Brushless motor and handpiece

Abstract

[Problem] To provide: a brushless motor in which the effect of suppressing heat generation is enhanced; and a handpiece equipped with such a brushless motor. [Solution] In an inner rotor magnet type brushless motor 1, a coil pattern 162 of each phase formed on a flexible substrate of a roll-wound stator coil is characterized in that a plurality of pattern parts 165 are arranged in parallel without providing an intermediate node from the start of winding to the end of winding, the end parts of one of the start of winding and the end of winding are knotted to each other as a common side node 165c, and the end parts of the other are knotted to each other as a terminal side node 165t of each phase.

Description

Brushless motor and handpiece

[0001] The present invention relates to an inner rotor magnet type brushless motor and a handpiece that drives a tool with such a brushless motor.

[0002] Conventionally, there are handpieces for polishing devices used in dental prosthetics, nail art, precision finishing of molds, and the like. Such handpieces rotate a tool located at the tip at high speed. Some handpieces have a built-in motor as a drive source for the tool. This motor is typically a slender, cylindrical brushless motor capable of rotating a rotor magnet at high speed. Recently, some brushless motors have been equipped with coils having the structure disclosed in Patent Document 1. The coil structure described in Patent Document 1 has a coil pattern formed as a conductor pattern on a flexible substrate rolled around the rotor magnet. This structure improves the space factor of the stator coil inside the motor and reduces the interphase resistance of the brushless motor. Therefore, applying this coil structure can result in a highly efficient brushless motor.

[0003] Japanese Patent Application Laid-Open No. 2022-181483

[0004] Here, it is desirable to minimize heat generation from the built-in motor of a handpiece. This is because heat generated by the motor itself reduces motor efficiency, and the heat transferred to the user's hand when the handpiece is held in hand for continuous operation can be difficult to handle. The generation of eddy currents in the coil pattern is believed to be the primary cause of heat generation when a brushless motor equipped with the coil structure of Patent Document 1 rotates at high speed. A common method for suppressing eddy currents is to block them by, for example, creating slits in the coil pattern. However, it has been confirmed that when a slender, compact inner-rotor magnet-type brushless motor rotates at high speed, heat generation in the coil pattern cannot be suppressed by conventional methods alone. Investigation of this heat generation revealed that it was due to significant amounts of currents other than eddy currents being generated inside the coil pattern, even when the rotor magnet rotates at high speed. This non-eddy current current is referred to as an AC circulating current.

[0005] Therefore, in view of the above circumstances, the present invention aims to provide a brushless motor that is more effective in suppressing heat generation in the coil pattern due to the generation of eddy currents and AC circulating currents, and a handpiece equipped with such a brushless motor.

[0006] In order to solve the above problems, the brushless motor is a motor with an inner rotor magnet type brushless structure, and includes: a shaft; a two-pole or four-pole rotor magnet fixed to the shaft; and a three-phase stator coil arranged to surround the rotor magnet in the circumferential direction and generating a magnetic field to rotate the rotor magnet. The stator coil includes a flexible substrate that is rolled up so as to surround the rotor magnet in the circumferential direction; and a three-phase coil pattern formed on the flexible substrate as a conductor pattern. The coil pattern for each phase has multiple pattern portions arranged in parallel from the start of winding to the end of winding without any intermediate nodes, and one end of the start of winding and the other end of the end of winding are connected to each other as a common node, and the other end is connected to each other as a terminal node for each phase.

[0007] In the brushless motor described above, the coil pattern formed on the flexible substrate in the stator coil has a structure in which multiple pattern portions are arranged in parallel, thereby reducing electrical resistance in the coil pattern for each phase. As a result, Joule heat generated when current is applied to the coil pattern for each phase is reduced. Furthermore, because each pattern portion has a thin, elongated shape from the beginning to the end of the winding, eddy currents are suppressed. In this way, the brushless motor described above reduces heat generation in the stator coil due to various factors.

[0008] Here, it is preferable that each of the multiple pattern portions has a straight portion extending in the width direction of the flexible substrate along the axial direction of the shaft, and an oblique portion extending from both ends of the straight portion at an angle with respect to the width direction toward the side edge of the flexible substrate, and that the width of the straight portion is equal to the width of the oblique portion in the length direction of the flexible substrate perpendicular to the width direction.

[0009] According to this configuration, the width of the straight line portion in each pattern portion is kept to a necessary minimum, which further reduces the generation of induced currents and eddy currents, thereby further enhancing the effect of suppressing heat generation.

[0010] It is also preferable that each of the multiple pattern portions is formed by one turn of the pattern consisting of a first half-winding pattern formed on one of the front and back surfaces of the flexible substrate and a second half-winding pattern formed on the other surface and connected to the first half-winding pattern at one end in the substrate thickness direction.

[0011] According to this configuration, since both the front and back surfaces of the flexible substrate are utilized, each pattern portion can be formed on the flexible substrate with increased formation density.

[0012] Furthermore, it is preferable that the other side ends of the multiple pattern portions that form the coil pattern of each phase are connected to each other as the terminal side nodes and protrude from the side edge of the flexible substrate to form connection terminals for each phase.

[0013] According to this configuration, the other side end portions of the plurality of pattern portions that form the coil pattern of each phase protrude from the side edge of the flexible substrate and can be used as connection terminals as they are.

[0014] In order to solve the above problem, the handpiece is characterized by comprising the above-mentioned brushless motor, a case that houses the brushless motor, and a tool part that protrudes at least partially from the case and is driven by the brushless motor.

[0015] The handpiece described above uses the brushless motor described above to drive the tool section, allowing for safe, long-term operation while maintaining stable, high-speed rotation. This is because heat generation in the stator coil of the brushless motor built into the handpiece can be suppressed, preventing a decrease in motor efficiency and preventing a rise in surface temperature that would interfere with holding the handpiece in one's hand and performing work.

[0016] The brushless motor and handpiece described above can enhance the effect of suppressing heat generation.

[0017] 1 is a perspective view of a brushless motor according to one embodiment, showing its internal structure in a cross section cut along the shaft axis.

[0023] FIG. 1 is a perspective view of a stator coil removed from the brushless motor shown in FIG. 1, seen from the circuit board side.

[0024] FIG. 2 is a perspective view of the stator coil shown in FIG. 2, seen from the output side of the brushless motor.

[0025] FIG. 3 is a schematic circuit diagram showing the stator coil shown in FIGS. 2 and 3.

[0026] FIG. 4 is a schematic view showing the coil pattern of the stator coil shown in FIGS. 2 and 3.

[0027] FIG. 5 is a schematic view showing the coil pattern for one phase and the nodes of each pattern.

[0028] FIG. 6 is a schematic view showing the coil pattern for one phase shown in FIG. 6 extended linearly.

[0029] FIG. 7 is a diagram showing a coil pattern with slits as a comparative example to the brushless motors shown in FIGS. 1 to 7.

[0029] FIG. 8 is a schematic view showing the coil pattern with slits shown in FIG. 7 extended linearly as in FIG. 7.

[0029] FIG. 9 is a graph comparing the case surface temperatures of three types of brushless motors: the comparative example shown in FIGS. 8 and 9, the embodiment shown in FIGS. 1 to 7, and a modified version of the embodiment.

[0029] FIG. 10 is a schematic view showing a handpiece incorporating the brushless motor shown in FIGS. 1 to 7 as a drive source.

[0018] An embodiment of a brushless motor and a handpiece will now be described.

[0019] FIG. 1 is a perspective view of a brushless motor according to an embodiment, showing its internal structure in a cross section cut along the shaft axis.

[0020] The brushless motor 1 shown in FIG. 1 is a motor with an inner rotor magnet type brushless structure, and includes a housing 11 , a yoke 12 , a shaft 13 , a rotor magnet 14 , a circuit board 15 , and a stator coil 16 .

[0021] The housing 11 includes a cylindrical housing main body 111 with a bottom, and a case cover 112 that closes the opening of the housing main body 111. A pair of ball bearings 113 that rotatably support the shaft 13 are provided inside the bottom wall portion 111a of the housing main body 111 and inside the case cover 112. An output port 111b is provided in the center of the bottom wall portion 111a of the housing main body 111, from which the output end 131 of the shaft 13 protrudes.

[0022] The yoke 12 is a cylindrical member made of a magnetic material and fixed to the inner circumferential surface of the housing main body 111. The yoke 12 houses the stator coil 16 inside and serves as a magnetic path for the magnetic field generated by the stator coil 16.

[0023] The shaft 13 is the output shaft of the motor, and is rotatably supported by the housing 11 via the pair of ball bearings 113 as described above.

[0024] The rotor magnet 14 is a cylindrical permanent magnet that is fixed to the shaft 13 via a pair of bushings 141 and is rotatable together with the shaft 13. The rotor magnet 14 is passed through by the shaft 13 in the axial direction D11 and is fixed at both ends to the shaft 13. Furthermore, although not specified here, the rotor magnet 14 is a four-pole or two-pole magnet.

[0025] The circuit board 15 is disposed inside the case cover 112, penetrating the end of the shaft 13. It is a printed wiring board that supplies current to the stator coil 16 and detects the rotational position. Motor wires 151 for supplying current to the stator coil 16 are connected to the circuit board 15. The brushless motor 1 of this embodiment is a three-phase motor with U, V, and W phases, and three motor wires 151 are connected, one for each phase. Three Hall elements 152 for position detection are mounted on the circuit board 15, and three Hall element wires 153 are connected, one for each Hall element 152. The motor wires 151 and the Hall element wires 153 extend through the case cover 112 to the outside of the motor.

[0026] The stator coil 16 is disposed between the yoke 12 and the rotor magnet 14, cylindrically surrounding the rotor magnet 14 in the circumferential direction D12. The stator coil 16 is a three-phase coil member that generates a magnetic field for rotating the rotor magnet 14 by energizing the circuit board 15. In this embodiment, the stator coil 16 has the following structure.

[0027] Fig. 2 is a perspective view of the stator coil removed from the brushless motor shown in Fig. 1, as seen from the circuit board side, and Fig. 3 is a perspective view of the stator coil shown in Fig. 2, as seen from the output side of the brushless motor. Fig. 4 is a schematic circuit diagram showing the stator coils shown in Figs. 2 and 3. Here, Fig. 4(A) shows the coil patterns collectively within each phase for ease of understanding. On the other hand, Fig. 4(B) shows a more detailed view, showing that multiple coils are arranged in series and parallel in each phase. Fig. 5 is a schematic diagram showing the coil patterns of the stator coils shown in Figs. 2 and 3.

[0028] The stator coil 16 includes a strip-shaped flexible substrate 161 rolled and wound around the rotor magnet 14 in the circumferential direction D12, and three-phase coil patterns 162 formed on the flexible substrate 161 as conductor patterns. In this embodiment, the strip-shaped flexible substrate 161 is rolled into a cylindrical shape. A U-phase coil pattern 162u, a V-phase coil pattern 162v, and a W-phase coil pattern 162w are star-connected on the flexible substrate 161 ( FIG. 4A ). The coil patterns 162 for each phase are formed by a pattern (solid line pattern in FIG. 5 ) formed on one surface (front surface) of the flexible substrate 161 and a pattern (dashed line pattern in FIG. 5 ) formed on the other surface (back surface) of the flexible substrate 161. The coil patterns 162 for each phase are short-circuited at one end of each of the winding start and end points to form a star-connected common portion 163. The other end of the coil pattern 162 for each phase protrudes from the side edge 161a of the flexible substrate 161 to form a connection terminal 164 for that phase. That is, the other end of the U-phase coil pattern 162u forms a U-phase terminal 164u, the other end of the V-phase coil pattern 162v forms a V-phase terminal 164v, and the other end of the W-phase coil pattern 162w forms a W-phase terminal 164w. These three connection terminals 164 are arranged in a line at approximately 120° intervals in the circumferential direction D12 when the flexible substrate 161 is rolled up. The above-mentioned motor electric wires 151 for supplying current are electrically connected to each connection terminal 164.

[0029] The configuration of the band-shaped flexible substrate 161 and the coil pattern 162 of each phase included in the stator coil 16 of this embodiment will be described in more detail. The band-shaped flexible substrate 161 is rolled four times. The coil pattern 162 has four coil pattern portions 162A arranged in parallel for each phase, and each coil pattern portion 162A is configured with two coils 162a connected in series ( FIG. 4B ). Each coil 162a is formed by connecting ten turns of a pattern formed on the front and back surfaces of the flexible substrate 161. When the flexible substrate 161 is rolled four times, the series-connected coils 162a face each other across the space inside the cylinder. Each roll layer of the four-fold roll has a coil 162a corresponding to one coil pattern portion 162A. The coils 162a of the same phase are arranged in parallel at the same position in the circumferential direction D12. That is, when the flexible substrate 161 is rolled, the coils are arranged in the order of U-phase, V-phase, W-phase, U-phase, V-phase, and W-phase at 60° intervals in the circumferential direction D12. At the side edge 161 a of the flexible substrate 161, connection terminals 164 for each phase protrude from each of the four rolled layers. As shown in FIGS. 2 and 3 , when the flexible substrate 161 is rolled, the connection terminals 164 are arranged so that they protrude in groups for the U-phase, V-phase, and W-phase at approximately 120° intervals in the circumferential direction D12. The connection terminals 164 are ultimately electrically connected in the U-phase, V-phase, and W-phase. In this way, the stator coil 16 formed into a cylindrical shape by multiple rolls of the strip-shaped flexible substrate 161 can have the connection terminals 164 (164u, 164v, 164w) taken out in a concentrated form for each phase by star connection. On the other hand, the star-connected common part 163 can be connected together with the connection terminal 164 at the other end of the cylindrical stator coil 16 in the axial direction of the cylinder. This makes it possible to prevent an increase in the axial dimension. Although not shown, the common part 163 can also be connected to the connection terminal 164 on the same side in the axial direction of the cylinder.In this case, the common side of each phase is taken out as a terminal, just as the connection terminals 164 are taken out from each roll layer of each phase, U, V, and W. The method of connection in this case will be described later together with the explanation regarding the electrical connection of the connection terminals 164 during assembly of the brushless motor 1.

[0030] FIG. 6 is a schematic diagram showing the coil pattern for one phase and the nodes of each pattern, and FIG. 7 is a schematic diagram showing the coil pattern for one phase shown in FIG. 6 extended linearly.

[0031] As shown in Figures 6 and 7, the coil pattern 162 for one phase is a pattern in which multiple (four in this embodiment) pattern portions 165 are arranged in parallel from the start of winding to the end of winding without any intermediate nodes. In other words, the coil pattern 162 for each phase, depicted by a single line in Figure 5, is composed of four pattern portions 165 shown in Figures 6 and 7. The four pattern portions 165 are connected to each other at one end of the start of winding or the end of winding as a common-side node 165c, and at the other end as a terminal-side node 165t for each phase. Although Figures 6 and 7 depict the four patterns as arranged adjacently in parallel, this is merely a schematic representation of the parallel arrangement; in reality, the patterns are not adjacent to each other, and one pattern is arranged on each layer of the four-rolled flexible substrate. Each pattern portion 165 has a front half winding pattern 166 (first half winding pattern) formed on the front surface of the flexible substrate 161 and a back half winding pattern 167 (second half winding pattern) formed on the back surface. These two half winding patterns form a pattern 168 for one winding. The front half winding pattern 166 and the back half winding pattern 167 are connected at one end to each other in the substrate thickness direction D13 of the flexible substrate 161 via, for example, a via, so that they form a continuous coil shape. As described above, the coil pattern 162 for each phase is a 10-winding pattern, and therefore each of the four pattern portions 165 is also a 10-winding pattern.

[0032] 2, 3, and 6, each of the front half winding pattern 166 and the back half winding pattern 167 in each pattern portion 165 has a straight portion 165a and a diagonal portion 165b. The straight portion 165a is a straight pattern that extends in the width direction D14 of the flexible substrate 161 along the axial direction D11 of the shaft 13. The diagonal portions 165b are a pair of diagonal patterns that extend from both ends of the straight portion 165a toward the side edges 161a of the flexible substrate 161, inclined with respect to the width direction D14. In this embodiment, the width W11 of the straight portion 165a is equal to the width W12 of the diagonal portions 165b in the length direction D15 of the flexible substrate 161 that is perpendicular to the width direction D14.

[0033] 7 is formed between the pattern 168 for one turn and the pattern 168 for the next turn in the 10-turn coil pattern 162. The transition portion 165d is a pattern that connects the pattern 168 for one turn and the pattern 168 for the next turn in the longitudinal direction D15 on the front or back surface of the flexible substrate 161.

[0034] The common-side nodes 165c formed at one end of the four pattern portions 165 constituting the coil pattern 162 for each phase are further short-circuited for three phases to form a star-connected common portion 163. The other end of the four pattern portions 165 are connected to each other as terminal-side nodes 165t and protrude from the side edge 161a of the flexible substrate 161 to form connection terminals 164 for each phase. Because the coil pattern portions 162A of each phase of the coil pattern 162 are arranged in parallel, multiple connection terminals 164 (164u, 164v, 164w) protrude for each phase, corresponding to the number of parallel arrangements. The multiple connection terminals 164 for each phase are gathered at approximately 120° intervals in the circumferential direction D12 and protrude for the U, V, and W phases. As described above, the motor wires 151 for each phase are connected to the connection terminals 164 for each phase. Connection terminal 164 and motor wire 151 are electrically connected via circuit board 15. When assembling brushless motor 1, the multiple connection terminals 164 for each phase are grouped together for the U, V, and W phases and protrude toward circuit board 15, facilitating assembly work such as electrical connection. Note that although the common-side node 165c has been described here as being disposed on the flexible substrate, if a common terminal is taken out on the same side in the axial direction of the cylinder as connection terminal 164, the common terminals for the three phases can be short-circuited on circuit board 15 to form a star-connected common portion.

[0035] Before describing the effects obtained by the brushless motor 1 of the embodiment described above, a comparative example will be described. In the present embodiment, the coil pattern 162 of each phase is configured by connecting four pattern portions 165 in parallel, whereas in the comparative example, the coil pattern of each phase is configured by a pattern with slits, as described below.

[0036] Fig. 8 is a diagram showing a coil pattern with slits as a comparative example to the brushless motors shown in Fig. 1 to Fig. 7. Fig. 9 is a schematic diagram showing the coil pattern with slits shown in Fig. 8 extended linearly in the same manner as Fig. 7.

[0037] First, in the coil pattern 562 of this comparative example, the width W51 of the straight portion 562a of the coil pattern 562 is widened to increase the pattern occupancy rate on a flexible substrate (not shown). Meanwhile, motors designed for relatively high-speed rotation require measures against eddy currents. In motor coils formed by rolling a printed circuit board into a cylindrical shape, slits are typically provided in the conductor pattern to address eddy currents within the coil itself. Therefore, multiple slits 562c are provided in the wide straight portion 562a to suppress the generation of eddy currents during motor operation. The formation of these slits 562c subdivides the coil pattern 562 in the pattern width direction D51, thereby suppressing the generation of eddy currents and reducing heat generated by the eddy currents. The ability to suppress the generation of eddy currents by forming slits in a conductor pattern is disclosed, for example, in Japanese Patent Laid-Open Publication No. 50-119903.

[0038] When such slit coil patterns 562 are formed on the front and back surfaces of a flexible substrate, the coil patterns 562 subdivided by the slits 562c are connected at connecting portions such as vias between the front and back surfaces. In other words, when the star-connected common portion 563 and the connection terminals 564 of each phase are set as the start and end of the winding of this coil pattern 562, multiple intermediate nodes 562d are provided between the start and end of the winding. Each intermediate node 562d is located at the boundary between the front half winding pattern 566 and the back half winding pattern 567 that form one winding's worth of pattern 568, and between the individual winding's worth of pattern 568. In this case, in the coil pattern 562 of the comparative example, the provision of the multiple intermediate nodes 562d forms a closed circuit surrounding each of the multiple slits 562c. When the motor is driven, a rotor magnet (not shown) moves in the pattern width direction D51 of the coil pattern 562, generating an induced potential difference in the pattern width direction D51 in the coil pattern 562. This induced potential difference generates an AC circulating current I51 in the closed circuit surrounding each slit 562c. In this comparative example, heat generation due to eddy currents is suppressed as described above, but on the other hand, heat generation due to this AC circulating current I51 occurs.

[0039] In contrast to this comparative example, the brushless motor 1 of the above-described embodiment can achieve the following effects. Specifically, according to this embodiment, the coil pattern 162 formed on the flexible substrate 161 of the stator coil 16 has a structure in which four pattern portions 165 are arranged in parallel, thereby reducing electrical resistance in the coil pattern 162 for each phase. As a result, Joule heat generated when current is applied to the coil pattern 162 for each phase is reduced. Furthermore, each pattern portion 165 is formed without any intermediate nodes from the beginning to the end of the winding, resulting in a thin, elongated shape. Thus, according to this embodiment, heat generation due to various factors in the stator coil 16 is reduced, thereby enhancing the heat generation suppression effect.

[0040] In this embodiment, the width W11 of the straight portion 165a of each pattern portion 165 is equal to the width W12 of the diagonal portion 165b in the longitudinal direction D15 of the flexible substrate 161. With this configuration, the width W11 of the straight portion 165b of each pattern portion 165 is kept to a necessary minimum.

[0041] Fig. 10 is a graph comparing the case surface temperatures of three brushless motors: the comparative example shown in Fig. 8 and Fig. 9, the embodiment shown in Fig. 1 to Fig. 7, and a modified version of the embodiment. The modified version here is one in which the width of the straight line portion of each of the four pattern parts that make up the coil pattern for each phase is wider than in the above-mentioned embodiment.

[0042] In the graph G11 of FIG. 10, the horizontal axis represents the rotor rotation speed (rpm), and the vertical axis represents the amount of rise in saturation temperature (° C.) on the case surface.

[0043] First, to conduct an experiment measuring the housing surface temperature for this embodiment, a brushless motor 1 was fabricated with the width W11 of the straight portion 165a of each of the four pattern portions 165 set to 0.28 mm. The increase in saturation temperature (°C) on the case surface was measured while increasing the rotor rotation speed (rpm). The experimental results are shown in graph G11 by the dashed line L11 connecting the black dots.

[0044] Next, when conducting experiments measuring the housing surface temperature for the modified example, the width of the straight section was set to 0.40 mm, wider than in the above-described embodiment. A brushless motor with the same structure as the embodiment was otherwise created, and the rise in saturation temperature (°C) on the case surface was measured while increasing the rotor rotation speed (rpm). The experimental results are shown in graph G11 by the dotted line L12 connecting the black dots.

[0045] Furthermore, in conducting the housing surface temperature measurement experiment for the comparative example, the width W52 of the thin line portion 562e, which was formed by dividing the straight portion 562a by the slit 562c, was set to 0.15 mm, and the width of the slit 562c was set to 0.3 mm. A brushless motor with the same structure as the embodiment was otherwise created, and the rise in saturation temperature (°C) on the case surface was measured while increasing the rotor rotation speed (rpm). The experimental results are shown in graph G11 by the dashed line L13 connecting the black dots.

[0046] In the comparative example in which multiple intermediate nodes 562d are provided, the heat generation due to the AC circulating current I51 described above is large, and as shown in graph G11 of FIG. 10, the rise in saturation temperature on the housing surface is the largest. On the other hand, in the embodiment and modified example without intermediate nodes, the rise in saturation temperature on the housing surface is significantly reduced compared to the comparative example. Furthermore, in the embodiment in which the width W11 of the straight portion 165a of each pattern portion 165 is narrowed to be equal to the width W12 of the diagonal portion 165b, the rise in saturation temperature on the housing surface is further reduced compared to the comparative example in which the straight portion is wider. It is believed that the rise in saturation temperature is significantly reduced by suppressing eddy current loss compared to the comparative example in which the straight portion is wider.

[0047] In this embodiment, each pattern portion 165 has a pattern 168 for one turn formed by a front half winding pattern 166 and a second half winding pattern 167. With this configuration, the front and back surfaces of the flexible substrate 161 are utilized, and therefore each pattern portion 165 can be formed on the flexible substrate 161 with increased formation density.

[0048] In this embodiment, the ends of the four pattern portions 165 constituting the coil pattern 162 for each phase are joined together at terminal-side nodes 165t and protrude from the side edge 161a of the flexible substrate 161 to form connection terminals 164 for each phase. The motor wires 151 for the corresponding phase are connected to the connection terminals 164 for each phase. With this configuration, the ends of the four pattern portions 165 for each phase can be used as the connection terminals 164 for the motor wires 151.

[0049] FIG. 11 is a schematic diagram showing a handpiece incorporating the brushless motor shown in FIGS. 1 to 7 as a drive source.

[0050] The handpiece 2 is a tool held by a user for use in a task and includes the brushless motor 1 of the above-described embodiment, a case 21, and a tool unit 22. The case 21 is a cylindrical case that houses the brushless motor 1 and is held by the user. The tool unit 22 protrudes at least partially from the case 21 and is a working part driven by the brushless motor 1 inside the case 21. The handpiece 2 is used for polishing tasks such as dental prosthetics, nail art, and precision finishing of molds, and includes devices such as electric routers and microgrinders. The brushless motor 1 mounted inside the handpiece 2, which can generally be held and operated by a user in one hand, has a long cylindrical shape and an outer diameter of approximately 8 mm to 22 mm. Inner rotor magnet type brushless motors such as the brushless motor 1, which have an outer diameter of approximately 8 mm to 22 mm, generally use a four-pole or two-pole rotor magnet.

[0051] The handpiece 2 of the embodiment described above can effectively suppress heat generation because the brushless motor 1 is used to drive the tool portion 22. Needless to say, the handpiece 2 of the embodiment can also achieve the other effects achieved by the brushless motor 1.

[0052] The above-described embodiment merely shows a typical example of a brushless motor and a handpiece, and the present invention is not limited to this embodiment. In other words, the brushless motor and the handpiece can be implemented in various modifications.

[0053] For example, in the above-described embodiment, the stator coil 16 configured with star connection shown in Fig. 4 is exemplified as an example of the stator coil. However, the connection of the stator coil is not limited to star connection and may be configured with delta connection.

[0054] In the above-described embodiment, the brushless motor 1 having a cylindrical can-like appearance shown in Fig. 1 is exemplified as an example of a brushless motor. However, the brushless motor is not limited to this, and the external shape can be set to any shape.

[0055] Furthermore, in the above-described embodiment, as an example of a coil pattern, a coil pattern 162 in which four pattern portions 165 are arranged in parallel is shown. However, the coil pattern is not limited to this, and as long as a plurality of pattern portions are arranged in parallel from the start of winding to the end of winding without providing any intermediate nodes, the specific number of pattern portions, the specific number of turns in the coil pattern, the circuit configuration, etc. are not important.

[0056] REFERENCE SIGNS LIST 1 Brushless motor 2 Handpiece 11 Housing 12 Yoke 13 Shaft 14 Rotor magnet 15 Circuit board 16 Stator coil 21 Case 22 Tool 111 Housing body 111a Bottom wall 111b Output port 112 Case cover 113 Ball bearing 131 Output end 141 Bush material 151 Motor wire 152 Hall element 153 Hall element wire 161 Flexible board 161a Side edge 162, 562 Coil pattern 162u U-phase coil pattern 162v V-phase coil pattern 162w W-phase coil pattern 163, 563 Common part 164, 564 Connection terminal 164u U-phase terminal 164v V-phase terminal 164w W-phase terminal 165 Pattern part 165a, 562a Straight section 165b, 562b Diagonal section 165c Common side node 165d Jumper section 165t Terminal side node 166, 566 Front half winding pattern 167, 567 Back half winding pattern 168, 568 Pattern for one winding 562c Slit 562d Midway node 562e Thin wire section D11 Axial direction D12 Circumferential direction D13 Board thickness direction D14 Width direction D15 Length direction G11 Graph I51 AC circumferential current L11 Dot-dash line L12 Dotted line L13 Dashed line W11, W51 Width of straight section W12 Width of diagonal section W52 Width of thin wire section

Claims

1. A brushless motor of an inner rotor magnet type comprising: a shaft; a two-pole or four-pole rotor magnet fixed to the shaft; and a three-phase stator coil arranged to surround the rotor magnet in the circumferential direction and generate a magnetic field to rotate the rotor magnet, wherein the stator coil comprises: a flexible substrate rolled up so as to surround the rotor magnet in the circumferential direction; and a three-phase coil pattern formed on the flexible substrate as a conductor pattern, wherein the coil pattern of each phase has multiple pattern portions arranged in parallel from the start of winding to the end of winding without any intermediate nodes, and one end of the start of winding and the end of winding are connected to each other as a common node, and the other end is connected to each other as a terminal node of each phase.

2. A brushless motor as described in claim 1, characterized in that each of the multiple pattern portions has a straight portion extending in the width direction of the flexible substrate along the axial direction of the shaft, and an oblique portion extending from both ends of the straight portion toward the side edge of the flexible substrate at an angle with respect to the width direction, and the width of the straight portion is equal to the width of the oblique portion in the length direction of the flexible substrate perpendicular to the width direction.

3. A brushless motor as described in claim 1, characterized in that each of the multiple pattern portions forms one winding of a pattern consisting of a first half-winding pattern formed on one of the front and back surfaces of the flexible substrate and a second half-winding pattern formed on the other surface and connected to the first half-winding pattern in the substrate thickness direction at one end.

4. A brushless motor as described in claim 1, characterized in that the other end portions of the multiple pattern portions that make up the coil pattern of each phase are connected to each other as the terminal side nodes and protrude from the side edge of the flexible substrate to form connection terminals for each phase.

5. A handpiece comprising: a brushless motor according to any one of claims 1 to 4; a case that houses said brushless motor; and a tool part that protrudes at least partially from said case and is driven by said brushless motor.

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