Controlling stepper motor with atteched encoder

[aratti]

Hi John, welcome to the forum!

How do you plan to feed the position value? By a keypad or via serial com.

I have written a code for driving stepper motor (that was few years ago) and position was fed via serial com. The code didn't use close loop but I will be happy to modify it for reading the encoder and turn it from open loop to close loop system

Let me know how many pulses per turn is your optical encoder and a little more on your project.

Cheers

Al.

[camcompco]

Hi Arrati (Al)
first off, thanks for the quick comments.

Well, i happen to have an idea for something that will have to move a given predefined distance in a pattern, not unlike out CNC friends, but my motions will be fixed from a given starting point, for example:

Move (by rotating a acme lead screw) a table to the right (x-axis) 100mm, then forward vie a different stepper/encoder (y-axis) 25mm, stay there for 5 seconds, reverse the y-axis direction 25mm, go further right (x-axis) 50mm, repeat the y-axis movement as before, do this a few more steps (further x and y movements) then return to home, wait until something happens elsewhere (mechanical trigger from other event) and repeat entire process over and over.

I plan on introducing sensors to actually trigger when the y-axis movements stop (they won't be 25mm always, they may be a function of a sensor (contact) being triggered, but the x axis movements will be constant.

This has to be an independent system, no "PC" interface allowed. In essence, it has to be a self contained unit that contains MCU, motors and the ability to know if a step was missed to keep going to "predefined" location. I will also have to introduce contacts so the movement can stop when the appropriate y-axis movement has taken place. The encoder has 400cpr.

thanks again!!!

Also, thanks for the kind welcome!!

[aratti]

Hi John, I am posting a working snippet for moving a stepper controlled by an optical encoder. The encoder is fed to Timer1 which act as a 16 bits counter and using DT interrupt on overflow it will stop the motor when position is reached. I have commented the code but if something is not clear please just ask!.

Hope you will find the code usefull as a base to start building your own.

Cheers

Al.

[camcompco]

Thanks for this. . .very excited to get home and give it a good look!!!
simply great that you take the time out to help a chap thousands of miles away. . . . .

I can't help but imagine that there are many others that will gain from this dialogue as well

Again, thanks!!!!

John (Camcompco)

[camcompco]

Sorry Al, maybe a dumb question here, but will I need to see these "include" files to understand things fully, just asking in the hopes that is the answer is yes you can attach them so when I get home i will better be able to look at things.

INCLUDE "DT_INTS-14.bas" ; Base Interrupt System
INCLUDE "ReEnterPBP.bas" ; Include if using PBP interrupts

thanks again!

[aratti]

Those two include files can be downloaded from Darrel site @ http://www.darreltaylor.com/DT_INTS-14/intro.html
Place both in the PBP folder.

Cheers

Al.

[camcompco]

Hello Al,

I just wanted to say that i am still working on this, didn't want to come of as rude for not following up. As it turns out I really needed to re-re-re read the picbasic pro manual, i was relying on the basic i learned back when i used Lotus 123, much has changed :-)

I am experimenting (trying) on the 18f4431, it has built in Quadrature feedback, sounds like it would be good for my app??? thoughts??

any who, will make sure to follow up soon,

All the best
John

[aratti]

Hi John, yes PBP manual is of great help.
As far as QUI is concerned, this technique increases by a factor of four the resolution of your encoder, so an encoder with 500 pulses per turn will result in a 2000 pulses per turn. This at a first glance could seems great but using a stepper could create some problem. Let me give you a numeric example.

You have a stepper with a resolution of 200 steps per turn, using half step driving you will obtain 400 steps per turn. An encoder of 100 pulses per turn will be your choise, using quadrature, otherwise compensating for lost steps could be a serious problem since the step movement of your motor is a fraction of the encoder quadrature count. (In case of an encoder of 500 pulses per turn your motor step will generate 5 encoder counts per motor step)
Just bear in mind this complication in choosing the encoder if you will use the quadrature.

PS. Is your stepper motor 200 steps per turn or higher?

Cheers

Al.