Press Brake CNC Control & G-Code

Yeah, both axis are actually pretty slow...

One motor is 1315rpm, it has a right angle 1:30 gearbox, so about 44rpm output. The encoder is 100pulses/rev, so about 4400pulses per minute, circa 74pulses per second. I suppose to be accurate, the parallel port will be reading twice as many pulses (A and , but it's pretty low frequency.

The other axis has the encoder on an output ball screw shaft. Not sure what the motor rpm or the gearbox reduction is, but there's also a chain drive (that syncs both shafts), and I think from memory that it's geared down there too. The rotation is not fast, even at full speed!

J

I'm needing to fit the IO now and get started with this, so trying to figure out what the best MESA boards will be.

So far I'm thinking
- 5i25 superport
- 7i77 6 axis servo card

At the moment I have a single VFD, but will likely add either a second VFD so both motors have dedicated VFD, -or- will fit a pair of direct drive servos (maybe clearpath etc) to replace one of the AC motors, leaving the original VFD to be used for dedicated control of the remaining AC motor. Both of these motors currently have encoders, so:

Servo 1: VFD 0-10V analogue
Servo 2: -none- (shared servo control via EMC)
Encoder 1: Y axis (beam bottom target)
Encoder 2: X axis (backgauge position)
Encoder 3: Y0 axis (beam actual position)

Now the 7i77 has only a single Enable per servo, whilst the VFD drive requires either a FWD or REV enable signal. I can maybe use Servo 1 enable for FWD and hijack the Servo 2 enable for REV - however as they're shared I need an enable for the corresponding motor contactor. Now the FWD/REV need to be isolated which the 7i77 does with the enables and the field IO can handle the motor contactors (I'll probably use solid state interface relays for both).

Long term I want to add probably 6 axis to the backguage, most likely using clear path servos or generic steppers. My thought is that I can use either a 7i76 and/or another 7i77 with the original 7i77 to give me the capacity and the right IO. I can even mix servo and steppers for the backgauges, using the 7i77 for the close loop axis and the 7i76 for the step/dir axis.

I don't actually need masses of IO, as other than the limit switches for the axis, most of the machines IO will be going through a new PLC. Any IO I need but isn't on the CNC IO I can get via ModBus. I want the MESA and LinuxCNC purely for the CNC aspect and will leave the PLC to handle core machine functionality, safety, interlocks, user actuation (pedal/hand controls) etc. The CNC side will handle the stroke distance, "soft" home positions, speed of machine (via digital input with PLC or over modbus, and PLC will enforce laser guard security at positioning speeds etc), encoder inputs for axis and positionig of axis.

Is this logic sound?? Am I picking the best combination of MESA boards for price and IO needed? I can't see a board that'll give me what I need without having to use multiple boards or without committing now to the IO for the future axis...

Suggestions welcome!

I should even pose another question:

If possible, how can I account for the shared VFD for the servos? Basically when Y is being positioned or moved X can't be and vice versa. I'm not having fixed homing as these axis are relative to the tooling, so I'll either measure their offset or touch the tooling etc, so there won't be a homing routine. Should also clarify, the encoders are not shared, so the position will always be tracked correctly, but it's actuation which is the issue. It's physically interlocked, with a bias to the first motor enabled.

But, I do need to enforce the logic so there's no craziness or fighting over axis in EMC!

Also, will EMC be okay with the same FWD/REV outputs being the same pins on both X and Y axis (i.e. when positioning ends, will EMC stop outputting on those pins)? The only difference being that the enables for each will be field IO.

I would advise not to use a separate PLC as everything can be handled by Linuxcnc as far as i know, it would require some programing but i doubt it would be hard.
7i77 has a single enable for 5 axis and a separate one for the spindle so you could use that, and forward and reverse can be sent to any output pin. Enable signals can also be sent to any output pin so they can be enabled separately for different purposes. The only diference is that field IO are not isolated from Vfield and ground, while enable outputs are isolated.
The " do not move X axis while Y is moving" can be aranged in hal with an XOR gate, same can be done for VFD if needed.
I would need to see the machine and analyse the inner workings to understand more and subsequently give more advice.
Regards,
Tom

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

If i understood correctly, you have 2 VFD to control, no servo drives, right?
VFD need 0-10V and have their own 10V reference voltage, mesa has +-10V outputs for analog servos with its own power supply so that can be tricky. I am sure Mesa can be configured to output just positive 10V, but still there is the VFD with its own power. So wiring just the GND and analog out from Mesa to the VFD and leaving +10V on the VFD unconnected should work, and avoid potencial diferences in volatge.
You should check this with PCW as this is all from memory, not from experience.
Theoreticaly it is all good, but theory and practice have a funny way of not beeing the same some times, in this case due to many diferent potencial diferences between electronic parts.