Abstract:
An optical sensing system for detecting objects passing through a volume of interest, wherein the sensing system has an emitter and a detector. The detector detects motion of object shadows generated as the object passes through the volume of interest between the emitter and detector. Motion detection algorithms, using computed motion vectors of the detected object, logically determine whether an object has traveled completely through the detection space, and can be used to discriminate a specific outcomes and/or impediments.

Description:
This application is a divisional of U.S. application Ser. No. 14/091,500 filed Nov. 27, 2013, which is based upon and claims benefit to U.S. Provisional Application Ser. No. 61/731,058 filed Nov. 29, 2012, the complete disclosures of which are hereby expressly incorporated by this reference. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention pertains to an optical sensing system for detecting moving objects. The sensing system may be used in any suitable application, including intrusion alarm systems, factory process monitors, vending machine dispensing sensors, and similar systems that require reliably sensing objects passing through a volume of interest. Although the invention may be used in any suitable application, for simplicity it will be described herein as used with a vending machine to detect whether an object has been properly vended. 
     Description of Related Art 
     In a typical vending machine, there is stored an array of articles ranging from small to large. Some vending machines contain relatively small objects such as metal screws, metal washers, or candy while other vending machines contain relatively large objects such as cans of soda and bags of snack foods. When a user makes the requisite payment or enters the proper access code to the machine and makes a desired selection on the selector panel, the selected product is released from its storage position by one of many known electromechanical mechanisms. It then tumbles downward, drawn by gravity, through a vend space between the front of the vend mechanisms and the back of the machine&#39;s front panel, into an outlet bin, from which the user can retrieve it. In many vending machines the machine&#39;s front panel is transparent thereby allowing the user to view the products before making a selection. 
     Several different problems may occur during the vending operation. For example, the vended product may get stuck in the machine before delivery to the user. Alternatively, the machine may dispense too many products to the user. Spatial orientation of packages and wrinkling of packaging, unusual random distribution of contents of a package, unusual random tumbling of a package through the vend space, an empty pocket in a dispensing mechanism, mis-feed of the dispensing mechanism, multi-feeds, and similar events all can cause mis-vending. In any case, certain actions need to be taken to provide a refund to the user, allow the opportunity to make another selection, or alert the machine owner that improper vending has occurred. 
     The physical characteristics of products dispensed from vending machines may vary widely. The products size may vary in volume and shape, typified by such product extremes as metalized plastic bags of snack food (typically 5×8×2 inches), thin paper cards (typically 3×5×0.060 inches), beverage cans (typically 6×2.5 diameter, inches), machine screws (1×0.125 diameter, inches), gum packages (typically 0.625×1.25×2.5 inches), and machine nuts (typically 0.125×0.125×0.040 inches). Such typical products may randomly tumble in three dimensions, such that the profile presented along any axis during the dispensing process may vary from the thinnest dimension to the widest dimension. 
     It is known in the art to provide an emitter and detector which provide a beam in a confined space through which the vended product will fall. A processer determines when a vended product breaks the beam to confirm that the product has been vended properly. In prior art devices, however, there is some chance that the falling product, through random orientation will fail to break the beam, or will apparently fail to break the beam, and therefore not be detected. There is also a possibility that in constricting the space through which the product must fall, random orientation will cause the product to bridge and become lodged in the constricted space, having been detected but not having been successfully vended. 
     Others have provided vend sensors in which the impact on the outlet chute of a comparatively heavy vended article such as a can or bottle, is sensed as a vibration. However, such sensing is not economically feasible where at least some of the products being vended are very light in weight, such as is the case where a small number of large potato chips are presented in a facially large but light in weight package made of synthetic plastic film. 
     A particularly difficult situation is presented when some of the products to be dispensed are large so that a large transverse cross-sectional area is required for the vend space, but others of the products are so small that an optical beam meant to be broken by the product could be missed due to random path of movement and changing spatial orientation of the falling product being vended. 
     There is therefore a need for an improved sensing system which overcomes these and other deficiencies in the prior art. 
     SUMMARY 
     Accordingly, it is an object of this invention to provide an optical sensing system which detects an object as it passes through a volume of interest. 
     It is another object of this invention to provide an optical sensing system which detects objects ranging from small to large orientation and dimensional ratios. 
     It is another object of this invention to provide an optical sensing system which is robust against external light sources and against intentional attempts to disrupt the detection system. 
     In one embodiment, the optical sensing system of the present invention is comprised of a light beam produced by an emitter and detected by a detector assembly, which may be a mosaic detector. The light beam may be collimated by the emitter or it may be collimated by a lens assembly spaced a certain distance from the emitter. In one embodiment, the optical sensor system uses a light source that is quasi-monochromatic and detectors that have peak sensitivity near the frequency of the light source, which helps filter out any ambient light that is not at that frequency. One embodiment includes a filter which passes only the narrow wavelength of the light source, thereby substantially rejecting ambient interfering light, such as may pass through a glass front vending machine, that may otherwise block or confuse the optical sensors. Lenses may be used to help remove ambient light that does not travel along the optical axis of the collimated light by directing it off axis so that it does not get focused on the detector. The optical sensing system of the present invention eliminates the problem of previous systems that require elaborate techniques to remove interference from ambient light and require extensive calibration to ensure that objects are detected. 
     For ensuring that a vending machine dispense cycle will continue until a product has descended through a volume of interest or an established time interval has elapsed, an optical beam produced by an emitter is established across the volume of interest through which a product must drop. The volume of interest in vending applications is referred to as the vending space. The beam may be projected across the vending space in either a vertical or horizontal direction, or a combination thereof. The beam has a first end and a second end where the first end is adjacent to the emitter and the second end is adjacent to the detector. Preferably, the beam is a tightly collimated light source, typically generated by a laser or light emitting diode (LED). If the light source is not collimated at the time of emission, one or more optical lenses may be used to collimate the light before it travels across the vending space. The beam may be any geometrical shape, including round. In one embodiment, the cross-section of the beam may be set (expanded) to fill the desired vending space according to the optics design. At the second end of the collimated light beam (e.g. the end opposite the emitter), an optical lens system focuses the collimated beam into a detector, which may be a mosaic detector such as a video motion sensor. The collimated beam allows reliable detection of very small objects because the relatively high number of individual photons that constitute the collimated light beam. The beam travels in a straight line (the optical axis) and is less susceptible to diffusion relative to non-collimated beams. The optical design of the collimating lenses sends the beam of light to the collecting lens system for the detector in such a manner that ambient light does not align with the optical axis of the direction of the beam of light and is not focused on the detector, because it is off axis. As described in more detail below, during operation a portion of the collimated beam is blocked by an intervening vended object passing through the vending space to produce a distinct shadow at the detector relative to the normal intensity of the light beam reaching the detector. 
     In addition to detecting the presence or absence of an object in the vend space, in some embodiments the detector can also detect the motion of dispensed object shadows generated as the dispensed object passes downward through the vending space. Detection of shadows (as opposed to front surface images) eliminates the need to process wide variations in color and reflectivity of the dispensed product. Motion detection algorithms, using computed motion vectors of the dispensed product, logically determine that a dispensed product has traveled completely through or has stalled within the vending space, and can be used to discriminate a specific vending cycle outcome and/or impediments. As described below, the detection algorithms may be set to detect items moving in a certain direction, at a certain speed or range of speeds, or items of a certain size or range of sizes. 
     In some embodiments, the detector is programmed with a set of rules to determine the range of motion vectors which the user has predefined as a successful vending cycle, thereby causing a logical output to be issued indicating to the vending machine that a successful dispensing action has occurred. In some embodiments a rule may be created which defines a successful vending cycle only if a shadow is detected in the downward direction moving at a predetermined velocity. Motion detection algorithms may be modified to allow the predetermined velocity, size, and direction characteristics to be tailored to user preferences for the properties of the vend object(s). In some embodiments the user may also define one or more separate sets of rules that define a static blockage of product (shadow with no motion), an attempt to enter the machine from the vending access opening in a theft attempt (shadow moving in the wrong direction), or other criteria as needed by the end use of the system. In some embodiments a rule may be created which instructs the machine to take no action if a stationary shadow having a predetermined size is detected. 
     In another embodiment, a system of one or more reflecting mirrors is interposed between the emitter and the detector for the purpose of reflecting the beam back and forth across the vending space any desired number of times to further illuminate the vending space by the multiple beam passes, with the intent of minimizing gaps between beam passes through which an object may pass undetected. This embodiment operates identically to the first embodiment, but allows use of a smaller cross-section optical lens system to cover the vending volume by employing multiple parallel collimated light beams rather than a single large diameter collimated beam. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are described in more detail with reference to the attached drawings, in which: 
         FIG. 1  is a block diagram showing an embodiment of the invention. 
         FIG. 2  is a side view of the block diagram shown in  FIG. 1 . 
         FIG. 3  is a front view of a vending machine showing any embodiment of the sensing system wherein the emitter and detector are located above the volume of interest. 
         FIG. 4  is a front view of a vending machine showing any embodiment of the sensing system wherein the beam is reflected off of a mirror thereby providing the emitter and detector are on the same side of the machine. 
         FIG. 5  is a top view of an embodiment of the sensing system wherein multiple autonomous emitter and detector pairs create multiple beams traversing the volume of interest. 
         FIG. 6  is a top view of an embodiment of the sensing system wherein a folding mirror is used to increase the volume of interest covered with a single emitter source and single detector. 
         FIG. 7  is a top view of an embodiment of the sensing system wherein multiple folding mirrors are used to increase the volume of interest coverage with a single emitter source and single detector. 
         FIG. 8  is a front view of a vending machine showing an embodiment of the sensing system wherein the beam(s) is (are) oriented vertically to detect a vertical vending space. 
         FIG. 9  is a perspective view of a mosaic detector showing the plurality of detection elements. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is related to an optical sensing system for use in any suitable application, including for sensing objects dispensed from a vending machine  15  by a dispensing mechanism  17 . The dispensing mechanism  17  is configured to perform vending operations in order to dispense an object  26  selected by a consumer. The invention is equally applicable to any suitable vending machine  15  having a volume of interest  16  (vend space) through which the object  26  must pass, independent of the specific electromechanical design and construction of the vending machine  15 . 
     One embodiment of the optical sensing system is schematically and diagrammatically illustrated in  FIG. 1  in which an emitter  10  projects a beam  14  of electromagnetic radiation (light) to a detector  12 . As illustrated below with reference to some specific embodiments, the beam  14  may be oriented in any suitable direction within the volume of interest  16 . For example, the beam  14  may be projected in one or more of front/back, left/right, up/down, or any angle therebetween. As shown in  FIG. 8 , for example, it is not necessary for the beam  14  to be projected at a right angle to the direction of travel of the vended object  26  as long as the vended object  26  is capable of breaking the beam  14  as it is being vended. The beam  14  has a first end adjacent to the emitter  10  and a second end adjacent to the detector  12 . In  FIG. 1 , the emitter  10  and detector  12  are adapted to be combined with opposite interior sides of the volume of interest  16 . The emitter  10  projects a single light source such as beam  14  and the detector  12  is adapted to detect the beam  14  and may be a single video sensor or mosaic detector. The beam  14  cross-section and orientation are selected to substantially span the volume of interest  16  for the product  26  to be dispensed. The arrow A in  FIGS. 1 and 2  shows the direction of travel of the product  26  being dispensed. 
     Any suitable emitter  10  may be used, including a laser diode, light emitting diode (“LED”), gas laser, incandescent light, fluorescent light, and high pressure gas discharge light. Power for the emitter  10  is typically provided from a conventional external power source, but may be integrated into the emitter  10  in some embodiments (such as battery power). In embodiments using a laser diode as the emitter, the laser diode power required for a typical vending machine  15  application is typically five milliwatts or less, well below safety thresholds even without beam expansion. The intensity of the light generated by the emitter  10  is proportional to the distance the light must travel from the emitter  10  to the detector  12 . If desired, the emitter  10 /detector  12  system may be switched on by the vending machine  15  master controller only when a vend cycle is in progress in order to conserve power when not in use. 
     Ambient light may pass through the transparent front  13  of the vending machine  15  into the volume of interest  16 . In one embodiment the wavelength of the beam  14  created by the emitter  10  may be selected by the user according to the choice of detector  12  or the ambient interfering light characteristics so as to optimize system performance. In areas where significant amounts of ambient light will reach the detector  12 , it may be desirable to select or limit the wavelength of light coming from the emitter  10  then tune the detector  12  to only detect the selected wavelength. This allows the system to tune out all wavelengths of ambient light except the one(s) selected by the user. This eliminates the need for calibration and synchronization functions which are required in prior art device. Red light (635 nm) is used in one embodiment One embodiment includes a filter which passes only the wavelength of the emitted beam  14 , thereby substantially rejecting ambient interfering light from reaching the detector  12 . 
     In the embodiment shown in  FIG. 1 , a lens assembly is used to increase the diameter of the beam  14 , then collimate the expanded beam  14 , then refocus the beam  14  as it enters the detector  12 . The lens assembly includes one or more of a first lens  18  which may be an expanding lens for expanding the beam  14  to an expanded diameter. A second lens  22  which may be a collimating lens for collimating the expanded beam to create a beam of light  14  comprised of generally parallel light rays of the desired final diameter. Typically the first two lenses  18 ,  22  are positioned near the first end of the beam  14  (near the emitter  10 ). A third lens  23  which may be a decollimating or first focusing lens for focusing the incoming collimated beam  14  to an intermediate diameter. A fourth lens  20  which may be a secondary focusing lens for focusing the intermediate beam  14  to a smaller size commensurate with the design of the specific detector  12 . The focused light is applied to the optical port of the detector  12  for analysis by the processor  21 . Typically the second two lenses  23 ,  20  are positioned near the second end of the beam  14  (near the detector  12 ). 
     In addition to expanding the diameter of the beam  14  and collimating the beam  14  through the volume of interest  16 , the lens assembly also serves to help prevent ambient light from reaching the detector  12  and interfering with detection. Ambient light which does not pass through one or more of lenses  22  and  23  at a specific angle (i.e., the angle of the light coming from the emitter  10 ) is directed by the lens  22 ,  23  off-axis to a focal point away from the detector  12 . 
     One or more of the emitter  10 , detector  12 , and lens assembly components may be mounted in one or more housings to help secure the components in their proper locations. 
     In one embodiment, the detector  12  is a subsystem comprising a mosaic of photo detectors  11 , a video processing means, motion algorithms, and rule programming. The mosaic of photo detectors  11  may have a defined array size and may be a video camera pixel array. An exemplary mosaic detector is shown in  FIG. 9  wherein the detector  12  comprises a plurality of detection elements  11 . As shown in  FIG. 9 , the exemplary mosaic detector  12  has an array of seven detection elements  11  along its length and five detection elements  11  along its width. Each detection element  11  is able to independently determine relative light levels such that full or partial shadows (relative to the normal intensity of the beam  14 ) cast on the detection elements  11  can be detected. Thus, motion, velocity, and size can be detected by the subsystem as an object  26  passes in front of the detection elements  11  as each individual detection element  11  sees changes in light levels. The mosaic sensor array provides better detection of objects passing through the beam of light  14  from the source, because it has a better signal to noise ratio compared to a linear array which has a better signal to noise ratio compared to a single detector. The mosaic sensor array can identify the direction an object is traveling as it passes through the beam  14  which the single detector and the linear array are not able to do. The one exception for the linear array is the special case for an object that is traveling parallel to the direction of the linear array. 
     The detector subsystem is typically integrated into a single, small circuit, which may include or otherwise be in communication with a processor  21  and firmware  23 . The subsystem can determine direction, position, velocity, and acceleration of objects passing in front of the array of detection elements  11 . The subsystem allows direct programming of rules (using various internally determined parameters, i.e., delta-x, delta-y, x-acceleration, y-acceleration, smoothing, x-velocity, y-velocity, etc.) into the device to define under what conditions a logical output state may be defined and so indicated. Such detector subsystem may include a processing function, typically expressed as N×M pixels (of the detection element  11  array), which output is used by the motion detection algorithms to extract the internal motion parameters. The video processing means is typically implemented in firmware  23  and/or in a processor (microcomputer)  21  to perform mathematical operations on the data values detected by the detection element  11  array. This allows the device to compare complex manipulations, apply mathematical functions, and compare matrix values with matrix values from a previous time of pixel light levels. The video processing compares patterns of light levels between frames, and makes decisions and inferences about the differences based on the rules and motion algorithms. 
     Some embodiments include methods of using the optical sensing system wherein one or more rules are created to define a successful vending cycle. Sensing of a product drop through the beam  14  involves comparing the vectors of any detected shadows reported by the motion detection algorithms of the detector  12 . The motion detection algorithms are typically implemented in firmware  23  and/or in a processor (microcomputer)  21 . If the reported vectors meet the requirements of the predefined rules, a dispense action logical signal is provided to the vending machine  15  master controller. Further actions may be undertaken by the vending machine  15  based upon this signal. 
     In one embodiment, a successful vending cycle is only achieved if a shadow is detected in the downward direction and/or is moving at a predetermined velocity. Motion detection algorithms may be modified to create rules which allow the predetermined velocity, size, and direction characteristics to be tailored to user preferences, or to specifically match each of a plurality of vended objects. In some embodiments the user may also define one or more separate sets of rules that define a static blockage of product (shadow with no motion), an attempt to enter the machine from the vending access opening in a theft attempt (shadow moving in the wrong direction), or other criteria as needed by the end use of the system. In some embodiments a rule may be created which instructs the machine to take no action if a stationary shadow having a predetermined size is detected. 
     The motion detection algorithms may vary widely depending on the speed of motion desired for detection. A first step is to determine the light level on all pixels in the detection element array  11  and to store those values in the processor&#39;s  21  buffer memory. Then the light level is determined again for all pixels in the array  11  a predetermined time after the initial light levels are determent (usually fractions of a second) and the second value is compared to the first value (in the buffer memory). A matrix of the differences between the two values is created and stored to buffer. The process is continued as light levels at a first time are compared to light levels at a second (later) time. The matrix of differences between the light levels at the first time and light levels at the second time are continually compared by the processor  21 . From the comparison of difference matrices, the direction and displacement of the differences is determined to give speed and direction (velocity). Further, the comparison of difference matrices can be used to determine the size of the object projected on the mosaic as larger objects will darken more detection elements  11  at a given time. 
     The detector  12  having the array of detection elements  11  detects the shadow of the vended object as the object passes in front of the beam  14 . The motion detection algorithms continuously analyze the relative differences and changes in the light falling on each element of the array  11 . The shadow may only be a slight darkening of a pixel or trail of pixels relative to the normal beam  14  intensity, rather than a total light/dark transition. The motion detection algorithms function with shades of gray in addition to total light/dark changes such that there is not a hard optical threshold at which detection occurs. The impact of brightness, and more specifically dealing with wide variation in dispensed product front surface color and reflectivity, is eliminated by the use of vend product shadows to be sensed by the invention. The motion detection algorithms examine and make decisions based on the relative differences among the pixels of the array  11  generated by the impinging shadow. 
     The smallest dispensed product detectable by the invention is one pixel area divided by the number of levels of gray scale. For example, if sixty-four levels of gray scale exist, then an object shadow 1/64th of the pixel area will cause a one-step light level output change detectable by the detector  12 . 
     A number of embodiments are possible to accommodate various volume of interest  16  geometries and physical vending machine  15  implementations.  FIGS. 1, 3, 5, and 7  show an embodiment wherein the emitter  10  is positioned at a first end of the volume of interest  16  such that the resulting collimated light beam  14  is directed across the desired axis/ area of the volume of interest  16  to the detector  12  at a second end of the volume of interest  16  where the detector  12  monitors for dispensed products  26  falling from a tray assembly  32  within the vending machine  15 . During normal operation, the dispensed products  26  fall into a bin  24  for retrieval by the consumer. In other words, in these embodiments, the first end of the beam  14  is projected from the first side of the volume of interest  16  and the second end of the beam  14  is received by a detector  12  at the opposite side of the volume of interest  16 . In contrast,  FIGS. 4 and 6  show embodiments where the beam  14  is reflected back to the first side of the volume of interest  16  by a mirror to allow the emitter  10  and detector  12  to be located on the same side of the volume of interest  16 . 
       FIG. 3  shows an embodiment wherein the emitter  10  and detector  12  are used with right angle mirrors  30  in order to conserve width within a vending machine  15 . In the embodiment shown, the emitter  10  and detector  12  may be located above the volume of interest  16  while the beam  14  is projected horizontally across the volume of interest  16  using mirrors  30 . 
       FIG. 4  shows an embodiment using a mirror  31  to reflect a single beam  14  back to the detector  12  located on the same side as the emitter  10 . This embodiment allows a single beam  14  to traverse the volume of interest  16  twice thereby increasing the detection area covered by the single beam  14 . 
       FIG. 5  is a top view showing an embodiment using multiple emitter  10   a ,  10   b ,  10   c /detector  12   a ,  12   b ,  12   c  pairs with each beam  14  traversing a different area of volume of interest  16 . It will be understood that any suitable number of emitter  10 /detector  12  pairs may be used. Each emitter  10   a ,  10   b ,  10   c /detector  12   a ,  12   b ,  12   c  operates autonomously to provide independent information to the processor  21 . The logical outputs can be logically combined in a desired manner or used separately so as to divide the volume of interest  16  into sectors. This embodiment may be used when it is important to know which sector of the volume of interest  16  a product has passed through. 
       FIG. 6  is a top view showing an embodiment wherein a folding mirror  35  (corner reflector) is used to double the monitored vending space  16  using only a single emitter  10  and detector  12  pair. It is irrelevant to the operation of the vending machine  15  in which pixel(s) motion is detected, just that motion was detected somewhere. In this embodiment the emitter  10  and detector  12  are located on the same side of the vending space  16 . 
       FIG. 7  is a top view of an embodiment wherein multiple folding mirrors  35  to monitor a larger vend space with only a single emitter  10 /detector  12  pair. This expands the embodiment of  FIG. 6  with additional folds of the beam  14 . Additional numbers of mirrors  35  may be used to further fold the beam  14  to increase the detection area of the vending space  16 . The number of folds that can be applied is limited only by the source brightness, mirror reflectivity, and tightness of collimation (beam divergence). Further, the gap between the beam  14  as it passes back and forth across the vending space  16  may be adjusted to user preference. In one embodiment, the mirrors  35  can be adjusted such that there is little or no gap between the reflected beam  14 . 
       FIG. 8  shows an embodiment wherein the beams  14  traverse the volume of interest  16  in a vertical direction. In the embodiment shown, a plurality of emitters  10  are positioned near the top (first end) of the machine and a plurality of corresponding detectors  12  are positioned near the bottom (second end) of the machine such that the emitters  10  create a vertical beam  14  through the volume of interest  16  which are received by the detectors  12 . In other embodiments the components may be reversed such that the detectors  12  may be near the top and the emitters  10  near the bottom. This embodiment is beneficial if it is important to know which column of products has been vended. In still other embodiments mirrors may be used to reflect a single beam  14  in generally parallel vertical alignment (similar to  FIG. 7  if it were rotated ninety degrees) to sense products vended from different trays. 
     Having thus described the invention in connection with the preferred embodiments thereof, it will be evident to those skilled in the art that various revisions can be made to the preferred embodiments described herein without departing from the spirit and scope of the invention. It is our intention, however, that all such revisions and modifications that are evident to those skilled in the art will be included with in the scope of the following claims.