PLC driven cutter machine

[Mill_Control]

I've been experimenting with the parameters available on the drive. I can definitely program the run speed and ramp up/ramp down characteristics I'm looking for.
Now I'm beginning to wonder how much I can do without getting a PLC into the mix.
I don't need the PLC for the E-stop or limit switches.
I cannot see getting the motor stopped and reversed without it though.

Like Lancie said reversing is easy with a couple relays. Wanting ~200 cycles pushes the job to the point where a programmable relay will be more cost effective than relay logic.

The cutter depth detection is what you really need to decide on before purchasing hardware because I doubt you'll be doing that with digital I/O. Either spec a plc that'll work with the planned depth detection method now or be prepared to eat the cost of the programmable relay if/when you have to add that functionality.

 

[OkiePC]

What is the cut sequence? Feed, stop, cut across, return? Is there a cutter up/down or engage/disengage action, and do we engage on the cut stroke then feed again or cut on the return stroke, or do we retract and return during the take-away and feed strokes?

I think the sequence needs to be better defined. Also, the limit switches would be hardwired to the fwd and rev run signals unless the drives are running with a single run command and a bipolar speed reference. In that case, they would be wired in series to a relay interrupting the run signal (or directly with the run signal if noise is not a concern).Then some provision would need to be made to over ride them but try to keep them hardwired. It might be easy for the operator to e-stop the machine or lock it out and push the device away from the limit, or it might be better to have a momentary over ride option.

It is highly recommended to use auxiliary contacts from the over travel limits to supply PLC inputs so that your program may know why it cannot control the actuator, take the appropriate fault action, and report the status to any HMI or indicator available.

The point of limit switches being hardwired is to protect your hardware if your PLC goes nuts or you program it to go nuts. Believe me, even after many years, I have made them do nutty things by mistake...One of my first jobs as a programmer...I was observing a machine and noticed very loose encoder cable. The machine was running okay, but when it stopped in waiting for a manual splice and button press, I took it upon myself to tighten that cannon plug. The operator was attending the other drum, and as he came toward me and I got the plug nice and tight, the drum width screw proceeded to extend past its physical limit and destroy about $8000 in parts. I was on the wrong side to reach any e-stop, and just knew that the code would surely stop it....I was not yet familiar with the spaghetti running some of the sub-stations of that machine, but I did later make that impossible as I was not the only one to crash a drum, it happened once a month for no good reason...so they thought, believe me, there were many reasons...

 

[Wefinish]

This Eaton EZ program set up for a EZ-512-DC-RC intelligent relay with 8 digital Inputs and 4 digital relay outputs should be a good start on the logic for your cutting machine. The 4 timers in the program will need to be adjusted so that your VFD is given RUN FORWARD, then STOP (while the VFD de-accelerates to a stop), then a RUN REVERSE, then STOP again, then repeat until the STOP button is pressed, or the E-Stop is pressed. The E-Stop should be hard-wired so that the VFD is stopped directly (bypassing the EZ relay).

Okay, I've taken a pretty good look at this Eaton 500 EZ and it just strikes me as a different type of PLC from the one I already have. Maybe it's advantage is in the way it communicates with the VFD but I'm unsure. At $450 I would have to be positive it is the right choice.
Maybe I'm just not understanding the difference between a PLC and an intelligent relay.

I have sent their customer support an e-mail asking them to look at this application on this forum. Maybe they can convince me that the EZ 500 is the right solution.

 

[Wefinish]

What is the cut sequence? Feed, stop, cut across, return? Is there a cutter up/down or engage/disengage action, and do we engage on the cut stroke then feed again or cut on the return stroke, or do we retract and return during the take-away and feed strokes?

The cutter on this machine is nontypical. It's more of a "Scratch" cutter. The PLC is being used to control the drive mechanism which will push and pull the cutter. So as far as cutter complexity, there really is none. That part of the machine will be strictly mechanical.

After this machine is up and running I am sure I will want to make many changes. But I will do that by building a second machine having used to this one to learn on. Then maybe I will worry about things like automated stop points determined by cutter progress.

 

[Lancie1]

Maybe it's advantage is in the way it communicates with the VFD but I'm unsure.

There is no need to "communicate" with the VFD with a COM protocol. Simply send the VFD an On/Off timed "Run Forward" command (using a standard digital output of almost any PLC) that gets your cutter within 4 seconds of the end, then kill the Run Fwd and let it deaccelerate to a stop (hopefully near the far-end Prox switch and before any hard mechanical stop), then give it a timed "Run Reverse" command with a 2nd PLC output that brings it back to within 4 seconds of the Home position, then again de-accelerate. Repeat until your Counter = 200, or you press the Stop button.

The EZ program was meant to be an example of how you can do the program using your Unitronics Jazz PLC. Keep It Simple. Use what you got.

At $450 I would have to be positive it is the right choice.

That seems to be on the high side. Check around. Newark Electronics lists the EZ-512-DC-RC at $178, with free downloadable software. You may not need the version with the built-in screen, and there are probably better deals at other places. You will need a few other items regardless of which PLC you use, such as a generic power supply (buy where you get the best deal), maybe a cable if you plan to develop your program on a PC and download to the PLC.

http://www.newark.com/eaton-moeller/easy512-ac-rc/programmable-logic-controller/dp/41M3162

 

[Wefinish]

I am currently using several of the D700 series drives. Mine in particular take 1 phase 120 and output 3 phase 230. Nice units, never had a problem with them. Setting up the parameters Lancie1 is talking about is a breeze.

Are you using them in conjunction with a PLC? If so, what kind of hardware/software communication link is being used? Maybe you are using an intelligent relay like the type suggested by Lancie1? That would be very interesting.

 

[Wefinish]

The EZ program was meant to be an example of how you can do the program using your Unitronics Jazz PLC. Keep It Simple. Use what you got.

Is this possible without any sort of ladder logic? Are you saying that the PLC only needs a couple conductors from its output to a pair of the inputs on the VFD?

No matter how simple I keep it, this is definitely the most complicated electronics project I have ever been involved with.

 

[Lancie1]

Is this possible without any sort of ladder logic? Are you saying that the PLC only needs a couple conductors from its output to a pair of the inputs on the VFD?

The program that I posted previously (Post #30) is the Eaton EZ ladder logic, similar to what you will need, whether it be Untronics Jazz, or Eaton EZ, or Omron ZEN, or any of the hundreds of other small available PLCs.

Yes, indeed, you only need about 3 conductors (for PLC to VFD): 1 from the COM terminal on your VFD control terminals to the Output COM on the PLC, and then from the PLC, 2 output conductors back to the VFD for "Run Forward" and "Run Reverse".

EDIT: I looked up the Jazz Jz10-11-R10, and see that it does not have a common output terminal, but instead has two terminals for each relay output. So if you use Outputs O0 and O1 for your Run Fwd and Run Rev, then you would jumper the VFD Com terminal to Jazz terminals 1 and 3, and connect Jazz terminal 2 to the VFD Run Fwd, and Jazz terminal 4 to VFD Run Reverse.

(Most VFDs have a built-in control voltage on the COM terminal, so you need dry relay contacts on your PLC). You would set up your VFD so that the absence of a Run command would be equivalent to a STOP command. That's all, no need to get into Modbus or some other comm protocol for this. You could of course, if you want to make it harder, more complicated, and more time-consuming to set up!

I see that your Unitronics Jazz is made for 24 VDC only, so you need to make sure that all your inputs are 24 VDC-compatible, and you probably will need the extra Jazz Add-On module to give you the capability to connect to a RS232 port on a computer. It appears that the Jazz only has 9-pin serial port comm capability, so if you have to connect to a modern computer with only USB ports, you will need a compatible USB-to-RS232 serial port adapter.

Is there a free download of the Jazz software? If so, I would like to get it and try it out. Does the Jazz have a built-in Simulator Mode as in the EZ and the ZEN, so that you can test your program to see if it runs (before actually hard-wring the Inputs and Outputs)?

 

[Lancie1]

Here is my previous EZ-512 ladder program translated into the Unitronic Jazz U90 ladder program. It is similar, except for a few differences.

The U90 ladder does not have a Counter, so you have to build your own from 3 other instructions. Also, the U90 software does not have Retentive-type timers, so if your power blinks, or if you need to stop a cut in the middle, you will not be able to do that, because all your timers will reset to 0. In other words, with this U90 ladder program you cannot stop and restart the cutter at the same place (without changes to the logic).

The U90 print-out is not so good, because it wastes a lot of paper space (8 pages to print 10 rungs). This program adds a bunch of titles and other page formatting that takes a lot of paper to print. It puts a rung comment on one page and the following rung on another page. The rungs are numbered differently from the EZ program, but follow the same logic sequence as closely as possible.

Maybe you can compare the 2 programs and get an idea of what you will need for your Cutting Machine.

 

[dploof23]

Are you using them in conjunction with a PLC? If so, what kind of hardware/software communication link is being used? Maybe you are using an intelligent relay like the type suggested by Lancie1? That would be very interesting.

Yes I am using a PLC. The communication consists of 2 digital outputs to turn on and off the forward and reverse run relays, and an analog output module to send a 4-20ma signal for speed control.

 

[Lancie1]

... and an analog output module to send a 4-20ma signal for speed control.

Wefinish could set up an analog output so that the Jazz HMI panel could send speed setpoints to the Mitsubishi D700 VFD, but I think his JZ10 Jazz model does not have analog outputs. From the U90 software Help menus, it appears that you have to upgrade to the JZ20-T18 to get analog outputs.

I think I would use the front-panel controls of the VFD to set the speed. It should not change very often. Also, 2 or 3 Preset speeds could be set in the VFD, and controlled by digital On/Off outputs from the Jazz JZ10.

Or use a Modbus comm link to the VFD to set the speed.