Re: [CAD_CAM_EDM_DRO] To convert Quadrature Encoder signals to Tachogenerator signals

Babar wrote:

>Yes , my aaplication is a DC servo motor for X-Axis of
>a turning center .Actually the motor and Drive
>(A20B-0007-0361) are both from Fanuc , The Drive have
>3 different modes of operations:
>
>1) Tacho 3V
>2) Tacho 6 V
>3) Pulse Encoder +F/V
>
>In my machine the servo motor does not have the Tacho
>and the drive was running in 3rd mode, the F/V logic
>was implemented in orignal CNC control, which I am
>replacing with Powerautomation GmbH CNC control.
>

Oh, we KNOW about this one! We ran into the same thing on
the Mazak conversion at Roland Freistad's. The servo amps
(Fanuc A06B, I vaguely recall) were velocity servos, plain.
The CNC control generated signals to simulate the tachometer
feedback, and sent this to the servo amp.

I'm not sure exactly what the group did to solve this problem,
but they apparently got a F/V converter that was made for
exactly this purpose.
OH, I finally found it, they changed out the amps to Servo Dynamics.
I still think they could have used the old ones, but the first machine
had phase-control SCR drives. UGH! Those SHOULD be changed!
See more detail than you want at
http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?MazakRetro

>
>Pete and Jon Elson are right about using the F to V
>circuit, The main problem for me is how to convert the
>sign of the analog voltage generated by the F/V, Jon,
>you have recommended some "Linear inverter"
>

This is a simple op-amp, with a switch to flip the polarity.
I will attempt ascii art here :




----/\/\/\/\--
| |
R R | |\ |
Input -------/\/\/\/\-----/\/\/\/\------ |-\ |
| | | \ |
| A o | \-------- Output
| R/2 R/2 | /
|-/\/\/\/\------/\/\/\/\---------|+ /
| | | /
| | |/
o | R |
B |--/\/\/\/\--| | . (Gnd)
|


In this circuit Ressistor R are all same value, R/2 are half that value.
When circuit point A is grounded, the amp is inverting, when circuit
point B is grounded, the circuit is non-inverting. You need to set
up MOS switches to do this grounding.

> and
>"quadrature to step/direction converter "
>

Here's a circuit right in our own files section. I put in the
triangle brackets, so hopefully the link will work right :
<http://f1.grp.yahoofs.com/v1/EBfRQ7c69mR-gvi4N1lI3XKhUbRmzFzc6htQVHMMV09BeMrVGS3RqYn-Mc4cpyQKnuJc11ymfTUWxYdX2oNB0zOGIIbW/CIRCUITS/Pulse%20Gen%20%20and%20Timing%20Circuits/Quad2StepDir.pdf>

>for this
>purpose ,could you please give me some link to where I
> can find these circuit schematics?The Pulse coder
>installed in the motor is of 2500 cpr.
>
>before this discussion ,I myself was planning to use
>the drive in mode 1 or 2 and for this purpose to use
>2 F/V ICs with a 4066 analog switch for the sign
>conversion of the analog voltage, but I don't know
>whether this circuit will be fast enough to meet the
>servo's requirement.
>
>
>

Yes, it should. The problem is there will be a discontinuity between
the two signs, which will cause instability at (near) rest. that's why
one circuit bot both directions is better. You put the smoothing after
the sign inverter. The 4066 swich is fine, but needs to be run from a
-5 +5 Volt supply so it can handle the range of analog signals. Then,
the signals to command the switches need to be level translated to
+/- 5 V levels (one transistor for each switch).

Jon