Patent ID: 6952009

Claim:
An apparatus for measuring displacement, the apparatus comprising: a machine element having a body defining an interior wherein the body has an interior surface and a length defined between a first end and a second end wherein the interior surface has a light-absorbing coating; a first wall at the first end wherein the first wall is planar and further wherein the first wall abuts the body of the machine element; a second wall at the second end substantially enclosing the interior; a shaft element movable within the machine element; a head element attached to the shaft element adjacent to the interior surface of the machine element; a light source on the first wall of the machine element wherein the light source extends inward with respect to the interior of the machine element wherein the light source emits a light into the interior of the machine element; and a sensor positioned on the first wall of the machine element wherein the sensor detects intensity of emitted light within the interior of the machine element which is not absorbed by the coating on the interior surface of the machine element wherein the intensity of light corresponds to a position of the head element within the machine element at a point between the first end and the second end.