Conveyor having rollers actuated by electromagnetic induction

Conveyor rollers rotated by electromagnetic induction to propel articles conveyed atop the rollers. A magnetic-field source induces a current in the electrically conductive rollers that causes them to rotate. The rollers can be mounted in conveyor belts or immobile mats. The magnetic-field source can be static if the rollers are advance through the field or dynamic. Alternatively, the rollers can be magnetic and induce a current in a stationary electrically conductive plate that creates interacting magnetic fields to rotate the rollers.

BACKGROUND

The invention relates generally to power-driven conveyors and more particularly to belt conveyors having electrically conductive rollers inductively actuated by interaction with a magnetic field.

Conveyor belts with article-supporting rollers are used to divert or orient articles as they are being conveyed. The belt rollers are rotated by contact with bearing surfaces or actuating rollers underlying the conveyor belt. As the belt advances, the belt rollers ride on the bearing surfaces or actuating rollers and are caused to rotate. The rotating belt rollers propel conveyed articles across or along the belt in the direction of the rollers' rotation. These belts are effective in sorting, orienting, registering, singulating, and otherwise diverting conveyed articles. But they do have some shortcomings. One shortcoming is noise. Contact between the belt rollers and the actuating rollers is noisy, especially at high belt speeds. Another shortcoming is roller wear. The frictional contact between the belt rollers and the bearing surfaces or actuating rollers wears away the belt rollers. And the need for frictional contact to rotate the belt rollers means that oil or other lubricants contaminating the conveyor cause the belt rollers to slip and alter the intended article trajectories. Furthermore, the rotational speed of the belt rollers and, consequently, the speeds of the articles depend on belt speed.

SUMMARY

These shortcomings are addressed by a conveyor embodying features of the invention. Such a conveyor comprises a conveyor belt having a plurality of electrically conductive rollers. A magnetic-field source generates a magnetic field that passes through the conveyor belt and induces a current in the electrically conductive rollers that causes the rollers to rotate.

Another version of such a conveyor comprises a magnetic circuit having a magnetic-field source forming a primary side of the magnetic circuit and an electrically conductive element forming a secondary side of the magnetic circuit. The magnetic-field source provides a primary magnetic field that induces a current in the electrically conductive element that creates a secondary magnetic field. A plurality of rollers forms a mat. Each of the rollers is either the magnetic-field source or the electrically conductive element; the other of the magnetic-field source and the electrically conductive element resides proximate the mat so that the primary and secondary magnetic fields coact to rotate the plurality of rollers.

In another aspect, a conveyor belt embodying features of the invention comprises a plurality of electrically conductive rollers that are adapted to interact with a magnetic field to induce a current in the rollers that causes them to rotate.

In yet another aspect of the invention, a method for conveying articles comprises: (a) supporting articles atop electrically conductive rollers in a conveyor belt; (b) subjecting the rollers to a magnetic field; (c) inducing a current in the electrically conductive rollers with the magnetic field to rotate the rollers; and (d) propelling articles along the conveyor belt with the rotating rollers.

DETAILED DESCRIPTION

A portion of a conveyor embodying features of the invention is shown inFIG. 1. The conveyor20comprises a conveyor belt22conventionally driven in a direction of belt travel24. The belt includes a plurality of rollers26arranged to rotate freely on axes28in the direction of belt travel24. The axes are defined by axles retained in the belt. In the example shown, the conveyor belt is a modular plastic conveyor belt constructed of a series of hingedly linked rows30of one or more belt modules having body sections extending from a first end to an opposite second in the direction of belt travel. The rollers26are mounted in cavities32in the belt with salient portions of the rollers protruding above an outer conveying surface34of the belt. Articles36are conveyed atop the belt rollers26. Although the rollers are shown residing in cavities in the module bodies of a modular plastic belt, they could be mounted atop the belt or extend through a bottom surface of the belt or be carried in a flat belt or a ceramic belt.

The rollers26, as also shown inFIG. 2, are cylindrical and made of an electrically conductive material, such as aluminum or copper. The aluminum or copper could form the outer surface of the rollers, or the aluminum or copper could be covered by another material, such as a plastic or elastomeric material that would exhibit desirable properties for contact with conveyed articles. The roller26is depicted inFIG. 2as a hollow conductive tube. Underlying the conveyor belt along a portion of the carryway is a magnetic-field source, such as the stator36of a linear induction motor. The stator has a series of poles38that are energized to produce a magnetic flux wave that travels along the length of the stator in a propagation direction40transverse to the direction of belt travel24in this example. As shown inFIGS. 3 and 4A-4C, the magnetic flux wave42traveling along the stator36induces a circulating current I in the electrically conductive roller26passing through the field. The current I produces a magnetic field that opposes the change in the flux of the magnetic field produced by the stator36. The interaction of the stator field (the primary field) with the induced field (the secondary field) produces a force that rotates the roller at a rotational speed ω and a tangential velocity v at the top of the roller opposite to the propagation direction40. In this way, the article36conveyed atop the rollers inFIG. 1will be pushed off the side of the belt22in the transverse direction44when it reaches the magnetic-field-producing stators36. If the propagation direction of the magnetic wave is reversed in the stator, the rollers26will rotate in the opposite direction and push the article36off the other side of the conveyor belt22. The axes of rotation28of the belt rollers are perpendicular to the stator-wave propagation direction40and parallel to the direction of belt travel24, which causes the rollers to push conveyed articles across the conveying surface34in the direction44perpendicular, or transverse, to the direction of belt travel. For this reason, the rollers26in the conveyor belt22ofFIG. 1are referred to as transverse rollers.

In the conveyor46shown inFIG. 5, a conveyor belt48has electrically conductive belt rollers50whose axes of rotation52are perpendicular to the direction of belt travel24. These rollers are referred to as in-line rollers because they propel conveyed articles36in or opposite to the direction of belt travel24. The stator52underlying the belt48on the carryway is rotated 90° from the stator36ofFIG. 1to produce a magnetic flux wave that has a propagation direction54in the direction of belt travel24to propel articles rearward on the conveying surface34of the belt. If the rearward tangential velocity of the rollers is equal to the forward speed of the belt, the conveyed article will remain stationary in space, which is useful in zero-back-pressure accumulation of backed-up articles. The belt speed and the propagation speed of the stator wave can be changed relative to each other to propel the articles rearward or forward. If the stator field is reversed, the belt rollers50rotate forward and accelerate articles at a speed faster than the belt speed to achieve article separation.

The conveyor56inFIG. 6uses a conveyor belt58that has obliquely arranged conductive belt rollers60to divert conveyed articles36across the conveying surface of the belt along trajectories oblique to the direction of belt travel24. The rollers60are freely rotatable on oblique axes62. A magnetic-field-producing stator64creates a magnetic wave that travels along the linear stator in a stator-wave propagation direction66perpendicular to the axes of the oblique rollers60. The forward-traveling stator wave causes the electrically conductive rollers to rotate opposite to the wave and push the articles obliquely rearward. If the stator field is reversed, the rollers reverse their rotation and push the articles36obliquely forward.

Although the conductive rollers in the conveyors ofFIGS. 1, 5, and 6are shown in endless conveyor belts, or mats, capable of advancing in a direction of belt travel, the rollers could also be embedded in or mounted on fixed, immobile mats. The mats could even be formed by a plurality of rollers or conveyor-belt sections long enough to extend over the stator. As another example,FIGS. 7A-7Bshow a turntable70topped with a stator72and a roller mat74having a plurality of freely-rotatable electrically conductive rollers76. The roller mat74could be realized, for example, as a few rows of the in-line-roller conveyor belt48ofFIG. 5. InFIG. 7A, the article36is fed or drawn onto the roller mat74in a first infeed direction78. The in-line rollers76are inductively actuated by the stator72with a magnetic stator wave traveling opposite to the first direction78. When the article36is centered on the turntable70, the stator is de-energized. The turntable is then rotated 90° counterclockwise as shown inFIG. 7Buntil the article is positioned as inFIG. 7C. The stator72is then re-energized to produce a magnetic wave that travels in a propagation direction80to rotate the rollers in the opposite direction and push the article36off the turntable in an outfeed direction perpendicular to its infeed direction78as shown inFIG. 7D. Of course, the turntable can be rotated to any outfeed angle.

Another arrangement of a fixed mat of rollers is shown in a conveyor section83configured as a sorter inFIG. 8. Three roller mats84,85,86are arranged in series, linked together, and supported in a frame88. Stators90,91,92underlie the mats. The first roller mat84has in-line rollers50used to draw an article36onto the conveyor. The first stator90propagates a magnetic wave in the first propagation direction94to rotate the rollers toward the second roller mat85. The speed of the propagating wave determines the rotational speed of the electrically conductive in-line rollers50. The roller speed can be set high enough to propel the article36all the way across the second roller mat85. Or it can be set low enough so that the article stops on the second roller mat85. If the article is not propelled past the second mat, the second stator91can be energized to produce a magnetic wave that travels in either transverse direction96to rotate the transverse electrically conductive rollers26in the opposite direction and direct the article36off a selected side of the conveyor. Articles36that are propelled past the second roller mat85onto the third roller mat86are directed off the end of the conveyor section83. The third stator92generates a magnetic flux wave that travels in the same propagation direction94as the first stator90to propel the article36off the end. The fields produced by the first and third stators90,92can be reversed, and articles can be fed onto the sorter and off its end in the opposite direction.

The stators shown underlying moving conveyor belts inFIGS. 1, 5, and 6can be replaced by magnets, such as permanent magnets or electromagnets arranged with alternating polarities along the direction of belt travel. The static, but spatially varying, magnetic field produced by these time-invariant magnetic-field sources can rotate the rollers as long as the roller belt is advancing in the direction of belt travel. In that way, the rollers “see” a magnetic field that is changing as the belt advances in the direction of belt travel through the magnetic field. The spatial variation in the magnetic field encountered by the rollers as they advance with the belt induces a current in the electrically conductive rollers that causes them to rotate. Once the belt stops, however, no current is induced in the rollers, which will then coast to a stop. As shown inFIG. 9, the permanent magnets underlying the rollers100can be arranged in a Hallbach array102, which increases the magnitude of the magnetic field above the array and decreases it below the array. The arrows on each magnet in the Hallbach array indicate the direction of the magnetic field along that face of the magnet. Because the rollers are advanced by the belt through a stronger magnetic field, the magnetic coupling and the roller torque are increased. Helical slots104in the periphery of the electrically conducted rollers100ofFIG. 9bias the rotation direction.

In the examples described thus far, stators and magnets served as sources, or primaries, of a magnetic circuit and electrically conductive rollers served as secondaries of the magnetic circuit. But the principle of operation could be reversed by making the roller a magnet (the primary) and underlying the conveyor belt with a conductive strip (the secondary) as shown inFIG. 10. The magnetic roller106acts as a source producing a magnetic field. Magnetic poles108are separated by helical slots110in the periphery of the roller. As the roller advances in the direction of belt travel24, the twisted poles induce a current in an underlying electrically conductive element, such as a metallic strip or plate112, that creates an induced magnetic field. The interaction of the primary magnetic field produced by the magnetic roller with the induced magnetic field in the electrically conductive element produces a force that causes the freely rotatable magnetic roller106to rotate.

As shown inFIG. 11, the stators114are controlled by a motor drive system116, such as a variable-frequency drive, that is coupled to a system controller118that can be used to coordinate stator frequency with belt speed and belt stopping and starting.

Although the invention has been described with the electrically conductive and magnetic belt rollers as article-supporting rollers, the rollers are not limited to use as rollers that contact articles directly. For example, the electrically conductive or magnetic belt rollers could be used to contact the carryway to help propel the conveyor belt, itself, along its path. Or the electrically conductive or magnetic belt rollers could be used to drive other rollers or non-roller components in the belt.