Accelerometers Gyros?

Log in or register to post comments
Go To Last Post
15 posts / 0 new
Author
Message
drt80
drt80's picture
Level: Resident
Joined: Fri. May 23, 2008
Posts: 806 View posts
Location: Pune, India
#1
Posted by drt80: Mon. Mar 30, 2009 - 12:37 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi,

I am in a design phase of a project, where I need to do the following:

Sense the rotation of a shaft. The shaft moves very slowly. It moves once every 6-10 seconds and the rotation is about 0.1 degs. I want to sense the rotation in degrees and would want to know the position in degrees (resolution of 0.1 deg) at any given time.

I have been searching here and google, but I have not been able to understand whether an accelerometer or a gyro would be useful here.

I have read about inclinometers from analog devices:

http://www.analog.com/en/mems-an...

These inclinometers internally use 2-axis accelerometers, so I think this can be done. But, just want to be sure.

Can anyone comment on this?

Thanks,
-Deven

Tags:

Learning and Information, General Electronics
Top
dezellis
dezellis's picture
Level: Hangaround
Joined: Mon. Mar 5, 2001
Posts: 130 View posts
Location: UK (West Yorkshire)
Posted by dezellis: Mon. Mar 30, 2009 - 02:01 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi,
I would have thought that this application is normally the realm of high resolution rotary encoders but I suspect they are not inexpensive http://www.motioncontrol.com/pro...
I can't really comment on the ADIS16203 solution I have never seen this application before, however, I suspect it will not give the consistency that you probably require.
I am curious regarding the actual application and the shaft size etc.

Top
ikdor
ikdor's picture
Level: Wannabe
Joined: Wed. Dec 5, 2001
Posts: 85 View posts
Location: Netherlands
Posted by ikdor: Mon. Mar 30, 2009 - 02:37 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

All gyros on the cheap side of million dollar ring laser gyros would not work, and even those have drift. Generally it's a bad idea.

You could use a two axis accelerometer glued to a shaft and do a cordic algorithm, but it is unlikely that you will get a usefull resolution close to 0.1 degrees. Check the accelerometer datasheets and calculate it yourself.
Also the electronics will be rotating in that setup, making a mess of the wiring.
A better solution would be a shaft encoder, either an optical or a magnetic one. Be warned though that 0.1 degrees resolution and accuracy are different things.

Good luck,
Igor
Shameless plug: http://www.skf.com/portal/skf/home/product_pages?contentId=001461&lang=en

Top
drt80
drt80's picture
Level: Resident
Joined: Fri. May 23, 2008
Posts: 806 View posts
Location: Pune, India
Posted by drt80: Mon. Mar 30, 2009 - 03:09 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

dezellis wrote:
Hi,
I would have thought that this application is normally the realm of high resolution rotary encoders but I suspect they are not inexpensive http://www.motioncontrol.com/pro...
I can't really comment on the ADIS16203 solution I have never seen this application before, however, I suspect it will not give the consistency that you probably require.
I am curious regarding the actual application and the shaft size etc.

Ya.... i have thought of the encoder solution. Actually, I want the solution to be compact. There is hardly any space to mount the encoder on the shaft. The shaft is of 20 mm diameter.

Thanks for your reply,
-Deven

Top
drt80
drt80's picture
Level: Resident
Joined: Fri. May 23, 2008
Posts: 806 View posts
Location: Pune, India
Posted by drt80: Mon. Mar 30, 2009 - 03:14 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

ikdor wrote:
All gyros on the cheap side of million dollar ring laser gyros would not work, and even those have drift. Generally it's a bad idea.

You could use a two axis accelerometer glued to a shaft and do a cordic algorithm, but it is unlikely that you will get a usefull resolution close to 0.1 degrees. Check the accelerometer datasheets and calculate it yourself.
Also the electronics will be rotating in that setup, making a mess of the wiring.
A better solution would be a shaft encoder, either an optical or a magnetic one. Be warned though that 0.1 degrees resolution and accuracy are different things.

Good luck,
Igor
Shameless plug: http://www.skf.com/portal/skf/home/product_pages?contentId=001461&lang=en

The resolution is one of the concerns. Other being the movement of the shaft. The movement of the shaft is very less, 0.1 degrees. Will the accelerometer be able to detect the change?

I am trying to find out the algorithms to calculate the actual rotation from the accelerometer parameters. If you know of some websites or name of certain algos, that would be great.

Thanks for your reply,
-Deven

Top
drt80
drt80's picture
Level: Resident
Joined: Fri. May 23, 2008
Posts: 806 View posts
Location: Pune, India
Posted by drt80: Mon. Mar 30, 2009 - 03:15 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

@ikdor: I see you mention a cordic algorithm. I will try to find out more about it.

-Deven

Top
Bronze Markbobgardner
bobgardner's picture
Level: 10k+ Postman
Joined: Wed. Sep 4, 2002
Posts: 26609 View posts
Location: Orlando Florida
Posted by bobgardner: Mon. Mar 30, 2009 - 03:19 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You can buy the parallax 3 axis accelerometer at radioshack for about $40. It has a Microchip 12 bit a/d converter on it and the accelerometer. Uses SPI. I have routines to read the accelerometers I can post. Just clamp it in a vise and see how close you can measure tilt.

Imagecraft compiler user

Top
drt80
drt80's picture
Level: Resident
Joined: Fri. May 23, 2008
Posts: 806 View posts
Location: Pune, India
Posted by drt80: Mon. Mar 30, 2009 - 04:55 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Well, I guess I can try it out. But should be a while before I do it. I want to finish my ground work before I order anything.
I am based in India, so need to think before buying (importing).

BTW, I will be interfacing it to one of the AVR32 devices. For trials the AT32UC3A0512 and a different AVR32 for the final design.

-Deven

Top
barnacle
barnacle's picture
Level: Raving Lunatic
Joined: Tue. Jan 3, 2006
Posts: 6742 View posts
Location: Berlin DE
Posted by barnacle: Mon. Mar 30, 2009 - 07:09 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Off the wall... how about a vernier scale wrapped around the shaft? A fixed number of narrow stripes running longitudinally along the shaft (i.e. round the circumference) and a scribed transparent grid at a slight angle; observe the position of the moire patterns.

Neil Barnes
www.nailed-barnacle.co.uk

Top
digitool
digitool's picture
Level: Posting Freak
Joined: Wed. Jul 2, 2003
Posts: 1012 View posts
Location: Tricky Dicky City
Posted by digitool: Mon. Mar 30, 2009 - 11:12 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Here is a link for some rotary encoders that might fit your needs.

http://usdigital.com/products/en...

Top
DocJC
DocJC's picture
Level: 10k+ Postman
Joined: Tue. Dec 11, 2007
Posts: 13553 View posts
Location: Cleveland, OH
Posted by DocJC: Tue. Mar 31, 2009 - 01:17 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Does it only rotate in one direction?

Is it always 0.1 deg per activation?

How about an optical sensor to detect a Zero Point and just counting the drive pulses to the system driving it?

JC

Top
glitch
glitch's picture
Level: Raving Lunatic
Joined: Sat. Jan 12, 2002
Posts: 8620 View posts
Location: Canada
Posted by glitch: Tue. Mar 31, 2009 - 01:22 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

another option is a resolver

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

Top
drt80
drt80's picture
Level: Resident
Joined: Fri. May 23, 2008
Posts: 806 View posts
Location: Pune, India
Posted by drt80: Tue. Mar 31, 2009 - 03:59 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks for the comments!

Now that I have some hints, I will do some search/research for a day or two and get back.

-Deven

Top
ubarch
ubarch's picture
Level: Hangaround
Joined: Wed. Apr 12, 2006
Posts: 117 View posts
Posted by ubarch: Thu. Apr 2, 2009 - 12:47 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Austria Microdevices makes some very small, relatively cheap encoders that I believe are based on the Hall effect. A magnet is mounted on the moving part, and an IC is mounted in a fixed position close to the magnet. They have shaft encoders and axial encoders. The former involves a magnetic strip that you wrap around the shaft, and the latter involves a small magnet that you attach to the end of a shaft.

Top
drt80
drt80's picture
Level: Resident
Joined: Fri. May 23, 2008
Posts: 806 View posts
Location: Pune, India
Posted by drt80: Fri. Apr 3, 2009 - 08:36 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Update!

I think I will go with the encoder solution. Still do not know which one, but will try to find one locally.

The accelerometer solution is on "hold". At least for now. But, it seems a nice mini project 8).

-Deven

Top