JPH06351209A - Brushless motor - Google Patents

Abstract

PURPOSE:To obtain a brushless motor whose durability is excellent by a method wherein a cylindrical surrounding member is made of zirconia sintered body and the strength of a member constituting a radial air bearing is improved. CONSTITUTION:In the case of a brushless motor which is used to give a rotary driving force to the side of a hand piece for a dental grinding apparatus, a sleeve 21 as a cylindrical surrounding member is arranged at the outside of a tubular cover 16. The sleeve 21 is formed of a cylindrical member composed of a ceramic sintered body, its wall thickness is set at 2 mm or lower, and its outside diameter is set at 50 mm or lower. In addition, in order to ensure the contact sliding property with the outer circumferential face of the tubular cover 16, the average roughness in the central line of its inner wall surface is set at about 0.01 to 0.1mum. Then, when the apparatus is dropped in a state that the brushless motor, an attachment and the hand piece have been mounted integrally, it is confirmed that the apparatus is provided with a shock-resistant strength of nearly three times as compared with that of a sleeve made of sintered alumina. As a result, the durability of the apparatus can be enhanced surely.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor, and more particularly to a brushless motor suitable for use as a rotary driving means for a dental polishing apparatus.

[0002]

2. Description of the Related Art Conventionally, a non-commutator motor (so-called brushless motor) is widely known in which mechanical contact parts such as brushes and commutators are removed from a DC motor and an electronic commutation mechanism is adopted instead of them. ing.

Generally, this type of motor employs a structure in which a rotor rotatably supported by a bearing is rotationally driven based on a magnetic interaction between a field magnet and an armature coil. Further, it is known that the brushless motor having such a structure has some preferable characteristics such as high rotatability, high acceleration and quietness.

As a specific example of an instrument using a brushless motor having such characteristics as a rotation driving means, for example, there is a dental polishing device used for polishing / cutting a patient's tooth in dentistry.

This type of device is usually constituted by a gripping part called a handpiece having a polishing drill at its tip and a rotary drive means for rotating the drill at a high speed, that is, a brushless motor. . And
In the brushless motor for the above-mentioned device, two types of bearings, which are a radial bearing and a thrust bearing, are generally provided as means for rotatably supporting the rotor.

Conventionally, in the brushless motor used in the dental polishing apparatus, a contact type such as a rolling bearing or a sliding bearing has predominated as a radial bearing structure. However, since the contact type bearing has a disadvantage that it is quickly worn and deteriorated, a non-contact type air bearing has recently attracted attention as an alternative.

Here, the radial air bearing means that a cylindrical enclosing member is arranged around the rotor, and a pressure gas film is formed in the clearance between the two by static pressure or dynamic pressure to receive the load of the rotor. It refers to the bearing to be tried.

Further, armature coils, sensors and the like are arranged on the outer peripheral surface of the cylindrical surrounding member which constitutes the radial bearing, and they are connected by a metallized wiring pattern or the like. As a material for forming such a cylindrical surrounding member, conventionally, a ceramic sintered body such as silicon carbide or alumina having excellent contact slidability is used.

[0009]

However, in the case of a brushless motor having a cylindrical surrounding member made of silicon carbide or alumina sintered body, the cylindrical surrounding member is cracked when a large impact is applied to the device, There is a problem that it becomes unusable.

And in the actual dental care field,
For example, when the device is separated from the connector and handled, the above problem is likely to occur when the device is dropped from a height of several tens of cm.

In particular, with the recent demand for frequent sterilization and disinfection of dental polishing equipment, it is said that the probability of cracking of the cylindrical surrounding member due to such drop is naturally increasing. I have no choice.

Therefore, as a method of preventing the occurrence of cracks, it is naturally conceivable to take measures such as increasing the strength by making the cylindrical surrounding member thicker. However, such a measure is not a good measure because it increases the distance between the field magnet and the armature coil and reduces the rotating torque. In addition, increasing the thickness of the cylindrical surrounding member increases the motor diameter and the overall weight of the device, and is not preferable.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a brushless motor having excellent durability by improving the strength of the members constituting the radial air bearing. .

[0014]

In order to solve the above-mentioned problems, according to the present invention, a rotor having a field magnet,
In a brushless motor provided with a radial air bearing for rotatably supporting the rotor, and an armature coil arranged on the outer peripheral surface of a ceramic cylindrical enclosing member forming the radial air bearing, The gist is that the cylindrical surrounding member is made of a zirconia sintered body.

[0015]

According to this structure, since the highly tough zirconia sintered body is used as the cylindrical surrounding member, the cylindrical surrounding member may be cracked even when it is shocked by being dropped. Never.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied in a dental polishing apparatus will be described in detail below with reference to FIGS.

First, the handpiece 32 of the dental polishing apparatus.
The configuration on the brushless motor M side for giving the rotational driving force to the side will be mainly described. As shown in FIG. 1, the end plate 2 is provided at the inner rear end of the substantially cylindrical casing 1.
Is stuck. An insertion hole 2a is provided in the center of the end plate 2 so as to be transparent. Between the outer peripheral surface of the end plate 2 and the inner peripheral surface of the casing 1, a resin seal ring 3 called a so-called O-ring is interposed. The end plate 2 and the seal ring 3 are arranged as described above, so that the rear end portion of the casing 1 is closed.

A mounting ring 4 is formed near the tip of the casing 1 along the inner peripheral surface of the casing 1.
An attachment 5 as shown in FIG. 1 is detachably attached to the tip of the casing 1 via an annular packing 6. An insertion hole 5a is formed in the center of the attachment 5 so as to extend along the axial direction.

Then, the attachment 5 and the packing 6
By arranging and as described above, the tip portion of the casing 1 is in a closed state. Further, a motor chamber 7 having a substantially circular cross section is formed in a region surrounded by the end plate 2 and the attachment 5 in the casing 1.

As shown in FIG. 1, a power transmission shaft 11 is housed in the motor chamber 7. The rear end of the power transmission shaft 11 is inserted into the insertion hole 2 a of the end plate 2. On the other hand, the tip of the shaft 11 is inserted into the insertion hole 5 a of the attachment 5.

When the shaft 11 is arranged in the motor chamber 7, a clearance S3 having a predetermined width is formed between the outer peripheral surface of the shaft 11 and the inner peripheral surfaces of the insertion holes 2a and 5a. . Therefore, the shaft 11 has two insertion holes 2
It is possible to rotate in a non-contact state with the inner peripheral surfaces of a and 5a.

A pair of annular bushes 12 are formed around the power transmission shaft 11 in the motor chamber 7.
a and 12b are fixed at a predetermined interval. The field magnet 1 is provided between the bushes 12a and 12b.
3 is held. Both bushes 12a and 12b are formed of a magnetic material in order to prevent leakage of magnetic flux in the axial direction of the field magnet 13.

As shown in FIG. 4, the field magnet 1
3 is four permanent magnet pieces 1 around the shaft 11.
It is configured by combining 4 in a cylindrical shape. Further, the respective permanent magnet pieces 14 constituting the field magnet 13 are in a state of being alternately arranged so that adjacent magnetic poles are different from each other.

As shown in FIG. 1, both bushes 12 are
Fitting step portions 15 are annularly cut out on the outer peripheral portions of a and 12b on opposite sides. A tubular cover 16 made of a ceramic material such as a silicon carbide sintered body is fitted between these fitting step portions 15. The cylindrical cover 16 surrounds the outer peripheral surface of the field magnet 13.

An annular magnet 17a as a rotor-side magnetic member is fixed to the rear end of the rear bush 12a. On the other hand, an annular magnet 19a as a casing-side magnetic member is attached to the inner peripheral surface of the fitting stepped portion 15 formed on the end plate 2 so as to face the annular magnet 17a.

Similarly, an annular magnet 17b serving as a rotor-side magnetic member is provided on the front end side of the front bush 12a.
Is stuck. On the other hand, an annular magnet 19b serving as a casing-side magnetic member is attached to the inner peripheral surface of the mounting ring member 20 projecting from the attachment 5 at the tip of the casing 1 so as to face the annular magnet 17b.

The annular magnets 17a, 19a facing each other on the rear side of the rotor 28 and the annular magnets 17b, 19b facing each other on the front side of the rotor 28 are:
In both cases, the same magnetic poles are arranged so as to face each other. Therefore, these two sets of magnets 17a and 19a
The a, 17b and 19b are in a state of being separated from each other with a predetermined gap (clearance) S1 by the magnetic repulsive force of each other. As a result, the power transmission shaft 11
Is restricted from moving in the thrust direction.

That is, in this embodiment, the bushes 12a and 12b, the field magnet 13, the cylindrical cover 16 and the annular magnets 17a and 17 are provided for the power transmission shaft 11.
The rotor 28 is configured by integrally fixing b. Further, in this embodiment, the pair of annular magnets 17a and 19a constitutes a rear thrust magnetic bearing. Similarly, the pair of annular magnets 17b, 19b constitutes a thrust magnetic bearing on the front side.

As shown in FIG. 1, a sleeve 21 as a cylindrical surrounding member is arranged outside the cylindrical cover 16. The sleeve 21 is supported between a fitting step 22 formed on the end plate 2 and a fitting step 23 formed on the mounting ring 4.

As shown in FIG. 1, a cylindrical yoke 29 is assembled inside the casing 1.
The yoke 29 is configured by laminating a plurality of ring-shaped silicon steel plates.

A storage space 10 is formed between the yoke 29 and the sleeve 21. The sleeve 21 has a plurality of ventilation holes 26 that connect the storage space 10 side and the rotor 28 side.
Is transparently installed. As shown in FIGS. 1 and 2, the end plate 2 has an air introduction hole 8 formed therethrough. A blower 30 is connected to the air introduction hole 8 via an air hose in a connector (not shown). Therefore, the high-pressure air sent from the blower 30 is supplied to the gap formed by the rotor 28 and the sleeve 21 via the air hose, the air introduction hole 8, the storage space 10 and the ventilation hole 26.

That is, the rotor 28 is held in the sleeve 21 in a non-contact state by the pressure of the air supplied from the blower 30. At this time, the rotor 2
8 and the inner peripheral surface of the sleeve 21 have a clearance S2.
Is maintained, and the power transmission shaft 11 and the insertion holes 2a and 5a
A clearance S3 is maintained between and. Further, in this embodiment, the cylindrical cover 16 and the sleeve 2 described above are used.
Thus, 1 and 1 constitute a radial air bearing.

The clearance S2 illustrated in FIG.
Is wider than it actually is to emphasize the presence of air passages. The actual clearance S2 is extremely narrow, such as several .mu.m to several tens of .mu.m, to the extent that air can leak. In the hydrostatic bearing structure for the brushless motor M, the clearance S
It is desirable to set the value of 2 in the range of 10 μm to 50 μm. In this embodiment, the value of the clearance S2 is set to about 20 .mu.m so that it falls within the preferable range.

As shown in FIGS. 1 and 4 to 6, on the outer peripheral surface of the sleeve 21, three armature coils 27 are arranged at equal intervals along the circumferential direction. Further, in the central portion on the outer peripheral surface of the sleeve 21 and in the winding region of the armature coil 27, three Hall elements 31 are provided at equal intervals along the circumferential direction.

Each hall element 31 has a power supply connection terminal 31.
a, a ground terminal 31b, and a signal terminal 31c. Each of the terminals 31a to 31c has a sleeve 2
The same kind of components are electrically connected to each other through the wiring 71 metallized on the outer peripheral surface of 1. The winding end portions 27a of the armature coils 27 are also electrically connected to each other by another wiring 72 metalized on the outer peripheral surface of the sleeve 21.

The hall elements 31 are for detecting changes in magnetic poles when the permanent magnet pieces 14 constituting the rotor 28 rotate. And each armature coil 2
The energization amount and energization direction to 7 are controlled based on the detection result from each Hall element 31.

At this time, the magnetic field sequentially generated by each armature coil 27 and the field magnet 13 of the rotor 28.
The rotation of the rotor 28 is controlled based on the interaction with the. The brushless motor M of the dental polishing device is configured as described above.

Next, the structure of the handpiece 32 will be described. As shown in FIG. 1, a handpiece 32 is attached to the outer side of the attachment 5 on the tip side of the brushless motor M. The handpiece 32 has a substantially cylindrical shape and a tapered shape. That is, the handpiece 32 has a shape that a dentist who is a user can easily hold when polishing a tooth.

As shown in FIG. 1, the handpiece 32
A handpiece side shaft 33 is rotatably housed inside the shaft along the axial direction thereof. This shaft 3
The tip portion of 3 is in a state of protruding from the tip portion of the handpiece 32. Then, a drill 34 for polishing the patient's teeth is attached to the portion.

A coupling 35 is provided at the tip of the power transmission shaft 11. Therefore, when the handpiece 32 and the casing 1 of the brushless motor M are connected via the attachant 5, the power transmission shaft 11 and the handpiece side shaft 3 are coupled by the coupling 35.
3 and 3 are connected and driven. In the vicinity of the drill 34 at the tip of the handpiece 32, an air jet, a water jet, and a light irradiation port (all not shown) are provided to assist the tooth polishing work.

As shown in FIG. 2, the end plate 2
A pair of through holes 9 are formed in the. Similarly, the mounting ring 4 is also formed with a pair of through holes (not shown) at positions corresponding to the pair of through holes 9. The water supply pipe 9a and the optical fiber 9b are arranged one by one on the path connecting the through hole 9 of the end plate, the storage space 10 and the through hole of the mounting ring 4. Also, the water supply pipe 9a and the optical fiber 9b
Is the water supply pipe 39 on the attachment 5 side shown in FIG.
a and the optical fiber 39b, respectively.

Therefore, water supplied from a water supply pump (not shown) and sent through the water supply pipes 9a and 39a is ejected from the water ejection port at the tip of the handpiece 32. Further, from the light irradiation port at the tip of the handpiece 32, a light generator (not shown) and the optical fiber 9b,
The light transmitted through 39b is emitted.

As shown in FIG. 2, the end plate 2
A plurality of connector pins 36 are provided upright so as to surround the insertion hole 2a. The base ends of these connector pins 36 are electrically connected to the wiring 71 on the outer peripheral surface of the sleeve 21. The tip of each connector pin 36 can be inserted into and removed from a pin hole (not shown) provided in the same number on the connector side. Therefore, when the connector is attached, the brushless motor M side and the control unit side (not shown) are electrically connected via the connector pin 36.

As shown in FIGS. 1 and 3, in the handpiece 32, a passage 5b is formed which connects the insertion hole 5a of the attachment 5 and the tip of the handpiece 32. And the attachment 5 from the motor chamber 7 side
The air discharged to the side is guided to the air ejection port through this passage 5b and then discharged to the outside from the air ejection port.

The operation of the dental polishing apparatus configured as described above will be briefly described. At the time of use, first, the handpiece 32 and the attachment 5 are integrally mounted on the casing 1. In this state, by energizing each armature coil 27, the rotor 28 starts rotating. At this time, the load of the rotor 28 in the thrust direction is due to the two pairs of annular magnets 17a, 19a and 17b, 19b.
It is accepted by the magnetic repulsion force of. In addition, the rotor 28
The radial load of is received by the pressurized air introduced between the cover 16 and the sleeve 21. Therefore, the rotor 28 can rotate at high speed and stably without contacting each member in the motor chamber 7. The rotational force of the rotor 28 is generated by the power transmission shaft 11,
It is transmitted via the coupling 35 and the handpiece side shaft 33, and as a result, the polishing drill 34 is rotationally driven.

Next, the properties of the sleeve 21 which constitutes the radial air bearing of the brushless motor M and the manufacturing method thereof will be described. As shown in FIG. 5, the sleeve 21 is a cylindrical member made of a ceramics sintered body. In this brushless motor M, the thickness of the sleeve 21 is 2 mm or less, more preferably 0.5 mm to 1.5 mm.
It is good to set to about mm. When the thickness of the sleeve 21 becomes thicker than 3 mm, the armature coil 27 and the rotor 28
This is because the distance between the field magnet 13 and the field magnet 13 becomes extremely large, and the rotational torque of the motor is significantly reduced.

The outer diameter of the sleeve 21 is preferably set to 50 mm or less, more preferably about 10 mm to 20 mm. This is because if the outer diameter of the sleeve 21 is larger than 50 mm, deformation or the like is likely to occur at the time of manufacture, and it becomes difficult to obtain a product with good dimensional accuracy. In the present embodiment, considering the above circumstances, the outer diameter, the wall thickness and the total length of the sleeve 21 are 13 mmφ, 1 mm and 45 mm, respectively.
Is set to.

Further, in order to secure the contact slidability with the outer peripheral surface of the tubular cover 16, the center line average roughness Ra of the inner wall surface of the sleeve 21 in this embodiment is about 0.01 μm to 0.1 μm.
It is set to about m. Since the sleeve 21 is extremely dense, the porosity is less than 3%.

In this embodiment, PSZ (Partially Stab) is used as the ceramic sintered body material formed by the sleeve 21.
ilized Zirconia: partially stabilized zirconia) is used. PSZ is characterized by being easier to manufacture (mainly sintering) and processing than non-oxide ceramics such as silicon nitride and silicon carbide, and having extremely excellent toughness at room temperature. It is generally known that PSZ is a ceramic obtained by adding another compound (stabilizer) to simple substance of zirconia, and is a ceramic that is reinforced by skillfully utilizing the phase transformation of crystal. ing.

Generally, PSZ is the species of stabilizer used.
It is possible to classify by type. Its representative
As for, magnesia (MgO) system and yttria (Y
₂O ₃) Two of the systems are well known. And this implementation
In the example, a sleeve 21 made of MgO-based PSZ is used.
Has been.

For example, in the case of producing a MgO-based PSZ, first, a compact having a predetermined shape is produced by using a mixed powder of zirconia simple substance and MgO. That is, in the case of this embodiment, a cylindrical molded body is produced here. Then, the molded body is fired at a high temperature of 1750 ° C. or higher. By this step, a cubic phase single phase sintered body is obtained. Further, the sintered body is 1100 ° C to 1500 ° C.
Aging (heat treatment for improving characteristics) is performed in a two-phase mixed region of cubic crystal and tetragonal crystal at ℃. By this step, a cylindrical PSZ having fine tetragonal phase particles is obtained.

The physical and electrical characteristics of PZT used as the material for forming the sleeve 21 in this embodiment are as follows. That is, the density (g / cm ³ ) is 6.
1, bending strength (kg / mm ² ) is 112, fracture toughness K _IC (M
pa · m ^1/2 ) 6-8, Micro Vickers hardness (kg
/ mm ² ) is 1500, and the longitudinal elastic modulus (× 10 ⁴ kg / mm ² ) is 2.
0, thermal shock resistance ΔT (℃) 250, thermal conductivity (cal / cm
・ Sec ・ ℃) 0.007, coefficient of thermal expansion (ppm / ℃)
Is 8.3, the volume resistivity (Ω · cm) is> 10 ¹⁰ , and the relative dielectric constant is 9. That is, it is understood that this PSZ has excellent characteristics such as high strength and high toughness when compared with ordinary ceramic materials.

As a test for evaluating the strength of the sleeve 21 of the brushless motor M in the dental polishing apparatus of this embodiment, the following impact test was conducted.
This test is a test assuming a case where the dentist accidentally drops the device when the device is separated from the connector and handled.

More specifically, with the brushless motor M, the attachment 5 and the handpiece 32 mounted integrally, the device is allowed to freely fall from various heights and the height at which the sleeve 21 is cracked. (Cm) was investigated. Further, here, an apparatus (comparative example) including a sleeve made of an alumina sintered body was produced, and the same impact test was performed on the apparatus. The sleeve of this comparative example is different only in material, and other elements such as shape and size are the same as those of the sleeve 21 of the example.

As a result of the above test, it was found that in the case of the device of the comparative example, the sleeve was broken when dropped from a height of about 40 cm. On the other hand, in the case of the apparatus of the example, it was found that the sleeve 21 cracks when dropped from a height of about 110 cm. Therefore, it was confirmed that the sleeve 21 of the example made of PSZ has almost three times the impact resistance strength of the sleeve of the comparative example.

That is, when the sleeve 21 of this embodiment is used as a constituent element of the radial air bearing, the strength of the radial air bearing is surely improved, and thus the brushless motor M
As a result, the durability of the dental polishing device is improved. Further, by adopting PSZ having high strength and high toughness as in this embodiment, it is possible to improve the strength of the device without increasing the thickness of the sleeve 21 itself. Moreover, this embodiment is advantageous in that there is no disadvantage such as deterioration of rotor rotation efficiency due to thickening of the sleeve 21.

The PSZ used as the material of the sleeve 21 in this embodiment has excellent physical characteristics (high strength, high dust resistance, abrasion resistance, etc.) and excellent electric characteristics. It also has (electrical insulation, relative dielectric constant, etc.).

Therefore, the PSZ sleeve 21 is extremely advantageous in that it has electrical characteristics comparable to those of the well-known sleeve materials such as silicon carbide, alumina, silicon nitride and sialon.

The present invention is not limited to the above embodiments, but can be modified as follows. For example, (a) the ceramic sintered body formed by the sleeve 21 is
It is not necessarily limited to the PSZ as shown in the examples. Of course, normal zirconia alone, which also has high strength and high toughness, and FSZ (Full Stabilized Zirc)
onia: stabilized zirconia) may be used.
Moreover, not only zirconia simple substance, PSZ and FSZ,
For example, a ceramics sintered body such as zircon (ZrSiO ₄ ) may be used.

(B) In addition to MgO and Y ₂ O ₃ described above, for example, ceria (CeO ₂ ), alumina (Al ₂
O ₃ ) and calcia (CaO) can be used.

(C) Of course, the cylindrical cover 16 constituting the radial air bearing on the rotor side may be made of zirconia sintered body such as PSZ or FSZ. With such a configuration, the durability and abrasion resistance of the brushless motor M are further improved, which is extremely suitable.

(D) The brushless motor M of the present invention is not limited to a dental polishing apparatus, and may be used for other medical equipment for polishing and cutting bone tissue other than teeth, machine tools, etc. It is also possible to embody the brushless motor used.

[0063]

As described above in detail, according to the brushless motor of the present invention, the cylindrical enclosing member forming the radial air bearing is made of a zirconia sintered body having high strength and high toughness, so that the strength is improved. Therefore, the excellent effect that the durability of the device can be surely improved is exhibited.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment in which a brushless motor of the present invention is embodied in a dental polishing apparatus.

FIG. 2 is an enlarged side view of the dental polishing apparatus as viewed from the connector side.

FIG. 3 is an enlarged sectional view taken along line AA of the dental polishing apparatus.

FIG. 4 is an enlarged sectional view taken along line BB of the dental polishing apparatus.

FIG. 5 is an exploded perspective view showing a sleeve, a rotor and a cushion.

FIG. 6 is a schematic development view showing an outer peripheral surface of a sleeve.

[Explanation of symbols]

13 ... Field magnet, 28 ... Rotor, 21 ... Sleeve as a cylindrical surrounding member, 27 ... Armature coil, M ... Brushless motor.

Claims (1)

[Claims] 1. A rotor (28) having a field magnet (13), a radial air bearing for rotatably supporting the rotor (28), and a ceramic cylinder forming the radial air bearing. Shape surrounding member (2
A brushless motor (M) having an armature coil (27) arranged on the outer peripheral surface of 1), wherein the cylindrical surrounding member (21) is made of a zirconia sintered body. .