BUG? CoDeSys AXIS_REF 32bit position rollover

2020-02-27T18:37:51.291000Z

Originally created by: Nicolai_Hanssing

The lack of precision in previous post, is due to a bug wich I have posted in a new thread.

I have now found a way(?) to convert an actual 32bit position, and transform it into the TechUnits-domain for a rotary axis (modulo):

(* Lets try to calculate actual position from dwActpos *)
(* OBS: pAx : POINTER TO AXIS_REF *)
ActPosition := ((pAx^.dwActPosition-pAx^.dwPosOffsetForResiduals) MOD pAx^.dwOneTurn)/pAx^.fScalefactor;
TmpLReal := pAx^.fOffsetPosition-TRUNC(pAx^.fOffsetPosition / pAx^.fPositionPeriod)*pAx^.fPositionPeriod;
ActPosition := ActPosition - TmpLReal;
WHILE ActPosition>=pAx^.fPositionPeriod DO
  ActPosition:=ActPosition-pAx^.fPositionPeriod;
END_WHILE
WHILE ActPosition<0 DO
  ActPosition:=ActPosition+pAx^.fPositionPeriod;
END_WHILE

I however dont understand why the value in AXIS_REF.fOffsetPosition is not kept within .fPositionPeriod?

When perofrming multiple MC_SetPos() calls the value can become extremely large, causing many iterations in the while-loops, wich is inefficient, so I had to add the TRUNC() calculation to keep it O(1) effecient.

It will also lead to loss of precision eventually when the LREAL value gets big enough!

I realise that increment-precision is kept until 2^51 for double precision LREAL, but it still seems wrong?

Is this intended by 3S?

Regards

Nicolai

BUG? CoDeSys AXIS_REF 32bit position rollover

2020-02-27T18:37:50.117000Z

Originally created by: Nicolai_Hanssing

Changing the axis to a modolu-axis, causes the discrepency to not appear when position-rollover from drive occurs.

However if I run the axis with modulo, how can I correctly transform the 32bit DINT feedback-value to an actual positionvalue?

My investigations so far has led me to the follwoing construct:

(* pAx is a pointer to AXIS_REF. *)
(* Lets calculate actual position from dwActpos (modulo axis) *)
 dwOffset := LREAL_TO_DWORD(pAx^.fOffsetPosition*pAx^.fScalefactor);
 ActPosition := 
  ((pAx^.dwActPosition-dwOffset) MOD pAx^.dwOneTurn) / pAx^.fScalefactor;

Firstoff I need to treat the feedback-value as DW instad of DI?

Then get the current offset and convert to DW by scalefactor (not precise, anyone know where to get the DW-offsetvalue to avoid rounding-errors?).

Apply axis modulo as found in AXIS_REF.dwOneTurn.

However this is not precise!

I think it is due to rounding-errors in the calculation of dwOffset.

So anyone have a sure, fast and precise way of transforming a 32bit DINT value to a corresponding AXIS_REF.fActPosition-domain?

Notes on application: We're reading a 32bit capture-positon in the drive, wich is currently not supported by MC_TouchProbe(), and therefor need to do this conversion.

BUG? CoDeSys AXIS_REF 32bit position rollover

2020-02-27T18:37:46.896000Z

Originally created by: Nicolai_Hanssing

System: CoDeSys 2.3.7.5 with Infranor CD1k CanOpen drives

Target: WinCE Cybelec

When using an axis with linear configuration I get some wrong behaviour when the feedback-position (DINT) rolls over at 2^31:

The raw 32bit feedback-position from the drive is available in:

AXIS_REF.dwActPosition (OBS: this is unsigned version, but it matches the binary transmission from the drive)

AXIS_REF.fActPosition - Current actual positon, scaled.

AXIS_REF.fSetPosition - Current setpoint from Position-profiler, scaled.

Now all these values are fine until the drive roll-over of the 32bit SIGNED position: 16#80000000 (2^31)

The setpoint for the drive is continous, when the roll-over hapens (ie. no following error), but is this is by luck i dont know....

'AXIS_REF.fActPosition' changes sign, and follows the dwActPosition, if that is typecasted into a DINT.

But 'AXIS_REF.fSetPosition' does not, it continous to grow.

So you get a large difference (2^32) between fActPosition and fSetPosition. This does not make sense, and is a bug....

Exspected behaviour would be one of the two below:

a) Act/Set-Position would both change sign.

b) Act/Set-Position would both be continous.

So we have this bug, but is it CoDeSys or is there something wrong with the Drive-libs?

I have some question I hope some will be able to answer:

What is the largest linear position, for a linear axis in the profiler?

How is the relation-ship between fSetPos (From profiler) and Actual command defined, when a roll-over has occured on either feedback or command-setpoint?

Please feel free to only answer part of the questions in seperate posts.

I'll try to see if I can provoke more strange behavior.

Regards

Nicolai Hanssing

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