Encoders not working correctly

[ozturbo]

Hello,

I am working on retrofitting a cnc with a mesa 5i20, 7i33, and 7i37. I finally got to the point today where everything is pretty much ready for testing. I have a problem though. The x encoder works fine, emc shows counts in positive and negative. The y encoder shows only negative movements, when i spin the motor clockwise it pulses +-.0001. and the z axis does not work at all. Any help is appreciated thanks.

[PCW_MESA]

Originally Posted by ozturbo Hello, I am working on retrofitting a cnc with a mesa 5i20, 7i33, and 7i37. I finally got to the point today where everything is pretty much ready for testing. I have a problem though. The x encoder works fine, emc shows counts in positive and negative. The y encoder shows only negative movements, when i spin the motor clockwise it pulses +-.0001. and the z axis does not work at all. Any help is appreciated thanks.

Sounds like the quadrature signals are not clean, I would check these things:

1. Is 7I33 jumpered properly to match encoder type? (TTL or differential)
( using TTL encoders when the 7I33 is jumpered for differential will
generate the type of behaviour you are seeing)

2. Measure 5V power to encoders

3. Check encoder wiring carefully

4. Trace the encoder signals from the encoder to the 5I20 either using a voltmeter or LED and resistor.

5. View the encoder signals with an oscilloscope if you have one.

Peter Wallace

[ozturbo]

From what i understand the encoders are differential they have a a/ b b/ z z/. They are all the same encoders and x works fine. I'm measuring 4.86 volts on the encoder power coming from the mesa card. One thing I noticed is if I plug in the 7i37 also, the 7i33 will power on briefly then the led's will dim out. I am thinking that the 50 pin connector can't supply enough power for all the encoders. I will try hooking the cards up to an external 5v supply.
Also, i will check the wiring, it seemed correct but they have been spliced together in 2 locations so something may have came loose as I was messing with them.

[PCW_MESA]

Originally Posted by ozturbo From what i understand the encoders are differential they have a a/ b b/ z z/. They are all the same encoders and x works fine. I'm measuring 4.86 volts on the encoder power coming from the mesa card. One thing I noticed is if I plug in the 7i37 also, the 7i33 will power on briefly then the led's will dim out. I am thinking that the 50 pin connector can't supply enough power for all the encoders. I will try hooking the cards up to an external 5v supply. Also, i will check the wiring, it seemed correct but they have been spliced together in 2 locations so something may have came loose as I was messing with them.

Note: if you supply external power to the encoders (because the 400 mA or so of cable supplied power is insufficient), it must be done in one of two ways:

1. Connect external 5V power to just the encoders, NOT the 7I33!

2. If you supply 5V power to the 7I33, it must come from the PC that has the 5I20 installed.

When we do a 7I33 card revision we will change the power wiring so that the external power connector only powers the encoders, but for now, the above wiring limitations must be observed.

Peter Wallace

[ozturbo]

Ok thanks, I know the computer doesn't have any 5v connectors available. I will try powering the encoders separately.

[ozturbo]

Ok, I got all the encoders to atleast work now, but I have some issues I don't understand. First, the z axis encoder was bad so that was it's problem. The issue I have now is all three encoders are the same, but I can't get the z and y to work with a a/ b b/ only a and b connected, but x work with everything hooked up without a problem. Any suggestions.

[PCW_MESA]

Originally Posted by ozturbo Ok, I got all the encoders to atleast work now, but I have some issues I don't understand. First, the z axis encoder was bad so that was it's problem. The issue I have now is all three encoders are the same, but I can't get the z and y to work with a a/ b b/ only a and b connected, but x work with everything hooked up without a problem. Any suggestions.

That sounds like the Z and Y encoders have trouble driving the differential input termination which points to some kind of wiring issue or wrong encoder type selection on the 7I33:

for example if you have the 7I33 set for TTL but use differential encoders, this sort of behavior is likely. What happens is that the individual A or /A signal will drive the TTL inputs as long as they are not terminated (both A and /A connected) as soon as you connect both A and /A they have to drive the differential termination resistor, reducing their signal swings to the point that they will no longer drive to valid TTL levels.

Assuming the encoders are differential, I would first verify the the 7I33 is jumpered for differential mode on all channels and next measure the actual encoder signals.

Normally, I would check the encoder signals with an oscilloscope, but if you don't have an oscilloscope, a voltmeter will do. The A, /A and B,/B lines are complementary, that is if one is at a logic high level, the other should be at a logic low level, that is they are just logically inverted from each other.

If you measure the A and /A voltages to ground (while connected to the 7I33 and motor power leads disconnected), one should be at a high voltage and one at a low voltage, the high voltage should be somewhere around 2.4 to 5V and the low voltage should be less than 1V. If you move the motor shaft slightly you should be able to get the high and low signals to reverse. The B and /B signals should behave identically.

Peter Wallace