Abstract:
A conveyor accumulator is configured to buffer a stream of articles moving along a conveyor path. The conveyor accumulator comprises an in-feed accumulator for diverting a flow of articles from an upstream source to various downstream output locations. The conveyor accumulator also comprises a mass storage accumulator connected downstream of and to the in-feed accumulator. The mass storage accumulator has a plurality of lanes. The conveyor accumulator further comprises an out-feed accumulator connected downstream of and to the mass storage accumulator for diverting the flow of articles from various upstream sources to a downstream output location.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage application of International Patenet Application No. PCT/US11/63577, filed Dec. 6, 2011, which is incorporated herein by reference in its entirety and which claims the benefit of U.S. application Ser. No. 12/961,176 filed on Dec. 6, 2010, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates generally to power-driven conveyor systems. Specifically, the invention relates to horizontally oriented sections for accumulating items and controlling the flow of items moving between an upstream source and a downstream destination. 
     In production environments, balancing the flow between an upstream process or delivery station and a downstream process or receiving station is important. Accumulators have been utilized to accumulate articles when the downstream receiving station is either shut down or is operating at intake speed that is slower than the rate at which articles are being fed to it by the upstream delivery station. A problem with prior art horizontal accumulators is that the accumulators require a relatively large footprint to provide the needed buffer capacity (in some cases two to three times the footprint for a given capacity because of the drive and wheel arrangements), cannot accomplish a 90-degree transfer of articles in a direction of product flow without compressing the articles when the transfer device repositions itself upstream of its current position, and cannot independently and simultaneously control a plurality of lanes which provide buffer capacity between the in-feed and out-feed side of the accumulator. The shortcomings of these accumulators are especially problematic in high speed production operations such as those found in the food processing, handling and packaging industry. 
     One horizontal accumulator designed specifically for high-speed operations is disclosed in U.S. Pat. No. 4,513,858. The accumulator disclosed therein operates on a first-in-first-out (FIFO) principle so that regardless of whether the upstream or downstream station is malfunctioning, the articles exit the accumulator in the same order that they arrive. To achieve FIFO, the accumulator has a plurality of fixed pulley wheels located at each end which guide an endless carrier or conveyor along a serpentine path. Located between the fixed pulley wheels is a plurality of interconnected pairs of pulley wheels which also help guide the endless conveyor. A slide assembly connects each of the interconnected pairs. The slide assemblies move toward one end of the accumulator or the other and carry the interconnected pair along to provide more or less carrying capacity and, therefore, more or less travel time between the in-feed and out-feed side of the accumulator. 
     A rather complicated in-feed and out-feed drive mechanism controls, respectively, the accumulation of the incoming and outgoing items. These two drive mechanisms, which are located on opposing sides of the accumulator, must always rotate opposite one another. Further, the mechanisms require a number of pulley wheels and belts to achieve the desired direction of endless conveyor travel. Periodic reversals of direction and looping are needed to prevent slack in the endless conveyor. 
     Because of the above arrangement, each interconnected pair of pulley wheels rotates when at least one of the in-feed or out-feed side drive mechanisms is engaged because one or more of the fixed pulley wheels are being driven by the engaged drive mechanism. The only way to stop the rotation of the interconnected pair of pulley wheels is to idle or stop both the in-feed and out-feed drive mechanisms. Therefore, when one or both of the drive mechanisms is engaged, product is always advancing toward the out-feed side of the accumulator regardless of whether the interconnected pair of pulley wheels is advancing toward one end of the accumulator. 
     Additionally, in order for the interconnected pair of pulley wheels to shorten or lengthen the exposed length of the endless conveyor in response to a speed difference between the drive mechanisms, they must move in the same direction of travel and pull the endless conveyor toward one end or the other. If the fixed pulleys, which essentially pin the endless conveyor at each end, were replaced by a sprocket arrangement, the only way to create a speed difference between the interconnected pair of pulley wheels would be to place the drive mechanisms on opposite ends of the accumulator, with one drive mechanism driving one of the pulley wheels in the pair and the other drive mechanism driving the other wheel. Additionally, the pair of pulley wheels by themselves cannot reverse travel without losing the conveyor because the slide assembly is a fixed body with no means, such as spring loading, to compensate for slack in the conveyor when reversing the travel. Lastly, this accumulator is highly questionable at best for use in high speed operations, and is mostly likely not at all suitable for use in high speed operations. 
     Another horizontal accumulator which is suitable for high-speed operations is disclosed in DE Pat. No. 103 12 695. A commercial embodiment of this accumulator is the MEURER HSP™ horizontal buffer (Meurer Verpackungssysteme GmbH &amp; Co. KG, Fürstenau, DE). The accumulator has an in-feed transfer unit, a mirror-image out-feed transfer unit and a plurality of storage lines or lanes located between the in-feed and out-feed transfer units. The transfer of articles is direct between the transfer units and the plurality of lanes. 
     Because of its design, the accumulator has a number of limitations. The design is complex, requiring a relatively large number of parts. Articles being carried on the in-feed and out-feed units must be carried across a long dead plate by many small belts which can fail, leading to article damage. Additionally, the design requires a lot of safety covers which limit access and make maintenance more difficult. 
     Another limitation of the accumulator is that the in-feed and out-feed transfer devices take product directly from a running conveyor with no means to alter, control or absorb the flow. As such, the incremental indexing of the transfer unit on the in-feed side from one storage lane to an adjacent storage lane of the accumulator during loading must occur against the article flow because if it is instead incrementally indexed in the direction of the flow, significant article compression would occur when the transfer unit thereafter transfers back directly from the last to the first lane. In other words, to avoid significant article compression, the transfer unit travels with the article flow when it transfers back directly from the last to the first lane, and therefore travels against the flow when incrementally indexing. The designers, therefore, traded off compressing the articles slightly but more frequently versus compressing them more greatly but less often. Even so, at least some article compression occurs on the in-feed side during the incremental indexing because it does occur against the article flow. Article compression is particularly problematic because compression can cause damage to the article or its packaging. 
     In a similar manner, this accumulator also creates gaps in article flow on the out-feed side because it has no means to compensate for the travel time required for the out-feed transfer unit to reposition itself. Moreover, because two storage lanes cannot simultaneously start, any time the downstream receiving station goes down the in-feed transfer unit must immediately index, thereby creating a gap in article flow when conveying is resumed. 
     Additionally, it is difficult to offer different in-feed and out-feed locations. The transfer unit either indexes from one lane to the next against product flow or travels with product flow to move from the last to the first lane. There is no disclosed control means for repositioning the transfer unit from the last lane to the second-to-last lane or repositioning the transfer unit from any lane to any given other lane upstream or downstream of its current lane position. Lastly, the transfer unit cannot move independently of the in-feed or out-feed conveyor. 
     The only way for the accumulator to control the flow of articles when the downstream receiving station malfunctions is to stop the transfer unit on the out-feed side, reduce the speed of the lane until it is filled, and then stop this lane and start a second, adjacent lane. Neither the in-feed unit nor the out-feed unit can adjust the length of exposed carrying surface to provide momentary, additional buffer capacity. Further, neither transfer unit can retrace its path without causing product compression. 
     Still yet another limitation of the accumulator is that it relies upon a complex drive pinion and drive motor arrangement. The drive motors are pivotally arranged on moveable carriages such that the motors can be independently connected to each of the drive pinions. A complex belt and pulley idler or clutch arrangement resides between the motors and the drive pinion. When the drive pinion engages, it moves a lane from an idle state to a travel state. Although one lane can move from travel to idle as another lane moves from idle to travel, only one lane can be in the travel state at any given time. The accumulator cannot run two lanes simultaneously nor can it accelerate one lane as another decelerates. 
     Yet another accumulator is disclosed in U.S. Pat. No. 6,725,998, which stores accumulated articles in a vertical spiral and uses a transport member to adjust the buffer capacity of the accumulator. A commercial embodiment of this accumulator is the 6400 DYNAC® accumulator which at the time of filing of the parent application referenced above was made and sold by Hartness International, Inc. (Greenville, S.C.). 
     The transport member moves along a path parallel to an in-feed conveyor and an out-feed conveyor and deflects articles from the in-feed to the out-feed conveyor. Depending on the relative speeds of the two conveyors, the transport member moves to increase or decrease the quantity of items which can be stored on the conveyors. However, each conveyor extends past the transport member and there is no conveyor looping around the transport member. The exposed length of conveyor on both the in-feed and out-feed side remains constant but the available length for storage changes based upon the relative position of the transport member. Further, the in-feed storage capacity cannot change independently of the out-feed storage capacity and vice versa. Although the vertical spiral and transport member arrangement performs well for its intended purpose, the conveying speed is limited by amongst other things incline and inertia. Also, the 180° transfer from one conveyor to the other can be difficult because the transfer takes place along curves and at angles and the articles must be gripped, lifted, moved and placed. 
     SUMMARY OF THE INVENTION 
     A system and method of providing accumulation and flow control between an upstream delivery station and a downstream receiving station includes an in-feed accumulator, a mass storage accumulator, and an out-feed accumulator. Articles processed by the upstream delivery station are accumulated on or conveyed by the in-feed accumulator and then transferred to one of the lanes of the mass storage accumulator. This transfer is indirect, resulting in a direction of article flow different than that of article flow on the in-feed accumulator. Articles being accumulated on and conveyed by the mass storage accumulator are then transferred onto an out-feed accumulator. This transfer is also indirect, resulting in a direction of article flow different than that of the mass storage accumulator. 
     The in-feed and out-feed accumulators (“the feed accumulators”) each have an endless conveyor that moves between first second positions. As each of the endless conveyors moves between different positions, the length of its exposed carrying surface, and therefore its carrying capacity, changes. During its travel between the first and second position, the conveyor may be transporting product faster, slower, or at the same rate as its carrying capacity is growing or shrinking. The ability of the endless conveyor to extend or retract allows the feed accumulator to maintain a constant density of article flow. Additionally, the endless conveyor can momentarily reverse its direction of rotation, as needed when the transfer device moves against the flow of articles, thereby providing additional time for the transfer device to reposition itself before receiving additional articles. 
     The endless conveyor of the feed accumulator is preferably guided by first and second U-turn wheels, located in different horizontal planes, and being linked to each other in a manner such that they translate in equal and opposite directions relative to each other. A first and second drive motor, preferably located on a single end of the feed accumulator, control the position and rotational speed of the U-turn wheels. The position and rotation of the endless conveyor responds to a speed difference and/or a rotational speed difference between the first and second motors. As the length of the exposed carrying surface increases, the length of the unexposed carrying surface decreases, and vice versa. 
     The indirect transfer between the feed accumulator and the mass storage accumulator occurs by way of an intermediate transfer device that moves independently from the endless conveyor of the in-feed accumulator. The transfer device preferably indexes in the direction of article flow. As the transfer device indexes between a first and second position, the density of article flow is not affected. In other words, indexing does not compress or alter the spacing between the articles. Because the endless conveyor moves independently from the transfer device, it can extend or retract to accommodate indexing of the transfer device and compensate for the indexing time. The endless conveyor may also reverse its travel when the conveyor retracts to allow the transfer device additional time to position itself. 
     The transfer device is preferably a transfer apparatus having a lane defined by first and second curved vertical surfaces that guide articles flowing into the mass storage accumulator and change their direction of travel. The first and second curved surfaces may take many forms. For example, the first curved surface may be a vertically oriented rail and the second curved surface may be a vertically oriented endless belt with a plurality of flexible fins. To prevent interference between the transfer apparatus and the mass storage accumulator, as the transfer apparatus indexes to a different lane of the mass storage accumulator, a pivot or lifting mechanism is preferably provided for raising the nose end of the transfer apparatus so it clears the conveying sections which define each lane. The lifting mechanism is preferably a roller and cam plate arrangement. 
     The mass storage accumulator preferably includes a plurality of independent conveyor lanes. Each lane may be selectively driven by either of two motors. The first motor may be a different rated motor than the second motor. The first motor preferably serves as a receiving motor for driving a lane when products are being loading onto said lane, and the second motor preferably serves as a discharge motor for driving a lane when products are being loading onto said lane. Each lane in the plurality of lanes preferably has its own first and second clutches, one of which is preferably operatively connected to the first motor and the other of which is preferably connected to the second motor. The first clutches of all lanes are preferably operatively connected to the first drive motor via a common drive shaft or axle. Similarly, all of the second clutches are preferably operatively connected to the second drive motor via another common drive shaft. The two drive motors are not necessarily always running but could be, as needed. 
     Because the clutches for each lane are connected in series, and because each lane can be operatively connected to the receiving motor or the discharge motor via the clutches, two or more lanes can simultaneously, instantaneously, and independently move between various states as the respective first or second clutch of the lane engages or disengages and as the receiving and discharging motors vary their speeds. For example, one lane driven by the first motor can stop or decelerate as another lane driven by the second motor starts or accelerates; one lane can be running at a different speed than another lane as each can be driven by a different motor; or two lanes driven by the same motor can simultaneously stop at the same time that a different two lanes driven by the other motor simultaneously start. Of course these functions could be performed instead by providing each lane with its own drive motor, but the costs would be far greater. 
     The in-feed accumulator may be modified for use as a stand-alone accumulator without the need for the mass storage accumulator. When used as a stand-alone accumulator, the transfer is direct between the in-feed and out-feed portions of its endless conveyor, and thus also between the upstream delivery station and the downstream receiving station, respectively. The central portion of the feed accumulator includes the upper and lower U-turn wheels which guide the endless conveyor and traverse in a direction adjacent to the in-feed and out-feed portions of the endless conveyor, thereby extending and retracting the length of exposed endless conveyor. Alternatively, non-rotating guides could be used in place of the wheels to direct the conveyor around the U-turns. 
     The present invention provides for a horizontal accumulator having many advantages. It provides a much larger accumulation capacity in a much smaller footprint relative to many other horizontal prior art accumulators. The accumulator lends itself to modular design and, therefore, is easier and less costly to size, install, retrofit, maintain, or repair according to a particular application than many prior art accumulators. The accumulator allows for optimal in-feed and out-feed locations depending on the current state of the upstream delivery station, downstream receiving station and the accumulator itself. The accumulator accommodates and reduces inherent variability in article flow. In other words, the accumulator maintains or provides a relatively constant flow density of articles and does not create variability in article flow due to how it accumulates, transfers and conveys articles. The accumulator transfers items from one accumulator to another without the conveyor sliding under the article, compressing adjacent articles, or in any way damaging the articles being conveyed and transferred. The accumulator ensures no damage to the product during indexing of the transfer device. The accumulator isolates questionable articles in position for rework or auto-pulls audit samples, if required. The accumulator allows two or more conveying lanes to simultaneously, instantaneously, and independently change their respective conveying states. The accumulator eliminates the use of water or dry lubricant and tolerates any line lubricant carryover. The accumulator is characterized by a smaller shipping volume and, therefore, has less shipping cost. The accumulator reduces operational cost, eliminates or minimizes the use of doors, and provides improved maintenance access and fewer safety issues. The accumulator is able to handle high product flow rates. And still further, the accumulator can be used to transfer items which, due to instability, could not transferred using prior art accumulators. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is top plan view of a prior art accumulator in accordance with U.S. Pat. No. 4,513,858. The accumulator has a plurality of interconnected paired pulley wheels located adjacent one another in the same horizontal plane. An endless carrier or conveyor is guided along a serpentine path by the paired pulley wheels and a plurality of fixed pulley wheels located at each end of the accumulator. An in-feed and out-feed drive mechanism, located on opposite ends of the accumulator, drive the endless conveyor. The interconnected pair of pulley wheels responds to a speed difference between the drive mechanisms and pulls the endless conveyor toward one end of the accumulator. The length of the exposed carrying surface provided by the endless conveyor, and therefore its carrying capacity, remains fixed but is reallocated between the in-feed side and out-feed side as the situation requires. 
         FIG. 2  is a top plan view of another prior art accumulator, that of DE Pat. No. 103 12 695. Because the transfer device of that accumulator loads against article flow, it compresses the items when indexing to load a new lane. If the transfer device were to index load with article flow, it would nonetheless compress the items during its return travel. Further, the accumulator creates gaps in article flow on the out-feed side because of (1) the return travel time required to reset the transfer device to the next or new lane; (2) the use of a discrete drive mechanism (see  FIG. 3 ) which, like return travel, increases cycle time; and (3) the accumulator lacking means to compensate for increased cycle time. Additionally, it is difficult to offer different in-feed and out-feed locations. 
         FIG. 3  is a side elevational view of the accumulator of  FIG. 2 . A drive pinion and pivotal drive motor arrangement controls the movement of each storage line or lane. When engaged, the drive pinion moves the lane from an idle state to a travel or convey state. Although one lane can theoretically move from travel to idle as another lane moves from idle to travel, because of the discrete nature of the drive mechanism the movement is not simultaneous. Further, the acceleration and deceleration of the two lanes are not independent of one another. Because one drive must completely disengage before it can shift to the next lane and re-engage, a time lag exists between one lane starting and the other lane stopping. In other words, two or more lanes cannot change their respective states simultaneously. 
         FIG. 4  is a top plan view of the prior art accumulator disclosed in U.S. Pat. No. 6,725,998. The accumulator stores items in a vertical spiral and uses a transport member to move along a path parallel to an in-feed conveyor and an out-feed conveyor. The transport member deflects articles from the in-feed conveyor to the out-feed conveyor. Depending on the relative speeds of the two conveyors, the transport member moves to increase or decrease the quantity of items which can be stored on the conveyors. However, the in-feed storage capacity cannot be adjusted without also adjusting the out-feed storage capacity. 
         FIG. 5  is a top plan view of a preferred embodiment of a horizontal accumulator made according to this invention for controlling the flow of items between an upstream and downstream processing operation. Accumulator capacity is provided by an in-feed and out-feed side accumulator and a mass storage device or accumulator having a plurality of storage lines or lanes located between the in-feed and out-feed accumulators. The transfer of items between the in-feed and out-feed accumulators and the plurality of lanes is not direct. Rather, the transfer occurs by way of an intermediate transfer device that provides accumulation and flow control and moves independently from the accumulator that it services. The in-feed and out-feed accumulators can adjust the length of its respective endless conveyor to provide more or less carrying capacity while the conveyor is not rotating. Under steady state flow conditions, both feed accumulators maintain the endless conveyor in a same position and the transfer device transfers items to and from the same lane in the plurality of lanes. 
         FIG. 6  is a side elevational view of the in-feed accumulator of  FIG. 5  with the accumulator housing partially removed, the out-feed side accumulator being a mirror image. An endless conveyor is guided by two wheels physically and flexibly connected together and located in different horizontal planes. 
         FIG. 7  is an elevational view of the drive motor end of the in-feed accumulator. One drive motor controls the speed and direction of the left half of its endless conveyor and another drive motor controls the speed and direction of the right half of the endless conveyor. The endless conveyor rotates and the U-turns move to different positions in response to speed and rotation differences between the two drive motors. When the motors drive the two halves of the endless conveyor in opposite directions and at the same speed, the U-turns of the endless conveyor maintain a constant position. 
         FIG. 8  is a top plan view of the in-feed accumulator of  FIG. 5 , illustrating the endless conveyor in a first position while rotating. Articles being conveyed flow along the upward facing portion of the endless conveyor and are transferred to a storage lane. When being repositioned, the upper and lower U-turns traverse in opposite directions and the endless conveyor extends or retracts. 
         FIG. 9  is a top plan view of the in-feed accumulator of  FIG. 5 , illustrating the endless conveyor moving to a second position, while the U-turns remain stationary. During this reverse travel, the exposed individual carrier segments maintain the position relative the U-turn that each was in at the start of the reverse travel (see carrier segments  23   A ,  23   B  and  23   C  in  FIGS. 8 and 9 ). 
         FIG. 10  is a top plan view of the intermediate transfer device shown on the accumulator shown in  FIG. 5 . The transfer device loads in the direction of the flow of articles and has mechanical means that allow it to reposition against the flow of articles without compressing the items (i.e., decreasing the spacing between items and causing items to touch). One curved surface of the transfer device is an endless belt having outward extending flexible ribs. 
         FIG. 11  is a partial elevational view of the nose end of the intermediate transfer device of  FIG. 5  when positioned to transfer articles between a feed side accumulator and one lane of the mass storage accumulator. 
         FIG. 12  is a view taken along section line  12 - 12  of  FIG. 11 . The nose end of the intermediate transfer device includes lifting means in communication with a cam plate. When the lifting means are positioned over the low cam positions of the cam plate, the nose end of the transfer device is in a substantially horizontal orientation. 
         FIG. 13  is a partial elevational view of nose end of intermediate transfer device of  FIG. 5  as it indexes from one lane to the next lane. As the transfer device indexes from one lane to the next, the lifting means lifts the nose end of the transfer device to avoid any interference with the carrier segments of the mass storage accumulator. 
         FIG. 14  is a view taken along section line  14 - 14  of  FIG. 13 . When the lifting means are positioned over the high cam positions of the cam plate, the nose end of the transfer device pivots or raises upward. 
         FIG. 15  is a partial elevational front view of the cam plate of  FIGS. 11 to 14  relative to the mass storage accumulator of  FIG. 5 . 
         FIG. 16  is a side elevational view of the plurality of lanes shown in  FIG. 5 . Each lane can be driven by either its first or second clutch. Although the first and second clutches are shown as upper and lower clutches, they could also be located on opposite ends of the respective lane, side-by-side, or anywhere wherever is practical along the lane&#39;s endless conveyor. That being said, all of the upper clutches share a common axle driven by an upper drive motor and all of the lower clutches share an axle driven by a lower drive motor. The upper and lower drive motors may be different rated motors. Each clutch is independent of the other and moves between a disengaged and engaged state. When in the engaged state with the respective motor operating, the lane is in a conveying or travel state. For example, an upper or lower clutch in one lane may engage at the same time that an upper or lower clutch in another lane disengages. Two or more adjacent upper or lower clutches may be engaged at the same time to accommodate flow or create a wider lane. 
         FIG. 17  is a side elevational view of the plurality of lanes of  FIG. 5 , showing the side opposite to that shown in  FIG. 16 . Various sensors, such as photoelectric eyes, may be used to monitor and communicate information about the status and position of articles being conveyed by the lanes. Other sensors, such as encoders, may be used to monitor and communicate information about the number of revolutions of the upper and lower motor drive shafts. 
         FIG. 18  is a partial cut-away elevational front view of the plurality of lanes of  FIG. 5  at the out-feed end, illustrating each lane having an upper and lower clutch connected in series. A clutch may be bypassed without having to take the lane or the entire plurality of lanes out of service. 
         FIG. 19  is a view taken along section line  19 - 19  of  FIG. 18 , illustrating the arrangement of an upper and lower clutch pair. 
         FIG. 20  is the accumulator of  FIG. 5  superimposed over of the prior art accumulator of  FIG. 1 . Both accumulators have been sized to have the same capacity. The accumulator of  FIG. 5  requires a much smaller footprint to provide the same capacity as that of the prior art accumulator. 
         FIG. 21  is the in-feed and out-feed accumulator of  FIG. 5  drawn adjacent to the paired interconnected pulley wheels of the prior art accumulator of  FIG. 1 . Because the paired pulley wheels are located in the same horizontal plane, the footprint of this prior art accumulator is much larger than that of the in-feed and out-feed accumulator of  FIG. 5  in order to provide the same carrying capacity. 
         FIG. 22  is an alternate embodiment of the in-feed or out-feed accumulator of  FIG. 5 , configured for use as a stand-alone accumulator. Unlike the feed accumulators of  FIG. 5 , the feed accumulator of  FIG. 22  includes in-feed and out-feed runs or portions of the endless conveyor. The upper and lower U-turns located in the mid-portion of the accumulator traverse adjacent to the in-feed and out-feed portion of the endless conveyor. The drive motors are mounted opposite one another, on the in-feed and out-feed portions, respectively. 
         FIG. 23  is a top plan view of the horizontal accumulator of  FIG. 5  with an alternate intermediate transfer device. Unlike the oblique lead-in, flexible-fin transfer device of  FIG. 5  (and  FIG. 10 ), the transfer device of  FIG. 23  is a true 90-degree transfer device with its inlet portion running substantially coaxial with the endless conveyor passing underneath the inlet portion. 
         FIG. 24  is a top plan view of the in-feed or out-feed accumulator for explaining the relationship between speed V, relative conveyor direction R, and upper U-turn position on the endless conveyor  21 . 
         FIG. 25  is a top plan view of the horizontal accumulator showing examples of control and sensing devices for controlling product flow through the accumulator. 
         FIG. 26  is a top plan view of the horizontal accumulator showing a partially accumulated state. Articles are shown being received and discharged simultaneously. 
     
    
    
     The preferred embodiments illustrated in the drawing will be described with reference to the following element numbers:
       10  Horizontal accumulator     20  In-feed/out-feed accumulator     21  Endless carrier or conveyor     23  Carrier segment     25  Sprocket-and-wheel arrangement     27  U-turn wheel     29  Platform or plate for  27       31  Channel     33  Housing     35  First end of  33       37  Second end of  33       39  Drive motor     41  Tether or cable     43  Spring     50  Mass storage device or accumulator     51  Storage line or lane     53  Endless carrier or conveyor     55  Carrier segment     57  Gap or space between adjacent lanes  51       59  Electro-magnetic clutch     61  Shaft or axle     63  Drive motor     65  Sprocket     67  Left or right side of  50       69  Shaft or axle     70  Intermediate transfer device     71  transfer member     73  Belt in communication with transfer member  71       75  Nose end     77  Lower surface of  75       79  Lifting means     81  Roller     83  Bracket     85  Fastener     87  Upper end of  83       89  First curved surface of  70       91  Lane     93  Entry portion of lane  89       95  Second curved surface     97  Endless belt     99  Flexible fins     100  Cam plate     101  Undulating upper surface     103  Low cam or low cam position     105  High cam or high cam position     113  Photo-optic or photo-electric eye   PE 1 - 5  Photocells   S 1 - 4  Servo motors   E 1 - 4  Encoders   

     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A horizontal accumulator in accordance with this invention may be used in many different industries to control the rate of flow of articles between an upstream delivery station and a downstream receiving station. The accumulator is particularly well-adapted for use in applications involving an upstream delivery station, which may be a filling station for placing contents into a package, and a downstream receiving station in which the package may be placed in boxes. Because of its unique and inventive structure, the accumulator in comparison to prior art accumulators (see  FIGS. 1 to 4 ) provides far greater programming flexibility and control to accommodate and reduce variability in article flow on both the in-feed and out-feed side of the accumulator. The accumulator also provides a carrying capacity equivalent to prior art horizontal accumulators but in a much smaller footprint (see  FIGS. 16 to 18 ). 
     Referring to the drawings, and first to  FIG. 5 , a preferred embodiment of a horizontal accumulator  10  made according to this invention includes a mass storage device or accumulator  50  located between an in-feed accumulator  20   I  and an out-feed accumulator  20   O . The in-feed accumulator  20   I  is located at one end of mass storage accumulator  50  and the out-feed accumulator  20   O  is located at the other end. 
     The accumulators  20   I ,  50 , and  20   O  collectively function as a “shock absorber” when the flow of articles being conveyed between the upstream delivery station and downstream receiving station becomes variable or “lumpy.” Throughout this disclosure, such articles being conveyed are referred to as articles and are referenced in the drawing figures by the letter “A”. The accumulators  20   I ,  50 , and  20   O  perform this shock absorbing function by working in concert to smooth out article flow when article flow does become lumpy, and by providing first-in-first-out article flow regardless of the current status of the upstream delivery station or the downstream processing station. Various sensors of types well-known in the art are used to collect status information and facilitate communication between and within the feed accumulators  20  and  50 . 
     The mass storage accumulator  50  includes a plurality of storage lines or lanes  51  that provide most of the accumulation or buffer capacity of accumulator  10 . The lanes  51  convey articles received from the in-feed accumulator  20   I  to the out-feed accumulator  20   O . The transfer of individual articles between the feed accumulator  20   IorO  and the mass storage accumulator  50  is not direct. Rather, the transfer occurs by way, of an intermediate transfer device  70  that moves independently relative to other portions of the accumulator  10  of the feed-side accumulator  20  that it services, thereby providing another means for accumulation and flow control. 
     In describing how this indirect transfer takes place, throughout this detailed description the current lane at which intermediate transfer device  70  is positioned is referred to as lane  51   N , lane  51   N+1  is the next lane in the direction of article flow, and lane  51   N−1  is the next lane in the direction opposite that of article flow. On the in-feed side, the transfer device  70   I  is positioned at the filling lane  51   N . On the out-feed side, the transfer device  70   O  is positioned at the emptying lane  51   N . 
     Depending on the status of the upstream delivery station, the downstream delivery station, and the mass storage accumulator  50 , the filling lane  51   N  may be a different lane than the emptying lane  51   N , with the respective intermediate transfer devices  70  being positioned accordingly. By way of example and referring to the lane nearest the left side  67   LEFT  of the mass storage accumulator  50  as the first lane, the filling lane  51   N  might be the first lane and the emptying lane  51   N  might be the third or fourth lane. If the two lanes  51   N  are different lanes, filling lane  51   N  may be running at a different speed than the emptying lane  51   N . Additionally, the transfer device  70  may need to index multiple lanes  51  on either the in-feed or out-feed side. For example, if the transfer device  70   I  is positioned at the last lane (i.e., the lane furthest from the first lane), it may be necessary for the transfer device  70   I  to index back to the first lane  51 . 
     In general terms, the transfer device  70  is capable of indexing itself N+Δ or N−Δ lanes  51 , where Δ is the lane increment (e.g. 1, 2, 3 . . . total lanes). There are two exceptions. When the transfer device  70  is positioned at the first lane  51 , it cannot index in the negative direction because there are no more upstream lanes  51  to which to index. Similarly, when the transfer device  70  is positioned at the last lane  51  it cannot index in the positive direction because there are no more downstream lanes  51  to which to index. 
     The structure of the in-feed accumulator  20   I  is the same as that of the out-feed accumulator  20   O  in all respects. The only difference between the two feed accumulators  20   I&amp;O  is that the in-feed side accumulator  20   I  is under the control of in-feed side logic and is configured to receive articles from the upstream delivery station and send those articles to the mass accumulator  50  whereas the out-feed side accumulator  20   O  is under the control of out-feed side logic and is configured to receive articles from the mass accumulator  50  and send those articles to the downstream receiving station. For ease of reference, throughout the remainder of this detailed description the in-feed and out-feed accumulators  20   I&amp;O  are sometimes referred to as feed accumulator  20  or feed accumulators  20 . 
     Because the intermediate transfer device  70  is independent of its respective feed side accumulator  20 , the endless conveyor  21  of the feed side accumulator  20  can extend or retract (or extend and extend again or retract and retract again) between a first position and a second position as the transfer device  70  is moving in the same or opposite direction. For example, if the transfer device  70   I  is transferring articles from the in-feed side accumulator  20   I  to the mass storage accumulator  50  in the direction of article flow (which is preferable) and the transfer device  70   I  needs to reposition or index to the next lane  51   N+1 , the endless conveyor  21   I  can momentarily extend (move opposite the transfer device  70   I ) and then retract to accommodate the indexing time and close any increased spacing in article flow caused by the index. Therefore, the speed at which the conveyor  21   I  extends may be different than the speed at which it retracts. Further, the speed at which the transfer device  70  indexes and the endless conveyor  21  extends or retracts may be different speeds. Additionally, regardless of whether the endless conveyor  21  is extending or retracting to accommodate indexing of the transfer device  70 , the rotation of the conveyor  21  does not necessarily need to speed up or slow down. 
     Under steady state flow conditions like that shown in  FIG. 5 , both feed accumulators  20  maintain their respective endless conveyor  21  in a same position and each transfer device  70  services the same lane  51   N  as the filling and emptying lane (the first lane  51  in this example). The endless conveyors  21  do not need to extend or retract from their current positions to accommodate either the rate of article flow, variability in article flow, or the indexing of the intermediate transfer device  70 . Further, the intermediate transfer devices  70  does not need to reposition or index from one lane  51   N  to a next lane  51   N+1 or N−1 . 
     When steady state flow conditions are interrupted, the feed side accumulators  20  can each adjust the exposed length of its endless conveyor  21 , as well as the speed of the endless conveyor  21 , to provide different carrying capacity, different total transit time, or different carrying capacity and transit time. Adjusting the speed of endless conveyor  21  may include stopping the rotation of the conveyor  21  around its U-turn wheel  27  or guide as its exposed length is adjusted, which is done simply by operating both the left drive motor  39   L  and the right drive motor  39   U  at the same speed and in the same direction. Additionally, a filling or emptying lane  51   N  of the mass storage accumulator  50  may be slowed down, speeded up or completely stopped and a next filing or emptying lane  51   N+1 or N−1  (or any other filling or emptying lane  51   N+Δ or N−Δ ) simultaneously, instantaneously and independently started. 
     When the filling lane  51   N  is full of articles or stopped, the intermediate transfer device  70  on the in-feed side indexes to the next available filling lane  51   N+Δ or N−Δ . Further, two lanes  51  may be running at the same time and at different speeds (or at different rates of acceleration and deceleration), and may be simultaneously, instantaneously, and independently started. 
     Referring to  FIGS. 5 to 9 , the endless conveyor  21 , which may be constructed of linked carrier segments  23 , is guided by a sprocket-and-wheel arrangement  25  that places one portion of the conveyor  21  in a different horizontal plane than the remaining portion. A curved rail (not shown) guides articles being carried by endless conveyor  21  as the articles move around the U-turn wheels  27   U . It should be appreciated that although in the preferred embodiment of the invention, the conveyor extends around U-turn wheels, the U-turns could also extend partially around non-rotatable guides. Moreover, the U-turns need not necessary have a semicircular shape and could comprise several smaller turns with various shapes. That being said, the wheels  27   U&amp;L  each ride on a respective platform or plate  29  received by opposing longitudinally extending channels  31  of the accumulator housing  33 . The movement of the plate  29  is responsive to its wheel  27  and the speed and rotational differences between the motors  39   U&amp;L . Each plate  29  is tethered to the other plate  29  by a cable  41 , thereby placing the wheels  27   U&amp;L  in a master-slave relation to one another (i.e., when one wheel is forced to move, the other must also move). 
     Because of the master-slave relation, when the upper wheel  27   U  of the in-feed accumulator  20   I  traverses toward the first end  35  of the accumulator housing  33 , the lower wheel  27   L  traverses toward the second end  37  and the endless conveyor  21  extends between first and second positions. Conversely, when the upper wheel  27   U  traverses toward the second end  37 , the other wheel  27   L  traverses toward the first end  35  and the endless conveyor  21  retracts between a second and first position. In general terms, the total exposed length of the in-feed endless conveyor  21  is at a maximum when its upper wheel  27   U  (and therefore its upper plate  29   u ) is at the end of its travel toward the first end  35  of housing  33  and wheel  27   U  (and therefore plate  29   U ) is at the end of its travel toward the second end  37  of housing  33 . Similarly, the total exposed length is at its minimum when the upper wheel  27   U  is at the end of its travel toward the second end  37  of housing  33  and the other wheel  27  is at the end of its travel toward the first end  35  of housing  33 . 
     Although the wheels  27  are in a master-slave relation, each wheel  27   UorL  is driven independently of the other wheel  27   LorU  by its respective drive motor  39   UorL . Because each wheel  27  responds to a speed and rotation of its drive motor  39 , and because the wheels  27  are in a master-slave relation to one another, the position and direction of rotation of the endless conveyor  21  responds to a speed “V” and rotational “R” difference of the drive motors  39 . Preferably, one of the drive motors  39   UorL  runs at a constant speed and serves as a governor with the speed of the other drive motor  39  being varied according to current feed conditions. The speed of the motor  39  serving as the governor on the in-feed side is set according to the incoming feed rate. On the out-feed side, the governor motor  39  is set according to the out-going feed rate. 
     The effect of the drive motors  39  on the endless conveyor  21  is summarized below in the following table: 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Effect of Differences in Speed V, Relative Conveyor Direction R, 
               
               
                 and Upper U-Turn Position on Endless Conveyor 21 (refer to FIG. 24). 
               
             
          
           
               
                   
                   
                 Drive Motor 39U 
                   
                   
               
               
                   
                 Drive Motor 39L 
                 In-feed 
                   
                 U-Turn 
               
               
                   
                 In-feed 
                 Accumulator 
                   
                 Extend or 
               
               
                   
                 Accumulator 
                 Exit Out-feed 
                 U-Turn 
                 Retract 
               
               
                   
                 Entrance Out-feed 
                 Accumulator 
                 Extend/ 
                 Speed 
               
               
                 Scenario 
                 Accumulator Exit 
                 Entrance 
                 Retract 
                 V(UT) 
               
               
                   
               
             
          
           
               
                 1 
                 V 
                 R 
                 V 
                 R 
                 Stationary 
                 Stationary 
               
               
                 2 
                 V + ΔV 
                 R 
                 V 
                 R 
                 Extend 
                 ΔV/2 
               
               
                 3 
                 V 
                 R 
                 V + ΔV 
                 R 
                 Retract 
                 ΔV/2 
               
               
                 4 
                 V 
                 −R 
                 V 
                 R 
                 Retract 
                 V 
               
               
                 5 
                 V 
                 R 
                 V 
                 −R 
                 Extend 
                 V 
               
               
                 6 
                 V + ΔV 
                 R 
                 V 
                 −R 
                 Extend 
                 V + ΔV/2 
               
               
                 7 
                 V 
                 R 
                 V + ΔV 
                 −R 
                 Extend 
                 V + ΔV/2 
               
               
                   
               
             
          
         
       
     
     The capability of endless conveyor  21  to traverse in a continuous (non-discrete) manner between a first and second position without rotation is one of the unique and inventive features of the feed side accumulators  20  and of the entire accumulator  10 . To prevent the endless conveyor  21  from being “spit out” by the upper wheel  27   U  as the endless conveyor  21  traverses without rotation of that wheel, one end of the cable  41  is connected to a spring  43 , which is affixed to the lower plate  29   L . Spring  43  allows cable  41  to take up any slack between the wheels  27  as one wheel  27   UorL  pulls and the other wheel  27   LorU  pushes. 
     When the endless conveyor  21  is moving between the first and second positions without rotation, its already exposed carrier segments  23  preferably do not advance (or retreat). For example, assume that the out-feed endless conveyor  21  is in the position shown in  FIG. 8  when the upper wheel  27   U  starts to traverse back toward the first end  35  (right) of the accumulator housing  33  (see scenario 4 of Table 1 and  FIG. 24 ). At the end of its traverse, the upper wheel  27   U  ends in the position shown in  FIG. 9 . Exposed carrier segments  23   A&amp;D  remain in their same position throughout the traverse. The unexposed segments  23   B&amp;C  at the start of the traverse become exposed at some point during the traverse. 
     Note that, in addition to “backing up” the endless conveyer  21  toward the first end  35  without wheel rotation, the endless conveyor  21  may also be reversed with counter rotation of the conveyor at the U-turn wheels or guides for timing purposes (see scenarios 5, 6, and 7 of Table 1 and  FIG. 24 ). This allows the intermediate transfer device  70  additional time, if required, for the transfer device  70  to index to a proper position relative to a lane  51  and verify that position before starting the actual transfer of articles between feed accumulator  20  and the lane  51 . To avoid compressing incoming articles, the length of the upper portion of the endless conveyor is increased at a rate greater than the speed at which the conveyor is being reversed. 
     Another unique, inventive feature is the placement of the wheels  27  in different horizontal planes. This placement allows the drive motors  39  to be located at the same end of the feed accumulator  20 , thereby giving the feed accumulator  20  a smaller footprint. The wheel placement also allows the wheels  27 , and therefore the endless conveyor  21 , to have a greater length of travel within this smaller footprint. 
     The feed accumulator  20  provides a greater carrying capacity within its footprint than prior art accumulators which place the wheels in the same horizontal plane (see  FIGS. 20 &amp; 21 ). Placing the wheels in the same horizontal plane results in a footprint approximately 30 to 40 percent longer than that of feed accumulator  20 , which has its wheels  27  placed in different horizontal planes. The indirect drive placed at each end of the prior art accumulator also extends its length by about 10 to 20 percent compared to that the accumulator  20  of the invention, which has its drive motors placed at the same end. The prior art accumulator also cannot reverse its travel without losing its conveyor because the slide assembly which carries the interconnected pulley wheels is a fixed body with no means, such as spring loading, to compensate for slack in the conveyor when reversing the travel. 
     Referring now to  FIGS. 5 and 8  to  15 , each feed accumulator  20  cooperates with a respective intermediate transfer device  70  that is detachably secured to a transfer member  71 . The transfer member  71  traverses left-to-right and right-to-left by means of an endless belt  73  controlled by a stepper or servo motor (see S 3  and S 4  in  FIGS. 25 and 26 ). The stepper or servo motor S 3 , S 4  controls the speed and direction of rotation of the endless belt  73  and, therefore, the speed and direction of travel of transfer device  70 . 
     The intermediate transfer device  70  preferably has the ability to pivot or lift its nose end  75  when indexing from one lane  51  to another lane  51 , thereby avoiding any interference with the lanes  51  during indexing. Each lane  51  is an endless conveyor  53  typically made up of linked carrier segments  55  (i.e., a slat chain conveyor). Any given carrier segment  55  in one lane  51  may not lie exactly in the same horizontal plane as a carrier segment  55  laying adjacent to it in the next lane  51  (carrier segments  55   N  and  55   N±1 , respectively). Further, one carrier segment  55  may lie partly ahead or behind another adjacent segment in the next lane  51 . Also, as a carrier segment  55  begins to expose its carrying surface on the in-feed end of mass accumulator  50  (or hide that surface on the out-feed end), a leading portion of the carrier segment might lie slightly above that of an adjacent carrier segment. If any of these interference situations occurs at the same time that the transfer device  70  needs to reposition or index to the next lane  55   N±1  (or to any lane  55   N±Δ ), the device  70  might hit the carrier segment  55  and cause damage to the lane  51   N  or  51   N±1 , the transfer device  70 , or articles being transferred. 
     Referring specifically to  FIGS. 11 to 15 , to pivot or lift the nose end  75 , the intermediate transfer device  70  has lifting means  77  located toward the nose end  75 . In a preferred embodiment, the lifting means  79  includes rollers  81  positioned below the transfer member  71  and configured to ride over the undulating upper surface  101  of a cam plate  100 . Each roller  81  has a bracket  83  connected to its axle that receives a fastener  85 . The fastener  85  passes through the transfer member  71  until its upper end  87  comes into contact with the lower surface  77  of the nose end  75 . 
     The cam plate  100  is arranged relative to the mass storage accumulator  50  so that each low cam position  103  is directly opposite the median line of each lane and each high cam position  105  is between lanes, that is, the gap  57  formed by the opposing longitudinal edges of adjacent lanes  51 . When the rollers  81  are in the low cam position  103 , the nose end  75  of the transfer device  70  is in a normal horizontal orientation. As the transfer device  70  indexes from lane  51   N  to lane  55   N±1 , the rollers  81  ride up and onto the high cam position  105 , lifting the nose end  75  and allowing it to clear the carrier segments  51   N  and  51   N±1 . In a preferred embodiment of the cam plate  100 , the high cam position  105  lifted the nose end  75  of the transfer device  70  a maximum of about 2 mm. 
     The intermediate transfer device  70  provides an indirect transfer between the feed accumulator  20  and the mass storage accumulator  50  by way of two opposing, spaced-apart curved surfaces  89 ,  95 . The curved surfaces  89 ,  95 , which need not be similar in structure, form a lane  91 . The curved surfaces  89 ,  95  may be arranged relative to one another so that an incoming article to lane  91  enters the lane  91  oblique to the article flow on endless conveyor  21  rather than enter orthogonal to it. This oblique entry angle is accomplished in one preferred embodiment by the curved surfaces  89 ,  95  forming about a 45-degree lead-in or entry portion  93  of the lane  91  of the transfer device  70 . The articles are received by the entry portion  93  and then guided by the curved surfaces  89 ,  95  to accomplish the 90-degree transfer. 
     The first curved surface  89  may be a curved rail or a curved wall having a plurality of beads or rollers (not shown). The second curved surface  95  may be an endless belt  97  guided by a chain-and-sprocket arrangement and controlled by a stepper or servo motor S 1  or S 2 . Preferably, the belt  97  includes a plurality of flexible fins  99  that come into contract with articles flowing into the lane  91  of the transfer device  70  and help guide those articles along the lane. 
     When used in combination with the cam plate  100 , the stepper or servo motor S 1  or S 2  used to control the endless belt  95  is preferably located toward the nose end  75  of the transfer device  70  to make the transfer device  70  nose-heavy. Being nose-heavy helps the nose end  75  remain in communication with the fasteners  85  and helps the rollers  81  remain in communication with the cam plate  100  as the transfer device  70  traverses left-to-right and right-to-left. 
     The lane  91  formed by the curved surfaces  89 ,  95  provides a lane width appropriate for the article being processed by the upstream processing station and received by the downstream receiving station. If the upstream processing station changes over to a different article that requires a different lane width, the intermediate transfer device  70  may be removed from the slide  71  and replaced by a different, appropriately sized transfer device  70 . For example, the different article may be one that is wider than a single lane  51  of the mass storage accumulator  50  and, therefore, requires that two adjacent lanes  51  be moved in concert with one another. A nonadjustable transfer device  70  configured to receive an article equal to or less than the width of a single lane  51  could not accommodate this different article and would need to be changed out for a transfer device  70  that could accommodate it. Alternatively, the width of the lane  51  of the transfer device  70  could be adjustable. 
     Referring now to  FIG. 23 , the intermediate transfer device  70  may be a true 90-degree transfer device  70   ALT . Unlike the transfer device  70  of  FIGS. 5 and 8  to  10  with its oblique lead-in or entry portion  93 , the transfer device  70   ALT  shown in  FIG. 23  has its entry portion  93   ALT  arranged coaxial to the endless conveyor  21  that passes underneath it. Like the other transfer device  70 , the transfer device  70   ALT  shown in  FIG. 23  remains independent of the endless conveyor  21 . 
     The intermediate transfer device  70  being independent of the endless conveyor  21  is yet another unique and inventive feature of accumulator  10 . Independence allows the transfer device  70  to transfer articles in the direction of article flow and articles are not compressed as the transfer device  70  indexes from lane  51   N  to lane  51   N+1 . “Not compressed” means that the article flow density does not increase. In other words, the spacing between adjacent articles on the endless conveyor  21  does not decrease as the transfer device indexes, no article slides away from its current position along the endless conveyor  21 , and no article comes into contact with any adjacent article because of the indexing. This holds true regardless of whether the transfer device  70  is indexing to lane  51   N+1  or lane  51   N−1 . 
     If the transfer device  70  transferred articles in a direction opposite that of article flow (that is, indexing from lane  51   N  to lane  51   N−1 ), no articles would compress because the U-turn  27   U  can move in the same direction and away from the transfer device  70 , thereby carrying articles away from the transfer device  70  as it indexes and as the exposed portion of the endless conveyor is extended. This is in contrast to the prior art accumulator shown in  FIGS. 2 and 3 . The prior art accumulator must index its transfer unit against article flow in order to have a short indexing distance and therefore minimize the amount of compression. The prior art transfer device then moves with article flow on its long index between the last and first lane so that little or no compression occurs. However, the long index time creates variability in article flow. 
     Additionally, because the intermediate transfer device  70  can index before (or after) the endless conveyor  21  repositions, the transfer device  70  can move at half the rate it would have to move if it were physically connected to the wheel  27   U . Further, the transfer device  70  can index without an article moving into it. Last, the endless conveyor  21  can momentarily traverse in a direction opposite that of the transfer device  70  as it indexes to lane  51   N+1  or as the transfer device  70  indexes between the last lane  51  and the first lane  51 . 
     The intermediate transfer device  70  may be mechanically connected to the plate  29   U  of the feed side accumulator  20  but this is not preferred for use in high speed operations. When mechanically connected in this way, the transfer device  70  moves in unison with the plate  29   U . 
     Referring now to  FIGS. 5 and 15  to  19 , each lane  51  of the mass storage accumulator  50  is in communication with a sprocket  61   U&amp;L  that engages the carrier segments  55  and its respective electro-magnetic clutches  59   U&amp;L  (“Electro-magnetic clutch” is referred to as “clutch” in the following and alternatively could be substituted by motors or other clutches). The clutches  59   UorL  of two or more lanes  51  may be configured in a modular arrangement, with a set of clutches  57   UorL  mounted on the same shaft or axle  61   UorL  with the axles  61  then connected to accommodate a wider configuration of the mass storage accumulator  50 . 
     The shaft or axle  61   U  of the upper clutches  59   U  are in communication with an upper drive motor  63   U . The axle  61   L  of the lower clutches  59   L  is in communication with a lower drive motor  63   L . The drive motors  63  are preferably located within the footprint of the plurality of lanes  51  and a respective shaft or axle  69 . Each axle  69   UorL  shares a chain drive with its corresponding axle  61   UorL , respectively. The drive motors  63   U&amp;L  may have different power ratings. 
     When the accumulator  10  is operating, both drive motors  63  may be running at their respective, predetermined constant speed and driving their respective axle  61 . By engaging one of the clutches  57   UorL  of a lane  51 , the lane  51  moves from an idle state to a traveling or conveying state. The motors  63  may be modulated based on in-feed and out-feed conditions, thereby changing the speed at which any given lane  51  travels. Encoders E 2 , E 3  may be used to record the number of rotations of the motors  63  for purposes of tracking product movement. A pair of opposing photo-electric eyes  113  may also be used to monitor the status of article flow on lanes  51 . 
     Having the clutches  59   UorL  on the same axle  61  in communication with the same drive motor  63   UorL  allows two or more lanes  51  to be simultaneously, instantaneously and independently stopped or driven by the drive motor. This arrangement of the clutches  59  also allows for some number of the clutches  59   UorL  to be electronically bypassed without impact the operation of the drive motors  63   U&amp;L  and the remaining clutches  59   U&amp;L . The mass storage accumulator  50 , and therefore the accumulator  10 , can therefore run continuously. 
     Each clutch  59   UorL  is independent of the other clutch  59   LorU  to which it is connected in series. Each clutch  59  is also independent of any other clutch  59   UorL  in any other lane  51 . The upper clutches  59   U  and the upper drive motor  63   U  may be under the control of the in-feed logic while the lower clutches  59   L  and lower drive motor  63   L  are under the control of the out-feed logic (or vice versa). Each clutch  59 , when engaged, allows for control of the speed, acceleration and deceleration of its respective lane  51 . 
     One of the unique and inventive features of the mass storage accumulator  50  is that the clutches  59   U&amp;L  are connected in series on the same lane  51 . Another unique and inventive feature is that the clutches  59   UorL  are arranged side-by-side on the same axle  61 . This arrangement allows at least two different lanes  51  to be in the traveling or conveying state at the same time. This also allows at least two different lanes  51  to simultaneously and instantaneously move into a conveying state. Still further, this allows one lane  51  to run at a different speed than another lane  51  or to accelerate or decelerate at a different rate. Additionally, this configuration allows for instantaneous stopping of one lane  51  while at the exact same time starting another lane  51 . As a result, the mass storage accumulator has a much faster cycle time than that of prior art accumulators in moving between lanes and the ability to close or reduce any gap that might occur in the article flow. Throughout this disclosure, the term “gap” refers to spacing between adjacent articles different than the spacing created by the processing rate of the upstream delivery station. For example, the spacing of articles on a drink box packaging line might be about one-half inch when the upstream delivery station is processing drink boxes. This constant spacing is interrupted whenever the upstream delivery station momentarily goes down, thereby creating gaps in the product flow. 
     In comparing the capability of the accumulator  10  and mass storage accumulator  50  to that of the prior art accumulator shown in  FIGS. 2 and 3 , the prior art accumulator can shift from one lane to the next but, because of its means to do so, a time lag exists between one lane starting and the other lane stopping. To move a lane into a conveying state when another lane is in the conveying state, the currently conveying lane must completely disengage before the drive and pinion gear mechanism can shift to the next lane and re-engage. Therefore, only one lane can be in the conveying state at any given time. Further, the acceleration and deceleration of the two lanes are not independent of one another. Because of its structure, this prior art accumulator has a slower cycle time than that of accumulator  10  and mass storage accumulator  50  of the invention, and only can close or reduce any gap that may be present in the article flow by pausing the loading of the lane. Additionally, that prior art accumulator cannot return those articles to the customer conveyor without creating a gap in article flow. 
     The manner by which the accumulator  10  and mass storage accumulator  50  compensates and corrects for variability in article flow is a unique and inventive feature. Simply stated, the structure of the accumulator  10  allows the accumulator  10  to take advantage of increased programming flexibility and control. The same control software applied to prior art accumulators, such as those illustrated in  FIGS. 1 to 4 , would be limited in what it could accomplish because of the mechanical limitations inherent in the design of those prior art accumulators. 
     By way of example, when loading a lane  51   N  of the mass storage device  50 , the lane&#39;s respective upper clutch  59   U  is engaged and the in-feed motor  63   U  comes under the control of in-feed logic. The out-feed motor  63   L  may also be running but the lower clutch  59   L  associated with the lane  51   N  is disengaged. If the upstream delivery station is momentarily down (about 2 or 3 seconds) and then up, incoming articles begin arriving in a “lumpy,” rather than constant flow pattern because there is now a gap in the article flow. The in-feed motor  63   U  modulates according to the incoming article flow as does the in-feed accumulator  20   I  which may slow or stop. At the same time a different emptying lane  51   N  may be discharging articles, with its respective clutch  59   L  engaged and the out-feed motor  63   L  coming under the control of out-feed logic. The emptying lane  51   N  may be running at a faster speed than filling lane  51   N  and might have to slow or stop. 
     Now, assume that the downstream receiving station is momentarily down (about 2 or 3 seconds). The endless conveyor  21   O  can extend all the way to the second end  37  of the accumulator housing  33  while the transfer device  70   O  continues to transfer articles to the conveyor  21   O  without moving away from the current emptying lane  51   N . When the downstream delivery station is back up and running, the out-feed conveyor  21   O  remains in its current position and, when the current emptying lane  51   N  is empty, the lane  51   N  is stopped and the transfer device  70   O  indexes at the same time to a another lane  51   N+1 . 
     If the same scenario were to occur with the prior art accumulator of  FIGS. 2 and 3 , the transfer unit would have to index immediately when the downstream receiving station goes down. The reason for this is that the prior art accumulator cannot simultaneously and instantaneously stop one lane and start the next lane. There is always a delay between stopping one lane and starting the next. Therefore, the prior art accumulator introduces gaps in the out-feed side any time the downstream receiving station goes down. 
     Table 2 below provides examples of the various states that two lanes  51   N&amp;N±Δ  can be in at the same time and the states to which each can independently, simultaneously, and instantaneously change at the same time. One lane  51   N  is the filling lane and the other lane  51   N±Δ  is the emptying lane. The acceleration or deceleration of each lane  51  is a function of the modulation of the drive motor  63   UorL  to which it is engaged. When a clutch  59   UorL  of a lane  51  is engaged, the lane  51  is in the travelling state and running at rate of speed determined by the in-feed or out-feed logic controlling the respective drive motor  63 . Note that Table 2 could be expanded to show four lanes  51  or other even multiples of lanes  51 . For example, at the same time one filling lane  51  may be slowing, another filling lane  51  may be starting, one emptying lane  51  may be slowing, and another emptying lane  51  starting. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Example: engaged (E), engaged accelerating (E A ), engaged 
               
               
                 decelerating (E D ) and disengaged (D) states of clutch series 59 U&amp;L   
               
               
                 for each of two lanes 51 N&amp;N±Δ  at a same time. 
               
             
          
           
               
                   
                 51 N   
                 51 N±Δ   
               
               
                   
                 59 U , 59 L   
                 59 U , 59 L   
               
               
                   
               
               
                 I 
                 D, D 
                 D, D 
               
               
                 II 
                 E, D 
                 D, D 
               
               
                   
                 E A , D 
                 D, D 
               
               
                   
                 E D , D 
                 D, D 
               
               
                 III 
                 D, D 
                 E, D 
               
               
                   
                 D, D 
                 E A , D 
               
               
                   
                 D, D 
                 E D , D 
               
               
                 IV 
                 D, E 
                 D, D 
               
               
                   
                 D, E A   
                 D, D 
               
               
                   
                 D, E D   
                 D, D 
               
               
                 V 
                 D, D 
                 D, E 
               
               
                   
                 D, D 
                 D, E A   
               
               
                   
                 D, D 
                 D, E D   
               
               
                 VI 
                 E, D 
                 E, D 
               
               
                   
                 E A , D 
                 E, D 
               
               
                   
                 E D , D 
                 E, D 
               
               
                   
                 E, D 
                 E A , D 
               
               
                   
                 E, D 
                 E D , D 
               
               
                   
                 E A , D 
                 E A , D 
               
               
                   
                 E A , D 
                 E D , D 
               
               
                   
                 E D , D 
                 E A , D 
               
               
                   
                 E D , D 
                 E D , D 
               
               
                 VII 
                 E, D 
                 D, E 
               
               
                   
                 E A , D 
                 D, E 
               
               
                   
                 E D , D 
                 D, E 
               
               
                   
                 E, D 
                 D, E A   
               
               
                   
                 E, D 
                 D, E D   
               
               
                   
                 E A , D 
                 D, E A   
               
               
                   
                 E A , D 
                 D, E D   
               
               
                   
                 E D , D 
                 D, E A   
               
               
                   
                 E D , D 
                 D, E D   
               
               
                 VIII 
                 D, E 
                 E, D 
               
               
                   
                 D, E A   
                 E, D 
               
               
                   
                 D, E D   
                 E, D 
               
               
                   
                 D, E 
                 E A , D 
               
               
                   
                 D, E 
                 E D , D 
               
               
                   
                 D, E A   
                 E A , D 
               
               
                   
                 D, E A   
                 E D , D 
               
               
                   
                 D, E D   
                 E A , D 
               
               
                   
                 D, E D   
                 E D , D 
               
               
                 IX 
                 D, E 
                 D, E 
               
               
                   
                 D, E A   
                 D, E 
               
               
                   
                 D, E D   
                 D, E 
               
               
                   
                 D, E 
                 D, E A   
               
               
                   
                 D, E 
                 D, E D   
               
               
                   
                 D, E A   
                 D, E A   
               
               
                   
                 D, E A   
                 D, E D   
               
               
                   
                 D, E D   
                 D, E A   
               
               
                   
                 D, E D   
                 D, E D   
               
               
                   
               
             
          
         
       
     
     Referring now to  FIG. 22 , the in-feed or out-feed accumulator  20  of  FIG. 5  may be configured for use as a stand-alone accumulator  20   SA . Unlike the oblong shaped of the endless conveyor  21  of the in-feed accumulator  20 , the stand-alone accumulator  20   SA  has a straight, in-feed run portion  21   I  of its endless conveyor  21  and a straight, out-feed run portion  21   O . The portion of the endless conveyor  21  guided by the U-turn  27  is located in the mid-portion  21   M  of the endless conveyor  21 . The mid-portion  21   M  traverses relative to the in-feed and out-feed portions  21   I&amp;O . 
     Similar to the in-feed accumulator  20  described above, the mid-portion  21   M  of the endless conveyor  21  of the stand-alone accumulator  20   SA  can traverse between a first and second position with or without rotation in the same manner as that of the in-feed accumulator  20 . However, the drive motors  39  are mounted opposite one another on the in-feed and out-feed portions  21   I&amp;O , respectively. Additionally, a customer-supplied motor or a motor of a downstream delivery station is in communication with the out-feed portion  21   O  of conveyor  21 . 
     Returning now to  FIG. 5 , earlier it was noted that the clutches  59  of the mass storage accumulator  50  may be modularized sets of clutches  59  that are assembled together to create a mass storage accumulator  50  having a particular width. The mass storage accumulator  50  may also be a modular design so that it can be scaled up or down according to the demands of a particular application. The in-feed accumulator  20  may also be made available in a standard length to match the size of the mass storage accumulator  50 . When shipping the accumulator  10  to a site, both the in-feed and out-feed accumulators  20  may be placed on and secured to mass storage accumulator  50  such that no further assembly will be required. Further, the various modular components of the accumulator  10  may be arranged to reduce the overall shipping footprint. 
     Having described various structural components and the functionality of various aspects of the preferred embodiment, several scenarios of the operation of the preferred embodiment of the accumulator will be described. 
     Initial Startup and Steady State Operation 
     Referring to  FIGS. 25 and 26 , when articles initially arrive at a first photocell PE 1 , the in-feed accumulator motors  39 U I ,  39 L I , a first servo motor S 1 , the mass storage in-feed drive motor  63 U, the in-feed clutch (shown as  59   U  in  FIG. 18 ) for lane  51   N , the second servo motor S 2  and the out-feed accumulator motors  39 U O  and  39 L O  are all energized. All of these motors are initially operated at a matched speed, with the in-feed and out-feed accumulator motors  39 U I&amp;O  and  39 L I&amp;O  turning in opposite directions and all operating the conveyor in the normal direction of article flow. 
     As a result, articles will flow steadily from the in-feed accumulator to the out-feed accumulator. During this state, small gaps in article flow measured by the first photocell PE 1  can be ignored by the system since there are no articles stored on the accumulator, and therefore there are no articles available to fill in any gaps in the flow of articles. Any durational gap between articles, as measured by the first photocell PE 1 , that exceeds the time required for an article to travel the entire length of the machine, is an indication that all articles have exited the machine. In response, the system preferably shuts down most components and thereafter waits for an additional incoming article to be detected by the first photocell PE 1 . 
     During steady state operation (i.e., when articles are flowing through the machine uninterrupted), the first photocell PE 1  can detect articles that have become too closely packed on the customer&#39;s in-feed accumulator. Should the first photocell PE 1  detect a tightly packed group of articles approaching the machine in-feed accumulator, a short delay timer will allow the leading edge of this group to reach the in-feed endless conveyor  21   I . All of the motors and servos which are operating at matched speed except the lower out-feed accumulator motor  39 L O  (which controls the speed at which articles flow out of the out-feed accumulator) will accelerate. As a result, the U-turn  27 U O  of the out-feed accumulator  20   O  will slightly extend due to the upper out-feed motor  39 U O  running slightly faster than the lower out-feed motor  39 L O . As a result, the horizontal accumulator  10  will have inserted the correct gap between the previously tightly packed articles, maintaining a consistent spacing through the machine. 
     Once the U-turn  27 U O  of the out-feed accumulator  20   O  has left its home position relative to the out-feed transfer device  70 ALT O , the machine&#39;s programmable controller (PLC) will utilize a second photocell PE 2  to detect status signals downstream of the out-feed accumulator  20   O  and will modulate or accelerate as needed to empty this small surge from the out-feed accumulator  20   O . By increasing the speed of the lower out-feed motor  39 L O , without an equal increase in the speed of the upper out-feed motor  39 U O , article output will increase and the U-turn  27 U O  of the out-feed accumulator  20   O  will retract. Once the U-turn  27 U O  has reached its home position relative to transfer device  70 ALT O , the lower out-feed motor  39 L O  will cease independent operation and return to the same speed as the other motors and servos. 
     Steady State with Momentary Downstream Stoppage 
     As previously mentioned during steady state operation, the speed of the in-feed and out-feed accumulator motors  39 R I&amp;O ,  39 L I&amp;O , the in-feed drive motor  63 U of the mass storage accumulator  50 , the first servo motor S 1 , and the second servo motor S 2  are controlled via the PLC and modulate together as one unit. The out-feed drive motor  63 L of the mass storage accumulator  50  does not need to run until articles have been loaded thereon and the in-feed transfer device  70 ALT I  has indexed off of lane  51   N . 
     When the PLC receives a stop signal from the customer&#39;s downstream machine or when the second photocell PE 2  has detected a backup condition, the lower out-feed motor  39 L O  of the out-feed accumulator  20   O  will stop or remain stopped. All other motors upstream will continue to run as previously described. As a result, the out-feed accumulator U-turn  27 U O  will extend (because the lower out-feed motor  39 L O  of the out-feed accumulator  20   O  continues to run) and no articles will be discharged from the out-feed accumulator. If the stop condition is cleared before the U-turn  27 U O  reaches the maximum travel position as determined by a first encoder E 1 , then the out-feed motor  39 L O  of the out-feed accumulator  20   O  will restart and run faster than normal until all of the articles that were absorbed by the out-feed buffer have been emptied and the U-turn  27 U O  returns to its home position relative to the out-feed transfer device  70 ALT O . At this point the machine will return to a steady state condition and the out-feed motor  39 L O  will drop its speed to match the speeds of the other motors. 
     Full Stop Downstream with in-Feed Indexing from Lane  51   N  to Lane  51   N+1    
     When the PLC receives a stop signal from the customer downstream machine or when the second photocell PE 2  has detected a backup condition, the lower out-feed motor  39 L O  of the out-feed accumulator  20   O  will stop. All other motors and servos will continue to run or operate as previously described. As discussed above, this causes the out-feed U-turn  27 U O  to extend so as to buffer articles. 
     As the out-feed U-turn  27 U O  of the out-feed accumulator  20   O  nears full extension, as detected by the first encoder E 1 , an index cycle is initiated. The PLC will look to a third photocell PE 3  located on the in-feed transfer unit  70 ALT I  to detect the leading edge on the next article. When that leading edge is detected by the third photocell PE 3 , two actions will occur more or less simultaneously. First, a delay timer will begin and allow the article to travel to a predetermined position. This position is such that the article will still be gripped by the transfer device  70 ALT I , trapping it prior to indexing, but also forward enough that any article or articles preceding it will have move onto the mass storage accumulator  50  unhindered. At the completion of this time, the first servo motor S 1  will stop. Additionally, the in-feed clutch for lane  51   N+1  will be energized. More or less simultaneously with the stopping of the first servo motor S 1 , a third servo motor S 3  will index the in-feed transfer device  70 ALT I  to the next lane  51   N+1 . Just prior to the in-feed transfer device  70 ALT I  arriving at its correct position at that next lane  51   N+1 , the first servo motor S 1  will accelerate to discharge articles onto the new lane  51   N+1  (which is then in motion). 
     As product begins to fill the new lane  51   N+1  of the mass storage accumulator  50 , the leading edge of the first article released thereon is sensed by a fourth photocell PE 4 . At this point, a second encoder E 2 , corresponding to the in-feed motor  63 U of the mass storage accumulator  50 , is set to zero and starts counting pulses so that the PLC can keep track of the estimated distance that the articles have traveled along the new lane  51   N+1  following their placement thereon. 
     As discussed above, the in-feed transfer device  70 ALT I  indexed away from the U-turn  27 U I  of the in-feed accumulator  20   I . As such, the in-feed transfer device  70 ALT I  moved with the flow of the article (i.e., away from the incoming articles). Hence, no article compression occurs on the in-feed accumulator  20   I  while the first servo motor S 1  is stopped and the in-feed transfer device  70 ALT I  is indexing. Following the indexing of the in-feed transfer device  70 ALT I , the lower in-feed motor  39 L I  is accelerated in order to bring the U-turn  27 U I  of the in-feed accumulator  20   I  back into its normal position relative to the in-feed transfer device  70 ALT I . During this procedure, the first servo motor S 1  and the in-feed drive motor  63 U of the mass storage accumulator  50  are also increased to maintain consistent spacing of the articles on the lane on which they are being placed. Once the in-feed U-turn  27 U I  has reached its normal position closer to the in-feed transfer device  70 ALT I , then the lower in-feed motor  394  the first servo motor S 1 , and the in-feed drive motor  63 U of the mass storage accumulator  50  will return to their normal operating speed. 
     While loading articles onto a lane other than 51 N , the out-feed drive motor  39 L O  may have started to feed the downstream equipment. In this situation the out-feed operation of the machine and the in-feed operation of the machine (loading and unloading) have now begun to operate independently. 
     Unlike during normal steady state conditions, during full stop downstream with in-feed indexing conditions the in-feed operation also changes in that if a gap between articles is sensed by the first photocell PE 1 , all elements of the in-feed operation will immediately stop until more articles are detected at the first photocell PE 1 . This ensures that the gap is removed and thereby maximizes the storage capacity of the accumulator  10 . 
     Indexing from Lane  51   N+1  To  51   N+2  To  51   N+Δ   
     When the PLC determines from the second encoder E 2  that the lane  51   N+1  being filled of the mass storage device is almost-full (which corresponds to being about eight inches from the maximum allowed travel, the PLC will again look to the third photocell PE 3  to detect the leading edge of an article that is about to be placed on the mass storage accumulator. Additionally, the in-feed clutch  59 U N+2  for the next lane  51   N+2  will energize. The in-feed clutch  59 U N+1  of the current lane  51   N+1  remains energized until that lane has reached its maximum allowed travel. This ensures that the last article that has been placed onto the lane  51   N+1  has cleared the fourth photocell PE 4  and that it is therefore safe to index the in-feed transfer device. 
     After indexing to the next lane  51   N+2 , the accumulator  10  will iterate the steps described above to fill as many lanes  51  of the mass storage device as are needed until conditions downstream of the accumulator  10  change or the accumulator reaches maximum capacity. 
     In high-speed operations, an additional action involving the in-feed accumulator U-turn  27 U I  during indexing may be performed. Unlike the indexing described above where the in-feed U-turn  27 U I  will follow in what could be described as an “inch-worm” motion (i.e., the in-feed transfer device  70 ALT I  indexes first, and thereafter the in-feed accumulator U-turn  27 U I  follows, the in-feed U-turn  27 U I  may follow in what could be described as an “accordion” motion during high speed operations or when articles being conveyed are relatively unstable. The accordion motion allows for additional accumulation on the in-feed accumulator  20   I  during the indexing cycle. In order to accomplish this, the in-feed U-turn  27 U I  will extend away from the in-feed transfer device  70 ALT I  while the in-feed transfer device is moving in the opposite direction indexing from one lane to the next. To accomplish this movement, the lower in-feed motor  39 L I  will momentarily slow while the third servo motor S 3  is moving the in-feed transfer device  70 ALT I  to the next lane. Then, following the completion of the indexing of in-feed transfer device  70 ALT I , the lower in-feed motor  39 L I  will be accelerated to a rate faster than the upper in-feed motor  39 U I  is running to bring the in-feed U-turn  27 U I  back to its home position relative to to the in-feed transfer device  70 ALT I . 
     Out-Feed Stoppage Corrected, Out-Feed Restarts, in-Feed Still Loading 
     When the PLC receives a downstream clear signal and the second photocell PE 2  is open, then out-feed clutch for the first lane  51   N  will be energized and out-feed drive motor  63 L of the mass storage accumulator  50 , the out-feed motors  39 U O&amp;L  of the out-feed accumulator  20   O , and the servo motor S 2  of the out-feed transfer device  70 ALTo will all begin to run with their speeds controlled in unison. Thereafter, articles will begin exiting the first lane  51   N . These motors will run according to the demand of the customer&#39;s downstream machine, and their speeds will modulate simultaneously based on the length of queue at the downstream machine as determined by the second photocell PE 2  or some other downstream detector. 
     It should be appreciated that the out-feed U-turn  27 U O  remains fully extended (near the last lane  51   N+Δ ). The extra amount of articles on the out-feed conveyor  21   O  will be reserved for use in eliminating gaps created during indexing cycles of the out-feed transfer device  71 ALT o . 
     When a third encoder E 3  has detected that the conveyor chain or belt of the first lane  51   N  has traveled sufficient distance to ensure that all articles have been cleared from first lane, the servo motor S 2  of the out-feed transfer device  70 ALTo will stop or slow down, the out-feed clutch  59 L N+1  for next incremental lane  51   N+1  will energize almost simultaneously, and a fourth S 4  servo motor will index the out-feed transfer device  70 ALT O  to the next lane  51   N+1  During this time, the lower out-feed motor  39 L O  will continue to run feeding out articles as needed. Should it be necessary to prevent gaps between articles on the out-feed accumulator  20   O  resulting from the out-feed transfer device  70 ALT o  indexing procedure during any of the stoppages during indexing, the upper out-feed motor  39 U O  can be slowed or stopped momentarily. As a result, the out-feed U-turn  27 U O  will retract towards the first lane  51   N  of the mass storage accumulator  50  to ensure that product can continue to be discharged from the accumulator  10 . This also prevents any product gap from forming at the exit or inlet of the out-feed transfer device  71 ALT O . 
     After the out-feed transfer device  70 ALT O  has indexed to the next lane, the out-feed lower drive motor  63 L of the mass storage accumulator  50 , the second servo S 2  on the out-feed transfer device  70 ALT O , and the upper out-feed motor  39 U O  will be accelerated to a higher speed than the rate at which the lower out-feed motor  39 L O  is running (i.e., faster than demand). This moves the out-feed U-turn  27 U O  to its maximum extension (past lane  51   N+Δ ). After the out-feed U-turn  27 U O  reaches its maximum extension, such motors slow back down to the speed of the upper out-feed motor  39 U O . Preferably, only when all articles on the accumulator  10  are moving does the out-feed U-turn  27 U O  return to its home position relative to the out-feed transfer device  70 ALT O . 
     In-Feed Transfer has Reached the Final Lane and at Least One Other Lane is Unloaded 
     After the in-feed transfer device  70 ALT I  has reached the last lane  51   N+Δ , then in-feed transfer device  70 ALT I  and the in-feed U-turn  27 U I  will return to the first lane  51   N . This is done without interfering with articles flowing into the accumulator  10  and without compacting articles adjacent the in-feed transfer device  70 ALT I . In other words, the articles on the in-feed accumulator conveyor  21   I  maintain their spacing from their adjacent articles. To accomplish this, several things occur. The in-feed upper motor  39 U I  continues at normal speed rate while the in-feed lower motor  39 L I  reverses rotation so that it rotates in the same direction as the upper in-feed motor  39 U I , thereby causing the in-feed U-turn  27 U I  to extend to absorb the articles both on and entering the in-feed accumulator conveyor  21   I  as the in-feed transfer device  70 ALT I  moves back against article flow. By controlling the direction and speed of the upper in-feed motor  39 U I , complete control of the rotational movement of the conveyor  20   I  around the in-feed U-turn  27 U I  is achieved, thereby avoiding article compaction. The third servo motor S 3  simultaneously indexes the in-feed transfer device  70 ALT I  all the way from the last lane  51   N+Δ  of the mass storage device  50  to the first lane  51   N . Preferably the speed of this movement matches the reversal speed of the lower in-feed motor  39 L I . After the in-feed transfer device  70 ALT I  reaches the first lane  51   N , the lower in-feed motor  39 L I  reverses rotation again, thereby causing articles to move toward the in-feed transfer device  70 ALT I , which begins discharging articles onto the first lane  51   N  in the manner described above. 
     Out-Feed Catches Up to in-Feed 
     Since the discharge rate is greater than the intake rate, at some time after the discharge of stored articles from the mass storage accumulator  50  has commenced, the out-feeding lane will “catch-up” with the in-feeding lane. This is referred to as a “same lane condition.” 
     Assuming this “catch-up” occurs on a lane other than the first lane  51   N , the machine is considered empty but out of position. The lane transporting the articles initially is being driven by the in-feed drive motor  63 U of the mass storage accumulator  50  via the lane&#39;s in-feed clutch. More or less simultaneously, the control for this lane will be switched to the out-feed drive motor  63 L of the mass storage accumulator  50  and via the lanes out-feed clutch, and the in-feed transfer device  70 ALT I  and the in-feed U-turn  27 U will traverse back to the first lane  51   N  in the manner described above. Also more of less simultaneously, the first lane  51   N  engages the in-feed drive motor  63 U in preparation of receiving articles. 
     When the in-feed transfer device  70 ALT I  is positioned at the first lane  51   N , it will begin to release articles onto that lane. The out-feed transfer device  70 ALT O  continues to unload articles from the other lane  51   N+Y  and will traverse back to the first lane  51   N  after emptying that other lane. While the second servo motor S 2  is stopped during the indexing of the out-feed transfer device  70 ALT O , the out-feed upper motor  39 U O  reverses direction to retract the out-feed U-turn  27 U O  to avoid creating article gaps on the out-feed conveyor  21   O  adjacent the out-feed transfer device. Upon completing the indexing, the second servo S 2  and the upper out-feed motor  39 U O  of the out feed accumulator  20   O  resume their normal rotation and the machine is then back in steady state mode. 
     While accumulator  10  and a method for its use have been described in detail, persons of ordinary skill in the art can make changes to its structure or method of use without departing from the spirit and scope of this disclosure. Therefore, a horizontal accumulator made and used according to this invention is only limited by the scope of the claims.