Contact image sensor for eliminating moire and banknote authentication device using the same

Abstract

The utility model discloses a kind of contact image sensor of eliminating moire and the currency verification device applying it, contact image sensor includes shell, optical lens, first light source, second light source and photosensitive element, optical lens is columnar lens and vertically arranged in shell, first light source and second light source are separately arranged in the both sides of columnar lens and the light-emitting surface is inclined towards the side where columnar lens is, photosensitive element is located directly below optical lens, diffusion sheet is arranged between optical lens and photosensitive element, light emitted by light source is formed reflected light after being reflected by to-be-scanned object, reflected light is received by photosensitive element after being scattered by diffusion sheet after being shot into optical lens, the haze of diffusion sheet is 40~60%.The contact image sensor is applied to currency verification device, in the case where focal length is not changed, light is scattered to multiple directions using the diffusion sheet added, so that light becomes more soft and uniform, moire is reduced or even eliminated, and the accuracy of identifying the authenticity of banknotes is improved.

Description

Technical Field

[0001] This utility model relates to the field of sensor equipment technology, and more specifically to a contact image sensor for eliminating moiré patterns and a banknote verification device using the same. Background Technology

[0002] Moiré patterns are a new type of wavy interference pattern that arises when the spatial frequencies of the pixels on the image sensor are close to the spatial frequencies of the stripes in the image. More specifically, the image sensor consists of many tiny pixels arranged in a grid-like structure. When the image sensor photographs a striped object, the stripes on the stripes also form a grid-like structure on the image sensor. If the spatial frequencies of these two grid-like structures are close, moiré patterns will occur. Figure 1 As shown, Image 1 and Image 2 are two identical concentric circle images, and when superimposed, a moiré pattern appears.

[0003] Existing contact image sensors scan banknote images, such as Figure 2 As shown, the presence of moiré patterns in the image can cause the algorithm to fail to identify the fake product, thus affecting the accuracy of the authentication.

[0004] Existing contact image sensors incorporate a cylindrical lens, which focuses light from one point to another. To mitigate moiré patterns, the focal length of the cylindrical lens is typically reduced, for example... Figure 3 This diagram illustrates the focal point of a cylindrical lens. This method can alter the spacing between pixel groups on the sensor and the texture on the banknote, thereby reducing moiré patterns. However, this method has some drawbacks, mainly: (1) Changing the focus is not effective in reducing moiré patterns and cannot completely solve the problem of moiré patterns.

[0005] (2) In order to completely eliminate moiré patterns, it would be necessary to move too far away from the focal point, which is not structurally feasible, and the degree of image blur will affect the algorithm's judgment. Figure 4 The contact image sensor scanned the image after the focus was disrupted. Although the moiré pattern on the image disappeared, it reduced the sharpness of the image and made the image blurry, resulting in the failure to identify the serial number.

[0006] (3) Due to defocusing, the height of the contact image sensor will increase, which may cause incompatibility with existing machine structures. For example Figure 5 The image shows a size comparison of the banknote verification module after the focus is lost. While keeping the banknote passage unchanged, the overall height of the contact image sensor will increase, resulting in a higher total height.

[0007] Therefore, it is necessary to develop an improved contact pattern sensor that can be applied to existing devices and eliminate moiré patterns. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a contact image sensor that can effectively eliminate moiré patterns without changing the focal length.

[0009] According to one aspect of the present invention, a contact image sensor for eliminating moiré patterns is provided, comprising a housing, an optical lens, a first light source, a second light source, and a photosensitive element. A light-transmitting glass plate is provided on the housing, and the upper surface of the light-transmitting glass plate forms a scanning surface that mates with the object to be scanned. The optical lens is a cylindrical lens and is vertically disposed within the housing. The first light source and the second light source are respectively disposed on both sides of the cylindrical lens, with their light-emitting surfaces inclined towards the side where the cylindrical lens is located. The photosensitive element is mounted on a PCB substrate and fixed within the housing, and is located directly below the optical lens. A diffuser is provided between the optical lens and the photosensitive element, and the diffuser is parallel to the light-transmitting glass plate. Light emitted by the first and second light sources is reflected by the object to be scanned to form reflected light. The reflected light enters the optical lens, is scattered by the diffuser, and is then received by the photosensitive element.

[0010] In some implementations, the haze of the diffuser is 40% to 60%, and the transmittance of the diffuser is greater than 80%.

[0011] In some embodiments, the housing has a lens mounting slot, the bottom of which is a hollow channel, a cavity is located above the photosensitive element, the top of which is a flat surface, the hollow channel extends to the top of the cavity, the width of the cavity is greater than the width of the hollow channel, and a diffuser is mounted on the top of the cavity.

[0012] In some embodiments, the upper surface of the diffuser is adhered to the top of the cavity, and the diffuser and the light-transmitting glass plate are arranged horizontally.

[0013] In some implementations, the first light source and the second light source form a dual-sided illumination light source, with the first light source and the second light source forming an angle of 30 to 60 degrees with the horizontal plane, respectively.

[0014] According to another aspect of the present invention, a banknote verification device is provided, which applies the above-mentioned contact image sensor for eliminating moiré patterns. The banknote verification device has two sets of contact image sensors for eliminating moiré patterns, which are disposed on both sides of the banknote passage and arranged vertically.

[0015] Compared with the prior art, the beneficial effects of this utility model are: The contact image sensor for eliminating moiré patterns provided by this utility model is an improvement on the existing contact image sensor structure. Without changing the focal length, a diffuser is added between the optical lens and the photosensitive element. After light is emitted from the light source, it is reflected on the surface of the object to be scanned. Then, the light passes through the optical lens, the diffuser, and finally reaches the photosensitive element for imaging. By adding a diffuser in the imaging light path, the light is scattered in multiple directions, making the light softer and more uniform. The imaging of the light on the photosensitive element becomes more diffused, thereby reducing the interference between the image texture of the scanned object and the pixel group, thus reducing or even eliminating moiré patterns.

[0016] Different levels of haze in diffusers result in different imaging effects. Without a diffuser, the image is clear, but as the haze increases, the image becomes increasingly blurry. This contact image sensor is used in banknote verification devices. The diffuser used in the contact image sensor needs to have its haze controlled between 40% and 60% to ensure that moiré patterns are eliminated without affecting the algorithm's judgment, thereby improving the accuracy of banknote authentication.

[0017] This contact image sensor adds a diffuser to the existing structure with minimal structural changes and does not alter the focal length. When applied to banknote verification devices, the total height of the upper and lower sets of contact image sensors remains unchanged, making it suitable for improvements to existing equipment and significantly reducing development and improvement costs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of moiré pattern generation; Figure 2 These are scanned images obtained from existing contact image sensors, and the images contain moiré patterns. Figure 3 It is the focal position of existing contact image sensors; Figure 4 These are scanned images obtained by existing contact image sensors when the focal point is disrupted; Figure 5 This is a size comparison diagram showing whether the banknote detector is in focus or not when the fragment is broken. Figure 5 A is a schematic diagram of the original banknote verification device. Figure 5 B is a schematic diagram of the banknote verification device when it loses focus; Figure 6 This is a schematic diagram of one embodiment of a contact image sensor according to the present invention; Figure 7 This is a schematic diagram of one embodiment of a banknote verification device according to the present invention; Figure 8 These are images showing the effects of using different haze diffusers; Figure 9These are scanned images of banknotes under different levels of haze diffusion. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments.

[0020] like Figure 6 As shown, a contact image sensor for eliminating moiré patterns according to one embodiment of the present invention includes: a housing 1, an optical lens 3, a first light source 4, a second light source 5, and a photosensitive element 6. This contact image sensor can be applied to devices such as banknote verification devices and bill scanners, and can eliminate moiré patterns on images.

[0021] A horizontally placed light-transmitting glass plate 2 is mounted on the housing 1, and the upper surface of the light-transmitting glass plate 2 forms a scanning surface 21 that mates with the object to be scanned. The optical lens 3 is a cylindrical lens, and the housing 1 has a lens mounting groove 11 with a hollow channel 12 at the bottom. The optical lens 3 is vertically positioned within the lens mounting groove 11 of the housing 1, located in the middle of the housing 1. A first light source 4 and a second light source 5 are respectively located on both sides of the optical lens 3, with the light-emitting surfaces of the two light sources tilted towards the side where the optical lens 3 is located. The angle A formed by the first light source 4 and the horizontal plane, and the second light source 5 and the horizontal plane, is 30-60 degrees, forming a dual-sided light source. A photosensitive element 6 is mounted on a PCB substrate 61 to form a photosensitive assembly, and then fixed inside the housing 1. The photosensitive element 6 faces upward, and there is a cavity 13 above the photosensitive element 6. The top 14 of the cavity 13 is a plane, and the hollow channel 12 extends to the top 14 of the cavity 13. The width of the cavity 13 is greater than the width of the hollow channel 12. The upper surface of the diffuser 7 is attached to the top 14 of the cavity 13, and the photosensitive element 6 is located directly below the optical lens 3.

[0022] The diffuser 7 is arranged parallel to the light-transmitting glass plate 2. The light emitted by the first light source 4 and the second light source 5 is reflected by the object to be scanned to form reflected light. After the reflected light enters the optical lens 3, it is scattered by the diffuser 7 and then received by the photosensitive element 6.

[0023] Different levels of haze in the diffuser 7 result in different imaging effects. Without the diffuser 7, the image is clear; as the haze of the diffuser 7 increases, the image becomes increasingly blurry. Figure 8 As shown. In this embodiment, preferably, the haze of the diffuser 7 is 40%~60%, and the transmittance of the diffuser 7 is greater than 80%.

[0024] Applying the aforementioned contact image sensor to a banknote verification device requires two sets of contact image sensors. These two sets of contact image sensors are arranged vertically, respectively on both sides of the banknote passage 100. Figure 7 As shown.

[0025] After applying this new type of contact image sensor to the banknote verification device, the banknotes were scanned, such as... Figure 9 As shown, it can be seen that using a diffuser 7 with a haze between 40% and 60% significantly improves the moiré pattern on the image; when the haze of the diffuser 7 is higher than 60%, although the moiré pattern on the image is eliminated, the image will also be excessively blurred, affecting the algorithm's judgment.

[0026] The contact image sensor for eliminating moiré patterns provided in this application is an improvement on the existing contact image sensor structure. Without changing the focal length, a diffuser 7 is added between the optical lens 3 and the photosensitive element 6. After light is emitted from the light source, it is reflected by the surface of the object to be scanned. The light then passes through the optical lens 3, the diffuser 7, and finally reaches the photosensitive element 6 for imaging. The diffuser 7 is added to the light path of the image formation, scattering the light in multiple directions, making the light softer and more uniform, and resulting in a more diffused image on the photosensitive element. This method can make the details between the pixels on the photosensitive element and the texture of the object being photographed less noticeable, thereby reducing or even eliminating moiré patterns.

[0027] The contact image sensor requires minimal structural modifications compared to existing designs. When applied to banknote verification devices, the total height of the upper and lower sets of contact image sensors remains unchanged, without affecting the dimensions of other components in the verification device. It can be directly applied to the improvement of existing equipment, thus significantly reducing development costs and the cost of improving existing banknote verification devices, enabling the new contact image sensor to be applied as soon as possible.

[0028] The above descriptions are merely some embodiments of this utility model. It should be noted that those skilled in the art can make other modifications and improvements without departing from the inventive concept of this utility model, and these all fall within the protection scope of this utility model.

Claims

1. A contact image sensor for eliminating moiré patterns, comprising a housing (1), an optical lens (3), a first light source (4), a second light source (5), and a photosensitive element (6), wherein a light-transmitting glass plate (2) is provided on the housing (1), the upper surface of the light-transmitting glass plate (2) forms a scanning surface (21) that cooperates with the object to be scanned, the optical lens (3) is a cylindrical lens and is vertically disposed inside the housing (1), the first light source (4) and the second light source (5) are respectively disposed on both sides of the optical lens (3) and the light-emitting surface is inclined toward the side where the optical lens (3) is located, the photosensitive element (6) is mounted on a PCB substrate (61) and fixed inside the housing (1), the photosensitive element (6) is located directly below the optical lens (3), characterized in that, A diffuser (7) is provided between the optical lens (3) and the photosensitive element (6). The diffuser (7) is arranged parallel to the light-transmitting glass plate (2). The light emitted by the first light source (4) and the second light source (5) is reflected by the object to be scanned to form reflected light. The reflected light enters the optical lens (3) and is scattered by the diffuser (7) before being received by the photosensitive element (6).

2. The contact image sensor for eliminating moiré patterns according to claim 1, characterized in that, The haze of the diffuser (7) is 40%~60%, and the transmittance of the diffuser (7) is greater than 80%.

3. The contact image sensor for eliminating moiré patterns according to claim 2, characterized in that, The housing (1) has a lens mounting groove (11), the bottom of the lens mounting groove (11) is a hollow channel (12), the photosensitive element (6) has a cavity (13) above it, the top (14) of the cavity (13) is a plane, the hollow channel (12) extends to the top (14) of the cavity (13), the width of the cavity (13) is greater than the width of the hollow channel (12), and the diffuser (7) is mounted on the top (14) of the cavity (13).

4. The contact image sensor for eliminating moiré patterns according to claim 3, characterized in that, The upper surface of the diffuser (7) is adhered to the top (14) of the cavity (13).

5. The contact image sensor for eliminating moiré patterns according to claim 1, characterized in that, The first light source (4) and the second light source (5) form a double-sided light source, with the first light source (4) and the second light source (5) forming an angle of 30 to 60 degrees with the horizontal plane, respectively.

6. A banknote verification device, characterized in that, The banknote verification device employs a contact image sensor for eliminating moiré patterns as described in any one of claims 1 to 5, and has two sets of contact image sensors for eliminating moiré patterns disposed on both sides of the banknote passage and arranged vertically.

Images