Detecting the presence of plants on the ground

A system for detecting the presence of a plant on the ground includes a light module configured to emit a light beam having a shape with a length longer than a width. The system may include one or more lenses each having one or more photodetectors. The photodetectors may be arranged in a side-by-side configuration and are configured to receive reflected portions of the light beam. The lenses may be configured to direct the reflected portions of the light beam onto the photodetectors.

FIELD OF THE INVENTION

Embodiments described herein relate generally to detecting the presence of plants on the ground, and more particularly, to systems that improve the detection of plants on the ground.

BACKGROUND

The spectral reflectance of plants compared to that of soil can be used to detect the presence of plants on the ground. This is illustrated inFIG. 1, which is an exemplary plot of the reflectance versus wavelength of a living plant1compared to that of bare soil2. Due to the differences between the spectral reflectance characteristics, it is possible to differentiate the living plant1from the bare soil2. For example, light beams of two different wavelengths W1, W2can be transmitted toward the ground, and the intensities of the different wavelengths of scattered light returning from the ground can be compared to determine if there is a plant1or just bare soil2. This is because light at the different wavelengths is absorbed by the living plant1and the bare soil2differently. For example, the living plant1may mostly absorb red light at wavelengths of between about 650 nm and 700 nm (W1), and the living plant1may mostly reflect near infrared light at wavelengths above about 720 nm (W2). In contrast, the bare soil2may have a similar reflectance at each of the wavelengths W1, W2.

Detecting a plant in this manner can allow herbicide sprayer systems to reduce the amount of chemicals required to eradicate weeds in a field. For example, a field may be scanned using light beams of two different wavelengths, and each time a weed (or plant) is detected, a valve may be opened to spray herbicide on the weed. A considerable savings may be realized since the herbicide is not sprayed unnecessarily onto the bare soil.

SUMMARY

Embodiments described herein provide improved detection of plants on the ground. In an embodiment, for example, a system includes photodetectors arranged in a side-by-side configuration. When detecting reflected portions of a light beam, gain values applied to amplifiers associated with at least some of the photodetectors can be adjusted to improve a signal-to-noise ratio of the photodetectors. Also, in some embodiments, a field of view of the photodtectors can be controlled by limiting an active number of the photodetectors. Additionally, the photodetectors may be configured to determine an approximate relative position of the plants on the ground. Depending on the embodiment, one or more of these features and/or benefits may exist. Exemplary embodiments are described throughout the specification with reference to the appended drawings.

In accordance with an embodiment, for example, a system for detecting the presence of a plant on the ground includes a light module and a photodetector system. The light module is configured to emit a light beam having a shape with a length longer than a width. The light beam comprises light at a first wavelength and light at a second wavelength different from the first wavelength. The light at the first wavelength is modulated with a first signal having a first phase, and the light at the second wavelength is modulated with a second signal having a second phase different from the first phase. The photodetector system includes photodetectors configured to receive reflected portions of the light beam. The photodetector system includes a first plurality of photodetectors arranged in a side-by-side configuration, and a first lens configured to receive first reflected portions of the light beam and direct the first reflected portions of the light beam onto the first plurality of photodetectors. The first reflected portions of the light beam have the shape with a length longer than a width. The width of the first reflected portions of the light beam impinging on the first plurality of photodetectors is less than a width of any one of the first plurality of photodetectors, and the length of the first reflected portions of the light beam impinging on the first plurality of photodetectors is greater than a length of any one of the first plurality of photodetectors and extends across multiple ones of the first plurality of photodetectors in the side-by-side configuration. The photodetector system also includes a second plurality of photodetectors arranged in the side-by-side configuration, and a second lens configured to receive second reflected portions of the light beam and direct the second reflected portions of the light beam onto the second plurality of photodetectors. The second reflected portions of the light beam have the shape with a length longer than a width. The width of the second reflected portions of the light beam impinging on the second plurality of photodetectors is less than a width of any one of the second plurality of photodetectors, and the length of the second reflected portions of the light beam impinging on the second plurality of photodetectors is greater than a length of any one of the second plurality of photodetectors and extends across multiple ones of the second plurality of photodetectors in the side-by-side configuration.

In an embodiment, the second lens is arranged to shift a location of the second reflected portions of the light beam impinging on the second plurality of photodetectors compared to a location of the first reflected portions of the light beam impinging on the first plurality of photodetectors. The second reflected portions of the light beam impinging on the second plurality of photodetectors may be shifted in a direction of the side-by-side configuration by a distance less than a length of any one of the second plurality of photodetectors.

In one embodiment, the first plurality of photodetectors are configured to function electrically as a single photodiode, and the second plurality of photodetectors are configured to function electrically as a single photodiode. In another embodiment, the first plurality of photodetectors are configured to function electrically as individual photodiodes or as groups of multiple photodiodes, and the second plurality of photodetectors are configured to function electrically as individual photodiodes or as groups of multiple photodiodes.

In one embodiment, the photodetector system also includes a mask shaped to prevent end parts of the first reflected portions of the light beam in the length direction from impinging on at least some of the first plurality of photodetectors depending on a location where the first reflected portions of the light beam impinges on the first plurality of photodetectors in the width direction. In another embodiment, the mask is shaped to limit a field of view of the first plurality of photodetectors depending on a location where the first reflected portions of the light beam impinge on the first plurality of photodetectors in the width direction.

In another embodiment, the photodetector system is configured to limit a field of view of the first plurality of photodetectors by limiting a number of active ones of the first plurality of photodetectors.

In another embodiment, the photodetector system is configured to increase a gain value applied to amplifiers of outer ones of the first plurality of photodetectors in the side-by-side configuration compared to a gain value applied to amplifiers of inner ones of the first plurality of photodetectors in the side-by-side configuration.

In another embodiment, the photodetector system is configured to generate a signal and provide the signal to a controller depending on a sequence of electrical signals generated by the first plurality of photodetectors.

In yet another embodiment, the photodetector system is configured to determine an approximate position of the plant on the ground and to provide a signal to a controller depending on the approximate position of the plant on the ground.

In accordance with another embodiment, a system for detecting the presence of a plant on the ground includes a light module that is configured to emit a light beam having a shape with a length longer than a width. The light beam comprising light at a first wavelength and light at a second wavelength different from the first wavelength. The system also includes a plurality of photodetectors arranged in a side-by-side configuration and configured to receive reflected portions of the light beam, and a lens configured to receive reflected portions of the light beam and direct the reflected portions of the light beam onto the plurality of photodetectors. The reflected portions of the light beam have the shape with a length longer than a width. The width of the reflected portions of the light beam impinging on the plurality of photodetectors is less than a width of any one of the plurality of photodetectors, and the length of the reflected portions of the light beam impinging on the plurality of photodetectors is greater than a length of any one of the plurality of photodetectors and extends across multiple ones of the plurality of photodetectors in the side-by-side configuration.

In one embodiment, the plurality of photodetectors are configured to function electrically as a single photodiode. In another embodiment, the plurality of photodetectors are configured to function electrically as individual photodiodes or as groups of multiple photodiodes.

In another embodiment, the system also includes a mask shaped to limit a field of view of the plurality of photodetectors depending on a location where the reflected portions of the light beam impinge on the plurality of photodetectors in the width direction.

In yet another embodiment, the system also includes a controller configured to increase a gain value applied to amplifiers of outer ones of the plurality of photodetectors in the side-by-side configuration compared to a gain value applied to amplifiers of inner ones of the plurality of photodetectors in the side-by-side configuration.

In accordance with yet another embodiment, a system for detecting the presence of a plant on the ground includes a light module configured to emit a light beam having a shape with a length longer than a width. The light beam comprises light at a first wavelength and light at a second wavelength different from the first wavelength. The system also includes a first photodetector and a first lens configured to receive first reflected portions of the light beam and direct the first reflected portions of the light beam onto the first photodetector. The first reflected portions of the light beam have the shape with a length longer than a width. The system also includes a second photodetector and a second lens configured to receive second reflected portions of the light beam and direct the second reflected portions of the light beam onto the second photodetector. The second reflected portions of the light beam have the shape with a length longer than a width.

In an embodiment, the second lens is arranged to shift a location of the second reflected portions of the light beam impinging on the second photodetector compared to a location of the first reflected portions of the light beam impinging on the first photodetector.

In another embodiment, the first photodetector comprises a first plurality of photodetectors arranged in a side-by-side configuration, and the second photodetector comprises a second plurality of photodetectors arranged in a side-by-side configuration.

In yet another embodiment, the first photodetector is configured to generate a signal and provide the signal to a controller depending on a sequence of electrical signals generated by the first photodetector.

DETAILED DESCRIPTION

Embodiments described herein provide improved detection of plants on the ground. Some embodiments may include one or more lenses each associated with one or more photodetectors. The photodetectors may be arranged in a side-by-side configuration and are configured to receive reflected portions of a light beam. The lenses may be configured to direct the reflected portions of the light beam onto the photodetectors.

FIG. 2is a simplified schematic diagram of an exemplary herbicide sprayer system that may benefit from the embodiments described herein. The herbicide sprayer system is used merely as an example, and it should be appreciated that the embodiments described herein may be used with other types of plant detection systems.

In the herbicide sprayer system shown inFIG. 2, a first diode3emits light at a first wavelength and a second diode4emits light at a second wavelength. In this example, the drive currents of the diodes3,4are each modulated with respective modulation signals that are of the same frequency but different phase. The light from the diodes3,4passes through an emitter lens5and is directed toward an object on the ground (in this case a plant6). Some of the light impinging on the plant6is reflected and passes through a detector lens7and an aperture plate8before impinging on a photodetector9. A resonant circuit10is tuned to the frequency of the modulation signals.

The phase of the scattered light impinging upon the photodetector9is used to assess the spectral reflectance characteristic of the scattered light and therefore to characterize the object (e.g., the plant6on the ground) from which the light is scattered. For example, if the light from the diode4were completely absorbed by the plant6, then the only light received by the photodetector9would be from the diode3. The photodetector9would therefore be modulated with a signal approximately in phase with the modulation signal driving the diode3.

If, on the other hand, no light from the diode3were scattered from the plant6, then the only light received by the photodetector9would be from the diode4. Consequently, the oscillation induced in resonant circuit10would have a second phase relationship with respect to the phase of the modulation signal used to drive the diode3.

The foregoing example represent extreme cases. In practice, the photodetector9typically receives some light from each of the diodes3,4. Then, depending on the relative reflectance values, the phase of the resonant circuit10is between the first and second extreme phase relationships described above.

A phase detector detects the phase of the oscillation induced in resonant circuit10, providing phase information indicative of the relative strengths of the scattered light beams from the diodes3,4. If this phase information is consistent with the spectral reflectance characteristic of a plant6, then a solenoid valve11is opened to spray herbicide onto the plant6. Conversely, if the phase information is consistent with the spectral reflectance characteristic of soil, the solenoid valve11remains closed.

It should be appreciated that the schematic diagram shown inFIG. 2depicts an exemplary herbicide sprayer system. The embodiments described herein are not limited to this system, and they may be implemented in other systems that may include different and/or additional components. As examples, some systems may utilize time-division multiplexing of the light at the different wavelengths, or other systems may separate the light into different channels using optical filters, rather than using the phase shift technique described with regard toFIG. 2. Also, some systems may utilize light at more than two different wavelengths.

FIG. 3is a simplified cross-sectional view of a portion of an exemplary herbicide sprayer system. The portion shown in this figure includes some components for detecting the presence of plants on the ground such as a housing109, diodes100(e.g., light emitting diodes), an emitter mask110, an emitter lens111, a detector lens113, a detector mask114, a photodetector103, and a printed circuit board112. The emitter mask110and/or detector mask114may be optional in some embodiments. The diodes100may be configured to emit light at different wavelengths as discussed previously (e.g., W1, W2). Portions of the emitted light are reflected by plants and/or bare soil. Reflected portions of the light are received at the photodetector103, and signals from the photodetector103may be used to detect the presence of the plants on the ground.

FIG. 3does not specifically show all the circuitry and/or hardware components for performing functions such as generating the light, detecting the light, analyzing the spectral reflectance characteristics, and controlling valves associated with the sprayer system.

In actual implementations, a plurality of the herbicide sprayer systems may be arranged adjacent to each other on an implement that is coupled to a tractor or another type of farm equipment. A height of the herbicide sprayer systems above the ground may be adjusted to provide nearly full coverage of the ground under the implement. In some arrangements, the light beams emitted from the herbicide sprayer systems have little to no overlap on the ground to avoid detection and double spraying of plants by adjacent systems.

FIGS. 4A-4Bare simplified drawings of a portion of a system for detecting the presence of plants on the ground in accordance with an embodiment. The portion shown inFIG. 4Amay be part of a larger herbicide sprayer system. This figure provides a perspective view of a housing409, an emitter lens411, and a detector lens413. The emitter lens411and/or the detector lens413may alternatively be protective covers that protect underlying lenses and are at least partially transparent to light emitted and received by the system.

Diodes within the housing409may be configured to emit light at different wavelengths. The diodes and emitter lens411may be part of a light module that is configured to emit a light beam. The light beam is directed toward the ground, and reflected portions of the light beam may be received by the detector lens413and directed towards a plurality of photodetectors. The detector lens413and photodetectors may be part of a photodetector system that is configured to receive reflected portions of the light beam.

FIG. 4Bprovides an example of photodetectors426arranged in a side-by-side configuration. Each photodetector may have a rectangular shape so that sides abut one or more adjacent photodetectors. Each photodetector is typically on the order of a few millimeters per side in length. The side-by-side configuration of the photodetectors426may extend approximately parallel to a length of the reflected portions of the light beam. The side-by-side configuration may extend along any axis depending on the configuration of the light module and any optical members altering an orientation of the light beam.

The photodetectors426may be disposed within the housing409and arranged to receive reflected portions of the light beam from the detector lens413. In some embodiments, the photodetectors426are configured to function electrically as a single photodiode. For example, the photodetectors426may be electrically coupled in parallel and configured to generate a single electrical signal.

In other embodiments, the photodetectors426may be configured to function electrically as individual photodiodes or as groups of multiple photodiodes. For example, the photodetectors426and associated circuitry may be configured so that each photodetector generates a separate electrical signal. Alternatively, the photodetectors426and associated circuitry may be configured so that groups of the photodetectors426generate a single electrical signal (e.g., groups of two photodetectors, groups of three photodetectors, etc.).

FIGS. 5A-5Care simplified drawings of a portion of a system for detecting the presence of plants on the ground in accordance with another embodiment. The portion shown inFIG. 5Amay be part of a larger herbicide sprayer system. This figure provides a perspective view of a housing509, an emitter lens511, and detector lenses513a,513b. The housing509and emitter lens511are similar to their corresponding features inFIG. 4Aand will not be described separately. This embodiment is different fromFIG. 4Ain that it includes two detector lenses513a,513b. Reflected portions of the light beam are directed by the first detector lens513ato one or more first photodetectors and by the second detector lens513bto one or more second photodetectors.

FIG. 5Bprovides an example of a single photodetector528that may be used in some embodiments. Two such photodetectors528may be disposed within the housing509, and each photodetector528may be arranged to receive reflected portions of the light beam from an associated one of the detector lenses513a,513b. The detector lenses513a,513bmay be arranged to receive non-overlapping or overlapping portions of the reflected light beam. Using multiple lenses513a,513band photodetectors528can increase an effective field of view of the system. Alternatively, using multiple lenses513a,513band photodetectors528can provide multiple images of the same reflected portions of the light beam.

FIG. 5Cprovides an example of a plurality of photodetectors526arranged in a side-by-side configuration that may be used in some embodiments. The photodetectors526are similar to the photodetectors426shown inFIG. 4Band can be configured to function in a similar manner. Similar features will not be described separately. A first one of the plurality of photodetectors526may be disposed within the housing509and arranged to receive reflected portions of the light beam from the first detector lens513a, and a second one of the plurality of photodetectors526may be disposed within the housing509and arranged to receive reflected portions of the light beam from the second detector lens513b.

FIGS. 6A-6Bare simplified drawings illustrating the scanning of a plant on the ground in accordance with an embodiment. This example assumes a system similar to that shown inFIG. 5Awith a plurality of photodetectors similar to those shown inFIG. 5C.FIG. 6Ashows a light beam632having a shape with a length longer than a width. The narrow width allows the light beam632to be scanned across the ground, or as shown inFIG. 6A, to be scanned across a plant634on the ground, while providing an increased signal-to-noise ratio (SNR) compared to beams of a larger width.

Although not specifically shown, the light beam632may be generated by one or more diodes and focused by an emitter lens. As explained previously, the light beam632may include light at a first wavelength and light at a second wavelength different from the first wavelength. Because the plant634has different spectral reflectance characteristics than the surrounding bare soil, portions of the light beam632impinging on the plant634will reflect differently than portions of the light beam632impinging on the bare soil.

Reflected portions of the light beam are received by one or more lenses and directed to one or more photodetectors. In this example, first reflected portions of the light beam632aare directed to first photodetectors630aas shown on the left side ofFIG. 6B, and second reflected portions of the light beam632bare directed to second photodetectors630bas shown on the right side ofFIG. 6B. Although not specifically shown, the first reflected portions of the light beam632aand the second reflected portions of the light beam632bare each directed onto the photodetectors630a,630brespectively by associated first and second lenses (similar to lenses513a,513bshown inFIG. 5A).

As shown inFIG. 6B, the first and second reflected portions of the light beam632a,632beach have the shape with a length longer than a width (similar to the shape of the emitted light beam). Widths of the first and second reflected portions of the light beam632a,632bimpinging on the photodetectors630a,630brespectively are each less than a width of any one of the photodetectors630a,630b. Lengths of the first and second reflected portions of the light beam632a,632bimpinging on the photodetectors630a,630brespectively are each greater than a length of any one of the photodetectors and extend across multiple ones of the photodetectors in the side-by-side configuration.

In this example, the first and second reflected portions of the light beam632a,632binclude reflected light from the entire length of the light beam632(a field of view of the first and second lenses each encompass the entire light beam). However, a location of the second reflected portions of the light beam632bon the photodetectors630bis shifted compared to a location of the first reflected portions of the light beam632aon the photodetectors630a. This can be seen inFIG. 6B, where the first reflected portions of the light beam632aare approximately centered on the first photodetectors630a, and the second reflected portions of the light beam632bare shifted to the right on the second photodetectors630b. The second reflected portions of the light beam632bare shifted in a direction of the side-by-side configuration (in the length direction) by a distance less than a length of any one of the photodetectors.

The second reflected portions of the light beam632bare shifted to eliminate any “blind spots” in the collective field of view of the first and second photodetectors. A “blind spot” is illustrated on the left side ofFIG. 6B, where a part of the first reflected portions of the light beam632athat is impacted by the plant634afalls on a boundary between two of the photodetectors630a. The plant634ais included in the figure to represent the part of the first reflected portions of the light beam632awhere an intensity of the reflected light will be reduced because of the presence of the plant634on the ground. Because the part of the first reflected portions of the light beam632athat is impacted by the plant634afalls on the boundary between two of the photodetectors630a, it is possible that the signal will not be sufficient to detect the plant thus causing a “blind spot.”

A location of the second reflected portions of the light beam632bon the photodetectors630bis shifted so that any “blind spots” on the photodetectors630aare not “blind spots” on the photodetectors630b(and vice versa). This is shown inFIG. 6B, where a part of the second reflected portions of the light beam632bthat is impacted by the plant634bfalls completely on one of the photodetectors630b. Because the part in not on a “blind spot,” the signal will be greater and it should be sufficient to detect the plant.

The example shown inFIGS. 6A-6Balso illustrates how the photodetectors630a,630bcan be used to determine an approximate position of the plant634on the ground relative to the light beam632. Using the photodetectors630bas an example, each individual photodetector receives reflected light from a particular part of the light beam632. Detection of a plant by one of the photodetectors is an indication that there is a plant within the corresponding part of the light beam632on the ground. A signal can be sent to a controller indicating the approximate position of the plant on the ground. The controller may use this information, for example, to open a particular valve of the sprayer system that is most closely aligned with the position of the plant.

FIGS. 7A-7Care simplified drawings of a mask shaped to limit a field of view of a group of photodetectors in accordance with an embodiment.FIG. 7Ashows a mask740having an aperture742. InFIG. 7B-7C, an outline of the aperture742is superimposed on photodetectors744. Reflected portions of a light beam746passing through the aperture742impinge on the photodetectors744. Reflected portions of the light beam746that are outside the aperture742are blocked by the mask740.

As a height of the system above the ground is changed, a location where the reflected portions of the light beam746impinge on the photodetectors744changes in a width direction (height of the photodetectors744inFIGS. 7B-7C). This is because the emitted light beam and/or the reflected portions of the light beam are at a slight angle as shown inFIG. 3.

In some embodiments, the aperture is arranged to block end parts of the reflected portions of the light beam746from impinging on some of the photodetectors744. The extent of the blocking depends on the location where the reflected portions of the light beam746impinge on the photodetectors744in the width direction.

This is shown inFIG. 7C, where end parts of the reflected portions of the light beam746are outside the aperture742and thus blocked from reaching outer ones of the photodetectors744. This may be useful, for example, when a height of the system above the ground is increased causing a length of the light beam impinging on the ground to increase (an increase in a field of view).

Blocking some of the photodetectors744can limit a field of view to prevent overlap between adjacent systems in implementations where multiple systems are arranged, for example, on an implement coupled to a tractor or another type of farm equipment.

FIGS. 8-9are simplified drawings of photodetectors arranged in side-by-side configurations in accordance with some embodiments.FIG. 8shows photodetectors850a-850farranged in a side-by-side configuration. In this example, a field of view of the photodetectors850a-850fis limited by turning off or disregarding signals from the outer photodetectors850aand850f. The remaining photodetectors850b,850c,850d,850eremain active. Other ones of the photodetectors850a-850fmay be limited in other embodiments.

FIG. 9shows photodetectors960a-960farranged in a side-by-side configuration. In this example, a gain value applied to amplifiers of outer ones of the photodetectors (e.g.,960aand960f) may be increased compared to gain values applied to amplifiers of inner ones of the first plurality of photodetectors (e.g.,960b,960c,960d,960e). Increasing the gain can improve a signal-to-noise (SNR) ratio because an intensity of reflected portions of a light beam generally decreases with distance from a center of the light beam. A gain value applied to amplifiers of other ones of the photodetectors960a-960fmay also be increased or decreased depending on particular conditions and applications.

FIG. 10is a simplified drawing illustrating a hand gesture used to generate signals for a controller in accordance with an embodiment. A sequence of electrical signals generated by photodetectors1044can be used to generate a signal for manual control of a herbicide sprayer system. For example, moving a user's hand (or anything that blocks the light beam) from right to left creates a sequence of signals that can be used by a controller to take some pre-determined action (e.g., opening or closing a valve of the herbicide sprayer system). This can be useful, for example, when the user is working on the herbicide sprayer system.

FIG. 11is a simplified drawing of photodetectors providing signals to a controller in accordance with an embodiment. In this example, photodetectors1180a-1180fare each configured to provide a signal to controller1182. Different gestures, as explained with regard toFIG. 10, can be associated with different actions by the controller.

The controller1182typically includes familiar software and hardware components. For example, it may include one or more operating systems, processors, local or remote memories for storage, I/O devices, and system buses interconnecting the hardware components. RAM and disk drives are examples of memories for storage of data and computer programs. Other types of local memories include magnetic storage media, optical storage media, flash memory, networked storage devices, and the like.

While the present invention has been described in terms of specific embodiments, it should be apparent to those skilled in the art that the scope of the present invention is not limited to the embodiments described herein. For example, features of one or more embodiments of the invention may be combined with one or more features of other embodiments without departing from the scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. Thus, the scope of the present invention should be determined not with reference to the above description, but should be determined with reference to the appended claims along with their full scope of equivalents.