Abstract:
A drive roller has a brushless D.C. motor with a stator or armature mounted on a fixed shaft and directly driving a 16 pole permanent magnet rotor mounted inside a roller tube. A motor controller drive supplies three-phase power to a Y-connected three phase winding having three groups of two coils, forming twelve electromagnets which drive the rotor. The modular motor is readily built in one inch increments to supply one lb-in of torque for each increment. The controller operates at a relatively low frequency of 15-75 Hz. Hall effect sensors provide feedback on motor speed and position. The armature laminations are relatively thick because of the relatively low power necessary to drive the motor and the resultant relatively low eddy currents present in the motor core. A 4.0 lb-in torque motor with a rotor and stator length of four inches will draw approximately 0.8 amps consuming about 15 Watts.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 09/294232 filed Apr. 19, 1999, which is a continuation-in-part of application Ser. No. 08/931593 filed Sep. 16, 1997, now U.S. Pat. No. 5,918,728 both of which are incorporated by reference herein. 
    
    
     STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     BACKGROUND OF THE INVENTION 
     The present invention relates to roller conveyors and motorized rollers used to move packages along roller conveyors. 
     Roller conveyors are used to move packages, trays, or containers where accumulation of individual containers is required. Roller conveyors may be advantageously used when items are accumulated from a number of locations and dispatched to multiple destinations, for example in moving sorted mail contained in trays from sorting locations to a loading dock where mail destined for a particular vehicle or container is accumulated. Roller conveyors consist of a roller tube which is mounted for rotation about the cylindrical axis of the roller. The rollers are spaced on the conveyors so that the minimum sized package is supported by at least three rollers at all times. Drive rollers are positioned between idler rollers and used to move and stop packages on the conveyor. The spacing and number of drive rollers relative to idler rollers depends on the size of the packages anticipated and the torque or drive force which is required. Groups of drive rollers may be used if greater drive force is required. 
     Although drive rollers may be driven by belts from external motors, the typical modern approach is to use rollers with internal electric motors which are mounted to a fixed shaft and drive the roller through a gear system. The use of internal-motor-driven rolls simplifies the assembly of the roll conveyor and eliminates a large number of pulleys and external motors which occupy space and require guards to protect workers. 
     Roller conveyors can be used to precisely control the motion of many packages with each motor under the control of a central computer or programmable controller. By controlling the individual drive motors, a package can be moved forward or can be brought to a stop by using the drive rollers as a brake. The rollers can operate individually or as an integrated system to accumulate packages with zero pressure, and release packages in a slug release or singulation mode. A roller conveyor can be used to combine streams of packages onto a single conveyor going to a single or multiple destinations. Packages on a first conveyor line which intersects a second conveyor line can be held and injected one by one as space becomes available on the second conveyor. Thus the conveyors will typically be used with multiple sensors which sense the passage of discrete packages, and a controller which is designed and programmed for a particular application. 
     Standard rollers of both the drive and idler types are 1.9 inches in diameter. The drive rollers are typically supplied as a sealed unit and utilize small high speed brush motors. The roller sealed units are typically disposed of when the brushes wear out. The typical life of a drive roller and motor unit is less than 2,000 hours. A typical drive roller costs $90.00 and has a service life of less than one year. Although units using brushless D.C. motors are known, the life of the units is still limited by the life of the gears which drive the roller tube. 
     Cost is a very important consideration in the design of drive rollers for roller conveyors. A typical installation may contain hundreds to thousands of feet of conveyor and, with one drive roller spaced every two to three feet, the number of drive rollers which must be purchased yearly to maintain such a system can be a considerable expense. 
     Although most roller conveyors use rollers having a diameter of 1.9 inches, the length of the rollers varies, and drive rollers are provided in a number of standard lengths. 
     What is needed is a drive roller with a longer life and a lower cost. 
     SUMMARY OF THE INVENTION 
     The drive roller of this invention utilizes a brushless D.C. motor which has a stator or armature mounted on a fixed shaft which directly drives a permanent magnet rotor mounted inside a roller tube. A motor controller drive supplies three-phase 24-volt power to a Y-connected three phase winding which is composed of three groups of four coils. Thus twelve electromagnets are formed. The electromagnets are used to drive the permanent magnet rotor which has sixteen poles. The brushless D.C. motor is of a modular design and can be easily built in two inch length increments to supply 2 lb-in of torque for each two-inch increment. The motor controller operates at a relatively low variable frequency of 15-75 Hz. Because of the low drive frequency, hysteresis losses in the armature laminations are extremely low and ordinary mild steel can be used to form them. The armature laminations making up the brushless D.C. motor core are also relatively thick because of the relatively low frequency power necessary to drive the motor and the resultant relatively low eddy currents present in the motor core. For a motor with a 4.0 lb-in design torque and a rotor and stator length of four inches, the current draw will be approximately 1.5 amps at rated torque consuming about 35 watts of power. The motor will drive the roller at approximately 265 rpm which corresponds to a conveyor speed of approximately two feet per second or 120 feet per minute. 
     Because the only moving parts of the drive roller are the bearings, which have a life of approximately 100,000 hours, the overall life of the drive unit is expected to be considerably more then ten times that of conventional units. In addition, the cost of the units is expected to be less than existing units because of the elimination of gears and brushes. The motor itself utilizes low-cost ferrite magnets in the rotor and low-cost armature cores utilizing mild steel and relatively few laminations. Further, the construction of the motor is simplified because the windings are inserted into the core from the outside of the core and thus are cost-effectively manufactured. 
     It is an object of the present invention to provide a drive roller for a roller conveyor which has a longer operational life. 
     It is a further object of the present invention to provide a drive roller for a roller conveyor which is designed for cost-effective production. 
     It is another object of the present invention to provide a drive roller in which the drive speed can be precisely controlled. 
     It is also an object of the present invention to provide a drive roller for a roller conveyor which can be used to position articles on a roller conveyor. 
     Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a drive roller of this invention, partially broken away in section, and shown in relation to a conveyor with a schematic illustration of the control system therefor. 
     FIG. 2 is a cross-sectional view of an alternative embodiment of the drive roller of FIG.  1 . 
     FIG. 3 is an exploded isometric view of the drive roller of FIG.  2 . 
     FIG. 4 is a cross-sectional view of the drive roller of FIG. 2 being inserted into a conveyor frame, with the spring loaded hexagonal roller mount shown depressed. 
     FIG. 5 is a cross-sectional view of the drive roller of FIG. 4, with the spring loaded hexagonal motor mount shown extended into the conveyor frame. 
     FIG. 6 is an end view of the stator of the motor of FIG. 2 showing six coil windings. 
     FIG. 7 is a schematic of the Y-connected coils of FIG.  6 . 
     FIG. 8 is a cross-sectional view of another embodiment of the drive roll of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring more particularly to FIGS. 1-8, wherein like numbers refer to similar parts, as shown in FIG. 1, a number of drive rollers  20  are mounted in a frame  34  along with idler rollers  66  to form a roller conveyor  21 . Each drive roller  20  has a stator  40  with Y-connected windings which is fixed to an axially extending shaft  28  which supports a roller tube  22  and permanent magnet rotor  62  on bearings  30 ,  32 . Each roller tube  22  is sealed with a first end cap  24  and second end cap  26 . The roller tube  22  is mounted for rotation on the shaft  28  by first bearings  30  and second bearings  32  which are mounted in the first end cap  24 , and the second end cap  26  respectively. The drive roller shaft  28  extends through and beyond the end caps  24 ,  26  on both ends of the tube  22  and extends into holes  36  in the frame  34 . The ends of the shaft  28  are preferably nonround to engage fixedly within the frame holes  36  to prevent rotation of the shaft. 
     A brushless D.C. motor  38  is contained within the roller tube  22 . The motor has a stator  40  mounted to the shaft  28 . The stator  40  consists of forty laminations  42  which form a core  44  on which coils  52  are wound. The laminations  42  are approximately {fraction (1/10)}th of an inch thick and are constructed of mild steel to minimize cost. The core  44  constructed from the laminations  42  has twelve slots  48  separated by T-shaped core posts  50 . Three groups of four coils  52  are wound on the core  44 . Each coil consists of 65 turns of No. 26 copper wire. The four coils  52  of each group are positioned sequentially with coils of the other two groups so that no two coils from the same group are adjacent, but alternate in regular order as is conventional for the windings of an electric motor. Each group of four coils is wound from a single wire  53  which has two ends  54 . The three wires are connected together at a first end  54  of the single wires  53  to form a Y-connected winding, and the other ends  54  of the wires  53  are the leads through which one of three phases of electric power is supplied. 
     The construction of the stator  40  facilitates low-cost fabrication by allowing the wires  53  forming the winding  52  to be inserted through slots  46  between the T-shaped core posts  50 . Because the slots are on an outwardly facing portion of the stator  40 , they are easily accessed for automatic winding of the wires  53  within the slots  46 . This allows the use of lower cost machinery which can operate at higher speeds. 
     The ends  54  of the wires  53  are led through a hole  56  in the side of the shaft  28 . The hole  36  leads to an axial bore  58  which allows the wires to pass through the center of the shaft  28  and through the bearing supporting the shaft. The ends  54  of the wires  53  are connected to a motor controller  60 . The motor controller  60  supplies three phase twenty-four volt current to the windings on the core  44  of the motor  38 . 
     A permanent ferrite magnetic shell  64  serves as the rotor  62  of the drive roller motor  38 . The shell  64  has sixteen poles: eight north N, and eight south S. The 3/4 ratio between stator electromagnetic poles and the rotor permanent magnetic poles helps to minimize losses in the motor. 
     The roller tube  22  will typically have a diameter of 1.9 inches, which is the industry standard for roller conveyors, and typically will have a length of at least ten inches. The ferrite magnetic shell  64  is bonded to the interior of the roller tube  22  by an adhesive, for example adhesive 2214 available from the 3M Corporation. 
     Current is supplied to the windings as is conventionally done in electric motors so that the induced electromagnets formed by the windings on the core react against the magnetic field of the permanent magnets of the shell  64  causing the magnetic shell and the affixed roller tube  22  and end caps  24 ,  26  to rotate about the shaft  28  on the bearings  30 ,  32 . The design of the motor will produce approximately four inch-pounds of torque. The motor is designed for a velocity of approximately 265 rpm at full speed. This corresponds to roller surface speed of about 2.2 ft/s or about 1.5 miles per hour. The velocity of the rollers can be controlled or decreased by varying the frequency of the drive current between fifteen and seventy-five Hertz, more typically between thirty and fifty Hertz. 
     Drive rollers  20  are interspersed on the frame  34  intermediate between one or more like diameter idler rollers  66 . The idler rollers  66  are similar in overall construction to the drive rollers  20 , except that they do not contain a motor and are not driven. Roller conveyors  21  are designed so that the particular packages, boxes or trays  67  which are moved along the conveyor surface  68  are supported at all times by at least three rollers—either drive rollers  20  or idler rollers  66 . The spacing of the drive rollers  20  is typically such that only one is engaged with a tray  67  at a time. For example, if the trays  67  are about thirty inches long, the drive rollers  20  could be spaced about three feet apart so that only one drive roller  20  is engaged with a tray  67  at one time. 
     The design of the conveyor system  70  allows the position of individual trays  67  to be controlled. The presence and placement of a tray  67  can be detected with conventional sensors (not shown). A programmable controller  74  utilizing information from conventional sensors causes a particular package to be accelerated and moved or stopped at a particular location by using the controlled drive rollers  20  to drive and brake individual trays  67 . If a tray  67  is by chance not positioned directly over a drive roller  20  an adjacent tray can be used to push it. 
     Roller conveyors are particularly useful when it is desirable to queue up packages and then introduce individual packages from one conveyor  21  onto another conveyor  76  as space becomes available on the target conveyor. 
     Roller conveyor systems can be extremely large and complicated, as, for example, are those systems used by the United States Postal Service at major sorting hubs. At these postal hubs mail is sorted by destination and loaded onto trays. A roller conveyor system will utilize a programmable controller to move sorted mail to distant points where mail going to a common destination can be loaded on a single truck or into a single container for transport to that destination. 
     The construction of the drive roller  20  of the present invention discussed above may be varied to obtain drive rollers of varying torque. By fabricating the permanent magnet shell in two inch lengths, the motor&#39;s drive power can be increased or decreased by using one, two, or three magnetic shell sections. If a design having a torque of two inch-pounds is desired, thirty-three core laminations are used and 130 turns of No. 29 copper wire are used in each coil. If on the other hand, a torque of six inch-pounds is desired, three magnetic shell sections are aligned axially along the shaft and the core of the stator is formed with ninety-nine laminations and the coils are wound with 42 turns of No. 24 copper wire. 
     An alternative drive roller  78  is shown in FIGS. 2-7. The alternative drive roller  78  differs from the drive rollers  20  principally in providing a mechanism for collapsing one side on the shaft supporting the drive roller, having six motor windings instead of twelve, employing a Hall effect sensor, and having a modular rotor magnet fabricated out of flexible bonded NdFeB. 
     The drive roller  78  has a roller tube  80  which is rotatably mounted about a shaft  82 . The tube  80  has a nominal diameter of 1.875 inches which conforms to the industry standard of about 1.9 inches for most roller conveyor rollers. The tube  80  is mounted to the shaft by a first end cap  84  which supports a first bearing  86 . The first bearing engages a bearing insert  88  fabricated of injection molded plastic such as Delrin. The bearing insert  88  in turn slips over a hexagonal shaft extension  90  which mounts on the shaft  82 . The shaft extension  90  is constructed from noncorrosive metal powder and has a first end  92  which forms a tapered hexagon for mating with a hexagonal hole  94  in a conveyor frame  96  as shown in FIG.  3 . 
     A second end cap  98  mounts the opposite end of the roller tube  80  by way of a second bearing  100  to a bearing insert  102  which mounts over a shaft extension  104  having a tapered hexagonal end  106 . The shaft extension  104  is slidingly mounted to the shaft  82 . The shaft extension  104  has a flange  108  which engages a spring  110  which biases the shaft extension  104  outwardly of the shaft  82 . As shown in FIG. 4, the shaft extension  104  can be moved against the spring  110  bringing the hexagonal end  106  flush with the outwardly facing surface of the second end cap  98 . The roller  78  can thus be positioned between parallel portions of the conveyor frame  96  as shown in FIG.  3 . When the tapered hexagonal end  106  is aligned with a hexagonal hole  94 , the spring  110  extends the shaft extension  104 , locking the roller  78  to the conveyor frame  96  as shown in FIG.  5 . The shaft extensions  90 ,  104  have hexagonal tapered surfaces  112  of about one degree. The taper assures a snug engagement with the conveyor frame  96  despite slight variations in tolerances in the holes  94  due to wear or manufacturing tolerances. 
     A permanent magnetic shell  114  is bonded within the rotor tube  80  to form the rotor  129  of the motor  132 . The magnetic shell is constructed as an extruded or injection molded part of flexible bonded NdFeB Grade: FXND-5 available from Kane Magnetics at http://www.kanemagnetics.com/ This type of magnet combines superior magnetic properties with flexibility and reasonable cost. The magnetic shell  114  has sixteen magnetic poles similar to the magnetic shell  64  shown in FIG.  1 . The magnetic shell  114  has a radial thickness of approximately {fraction (1/10)}th inch and is fabricated in cylindrical sections  116  approximately one inch long. The cylindrical sections  116  are positioned in angular relationship to one another by alignment tabs  118  and alignment notches  120  which cause the magnetic poles to be aligned. The number of cylindrical sections  116  may be between one and six and produce one to six lb-in nominal torque. 
     The stator  122 , shown in FIG.  2  and FIG. 6, is composed of laminations  124  having twelve slots  126  similar to the laminations  48  shown in FIG.  1 . Between each slot are T-shaped core posts  128 . The laminations have a thickness of about 0.062 inches and are constructed of steel from Tempel Steel Co. of 1008 to 1018 C. R. S. The laminations  124  should be precisely aligned and may be held together and insulated by using 3M Scotchcast. To simplify winding, six coils  130  of one-hundred turns of twenty-five gauge magnetic wire are wrapped within the twelve slots as shown in FIG.  6 . The coils are Y-connected electrically, as shown in FIG. 7, with three phase current from a motor controller  60  connected with the A B C phases. The end wires  131 ,  133 ,  135  are led through a central hole  137  in the shaft  82 . The six coils  130  produce twelve poles and thus the 3/4 ratio between stator and rotor  129  is maintained. A gap of about twenty thousandths is maintained between the stator laminations and the magnetic shell  114 . 
     To allow closed loop control of the motor  132  formed by the magnetic shell  114  and the stator  122 , a plurality of Hall effect sensors are mounted on a mounting assembly  134  formed of grade LE Ryertex plastic. The mounting assembly  134  positions three Hall effect sensors  136  spaced 37.5 degrees apart. The spacing of the Hall effect sensors  136  allows all three phases to be monitored so that the Hall effect sensors can be used to switch power to the winding sequentially to drive the motor  132 . The sensors  136  extend from the mounting assembly  134  to overlie the laminations  124  beneath the magnetic shell  114  of the rotor  129 . In this way no additional magnet is required to drive the Hall effect sensors  136 . Five leads  138  from the Hall effect sensors  136  are also routed through the hole  137  in the shaft  82  and connected to circuitry (not shown) which forms part of the controller  60  shown in FIG.  1 . 
     The motors  38 ,  78  are preferably controlled by motor controllers  60  which communicate with a programmable controller  74 . The programmable controller may be an industrial PC which communicates with controllers  60  connected to individual motors  38 ,  78  over a RS232 bus to set speed, set current limit, set hold mode, and/or current limit. The motor controllers can be three phase twenty-eight volt three amp supply, which utilizes the output from the Hall effect sensors for commutation and speed control. The design of the controllers  60  may utilize a MC33035 Brushless DC Motor Controller chip available from Motorola see http://mot2.mot-sps.com/books/dl128/pdf/mc33035rev3.pdf. 
     Individual eight bit words can be sent over the RS232 bus so that current limit and roller speed limit may be set on a scale of 0 to 255. Individual bus commands can be used to read roller speed and roller current. Control to effect breaking and holding of packages is also possible. 
     The construction of the motor  38  is designed to minimize cost and maximize reliability. Reliability is enhanced by the reduction in the number of wearing moving parts. The only parts subject to wear are the bearings, which rotate with respect to the rigid shaft. There is no wear between the rotor and the stator, because the magnetic shell is supported in closely spaced relation to the stator. Bearings typically have a wear life in the range of one-hundred thousand hours, which is much longer than the wear life of conventional gears and brushes. The design of the motor  38  allows for the use of low-cost components. 
     The stator design allows the armature to be wound on the outside of the stator which minimizes fabrication costs. The conveyor motors, particularly motor  132 , produces a relatively high torque per amp per linear inch of motor, making it feasible to produce the gearless motorized roller with resulting high reliability, low noise and long life. Efficiency is normally not a large concern in the design of roller conveyors from a cost standpoint because of the relatively small amount of power consumed. 
     Efficiency is important, however, in maintaining the rolls at a low temperature. It is generally desirable to keep the surface of the roller tube  22  below about 110 degrees Fahrenheit to prevent material used in packaging from melting and adhering to the drive rollers. 
     Another embodiment drive roll  139  is shown in FIG.  8 . Drive rolls  20 ,  78 ,  139  are made in a number of lengths from approximately ten inches to as much as sixty inches long depending on the conveyor application. Some lengths are more widely used than others for example ten, twenty-four and thirty-two inches. Not infrequently, rolls of a particular length will be built for a single customer or large installation. This requires stocking, or manufacturing to order, a large number of different roller tube  80  sizes and shafts  82 . The drive roll  139  allows a basic unit  140  including the drive motor  132  to be customized as to length by the addition of a roller tube extension  142 , and using a length specific shaft  144 . 
     This modularity is accomplished by forming the rotor tube  146  with a closed end  148  which accommodates a plastic spacer  150  and a third intermediate bearing  152 . The closed end  148  has an opening through which the shaft  144  extends. A portion  154  of the roller tube  146  adjacent the closed end  148  has a slightly reduced diameter which forms an interference fit with the inside  156  of a portion of the roller tube extension  142 . The overlap between the tube extension  142  and the roller tube  146  may be glued, welded, or brazed or a simple interference fit may be sufficient. 
     It should be understood that in addition to increasing the power of the motor in a single drive roller it is also possible to group rollers together to increase the amount of driving force available. 
     It should also be understood that the motor  38 ,  78  can be constructed to operate on power having two or more phases of drive current. In addition, the number of coils, number of wires, and number of turns per coil, together with wire gauge, are design variables, which will vary with the number of drive current phases, and the voltage of the drive current, used with the motor, and the amount of torque for which the motor is designed. 
     It should be understood that various types of sensors other then Hall effect can be used to determine the rotation rate and angular position of the rotor. Examples include Giant Magnetoresistive (GMR) type sensors available from Nonvolatile Electronics, Inc., Eden Prairie, Minn., http://www.nve.com, flux gate sensors, optical and magnetic shaft encoders and similar devices. 
     It should be understood that the frequency of the drive current is varied and so the drive could be described as a variable frequency drive and was so described in my earlier U.S. Pat. No. 5,918,728. However that term is normally used to ascribe an AC motor drive and the more proper term is a commutated brushless DC motor controller, or just DC motor controller, as has been used herein for greater clarity. 
     It should be understood that the design described in FIG. 1 shows an open loop motor controller which varies the current frequency to control motor speed. The embodiments of FIGS. 2-8 show the utilization of feedback to provide drive current at a frequency and waveform which is optimized to accelerate/decelerate or maintain at speed the motor. 
     It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces such modified forms thereof as come within the scope of the following claims.