Magnetic heading reference

Claim 2

Means for detecting relative angular displacement comprising: a source of unpolarized light; polarizing means disposed in the path of light from said source to cause the light passing therethrough to be polarized; analyzing means disposed in the path of said polarized light comprising a central polarized area and an outer polarized area surrounding said central polarized area, said central and outer polarized areas being arranged to have their respective directions of polarization at an angle to each other; a first photo-responsive means positioned to receive the light which first passes through said polarizing means and then through said central polarized area of said analyzing means; and a second photo-responsive means positioned to receive the light which first passes through said polarizing means and then through said outer polarized area of said analyzing means; said analyzing means and said polarizing means being angularly displaceable relative to each other.

Claim 3

Means for detecting relative angular displacement as claimed in claim 1 wherein said polarized light is arranged to radiate in substantially equal intensity in the directions of said first and second photo-responsive means.

Claim 4

Means for detecting relative angular displacement as claimed in claim 1 wherein the respective directions of polarization of said central and outer polarized areas are arranged at right angles to each other.

Claim 5

Means for detecting relative angular displacement as claimed in claim 1 further including electrical circuit means operatively associated with said first and second photo-responsive means, said first and second photo-responsive means providing respective output signals each respresentative of the amount of light incident on the corresponding photo-responsive means, said electrical circuit means providing a further signal indicative of the differential between said output signals.

Claim 6

Means for detecting relative angular displacement as claimed in claim 1 further including positioning means for angularly positioning said analyzing means with respect to said polarizing means.

Claim 7

Means for detecting relative angular displacement as claimed in claim 5 wherein said analyzing means lies in a plane and said positioning means is arranged to rotate said analyzing means in said plane.

Claim 8

Means for detecting relative angular displacement as claimed in claim 6 wherein said means for detecting relative angular displacement operates to detect angular displacement of a first member relative to a second member, said polarizing means being affixed to said first member and said analyzing means being affixed to said second member, said first member having a center of rotation and said second member having an axis of rotation which offset from the center of rotation of said first member.

Claim 9

Means for detecting relative angular displacement as claimed in claim 7 wherein said central polarized area of said analyzing means has a circular outer edge and said first and second members are arranged such that an imaginary line passing through said center of rotation perpendicular to the plane of said analyzing means intersects said plane at a point on said circular outer edge of said central polarized area.

Claim 10

Means for detecting relativE angular displacement as claimed in claim 1 wherein said central polarized area of said analyzing means has a circular outer edge.

Claim 11

Means for detecting relative angular displacement as claimed in claim 9 wherein said polarizing means has a center of rotation and said analyzing means and said polarizing means are arranged such that an imaginary line passing through said center of rotation perpendicular to said analyzing means intersects a point on said circular outer edge of said central polarized area of said analyzing means.

Claim 12

Means for detecting relative angular displacement as claimed in claim 10 further including positioning means for angularly positioning said analyzing means about an axis parallel to said line.

Claim 13

Means for detecting relative angular displacement as claimed in claim 11 wherein said first photo-responsive means is disposed in substantial axial alignment with said central polarized area.

Claim 14

Means for detecting relative angular displacement as claimed in claim 13 wherein said first photo-responsive means is disposed immediately behind said central polarized area on the side of said analyzing means opposite said polarizing means.

Claim 15

Means for detecting relative angular displacement as claimed in claim 12 wherein said second photo-responsive means is disposed diametrically opposite said first photo-responsive means relative to said axis.

Claim 16

Means for detecting relative angular displacement as claimed in claim 14 wherein said first and second photo-responsive means are disposed in side-by-side fashion.

Claim 17

Means for detecting relative angular displacement as claimed in claim 15 wherein said first and second photo-responsive means are disposed immediately behind said analyzing means on the side thereof opposite said polarizing means.

Claim 18

Means for detecting relative angular displacement as claimed in claim 9 wherein said outer polarized area has a circular inner periphery matching the outer circular periphery of said central polarized area.

Claim 19

Means for detecting relative angular displacement as claimed in claim 1 wherein said first and second photo-responsive means each comprises a photo-sensitive area responsive to light incident thereon falling within a limited solid angle, said first and second photo-responsive means being positioned such that light from said source which passes through said central polarized area of said analyzing means subtends substantially the entire solid angle associated with the photo-sensitive area of said first photo-responsive means and the light from said source passing through said outer polarized area of said analyzing means subtends substantially the entire solid angle associated with the photo-senesitive area of said second photo-responsive means.

Claim 20

A magnetic heading reference comprising: a housing forming an enclosure; magnetic means disposed within said enclosure for alignment with the horizontal component of the prevailing external magnetic field; a source of unpolarized light on said housing; polarizing means carried by said magnetic means and disposed in the path of light from said source such that the light passing through said polarizing means becomes polarized and has a direction of polarization representative of the direction of said horizontal component of the prevailing external magnetic field; analyzing means on said housing disposed in the path of said polarized light, said analyzing means comprising a first region of polarization and a second region of polarization, said two regions of polarization having their respective directions of polarization at an angle to each other, a first photo-responsive means disposed on said housing to receive light which first passes through said polarizing means and then through said first region of polarization; a second photo-responsive means disposed on said housing to receive light which first passes through said polarizing means and then through said second region of polarization; and positioning means for positioning said analyzing means with respect to said housing.

Claim 21

A magnetic heading reference comprising: a housing forming an enclosure; magnetic means disposed within said enclosure for alignment with the horizontal component of the prevailing external magnetic field; a source of unpolarized light on said housing; polarizing means carried by said magnetic means and disposed in the path of light from said source such that the light passing through said polarizing means becomes polarized and has a direction of polarization representative of the direction of said horizontal component of the prevailing external magnetic field; analyzing means on said housing disposed in the path of said polarized light, said analyzing means comprising a first region of polarization and a second region of polarization, said two regions of polarization having their respective directions of polarization at an angle to each other, a first photo-responsive means disposed on said housing to receive light which first passes through said polarizing means and then through said first region of polarization; a second photo-responsive means disposed on said housing to receive light which first passes through said polarizing means and then through said second region of polarization; and positioning means for positioning said analyzing means with respect to said housing.

Claim 22

A magnetic heading reference as claimed in claim 19 wherein said analyzing means comprises a disc containing said first and second regions of polarization, said positioning means being arranged to rotate said disc about an axis.

Claim 23

A magnetic heading reference as claimed in claim 20 wherein said magnetic means is arranged to rotate about a point and said axis is offset with respect to the point about which said magnetic means rotates.

Claim 24

A magnetic heading reference as claimed in claim 21 wherein said first region of polarization has a circular outer periphery and said second region of polarization surrounds said first region of polarization.

Claim 25

A magnetic heading reference as claimed in claim 22 wherein the periphery of said first region of polarization is substantially tangent to a line passing through the point about which said magnetic means rotates perpendicular to said axis.

Claim 26

A magnetic heading reference as claimed in claim 23 including manually operable means for operating said positioning means to rotate said disc.

Claim 27

A magnetic heading reference as claimed in claim 24 wherein said manually operable means comprises a thumbwheel knob.

Claim 28

A magnetic heading reference as claimed in claim 22 wherein said first photo-responsive means is disposed in axial alignment with said first region of polarization.

Claim 29

A magnetic heading reference as claimed in claim 26 wherein said second photo-responsive means is disposed along side said first photo-responsive means.

Claim 30

A magnetic heading reference as claimed in claim 27 wherein said first photo-responsive means is disposed to respond substantially exclusively to light passing through said first region of polarization and said second photo-responsive means is disposed to respond substantially exclusively to light passing through said second region of polarization.