Cart management system
FIELD OF THE INVENTION 
     The invention is directed to a system for the management of carts such as luggage carts, shopping carts, strollers and the like. More particularly, the invention is directed to an automated stand alone cart management system allowing for the storage, vending and return of a plurality of carts. 
     BACKGROUND OF THE INVENTION 
     Carts have a wide variety of applications in public places such as airports, shopping centers, parks, zoos, etc. For example, in airports, luggage carts have become popular for assisting air travellers with transporting luggage to and from planes and ground transportation. 
     A large public facility such as an airport may require hundreds or thousands of carts to satisfy the demands of air travellers. Many airports, especially in Europe, own and provide these carts as a service to their customers. However, the carts often become a nuisance in the airport as many customers do not return the carts to a central area after using them. Unreturned carts can be safety hazards and disrupt pedestrian and motor traffic. Further, the carts are often not maintained properly and can break down. 
     Automated cart management systems have become popular in the United States for managing and vending a large number of carts for use by the general public. These systems typically retain a number of carts within a track or rail, and allow for vending and return of carts without the need for a human attendant. An attendant is needed only to periodically check the system to collect currency and perform routine maintenance. Furthermore, cart management systems provide an additional source of revenue for an airport. 
     Most cart management systems use carts which are specifically designed for use in the systems. Many retain a wheel or a specialized &#34;key&#34; on a cart. Consequently, most cart management systems are sold as complete systems having specialized cart management units and carts. 
     Many public facilities, especially in Europe, already own carts but do not have cart management units for vending the carts. While these facilities would like to convert their own carts to automated systems, to date there have been few alternatives, short of purchasing a new cart management system with all new carts, for doing so. Therefore, there is a need for a cart management system which may be used to retrofit existing carts for incorporation therein in an automated system. 
     Cart management systems also provide an added benefit in that the number of unreturned carts left around a public facility is often reduced. Many cart management systems are designed to offer a &#34;reward&#34; for returning the cart to the system, which encourages customers to return their carts once they are done with them. Even if the customer who rended the cart does not return the cart, another person can collect the cart and return it for the reward. It has been found that the reward system significantly cuts down on the number of unreturned carts, thus reducing safety hazards and traffic congestion as a result of unreturned carts. 
     By providing the potential for rewards in a cart management system, however, hustlers may attempt to cheat the system and repetitively retrieve rewards by making the system think carts are being returned when in fact they are not. Many cart management units are susceptible to theft of large amounts of reward money as a result of clever hustlers. Therefore, a need has also arisen for a cart management system which is resistant to theft from hustled rewards. 
     SUMMARY OF THE INVENTION 
     The invention addresses these and other problems in the prior art in providing an automated cart management system which is readily usable with a variety of carts, even existing carts not specifically designed and manufactured for use in the cart management system. Preferred systems retain cart keys attached to carts in a retaining rail, and utilize a paddlewheel mechanism to selectively control the vending and returning of carts. Furthermore, sophisticated and substantially fault-free electronic control over the vending and returning of carts is provided through the use of various position and proximity sensors. Consequently, the invention is particularly well suited for facilities owning one or more different types of carts as these carts may all be integrated into a single automated cart management system which is resistant to &#34;hustling&#34;, particularly to the theft of rewards which are dispensed by the system. 
     Therefore, in accordance with one aspect of the invention, a cart management apparatus for retaining carts of the type having a cart key mounted thereto at a predetermined height is provided. The apparatus includes a retaining rail having an open end for receiving a cart key of a cart; a rotatably mounted paddlewheel including a plurality of paddles extending radially from a rotational axis thereof for selectively retaining the cart with the cart key retained in the rail; and an electromagnetic brake, coupled to the paddlewheel, for selectively inhibiting rotation of the paddlewheel and thereby restricting removal of the cart key from the retaining rail. 
     In accordance with another aspect of the invention, a cart management apparatus for retaining carts of the type having a cart key mounted thereto at a predetermined height is provided, which includes a retaining rail having an open end for receiving a cart key and an access aperture defined in at least one side thereof; a paddlewheel, including a plurality of paddles extending radially from a rotational axis thereof, and rotatably mounted with at least one paddle projecting through the access aperture of the retaining rail; locking means, coupled to the paddlewheel for selectively inhibiting rotation of the paddlewheel and thereby restricting removal of the cart key from the retaining rail; and a one-way clutch, coupled to the paddlewheel, for allowing rotation of the paddlewheel in a return direction and thereby allowing the cart key to be inserted into the retaining rail. 
     According to an additional aspect of the invention, a cart management apparatus for retaining carts of the type having a cart key mounted thereto at a predetermined height is provided, including a retaining rail having an open end for receiving a cart key and an access aperture defined in at least one side thereof; a paddlewheel including first and second paddles extending radially from a rotational axis thereof for selectively retaining the cart key in the retaining rail; and paddlewheel position sensing means for sensing the rotational position of the paddlewheel. The first and second paddles have notches defined at first and second predetermined radial distances from the rotational axis of the paddlewheel, respectively, and the paddlewheel position sensing means includes first and second sensors arranged at the first and second predetermined radial distances for detecting the notches on the first and second paddles, respectively. 
     According to a further aspect of the invention, a cart management system for vending carts is provided, including a cart key mounted to a cart at a predetermined height; retaining means for selectively retaining the cart key; and key identification sensing means for identifying the cart when the cart key is retained by the retaining means. The key identification sensing means includes first transmitting means, disposed within the cart key, for providing an identification signal indicative of the cart, and first receiving means, coupled to the retaining means, for detecting the identification signal when the cart key is retained by the retaining means. 
     According to another aspect of the invention, a method of vending carts in a cart management apparatus of the type including a retaining rail having an open end for receiving cart keys mounted on the carts and a rotatably mounted paddlewheel including a plurality of paddles extending radially from a rotational axis thereof for selectively retaining carts with cart keys retained in the rail is provided. The method includes the steps of detecting insertion of a cart key into the retaining rail; identifying the cart key and determining whether the cart key is a valid key; sensing when the key is fully retained within the rail by the paddlewheel; and dispensing a reward when a valid key is identified and the key is fully retained within the rail. 
     These and other advantages and features, which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention and the advantages and objectives obtained by its use, reference should be made to the drawing which forms a further part hereof and to the accompanying descriptive matter, in which there is described a preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1a is a perspective view of a preferred cart management system consistent with the invention. 
     FIG. 1b is an enlarged partial fragmentary perspective view of the cart management system of FIG. 1a, with an access panel removed therefrom showing the paddlewheel mechanism and sensors retained therein. 
     FIG. 2 is a partial fragmentary perspective view of the cart key of FIG. 1a. 
     FIG. 3 is an end elevational view through the open end of the retaining rail, showing a cart key retained therein. 
     FIG. 4 is a partial fragmentary perspective view of the retaining rail, paddlewheel mechanism and sensors for the cart management system of FIGS. 1a and 1b. 
     FIG. 5a is an exploded perspective view of the paddlewheel mechanism of FIG. 4. 
     FIG. 5b is a top plan view of the paddlewheel of FIG. 5a. 
     FIG. 5c is a top plan view of an alternate paddlewheel suitable for use with the paddlewheel position sensor in the system of FIGS. 1a and 1b. 
     FIG. 6 is a top cross-sectional view of the centering mechanism and dampening mechanism for the paddlewheel mechanism of FIG. 4. 
     FIG. 7 is a schematic diagram of the electronic components in the cart key and key identification sensor for the system of FIG. 1a. 
     FIG. 8 is a schematic diagram of the electronic components in the controller for the system of FIG. 1a. 
     FIGS. 9a-d are flowchart diagrams showing the operation of a preferred control system for the system of FIG. 1a. 
     FIG. 9e is a flowchart diagram of an alternate key carts in/out routine to that of FIG. 9d. 
     FIGS. 10a-f are functional top plan views showing various stages in the return of a cart into the cart management system of FIG. 1a. 
     FIG. 11 is a functional top plan view showing an alternate positioning for the key identification sensor of the cart management system of FIG. 1a. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning to the Drawing, wherein like numbers denote like parts throughout the several views, FIGS. 1a and 1b show a preferred cart management system 10 consistent with the invention, including a cart management unit 50 for retaining and vending a plurality of carts such as luggage cart 20. Cart management unit 50 includes a retaining rail 52, supported off the ground by a plurality of supports 54, for receiving and vending carts through an open end 56 thereof. A paddlewheel mechanism 60 projects into the retaining rail to control the insertion and removal of carts into and out of the system, and a controller 58 provides electronic control over system 10, including controlling paddlewheel mechanism 60, accepting currency and dispensing rewards. 
     Cart 20 is preferably a nestable luggage cart, such as those available from a number of vendors, including Smarte Carte, Inc. Other types of carts, including shopping carts, strollers, etc. may also be used consistent with the invention. Furthermore, while the preferred carts are nestable to reduce the amount of rail needed to retain a number of carts, non-nestable carts may also be used. 
     A cart key 30 is utilized on cart 20 to cooperate with retaining rail 52 in retaining cart 20 in cart management unit 50. As shown in FIG. 2, key 30 includes a mounting bracket 32 with saddle clamp 31 that removably fixes key 30 on an upward support 22 near the rear of cart 20 at a predetermined height from the ground surface. The height of key 30 preferably ranges from about 9 to 14 inches, more preferably about 12 inches in height. Alternate mounting methods, including permanent mounting methods such as welding may be used to mount key 30 to cart 20. 
     Cart key 30 may be installed on luggage carts, shopping carts, strollers, etc. Furthermore, it may be installed at different places on a cart, including vertical or horizontal supports, wheel housings, or baskets of a cart. It will be appreciated that the design of the key clamp will vary accordingly with the placement of the key on a cart. In addition, it will be appreciated that the wheels of the carts themselves may be used as the keys for retaining the carts in the retaining rail. 
     The preferred design of cart key 30 therefore enables carts which are not integrated into an existing cart management system (and thus do not have keys mounted thereon), as well as carts integrated into other automated systems (having other keys mounted thereon), to be utilized in the preferred cart management system 10. Consequently, the preferred system 10 may be utilized as a significantly standardized system for use with a wide variety of carts. It will be appreciated, however, that the preferred system 10 may also utilize new carts which are specifically designed for use with the system. 
     Cart key 30 includes first and second rollers 36 and 38 rotatably mounted to a base portion 34 of bracket 32 through bolts 39. A support 33 may also be used to reinforce base 34 against saddle clamp 31. 
     Rollers 36 and 38 are preferably made of a plastic such as Versathane® polyurethane. Other materials, including Nylon may also be used. First roller 36 preferably includes electronics (discussed below) which provide an identification signal utilized by cart management unit 50 to identify the particular cart to which key 30 is attached. In the preferred embodiment, however, second roller 38 is inactive, i.e., no electronics are included therein. 
     The two roller construction of key 30 offers several benefits. First, the longitudinally aligned rollers help in centering the key in retaining rail 52. Furthermore, the rollers facilitate the movement of cart 20 along the rail, by rolling against the internal sides of the rail, by maintaining the key centered in the rail, and by preventing the cart from being twisted while the key is retained in the rail. The use of a second roller also has the benefit of preventing the first roller from being pulled back into proximity with a sensor once the key is inserted into the rail, providing one of the hustler-prevention measures in the preferred system 10 (discussed in greater detail below). 
     Rollers 36 and 38 are preferably rotatable on base 34. As discussed above, by being rotatable, movement of the key along the retaining rail is facilitated. However, the rollers may be replaced by fixed members, although greater friction may result within the rail. 
     In addition, rollers 36 and 38 preferably rotate about vertical axes. As seen in FIG. 3, this arrangement provides a degree of clearance within rail 52 to compensate for variations in key height between carts, or to compensate for variations in ground surfaces (e.g. bumps or cracks) which may vary key height as a cart rolls down the retaining rail. Carts may be significantly less likely to catch in the retaining rail as a result of key height imperfections with this design. It will be appreciated that the rollers could instead rotate about horizontal axes (or may even be the wheels of the cart themselves) consistent with the invention. 
     Returning to FIG. 1a, cart management unit 50 is used to retain and control the vending of carts 20. Unit 50 includes a controller 58 which provides electronic control over the vending, return, reward and change dispensing, and payment functions of cart management system 10. The primary operational components of controller 58 will be discussed below with relation to FIG. 8; however, the components shown in FIG. 1, which make up the user interface for system 10, will be described briefly. 
     A display 58a is included to provide prompts and convey information to a user. Display 58a may be any of a number of types of alphanumeric displays, including LED, LCD, Vacuum, or CRT displays, for example a 16 character No. L2014B1J000 LCD display manufactured by Seiko. 
     Payment is accepted from a customer through one of three mechanisms. The first, card reader 58b accepts payment from a credit or debit card, which may also include a modem and communications link to verify a card before accepting payment. One preferred card reader is the EasyReader card reader manufactured by CommStar, Inc. The second, bill reader 58c accepts payment from the insertion of dollar bills in different denominations. One preferred bill reader is the CBA-2 bill reader manufactured by Rowe. The third, coin reader 58d accepts payment in coin currency. One preferred coin reader is the C235 Sentinal coin reader manufactured by Coin Controls. The use and operation of each of these types of readers is known in the art, and it will be appreciated that payment may be accepted in any combination of the above devices. 
     The user interface for controller 58 also includes a change dispenser 58e which returns change and/or rewards to a customer in coin currency, such as the Mark II change dispenser manufactured by Coin Controls. Change and rewards may also be returned by a bill dispenser or by crediting a credit or debit account; however, typically a return in coin currency is sufficient for most situations. 
     Several access panels are also provided on unit 50 for performing routine maintenance of the system. For example, three access panels 59a, 59b and 59c are shown in FIG. 1. The panels are preferably locked to permit access only to authorized personnel. It will be appreciated that the arrangement and number of panels may vary. 
     A retaining rail 52 is supported by a number of vertical supports 54 at a predetermined height. As shown in FIG. 3, rail 52 is preferably rectangular in cross section with a downwardly open slot extending along the length of the rail. It will be appreciated that the height and cross-sectional shape of the rail will be dictated primarily by the height and shape of keys 30 on carts 20. For example, if the keys include rollers which rotate about horizontal axes, the slot in the rail would be open to the side of the rail. 
     The length of rail 52 will vary depending upon the number of carts which are to be retained. The rail is preferably a modular design, whereby fixed lengths of rails may be joined together in any manner known in the art to provide the necessary length. 
     The preferred system 10 utilizes a single unit 50 to vend and return carts, resulting in last in-first out cart vending. Consequently, rail 52 is preferably open only at one open end 56, with the opposite end otherwise obstructed. However, an alternate embodiment may include separate control units at each end of the rail for first in-first out vending, whereby carts would be returned at one end of the system and vended at the other end. 
     As shown in FIG. 4, a paddlewheel mechanism 60 provides an obstruction in retaining rail 52 through an access aperture 55 in the rail. As best shown in FIG. 5a, the primary components of paddlewheel mechanism 60 are paddlewheel 80, one-way clutch 61 and electromagnetic brake 65. 
     FIGS. 5a and 5b show paddlewheel 80 in greater detail. Paddlewheel 80 preferably includes four paddles 82a-d radially extending from the rotational axis of the paddlewheel. Any number of paddles, e.g., as few as two, may be used. Further, paddlewheel 80 preferably rotates about a vertical axis, which enables the rollers of cart key 30 to roll along the paddles as the key is pushed through the rail past paddlewheel mechanism 60, thereby reducing the friction encountered by the cart key in the rail. Consequently, for rollers which rotate instead about horizontal axes, paddlewheel 80 may rotate about a horizontal axis as well. Alternatively, paddlewheel 80 may rotate about a transverse axis to that of key rollers 36 and 38. 
     Paddles 82a-d of paddlewheel 80 preferably engage a cart key through access aperture 55 in retaining rail 52. Alternatively, the paddles may engage other components of a cart, either retained within a secondary retaining rail or not, e.g., coupled with a cart key retained in rail 52. 
     One-way clutch 61 includes a slotted member 63 which is rotatable in a main housing 64 mounted to paddlewheel 80 through a plurality of bolts extending through apertures 85 and 62 in paddlewheel 80 and housing 64, respectively. A shaft 69 is in turn coupled to the slotted member 63, which has a slotted aperture therein for cooperatively retaining a key on shaft 69. 
     One preferred design for clutch 61 is an over-running/indexing/backstopping type clutch, such as the FSO 300 clutch manufactured by Warner Electric. This type of clutch permits paddlewheel 80 and clutch main housing 64 to rotate in a counter-clockwise direction with respect to shaft 69 and slotted member 63 (when viewed from the top). This enables the paddlewheel to rotate freely when a cart key is being inserted into retaining rail 52 (i.e., in an insertion or returning direction) as a cart is being returned. 
     The lower end of shaft 69 is retained by a bearing 69a (shown in FIG. 4) that secures the shaft in the unit while permitting shaft 69 to rotate in relation thereto. The lower end of shaft 69 also includes an annular Groove 69b (FIG. 5a) which is secured by a Waldes Truarc #5133-74 e-ring circular clip 69c, which supports clutch 61 and paddlewheel 80 on shaft 69. The opposite end of shaft 69 projects through an electromagnetic brake 65 and is retained by a slotted member 67 which is selectively rotatable within a main housing 66. Brake 65 selectively inhibits rotation of paddlewheel 80 to restrict removal of a cart key from rail 52 in a removal or vending direction. 
     Brake 65 is preferably an electrically actuated spring applied friction brake which is normally biased to a locked stated in the absence of an electrical control signal, such as the ERS-68 electromagnetic brake manufactured by Warner Electric. Upon the application of an electrical signal (at least 24 VDC in the case of the preferred brake), slotted member 67 is permitted to rotate freely within housing 66. In the alternative, electromagnetic brake 65 may be biased normally to an unlocked state; however, in such a case, the brake would draw more power since the brake is typically locked the majority of the time, being unlocked only when a cart is vended. 
     Different locking mechanisms may be used in the alternative to electromagnetic brake 65. Examples include solenoid and controlled mechanical mechanisms, ratchet release control mechanisms, etc. 
     Either the one-way clutch or the electromagnetic brake may be used independent of the other in the control of paddlewheel 80. However, it has been found that the combination clutch and brake offers simple, efficient and low power control over paddlewheel 80. For example, the one-way clutch enables carts to be returned without applying power to the brake, since the clutch permits rotation of the paddlewheel in an insertion direction. In addition, since the clutch permits free rotation in this direction, certain components of the system such as key identification sensor 120 do not need to be continuously active to sense when a cart is being returned, rather, the insertion of the cart itself can be detected by a sensor to &#34;wake up&#34; the system to handle the cart return and reward operations. With this configuration, the only time in which power need be applied to the brake is when a cart is being vended, after sufficient currency has been inserted by a customer. Consequently, less power is utilized by the system. Further, the system is more reliable given that a cart can only be released from the system only when power is applied to brake 65 by controller 58. 
     A centering mechanism is also preferably incorporated in paddlewheel mechanism 60 to center the paddlewheel at predetermined positions, preferably with a paddle projecting into retaining rail 52 generally orthogonal to the longitudinal axis thereof. By maintaining the paddlewheel at predetermined positions when at rest, the position of the paddlewheel is significantly easier to detect and control with less complex and expensive sensors. Otherwise, a positional sensor may be incorporated into the paddlewheel mechanism to provide a signal representative of the precise angular position of the paddlewheel; however, such a sensor would most likely be more expensive and complex, and would require more elaborate software control by controller 58. 
     As shown in FIG. 6, in the centering mechanism, a spring-loaded centering device 90 engages a plurality of cam follower rollers 94 coupled to the paddlewheel 80. Centering device 90 includes a spring loaded cam 92 having tapered edges which engage the cam follower rollers 94 and urge the paddlewheel to one of four positions. In the preferred embodiment, the cam edge is formed by a pair of planar surfaces joined at an apex. However, it will be appreciated that other known edge profiles, including curved, may be used to vary the camming action applied by the device on paddlewheel 80. 
     Cam follower rollers 94 are preferably rotatably mounted on bolts threaded through the underside of paddlewheel 80. The number, spacing and placement of the rollers will be dependent upon the number of paddles and the desired centering action (e.g., the amount of centering force applied) applied by the mechanism. For four paddles, four evenly positioned rollers 94 are preferred, with the desired angular positions of the paddlewheel being at the midpoints between adjacent pairs of rollers. The paddlewheel will be urged to the point at which the compression of the spring in centering device 90 is minimized, which is at these midpoint positions since cam 92 of device 90 is the least compressed at these positions. 
     It will also be appreciated that the rollers may be fixably mounted to the paddlewheel/clutch assembly. However, this would increase the friction between rollers 94 and centering device 90, thus making the paddlewheel harder to turn. 
     A dampening mechanism may also be optionally incorporated in paddlewheel mechanism 60 to smooth out the rotation of the paddlewheel. It has been found that due to the centering force applied by the centering mechanism, the paddlewheel may have the tendency to overshoot the predetermined rotational position. Through the use of a dampening mechanism, the conversion of the potential energy stored in the centering mechanism to the kinetic energy of the paddlewheel is tempered, whereby the rotation of the paddlewheel induced by the centering mechanism is moderated to prevent the paddlewheel from overshooting the predetermined positions. 
     The dampening mechanism utilizes a damper device 95 having a cam 96 which is similar in configuration to cam 92 of centering device 90, having tapered edges which can have many different cam surface profiles. Cam 96 moves relative to damper device 95 through a hydraulic piston and cylinder assembly, e.g., an air cylinder similar in operation to a shock absorber, such as the MC150 manufactured by Ace Controls Inc. This type of assembly is resistant to changes in velocity, thereby providing relatively uniform motion for cam 96, and consequently, uniform motion for paddlewheel 80. 
     The dampening mechanism also utilizes cam follower rollers 94 which are rotatably mounted on the underside of paddlewheel 80. The dampening device 95 is preferably oriented about 45 degrees (or alternatively, at 135, 225 or 275 degrees) offset from the position of centering device 90. In this orientation, the maximum dampening effect of the dampening mechanism is coordinated with the position of maximum potential energy for the centering mechanism. In an alternate embodiment, rollers 94 may be mounted to the top side of paddlewheel 80, or to a separate member which rotates in cooperation with the paddlewheel. Further, separate rollers may be used for the dampening and centering mechanisms, respectively, however, it has been found that the use of a single set of rollers reduces the number of parts and permits easier assembly. 
     Returning again to FIG. 1b, cart management system 10 uses a plurality of sensors for tracking the movement of carts through the retaining rail 52. A first sensor, cart in/out sensor 100, is mounted proximate end 56 of retaining rail 52 in a sensor aperture 57. This sensor includes an arm projecting into rail 52. A cart key moving past sensor 100 engages the arm and rotates it about an axis transverse to the longitudinal axis of the rail. 
     Sensor 100 is preferably a two-way sensor which provides separate signals for detecting whether a cart key is moving in or out of rail 52. This type of sensor is exemplified by the Limit Switch manufactured by Micro Switch. Other known sensors, including mechanically actuated, magnetic, or capacitive proximity sensors, etc. may be used, further including binary sensors which only detect whether a key is present, rather than detecting the direction in which the key is moving. In addition, sensor 100 may be omitted, with its functions instead incorporated into the software and the other sensors. 
     Sensor 100 is used to count carts in and out of the system. Furthermore, sensor 100 may be used to activate controller 58 to turn on key identification sensor 120, among other operations (e.g., wake the controller from a &#34;sleep&#34; state) when a cart key is inserted into rail 52. Consequently, substantially automatic operation is provided since a user does not need to manually activate the system prior to returning the cart. 
     As best shown in FIG. 4, and functionally in FIG. 5b, a second sensor, a paddlewheel position sensor 110, is used to detect which paddle 82a-d is positioned within retaining rail 52. In the preferred embodiment, three separate proximity detectors 111, 112 and 113 are used to detect notches 83a-c cut into different paddles. The detectors are arranged along a radial line at distances r 1 , r 2  and r 3 , respectively, from the rotational axis of paddlewheel 80. 
     The angular position of the detectors is preferably 90 degrees from the angular position of the paddle projecting into rail 52, although the detectors may also be oriented at 0, 180 or 270 degrees therefrom. The detectors are preferably positioned directly over one of the paddles when the paddlewheel is at a centered position so the paddle may be identified when centered. It will be appreciated, however, that the arrangement and number of detectors will vary with the arrangement and number of paddles. 
     As seen in FIGS. 5a and 5b, notches are cut into the top edges of the paddles on paddlewheel 80. Alternatively, the notches and detectors may be located on the underside of the paddlewheel, or on a separate member which rotates in cooperation with the paddlewheel. Notch 83a is formed on paddle 82a at distance r 1  from the rotational axis of paddlewheel 80. Similarly, notch 83b is formed on paddle 82b at distance r 2 , and notch 83c is formed on paddle 82c at distance r 3 . Paddle 82d does not have a notch. It will be appreciated that the arrangement of these notches on the paddles may vary. 
     Detectors 111, 112 and 113 are proximity type detectors such as the Inductive proximity sensors manufactured by Turck Inc, which generally include a coil and ferrite core arrangement, an oscillator circuit, a detector circuit, and a solid-state output circuit. The oscillator circuit drives the coil and emits a high frequency field therefrom. A metal object placed closed to the coil collects eddy currents and reduces the energy in the oscillator circuit. The detector and solid-state output circuits detect the loss of energy in the oscillator circuit and provide a digital output representative thereof. Other known types of detectors may also be used. 
     With detectors 111, 112 and 113, each notch in a paddle is indistinguishable from the detected condition when no paddle is underneath the detectors. Therefore, each paddle is identified by paddlewheel position sensor 110 as follows. Each paddle 82a-d has a unique identification as a result of the presence and position of the notch on the paddle. Assuming a &#34;1&#34; indicates the detection of the metallic material in a paddle, and a &#34;0&#34; indicates no metallic material detected, detectors 111, 112 and 113 will output in one of five states, as shown in Table I: 
     
                       TABLE I                                                     
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             Detector                                                     
Condition      111         112    113                                     
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1) Between paddles                                                        
               0           0      0                                       
2) Paddle 82a  0           1      1                                       
3) Paddle 82b  1           0      1                                       
4) Paddle 82c  1           1      0                                       
5) Paddle 82d  1           1      1                                       
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     In the alternative, a single detector could be used to detect when a paddle passed a certain position, with the software being used to increment or decrement a count to keep track of which paddle is projecting into rail 52. One potential problem with this alternate configuration, however, is that a hustler could break the clutch or brake and &#34;jiggle&#34; the paddlewheel back and forth across a detector to simulate multiple cart returns. In the preferred configuration, on the other hand, controller 58 will have a reliable identification of which paddle is positioned under sensor 110, and knowing in which order the paddles are arranged, will not be susceptible to this particular hustling technique since the controller will know precisely which paddle should be expected in a proper return. 
     Different paddlewheels with various combinations of notches on the paddles may be used with paddlewheel position sensor 110. For example, as shown in FIG. 5c, an alternate paddlewheel 80&#39; includes paddles 82a&#39;-82d&#39;. Paddlewheel position sensor 110 again has detectors 111, 112 and 113 disposed at radii r 1 , r 2  and r 3 , respectively. In this embodiment, paddle 82a&#39; does not include a notch. Paddle 82b&#39; includes a notch 83b&#39; at radius r 2 , and paddle 82c&#39; includes a notch 83c&#39; at radius r 3 . In addition, paddle 82d&#39; includes a notch 83d&#39; that spans from radius r 2  to radius r 3 . No notches are disposed at radius r 1  ; therefore, detector 111 may be used independently as a &#34;centered&#34; sensor which senses whenever a paddle is positioned directly below position sensor 110. The identification of which paddle is in this position is detected by the combination of detectors 112 and 113. Table II shows the detector outputs for paddlewheel 80&#39;: 
     
                       TABLE II                                                    
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             Detector                                                     
Condition      111         112    113                                     
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1) Between paddles                                                        
               0           0      0                                       
2) Paddle 82a  1           1      1                                       
3) Paddle 82b  1           0      1                                       
4) Paddle 82c  1           1      0                                       
5) Paddle 82d  1           0      0                                       
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     The alternative arrangement shown in FIG. 5c has the advantage of being able to detect whether a paddle is centered in a position with detector 111 alone (1=paddle, 0=no paddle), then being able to detect which paddle is located under the sensor using only detectors 112 and 113. This arrangement tends to simplify the software code necessary for detecting paddlewheel positions. 
     This alternative arrangement also is particularly useful for embodiments in which in/out sensor 100 is not used, and it enables detectors 112 and 113 to be disabled much of the time, saving processing time and power requirements. For example, when a paddle is centered under sensor 110, there is typically no need to enable detectors 112 and 113. Detector 111 may be checked periodically (e.g., every 0.1 second) to determine whether movement of the paddle has occurred (e.g., in a cart return situation), or may be tied to an interrupt line to awaken the system when movement of the paddlewheel is detected (effectively performing the same function as sensor 100). Then, when movement of the paddle away from detector 111 occurs, the system can then activate detectors 112 and 113 to assist in identifying the next paddle. Once the next paddle is identified, detectors 112 and 113 may be disabled, and detector 111 may return to the sleep state. It will be appreciated that a paddle will generally be located under sensor 110 almost all of the time, therefore, the usage of detectors 112 and 113 is greatly reduced in this manner. 
     An alternative embodiment of paddlewheel position sensor 110 utilizes a pair of detectors arranged along a radial line at first and second distances from the rotational axis of paddlewheel 80. One pair of oppositely disposed paddles, e.g. paddles 82a and 82c, have notches at the first distance, and the other pair, paddles 82b and 82d, have notches at the second distance. Again, assuming &#34;1&#34; denotes the detection of paddle metallic material, and &#34;0&#34; denotes the absence of metallic material, the first and second detectors would output in three different states, as shown in Table III: 
     
                       TABLE III                                                   
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Condition    First Detector                                               
                         Second Detector                                  
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1) Between paddles                                                        
             0           0                                                
2) Paddles 82a/82c                                                        
             0           1                                                
3) Paddles 82b/82d                                                        
             1           0                                                
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     In this alternative embodiment, controller 58 would be programmed with the arrangement of paddles, and therefore, would be able to determine which paddle is under the first and second detectors. Consequently, the aforementioned hustling scheme would also not pose a problem for this alternate embodiment. 
     It will be appreciated that both of the preferred paddlewheel position sensor designs are relatively simple and inexpensive, and are comparatively easy to implement in controller 58. Other position sensors, including angular position sensors, may be used in the alternative. 
     As shown in FIG. 1b, a third sensor, key identification sensor 120, is positioned along rail 52 immediately beyond paddlewheel mechanism 60. This sensor confirms that a cart key for a returned cart has been fully inserted into rail 52 and retained by paddlewheel mechanism 60. Furthermore, this sensor may also be used to identify the cart key as belonging to system 10 for the purpose of refunding a reward and further protecting from hustlers. 
     The first of the above-described functions for sensor 120 may be accomplished by many types of sensors, including those described above in relation to first sensor 100. The second function, however, identifying the cart key, requires some additional degree of cooperation between key 30 and sensor 120. 
     The preferred design for the key identification sensor 120 is shown schematically in FIG. 7. Sensor 120 includes a transmitter 121, a receiver 126 and a key detector circuit 130 coupled to the transmitter and receiver. Also shown in FIG. 7 is a cart key 30 having a receiver 140 coupled to a transmitter 145. When cart key 30 is in close proximity to sensor 120, transmitter 121 of sensor 120 is electromagnetically coupled to receiver 140 of key 30, and receiver 126 of sensor 120 is electromagnetically coupled to transmitter 145 of key 30. When this coupling occurs, key detector circuit 130 generates a signal KEY 13  PRESENT indicating that a valid key has been detected. 
     The operation of sensor 120 and key 30 is as follows. Transmitter 121 of sensor 120 is any known oscillator circuit capable of generating a fixed frequency signal at a frequency F 1 , which is preferably any frequency between about 30 Khz and 200 Khz. For example, transmitter 121 may include an oscillator 125 and an amplifier 124 connected to a parallel L-C circuit comprised of a wire coil 122 and a capacitor 123. The inductance and capacitance of coil 122 and capacitor 123, respectively, are selected to generate the frequency F 1 , in a manner known in the art. The fixed frequency signal is emitted from coil 122 for a short distance from the coil, preferably about 0.5 to 2.0 inches. The distance is selected such that a key will only be detected when it is in retaining rail 52 directly opposite sensor 120. 
     The signal emitted by coil 122 is received by receiver 140 when the key is in close proximity to sensor 120. Receiver 140 includes a parallel-resonant network including a coil 141 and capacitor 142 connected in parallel, with the inductance and capacitance of the coil and capacitor, respectively, selected such that receiver 140 is tuned to resonate at frequency F 1 . 
     Receiver 140 is coupled to key transmitter 145, which includes a parallel-resonant network of coil 146 and capacitor 147. One end of the parallel-resonant network of transmitter 145 is connected to a center tap off of coil 141. The other end of the transmitter network is connected through a pair of diodes 143 and 144 to the ends of coil 141 of receiver 140. The inductance and capacitance of coil 146 and capacitor 147, respectively, of transmitter 145 are selected such that, when a signal (e.g., generated by transmitter 121 of sensor 120) is present with sufficient strength, the induced alternating voltage potential at each end of coil 141 with respect to its center tap is coupled into the parallel-resonant network of transmitter 145 through diodes 143 and 144. Since the alternating voltage at each end of coil 141 is 180 degrees out of phase with the other end, and since the diodes pass the positive cycle of each, the exciting signal into the parallel-resonant network of transmitter 145 is exactly double the frequency of the receiver&#39;s oscillation. This causes the parallel-resonant network of transmitter 145 to resonate at a frequency F 2 , which is exactly double the frequency F 1 . Preferably, the strength of this signal is sufficient to couple with receiver 126 of sensor 120 only when the key is directly opposite the sensor in the track. 
     It will be appreciated that since receiver 140 is tuned to resonate at frequency F 1 , the receiver will not resonate as a result of applied signals at other frequencies, and consequently will not have enough energy to excite transmitter 145 to emit a return signal. Furthermore, since transmitter 145 is tuned to resonate at frequency F 2 , the transmitter will not emit signals at any other frequency. 
     Receiver 126 of sensor 120 includes a parallel-resonant network of coil 127 and capacitor 128, the inductance and capacitance of which are selected such that receiver 126 is tuned to pick up a signal with frequency F 2 . Receiver 126 will not efficiently pick up other signals. The resonant signal of the parallel-resonant network is amplified and converted to a pulse train by pulse shaper 129. Pulse shaper 129 may be a simple comparator, or another known device which provides a binary pulse train output from an oscillating AC signal. 
     From the known frequencies F 1  and F 2 , key detector 130 can determine whether a valid key is being detected by sensor 120 as follows. The output from pulse shaper 129 is fed into a divide-by-eight counter 132 which produces an output with a frequency that is 1/8th the frequency of the pulse train generated by pulse shaper 129. The configuration of a counter to operate as a divide-by-eight frequency generator is known in the art. 
     The output of oscillator 125 of transmitter 121 is fed into a divide-by-four counter 131 which produces an output with a frequency that is 1/4th the oscillator frequency F 1 . The configuration of a counter to operate as a divide-by-four frequency generator is also known in the art. 
     The output of counter 131 is fed into the reset input of counter 132. Through this combination, the only time in which the output of counter 132 is forced high occurs when receiver 126 resonates to apply a signal to counter 132 at frequency F 2 , since frequency F 2  is selected to be twice that of frequency F 1 . If a pulse train was provided by pulse shaper 129 which was lower than frequency F 2 , the counter 132 would be reset by counter 131 before its output would be forced high. This effectively prevents a signal at frequency F 1  (due to, for example, a hustler placing a metal object proximate sensor 120 to reflect the transmitted signal from transmitter 121) from indicating a key present condition due to the transmitted signal at frequency F 1  being picked up and amplified by receiver 126. 
     The output of counter 132 is fed to the clock input of a latch 133. The data input D of latch 133 is connected to the output of a first timer (T1) 134. Timer 134 accepts a START --  SENSE signal 136 from controller 58 (not shown in FIG. 7) through a interface 138. Timer 134 is any known timer which is configured to output a high signal for a fixed period of time after being initiated by a high input signal thereto. In the preferred embodiment, timer 134 provides a positive voltage at the data input of latch 133 for about 5 to 15 seconds, preferably about 10 seconds, after START --  SENSE is asserted by controller 58. 
     With the data input of latch 133 connected to timer 134 and the clock input connected to counter 132, the output Q of latch 133 will only be forced high when a key is detected in the time frame set by timer 134 (i.e., when the data and clock inputs are both high). Therefore, a user only has a certain period of time after sensor 120 has been activated to insert the cart key far enough into rail 52 to be detected by sensor 120. 
     The output Q of latch 133 is returned to controller 58 as a KEY --  PRESENT signal 137 through interface 138. A second timer (T2) 135 is used to reset the KEY --  PRESENT signal after a predetermined period of time. Timer 135 is activated by the output of counter 132, and therefore, will be initiated when the clock input of latch 133 is forced high by counter 132. The output of timer 135 is fed to the reset input of latch 133, whereby after a fixed period of time after the clock input of latch 133 is forced high, preferably about 10 seconds, the output will be reset to low. The action of timer 135 keeps the KEY --  PRESENT signal active long enough for controller 58 to detect the signal if it is operating in a polling mode. 
     Various modifications to the design of sensor 120 and key 30 may be made consistent with the invention. For example, transmitter 121 of sensor 120 may be controlled by the START --  SENSE signal 136 to oscillate only when directed by controller 58. Furthermore, sensor 120 may be used to verify that no pulses are received during a time window in which transmitter 121 is shut off. 
     Other sensor/key configurations may also be used consistent with the invention. For example, other proximity identification systems, even those which can provide separate identification codes for each key (to enable the system to keep track of each individual cart in the system), may also be used; however, these more sophisticated systems are comparatively more expensive, and would require more sophisticated control than the comparatively simple and inexpensive preferred sensor 120. 
     Receiver 140 and transmitter 145 of key 30 are preferably mounted within the first roller 36 thereof. In the preferred embodiment the components of the receiver and transmitter are formed on a circular fiberglass circuit board which is adapted for mounting within a covered recess on roller 36. Coils 141 and 146 are preferably formed as circuit board traces on the circuit board, and the diodes and capacitors are mounted to the board, in a manner known in the art. Alternatively, coils 141 and 146 may be wound coils of wire mounted about the periphery of a disk. 
     It will be appreciated that frequencies F 1  and F 2  may be selected to customize cart keys 30 and sensor 120 of the preferred cart management system 10. Consequently, different installations can utilize different frequencies, so that keys from one facility will not work with another facility. This also prevents hustlers for obtaining universal keys that will work on all installations. 
     As was described previously, second roller 38 of cart key 30 is inactive. One purpose for roller 38 is to prevent roller 36 from being pulled back into proximity with sensor 120 after paddlewheel 80 has been incremented by insertion of a cart fully into rail 52. Once the paddlewheel has been incremented, one-way clutch 61 and brake 65 restrict the rotation of the paddlewheel in the opposite direction, and the placement of sensor 120 immediately behind paddlewheel mechanism 60 also cooperates in keeping roller 36 from being detected a second time by sensor 120 after a valid key has already been detected. 
     FIG. 8 shows a schematic diagram for the primary electronic components of controller 58. Program code for controller 58 is executed in a processor 152. The program code is stored in a combination of read only memory 156 and a portion of a battery-backed random access memory 154. A remaining portion of random access memory 154 is used for working memory. Many different known microprocessors or microcontrollers may be suitable for use as processor 152, for example, the 8031 processor manufactured by Intel. 
     It will be appreciated by one skilled in the art that various support circuitry will be required for processor 152 such as a power supply circuit, a crystal oscillator, data buffers, and other necessary components. Further, it will be appreciated that the configuration, installation and operation of processor 152, ROM 156, ROM 154 and the other required support circuitry are well known in the art. 
     Processor 152 has a number of inputs and outputs through which it communicates with several subgroups of external components within controller 58. For example, one subgroup includes the display panel components that provide the primary user interface, including display 58a, card reader 58b, bill reader 58c, coin reader 58d, and coin dispenser 58e, and which must be capable of receiving and transmitting information to and from processor 152. 
     A display panel input/output block 157 is shown between the display panel components and processor 152 for handling the information exchange therebetween. Display panel I/O block 157 is shown generically, as the display panel components may be interconnected with processor 152 in a number of manners. For example, each of the components may be assigned address space and connected to the address and data buses of processor 152 in a known manner. Alternatively, the information exchange may be handled through serial or parallel communication through one or more dedicated I/O ports from processor 152. It will further be appreciated that different buffers, multiplexers, and other communication devices may also be necessary depending on the particular selected manner for exchanging data between the display panel components and processor 152. 
     Components 58a-58e are preferably commercially available items, and consequently, the use, control, and information exchange protocols necessary for control of these items via a processor such as processor 152 is known in the art. Furthermore, since card reader 58b may also include credit card verification from a remote site, an optional modem 158 maybe interconnected thereto for handling the remote communication. The required peripheral devices, connections and control operations for controlling modem 158 are also known in the art. 
     A second subgroup of components which are driven by processor 152 are the cart in and cart out count displays 151a and 151b and the key cart in/out switch 153. The switch and displays are preferably located behind an access panel whereby only authorized maintenance personnel have access to the components. The cart in count display 151a displays the number of carts which are currently retained within system 10. Cart out count display 151b provides a display of the number of carts which are currently in use by customers. As shown in FIG. 8, both displays may be controlled through the display panel input/output circuitry 157. The displays are preferably selected from commercially available components such as CUB 3LR displays manufactured by Red Lion Controls, and consequently, the transfer of information between the displays and processor 152 is known in the art. In an alternative embodiment, the cart counts may be displayed on a single view register, or even on display 58a, accessed by a push button behind an access panel. An operator would be able to toggle through different views to get separate counts of carts in, carts out, carts used, carts vended, etc. 
     Key cart in/out switch 153 is used to select an alternate, maintenance mode of operation for processor 152 which automatically releases electromagnetic brake 65 to enable maintenance personnel to add or remove carts from the system. Switch 153 may be interconnected to processor 152 to any number of known manners, e.g., through a dedicated input/output, as an address in the processor addressing space, or as an external interrupt. 
     A third subgroup of components which are controlled by processor 152 are the cart in/out sensor 100, the paddlewheel position sensor 110, and the key identification sensor 120. Cart in/out sensor 100 preferably provides two separate outputs which indicate, respectively, whether a cart is being inserted into rail 52 or removed from rail 52. Paddlewheel position sensor 120 includes detectors 111, 112, 113, each of which has an output which is asserted whenever metallic material is detected in close proximity to the detectors. Furthermore, as discussed above with reference to FIG. 7, key identification sensor 120 receives an input START --  SENSE which is asserted by processor 152 to initiate sensor 120 for detecting a valid key. Sensor 120 also provides an output KEY --  PRESENT which is asserted when sensor 120 detects a valid key. It will be appreciated that the input/output signals to and from sensors 100, 110, 120 may be interconnected with processor 152 through any of the above-described known manners. 
     A fourth subgroup of components driven by processor 152 is the electromagnetic brake 65. As discussed above, brake 65 is normally biased to a locked position, and is unlocked through the application of a 24 VDC signal. Since many processors operate at 3 or 5 VDC, a brake driver 155 is preferably interposed between brake 65 and processor 152 to provide the necessary voltage amplification for driving brake 65 in response to a low voltage input signal asserted by processor 152. Many suitable amplifier circuits are known in the art. 
     Controller 58 preferably is configured to operate in the manner shown in FIGS. 9a-d. The program code necessary for performing the operations disclosed herein will be dependent upon the particular processor and programming language utilized in controller 58. Consequently, it will be appreciated that the generation of program code from the disclosure presented herein would be within the skill of an ordinary artisan. 
     Main routine 200 for the operation of controller 58 is shown in FIG. 9a. The first step in this routine is an initialization step 202, wherein various housekeeping functions such as initializing variables, setting up interrupts, etc., is performed. 
     Next, routine 200 proceeds to block 204 to determine whether the key cart in/out switch is set. As discussed above, this switch will be set by a maintenance personnel when it is desired to add or remove carts from the system. If this switch is set, the routine proceeds to block 260 to call the key cart in/out subroutine which handles this alternate mode of operation. This routine is discussed below with reference to FIG. 9d. 
     If the key cart in/out switch is not set, as will be typically found in the normal operational mode of the system, control passes to block 206 to determine whether a &#34;cart in&#34; condition is detected, indicating that a cart is being returned. In the preferred embodiment, this condition is sensed by detecting a &#34;cart in&#34; sensed by sensor 100. However, in the alternate embodiment described above wherein sensor 100 is not used, the &#34;cart in&#34; condition may be detected by sensor 110 as a cart inserted into rail 52 will be allowed to rotate paddlewheel 80 by virtue of one-way clutch 61. The initial rotation of paddlewheel 80 as a result of a cart being inserted into the rail is sensed when detectors 111-113 all indicate no metallic material detected (corresponding to the &#34;between paddle&#34; condition in Table I above), or, for the paddlewheel of FIG. 5c, when detector 111 indicates no metallic material detected. 
     Once the &#34;cart in&#34; condition is detected, control passes to block 240 to call the return cart routine, which is discussed in greater detail below with reference to FIG. 9c. On the other hand, if the cart in condition is not detected, control passes to block 208 to determine whether a vend request has been initiated. 
     Any number of conditions may initiate a vend request. For example, a user may depress a pushbutton on the display panel to request a cart vend. Alternatively, the vend request may be initiated automatically by the insertion of a credit or debit card into card reader 58b, the insertion of a dollar bill into bill reader 58c, or the insertion of a coin into coin reader 58d, all of which indicate that a customer is preparing to obtain a cart. 
     If no vend request is received, control returns to block 204 to again cycle through the main loop of routine 200. However, if a vend request is received, control passes to accept payment routine 210 to control the various payment accepting devices and determine whether sufficient funds have been inserted into the system to initiate a cart vend operation. The program flow of accept payment routine 210 is generally known in the art, and will be dependent upon a number of factors, e.g., the cost of a cart, the number/types of payment devices present on the system, etc. 
     After the accept payment routine 210 is called, control passes next to block 212 to determine whether a correct payment has been received. If the correct payment is not received, control passes back to block 204 to cycle through the main loop. In addition, any necessary additional functions, such as refunding any partial payments, would be performed at this time. 
     If the correct payment is received, block 210 passes control to block 220 to call the vend cart routine. The operation of this routine is discussed below with reference to FIG. 9b. After routine 220, control returns to block 204 to cycle again through the main loop of routine 200. 
     It will be appreciated that any of the subroutines discussed above may be initiated by means of interrupts as opposed to being continuously cycled through in a main routine. It will also be appreciated that other functions, such as various general housekeeping routines, may also be included in the main routine. Furthermore, it will be appreciated that various fault detection and self-test routines may be utilized in routine 200 and further that a diagnostic or program mode may be incorporated therein to allow modification and customization of the main routine for a particular installation (e.g., changing the amount of the vending cost and the reward dispensed). Other modifications to routine 200 will be appreciated by one skilled in the art. 
     Turning to FIG. 9b, the vend cart routine 220 is discussed in greater detail. The first step in this routine is to release electromagnetic brake 222, which is preferably performed by asserting a signal to brake driver 155. This releases paddlewheel 80 and allows a customer to pull the last cart past paddlewheel 80 and out of rail 52. When one cart is pulled out of rail 52, paddlewheel 80 will be incremented to the next paddle. Therefore, in block 224, routine 220 waits until the next paddle is detected by sensor 110, which indicates that the cart key of the cart being vended has been moved past paddlewheel 80. At this point, routine 220 proceeds to block 226 to relock electromagnetic brake 65, thereby restricting the rotation of paddlewheel 80 further. Next, routine 220 waits in block 228 until a &#34;cart out&#34; condition is sensed by sensor 100. Once this condition is sensed, the cart key of the vended cart has been removed from retaining rail 52. At this point, the number of carts retained by system 10 (&#34;carts in&#34;) is decremented, and the number of carts rended (&#34;carts out&#34;) is incremented, in block 230. It will be appreciated that alternatively only one variable may be maintained related to the number of carts in or out, with the other value being calculated based upon the known number of carts in the system. 
     As discussed above, in an alternative embodiment, cart in/out sensor 100 may be omitted, with its functions incorporated into sensor 110. In this case, the &#34;cart out&#34; condition detected in block 228 would not be required since sensor 110 would indicate a &#34;cart out&#34; condition by detecting a 90 degree rotation of the paddlewheel. Consequently, the next paddle detected block 224 which detects when a rotation of the paddlewheel has occurred may be suitable to verify that the cart key of the vended cart is beyond paddlewheel 80 and no longer captured in the system. Therefore, it will be appreciated that the separate cart out detection block 228 is optional. 
     Turning next to FIG. 9c, the return cart routine 240 is described. In addition, reference is also made to FIGS. 10a-f, which show schematically the physical insertion of a cart key into rail 52 during the return of a cart. FIG. 10a shows the rollers 36, 38 of a cart key inserted into rail 52, and with paddle 82a disposed under sensor 110. FIG. 10b shows roller 36 passing sensor 100 and initiating a &#34;cart in&#34; condition, which is detected in block 206 of main routine 200 in the preferred embodiment (shown in FIG. 9a). 
     In routine 240, the first step is to activate key identification sensor 242, which is preferably performed by asserting the START --  SENSE signal to sensor 120. Next, at block 244 the system determines whether the key for the return cart is a valid key in the manner described above. 
     If a valid key is detected by sensor 120, a flag is set in block 246 and control passes to block 248. Otherwise, the valid key flag will indicate an invalid key, and control will still pass to block 248. In block 248, the system cycles until the next paddle is detected by sensor 110. As discussed above, the next paddle can be detected by checking detectors 111-113 for paddlewheel 80 of FIG. 5b, or by checking only sensor 111 for paddlewheel 80&#39; of FIG. 5c. 
     As shown in FIGS. 10c and 10d, roller 36 of key 30 will preferably pass sensor 120 prior to a full 90° rotation of paddlewheel 80 (which is depicted in FIG. 10e). Consequently, the detection of a valid key will preferably occur before the next paddle is detected by sensor 110. As shown in FIG. 11, sensor 120 will preferably be disposed within the area in the rail defined by the rotation of paddlewheel 80 (circumscribed by dashed line 300 in FIG. 11) so that the key will be identified prior to detecting the next paddle. 
     The preferred orientation of sensor 120 provides an important safeguard against reward theft. Otherwise, if the key was not read until after the paddlewheel incremented positions, a hustler would be able to rotate the paddlewheel a small amount by hand to simulate a returned cart and activate the system. Next, the hustler could pull the rearmost cart in the rail back into the reader position to enable sensor 120 to identify the key, and then rotate the paddlewheel to the next position by hand and receive a reward. 
     In addition, due to the preferred positioning of sensor 120 within the area defined by paddlewheel 80, the next paddle of the paddlewheel will preferably project into retaining rail 52 before roller 36 passes sensor 120. Consequently, at that point, the cart key would not be able to be pulled out of retaining rail 52 due to the obstruction presented by the next paddle. 
     With the preferred position of sensor 120 in rail 52, an additional level of theft prevention may be provided. As is exemplified by FIG. 10f, once paddlewheel 80 has been incremented to the next centered paddle position, roller 36 of key 30 may not be pulled back into proximity with sensor 120 by virtue of roller 38 contacting paddlewheel 80. 
     Furthermore, as shown in FIG. 11, positioning a key identification sensor 120&#39; more proximate the centered position of a paddle may also be beneficial. In this situation, even if roller 38 is broken off key 30 by a hustler, key 36 still is unable to fully retracted over sensor 120&#39; and identified due to the centered paddlewheel. Other positions for sensor 120 within the preferred range may also be used consistent with the invention. 
     Returning to FIG. 9c, after the next paddle is detected at block 248, indicating that a 90° rotation of paddlewheel 80 has occurred, block 249 checks if a valid key was detected by checking the valid key flag. If a valid key was detected, a reward is dispensed in block 250 by activating coin dispenser 58e to dispense the proper amount of the reward. The operation of this step will vary upon the particular coin dispenser utilized in a manner known in the art. If the valid key flag is not set, control instead passes to block 251 to display on display 58a that an invalid key was detected, and no reward is dispensed. In either instance, control next passes to block 252 to increment the number of captured carts and decrement the number of vended carts before control is returned to main routine 200. 
     Turning to FIG. 9d, the alternate maintenance mode of controller 58, which is initiated by key cart in/out switch 153, is shown in key carts in/out routine 260. In this routine, electromagnetic brake 65 is released in block 261 to permit free insertion and removal of carts by a maintenance personnel. A &#34;cart in&#34; condition is checked for in block 262. This may be detected by sensor 100. If a &#34;cart in&#34; condition is detected, control passes to block 264 to wait until the next paddle is detected, indicating that a cart has been advanced past paddlewheel 80. At this point, in block 266, the number of captured carts may be incremented and the number of vended carts may be decremented. Then, before returning to main program 200, brake 65 may be locked in block 274. In block 266, the total number of carts in the system may also be incremented, for example, by selecting another position of switch 153 or by toggling a second switch (not shown), signifying that new carts are being added to the system. 
     If a &#34;cart in&#34; condition is not detected in block 262, control passes to block 268 to determine whether a &#34;cart out&#34; condition is being sensed. This condition is sensed by sensor 100 in the preferred embodiment. If no &#34;cart out&#34; condition is detected, control passes directly to block 274 to once again lock brake 65 before returning to main routine 200. 
     If, however, a &#34;cart out&#34; condition is detected, control is passed to block 272 to decrement the number of captured carts and increment the number of vended carts. Also, the total number of carts in the system may be decremented as described above. Next, in block 274, the brake is locked before control is returned to main routine 200. 
     It will be appreciated that once the &#34;cart out&#34; condition is sensed by sensor 100, paddlewheel 80 will already have been incremented to the next paddle position, so this condition does not necessarily need to be detected. 
     In the alternative embodiment discussed above which does not utilize a sensor 100, the key carts in/out routine would be somewhat simplified, as exemplified in routine 280 in FIG. 9e. First, brake 282 would be released as above. Next, in block 284, the system waits until a paddle is not detected by sensor 110 (i.e., when a &#34;between paddles&#34; condition is detected), indicating that a cart is being inserted or removed from the rail. For paddlewheel 80 (FIG. 5b), this would be detected when detectors 111-113 indicate no paddle, and for paddlewheel 80&#39; (FIG. 5c), this would be detected when detector 111 indicates no paddle. 
     Once the paddlewheel has left a centered position, control passes to block 286 to wait until the next paddle is detected, in the same manner for each paddlewheel embodiment (80 or 80&#39;) as discussed above for block 284. 
     Then, in block 288, the system determines from the new paddle position whether a &#34;cart in&#34; or &#34;cart out&#34; condition has occurred. For paddlewheel 80 of FIG. 5b, detectors 111-113 would all be polled as described above. For paddlewheel 80&#39; of FIG. 5c, only detectors 112 and 113 need be activated after the new paddle is sensed by detector 111. Since the arrangement of paddles is stored in the system, a clockwise or counterclockwise rotation of the paddlewheel may be distinguished, with the cart in and cart out counts adjusted accordingly in blocks 290 and 292. Then, the brake is locked in block 294 before control returns to routine 200. 
     In another alternate embodiment of the invention, the key carts in/out routine may be controlled as an interrupt which is signalled by the position of the key carts in/out switch 153. In this instance, the control over brake 65 may be tied to the position of switch 153, thereby reducing the repetitive cycles in which the brake is transitioned between locked and unlocked states. 
     The above combination of sensors and components operating in the manner disclosed herein provides several levels of protection against the theft of rewards due to hustlers. The size and shape of the paddle permits only one key to be inserted into the rail at a time. The limited size of the slot in the bottom of the rail makes it difficult to access the paddlewheel and other internal components of the system. The centering mechanism makes it difficult to hold the paddlewheel in intermediate positions between centered positions. The combination of sensors 100, 110 and 120 are coordinated by the controller to dispense rewards only when a predetermined set of conditions occur in a predetermined order. Each paddle on the paddlewheel is separately identifiable, enabling the controller to distinguish between a rotation to a next paddle and &#34;jiggling&#34; proximate one paddle position. Also, as described above, the positioning of sensor 120 in the path of paddlewheel 80 prevents a cart key already inserted in the rail from being used to dispense additional rewards. Other theft preventive measures and benefits, including the others described above, will be appreciated by one of ordinary skill in the art. 
     Therefore, it will be appreciated that the invention provides cart management systems which may be used in a variety of application with a variety of carts, and with sophisticated electronic control that is highly resistant to theft from hustling. As one skilled in the art will appreciate that various modifications may be made to the preferred embodiments without departing from the spirit and scope of the invention, the invention thus resides in the claims hereafter appended.