×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Position measurement problem using encoders

Position measurement problem using encoders

Position measurement problem using encoders

(OP)
Hello,
I am trying to measure the position from 2 linear encoders (XY Plance).
My hardware setup is such as:

2 Encoders (Heidenhain) provide sine wave position signal (signal period 2 µm, frequency appx. 50KHz ). Signal is then digitized and interpolated (Sine wave to TTL, 200 times) using an interpolator box (Heidenhain). Position is then calculated using a counter board.

But I do not getting correct position signal. Encoders are used to trace a circular motion. But recorded motion is an uneven circle with incorrect scale.

What could be the possible reason?
I would be thankful for any suggestion.
Simasa
 

RE: Position measurement problem using encoders

If the diameter of your circle is small, it is probably a mechanical problem with coupling between movement and encoders. Often overlooked, but very common.

If the diameter is relatively large, 100 mm or so, the mechanical problems usually are easily mastered. You have to turn to the manufaturer for advice. Those encoders are not known to have any problems.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Position measurement problem using encoders

(OP)
The radius used is 150 mm. I think too that the encoders are functioning right.
I just thought about the possibility that the input frequency of 50 KHz might be high for the interpolator (200 times interpolation). May be I should try to reduce the interpolation factor (not sure).
could it be a possible reason?
I would be thankful for some further suggestion.
simasa

RE: Position measurement problem using encoders

2 um and 50 kHz equals 100 000 um/second or 6 m/minute. What does the data sheet say about speed? There is usually a maximum allowed speed.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Position measurement problem using encoders

(OP)
Maximum allowed frequency for 200 times interpolation (currently set) mensioned in data sheet is 12.5 kHz. The current input frequency which I have been trying id from 10-50 KHz. I do not have possibility to test with input signal below 10 KHz.

It seems violating the allowable input frequency range.
Would be the reason?

Some extra detail: Position output signal of X and Y motion should appear to be proper sine wave form (As motion along XY-Plane is a circular motion). I am getting a kind of sine wave with sharp edges.
I would be thankful for some further suggestion.
simasa
 

RE: Position measurement problem using encoders

The "Doktor" (Heidenhain, that is) opens his office tomorrow. I think that you need to dicuss a faster system. As you say, you are violating the speed limit set for the system. It does work with less interpolation, I assume?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Position measurement problem using encoders

Take a look at the Heidenhain IK 220.

http://www.heidenhain.com/index.php?WCMSGroup_479_177=839&WCMSGroup_2238_177=479&WCMSGroup_839_177=841&WCMSArticle_Template_45_13224=HeidenhainProduktDB&op=catview&search=category&CS_UID=18506

The IBV660B limitation is the output edge speed.  
12,500 x 200 x 4 = 10,000,000 edges/sec which is the maximum edge rate out of the IBV660B

The encoder signals are adjusted for amplitude, etc. via Pots in the APE boxes at the end of the encoder read head cable.  Heidenhain sells calibration units to use to do this.

 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources