Motor

Abstract

To reduce influence of electromagnetic noise on electronic components arranged around a motor.SOLUTION: A stepping motor includes: a stator 16 that forms a magnetic circuit and has pole teeth yokes 3, 4, 7, 8 and excitation coils 5, 6 for exciting the yokes 3, 4, 7, 8; and a rotor 17 having a rotor magnet 9 and a shaft 10 on which the rotor magnet 9 is fixed. The yokes 3, 4, 7, 8 have a pair of cylindrical out yokes 3, 4 constituting an outer shape of the stepping motor, and a pair of in yokes 7, 8 having pole teeth disposed adjacent to the pole teeth of the out yokes 3, 4 in a circumferential direction. The pair of out yokes 3, 4 are welded and fastened in a mutually thrusting state. At least six or more welded joint portions L1 are provided. A ratio occupied by the welded joint portions L1 with respect to the entire circumference in the circumferential direction of the out yokes 3, 4 is about 14% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a stepping motor or the like that is provided with a rotor made up of a shaft and magnet that rotates within a stator, and a yoke (stator) that is magnetized by exciting a coil. [Background technology]

[0002] In conventional motors, as described in Patent Document 1, for example, the fitting depth of the annular step provided on the inner surface of the edge of one end opening of two outer yoke (frame) cylinders is set shallower than the plate thickness of the inner yoke where the outer edge of the inner yoke housed in the frame fits into the annular step of the out yoke, thereby butting the stators (inner yokes) together and eliminating stator tilt, thereby preventing a decline in motor performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 5-33673 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the technology described in Patent Document 1, there is a gap between the butted portions of the out yokes, leaving the inner yoke inside the out yoke (frame) exposed in the radial direction. This causes magnetic flux generated inside the motor to leak through the gap between the out yokes, i.e., from the inner yoke in the radial direction of the motor, which can cause electromagnetic noise effects on sensors used in cameras, for example. In particular, high-frequency noise (several kHz or higher) from the drive circuit that drives the motor can cause problems. In recent years, as cameras have become more compact (e.g., mirrorless cameras), the distance between sensors and motors has become shorter, creating a demand for reducing the effects of electromagnetic noise on electronic components such as sensors located around the motor. [Means for solving the problem]

[0005] In view of the above, the stepping motor according to the present invention comprises: a stator having a yoke that forms a magnetic circuit and has pole teeth, and an excitation coil that excites the yoke; a rotor having a rotor magnet and a shaft to which the rotor magnet is fixed; A stepping motor comprising: the yoke includes a pair of cylindrical outer yokes that form the outer shape of the stepping motor, and a pair of inner yokes that have pole teeth arranged adjacent to the pole teeth of the outer yokes in the circumferential direction, The pair of outer yokes are fastened together by welding while butting against each other, and the welded joints are provided in at least six locations, and the proportion of the joints relative to the entire circumferential circumference of the outer yoke is approximately 14% or more. [Effects of the Invention]

[0006] According to the present invention, it is possible to reduce the influence of electromagnetic noise on electronic components arranged around the motor. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is an exploded perspective view of a motor according to a first embodiment of the present invention; [Figure 2] 1A and 1B are top and side views of a motor according to a first embodiment of the present invention; [Figure 3] 1 is a cross-sectional view of a motor according to a first embodiment of the present invention; [Figure 4] 10 is a side view of a motor according to a second embodiment of the present invention; [Figure 5] 10 is a side view of a motor according to a third embodiment of the present invention; [Figure 6] Illustrative diagram of eddy currents [Figure 7] Graph showing the magnetic flux leakage improvement effect of the present invention [Figure 8] Explanatory diagram of a conventional example DETAILED DESCRIPTION OF THE INVENTION

[0008] Example 1 1 to 3 are explanatory diagrams showing the structure of a PM (permanent magnet) stepping motor according to a first embodiment of the present invention.

[0009] FIG. 1 is an exploded perspective view of a stepping motor according to this embodiment, with the left side being the output side of the motor. The opposite side in the axial direction is referred to as the rear end side. The rotor 17 is composed of a rotatably supported shaft 10 made of a magnetic material such as stainless steel, and a rotor magnet 9 that is magnetized with alternating north and south poles along the circumferential direction. Washers 11 are inserted on both sides of the rotor magnet 9 in the axial direction.

[0010] The stator 16 is composed of a pair of inner yokes 7, 8 each made of a soft magnetic material such as pure iron and having a plurality of comb teeth (pole teeth) arranged alternately in the circumferential direction, a pair of outer yokes 3, 4 each made of a soft magnetic material such as pure iron and having a plurality of comb teeth arranged alternately in the circumferential direction and adjacent to the comb teeth of the inner yokes 7, 8 in the circumferential direction, an excitation coil 5 arranged between the inner yoke 7 and the outer yoke 3 to excite each yoke, and an excitation coil 6 arranged between the inner yoke 7 and the outer yoke 3 to excite each yoke. The magnetic field excited by the excitation coils 5, 6 flows through a magnetic circuit formed by the inner yokes 7, 8 and the outer yokes 3, 4, causing the rotor 17 to rotate.

[0011] Bearings 2 and 4 are provided at both axial ends of shaft 10 for rotor 17 that rotates inside stator 16. Bearing 2 on the rear end side is formed into a hollow cylinder by molding, and is positioned coaxially by its outer diameter and the inner diameter of out yoke 3. Bearing 4 on the output side is made of metal and is fixed to flange 15 by crimping.

[0012] The rotor 17 is coaxially disposed within the stator 16, with a predetermined gap between it and the comb teeth of each yoke. The bearing 14 is fixed by crimping to a flange 15, which serves as a mounting plate, and the inner diameter of the outer yoke 4 and the inner diameter of the bearing 14 are positioned coaxially. A recess 18 (see Figure 3) for installing a coil spring is provided on the surface of the bearing 14 facing the rotor magnet, and a coil spring 12 is provided so as to be sandwiched between a washer 13 provided in this recess 18 and a washer 11 on the end face of the rotor magnet, thereby urging the rotor magnet 9 toward the rear end of the motor. Furthermore, a washer 17 press-fitted and held onto the shaft 10 is provided on the rear end of the shaft 10, and is in abutment (surface contact) with a rear end bearing 2 molded from LCP, for example.

[0013] The magnetic material SUS430 is used for the retainer plate 1 to prevent magnetic flux leakage from the center of the shaft 10 to the outside of the motor. In this embodiment, SUS304 is used for the flange 15 attached to the output side, but it may also be made of a magnetic material such as SUS430 to prevent magnetic flux leakage, and it is preferable that the resistivity ρ of the material of the retainer plate 1 and flange 15 is 65×10^-8 [Ωm] or less.

[0014] In addition, in this embodiment, SUS420 is used for the shaft 10, but in terms of magnetic flux leakage, there is a phenomenon in which magnetic flux tends to leak outward along the central axis of the shaft 10, so it is more preferable to use an austenitic non-magnetic material.

[0015] In the above configuration, when the excitation coils 5 and 6 are energized, the inner yokes 7 and 8 and the outer yokes 3 and 4 are excited, magnetizing each comb tooth, which repels and attracts the magnetized poles of the rotor magnet 9, generating torque, driving the rotor 17 to rotate as the excitation coils 5 and 6 are energized, and transmitting driving force from the shaft 10 to the outside. At that time, magnetic flux generated from the coils 5 and 6 and the rotor magnet 9 flows from the comb teeth of the inner yoke 8 (7) of the motor to the outer yoke 4 (3) in the outer radial direction. In the following explanation, the pair of the inner yoke 8 and the outer yoke 4 will be explained due to their symmetry, but the same applies to the pair of the inner yoke 7 and the outer yoke 3.

[0016] 3, the inner diameter portion 4a1 of the outer tube portion 4a of the cylindrically formed out-yoke 4 is fitted with the outer diameter portion 8a of the in-yoke 8, and if there is no large gap at the fitted portion and no gap at the butt portion of the out-yokes 4, i.e., the center of the stator 16 in the thrust direction, and they are electrically coupled, magnetic flux does not leak toward the outer diameter of the motor, but flows toward the inner diameter after passing through the outer tube portion 4a of the out-yoke 4, and then flows to the comb teeth of the out-yoke 4. However, if there is a large gap between the out-yokes 4, or if there is a small gap without electrical coupling, or if there is a small electrical coupling, high-frequency electromagnetic noise (magnetic flux) generated from the circuit device that drives the motor, for example, when it tries to flow from the inner yoke to the out-yoke, the flow of magnetic flux is obstructed by eddy currents generated inside the out-yoke, and the magnetic noise has no escape route and leaks out of the motor (into the air) through the gap between the out-yokes.

[0017] In a conventional motor having out yokes 4 butted together as shown in Fig. 8, when terminal portion 119 is at 12 o'clock when viewed from the output shaft side of motor shaft 110, laser irradiation is performed at two locations, one on the right side at 3 o'clock and one on the left side at 9 o'clock, or two locations on each side, for a total of four locations (four locations at 2 o'clock, 4 o'clock, 8 o'clock, and 10 o'clock in Fig. 8), so that the out yokes are at least secured together. In contrast, in this embodiment, as shown in Fig. 2, the out yokes are fastened together by welding using laser irradiation at a total of eight locations, four locations on the right and left sides, to ensure a reliable electrical connection.

[0018] In terms of the laser irradiation angle shown in Figure 2, the angle X of one laser irradiation area L1 (welding spot diameter) is 8.6°, so the total angle of the eight laser irradiation areas is 68.8°, which accounts for approximately 19.1% of the 360° circumference. Furthermore, the terminals 19 and the mounting portions 15a on the flanges 15 must protrude outward from the gaps between the out-yokes 4. The butting range (angle) Y is 126° on each side, meaning the out-yokes 4 are butted together for a total of 252°, which accounts for approximately 27.3% of this 252°. If, as in the past, a total of four laser irradiation areas were used, the total laser irradiation angle would be 34.4° (8.6° x 4 areas), which accounts for 9.6% of the 360° circumference. Furthermore, the butting range (angle) Y of the out-yokes is 126° on each side, so the out-yokes are butted together a total of 252°, with 34.4° accounting for approximately 13.7% of this 252°. Note that laser irradiation not only affects the out-yokes themselves, but also electrically bonds the out-yoke and inner yoke, reducing magnetic resistance caused by the gap between the inner and outer yokes. Therefore, it is preferable that the inner yoke 8 and the out-yoke 4 are also electrically bonded by laser irradiation, as shown in laser irradiated area L1 (joint) in Figure 3(b).

[0019] When the out-yokes are electrically coupled by laser irradiation, the gap between the out-yokes is reduced more effectively than when the electrical coupling is weaker, which effectively reduces magnetic flux leakage. Furthermore, as shown in FIG. 6 , eddy currents are generated around a line connecting two or more laser-irradiated areas. This eddy current generates a counteracting magnetic flux that would otherwise leak outside the motor, effectively suppressing magnetic flux leakage outside the motor. In this embodiment, by appropriately securing the welding area, this eddy current is appropriately generated on the outer surface of the out-yoke, effectively reducing magnetic flux leakage from the gap between the out-yokes. For this reason, electrically coupling the inner yoke 8 and the out-yoke 4 by laser irradiation is preferable because it allows the eddy current to be concentrated on the outer surface of the out-yoke 4. Furthermore, it is preferable to appropriately space the locations where this eddy current occurs on the outer cylindrical portion 4a of the out-yoke 4. In this embodiment, the laser irradiation diameter is set to 0.6 to 0.7 mm for a motor outer diameter of 7.8 mm, and the distance between the centers of the laser irradiation diameters is approximately 1 mm in the circumferential direction.

[0020] Figure 7 shows the results of measurements of magnetic flux leakage when the number of laser irradiation points is four (a conventional example) and when the number of laser irradiation points is eight (eight) in this example. Figure 7(a) shows the results of measurements of the magnetic flux generated by the motor at a position 20 mm away from the non-output side (rear end side) of the stepping motor to which this example is applied, in the measurement environment shown in Figure 7(b). The magnetic flux leakage was 83.9 dB when the number of laser irradiation points was four, while it was 84.8 dB when the number of laser irradiation points was eight, indicating that the effect of magnetic flux leakage was improved by 0.9 dB. It should be noted that the total laser irradiation angle can be increased by increasing the laser irradiation diameter, for example, by increasing the laser spot diameter when the number of laser irradiation points is four or less. However, in this case, there is a risk of irradiating the mold bobbin flanges 5a and 6a (see Figure 3(b)) of the coils 5 and 6, which are arranged so as to contact the flanges 7a and 8a of the inner yokes 7 and 8 inside the outer cylindrical portions 3a and 4a of the outer yokes 3 and 4. Therefore, since the laser irradiation diameter needs to be set to approximately equal to or less than the thickness of the overlapping flanges 7a and 8a of the inner yoke, it is difficult to increase the total value of the laser irradiation angle by increasing the laser irradiation diameter.

[0021] From the above, it can be seen that the greater the total angle at which the out-yokes are joined together in the circumferential direction, the more magnetic flux leakage can be reduced. It is desirable that the laser irradiation number be at least three times twice (a total of six or more), and that the total laser irradiation angle be 51.6° or more around the entire circumferential direction, i.e., 14.3% or approximately 14% or more of the entire 360°. Furthermore, if the butting range of the out-yokes is 252°, it is desirable that the angle be 20.5° or approximately 20% or more. This also has the advantage of reducing the impact of electromagnetic noise on sensors, for example, due to magnetic flux leakage, even when the device is installed in precision equipment such as a camera.

[0022] Example 2 A second embodiment of the present invention will now be described. In this embodiment, laser irradiation is performed on almost the entire area of ​​the portion where the outer diameter of the inner yoke and the inner diameter of the outer tubular portion of the outer yoke fit together in the first embodiment, i.e., the portion where the outer yokes butt together, thereby reliably eliminating any gaps. In the following description, the same reference numerals will be used for parts common to the first embodiment, and their description will be omitted.

[0023] As shown in FIG. 4, when the terminal portion 19 is positioned at 12 o'clock when viewed from the output shaft side of the shaft 10, ten laser irradiation portions L1 are provided at each of the three and nine o'clock positions, ensuring reliable electrical coupling between the out-yokes at a total of 20 positions. Using the laser irradiation angle shown in FIG. 1, the angle X for one position is 8.6°, resulting in a total of 172° for the 20 positions, which accounts for approximately 50% of the 360° circumference. Furthermore, the butting range (angle) Y between the out-yokes is 126° on each side, resulting in a total of 252° of butting between the out-yokes in the circumferential direction. Of this 252°, the 172° of the welding area accounts for approximately 70%. Although not shown in the figure, the laser irradiation range may be the same as the 252° of the out-yoke butt joints by eliminating the laser irradiation interval and increasing the number of laser irradiation portions. Although this embodiment requires more labor and cost for welding than Example 1, it has the advantage of further reducing the impact of electromagnetic noise on the sensor due to magnetic flux leakage.

[0024] Example 3 Example 3 of the present invention will be described. This example has the same configuration as Example 1 or 2, but is configured such that the laser irradiation portions L1 are continuously irradiated so as to overlap (continuous welding). The embodiment is shown in Fig. 5, and by irradiating the laser irradiation portions L1 so as to overlap each other, gaps between the laser irradiation portions L1 in the circumferential direction can be reliably eliminated, which has the advantage of reducing the influence of electromagnetic noise on the sensor due to magnetic flux leakage.

[0025] The above-described embodiments are merely examples of the stepping motor according to the present invention, and various modifications are possible. For example, instead of the spot welding using laser irradiation as described above, continuous welding may be performed using heat conduction welding or seam welding. [Explanation of symbols]

[0026] 1 Presser plate 2 Rear end bearing 3 Out York 4 Out York 5 Excitation coil 6 Excitation coil 7. York 8. York 9 Rotor magnet 10 Shaft (rotating axis) 11 Washer 12 Coil spring 13 Washer 14 Tip bearing 15 flange 16 Stator 17 rotor 18 Tip bearing recess 19 Terminal section L1 Laser irradiation part

Claims

1. a stator having a yoke that forms a magnetic circuit and has pole teeth, and an excitation coil that excites the yoke; a rotor having a rotor magnet and a shaft to which the rotor magnet is fixed; A stepping motor comprising: the yoke includes a pair of cylindrical outer yokes that form the outer shape of the stepping motor, and a pair of inner yokes that have pole teeth arranged adjacent to the pole teeth of the outer yokes in the circumferential direction, A stepping motor characterized in that the pair of out yokes are fastened together by welding while being butted against each other, there are at least six or more welded joints, and the joints account for approximately 14% or more of the entire circumferential circumference of the out yoke.

2. 2. The stepping motor according to claim 1, wherein the joint portion occupies approximately 20% or more of the area of ​​the butted portion where the out yokes are butted together.

3. 3. The stepping motor according to claim 2, wherein the joints are continuously provided so as to overlap in the circumferential direction.

4. 3. The stepping motor according to claim 2, wherein a magnetic pressing plate is provided on the opposite side of the output of the stepping motor.

5. 4. The stepping motor according to claim 3, wherein a magnetic flange is provided on the output side of the stepping motor.

6. 5. The stepping motor according to claim 4, wherein the shaft is made of a non-magnetic material.

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