Patent Document

BACKGROUND 
     The invention relates generally to power-driven conveyors and, more particularly, to conveyors and methods for controlling the gap between consecutive articles, such as packages, conveyed in a single file. 
     In some conveyor applications, it is important to control the spacing, or gap, between the tail end of a leading package and the head end of a trailing package. If the gaps are too great, throughput is decreased. If the gaps are too small, consecutive packages interfere with each other at downstream processing or sorting locations. Controlling these gaps is especially difficult when the packages vary in size, shape, or orientation. Thus, there is a need for a conveyor that can control the spacing between consecutive packages. 
     SUMMARY 
     This need and other needs are satisfied by a spacing conveyor embodying features of the invention. One version of such a spacing conveyor comprises a conveying surface, such as a conveyor belt, having retractable stops at spaced apart locations along the length of the conveying surface and article-supporting rollers protruding above the conveying surface to a roller top level. The conveying surface advances from an upstream end to a downstream end in a conveying direction. A bearing surface near the conveying surface contacts the rollers and causes them to rotate as the conveying surface advances. The rotating rollers propel articles supported atop the rollers along the conveying surface in the conveying direction. An actuator is selectively movable into contact with the retractable stops to move them from a retracted position below the roller top level to a blocking position above the roller top level. In the blocking position, the stop is positioned to receive an article propelled forward by the rollers. A sensor upstream of the actuator measures the length of a conveyed article and provides a corresponding length signal. A controller, responding to the length signal, selectively actuates the actuator to move selected stops to the stop position according to the length of the conveyed article and a predetermined spacing between consecutive articles. 
     Another version of a spacing conveyor comprises a conveyor belt advancing along a carryway from an upstream end to a downstream end in a conveying direction. The conveyor belt includes a series of rows of belt modules linked together at hinge joints between adjacent rows into an endless conveyor belt having outer and inner sides. Retractable stops are positioned at spaced apart locations along the length of the conveyor belt. Article-supporting rollers have salient portions that protrude above the outer side to a roller top level. The salient portions are accessible from the inner side. A bearing surface next to the inner side of the belt loop contacts the salient portions of the rollers, which causes them to rotate as the belt advances in the conveying direction. The rollers propel articles supported atop the rollers along the outer side in the conveying direction. A sensor upstream of the bearing surface measures the length of a conveyed article. An actuator is selectively movable between two positions depending on the measured length of a conveyed article advancing onto the conveyor belt. The actuator contacts the retractable stops to move them from a retracted position below the roller top level to a blocking position above the roller top level. In the blocking position, the stop receives articles propelled by the rollers. 
     In yet another aspect of the invention, a method for controlling the gap between consecutive articles on a conveyor comprises: (a) moving a first stop of a stop of series of regularly spaced stops advancing with a spacing conveyor in a conveying direction into a blocking position; (b) measuring the length of an article being fed onto the spacing conveyor at an infeed; (c) propelling the article along the spacing conveyor to the first stop; and (d) moving a second stop into a blocking position, wherein the second stop is the stop that trails the first stop in the conveying direction by the smallest distance greater than or equal to the length of the article plus a predetermined minimum gap between consecutive articles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These features and aspects of the invention, as well as its advantages, are better understood by referring to the following description, appended claims, and accompanying drawings, in which: 
         FIG. 1  is a side elevation view, partly cut away, of a portion of a conveyor system including a spacing conveyor embodying features of the invention; 
         FIG. 2  is a top plan view, partially cut away, of a portion of the conveyor of  FIG. 1 ; 
         FIG. 3  is a block diagram illustrating the control of the conveyor of  FIG. 1 ; and 
         FIG. 4  is a side schematic of the conveyor of  FIG. 1  illustrating one way of controlling the gap between consecutive packages. 
     
    
    
     DETAILED DESCRIPTION 
     A spacing conveyor embodying features of the invention is shown in a conveyor system in  FIG. 1 . The conveyor system comprises a spacing conveyor  10  downstream of an infeed conveyor  12 . Both conveyors advance in the conveying direction  14 , with the infeed conveyor feeding articles, such as packages  16 , single file onto the upstream end  18  of the spacing conveyor across a transfer plate  20 . The spacing conveyor transports the packages it receives toward its downstream end  19 . 
     In a preferred embodiment, both the infeed conveyor and the spacing conveyor are realized as conveyor belts, such as modular plastic conveyor belts. The infeed belt  22  is shown as composed of a series of rows  24  of belt modules linked together by hinge pins  26  at hinge joints  28  between adjacent rows. The belt articulates at the hinge joints around drive sprockets  30  at its downstream end. The drive sprockets are mounted conventionally on a shaft (not shown) through central sprocket bores  34 . The drive shaft is coupled to a motor (not shown), which rotates the shafts and the sprocket and drives the belt. The infeed belt shown in  FIG. 1  is also characterized by article-supporting rollers  36  protruding past the outer surface  33  of the belt. But an infeed belt without rollers could be used as well. 
     Like the infeed belt, the spacing belt  38  is preferably a modular plastic conveyor belt with rollers  36  protruding past inner and outer surfaces  40 ,  41  of the belt loop. The belt is trained between one or more drive sprockets  42  at the downstream end and one or more idle sprockets  43  at the upstream end. Salient portions  44  of the rollers extend past the inner surface of the spacing belt into contact with bearing surfaces  46  underlying and supporting the belt on the rollers along an upper carryway portion  48  of the conveying path. As shown in  FIG. 2 , the bearing surfaces are positioned under the rollers along the carryway. The forward motion of the belt causes the rollers riding on the bearing surfaces to rotate in the direction of arrow  50  on axles  49 . Packages  17  atop the rotating rollers are propelled in the conveying direction  14  by the rollers along the belt&#39;s outer conveying surface  41  at a speed greater than the speed of the belt. The bearing surfaces may be realized as one or more continuous surfaces underlying each lane of rollers or as segmented surfaces that could be selectively raised and lowered as indicated by arrow  51  or otherwise moved into and out of contact with the belt rollers by hydraulic, pneumatic, or electromechanical devices, to accelerate packages or not, as required. 
     The spacing belt also includes retractable stops  52  at spaced apart locations along the length of the belt. The stops in the example belt of  FIGS. 1 and 2  are positioned on the hinge rod  26  between every third belt row. But the stops could be positioned between every row or spaced even farther apart than shown. The stops shown in the example have a plate-like portion  54  with a face  56  that receives a package propelled along the belt when the stop  52  is in a blocking position with its face above the roller top level  58 . The plate-like portions are connected to roller portions  60  at each end, as shown in the cut away sections along the carryway in  FIG. 1 . The roller portions reside in gaps  62  between adjacent belt rows. A bore  64  through the roller portions receives the hinge rod  26 , which serves as an axle on which the stop can rotate. Actuators  66  positioned along the carryway at one or more positions along the length of the conveyor are selectively movable into and out of contact with the retractable stops, such as up and down as indicated by arrow  68 . The actuators are laterally aligned with the roller portions of the stops. 
     The actuators, which may be moved by any conventional means, such as hydraulics, pneumatics, electromagnetics, mechanical systems, or air bursts, have an upper cam surface  70  with an entrance ramp  72  on which the stop&#39;s roller portion  60  can ride as a cam follower. When in contact with the actuator&#39;s cam surface, the stop rotates on the hinge rod into the blocking position. 
     The stops are bistable with two stable positions: (a) the blocking position  52 ; and (b) a retracted position  52 ′. In the retracted position, the stop is below the roller top level  58  and cannot interfere with conveyed packages. Because the stops are bistable, once an actuator engages a stop on the carryway, the stop remains in the blocking position until gravity causes it to return to its refracted position as the belt articulates about the idle sprocket  43  on its return to the carryway. Thus, all the stops are automatically returned to their retracted positions just before entering the carryway. 
     A sensor  74 , such an optical sensor, is shown in  FIG. 1  positioned at the downstream end of the infeed conveyor  12 . The sensor, which may include a light source emitting a light beam across the conveyor to a photodetector, is used to measure the length of each package. The passage of a package through the beam shadows the photodetector for a time proportional to the length of the package. As shown in  FIG. 3 , the sensor outputs a signal  75  on a signal line  76  indicative of the time the beam is shadowed, which is proportional to the length of a passing package. The signal is sent to a controller  78 , such as a programmable logic controller, a microcontroller, or other intelligent controller. With knowledge of the speed of the infeed conveyor, the controller can compute the length of the package by multiplying the speed by the time the beam was shadowed by the package. The controller then controls the activation of the one or more actuators  66  over control lines  68  to optimize the gap between consecutive packages. 
     The operation of the spacing conveyor as controlled by the controller is illustrated in  FIG. 4 . In the exemplary operating mode depicted, the controller is programmed to maintain a selectable or predetermined nominal gap G of D±D/2 (0.5 D to 1.5 D) between consecutive packages, where D is the distance between the positions of consecutive stops  52 . Thus, in this example, the minimum allowed gap is 0.5 D. A first package P 1  whose length l 1  has been measured by the sensors is propelled atop the rollers on the spacing conveyor to a stop  52 A in the blocking position. Because the length of the package is between 2D and 3D, i.e., 2D&lt;l 1 &lt;3D, the controller does not send actuation signals to the actuators to move the following two stops  52 B and  52 C to the blocking position. They remain in the retracted position below the roller top level and out of contact with the package P 1 . Because l 1 ≲2.5 D, or, more generally, (l 1  modulo D)≲0.5 D, the controller sends a signal to the actuator to move the next stop  52 D to the blocking position. This sets a gap between the tail end of the package P 1  and the head end of the trailing package P 2  as G 1 =3D−l 1 ≳0.5D. In other words, the second blocking stop  52 D is the stop that trails the first blocking stop  52 A by the smallest distance greater than or equal to the sum of the length of the package and the minimum gap allowed, or (l 1 +0.5 D) in this example. The package P 2  has a length l 2  as measured by the sensor and reported to the controller. After the trailing package P 2  is fed onto the spacing belt, it is accelerated forward to the stop  52 D already in the blocking position. Because l 2 ≳2.5 D, or, more generally, (l 2  modulo D)≳0.5 D, the controller sends a control signal to the actuator to move the second trailing stop  52 H to the blocking position. The stop  52 G between the tail end of the package P 2  and the next blocking stop  52 H is maintained in its retracted position to ensure that a gap of at least D/2 is maintained. In this case, the gap G 2  between the tail end of the package P 2  and the front end of a trailing package is given by G 2 =4D−l 2 ≳1.5D. In this way, the spacing conveyor maintains a gap of 0.5 D to 1.5D between consecutive packages. Of course, it would be possible to program the controller to interpose greater gaps between consecutive packages. For example, where two lanes of packages are being conveyed on opposite sides of the spacing conveyor, either on a single belt with independently actuated stops or on each of a pair of side-by-side belts, it would be possible to stagger the packages from one lane to the other in anticipation of a clean merge downstream. In such a case, the gaps between consecutive stops in each package lane would have to be great enough to account for a staggered package in the other lane. And it is possible to achieve tighter controlled gaps by spacing the stops closer together along the length of the conveyor. 
     Although the spacing conveyor has been described in detail with reference to a preferred version, other versions are possible. For example, flat belts, slat conveyors, or other moving conveying surfaces with protruding rollers and retractable stops could be used instead of modular plastic conveyor belts. As another example, the stops do not have to rotate on hinge rods. They could alternatively pop up linearly when activated or be forced mechanically back to their retracted position. As yet another example, any sort of sensor that can measure the length of the packages can be used. And the actuators could be realized as rollers or as telescoping cam surfaces that may be extended along the length of the carryway to activate a selected number of consecutive stops. Furthermore, the description was written as though the length of a package is its actual length when properly oriented. But, for packages oriented off-axis or for non-rectangular packages or articles, the length of the package would be the length of the longest line segment through the package parallel to the conveying direction, and not its actual length. So, as these few examples suggest, the spirit and scope of the claims are not meant to be limited to the preferred version described in detail.

Technology Category: 7