Need Help!- EMC2 to IMserv hardware

[twells]

I have a sherline lathe with an IMserv servo control system. I would like to use the hardware and eliminate the deskcnc softeware and drive it with emc2.
Has anyone done that before and can help me over some of the pitfalls? It seems to me that i could bypass the propritary controler card that is serial driven by deskcnc and send the step/direction from the parallel port directly to the servo amps step/dir inputs. Given that the grounds and voltages remain on the amps. The amps are "sv-500's" and have a manual PID adj. on the card. I've read that this could be a problem but i'm willing to try. i'm hoping to get some ideas. I have a 4 axis mill and use emc2 on it and i'm realy happy with it.. NOT so happy with deskcnc..
thanks..

[jmelson]

Originally Posted by twells I have a sherline lathe with an IMserv servo control system. I would like to use the hardware and eliminate the deskcnc softeware and drive it with emc2. Has anyone done that before and can help me over some of the pitfalls? It seems to me that i could bypass the propritary controler card that is serial driven by deskcnc and send the step/direction from the parallel port directly to the servo amps step/dir inputs. Given that the grounds and voltages remain on the amps. The amps are "sv-500's" and have a manual PID adj. on the card. I've read that this could be a problem but i'm willing to try. i'm hoping to get some ideas. I have a 4 axis mill and use emc2 on it and i'm realy happy with it.. NOT so happy with deskcnc.. thanks..

Well, it looks like the drive is pretty similar to a Gecko 320, just lower power. Depending on encoder resolution, it ought to work with software step generation from EMC. Possibly you would need a breakout board to create step pulse signals compatible with the drive, but most likely not.
The only posible problem is that the Sherline has a 20 TPI leadscrew, and with a relatively modest encoder resolution, you might need a lot of step pulses per second to get reasonable speed.

Quick calculation, assuming 250 cycle/rev encoder : 30 IPM * 20 TPI * 1000 = 600,000 pulses / minute or 10000 pulses per second = no problem for EMC2. Now, I seem to recall that the IMserv setup has a gearbox on the motor with somthing like a 7:1 ratio. Is that correct? Now, with all the same numbers, you need 70,000 step pulses/second to even hit 30 IPM! Now, you have a problem. But, the drives have a 4:1 step multiplier, is that optional or a permanent feature?
If always set for 4X multiplier, then 70K goes down to 17,500, back into the perfectly OK for software step generation in EMC2.

Anyway, if you find you DO need higher step rates, there are several hardware step generator boards available. I make the Pico Systems Universal Stepper Controller, there are also some options from Mesa.

Jon

[twells]

Thanks so much jon.. I took a look at one of the drives and found the ratio to be 2.8235 to 1.. it doesn't sound right but i double counted the teeth on the sprockets in the gear box 17:48. They are globe motors 30.3 volt and the encoder is an avago heds-5505 a06 giving 500 pulses per rev. With the math you helped me with i think i have a starting point. Also i'm going to go though some of the detail set up values for the deskcnc app and see what it is using. It might not cross over or relate to what emc is looking for but i will see. i plan on getting started on this project in a week or so, so i'll let you know. Thanks again..

[jmelson]

Originally Posted by twells Thanks so much jon.. I took a look at one of the drives and found the ratio to be 2.8235 to 1.. it doesn't sound right but i double counted the teeth on the sprockets in the gear box 17:48. They are globe motors 30.3 volt and the encoder is an avago heds-5505 a06 giving 500 pulses per rev. With the math you helped me with i think i have a starting point. Also i'm going to go though some of the detail set up values for the deskcnc app and see what it is using. It might not cross over or relate to what emc is looking for but i will see. i plan on getting started on this project in a week or so, so i'll let you know. Thanks again..

OK, 500 pulses/rev = 2000 quadrature counts/rev. 2000 * 2.8235 * 20 TPI = 112940 counts/inch.
Now, supposedly the SV500 multiplies steps by 4, so that would be 28235 step pulses per inch.
To go 60 IPM (1 IPS) you only need 28235 steps/second, so if all this is right, software step generation should work fine. Hmmm, 28235 <==> 2.8235, interesting number conversions!

Jon