JPS6216088A - Driving circuit for dc motor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a motor servo circuit for an electronic still camera, and particularly to a method for shortening the time it takes for one motor to reach a specified speed when starting the motor.

[Background of the invention]

In electronic still cameras, when the shutter button is pressed, power is supplied to the drive circuit of the motor for rotating the recording medium, the motor starts, and the video signal is recorded on the recording medium after waiting for the motor to reach the specified rotation speed. Ru. (Unexamined Japanese Patent Publication No. 59-278
). Here, the shutter opens after the motor reaches a specified number of rotations, and at the same time records from the image sensor to the recording medium.The shutter opens at the same time as the shutter button is pressed, and video information is captured until the motor reaches the specified number of rotations. There is a method in which the data is stored in an element and recorded after the motor reaches a specified rotation speed. At this time, in order to obtain a good photo opportunity and to avoid accumulation of noise in the image sensor, it is desirable to shorten the motor startup time.

Conventionally, as a method for shortening the motor startup time, a method of switching the gain of the control system at an appropriate time (Japanese Patent Laid-Open No. 58-1
03885) or a method in which the phase compensation circuit is separated at startup (Japanese Patent Application Laid-open No. 155687/1987) is known. However, since these methods change the characteristics of the servo section at startup, the circuitry becomes complicated.

In addition, due to phase compensation of the servo section, the rise of the servo section is slow and often causes malfunctions at startup, so there is a method that does not apply control at startup. [Object of the Invention] The object of the present invention is to Just by making a simple addition to the drive circuit,
An object of the present invention is to provide a drive circuit that shortens the starting time of a DC motor.

[Summary of the invention]

The gist of the present invention is that in a system that uses pulse width modulation to control the rotational speed of a DC motor, when the motor is started, pulse width modulation is not performed and current continues to flow through the motor coil without interruption. Pulse width modulation control is performed after the motor speed reaches around the specified speed.

[Embodiments of the invention]

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

FIG. 1 is a block diagram of a motor drive circuit according to the present invention;
FIG. 2 is a waveform diagram of the main part of FIG. 1.

In FIG. 1, 1 is a Hall element, 2 is a polarity discrimination circuit,
3 is an absolute value circuit, 4 is a pulse width modulation circuit (hereinafter abbreviated as PWM circuit), 5 is an OR circuit, 6 is an FG, 7 is a frequency-voltage conversion circuit, 8 is a comparator, 11 is a motor drive unit, 20
is the motor coil.

Next, the operation will be explained. The Hall sensor 1 detects the position of the magnetic pole of the motor and outputs a Hall signal (a). The polarity determination circuit 2 detects the polarity of the Hall signal (a) and outputs a polarity signal (b). The absolute value circuit 3 receives the Hall signal (a)
detects the absolute value of and outputs an absolute value signal (c). P.W.
The M circuit 4 pulse width modulates the absolute value signal (C) and outputs a pulse width modulation signal (hereinafter abbreviated as PWM signal) (d).

On the other hand, the frequency generator 6 outputs the FG multiplied signal e) having a frequency proportional to the speed of the motor, and the frequency-voltage conversion circuit 7 converts the frequency of the FG multiplied signal e) into a voltage, and converts the frequency of the FG multiplied signal e) to a speed error signal ( f). Comparator 8 compares the speed error signal (f) with a reference voltage and outputs a start signal (g). This starting signal (g) is 1 high during the period until the motor reaches the specified speed (hereinafter referred to as starting time), and 10 high during the period after the motor reaches the specified speed (hereinafter referred to as steady state). 9 is a constant voltage, and 1 is a constant voltage.
0 is the ground terminal.

The OR circuit 5 creates a logical sum of the PWM signal (d) and the activation signal (g) and outputs a drive signal (h). This drive signal (h) always maintains a 1 high 1 state during startup, and transmits the PWM signal (g) as it is during normal operation.

The motor drive unit 11 has a polarity signal (1)) and a drive signal (
h) is input. As will be described later, the drive signal (h) turns on and off the current flowing through the motor coil 20, and the one-polarity signal (b) determines the direction of the current flowing through the motor coil 20.

Next, the internal operation of the motor drive section 11 will be explained.

AND circuits 12 and 13 mask the drive signal (h) with a polarity signal (b) and its inversion (6), respectively, and output signals (i) and (j). Signal (1) is high.

When there are 10 signals (j), the transistor 14°1
5 and 16 on, transistors 17.18 and 1
9 is turned off, current flows sequentially from the power supply terminal 21 to the transistors 15. Motor coil 20. Through the transistor 16, the ground terminal 22VC flows into the ground terminal 22VC.

Further, when the signal (i) is 10' and the double signal j) is 1 high, transistors 14, 15 and 16 are off.

Since transistors 17, 18 and 19 are turned on,
Current flows sequentially from the power supply terminal 21 to the transistor 18° motor coil 20. It flows into the ground terminal 22 via the transistor 19. Also, both signals (i) and (j) are 1
When the voltage is 0', all transistors are off, so no current flows through the motor coil 20. It is impossible for signals (i) and (j) to be 1 high' at the same time.

Therefore, when the drive signal (h) is 1 high, the signal (i
) or U) becomes 1 no.i', so a current flows on the motor coil 20. Furthermore, at this time, if the polarity signal (b) is high, the current flows on the motor coil 20 in the direction of A, and if the polarity signal (b) is high, the current flows on the motor coil 20 in the direction of B. flows to Furthermore, when the number of drive signals (h) is 10', no current flows through the motor coil 20.

At startup, the startup signal (g) is at a high level of 1, so current continues to flow through the motor coil 20 without interruption.
Continue accelerating the motor. Therefore, the time to reach the steady speed can be shortened. Note that if the speed error signal (f) takes an abnormal value at startup due to the saturation characteristics or rise characteristics of the frequency-voltage conversion circuit 7, , a timer shown in FIG. 3 can also be used. The output signal (g') of this timer 23 maintains 1 high for a certain period of time from the start of the motor, and then changes to 10'. The holding time of the 'high' state is set to the startup time determined experimentally in advance.In the circuit shown in Figure 3,
Since no control unit is included, malfunction of the control unit at startup can be avoided.

FIG. 4 is another example of a motor drive circuit according to the present invention. In FIG. 4, a speed command signal 101 is pulse width modulated by a PWM circuit 102 to turn a switching transistor 103 on and off. As a result, the current from the power source 104 is intermittent. This intermittent current is applied to the coil 106. Smoothing circuit 10 consisting of a diode 107° and a capacitor 108
5 and then supplies it to the motor 109, thereby rotating the motor 109 at a speed according to the speed command signal 101.

On the other hand, the frequency generator 110 outputs F(3 signals) having a frequency proportional to the speed of the motor 109.

The frequency-voltage conversion circuit 111 converts the FG flaw signal frequency into voltage and outputs a speed error signal.

Comparator 114 compares the speed error signal with a reference voltage;
Outputs a start signal. This starting signal is set to 5 so that it becomes 10' at startup and 1 high' at steady state.

Therefore, at startup, current is supplied from the power supply 104 to the motor 109 via the switching transistor 115. Therefore, there is no voltage drop in the large current filter 106 that flows during startup, and the power supply voltage is applied to the motor 109 almost as is, accelerating the motor 109 and shortening the startup time.

Note that, as already mentioned, it is also possible to use the output of the timer as the activation signal. This method is shown in FIG. 116
is a timer, which outputs 10' for a certain period of time from the start of the motor 17), and then outputs the power recovery high.The holding time of the 'low' state is set to the starting time determined experimentally in advance. I'll keep it.

〔Effect of the invention〕

As described above, according to the present invention, the startup time of the DC motor can be shortened by simply adding a simple addition to the drive circuit.

[Brief explanation of the drawing]

1 and 3 are block diagrams of a motor drive circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram of the main part of FIG. 1, and FIGS. 4 and 5 are another motor drive circuit according to the present invention. It is a block diagram of a circuit. 1...Hall element, 2...Polarity discrimination circuit,
3... Absolute value circuit, 4... PWM circuit, 5...
...OR circuit, 6...frequency generator, 7...
- Frequency-voltage conversion circuit, 8... Comparator, 11... Drive section, 12.
13...AND circuit, 2o...motor coil, 2
3...Timer. Figure 1 IO Figure 3 Figure 1 +++++++++++-J Figure 2

Claims (1)

[Claims] 1. A DC motor, a Hall element that detects the position of the DC motor, a pulse width modulation circuit that pulse width modulates the output signal of the Hall element and outputs a pulse width modulation signal, and a motor coil that uses this pulse width modulation signal. In a DC motor drive circuit comprising a drive unit that controls the speed of the DC motor by turning on and off a drive transistor, means for outputting a starting signal during a period from when the DC motor starts to reach a specified speed; , means for keeping the pulse width modulation signal in an ON state at all times while the start signal is being outputted.