Relative movement detecting apparatus using a detector positioned in a region of natural interference

An apparatus for detecting relative movement comprising

• a diffraction grating relatively movable with respect to a source and having a period P and a characteristic which diffracts light at a preselected wavelength .lambda. into positive and negative diffraction orders which interfere with one another in a region of natural interference adjacent the diffraction grating;
• a light source providing a beam of light of wavelength .lambda.;
• a polarizing beam splitter;
• a quarter-wavelength phase retarder, wherein the polarizing beam splitter is positioned in a path of the beam to reflect substantially all of the beam through the phase retarder and onto the diffraction grating, and further wherein the polarizing beam splitter and the phase retarder are positioned so that positive and negative diffraction orders diffracted from the diffraction grating pass through the phase retarder and the polarizing beam splitter;
• and
• a detector having a sensing plane positioned within a region of natural interference between positive and negative diffraction order beams from the diffraction grating which have passed through the phase retarder and the polarizing beam splitter.

An apparatus capable of detecting relative movement of a member which includes a diffraction grating having a period P and a characteristic which diffracts light at a preselected wavelength .lambda. into positive and negative diffraction orders that interfere with one another in a region of natural interference adjacent the diffraction grating, the apparatus comprising

• a head structure;
• a carrier structure supported by the head structure;
• a light source which provides collimated, monochromatic of the pre-selected wavelength .lambda. and supported by the head structure;
• a periodic detector positioned on the carrier structure, having a sensing plane and a having a period which is a function of the preselected wavelength .lambda. and the period P of the diffraction grating, wherein the periodic detector provides an output signal in response to light incident thereon;
• electronic circuitry positioned on the carrier structure, for conditioning the output signal from the periodic detector;
• a mirror structure supported by the head structure;
• wherein the mirror structure has a position on the head structure with respect to the light source so as to be capable of directing onto the periodic detector natural interference between positive and negative diffraction orders which are diffracted by the diffraction grating in response to light incident on the diffraction grating from the light source when the head structure is positioned adjacent the diffraction grating.

An apparatus for detecting relative movement comprising

• a diffraction grating relatively movable with respect to a source and having a period P and a characteristic which diffracts light at a preselected wavelength .lambda. into positive and negative diffraction orders which interfere with one another in a region of natural interference adjacent the diffraction grating;
• means for illuminating with first and second beams of light of wavelength A a region of said diffraction grating;
• a multi-element detector having a sensing plane positioned within the region of natural interference of the diffraction grating between positive and negative diffraction orders from the first and second beams of light;
• wherein the multi-element detector has a period which is a function of the preselected wavelength .lambda. and the period P of the diffraction grating, wherein the multi-element detector provides an output signal in response to light incident thereon, whereby the multi-element detector responds principally to interference at said sensing plane between the positive and negative diffraction orders diffracted from said diffraction grating.