JP2006325311A - Dc brushless motor apparatus and rotary vacuum pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC brushless motor apparatus synchronously driven, even if there is phase difference between the magnetic pole position of a motor rotor and a sensor signal. <P>SOLUTION: Rotational position sensors 47a-47c are synchronized with the rotated rotor, and output gap signals G1-G1, corresponding to a gap between a sensor target 46 integrally rotating along with the motor rotor 62. A delay time calculating section 75 calculates a delay time Δt, based on a rotor rotational frequency f detected by a rotational speed detecting section 74 and a phase angle θ, previously stored in a phase difference storing section 76. A signal delay section 73 corrects the delays in the gap signals G1-G3 based on the calculated delay time Δt, and calculates the rotational position signals S1-S3. A motor driving waveform generating circuit 72 generates a waveform pattern of voltages applied to U, V, W phases in a motor stator 61, based on the rotational position signal S1-S3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a DC brushless motor device and a rotary vacuum pump equipped with the DC brushless motor device.

  The turbo molecular pump (TMP) performs evacuation by rotating at high speed a rotor on which rotor blades are formed with respect to fixed blades. A DC brushless motor is known as a motor for rotating the rotor. In general, in a DC brushless motor, a Hall element is used to detect the magnetic position of the rotor and detect the rotational position of the rotor.

  However, since the Hall element is inferior in radiation resistance and heat resistance to other parts of the pump body, a technique using an inductance sensor instead of the Hall element has been proposed (for example, see Patent Document 1). In this method, instead of directly detecting the magnetic pole of the motor rotor, a target having a concavo-convex surface is mounted on the rotating shaft, and an inductance sensor is arranged so as to face the concavo-convex surface to detect a change in the distance to the target. To detect the rotational position.

JP 2001-231238 A

  However, in the inductance sensor method as described above, when the target is fixed to the rotating shaft, it is necessary to accurately match the phase of the magnetic pole position of the motor rotor and the target. It was difficult to match.

The invention of claim 1 is applied to a DC brushless motor device that generates a motor drive signal based on a rotational position signal that is magnetic pole position information of the motor rotor, and rotates the motor rotor in synchronization with the magnetic pole position by the motor drive signal. , A signal generation means for generating a synchronization signal synchronized with the rotation of the motor rotor, a storage means for storing phase difference information between the synchronization signal and the rotation position signal in advance, and detecting the rotation speed information of the motor rotor based on the synchronization signal A rotation speed detection means, a signal calculation means for calculating a rotation position signal by correcting the synchronization signal obtained during rotation of the motor rotor based on the rotation speed information and the phase difference information stored in the storage means, and a signal Drive signal generation means for generating a motor drive signal based on the rotational position signal calculated by the calculation means To.
According to a second aspect of the present invention, in the DC brushless motor device according to the first aspect, the signal generating means is provided with one sensor for outputting a synchronizing signal, and the signal calculating means is driven by the motor in synchronization with the rotational position signal. When generating the signal, the motor drive signal is generated based on the period of the rotational position signal acquired in the past from the rotational position signal.
According to a third aspect of the present invention, in the DC brushless motor device according to the first or second aspect, the DC brushless motor device further comprises phase difference calculation means for calculating phase difference information based on a back electromotive voltage of at least one phase of the motor stator, and storage means. Stores the phase difference information calculated by the phase difference calculation means.
According to a fourth aspect of the present invention, in the DC brushless motor device according to the third aspect of the present invention, (a) until the motor rotor reaches a predetermined rotational speed from the stopped state, a rotational drive signal not based on the rotational position signal is generated by the drive signal generating means. (B) When the motor rotor is rotated asynchronously, (b) when the motor rotor reaches a predetermined rotational speed, the phase difference information is calculated by the phase difference calculation means, and the calculation result is stored in the storage means. After the calculation result is stored, the signal calculation unit calculates the rotation position signal based on the phase difference information stored in the storage unit, and (d) the drive signal generation unit generates a motor drive signal based on the calculated rotation position signal. And motor starting control means for synchronously driving the motor rotor.
A rotary vacuum pump according to a fifth aspect of the invention is characterized in that the DC brushless motor device according to any one of the first to fourth aspects is provided as a rotational drive means of a pump rotor.

  According to the present invention, the rotation position signal is calculated by correcting the synchronization signal obtained in synchronization with the rotation of the motor rotor based on the rotation speed information and the phase difference information, and the motor drive signal is generated from the rotation position signal. Thus, synchronous driving is possible even if there is a phase difference between the magnetic pole position of the motor rotor and the synchronization signal. Therefore, it is not necessary to perform phase alignment strictly at the time of assembly, and the assembly work is simplified.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
-First embodiment-
FIG. 1 is a diagram showing a first embodiment of a DC brushless motor device according to the present invention, and is a block diagram showing a schematic configuration of a magnetic bearing type turbo molecular pump in which the DC brushless motor device is incorporated. The turbo molecular pump includes a pump body 1 and a power supply device 2. In the example shown in FIG. 1, the pump main body 1 and the power supply device 2 are configured to be connected by a cable. However, the pump main body 1 and the power supply device 2 may be configured integrally.

  The pump body 1 is provided with a rotor 4 formed with rotor blades to be described later. The rotor 4 is supported in a non-contact manner by a magnetic bearing 5 and is driven to rotate by a motor 6. A DC brushless motor is used as the motor 6. On the other hand, the power supply device 2 includes a motor control unit 7 that drives a DC brushless motor, and a bearing control unit 8 that controls the excitation current supplied to the magnetic bearing 5 so that the rotor 4 is supported at a predetermined floating position. I have.

  FIG. 2 is a cross-sectional view showing details of the pump body 1. The rotor 4 disposed inside the casing 10 of the pump body 1 is formed with a plurality of stages of rotary blades 41 and a screw rotor portion 42. Fixed blades 43 are alternately arranged between the stages of the rotary blades 41 arranged vertically. Further, a screw stator portion 44 is disposed on the base 3 so as to face the rotating screw rotor portion 42.

  A motor rotor 62 of the DC brushless motor 6 is mounted on the shaft portion 45 of the rotor 4, and a permanent magnet is built in the motor rotor 62. On the other hand, a motor stator 61 having a U-phase winding, a V-phase winding, and a W-phase winding for forming a rotating magnetic field is provided on the base 3 side. A sensor target 46 is provided at the lower end of the shaft portion 45, and a rotational position sensor 47 is provided at a position facing the sensor target 46.

  The rotational position sensor 47 is a distance sensor that detects a distance from the sensor target 46, and an inductance sensor is used in the present embodiment. The rotational position sensor 47 is not limited to that described above as long as it outputs a signal synchronized with the rotor rotation.

  3A and 3B are diagrams showing the positional relationship between the sensor target 46 and the rotational position sensor 47. FIG. 3A shows the case where the rotational position sensor 47 is arranged in the axial direction of the sensor target 46, and FIG. The case where the position sensor 47 is arranged in the radial direction of the sensor target 46 is shown. In the case of FIG. 3A, the lower surface of the sensor target 46 is an uneven surface having a level difference h, and the convex surface 46a and the concave surface 46b are distributed by 180 degrees with respect to the rotation angle.

  On the other hand, when the rotational position sensors 47a to 47c are arranged in the radial direction as shown in FIG. 3B, the convex surface 46a and the concave surface 46b of the step h are formed on the outer peripheral surface of the sensor target 46 that is the sensor facing surface. Has been. In any case, three rotational position sensors 47a, 47b, 47c are arranged so as to face these surfaces 46a, 46b. The rotational position sensors 47a, 47b, 47c are arranged around the rotation axis J at intervals of 120 degrees. Since the distance when the output signals of the rotational position sensors 47a to 47c face the surfaces 46a and 46b differs depending on whether they face the convex surface 46a or the concave surface 46b, the output signals at that time also differ. Become.

  The magnetic bearing 5 (see FIG. 1) for supporting the rotor 4 in a non-contact manner includes electromagnets 51 and 52 constituting a radial magnetic bearing and an electromagnet 53 constituting an axial magnetic bearing as shown in FIG. A shaft control type magnetic bearing is constructed. Corresponding to the radial electromagnets 51 and 52 and the axial electromagnet 53, radial displacement sensors 55 and 56 and an axial displacement sensor 57 for detecting the position of the rotor 4 are provided. 11 and 12 are emergency mechanical bearings, and 13 is a connector to which a cable connecting the pump body 1 and the power supply device 2 is connected.

  FIG. 4 is a block diagram showing a schematic configuration of the motor stator 61, the motor rotor 62, the sensor target 46, the rotational position sensors 47a, 47b, 47c, and the motor control unit 7 constituting the DC brushless motor device. FIG. 4 shows an example in which the rotational position sensors 47a to 47c are arranged in the radial direction of the sensor target 46 (FIG. 3B). A drive voltage is applied to a U-phase winding, a V-phase winding, and a W-phase winding provided in the motor stator 61 by a motor drive waveform generation circuit 72 connected to a power source 71.

  The signals G1 to G3 output from the rotational position sensors 47a, 47b, and 47c are signals corresponding to the gap between the rotational position sensors 47a to 47c and the sensor target 46 as described above. When the sensor target 46 is fixed to the shaft portion 45 (see FIG. 2), the sensor target 46 is assembled so that the position of the stepped portion 46c of the sensor target 46 coincides with the position of the boundary surface between the N pole and the S pole of the motor rotor 62. However, in the example shown in FIG. 4, the angle θ is shifted due to an assembly error. Therefore, these gap signals G1 to G3 cannot be directly input to the motor drive waveform generation circuit 72 as rotational position signals. In the present embodiment, the gap signals G1 to G3 are once input to the signal delay unit 73.

  The signal delay unit 73 delays the gap signals G1 to G3 to generate correct rotational position signals S1 to S2, and outputs the rotational position signals S1 to S3 to the motor drive waveform generation circuit 72. is there. FIG. 5 shows each waveform pattern (time chart) of the voltages applied to the gap signals G1 to G3, the rotational position signals S1 to S3, and the U-phase winding, V-phase winding, and W-phase winding. . When the rotational position sensors 47a, 47b, 47c are opposed to the convex surface 46a of the sensor target 46, the gap signals G1 to G3 are in the high state, and conversely, when the rotational position sensors 47a, 47b, 47c are opposed to the concave surface 46b, the gap signals G1 to G3 are in the low state.

Since the rotational position sensors 47a, 47b, and 47c are arranged every 120 degrees, the gap signal G2 is out of phase with the gap signal G1 by 120 degrees. Similarly, the gap signal G3 is changed to the gap signal G2. In contrast, the phase is shifted by 120 degrees. The time difference between the rising edge of the correct rotational position signal S1 and the rising edge of the gap signal G1 to be input to the motor drive waveform generation circuit 72, that is, the delay time is caused by the phase angle θ which is the angle shift shown in FIG. appear. This delay time Δt can be calculated by the following equation (1) using the rotor rotation frequency f and the angle θ.
Δt = (1 / f) · (θ / 360) (1)

  In FIG. 4, the rotational speed detector 74 calculates the rotational frequency f of the motor rotor 62 based on the gap signal G1 of the rotational position sensor 47a, and outputs the calculated rotational frequency f to the delay time calculator 75. The phase difference storage unit 76 stores a phase angle θ in advance. The delay time calculation unit 75 calculates the delay time Δt by Expression (1) based on the rotation frequency f calculated by the rotation speed detection unit 74 and the phase angle θ stored in the phase difference storage unit 76. The signal delay unit 73 calculates correct rotational position signals S1 to S3 based on the input delay time Δt and the gap signals G1 to G3, and outputs them to the motor drive waveform generation circuit 72.

  The motor drive waveform generation circuit 72 generates U-phase, V-phase, and W-phase voltage waveform patterns as shown in FIG. 5 by performing logical operations based on the rotational position signals S1 to S3. Note that the rotation frequency f cannot be calculated when the rotor 4 is in a stopped state, such as at the start of rotation. Therefore, at the time of start-up, voltage waveform patterns U, V, and W as shown in FIG. 5 are generated asynchronously with the magnetic pole position of the motor rotor 62, and the cycle is sequentially shortened to bring the rotor 4 to a predetermined rotational speed. To accelerate. When the rotor rotational speed reaches a predetermined rotational speed at which the rotational frequency f by the rotational speed detection unit 74 can be acquired, the rotational frequency f is detected and phase correction corresponding to the phase angle θ by the signal delay unit 73 is performed. And go to synchronous operation.

  As described above, the correct rotation position signals S1 to S3 are calculated by correcting the gap signals G1 to G3 output from the rotation position sensors 47a to 47c with the delay time Δt calculated from the rotation frequency f and the phase angle θ. Since the motor drive signals U, V, and W are generated based on the rotational position signals S1 to S3, synchronous driving is possible even if there is a phase angle θ between the magnetic pole position of the motor rotor and the synchronous signal. . For this reason, when the sensor target 46 is fixed to the shaft portion 45, the position of the stepped portion 46c does not need to be exactly matched with the position of the boundary surface between the N pole and the S pole of the motor rotor 62. Can be planned.

  In the present embodiment, a two-pole motor has been described as an example. However, the present invention can be similarly applied to motors having other numbers of poles by changing the number and arrangement of rotational position sensors. As a method of obtaining the phase angle θ stored in advance in the phase difference storage unit 76, for example, the angle deviation may be actually measured, or the rotor 4 is rotated by an external driving force (for example, manually rotated). Or the back electromotive force induced in each phase at that time. The obtained phase angle θ is stored in advance in the phase difference storage unit 76 before shipment.

-Second Embodiment-
FIG. 6 is a diagram showing a second embodiment of the DC brushless motor device according to the present invention, and is a block diagram similar to FIG. 4 described above. In the first embodiment described above, the three rotational position sensors 47a to 47c are used as shown in FIG. 4, but in the second embodiment, the motor rotational control is performed using one rotational position sensor 47a. Do. The gap signal G1 output from the rotational position sensor 47a is input to the signal delay unit 73 and the rotational speed detection unit 74 as in the first embodiment.

  Then, the delay time calculation unit 75 calculates a delay time Δt based on the phase angle θ stored in the phase storage unit 76 and the rotor rotational frequency f calculated by the rotation speed detection unit 74, and the signal delay unit 73. Output to. The signal delay unit 73 generates a correct rotation position signal S1 based on the gap signal G1 and the calculated delay time Δt, and outputs the rotation position signal S1 to the motor drive waveform generation circuit 72.

  In the case of the apparatus including the three rotational position sensors 47a to 47c as in the first embodiment, 120 degrees is obtained by correcting the phase of the gap signals G1 to G3 of the rotational position sensors 47a to 47c. Rotation position signals S1 to S3 having phases shifted from each other were obtained. Therefore, the voltage waveform patterns U, V, and W can be generated by a logical operation using the rotation position signals S1 to S3.

  However, in the present embodiment, only one rotational position signal S1 can be obtained as shown in FIG. Therefore, the rotation speed detection unit 74 calculates the rotation period T1 = 1 / f, and the motor drive waveform generation circuit 72 uses the rotation period T1 and the rotation position signal S1 to determine voltage waveform patterns of the U phase, V phase, and W phase. Is generated.

  FIG. 7 is a diagram for explaining a pattern generation method. Here, the drive pattern switching time T1 / 6 is generated by dividing the time of one rotation from the previous rotation speed data into six, and the same pattern as the voltage waveform patterns U, V, and W of FIG. To generate. First, when the gap signal G1 is acquired, the signal delay unit 73 generates the rotational position signal S1 based on the delay time Δt calculated by the delay time calculation unit 75. The cycle of the rotational position signal S1 is the same as the cycle T1 of the gap signal S1 calculated by the rotational speed detector 74.

  Next, when the rotation position signal S1 in the second cycle is generated, generation of the voltage waveform patterns U, V, and W is started in synchronization with the rise of the signal. And the waveform pattern produced | generated is switched whenever time T1 / 6 passes. On the other hand, in the signal delay unit 73, the rotation signal S <b> 1 in the second cycle is generated and input to the motor drive waveform generation circuit 72. The period of the rotation signal S1 in the second period is T2. Since the rotor rotational speed changes during acceleration and deceleration, generally T2 ≠ T1.

  In the example shown in FIG. 7, T2 <T1 (acceleration state). As described above, generation of the voltage waveform patterns U, V, and W in the first cycle is started in synchronization with the rising edge of the rotation signal S1 in the second cycle, and the waveform is switched every T1 / 6. That is, the voltage waveform patterns U, V, and W in the first cycle are generated assuming that the cycle is T1. However, the rise of the rotation signal S1 in the second cycle occurs after time T2 from the start of generation of the voltage waveform patterns U, V, and W in the first cycle, and therefore, among the waveform patterns formed every T1 / 6. The generation time of the sixth waveform pattern is shorter than T1 / 6.

  Also in the present embodiment, as in the first embodiment described above, if the engine is started asynchronously and the rotational speed detection unit 74 can acquire the rotor rotational frequency, the signal delay unit 73 is used. The phase correction corresponding to the phase angle θ is performed to shift to the synchronous operation.

  As described above, in the second embodiment, generation of the voltage waveform patterns U, V, and W for each period is started in synchronization with the rising edge of the rotational position signal S1, and the rotation period acquired before that is divided into six. The waveform pattern is switched at the specified time. In the example described above, the cycle of the first rotation position signal S1 is used, but the cycle of the rotation position signal S1 acquired two or more times before may be used. In the present embodiment, the same effects as those of the first embodiment can be achieved, and further, the cost can be reduced by reducing the number of rotational position sensors to one, and the sensor installation space can be reduced. Reduction and improvement of installation flexibility can be achieved.

-Third embodiment-
FIG. 8 is a block diagram showing a third embodiment of the DC brushless motor apparatus according to the present invention. The block diagram shown in FIG. 8 differs from the block diagram of FIG. 6 described above in that a difference calculation unit 77 and a phase difference measurement unit 78 are provided. In the first and second embodiments described above, the phase angle θ is stored in advance in the phase difference storage unit 76. However, in this embodiment, the phase angle θ is automatically detected during the rotation start operation to store the phase difference. It was made to memorize in part 76.

  Hereinafter, a detection operation when the phase angle θ is automatically detected will be described. First, as in the first embodiment described above, the engine is started asynchronously, and once the rotation speed is reached, the drive voltage is turned off. The difference calculation unit 77 receives the back electromotive voltage induced in the U phase and the neutral point voltage, and “(difference) = (back electromotive voltage) − (neutral point voltage)” is calculated there. FIG. 9A is a diagram showing an example of the difference signal, and shows one period of the periodic difference signal, that is, one rotation of the rotor. Here, since a two-pole motor is described as an example, the positive / negative of the difference signal appears once every rotation.

The phase difference measuring unit 78 detects a point (zero cross point) at which the difference signal becomes zero. It has been known that there is a phase difference of 30 degrees between the zero cross point P and the rotational position signal S1 detected by a conventional Hall sensor or the like. On the other hand, the gap signal G1 (see FIG. 9C) input to the phase difference measuring unit 78 is out of phase with the difference signal in FIG. 9A. Therefore, the phase difference measuring unit 78 detects the time difference T between the timing at which the zero cross point P is detected and the rising timing of the gap signal G1, the predetermined phase difference of 30 degrees, and the rotation period detected by the rotation speed detecting unit 74. Based on T1, the phase difference θ (= phase angle θ) between the gap signal G1 and the rotational position signal S1 is calculated by the following equation (2).
θ = (T / T1) × 360-30 (2)

  This phase difference θ is stored in the phase difference storage unit 76 as the phase angle θ. Once the phase angle θ is acquired, the rotational position signal S1 is generated by the signal delay unit 73 and the motor is driven in synchronization with the magnetic pole position of the motor rotor 62, as in the case of the second embodiment described above. Do. The method for obtaining the zero cross point described above is the same as the method used in the conventional sensorless motor, but in this embodiment, the motor drive voltage is turned off and the back electromotive force is measured. Therefore, switching noise or the like during PWM driving is not superimposed, and the timing of the zero cross point can be easily acquired with a simple circuit configuration.

  That is, the rotational position sensor 47a is a cost increase factor as compared with the conventional sensorless driving method, but since the control system is simplified, there is a total cost reduction effect. In addition, the control itself becomes simpler than the sensorless case, and the stability is improved.

In the above-described embodiment, the U-phase counter electromotive voltage is used, but a V-phase or W-phase counter electromotive voltage may be used. Also, the counter electromotive voltage of one of the U, V, and W phases is measured, and an intermediate voltage (Vmax−Vmin) / 2 between the maximum value Vmax and the minimum value Vmin (= 0 V) is obtained. The timing at which the measured back electromotive voltage coincides may be used instead of the zero cross point described above. In that case, the phase difference θ is calculated by the equation (2) as described above.
Furthermore, a difference between the counter electromotive voltages of the two phases, for example, a difference between the U phase counter electromotive voltage and the V phase counter electromotive voltage may be used. In that case, the phase difference θ is calculated by the following equation (3).
θ = T / T1 × 360 (3)

  In the above-described embodiment, the DC brushless motor apparatus mounted on the turbo molecular pump has been described as an example. However, the DC brushless motor apparatus according to the present invention is not limited to the turbo molecular pump, and drives a pump rotor of a rotary vacuum pump. It can be used as a device.

  In the correspondence between the embodiment described above and the elements of the claims, the sensor target 46 and the rotational position sensors 47, 47a to 47c are signal generating means, the phase angle θ is phase difference information, and the rotational frequency f is rotational. For the speed information, the signal delay unit 73 and the delay time calculation unit 75 are signal calculation means, the motor drive waveform generation circuit 72 is drive signal generation means, the motor control unit 7 is motor start control means, and the phase difference measurement unit 78 is Each of the phase difference calculation means is configured. The above description is merely an example, and when interpreting the invention, there is no limitation or restriction on the correspondence between the items described in the above embodiment and the items described in the claims.

It is a figure which shows 1st Embodiment of the DC brushless motor apparatus by this invention. 2 is a cross-sectional view showing details of the pump body 1. FIG. It is a figure which shows the relationship between the sensor target 46 and the rotational position sensor 47, (a) shows the case where the rotational position sensor 47 is arrange | positioned in an axial direction, (b) arranges the rotational position sensor 47 in a radial direction. Shows the case. It is a block diagram which shows the structure of DC brushless motor apparatus. It is a figure which shows the waveform pattern of the applied voltage applied to gap signal G1-G3, rotational position signal S1-S3, and U, V, and W phase. It is a block diagram which shows 2nd Embodiment of the DC brushless motor apparatus by this invention. It is a figure explaining a pattern generation method. It is a block diagram which shows 3rd Embodiment of the DC brushless motor apparatus by this invention. It is a figure explaining detection operation | movement of phase angle (theta), (a) shows a difference signal, (b) shows rotation position signal S1, (c) shows gap signal G1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pump main body 2 Power supply device 4 Rotor 6 Motor 7 Motor control part 46 Sensor target 47, 47a-47c Rotation position sensor 61 Motor stator 62 Motor rotor 72 Motor drive waveform generation circuit 73 Signal delay part 74 Rotation speed detection part 75 Delay time calculation part 76 Phase difference storage unit 77 Difference calculation unit 78 Phase difference measurement unit

Claims (5)

In a DC brushless motor device that generates a motor drive signal based on a rotation position signal that is magnetic pole position information of a motor rotor, and rotates the motor rotor in synchronization with the magnetic pole position by the motor drive signal.
Signal generating means for generating a synchronization signal synchronized with the rotation of the motor rotor;
Storage means for storing in advance phase difference information between the synchronization signal and the rotational position signal;
Rotational speed detection means for detecting rotational speed information of the motor rotor based on the synchronization signal;
Signal calculating means for calculating the rotational position signal by correcting the synchronization signal obtained during rotation of the motor rotor based on the rotational speed information and the phase difference information stored in the storage means;
A DC brushless motor device comprising drive signal generation means for generating the motor drive signal based on the rotational position signal calculated by the signal calculation means. The DC brushless motor device according to claim 1,
The signal generating means is provided with one sensor that outputs the synchronization signal,
When generating the motor drive signal in synchronization with the rotational position signal, the signal calculation means generates the motor drive signal based on a period of the rotational position signal acquired in the past from the rotational position signal. A DC brushless motor device characterized by that. In the DC brushless motor device according to claim 1 or 2,
Phase difference calculation means for calculating the phase difference information based on a back electromotive voltage of at least one phase of the motor stator is provided, and the storage means stores the phase difference information calculated by the phase difference calculation means. DC brushless motor device. In the DC brushless motor device according to claim 3,
(A) Until the motor rotor reaches a predetermined rotational speed from a stopped state, a rotational drive signal not based on the rotational position signal is generated by the drive signal generation means to rotate the motor rotor asynchronously; (b) When the motor rotor reaches a predetermined rotational speed, the phase difference calculation means calculates phase difference information and stores the calculation result in the storage means. (C) After the calculation result is stored, the storage means stores the calculation result. Based on the stored phase difference information, the signal calculation means calculates a rotational position signal, and (d) a motor drive signal based on the calculated rotational position signal is generated by the drive signal generation means to synchronously drive the motor rotor. A DC brushless motor device comprising motor starting control means for performing   A rotary vacuum pump comprising the DC brushless motor device according to any one of claims 1 to 4 as a rotational drive means of a pump rotor.

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