Re: step/dir servo (Gecko drives)

--- In CAD_CAM_EDM_DRO@egroups.com, Jon Elson <jmelson@a...> wrote:

> Probably most of it. The PWM drive can only produce an output

voltage a

> little less than the
> DC supply, perhaps 90 - 95% of the supply voltage, depending on how
> close it can go
> to 100% modulation. (Mine can go to 100%, but you still lose a

little

> voltage across the
> transistors. Also, if you drive the servo into saturation, it
> introduces a discontinuity
> in the transfer function, which upsets the stability of the servo

loops,

> so you shouldn't
> really count on going to saturation for best results.)
>
> Also, the series resistance of the motor armature windings is in

series

> with the
> source. If your motors have a 1 Ohm winding, and the amplifier's

FETs

> have
> an equivalent of, say, 2 Ohms, then you have 3 Ohms in series with

the

> power
> source. So, if your motors need 3 amps to move the machine under

some

> (presumably light) load, the voltage drop is 3 Ohms x 3 Amps = 9

Volts.

> If your supply is 75 V, 90% of that is 67.5, then 67.5 - 9 = 58.5 V.
> Given
> these rough numbers, you should be able to get a rapid feed rate

equal

> to
> the motor's free-running speed at 58.5 V when loaded by the machine.
>
> This should give you a very rough idea how to guesstimate the

required

> voltage to get some specific performance, within maybe 15% accuracy.
>
> Jon

Hi,

Actually the drive resistance is on the order of 1/8 of an ohm and
the modulation limit setpoints are at 1.5% and 98.5%. This is to
allow proper operation of the top MOSFET boot-strap gate drive supply
circuit.

I just ran a panel (12 drives) thru the SMT machine of the production
G320s and hand assembled one drive to test the production boards for
errors. It worked to my satisfaction.

I get the pulse multiplier boards in early next week. If they work as
well as the breadboard then it should get interesting.

Mariss