Bi-directional, self imaging grating detection apparatus

Claim 2

A bi-directional, self-imaging grating detection apparatus comprising: a grating comprising a strip of transparent material having first and second sets of light interrupting opaque lines thereon, said first set of lines being positioned above said second set of opaque lines and laterally offset therefrom; a source-detector assembly comprising first and second pairs of light source and detection devices, each of said pairs comprising a light source means and a light detection means, and positioned on one side of said grating; at least one of said devices of one of said pairs being aligned with said first set of light interrupting opaque lines and the other of said devices of said pair being aligned with the other set of light interrupting opaque lines; an imaging reflective surface on the opposite side of said strip having a central axis which passes through a point mid way between the light source means and light detection means of each of said pairs of light source and detection devices, means for effecting relative movement between said grating and said source-detector assembly whereby the images detected in the moving system by the detectors are offset to thereby effect a signal output by said detectors of a different phase relation.

Claim 3

A bi-directional, self-imaging grating detection apparatus in accordance with claim 1 in which said imaging reflective surface comprises a segment of a spherical surface.

Claim 4

A bi-directional, self-imaging grating detection apparatus in accordance with claim 2 wherein said grating lies in a plane which is perpendicular to said control axis and passes through a point coincident with the center of the spherical segment surface so as to obtain a magnification of 1X.

Claim 5

A bi-directional, self-imaging grating detection apparatus in accordance with claim 1 wherein said imaging reflective surface comprises a concave mirror, said concave mirror having a radius of curvature equal to the distance between said mirror and said grating along said central axis.

Claim 6

A bi-directional, self-imaging grating detection apparatus in accordance with claim 1 wherein said control axis of said imaging reflective surface passes through said grating and said source detector assembly, each of said source means of a pair being located the same distance from said control axis as the detection means of said pair.

Claim 7

A bi-directional, self-imaging grating detection apparatus in accordance with claim 5 wherein the said source means and detection means of each of said pairs is located the same distance from the central axis of said imaging reflective surface.

Claim 8

A bi-directional, self-imaging grating detection apparatus in accordance with claim 1 wherein said lateral offset of said first set of lines with respect to said second set of lines is 90°.

Claim 9

A bi-directional, self-imaging grating detection apparatus in accordance with claim 1 wherein said opaque lines of said first and second sets are positioned at an angle of 45° to reduce the effect of astigmatic aberration.

Claim 10

A bi-directional, self-imaging grating detection apparatus in accordance with claim 1 wherein said first and second sets of light interrupting opaque lines are spaced uniformily apart, forming transparent line patterns therebetween so that said opaque lines are interdigitated with said transparent lines.

Claim 11

A bi-directional, self-imaging grating detection apparatus in accordance with claim 9 in which the width of each of said opaque lines is greater than the width of an adjacent transparent lines.

Claim 12

A bi-directional, self-imaging grating detection apparatus in accordance with claim 10 in which said opaque line and transparent line combination are represented by a 60% opaque line width and a 40% transparent line width.

Claim 13

A bi-directional, self-imaging grating detection apparatus in accordance with claim 1 wherein said height of said second set of opaque lines is greater than the height of said first set of opaque lines.

Claim 14

A bi-directional, self-imaging grating detection apparatus in accordance with claim 1 including a lens over each of said source and detection devices of said source and detection pairs.

Claim 15

A bi-directional, self-imaging grating detector in accordance with claim 13 wherein each of the lens has an axis which is offset from the central axis of each of the devices and towards said central axis.

Claim 16

A bi-directional, self-imaging grating detection apparatus in accordance with claim 3 wherein said control axis of said spherical segment surface passes through said grating and said source detector assembly, each of said source means of a pair being located the same distance from said control axis as the detection means of said pair.

Claim 17

A bi-directional, self-imaging grating detection apparatus in accordance with claim 15 including a lens over each of said source and detection devices of said source and detection pairs.

Claim 18

A bi-directional, self-imaging grating detector in accordance with claim 16 wherein each of the lens has an axis which is offset from the central axis of each of the devices and towards said central axis.

Claim 19

A grating and detection apparatus in combination, comprising: a grating having first and second sets of light interrupting opaque lines thereon interdigitated with light transmissive or transparent lines thereon, said first set of lines being superimposed of said second set of lines and lateraly offset therefrom; a source-detector assembly comprising first and second pairs of light source and detection devices, each of said pairs comprising a light source means and a light detection means, and positioned on one side of said grating; at least one of said devices of one of said pairs being aligned with said first set of light interrupting opaque lines and the other of said devices of said pair being aligned with the other set of light interrupting opaque lines; a spherical segment mirror surface on the opposite side of said grating having a control axis which passes through a point midway between said light source and detection devices, said mirror surface having a radius of curvature equal to the distance along said central axis of said mirror surface from said grating; lens means over said source means and light detection means to focus light eminating from said source means and light received by said detection means; means for effecting relative movement between said grating and said source-detector assembly whereby the images detected in the moving system by the detectors are offset to thereby effect a signal output by said detectors of a different phase relation.

Claim 20

A grating and detection apparatus in combination, comprising: a grating having first and second sets of light interrupting opaque lines thereon interdigitated with light transmissive or transparent lines thereon, said first set of lines being superimposed of said second set of lines and lateraly offset therefrom; a source-detector assembly comprising first and second pairs of light source and detection devices, each of said pairs comprising a light source means and a light detection means, and positioned on one side of said grating; at least one of said devices of one of said pairs being aligned with said first set of light interrupting opaque lines and the other of said devices of said pair being aligned with the other set of light interrupting opaque lines; a spherical segment mirror surface on the opposite side of said grating having a control axis which passes through a point midway between said light source and detection devices, said mirror surface having a radius of curvature equal to the distance along said central axis of said mirror surface from said grating; lens means over said source means and light detection means to focus light eminating from said source means and light received by said detection means; means for effecting relative movement between said grating and said source-detector assembly whereby the images detected in the moving system by the detectors are offset to thereby effect a signal output by said detectors of a different phase relation.