Abstract:
An arrangement for depicting a linear optical marking on a surface, including a radiation source emitting light, such as laser radiation, as well as a first lens arranged in the beam path having a first and a second surface penetrated by the radiation, of which one surface features a parabolic or elliptical trace at least partially in cross section, formed of curved sections of different radii, the trace extending symmetrically with respect to a plane of symmetry of the lens, along which runs the beam directed in parallel, preferably by means of a second lens. In order to achieve a uniform power distribution along the line, it is proposed that the first surface formed of sections with different radii faces the radiation.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns an arrangement for depicting a linear optical marking on a surface, such as a periphery such as a wall surface of a room, comprising a radiation source emitting light or laser radiation, as well as a first lens arranged in the optical path having a first and a second surface penetrated by the radiation, of which one surface consists at least in part of curved sections with different radii in cross section, having in particular an at least partially parabolic or elliptical trace in cross section, and extends symmetrically with respect to the plane of symmetry of the first lens, along which the parallel radiation travels. 
     DE-A-102 17 108 discloses a laser irradiating apparatus which is used in the construction industry. In order to generate a line without interruption running across a wide angle, it is provided that a laser beam bundle passing through a collimator lens falls on a rod lens, which has a semitransparent surface on the light source side, in order to reflect a linear light beam in the direction of the light source. The non-reflected light passes thus through a completely transparent surface of the rod lens, which faces away from the light source, and is refracted in order to generate a linear light beam in a second direction, which is opposite from the first direction. 
     U.S. Pat. No. 6,502,319 provides several cylindrical lenses or mirrors, by means of which the light beam emitted by the light source is distributed to the required extent, in order to depict a line of visible light on a surface, which starts directly in front of a housing where the light source is accommodated. 
     Light beam leveling devices according to DE-U-203 04 117 and DE-U-203 04 114 have line lenses consisting of sections with different focal lengths in front of a light source, by which a linear light beam is to be generated. 
     DE-C-199 53 114 proposes the use of two lateral projection devices arranged side by side, each comprising a light source and an optical unit arranged in its beam path, for the purpose of generating two lines intersecting at a right angle on a workpiece under an optical marking system. In order to spread the light beam, U.S. Pat. No. 3,984,154 provides a lens which has the shape of a hollow cylinder section, on whose one edge surface a collimator laser beam impinges. The inner surface of the lens has a reflecting layer for the purpose of reflecting the light to a sufficient extent to the outside. 
     In JP-A-2004094123, a rod lens, whose outer surface is provided in sections with a reflecting layer, so that the impinging light is directly reflected, is utilized to generate linear markings. Light can pass through the lens in the areas in which a corresponding reflection layer is not provided. 
     A lens utilized according to U.S. Pat. No. 6,935,034 to spread a laser beam features a rectangular geometry with a rounded edge facing away from the light source for the purpose of achieving the desired spread of the light that passes through the lens. 
     A crossline laser is disclosed in EP-A-1 795 863. The lenses used have a first planar surface on which the laser impinges in order to then be refracted on the surface, which is elliptical in cross section and faces away from the beam, whereby an optical line is generated, which is projected as a marking on a surface. The intensity distribution along the line is not uniform. Rather, the intensity is greater in the central area of the line and decreases towards the outside. 
     A laser beam impinges on the flat rear side of a half-cylinder lens in order to linearly spread a laser beam according to U.S. Pat. No. 5,782,093. 
     A refractive-diffractive hybrid lens for forming a beam of high power diode lasers is known from DE-A-103 54 780. The lens is composed of a rectangular section and a cylindrical section, through which the light passes first. 
     An apparatus for depicting a linear optical marking according to DE-U-20 2004 007 476 features a channel-shaped lens, whose curved sections run along both sides of a plane which extends perpendicularly to the radiation impinging the lens. 
     According to DE-A-195 28 198, a laser beam impinges on a cylindrical lens in order to be linearly depicted by the latter on sensors, with which the intensity distribution of the laser beam is measured. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to further develop an arrangement of the initially mentioned kind in such a way that a line can be generated, which is relatively long and features a uniform intensity distribution over a wide area, in particular a more uniform intensity distribution than that of the known arrangements. 
     The object is attained according to the invention essentially in that the first surface composed of sections having different radii faces toward the radiation. 
     As a deviation from the known lenses, which refract a light bundle to a line, that is, spreading lenses featuring a flat side, the refraction according to the invention is carried out at two contours, that is, surfaces, of which the first is curved, whereby not only a more uniform intensity distribution along the line is obtained, but a considerably longer line is generated in comparison with lenses of the same size, in which a refraction occurs only at one surface. 
     The uniformity of the light intensity along the line according to the invention also has the advantage that more power can be incorporated overall into the laser line, without exceeding the laser safety class already in the central area of the line. 
     It is particularly provided that the light source—if required with an associated optical unit—emits an elongated elliptical light bundle, whose longitudinal axis runs vertical to the plane of symmetry. Here the light bundle should impinge on the first surface while it is symmetrically distributed with reference to the axis of symmetry, whereby preferably the relationship of the longitudinal extension L of the light beam with respect to the transversal extension B of the lens vertically to the plane of symmetry is 2:3≦L:B≦1:1. If higher losses or a worse efficiency factor can be tolerated, then values deviating from those above can of course also be considered. 
     Furthermore, the first surface is characterized in that the light bundle impinges fully on the first surface at a distance from the vertex of the first surface, wherein 0.5 L≦a≦1.5 L, with L=length of the light bundle. 
     In order to optimize the generated optical line, the first surface should in addition be curved in such a way that the maximum refraction angle α amounts to 50°≦α≦80°, in particular 55°≦α≦70°. 
     The first surface should have a radius of curvature r 1  at the vertex, with 0.45 mm≦r 1 ≦1.1 mm. The values are dependent upon the material and refraction index, so that other value ranges can also be taken into consideration. 
     In order to prevent a blurred appearance of the optical line, it is provided that the first surface is depicted with reduced reflection or is provided with a corresponding layer. 
     In order to achieve a further uniformity of the intensity of the line, a preferred further development of the invention provides that the second surface is curved or arched, wherein a concave or convex trace is considered. The second surface is formed in particular by a section of a cylindrical surface. 
     The second surface can have a radius of curvature r 2 , with 15 mm≦r 2 ≦25 mm. 
     The invention provides in addition that a laser light source, such as a laser diode emitting polarized light, is utilized as light source. Radiation that is polarized parallel to the longitudinal axis of the elliptical light bundle should especially be used. The invention is not abandoned, however, when polarization is vertical to the longitudinal axis of the light beam. 
     The lens itself can be made of plastic, in particular in the form of a cast part. 
     In a further development, the invention provides that the second surface has a diffractive configuration or is provided with a diffractive element. 
     The invention is characterized in particular by a crossline laser device in which a first arrangement according to the invention for generating a first linear optical marking and a second arrangement according to the invention for generating a second linear optical marking, which is vertical to the first linear optical marking, is arranged as a unit in a housing, which oscillates or is adjustable in dependence upon gravitational forces or by means of a motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details, advantages and features of the invention are disclosed, not only in the claims, the features inferred therefrom—per se or in combination—but also from the following description of the embodiments represented in the drawings. 
       In the drawings: 
         FIG. 1  shows a lateral view of a crossline laser device; 
         FIG. 2  shows a frontal view of the crossline laser device of  FIG. 1 ; 
         FIG. 3  shows a cross section through a lens according to the invention; 
         FIG. 4  shows a schematic representation of a beam path through a lens according to the invention; 
         FIG. 5  shows a frontal view of the lens of  FIG. 4 ; 
         FIG. 6  shows a schematic representation of the beam path through an embodiment of a lens according to the invention; 
         FIG. 7  shows a schematic representation of a beam path through a further embodiment of a teaching of the invention; 
         FIG. 8  shows intensity distributions of beams distributed by means of lenses; and 
         FIGS. 9-11  show schematic representations of beams which pass through lenses according to the state of the art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Line or crossline laser devices are used in order to depict lines or intersecting lines as auxiliary lines for work to be carried out, especially in the construction field.  FIGS. 1 and 2  show purely schematically an arrangement of a line or crossline laser device oscillating suspended within a housing, which arrangement comprises light sources such as laser sources, in particular laser diodes with an optical unit connected upstream, which can be generally designated a pendulum  10 . The pendulum  10  proceeds from a bearing  12 . In a crossline laser, two lines  14 ,  16 , which intersect each other at an angle of 90° and can be projected onto a surface, are then generated by means of light sources, such as laser diodes and the upstream optical unit, through especially shaped lenses. 
     For this purpose, the beam emitted by the laser light source, such as a laser diode, is directed toward the lens  18 ,  20 , by means of which the laser beam is refracted in order to form the lines  14 ,  16 . 
     Lenses utilized according to the state of the art are represented purely schematically in  FIGS. 9-11  with the associated beam paths. The same reference numerals are used therein to identify identical elements. 
     The beam originating from a laser source  20 , such as a laser diode, is aligned in parallel by means of a lens  22  in order to pass vertically through a boundary surface  24  of a lens  26 , which has on its rear a surface  28  consisting of sections with mutually differing curvature radii and having an elliptical shape especially in cross section. A lens such as this, which corresponds to EP-A-1 795 863, consequently effects a refraction of the beam only at one contour, namely on the curved surface  28 . In this way a line  30  is produced, for example on a wall surface, which shows an irregular power or intensity distribution, as should be illustrated purely schematically by means of the spaces of the beams. 
     A cylindrical lens  32  is shown in  FIG. 10 , on which a bundle of parallel beams impinges, wherein a refraction caused by the cylindrical geometry takes place, such that the line  30  projected on a surface likewise varies in intensity along its longitudinal axis, that is, it is considerably weaker in the margin area than in the central area. A corresponding cylindrical lens is known, for example, from DE-A-102 17 108. 
     A lens  34  according to  FIG. 11 , which is formed by a cylindrical section, likewise shows an irregular intensity distribution along the line  30 , as should be conveyed schematically by the spacing of the individual beams. The intensity is many times greater than in the border area in comparison to the embodiments of  FIGS. 9-10 . A corresponding lens is known, for example, from U.S. Pat. No. 5,782,003. 
     A lens  36  for generating a linear optical marking featuring two refracting contours according to  FIGS. 4 ,  6  and  7 , that is surfaces  38 ,  40 , of which the surface facing the beam consists of sections of different curvature radii and has an almost hyperbolic or elliptical shape in cross section, is proposed according to the invention. This can be seen purely schematically in the figures. The corresponding surface  38 , which is also called the first surface, is composed of areas  44 ,  46  that run symmetrical to the plane of symmetry  42 . 
     If a Cartesian coordinate system with X, Y and Z axes, wherein the Z axis is vertical to the drawing plane, is plotted on the lens  36 , both the first and the second surface  38 ,  40  have X and Y coordinates, which are respectively independent of the Z coordinates in at least one section of the Z axis. The first surface  38  features sections with different radii in the X-Y plane of the coordinate system. 
     The beam bundle originating from a light source, such as a laser diode  20 , according to the representation shown in  FIGS. 9-11 , consists of beams running parallel to the X axis and therewith to the plane of symmetry  42  with respect to the X-Z plane, which impinge on the first surface  38 , that is, the areas  44   46  that are symmetrical with respect to the plane of symmetry  42 . In agreement with the representation of  FIG. 5 , which shows a front view of the lens  36 , that is, a plan view of the surface  38  with the sections  44 ,  46 , the beams form a beam bundle  48  having an elliptical cross section, whose longitudinal axis is aligned along the Y axis, that is, vertically to the plane of symmetry  42 . The outer marginal beams, that is, the beams  50  that form the vertices of the beam bundle  48 , should have a distance L with respect to each other, that is, a distance L/2 from the X axis or plane of symmetry  42 , which is smaller than the maximum width B of the lens  36  transversely to the plane of symmetry  42 , that is, along the Y axis. This maximum width is predetermined by the rear side surface  40 . Only the upper marginal beam  50  is shown in the drawing. 
     L is preferably about ⅔ of B or greater, even though the beam bundle  48  can have a length which is equal to the width of the lens  36  according to the schematic representation of  FIGS. 6 and 7 . 
     Particularly uniform intensity distributions can be obtained when the light bundle  48  fully impinges on the surface  38  at the distance a from the vertex  54  of the surface  38 , whereby especially 0.5≦a≦1.5 L. 
     The surface  38  is preferably curved in such a way that the refraction angle α of the marginal beams  50  is between 50° and 80°, in particular between 55° and 70°. In addition, the surface  38  in the vertex  54  should feature a curvature r 1  of between 0.45 mm and 1.1 mm. 
     If the rear side surface  14  has a planar configuration according to the representation of  FIG. 4 , then the lens  36  is can be provided with a rear surface  56  according to the schematic representation of  FIG. 3 , which features a concave trace, that is, it is curved inwardly. The surface  56  should likewise be symmetrical to the plane of symmetry  42  and should have a radius of between 19 mm and 21 mm. 
     Typical dimensions of the lens  36  can be inferred from  FIG. 3 . The lens can thus feature a height H between 4 and 7 mm in X direction, whereas the width B is between 4 mm to 6 mm. The first surface  38  can be provided in addition with an anti-reflective coating in order to minimize the reflection of beams on the surface. 
       FIGS. 6 and 7  should illustrate the schematic trace of the beams, which are refracted by means of a lens according to the invention, in order to project a line  30  on a surface, which line features a uniform intensity distribution along its length. The lens shown in  FIG. 6  corresponds to that of  FIG. 3  and is identified with reference numeral  36 . 
     A lens  57 , which can be seen in  FIG. 7 , is comparable to the first surface  38  of the previously described lens  36 . On the other hand, the second surface  58  facing away from the beam has a convex shape, and can have a radius of curvature of between 15 and 25 mm. 
     It also becomes clear from  FIGS. 6 and 7  that the surface  36  does not generate a focal point, but a focal line, which can be located inside, outside, or both inside and outside of the lens  36 . 
     It is also possible, independently of this, to provide the second surface  40 ,  56 ,  58  with a diffractive configuration or with a diffractive element. 
     It should become clear with reference to  FIG. 8  that a uniform intensity distribution along the line  30  can be achieved with the lenses  36 ,  38  according to the invention. The curve  60 , which is formed by the filled triangles, thus represents an intensity distribution of a cylindrical lens, as can be seen in  FIG. 11 . It can be perceived that the intensity decreases sharply from the center of the curve  60  towards the outside. Consequently, if one intends to attain sufficient intensity in the margin area of the line, the intensity would be so strong in the central area that it could possibly represent a danger to the user. On the other hand, intensity that remains the same over a large angular range can be obtained for a line that can be projected with a lens  36 ,  38  according to the invention, as is conveyed by the curve  62  represented by filled squares. The advantage is thus obtained that more power can be introduced over the entire line; with the consequence that sufficient intensity is also attained in a greater angular range, without having to exceed the laser safety class in the central area. There is thus no danger to a user.