Can an Acorn replace an industrial PLC/VMC control?

[hackish]

I bought an older VMC and it has a Meldas 520M control. I am wondering if the Acorn is going to be capable of replacing this so it is not a downgrade. My primary reason to change is the old control has limited data / buffering capabilities and high speed movement get very jerky as the drip feeding can't transfer the data in fast enough for complex 3 and 4 axis moves.

Can the acorn be programmed like a PLC? Specifically, fault codes are important as this is a big heavy machine and all inputs/outputs need to be validated for safety. For example, if the high speed spindle gear is commanded but doesn't engage, it needs to move the spindle and retry at least a few times, then fail if not successful because powering a 10hp motor if the gearbox didn't complete its movement is going to break expensive parts! Or another one, if for some reason the ATC does not extract the tool and reach the full down position, it should not be commanded to retract.

Can it really do 4 axis? Some people online say yes, but the documentation says it will only do 3.

Does the interpreter do true lookahead for accel/decel? I'm not an HSM wizard, but even the old meldas control has a whole section on how it looks at incoming instructions to pre-calculate the machine kinetics so it hits the proper points on the paths without over-running them. Although this is just a hobby type deal, I bought a VMC so I could produce accurate parts and I wouldn't be happy if the accuracy suffers.

Is there a way to store the servo initialization commands in the acorn so they are sent to each of the controls on startup? I think the controls use some sort of modbus or serial interface to get all of their settings, and occasionally they might need to signal a fault due to over-torque or some other reason. The existing control stops if there is any error, so I would want to ensure this level of safety is retained.

I understand there is going to be a bit of a learning curve, and the price point of the acorn is very low compared to what I'm asking, but I don't want to embark on this path and put my toy out of commission if the capabilities are not going to be sufficient from the start.

[cnckeith]

I bought an older VMC and it has a Meldas 520M control. I am wondering if the Acorn is going to be capable of replacing this so it is not a downgrade. My primary reason to change is the old control has limited data / buffering capabilities and high speed movement get very jerky as the drip feeding can't transfer the data in fast enough for complex 3 and 4 axis moves.

Can the acorn be programmed like a PLC? < yes> Specifically, fault codes are important as this is a big heavy machine and all inputs/outputs need to be validated for safety. For example, if the high speed spindle gear is commanded but doesn't engage, it needs to move the spindle and retry at least a few times, then fail if not successful because powering a 10hp motor if the gearbox didn't complete its movement is going to break expensive parts! Or another one, if for some reason the ATC does not extract the tool and reach the full down position, it should not be commanded to retract.

Can it really do 4 axis? Some people online say yes, but the documentation says it will only do 3.
<yes on 4 axis, (where did you see documentation saying only 3?)>

Does the interpreter do true lookahead for accel/decel? < yes 1000 line lookahead and also has g code smoothing feature> I'm not an HSM wizard, but even the old meldas control has a whole section on how it looks at incoming instructions to pre-calculate the machine kinetics so it hits the proper points on the paths without over-running them. Although this is just a hobby type deal, I bought a VMC so I could produce accurate parts and I wouldn't be happy if the accuracy suffers.

Is there a way to store the servo initialization commands in the acorn so they are sent to each of the controls on startup? I think the controls use some sort of modbus or serial interface to get all of their settings, and occasionally they might need to signal a fault due to over-torque or some other reason. The existing control stops if there is any error, so I would want to ensure this level of safety is retained. < not quite sure what you mean with this one, what specific feature do you need?, fault signals from a drive are sent into Acorns inputs, Acorn does not use modbus or serial interface>

I understand there is going to be a bit of a learning curve, and the price point of the acorn is very low compared to what I'm asking, but I don't want to embark on this path and put my toy out of commission if the capabilities are not going to be sufficient from the start. < you might want to look at the Oak CNC controller combined with a new set of Axis motors and drives , this is better suited for a large VMC than Acorn>

[hackish]

Hi,

Can it really do 4 axis? Some people online say yes, but the documentation says it will only do 3.
<yes on 4 axis, (where did you see documentation saying only 3?)>
https://www.centroidcnc.com/centroid_di ... oller.html
It says 3 axis simultaneous where I want 4 axis simultaneous.

Is there a way to store the servo initialization commands in the acorn so they are sent to each of the controls on startup? I think the controls use some sort of modbus or serial interface to get all of their settings, and occasionally they might need to signal a fault due to over-torque or some other reason. The existing control stops if there is any error, so I would want to ensure this level of safety is retained. < not quite sure what you mean with this one, what specific feature do you need?, fault signals from a drive are sent into Acorns inputs, Acorn does not use modbus or serial interface>
Ok, I didn't know it flagged faults just as binary input signals. The real issue is that the drives seem to require some initialization commands on startup as the PLC does a bunch of checks for oil, air pressure and so on before the axes get enabled.

I understand there is going to be a bit of a learning curve, and the price point of the acorn is very low compared to what I'm asking, but I don't want to embark on this path and put my toy out of commission if the capabilities are not going to be sufficient from the start. < you might want to look at the Oak CNC controller combined with a new set of Axis motors and drives , this is better suited for a large VMC than Acorn>

I looked at the oak controller, but in my case, the machine already has the proper servos, drives and power supplies. Replacing them all would cost $10k+ which is more than the machine is worth. The acorn definitely packs an amazing amount of punch for the price, but I was a little concerned that I'd be asking too much out of it. Since the entire machine is already wired with the limit switches, resolvers, relays, pneumatics and all that, it looked like the Acorn might be a fairly easy solution to wire in even if only to try before making any permanent changes to the machine. While the industrial controls are very solid and reliable, they don't exactly make technical details that readily available, and many times you have to pay big dollars just to have options like rigid tapping enabled.

Maybe there is a PLC that could handle all of these functions while just providing a simple interface to the acorn so it can handle the motion control work and the PLC can handle the more complex logic like initializing the servos and the spindle drive.

[suntravel]

Only free version ist limited to 3 axis simultaneous...

Uwe

[cnckeith]

what kind of servo drives are they?

Acorn is a step and direction based cnc controller. the drives would need to accept step and direction signals to work with Acorn.

[cncsnw]

I looked at the oak controller, but in my case, the machine already has the proper servos, drives and power supplies. Replacing them all would cost $10k+ which is more than the machine is worth. The acorn definitely packs an amazing amount of punch for the price, but I was a little concerned that I'd be asking too much out of it. Since the entire machine is already wired with the limit switches, resolvers, relays, pneumatics and all that, it looked like the Acorn might be a fairly easy solution to wire in even if only to try before making any permanent changes to the machine.

I think you do not have a clear picture of the difference between the Oak and the Acorn.

Both are just controller boards, which interface to whatever drives and control components you choose to supply.

The main difference is that the Oak is a closed-loop controller (it reads encoder feedback from each axis) and can run analog drives (e.g. velocity-mode or torque-mode control) as well as position-mode drives. The Acorn is an open-loop controller which cannot read or use encoder feedback from the axes, and which can only run step-and-direction position-mode control.

The rest of the control hardware you surround them with is up to you.

If your VMC is old enough to have used a Meldas 520 control, it is unlikely that its drives will run in a step-and-direction position mode. That means that you would need to install new servo drives and motors in order to use Acorn. There is a modest chance that they will run in analog velocity mode, but to use them with Oak you would need to find a way to get quadrature differential encoder positions out. Oak will not read resolvers.

[hackish]

what kind of servo drives are they?

Acorn is a step and direction based cnc controller. the drives would need to accept step and direction signals to work with Acorn.

The servos are Meldas MDS-B series. I'll have to look at the motors part numbers, but I think they are 2kw for X/Y and 4kw for Z. Each one has the AC servo and encoder going onto to their respective servo amp.

I spent several hours trying to find full documentation on the servo amps, but so far I haven't found anything. I was expecting that they could take direction and step inputs. Since the motion control computer and PLC are each separate, I'm not sure how they'd have accurate simultaneous control of all the axis if they were expecting serial commands for every movement.

[hackish]

The main difference is that the Oak is a closed-loop controller (it reads encoder feedback from each axis) and can run analog drives (e.g. velocity-mode or torque-mode control) as well as position-mode drives. The Acorn is an open-loop controller which cannot read or use encoder feedback from the axes, and which can only run step-and-direction position-mode control.

The rest of the control hardware you surround them with is up to you.

If your VMC is old enough to have used a Meldas 520 control, it is unlikely that its drives will run in a step-and-direction position mode. That means that you would need to install new servo drives and motors in order to use Acorn. There is a modest chance that they will run in analog velocity mode, but to use them with Oak you would need to find a way to get quadrature differential encoder positions out. Oak will not read resolvers.

The trouble I've had with understanding this is that I've never seen a servo controller that needed external feedback. You tell it where to go, and it does it courtesy of its own encoder installed on the servo motor. If it exceeds the torque - let's say you crash the machine, it asserts an error signal, and you expect the PLC to stop the party. The work I did on minas controls were done in a similar fashion, and the acorn board just hooked up and off it went. Since they were a bit newer, all of the settings and initialization were flashed into the servo control beforehand, so they would boot and initialize and you only had to wait for the drive ready signal before asserting the motion enable pin.

There meldas servo controls don't seem to have documentation to say how they actually work, but I suspect each time they start, you have to upload the configuration to them since it's stored in the actual Meldas CPU unit (thanks to an old school battery RAM backup). I know they have modbus at least, but it isn't clear how they are actually controlled. Since I see it is daisy chained, it isn't clear how the axes stay in sync with the older baudrate communications they used in the 1990's.

Maybe I'm missing something with my understanding of this system.

[cncsnw]

My experience has been different.

Nearly every industrial CNC control I have encountered from the 1980's, 1990's and 2000's has closed the position loop at the CNC controller. The servo amplifiers nearly always run in an analog velocity mode.

The CNC controller receives position feedback; runs its PID calculation; and decides how much velocity to request from each axis drive.