Emc and servos

[cnc-it]

Hi I'm just starting to learn about EMC and was wondering what feedback is needed from servo motors.
Am I correct that if I have encoders but no tachos then I will need a frequency to velocity converter to give EMC both position and speed feedback.

I have Fanuc dc yellow cap motors and Fanuc analogue drives.

By the way how well does G41 G42 cutter comp work in EMC...is it reliable..?

John.

[jmelson]

Originally Posted by cnc-it Hi I'm just starting to learn about EMC and was wondering what feedback is needed from servo motors. Am I correct that if I have encoders but no tachos then I will need a frequency to velocity converter to give EMC both position and speed feedback.

No, you do not need tachometers for EMC. If you use an analog velocity servo amp such as a Copley, AMC, Servo Dynamics, etc. that requires velocity feedback, then it will need a tachometer.

I have Fanuc dc yellow cap motors and Fanuc analogue drives.

OK, so the Fanuc control generates the velocity signal from the encoder pulses. There are boxes to do this, but they get fairly expensive. The Fanuc amps can be set for torque mode, but that requires some rewiring and a total retuning.

By the way how well does G41 G42 cutter comp work in EMC...is it reliable..? John.

G41/42 work quite well, but they do require strictly avoiding gouging the work side.
Some controls are quite forgiving on that. The techniques to avoid the gouges are pretty simple when setting up lead-in and lead-out points.

Jon

[atex57]

Lead-in and inside corner radius approaches have changed considerably lately. I am running 2.3.4 on my Wells-Index and can command it to do a inside square pocket without using inside radii. The tool simply drives to the tangent point of the next wall and makes a corner leaving the radius of the cutter. Makes it much simpler on inside pockets. You do still have to use a lead-in but it can actually be from the opposite direction from the previous conventions. The lead-in must be long enough that the radius of the cutter can clear the next line. Ed.

[cnc-it]

Thanks for the replies guys, just what I was after.
I didn't know my drives could be set for torque mode..will have to look into this one!

John.

[kudos]

with fanuc yellow caps and drives should't it be more of a case supply a +/-10v analog from EMC to drives, while reading encoder from motor for position and PID loop

do your motors have a tacho? most do which the drive will use for speed feedback, this normal goes straight into the drive so servo is in Velocity mode.

EMC can then close the loop for you again from the PID in EMC
ud need something like mesa cards to give you the analog out.

rob

[elrado]

Hi

I could offer two chanel encoder-to-tacho signal converter, which distributes the encoder signals to the CNC at a reasonable price - 100 EUR.
Also I could offer FANUC caompatible servoamplifiers for all FANUC yellow cap motors. Analog DC4QR (supports current mode) and digital DC4QR-D (suppoorts STEP/DIR interface)
For more information www.semis.hit.bg

Best regards
Radoslav Tchipanov

[jmelson]

Originally Posted by kudos with fanuc yellow caps and drives should't it be more of a case supply a +/-10v analog from EMC to drives, while reading encoder from motor for position and PID loop do your motors have a tacho? most do which the drive will use for speed feedback, this normal goes straight into the drive so servo is in Velocity mode. EMC can then close the loop for you again from the PID in EMC ud need something like mesa cards to give you the analog out. rob

The Fanuc Yellow Cap motors generally do NOT have a tachometer. That function was performed by the CNC control, converting encoder counts to an analog velocity signal to close the velocity loop at the servo amp. When you pull the old control out, you lose that function.

Yes, in theory, you could use the analog output of the Mesa to do this, but it needs to have pretty good resolution. The Pico Systems PPMC has a 16-bit DAC, so you get 8192 discrete values in both positive and negative polarities. I think the Mesa only has a 12-bit DAC, so you only get 2048 values in each polarity. I don't know if this granularity would affect the stability of the servo
amp.

Jon

[kudos]

Originally Posted by jmelson The Fanuc Yellow Cap motors generally do NOT have a tachometer. That function was performed by the CNC control, converting encoder counts to an analog velocity signal to close the velocity loop at the servo amp. When you pull the old control out, you lose that function Jon

I see what you mean never really noticed this before looking into it, had a look in tech manuals and at one of the machines today
i see you can use a tacho tho with drives no problem if u had one or could pick one up
just need a 7.5V/1000RPM & drive jumper change etc
then ether move the encoder to the screw or make a spacer or something up for both to live on the motor end.

to buy a tacho might cost as much as a converter board though i guess?

rob

[elrado]

Two channel encoder -to tacho converter (i.e. for two axis) costs 100 EUR
Radoslav

[cnc-it]

Thanks elrado I have your site on my favorites now. Looks to be just what is needed. A tach signal could be fed to the drive and the encoder signal to EMC...?

John.