Abstract:
A detector for detecting cargo in a container has a controller block, a transmitter for transmitting light into the field of view, a receiver for receiving reflected light, and a threshold comparator for determining whether the received light meets a threshold for cargo detection. The receiver includes a DC block for removing effects of ambient light. The detector performs detection multiple times and averages the results, which can be compared with a previously stored condition of cargo presence or absence to increase the detection accuracy further.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a system and method for detection of cargo and more particularly to such a system and method which can detect pallet-sized objects at a distance without being affected by ambient light such as sunlight. 
     DESCRIPTION OF RELATED ART 
     Reliable and inexpensive detection of pallet-sized objects within a defined area is a capability which has long been desired by the transportation and shipping industries. Those companies keep trailers/containers at secure lots, truck stops, customer facilities, and other designated areas depending upon need, convenience, and cost. In most cases, loading and unloading those containers is the responsibility of the customer; as a consequence, the shipper often does not know when their containers are ready for pickup. Knowing when their containers are loaded or unloaded allows the shipping companies to reduce their operating costs by using their containers more efficiently and enables them to identify and charge customers who do not promptly empty received containers but rather use them as storage facilities. 
     Previously disclosed object detectors use one of five techniques: ultrasonic detection, microwave detection, image detection, coherent light detection and non-coherent light detection. 
     Ultrasonic detectors emit pulses of high-frequency sound waves and then listen for the sound energy to be reflected back from nearby objects. In open area deployments, any reflected sound energy would signal the presence of an object. However, in confined space deployments such as a cargo container, sound energy will always be reflected back to the detector by the walls, floor and ceiling of the container. In that case, it is necessary for the detector to distinguish between those ever present reflections and reflections from additional objects in the container. Classification of the different reflections may be done by measuring the amplitude and/or time delay of the reflection in order to obtain distance information for the source of the reflection. 
     Microwave detectors emit microwave frequency electromagnetic energy and then similarly listen for the microwave energy to be reflected back to the detector. In enclosed spaces, those detectors use the amplitude of the reflected energy to detect the presence or movement of objects. 
     Image detectors use a digital camera or other suitable imaging device to capture an image of the inside of the container. That image is then digitally processed by software algorithms to determine if there are objects present in the image other than the components of an empty container. That detection method usually requires each detector to be trained to recognize the empty state of the container it is monitoring. 
     Coherent light detectors come in two different implementations. The first emits a beam of laser light (usually red or infrared) and watches for the light energy to be reflected back from an object. As with the acoustic detectors, the detector must be able to distinguish between light reflected from an object and light reflected from the inside of the container. Again, that determination can be made by measuring the amplitude or the time delay of the reflection in order to obtain distance information for the source of the reflection. The second implementation emits a beam of laser light towards a remotely located receiver. With that setup, detection of the light beam by the receiver indicates the absence of an object. If an object is present, it blocks the light beam, making its presence known to the receiver. 
     Non-coherent light detectors operate very similarly to coherent light detectors except that the light source is not coherent, i.e. it is not a laser. 
     However, the known techniques have the following drawbacks. For ultrasonic and microwave detectors, the need to eliminate readings from spurious reflections increases computational complexity and thus power draw. For image detectors, the training of each detector and the image processing increase complexity, cost, and power draw. For light detectors, either coherent or incoherent, the level of ambient light can effect the accuracy of detection. Also, when the detected signal is at or near a threshold, accurate detection can be difficult. For those reasons, light detection has not previously been used to detect the presence of cargo in a confined area. 
     SUMMARY OF THE INVENTION 
     There is thus a need in the art for a technique for cargo detection in a container which overcomes the above drawbacks. 
     It is therefore an object of the invention to provide a cargo detector with a low power draw. 
     It is another object of the invention to provide a cargo detector which is computationally simple. 
     It is still another object of the invention to provide a cargo detector which is not affected by spurious reflections. 
     It is still another object of the invention to provide a cargo detector which is not affected by ambient light levels. 
     It is still another object of the invention to provide a cargo detector which can accurately detect cargo even when the detection signal is at or near a threshold. 
     To achieve the above and other objects, the present invention is directed to a detector and method for detection of objects at relatively large distances and preferably for detection of pallet-sized objects (cargo) at distances of up to 40 feet. A preferred embodiment operates on the non-coherent light detection principle, in which it emits non-coherent light while watching for the light energy to be reflected back from an object within its field of view. The presence or absence of cargo is then determined based on the amplitude of the reflected light. The principles of operation are equally applicable to coherent light detection. The detector includes a DC block to remove the ambient light response. 
     The detector measures the reflected light power several times and averages the readings to reduce measurement noise. It can then compare the result of detection to the currently stored cargo state (empty or not empty) to determine whether it needs to take more measurements for greater accuracy. 
     The concept of using reflected light to detect the presence of an object is not by itself novel. However, the adaptation of such technology to detecting the presence of cargo within a confined area is new. The preferred embodiment can reliably detect objects at distances of 0-30 feet at a minimum and preferably up to 40 feet. Furthermore, the detector according to the preferred embodiment consumes very little current in order to maximize battery life. The present embodiment typically consumes 60 mAh/year when connected to a GlobalWave MT2000 transceiver and depending on the installation can detect objects over 40 feet away. 
     A reliable optical cargo detector has been invented. The detector is unaffected by ambient light including direct sunlight, can detect pallet sized objects up to 40 feet away within the confines of a 53 foot container and typically consumes only 60 mAh/year when connected to a GlobalWave MT2000 Transceiver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment will be set forth in detail with reference to the drawings, in which: 
         FIG. 1  is a block diagram of the detector according to the preferred embodiment; 
         FIG. 2  is a block diagram of the transmitter of the detector of  FIG. 1 ; 
         FIG. 3  is a block diagram of the receiver of the detector of  FIG. 1 ; 
         FIG. 4  is a flow chart of a single detection algorithm performed by the detector of  FIG. 1 ; and 
         FIG. 5  is a flow chart of a cargo state detection algorithm for improving the accuracy of the algorithm of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment will be set forth in detail with reference to the drawings, in which like reference numerals refer to like elements throughout. 
       FIG. 1  is a block diagram of the preferred embodiment of the invention. As shown in  FIG. 1 , the detector  100  includes a controller block  102  which enables and disables a transmitter block  104  and receiver block  106  as required and reads a detection result from a threshold comparator  108 . The transmitter block  104  emits electromagnetic radiation E into an area in which cargo is to be detected (that is, the field of view of the detector  100 ). The receiver block  106  detects the reflected electromagnetic radiation R. The temperature compensating threshold comparator  108  discriminates over temperature between background reflections and those from an object placed within the field of view of the detector  100 . All components of the detector  100  are powered by a power source such as a battery  110 . 
     In the preferred embodiment, the controller  102  includes a microprocessor  112  with a built-in temperature sensor and analog-to-digital converter. Those capabilities allow the threshold comparator  108  to be incorporated into the controller block  102  by measuring the received power with the analog-to-digital converter and performing the temperature compensation and threshold comparison in software. Also included in the preferred embodiment is a pair of lenses, a first lens  114  to focus the light output from the transmitter  104  and a second lens  116  to concentrate the reflected light energy into the receiver  106 . Those lenses serve to increase the range of the detector  100  and are therefore optional, depending on the desired field of view. 
       FIG. 2  shows a detailed block diagram of the transmitter  104 . The transmitter  104  includes a modulation source  202  used to modulate the light intensity emitted by the detector  100 , a driver block  204  to power the light source and an LED  206  to transform the electrical output of the driver into non-coherent light E. For the coherent light option, the LED would be replaced with a laser diode. 
       FIG. 3  shows a detailed block diagram of the receiver  106 . The receiver  106  includes a photodetector (photodiode)  302  for detecting the reflected light R, an amplifier block  304  to amplify the output of the photodiode, a DC block  306  to remove the ambient light response, and a power detector  308  to further amplify the signal and to measure the amplitude of the reflected light response. In the block diagram, the DC block  306  is shown after the amplifier for simplicity. In the preferred embodiment, the DC block  306  is actually incorporated into the amplifier block  304  to improve the performance of the amplifier block  304 . 
       FIG. 4  shows the algorithm used to perform a single detection. The algorithm starts in step  402  by turning on the transmitter and receiver. In step  404 , the averaging count is initialized. After a short delay in step  406 , the algorithm measures the reflected light power in step  408  and increments the averaging count in step  410 . The algorithm performs steps  406 ,  408  and  410  a number of times (e.g., 8). Once it is determined in step  412  that the number of times has been reached, the algorithm turns off the transmitter and receiver in step  414 . The readings are averaged in step  416  to reduce the measurement noise and then adjusted in step  418  to compensate for temperature. Finally, the adjusted result is compared to the detection threshold in step  420  to determine whether an object is detected, as in step  422 , or not detected, as in step  424 . 
     The algorithm of  FIG. 4  has no built-in hysteresis, so that an object at the limit of detection can cause the algorithm to randomly toggle between detection and non-detection of an object. To solve that particular problem in a cargo sensing application, the algorithm of  FIG. 5  is used. 
     The algorithm of  FIG. 5  starts by performing the single detection algorithm of  FIG. 4  in step  502 . If it is determined in step  504  that the result of the single detection algorithm is the same as the currently stored cargo state (empty or not empty), the cargo state is left unchanged, and the algorithm terminates in step  506 . However, if it is determined in step  504  that the result of the single detection algorithm is not the same as the currently stored cargo state (i.e. the state appears to have changed), the algorithm then verifies the state change by taking up to N additional single detection measurements. More specifically, a count is initialized in step  508 . After a delay in step  510 , the algorithm performs a single detection in step  512 , using the algorithm of  FIG. 4 . If it is determined in step  514  that the state has not changed, the state is left unchanged, and the algorithm terminates in step  516 . If it is determined in step  514  that the state has changed, the count is incremented in step  518 . Steps  510 ,  512 ,  514  and  518  are repeated until either step  516  is reached or it is determined in step  520  that the count has reached a predetermined maximum value. In the latter situation, it is determined that all of the follow-up measurements agree with the first measurement, and the cargo state is officially changed in step  522 . If any of the follow-up measurements disagrees with the first measurement, the cargo state is left unchanged, and, as noted above, the algorithm immediately terminates in step  516 . 
     While a preferred embodiment of the present invention has been set forth in detail above, those skilled in the art who have reviewed the present disclosure will readily appreciate that other embodiments can be realized within the scope of the present invention. For example, numerical values are illustrative rather than limiting. Also, as noted above, the detector can use either coherent or incoherent light; those skilled in the art will understand how to implement either. Moreover, components shown as discrete can be consolidated, while a component having multiple functions can be implemented as multiple discrete components. The same is true with method steps. Furthermore, the invention can be implemented to use transmissive rather than reflective detection. Therefore, the present invention should be construed as limited only by the appended claims.