Re: [CAD_CAM_EDM_DRO] Re: Out of Estop.. BUT

imranjawaid@... wrote:

> > Well, the jerky motion is strange. How does this amp get velocity
> > feedback? Does it take the encoder signals, or is there a tach?
>
> The Amp Drive have three connectors
> CN1 -( Gets the DAC input <------- STG2 card)
> CN2 -( Get the encoder input --------> amp drive)
> CN3 -(Amp drive Sends the encoder singnals to the
> STG2 <-----Amp driver, i.e A+/- , B+/- , Marker +/- without the
> encoder 0v & 5V opartion voltage)

Ah, yes, instead of a DC tach, it uses the encoder for velocity
feedback. The problem is it has no velocity info between encoder
pulses, and the velocity info it does have gets 'bumpy' when the
speed is extremely low. My servo system, with DC tachs, can go
down to about .01 IPM before the stick-slip of the table overwhelms
the tach signal, and it starts to bump. This is so slow, you really
can't even see it, but you can read it off the position display.
The only way to do better is to go to a finer resolution encoder.

Matt Shaver and I tossed this problem about for some time, as
he wanted me to design an encoder to tach converter. My read
was that it would be VERY hard to do, and get both very fast
update at high speed and freedom of fluctuations in the output
at very low speeds. My servo system has meaningful bandwidth
up to sevral KHz, and so the delay of the conversion would have
to be kept very low. This is a killer digital filtering problem, and
is probably totally insoluble any other way.

Jon