Servo amp question
 

I'm using a dc motor & a servo amp to run the lead screw on my lathe.
The servo amp is an Advanced Motion Controls model 25A20:
http://www.a-m-c.com/download/datasheet/25a20i.pdf

I'm setting the speed with an analog input on pins 4 & 5 ("REF"). This
is described as "Differential Reference Input (±10 V Operating Range,
±15 V Maximum Input)". My assumption was that this voltage could go to
15v, but beyond 10v there would be no additional effect on the output.
I was wrong. The output continues to increase as REF increases to 15v.
I didn't check if it was linear in the 10 - 15v range.

The question is: is it a bad idea to use it in the 10-15v range? It
might be useful to have the extra output in certain special cases. E.g.
rapid reverse.

Thanks,
Bob

PS - is there another NG that might be better posted to?

Servo amp question
 

Bob Engelhardt fired this volley in
:
PS - is there another NG that might be better posted to?

Yep... sign up in CNCZone.com, and join the fora there, where there are
folks who do this stuff every day.

LLoyd

Servo amp question
 

On Fri, 16 Jan 2009 21:58:54 -0500, Bob Engelhardt
wrote:

I'm using a dc motor & a servo amp to run the lead screw on my lathe.
The servo amp is an Advanced Motion Controls model 25A20:
http://www.a-m-c.com/download/datasheet/25a20i.pdf

I'm setting the speed with an analog input on pins 4 & 5 ("REF"). This
is described as "Differential Reference Input (±10 V Operating Range,
±15 V Maximum Input)". My assumption was that this voltage could go to
15v, but beyond 10v there would be no additional effect on the output.
I was wrong. The output continues to increase as REF increases to 15v.
I didn't check if it was linear in the 10 - 15v range.

The question is: is it a bad idea to use it in the 10-15v range? It
might be useful to have the extra output in certain special cases. E.g.
rapid reverse.

I've used a lot of AMC amps and don't recall having to go beyond a 10V
input to get full output. Do you have the gain pot turned all the way
up? I assume you're running in voltage mode, not current mode, yes?

The input is probably limited to +-15V because the op amp at the input
has a +-15V supply and most op amps don't like voltages outside their
supply on the inputs. If you need a 15V reference to get full output,
it shouldn't be a problem. But I think you should be able to get there
with a 10V signal, or even less.

--
Ned Simmons

Servo amp question
 

"Bob Engelhardt" wrote in message
...
I'm using a dc motor & a servo amp to run the lead screw on my lathe. The
servo amp is an Advanced Motion Controls model 25A20:
http://www.a-m-c.com/download/datasheet/25a20i.pdf

I'm setting the speed with an analog input on pins 4 & 5 ("REF"). This is
described as "Differential Reference Input (±10 V Operating Range, ±15 V
Maximum Input)". My assumption was that this voltage could go to 15v, but
beyond 10v there would be no additional effect on the output. I was wrong.
The output continues to increase as REF increases to 15v. I didn't check
if it was linear in the 10 - 15v range.

The question is: is it a bad idea to use it in the 10-15v range? It might
be useful to have the extra output in certain special cases. E.g. rapid
reverse.

Thanks,
Bob

PS - is there another NG that might be better posted to?

+ & - 10V is a pretty common servo connection. You should be able to adjust
gain and perhaps signal pots to give you the full speed at 10V input if that
is what you desire. I'd recommend adjusting the drive to give you the
speeds you need (or maximum speed) with the 10V input, it may be easier on
the electronics and would be more likely to be compatible if you needed to
replace the drive some day. My CNC lathe has 240ipm rapids and this is done
with a +-10V input to the servo drives.

RogerN

Servo amp question
 

Bob,
Normally, the differential input is supposed to generate a linear output of
the amp, where the amp output between min and max is a differential function
between 0 and the reference voltage you apply to the ref pin. I believe the
15 volt number you quoted is the max reference voltage you are allowed to
use by the manufacturer, not a must be number. This is how OP amps work. The
amp is linear. You, as the end user, determine the linearity range by
voltage assignment to the ref pin.
Steve

"Bob Engelhardt" wrote in message
...
I'm using a dc motor & a servo amp to run the lead screw on my lathe. The
servo amp is an Advanced Motion Controls model 25A20:
http://www.a-m-c.com/download/datasheet/25a20i.pdf

I'm setting the speed with an analog input on pins 4 & 5 ("REF"). This is
described as "Differential Reference Input (±10 V Operating Range, ±15 V
Maximum Input)". My assumption was that this voltage could go to 15v, but
beyond 10v there would be no additional effect on the output. I was wrong.
The output continues to increase as REF increases to 15v. I didn't check
if it was linear in the 10 - 15v range.

The question is: is it a bad idea to use it in the 10-15v range? It might
be useful to have the extra output in certain special cases. E.g. rapid
reverse.

Thanks,
Bob

PS - is there another NG that might be better posted to?

Servo amp question
 

Bob,
One more point. Op amps are really neat. I quoted the case of a static
voltage at the ref pin, but it can also be dynamic, where you may wish to
adjust the output of the motor drive dependant on carriage velocity. You
would then find a tachometer (linear DC generator) and apply that voltage
through another Op amp to the reference pin on the motor driver. If you use
a negative voltage and not ground it is also possible to use the motor drive
as a dynamic brake. You have lots and lots of options here. The data sheet
from the manufacturer is your friend.
Steve

"Bob Engelhardt" wrote in message
...
I'm using a dc motor & a servo amp to run the lead screw on my lathe. The
servo amp is an Advanced Motion Controls model 25A20:
http://www.a-m-c.com/download/datasheet/25a20i.pdf

I'm setting the speed with an analog input on pins 4 & 5 ("REF"). This is
described as "Differential Reference Input (±10 V Operating Range, ±15 V
Maximum Input)". My assumption was that this voltage could go to 15v, but
beyond 10v there would be no additional effect on the output. I was wrong.
The output continues to increase as REF increases to 15v. I didn't check
if it was linear in the 10 - 15v range.

The question is: is it a bad idea to use it in the 10-15v range? It might
be useful to have the extra output in certain special cases. E.g. rapid
reverse.

Thanks,
Bob

PS - is there another NG that might be better posted to?

Servo amp question
 

Bob Engelhardt wrote:

The question is: is it a bad idea to use it in the 10-15v range? It
might be useful to have the extra output in certain special cases. E.g.
rapid reverse.

Are you just doing a battery box test at the moment?
What voltage range does your control emit? Your voltage range may have been decided for
you already.

Wes

Servo amp question
 

Bob Engelhardt wrote:

I'm using a dc motor & a servo amp to run the lead screw on my lathe.
The servo amp is an Advanced Motion Controls model 25A20:
http://www.a-m-c.com/download/datasheet/25a20i.pdf

I'm setting the speed with an analog input on pins 4 & 5 ("REF"). This
is described as "Differential Reference Input (±10 V Operating Range,
±15 V Maximum Input)". My assumption was that this voltage could go to
15v, but beyond 10v there would be no additional effect on the output. I
was wrong. The output continues to increase as REF increases to 15v. I
didn't check if it was linear in the 10 - 15v range.

The question is: is it a bad idea to use it in the 10-15v range? It
might be useful to have the extra output in certain special cases. E.g.
rapid reverse.

Thanks,
Bob

PS - is there another NG that might be better posted to?


The standard control voltage used are +/- 10 vdc. The 15 volt spec. is
the maximum that the servo amp can handle. The input voltage vs. the
speed of the drive is determined by the gain of the drive. The output
of the drive is determined by the hp rating of the drive itself and the
asssociated servo motor. At the full 10 volt +- rating you should be
operating the drive at near the full hp rating of the drive and motor.
This is accomplished by adjusting the gain of the drive and at the same
time measuring the output power to the motor or input current to the
drive and checking it with the mfgr specs.

have fun..


John

Servo amp question
 

Thanks for all the responses. To clarify what I'm doing: I had set the
gain on the servo to give a maximum feed rate of 1/2" / second, with a
10v input. I have an op-amp controller feeding the servo 0 - 10v. But
I can get an out-of-bounds condition where the op amp output is 15v.

So I think that I'll put a 10v zener clamp on my controller output for
the forward feed, but use -15v for the more-rapid reverse.

Bob

BTW - this is turning out very nicely & I expect to be writing it up for
the DropBox.