JPS60128887A - Controller of brushless motor - Google Patents

Abstract

PURPOSE:To shorten a starting time and to raise a drive voltage at the normal time by switching the impedance of a stator winding at between accelerating and normal times. CONSTITUTION:Since switching transistors Q1A, Q2A, Q3A are turned ON at the acceleration time, a motor coil resistance decreases. Accordingly, a motor stator winding resistance value decreases, and the starting time reduces. Since a servo voltage Vs is set in advance to a value as near as the value of a DC voltage Vcc by main coils L1, L2, L3 at the normal time, a voltage VCE between the collector and the emitter of a drive transistor Q4 decreases, and the collector loss can be accordingly set to a small value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a brushless motor control device for controlling the rotational phase and rotational speed of a brushless motor used in a recording/reproducing device such as a video tape recorder.

[Technical background of the invention and its problems] During recording, a video tape recorder rotates a plurality of rotary heads at low speed to record one finild's worth of video signals as one diagonal track on the tape. During playback, each head alternately and accurately traces the track to pick up the recorded signal.

In order to perform such operations, a brushless motor is usually used to drive the rotation of the rotating disk, and a motor servo mechanism is used to control the rotational phase and number of rotations.

Conventionally, a brushless motor is constructed as shown in FIG.

As shown in FIG. 1, a brushless motor M using a position detection element (Hall element) has a shaft of 1 degree and a bearing of 2 degrees. Rotor magnet 3. It is composed of a motor coil (stator coil) 41 and a position detection element 5, a rotor magnet 3 is arranged around a shaft 1, and the shaft 1 is rotatably arranged in a bearing 2 provided at the center of the motor coil 4. ing. Further, the position detection element 5 is arranged on the stator side close to the rotor magnet 3. Then, the position of the rotor magnet 3 is detected by the position detection element 5, and after signal processing such as amplification and waveform shaping is performed, a drive current is applied to the motor coil 4.

A conventional brushless motor and its motor servo mechanism are constructed as shown in FIG.
is equipped with three motor coils Ll + 12 *L3,
Three position detection elements 5a and 5b arranged on the stator side
, 5c, the current switching switch transistor Q+ uses the position detection pulse from 5c.

Q2. Switch Q'3 sequentially to three coils L+.

12. By passing drive currents with different phases through Ls, the motor is rotated with an average torque. A servo voltage Vs is supplied to the motor coils L+, 12, and L3 from a DC voltage source Vcc via a drive transistor (power transistor) Q4, and a voltage is applied to each coil by switching the current switching switch transistors Q+, Q2, and Q3. A drive current is provided, which can be varied by controlling the base current of transistor Q4. A rotary disk 6 is connected to the shaft of the brushless motor M, and rotates as the motor M rotates. A speed detection radar 7 is arranged near the rotating disk 6, so that the rotational phase and number of rotations can be detected.

The detection pulse P1 detected by the detection radar 7 is compared with a reference signal P2 giving a target rotation speed by a speed detector 8,
Generates a voltage according to the rotational speed of the motor and supplies it to the next stage amplifier 9.
After amplifying the signal, the drive transistor Q4 is driven.

In such a configuration, the servo voltage VST at the time of electromotive force
There is a relationship between VS and the steady state servo voltage Vs of VS<, VST, and for these servo voltages VST and VS, there is a relationship between the rotational torque T and the rotational speed M as shown in Fig. 3. There is. As you can see from this diagram, the target rotation speed N
For a steady torque To corresponding to o, the starting voltage VS
There is a large gap between T and the steady voltage Vs. In addition, 8
The points are operating points during servo operation.

By the way, in order to realize a motor servo device with good acceleration and low power consumption during steady state, it is necessary to
It is necessary to select the value of c and the characteristics of the motor M.

Good acceleration and power consumption have a contradictory relationship.

In general, the motor starting time [is t = - (RJ/KTKE) In (1 - (No /
N1)) ...(1) Approximately expressed as follows. Here, R is the motor stator winding resistance, J is the inertia of the motor and load, KT is the motor torque constant, KE is the back electromotive force constant, No is the target rotation speed,
N1 is the motor rotation speed when the maximum value of the servo voltage Vs is applied.

Therefore, in order to improve the acceleration performance, that is, to shorten the starting time t, the first step is to increase the rotational speed N1 when the maximum servo voltage Vs is applied, that is, to increase the voltage value of the DC voltage source Vcc. The second step is to lower the motor stator winding resistance R, and the third step is to reduce the motor torque constant K.
It is conceivable to increase ε in T and the back electromotive force constant.

5- In the first method, a DC voltage source V supplying a high voltage value
cc is required, and as a result, the collector-emitter voltage VCE of drive transistor Q4 in steady state
becomes larger. Therefore, a problem arises in that the collector loss Pc in the transistor Q4 is large and a heat sink or the like is required. As a countermeasure to this problem, a method can be considered to reduce the collector loss Pc of the transistor Q4 and supply a high DC voltage. In this method, as shown in FIG. 4, a pulse width modulation circuit 10 is interposed between an amplifier 9 and a drive transistor Q4, and a pulse output is obtained at the emitter output terminal of the transistor Q4. This is a system in which the voltage is further converted into a DC voltage by a smoothing filter such as a coil L+, a capacitor C+, etc., and the motor M is driven. However, this method has disadvantages in that it generates noise and has a complicated circuit configuration, which is disadvantageous in terms of cost. Also, the above-mentioned No. 2. By the third method, the motor stator winding resistance R can be reduced and KTKε
There is a problem in that making the value extremely small is disadvantageous in giving priority to the efficiency of the motor in steady state, and therefore cannot be done in practice.

Therefore, in the past, when controlling the speed of a brushless motor, startup time, that is, acceleration performance, was often treated as a secondary issue.

[Object of the Invention] In view of the above-mentioned points, the present invention provides a control device for a brushless motor that has good acceleration performance, maximizes motor efficiency in steady state, and reduces loss in drive transistors. There is a particular thing.

[Summary of the Invention] The brushless motor control device of the present invention is configured such that the impedance of the stator winding (motor coil) of the brushless motor can be switched between acceleration and steady state, and the winding impedance can be switched between current and steady states. This is configured to be performed using a comparison signal between the motor rotation speed and a target value.

[Embodiments of the invention] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 5 is a circuit diagram showing an embodiment of a brushless motor control device according to the present invention. However, the same or equivalent parts as in FIG. 2 will be described with the same reference numerals.

In FIG. 5, reference numerals 5a, 5b, and 5c are position detection elements such as Hall elements, which detect the position of a rotor magnet (not shown), and send position detection pulses with different phases to a current switching switch transistor Q+.

Q2, Qa and these transistors Q+.

By sequentially switching Q2 and Qs, the three motor coils L+
, L2, and Ls are caused to flow drive currents having different phases. Motor coil L+, L2.

A servo voltage Vs is supplied to Ls from a DC voltage source Vcc via a drive transistor Q4. Motor coils L+, 12, and Ls have coils L+A, L2A, and L3A connected to switch transistors Q, respectively.
The switching transistors Q+A, Q2A, and QaA are connected in parallel by switching IAlQ2AlQ3A, and the switching of the switching transistors Q+A, Q2A, and QaA is controlled by the output voltage of the acceleration signal generator 11. Motor M configured in this way
A rotating disk 6 is connected to A (indicated by a broken line frame) and rotates as the motor MA rotates.

A detection head 7 is disposed near the rotating disk 6 to detect the rotational phase and number of rotations.

The detection pulse P1 detected by the detection radar 7 is compared with the reference signal P2 which gives the target rotation speed in the speed detector 8, generates a voltage according to the rotation speed of the motor, and is amplified by the next stage amplifier 9 and then driven. It is designed to be supplied to the base of the transistor Q4. On the other hand, an acceleration signal generator 11 is connected to the speed detector 8, which determines whether the current period of the pulse P1 indicating the rotational speed of the motor is larger or smaller than the target value P2, and displays the result of the determination. Outputs an acceleration signal P3. Main coils L+, L2, L inside the above motor MA
The coils L+Al L2 are connected in parallel with s, respectively.
A and L3A are wound overlappingly with the main coils L+, 12 and Ls, and their wire diameters and number of turns do not necessarily match those of the main coils L+, L2 and Ls. That is, the main coil L+ that operates normally,
The wire diameter of L2 and Ls with two turns has maximum efficiency near steady torque, and the servo voltage Vs at the operating point during steady operation
is selected so that it has a high value as close as possible to the voltage value of the DC voltage source marked V. Also 1, parallel coil L+ A, L
2A and L3A reduce the total impedance of the coils connected in parallel so that only the starting characteristics are satisfied.
It is configured to increase the magnetic flux density generated in the wound coil.

In such a configuration, switch transistors QIA, Q
2A and QaA are switched and controlled by the output voltage of the acceleration signal generator 11 when the motor rotation speed does not reach the target value. In addition, the servo voltage Vs at steady state satisfies the condition Vo<VSM^×, when the motor rotation speed is equal to the target value, the servo voltage at the maximum load torque is Vo, and the maximum value of the servo voltage is VSsAx. This is the maximum Vo value.

During acceleration, switch transistors Q1A and Q2A.

Since GhA is turned on, the motor coil resistance decreases by 10-, so the R value in equation (1) described above decreases, and the startup time . During normal operation, the main coils L+ and L2 are connected in advance.
, La, the servo voltage Vs is set as close as possible to the value of the DC voltage Vcc, so the collector-emitter voltage σ of the drive transistor Q4 is small, and therefore the collector loss Pc can be set small. Servo voltage VST at startup and servo voltage Vs at steady state
There is a relationship of Vs 1VVs T between these servo voltages VST and VS, and a relationship as shown in FIG. 6 exists between rotational torque T and rotational speed N.

For steady torque To corresponding to target rotation speed No.
There is no large difference between the starting voltage VST and the steady voltage Vs, and the motor MA operates steadily at eight points. Further, when the rotation speed of the motor MA does not reach the target value No., for example, at the time of startup, FIG. 7(a) shows.

As shown in (b), the period until the target rotational speed No is reached is 0, when the acceleration signal P3 is output from the acceleration signal generator 11 and the switch transistor QIA.

Q2A and Q3A are turned on, and during this period starting voltage VST is supplied to the motor coil.

FIG. 8 is a circuit diagram showing another embodiment of the brushless motor control device according to the present invention, in which three motor coils are main coils L+a, 12Bl, L3e, and coil L+c connected in series with these, respectively.

Consisting of L2C113C, series coil L+c.

A switch transistor O1s is installed at both ends of L2C and L3C.
, Q2 e , and Qs e have collectors and emitters connected in parallel. and these switch transistors Q+ e + Q2 e .

Acceleration signal generator 11 shown in Fig. 5 is installed on each base of 03B.
In this case, the acceleration signal P3 is supplied. Therefore, the common connection end of the main coils LIB, 12B, and 1.3B is connected to the emitter of the drive transistor Q4 to supply the servo voltage Vs, and one end of the series coils LIC, L2C1L3C is connected to the current switching terminal, respectively. It is connected to the collectors of the switch transistors Q+, Q2, and Qs.

In such a configuration, during acceleration, the switch transistor Q
+ e , Q2 s + Q3 e are turned on, so the motor coil resistance decreases, and the R value in equation (1) described above decreases, so the startup time t decreases. During normal operation, the coils are connected in series, so the number of windings is large, and the motor's back electromotive force constant increases, increasing the servo voltage Vs and increasing the collector-emitter voltage VC of the drive transistor Q4.
E decreases, and collector loss Pc decreases.

Note that whether the motor coils are connected in parallel as shown in Fig. 5 or in series as shown in Fig. 8 is a matter of configuration and depends on performance. This is not a particular problem.

[Effects of the Invention] As described above, according to the present invention, the impedance of the stator winding of a brushless motor is configured to be switchable between acceleration and steady state, and the winding impedance is switched depending on the current motor rotation speed. Since this is performed using a comparison signal between the target value and the target value, it is possible to shorten the startup time, increase the drive voltage in steady state, and reduce the collector loss of the drive transistor. Therefore, the acceleration characteristics and power consumption of the motor are improved. In addition, with the above configuration, the starting characteristics can be considered separately from the steady-state characteristics, so each characteristic can be set to be optimal.
It is possible to operate at maximum efficiency even in steady state.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the configuration of a brushless motor, Fig. 2 is a circuit diagram showing a conventional brushless motor control device, and Fig. 3 is an operational explanation showing the relationship between rotational torque and rotational speed in the device shown in Fig. 2. 4 is a circuit diagram showing another conventional example,
FIG. 5 is a circuit diagram showing an embodiment of a brushless motor control device according to the present invention, FIG. 6 is an operation explanatory diagram showing the relationship between rotational torque and rotational speed in the device shown in FIG. 5, and FIG. FIG. 5 is an operational explanatory diagram showing the starting characteristics of the device, and FIG. 8 is a circuit diagram showing another embodiment of the present invention. 5a, 5b, 5c...position detection element, 6...rotating disk, 7...rotation speed detection head, 8...speed detector, 9...amplifier, 14-11...acceleration signal Generator, Q+, Q2, Q3... Current switching switch transistor, Q4... Drive transistor, Q+ A, Q2 A, Qs A and Q+ s, Q2
s. Q3e...Switch transistor for impedance switching, L+, L2, L3 and LlA, L2A, L3A...
・Stator winding (motor coil), L+ e, 12B,
13B and L + c, L 2 C1L3C... Stator winding (motor coil), Vcc... DC voltage source, Vs... Servo voltage (drive voltage), P+... Rotation speed detection pulse, P2.・Reference signal,
P3...Acceleration signal, MA...Brushless motor. Agent Patent attorney Kensuke Norichika (and 1 other person) 15-

Claims (1)

[Claims] In a brushless motor control device that detects the motor rotation speed, compares it with a target value, and controls the motor drive voltage based on the deviation value, the impedance of the motor's stator winding can be switched between acceleration and steady state. and a signal generating means that compares the detected motor rotation speed with a target value and generates a control signal indicating the result. A control device for a brushless motor, characterized in that it is configured to switch winding impedance by and.