Press Brake CNC Control & G-Code

Hi Tom

The PLC is needed for the intrinsic safety - there's some legal requirements for safety including response times for stopping the machine, which will be enforced by the PLC.

At present the electrics are split into a contactor controlled machine logic/safety system (at 24vac) and NC operated axis (at 24vdc), so it's replacing these like for like.

My struggle is trying to pick the right combination of MESA boards for the axis control, but I'm happy that you've not advised against the choice of a 7i77!! The field IO will be isolated by virtue of use of interface relays and use of dry contacts...

Jon

Two 'virtual' VFD, but it's physically one VFD and a pair of contactors that switch which motor is being controlled by the VFD. The old wiring then uses two sets of FWD/REV inputs, so that the VFD can be controlled by the NC when it switches axis (no special config with the NC required). Not sure the original reasoning (other than cost), but it's been wired so that as long as only one is being controlled at a time, the contactors and relays ensure the right NC output controls the VFD and the right motor is being fed from the VFD.

They're closed loop AC motors (both have their own encoders), but not true servos. My thought was that a servo board has a 0-10V output per motor, and has an encoder input per motor. Long term I'll be using a few servos, probably Clear Path, but even then, not sure whether to use them in stepper config (SD series) or via software (SC series). That's probably a call out question - can LinuxCNC work with the SC series ClearPath servos? Or is the stepper config better?

You're correct about the reference voltage versus the servo not having reference voltages. D'oh. Reading too many manuals and must have overlayed what I read for a different MESA board, and thought the servo outputs could take a ref voltage.

I'll be keeping the VFD for the Y axis, but the X axis I likely will swap out to direct drives (again, servo or stepper TBC). This means I could get away with using the spindle output from a 7i76 - hook the VFD to the spindle control (which also has ENABLE and DIR floating signals), and then have one encoder going through the spindle encoder... So, if I use the 7i76, I get 4x stepper axis that I can use with the ClearPath SD or any generic stepper I use. But I'm short of 2x encoder channels still.

So I need some other way of getting another 4 stepper channels and 2x encoder channels on top...

If I use steppers, I may want to fit encoders on a few axis, purely for relative homing, but the majority would just be open loop. So is there a serial daughterboard that can handle the encoders, allowing me to get another 7i76 in the future when I need those extra axis, without hogging the second interface on the 5i25 now? The 7i85 is also an option, but limits how I can drive motors in the future (unless I can get serially controlled motors).

So, revision:
- 5i25
- 7i76 (4 axis step/dir + spindle/encoder)
- 7i85 (4 channel encoder)

Any suggestions as to alternative combinations of IO card and daughtercards?

Do I maybe go for a 5i24, a 7i34 (8-channel encoder) plus 2x 7i76 (using HD-DB adapters)??

Meh... Advice please! I need to order the boards on today or Monday so I get them midweek to get the install underway...

The Clearpath SD is the one to use with LinuxCNC. The others are for say conveyor belt applications not for CNC motion control. If you were going to use them, I thought their claim to fame was they responded to standard step and direction signals and the encoder is wired internally eg. they only need Step and Direction from LCNC. So in that case the 7i76e might be all you need.

Thanks Tom & Rod...

Thinking that the 7i76E is the way to go. I was hung up on the PCI card approach, but I like that the 7i76E also offers two daughterboard ports, so I can get the encoders I need now with a 7i85, and then when I add other axis I can choose a 7i77 or 7i76 - but it'll probably be one of the latter as I'll use the SD clearpaths or some nice steppers I have.

I'll keep the Ethernet connectivity on separate VLANs and hardware, but is there anything to be aware of or caveats with Ethernet boards? I've not payed much attention to be docs regarding them, but gather need a realtime Ethernet driver of some kind for the host?

What is the preferred route now for new installs? I'm also needing to buy a 7i76 and 5i25 for a CNC router - should I be considering a 7i76E?? I've just upgraded a CNC mill with a 5i25/7i76 and very happy - the computer however is circa 7yrs old (an HP xw420) and seems to have some latency issues that I need to sort. Will that age of computer handle the 7i76E, or should I be looking for something newer (I've got another xw420 ear marked for the router or press brake).

Jon

Jon,

I found I needed 64 bit hardware for my 7i76e and it seems you have that. Other than that,
Just follow CNCnoobs Mint Installation tutorial as you have to install the PREEMPTIVE kernel so you can't use the ISO.

There is also a very good pinout of the 7i76e on the forum here.

Thanks Rod...

Need to have a think overnight, but tempted now to use a 7i76E for the CNC router too...

The added advantage, is that I have a small engraver that needs upgrading - using a 7i76E for both means I can use one PC for now for the router and engraver, and just switch between configs as needed.

How would an Atom D525 with gigE handle it??