Definitions

• This invention relates to an improved motor driven roller in which the motor is located inside the roller and, more particularly, to such a motor driven roller in which the motor directly drives the roller.
• Motor-driven rollers are used in a variety of applications. Among these applications are the rollers used in exercise treadmills and in material handling conveyors. The specific embodiment of the invention, described in this patent specification, is directed to a conveyor application. However, it will be appreciated the invention is applicable to motor driven rollers used in other systems, such as treadmills.
• a brushless, permanent magnet, d.c. motor is housed inside the roller itself.
• the motor which is necessarily limited in size, has a relatively low torque.
• a conveyor roller has an inside diameter of less than two inches.
• a reducing gear is needed to couple the motor rotor to the roller in order to generate the torque required for the conveyor roller application.
• a resilient clutch is used to uncouple the motor from the roller in those situations where the roller becomes stuck. While generally satisfactory, the reducing gear requires maintenance and is subject to breaking down, which requires disassembly of the roller and repair or replacement of the broken parts .
• An object of this invention is the provision of an electronically controlled, high torque d.c. motor assembly housed inside the roller and directly connected to it, which eliminates the need for a reduction gear and a clutch control used in the prior art.
• this invention contemplates the provision of a motorized roller in which a cylindrical permanent magnet is secured to the inside surface of the roller. Longitudinal segments are magnetized to form poles of alternate north and south magnetic polarity. These magnet poles are the rotor of an inside-out brushless d.c. motor, the stator of which is formed by coils in slots in a toothed structure mounted on a stationary shaft about which the permanent magnet rotor and the roller to which it is attached rotates.
• the number of rotor poles is, or is close to, the maximum number of poles that can be formed about the circumference of the cylindrical permanent magnet, given the constraint on the diameter of the permanent magnet since it much fit within the roller, and the constraint of practical manufacturing limitations.
• the required thickness of the back iron which is needed to generate a high flux density in the air gap, which in turn is necessary to generate a high torque output per unit volume. It will be appreciated that the required back iron thickness is approximately equal to the ratio of the number of magnetic flux lines per pole to the acceptable back iron flux density level. As the number of poles increases, the magnetic lines per pole decrease, since the magnetic flux is evenly distributed among the poles.
• the stator coils are electronically commutated to provide brushless operation.
• One end of the stator shaft extends beyond the end of the roller and is secured to a suitable frame member. Wires in a passage in the shaft carry current to the coils.
• six-step switching is used to commutate the stator coils and the commutation angle can be advanced as the motor speed increases in order to maintain a desired torque.
• the motor extends the length of the roller. In another embodiment, the motor extends for only a part of the length of the roller.
• the permanent magnet in which the poles are formed may be secured to the inside of the roller by means of a suitable adhesive.
• the roller itself serves as the back iron to provide a low reluctance path to complete the magnetic circuit between adjacent poles.
• the entire motor assembly is secured in a metal housing, which is then secured to the roller by force fit or other suitable means.
• the metal housing serves as the back iron member.
• Fig. 1 is a longitudinal, sectional view of one embodiment of motor and roller combination in accordance with the teachings of the invention.
• Fig. 1A is a transverse sectional view taken in the plane indicated by line 1A--1A in Fig. 1.
• Fig. IB is an enlarged fragmentary view of a portion of Fig. 1A.
• Fig. 2 is a longitudinal, sectional view of a second embodiment of the motor and roller combination in accordance with the teachings of the invention.
• Fig. 2A is a transverse sectional view taken in the plane indicated by line 2A--2A in Fig. 2.
• Fig. 3 is a schematic view of a modified form of the roller and motor combination of either Fig. 1 or Fig. 2 in which the motor extends for only a part of the length of the roller.
• Fig. 4 is a schematic view similar to Fig. 3 where the motor extends substantially the entire length of the roller.
• Fig. 5 is a schematic drawing of a control system for the roller motor of a conveyor roller driven by an inside- out, brushless, permanent magnet, d.c. motor in accordance with the teachings of this invention.
• a cylinder 10 having a plurality of permanent magnets 12 is secured to the inside surface of a conveyor roller 14 by a suitable adhesive, for example.
• the thickness "t" of a typical conveyor roller wall is approximately roughly 1/16 of an inch.
• the permanent magnets 12 may be of any suitable magnetic material, such as neodium-iron-boron.
• longitudinal segments 12 of the cylinder 10 are magnetized to form magnetic poles with adjacent segments of opposite magnetic polarity, as indicated by the letters N and S in Fig. IB.
• the magnetized segments 12 are separated by narrow gaps of material 13 that are not magnetized under ordinary operating conditions.
• Magnetic Flux Magnetic Flux Density X Magnet Area
• a laminated toothed member 16 which is affixed to a shaft 18, is separated from the inner surfaces of cylinder 10 by an air gap 19.
• Stator coils 15 are disposed in slots 22 formed by teeth 26.
• the coils 15 each have at least thirteen turns, with only one turn per coil being shown for illustration purposes.
• Each coil 15 encircles only a single tooth 26.
• the coils 15 carry current supplied in three phases, A, B and C.
• a three-phase stator is used, with four coils per phase and two coil half-sections in each slot 22.
• Slot 1 is designated SI in Figs. 1A and 2A. Slot 1 is located between “tooth 12" and "tooth 1" of the stator 16.
• the phase A coils are disposed in the slots 22 to encircle “tooth 12" , “tooth 1", “tooth 6" and “tooth 7.”
• the phase B coils are disposed in the slots 22 to encircle “tooth 2", “tooth 3", "tooth 8" and “tooth 9".
• the phase C coils are disposed in the slots 22 to encircle "tooth 4", “tooth 5", "tooth 10" and "tooth 11".
• the motor of the present invention develops a high back EMF so as to provide a higher ratio of stator voltage to rotor speed than the prior art. In the prior art, this ratio was about 1.5.
• a ratio of 10 RMS volts per 1000 RPM of rotor speed can be obtained, with the nominal stator voltage on each of the three phases being a 24 -volt RMS PWM signal. By varying the number of turns, other guages of wire will provide the same results. If the nominal stator voltage were doubled to 48 RMS volts, then this ratio would be doubled to 20 RMS volts per 1000 RPM to provide suitable performance .
• the coils are electronically co mutated, for example, by a six-step commutation control algorithm. Although six- step commutation is preferred, other types of commutation including sine wave commutation may be employed. Here it will be appreciated this brushless commutation requires a means to determine the angular position of the rotor with respect to the stator coils 15.
• Three Hall effect sensors 23 are angularly spaced 120° apart and are supported on an annular circuit board 20. As the pole segments 12 pass by, sets of three signals are provided from the Hall effect sensors 23, and these three-signal sets are decoded to determine angular position signals which are then used for controlling commutation.
• the number of pole segments 12 is preferably made as large as it is practical to manufacture without reducing the magnetizable area. For example, with the inside diameter of the magnetic cylinder 10 on the order of one inch, it is practical to form about twelve pole piece segments.
• the thickness of the back iron required of a low reluctance magnetic flux return path is decreased so that the roller 14 can provide this function, resulting in an increased torque output per unit volume .
• the flux lines per pole decreases, since the density is distributed evenly among the number of poles. Consequently, the thickness of the back iron decreases as the number of poles increases .
• the minimum number of poles for any motor is two.
• the ratio of the back iron thickness for a two pole to the back iron thickness for a motor with "N" poles is approximately N divided by 2.
• at least six poles and preferably ten poles should be used.
• the shaft 18 extends outwardly from the roller so that it can be secured to the frame of the conveyor.
• the outer peripheral surfaces of a pair bearings 30 and 32 at this end of the shaft are affixed to the inner surface of the roller 14.
• the outer peripheral surface of another bearing 34, at the other end of the shaft 18, is also affixed to the inner surface of the roller 14.
• bearings are all rotatably mounted on the shaft 18 and allow the permanent magnet 10 along with the roller 14 to which it is affixed to rotate relatively to the fixed shaft 18 while maintaining the air gap 19 between the inner surface of the magnets and the outer periphery of toothed member 16.
• Conductors 37 are disposed in a passageway 36 in the shaft 18, including three phase conductors to provide power to the stator coils 15 from an external power source.
• the roller motor is first assembled in a cylindrical metal housing 40 which, in turn, is secured to the inner surface of the roller 14.
• the thickness of the wall of the housing is preferably minimized in order to maximize the diameter of the cylinder 10 which in turn maximizes torque.
• the housing 40 is secured to the roller 14 by a forced friction fit between the outer surface of the housing 40 and the inner surface of the roller 14 for at least a portion of their lengths. That is, the nominal outside diameter of the housing is slightly larger than the nominal inside diameter of the roller for at least a portion of their lengths.
• the housing 40 is closed at one end and a bearing 42 rotatably supports this end of the housing on the shaft 18.
• adhesive may be used to secure the housing 40 to the roller 14, or the adhesive may be used in addition to the press fit.
• the housing 40 provides the back iron path for the pole segments 12.
• the motor here indicated by the reference number 46
• the shaft 18 in this embodiment needs to extend the length of the roller, but may be supported by a bearing 47 inside the roller.
• the other side of the roller 14 is supported by a shaft 49 affixed to the frame 48 and a bearing 50 rotatable about the shaft and affixed to the roller 14.
• the motor 46 does extend substantially the entire length of the roller.
• the volume of the motor increases, and the torque which it can generate, which is a function of volume, also increases.
• Fig. 5 is a schematic diagram illustrating one embodiment of how the roller motor can be energized.
• a six-step commutating controller 52 connects a three-phase power supply 54 to the motor's stator coils (shown in Figs. 1 and 2) through three phase conductors 55 entering through the shaft of the roller 14.
• the rotor position sensors 23 (for example a Hall effect sensor) (shown in Figs. 1 and 2) provide commutating signals to controller 52 through three sense lines 57.
• a current sensing line 56 provides a signal to the controller 52 to indicate when a roller is stuck (i.e. the input current excess a predetermined threshold) so that the controller can cut off power to the jammed roller.
• the controller 52 can provide short duration power pulses to the motor after power has been cut off, to see if the roller has become freed, and if it has to resume supplying power to the motor.

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• Rollers For Roller Conveyors For Transfer (AREA)

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Cited By (6)

• 1999
  • 1999-06-11 AU AU44346/99A patent/AU4434699A/en not_active Abandoned
  • 1999-06-11 EP EP99927446A patent/EP1086522A1/de not_active Withdrawn

Non-Patent Citations (1)

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