Abstract:
The present invention teaches and discloses method and apparatus for alerting a grocery store check out cashier of merchandise placed on the bottom tray of a typical grocery shopping cart. A passive RFID transponder is incorporated into the structure of the cart which when interrogated by an associated reader, located at the cashier&#39;s check out station, responds with a signal verifying the presence, or absence, of an unseen item upon the carts bottom tray.

Description:
RELATED APPLICATIONS 
     This application claims the priority of Provisional Patent Application Ser. No. 60/604,808 filed on Aug. 27, 2004 Titled “Bob Sensor System” and Provisional Patent Application Ser. No. 60/642,556 filed on Jan. 11, 2005 Titled “Object Sensing System.” 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to Radio Frequency Identification (RFID) technology. More specifically the present invention relates to using RFID technology to detect the presence of merchandise placed upon the bottom tray or rack of a typical grocery shopping cart by a consumer 
     BACKGROUND OF THE INVENTION 
     A typical grocery shopping cart as used in grocery stores comprises a base frame, supporting wheels and a bottom rack or tray for carrying large bulky purchases such as bags of dog food and the like, an upper basket extending over top of the bottom tray, and a handle bar for pushing the cart about the store. 
     When the top basket is relatively full, items placed upon the bottom tray are, many times, hidden from view and may go unnoticed by the check out cashier. 
     Thus an effective means is needed to detect items, placed on the bottom tray of a grocery shopping cart, that may be hidden from view of the check out cashier. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention teaches an improved method and apparatus for the detection of articles of purchase placed upon the lower shelf or tray of a typical grocery shopping cart at the check-out cashier&#39;s station that otherwise may go unnoticed. 
     Our invention comprises a weight sensing grocery cart, bottom tray, employing a passive RFID transponder module that will respond to an interrogating RFID signal, as the grocery cart is passed through a grocery cart check out station, when a product is present upon the grocery cart bottom tray. 
     Products placed upon the grocery cart&#39;s bottom tray are detected by a logic sensing radio frequency microchip and antenna incorporated into the bottom tray. A radio frequency identification transmitter/receiver with an antenna is located in the check out station area and coupled to an alert warning device located in proximity of the check out cashier, or coupled to an otherwise automated system that alerts the check out cashier to the presence of an unnoticed product on the bottom tray of the grocery cart. 
     When an item is placed on the grocery cart&#39;s bottom tray, the item activates a weight sensing switch mechanism incorporated within the bottom tray. As the tray is passed through the check out station detection area, the radio frequency transmitter/receiver, in the detection area, activates a microchip incorporated into the cart&#39;s bottom tray. The microchip then senses the state of the weight sensing switch mechanism within the tray and transmits this information back to the check out station transmitter/receiver. A signal is then sent to an alert device whereby the “operator” is notified of the presence of an item on the bottom tray. The “operator” may be a person, namely a check out cashier, or may be hardware such as a computer or programmable logic controller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  presents a side elevational view of a typical grocery shopping cart embodying the present invention. 
         FIG. 2  presents a rear elevational view of the grocery shopping cart in  FIG. 1  shown passing through a typical grocery store cashier&#39;s check out station. 
         FIG. 3  presents a top view of the lower shelf of the grocery cart shown in  FIG. 1  and taken along lines  3 — 3  in  FIG. 1 . 
         FIG. 4  is a bottom view of the lower shelf of the grocery cart shown in  FIG. 1  and taken along lines  4 — 4  in  FIG. 2 . 
         FIG. 4A  is a crossectional view taken along line  4 A— 4 A in  FIG. 4 . 
         FIG. 4B  is a crossectional view taken along line  4 B— 4 B in  FIG. 4 . 
         FIG. 4C  is a crossectional view taken along line  4 C— 4 C in  FIG. 4 . 
         FIG. 4D  is a crossectional view taken along line  4 D— 4 D in  FIG. 4 . 
         FIG. 5A  is a crossectional view taken along line  5 A— 5 A in  FIG. 3 . 
         FIG. 5B  is a crossectional taken along line  5 B— 5 B in  FIG. 3 . 
         FIG. 6A  is a crossectional view taken along line  6 A— 6 A in  FIG. 4 . 
         FIG. 6B  is a crossectional view taken along line  6 B— 6 B in  FIG. 4 . 
         FIG. 7A  is a crossectional view taken along line  7 A— 7 A in  FIG. 4 . 
         FIG. 7B  is a crossectional view taken along line  7 B— 7 B in  FIG. 4 . 
         FIG. 8  presents a schematic of the passive transponder circuit on the shopping cart shown in  FIG. 1 . 
         FIG. 9  presents a schematical illustration of a reader system that may be installed at a typical cashier&#39;s check out station. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a typical grocery store shopping cart  10  commonly used in modern day supermarkets. Shopping cart  10  generally comprises a basket  12  for receiving the shoppers selected purchases, an undercarriage structure assembly  14  for supporting basket  12 , and providing a handle  16  for pushing the cart and supporting wheels  18 . 
     As illustrated in  FIGS. 1 through 3 , a bottom tray assembly  20 , supported by undercarriage  14 , is typically provided for the placement of large and/or bulky items selected for purchase. In the present embodiment of the invention tray assembly  20  is hingedly supported at the front end of cart  10  by hinged support assembly  25  and at the rear by a laterally extending support bar  22 . Hinge support assembly  25  attaches bottom tray  20  to the front end of undercarriage assembly  14  and permits the rear portion of bottom tray  20  to be raised and lowered, thereby permitting the telescopingly storage of carts  10  when not in use. Hinge support assembly  25  also permits bottom tray  20  to “float” vertically as described in further detail below. 
     Turning now to  FIGS. 4 through 4D , bottom tray assembly  20  primarily comprises a planar grid structure having a multiplicity of longitudinal longerons  30  and laterally intersecting orthogonal members  32  within a surrounding frame  34 . Included within the planer grid structure of bottom tray assembly  20  is a planer rectangular structure  35  comprised of enlarged portions of intersecting longerons  38  and  39  and orthogonal members  40  and  41 . Extending longitudinally outward from opposite sides of rectangular structure  35  are similarly enlarged longerons  42  and  44  extending forward toward the front end of tray  20  and toward the rear of tray  20  respectively. 
     Referring now to  FIGS. 3 , through  5 B, the forward portion of surrounding frame  34  includes a “floating” hinge assembly  50  comprising an inverted “U” shaped channel member  52  that engages front end support rod  45 . Support rod  45  comprises a single rod extending through the lateral length of hinge assembly  50  and is affixed to cart undercarriage assembly  14  as best illustrated in  FIG. 3 . 
     At opposite lateral ends of channel member  52  are vertically aligned compression springs  62 A and  62 B positioned between support rod  45  and the top of channel member  52  whereby tray assembly  20  floats a predetermined distance above support rod  45  and is also free to rotate about support rod  45  thereby permitting carts to be telescopingly stored when not in use. 
     Referring now to  FIGS. 3 ,  4 ,  6 A and  6 B. The rear portion of tray  20  includes rear channel support member  61  having rear support bar  22  passing therethrough as best illustrated in  FIGS. 6A and 6B . Similar to the forward portion of tray  20 , a pair of oppositely positioned, vertically aligned, compression springs  65 A and  65 B are positioned between rear support bar  22  and the top of rear channel support member  61  as best illustrated in  FIGS. 6A and 6B . Compression springs  65 A and  65 B cause the rear portion of tray  22  to float at a predetermined distance above rear support bar  22 . 
     By the action of compression springs  62 A,  62 B,  65 A and  65 B tray  20  floats above forward support rod  45  and rear support bar  22 . 
     Referring now to  FIGS. 4 ,  7 A and  7 B. An electrical “on-off” switch assembly  76  and  78  is positioned within rear channel  61  and front channel  52 . Switch  76  is positioned above rear support bar  22  and switch  78  is positioned above front support rod  25  as illustrated in  FIGS. 7A and 7B . Switches  76  and  78  are simple on/off, single pole/single throw, switches having a suitable plunger type operator  77  and  79  respectively. Although only two on/off switches are illustrated, any number of on/off switches may be used as desired. 
     In operation, tray  20  is floatingly suspended above front support rod  22  and rear support bar  25  by action of compression springs  62 A,  62 B,  65 A, and  65 B such that switches  76  and  78  are in the non-activated (open) configuration. When an object is placed upon tray  20 , the appropriate compression spring, or springs  62 A,  62 B,  65 A and/or  65 B are compressed whereby at least one of the switches,  76  or  78 , is activated (closed) by switch plunger  79  and/or  78  coming into contact with front support rod  45  and/or rear support bar  22 . 
     Turning now to  FIGS. 4 and 8 , a passive transponder device is attached to, or otherwise integrated into, enlarged orthogonal members  40 ,  41 , and longerons  38  and  39 . Attached to or otherwise integrated therewith, is an onboard transponder microprocessor module  46  having therein microprocessor  70  and associated elements as illustrated in  FIG. 8 . 
     The passive transponder circuit comprises antenna  82 , capacitor  72 , for tuning antenna  82 , and one or more weight sensing switches  76  and  78  wired in series with resistor  74  by way of hard wiring  84  and  86  extending through enlarged longerons  42  and  44  as best illustrated in  FIGS. 4C and 4A  respectively. A suitable microprocessor chip  70  is Microprocessor Model MCRF-202 manufactured by Microchip, Inc., of Chandler, Ariz. Antenna  82  comprises multiple loops of cooper wire embedded within, or otherwise attached to orthogonal members  40  and  41  and longerons  38  and  39  of tray  20  thereby forming a loop antenna. See  FIGS. 4B and 4D . Capacitor  72  is arranged in parallel with antenna  82  thereby tuning the natural frequency of the circuit to maximize response at the desired operating frequency within the range of 100 to 400 kHz. Other frequencies may be used, however, the range of 100 to 400 kHz has been found to provide the preferred read range and antenna size. 
       FIG. 2  illustrates a typical grocery store cashier&#39;s check out station  26  embodying the present invention. Contained within check out station  26  is an RFID Inc. Model 5000-1E-RW transponder reader  92  with an associated RFID Inc. Model 5160 Reader Head antenna  94  (manufactured by RFID Inc., of Aurora, Colo.) embedded within floor  100 . 
     Tray  20  contains no active power source. Power for the passive transponder circuit is generated by the reader antenna  94  exciting an oscillating electromagnetic field at a frequency corresponding with the natural frequency of the tuned transponder antenna  82 . The oscillating electromagnetic field from reader antenna  94  causes electrical currents to oscillate in antenna  82  of the on board transponder. Microprocessor chip  70  rectifies this current and converts the energy into a DC voltage current source sufficient to operate microprocessor  70 , 
     Upon powering of microprocessor  70 , a voltage is applied across parallel switches  76  and  78 , in series with resister  74 , and a voltage is sensed by the microprocessor sensor pin between resister  74  and switches  76  and  78 . In the event switches  76  and  78  are in the open state, thereby indicating that no items are present on tray  20 , the voltage sensed is in a high state because no voltage drop across resister  74  has been detected. 
     However, if at least one switch,  76  or  78 , is closed, thereby indicating the presence of an item upon tray  20 , the voltage sensed is in a low state because a voltage drop across resister  74  has been detected. 
     Upon sensing the state of voltage in hard wiring  84 , microprocessor  70  will transmit a pre-programmed bit pattern by momentarily grounding, or otherwise disturbing transponder antenna  82  in a predetermined manner thereby modulating the amplitude of the transponder antenna  82  voltage and resulting emitted radio frequency signal amplitude. The bit pattern must be transmitted with a predetermined protocol, such as Manchester, Frequency Shift Keying (FSK), or any other serial data transmission protocol, to allow the reader  92  to properly interpret the data being received from transponder module  46 . 
     The transponder antenna disturbance and resulting radio frequency signal is sensed by reader antenna  94  and transmitted to reader module  92  through hard wiring  93  and therein converted, by reader module  92 , back into the original digital bit pattern. This bit pattern may be further processed by reader module  92  and transmitted through hard wiring  95  to any external system, such as a visual monitor  96 , store database  94  or any other suitable alert devise  98 . 
     The preferred location of reader antenna  94 , in a retail store application, is embedded in the floor  100  adjacent the cashier&#39;s check out stand  26  where customers typically unload the cart as illustrated in  FIG. 2 . It may be desirable to place a second reader antenna down stream of the first reader antenna  94  to check that an object detected by the first reader antenna had, in fact, been removed. Thus the cashier may be assured that all items have been accounted for before the transaction can be finalized. 
     The transponder microprocessor  70  is configured to transmit a string of bits to reader  92  when interrogated. The bit pattern transmitted may be configured and stored in the read only memory of microprocessor  70  in any number of ways to allow for identification of the particular grocery cart by a unique serial number, cart manufacturer, state of the weight sensing switches  77  and  79 , an/or any other information that may be encoded in a bit stream. 
     Microprocessor  70  may transmit a pre-programmed bit pattern normally or inverted, depending on the state of weight sensing switches  77  and  79 , thus if all switches are in the open condition, indicating that tray  20  is empty, the bit pattern will be transmitted normally. However, if one of the switches  77  or  79  is closed an inverted bit pattern would be transmitted. This feature may provide for self-diagnostics of tray  20 . Thus if the cart passes through the detection area and no bit stream is transmitted, the cashier may be alerted to a defective transponder on that particular grocery cart. 
     It is evident that many alternatives, modifications, and variations of the present invention will be apparent to those skilled in the art in light of the foregoing teachings. Accordingly, the invention is intended to embrace all such alternatives, modifications, and variations as may fall within the spirit and scope of the appended claims.