CN1781110A - An optical system - Google Patents

Abstract

The invention relates to an optical system for imaging an object on an image sensor, said system having an optical axis extending through an aperture and through image-forming means the comprise an aspheric light-beam-refracting surface. According to the invention an aspheric image-forming element, such as the lens (4), is combined with a small aperture (5). The aperture (5) and its location in relation to the lens (4) is to be configured such that the beam path is accomplished as shown in Figure 1, from where it will appear that light beams from the point A is refracted through such portions of the aspheric surface that do not overlap the portions of the aspheric surface where the light beams from C to D are refracted. Therefore the two said areas of the lens surface may be configured such the they each take into account the different focal distances to the respective parts of the label (2).

Description

optical system

technical field

The present invention relates to an optical system for imaging an object onto an image sensor, said system having an optical axis extending through a diaphragm and through an imaging device comprising an aspherical beam-refracting surface.

The invention relates particularly, but not exclusively, to reading information on vials of medicines which may contain insulin. This marking contains information about the contents of the container, expiry date, production date, batch number, etc.

Background technique

We know that various types of barcodes, matrix codes and code readers are available for this purpose. The construction of the code reader is mainly based on two principles. The first principle is that a scanning collimated beam with a small cross-section is used to illuminate the code point by point, which is usually used to determine the code on the code by means of a combination of a laser beam reflected from a circularly moving mirror and a photodetector. The reflected light intensity of the reflected light point.

Another principle is the use of a diffuse light source and an optical system capable of clearly detecting the diffuse light code on the image sensor. The scanning structure of the matrix code is far more complicated than that of the bar code, generally speaking, because the illumination of the matrix code requires the light beam to move in two dimensions. Often, it is difficult to ensure the reliability of the structure of moving parts in equipment due to the wear and tear caused by users in daily use, where there is a high demand for miniaturization. This situation combined with the ever-falling price of image sensors makes systems with image sensors very attractive for the readout of matrix codes.

For example, systems based on barcode reading are known from the disclosures in US Patent No. 4,978,335 and US Patent No. 5,821,524, while systems with two-dimensional matrix codes are described in Japanese Patent Application No. 2001-075480 and 11-3167877 . The former also mentions the use of a CCD camera to read codes, however, when considering the following conditions, it does not provide a method that can actually image a two-dimensional information matrix onto a CCD camera.

Prior art image sensor optics for code readers have an operating range whose focal length is typically never less than 30 mm to 500 mm. A very important aspect of the present invention is that the matrix code can be read by means of such a compact optical system, which can be integrated with the dosing device for dispensing insulin. Therefore, the information on the medicine bottle can be calculated within the drug delivery device, although the present invention is also applicable to conventional barcodes, but their information density is usually too small to be efficient by using the calculation unit in the drug delivery device. The invention now described involves two-dimensional matrix coding, from which two problems arise: one is the exact positioning of the matrix code relative to the optical system, and the other is accurate imaging of the matrix code onto the sensor, even at the desired focal length Being much smaller than 30mm, it can ensure that only a small distortion will be produced under poor focus conditions.

This problem is due to the overall limited depth of field and increased optical distortion at small focal lengths. Defective focusing and non-linear positional shifts of the code position on the image sensor make the decoding algorithm unstable or impossible to decode at all. In addition to this problem, the requirements of the cylindrical surface of the ampoule on the system tolerances are exactly the depth of field and the non-linear position transformation. The main problem is that the beams from the extremes of the object travel farther to reach the image plane than the beams from the center of the matrix code.

GB 2 287 551, US 5 305 147, and US 5 311 364 describe optical systems with short focal length aspheric lenses. These prior art systems are very complex and expensive since their aim is usually a large collimation stop and low distortion.

Contents of the invention

It is an object of the present invention to provide an optical system of the above-mentioned type in which there is very little distortion in poor focus by means of inexpensive and reliable optical elements.

The object of the invention is achieved by means of a system comprising a diaphragm configured and positioned relative to the aspherical beam-refracting surface so that two image point beams at different distances from the optical axis are captured by the different surfaces of the aspheric surface partial deflection.

In this document, an aspheric surface refers to a non-planar and non-spherical surface which, according to the invention, is capable of compensating for optical aberrations using the disclosed diaphragm size and position. The aspheric surface can be a double curved surface, such as a paraboloid, and a single curved surface mainly along the elongated direction, such as a cylindrical surface. An aspheric surface can be used solely as a focusing element in a system, or it can be used primarily as a correcting element in combination with other optical elements.

According to the invention, the diameter of the diaphragm is such that light beams from the edge of the object are refracted by points on the aspheric surface, excluding the apex of the aspheric surface. This compensates for the difference in distance between the object and the image plane, depending on whether the beam being observed comes from the far end or the center of the object. The two extreme different distances require different focal lengths, which can be precisely realized with the optical system according to the invention.

The aperture sizes of the stop to the object and the image plane respectively are of such a size that the portion of the aspheric surface that refracts the beam from the edge of the object does not overlap with the portion of the asphere that refracts the beam from the center of the object.

Preferably, aspheric lens elements are used, but the principles of the invention also include the use of aspheric mirrors.

Beam refracting surfaces are refractive and reflective optical elements whose properties can be described by geometric optics (ray tracing model). Beam refracting surfaces can also refer to optical elements that are partially or completely based on the phenomenon of diffraction.

According to a preferred embodiment, the aspheric lens is an injection molded lens and the stop is a circular stop.

According to another embodiment, the diaphragm can be an elongated diaphragm, whereby light beams in one direction, ie along a plane containing the optical axis, can be refracted by the central and peripheral regions of the lens. Since matrix codes are usually one-way rather than two-way curved, optical errors are not particularly large. Preferably, the elongated stop aperture is used in combination with an elongated lens, the elongated lens having an aspheric curvature on its surface, which spans the longitudinal direction of the lens.

According to a preferred embodiment, the system comprises an injection molded housing provided with an aperture integral with the housing and comprising securing means for the imaging means. Several lenses may be contained in the housing, preferably the housing contains mounting means for one or more light sources or light guides. Since the housing can also include a fixture for the image sensor, it is possible to form an optical system that contains inexpensive means, simple optical elements are positioned precisely, and substantially distortion-free imaging of curved objects can be achieved on planar object sensors, whereas At the same time the optical distance between the object and the image sensor is very small, eg less than 30mm.

Still small distortions can occur with the optical system according to the invention, which can be further reduced by means of known image correction circuits and receiving digital image data from the image sensor. The correction circuit may be based on digital polynomial functions.

Due to its very compact and reliable design, the invention is particularly suitable for inclusion in a dosing meter or BGM.

Description of drawings

The invention is described below with reference to the accompanying drawings, in which:

Fig. 1 represents according to the technical principle of the present invention;

Fig. 2 represents known two-dimensional matrix code;

Figure 3 is a cross-sectional view of an optical sensor according to the present invention; and

FIG. 4 is an exploded view of the embodiment shown in FIG. 3 .

Detailed ways

Referring now to Figure 1, in which the principles of the present invention are first explained.

In Fig. 1, it depicts part of the surface 1 of a cylindrical vial with a label 2 (see Fig. 2). Furthermore, an optical sensor or camera chip 3 , a lens 4 and a diaphragm 5 are drawn. From Figure 1, it can be clearly seen that the propagation path of the beam from point A to point B is larger than the propagation path of the beam from point C to point D. For example, if the triangulation method is used on the optical system, the deviation of the optical path length can reach 12%. The effect of the present invention is that the optical system can be made very compact. If the imaging optical length is 12mm, the 12% is equivalent to 1.4mm, which is close to the theoretical depth of field of the system with a diaphragm aperture of 0.5mm. For the optical path length plus all the uncertainties in the mechanical connection, a depth of field of 1.4 mm is sufficient to have the effect. This means that it is practically impossible to construct a 12 mm path length optical system with sufficient quality by means of the structural principles of the prior art. While the aperture of the diaphragm is very important for depth of field, once it is less than about 0.5mm, it adds unwanted diffraction phenomena, and the light intensity of the sensor drops to such a level that it is useless for the associated light source and sensor.

According to the invention, an aspherical surface imaging element such as lens 4 is combined with a small stop of 0.5 mm. The diaphragm and its position relative to the lens 4 are configured in such a way that it forms an optical path as shown in Figure 1. It can be clearly seen from Figure 1 that the part of the light beam from point A refracted through the aspheric surface is the same as that from The part of the light beam refracted from point C to point D passing through the aspheric surface does not overlap. Therefore, the two said regions of the lens surface can be configured such that they have different focal distances to their respective parts on the label 2 .

With the aid of well-known techniques, it is actually possible to design lenses that work according to the principles of the present invention, for example, according to the following formula:

$\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cr"\; filenames="A20048001180500101.png"\; state="\{\{state\}\}">cr</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="A20048001180500101.png"\; state="\{\{state\}\}">r</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}$

in

1/c=-1.24042

k=-0.786851

r is the radial coordinate in the coordinate system whose origin is the apex of the lens.

FIG. 2 shows an example of a known two-dimensional matrix code 6 comprising a plurality of dots, for example dark dots 7 and bright dots 8 . Such matrix codes are known, for example, from US Patent No. 5,126,542, where light and dark dots represent 0 and 1 respectively of digital information. This two-dimensional matrix code has quite high information density compared with the bar code, although the present invention is also applicable to the bar code, but when utilizing the two-dimensional matrix code, the advantage of the present invention is particularly obvious, when the matrix code is in a circle Imaging problems with imaging of such codes arise when surfaced, for example, the label on an insulin ampule.

The label curvature and very short focal length associated with this utilization of the present invention can result in such a combination of optical errors that it is practically impossible to correct for such optical errors with known digital imaging software programs. This problem is solved by means of the present invention in combination with known digital image correction techniques, eg pincushion distortion and/or barrel distortion can be reduced.

Figure 3 is a cross-sectional view of a preferred embodiment of the present invention.

FIG. 3 shows vial 11 with label 12 supported on base 28 . By means of an optical system mounted on the circuit board PCB 14, the information on the label can be read. Also mounted on the circuit board are light emitting diodes 15 and 16 and an image sensor 17 . Also shown in Figure 4 is the optical system.

Reference numeral 18 is used to designate a photoconductor member which can receive light from the light emitting diodes 15 and 16 . The light conductor element has polished surfaces 19-21 so that after the light exits through the matte surface 22, a uniform and diffuse distribution of light is directed towards the label 12. A thin transparent protective barrier 23 is arranged on the outer side of the matte side of the light conductor element 18 for cleaning the optical system.

Part 24 of the light conductor element 18 is configured as an aspheric lens 24 and has a stop 25 , see stop 5 shown in FIG. 1 . In addition, an opaque screen 26 is formed to ensure that extraneous light cannot enter the image sensor, which only receives light from the label and through the lens 24 . The above-mentioned elements are surrounded by a casing 27 , which is explained in more detail below with reference to FIG. 4 .

FIG. 4 is an exploded view of the embodiment shown in FIG. 3 . The housing 27 is a separate injection molded part which contains a not shown transverse beamlet 29 in which the diaphragm 25 is arranged. As mentioned above, the light conductor element 18 comprises a lens 24, and it can be seen from the above explanation that it is important according to the invention that the alignment of this lens with respect to the diaphragm 25 is very precise. In the exemplary embodiment shown, this is achieved by means of guide surfaces 30 , 31 on the light conductor element 18 , the surfaces of which engage in grooves in the injection-molded element 27 , as can be clearly seen in FIG. 4 . In this way, the relative position between the lens 24 and the diaphragm 25 is very precise. The positioning of the image sensor 17 relative to the optical element can be realized by a common method, for example, the assembled two parts include bosses and recesses.

Claims (20)

1. one kind is used for the optical system of imaging object to the imageing sensor, described system has and extends through diaphragm and the optical axis by imaging device, imaging device comprises non-spherical beams plane of refraction, it is characterized in that, the configuration of diaphragm and the position in optical system are such, and the surface portion that has the light beam of two picture point of different distance to be had nothing in common with each other on the non-spherical basically with optical axis reflects.

2. according to the optical system of claim 1, it is characterized in that imaging device comprises: non-spherical lens.

3. according to the optical system of claim 1, it is characterized in that imaging device comprises: non-spherical reflector.

4. according to the optical system of claim 1, it is characterized in that imaging device comprises: diffraction lens.

5. according to the optical system of claim 2, it is characterized in that lens are injection molding lens.

6. according to the optical system of claim 1, it is characterized in that diaphragm is a circular iris.

7. according to the optical system of claim 1, it is characterized in that diaphragm is the thin-and-long diaphragm.

8. according to the optical system of claim 7, it is characterized in that lens are to have the thin-and-long lens that travelling belt limits non-spherical, travelling belt is parallel to the vertical of lens.

9. according to any one optical system among the claim 1-7, it is characterized in that it comprises the injection molding shell that disposes diaphragm, diaphragm and shell form integral body, and comprise the stationary installation that is used for imaging device.

10. according to the optical system of claim 4, it is characterized in that the several lens of configuration in the shell.

11. the optical system according to claim 9 or 10 is characterized in that, a plurality of catoptrons of configuration in the shell.

12. the optical system according to claim 9-11 is characterized in that, shell comprises the stationary installation that is used for one or more light sources.

13. the optical system according to claim 12 is characterized in that shell comprises optical conductor.

14. the optical system according to claim 12 or 13 is characterized in that, shell comprises the stationary installation that is used for imageing sensor.

15. the optical system according to claim 8-14 is characterized in that, the light path between object and the imageing sensor is less than 30mm.

16. the optical system according to claim 1-13 is characterized in that, imageing sensor can produce Digital Image Data.

17. the optical system according to claim 16 is characterized in that, a kind of image calibrating circuit is provided, it is disposed for adjusting view data, and it can reduce optical imaging error.

18. the optical system according to claim 15 is characterized in that, provides adjustment by means of digital polynomial function.

19. the optical system according to claim 1-18 is characterized in that, it is integrated in the administration device that is used for the treatment of.

20. the optical system according to claim 1-14 is characterized in that, it is integrated in the blood-glucose measurement mechanism, is used to read the information of label on this device.

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