回覆: Value of Renishaw absolute encoder exceeds its maximum

[Chiang, Liang-Chih [江良志] via Tech-talk <tech-talk at aps.anl.gov>]

Hi, some update.

The problem is that the encoder readhead is 26-bit,

when the encoder raw value exceeds 2^26, the encoder value will start from 0.

Negative limit switch: 59,829,149

Positive limit switch: 899,833 (correct value should be 68,008,697 = 899,833+2^26)

One  solution is to use the field of  RDBL, RRES,  and URIP of motor record.

Set RRES (encoder resolution).
Set URIP=1, UEIP=0.

Read the encoder raw value from REP,

when the raw value is below, say 1,000,000, add 2^26 to it,

set RDBL to the new encoder value.

Then the motor record will get the corrected encoder value from RDBL.

Best regards.

LiangChih Chiang

NSRRC, Beamline group

Email：chiang.lc at nsrrc.org.tw 

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寄件者: Chiang, Liang-Chih [江良志] <chiang.lc at nsrrc.org.tw>
寄件日期: 2023年3月24日 下午 03:31
收件者: Torsten Bögershausen <torsten.bogershausen at ess.eu>
副本: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
主旨: 回覆: Value of Renishaw absolute encoder exceeds its maximum

 

Hi, Torsten Bögershausen,

thanks for replying.

After examining the positions of encoder reader and scale,

it may be ok to adjust the position of the reader reader downward a little bit.

Best regards.

LiangChih Chiang
 NSRRC
 Beamline Group
 email：chiang.lc at nsrrc.org.tw

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寄件者: Torsten Bögershausen <torsten.bogershausen at ess.eu>
寄件日期: 2023年3月24日 下午 12:59
收件者: Chiang, Liang-Chih [江良志] <chiang.lc at nsrrc.org.tw>
副本: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
主旨: Re: Value of Renishaw absolute encoder exceeds its maximum

 

Hej LiangChih Chiang,
there is no good solution to handle this in software, as far as I know.
The best thing would be to talk out the encoder (mechanically),
rotate it by hand so that the value of the encoder at the negative
limit switch is close to zero, with  a little margin.
Say 1000 or so, as an example.
Put the encodet back into the mechanics, and verify that there is no
Overflow / wrap around through the whole driving range from
Low- to the high limit switch.




> On 24 Mar 2023, at 04:32, Chiang, Liang-Chih [江良志] via Tech-talk <tech-talk at aps.anl.gov> wrote:
>
> Hello,
>
> I use Galil DMC-4080 controller to read Renishaw absolute encoders(26 bits).
> So far so good.
>
> However, I conjectured that I encounter the situation where encoder's value
> exceeds its maximum(2^26 = 67,108,864).
>
> 66,000,166 is the encoder value initially.
> 59,829,149 when going to negative limit switch, which is ok.
> 899,833 when going to positive limit switch, which is abnormal.
>
> What could I do to handle this situation?
> 1.  Replace the encoder scale.
> 2.  Can I remedy it in EPICS? How? I have no idea.
>
>
> Best regards.
>
>
> LiangChih Chiang
> NSRRC
> Beamline Group
> email：chiang.lc at nsrrc.org.tw