I started wiring everything in as professional manner as I am able to
do. I use DIN rail to mount as much stuff as possible, use DIN
terminals wherever possible, and I route wires through wire channels.

I connected my AMC 30A8T drive to the power supply and tachometer, so
that it would operate in tach mode. I made sure that all DIP switches
are set properly for tach mode.

Pictures of wiring are here.

http://igor.chudov.com/projects/Brid...iring-7670.jpg

The good news is that after some false tries, tach mode works
great. The X axis moves at about 70 IPM max, or super slow, as
commanded. I use a separate little power supply for commands. The
drive develops 68VDC and appx. 3 amps to move the table at highest
speed.

The more disconcerting news is that if a tach cable is not connected,
the drive goes into a runaway mode EVEN IF NO INPUT SIGNAL is
present (inputs shorted to each other).

This means that if I do a shoddy job wiring those tach contacts, or
the open barrel terminals fall out, or anything else, I will be in a
world of hurt.

I know that EMC has some protection against following error, but I am
not sure how robust is that.

Besides a lot of simple jobs facing me, I have a big job, which is
installing new encoders and making mount plates for same.

After this, I will try to create a "One-Axis CNC" machine without
worrying about other axes.

Anyway, I have one little thing to celebrate (the tach mode).

I also have a good grip on using that open barrel terminal crimper and
all crimps now come out looking good. I do a pull test on each, of
course.

i

....
Anyway, I have one little thing to celebrate (the tach mode).

I also have a good grip on using that open barrel terminal crimper and
all crimps now come out looking good. I do a pull test on each, of
course.

I've never played with a tach. I'm assuming you still give the AMC drive
a -10 to 10 volt signal for direction and speed and the control does the
PID. I had read somewhere that a tach would help in super slow applications,
like a wire edm where feeds are .0X ipm. Let me know if you see benefits.

I ordered one of the crimpers you suggest, got to be better than mine.

Karl

On 2010-07-09, Karl Townsend wrote:
...
Anyway, I have one little thing to celebrate (the tach mode).

I also have a good grip on using that open barrel terminal crimper and
all crimps now come out looking good. I do a pull test on each, of
course.

I've never played with a tach. I'm assuming you still give the AMC drive
a -10 to 10 volt signal for direction and speed and the control does the
PID. I had read somewhere that a tach would help in super slow applications,
like a wire edm where feeds are .0X ipm. Let me know if you see benefits.

Yes, you give the drive a signal and the control minimizes the error
between the speed as reported by tach, and speed as commanded by the
signal.

The drive is, therefore, able to produce very precise speed.

I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.

I was told (and it makes sense) that ability to set velocity precisely
is useful for a lot of machining operations, smooth finish etc. You
could have your cutter move along some curvy curve and follow it
precisely and dynamically. The servo drives closes the velocity loop
continuously. The PC control does not have to close the velocity loop
by itself 5000 times a second based on encoder readings.

I ordered one of the crimpers you suggest, got to be better than mine.

I would say, waste about 5-10 connectors to get a hang of it. The
connector can go in only one way. The crimper has an internal step,
kind of.

I still have no estop stuff done, I just pull out a fuse holder by
hand if something goes wrong.

I try to get at least something done every day.

Bought a BIG BOX of DIN terminals:

http://cgi.ebay.com/ws/eBayISAPI.dll...m=320556561707

i

On 2010-07-09, Ignoramus30064 wrote:
On 2010-07-09, Karl Townsend wrote:
...
Anyway, I have one little thing to celebrate (the tach mode).

I also have a good grip on using that open barrel terminal crimper and
all crimps now come out looking good. I do a pull test on each, of
course.

I've never played with a tach. I'm assuming you still give the AMC drive
a -10 to 10 volt signal for direction and speed and the control does the
PID. I had read somewhere that a tach would help in super slow applications,
like a wire edm where feeds are .0X ipm. Let me know if you see benefits.

Yes, you give the drive a signal and the control minimizes the error
between the speed as reported by tach, and speed as commanded by the
signal.

The drive is, therefore, able to produce very precise speed.

I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.

I was told (and it makes sense) that ability to set velocity precisely
is useful for a lot of machining operations, smooth finish etc. You
could have your cutter move along some curvy curve and follow it
precisely and dynamically. The servo drives closes the velocity loop
continuously. The PC control does not have to close the velocity loop
by itself 5000 times a second based on encoder readings.

i mean 1,000 times pre second

i

I ordered one of the crimpers you suggest, got to be better than mine.

I would say, waste about 5-10 connectors to get a hang of it. The
connector can go in only one way. The crimper has an internal step,
kind of.

I still have no estop stuff done, I just pull out a fuse holder by
hand if something goes wrong.

I try to get at least something done every day.

Bought a BIG BOX of DIN terminals:

http://cgi.ebay.com/ws/eBayISAPI.dll...m=320556561707

i

I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.

Disclaimer:My control uses a Galil dedicted real time controller so your
results may differ.

Torque mode is the preferred mode for most all applications, certainly for
what you're doing. Precise smooth control is not an issue at all with lathe
and mill applications.

Karl

On 2010-07-09, Karl Townsend wrote:

I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.

Disclaimer:My control uses a Galil dedicted real time controller so your
results may differ.

Torque mode is the preferred mode for most all applications, certainly for
what you're doing. Precise smooth control is not an issue at all with lathe
and mill applications.

Karl, could you explain to me, why do you think so? Wouldn't the
milling table move at very high rates of speed if it encountered no
resistance, in torque mode?

i

"Ignoramus30064" wrote in message
...
On 2010-07-09, Karl Townsend wrote:

I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.

Disclaimer:My control uses a Galil dedicted real time controller so your
results may differ.

Torque mode is the preferred mode for most all applications, certainly
for
what you're doing. Precise smooth control is not an issue at all with
lathe
and mill applications.

Karl, could you explain to me, why do you think so? Wouldn't the
milling table move at very high rates of speed if it encountered no
resistance, in torque mode?

i

http://www.a-m-c.com/content/support/FAQ.html#setup03

read question 3

On 2010-07-09, Karl Townsend wrote:

"Ignoramus30064" wrote in message
...
On 2010-07-09, Karl Townsend wrote:

I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.

Disclaimer:My control uses a Galil dedicted real time controller so your
results may differ.

Torque mode is the preferred mode for most all applications, certainly
for
what you're doing. Precise smooth control is not an issue at all with
lathe
and mill applications.

Karl, could you explain to me, why do you think so? Wouldn't the
milling table move at very high rates of speed if it encountered no
resistance, in torque mode?

i

http://www.a-m-c.com/content/support/FAQ.html#setup03

read question 3



Karl, that does not really answer my question (about possible high
speed).

i

Ignoramus30064 wrote:

On 2010-07-09, Karl Townsend wrote:

"Ignoramus30064" wrote in message
...
On 2010-07-09, Karl Townsend wrote:

I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.

Disclaimer:My control uses a Galil dedicted real time controller so your
results may differ.

Torque mode is the preferred mode for most all applications, certainly
for
what you're doing. Precise smooth control is not an issue at all with
lathe
and mill applications.

Karl, could you explain to me, why do you think so? Wouldn't the
milling table move at very high rates of speed if it encountered no
resistance, in torque mode?

i

http://www.a-m-c.com/content/support/FAQ.html#setup03

read question 3



Karl, that does not really answer my question (about possible high
speed).

i

Axis speed is controlled by the CNC control giving the motion commands,
not by the servo drive. The CNC control doesn't say "move to position X"
and the drive goes full tilt to that position. The CNC control manages
the movement to move at the specified feed or rapid rate, i.e. G01 X10
F25 moves from the current X position to X10 at a 25 inch per minute
rate.

On 2010-07-09, Pete C. wrote:

Ignoramus30064 wrote:

On 2010-07-09, Karl Townsend wrote:

"Ignoramus30064" wrote in message
...
On 2010-07-09, Karl Townsend wrote:

I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.

Disclaimer:My control uses a Galil dedicted real time controller so your
results may differ.

Torque mode is the preferred mode for most all applications, certainly
for
what you're doing. Precise smooth control is not an issue at all with
lathe
and mill applications.

Karl, could you explain to me, why do you think so? Wouldn't the
milling table move at very high rates of speed if it encountered no
resistance, in torque mode?

i

http://www.a-m-c.com/content/support/FAQ.html#setup03

read question 3



Karl, that does not really answer my question (about possible high
speed).

i

Axis speed is controlled by the CNC control giving the motion commands,
not by the servo drive. The CNC control doesn't say "move to position X"
and the drive goes full tilt to that position. The CNC control manages
the movement to move at the specified feed or rapid rate, i.e. G01 X10
F25 moves from the current X position to X10 at a 25 inch per minute
rate.

But how does the control tell the drive what speed to use, if the
drive is in torque mode?

I do not quite understand this.

i

But how does the control tell the drive what speed to use, if the
drive is in torque mode?

I do not quite understand this.

i

The control is smart, the drive is dumb. The control only tells the drive
what to until the next refresh. The control looks at actual position vs.
command position, acceleration, etc. and makes a decision for how much
motion till the next refresh to solve the positioning problem. The dumb
drive just gets a voltage and does what its told.

karl

I'm sure a EE could give a far more elegant description.

On Fri, 09 Jul 2010 11:46:37 -0500, Ignoramus30064
wrote:

On 2010-07-09, Pete C. wrote:

Ignoramus30064 wrote:

On 2010-07-09, Karl Townsend wrote:

"Ignoramus30064" wrote in message
...
On 2010-07-09, Karl Townsend wrote:

I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.

Disclaimer:My control uses a Galil dedicted real time controller so your
results may differ.

Torque mode is the preferred mode for most all applications, certainly
for
what you're doing. Precise smooth control is not an issue at all with
lathe
and mill applications.

Karl, could you explain to me, why do you think so? Wouldn't the
milling table move at very high rates of speed if it encountered no
resistance, in torque mode?

i

http://www.a-m-c.com/content/support/FAQ.html#setup03

read question 3



Karl, that does not really answer my question (about possible high
speed).

i

Axis speed is controlled by the CNC control giving the motion commands,
not by the servo drive. The CNC control doesn't say "move to position X"
and the drive goes full tilt to that position. The CNC control manages
the movement to move at the specified feed or rapid rate, i.e. G01 X10
F25 moves from the current X position to X10 at a 25 inch per minute
rate.

But how does the control tell the drive what speed to use, if the
drive is in torque mode?

I do not quite understand this.

i

When the amp is set to velocity mode, the setting when you're using a
tach, it acts as a voltage to voltage amplifier. In torque mode, which
as Karl said is what the vast majority of motion control apps use, the
amp's output *current* is proportional to the command voltage. If the
controller sees, via the encoder feedback, that the motor is moving
too slowly it increases the command signal, the amp increases current,
motor torque goes up, and speed increases. Repeat until the controller
is satisfied.

I've designed and built 15 or 20 different systems with perhaps 50
servo axes over the last 20 years, and I can think of only one
instance that used tach feedback, and even that was synthesized from
an encoder signal. And in that case there was no traditional
controller.

Re your earlier remark that tach feedback decreases the load on the
controller -- every modern digital motion controller I've worked with
is constantly updating the servo loop unless you specifically tell it
not to. The typical rate is in the range of 10 KHz.

--
Ned Simmons

On 2010-07-09, Ned Simmons wrote:
On Fri, 09 Jul 2010 11:46:37 -0500, Ignoramus30064
wrote:

On 2010-07-09, Pete C. wrote:

Ignoramus30064 wrote:

On 2010-07-09, Karl Townsend wrote:

"Ignoramus30064" wrote in message
...
On 2010-07-09, Karl Townsend wrote:

I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.

Disclaimer:My control uses a Galil dedicted real time controller so your
results may differ.

Torque mode is the preferred mode for most all applications, certainly
for
what you're doing. Precise smooth control is not an issue at all with
lathe
and mill applications.

Karl, could you explain to me, why do you think so? Wouldn't the
milling table move at very high rates of speed if it encountered no
resistance, in torque mode?

i

http://www.a-m-c.com/content/support/FAQ.html#setup03

read question 3



Karl, that does not really answer my question (about possible high
speed).

i

Axis speed is controlled by the CNC control giving the motion commands,
not by the servo drive. The CNC control doesn't say "move to position X"
and the drive goes full tilt to that position. The CNC control manages
the movement to move at the specified feed or rapid rate, i.e. G01 X10
F25 moves from the current X position to X10 at a 25 inch per minute
rate.

But how does the control tell the drive what speed to use, if the
drive is in torque mode?

I do not quite understand this.

i

When the amp is set to velocity mode, the setting when you're using a
tach, it acts as a voltage to voltage amplifier. In torque mode, which
as Karl said is what the vast majority of motion control apps use, the
amp's output *current* is proportional to the command voltage. If the
controller sees, via the encoder feedback, that the motor is moving
too slowly it increases the command signal, the amp increases current,
motor torque goes up, and speed increases. Repeat until the controller
is satisfied.

I've designed and built 15 or 20 different systems with perhaps 50
servo axes over the last 20 years, and I can think of only one
instance that used tach feedback, and even that was synthesized from
an encoder signal. And in that case there was no traditional
controller.

Re your earlier remark that tach feedback decreases the load on the
controller -- every modern digital motion controller I've worked with
is constantly updating the servo loop unless you specifically tell it
not to. The typical rate is in the range of 10 KHz.


OK. So, I think that I am making a mistake by using tachometer and
instead, I should go to torque mode. It will actually be easier to
use torque mode, anyway. If everyone does it, so will I. It is also
safer and I can remove a whole bunch of cables from the control that I
do not need. Seems to be a win-win all around.

i

On 2010-07-09, Karl Townsend wrote:

But how does the control tell the drive what speed to use, if the
drive is in torque mode?

I do not quite understand this.

i

The control is smart, the drive is dumb. The control only tells the drive
what to until the next refresh. The control looks at actual position vs.
command position, acceleration, etc. and makes a decision for how much
motion till the next refresh to solve the positioning problem. The dumb
drive just gets a voltage and does what its told.

Karl, you and Ned have convinced me.

I am actually very happy, because I would get rid of a lot of cables
inside the control box, less complexity, less fear of tachs going bad
on me and the drives going berserk, etc.

I will use torque mode.

One last question, if someone could enlighten me, whi torque mode and
not "voltage mode"?

I am not trying to invent a better wheel with 4 minutes of experience,
or think that I know better than everyone, I just want to understand.

i

Ignoramus6355 wrote:

The more disconcerting news is that if a tach cable is not connected,
the drive goes into a runaway mode EVEN IF NO INPUT SIGNAL is
present (inputs shorted to each other).

This means that if I do a shoddy job wiring those tach contacts, or
the open barrel terminals fall out, or anything else, I will be in a
world of hurt.

I know that EMC has some protection against following error, but I am
not sure how robust is that.

Make sure the encoder wiring is good or your control has no way to know you have an axis
that is running away. The only thing your control can do is put your system in e-stop.

I had a waterjet cell that profiled headlinders for explorers. The drives were DC and
used a tach. I always kept in mind that one wire broken could cause a lot of grief and
danger. Not a real problem to the operators but if I'm inside teaching a profile, I
better be somewhere a run away can't get me.

As far as your tach, have you opened the motor and looked at the brushes? If the brushes
are worn down, trouble is on the horizon. I've never had problems with tach brushes
during the time period I had to deal with dc drives, usually the motor brushes that have a
more demanding task fail. Oh, while you are in there, blow out the dust.


Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller

On 2010-07-09, Ignoramus6355 wrote:
I started wiring everything in as professional manner as I am able to
do. I use DIN rail to mount as much stuff as possible, use DIN
terminals wherever possible, and I route wires through wire channels.

I connected my AMC 30A8T drive to the power supply and tachometer, so
that it would operate in tach mode. I made sure that all DIP switches
are set properly for tach mode.

Pictures of wiring are here.

http://igor.chudov.com/projects/Brid...iring-7670.jpg


Looks nice.

The good news is that after some false tries, tach mode works
great. The X axis moves at about 70 IPM max, or super slow, as
commanded. I use a separate little power supply for commands. The
drive develops 68VDC and appx. 3 amps to move the table at highest
speed.

Without cutting load, of course.

The more disconcerting news is that if a tach cable is not connected,
the drive goes into a runaway mode EVEN IF NO INPUT SIGNAL is
present (inputs shorted to each other).

Usually, there is a zero trimpot on the servo amp (drive) which
will first off eliminate drive with zero input signal voltage. When
this is done, it might also eliminate the runaway problem with no tach
feedback connected -- but I'm not sure of that.

I presume the black module near the bottom marked 'X' is the
servo amp?

This means that if I do a shoddy job wiring those tach contacts, or
the open barrel terminals fall out, or anything else, I will be in a
world of hurt.

So -- this is a motivation to do it right. :-)

I know that EMC has some protection against following error, but I am
not sure how robust is that.

Besides a lot of simple jobs facing me, I have a big job, which is
installing new encoders and making mount plates for same.

After this, I will try to create a "One-Axis CNC" machine without
worrying about other axes.

Anyway, I have one little thing to celebrate (the tach mode).

Indeed -- congratulations.

I also have a good grip on using that open barrel terminal crimper and
all crimps now come out looking good. I do a pull test on each, of
course.

Especially with the new motivation. :-)

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 2010-07-09, Karl Townsend wrote:

I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.

Disclaimer:My control uses a Galil dedicted real time controller so your
results may differ.

Torque mode is the preferred mode for most all applications, certainly for
what you're doing. Precise smooth control is not an issue at all with lathe
and mill applications.

The place where this is most likely to make a difference is
cutting a line which almost but not quite parallels an axis of the
machine. This means that one axis is moving at a speed which is
determined by the appropriate feed rate for the tool/material
combination, and the other axis is moving at a very slow creep. An
example would be turning (or milling) a shallow taper. While turning,
maybe Morse, even more so for the taper of a tapered arbor.

If the controller is monitoring the encoders frequently enough,
and the encoders have sufficient resolution, you are fine anyway.
However, with a coarser resolution encoder, the ability to command a
precise slow speed means that you can trust it to maintain the very
shallow angle between encoder pulses. The Galil, with a set of
sufficient resolution encoders probably does not truly need the tach
feedback -- but even it might find the job easier with that.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 2010-07-09, Karl Townsend wrote:

But how does the control tell the drive what speed to use, if the
drive is in torque mode?

I do not quite understand this.

i

The control is smart, the drive is dumb. The control only tells the drive
what to until the next refresh. The control looks at actual position vs.
command position, acceleration, etc. and makes a decision for how much
motion till the next refresh to solve the positioning problem. The dumb
drive just gets a voltage and does what its told.

In which case, it is possible for the computer acting as the
control to lock up (BSOD for Windows) just after issuing a command for
high torque, leaving the motor running quite rapidly until it hits a
stop.

Less likely to happen with the linux backed EMC, but still
possible if there is a hardware failure in the computer.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"DoN. Nichols" wrote:

On 2010-07-09, Karl Townsend wrote:

But how does the control tell the drive what speed to use, if the
drive is in torque mode?

I do not quite understand this.

i

The control is smart, the drive is dumb. The control only tells the drive
what to until the next refresh. The control looks at actual position vs.
command position, acceleration, etc. and makes a decision for how much
motion till the next refresh to solve the positioning problem. The dumb
drive just gets a voltage and does what its told.

In which case, it is possible for the computer acting as the
control to lock up (BSOD for Windows) just after issuing a command for
high torque, leaving the motor running quite rapidly until it hits a
stop.

Less likely to happen with the linux backed EMC, but still
possible if there is a hardware failure in the computer.

This is where watchdog timers come into play. I presume the I/O boards
Iggy is using have such a feature since the ones for Mach3 do. The
watchdog timer monitors a signal from the PC that is supposed to cycle
continuously as the program operates normally, if the signal doesn't
cycle in a second or so, the watchdog timer times out and forces an
E-stop.

On 2010-07-09, Pete C. wrote:

"DoN. Nichols" wrote:

On 2010-07-09, Karl Townsend wrote:

But how does the control tell the drive what speed to use, if the
drive is in torque mode?

I do not quite understand this.

i

The control is smart, the drive is dumb. The control only tells the drive
what to until the next refresh. The control looks at actual position vs.
command position, acceleration, etc. and makes a decision for how much
motion till the next refresh to solve the positioning problem. The dumb
drive just gets a voltage and does what its told.

In which case, it is possible for the computer acting as the
control to lock up (BSOD for Windows) just after issuing a command for
high torque, leaving the motor running quite rapidly until it hits a
stop.

Less likely to happen with the linux backed EMC, but still
possible if there is a hardware failure in the computer.

This is where watchdog timers come into play. I presume the I/O boards
Iggy is using have such a feature since the ones for Mach3 do. The
watchdog timer monitors a signal from the PC that is supposed to cycle
continuously as the program operates normally, if the signal doesn't
cycle in a second or so, the watchdog timer times out and forces an
E-stop.

I think that Jon's PPMC has some kind of a watchdog.

i

Ignoramus6355 wrote:
The more disconcerting news is that if a tach cable is not connected,
the drive goes into a runaway mode EVEN IF NO INPUT SIGNAL is
present (inputs shorted to each other).

Yes, of course. Any servo needs to have its "loop" closed at all times.
It may be that if you put a 10 K Ohm resistor across the tach input
terminals on
the servo amp, then an open tach circuit will no longer cause a runaway.
This means that if I do a shoddy job wiring those tach contacts, or
the open barrel terminals fall out, or anything else, I will be in a
world of hurt.

Well, the tach can also have the brushes go bad, the wire can fail due
to flexing, etc.
I know that EMC has some protection against following error, but I am
not sure how robust is that.

It is unlikely the tach AND the encoder will fail at the same time.

I just got in the boards for my "Copley interface", which will also work
on the AMC amps
(they are the same). The servo amp needs a contact closure to ground to
enable it, and
produces a 5 V signal when it goes into fault status. A quirk is that
when disabled, it shows
fault status. So, this board suppresses the fault indication for a
moment until the amp has
gotten enabled. The signal from one of the DIO SSR's can be used to
send the enable to the
servo amps. By default, EMC2 does not go to E-stop on a following
error, allowing the
servo amps to drift (or continue to run away, if that was the cause). I
have to find out
how to modify the ppmc_io.hal file to make this happen.

Jon

On 2010-07-10, Jon Elson wrote:
Ignoramus6355 wrote:
The more disconcerting news is that if a tach cable is not connected,
the drive goes into a runaway mode EVEN IF NO INPUT SIGNAL is
present (inputs shorted to each other).

Yes, of course. Any servo needs to have its "loop" closed at all times.
It may be that if you put a 10 K Ohm resistor across the tach input
terminals on
the servo amp, then an open tach circuit will no longer cause a runaway.
This means that if I do a shoddy job wiring those tach contacts, or
the open barrel terminals fall out, or anything else, I will be in a
world of hurt.

Well, the tach can also have the brushes go bad, the wire can fail due
to flexing, etc.
I know that EMC has some protection against following error, but I am
not sure how robust is that.

It is unlikely the tach AND the encoder will fail at the same time.

I just got in the boards for my "Copley interface", which will also work
on the AMC amps
(they are the same). The servo amp needs a contact closure to ground to
enable it, and
produces a 5 V signal when it goes into fault status. A quirk is that
when disabled, it shows
fault status. So, this board suppresses the fault indication for a
moment until the amp has
gotten enabled. The signal from one of the DIO SSR's can be used to
send the enable to the
servo amps. By default, EMC2 does not go to E-stop on a following
error, allowing the
servo amps to drift (or continue to run away, if that was the cause). I
have to find out
how to modify the ppmc_io.hal file to make this happen.

Jon

Jon, the way I am planning to do things, estop will cut power to servo
amps and will also stop the spindle by interrupting its signal circuit.

I would like to know, what do you think is the best mode to run these
amps: voltage mode, torque mode or tach mode? Any thoughts on this?

By the way, I wired in your PPMC and it powers find every time.

I have not connected it to a PC after placing it inside the mill.

i

Karl Townsend wrote:
I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.


Disclaimer:My control uses a Galil dedicted real time controller so your
results may differ.

Torque mode is the preferred mode for most all applications, certainly for
what you're doing. Precise smooth control is not an issue at all with lathe
and mill applications.

Why do you say this? Most of the older machines had tach feedback and
velocity servo
amps, and many still do, in one form or another. Are you serious that
"precise smooth control"
is not an issue in machining applications? Or, are you saying that
torque mode control can be just as
smooth?

The problem with no-tach servo control is that at SOME point, as you go
slower, the encoder
counts come in farther and farther apart in time, and the CNC control
has no velocity
information between encoder counts. This is why some CNC controls
(Fanuc, for example)
moved to ever higher and higher encoder counts, now Fanuc is at 4
million counts/rev.
Try pricing a million cycle/rev encoder!

When I first set up my Bridgeport, I wanted to see how well the velocity
servo loop worked,
so I moved at ever slower rates until the movement started to become
irregular. That was at
about 0.01 IPM, or 3 encoder counts/second on this setup. With the EMC2
servo loop
operating at 1000 cycles/second, that meant it was going 333 updates
before seeing each count.
But, the velocity servo was keeping the movement quite steady.


Jon

Ignoramus30064 wrote:
But how does the control tell the drive what speed to use, if the
drive is in torque mode?

I do not quite understand this.

The control has the velocity loop in software. It reads the encoder and
subtracts
new pos from last pos to compute velocity. Commanded velocity - actual
velocity
is the velocity error output, and is fed out as a torque command. This
is IDENTICAL
to what a velocity servo amp does (usually with op amps and resistors)
except it is
done by computation. The one place this falls down is if the machine is
moving slowly
enough that you get NO encoder counts in a servo period, then there is
no way to
calculate velocity.

Jon

Ignoramus30064 wrote:


Karl, you and Ned have convinced me.

I am actually very happy, because I would get rid of a lot of cables
inside the control box, less complexity, less fear of tachs going bad
on me and the drives going berserk, etc.

I will use torque mode.

One last question, if someone could enlighten me, whi torque mode and
not "voltage mode"?

I am not trying to invent a better wheel with 4 minutes of experience,
or think that I know better than everyone, I just want to understand.

Why ruin what you already have working? What is the resolution of your
encoder?
Calculate what velocity will have less than 10 encoder counts coming in
per second,
and if this is any rational velocity like you might have while orbiting
a circular path,
then you will descend into stepwise movement. Don't fear a tach,
they've been used
for 50 years now in motion control systems.

Jon

On 2010-07-10, Jon Elson wrote:
Ignoramus30064 wrote:


Karl, you and Ned have convinced me.

I am actually very happy, because I would get rid of a lot of cables
inside the control box, less complexity, less fear of tachs going bad
on me and the drives going berserk, etc.

I will use torque mode.

One last question, if someone could enlighten me, whi torque mode and
not "voltage mode"?

I am not trying to invent a better wheel with 4 minutes of experience,
or think that I know better than everyone, I just want to understand.

Why ruin what you already have working? What is the resolution of your
encoder?
Calculate what velocity will have less than 10 encoder counts coming in
per second,
and if this is any rational velocity like you might have while orbiting
a circular path,
then you will descend into stepwise movement. Don't fear a tach,
they've been used
for 50 years now in motion control systems.

Jon

Jon, my encoders are sinusoidal and thus I believe them to be
incompatible.

i

On Fri, 9 Jul 2010 12:00:04 -0500, "Karl Townsend"
wrote:


But how does the control tell the drive what speed to use, if the
drive is in torque mode?

I do not quite understand this.

i

The control is smart, the drive is dumb. The control only tells the drive
what to until the next refresh. The control looks at actual position vs.
command position, acceleration, etc. and makes a decision for how much
motion till the next refresh to solve the positioning problem. The dumb
drive just gets a voltage and does what its told.

karl

I'm sure a EE could give a far more elegant description.

A cultural note: that's a Minnesota rocket, by golly.

"Jon Elson" wrote in message
...
Karl Townsend wrote:
I could never get it to run at super slow speed in voltage mode, but
could easily do so in tach mode. It was kind of nice to see.


Disclaimer:My control uses a Galil dedicted real time controller so your
results may differ.

Torque mode is the preferred mode for most all applications, certainly
for what you're doing. Precise smooth control is not an issue at all with
lathe and mill applications.

Why do you say this? Most of the older machines had tach feedback and
velocity servo
amps, and many still do, in one form or another. Are you serious that
"precise smooth control"
is not an issue in machining applications? Or, are you saying that torque
mode control can be just as
smooth?

Jon, I'm just saying the first rule of good engineering is KISS.

Torque mode is simple and will work very well for Iggy.

Karl

Ignoramus30064 wrote:

On 2010-07-10, Jon Elson wrote:
Ignoramus30064 wrote:


Karl, you and Ned have convinced me.

I am actually very happy, because I would get rid of a lot of cables
inside the control box, less complexity, less fear of tachs going bad
on me and the drives going berserk, etc.

I will use torque mode.

One last question, if someone could enlighten me, whi torque mode and
not "voltage mode"?

I am not trying to invent a better wheel with 4 minutes of experience,
or think that I know better than everyone, I just want to understand.

Why ruin what you already have working? What is the resolution of your
encoder?
Calculate what velocity will have less than 10 encoder counts coming in
per second,
and if this is any rational velocity like you might have while orbiting
a circular path,
then you will descend into stepwise movement. Don't fear a tach,
they've been used
for 50 years now in motion control systems.

Jon

Jon, my encoders are sinusoidal and thus I believe them to be
incompatible.

i

Er, you got the US Digital ones to install in place of the old ones,
didn't you? You certainly aren't going to get your CNC control working
without working encoders.

On 2010-07-10, Pete C. wrote:

Ignoramus30064 wrote:

On 2010-07-10, Jon Elson wrote:
Ignoramus30064 wrote:


Karl, you and Ned have convinced me.

I am actually very happy, because I would get rid of a lot of cables
inside the control box, less complexity, less fear of tachs going bad
on me and the drives going berserk, etc.

I will use torque mode.

One last question, if someone could enlighten me, whi torque mode and
not "voltage mode"?

I am not trying to invent a better wheel with 4 minutes of experience,
or think that I know better than everyone, I just want to understand.

Why ruin what you already have working? What is the resolution of your
encoder?
Calculate what velocity will have less than 10 encoder counts coming in
per second,
and if this is any rational velocity like you might have while orbiting
a circular path,
then you will descend into stepwise movement. Don't fear a tach,
they've been used
for 50 years now in motion control systems.

Jon

Jon, my encoders are sinusoidal and thus I believe them to be
incompatible.

i

Er, you got the US Digital ones to install in place of the old ones,
didn't you? You certainly aren't going to get your CNC control working
without working encoders.

Yes, I got US digital encoders and am now working on mounting them.

i

Karl Townsend wrote:

"Jon Elson" wrote in message
...


Why do you say this? Most of the older machines had tach feedback and
velocity servo
amps, and many still do, in one form or another. Are you serious that
"precise smooth control"
is not an issue in machining applications? Or, are you saying that torque
mode control can be just as
smooth?


Jon, I'm just saying the first rule of good engineering is KISS.

Torque mode is simple and will work very well for Iggy.

Depending on how smooth he wants it, and what his encoder resolution
works out to,
maybe yes, and maybe no. The whole basis of my argument for the tach
feedback is the
velocity servo is a continuous-time system, the DC tach and velocity
error amplifier are
not sampled in any way. (Yes, the PWM modulator, etc. downstream in the
typical servo
amp then makes it discontinuous-time, but the PWM frequency is high
enough that this
shouldn't interfere with my argument.)

Deriving velocity info from an encoder effectively samples the
information both in
position (encoder resolution) and in time (servo sampling rate), thus
introducing
a type of noise into the system, but also making the system run
open-loop between
encoder counts. At low speeds, this requires much lower gain of the
velocity loop, or
you get a step-wise response at each encoder count.

This is why Fanuc, for example, uses encoders with a million lines/rev.

Jon

Ignoramus30064 wrote:

Jon, the way I am planning to do things, estop will cut power to servo
amps and will also stop the spindle by interrupting its signal circuit.

Well, you might want to think about having a braking resistor switched
in when the
servo power is cut off. Something like a 10 Ohm 25 W resistor on the NC
relay
contacts that drains energy from the motors via the DC bus.
I would like to know, what do you think is the best mode to run these
amps: voltage mode, torque mode or tach mode? Any thoughts on this?

I would run in velocity (tach) mode. You have the tachs on the machine
now, all
it takes is a little bit of wire to connect them. You should be able to
get smooth motion even
at low speeds with the tachs. I am using velocity servo mode on my
Bridgeport, and never
had a problem with them.

Jon

Ignoramus30064 wrote:
On 2010-07-10, Jon Elson wrote:

Ignoramus30064 wrote:

Karl, you and Ned have convinced me.

I am actually very happy, because I would get rid of a lot of cables
inside the control box, less complexity, less fear of tachs going bad
on me and the drives going berserk, etc.

I will use torque mode.

One last question, if someone could enlighten me, whi torque mode and
not "voltage mode"?

I am not trying to invent a better wheel with 4 minutes of experience,
or think that I know better than everyone, I just want to understand.


Why ruin what you already have working? What is the resolution of your
encoder?
Calculate what velocity will have less than 10 encoder counts coming in
per second,
and if this is any rational velocity like you might have while orbiting
a circular path,
then you will descend into stepwise movement. Don't fear a tach,
they've been used
for 50 years now in motion control systems.

Jon


Jon, my encoders are sinusoidal and thus I believe them to be
incompatible.

Well, yes, we went through that, but you said you were going to install
new encoders soon.

Jon

On 2010-07-10, Jon Elson wrote:
Calculate what velocity will have less than 10 encoder counts coming in
per second,
and if this is any rational velocity like you might have while orbiting
a circular path,
then you will descend into stepwise movement. Don't fear a tach,
they've been used
for 50 years now in motion control systems.

Jon


Jon, my encoders are sinusoidal and thus I believe them to be
incompatible.

Well, yes, we went through that, but you said you were going to install
new encoders soon.

Yes, I have new encoders.

I think that tach mode is still within the KISS principle.

i