Picture

http://igor.chudov.com/misc/ebay/tmp...l/IMG_9530.JPG

This mill is a lot like my own Bridgeport Interact, except that it is
stepper motor powered, and mine is servo motor powered.

Steppers are a plus if you want to use Windows based Mach3, otherwise
servos are better.

I was told that it worked, however, I cannot be sure of this until I
bring it to my warehouse and test.

220v 3 phase.

i

Ignoramus30438 fired this volley in
:

http://igor.chudov.com/misc/ebay/tmp...l/IMG_9530.JPG

Oh, IG! You'll play hell getting much more than scrap value for that
unless your helper puts some _serious_ cleaning time into it.

(how much? G)

Lloyd

On 2012-06-09, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus30438 fired this volley in
:

http://igor.chudov.com/misc/ebay/tmp...l/IMG_9530.JPG

Oh, IG! You'll play hell getting much more than scrap value for that
unless your helper puts some _serious_ cleaning time into it.

(how much? G)


I have not decieded, but it will not be the top price and further
discount will be given to this ng. i will know when i bring it in.

i
KK
Lloyd

I ran one of these for quite a while. VERY rigid machine. Control was
a POS. Put Mach control on and be happy. it will take some serious
drivers to get the most out of this. I don't think Gecko goes that
big.

I'd suggest a VFD for the spindle.

Karl

Ignoramus9564 fired this volley in
:

The control on my Bridgeport was a POS too. It (Heidenhain) was great
for its time, of course, that that was 25 years ago. My control was
dead when I bought my mill.


Heh! I'm running on original electronics in my R2E4! But then, the
technology in that machine is what I made my first career around, so it's
"comfortable".

OTOH, there are a lot of features I'd love the mill to have, and only
going to EMC is going to solve that!

Lloyd

On 2012-06-09, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus9564 fired this volley in
:

The control on my Bridgeport was a POS too. It (Heidenhain) was great
for its time, of course, that that was 25 years ago. My control was
dead when I bought my mill.


Heh! I'm running on original electronics in my R2E4! But then, the
technology in that machine is what I made my first career around, so it's
"comfortable".

OTOH, there are a lot of features I'd love the mill to have, and only
going to EMC is going to solve that!

I love EMC and what it lets me do, the comfort and the convenience.

i

On 6/9/2012 4:44, Ignoramus30438 wrote:
This mill is a lot like my own Bridgeport Interact, except that it is
stepper motor powered, and mine is servo motor powered.

Steppers are a plus if you want to use Windows based Mach3, otherwise
servos are better.

Servos work fine with mach3 too.. Just use a servo controller that
accepts step and dir pulse inputs, like Granite devices VSD-E, for
easy interface..

Kristian Ukkonen.

On Sun, 10 Jun 2012 11:41:24 +0300, Kristian Ukkonen
wrote:

On 6/9/2012 4:44, Ignoramus30438 wrote:
This mill is a lot like my own Bridgeport Interact, except that it is
stepper motor powered, and mine is servo motor powered.

Steppers are a plus if you want to use Windows based Mach3, otherwise
servos are better.

Servos work fine with mach3 too.. Just use a servo controller that
accepts step and dir pulse inputs, like Granite devices VSD-E, for
easy interface..

Looks like about a $300-350 per axis addition, plus servo. Pricy!

--
Do not let your fire go out, spark by irreplacable spark.

In the hopeless swamps of the not quite, the not yet, and
the not at all, do not let the hero in your soul perish
and leave only frustration for the life you deserved, but
never have been able to reach.

The world you desire can be won, it exists, it is real,
it is possible, it is yours.
-- Ayn Rand

Kristian Ukkonen fired this volley in
:

Servos work fine with mach3 too.. Just use a servo controller that
accepts step and dir pulse inputs, like Granite devices VSD-E, for
easy interface..

I was told by the guys at MachMotion.com that Mach cannot keep up with
fine resolver or encoder inputs at any reasonable speeds. It must have a
physical motion controller between the computer and the drives in order
to handle things like threading or helical interpolation.

They represented that as a defect, and suggested that if I wanted to do
software gearing for threading ops, I should explore either EMC, or a
very expensive motion controller (that they would sell to me, but didn't
recommend, because of the cost of the lathe I wanted to convert).

LLoyd

On 2012-06-10, Kristian Ukkonen wrote:
On 6/9/2012 4:44, Ignoramus30438 wrote:
This mill is a lot like my own Bridgeport Interact, except that it is
stepper motor powered, and mine is servo motor powered.

Steppers are a plus if you want to use Windows based Mach3, otherwise
servos are better.

Servos work fine with mach3 too.. Just use a servo controller that
accepts step and dir pulse inputs, like Granite devices VSD-E, for
easy interface..

It is like saying, you can still walk with crutches if there kis
nothing wrong with your legs.

i

On 6/10/2012 16:10, Ignoramus15748 wrote:
On 2012-06-10, Kristian wrote:
On 6/9/2012 4:44, Ignoramus30438 wrote:
This mill is a lot like my own Bridgeport Interact, except that it is
stepper motor powered, and mine is servo motor powered.

Steppers are a plus if you want to use Windows based Mach3, otherwise
servos are better.

Servos work fine with mach3 too.. Just use a servo controller that
accepts step and dir pulse inputs, like Granite devices VSD-E, for
easy interface..

It is like saying, you can still walk with crutches if there kis
nothing wrong with your legs.

Pardon my English, but I didn't catch if that was a negative
or positive comment. I presume negative.

As far as I understand the problems with steppers a
- lose torque at high RPM
- misses steps

The servo amp with step/dir input solves these.

The torque remains high at high RPM like any servo motor.
The missed steps are not possible because the step/dir only
inputs to the servoamp position counter, so the actual motor
is still a closed-loop servo which can't "miss steps" as
the position feedback comes from a physical encoder.

There is also electronic gear in the servoamp, so it is
possible to have one input step to mean 0.01 or 100 or
whatever encoder steps. I use this with 100:1 electronic
gear in CNC mill spindle drive with MACH3 using step/dir
signal to servo amp.. Works ok with PC parallel port.

Of course, mach3 is not equivalent to some Fancy CNC
control from Siemens, Fanuc etc. but the cost is also
significantly less. The step/dir input servodrive makes
it possible to interface Mach3 to existing servomotors/
encoders.

Kristian Ukkonen.

On 6/10/2012 14:26, Larry Jaques wrote:
On Sun, 10 Jun 2012 11:41:24 +0300, Kristian Ukkonen
On 6/9/2012 4:44, Ignoramus30438 wrote:
This mill is a lot like my own Bridgeport Interact, except that it is
stepper motor powered, and mine is servo motor powered.

Steppers are a plus if you want to use Windows based Mach3, otherwise
servos are better.

Servos work fine with mach3 too.. Just use a servo controller that
accepts step and dir pulse inputs, like Granite devices VSD-E, for
easy interface..

Looks like about a $300-350 per axis addition, plus servo. Pricy!

Servos are not cheap. However, there is the double-axis model
where one of those serveamps runs two motors, halving the
price per motor.
http://www.granitedevices.fi/index.p...vo-drive-vsd-e
http://www.granitedevices.fi/index.p...e-dualdc-servo
I'm just a happy customer.

The main point was that if you have an existing CNC device
with servos and you wish to modernize it, one quite good option
(for amateurs) is Mach3 with a servo-amplifier having step/dir
input for direct interfacing to parallel port.

I just did that with Emco VMC100. The axis are actually 5-phase
steppers, and the spindle is servo-motor. I used Granite-devices
VSDEPI board to interface PC to the servoamp VSD-E and three stepper
drivers (vexta 2.8A drives). Those stepper drives I got used from
ebay, the granite stuff I had to buy new. Also I got a cheap
chinese modbus pendant for it. So far, I have been happy.

Kristian Ukkonen.

On Sun, 10 Jun 2012 16:43:35 +0300, Kristian Ukkonen
wrote:

On 6/10/2012 14:26, Larry Jaques wrote:
On Sun, 10 Jun 2012 11:41:24 +0300, Kristian Ukkonen
On 6/9/2012 4:44, Ignoramus30438 wrote:
This mill is a lot like my own Bridgeport Interact, except that it is
stepper motor powered, and mine is servo motor powered.

Steppers are a plus if you want to use Windows based Mach3, otherwise
servos are better.

Servos work fine with mach3 too.. Just use a servo controller that
accepts step and dir pulse inputs, like Granite devices VSD-E, for
easy interface..

Looks like about a $300-350 per axis addition, plus servo. Pricy!

Servos are not cheap.

That's why I'll be using steppers.



However, there is the double-axis model
where one of those serveamps runs two motors, halving the
price per motor.
http://www.granitedevices.fi/index.p...vo-drive-vsd-e
http://www.granitedevices.fi/index.p...e-dualdc-servo
I'm just a happy customer.

Cool!


The main point was that if you have an existing CNC device
with servos and you wish to modernize it, one quite good option
(for amateurs) is Mach3 with a servo-amplifier having step/dir
input for direct interfacing to parallel port.

Yes, good point.


I just did that with Emco VMC100. The axis are actually 5-phase
steppers, and the spindle is servo-motor. I used Granite-devices
VSDEPI board to interface PC to the servoamp VSD-E and three stepper
drivers (vexta 2.8A drives). Those stepper drives I got used from
ebay, the granite stuff I had to buy new. Also I got a cheap
chinese modbus pendant for it. So far, I have been happy.

Great. I hope to have my CNC router up and running by mid July. I'm
slowly but surely getting my shop cleared out enough to finish it, but
I've had ten years to stuff it, so it's slow going.

Here's the metal portion of it so far: http://tinyurl.com/8329kzz
Once I clear the shop enough, I'll strip it, paint it, finish a few
clearance mods on the gantry, and start to test.

--
Doctors prescribe medicine of which they know little,
to cure diseases of which they know less,
in human beings of which they know nothing.
--Francois-Marie Arouet Voltaire, about 250 years ago

On 2012-06-10, Kristian Ukkonen wrote:

On 6/10/2012 22:27, Ignoramus15748 wrote:
On 2012-06-10, Kristian wrote:
There is also electronic gear in the servoamp, so it is
possible to have one input step to mean 0.01 or 100 or
whatever encoder steps. I use this with 100:1 electronic
gear in CNC mill spindle drive with MACH3 using step/dir
signal to servo amp.. Works ok with PC parallel port.

What is this electronic gear, is that for threading?

It is just possible to match the pulse output capability
of the controller and the servodrive.

At my spindle, I would need 3000RPM * 2000ppr / 60 min/s = 100kHz
pulse rate at step input to get full speed. With 100:1 electronic
gear, I get the same speed with 1kHz pulse rate, which is realistic
with PC parallel port.

Of course, the spindle angular accuracy is also just
2000/100=20 pulses per revolution. Works for me as I just
need the spindle servo control for running tool changer
(which is a EMCO hack where tool changer carousel runs with
spindle servo motor through a gear touching spindle gear
only in tool change position of Z, outside normal Z range).

This kind of little machine (google image found this link, not mine)
http://www.ebay.com/itm/EMCO-CNC-Mil...-/190679550995
I replaced the right electronics unit with a little box of
modern electronics, bolted to the side of the main unit.

Kristian Ukkonen.

Very nice. You can make small stuff with it, like jewelry or
whatnot. Looks very practical and sophisticated.

Here's my mill

http://igor.chudov.com/projects/Brid...ct-2-CNC-Mill/


i

On Sun, 10 Jun 2012 15:47:19 -0500, Ignoramus15748
wrote:

On 2012-06-10, Kristian Ukkonen wrote:

On 6/10/2012 22:27, Ignoramus15748 wrote:
On 2012-06-10, Kristian wrote:
There is also electronic gear in the servoamp, so it is
possible to have one input step to mean 0.01 or 100 or
whatever encoder steps. I use this with 100:1 electronic
gear in CNC mill spindle drive with MACH3 using step/dir
signal to servo amp.. Works ok with PC parallel port.

What is this electronic gear, is that for threading?

It is just possible to match the pulse output capability
of the controller and the servodrive.

At my spindle, I would need 3000RPM * 2000ppr / 60 min/s = 100kHz
pulse rate at step input to get full speed. With 100:1 electronic
gear, I get the same speed with 1kHz pulse rate, which is realistic
with PC parallel port.

Of course, the spindle angular accuracy is also just
2000/100=20 pulses per revolution. Works for me as I just
need the spindle servo control for running tool changer
(which is a EMCO hack where tool changer carousel runs with
spindle servo motor through a gear touching spindle gear
only in tool change position of Z, outside normal Z range).

This kind of little machine (google image found this link, not mine)
http://www.ebay.com/itm/EMCO-CNC-Mil...-/190679550995
I replaced the right electronics unit with a little box of
modern electronics, bolted to the side of the main unit.

Kristian Ukkonen.

Very nice. You can make small stuff with it, like jewelry or
whatnot. Looks very practical and sophisticated.

Here's my mill

http://igor.chudov.com/projects/Brid...ct-2-CNC-Mill/


i
pic is still in the garage. Thought you gave that space back to your
boss.

Karl

On 2012-06-10, Karl Townsend wrote:
On Sun, 10 Jun 2012 15:47:19 -0500, Ignoramus15748
wrote:

On 2012-06-10, Kristian Ukkonen wrote:

On 6/10/2012 22:27, Ignoramus15748 wrote:
On 2012-06-10, Kristian wrote:
There is also electronic gear in the servoamp, so it is
possible to have one input step to mean 0.01 or 100 or
whatever encoder steps. I use this with 100:1 electronic
gear in CNC mill spindle drive with MACH3 using step/dir
signal to servo amp.. Works ok with PC parallel port.

What is this electronic gear, is that for threading?

It is just possible to match the pulse output capability
of the controller and the servodrive.

At my spindle, I would need 3000RPM * 2000ppr / 60 min/s = 100kHz
pulse rate at step input to get full speed. With 100:1 electronic
gear, I get the same speed with 1kHz pulse rate, which is realistic
with PC parallel port.

Of course, the spindle angular accuracy is also just
2000/100=20 pulses per revolution. Works for me as I just
need the spindle servo control for running tool changer
(which is a EMCO hack where tool changer carousel runs with
spindle servo motor through a gear touching spindle gear
only in tool change position of Z, outside normal Z range).

This kind of little machine (google image found this link, not mine)
http://www.ebay.com/itm/EMCO-CNC-Mil...-/190679550995
I replaced the right electronics unit with a little box of
modern electronics, bolted to the side of the main unit.

Kristian Ukkonen.

Very nice. You can make small stuff with it, like jewelry or
whatnot. Looks very practical and sophisticated.

Here's my mill

http://igor.chudov.com/projects/Brid...ct-2-CNC-Mill/


i
pic is still in the garage. Thought you gave that space back to your
boss.

Yes, I moved it to my warehouse.

i

On Sun, 10 Jun 2012 14:22:52 -0500, Ignoramus15748
wrote:

On 2012-06-10, Larry Jaques wrote:
Here's the metal portion of it so far: http://tinyurl.com/8329kzz
Once I clear the shop enough, I'll strip it, paint it, finish a few
clearance mods on the gantry, and start to test.

Looks awesome!

I will have some router heads for sale. They might be too big for this
one, though.

I have a 2-1/4 HP Hitachi M12VC and a pair of precision collets for it
which ought to handle the task well. Some day, when it grows up, it
may have a real spindle on it.

--
Doctors prescribe medicine of which they know little,
to cure diseases of which they know less,
in human beings of which they know nothing.
--Francois-Marie Arouet Voltaire, about 250 years ago

On 2012-06-10, Kristian Ukkonen wrote:
On 6/9/2012 4:44, Ignoramus30438 wrote:
This mill is a lot like my own Bridgeport Interact, except that it is
stepper motor powered, and mine is servo motor powered.

Steppers are a plus if you want to use Windows based Mach3, otherwise
servos are better.

Servos work fine with mach3 too.. Just use a servo controller that
accepts step and dir pulse inputs, like Granite devices VSD-E, for
easy interface..

In my opinion, the drivers which accept step and direction
pulses to run a servo motor throw away some of the benefits of servo
motors, including smooth motion and the ability to traverse
intermediate values without leaving steps in the workpiece. After all
-- even though the motor is capable of intermediate positions, the
controller is not capable of commanding them to reach those positions
if it has to treat them as steppers.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
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 11 Jun 2012 03:29:58 GMT, the renowned "DoN. Nichols"
wrote:

On 2012-06-10, Kristian Ukkonen wrote:
On 6/9/2012 4:44, Ignoramus30438 wrote:
This mill is a lot like my own Bridgeport Interact, except that it is
stepper motor powered, and mine is servo motor powered.

Steppers are a plus if you want to use Windows based Mach3, otherwise
servos are better.

Servos work fine with mach3 too.. Just use a servo controller that
accepts step and dir pulse inputs, like Granite devices VSD-E, for
easy interface..

In my opinion, the drivers which accept step and direction
pulses to run a servo motor throw away some of the benefits of servo
motors, including smooth motion and the ability to traverse
intermediate values without leaving steps in the workpiece. After all
-- even though the motor is capable of intermediate positions, the
controller is not capable of commanding them to reach those positions
if it has to treat them as steppers.

Enjoy,
DoN.

What difference does it make if the steps are small enough?

Digital commands will always have some finite resolution, even if it's
nanometers.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

"Karl Townsend" wrote in message
...
I ran one of these for quite a while. VERY rigid machine. Control was
a POS. Put Mach control on and be happy. it will take some serious
drivers to get the most out of this. I don't think Gecko goes that
big.

If its servo no problem for that size machine. The G320X is rated 80VDC 20
amps. Viper is rated higher, but support is slower.

If its stepper, most people think of the G540 which really doesn't handle
much larger than about 380oz/in and then only those that will get to full
torque at 50VDC and 3.5 amps or less per stepper. However while the G540 is
a nicely packaged combo of a breakout and 4 250 stepper drivers its one of
the less powerful controllers they sell.

The 201, 203, 210, and 213 will all handle 80VDC and 7 amps per driver.

The claim they design with about a 20% safety margin.

I'd suggest a VFD for the spindle.

Absofrigginglutely. VFDs are awesome. I will probably wind up with 3 of
them inside the high voltage cabinet on the Hurco by the time I get it done.
I already have two in there. (Main spindle and spindle cooling fan
currently, going to add a 4th vertical axis (Linear A that I can swap with Z
when I need it) with a high speed spindle eventually.)

....
If its stepper, most people think of the G540 which really doesn't handle
much larger than about 380oz/in and then only those that will get to full
torque at 50VDC and 3.5 amps or less per stepper. However while the G540 is
a nicely packaged combo of a breakout and 4 250 stepper drivers its one of
the less powerful controllers they sell.


prettys sure its a 2000 oz/in stepper that doesn't do microstepping.
It may do 1/2 steps IIRC. I seem to remember my AHHA drivers were
rated 12amp at 50 volt and they were still undersize.

Karl

On 2012-06-11, Spehro Pefhany wrote:
On 11 Jun 2012 03:29:58 GMT, the renowned "DoN. Nichols"
wrote:

On 2012-06-10, Kristian Ukkonen wrote:

[ ... ]

In my opinion, the drivers which accept step and direction
pulses to run a servo motor throw away some of the benefits of servo
motors, including smooth motion and the ability to traverse
intermediate values without leaving steps in the workpiece. After all
-- even though the motor is capable of intermediate positions, the
controller is not capable of commanding them to reach those positions
if it has to treat them as steppers.

Enjoy,
DoN.

What difference does it make if the steps are small enough?

Because the steps may *not* be small enough. This is certainly
the case with my Emco-Maier Compact-5/CNC lathe. A little lathe made
mostly for teaching CNC machining. The minimum step (from the program
point of view) is either 0.01mm or 0.001" depending on the position of a
front panel switch. The steps are in metric units, so the inch units
wind up with patterns like:

0.001-0.002- -0.004 0.005- -0.007

And -- to make it worse, the cross-feed steps have to translate into
diameter, so a slow taper like a Morse is visibly stepped.

And if you are going to say -- finer steps and step faster, that
machine *can't* step fast enough as it is. As an example, when
threading with a fairly coarse thread, you have to slow down to 180 RPM
(or sometime slower) on the spindle so the CPU can keep up with stepping
the longitudinal feed at the right times. The CPU is an ancient 6502,
and has little enough memory so finer steps would reduce the nubmer of
program lines possible -- because the input is fixed format.

Digital commands will always have some finite resolution, even if it's
nanometers.

Of course. But steppers run fast can introduce resonance in the
leadscrews -- and the same applies to servos pretending to be steppers.

Oh yes -- the fineness of the steps with a servo pretending to
be a stepper is limited by the resolution of the encoder on the servo's
shaft. Used as a true servo, the computer simply outputs a voltage
saying "go so many RPM" and the servo amp takes care of keeping that
happening. The computer simply checks every so often to make sure that
the speed is right, and if it is a little too fast or slow, it changes
the output voltage just enough to fix that speed. And this gives a
smooth travel between the two end points, even in the areas where the
encoders don't have resolution to tell the difference.

The only disadvantage to true servo operation that I can see is
that if the computer hangs up (say a Windows box which experiences BSOD
-- Blue Screen Of Death), each axis will keep going at the last
commanded speed -- until it hits a limit which should be wired to shut
it down fully. With steppers, a hung computer will stop outputing
pulses, and the motor will stop. Likely a spoiled job in either case,
but less potentially exciting with the steppers.

And with servos in home machines, it is likely being controlled
by what used to be called EMC, and is now LinuxCNC, which runs in a real
time engine under the linux OS' kernel, so a hang is less likely.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
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 6/12/2012 6:58, DoN. Nichols wrote:
The only disadvantage to true servo operation that I can see is
that if the computer hangs up (say a Windows box which experiences BSOD
-- Blue Screen Of Death), each axis will keep going at the last
commanded speed -- until it hits a limit which should be wired to shut
it down fully. With steppers, a hung computer will stop outputing
pulses, and the motor will stop. Likely a spoiled job in either case,
but less potentially exciting with the steppers.

There is a solution for this also, pulse input that requires
pulses from the controller all the time, and if pulses stop
(controller hangs), it disables drives. My mach3 system is
built like that. In Mach3 it is called "change pump" output.

Kristian Ukkonen.

Kristian Ukkonen fired this volley in
:

My mach3 system is
built like that. In Mach3 it is called "change pump" output.

In other parlances, that's called a "dead man signal". Common on all
mission-critical computers.

The name comes from the pedal or lever that railroad engineers had to keep
depressed all the time for the locomotive to move. If they fell off the
"dead man switch", the engine stopped.

Lloyd

On Tue, 12 Jun 2012 22:48:58 +0300, Kristian Ukkonen
wrote:

On 6/12/2012 6:58, DoN. Nichols wrote:
The only disadvantage to true servo operation that I can see is
that if the computer hangs up (say a Windows box which experiences BSOD
-- Blue Screen Of Death), each axis will keep going at the last
commanded speed -- until it hits a limit which should be wired to shut
it down fully. With steppers, a hung computer will stop outputing
pulses, and the motor will stop. Likely a spoiled job in either case,
but less potentially exciting with the steppers.

There is a solution for this also, pulse input that requires
pulses from the controller all the time, and if pulses stop
(controller hangs), it disables drives. My mach3 system is
built like that. In Mach3 it is called "change pump" output.

I believe you meant "charge pump", Kristian.

--
Doctors prescribe medicine of which they know little,
to cure diseases of which they know less,
in human beings of which they know nothing.
--Francois-Marie Arouet Voltaire, about 250 years ago

Lloyd E. Sponenburgh wrote:
Kristian fired this volley in
:

My mach3 system is
built like that. In Mach3 it is called "change pump" output.

In other parlances, that's called a "dead man signal". Common on all
mission-critical computers.

The name comes from the pedal or lever that railroad engineers had to keep
depressed all the time for the locomotive to move. If they fell off the
"dead man switch", the engine stopped.

Unless the engineer put a big piece of
wood on it to hold it down.

My dad was a trainman and I rode the engine
a few times as a boy.

On 2012-06-12, Kristian Ukkonen wrote:
On 6/12/2012 6:58, DoN. Nichols wrote:
The only disadvantage to true servo operation that I can see is
that if the computer hangs up (say a Windows box which experiences BSOD
-- Blue Screen Of Death), each axis will keep going at the last
commanded speed -- until it hits a limit which should be wired to shut
it down fully. With steppers, a hung computer will stop outputting
pulses, and the motor will stop. Likely a spoiled job in either case,
but less potentially exciting with the steppers.

There is a solution for this also, pulse input that requires
pulses from the controller all the time, and if pulses stop
(controller hangs), it disables drives. My mach3 system is
built like that. In Mach3 it is called "change pump" output.

But since Mach3 does not do "true servo" operation -- only
servos pretending to be steppers, so if the computer hangs up, Mach3
stops producing pulses anyway.

The "servo pretending to be a stepper" is accomplished by a
counter controlled by the step and direction pulses, and another one by
the encoder on the servo motor. The Gecko servo driver is an example of
this design.

Typically, there will be a circuit comparing the count in each
of the two counters, and producing a voltage proportional to the
difference between the two counts. The step and direction pulses get a
burst to move to a higher value, and the voltage difference starts the
motor moving (speed dependent on the difference) which starts counting
encoder pulses until the two are equal again. This circuitry is totally
separate from the computer, so if the computer hangs it stops outputting
pulses, so there is no problem. (This unless the computer is asked to
be part of the driver too, which I have not yet encountered.

So the only place where I would expect this problem to show up
is when using a servo as a true servo -- controller outputs a desired
speed voltage, not pulses, and the servo amp (driver) simply runs the
motor at that speed until it is changed.

As for the hanging problem, computers designed to run unix have
in their hardware a "watchdog timer" -- the OS pokes at it once every so
many milliseconds, and if it does not get a poke in so-many + 10% or so
milliseconds, it generates a pulse which resets the computer, starting a
reboot, and hopefully, the card generating the speed command voltages
will sense that reset and adjust the output voltages to zero. But in
any case, the axes with true servos should have limit switches to shut
down the servo amps to prevent crashes. Again -- something which does
not depend on the computer.

Enjoy,
DoN.

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