Plant sensor

Abstract

This plant sensor comprises a first light source (6) that emits first measurement light (3a) including a first wavelength band, a second light source (7) that emits second measurement light (3b) including a second wavelength band, a first lens (8) that converts the first measurement light into a parallel light beam, a second lens (9) that converts the second measurement light into a parallel light beam, a measurement light deflecting member (11) that is provided on a common optical path of the first measurement light and the second measurement light and that deflects either the first measurement light or the second measurement light such that the first measurement light and the second measurement light are coaxial, a reference light deflecting member (15) that extracts a part of each measurement light as reference light (26), a reference light receiving unit (16) that receives the reference light, a light receiving unit (18) that receives first reflected measurement light (5a) and second reflected measurement light (5b) from a measurement target, and a control unit (19) that computes the growth status of the measurement target on the basis of the received amount of the reference light and the received amount of each reflected measurement light, wherein a light receiving surface area of the reference light deflecting member is smaller than the area of the light beam cross-section of each measurement light, and the reference light deflecting member is disposed so as to be capable of extracting light in a central portion of the light beam cross-section of each measurement light.

Description

Plant Sensor

[0001] The present invention relates to a plant sensor that irradiates agricultural crops with measurement light and analyzes the reflected light to measure the growth status of the crops.

[0002] Detecting the growth status of plants, especially agricultural crops, is important for agricultural production management. Conventionally, the growth status of plants is detected by irradiating the plants with detection light diffused in one direction and detecting the reflected detection light from the plant leaves. In this case, the reflected detection light includes the reflected detection light from the soil as well as the plant leaves, so the detection result contains noise.

[0003] Another method is to irradiate a plant with two detection lights of different wavelengths and compare the amount of light reflected from the plant leaves to remove noise such as reflected detection light from the soil and improve detection accuracy.

[0004] Furthermore, a part of the detection light is extracted as reference light using a half mirror or the like, and the amount of the detection light is accurately measured based on the reference light to accurately determine the ratio of the reflected detection light to the detection light. However, this requires a lens to focus the extracted reference light and, depending on the amount of reference light, an attenuation filter, which may increase the number of parts and the size of the optical system.

[0005] JP 2012-247235 A JP 2019-45445 A

[0006] The present invention provides a plant sensor that reduces the number of parts and the size of the optical system.

[0007] The present invention relates to a plant sensor comprising: a first light source that emits first measurement light including a first wavelength band; a second light source that emits second measurement light including a second wavelength band; a first lens that converts the first measurement light into a parallel beam; a second lens that converts the second measurement light into a parallel beam; a measurement light deflecting member that is arranged on a common optical path of the first measurement light and the second measurement light and deflects either the first measurement light or the second measurement light so that the first measurement light and the second measurement light are coaxial; a reference light deflecting member that extracts a portion of each measurement light as reference light; a reference light receiving unit that receives the reference light; a light receiving unit that receives the first reflected measurement light and the second reflected measurement light from the measurement object; and a control unit that calculates the growth status of the measurement object based on the received light amount of the reference light and the received light amount of each reflected measurement light, wherein the light receiving area of ​​the reference light deflecting member is smaller than the area of ​​the cross section of the beam of each measurement light, and the reference light deflecting member is positioned so as to be able to extract the light at the center of the cross section of the beam of each measurement light.

[0008] The present invention also relates to a plant sensor in which the reference light deflection member is longer than the radius of the light beam of each measurement light, passes through the center of each measurement light, and is arranged to extend outside each measurement light.

[0009] The present invention also relates to a plant sensor further comprising an optical fiber, a third lens that focuses each measurement light onto the light receiving end surface of the optical fiber, and a fourth lens that converts each measurement light irradiated from the exit end surface of the optical fiber into a parallel beam, and the reference light deflection member is configured to extract the reference light from each measurement light that has been converted into a parallel beam by the fourth lens.

[0010] The present invention also relates to a plant sensor further comprising an optical fiber, a third lens that focuses each measurement light onto the light receiving end surface of the optical fiber, and a fourth lens that converts each measurement light irradiated from the exit end surface of the optical fiber into a parallel beam, and the reference light deflection member is configured to extract the reference light from each measurement light irradiated from the exit end surface of the optical fiber.

[0011] The present invention also relates to a plant sensor configured such that the first light source and the second light source are LEDs, the first lens and the second lens are TIR lenses, a first wavelength selection member that transmits only light of a first wavelength band is provided on the optical path of the first measurement light, and a second wavelength selection member that transmits only light of a second wavelength band is provided on the optical path of the second measurement light.

[0012] The present invention also relates to a plant sensor in which the control unit calculates the actual light intensity of each measurement light based on the light intensity of each measurement light set in the first light source and the second light source, the received light intensity of the reference light, and the ratio of the reference light to each measurement light, and is configured to calculate the fluctuation in the light intensity of each measurement light based on the set light intensity and the actual light intensity.

[0013] Furthermore, the present invention relates to a plant sensor that further includes a memory unit in which a database correlating the growth status of the measurement object with the reflectance of the reflection measurement light is stored, and the control unit is configured to calculate the reflectance of the reflection measurement light based on the actual light amount and the received amount of the reflection measurement light, and to measure the growth status of the measurement object based on the reflectance and the database.

[0014] According to the present invention, a first light source emitting a first measurement light including a first wavelength band, a second light source emitting a second measurement light including a second wavelength band, a first lens that converts the first measurement light into a parallel beam, a second lens that converts the second measurement light into a parallel beam, a measurement light deflection member that is provided on a common optical path of the first measurement light and the second measurement light and deflects one of the first measurement light and the second measurement light so that the first measurement light and the second measurement light are coaxial, a reference light deflection member that extracts a part of each measurement light as a reference light, a reference light receiving unit that receives the reference light, and a measurement object. The optical system has a light receiving unit that receives the first reflected measurement light and the second reflected measurement light from the object, and a control unit that calculates the growth status of the object to be measured based on the received amount of the reference light and the received amount of each reflected measurement light, and the light receiving area of ​​the reference light deflection member is smaller than the area of ​​the cross section of the beam of each measurement light, and the reference light deflection member is configured to be positioned so that it can extract the light at the center of the cross section of the beam of each measurement light, so there is no need to provide a lens for focusing the reference light or an attenuation filter for reducing the amount of light of the reference light, and it is possible to reduce the number of parts and make the optical system more compact.

[0015] FIG. 1 is an explanatory diagram illustrating an example of use of a plant sensor according to a first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating the configuration of the plant sensor according to the first embodiment of the present invention. FIG. 3 is an explanatory diagram illustrating the relationship between a beam splitter and a fourth lens. FIG. 4 is an explanatory diagram illustrating the beam profile of measurement light. FIG. 5(A) is an explanatory diagram illustrating a first modified example, and FIG. 5(B) is an explanatory diagram illustrating a second modified example. FIG. 6 is a schematic diagram illustrating the configuration of a plant sensor according to a second embodiment of the present invention. FIG. 7 is a schematic diagram illustrating the configuration of a plant sensor according to a third embodiment of the present invention. FIG. 8 is an explanatory diagram illustrating a lens according to the third embodiment. FIG. 9 is an explanatory diagram illustrating a lens according to a modified example of the third embodiment.

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] FIG. 1 shows an outline of a plant sensor according to a first embodiment of the present invention.

[0018] In Fig. 1, 1 denotes a mobile object such as a tractor, and 2 denotes a predetermined number (two in Fig. 1) of plant sensors provided on the mobile object 1. The plant sensor 2 alternately irradiates a measurement object 4 (e.g., agricultural crops) in a field or the like with laser beams (measurement light 3) of two wavelengths. The plant sensor 2 also detects the amount of light received for each wavelength of the measurement light 3 (reflected measurement light 5) reflected by the measurement object 4, and measures the reflectance for each wavelength based on the amount of light received.

[0019] The plant sensor 2 emits two types of measurement light with different wavelengths, and these two types of measurement light are collectively referred to as the measurement light 3. Similarly, the measurement object 4 reflects two types of reflected measurement light, and these two types of reflected measurement light are collectively referred to as the reflected measurement light 5.

[0020] The plant sensor 2 can measure the growth status of the measurement object 4 based on the reflectance for each wavelength at the irradiation position of the measurement light 3 .

[0021] Here, examples of two wavelengths used as the measurement light 3 include 735 nm as a first wavelength band (red visible light) and 808 nm as a second wavelength band (infrared light). When a first measurement light 3a having a wavelength near 735 nm (e.g., 735±20 nm) in the first wavelength band is used as the measurement light 3, if the measurement object 4 contains nitrogen, the measurement light 3a is reflected by the measurement object 4, but the amount of the reflected measurement light 5 does not change regardless of the nitrogen content.

[0022] On the other hand, when the second measurement light 3b having a wavelength in the second wavelength band around 808 nm (for example, 808±15 nm) is used as the measurement light 3, if the measurement object 4 contains nitrogen, the second measurement light 3b is reflected by the measurement object 4, and it is known that the reflectance varies depending on the nitrogen content, and the amount of reflected light increases as the content increases.

[0023] It is also known that crop leaves contain nitrogen, and that when the growing conditions are good the nitrogen content is high, and when the growing conditions are poor the nitrogen content is low.

[0024] In addition to the measurement object 4, soil, for example, may also contain nitrogen, but when comparing the reflectance of soil with that of leaves, the reflectance of soil is significantly smaller than that of leaves. Therefore, by comparing only the amount of reflected light regardless of wavelength, it is possible to determine whether the light is reflected by soil or leaves, and therefore noise can be removed by removing the reflected measurement light 5 that is determined to be reflected by soil.

[0025] As described above, the measuring light 3 is alternately irradiated with the first measuring light 3a having a wavelength near 735 nm and the second measuring light 3b having a wavelength near 808 nm. That is, the first measuring light 3a and the second measuring light 3b are irradiated on the same or approximately the same optical axis and onto the same or approximately the same irradiation area. The amount of reflected light of the reflected measuring light 5 is affected by the condition of the reflecting surface, such as cleanliness or dirt. However, since the measuring light 3 of two wavelengths is irradiated onto the same area of ​​the reflecting surface, the influence of the condition of the reflecting surface on the measuring light 3 of each wavelength is the same.

[0026] Therefore, it is determined that the amount of received light of the second reflected measurement light 5b having a wavelength around 808 nm depends on the amount of nitrogen contained, and therefore the nitrogen content ratio of the measurement object 4 can be obtained based on the first reflected measurement light 5a and the second reflected measurement light 5b. Furthermore, if the nitrogen content ratio of the leaves of a crop corresponding to the growth status is obtained in advance, the growth status of the crop of the measurement object 4 can be determined.

[0027] The nitrogen content ratio of the measurement object 4 can be expressed as the content ratio S = (R2 / R1-1) x 100, where R1 is the reflectance in the first wavelength band (735 nm) and R2 is the reflectance in the second wavelength band (around 808 nm).

[0028] FIG. 2 shows a schematic configuration diagram of the plant sensor 2 according to the first embodiment of the present invention.

[0029] The plant sensor 2 includes a first light source 6, a second light source 7, a first lens 8, a second lens 9, a dichroic mirror 11 as a measurement light deflection member, a third lens 12, an optical fiber 13, a fourth lens 14, a beam splitter 15 as a reference light deflection member, a reference light receiving unit 16, a diffusion optical element 17, a light receiving unit 18, a control unit 19, a memory unit 20, etc., and each component is housed in a housing 21. A window 22 having a predetermined opening area is formed in the housing 21. The control unit 19 may be a CPU specialized for this device or a general-purpose CPU.

[0030] The first light source 6 is, for example, a laser diode, and is configured to emit the first measurement light 3 a having a wavelength in a first wavelength band (near 735 nm) onto the first measurement optical axis 23 a at a predetermined divergence angle, while the second light source 7 is, for example, a laser diode, and is configured to emit the second measurement light 3 b having a wavelength in a second wavelength band (near 808 nm) onto the second measurement optical axis 23 b at a predetermined divergence angle.

[0031] The first lens 8, the dichroic mirror 11, the third lens 12, and one end face (hereinafter referred to as the light-receiving end face) of the optical fiber 13 are arranged on the first measurement optical axis 23a. The second lens 9 and the dichroic mirror 11 are arranged on the second measurement optical axis 23b, and the third lens 12 and the light-receiving end face of the optical fiber 13 are arranged on the reflected optical axis of the dichroic mirror 11. That is, the dichroic mirror 11 is arranged at the intersection of the first measurement optical axis 23a and the second measurement optical axis 23b, and on the common optical path of the first measurement light 3a and the second measurement light 3b.

[0032] In addition, the fourth lens 14, the beam splitter 15, and the diffusing optical element 17 are arranged on the emission optical axis of the first measurement light 3a and the second measurement light 3b irradiated from the other end face (hereinafter referred to as the emission end face) of the optical fiber 13, and the reference light receiving unit 16 is arranged on the reflected optical axis of the beam splitter 15.

[0033] The first lens 8 collimates the first measurement light 3 a, and the second lens 9 collimates the second measurement light 3 b. The dichroic mirror 11 has optical properties of transmitting light in a first wavelength band and reflecting light in a second wavelength band. That is, the dichroic mirror 11 transmits the first measurement light 3 a and deflects the second measurement light 3 b at a right angle so that the second measurement optical axis 23 b coincides with the first measurement optical axis 23 a.

[0034] In addition, the first measurement optical axis 23a and the second measurement optical axis 23b, which are aligned by the dichroic mirror 11, are collectively referred to as the measurement optical axis 23, and the first measurement light 3a and the second measurement light 3b, which are irradiated coaxially on the measurement optical axis 23, are collectively referred to as the measurement light 3.

[0035] The third lens 12 focuses the first measurement light 3 a and the second measurement light 3 b, which are transmitted or reflected by the dichroic mirror 11 so as to be coaxial or approximately coaxial, onto the light-receiving end surface of the optical fiber 13 .

[0036] The optical fiber 13 emits the first and second measuring beams 3 a and 3 b incident on the light-receiving end face from the light-emitting end face. The optical fiber 13 is configured to mix the first and second measuring beams 3 a and 3 b while they travel through the optical fiber 13. In the first embodiment, to promote the mixing action, the optical fiber 13 is wound around a rod-shaped member (not shown) to form a mode scrambler 24, and the mode scrambler 24 performs mode scrambling.

[0037] Mode scrambling induces mutual exchange of optical power between modes within the light guide path of the optical fiber 13, and mode scrambling is performed by winding the optical fiber 13 within the range of the allowable bending radius in the mode scrambling section 24.

[0038] Therefore, the first measuring light 3 a and the second measuring light 3 b irradiated from the exit end face of the optical fiber 13 have uniform intensity when viewed in a plane (beam cross section) perpendicular to the traveling direction and are non-polarized (randomly polarized). As a result, the beam cross sections of the first measuring light 3 a emitted from the first light source 6 and the second measuring light 3 b emitted from the second light source 7 are elliptical, but the first measuring light 3 a and the second measuring light 3 b emitted from the exit end face of the optical fiber 13 become circular in shape to match the shape of the exit end face of the optical fiber 13 due to the mixing action in the optical fiber 13.

[0039] The fourth lens 14 collimates the first measurement light 3a and the second measurement light 3b irradiated from the exit end face of the optical fiber 13. As shown in FIGS. 2 and 3, the beam splitter 15 has a predetermined width and a length longer than the beam radii of the first measurement light 3a and the second measurement light 3b. The beam splitter 15 is positioned so as to pass through the centers of the first measurement light 3a and the second measurement light 3b and extend to the outside of the first measurement light 3a and the second measurement light 3b, and is supported externally. That is, the beam splitter 15 is supported as a cantilever. The beam splitter 15 has optical properties of reflecting a portion of the incident first measurement light 3a and the second measurement light 3b, for example, 0.5% to 10%, at a right angle onto the reference optical axis 25 as reference light 26 (first reference light 26a, second reference light 26b), and receiving the reference light receiving unit 16, while transmitting the remaining portion.

[0040] 4 shows the beam profile (cross section of the beam) of the first measurement light 3a or the second measurement light 3b (the measurement light 3) transmitted through the fourth lens 14. As shown in FIG. 4, the measurement light 3 has a strong relative light intensity at the center and a weak relative light intensity at the ends due to changes in the bending state of the optical fiber 13 and fluctuations in the light intensity of the light sources (the first light source 6 and the second light source 7). Therefore, at the center of the beam profile where the relative light intensity is strong, a relative light intensity more proportional to the fluctuations in the light intensity of the light sources 6 and 7 can be extracted, so it is desirable to position the beam splitter 15 so that the measurement light 3 at the center can be extracted.

[0041] The reference light receiving unit 16 is, for example, a photodiode (PD) or an avalanche photodiode (APD). The reference light receiving unit 16 is capable of detecting the received light amounts of the first reference light 26 a and the second reference light 26 b incident along the reference light axis 25. The received light amounts of the first reference light 26 a and the second reference light 26 b detected by the reference light receiving unit 16 are transmitted to the control unit 19 in real time as received light amount data.

[0042] Furthermore, since the beam profile of the measurement light 3 is known, and the size and installation position of the beam splitter 15 are also known, the ratio of the reference light 26 to the measurement light 3 can be calculated, and the actual light amount of the measurement light 3 can be calculated based on this ratio and the received light amount data of the reference light 26.

[0043] The diffusing optical element 17 may be a one-dimensional diffusing optical element that diffuses the first measuring light 3 a and the second measuring light 3 b in one direction, such as a cylindrical lens having a concave surface and a convex surface, or a one-dimensional surface diffusing optical element, or a rotationally symmetric diffusing optical element that diffuses the first measuring light 3 a and the second measuring light 3 b concentrically, such as a convex lens, a concave lens, or a surface diffusing optical element.

[0044] The light receiving unit 18 is a light receiving element, such as a photodiode (PD) or an avalanche photodiode (APD), provided on the light receiving optical axis 27. The light receiving unit 18 is capable of detecting the received light amounts of the first reflected measurement light 5a and the second reflected measurement light 5b incident along the light receiving optical axis 27. The received light amounts of the first reflected measurement light 5a and the second reflected measurement light 5b detected by the light receiving unit 18 are transmitted to the control unit 19 in real time as received light amount data.

[0045] Furthermore, the window 22 is disposed on the optical path of the reflected measurement light 5, and is vapor-deposited with a material having an absorption band in a wavelength band other than the first and second wavelength bands, or a dichroic film that reflects light of wavelengths other than the first and second wavelength bands. That is, the window 22 is configured to transmit only the first reflected measurement light 5 a and the second reflected measurement light 5 b.

[0046] The control unit 19 executes various programs stored in the storage unit 20, which will be described later. As a result, the control unit 19 controls the first light source 6 and the second light source 7 to emit light at a predetermined amount, and controls the measurement process of the growth state of the measurement target 4 based on the reflected measurement light 5 (the first reflected measurement light 5 a and the second reflected measurement light 5 b) received by the light receiving unit 18.

[0047] The storage unit 20 stores a sequence program for activating the first light source 6 and the second light source 7 and alternately irradiating the first measurement light 3a and the second measurement light 3b to the measurement object 4 at a predetermined light intensity, a judgment program for judging the growth state of the measurement object 4 based on the received light intensity data received by the light receiving unit 18, a noise removal program for removing noise data from the received light intensity data, a light intensity calculation program for calculating the actual light intensity of the measurement light 3 irradiated to the measurement object 4 based on the received light intensity data of the reference light 26 received by the reference light receiving unit 16, and a control program for feedback control of the first light source 6 and the second light source 7 based on the calculated actual light intensity of the measurement light 3 and the set light intensity of the measurement light 3 set by the first light source 6 and the second light source 7. In addition, the noise removal program is set with a threshold value required for noise judgment, such as a threshold value related to the received light intensity. Furthermore, the storage unit 20 stores a database in which the nitrogen content ratio of leaves corresponding to the growth state of the measurement object 4, which is an agricultural product, is associated with the reflectance.

[0048] Next, a case where the growth status of the measurement target 4 is measured by the plant sensor 2 will be described.

[0049] When a command to start measurement is input to the plant sensor 2 by various means, such as the control terminal of the mobile body 1, a portable terminal carried by the operator, or an operating unit (not shown) provided on the plant sensor 2, the control unit 19 alternately pulses the first measurement light 3a and the second measurement light 3b so that the first light source 6 and the second light source 7 receive a predetermined amount of light.

[0050] The first measurement light 3 a diffused at a predetermined divergence angle on the first measurement optical axis 23 a is converted into a parallel beam by the first lens 8, then passes through the dichroic mirror 11, and is focused by the third lens 12 toward the light-receiving end surface of the optical fiber 13.

[0051] The first measurement light 3 a introduced into the optical fiber 13 is mixed while traveling inside the optical fiber 13, particularly while passing through the mode scrambling unit 24, so that the beam profile is homogenized and the polarization direction is randomly polarized.

[0052] The first measurement light 3 a passing through the optical fiber 13 is diffused at a predetermined divergence angle and enters the fourth lens 14, where it is converted into a parallel beam by the fourth lens 14. Of the first measurement light 3 a passing through the fourth lens 14, a portion including the central portion in the plane enters the beam splitter 15, and the remaining portion passes through the periphery of the beam splitter 15.

[0053] A part of the first measurement light 3 a incident on the beam splitter 15 is reflected at a right angle along the reference optical axis 25 as the first reference light 26 a, and the remaining part is transmitted. The first reference light 26 a reflected by the beam splitter 15 is incident on the reference light receiving unit 16. The reference light receiving unit 16 detects the amount of received light of the incident first reference light 26 a and outputs it to the control unit 19 as received light amount data.

[0054] The first measuring light 3 a that has passed around the beam splitter 15 and the first measuring light 3 a that has been transmitted through the beam splitter 15 are diffused by the diffusing optical element 17 and irradiated onto the measurement object 4 .

[0055] The first measurement light 3a is reflected at a predetermined reflectance based on the nitrogen content ratio of the measurement target 4, and the first reflected measurement light 5a is received by the light-receiving unit 18 through the window 22. The light-receiving unit 18 outputs the received light amount of the first reflected measurement light 5a as received light amount data to the control unit 19. Here, the window 22 is vapor-deposited with a film having optical properties that transmit only the first reflected measurement light 5a and the second reflected measurement light 5b, so that light other than the reflected measurement light 5a, such as external light, is blocked, and only the first reflected measurement light 5a is received by the light-receiving unit 18.

[0056] Similarly, the second measurement light 3b diffused at a predetermined divergence angle on the second measurement optical axis 23b is converted into a parallel beam by the second lens 9, reflected by the dichroic mirror 11, and focused by the third lens 12 toward the light-receiving end surface of the optical fiber 13.

[0057] The second measurement light 3b introduced into the optical fiber 13 is mixed while passing through the optical fiber 13 and is emitted from the exit end face at a predetermined divergence angle. The second measurement light 3b is converted into a parallel beam by the fourth lens 14.

[0058] A part of the second measurement light 3b transmitted through the fourth lens 14 is incident on the beam splitter 15, and the remaining part passes around the beam splitter 15 and is incident on the diffusing optical element 17. Furthermore, a part of the second measurement light 3b incident on the beam splitter 15 is reflected at a right angle onto the reference optical axis 25 as a second reference light 26b, and the remaining part is transmitted through the beam splitter 15 and is incident on the diffusing optical element 17.

[0059] The second reference light 26b reflected by the beam splitter 15 is incident on the reference light receiving unit 16, and the reference light receiving unit 16 detects the amount of light received by the incident second reference light 26b and outputs it to the control unit 19 as light receiving amount data.

[0060] Furthermore, the second measurement light 3b incident on the diffusing optical element 17 is diffused in a predetermined direction and irradiated onto the measurement target 4. The second reflected measurement light 5b reflected based on the nitrogen content ratio of the measurement target 4 is received by the light receiving unit 18 through the window 22. The light receiving unit 18 outputs the received light amount of the second reflected measurement light 5b to the control unit 19 as received light amount data. At this time, external light and the like are blocked by the window 22, and only the second reflected measurement light 5b is received by the light receiving unit 18.

[0061] Therefore, the reference light receiving unit 16 alternately receives the first reference light 26a and the second reference light 26b and alternately sends data on the amount of received light to the control unit 19, and the light receiving unit 18 alternately receives the first reflected measurement light 5a and the second reflected measurement light 5b and alternately sends data on the amount of received light to the control unit 19.

[0062] The control unit 19 calculates the actual light intensity of the first measuring light 3a based on the received light intensity data of the first reference light 26a and the ratio of the first reference light 26a to the first measuring light 3a, and calculates the actual light intensity of the second measuring light 3b based on the received light intensity data of the second reference light 26b and the ratio of the second reference light 26b to the second measuring light 3b. The control unit 19 also calculates the difference between the actual light intensity of the first measuring light 3a and the light intensity set in the first light source 6, i.e., the light intensity fluctuation, and calculates the difference between the actual light intensity of the second measuring light 3b and the light intensity set in the second light source 7, i.e., the light intensity fluctuation.

[0063] Furthermore, the control unit 19 may automatically adjust the light intensities of the first light source 6 and the second light source 7 based on the calculated fluctuation in light intensity so that the actual light intensity matches the set light intensity.

[0064] In addition, the control unit 19 calculates the reflectance of the first measuring light 3a and the second measuring light 3b based on the actual light amount of the first measuring light 3a and the second measuring light 3b and the received light amount of the first reflected measuring light 5a and the second reflected measuring light 5b input from the light receiving unit 18.

[0065] Furthermore, the control unit 19 compares the calculated reflectance with the nitrogen content ratio of the leaves of the measurement object 4 corresponding to the growth status acquired in advance and the reflectance at that time (database), determines the growth status of the measurement object 4 based on the comparison result, and transmits the determined growth status to the control terminal of the mobile object 1 or the worker's mobile terminal, etc., thereby completing the measurement. Note that the amount of fertilizer required for the measurement object 4 may also be calculated in accordance with the growth status of the measurement object 4, and fertilization may be performed automatically.

[0066] As described above, in the first embodiment, the beam splitter 15 is provided in the optical path of the measurement light 3, and a part of the measurement light 3 is extracted as the reference light 26. Based on the received light amount of the reference light 26, the difference between the light amount (set light amount) of the measurement light 3 set based on the received light amount of the reference light 26 and the light amount (actual light amount) of the measurement light 3 irradiated onto the measurement object 4, i.e., the light amount fluctuation, can be calculated.

[0067] Therefore, by using the fluctuating light intensity of the measurement light 3 as the actual light intensity, it is possible to prevent calculation errors in the reflectance of the reflected measurement light 5 for the measurement object 4, thereby improving the measurement accuracy of the growth status of the measurement object 4.

[0068] Furthermore, the beam splitter 15 has a smaller beam diameter than the measurement light 3, so that a portion of the measurement light 3 is incident on the beam splitter 15. Therefore, there is no need to increase the size of the beam splitter 15, and the beam diameter of the reference light 26 reflected by the beam splitter 15 is also small, so there is no need to use a lens for focusing the reference light 26, and it is possible to reduce the number of parts and make the optical system more compact.

[0069] Furthermore, the beam splitter 15 is configured to allow a portion of the measurement light 3 to be incident thereon and to extract a portion of the incident measurement light 3 as the reference light 26. Therefore, even if the amount of light of the reference light 26 is small and the amount of light of the measurement light 3 is large, saturation of the optical system can be prevented without providing a neutral density filter.

[0070] Furthermore, the beam splitter 15 is arranged so as to pass through the center of the beam profile of the measurement light 3. Therefore, the measurement light 3 in the central portion, where the relative light intensity is high, can be extracted as the reference light 26, and the reference light 26 that is accurately proportional to the fluctuation in the light intensity of the light sources 6 and 7 can be extracted, further improving the measurement accuracy.

[0071] In the first embodiment, the first light source 6 and the first lens 8 are arranged on the transmission side of the dichroic mirror 11, and the second light source 7 and the second lens 9 are arranged on the reflection side of the dichroic mirror 11. However, it goes without saying that the second light source 7 and the second lens 9 may be arranged on the transmission side of the dichroic mirror 11, and the first light source 6 and the first lens 8 may be arranged on the reflection side of the dichroic mirror 11.

[0072] 5A and 5B show modified examples of the first embodiment. In the first modified example shown in Fig. 5A, a beam splitter 28 serving as a reference beam deflection member is longer than the beam diameter of the measurement beam 3. In addition, both ends of the beam splitter 28 extend beyond the luminous flux of the measurement beam 3, and the beam splitter 28 is supported at both ends by the extending portions. Therefore, the beam splitter 28 can be stably held.

[0073] 5B, the beam splitter 29 serving as the reference beam deflection member is rectangular in size so as to be able to extract only the light at the center of the beam profile of the measurement beam 3, and the beam splitter 29 is supported on its entire periphery by a holder 31 that extends to the outside of the luminous flux of the measurement beam 3. Therefore, even in the second modification, the beam splitter 29 can be stably held.

[0074] Next, a second embodiment of the present invention will be described with reference to Fig. 6. In Fig. 6, the same components as those in Fig. 2 are given the same reference numerals, and the description thereof will be omitted.

[0075] In the second embodiment, a beam splitter 32 serving as a reference beam deflection member is disposed between the exit end face of the optical fiber 13 and the fourth lens 14. The other configurations are the same as those in the first embodiment.

[0076] In the second embodiment, the reference light 26 is extracted from the measurement light 3 before it is collimated by the fourth lens 14. That is, the beam diameter of the measurement light 3 at the position where the beam splitter 32 extracts the reference light 26 is smaller than the beam diameter of the measurement light 3 that has been collimated.

[0077] Therefore, the beam splitter 32 can be made shorter in width and length than the beam splitter 15 in the first embodiment, which allows the optical system to be made even more compact.

[0078] The reference light 26 reflected by the beam splitter 32 has a predetermined divergence angle, but since the beam diameter of the reference light 26 when received by the reference light receiving unit 16 is smaller than that of the reference light receiving unit 16, there is no need to provide a separate lens to focus the reference light 26.

[0079] Next, a third embodiment of the present invention will be described with reference to Figures 7 and 8. In Figures 7 and 8, the same reference numerals are used to designate the same components as in Figure 2, and the description thereof will be omitted.

[0080] The plant sensor 2 according to the third embodiment includes a first light source 36, a second light source 37, a first lens 38, a second lens 39, a first wavelength selecting member 41, a second wavelength selecting member 42, a dichroic mirror 11 as an optical axis deflector, a beam splitter 15, a reference light receiving unit 16, a surface diffusion optical element 43, a window 44, a light receiving unit 18, a control unit 19, a memory unit 20, etc., and each of these components is housed in a housing 21. The surface diffusion optical element 43 may be, for example, a film coated with resin, and fine irregularities made with a mold pressed against the resin to transfer the irregularities.

[0081] The first light source 36 is, for example, an LED, and is configured to diffuse the first measurement light 3a of 735±20 nm, which includes the first wavelength band, and the second light source 37 is, for example, an LED, and is configured to diffuse the second measurement light 3b of 808±15 nm, which includes the second wavelength band.

[0082] 8, the first lens 38 is a TIR (Total Internal Reflection) lens, and has a recess 38a formed in the center, in which the first light source 36 is disposed. The first lens 38 also has an aspherical transmitting surface 38b formed in the center of the exit surface, and an aspherical reflecting surface 38c formed on the periphery.

[0083] The transmitting surface 38b is configured so that the first measuring light 3a emitted from the first light source 36 and incident at a small angle from the bottom surface of the recess 38a to the first lens 38 is incident thereon, and the first measuring light 3a is deflected to become a straight light substantially parallel to the first measuring optical axis 23a when passing through the transmitting surface 38b. Here, substantially parallel includes a case where the first measuring light 3a is parallel and a case where the first measuring light 3a can be regarded as substantially parallel.

[0084] The reflecting surface 38c is configured to receive the first measuring light 3a emitted from the first light source 36 and incident on the first lens 38 from the side surface of the recess 38a at a large incident angle, and deflects the first measuring light 3a to become a straight light beam substantially parallel to the first measuring optical axis 23a when totally reflected by the reflecting surface 38c. That is, the first lens 38 is configured to deflect the first measuring light 3a diffused over a wide range from the first light source 36 with high efficiency to become a substantially parallel light beam along the first measuring optical axis 23a.

[0085] The second lens 39 has the same structure as the first lens 38, and is configured to deflect the second measurement light 3b diffused over a wide range from the second light source 37 with high efficiency so that it becomes an approximately parallel light beam along the second measurement optical axis 23b.

[0086] The first wavelength selecting member 41 is, for example, a bandpass filter configured to transmit only light in a first wavelength band, for example, light with a full width at half maximum of 735±5 nm, while the second wavelength selecting member 42 is, for example, a bandpass filter configured to transmit only light in a second wavelength band, for example, light with a full width at half maximum of 808±5 nm.

[0087] In the third embodiment, the first measurement light 3 a diffused and emitted from the first light source 36 is converted into a substantially parallel beam by the first lens 38 and transmitted through the dichroic mirror 11. A part of the first measurement light 3 a transmitted through the dichroic mirror 11 is incident on the beam splitter 15, and the remaining part passes around the beam splitter 15 and is incident on the surface diffusion optical element 43.

[0088] Furthermore, a part of the first measurement light 3 a incident on the beam splitter 15 is reflected at a right angle along the reference optical axis 25 as a first reference light 26 a and is incident on the reference light receiving unit 16, and the remaining part is transmitted through the beam splitter 15 and is incident on the surface diffusion optical element 43. The reference light receiving unit 16 detects the amount of received light of the incident first reference light 26 a and outputs it to the control unit 19 as received light amount data.

[0089] The first measurement light 3a incident on the surface diffusion optical element 43 is diffused in a predetermined direction and irradiated onto the measurement target 4 (see FIG. 1). The first reflected measurement light 5a reflected based on the nitrogen content ratio of the measurement target 4 is received by the light receiving unit 18 through the window 22. The light receiving unit 18 outputs the received light amount of the first reflected measurement light 5a to the control unit 19 as received light amount data.

[0090] Similarly, the second measurement light 3b diffused and emitted from the second light source 37 is converted into a substantially parallel beam by the second lens 39 and deflected by the dichroic mirror 11 so as to be coaxial with the first measurement light 3a. A part of the second measurement light 3b reflected by the dichroic mirror 11 is incident on the beam splitter 15, and the remaining part passes around the beam splitter 15 and is incident on the surface diffusion optical element 43.

[0091] Furthermore, a part of the second measurement light 3b incident on the beam splitter 15 is reflected at a right angle along the reference optical axis 25 as a second reference light 26b and is incident on the reference light receiving unit 16, and the remaining part is transmitted through the beam splitter 15 and is incident on the surface diffusion optical element 43. The reference light receiving unit 16 detects the amount of received light of the incident second reference light 26b and outputs it to the control unit 19 as received light amount data.

[0092] The second measurement light 3b incident on the surface diffusion optical element 43 is diffused in a predetermined direction and irradiated onto the measurement target 4 (see FIG. 1). The second reflected measurement light 5b reflected based on the nitrogen content ratio of the measurement target 4 is received by the light receiving unit 18 through the window 22. The light receiving unit 18 outputs the received light amount of the second reflected measurement light 5b to the control unit 19 as received light amount data.

[0093] Therefore, the reference light receiving unit 16 alternately receives the first reference light 26a and the second reference light 26b and alternately sends data on the amount of received light to the control unit 19, and the light receiving unit 18 alternately receives the first reflected measurement light 5a and the second reflected measurement light 5b and alternately sends data on the amount of received light to the control unit 19. The processing after receiving the reference light 26 and the reflected measurement light 5 is the same as in the first embodiment.

[0094] In the third embodiment, LEDs are used as the light sources 36 and 37, and TIR lenses are used as the lenses 38 and 39. Therefore, there is no need to mix the measurement light 3 by passing it through the optical fiber 13 (see FIG. 2), and the third lens 12, the optical fiber 13, and the fourth lens 14 in the first embodiment can be omitted, which significantly reduces the number of parts, reduces manufacturing costs, and significantly downsizes the optical system.

[0095] Furthermore, since the first wavelength selection member 41 is arranged on the optical path of the first measurement light 3a and the second wavelength selection member 42 is arranged on the optical path of the second measurement light 3b, even if an LED that includes light other than the first wavelength band and the second wavelength band is used as the light source, only the measurement light 3 of the first wavelength band and the second wavelength band can be used, thereby improving measurement accuracy.

[0096] Furthermore, since the surface diffusing optical element 43 is used to diffuse the measuring light 3, the beam profile of the measuring light 3 can be made more uniform than when a lens is used.

[0097] 9 shows a modification of the third embodiment. In this modification, the shapes of the first lens 45 and the second lens 46 are different from those of the first lens 38 and the second lens 39 of the third embodiment. Since the first lens 45 and the second lens 46 have the same structure, only the first lens 45 will be described below.

[0098] The first lens 45 has a recess 45a whose bottom surface is an aspherical transmitting surface 45b, and an exit surface which is entirely flat. The other configurations are the same as those of the first lens 38. In the first lens 45, light of the first measuring light 3a having a small incident angle is deflected into a straight light in the process of passing through the transmitting surface 45b, and light of a large incident angle is totally reflected by the reflecting surface 45c to become a straight light.

[0099] The present invention is not limited to the lenses shown in the third embodiment and the modified example of the third embodiment, and any TIR lens or collimator lens that can change diffused light into straight light can be applied to the present invention.

[0100] Furthermore, in the first to third embodiments, a tractor is used as an example of a mobile body on which the plant sensor 2 is installed, but the plant sensor 2 may also be installed on an aircraft such as a UAV, or may be carried by a worker.

[0101] 2 Plant sensor 3 Measurement light 4 Measurement object 5 Reflected measurement light 6 First light source 7 Second light source 8 First lens 9 Second lens 11 Dichroic mirror 15 Beam splitter 16 Reference light receiving unit 18 Light receiving unit 19 Control unit 26 Reference light

Claims

1. A plant sensor comprising: a first light source that emits a first measurement light including a first wavelength band; a second light source that emits a second measurement light including a second wavelength band; a first lens that converts the first measurement light into a parallel beam; a second lens that converts the second measurement light into a parallel beam; a measurement light deflection member that is provided on a common optical path of the first measurement light and the second measurement light and deflects one of the first measurement light and the second measurement light so that the first measurement light and the second measurement light are coaxial; a reference light deflection member that extracts a portion of each measurement light as a reference light; a reference light receiving unit that receives the reference light; a light receiving unit that receives the first reflected measurement light and the second reflected measurement light from a measurement object; and a control unit that calculates the growth status of the measurement object based on the received light amount of the reference light and the received light amount of each reflected measurement light, wherein the light receiving area of ​​the reference light deflection member is smaller than the area of ​​the cross section of the beam of each measurement light, and the reference light deflection member is positioned so as to be able to extract light at the center of the cross section of the beam of each measurement light.

2. The plant sensor according to claim 1, wherein said reference beam deflecting member is longer than the radius of the beam of each measurement beam, passes through the center of each measurement beam, and is disposed so as to extend to the outside of each measurement beam.

3. A plant sensor as claimed in claim 1, further comprising an optical fiber, a third lens for focusing each measurement light on the light receiving end face of the optical fiber, and a fourth lens for converting each measurement light irradiated from the exit end face of the optical fiber into a parallel beam, and the reference light deflection member is configured to extract the reference light from each measurement light converted into a parallel beam by the fourth lens.

4. A plant sensor as claimed in claim 1, further comprising an optical fiber, a third lens for focusing each measurement light on the light receiving end face of the optical fiber, and a fourth lens for converting each measurement light irradiated from the exit end face of the optical fiber into a parallel beam, wherein the reference light deflection member is configured to extract the reference light from each measurement light irradiated from the exit end face of the optical fiber.

5. A plant sensor as claimed in claim 1, wherein the first light source and the second light source are LEDs, the first lens and the second lens are TIR lenses, a first wavelength selection member that transmits only light of a first wavelength band is provided on the optical path of the first measurement light, and a second wavelength selection member that transmits only light of a second wavelength band is provided on the optical path of the second measurement light.

6. A plant sensor according to any one of claims 1 to 5, wherein the control unit is configured to calculate the actual light intensity of each measurement light based on the light intensity of each measurement light set in the first light source and the second light source, the received light intensity of the reference light, and the ratio of the reference light to each measurement light, and to calculate the fluctuation in the light intensity of each measurement light based on the set light intensity and the actual light intensity.

7. A plant sensor as claimed in claim 6, further comprising a memory unit in which a database correlating the growth status of the measurement object with the reflectance of the reflection measurement light is stored, and the control unit is configured to calculate the reflectance of the reflection measurement light based on the actual amount of light and the amount of the reflection measurement light received, and to measure the growth status of the measurement object based on the reflectance and the database.

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