Hello Guest it is January 15, 2021, 09:26:37 AM

Author Topic: Microstep with encoder  (Read 82 times)

0 Members and 1 Guest are viewing this topic.

Microstep with encoder
« on: December 27, 2020, 10:02:38 AM »
Hello, I’m building a CNC router. I have ball screws 2010 with closed loop Nema34. The encoder have 1000 CPR. My calculations for 20 micro steps :
(200 steps motors X 20) / 10 = 4000 / 10 = 400 counts per units in Mach4
Accuracy 1 / 400 = 0.0025mm

Do you agree with me ?
I’ve already used open loop stepper motors, but never with closed loop systems. I don’t know which value of micro step I have to use with an encoder of 1000 CPR ?

Thank you for your help
Re: Microstep with encoder
« Reply #1 on: January 01, 2021, 03:23:30 PM »
Hi,
I would double check the:
Quote
. The encoder have 1000 CPR.
I rather suspect that the encoder is 1000 line per rev which would make it, with quadrature encoding, 4000 count per revolution.
Almost all of the closed loop steppers I've seen advertised are 1000 line, a subtle difference in terminology.

I'm not sure that microstepping has any relevance, the best resolution you can obtain is determined by the finest resolution of your encoder,
1000 count per your post or 4000 count per my guess.

One of the few and genuine advantages that closed loop steppers offer over open loop steppers is resolution. With open loop steppers no matter
what you microstep settings are you can really only expect genuine resolvable steps of half full steps, ie 400 steps per rev.  Closed loop steppers
can however genuinely interpolate between steps up to the max resolution of the encoder.

I otherwise agree with your calculation. May I suggest plug the numbers into the Mach4 Control plugin and try it. You'll soon see if when you MDI a
100 mm move whether it moves 100mm or not.

Craig
My wife left with my best friend...
     and I miss him!
Re: Microstep with encoder
« Reply #2 on: January 01, 2021, 10:19:11 PM »
Hi Craig
Thank you for your answer.
Informations about motor
https://www.omc-stepperonline.com/closed-loop-stepper-motor/p-series-nema-34-closed-loop-stepper-motor-8-5nm-1203-94oz-in-with-encoder-1000cpr.html?mfp=161-motor-nema-size%5BNema%2034%5D
P Series Nema 34 Closed Loop Stepper Motor 8.5Nm/1203.94oz.in with Encoder 1000CPR
Encoder Specification
Output Circuit Type: Differential type
Output Signal Channels: 2 channels
Supply Voltage Min: 5V
Supply Voltage Max: 5V
Output High Voltage: <4V
Output Low Voltage: <1V


Driver
https://www.omc-stepperonline.com/closed-loop-stepper-driver/closed-loop-stepper-driver-0-8-2a-24-110vdc-18-80vac-for-nema-34-stepper-motor.html

So if I understand I must choose a microstep to match the encoder max value If the value of encoder is 1000 I must set the micro step to 5 (1000/200) ?
Re: Microstep with encoder
« Reply #3 on: January 01, 2021, 11:19:36 PM »
Hi,
well the advertising material certainly says 1000 counts per rev.

In any event the encoder resolution is what it is, you need to set the microstepping, and your proposal of 20 microsteps
per full step for 4000 pluses/rev sounds good. That would result in 400 steps/unit in Machs motor tuning page.

Quote
So if I understand I must choose a microstep to match the encoder max value If the value of encoder is 1000 I must set the micro step to 5 (1000/200) ?

No, you can set the microstepping higher than the encoder resolution but the actual resolution you are going to achieve is determined by the encoder.
Given that your proposed micro stepping regime is at a higher rate than the encoder suggests that you will be able to extract ALL the resolution the motor is capable of.

Craig
« Last Edit: January 01, 2021, 11:24:38 PM by joeaverage »
My wife left with my best friend...
     and I miss him!
Re: Microstep with encoder
« Reply #4 on: January 01, 2021, 11:28:07 PM »
Ok
Thank you