Linear motor and methods for reducing raster phenomena

Abstract

Linear motor, which includes: a field magnet part (5) with a plurality of permanent magnets (21) arranged to alternately form north and south poles; a core (14) with a plurality of projecting posts (14a, 14b, 14c) which are arranged facing the field magnet part (5); a three-phase winding (16) wound around the projecting posts (14a, 14b, 14c) of the core (14); an armature (10) which has the three-phase winding (16) and the core (14) and moves linearly relative to the field magnet part (5); an additional core (18) of a magnetic body, which is present on at least one side of the runner (10) in a direction of relative motion of the runner (10); and wherein a distance (P1) between a center of the additional core (18) and a center of a middle projecting post (14b) from the projecting posts (14a, 14b, 14c) in the direction of relative motion of the runner (10) is specified such that it is substantially 1 / 4 x (2N+1) x a magnetic pole spacing (P2) between north poles of the field magnet part (5) (N: an integer equal to or greater than 1), wherein a gap is present between the additional core (18) and the core (14) or a non-magnetic material is arranged between them to prevent the projecting posts (14a, 14c) at the end of the core (14) and the additional core (18) from forming a magnetic circuit.

Description

Technical field

[0001] The present invention relates to a linear motor with a rotor that moves linearly relative to a stator, and in particular to a linear motor that has an additional core to reduce raster phenomena of the linear motor, and to a method for reducing raster phenomena of the same. Technical background

[0002] In a linear motor, a rotor moves linearly relative to a stator. The stator of the linear motor contains a multitude of permanent magnets arranged so that the north and south magnetic poles alternate. The rotor is mounted to the stator across a gap. To maintain a constant gap between the stator and the rotor, the linear movement of the rotor is guided by a guide device, such as a linear guide or a bearing.

[0003] The rotor contains a magnetic core facing the permanent magnets. This core has multiple projecting posts that extend towards a field magnet section. Each of these posts is wound with three-phase windings representing phases U, V, and W. When a three-phase alternating current with a phase difference of 120° is passed through these windings, a moving magnetic field is generated. The interaction of this moving magnetic field, generated by the three-phase windings and the magnetic field generated by the permanent magnets, causes the rotor to move linearly.

[0004] The core is present to amplify the magnetic field generated by the windings. The core is made of a magnetic material, such as silicon steel. Therefore, even when no current is flowing through the windings, magnetic attraction is generated between the protruding posts of the core and the permanent magnets. As the rotor moves along the stator, the protruding posts of the core are attracted to either the front or rear permanent magnets due to this magnetic attraction. Consequently, the magnetic attraction applied to the rotor varies periodically with respect to the pole spacing of the permanent magnets. This periodic change in attraction is known as cogging. Even when current is flowing through the windings, cogging persists and can be disruptive.

[0005] One method for eliminating grid distortion is, as in Fig. Figure 11 shows a known linear motor having additional magnetic poles 2a and 2b of magnetic bodies located at respective ends of the core 1 of the rotor in the direction of motion (see patent documents 1 and 2). In this linear motor, the additional magnetic poles 2a and 2b are present to increase the magnetic flux of the projecting posts 1a and 1b at respective ends in the direction of motion of the core 1. If the additional magnetic poles 2a and 2b were not present, it would be difficult to form a magnetic circuit of the projecting posts 1a and 1b at the respective ends, and the magnetic flux of the projecting posts 1a and 1b at the respective ends would be weaker than that of the central projecting post 1c.If the magnetic flux at the protruding posts 1a and 1b becomes weak at their respective ends, the magnetic flux of these posts and the magnetic flux of the central protruding post 1c are not in equilibrium, resulting in grid distortion. The additional cores 2a and 2b are present to increase the magnetic flux of the protruding posts 1a and 1b at their respective ends and to resolve this imbalance.

[0006] US 2003 / 0 098 620 A1 reveals a permanent magnet synchronous linear motor with reduced cogging torque and improved performance.

[0007] JP S60-30195 B2 discloses a linear electrical machine equipped with a field part having multiple magnetic poles and an armature core having multiple protruding poles for the winding arranged opposite the field part; wherein at least one of the parts, field part and armature core, is equipped with an additional protruding pole consisting of a magnetic body opposite the field part, at least one of the two ends of the armature core and the adjacent protruding poles of the winding.

[0008] JP 2005- 253 259 A discloses a linear electromagnetic actuator with a core in an armature, in particular a method for effectively reducing the detent force in a linear electromagnetic actuator. [Patent document 1]: Japanese Utility Model Disclosure JP H07 - 53 427 A [Patent Document 2]: Japanese Patent Application Disclosure JP S55 - 68 870 A Disclosure of the invention Problems to be solved with the invention

[0009] However, when additional cores are present to increase the magnetic flux of the protruding posts at the respective ends of the core, these newly added cores cause rasterization. To reduce rasterization caused by the additional cores, a new countermeasure is required. Therefore, the use of the conventional method for reducing rasterization as a general countermeasure is complicated by several interrelated factors.

[0010] The inventors noticed that the magnetoresistance at the protruding post in the middle of the core is low, the magnetic flux is easily conducted, and a waveform of the detent force generated throughout the core (see Fig. 7, where the horizontal axis indicates the core phase and the vertical phase indicates the cogging force) is synchronous with a waveform of a cogging force generated in the central projecting post. Furthermore, they have discovered that the cogging force of the entire core can be reduced by generating a cogging force at the additional cores which has a waveform that cancels out the waveform of the cogging force generated at the central projecting post.

[0011] The present invention was made in light of the above, and one objective of the invention is to provide a linear motor and a method for reducing raster phenomena in a linear motor, which are novel and with which raster phenomena can be reduced. Means of solving the problems

[0012] To solve the problems listed above, the invention according to claim 1 is a linear motor comprising: a field magnet part with a plurality of permanent magnets arranged to form alternating north and south poles; a core with a plurality of projecting posts facing the field magnet part; a three-phase winding wound around the projecting posts of the core; an armature comprising the three-phase winding and the core, moving linearly relative to the field magnet part; and an additional core of a magnetic body present on at least one side of the rotor in a direction of relative movement of the rotor.and wherein a distance between a center of the additional core and a center of a middle projecting post from the projecting posts in the direction of relative motion of the runner is specified such that it is substantially 1 / 4 x (2N+1) x a magnetic pole spacing between north poles of the field magnet part (N: an integer equal to or greater than 1), wherein a gap is present between the additional core and the core, or a non-magnetic material is arranged between them, to prevent the projecting posts at the end of the core and the additional core from forming a magnetic circuit.

[0013] The invention according to claim 2 is characterized in that, in the linear motor according to claim 1, the additional core has a front end part and a support part, and the thickness of the front end part in the direction of movement is smaller than the thickness of the support part in the direction of movement.

[0014] The invention according to claim 3 is characterized in that, in the linear motor according to claim 2, the front end part of the additional core is cut off on a side facing the core, so that the thickness becomes smaller in the direction of movement.

[0015] The invention according to claim 4 is characterized in that, in the linear motor according to one of claims 1 to 3, the additional core is present on each side of the runner in the direction of movement such that the runner is enclosed between the additional cores.

[0016] The invention according to claim 5 is characterized in that, in the linear motor according to one of claims 1 to 3, the three-phase winding is a group of windings of phases U, V and W, each of which is wound around the protruding posts and arranged in the direction of movement, and the middle protruding post is a post that is positioned in the middle of the three protruding posts in the direction of movement.

[0017] The invention according to claim 6 is a method for reducing rasterization in a linear motor comprising a field magnet part with a plurality of permanent magnets arranged to form alternating north and south poles; a core with a plurality of projecting posts facing the field magnet part; a three-phase winding wound around the projecting posts of the core; an armature comprising the three-phase winding and the core and moving linearly relative to the field magnet part; and an additional core of a magnetic body present on at least one side of the armature in a direction of relative movement of the rotor;wherein the method for reducing raster phenomena in a linear motor comprises: arranging the additional core such that a distance between a center of the additional core and a center of a middle projecting post from the projecting posts in the direction of relative motion of the rotor is substantially 1 / 4 x (2N+1) x a magnetic pole spacing between N north poles of the field magnet part (N: an integer equal to or greater than 1), and creating a gap between the core and the additional core or arranging a non-magnetic material between them to prevent the projecting posts at the end of the core and the additional core from forming a magnetic circuit. Effects of the invention

[0018] According to the invention of claim 1, since the additional core is arranged essentially at a position an odd multiple of a magnetic pole spacing x 1 / 4 from the central projecting post, it is possible to generate a detent force at the additional core that cancels out the detent force generated by the central projecting post. This means that it is possible to reduce the grid appearance across the entire core.

[0019] According to the invention as described in claim 1, since the gap is formed between the core and the additional core, or the non-magnetic material is arranged between them, it is further possible to prevent the protruding posts at the respective ends of the core and the additional core from forming a magnetic circuit. This makes it possible to reduce the influence of the conventional measure against grid distortion, which increases the magnetic flux of the protruding posts at the respective ends of the core, thus reliably reducing grid distortion.Furthermore, since the core and the additional core are separate components, even if there is a deviation from the design parameters regarding the dimensions of the manufactured additional core, or if, in addition to the components of the linear motor, a component that causes grid distortion is present between the stator and the rotor, it is not necessary to manufacture the core again, whose manufacturing process is complicated, but only to replace the additional core.

[0020] According to the invention as per claim 2, the additional core can be separated from the core while simultaneously maintaining a constant distance between the additional core and the central projecting post. This prevents the projecting posts at the respective ends of the core and the additional core from forming a magnetic circuit. Furthermore, the support part is thicker than the front end part, allowing the additional core to be easily attached to the table or the like. Additionally, because the attraction acting on the additional core can be reduced, it becomes possible to decrease the load on a guide element for guiding the linear movement of the runner.

[0021] According to the invention according to claim 3, it is possible to reduce the total length of the core including the additional core, while at the same time forming the gap between the protruding posts at the respective ends of the core and the additional core.

[0022] According to the invention according to claim 4, it is possible to reduce the locking force generated by the central projecting post in a uniformly balanced manner by using the additional cores present on the respective sides of the anchor.

[0023] According to the invention according to claim 5, it is possible to effectively reduce the locking force on the middle projecting post of the three projecting posts.

[0024] According to the invention of claim 6, since the additional core is arranged essentially at a position an odd multiple of a magnetic pole spacing x 1 / 4 from the central projecting post, it is possible to generate a detent force on the additional core that cancels out the detent force generated by the central projecting post. This means that it is possible to reduce the grid distortion across the entire core. Brief description of the drawings Fig. Figure 1 is a perspective view of a linear motor according to an exemplary embodiment of the present invention (including a partial sectional view of a table). Fig. Figure 2 is a front view of the linear motor. Fig. Figure 3 is a cross-sectional view along the direction of movement of a runner. Fig. 4A to 4B are detailed views of an additional core ( Fig. 4A is a top view, and Fig. 4B is a side view). Fig. Figure 5 is a perspective view of a field magnet part. Fig. Figure 6 is a top view of the field magnet part. Fig. Figure 7 is a diagram showing the detent forces generated on protruding posts. Fig. Figure 8 is a diagram showing the cogging force generated by the entire core as well as the cogging forces generated by the additional cores. Fig. Figure 9 is a view that shows a relationship between a magnetic pole spacing between north poles of the field magnet part and a distance P1 between the center of the middle projecting post of phase W and the center of the additional core. Fig. 10A and Fig. 10B are diagrams that serve to compare the raster phenomena before and after the application of the additional core ( Fig. Figure 10A shows the grid phenomena before the additional core is attached and Fig. Figure 10B shows the grid patterns after the addition of the extra core). Fig. Figure 11 is a schematic view representing a linear motor in which the conventional measure against raster phenomena is taken. Reference sign 5 Field magnet part 10 anchors 14 core 14a, 14b, 14c projecting posts 14b middle projecting post 16 three-phase winding 18a Support part of the additional core 18b front end part of the additional core 18 additional cores 21 Permanent magnet P1 Distance from the center of the additional core to the center of the middle projecting post P2 Magnetic pole spacing between N poles of the field magnet part Implementation of the invention

[0025] With reference to the accompanying drawings, exemplary embodiments of the present invention are described in detail below. Fig. Figure 1 is a perspective view of a linear motor according to an exemplary embodiment of the present invention (including a sectional view of a table), and Fig. Figure 2 is a front view of the same. A field magnet part 5, serving as a stator for the linear motor, is mounted on an elongated base 4. Linear guides 9 for guiding linear movements of a table 3 are mounted on the base 4. The table 3 is attached to the upper movable blocks 7 of the linear guides 9. An armature 10, serving as a rotor for the linear motor, is suspended between the linear guides 9 on both sides of the underside of the table 3. A gap g is, as shown in the front view in Fig. Figure 2 shows a gap formed between the armature 10 and the field magnet part 5. The linear guides 9 keep this gap constant regardless of the movement of the table 3.

[0026] The base 4 has a bottom wall 4a and a pair of side walls 4b, which are located on the respective sides in the width direction of the bottom wall 4a. Track rails 8 of the linear guides 9 are attached to the top of the bottom wall 4a. Movable blocks 7 are slidably mounted on each track rail 8. A plurality of balls (not shown) are arranged to roll between the track rail 8 and each movable block 7. A circular ball recirculation channel is provided in the movable block 7 for the circulation of the balls. When the movable block 7 slides relative to the track rail 8, the multiple balls roll between it and circulate in the ball recirculation channel. This allows the movable block 7 to slide freely relative to the track rail 8.

[0027] The table 3 is attached to the top of each movable block 7 of the linear guide 9. The table 3 is made of a non-magnetic material, such as aluminum. A movable object is attached to the table 3. Furthermore, a position sensing unit 12, such as a linear scale, is attached to the table 3, which detects the position of the table 3 relative to the base 4. A position signal detected by the position sensing unit 12 is sent to a control unit, which controls the linear motor. The control unit regulates a current supplied to the armature 12 so that the table 3 is moved according to a position command from a control unit at a higher level.

[0028] Fig. Figure 3 is a sectional view along the direction of movement of the armature 10. The armature is located on the underside of the table 3 via an insulating material 13. The armature 10 has a core 14 made of a magnetic material, such as silicon steel, and a three-phase winding 16 wound around projecting posts 14a, 14b, and 14c of the core 14. The core 14 has a support plate 14d attached to the underside of the table 3, as well as the comb-shaped projecting posts 14a, 14b, and 14c extending downwards from the support plate 14d. The number of projecting posts 14a, 14b and 14c is a multiple of 3 and is 3 in this exemplary embodiment. The projecting posts 14a, 14b and 14c are arranged in the direction of movement of the anchor 10, with a fixed distance maintained between them.The three protruding posts 14a, 14b, and 14c are wound with windings 16a, 16b, and 16c of phases U, V, and W. The three-phase winding 16 carries three-phase alternating current with a phase difference of 120°. After the three-phase winding 16 has been wound around the protruding posts 14a, 14b, and 14c, it is encapsulated with plastic.

[0029] Paired additional cores 18 are attached to the underside of the table 3 such that they enclose the armature 10. The additional cores 18 and the core 14 of the armature 10 are separate components. Furthermore, a gap W is formed between the core 14 and each of the additional cores 18. The additional core 18 consists of a magnetic material, such as silicon steel or rolled steel with a general structure. Since no winding is wound on any of the additional cores 18, the additional core 18 does not act as an electromagnet.

[0030] Fig. 4A and Fig. 4B are detailed views of the additional core 18. Fig. 4a is a top view of the additional core 18, and Fig. Figure 4B is a side view of the additional core 18. The additional core 18 is approximately plate-shaped overall. The lateral width of the additional core 18 is nearly the same as that of the core 14. The additional core 18 has a support part 18a, which is attached to the table 3, and a front end part 18b, which is located closer to the field magnet part 5. The support part 18a has a screw hole 18c for attaching the additional core 18 to the table 3. One side of the front end part 18b, facing the armature 10, is truncated along its entire length in the width direction. This truncated part 18d is present so that the front end part 18b is thinner than the support part 18a.

[0031] There, as in Fig. As shown in Figure 3, the gap W between core 14 and the additional cores 18 makes it possible to prevent the protruding posts 14a and 14c at the respective ends of core 14 and the additional cores 18 from forming a magnetic circuit. This reduces the influence of the conventional method for reducing grid distortion, which increases the magnetic flux of the protruding posts 14a and 14c at the respective ends of core 14.

[0032] Furthermore, since the front end portion 18b of each additional core 18 is thin, it is possible to separate the additional core 18 from the core 14 as much as possible while simultaneously keeping the distance P1 between the additional core 18 and the central projecting post 14b constant. This makes it possible to prevent the projecting posts 14a and 14c at the respective ends of the core 14 and the additional cores 18 from forming a magnetic circuit.

[0033] Fig. Figure 5 represents the field magnet section 5, which is attached to the top of the base 4. The field magnet section 15 has a yoke 20 in the form of a thin plate and a plurality of permanent magnets 21 arranged in a row on the yoke 20. Each permanent magnet 21 is a rare-earth magnet, such as a neodymium magnet, with a strong coercive force. The north pole or the south pole is formed on the front of the plate-shaped permanent magnet 21, and the other pole is formed on the back. The permanent magnets 21 are arranged on the yoke 20 such that the north and south poles alternate along the longitudinal direction. The permanent magnets 21 are attached to the yoke 20 by adhesive bonding.

[0034] The yoke 20 is made of a magnetic material, such as silicon steel or rolled steel with a general structure. The yoke 20 is designed as an elongated plate. The permanent magnets 21 attached to the yoke 20 are covered by a cover plate (represented by the dashed-column line). The cover plate 22 is also attached to the yoke 20 by adhesive bonding. The yoke 20, to which the permanent magnets 21 and the cover plate 22 are attached, is mounted to the base 4 using a fastener, such as a screw 23. The field magnet part 5 forms a unit, and multiple field magnet parts 5 are grouped together to form a unit corresponding to the length of the base 4 and are attached to the base 4. The base 4, to which the field magnet parts 5 are attached, is fastened to a bed (not shown) using a fastener, such as a screw 24.

[0035] Fig. Figure 6 is a top view of the field magnet part 5. In this exemplary embodiment, the planar shape of each permanent magnet 21 is that of a parallelogram. The distance from the center of one north-pole permanent magnet 21a to the center of another north-pole permanent magnet 21a is a magnetic pole spacing P2 between north poles of the field magnet part 5. It goes without saying that the magnetic pole spacing P2 between north poles of the field magnet part is twice as long as the magnetic pole spacing P3 between north and south poles and the same as the magnetic pole spacing between south poles.

[0036] With reference to Fig. Figures 7 to 9 describe a method for reducing rasterization according to the present invention. When the core 14, made of magnetic material, is moved over the permanent magnets 21 of the field magnet part 5, magnetic attraction is generated between the permanent magnets 21 and the core 14. Of this magnetic attraction, a component generated in the direction of movement of the armature 10 is relevant for rasterization. A component perpendicular to the direction of movement of the armature 10 (attraction in the vertical direction) is absorbed by the linear guides 9 and is not relevant for rasterization.

[0037] When no current is passed through the three-phase winding 16, the armature 10 moves linearly relative to the field magnet part 5. Then, the projecting posts 14a, 14b, and 14c of the core 14 are attracted by the front permanent magnets 21 or the rear permanent magnets 21 in the direction of movement. This periodic change in attraction is called the lattice phenomenon.

[0038] Fig. Figure 7 is a diagram showing the cogging force generated at each of the projecting posts 14a, 14b, and 14c when the armature 10 is moved from -180° to 0° electrical (1 / 2 of the magnetic pole spacing between the north posts). The cogging forces generated at the projecting posts 14a, 14b, and 14c of phases U, V, and W are represented as sine waves whose phases differ by 120°, with equal currents flowing through the three-phase windings of phases U, V, and W. When the amplitudes of the three sine waves are equal, the cogging force of the entire core, resulting from the combination of the cogging forces of the three projecting posts 14a, 14b, and 14c, is always zero, regardless of the position of the armature 10. That is, no cogging phenomena are generated.

[0039] The magnetoresistance of the central projecting post 14b of phase W is the lowest, and the magnetic flux can easily pass through it. When comparing the detent forces of the projecting posts U, V, and W, the detent force of the central projecting post 14b of phase W is the largest, and the detent forces of the projecting posts 14a and 14c at the respective ends are smaller. Given this, the detent force of the entire core is generated synchronously with the detent force of the central projecting post 14b of phase W. If the additional cores 18 can generate a detent force sufficient to cancel the detent force of the projecting post of phase W, the detent force of the entire core can be reduced.

[0040] Fig. Figure 8 is a diagram comparing the waveform of the cogging force generated at the entire core with the waveforms of the cogging forces generated at the additional cores 18. The waveforms of the cogging forces generated at the additional cores (1) and (2) are electrically offset by 90 degrees relative to the cogging force waveform of the entire core and serve as waveforms by which the cogging force of the entire core can be reduced. Furthermore, the cogging force waveform resulting from combining the waveforms of the additional cores (1) and (2) is an inversion of the waveform of the entire core. Therefore, the cogging force resulting from combining the cogging forces of the entire core and the additional cores (1) and (2) is always zero, regardless of the electrical angle of the armature 10.

[0041] In order for the additional cores 18 to generate the detent force required to cancel the detent force of the entire core, only the phase of the central projecting post 14b of phase W needs to be shifted by 90 electrical degrees relative to the phase of the additional core 18. That is, the distance P1 from the center of the central projecting post 14b of phase W and the center of the front end portion 18b of the additional core 18 is an odd multiple of one-quarter of the magnetic pole spacing P2 between the north poles of the field magnet portion 5. When set to be an even multiple of one-quarter of the magnetic pole spacing, the detent force of the additional core 18 reinforces the detent force of the projecting post 14b of phase W.

[0042] Taking into account the available space for additional cores 18 or the actual occurrence of grid distortion, the distance P1 between the center of the projecting post 14b of phase W and the center of the additional core 18 can be shifted slightly relative to an odd multiple of a quarter of the magnetic pole spacing. This case can be included within the scope of protection of the present invention, which provides that the distance P1 is essentially an odd multiple of a quarter of the magnetic pole spacing. Examples

[0043] A linear motor is used whose magnetic pole spacing between the north poles of the field magnet part is 5.39 mm. If this is due to the in Fig. Applying formula 9, the distance P1 between the center of the projecting post 14b of phase W and the center of the additional core 18 is 39 x (1 / 4) x 5 = 48.75 mm. In fact, the additional core 18 is located at position 39 x (1 / 4) x 4.8 = 48.75 mm. Grid phenomena are then compared before and after the installation of the additional core 18.

[0044] Fig. 10A and Fig. 10B presents the results of the comparison of grid phenomena. Fig. Figure 10A shows the grid pattern before the addition of the extra core 18, and Fig. Figure 10B shows the grid pattern after the addition of the extra core 18. This shows that the grid force can be reduced by approximately 50% from 11.4 N to 5.86 N by adding the extra core 18.

[0045] The present invention is not limited to the exemplary embodiment described above and can be implemented in various forms without deviating from the scope of protection of the present invention. For example, if three projecting posts form a group, two groups of projecting posts, i.e., six projecting posts, may be present. In this case, two middle projecting posts are present, and the midpoint of the two projecting posts is treated as the midpoint of the middle projecting post. If a total of nine projecting posts are present, the fifth projecting post from the end is treated as the middle projecting post.

[0046] Furthermore, the additional cores need not be present on the respective sides of the anchor, or an additional core may be present on only one side of the anchor. The front end of the additional core need not be thin or may have a straight cross-section that does not change from the support part to the front end. A non-magnetic material may be placed between the additional core and the main core in place of the gap. The additional core may be located on the side of the table rather than on the underside.

[0047] Furthermore, although in the exemplary embodiment described above the armature is moved as the runner and the field magnet part is stationary as the stator, the field magnet part can be moved and the armature can be stationary.

[0048] The present application is based on Japanese patent application No. 2007-240143, filed on September 14, 2007.

Claims

[1] Linear motor comprising: a field magnet part (5) with a plurality of permanent magnets (21) arranged to alternately form north and south poles; a core (14) with a plurality of projecting posts (14a, 14b, 14c) which are arranged facing the field magnet part (5); a three-phase winding (16) wound around the projecting posts (14a, 14b, 14c) of the core (14); an armature (10) which has the three-phase winding (16) and the core (14) and moves linearly relative to the field magnet part (5); an additional core (18) of a magnetic body, which is present on at least one side of the runner (10) in a direction of relative motion of the runner (10); and wherein a distance (P1) between a center of the additional core (18) and a center of a middle projecting post (14b) from the projecting posts (14a, 14b, 14c) in the direction of relative motion of the runner (10) is specified such that it is substantially 1 / 4 x (2N+1) x a magnetic pole spacing (P2) between north poles of the field magnet part (5) (N: an integer equal to or greater than 1), wherein a gap is present between the additional core (18) and the core (14) or a non-magnetic material is arranged between them to prevent the projecting posts (14a, 14c) at the end of the core (14) and the additional core (18) from forming a magnetic circuit. [2] Linear motor according to claim 1, wherein the additional core (18) has a front end part (18b) and a support part (18a) and the thickness of the front end part (18b) in the direction of movement is less than the thickness of the support part (18a) in the direction of movement. [3] Linear motor according to claim 2, wherein the front end part (18b) of the additional core (18) is cut off on a side facing the core (14) so ​​that the thickness becomes smaller in the direction of movement. [4] Linear motor according to any one of claims 1 to 3, wherein the additional core (18) is present on each side of the runner (10) in the direction of movement such that the runner (10) is enclosed between the additional cores (18). [5] Linear motor according to any one of claims 1 to 4, wherein the three-phase winding (16) is a group of windings (16a, 16b, 16c) of phases U, V and W, each wound around the projecting posts (14a, 14b, 14c) and arranged in the direction of movement, and the middle projecting post (14b) is a post (14b) positioned in the middle of the three projecting posts (14a, 14b, 14c) in the direction of movement. [6] A method for reducing latency in a linear motor comprising a field magnet part (5) with a plurality of permanent magnets (21) arranged to alternately form north and south poles; a core (14) with a plurality of projecting posts (14a, 14b, 14c) facing the field magnet part (5); a three-phase winding (16) wound around the projecting posts (14a, 14b, 14c) of the core (14); an armature (10) comprising the three-phase winding (16) and the core (14) moving linearly relative to the field magnet part (5); and an additional core (18) of a magnetic body located on at least one side of the rotor (10) in a direction of relative motion of the rotor (10); wherein the method for reducing latency in a linear motor comprises: Arranging the additional core (18) such that a distance (P1) between a center of the additional core (18) and a center of a middle projecting post (14b) from the projecting posts (14a, 14b, 14c) in the direction of relative motion of the runner (10) is substantially 1 / 4 x (2N+1) x a magnetic pole spacing (P2) between N north poles of the field magnet part (5) (N: an integer equal to or greater than 1), and Creating a gap between the core (14) and the additional core (18) or arranging a non-magnetic material between them to prevent the projecting posts (14a, 14c) at the end of the core (14) and the additional core (18) from forming a magnetic circuit.

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