WO1998057539A1

WO1998057539A1 - Detecting plants in a field using a plurality of power multiplexed sensor units

Info

Publication number: WO1998057539A1
Application number: PCT/US1998/011406
Authority: WO
Inventors: Malcolm L. Kinter; James L. Beck
Original assignee: Patchen, Inc.
Priority date: 1997-06-18
Filing date: 1998-06-12
Publication date: 1998-12-23
Also published as: AU8252998A

Abstract

An apparatus for detecting plants in a field has a plurality of optical sensor units which are scanned in parallel paths across a field. In some embodiments, the sensor units are mounted along a boom and all draw electrical power from a common power conductor that extends down the boom. In a first time period, light sources of a first of the sensor units are activated to draw power from the power conductor whereas light sources of a second of the sensor units are not activated. Then, in a second time period, light sources of the second sensor unit are activated to draw power from the power conductor and the light sources of the first sensor unit are not activated. Less peak power is therefore transferred over the power conductor at a given time and a lightweight and less expensive power conductor can be used.

Description

DETECTING PLANTS IN A FIELD USING A PLURALITY OF POWER MULTIPLEXED SENSOR UNITS

FIELD OF THE INVENTION

This invention relates to detecting objects (for example, plants) in a field using a plurality of optical sensor units.

BACKGROUND INFORMATION

Commonly-owned U.S. Patent No. 5,296,702 entitled "Structure And Method For Differentiating One Object

From Another Object" discloses a sensor unit which uses the different spectral reflectance characteristics of living plants and of soil to differentiate living plants from soil in a field. Figure 1 (Prior Art) is a graph which illustrates the different spectral reflectance characteristics of a living plant (shown in curve 100) and of soil (shown in curve 101) . In some embodiments of the sensor unit, substantially monochromatic light of a first wavelength (for example, 670 nm) is transmitted onto a surface of the field and the light reflected from the surface is detected by a detector in the sensor unit. Similarly, substantially monochromatic light of a second wavelength (for example, 750 nm) is transmitted onto the same surface of the field and the light reflected is detected by the detector. If the difference in reflectance at the two wavelengths corresponds with curve 100, then the reflectance is indicative of a plant. If, on the other hand, the difference in reflectance at the two wavelengths corresponds with curve 101, then the reflectance is indicative of soil. Such a sensor unit has important uses in agriculture.

When growing row crops (for example, cotton) , it is often desirable to kill weeds growing in the "middles" between rows of crops. The entire middle can be blanke -sprayed with a herbicide to kill the weeds, but much of the middles are not covered in weeds . Much herbicide will therefore be sprayed onto bare soil and wasted. Blanket -spraying is therefore expensive due to large amounts of herbicide being wasted. Furthermore, blanket -spraying raises environmental concerns due to the use of unneeded herbicide.

Herbicide is selectively administered into a crop middle by scanning the sensor unit described above down the middle. If a plant (i.e., a weed) is detected in the middle, then a solenoid spray valve is activated to spray herbicide onto the plant. If no plant is detected in the middle, then the solenoid spray valve remains closed and herbicide is not wasted on the bare soil. Multiple middles are sprayed concurrently by attaching multiple sensor units to a boom so that each sensor units scans a different middle.

Each sensor unit consumes about 60 milliamperes to keep the solenoid valve open and up to 400 milliamperes to generate the light of the first and second wavelengths. Where dozens of sensor units are provided on a boom, a large amount of power is required to power the sensor units. Large cables may be required to carry that large amount of power. Power requirements and weight limitations may therefore reduce the practicality of using a large, multi-sensor unit sprayer. A lightweight and economical agricultural implement is desired whereby a large number of sensor units are used together at one time.

SUMMARY

An apparatus for detecting plants in a field has a plurality of optical sensor units which are scanned in parallel paths across a field. In some embodiments, the sensor units are mounted along a boom and all draw power from a common power conductor that extends down the boom. In a first time period, light sources of a first of the sensor units are activated to draw power from the power conductor whereas light sources of a second of the sensor units are not activated. Then, in a second time period, light sources of the second sensor unit are activated to draw power from the power conductor and the light sources of the first sensor unit are not activated. Less peak power is therefore transferred over the power conductor at a given time and a lightweight and less expensive power conductor can be used.

This summary does not purport to define the invention. The invention is defined by the claims. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 (Prior Art) is a graph illustrative of the spectral reflectance characteristics of a living plant and of soil; Figure 2 is a perspective view of a use of a spray implement in accordance with an embodiment;

Figure 3 is a sectional diagram of a portion of the spray implement of Figure 2 ;

Figure 4 is a sectional diagram of a portion of two sensor units 10A and 10B of Figure 3;

Figure 5 is a schematic diagram of a suitable light source for sensor units of the present invention;

Figure 6 is a timing diagram of the light source current according to one embodiment of the invention; and

Figure 7 is a timing diagram of light source current according to another embodiment of the invention.

Use of similar reference numbers in different figures indicates the same or like elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 2 is a perspective view of a tractor 3 moving a spray implement 4 through a cotton field in accordance with one embodiment. Cotton crop plants are located in rows 1. Weeds to be sprayed are located in middles 2. Spray implement 4 includes a boom 5 (which can be folded and unfolded via hydraulic cylinders 6) , plastic spray hoods 7 positioned over middles 2 containing a plurality of sensor units and solenoid- activated spray valves (not shown) , boom extensions 8 connecting boom 5 to the spray hoods 7, herbicide plumbing and electrical wiring (not shown) , a spray tank 9, and a central control and display circuit (not shown). For additional details, see commonly-owned U.S. Patent App. Serial No. 08/808,497, entitled "An Agricultural Implement Having Multiple Agents For Mapping Fields", filed February 27, 1997 (the content of which is incorporated herein by reference) . Figure 3 is a simplified sectional diagram of the right hand side of spray implement 4 of Figure 2. The outermost spray hood 7 contains one sensor unit 10, whereas each of the remaining inner spray hoods contains three sensor units 10. There are therefore a total of thirty-two sensor units 10 controlled by control circuit 11. In this embodiment, the outermost spray hoods are 14 inches wide, the inner spray hoods are 32 inches wide, and the hoods are spaced on 40 inch centers. Other numbers, sizes, and separations of spray hoods are possible. To further expand spray implement 4, a central control unit (not shown) may be added for controlling multiple control circuits 11, with each control circuit 11 controlling up to thirty- two sensor units 10. Control circuit 11 and sensor units 10 are powered, for example, from a battery 11A attached to the tractor. Electrical power (from battery 11A in this case) is supplied to a first sensor unit 10A via a first length of power conductor in a cable 12. A second sensor unit 10B receives power (from battery 11A in this case) via a second length of power conductor in a second cable 13, which is coupled to the first length of power conductor in cable 12 through sensor unit 10A. Power is supplied to the remaining sensor units via power conductors in cables 14-27 in a daisy-chain fashion, as shown in Figure 3. Each sensor unit 10 controls an associated solenoid-activated spray valve (not shown) for selectively spraying herbicide based on the individual sensor unit detection's. For additional details on a suitable solenoid-activated spray valve, see commonly-owned U.S. Patent App . Serial No. 08/664,600, entitled "High Speed Solenoid Valve Cartridge For Spraying An Agricultural Liquid In A Field", filed June 17, 1996 (the content of which is incorporated herein by reference) . A valve cartridge with a pressure sensor mounted to detect fluid pressure between the solenoid valve and the nozzle can be employed to detect cartridge malfunction . An SCC30G pressure sensor from SenSym of Milpitas, California can be employed.

Figure 4 is a simplified diagram illustrating sensor units 10A and 10B of spray implement 4 of Figure 3. A first length of power conductor 28 of cable 12 is coupled to sensor unit 10A. A second length of power conductor 29 of cable 13 couples sensor unit 10A to sensor unit 10B. The other lengths of power conductors 30 and 31 of cables 12 and 13, respectively, are ground conductors. Connectors 12B, 13A, 13B and 14A are Molex connectors . In one embodiment, the cables 12 and 13 contain five twisted-pairs: one 18 -gauge pair to supply power to the light sources of the sensor units, one for the logic circuitry of the sensor units, one for the solenoid-activated spray valves of the sensor units, and two 22-gauge pairs for signal lines. The twistedpairs for the solenoid-activated spray valves and the signal lines are separately shielded. These shields are coupled to battery ground. In some embodiments, cables 12, 15, 18, 21, 24 and 27 are about nine feet long and cables 13, 14, 16, 17, 19, 20, 22, 23, 25 and 26 are about eighteen inches long.

In Figure 4, sensor unit 10A includes a first light source Al which emits light of a first wavelength (for example, 670 nm) and a second light source A2 which emits light of a second wavelength (for example, 750 nm) , both at a surface 37 of the field. A light detector 32 detects light reflected from light sources Al and A2. Similarly, sensor unit 10B includes a first light source Bl which emits light of the first wavelength, a second light source B2 which emits light of the second wavelength, and a light detector 33. See the following commonly-owned patents and applications (the contents of which are incorporated herein by reference) for additional details on the structure and operation of various suitable sensor units: U.S. Patent No. 5,296,702, entitled "Structure And Method For Differentiating One Object From Another Object"; U.S. Patent App . Serial No. 08/276,002, entitled "Apparatus And Method For Determining A Distance To An Object In A Field For The Controlled Release Of Chemicals On Plants, Weeds, Trees Or Soil And/Or Guidance Of Farm Vehicles", filed July 15, 1994; U.S. Patent App. Serial No. 08/626,857, entitled "Apparatus And Method For Spraying Herbicide On Weeds In A Cotton Field", filed April 3, 1996; U.S. Patent App. Serial No. 08/705,381, entitled "Photodetector Circuit For An Electronic Sprayer", filed August 28, 1996; and U.S. Patent App. Serial No. 08/740,592, entitled "Detecting Plants In A Field By Detecting A Change In Slope In A Reflectance Characteristic", filed October 31, 1996.

In some embodiments, the light sources are Aluminum Gallium Arsenide (AlGaAs) light emitting diodes (LEDs) . One such suitable light source, shown in Figure 5 and labeled Al for illustration purposes, consists of two parallel chains of three diodes 34 connected in series with an npn transistor 35 and a resistor 36. About 400 milliamperes flows through each light source, with about 200 milliamperes flowing through each diode chain when the light source is on. In addition to the current drawn by the light sources, each sensor unit draws about 100 milliamperes for the logic circuitry of the sensor unit and about 60 milliamperes for each solenoid-activated spray valve when open (the solenoid-activated operated spray valve can be considered part of the associated sensor unit) . In the embodiment of Figure 3, sixteen sensor units 10 are coupled downstream of first length of power conductor 28 of cable 12. If all the light sources of the first wavelength in these sixteen sensor units are on at the same time, then over 6 amperes of current would be drawn through power conductor 28 just due to the light sources of the first wavelength. In such a situation, expensive, large and heavy power conductors for carrying such large currents may be necessary to prevent undesirably large voltage drops from developing across the power conductors in cables 12-27. These problems worsen as more sensor units are added to the ends of boom 5. Figure 6 illustrates the operation of spray implement 4 in accordance with one embodiment. The light sources of first sensor unit 10A are energized in a first time period 38 but not in a second time period 39. Similarly, the light sources of second sensor unit 10B are energized in second time period 39 but not in the first time period. In this way, the light sources of a sensor unit are energized a smaller proportion of the time. There can be two classes of sensor units, the light sources of each sensor unit of a class being energized in every other time period. There can be three classes of sensor units, the light sources of each sensor unit of a class being energized in every third time period. There can be four classes of sensor units, the light sources of each sensor unit of a class being energized in every fourth time period, and so forth.

In the example of Figure 6, light source Al of sensor unit 10A (Al emits light of a first wavelength, for example 670 nm) is energized in first time period 38 with a 50/50 duty cycle, 455 kHz drive current. The

-9- SUBST1TUTE SHEET (RULE 26) resulting light is transmitted onto surface 37 of the field and a portion of that light is reflected and detected by detector circuitry 32. The light source Bl of sensor unit 10B that emits light of the first wavelength is not energized in this time period 38. Next, light source A2 (emits light of a second wavelength, for example, 750 nm) of sensor unit 10A is energized with a 50/50 duty cycle, 455 kHz drive current. The resulting light is transmitted onto surface 37 and a portion of that light is reflected and detected by detector circuitry 32. The detector circuitry 32 is tuned to the 455 kHz modulation frequency so that the reflected light from light sources Al and A2 is discriminated from background ambient light. After light from light sources Al and A2 has been detected, the sensor unit 10A determines whether the reflected light is indicative of the spectral characteristic of a plant. This determination can be made in the early part of second time period 39. In time period 39, light sources Bl and B2 of sensor unit 10B are energized and the light sources Al and A2 of sensor unit 10A are not energized. The amount of current flowing through first length of power conductor 28 is reduced because only one of the light sources Al , A2 , Bl and B2 is drawing current at a time.

Figure 7 illustrates the operation of spray implement 4 in accordance with another embodiment . In this embodiment, each sensor unit has four light sources WL1, WL2 , WL3 and WL4 (each light source is a group of LEDs) . There are two classes of sixteen sensor units. The light sources of the first class 41 are energized in the first time period 42 but not in the second time period 43, whereas the light sources of the second class 44 are energized in the second time period 43 but not in the first time period 42. Each light source draws about 400 milliamperes when on. Each light source is on about one sixteenth of the time. About 3.2 amperes of current is drawn across first length of power conductor 28 to power the control logic of the sensor units. Between zero and about 1.9 amperes is drawn across first length of power conductor 28 for the solenoid-activated spray valves, depending on how many of the thirty-two are controlled to be open. The total current supplied across conductor 28 therefore ranges between about 6.4 and 8.3 amperes. Lengths of power conductors can be directly connected together inside sensor units as illustrated in Figure 4, the lengths of power conductor can be indirectly connected via other circuitry including power-conditioning circuitry in the sensor units, and/or the lengths of power conductor can be parts of a single length of power conductor, the sensor units being connected to that single length via individual connections . Embodiments are described wherein only one light source of a sensor unit is on at a time, but other embodiments are possible. For example, two light sources modulated with 50/50 duty cycle drive currents that are phase shifted with respect to one another can be used in accordance with the teachings in U.S. Patent No. 5,296,702. In some time periods, no light sources are on thereby reducing power consumption. The time between successive transmissions of all the light sources of a sensor unit is the time between successive determinations of whether the surface is a plant or soil. Accordingly, the degree to which power consumption is reduced may be a function of the speed that the sensor units are moved over the field and the desired distance between locations on the field where plant/soil determinations are made and a solenoid- activated spray valve can be opened or closed. In one embodiment, time periods 42 and 43 are about 500 microseconds each amounting to a distance of approximately 0.18 inches between plant/soil determinations for tractor 3 moving at approximately 10 mph. In some embodiments a speed detector on tractor 3 is in communication with the sensor units 10 via the signal lines of the cables.

Although the present invention is described in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. For example, applications beyond agricultural spraying should be appreciated, such as automatic hoeing, weed removal along roadsides and rail ways, mapping and vehicle guidance. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.

Claims

CLAIMSWhat is claimed is:

1. An apparatus for detecting plants in a field, comprising: a first length of power conductor; a first sensor unit comprising a light source Al and a first light detector, light LAI emitted from said light source Al reflecting off a first surface area of said field in a first time period and being detected by said first light detector, an amount of electrical energy EA1 being transferred through said first length of power conductor during said first time period to power said light source Al to generate said light LAI; a second length of power conductor; and a second sensor unit comprising a light source Bl and a second light detector, light LB1 emitted from said light source Bl reflecting off a second surface area of said field in a second time period and being detected by said second light detector, an amount of electrical energy EBl being transferred through said first length of power conductor and then through said second length of power conductor during said second time period to power said light source Bl to generate said light LB1, said light source Bl emitting substantially no light during said first time period, said light source Al emitting substantially no light during said second time period.

2. The apparatus of Claim 1, wherein said first sensor unit further comprises a light source A2 , light LA2 emitted from said light source A2 reflecting off said first surface area in said first time period and being detected by said first light detector, an amount of electrical energy EA2 being transferred through said first length of power conductor during said first time period to power said light source A2 to generate said light LA2 ; and wherein said second sensor unit further comprises a light source B2 , light LB2 emitted from said light source B2 reflecting off said second surface area in said second time period and being detected by said second light detector, an amount of electrical energy EB2 being transferred through said first length of power conductor and then through said second length of power conductor during said second time period to power said light source B2 to generate said light LB2.

3. The apparatus of Claim 1, further comprising means for carrying said first and second sensor units over said field such that said first and second sensor units scan strips of said field which are parallel to one another.

4. The apparatus of Claim 3, wherein said means for carrying is a boom, said first sensor unit is fixed to said boom at location separate from a location where said second sensor unit is fixed to said boom, said first length of power conductor being greater than 60 inches in length.

5. The apparatus of Claim 1, wherein said first length of power conductor is greater than 60 inches in length.

6. The apparatus of Claim 5, wherein said second length of power conductor is greater than 12 inches in length.

7. The apparatus of Claim 5, wherein said second length of power conductor is greater than 60 inches in length.

8. The apparatus of Claim 2, wherein each of said light sources Al, A2 , Bl, and B2 comprises a plurality of LEDs, said light LAI and LB1 being substantially monochromatic light of the same first wavelength, said light LA2 and LB2 being substantially monochromatic light of the same second wavelength, said first wavelength being different from said second wavelength.

9. The apparatus of Claim 1, wherein said light source Al comprises a first plurality of LEDs, said first LEDs being turned on and off multiple times during said first time period, said first LEDs drawing a current of at least 100 milliamperes over said first power conductor when said first LEDs are on during said first time period, and wherein said light source Bl comprises a second plurality of LEDs, said second LEDs being turned on and off multiple times during said second time period, said second LEDs drawing a current of at least 100 milliamperes over said first power conductor and said second power conductor when said second LEDs are on during said second time period.

10. The apparatus of Claim 1, wherein said first length and said second length of power conductor are parts of the same single length of power conductor.

11. The apparatus of Claim 1, wherein said first length of power conductor is coupled to said first sensor unit, and wherein said second length of power conductor is coupled to said first sensor unit and said second sensor unit, the first and second lengths of power conductors not being parts of the same single length of power conductor.

12. The apparatus of Claim 1, wherein only one of said light sources Al and Bl emits light during said first time period.

13. The apparatus of Claim 2, wherein said light sources Al and A2 emit light at different times in said first period, and wherein said light sources Bl and B2 emit light at different times in said second period.

14. The apparatus of Claim 2, wherein said light sources Al and A2 emit light simultaneously during said first time period, and wherein said light sources Bl and B2 emit light simultaneously during said second time period.

15. An apparatus for detecting plants in a field, comprising: a power conductor; a plurality of substantially monochromatic light sources A, B and C; means for powering said substantially monochromatic light sources sequentially from said power conductor such that only one of said substantially monochromatic light sources draws current from said power conductor at a time; and means for detecting plants by detecting light from said substantially monochromatic light sources A, B and C that has reflected off plants in said field.

16. The apparatus of Claim 15, wherein said substantially monochromatic light sources A, B and C all emit light of substantially the same wavelength.

17. The apparatus of Claim 15, further comprising three solenoid-activated spray valves coupled to said means for detecting.

18. The apparatus of Claim 15, wherein said power conductor extends from said light source A to said light source B, and from said light source B to said light source C.

19. An apparatus for detecting plants in a field, comprising:

N sensor units;

N sets of M light sources, each set contained within one of said N sensor units, some of said N sensor units not transmitting light during a time period when another of said N sensor units is transmitting light, said time period being at least 200 microseconds in duration; a power conductor coupling each of said N*M light sources to a power source; and means for detecting plants in said field by comparing light from said light sources of said N sensor units that has reflected off said plants in said field.

20. The apparatus of Claim 19, wherein N is a number greater than 4.

21. The apparatus of Claim 20, wherein each of said N sensor units is of one of K classes of sensor units.

22. The apparatus of Claim 21, wherein each of said N sensor units emits light only during one period of every K periods of time.

23. The apparatus of Claim 22, wherein each of said M light sources within each of said N sensor units- emits light at a different time during one of said K periods of time.

24. The apparatus of Claim 22, wherein said light sources of said another sensor unit are modulated on and off in said time period with 50/50 duty cycle drive currents .

25. The apparatus of Claim 19, wherein said N sensor units are spaced at least 12 inches apart from one another.

26. The apparatus of Claim 25, wherein N is a number greater than 8.

27. A method, comprising: in a first time period, transferring a first amount of energy over a first length of conductor to a first sensing device A, said first sensing device A converting a portion of said first amount of energy into substantially monochromatic light LI, said substantially monochromatic light LI being transmitted onto a first surface area of a field; in a second time period, transferring a second amount of energy over said first length of conductor and then over a second length of conductor to a second sensing device B, said second sensing device B converting a portion of said second amount of energy into substantially monochromatic light L2 , said substantially monochromatic light L2 being transmitted onto a second surface area of said field, said first sensing device A receiving at least twice as much energy in said first time period from said first length of conductor than said second sensing unit B receives from said second length of conductor in said first time period, said second sensing device B receiving at least twice as much energy from said second length of conductor in said second time period than said first sensing device A receives from said first length of conductor during said second time period; and moving said first sensing device A and said second sensing device B with respect to said field such that the first and second surface areas scan parallel paths across said field.

28. The method of Claim 27, wherein said first sensing device outputs light less than one eighth of the time, and wherein said second sensing device outputs light less than one eighth of the time.

29. The method of Claim 27, wherein said first length of power conductor is greater than 12 inches in length, and wherein second length of power conductor is greater than 12 inches in length.