Abstract:
A control for stopping the rotation of the output shafts of a plurality of multiplexed motors configured in columns and rows with the first connector of each motor in a given column connected in parallel and with the second connector of each motor of a given row of motors connected in parallel. Each motors includes a switch positioned to be actuated when the output shaft of the motor is in its home orientation. One contact of the switch is connected to a first contact of the motor and therefor receives power when the switch for the column is energized. The second connector of each switch in a given row are connected in parallel to a detector for detecting a change in electric potential. The detector will detect a change in potential when the rotating shaft of an energized motor rotates its output shaft to its home position thereby closing its associated switch.

Description:
The present invention relates to controlling electrically multiplexed gear motors in a vending machine and in particular to an improved method of detecting when the gear motors have returned to their home position. 
   BACKGROUND OF THE INVENTION  
   Vending machines used to dispensed candy and snack products are adapted to offer a very large selection of products from a single machine. Each of the products being offered is dispensed by a single dispensing device including a spiral shaped coil or auger driven by an electrically operated gear motor. The snack products are positioned linearly between the coils of the auger and the gear motor rotates the augur, usually through a single 360 degree rotation, to dispense a single product. The wiring for the gear motors that drive the various augurs are arranged in rows and columns and a controller applies power through a multiplex circuit to drive the motor for dispensing the product that a customer has selected. Once the customer has selected a product, the controller applies power to the appropriate motor by closing switches to the wires for the correct column and row of the motor operating the auger. The gear motor and augur continue to rotate through a cycle (which may be 360 degrees) after which the augur returns to its home position. A cam on the output shaft of the gear motor operates a switch creating an electric signal to the electronic controller after which the controller terminates power to the gear motor causing it to stop in the home position. 
   A vending machine for dispensing snack products and candy may have fifty or more independently operated gear motors for dispensing products. The electronics for the vending machine therefore must include a sensor for sensing when the shafts for each of the fifty or more rotatable shafts has reached its respective home position. Although the metal parts of a vending machine are useable for a ground, existing vending machines employ at least one wire directed to each of the gear motors to provide the needed feedback to the controller for terminating power to the gear motors after they have completed rotation through 360 a cycle. It should be appreciated that most products are dispensed with the gear motor rotating through a 360 degree cycle, but some products may require less than a full rotation and other products may require more than full rotation of the shaft. Where the machine employs a large number of gear motors, the wire harness complexity increases. It would be desirable, therefore, to provide an improved method of controlling the gear motors of a vending machine such that each gear motor of the machine will provide a signal to the controller when the associated rotatable shaft has returned to its home position, without requiring a wire attached to each of the individual motors. 
   SUMMARY OF THE INVENTION  
   Briefly, the present invention is embodied in a control for a vending machine of the type having a plurality of gear motors each of which must rotate an output shaft through 360 degrees to dispense a product. In the preferred embodiment, the vending machine has a plurality of vertically stacked trays, with each of the trays having six to ten gear motors and their associate augurs aligned in side by side fashion. The gear motors of each tray therefore form a row of a multiplexed circuit having columns and rows. Each of the motors has a first and second contact, with the second contact of each of the motors in a tray connected in parallel. The trays are stacked one above another in the machine, and the gear motors of the stacked trays are electronically configured in columns with the first contact of each of the motors of a column also connected in parallel. Electrical power to each of the columns and to each of the rows are independently switched open or closed by the controller, such that a selected motor can be energized by closing the switches for both the column and row of the selected gear motor. Such multiplexing circuits are well known in the art. 
   In accordance with the invention, each of the gear motors has associated therewith an electric switch which is activated by a cam connected to the output shaft of the gear motor such that the switch is activated when the shaft has returned to the home position. The switch for each of the gear motors has a first contact that is electrically connected to the first contact of the associated gear motor. The second contacts for all of the gear motors in a single tray are connected in parallel and are connected to a detector circuit within an electronic controller for detecting a change in the electric potential at the common connection of the second contacts of the row of gear motors. 
   A tray of a vending machine configured in accordance with the present invention has an electrical connector for each of the first contacts of the gear motors and a single connector for the second contacts of the gear motor, since all second contacts are connected in parallel, and a common connector for the second pole of the switches of the gear motors of the tray. 
   In the preferred embodiment, the circuit includes a semi-conductor element, such as a diode, to prevent reverse flow of current through the switch associated with each of the gear motors during the operation of one of the gear motors. The switches are configured to change state when the cam on the output shaft is in the home position. When power is applied to one of the selected gear motors, the energized motor will commence the rotation of the shaft and move the cam away from the switch, changing the state of the switch. Electric current will therefore pass through the line connecting the column of gear motors and will be applied to the coils of the selected motor. Once the motor has rotated the shaft and cam through 360 degrees, the cam will again change the state of the associated switch connecting the first pole of the motor to the detector line and thereby changing the potential between the detector line and ground. The controller that directs power to the gear motor responds to the detection of a change in potential in the detector line and terminates power to the two poles of the gear motor by opening the switch to the appropriate column and row and stopping the gear motor with the cam in its home position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS  
     A better understanding of the invention will be had after a reading of the following detailed description taken in conjunction with the drawings, wherein: 
       FIG. 1  is an isometric view, partially broken away, of a vending machine embodying the invention; 
       FIG. 2  is a front view of the configuration of the trays and dispensing coils of the vending machine shown in  FIG. 1 ; 
       FIG. 3  is a fragmentary, top elevational view of one of the trays shown in  FIG. 2 , consisting of a plurality of parallel oriented gear motors and dispensing coils; 
       FIG. 4  is a rear view of a gear motor showing the associated cam and controlling switch; 
       FIG. 5  is a schematic view of the detecting circuit for six of the gear motors of the vending machine shown in  FIG. 1 ; and, 
       FIG. 6  is a fragmentary enlargement of  FIG. 5  showing a single gear motor. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
   Referring to  FIGS. 1 through 4 , a vending machine  10  includes a selection panel  11 , a money reception  12 , and a dispensing tray  13  for dispensing a product to a customer. The machine  10  also has a plurality of trays  14 ,  15 ,  16 ,  17 ,  18  for dispensing products. Along each of the trays  12 – 18 , of which tray  14 , a fragment of which is depicted in  FIG. 3 . is typical of each, are a plurality of dispensing augurs  20 — 20 . Each of the dispensing augurs  20  includes a spiral coil  22  driven by a gear motor  24  having an output shaft  26 . As best shown in  FIG. 4 , on the rearward end of the output shaft  26  is a cam  28  and adjacent cam  28  is an electric switch  30  having an actuator  32 . As depicted in  FIG. 4 , the switch  30  is actuated when the cam  28  engages the actuator  32 . 
   The motors  24  are electrically operated, and therefore have first and second electrical contacts  34 ,  36  respectively for applying an electric potential across the coils thereof. In  FIG. 5 , the first contacts for the last three motors  24   d ,  24   e , and  24   f  are not marked with the indicia number  34 , but the first contact of these three motors is in the same relative position as those marked  34  in the first motors  24   a ,  24   b , and  24   c  and the last three motors will be described as having first contacts  34  even though these indicia numbers are not marked. Each motor  24  also has first and second contact  38 ,  40  for the associated electric switch  30 . 
   For simplicity,  FIG. 5  depicts a circuit having only six dispensing elements for which there are six gear motors numbered  24   a ,  24   b ,  24   c ,  24   d ,  24   e , and  24   f . Gear motors  24   a ,  24   b , and  24   c  are configured in the first tray  14  and gear motors  24   d ,  24   e , and  24   f  are configured in the second tray  15 . 
   Referring to  FIGS. 1 ,  4 ,  5  and  6 , the second contact  36  of the gear motors  24   a ,  24   b ,  24   c  of tray  14  are connected in parallel by common connecting wire  42  to a switch  44  for connecting and disconnecting the common connector and the second contacts  36  to a first pole  43  of an electric power source  45 . In similar fashion, the second contacts  36  of the gear motors  24   d ,  24   e , and  24   f  of tray  15  are connected in parallel by common connector line  46  to a switch  48  for connecting and disconnecting power to the first pole  43  of the source  45  of electric power. 
   The first contact  34  of the various electric motors  24  are also connected in columns. Specifically, the first contacts  34  of gear motors  24   a  and  24   d  are connected in parallel by a common connector line  54 , the first contacts  34  of gear motors  24   b  and  24   e  are connected in parallel by common connector line  56 , and the first contacts  34  of gear motors  24   c  and  24   f  are connected in parallel by common connector line  58 . 
   In accordance with current technology the gear motors  24   a – 24   f  are powered by an electronic controller  66  having internally all functions needed to operate the motors. Accordingly, common connector line  54  is connected through a switch  60  provided within the controller  66  for connecting and disconnecting the contacts  34  of gear motors  24   a  and  24   d  to the second pole  47  (in this case the high side) of the source  45  of electric power. In similar fashion, common connector line  56  is connected through a second switch  62  within controller  66  for connecting and disconnecting the first contacts  34  of gear motors  24   b  and  24   e  to the second pole  47  (the high side) of a source of electric power  45 , and common connector line  58  is connected through a third switch  64  for connecting and disconnecting contacts  34  of gear motors  24   c  and  24   f  to the second pole (high side) of the source of electric power  45 . In the preferred embodiment the switches  44 ,  48 ,  60 ,  62 ,  64  are actuated within the controller  66  and the power supply  45  is built into the controller  66  although it should be appreciated that all the switches  44 ,  48 ,  60 ,  62 ,  64  could be operated from outside the controller  66  and the power supply  45  could also be external of the controller  66 . 
   The circuit consisting of the connecting lines  42 ,  46 ,  54 ,  56 , and  58  and the various switches  44 ,  48 ,  60 ,  62 , and  64  provide for the multiplexing of the motors  24   a – 24   f . The controller  66  will close the switch  44 ,  48  for the appropriate tray or row  14 ,  15  and the switch  60 ,  62 ,  64  for the appropriate column, and power  45  will be applied to the one gear motor  24  associated with the product selected by a customer for dispensing. Once the controller  66  has directed power through the appropriate switches to the selected gear motor  24 , the gear motor  24  will commence rotating its associated output shaft  26  and will continue rotating the shaft  26  until a signal is received indicating that the rotating output shaft  26  has returned to its home position, after which the controller  66  will open the associated switches  44 ,  48 ,  60 ,  62 ,  64  and terminate power to the operating gear motor  24  as is further described below. 
   Referring to  FIGS. 4 ,  5  and  6 , in accordance with the invention the first contact  38  of the switch  30  associated with each gear motor  24  is electrically connected by connector  68  to the first contact  34  of the associated gear motor  24 . Also, the second contacts  40  of the switches  30  of all the gear motors  24   a ,  24   b ,  24   c  of the first row identified as tray  14  are connected in parallel by a common connector line  70  to a detector  71 , which is built into the controller  66 , for detecting a change in the electric potential in line  70 . The controller  66  will terminate power to the energized motor  24  in row  14  when a change in electric potential is detected by the detector  71  as is further described below. In similar fashion, the second contacts  40  of the switches  30  of gear motors  24   d ,  24   e ,  24   f  of the second row, identified as tray  15 , are connected in parallel through common connector line  72  to a second detector  73  in controller  66  for detecting a change in the electric potential in line  72 . The controller  66  will terminate power to an energized motor in row  15  when a change in the electric potential in line  72  is detected as is further described below. 
   A semi-conductor  74 , such as a diode, in the circuit of the switch  30  prevents the leakage of electric power from an energized gear motor to other gear motors mounted on the same tray as the gear motor being energized. It should be appreciated that the polarity of the semi-conductor  74  must be reversed if the polarity of the power source  45  is reversed. 
   When power is applied to one of the gear motors, for example gear motor  24   a , by opening switches  44  and  60  electrical power from source  45  is applied across the contacts  34  and  36  of gear motor  24   a  energizing the gear motor  24   a . Rotation of the gear motor  24   a  causes the output shaft  26  to move the flat of the cam  28  off actuator  32  thereby opening the associated switch  30 . With the switch  30  open, there is no electrical connection between pole  47  of the electrical power source  45  and line  70 . The switch  30  remains open until the gear motor  24   a  has completed a cycle (which typically is 360 degrees but may be greater or less than 360 degrees) and the cam  28  again engages the actuator  32  and closes the switch  30 . When the switch  30  is again closed, contact pole  47  of the source of electrical power  45  is connected to detector line  70  changing the electric potential in line  70 . When the controller  66  detects a change in the potential of line  70  it will open the switch  44  to the tray  14  and switch  60  the first column thereby terminating power to the gear motor  24   a.    
   As can be seen, the controller of the present invention does not require a separate connector wire to each of the six motors depicted in order to detect that the operating gear motor has completed a 360 degree cycle. In the depicted embodiment, with two trays of three gear motors each, only two detector wires,  70 ,  72  are needed to monitor all six of the gear motors  24   a – 24   f . Accordingly, fewer wires are needed to monitor the operation of the various gear motors of a vending machine  10 , thereby simplifying the manufacture of the machine and reducing the amount of time required to install the electrical connections. 
   It should also be appreciated that while the second contacts  40  of the switches  30  have been described as being connected in parallel to detectors  71 ,  73  for the respective rows  14 ,  15  and the first connectors of the switches  30  have been described as being connected to pole  47  of the source  45  of electric power the structure could be reversed. In that case the second contacts  40  of switches  30  would be connected in parallel and to a detector for detecting a change in potential and the first contacts  38  of the switches  30  would be connected to pole  43  of the source  45  of electric power. The use of the terms “column” and “row” are interchangeable because the circuit is not dependent upon vertical and horizontal orientations but upon the existence of a grid of multiplex of motors. 
   While the present invention has been depicted with respect to a single embodiment, it will be appreciated that many modifications and variations may be made without departing from the true spirit and scope of the invention. It is therefore the intent of the appendant claims to cover all such variations and modifications which fall within the true spirit and scope of the invention.