Abstract:
An infeed station for conveying and positioning a stack of carton blanks for sequential removal by a carton feeder, for automatically adjusting the rate of advancement of the carton blanks to compensate for excessive tilting and gaps between the carton blanks, and for providing alerts to signal the need for operator intervention or automatic shutdown. The infeed station includes a hopper and a magazine that receives carton blanks from the hopper. The magazine includes a sensing mechanism including a control sensor and a warning sensor mounted in proximity to the carton blanks in the infeed station, and a processor that, according to a condition signaled by the sensing mechanism, controls the rate at which advancing belts advance a queue of carton blanks toward the magazine.

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Application No. 60/696,379, filed Jul. 1, 2005, the entirety of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to machines for erecting cartons, and more particularly, a carton magazine with a control sensor that compensates for inconsistent loading of cartons in a packaging machine. 
     BACKGROUND OF THE INVENTION 
     A continuous-motion automatic packaging machine rapidly applies secondary packaging to multiple individually packaged products such as canned or bottled consumables for greater ease of transportation, storage, sale, and consumer utilization. A typical packaging machine integrates several modular stations, including a carton erector, case packer, carton sealing station, palletiser, and interconnecting conveyor systems that convey the products through the various modular stations and into each of a series of cartons. It is known to provide a packaging machine with a modular or integral carton feeder that erects cartons, such as sleeve type cartons provided as carton blanks that are partially assembled and collapsed into tubular sleeves prior to being fed into the packaging machine. A typical carton feeder includes three rotary vacuum wheels, each including vacuum cups for engaging and disengaging cartons that are selectively activated and deactivated by means of valves controlled by a computer processor. 
     When the packaging machine is running, it is critical to supply the carton feeder with a steady stream of carton blanks, which may be folded beforehand and secured into a pre-erected configuration, such as flattened tubular sleeves or flattened basket-style carriers. An operator loads the carton blanks into a hopper, which then conveys the carton blanks to the feeder on advancing belts that are continuously or intermittently driven. In order for the feeder wheel to efficiently engage each carton, the cartons must be consistently stacked. Thus, such packaging machines are sensitive to the manner in which the operator fills the hopper—requiring loading to be extremely orderly and consistent. Gaps between carton blanks cause the blanks to tilt, resulting in more frequent misses by the feeder wheel. Conversely, overcompensating for gaps by overdriving the advancing belts of the hopper causes the carton blanks to press against one another excessively, again increasing the occurrence of misses by the feeder wheel as well as increasing the likelihood that carton blanks will be expelled prematurely. 
     Attempts to compensate for this sensitivity include creating a pressure break that reduces the pressure translated from the line of carton blanks in the hopper to the feeder wheel. The pressure break is created by interposing a magazine between the feeder wheel and the hopper. The transition between the hopper and the magazine is stepped down significantly such that the cartons blanks in the magazine are several inches lower than the carton blanks in the hopper. Because the hopper is separate from the magazine, the magazine needs separately driven roller belts to convey carton blanks toward the feeder wheel. Although such configurations may reduce the pressure in the magazine, there is still no guarantee that the advancing belt will not run excessively to exceed the ability of the pressure break to adequately relieve the pressure. Furthermore, the inclusion of separate roller belts significantly limits the ability of such magazines to support the weight of the carton blanks. 
     There is a need, therefore, for a packaging machine having an infeed station that is less sensitive to filling anomalies, and that reduces the likelihood of misfeeds. 
     SUMMARY OF THE INVENTION 
     The various embodiments of the present invention overcome the shortcomings of the prior art by providing systems and methods for operating an infeed station. The infeed station includes a magazine that is tolerant of inconsistent loading of a hopper and includes a sensing mechanism that limits the pressure on the carton blanks in the carton magazine. The magazine includes fixed supports that can bear the weight of numerous carton blanks. 
     Generally described, the systems and methods of the present invention include an infeed station for stacking the carton blanks for sequential removal by a carton feeder. The infeed station includes a hopper and a magazine for receiving carton blanks from a hopper. The magazine includes a sensing mechanism including a control sensor and optionally, a warning sensor, that are mounted in proximity to the carton blanks in the infeed station. The sensing mechanism controls advancing belts that are associated with the hopper, for example, to advance additional carton blanks into or toward the magazine or to close gaps between a queue of carton blanks already loaded in the hopper. Generally described, the sensing mechanism detects conditions such as whether carton blanks in the infeed station are excessively tilted and whether the hopper and the magazine are full, and signals a corresponding condition to a PLC (Programmable Logic Controller) or other processor. If the infeed station is fully loaded and the carton blanks are sufficiently upright, the PLC slows, disables, disengages, or brakes the advancing belts or otherwise prevents a drive system from causing the belts to advance beyond what is needed to sustain the fully loaded condition. 
     The hopper queue is separated from the magazine stack by a transition region created by disposing the magazine at a slightly lower elevation with respect to the hopper. Thus, carton blanks conveyed in the hopper drop down into the magazine upon being conveyed into the transition region. The relative disparity in elevation also causes at least the frontmost carton blanks in the hopper queue, i.e. just upstream from the transition region, to tilt toward or lean slightly against the stack in the magazine. This pressure, combined with a bottom surface of the magazine that slopes toward the carton feeder, drives the stack toward the carton feeder. The pressure is limited, however, by ensuring that the carton blanks in the hopper queue do not lean excessively onto the stack. 
     To detect excessive tilting or leaning, which also may indicate that the magazine is not full, the control sensor monitors the elevation of the top edges of the endmost carton blanks in the hopper queue. This elevation indicates whether the carton blanks in the hopper queue are tilting or leaning excessively toward the stack. When the carton blanks tilt or lean excessively, the distance between the top edges of the carton blanks and the control sensor exceeds the sensing range of the control sensor, and a corresponding state is indicated by the control sensor. This state or a condition defined by multiple states is detected by the PLC, which causes the advancing belts to advance, thereby raising the elevation of the endmost carton blanks in the hopper queue and filling the magazine. If advancing the advancing belts does not fill the magazine, the sensing mechanism detects that the queue has been depleted and the packaging machine is eventually shut down by the PLC. In other instances, the configuration permits running the advancing belts of the hopper as needed to ensure a steady supply of carton blanks to the magazine. 
     The invention reduces the sensitivity of the packaging machine to loading anomalies in which the operator fails to load cartons in such a manner to eliminate gaps between adjacent carton blanks. In addition, a warning sensor is provided to alert the operator of the need to load additional carton blanks in the hopper to ensure continuous operation of the packaging machine. In the embodiments described herein, the warning sensor is disposed beneath the advancing belts and upstream from the magazine to detect carton blanks passing above it on the advancing belts. If carton blanks are not detected for a given period of time, an audible, visible, vibratory or other detectable warning signal is issued to notify a human or automated operator to load the hopper. 
     An aspect of the invention is the interoperability of the warning sensor and the control sensor. Specifically, the states of both sensors can be combined to define certain conditions to which the PLC will respond or trigger a response. If both sensors detect carton blanks, then the PLC does not advance the belts. If the warning sensor detects carton blanks in the hopper queue, but the control sensor does not detect carton blanks at the proper elevation, the advancing belts advance to right the carton blanks entering the transition region, thereby ensuring a full magazine and preventing excessive tilting or leaning of carton blanks in the hopper queue. If the warning sensor does not detect carton blanks and the control sensor does detect carton blanks at the proper elevation, a warning signal is issued to notify the operator to load more cartons. The warning signal may be delayed for a given period of time in case the failure of the warning sensor to detect is simply caused by gaps between adjacent cartons due to filling anomalies. Several repeating or escalating warning signals may issue to indicate as time elapses after the first warning signal to indicate the urgency of preventing the hopper from completely being depleted before the operator reloads. If the warning sensor fails to detect carton blanks in the queue in the hopper, and the control sensor also fails to detect carton blanks, then the packaging machine shuts down due to lack of carton blanks. The shut down may also be delayed for a predetermined time calculated to fully exhaust the supply of carton blanks in the magazine prior to the failure of the control sensor to detect carton blanks. 
     According to another aspect of the invention, the magazine includes bottom supports that can bear the weight of as many carton blanks as the magazine can hold. The supports are substantially rigid with generally smooth upper surfaces that minimize the friction imparted to the bottom edges of the carton blanks that move across the supports and into the carton feeder. The carton blanks are driven across the supports by the controlled amount of pressure generated by the top edges of the carton blanks in the hopper queue, which ideally lean slightly onto the stack of carton blanks in the magazine. 
     The foregoing has broadly outlined some of the aspects and features of the present invention, which should be construed to be merely illustrative of various potential applications of the invention. Other beneficial results can be obtained by applying the disclosed information in a different manner or by combining various aspects of the disclosed embodiments. Accordingly, other aspects and a more comprehensive understanding of the invention may be obtained by referring to the detailed description of the exemplary embodiments taken in conjunction with the accompanying drawings, in addition to the scope of the invention defined by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial perspective view of an infeed station of a packaging machine that incorporates an exemplary magazine and an exemplary carton hopper according to the present invention. 
         FIG. 2  is a block diagram showing the functional connections and the flow of data between certain of the various elements of an embodiment of the present invention. 
         FIG. 3  is a diagram showing the sensing window of a sensor that is integral to the infeed station of  FIG. 1 . 
         FIG. 4  is a perspective view of the magazine of  FIG. 1 . 
         FIG. 5  is an exploded view of the magazine of  FIG. 4 . 
         FIG. 6  is an exploded view of the carton hopper of  FIG. 1 . 
         FIG. 7  is a side elevation view of the infeed station of  FIG. 1 . 
         FIG. 8  is a chart showing the interoperability of the warning and control sensors according to certain embodiments of the invention. 
         FIGS. 9 and 10  illustrate certain states of the carton blanks within the infeed station of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein. It must be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms, and combinations thereof. As used herein, the word “exemplary” is used expansively to refer to embodiments that serve as illustrations, specimens, models, or patterns. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. In other instances, well-known components, systems, materials, or methods have not been described in detail in order to avoid obscuring the present invention. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     Referring now to the drawings in which like numerals indicate like elements throughout the several views, the drawings illustrate certain of the various aspects of exemplary embodiments of an infeed station of the present invention. The infeed station is shown and described in the context of an exemplary packaging machine for erecting and loading paperboard cartons, article carriers, or other packages, although the principles and features of the invention are useful in similar packaging machines and with articles similar to the cartons described. As such, the exemplary cartons may be formed from materials other than paperboard, and indeed from any suitable sheet material that is substantially flat or foldable into a flattened, such as but not limited to, corrugated board, plastic, and the like. 
     An exemplary infeed station  100  for a carton feeder F of an exemplary packaging machine is shown in  FIG. 1 . The infeed station  100  includes a hopper  102  and a magazine  104 . The hopper  102  holds a queue Q (shown in  FIG. 7 ) of carton blanks C that stand on their bottom edges and the magazine  104  holds a stack T of carton blanks C that stand on their bottom edges. The queue Q of carton blanks C are conveyed from the hopper  102  into the magazine  104 , where the carton blanks C are held in the stack T prior to being removed one by one by vacuum cup stations S on a pickup wheel  116  of the carton feeder F (partially obstructed). Thereby, carton blanks C move from the rear of the infeed station  100  toward the front of the infeed station  100 . As used herein, the terms “rear” and “front” refer to relative positions of objects along the length of the infeed station  100  and, specifically, along the path of the carton blanks C within the infeed station  100 . 
     The hopper  102  includes a conveyor  111  or other means for conveying the queue Q of carton blanks C into the magazine  104 . The bottom edges of the queue Q of carton blanks C rest transversely across means for conveying of the hopper  102 . In the exemplary embodiment, the conveyor  111  includes a set of one or more advancing belts  110 , although any suitable apparatus for orderly conveyance or other means for conveying can be substituted, including a single advancing belt, a vibrating table, a system of carts, a roller bed, a conveying surface, and the like. 
     The advancing belts  110  shown in  FIG. 1  are toothed or serrated roller belts, which are known for use in various conveying applications. In the exemplary embodiment, the advancing belts  110  are run in a single direction to move the queue Q of carton blanks C forward toward the magazine  104 . However, reciprocating belts, which convey a load of carton blanks C to the magazine  104  and then reverse to be reloaded, are contemplated as well. In any event, the advancing belts  110  may be driven by a single motor (not shown) or a synchronized set of motors (not shown). The operation and drive speed of the motor or motors is controlled by a programmable logic controller (PLC)  200  (shown in  FIG. 2 ) or other processing device that includes program logic and circuitry which facilitates controlling motors and other peripheral devices. 
     The exemplary hopper  102  further includes guides  106 ,  108  that provide lateral support to opposing side edges of the carton blanks C in the queue Q. Guide  106  extends along the entire length of the advancing belts  110 , as shown in  FIG. 6 . Guide  108  is disposed adjacent to the magazine  104  and is adjustable such that the distance between the guides  106 ,  108 , or otherwise the width of the hopper  102 , can be changed to accommodate carton blanks C having various dimensions. Referring to  FIG. 6 , the guide  108  can be adjusted by loosening thumb screws  602  and sliding the screws  602  within respective slots  604  that are machined in a hopper table  606 . 
       FIGS. 4 and 5  provide additional detail regarding the major components of the exemplary magazine  104 . The magazine  104  is mounted to the frame (not shown) of the packaging machine via vertical support plates  400 ,  402 . An upper detent bar  404  and a lower detent plate assembly  418  extend horizontally between two vertical tracks  406 ,  408 . The upper detent bar  404  is adjustably engaged by the tracks  406 ,  408 , with its adjustment being controlled via chain  410 , so that its elevation relative to a bottom surface  708  (shown in  FIG. 7 ) of the magazine  104  can be changed to accommodate carton blanks C of various dimensions. The front end of the bottom surface  708  of the magazine  104  is angled downward such that carton blanks C entering the rear end of the magazine  104  from the hopper  102  slide toward the front end of the magazine  104 . In certain embodiments, the magazine  104  also includes a vibration generator that shakes or otherwise vibrates to align the carton blanks C with respect to one another in the proper position for removal from the front end of the magazine  104 . Several prongs  414  that are mounted on the underside of the upper detent bar  404  serve to guide the top edges of carton blanks C from the hopper  102  into the magazine  104 , as well as through the magazine  104 , without generating excessive friction that would impede the motion of the carton blanks C. Similarly, supports  416  are mounted to the lower detent plate assembly  418  to support the bottom edges of carton blanks C. Referring to  FIGS. 5 and 7 , support rollers  420 , lower detents  702 , and upper detents  704  prevent the stack T of carton blanks C from escaping through the front end of the magazine  104  prior to being removed by the pickup wheel  116  of the carton feeder F. The support rollers  420  are mounted on a medial detent bar  422 . The lower detents  702  protrude slightly above the bottom surface  708  of the magazine  104  or otherwise above a plane that is defined by the upper surface of the supports  416 . The upper detents  704  protrude below the lower surface of the prongs  414 . 
     The ability of the lower detents  702  to retain the carton blanks C in the magazine tends to be undesirably overcome as excessive pressure is applied to the stack T of carton blanks C in the magazine  104 . Excessive pressure is prevented at least in part by maintaining a transition region G between the queue Q of carton blanks C in the hopper  102  and the stack T of carton blanks C in the magazine  104 . The transition region G is maintained in part by varying the relative elevation and angle of disposition of a bottom surface  706  of the hopper  102 , as defined by the upper surfaces of advancing belts  110 , relative to the bottom surface  708  of the magazine  104 , as defined by the upper surfaces of the supports  416 . For example, the bottom surface  708  of the magazine  104  is disposed at an acute angle A (shown in  FIG. 9 ) with respect to the bottom surface  706  of the hopper  102 . In addition, the front edge of the bottom surface  706  of the hopper  102  is elevated above the rear edge of the bottom surface  708  of the magazine  104  by a distance D (shown in  FIG. 9 ) or otherwise the maximum elevation of the bottom surface  708  of the magazine  104  is lower than the elevation of the bottom surface  706  of the hopper  102 . In other words, no part of the supportive portion of the bottom surface  708  of the magazine  104  breaks the plane of the bottom surface  706  of the hopper  102 . The frontmost carton blanks C in the queue Q are tilted forward to pass through the transition region G and the top edges of the frontmost carton blanks C in the queue Q are engaged by the prongs  414  such that the top edges of the frontmost carton blanks C in the queue Q align with the top edges of the carton blanks C in the stack T. Additionally, the upper portion of the frontmost carton blank C in the queue Q abuts the upper portion of the rearmost carton blank C in the stack T. Thereby, the transition region G ensures that any pressure exerted by the queue Q of carton blanks C in the hopper  102  on the stack T of carton blanks C in the magazine  104  is concentrated on the upper portion or upper edges of the stack T of carton blanks C, which is supported by the much more substantial upper detents  704 . 
     Referring to  FIGS. 1 and 7 , the infeed station  100  further includes sensors  112 ,  114  that are positioned to detect certain states which are present in the infeed station  100  and to provide signals to the PLC  200  reflecting those states. Generally speaking, the sensors  112 ,  114  are positioned to, detect the presence or absence of certain portions of carton blanks C at certain locations along the length of the infeed station  100 , as described in further detail below. Thereby, the sensors  112 ,  114  output or indicate states which define a condition and the PLC  200  issues or triggers a corresponding response. 
     Both sensors  112 ,  114  may be of the same type, which in the embodiment described is an ultrasonic threaded cylindrical proximity sensor with an 18 mm diameter, such as the SM650A-216-00 Superprox® model manufactured by Hyde Park Electronics LLC of Dayton, Ohio, although any suitable known or yet to be developed sensor may be used to detect presence or proximity or any other suitable parameter that would trigger the desired response as described herein. With reference to  FIG. 3 , the exemplary sensors  112 ,  114  are normally configured to detect objects within a fixed sensing field or window W, which is defined by a near limit L 1 , a far limit L 2 , and a beam width. The beam width may be variable along a notional central axis that extends perpendicularly from a sensing face  300  of the sensor  112 ,  114 . Each sensor  112 ,  114  has a maximum beam width, referred to herein as scope H, that is measured in a direction that is substantially perpendicular to the notional central axis of the sensor  112 ,  114 . The distance between the sensing face  300  of the sensor  112 ,  114  and the far limit L 2  is also referred to as a sensing range R. 
     The sensor  112 ,  114  is configured such that it does not detect objects outside the window W. Specifically, the sensor  112 ,  114  does not detect objects located in a deadband region, which is the space between the sensing face  300  of the sensor  112 ,  114  and the near limit L 1 , or objects located beyond the sensing range R. In certain embodiments, the near limit L 1  of the sensors  112 ,  114  is one inch and the far limit L 2  is two inches, yielding a sensing window W with a length of one inch in the direction defined by the notional central axis. 
     Each sensor  112 ,  114  changes state to reflect the presence or absence of objects within the window W of the sensor  112 ,  114 . The state of each sensor  112 ,  114  is periodically or continuously scanned or sampled by the PLC  200  and the combined states define a condition which corresponds to a command to be triggered or issued by the PLC  200 . In the exemplary embodiment, each of the sensors  112 ,  114  outputs one of two state indicators. When an object is detected in the window W of the sensor  112 ,  114 , the sensor  112 ,  114  outputs or indicates a “detected” state and when an object has not been detected in the window W of the sensor  112 ,  114 , the sensor  112 ,  114  outputs or indicates a “not detected” state. Alternatively, rather than outputting a state, the sensor may output a quantitative measurement of a parameter that is processed by the PLC  200 . For example, the parameter may be a distance from the sensor and the distance can be processed by the PLC  200  to define multiple states including a state that indicates a loading error. 
     It is envisaged that the sensor  112 ,  114  indicates a state when the parameter detected by the sensor  112 ,  114  falls between certain predefined limits. Further, if the parameter detected is proximity or presence, the sensor may indicate a state only if the parameter falls between certain predefined limits for a certain amount of time. The predefined limits can be integral to the sensor or incorporated into the PLC program. As a hypothetical, the PLC may sample the output signal, i.e. the state, of a sensor X times per second. However, the PLC may be programmed to trigger a particular response only if the states of the sensors indicate a corresponding condition in Y consecutive samples, or if a condition is met for any percentage of Y consecutive samples. It should be understood that the samples of the states of the sensors can be processed and combined in any manner, by circuitry integral to the sensor or programmed into the PLC, to define a condition which is sampled by the PLC in order to determine a response. 
     Referring to  FIG. 7 , for the infeed station  100  to function properly, carton blanks C from the queue Q are added to the stack T of carton blanks C as the carton feeder F removes carton blanks C from the stack T such that the infeed station  100  provides a continuous supply of carton blanks C to the carton feeder F. Accordingly, the advancing belts  110  are controlled such that the advancing belts  110  are driven to add carton blanks C from the queue Q to the stack T and stopped to prevent excessive back pressure on the stack T. The sensor  114  is positioned to determine when carton blanks C are to be added to the stack T or otherwise to determine when the stack T is suitably full. 
     Certain parameters of the stack T and the queue Q reflect the fullness of the stack T. Referring to  FIGS. 9 and 10 , as the frontmost carton blanks C are removed from the stack T by the carton feeder (not shown), the depth of the stack T is reduced and the remaining carton blanks C move incrementally forward. Consequently, frontmost carton blanks C in the queue Q, which lean against the upper portion of the rearmost carton blanks C in the stack T, tilt forward thereby reducing the elevation E 2  of the top ends of the carton blanks C in the queue Q relative to the bottom surface  706  of the hopper  102 . The elevation E 2  of the top ends of the carton blanks C in the queue Q depends on the depth of the stack T and both these parameters reflect the fullness of the stack T. Further, the depth of the queue Q to reflects whether or not the queue Q is suitably full. 
     The warning sensor  112  is positioned so as to detect the presence or absence of carton blanks C in the hopper  102  at a distance X 1  (shown in  FIG. 9 ) from the front edge of the bottom surface of the hopper  102 . The distance X 1  is determined to reflect a depth of the queue Q of carton blanks C at which the queue Q is considered suitably full. In the embodiment shown in  FIGS. 1 and 7 , the warning sensor  112  is disposed between adjacent advancing belts  110  so as to be perpendicular to and below the bottom surface  706  of the hopper  102 . That is, to avoid interfering with the procession of carton blanks C in the hopper  102 , the sensing face  300  (shown in  FIG. 3 ) of the warning sensor  112  extends no further than the elevation of the valleys between the teeth in the advancing belts  110 . Moreover, the distance between the bottom surface  706  and the sensing face  300  of the warning sensor  112  is constrained at least in part by the characteristics of the particular sensor used including the limits L 1 , L 2  of the sensing window W. The warning sensor  112  is directed upward to detect the presence or absence of carton blanks C above the warning sensor  112  on the advancing belts  110  of the hopper  102 . The warning sensor  112  is thereby positioned such that the sensing window W is disposed in a space that is adjacent to and above the bottom surface  706 , for example, to detect the presence of the bottom edges of carton blanks C in the queue Q. Those skilled in the art will readily appreciate that the sensors  112 , may be positioned in alternate locations, including along the sides of the hopper  102  and directed inward, above the hopper  102  and directed downward, or at any vantage point that offers an unobstructed path to detect the presence or absence of carton blanks C in the hopper  102 . 
     The control sensor  114  is positioned to detect the presence of carton blanks C in or around the transition region G between the hopper  102  and the magazine  104  and in doing so reflect whether the stack T is suitably full. The control sensor  114  is mounted between prongs  414 , above a plane defined by the bottom surfaces of the prongs  414 , and approximately at a distance X 2  from the front end of the magazine  104 . The distance X 2  corresponds to the depth of the stack T at which the magazine  104  is considered suitably full. Further, the distance X 2  is defined between a plane that is defined by the surface of the frontmost carton blank C in the stack T and the notional central axis of the sensor  114 . Referring to  FIG. 4 , the control sensor  114  is mounted to the upper detent bar  404  by a mounting plate  412  that extends from the upper detent bar  404  toward the hopper  102 . The length of the mounting plate  412  is at least partially determinative of the extent to which the control sensor  114  is offset from the upper detent bar  404 . The distance between the plane defined by the bottom surfaces of the prongs  414  and the sensing face  300  is controlled at least in part by the characteristics of the particular sensor used including the limits L 1 , L 2  of the sensing window W. The control sensor  114  is directed downward to detect the presence or absence of carton blanks C disposed or passing below the control sensor  114 . The control sensor  114  is thereby positioned such that the sensing window W is disposed in a space that is adjacent to and below the prongs  414 . Thereby, the control sensor  114  can detect the presence of the top edges of carton blanks C that are suitably upright in the stack T and/or the queue Q. Specifically, the control sensor  114  is positioned to detect the presence of the top edges of the frontmost carton blanks C in the queue Q when the elevation E 2  of the queue Q is such that the top edges of frontmost carton blanks C in the queue Q are adjacent to the prongs  414  or otherwise such that the elevation E 2  corresponds to an elevation E 3  relative to the bottom surface  708  of the magazine  104 . The dimensions and position of the window W of the sensor  114  define the elevation E 3 . In the exemplary embodiment, the elevation E 3  is measured relative to the bottom surface  708  of the magazine  104 . However, the elevation E 3  can be measured relative to any surface including the bottom surface  706  of the hopper  102 . It should be noted that the elevation at which the top ends of the frontmost carton blanks C in the queue Q are present in the window W is dependent on the size and shape of the window W and the sensor  114  can be positioned to adjust the elevation at which the top ends of the frontmost carton blanks C in the queue Q are present in the window W. 
     It should be noted that the extent of the scope H and the thickness of the carton blanks C determine the number of carton blanks C that are detected by each sensor  112 ,  114 . In the exemplary embodiments, the sensor  112 ,  114  may signal a condition when one or more of the carton blanks C within the scope H are detected. In alternative embodiments, a certain number of carton blanks C are preferred to be detected in order to indicate a state. 
     It should be understood that the limited sensing range R of the control sensor  114  offers the advantage of ignoring any carton blank C that is aligned in the direction of the control sensor  114 , but is tilted to an unacceptable degree such that the top edge of the carton blank C is disposed below an elevation corresponding to the elevation E 3 . For example, in the exemplary embodiment, the two inch sensing range R ensures that any carton blank C that is tilted such that its upper edge is more than two inches away from the sensing face  300  is not detected by the control sensor  114 . Thus, if a carton blank C is tilted beyond a predetermined acceptable angle, its upper edge will escape the sensing range R. In response, the PLC  200  is programmed to increase the rate of advancement of the advancing belts  110  to correct the tilt of the excessively tilted carton blanks C. The duration of this increase may be limited so as to distinguish between a temporary condition, i.e., a tilted carton blank C, and a condition that will persist without intervention, i.e., absence of carton blanks C. 
     The sensors  112 ,  114  are positioned on the infeed station  100  and the PLC  200  can be programmed, as described below, such that the driving mechanism for the advancing belts  110  is controlled to properly feed carton blanks C through the infeed station  100 . Specifically, the command issued or the response triggered by the PLC  200  is dependent on the condition that is defined by the states that are indicated by the sensors  112 ,  114 . For example, a condition “A” is defined when the warning sensor  112  indicates a “detected” state and the control sensor  114  indicates a “detected” state. In this instance, the depth of the stack T and the depth of the queue Q are such that the magazine  104  and the hopper  102  are suitably full. When condition “A” is scanned or sampled by the PLC  200 , the PLC  200  disables the advancing belts  110  or otherwise does not command the advancing belts  110  to be driven. 
     A condition “B” is defined when the warning sensor  112  indicates a “detected” state and the control sensor  114  indicates a “not detected” state. In this instance, the depth of the queue Q is such that the hopper  102  is suitably full, but the depth of the stack T is such that the magazine  104  is not suitably full and the queue Q is substantially tilted. In response to condition “B”, the PLC  200  causes the advancing belts  110  to be driven to move the frontmost carton blanks C in the queue Q through the transition region G to be added to the stack T and/or to cause the carton blanks C in the queue Q to become substantially upright. In other words, the elevation E 2  of the top ends of the carton blanks C in the queue Q relative to the bottom surface  706  of the hopper  102  is increased. 
     A condition “C” is defined when the warning sensor  112  indicates a “not detected” state and the control sensor  114  indicates a “detected” condition. In this instance, the depth of the stack T is such that the magazine  104  is suitably full but the depth of the queue Q is such that the hopper  102  is not suitably full. Accordingly, with continued operation in this state, the queue Q cannot continue to replenish the stack T. In response to condition “C”, the PLC  200  issues a warning signal to an operator from an alarm output  202 . The warning signal may include an audible, visible, or vibratory alert, or any other signal or event that is detectable by a human or automated operator, such as a computerized voice. Therefore, the alarm output  202  may be any suitable output device, such as a siren, display screen, vibration table, speaker, and the like. 
     A condition “D” is defined when the warning sensor  112  indicates a “not detected” state and the control sensor  114  indicates a “not detected” condition. In this instance, the depth of the stack T is such that the magazine  104  is not suitably full and the depth of the queue Q is such that the hopper  102  is not suitably full. Accordingly, with continued operation in this state, infeed station  100  cannot continuously feed carton blanks C to the carton feeder F. In response to condition “D”, the PLC  200  shuts the packaging machine down. 
     Referring to  FIG. 2 , the PLC  200  may be programmed directly, or the logic programs may be downloaded or relayed from a computer (not shown). The PLC  200  has either modular or integral input/output circuitry that monitors the signals of field connected sensor inputs, including sensors  112  and  114 , and controls attached output actuators, including devices such as motor starters, solenoids, pilot lights/displays, drives, vacuum valves, and the like (not shown) according to the programs stored in the random-access (RAM) portion of memory  204 . A system bus  206  couples memory  204 , sensor inputs, and output actuators to the PLC  200 . If the PLC  200  receives programming from a computer, the computer typically further includes additional computer-readable media, such as low speed storage, such as a hard disk drive or a magnetic disk drive, and the like, to read from or write to a removable disk, and an optical disk drive for reading a CD-ROM disk or to read from or write to other optical media. The hard disk drive, magnetic disk drive, and optical disk drive include a hard disk drive interface, a magnetic disk drive interface, and an optical drive interface, respectively (not shown), for coupling the drives to the system bus  206 . The drives and their associated computer-readable media provide nonvolatile storage for the computer. Although the description of computer-readable medium above refers to a hard disk, a portable USB drive, a removable magnetic disk, a CD-ROM disk, other types or media readable by a computer, such as magnetic cassettes, flash memory cards, digital video disks, Bernoulli cartridges, and the like, can also be used. 
     A number of program modules can be stored in the drives and in the RAM portion of memory  204 , including an operating system, one or more application programs, a shared code library, and a browser program module. A user may enter commands and information into the computer through a human/machine interface (HMI)  208 , such as but not limited to a keyboard and pointing device, such as a mouse. The HMI  208  may incorporate other input/output devices such as a microphone, joystick, scanner, pushbuttons, LEDs, and the like. These and other input/output devices may be connected to the PLC  200  or the processing unit of the computer through a serial port interface coupled to the system bus  206 , but can be connected by other interfaces, such as a universal serial bus (USB) (not shown). The input/output devices include a monitor or other type of display device connected to the system bus  206  via an interface, such as a video adapter. In addition to the monitor, computers typically include other peripheral output devices, such as speakers or printers. 
     According to an exemplary method, the carton blanks C are loaded into the hopper  102  and into the magazine  104 , and the PLC  200  begins scanning or sampling the condition defined by the states that are indicated by the warning sensor  112  and the control sensor  114 . As shown for condition “A” in the chart of  FIG. 8 , the warning sensor  112  detects the carton blanks C in the hopper  102 , and assuming the carton blanks C were properly loaded, the control sensor  114  detects the top edges of the frontmost carton blanks C in the queue Q. The output of each of the sensors  112 ,  114  indicates a “detected” state, thereby defining the condition “A”, so the PLC  200  takes or triggers no action with respect to the advancing belts  110 . Meanwhile, the carton feeder wheel  116  removes carton blanks C from the magazine  104 , commonly at high rates of speed such as five per second, thereby decreasing the depth of the stack T. As the depth of the stack T decreases, the tilt of the carton blanks C in the queue Q increases, causing the elevation E 2  of the top edges of the frontmost carton blanks C to fall below the sensing range R of the control sensor  114 . Thereby, the PLC  200  detects condition “B” and, in response, advances the advancing belts  110  to return the system to condition “A”. In the event that the queue Q is depleted, the warning sensor  112  fails to detect carton blanks C in the hopper  102  and the PLC  200  detects condition “C”, which indicates that the depth of the queue Q is less than a predetermined limit and may be depleted if the hopper  102  is not reloaded. In response, the PLC  200  causes a warning signal to issue via alarm output  202 . According to certain embodiments, the PLC  200  is programmed to only issue the warning signal after the output of the warning sensor  112  has been off for a certain period of time, e.g., 30 seconds. This is to prevent alerting the operator to load carton blanks C when the sensor  112  has merely detected transient gaps between carton blanks C that are already loaded in the hopper  102 . If carton blanks C are not loaded in the hopper  102  in response to the warning signal, the queue Q is eventually depleted, and the control sensor  114  fails to detect the top edges of carton blanks C in the queue Q or in the stack T. Condition “D” is then detected, causing the PLC  200  to shut the packaging machine down when the program conditions are met, including applying any predefined delays. 
     Those skilled in the art will readily appreciate that, as used herein the phrases “advancing the advancing belts” or “stopping the advancing belts” (and variants thereof) may refer to alterations of the rate of advancement of the carton blanks relative to the normal operating speed of the advancing belts. In other words, it is contemplated that when the hopper is full, the advancing belts advance continuously according to the rate at which the feeder removes carton blanks from the magazine. When cartons tilt, the advancing belts simply increase the rate of advancement above the normal operating speed to compensate and close the gap. Once the gap is eliminated, the advancing belts return to normal operating speed, and thus, may never completely stop. 
     The present invention has been illustrated in relation to a particular embodiment which is intended in all respects to be illustrative rather than restrictive. Those skilled in the art will recognize that the present invention is capable of many modifications and variations without departing from the scope of the invention. For example, design choices such as the type of sensors and PLCs or variations in programming will introduce certain delays in the timing of the certain of the events described above. The scan rate of the particular PLC will determine how long a condition or state may exist before the PLC controls peripheral devices accordingly. The characteristics of the motor and drive system controlling the advancing belts may include limitations that demand additional logic and/or delays to avoid exceeding such restrictions as duty cycle and maximum allowable starting frequency. Similarly, the placement of sensors may also vary according to the depth of the magazine, length of the hopper, speed of the packaging machine, carton type and dimensions, frequency and speed of the operator to reload the hopper, and similar parameters. With respect to the type of sensors used, sensors having an on/off delay may be preferred in certain applications such as to prevent excessive starting of the advancing belt motors due to transient gaps between carton blanks C. 
     As used herein, directional references such as “top”, “base”, “bottom”, “end”, “side”, “inner”, “outer”, “upper”, “middle”, “lower”, “front” and “rear” do not limit the respective walls and edges of the cartons or carton blanks to such orientation, but merely serve to distinguish these walls from one another. 
     Those skilled in the art will also appreciate that the packaging machine described represents only one example of the various packaging machine types and configurations that will be suitable for implementation of the various embodiments of the invention. In addition, any suitable picking and placing device may be used in addition to or instead of vacuum cup stations, including magnets, non-permanent adhesives, and the like. The exemplary vacuum stations may utilize any negative pressure generating devices and principles, including without limitation, Venturi or Bernoulli vacuum devices, which may but do not necessarily contact the surface of the article to be engaged and disengaged. Accordingly, the scope of the present invention is described by the claims appended hereto and supported by the foregoing.