BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to the art of vending machines and, more particularly, to a system for detecting a transfer of a selected product from one of a plurality of shelves to a product delivery device through movement imparted to a motor operatively connected to the product delivery device. 
     2. Discussion of the Prior Art 
     Vending machines for dispensing canned and/or bottled beverages have long been known. Early model vending machines release similarly sized bottles, one at a time, following deposit of a required purchase amount. In order to withdraw the selected product from the vending machine, the purchaser was required to, for example, manually remove a beverage container through a release mechanism on a shelf. Over time, manufacturers developed various mechanisms for releasing products from vending machines. The mechanisms range from a more conventional arrangement wherein products are guided to a chute, often times along a serpentine path, into a delivery port, to a more unique arrangement that shifts a transport carrier to a point adjacent a selected product, receives the selected product and then delivers the selected product to the adjacent delivery port. 
     Unlike the more conventional arrangements where the release and delivery of a product is readily determined, in the more unique arrangements, often times one or more cycles must be completed if a product is not properly released. If the product does not transfer into the transport carrier, there is nothing to deliver to the consumer. If the vending machine fails to deliver a product, the consumer is either refunded the purchase amount or the vending machine will initiate another vending cycle and make a second attempt to deliver the selected product. In either case, the vending cycle must typically near completion before the vending machine determines that the product has been delivered to the consumer. The time required to make this determination may lead to consumer frustration. 
     In order to address this problem, manufacturers have employed various sensors to determine whether a product has been properly transferred to a transport carrier. In accordance with one such arrangement, a sensor, such as an optical beam, is positioned in the transport carrier. When the selected product is transferred into the transport carrier, the beam is interrupted or broken. When the beam is broken, a signal is sent to a control indicating that a product is present in the transport carrier. While effective, occasionally the product does not enter the cup properly and the beam remains unbroken. In this case, the vending machine attempts to deliver a second product into the transport carrier or, if the product is sold out, ceases the vend operation and refunds the purchase amount, leaving the customer without the desired product. 
     Thus, despite the existence of product detection systems in the prior art, there still exists a need for a system that detects the receipt of a selected product in a vending machine product delivery device. More specifically, there exists a need for a product detection system that can reliably detect the presence of a product at an initial stage of a vending operation. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a vending machine having a product detection system that senses whether a selected product has transferred from a product staging area or queue into a product transport system. The vending machine includes a cabinet and a plurality of product support shelves, each of which includes multiple dividers that establish a plurality of product queues. Upon receipt of a purchase amount and the selection of a desired product, the vending machine initiates a vending operation. A controller activates the product transport system which drives a motor that shifts a product delivery device to a position adjacent one of the plurality of product queues. The selected product is then released from the product queue into the product delivery device and transported to a product delivery portion of the vending machine. 
     In accordance with the invention, upon being released, the selected product is deposited or dropped into the product delivery cup. As the product is received, a downward force is imparted to the product delivery device. The downward force carries or transfers through the product transport system to the motor. A sensor, operatively associated with the motor, detects the force and signals the controller that the product has transferred into the product delivery device. Once the signal is received, the controller continues the vending operation. Preferably, the sensor is constituted by an optical encoder mounted to the motor. Movement of the optical encoder in the absence of a drive signal from the controller indicates that the product has successfully transferred into the product delivery device. In accordance with one aspect of the invention, the product detection system also includes a capacitive-type sensor positioned in the delivery device. The capacitive-type sensor also signals the controller that the product is resting in the product delivery device. In this manner, the capacitive-type sensor confirms the signal received from the optical encoder. 
     Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of a preferred embodiment when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevational view of a vending machine including a product detection system constructed in accordance with the present invention; 
         FIG. 2  is an elevational view of the vending machine of  FIG. 1  with the door of a product storage zone shown open; 
         FIG. 3  is a partial, perspective view of a product being released into a product delivery device; and 
         FIG. 4  is a partial, perspective view of the product resting in the product delivery device after having triggered the product detection system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With initial reference to  FIGS. 1 and 2 , a vending machine generally indicated at  2  includes a cabinet  4 . As shown, cabinet  4  includes top, bottom and opposing side walls  6 - 9 . Arranged below bottom wall  7  are various leg members  10  and  11  for positioning vending machine  2  upon a supporting surface (not shown). In the preferred embodiment shown, vending machine  2  is divided into a plurality of zones, with each zone being associated with a particular portion of a vending operation. Towards that end, vending machine  2  includes a storage and display zone  14 , a currency receiving zone  15  and a dispensing zone  16 . 
     As illustrated, storage/display zone  14  is provided with a plurality of product support shelves  20 - 24  for supporting and displaying a plurality of product containers, one of which is indicated at  26 . Each of the plurality of product support shelves  20 - 24  includes a plurality of dividers, one of which is indicated at  28 , that establish a plurality of product queues, one of which is indicated at  30 , on product support shelf  20 . Each of the plurality of product queues  30  includes an associated dispensing or escapement mechanism  33  that is selectively operated to release a product container  26  from storage/display zone  14  for delivery to a consumer. However, the actual construction and operation of dispensing mechanism  33  does not constitute part of the present invention. Instead, various known dispensing mechanisms could be employed, including that set forth in detail in commonly assigned U.S. Pat. No. 6,571,988 entitled “Article Release Mechanism For a Vending Machine” issued on Jun. 3, 2003 which is incorporated herein by reference. In a manner known in the art, storage/display zone  14  includes top, bottom and opposing side walls  37 - 40  and is provided with a door  46  having a glass panel  47  that enables a consumer to view and choose between the variety of product containers  26  available for purchase located within vending machine  2 . 
     Arranged alongside storage/display zone  14  is currency receiving zone  15 . In the embodiment shown, currency receiving zone  15  includes a currency receiving center  50  for inputting a required purchase price to initiate currency during a vend transaction or operation. Currency receiving center  50  includes a bill acceptor/validator  52 , a multi-price coin mechanism  53  and a keypad  55  for inputting particular product selections. Currency receiving center  50  also includes a display  57  for providing information to the consumer, as well as validating the particular selection made. Finally, a coin return slot  59  is provided for returning any required change to the consumer at the completion of the vend operation. Arranged below currency receiving zone  15 , dispensing zone  16  includes a delivery port  65  that enables a consumer to retrieve a dispensed product from vending machine  2 . In the embodiment shown, currency receiving zone  15  and dispensing zone  16  are provided on a door  70  that overlaps door  46  and therefore must be opened prior to opening door  46 . To this end, door  70  is preferably provided with a lock  75  that prevents unauthorized access to vending machine  2 . 
     In the embodiment shown, vending machine  2  includes a product transport system  90  that receives a selected one of the plurality of product containers  26  from one of the plurality of product queues  30 . Once the selected product is received, transport system  90  carries the selected product towards delivery chamber  65 . As referenced in  FIG. 2 , product transport system  90  includes a first, laterally extending guide rail  95  arranged on lower wall  38  of product storage zone  14 , a second, laterally extending guide rail  96  arranged on upper wall  37  and an upstanding carriage rail  100  that extends across storage/delivery zone  14  between first and second guide rails  95  and  96 . Product transport system  90  also includes a first motor or horizontal axis translation mechanism  104  for shifting carriage rail  100  between the plurality of product queues  30  and a second motor or vertical axis translation mechanism  107  coupled to a drive belt (not labeled) that selectively shifts a product delivery device, preferably in the form of a delivery cup  114  slidably supported by carriage rail  100 , between the plurality of product shelves  20 - 24 . Although various product transport systems can actually be employed in the present invention, details of the preferred product transport system  90  can be found in commonly assigned pending U.S. patent application Ser. No. 11/249,526 entitled “Product Transport System For a Vending Machine” filed on Oct. 14, 2005 incorporated herein by reference. 
     As will be discussed more fully below, second motor  107  has associated therewith an optical encoder  120  that, in addition to providing feedback to a vending controller  121  regarding a particular position of product delivery cup  114 , is coupled to a product detection system  122  to signal vending controller  121  that a product has passed from one of the plurality of product queues  30  into product delivery cup  114 . While shown as a separate component, product detection system  122  is preferably incorporated into vending controller  121 . In any event, optical encoder  120  is operatively associated with motor  107 , preferably associated with an output shaft (not shown) of motor  107 . Optical encoder  120  senses rotation of motor  107  and provides position signals to vending controller  121  to determine when product delivery cup  114  is properly positioned at the particular product queue  30  containing the selected product. As will be discussed more fully below, once product delivery cup  114  is positioned at product queue  30 , vending controller  121  should not receive any signals from optical encoder  120  until product delivery cup  114  is moved towards dispensing zone  16 . 
     Reference will now be made to  FIGS. 3-4  in describing particulars of product delivery cup  114 . As shown, product delivery cup  114  includes a base portion  130  having a product support surface  132 , a carriage portion  134  that is shiftably mounted to carriage rail  100  through a drive belt (not shown), and a shroud portion  138  pivotally mounted to carriage portion  134 . Shroud portion  138  includes side walls  140  and  141  and a front wall  142  that collectively define a product receiving cavity  145 . It should be noted that shroud portion  138  also includes a rear wall (not shown), that is lower than front wall  142 , thereby enabling a product container  26  to be transferred into product delivery cup  114 . In any case, shroud portion  138  includes a laterally outwardly projecting extension or discharge element  155  having an up-turned portion  157  provided at an upper portion (not separately labeled) of side wall  140 . Discharge element  155  engages with structure (not shown) provided on side wall  40 , causing shroud portion  138  to pivot about an axis defined by a pin  161  to discharge product container  26  into delivery port  65 . However, as discharging or releasing product container  26  from product delivery cup  114  does not fall within the scope of the present invention, these details will not be discussed more fully herein. Instead, the details of releasing product container  26  into delivery chamber  65  can be found in commonly assigned pending U.S. patent application Ser. No. 11/249,527, entitled “Product Discharge and Delivery System For a Vending Machine” filed Oct. 14, 2005 incorporated herein by reference. 
     In accordance with the invention, at the start of the vending operation, product transport system  90  shifts product delivery cup  114  to a position adjacent one of the plurality of product queues  30  within which resides the selected product container  26 . At this point, dispensing mechanism  33  is activated to release the selected product container  26  into product receiving cavity  145 . As the selected product impacts product support surface  132 , a force “m” is imparted to motor  107  through the drive belt (not shown) resulting in an unexpected movement of optical encoder  120 . That is, as discussed above, once product delivery cup  114  is properly positioned at product queue  30 , there should be no movement of motor  107  detected by optical encoder  120  until vending controller  121  signals product transport system  90  to shift delivery cup  114  toward dispensing zone  16 . Thus, any movement sensed by optical encoder  120  prior to the signal sent from vending controller  121  to shift product delivery cup  114  towards dispensing zone  16  is unexpected. Any unexpected movement of motor  107  that occurs after product delivery cup  114  is properly positioned and prior to being operated to shift the selected product toward dispensing zone  16  is detected by optical encoder  120  and passed to product detection system  122 . The unexpected movement signals product detection system  122  that product container  26  has properly transferred into product delivery cup  114 . 
     In accordance with one aspect of the invention, after dispensing mechanism  33  is operated to release product container  26  into product receiving cavity  145 , product delivery cup  114  is shifted towards dispensing zone  16  and product container  26  released into delivery port  65 . A sensor (not shown) in delivery port  65  confirms receipt of product container  26 . If no confirmation signal is received, the signal from product detection system  122  indicating that a product failed to dispensed is confirmed and either a new vending cycle is attempted or the consumer is refunded the purchase price. In accordance with another aspect of the invention, product detection system  122  includes a redundancy system in the form of a capacitive-type sensor  240  located in base portion  130 . That is, capacitive-type sensor  240  also detects a presence of product container  26  on product support surface  132  and signals product detection system  122 , confirming the signal passed from optical encoder  120 . In this manner, the presence of product container  26  in product delivery cup  114  is confirmed prior to attempting to complete the vend cycle. 
     With this arrangement, vending controller  122  is assured that the selected product container  26  resides in product receiving cavity  145  before continuing with the vending operation. In the event that no signal is received from product detection system  122 , vending controller  121  can either shift product delivery cup  114  to an adjacent product queue holding a similar product or, if no other identical products are available, enable an alternate selection or simply refund the purchase amount to the consumer. In any case, once the selected product container  26  has been received in product delivery cup  114 , product transport vending controller  121  signals product transport system  90  to shift product delivery cup  114  towards a portal (not shown) which is formed in side wall  40  of product storage and display zone  14 . Once in position, the selected product is released into delivery port  65 . 
     Although described with reference to a preferred embodiment of the invention, it should be readily understood that various changes and/or modifications can be made to the invention without departing from the spirit thereof. For instance, while described as employing an optical encoder to sense the unexpected movement of the motor, changes in holding current that maintains the product delivery cup adjacent the product queue can also be employed. Also, while sensor  140  is described as a capacitive-type sensor, other types of sensors can also be utilized to sense the presence of the selected product. Finally, while the product delivery device is shown and described as a product delivery cup, other devices, including a conveyor belt, could also be employed. In general, the invention is only intended to be limited by the scope of the following claims.
A vending machine includes a product detection system for signaling a vending controller that a selected product has released from a product support shelf. The vending machine includes a product delivery device that, upon initiation of a vending operation, transports the selected product from the product support shelf towards a delivery area. Upon initiation of a vending operation, a motor moves a product delivery device to a position adjacent the selected product. A dispensing mechanism then releases the selected product which falls into the delivery device, imparting a downward force which is sensed at the motor. A sensor detects the downward force and signals the vending controller that the product has been received by the product delivery device. At this point, the vending controller continues with the vending operation.