cylindrical linear motor

Abstract

To provide a cylinder type liner motor capable of improving a mass thrust density.SOLUTION: A cylinder type liner motor 1 comprises: a field magnet 6 that has a cylinder shape and includes an N pole and an S pole which are alternately arranged in an axial direction; an armature E that is arranged on an inner peripheral side or an outer peripheral side of the field magnet 6 and can be moved in the axial direction to the field magnet 6; and an inner tube 9 that has a cylinder shape and is formed of a soft magnetic body arranged on the armature side of the field magnet 6. The inner tube 9 comprises a narrow part 9b narrowing a magnetic path area provided in a peripheral direction without across one magnetic pole of the field magnet 6 in the axial direction, between magnetic poles on an inner periphery or an outer periphery.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cylindrical linear motor. [Background technology]

[0002] Some cylindrical linear motors are configured with a cylindrical field magnet formed by stacking multiple annular permanent magnets so that north and south poles appear alternately in the axial direction, and an armature that is positioned on the inner periphery of the field magnet and is movable axially relative to the field magnet (see, for example, Patent Document 1).

[0003] In such conventional cylindrical linear motors, a non-magnetic inner tube is provided between the field magnet and the armature, and the inner tube prevents interference between the armature and the permanent magnet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-097377 Summary of the Invention [Problem to be solved by the invention]

[0005] In such cylindrical linear motors, a non-magnetic inner tube is provided between the field magnet and the armature, which increases the magnetic air gap between the field magnet and the armature, limiting the ability to apply a large magnetic field to the armature.However, if the inner tube were simply made of a soft magnetic material, the magnetic flux of the field magnet would pass through the inner tube, making it difficult to apply a large magnetic field to the armature.

[0006] As such, with conventional cylindrical linear motors, there is a limit to how large a magnetic field can be applied to the armature from the field magnet, making it difficult to further improve the mass thrust density. Here, mass thrust density is the value obtained by dividing the maximum thrust of a cylindrical linear motor by its mass, and the greater the mass thrust density, the greater the thrust per mass of the cylindrical linear motor.

[0007] SUMMARY OF THE INVENTION An object of the present invention is to provide a cylindrical linear motor that can improve the mass thrust density. [Means for solving the problem]

[0008] In order to achieve the above object, the cylindrical linear motor of the present invention comprises a cylindrical field magnet having N poles and S poles arranged alternately in the axial direction, an armature arranged on the inner periphery of the field magnet and movable axially relative to the field magnet, and a cylindrical inner tube made of a soft magnetic material arranged on the armature side of the field magnet, the inner tube having a narrow portion between the magnetic poles that narrows the cross-sectional area of ​​the magnetic path in the circumferential direction without axially spanning one of the magnetic poles of the field magnet.

[0009] In a cylindrical linear motor configured in this manner, narrowed portions that narrow the cross-sectional area of ​​the magnetic path in the circumferential direction are provided between the magnetic poles of the field magnet in the inner tube. By providing narrowed portions that narrow the cross-sectional area of ​​the magnetic path in the inner tube in this way, even if the inner tube is made of a soft magnetic material, the magnetic field can be made to act efficiently on the armature, and by shortening the distance between the field magnet and the armature, a large magnetic field can be made to act on the armature.

[0010] The inner tube may have a slit on one of the inner periphery or outer periphery, and the armature may be disposed on the other of the inner periphery or outer periphery of the inner tube, with the slit forming a narrowed portion that narrows the cross-sectional area of ​​the magnetic path.

[0011] In a cylindrical linear motor configured in this manner, a slit is provided on the field side of the inner tube, which makes it easy to form a narrow space that narrows the cross-sectional area of ​​the magnetic path between the north and south poles of the field magnet in the inner tube.

[0012] Furthermore, in a cylindrical linear motor configured in this manner, the slits are provided on the surface of the inner tube opposite the armature, and therefore no slits are provided on the surface facing the armature, so there are no irregularities, and the inner tube can be used to guide the axial movement of the armature, further narrowing the radial gap between the armature and the field magnet.

[0013] Furthermore, in a cylindrical linear motor configured in this manner, the inner tube can be used to guide the axial movement of the armature, eliminating the need to provide a separate guide mechanism for guiding the axial movement of the armature.

[0014] Therefore, with a cylindrical linear motor configured in this manner, not only is it lightweight because it does not require the installation of a separate guide mechanism, but it also allows a large magnetic field to act on the armature and further narrows the radial magnetic air gap between the armature and the field magnet, thereby increasing the thrust, and as a result, the mass thrust density can be further improved.

[0015] Furthermore, in a cylindrical linear motor in which the slit has an opening on either the inner or outer circumference of the inner tube and the cross-sectional shape of the slit is narrower at the tip on the armature side than the axial width at the opening, the sudden change in the cross-sectional area of ​​the magnetic path at the portion of the inner tube where the slit is provided is mitigated, thereby reducing the cogging thrust caused by providing the slit in the inner tube.

[0016] Furthermore, the slits in the inner tube may be provided at an angle relative to the axial direction of the inner tube. In a cylindrical linear motor in which the slits are provided at an angle relative to the axis of the inner tube in this manner, the cogging thrust caused by providing the slits in the inner tube can be reduced by the skew effect. [Effects of the Invention]

[0017] According to the cylindrical linear motor of the present invention, the mass thrust density can be improved. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a longitudinal sectional view of a cylindrical linear motor according to an embodiment of the present invention; [Figure 2] FIG. 2 is a side view of an inner tube of the cylindrical linear motor according to the embodiment. [Figure 3] Fig. 3(a) is a cross-sectional view of a slit portion of an inner tube of a cylindrical linear motor according to a first modified example of an embodiment. Fig. 3(b) is a cross-sectional view of a slit portion of an inner tube of a cylindrical linear motor according to a second modified example of an embodiment. Fig. 3(c) is a cross-sectional view of a slit portion of an inner tube of a cylindrical linear motor according to a third modified example of an embodiment. Fig. 3(d) is a cross-sectional view of a slit portion of an inner tube of a cylindrical linear motor according to a fourth modified example of an embodiment. [Figure 4] Fig. 4(a) is a partial side view of an inner tube of a cylindrical linear motor according to a fifth modified example of an embodiment, Fig. 4(b) is a partial side view of an inner tube of a cylindrical linear motor according to a sixth modified example of an embodiment, and Fig. 4(c) is a partial side view of an inner tube with an undesirable slit. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described below based on the embodiments shown in the drawings. As shown in Fig. 1, a cylindrical linear motor 1 in one embodiment is configured to include a cylindrical field magnet 6 having N poles and S poles alternately arranged in the axial direction, an armature E arranged on the inner periphery of the field magnet 6 and movable in the axial direction relative to the field magnet 6, and a cylindrical inner tube 9 made of a soft magnetic material arranged on the armature E side of the field magnet 6.

[0020] Each part of the cylindrical linear motor 1 will be described in detail below. In this embodiment, the field magnet 6 is cylindrical and includes annular main pole permanent magnets 6a and annular sub pole permanent magnets 6b that are alternately stacked and inserted in the axial direction. A back yoke 8 made of a cylindrical magnetic material is attached to the outer periphery of the field magnet 6. The field magnet 6 and back yoke 8 are housed in an annular gap formed between a cylindrical non-magnetic barrel 7 and a cylindrical soft magnetic inner tube 9 inserted into the barrel 7.

[0021] 1, the triangles on the main pole permanent magnet 6a and the sub-pole permanent magnet 6b indicate the magnetization direction, with the main pole permanent magnet 6a being magnetized in the radial direction and the sub-pole permanent magnet 6b being magnetized in the axial direction. The main pole permanent magnets 6a and the sub-pole permanent magnets 6b are arranged in a Halbach array, with south and north poles alternating in the axial direction on the inner periphery of the field magnet 6. The main pole permanent magnets 6a of the field magnet 6 are magnetized so that north and south poles alternate on the inner periphery in the axial direction of the field magnet 6, and the sub-pole permanent magnets 6b form the boundary between the north and south poles in the field magnet 6.

[0022] Furthermore, the axial length of the permanent magnet 6a of the main magnetic pole is longer than the axial length of the permanent magnet 6b of the sub-pole. Increasing the axial length of the permanent magnet 6a of the main magnetic pole reduces the magnetic resistance between the permanent magnet 6a of the main magnetic pole and the armature E, and increases the magnetic field acting on the armature E, thereby improving the mass thrust density of the cylindrical linear motor 1.

[0023] Furthermore, in the cylindrical linear motor 1 of this embodiment, a back yoke 8 is provided around the permanent magnets 6a and 6b. Without the back yoke 8, shortening the axial length of the permanent magnets 6b of the sub-pole increases magnetic resistance outside the permanent magnets 6a of the main pole at the axial center, reducing the field magnetic flux. This reduces the degree of thrust improvement of the cylindrical linear motor 1 when the axial length of the permanent magnets 6a of the main pole is increased. In contrast, providing a back yoke 8 around the permanent magnets 6a and 6b ensures a magnetic path with low magnetic resistance, thereby suppressing the increase in magnetic resistance caused by shortening the axial length of the permanent magnets 6b of the sub-pole. Therefore, making the axial length of the permanent magnets 6a of the main pole longer than that of the permanent magnets 6b of the sub-pole and providing a cylindrical back yoke 8 around the permanent magnets 6a and 6b can significantly improve the mass thrust density of the cylindrical linear motor 1. 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 magnetic pole.

[0024] Furthermore, the armature E is inserted on the inner periphery side of the field 6, and the field 6 applies a magnetic field to the armature E. Note that the field 6 only needs to apply a magnetic field to the movable range of the armature E, so the installation range of the permanent magnets 6a, 6b can be determined according to the movable range of the armature E. Therefore, the permanent magnets 6a, 6b do not need to be installed in the range of the annular gap between the barrel 7 and the inner tube 9 that does not face the armature E. Note that, in this embodiment, the field 6 is composed of permanent magnets 6a, 6b stacked in a Halbach array, but as long as N poles and S poles appear alternately on the inner periphery, the field 6 may be composed of permanent magnets stacked in an array other than the Halbach array.

[0025] As shown in FIGS. 1 and 2, the inner tube 9 is a cylinder made of a soft magnetic material and fitted onto the inner periphery of the field magnet 6 on the armature E side, and has slits 9a on the outer periphery facing the field magnet 6 at positions radially opposing the N and S poles of the field magnet 6. Since the armature E is inserted into the inner periphery of the inner tube 9, it is sufficient for the inner tube 9 to be positioned on the inner periphery of the field magnet 6, but it is preferable for the inner tube 9 to be fitted onto the inner periphery of the field magnet 6 so as not to form an air gap between it and the field magnet 6. Each slit 9a is provided in the circumferential direction without axially spanning one of the magnetic poles of the field magnet 6, and as shown in FIG. 2, it is formed as an annular groove provided around the entire outer periphery of the inner tube 9 along the circumferential direction.

[0026] The field magnet 6 is composed of permanent magnets 6a and 6b stacked in a Halbach array, and the boundary between the N and S magnetic poles is in the range where it faces the sub-pole permanent magnet 6b in the axial direction. In the cylindrical linear motor 1 of this embodiment, the slit 9a is formed in the range where it faces the sub-pole permanent magnet 6b between the magnetic poles.

[0027] By providing slits 9a in the inner tube 9 at positions facing the gap between the N and S poles of the field magnet 6, the radial thickness of the narrowed portion 9b where the slits 9a are provided in the inner tube 9 is reduced, and providing the slits 9a in the inner tube 9 forms a narrowed portion 9b in the inner tube 9 that narrows the cross-sectional area of ​​the magnetic path. When the slits 9a are provided in the inner tube 9 in this manner, the magnetic field lines in the field magnet 6 exit from the N pole and pass through the wall thickness of the inner tube 9 toward the S pole, but the cross-sectional area of ​​the magnetic path is narrowed in the narrowed portion 9b where the slits 9a are provided in the inner tube 9. If the narrowed portion 9b that narrows the cross-sectional area of ​​the magnetic path is not formed in the inner tube 9 made of a soft magnetic material at a position facing the gap between the magnetic poles of the field magnet 6, most of the magnetic field lines exiting from the N pole of the field magnet 6 will pass through the wall thickness of the inner tube 9 and return to the S pole of the field magnet 6, making it difficult for the magnetic field of the field magnet 6 to act on the armature E side on the inner periphery of the inner tube 9. In contrast, the cross-sectional area of ​​the magnetic path is narrow in the narrow portion 9b where the slit 9a of the inner tube 9 is provided, and the magnetic flux is saturated in the narrow portion 9b. As a result, many of the magnetic lines of force emanating from the N pole of the field 6 pass radially through the thickness of the inner tube 9, pass once through the armature E, and then pass radially through the thickness of the inner tube 9 again to return to the S pole, as shown by the dashed dotted line in Figure 2.

[0028] Therefore, by providing the inner tube 9 with slits 9a at positions facing the north and south magnetic poles of the field magnet 6, it is possible to allow many of the magnetic field lines of the field magnet 6 to pass through the armature E inside the inner tube 9.Furthermore, since the inner tube 9 is made of a soft magnetic material and can be positioned so that the distance between the inner tube 9 and the armature E is extremely short, a large magnetic field can be applied to the armature E inserted into the inner tube 9.

[0029] The slits 9a are formed by forming a narrow portion 9b where the magnetic lines have difficulty passing through at a location facing the N and S poles of the field magnet 6 of the inner tube 9, thereby allowing the magnetic lines to pass through the armature E inside the inner tube 9. Therefore, instead of being formed as a continuous annular groove in the circumferential direction of the inner tube 9, the slits 9a may also be formed as intermittent grooves in the circumferential direction.

[0030] Furthermore, the width of the slits 9a can be changed as desired, but a narrower width is preferable because the narrower the width of the slits 9a in the inner tube 9, the stronger the magnetic field that can act on the armature E. Furthermore, since the slits 9a must be provided so as not to straddle the entire length of the N pole or S pole of the field magnet 6, the width between the slits 9a, 9a must be at least wider than the axial width of the permanent magnet 6a of the main magnetic pole.

[0031] Furthermore, the depth of the slit 9a can be changed as desired, but since making the magnetic path cross-sectional area at the location where the slit 9a is formed in the inner tube 9 as narrow as possible will increase the magnetic field that can act on the armature E, it is better to make the slit as deep as possible within the range that ensures the strength required of the inner tube 9.

[0032] In the cylindrical linear motor 1 of this embodiment, the wall thickness of the inner tube 9 is made thinner at the narrow portion 9b where the slit 9a is formed than at the portion where the slit 9a is not formed, thereby forming the narrow portion 9b where the magnetic path cross-sectional area is narrowed. However, since the narrow portion 9b where the magnetic path cross-sectional area is narrowed is a portion of the inner tube 9 where the cross-sectional area is narrower than other portions of the inner tube 9 in the cross section of the inner tube 9, if the wall thickness of the inner tube 9 is sufficiently thick, an air gap may be formed in the inner tube 9 by embedding an air gap or a non-magnetic material in the wall thickness, thereby forming the narrow portion 9b where the magnetic path cross-sectional area is narrowed in the inner tube 9. Furthermore, the narrow portion 9b where the magnetic path cross-sectional area is narrowed may be formed in the inner tube 9 by forming a slit on the inner circumference of the inner tube 9 facing the armature E. In other words, the narrow portion 9b where the magnetic path cross-sectional area is narrowed may be provided on either the inner circumference or the outer circumference of the inner tube 9.

[0033] In addition, when the field magnet 6 is not stacked in a Halbach array, and the field magnet is formed by stacking radially magnetized permanent magnets on the inner and outer periphery so that N and S poles appear alternately in the axial direction, each permanent magnet forms an N and S magnetic pole, so that narrow portions 9b that narrow the cross-sectional area of ​​the magnetic path can be provided by providing slits 9a or the like at least along the boundary between adjacent permanent magnets, or at least a portion of the slits 9a passing through the boundary so as not to straddle one permanent magnet in the axial direction.

[0034] 1 are closed by a cap 16, and the right ends of the barrel 7, back yoke 8 and inner tube 9 in FIG. 1 are closed by an annular head cap 15.

[0035] 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.

[0036] In this embodiment, the core 2 is made of permendur material and comprises a cylindrical yoke 2a, a ring-shaped yoke, a plurality of teeth 2b with a rectangular axial cross section arranged circumferentially and axially spaced apart on the outer periphery of the yoke 2a on the field side, and slots 2c formed by gaps between the teeth 2b, 2b, into which the windings 3 are attached.

[0037] As described above, the yoke 2a is cylindrical, and has a thickness such that its cross-sectional area is equal to or greater than the cross-sectional area of ​​the magnetic path in the teeth 2b.

[0038] 1 and 2, in this embodiment, seven teeth 2b are arranged at equal intervals in the axial direction on the outer periphery of the yoke 2a, and slots 2c, which are annular grooves into which the windings 3 are fitted, are formed between the teeth 2b on the outer periphery side that faces the field 6 of the core 2. In this embodiment, the cross-sectional shape of the teeth 2b is rectangular, but they may also be trapezoidal, with the width on the inner periphery, or base end, being greater than the width on the outer periphery, or tip end, so that a large magnetic path cross-sectional area can be secured on the base end side.

[0039] In this embodiment, a total of six slots 2c, each consisting of 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 at equal intervals in the axial direction on the outer periphery of the core 2.

[0040] The slots 2c are fitted with windings 3 wound around them. The windings 3 are three-phase windings consisting of U-phase, V-phase, and W-phase. The windings 3 for each phase are fitted in six slots 2c so as to be arranged appropriately according to the magnetic pole arrangement of the field magnet 6.

[0041] The armature E configured in this manner is attached to the outer periphery of the tip of a rod 11 made of a non-magnetic material, which serves as the output shaft, and is inserted into the field magnet 6 together with the rod 11 so as to be freely movable.

[0042] The rod 11 protrudes outside the cylindrical linear motor 1 through a head cap 15 attached to the right end of the barrel 7 in FIG. 1. Annular sliders 12 and 13, each having annular wear rings 12a and 13a on its outer periphery that come into sliding contact with the inner periphery of the inner tube 9, are attached to the left and right sides of the armature E of the rod 11 in FIG. 1.

[0043] The armature E is clamped between sliders 12 and 13 and fixed to the rod 11, and the sliders 12 and 13 are slidably inserted into the inner periphery of the inner tube 9, so that there is no axial wobble relative to the field magnet 6 and the armature E can move in the axial direction without interfering with the inner tube 9. In this way, the armature E's axial movement relative to the field magnet 6 is guided by the inner tube 9.

[0044] In this way, the inner tube 9 can increase the magnetic field that the field magnet 6 applies to the armature E, and plays a role in guiding the axial movement of the armature E in cooperation with the sliders 12, 13. Furthermore, 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, allowing the cylindrical linear motor 1 to smoothly extend and retract. Note that it is sufficient for the inner tube 9 to indirectly or directly guide the axial movement of the armature E, and therefore the concept of the inner tube 9 guiding the axial movement of the armature E also includes a mode in which the inner tube 9 guides the movement of the armature E by utilizing the sliders 12, 13.

[0045] Although not shown, the rod 11 is cylindrical, and power can be supplied to the windings 3 from an external power source installed outside the cylindrical linear motor 1 via an electric wire (not shown) that passes through the rod 11.

[0046] For example, by sensing the electrical angle of the windings 3 relative to the field 6 and switching the energization phase based on that electrical angle while controlling the amount of current in each winding 3 by PWM control, it is possible to control the thrust and the direction of movement of the armature E in the cylindrical linear motor 1. Note that the above-described control method is one example and is not limited to this. Furthermore, when an external force acts to relatively displace the armature E and the field 6 in the axial direction, energization of the windings 3 or induced electromotive force generated in the windings 3 can generate thrust that suppresses the relative displacement, allowing the cylindrical linear motor 1 to damp the vibration and movement of the equipment caused by the external force, and also enabling energy regeneration to generate electric power from the external force.

[0047] The cylindrical linear motor 1 configured as described above comprises a cylindrical field magnet 6 having N poles and S poles arranged alternately in the axial direction, an armature E arranged on the inner periphery of the field magnet 6 and movable axially relative to the field magnet 6, and an inner tube 9 made of a soft magnetic material arranged on the armature side of the field magnet 6, the inner tube 9 having a narrow portion 9b between the magnetic poles that narrows the cross-sectional area of ​​the magnetic path in the circumferential direction without spanning one of the magnetic poles of the field magnet in the axial direction.

[0048] In the cylindrical linear motor 1 configured in this manner, narrow spaces 9b that narrow the cross-sectional area of ​​the magnetic path in the circumferential direction are provided between the magnetic poles of the field magnet 6 in the inner tube 9. By providing the narrow spaces 9b that narrow the cross-sectional area of ​​the magnetic path in the inner tube 9 in this manner, the magnetic field can be made to act efficiently on the armature E even if the inner tube 9 is made of a soft magnetic material, and by shortening the distance between the field magnet 6 and the armature E, a large magnetic field can be made to act on the armature E inside the inner tube 9.

[0049] Therefore, according to the cylindrical linear motor 1 of this embodiment, the radial magnetic air gap between the armature E and the field magnet 6 can be narrowed, and a large magnetic field can be applied to the armature E inside the inner tube 9, thereby improving the mass thrust density.

[0050] The inner tube 9 has a slit 9a on the outer periphery, an armature E is disposed on the inner periphery of the inner tube 9, and a narrow portion 9b that narrows the cross-sectional area of ​​the magnetic path is formed in the inner tube 9 by the slit 9a.

[0051] In the cylindrical linear motor 1 configured in this manner, slits 9a are provided on the outer periphery of the inner tube 9. By providing the slits 9a in the inner tube 9 in this manner, narrow spaces 9b that narrow the cross-sectional area of ​​the magnetic path can be easily formed between the N pole and S pole of the field magnet 6 of the inner tube 9.

[0052] Furthermore, since the slits 9a are provided on the surface of the inner tube 9 opposite the armature E side, no slits are provided on the surface facing the armature E side, so there are no irregularities, and the sliders 12, 13 arranged on both sides of the armature E can be made to slide directly against the side surface of the armature E of the inner tube 9 to guide the axial movement of the armature E.

[0053] In this way, in the cylindrical linear motor 1 of this embodiment, the inner tube 9 can be used to guide the axial movement of the armature E, so there is no need to provide a separate guiding mechanism to guide the axial movement of the armature E, and the sliders 12, 13 provided adjacent to the armature E can be made to slide against the inner tube 9 to restrict the radial movement of the armature E, so even if the radial gap between the armature E and the inner tube 9 is narrowed, contact between the armature E and the inner tube 9 can be prevented.

[0054] Therefore, according to the cylindrical linear motor 1 of this embodiment, not only is it lightweight because it does not require the installation of a separate guide mechanism, but it is also possible to apply a large magnetic field to the armature E inside the inner tube 9 and further narrow the radial magnetic air gap between the armature E and the field magnet 6, thereby increasing the thrust, and as a result, the mass thrust density can be further improved.

[0055] While the cross-sectional shape of the slits 9a has been described above as rectangular, it may also be trapezoidal, triangular, semicircular, or other shapes in which the axial width narrows toward the armature E, as shown in Fig. 3, or a U-shape in which the axial width gradually narrows from midway toward the armature E. In this way, with a cylindrical linear motor 1 in which the slits 9a have openings on the field side and the cross-sectional shape of the slits 9a is narrower at the ends on the armature E side than at the axial width at the openings, a sudden change in the cross-sectional area of ​​the magnetic path at the portion of the inner tube 9 where the slits 9a are provided is alleviated, and therefore the cogging thrust caused by providing the slits 9a in the inner tube 9 can be reduced.

[0056] Furthermore, although the slits 9a are provided along the circumferential direction on the outer periphery of the inner tube 9 as described above, they may also be provided at an angle with respect to the axial direction of the inner tube 9 when viewed from the side, as shown in Fig. 4. In this case, the slits 9a may be formed as annular grooves that are inclined with respect to the axis of the inner tube 9, as shown in Fig. 4(a), or may be provided spirally with respect to the outer periphery of the inner tube 9, as shown in Fig. 4(b). However, when the slits 9a are provided at an angle with respect to the axis of the inner tube 9 when viewed from the side, it is not preferable for the slits 9a to be provided across the N pole or S pole of the field magnet 6 in the axial direction, as shown in Fig. 4(c), because this reduces the magnetic flux of the magnetic lines of force passing through the armature E inside the inner tube 9. In the cylindrical linear motor 1 of this embodiment, the field 6 is formed of permanent magnets 6a, 6b stacked in a Halbach array, so if slits 9a or the like are formed between the permanent magnets 6a, 6a of the main magnetic pole, i.e., within the axial width of the permanent magnets 6b of the sub-magnetic pole, to provide narrow portions 9b that narrow the cross-sectional area of ​​the magnetic path, the magnetic field can be efficiently applied to the armature E inside the inner tube 9. If the field 6 is not stacked in a Halbach array and the field is formed by stacking radially magnetized permanent magnets on the inner and outer peripheries so that N and S poles appear alternately in the axial direction, each permanent magnet will form an N and S magnetic pole, so it is only necessary to provide narrow portions 9b that narrow the cross-sectional area of ​​the magnetic path by providing slits 9a or the like at least along the boundary between adjacent permanent magnets or so that at least a portion of the slits passes through the boundary so as not to straddle one permanent magnet in the axial direction.

[0057] In this way, with a cylindrical linear motor 1 in which the slits 9a are arranged in an inclined position relative to the axis of the inner tube 9 when viewed from the side, the skew effect can reduce the cogging thrust caused by providing the slits 9a in the inner tube 9.

[0058] Although the cylindrical linear motor 1 of this embodiment is structured so that the armature E is provided on the inner periphery of the field magnet 6, it is also possible to adopt a structure in which the cylindrical armature E is provided on the outer periphery of the field magnet 6. In this case, an inner tube 9 may be disposed on the outer periphery of the field magnet 6 on the armature E side, and a slit 9a or the like may be provided in the inner tube 9 to provide a narrowed portion 9b that narrows the cross-sectional area of ​​the magnetic path. Even with a cylindrical linear motor 1 configured in this manner, a narrowed portion 9b that narrows the cross-sectional area of ​​the magnetic path is formed in a portion of the inner tube 9 that faces between the magnetic poles of the field magnet 6, thereby narrowing the magnetic air gap between the field magnet 6 and the armature E. This allows a strong magnetic field to act on the armature E on the outer periphery of the inner tube 9, thereby improving the mass thrust density. Furthermore, when a slit 9a is provided on the inner periphery of the inner tube 9 to form a narrowed portion 9b that narrows the cross-sectional area of ​​the magnetic path, the axial movement of the armature E located on the outer periphery can be guided by the outer periphery of the inner tube 9, eliminating the need for an additional guide mechanism and further improving the mass thrust density. Even with a cylindrical linear motor 1 configured in this manner, the cogging thrust caused by providing the slits 9a in the inner tube 9 can be reduced by making the cross-sectional shape of the slits 9a such that the axial width at the tip on the armature E side is narrower than the axial width at the opening, or by arranging the slits 9a in an attitude that is inclined with respect to the axis of the inner tube 9 when viewed from the side.

[0059] Although the preferred embodiment of the present invention has been described in detail, modifications, variations and changes can be made thereto without departing from the scope of the appended claims. [Explanation of symbols]

[0060] 1... Cylindrical linear motor, 6... Field magnet, 9... Inner tube, 9a... Slit, 9b... Narrow space, E... Armature

Claims

1. a cylindrical field magnet having north and south poles alternately arranged in the axial direction; an armature disposed on an inner or outer peripheral side of the field magnet and movable in an axial direction relative to the field magnet; an inner tube that is cylindrical and made of a soft magnetic material and that is arranged on the armature side of the field magnet, The inner tube has a narrow portion between magnetic poles that narrows the cross-sectional area of ​​the magnetic path in the circumferential direction without spanning one magnetic pole of the field magnet in the axial direction. A cylindrical linear motor characterized by:

2. The inner tube has a slit on one of the inner circumference and the outer circumference, the armature is disposed on the other of the inner periphery or the outer periphery of the inner tube, The narrow space is formed by the slit.

2. The cylindrical linear motor according to claim 1.

3. the slit has an opening on one of the inner periphery and the outer periphery of the inner tube, The cross-sectional shape of the slit is such that the axial width at the tip on the armature side is narrower than the axial width at the opening.

3. The cylindrical linear motor according to claim 2.

4. The narrow space is provided at an angle with respect to the axial direction.

4. The cylindrical linear motor according to claim 1, wherein the first and second rotors are arranged parallel to each other.

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