Layer shift detection?
-
@zapta A closed loop motor/system wouldn't be able correct for all errors. If a print warps and stands up and blocks the nozzle, a closed loop system is going to try to force the nozzle to the correct position. That could cause problems.
I think a closed loop stepper is best used in a system where an object has to move to a target location, like maybe a pick and place machine, as opposed to something that is moving continuously along a specific path.
-
I know this will not help any current user but I wonder if someone will push a controller board that utilize closed-loop stepper drivers.
I have some experience with leadshine and some other proprietary closed-loop stepper drivers and I really like how they work. They take step/dir/en input and can easily be used with any available control board but it's waste of money to have 5-6 drivers on board that you are not using and just bypassing them to use external drivers. In addition you can't control any of the fancy features (current, type of operation etc).
What I'd love to see is a controller that utilize existing (or new) open source closed loop drivers. For e.g. this one looks good:
https://github.com/makerbase-mks/MKS-SERVO42Bthis one looks less powerful but could be cheaper option:
https://www.ustepper.com/what-is-ustepper/Imagine for example Duet3 board, with duet toolboard's that have MKS-SERVO42B driver or something similar for each axes? Or for example duet3 that have 3 TMC's and 3 MKS-SERVO42B and optional can-fd toolboards with MKS-SERVO42B in addition to existing TMC ones ...
maybe just create toolboard with MKS-SERVO42B ?
-
@arhi said in Layer shift detection?:
maybe just create toolboard with MKS-SERVO42B ?
Potentially it could fit the Duet CAN bus architecture. A small toolboard next to each close loop stepper with 4 wires for power and data. Silicon is getting more capable and less expensive.
-
Yes, could probbly be another can-fd tool in the chain. Question is more about support. Whatever driver is chosen it would have to be integrated with RRF so that current and other settings can be set trough g-code like tmc is configured now. I'd like to see then a DUET3LITE that has no integrated drivers, just a can master and some IO (heaters, extruder encoder and STEP/DIR/ENABLE for the 6 onboard drivers that exist now)
-
I might be thinking of a different printer, but their higher-end machines use a laser profilometer for in-process inspection. Detecting a 'dislocation' would likely be possible this way.
https://markforged.com/blog/in-process-inspection-improving-3d-printed-parts/
EDIT: Not to hijack this thread, but I just came across their patent application (pending) for the technology I linked
https://patents.google.com/patent/US20190009472A1/en?assignee=markforged&oq=markforged&page=3
-
@mrehorstdmd said in Layer shift detection?:
@zapta A closed loop motor/system wouldn't be able correct for all errors. If a print warps and stands up and blocks the nozzle, a closed loop system is going to try to force the nozzle to the correct position. That could cause problems.
I think a closed loop stepper is best used in a system where an object has to move to a target location, like maybe a pick and place machine, as opposed to something that is moving continuously along a specific path.
Sorry but this is so much misinformation.
I can´t help but disagree with that. The print head (with a servomotor) will always try to reach the position given by the microcontroller, and as long as the printhead is held up it will stay there, and as soon as the dictated direction changes and the print head can "slip by" it will go to the new correct location.
Also, all servos can throw out an alarm when there is a specified lag behind the commanded position. I have configured my JMC servo to throw an error if either a specified Amp draw is reached (in my case 9A) or it lags at least 200 steps behind the commanded position. It will throw an alarm and stop, and wait for a reboot.
You can connect the alarm to a free endstop and configure that as an E-stop.I have long said that steppers are long overdue for being phased out, with servos coming down in price so drastically.
Just take this for example, this is the servo i`m using.It´s a 180W nema 23 size servomotor with an included onboard driverboard.
It costs 106 € including shipping (70 without, for when buying multiple)
Now, considering that a good quality stepper already costs 40€ plus the stepper driver (I dont know how much, maybe 10-20€ for the chip?) which equals to 50-60€, you begin to question the reason behind steppers, apart from "it´s always been steppers".
Just some of the benefits:- Closed loop
- Automatic e-stop when an alarm is detected, within microseconds, not at the end of the layer and without homing
- You only need to route power, step and direction to the servo, which means you can share power lines.
- You won´t get als much electrical interference due to inductance like with steppers. Which means you can run thermocouple lines closer to the rest.
- They can rev much higher than steppers, the nema 23 can do 3000 rpm with full torque up to 2000 rpm.
- They have a very smooth motion profile from the start, no 256-interpolation necessary. You can configure them with up to 160.000 steps per revolution if you wish. Not necessary though, i run mine with 5000 steps per rev.
- Dramatically lower power consumption, the servo only consumes power when you accelerate it or turn a load.
Steppers always consume the specified amperage x voltage. - You can configure the servos to deliver more power for a shorter period of time (duty cycle). They are rated for example for 180W at 100% duty cycle. You can run them at 540W, or 300% for a duty cycle of 10% Which means normally 1 minute running at 300%, then 9 minutes cooling off at reduced load.
- (added) They are DEAD SILENT. Not a whisper coming from them, even going at 400mm/s or accelerating at 5g. No stealthchop necessary.
I could list some more, but i think that is enough for now.
Also, you can get the nema 17 version for 62€.
I have long asked dc42 why he focuses so much on integrated stepper drivers.
A cheaper board with no stepper drivers and only the pinouts for external drivers would be a real seller.
I am so happy with my nema23 servos, my next printer will have all axes equipped with it.
The servo is so powerful, it can accelerate my 5kg gantry with 5g (~50.000 mm/s²) if i want it to, and not a single skipped step in sight.I think it´s a shame that the industry is moving towards linear servomotors already, and we can´t even adapt normal rotational servomotors yet.
-
@NitroFreak said in Layer shift detection?:
I have long asked dc42 why he focuses so much on integrated stepper drivers.
A cheaper board with no stepper drivers and only the pinouts for external drivers would be a real seller.
I am so happy with my nema23 servos, my next printer will have all axes equipped with it.
The servo is so powerful, it can accelerate my 5kg gantry with 5g (~50.000 mm/s²) if i want it to, and not a single skipped step in sight.I think it´s a shame that the industry is moving towards linear servomotors already, and we can´t even adapt normal rotational servomotors yet.
I've had tons of discussions with people using servos who have never used an integrated stepper driver before. What they don't realize is that these integrated drivers already work close to how a closed loop system would, because they, pardon my Chinese, adjust the control parameters on the fly based on the back EMF and they are darn good at it. So good at it, that it's creepy.
You are right about servos, but integrated drivers have a place and are the cozy future. I'm impressed what they can do on my printer with Nema17. I think dc42 didn't think most people would try slapping multiple 10kg gantries onto them, and I think most people don't.
-
@NitroFreak said in Layer shift detection?:
I have long asked dc42 why he focuses so much on integrated stepper drivers.
He stated (in other threads) that expansion boards with no drivers, and outputs for external drivers, are on the roadmap for Duet 3. No dates, yet.
Delta / Kossel printer fanatic
-
@Edgars-Batna said in Layer shift detection?:
I've had tons of discussions with people using servos who have never used an integrated stepper driver before. What they don't realize is that these integrated drivers already work close to how a closed loop system would, because they, pardon my Chinese, adjust the control parameters on the fly based on the back EMF and they are darn good at it. So good at it, that it's creepy.
You are right about servos, but integrated drivers have a place and are the cozy future. I'm impressed what they can do on my printer with Nema17. I think dc42 didn't think most people would try slapping multiple 10kg gantries onto them, and I think most people don't.
I have used them (I have 2 duet 2´s) and even with them working well, they can´t reliably detect a missed step.
What i don´t understand about the duet 3´s is that they are obviously geared towards those multiple 10kg gantries with big steppers moving them, seeing as they have 4A drivers.
BUT, Why does it still only have 30V maximum rating? It does not make sense for big steppers. At least go to 48V to use the cheap server power supplies.
I´m not going to mention that those bigger steppers are even more expensive and cut well into the territory of a nema23 servo.Also, i forgot one of the most important aspects about servos, so here we go:
- they are dead silent! No stealthchop required!
-
@Danal said in Layer shift detection?:
@NitroFreak said in Layer shift detection?:
I have long asked dc42 why he focuses so much on integrated stepper drivers.
He stated (in other threads) that expansion boards with no drivers, and outputs for external drivers, are on the roadmap for Duet 3. No dates, yet.
You got me wrong, i dont want to buy a duet 3 with 6 expensive drivers only to expand it with another board that adds additional cost.
Give me a Duet 3 without any stepper drivers that has the breakout pins right on the board, and I´d be so happy.
What do people use those huge stepper drivers for anyway?
-
@NitroFreak said in Layer shift detection?:
@Danal said in Layer shift detection?:
@NitroFreak said in Layer shift detection?:
I have long asked dc42 why he focuses so much on integrated stepper drivers.
He stated (in other threads) that expansion boards with no drivers, and outputs for external drivers, are on the roadmap for Duet 3. No dates, yet.
You got me wrong, i dont want to buy a duet 3 with 6 expensive drivers only to expand it with another board that adds additional cost.
Give me a Duet 3 without any stepper drivers that has the breakout pins right on the board, and I´d be so happy.
I get it. I'm just repeating what Dave said.
What do people use those huge stepper drivers for anyway?
Printers.
-
@Danal said in Layer shift detection?:
Printers.
I get it, but why? If you have to use nema 34´s, you are already more expensive than servos that have similar power output.
Servos have the advantage that they are very power dense, so they require less metal and copper to output the same power (factor 3)
They are only more expensive because they require the encoder and feedback loop, but those stay constant with size going up, so they amortize really quickly going up in size and stepper nema 23 setups with similar power output already cost more. -
@NitroFreak said in Layer shift detection?:
i dont want to buy a duet 3 with 6 expensive drivers
You are kidding, right? Duet 3 uses TMC5160A-TA. These are DigiKey Qty 2000, $3.11 each. I'm sure the board builders get them for under $3. Removing six of them cuts $18 or less from the internal cost. Maybe $18.50 if you count the passives.
Like any technology, that number will fall over the lifecycle of the D3.
I'd think the more important thing is the lack of pins for Step/Dir/Ena, or SPI equivalent, that are fully supported for external drivers. Expansions will provide that.
Delta / Kossel printer fanatic
-
@NitroFreak said in Layer shift detection?:
If you have to use nema 34´s
Very, very, few of these in Hobbyist printers. TMC5160 may be a bit of overkill for Nema17 if one looks only at current; at the same time, it is the "latest and greatest" at things like interpolation, whatever.
And the points I made about price above, they get even less if you compare a prior generation to the 5160. In other words, the incremental cost of "latest greatest" is probably under $6 per board, even if "latest greatest" is not strictly speaking 'required' for most of D3 installations.
-
And, having said all of that, my second or third post in this thread was "Also, the 'real' way to do this is closed loop...".
So I am totally with you on servos (or equivalent). I'm just pointing out that the factual cost of those TMC drivers is only a few percent of the board cost.
I'd love to see more direct support for closed loop.
-
@Danal said in Layer shift detection?:
@NitroFreak said in Layer shift detection?:
i dont want to buy a duet 3 with 6 expensive drivers
You are kidding, right? Duet 3 uses TMC5160 DigiKey Qty 2000 they are $3.11 each. I'm sure the board builders get them for under $3.
Removing six of them cuts $18 from the internal cost. Maybe $18.50 if you count the passives.
Yes, i can see that you know how pricing works. If you consider that the components cost maybe 80$ ( the processor costs 8€, the rest is cents) cutting 25% of the internal costs is quite a bit. Now, hoping that they keep the profit margin % the same, those 18$ can easily amount to 50$ saved on the final product. And especially considering that one does not need to buy the separate 30€ expansion breakout board (why can the breakout pins not be on the board from the start?) That is a substantial chunk of change. Also the PCB itself shrinks, further reducing cost.
So no, i am not kidding. -
@NitroFreak Interesting. If the servo gets hung up, or misses steps, is there some means of feeding that information to the extruder so it won't keep trying to squirt plastic?
-
@mrehorstdmd said in Layer shift detection?:
@NitroFreak Interesting. If the servo gets hung up, or misses steps, is there some means of feeding that information to the extruder so it won't keep trying to squirt plastic?
Yes, the servo has an alarm output that switches from 0 to 5v where you can run (dont have to) a wire from the servo to the duet which treats it as an endstop. You can configure that endstop as an emergency stop.
https://duet3d.dozuki.com/Wiki/Connecting_an_Emergency_Stop -
@NitroFreak But it doesn't "recover" from lost steps, etc., merely shuts down the print?
I like the idea of silent operation- I have a sand table that could use some additional quieting down...
I'm looking at the NEMA-17 motor/driver you linked and the torque spec looks really low. 0.48 Nm can't be right for 52W motor, unless that's torque at maximum rpm. How do you select these things for a given application?
I found the manual here. Are there any special tricks required to interface these to a Duet board?
Do you notice any differences between steppers and servos in terms of things like ringing in prints?
-
@NitroFreak Parts cost is the only driver of price? Assembly labor? Firmware is not a contributor? Trade show marketing (well... not right now)? Support? A dozen things I forgot? Price and cost are only very loosely related, and neither of us really knows how Duet3D chooses to run internally. Therefore, let's turn the question around:
Retailers have posted prices of $230 USD or 250€ to 260€ today for a 6HC, what would you expect to pay for a driverless "base" board?
Delta / Kossel printer fanatic
