4th Axis erros

[charlie]

Hi all, thanks in advance for any help or ideas.

My machine is a 3 axis bed mill with a Yuasa UDX-14001 4th axis unit on it (see images). The control is an M400S, system ID 0611071030. Report attached.

Recently, during a long job, the 4th axis started to drift. This became apparent as the job (generated in CAM, and run previously with success) involved machining geometry that consisted of a pattern of 22 identical features evenly spaced about the axis of the part. The first and last features were overlapping slightly. I confirmed this by commanding the 4th axis to 0 deg, making a line across the chuck and the stationary body. I then commanded 360 deg and observed that the lines didn't line up. I commanded 720 and the lines were further out, 1080 and so on. I initially thought that someone must have changed a ratio parameter or something but then repeated the test at different feed rates and got different results again (the misalignment wasn't constant).

The next step was to open up the 4th axis unit. I took the servo housing off and a bunch of coolant ran out. *Alarm bells*. I jumped to the conclusion that the encoder must be liquid damaged and decided to give the entire unit a full teardown on the basis that it needed a proper clean and inspection to deal with the coolant leak.

The teardown took an hour or so, and coolant also seemed to have made its way into the gearbox side of the unit as the oil was quite milky. During the teardown, we also removed the front cover (ie Mount plate) from the servo and pulled the shaft/armature/encoder assembly out for a closer look. There was a bit of a stench coming from the assembly which was a worry. We cleaned these parts (including the encoder board) with spray can of electrical component cleaner and then ran the air duster over it and then dried it with a heater. Not sure if this was a good idea or not.

Next, we reassembled the servo, and then assembled the servo to the rest of the 4th axis unit and connected to the machine (leaving the main servo casing off so that we could observe the servo's behaviour. The machine homed x, y and z fine but the 4th axis was erratic and then threw an error (I can't remember exactly which one - "position error" I believe). I jogged the motor a few times, and a few sparks came out from the gland where the power cables go into it, and it began to run faster and eventually settled into running in a short, consistent bursts and throwing an error "Full power without motion." I suspect the sparks were because I also had the brushes out (to clean them) and they were presumably re-seating (I've since read that the brushes on DC servos should never be removed - whoops).

I metered the servo power leads and got 0.6 ohm. Open-loop to the body and earth lead.

What is most interesting is that I get two different errors based on the jog feed rate override knob setting.
At the lowest speed, it's "411 A axis(4) full power without motion."
At about 25% this error becomes "410 A axis (4) position error"
See the video here: https://share.icloud.com/photos/0OnQZZ- ... xh49ovQJCw
The same thing happens when switching between inc and cont modes.

I have also taken a video of the PID page during jog attempts. The encoder counts seem to be non-existent, but the "SUM" value briefly shows numbers:
https://share.icloud.com/photos/0xUQyap ... aWKVYwWCGQ

Another thing: during the homing sequence, the 4 red Axis error LEDs on the drive remain off until the sequence gets to the 4th axis. At this point all 4 LED's become illuminated.

Basically, I'm working on the assumption that the problem lies with either the servo, encoder or the drive. My main question is what do I need to do to determine which component is faulty, and how do I fix it?

Thanks again for any help.

Charlie

[cncsnw]

You have no encoder feedback from the motor to the CPU10 board. This is probably because the encoder was damaged by the coolant, although it could also be a cable or connection problem.

In this situation, "410 ... position error" and "411 ... full power without motion" mean essentially the same thing: no matter what the control asks the servo drive to do, there is no visible movement of the motor. As far as the control is concerned, "visible movement" means encoder counts.

At a minimum, replace the encoder. If budget allows, replace the whole motor.

[martyscncgarage]

You should not be stuck with the Renco encoder. Measure the shaft the encoder is attached to. Go to Automationdirect.com OR contact Centroid with the shaft measurement. They may be able to supply you with a new encoder AND a cable.

Just be sure you are looking for a line driver/differential 5VDC encoder.

Marty

[charlie]

Hi guys - thanks for the replies. I have just been in touch with Centroid regarding a replacement encoder.

[charlie]

A quick update: I've got the new encoder installed and working which is great. Thanks, everyone for your help and comments above. Note: I did need to reverse the servo power wires as the new encoder presumably counts +ve in the opposite direction to the last.

Next problem: I'm now trying to sort out the 4th axis brake/clamp while I have the thing apart. It doesn't work when commanded via MDI: it just says "312 Waiting for PLC Operation..."

The 4th axis has a Koganei air valve (100E1-SR). 2 position, 3 port, normally closed. More info here: https://official.en.koganei.co.jp/product/100_ALL
I've noticed that the valve is energised by default, so have plumed the pressure line to the "R" port (I believe this is how it was when I first opened it up).
It also has a pressure switch (for confirmation).

What I've done so far:

• Confirmed electrical connection to the valve with a multimeter (I read 30V in almost all senarios). Note: this drops to 0V when I hit e-stop. It becomes (and remains) live again when I release e-stop and then jog the 4th

• Confirmed that the pressure switch is switching

• Read this post and added M10 and M11 macros to my cnc10 folder (both were missing)

• Uncommented "Clamp = M10 AND CNC_Program_Running" in the "m400cpu.src" file & re-compiled

• Re-commented "Clamp = M10 AND CNC_Program_Running" in the "m400cpu.src" file & re-compiled (as the above didn't solve the problem)

• Noticed that one of the Aux LED lines in the m400cpu.src files is labled "Brake_LED" as opposed to what I assume was the defaul (Aux_1_LED?)

What I'm trying to achieve:
The normal function of the clamp. I assume this means that I can:

• Activate and deactivate the clamp via MDI with M10 and M11 commands

• Activate and deactivate from a CAM program

• Jog the 4th axis with the clamp activating and deactivating as/if required (how is it normally treated during manual jogs?)

Recent report attached. Any help, much appreciated.

report.zip

(272.78 KiB) Downloaded 141 times

[cncsnw]

Because you are just using default behavior for M10 and M11 (i.e. M10 = "M94/4", and M11 = "M95/4") there is no need for macro files. The default behavior is built into CNC10.

Because you have a two-part, CNC10-style PLC program, the relevant logic is in the PC side of the PLC program (in your case, currently, m400pc.src).

Your PLC program defines the Clamp output to be OUT11. It will turn on OUT11 whenever an M10 request is present. You should be able to confirm this by watching OUT11 on the Alt-i PLC Diagnostic display while you use MDI to run M10 and M11.

Is the clamp solenoid valve coil wired through OUT11 on the RTK2 PLC unit? Your text suggests that perhaps someone wired it through the 4th-axis brake terminals of the servo drive instead. Follow the wires and tell us or show us what terminals it is connected to.

If you wire the solenoid valve coil through OUT11 on the RTK2 PLC unit, then you will be able to control it with M10 and M11, both at the MDI prompt and in CAM-generated CNC programs (as long as your CAM software puts in M10 and M11 in appropriate places).

If you instead wire the solenoid valve coil through the 4th-axis brake terminals of the servo drive, then it will be released whenever the axis is enabled, and applied whenever the axis is disabled. You will not be able to reliably use M10 and M11. You could get partial functionality by writing a custom M10 macro which just says "M93/A". Since that would release power on the A axis (removing the enable), the servo drive would turn off its brake-release relay. However, you cannot count on the axis remaining disabled through tool changes or job finish / restart.

It is not possible to have the clamp automatically released and applied just because you are jogging the axis, or have stopped jogging the axis (or, similarly, just because CNC codes happen to be moving the axis or not). The Centroid control does not work that way.

References to a "brake" in your PLC program relate to a spindle brake, not the rotary axis clamp. The rotary axis clamp is called "clamp".

Also, what is the Centroid control serial number, from the side of the console? It is probably in the 106xx or 107xx neighborhood. It appears to be a console upgrade of an earlier M400, which would have a 6000-series serial number on the door of the electrical cabinet.