Linear motor with varying width slider teeth

Abstract

A linear motor includes a stator having a plurality of salient poles, and a slider configured to move along a direction of extension of the stator. A U-phase coil core of the slider includes a yoke, a plurality of teeth, permanent magnets provided in respective magnet-receiving cavities located between the teeth, coil-receiving cavities formed on outer sides of the teeth set, and a U-phase coil wound in the coil-receiving cavities. The plurality of teeth project radially from the yoke toward the stator, and the width of each of the teeth as measured at the yoke side is narrower than its width as measured at the stator side.

Claims

1. A linear motor comprising: a stator having a plurality of salient poles arranged at uniform intervals along a direction of extension; and a slider provided facing the stator and configured to move along the direction of extension of the stator, wherein the slider comprises: a yoke; a plurality of teeth projecting from the yoke toward the stator and located sequentially along a direction of movement; permanent magnets provided in respective magnet-receiving cavities located between the teeth; coil-receiving cavities formed on outer sides of a teeth set composed of the plurality of teeth; and a coil wound in the coil-receiving cavities, and wherein the plurality of teeth project radially from the yoke toward the stator, and a width of each of the teeth as measured at a yoke side is narrower than its width as measured at a stator side, and widths of all of the teeth as measured at their respective ends at the yoke side are equal to each other.

2. The linear motor according to claim 1, wherein the plurality of teeth project radially from the yoke toward the stator at equiangular intervals.

3. The linear motor according to claim 1, wherein each of teeth located toward the front in the teeth set has its tip slanted frontward relative to a facing direction orthogonal to the direction of movement, each of teeth located toward the rear in the teeth set has its tip slanted rearward relative to the facing direction, and a space in front of a front-end tooth located at a front end of the teeth set in the direction of movement and a space behind a rear-end tooth located at a rear end of the teeth set in the direction of movement respectively constitute the coil-receiving cavities.

4. The linear motor according to claim 2, wherein each of teeth located toward the front in the teeth set has its tip slanted frontward relative to a facing direction orthogonal to the direction of movement, each of teeth located toward the rear in the teeth set has its tip slanted rearward relative to the facing direction, and a space in front of a front-end tooth located at a front end of the teeth set in the direction of movement and a space behind a rear-end tooth located at a rear end of the teeth set in the direction of movement respectively constitute the coil-receiving cavities.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Embodiment(s) of the present disclosure will be described based on the following figures, wherein:

(2) FIG. 1 is a cross-sectional view showing a schematic configuration of a linear motor according to an embodiment;

(3) FIG. 2 is a cross-sectional view showing a U-phase coil core of the linear motor according to the embodiment;

(4) FIG. 3 is an explanatory diagram showing magnetic flux flow at a time when a current is caused to flow in a U-phase coil on the U-phase coil core of the linear motor according to the embodiment;

(5) FIG. 4 is a cross-sectional view of a U-phase coil core of a linear motor according to a conventional art;

(6) FIG. 5 is an explanatory diagram showing magnetic flux flow at a time when a current is caused to flow in a U-phase coil on the U-phase coil core of the linear motor according to the conventional art;

(7) FIG. 6 is a diagram showing an example cross-sectional structure of the linear motor according to the conventional art;

(8) FIG. 7 is a diagram showing an example cross-sectional structure of another linear motor according to a conventional art; and

(9) FIG. 8 is a diagram showing an example cross-sectional structure of another linear motor according to a conventional art.

DESCRIPTION OF EMBODIMENTS

(10) A linear motor 100 according to an embodiment will now be described by reference to the drawings. As shown in FIG. 1, the linear motor 100 is composed of a stator 10 and a slider 20. Here, in each of the drawings, an X direction denotes a direction of extension of the stator 10 or a direction of movement of the slider 20. A Y-direction denotes a facing direction orthogonal to the X direction which is the direction of movement. In the following description, a negative side of the X direction is referred to as a frontward direction of the slider 20, and a positive side of the X direction is referred to as a rearward direction of the slider 20.

(11) The stator 10 is formed by, for example, laminating silicon steel sheets. The stator 10 is composed of an elongate stator yoke 11 extending in the X direction, and a plurality of salient poles 12 projecting from an end face, in the Y direction, of the stator yoke 11 toward a positive side of the Y direction. The salient poles 12 are located sequentially along the X direction at uniform intervals of pitch STP.

(12) The slider 20 is formed by, for example, laminating silicon steel sheets, and faces the stator 10 in the Y direction. The slider 20 is composed of a U-phase coil core 30, a W-phase coil core 40, and a V-phase coil core 50 located sequentially along the X direction. The length of the slider 20 in the X direction is SLLT1, and its height in the Y direction is SLH. The length, in the X direction, of all of the U-phase coil core 30, the W-phase coil core 40, and the V-phase coil core 50 is length SLL1.

(13) The U-phase coil core 30 comprises a yoke 31 having a height LY in the Y direction, and a plurality of teeth 32a-32f which project from the yoke 31 toward the stator 10 toward a negative side of the Y direction and which are arranged sequentially along the X direction. In magnet-receiving cavities 33 located between the teeth 32a-32f, permanent magnets 34a-34e are mounted respectively. Further, the teeth 32a-32f constitute one teeth set 32S, and on outer sides of the teeth set 32S, coil-receiving cavities 35 are formed. The length of the teeth set 32S in the X direction as measured at the yoke side is TWA. The width of each coil-receiving cavity 35 in the X direction as measured at the yoke side is D, and its length in the Y direction is SLTH. A U-phase coil 36 is wound in the coil-receiving cavities 35 in parts denoted by U and X. Here, when making no distinction among the respective teeth 32a-32f and among the respective permanent magnets 34a-34e, these will be simply referred to as the teeth 32 and the permanent magnets 34.

(14) Each of the W-phase coil core 40 and the V-phase coil core 50 has the same structure as the U-phase coil core 30, and comprises a yoke 41, 51 and a plurality of teeth 42, 52. In magnet-receiving cavities 43, 53 located between the teeth 42 and between the teeth 52, permanent magnets 44, 54 are mounted respectively. Further, in coil-receiving cavities 45, 55 located on outer sides of the teeth 42 constituting one set and on outer sides of the teeth 52 constituting one set, a W-phase coil 46 and a V-phase coil 56 are wound. The W-phase coil 46 is wound in parts denoted by W and Z in FIG. 1, and the V-phase coil 56 is wound in parts denoted by V and Y in FIG. 1.

(15) The teeth 32 of the U-phase coil core 30, the teeth 42 of the W-phase coil core 40, and the teeth 52 of the V-phase coil core 50 are arranged by being respectively shifted in the X direction relative to the salient poles 12 of the stator by a pitch STP/3, which corresponds to an electrical angle of 120 degrees. Each of the spacing between the teeth 32 and the teeth 42 across the coil-receiving cavities 35, 45 and the spacing between the teeth 42 and the teeth 52 across the coil-receiving cavities 45, 55 is SLPW, which is identical to that of the conventional art shown in FIG. 6, and is defined by Equation 2.

(16) Next, the structure of the U-phase coil core 30 will be described in detail by reference to FIG. 2. As shown in FIG. 2, the teeth 32a-32f project toward the stator 10 in a manner slanted relative to the Y direction. As shown in FIG. 2, assuming that an axis located at the center of the U-phase coil core 30 in the X direction and extending toward the negative side of the Y direction is a Y1 axis, two central teeth 32c, 32d of the U-phase coil core 30 are slanted frontward and rearward, respectively, relative to the Y1 axis by an angle of 1. Further, two teeth 32b, 32e located adjacently on outer sides thereof are slanted frontward and rearward relative to the central teeth 32c, 32d at an angle of 21. Furthermore, a front-end tooth 32a and a rear-end tooth 32f, which are the outermost teeth, are slanted frontward and rearward relative to the teeth 32b, 32e at an angle of 21. In this way, in the teeth set 32S, each of the teeth 32a-32c located toward the front has its tip slanted frontward relative to the Y1 axis, and each of the teeth 32d-32f located toward the rear has its tip slanted rearward relative to the Y1 axis.

(17) Here, since the angle between the two central teeth 32c, 32d is 21, each of the teeth 32a-32f is arranged at an angle of 21 relative to its adjacent teeth, and the teeth 32a-32f project radially from the yoke 31 toward the stator 10 at equiangular intervals of the angle 21. Further, a space in front of the front-end tooth 32a of the teeth set 32S in the X direction and a space behind the rear-end tooth 32f of the teeth set 32S in the X direction respectively constitute the coil-receiving cavities 35.

(18) At respective centers of parts between the teeth 32a-32f, the magnet-receiving cavities 33 are provided. The magnet-receiving cavities 33 are slits having a constant width E, in which the permanent magnets 34 having a rectangular cross section are mounted as shown in FIG. 2. Although each of the teeth 32a-32f is arranged at an angle of 21 relative to its adjacent teeth, each magnet-receiving cavity 33 has a rectangular cross section, and its two opposite sides are parallel. Accordingly, a front surface and a rear surface of each tooth 32a-32f are not parallel to each other, and the width decreases from near the stator 10 toward the yoke 31. As shown in FIG. 2, a width TW1 of each tooth 32a-32f at the yoke side is narrower than its width TW2 at the stator side.

(19) Further, when midpoints of tip end sides of the respective teeth 32a-32f are referred to as the centers of the teeth 32a-32f, pitches SLP between the centers of the teeth 32a-32f in the X direction satisfy Equation 1 relative to the pitch STP of the salient poles 12 of the stator 10 as in the conventional art, and all of the pitches SLP are identical in size. Here, the width of the salient poles 12 of the stator 10 is equivalent to that in the conventional art.

(20) Since the magnet-receiving cavities 33 are provided at the centers of the parts between the teeth 32a-32f, each of the magnet-receiving cavities 33 is arranged at an angle of 21 relative to its adjacent magnet-receiving cavities 33, and the magnet-receiving cavities 33 extend radially from the yoke 31 toward the stator 10 at equiangular intervals of the angle 21, in a manner similar to the teeth 32a-32f.

(21) In the magnet-receiving cavities 33, the permanent magnets 34a-34e are mounted respectively. The permanent magnets 34a-34e have a rectangular cross section with a width E. As in the conventional art, the permanent magnets 34a-34e are mounted such that the magnetic poles are oriented in a direction orthogonal to longer sides of the permanent magnets 34a-34e, and such that poles of the same polarity face each other across the teeth 32a-32e.

(22) Since the permanent magnets 34a-34e are mounted in the magnet-receiving cavities 33, each of the permanent magnets 34a-34e is arranged at an angle of 21 relative to its adjacent permanent magnets, and the permanent magnets 34a-34e are arranged such that directions of the longer sides extend radially from the yoke 31 toward the stator 10 at equiangular intervals of the angle 21.

(23) According to the above-described configuration, a length TWB of the teeth set 32S in the X direction as measured at the stator side is as below.
TWBTW26+5E(Equation 4)

(24) Here, since the width TW2 of the teeth 32a-32f as measured at the stator side is approximately equal to the width TW0 of the conventional-art teeth 5 shown in FIG. 4, and the width E of the permanent magnets is also approximately equal to the width E of the conventional-art permanent magnets 3, TWB is approximately equal to a length TWA0 of the conventional-art teeth set in the X direction. In Equation 4, influences of the angles of slant of the teeth 32a-32f and the permanent magnets 34a-34e are small, and are therefore ignored.

(25) Meanwhile, a length TWA of the teeth set 32S in the X direction as measured at the yoke side is as below.
TWATW16+E5(Equation 5)
In Equation 5, influences of the angles of slant of the teeth 32a-32f and the permanent magnets 34a34e are ignored as in Equation 4.

(26) Since TW1<TW2 as noted above, the following holds true.
TWA<TWBlengthTWA0of conventional-art teeth set in X direction(Equation 6)

(27) As such, in the U-phase coil core 30 of the linear motor 100 according to the present embodiment, the length TWA of the teeth set 32S in the X direction as measured at the yoke side becomes shorter than the length TWA0, in the X direction, of the conventional-art teeth set shown in FIG. 4. As a result, when the length SLL1 of the U-phase coil core 30 in the X direction is made identical to the X-direction length SLL0 of the conventional-art U-phase coil core 1a, the X-direction width D, as measured at the yoke side, of the coil-receiving cavities 35 formed on the outer sides of the teeth set 32S can be increased as compared to the width DO of the conventional-art coil-receiving cavities 8.

(28) Here, as described above by reference to FIG. 1, the spacing between the teeth 32, 42 across the coil-receiving cavities 35, 45 is SLPW, which is identical to that of the conventional art shown in FIG. 6, and the width TW2 of the tip end of the teeth 32 is approximately equal to the width TW0 of the conventional-art teeth 5 shown in FIG. 4, so that a width Ds of the coil-receiving cavities 35 as measured at the stator side is as below.
Ds=(SLPWTW2)/2(SLPWTW0)/2=D0(Equation 7)
The width Ds is approximately identical to the width DO of the coil-receiving cavities 8 in the conventional-art U-phase coil core 1a shown in FIG. 4.

(29) Next, flow of magnetic flux generated in the teeth 32a-32f when a current is caused to flow in the coil 36 will be described by reference to FIG. 3. When a current is caused to flow in the coil 36, magnetic flux generated in accordance with the right-hand corkscrew rule serves to strengthen or weaken the magnetic flux in the teeth 32a-32f as in the conventional art. As shown in FIG. 3, the leftmost permanent magnet 34a has its N pole on the left and its S pole on the right, and the permanent magnets 34b-34e are then sequentially arranged such that poles of the same polarity face each other. In this arrangement, when a current is caused to flow such that the current flow in a portion of the coil 36 shown on the left side is in a direction from within to out of the drawing plane and the current flow in a portion of the coil 36 shown on the right side is in a direction from outside and into the drawing plane, magnetic flux is generated in the part between the coil 36 portions in a direction toward the positive side of the Y direction according to the right-hand corkscrew rule. As a result, magnetic flux generated from the N poles of the permanent magnets 34a-34e and advancing toward the stator 10 toward the negative side of the Y direction is weakened, while magnetic flux advancing in the direction opposite to the stator 10 toward the positive side of the Y direction is strengthened. Further, magnetic flux advancing from the stator 10 toward the permanent magnets 34a-34e toward the positive side of the Y direction and entering into the S poles of the permanent magnets 34a-34e is strengthened, while magnetic flux advancing from the yoke 31 toward the negative side of the Y direction and entering into the permanent magnets 34a-34e is weakened.

(30) In the linear motor 100 of the present embodiment, the width TW1 of the teeth 32a-32f in the X direction as measured at the yoke side is narrower than the width TW2 in the X direction as measured at the stator side, so that, as compared to the case of the conventional structure, magnetic resistance in the yoke side end part of the teeth 32a-32f is higher, and magnetic flux encounters more difficulty passing therein. Since the width TW1 of the teeth 32a-32f at the yoke side is narrower than the width TW0 of the conventional-art teeth 5, and magnetic resistance in that part is higher by (TW0/TW1) times, the difficulty for magnetic flux to pass therein is increased at that ratio.

(31) Generally, magnetic flux flows more in a direction involving low magnetic resistance and facilitating flow of the magnetic flux, and when magnetic resistance is increased, magnetic flux passing in that part becomes reduced. Accordingly, when magnetic resistance at the yoke side of the teeth 32a-32f is increased, magnetic flux advancing from the teeth 32a-32f toward the yoke 31 in the direction opposite the stator 10 becomes reduced, so that magnetic flux passing through the yoke 31 and connecting to adjacent phases becomes reduced. For this reason, magnetic flux saturation in the yoke 31 is less likely to occur as compared to the case of the conventional-art slider 1, and the height LY of the yoke 31 in the Y direction can therefore be made smaller than the yoke height LY0 in the conventional art shown in FIG. 4. In a case where the height SLH of the slider 20 is to be maintained, by reducing the height LY of the yoke 31 in the Y direction, the height SLTH of the coil-receiving cavities 35 in the Y direction can be increased by that amount as compared to the height SLTH0 of the conventional-art coil-receiving cavities 8 in the Y direction.

(32) As described above, in the U-phase coil core 30 of the linear motor 100 of the present embodiment, the teeth 32a-32f project radially from the yoke 31 toward the stator 10, and the width TW1 of the teeth 32a-32f as measured at the yoke side is narrower than the width TW2 as measured at the stator side. By means of this configuration, when the X-direction length SLL1 and the height SLH of the U-phase coil core 30 are made identical to the length SLL0 and the height SLH0 of the U-phase coil core 1a of the conventional art shown in FIG. 4, the width D in the X direction at the yoke side and the height SLTH in the Y direction of the coil-receiving cavities 35 can be made respectively larger than the width D0 in the X direction and the height SLTH0 in the Y direction of the conventional-art coil-receiving cavities 8, and the cross-sectional area of the coil-receiving cavities 35 can be increased as compared to the cross-sectional area of the conventional-art coil-receiving cavities 8. It is therefore possible, without increasing the volume of the U-phase coil core 30, to increase the amount of the coil 36 wire as compared to the amount of the coil 4 wire in the conventional-art U-phase coil core 1a, thereby enabling an increase in thrust force and a reduction in heat generation in the U-phase coil core 30.

(33) While the details of the structure of the U-phase coil core 30 have been described above, the structures of the W-phase coil core 40 and the V-phase coil core 50 are identical with that of the U-phase coil core 30. When the X-direction length SLL1 and the height SLH of the W-phase coil core 40 and the V-phase coil core 50 are made identical to the length SLL0 and the height SLH0 of the W-phase coil core 1b and the V-phase coil core 1c of the conventional art shown in FIG. 4, the width D in the X direction at the yoke side and the height SLTH in the Y direction of the coil-receiving cavities 45, 55 can be made respectively larger than the width DO in the X direction and the height SLTH0 in the Y direction of the conventional-art coil-receiving cavities 8, and the cross-sectional area of the coil-receiving cavities 45, 55 can be increased as compared to the cross-sectional area of the conventional-art coil-receiving cavities 8.

(34) Accordingly, in the slider 20 formed by connecting the U-phase coil core 30, the W-phase coil core 40, and the V-phase coil core 50 along the X direction, when the length SLLT1 in the X direction and the height SLH in the Y direction of the slider 20 are made identical to the length SLLT0 in the X direction and the height SLH0 in the Y direction of the slider 1 of the conventional art shown in FIG. 6, the width D in the X direction at the yoke side and the height SLTH in the Y direction of the coil-receiving cavities 35, 45, 55 can be made respectively larger than the width D0 in the X direction and the height SLTH0 in the Y direction of the conventional-art coil-receiving cavities 8, and the cross-sectional area of the coil-receiving cavities 35, 45, 55 can be increased as compared to the cross-sectional area of the conventional-art coil-receiving cavities 8. Therefore, in the linear motor 100 of the present embodiment, it is possible, without increasing the motor volume, to increase the amount of the coil 36 wire of the respective phases as compared to the amount of the coil 4 wire of the respective phases in the conventional art, thereby enabling an increase in thrust force and a reduction in heat generation in the slider 20.

(35) In a case where improvements in characteristics are not particularly necessary, the motor volume may be reduced to achieve downsizing. Specifically, the height SLH of the slider 20 may be made smaller by reducing the height LY of the yoke 31 or the height SLTH of the coil-receiving cavities. Alternatively, since the flowing current value for generating the same amount of thrust force can be reduced, there are less risks of demagnetization of the permanent magnets 34a-34e, so that the width E of the permanent magnets 34a-34e may be made smaller to thereby shorten the overall length of the slider 20.

(36) Although it has been described above that, in the U-phase coil core 30, the angle of slant of the individual teeth 32a-32f relative to each other, the individual coil-receiving cavities 33 relative to each other, and the individual permanent magnets 34a-34e relative to each other is 21, this is not a requirement, and the angle of slant relative to each other may be different. Further, it may be the case that not all of the individual teeth 32a-32f, the individual coil-receiving cavities 33, and the individual permanent magnets 34a-34 project radially. For example, it may be configured such that: the teeth 32c-32d, the coil-receiving cavity 33, and the permanent magnet 34c, which are located at the central part of the teeth set 32S, extend in the Y direction toward the stator 10 without slanting; the teeth 32a-32b, the coil-receiving cavities 33, and the permanent magnets 34a-34b, which are located at the front part of the teeth set 32S, have their tip parts slanted frontward relative to the Y direction; and the teeth 32e-32f, the coil-receiving cavities 33, and the permanent magnets 34d-34e, which are located at the rear part of the teeth set 32S, have their tip parts slanted rearward relative to the Y direction. This applies similarly to the W-phase coil core 40 and the V-phase coil core 50.

(37) Although it has been described above that the pitch STP of the salient poles 12 of the stator 10 is double the pitch SLP of the teeth 32, it is not particularly necessary that the pitch STP is double. Changes may arbitrarily be made thereto according to the method of control of the linear motor 100 or the number of the teeth 32.