I hope someone can shed some light on a problem I am having with a DC brushed Servo motor in a factory made laser engraver.
The machine is no longer supported by the US manufacturer because it is 19 years old. Talking to them is useless. Same problem with the motor manufacturer, even though they appear to make the same motors for OEM configurations.
I am not an electronics technician, but i have a very good understanding of general electronics, electric and repairs. What I try to describe may not be the correct terminology, but hopefully I'll get the idea across! Here is the problem:
The laser engraver uses (2) 48 volt brushed DC servo motors for the X and Y axis control. The motors do not have any gear reduction or reduction in the way of different sized pulleys on the belts that drive the carriage. The Y axis is generally rotating fairly slow as it moves. Probably in the range of 30-100 rpm for moving to the start/home positions, etc. When the laser is in "vector cutting" mode, as in a CNC type use, it rotates very slowly when the speed is set to the minimum ranges of the driver (in the PC or machine control panel). The machine is supposed to be able to be controlled in speed setting from 1-100% for various engraving/cutting and applications.
When the speed is set to most settings below 10% the Y axis motor will set up a severe vibration that affects the speed and causes "jerky/stalling/erratic" movement. It seems to be fine above that speed. It does not always start vibrating instantly at a given low speed but can start after 4-6 rpms.
One old bulletin from the manufacturer states that "the Y motor is set to low gain on start-up and will not vibrate, but when it is engraving the gain is set high, and the machine will vibrate if the short belt is loose".
They are referring to the timing belt from the motor to the axle shaft that drives the Y axis. I have tightened to their recommendations , and tried a variety of different belt settings, tighter and more loose , but no joy. I have removed the motor from the mount and held it in my hand with no load and get the same vibration, so I don't think it is "machine" related bearings, loading, etc.
Since the motor manufacturer does not offer any parts or motors, I have disassembled the motor to check it over. I thought the ball bearings were too loose, so replaced those with new R4A-ZZ-C3 ball bearings, I removed any end play on the shaft, checked the encoder for dirt, dust, etc. (none), checked the brushes for wear, brushes looked almost new, maybe not quite seated in to the armature/rotor yet, as they were worn only on half of the rectangle surface, they may a have been replaced shortly before I bought the unit. The bars on the armature/rotor are clean, smooth, not worn, the gaps between are void of build-up, and in general look very good.
At this point I'm considering all options.
I probably can't change the frequency or pulses sent by the proprietary controller board.
I can't find a replacement motor yet on e-bay, but don't necessarily think it's the motor at this time.
Could it be the frequency that is being sent to the motor is setting up a resonant frequency within the motor?
Should I remove the motor and run it with a dc power supply to seat the brushes better (for full contact)?
Would a resistor in series to the motor or capacitor across the motor do any good? I don't want to blow the control board.
I have considered changing the ratio on the motor drive to a 2:1 ratio and changing the encoder wheel from 512 cpr to 256 cpr so the motor will rotate at twice the speed and maybe avoid the problem.
Any ideas or comments are appreciated.
Sorry so long!
Thanks,
Jeff
The machine is no longer supported by the US manufacturer because it is 19 years old. Talking to them is useless. Same problem with the motor manufacturer, even though they appear to make the same motors for OEM configurations.
I am not an electronics technician, but i have a very good understanding of general electronics, electric and repairs. What I try to describe may not be the correct terminology, but hopefully I'll get the idea across! Here is the problem:
The laser engraver uses (2) 48 volt brushed DC servo motors for the X and Y axis control. The motors do not have any gear reduction or reduction in the way of different sized pulleys on the belts that drive the carriage. The Y axis is generally rotating fairly slow as it moves. Probably in the range of 30-100 rpm for moving to the start/home positions, etc. When the laser is in "vector cutting" mode, as in a CNC type use, it rotates very slowly when the speed is set to the minimum ranges of the driver (in the PC or machine control panel). The machine is supposed to be able to be controlled in speed setting from 1-100% for various engraving/cutting and applications.
When the speed is set to most settings below 10% the Y axis motor will set up a severe vibration that affects the speed and causes "jerky/stalling/erratic" movement. It seems to be fine above that speed. It does not always start vibrating instantly at a given low speed but can start after 4-6 rpms.
One old bulletin from the manufacturer states that "the Y motor is set to low gain on start-up and will not vibrate, but when it is engraving the gain is set high, and the machine will vibrate if the short belt is loose".
They are referring to the timing belt from the motor to the axle shaft that drives the Y axis. I have tightened to their recommendations , and tried a variety of different belt settings, tighter and more loose , but no joy. I have removed the motor from the mount and held it in my hand with no load and get the same vibration, so I don't think it is "machine" related bearings, loading, etc.
Since the motor manufacturer does not offer any parts or motors, I have disassembled the motor to check it over. I thought the ball bearings were too loose, so replaced those with new R4A-ZZ-C3 ball bearings, I removed any end play on the shaft, checked the encoder for dirt, dust, etc. (none), checked the brushes for wear, brushes looked almost new, maybe not quite seated in to the armature/rotor yet, as they were worn only on half of the rectangle surface, they may a have been replaced shortly before I bought the unit. The bars on the armature/rotor are clean, smooth, not worn, the gaps between are void of build-up, and in general look very good.
At this point I'm considering all options.
I probably can't change the frequency or pulses sent by the proprietary controller board.
I can't find a replacement motor yet on e-bay, but don't necessarily think it's the motor at this time.
Could it be the frequency that is being sent to the motor is setting up a resonant frequency within the motor?
Should I remove the motor and run it with a dc power supply to seat the brushes better (for full contact)?
Would a resistor in series to the motor or capacitor across the motor do any good? I don't want to blow the control board.
I have considered changing the ratio on the motor drive to a 2:1 ratio and changing the encoder wheel from 512 cpr to 256 cpr so the motor will rotate at twice the speed and maybe avoid the problem.
Any ideas or comments are appreciated.
Sorry so long!
Thanks,
Jeff