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PICList Thread
'Linear quad. encoders.'
2000\05\10@162627 by John

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Hello PIC.ers,         (longish post)

After years of dealing with quad. optical rotary encoders and the counting
circuitry associated with them, I have only come across very few makers
of the linear variety.

HP make the HEDS9200 encoder, and you use their matching code strip to get
resolution as fine as 360 counts/inch.
USDigital offer the same device & it is easier to obtain their's
than HP's.
(HP is represented heavily in SA, USDigital isn't...   go figure..  )
Also, USD have been promptly very helpful to me but I'll still be left with
an incomplete answer - has anyone out there in PICland ever put one of
these devices into a 'plunger - type' housing, or seen it done?
I need to end up with an assembly with a spring-loaded (or maybe gravity)
plunger sticking out the bottom as mechanical dial gauges have.

The HEDS parts usually do duty in apps. where the opto. and code strip
are mounted on separate mechanical components which are themselves
confined to move in very restricted ranges, e.g. milling machine slides,
printer carriages, etc. with good lateral stability.

The sensor WILL be used in a PIC app. (16f877 or 16c74) for measurement
and control of a hydraulic press doing tests on granular load-bearing
material, to derive stress-strain relationships.
The closed loop controller (16c74 based, made in this shop) for the machine
already exists, but an appropriate displacement sensor doesn't.
If a HEDS-based sensor can be made to work, it will be massively cheaper
(ratio 1:5 or so) than the other established displacement transducers
like LVDTs, capacitive plungers or non-contact optics.
These have generally better resolution, but that's overkill in these jobs.
Afterwards, I'll have a bunch of other related apps. which have been crying
out for this for many years.

Comments anyone? Suppliers? Alternatives?
If JS Controls started _making_  these as a new business line,
would folks out there like to buy them from me?


TIA & bestos,   John


e-mail from the desk of John Sanderson, JS Controls.
Snailmail:          PO Box 1887, Boksburg 1460, Rep. of South Africa.
Tel/fax:            Johannesburg  893 4154
Cellphone no:   082 469 0446
email:                spam_OUTjsandTakeThisOuTspampixie.co.za
Manufacturer & purveyor of laboratory force testing apparatus, and related
products and services.

2000\05\12@124044 by Mike Gann

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John -

Here is a description of an enclosure for the US Digital Strips and
read heads. It came from a Machining mailing list CAD_CAM_EDM_DRO
on egroups.com. The author of the note was Dan Mauch. Also, here is a
link to a picture of the enclosure, mounted on a milling machine.

www.metalworking.com/dropbox/_1998_retired_files/DROXencoder.jpg
http://www.metalworking.com/dropbox/_1998_retired_files/DROX1encoder.jpg

"I will try and find some picurrees of my enclosed US digital linear
strips.
Essentially,  it is a 1X2 rectangular aluminum tubing. I made end caps
that
are inserted into the ends of the tubing and serve as a seal, a mounting
flange and a location stop.
The linear strip was mounted onto a pieces of 1/4" square aluminum stock
with 2 mill double sided tape. The strip is so light and with the
rigidity
of the mylar there has been no problems with this technique after one
year
of operation. The 1/4 stock with linear strip is epoxied into the 1X2
housing on one edge . Whereas there is no phyical contact with the
encoder
strip epoxy is an easy way of securing the strip to the housing
The encoder head is mounted on a polypropylene slider that positions the
encoder head to run over the linear strip. The slider is moved by a
piece of
5/16"D aluminum tubing that serves as a cable conduit and as a push rod
for
the slider. The endcap on one side has a hole bored to allow the 5/16
pushrod to line up with the slider .
I think a picture of my encoder set up is in http://www.metalworking.com in the
drop box under droxencoder.jpg
   Dan"

Mike Gann

John wrote:
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