cogo...@verizon.net wrote: > where I work we have a Shizuoka with an old Bandit control. The three servo > drives still appear to work. It has tachometer feedback to the servo drives, > and resolver feedback to the computer portion, which is in a coma. > > I would like to convert this to an EMC2 servo system with quadrature > encoders for feedback to EMC2, and for the proof of concept, I'd like to have > EMC2 do pulse-width-modulation of 3 parallel port pins, which I would convert > to +- 10V with a quad op amp and filter circuit (already have those parts). > Since I'd be spending someone else's money, I'd like to avoid buying a Pluto > servo board, or a MESA 5i20 until I can prove it can cut parts. I'm also > planning on doing an "open quadrature encoder" project, to save some bucks up > front, and hopefully come up with a cheap and fairly reliable replacement for > expensive encoders. > > I have a resolver to quadrature converter board (see http://pico-systems.com/resolver.html ) This will save you from having to retrofit encoders into the machine.
I think the software-generated PWM to +/- 10 V analog is going to be too low a frequency, or too coarse a percentage resolution to work smoothly. Why not use a real DAC for the purpose? I am using my own PPMC boards with analog velocity servo amps. I started with a Servo-to-Go board with analog output, and used it from 1999 to 2007. I've been using my PPMC since then on my Bridgeport. That is my production machine, so I need a good reason to change anything, or I would have moved to my own hardware a lot sooner. See the PPMC at http://pico-systems.com/PPMC.html > The Question: Where can I find info that would help me set up the HAL to > input from a quadrature encoder on two parallel port pins (the easy part), > and output a pulse width modulated stream on another pin of the parallel port > (the hard part), while using this to control the position of a servo motor? > > I suspect that if I had a fast PC, with a fast thread running about 25uSEC, > even if I were satisfied with low bit resolution in the PWM, the filter would > slow down the +-10V output to the point where the machine would probably be > stepper slow, or even slower; but if it could (slowly) cut parts out > reliably, and with precision, it would be easy to justify getting a servo > card for the machine. This machine would be backup for our Fadal 4020 > > The 5V power supply for the controller had died, and I bought some > transistors and repaired it, but it still won't cut parts. That's why the > caution about investing in it. > I don't understand why you'd want to do a halfway job, just to "prove it can cut parts." Lots of people are cutting parts with EMC, even in big shops that service the aerospace market. All your effort would just have to be re-done once you moved to a board with a real DAC on it. If you just want to prove the servo amps are still alive, you can do that with a 9 V battery and a potentiometer, or even just a single AA cell connected to the command input. (You need to jumper whatever relay enables the amp.) Jon ------------------------------------------------------------------------------ Open Source Business Conference (OSBC), March 24-25, 2009, San Francisco, CA -OSBC tackles the biggest issue in open source: Open Sourcing the Enterprise -Strategies to boost innovation and cut costs with open source participation -Receive a $600 discount off the registration fee with the source code: SFAD http://p.sf.net/sfu/XcvMzF8H _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
