Cylindrical linear motor

Abstract

To provide a cylindrical linear motor which can achieve both of enhancement of the thrust and a reduction in manufacturing cost.SOLUTION: A cylindrical linear motor 1 includes: a cylindrical field magnet F; and an armature E which is disposed on an inner circumference of the field magnet F and is movable in the axial direction with respect to the field magnet F. The field magnet F includes: a plurality of annular permanent magnets 3a, 3b which are magnetized in the axial direction, and which are arranged such that their magnetization directions may alternate in the axial direction of the field magnet F; an annular yoke 2b, made of a soft magnetic material, which is interposed between the permanent magnets 3a, 3b. The permanent magnets 3a, 3b each have a protruding shape where, in an axially cut cross section, an axial length on the armature side is shorter than an axial length on the side opposite to the armature side.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Generally, a cylindrical linear motor is configured with a cylindrical field magnet formed by arranging multiple permanent magnets so that north and south poles appear alternately, and an armature that faces the inner or outer periphery of the field magnet and can move in the longitudinal direction of the field magnet.

[0003] In order to increase the thrust of such a cylindrical linear motor, it is necessary to increase the magnetic field that the field magnet applies to the armature. One method for increasing the magnetic field is to arrange the permanent magnets in a Halbach array, which concentrates a lot of magnetic flux on the armature side.

[0004] By arranging the permanent magnets in the field magnet in a Halbach array in this manner, the third and fifth order components contained in the waveform of the gap magnetic flux density distribution at a position slightly away from the surface of the field magnet facing the armature are reduced, and the waveform becomes closer to a sine wave and the amplitude of the waveform increases, thereby improving the thrust of the cylindrical linear motor (see, for example, Patent Document 1).

[0005] However, in a cylindrical linear motor, the field magnet must be formed in a cylindrical shape, and if the permanent magnets are arranged in a Halbach array, expensive permanent magnets with a radial magnetization direction are required, resulting in high manufacturing costs.

[0006] In contrast, in a cylindrical linear motor that uses permanent magnets magnetized in the axial direction, the field magnet can be formed by stacking annular permanent magnets magnetized in the axial direction so that the magnetization direction alternates in the axial direction of the field magnet, and manufacturing costs can be reduced because inexpensive permanent magnets magnetized in the axial direction can be used (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2011-24379 A [Patent Document 2] Patent No. 6314833 Summary of the Invention [Problem to be solved by the invention]

[0008] However, a cylindrical linear motor in which axially magnetized ring-shaped permanent magnets are simply stacked so that the magnetization direction alternates in the axial direction of the field magnet is unable to concentrate magnetic flux on the armature side, and therefore has lower thrust than a cylindrical linear motor equipped with a field magnet that uses a Halbach array, although it is inexpensive.

[0009] On the other hand, a cylindrical linear motor equipped with a field magnet using a Halbach array has the advantage of being able to produce a large thrust, but has the problem of high manufacturing costs. In this way, with conventional cylindrical linear motors, increasing the thrust results in high costs, while reducing the manufacturing cost results in a decrease in thrust, making it difficult to achieve both increased thrust and reduced costs.

[0010] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a cylindrical linear motor that can achieve both improved thrust and reduced manufacturing costs. [Means for solving the problem]

[0011] In order to achieve the above object, a cylindrical linear motor of the present invention comprises a cylindrical field magnet, and an armature arranged on the inner or outer circumference of the field magnet and movable in the axial direction relative to the field magnet, the field magnet has a plurality of permanent magnets that are annular, magnetized in the axial direction, and arranged so that the magnetization direction alternates in the axial direction of the field magnet, and a yoke that is annular, made of a soft magnetic material, and interposed between the permanent magnets, and the permanent magnets have a convex shape in a cross section taken in the axial direction, with the axial length on the armature side being shorter than the axial length on the anti-armature side.

[0012] In a cylindrical linear motor configured in this manner, the magnetic flux from the portion of the permanent magnet with a short axial length on the armature side and the portion with a long axial length on the anti-armature side passes through the yoke, which allows magnetic passage, toward the armature side, increasing the magnetic flux density in the range radially opposing the yoke, so that the waveform of the gap magnetic flux density distribution on the outer periphery of the armature becomes closer to a sine wave compared to a field magnet configured by stacking axially magnetized annular permanent magnets with rectangular cross sections so that the magnetization directions are alternating. As a result, the amplitude of the waveform of the gap magnetic flux density distribution on the outer periphery of the armature becomes larger, making it possible to increase the magnetic field acting on the armature housed inside the sleeve.

[0013] In addition, the cylindrical linear motor may include a sleeve formed of a soft magnetic material and having a cylindrical portion that fits onto the armature side of the permanent magnet, the sleeve having a yoke integral with the cylindrical portion, and the yoke may be interposed over the entire area between the portion of the permanent magnet with a short axial length on the armature side and the portion of the permanent magnet with a long axial length on the anti-armature side.

[0014] In a cylindrical linear motor configured in this manner, the permanent magnets are entirely interposed between the yokes, and the magnetic flux emanating from the armature-side surface and both axial end surfaces of the permanent magnets at the portion with a short axial length on the armature side and the portion with a long axial length on the non-armature side passes through the yoke, which is magnetically easy to pass through, toward the armature side, so that the magnetic flux density in the range radially opposed to the yoke becomes higher, and the waveform of the gap magnetic flux density distribution on the outer periphery of the armature becomes closer to a sine wave than in a field magnet configured by stacking axially magnetized annular permanent magnets with rectangular cross sections so that the magnetization directions are alternating. Therefore, in a cylindrical linear motor configured in this manner, the amplitude of the waveform of the gap magnetic flux density distribution on the outer periphery of the armature becomes larger, and the magnetic field acting on the armature housed inside the sleeve can be made even larger.

[0015] Furthermore, the cylindrical linear motor may include a sleeve formed of a soft magnetic material and having a cylindrical portion that fits onto the armature side of the permanent magnet, the sleeve having a yoke integral with the cylindrical portion, the yoke being interposed between the portions of the permanent magnet with a short axial length on the armature side, and a magnetic gap being provided between the portions of the permanent magnet on the anti-armature side of the yoke with a long axial length on the anti-armature side.

[0016] In the cylindrical linear motor thus constructed, the axial length of the permanent magnet on the armature side is shorter than the axial length on the non-armature side, and a magnetic gap is provided on the non-armature side of the yoke between the portion of the permanent magnet with the long axial length on the non-armature side, so that the magnetic flux emitted from the armature side surface and both end faces in the axial direction of the portion of the permanent magnet with the short axial length on the armature side and the portion with the long axial length on the non-armature side passes through the yoke, which is magnetically easy to pass through, toward the armature side, and the magnetic flux density in the range radially opposite the yoke becomes high, so that the waveform of the gap magnetic flux density distribution on the outer periphery of the armature becomes closer to a sine wave than a field magnet formed by stacking annular permanent magnets with rectangular cross sections and axial magnetization in alternating magnetization directions. Therefore, in the cylindrical linear motor thus constructed, the amplitude of the waveform of the gap magnetic flux density distribution on the outer periphery of the armature becomes larger, and the magnetic field acting on the armature housed in the inner periphery of the sleeve can be further increased. Effect of the Invention

[0017] According to the cylindrical linear motor of the present invention, it is possible to achieve both an improvement in thrust and a reduction in manufacturing costs. [Brief description of the drawings]

[0018] [Figure 1] 1 is a vertical cross-sectional view of a cylindrical linear motor according to an embodiment; [Diagram 2] 4 is an enlarged cross-sectional view of a field magnet of a cylindrical linear motor according to one embodiment. [Diagram 3] FIG. 4 is a vertical sectional view of a cylindrical linear motor in a first modified example of the embodiment. [Figure 4]FIG. 11 is a vertical sectional view of a cylindrical linear motor according to a second modified example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention will be described below based on the embodiment shown in the drawings. A cylindrical linear motor 1 in one embodiment is configured with a cylindrical field magnet F and an armature E that is disposed on the inner circumference of the field magnet F and is movable in the axial direction relative to the field magnet F, as shown in Figure 1.

[0020] Each component of the cylindrical linear motor 1 will be described in detail below. In this embodiment, the field F is cylindrical, annular, and magnetized in the axial direction, and includes a plurality of permanent magnets 3a, 3b arranged so that the magnetization directions alternate between the left and right in Fig. 1, which is the axial direction of the field F, and a yoke 2b annular and made of a soft magnetic material interposed between the permanent magnets 3a, 3b. Note that the triangular marks attached to the permanent magnets 3a, 3b in each figure indicate the magnetization directions.

[0021] In this embodiment, the field magnetic field F includes a cylindrical sleeve 2 on whose outer periphery the permanent magnets 3a and 3b are attached. As shown in Fig. 1 and Fig. 2, the sleeve 2 is made of a soft magnetic material, and includes a cylindrical portion 2a fitted to the inner periphery of the permanent magnets 3a and 3b, a plurality of annular yokes 2b provided circumferentially on the outer periphery of the cylindrical portion 2a and spaced apart in the axial direction, and a plurality of annular grooves 2c formed by annular gaps along the circumferential direction between the yokes 2b of the cylindrical portion 2a.

[0022] In this embodiment, the sleeve 2 is formed by processing the outer periphery of one cylindrical soft magnetic material to provide an annular groove 2c, and is provided with a cylindrical portion 2a and a yoke 2b that protrudes from the outer periphery of the cylindrical portion 2a in a flange-like shape. As shown in FIG. 2, fillet processing is performed on both axial ends of the bottom of the annular groove 2c in the sleeve 2, that is, on the outer periphery of the cylindrical portion 2a and the root portions on both axial sides of the yoke 2b, and a curved surface 2d is formed from the root of the yoke 2b to the outer periphery of the cylindrical portion 2a. In this embodiment, the axial width of each annular groove 2c is all equal and is longer than the axial width of the yoke 2b. The annular grooves 2c are provided at equal intervals on the outer periphery of the sleeve 2. In this embodiment, the yokes 2b are provided on both ends of the sleeve 2, but it is not necessary to provide the yokes 2b on both ends by making the ends of both ends of the sleeve 2 annular groove 2c. In addition, in this embodiment, the sleeve 2 is integrally provided with the cylindrical portion 2a and the yoke 2b, but the cylindrical portion 2a and the yoke 2b may be configured as separate parts.

[0023] Each of the permanent magnets 3a, 3b is annular, and in a cross section cut along the axial direction, the inner peripheral portion 3a1, 3b1 on the armature side has a convex cross section with a long axial length of the outer peripheral portion 3a2, 3b2 on the anti-armature side. The axial center of the inner peripheral portion 3a1, 3b1, which is the portion with a short axial length of each permanent magnet 3a, 3b, and the axial center of the outer peripheral portion 3a2, 3b2, which is the portion with a long axial length, coincide with each other in the axial direction, and the cross-sectional shape of each permanent magnet 3a, 3b is symmetrical with respect to a line passing through the axial center. The radial thickness of the inner peripheral portion 3a1, 3b1 and the outer peripheral portion 3a2, 3b2 may be designed to be equal but different as illustrated. When the terminal permanent magnets are provided on the end side of the yokes 2b at both axial ends of the sleeve 2, the terminal permanent magnets may have the same shape as the permanent magnets 3a, 3b, for example. However, if it is desired to avoid a stepped end of the field magnet F, one side of the outer circumferential portions 3a2, 3b2 may be cut off in the radial direction, or the permanent magnets 3a, 3b may be cut in half at the center in the axial direction.

[0024] Moreover, each permanent magnet 3a, 3b is formed into an annular shape by combining magnet pieces having a shape obtained by dividing a cylinder into a plurality of pieces in the circumferential direction. In this embodiment, the magnet pieces are semi-cylindrical when viewed from the axial direction, and the cylindrical permanent magnets 3a, 3b are formed by combining two magnet pieces with their circumferential ends facing each other. Since the permanent magnets 3a, 3b are thus formed by magnet pieces divided in the circumferential direction, they can be easily and naturally installed in the annular groove 2c provided on the outer periphery of the sleeve 2.

[0025] As described above, the permanent magnets 3a, 3b are formed into an annular shape by combining multiple magnet pieces, but if the cylindrical portion 2a and the yoke 2b are configured as separate parts, or if the cylindrical portion 2a is not provided, the permanent magnets 3a, 3b may be formed as a single annular magnet instead of being formed of multiple magnet pieces combined into a cylindrical shape, and the permanent magnets 3a, 3b and the yoke 2b may be stacked alternately to assemble the field magnet F. Also, in this case, instead of or in addition to being divided in the circumferential direction, the permanent magnets 3a, 3b may be formed by combining magnet pieces divided into inner peripheral portions 3a1, 3b1, which are portions of the permanent magnets 3a, 3b with a short axial length, and outer peripheral portions 3a2, 3b2, which are portions of the permanent magnets 3a, 3b with a long axial length.

[0026] Furthermore, the permanent magnets 3a, 3b are formed by combining magnet pieces divided in half in the circumferential direction into a cylindrical shape, but may be formed of magnet pieces divided into three or more parts in the circumferential direction.

[0027] Furthermore, the inner circumferences at both axial ends of the inner circumference parts 3a1, 3b1 of the permanent magnets 3a, 3b are chamfered to provide inclined surfaces 3a11, 3b11. The axial length of the inner circumference parts 3a1, 3b1 of the permanent magnets 3a, 3b is approximately the same as the axial length of the annular groove 2c but is slightly smaller, so that the inner circumference parts 3a1, 3b1 of the permanent magnets 3a, 3b can be fitted into the annular groove 2c.

[0028] Furthermore, the magnetization direction of the permanent magnets 3a, 3b is magnetized in the axial direction, with one axial end being an N pole and the other axial end being an S pole. The S poles and N poles of the permanent magnets 3a, 3b are arranged in opposite directions and are installed alternately in the annular groove 2c of the sleeve 2. In this way, the permanent magnets 3a, 3b are arranged so that the magnetization direction alternates in the axial direction of the field magnet F.

[0029] When the permanent magnets 3a, 3b configured in this way are alternately mounted in the annular groove 2c of the sleeve 2, the inner circumferential portion 3a1 of the adjacent permanent magnet 3a and the inner circumferential portion 3b1 of the permanent magnet 3b face each other with the N poles and S poles sandwiching the yoke 2b, and the outer circumferential portion 3a2 of the permanent magnet 3a and the outer circumferential portion 3b2 of the permanent magnet 3b face each other with a small gap between their end faces. Note that the axial lengths of the outer circumferential portions 3a2, 3b2 of the permanent magnets 3a, 3b may be such that the axial end faces of the outer circumferential portions 3a2, 3b2 are just in contact with each other when the inner circumferential portions 3a1, 3b1 are accommodated in the annular groove 2c of the sleeve 2, but if they are set to face each other with a small gap between them, the gap absorbs dimensional errors of the permanent magnets 3a, 3b, which is advantageous in that it is easy to assemble the permanent magnets 3a, 3b to the sleeve 2.

[0030] In the cylindrical linear motor 1 of this embodiment, one magnetic pole is formed from the axial center of the permanent magnet 3a, including the yoke 2b, to the axial center of the adjacent permanent magnet 3b, and the N poles of the permanent magnets 3a, 3b, which have their N poles facing each other, and the yoke 2b sandwiched between the N poles, function as one N pole, and the S poles of the permanent magnets 3a, 3b, which have their S poles facing each other, and the yoke 2b sandwiched between the S poles, function as one S pole.

[0031] In the field F configured in this manner, the axial length of the inner periphery 3a1, 3b1 of the permanent magnets 3a, 3b on the armature side is shorter than the axial length of the outer periphery 3a2, 3b2 on the anti-armature side, and the magnetic flux of the inner periphery 3a1, 3b1 and the outer periphery 3a2, 3b2 passes through the yoke 2b, which is magnetically easy to pass through, toward the armature side, thereby increasing the magnetic flux density in the range radially opposing the yoke 2b. Therefore, compared to a field configured by simply stacking axially magnetized annular permanent magnets with rectangular cross sections so that the magnetization directions are alternating, the waveform of the gap magnetic flux density distribution on the outer periphery of the armature E becomes closer to a sine wave and the amplitude of the waveform becomes larger, making it possible to increase the magnetic field acting on the armature E housed in the inner periphery of the sleeve 2.

[0032] In addition, curved surfaces 2d are formed by filleting at the corners of the bottom (the outer periphery of the cylindrical portion 2a) and the side wall (the base of the yoke 2b) at both axial ends of the annular groove 2c, and inclined surfaces 3a11, 3b11 are formed by chamfering on the inner circumference at both axial ends of the inner periphery 3a1, 3b1 accommodated in the annular groove 2c of the permanent magnets 3a, 3b. Therefore, as shown in FIG. 2, when the inner periphery 3a1, 3b1 of the permanent magnets 3a, 3b is attached to the annular groove 2c, the curved surface 2d of the annular groove 2c and the inner periphery 3a1, 3b1 face each other so as not to interfere with each other, forming a gap G between them, and the axial end faces of the inner periphery 3a1, 3b1 of the permanent magnets 3a, 3b can come into surface contact with the side of the yoke 2b.

[0033] When the outer periphery of a cylindrical base material is cut to form the annular groove 2c, it is difficult to machine the corners at both axial ends of the bottom of the annular groove 2c at right angles. If no measures are taken, the corners of the inner peripheries 3a1, 3b1 of the permanent magnets 3a, 3b will ride up onto the corners, causing the inner peripheries 3a1, 3b1 of the permanent magnets 3a, 3b to float off the outer periphery of the cylindrical portion 2a, which is the bottom of the annular groove 2c, or preventing surface contact between the side wall of the yoke 2b and the end faces of the inner peripheries 3a1, 3b1 of the permanent magnets 3a, 3b, which may result in the position of the permanent magnets 3a, 3b relative to the annular groove 2c being inconsistent in each annular groove 2c.

[0034] In contrast to this, as described above, if the curved surface 2d is formed by fillet processing and the inner peripheral edges at both axial ends of the inner peripheral portions 3a1, 3b1 of the permanent magnets 3a, 3b are chamfered to provide inclined surfaces 3a11, 3b11 to avoid interference with the curved surface 2d, a gap G is formed between the corners at both axial ends of the bottom of the annular groove 2c and the inner peripheral portions 3a1, 3b1 at both ends of the permanent magnets 3a, 3b.When the permanent magnets 3a, 3b are fitted into the annular groove 2c, the permanent magnets 3a, 3b can be positioned by the yoke 2b which forms the side wall of the annular groove 2c. When a gap G is formed between the corners at both axial ends of the bottom of the annular groove 2c and the inner peripheral edges at both axial ends of the inner peripheral parts 3a1, 3b1 of the permanent magnets 3a, 3b, the side wall of the yoke 2b and the end faces of the inner peripheral parts 3a1, 3b1 of the permanent magnets 3a, 3b can be in surface contact with each other, so that it is possible to prevent stress from concentrating on a part of the permanent magnets 3a, 3b due to the axial load received when the armature E is driven. In addition, in the cylindrical linear motor 1 of this embodiment, the permanent magnets 3a, 3b are fixed to the annular groove 2c using an adhesive, and when a gap G is formed between the corners at both axial ends of the bottom of the annular groove 2c and the inner peripheral edges at both axial ends of the inner peripheral parts 3a1, 3b1 of the permanent magnets 3a, 3b as described above, excess adhesive escapes into the gap G and is accommodated therein, so that it is possible to prevent the permanent magnets 3a, 3b from being unable to be positioned properly in the annular groove 2c due to the presence of the adhesive. However, the fillet processing at both ends of the bottom of the annular groove 2c and the chamfering of the inner peripheral edges at both axial ends of the inner peripheral portions 3a1, 3b1 of the permanent magnets 3a, 3b may be omitted if not required.

[0035] In order to provide gaps G at the corners at both axial ends of the annular groove 2c and at the inner circumferential edges at both axial ends of the inner circumferential portions 3a1, 3b1 of the permanent magnets 3a, 3b, a groove may be provided by machining the entire circumference of the portion of the cylindrical portion 2a adjacent to the yoke 2b which is the axial end of the bottom of the annular groove 2c. In this case, it is not necessary to chamfer the inner circumferential edges at both axial ends of the inner circumferential portions 3a1, 3b1 of the permanent magnets 3a, 3b. In addition, when providing gaps G between the corners at both axial ends of the annular groove 2c and the inner circumferential edges at both axial ends of the inner circumferential portions 3a1, 3b1 of the permanent magnets 3a, 3b, the inner circumferential edges at both axial ends of the inner circumferential portions 3a1, 3b1 of the permanent magnets 3a, 3b can be chamfered to provide inclined surfaces 3a11, 3b11 or curved surfaces, so that fillet processing is not required for the corners at both axial ends of the bottom of the annular groove 2c. In this case, when gaps G are formed between the corners at both axial ends of the annular groove 2c and the inner circumferential edges at both axial ends of the inner circumferential portions 3a1, 3b1 of the permanent magnets 3a, 3b so that the inner circumferential edges at both axial ends of the inner circumferential portions 3a1, 3b1 of the permanent magnets 3a, 3b can come into surface contact with the side of the yoke 2b., the fillet processing may be omitted.

[0036] The field magnet F configured in this manner is housed in a cylindrical barrel 5 made of a non-magnetic material. The left ends of the barrel 5 and the field magnet F in FIG. 1 are closed by a cap 6, and the right ends of the barrel 5 and the field magnet F in FIG. 1 are closed by an annular head cap 7. In the cylindrical linear motor 1 of this embodiment, the field magnet F is covered by the barrel 5 made of a non-magnetic material, which protects the permanent magnets 3a, 3b attached to the outer periphery of the sleeve 2 and prevents the permanent magnets 3a, 3b from scattering from the sleeve 2, and also prevents external dust containing iron from being attracted by the field magnet F by the barrel 5.

[0037] Next, the armature E is configured to include a cylindrical core 8, a winding 9 attached to the core 8, and a guide 10 in sliding contact with the inner peripheral surface of the sleeve 2, and is inserted into the field magnet F so as to be freely movable in the axial direction. That is, in this embodiment, the armature E is disposed on the inner peripheral side of the field magnet F, and can move relative to the field magnet F in the axial direction.

[0038] In this embodiment, the core 8 is configured to include a cylindrical yoke 8a, a plurality of teeth 8b having a rectangular axial cross section that are annular and arranged circumferentially and axially spaced apart from one another on the outer periphery of the yoke 8a, which is the field side of the core 8, and slots 8c formed by the gaps between the teeth 8b, 8b, into which the windings 9 are attached.

[0039] As described above, the yoke 8a is cylindrical, and the thickness is ensured so that the cross-sectional area is equal to or larger than the magnetic path cross-sectional area of ​​the teeth 8b. In this embodiment, as shown in Fig. 1 and Fig. 2, seven teeth 8b are arranged at equal intervals in the axial direction on the outer periphery of the yoke 8a, and a slot 8c, which is an annular groove in which the winding 9 is fitted, is formed between the teeth 8b, 8b on the outer periphery side that is the field magnet F side of the core 8. In this embodiment, the cross-sectional shape of the teeth 8b is rectangular, but it may be trapezoidal in which the width on the inner periphery, the base end side, is larger than the width on the outer periphery, the tip side, so that a large magnetic path cross-sectional area on the base end side can be ensured.

[0040] In this embodiment, a total of six slots 8c each made of annular grooves are provided between adjacent teeth 8b, 8b in Fig. 1. The slots 8c are provided along the circumferential direction of the core 8 and are arranged at equal pitches in the axial direction on the outer periphery of the core 8.

[0041] The windings 9 are wound around the slots 8c. The windings 9 are three-phase windings having U, V, and W phases. The windings 9 for each phase are mounted in the six slots 8c in an appropriate arrangement according to the magnetic pole arrangement of the field magnet F.

[0042] The armature E thus constructed is attached to the outer periphery of the tip of a rod 11 which is an output shaft and is made of a non-magnetic material, and is inserted into the field magnet F together with the rod 11 so as to be freely movable.

[0043] The rod 11 protrudes out of the cylindrical linear motor 1 through a head cap 7 attached to the right end of the field magnet F in Fig. 1. Annular guides 10, 10 having annular wear rings 10a on their outer periphery that come into sliding contact with the inner circumferential surface of the sleeve 2 in the field magnet F are attached to the left and right sides of the core 8 of the rod 11 in Fig. 1.

[0044] In this way, the core 8 is sandwiched by the guides 10, 10 from both sides in the axial direction and fixed to the rod 11. The armature E is provided with the guides 10, 10, which are slidably inserted into the inner peripheral surface of the sleeve 2, so that the armature E can move in the axial direction without axial wobble or interfering with the field magnet F. In this way, the armature E's axial movement relative to the field magnet F is guided by the sleeve 2.

[0045] Moreover, the sleeve 2 made of a soft magnetic material reduces the magnetic gap with the armature E, thereby increasing the magnetic field that the field magnet F acts on the armature E, and plays a role in guiding the axial movement of the core 8 in cooperation with the guides 10, 10. Furthermore, the outer diameter of the core 8 is smaller than the inner diameter of the cylindrical portion 2a of the sleeve 2, so it does not interfere with the sleeve 2, allowing the cylindrical linear motor 1 to expand and contract smoothly.

[0046] Although not shown, rod 11 is cylindrical, and power can be supplied to windings 9 from an external power source installed outside cylindrical linear motor 1 via an electric wire (not shown) that passes through rod 11.

[0047] For example, by sensing the electrical angle of the windings 9 with respect to the field F, switching the energized phase based on the electrical angle, and controlling the amount of current in each winding 9 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-mentioned control method is an example and is not limited to this. Furthermore, when an external force acts that causes a relative displacement between the armature E and the field F in the axial direction, a thrust that suppresses the relative displacement can be generated by energizing the windings 9 or by induced electromotive force generated in the windings 9, allowing the cylindrical linear motor 1 to damp the vibration and movement of the equipment caused by the external force, and energy regeneration that generates electric power from the external force is also possible.

[0048] As described above, the cylindrical linear motor 1 of this embodiment comprises a cylindrical field F and an armature E that is arranged on the inner periphery of the field F and is movable in the axial direction relative to the field F. The field F comprises a plurality of permanent magnets 3a, 3b that are annular, magnetized in the axial direction, and arranged so that the magnetization direction alternates in the axial direction of the field F, and a yoke 2b that is annular, made of a soft magnetic material, and interposed between the permanent magnets 3a, 3b. The permanent magnets 3a, 3b have a convex shape in an axial cross section such that the axial length on the armature side is shorter than the axial length on the anti-armature side.

[0049] According to the cylindrical linear motor 1 configured in this manner, the axial length of the inner peripheral parts 3a1, 3b1 on the armature side of the permanent magnets 3a, 3b is shorter than the axial length of the outer peripheral parts 3a2, 3b2 on the anti-armature side, and magnetic flux flows from the axial end faces of not only the inner peripheral parts 3a1, 3b1 but also the outer peripheral parts 3a2, 3b2 through the yoke 2b, which is magnetically easy to pass through, toward the armature side, so that the magnetic flux density in the range radially facing the yoke 2b becomes high, so that the waveform of the gap magnetic flux density distribution on the outer periphery of the armature E becomes closer to a sine wave, compared to a field magnet configured by stacking axially magnetized annular permanent magnets with rectangular cross sections so that the magnetization directions are alternated. Therefore, the amplitude of the waveform of the gap magnetic flux density distribution on the outer periphery of the armature E becomes large, and the magnetic field acting on the armature E housed in the inner periphery of the sleeve 2 can be increased.

[0050] In this way, the cylindrical linear motor 1 in this embodiment can utilize inexpensive axially magnetized permanent magnets 3a, 3b while being able to increase the magnetic field acting on the armature E, thereby making it possible to achieve both improved thrust and reduced manufacturing costs.

[0051] Moreover, the cylindrical linear motor 1 of this embodiment includes a sleeve 2 formed of a soft magnetic material and having a cylindrical portion 2a that fits into the armature side of the permanent magnets 3a, 3b, and the sleeve 2 includes a yoke 2b integral with the cylindrical portion 2a. In the cylindrical linear motor 1 configured in this manner, the permanent magnets 3a, 3b are mounted in the annular groove 2c formed between the yokes 2b, 2b formed on the outer periphery of the sleeve 2. Therefore, if the position and dimensions of the annular groove 2c of the sleeve 2 are precisely controlled, even if there is a dimensional error in the axial length of the permanent magnets 3a, 3b, the dimensional error of the permanent magnets 3a, 3b is not accumulated in the axial direction of the sleeve 2, and the installation error of each of the permanent magnets 3a, 3b with respect to the sleeve 2 is within the axial range of the annular groove 2c. Therefore, according to the cylindrical linear motor 1 configured in this manner, the axial deviation of the installation positions of the permanent magnets 3a, 3b with respect to the sleeve 2 from the design value is reduced, so that the cogging thrust when the armature E is driven can be reduced. Furthermore, in the cylindrical linear motor 1 configured in this manner, the armature E is provided with the guide 10 that is in sliding contact with the inner peripheral surface of the sleeve 2, so that the armature E does not become eccentric in the radial direction with respect to the sleeve 2, and the relative radial positions of the permanent magnets 3a, 3b and the armature E are stable, enabling a stable thrust to be generated. As described above, the cylindrical linear motor 1 of this embodiment makes it possible to generate a stable thrust while reducing the cogging thrust.

[0052] Furthermore, in the cylindrical linear motor 1 of this embodiment, the cylindrical portion 2a of the sleeve 2 made of a soft magnetic material is disposed between the permanent magnets 3a, 3b and the armature E, and the guides 10, 10 can prevent the core 8 from interfering with the sleeve 2 even if the core 8 is disposed very close to the sleeve 2, so that the magnetic field generated by the permanent magnets 3a, 3b can be made to act on the armature E efficiently and the gap between the permanent magnets 3a, 3b and the core 8 can be made extremely small, allowing a large magnetic field to act on the armature E. Thus, according to the cylindrical linear motor 1 of this embodiment, a large magnetic field can be made to act on the armature E inside the field magnet F, and the magnetic air gap in the radial direction between the armature E and the field magnet F can be made even narrower, allowing the thrust to be increased, and as a result, the mass thrust density can be improved.

[0053] Furthermore, in the cylindrical linear motor 1 of this embodiment, the guide 10 of the armature E is brought into sliding contact with the sleeve 2 of the field F 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.

[0054] In addition, as long as the guide 10 is not opposed, an auxiliary field magnet may be provided on both or one axial side of the sleeve 2, which is cylindrical and made of a soft magnetic material and has an annular groove on its outer periphery in which a permanent magnet is attached, and which constitutes part of the field magnet.

[0055] In addition, in the cylindrical linear motor 1 of this embodiment, a gap G is provided between both axial ends of the bottom of the annular groove 2c in the sleeve 2 and the inner peripheral edges of both axial ends of the inner peripheral parts 3a1, 3b1 of the permanent magnets 3a, 3b. According to the cylindrical linear motor 1 configured in this manner, a gap G is formed between the corners at both axial ends of the bottom of the annular groove 2c and the inner peripheral edges at both axial ends of the inner peripheral parts 3a1, 3b1 of the permanent magnets 3a, 3b, so that the yoke 2b, which is the side wall of the annular groove 2c, and the axial ends of the inner peripheral parts 3a1, 3b1 of the permanent magnets 3a, 3b can come into surface contact with each other, and the permanent magnets 3a, 3b can be positioned in the annular groove 2c using the yoke 2b. Therefore, according to the cylindrical linear motor 1 configured in this manner, the permanent magnets 3a, 3b can be positioned at a desired position in the annular groove 2c, so that the permanent magnets 3a, 3b can be positioned at an appropriate position relative to the sleeve 2, and the cogging thrust during driving of the armature E can be further reduced. Furthermore, in the cylindrical linear motor 1 configured in this manner, the side wall of the yoke 2b and the end faces of the permanent magnets 3a, 3b can be in surface contact with each other, which makes it possible to avoid stress concentration on some of the permanent magnets 3a, 3b due to the axial load received when the armature E is driven. In addition, in the cylindrical linear motor 1 of this embodiment, when the permanent magnets 3a, 3b are fixed to the annular groove 2c using an adhesive, excess adhesive escapes and is accommodated in the gap G, which makes it possible to prevent the permanent magnets 3a, 3b from being positioned in the correct position within the annular groove 2c due to the presence of adhesive.

[0056] In addition, in the cylindrical linear motor 1 of the embodiment described above, the axial end faces of the outer peripheries 3a2, 3b2 of the permanent magnets 3a, 3b are in contact with each other or are opposed to each other with a small gap therebetween, but as in the cylindrical linear motor 1A of the first modified example shown in Figure 3, the cross-sectional shape of the yoke 2e in the sleeve 2 taken in the axial direction may be a convex shape with a convex portion on the outer periphery, and the permanent magnets 3a, 3b may be mounted between the yokes 2e, 2e.

[0057] The sleeve 2 in the cylindrical linear motor 1A of the first modification is made of a soft magnetic material, and includes a cylindrical portion 2a fitted to the inner circumference of the permanent magnets 3a and 3b, a plurality of annular yokes 2e arranged circumferentially on the outer circumference of the cylindrical portion 2a at intervals in the axial direction, and a plurality of annular grooves 2f formed by annular gaps along the circumferential direction between the yokes 2e, 2e of the cylindrical portion 2a, and includes the yoke 2e protruding like a flange on the outer circumference of the cylindrical portion 2a as an integral, inseparable unit. Note that the cylindrical portion 2a and the yoke 2e may be formed as separate parts.

[0058] 3, the yoke 2e is annular, with an inner peripheral portion 2e1 on the cylindrical side having a long axial length and an outer peripheral portion 2e2 on the anti-cylindrical side having a short axial length, and the cross section cut in the axial direction has a convex shape with a convex portion on the outer peripheral side. The radial thickness of the inner peripheral portion 2e1 of the yoke 2e is approximately equal to the radial thickness of the inner peripheral portions 3a1, 3b1 of the permanent magnets 3a, 3b, and the radial thickness of the outer peripheral portion 2e2 is approximately equal to the radial thickness of the outer peripheral portions 3a2, 3b2 of the permanent magnets 3a, 3b.

[0059] Therefore, the annular groove 2f between the yokes 2e, 2e, unlike the yoke 2e, has a short axial length on the inner side which is the cylindrical portion side and a long axial length on the outer side which is the anti-cylindrical portion side, and its axial cross-sectional shape matches the axial cross-sectional shape of the permanent magnets 3a, 3b, so that the permanent magnets 3a, 3b can be accommodated inside.

[0060] Although not shown in detail, both axial ends of the bottom of the inner and outer circumferential portions of the annular groove 2f in the sleeve 2, i.e., the outer periphery of the cylindrical portion 2a, the base portions on both axial sides of the yoke 2e, and the axial corners on both axial sides of the step portion of the yoke 2e, may be filleted or grooved, as in the sleeve 2 of the cylindrical linear motor 1 of one embodiment, to avoid interference with the corners on both axial ends of the permanent magnets 3a, 3b.

[0061] In this embodiment, the cross-sectional shapes of the annular grooves 2f are all equal, and the annular grooves 2f are provided at equal intervals on the outer periphery of the sleeve 2. Therefore, the yokes 2e are also provided at equal intervals on the outer periphery of the sleeve 2. In this embodiment, the end yokes 2g, 2g provided at both ends of the sleeve 2 have a shape obtained by cutting the yoke 2e in half at the center in the axial direction. It is not necessary to provide end yokes 2g, 2g at both ends by making the ends of the sleeve 2 annular grooves.

[0062] The permanent magnets 3a and 3b are mounted in the annular groove 2f between the yokes 2e and 2e of the sleeve 2 configured in this way so that their magnetization directions are alternated. Then, the inner peripheral portion 2e1 of the yoke 2e is interposed between the inner peripheral portions 3a1 and 3b1 of the permanent magnets 3a and 3b, so that the axial end faces of the inner peripheral portions 3a1 and 3b1 face the axial end face of the inner peripheral portion 2e1 of the yoke 2e in the axial direction, and the inner peripheral portion 2e1 of the yoke 2e is interposed between the outer peripheral portions 3a2 and 3b2 of the permanent magnets 3a and 3b, so that the axial end faces of the outer peripheral portions 3a2 and 3b2 face the axial end face of the outer peripheral portion 2e2 of the yoke 2e in the axial direction. In this way, the permanent magnets 3a and 3b are interposed over the entire area between the yokes 2e and 2e, and are entirely housed in the annular groove 2f between the yokes 2e and 2e when viewed from the axial direction.

[0063] Although not shown in the figure, the inner circumferences of the inner circumferential portions 3a1, 3b1 and the outer circumferential portions 3a2, 3b2 of each permanent magnet 3a, 3b are chamfered at both axial ends, so that even when the permanent magnets 3a, 3b are housed in the annular groove 2f between the yokes 2e, 2e, the permanent magnets 3a, 3b are prevented from floating up from the outer circumference of the cylindrical portion 2a.

[0064] Like the cylindrical linear motor 1, the cylindrical linear motor 1A of this embodiment also forms one magnetic pole from the axial center of the permanent magnet 3a, including the yoke 2e, to the axial center of the adjacent permanent magnet 3b, and the N poles of the permanent magnets 3a, 3b, which have their N poles facing each other, and the yoke 2e sandwiched between the N poles, function as one N pole, and the S poles of the permanent magnets 3a, 3b, which have their S poles facing each other, and the yoke 2e sandwiched between the S poles, function as one S pole.

[0065] In the field F configured in this manner, the axial length of the inner periphery 3a1, 3b1 of the permanent magnets 3a, 3b on the armature side is shorter than the axial length of the outer periphery 3a2, 3b2 on the anti-armature side, and the magnetic flux of the inner periphery 3a1, 3b1 and the outer periphery 3a2, 3b2 passes through the yoke 2e, which is magnetically easy to pass through, toward the armature side, and the magnetic flux density becomes high in the range radially opposing the yoke 2e. Therefore, compared to a field configured by simply stacking axially magnetized annular permanent magnets with rectangular cross sections so that the magnetization directions are alternated, the waveform of the gap magnetic flux density distribution on the outer periphery of the armature E becomes closer to a sine wave and the amplitude of the waveform becomes larger, making it possible to increase the magnetic field acting on the armature E housed in the inner periphery of the sleeve 2. In addition, in the cylindrical linear motor 1A of the first modification, the outer peripheral portion 2e2 of the yoke 2e is sandwiched between the outer peripheral portions 3a2, 3b2, which are the portions of the permanent magnets 3a, 3b that have a long axial length, so that the magnetic flux emanating not only from the inner peripheral surfaces on the armature side of the outer peripheral portions 3a2, 3b2 but also from the end faces in the axial direction is directed toward the inner peripheral portion 2e1 of the yoke 2e. Therefore, in the cylindrical linear motor 1A of the present embodiment, the magnetic flux can be concentrated in the range radially facing the inner peripheral portion 2e1 of the yoke 2e more than in the cylindrical linear motor 1, so that the waveform of the gap magnetic flux density distribution on the outer periphery of the armature E becomes closer to a sine wave, the amplitude of the waveform becomes larger, and the magnetic field acting on the armature E housed in the inner periphery of the sleeve 2 can be further increased.

[0066] As described above, the cylindrical linear motor 1A in the first modified example of this embodiment includes a cylindrical field F and an armature E that is arranged on the inner periphery of the field F and is movable in the axial direction relative to the field F. The field F includes a plurality of permanent magnets 3a, 3b that are annular, magnetized in the axial direction, and arranged so that the magnetization direction alternates in the axial direction of the field F. The sleeve 2 is made of a soft magnetic material and has a cylindrical portion 2a that fits on the armature side of the permanent magnets 3a, 3b and a yoke 2e that is annular, integrated with the cylindrical portion 2a, and interposed between the permanent magnets 3a, 3b. The permanent magnets 3a, 3b have a convex shape in a cross section taken in the axial direction, with the axial length on the armature side being shorter than the axial length on the anti-armature side. The yoke 2e is interposed over the entire area between inner peripheries (portions) 3a1, 3b1 of the permanent magnets 3a, 3b that have a shorter axial length on the armature side and outer peripheries (portions) 3a2, 3b2 that have a longer axial length on the anti-armature side.

[0067] According to the cylindrical linear motor 1A configured in this manner, the axial length of the inner circumferential portions 3a1, 3b1 of the permanent magnets 3a, 3b on the armature side is shorter than the axial length of the outer circumferential portions 3a2, 3b2 on the anti-armature side, and the permanent magnets 3a, 3b are entirely interposed between the yokes 2e, 2e. Therefore, the magnetic flux emitted from the armature side surfaces and both axial end faces of the inner circumferential portions 3a1, 3b1 and the outer circumferential portions 3a2, 3b2 passes through the yoke 2e, which is magnetically easy to pass through, toward the armature side, and the magnetic flux density in the range radially opposing the yoke 2e becomes higher. As a result, the waveform of the gap magnetic flux density distribution on the outer periphery of the armature E becomes closer to a sine wave than in a field magnet configured by stacking axially magnetized, annular permanent magnets with rectangular cross sections so that the magnetization directions are alternately alternating. Therefore, the amplitude of the waveform of the gap magnetic flux density distribution on the outer periphery of the armature E becomes even larger, and the magnetic field acting on the armature E housed on the inner periphery of the sleeve 2 can be made even larger.

[0068] In this way, in the cylindrical linear motor 1A of the present embodiment, while utilizing inexpensive axially magnetized permanent magnets 3a, 3b, the magnetic field acting on the armature E can be made even larger, thereby enabling a reduction in manufacturing costs while further improving thrust.

[0069] Moreover, the cylindrical linear motor 1A of this embodiment includes a sleeve 2 formed of a soft magnetic material and having a cylindrical portion 2a that fits into the armature side of the permanent magnets 3a, 3b, and the sleeve 2 includes a yoke 2e that is integral with the cylindrical portion 2a. In the cylindrical linear motor 1A configured in this manner, the permanent magnets 3a, 3b are attached to the annular grooves 2f formed in the yokes 2e, 2e formed on the outer periphery of the sleeve 2. Therefore, if the position and dimensions of the annular groove 2c of the sleeve 2 are precisely controlled, even if there is a dimensional error in the axial length of the permanent magnets 3a, 3b, the dimensional error of the permanent magnets 3a, 3b is not accumulated in the axial direction of the sleeve 2, and the installation error of each of the permanent magnets 3a, 3b with respect to the sleeve 2 is within the axial range of the annular groove 2f. Furthermore, in the cylindrical linear motor 1A, the yoke 2e is positioned entirely between the permanent magnets 3a, 3b in the axial direction, so that the permanent magnets 3a, 3b do not directly interfere with each other. This makes it less susceptible to the effects of dimensional errors in the permanent magnets 3a, 3b, and allows the permanent magnets 3a, 3b to be more appropriately positioned in the sleeve 2.

[0070] Therefore, according to the cylindrical linear motor 1A in the first modified example configured in this manner, the axial deviation of the installation positions of the permanent magnets 3a, 3b relative to the sleeve 2 from the design value is further reduced, thereby further reducing the cogging thrust when the armature E is driven.

[0071] Furthermore, in the cylindrical linear motor 1 of the embodiment described above, the axial end faces of the outer peripheries 3a2, 3b2 of the permanent magnets 3a, 3b are in contact with each other or are opposed to each other with a small gap therebetween, but as in the cylindrical linear motor 1B of the second modified example shown in Figure 4, the axial width of the yoke 2b in the sleeve 2 may be increased to intentionally provide a gap between the outer peripheries 3a2, 3b2 of the permanent magnets 3a, 3b mounted in the annular groove 2c between the yokes 2b, 2b, so that a magnetic gap 20 is formed between the outer peripheries 3a2, 3b2 on the outer periphery side of the yoke 2b.

[0072] In the field F configured in this manner, a magnetic gap 20 is provided between the outer peripheral portions 3a2, 3b2, which are the portions of the permanent magnets 3a, 3b that have a long axial length, so that the magnetic flux emitted from the axial ends of the outer peripheral portions 3a2, 3b2 also heads toward the yoke 2b provided on the inner peripheral side, and is less likely to pass through the outer peripheral side, which is the anti-armature side, of the permanent magnets 3a, 3b, and the magnetic flux heading toward the inner peripheral side, which is the armature side, increases accordingly, and the magnetic field acting on the armature E housed in the inner periphery of the sleeve 2 can be increased. In addition, in the cylindrical linear motor 1B of the second modified example, a magnetic gap 20 is provided between the outer peripheral portions 3a2, 3b2, which are the portions of the permanent magnets 3a, 3b that have a long axial length, on the anti-armature side of the yoke 2b, so that most of the magnetic flux emitted from the axial end faces of the outer peripheral portions 3a2, 3b2, together with the magnetic flux emitted from the inner peripheral surfaces on the armature side of the outer peripheral portions 3a2, 3b2, heads toward the inner peripheral portion 2e1 of the yoke 2b. Therefore, in the cylindrical linear motor 1B of this embodiment, the magnetic flux can be concentrated in the area radially opposite the yoke 2b more than in the cylindrical linear motor 1, the waveform of the gap magnetic flux density distribution on the outer periphery of the armature E becomes closer to a sine wave, the amplitude of the waveform becomes larger, and the magnetic field acting on the armature E housed in the inner periphery of the sleeve 2 can be made even larger.

[0073] As described above, the cylindrical linear motor 1B in the first modified example of the present embodiment includes a cylindrical field magnet F and an armature E that is disposed on the inner periphery of the field magnet F and is movable in the axial direction relative to the field magnet F. The field magnet F includes a plurality of permanent magnets 3a, 3b that are annular, axially magnetized, and arranged such that the magnetization directions alternate in the axial direction of the field magnet F, a cylindrical portion 2a that fits onto the armature side of the permanent magnets 3a, 3b, and a yoke 2b that is annular, integrated with the cylindrical portion 2a, and interposed between the permanent magnets 3a, 3b. and a sleeve 2 formed of a soft magnetic material, the permanent magnets 3a, 3b have a convex shape in an axial cross section with the axial length on the armature side shorter than the axial length on the anti-armature side, the yoke 2b is interposed between inner peripheries (portions) 3a1, 3b1 of the permanent magnets 3a, 3b which have a shorter axial length on the armature side, and a magnetic gap 20 is provided between outer peripheries (portions) 3a2, 3b2 which are on the anti-armature side of the yoke 2b and have a longer axial length on the anti-armature side of the permanent magnets 3a, 3b.

[0074] According to the cylindrical linear motor 1B configured in this manner, the axial length of the inner circumferential portions 3a1, 3b1 on the armature side of the permanent magnets 3a, 3b is shorter than the axial length of the outer circumferential portions 3a2, 3b2 on the anti-armature side, and a magnetic gap 20 is provided between the outer circumferential portions 3a2, 3b2 of the permanent magnets 3a, 3b on the anti-armature side of the yoke 2b. Therefore, the magnetic flux emitted from the inner circumferential portions 3a1, 3b1 and the inner circumferential surfaces and axial end faces on the armature side of the outer circumferential portions 3a2, 3b2 passes through the yoke 2b, which is magnetically easy to pass through, toward the armature side, and the magnetic flux density in the range radially opposing the yoke 2b becomes high. As a result, the waveform of the gap magnetic flux density distribution on the outer periphery of the armature E becomes closer to a sine wave than in a field magnet configured by stacking axially magnetized annular permanent magnets with rectangular cross sections so that the magnetization directions are alternately arranged. Therefore, the amplitude of the waveform of the gap magnetic flux density distribution on the outer periphery of the armature E becomes even larger, and the magnetic field acting on the armature E housed on the inner periphery of the sleeve 2 can be made even larger.

[0075] In this way, in the cylindrical linear motor 1B of the present embodiment, while utilizing inexpensive axially magnetized permanent magnets 3a, 3b, the magnetic field acting on the armature E can be made even larger, thereby enabling a reduction in manufacturing costs while further improving thrust.

[0076] In this embodiment, the armature E is inserted on the inner periphery of the field F, but a cylindrical armature E may be disposed on the outer periphery of the field F. In this manner, when the armature E is disposed on the outer periphery of the field F, the field F is annular, and a plurality of permanent magnets are magnetized in the axial direction and arranged so that the magnetization directions alternate in the axial direction of the field F. The axial length of the outer periphery side portion of the field F may be made shorter than the axial length of the inner periphery side portion.

[0077] In addition, in the cylindrical linear motors 1, 1A, and 1B of the embodiment, the sleeve 2 has a cylindrical portion 2a and a yoke 2b integrally formed on the outer periphery of the cylindrical portion 2a. However, since the cylindrical portion 2a has magnetic resistance even though it is made of a soft magnetic material, the thinner the radial thickness of the cylindrical portion 2a, the stronger the magnetic field that can be applied to the armature E. On the other hand, the thinner the thickness of the cylindrical portion 2a, the weaker the strength of the sleeve 2 becomes, making it difficult to use the sleeve 2 as a member for holding the field magnet F. Therefore, a rib that intersects with the yoke 2b along the axial direction may be provided on the outer periphery of the cylindrical portion 2a to thin the radial thickness of the cylindrical portion 2a and increase the magnetic field that is applied to the armature E, while suppressing the weakening of the cylindrical portion 2a. When the armature E is disposed on the outer periphery of the field magnet F, a rib may be provided on the outer periphery of the cylindrical portion 2a of the sleeve 2. The number of ribs and their cross-sectional shape can be set as desired as long as the strength of the cylindrical portion 2a can be ensured. If ribs are provided, the permanent magnets 3a, 3b can be divided in the circumferential direction so that the permanent magnets 3a, 3b can avoid the ribs.

[0078] Although the preferred embodiment of the present invention has been described in detail above, modifications, variations and changes can be made thereto without departing from the scope of the appended claims. [Explanation of symbols]

[0079] 1, 1A, 1B... cylindrical linear motor, 2b, 2e... yoke, 3a, 3b... permanent magnet, 3a1, 3b1... inner periphery (portion of permanent magnet with short axial length), 3a2, 3b2... outer periphery (portion of permanent magnet with long axial length), 20... magnetic gap, E... armature, F... field magnet

Claims

1. A cylindrical field magnet, an armature disposed on an inner periphery or an outer periphery of the field magnet and movable in an axial direction relative to the field magnet; The field magnet is A plurality of permanent magnets are annular, axially magnetized, and arranged such that the magnetization directions alternate in the axial direction of the field magnet; a yoke having an annular shape, made of a soft magnetic material, and interposed between the permanent magnets; The permanent magnet has a convex shape in an axial cross section, the axial length of which on the armature side is shorter than the axial length on the non-armature side. A cylindrical linear motor.

2. a sleeve made of a soft magnetic material and having a cylindrical portion that fits onto the armature side of the permanent magnet; the sleeve has the yoke integral with the cylindrical portion, The yoke is interposed over the entire area between a portion of the permanent magnet that is short in axial length on the armature side and a portion of the permanent magnet that is long in axial length on the anti-armature side.

2. The cylindrical linear motor according to claim 1 .

3. a sleeve made of a soft magnetic material and having a cylindrical portion that fits onto the armature side of the permanent magnet; the sleeve has the yoke integral with the cylindrical portion, The yoke is interposed between the portions of the permanent magnets that are on the armature side and have a short axial length, A magnetic gap is provided between the yoke and the permanent magnet on the opposite armature side, the axial length of which is longer than the armature side.

2. The cylindrical linear motor according to claim 1 .

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