Brushless motor and handpiece

Abstract

[Problem] To provide a brushless motor that suppresses heat generation by restraining eddy currents during high-speed rotation, and that can also continuously rotate stably at high speeds, and to provide a handpiece that incorporates the brushless motor. [Solution] In a rotor 10, a yoke 13 has a hollow cylindrical shape which has a larger inner diameter than the outer diameter of a cylindrical portion of a magnet 11, and a holder 14 holds the magnet 11 and the yoke 13 coaxially. In a stator 20, a sleeve 22 has a hollow cylindrical shape in which the inner and outer diameter are larger than the outer diameter of the cylindrical portion of the magnet 11 and smaller than the inner diameter of the cylindrical portion of the yoke 13, and the sleeve 22 holds three coils 21 at equal intervals. In addition, the coils 21 are configured to be positioned in a space between the outer surface of the cylindrical portion of the magnet 11 and the inner surface of the cylindrical portion of the yoke 13.

Description

Technical Field

[0001] The present invention relates to a brushless motor and a handpiece incorporating the brushless motor as a drive source.

Background Art

[0002] Conventionally, some handpieces of polishing devices used for dental laboratory work, nail art, precision finishing of molds, etc. incorporate a brushless motor as a drive source (see, for example, Patent Document 1). The brushless motor for this application needs to perform high-speed rotation of about 40,000 rpm.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the brushless motor as described in the above prior art is rotated at high speed, heat generation due to eddy currents occurs. This heat generation reduces the efficiency of the motor, and in a handpiece that a person holds and continuously operates, the heat transmitted to the fingertips of the person may become an obstacle in handling.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to achieve both high-speed rotation and prevention of heat generation due to eddy currents, and to provide an optimal brushless motor for incorporation in tools such as a handpiece that a person holds and operates, and a handpiece incorporating the brushless motor as a drive source.

Means for Solving the Problems

[0006] One solution to the above problem is a brushless motor having a rotor and a stator, wherein the rotor comprises a magnet, a yoke, a holder, and a balance ring, and the stator comprises a coil and a sleeve. The magnet is elongated cylindrical in shape. The yoke is hollow cylindrical with an inner diameter larger than the outer diameter of the cylindrical part of the magnet. The holder coaxially holds the magnet and the yoke. The balance ring is fixed to the end of the yoke. There are at least three coils. The sleeve is hollow cylindrical with an inner and outer diameter larger than the outer diameter of the cylindrical part of the magnet and smaller than the inner diameter of the cylindrical part of the yoke, and holds the coils at equal intervals. The coils are positioned in the space between the outer surface of the cylindrical part of the magnet and the inner surface of the cylindrical part of the yoke. Furthermore, a brushless motor with this configuration is built into a handpiece. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a brushless motor that suppresses heat generation by suppressing eddy currents during high-speed rotation, and that can continuously rotate stably at high speed, as well as a handpiece that can be held in a person's hand and used for safe work over long periods of time. [Brief explanation of the drawing]

[0008] [Figure 1] This is a structural diagram showing an example of a brushless motor according to the present invention. [Figure 2] This is a cross-sectional view showing the rotor section of the brushless motor. [Figure 3] This is a diagram showing the stator section of the brushless motor. [Modes for carrying out the invention]

[0009] One of the features of this embodiment is that the brushless motor is configured as follows. A brushless motor having a rotor and a stator, wherein the rotor comprises a magnet, a yoke, a holder, and a balance ring, and the stator comprises coils and a sleeve. The magnet is elongated cylindrical in shape. The yoke is hollow cylindrical with an inner diameter larger than the outer diameter of the cylindrical part of the magnet. The holder coaxially holds the magnet and the yoke. The balance ring is fixed to the end of the yoke. There are at least three coils. The sleeve is hollow cylindrical with an inner and outer diameter larger than the outer diameter of the cylindrical part of the magnet and smaller than the inner diameter of the cylindrical part of the yoke, and holds the coils at equal intervals. The coils are positioned in the space between the outer surface of the cylindrical part of the magnet and the inner surface of the cylindrical part of the yoke. With this configuration, the rotor yoke and magnet rotate together, making it less susceptible to the effects of changes in the magnetic field at the yoke. This suppresses heat generation due to eddy currents, especially at high rotational speeds, allowing for continuous and stable rotation. Furthermore, because this brushless motor configuration achieves both high rotational speed and prevention of heat generation due to eddy currents, it is ideal for integration into tools such as handpieces that are held by a person during operation.

[0010] Another feature, in addition to the above, is the sensorless drive system that detects the rotor's position by detecting the back electromotive force generated in the coil due to the rotor's rotation. With this configuration, the current consumption of the drive circuit, including FETs, can be reduced compared to the case where rotational control at high speed is maintained while acquiring the absolute position of the rotor with a Hall sensor, thus keeping the heat generated in the drive circuit low.

[0011] Another feature, in addition to the features mentioned above, is that the housing that houses the rotor and stator is made of a non-magnetic material. With this configuration, the housing is not affected by changes in the magnetic field, thus preventing the generation of eddy currents in the housing and the resulting heat generation.

[0012] Another feature, in addition to the features mentioned above, is that the sleeve is made of a thermally conductive resin. According to this configuration, the heat generated by the coil can be efficiently dissipated.

[0013] As another feature, in addition to the above features, the holder also has a function of adjusting the balance of the rotor. According to this configuration, the rotor balance for high-speed rotation can be more appropriately adjusted.

[0014] Also, when the brushless motor according to the above embodiment is incorporated in the handpiece, more characteristic effects can be obtained. The handpiece of this configuration incorporates a brushless motor that can suppress heat generation due to eddy currents and heat transfer to the housing during driving as much as possible. According to the handpiece of this configuration, it is possible to perform safe and long-term work while maintaining driving by stable high-speed rotation. This is because it has a structure that can prevent the efficiency of the motor from being reduced by eddy currents during high-speed rotation and can prevent heat that hinders work when held by hand.

Example

[0015] Next, a preferred embodiment having the above features will be described in detail based on the drawings. In this embodiment, the "axial direction" means the direction of the rotation center axis of the rotor. Also, the "radial direction" means the direction perpendicular to the rotation center axis of the rotor.

[0016] FIG. 1 is a longitudinal sectional view showing the structure of a brushless motor 1 showing an example of the brushless motor according to the present invention. FIG. 2 is a longitudinal sectional view showing the rotor portion of the brushless motor 1. FIG. 3 is a view showing the stator portion of the brushless motor 1, and FIG. 3(a) is a view of the cross section indicated by A-A in FIG. 3(b).

[0017] The brushless motor 1 is an inner rotor type brushless motor including a rotor 10, a stator 20, a housing 30, and a flange unit 40. The rotor 10 is rotatably supported on both axial sides by the bearing members 31 and 41. The stator 20, the housing 30, and the flange unit 40 are integrally and fixedly arranged.

[0018] The rotor 10 is composed of a magnet 11, a shaft 12, a yoke 13, a holder 14, a balance ring 15, and a fixed bush 16. The magnet 11 is a long cylindrical shape and is a four-pole permanent magnet arranged such that N poles and S poles alternately appear on the outer peripheral surface of the cylinder. The shaft 12 is formed in a long cylindrical shape from a hard material such as stainless steel. This shaft 12 is inserted through the center of the magnet 11 in a penetrating manner, and the front and rear end portions thereof protrude from the front and rear end portions of the magnet 11, respectively. The yoke 13 is formed in a hollow cylindrical shape from a magnetic material. This yoke 13 is arranged such that the inner peripheral surface of the hollow cylindrical shape faces the outer peripheral surface of the magnet 11. The holder 14 holds the magnet 11, the shaft 12, and the yoke 13 coaxially. The balance ring 15 has a ring shape with approximately the same inner and outer diameters as the yoke 13 and is fixed to the end portion of the yoke 13 by press fitting. The fixed bush 16 holds the magnet 11 and the shaft 12 coaxially.

[0019] The stator 20 is composed of three coils 21 and a sleeve 22. The main part of the sleeve 22 has a hollow cylindrical shape, and three coils 21 are held on the outer peripheral side thereof at equal intervals by integral molding. The sleeve 22 is formed of a resin having thermal conductivity.

[0020] The hollow cylindrical shape of the sleeve 22 has an outer diameter larger than the outer diameter of the cylindrical portion of the magnet 11 and an inner diameter smaller than the inner diameter of the cylindrical portion of the yoke 13. Therefore, the coil 21 held in the sleeve 22 is located in the space between the outer circumferential surface of the cylindrical portion of the magnet 11 and the inner circumferential surface of the cylindrical portion of the yoke 13.

[0021] Three coils 21 are arranged on the inner circumferential surface of the hollow cylindrical sleeve 22 so as to face the outer cylindrical surface of the magnet 11. The rotor 10 is rotated by sequentially energizing the three coils while detecting the position of the magnet 11 using the back electromotive force generated in the coil 21 by the rotation of the rotor 10.

[0022] The housing 30 is made of a non-magnetic material and is formed in a roughly cylindrical, elongated shape, housing the rotor 10 and stator 20 inside. The housing 30 and the stator 20 are fixed together as a single unit. Furthermore, the housing 30 has a bearing member 31 positioned on one side in the axial direction to rotatably support the shaft 12 of the rotor 10.

[0023] The flange unit 40 consists of a flange 42 and a circuit board 43, among other things. The flange 42 of the flange unit 40 is formed in a substantially cylindrical shape, and a circuit board 43 consisting of three electrically connected substrates 43a, 43b, and 43c is fixedly housed inside it. The flange 42 is fixed to the housing 30 at the open end side of the inner circumferential surface of the housing 30 (the side opposite the bearing member 31 in the axial direction).

[0024] A bearing member 41 is positioned on one side of the flange 42 in the axial direction, and together with the bearing member 31, it rotatably supports the shaft 12. A plate-shaped cover member 44 is attached to the open end side of the inner circumferential surface of the flange 42 (the side opposite to the bearing member 41 in the axial direction). Furthermore, a terminal 45 is positioned on the open end side of the inner circumferential surface of the flange 42 so as to protrude from the cover member 44. Terminal 45 is for supplying power to the motor 1 and is electrically connected to the circuit board 43.

[0025] The circuit board 43 is for driving and controlling the brushless motor 1. This circuit board 43 includes a number of coils 21 (three in this embodiment) and switching elements such as FETs that are electrically connected to each coil 21 and switch the direction of the current flowing through each coil 21, as well as control elements that control the switching operation of these switching elements. The drive control of the brushless motor 1 is performed by detecting the position of the rotor 10 (magnet 11) from the back electromotive force generated in the coils 21 by the rotation of the rotor 10 (magnet 11).

[0026] Next, the characteristic effects of the brush motor 1 with the above configuration will be explained in detail.

[0027] Since the yoke 13 and magnet 11 of the rotor 10 rotate together, the rotor 10 is less susceptible to changes in the magnetic field at the yoke 13 during rotation. Especially at high speeds, the yoke 13 prevents the magnetic force of the magnet 11 from leaking outside the housing 30, suppresses the generation of eddy currents and the resulting heat generation, and enables continuous and stable rotation. Therefore, the brushless motor 1 can achieve both high-speed rotation and prevention of heat generation due to eddy currents.

[0028] The brushless motor 1 uses a sensorless drive system that detects the position of the rotor 10 by the back electromotive force generated in the coil 21 due to the rotation of the rotor 10. This allows for a fundamentally lower current consumption of the drive circuit, including FETs, compared to, for example, a system that maintains high-speed rotation control while acquiring the absolute position of the rotor 10 using a sensor such as a Hall sensor. As a result, heat generation on the circuit board 43, which includes the drive circuit, can be kept low.

[0029] Since the housing 30 is made of a non-magnetic material, it is not affected by changes in the magnetic field when the rotor 10 (magnet 11) rotates, thus preventing the generation of eddy currents in the housing and the resulting heat generation.

[0030] Since the sleeve 22 holding the coil 21 is made of a heat-conductive resin, the heat generated by the coil 21 during operation of the brushless motor 1 can be efficiently dissipated.

[0031] The holder 14 and balance ring 15 function as adjustment parts for the rotational balance of the rotor 10 by cutting or drilling holes in parts of them. By more appropriately adjusting the rotor balance for high-speed rotation, even slight imbalances in the rotor that cause harmful vibrations and noise in the high-speed rotation range can be eliminated. Using a material with a high specific gravity, such as a copper alloy, for the holder 14 and balance ring 15 will yield a greater effect on balance adjustment.

[0032] As described above, the brushless motor 1 can continuously rotate stably while suppressing heat generation, making it suitable for use as a power source in tools such as handpieces that are held in the hand for work, and for integration into such tools. More specifically, even when the brushless motor 1 is driven continuously for more than 10 minutes under no load with a voltage of 24V applied, the surface temperature of the housing 30 does not exceed 39°C. Therefore, when the brushless motor 1 is integrated as a power source, especially in handpieces for nail polishing, there is no risk of the part held in the hand becoming too hot and hindering work, allowing for stable operation over long periods of time.

[0033] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and can be modified as appropriate without altering the gist of the invention. [Explanation of symbols]

[0034] 1: Brushless motor 10: Rotor 11: Magnet 12: Shaft 13: York 14: Holder 15: Balance Ring 16: Fixed bushing 20: Status 21: Coil 22: Sleeves 30: Housing 31: Bearing member 40: Flange Unit 41: Bearing member 42: Flange 43: Circuit board 44: Cover component 45: Terminals

Claims

1. A brushless motor having a rotor and a stator, The facility comprises a housing that accommodates the rotor and the stator, A flange is fixed to the housing, The rotor comprises a magnet, a yoke, a holder, a fixing bush, a shaft, and a balance ring. The stator comprises a coil and a sleeve, The aforementioned magnet has a long cylindrical shape, The yoke has a hollow cylindrical shape with an inner diameter larger than the outer diameter of the cylindrical part of the magnet. The holder holds the magnet and the yoke coaxially, The aforementioned fixed bush holds the magnet and the shaft coaxially. The shaft is rotatably supported by a bearing member arranged in the housing and a bearing member arranged in the flange. The balance ring is fixed to the end of the yoke, The aforementioned coil has at least three units. The sleeve has a hollow cylindrical shape, with an inner and outer diameter larger than the outer diameter of the cylindrical portion of the magnet and smaller than the inner diameter of the cylindrical portion of the yoke, and holds the coils at equal intervals. A brushless motor characterized in that the coil is located in the space between the outer circumferential surface of the cylindrical portion of the magnet and the inner circumferential surface of the cylindrical portion of the yoke.

2. The brushless motor according to claim 1, characterized in that it is a sensorless drive system that detects the position of the rotor by the back electromotive force generated in the coil due to the rotation of the rotor.

3. The brushless motor according to claim 1 or 2, characterized in that the housing is formed of a non-magnetic material.

4. The brushless motor according to any one of claims 1 to 3, characterized in that the sleeve is formed of a resin having thermal conductivity.

5. The brushless motor according to any one of claims 1 to 4, characterized in that the holder is equipped with a function for adjusting the balance of the rotor.

6. A handpiece incorporating a brushless motor as described in any one of claims 1 to 5 as a drive source.

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