Best practice for mill VFD control wiring


I am back from my RV trip. (which went very well)
This post is in regards to that Arboga EM825 mill that I am working
on. It is three phase and works well. This is a 1.1 HP, 3 phase
mill/drill with geared drive. It does not have and has never have a
reverse switch of any kind.
My plan is to convert it to single phase by means of adding a VFD, do
a nice job at that, and sell it to single phase people.
I use a Toshiba VF-A3 drive, the same one as what Pete C and Ivan
Vegvary have.
So far, I got to the point of having the drive mounted and I use panel
controls to run the mill. So now it does run great from single
phase. This is not the most convenient and not the safest option due
to where the drive is mounted (low height).
I would like feedback about the following plan:
* Mount drive out of the way to the right of the base.
*
Use the original START/STOP buttons on the right side for START and
STOP control of VFD.
* Add a panel on the left side, composed of
o SPDT On-On switch to switch FORWARD and REVERSE
o Potentiometer to adjust mill speed from 0 to 80 Hz.
(the higher limit is the VFD setting).
*
Program acceleration time to be 1 second and deceleration time to be
0.4 seconds.
Is that plan basically sufficient and does it constitute "best
practices"?
My own reasoning is that START/STOP is basically a safety function and
it would be good to retain it in its original design for legal
reasons.
i
Reply to
Ignoramus25401
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If you're really concerned about legal reasons don't alter the controls. Stop buttons normally hard interrupt a contactor, a VFD control is a soft control. We had one piece of equipment, a portable floor grinder, which had a VFD and a stop button, the stop button actually killed all of the power, including the VFD. The design you are describing is an improvement over using the controls on the VFD and sounds fine for your own home use.
Reply to
ATP*
OK, then, I can alter my plan:
* Original START/STOP buttons would control incoming power to VFD * The operator control panel would include: o speed control pot o On-Off-On switch to control FORWARD/STOP/REVERSE
This way, the only use for the original buttons would be some sort of emergency, but the STOP button ensures safe and complete shutdown regardless of any wiring or programming mistakes.
At the same, normally, the on/off/on switch would be used to run and stop the mill.
Any thoughts? Bruce Bergman?
i
Reply to
Ignoramus25401
I agree that a big red 'OFF' button should kill everything, VFD included.
I tend to like all the controls in one spot with the panic controls on the top with the regular controls lower on the same panel. No sense having an operator have to think about if a situation is a big deal and have to move to a different panel. Milliseconds matter at this point.
Ignoramus25401 wrote:
Reply to
RoyJ
My plans solidified a little bit. I will use the original START/STOP to supply or kill power coming _INTO_ the VFD.
I will install an Allen Bradley 800T style lever switch with XA switches, that has three positions, to provide FORWARD/OFF/REVERSE functionality. The lever switch has an extra convenience of being equivalent, on tactile level, to the direction of intended rotation (turn to the right for clockwise, turn to left for counterclockwise).
In addition I will mount some speed control pot near the lever.
i
Reply to
Ignoramus25401
Could you take advantage of dynamic braking by turning off the power like that?
--Winston
Reply to
Winston
Here's what we have at work. A fused disconnect feeding the VFD and an E-stop circuit killing power after the drive to the motor, auxiliary contacts on the contactor between VFD and motor go to drive enable. The normal stop/start buttons would wire to inputs to the VFD, a selector switch to select forward/reverse, you could add a potentiometer for speed control. This way, drive gets to control the stop under normal circumstances and motor is instantly disconnected when E-Stop is pressed. You could add additional contacts to kill power to the VFD if you wanted to but most of the time the VFD will stop the spindle quicker with the power on then just killing power to it. Note that if you remove power before the VFD you're not killing power to the motor until the VFD capacitors discharge.
On some machines we use a timing relay to keep power on the drive for a couple of seconds while stopping the motor, the motor stops much quicker with the drive then it does by just removing power. We have some drives that can have a separate 24V DC logic power, you can kill power to the drive and not lose the power to the drives computer. This is done on our ProfiBus drives that are on the PLC's network.
Our drives are in a control cabinet and power coming out of the cabinet is removed in E-stop condition except control power. Those that claim you have to kill everything on an E-stop don't kill the incoming power from their utility pole, so even they don't kill "everything". What I described is what works in a ~35 year old 60+ acre factory with probably over 1000 VFD's and an electric bill of over $1 million per month. If there were ever a safety incident power would be required to be removed before the drives. Some of our techs have worked where they kill power to the whole machine on E-stop and it makes people very reluctant to use the E-stop because of the uncontrolled crash and difficulty restarting.
RogerN
Reply to
RogerN
No, but I think of that stop button as a safety stop to stop the machine when something goes haywire.
Under more normal circumstances, something else would be used to stop the spindle. As of now, I set it to stop in 0.5 second using dynamic braking. Any time shorter than that gives a weird feeling that the machine is fake.
i
Reply to
Ignoramus18810
set the deceleration to "coast" - otherwise your customer will be unhappy
Reply to
Bill Noble
Why in Croms name do you set decel to "coast"??????
Big assed chuck you dont want to unscrew when running the lathe in reverse????
Whenever a Liberal utters the term "Common Sense approach"....grab your wallet, your ass, and your guns because the sombitch is about to do something damned nasty to all three of them.
Reply to
Gunner Asch
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Though if the motor is running at fairly high power, that will be pretty quick anyway.
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This is what makes me reluctant to use the E-stop on my little Emco-Maier Compact-5/CNC lathe (it's only a 5" swing, so there is not too much danger when something *does* go wrong). You hit the E-stop, and not only does it dump power from the spindle motor and the stepper motors -- it also dumps it from the computer. If I've just spent some time keying in a program and not saved it since several changes, I lose that too -- and I have to redefine the zeros for the axes -- unless I am lucky enough to have it at the home position (defined as where it is when you start the program). There are no reference limit switches to allow it to restore to a known point on its own.
Enjoy, DoN.
Reply to
DoN. Nichols
What I've always preferred is keeping control and input power on but killing output power on E-Stop. That way you keep your controls but disconnect the potential for movement. For example with your Compact 5 I would keep power to the computer and encoders, if it uses steppers perhaps chop the current in half or so. Kill power to the spindle motors and servo drives but not their feedback devices. That way an E-stop is going to stop motion and keep position, program, etc..
RogerN
Reply to
RogerN
This is a mill. I cannot think of anyone who would not want to have quick deceleration, as well as electronic reverse.
i
Reply to
Ignoramus18810
Big Gold Star!!!
Gunner
Whenever a Liberal utters the term "Common Sense approach"....grab your wallet, your ass, and your guns because the sombitch is about to do something damned nasty to all three of them.
Reply to
Gunner Asch
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Unfortunately -- the power for the spindle motor, the steppers and the computer come from the same power supply -- and it is all shut off by the E-stop button. To restore power you have to first release the E-stop button (by twisting the mushroom), and then use the key to switch the AC power off and back on.
And -- there is not really room in there to add separate circuitry with relays and such to selectively power down the steppers and the spindle motor.
And -- since it uses stepper motors instead of servos, drop power to the steppers and spindle but keep power on the computer and you get another problem. There is no position feedback -- it trusts that the steppers have gone to where they were told to do, so you have no idea how far out of sync the actual position of the motors and the computer's idea of where they are may be.
And there is not really room to expand the program to allow a graceful stop to the CPU. It is running on a 6502 (64 K address space), and has about half of the address space taken by the firmware, and the other half for user programs. And the system's program is in machine code (of course, given how little space there is), and totally undocumented, unless someone has a chance to get into Emco's history files. :-)
Some of these days, I'll take a dead spare that I have and built a servo based controller around it using EMC, so I'll have a lot more control over things.
Enjoy, DoN.
Reply to
DoN. Nichols
Something that might be a possibility for you. If you found the signals to your stepper motor drives you might be able to use a separate PC with a parallel port breakout board. Sort of disconnect the EMCO PC and use your own PC running EMC or similar. Perhaps you already have home switches but it would help me if I had home switches so I could set a reference point and position my cutting tools from a known position. Right now I just jog and take a cut, measure, set the axis to the radius.
My lathe is an old Anilam 14 X 20 lathe that came with good hardware and electronics except the controls were bad. I put a PC running EMC2 and I like it. My first test run I cut the EMC lathe pawn program cutting a stainless steel pawn in 3 minutes and I don't have the coolant running yet. Stainless was coming off red hot so I don't think I can speed it up without burning tooling until I get the coolant pump running.
I found the original spindle encoder was bad so I ordered one from Automationdirect.com and it cuts threads very nice now. The spindle motor is 7.5HP and I have single phase here, so I put on a 10HP Hitachi VFD and am using EMC to control my spindle speeds with RPM feedback from the encoder. I still need to wire the limit and home switches, the coolant pump, and the gearbox lube circulation / cooling pump.
I have an Anilam CNC Bridgeport mill that uses DRO scales and servo motors that I hope to be my next EMC conversion. I called Anilam about an I/O option for the controls and it was going to cost more for simple spindle ON/OFF then an entire EMC conversion will cost. But with the EMC conversion I get spindle speed, spindle forward/reverse, and can add a spindle encoder to get rigid tapping. And there's a possibility to add a 4th axis...
RogerN
Reply to
RogerN
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The stepper motor drives plug directly into the CPU board, and derive power from it.
No PC there (if you mean personal computer, instead of printed circuit). It is a large printed circuit board with the keypad, a several digit LED display, other keys for jogging and other positioning, outputs to control a tool turret (which also has no absolute home position, and the commands in the programs are "advance three stations" instead of "go to station 5", so it gets lost too when a program is interrupted (or if you forget to do enough advances at the end of the program to return to station 1. :-)
No such luck. Nor is there much room to add such.
Note that home switches are not accurate enough to reliably set zero from them. Typically, it is necessary to have linear encoders or rotary encoders with an index position as well as the increment encoders. So -- with linear encoders, you move until you encounter the index position, and then keep going until you are at a count zero point within that zone. With rotary encoders it is similar, except that you need a mechanical switch to say "this time around is when you pay attention to the index spot". :-)
That is big enough to have room to hang anything you need on it. And Anilam controls were nice. I worked with one on a Bridgeport clone a few years before I retired. I found some intersting things that you could do with an Anilam and a PC to dump the entire set of canned cycles to. This allowed me to write canned cycles to engrave letters using the Hershey letter sets.
Hmm ... if you're using clamped carbide inserts, they will happily cut with red hot chips. The only thing to worry about is whether the holder is getting hot enough to give.
But you certainly don't want to hit a carbide insert with coolant after it gets that hot -- it is likely to crack.
Great!
Does it work as it stands? You certainly will have a lot of working hardware, including servo motors already mounted, even if you do go to EMC2. What interface are you planning to use -- driving the existing servo amplifiers with analog signals from a card like the Servo To Go cards, or going with the drivers which make the servo motors look like steppers to the controller? My preference is the former, once I finish converting the Bridgeport BOSS-3 to use servos instead of steppers. (I really *don't* like steppers for many reason.)
Ouch!
Or more than a 4th axis -- say an index/dividing head on top of a rotary table to get more creative angles. The Servo-To-Go card will drive 8 axes, though I think that there was some kind of problem which limited it to six axes with the earlier EMC at least.
Anyway -- the Bridgeport is the first target for EMC, then the *spare* Compact-5 with the dead electronics to replace with EMC and servo motors in place of steppers. This also means a small VFD for the spindle motor so I get speed control too. Right now, it is a DC spindle motor which is selected on or off, and the speed set by a front panel pot only. I had considered adding a small relay in there and a second front panel pot, so I could switch between two speeds in the middle of a program. The primary reason for this is that it is serious limited in spindle speed when threading (typically if the spindle speed is above 200 RPM, it displays an error code on the LED display, and a "TOO FAST" warning on the video display (which is normally good for 16 lines of program and status).
Good Luck, DoN.
Reply to
DoN. Nichols
I was thinking of a switch and an index. On one project that wasn't real critical, we used a prox switch to home from and for an experiment I mounted my dial indicator to test home repeatability. It came to zero on repeated homings and seemed to be 0.001" accurate, but that could have changed with temperature or anything else over time that I wouldn't have detected. On homing without a switch I guess a person could jog to a mark on the slide and have an index mark on a dial, pulley, or something on the screw to jog alignment to set a known home position.
I ended up using a Mesa 5i20 board, $199 instead of $800 for the servo's to go board. This allows me to connect directly to the original amplifiers. I'm not certian but I think you can use 2 5i20 boards for 8 servos and encoders. On the conversion I plan to use the same connectors as Anilam so I can unplug my Crusader II control and plug in the EMC control. That way I could switch back to the original control until I get EMC tuned in. My crusader II control works fine but sometimes a row of buttons doesn't work, I made a jumper wire to push the AUX button so I can transfer programs to a laptop.
EMC does 6 coordinate axis but can use 8 servo axis to get there.
I cut some threads at 800 RPM, doesn't take long! The index comes around a lot more than a thread dial so it just looks like a continuous cut. About makes you sick after doing it by hand. My friend cut some hydraulic cyl. ends and got them down to about a half hour. I programmed it in the CNC lathe and it took 3 minutes :-)
RogerN
Reply to
RogerN
That is pretty good. How fast was the approach?
Yes -- except that there are no dials on the Compact-5/CNC. Just small (8mm or so) ball screws driven by stepper motors with a short timing style belt (about 4mm wide) in a very tiny housing with no room to add any kind of index sensor. Once I modify one to use servo motors, I will have to re-do the couplings so I can add an index. I will really need a rotary encoder on the leadscrew to get position feedback anyway, and if there is one with an index encoder as well, that should work -- perhaps with the addition of a position sensor switch.
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That looks interesting, and may allow me to use EMC2 in a Sun UltraSPARC system running Solaris 10, instead of a PC running linux. If all else fails, I could install linux in the UltraSPARC system. The need for the ISA bus for the Servo To Go board was locking me to older PC hardware.
Solaris 10 comes with built-in real-time capability, instead of having to jack up the linux kernel and run it on top of a separate real-time micro-kernel.
Great!
Hmm ... the Anilam Crusader II used entirely capacitive sensor switch areas on a rigid panel, IIRC. (It has been probably twenty years since I last saw one.) I wonder where the problems are in the front panel. (Or was the AUX button a real separate switch?)
O.K.
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Even with the slower speeds for the Compact-5/CNC while threading, it is impressive enough threading to a shoulder.
As for 800 RPM threads, I have cut those quite a few times on the purely manual 12x24" Clausing which I use. It is only when threading to a shoulder that I drop down into back gear for slower threading -- or really coarse threads.
Enjoy, DoN.
Reply to
DoN. Nichols
It was pretty slow, the control was a dedicated servo indexer. I usually find home kind of fast, go back off home a little bit, then home slow for more accuracy.
Sounds like they don't give you much room for anything! There's $99 servo motors here, not sure they'd work for your application or if you have something better in mind.
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Mine has a membrane keypad and I did a partial pinout using an ohmmeter. I soldered two wires on the header that when I touch the wires together it operates the AUX like the button does when it's working. When it's not working, the entire column of buttons doesn't work but enough works to transfer programs to/from the laptop.
For example, if I used EMC on my Bridgeport for my quill and added a servo for the knee, EMC would still consider that 3 axis (X,Y,Z) even though it was using 4 servos (quill and knee both on Z axis). The other 3 axis EMC supports are rotation about X,Y, & Z. That can define any 3D position and a 3D rotation angle, as far as I know that's any position at any angle. But to get to any position, any angle, it can use up to 8 servo (or stepper) motors.
The RPM on the threads isn't that impressive but their seems to be no noticeable pause between passes. It goes in, takes off cutting the thread, backs out, rapids (200 IPM on the lathe) to start. It's as if your thread dial is ready 400 times a minute (my spindle turns 2 revs per 1 encoder rev.). On my cylinder rod end program it turns 1" stainless steel to 3/4" dia X 3" and threads 3/4-16 for 1-1/2" of the end, complete with chamfers and blend from threaded to flat portion, 1 manual tool change, and done in about 3 minutes. Seems that everything I have test cut on the lathe so far is done in about 3 minutes.
Another feature that could be of interest to you. You should be able to use EMC with stepper motors and encoder feedback. It's of limited because if a stepper looses steps, increasing the speed doesn't seem to help :-) What I like about my mill is the use of linear DRO scales for position feedback. When I first got the mill it had some backlash between the screw and table due to bearings needing shimmed. The combination of tach feedback to the drive and scale feedback to the control produced a stable and accurate system even with almost 0.1" of backlash (or course it wouldn't have been very good on climb milling!). For your lathes, it may be beneficial to at least let you know if a stepper skipped steps and fault out instead of perhaps crashing.
RogerN
Reply to
RogerN

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