US3217590A - Apparatus for producing moire patterns for use in determining the relative position of a pair of elements - Google Patents

Apparatus for producing moire patterns for use in determining the relative position of a pair of elements Download PDF

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Publication number
US3217590A
US3217590A US194606A US19460662A US3217590A US 3217590 A US3217590 A US 3217590A US 194606 A US194606 A US 194606A US 19460662 A US19460662 A US 19460662A US 3217590 A US3217590 A US 3217590A
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US
United States
Prior art keywords
zones
elements
zone
pattern
pair
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Expired - Lifetime
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US194606A
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English (en)
Inventor
Harry J Lawrence
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AMERICAN DESIGN ENGINEERING CO
AMERICAN DESIGN ENGINEERING CORP
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AMERICAN DESIGN ENGINEERING CO
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Priority to US194606A priority Critical patent/US3217590A/en
Priority to GB16308/63A priority patent/GB1009699A/en
Priority to DE19631303561D priority patent/DE1303561B/de
Application granted granted Critical
Publication of US3217590A publication Critical patent/US3217590A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/36—Forming the light into pulses
    • G01D5/38—Forming the light into pulses by diffraction gratings
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
    • G01B21/02—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness
    • G01B21/06—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness specially adapted for measuring length or width of objects while moving
    • G01B21/065—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness specially adapted for measuring length or width of objects while moving for stretchable materials

Definitions

  • the invention concerns the establishment of a definite and well defined index pattern defined by overlapping elements having aligned cooperating areas of zones of different spatial density.
  • the areas or zones are, in accordance with the present invention, constructed to vary the configuration of the pattern in a direction substantially normal to the direction of movement of the elements for producing a desired index pattern.
  • moire bands are produced when two or more regularly spaced patterns which differ from one another by some slight constant difference are superimposed and the pattern moves if the patterns are moved relative to one another. These bands have been used as an index of such relative motion and have produced systems of high sensitivity to such relative motion.
  • the present invention makes it possible and practicable to locate these maxima and/or minima with high precision, without the necessity for employing additional averaging devices or methods.
  • the index pattern in accordance with the present invention is sufficiently discernible to be readable directly visually.
  • the individuaL zones forming graduation on the overlapping elements have converging side edges which define equally spaced points.
  • the superposed graduations of different spatial density then define an index pattern which varies not only along the length of the superposed graduations but transversely thereof as well.
  • the index pattern is directly related to and generally is an enlargement of the configuration of the individual zones and any desired pattern can therefore be obtained by proper configuration of the shapes of the individual zones.
  • FIG. 1 is a diagrammatic illustration of a pair of overlapping and relatively angularly displaceable discs including aligned patterns defining a movable index pattern which is positioned in accordance with the relative angular position of the discs;
  • FIG. 2 is an enlarged fragmentary view of a portion of FIG. 1 more clearly illustrating one form of the light grating system of the present invention
  • FIG. 3 is a substantially enlarged phantom view of the index pattern shown in FIG. 2;
  • FIG. 4 is a diagrammatic illustration of an embodiment of the invention incorporated in a pair of rectilinearly displaceable elements
  • FIG. 5 is a view of the elements shown in FIG. 4 in superposed relation to define an index pattern related to the relative position of the elements;
  • FIG. 6 is an enlarged phantom line view of the index pattern shown in FIG. 5
  • FIG. 7 is an illustration of a wedge shaped zone
  • FIG. 8 is the resulting index pattern when the wedge shaped zone is applied to rectilinearly movable elements such as shown in FIG. 5;
  • FIGS. 9 and 10 are views similar to FIGS. 7 and 8 showing an inverted wedge shaped sector or zone and the resulting index pattern when the zone configuration is applied to rotary apparatus;
  • FIGS. 11 and 12 are views similar to FIGS 7 and 8 illustrating a further modification of the zone configuration and the resulting index pattern.
  • the apparatus illustrated may be employed to measure the angular displacement or relative position between a pair of discs 1 and 2 each of which carries adjacent its periphery a symmetrical pattern or graduation of substantially identically shaped transparent zones or apertures 3 which are separated by opaque zones or areas.
  • the several zones shown in the drawings are substantially enlarged in both FIGS. 1 and 2 for purposes of clarity of explanation and convenience of pictorial representation.
  • discs 1 and 2 are concentrically located with respect to each other to superimpose the symmetrical graduations.
  • disc 2 moves with some external element; for example, a shaft 4 which is coaxially secured to the disc 2 and Whose angular position is to be determined.
  • the opposite disc I is fixed to a relatively stationary reference frame 5 having a known or controlled position relative to the shaft.
  • the number of zones 3 in the graduation on respective discs 1 and 2 differ by any small whole number which is small in comparison to the total number of zones on either disc. For example, if the basic number of zones on disc 1 is equal to 360 and it is desired to read the relative angular position in minutes, the disc 2 will be provided with 366 zones.
  • each of the individual zones 3 is a wedge shaped segment having straight side walls or edges 6 and 7 converging radially and ci rcumferentially inwardly.
  • the corresponding edges of all zones 3 are similar to each other and the edges 6 and 7 of each zone meet at point 8 with the points equally spaced on a circle having a center coinciding with the center of the corresponding disc.
  • each zone is bisected by a radial line from said common center or axis, the zone has a height 0 measured along the bisecting line between the point 8 and the base 811 which is a small multiple of the width of base 8a. Further, the radial distance from the center of the circle to point 8 is substantially greater than the zone height.
  • the overlap of immediately adjacent superimposed zones 3 on the discs 1 and 2 is varied and the total opening varied accordingly. Light proceeds axially through the apertures in the discs 1 and 2 in accordance with the openings defined by the overlapping discs generally in accordance with the conventional formation of moire bands or patterns.
  • the index pattern 9 is a unilateral expansion of an individual zone 3 with the point 10 of the index pattern defined by the individual superposed zones 3 within pattern 9 on discs 1 and 2.
  • the side edges of index pattern 9 are curved to the point 10. This results from the circumferential distribution of the zones.
  • the side edges of zones 3 convex the side edges of the index pattern may be made straight.
  • the index pattern 9 expands circumferentially and radially in accordance with the varying overlap of the zones 3 on discs 1 and 2.
  • the maximum height or radial dimension corresponds to the dimensions of the individual zones and the pattern width is an annular enlargement of one zone.
  • the degree of enlargement of pattern width is determined by the ratio between the width of the individual zone at its widest portion and the angular displacement between adjacent zones on the disc 1 carrying the smaller number of zones.
  • the total width of the index pattern 9 is equal to the smaller or base number of individaul zones on disc 1 divided by the difference between the number of zones on discs 1 and 2 times this ratio.
  • the priviously described spacing of 360 zones 3 on disc 1 establishes one degree between adjacent spaces. If the angle subtended by the base or the widest part of the individual zone 3 is assumed to be one quarter of a degree, the index pattern width is 360 divided by six times A divided by l or 15. The index pattern 9 thus subtends an angle of 15 or 7 /2 at each side of the point 10. The position of point 10 is readily discernible and a cooperating fixed scale 11 is shown adjacent the position of the pattern. Scale 11 is divided into any convenient fractions of the initial interval between spaces or zones in the present instance 1. For example, dividing the scale directly into 60 units, the typical distribution of zones 3 already described provides apparatus which reads in minutes.
  • the present invention as illustrated in FIGS. 1-3 provides a light grating means for relating angular motion without the necessity for the usual averaging devices or methods to accurately read the position of the light pattern.
  • FIGS. 4-6 inclusive, a suitable apparatus for that purpose is illustrated in a manner similar to that of the previous embodiment.
  • a graduated strip 12 is attached to and carried by the elements, not shown, whose translational position is to be determined with respect to some fixed object such as a machine frame, not shown.
  • the strip 12 is marked with a plurality of equally spaced transparent zones 13 spaced by opaque areas similar to the zones shown in FIGS. 1-3.
  • a second cooperating strip 14 is fixedly mounted with respect to the movement of the strip 12 and carried by a fixed reference frame 15.
  • Strip 14 is marked with a plurality of transparent zones 16 in parallel relation to the corresponding zones on the initial strip 12. However, the density of the light and dark bands or areas upon the second strip 14 is difi'erent from that of the first strip 12 by a small predetermined amount.
  • the fixed strip may be provided with 100 alternate transparent and opaque bands or zones per lineal inch of light and the second strip provided with 201 alternate clear and opaque bands or zones in each two inches of lineal segment.
  • the strips are superposed as indicated in FIG. 5 and establish a light pattern determined by the overlap of the zones on the respective strips 12 and 14.
  • the light pattern within any one period defined by the repetition of the relative number of zones on the strips varies both in the direction of relative movement of the strips and at an angle substantially normal thereto.
  • the index pattern 17 is formed which is a substantially unilateral enlargement of the individual zones and extends symmetrically to opposite sides of the superposed zones within one period on the strips 12 and 14 to define a readily discernible point 18.
  • the shape of the index pattern in the illustrated embodiments of the invention is controlled by the shape of the individual spaces and the desired pattern is essentially limited only by the possibility of producing properly shaped opaque or transparent zones.
  • the circumferential spacing of the zones causes the side edges of the index pattern to change from the precise shape of the individual zones.
  • practically any configuration can be provided by proper selection of the individual zones.
  • a wedge shaped zone 19 is shown in FIG. 7 having rectilinear side edges 20. If this zone configuration is applied to a linearly movable element such as shown in FIGS. 4 and 5, an index pattern having rectilinear side edges such as shown in FIG. 8 is obtained.
  • the precise shape or width of the pattern will be determined by the spacing of the zones and the width of the individual zones at its widest portion.
  • FIG. 9 is an inverted wedge shaped zone 21 and when applied to rotary apparatus such as discs 1 and 2 of FIGS. 1 and 2, the resulting index pattern is generally continuous curved pattern changing circumferentially and radially.
  • the index pattern may be internally shaped by corresponding shaping of the zones; for example, as shown in FIGS. 11 and 12.
  • FIG. 11 is a generally V-shaped zone 22. If zones 22 are applied to rectilinearly movable elements such as shown in FIGS. 4 and 5, an enlarged V-shaped index pattern shown in FIG. 11 is obtained.
  • the various index patterns may be made more pronounced and narrower by making the ratio between the individual pattern width and the interval spacing of zones smaller. This may be accomplished either by making the individual zones narrower at its widest point or the number of individual elements smaller or by increasing the interval between the adjacent zones or by a combination thereof.
  • the present invention thus provides a very simple and inexpensive means for employing a visible pattern effect which is readable by providing predetermined configurations of the light transmitting individual zones in accordance with a predetermined desired pattern.
  • the present invention thus provides a very simple means of completely controlling and determining moire patterns and avoiding the necessity although not rejecting the possible use of the heretofore employed averaging and other auxiliary devices.
  • Apparatus for determining an angular position a pair of at least partially overlapping elements rotatably movable with respect to one another around a common axis of rotation, each of said elements being provided with similarly positioned graduations in the form of closely spaced transparent zones including opposite sharply converging side edges defining an included angle substantially greater than the angle included by radial lines to said common axis of rotation and the height of each zone being a small multiple of the width, said zones being spaced from the common axis a distance substantially greater than the zone height and separated by opaque areas, all
  • Apparatus for determining relative position comprising a pair of at least partially overlapping elements movable relative to one another along one predetermined straight line of direction, each of said elements being provided with superimposed graduations in the form of closely spaced transparent zones each including opposite sharp- 1y converging side edges with the height of the zone being a small multiple of the width and separated by opaque areas with the graduations being maintained in the same overlapping relation in the direction normal to movement for all relative positions thereof, all of said zones on each element being of equal effective size and effective shape and all of said areas of each element being of equal effective size and effective shape, the spatial density of said zones on one of said elements being slightly different from that on the other of said elements.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optical Transform (AREA)
  • Eye Examination Apparatus (AREA)
US194606A 1962-05-14 1962-05-14 Apparatus for producing moire patterns for use in determining the relative position of a pair of elements Expired - Lifetime US3217590A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US194606A US3217590A (en) 1962-05-14 1962-05-14 Apparatus for producing moire patterns for use in determining the relative position of a pair of elements
GB16308/63A GB1009699A (en) 1962-05-14 1963-04-25 Apparatus for producing moire patterns
DE19631303561D DE1303561B (enrdf_load_stackoverflow) 1962-05-14 1963-05-14

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US194606A US3217590A (en) 1962-05-14 1962-05-14 Apparatus for producing moire patterns for use in determining the relative position of a pair of elements

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US3217590A true US3217590A (en) 1965-11-16

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DE (1) DE1303561B (enrdf_load_stackoverflow)
GB (1) GB1009699A (enrdf_load_stackoverflow)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4242000A (en) * 1977-09-09 1980-12-30 Bergkvist Lars A Arrangement at screens intended to give rise to a moire pattern
US4247769A (en) * 1978-12-21 1981-01-27 The Charles Stark Draper Laboratory, Inc. Apparatus for measuring angular and linear displacements
EP0359414A3 (en) * 1988-09-16 1990-12-12 Renishaw plc Scale for use with opto-electronic scale reading apparatus

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2302587B (en) * 1995-06-24 1998-04-08 British Aerospace Measuring relative deflection between two adjacent components

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1415627A (en) * 1919-11-07 1922-05-09 Howard S Levy Precision instrument
US2246001A (en) * 1940-04-01 1941-06-17 Associated Patentees Inc Light modulator
US2247076A (en) * 1939-08-25 1941-06-24 Gen Electric Tuning instrument
US2256170A (en) * 1941-01-24 1941-09-16 Associated Patentees Inc Propeller synchronizing and other instruments
US2280038A (en) * 1941-10-17 1942-04-14 Associated Patentees Inc Turn indicator
US2451972A (en) * 1945-12-03 1948-10-19 Associated Patentees Inc Optical indicator having cooperating grids
US2475490A (en) * 1948-03-20 1949-07-05 Gelardin Albert Direct reading, visual index forming intersection pattern thread and line counter
US2559915A (en) * 1949-12-28 1951-07-10 Gaebel Arthur Henry Half-tone screen determiner
US2788519A (en) * 1954-12-10 1957-04-09 Telecomputing Corp Position indicating device
US2817266A (en) * 1954-04-13 1957-12-24 Gelardin Albert Direct reading, visual index forming, intersection pattern thread and line counter

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1415627A (en) * 1919-11-07 1922-05-09 Howard S Levy Precision instrument
US2247076A (en) * 1939-08-25 1941-06-24 Gen Electric Tuning instrument
US2246001A (en) * 1940-04-01 1941-06-17 Associated Patentees Inc Light modulator
US2256170A (en) * 1941-01-24 1941-09-16 Associated Patentees Inc Propeller synchronizing and other instruments
US2280038A (en) * 1941-10-17 1942-04-14 Associated Patentees Inc Turn indicator
US2451972A (en) * 1945-12-03 1948-10-19 Associated Patentees Inc Optical indicator having cooperating grids
US2475490A (en) * 1948-03-20 1949-07-05 Gelardin Albert Direct reading, visual index forming intersection pattern thread and line counter
US2559915A (en) * 1949-12-28 1951-07-10 Gaebel Arthur Henry Half-tone screen determiner
US2817266A (en) * 1954-04-13 1957-12-24 Gelardin Albert Direct reading, visual index forming, intersection pattern thread and line counter
US2788519A (en) * 1954-12-10 1957-04-09 Telecomputing Corp Position indicating device

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4242000A (en) * 1977-09-09 1980-12-30 Bergkvist Lars A Arrangement at screens intended to give rise to a moire pattern
US4247769A (en) * 1978-12-21 1981-01-27 The Charles Stark Draper Laboratory, Inc. Apparatus for measuring angular and linear displacements
EP0359414A3 (en) * 1988-09-16 1990-12-12 Renishaw plc Scale for use with opto-electronic scale reading apparatus

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Publication number Publication date
DE1303561B (enrdf_load_stackoverflow) 1972-02-03
GB1009699A (en) 1965-11-10

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