S120 load gear position tracking

We have Sinamics S120 FW4.7 with servomotor 1FK7 with multiturn absolute encoder (4097 turns).
We use it for linear displacement of a cutting knife.
I noticed a problem when we would calibrate the encoder (set absolute encoder offset) with a rather high position value. I got F07443 fault. This seemed logical because I had left the position window that can be represented by the multiturn encoder.
Then I activated load gear position tracking for rotary axis, and my problem was gone.
However some questions :
1) If the drive is completely shuddown (no power or control voltage) to what extent can the motor axis be manually moved without causing problems when the power is connected again, I mean I want the actual position to be correct again after power is restored. What if my position was close to the virtual multiturn resolution before power down?
2) The activation of the load gear position tracking only worked if I choosed 'rotary axis'. If I choossed 'lineair axis' I got error 7443, although in fact my motor drives a lineair displacement.?

TechTeam

Hello,

1)When drive is completely shutdown (no power or control voltage) only your real multiturn of the encoder is relevant. When drive is powered off and you manually move it > than 1/2 multiturn (4096/2 = 2048) the drive has after power on again a false position.

What is the significance of this 1/2 a multiturn?  Can anyone give more details about what happens when you exceed more than 1/2 a multiturn while the power is off. 

If I understand correctly, if my multi-turn absolute encoder can track up to 4096 rotations before rolling back over to zero, I can rotate my encoder as many as 2048 turns while the power is off and have no problems, but if I rotate it 2049 or more there will be a false position.  I assume this false position refers to the value stored in p0483 (G1_XIST2).

Can anyone give an explanation using real numeric values to show what happens to the position while rotating the encoder beyond the 1/2 multiturn.

Thanks in advance.

Step1

Can anyone give an explanation using real numeric values to show what happens to the position while rotating the encoder beyond the 1/2 multiturn.

Thanks in advance.

Hello,

Looked through my projects just out of interest, because this issue is acute for me as well.

So I would say that 1/2 multiturn has nothing to do with this case.

Also, see encoder logic homemade chart attached where you'll find an explanation.

Msorich

Step1

 

TechTeam

Hello,

1)When drive is completely shutdown (no power or control voltage) only your real multiturn of the encoder is relevant. When drive is powered off and you manually move it > than 1/2 multiturn (4096/2 = 2048) the drive has after power on again a false position.

What is the significance of this 1/2 a multiturn?  Can anyone give more details about what happens when you exceed more than 1/2 a multiturn while the power is off. 

If I understand correctly, if my multi-turn absolute encoder can track up to 4096 rotations before rolling back over to zero, I can rotate my encoder as many as 2048 turns while the power is off and have no problems, but if I rotate it 2049 or more there will be a false position.  I assume this false position refers to the value stored in p0483 (G1_XIST2).

Can anyone give an explanation using real numeric values to show what happens to the position while rotating the encoder beyond the 1/2 multiturn.

Thanks in advance.

Okay… after thinking about it for a while I think I can answer my own question.Thank you very much Msorich for taking the time to look into this, but see if you can agree with how I explain this below.

Assumptions:

1. Absolute multi-turn encoder capable of tracking 4096 rotations.

2. No power is necessary to track the rotation number within this 4096 limit.

3. “Full multi-turn” = 4096 encoder shaft turns.

4. “Half multi-turn” = 2048 encoder shaft turns

The simplest way to understand why you cannot rotate this encoder greater than a “Half multi-turn” without power applied, is to look at the attached cases where I show the encoder’s rotation count number along with its “Half multi-turn” range.

Looking at the figure you can see that if you rotate the encoder shaft beyond its “Half multi-turn” range, the rotation count number is a value that you can arrive at by turning the encoder shaft beyond its “Half multi-turn” clockwise, or by turning the encoder shaft less than its “Half multi-turn” counter-clockwise.

Example:

1. See attached “Case 3”.

2. Machine is stopped with encoder’s multi-turn rotation count = 0.

3. System power is shut off (encoder and control system power is removed).

4. The encoder is manually rotated clockwise 2049 times.

5. Power is restored.

6. The control system has no way to know whether the encoder shaft was rotated clockwise 2049 times or counter-clockwise 2047 times… all it knows is the value of read by the controller is 2049.  Obviously this creates a tracking problem.

Well. Does youre encoder have any name? Just out of interest to look at its technical data.

Msorich

Msorich

Well. Does youre encoder have any name? Just out of interest to look at its technical data.

Msorich

 

No name... it is just a general example for any multi-turn absolute encoder.  Keep in mind that a multi-turn absolute encoder can count its turns even when the system power is turned off.  But when power is off, you cannot rotate the encoder shaft more than half its range without creating a tracking problem... for the standard EQN1337 encoder, this is 2048 revolutions.  For a single turn ECN1325 absolute encoder this is half a revolution.

Some multi-turn absolute encoders use gears internal to the encoder to keep track of how many times the encoder shaft is turned even when there is no power available.  Some multi-turn absolute encoders use batteries to keep track of how many times the encoder shaft is turned even when there is no power available.  There are other technologies out there as well that allow for counting revolutions of the encoder shaft even without external power.

But no matter which multi-turn absolute encoder you choose, there is a limit to how many turns that can be counted before it rolls over back to zero.  In my example I choose a multi-turn absolute encoder capable of counting 4096 rotations.

From the FH manual:

Absolute encoder adjustment

NOTICE

Adjustment only in a defined encoder range

During adjustment with the rotary absolute encoder, a range is aligned symmetrically around the zero point with half the encoder range within which the position is restored after switch off/on. If position tracking is deactivated (2720.0 = 0), only one encoder overflow is permitted to occur in this range (for further information, see Section Actual position value processing (Page 448)). Once adjustment has been carried out, the range must not be exited because a unique reference between the actual encoder value and the mechanical components cannot be established outside the range.

If the reference point p2599 is in the encoder range, the actual position value is set in line with the reference point during adjustment. Otherwise, it is set to a corrected value in the encoder range.

No overflow occurs with linear absolute encoders, which means that the position can be restored within the entire traversing range after switch off/on once adjustment has been carried out. During adjustment, the actual position value is set in line with the reference point.

Well.What about 12 bit resolution encoder + 13 bit multiturn capacity?

What happens in this case?

Msorich

Msorich

Well.What about 12 bit resolution encoder + 13 bit multiturn capacity?

What happens in this case?

Msorich

It is much the same no matter which absolute multi-turn encoder you choose.  An encoder with 13 bit multi-turn capacity can track 8192 rotations, so its "half multi-turn" = 4096.  This means you can rotate it 4096 rotations without power and have no trouble with position when power returns.

First, EQN it's not standard at all, it just first three letters of type Heidenhain's encoder 25 bit res +12 bit multiturn capacity, meaning 33554432 ppr and 4096 multiturn part.

Looked through its data, I learned that feature of safe information operates within its singleturn part. It's written in black & white there. This means within 33554432. Absolutely the same writes Siemens for their encoders and the same I wrote you above.

I have no clue where did you get "1/2 of multiturn part issue".

If you have issue you-called "beyond 1/2 of multiturn capacity", I would suppose that youre Drive, so to speak, operates is not in harmony with encoder. Because there shouldn't be any problems within singleturn resolution, which is much much far beyond 2048.

Considering that Heidenhain encoders have pretty high resolution by wide known reasons and as I wrote you above try to adapt encoder via p400 [9999], so-called "user defined encoder".

Hope this helps

Msorich