Apparatus for detecting relative movement

Apparatus for detecting relative movement comprising;

• a source of monochromatic light of wavelength .lambda.;
• a reflection diffraction scale relatively movable with respect to said source and having a period P and a characteristic which concentrates light diffracted at said wavelength .lambda. into the positive and negative first orders and which minimizes the zeroth order;
• means for directing light from said source onto a region of said scale having a width W along the length of the scale;
• a poly-phase periodic detector having a sensing plane spaced from said scale a distance less than ##EQU6## the period of said detector being equal to P/2 whereby said detector responds principally to interference at said sensing plane between the positive and negative first orders diffracted from said scale.

Apparatus for detecting relative movement comprising:

• a semiconductor laser providing monochromatic light of wavelength .lambda.;
• an elongate reflective diffraction scale longitudinally relatively movable with respect to said laser, said scale being ruled transversely to its length with a period P and a characteristic which concentrates light diffracted at said wavelength .lambda. into the positive and negative first orders and which minimizes the zeroth order;
• means for directing light from said laser onto a region of said scale having a width w along the length of the scale;
• a plurality of elongate photoelectric detectors arranged in a planar parallel array spaced from said scale a distance less than ##EQU8## said detectors being interconnected in a periodic multiphase array with the period being equal to P/2 whereby said detector responds principally to interference at said sensing plane between the positive and negative first orders diffracted from said scale.

Apparatus for detecting relative movement comprising:

• a diffraction grating relatively movable with respect to a source of light and having a period P and a characteristic which concentrates light diffracted at a preselected wavelength .lambda. into positive and negative first order beams which initially overlap and interfere with one another in a region of pre-separation interference and thereafter separate from one another;
• means for illuminating with light of wavelength .lambda., a region having a width W along the length of said grating;
• and
• a periodic detector having a sensing plane positioned within the region of pre-separation interference, wherein the period of said detector is equal to P/2 whereby said detector responds principally to interference at said sensing plane between the positive and negative first orders beams diffracted from said grating.

A method for detecting relative movement of an object comprising

• positioning a diffraction grating for movement with the object, wherein the diffraction grating has a period P and a characteristic which concentrates light diffracted at a preselected wavelength .lambda. into positive and negative first order beams which initially overlap and interfere with one another in a region of pre-separation interference and thereafter separate from one another;
• illuminating with light of wavelength .lambda., a region having a width W along the length of said grating;
• and
• positioning a sensing plane of a periodic detector within the region of pre-separation interference, wherein the period of said detector is equal to P/2 whereby said detector responds principally to interference at said sensing plane between the positive and negative first orders beams diffracted from said grating.