This is insane 🤯 I always wanted a high precision stage for microchip scanning photography but with this kid of lathe you changed my mind how to think about it and how to design no backlash one.
The friction drive is really neat. Since it's directly linked in terms of RPM and you're moving the Z such short distances, Is it difficult the drive that motor with the precision you want?
using Flexure to preload friction drive bar is a great ideal！heidenhain encoder can be interpolated by renishaw interpolator as far as encoder output is 1v vpp
Looking really good! The scale is beautiful. I love the V-groove friction drive, that's clever. Is the air isolation table custom? Looks like a big trampoline :D
at around 7:00 mark talking about feed motor bearing precision, that would also contribute to error in Z absolute position even with infinitely divided encoder on the motor shaft, hence the choice of direct measurement with linear scale was the right thing to do
Be aware of and don't underestimate the impact of the runout, bearing error etc in that motor will have on your system. I have a similar concept setup on my mill though at an order of magnitude or two looser tolerance lol. 0.001mm glass scales with spring loaded pair of ball nuts to give a zero backlash motion stage with a brushed motor direct driving the screw. The screw is slightly bent (as all screws are) about 3mm over a metre of screw. You can see the bend manifesting as periodic following error during rapid moves. The acceleration that would be required to take it out and give a smooth rapid velocity would be immense. So I have to take the hit to the tightness of the pid control at low speed to be able to keep the high speed motion. Not saying our situations are directly comparable given the scale differences and you can probably get around it by just capping your max feed rate. But it may be something to watch out for. Creep up on your speeds after tuning at low speeds. Be sure to check operation over a range of speeds, resonances spring up irritatingly. At your scale I'd be concerned about the periodic error that occurs as the balls in the bearings go past the peak load point. The differences between the balls themselves would likely be taken out without issue by the encoder system.
@@marcfaulk the issue there is as soon as it starts wearing it'll get slop or backlash in it. The best solution to this I've seen is to actually build a linear motor into the slide itself. No backlash and no linkages between drive and motion component. Harder to get the force though and more stuff to make but it's a neat solution.
If the control loop can’t null out the brushed motor bearing noise then just need air bearing motor lol. Fundamental rule of precision engineering right? If the thing isn’t precise enough, it just means you didn’t add enough air bearings.
@@andrewphillip8432 eh it was cheap and in an open loop controller you wouldn't have the issue. In terms of absolute position it's in the .01 mm range it's just a lot of noise added to the system.
Nothing wrong with a brushed DC motor. If you want detent free, super smooth operation they are still a great option. In that application it may be worth playing with input voltage to quite the motor more
Do you see any impact in position from the brushes sliding over the commutator? Like if you drove a full revolution, can you see where the brushes make and break?
Well the backlash is on the order of the elasticity and hysteresis of the hardened steel itself, like down on the molecular level. I’ve not been able to measure it myself.
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There is so little information on youtube about this topic.
Thank you for sharing your work with us!
This is insane 🤯
I always wanted a high precision stage for microchip scanning photography but with this kid of lathe you changed my mind how to think about it and how to design no backlash one.
Looks great, it’s really starting to come along!
The friction drive is really neat. Since it's directly linked in terms of RPM and you're moving the Z such short distances, Is it difficult the drive that motor with the precision you want?
Didn't think you could get the accurate with a brushed motor, impressive
Sometimes I want to give 2 likes to a video. I write this comment instead, for the algorithm.
Thanks man!
very cool!! i wonder what other uses you'll have for the insane resolution in the future.
using Flexure to preload friction drive bar is a great ideal！heidenhain encoder can be interpolated by renishaw interpolator as far as encoder output is 1v vpp
Tupperware dustshield? Vibe check: passed. ✅
Instant subscribe
Orphus compensated......naturally.
Wow, great project! Fellow Onshape user here.
Thanks, Onshape is the best!
Very interesting drive system.
Ah. And there are the IONIs :)
Looking really good! The scale is beautiful. I love the V-groove friction drive, that's clever. Is the air isolation table custom? Looks like a big trampoline :D
Thanks man. Table is old surplus.
at around 7:00 mark talking about feed motor bearing precision, that would also contribute to error in Z absolute position even with infinitely divided encoder on the motor shaft, hence the choice of direct measurement with linear scale was the right thing to do
Correct
This is why ballscrew is better, it is easier to achieve a lower axial runout than radial in a bearing, I think.
Be aware of and don't underestimate the impact of the runout, bearing error etc in that motor will have on your system. I have a similar concept setup on my mill though at an order of magnitude or two looser tolerance lol. 0.001mm glass scales with spring loaded pair of ball nuts to give a zero backlash motion stage with a brushed motor direct driving the screw.
The screw is slightly bent (as all screws are) about 3mm over a metre of screw.
You can see the bend manifesting as periodic following error during rapid moves. The acceleration that would be required to take it out and give a smooth rapid velocity would be immense. So I have to take the hit to the tightness of the pid control at low speed to be able to keep the high speed motion. Not saying our situations are directly comparable given the scale differences and you can probably get around it by just capping your max feed rate. But it may be something to watch out for. Creep up on your speeds after tuning at low speeds.
Be sure to check operation over a range of speeds, resonances spring up irritatingly. At your scale I'd be concerned about the periodic error that occurs as the balls in the bearings go past the peak load point.
The differences between the balls themselves would likely be taken out without issue by the encoder system.
At this scale and speed of operation, would a bushing work instead of the ball bearing?
@@marcfaulk the issue there is as soon as it starts wearing it'll get slop or backlash in it. The best solution to this I've seen is to actually build a linear motor into the slide itself.
No backlash and no linkages between drive and motion component. Harder to get the force though and more stuff to make but it's a neat solution.
If the control loop can’t null out the brushed motor bearing noise then just need air bearing motor lol. Fundamental rule of precision engineering right? If the thing isn’t precise enough, it just means you didn’t add enough air bearings.
Also wow, 3mm seems like kind of a lot of bend for a 1 meter ball screw!
@@andrewphillip8432 eh it was cheap and in an open loop controller you wouldn't have the issue. In terms of absolute position it's in the .01 mm range it's just a lot of noise added to the system.
Nothing wrong with a brushed DC motor. If you want detent free, super smooth operation they are still a great option. In that application it may be worth playing with input voltage to quite the motor more
I expect the voltage will also have an impact on position stiffness.
Gut instinct says that Seagate was using that for HDD manufacturing. Nothing wrong with a brushed DC motor!
Yeah how do you couple a close loop with scale of this precision with a DC motor?
Just like any other servo control system I guess.
Do you see any impact in position from the brushes sliding over the commutator? Like if you drove a full revolution, can you see where the brushes make and break?
Not thus far. Generally there is some amount of over lap in a brushed motor to prevent dead zones and jumps between commutator bars
@@cylosgarage must be a really nice motor! Who made it?
Would it be accurate to say that the friction bar drive has zero backlash?
Well the backlash is on the order of the elasticity and hysteresis of the hardened steel itself, like down on the molecular level. I’ve not been able to measure it myself.
@@cylosgarage I guess as long as you don't drive the motor hard enough that it overcomes the metal on metal friction right?
Please explain the meaning of the term "Orifice Compensation" in the context of the air bearing.
The restriction is just done via a small orifice on the bearing pad
Thank the precision engineering lords you are not using laser interferometry for location/encoder
it is indirectly used in LIP 382