Positional sensing

[Parsnip]

Please can someone provide a clue.
I need to monitor the position of a flag positioned on a leadscrew attached to a motor. All the movement is computer controlled and on startup moves the flag to break the beam of an opto sensor. The leadcrew is then activated and the flag moves until another opto sensor is activated (about 150mm). The problem is that the opto sensors are mounted on flimsy posts and can not be constrained in enough degrees of freedom.
Ideally I would like to use an alternative method and have been told about positional encoders, bar code readers etc - please can some genral help be provided to point me in the right direction.
Regards
Parsnip

 

[benta]

Well, if you have a leadscrew, the solution would be to measure revolutions/position.
Use a so called "Absolute" encoder", this could be mounted either at the motor end or on the end of your leadscrew.
Look here:

http://www.avagotech.com/products/category-detail.jsp?navId=H0,C1,C5231,C4935,C4975

Benta.

 

[waross]

benta has an excellent suggestion.
As an alternative limit switches may be mounted next to the leadscrew.
yours

 

[OperaHouse]

The problem sounds more mechanical. As an alternative a magnetic sensor may have some advantages in this situation.

 

[jraef]

I would opt for the absolute encoder, virtually impervious to environmental influences, vibration, magnetics, light scattering etc. etc.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[ScottyUK]

Define what accuracy you need. If you don't need better accuracy than the tolerance on the leadscrew, use it as part of the measuring device by counting screw revolutions and implying linear distance moved from the count. If you need better accuracy, consider magnetostrictive sensors or LVDT's - good for resolving down to a few microns. Below that you will need some fairly exotic (and expensive) hardware.

Heidenhain and Balluff are a couple of manufacturers to get you going - Heidenhain are arguably better known for their rotary encoders, Balluff for their linear types. Both very good.

http://www.heidenhain.com/

http://www.balluff.com

----------------------------------

I don't suffer from insanity. I enjoy it...

 

[Parsnip]

Thank you all for your help - the rotary encoders certainly look the way to go and having talked to our electronics/firmware guys it looks as though they will be compatible with what we have already designed.
Thanks all once again
Parsnip

 

[IRstuff]

Note that optical sensors also need to be somewhat shielded from ambient lighting, particularly in an application that's exposed to strong lights.

TTFN