GB2281664A

GB2281664A - Linear motor and elevator and conveyer using same

Info

Publication number: GB2281664A
Application number: GB9415733A
Authority: GB
Inventors: Hideki Nihei; Fumio Tajima; Shunichi Tanae
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1993-09-01
Filing date: 1994-08-03
Publication date: 1995-03-08
Also published as: GB9415733D0; JPH0775324A

Abstract

A primary part (10) serving as a moving member comprises a primary magnetic material (103), and primary coils (101) which are wound on an outer periphery of this magnetic material (103) in cross-sectional planes passing through the magnetic material perpendicularly to a direction of movement of a linear motor (1), and a pair of secondary parts (20) are provided over an entire stroke of the linear motor in such a manner that the primary part (10) is interposed between the secondary parts (20). Coil end portions, can be reduced in size, and therefore a relatively high efficiency can be achieved with the flat linear induction motor. A U-shaped primary member and an E-shaped secondary member may be used. The motor may be an induction motor or a synchronous motor. In the conveyor application the primary member may be wound to provide opposite thrust on respective secondary members so as to also drive the return portion (Fig. 16, 17). <IMAGE>

Description

LINEAR MOTOR, AND ELEVATOR AND CONVEYER USING SAME This invention relates to a linear motor for linear movement, and more particularly to a linear motor suited for use as a drive source for an elevator or the like.

It is thought that a suitable example of a linear motor requiring a large capacity to serve, for example, as a drive source for an elevator or the like is a linear induction motor.

As conventional linear induction motors, there are known a flat type linear induction motor and a cylindrical linear induction motor, as described in literature "Linear Motor and its Application" edited by Magnetic Actuator Research Technical Committee, Institute of Electrical Engineers (March, 1984).

A first prior art example is Japanese Patent Unexamined Publication No. 1-220691 disclosing a flat type linear induction motor serving as an auxiliary drive means for an inclined elevator. This publication describes that the flat type linear induction motor is used as the auxiliary drive means at part of a travel path of the inclined elevator having a hoist as a drive source. The auxiliary drive means is operated at part of the travel path, and therefore the drive distance is short, and in this construction a primary part is fixed while a secondary part is movable.

As a second prior art example, there are listed, for example, Japanese Patent Unexamined Publication Nos. 5-78060, 4-116081, 3-56382, 3-95083, 2-310281 and 57-175684, in which a flat type linear induction motor, different from that of the first prior art example, is used as a main drive source for an elevator. The flat type linear induction motors disclosed in these prior art publications are of such a construction that coils are arranged in a three-phase manner on one flat surface of a primary magnetic material.

As a third prior art example, there are listed, for example, Japanese Patent Unexamined Publication Nos.

2-233489 and 2-233490 which disclose a cylindrical linear induction motor achieving high efficiency and power factor. In the cylindrical linear induction motors disclosed in these prior art publications, usually, a secondary part of a simple construction is fixed, and a cylindrical secondary conductor is provided on the outside of a cylindrical secondary yoke of the secondary part, and a cylindrical primary core, having a doughnutshaped primary coil mounted on its inner surface, is further provided on the outside of the cylindrical secondary conductor through a gap. As a result, the primary part has a cylindrical shape, and faces the secondary conductor over an entire area thereof, and therefore a copper loss can be made small, and the lowering-of the efficiency can be suppressed.

In the first prior art example, a plurality of drive sources, that is, the hoist and the linear motor, have been required for driving the inclined elevator, and therefore this construction has not been applied to elevators of the ordinary type. Incidentally, the construction has been complicated, and the cost has been too high, and therefore it has been difficult to even achieve the inclined elevator.

Moreover, this linear motor is of such a construction that the primary part does not always face the secondary part over the entire surface, and those surfaces of the primary part which do not impart a magnetic flux to the secondary part do not contribute to a motor output, and therefore the efficiency has been greatly lowered.

The linear motor of the second prior art example is of such a construction that the coils are provided on one surface of the primary magnetic material in a three phase manner, as described above, and therefore the U-phase coil, while reaching the U-phase at the next slot, overlaps the V-phase and W-phase coils to form large coil end portions. Since these coil end portions do not face the secondary conductor, and therefore do not contribute to the production of a thrust, the resistance of the coils increases with the increase of the coil end portions. This has increased a copper loss, and has markedly lowered the efficiency of the motor.

The linear motor of the third prior art example has suffered from various problems since the cylindrical primary coils, the primary core, the secondary conductor and the secondary yoke are manufactured and combined together. Its details will now be described in the following.

In this linear motor, with respect to the primary part, slots are provided in the inner surface of the cylindrical primary core, and the primary coil of a doughnut-shape is provided in the slots. The manufacture is very difficult.

In order to provide the mechanism for maintaining an air gap at the thrust-producing portion, a travel surface is provided on the secondary part while rollers are provided on the primary part. In this case, the travel surface on the secondary conductor of the secondary part is required to have high flatness and hardness. To avoid this, if a travel surface for exclusive use is provided, those portions mechanically connected between the primary part and the secondary part are increased in length, and therefore the rigidity is lowered, and vibrations are liable to occur. To deal with this, the mechanism is more complicated and expensive.

Therefore, this prior art example has suffered from the problems that difficulty is encountered in connection with the manufacture and that the cost is high.

It is an object of this invention to provide a linear motor which addresses the various problems of the above prior art flat type linear motors and cylindrical linear motors, and achieves a relatively high efficiency, and also can be easily manufactured.

The present invention is characterized in that a primary part serving as a moving member comprises a primary magnetic material, and primary coils which are wound on an outer periphery of the magnetic material in cross-sectional planes passing through the magnetic material perpendicularly to a direction of movement of a linear motor, and that a pair of secondary parts are provided over an entire stroke of the linear motor in such a manner that the primary part is interposed between the secondary parts.

With the above construction of the present invention, shifting magnetic fields, generated at the primary coils of the moving member, produce thrusts at two opposed portions of the primary part and the secondary parts at the same time, thereby effecting the function of the linear motor.

In this linear motor, the two secondary parts always face the single primary part to produce the thrusts, and therefore there can be achieved the linear motor which has a small loss and a high efficiency. And besides, the primary part serves as a moving member while the secondary parts, which are simpler in construction and lower in cost than the primary part, are fixed, and therefore the inexpensive linear motor can be provided.

As compared with those portions of the primary coils, whose turns are disposed perpendicular to the direction of movement of the linear motor, provided at the thrust-producing portions, those portions (coil ends) of the primary coils not provided at the thrust-producing portions can be made shorter, thus reducing the dimension of the coil end portions not contributing to the motor output, and therefore the efficiency can be enhanced.

Particularly in one preferred embodiment of the present invention, the magnetic material of the primary part has a quadrilateral shape, and two opposite sides of this quadrilateral magnetic material serve as thrustproducing portions, and are made much longer than the other two sides of the primary part so that the magnetic material can be reduced in thickness as much as possible in so far as a required mechanical strength and an acceptable magnetic flux density are obtained. With this arrangement, there can be provided the flat type linear motor in which the influence of the coil end portions is very small.

In the drawings: Fig. 1 is a view schematically showing the appearance of a first embodiment of a linear induction motor of the present invention.

Fig. 2 is a cross-sectional view of the first embodiment of the linear induction motor of the present invention taken in a XY plane of Fig. 1.

Fig. 3 is a cross-sectional view of the first embodiment of the linear induction motor of the present invention taken in a XZ plane of Fig. 1.

Fig. 4 is a cross-sectional view of the first embodiment of the linear induction motor of the present invention taken in a YZ plane of Fig. 1.

Fig. 5 is a block diagram of a drive circuit of the first embodiment of the present invention.

Fig. 6 is a view schematically showing the appearance of a construction in which the first embodiment of the linear induction motor of the present invention is applied to an elevator.

Fig. 7 is a view schematically showing the appearance of a second embodiment of a linear induction motor of the present invention.

Fig. 8 is a cross-sectional view of the second embodiment of the linear induction motor of the present invention taken in a XY plane of Fig. 7.

Fig. 9 is a cross-sectional view of the second embodiment of the linear induction motor of the present invention taken in a XZ plane of Fig. 7.

Fig. 10 is a cross-sectional view of the second embodiment of the linear induction motor of the present invention taken in a YZ plane of Fig. 7.

Fig. 11 is a block diagram of a drive circuit of the second embodiment-of the present invention.

Fig. 12 is a view schematically showing the appearance of a construction in which the second embodiment of the linear induction motor of the present invention is applied to an elevator.

Fig. 13 is a view schematically showing the appearance of a third embodiment of the present invention in which a linear induction motor of the present invention is applied to an elevator.

Fig. 14 is a cross-sectional view of a fourth embodiment of a linear induction motor of the present invention taken in a XY plane.

Fig. 15 is a block diagram of a drive circuit of a fifth embodiment of the present invention.

Fig. 16 is a cross-sectional view of a primary part of a linear induction motor according to a sixth embodiment of the present invention.

Fig. 17 is a schematic cross-sectional view of a moving walk to which the sixth embodiment of the linear induction motor of the present invention is applied.

Figs. 18A, 18B and 18C are views explanatory of coil end portions of the prior arts.

Figs. 18D, 18E and 18F are views explanatory of coil end portions of the present invention.

A first embodiment of the present invention will now be described with reference to Figs. 1 to 6.

Fig. 1 schematically shows the appearance of a first embodiment of a linear induction motor of the present invention. In this Figure, the direction of movement of the linear induction motor is indicated by a Z-axis, and thrust-producing portions are disposed parallel to a ZX plane.

The linear induction motor comprises a primary part 10 receiving electric feed, and a secondary part 20 not receiving electric feed. The secondary part 20 is fixed, and longitudinal rollers 151 for supporting a load in a Y-direction, as well as transverse rollers 152 for supporting a load in an X-direction, are mounted on the primary part movable in a Z-direction.

The secondary part 20 comprises a secondary yoke 204 of a magnetic material which has a U-shape in an XY plane, and extends in the Z-direction, and secondary conductors 201 and 202 each in the form of a plate-like, electrically-conductive material extending in the Z-direction. The secondary conductors 201 and 202 are mounted on the inner surface of the secondary yoke 204.

The primary part 10 includes a plurality of primary coils 101 of an electrically-conductive material wound on a primary core 103 of a parallelepipedic shape in the Z-direction, the primary core of a magnetic material extending in the Z-direction.

Fig. 2 is a cross-sectional view of the first embodiment of the linear induction motor of the present invention taken in a XY plane. As shown in this Figure, the secondary yoke 204 is of a U-shape, and the secondary conductors 201 and 202 are provided respectively on the sides of the upper and lower portions (Fig. 2) of the secondary yoke directed toward the primary coils.

Magnetic fluxes, produced by energizing the primary coils 101, reach the upper portion, the lower portion and a left portion (Fig. 2) of the secondary yoke 204, respectively, and then the magnetic fluxes on the upper portion and the lower portion pass through the primary core 103 in the direction of travel of the linear motor, and return to the secondary yoke 204.

In addition to the thrust, attractive forces are produced between the primary part and the secondary part. These forces are shown in Fig. 2. The force F1 attracts the primary part toward the negative side in the Y-direction, the force F2 attracts the primary part toward the positive side in the Y-direction, and the force F3 attracts the primary part toward the negative side in the X-direction.

The attractive forces F1 and F2 act in opposite directions, respectively, and therefore the load acting on the longitudinal rollers 151 is zero if an ideal condition is achieved. Even if F1 and F2 become different from each other due to the difference between the gaps at the thrust-producing portions, the difference between the attractive forces is far smaller than in a flat linear induction motor in which an attractive force acts only on one side. Therefore, the stability generally equivalent to that achieved with a cylindrical linear induction motor can be obtained.

Furthermore, because of the attractive force F3, the transverse rollers 152 positively run on the left portion (in the drawings) of the secondary yoke. Therefore, the primary element will not excessively shake in the X-direction, thus achieving a stable operation.

With respect to the configuration of the primary coil 101, its upper and lower sides (in the drawings), contributing to the production of the thrust, are longer whereas its left and right sides are shorter.

By doing so, the coil end portions not contributing to the production of the thrust can be shortened. The coil end portion will be described later.

Fig. 3 is a cross-sectional view of the first embodiment of the linear induction motor of the present invention taken in an XZ plane. As shown in this Figure, the primary core 103 having the primary coils 101 mounted thereon is formed by laminating plate-like magnetic materials, such as a silicon steel plate, so that eddy currents due to magnetic fluxes will not be produced in the primary core 103, thereby preventing the efficiency from being lowered.

The plate-like magnetic material has a rectangular shape, and has grooves for enabling the primary coils 101 to be mounted thereon, as shown in Fig.

4. These magnetic materials are laminated to form the primary core 103, as shown in Fig. 3, and therefore this can be manufactured much more easily as compared with a cylindrical linear induction motor.

Instead of forming the grooves in the silicon steel plate, there can be used a method in which primary coils are mounted at a predetermined pitch on a primary core comprising laminated silicon steel plates of a rectangular shape, and then magnetic poles of a magnetic material are provided between the primary coils at thrust-producing portions, thereby providing a similar primary part.

In this case, the primary coils can be beforehand incorporated after the shaping, and therefore there is provided an advantage that the manufacture can be effected easily as compared with the above case in which the primary coils are wound on the primary core with the grooves.

As shown in Fig. 3, the primary core 103 is connected to a mechanism portion 105 of a U-shape, and the longitudinal rollers 151 and the transverse rollers 152 are mounted on the mechanism portion 105 so as to roll on the travel surfaces of the secondary yoke 204, thereby supporting the primary core in the X-direction and Y-direction in Fig. 2.

Fig. 4 is a cross-sectional view of the linear induction motor of the first embodiment taken in a YZ plane. As shown in this Figure, the plurality of primary coils 101 are wound in such a manner that they are divided into three phases. When supplying three-phase alternating current to these primary coils, shifting magnetic fields (rotating magnetic field in a rotating type) are produced relative to the secondary yoke 204, and eddy current flows in the secondary conductors 201 and 202, and the shifting magnetic field from the primary coils intersects this eddy current, thereby producing a thrust. This is similar to a torque-producing mechanism in a linear induction motor of the general type.

In the present invention, since the secondary part is fixed, the primary part is moved in the Z-direction by the produced thrust.

The primary coils 101 of the linear induction motor are connected to a three-phase inverter 301, and three-phase alternating current of arbitrary magnitude and frequency is supplied to the primary coils 101 by the three-phase inverter 301. The current is detected by current detectors 331 connected respectively to the coils of two phases in the linear induction motor, and a threephase current feedback signal If is calculated by a current calculator 332.

Here, the position of the moving primary part is detected by a position detector 311, and a position calculator 308 effects a suitable adjustment by a control parameter to provide a position feedback signal Pf. The speed of the primary part is detected by a speed detector 312, and a speed calculator 307 effects a suitable adjustment by a control parameter to provide a speed feedback signal Vf.

The position feedback signal Pf is compared with a position instruction Pc, and its error is adjusted by a control parameter in a position controller 306, and is outputted as a speed instruction Vc. This speed instruction vc is inputted into a speed controller 302.

Here, the speed instruction can be arbitrarily set in accordance with the position error. Therefore, smooth acceleration and deceleration as well as quick acceleration and deceleration can be achieved in accordance with the condition of the load and the operating condition.

In response to the speed instruction, the speed controller 302 calculates a drive frequency, exciting current and thrust current in accordance with the speed feedback signal Vf and the three-phase feedback signal If of the secondary part, and calculates a corresponding three-phase current instruction, and outputs the threephase current instruction to the three-phase inverter 301. Three-phase alternating current of arbitrary magnitude and frequency is applied from the three-phase inverter 301 to the primary coils 101 of the linear induction motor.

By doing so, the linear motor can be driven to an arbitrary position at an arbitrary speed in an arbitrary acceleration/deceleration pattern.

In this embodiment, the flat linear induction motor can be operated at an efficiency generally equivalent to that of a cylindrical linear induction motor, and therefore there can be obtained the linear induction motor which can be manufactured quite easily.

Fig. 6 shows an example in which the linear induction motor of the first embodiment of the present invention is applied to an elevator.

A cage 401 is supported on guides 405, and is movable upward and downward. The cage 401 is connected to the primary part 10 of the linear motor by a rope 402 through pulleys 403 and 404. The secondary part 20 is provided parallel to the cage 401, and the primary part 10 is movable along the secondary part 20.

By supplying three-phase alternating current to the primary part 10, the primary part 10 is moved upward and downward to move the cage 401 downward and upward.

Therefore, the need for a machine room housing a motor for winding up the elevator rope is obviated, thus providing advantages that the height of a building can be low and that the cost for the installation of the machine room is reduced.

In this example, the thrust-producing portions of the linear motor 1 are disposed perpendicular to that side face of the cage 401 facing the linear motor 1, and an opening in the secondary part 20 faces the cage, and by displacing the cage 401 and the primary part 10 in an upward-downward direction with respect to each other, the primary part 10 can be easily removed.

In this embodiment, although the invention is applied to the so-called rope-type elevator in which the primary part of the linear motor is provided at a counterweight, with the cage elevated through the rope, it can be applied to a so-called ropeless elevator in which a primary part is provided at a cage so as to directly move the cage. In this case, also, similar effects as in this embodiment can be obtained.

A second embodiment of the present invention will now be described with reference to Figs. 7 to 12.

Fig. 7 schematically shows a second embodiment of a linear induction motor of the present invention. In this Figure, the direction of movement of the motor is indicated by a Z-axis, and planes of gaps are disposed parallel to a ZX plane.

The linear induction motor comprises a primary part 10 receiving electric feed, and a secondary part 20 not receiving electric feed. The secondary part 20, assuming an E-shape in an XY plane, is fixed, and longitudinal rollers 151 for supporting a load in a Y-direction, as well as transverse rollers 152 for supporting a load in an X-direction, are mounted on the primary part 10 assuming a U-shape in the XY plane, the primary part 10 being movable in a Z-direction.

The secondary part 20 comprises a secondary yoke 204 of a magnetic material which has a U-shape in an XY plane, and extends in the Z-direction, and secondary conductors 201, 202 and 203 each in the form of a platelike, electrically-conductive material extending in the Z-direction. The secondary conductors 201 and 203 are mounted on the inner surface of the secondary yoke 204, and the secondary conductor 202 is provided between the primary part 10.

Fig. 8 is a cross-sectional view of the second embodiment of the linear induction motor of the present invention taken in an XY plane. As shown in this Figure, the secondary yoke 204 is of a U-shape, and upper and lower portions (Fig. 8) of this yoke constitute magnetic materials of the secondary part for first and second linear induction motors, respectively. The secondary conductor 201 is provided on that portion of the secondary yoke disposed adjacent to primary coils of the first linear induction motor, and the secondary conductor 203 is provided on that portion of the secondary yoke disposed adjacent to primary coils of the second linear induction motor, and the secondary conductor 202 is provided between these two conductors. The secondary conductor 202 serves as a secondary conductor for the first linear induction motor and also as a secondary conductor for the second linear induction motor.

Magnetic fluxes, produced by energizing the primary coils 101 of the primary part of the first linear induction motor, reach the upper and left portions (Fig.

8) of the secondary yoke 204 and a primary core 104 of the primary part of the second linear induction motor.

Magnetic fluxes, produced by energizing the primary coils 102 of the primary part of the second linear induction motor, reach the lower and left portions (Fig. 8) of the secondary yoke 204 and a primary core 103 of the primary part of the first linear induction motor.

Attractive forces, produced by the magnetic flux, reaching the primary core 104 of the secondary linear induction motor from the primary core 103 of the first linear induction motor, and the magnetic flux reaching the primary core 103 of the primary part of the first linear induction motor from the primary core 104 of the second linear induction motor, act between the primary core 103 of the first linear induction motor and the primary core 104 of the second linear induction motor. These primary cores are connected together by a mechanism portion, and will not be displaced relative to each other by the attractive forces.

A force F1 pulling the primary part upward (Fig. 8) is produced by the magnetic flux reaching the upper portion of the secondary yoke 204 of the secondary part from the primary core 103 of the first linear induction motor. A force F2 pulling the primary part downward (Fig. 8) is produced by the magnetic flux reaching the lower portion of the secondary yoke 204 of the secondary part from the primary core 104 of the second linear induction motor.

On the other hand, a force F3 pulling the primary part 10 left (Fig. 8) is produced by the magnetic flux reaching the left portion of the secondary yoke 204 of the secondary part from the primary core 103 of the first linear induction motor. Similarly, a force F4 pulling the primary part 10 left (Fig. 8) is produced by the magnetic flux reaching the left portion of the secondary yoke 204 of the secondary part from the primary core 104 of the second linear induction motor.

The pull forces F1 and F2 act in opposite directions, respectively, and therefore the load acting on the longitudinal rollers 151 is zero if an ideal condition is achieved. Even if F1 and F2 become different from each other due to the difference between air gaps, such a difference is far smaller as compared with a flat linear induction motor in which a pull force acts only on one side. This is generally equivalent to that of a cylindrical linear induction motor.

Furthermore, by controlling the pull forces F1 and F2, the overall pull force can be reduced.

On the other hand, because of the pull force F3, the transverse rollers 152 positively run on the left portion (in the drawings) of the secondary yoke. Therefore, the primary part will not excessively shake in the X-direction, thus achieving a stable operation.

The primary coils 101 has a parallelepipedic shape, and the thrust-producing portions, that is, its upper and lower sides (in the Figure) are longer whereas its left and right sides are shorter. By doing so, the coil end portions not contributing to the production of the thrust can be shortened. The coil end portions will be described later.

Fig. 9 is a cross-sectional view of the second embodiment of the linear induction motor of the present invention taken in an XZ plane. As shown in this Figure, the primary core 103, having the primary coils 101 of the first linear induction motor mounted thereon, is formed by laminating plate-like magnetic materials, such as a silicon steel plate, so that eddy currents due to magnetic fluxes will not be produced in the primary core 103, thereby preventing the efficiency from being lowered.

10. These magnetic materials are laminated to form the primary core 103, as shown in Fig. 9, and therefore this can be manufactured much more easily as compared with a cylindrical linear induction motor.

As shown in the drawings, the primary core 103 is connected to a mechanism portion 105 of a U-shape, and the longitudinal rollers 151 and the transverse rollers 152 are mounted on the mechanism portion 105 so as to roll on the travel surfaces of the secondary yoke 204, thereby supporting the primary core in the X-direction and Y-direction in Fig. 7.

What has been described with reference to Fig.

9 is the same with the primary coil 102 of the second linear induction motor.

Fig. 10 is a cross-sectional view of the second embodiment of the linear induction motor of the present invention taken in a YZ plane. As shown in this Figure, the primary part 10 comprises a first primary part 11 constituting the first linear induction motor, and a second primary part 12 constituting the second linear induction motor. The plurality of primary coils 101 of the first primary part, as well the plurality of primary coils 102 of the second primary part, are divided into three phases. When supplying three-phase alternating current to the primary coils, shifting magnetic fields (rotating magnetic field in a rotating type) are produced relative to the secondary yoke 204, and eddy currents flow in the secondary conductors 201, 202 and 203, and these eddy currents intersect the shifting magnetic fields from the primary coils, thereby producing a thrust, as described above for the preceding embodiment.

In the present invention, since the secondary parts are fixed, the primary parts are moved in the Z-direction by the produced thrust.

Fig. 11 is a block diagram of a drive circuit of the second embodiment of the present invention. As shown in this Figure, in the first linear induction motor, the primary coils 101 are connected to a threephase inverter 301, and three-phase alternating current is supplied to the primary coils 101 to produce a thrust, thereby moving the primary part. The second linear induction motor is of a similar construction.

Here, the position of the moving primary part is detected by a position detector 311, and a position calculator 308 effects a suitable adjustment by a control parameter to provide a position feedback signal Pf. The speed of the primary element is detected by a speed detector 312, and a speed calculator 307 effects a suitable adjustment by a control parameter to provide a speed feedback signal Vf.

The position feedback signal Pf is compared with a position instruction Pc, and its error is adjusted by a control parameter in a position controller 306, and is outputted as a speed instruction Vc. This speed instruction Vc is inputted into a speed controller 302 for the first linear induction motor and a speed controller 304 for the second linear induction motor.

The pull forces of the first and second linear induction motors are detected by pull force detectors 324 and 325, respectively, and are suitably adjusted by a control parameter in pull force calculators 322 and 323, respectively, and are compared with a reference pull force 321, and their errors are outputted to the speed controllers 302 and 304, respectively.

In response to the speed instruction, the speed controllers 302 and 304 calculate a drive frequency, exciting current and thrust current in accordance with the motor speed feedback Vf and three-phase current feedback If, and calculate respective three-phase current instructions, and output respective current instructions to the three-phase inverters 301 and 303. Three-phase alternating currents of arbitrary magnitude and frequency are applied respectively from the three-phase inverters 301 and 303 to the primary coils of the first and second linear induction motors.

In this embodiment, the pull forces of the first and second linear induction motors are calculated, respectively, and these forces are compared with the reference pull force, and their errors are outputted to the speed controllers 302 and 304 of the first and second linear induction motors, respectively. If the error of the pull force is positive (that is, the pull force is larger than the reference pull force), each of the speed controllers 302 and 304 decreases the thrust current. If the error of the pull force is negative (that is, the pull force is smaller than the reference pull force), each of the speed controllers 302 and 304 increases the thrust current.

By doing so, the pull forces vary in accordance with the increase and decrease of the thrust current, and therefore are controlled to be brought into agreement with the reference pull force. If in one of the first and second linear induction motors, the thrust current increases to increase the pull force, the thrust current decreases in the other motor to decrease the pull force by an amount corresponding to the amount of increase of the pull force in the one motor. Thus, the thrust, produced by the combination of the first and second linear induction motors, can be kept to a level determined in accordance with the speed control.

Therefore, in this embodiment, the pull forces of the first and second linear induction motors, directed respectively toward the secondary conductors at the thrust-producing portions, are controlled to be equal to each other, and the force hardly acts on the rollers and the travel path, and therefore there can be obtained the linear induction motor which produce less noises and vibrations and is excellent in durability.

It has been difficult to shorten the air gap in order to increase the thrust, since the increase of the pull force is larger than the increase of the thrust, which increases the burden on the support mechanism such as rollers. In this embodiment, the pull force can always be kept to zero, and therefore the thrust can be enhanced by shortening the air gap.

Fig. 12 is an example in which the second embodiment of the present invention is applied to an elevator. As shown in this Figure, a cage 401 is supported on guides 405, and is movable upward and downward. The cage 401 is connected to the primary part of the linear motor by a rope 402 through pulleys 403 and 404. The secondary part 20 is provided parallel to the cage 401, and the primary part 10 is movable along the secondary part 20.

Furthermore, this linear induction motor produces less noises and vibrations, and is excellent in durability, and therefore noises and vibrations of the elevator can be reduced, thereby improving the durability of the elevator.

Fig. 13 is a third embodiment in which the present invention is applied to an elevator. In this embodiment, those portions, identical respectively to those of the elevator of Fig. 6 to which the first embodiment is applied, are designated by identical reference numerals, respectively.

In this embodiment, motor guides 160 for guiding a primary part 10 are provided respectively on opposite sides of the primary part 10, and rollers 153 for rolling along the motor guides 160 are mounted on the primary part 10. The rollers 153 are provided at four corners of the primary part 10. At each of these corners, one roller for suppressing the displacement of the primary part 10 toward the motor guide is provided, and two rollers for suppressing the displacement of the primary part 10 toward secondary parts (that is, in a direction to vary an air gap) are provided at two thrustproducing portions, respectively. Thus, a total of 12 rollers are provided. With this arrangement, the primary part 10 travels along the motor guides 160 for exclusive use, and therefore fine gaps can be maintained, and the efficiency and power factor can be enhanced.

The thrust-producing portions are disposed parallel to an entrance/exist of a cage, and therefore a dead space can be reduced, and a floor area occupied by the cage and the linear motor can be reduced. And besides, the secondary parts 21 are not of a U-shaped configuration, but are of such a construction that the primary part 10 is interposed between the secondary parts, and therefore instead of the motor guides 160 for exclusive use, a rail for guiding a counterweight of the elevator can guide the movement of the linear motor.

Fig. 14 shows a fourth embodiment of the present invention in which the width of a motor is reduced. In Fig. 14, each of secondary conductors 201 and 202 corresponding to those of the embodiment of Fig.

2 is thickened at its end portions in its cross-sectional shape in the XY plane.

Usually, in order to make the secondary current density constant, the end portions of a secondary conductor must extend a pole pitch beyond the width of a primary core. This means that the amount of extending at each end portion is about 1/2 pole pitch. Therefore, the width of the secondary conductor and hence the width of the secondary part is larger.

By thickening the end portions of the secondary conductor as in the present invention, the width of the end portions can be reduced if the secondary current density is constant. Therefore, the width of the secondary part can be reduced, thereby achieving a compact design.

Fig. 15 shows a drive circuit as a fifth embodiment of the present invention for eliminating the influence of pull forces. The embodiment of Fig. 15 differs from the embodiment of Fig. 11 in that instead of controlling the pull forces of the first and second linear induction motors to be equal to each other, means for controlling gaps to be equal to each other is provided.

Those portions of this embodiment different from the embodiment of Fig. 11 will now be described.

Air gaps at thrust-producing portions of the first and second linear induction motors facing a magnetic yoke of a secondary part are detected respectively by gap detectors 329 and 330, and are suitably adjusted by a control parameter in gap calculators 327 and 328, respectively, and are compared with a reference gap 326, and their errors are outputted to speed controllers 302 and 304, respectively.

In this embodiment, the gaps of the first and second linear induction motors are calculated, respectively, and these gaps are compared with the reference gap, and their errors are outputted to the speed controllers 302 and 304 of the first and second linear induction motors, respectively. If the error of the gap is positive (that is, the gap is larger than the reference gap), each of the speed controllers 302 and 304 reduces the thrust current to decrease the pull force.

If the error of the gap is negative (that is, the gap is smaller than the reference gap), each of the speed controllers 302 and 304 increases the thrust current to increase the pull force.

With this arrangement, when one of the two gaps provided respectively in the first and second linear induction motors increases, so that the pull force at this side is reduced, the other gap decreases, so that the pull force at this side is increased. By this difference between the pull forces, the two gaps are always controlled to be brought into agreement with the reference gap.

If in one of the first and second linear induction motors, the thrust current increases to decrease the gap, the thrust current decreases in the other motor to decrease the pull force by an amount corresponding to the amount of increase of the pull force in the one motor. Thus, the overall thrust, produced by the first and second linear induction motors, can be kept to a level determined in accordance with the speed control.

Thus, in this embodiment, the gaps of the first and second linear induction motors are controlled to be equal to each other. Therefore, even if the use of the longitudinal rollers 151 shown in Figs. 7 to 10 is omitted, the motor can travel, while maintaining the predetermined gaps, and therefore there can be obtained the linear induction motor which produces less noses and vibrations, and is excellent in durability.

Fig. 16 shows the appearance of a primary part according to a sixth embodiment of the present invention.

In this embodiment, the manner of winding of the primary coils 101 in the embodiment of Fig. 4 is modified.

Details thereof will now be described.

A U-phase coil 111, a V-phase coil 112 and a W-phase coil 113 which are constituents of the primary coils 101 are so arranged that one sides of these coils facing one thrust-producing portion (disposed at the left side in Fig. 16) are reverse to the other sides of these coils facing the other thrust-producing portion (disposed at the right side) in an upward-downward direction. The upward and downward directions in Fig. 16 are the directions of shifting of the magnetic fields, and current is applied to the coils 101 in such a manner that the magnetic fields shift in these directions.

For example, when current is applied sequentially to the U-phase, V-phase and W-phase, the magnetic field shifts downward at the left side of Fig.

16. In contrast, the magnetic field shifts upward at the right side of Fig. 16. Therefore, the direction of the shifting magnetic field produced at the right thrustproducing portion is opposite to the direction of the shifting magnetic field produced at the left thrustproducing portion. In other words, the thrusts produced respectively at the right and left sides act in opposite directions, respectively.

Fig. 17 shows an example in which the sixth embodiment of the present invention is applied to a man conveyor. Fig. 17 shows a so-called moving walk for transporting passengers in a horizontal direction. The passengers stand on pallets 411, and the pallets are moved horizontally to convey the passengers. A plurality of pallets 411 are mechanically connected to one another to provide a pallet train, and the direction of movement of the pallets is changed by two rollers 410. The pallet train is driven in a circulating manner, and only the upper portion of the pallet train is used for conveying the passengers. A plurality of primary part 10 of Fig.

16 are provided between the upper and lower portions of the train of pallets 411, and are spaced at intervals. A secondary part 20 is provided on those surfaces of the pallets facing the primary parts 10.

With this construction, the magnetic fields, produced respectively on the upper and lower sides of the primary parts 10, act in opposite directions, respectively, as described above for Fig. 16. Therefore, for example, each primary part 10 can produce a left thrust relative to the upper portion of the pallet train, and also can produce a right thrust relative to the lower portion of the pallet train, so that the pallets can be smoothly driven to provide a moving walk.

As described above, the coil portions of the primary part at the non-thrust producing portions are shorter than the coil portions at the thrust-producing portions, and therefore the vertical dimension of the primary part in Fig. 17 is small, and the distance between the upper and lower portions of the pallet train can be reduced. This provides an advantage that the apparatus can be reduced in thickness.

Referring to other application than the above, the primary part of the embodiment of the present invention is mounted on a carriage of a conveyor apparatus disposed on rails for movement therealong, and the secondary part of the embodiment of the present invention is provided along the rails. With this arrangement, there can be obtained the conveyor apparatus which is simplified in construction by the use of the linear motor, and can be easily manufactured, and achieves a high efficiency.

The secondary part of the embodiment of the present invention is mounted on a movable portion of an escalator, and the primary part of the embodiment of the present invention is mounted on the ground. With this arrangement, there can be obtained the escalator which is simplified in construction by the use of the linear motor, and can be easily manufactured, and achieves a high efficiency.

In the above embodiments, although the longitudinal rollers for maintaining the gaps at the thrust-producing portions are provided at one ends of the thrust-producing portions, the rollers may be provided at both ends in such a manner that the thrust-producing portions are disposed between the rollers.

Although the rollers run over the magnetic material of the secondary part, the rollers may run over the electrically-conductive materials, that is, the secondary conductors.

Instead of the rollers and the travel surfaces, sliding members may be mounted on the primary part and the secondary part so that the gaps can be maintained through sliding contact.

The above-mentioned coil end portions will now be described with reference to Fig. 18 showing the structure of primary parts.

Figs. 18A, 18B and 18C show the structure of a conventional primary part, and Figs. 18D, 18E and 18F show the structure of a primary part of the present invention.

Figs. 18A and 18D are views showing the appearance of the primary parts, Figs. 18B and 18E are views showing only coils of the primary parts, and Figs.

18C and 18F are cross-sectional views of the primary parts.

In the structure of Fig. 18A, coils are provided on one flat surface of a magnetic material in a three-phase manner, and therefore for example, the U-phase coil, while reaching the U-phase at the next slot, overlaps the V-phase and W-phase coils to form large coil end portions. And besides, since the coils are wound at one flat surface, a plurality of coils are disposed at the coil end portions, and large ineffective portions Lbl of the coils as contrasted with effective portions Lal of the coils are formed, as can be seen from Fig. 18B, which results in the formation of the large coil end portions.

In contrast, in the present invention, the coils are wound on the outer periphery of the magnetic material of a rectangular parallelepipedic shape in cross-sectional planes through this magnetic material, as shown in Figs. 18D, 18E and 18F, and any one of the U-phase, V-phase and W-phase coils overlaps the other two at its connecting portions, and therefore the coil end portions can be made smaller. The magnetic material is formed into an acceptable minimum thickness, taking the magnetic flux and the strength into consideration, and therefore ineffective portions Lb2 of the coils can be made sufficiently short relative to effective portions Lbl of the coils, so that the lowering of an efficiency due to the coil end portions can be kept to a minimum.

In the above embodiments, although the linear induction motors have been described, a linear synchronous motor of a similar construction can be provided, in which case similar effects can be achieved by shortening coil end portions.

In the present invention, since those portions of the electrically-conductive materials not contributing to the motor output, that is, the coil end portions, can be made small, there can be obtained the flat linear motor generally equivalent in efficiency to a cylindrical linear motor. Thus, there can be obtained the linear motor which can be easily manufactured, and achieves a high efficiency.

Furthermore, since the construction and control means for balancing the pull forces are used, there can be obtained the linear motor in which the burden on the support mechanism for the rollers is low, and vibrations and noises are small, and the durability is excellent.

Claims

1. A linear motor comprising a primary part comprising coils, and a magnetic material; secondary parts each comprising an electrically-conductive material, a magnetic material, or a combination of an electrically-conductive material and a magnetic material, wherein a thrust is produced by opposed portions of said primary part and said secondary part; in which said primary part is mounted on a moving member, and has a quadrilateral shape in its cross-section perpendicular to a direction of movement of the linear motor; and opposite two of four sides of said quadrilateral primary part which respectively face said secondary parts to produce thrusts are longer than the other sides.

2. A linear motor comprising a primary part comprising coils, and a magnetic material; secondary parts each comprising an electrically-conductive material, a magnetic material, or a combination of an electrically-conductive material and a magnetic material, wherein a thrust is produced by opposed portions of said primary part and said secondary parts; in which a pair of said thrust-producing portions are formed at the same time by said primary part and said secondary parts which share said primary part, and are independent of each other.

3. A linear motor comprising a primary part comprising coils, and a magnetic material; secondary parts each comprising an electrically-conductive material, a magnetic material, or a combination of an electrically-conductive material and a magnetic material, wherein a thrust is produced by opposed portions of said primary part and said secondary parts; in which said thrust-producing portions are formed by said single primary part and said secondary parts which are provided in a manner to interpose said primary part therebetween.

4. A linear motor comprising a primary part comprising coils, and a magnetic material; secondary parts each comprising an electrically-conductive material, a magnetic material, or a combination of an electrically-conductive material and a magnetic material, wherein a thrust is produced by opposed portions of said primary part and said secondary parts; in which said primary coils are provided on a moving member, and are arranged along a direction of movement, and are wound on an outer periphery of said primary magnetic material in cross-sectional planes passing through said primary magnetic material perpendicularly to the direction of movement; and said secondary parts are opposed to each other over an entire travel stroke of said moving member in such a manner that said primary part is interposed between said secondary parts.

5. A linear motor comprising a primary part comprising coils, and a magnetic material; secondary parts each comprising an electrically-conductive material, a magnetic material, or a combination of an electrically-conductive material and a magnetic material, whereby a thrust is produced by opposed portions of said primary part and said secondary parts; in which said coils produce magnetic fluxes in said primary magnetic material in a direction of movement of the linear motor; and said secondary parts are provided in a manner to interpose said primary part therebetween, and share said primary coils so as to produce thrusts.

6. A linear motor comprising a primary part for producing shifting magnetic fields; and two secondary parts provided in a manner to interpose said primary part therebetween, whereby thrust-producing portions of the linear motor are formed by said two secondary parts and two surfaces of said primary part respectively facing said two secondary parts; in which there is provided a magnetic material disposed in opposed relation to other surfaces of said primary part; and there is provided guide means for guiding a relative movement between said primary part and said secondary parts, said guide means utilizing magnetic pull forces produced between said primary part and said magnetic material.

7. A linear motor comprising a primary part for producing shifting magnetic fields; and two secondary parts provided in a manner to interpose said primary part therebetween, whereby a thrust-producing portion of the linear motor is formed between each of said two secondary parts and each of two surfaces of said primary part respectively facing said two secondary parts; in which guide means for maintaining a gap between said primary part and each of said secondary parts at said thrust-producing portion is provided between a magnetic material of said secondary parts and said primary part.

8. A linear motor comprising a primary part comprising coils, and a magnetic material; secondary parts each comprising an electrically-conductive material, a magnetic material, or a combination of an electrically-conductive material and a magnetic material, whereby a thrust is produced by opposed portions of said primary part and said secondary parts; in which there are provided two said primary parts disposed parallel to each other; there is provided a secondary conductor which is interposed between and shared by said two primary parts; and there are provided two said secondary parts respectively facing those surfaces of said two primary parts facing away from said secondary conductor.

9. A linear motor comprising a primary part comprising coils, and a magnetic material; secondary parts each comprising an electrically-conductive material, a magnetic material, or a combination of an electrically-conductive material and a magnetic material, wherein said primary part is interposed between said secondary parts and a thrust is produced by two opposed portions of said primary part and said secondary parts; in which portions for respectively producing shifting magnetic fields acting respectively in opposite directions with respect to a direction of movement of the linear motor are provided at those two surfaces of said primary part serving to produce the thrust.

10. An elevator wherein a cage is moved upward and downward in an elevation path having a plurality of floors; in which secondary parts each comprising an electrically-conductive material, a magnetic material, or a combination of an electrically-conductive material and a magnetic material are provided on a rear side of said cage in the elevation path in parallel relation to an entrance/exit of said cage; a primary part comprising coils and a magnetic material is interposed between said secondary parts, opposed portions of said primary part and said secondary parts producing a linear motor thrust; and said cage is connected to said primary part by a rope so as to be driven.

11. A conveyor wherein pallets connected together in an endless manner are driven for conveying passengers; in which there is provided a primary part comprising coils and a magnetic material; a secondary part of an endless construction is mounted on an inner periphery of a train of said pallets in surrounding relation to a periphery of said primary part, said secondary element comprising an electrically-conductive material, a magnetic material, or a combination of an electrically-conductive material and a magnetic material; and two portions for respectively producing linear motor thrusts acting respectively in opposite directions are provided respectively at two opposed portions of said endless secondary part and said.primary part.

12. A linear motor substantially as herein described with reference to and as illustrated in Figs. 1 to 6, or Figs. 7 to 12 or Fig. 13 or Fig. 14 or Figs. 16 and 17 of the accompanying drawings.

13. An elevator substantially as herein described with reference to and as illustrated in Fig . 6 or Fig. 12 or Fig. 13.

14. A conveyer substantially as herein described with reference to and as illustrated in Fig. 17 of the accompanying drawings.