JP6952408B2 - A drive device for a brushless motor, a brushless motor, and a medical handpiece using the brushless motor. - Google Patents

Description

The present invention relates to a sensorless DC brushless motor that detects the position of the rotor with respect to the stator coil without using a sensor such as a Hall element. In particular, motor control capable of detecting the position of the rotor even in a low-speed rotation region. The present invention relates to a device, a brushless motor using this motor drive device, and a medical handpiece using this brushless motor.

Conventionally, a DC brushless motor (hereinafter, brushless motor) has been used as a drive source for a medical handpiece (hereinafter, handpiece) widely used for dental and surgical treatment. The handpiece cuts teeth and bones, and has a blade that rotates and cuts at the head portion. This blade is called a file or reamer and is a cutting tool.
Such handpieces need to be sterilized in advance to prevent infection to the patient or user during use. Therefore, the drive brushless motor used to rotate the blade of the handpiece is required to have performance capable of withstanding sterilization.
An autoclave is generally used for the sterilization process of such a handpiece. An autoclave is a device that sterilizes a handpiece by having a space inside the device to hold the handpiece, filling the space with water vapor of about 120 to about 135 degrees Celsius, and keeping it in a high temperature and high pressure state. ..

However, in a brushless motor that detects the relative position of the magnetic poles of the rotor magnet with respect to the stator coil using a magnetic pole position sensor such as a Hall element and drives the rotation based on this, the magnetic pole position sensor and its peripheral circuits have a high temperature.・ There is a risk of deterioration and failure due to high-pressure steam.
Therefore, as the drive motor used for the medical handpiece, a sensorless brushless motor that performs rotational drive control without using a magnetic pole position sensor is desired.

To control this sensorless brushless motor, there is a method of utilizing the counter electromotive voltage generated in the stator coil by the rotation of the rotor magnet. Although this method is relatively simple, it cannot be used because it is difficult to detect because the counter electromotive voltage becomes extremely small in the low speed region.
Therefore, for applications that drive in a low speed region, the phenomenon that the inductance of the stator coil changes depending on the position of the rotor is used.
Since the change in inductance occurs depending on the position regardless of the rotation speed of the rotor, it can be used at rest and in a low speed region. Various methods have been proposed for position sensorless control at rest and in a low speed region.

For example, in Patent Document 1, a short pulse current is sequentially passed through the stator coil in the forward and reverse directions, the induced voltage appearing in the non-energized phase is synthesized in the forward and reverse directions, and the current-carrying phase is determined based on the polarity determination of the induced voltage. The method of determining is disclosed.
Further, Patent Document 2 discloses a method of identifying a rotor stationary position based on a difference in kickback time caused by a difference in inductance that slightly changes depending on a difference in the stationary position of the rotor by passing a short pulse current. Has been done.
Further, Patent Document 3 discloses a method in which a motor is energized for a short time, a voltage induced in a coil in a non-energized phase is detected, and a magnetic pole position of a rotor is detected from the amplitude of the induced voltage.
Further, Patent Document 4 discloses a method of detecting a voltage induced in a coil of a non-energized phase, comparing it with a reference voltage, and switching the energized phase according to the result.

Japanese Unexamined Patent Publication No. 2001-275387 Japanese Unexamined Patent Publication No. 2002-335691 Japanese Unexamined Patent Publication No. 2003-189674 Japanese Unexamined Patent Publication No. 2009-189176

However, in the handpiece used in dentistry and surgery by the method disclosed in each patent document, there are various problems when the brushless motor for driving is driven at a low speed.
In the method disclosed in Patent Document 1, a short pulse current is sequentially passed through the stator coil in the forward and reverse directions. Therefore, if this is used for low-speed driving, a period opposite to the desired current flows. There is a problem that smooth operation is hindered due to the occurrence of.

Further, in the method disclosed in Patent Document 2, a short pulse current is passed, and a difference in kickback time caused by a difference in inductance that slightly changes due to a difference in the stationary position of the rotor is detected. This kickback time not only changes depending on the difference in the stationary position of the rotor, but also changes depending on the load during low-speed driving.
Therefore, there is a problem that it is difficult to apply it to a motor for driving a handpiece used in dental and surgical treatments, which has a load fluctuation related to cutting by a blade.

Further, in the methods disclosed in Patent Documents 3 and 4, the voltage induced in the coil of the non-energized phase is detected, and the amplitude thereof is referred to or compared with the reference value. The detection accuracy is easily affected by the variation of the stator coil that occurs.
Therefore, there is a problem that it is necessary to correct the value for each motor or each phase in order to suppress the influence of manufacturing errors and variations.

In particular, for dental and surgical handpieces that are used to control the rotation of the blade by driving a brushless motor at a low speed and gradually adjust the degree and degree of cutting of teeth and bones. When there are the above problems, it becomes difficult for the user to perform delicate operations.

The present invention is for solving the above-mentioned problems, and when the position of the rotor is detected by utilizing the phenomenon that the inductance of the stator coil changes depending on the position of the rotor, a current flows through the stator coil in one direction. After that, it is not necessary to flow in the opposite direction, and it is an object of the present invention to provide a driving method for smooth operation at a low speed.

In order to solve the problem, in a motor drive device that controls a brushless motor that is rotationally driven by three phases, a drive means that energizes the three phases, a control means that controls the drive means, and terminals of either phase. A voltage detecting means for detecting a voltage and a storage means for storing a detection value of the voltage detecting means are provided, and as a first state, in a state in which two of the three phases are energized to form an energized phase. , The voltage detecting means detects the first voltage of the non-energized phase among the phases and stores it in the storage means, and as the second state, the voltage in the state where all the phases are not energized. The detecting means detects the second voltage of the phase that was the non-energized phase in the first state and stores it in the storage means, and the controlling means is based on the first voltage and the second voltage by the driving means. If the energized phase is switched and the voltage detecting means is configured to detect the second voltage while the recirculation current continues to flow through the brushless motor after switching from the first state to the second state. good.

According to the present invention, in driving a sensorless brushless motor, when the position of the rotor with respect to the stator coil is detected by utilizing the phenomenon that the inductance of the stator coil changes depending on the position of the rotor, the motor terminal voltage is referred to. Since the position is detected by capturing the change in the inductance of the stator coil, the drive control can be performed at a low speed regardless of the change in the motor current due to the load fluctuation.

Schematic of a brushless motor and dental handpiece connected to a motor drive Circuit diagram of the drive unit and the brushless motor connected to this drive unit Schematic diagram showing the relationship between the rotor magnet and each phase in a brushless motor Graph showing the change of the inductance of each coil with respect to the angle θd of FIG. This is an example of the energized state of the motor, and is an equivalent circuit showing a state in which the V phase and the W phase are energized and the U phase is de-energized. Graph of neutral voltage with respect to rotor magnet phase Flowchart showing control steps of forward / reverse rotation control of motor Equivalent circuit of inverter and motor indicating the state where the U phase is the non-energized phase Equivalent circuit in the state immediately after turning off all switching elements from the state shown in FIG. A graph showing the state of the motor terminal voltage in the states of FIGS. 8 and 9. A graph showing how the first voltage and the second voltage, which are the neutral point voltages, are sampled from the motor terminal voltage. A graph showing the counter electromotive voltage generated in the U-phase, V-phase, and W-phase stator coils due to the rotation of the rotor magnet. A graph showing how the counter electromotive voltage of FIG. 12 is superimposed on the U-phase terminal voltage of FIG. A graph showing the waveform when voltage Vd is applied to both ends of a general coil and cutoff is repeated.

Hereinafter, embodiments of the invention will be described with reference to the drawings.
FIG. 1 shows a motor drive device M (hereinafter, drive device M) of the present invention, a sensorless DC brushless motor 4 (hereinafter, motor 4) driven by the drive device M, and a dental hand to which the motor 4 is connected. It is a figure which shows the schematic structure of piece H (hereinafter, handpiece H).
The handpiece H transmits the rotational torque obtained by the motor 4 to the blade Ha located at the front end head, and rotationally drives the blade Ha. The user grasps the handpiece H and cuts teeth and the like with a rotating blade Ha.

FIG. 2 shows a circuit diagram of the drive device M of the present invention and the motor 4 connected to the drive device M.
The drive device M includes an inverter 1, a control means 3, and a rotor position detection circuit 5 (hereinafter, position detection circuit 5). The control means 3 has a storage means. The motor 4 has three-phase stator coils Lu, Lv, Lw (hereinafter, coils Lu, Lv, Lw) and is connected to the inverter 1.
The inverter 1 is a driving means of the motor 4 and has six switching elements (U +, U−, V +, V−, W +, W−). The DC power supply 2 supplies the voltage Vd to the inverter 1. The control means 3 is a controller of the inverter 1, and turns on and off six switching elements as appropriate. As a result, the currents flowing through the coils Lu, Lv, and Lw change appropriately, and the rotor rotates.

The position detection circuit 5 is a circuit for detecting the relative position of the magnetic pole of the rotor magnet 4a with respect to the coils Lu, Lv, Lw in the motor 4, and the terminal connected to the coils Lu, Lv, Lw of the motor 4 and the inverter 1 Connect between. Further, the position detection circuit 5 includes voltage dividing circuits 5a, 5b, 5c and amplifiers 5d, 5e, 5f.
The voltage dividing circuits 5a, 5b, and 5c are voltage detecting means for detecting the motor terminal voltages Vu, Vv, and Vw. The voltage dividing circuits 5, 6 and 7 set the motor terminal voltages Vu, Vv and Vw to low voltages, respectively, and output the voltage signals S1, S2 and S3 to the control means 3. The control means 3 stores the input voltage signals S1, S2, and S3 in the storage means, and detects the center voltages Vn and Vn'described later based on the stored voltage signals S1, S2, and S3.
The amplifiers 5d, 5e, 5f amplify the interphase voltage of the motor terminal voltages Vu, Vv, Vw, and output the voltage signals S4, S5, S6 to the control means 3. The control means 3 stores the input voltage signals S4, S5, S6 in the storage means, and detects the counter electromotive voltages eu, ev, and ew based on the stored voltage signals S4, S5, and S6.

That is, the position detection circuit 5 detects the motor terminal voltages (Vu, Vv, Vw) corresponding to the coils of the three phases, and compares the voltages between the coils. Then, the detected signal related to the motor terminal voltage or the like is output to the control means 3. The control means 3 stores the detected value and the like related to the terminal voltage in the control means. The control means 3 controls the inverter 1 based on these detection signals to control the drive of the motor 4.
Vu is the U-phase terminal voltage, Vv is the V-phase terminal voltage, and Vw is the W-phase terminal voltage. Further, eu is a counter electromotive voltage generated in the U phase, ev is a counter electromotive voltage generated in the V phase, and ew is a counter electromotive voltage generated in the W phase.

Next, FIG. 3 is a schematic view showing the relationship between the rotor magnet 4a and each phase (U phase, V phase, W phase) in the motor 4. The angle θd indicates the angle formed by the U-phase coil Lu and the rotor magnet 4a. In other words, the angle θd is the angle of inclination of the magnetic pole direction straight line of the rotor magnet 4a with respect to the straight line connecting the rotation center of the rotor of the motor 4 and the magnetic center of the U-phase coil.

Next, FIG. 4 is a graph showing the change of the coil inductance with respect to the angle θd with time. That is, FIG. 4 shows how the coil inductance of each coil of the motor 4 changes depending on the value of the angle θd. Lu indicates the inductance of the U phase, Lv indicates the inductance of the V phase, and Lw indicates the inductance of the W phase.
The coil inductance (Lu, Lv, Lw) fluctuates so as to have a peak of 2 degrees between 0 degrees and 360 degrees when the motor 4 makes one rotation due to the influence of the magnetic flux of the rotating rotor magnet 4a.
Since the coil inductance fluctuates depending on the position of the rotor magnet 4a, the position of the rotor magnet 4a with respect to the stator coil can be detected by capturing this change. It should be noted that the actual change in the inductance of the motor 4 does not become a smooth sine wave due to the influence of magnetic flux saturation and the like, but it is shown schematically.

Here, in order to detect the change in the coil inductance, there is a method of comparing the length of the kickback time caused by the motor current as shown in Patent Document 2.
When the switching element of the inverter is turned off after the motor coil is energized, a kickback voltage is generated until the energy stored in the inductance of the coil is exhausted. As the inductance increases, the kickback time increases, so the position of the rotor magnet can be detected by comparing the length of the kickback time.
However, since the kickback time is also generated by the fluctuation of the motor current due to the increase or decrease of the motor load, it is difficult to apply the kickback time when the load fluctuates while driving the motor.

Therefore, as a method that is not affected by the change of the current flowing through the motor 4, there is a method of detecting the neutral point voltage Vn, Vn'of the motor 4 and detecting the change in the inductance of the motor 4.
The neutral point voltages Vn and Vn'are determined by the inductance ratio of the two phases of the energized phase immediately after the switching element of the inverter is turned on and off. Since the inductance ratio changes depending on the position of the rotor magnet 4a, the position of the rotor magnet 4a can be detected by capturing the changes in the neutral point voltages Vn and Vn'.
In the 120-degree energization control, when two of the three phases of the motor 4 are energized and no current is flowing through the coil of the non-energized phase, the neutral point voltage Vn, Vn'and the motor terminal of the non-energized phase The voltage is the same. In the present invention, the motor terminal voltage of the non-energized phase in a state where no current is flowing through the coil of the non-energized phase is detected, and the position of the rotor magnet 4a is detected based on this.

FIG. 5 shows an example of the energized state of the motor 4, showing a state in which the V phase and the W phase are energized and the U phase is de-energized. A voltage Vd is applied in the circuit.
In particular, FIG. 5A shows an equivalent circuit in a state where the switching elements V + and W− of the inverter 1 are turned on. Further, FIG. 5B shows an equivalent circuit in a state where the switching elements V− and W + of the inverter 1 are turned on.

The current flowing through the motor 4 flows from the V phase to the W phase coil in FIG. 5 (a), and flows from the W phase to the V phase in the state of FIG. 5 (b). That is, in the case of the state of FIG. 5 (b), the direction of current flow is opposite to the direction of current flow in the state of FIG. 5 (a).
At this time, no current flows in the U phase and it becomes a non-energized phase, and the neutral point voltage Vn and the U-phase motor terminal voltage Vu are the same. As described above, the coil inductance (Lu, Lv, Lw) changes as shown in FIG. 4 depending on the angle θd of the rotor magnet 4a.

Lv is represented by Equation 1 and Lw is represented by Equation 2. Here, L0 indicates a fixed value in which the inductance does not change, and L1 indicates a swing width in which the inductance changes. The actual inductance is the sum of the two.
Lv = L0-L1 · COS (2 (θd-2π / 3)) ---- Equation 1
Lw = L0-L1 · COS (2 (θd + 2π / 3)) ---- Equation 2

At this time, the neutral point voltage Vn is represented by Equation 3 in the energized state of FIG. 5 (a) and by Equation 4 in the energized state of FIG. 5 (a).
Vn = Lw / (Lv + Lw) ・ Vd ---- Equation 3
Vn'= Lv / (Lv + Lw) ・ Vd ---- Equation 4

FIG. 6 is a graph of the neutral point voltage with respect to the phase of the rotor magnet 4a. That is, FIG. 6 is a graph of Equations 3 and 4.
When θd is in the range of −30 degrees to +30 degrees, the non-energized phase is defined as the U phase. At this time, a voltage of Vn or Vn'appears in Vu depending on the direction of the current flowing through the motor 4.
The rotary drive of the motor 4 will be described. The control means 3 detects Vn and Vn'at this time and records them in the storage means, with the phase immediately after switching from one energized phase to another energized phase as θd1. Further, the amplitude A obtained by subtracting Vn'from Vn is recorded.

After that, Vn and Vn'are detected periodically and continuously, and Vn'is subtracted from Vn each time to calculate the amplitude B. When θd moves to θd2, the amplitude B has the opposite polarity to the amplitude A and has the same absolute value. When this condition is satisfied, the energizing phase is switched.
Generally, in 120-degree energization control, the energizing phase is switched every 60 degrees according to the position of the rotor magnet 4a. Therefore, when the above operation is repeatedly executed, the energizing phase changes every 60 degrees according to the position of the rotor magnet 4a. The motor can be driven to rotate.

Next, the forward / reverse rotation control of the motor 4 will be described with reference to FIG. 7. FIG. 7 is a flowchart showing a control step of forward / reverse rotation control of the motor 4.
Since the motor 4 of the present embodiment does not have a rotor position detecting means such as a Hall element, the initial position of the rotor magnet 4a cannot be estimated in a state where it is not rotationally driven. Therefore, the control means 3 obtains the position of the rotor magnet by using the initial position estimation method known in STEP1. As an initial position estimation method, for example, there is a method in which a pulse current that does not move the rotor is passed through the stator coil, the voltage of each rotor is detected, and estimation is performed based on the pulse current.

Next, in STEP 2, the control means 3 outputs an energization signal to the inverter 1 according to the position of the rotor magnet 4a to energize a predetermined stator coil. At this time, rotational torque is generated in the motor 4.
Next, in STEP 3, the position detection circuit 5 detects the motor terminal voltage of the non-energized phase and outputs it to the control means 3. When no current is flowing in the non-energized phase, the control means 3 detects and records Vn and Vn'because the motor terminal voltage is the same as the neutral point voltage.

Next, in STEP 4, the control means 3 subtracts Vn'from Vn to obtain the amplitude A, records the amplitude A in the storage means, and is the value obtained by subtracting Vn'from this Vn larger than the amplitude A? to decide.
When the value obtained by subtracting Vn'from Vn is larger than the amplitude A as shown on the left side of θd1 in FIG. 6, the process proceeds to STEP7. In this case, since the motor is rotating in the opposite direction in which θd decreases, in STEP 7, the control means 3 controls the inverter 1, switches to the energized phase suitable for the reverse direction, and shifts to STEP 2. In the example shown in the figure, it is U + and W−.

Next, when the value obtained by subtracting Vn'from Vn is smaller than the amplitude A, the process proceeds to STEP5. On the right side of θd2 in FIG. 6, the amplitude B obtained by subtracting Vn'from Vn is larger than the already recorded absolute value of the amplitude A, and the polarity is opposite.
In STEP 5, it is determined whether or not this condition is satisfied. If it is established, the motor is rotating in the positive direction in which θd increases, so that the motor shifts to STEP8, the control means 3 switches to the energized phase matching the forward rotation direction, and shifts to STEP2. In the example shown in the figure, V + and U− are ON for the switching element.
If it is not established, the process shifts to STEP 6 and shifts to STEP 2 without switching the energized phase. By repeating the above processing, the control means 3 drives and controls the motor 4 in the forward rotation and the reverse rotation.

Next, sampling of Vn and Vn'will be described.
In the example of FIG. 5 described above, in order to obtain Vn, Vn', it is necessary to energize V +, W− and V−, W + in the forward and reverse directions. However, as described in the problem of Patent Document 1, if the short pulse current is sequentially passed in the forward direction and the reverse direction, a period in which the current opposite to the desired current for rotating the motor flows is generated, so that the smoothness is achieved. It may interfere with the rotation operation. Therefore, in order to solve this problem, we focus on the motor terminal voltage at the kickback time.

FIG. 8 shows an equivalent circuit of the inverter 1 and the motor 4 showing a state in which the U phase is a non-energized phase. FIG. 8 shows the switching elements U + and U− of the inverter 1 omitted, and shows a state in which V + and W− are turned on.
The arrow indicates the flow of the current flowing through the motor 4, and the current is flowing from the V-phase coil to the W-phase coil.

FIG. 9 shows a state immediately after all the switching elements are turned off from the state of FIG. Since energy is stored in the coil inductance of the motor, the reflux current continues to flow for a short time even if all the switching elements are turned off.
The arrow in the figure indicates the path through which the reflux current flows. From the state of FIG. 8, the current continues to flow from the V-phase coil to the W-phase coil, but flows into the switching elements W + and V- from the opposite direction.

The state of FIG. 8 is represented by the equivalent circuit of FIG. 5 (a), and the state of FIG. 9 is represented by the equivalent circuit of FIG. 5 (b). That is, in order to obtain Vn and Vn', the equivalent circuit is the same when the V +, W− and V−, W + are energized in the forward and reverse directions and while the reflux current continues to flow.
Therefore, if Vn'is sampled and recorded during the period in which the reflux current is flowing, it is not necessary to energize in the opposite direction, and the motor can be driven smoothly.

Here, the state in which two of the three phases are energized to form the energized phase is defined as the first state. In the first embodiment, the first state is a state in which the V phase and the W phase are energized and the U phase is not energized. The center point voltage Vn in the first state is referred to as the first voltage Vn.
The second state is a state in which none of the three phases is energized (non-energized state). The center point voltage Vn'in the second state is referred to as the second voltage Vn'.

FIG. 10 is a graph showing the states of the motor terminal voltage (Vu, Vv, Vw) and the current (Iu, Iv, Iw) in the states of FIGS. 8 and 9.
The period of t1 is the first state, and the switching elements V + and W− are turned on. At this time, Vv = Vd, Vw = 0, and Vu = Vn.
The period of t2 is the second state, and the reflux current flows immediately after the switching elements V + and W− are turned off. At this time, Vv = 0, Vw = Vd, and Vu = Vn'.
The period of t3 is the second state in which the switching element is off, but no reflux current is flowing. Periods t1, t2, t3 are repeated to detect Vn and Vn'.

FIG. 10A shows the relationship between Vn and Vn'when Lw> Lv, and Vn>Vn'. FIG. 10B shows the relationship between Vn and Vn'when Lw <Lv, and Vn <Vn'. FIG. 10C shows the relationship between Vn and Vn'when Lw = Lv, and Vn = Vn'= Vd / 2.
In this way, the change in inductance, that is, the position of the rotor magnet 4a can be detected by comparing Vn and Vn', so that the voltage induced in the coil of the non-energized phase can be detected as in Patent Documents 3 and 4. It is not necessary to refer to the amplitude or compare it with the reference value, and it is possible to suppress the influence of the variation of the stator coil caused by the manufacturing error.

FIG. 11 shows how Vn and Vn'are sampled from the motor terminal voltage. Let P1 be the sampling point of Vn and P2 be the sampling point of Vn'.
When sampling Vn', immediately after switching from the period t1 which is the first state to the period t2 which is the second state, ringing occurs in the actual circuit, so it is detected at the sampling point P2 which avoids this. Record.
Further, during the period of t2, the reflux current gradually decreases, but the value of Vu gradually approaches Vd / 2, and at the same time as the period of t3 starts, the significant difference caused by the fluctuation of the inductance disappears.
Therefore, it is necessary to set the sampling point P2 as early as t2. On the other hand, the sampling point P1 when sampling Vn should be as close to the end of the period t1 as possible.

The reason for setting the sampling points P1 and P2 as described above is as follows.
FIG. 12 shows the counter electromotive voltages eu, ev, and ew generated in the U-phase, V-phase, and W-phase stator coils by the rotation of the rotor magnet 4a. When the non-energized phase is the U phase, the counter electromotive voltage eu is superimposed on the U phase terminal voltage.
FIG. 13 shows how the counter electromotive voltage of FIG. 12 is superimposed on the state of the U-phase terminal voltage of FIG.
The amplitude of the counter electromotive voltage increases in proportion to the number of revolutions. If the sampling interval between the sampling point P1 and the sampling point P2 becomes wide while the amplitude of the counter electromotive voltage increases, the difference in the counter electromotive voltage generated during this period increases, causing an error in the detection of the sampling point P1 and the sampling point P2. ..
In order to avoid this, the sampling point P1 is set as close to the end of the period t1 as possible to reduce the time difference from the sampling point P2.

FIG. 14 shows a waveform when a voltage Vd is repeatedly applied and cut off at both ends of a general coil. During the period of t4 and t6 where the coil current is changing, a self-induced voltage is generated in the coil. At this time, as shown in FIG. 5, the neutral point voltage Vn when two coils are connected in series is represented by the equation 3.
On the other hand, during the periods t5 and t7 of FIG. 14, since the coil current does not change, the self-induced voltage of the coil does not occur. At this time, as shown in FIG. 5, the neutral point voltage Vn when two coils are connected in series is represented by the equation 5. Rw is a W-phase resistor, Rv is a V-phase resistor, and Ru is a U-phase resistor.
Vn = Rw / (Rv + Rw) ・ Vd ---- Equation 5

The voltage difference between Equation 3 and Equation 5 corresponds to the difference between Vd / 2 and the sampling point P1 in FIG. 11, and the same applies to the sampling point P2.
For this reason, since there is a change in the coil current in the early stage of t2, the value is close to Equation 3, but in the latter stage, the value is close to Equation 5 because there is no change in the coil current.
Therefore, it is necessary to set the sampling point P2 as early as t2 in order to capture the significant difference caused by the fluctuation of the inductance.

Further, the periods of t2 and t3, which are non-energized periods, are necessary for detecting Vn and Vn', but as the rotation speed increases, the ratio of the non-energized period to the rotation cycle increases and the speed is controlled. Affects.
Therefore, when the speed increases to some extent, the control is switched to the known sensorless control that does not require a non-energized period. If the known sensorless control is a method that utilizes the counter electromotive voltage generated in the stator coil by the rotation of the rotor magnet 4a, the speed can be increased without any problem because the non-energized period is not required.

In FIG. 2, signals S1, S2, and S3 are referred to before switching to the known sensorless control, and signals S4, S5, and S6 are referred to after switching to the known sensorless signal. The signals S1, S2, and S3 are voltages for detecting the neutral point voltage Vn, Vn'by the control means 3 by setting the motor terminal voltages Vu, Vv, and Vw to low voltages by the voltage dividing circuits 5a, 5b, and 5c, respectively. Refer to as a signal.
On the other hand, the signals S4, S5 and S6 are voltages for amplifying the interphase voltage of the motor terminal voltages Vu, Vv and Vw by the amplifiers 5d, 5e and 5f and detecting the counter electromotive voltage eu, ev and ew by the control means 3. Refer to as a signal.

As described above, according to the present embodiment, when driving the sensorless DC brushless motor, the motor terminal voltage is detected when the position of the rotor with respect to the stator coil is detected by utilizing the phenomenon that the inductance of the stator coil changes depending on the position of the rotor. Since the position is detected by capturing the change in the inductance of the stator coil with reference to the reference, it is possible to provide a drive device for a brushless motor capable of performing drive control at a low speed regardless of a change in the motor current due to load fluctuation. ..

In addition, while the reflux current continues to flow in the stator coil of the brushless motor, the terminal voltage is detected, stored, and used for control. Therefore, when the terminal voltage is detected, the current flows in the stator coil in the opposite direction. It is possible to provide a drive device for a brushless motor that does not need to be used and can be driven at a low speed for smooth operation.

In addition, when detecting the position of the rotor of a brushless motor, even if there are variations in the motor caused by manufacturing errors, the voltage amplitude induced in the stator coil is not measured or compared with the reference value, so each motor Alternatively, it is possible to provide a drive device for a brushless motor that does not need to correct the detected value for each phase.

Further, by controlling the drive of the sensorless brushless motor by the drive device of the brushless motor of the present embodiment, it is possible to drive at a stable low speed rotation.

Further, by using the brushless motor driven by the driving device of the brushless motor of the present embodiment as the driving source of the handpiece, when the handpiece is used, the brushless motor is driven at a low speed, and the blade By controlling the rotation, it is possible to use it to adjust the degree and degree of cutting of teeth and bones little by little.
In particular, in medical settings such as dentistry and surgery, the user can perform delicate operations using the handpiece. For example, in dental treatment, when an opening for implanting an artificial tooth root of an implant is formed by cutting into the jawbone, it is necessary to rotate the blade of the handpiece at a low rotation, and the treatment can be performed by using the present invention. It will be easier to do.

Although the present invention has been described in the embodiment used for a medical handpiece, it can be applied to a sensorless brushless motor regardless of the field of use such as medical use or industrial use.

M Motor drive device H Handpiece Ha Blade 1 Inverter (drive means)
2 DC power supply 3 Control means 4 Sensorless DC brushless motor 4a Rotor magnet 5 Rotor position detection circuit 5a, 5b, 5c Pressure division circuit 5d, 5e, 5f Amplification circuit Vu Motor U-phase terminal voltage Vv Motor V-phase Terminal voltage Vw Motor W-phase Terminal voltage Ru Motor U-phase resistance Rv Motor V-phase resistance Rw Motor W-phase resistance Lu Motor U-phase inductance Lv Motor V-phase inductance Lw Motor W-phase inductance Vc Amplification circuit control power supply voltage Vd DC voltage U + Inverter switching element V + Inverter switching element W + Inverter switching element U-Inverter switching element V-Inverter switching element W- Inverter switching element Vn Motor neutral point voltage (first voltage value)
Vn'motor neutral point voltage (second voltage value)
θd Angle formed by U-phase coil Lu and rotor magnet 4a eu U-phase countercurrent voltage ev V-phase countercurrent voltage ew W-phase countercurrent voltage P1 Voltage sampling point P2 Voltage sampling point R General coil resistance IL General Current flowing through the coil VL Self-induced voltage of a general coil

Claims (4)

In a motor drive device that controls a brushless motor that is rotationally driven by three phases,
A driving means for energizing the three phases and
A control means for controlling the drive means and
A voltage detecting means for detecting the terminal voltage of any of the phases, and
A storage means for storing the detected value of the voltage detecting means is provided.
As a first state, in a state in which two of the three phases are energized to form an energized phase, the voltage detecting means is the first voltage of the non-energized phase among the phases. Is detected and stored in the storage means,
As a second state, when all the phases are not energized, the voltage detecting means detects the second voltage of the phase which was the non-energized phase in the first state and stores the memory. Remember in the means,
The control means switches the phase energized by the drive means based on the first voltage and the second voltage .
The voltage detecting means is brushless, which detects the second voltage while the reflux current continues to flow through the brushless motor after switching from the first state to the second state. Motor drive. In a motor drive device that controls a brushless motor that is rotationally driven by three phases,
A driving means for energizing the three phases and
A control means for controlling the drive means and
A voltage detecting means for detecting the terminal voltage of any of the phases, and
A storage means for storing the detected value of the voltage detecting means is provided.
As a first state, in a state in which two of the three phases are energized to form an energized phase, the voltage detecting means is the first voltage of the non-energized phase among the phases. Is detected and stored in the storage means,
As a second state, when all the phases are not energized, the voltage detecting means detects the second voltage of the phase which was the non-energized phase in the first state and stores the memory. Remember in the means,
The control means switches the phase energized by the drive means based on the first voltage and the second voltage.
After the drive means switches the energizing phase to rotationally drive the brushless motor, the control means subtracts the second voltage from the first voltage to obtain a first numerical value, and the storage means. Remember to
After that, the control means subtracts the second voltage from the first voltage, repeatedly obtains the second numerical value, and stores it in the storage means.
The control means is brushless, wherein when the second numerical value has the same polarity and absolute value as the first numerical value, the control means switches to the next energizing phase in order to rotate the motor. Motor drive. A brushless motor that is controlled by the drive device of the brushless motor according to claim 1 or 2. A medical handpiece using the brushless motor according to claim 3.

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