Author Topic: Chinese Digital Caliper As Encoder?  (Read 4208 times)

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Offline iplay1515

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Chinese Digital Caliper As Encoder?
« on: February 17, 2010, 02:05:21 PM »
Just wondering if Mach can use either the direct or modified output from the inexpensive Chinese digital calipers in a closed loop manner to help resolve backlash and other positioning errors??

It's my understanding that the Chinese calipers don't output the same quad signals that are standard on most encoders.


Offline Hood

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Re: Chinese Digital Caliper As Encoder?
« Reply #1 on: February 17, 2010, 02:55:37 PM »
Mach is open loop, you could probably write a macropump or plugin to fault on errors of position but not correct on the fly.
You would need to have some means of converting the output of the Chinese scales to TTL for Mach anyway.
Hood

Offline iplay1515

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Re: Chinese Digital Caliper As Encoder?
« Reply #2 on: February 17, 2010, 03:37:51 PM »
Thanks.

How does Mach handle backlash compensation, and where can I find detail information about this aspect of Mach?

Offline Hood

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Re: Chinese Digital Caliper As Encoder?
« Reply #3 on: February 17, 2010, 03:41:31 PM »
Do a search on the forum for Backlash and you should get some info. I have never used it myself so cant really advise on it.
Hood

Offline RICH

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Re: Chinese Digital Caliper As Encoder?
« Reply #4 on: February 17, 2010, 04:41:24 PM »
You measure the backlash and then go into config and implement it, here are some recomendations:

BACKLASH:

Here is what i would recommend for initial settings when using a machine with more than one axis.

"My"  50-50-50 rule of thumb.

Motor velocity setting: 50% of max velocity ( down from where you would start to miss steps post motor tuning )
Backlash Speed:          50%
Shuttle acceleration: .050 ( .5, or .050, or .0050 just an easly way to remember the setting )   

Then you can play with individual settings to get the system just so, such that you have no problems
during a two axis move. The motor acceleration can also be payed with.

RICH

Offline Dan13

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Re: Chinese Digital Caliper As Encoder?
« Reply #5 on: February 18, 2010, 01:13:55 PM »
Just as a note, digital callipers (not only Chinese, but also many of the expensive ones) are not as accurate as some people believe they are. Most of the manufacturers declare an accuracy of 0.02mm, but in practice the error can easily get as high as 0.05mm with temperature change that causes for the expansion or contraction of the PCB mount. Just be aware of the limitations of a digital calliper.

Daniel

Offline RICH

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Re: Chinese Digital Caliper As Encoder?
« Reply #6 on: February 18, 2010, 06:58:59 PM »
Have a look at this site as they provide info about chinese scales and kits.
Shame, built mine some time ago, and have the scales and still not using it...... ???
A friend loves his  ( for the money ) and uses them on his lathe.
 
http://www.shumatech.com/web/products/dro-350

RICH