Abstract:
A conveyor system includes a plurality of transit conveyors having a controller utilizing a logic scheme to selectively implement a time delay before authorizing transport of an article from an adjacent preceding conveyor to the transit conveyor, thereby maintaining and adjusting the gap between objects conveyed by the system. The invention includes a method of spacing the articles including (1) receiving an input signal with a controller associated with an individual transit conveyor indicating an article ready for transit from the preceding conveyor to the transit conveyor, (2) determining whether an object is present on the transit conveyor (3) generating a time delay when an article is present on the transit conveyor, and (4) transmitting an authorization signal to the preceding conveyor authorizing the transfer of an article from the preceding conveyor to the transit conveyor after the time delay has elapsed.

Description:
RELATED APPLICATION  
       [0001]    This application is a conversion of U.S. Provisional Application Serial No. 60/173,860, filed Dec. 30, 1999, upon which priority for this application is claim and the contents of which are incorporated herein for all purposes. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The invention relates, in general, to a method and apparatus for controlling material handling systems and, in particular, to controlling conveyor systems comprised of individually controllable conveyor segments.  
         BACKGROUND OF THE INVENTION  
         [0003]    Material handling systems in the past have been designed of two basic types. One type is a conveyor transportation system that uses long conveyor lines, comprised typically of belt conveyors, to transport on one conveyance all objects to be carried. Another type of conveyor transportation system uses a network of smaller conveyors, comprised typically of belt or roller conveyors, that are individually controlled to transport on the various conveyors all objects tot be carried. The present invention relates to material handling systems of the second type.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention provides an improved method and apparatus for controlling a series of conveyors. In this system, the conveyor zone controllers will make a decision as to conveyor speed and timing based on an algorithm using the information from one photo eye sensors and inputs from the previous and next conveyor zones.  
           [0005]    The system described herein is typically operated in one of two modes, a signal object or single tray mode when there is a need to have no more than one tray in a conveyor zone. Such applications include scales, scanning stations, and zones in front of or after certain special units. A disadvantage of this mode is that the throughput of a zone in this mode can be less than half that of a conveyor zone operating in the train mode. The second mode of operation is the train mode, typically used for long conveyor lines, which provides high transport speed but has the disadvantage of an increased tendency to create jams for busy conveyor lines having a lot of start and stop signals in a short period of time.  
           [0006]    Depending upon the configuration of the line, units designed according to the present invention can be connected in different ways with or without other special units. Each conveyor in a multiple-conveyor transportation system forms an individually controllable conveyor zone. Each conveyor zone is longer than the object to be carried and typically is used to store and convey a single object along the conveyor network. At least one sensor, typically a photoelectric cell, and control logic are present in each conveyor zone. The control logic may be implemented in the form of programmed instructions present on a memory device in the zone or conveyor controller or may be implemented in a hard wired circuit.  
           [0007]    The status of the sensors from a particular zone and adjacent zones preceding and following the particular zone are used by the controlling logic present in the particular zone to direct the flow of objects through the particular conveyor zone. Each conveyor zone has an electronic module containing circuitry for driving a motor, fixed or programable circuitry for evaluating the status of sensors, and circuitry for communicating with preceding and following zones. Additionally, general control and supervision over the entire conveyor network may be extended by providing circuitry for communication with a conveyor network controller.  
           [0008]    The invention disclosed herein provides a new control algorithm that improves both the single tray mode and train mode, but especially the train mode. The algorithm increases both the speed and reliability of a conveyor line along its entire length. The algorithm incorporates a “gap regeneration” technique. This is done using a time delay for the authorization form one unit to the previous unit and a set/reset procedure for the signal coming from the previous unit.  
           [0009]    The hardware boards and software programs traditionally employed for conveyor control typically incorporate special configuration devices such as dip switches and or software tools to configure a first, last or transit conveyor zone. These selections have traditionally been necessary to provide the proper functionality for a conveyor zone after a special unit (such as the first conveyor zone in the line), between other conveyor units (such as a transit conveyor) or before a special unit (such as the last conveyor zone in a line).  
           [0010]    In units designed according to the present invention, the option to set a zone as a first zone, last zone or transit zone is eliminated by using the module just as a transit zone. The options of the first zone and last zone are implemented in a separate module for hardware or subroutine for software. This structure increases the flexibility and simplifies the manufacturing and maintenance of the units.  
           [0011]    In one embodiment, the conveyor system includes a plurality of conveyors arranged end-to-end for transporting articles along the length thereof, including a plurality of transit conveyors, each disposed between adjacent conveyors. At least some of the transit conveyors include a controller for controlling the operation of the transit conveyor to receive conveyed articles from a preceding conveyor and convey the articles to a succeeding conveyor according to a predetermined logic scheme. Each controller maintains a selected spacing between articles conveyed from the transit conveyor to the succeeding conveyor by delaying transfer of articles to regenerate the spacing between articles which are spaced less than a predetermined distance apart in accordance with the logic scheme. In one embodiment, an adjacent preceding conveyor conveys an article to the transit conveyor only upon receiving an authorization from the transit conveyor controller and the transit conveyor transfers the article to the succeeding conveyor only upon receiving an authorization from the adjacent succeeding conveyor controller. The controller for each such transit conveyor selectively implements a time delay logic scheme to delay authorization for transport of an article from an adjacent preceding conveyor to the transit conveyor, thereby maintaining and adjusting the gap between objects conveyed by the system. Articles present on the conveyors are detected with sensors such as photo electric cells, proximity switches, contact switches, pressure switches or similar devices. In one embodiment, the predetermined logic scheme is embodied in a set of instructions programmed into a memory unit associated with the controller. In an alternate embodiment, the predetermined logic scheme is implemented with a hardwired circuit.  
           [0012]    The invention also provides a method of controlling the spacing of articles conveyed on a conveyor system including a plurality of transit conveyors arranged in an end to end fashion between adjacent preceding and succeeding conveyors. The method includes the steps of (1) receiving an input signal with a transit conveyor controller associated with an individual transit conveyor, the signal indicating the presence of an article ready for transit from the preceding conveyor to the transit conveyor, (2) determining whether an object is present on the transit conveyor (3) generating a time delay when an article is present on the transit conveyor, and (4) transmitting an authorization signal to the preceding conveyor, the signal authorizing the transfer of an article from the preceding conveyor to the transit conveyor after the time delay has elapsed. In one embodiment of the method, each transit conveyor controller receives and transmits authorization signals to and from a preceding transit conveyor and a succeeding transit conveyor. The step of determining whether an article is present on the transit conveyor preferably comprises transmitting a signal from a sensor associated with the transit conveyor to the transit conveyor controller.  
           [0013]    In another aspect the method may include the step of detecting whether a jam has occurred on the transit conveyor. The method may also include the step of detecting whether an article transferred to the transit conveyor has been conveyed across the conveyor in a predetermined period of time and generating an error signal when the object has not been conveyed across the conveyor within the time period. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0014]    Referring now to the drawings wherein like reference numerals refer to the same and similar elements and steps,  
         [0015]    [0015]FIG. 1 is a schematic representation of an authorization signal control system in accordance with one embodiment of the invention;  
         [0016]    [0016]FIG. 2 is a schematic representation of an motor control system in accordance with one aspect of the invention;  
         [0017]    [0017]FIG. 3 is a schematic representation of a jam error check logic control system in accordance with the invention;  
         [0018]    [0018]FIG. 4 is a schematic representation of a lost article error check logic control system in accordance with the invention; and  
         [0019]    [0019]FIG. 5 is a schematic representation of a conveyor system in accordance with the invention. 
     
    
       [0020]    These and other aspects and advantages of the invention will be further described in the following Detailed Description.  
       DETAILED DESCRIPTION  
       [0021]    While the making and using of various embodiments of the invention are discussed in detail below, it should be appreciated that the invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and are not to delimit the scope of the invention as claimed.  
         [0022]    Referring now to FIGS. 1 and 5, there is shown a schematic representation of a conveyor system  8  including a series of conveyors,  10 ,  12 , and  14  for conveying articles  6 . Each of conveyors  10 ,  12  and  14  are equipped with at least one photo electric cell  16 ,  18  and  20  respectively, (FIG. 5) and controllers  22 ,  24  and  26 , each including a logic scheme represented by circuit  100  (FIG. 1) for implementing the basic algorithm and functional aspects of the conveyor zone control of the invention. As will be appreciated, the logic scheme represented by circuit  100  may be embodied as a set of instructions programmed into a memory unit (not shown) in controller  22 . Photo electric cells  16 ,  18  and  20  detect the presence of conveyed articles on conveyors  10 ,  12 , and  14  respectively, and provide inputs for circuit  100  represented in FIG. 1. It will be appreciated that devices other than photo sensors, i.e., pressure sensors, proximity sensors, contact sensors and similar devices for detecting the presence or absence of an article or object may be readily employed in the practice of the invention.  
         [0023]    Turning now to FIG. 1, the circuit  100  presented therein represents control logic embodied in a controller for controlling a single zone conveyor. Circuit  100  is connected to the controls of a preceding unit through input  102  line and output line  104 . Circuit  100  is similarly connected to the succeeding conveyor though input line  108  and output line 106 . If the logic embodied in circuit  100  is present and implemented as software, e.g., a set of programmed instructions on controller  22 , input lines  102  and  108  along with output lines  104  and  106  represent transmission of software signals rather than the physical connections illustrated. In this case, the components illustrated in FIG. 1 represent functions and functionalities that would be embodied in a set of programmed instructions in a software embodiment.  
         [0024]    When an object on the preceding conveyor  10  is ready to be transferred from the preceding conveyor to the intermediate conveyor  12 , as sensed by photocell  16 , the control logic for the preceding conveyor will generate a signal on input line  102  that is carried by line  110  to logic unit  112 . Such a signal could comprise, for example, a rising or falling edge or signal amplitude, depending upon specific embodiment. In the embodiment illustrated in FIGS. 1 and 6, the signal on input line  102  is generated directly by photo electric cell  16 . Logic unit  112 , in response to an appropriate signal on line  102  will generate a pulse on line  114 . Logic unit  112  comprises a negative front detection logic unit that detects a transition from TRUE to FALSE in a signal.  
         [0025]    The output signal on line  114  from logic unit  112  is input to timer off delay unit  116  and to reset set/reset (bistable) logic unit  118 . Timer off delay unit  116  is a timer that delays an “off” transition, i.e., from TRUE to FALSE. Timer off delay unit  116  thus delays setting the signal from logic unit  112  to an off condition. Upon receiving an appropriate input signal from logic unit  112 , timer off delay unit  116  initiates a delay period after which an output TRUE signal is generated and communicated to inverter  122  on line  120 , indicating that the timer has timed out. The FALSE output from inverter  122  is communicated to OR gate  126  over line  124 . The signal from timer off unit is also transmitted to AND gate  212  in motor control circuit  200  (FIG. 2). As used herein the terms “AND gate” and “OR gate” incorporate devices and programmed instructions for implementing “AND” and “OR” boolean logic based upon the indicated inputs to the devices.  
         [0026]    As noted above, conveyor  12  is equipped with a photo electric cell  18  for sensing the presence of a conveyed article on the conveyor. The output signal of photo electric cell  18  reflects the presence or absence of a conveyed article on conveyor  12 . The output signal from photo electric cell  18  is input to inverter  136  over line  137  which, in turn, provides an output signal to the control circuit for conveyor  14  over line  106 . The signal  137  from photo electric cell  18  is also transmitted to logic unit  132  and inverter  140  over line  134 . Logic unit  132  is a positive from detection unit that detects a transition from FALSE to TRUE for an input signal.  
         [0027]    The signal from photo electric cell  18  is TRUE if the photo electric cell is not blocked, i.e., if an article is not present. Thus, the output of OR gate  150  will be TRUE if either (1) an article is not present or (2) a TRUE signal is received from AND gate  146  indicating that an authorization signal is received from succeeding conveyor  14  over line  108  and a TRUE signal is received over line  148  indicating that conveyor  10  is in the train mode.  
         [0028]    The output signal from logic unit  132  is the second signal input to OR gate  126 , along with the inverted output of timer off delay unit  116 . When either of the output signals from logic unit  132  or the output signal from timer off delay unit is TRUE, OR gate  126  transmits a TRUE signal to set set/reset logic unit  118  which in turn, transmits an auxiliary enable signal over line  144 , depending upon the status of the inputs from logic units  112  and  126 , respectively. Thus auxiliary enable signal transmitted over line  144  generated by set/reset logic unit  118  may be set by either a signal from photo electric cell  18  or a signal from the preceding conveyor  10 , transmitted over line  102  and is transmitted to AND gate  156 . Assuming that AND gate  156  is receiving a TRUE signal from inverter  162  over line  160 , indicating no jam as determined by jam detection circuit  300  (FIG. 3), and a TRUE signal from OR gate  150  over line  154 , then AND gate  156  transmits a TRUE signal to time delay unit  170  AND gate  172 . Time delay unit  170  us a timer on delay, it delays the “on” transition, i.e., from FALSE to TRUE. If AND gate  172  is receiving a TRUE signal from inverter  164  over line  160 , indicating that the “Train” mode is off, and a TRUE signal from AND gate  156 , AND  172  gate transmits a TRUE signal to OR gate  178  over line  174 . If OR gate  178  receives either a TRUE signal from AND gate  172  or a TRUE signal from time delay unit  170 , indicating that the timer has timed out, OR gate  178  transmits a TRUE signal over line  104  to control unit  22  of preceding conveyor  10 , indicating that an object may be conveyed to conveyor  12 . The signal from OR gate  178  is also transmitted to AND gate  208  in motor control circuit  200  (FIG. 2), along with the input signal from preceding conveyor  10  over line  102 .  
         [0029]    As previously noted, control circuit  100  also receives an input signal from succeeding conveyor  14  over input line  108 . The signal received over line  108  is input to AND gate  146 , along with the train mode input signal  148 . If both of these signals are true then AND gate  146  outputs a true signal  152  to OR gate  150 , that also receives signal  142  from inverter  140 . If either of these signals are TRUE, then OR gate  150  outputs a TRUE signal to AND gate  156 .  
         [0030]    A TRUE to FALSE (negative front) signal on line  104 , indicating the presence of article on conveyor  10  awaiting transfer to conveyor  12 , will result in a TRUE signal being transmitted from logic unit  112  over line  114  to set/reset logic unit  118 . The signal from logic unit  114  is also transmitted via timer off delay  116 , inverter  122  and OR gate  126  to set logic unit  118  to set back the auxiliary enable signal  144 . The auxiliary enable signal from set/reset logic unit  118  may also be set by the inverted signal from photo electric cell  18  as transmitted through inverter  136 , logic unit  132  (positive front detection) and OR gate  126 . The transmission of auxiliary enable signal is conditioned upon AND gate  156  receiving a TRUE signal from inverter  162  over line  160 , indicating that a jam is not present and receiving a TRUE signal  154  from OR gate  150 .  
         [0031]    The output of AND gate  156  will be TRUE when (1) no tray jam is detected as indicated by the signal received over line  160 , (2) AND gate  156  is receiving a TRUE signal from set/reset logic unit  118  over line  144 , and (3) AND gate  156  is receiving a TRUE signal over line  154  from OR gate  150 .  
         [0032]    The timing of the signal transmitted to preceding conveyor  10  is determined by whether conveyor  12  is set in the train mode. If conveyor  12  is set in the train mode, inverter  164  will communicate a FALSE signal over line  166  to AND gate  172 , preventing a TRUE signal transmitted over line  168  from reaching OR gate  178  in output line  104 . In this case, assuming that there is a TRUE signal on line  168 , the TRUE signal on line  168  will only be transmitted after the time delay on unit  170  times out, outputting a TRUE signal over line  176  to OR gate  178 , which in turn then transmits a TRUE, or authorization signal over output line  104 .  
         [0033]    Alternatively, if conveyor  12  is not set in the train mode, but rather is set in a single tray or single article mode, the output of inverter  164  will be TRUE, resulting in the transmission of a TRUE or authorization signal by OR gate  178  over output line  104 .  
         [0034]    As will be appreciated, an auxiliary enable or authorization signal over line  104  may be generated in two different ways. If conveyor  12  is in the train conveying mode, the combination of (1) a TRUE signal from set/reset unit  118 , (2) a TRUE signal from OR gate  150 , indicating either an authorization signal from conveyor  14  or a TRUE signal from photo electric cell  18  indicating no article present, and, (3) a TRUE signal from inverter  162 , indicating the absence of a jam, will result in a TRUE signal being generated by AND gate  156  and transmitted to timer on delay unit  170 . In this case, AND gate will receive a FALSE signal from inverter  164 , blocking transmission of a signal around timer on delay unit  170  on line  174 . After timer on delay unit  170  has timed out, an enable or authorization signal will be generated and transmitted via line  176  and OR gate  178  over line  104 .  
         [0035]    Alternatively, if conveyor  12  is in the single article conveying mode, a combination of (1) a TRUE signal from set/reset unit  118 , (2) a TRUE signal from OR gate  150 , indicating a TRUE signal from photo electric cell  18  indicating no article present, and, (3) a TRUE signal from inverter  162 , indicating the absence of a jam, will result in a TRUE signal being generated by AND gate  156  and transmitted to AND gate  172 . Since the conveyor is in the single article conveying mode, the inverted signal from inverter  164  will be TRUE, allowing transmission of a TRUE or authorization signal on line  174  through OR gate  178  to preceding conveyor  10  on line  104  without a time delay.  
         [0036]    As will be appreciated, control circuit  100  implements a “gap regeneration” control that maintains the gap between articles conveyed along conveyors  10 ,  12  and  14 .  
         [0037]    The gap regeneration is accomplished applying a set/reset procedure to the signal received from the preceding conveyor in combination with a time delay applied to the authorization signal sent to the preceding conveyor. The actual values of the time delay will, of course, vary with the specific application depending upon the speed at which the conveyors are operated, the desired size of the gap between conveyed articles, the physical dimensions of the conveyed articles and other application specific criteria. Additionally, as illustrated, the conveyor system utilizes belt conveyors, however, it will be appreciated that the inventive concepts described herein are equally applicable to systems employing other types of conveyors including, without limitation, powered roller type conveyors, chain conveyors and segmented tray type conveyors.  
         [0038]    It will also be appreciated that circuit  100  incorporates and illustrates those portions of the system of the invention relating to the interconnections and communications between control units for preceding and succeeding conveyors. In particular, it will be appreciated that the control circuit  100  will not require modification for use on an end conveyor unit, i.e., the first or last conveyor in a series of conveyor units.  
         [0039]    Turning now to FIG. 2 there is illustrated a diagram for the conveyor motor logic in the form of a circuit  200 . The signal present on line  226  is the motor on/off output for the circuit  200 . Circuit  200  receives as inputs the input signal on line  102  from preceding conveyor  10  on line  110  and the output of OR gate  178  though AND gate  208 . The signal from inverter  136  is received on line  134  and input to AND gate  210  along with the output signal  108  from the succeeding conveyor. The signal from timer off delay unit  116  is input to AND gate  212  via line  120 . The signal from set/reset logic device  118  is invert by inverter  202  and input to AND gate  212  via line  206 .  
         [0040]    The inputs from AND gates  208 ,  210  and  212  are input to OR gate  220 . The signal from OR gate  220 , along with an auxiliary status signal on line  204  are input into and gate  224 . The signal on line  204  represents the status of auxiliary conditions, i.e., safety devices, over current protection devices, and similar conditions that must be satisfied prior to setting the motor on/off signal to on. Thus, a “motor on” signal will be transmitted from AND gate  224  on line  226  when the signal on line  204  is TRUE and at least one of the following set of conditions are met: (1) a TRUE signal is received on line  102  from preceding conveyor  10 , and a TRUE signal is transmitted on line  104  from OR gate  178  as described above, i.e., the presence of authorization signals both too and from the preceding conveyor (2) a TRUE signal is transmitted from inverter  136  and a TRUE signal is transmitted on input line  108  from succeeding conveyor  14 , i.e., the presence of authorization signals both to and from the succeeding conveyor  14  and (3) a TRUE signal is received on line  120  from timer off device  116  and a TRUE signal is transmitted on line  144  from set/reset logic device  118 , i.e., when the timer off and a reset condition is not present.  
         [0041]    The control system of the invention also contains provisions for detecting and signaling two error conditions, a jam error and a lost article error. The logic for the jam error is schematically represented circuit  300  of FIG. 3. Circuit  300  receives the motor on signal from AND gate  224  on line  226  which is input to AND gate  302 . Circuit  300  also receives the signal from inverter  136  on line  134 , indicating the presence of an article on conveyor  12 . When both the “motor on” and “article present” signals are TRUE, AND gate  302  will transmit a TRUE signal to timer on delay device  306 , which after will transmit a TRUE output on line  308  after the timer times out. Timer delay device  306  is a timer on delay unit, it delays the “on” transition, e.g., from FALSE to TRUE.  
         [0042]    A change of state of the signal on line  304  from FALSE to TRUE resets timer on delay device  306 , beginning a timed interval. If, at the end of the timed interval, the input signals on lines  226  and  134  remain TRUE, the output of timer on delay device  306  is set to true on line  308 , indicating an error condition. A TRUE output on line  308  reflects the condition where the conveyor motor has been energized for a period equal to the time interval set by timer on delay device  306  while there has been no detectable change in part position, indicating that a jam of some sort has occurred. In the illustrated embodiment, the output of timer on delay device  306  is also input on line  158  of circuit  100 .  
         [0043]    Detection and signaling of the second error condition, a lost article is provided by the logic represented by circuit  400  of FIG. 4. A TRUE output on line  120  from timer off device  116  is input to logic device  402  which generates a pulse output to AND gate  410  over line  404 . Also input to AND gate  410  is the inverted output from logic set/reset unit  118  on line  408  from inverter  406 . The output from AND gate  410  is directed to set/reset logic unit  414  over line  412 . The output from inverter  136  is also input to set/reset logic unit  414 . In operation, the set/reset unit is set with signal from timer off delay unit  116  when set/reset unit  118  is reset and transmitted via AND gate  410 . If set/reset unit  414  is not reset by a signal from photo electric cell  18 , inverted by inverter  136 , before timer off logic unit  116  times out, set/rest unit  414  will generate a TRUE signal, indicating that an article has entered the conveyor zone, i.e., has been transferred onto conveyor  12 , but has failed to reach the photocell within the expected period of time.  
         [0044]    Although certain embodiments of the invention have been described for the purpose of illustration, numerous changes and modifications will become apparent to those skilled in the art without departing from the spirit and scope of the invention. Such changes or modifications are incorporated within the scope of the invention as defined in the appended claims.