Method for optimizing performance of optical encoders operating in a fluid
An unsealed optical encoder does not function properly in a fluid other than air because the optics do not function when interfaced with a medium having an index of refraction significantly higher than air. The collimating lens of an optical encoder has two refracting surfaces, at least one of the refracting surfaces being convex. An orthogonal cap of the present invention is attached over an optical encoder's collimating lens to create a sealed air cavity between the convex refracting surface of the collimating lens and the orthogonal cap. This placement of the orthogonal cap is such that the collimated light leaving the sealed air cavity may enter the surrounding medium at an angle that is normal to the surface of the medium, such as transparent oil, so that the collimated light does not bend even though the light is traveling from air to a much slower medium.
1. An optical encoder, capable of functioning while submersed in a fluid, comprising:
a caliper;
a code disc;
a sensing element;
a light source;
a collimating lens, with a first refracting surface and a second refracting surface, that properly collimates light from the light source when at least one of the refracting surfaces is substantially interfaced with a medium of air; and
a first orthogonal cap that creates a first sealed air cavity between one of the collimating lens's refracting surfaces and the first orthogonal cap, the first orthogonal cap being a substantially transparent sheet of non-focusing material that substantially lies in a plane that is perpendicular to the propagation of collimated light.
2. The optical encoder of claim 1 further comprising a lens tube that substantially surrounds a circumference of the collimating lens such that a height of the lens tube is parallel to the propagation of the collimated light, the lens tube having a crown end and a base end that each lie in planes that are perpendicular to a height of the lens tube, the crown end being closest to the second refracting surface and the base end being closest to the first refracting surface, the crown end being fixed to the first orthogonal cap so that at least part of the lens tube functions as a wall for the first sealed air cavity.
3. The optical encoder of claim 2 further comprising a second orthogonal cap that is fixed to the base end of the lens tube so that at least part of the lens tube functions as a wall for a second sealed air cavity.
4. The optical encoder of claim 2 wherein the first orthogonal cap is a substantially clear sheet of polycarbonate material having a uniform thickness.
5. The optical encoder of claim 4 wherein the first orthogonal cap is fixed to the crown end of the lens tube by a polycarbonate solvent weld.
6. The optical encoder of claim 1 wherein the caliper is coated with a material that protects the optical encoder against conductive fluids.