Abstract: A device for measuring the displacement of a movable object includes a stationary light source (10) that produces an incident light beam. A target feature (17), attached to, or integral with, the object, reflects the incident light beam and forms a first image of the light source in close proximity of the target feature. An imaging lens (26) receives the reflected light beam and reforms the first image of the light source as a second image on the photodetector (20). The photodetector, spaced from the object, receives the reflected light beam and produces an electric signal having a characteristic which is proportional to a received location on the photodetector of the second image and which represents a position of the object. The target feature includes a curved surface that reflects the light beam such that a small, point-like or line-like first image of the light source is formed and reformed as a second image on the photodetector.

Abstract: A method for fabricating an error-free linear position encoder incorporates the generation of fringes on a holographic plate by the interference of light from two point sources. The fringes are projected onto a curved holographic plate without intervening optical elements, the curve being such that the fringes have a constant pitch along the surface of the plate. A methodology for generating such a curve includes the creation of a graphic representation of the hyperbolic fringes generated by the interference between two coherent point sources, which would fall on an appropriately curved holographic plate. A numerical technique derived from the graphic representation produces a “constant-pitch” curve such that all of the fringes projected onto the curve are equidistant. The holographic plate, coated with a photosensitive material, is fabricated or formed in the shape of the constant-pitch curve.

Abstract: A device for measuring the displacement of a movable object includes a stationary light source that produces an incident light beam. A target feature, attached to, or integral with, the object, reflects the incident light beam. A stationary photodetector, spaced from the object, receives the reflected light beam and, in response thereto, produces an electric signal having a characteristic (such as amplituded) which is proportional to a received location on the photodetector of the reflected light beam and which represents a position of the object. An imaging lens receives the reflected light beam and focusses an image of the light source on the photodetector. The target feature includes a curved surface that reflects the light beam such that a small, point-like or line-like image of the light source is focussed on the photodetector. The displacement sensor device is particularly useful in a disk drive servo system application.

Abstract: A device for measuring the displacement of a movable object includes a stationary light source that produces an incident light beam. A target feature, attached to, or integral with, the object, reflects the incident light beam and forms a first image of the light source in close proximity of the target feature. An imaging lens receives the reflected light beam and reforms the first image of the light source as a second image on the photodetector. The photodetector, spaced from the object, receives the reflected light beam and, in response thereto, produces an electric signal having a characteristic (such as amplitude) which is proportional to a received location on the photodetector of the second image and which represents a position of the object. The target feature includes a curved surface that reflects the light beam such that a small, point-like or line-like first image of the light source is formed and reformed as a second image on the photodetector.

Abstract: A device for measuring the displacement of a movable object includes a stationary light source that produces an incident light beam. A target feature, attached to, or integral with, the object, reflects the incident light beam. A stationary photodetector, spaced from the object, receives the reflected light beam and, in response thereto, produces an electric signal having a characteristic (such as amplituded) which is proportional to a received location on the photodetector of the reflected light beam and which represents a position of the object. An imaging lens receives the reflected light beam and focusses an image of the light source on the photodetector. The target feature includes a curved surface that reflects the light beam such that a small, point-like or line-like image of the light source is focussed on the photodetector. The displacement sensor device is particularly useful in a disk drive servo system application.

Abstract: A device for measuring the displacement of a movable object includes a stationary light source that produces an incident light beam. A target feature, attached to, or integral with, the object, reflects the incident light beam. A stationary photodetector, spaced from the object, receives the reflected light beam and, in response thereto, produces an electric signal having a characteristic (such as amplituded) which is proportional to a received location on the photodetector of the reflected light beam and which represents a position of the object. An imaging lens receives the reflected light beam and focusses an image of the light source on the photodetector. The target feature includes a curved surface that reflects the light beam such that a small, point-like or line-like image of the light source is focussed on the photodetector. The displacement sensor device is particularly useful in a disk drive servo system application.

Abstract: A detector is described, intended for use in metrology systems of the type which produce interference fringe patterns which contain a phase which is characteristic of the parameter under measurement, particularly displacement or position. The detector is in the form of an array of elements whose outputs are electrically interconnected so as to form three or more signals displaced from one another in phase by a fixed amount. The detector is provided on a single monolithic, silicon substrate using microelectronics techniques.

Abstract: A metrology system includes means for generating an interference fringe pattern as a function of a parameter to be measured, transducer apparatus for simultaneously generating three intensity-modulated optical signals, I.sub.R, I.sub.S and I.sub.T, that are related to the interference fringe pattern; signal processing apparatus for accurately determining an aspect of the interference fringe pattern from the three signals; means for accumulating phase information proportional to the aspect of the interference fringe pattern; and means for converting the accumulated phase and aspect information to desired outputs indicative of the parameter to be measured.

Abstract: A lateral movement sensing system which utilizes a two-frequency laser to provide two laser beams to illuminate a surface of a laterally moveable body. A beam splitter divides the two-frequency laser into two beams, and the system detects the modulation frequency of the scattered light when the laterally moveable body is moving. This detected modulation frequency is compared to the frequency difference between the two beams. The phase difference between the detected modulation frequency and the difference frequency represents units of lateral displacement of the laterally moveable body.

Abstract: Frequency stabilization is disclosed for a laser device, wherein the laser tube is provided with end mirrors which are mounted in extensions at the respective ends of the laser tube. The laser tube extensions have reduced sections which are movable to allow adjustment of the end mirrors in the laser device. The reduced sections are preferably made of metallic material. The means to stabilize frequency provided is the application of heat or current or both to and around a reduced metallic section in the laser tube extension. This may be accomplished by the passing of current through a wire wrapped around the reduced metallic section. The passing of such current causes the reduced metallic section to contract and expand along an axis in line with the laser tube, and as well as a magnetic field is induced upon the gaseous medium within the laser tube. By such means controlled by suitable circuitry, laser frequency stabilization is accomplished.

Abstract: An improved mirror alignment control for dynamically aligning the reflecting mirrors bounding the optical path in an interferometer comprises a closed loop servo control which utilizes a two frequency laser beam to provide phase comparison between beams traversing differing portions of the optical paths in the interferometer to determine alignment of the mirrors, said phase comparison providing a correction signal to direct multi-axial alignment of at least one of the mirrors.

Abstract: A method and means for stabilizing the difference in frequencies between the frequency components of a two frequency laser beam influenced by Zeeman effect frequency splitting, accurately determines the frequency separation independently of the individual frequencies or intensities of either of the frequency components. Frequency stabilization is accomplished by mechanical and thermal adjustments to the lasing chamber length of the laser by a closed loop servo control referencing the frequency difference between laser beam components and a reference signal having a frequency equal to the desired frequency difference.

Abstract: An improved mirror scan control for driving a movable mirror in an interferometer with a constant scan velocity comprises a closed loop servo control which provides constant velocity mirror scan in response to a phase comparison of a signal derived from the beat frequency of a two frequency laser beam passing through the interferometer and a selected frequency reference signal, wherein the difference in frequencies or beat frequency of the two frequency laser beam is stabilized at a specified difference in frequencies. The mirror scan control employs a phase lock control loop which locks the frequency of the referenced signal with the frequency of the signal derived from the laser beam to provide precise mirror velocity control.