Need Help!- Possible bad encoder on X servo

[bherr]

After some troubleshooting I found that the encoder on the X axis servo is not counting. I ohm checked all the wires back to the TNC 155b Heindenhain controller and they are good. My question, is there a way to check the outputs of the encoder to confirm that it is bad and not something in the TNC controller. I've attached photos of the encoder, which I believe is a light emitting diode type of encoder.

Any help from the expects out there>

Dave smith of Philly saiid I should ship it to Clarkson co. in IL and that it could cost up to a $1000, ouch, so if I can verify and or get a replacement I I can change it out myself.

Ben

[machintek]

If you swap this motor with another axis, and the problem follows the motor, then the problem may be the encoder.
It can be checked with a power supply and a oscilloscope.
Are you getting a measuring system defective error?
Say hello to Dave Smith from me. We worked together from 82 to 87 out of the Bristol PA office.

George

[joejared]

If it's a bad encoder, you can get pretty inexpensive and compatible encoders from either US Digital or from or from Renco. If it's urgent, US Digital stocks them, while sometimes it takes time to get a Renco encoder.

[TOTALLYRC]

When I checked my encoder, known good vs questionable, using a dvom, the voltage on the A and B would either be high or low on the good one when turning the motor very slowly by hand. On the bad one it would sometimes give a middle of the road reading. So instead of ~0v and ~5 v, I would get ~2v, IIRC, then I swapped out the encoder and in my case single to differential line driver and the problems went away.
Of coure if you have a scope, just compare the output on a good one to the questionable one and it will be clear.

[bherr]

Originally Posted by machintek If you swap this motor with another axis, and the problem follows the motor, then the problem may be the encoder. It can be checked with a power supply and a oscilloscope. Are you getting a measuring system defective error? Say hello to Dave Smith from me. We worked together from 82 to 87 out of the Bristol PA office. George

George,
That Dave Smith is quite the gentleman and was very helpful. He had me power up the machine, but not hit the start cycle, then move the table by hand, in the X axis and watch the monitor. The X axis didn't count, while the Z & Y did. I have a scope so I could check it. If you have the procedure and voltage required, I'd appreciate the assistance.

Email is bherr@atlanticbb.net
Thanks,
Ben

[bherr]

Originally Posted by joejared If it's a bad encoder, you can get pretty inexpensive and compatible encoders from either US Digital or from or from Renco. If it's urgent, US Digital stocks them, while sometimes it takes time to get a Renco encoder.

joe,
Went to US digital, but couldn't find the encoder, so I sent them and email with the photos. Thanks for the help. If I had a procedure to test the encoder I could then determine what was bad and with my experience in electronics and with the help of my good friend, who also has 30+ years in Industrial electroincs, we could figure a fix.

Ben

[joejared]

Originally Posted by bherr joe, Went to US digital, but couldn't find the encoder, so I sent them and email with the photos. Thanks for the help. If I had a procedure to test the encoder I could then determine what was bad and with my experience in electronics and with the help of my good friend, who also has 30+ years in Industrial electroincs, we could figure a fix. Ben

You're not looking for an exact match, really, just one that will fit. Both companies sell modular encoders, and you're looking for the right shaft size and encoder counts. You may have to exchange A and B, or if you require commutator tracks, you'll be limited to purchasing them from Renco. Either way, what are the specifications of your motors, including the dimensions of the encoder mounting holes and their thread sizes? Swapping axis' is the usual in field test. With an Oscilloscope you could see the outputs, which are fairly well documented. I have a mini test plug for most motors I work with.

[Al_The_Man]

Before you try another encoder, find out it the encoder output is TTL or at least square wave.
The TNC 155 may use one of the other Heidenhain formats that are low voltage or current sinusoidal.
The Heidenhain controllers I have come across do use this format.
Al.

[One of Many]

Ben,

You might call up Clarkson and see if they have a used or new encoder for that SEM motor.

To check the encoder, either look at the machines schematics where the connector ends up on the input board or find the encoder model and look for a pinout diagram online.

Figure out which pin does what. Power, Ground, A, B, and Z is all you will have from the looks of the terminals on the encoder there. Take note of the voltage that powers up the encoder. It could be 5v or 12v with the outputs typically just below that no more than 1-1.5v. Set up the scope, logic probe or meter range likewise.

Since the machine should power up the device, ground the negative lead of your test equipment close by. Use the signal probe or test lead to verify supply power is getting to the encoder at each end of the cable, then while slowly turning the motor, each pin on the connector that you expect an output signal from. The A&B signals would be very close together pulses and the Z either 1-4 pulses per revolution. The Z pulses are a bit hard to find since there are so few.

The procedure would be the same of you decide to bench test the encoder. The only difference is that you will need to supply the power and ground as that model encoder requires.

Joe has the right idea, if you need to find an encoder on the cheap. The issue will be a different mounting and package size. Hollow shaft, PPR and voltage shouldn't be much of an issue. I'm not a fan of the inexpensive encoder from US Digital. At least get an industrial quality unit rather than one of the plastic types.....



DC

[bherr]

Originally Posted by joejared You're not looking for an exact match, really, just one that will fit. Both companies sell modular encoders, and you're looking for the right shaft size and encoder counts. You may have to exchange A and B, or if you require commutator tracks, you'll be limited to purchasing them from Renco. Either way, what are the specifications of your motors, including the dimensions of the encoder mounting holes and their thread sizes? Swapping axis' is the usual in field test. With an Oscilloscope you could see the outputs, which are fairly well documented. I have a mini test plug for most motors I work with.

Joe,
the motor is a SEM Type MT 30Z4-61
Max RPM =8300
Volts=140
Pulse Amps=50
Tacho= 9.5
Can you explain A vs B as I have no idea what your talking about.
Ben

[bherr]

Originally Posted by One of Many Ben, You might call up Clarkson and see if they have a used or new encoder for that SEM motor. To check the encoder, either look at the machines schematics where the connector ends up on the input board or find the encoder model and look for a pinout diagram online. Figure out which pin does what. Power, Ground, A, B, and Z is all you will have from the looks of the terminals on the encoder there. Take note of the voltage that powers up the encoder. It could be 5v or 12v with the outputs typically just below that no more than 1-1.5v. Set up the scope, logic probe or meter range likewise. Since the machine should power up the device, ground the negative lead of your test equipment close by. Use the signal probe or test lead to verify supply power is getting to the encoder at each end of the cable, then while slowly turning the motor, each pin on the connector that you expect an output signal from. The A&B signals would be very close together pulses and the Z either 1-4 pulses per revolution. The Z pulses are a bit hard to find since there are so few. The procedure would be the same of you decide to bench test the encoder. The only difference is that you will need to supply the power and ground as that model encoder requires. Joe has the right idea, if you need to find an encoder on the cheap. The issue will be a different mounting and package size. Hollow shaft, PPR and voltage shouldn't be much of an issue. I'm not a fan of the inexpensive encoder from US Digital. At least get an industrial quality unit rather than one of the plastic types..... DC

One of many,
I've looked thru my documentaion on the TNC155b and all my wiring diaigrams are in German. You wouldn't happen to have them in English?? If so can you email copies? Email is bherr@atlanticbb.net, or tell me were I can download them.
thanks much,
ben

[One of Many]

Originally Posted by bherr Joe, the motor is a SEM Type MT 30Z4-61 Max RPM =8300 Volts=140 Pulse Amps=50 Tacho= 9.5 Can you explain A vs B as I have no idea what your talking about. Ben

Ben,

Al brings up a good point to find out what type of encoder it is. If this is not a TTL/CMOS pulse type encoder, it might be harder to check with a meter or logic probe. A scope might be your only option.

I have had pulse type encoders that checked out fine with a logic probe, but when viewing the signals on a scope, the initial rise of the pulse was slow.

Simply put for incremental pulse encoders. The basic outputs are 2 signals 90 degees out of phase from each other. These are commonly refered to as A pulse and B pulse signals that rise and fall as the encoder rotates. Setting still, these 2 wires/lines/signals might be any combination of high or low. This format allows the control to differentiate the directional rotation by logic of which signal goes high or low first, relative to the next change in state-an up or down count. The Z pulse is primarily used at the homing sequence as a marker pulse after finding the homing switch.

DC