JPS6311875B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control device for an electric motor, and an object of the present invention is to enable stable speed control.

In general, the greater the number of pulses of a periodic signal required to control the speed of an electric motor, the wider the control frequency band can be obtained, making it possible to provide a high-performance electric motor. By the way, as a method of obtaining a periodic signal proportional to the rotational speed of an electric motor, there are an optical method and a magnetic method. However, in either method, there is a limit to the number of pulses because if the periodic signal is configured to have a large number of pulses, the generated voltage of the signal becomes small and electrical noise from the motor itself or from the outside becomes a problem.

The present invention corrects these deficiencies and provides a speed control device that can increase the number of pulses without reducing the S/N ratio of the frequency generator. Examples thereof will be described below based on the drawings.

In Figure 1, 1 is an electric motor, 2 and 3 are frequency generators driven by this electric motor 1, and the phase is 180°.
generate different signals. 4 and 5 are Schmitt trigger circuits for waveform shaping, 6 and 7 are monostable multivibrators, 8 is a waveform synthesizer for waveform synthesis, 9 is an inverter circuit, 10 is a sample command signal circuit for generating a sample command signal, 11 is a reference signal generation circuit, 12 is a sawtooth wave generation circuit, 13 is a sample hold circuit, and 14 is a power supply control circuit.

Figure 2 shows the signal waveforms of each part.
7, the outputs of the waveform synthesizer 8, the circuit 9, the sample command signal circuit 10, the reference signal generation circuit 11, the sawtooth wave generation circuit 12, and the sample hold circuit 13.

Next, the operation of this embodiment will be explained.

As the electric motor 1 rotates, frequency generators 2 and 3, which are periodic signal generating means, generate periodic signals proportional to the rotational speed. These periodic signals are sine waves, as shown in Figure 2 A and B, and have a phase difference of 180 degrees in electrical angle. Note that this phase difference will be described later. Waveform shaping the sine wave output signal by respective Schmitt trigger circuits 4 and 5,
The square wave output signals shown in FIG. 2C and D are obtained. The square wave output signal is applied to the monostable multivibrators 6 and 7, and synchronized and inverted at either the rising edge or the falling edge (in the embodiment, the rising edge), and the CR time constant shown in FIG. A signal with a pulse width of a predetermined time width T _a is obtained. The pulse signals obtained by the monostable multivibrators 6 and 7 are logically synthesized by a waveform synthesizer 8 to obtain a composite pulse signal of 1/2 period of the periodic signals A and B, as shown in FIG. This signal is inverted by an inverter circuit 9 and sample command signal circuit 10
2, a sample command signal is generated as shown in FIG. ing. Based on the reset pulse signal, the sawtooth wave generating circuit 12 generates the waveform shown in FIG. The sawtooth wave is sampled and held using the sample command signal, and a speed error output proportional to the phase difference (time difference) between the two signals is generated in a sample and hold circuit 13 serving as a comparison means. The error output signal is amplified and the power supply control circuit 1
4 controls the power supplied to the motor 1 so that the output period (frequency) of the frequency generators 2 and 3 connected to the motor shaft becomes close to the set value in the reference signal generation circuit 11. The speed is controlled by.

As described above, when there is a limit to the number of pulses due to the structure, electrical logic synthesis can obtain n times the number of pulses, which has the effect of improving control characteristics. However, it is expected that the phase relationship of the output signals obtained from the n frequency generators having a predetermined phase difference may deviate due to mechanical assembly errors or the like. In this case, the above-mentioned deviation in the phase relationship becomes a periodic variation, which affects the rotation of the electric motor. A solution to the above problem is shown in FIG.

Figures A and B are the output signals of the two frequency generators. Similarly, square waves C and D correspond to the waveforms A and B, respectively. The respective square wave signals are configured so that the set phase difference is 180 degrees in electrical angle, but here, a case will be described in which a phase error occurs by Δt from the set phase difference. Third
The predetermined period width is determined by the rising signal of the square wave in Figure C.
Waveform E of T _a is created using the CR constants of multivibrators 6 and 7. Then, it is adjusted by the CR constants of the multivibrators 6 and 7 so that the waveform has an adjustment period width T _b according to the rising signal of the square wave shown in FIG. 3D. That is, the CR constants of the multivibrators 6 and 7 are adjusted so that the falling signal period of the waveform G, which is a composite signal waveform of the waveform E and the waveform G, becomes the repetition period T. Note that the sample command signal, which is period information, is generated by a rising signal of a square wave, so the inverter circuit 9 inverts waveform G and creates waveform Q so that the rising signal period becomes a repeating period. , Hereafter, the same processing as shown in FIG. 2 is performed to control the electric motor.

Although the number of frequency generators is two for convenience, in reality, the rotor part of the frequency generator is common, and the stator part is a power generation configuration of, for example, magnetoelectric detection type magnetic teeth and zigzag power generation coil. In this case, the zigzag power generation coil can be provided on both sides of the film substrate, or the zigzag power generation coil can be divided on one side. Therefore, there may be a configuration in which the cost increase due to the increase in the number of frequency generators is small.

Further, in the above embodiment, the case where n=2 was explained as the number of frequency generators, but the present invention is not limited to this, and a configuration in which n=2 or more is also possible. Of course, in that case, it goes without saying that the configuration must be such that the set phase difference between the respective periodic signals is 360°/n.

Therefore, if the motor speed control device of the present invention is used as a drive source in a field that particularly requires miniaturization, such as tape recorder equipment, it can be made into equipment with good characteristics.

As is clear from the above embodiments, according to the present invention, the number of pulses can be substantially increased without reducing the generated voltage and by eliminating the adverse effects of noise, making it possible to perform accurate speed control. .

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a motor speed control device according to an embodiment of the present invention, Fig. 2 is a signal waveform diagram of the main parts, and Fig. 3 is a signal waveform diagram of each part when a setting phase error occurs. be. 1...Electric motor, 2, 3...Frequency generator, 6,
7... Monostable multivibrator, 8...
... Waveform synthesizer, 11 ... Reference signal generation circuit, 13
...Sample hold circuit, 14...Power supply control circuit.

Claims (1)

[Claims] 1. n frequency generators that obtain speed periodic signals that are proportional to the rotational speed of the electric motor and have different phases;
n pulse generating means for generating pulses of a constant time width from the output signals of the generators; waveform synthesizing means for synthesizing respective signal pulse waveforms obtained by the pulse generating means; and a reference speed signal for the electric motor. a reference period signal generating means for generating a reference period signal, a comparison means for comparing the composite pulse signal and the reference period signal to obtain an error signal thereof, and a power supply control means for controlling the supply of power to the electric motor based on the error signal. A speed control device for an electric motor. 2. The speed control device for an electric motor according to claim 1, wherein a pulse generating means capable of variably setting a signal pulse width is used as the pulse generating means. 3. The speed control device for an electric motor according to claim 1, characterized in that the waveform synthesizing means is provided with means for switching the phase of its output by 180°.