Low-cost contact image sensor and detection method
By using infrared receiving diodes with a diameter of 2mm and an interlaced light guide structure to replace the microlenses and complex photosensitive chips in traditional CIS, the cost and complexity of banknote counterfeit detection sensors have been reduced, achieving a resolution of 20DPI and a counterfeit detection effect.
Patent Information
- Application Number
- CN202511185435.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-22
- Publication Date
- 2026-01-13
AI Technical Summary
Traditional contact image sensors (CIS) are expensive for banknote authentication, making it difficult to meet the demand for low-cost competition.
Using infrared receiving diodes with a diameter of 2mm to replace tiny lenses and complex photosensitive chips, the staggered infrared receiving diodes, combined with light guide rods and LED emitting light sources, achieve image signal acquisition and conversion through a one-time injection molded machine housing.
It reduces production complexity and material costs while maintaining a resolution of 20 DPI, meeting the requirements for banknote authentication and achieving the same authentication effect as traditional CIS sensors.
Smart Images
Figure CN121335239A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of image sensor technology, and specifically to a low-cost contact image sensor and detection method. Background Technology
[0002] Traditional contact image sensors (CIS) are currently used in the financial equipment industry, primarily for image recognition and counterfeit detection of banknotes. They are characterized by high resolution (typically 100 DPI, 200 DPI, or 300 DPI) and fast response, but are very expensive. CIS technology involves closely arranging photosensitive sensors in a row or column, with an effective scanning length typically around 180 mm. This allows for rapid and direct capture of images or documents in close proximity. The products are usually rectangular, with light sources at both ends for exposure. Products used in financial equipment typically utilize red, green, blue, infrared, and UV light sources to generate images under different illumination conditions. During exposure, the image signal of the surface object is focused onto the photosensitive chip through a tiny fiber optic lens. The chip acquires the image at a specific frequency and ultimately outputs an analog electrical signal serially to a high-speed ADC chip for image signal analysis and conversion. For banknote counterfeit detection, such high image resolution is not necessary. Therefore, research and development of low-cost CIS sensors specifically for banknote counterfeit detection could be considered from this perspective.
[0003] Traditional CIS sensors, capable of capturing high-resolution images, require tiny lenses and complex photosensitive chips to receive these images. Their manufacturing process is complex, necessitating the use of high-end chip bonding machines, resulting in high product prices. Traditional CIS sensors can no longer meet the increasingly fierce demand for low-cost competition, especially against the backdrop of trade wars and a global economic downturn, where low-cost products are more likely to gain market acceptance. Summary of the Invention
[0004] In view of this, it is necessary to provide a low-cost contact image sensor and detection method that can reduce material costs and manufacturing complexity.
[0005] A low-cost contact image sensor for banknote counterfeit detection, meeting the resolution requirements for banknote counterfeit detection, includes an upper half and a lower half with the banknote channel as the axis of symmetry. The upper half and the lower half respectively include a machine housing, multiple LED emitting light sources, two light guide rods, several infrared receiving diodes, a constant current driving unit, and an ADC conversion unit. The machine housing has two light guide grooves and several regularly arranged light guide holes for receiving lamps. Each light guide rod has an LED emitting light source at both ends, and each infrared receiving diode is correspondingly located at the bottom of one of the light guide holes for receiving lamps. The output terminal of the constant current driving unit is connected to the LED emitting light source, and the constant current driving unit is used to provide a PWM signal to the LED emitting light source; the input terminal of the ADC conversion unit is connected to the infrared receiving diode, and the ADC conversion unit is used to perform analog-to-digital conversion on the signal received by the infrared receiving diode; the light emitted by the light guide rod is reflected by the banknote to be identified, enters the infrared receiving diode through the light guide hole of the receiving lamp, so as to realize the reception and conversion of the reflected light signal.
[0006] Preferably, the upper part and the lower part are symmetrically arranged, the machine housing has a predetermined height and length, the top surface of the machine housing in the height direction is provided with a glass layer, the bottom surface of the machine housing in the height direction is provided with a fiberglass board, and the glass layers of the upper part and the lower part are respectively located on both sides of the axis of symmetry.
[0007] Preferably, the light guide groove is elongated, and the length direction of the light guide groove is consistent with the length direction of the machine housing. Two light guide grooves are symmetrically arranged on the inner side of the outer side wall of the machine housing. There is a predetermined angle between the light guide groove and the side wall of the machine housing. Two light guide rods are respectively arranged at the bottom of the light guide groove. The light emission direction of the light guide rods is towards the glass layer and has a predetermined angle with the plane of the glass layer.
[0008] Preferably, a plurality of light guide holes for receiving lamps are regularly arranged between two light guide slots, and the plurality of light guide holes for receiving lamps are divided into two groups, with the two groups of light guide holes for receiving lamps arranged alternately on both sides of the centerline in the length direction of the machine housing; The light guide groove and the regularly arranged light guide holes of the receiving lamps in the machine housing are injection molded in one step.
[0009] Preferably, the system further includes a PCB circuit board, which is disposed on the inner side of the fiberglass board. A plurality of infrared receiving diodes are electrically connected to the PCB circuit board. The number and installation position of the infrared receiving diodes are the same as the number and installation position of the light guide holes of the receiving lamp, and are arranged in a one-to-one correspondence.
[0010] Preferably, the LED emitting light source adopts a light source with multiple different wavelengths, including one or more of red light, green light, blue light, infrared light, white light and UV light.
[0011] Preferably, the constant current driving unit includes a first transistor Q1, a third resistor R3, a fourth resistor R4, and a second transistor Q2 connected in series. The anode of the LED light source is connected to the power supply terminal, the cathode of the LED light source is connected to the collector of the first transistor Q1, the base of the first transistor Q1 is connected to the DAC chip through the tenth resistor R10, and the base of the second transistor Q2 is connected to the PWM signal through the eleventh resistor R11.
[0012] Preferably, the ADC conversion unit includes multiple analog switch chips and a high-speed ADC conversion circuit. Each analog switch chip is connected to multiple infrared receiving diodes. The analog switch chip is used for signal multiplexing of the multiple infrared receiving diodes. The analog switch chip is connected to the high-speed ADC conversion circuit through a flexible flat cable (FFC). The high-speed ADC conversion circuit is used to perform analog-to-digital conversion of the signal to realize the recognition of the received image signal.
[0013] Furthermore, a low-cost contact image sensor detection method is provided, using the low-cost contact image sensor described above for banknote counterfeit detection, the method comprising the following steps: Step 1: The LED light source is activated and emits light; Step two involves passing the banknote to be identified between two glass layers, the upper and lower halves of a low-cost contact image sensor. Step 3: The constant current driving unit drives the light guide rod to emit light. The light guide rod emits one or more of the following: red light, green light, blue light, infrared light, white light and UV light. The light guide rod evenly emits light onto the banknote to be identified. Step four: The light signal diffused by the banknote surface passes through the light guide hole of the receiving lamp and reaches the infrared receiving diode; Step 5: The infrared receiving diode converts the optical signal into an electrical signal and transmits it to the ADC conversion unit; Step six: The ADC conversion unit converts the analog signal into a digital signal and transmits it to the central processing unit; Step seven: The central processing unit identifies and synthesizes the image acquired under a monochromatic light source, and finally outputs the image signal of the banknote.
[0014] Preferably, the specific steps for starting and emitting light from the LED light source in step one include: Step 1.1: Power on the device and start it up to determine the reference clock; Step 1.2: The LED light source emits red light, green light, blue light, infrared light, white light and UV light in sequence for an integer multiple of the reference clock. The red light receiving diode receives the red light, green light, blue light, infrared light, white light and UV light in sequence and transmits them to the ADC conversion unit. Step 1.3: The central processing unit combines images generated by light of the same color into a monochrome image.
[0015] In the aforementioned low-cost contact image sensor and detection method, infrared receiving diodes with a diameter of 2mm are used instead of tiny lenses and complex photosensitive chips to receive images. The infrared receiving diodes are arranged in an alternating pattern, with a spacing of 1.27mm between adjacent diodes, achieving an effective scanning length of 90mm and a resolution of 20DPI, meeting the requirements for banknote image recognition and counterfeit detection. The light guide holes for the receiving lamps, arranged in an alternating pattern along the centerline of the machine housing, are injection molded in one piece, facilitating mold making and improving resolution. The encapsulated infrared receiving lamps are mature products on the market, inexpensive, readily available from numerous manufacturers, and easy to purchase. In terms of banknote counterfeit detection performance, this method maintains consistency with traditional CIS sensors while significantly reducing overall production complexity and material costs. The method of this invention is simple, easy to implement, low-cost, and easy to promote. Attached Figure Description
[0016] Figure 1 This is a schematic diagram (cross-sectional view) of the structure of a low-cost contact image sensor according to an embodiment of the present invention.
[0017] Figure 2 This is a schematic diagram of the light guide hole of the receiving lamp in a low-cost contact image sensor according to an embodiment of the present invention.
[0018] Figure 3 This is a schematic diagram of the circuit structure of the constant current drive unit of the low-cost contact image sensor according to an embodiment of the present invention.
[0019] Figure 4 This is a schematic diagram of the circuit structure of the infrared receiving diode of the low-cost contact image sensor according to an embodiment of the present invention.
[0020] Figure 5 This is a schematic diagram of the circuit structure of the ADC conversion unit of the low-cost contact image sensor according to an embodiment of the present invention.
[0021] Figure 6 This is a flowchart of a low-cost contact image sensor detection method according to an embodiment of the present invention.
[0022] Figure 7 This is a schematic diagram of the working process of the LED emitting light source in the detection method of the low-cost contact image sensor according to an embodiment of the present invention.
[0023] Figure 8 This is a schematic diagram of a banknote image identified by a low-cost contact image sensor according to an embodiment of the present invention. Figure 1(The upper half is a white light image, and the lower half is an infrared image and infrared features).
[0024] Figure 9 This is a schematic diagram of a banknote image identified by a low-cost contact image sensor according to an embodiment of the present invention. Figure 2 (The upper half is a white light image, and the lower half is an infrared image and infrared features). Detailed Implementation
[0025] This embodiment uses a low-cost contact image sensor and detection method as an example. The invention will be described in detail below with reference to specific embodiments and accompanying drawings.
[0026] Please see Figure 1 and Figure 2 This invention illustrates a low-cost contact image sensor 100 for banknote counterfeit detection, meeting the resolution requirements for banknote counterfeit detection. The sensor includes an upper half and a lower half with the banknote channel as a symmetrical axis. The upper half and lower half respectively include a housing 10, multiple LED emitting light sources, two light guide rods 50, several infrared receiving diodes 60, a constant current driving unit, and an ADC conversion unit. The housing 10 has two light guide grooves 11 and several regularly arranged light guide holes 12 for receiving lamps. Each light guide rod 50 has an LED emitting light source at both ends, and each infrared receiving diode 60 is correspondingly located at the bottom of one of the light guide holes 12. The output terminal of the constant current driving unit is connected to the LED emitting light source, and the constant current driving unit is used to provide a PWM signal to the LED emitting light source; the input terminal of the ADC conversion unit is connected to the infrared receiving diode 60, and the ADC conversion unit is used to perform analog-to-digital conversion on the signal received by the infrared receiving diode 60; the light emitted by the light guide rod 50 is reflected by the banknote to be identified, enters the infrared receiving diode 60 through the light guide hole 12 of the receiving lamp, so as to realize the reception and conversion of the reflected light signal.
[0027] Preferably, the upper part and the lower part are symmetrically arranged, the machine housing 10 has a predetermined height and length, the top surface of the machine housing 10 in the height direction is provided with a glass layer 20, the bottom surface of the machine housing 10 in the height direction is provided with a fiberglass board 40, and the glass layers 20 of the upper part and the lower part are respectively located on both sides of the axis of symmetry.
[0028] Specifically, the glass layer 20 is placed on the top of the machine housing 10 to allow light to pass through during banknote verification; the fiberglass board 40 is placed on the bottom of the machine housing 10 to enhance the strength of the machine housing 10 and prevent deformation of the housing.
[0029] Preferably, the light guide groove 11 is elongated, and the length direction of the light guide groove 11 is consistent with the length direction of the machine housing 10. Two light guide grooves 11 are symmetrically arranged on the inner side of the outer side wall of the machine housing 10. The light guide groove 11 and the side wall of the machine housing 10 have a predetermined angle. Two light guide rods 50 are respectively arranged at the bottom of the light guide groove 11. The light emission direction of the light guide rods 50 is towards the glass layer 20 and has a predetermined angle with the plane of the glass layer 20.
[0030] Specifically, the length direction of the light guide rod 50 is consistent with the length direction of the machine housing 10, and there is a predetermined width between the two light guide rods 50 to avoid blocking the reflected light signal.
[0031] Specifically, the width between the two light guide rods 50 is greater than the width of the two sets of staggered light guide holes 12 of the receiving lamps.
[0032] Specifically, in this embodiment, the two light guide rods 50 are symmetrically arranged on both sides of the center line of the machine housing, and the angle between the light emission angle of the light guide rod 50 and the plane of the glass layer 20 is 65°.
[0033] Preferably, a plurality of light guide holes 12 for receiving lamps are regularly arranged between two light guide grooves 11, and the plurality of light guide holes 12 for receiving lamps are divided into two groups, and the two groups of light guide holes 12 for receiving lamps are arranged alternately on both sides of the centerline in the length direction of the machine housing 10. The light guide groove 11 and the regularly arranged light guide holes 12 of the receiving lamps of the machine housing 10 are injection molded in one step.
[0034] Specifically, on both sides of the centerline along the length of the machine housing 10, there is a set of sequentially arranged light guide holes 12. The two sets of light guide holes 12 are staggered, and each light guide hole 12 is located on the perpendicular bisector of the line connecting the centers of two adjacent light guide holes 12 in the other set. That is, each light guide hole 12 and the two adjacent light guide holes 12 in the other set form an equilateral triangle, and the center of each light guide hole 12 and the center of the two adjacent light guide holes 12 in the other set are located at the vertices of the equilateral triangle.
[0035] Specifically, in this embodiment, the aperture of each light guide hole 12 is 1.8 mm, the diameter of each infrared receiving diode 60 is 2 mm, and the center of the light guide hole 12 coincides with the center of the infrared receiving diode 60, so that all the light in the light guide hole 12 can be received by the infrared receiving diode 60.
[0036] The light guide holes 12 of the receiving lamps in the same group are arranged sequentially, and the light guide holes 12 of the receiving lamps in different groups are arranged alternately, so that the distance between the centers of adjacent light guide holes 12 of the receiving lamps in different groups is 1.27mm, that is, the spacing between the infrared receiving diodes 60 is 1.27mm, which meets the image resolution requirement of 20DPI.
[0037] Preferably, the system further includes a PCB circuit board 30, which is disposed inside the fiberglass board 40. A plurality of infrared receiving diodes 60 are electrically connected to the PCB circuit board 30. The number and installation position of the infrared receiving diodes 60 are the same as the number and installation position of the light guide holes 12 of the receiving lamp, and are arranged in a one-to-one correspondence.
[0038] Specifically, in this embodiment, the infrared receiving diode 60 is a 2mm black round-headed infrared LED receiving tube with a receiving wavelength range of 400-1100nm.
[0039] Preferably, the LED emitting light source adopts a light source with multiple different wavelengths, including one or more of red light, green light, blue light, infrared light, white light and UV light.
[0040] Specifically, the LED emitting light source outputs light sources of different wavelengths, enabling the infrared receiving diode 60 to acquire image signals under different light sources.
[0041] Specifically, the constant current driving unit and the ADC conversion unit are disposed on the PCB circuit board 30.
[0042] Preferably, please refer to Figure 3 The constant current driving unit is shown, which includes a first transistor Q1, a third resistor R3, a fourth resistor R4, and a second transistor Q2 connected in series. The anode of the LED light source is connected to the power supply terminal, the cathode of the LED light source is connected to the collector of the first transistor Q1, the base of the first transistor Q1 is connected to the DAC chip through the tenth resistor R10, and the base of the second transistor Q2 is connected to the PWM signal through the eleventh resistor R11.
[0043] Specifically, the DAC signal is used to adjust the transmit current during calibration, the PWM signal is used to adjust the exposure time during operation, and the third resistor R3 and the fourth resistor R4 are used to limit the maximum output current value.
[0044] Specifically, in this embodiment, the function of the DAC chip in sending DAC signals is to adjust the transmitting lamp current based on the signal of the reference material, so that the signals of the receiving lamps are at the same level.
[0045] Before the image sensor is installed in the product, a signal calibration is required using a reference object to ensure that the signal of the infrared receiving diode 60 remains consistent. When banknotes of different colors pass through the image sensor, the signal change ratio can be displayed in different colors.
[0046] Preferably, please refer to Figure 4 and Figure 5 The diagram shows the ADC conversion unit, which includes multiple analog switch chips and a high-speed ADC conversion circuit. Each analog switch chip is connected to multiple infrared receiving diodes 60. The analog switch chip is used for signal multiplexing of the multiple infrared receiving diodes 60. The analog switch chip is connected to the high-speed ADC conversion circuit through a flexible flat cable (FFC). The high-speed ADC conversion circuit is used to perform analog-to-digital conversion of the signal to realize the recognition of the received image signal.
[0047] Specifically, in this embodiment, the analog switch chip uses a 74HC4051 analog gating chip to realize the multiplexing of analog signals. Each 74HC4051 analog gating chip can connect to eight infrared receiving diodes 60.
[0048] In this embodiment, there are a total of 72 infrared receiving diodes 60, divided into 9 groups. Each group consists of 8 infrared receiving diodes 60 and is connected to a 74HC4051 analog gating chip. The 74HC4051 analog gating chip performs time-division multiplexing of the analog signal and transmits it to the high-speed ADC conversion circuit.
[0049] Specifically, the total length of the contact sensor is 1.5mm, which is sufficient for the narrow edge movement of banknotes during feeding.
[0050] In this embodiment, Figure 1 A cross-sectional view of the CIS sensor is shown. Figure 2 The top view of the CIS sensor is shown. The total length of the sensor is 105mm, which is suitable for the narrow edge of the banknote feeding motion. The spacing of the receiving LEDs is 1.27mm.
[0051] The system includes four LED emitting light sources, which can integrate multiple light sources. The LED emitting light sources are located at the top of a light guide rod, which evenly directs the light emitted from the LEDs at both ends towards the center. A PCB circuit board is used for the circuitry driving and signal processing of the emitting and receiving lamps. A glass layer prevents dust from falling into the receiving light guide hole and provides a solid surface for the banknote movement. The machine housing and the central light guide hole are integrally injection molded. Infrared receiving diodes are mounted on the PCB circuit board. The receiving light guide holes are arranged in the center of the machine housing. These holes, with a diameter of 1.8mm, are used to receive image signals from the banknote surface. The staggered placement of these holes maximizes the aperture size, facilitating mold making and improving resolution.
[0052] Figure 3 This is a constant current drive circuit for an LED light source emitter. The DAC signal is used to adjust the emission current during calibration, the PWM signal is used to adjust the exposure time during operation, and resistors R3 and R4 limit the maximum output current. The light source can be any combination of red, green, blue, infrared, white, or UV light. The exposure time can be automatically adjusted by software based on the received signal value.
[0053] Figure 4 and Figure 5 The circuit connects the infrared receiving diodes and the ADC conversion unit. The infrared receiving diodes are 2mm black round-headed infrared LEDs with a wavelength range of 400-1100nm. Eight infrared receiving diodes are grouped together and switched using a 74HC4051 analog gating chip, ultimately outputting a single signal to the high-speed ADC conversion circuit on the main board. The entire product uses 9 groups, totaling 72 infrared receiving diodes, with a spacing of 1.27mm, achieving an image resolution of 20DPI.
[0054] The working principle of the entire product is as follows: when an object such as a banknote arrives at the glass surface of the CIS, the software controls a PWM signal to activate the LED light source. The light is then evenly distributed through a light guide and directed at the object. The light undergoes diffuse reflection on the object's surface, and the intensity of the reflected light signals reaches the infrared receiving diodes through the light guide holes, ultimately generating electrical signals of varying intensity. When the light is alternately emitted, each light source produces an image corresponding to that light source. The signals from the 72 sets of infrared LED receiving diodes in the CIS module are switched via analog switches and then connected to the motherboard via FFC lines for ADC conversion, ultimately outputting multiple complete image signals under different light sources.
[0055] And, please see Figure 6 This paper illustrates a low-cost contact image sensor detection method for banknote authentication using the low-cost contact image sensor described above. The method includes the following steps: Step S10: The LED light source is activated and emits light.
[0056] The specific steps include: Step S11: Power on the device and start it up to determine the reference clock.
[0057] Step S12, as follows Figure 7 As shown, the LED light source emits red, green, blue, infrared, white, and UV light in sequence for a duration that is an integer multiple of the reference clock. The red light receiving diode receives the red, green, blue, infrared, white, and UV light in sequence and transmits them to the ADC conversion unit.
[0058] In step S13, the central processing unit combines images generated by light of the same color into a monochrome image.
[0059] Specifically, the LED emitting light source outputs light in different wavelengths, enabling the infrared receiving diode to collect image signals under different light sources.
[0060] Specifically, in step S10, the central processing unit adjusts the light signal received by the infrared receiving diode by obtaining the image acquired under a monochromatic light source.
[0061] Step S20 involves passing the banknote to be identified between two glass layers of the upper and lower halves of a low-cost contact image sensor.
[0062] In step S30, the constant current driving unit drives the light guide rod to emit light. The light guide rod emits one or more of the following: red light, green light, blue light, infrared light, white light, and UV light. The light guide rod evenly emits light onto the banknote to be identified.
[0063] In step S40, the light signal diffused by the banknote surface reaches the infrared receiving diode through the light guide hole of the receiving lamp.
[0064] In step S50, the infrared receiving diode converts the optical signal into an electrical signal and transmits it to the ADC conversion unit.
[0065] In step S60, the analog signal of the ADC conversion unit is converted into a digital signal and transmitted to the central processing unit.
[0066] In step S70, the central processing unit identifies and synthesizes the image acquired under a monochromatic light source, and finally outputs the image signal of the banknote.
[0067] Specifically, such as Figure 7As shown, the constant current driving unit drives the LED emitting light source to emit one or more of the following: red light, green light, blue light, infrared light, white light, and UV light. The monochromatic light is emitted for a predetermined duration. The central processing unit combines the banknote images obtained under the same monochromatic light source into a monochromatic light image, and then the central processing unit performs counterfeit detection on the monochromatic light image.
[0068] In the infrared signal receiving section, the technical solution of this invention adopts a staggered arrangement of double-row receiving holes, avoiding the problem of difficult mold implementation due to size limitations and ensuring a resolution of 20 DPI. The transmission path of the received light uses a low-cost solution with simple plastic housing openings, eliminating the traditional and expensive lens structure, and is injection molded in one piece, reducing accuracy errors caused by installation. The angle of the receiving hole is perpendicular to the glass surface, and the light-emitting guides on both sides are tilted at a 65° angle to the glass surface, ensuring that the light path reflects back from the banknote surface and enters the receiving hole. The infrared receiving lamp converts 72 optical signals into analog signals, which are then switched by nine 74HC4051 chips, outputting eight analog signals for further amplification and processing. When a solid-color reference paper is placed between the CIS, the software sets the target value for the 72 infrared receiving lamps and adjusts the PWM signal to control the emitted light intensity based on the target value, ensuring that the emission duty cycle is at an appropriate value. Under appropriate light intensity conditions, the software then modifies and adjusts the received signal value to obtain 72 adjustment coefficients and compensation algorithms, ensuring that the values of the 72 points are within a certain error range. When collecting different banknotes, these 72 coefficients are used to calculate and obtain the true image data.
[0069] The final acquired image is as follows Figure 8 and Figure 9 As shown.
[0070] In the aforementioned low-cost contact image sensor and detection method, infrared receiving diodes with a diameter of 2mm are used instead of tiny lenses and complex photosensitive chips to receive images. The infrared receiving diodes are arranged in an alternating pattern, with a spacing of 1.27mm between adjacent diodes, achieving an effective scanning length of 90mm and a resolution of 20DPI, meeting the requirements for banknote image recognition and counterfeit detection. The light guide holes for the receiving lamps, arranged in an alternating pattern along the centerline of the machine housing, are injection molded in one piece, facilitating mold making and improving resolution. The encapsulated infrared receiving lamps are mature products on the market, inexpensive, readily available from numerous manufacturers, and easy to purchase. In terms of banknote counterfeit detection performance, this method maintains consistency with traditional CIS sensors while significantly reducing overall production complexity and material costs. The method of this invention is simple, easy to implement, low-cost, and easy to promote.
[0071] It should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can be modified and varied in various ways. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of protection of the present invention.
Claims
1. A low cost contact image sensor for banknote authentication, which meets the resolution requirements for banknote authentication, characterized in that, The banknote channel includes an upper half and a lower half of a symmetry axis, the upper half and the lower half respectively include a machine shell, a plurality of LED light sources, two light guide rods, a plurality of infrared receiving diodes, a constant current driving unit and an ADC conversion unit; the machine shell has two light guide grooves and a plurality of regularly arranged receiving lamp light guide holes; each of the two light guide rods is provided with one of the LED light sources at each end, and each of the infrared receiving diodes is arranged at the bottom of one of the receiving lamp light guide holes; The output end of the constant current driving unit is connected to the LED light source, and the constant current driving unit is used to provide a PWM signal for the LED light source; the input end of the ADC conversion unit is connected to the infrared receiving diode, and the ADC conversion unit is used to perform analog-to-digital conversion on the signal received by the infrared receiving diode; the light emitted by the light guide rod is reflected by the banknote to be identified, enters the infrared receiving diode through the receiving lamp light guide hole, so as to realize the reception and conversion of the reflected light signal.
2. The low cost contact image sensor of claim 1, wherein, The upper half and the lower half are symmetrically arranged, the machine shell has a predetermined height and length, the top surface of the machine shell in the height direction is provided with a glass layer, the bottom surface of the machine shell in the height direction is provided with a glass fiber plate, and the glass layer of the upper half and the lower half is arranged on both sides of the symmetry axis respectively.
3. The low cost contact image sensor of claim 2, wherein, The light guide groove is in a strip shape, the length direction of the light guide groove is consistent with the length direction of the machine shell, and the two light guide grooves are symmetrically arranged on the inner side of the outer side wall of the machine shell, the light guide groove and the side wall of the machine shell have a predetermined included angle, and the two light guide rods are arranged at the bottom of the light guide groove, the light emitting direction of the light guide rod is towards the glass layer, and the light emitting direction of the light guide rod has a predetermined included angle with the plane of the glass layer.
4. The low cost contact image sensor of claim 3, wherein, The plurality of receiving lamp light guide holes are regularly arranged between the two light guide grooves, and the plurality of receiving lamp light guide holes are divided into two groups, and the two groups of receiving lamp light guide holes are arranged on both sides of the center line of the length direction of the machine shell. The light guide groove and the regularly arranged plurality of receiving lamp light guide holes of the machine shell are injection molded at one time.
5. The low cost contact image sensor of claim 2, wherein, Further comprising a PCB circuit board, the PCB circuit board is arranged on the inner side of the glass fiber plate, and a plurality of infrared receiving diodes are electrically connected to the PCB circuit board, the number and mounting position of the infrared receiving diodes are the same as and one-to-one corresponding to the number and mounting position of the receiving lamp light guide holes.
6. The low cost contact image sensor of claim 1, wherein, The LED light source adopts a light source with a plurality of different wave bands, and the plurality of different wave bands include one or more of red light, green light, blue light, infrared light, white light and UV light.
7. The low cost contact image sensor of claim 1, wherein, The constant current driving unit comprises a first triode Q1, a third resistor R3, a fourth resistor R4 and a second triode Q2 connected in series, an anode of the LED light emitting source is connected to a power supply end, a cathode of the LED light emitting source is connected to a collector of the first triode Q1, a base of the first triode Q1 is connected to a DAC chip through a tenth resistor R10, and a base of the second triode Q2 is connected to a PWM signal through an eleventh resistor R11.
8. The low cost contact image sensor of claim 1, wherein, The ADC conversion unit comprises a plurality of analog switch chips and a high-speed ADC conversion circuit, each of the analog switch chips is connected with a plurality of infrared receiving diodes, the analog switch chip is used for signal multiplexing of the plurality of infrared receiving diodes, the analog switch chip is connected to the high-speed ADC conversion circuit through a flexible flat cable (FFC) line, and the high-speed ADC conversion circuit is used for completing analog-digital conversion of a signal to realize identification of a received image signal.
9. A method of detecting with a low-cost contact image sensor, using a low-cost contact image sensor according to any one of claims 1 to 8, for the authentication of banknotes, characterized in that The method comprises the following steps: Step one, the LED light emitting source is started and emits light; Step two, the banknote to be identified passes between two glass layers of the upper half and the lower half of the low-cost contact image sensor; Step three, the constant current driving unit drives the light guide rod to emit light, the light guide rod emits one or more of red light, green light, blue light, infrared light, white light and UV light, and the light guide rod uniformly emits light to the banknote to be identified; Step four, the light signal after diffuse reflection on the surface of the banknote reaches the infrared receiving diode through the receiving lamp light guide hole; Step five, the infrared receiving diode converts the light signal into an electric signal and transmits it to the ADC conversion unit; Step six, the ADC conversion unit converts the analog signal into a digital signal and transmits it to the central processing unit; Step seven, the central processing unit identifies and synthesizes the images collected under the monochromatic light source, and finally outputs the image signal of the banknote.
10. The low-cost contact image sensor detection method of claim 9, wherein, The specific steps of step one, starting and emitting light of the LED light emitting source, comprise: Step 1.1, the device is powered on to determine a reference clock; Step 1.2, the LED light emitting source emits red light, green light, blue light, infrared light, white light and UV light in sequence, the duration is an integer multiple of the reference clock, the red light receiving diode receives red light, green light, blue light, infrared light, white light and UV light in sequence, and transmits them to the ADC conversion unit; Step 1.3, the central processing unit synthesizes images generated by the same color light into a monochrome image.