lol, affects all points in the cell and the dift is a similar distance but changes direction depending on what userframe the program is calling.

    The latest idea from Fanuc support is that some of the joints on this robot can skip teeth by the style "non-wearing" syle of gearing they use, since we have frequent crashes when loading the raw material into the cnc it could cause this. They claim that a strong push or pull on the EOAT can cause a gear to skip

    We have 8 identical cells and programs with R-30iB TP and Fanuc M-20iB 25. They are loading small blocks of material into a CNC then removing the finished peice, deburring the part edges, serializing the parts, visually inspecting the serialization, then placing the finished parts into a bin. We are trying to hold around .025" at our tightest tolerance. "Drift" has been observed in 2 of the cells after 2 months, however, the other cells "fall out" of program quality in a similar timeline.

    The finished parts are being gripped in the center and are thin curved pieces, the end effector has 3D printed fingers that match the curve of the part. After being removed from the machine, the robot brings the part to a re-grip stand. re-grips, then begins deburring the edges on a number of different deburring wheels. The whole robotic process takes about 10 minutes per part.

    The arm will flex when pressure is applied to it, but it does not feel "sloopy" or "loose" after pressure is applied it will move back to it's orignal location

    I appretiate all the help. We have considered laser scanning to determine the source of movement but have not pulled the trigger on that just yet. We are hoping the in cell quick mastering every 2 months will hold us over while we can look into other potential solutions. Fanuc tech support mentioned that some users will mount a calibration grid in the cell and use iRVision mounted on the robot to auto calibrate after X amount of cycles.

    The robots are mounted on a large metal skid, along with everything else in the cell, so if there was expansion or changes on the concrete floor I would think it would be uniform change. Also our shop is temperature controlled to stay within 65-70* all year.

    The end of arm tooling is 1.1FT off the faceplate, it is an aluminum cylinder with a Shunk end effector. The grip of the parts being minipulated is very consitant, it does not slide or rotate in the jaws.

    The cells have not had any PM done to them just yet, I am looking into having that done, according to the fanuc manual it seems like some basic checks, the only "bigger" item would be greasing the joints.

    Both times the drift was about at the tcp was 1mm or so and we mapped out the drift on points around the cell and it did not appear to come from the base of the robot, also the end effector does not feel lose, however there was no great way to measure it.

    We re-mastered the cell to align the joint witness marks, took a photo, then after the cell fell out of precision again, compared the witness marks and they were off around half to 3/4 of a witness mark thikness on J2, J3. The witness marks were aligned in the zero program, so after there was drift noticed we would re-run te zero program and see that the robot thinks it is at 0 however, the witness marks are no longer the same.

    They are M-20ib/25, when pulling on the arm / end effector there is some flex but it goes back to the original position, I am not sure if I would call it slop tho, it feels solid not like there is slop between the gears or something, but I am able to flex the arm and move the TCP it quite a bit, maybe 5mm or so before it "springs" back to its original position. Should the arm be rock solid when ir pull on the end effector?

    So you think there maybe a faulty reducer in one or more of the joints causing the "drift"? I was able to observe "drift" in the whitness marks in 2 identical robots and cells in joints 2 and 3, both after about 2 months per robot/cell, would this be enough evidence to look into replacing those reducers, these robots and cells were only installed 2 years ago and have a payload of only 2 lbs, also the programs never exceed 50% speed, so it's troubling to think backlash or other mechanical issues could happed with this type of workload.

    The help is greatly appricited I hope to someday give back to the boards and help others, this has been a reacurring theme across our 10 cells and has us in a never ending "touchup", re-programming loop!

    Talking with Fanuc tech support, they recommended this as a solution to our issues, we have noticed that our prgrammed points are not repeatable. We see about 1mm in error after about 2 months. We have checked fixturing androbot mounting and they believe it is a backlashing issue. Our robot witness marks were aligned then drifted after 2 months

    I cannot master to my whitness marks inside the cells, however, I can master to a common fixture point. If I wanted to do this would I jog the robot in joint mode to that point, and register it as a quick master ref position, then monthly or whenever, I can jog back to that position and perform a quick mastering and calibrate? Am I understanding that correctly, or how would i re-teach that master location if I have an issue with the arm? Thanks a bunch

    1.How did you check the drifting ?

    The EOAT was measured before and after the points seemed to "shift".

    2.In which direction does the drift occur ?

    Was only able to notice Y+ , X-, and Z+

    3.did you try rotating the TCP using the tool frame ?

    The movement rotates very well about Z, however, when rotating about X or Y it tends to "drift" from side to side. This was noticed before the cell had issues as well. How would an inaccurate TCP cause the robot to suddenly become less repeatable? the TCP taught or manually entered ?

    manually entered

    5.are you sure it was taught precisely ?


    6.Did you put the robot to 0 position and check the marks ?

    The marks are close, J3,J4 are about a line thickness off but very close.

    7.Put your robot in home position and apply some force by hand on the wrist. Try moving the end effector by hand (like trying to rotate the robot) and up down, this way you can check your reducers for plays

    Seems very firm and steady


    Tech support mentioned that the majority of axis drive mechanisms in this robot are harmonic reducers and that the potential for slip and or drift after a collision is high compared to rotary vector drives. Could this be a concern with crashes or rubbing in and out of fixtures?

    The drift does not seem to be in an arch to the world frame / center of the robot (our robots are offset 60* in the cells)


    Our 10 identical automation cells with M-20iB/25 robots are "drifting" about 1.5mm over the course of 2 months. After speaking with Fanuc's tech support I have heard different theories on the issues like; lose base bolts, lose end effectors or the joints being knocked out after a crash, or fading due to the arm rubbing in and out of fixtures. Fanuc recommends that we purchase the iRVision and re-master the robot every month or so.

    • If we vision master every month or whenever we notice drift, will it automatically shift all of our program points frames etc?
    • Should we also be looking into robot calibration? A drifing point could either be the robots calibration fading or it's mastering location or both?

    These robots have never been mastered or calibrated since they were put in by the integrator 2 years ago. Calibration would also allow for offline programming and cell mirroring, which could come in handy


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