CN115615541A - A Photoelectric Sensor with Dual Emission Wavelength Light Source Design - Google Patents

Abstract

The invention relates to the technical field of reflective and through-beam photoelectric sensors, in particular to a photoelectric sensor technology with dual emission wavelength light source design. The invention is mainly specially designed for the light source of the light emitting unit and the light receiving unit, so that the sensor has strong anti-environmental light interference ability and the convenience and accuracy of debugging and installation.

Description

A Photoelectric Sensor with Dual Emission Wavelength Light Source Design

【Technical field】

The invention relates to the technical field of reflective and through-beam photoelectric sensors, in particular to a photoelectric sensor technology with dual emission wavelength light source design.

【Background technique】

The working principle of the reflective photoelectric sensor is shown in Figure 1. The existing light receiving unit 12 and the existing light emitting unit 13 are all in the closed space of the sensor, and the sensor light emitting unit will emit light. When the set detection range When an object 15 appears inside, the light emitted by the sensor emitting unit will be reflected by the object, and part of the reflected light will be received by the light receiving unit to generate an electrical signal, and then the electrical signal will be transmitted to the processing circuit by the signal output line 14, and then the sensor will issue an instruction Signal.

The principle of the through-beam photoelectric sensor is shown in Figure 2. The existing light-emitting unit 12 and the existing light-receiving unit 13 are separated. When there is no object 15 between the light-emitting unit and the light-receiving unit, the light-receiving unit can receive Light, when the object to be detected enters the detection range, it will block the light beam so that the light receiving unit cannot receive the light emitted by the light emitting unit, and transmit it to the processing circuit through the signal output line 14, thereby detecting the change of the light signal, and the receiving end makes a reaction.

Existing light sources at the emitting end of photoelectric sensors generally use single-wavelength red light or near-infrared light, and the more commonly used wavelengths are around 650nm, around 850nm or 940nm. Red light is used as the light source because it is easy to identify when the beam hits the object, and it is also a common practice in the field of industrial automation. However, photoelectric sensors that use red light as the light source at the transmitting end are more susceptible to interference from various light sources in the environment, because the ambient light generally contains light waves around 650nm, especially in recent years with the popularization of LED lighting, and the brightness of LED lighting sources is high. It is easy to cause disturbance. However, the near-infrared light is used as the light source sensor at the transmitting end. Since it is invisible light, the light spot emitted by the sensor cannot be seen with the naked eye. When debugging and installing, it is impossible to accurately find the center of the light spot, and it is not easy to detect objects or quasi-receivers. In addition Whether the light-emitting element of the sensor is working normally cannot be judged intuitively.

【Content of invention】

In view of the above problems, the present invention mainly focuses on the special design of the light source and light receiving unit of the light emitting unit, so that the sensor has a strong ability to resist ambient light interference and the convenience and accuracy of debugging and installation. The light-emitting element adopts a light source emitting two wavelengths, including two independent light-emitting chips of visible light and near-infrared light, and the light-emitting chip may be an LED. The notable feature of the present invention is that through the special layout of two light-emitting chips emitting different wavelengths, as shown in Figure 4 and Figure 5, the light-emitting chips of the light source are stacked in close contact in space, and the infrared light-emitting chips are close to the lens. On one side, the red light-emitting chip is on the other side. The light-emitting surfaces of the two light-emitting chips face the emitting lens. The area of the red light chip is larger than that of the near-infrared light chip. At the same time, the central axis of the two light-emitting chips coincides, or the center axis distance error It should be less than 5mm, the purpose is to make the center of the spot after the beam passes through the lens coincide or close to coincide;

The present invention uses light capable of emitting two wavelengths as a light source, and the emitted light beams of two wavelengths include visible light and near-infrared light, and the centers of the spots of visible light and near-infrared light coincide or nearly coincide. In this way, during the installation and debugging process, it is very convenient to find the exact position of the light irradiation by observing the visible light spot, so that the measured object is correctly placed within the detection range of the sensor. , the visible light spot can be used as a reference for the range of the near-infrared light spot. In addition, in the light-receiving unit, a narrow-band filter is added in front of the light-receiving element (usually a silicon-based photosensitive element, and different devices are used according to requirements) to filter light other than the near-infrared light source, and the near-infrared light is used as the receiving detection light, avoiding the use of The interference of visible light in the environment can achieve the purpose of stable detection.

The present invention relates to the technical field of a photoelectric sensor with a dual emission wavelength light source design, and in particular to the technical field of a reflective and through-beam photoelectric sensor. The structure of a photoelectric sensor with a dual emission wavelength light source design includes a light emitting unit, An optical receiving unit and a signal processing unit, wherein:

The light emitting unit is composed of a driving power circuit, a dual-wavelength emitting light source and a emitting lens. The driving power circuit is connected to the dual-wavelength emitting light source. The dual-wavelength emitting light source is composed of two special layouts of light-emitting chips emitting different wavelengths. The emitting lens is connected and fixed by a fixing device, and a certain distance is kept as required, and the driving circuit provides power to the light source;

The light receiving unit consists of a beam receiving lens, an optical filter and a photosensitive element. The beam receiving lens, optical filter and photosensitive element are connected and fixed by a fixing device. The function of the beam receiving lens is to collect the light reflected back from the measured object or emitted by the transmitter. and make it converge to the light-receiving surface of the photosensitive element. The function of the optical filter is to filter out the light in the wavelength range of visible light, only allowing near-infrared light to pass through, and eliminating the interference of visible light; considering the limited space in the sensor, the receiving unit The filter can also be removed, and the surface of the receiving lens can be coated with a filter film to filter light other than the wavelength of the emitted light;

The signal processing unit includes a series of electrical signal processing elements, which are connected to the light receiving unit through electrodes. The function of the signal processing unit is to amplify the electrical signal output by the photosensitive element and process it into a standard signal that can communicate with the outside of the sensor;

Further, it is characterized in that: the dual-wavelength emission light source includes a visible light wavelength light source and a near-infrared wavelength light source, and includes two independent light-emitting chips for visible light and near-infrared light, wherein the light-emitting chip can be an LED;

Further, it is characterized in that: through the special layout of two light-emitting chips emitting different wavelengths, the light-emitting chips of the light source are stacked in space, wherein the infrared light-emitting chip is on the side close to the lens, and the red light-emitting chip is on the other side. On the other hand, the diameter of the red light chip is larger than the diameter of the infrared light chip, and at the same time, the beam axes (104) of the two light-emitting chips coincide, and the distance between the central axes is less than 5mm;

Further, the special layout of two light-emitting chips emitting different wavelengths, the diameter of the red chip is D1, the diameter of the infrared chip is D2, and the diameter of the emitting lens is D3. The function of the emitting lens is to emit light to the light source according to the needs of the usage scene The light is converged so that the beam energy is concentrated within the range to be detected; where D1, D2, and D3 must meet the following conditions:

D1≤D3/10, because the LED is regarded as a point light source when the lens is designed, the prerequisite is that the diameter of the light source must be less than 1/10 of the lens;

D1-D2≥2μm, according to experiments, if the red light-emitting area is too small, the red light spot cannot be observed;

D2≥10μm is to ensure that the intensity of infrared light is enough to detect objects. The actual test found that when the diameter of the light-emitting chip is smaller than this value, the sensor cannot work normally because the signal received by the sensor receiving unit is too weak, that is, the light source. Insufficient radiant flux emitted;

The ranges of D1, D2, and D3 discussed here are limited to photoelectric sensors in actual use. In this type of photoelectric sensor structure, the distance between the light source chip and the center point of the lens is within the range of 2-30mm.

Further, it is characterized in that: the design of the transmitting end lens should follow the focal length relationship f _red <f _design <f _infrared , because the focal length formula of the emitting end lens (103) is as follows:

n is the refractive index of the glass, d is the center thickness of the lens, when d=0, it is a thin lens, f is the focal length, and r is the spherical radius of the lens. Because different wavelengths have different propagation speeds in the glass, the refractive index is also different, so the focal length is also different, that is, the same lens has different focal lengths at different wavelengths. According to Cauchy's formula, the longer the wavelength, the smaller the refractive index; according to the lens focal length formula, the smaller the refractive index, the longer the focal length.

The relationship between the vertical axis magnification β and the focal length f is, where x is the distance of the image

In order to make the red light and the near-infrared light coincide after the light spot centers after passing through the lens, and reduce the overlapping of the light spot range as much as possible, therefore, the design of the transmitting end lens (103) should follow f _{red light} <f _design <f _infrared .

Compared with the prior art, the present invention has the following advantages:

The present invention is developed in view of the above situation. Considering that the light source has two wavelengths of red light and near-infrared light, the lens passing through the light emitting unit will produce axial chromatic aberration and lateral chromatic aberration, especially the lateral chromatic aberration has a relatively large impact on the coverage of the spot . The focal length formula of the lens is as follows

n is the refractive index of the glass, d is the center thickness of the lens, when d=0, it is a thin lens, f is the focal length, and r is the spherical radius of the lens. Because different wavelengths have different propagation speeds in the glass, the refractive index is also different, so the focal length is also different, that is, the same lens has different focal lengths at different wavelengths. According to Cauchy's formula, the longer the wavelength, the smaller the refractive index; according to the lens focal length formula, the smaller the refractive index, the longer the focal length.

The relationship between the vertical axis magnification β and the focal length f is, where x is the distance of the image

In order to make the center of the spot of red light and near-infrared light coincide after passing through the lens, and at the same time minimize the overlapping of the spot range, the design of the lens should follow the focal length f _{red light} < f _design < f _infrared . Therefore, the lens of the emitting part of the sensor is also designed through a special achromatic design, so that the center of the spot of the emitted red light and the center of the near-infrared light coincide or nearly coincide. The light-receiving unit part is equipped with a narrow-band filter to allow only the near-infrared light emitted by the light source to reach the photodetector. The purpose of this design is that the position of the light spot is always visible during the installation and debugging process, which has the function of positioning and is convenient for debugging. At the same time, the sensor is not disturbed by the visible light of the lighting equipment in the environment during the actual use of the sensor.

【Description of drawings】

Figure 1 is a schematic diagram of an existing reflective sensor;

Figure 2 is the schematic diagram of the existing through-beam sensor; the detection basis is based on whether the projected light is blocked or not;

Fig. 3 is a kind of schematic diagram of the photoelectric sensor with dual emission wavelength light source design of the present invention;

Fig. 4 is a top view of the dual-wavelength transmitting units of the present invention in a spatially stacked manner;

Fig. 5 is a perspective view of the dual-wavelength transmitting units of the present invention in a spatially stacked manner;

Fig. 6 is a working diagram of the dual-wavelength emitting unit of the present invention.

【detailed description】

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and implementation examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Please refer to Fig. 3-Fig. 6, the present invention provides a kind of photoelectric sensor with double emission wavelength light source design, comprises the following steps:

A structure of a photoelectric sensor 1 with a dual emission wavelength light source design includes a light emitting unit 10, a light receiving unit 20 and a signal processing unit 30, wherein:

Described light emitting unit 10 is made up of driving power supply circuit 101, double-wave emitting light source 102 and emitting lens 103, double-wavelength emitting light source 102, driving power supply circuit 101 are connected with double-wavelength emitting light source 102, double-wavelength emitting light source 102 and emitting lens 103 is connected and fixed by a fixing device, wherein the drive circuit 101 provides power to the light source;

Described light receiving unit 20 comprises light beam receiving lens 201, optical filter 202 and photosensitive element 203 are formed, and light beam receiving lens 201, optical filter 202 and photosensitive element 203 are connected and fixed by fixing device, and the function of light beam receiving lens 201 is to collect the The light reflected back by the measured object or the light emitted by the emitter is converged to the light-receiving surface of the photosensitive element 203. The function of the optical filter 202 is to filter out the light in the wavelength range of visible light, and only allow near-infrared light to pass through. Visible light interference;

The signal processing unit 30 includes a series of electrical signal processing elements, which are connected to the light receiving unit 20 through the electrodes 301 . The function is to amplify the electrical signal output by the photosensitive element 203 and process it into a standard signal that can communicate with the outside of the sensor.

The dual-wavelength emitting light source 102 includes a visible light wavelength light source 104 and a near-infrared wavelength light source 105, and the visible light wavelength light source 104 and the near-infrared wavelength light source 105 use independent light-emitting chips to emit light. The visible light wavelength light source 104 uses a red light-emitting chip to emit visible light, and the near-infrared wavelength light source 105 uses an infrared light-emitting chip to emit near-infrared light; the light-emitting chip can be an LED. The remarkable feature of the present invention is that through the special layout of two light-emitting chips emitting different wavelengths, the light-emitting chips of the light source are stacked in space, wherein the infrared light-emitting chip is on the side close to the lens, and the red light-emitting chip is on the other side , the diameter of the red light-emitting chip is greater than that of the infrared light-emitting chip, and the central axes of the two light-emitting chips coincide, and the distance between the center of the red light-emitting chip and the central axis of the infrared light-emitting chip is less than 5mm.

The diameter of the red light-emitting chip is D1, the diameter of the infrared light-emitting chip is D2, and the diameter of the emitting lens 103 is D3, wherein D1, D2, and D3 must meet the following conditions:

D1≤D3/10, because the light-emitting chip is regarded as a point light source when the lens is designed, and the prerequisite is that the diameter of the light source must be smaller than 1/10 of the lens;

D1-D2≥2μm, because according to the actual test experience, if the red light emitting area is too small, the red light spot cannot be observed;

D2≥10μm is to ensure that the intensity of the infrared light is sufficient to detect objects. The actual test found that when the diameter of the light-emitting chip is smaller than this value, the sensor cannot work normally, that is, the luminous intensity of the light source is insufficient;

The ranges of D1, D2, and D3 discussed here are limited to photoelectric sensors in actual use. In this type of photoelectric sensor structure, the distance between the light source chip and the center point of the lens is within the range of 2-30mm.

The function of the lens is to converge the light emitted by the light source according to the needs of the use scene, so that the beam energy can be concentrated within the range that needs to be detected;

1. The first specific embodiment:

The structure of the present invention includes a light emitting unit 10 , a light receiving unit 20 and a signal processing unit 30 .

Wherein, the diameter D1 of the red light emitting chip is 0.5 mm, the diameter D2 of the infrared light emitting chip is 0.3 mm, and the diameter D3 of the emitting lens 103 is 6 mm.

Contains two independent light-emitting chips for visible light and near-infrared light, wherein the wavelength of visible light is 650nm, and the wavelength of near-infrared light is 850nm. According to the characteristics of the LED light source and the use requirements, and after considering the achromatic aberration, the actual design of the focal length f of the lens 103 at the transmitting end is _designed to be 5.2mm

2. The second specific embodiment:

The red light-emitting chip is square, the side length D1 is 0.6mm, the infrared light-emitting chip is also square, the side length D2 is 0.3mm, and the diameter of the emitting lens D3 is 6mm. The emission wavelength of the red light-emitting chip is 660nm, and the emission wavelength of the infrared light-emitting chip is 910nm. According to the characteristics of the LED light source and the use requirements, and after considering the achromatic aberration, the actual design of the focal length f of the lens 103 at the transmitting end is _designed to be 5.2mm

3. The third specific embodiment:

When it is necessary to detect a large object, and the object has a small area of holes locally or the reflectivity is very low (for example, below 5%), the red light-emitting chip is a square, the side length D1 is 1mm, and the infrared light-emitting chip is circular, with a diameter of D2 is 0.8mm, and the lens diameter is 10mm.

The emission wavelength of the red light-emitting chip is 620nm, and the emission wavelength of the infrared light-emitting chip is 880nm.

According to the characteristics of the LED light source and the use requirements, and after considering the achromatic aberration, the actual design of the focal length f of the emitting end lens (103) is _designed to be 5.5 mm.

4. The fourth specific embodiment:

When detecting small or tiny objects, a smaller spot size is required. The red light-emitting chip is circular with a diameter of 0.3 mm, the infrared light-emitting chip is circular with a diameter of 0.2 mm, and the diameter of the emitting lens 103 is 5 mm.

The emission wavelength of the red light-emitting chip is 640nm, and the emission wavelength of the infrared light-emitting chip is 930nm.

According to the characteristics of the LED light source and the use requirements, and after considering the achromatic aberration, the focal length f of the lens 103 at the transmitting end is actually _designed to be 5.2 mm.

Compared with the prior art, the present invention has the following advantages:

The present invention is developed in view of the above situation. Considering that the light source has two wavelengths of red light and near-infrared light, axial chromatic aberration and lateral chromatic aberration will occur through the lens of the light emitting unit, especially lateral chromatic aberration has a relatively large impact. The focal length formula of the lens is as follows

n is the refractive index of the glass, d is the center thickness of the lens, when d=0, it is a thin lens, f is the focal length, and r is the spherical radius of the lens. Because different wavelengths have different propagation speeds in the glass, the refractive index is also different, so the focal length is also different, that is, the same lens has different focal lengths at different wavelengths. According to Cauchy's formula, the longer the wavelength, the smaller the refractive index; according to the lens focal length formula, the smaller the refractive index, the longer the focal length.

The relationship between the vertical axis magnification β and the focal length f is, where x is the distance of the image

In order to make the red light and near-infrared light coincide with the center of the spot after passing through the lens, and at the same time minimize the overlapping of the spot range, the _design of the lens should follow fred _light <fdesign< _finfrared . Wherein f _{red light} is the focal length of the red light-emitting chip, f _design is the focal length of the emitting end lens 103, and f _infrared is the focal length of the infrared light-emitting chip; therefore the lens of the sensor emitting part is also designed through a special achromatic aberration, so that the emitted red light The spot center of the near-infrared light coincides or nearly coincides with the spot center of the near-infrared light. The light-receiving unit part is equipped with a narrow-band filter to allow only the near-infrared light emitted by the light source to reach the photodetector. The purpose of this design is that the position of the light spot is always visible during the installation and debugging process, which has the function of positioning and is convenient for debugging. At the same time, the sensor is not disturbed by the visible light of the lighting equipment in the environment during the actual use of the sensor.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any modifications made within the concept of the present invention, equivalent replacements and improvements, etc. should be included in the scope of patent protection of the present invention. Inside.

Claims (5)

1. A photosensor with a dual emission wavelength light source design comprising a light emitting unit (10), a light receiving unit (20) and a signal processing unit (30), characterized by the following further comprising the features:

the light emitting unit (10) is composed of a driving power circuit (101), a dual-wavelength light emitting source (102) and an emitting lens (103), the driving power circuit (101) is connected with the dual-wavelength light emitting source (102), the dual-wavelength light emitting source (102) is composed of two light emitting chips emitting different wavelengths, the dual-wavelength light emitting source (102) and the emitting lens (103) are fixedly connected through a fixing device, and the dual-wavelength light emitting source (102) and the emitting lens (103) are arranged at intervals.

The light receiving unit (20) comprises a light beam receiving lens (201), an optical filter (202) and a photosensitive element (203), the light beam receiving lens (201), the optical filter (202) and the photosensitive element (203) are fixedly connected through a fixing device, the light beam receiving lens (201) has the function of collecting light reflected by a measured object or light emitted by a transmitter and enabling the light to be converged on a light receiving surface of the photosensitive element (203), and the optical filter (202) has the function of filtering light in a visible light wavelength range, only allowing near infrared light to pass through and eliminating visible light interference;

the signal processing unit (30) is connected with the light receiving unit (20) through electrodes, and the signal processing unit (30) amplifies and processes the electric signals output by the photosensitive element (203) into standard signals capable of communicating with the outside of the sensor.

2. A photosensor having a dual emission wavelength light source design according to claim 1 wherein:

the dual-wavelength emission light source (102) comprises a visible light wavelength light source (104) and a near infrared wavelength light source (105), and the visible light wavelength light source (104) and the near infrared wavelength light source (105) adopt independent light emitting chips to emit light.

3. The photosensor with dual emission wavelength light source design of claim 2, wherein the visible light wavelength light source (104) emits visible light using a red light emitting chip and the near infrared wavelength light source (105) emits near infrared light using an infrared light emitting chip; the infrared light-emitting chip is close to one side of the emission lens (103), the red light-emitting chip is arranged on the other side, the diameter of the red light-emitting chip is larger than that of the infrared light-emitting chip, the beam axes of the two light-emitting chips are coincided, and the distance between the center of the red light-emitting chip and the center of the infrared light-emitting chip is smaller than 5mm.

4. A photosensor having a dual emission wavelength light source design as claimed in claim 2 wherein: the diameter of the red light emitting chip is D1, the diameter of the infrared light emitting chip is D2, the diameter of the transmitting lens (103) is D3, and the transmitting lens has the function of converging light emitted by a light source according to the use scene so that the energy of light beams is concentrated in the range needing to be detected; wherein D1, D2 and D3 satisfy the following conditions:

d1 is less than or equal to D3/10, because the light-emitting chip is regarded as a point light source when the lens is designed, wherein the diameter of the light source must be less than 1/10 of the lens;

d2 is more than or equal to 10 mu m, which is used for ensuring that the intensity of infrared light emitted by the infrared light-emitting chip is enough to detect an object, and if the diameter of the light-emitting chip is smaller than the value, the sensor cannot work normally because the signal received by the sensor receiving unit is too weak, namely the radiation flux emitted by the light source is insufficient;

D1-D2 is more than or equal to 2 mu m, and if the area of the red light emitting chip is too small, red light spots cannot be observed;

d1 The range of D2 and D3 is limited to the photoelectric sensor in practical use, and the distance between the light source light-emitting chip and the central point of the lens in the photoelectric sensor structure is in the range of 2-30 mm.

5. A photosensor having a dual emission wavelength light source design as claimed in claim 2 wherein: the design of the emission lens (103) should follow f _{Red light} ＜f _{Design of} ＜f _{Infrared ray} Wherein f is _{Red light} Is the focal length of the red light emitting chip, f _{Design of} Is the focal length of the emitting end lens (103), f _{Infrared ray} Is the focal length of the infrared light emitting chip;

the focal length formula of the transmitting end lens (103) is as follows:

n is the refractive index of the glass, d is the central thickness of the lens, f is the focal length, r is the spherical radius of the lens, and the focal lengths are different because the propagation speeds of different wavelengths in the glass are different and the refractive indexes are also different, namely the focal lengths of the same lens are different under different wavelengths; according to the Cauchy's formula, the longer the wavelength, the smaller the refractive index; according to a lens focal length formula, the smaller the refractive index is, the longer the focal length is;

the relationship between the vertical axis magnification β and the focal length f is that, where x is the distance of the image

In order to ensure that the centers of light spots of the visible light wavelength light source (104) and the near infrared wavelength light source (105) are superposed after light passes through the lens, and simultaneously, the light spot ranges are reduced to the greatest extent,therefore, the design requirement f of the emission end lens (103) _{Red light} ＜f _{Design of} ＜f _{Infrared ray} 。

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