JP3162460B2 - Rotation speed control device for dental air turbine type handpiece - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an air turbine type handpiece used for dental grinding treatment, which automatically controls the number of rotations of a cutting tool which fluctuates due to a change in the rotational load of the cutting tool during the grinding process. Regarding improvement.

[0002]

2. Description of the Related Art A tooth grinding handpiece is obtained by rotating a cutting tool attached to a head of a handpiece at a high speed.
The air turbine type handpiece is used for forming a cavity of a tooth contact portion and shaping a surface portion, and an air turbine type handpiece rotates a turbine blade provided in the head portion by compressed air injection energy, and includes a turbine blade. In this method, a tool connected to the rotor is rotated.

[0003] Air turbine type handpieces are widely used because they can easily obtain high-speed rotation despite their relatively simple structure. However, when the load torque fluctuates due to an external force that causes a rotating tool to come into contact with the tooth hard tissue. In addition, when the number of revolutions greatly fluctuates and the number of revolutions decreases, the sharpness deteriorates.

[0004] Conventional techniques for controlling the rotation speed of a tooth cutting tool include a rotor rotation speed detected by an optical sensor,
Comparing with the set number of revolutions input to the setting circuit, adjusting the pressure regulating valve of the pressurized air pipe with the comparison signal, adjusting the compressed air injection energy to the turbine blades, keeping the rotor number of revolutions constant, There is known a system that suppresses rotation speed fluctuation due to fluctuation in rotation torque.

This air pressure control system exhibits a rotation speed control function when there is no load or during a period of constant light cutting, but since air is a compressible fluid, the air pressure control valve and the injection nozzle are not connected to each other. If the pipeline is long, the pressure response is slow, for example,
When the tool is removed from the tooth from the cutting state with a constant load to be in a no-load state, or when the load is suddenly changed, the rotation speed control is almost impossible.

On the other hand, the present applicant has incorporated a permanent magnet into the rotor, fixed the coil on the inner surface of the housing, and calculated the rotor speed from the excitation voltage generated in the coil by the rotating magnetic field of the magnet. Then, a rotation speed control device for braking the rotor rotation speed by controlling the load current of the coil based on the output signal compared with the set rotation speed has been proposed (Japanese Patent Application Laid-Open No. 63-143054).

[0007]

The above-described rotational speed control device comprising the permanent magnet of the rotor and the coil of the housing has an effect of suppressing a rapid increase in the rotational speed due to a sudden decrease in the cutting torque of the rotating tool. However, even with this device, the surgeon cannot cope with a sharp decrease in the rotational speed in heavy cutting in which the rotational torque is suddenly increased by increasing the external force of the cutting tool in contact with the teeth. If cutting is continued at a low level, wear and loss of the ball bearings and air bearings that support the rotor will become a problem, and even the surgeon will adjust the contact force of the cutting tool to the teeth themselves to keep the rotation speed constant. Some were forced to maintain it, and some were mentally burdensome.

The present invention provides a rotational speed control apparatus for a dental air turbine type handpiece having a high response speed and a wide constant speed control range, following such a rapid change in the rotational speed of the cutting tool. What you want to do.

[0009]

SUMMARY OF THE INVENTION The present invention provides a dental air turbine comprising a rotor including a turbine blade which is rotated by jetting pressurized air and a housing surrounding and supporting the rotor. In the rotation speed control device for a mold handpiece, a permanent magnet provided on all or a part of the rotor including the turbine blades, a coil arranged in the housing and forming a brushless motor together with the permanent magnet, A current or voltage is supplied to control the rotation of the rotor, and a current or voltage to be supplied to the coil is controlled based on a synchronization signal synchronized with the rotation of the permanent magnet. And a rotation speed control unit that automatically holds the rotation speed of the rotor at a rotation speed near a set value by a power generation function or a braking function. It is.

[0010]

In the present invention, the rotor including the turbine blades is rotated by the injection of the pressurized air to the turbine blades, and the permanent magnet of the rotor including the turbine blades is rotated to form a rotating magnetic field and surround the rotor. A coil is fixed to the housing, and a permanent magnet of the rotor and a coil of the housing constitute a motor unit.

The rotation speed control unit supplies a synchronous current to the coil of the motor unit to cause the coil to form an alternating magnetic field or a rotating magnetic field. The control unit controls the same phase as the excitation voltage generated in the coil by the rotating magnetic field of the permanent magnet. When a current or a control voltage is supplied to the coil, the motor enters an electric state and accelerates the rotation of the rotor. On the other hand, if a synchronous current having a phase opposite to that of the excitation voltage generated by the power generation is supplied to the coil, the motor enters a power generation state or a braking state, and the rotation of the rotor is reduced. In the following description, the case where the current flows into the motor coil is defined as the same phase, and the case where the current is extracted from the motor coil is defined as the opposite phase.

The brushless motor section of the present invention constitutes a permanent magnet synchronous motor or a permanent magnet brushless motor. When the torque angle of the alternating magnetic field of the coil with respect to the rotating magnetic field of the permanent magnet is about 1 / 2π, the maximum efficiency of the motor is reduced. A torque is generated, and a braking torque with a maximum efficiency is generated when the torque angle is about -1 / 2π. When the current supplied to the coil matches the rotation frequency of the permanent magnet and is adjusted to a phase within the above torque angle range, the current or voltage supplied to the coil is controlled to adjust the rotation speed of the rotor. Can be.
Since the driving source of the rotation of the rotor is exclusively based on the compressed air injection energy, the motor unit in the present invention only needs to have a function of compensating for the fluctuation of the load torque of the cutting tool in use, and has a rotation starting ability. There is no need to use a single-phase coil motor with one pole pair.

The rotation speed control unit adjusts the magnitude and phase of the voltage and current supplied to the coil by using an output signal obtained by comparing the measured value of the rotation speed of the rotor with the set value, thereby obtaining the AC synchronous current of the coil.・ If the voltage is controlled and the rotor speed becomes larger than the set value, the braking torque acts on the rotor having the permanent magnet by the power generation / braking function of the motor, so the speed is reduced to the set value and becomes constant. . When the rotation speed becomes smaller than the set value, the rotor is driven by an electric torque by the electric function of the motor to accelerate to the rotation speed of the set value and become constant.

[0014] Since the response speed of the motor and the rotation speed control unit is fast, even if the cutting torque of the rotor suddenly changes in the tooth cutting process, the fluctuation of the rotation speed of the rotor can be suppressed to a level that causes no practical problem. .

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a longitudinal sectional view of a head portion of an air turbine type handpiece. An example of a handpiece of a type in which a shaft 13 of a rotor 1 is supported by a ball bearing 2 inside a housing 3 of the head portion is shown. Is shown.

The rotor 1 is provided with turbine blades 11 on its outer periphery, and compressed air is injected into the turbine blades 11 from an air supply line 4 from a joint pipe portion 8 integrally connected to the housing 3.
The rotor rotates at high speed.

A pair of coils 71 and 72 are mounted on the inner surface of the housing adjacent to the outer periphery of the turbine blade 11 at positions opposed to each other about the rotation axis of the rotor 1. The coils 71 and 72 may be formed by winding a large number of fine copper wires,
It is composed of a conductor thin layer wound on a printed circuit board,
This is preferable in that the entire coil can be easily mounted and arranged on the inner surface of the housing.

FIG. 2A is a cross-sectional view including the rotor 1 of the head portion shown in FIG. 1. In this embodiment, the rotor 1 itself is formed of a ferromagnetic permanent magnet, and a pair is formed in a radial direction of the rotor. Are magnetized by the magnetic poles to form a rotor, and the coils 71 and 72 function as stators to constitute a single-phase permanent magnet synchronous motor unit. The permanent magnet has a large coercive force even when the rare-earth cobalt magnet is small, and is advantageous for forming a turbine airfoil.

Further, in this embodiment, the housing 3 (31) itself is made of a soft ferromagnetic material to provide a magnetic path (yoke) for a rotating magnetic field due to the rotation of the magnetized rotor 1, thereby reducing eddy current loss due to the rotation of the magnetic field. The braking torque is reduced. As this soft ferromagnetic material, mild steel or the like whose surface is rust-proof plated can be used.

FIG. 3 is a block diagram of the rotation speed control device according to the present invention.
The air turbine unit and the motor unit are integrally formed in the turbine including the housing 3 and the housing 3. The air turbine unit may be provided with a compressed air control unit 43 that performs constant pressure control by a pressure adjustment valve 41 provided in the air pipeline 4. Also,
It is also possible to automatically operate the pressure control unit 43 to adjust the rotation speed of the rotor at a constant load.

The rotation speed control section 6 of the present invention controls the motor section. In the following description, first, a current control method for controlling the alternating current supplied to the coil 7 of the motor section will be described. The rotation speed control unit 6 inputs the rotation speed measurement signal B from the rotation speed detection unit 66 and the rotation speed setting signal A set by the rotation speed setting unit 61 to the comparison unit 62 and outputs the rotation speed difference signal A
-B is generated, and the difference signal (A-B) is used to calculate
3, the current control unit 64 proportionally controls the alternating current supplied to the coil 7 of the motor unit.

Since the AC voltage D excited by the rotation of the permanent magnet of the rotor 1 appears in the coil 7, the synchronous signal detecting section 65 detects the AC exciting voltage D and generates a synchronous signal C having a constant amplitude. The data is input to the calculation unit 63. Since the AC excitation voltage D generated in the coil 7 is synchronized with the rotating magnetic field of the magnetized rotor, the synchronization signal C is also always in a synchronized state. If a multiplier for calculating the product of the difference signal (AB) is used, the current control unit 64 receives the synchronized product signal C × (AB) and outputs an AC current proportional to the product signal. It is supplied to the coil 7.

In this case, since the coil excitation voltage D and the coil supply current have a phase difference of about 1 / 2π, the synchronization signal detecting section 65 provides a signal for delaying the phase of the synchronization signal by about 1 / 2π. It is preferable to provide a phase shifter as the phase means for adjusting the torque angle described below. When an integrating circuit is used as a phase shifter, an AC excitation voltage D [∝ω of a sine wave sin (ωt) whose amplitude is proportional to the rotational angular velocity ω of the rotor is used.
When sin (ωt)] is integrated, a cosine-wave synchronization signal C [∝-cos (ωt) = sin (ωt−1 / 2) having a constant amplitude is obtained.
π)] is obtained, so that the phase difference and the constant amplitude can be easily adjusted.

The synchronizing signal E output from the synchronizing signal detector 65
Is detected by the rotation speed detection unit 66 only as the rotation speed component of the rotor, output as the actual rotation speed measurement signal B, and input to the comparison unit 62 as described above. Further, the rotation speed is displayed on the display section 67 by the rotation speed measurement signal B.

In the use of the present apparatus, when the rotation speed of the turbine rotor is a constant speed rotation equal to the set value preset in the rotation speed setting section 61, the measured speed signal B and the set signal A are equal. The difference signal (A−
B) becomes zero, the current control unit 64 is set to the state of current interruption, no current flows through the coil 7, and the motor unit does not operate (this state corresponds to a no-load power generation state).

When the rotation speed of the turbine rotor becomes smaller than the set value during use of the handpiece, the measured rotation speed value B of the rotation speed detection unit 66 becomes smaller than the set value A. (AB) becomes, for example, a positive value, and is calculated by the product signal C × (AB) from the arithmetic unit 63,
4 is a positive torque angle to the coil 7 of the motor, preferably 1/2
By supplying a synchronous alternating current of π, an electric torque is applied to the rotor to increase the rotation speed. The supply current to this coil 7 is
The phase is the same as the phase of the coil generated voltage in the no-load power generation state.
In the speed increasing process, as the rotor speed approaches the set speed, the difference signal (AB) decreases, and the current supplied to the coil 7 also decreases.

On the other hand, when the rotor speed becomes larger than the set value, the difference signal (AB) becomes a negative value by performing the reverse operation, and the product signal C × (A− B)
Is inverted, and the current control unit 64
Supply a synchronous AC current with a negative torque angle, preferably -1 / 2π, so that the motor section applies a braking torque to the rotor to reduce the rotor speed to a set value. In this braking process, the current supplied to the coil 7 is in the opposite phase to the phase of the coil excitation voltage in the no-load power generation state.

FIG. 3 shows an example in which the AC excitation voltage D of the coil 7 is used as an input signal to the synchronization signal detection unit 65 of the rotation speed control unit 6. However, as shown in FIG. An example is shown below in which a signal from the synchronization sensor 9 for detecting the rotation signal is input to the synchronization detection unit 65 and the motor unit is a permanent magnet brushless motor.

As an example of the synchronous sensor 9, as shown in FIG. 2A, a Hall element 91 attached to the inner surface of the housing close to the turbine blade can be used. The position of the Hall element 91 is set with respect to the coil 7 (71, 7
The position of the line orthogonal to the line connecting 2) is convenient for setting the torque angle of the voltage supplied to the coil 7.

The Hall element 91 is a permanent magnetized rotor 1
A synchronous AC output proportional to the magnetic field strength of the rotating magnetic field is output, but the signal voltage of the Hall element 91 does not depend on the rotation speed. FIG. 4 is a circuit diagram of a simple configuration of the rotation speed control device in the case where a Hall element is used for the synchronization sensor 9. The output signal D 'from the Hall element 91 is a synchronous signal composed of a filter and an amplifier. The signal detector 65 detects the synchronization signal C
And is input to the multiplier of the operation unit 63. The filter includes harmonic components resulting from the non-sinusoidal nature of the rotating magnetic field of the rotor,
A low-pass filter (LPF) for removing high-frequency components due to a high-frequency magnetic field formed by rotation of a magnetic focusing portion at the tip of each blade of a turbine blade of the rotor. A synchronization signal C is a fundamental wave synchronized with the rotor rotation. A sine wave is obtained.

Using the synchronization signal C as a rotation speed signal D, a rotation speed detection unit 66 comprising a frequency-voltage (FV) converter obtains a DC rotation speed measurement signal B whose voltage is proportional to the frequency.
It is input to the comparison unit 62. As a frequency-voltage converter,
A method of differentiating the sine wave of the rotational speed signal D with a differentiating circuit to obtain a direct current with a rectifying-smoothing circuit, or generating a trigger pulse for each phase inversion of the sine wave of the rotational speed signal D to generate a monostable FF
A method of generating a pulse having a fixed time width by a circuit and smoothing the pulse to obtain a DC voltage is used.

In the rotation speed setting section 61, the rotation speed is set by the variable resistor VR, and the difference signal (A−A) is set by the differential amplifier of the comparison section 62 to which the setting signal A and the actual measurement signal B are inputted.
B) and outputs the product signal C × (A−
Obtain B). The current control unit 64 may be a low-frequency power amplifier, but in this example, the directly connected output transistors are switched every half cycle of the input signal C (A-B), and the AC is proportional to the input signal. The current is supplied to the coil 7 to control the current of the coil.

As the synchronous sensor 9, a coil for detecting a rotating magnetic field can be used instead of the Hall element 91, in addition to a magnetoresistive element and an optical sensor. The detection coil 9
FIG. 5 shows an example of the arrangement of the rotor 3. A small disk-shaped permanent magnet 92 is provided on the shaft end surface of the rotor 1, and a detection coil 93 is provided on the housing side outside the permanent magnet 92. Since the rotation also rotates the permanent magnet disk 92, an AC signal synchronized with the rotation is induced in the detection coil 93, and the AC signal is input to the synchronization signal detection unit 65.

The output from the detection coil 93 having such an arrangement can be arranged so as to have only a sine wave and a small harmonic component, and to be able to ignore the influence of the magnetic field of the motor section.
It is preferable that the synchronization detection unit 65 is provided with a synchronization oscillator or a sine wave shaping circuit that can obtain a synchronization signal C having a constant amplitude without using a filter. Since the voltage of the output signal from the detection coil 93 is proportional to the number of rotations of the rotating magnetic field, the output signal is used as a rotation number measurement signal B by the rotation number detection unit 66 using a DC signal that has been subjected to double-wave rectification and smoothed. You may. In this case, the excitation voltage D of the coil 7 can be directly used as the signal input to the synchronization detection unit 65.

In FIG. 5, the position of the detection coil 93 with respect to the magnetic pole of the disk-shaped permanent magnet is made to correspond to the position of the coil 7 with respect to the magnetic pole of the rotor 1. Therefore, the output signal of the detection coil 93 indicates the rotation of the rotor. It is easy to satisfy the condition of the optimum torque angle ± 1 / 2π with respect to the magnetic field.

In the above example, the current control method for controlling the alternating current supplied to the coil 7 of the motor unit has been described. However, at least in the electric process, a voltage control method for controlling the supplied alternating voltage to the coil 7 may be employed. . FIG. 6 shows a circuit diagram of a main part of the rotation speed control unit 6 of the voltage control method. The current control unit 64 in the figure constitutes a voltage feedback type operational amplifier. The section 64 supplies a synchronous AC voltage proportional to the product signal C × (A−B) from the multiplier 63 to the coil 7 to generate an electric torque. On the other hand, in the braking process, a reverse-phase current is supplied to the coil 7 to generate a braking torque. The resistors R ₁ and R ₂ on the base side of the output transistors T ₁ and T ₂ are for preventing coil overcurrent during the braking process. For this purpose, resistors are inserted in the connection 73 of the coil 7. May be.

FIG. 6 shows an example in which the synchronizing signal detecting section 65 outputs the synchronizing signal C by using the excitation voltage D of the coil 7 of the motor section.
5 is connected to a phase shifter φ together with a filter (LPF). The excitation voltage D from the coil and the current supplied to the coil
Since the phase difference from the voltage is about 1 / 2π, the phase shifter φ delays the phase of the synchronization signal C by about 1 / 2π more than the phase of the excitation voltage D to adjust the phase to the above-described best torque angle. Things. This phase shift may be performed additively by the filter (LPF) and the phase shifter φ, or the filter (LPF) may also serve as the phase shifter φ.

FIG. 2B shows another embodiment of the rotor 1. The rotor 1 itself is formed of a non-magnetic metal or ceramics, and a pair of permanent magnet pieces 12, 12 are embedded therein. This is an example in which the entire rotor 1 is a permanent magnet rotor.

In FIG. 2B, the outermost part of the housing 3 is formed of a non-magnetic material, for example, an austenitic stainless steel, and a soft magnetic material constituting the yoke 32 inside thereof.
For example, it is made of silicon steel or ferrite porcelain ring. Further, the inner layer portion 33 is lined with a hard synthetic resin.

In the above embodiment, a ball bearing type handpiece has been exemplified.
The present invention can be applied to an air bearing type handpiece in exactly the same manner. Further, the present control device can be applied to a straight handpiece other than the contra-angle handpiece of the above embodiment.

FIG. 7 schematically shows the rotational torque-rotation speed characteristics of the rotor of the handpiece provided with the rotation speed control device of the present invention. In the figure, the curve a indicates the case where the rotation speed control is not performed.
This shows the control characteristics in a state where the pressure of the air pipeline 4 to the turbine blade 11 is controlled to be constant, and ωt is the number of revolutions at no load when the cutting tool of the handpiece is in the idling state.

When the set number of revolutions is set to ω ₂ and the number of revolutions control device is operated, its characteristic is that the torque of the cutting tool, that is, the rotational torque of the rotor fluctuates as shown by the b ₂ curve. rpm with a torque control range also is maintained substantially constant in the set rotation speed omega _2. In practice, in the case of performing the light cutting against tooth at high speed rotation, b ₃ is set to set speed omega ₃ as shown curve, almost constant rotational speed during idling and during cutting of the cutting tool is obtained Can be In particular, since the control system of the present apparatus has a high response speed, it can follow a sudden change in the load torque of the cutting tool, and can reduce the change in the rotational speed.

Further, the difference signal (AB) from the comparing section 62
Thus, the pressure regulating valve 4 by the compressed air control unit 43 in FIG.
It is also possible to proportionally control the outlet side pressure. With this configuration, even when the rotation speed of the rotor deviates from the controllable rotation speed range of the motor unit during use of the hunt piece, the pressure generated by the turbine blades is adjusted by the compressed air control unit 43 to reduce the rotation speed. It can be quickly adjusted within the control range of the motor unit.

[0045]

According to the rotation speed control device of the present invention, a brushless motor portion is provided on the rotor of the head portion of the handpiece, and the rotation of the rotation speed due to the fluctuation of the load torque of the rotor is detected, and the motor portion is electrically driven to the rotor. By applying torque and braking torque, the air turbine torque can be compensated and controlled to a rotational speed substantially equal to the set rotational speed, and since the response speed of this control system is high, during the tooth cutting by the handpiece, Even if there is a rapid change in the cutting torque, the change in the rotor speed can be suppressed to a small value.

During a light cutting operation, the cutting operation can be performed at a high speed and a constant rotation speed even while the cutting tool is spinning and cutting, so that the sharpness peculiar to this kind of air turbine type handpiece is exhibited. Therefore, a clean tooth surface can be realized regardless of the cutting load.

The sudden stop at the beginning of cutting of the cutting tool and the high-speed idling at the end of cutting can also be prevented by exerting rapid acceleration and sudden deceleration of the motor unit, and there is no need to wait for the rotation speed to recover after the sudden stop. The cutting treatment can be performed quickly and safely for the practitioner without having to worry about an unexpected situation due to high-speed idling.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a head portion of an air turbine type handpiece.

FIG. 2 is a cross-sectional view (A, B) of the head unit in FIG. 1;

FIG. 3 is a block tiregram of a rotation speed control unit.

FIG. 4 is a circuit diagram according to an embodiment of a rotation speed control unit.

FIG. 5 is a perspective view of a rotor provided with a synchronization sensor.

FIG. 6 is a partial circuit diagram according to another embodiment of the rotation speed control unit.

FIG. 7 is a characteristic diagram of rotational torque versus rotational speed of a rotor.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Rotor 11 Turbine blade 12 Permanent magnet piece 13 Rotor shaft 2 Ball bearing 3 Housing 4 Air line 6 Revolution control part 7 Coil 9 Synchronous sensor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-143054 (JP, A) JP-A-62-101804 (JP, A) JP-A-62-101805 (JP, A) JP-A-58-108 103448 (JP, A) JP-A-52-118894 (JP, A) JP-A 62-107812 (JP, U) JP-A 60-149620 (JP, U) JP-A 61-139208 (JP, U) 63-120597 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61C 1/00-1/08

Claims (6)

(57) [Claims] An apparatus for controlling a rotational speed of a dental air turbine type handpiece comprising a rotor for driving a dental handpiece comprising a rotor including turbine blades rotated by jetting of pressurized air and a housing surrounding and supporting the rotor. In the above, a permanent magnet which constitutes all or a part of the rotor including turbine blades, a coil which is arranged in the housing and forms a brushless motor together with the permanent magnet, and supplies a current or a voltage to the coil, It controls the rotation of the rotor and outputs a synchronization signal synchronized with the rotation of the permanent magnet, controls the current or voltage supplied to the coil based on the signal, and controls the electric function and the power generation function of the brushless motor unit. A rotation speed control unit for automatically holding the rotation speed of the rotor at a rotation speed near a set value by a braking function. Speed control device for dental air turbine type handpieces. 2. A synchronous signal detecting section for detecting a voltage induced in the coil in synchronization with the rotation of the permanent magnet and outputting a synchronous signal, and detecting a rotational number of the rotor. A rotation speed detection unit, a rotation speed setting unit for setting the rotation speed of the rotor, and a difference signal between a rotation speed measurement signal from the rotation speed detection unit and a rotation speed setting signal from the rotation speed setting unit. A comparison unit, a calculation unit that outputs a coil control signal obtained based on the difference signal and the synchronization signal, and a current control unit that controls a supply current or a supply voltage of the coil based on the coil control signal. The rotation speed control device for a handpiece according to claim 1, wherein: 3. The handpiece rotation speed control according to claim 2, wherein said synchronization signal detection section includes phase shift means for synchronizing a voltage induced in said coil with rotation of said permanent magnet. apparatus. 4. The apparatus according to claim 1, wherein the coil is a conductor wound around a printed circuit board. 5. A yoke made of a soft ferromagnetic material is provided around the outer periphery of the turbine blade either integrally with the housing or separately inside the housing. Item 2. The rotation speed control device for a handpiece according to Item 1. 6. A rotational speed control device for a dental air turbine type handpiece comprising a rotor for driving a dental handpiece, comprising a rotor including turbine blades rotated by jetting of pressurized air and a housing surrounding and supporting the rotor. At
All or a part of the rotor including the turbine blades is formed as a permanent magnet, and a coil is arranged and held in the housing to form a brushless motor portion. A rotation control device for a dental air turbine handpiece, wherein the rotation of the brushless motor is simultaneously obtained by supplying a synchronous current or a synchronous voltage synchronized with the rotation of the permanent magnet.