Linear motor

Abstract

To provide a technique capable of improving the performance of sensor-less control of a linear motor in terms of a structure.SOLUTION: A linear motor 1 according to one embodiment of the present disclosure includes an armature 10 and a field 20 that are disposed to face each other in a relatively movable manner in an X-axis direction. The armature 10 includes a plurality of coils 12 that are each wound around a core 11 and are arranged along the X-axis direction. The field 20 is disposed to face the armature 10 in a Z-axis direction orthogonal to the X-axis direction, and includes a plurality of permanent magnets 21 arranged along the X-axis direction and a plurality of soft magnetic bodies 23 arranged to be disposed alternately with the permanent magnets 21 along the X-axis direction. In the X-axis direction, a ratio x of a width LMC of a portion of the core 11 facing the field 20 with respect to a coil pitch PC at which the coils 12 are arranged is 0.53 or less.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to linear motors. [Background technology]

[0002] For example, sensorless control is known in which the magnetic pole position is estimated by utilizing the induced voltage or saliency of the motor, thereby controlling the motor without using a position sensor or a speed sensor.

[0003] In particular, in the case of a linear motor, which operates at a relatively slow speed compared to a rotating machine, the induced voltage decreases, so sensorless control is performed by utilizing saliency (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-171669 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the characteristics of the linear motor related to the saliency may change depending on the current conditions of the linear motor. For example, under medium to high load current conditions where a relatively large current flows, the magnetic saturation of the linear motor becomes significant, causing a change in the inductance characteristics, which may result in a change in the characteristics of the linear motor related to the saliency. Therefore, the change in the characteristics related to the saliency in response to the change in the current conditions may reduce the estimation accuracy of the magnetic pole position, which may result in a deterioration in the control performance of the linear motor.

[0006] In view of the above-mentioned problems, an object of the present invention is to provide a technique capable of improving the performance of sensorless control of a linear motor from a structural standpoint. [Means for solving the problem]

[0007] In order to achieve the above object, in one embodiment of the present disclosure, A linear motor including an armature and a field magnet arranged opposite each other so as to be capable of relative movement, the armature includes a plurality of windings each wound around a first core and aligned along the direction of the relative movement; the field magnet includes a plurality of permanent magnets arranged along the direction of the relative movement so as to face the armature in a direction perpendicular to the direction of the relative movement, and a plurality of second iron cores arranged so as to be alternately arranged with the permanent magnets along the direction of the relative movement, a first ratio of a dimension of a portion of the first core facing the field magnet to a pitch at which the windings are arranged in the direction of the relative movement is 0.53 or less; A linear motor is provided. Effect of the Invention

[0008] According to the above-described embodiment, the performance of the sensorless control of the linear motor can be improved from the structural aspect. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a side cross-sectional view showing an example of a linear motor. [Diagram 2] FIG. 2 is a plan sectional view showing an example of an armature. [Diagram 3] FIG. 2 is a diagram illustrating an inductance locus of a linear motor. [Figure 4] 13 is a diagram showing a change in inductance locus accompanying a change in current condition of a linear motor according to a comparative example. FIG. [Diagram 5] 1 is a diagram for explaining dimensions of components of a linear motor related to the inductance characteristics of the linear motor; [Figure 6] FIG. 13 is a diagram showing an example of an analysis result regarding the relationship between the ratio of the width of the core end in the Z-axis direction to the coil pitch and the ratio of the length of the soft magnetic member to the magnetic pole pitch, and the slope of the inductance locus of a linear motor under specific current conditions. [Figure 7] FIG. 13 is a diagram showing changes in inductance locus with changes in current conditions for an example linear motor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment will be described with reference to the drawings.

[0011] [Linear motor overview] An overview of a linear motor 1 according to this embodiment will be described with reference to FIGS.

[0012] Fig. 1 is a side cross-sectional view showing an example of a linear motor 1. Specifically, Fig. 1 is a cross-sectional view taken along a plane parallel to the X-axis and Z-axis of the linear motor 1. Fig. 2 is a plan cross-sectional view showing an example of an armature 10. Specifically, Fig. 2 is a cross-sectional view taken along line AA in Fig. 1.

[0013] In the following description, an orthogonal coordinate system defined by the X-axis, Y-axis, and Z-axis in the drawings may be used. The positive X-axis direction and the negative X-axis direction may be collectively referred to as the X-axis direction, the positive Y-axis direction and the negative Y-axis direction may be collectively referred to as the Y-axis direction, and the positive Z-axis direction and the negative Z-axis direction may be collectively referred to as the Z-axis direction.

[0014] The linear motor 1 according to this embodiment may be incorporated into the opening and closing mechanisms of various sliding doors, such as railway car doors, station platform doors, etc. The linear motor 1 according to this embodiment may also be mounted on machine tools, such as semiconductor manufacturing equipment and machining centers.

[0015] 1 and 2, the linear motor 1 includes an armature 10 and a field magnet 20. In Fig. 1, the letters "N" and "S" drawn on the field magnet 20 represent the magnetic poles (north pole and south pole) of a permanent magnet 21. In Fig. 2, the dashed line drawn on the armature 10 represents the cross-sectional shape of both ends of the core 11 in the Z-axis direction.

[0016] The armature 10 is disposed facing each of the field magnet portions 20A, 20B on both sides in the positive direction and the negative direction of the Z axis via a predetermined gap (also referred to as an "air gap") AG. In this example, the armature 10 is a mover. The armature 10 is supported by a support mechanism such as a slide rail or a linear guide so as to be movable in the X axis direction. This allows the armature 10 to move in the X axis direction by a magnetic force acting between the armature 10 and the field magnet 20. The armature 10 includes a core (also referred to as an "iron core") 11, a coil (also referred to as a "winding") 12, and a holding portion 13.

[0017] Core 11 functions as a magnetic path for the magnetic field generated by the armature current of coil 12 and the magnetic field from permanent magnet 21 of field magnet 20. Core 11 is made of a soft magnetic material. The soft magnetic material used for core 11 is, for example, an iron-based material such as cast iron or structural steel. The soft magnetic material used for core 11 may also be a functional material such as an electromagnetic steel sheet or a powder magnetic core. In this example, a plurality of cores 11 (six cores) are provided, the same number as the coils 12.

[0018] 1 and 2, for example, core 11 has a rectangular column shape extending in the Z-axis direction, and is formed so that the cross-sectional shapes of both ends in the Z-axis direction are larger than the cross-sectional shape of the center in the Z-axis direction. As a result, even if core 11 attempts to move in the positive direction of the Z-axis, the end of core 11 in the negative direction of the Z-axis abuts against holding portion 13, and as a result, core 11 cannot move in the positive direction of the Z-axis, thereby preventing core 11 from falling off from armature 10 as it moves in the positive direction of the Z-axis. Similarly, the same action can prevent core 11 from falling off from armature 10 as it moves in the negative direction of the Z-axis.

[0019] When an armature current flows through coil 12, the coil generates a thrust force for the mover (armature 10) by interaction with the magnetic field generated from field magnet portions 20A and 20B. Coil 12 is formed by winding a conductive wire around core 11.

[0020] In this example, a plurality of (six) coils 12 are provided. The plurality of coils 12 are arranged in the X-axis direction. For example, three-phase AC power of U phase, V phase, and W phase is supplied to the plurality of coils 12. Specifically, the three-phase AC power may be supplied in the order of U phase (+), U phase (-), V phase (-), V phase (+), W phase (+), and W phase (-) from the coil 12 at the end in the negative direction of the X-axis in the drawing toward the positive direction of the X-axis.

[0021] An insulating part (not shown) is provided between the core 11 and the coil 12 (conductor) to ensure insulation between them. The insulating part is an insulating member that ensures insulation between the core 11 and the entire coil 12, such as insulating paper, an insulator, a bobbin, or an insulating coating on the surface of the core 11. The insulating coating on the core 11 is, for example, an insulating powder coating. The insulating part may also be an insulating film coated on the conductor of the coil 12.

[0022] The holding portion 13 integrally holds the multiple cores 11 and the multiple coils 12. The holding portion 13 is made of, for example, molded resin, and both ends of the multiple cores 11 in the axial direction (Z-axis direction) are held so as to be exposed from the holding portion 13. In addition, both ends of the multiple cores 11 in the axial direction (Z-axis direction) may be covered by the holding portion 13 and held so as not to be exposed from the holding portion 13.

[0023] The field magnet 20 generates a magnetic field that acts on the armature 10. In this example, the field magnet 20 is a stator. As shown in Fig. 1, the field magnet 20 is provided so as to extend in the X-axis direction, and the dimension in the X-axis direction is determined according to the amount of movement in the X-axis direction of the armature 10 as a mover.

[0024] The field magnet 20 includes field magnet portions 20A and 20B.

[0025] The field magnet parts 20A, 20B are provided so as to extend in the X-axis direction substantially parallel to each other. The term "substantially" is intended to allow for, for example, manufacturing errors, and will be used in the same manner hereinafter. A predetermined distance is provided between the field magnet parts 20A, 20B in the Z-axis direction, and this distance is set to be somewhat larger than the dimension of the armature 10 in the Z-axis direction. For example, the distance between the field magnet parts 20A, 20B corresponds to the dimension of the armature 10 in the Z-axis direction plus the movable amount in the Z-axis direction of the support mechanism of the armature 10 (for example, a slide rail or linear guide) and a predetermined margin. This allows the armature 10 as a mover to move in the X-axis direction without coming into contact with the field magnet parts 20A, 20B.

[0026] Field magnet portions 20A, 20B are disposed to face each other in the positive Z-axis direction and the negative Z-axis direction, respectively, when viewed from armature 10. Field magnet portions 20A, 20B each generate a magnetic flux that links with the multiple coils 12 of armature 10.

[0027] Each of the field magnet portions 20A and 20B includes a plurality of permanent magnets 21, a back yoke 22, and a soft magnetic member .

[0028] The multiple permanent magnets 21 are arranged side by side in the X-axis direction so as to face the armature 10 in the Z-axis direction. For example, as shown in Fig. 1, the multiple permanent magnets 21 each have a substantially rectangular parallelepiped shape with sides in the X-axis direction, Y-axis direction, and Z-axis direction, and are arranged side by side at substantially equal intervals in the X-axis direction. Each of the multiple permanent magnets 21 is magnetized in the Z-axis direction such that the field magnet 20 faces the armature 10, and is arranged such that the magnetic pole of the end face in the Z-axis direction facing the armature 10 is different from other permanent magnets 21 adjacent in the X-axis direction.

[0029] The permanent magnet 21 is rare earth-free, that is, a permanent magnet that does not use any rare earths (rare earth elements). For example, the permanent magnet 21 is lanthanum-free, that is, a ferrite magnet that does not use any lanthanum. The permanent magnet 21 may also be rare metal-free, that is, a permanent magnet that does not use any rare metals including rare earths. For example, the permanent magnet 21 is lanthanum-free and cobalt-free, that is, a ferrite magnet that does not use any lanthanum or cobalt.

[0030] The field magnet portion 20A and the field magnet portion 20B are configured so that the magnetic specifications (e.g., shape, size, residual magnetic flux density, etc.) and arrangement specifications (e.g., arrangement positions of the permanent magnets 21 in the X-axis direction and arrangement manner including the presence or absence of a Halbach array, etc.) of the permanent magnets 21 are substantially the same. This allows the field magnet portion 20A and the field magnet portion 20B to generate substantially symmetrical magnetic fields in spaces facing each other in the Z-axis direction.

[0031] The back yoke 22 is disposed adjacent to an end face of the permanent magnet 21 on the opposite side to the side on which the armature 10 is present in the Z-axis direction. The back yoke 22 functions as a magnetic path between adjacent permanent magnets 21. The back yoke 22 is formed of a soft magnetic material. The soft magnetic material used for the back yoke 22 is, for example, an iron-based material such as cast iron or structural steel. The soft magnetic material used for the back yoke 22 may also be a functional material such as an electromagnetic steel sheet or a powder magnetic core.

[0032] The soft magnetic member 23 is formed of a soft magnetic material and is disposed between adjacent permanent magnets 21 in the X-axis direction so as to be adjacent to the permanent magnets 21. For example, the soft magnetic material is an iron-based material such as cast iron or structural steel. The soft magnetic material may also be a functional material such as an electromagnetic steel sheet or a powder magnetic core. For example, as shown in FIG. 1, the soft magnetic member 23 has a substantially rectangular parallelepiped shape with sides in the X-axis direction, the Y-axis direction, and the Z-axis direction, and abuts against the permanent magnets 21 at both ends in the X-axis direction. This allows the field magnet parts 20A and 20B to have a saliency with uneven magnetic resistance (reluctance) with respect to the magnetic field of the armature 10 in the X-axis direction, which is the moving direction of the mover (armature 10). Therefore, the linear motor 1 can utilize not only the magnetic force between the armature 10 and the field magnet 20 but also the reluctance force as a driving force. This allows the thrust of the linear motor 1 to be improved. Furthermore, by utilizing the saliency of the field magnet 20 (field magnet portions 20A, 20B), it becomes possible to estimate the position of the mover (armature 10) in the X-axis direction, making it possible to omit a sensor such as an encoder for detecting the position of the armature 10.

[0033] The number of magnetic poles and the number of slots of the linear motor 1 may be any combination. For example, as shown in Fig. 1, the permanent magnets 21 of the field magnet 20 and the coils 12 of the armature 10 are arranged in a relationship of 5 poles and 6 slots in the X-axis direction. Specifically, the permanent magnets 21 and the coils 12 are arranged in the X-axis direction such that the number of coils 12 (the number of slots) is 6 for a section in which the number of permanent magnets 21 (the number of magnetic poles) is 5. Furthermore, the combination of the number of magnetic poles and the number of slots of the linear motor 1 may be 2 poles and 3 slots, 4 poles and 3 slots, 7 poles and 6 slots, or the like, instead of 5 poles and 6 slots.

[0034] [Outline of linear motor position estimation method] Next, an overview of a method for estimating the position of the linear motor 1 will be described with reference to FIG.

[0035] FIG. 3 is a diagram showing a schematic diagram of the inductance locus of the linear motor 1. As shown in FIG.

[0036] The inductance locus can be obtained by plotting the inductance of the linear motor 1 for one pitch period (phase 360 ​​degrees) in the X-axis direction as a vector locus on a dq coordinate system, with the magnetic pole position of the permanent magnet 21 as the d-axis and the position of the soft magnetic member 23 as the q-axis. The inductance value is calculated from the voltage applied to the armature 10 of the linear motor 1 and the current flowing through the armature 10 at that time.

[0037] The control system of the linear motor 1 includes a drive device and a control device, neither of which is shown.

[0038] The driving device supplies power to the linear motor 1 to drive the linear motor 1. The driving device is, for example, a power conversion device, and drives the linear motor 1 by generating three-phase AC of a predetermined voltage and frequency from DC or AC supplied from an external power source and supplying it to the armature 10 of the linear motor 1.

[0039] The control device controls the drive device to thereby perform drive control of the linear motor 1.

[0040] As described above, the control device estimates the position in the X-axis direction of the armature 10 as a mover by utilizing the saliency of the field magnet 20. This allows the control device to calculate an estimate of the speed of the armature 10 based on the estimate of the position in the X-axis direction of the armature 10. Then, the control device can perform position control and speed control of the armature 10 based on the estimate of the position in the X-axis direction and the speed in the X-axis direction of the armature 10.

[0041] 4, the inductance characteristic of the linear motor 1 having salient poles is represented by an elliptical inductance locus whose short side is the d-axis and whose long side is the q-axis. The control device can estimate the position of the armature 10 in the X-axis direction by using such an inductance locus as a premise.

[0042] For example, the control device assumes that the γ-axis and δ-axis correspond to the d-axis and q-axis, and applies a high-frequency AC voltage for position detection in the γ-axis direction. At this time, the interference current i δ A current i δ becomes 0 (zero) when the γ-axis and the d-axis coincide with each other. Therefore, the control device adjusts the γ-axis and δ-axis so that the interference current iδ becomes zero, thereby causing the γ-axis to coincide with the d-axis, and as a result, it is possible to estimate the position in the X-axis direction corresponding to the γ-axis as the magnetic pole position.

[0043] [Changes in inductance characteristics of the linear motor according to the comparative example] Next, with reference to FIG. 4, a change in the inductance characteristic of the linear motor according to the comparative example will be described.

[0044] FIG. 4 is a diagram showing changes in inductance locus accompanying changes in current conditions of the linear motor according to the comparative example.

[0045] FIG. 4 illustrates inductance loci 40 to 43 under different current conditions of a linear motor according to a comparative example, with the armature current increasing in the order of inductance locus 40, inductance locus 41, inductance locus 42, and inductance locus 43.

[0046] As shown in Fig. 4, the inductance locus of the linear motor according to the comparative example shifts the phase at which the inductance is minimum from the d-axis as the armature current increases. This is because magnetic saturation occurs as the armature current increases, causing mutual interference between the d-axis and the q-axis. As a result, the inductance locus of the linear motor according to the comparative example has the major and minor axes inclined from the d-axis and q-axis when the armature current is relatively large.

[0047] For example, when the control device performs the above-mentioned position estimation method on the linear motor according to the comparative example in a state where the armature current is relatively large, the control device estimates the position corresponding to the minor axis of the tilted inductance locus, not the d-axis, as the magnetic pole position. Therefore, a relatively large error occurs between the actual magnetic pole position and the estimation result, which may result in deterioration of control performance or, in the worst case, failure to control.

[0048] [Structure of a linear motor] Next, the structure of the linear motor 1 according to this embodiment will be described with reference to FIGS.

[0049] FIG. 5 is a diagram for explaining the dimensions of the components of the linear motor 1 related to the inductance characteristics of the linear motor 1. FIG. C Width L of the end of the core 11 in the Z-axis direction MC Ratio x, and pole pitch P MG The length L of the soft magnetic member 23 SC 7 is a diagram showing an example of an analysis result relating to the relationship between the ratio a and the slope θ of the inductance locus of the linear motor 1 under specific current conditions. Fig. 7 is a diagram showing changes in the inductance locus accompanying changes in the current conditions of an example of the linear motor 1.

[0050] The specific current condition corresponds to a medium to high load current condition where the inclination θ of the inductance locus is likely to become large due to magnetic saturation or the like, that is, a current condition where a relatively large armature current flows.

[0051] As shown in Figure 5, the coil pitch P C represents the pitch of the coil 12 in the X-axis direction. Also, the width L of the end of the core 11 in the Z-axis direction MC represents the dimension in the X-axis direction of the end portion in the Z-axis direction of the core 11. Also, the magnetic pole pitch P MG represents the pitch of the arrangement of the permanent magnets 21 in the X-axis direction. SC represents the dimension of the soft magnetic member 23 in the X-axis direction.

[0052] As shown in FIG. 6, the slope θ of the inductance locus of the linear motor 1 has a ratio x (=L MC / P C ) is significantly affected by the width L of the end of the core 11 in the Z-axis direction. MC is relatively large, in which case magnetic flux tends to concentrate in core 11, making it easier for magnetic saturation to occur in coil 12.

[0053] In particular, in the range where the ratio x exceeds 0.53 to 0.61, the slope θ of the inductance locus exceeds 20° and increases rapidly with an increase in the ratio x. Therefore, for example, the structure of the linear motor 1 is determined so that the ratio x is 0.53 or less.

[0054] As shown in FIG. 6, the slope θ of the inductance locus of the linear motor 1 is affected by the ratio a (=L SC / P MG ) is affected by the length L of the soft magnetic member 23. Specifically, the slope θ of the inductance locus of the linear motor 1 increases as the ratio a increases. SC is relatively large, and in this case, the magnetic flux linking the coil 12 through the soft magnetic member 23 becomes relatively large, which makes it easier for magnetic saturation to occur in the coil 12.

[0055] Therefore, the condition regarding the ratio x may be determined taking into consideration the ratio a. For example, the structure of the linear motor 1 is determined so as to satisfy the condition of the following formula (1) which expresses the relationship between the ratio x and the ratio a.

[0056]

number

[0057] The upper limit of the ratio x defined by formula (1) is represented by the dashed line in Fig. 6. As a result, the larger the ratio a is, the smaller the upper limit of the ratio x (dashed line in Fig. 6) is, so that the slope θ of the inductance locus of the linear motor 1 can be more appropriately suppressed.

[0058] For example, inductance loci 70 to 73 are drawn under different current conditions of the linear motor 1, and the armature current increases in the order of inductance locus 70, inductance locus 71, inductance locus 72, and inductance locus 73.

[0059] In this example, the coil pitch P C Width L of the end of the core 11 in the Z-axis direction MC By appropriately determining the ratio x, the slope θ of the inductance locus of the linear motor 1 is kept very small even if the armature current increases.

[0060] In this way, in this example, in the linear motor 1, the coil pitch P C Width L of the end of the core 11 in the Z-axis direction MC By appropriately determining the ratio x, it is possible to suppress magnetic saturation of the linear motor 1 under medium to high loads and suppress the inclination θ of the inductance locus. Therefore, the control device can maintain a relatively high accuracy in estimating the position of the armature 10 in the X-axis direction, and as a result, it is possible to more appropriately control the position and speed of the linear motor 1.

[0061] [Other embodiments] Next, another embodiment will be described.

[0062] The above-described embodiment may be modified or altered as appropriate.

[0063] In the above-described embodiment and its modified and altered examples, the permanent magnet 21 may be a permanent magnet using rare earth or rare metal. For example, the permanent magnet 21 is a neodymium magnet or a ferrite magnet using cobalt or lanthanum.

[0064] Furthermore, in the above-described embodiment and its modified and altered examples, when the permanent magnets 21 and the coils 12 are arranged in a 5-pole, 6-slot relationship in the X-axis direction, the number of coils 12 in the armature 10 may be a multiple of 6 that is 7 or greater. The same applies to combinations of the number of magnetic poles and the number of slots in the linear motor 1, such as 2 poles and 3 slots, 4 poles and 3 slots, 7 poles and 6 slots, etc.

[0065] In the above-described embodiment and its modified and altered examples, the back yoke 22 and the soft magnetic member 23 may be integrally formed as a single member.

[0066] In addition, in the above-described embodiment and its variations and modifications, the back yoke 22 may be omitted.

[0067] In the above-described embodiment and its variations and modifications, the cross-sectional shape of the core 11 at both ends in the Z-axis direction may be substantially the same as the cross-sectional shape of the center portion in the Z-axis direction.

[0068] In the above-described embodiment and its modified and altered examples, the linear motor 1 may have the armature 10 as the stator and the field magnet 20 as the mover. In this case, the armature 10 is provided so as to extend between both ends of the movable range in the X-axis direction. In this case, the field magnet 20 has field magnet portions 20A and 20B connected so as to surround the armature 10 in the Z-axis direction and the Y-axis direction.

[0069] In the above-described embodiment and its variations and modifications, the moving path of the mover of the linear motor 1 may include at least a part of a path that follows a curve.

[0070] [Effect] Next, the operation of the linear motor according to this embodiment will be described.

[0071] In this embodiment, the linear motor includes an armature and a field magnet that are arranged opposite to each other so that they can move relative to each other. The linear motor is, for example, the linear motor 1 described above. The armature and the field magnet are, respectively, the armature 10 and the field magnet 20 described above. Specifically, the armature includes a plurality of windings that are wound around a first core and arranged along the direction of relative movement of the armature and the field magnet. The first core is, for example, the core 11 described above. The winding is, for example, the coil 12 described above. The direction of relative movement of the armature and the field magnet is, for example, the X-axis direction described above. The field magnet includes a plurality of permanent magnets and a plurality of second cores. The permanent magnet is, for example, the permanent magnet 21 described above. The second core is, for example, the soft magnetic member 23 described above. More specifically, the multiple permanent magnets are arranged to face the armature in a direction perpendicular to the direction of relative movement between the armature and the field, and are aligned along the direction of relative movement between the armature and the field. The direction perpendicular to the direction of relative movement between the armature and the field is, for example, the Z-axis direction described above. The multiple second iron cores are aligned so as to be alternately arranged with the permanent magnets along the direction of relative movement. In addition, in the direction of relative movement between the armature and the field, a first ratio of the dimension of the portion of the first iron core facing the field to the pitch at which the windings are arranged may be 0.53 or less. The pitch at which the windings are arranged may be, for example, the coil pitch P described above. C The dimension of the portion of the first iron core facing the field magnet is, for example, the above-mentioned width L MC The first ratio is, for example, the ratio x described above.

[0072] This allows the dimensions of the portion of the first iron core facing the field to be relatively small. This makes it possible to suppress magnetic saturation of the windings in medium to high load operating conditions where the armature current of the linear motor is relatively large, and to suppress the inclination of the inductance locus, thereby improving the estimation accuracy of the position of the mover of the linear motor. This makes it possible to improve the performance of the sensorless control of the linear motor from a structural standpoint.

[0073] In this embodiment, the above relational expression (1) may be established when the first ratio is x and the second ratio of the size of the second core to the pitch at which the multiple permanent magnets are arranged in the direction of relative movement of the armature and the field is a. The pitch at which the multiple permanent magnets are arranged may be, for example, the above-mentioned magnetic pole pitch P MG The dimensions of the second core are, for example, the length L of the second core described above. SC The second ratio is, for example, the above-mentioned ratio a.

[0074] As a result, the first ratio is determined so that the larger the second ratio, the smaller the first ratio. Therefore, even if the magnetic flux linking the winding through the second core is relatively large because the second ratio is relatively large, the first ratio is determined to be relatively small in accordance with the second ratio, thereby suppressing magnetic saturation of the winding in medium to high load operating states. This makes it possible to further improve the accuracy of estimating the position of the mover of the linear motor.

[0075] In the present embodiment, the first core may have a portion facing the field magnetic field that is larger in size than the other portions in the direction facing the field magnetic field.

[0076] Thereby, for example, by adjusting the ratio x, it is possible to make the dimension of the portion of the first core that faces the field magnet relatively small, while suppressing the first core from falling off the armature.

[0077] In this embodiment, the permanent magnet may be rare earth-free.

[0078] This makes it possible to configure a linear motor using rare earth-free permanent magnets that have a relatively small residual magnetic flux density.

[0079] In this embodiment, the permanent magnet may be formed without using rare metals.

[0080] This makes it possible to configure a linear motor using rare metal-free permanent magnets with a relatively small residual magnetic flux density.

[0081] In addition, in this embodiment, the permanent magnet may be a lanthanum-free and cobalt-free ferrite magnet.

[0082] This makes it possible to configure a linear motor using lanthanum-free and cobalt-free ferrite magnets that have a relatively small residual magnetic flux density.

[0083] Although the embodiments have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist described in the claims. [Explanation of symbols]

[0084] 1. Linear motor 10 Armature 11 cores 12 Coils 13 Holding part 20 Field magnet 20A field magnet 20B Field magnet section 21 Permanent magnets 22 Back Yoke 23 Soft magnetic materials AG void

Claims

1. A linear motor including an armature and a field magnet arranged opposite each other so as to be capable of relative movement, the armature includes a plurality of windings each wound around a first iron core and aligned along the direction of the relative movement; the field magnet includes a plurality of permanent magnets arranged along the direction of the relative movement so as to face the armature in a direction perpendicular to the direction of the relative movement, and a plurality of second iron cores arranged so as to be alternately arranged with the permanent magnets along the direction of the relative movement, a first ratio of a dimension of a portion of the first core facing the field magnet to a pitch at which the windings are arranged in a direction of the relative movement is 0.53 or less; Linear motor.

2. When the first ratio is x and a second ratio of a dimension of the second iron core to a pitch at which the plurality of permanent magnets are arranged in the direction of the relative movement is a, the following relational expression is established:

2. The linear motor according to claim 1. [0010]

3. The first iron core has a portion facing the field magnetic field that is larger in size than the other portion in a direction facing the field magnetic field.

3. The linear motor according to claim 1 or 2.

4. The permanent magnet is rare earth-free.

3. The linear motor according to claim 1 or 2.

5. The permanent magnet is rare metal-free.

5. The linear motor according to claim 4.

6. The permanent magnet is a lanthanum-free and cobalt-free ferrite magnet.

6. The linear motor according to claim 5.

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