Abstract:
A system and method for determining material yield and/or loss from a harvesting machine using acoustic sensors and advanced signal processing capabilities is presented. The system consists of a sensor housing with an opening on one side of the sensor housing, a strike plate designed to fit into the opening, and an electronics module comprising a microphone and a signal processor designed to capture the sound waves created when material impacts on the strike plate, and convert them into an audio signal indicating the amount of material impacting the sensor at a given time.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority in U.S. Patent Application Ser. No. 61/560,201, filed Nov. 15, 2011, and is related to U.S. patent application Ser. No. 13/046,549 entitled Air Seeder Monitoring and Equalization System Using Acoustic Sensors, filed Mar. 11, 2011, which are both incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the invention 
     The present invention relates generally to a system for detecting the amount of crop material present in an agricultural machine, and more particularly to a system using one or more acoustic sensors which can be used for detecting the amount of crop lost from a harvester, as well as the amount of crop yielded by the harvester. 
     2. Description of the Related Art 
     An agricultural combine, also referred to as a harvester, is a vehicle used to gather a crop from a field once the crop has reached maturity. The combine is driven through a field, and the plants (crop) in that field are pulled into an attachment called a header on the front of the machine. As the plants are pulled into the header, they are cut and fed into a threshing unit internal to the combine. In general terms, the threshing unit forces the cut plants to be rubbed between a rotating drum, or rotor, and a concave surface in order to separate the nutrient component (such as grain) from the remainder of the plant (the chaff). Most of the separated grain falls below the drum to a set of sieves, and then through the sieves where it is collected and transported via an elevator to a grain tank. The chaff material is passed over a series of conveyors called “straw walkers” which move the chaff toward the back of the machine. Air is blown through the sieves and the straw walkers, and the chaff is blown up off of the straw walkers and out the back of the combine. Some additional grain that remains in the chaff as it moves over the straw walkers, being heavier than the chaff and less susceptible to the blowing air, will fall through into the sieves to be collected in the grain tank. 
     The settings on the combine, and in particular the settings of the sieves in the combine, can, if not properly adjusted, cause amounts of grain to be lost out the back of the combine along with the chaff, resulting in lower crop yields. In addition, factors such as the speed of the combine through the field, ambient environmental conditions, crop moisture content, and crop type can affect the amount of crop that is lost during the harvesting process. In order to know how to adjust the combine settings properly, the operator needs to have an indication of how much crop is being lost at any given moment. This information is typically gathered through the use of a grain loss sensor, which is capable of detecting when crop material is being lost out the back of the combine, and can distinguish crop material from waste material (such as chaff). 
     A typical grain loss sensor utilizes a piezoelectric pad or membrane, typically located at the back of the sieves where material is falling or being blown out of the combine. Although both grain material and chaff material are ejected from the back of the combine, the grain is generally heavier and falls closer to the back of the machine, while the lighter chaff is blown farther away. The piezoelectric pad is placed close to the back of the machine, pad facing up, such that falling crop or kernels of grain, rather than chaff, will strike the pad. When the kernels impact the sensor, the deformation of the piezoelectric pad generates a measurable voltage due to piezoelectric effect, which electrical signals can be detected and interpreted as the presence of lost crop material. 
     Piezoelectric grain loss sensors suffer from several disadvantages. Since a portion of the piezoelectric pad has to be deformed by the grain strikes in order to be detected, the piezoelectric material must cover the entire surface where detection is required. However, to cover the entire width of the back of a combine, a very large piezoelectric pad would be required to cover the span and depth of the area. This would result in a very expensive sensor. Instead, combine manufacturers typically install two or three smaller sensors in key areas at the rear of the vehicle where the heaviest flow of material is expected. As a combine moves and tilts while operating on a sloping surface, the sensors often move out of these expected material flow zones, and the grain loss rates measured are artificially low. 
     Also, since a direct strike is required, the piezoelectric material itself must be exposed to the elements, and is exposed not only to being struck by grain, rocks, and other material, but also to the direct sun, precipitation, dust, and extremes in temperature. As a result, the sensors must frequently be cleaned, repaired, and replaced. 
     Existing piezoelectric sensors have a very limited ability to distinguish between types of material hitting their surfaces. Most of these prior art sensors will count a pebble or rock hit as a grain hit. This also limits the ability of the piezoelectric sensors to provide accurate loss rates. 
     The ideal technology for implementing a grain loss sensor would be flexible enough so that it could be adapted for use as a yield sensor in the same combine. A yield sensor is used to measure the amount of material that is harvested and successfully captured in the grain tank. This information is best captured in real-time, as an amount of material or flow rate, so that yield mapping applications can be implemented. A yield-mapping application combines information on the instantaneous flow rate of material with location information (such as that from a GNSS system such as GPS) to create a map showing amount of material (yield) mapped to specific locations in the field. The yield map can then be used by the farmer or operator to determine where and in what amounts to apply chemicals (such as fertilizers, pesticides, etc.) to boost the overall output of the field. 
     Unfortunately, a piezoelectric sensor is not well suited for measuring yield. The piezoelectric sensor could be placed at the top of the clean grain elevator, where grain is delivered (typically by chain-driven paddles moving up an enclosed elevator shaft). However, the amounts of material hitting the piezoelectric sensor would quickly overwhelm the sensitivity capabilities of the sensor, and the constant pummeling of material against the pad would likely damage or wear out the sensor quickly. Some combines use mechanical means for sensing yield, such as causing a flap to be pushed open to varying degrees by the material flowing into the grain tank based on the amount of material present. These mechanical sensing means for yield are inaccurate and subject to breakdown. 
     What is needed in the art is a new type of material sensing technology which can overcome the limitations described above associated with piezoelectric sensors, yet which is flexible enough to allow it to be adapted for use in yield sensing. 
     SUMMARY OF THE INVENTION 
     In accordance with the teachings of the present invention, a system and method for determining material yield and/or loss from a harvesting machine using acoustic sensors and advanced signal processing capabilities is disclosed. 
     In one aspect of the invention, a material loss sensor is disclosed, comprising a sensor housing with a first opening on a first side of the sensor housing, a strike plate designed to fit into the first opening on the first side of the sensor housing, and an electronics module comprising a microphone and a signal processor wherein the strike plate forms an environmental seal against the sensor housing, the electronics module extends at least partially into the sensor housing, the microphone is capable of detecting sound waves generated by the impact of particles on an exterior surface of the strike plate, the microphone converts the sound waves into a raw data signal and sends the raw data signal to the signal processor, and the signal processor processes the raw data signal and determines which portions of raw data signal correspond to the particle impacts and converts this information into an amount of material impacting the strike plate. 
     In another aspect of the invention, a material yield sensor comprising a sensor housing with a first opening on a first side of the sensor housing, a strike plate designed to fit into the first opening on the first side of the sensor housing, and an electronics module comprising a microphone and a signal processor wherein the strike plate forms an environmental seal against the sensor housing, the electronics module extends at least partially into the sensor housing, the microphone is capable of detecting sound waves generated by the impact of particles on an exterior surface of the strike plate, the microphone converts the sound waves into a raw data signal and sends the raw data signal to the signal processor, and the signal processor processes the raw data signal and determines the amount of sound power represented by the raw data signal and converts this information into a relative amount of material impacting the strike plate. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows an exploded isometric view of one embodiment of an acoustic grain loss sensor. 
         FIG. 2  shows a non-exploded isometric view of one embodiment of an acoustic grain loss sensor. 
         FIG. 3  shows a front view of one embodiment of an acoustic grain loss sensor. 
         FIG. 4  shows a side view of a combine, showing the main internal components and one possible mounting location for an acoustic grain loss sensor. 
         FIG. 5  shows a close up view of the ends of the straw walkers in a combine in relation to an acoustic grain loss sensor, showing how grain and chaff material may strike the sensor. 
         FIG. 6A  shows a flowchart for a simplified version of one embodiment of an algorithm that may be used to process the acoustic signals detected by an acoustic grain loss sensor. 
         FIG. 6B  shows a flowchart for a more complex version of one embodiment of an algorithm that may be used to process the acoustic signals detected by an acoustic grain loss sensor. 
         FIG. 7  shows an alternate embodiment of the acoustic sensor being used as a yield sensor, to detect the amount of grain entering the grain tank on the combine. 
         FIG. 8  is a simplified block diagram of one possible embodiment of an electronics module for use in an acoustic sensor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference now to the drawings, and in particular to  FIGS. 1 through 8  thereof, a new acoustic-based material sensing system embodying the principles and concepts of the present invention will be described. 
       FIG. 1  shows an isometric view of one embodiment of an acoustic grain loss sensor  100 .  FIG. 1  is shown as an exploded view to better illustrate the construction of the grain loss sensor, as one distinct advantage of this sensor over prior art grain loss sensors is the simplicity and ruggedness of its construction. 
     In the embodiment of the acoustic grain loss sensor  100  shown in  FIG. 1 , a sensor case  110  forms an acoustic cavity through which sound waves can travel. The sensor case  110  is created such that it has small channels  110   a  on either side of its top surface such that a sensor strike plate  120  can be slid into place and held securely in channels  110   a . Two sensor end caps  130  are placed at either end of the sensor case  110 , completing the housing assembly and holding the sensor strike plate  120  in place. Finally, an electronics module  140 , containing a microphone and other electronic components (detailed in later figures) is mounted into an opening in the bottom of the sensor case  110  such that the acoustic grain loss sensor  100  is environmentally sealed and such that the microphone extends up into the sensor case  110 . 
       FIG. 2  shows an alternate non-exploded isometric view of the same embodiment of the acoustic grain loss sensor  100  illustrated in  FIG. 1 , and is provided to show how this embodiment of the acoustic grain loss sensor  100  may appear when fully assembled.  FIG. 3  shows a front view of this same embodiment. 
     The following discussion refers collectively to  FIGS. 1, 2, and 3 . The general concept behind the acoustic grain loss sensor  100  as shown in  FIGS. 1, 2, and 3  is as follows. The acoustic grain loss sensor  100  is mounted on a combine or other agricultural vehicle such that it is located directly in the path of a flow of material. For the grain loss sensor application discussed here, that flow of material is the grain and chaff material that is falling or being blown out of the back of a combine. The acoustic grain loss sensor  100  is mounted such that the sensor strike plate  120  will be directly impacted by the material that is flowing. The impact of the grain (or other material) on the sensor strike plate  120  will generate a ringing sound pattern which will reverberate through the sensor case  110 . The design of the sensor case  110  and the sensor end caps  130  are such that the sound waves generated by the impact on the sensor strike plate  120  will be guided toward the electronics module  140 , where they will be picked up by the microphone and processed by the electronics present on the module (as discussed and illustrated in later figures). 
     In one embodiment, the sides  130   a  of the sensor end caps  130  are designed to be slanted, so that they will not reflect sound waves directly back toward the opposite side  130   a . Sensor end caps  130  with perpendicular and parallel sides  130   a  will likely cause sound waves to bounce back and forth, creating and propagating a standing wave which would cause erroneous readings leading to misidentification of the material hitting the sensor strike plate  120 . 
     The technical design of the acoustic grain loss sensor  100  is crucial to its performance. The materials used for the sensor strike plate  120 , sensor case  110 , and sensor end caps  130 , as well as the internal and external geometry of these components, will determine the frequency and wavelength of the sound waves created inside the sensor  100  by an impact on the strike plate  120 . The choice of materials can be made in order to “tune” the frequency of the sound waves being detected by the electronics module  140 . Ideally, the acoustic grain loss sensor  100  design will be used to tune the range of frequencies detected by various kinds of impacts on the strike plate  120  such that the frequencies can be easily isolated from the background noise of the combine and the environment. 
     One preferred material used for the sensor strike plate  120  is a sheet of stainless steel. This material stands up well to the environmental challenges inherent in a combine (dust, humidity, rocks, etc.) and passes sounds well into the acoustic grain loss sensor  100 . The thickness of the strike plate  120  can be controlled to change the frequency characteristics of the sounds waves generated. Of course, any appropriate material which can absorb impacts and survive the environment can be used for the sensor strike plate  120 . 
     The sensor case  110  may be constructed from a flat sheet of metal, or may be molded or cast into its final shape. In one alternate embodiment, if the sensor case  110  is molded from a plastic material, it would be possible to also directly mold the end caps  130  into the case  110 , such that both case  110  and end caps  130  are combined into a solid piece. 
     The materials selected for the sensor case  110  and sensor end caps  130  will be such that the desired frequency response range is generated. Any appropriate material may be used to achieve this response range. One skilled in the art will recognize that various form factors and geometries can be used to modify the performance of the acoustic grain loss sensor  100 , with the critical factor being how the sound waves are directed into the electronics module  140 . 
     In one embodiment of the acoustic grain loss sensor  100 , a gasket or sealant material would be used between the sensor strike plate  120 , sensor end caps  130 , electronics module  140 , and the sensor case  110 , such that an airtight seal is created. This airtight seal would limit the amount of “noise” generated by the movement of air (caused by the environment or moving equipment) throughout the sensor  100 . 
       FIG. 4  shows a side view of a combine, showing the main internal components and one possible mounting location for the acoustic grain loss sensor  100  of  FIGS. 1, 2, and 3 . A typical combine  200  drives through a field in order to harvest the crop. As the combine  200  moves through the crop, the crop is pulled into the header  210  which cuts the crop and pulls it up inside the combine  200 . Once past the header  210 , the crop is pulled further into the combine  200  by a belt or auger  220 . The crop passes between a rotor  230  and a concave  235 , where the grain is separated from the rest of the plant by a rubbing or friction between the rotor  230  and concave  235 . Most of the grain falls through openings in the concave  235  and lands on sieves  250 , which act as filters to further separate additional non-grain material (chaff) from the grain before the grain drops through the sieves  250  and is collected by augers  220  which transport it to a grain tank (not shown in  FIG. 4 , but shown in later figures). Most of the non-grain material (chaff) that comes out of the concave  235  is thrown up on the straw walkers  240 , which are a series of separately moving conveyors which move in a cyclic pattern and which move the chaff toward the back of the combine  200 . Air is blown up through the sieves  250  and straw walkers  240  in order to blow the lighter chaff up and toward the back of the combine  200  while the heavier grain particles fall through the straw walkers  240  and sieves  250  to be collected for transport to a clean grain tank. 
     In the embodiment shown in  FIG. 4 , the acoustic grain loss sensor  100  is mounted behind the straw walkers  240 , such that any grain that is being lost out the back of the combine  200  (instead of falling through the walkers  240  and sieves  250 ) will impact the sensor and be detected. More than one acoustic grain loss sensor  100  may be mounted on the combine  200  in other locations where grain is being lost. Alternately, the size of the acoustic grain loss sensor  100  may vary. One longer sensor  100  may be used to cover the entire width of the back of the combine  200 , or two or more sensors  100  may be used to each cover a portion of the distance. In one embodiment, each straw walker  240  could have its own acoustic grain loss sensor  100  mounted directly to it, such that the sensor  100  moves back and forth in a reciprocating path along with its corresponding straw walker  240 , to maximize the amount of grain loss it sees. 
       FIG. 5  shows a close up view of the ends of the straw walkers  240  in the combine  200  in relation to an acoustic grain loss sensor  100 , showing how material may strike the sensor. Since chaff  315  is lighter than grain  310 , most of the chaff  315  is blown off of the straw walker  240  such that it falls beyond the acoustic grain loss sensor  100 . The heavier grain  300 , however, falls closer to the ends of the straw walkers  240 , and thus mostly impacts the sensor strike plate  120  of the acoustic grain loss sensor  100 . It is likely that some grain  310  will fall beyond the sensor  100 , and some chaff  315  will fall on the sensor  100 , so it may be important for the sensor to be able to distinguish between the impact of a lighter material and that of a heavier one. 
       FIG. 6A  shows a flowchart for a simplified version of one embodiment of an algorithm that may be used to process the acoustic signals detected by an acoustic grain loss sensor. A raw signal  400  is created when the microphone on the electronics module  140  detects the sound waves created by impacts on the acoustic grain loss sensor  100 . This raw signal  400  is likely characterized by a lot of noise that makes the signal  400  difficult to process. Therefore, the raw signal  400  is first passed through a band pass filter  405  to remove some of the noise that does not fit a particular frequency range (as determined by the design of the acoustic grain loss sensor  100 ). The result is a filtered signal  400   a  that is much cleaner but which still does not clearly show grain impacts from chaff impacts and other ambient noise. The filtered signal  400   a  is then run through an acoustic energy measurement process  410 , during which each point on the filtered signal  400   a  is squared to create its absolute value and the filtered signal  400   a  is further processed to create signal  400   b , which contains distinguishable “hills” representing impact energies (that is, representing individual impacts of some kind on the sensor strike plate  120 ). 
     In step  415 , an acoustic event detection is performed by determining which of the hills in the  400   b  signal rise above a predetermined threshold  412 , which indicates that those locations represent peaks  400   c  which can be associated with impacts that were very likely caused by grain. Those hills in  400   b  which fall below the threshold  412  are likely caused by impacts related to chaff. 
     Finally, a multiple impact detection step  420  is performed, which further processes the peaks  400   c  to determine if they rise above a second predetermined threshold  422 . Those peaks  400   c  which rise above threshold  422  are likely caused by the impacts of two or more grains striking at the same time (increasing the sound noise generated over a single strike). These multiple grain impacts can be taken into account when determining the amount of grain loss. 
       FIG. 6B  shows a flowchart for a more complex version of the algorithm from  FIG. 6A . In parallel with steps  405 ,  410 ,  415 , and  420  (as shown on  FIG. 6A ), additional steps are added to better identify the source of the impact signals. Information based on the time domain features  425  (such as the zero crossing rate of the raw data signal  400 ) is combined with information based on the frequency domain features  430  (such as the short term fast Fourier transform of the variance of the raw data signal  400 ) and the acoustic event detection process  415 . This information is fed into a neural network  435  which uses this information, along with stored information related to impact profiles for various grain types, chaff types, and MOG (material other than grain) types, to determine if the impact was caused by a seed or something other than a seed. Although the steps provided in  FIG. 6A  are likely adequate to provide a reasonable grain loss measure, these additional steps can provide more detailed information. 
     It should be noted that the steps shown in  FIGS. 6A and 6B  are not meant to be limiting in any way, and that various other steps could be added or substituted for the steps shown in these figures. These figures are meant to be indicative of the types of processing that can be done by an acoustic grain loss sensor. 
       FIG. 7  shows an alternate embodiment of the acoustic sensor being used as a yield sensor, to detect the amount of grain  310  entering the grain tank on the combine  200 .  FIG. 7  shows an interior view of the clean grain elevator in a combine. Paddles  500  mounted on a chain drive  510  move grain particles  310  up into a grain elevator. The paddles  500  eject the grain particles  310  at the top of their travel, and the grain particles  310  fly into an entry way for a grain holding tank. An acoustic yield sensor  100   a  is mounted in the entry way such that the grain particles  310  impact the yield sensor&#39;s strike plate  120   a  before being deflected down into the grain holding tank. The impact of the particles  310  on the strike plate  120   a  creates sound waves in the sensor  100   a  which are detected and processed by the electronics module  140   a.    
     The physical construction of the acoustic yield sensor  100   a  is almost identical to that of the acoustic grain loss sensor  100  of earlier figures, except that it is configured to fit in the grain holding tank entry way and designed acoustically to be optimized for this application. However, the main components shown in  FIGS. 1, 2, and 3  for the acoustic grain loss sensor  100  should have their counterparts in the design of the acoustic yield sensor  100   a.    
     The processing required for the acoustic yield sensor  100   a , however, will likely be different than that required for the acoustic grain loss sensor  100 . For the acoustic grain loss sensor  100 , the goal was to isolate individual impacts and to determine if they matched a certain profile (to see if they were grain or MOG). This required processing the signals in the time domain for the grain loss sensor  100 . For the acoustic yield sensor  100   a , the material is nearly  100  percent pure grain and impacting the yield sensor  100   a  at a significantly higher rate, which is an almost continuous flow of material. The processing for the yield sensor  100   a  signals, therefore, is best done in the frequency domain, and the incoming data will represent the “sound power” of the impact. This approach is similar to that taken by the inventors in the related U.S. patent application Ser. No. 13/046,549, entitled “Air Seeder Monitoring and Equalization System Using Acoustic Sensors” by Gelinske et al. This application is therefore included herein in its entirety by reference. 
       FIG. 8  is a simplified block diagram of one possible embodiment of an electronics module  140  for use in an acoustic sensor. A key component in the electronics module  140  is the MEMS (micro-electro-mechanical system) microphone  605 , which is mounted on a printed circuit board (PCB) within the electronics module  140 . The microphone  605  picks up sound created by the impacts of particles on the sensor strike plate  120 . A general processor  620  is provided to handle routine tasks within the electronics module  140 , such as executing the operating system tasks required to run the system. A special audio processor  625  is provided specifically for processing the audio signals received by the acoustic sensor (either  100  or  100   a , or any alternate version thereof). In the preferred embodiment, the audio processor  625  is a high-end audio frequency processor, ideally suited for processing the frequency-based audio data captured from the acoustic sensors  100 / 100   a.    
     A communications module  630  is responsible for sending messages to and receiving messages from other parts of the combine, such as a display in the combine cab. These messages could be in any appropriate format, but are likely sent in an industry standard protocol such as CAN (Controller Area Network). 
     A power supply circuit  610  processes and filters the power input to the module  140 , and steps the voltages up or down for subcircuits as necessary. An input/output processing circuit  615  is responsible for handling any inputs  642  that may come into the module  140  or outputs  644  that may be sent by the module  140 . These inputs  642  and outputs  644  may be any number of items, including signals from external systems including power inputs. The inputs  642  and outputs  644  are routed into the electronics module  140  through one or more connectors  640 . 
     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims. In particular, the components of the present invention, described herein and in the accompanying drawings, may be used in different configurations and combinations than described in the examples described above.