JPH02219491A - Revolution detecting circuit of brushless motor - Google Patents

Abstract

PURPOSE:To reduce the number of parts of a revolution detecting means by knowing the number of revolutions through detecting the period of a counter- electromotive force generated in a coil. CONSTITUTION:Respective terminals of a brushless motor 1 are connected with comparators 3a, 3b, 3c via a resistor 2 so that a voltage between two terminals is referred to. Said comparators 3a, 3b, 3c output a high level signal to CPU 5, when the input is positive, and a low level signal thereto, when said input is negative. The output of one of the comparators (output of the comparator 3a) is inputted to a frequency-dividing circuit 4, divided into 1/4 period, and inputted to the CPU 5 as an index signal 7. The CPU 5 refers to said signals to control a driver 6 and to maintain the appropriate number of revolutions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rotation speed detection circuit for a brushless motor.

[Conventional technology]

Conventionally, the rotation speed of this type of brushless motor has been detected using pulses generated when a magnet attached to the rotor passes near a fixed Hall element or the like. Referring to FIG. 3, a magnet 32 is attached to the rotor 28, and each time the rotor 28 rotates, the magnet 32 passes near the Hall element 33, and the signal generated by the Hall element is transmitted to the CP.
The rotation speed is detected by inputting it to U21.

Next, driving of the brushless motor will be explained with reference to the drawings.

Basically, a brushless motor is driven by changing the direction of current flowing through a coil, thereby causing magnetic flux to act on the rotor. Brushless motor 27 shown in FIG.
has three phases, that is, three coils in three directions. The coil is coil A29. There are B2O and C31, which are arranged at an angle of 120° from each other. Current flowing through these coils is supplied from a driver 26 controlled by the CPU 21. The driver 26 is a switch (SWAI, A2°Bl, B2
．． CI, C2) modules A22, B23. C
24, and a DC power source 25 for supplying current.

Hereinafter, the operation of the driver 26 will be explained with reference to FIG.

The ching operation will be explained. In the figure, what is written at the top is a schematic diagram showing the relationship between the coil and the magnetic flux direction (arrow), and corresponds to the timing directly below. That is, in the section (■), 5WBI and swci are in the ON state, and current flows from the coil 031 to the coil B30, generating magnetic flux in the direction of each coil, and as a result, magnetic flux in the direction of the arrow is generated. In the section ■, 5WAI and 5WB2 are O
Since it is N, the direction of the magnetic flux changes. Thereafter, the direction of the magnetic flux changes in a rotating manner in the same manner, causing the rotor 28 to rotate. Here, the rotation of the rotor 28 and the rotation of the magnetic flux are not completely synchronized, and there is inevitably a delay in the rotation of the rotor 28, especially at startup. For this reason, the CPU 21 monitors the rotational speed of the rotor 28 itself using the method described above, and controls the rotor 28 by forming a closed loop.

[Problem to be solved by the invention]

The rotational speed detecting means of the conventional apparatus described above requires a magnet and a Hall element for detection, which has the drawback of increasing the number of parts and increasing costs.

[Means to solve the problem]

The rotation speed detection circuit for a brushless motor according to the present invention recognizes the rotation speed based on the period of the back electromotive force generated in the coil.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

The present embodiment shown in FIGS. 1 and 2 relates to a three-phase eight-pole brushless motor device.

Each terminal of the brushless motor 1 is connected to comparators 3a, 3b, and 3c via a resistor 2, and the voltage between the two terminals is referenced. The comparators 3a, 3b, and 3c output a high level to the CPU 5 if the input is positive, and a low level if the input is negative. One of the outputs (the output of the comparator 3a) is input to the frequency divider circuit 4, and is frequency-divided into 1/4 period.

In this embodiment, since an 8-pole brushless motor is used, the frequency is divided by this period ratio. The frequency-divided output is input to the CPU 5 as an index signal 7. The CPU 5 refers to these signals and controls the driver 6 to maintain an appropriate rotational speed.

The operation of this embodiment will be explained below with reference to FIG.

Since the brushless motor 1 has a coil between its terminals, when a rotor having magnets rotates therein, a voltage (interphase back electromotive force) is generated between the terminals.

Between one terminal, this back electromotive force changes sinusoidally as shown in FIG. 2(a). In this example, an 8-pole rotor is used, so the period ratio between the back electromotive force and the rotation of the rotor is 1:4.
This is the frequency dividing ratio selection criterion of the frequency dividing circuit 4 described above. This back electromotive voltage is converted into a comparator output of a rectangular wave as shown in FIG. 2(b) by a comparator, and is further frequency-divided to become an output of a frequency dividing circuit as shown in FIG. 2(c). Through the above processing, the index signal 7 having the same period as the rotation of the rotor is generated.

The CPU 5 recognizes the relative positional relationship between the coil and rotor of the brushless motor 1 from the outputs of the three comparators, and the rotation speed from the index signal 7. C with reference to these
PU5 controls driver 6. Here, it is necessary to shift the timing when applying the driving power and when referring to the back electromotive voltage. Control for this purpose is also performed by the CPU 5.

In this embodiment, the output signal of each comparator is
Although the processing is performed by the PU, it is also possible to drive the driver 6 using a simple signal processing circuit instead of the CPU.

In the above embodiment, since no index signal is generated when the brushless motor is started, a pseudo signal is added.

〔Effect of the invention〕

As explained above, the present invention determines the rotational speed of a brushless motor by detecting the period of the back electromotive force generated in the coil of the brushless motor, so it can be configured with fewer parts than conventional circuits and has fewer malfunctions and breakdowns. It is effective in providing

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a diagram showing the operation of the circuit, Fig. 3 is a block diagram showing an example of a conventional device, and Fig. 4 is a diagram showing the switching of a coil in a conventional example. FIG. 1...Brushless motor, 2...mark/resistance, 3
a. 3b, 3c...Comparator, 4...
Frequency divider circuit, 5...CPU, 6...driver, 7...inch. signal, 8 spindle motor/rotor, 9... river/magnet, 10... Hall IC. Agent Patent Attorney Hara Uchihara

Claims (1)

[Scope of Claim] A rotation speed detection circuit for a brushless motor, which has a rotor having a plurality of permanent magnets and is driven by switching currents flowing through a plurality of coils fixedly arranged near the rotor. A circuit for detecting a back electromotive voltage generated in the plurality of coils as a rotor rotates, a circuit for detecting a period of the detected back electromotive voltage, and a circuit for calculating the rotation speed of the rotor from the period. A rotation speed detection circuit for a brushless motor, comprising: