Abstract
A retroreflector includes an arrangement of triples, each having three side surfaces, which are disposed in the manner of a cube corner and stand approximately perpendicular on one another. The retroreflector can be produced from a carrier material by injection molding. An optical silicone resin is used as the carrier material. The retroreflector is based on triple mirrors that are both easily unmolded from a die and easily applied to curved surfaces even after unmolding or are usable for reflection of ultraviolet light.
Claims
1. A forming die for the producing a retroreflector, wherein the retroreflector comprises an arrangement comprising a plurality of mirrored or totally reflective triples, each triple having first, second, and third side surfaces perpendicular to each other; wherein the first, second, and third side surfaces are disposed as cube corners; and wherein the retroreflector is produced by injection molding from a carrier material comprising an optically transparent silicone resin; wherein the forming die comprises: a die body delimited by a die surface; wherein the die surface has a plurality of triples; wherein each triple has first, second, and third forming surfaces that border on one another and intersect one another at an angle between 85° and 95°; wherein the first, second, and third forming surfaces of each triple come together in a triple center; wherein an axis of symmetry of the respective triple extends through the triple center; wherein a tool body is heated; and wherein the die body has at least one die element perpendicular to an unmolding direction that counters unmolding.
2. The forming die according to claim 1, wherein the forming die is produced by micro-cutting or by galvanic forming of a microsection.
3. A method for the production of a retroreflector, wherein the retroreflector comprises an arrangement comprising a plurality of mirrored or totally reflective triples, each triple having first, second, and third side surfaces perpendicular to each other; wherein the first, second, and third side surfaces are disposed as cube corners; and wherein the retroreflector is produced by injection molding from a carrier material comprising an optically transparent silicone resin; wherein the method comprises: i. separately placing at least first and second components of an injection-molding material comprising an optical silicone into an injection-molding machine, in a volume ratio of 1:1; ii. mixing the components in a screw of the injection-molding machine and pressing the components into an injection-molding mold using a forming die, wherein the screw is kept at a temperature between 10° C.; and 30° C.; iii. pressing the components into an injection-molding mold, wherein the injection-molding mold is heated to a temperature between 130° C. and 200° C.; iv. curing the components in the injection-molding mold to form the retroreflector; and v. unmolding the retroreflector from the injection-molding mold.
4. An optical sensor apparatus comprising: (a) a retroreflector, wherein the retroreflector comprises an arrangement comprising a plurality of mirrored or totally reflective triples, each triple having first, second, and third side surfaces perpendicular to each other; wherein the first, second, and third side surfaces are disposed as cube corners; and wherein the retroreflector is produced by injection molding from a carrier material comprising an optically transparent silicone resin; (b) a light emitter for emitting ultraviolet light; and (c) a light receiver for receiving light emitted by the light emitter; wherein the retroreflector is disposed in a beam path of the light in such a manner that the retroreflector retroflects the light emitted by the light receiver.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.
[0052] In the drawings,
[0053] FIG. 1 shows a usual retroreflector geometry;
[0054] FIG. 2 shows an individual triple, to explain an undercut;
[0055] FIG. 3 shows an exemplary retroreflection on curved surfaces;
[0056] FIG. 4 shows an example of a retroreflective hemisphere;
[0057] FIG. 5 shows a mold insert for a hemisphere according to FIG. 4 in the closed state;
[0058] FIG. 6 shows a mold insert for a hemisphere according to FIG. 4 in a view at a slant from the front;
[0059] FIG. 7 shows typical angle distributions for triples on a level surface or a curved surface;
[0060] FIG. 8 shows application of an elastic reflector to a curved surface; and
[0061] FIG. 9 shows a schematic representation of a retroreflector.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0062] FIG. 1 shows a usual geometry of a retroreflector 1 as described in DE 102 16 579 A1, for example. The retroreflector 1 is formed by a regular arrangement of individual triples 3. Each triple 3 has three optically active boundary surfaces, at which a transition from an optically denser medium, in other words a material having a higher index of refraction, to an optically thinner medium, in other words a material having a lower index of refraction, or the opposite transition can take place. These boundary surfaces can also be referred to as first, second, and third side surfaces 5, 7, 9. In a usual geometry, light enters into the optically denser medium at a light entry surface that lies opposite the reflector side, and impacts the triples 3 at an angle at which total reflection takes place. The light beam is reflected once at each of the side surfaces 5, 7, 9. During each reflection, a component of the dispersion vector changes its sign. After triple reflection, the reflected light reflected beam 29 leaves the retroreflector 1 again, parallel to the direction of the incident beam 27.
[0063] In this regard, the surfaces 5, 7, and 9 enclose a right angle with one another. In the example of FIG. 1, the surfaces 5 and 7 intersect at the first edge 11 having the edge length a, the surfaces 5 and 9 intersect at the edge 13 having the edge length b, and the surfaces 7 and 9 intersect at the edge 15 having the edge length c. The intersection point of all three surfaces 5, 7, 9 forms the apex 17. An axis of symmetry 19 can be laid through the apex 17, which axis encloses the same angle with regard to all the side surfaces 5, 7, 9. As can be seen in FIG. 1, the triples 3 stand at a slight slant. In other words a tilt 23 is present. The axis 19 of the triples 3 is not parallel to a normal line vector of a plane 25 in which the triples are disposed.
[0064] FIG. 2 shows a top view of an individual triple 3 of a retroreflector 1 as in FIG. 1. In FIG. 2 a), a triple without a tilt is shown. The axis of symmetry 19 is collinear with a normal line vector of a plane 25 of the triple according to FIG. 1. A possible rotation 21 of the triple 3 about the axis 19 is indicated by an arrow having the reference symbol of the angle of rotation Φ. The angle α of the first side surface 5 relative to the axis of symmetry 19 of the triple 3 amounts to 35.26°. The angle β of the second side surface 7 relative to the axis of symmetry 19 of the triple 3 corresponds to the angle of the diagonal of a cube and amounts to 54.74°. The sum of α and β and thereby the intersection angle of the first side surface 5 with the second side surface 7 amounts to precisely 90°. The third side surface 9 lies in the plane of the drawing here and also encloses a right angle with the two other side surfaces 5, 7.
[0065] FIGS. 2 b) to d) show the triple with three different tilt angles Θ. In FIG. 2 b) the tilt angle Θ is less than 54.74°; in FIG. 2 c the tilt angle Θ amounts to precisely 54.74°. In other words, the first side surface 5 lies coplanar to the plane 25 of the triple. In FIG. 2 d), the tilt angle Θ is greater than 54.74°. It is understood that the triples can also be rotated 21 and tilted 23 in combined manner.
[0066] The triples 3 shown in FIGS. 2 b) and 2 c) can be unmolded from an imaginary die in an unmolding direction 31, without undercut. The triple 3 shown in FIG. 2 d) has an undercut 33. The region indicated with 33 is perpendicular to the unmolding direction 31, counter to unmolding. The triple shown in FIG. 2 d) can therefore be unmolded only if it consists, according to the invention, of an elastic material, for example silicone.
[0067] FIG. 3 shows, as an example, retroreflection at a curved surface 135. In the view of FIG. 3, only two of the side surfaces 105, 107 of the triples 103 are shown. Incident light 127 first impacts the first side surface 105, is reflected there, and then impacts the second side surface 107 and is reflected there. Reflection at the third side surface 109 is not shown. The sequence of impact of the incident light beam 127 on the side surfaces 105, 107, 109 can be permuted as desired. In FIG. 3, the region of the light entry surface that precisely illuminates one triple 103 is indicated with an arrow as aperture 143. Because the surface 135 is curved, the aperture 143 is also curved. In order for the offset not to bring about a change in direction of the reflected beam 129 relative to the incident beam 127 during retroreflection of the light beam, the radius of the sphere or, in general, the local radius of curvature of the curved surface 135 must be greater than the greatest edge length of the triple at least by a factor of 10, preferably at least by a factor of 50, particularly preferably at least by a factor of 100. Furthermore, it is shown, as an example, that the axis 119 of the triple 103 points in the radial direction R.
[0068] FIG. 4 shows the view of the retroreflector 101 in the form of a retroreflective hemisphere 141. The curved surface 135 therefore has a spherical shape. The curved surface 135 can consequently be represented by a sphere coordinate system having a radial vector R (see FIG. 3), a polar angle φ, and an azimuth angle θ. Therefore two curvature directions are present. In this view, all the side surfaces 105, 107, 109 of a triple 103 as well as the first, second, and third edges 111, 113, 115 can be seen. The edges 111, 113, 115 intersect in the apex 117. The triples 103 are clearly shown too large in the drawing, in relation to the hemisphere radius, for reasons of recognizability. If one puts two such components together at the circumference, a reflective full sphere occurs, which reflects approximately at the spatial angle 4π. Such spheres, having a suitable diameter, can also be used as operation markers, for example.
[0069] FIGS. 5 and 6 show a mold having a mold insert 151 for the production of a retroreflector 101 from FIG. 4. The first forming surface 155 of a triple 153 of the mold insert 151 corresponds to the first side surface 105 of a triple 103 of the retroreflector 101. The reference symbols of the mold insert 151 differ from the reference symbols of the retroreflector 101 by 50, in each instance. The same holds true analogously for the second and third forming surfaces 157 and 159, the first, second, and third edges 161, 163, 165, the triple center 167, and the axis of symmetry 169 of the triple 153.
[0070] In FIG. 5, the mold is shown in a closed state. An unmolding direction 131 is perpendicular to the flat base surface of the mold die. Undercuts 133 can be clearly seen in the lower region, close to the base plate of the mold die. For reasons of clarity, a heating system for the mold, which is required for curing the silicone, was left out of the drawing.
[0071] FIG. 6 shows the mold insert in the open state.
[0072] In FIG. 7, an intensity distribution I is plotted above an observation angle γ in arbitrary units. FIG. 7 a) shows the angle distribution of the retroreflected light in the case of an ideal triple and a flat aperture surface. The peak width at half height is zero, except for any resolution due to the representation. FIG. 7 b) shows the angle distribution for the same ideal triple but with a curved aperture surface 143 (see FIG. 3). Here, the curvature radius is selected in such a manner that approximately a peak width at half height of the angle distribution of 0.5° is obtained.
[0073] FIG. 8 symbolically shows adaptation of an elastic retroreflector 201, shown in two dimensions, and injection-molded in a flat plane, to a curved surface 235 of an object 237. FIG. 8 a) shows the retroreflector 201, in this regard, before it is applied to the object 237. FIG. 8 b) shows the retroreflector 201 and the object 237 after application of the retroreflector. In FIG. 8, in particular, the sizes of the triples 203 are shown with great exaggeration. As a result, the deformations, in particular of the triples 203, are shown with great exaggeration in FIG. 8 b). In reality, a local curvature radius of the curved surface 235 is greater than the edge lengths or the widths across flats of the triples 203 by at least a factor of 50, even better by at least a factor of 100.
[0074] In FIG. 8, due to the symbolic two-dimensional representation, only two side surfaces 205, 207 or two edges, namely first and second edges 211, 213 of a triple 203 are shown in the drawing, in each instance. The edges intersect at the apex 217. The axis of symmetry 219, which passes through the apex 217 and encloses the same angle with the first and second side surfaces 205, 207, lies parallel to the normal line vector of a plane 225 in FIG. 8 a), in other words before the elastic retroreflector 201 is affixed to the object 237. The plane 225 corresponds to a flat wall in an injection-molding mold, not shown. After application, the axis of symmetry 219 follows the curved surface 235 of the object 237 in the example of FIG. 8 b). The elastic deformations of the retroreflector 201, shown in exaggerated manner in FIG. 8 b), can have a negative effect on the reflection behavior of the reflector, on the one hand, but on the other hand can also be used to achieve a desired angle distribution, for example.
[0075] FIG. 9 shows a schematic 2D representation of a retroreflector 301 according to the invention, which is intended for use in a sensor device, in which ultraviolet light emitted from a light source, not shown, in other words an incident beam 327, for example having a wavelength of 280 nm, is guided to a light recipient, not shown, as a retroflected beam 329. The retroreflector 301 has an arrangement of triples 303, each having three side surfaces that stand almost perpendicular on one another, of which a first side surface 305 and a second side surface 307 are shown.
[0076] The retroreflector 301 in FIG. 9 is not curved, in other words it is configured to be flat. Nevertheless, the elastic property of silicone can be utilized so as to press an undercut 333 of the retroreflector 301 or preferably a groove, into a holder 339, preferably a rigid holder 339, or to place it over the holder.
[0077] At the location of the undercut 333 or the groove, the retroreflector 301 can be attached to the holder. Thanks to the elastic material of the silicone, a closed rear surface can be created in this way. It is therefore possible to do without welding.
[0078] Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.
