BACKGROUND

The invention relates to power-driven conveyors and more particularly to motorized rollers.

Motorized rollers are commonly used to propel a series of conveyor rollers or conveyor belts. As shown in Figures la and lb, motorized rollers 20 typically include an electric motor 22 whose output shaft 24 is coupled to a reduction gear 26 that drives an outer cylindrical shell 28. The motor 22 and the reduction gear 26 are housed inside the hollow cylindrical shell 28. Stationary end shafts 30 extend out from end caps 32 for mounting the motorized roller 20 to the side walls of a conveyor. At least one of the stationary shafts 30 can be hollow to admit power and control cables 34 to the motor 22. The outer cylindrical shell 28 rotates about an axis of rotation 36 coincident with the shafts 24, 30. The shell 28 can directly drive a tensioned conveyor belt; it can propel articles directly and drive other idle rollers to drive articles via one or more transmission belts; or it can have or be outfitted with lagging that has drive surfaces to positively drive a toothed belt.

Motorized rollers are generally small in diameter so that they can be closely spaced in a powered roller conveyor. But the small outside diameter of motorized rollers limits the size of the internal electric motor and the maximum torque available for a given roller speed.

SUMMARY

One version of a drive system embodying features of the invention comprises a motorized roller and an external stator. The motorized roller includes a primary motor and an outer cylindrical shell rotated in a direction of rotation by the primary motor about an axis of rotation. The outer cylindrical shell includes electrically conductive or magnetic material. The external stator is disposed proximate the outer cylindrical shell and external to the motorized roller. The stator produces a magnetic flux wave that travels circumferentially along a portion of the outer cylindrical shell and interacts with the electrically conductive or magnetic material to produce a torque rotating the outer cylindrical shell about the axis of rotation.

Another version of a drive system comprises a stationary roller having an outer cylindrical shell and an external magnetic-field source disposed proximate the outer cylindrical shell. The outer cylindrical is rotated in a direction of rotation about an axis of rotation by a primary drive. The outer cylindrical shell includes electrically conductive or magnetic material. The external magnetic-field source is external to the roller and produces a magnetic field that cuts the outer cylindrical shell and interacts with the electrically conductive or magnetic material to produce a torque rotating the outer cylindrical shell about the axis of rotation.

In another aspect of the invention a method for increasing or decreasing the torque of a motorized comprises: (a) mounting a curved stator external and proximate to a roller having an outer cylindrical shell and driven with a first torque by a primary drive; and (b) producing a magnetic field with the stator that travels along the outer cylindrical shell in a first direction to produce a second torque that boosts the first torque rotating the outer cylindrical shell or in an opposite second direction to produce a second torque that bucks the first torque rotating the outer cylindrical shell.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures la and lb are isometric and cutaway side views of a prior- art motorized roller;

Figure 2 is a hybrid isometric view and block diagram of a boost drive embodying features of the invention;

Figures 3a and 3b are isometric views of motorized rollers as in Figure 2 with drive members extending from the periphery of the cylindrical shell at the edges of the shell in Figure 3a and in an internal region of the shell in Figure 3b;

Figure 4a is a side elevation view of a motorized roller with a boost drive as in Figure 2 positively driving a conveyor belt; Figure 4b is a side elevation view of a series of idle rollers driven by a motorized roller as in Figure 2;

Figure 5 is an isometric view of a boost drive as in Figure 3b, but with an array of permanent magnets;

Figure 6 is an isometric view of a boost drive as in Figure 5, but with staggered permanent-magnet bands;

Figure 7 is an enlarged view of Figure 6 showing the array of permanent magnets arranged in a Hallbach array.

Figure 8 is an isometric view of a boost drive for a toothed motorized roller with an array of magnetically soft poles in the motorized-roller outer shell. Figure 9 is an isometric view of the boost drive of Figure 8 with offset poles;

Figure 10a is an isometric view of a boost drive as in Figure 3a, but with poles that extend across the width of the outer shell; and Figure 10b is a stylized graph of belt tension due to chordal action and belt tension due to cogging;

Figure 11 is an isometric view of an external stator as in Figure 2 acting on an idle roller to damp speed variations; and

Figure 12a is an isometric view of external bands of permanent magnets for producing drag on an idle roller; and Figure 12b is an enlarged view of the permanent magnets of Figure 12b arranged in a Hallbach array.

DETAILED DESCRIPTION

A boost drive system for a motorized roller embodying feature of the invention is shown in Figure 2. A stator 40 is positioned close to the outer cylindrical shell 28 of a motorized roller 20 mounted stationary at a fixed position in a conveyor frame (not shown). The motorized roller's primary drive is its integral electric motor. The stator 40 has an array of poles 42 terminating in pole faces 44 proximate the shell 28. Each of the poles 42 is surrounded by windings 46, such as three-phase windings. The pole faces 44 define a curved plane whose shape is complementary to the outer shell 28 of the motorized roller 20 across an air gap 45. The stator 40 is an external magnetic-field source positioned close to the outer shell 28.

The stator 40 extends axially along the majority of the length of the motorized roller 20 and circumferentially along only a portion of the outer cylindrical shell 28. The stator 40 produces a magnetic flux wave that travels circumferentially through the air gap 45 and along the outer shell 28. The outer shell 28 includes electrically conductive material or magnetic material. The motorized roller's primary motor rotates the outer shell 28 in a direction of rotation 43. The magnetic flux wave produced by the stator 40 induces currents in the electrically conductive material or attracts the magnetic material, which produces a torque 41 in the shell 28 about the axis of rotation 36. The torque 41 due to the external stator 40 augments the torque produced by the motorized roller's internal primary motor (22, Figure lb) in a boost-drive system. A controller 48 powers and coordinates the operation of the stator 40 and the motorized roller 20 over power and control lines 50, 51. Figures 3a and 3b show motorized rollers 20 with drive elements extending radially outward from the outer cylindrical shell 28. In Figure 3a the drive elements are teeth 52 formed on the peripheries of sprocket rings 54 mounted on the two opposite ends of the outer shell 28 so that they don't interfere with the positioning of the stator 40 close to the outer shell. In Figure 3b the drive elements are teeth 56 that are arranged in circumferential lanes 58 on the outer cylindrical shell 28. The teeth 56 can be welded to the outer shell 28 or formed on lagging attached to the shell. Notches 60 formed in the stator 40' are axially aligned with the lanes 58 of drive elements 56 so that the stator can be positioned close to the outer shell 28 of the motorized roller 20 to boost the torque provided by the motorized roller's primary motor.

The boost-drive system of Figures 3a and 3b is shown positively driving a conveyor belt 60 in Figure 4a. Drive faces 62 on the drive elements 56 engage drive-receiving surfaces on the inner side 64 of the belt 60 to drive the belt in the direction of arrow 66. The stator 40 is shown conveniently mounted close to the motorized roller 20 between upper and low belt runs 68, 69.

Figure 4b shows the motorized roller 20 driving a series of idle rollers 70. A series of transmission belts 72 interconnect the outer shell 28 of the motorized roller 20 to the outer shells 74 of the idle rollers 70 and transmit the power from the motorized roller to the idle rollers. In this example the boost drive's stator 40 is mounted below the motorized roller 20 in the conveyor frame (not shown).

When the outer cylindrical shell is made of or includes electrically conductive material, such as aluminum or copper, the stator's magnetic flux wave induces currents in the shell. The induced currents produce reaction magnetic fields that interact with the stator flux wave to produce a torque on the shell. Thus, the outer shell acts as the rotor in an induction motor formed with the stator. As shown in Figure 3a, an inner cylinder 75 backs the outer cylindrical shell 28. The inner cylinder 75 is made of a magnetically soft material, such as carbon steel, to complete the magnetic circuit with the stator 40.

Figure 5 shows an outer cylindrical shell 76 that includes magnetic material in the form of circumferential bands 78 of permanent magnets 80. The bands are spaced apart axially on the shell 76. The magnetic flux wave produced by the stator 40' interacts with the magnetic field of the permanent magnets to create a synchronous permanent-magnet or stepper motor. Permanent magnets of common polarity are axially aligned across all four bands 78. In Figure 6 the bands 79 of permanent magnets 80 are shown with circumferentially alternating north (N) and south (S) poles around the outer cylindrical shell 76. The bands 79 are circumferentially offset from one another so that poles of the same polarity are not axially aligned from band to band. With the poles staggered in this manner, cogging of the outer shell 76 at low belt speeds is reduced. For example, if the magnet bands 79 are advanced 90° magnetically from band to band in the axial direction, the cogging action is broken into four components, each occurring 90° out of phase from its neighboring bands with a frequency of four times the cogging frequency of the unstaggered bands 78 of Figure 5 and one-fourth the cogging amplitude. In this arrangement corresponding magnet poles from band to band lie on a helical curve on the outer cylindrical shell 76. The bands 78' of permanent magnets are arranged in a Hallbach array in Figure 7 to focus the magnetic field of the magnets outward into the gap 82 between the stator poles and the magnets 80 for better magnetic coupling and higher torque.

Figures 8 and 9 show a motorized roller with an outer cylindrical shell containing an array of pole pieces 86 made of a magnetically soft material. The poles 86 are

circumferentially and axially spaced apart along and across the outer shell 84. The shell 84 with its soft magnetic poles 86 forms a reluctance motor with the stator 40'. The soft magnetic poles 86, seeking to minimize the reluctance of the magnetic circuit they form with the stator poles 42, are pulled along by the stator's magnetic flux wave, which produces a torque on the shell. To minimize cogging effects at low speeds, the rotor poles 86, like the permanent-magnet bands 79 of Figure 6, are staggered (offset circumferentially) in Figure 9 so that no two poles of the same polarity are aligned axially.

In Figure 10a a motorized roller 87 is shown with an outer cylindrical shell 88 having elongated permanent magnets 90 extending axially along the shell. (Bands of permanent magnets, as in Figure 5, would behave similarly.) The permanent-magnet motor so formed with the stator 40 causes a regular variation in belt tension and speed that is due to cogging. The period of the cogging is related to the circumferential spacing (the pole pitch) of the permanent magnets 90. That relationship 92 is shown in Figure 10b. When the motorized roller 87 is used to drive an articulating conveyor belt, such as the belt 60 in Figure 4a, the belt is subject to chordal action, which causes a variation in belt tension and speed. The period of that variation is related to the pitch (the circumferential spacing of the teeth 52 on the sprockets). The effect of chordal action on the belt tension 94 is shown in Figure 10b. If the tooth pitch is the same as the pole pitch, the periods of the variations in belt tension and speed due to cogging 92 and to chordal action will be the same. By adjusting the phase φ of the poles 90 relative to the drive faces 62 of the teeth 52, the cogging variation can be made 180° out of phase with the chordal action variation. The result 96 is full or partial

cancellation of chordal action by cogging and smoother belt motion as shown in Figure 10b.

Figure 11 shows a stator 40 acting on the outer cylindrical shell 28' of an idle roller or pulley 100, such as for a conveyor belt (not shown) advancing in a direction of belt travel 102 along an upper carry way. The idle roller 100 is engaged directly or indirectly via sprockets or other intervening drive elements with the driven conveyor belt serving as the idle roller's primary drive. The curved stator is positioned close to the shell 28' between the carryway and the belt's lower returnway as in Figure 4a. In this example the shell 28' is made of an electrically conductive material to function as the rotor of an induction motor having the stator 40. A controller, such as the controller 48 in Figure 2, coordinates the belt's primary drive motor with the operation of the idle roller's stator 40. The magnetic field of the stator 40 is pulsed to induce currents in the conductive outer shell 28' that oppose or aid the rotation 104 of the idle roller with torque pulses 106 opposite to or in the same direction as the primary rotation 104. In this way the external stator 40 is used to damp speed variations in the belt with the external stator 40 causing a torque that bucks the idle roller's rotation. As for the boost drives, magnetic material, such as soft-iron pieces or permanent magnets, could be embedded in the outer shell 28' to achieve damping using reluctance-motor or synchronous-motor techniques.

An alternative way to damp speed variations is with curved bands of permanent magnets 108 mounted external to the electrically conductive outer cylindrical shell 28' of an idle roller 110 across an air gap as in Figure 12a. (To simplify the drawing, mounting structure is not shown.) Like the stator 40 in Figure 11, the curved array of permanent magnets 108 forms an external magnetic-field source positioned close to the cylindrical shell 28' to affect its rotation. In this case the permanent magnets 108 form a permanent-magnet stator producing a static magnetic field. As the idle roller rotates in a direction of rotation 112, the static magnetic field produced by the permanent magnets 108 induces eddy currents in the conductive outer shell 28'. The eddy currents produce reaction fields that interact with the permanent-magnet field to create a drag force 114 on the shell 28' opposing the primary rotation 112 due to the idle roller's engagement with a driven conveyor belt (not shown). The drag force 114 damps speed pulsations in the belt and idle roller. As shown in Figure 12b, the permanent-magnet bands can be arranged in Hallbach arrays 116 to increase the magnetic-field strength crossing the air gap 118 between the Hallbach arrays 116 and cutting the conductive cylindrical shell 28'.

The term motorized roller is meant to encompass drum drives, motorized pulleys, and any motorized conveyor drive that has an axially elongated cylindrical outer drive shell, whether or not the motor is housed within the shell.