@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.