cylindrical linear motor

Abstract

To provide a cylindrical linear motor with which, when equipped with a yoke, yet it is possible to improve mass thrust density.SOLUTION: In order to achieve the above objective, a cylindrical linear motor 1 pertaining to the present invention comprises: a cylindrical magnetic field 6 having a stacked magnet body 10 which is constructed with a plurality of annular permanent magnets 10a, 10b that is stacked one on another in such a way that N and S poles are alternately arranged in an axial direction, and a cylindrical yoke 8 which is constructed with a magnetic body that is disposed on an inner circumference and / or an outer circumference of the stacked magnet body 10; and an armature 2 which is disposed on a counter-yoke side that is the inner or outer circumferential side of the stacked magnet body 10 and is capable of moving toward the magnetic field 6 in the axial direction of the magnetic field 6. The yoke 8 includes a notch 30a which is formed along the axial direction penetrating a wall thickness of the yoke 8, and of which an axial length L1 that is along the axial direction of the yoke 8 is longer than a circumferential length L2 that is along a circumferential direction of the yoke 8.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] A cylindrical linear motor, for example, includes a core having a number of teeth arranged in the axial direction on its outer periphery, an armature having U-phase, V-phase, and W-phase windings fitted in slots between the teeth, and a field magnet facing the armature, which has a laminated magnet body formed by stacking a number of annular permanent magnets so that south and north poles are arranged alternately in the axial direction.

[0003] In a cylindrical linear motor configured in this manner, by applying current appropriately to the U-phase, V-phase, and W-phase windings of the armature, attractive and repulsive forces in the axial direction are generated between the permanent magnets in the field and the armature, driving the armature or field as a mover.

[0004] In such cylindrical linear motors, the field magnet may have a yoke made of a ferromagnetic cylinder around the outer periphery of the laminated magnet body in order to efficiently direct the magnetic field lines of the permanent magnets in the field magnet toward the armature side and improve the thrust of the cylindrical linear motor (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-86725 Summary of the Invention [Problem to be solved by the invention]

[0006] Although the yoke improves the thrust of the cylindrical linear motor, it is a ferromagnetic material and therefore has a large mass, which can reduce the mass thrust density of the cylindrical linear motor. Here, mass thrust density is the value obtained by dividing the maximum thrust of the cylindrical linear motor by its mass, and the larger the mass thrust density value, the greater the thrust per mass of the cylindrical linear motor. Therefore, the mass thrust density value is an index for evaluating the thrust output efficiency using the size of the cylindrical linear motor as a scale.

[0007] As described above, although the thrust of a cylindrical linear motor is improved by providing a yoke, if the mass of the cylindrical linear motor becomes too large due to the provision of a yoke, even if the thrust is improved, there is a problem in that the mass thrust density decreases and the thrust output efficiency deteriorates.

[0008] Therefore, an object of the present invention is to provide a cylindrical linear motor that can improve the mass thrust density even when equipped with a yoke. [Means for solving the problem]

[0009] In order to achieve the above object, the cylindrical linear motor of the present invention comprises a laminated magnet body formed of a plurality of annular permanent magnets stacked so that N poles and S poles are arranged alternately in the axial direction, a cylindrical field magnet having a cylindrical yoke formed of a magnetic material arranged on either the inner or outer periphery of the laminated magnet body, and an armature arranged on the inner or outer periphery of the laminated magnet body, opposite the yoke, and movable in the axial direction of the field magnet relative to the field magnet, the yoke having a notch formed along the axial direction, penetrating the thickness of the yoke, and whose axial length along the axial direction of the yoke is longer than the circumferential length along the circumferential direction of the yoke.

[0010] In a cylindrical linear motor configured in this manner, a yoke with low magnetic resistance is provided on the anti-armature side of the laminated magnet body, which allows the field magnetic flux acting on the armature side to be increased, and the provision of a notch in the yoke allows the yoke to be made lighter.

[0011] Furthermore, although the cross-sectional area of ​​the magnetic path of the yoke is reduced by providing the notches in the yoke, the notches are aligned along the axial direction of the yoke, and the axial length along the axial direction of the yoke is longer than the circumferential length along the circumferential direction of the yoke, so that the direction of progression of the magnetic flux of the laminated magnet body coincides with the axial direction within the yoke, it is possible to suppress a decrease in the magnetic resistance of the yoke due to the provision of the notches.

[0012] Also, the notch ratio, which is the ratio of the volume difference obtained by subtracting the volume of the yoke having the notches from the volume before the notches are formed in the yoke without the notches, to the volume before the notches are formed, may be set to 12% or less. Ta As a result, the mass thrust density can be stably improved. [Effects of the Invention]

[0013] According to the cylindrical linear motor of the present invention, even if a yoke is provided, the mass thrust density can be improved. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a longitudinal sectional view of a cylindrical linear motor according to an embodiment of the present invention; [Figure 2] 2 is a side view of a yoke of a cylindrical linear motor according to an embodiment, viewed from a radial direction. FIG. [Figure 3] FIG. 2 is a partially enlarged vertical cross-sectional view of a field magnet of a cylindrical linear motor according to an embodiment. [Figure 4] 10 is a graph showing the relationship between the notch ratio and the mass thrust density of a cylindrical linear motor. DETAILED DESCRIPTION OF THE INVENTION

[0015] 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 with a laminated magnet body 10 formed of multiple annular permanent magnets 10a, 10b that are laminated on the inner periphery so that N poles and S poles are arranged alternately in the axial direction, a cylindrical field magnet 6 having a cylindrical yoke 8 formed of a magnetic material and arranged on the outer periphery of the laminated magnet body 10, and an armature 2 that is movable in the axial direction of the field magnet 6 relative to the field magnet 6.

[0016] Below, we will explain in detail each part of the cylindrical linear motor 1. The armature 2 is composed of a core 3 and a winding 5. The core 3 is composed of a cylindrical core body 3a and a plurality of annular teeth 3b provided at intervals in the axial direction on the outer periphery of the core body 3a.

[0017] As described above, the core 3 is cylindrical, and as shown in Fig. 1, it has ten teeth 3b arranged at equal intervals in the axial direction on the outer periphery of the core body 3a, and slots 4, which are gaps into which windings 5 ​​are attached, are formed between the teeth 3b. In this embodiment, a total of nine slots 4, which are gaps, are provided between adjacent teeth 3b in Fig. 1. The windings 5 ​​are wound around and attached to these slots 4. The windings 5 ​​are made up of three-phase windings: a U-phase winding, a V-phase winding, and a W-phase winding.

[0018] Each tooth 3b is annular and, except for the teeth 3b located at both ends of the core 3, is an isosceles trapezoid in the axial direction, with the outer circumferential end being narrower than the inner circumferential end, and both axial side surfaces are tapered at equal angles relative to the outer circumferential end. As shown in Fig. 1, the terminal teeth 3b have a cross-sectional shape in which the other teeth 3b are cut in half along a plane perpendicular to the axis of the core 3. The cross-sectional shape of the teeth 3b may be a shape other than an isosceles trapezoid, such as a rectangle.

[0019] The armature 2 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. The rod 11 includes a cylindrical first rod 20 and a cylindrical second rod 21, which has a core 3 attached to its outer periphery and is screwed onto the inner periphery of the first rod 20.

[0020] The first rod 20 is cylindrical and includes a rod body 22 having screw portions 22a and 22b on the outer periphery at the left end in FIG. 1 and on the inner periphery at the right end in FIG. 1, respectively, and a rod cap 23 having a bracket 23a for attaching the cylindrical linear motor 1 to equipment and screwed onto the screw portion 22a at the left end in FIG. 1 of the rod body 22 to close the left end of the rod body 22.

[0021] An annular slider 25 is fitted to the outer periphery of the right end of the rod main body 22 in FIG. 1. The slider 25 includes a sliding contact portion 25a that slides against the inner periphery of a cylindrical portion 9b (described later), a small-diameter portion 25b that is provided on the base end side of the rod 11, which is to the left of the sliding contact portion 25a in FIG. 1, and has an outer diameter smaller than that of the sliding contact portion 25a, an annular groove 25c that is provided circumferentially on the outer periphery of the small-diameter portion 25b, and a flange 25d that is provided on the inner periphery of the right end in FIG. 1. A rubber seal ring 26 serving as an elastic body is fitted in the annular groove 25c of the slider 25. The inner diameter of the flange 25d is equal to or larger than the inner diameter of the rod main body 22 but smaller than the outer diameter of the rod main body 22. When the slider 25 is fitted to the rod main body 22, the flange 25d abuts against the right end surface of the rod main body 22 in FIG. 1.

[0022] The second rod 21 includes a cylindrical core retaining tube 21a on whose outer periphery the core 3 is attached, and an annular slider 21b provided on the outer periphery of the tip of the core retaining tube 21a, which is the right end in FIG. 1. A threaded portion 21c is provided on the outer periphery of the base end of the core retaining tube 21a, which is the left end in FIG. 1. The base end of the core retaining tube 21a is provided on the inner periphery thereof, with a large inner diameter portion 21d having a larger inner diameter than other portions. When the base end of the core retaining tube 21a is inserted into the inner periphery of the rod main body 22 of the first rod 20 at the right end in FIG. 1 and the threaded portion 21c is screwed into the threaded portion 22b, the first rod 20 and the second rod 21 are connected. In this manner, in this embodiment, the rod 11 is cylindrical and is composed of the first rod 20 and the second rod 21.

[0023] Furthermore, the core 3 is fitted onto the outer periphery of the core holding cylinder 21a of the second rod 21. The outer diameter of the core holding cylinder 21a is smaller than the outer diameter of the rod main body 22 of the first rod 20. Therefore, when the second rod 21, on which the armature 2 is mounted, is connected to the first rod 20, on which the slider 25 is mounted, in the manner described above, the armature 2 and the slider 25 are sandwiched and fixed between the right end of the first rod 20 in FIG. 1 and the slider 21b of the second rod 21. When the armature 2 is mounted on the rod 11 in this manner, the core 3 is fixed to the rod 11 in a manner sandwiched between the slider 21b and the slider 25. Note that, although the armature 2 is configured to have only a single core 3 in this embodiment, it may be configured to have multiple cores 3 to improve thrust, etc.

[0024] Next, the rod 11 is provided with a cover 17 that covers the outer periphery of the rod 11 and forms a gap G. Specifically, the cover 17 is cylindrical, and is attached to the rod 11 with one end fitted onto the outer periphery of an annular cover end 18 provided on the outer periphery of the rod 11 and the other end fitted onto the outer periphery of the small diameter portion 25b of the slider 25.

[0025] Lead wires L that connect the windings 5 ​​of each phase attached to the core 3 to an external drive circuit (not shown) are housed in the gap G between the cover 17 and the rod 11, and the wiring work between the windings 5 ​​and the lead wires L can be performed with the cover 17 removed, making the assembly work of the cylindrical linear motor 1 easier.

[0026] On the other hand, in this embodiment, the stator is configured to include a field 6 made up of a cylindrical laminated magnet body 10 and a yoke 8 made of a cylindrical magnetic material that is press-fitted onto the outer periphery of the laminated magnet body 10, a cylindrical guide tube 9 made of a non-magnetic material that is inserted into the inner periphery of the laminated magnet body 10, and a cylindrical barrel 7 made of a non-magnetic material into which the guide tube 9 and field 6 are inserted.

[0027] The barrel 7 is made of a non-magnetic material and has a threaded portion 7a provided on the inner periphery of the open end on the left side in FIG. 1 and a threaded portion 7b provided on the outer periphery of the open end on the right side in FIG. 1. A bottom cap 12 is screwed onto the outer periphery of the open end on the right side in FIG. 1 of the barrel 7, closing the open end on the right side in FIG. 1. The bottom cap 12 is cylindrical with a bottom 12a and a tubular portion 12b, and is attached to the barrel 7 by screwing the tubular portion 12b onto the outer periphery of the barrel 7. A bracket 12c is provided on the tubular portion 12b of the bottom cap 12, allowing the cylindrical linear motor 1 to be attached to a device. The bottom 12a of the bottom cap 12 faces the right end of the field magnet 6 in FIG. 1.

[0028] The guide tube 9 is made of a non-magnetic material and is configured to include an annular head portion 9a that is attached by screwing to the open end at the left end in Fig. 1 of the barrel 7, and a tubular portion 9b that is thinner in thickness than the head portion 9a and extends from the inner periphery of the right end in Fig. 1 of the head portion 9a and is inserted into the inner periphery of the field magnet 6. Therefore, the right end in Fig. 1 of the head portion 9a of the guide tube 9 faces the left end in Fig. 1 of the field magnet 6 that is arranged on the outer periphery of the tubular portion 9b.

[0029] The guide tube 9 also has a curved surface 9c at the boundary between the right end of the head portion 9a in Figure 1 and the cylindrical portion 9b, so that even if an axial force acts only on the head portion 9a, stress does not concentrate at the boundary between the head portion 9a and the cylindrical portion 9b. To avoid such stress concentration, a tapered surface may be provided at the boundary between the head portion 9a and the cylindrical portion 9b.

[0030] The field 6 is configured with a laminated magnet body 10 formed of a plurality of annular permanent magnets 10a serving as main magnetic poles and a plurality of annular permanent magnets 10b serving as sub-magnetic poles, which are alternately stacked and inserted in the axial direction, and a cylindrical yoke 8 bonded to the outer periphery of the laminated magnet body 10.

[0031] The laminated magnet body 10 is composed of multiple annular permanent magnets 10a that serve as main poles and multiple annular permanent magnets 10b that serve as sub-pole poles, stacked alternately in the axial direction. The permanent magnets 10a and 10b are stacked with an adhesive between them to prevent them from scattering. Note that the triangular marks on the main pole permanent magnets 10a and sub-pole permanent magnets 10b in FIG. 1 indicate the magnetization direction, with the main pole permanent magnets 10a being magnetized radially and the sub-pole permanent magnets 10b being magnetized axially. The main pole permanent magnets 10a and sub-pole permanent magnets 10b 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.

[0032] Furthermore, in the cylindrical linear motor 1 of this embodiment, the axial length of the permanent magnet 10a of the main magnetic pole is longer than the axial length of the permanent magnet 10b of the sub-pole. In this way, if the axial length of the permanent magnet 10a of the main magnetic pole is increased, the magnetic resistance between the permanent magnet 10a of the main magnetic pole and the core 3 can be reduced, and the magnetic field acting on the core 3 can be increased, thereby improving the thrust of the cylindrical linear motor 1. In this embodiment, the axial length of the permanent magnet 10a of the main magnetic pole is longer than the axial length of the permanent magnet 10b of the sub-pole, but this is not limiting and the axial lengths of the two can be set as desired by design.

[0033] Furthermore, in the cylindrical linear motor 1 of the present invention, a yoke 8 is provided around the permanent magnets 10a and 10b. Without the yoke 8, shortening the axial length of the permanent magnets 10b of the sub-pole increases the magnetic resistance outside the permanent magnets 10a of the main pole at the axial center, reducing the field magnetic flux. This reduces the degree of improvement in thrust of the cylindrical linear motor 1 when the axial length of the permanent magnets 10a of the main pole is increased. In contrast, providing a yoke 8 around the permanent magnets 10a and 10b 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 10b of the sub-pole. Therefore, making the axial length of the permanent magnets 10a of the main pole longer than that of the permanent magnets 10b of the sub-pole and providing a cylindrical yoke 8 around the permanent magnets 10a and 10b can significantly improve the thrust of the cylindrical linear motor 1. The thickness of the yoke 8 may be set to a thickness suitable for suppressing an increase in the external magnetic resistance of the permanent magnet 10a of the main magnetic pole.

[0034] As shown in Fig. 1, the yoke 8 is formed by stacking multiple yoke segments 30. As shown in Fig. 2, each yoke segment 30 is cylindrical and has four notches 30a formed along the axial direction and penetrating the wall thickness of the yoke segment 30. The yoke segments 30 are sequentially attached to the outer periphery of the laminated magnet body 10 as described above and stacked on the outer periphery of the laminated magnet body 10 to form the yoke 8 that covers the outer periphery of the laminated magnet body 10. The notches 30a are rectangular, with the four corners chamfered in an R or C shape.

[0035] As described above, because each yoke segment 30 has a notch 30a, the overall mass of the yoke 8 is smaller than when the yoke 8 does not have the notch 30a. Furthermore, the axial length L1 of the notch 30a along the axial direction of the yoke 8 is longer than the circumferential length L2 of the notch 30a along the circumferential direction of the yoke 8. Since the notches 30a are provided along the axial direction of the yoke 8, the provision of the notches 30a can reduce the mass of the yoke 8 while suppressing an increase in magnetic resistance in the yoke 8 due to the provision of the notches 30a. Therefore, by providing the notches 30a in the yoke 8, it is possible to suppress an increase in the weight of the cylindrical linear motor 1 due to the provision of the yoke 8 on the outer periphery of the laminated magnet body 10. Furthermore, because the four corners of the notches 30a are chamfered in an R-shape or a C-shape, magnetic flux passing through the yoke 8 near the notches 30a can pass smoothly through the yoke 8.

[0036] The axial length of the yoke 8 is set to be equal to or longer than the axial length of the laminated magnet body 10, but is set to a length that prevents the permanent magnets 10a, 10b from unnecessarily applying a magnetic field outside the stroke range of the core 3, thereby preventing a decrease in thrust. The axial length of the yoke 8 may be set to be equal to the overall length of the laminated magnet body 10. If the axial length of the yoke 8 is longer than the overall length of the laminated magnet body 10, the magnetic field lines at the ends of the laminated magnet body 10 will not leak into the atmosphere, preventing a decrease in thrust of the cylindrical linear motor 1. In this way, the axial length of the yoke 8 can be made longer than the axial length of the laminated magnet body 10 by making the axial length of the yoke 8 longer than the axial length of the laminated magnet body 10, simply by making the axial length of the yoke 8 longer than the maximum axial length that the laminated magnet body 10 can assume due to processing errors in the permanent magnets 10a, 10b.

[0037] The axial length of the yoke segments 30 other than those at both axial ends of the yoke 8 is set to twice the length of the magnetic pole pitch P of the field magnet 6. The yoke segments 30 at both axial ends of the yoke 8 may be set so that the overall length of the yoke 8 is equal to or greater than the overall length of the field magnet 6 when all of the yoke segments 30 are stacked. If the axial lengths of the yoke segments 30 at both axial ends of the yoke 8 are short and it is difficult to provide the notches 30a, the notches 30a may not be provided in the yoke segments 30 at both axial ends of the yoke 8. If the yoke 8 is formed as a single unit rather than by stacking separate yoke segments 30, it is sufficient to provide a notch along the axial direction in the yoke 8. The notches 30a are formed as holes, leaving the ends of the yoke segments 30 uncut, but may be formed so as to open at one end of the yoke segments 30. Furthermore, four notches 30a are provided in the circumferential direction of the yoke segment 30, but it is sufficient to provide at least one or more, so only one may be provided in the circumferential direction, or multiple notches 30a may be provided lined up in the axial direction.

[0038] 3, the magnetic pole pitch P of the field magnet 6 extends from the center of the permanent magnet 10a of the main pole to the center of the permanent magnet 10a of the adjacent main pole, sandwiching the permanent magnet 10b of the sub-pole. The path of the magnetic field lines forms a loop, passing from the permanent magnet 10a of the main pole through the armature 2 to the permanent magnet 10a of the adjacent main pole, in the range from the center of the permanent magnet 10a of the main pole to the center of the permanent magnet 10a of the adjacent main pole, sandwiching the permanent magnet 10b of the sub-pole.

[0039] Therefore, if the axial length of the yoke segments 30 is set to an integer multiple of the magnetic pole pitch P and at least the axial end portions 30b of the yoke segments 30 are positioned on the outer periphery of the permanent magnets 10a of the main poles, the magnetic field lines of the laminated magnet body 10 will cross multiple yoke segments 30, but leakage of the magnetic field lines to the outside can be suppressed while suppressing an increase in the magnetic resistance of the yoke 8.

[0040] Because the yoke 8 is formed by stacking a plurality of yoke segments 30 in this way, it is extremely easy to attach the yoke segments 30, which are much shorter than the overall length of the yoke 8, one by one around the outer periphery of the laminated magnet body 10, compared to when the yoke 8 is a single piece and not composed of yoke segments 30. Therefore, the work of attaching the yoke 8 to the outer periphery of the laminated magnet body 10 is easy, which greatly simplifies the assembly of the cylindrical linear motor 1. Note that the laminated magnet body 10 in the cylindrical linear motor 1 is formed by laminating and adhering the permanent magnets 10a, 10b, but it is also possible to divide the laminated magnet body 10 in the axial direction according to the overall axial length of the yoke segments 30 to manufacture laminated magnet segments in which several permanent magnets 10a, 10b are stacked, and then manufacture a plurality of split field assemblies in which yoke segments are attached to the outer peripheries of the laminated magnet segments, and then stack the split field assemblies to manufacture the field 6.

[0041] Furthermore, if the axial length of the yoke segments 30 is ideally an integer multiple of the magnetic pole pitch P and the yoke segments 30 are attached to the outer periphery of the laminated magnet body 10 so that both ends of the yoke segments 30 are positioned at the center of the permanent magnets 10a of the main pole in the laminated magnet body 10, the magnetic field lines will not cross the gaps between the multiple yoke segments 30, minimizing the magnetic resistance of the yoke 8 and suppressing leakage of the magnetic field lines to the outside. As mentioned above, in the case of permanent magnets 10a, 10b in the Halbach array, the path of the magnetic field lines runs from the center of the permanent magnet 10a of the main pole to the center of the permanent magnet 10a of the adjacent main pole, across the permanent magnet 10b of the sub-pole, passing through the armature 2 and forming a loop. Therefore, in the cylindrical linear motor 1 of this embodiment, the yoke segments 30 abut on each other at the outer periphery of the axial center of the permanent magnets 10a of the main magnetic pole, so that the magnetic field lines of the field magnet 6 do not cross the gap between the yoke segments 30, and consideration is given to preventing a decrease in the thrust of the cylindrical linear motor 1 even when the yoke 8 is formed from multiple yoke segments 30. In this way, even when the yoke 8 is formed by stacking multiple cylindrical yoke segments 30, the magnetic field strength toward the inner periphery of the field magnet 6 is comparable to that of a yoke made of a single cylindrical body. In other words, by aligning the abutment surfaces of the yoke segments 30 with the axial center of the permanent magnets 10a of the main magnetic pole, good assembly of the cylindrical linear motor 1 and prevention of a decrease in thrust can both be achieved.

[0042] Note that the axial length of the yoke segments 30 is preferably an integer multiple of the magnetic pole pitch P, but even if the length is set to a length other than an integer multiple of the magnetic pole pitch P, the yoke 8 can be provided with a magnetic circuit with low magnetic resistance and the effect of increasing the field flux acting on the armature 2 can be achieved, so it is also possible to set the axial length of the yoke segments 30 to a length other than an integer multiple of the magnetic pole pitch P. Also, in this embodiment, the laminated magnet body 10 is composed of permanent magnets 10a, 10b stacked in a Halbach array, but it may also be configured by sequentially stacking an annular permanent magnet that is radially magnetized and has an N pole on its inner periphery and an annular permanent magnet that is radially magnetized and has an S pole on its inner periphery.

[0043] 3, in the cylindrical linear motor 1 of this embodiment, chamfered portions C are provided on the edges of the inner circumference at both axial ends of the yoke segments 30. By providing chamfered portions C on the inner circumference at both axial ends of the yoke segments 30 in this manner, when the yoke segments 30 are fitted onto the outer peripheries of the permanent magnets 10a, 10b, the permanent magnets 10a, 10b slide along the chamfered portions C and are guided into the yoke segments 30, making the assembly of the cylindrical linear motor 1 even easier.

[0044] The armature 2 is inserted inside the field magnet 6 so as to be movable in the axial direction, and the field magnet 6 applies a magnetic field to the core 3. Note that the field magnet 6 only needs to apply a magnetic field within the movable range of the core 3, so the installation range of the permanent magnets 10a, 10b can be determined according to the movable range of the core 3. Therefore, it is not necessary to install the permanent magnets 10a, 10b in the range of the annular gap between the barrel 7 and the cylindrical portion 9b that does not face the core 3.

[0045] An annular head-side spacer 40, the field magnet 6, and an annular end-side spacer 41 are housed between the outer periphery of the cylindrical portion 9b and the inner periphery of the barrel 7. The head-side spacer 40 is cylindrical and has a shape in which the outer diameter on the anti-field magnet side, which is the left side in FIG. 1, is larger than the outer diameter on the field magnet side, which is the right side in FIG. 1, and is equipped with a large-diameter portion 40a and a small-diameter portion 40b, with the left end of the large-diameter portion 40a in FIG. 1 abutting against the right end face in FIG. 1 of the head portion 9a of the guide tube 9, and the right end of the small-diameter portion 40b in FIG. 1 abutting against the left end of the field magnet 6.

[0046] The end-side spacer 41 is cylindrical and has a shape in which the outer diameter on the anti-field side, which is the right side in FIG. 1, is larger than the outer diameter on the field side, which is the left side in FIG. 1, and is provided with a large-diameter portion 41 a and a small-diameter portion 41 b, with the right end of the large-diameter portion 41 a in FIG. 1 abutting against the left end surface of the bottom 12 a of the bottom cap 12 in FIG. 1, and the left end of the small-diameter portion 41 b in FIG. 1 abutting against the right end 6 b of the field 6.

[0047] 1, an annular head spacer 40, field magnet 6, and an annular end spacer 41 are fitted onto the outer periphery of the cylindrical portion 9b, and after the head portion 9a of the guide tube 9 is screwed into the barrel 7, a bottom cap 12 is attached to the right end of the barrel 7 in FIG. 1. This causes the head spacer 40, laminated magnet body 10, and end spacer 41 to be sandwiched between the head portion 9a of the guide tube 9 and the bottom portion 12a of the bottom cap 12, and the laminated magnet body 10 is fixed to the inner periphery of the barrel 7. Note that the yoke 8 attached to the outer periphery of the laminated magnet body 10 is not sandwiched axially between the head portion 9a and the bottom cap 12, but is adhered to the laminated magnet body 10 and does not move within the barrel 7.

[0048] In addition, an annular sealing member 28 is provided on the inner circumference of the head portion 9a, which is in sliding contact with the outer circumference of the cover 17 that covers the outer circumference of the first rod 20, preventing dust, water, etc. from entering the cylindrical linear motor 1.

[0049] The rod 11 with the armature 2 attached is inserted into the guide tube 9 so as to be movable in the axial direction, and the sliders 21b and 25 slide against the inner periphery of the cylindrical portion 9b to guide the axial movement of the armature 2. In this way, the armature 2 is inserted into the inner periphery, which is the side opposite the yoke, of the laminated magnet body 10. The guide tube 9 functions as a guide to guide the axial movement of the armature 2 relative to the field 6, and the surface of the guide tube 9 facing the armature 2 has no notches or grooves that would hinder the smooth movement of the armature 2.

[0050] The cylindrical portion 9b forms a gap between the outer periphery of the core 3 and the inner periphery of each permanent magnet 10a, 10b, and also plays a role in guiding the axial movement of the core 3 in cooperation with the sliders 21b, 25. In this embodiment, the armature 2 is configured to have only a single core 3, but if the armature has multiple cores 3, sliders that come into sliding contact with the inner periphery of the cylindrical portion 9b may be provided not only at both axial ends of the armature 2 but also between the cores 3, 3.

[0051] Furthermore, a guide rod 16 is attached to the inner periphery of the bottom 12a of the bottom cap 12. The guide rod 16 has a base end 16a fixed to the inner periphery of the bottom 12a, and a guide portion 16b extending from the base end 16a toward the rod 11 and slidably inserted into the rod 11, and is always in sliding contact with the inner periphery of the rod 11 even when the cylindrical linear motor 1 extends or retracts. More specifically, the guide portion 16b of the guide rod 16 is slidably inserted toward the tip side of the large inner diameter portion 21d of the second rod 21.

[0052] In this way, in the cylindrical linear motor 1 of this embodiment, the guide rod 16 is in sliding contact with the inner circumference of the rod 11, and the sliders 21b, 25 are in sliding contact with the cylindrical portion 9b, so the armature 2 can move smoothly in the axial direction together with the rod 11 without becoming eccentric relative to the field 6, but the guide rod 16 may be eliminated.

[0053] Furthermore, in the cylindrical linear motor 1 configured in this manner, the cylindrical portion 9b, which guides the axial movement of the armature 2 and prevents the armature 2 from becoming eccentric relative to the field magnet 6, is integrally structured with the head portion 9a, so distortion is less likely to occur in the cylindrical portion 9b and the head portion 9a, and the sliders 21b and 25 can slide smoothly on the inner circumference of the cylindrical portion 9b, allowing it to expand and contract smoothly.

[0054] The cylindrical linear motor 1 is driven by a controller that detects the position of the rod 11 relative to the field 6 using a stroke sensor (not shown), grasps the electrical angle of the core 3 relative to the field 6, switches the energized phase, and controls the amount of current in each winding 5 using PWM control to control the thrust and the movement direction of the armature 2 in the cylindrical linear motor 1. Note that the control method of the controller described above is one example and is not limited to this. Furthermore, when an external force acts to relatively displace the armature 2 and the field 6 in the axial direction, a thrust that suppresses the relative displacement is generated by energizing the windings 5 ​​or by induced electromotive force generated in the windings 5, 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.

[0055] In the cylindrical linear motor 1 of this embodiment, the weight of the yoke 8 is reduced by providing a notch 30a in the yoke 8 in the field magnet 6. The yoke 8 provided with the notch 30a has a larger magnetic resistance than a yoke having the same inner and outer diameters and axial length as the yoke 8 but without a notch, and therefore the field magnetic flux in the field magnet 6 is smaller.

[0056] Here, the volume of a yoke without notches, that is, a yoke with the same inner and outer diameters and axial length as yoke 8 but without notches, is defined as pre-notch volume A, the difference obtained by subtracting the volume of yoke 8 with notches 30a from pre-notch volume A is defined as volume difference B, and the ratio of volume difference B to pre-notch volume A is defined as notch ratio ρ. The notch ratio ρ for yoke 8 can be calculated by ρ = B / A × 100. The larger the volume of notches 30a, the larger the value of notch ratio ρ.

[0057] Fig. 4 shows how the mass thrust density of cylindrical linear motor 1 changes when the cutout ratio ρ is changed. As cutout 30a becomes larger, the weight of yoke 8 becomes lighter, but on the other hand, the cross-sectional area of ​​the magnetic path decreases, increasing the magnetic resistance in yoke 8 and reducing the field magnetic flux that field 6 exerts on the armature 2 side.

[0058] 4, as the cutout ratio ρ is increased from 0, initially the volume of the cutouts 30a is small and the cross-sectional area of ​​the magnetic path of the yoke 8 is large, reducing the magnetic resistance of the yoke 8 little, and the provision of the cutouts 30a reduces the weight of the yoke 8, thereby improving the mass thrust density of the cylindrical linear motor 1. This trend continues as the cutout ratio ρ is between 5% and 6%, but as the cutout ratio ρ increases beyond 6%, the mass thrust density tends to decrease, and when the cutout ratio ρ reaches 12%, the mass thrust density when a field magnet 6 equipped with a yoke 8 with a cutout ratio of 12% is used in a cylindrical linear motor 1 becomes approximately the same as the mass thrust density of a cylindrical linear motor in which a yoke with the same inner and outer diameters and axial length as the yoke 8 but without cutouts is attached to the outer periphery of the laminated magnet body 10. Furthermore, if the notch ratio ρ exceeds 12% and becomes larger than this, the mass thrust density of the cylindrical linear motor 1 will be lower than the mass thrust density of a cylindrical linear motor in which a yoke with the same inner and outer diameters and axial length as the yoke 8 but no notches is attached to the outer periphery of the laminated magnet body 10, resulting in a deterioration in the mass thrust density.

[0059] From the above, if the notch ratio ρ of the yoke 8 is set in the range of 4% to 8% and the notch 30a is formed in the yoke 8, the mass thrust density of the cylindrical linear motor 1 can be effectively improved by reducing the weight of the yoke 8 even if the magnetic resistance of the yoke 8 increases. It was also found that the mass thrust density of the cylindrical linear motor 1 can be improved by setting the notch ratio ρ of the yoke 8 in the range of more than 0% to 12%.

[0060] As described above, the cylindrical linear motor 1 of the present invention comprises a laminated magnet body 10 formed of a plurality of annular permanent magnets 10a, 10b stacked so that N poles and S poles are arranged alternately in the axial direction, a cylindrical field magnet 6 having a cylindrical yoke 8 formed of a magnetic material and arranged on the outer periphery of the laminated magnet body 10, and an armature 2 arranged on the opposite side of the yoke on the inner periphery of the laminated magnet body 10 and movable in the axial direction of the field magnet 6 relative to the field magnet 6, and the yoke 8 has a notch 30a formed along the axial direction, penetrating the thickness of the yoke 8, and having an axial length L1 along the axial direction of the yoke 8 longer than a circumferential length L2 along the circumferential direction of the yoke 8.

[0061] In the cylindrical linear motor 1 configured in this manner, by providing a yoke 8 with low magnetic resistance on the side opposite the armature 2 of the laminated magnet body 10, it is possible to increase the field magnetic flux that the field 6 exerts on the armature 2 side, and by providing a notch 30a in the yoke 8, it is possible to reduce the weight of the yoke 8.

[0062] Furthermore, although the provision of the notch 30a in the yoke 8 reduces the cross-sectional area of ​​the magnetic path of the yoke 8, the notch 30a is aligned along the axial direction of the yoke 8, and the axial length L1 along the axial direction of the yoke 8 is longer than the circumferential length L2 along the circumferential direction of the yoke 8, and the direction of progression of the magnetic flux of the laminated magnet body 10 coincides with the axial direction within the yoke 8, so that the reduction in magnetic resistance of the yoke 8 due to the provision of the notch 30a can be suppressed.

[0063] Furthermore, because the armature 2 is guided by the guide tube 9, which does not have any notches or grooves that would hinder the movement of the armature 2, the cylindrical linear motor 1 can smoothly extend and retract. When multiple yoke segments 30 are stacked and attached to the outer periphery of the laminated magnet body 10 to form the yoke 8, the notches 30a provided in each yoke segment 30 do not have to be arranged in a straight line in the axial direction, and the number of notches 30a provided in all yoke segments 30 does not have to be the same. Furthermore, the shape and dimensions of the notches 30a provided in the yoke segments 30 do not have to be the same for all yoke segments 30. When the yoke 8 is formed from a single tube rather than from yoke segments 30, a long notch may be provided along substantially the entire axial length of the yoke 8, or multiple independent notches may be provided along the axial direction, or multiple notches may be arranged in a staggered pattern, offset in both the circumferential and axial directions.

[0064] Furthermore, if the notch ratio ρ, which is the ratio of the volume difference B obtained by subtracting the volume of the yoke 8 having the notches 30a from the volume A before the notches are formed in the yoke, to the volume A before the notches are formed, is set to 12% or less, the mass thrust density of the cylindrical linear motor 1 can be stably improved. Furthermore, if the notch ratio ρ is set in the range of 4% to 6%, the effect of improving the mass thrust density of the cylindrical linear motor 1 can be further enhanced.

[0065] In the cylindrical linear motor 1 of this embodiment, the yoke 8 is fixed to the outer periphery of the laminated magnet body 10, but in the case of a cylindrical linear motor having a structure in which the field magnet 6 is inserted inside the armature 2, it is sufficient to attach a yoke 8 with a notch to the inner periphery of the laminated magnet body 10.

[0066] 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]

[0067] 1... cylindrical linear motor, 2... armature, 6... field magnet, 8... yoke, 10... laminated magnet body, 10a... main pole permanent magnet, 10b... sub pole permanent magnet, 30a... notch

Claims

1. a cylindrical field magnet having a laminated magnet body formed of a plurality of annular permanent magnets stacked so that N poles and S poles are alternately arranged in the axial direction, and a cylindrical yoke formed of a magnetic material and arranged on either the inner periphery or the outer periphery of the laminated magnet body; an armature disposed on the inner or outer periphery of the laminated magnet body, but opposite the yoke, and movable in the axial direction of the field magnet relative to the field magnet, The yoke has a notch formed along the axial direction, penetrating the thickness of the yoke, and having an axial length along the axial direction of the yoke longer than a circumferential length along the circumferential direction of the yoke. A cylindrical linear motor characterized by:

2. The notch ratio is the ratio of the volume difference obtained by subtracting the volume of the yoke having the notch from the volume before the notch is formed in the yoke, and the notch ratio is set to 12% or less.

2. The cylindrical linear motor according to claim 1.

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