Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
  • G02B26/10—Scanning systems
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/08—Mirrors
  • G02B5/09—Multifaceted or polygonal mirrors, e.g. polygonal scanning mirrors; Fresnel mirrors
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
  • G02B26/10—Scanning systems
  • G02B26/12—Scanning systems using multifaceted mirrors
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/08—Mirrors
  • G02B5/10—Mirrors with curved faces

Definitions

• the present invention relates to a scanning system and apparatus for use in a scanning system, particularly, but not exclusively, such a scanning system and apparatus for use in image projection.
• the present invention provides a scanning system comprising: first scanner means; a light source arranged to direct a beam of photons to impinge on the first scanner means to effect scanning of photons in a first general scan direction; second scanner means arranged to effect scanning of said photons in a second general scan direction substantially at right angles to said first general scan direction thereby enabling an image to be perceived.
• the first scanner means is arranged to effect a linear photon sweep or trace "line scan” across the second scanner means, the second scanner means scanning the line trace to effect a two dimensional "frame scan” image.
• the light beam directed toward the first scanner means is preferably modulated.
• synchronisation means is provided for the system arranged to enable modulated light sequences scanned from at least one of the scanner means to be accurately repeated, the synchronisation means comprising: i) a synchronisation beam distinct from the modulated image forming beam, the synchronisation beam being directed to impinge on at least one (preferably both) of the scanner means; and, ii) sensor means arranged to sense the synchronisation beam reflecting from the scanner means.
• the synchronisation beam and the sensor means of the synchronisation means are configured such the sensor means senses the reflected beam proximate the beginning of the scan sweep of the reflected synchronisation beam.
• the synchronisation means advantageously comprises separate synchronisation beams (each distinct from the modulated image forming beam) , each synchronisation beam being directed toward a separate one of the first and second scanner means.
• Separate respective sensors are preferably provided, each arranged to detect respective synchronisation beams reflected from respective scanner means.
• the system preferably also provides a reference enabling a phase relationship between the scan rate of the first and second scanner means to be maintained.
• one or both of the first and second scanner means comprises reflector means having one or more light reflecting surfaces arranged to effect scanning of the light photons.
• the reflector means comprise rotatable mirrors preferably a first one comprising the first scanner means and a second one comprising the second scanner means.
• the mirrors comprising the respective scanner means are arranged to be driven by respective motors.
• the first scanner means may comprise a rotatable ultifaceted polygonal mirror
• the second scanner means preferably comprising a driven rotatable element having a reflective surface extending about a rotational axis for reflecting the light beam, the reflective surface having a generally continuously curved surface profile about the rotational axis except for at least one localised angular step or discontinuity.
• the mirrors are rotated at differing respective speeds, the first rotatable scanner mirror effecting the "line scan” being rotated at a substantially greater speed that the rotational speed of the second rotatable scanner element effecting the "frame scan".
• a rotatable reflector element having a reflective surface as defined having relatively few (preferably only one or two) localised steps or discontinuities provides significant technical advantages when used as a "frame” scanner downstream of a rotatable polygonal mirror having a relative multiplicity of facets used as a "line” scanner. This is because, for example, the low number of scans per revolution of the "frame” scanner relative to the "line” scanner enhances the resolution of the image. Furthermore, the "frame” scanner may be run at relatively high rotational speeds at which rotational stability is greater.
• the invention provides scanner means for scanning a light beam, the scanner means comprising a driven rotatable element having a reflective surface extending about a rotational axis for reflecting the light beam, the reflective surface having a generally continuously curved surface profile about the rotational axis except for at least one localised angular step or discontinuity, the curved surface profile and localised angular step or discontinuity being configured such that for the scanner rotating at a constant rotational speed with the light beam impinging upon the reflective surface, the beam is scanned to move across a flat screen at substantially a constant speed.
• An advantage of such a linear scan is that the intensity and resolution of particular pixels making up the projected image should be independent of their respective locations in the image because the photon density would be uniform over the total extent of the image for an unmodulated scanning beam.
• the generally continuously curved profile of the mirror surface is preferably not of a continuous degree of curvature; rather the degree of curvature varies about the axis.
• the locus of the mirror surface about the rotational axis is asymmetrical about at least one axis of symmetry extending transversely through the rotational axis.
• the locus of the mirror surface about the rotational axis is symmetrical about two or less (preferably only one) axes of symmetry extending transversely through the rotational axis.
• the scanner means effects a single scan of light photons per revolution of the driven rotatable element.
• two steps or discontinuities may be provided relatively spaced at 180° intervals about the rotational axis; in this embodiment two scans of light photons are effected per revolution.
• the localised step or discontinuity serves to reset the frame scan to its start position and initiate the "screen refresh" of the perceived image.
• the driven rotatable element is balanced to reduce vibration and out of balance forces when in operation.
• Figure 1 is a schematic representation of a scanning system according to the invention for use in projecting an image
• Figure 2 is a schematic block diagram of the system of Figure 1;
• Figure 3 is a schematic representation similar to Figure 1 showing an alternative scanning system according to the invention
• Figure 4 is a schematic perspective and plan view of a first embodiment of scanner means according to the invention.
• FIG. 5 is an explanatory diagram showing the linear scan produced by the scanner means according to the invention.
• Figure 6 is a schematic representation of an alternative embodiment of scanner means according to the invention.
• a projection system comprises a modulated laser light source 1 arranged to direct generated photons to a first scanner 10 (line scanner) , to be reflected toward a second scanner 20 (frame scanner) subsequently to produce an image 2 on a screen 3.
• the first scanner comprises a multi-facetted polygonal mirror 11 driven by an a.c. synchronous motor 12 to rotate at very high speed (typically, for example 80,000 r.p.m.).
• the first scanner 10 scans photons to produce a "line scan" (which ultimately represents the horizontal scan on the formed image) each facet producing one scan line.
• second scanner 20 which again comprises a rotating curved mirror 21 (driven by motor 22) having its axis orientated perpendicularly to the rotational axis of the first mirror 11.
• Each successive scan line impinging on the curved facet of the second mirror 21 is reflected onto the screen, the progressive rotation of the facet causing successive scan lines to be displaced vertically on the screen 3 such that the reflective surface of the second mirror 21 provides a "frame scan" producing a completed screen of information or "image”.
• a synchronisation system comprising a synchronisation laser light source 4 and photodetectors 5,6 are provided.
• Laser light source 4 produces respective beams, each directed to impinge upon a respective scanner mirror 11,21.
• Photodetectors 5,6 are positioned so as to detect a respective reflected synchronisation beam at a point in time corresponding to the initiation of a line scan and frame scan (of the modulated image producing beam) respectively.
• the modulation pattern that controls the photon generator 1 is generated by a processor and control unit 7.
• the principle of operation is similar to conventional TV/monitor technology where a serial modulation pattern is produced, the speed and timing being governed by the scan speed and the synchronisation respectively.
• Control unit 7 therefore receives inputs from the photodetectors 5,6 to determine the synchronisation of the beam modulation and the rotation of mirrors 11 , 21 .
• both first and second mirrors 11,21 In order to maintain a stable image of the correct aspect ratio with the required number of scan lines per frame, the rotational speed of both first and second mirrors 11,21 has to be exactly pre-determined or controlled.
• A.C. hysteresis motors may be used, their speed being determined by the frequency of the a.c. supplied to them. Both frequencies are derived from one high frequency master clock (divided down by the appropriate amount) thus once the mirrors 11,21 are revolving at the required speed, their exact ratio and relative phase is maintained constant to avoid the image "tumbling" or wandering on the screen (such as occurs for example with loss of synchronisation on a faulty television picture) .
• the scanning system is used with apparatus which permits the resolution of the image to change (for example the image resolution on a computer display screen changing from 1024 x 768 pixels to 640 x 480 pixels) the change of resolution can be detected and the speed of the motors 12,22 adjusted to compensate thereby enabling the image size to remain constant.
• Speed of rotation of the mirrors 11,21 is also controlled by the processor controller 7.
• the scanner 20 comprises rotatable element 21 rotatably mounted on a motor assembly 22, and provided with a curved peripheral reflective surface 23 extending about its rotational axis.
• the locus of the curved reflective surface about the axis is not symmetrical about more than one axis of symmetry and is generally substantially continuously curved except for one major step (or discontinuity) 24 which acts to reset the scan to its original position as the step rotates through the light beam.
• the reflective surface is generally continuously curved about the rotational axis, the degree of curvature varies about the axis.
• the important feature about the curved reflective surface extending about the axis is that it is configured to provide at least a close approximation to a linear scan in which, for a constant rotational speed of element 21 the reflected beam moves at a substantially constant linear speed on a flat screen. As shown in figure 5, for an exact linear scan the incremental time ⁇ t for the beam to travel a uniform incremental distance ⁇ y on the screen is constant.
• A is the scan angle and R is the radius of the inscribed circle.
• the scanner 40 (shown in figure 6) is an alternative to the scanner 20 of Figure 4 and comprises a rotatable element 41 mounted on a driving motor assembly 42.
• the curved peripheral reflective mirror surface 43 is provided with two discontinuities or steps 44,45 spaced at 180° about the rotational axis.
• the locus of surface 43 about the rotational axis therefore has two axes of symmetry passing transversely through the rotational axes (perpendicular to one another) .
• the surface 43 ensures two scans are effected per revolution about the rotational axis.
• the locus of the curved mirror surface about the rotational axis for rotatable element 42 can be expressed mathematically using the following expressions: and
• A is the scan angle and R is the radius of the inscribed circle.
• a scan lens 15 may be provided in the path of light reflected from the first mirror 11 to ensure the reflected light is adapted to be focused on a flat (planar) surface (not a curved focal surface as would be the case for unadapted reflected light) .
• an arrangement of aspherical lenses 9 is introduced in the path of the scanned light.
• the modulated light source 1 comprises respective red, green and blue lights.
• a scanning system is suitable for use in a projection system, particularly a virtual reality display system such as a direct retinal projection arrangement or head mounted display.
• the system may be used in "head up display” applications in which an image is projected onto a transparent screen enabling the user to simultaneously see through the screen and observe an image projected onto the screen.
• the scanning system would be suitable for industrial marking applications, in which visible laser light would be replaced with higher energy sources such as a high power carbon dioxide laser source.
• the system may further more be adapted to act as a camera system, such as a video camera system. In this application, the light source is replaced with photosensors/photodetectors. It is believed that such a system is both novel and inventive per se.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Mechanical Optical Scanning Systems (AREA)
• Vehicle Body Suspensions (AREA)
• Measurement And Recording Of Electrical Phenomena And Electrical Characteristics Of The Living Body (AREA)
• Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=10784958

Family Applications (1)

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Families Citing this family (7)

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• 1995
  • 1995-12-05 GB GBGB9524884.5A patent/GB9524884D0/en active Pending
• 1996
  • 1996-12-04 CN CN96198803A patent/CN1203677A/zh active Pending
  • 1996-12-04 CA CA002239455A patent/CA2239455A1/en not_active Abandoned
  • 1996-12-04 EP EP96941124A patent/EP0865625A2/de not_active Withdrawn
  • 1996-12-04 AU AU10374/97A patent/AU1037497A/en not_active Abandoned
  • 1996-12-04 WO PCT/GB1996/002993 patent/WO1997021131A2/en not_active Ceased
  • 1996-12-04 KR KR1019980704211A patent/KR19990071924A/ko not_active Withdrawn
  • 1996-12-04 JP JP9521080A patent/JP2000501520A/ja active Pending
  • 1996-12-04 EA EA199800512A patent/EA199800512A1/ru unknown

Non-Patent Citations (1)

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