Position sensor with grating to detect moving object with periodic pattern

A device for detecting the position of a medium having a periodic pattern, comprising:

• a light source mounted to direct a beam of light at said medium;
• a multiple element detector mounted to intercept a reflected beam of light from said medium, wherein said reflected beam of light diverges from said light source to said medium and from said medium to said detector;
• a periodic structure for varying the area of said detector exposed to said beam of light over at least a first element of said multiple element detector, a period of said periodic structure given by MT0/n, where M=(Z1+Z0)/Z0 is a magnification factor determined by the distance Z0 between said light source and said medium and the distance Z1 between the detector and the medium, T0 is the period of the periodic pattern on the medium and n is an integer number, the period of said periodic structure corresponding to a harmonic of a frequency of said periodic pattern of said medium;
• a diffraction grating mounted between said medium and said detector for directing said reflected light to said detector;
• wherein said periodic structure is mounted on said diffraction grating, and wherein different zones of said periodic structure have different periods of said diffraction grating to diffract said reflected light to different elements of said detector;
• and
• wherein said detector comprises three light sensitive elements having either 120degree phase difference or 90 degree phase difference in the detector pattern for providing differential detector signals.

A device for detecting the position of a medium having a periodic pattern, comprising:

• a multiple element detector;
• a laser mounted adjacent said detector;
• a first diffractive lens mounted between said laser and said medium to form a line image on said medium, said line being normal to said periodic pattern;
• and
• a second diffractive lens mounted between said medium and said detector to direct a reflection of said laser beam to different elements of said detector.

A device for detecting the position of said device with respect to a medium having a periodic pattern which is periodic in two directions, comprising:

• a light source mounted to direct a beam of light at said moving medium;
• first and second detectors mounted to intercept a reflected beam of light from said medium, wherein said reflected beam of light diverges from said light source to said medium and from said medium to said detectors;
• a first periodic structure for varying the area of said first detector exposed to said reflected beam of light along a first axis, the period of said periodic structure corresponding to a frequency of said periodic pattern in a first direction;
• and
• a second periodic structure for varying the area of said second detector exposed to said reflected beam of light along a second axis, the period of said periodic structure corresponding to a frequency of said periodic pattern in a second direction.