Linear motor

Abstract

To provide a linear motor with a core capable of suppressing the influence of cogging.SOLUTION: A coreless linear motor disposed on at least one side in a moving direction of the movable element of the iron-core linear motor, wherein the coreless linear motor includes a core having a plurality of magnetic pole teeth and a coil wound around the magnetic pole teeth, and is controllable to generate a force in a direction in which a cogging force generated in the iron-core linear motor is canceled out.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] One method for linearly moving a moving body to transport parts, etc., is to use a rotating device and a ball screw. However, there is a limit to the speed at which a ball screw can move, and there is a limit to how fast it can be. In addition, the use of a rotating device can cause problems such as grease scattering.

[0003] For this reason, linear motors, which allow for a clean working environment and enable high speed and precision, are used in semiconductor manufacturing equipment, for example. Linear motors have high positional precision due to low thermal conductivity to the surrounding area, and by connecting multiple stators, they can easily be made long stroke.

[0004] One such linear motor that has been proposed is one in which multiple permanent magnets are arranged on a field core arranged on the stator side so that their magnetism is alternately reversed, and a mover is arranged facing the field poles with a gap between them (Patent Document 1).Patent Document 1 describes a linear motor in which coils are wound around some of the teeth that make up the armature of the mover, and no coils are wound around other teeth. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-176299 Summary of the Invention [Problem to be solved by the invention]

[0006] Linear motors can be broadly divided into iron-core type (hereinafter sometimes referred to as "core type") linear motors and coreless type linear motors. Iron-core type linear motors can generate large thrust, but they have the problem of generating cogging force. Cogging force is generated when the core tries to move to a stable position due to the magnetic force of the permanent magnet.

[0007] For example, when the mover is moved from a stable position due to the relationship between the attractive and repulsive forces between the core and the permanent magnet, a force is generated that tries to return it to its original stable position. If the mover is moved further in this state, the force that tries to return it to its original stable position weakens, and as it approaches the next stable position, a force that tries to move it forward to the next stable position is generated. Because such forces occur periodically, even when the armature is not energized, for example, a force that inhibits or promotes the generated thrust in the thrust direction is generated depending on the pitch of the permanent magnet, which adversely affects positional accuracy.

[0008] On the other hand, coreless linear motors do not generate this type of cogging force. However, because coreless linear motors have a low thrust density, the motor volume increases when trying to generate the same thrust as an iron-core linear motor, making them unsuitable for miniaturization. For this reason, when large thrust is required in a small space, it is essential to use an iron-core linear motor, and the challenge is how to suppress cogging, which has a negative effect on positioning accuracy.

[0009] Conventional countermeasures to cogging include, for example, providing a skew angle to the permanent magnet or optimizing the tip shape of the core. However, these methods can also reduce thrust and do not completely eliminate cogging. Another method is to have the linear motor cancel out the cogging force by passing a current in the opposite phase to the cogging force on the control side, but this requires tuning for each motor, making it less versatile.

[0010] The present invention has been made in view of the above problems, and has an object to provide an iron-core linear motor that can suppress the effects of cogging. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, the first invention is a linear motor having an iron-cored linear motor including a stator in which a plurality of permanent magnets are arranged so that their magnetic poles alternate, a core having a plurality of magnetic pole teeth and a coil wound around the magnetic pole teeth, and a mover that is movable relative to the stator, and a coreless linear motor that is arranged on at least one side of the moving direction of the mover of the iron-cored linear motor, wherein the coreless linear motor is controlled so that it can generate a force in a direction that cancels out the cogging force generated in the iron-cored linear motor.

[0012] It is desirable that the current cycles of the iron-core linear motor and the coreless linear motor are synchronized.

[0013] The width of the coreless coil constituting the coreless linear motor, which is the length in the moving direction of the mover, may be approximately the same as the width of the permanent magnet, which is the length in the moving direction of the mover.

[0014] The coreless linear motor may be made up of a plurality of coreless coils, and the plurality of coreless coils may be arranged in parallel in the direction of movement of the mover.

[0015] The distance between the coreless linear motor and the stator of the iron-core linear motor may be closer than the distance between the mover and the stator of the iron-core linear motor.

[0016] According to the present invention, a coreless linear motor is fixed to the mover of an iron-core linear motor. In this configuration, the coreless linear motor is controlled to generate a force (thrust) in a direction that cancels the cogging force generated in the iron-core linear motor. Alternatively, the current cycles of the iron-core linear motor and the coreless linear motor are synchronized. This makes it possible to suppress the effects of cogging.

[0017] By roughly matching the width of the coreless coil (length in the direction of movement of the mover) that constitutes such a coreless linear motor with the width of the permanent magnet in the stator, the coreless linear motor can generate a force that efficiently cancels out the cogging force.

[0018] In this case, by arranging multiple coreless coils side by side, the thrust force of the coreless linear motor can be increased, making it possible to deal with cogging forces that cannot be counteracted by a single coreless coil.

[0019] In addition, by making the distance between the coreless coil of a coreless linear motor and the stator of an iron-cored linear motor closer than the distance between the coil mover and the stator of an iron-cored linear motor, the thrust force of the coreless linear motor can be increased. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide an iron-core linear motor that can suppress the effects of cogging. [Brief explanation of the drawings]

[0021] [Figure 1] 1A is a front view of the linear motor 1, and FIG. 1B is a bottom view of the linear motor 1. FIG. [Figure 2] 1(a) is a cross-sectional view of the mover 3 taken along line AA in FIG. 1(a), and FIG. 1(b) is an enlarged view of part H in FIG. 1(a). [Figure 3] A partially enlarged cross section of line BB in Figure 1(b). [Figure 4]FIG. 2 is a diagram showing the configuration of a control system for a sub-motor 9. [Figure 5] 10 is a diagram showing the canceling effect of cogging forces. DETAILED DESCRIPTION OF THE INVENTION

[0022] The linear motor of the present invention comprises an iron-cored linear motor having a stator in which a plurality of permanent magnets are arranged with alternating magnetic poles, a core having a plurality of magnetic pole teeth and a coil wound around the magnetic pole teeth, and a mover that is movable relative to the stator; and a coreless linear motor that is arranged on at least one side of the iron-cored linear motor in the direction of movement of the mover, and is characterized in that the coreless linear motor is controlled so that it can generate a force in a direction that cancels out the cogging force generated in the iron-cored linear motor. It is desirable that the current cycles of the iron-core linear motor and the coreless linear motor are synchronized. The width of the coreless coil constituting the coreless linear motor, which is the length in the moving direction of the mover, may be approximately the same as the width of the permanent magnet, which is the length in the moving direction of the mover. The coreless linear motor may be made up of a plurality of coreless coils, and the plurality of coreless coils may be arranged in parallel in the direction of movement of the mover. The distance between the coreless linear motor and the stator of the iron-core linear motor may be closer than the distance between the mover and the stator of the iron-core linear motor.

[0023] A linear motor according to an embodiment of the present invention will be described below. Fig. 1(a) is a front view of the linear motor 1, and Fig. 1(b) is a bottom view of the linear motor 1. Note that in the following figures, the linear guide, cables, and other components, as well as the resin that coats the coils, are not shown. The left-right direction in Fig. 1 is the direction of movement of the mover 3.

[0024] The linear motor 1 is composed of an iron-core linear motor (hereinafter referred to as the "main motor 2") and a coreless linear motor (hereinafter referred to as the "sub-motor 9"). The main motor 2 is composed of a mover 3, a stator 5, etc. The stator 5 has multiple permanent magnets 7 arranged in parallel so that their magnetic poles are alternately reversed in the direction of movement of the mover 3. Note that in Figure 1, the permanent magnets 7 are arranged side by side at a predetermined skew angle (θ in the figure) with respect to the direction perpendicular to the direction of movement of the mover 3, but it is not necessary to set a skew angle. A skew angle can be set as needed.

[0025] The mover 3 is disposed facing the stator 5 at a predetermined distance from the stator 5, and is movable relative to the stator 5. The mover 3 is supported by a predetermined linear guide, and is movable while maintaining a distance from the stator 5 against the attractive force of the stator 5.

[0026] 2(a) is a cross-sectional view of the mover 3 taken along line AA in FIG. 1(a). The mover 3 has a core 13 having a plurality of magnetic pole teeth 14, and a coil 11a wound around each of the magnetic pole teeth 14 of the core 13. A plurality of magnetic pole teeth 14 are arranged in the direction of movement of the mover 3. In other words, the linear motor 1 is a so-called moving coil type (MC type) in which an armature having a plurality of magnetic pole teeth and a plurality of coils is arranged on the mover side. For example, the coils are arranged in the order of U-phase, V-phase, and W-phase of the three phases in the direction of movement of the mover 3.

[0027] A sub-motor 9 is disposed on one side of the moving element 3 in the direction of movement. The sub-motor 9 is composed of a coil 11b, which is a coreless coil, and a stator 5. The stator 5 is also used as the stator 5 of the main motor 2. In the illustrated example, two coils 11b are arranged in parallel in the direction of movement of the moving element 3, but one coil or three or more coils may be used. When multiple coils 11b are arranged in parallel, they are connected in series. When multiple coils 11b are used, the sub-motors 9 may be disposed on both sides of the moving element 3 in the direction of movement.

[0028] Furthermore, it is preferable that the distance (gap) between the coil 11b in the sub-motor 9 and the stator 5 of the main motor 2 is closer (narrower) than the distance (gap) between the coil 11a (the surface of the mover 3 facing the stator 5) of the main motor 2 and the stator 5. Since the magnetic force from the permanent magnet 7 becomes significantly weaker with increasing distance from the permanent magnet 7, it is desirable that the distance between the coil 11b and the stator 5 is shorter from the viewpoint of efficiency.

[0029] Figure 2(b) is an enlarged view of part H in Figure 2(a). By arranging the coil 11b so that the lower end of the coil 11b protrudes further toward the stator 5 (downward in the figure) than the lower end of the coil 11a, the distance between the coil 11b of the sub-motor 9 and the stator 5 of the main motor 2 can be made smaller than the distance between the coil 11a of the main motor 2 and the stator 5.

[0030] In this case, if only one coil 11b is insufficient in terms of the force (thrust) required to cancel out the cogging force, the sub-motor 9 can be configured with multiple coils 11b as shown in the figure, and multiple coils 11b can be arranged in parallel in the direction of movement of the mover 3.

[0031] For example, the cogging force increases in proportion to the maximum thrust of the mover 3. Therefore, a mover 3 with a larger thrust requires a sub-motor capable of generating a larger force (thrust) to cancel out the cogging force. Note that, for example, a linear motor capable of generating a thrust of about 1500 N has a cogging force of about 20 N, so the sub-motor 9 only needs to be capable of generating a thrust of about 20 N. For example, to generate a thrust of about 20 N, one coil 11b is sufficient.

[0032] 3 is a partially enlarged view of the cross section taken along line BB in FIG. 1(b). As described above, in this embodiment, the permanent magnet 7 is arranged with a predetermined skew angle. Meanwhile, the magnetic pole teeth 14 and the coil 11a are arranged so as to be perpendicular to the moving direction of the mover 3. Furthermore, the coil 11b constituting the sub-motor 9 is arranged at approximately the same angle as the permanent magnet 7 with respect to the direction perpendicular to the moving direction of the mover 3. In other words, the coil 11b and the permanent magnet 7 are arranged so that their longitudinal directions are approximately parallel when viewed from the front. Note that when the permanent magnet 7 is arranged so as to be perpendicular to the moving direction of the mover 3 (when no skew angle is provided), the coil 11b is also arranged in a direction perpendicular to the moving direction of the mover 3.

[0033] Here, the length (D in the figure) of coil 11b constituting sub-motor 9 in the direction of movement of mover 3 is referred to as the width of coil 11b. Similarly, the length (C in the figure) of permanent magnet 7 in the direction of movement of mover 3 is referred to as the width of permanent magnet 7. In this case, width D of coil 11b and width C of permanent magnet 7 are approximately the same. In order to allow the magnetic flux of permanent magnet 7 to efficiently penetrate coil 11b, it is desirable that width D of coil 11b and width C of permanent magnet 7 are approximately the same.

[0034] The width of the coil 11a is not particularly limited, but for example, the width of the coil 11a can be made wider than the width of the permanent magnet 7, in which case the width of the coil 11b will be narrower than the width of the coil 11a.

[0035] Furthermore, there is no particular limitation on the method of fixing the sub-motor 9 to the mover 3 of the main motor 2. As mentioned above, the coils 11a and 11b are usually coated with resin, and therefore they may be coated integrally with resin. Furthermore, if a cooling section for cooling the core 13 and the coil 11a is provided on the back side of the coil 11a to cool the mover 3, the cooling section arranged on the back of the core 13, etc. may be joined to the sub-motor 9 via a heat transfer member. In this way, heat generated in the sub-motor 9 can be transferred to the cooling section and dissipated.

[0036] Next, the function and control of the sub-motor 9 will be explained. Figure 4 is a diagram showing the configuration for controlling the sub-motor 9. As mentioned above, the mover 3 of the main motor 2 tries to stay in a stable position in response to attraction and repulsion with the permanent magnet 7, so a cogging force is generated in the direction of movement. In other words, the direction and force of the cogging force change periodically depending on the position of the mover 3 relative to the stator 5.

[0037] In this embodiment, a position sensor 15 is provided as a position detection means capable of detecting the position of the mover 3 relative to the stator 5. The position sensor 15 may be, for example, a Hall element, but is not limited to this. For example, one position sensor 15 may be provided on the side of the sub-motor 9 opposite the mover 3. In this case, the main motor 2 and the sub-motor 9 share the same position sensor 15. In addition to the above configuration, another position sensor 15 may be provided at an arbitrary position on the mover 3 of the main motor 2, or the main motor 2 and the sub-motor 9 may each detect their positions using different position sensors 15.

[0038] In this embodiment, in addition to the control unit that controls the current supplied to the main motor 2, a control unit 17 is provided that controls the current supplied to the sub-motor 9 (coil 11b) in accordance with the position of the mover 3 or the position of the sub-motor 9 detected by the position sensor 15. For example, the control unit 17 is connected to the power supply 19 or an adjuster of the power supply 19, and can adjust the current flowing from the power supply 19 to the coil 11b. The amount of adjustment of the power supply 19, etc., in accordance with the position may be set in advance and stored in a storage unit (not shown), and the control unit 17 may read out the conditions as appropriate.

[0039] When the control unit 17 controls the current supplied to the sub-motor 9 (coil 11b), it is desirable that the current cycles of the main motor 2 and the sub-motor 9 are synchronized, for example, as shown in FIG. 5, which will be described later.

[0040] As described above, the magnitude and direction of the cogging force differ depending on the position of the mover 3. For this reason, the current (voltage) flowing through the coil 11b is controlled so that a force (thrust) in the opposite direction is applied to the cogging force generated in response to the position of the mover 3. In this way, the control unit 17 controls the sub-motor 9 (coil 11b) so that a force is generated in the direction that cancels out the cogging force generated when the mover 3 moves relative to the stator 5. In other words, by generating a thrust in the sub-motor 9 (coil 11b) that is in the opposite phase and synchronized with the cogging force, the cogging force can be significantly reduced.

[0041] There is no particular limitation on the method of controlling the sub-motor 9. As long as it is possible to cause the sub-motor 9 to generate a thrust force that is set in advance in accordance with the position of the mover 3, other configurations may be used.

[0042] 5 is a diagram showing the cogging force generated when the sub-motor 9 is not used, and the cogging force after part of the cogging force is canceled out by the sub-motor 9. In the figure, E is the cogging force generated when the mover 3 is moved relative to the stator 5 without using the sub-motor 9. In other words, it is the cogging force generated in a conventional linear motor that does not use the sub-motor 9.

[0043] In contrast, F in the figure is the thrust (calculated value) generated by the sub-motor 9 according to the position of the mover 3. As shown in the figure, the sub-motor 9 can generate a predetermined thrust by adjusting the current flowing through the coil 11b according to the position of the mover 3.

[0044] In the figure, G is the actual cogging force measured when the sub-motor 9 was operating. Although it was not possible to completely eliminate the cogging force using the sub-motor 9, by using the sub-motor 9 to cancel out the cogging force generated by conventional linear motors, it was possible to reduce the cogging force to about one-third.

[0045] The control unit 17 may use the residual cogging force obtained in this manner while the sub-motor 9 is operating to perform feedback control and / or feedforward control to correct the control conditions of the sub-motor 9. For example, if a thrust command that cancels out the residual cogging force is stored in the control unit 17, the cogging force can be further reduced.

[0046] As described above, according to the linear motor 1 of this embodiment, the sub-motor 9, which is a coreless linear motor, is arranged on at least one side of the main motor 2, which is an iron-core linear motor, in the direction of movement of the mover 3. The sub-motor 9 is controlled so that it generates a force in a direction that cancels out the cogging force generated in the main motor 2. This configuration makes it possible to suppress the effects of cogging. Furthermore, by synchronizing the current cycles of the main motor 2 and the sub-motor 9 using the control unit 17 or the like, the cogging force can be significantly reduced. In this case, the current to the coil 11a does not change, so there is almost no reduction in thrust.

[0047] Furthermore, as mentioned above, the sub-motor 9 does not need a large thrust, so the size of the linear motor 1 does not become excessively large.

[0048] Furthermore, if the permanent magnets 7 are arranged with a skew angle, it is expected that the cogging force will be further reduced. In this case, by arranging the coils 11b of the sub-motor 9 so that they face the permanent magnets 7 with approximately the same skew angle, it is possible to obtain a stable thrust force from the sub-motor 9.

[0049] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the technical scope of the present invention is not limited to the above-described embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the technical ideas described in the claims, and it is understood that these modifications and alterations also fall within the technical scope of the present invention. [Explanation of symbols]

[0050] 1...Linear motor 2...Main motor 3……Movable element 5……Stator 7...Permanent magnet 9...Sub motor 11a, 11b... Coil 13...Core 14...Magnetic pole teeth 15...Position sensor 17...Control unit 19……Power supply

Claims

1. a stator in which a plurality of permanent magnets are arranged so that their magnetic poles alternate; an iron-core linear motor including a mover having a core with a plurality of magnetic pole teeth and a coil wound around the magnetic pole teeth, the mover being movable relative to the stator; a coreless linear motor disposed on at least one side of the iron-core linear motor in the moving direction of the mover, The coreless linear motor is controlled so as to generate a force in a direction that cancels out the cogging force generated in the iron-core linear motor.

2. 2. The linear motor according to claim 1, wherein the current cycles of said iron-core linear motor and said coreless linear motor are synchronized.

3. 3. The linear motor according to claim 1, wherein the width of the coreless coil constituting the coreless linear motor, which is the length in the direction of movement of the mover, is approximately the same as the width of the permanent magnet, which is the length in the direction of movement of the mover.

4. 3. The linear motor according to claim 1, wherein the coreless linear motor comprises a plurality of coreless coils, the plurality of coreless coils being arranged in parallel in the direction of movement of the mover.

5. 3. The linear motor according to claim 1, wherein the distance between the coreless coil of the coreless linear motor and the stator of the iron-core linear motor is shorter than the distance between the mover and the stator of the iron-core linear motor.

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