Wether it would work or not I couldn't tell you. But I should say this -
The Fanuc drives I have experience with would not tolerate ANY
delays. If the motor makes even the slightest move without response from a
tach signal the drive will throw a TG alarm (Tacho Generator Failure). Keep
in mind that a true servo is always moving, be it ever so slightly, so it
will always see something from the tach. If those hurdles can be leaped over
it should work. The device would have to be able to be scaled for output so
you could use it for different servo systems as they all have different rpm
and tach outputs. Some use 3vdc/1000, 6vdc/1000, 7vdc/1000 etc. So the
output needed would depend on the servo system.
Dave
----- Original Message -----
From: "cogoman" <cogo...@verizon.net>
To: <emc-users@lists.sourceforge.net>
Sent: Saturday, March 20, 2010 4:02 PM
Subject: Re: [Emc-users] G52 and Fanuc conversion to EMC
> That price seems overkill to me too. I have been thinking about
> trying to develop a product for just this kind of situation. The
> solution seems simple, and inexpensive. Take an AVR microcontroller and
> have it monitor the Q-encoder signals. The program would start out
> counting the time between changes of the signals. When the RPMs get
> high enough it could switch to counting encoder events for a certain
> small amount of time. The RPM that is found would be converted to a DC
> voltage by a PWM signal from one of the counters. The PWM would always
> be clocked at a few MHz, so the RC filter would have a high corner
> frequency, and the DC voltage would be able to change faster than most
> (if not all) servo systems. For older servo motors that top out at
> about 2500 RPM this should be overkill.
> I originally had envisioned one uC at the encoder end that could
> generate A/-A, B/-B, and index pulse driven between +5V and ground
> (probably good for most noisy systems), as well as generating the analog
> voltage, but you probably wouldn't want a sensitive analog voltage
> traveling any length through an electrically noisy machine, so the
> quadrature to tachometer function would probably have to be done by a
> separate board and uC located in the same box as the servo drives. One
> positive, by locating it there you could probably have a uC with greater
> pin count and multiple timer/counters do quadrature to DC conversions
> for multiple channels at once.
> Unfortunately, this is still just an idea hamster's dream, as I
> haven't worked on it at all yet.
> Can I get a consensus on this one issue? Should the output of this
> device be +-10V? Seems to me that +-10V would be just right to make use
> of most older servo drives. Would $25 for a board that could convert 4
> channels to a tachometer voltage be overpriced (the board would be
> pretty basic, not having screw terminals, but holes for soldering in
> wires to connect it in).
>
>>>> I think I have located the answer for keeping the encoders
>>>> on
>>>> the motors. Follow this link:
>>>>
>>>> http://www.usdigital.com/products/etach2/
>>>>
>>>> Please tell me what you think.
>>>>
>>>> Dave
>>>>
>>>>
>>> Waaaayy out of my price range at $195/channel.
>>>
>
>
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