Inputs/Outputs

I've been starting to design the electronic system which will control my CNC mill and already I have hit a potential problem. My problem it seems is the number of inputs and outputs available through a parrallel port. I'm designing a four axis machine so that will be 1 limit switch for each end of each axis = 8 limit switches !.

8 inputs just for limits seems a little excessive, even for a 3 axis, by my reaconing 6 would be required.

Is there an error in my thinking here or is this normal and accepted ?

here a link to a Bobcad thread kind of on the same line as your question http://216.117.147.20/bobcadsupport/...read.php?t=799

Thanks for the quick reply but are you sure that is the right link ? " RS-232 Communications and Pinout" - I've had a read through and I cant find anything relevent.

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Originally Posted by UKRobotics

I've been starting to design the electronic system which will control my CNC mill and already I have hit a potential problem. My problem it seems is the number of inputs and outputs available through a parrallel port. I'm designing a four axis machine so that will be 1 limit switch for each end of each axis = 8 limit switches !.

8 inputs just for limits seems a little excessive, even for a 3 axis, by my reaconing 6 would be required.

Is there an error in my thinking here or is this normal and accepted ?

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You could use one home switch per axis (and use it as limit also, in TurboCNC you can do that, probably in other programs) and on the other side wire all the limit switches in series.

If your machine limits out it will stop no matter which axis overtravelled. Then you can look at the position display to determine which axis it was.

This would only take 5 inputs for a 4-axis. Another option is of course to add another parallel port.

Nikolas

dom: actually you probably want three inputs per axis, two limits and a home. Now if your running out of io you could always add a second parallel port card, and use that. What software are you running? Things like rs232 input depend on your package, and how much work you want to put into it.

PS: it really is a small world, just checked your webpage out, didnt expect to find anyone else from reading uni here.

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Originally Posted by daedalus

PS: it really is a small world, just checked your webpage out, didnt expect to find anyone else from reading uni here.

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Indeed it is. What are you studying & what year are you in ? - I'm guessing eng/cyb cause of the CNC connection but you could prove me wrong.

Do you have msn messenger or anything like that ?

CNCGR - I'm running Mach 3 through a parrallel port. My plan was already to have x-, y- and z+ as combined home and limits. As for having + and - limits for each axis also on the same pin, it is a possibility but I would have liked to have done it 'properly'.

Do you know if mach has an option to automatically reverse off a limit once hit or does it always have to be done manually. If the former is true then it would make sense to have separate inputs for + and - otherwise i might was well stick +, - and home all on one pin.

I have already considered another parrallel port card but even with that I worry about running out of inputs and outputs. In addition to the limit switches I also need inputs and outputs for charge pump, VDF, spindle reverse, estop, x,y,z,a axis motor encoders, x,y,x,a step/dir, an MPG, switches to jog each axis, power drawbar, ATC, suds pump, auto lube system, lights, vacuum table and no doubt more things I havent thought of.

Keep in mind that you can AND some of the limits together - that's what they do on my NC lathe.

My Bridgeport mill has softcoded limits in the program and only home switches on the X, Y and Z axis.

Or you could always add another parallel port.... (creative thought, no???)

Most software I have run across either relies on the limits being wired in an "AND" or "OR" configuration.

Here is one example of switch wiring:
http://www.pminmo.com/wiki/index.php...limit_switches

OK, So lets suppose that I need 4 pins for limt switches and one pin for an e-stop.

How many pins will I need for each servo drive/encoder ?

Is there some sort of wiring standard which suggests which pins should be used for which axis and which purpose or does it not matter at all .

I would be interested to see what pins/wiring setups other people on here have used successfully for a 3 or 4 axis machine.

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Originally Posted by UKRobotics

Thanks for the quick reply but are you sure that is the right link ? " RS-232 Communications and Pinout" - I've had a read through and I cant find anything relevent.

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I read this thread last night after work about 3am and your right it has nothing to do with you issue at first I thought you need info from controller to pc not pc to axis

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Originally Posted by UKRobotics

Do you know if mach has an option to automatically reverse off a limit once hit or does it always have to be done manually. If the former is true then it would make sense to have separate inputs for + and - otherwise i might was well stick +, - and home all on one pin.

I have already considered another parrallel port card but even with that I worry about running out of inputs and outputs. In addition to the limit switches I also need inputs and outputs for charge pump, VDF, spindle reverse, estop, x,y,z,a axis motor encoders, x,y,x,a step/dir, an MPG, switches to jog each axis, power drawbar, ATC, suds pump, auto lube system, lights, vacuum table and no doubt more things I havent thought of.

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Haven't used Mach, sorry. TurboCNC just stops.

Two // ports will give you 24 outputs and 10 input, I think they should cover it, and you can still add a third.

You can use a keyboard controller to make a pendant instead of using up I/Os for jogging. Also, I don't think you'll ever need all these at the same time, you could reconfigure I/Os as needed.

As for wiring the motors, it's best that each motor has it's step and dir on the same port, preferably the data port (pin 2 to 9).

Nikolas

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Originally Posted by UKRobotics

How many pins will I need for each servo drive/encoder ?

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The servo encoder feedback is done inside the servo, so you don't need an input to the PC. You could add an additional encoder (e.g. linear scale) as you could in a stepper system (Mach has encoder input, TCNC not) but it's not neccessary.

The I/O limit is a hassle, no doubt. You will want to choose one of the AND/OR schemes to reduce the inputs needed for homes and limits. A keyboard emulator board will save some inputs by converting them to keystroke equivalents. You may lose some feel, so don't use that approach for anything that is too time critical. I certainly wouldn't connect the limits that way! Save some for spindle and coolant control too.

Strategies to gain more inputs:

- Run 2 breakout boards on 2 parallel ports. Can be made to work,but is finicky.

- Check into a ModIO board. Hohman designs has a nice one. This let's you run a bunch of I/O through your USB. Think of it as a substitute for the 2nd parallel port but not for the first, you still want a breakout card.

- If you software supports it, look at a GRex. Tons of I/O, both for switches (on/off) and analog (speed controls and the like). This is the path I'm working on, basically because it just seemed simpler and more elegant to go to one box to get all the I/O.

Best,

BW

Or....look at our Mini-IO-Combo. All in one box with 5 inputs on Port one, (plus 12 buffered outputs (two drive high current relays on a remote card [included]) and the port 2 input has a small remote breakout card that gives you 13 more inputs and 4 more outputs. Our new 12 function MPG/Pendant plugs into that port (but you lose the use of the 13 inputs for other functions). Everything fits in a compact instrument enclosure including the power supplys and the connections are all made via standard DB 25 and db9 computer cables to the rear of the case. Relays can be 25ft away and the card has 5 isolated inputs for homes and series connected limits.

Comes with profiles for MACH3 with all the pins setup. Manual is on the website.

Http://www.CandCNC.com/Mini-IOProductsChart.htm

All of the inputs (except for the MPG inputs) are opto isolated and a true floating supply is there to drive the load side of the inputs (split grounds to eliminate conducted noise).

Does the G100 have isolation on the inputs? In noisy environments isolated inputs can make a big difference in stray signals tripping limits or other trigger inputs.

Tom Caudle
CandCNC