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
  • G02B26/108—Scanning systems having one or more prisms as scanning elements

Definitions

• the invention relates to a device for deflecting a
• Beam bundle at a predeterminable angle Beam bundle at a predeterminable angle.
• the invention relates to a device in which the beam is deflected by means of a deflecting prism which can be rotated about the axis of the incident beam and whose beam entry surface is perpendicular to the axis of rotation. If necessary, the deflected beam is imaged on a surface to be scanned using an imaging system assigned to the deflecting prism.
• Such devices are used for example in scanner systems.
• a beam of rays emitted by a light source is deflected by a rotating deflecting element and imaged as a light spot on a surface to be scanned.
• the light spot depicted describes a linear movement on the surface.
• the surface is scanned line by line. This is achieved, for example, in that the surface to be scanned is applied to a roller which rotates step by step about its figure axis.
• the accuracy of the scanner system depends crucially on how straight the scanning lines run on the surface to be scanned.
• a source of error which leads to deviations from a straight-line scanning is that the axis of rotation of the deflecting element is caused to flutter or vibrate (wobble) by manufacturing or wear-related inaccuracies in the pivot bearings.
• the flutter movement is increasingly transmitted to the movement of the deflected bundle of rays.
• the illustrated light point then does not perform a linear but a wave-like movement.
• DE-PS 37 07 023 specifies two different beam guides.
• the beam is totally reflected twice in succession by the side surfaces after it has entered through a surface perpendicular to the beam, before it penetrates the exit surface perpendicular to the input surface.
• the side length of the square prism must be approximately 3.5 times as large as the beam diameter.
• Such prisms are comparatively large and are not suitable for use in scanner systems in which the deflection prism rotates at high speed.
• a second beam guide is therefore specified, in which the square prism has a smaller volume and weight than a pentaprism for a given cross section of the beam.
• the beam is reflected four times inside the prism. The reflection takes place on two surfaces at an angle which is smaller than the angle of the total reflection. That's why they have to both surfaces are provided with a reflection layer.
• the invention is based on the object of specifying a deflection prism for a scanner system which reacts insensitively to tilting of the prism axis against the direction of the incident beam, which has the smallest possible volume and weight and which is easy to manufacture.
• the deflection in the device according to the invention takes place partly by reflection and partly by refraction.
• the two reflections within the prism have the effect that a tilt of the prism against the beam axis has a weaker effect on the beam deflection by a factor of 10 than, for example, the tilt of a mirror.
• a vibration movement of the axis of rotation affects the deflected beam 10 times less than when a mirror is used, so that the accuracy requirements for the position of the axis of rotation relative to the deflection prism are lower than in known solutions.
• the contribution of the refraction to the deflection of the beam causes an inaccuracy of the angle between two prism surfaces to be compensated for by a slight tilt. This results in lower requirements for the tolerances in the manufacture of the deflection prism according to the invention than in the manufacture of a square prism according to Wollaston.
• the deflection prism according to the invention has only three optical surfaces, which simplifies the manufacturing process compared to the square prism.
• the use of the triangular prism within a device of the generic type proves to be particularly advantageous with regard to the volume, the weight and the distance between the axis of rotation and the most distant prism part which determines the input focal length.
• the triangular prism according to the invention has less than half the minimum weight of a corresponding square prism according to Wollaston and the input focal length is about a third smaller.
• any deflection angle can be achieved in a simple manner by machining only one surface.
• a deflection angle of 90 ° proves to be particularly favorable.
• the surface on which the beam experiences the second reflection is provided with a reflective layer.
• the angles between the optical surfaces can vary within a wide range.
• the angle between the entrance and beam exit surface must be greater than the critical angle of total reflection and can be selected between 45 ° and approximately 90 °.
• a laser diode is used as the light source and diffraction-limited optics (F-theta optics) are used as the imaging system (claim 6) assigned to the deflection prism.
• F-theta optics diffraction-limited optics
• This development takes advantage of the fact that, due to the refraction of the light beam at the beam exit surface, a light beam entering with a circular cross section is given an elliptical cross section on the beam exit side. The ratio of the axes is approximately 1: 0.85. If the beam of the laser diode, which generally has a cross-section deviating from the circular shape, passes through the triangular prism, this deviation is at least partially compensated for.
• Fig. 1 a the deflection of a beam on one
• Wollaston Fig. 2 b shows a section through an inventive
• Deflection elements are shown in all the figures, which deflect the incoming beam by 90 °.
• the light sources, the brackets and bearings of the deflecting elements and the associated imaging systems have not been shown.
• FIG. 1 b shows a triangular prism according to the invention with the non-mirrored surfaces (4, 5) and the mirrored surface (6), on which a beam of rays impinges.
• the prism according to the invention is thus less sensitive to tilting than the mirror by a factor of 10.
• FIG. 2a shows a square prism according to Wollaston for comparison with a prism according to the invention. It has two non-mirrored surfaces 9, 10, which form a right angle, " as well as two mirrored surfaces 11, 12. The surfaces 10, 11 and the surfaces 9, 12 enclose an angle of 67.5 °.
• the emerging beam is deflected by 90 ° with respect to the incoming beam, and the beam axis (14) is also the axis of rotation of the quadrangular prism 10 and the cut edge between the surfaces 9 and 12.
• the beam has a distance x of, for example, 0.15 d (d: diameter of the beam line) compared to surface 10 ritts beam).
• the distance x is required so that too when the prism axis of rotation is tilted, a beam of rays is deflected correctly.
• FIG. 2b shows a triangular prism according to the invention which is suitable for deflecting a beam with the same cross section d as in FIG. 2a. It has two non-mirrored surfaces 4, 5 which form an angle of 50 ° and a mirrored surface 6 which forms an angle of 37.5 ° with surface 5.
• the beam of rays leaves the prism at an angle ⁇ with respect to the surface normal of the beam exit surface.
• the axis of rotation of the triangular prism is oriented approximately perpendicular to the prism surface 4.
• FIG. 2b The ideal case of a non-tilted axis of rotation is shown in FIG. 2b.
• the beam in turn has the cross section d.
• the width of the beam entry surface 4 projects beyond the cross-section of the beam on both sides by an amount x of, for example, 0.1 d, so that a complete deflection of the beam is guaranteed when the axis of rotation is tilted.
• the triangular prism takes up less than half the space, saving more than half of the material.
• the entrance focal length is also significantly reduced compared to the Wollaston square prism.
• the numerical values of the exemplary embodiments do not represent any restriction of generality. The choice of the angles depends both on the respective application and on the refractive power of the prism material used.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Elements Other Than Lenses (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=6381970

Family Applications (1)

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Family Cites Families (7)

• 1989
  • 1989-06-02 DE DE19893918075 patent/DE3918075C1/de not_active Expired - Fee Related
• 1990
  • 1990-05-31 WO PCT/DE1990/000410 patent/WO1990015354A1/de not_active Application Discontinuation
  • 1990-05-31 EP EP19900908189 patent/EP0428662A1/de not_active Withdrawn

Non-Patent Citations (1)

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