Cylindrical linear motor

Abstract

To provide a cylindrical linear motor which can further reduce cogging thrust.SOLUTION: A cylindrical linear motor 1 comprises: a field magnet 6 in which N poles and S poles are alternately arranged in an axial direction; and an armature E which can move in the axial direction with respect to the field magnet 6. The armature E includes: a cylindrical core 2 which is a magnetic body; and windings 3 attached to the core 2. The core 2 includes: a plurality of teeth 2b with trapezoidal axial cross sections; a slot 2c to which the windings 3 are attached; auxiliary salient poles 2e1 and 2e2 provided on end sides of teeth 2b1 and 2b2 at both axial ends; and chamfered parts 2d1 and 2d2 provided around a field magnet side on end sides of the auxiliary salient poles 2e1 and 2e2. An axial length X of end faces 2b11, 2b21, 2e11 and 2e21 of the teeth 2b1 and 2b2 and the auxiliary salient poles 2e1 and 2e2 in both ends, which face the field magnet 6, is set to reduce cogging thrust by the core 2 with cogging thrust by the auxiliary salient poles 2e1 and 2e2 of the core 2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a tubular linear motor.

Background Art

[0002] A tubular linear motor includes, for example, a cylindrical stator case, a core having a plurality of teeth mounted on the inner circumference of the stator case and arranged axially side by side on the inner circumference, and a U-phase, a V-phase, and a W-phase winding mounted in slots between the teeth. And a stator, and a rotor movably inserted into the inner circumference of the stator and provided with a plurality of permanent magnets on the outer circumference.

[0003] In the tubular linear motor configured as described above, in order to smooth the change in magnetic flux at both ends of the core and reduce the cogging thrust generated when the rotor moves axially with respect to the stator, auxiliary salient poles are provided at both axial ends of the core. (For example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In such a tubular linear motor, the cogging thrust due to the end effect can be reduced by providing auxiliary salient poles. However, since the cogging due to the core includes harmonic components, the cogging thrust cannot be sufficiently reduced. Therefore, further reduction of the cogging thrust is desired. The cogging thrust due to the core refers to the unbalanced force generated because the tooth shape at the core end is different from the tooth shape at the core middle part, and the period of the cogging thrust due to the core is 2N (N is a natural number) per electrical angle cycle.

[0006] Therefore, an object of the present invention is to provide a tubular linear motor capable of further reducing cogging thrust.

Means for Solving the Problems

[0007] To achieve the above object, the tubular linear motor of the present invention ,shaft includes a field magnet in which N poles and S poles are alternately arranged in a direction, and an armature that is movable axially with respect to the field magnet. The armature has a magnetic body that is a cylindrical core and windings mounted on the core. The core has a cylindrical yoke, a plurality of teeth that are provided annularly along the circumferential direction on the field magnet side of the inner circumference or outer circumference of the yoke and have a trapezoidal cross-section in the axial direction, slots in which windings formed in the gaps between the teeth are mounted, auxiliary salient poles provided on the end sides of the teeth at both axial ends, and chamfered portions provided around the end sides of the auxiliary salient poles on the field magnet side and spaced apart from the field magnet toward the end sides. The axial lengths of the end faces of the teeth and the auxiliary salient poles at both ends facing the field magnet at a constant interval are set to a length that is half of the pole pitch.

[0008] In the tubular linear motor configured as described above, since the core has teeth with a trapezoidal cross-section and the core has chamfered portions at the auxiliary salient poles at both axial ends, the waveforms of the cogging thrust due to the core and the cogging thrust due to the auxiliary salient poles of the core become sinusoidal waveforms with less distortion. Further, since the axial lengths of the end faces of the teeth and the auxiliary salient poles at both ends facing the field magnet are set so as to reduce the cogging thrust due to the core by the cogging thrust due to the auxiliary salient poles of the core, the phases of the cogging thrust due to the core with a sinusoidal waveform with less distortion and the cogging thrust due to the auxiliary salient poles of the core can be adjusted so that the thrusts cancel each other out by the setting of the length. Furthermore, with a cylindrical linear motor configured in this manner, the waveform of the cogging thrust due to the core and the waveform of the cogging thrust due to the auxiliary salient pole of the core are exactly in opposite phases, so they cancel each other out efficiently, minimizing the overall cogging thrust of the cylindrical linear motor.

[0009] In addition, the core in the tubular linear motor includes a central core split body including teeth at both axial ends, a pair of spacers that are annular and laminated on both axial ends of the central core split body respectively, and a pair of end-side core split bodies that are annular and laminated on the side opposite to the central core split body in the axial direction of the spacers and have the chamfered portions. The spacers and the end-side core split bodies may function as auxiliary salient poles. According to the tubular linear motor configured in this way, by replacing the spacers, the axial position of the end-side core split body with respect to the central core split body can be adjusted so that the cogging thrust by the core and the cogging thrust by the auxiliary salient poles of the core can be efficiently canceled out.

[0010] Furthermore, the core in the tubular linear motor includes a central core split body including teeth at both axial ends, and a pair of end-side core split bodies that are annular and laminated on both axial ends of the central core split body respectively and have chamfered portions. The end-side core split bodies may function as auxiliary salient poles. According to the tubular linear motor configured in this way, if an end-side core split body having an optimal axial length according to the number of pole slots of the tubular linear motor is used, the cogging thrust by the core and the cogging thrust by the auxiliary salient poles of the core can be efficiently canceled out without changing the design of the central core split body.

Advantages of the Invention

[0012] According to the tubular linear motor of the present invention, the cogging thrust can be further reduced.

Brief Description of the Drawings

[0013] [Figure 1] It is a longitudinal sectional view of a tubular linear motor in an embodiment. [Figure 2] It is a partially enlarged view of the armature of the tubular linear motor in an embodiment. [Figure 3] It is a diagram showing the waveform of the cogging thrust by the core, the waveform of the cogging thrust by the auxiliary salient poles of the core, and the waveform of the overall cogging thrust of the tubular linear motor. [Figure 4]It is a longitudinal sectional view of a core of a tubular linear motor in a first modification of an embodiment.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described based on the embodiments shown in the drawings. As shown in FIG. 1, a tubular linear motor 1 in an embodiment includes an armature E having a tubular field magnet 6 in which N poles and S poles are alternately arranged in the axial direction, a tubular core 2, and windings 3 attached to the core 2.

[0015] Hereinafter, each part of the tubular linear motor 1 will be described in detail. In the present embodiment, the field magnet 6 includes an annular main pole permanent magnet 6a and an annular sub-pole permanent magnet 6b that are alternately laminated and inserted in the axial direction, and is configured to be tubular. Further, a tubular back yoke 8 is attached to the outer periphery of the field magnet 6. The field magnet 6 and the back yoke 8 are accommodated in an annular gap formed between a cylindrical non-magnetic outer tube 7 and a cylindrical non-magnetic inner tube 9 inserted into the outer tube 7.

[0016] Note that the triangular marks shown on the main pole permanent magnet 6a and the sub-pole permanent magnet 6b in FIG. 1 indicate the magnetization directions. The magnetization direction of the main pole permanent magnet 6a is in the radial direction, and the magnetization direction of the sub-pole permanent magnet 6b is in the axial direction. The main pole permanent magnet 6a and the sub-pole permanent magnet 6b are arranged in a Halbach array, and on the inner peripheral side of the field magnet 6, the S poles and N poles appear alternately in the axial direction.

[0017] Also, the axial length L1 of the permanent magnet 6a of the main pole is longer than the axial length L2 of the permanent magnet 6b of the sub-pole. In the present embodiment, the axial length L1 of the permanent magnet 6a of the main pole and the axial length L2 of the permanent magnet 6b of the sub-pole are set so as to satisfy 0.2 ≦ L2 / L1 ≦ 0.5. If the axial length L1 of the permanent magnet 6a of the main pole is increased, the magnetic resistance between the permanent magnet 6a of the main pole and the core 2 can be reduced, and the magnetic field acting on the core 2 can be increased, so that the mass thrust density of the tubular linear motor 1 can be improved.

[0018] Also, in the tubular linear motor 1 of the present embodiment, a back yoke 8 is provided on the outer periphery of the permanent magnets 6a and 6b. When the back yoke 8 is not provided, if the axial length L2 of the permanent magnet 6b of the sub-pole becomes short, the magnetic resistance outside the magnet at the axial center portion of the permanent magnet 6a of the main pole increases, and the field magnetic flux decreases. Therefore, the degree of improvement in the thrust of the tubular linear motor 1 when the axial length L1 of the permanent magnet 6a of the main pole is increased becomes small. On the other hand, when the back yoke 8 is provided on the outer periphery of the permanent magnets 6a and 6b, a magnetic path with low magnetic resistance can be secured, so that an increase in magnetic resistance caused by shortening the axial length L2 of the permanent magnet 6b of the sub-pole is suppressed. Therefore, when the axial length L1 of the permanent magnet 6a of the main pole is made longer than the axial length L2 of the permanent magnet 6b of the sub-pole and the cylindrical back yoke 8 is provided on the outer periphery of the permanent magnets 6a and 6b, the mass thrust density of the tubular linear motor 1 can be greatly improved. The thickness of the back yoke 8 may be set to a thickness suitable for suppressing an increase in the external magnetic resistance of the permanent magnet 6a of the main pole.

[0019] Note that the permanent magnet 6b of the auxiliary pole is a permanent magnet having a coercive force higher than that of the permanent magnet 6a of the main pole. The residual magnetic flux density and the coercive force in a permanent magnet are closely related to each other. Generally, when the residual magnetic flux density is increased, the coercive force decreases, and when the coercive force is increased, the residual magnetic flux density decreases, which is an inverse relationship. In the Halbach array, since a large magnetic field is applied to the permanent magnet 6b of the auxiliary pole in the demagnetization direction, the coercive force of the permanent magnet 6b of the auxiliary pole is increased to suppress demagnetization so that a large magnetic field can act on the core 2. On the other hand, the strength of the magnetic field acting on the core 2 depends on the number of magnetic field lines of the permanent magnet 6a of the main pole. Therefore, a permanent magnet with a high residual magnetic flux density is used for the permanent magnet 6a of the main pole to act a large magnetic field on the core 2. In the present embodiment, when making the coercive force of the permanent magnet 6b of the auxiliary pole higher than that of the permanent magnet 6a of the main pole, the material of the permanent magnet 6b of the auxiliary pole is a material having a higher coercive force than the material of the permanent magnet 6a of the main pole. Therefore, by selecting the material, the combination of the permanent magnet 6a of the main pole and the permanent magnet 6b of the auxiliary pole can be easily realized. In the present embodiment, the permanent magnet 6a of the main pole is composed of a material having a high residual magnetic flux density mainly composed of neodymium, iron, and boron, and the permanent magnet 6b of the auxiliary pole is composed of a magnet that is difficult to demagnetize by increasing the addition amount of heavy rare earth elements such as dysprosium and terbium to the above material.

[0020] Further, the core 2 is inserted on the inner peripheral side of the stator, and the field magnet 6 acts a magnetic field on the core 2. Note that since the field magnet 6 only needs to act a magnetic field on the movable range of the core 2, the installation range of the permanent magnets 6a and 6b may be determined according to the movable range of the core 2. Therefore, in the annular gap between the outer tube 7 and the inner tube 9, it is not necessary to install the permanent magnets 6a and 6b in a range where they cannot face the core 2. Note that the field magnet 6 is composed of the permanent magnets 6a and 6b laminated in the Halbach array in the present embodiment. However, since it is only necessary that the N pole and the S pole appear alternately on the inner periphery, it may be composed of permanent magnets laminated in an array other than the Halbach array.

[0021] The left ends of the outer tube 7, back yoke 8 and inner tube 9 in FIG. 1 are closed by caps 14, and the right ends of the outer tube 7, back yoke 8 and inner tube 9 in FIG. 1 are closed by an annular head cap 15.

[0022] The armature E is configured to include a cylindrical core 2 and a winding 3 attached to the core 2, and is inserted into the inner tube 9 so as to be movable in the axial direction. That is, in this embodiment, the armature E is disposed on the inner peripheral side of the field magnet 6, and can move relative to the field magnet 6 in the axial direction.

[0023] In this embodiment, the core 2 is made of permendur material and comprises a cylindrical yoke 2a, a plurality of annular teeth 2b with trapezoidal axial cross sections arranged circumferentially and axially spaced apart on the outer periphery of the yoke 2a on the field side, slots 2c formed by gaps between the teeth 2b, 2b in which the windings 3 are fitted, auxiliary salient poles 2e1, 2e2 respectively provided on the axial end sides of the teeth 2b1, 2b2 at both axial ends of the core 2 among the teeth 2b, and chamfered portions 2d1, 2d2 provided around the outer periphery on the field side of the auxiliary salient poles 2e1, 2e2.

[0024] As mentioned above, the yoke 2a is cylindrical, and its thickness is ensured so that its cross-sectional area is greater than or equal to the cross-sectional area created when the teeth 2b are cut with a cylinder centered on the axis of the core 2, from the inner circumference to the outer circumference of the teeth 2b.

[0025] In this embodiment, as shown in FIGS. 1 and 2, 13 teeth 2b are provided on the outer periphery of the yoke 2a at equal intervals in the axial direction. On the outer peripheral side of the core 2 on the field magnet 6 side, a slot 2c is formed, which is an annular groove where the winding 3 is mounted between the teeth 2b, 2b. In this embodiment, the teeth 2b have a trapezoidal cross-sectional shape, and the width of the base end side on the inner periphery is larger than the width of the tip end side on the outer periphery, so as to ensure a larger magnetic path cross-sectional area on the base end side. More specifically, each tooth 2b has a trapezoidal cross-section, but the teeth 2b other than the teeth 2b1, 2b2 arranged at both ends in the axial direction of the core 2 have an isosceles trapezoidal shape. In this embodiment, the teeth 2b1, 2b2 arranged at both ends in the axial direction of the core 2 have a cross-sectional shape obtained by dividing the tooth 2b in half at the center in the axial direction, and the axial width of the outer periphery of the teeth 2b1, 2b2 is 1 / 2 of the axial width Y of the outer periphery of the tooth 2b. Therefore, in this embodiment, the auxiliary salient poles 2e1, 2e2 are formed at both ends of the core 2 from a point Y / 2 from the slot 2c side end of the teeth 2b1, 2b2 at the end of the core 2, and are integrally inseparable from the end teeth 2b1, 2b2. Note that the axial width of the outer periphery of the end tooth 2b is set to Y / 2, but it can be arbitrarily changed.

[0026] In this embodiment, a total of 12 slots 2c, which are annular grooves, are provided between adjacent teeth 2b, 2b in FIG. 1. A plurality of slots 2c are provided along the circumferential direction of the core 2, and are arranged on the outer periphery of the core 2 at equal pitches in the axial direction.

[0027] And the winding 3 is wound and mounted in this slot 2c. The winding 3 is a three-phase winding of U-phase, V-phase, and W-phase. The windings 3 of each phase are mounted in the 12 slots 2c so as to have an arrangement suitable for the pole arrangement of the field magnet 6.

[0028] Also, in FIGS. 1 and 2, the core 2 is provided with chamfered portions 2d1, 2d2 which are provided on the end sides of the auxiliary salient poles 2e1, 2e2 provided on the end sides of the teeth 2b1, 2b2 provided at both axial ends, and which are chamfered in an R shape around the outer peripheral side which becomes the field side.

[0029] The armature E configured in this way is attached to the outer periphery of the tip of a rod 11 formed of a non-magnetic material which is an output shaft, and is movably inserted into the field 6 together with the rod 11. In the tubular linear motor 1 of the present embodiment, the field 6 and the armature E configured as described above constitute an 8-pole 9-slot linear motor. Note that the combination of the number of poles and the number of slots can be changed as appropriate.

[0030] The rod 11 projects outside the tubular linear motor 1 through the inside of a head cap 15 attached to the right end in FIG. 1 of the outer tube 7. Also, sliders 12, 13 which are in sliding contact with the inner periphery of the inner tube 9 are attached to the left and right of the armature E of the rod 11 in FIG. 1. The armature E is sandwiched by the sliders 12, 13 and the core 2 is fixed to the rod 11. Further, since the sliders 12, 13 are in sliding contact with the inner periphery of the inner tube 9, the armature E does not shift axially with respect to the field 6, and thus can move axially without interfering with the inner tube 9.

[0031] In this way, the inner tube 9 forms a high-magnetic-resistance gap between the outer circumference of the core 2 and the inner circumference of the field magnet 6, and cooperates with the sliders 12 and 13 to guide the axial movement of the armature E. The outer diameter of the core 2 is smaller than the inner diameter of the inner tube 9 and does not interfere with the inner tube 9, so that the tubular linear motor 1 can smoothly expand and contract. However, it may also be in sliding contact with the inner circumference of the inner tube 9. Note that the inner tube 9 may be formed of a non-magnetic material, but when formed of a synthetic resin, the effect of improving the thrust density of the tubular linear motor 1 is enhanced. When the inner tube 9 is manufactured from a non-magnetic metal, eddy currents are generated inside the inner tube 9 when the armature E moves axially, and a force is generated that hinders the movement of the armature E. On the other hand, if the inner tube 9 is made of a synthetic resin, no eddy currents are generated, so that the thrust of the tubular linear motor 1 can be more effectively improved, and the mass of the tubular linear motor 1 can be reduced. Note that when the inner tube 9 is made of a synthetic resin, if it is manufactured from a fluororesin, friction and wear between the inner tube 9 and the sliders 12 and 13 can be reduced. Further, the inner tube 9 may be formed of other synthetic resins, or the inner circumference of the inner tube 9 formed of other synthetic resins may be coated with a fluororesin to reduce friction and wear.

[0032] Note that although not shown in the figure, the rod 11 is cylindrical, and power can be supplied from an external power source installed outside the tubular linear motor 1 to the winding 3 through a wire (not shown) passed through the rod 11.

[0033] Then, for example, by sensing the electrical angle of the winding 3 with respect to the field magnet 6, performing conduction phase switching based on the electrical angle, and controlling the current amount of each winding 3 by PWM control, the thrust in the tubular linear motor 1 and the moving direction of the armature E can be controlled. Note that the above-described control method is only an example and is not limited thereto. Further, when an external force that causes relative displacement between the armature E and the field magnet 6 in the axial direction acts, a thrust that suppresses the relative displacement is generated by energizing the winding 3 or the induced electromotive force generated in the winding 3, so that vibration and movement of the device due to the external force can be damped in the tubular linear motor 1, and energy regeneration that generates electric power from the external force is also possible.

[0034] In the cylindrical linear motor 1 of the present embodiment, the core 2 includes teeth 2b having a trapezoidal cross-section. attitude Thus, when the core 2 includes teeth 2b having a trapezoidal cross-section, the magnetic flux lines from the field magnet 6 side penetrate not only the outer peripheral ends of the teeth 2b but also the side surfaces at both axial ends. Therefore, as shown by the waveform A in FIG. 3, the waveform of the cogging thrust by the core 2 has less harmonic distortion and is closer to a sine wave compared to a conventional cylindrical linear motor using a core with rectangular cross-section teeth. Note that the period of the cogging thrust by the core 2 is determined by the number of slots and the number of poles. Since the cylindrical linear motor 1 of the present embodiment is an 8-pole 9-slot linear motor, it is 5 degrees, which is the value obtained by dividing 360 degrees by the least common multiple of 8 and 9.

[0035] Also, in the cylindrical linear motor 1 of the present embodiment, chamfered portions 2d1, 2d2 that are spaced farther from the field magnet 6 toward the end sides are provided around the outer periphery on the field magnet side of the end sides of the auxiliary salient poles 2e1, 2e2 provided at the end sides of the teeth 2b1, 2b2 at both axial ends of the core 2. Thus, when the core 2 includes chamfered portions 2d1, 2d2 that move away from the field magnet 6 at both axial ends of the auxiliary salient poles 2e1, 2e2, the change in magnetic flux at both axial ends of the armature E becomes smooth. As shown by the waveform B in FIG. 3, the waveform of the cogging thrust by the auxiliary salient poles 2e1, 2e2 of the core 2 has less harmonic distortion and is closer to a sine wave compared to a conventional cylindrical linear motor without chamfered portions. Here, the cogging thrust by the auxiliary salient poles of the core 2 is the force acting on the open surfaces of the auxiliary salient poles 2e1, 2e2. The waveform distortion can be reduced by the shape of the chamfered portions 2d1, 2d2 of the auxiliary salient poles 2e1, 2e2, and the phase can be adjusted by setting the axial length (thickness) from the end portions on the slot 2c side of the teeth 2b1, 2b2 to the chamfered portions 2d1, 2d2 of the auxiliary salient poles 2e1, 2e2.

[0036] As described above, in the cylindrical linear motor 1 of the present embodiment, since the core 2 includes the teeth 2b having a trapezoidal cross section, the waveform of the cogging thrust by the core 2 becomes a sine wave with little distortion. Since the core 2 includes the chamfered portions 2d1 and 2d2 at the auxiliary salient poles 2e1 and 2e2 at both axial ends, the waveform of the cogging thrust by the auxiliary salient poles 2e1 and 2e2 of the core 2 becomes a sine wave with little distortion.

[0037] As described above, since the waveforms of both the cogging thrust by the core 2 and the cogging thrust by the auxiliary salient poles 2e1 and 2e2 of the core 2 are waveforms close to a sine wave, if the phases are adjusted so as to cancel out the cogging thrust by the core 2 and the cogging thrust by the auxiliary salient poles 2e1 and 2e2 of the core 2, the overall cogging thrust of the cylindrical linear motor 1 can be suppressed.

[0038] Therefore, in the tubular linear motor 1 of the present embodiment, the axial length X of the end faces 2b11 and 2b21 facing the field magnet 6 of the teeth 2b1 and 2b2 at both ends and the end faces 2e11 and 2e21 facing the field magnet 6 of the auxiliary poles 2e1 and 2e2 is set so that the cogging thrust by the core 2 can be reduced by the cogging thrust by the auxiliary poles 2e1 and 2e2 of the core 2. Specifically, when the distance between the core 2 and the field magnet 6 from the end on the slot 2c side of the tooth 2b1 (2b2) to the chamfered portion 2d1 (2d2) of the auxiliary pole 2e1 (2e2) is the shortest and the total axial length X of the end faces 2b11 (2b21) and the end faces 2e11 (2e21) facing the field magnet 6 at a constant interval with respect to the field magnet 6 is changed, the phase difference between the waveforms of the cogging thrust by the auxiliary poles 2e1 and 2e2 of the core 2 and the waveform of the cogging thrust by the core 2 can be adjusted. Therefore, in the tubular linear motor 1 of the present embodiment, the length X is set so that the difference between the phase of the waveform of the cogging thrust by the core 2 and the phase of the waveform of the cogging thrust by the auxiliary poles 2e1 and 2e2 of the core 2 becomes 180 degrees, so that the cogging thrust by the core 2 and the cogging thrust by the auxiliary poles 2e1 and 2e2 of the core 2 cancel each other out. More specifically, in the tubular linear motor 1 of the present embodiment, the length X is set to half the pole pitch. As shown in FIG. 3, the waveform A of the cogging thrust by the core 2 and the waveform B of the cogging thrust by the auxiliary poles 2e1 and 2e2 of the core 2 appear with a 180-degree phase difference and cancel each other out, so that the waveform C of the overall cogging thrust of the tubular linear motor 1 can be minimized.

[0039] Note that in order to minimize the overall cogging thrust of the tubular linear motor 1, the axial length X of the end faces 2b11 and 2b21 facing the field magnet 6 most on the field magnet 6 side of the teeth 2b1 and 2b2 and the end faces 2e11 and 2e21 of the auxiliary poles 2e1 and 2e2 may be set so that the difference between the phase of the waveform A of the cogging thrust by the core 2 and the phase of the waveform B of the cogging thrust by the auxiliary poles 2e1 and 2e2 of the core 2 becomes 180 degrees. However, the length X can be freely set as long as the overall cogging thrust of the tubular linear motor 1 can be reduced.

[0040] As described above, the tubular linear motor 1 of the present embodiment includes a field magnet 6 in which N poles and S poles are alternately arranged in the axial direction, and an armature E that is movable in the axial direction with respect to the field magnet 6. The armature E includes a cylindrical core 2 made of a magnetic material and a winding 3 attached to the core 2. The core 2 has a plurality of teeth 2b provided annularly along the circumferential direction on the outer periphery and having a trapezoidal cross-section in the axial direction, slots 2c in which the windings 3 formed in the gaps between the teeth 2b, 2b are attached, auxiliary salient poles 2e1, 2e2 provided at the end sides of the teeth 2b1, 2b2 at both ends in the axial direction, and chamfered portions 2d1, 2d2 provided around the field magnet side at the end sides of the auxiliary salient poles 2e1, 2e2 and spaced apart from the field magnet 6 toward the end sides. The axial lengths X of the end faces 2b11, 2b21, 2e11, 2e21 of the teeth 2b1, 2b2 and the auxiliary salient poles 2e1, 2e2 at both ends facing the field magnet 6 at a constant interval are set so as to reduce the cogging thrust by the core 2 with the cogging thrust by the auxiliary salient poles 2e1, 2e2 of the core 2.

[0041] In the tubular linear motor 1 configured as described above, since the core 2 includes teeth 2b having a trapezoidal cross-section and the core 2 includes chamfered portions 2d1, 2d2 at the auxiliary salient poles 2e1, 2e2 at both ends in the axial direction, the waveforms of the cogging thrust by the core 2 and the cogging thrust by the auxiliary salient poles 2e1, 2e2 of the core 2 become sinusoidal waveforms with less distortion. Further, since the axial lengths X of the end faces 2b11, 2b21, 2e11, 2e21 of the teeth 2b1, 2b2 and the auxiliary salient poles 2e1, 2e2 at both ends facing the field magnet 6 are set so as to reduce the cogging thrust by the core 2 with the cogging thrust by the auxiliary salient poles 2e1, 2e2 of the core 2, the phases of the cogging thrust by the core 2 with a sinusoidal waveform with less distortion and the cogging thrust by the auxiliary salient poles 2e1, 2e2 of the core 2 can be adjusted so that the thrusts cancel each other out by setting the length X. Therefore, according to the tubular linear motor 1 of the present embodiment, the cogging thrust by the core 2 can be reduced by the cogging thrust by the auxiliary salient poles 2e1, 2e2 of the core 2, and the overall cogging thrust of the tubular linear motor 1 can be reduced.

[0042] Furthermore, when the axial lengths X of the end faces 2b11, 2b21, 2e11, 2e21 of the teeth 2b1, 2b2 and the auxiliary salient poles 2e1, 2e2 at both ends facing the field magnet 6 are set such that the phase of the cogging thrust by the core 2 and the phase of the cogging thrust by the auxiliary salient poles 2e1, 2e2 of the core 2 are 180 degrees, the waveform A of the cogging thrust by the core 2 and the waveform B of the cogging thrust by the auxiliary salient poles 2e1, 2e2 of the core 2 are exactly out of phase and can efficiently cancel each other out, minimizing the overall cogging thrust of the tubular linear motor 1.

[0043] In addition, like the tubular linear motor 1A of the first modification of the embodiment shown in FIG. 4, the core in the armature E1 is composed of a central core split body 21 including the teeth 2b1, 2b2 at both axial ends, a pair of spacers 22, 22 that are annular and laminated on both axial ends of the central core split body 21 respectively, and a pair of end-side core split bodies 23, 23 that are annular and laminated on the side opposite to the central core split body in the axial direction and have chamfered portions 23a, 23a. The spacers 22 and the end-side core split bodies 23 may function as auxiliary salient poles. These central core split body 21, spacers 22, 22 and end-side core split bodies 23, 23 are made of a magnetic material.

[0044] The central core split body 21 includes a cylindrical yoke 21a and an annular tooth 21b having a trapezoidal cross section provided on the outer periphery of the yoke 21a. The axial lengths of the teeth 21b1, 21b2 at both ends are shorter than those of the other teeth 21b. The winding 3 is mounted in a slot 21c formed by the gaps between the teeth 21b. The spacers 22, 22 are annular, and their outer peripheral surfaces face the field magnet 6. Also, the outer peripheral surface of the end-side core split body 23 is a curved surface formed by chamfering into an R shape, and the chamfered portion 23a is formed over the entire outer periphery. When the spacers 22, 22 are stacked on both axial ends of the thus configured central core split body 21, and further the end-side core split bodies 23, 23 are laminated from the outside of the spacers 22, 22, a core 2 having the same shape as the core 2 in the tubular linear motor 1 of the embodiment can be formed.

[0045] The end - side core segments 23, 23 are provided with chamfered portions 23a, 23a in order to reduce the distortion of the waveform of the cogging thrust caused by the auxiliary poles of the core 2. The spacer 22 is provided to adjust the phase of the waveform of the cogging thrust of the auxiliary poles of the core 2 with respect to the phase of the waveform of the cogging thrust of the core 2. Here, if a plurality of spacers 22 with different axial lengths are prepared, by replacing the spacer 22, the position of the end - side core segment 23 that generates the cogging thrust by the auxiliary poles of the core 2 can be adjusted with respect to the central core segment 21 that generates the cogging thrust by the core 2.

[0046] Therefore, in this way, for the tubular linear motor 1A constituted by the core 2 including the central core segment 21 including the teeth 2b1, 2b2 at both axial ends, a pair of spacers 22, 22 that are annular and laminated on both axial ends of the central core segment 21 respectively, and end - side core segments 23, 23 that are annular and laminated on the opposite side of the central core segment in the axial direction of the spacers 22, 22 and have chamfered portions 23a, 23a, by replacing the spacer 22, the axial positions of the end - side core segments 23, 23 can be adjusted with respect to the central core segment 21 so that the cogging thrust by the core 2 and the cogging thrust by the auxiliary poles of the core 2 can be efficiently canceled out.

[0047] Note that not all of the outer peripheral surface of the end - side core segment 23 needs to be the chamfered portion 23a, and a part of the outer peripheral surface of the end - side core segment 23 within the range of the length X described above may be configured. Also, the spacer 22 may be configured to include all of the outermost peripheral surfaces of the teeth 2b1, 2b2 on both axial sides of the core 2. In this way, the auxiliary poles may be constituted only by the spacer 22 and the end - side core segment 23, or the spacer 22 and the end - side core segment may constitute not only the auxiliary poles but also a part or all of the teeth at both ends of the core 2, or the spacer 22 and the end - side core segment 23 may constitute a part of the auxiliary poles.

[0048] Furthermore, although not shown in the drawings, the core 2 may be composed of a central core segment 21 and end core segments 23, 23 that are laminated at both ends of the central core segment 21 in the axial direction and have chamfered portions 23a, 23a, with the spacer 22, 23 omitted. The end core segments 23 may function as auxiliary poles. In this case, instead of making the entire outer peripheral surface of the end core segment 23 a chamfered portion 23a, a part or all of the outer peripheral surface of the end core segment 23 within the range of the length X described above may be configured. Also, the auxiliary poles may be constituted only by the end core segments 23, or the end core segments 23 may constitute a part or all of the auxiliary poles and the teeth 2b1, 2b2 at both ends of the core 2, or the end core segments 23 may constitute a part of the auxiliary poles. According to the tubular linear motor configured as described above, by using the end core segments 23, 23 having an optimal axial length according to the number of pole slots of the tubular linear motor, without changing the design of the central core segment 21, the cogging thrust by the core 2 and the cogging thrust by the auxiliary poles 2e1, 2e2 of the core 2 can be efficiently canceled out.

[0049] In the tubular linear motors 1, 1A of each embodiment, the chamfered portions 2d1, 2d2, 23a are formed as curved surfaces with a cross-sectional R shape. However, as long as they are formed on both axial ends of the teeth 2b1, 2b2 or the end core segments 23 on the field side and are chamfered so as to move away from the field 6, they may be formed as tapered surfaces with a C shape.

[0050] Note that the tubular linear motor 1 of the present embodiment has a structure in which the armature E is provided on the inner periphery of the field 6, but it is also possible to adopt a structure in which the armature E is provided on the outer periphery of the field 6. In that case, teeth may be provided on the inner peripheral side of the core 2 that becomes the field side, windings 3 may be mounted in the slots formed between the teeth, and chamfered portions may be provided around the inner periphery of the auxiliary poles at both axial ends of the core 2 on the field side. Then, in this case, the axial length of the inner peripheral surface facing the field from the slot side end of the teeth of the core to the chamfered portion of the auxiliary pole may be set so as to reduce the cogging thrust by the core 2 with the cogging thrust by the auxiliary poles of the core 2.

[0051] As described above, the preferred embodiments of the present invention have been described in detail, but modifications, deformations, and changes are possible without departing from the scope of the claims.

Explanation of Reference Numerals

[0052] 1, 1A... cylindrical linear motor, 2... core, 2a, 21a... yoke, 2b1, 2b2... teeth at both ends, 2b11, 2b21, 2e11, 2e21... end faces, 2c, 21c... slots, 2d1, 2d2, 23a... chamfered portions, 2e1, 2e2... auxiliary salient poles, 3... winding, 6... field magnet, 21... central core split body, 22... spacer, 23... end-side core split body, E, E1... armature

Claims

1. A field magnet in which N poles and S poles are alternately arranged in the axial direction, and an armature movable axially with respect to the field magnet, wherein the armature is a magnetic body and has a cylindrical core, and a winding mounted on the core, wherein the core has a cylindrical yoke, a plurality of teeth provided annularly along the circumferential direction on the field magnet side of the inner circumference or the outer circumference of the yoke, and having a trapezoidal cross-section in the axial direction, a slot in which the winding formed in the gap between the teeth is mounted, auxiliary salient poles provided at the end sides of the teeth at both axial ends, and a chamfer provided at the end side of the auxiliary salient pole and extending around the field magnet side, and being spaced away from the field magnet toward the end side, wherein the axial lengths of the end faces of the teeth at both ends and the auxiliary salient poles facing the field magnet at a constant interval are set to a length of half of the pole pitch. A tubular linear motor characterized by the above.

2. The core has a central core split body including the teeth at both axial ends, a pair of spacers which are annular and laminated on both axial ends of the central core split body respectively, and a pair of end-side core split bodies which are annular and laminated on the side opposite to the central core split body in the axial direction of the spacer and include the chamfer, wherein the spacer and the end-side core split body function as the auxiliary salient poles. The tubular linear motor according to Claim 1, characterized by the above.

3. The core has a central core split body including the teeth at both axial ends, and a pair of end-side core split bodies which are annular and laminated on both axial ends of the central core split body respectively, include the chamfer, and function as the auxiliary salient poles. The tubular linear motor according to Claim 1, characterized by the above.

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