Re: Best practice for mill VFD control wiring

On 2009-08-26, RogerN <regor@xxxxxxxxxxx> wrote:

"DoN. Nichols" <dnichols@xxxxxxxxxxx> wrote in message
news:slrnh98vli.9io.dnichols@xxxxxxxxxxxxxxxxxxxxx
On 2009-08-25, RogerN <regor@xxxxxxxxxxx> wrote:


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..

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.

[ ... ]

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.

The stepper motor drives plug directly into the CPU board, and
derive power from it.

Sort of disconnect the EMCO PC and use your
own PC running EMC or similar.

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. :-)

Perhaps you already have home switches

No such luck. Nor is there much room to add such.

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.

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". :-)

My lathe is an old Anilam 14 X 20 lathe that came with good hardware and
electronics except the controls were bad.

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.

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.

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.

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.

Great!

I have an Anilam CNC Bridgeport mill that uses DRO scales and servo motors
that I hope to be my next EMC conversion.

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.)

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.

Ouch!

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...

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.

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