Abstract:
A triple-sensor motion detector is provided for illuminating the approach to a display case or other object. The triple-sensor motion detector provides a field of detection that spans the front width of the case, yet does not include the areas along the sides of the case. The detector reduces inadvertent triggering of the illumination by persons approaching the side of the case or approaching another case on the other side of an aisle.

Description:
BACKGROUND INFORMATION 
     1. Field of the Invention 
     The invention relates to a motion detection system for display cases. 
     2. Description of the Prior Art 
     Passive infrared (PIR) detectors are often used to trigger illumination. Retail stores, particularly grocery stores, store goods in cases. Some of the upright refrigerated cases have doors on them, others are chest-type refrigerated cases, which are open and readily accessible from above. Often, these cases are constantly illuminated, to better display the goods stored within. For reasons of economy, store owners or operators now frequently desire to keep the illumination turned off, except when a customer approaches the case. There are several known motion detection devices that use PIR motion sensors to control the illumination of display cases. One uses a single PIR motion detector sensor  1  placed centrally on the front face of the case. See  FIG. 1 . The field of detection or field of view fans out in a cone shape from the sensor and leaves large areas toward the side edges of the case uncovered by the field of view, as shown by the polar plot. The polar plot indicates the sensitivity of the detector, on a scale of 1 to 10, 10 indicating maximum sensitivity. The large areas uncovered by the field of view are null areas N and are less than 5 on the sensitivity scale. The device also detects motion that is too far away from the case, because the greatest sensitivity is in a normal direction to the case. The field of detection is limited to 60 degrees and does not provide 180 degrees field of view, which is required in order to accurately “see” a customer approaching from the sides of a refrigeration case. 
     A second device uses two PIR motion detector sensors  2  located centrally on the front of the case C, with their axes angled 65 degrees azimuthally to provide a field of detection that is approximately 140 degrees. See  FIG. 2 . The field of detection from the two sensors covers only partially the central portion of the case, as indicated by the null area in the detection coverage, and also has null areas on either side of the case. Assuming that refrigeration cases are arranged close to each other in rows with the front of the cases of two rows facing each other across an aisle, the dual-sensor device on one case may detect a customer who is approaching a case on the other side of the aisle, yet will fail to detect a customer approaching close to the side of the case. If the device is used on a case that is located at the end of the aisle, such that customers typically approach it on a path that is close to being normal to the case, the device will not trigger until the customer is relatively close. Also, because of the pronounced sensitivity at 30 and 330 degrees, the device will trigger unnecessarily when customers are detected at a greater than desired distance. 
     Motion detection lighting systems are typically subjected to large numbers of activation cycles during their lifetimes and the number can often exceed the estimated life of a mechanical relay. Some of these lighting systems have ballasts or power supplies that have a high in-rush starting current. This repetitive high starting current decreases the life of the mechanical relay and the power supply. 
     What is needed is a detection system that detects motion in the front of a display case adequately, without unnecessarily detecting motion off to the side of the case or too far away in front of the case. What is further needed is such a system that avoids null areas in a desired and foreseeable approach path and avoids detection beyond the side edges of the case. What is yet further needed is a device that is simply and quickly incorporated into existing circuitry. What is still yet further needed is such a system with improved reliability. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is a motion detection system, comprising a motion detector module and a power switching module for controlling selective illumination of an area of approach to a specific object or area, such as, for example, a display case, a staircase, a doorway, an obstacle, etc. The motion detection module senses motion and activates the power switching module, which interfaces between a conventional lighting system and the motion detector module. The motion detector module comprises three PIR sensors, i.e., a central sensor and two side-looking or outboard sensors. This triple-sensor motion detector provides useful and intended motion detection across the front face of a display case or other object to be illuminated and reduces the occurrence of inadvertent triggering of the illumination. The inventor has determined that the set of three PIR sensors, properly angled, provides the best field of detection, one that eliminates unnecessary overlap and allows greater control over the size and shape of the field of detection. 
     Each of the three PIR sensors is aimed with a specific azimuth and elevation angle in relation to the case to produce a desired unit pattern. Each PIR sensor is chosen to be either a dual sensing element or quad sensing element to achieve the best sensing characteristics for the position that the sensor is in. The rotational angle of the sensor in relation to the case is adjusted to provide optimum performance. Each sensor is fitted with a Fresnel lens that focuses the IR energy from the person or target, allowing the sensor to detect at a greater distance. The gain of the circuit that processes the signal from the particular sensor may be adjusted to control the overall sensitivity of the sensor. If it is desirable to block detection in a specified direction, a physical barrier to IR radiation may be employed. The combination of sensors is used to achieve the desired pattern, with each sensor set up as previously described and the signals of all the sensors combined electronically. The motion detector according to the invention may be adjusted to accommodate a wide range of sizes of display cases, for example, from two-door cases all the way up to six-door cases, by adjusting all of the previously mentioned parameters. The previously explained parameters may also be used to adjust the motion detector, such that small animate bodies, such as toddlers or pets, i.e., cats or dogs, do not create false triggers. 
     The power switching module supplies power to the conventional lighting fixtures when motion is detected by the motion detector module. This power switching module may be a conventional electromechanical relay or a unit specifically constructed to work with the motion detector module. So, for example, the motion detection module according to the invention may be provided as a module that is easily electrically coupled to an existing mechanical relay, or may be provided as a complete unit, with the power switching module and the motion detection module provided as a single packaged unit. In conventional lighting control systems, a relay coil is typically used to switch power to lighting fixtures. The switch on the relay coil typically operates with low voltage (24 VAC). When provided as a module to be coupled with an existing mechanical relay, the motion detector module is simply wired in series with the relay coil circuit of the power control system. The motion detector module enables or disables activation of the relay coil, based on the presence of detected motion. Ideally, the motion detector module is self-powered and does not require a separate power connection, although it is possible to provide a motion detector module according to the invention that is not self-powered. 
     A solid state relay may be used in place of the mechanical relay, the advantage of the solid state relay being that it does not degrade or wear-out with high cycling rates. The solid state relay may also be selectively turned on at the zero-crossing of the power AC sine-wave, thus greatly lowering the in-rush starting current of the power supply. Additionally, the power module may have a temperature-dependant current-limiting resistor to further limit the in-rush starting current. 
     The triple-sensor motion detector results in greater energy savings than detectors having a single sensor or two sensors. It reduces or eliminates faulty detection of persons or targets who are not approaching the display case, for example, customers approaching a refrigeration case on the opposite side of the aisle or walking along the side of a case and who are not within a predefined area of approach. This reduces the amount of time illumination is unnecessarily turned on, which reduces energy consumption. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. The drawings are not drawn to scale. 
         FIG. 1  is a top plane view in polar coordinates, showing the field of detection of a single-sensor motion detector (prior art). 
         FIG. 2  is a top plane view in polar coordinates, showing the field of detection of a dual-sensor motion detector (prior art). 
         FIG. 3  is a top plane view in polar coordinates, showing the field of detection of a triple-sensor motion detector according to the invention. 
         FIG. 4  is a side elevational view in polar coordinates of the triple-sensor motion detector of  FIG. 3 , mounted on a refrigeration case, illustrating the limited field of detection in the elevational plane. 
         FIG. 5  is a perspective view of the three sensors, illustrating the individual mechanical adjustments of the sensors. 
         FIG. 6  is a front elevational view of the triple-sensor motion detector, showing the downward orientation of the three sensors. 
         FIG. 7  is a perspective view of the triple-sensor motion detector according to the invention. 
         FIG. 8  is an exploded view of a sensor and a lens. 
         FIG. 9  is a schematic of a motion sensor according to the invention connected with a three-wire connection into existing circuitry. 
         FIG. 10  is a schematic of a motion sensor according to the invention, showing a two-wire connection into existing circuitry. 
         FIG. 11  is a schematic diagram of the triple-sensor motion detector, sheet  1  of  6 . 
         FIG. 12  is a schematic diagram of the triple-sensor motion detector, sheet  2  of  6 . 
         FIG. 13  is a schematic diagram of the triple-sensor motion detector, sheet  3  of  6 . 
         FIG. 14  is a schematic diagram of the triple-sensor motion detector, sheet  4  of  6 . 
         FIG. 15  is a schematic diagram of the triple-sensor motion detector, sheet  5  of  6 . 
         FIG. 16  is a schematic diagram of the triple-sensor motion detector, sheet  6  of  6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully in detail with reference to the accompanying drawings, in which the preferred embodiments of the invention are shown. This invention should not, however, be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be complete and will fully convey the scope of the invention to those skilled in the art. 
       FIGS. 3 and 4  are top plane and elevational plane views, respectively, of the field of detection of a triple-sensor motion detector  100  according to the invention. The intended purpose of the triple-sensor motion detector  100  is to precisely shape a field of detection, particularly in an approach area to a display case or some other specific object or area, in order to eliminate unnecessary triggering of illumination because a person has incidentally wandered close to the display case or other specific object or area. As used hereinafter, a desired approach area is a predetermined area in front of the object or area to be illuminated; an undesired approach area is the area beyond, yet adjacent to, the desired approach area. A very suitable application for the triple-sensor motion detector according to the invention, for example, is to control the illumination of display cases in stores, such as refrigeration cases in grocery stores. Hereinafter, reference will be made to a display case. It is understood, that this term is representative only and is not in any way limiting with regard to the invention, but rather, that the motion detection system may be used to illuminate the area of approach of various and myriad types of objects and areas. 
     The triple-sensor motion detector  100  comprises a configuration of three motion sensors  10 , which are shown in greater detail in  FIGS. 5-8 . The field of detection is shown in polar coordinates and the changing sensitivity of the motion sensors  10  is indicated on a scale of 0 to 10, 10 indicating maximum sensitivity. The three sensors  10  are individually designated as  10 A, a centrally located sensor, and  10 B and  10 C, two side-looking or outboard sensors. Each sensor  10  has a field of detection  12 , individually designated as a central field of detection  12 A and two side-locking fields,  12 B and  12 C. Areas in the polar projection that are not within the field of detection or are less than 5 on the sensitivity scale are identified as null areas N. The triple-sensor motion detector  100  according to the invention is shown here mounted on a display case C. 
       FIG. 4  illustrates the field of detection in elevation of the triple-sensor motion detector  100 . The display case C is shown installed on a floor F. The illustration shows a 50-degree downward elevation angle of a pattern that may be adjusted to control the distance at which targets are detected. 
       FIGS. 5 and 6  show the three sensors  10 A- 10 C assembled on a circuit board  16  of the triple-sensor motion detector  100 . All three of the sensors are oriented such, that the field of detection is pointing downward. The ideal azimuth and elevation angles for the sensors  10  are determined for each individual sensor, in order to achieve the desired shape of the field of detection, as shown in  FIGS. 3 and 4 . The sensitivity of the sensors may also be individually adjusted by controlling the gain of each amplifier that processes the signal for each individual sensor. Examples of suitable sensors  10  are the RE200B, a dual sensor, used for the outboard sensors  10 B and  10 C, and the SBA42-54W, a quad sensor, used for the central sensor  10 A. Both sensors are available from Nippon Ceramic Co., Ltd. of Japan. 
       FIG. 8  is an exploded view of an IR Fresnel lens  20  that fits over the sensor  10 . The lenses  20  are individually labeled as  20 A,  20 B, and  20 C and each lens  20  may be different for each sensor  10 . The Fresnel lenses  20  are used to shape the field of detection of each sensor  10  by focusing the IR signal and thereby allowing each sensor  10  to detect at a greater distance with a specific pattern. In the embodiment shown, the lens  20  fits snugly onto the front of the sensor  10 . Such lenses are available in a variety of patterns. A very suitable lens  20  is one that generates a fan beam pattern, such as the NCL-3IL from Nippon Ceramic Co., Ltd. of Japan. 
       FIG. 7  is a perspective view of the triple-sensor motion detector  100 , ready for installation. A housing  30  encloses the sensors  10  and a sensor cover  40  covers the three sensors  10 . The sensor cover  40  may be specially adapted to restrict the sideward field of detection. For example, an IR blinder  45 , i.e., a physical barrier that blocks infrared radiation, may be provided on each end of the cover  40  to limit the side-looking field of detection of the sensors  10 B and  10 C. It is understood that, depending on the specific application of the triple-sensor motion detector  100 , the cover  40  may be adapted accordingly. 
       FIGS. 9 and 10  are schematic illustrations of two alternative control circuits  200  for controlling illumination of lighting fixtures  230 .  FIG. 10  is a schematic illustration of a control circuit  200  that is a two-wire connection of the triple-sensor motion detector  100  with an existing switching relay  210 . A controller  220  is used to control the illumination device  230  for the refrigeration or display case C. Two connections C 1  and C 2  connect the sensor  100  with the controller  220 . These two connections C 1 ,C 2  allow the triple-sensor motion detector  100  to control the switching relay  210  and obtain power for operation of the motion detection module  100 . The control circuit  200  is designed to draw a small current through the coil of the relay  210  to power the triple-sensor motion detector  100 , without activating the relay  210 . When the controller  220  is activated by the motion detection module  100 , an increased amount of current is allowed to flow, which then activates the relay  210  and continues to power the controller  220 . This completes the circuit  200  and activates the illumination device  230 .  FIG. 9  is a schematic illustration of a common three-wire circuit  200 . The motion detection module  100  has a power source, typically 24 VAC, and switches on the controller  220  when motion is detected. Two conductors couple the motion detection module  100  to the switching relay circuit  210 . A third conductor provides power to operate the motion detection module  100 . A common ground with the relay  210  completes the power circuit. 
     The motion detection module  100  may be provided as a module that is to be connected with existing circuitry  200 . Alternatively, the motion detection module  100  and the control circuit  200  may be incorporated into a unitary package. A solid-state relay may be used instead of a mechanical relay. Each of the motion sensors  10  may be provided with a switch that will allow the end-user to adjust the time delay between a triggering and a cessation of power to the illumination device. 
       FIGS. 11-16  are schematic diagrams of the triple-sensor motion detector  100 .