Re: [CAD_CAM_EDM_DRO] Re: Better servo performance: Ameteks at 60V, 80V ?

ja_erickson wrote:

>
> I'm in the process of retrofitting a bridgeport boss 5 mill
> and have purchsed some ametek motors that are rated at 40 volts
> also.
>
> and if i remember correctly these motors have a 2000 count encoder
> on them,i was told that by using a 1000 count encoder that the overall
> r.p.m.'s of the motors would increase.

(Are those 2000 CPR or 2000 steps-in-quadrature? .... big difference!).

Here's my nickles worth (2 cents after taxes...):

DeanC ( http://www.axxustech.com/ ) once told me, the supplied voltage
to the Ametek motors could be increased (while limiting the maximum
step rate in the software). I think he was monitoring the voltage
at the motors, at the variously faster step rates.

Of course, you have to use restraint, because then increasing the step
rate of the software, increases the voltage seen at the motors (perhaps
beyond their tolerance). Please contact Dean directly if you have questions
on his method.

I have no experience with the 40V Ameteks myself, but to answer your second
question (in my 90VDC 2500rpm motor context):

- Using a 75VDC powersupply driving the 80VDC max Gecko G320/G340 there
is no over-voltage concern. However, the maximum rpm is then limited
to 2500rpm * 75VDC/90VDC = 2083 rpm = 34.72 rps

- Suppose your step engine (either software or hardware) can emit 25,000
steps/sec max. Then an optimal rotary encoder (I'm assuming the encoder is
mounted on the motor shaft) would be 25,000/34.72 = 720 steps-in-quadrature / revolution
(or 720/4= 180 CPR cycles per revolution).

- Suppose you actually had a 200 CPR encoder. Your step emitter source
will be limiting your fastest speed to less than the theoretical maximum motor speed.

- If you wanted to get the maximum speed from your motor (with your 25K step source),
you would need to DECREASE your resolution down to 180 CPR. However, 180 CPR
is uncommon, so you might consider a 150 CPR = 600 steps-in-quadrature encoder.
Then your performance (but not your resolution) would be optimal under the
circumstances (the circumstance being: voltage, motor rpm at that voltage,
the max frequency of your step source, and the encoder resolution).

Hope that helps.

Doug Fortune
http://www.cncKITS.com




















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