Encoders for a Stepper System with a 7i85s

Utilitas wrote:

I also did some more digging and found the usdigital website again. (I had stumbled upon it much earlier while I was
looking at steppers a couple weeks ago, then forgot what their website was) They also have a somewhat modular
system of encoders but of an "optical" type. They are notably more expensive, but do represent another potential
option in the US.
 

And for my next point of reference, I'm using US Digital encoders for both my mill spindle motor and lathe high-res spindle encoder.

The mill encoder is a 4096 ppr and runs up to 8k RPM.
Lathe encoder is a 10000 ppr and runs up to 3500 RPM.

Both encoders are differential line driver outputs.  The mill encoder is an E6 mounted on the motor, and the lathe is an S6 model belt driven from the spindle.

I did have to turn the input filter off on the 7i96s for the high-res encoder as it was a little flakey near the upper end of the RPM range with the filter on.

Very pleased with both encoders.  TBH, I probably would have used a US Digital (instead of the AMT) on my lathe motor had I known about them at the time, but the CUI is working fine in this application and it's rather less expensive.

blazini36 wrote:

As for encoders I don't think anyone knows what on earth a "capacitive" encoder is. Really, don't get too caught up in magnetic or optical cuz if it's rated for a speed it will produce clean pulses throughout that speed. If it bothers you that much research the difference between photo diodes and hall effect sensors because that is the difference between optical and magnetic encoders. I guess in that same vein capacitive encoders are akin to capacitive proximity switches but I never use those so I have no idea.

 

The CUI AMT10x series of encoders have a low-resolution disc that has interrupted metal plates that line up with plates on the sensor section.  Capacitance between these plates is sensed by the electronics.  The electronics then interpolates the position of the disc to deliver the desired resolution.  There is a cable you can buy that had a single-ended to differential converter on it.
One small issue with these encoders is that they synthesize a velocity of the encoder and use this during the interpolation.  This causes a slight delay (3-5 ms) in the response to sudden velocity changes.  This may cause stability issues in some servo systems.  Initially, I thought this was a serious problem, but after using them, it seems it does NOT cause much trouble.

Jon


 

A 3-5ms delay is pretty bad. I recall the thread where this came up with DMM servos, if it wasn't an issue no one would have noticed it.

Weak output and 3-5ms delay, not sure I'd bother to consider using these.

Well, it is not a delay in the quadrature output, but a delay in responding to changes in velocity. Apparently, that upsets servo loops less than just plain position delay,
Jon