I have finished setting up the Liteplacer. Homing and look for the exact position with a ruler. If I move the machine 2 or 3 times using TESTXY and then have to be at the 0 point again at some point, I have a 1-2mm offset position. Do the motors skip a few steps? I've already set 3/4 of the current on the potentiometer on the TinyG and the motors get warm after a short period of operation.
What can I do?
Repeatability more than 1mm offset after 2 times TestXY?
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elcomportal
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- Joined: Mon Mar 06, 2023 5:34 am
Re: Repeatability more than 1mm offset after 2 times TestXY?
The moving parts are so light that the motors are unlikely to skip. If they are driven too hard, they tend to stall, and that is easy to notice. More likely, something is skipping. Please look at the bolts that fix the parts that connect to the belt and tighten if needed, including the motor fixing and the pulley set screws. Also, make sure that the belt ends have no play. Try also slack compensation.
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elcomportal
- Posts: 5
- Joined: Mon Mar 06, 2023 5:34 am
Re: Repeatability more than 1mm offset after 2 times TestXY?
Thank you for your answer.
I think, the cables are too inflexible. This is all too difficult. I'll try not to work with the chains, but to let the cables hang from above so that the motors don't have to bend the cables in the chain. How easy or difficult should the X and Y axes be to move? I entered 1 each in the fields for acceleration and speed and the motors make strange noises, especially the X-axis when braking.
I think, the cables are too inflexible. This is all too difficult. I'll try not to work with the chains, but to let the cables hang from above so that the motors don't have to bend the cables in the chain. How easy or difficult should the X and Y axes be to move? I entered 1 each in the fields for acceleration and speed and the motors make strange noises, especially the X-axis when braking.
Re: Repeatability more than 1mm offset after 2 times TestXY?
> How easy or difficult should the X and Y axes be to move?
With power off, there is some resistance, but the axis should move relatively easily, like pushing with one or two fingers.
> I entered 1 each in the fields for acceleration and speed and the motors make strange noises, especially the X-axis when braking.
Please click the "Reset to defaults" button under Control Board Settings. This will write a good but conservative (=somewhat slow) settings to the TinyG board. These should be a good starting point.
With power off, there is some resistance, but the axis should move relatively easily, like pushing with one or two fingers.
> I entered 1 each in the fields for acceleration and speed and the motors make strange noises, especially the X-axis when braking.
Please click the "Reset to defaults" button under Control Board Settings. This will write a good but conservative (=somewhat slow) settings to the TinyG board. These should be a good starting point.
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elcomportal
- Posts: 5
- Joined: Mon Mar 06, 2023 5:34 am
Re: Repeatability more than 1mm offset after 2 times TestXY?
Hello, thank you again for your answer. Now it work fine, but a little thing:
If i make a Homeing the machine move to the zero point. Then i click at "TEST XY", the machine move, i click at "TEST XY" again and the machine move back to the zero point. But it is now a mm more left and a mm to the back, not in the middle of my dot. Now, when i move the machine, it will go to exactly this point, every time to this point. When i click HOME it will go to the middle of my zero point, but after a move it have "a new zero point". What can i do?
If i make a Homeing the machine move to the zero point. Then i click at "TEST XY", the machine move, i click at "TEST XY" again and the machine move back to the zero point. But it is now a mm more left and a mm to the back, not in the middle of my dot. Now, when i move the machine, it will go to exactly this point, every time to this point. When i click HOME it will go to the middle of my zero point, but after a move it have "a new zero point". What can i do?
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- zero_point.jpg (196.6 KiB) Viewed 8498 times
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- zero after a move.jpg (307.47 KiB) Viewed 8498 times
Re: Repeatability more than 1mm offset after 2 times TestXY?
The test functions are simple: If the machine is at home mark, the machine is moved at machine limit set at machine size boxes. If machine is elsewhere, it is moved to zero.
Apparently you have some slack in your system. Please check that the pulley set screws are tight and the belt attachments are snug and don't move. You can also use the location marks (one at zero, others at different areas of the machine) to test if the issue is related to some area in the machine. For example, place a mark ten cm or so from the zero, and go there. Command the machine to go back to zero (either by mark set there or by the Go button using absolute coordinates) and see if the issue is with all moves or only some. See also, that the cables are not pushing the gantry off position. At this point, I have no explanation why the first move is so much different than the rest.
Btw, there is a slack compensation function that makes the machine to approach target point always from same direction and same speed. This can be used to compensate possible small remaining slack. However, this is not that, you should get way past sub-mm repeatability without this function.
Apparently you have some slack in your system. Please check that the pulley set screws are tight and the belt attachments are snug and don't move. You can also use the location marks (one at zero, others at different areas of the machine) to test if the issue is related to some area in the machine. For example, place a mark ten cm or so from the zero, and go there. Command the machine to go back to zero (either by mark set there or by the Go button using absolute coordinates) and see if the issue is with all moves or only some. See also, that the cables are not pushing the gantry off position. At this point, I have no explanation why the first move is so much different than the rest.
Btw, there is a slack compensation function that makes the machine to approach target point always from same direction and same speed. This can be used to compensate possible small remaining slack. However, this is not that, you should get way past sub-mm repeatability without this function.