Abstract:
An electromagnetic propulsion system for electrically conductive articles, such as aluminum beverage cans. Currents in coils disposed along a passageway induce currents in aluminum cans in the passageway. The electromagnetic fields produced by the coil currents and the eddy currents in the cans interact to produce forces that propel the cans along the passageway. A coil drive supplies the coils with a low-frequency current to propel the cans and a high-frequency current to heat the cans. The coils are arranged as solenoids encircling the passageway or as planar arrays bracketing the passageway. Besides being used to propel aluminum cans, the coils can be used to spin cans. The electromagnetic propulsion systems are shown in can washers and dryers.

Description:
BACKGROUND 
       [0001]    The invention relates generally to power-driven conveyors and more particularly to electromagnetic conveyors. 
         [0002]    Transporting aluminum beverage cans on conveyor belts through the can-manufacturing process without tipping or damaging the fragile, lightweight cans is difficult. Coated or decorated cans are cured and wet cans are dried in bulk in large ovens. But large ovens are not energy efficient. Solenoidal induction heaters are used to heat cans, but the heaters use a conveyor chain or a pin conveyor to transport the cans. Cans are washed and rinsed in bulk in large washers that are not energy efficient. The washers consume large amounts of water and cleaning solution. The large conveyor belts conveying the cans in bulk through the washers must be able to withstand the cleaning chemicals and the dryer heat. And, because the lidless cans are cleaned upside down to drain, they must be inverted right-side up after cleaning to be transported reliably to downstream processing. 
       SUMMARY 
       [0003]    A propulsion system for electrically conductive articles comprises a passageway that extends in length from an entrance at a first end to an exit at an opposite second end. Electrically conductive articles are admitted into the passageway through the entrance and leave the passageway through the exit. Primary coils are positioned adjacent to the passageway along its length. A coil drive provides currents in the primary coils that produce a primary electromagnetic field that induces currents in the electrically conductive articles in the passageway. The induced currents create secondary electromagnetic fields in the electrically conductive articles that interact with the primary electromagnetic field to produce a drive force directed against the electrically conductive articles to propel them from the entrance and through the exit of the passageway. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a part-isometric-part-schematic of a portion of one version of a solenoidal can-propulsion system embodying features of the invention; 
           [0005]      FIG. 2  is an isometric view of a portion of another version of a solenoidal can-propulsion system as in  FIG. 1 , but with a rectangular cross section; 
           [0006]      FIG. 3  is an isometric view of a portion of another version of a solenoidal can-propulsion system as in  FIG. 2  for conveying two cans side by side; 
           [0007]      FIG. 4  is an isometric view of a portion of another version of a can-propulsion system embodying features of the invention with drive coils in side walls; 
           [0008]      FIG. 5  is a part-isometric-part-schematic of a portion of one of the side walls of the can-propulsion system of  FIG. 4  including can heating; 
           [0009]      FIG. 6  is an isometric view of a portion of another version of a can-propulsion system with drive coils in the floor; 
           [0010]      FIG. 7  is an isometric view of a can washer-dryer using a can-propulsion system as in  FIG. 1 ; 
           [0011]      FIG. 8  is an isometric view of washing and drying portions of the can washer-dryer of  FIG. 7 ; 
           [0012]      FIG. 9  is an isometric view of the can-righting solenoidal portion of the can washer-dryer of  FIG. 7 ; 
           [0013]      FIG. 10  is an isometric view of a can washer using a can-propulsion system as in  FIG. 4 ; 
           [0014]      FIG. 11  is an isometric view of a portion of one side wall of the can washer of  FIG. 10  with a scrubber; 
           [0015]      FIG. 12  is an isometric view of a hinged version of the can-propulsion system of  FIG. 4 ; 
           [0016]      FIG. 13  is an isometric view of one side wall of a can-propulsion system as in  FIG. 4  with an array of permanent magnets in the side wall; 
           [0017]      FIG. 14  is an isometric view of the can washer of  FIG. 10  with a can inverter at the output; and 
           [0018]      FIG. 15  is an isometric view of a can-propulsion system as in  FIG. 4  with a 180° twist to invert a can. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    One version of a can-propulsion system is shown in  FIG. 1 . The propulsion system includes three sets of primary coils  20 A-C wound around a coil form  22  along its length to form a solenoid  23 . The coils are energized by a coil drive, such as a three-phase current amplifier  24  providing currents to the three sets of coils. The energized coils produce an electromagnetic flux wave that travels along the length of the coil form  22  in a direction of propagation  26 . The coil form  22  of the solenoid is elongated in the direction of propagation and made of a non-metallic material with a low-friction interior wall  28 . The interior wall  28  bounds an enclosed passageway  30  that extends the length of the solenoid  23  from an entrance  32  to an exit  33 . An electrically conductive article, such as an aluminum can C, inserted into the entrance  32  is propelled through the solenoid  23 . The traveling electromagnetic flux wave induces currents in the aluminum can C that produce secondary, reaction electromagnetic fields that oppose the primary field of the solenoid. The interaction of the fields produces a net force F pushing the can C in the direction of propagation  26  through the passageway  30  and out the exit  33 . The cross section of the solenoid&#39;s coil form  22  is circular to admit cans into the passageway top or bottom first. The inside diameter of the coil form is slightly greater than the outside diameter of the can C. That slight difference in diameters is enough to propel the can through the passageway  30  with minimal contact with the interior wall  28 . The close tolerance also allows the coils  20  to be close to the can C to couple more electromagnetic flux into the can. The coil form  22  can include fluid drainage holes. 
         [0020]    Besides propelling cans C, the solenoid  23  can also heat cans. The current amplifier produces currents with two components: a low-frequency component  34  used primarily to create the can-propelling force F, and a higher-frequency component  35  used primarily to inductively heat the cans. The higher-frequency current component induces high-frequency eddy currents in the cans C as they traverse the passageway  30 . The high-frequency eddy currents heat the cans. 
         [0021]      FIG. 2  shows a solenoidal can heater and propulsion system with a passageway  36  having a rectangular cross section. The coils  38 A-C are wound around a rectangular coil form  40  and energized by a current amplifier as in  FIG. 1 . The rectangular passageway  36  accommodates cans C upright or upside down. The solenoid  42  in  FIG. 3  also has a rectangular cross section, but has a wider passageway  43  to accommodate a pair of cans C, side by side. The solenoid  42  is shown surrounded by a backing  44  made of a magnetically permeable material, such as a ferrite, that reduces flux leakage and increases the flux density in the passageway  43 . Such a ferrite backing could be used with the other can-propulsion systems described in this description. Both the coil form  40  and the backing  44  can include drainage holes. 
         [0022]    Instead of a solenoid, the electromagnetic propulsion system of  FIG. 4  has first and second coil sets  46 ,  47  supported by a pair of side walls  48 ,  49  flanking and defining a central passageway  50 . The passageway has a rectangular cross section to admit cans C side first, upright or upside down. The passageway  50  is substantially enclosed, except for entrances and exits and upper and lower slots  52 ,  53  between the side walls  48 ,  49 . The slots  52 ,  53  are too narrow for the cans C to pass through. The only path for the cans is through the entrance and the exit. As shown in  FIG. 5 , the coils  46  in the side wall  48  are driven by a coil drive  54  like that of  FIG. 1 . The coil drive  54  provides a high-frequency heating current component  35  in addition to the low-frequency propulsion component  34 . The other half of the coils (not shown to simplify the drawing) can be driven by the same coil drive. 
         [0023]    The coils  56  in the propulsion system  58  of  FIG. 6  are shown embedded in a floor  60  defining the bottom of a passageway. The complementary top ceiling portion is not shown, but is similar to the floor  60 . Together, the bottom floor and the top ceiling sections form the passageway with an entrance and an exit at opposite ends. 
         [0024]    A solenoidal can washer-dryer system is shown in  FIGS. 7-9 . The system includes a washer section  62 , a dryer section  64 , a righter section  66 , and a drive section  68 . All the sections are solenoidal. The washer section  62  includes a first propulsion section  70  comprising a passageway  72  through two circular solenoid sections  74 ,  75  split by an access opening  76  through which water or cleansing fluid can be applied to the cans C by fluid ports, such as nozzles  78 . The access opening  76  is not wide enough for the can C to lose significant propulsion or to escape through. The next solenoidal section of the washer  70  is a spin section  80 . In addition to the primary propulsion coils  82 , the spin section  80  has spin coils  84  circumferentially spaced around the periphery of the central passageway. The spin coils  84  carry currents perpendicular to the primary coil currents to produce an electromagnetic flux wave that circulates around the girth of the passageway. The spin wave induces currents in the cans C that causes them to spin, or roll, rapidly about the long axis of the cans. Oils and other liquids are spun off the rapidly spinning cans by centrifugal force. The spinning momentum is maintained as the cans enter a rinse section  86 . The rinse section  86  is a propulsion section shown identical to the first propulsion section  70 , except that the fluid ports  88  spray rinse water or steam on the cans C through an opening  89 . The dryer section  64  is shown with spin coils  84  as well as drive coils  82 . The primary propulsion coils  82  are energized with both high- and low-frequency current components to heat and propel the cans C as they are spun through the dryer section  64 . The interior walls bounding the passageway could be lined with bristles or other scrubbing elements to scrub the exteriors of the cans. 
         [0025]    After leaving the dryer section  64 , the cans are propelled top or bottom first into a propulsion section  90  of the righter section  66 . The righter  66  transitions the cans from top or bottom first to side first, upright or upside down. To facilitate draining, the cans C are converted in the righter  66  to an upside down orientation. The circular propulsion section  90  propels cans into a rectangular righting solenoid  92  wound around a rectangular coil form  93  whose cross sectional area monotonically increases from an entrance end  94  to an exit end  95 . In the version shown in  FIG. 7 , the floor  96  of the righting solenoid  92  diverges from the ceiling  97  toward the exit end  95 . A permanent magnet  98  along the long side of the righting solenoid  92  near the exit end  95  induces eddy currents in the lower portion of the cans that produce a drag force that rights the cans. In this way the righting section  66  changes the orientation of the cans from top or bottom leading to side first, upright or upside down. The permanent magnet can be embedded in the righter&#39;s widening rectangular coil form  93  or mounted outside it. The final propulsion section  68 , which is a rectangular solenoid  100 , then conveys the upright or upside down cans to downstream processing. 
         [0026]    Another version of a can washer is shown in  FIG. 10 . This version uses the propulsion system of  FIG. 4  to convey the cans C. Fluid ports, such as cleaner nozzles  102  and rinse nozzles  104 , direct liquid cleanser and rinsing water or steam at the cans C through the upper and lower slots  52 ,  53  opening into the rectangular passageway  50 . The lower slot  53  provides drainage for the cleanser and rinse water. The left and right coil sets  46 ,  47  can be driven with currents that produce flux waves traveling in opposite directions to cause the cans to spin about their long axes  106 . The magnitudes of the two currents are different to produce oppositely directed forces f 1 , f 2  of different magnitudes on opposite sides of the cans. The net force F is directed in the conveying direction to propel the spinning cans through the passageway  50 . As shown in  FIG. 11 , a scrubber in the form of bristles  108  lines a portion of the side wall  48  of the washer to scrub oils from the sides of the cans C. The scrubber can be on one side only if the cans are being spun. If not, the scrubber can line both interior side walls. 
         [0027]      FIG. 12  shows a hinged version of the propulsion system of  FIG. 4  or the can washer of  FIG. 10 . Hinges  110  on one side of the side walls  48 ,  49  join the two halves of the propulsion system together for easy cleaning and maintenance, such as replacing scrubbing pads  111 . 
         [0028]    As shown in  FIG. 13 , one of the side walls  112  for use with an opposite side wall having drive coils has an array of permanent magnets  114  lining the interior wall  116 . Alternatively, the magnets could be recessed into or embedded in the side wall  112 . The permanent magnets induce currents in the cans propelled by coils in the other half of the propulsion system. The induced currents produce fields that provide a drag on the cans to make them spin. The magnets can be arranged in a Hallbach array to increase the flux density in the passageway. 
         [0029]      FIG. 14  shows an inverter  118  at the exit of the can washer  120  of  FIG. 10 . The inverter  118  provides a 180° bend in the short side  122  of the passageway  50  to turn upside-down cans C u  entering the washer right-side up upon exit. A second 180° bend  119  in the long side  123  of the passageway  50  reverses the direction of travel of the right-side-up can C r . A bend in the short side  122  changes the elevation of the passageway. And another way to change an upside-down can C u  to a right-side-up can C r  is shown in the 180° twist passageway  124  of  FIG. 15 . The bends  118 ,  119  and the twist  124  can be passive passageways, i.e., without coil propulsion, or can be propulsion passageways adjacent to drive coils as in  FIG. 4 .