M P G control

[colin1544]

Hello I am looking for some help and guidance I have a DOS version Ajax mill setup and would like to put a M P G hand control on my machine, and I am wondering if anyone has used a different M P G control from a different supply other than the one supplied by Ajax as they are quite resonable on the net and Ebay,if so and it works OK could you send me details of the wiring and setup needed for this. Cheers Colin

[Al_The_Man]

The vast majority of MPG's out there are 100p/turn.
many being 5v differential, there are a couple of differences in that some are single A/B output and more rarer are 12vdc supply but 5v A/B signal, these are sometimes used by the older Mazak/Mitsubishi.
Al.

[cncsnw]

Do you have the T-shaped pendant with a plastic housing, a rectangular pendant with a metal housing; or no pendant at all?

With the T-shaped pendant, you can only use a Centroid MPG, because the pendant expects to communicate with an MPG that contains its own Centroid processor.

With the newer rectangular pendant, you need a sufficiently recent version that it has a header on the jog panel board inside for the newer "dumb" MPG's: those which just output selector switch contacts and handwheel pulses without trying to process them themselves.

If you have a rectangular pendant and are not sure what MPG it supports, remove the face plate (4 screws) and post a good photo of the board you find on the back side.

If you have no jog pendant at all, you will need to buy one of those first. The MPG handwheel pendant connects to the jog panel board; not directly to the CPU7.

[JWWalthall]

Just to follow up on this . Can you use a non Ajax control pendent with the control? I have the newer control pendent ,(not the t handle). In my wiring schematic it shows the pin outs for the MPG is this all I need or does the Ajax MPG have a pic imbedded in it to count pulses. I have all the parts that I need but am confused if this will work.

J Walthall

[cncsnw]

If you have the newest style pendant (shipped within the last four or five years), and your schematic shows pins for each axis select switch position, each increment select position, and A and B pulse channels, then yes: you can build your own MPG pendant from parts, or likely adapt a similar MPG built for another control system.

[ewest]

You can absolutely use a different MPG with Ajax, just as long as the encoder puts out DIFFERENTIAL output - that is there's a +5, Gnd, A-, A+, B- and B+ lead. Differential means that instead of +5 and 0V between A or B and GND, the A+/A-, (and B+/B- leads too) swap polarity in respect to one another to indicate 0 and 1, as opposed to a single line going high or low with respect to GND. This scheme is implemented to reduce electrical noise, and you want to use this wherever possible. Electrical noise = missed steps or dropped encoder pulses = trash parts = wasted money. You can use a chip called a "DS26LS31CM" made by national semiconductor to change TTL encoders to differential output. Needs no external components. They're around a buck. Mount it as close as possible - preferably ON the encoder. Look here. I used a "CNC4PC.COM" MPG unit with my Ajax MPU11. Works fine. I think the chips come in non surface mount, but I like not drilling holes so that's what I used. Make sure your connections are solid. The CNC4PC MPG had single ended TTL outputs, so I had to make the board. It lives in the MPG itself, soldered in place. I used two spare lines in the cable to run the A- and B- wires.

[cnckeith]

ewest, thanks for the info on the CNC4PC mpg mod.

some guys on the ajaxbb are talking about those as well.
I posted your info there, i thought they would find it helpful as well.

http://ajaxcnc.com/ajaxbb/viewtopic....347304288#p105

[rppman]

Ewest, I also have the mpg2 and ajax mpu 11. I was having a hard time finding the chip you are talking about so I am going to just order the line drive output mpg wheel and switch them out. My question to you is, are you using the e-stop switch on the mpg2 with the ajax syatem? I was looking at the limits of the switch and they seem small. Like .5 amp max. Wouldn't the ajax rounting through the coil and other boards draw more than .5 amps? The stop switch is a 4 pole and I think it would work but I am unsure about the amp limits? Thanks for any input. Scott

[Al_The_Man]

Originally Posted by rppman I was having a hard time finding the chip you are talking about so I am going to just order the line drive output mpg wheel and switch them out.

You can get 26LS31 is all over the place, One of the nice suppliers is DigiKey.
Make sure you get the DIP version, unless you are in to SMT, (surface mount).
Al.

[cncsnw]

Wouldn't the ajax rounting through the coil and other boards draw more than .5 amps?

The E-stop contactor coil is the only load. Routing through the servo drive's fault relay, through any other E-stop pushbuttons, and optionally through a PLC output relay does not increase the current draw.

You would need to locate specs for your E-stop contactor to check the load. The "inrush" (current as the contactor closes) is likely to be over 0.5A, especially if you are using a 24V coil. The "sealed" current (continuous draw to keep the contactor closed) will be a lot lower (though it might still be over 0.5A for a large contactor with a 24V coil).

If you really want to use the MPG E-stop button, but it can't carry the load of your E-stop contactor, you could always introduce an ice-cube relay (E-stop button switches the relay; relay NO contacts switch the contactor coil circuit).

[rppman]

Ok thanks for the replies...

[rppman]

Does anyone know where to get a "cube relay" that would meet my requirements? Contactor coil voltage is 24vac. And the e-stop max. Amperage is .5 amp. Thanks scott