Centroid Community CNC Support Forum

Hi,

I have an “all in one DC” Ajax drive and am using the Centroid software, and the Ajax jog panel.

I have 3, 1997 Hurco Hawk mills that were taken out of service for unknown reasons. The servomotors have different encoders, and I don’t know what was original, or a replacement. I looked at one of them, and it gave me the color code for the 5v, 0v, A, A-, B, B-, Z, Z- so I proceeded to wire up the Ajax. Another encoder I looked at was about the diameter of a dime, and was from Denmark. The one with the color code was a sumtak-015-2500, which seems to be an obsolete encoder. The motor that works is the y axis motor and is inside the casting, so lazy me, I didn’t want to pull it out and look at it.

The drive wouldn’t let the e stop contactor pull in. I tried the motors one at a time, and only one worked. Tell me if I’m wrong, but I believe the drive wants to be happy with the encoder, or it won’t let the e stop contactor pull in. Even if you don’t hook the motor power cable up, if the drive likes the encoder, the e stop contactor will pull in.

I tried the one motor, the drive likes, in all three axis, and all of the drive’s axis work fine, it must be the encoders. 1 motor works of the 4 motors I tried. 2 of the motors, if you turn the shaft c-clockwise the encoder counts in the pid screen get bigger like they should, but still don’t work, one encoder is just dead.

I believe the motors themselves are ok. The shafts spin freely, and when I short out the power pins, the motors turn way harder, and they work fine with my 18volt drill battery.

Why won’t the 2 motors, that have the encoders that seem to work, allow the e stop circuit to pull in? What does the drive want to see from the encoders, to allow the e stop to energize?

I see you don’t want “TTL” encoders, and I have no idea how I can tell the difference between non TTL or TTL. (Whatever that is) Maybe I have TTL’s? I dunno.

Another thing I noticed on the sumtak encoder, it draws 150ma, which I think is a lot for an encoder, and I don’t know if that is a problem for Ajax.

Any suggestions are appreciated. (I already thought of buying new encoders)

Thanks,
Bill

The drive wouldn’t let the e stop contactor pull in. I tried the motors one at a time, and only one worked. Tell me if I’m wrong, but I believe the drive wants to be happy with the encoder, or it won’t let the e stop contactor pull in. Even if you don’t hook the motor power cable up, if the drive likes the encoder, the e stop contactor will pull in.

More or less.

The MPU11 (which in your case is part of the same All-in-one unit) will report a "Stall" condition if any axis which you try to enable does not have a good encoder connected. The stall condition is considered a fault in the PLC, and like all faults, will cause the E-stop contactor to open (by way of the OUT1 relay, which is part of the E-stop contactor coil circuit).

What is a good encoder connection?

First, it needs to have valid differential signals on all channels (or at least A and B; I don't know if it requires a valid signal on Z). A valid differential signal means at least a certain minimum voltage difference between differential pairs: between A and /A, and between B and /B. I am not certain what the minimum voltage difference is, but the MPU11 manual suggests it is about 3.0 volts. This is unfortunate, because some otherwise perfectly suitable encoders only put out around 2.5V across their differential pairs.

The MPU11 will also report a Stall if it detects a "quadrature error". This would mean that both the A channel and the B channel changed state at the same time. That is supposed to be impossible with a properly functioning quadrature encoder (it would be saying the encoder had moved two counts instantaneously, in an indeterminate direction).

Quadrature errors could indicate momentary loss of power to the device, or to a portion of it. For example, if the line driver chip stays alive (so the differential output is good) but, at a time when both channels are on, the LED or detector goes out and/or comes back, the output will cause both channels to go off and/or on simultaneously.

If you want to troubleshoot it (instead of just replacing the encoders) then you need to buy or make a 9-pin breakout device so you can clip test leads onto the encoder channels and see what is happening: measure the differential voltages, and perhaps watch the channels on an oscilloscope.

You can also use Parameters 332 and 334 to do trial-and-error testing for different encoder errors. For example, P332= 4 will suppress the detection of differential errors on the third (Z) axis encoder. P334 = 4 will suppress the detection of quadrature errors on the Z encoder. If you suppress one or the other error type, and the control then tolerates the encoder and lets you run the axis, then you know (approximately) what the problem is. These parameters should be used for testing and troubleshooting only; not to run your machine indefinitely with unsuitable encoders.

Hi,

BTW, I forgot to tell you these are 2500 line encoders, and when I made a full rev of the motor, the pid screen said 10,000 which would be correct. I also checked the 5volts coming from the Ajax drive, which started out a little over 5volts, and only dropped a little with 3 of the motors plugged in, still over 5v.

I hooked up an external power source of 4.622 volts, and sent the voltage to an encoder on one of the motors that wouldn’t allow the e stop to pull in. I hooked 2 meters up, 1 to “B” and 1 to “B-“. One meter would read 5.960 volts and the other would read .190 (point one nine) and they would flip flop as I turned the motor shaft. I don’t know how the voltage grew more than 1volt, but I think the voltage difference is ok. (I have Fluke meters not junk ones)

I changed parameter 334 to 4 and no change. (P332 at 0)

I changed parameter 332 to 4 (P334 to 0) and e stop pulled in! My problem seems to be differential.

What do you think I should do? Of course I want to know the parameters to suppress differential errors on X and Y axis, and it would be miller time, but I suspect its not that easy.

What do you suggest?

Thanks, Bill