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Author Topic: Servo motor inputs to Vital DSPMC  (Read 8722 times)

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Servo motor inputs to Vital DSPMC
« on: May 02, 2012, 06:07:36 AM »
Hi all

I am having trouble getting the servo motors on my Morbidelli U50 retrofit with Mach3 and Vital DSPMC running over 7Meters / Minute. According to the maths they should be capable of 40M/Min the old controller had them running at 30M/Min max.

The encoders are 500 CPR (2000 QCPR) single ended going into positive terminal of the DSPMC. I saw in a post “Tuning dspMC with Axis Works.
« on: December 23, 2008, 10:14:51 AM »” that “Totallyrc / Mike” asked the poster

“4.Are the encoders differential or single ended with converter board?”

Do I need something like this "converter board" on the input to the DSPMC ?
If so any suggestions?.

Also any user settings for the PID would be useful.
I am running about 4000P 0I 100000D 100G

Regards Rob
Re: Servo motor inputs to Vital DSPMC
« Reply #1 on: May 02, 2012, 05:29:58 PM »
hi Rob,

you do need the single-ended to Differential driver module for all shaft encoders.  you can also build yourself using the am26ls31 chip.

Re: Servo motor inputs to Vital DSPMC
« Reply #2 on: May 02, 2012, 05:49:43 PM »
Hi Rufi

A Big thanks for your prompt and helpful reply.
Do you have any suggestions of over the counter units that have been used successfully?

Regards Rob
Re: Servo motor inputs to Vital DSPMC
« Reply #3 on: May 02, 2012, 11:22:00 PM »
I don't understand what you mean by 'counter units that have been used successfully'!
Re: Servo motor inputs to Vital DSPMC
« Reply #4 on: May 03, 2012, 12:33:40 AM »
Apologies. my spelling is atrocious alas
I meant Converter units as converting from single ended to differential encoder wiring.

I know a CNC machine guru who can design and make me an interface but he is very busy so if there is an of the shelf unit it may be more appropriate.

Cheers Rob
Re: Servo motor inputs to Vital DSPMC
« Reply #5 on: May 03, 2012, 03:09:34 PM »
Hi Rob,
I am using these with the amt encoders but they should work with a standard encoder. I would check with AMT just to be sure.


We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.
Re: Servo motor inputs to Vital DSPMC
« Reply #6 on: May 06, 2012, 12:52:46 PM »
Regarding the converter to change from single ended encoder to differential, the "Line Driver Module" sold by CNC4PC will do the job. It is the DG6 module, which takes input A,B,Z, 5v, GND from the encoder, and outputs A+, A-, B+, B-, Z+, Z- 5v, GND through a RJ45 connector. The J6 board, and the J7 have connections for A+, A- ....etc., for each axis. The A-, B-, Z- signals are not regular ground connections. Do not connect them to ground.
Make sure to do a continuity check from each terminal on the J6, or J7 board back to the RJ45 connector which plugs into the module. It is easy to mix up the wires. I used a RJ45 female connector with numbered screw terminals, which you can plug the RJ45 plug into. You have to splice the original encoder wires onto short Cat5 connector cable+end to make up the connection to the DG6 module. The module is less than $10.00, and has a web site to get all the wire date info.

Pay attention to the "Encoder Polarity" check box on the dspmc set-up page. You can specify Positive, or Negative in a drop down box. One way the motor will not work, one way it will. I had a frustrating time trying to get the machine working, until I fiinally tried that check box.

If your encoder wiring does not have the necessary (8)wires with shielding, you will have to change it over.

Do one axis at a time, and get it working before doing a second.

Hope this helps.

Re: Servo motor inputs to Vital DSPMC
« Reply #7 on: May 11, 2012, 05:22:05 AM »
Hi All
Thanks with your help on this. With the information you gave and a chat to a friend Russel who is a professional CNC electronics specialist we got it solved. Two of the motors are running at Max seed the third is down a bit but above the level that Morbidelli used on the Tria 6000 controller.

Rulphi suggestions on the am26ls31 chip was spot on. Alas due to my knowledge level, I assumed that there would need to be discrete componentry added to it to make it a functioning unit. Russel told me to wire it up as it is and to connect the unused input ether hight or low so I did.

Thanks “mrprecise44” for your comments. The design is working but yesterday when I connected the belts there is some cross talk between the axis’s, which is changeable by how I position the fly leads. So today I have purchased some Screen Cat 5 cable and will re do the interface paying close attention to screening.

I have attached an interconnection diagram to help others reading this post.

Thanks to you all.
Regards Rob
« Last Edit: May 11, 2012, 05:25:29 AM by Rob west »
Re: Servo motor inputs to Vital DSPMC
« Reply #8 on: May 11, 2012, 12:04:50 PM »
hi Rob,

The diff. driver chip should be located very close to the shaft encoder, may be only few inches leads.   the differential output signals should be on the long cable.

may be you have the driver chip mounted close to the dspmc and thats why you are seeing the cross talk.

also use encoder debounce setting on the system page to further remove noise on encoder lines.