JPH05212060A - Rotating speed controller for air turbine type hand piece for dental purpose - Google Patents

Abstract

PURPOSE:To improve the responsiveness of rotating speed control by regulating the magnitude and phase of the supply voltage and current to a coil according to the output signal obtd. by comparing the actually measured value and set value of the rotating speed of a rotor, and controlling the AC synchronizing current and voltage of the coil. CONSTITUTION:The hand piece for dental purposes has a driving section constituted by housing a rotor contg. turbine vanes to be rotated by the ejection of pressurizing air within a housing. A coil is disposed in the housing of such driving section to constitute a brushless motor section. The energization to the coil is controlled by a rotating speed control section 6. In rotating speed control section, namely, the actually measured rotating speed signal B from a rotating speed detecting section 66 and the rotating speed set signal A by a rotating speed setting section 61 are compared in a comparing section 62. The supply AC current to the coil of the motor section is proportionally controlled with a current control section 64 via arithmetic section 63 by the resulted differential signal, by which the rotating speed of the rotor is so controlled as to be maintained within a specified control range.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art A handpiece for tooth grinding is produced by rotating a cutting tool attached to the head of the handpiece at high speed.
The air turbine type handpiece, which is used for forming a cavity in the tooth caries and for chamfering and shaping the surface, includes a turbine blade that rotates the turbine blade provided in the head portion with compressed air jet energy. This is a method of rotating a tool connected to the rotor.

The air turbine type handpiece is widely used because it can be easily rotated at a high speed even though it has a relatively simple structure. However, the load torque varies every time due to an external force that abuts the rotating tool on the tooth hard tissue. Moreover, when the rotational speed fluctuates greatly and the rotational speed decreases, the sharpness deteriorates.

As a conventional technique for controlling the rotational speed of a tooth cutting tool, the rotor rotational speed detected by an optical sensor,
Compared with the set speed input to the setting circuit, adjust the pressure adjusting valve of the pressurized air pipe with the comparison signal, adjust the compressed air injection energy to the turbine blade, and keep the rotor speed constant, There is known a system that suppresses fluctuations in rotation speed due to fluctuations in rotation torque.

This air pressure control system exerts a rotation speed control function when there is no load or during constant light cutting, but since air is a compressible fluid, it is between the pressure regulating valve and the injection nozzle. When the pipeline is long, the pressure response is low, for example,
The rotational speed control was almost impossible when the tool was removed from the tooth from the tooth under a constant load to leave it unloaded, or when there was a sudden load change.

On the other hand, the applicant of the present invention incorporates a permanent magnet into the rotor, fixes the coil on the inner surface of the housing, and calculates the rotor rotation 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 was proposed (Japanese Patent Laid-Open No. 63-143054).

[0007]

The rotation speed control device composed of the permanent magnet of the rotor and the coil of the housing described above has an effect of suppressing a sharp increase in the rotation speed due to a rapid reduction in the cutting torque of the rotating tool. However, even in this device, the surgeon cannot cope with a sharp decrease in the rotation speed in the case of heavy cutting in which the rotating torque abruptly increases by increasing the external force with which the cutting tool comes into contact with the tooth. If the cutting is continued in a low condition, the wear and damage of the ball bearings and the air bearings that support the rotor become a problem, and even the surgeon can adjust the contact force of the cutting tool to the teeth himself to keep the rotation speed constant. There were some who were forced to perform maintenance operations and had a heavy mental burden.

The present invention provides a rotation speed control device for a dental air turbine type handpiece having a wide response speed and a wide constant speed control range by following such a rapid change in the cutting tool rotation speed. Is what you are trying to do.

[0009]

SUMMARY OF THE INVENTION A dental air turbine type handpiece rotation speed control system according to the present invention comprises a rotor including turbine blades rotated by jetting of pressurized air and a housing surrounding and supporting the rotor. In a rotation speed control device of a dental air turbine type handpiece which constitutes a drive part of a handpiece for use, all or part of the rotor including turbine blades is a permanent magnet, and a coil is arranged and held in the housing, A brushless motor unit that controls the synchronous current or synchronous voltage of the coil to automatically maintain the rotor speed at a speed near the set value by the electric function and power generation function or braking function of the motor unit. It is characterized by having a number control unit.

[0010]

In the present invention, the injection of the compressed air to the turbine blade causes the rotor including the turbine blade to rotate, and the permanent magnet of the rotor including the turbine blade rotates to form a rotating magnetic field, which surrounds the rotor. A coil is fixed to the housing, and the permanent magnet of the rotor and the coil of the housing form a motor unit.

The rotation speed control section supplies a synchronous current to the coil of the motor section to form an alternating magnetic field or a rotating magnetic field in the coil, but controls the phase of the excitation voltage generated in the coil by the rotating magnetic field of the permanent magnet. When the current or the control voltage is supplied to the coil, the motor is in an electrically driven state and accelerates the rotation of the rotor. On the other hand, if a synchronous current having an opposite phase to the excitation voltage generated by power generation is supplied to the coil, the motor is in a power generation state or a braking state, and the rotation of the rotor is decelerated. In the following description, the case where a current is applied to the motor coil is the same phase, and the case where a current is extracted from the motor coil is the opposite phase.

The brushless motor section of the present invention constitutes a permanent magnet synchronous motor or a permanent magnet brushless motor, and the maximum efficiency electric drive is achieved 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 1/2 π. The torque is expressed, and the braking torque of maximum efficiency is expressed 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 the phase within the above torque angle range, the rotation speed of the rotor is adjusted by controlling the current or voltage supplied to the coil. You can
Since the drive source for the rotation of the rotor is exclusively by the compressed air injection energy, the motor unit in the present invention only needs to have the function of compensating for the fluctuation of the load torque of the cutting tool in use, and has the rotation starting ability. It is not necessary and therefore a single-phase coil motor with one pole pair may be used.

The rotation speed control unit adjusts the magnitude and phase of the voltage / current supplied to the coil by the output signal obtained by comparing the measured value and the set value of the rotation speed of the rotor, and thereby the AC synchronous current of the coil.・ When the voltage is controlled and the rotor speed becomes higher than the set value, braking torque acts on the rotor with permanent magnets by the motor's power generation / braking function, so the speed is reduced to the set value and becomes constant. .. When the rotation speed becomes lower than the set value, electric torque is applied to the rotor by the electric function of the motor, and the rotor is accelerated to the set speed and becomes constant.

Since the response speeds of the motor and the rotation speed control unit are fast, even if the cutting torque of the rotor suddenly changes during the tooth cutting process, the fluctuation of the rotation speed of the rotor can be suppressed to such a degree that there is no practical problem. ..

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a rotation speed control device for an air turbine type handpiece according to 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 type of handpiece in which a shaft 13 of a rotor 1 is supported by a ball bearing 2 inside a housing 3 of the head portion. Indicates.

The rotor 1 is provided with turbine blades 11 on the outer periphery thereof, and compressed air is injected into the turbine blades 11 from an air supply pipe 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 attached to the inner surface of the housing near the outer circumference of the turbine blade 11 at positions facing each other around the rotation axis of the rotor 1. The coils 71 and 72 may be formed by winding a number of thin copper wires,
It consists of a thin conductor layer wound on a printed circuit board.
This is preferable because the entire coil can be easily mounted and arranged on the inner surface of the housing.

FIG. 2A shows the rotor 1 of the head portion of FIG.
In this example, the rotor 1 itself is formed of a ferromagnetic permanent magnet, and is magnetized into a pair of magnetic poles in the radial direction of the rotor to become a rotor.
The stators 1 and 72 constitute a single-phase permanent magnet synchronous motor unit. The permanent magnet has a large coercive force even if the rare earth cobalt magnet is small, and is convenient for forming a turbine blade shape.

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

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

The rotation speed control unit 6 of the present invention controls the motor unit. In the following description, first, a current control system for controlling the alternating current supplied to the coil 7 of the motor unit 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 to input the rotation speed difference signal A.
-B is generated, and the calculation unit 6 is operated by the difference signal (A-B).
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 synchronization signal detecting section 65 detects the AC excitation voltage D and generates the synchronization signal C having a constant amplitude. Input to the calculation unit 63. Since the AC excitation voltage D generated in the coil 7 is in synchronization with the rotating magnetic field of the magnetized rotor, the synchronization signal C is also always in the synchronization state. If it is a multiplier that calculates the product of the difference signal (A−B), the current control unit 64 receives the synchronized product signal C × (A−B) and outputs an alternating current proportional to the product signal. Supply to the coil 7.

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

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

In the use of this device, when the turbine rotor is rotating at a constant speed equal to the preset value set in the rotary speed setting section 61, the actual speed signal B and the set signal A are equal to each other. The difference signal (A-
B) becomes zero, the current control unit 64 is in the current cutoff state, no current flows through the coil 7, and the motor unit does not operate (this state corresponds to the no-load power generation state).

When the rotation speed of the turbine rotor becomes lower than the set value during use of the handpiece, the actually measured rotation speed B of the rotation speed detection unit 66 becomes smaller than the set value A. In this example, the difference signal (A-B) becomes a positive value, for example, and the product signal C × (A-B) from the calculation unit 63 causes the current control unit 6 to
4 is a positive torque angle in the coil 7 of the motor, preferably 1/2
A synchronous alternating current of π is supplied to give an electric torque to the rotor to accelerate the rotation. The current supplied to this coil 7 is
It is in phase with the phase of the voltage generated by the coil in the no-load power generation state.
In this speed-up process, as the rotor rotation speed approaches the set rotation speed, the difference signal (AB) becomes smaller and the supply current to the coil 7 also becomes smaller.

On the other hand, when the number of rotations of the rotor becomes larger than the set value, the reverse operation is performed and the difference signal (AB) becomes a negative value, for example, and the product signal C × (A− B)
Phase inverts, and the current control unit 64 controls the coil 7 of the motor unit.
Since a synchronous AC current having a negative torque angle, preferably −1 / 2π, is supplied to the motor, the motor section applies a braking torque to the rotor to decelerate the rotor rotation speed to a set value. In this braking process, the current supplied to the coil 7 is in a phase opposite 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 the input signal to the synchronizing signal detecting section 65 of the rotation speed control section 6, but as shown in FIG. An example in which a signal from the synchronization sensor 9 for detecting the rotation signal of No. 1 is input to the synchronization detection unit 65 so that the motor unit is a permanent magnet brushless motor will be described below.

As an example of the synchronous sensor 9, as shown in FIG. 2 (A), 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 such that 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 rotor 1 which is permanently magnetized.
Although a synchronous alternating current proportional to the magnetic field strength of the rotating magnetic field is output, the signal voltage of the Hall element 91 does not depend on the rotation speed. FIG. 4 shows 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, but the output signal D ′ from the hall element 91 is a synchronization circuit including a filter and an amplifier. The signal detector 65 causes the synchronization signal C
Is obtained and input to the multiplier of the arithmetic unit 63. The filter has harmonic components that result from the non-sinusoidal nature of the rotating magnetic field of the rotor,
A reducing pass filter (LPF) for removing a high frequency component due to a high frequency magnetic field formed by rotation of a magnetic focusing portion at each tip of each blade of a rotor blade of a rotor. A synchronization signal C is a fundamental wave synchronized with rotor rotation. A sine wave is obtained.

The synchronizing signal C is used as the rotation speed signal D, and the rotation speed detecting unit 66 composed of a frequency-voltage (FV) converter obtains a DC rotation speed measurement signal B whose voltage is proportional to the frequency.
Input to the comparison unit 62. As a frequency-voltage converter,
A method of differentiating the sine wave of the rotation speed signal D with a differentiating circuit to obtain a direct current with a rectification-smoothing circuit, or generating a trigger pulse for each phase inversion of the sine wave of the rotation speed signal D, to obtain a monostable FF.
A method is used in which a pulse is generated by a circuit with a constant time width and smoothed to obtain a DC voltage.

In the rotation speed setting unit 61, the rotation speed is set by the variable resistor VR, and the difference signal (A-
B), and the product signal C × (A−
B) is obtained. The current control unit 64 may be a low-frequency power amplifier, but in this example, the directly connected output transistor is switched in every half cycle of the input signal C (AB) to generate an alternating current proportional to the input signal. A current is supplied to the coil 7 to control the current of the coil.

Instead of the hall element 91, the synchronous sensor 9 may use a magnetoresistive element, an optical sensor, or a coil for detecting a rotating magnetic field. The detection coil 9
FIG. 5 shows an example of the arrangement of No. 3 of the rotor 1. A small disk-shaped permanent magnet 92 is surface-mounted 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 permanent magnet disk 92 also rotates due to the rotation, 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 is substantially a sine wave and has less harmonic components, and the output can be arranged so that the influence of the magnetic field of the motor can be ignored.
The sync detector 65 may be provided with a filter and a sync oscillator or a sine wave shaping circuit capable of obtaining a sync signal C having a constant amplitude. Since the voltage of the output signal from the detection coil 93 is proportional to the rotation speed of the rotating magnetic field, this output signal is used by the rotation speed detection unit 66 for the rotation speed actual measurement signal B by using the DC signal smoothed after the double-wave rectification. May be. 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.

Further, 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 is the rotation of the rotor. It is easy to satisfy the condition of the optimum torque angle ± 1/2 π 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 section has been described, but a voltage control method for controlling the alternating voltage supplied to the coil 7 may be employed at least in the electric process. .. FIG. 6 shows a circuit diagram of a main part of the rotation speed control unit 6 of the voltage control system. The current control unit 64 in the figure constitutes a voltage feedback type operational amplifier, and the current control unit in the motor drive process controls the current. The unit 64 supplies a synchronous AC voltage proportional to the product signal C × (A−B) from the multiplier 63 to the coil 7 to generate electric torque. On the other hand, in the braking process, currents of opposite phases are supplied to the coil 7 to generate 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 in the braking process. For this purpose, resistors are inserted in the connection 73 of the coil 7. You may.

Further, FIG. 6 shows an example in which the synchronizing signal C is output to the synchronizing signal detecting section 65 by utilizing 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). Excitation voltage D from coil and current supplied to coil
Since the phase difference from the voltage is about 1 / 2π, the phase shifter φ adjusts the phase of the synchronizing signal C by delaying the phase of the excitation voltage D by about 1 / 2π to obtain the above-mentioned best torque angle. It is a thing. This phase shift may be performed additively by the filter (LPF) and the phase shifter φ, or the filter (LPF) may double as the phase shifter φ.

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

Further, in FIG. 2B, the outermost part of the housing 3 is made of a non-magnetic material such as austenite stainless steel, and the soft magnetic material constituting the yoke 32 is provided inside the housing 3.
For example, a silicon steel plate or a ferrite porcelain ring is used for the interior. Further, the inner layer portion 33 is lined with a hard synthetic resin.

Although the ball bearing type handpiece is exemplified in the above embodiment, the rotation speed control device of the present invention is
It can be applied to an air bearing type handpiece in exactly the same manner. In addition to the contra-angle handpiece of the above embodiment, the present control device can be applied to straight handpieces.

A schematic diagram of the rotational torque-rotational speed characteristic diagram of the rotor of the handpiece provided with the rotational speed control device of the present invention,
As shown in FIG. In the figure, a curve shows static characteristics when the rotation speed is not controlled and the pressure of the air pipe 4 to the turbine blade 11 is controlled to be constant, and ω _t is a cutting tool of the handpiece. Is the number of revolutions when there is no load when is idle.

When the set rotation speed is set to ω ₂ and the rotation speed control device is operated, the characteristic is that the torque of the cutting tool, that is, the rotation torque of the rotor fluctuates as shown by the curve b _2. In the torque control range, the rotation speed is kept substantially constant at the set rotation speed ω ₂ . Practically, when performing light cutting on a tooth at high speed, by setting the set speed ω ₃ as shown by the b ₃ curve, almost constant rotation speed can be obtained between idling and cutting of the cutting tool. Be done. In particular, since the control system of this device has a high response speed, it is possible to follow a sudden change in the load torque of the cutting tool, and the change in the rotation speed can be reduced.

The difference signal (A-B) from the comparison unit 62
The pressure control valve 4 by the pneumatic control unit 43 in FIG.
It is also possible to perform proportional control of the outlet side pressure of 1. 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 compressed air control unit 43 adjusts the generated torque of the turbine blade 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, the rotor of the head portion of the handpiece is provided with the brushless motor portion, and the motor portion drives the rotor by detecting the rotation speed variation due to the load torque variation of the rotor. Torque and braking torque can be applied to compensate for the air turbine torque and control the rotation speed to be almost equal to the set rotation speed. Since the response speed of this control system is high, it can Even if there is a rapid change in the cutting torque, the change in the rotor speed can be suppressed to a small level.

During the light cutting work, the work can be performed at a constant high speed even during idling and cutting of the cutting tool. Therefore, the sharpness peculiar to this type of air turbine handpiece is exhibited. Therefore, a clean cutting tooth surface can be realized regardless of the cutting load.

A sudden stop of the cutting tool at the beginning of the cutting and a high speed idling at the end of the cutting can be prevented by exerting a sudden acceleration or a rapid deceleration of the motor part, and it is not necessary to wait for the recovery of the rotational speed after the sudden stop. It is possible to perform cutting treatment promptly and safely for the practitioner without having to worry about an unexpected situation caused by high-speed spinning.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a head portion of an air turbine type handpiece.

2 is a cross-sectional view (A, B) of the head portion of FIG.

FIG. 3 is a block tire gram 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 including a synchronization sensor.

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

FIG. 7 is a rotation torque-rotation speed characteristic diagram of the rotor.

[Explanation of sign]

 1 Rotor 11 Turbine Blade 12 Permanent Magnet Piece 13 Rotor Axis 2 Ball Bearing 3 Housing 4 Air Pipeline 6 Rotation Speed Control Section 7 Coil 9 Synchronous Sensor

Claims (5)

[Claims] 1. A rotational speed control device for a dental air turbine type handpiece comprising a drive unit for a dental handpiece, which comprises a rotor including turbine blades that rotate by jetting pressurized air and a housing that surrounds and supports the rotor. In, the whole or part of the rotor including the turbine blade is made a permanent magnet, the coil is arranged and held in the housing to form a brushless motor section, and the synchronous current or the synchronous voltage of the coil is controlled, Rotational speed control of a dental air turbine type handpiece characterized by having a rotational speed control section for automatically maintaining the rotational speed of the rotor at a rotational speed near a set value by an electric function and a power generation function or a braking function of the motor section. apparatus. 2. The rotation speed control unit detects and outputs a synchronization signal synchronized with the rotation of the permanent magnet, a synchronization signal detection unit, a rotation speed detection unit that detects the rotation speed of the rotor, and a rotation speed setting unit. And a comparison unit that outputs a difference signal between the rotation speed measurement signal from the rotation speed detection unit and the rotation speed setting signal from the rotation speed setting unit, and a coil control signal from the difference signal and the synchronization signal. 2. The rotation number control device for a handpiece according to claim 1, further comprising: a calculation unit for controlling the supply current or the supply voltage of the coil according to the coil control signal. 3. The synchronization signal detecting section uses an excitation voltage of the coil as an input signal, and includes a phase shift means, and a supply current or a supply voltage of the coil from the excitation voltage by the phase shift means. 3. The synchronizing signal adjusted to a desired torque angle of the motor section is output.
A rotation speed control device for the handpiece described. 4. The rotation number control device for a handpiece according to claim 1, wherein the coil is a conductor attached to and wound on a printed circuit board. 5. The handpiece according to claim 1, wherein a yoke made of a soft ferromagnetic material is provided integrally with the housing or as a separate body inside the housing, and around the outside of the turbine blade. Speed controller.