Haas Servo Rotary Table

[Dennis Tillman]

Hi folks,
I'm new to the forum so if I choose the wrong group to post this to please let me know.
We have a HAAS SRT (Servo Rotary Table) that immediately reports an over temperature error when the Cycle Start button is pressed. We have traced the signal through several ICs on the CPU Controller card and the error is definitely NOT being caused by an over temperature. We have replaced the CPU Controller card with a new one from the factory and the problem persists. The thermistor that HAAS uses to detect the over temperature condition is working correctly and nothing is hot.
HAAS apparently has a policy of telling owners as little as possible about how their stuff works. We do know, according to a HAAS technician, that other things, such as incorrect voltages, can also cause the SRT display to say there is an over temperature error. So we checked all the voltages. They appear to be nominal. Three of the voltage regulators are on the CPU card which was replaced. So those 3 supplies cannot be at fault. The fourth supply (+160V DC) is on a seperate PC board which is working perfectly.

Any suggestions would be appreciated for how to proceed or what else to look for.

HAAS SRT Details: Controller S/N 3307, Rotary Table S/N 617, using 17 pin Amphenol connector.

Thanks, Dennis Tillman, Shareway Industries

[Al_The_Man]

You seem to have covered most bases, I assume the temp device is the usual N.C. thermal switch, or is it an actual thermistor?
Is there continuity back to the controller?
Al.

[Geof]

You may have an open circuit somewhere. I cannot make any suggestions where, but with the Haas rotary tables if you activate the 4th axis in the Settings but do not plug the table into the machine the error you get is Over Temperature. This suggest to me that if the controller cannot detect any signal from the temperature detector it gives this alarm...which is why I suspect it could be an open circuit in this line.

[philserveng]

try to link out the thermister on the machine side, if you are sure the motor and servo are not hot, then you can't do any damage. if the unit works, then you have a broken wire on the thermister circuit, and you can trace it using the ohms setting on a multimeter and the wiring diagrams.

[Dennis Tillman]

Originally Posted by Al_The_Man You seem to have covered most bases, I assume the temp device is the usual N.C. thermal switch, or is it an actual thermistor? Is there continuity back to the controller? Al.

Oops, I meant thermal switch, not thermistor. We tested the thermal switch and it is OK. It never even has a chance to get hot and neither does the power resistor it is strapped to. We also checked the entire input circuit the thermal switch connects to by applying a short and an open to the input circuit. Thermal switches are either open or closed, they are not proportional so a short or an open is all you get. We were able to trace the logic signal generated by the thermal switch through several Integrated Circuits on the controller PC board. The signals were all what you would expect and they switched from 0 to 1 (and vice versa) depending on whether the thermal switch was open or closed. We got to the point where the signal was multiplexed onto the data bus (via a 74LS244 tri-state driver) and could not trace it any further. But I thought it was odd that (as near as I could tell) the signal from the thermal switch wasn't being handled by one of the PIO (Parallel Input/Output) chips. Instead it seems to bypass them. Perhaps it is being read directly by the CPU. I have no schematic so I could not trace this any further. Schematics would be a great help but HAAS is not forthcoming with information.

Dennis TIllman, Shareway Industries

[Dennis Tillman]

Originally Posted by Geof You may have an open circuit somewhere. I cannot make any suggestions where, but with the Haas rotary tables if you activate the 4th axis in the Settings but do not plug the table into the machine the error you get is Over Temperature. This suggest to me that if the controller cannot detect any signal from the temperature detector it gives this alarm...which is why I suspect it could be an open circuit in this line.

Thanks for the heads up about the alternate cause of the alarm. Thermal switches are either open or closed so by using an open or a short I traced the thermal switch signal through several ICs on the controller card and the signals were exactly what you would expect (logic 0 or 1). I finally get to a 74LS244 tri-state driver which appears to multiplex the signal onto the data bus and I can go no further. This was all done without a schematic so I was really at a disadvantage. If I had more information I could have gone further. As near as I can tell the controller CPU should be able to detect this signal given how far I was able to trace it on the board. The fact that we replaced the controller card with a new one (from HAAS) and had the exact same problem is an indication that the cause is somewhere else (as you are suggesting). I will look for an open circuit very carefully.

I was starting to suspect that there might have been other causes for the Over Temperature alarm. It seems pretty dumb to have one error message for a multitude of possible error conditions but I didn't design this so I do not know what constraints the designers were up against.

Thanks, Dennis Tillman, Shareway Industries

[Dennis Tillman]

Originally Posted by philserveng try to link out the thermister on the machine side, if you are sure the motor and servo are not hot, then you can't do any damage. if the unit works, then you have a broken wire on the thermister circuit, and you can trace it using the ohms setting on a multimeter and the wiring diagrams.

Hi Phil,
Correction, its a thermal switch, not a thermistor. Sorry for any confusion that might have caused. The thermal switch is strapped to a power resistor that is on the 160 VDC power supply. This 160 VDC power supply is on its own small PC board inside the controller. This power supply is working properly (I checked every component on it). This power supply isn't really involved in causing the over temp error for three reasons (in my humble opinion). 1) The error occurs immediately when you press Cycle Start, long before the power resistor could possibly heat up; 2) the power resistor is cold; 3) The thermal switch connects directly to the CPU card where its state (open or closed) is being directly measured.

We have no wiring diagrams. Do you? I traced these signals the hard way with a multimeter until I could go no further.

One other possibility comes to mind: The over temperature error being reported has nothing to do with the power resistor on the 160 VDC power supply board. Instead, there is something else being monitored by the CPU for its temperature. If this is the case then I have been on a wild goose chase. I will look for another possible cause for this error next.

Thanks for your suggestions, Dennis Tillman, Shareway Industries

[Al_The_Man]

If when the OT occurs it refers to the rotary table, then logically if there is any other devices it is centered around the RT.
I have not had direct experience with your particular system, but past experience with other systems has shown that some indicate an overheat which is not directly overheat caused.
For e.g., Fanuc somtimes indicate an O.T. as well as O.C. on a servo motor & drive.
In other words if a drive has a shorted IGBT you can get a O.T. alarm as the controller interprets this as overload & overheat.
The other locations of where temp detectors are placed are, Drive heat sinks, embedded in Transformer windings etc.
Seems odd the temp sensor by-passes the I/O input device?
Is it possible to remove power from the drive itself at power up without getting an alarm, just to test this theory?
Al.

[Dennis Tillman]

Originally Posted by Al_The_Man ...Seems odd the temp sensor by-passes the I/O input device? Is it possible to remove power from the drive itself at power up without getting an alarm, just to test this theory? Al.

Yes, that is odd. I have 30+ years experience with microprocessors and I haven't seen that done before. But I don't know what constraints the developers were under so it may have been the right thing to do in this case. HAAS is no help.

As far as removing power from drive, that is genearally how we have been checking out the controller but when the drive is hooked up we get the same result ayway. One suggestion Philserving made was to look for an open in the cable from the drive to the controller. Combine Phil's suggestion with your comments about there being more than one thermal switch (on the motor or transformer and that is a real possibility. I hope to get to it today or tomorrow.

It would be really nice to have any documentation at all. As it is all we have is the user manual which seems to devote an inordinate amount of copy to HAAS expounding on how wonderful they are as a company and how lucky we are to have bought one of their products. All in all, its useless.

Dennis

[Dennis Tillman]

Thanks to all for your help. Had I paid more attention to the exact error message on the controller I might have had more success in my initial attempts to get to the bottom of this. The error was 'AIR HOT'. My boss reasonably assumed this was caused by an over temperature condition and began at the logical place for such an error: the thermal overload switch. I carried his investigation of this switch as far as I could and eventually reached a dead end.

Fortunately I contacted this group. My boss, on the other hand, contacted someone at Haas who "helped" him by explaning that this error could also be caused by incorrect voltages. This "help" led us on a wild goose chase. I wasted a week checking out perfectly good power supply voltages based on what the Haas technician told my boss.

What the Haas technician DIDN'T say was that the pressure switch on the air supply can cause this. He never bothered to mention that the error message 'AIR HOT' was telling the operator that there was EITHER an over temperature OR insufficient air pressure.

Once I took in to consideration what this forum had to say, I had lots of good ideas for where to look for the cause. It turns out the pressure switch was flaky and didn't close when pressure was applied. Placing a jumper across its contacts proved this.

Unfortunately the Haas then reports an 'ENCODER' error which I was able to diagnose very quickly as a bad or missing index pulse coming out of the encoder. The encoder is a Haas branded unit which I can't fix so we sent the entire drive back to Haas for repair. In the end I'm disappointed that I was not able to fix the unit and get it back into production but at least now I know what's wrong with it. I also know I'm better off without Haas' help

Thanks for all your good ideas. Dennis

[Geof]

Originally Posted by Dennis Tillman .... The error was 'AIR HOT'. ... 'AIR HOT' was telling the operator that there was EITHER an over temperature OR insufficient air pressure......

I have several Haas machines and have often been amused/frustrated over the obscure error or alarm messages that occasionally pop up.

Your 'AIR HOT' is the obscurist I have ever come across. 'Obscurist" is that really a word? Anyway I trhink it explains what I mean.