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US 5,107,107 AGranted
Laser optical disk position encoder with active heads
AssigneeThe United States of America as represented by the Administarator of the National Aeronautics and Space Administration
InventorEric P. Osborne
Life of this patent
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Abstract
An angular position encoder is provided that minimizes the effects of eccentricity and other misalignments between the disk and the read stations by employing heads which incorporate beam steering optics with the ability to actively track the disk in directions along the disk radius and normal to its surface. The device adapts features prevalent in optical disk technology toward the application of angular position sensing. A reflective disk and the principles of interferometry are employed. The servo controlled steering optics move so as to acquire a track on the disk lying at a predetermined radius and distance below the head, and then adjust position and orientation in order to maintain view of the disk track as required. Thus, the device is actively self-aligning.
Claims12
An encoder employing constructive interferometry comprising:
- a code disk rotatable about an axis in a plane and having a plurality of bi-level surfaces spaced equidistantly apart by a predetermined pitch on a circumferential part of one face of said disk in said rotation plane, said bi-level surfaces extending circumferentially about said rotation axis wherein said bi-level surfaces have a uniform reflectivity, said bi-level surfaces lying in one of either of two parallel planes differing in elevation by a fraction of a wavelength of light;
- and
- sensing means disposed opposite said circumferential part of said one face of said code disk and facing said bi-level surfaces, wherein said sensing means are kinematically mounted allowing motion with respect to said one face of said disk thereby allowing said sensing means to acquire and continually track said bi-level surfaces, and wherein the position and orientation of said sensing means are established through closed loop control circuitry capable of evaluating the relative position and orientation of said sensing means with respect to said bi-level surfaces.
An encoder employing constructive interferometry comprising:
- a code disk rotatable about an axis in a plane and having a plurality of bi-level surfaces spaced equidistantly apart by a predetermined pitch on a circumferential part of one face of said disk in said rotation plane, said bi-level surfaces extending circumferentially about said rotation axis wherein said bi-level surfaces have a uniform reflectivity, said bi-level surfaces lying in one of either of two parallel planes differing in elevation by a fraction of a wavelength of light;
- sensing means disposed opposite said circumferential part of said one face of said code disk and facing said bi-level surfaces, wherein said sensing means are kinematically mounted allowing motion with respect to said one face of said disk thereby allowing said sensing means to acquire and continually track said bi-level surfaces, and wherein the position and orientation of said sensing means are established through closed loop control circuitry capable of evaluating the relative position and orientation of said sensing means with respect to said bi-level surfaces;
- said sensing means further comprises:
- transmitter means for directing a coherent light beam through an aperture toward said one face of said code disk;
- receiver means for detecting the light reflected off said one face of said code disk;
- electronic circuitry for evaluating the detected light thereby interpreting the distance between said code disk and beam steering optics located within said head sensing means, the focus parameter, and also interpreting the track position of said code disk relative to said aperture, the radial track parameter, said circuitry having the capability of producing error signals proportional to both said parameters;
- and
- servo controlled means for directing said beam steering optics so as to follow both axial variations and radial motion of said code disk, wherein said focus and tracking error signals are fed back to said servo controlled means for correction of said beam steering optical device.
5 more elements
An encoder comprising:
- a code disk rotatable about an axis in a plane and having a plurality of demarcated elements spaced equidistantly apart by a predetermined pitch on a circumferential part of one face of said code disk in said rotation plane, said demarcated elements extending circumferentially about said rotation axis;
- and
- sensing means disposed opposite said circumferential part of said one face of said code disk facing said bi-level surfaces, wherein said sensing means are kinematically mounted allowing motion with respect to said one face of said disk thereby allowing said sensing means to acquire and continually track said demarcated elements, and wherein the position and orientation of said sensing means are established through closed loop control circuitry capable of evaluating the relative position and orientation of said sensing means with respect to said demarcated elements.
A method for the application of angular position sensing comprising the steps of:
- (a) aligning a beam steering optical system located within a read station such that said system directs a coherent beam of light so that said light strikes a code disk within a defined band of tracks;
- (b) rotating said code disk at a constant rate;
- (c) activating a first magnetic actuator to move an objective lens located within said beam steering optical system such that the light beam is focused upon an information layer within said code disk, and constantly maintaining the distance between said objective lens and said information layer of said code disk;
- (d) activating a second magnetic actuator to move said objective lens such that said light beam is centered above the closest track located within said band of tracks of said code disk;
- (e) evaluating the optical signal received by a detector located within said read station to determine the frequency of variation of the optical signal received by said detector as a result of said disk motion;
- (f) repeating steps (d) and (e) for the adjacent tracks of said code disk until the track with the highest frequency of variation of the optical signal received by said detector is located;
- (g) maintaining the radial alignment of said objective lens relative to said track;
- and
- (h) monitoring the optical signal received by said detector to determine relative changes in angular orientation of said disk.
6 more elements
A method for the application of angular position sensing comprising the steps of:
- (a) aligning a beam steering optical system located within a read station such that said system directs a coherent beam of light so that said light strikes a code disk within a defined band of tracks;
- (b) dithering said code disk at a constant frequency;
- (c) activating a first magnetic actuator to move an objective lens located within said beam steering optical system such that the light beam is focused upon an information layer within said code disk, and constantly maintaining the distance between said objective lens and said information layer of said code disk;
- (d) activating a second magnetic actuator to move said objective lens such that said light beam is centered above the closest track located within said band of tracks of said code disk;
- (e) evaluating the optical signal received by a detector located within said read station to determine the frequency of variation of the optical signal received by said detector as a result of said disk motion;
- (f) repeating steps (d) and (e) for the adjacent tracks of said code disk until the track with the highest frequency of variation of the optical signal received by said detector is located;
- (g) maintaining the radial alignment of said objective lens relative to said track;
- and
- (h) monitoring the optical signal received by said detector to determine relative changes in angular orientation of said disk.
6 more elements
Dependencies are inferred from the claim text.