JPH04145889A - Speed controller for dc motor - Google Patents

Abstract

PURPOSE:To improve the efficiency of the title controller without requiring any space by providing a means which detects the induced voltage of a motor while the power supply to the motor is stopped and another means which controls the power supplying time to the motor on the basis of the detected voltage. CONSTITUTION:The high-level time of a pulse generation circuit 6 is adjusted in accordance with the output a sampled operational amplifier 4 and the high- level time of the circuit 6 is held by a sample and hold circuit 5. The circuit 5 is set to a holding state while a high level is supplied to a terminal 5a. Accordingly, the magnitude of the induced voltage of a motor 1 controls the power supplying time to the motor 1. For example, the power supplying time becomes longer during the period (b), since a load is applied to the motor 1 and the induced voltage drops. The power supplying time becomes shorter during the period (c) in order to reduce the rotating speed of the motor, since the rotating speed of the motor is so fast that the induced voltage becomes higher.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a speed control device for a DC motor that controls a motor to a constant speed.

[Conventional technology] Since the rotation speed of a DC motor changes with load fluctuations, conventionally an optical or magnetic pole detection type rotary encoder is attached to the motor shaft to detect the rotation speed and adjust the rotation speed accordingly. The speed is controlled by converting the power into a voltage, etc., and controlling the power supplied to the motor based on that.

Furthermore, as a speed control method that does not use an encoder, an electronic governor method and the like5 are generally known.

[Problems to be Solved by the Invention] However, in the conventional example described above, since the encoder is attached to the motor, additional space is required for attaching the motor, and the cost increases due to the encoder.

Furthermore, control using the electronic governor method has disadvantages such as low efficiency and being affected by fluctuations in the winding resistance inside the motor due to temperature changes.

SUMMARY OF THE INVENTION The object of the present invention is to overcome the above-mentioned drawbacks and to provide a space-saving and efficient speed control device for a DC motor.

[Means for Solving the Problems] In order to achieve the above object, according to the present invention, the speed of the motor is controlled by dividing the time when power is supplied to the motor and the time when power supply to the motor is stopped. In a speed control device for a DC motor, means for detecting the induced voltage of the motor during the time when the power supply to the motor is stopped, and means for controlling the time of power supply to the motor based on the detected voltage. By providing this, constant speed control is achieved.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

Figure 1 shows a motor speed control circuit, where 1 is a DC motor to be controlled, 2 is a flywheel diode, 3 is a reference voltage generation circuit that generates a reference voltage for setting the rotation speed of motor 1, and 4 5 is an operational amplifier that compares and calculates the reference voltage from the reference voltage generation circuit 3 and the induced voltage of the motor 1, and 5 samples the output from the operational amplifier 4 when the power supply to the motor 1 is stopped, that is, when the terminal 5a is at a low level. However, when the terminal 5a for supplying power to the motor 1 is at a high level, it is a sample and hold circuit that functions to hold the voltage. 6 is a sample and hold circuit 5
This is a pulse generation circuit that changes the width of the high level of the pulse according to the output from the pulse generator. Reference numeral 7 designates a DC motor drive circuit, and power is supplied to the motor 7 when the input to the drive circuit 7 is at a high level, that is, when the pulse output from the pulse generating circuit 6 is at a high level.

Next, the operation of the motor speed control circuit shown in FIG. 1 will be explained.

The pulses output from the pulse generation circuit 6 are applied to the motor drive circuit 7 and the sample and hold circuit 5. When the output pulses of the pulse generation circuit 6 are at a high level, power is supplied to the motor 1, and when the output pulses are at a low level. At this time, the power supply to the motor 1 is stopped and constant speed control of the motor 1 is performed. When the output of the pulse generation circuit 6 is at a low level, the sample and hold circuit 5 samples the output of the operational amplifier 4. At this time, the output of the operational amplifier 4 is a calculated value of the reference voltage from the reference voltage generation circuit 3 and the induced voltage of the motor l.

The high level time of the pulse generating circuit 6 is adjusted according to the sampled output of the operational amplifier 4, and the high level time of the pulse generating circuit 6 is held by the sample and hold circuit 5. This sample and hold circuit 5 is in a hold state while a high level is applied to the terminal 5a.

Therefore, the magnitude of the induced voltage of motor 1 controls the power supply time to motor 1, and this state is
Let's explain with a diagram. Figure 2 shows the voltage waveform of the electrodes of the motor 1, and the reference voltage generation circuit 3 is set so that the induced voltage when the motor 1 is rotating normally is at the level β shown by the dotted line in Figure 2. Setting the voltage. In FIG. 2, a normal rotational speed is obtained at time A. During the initial period, the motor is loaded and the induced voltage drops, so the power supply time increases accordingly. In Ha, the motor's rotational speed became too high, causing the induced voltage in the motor to become too high, so in order to lower the rotational speed, the time required to supply power to the motor was shortened.

And at the second time, the rotation speed is normal.

In this way, fluctuations in the rotational speed can be detected as fluctuations in the induced voltage of the motor itself, without using an encoder, and constant speed control can be performed based on this.

[Other Embodiments] Next, other embodiments of the present invention will be described with reference to FIGS. 3 to 5.

FIG. 3 shows a motor drive control circuit, and the same parts as in FIG. 1 are given the same reference numerals, and the different parts will be explained. In FIG. 3, 8 is a microcomputer, 8a is a terminal for sampling the output voltage from the operational amplifier 4, and 8b is a terminal for outputting pulses for driving the motor.

Next, the control flow shown in FIG. 3 will be explained with reference to the voltage waveform of the electrodes of the DC motor shown in FIG. 4 and the flowchart shown in FIG. 5.

In step S1, it is determined whether the pulse output from the terminal 8b is at low level, and if it becomes low level (
When tl is reached in Fig. 4), wait until a certain period of time has elapsed (tl in Fig. 4) in step S2, and when t2 is reached, in step S3, the back electromotive force of the DC motor, that is, the operational amplifier 4 Sample the output voltage of Then, the sampled voltage is A/D converted in step S4,
In accordance with this A/D converted voltage, the width of the high level of the pulse to be output from the terminal 8b is determined in step S5, and the pulse is output in step S6.

[Effects of the Invention] As explained above, according to the present invention, fluctuations in the rotation speed due to load torque etc. are detected as fluctuations in the induced voltage of the motor itself, and constant speed control is performed based on this, thereby improving the conventional method. There is no need for an encoder to detect the rotation speed, and the motor does not require space to install, making it possible to reduce the size and cost, and to provide an efficient DC motor speed control device. be.

[Brief explanation of the drawing]

FIG. 1 is a speed control circuit diagram of a DC motor according to the first embodiment of the present invention, FIG. 2 is a voltage waveform diagram of the electrodes of the DC motor shown in FIG. 1, and FIG. A speed control circuit diagram of the DC motor according to the embodiment, FIG. 4 is a voltage waveform diagram of the electrodes of the motor shown in FIG. 3, and FIG. 5 is a flowchart of the circuit shown in FIG. 3. ■...DC motor 3...Reference voltage generation circuit 4
... Arithmetic amplifier 7 ... Motor drive circuit 8.
...Microcomputer Figure 4

Claims (1)

[Claims] In a DC motor speed control device that controls the speed of the motor by alternately repeating the time when power is supplied to the motor and the time when power supply to the motor is stopped, the period during which the power supply to the motor is stopped. A speed control device for a DC motor, comprising means for detecting an induced voltage of the motor, and means for controlling power supply time to the motor based on the detected voltage.