How to connect Encoder Feedback (diff A/B/Z)
29 May 2011 15:19 #10152
by andypugh
Replied by andypugh on topic Re:How to connect Encoder Feedback (diff A/B/Z)
It's a little late now, but whilst step-direction servo systems can work well, the preferred way with EMC2 is to use "dumb" drives with the control loop (and tuning of that loop) done in software on the controller PC.
Such dumb drives need an interface to EMC2 other than the parallel port, both Pico systems and Mesa electronics make very popular interfaces which either plug into the parallel port (but use it as a communications interface, not individual bits). These are the Pico PPMC and the Mesa 7i43. Mesa also do a range of PCI cards with the same functionality. Both manufacturers also make servo drives, too. (Which tend to be relatively inexpensive, as they contain no cleverness), but as you already have drives you should stick with them.
The previous respondents have tried hard to not push a particular solution, as one of them is Pico, and one of them is Mesa.
The basic message is as Pete described, you will quickly run into speed issues counting quadrature with software, rather faster than you will run out of step rate, because you have more encoder edges than steps in every rev.
Switching to an external step-generator / encoder counter will give you a lot more performance, and a lot more IO lines to use for other things.
The Mesa 7i43 is around $90 for 48 IO lines and hardware stepgens/counters. However, you will tend to also need a daughter-card such as the for differential encoder termination, stepgen buffering and PWM-voltage conversion. I _think_ that the 7i47S ($80) would suit your drives and encoders but you would need to check with Mesa
www.mesanet.com/
The Pico Universal Stepper Controller is $250 and has PC interface, step generators and encoder interface all on one board:
pico-systems.com/univstep.html
Of course, if you are not running out of encoder sampling speed, then your current hardware is probably OK (and you might well find that the encoders work fine simply by connecting all -ve lines to p-port grnd.)
Such dumb drives need an interface to EMC2 other than the parallel port, both Pico systems and Mesa electronics make very popular interfaces which either plug into the parallel port (but use it as a communications interface, not individual bits). These are the Pico PPMC and the Mesa 7i43. Mesa also do a range of PCI cards with the same functionality. Both manufacturers also make servo drives, too. (Which tend to be relatively inexpensive, as they contain no cleverness), but as you already have drives you should stick with them.
The previous respondents have tried hard to not push a particular solution, as one of them is Pico, and one of them is Mesa.
The basic message is as Pete described, you will quickly run into speed issues counting quadrature with software, rather faster than you will run out of step rate, because you have more encoder edges than steps in every rev.
Switching to an external step-generator / encoder counter will give you a lot more performance, and a lot more IO lines to use for other things.
The Mesa 7i43 is around $90 for 48 IO lines and hardware stepgens/counters. However, you will tend to also need a daughter-card such as the for differential encoder termination, stepgen buffering and PWM-voltage conversion. I _think_ that the 7i47S ($80) would suit your drives and encoders but you would need to check with Mesa
www.mesanet.com/
The Pico Universal Stepper Controller is $250 and has PC interface, step generators and encoder interface all on one board:
pico-systems.com/univstep.html
Of course, if you are not running out of encoder sampling speed, then your current hardware is probably OK (and you might well find that the encoders work fine simply by connecting all -ve lines to p-port grnd.)
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