1. Field of the Invention
The invention concerns a device to graphically reproduce the surface of objects in which the objects are placed on the scanning area of a scanning prism, and in which there is an array of further prisms in the path of the detection beam between the scanning prism and an optoelectronic sensor. Such optical devices are particularly well suited for taking finger-prints.
2. Background
Processes and devices for reproducing objects using the optical principle of the disturbed total reflection are known from the state of the art.
In this connection, DE 34 21 220 C2 describes a “device for the distortion-free graphical reproduction of objects placed at an oblique angle to the scanning area,” in which a reflective prism is used as scanning prism. The object must be pressed from the outside onto a scanning area of the scanning prism, while, inside the scanning prism, the light is aimed at the scanning area. The light is reflected inside the scanning prism by the scanning area and in the process collects image information of the surface segment of the object resting on it.
This device, which serves in particular to collect, examine and identify fingerprints, is characterized by the fact that there are two deflecting prisms between the scanning prism and the face-side end section of the device, one of which serves to anamorphotically enlarge the object to be reproduced and the other to compensate for astigmatism, and that there is a lens that precedes an optical reproduction device or an optical analysis device.
The two deflecting prisms in combination are intended to facilitate anamorphotic enlargement without astigmatism when the planes of the image and the object are close, resulting in a low-distortion and high-resolution picture.
However, a significant disadvantage of this device is the course of the path of the beam caused by the use of the deflecting prisms; thus, only instruments with relatively large rated volume and in particular large rated heights are possible following this principle.
To that extent, this device does not satisfy the often-voiced call for a compact, space-saving device design.
Against that background, the invention has the purpose of improving the device described above in such a way that such devices can be designed with reduced rated volume and, in particular, reduced rated height.
The invention solves this problem in that at least one of the other prisms arranged in the path of the deflection beam is designed as a reflective prism with an incoming beam area, a reflective back area onto which the incoming light falls inside the prism, as well as an exiting beam surface.
Since the optical path now is no longer guided through deflecting prisms as in prior art because of the use of reflective prisms, a substantial reduction in the rated height of the devices built according to the characteristics of the invention becomes possible.
The reflective prisms can be designed to great advantage in such a way that the incoming beam surface and the exiting beam surface are located in a common prism area, so that the detection beam exits the prism through the same area through which it enters the prism.
According to the invention, both the prism for anamorphotic enlargement and the prism to compensate for astigmatism can be designed as reflective prisms. However, embodiments are also conceivable in which either only one or the other prism is designed as a reflective prism.
In this way, it is possible to make the device more compact as needed even as the length of the optical path remains the same.
Reflective prisms can, for example, be manufactured by providing a surface opposite the incoming beam surface of the prism, described as the back area in the invention, a mirrored surface or by pasting this area to a mirrored surface.
In a preferred embodiment of the device according to the invention there is also at least one plane mirror in the path of the detection beam between the scanning prism, and a lens that precedes the optoelectronic sensor to deflect the path of the beam for the purpose of bending.
This bending serves to further reduce the distance between the scanning prism and the optoelectronic sensor while, at the same time, maintaining the required optical path by aiming the beam, for example, from one prism first to a plane mirror and then from the latter to another prism, or from the plane mirror to at least one other plane mirror, forming in the process a more or less acute angle with the connecting line between the prisms.
In tested and tried embodiments of the invention there are two, or even three, plane mirrors between the prism for anamorphotic enlargement and the prism to compensate for the astigmatism.
Between the prism to compensate for the astigmatism and the optoelectronic sensor is a lens from which the detection beam is aimed at the optoelectronic sensor. In an additional embodiment of the invention, it is also possible to place at least one other optical element between the lens and the optoelectronic sensor that deflects the beam yet again and thereby allows for a reduction in the rated length of the device. Such an optical element is preferably a plane mirror.
The scope of the invention also allows for the replacement of the prism to compensate for astigmatism by a cylinder lens in order to achieve a technically desired effect.
The invention will be explained in more detail in the examples of embodiment that follow. The respective drawings show
For this purpose, light is beamed in one light beam path 5.1 through an incoming beam surface 6 into the scanning prism 1 and reflected inside the scanning prism 1 off the scanning area 2. In the process, the light registers image information, for example the papillary line pattern of a finger resting on it, exits again from the scanning prism 1 in one detection beam 5.2 through the exiting beam surface 7 and arrives at another prism 8 for anamorphotic enlargement.
The prism 8 of the invention is designed as a reflective prism, and thus has a mirrored surface on the back area 9. Because of this, the detection beam 5.2 entering into prism 8 through the prism area 10 does not exit again from the opposite surface and is only deflected in the process, as is usual with the current state of the art, but is reflected off the back area 9 and exits again through the prism area 10.
This has the advantage that only small prism angles are necessary because of the mirrored surface, which makes bending possible already at that stage.
In its further course, the detection beam 5.2 falls on a first reflector 11, is deflected by it in the direction of a second reflector 12 and falls on a prism 13 that serves to correct the astigmatism and is designed as a deflecting prism in this case.
Between the prism 13 and the optoelectronic sensor 4 is a lens 14 from which the detection beam 5.2 is aimed at the receiving area of the optoelectronic sensors 4.
Here, l1 stands for the rated length and h1 stands for the rated height of an optical device designed following the characteristics of the invention. It can be seen that the rated length l1 is much shorter than the optical path of the detection beam 5.2 from the scanning prism 1 to the optoelectronic sensor 4, and that the rated height h1 is substantially less than what is known from prior art devices in which the detection beam is at this spot carried through a deflecting prism.
The reduction in the rated length l1 and especially in the rated height h1 is achieved by designing the prism 8 as a reflective prism and by repeatedly changing the direction of the detection beam 5.2 at the reflectors 11 and 12.
Unlike the possible embodiments of the invention according to the previous example,
In the third exemplary embodiment according to
In another conceivable example, not illustrated here, another plane mirror, which would deflect detection beam 5.2 one more time, thus making another shortening of the rated length of the device possible, can be placed between the lens 14 and the optoelectronic sensor 4.
1 Scanning prism
2 Scanning area
3 Object
4 Optoelectronic sensor
5.1 Light beam
5.2 Detection beam
6 Incoming beam surface
7 Exit beam surface
8 Prism
9 Back area
10 Prism area
11, 12 Reflectors
13 Deflecting prism
14 Lens
15 Reflector
16, 17 Reflectors
18 Prism
Number | Date | Country | Kind |
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102 23 107.9 | May 2002 | DE | national |
This application claims priority to PCT Application No. PCT/EP03/03527, filed Apr. 4, 2003, and German Application No. DE 102 23 107.9, filed May 22, 2002.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP03/03527 | 4/4/2003 | WO | 5/27/2005 |