Patent ID: 7180053

Claim:
An apparatus for monitoring position, the apparatus comprising: a cylinder having walls defining an interior and further having a length defined between a first end and a second end wherein the first end is opposite to the second end of the cylinder; a first wall at the first end of the cylinder; a shaft having a length defined between a first end and a second end wherein a portion of the shaft is within the interior of the cylinder wherein the second end of the shaft moves between the first end of the cylinder and the second end of the cylinder within the interior of the cylinder wherein the second end of the shaft moves from a first position within the interior of the cylinder to a second position within the interior of the cylinder wherein the second end of the shaft transposes the interior of the cylinder between the first end and the second end of the cylinder; a second wall at the second end of the cylinder wherein the second position of the second end of the shaft is located between the first position and the second wall at the second end of the cylinder; an aperture within the first wall at the first end wherein light projects through the aperture into the cylinder; and a sensor at the second wall of the cylinder wherein the sensor detects intensity of light within the interior of the cylinder at the second end of the cylinder which is not absorbed by the shaft and the interior of the cylinder wherein the intensity of light detected by the sensor at the second wall corresponds to the second position of the shaft in the interior of the cylinder wherein a distance between the second end of the shaft and the second wall corresponds to the intensity of light detected by the sensor at the second wall.