Laser for revolution counting...

[Wond3rboy]

Hi i want to know in what ways one can use a laser for counting the rotations of a wheel. Here are a few that i thought of(simple)

1. Use a Reciver(LDR or something) on the other end and point the laser trough the rims.

2. Use some sort of reflector(not very efficient since the 'reflector' can get dirty, inaddition to all the other problems).

Any more??

 

[dknguyen]

Depends on what kind of wheel you are trying to measure. Some don't even use a laser. They seem to just use ambient light (non-fluorescent) and count the "dark".

Others don't need a reflector either. THey just read the diffuse reflection off of the wheel.

 

[Boncuk]

If you can make some small grooves (0.1mm) into the wheel the laser will "see" the wheel rotating until it's surface has become perfectly smooth and even by dirt.

Look at a CD. You can't see the pits in the aluminum, but the laser can clearly "see" them.

Boncuk

 

[Wond3rboy]

Thanks for your replies.I want to measure the speed of a vehicle's wheel.So i thought that a laser would be a better approach. Tachometers are available to to calculate the RPM.

About the diffused reflection by the tire, since it can get dirty it will become un predictable.

 

[Boncuk]

Look at the complete wheel arrangement of a car using ABS (anti-blocking-system) There is another wheel mounted on the axle of each wheel. It looks like a sprocket and is used in combination with Hall sensors.

If the car has become dirty enough to make the sprocket even the system still recognizes the precise rpm of each individual wheel.

May be it's a good idea to get away from laser detecting and use Hall sensors instead.

Boncuk