Closed-loop control of a Router's rpm using pwm'd mosfets

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cmartinez

Joined Jan 17, 2007
7,024
You know what? ... I like this circuit so much that I think I'm actually going to build it ... and I'll be using it to control the speed of a Milwawkee 5625-20 router, whose original controller works just fine (in fact, it actually works beautifully), but its lowest speed is too high for the things that I want to do with it... like cutting soft plastics that melt at the 10,000 rpm that it delivers at its lowest speed setting.

Here's my first attempt at a sim of the original circuit. But since this is a closed-loop concept, I have no idea as to how to sim the revs of a real motor. So what I did was include a variable frequency source (shown at the left), that simulates the encoder's output of a motor varying its speed, and fed it to the circuit on the right. I also adjusted some of the resistors to more standard, commercially available values.

upload_2018-7-21_21-11-27.png


From what I'm seeing, the circuit seems to be working fine. What I have to do now is add a couple of back-to-back n-Fets to switch AC instead of just DC, plus an opto-isolated driver using a floating-type power supply. I'll be back later with said circuits, plus a few tweaks. Including how I plan to use the magnetic encoder already installed in the router. Who knows... after I'm done it might be a circuit worthy of being included in the finished projects forum.

I've started a new thread inviting the previous participants, to avoid hijacking the original one.

@Bernard, @MaxHeadRoom, @pratto, @KeepItSimpleStupid, @ebeowulf17
 

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Thread Starter

cmartinez

Joined Jan 17, 2007
7,024
There you go, this is the back-to-back n-Fet circuit and driver I'm going to use for this particular application. It was generously posted by @JDT a while back. But he hasn't been seen around this place in a long time, from what I gather.

AC-MOSFET-DRIVER.png

Anyway, credit's given when credit's due ... I don't like to post someone else's circuits without acknowledging their source... that would be just rude.
 

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cmartinez

Joined Jan 17, 2007
7,024
Did you consider using DC to run it with regular PWM?
Also a member here, @THE_RB, that hasn't been seen for a while put together a marketed product that goes down to 5krpm with feedback control using a Triac and Picmicro.
http://www.vhipe.com/product-private/SuperPID.htm
Max.
Yeah, I remember that product. And it seems impressive. Thing is, he's using a triac, and I've already tried using triacs before for this same purpose. Unfortunately, the response time of that sort of circuit is too slow for what I want, and the router's (or spindle or whatever) rpm jump around a bit too much for my taste.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,024
I actually picked one up in the original promotion, it ran really smooth and the accuracy is spot on according to the readout.
Since sold it due to the application gone.
There is a really long thread on the initial launch on the CNCzone from Roman.
https://www.cnczone.com/forums/diy-cnc-router-table-machines/112658-cnc-manufacturing-forum.html
Max.
I also forgot to mention that I'd like to control the router's speed well below the 5,000 rpm that that product boasts as minimum ... besides, building the thing will be fun for me ... :)
 

MaxHeadRoom

Joined Jul 18, 2013
20,936
It should be an interesting project considering the rpm range and the fact it is a series field motor.
I would think the PWM duty cycle range will be stretched thin over 10 bits.
Or you don't anticipate this?
Max.
 

danadak

Joined Mar 10, 2018
4,057
One possibility, down to 500 rpm -

http://www.cypress.com/documentation/application-notes/an93637-psocr-4-sensorless-field-oriented-control-foc

upload_2018-7-22_15-24-41.png

There is a kit, a little pricey, that has all the power driving and sample motor.

The heart of the implementation however could be done on this $ 4 board -

http://www.cypress.com/documentation/development-kitsboards/psoc-4-cy8ckit-049-4xxx-prototyping-kits, either the 4200 or 4200M (more capability) boards.

Tool, compiler free. Creator.

http://www.cypress.com/products/psoc-creator-integrated-design-environment-ide


Regards, Dana.
 
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Thread Starter

cmartinez

Joined Jan 17, 2007
7,024
It should be an interesting project considering the rpm range and the fact it is a series field motor.
I would think the PWM duty cycle range will be stretched thin over 10 bits.
Or you don't anticipate this?
Max.
Actually, bits don't apply in this approach. It's the frequency obtainable from the encoder and its conversion to a proportional voltage that dictates the maximum rpm resolution possible.
 
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