Hello to all,

We have a CU320 controlling three servo motors. If 480V power supply to the machine does down, after power returns all three axes positions show very high values e.g. -13134.42mm for a slide that is only 250mm long. This is a new issue on a five year old machine.

Please offer advice on what this might be.

I suppose the basic positioner is used?

Do you have linearaxis and have you changed sth. on your mechanic – maybe disconnected and connect again and used a simple “Position setting” instead of absolute encoder homing procedure?

Is position tracking activated ? (maybe you have switched off on an other position as before and the absolute encoders where outside of +/-2048 rev (for that position tracking should be used))

It's hard to guess how the programmer set up the system, but just trying to talk this out:

The cyclic absolute encoder position can be stored in either the PLC or CU320 depending on how it was set up.

PLC:

if the PLC is using the technology option, the multiturn cyclic absolute encoder position is stored in the Axis structure. Part of this is retain data for remembering how many times the encoder rolled over, especially if it is a singleturn encoder.

If the PLC is forgetting this number, its battery backup is dead. Or in general if it didn't ever have a battery, its internal capacitor for remembering retain data has reached the end of its life and no longer stores a charge. Either of these would explain why it could be suddenly forgetting what it was always remembering in the past.

CU320:

I personally have a knowledge gap surrounding what happens when the cyclic absolute position is stored in the CU320, as it does not have battery backup. My thought is, there would be a mechanical positional range when the system powers up that produces a correct result, but outside of that range it would produce numbers wildly outside what makes sense.

Let's say for example that normal traveling range is 0 to 500 mm. But it can creep a little bit, and its actual position when it powers off is -0.0000005 mm. Now when it powers back on, it could be something wildly different like 203902385 mm or whatever depending on the gearbox ratio entered. This is due to it having to guess when it powers back on. Or rather it doesn't really guess, just that the multiturn count is set back to 0, or maybe back to what was last saved to CF.

Hi,

Joeman explained it well. But what we really need to know is which kind of position control and position evaluation is used and also important: which type of encoder is used?

So please answer: TO in SIMATIC or EPOS in SINAMICS used? And which kind of encoder (incremental, singleturn absolute, multiturn absolute)? And which way the encoders were homed (absolute encoder adjustment)?

For EPOS in case of absolute encoder adjustment it is important that the encoder is not turned further for more than half of the encoder revolution (or more than half of the multiurn revolutions) as long as the drive is powered Off.