JPH0452075B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a motor speed control circuit that performs feedback control based on a signal from a detection element that detects the rotational speed of a DC motor.

[Background technology] When positioning a wood screw with an electric screwdriver or positioning a hole with a drill,
Slow startup is desired, but in conventional startup circuits, although there is some inertia in the motor and drive unit until the set speed (low speed) is reached, the speed is quickly reached as shown in Figure 4a. Therefore, there was a problem of overshooting. This is because a control circuit with fast response speed is required in order to keep the speed constant or change speed smoothly when the load suddenly changes or the set speed changes, so this performance also appears at startup. Incidentally, FIG. 4b shows a starting pulse waveform for starting the motor.

[Object of the Invention] The present invention has been provided in view of the above-mentioned points, and it is an object of the present invention to provide a speed control circuit for a motor that can start and control the speed smoothly from a low rotational speed with almost no overshoot. The purpose is to

[Disclosure of the Invention] An embodiment of the present invention will be described below with reference to the drawings. First, the overall circuit operation will be explained. FIG. 1 shows a block diagram of the speed control circuit, and FIG. 2 shows its time chart in steady state. Speed detection circuit 1 that outputs a signal proportional to the motor rotation speed includes a frequency generator FG and an operational amplifier.
It consists of OP ₁ , resistors _RF , RS _{, etc.} The sample/reset pulse generation circuit 2, which is a timing pulse generation circuit that generates timing pulses such as sample pulses and reset pulses, is composed of a trapezoidal wave circuit 11 that generates a trapezoidal wave, a hysteresis comparator _OP2 , and an IC. A trapezoidal wave circuit 11, which inputs a trapezoidal wave to the sample/reset pulse generator 2a, is comprised of a constant current source I ₁ , a capacitor _CR, and the like. The sawtooth wave generation circuit 3, which generates a sawtooth wave using the reset pulse of the sample/reset pulse generator 2a, is composed of a constant current source I ₂ , a capacitor _CT, etc.
A sample and hold circuit 4 that samples and holds a sawtooth wave voltage using the sample pulse a is comprised of buffers 4a and 4b, a capacitor C _H , and the like. The speed variable circuit 7 for setting an appropriate speed consists of a resistor _RX , a volume VR, a buffer 7a, etc., and its output is input to an error amplifier 12 and compared with the output from the sample and hold circuit 4, and the difference is inverted and amplified. be done. Furthermore, error amplifier 1
The output of 2 is compared with the reference triangular wave from the reference triangular wave generating circuit 5 by a comparator 13 which is a comparison circuit, and when the output of this comparator 13 is at H level, the output circuit 8 is driven. And output circuit 8
The power that configures the switching circuit with the output of
The MOSFET 14 is turned on and the motor M is driven. Further, the power source is a battery B, and the voltage is boosted by a booster circuit 10 and supplied to the motor M. The F-V conversion circuit that performs F-V conversion on the speed signal of the motor M is composed of a sawtooth wave generation circuit 3 and a sample hold circuit 4.

Next, the operation will be explained with reference to FIGS. 1 and 2.
Note that a to j in FIG. 2 indicate waveforms at points a to j in FIG. 1. A speed signal proportional to the rotational speed of the motor M is outputted by a frequency generator FG, and the outputted speed signal is amplified by R _F /R _S times by an operational amplifier _OP1 . The output of the operational amplifier OP ₁ as shown in FIG. 2a is input to a hysteresis comparator OP ₂ to obtain a square wave pulse with a frequency proportional to the rotational speed as shown in FIG. 2b. This square wave causes the trapezoidal wave circuit 11 of the sample/reset pulse generating circuit 2 to generate a trapezoidal wave as shown in FIG. 2c. The rise of this trapezoidal wave is compared with the reference voltages V ₁ , V ₂ , V ₃ from the reference voltage generation circuit 6 (Fig. 2 c), and the sample pulse (Fig. 2 e) and reset pulse (Fig. 2 d) are compared. determine the timing of occurrence. On the other hand, in the sawtooth wave generation circuit 3, the capacitor _CT is charged by the constant current source _I2 , and when _the reset pulse is generated, as shown in FIG. Generates a sawtooth wave as shown. Sample hold circuit 4
Now, when a sample pulse occurs, the sawtooth wave voltage at that time is sampled and held by charging or discharging the hold capacitor C _H. Therefore, a DC signal proportional to the rotational speed as shown in FIG. 2g is outputted to the sample and hold circuit 4.

The error amplifier ₁₂ inverts and amplifies the difference _{between the} voltage _V The reference triangular wave of the reference triangular wave generating circuit 5 is compared with the comparator 13, and the result shown in FIG.
A square wave is obtained as shown in . This square wave is output through the output circuit 8 to obtain a gate voltage as shown in FIG.
The power supply to the DC motor M is controlled by PWM. The lock protection circuit 9 has the following functions. That is, when an overload is applied to the motor M, the rotation speed of the motor M decreases. Therefore, the output frequency of the frequency generator FG becomes smaller,
The output voltage of the sample hold circuit 4 increases.
This voltage is detected by the voltage divided by resistors R _L1 and R _L2 and the comparator 15, and when the rotation speed falls below the set value, the output pulse is cut off and the motor M
This is to stop the

Next, the operation immediately after turning on the power switch, that is, immediately after the power is turned on, will be described. When the power is turned on, capacitor _CR of sample/reset pulse generation circuit 2 begins to be charged. A sample pulse is generated at the rising edge. However, at this time, the capacitor of sawtooth wave generation circuit 3
Since _CT is also being charged, the sample and hold voltage is also low. For this reason, the error amplifier 12
The voltage inverted and amplified by
level, and the gate signal of the power MOSFET 14 is not output, so the motor M will not start.

Next, the starting circuit 16, which is the gist of the present invention, will be explained. This starting circuit 16 includes resistors _R1 to _R5 , a capacitor _C1 , and a comparator 1 as shown in FIG.
A resistor _R1 is inserted and connected between the inverting input terminal of the PWM comparator 13 and the output terminal of the error amplifier 12, and the comparator 1
3 and the comparator 1 of the starting circuit 16.
A resistor _R2 is connected between the output terminal of 6a and the output terminal of 6a.
A resistor _R3 is connected to the inverting input terminal of the comparator 16a.
A reference voltage divided by R ₄ is input, and a connection portion between resistor R ₅ and capacitor C ₁ is connected to the non-inverting input terminal of comparator 16a. Therefore,
The charging voltage of the capacitor _C1 is applied to the non-inverting input terminal of the comparator 16a.

Therefore, when power is applied, resistors R ₃ and R ₄
A reference voltage determined by is applied to the comparator 16a of the starting circuit 16, while the capacitor _C1 is charged with a time constant determined by the resistor _R5 and the capacitor _C1 ,
This voltage is compared by a comparator 16a. While the voltage of capacitor _C1 is low, comparator 16a
Since the output of the error amplifier 12 becomes L level and the voltage of the sample hold capacitor C _H is low at startup, the output of the error amplifier 12, which is at H level, is connected to the resistor _R1.
Divided by resistance with R ₂ , PWM comparator 13
Enter. Here, by setting the resistor-divided voltage within the voltage amplitude range of the reference triangular wave of the reference triangular wave generating circuit 5, a pulse is output from the comparator 13 and the motor M is started. Since the starting current of the motor M is passed in a pulsed manner as shown in FIG. 3b, the motor M is started slowly as shown in FIG. 3a. As shown in Figure 3c, capacitor C ₁
When the charging voltage reaches the midpoint voltage between the resistors R ₃ and R ₄ , the output of the comparator 13 becomes H level.
Since the output stage of the comparator 13 is an open collector, no current flows through the resistor R ₂ , and the output of the error amplifier 12 is directly input to the PWM comparator 13 . When the motor M is started and a speed signal is input from the speed detection circuit 1, the voltage of the capacitor _CH of the sample hold circuit 2 is charged to a voltage proportional to the speed, and normal control is performed. Incidentally, FIG. 3d shows a starting pulse at the time of starting, and shows the output of the comparator 13, and shows a waveform opposite to the output level of the comparator 13. Also, capacitor
When _C1 is charged and comparator 13 is inverted,
At this time, the sample and hold circuit 2 capacitor
Since C _H is also highly charged, the output of the error amplifier 12 decreases, and as a result, the pulse width of the pulse waveform of the output circuit 8 changes as shown in Figure 3b, causing the speed of the motor M to reach the set speed. reach it. Thereafter, normal control is performed as described above.

[Effects of the Invention] As described above, the present invention includes a speed detection circuit that outputs a signal proportional to the rotation speed of a motor, a timing pulse generation circuit that generates a timing pulse based on the speed signal from the speed detection circuit, and a timing pulse. an F-V conversion circuit that performs F-V conversion of a motor speed signal using timing pulses of the generation circuit;
A comparison circuit that compares the F-V converted signal from the F-V conversion circuit with a predetermined reference triangular wave from the reference triangular wave generation circuit, and a switching circuit that supplies drive power to the motor using the output of the comparison circuit. In a motor speed control circuit, a comparator compares the voltage of a capacitor charged at startup with a preset reference voltage, and the F-V converted signal voltage is divided by resistance using the output voltage of the comparator to generate a reference triangular wave. A starting circuit for starting the motor with a pulse waveform to prevent overshoot is constructed with a resistor that makes a part of the voltage higher than the F-V converted signal voltage. Until the capacitor is charged, the output voltage of the comparator is used to divide the F-V converted signal voltage with a resistor to make a part of the reference triangular wave higher than the F-V converted signal voltage. , it is possible to start the motor with a pulse waveform, and as a result, compared to the conventional method where the motor quickly reaches the set speed at startup, the motor can be started slowly and smoothly, and the set speed can be reached with almost no overshoot. Moreover, since the startup circuit is composed of a comparator, a capacitor, and a resistor, the circuit configuration can be simplified and the circuit can be configured without increasing costs too much. be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a time chart in a steady state, FIG. 3 is a time chart at startup, and FIG. 4 is an explanatory diagram of the operation of the conventional example. 1 is a speed detection circuit, 4 is a sample hold circuit, 5 is a reference triangular wave generation circuit, 16 is a startup circuit,
M indicates a motor.

Claims (1)

[Claims] 1. A speed detection circuit that outputs a signal proportional to the rotation speed of the motor, a timing pulse generation circuit that generates a timing pulse based on the speed signal from the speed detection circuit, and a timing pulse generation circuit that generates a motor speed signal using the timing pulse of the timing pulse generation circuit. an F-V conversion circuit that performs F-V conversion of the signal; a comparison circuit that compares the F-V converted signal from the F-V conversion circuit with a predetermined reference triangular wave from the reference triangular wave generation circuit; In a motor speed control circuit that includes a switching circuit that supplies drive power to the motor, a comparator that compares the voltage of a capacitor charged at startup with a preset reference voltage, and a comparator that compares the F-V converted signal voltage. A starting circuit for overshoot prevention, which starts the motor with a pulse waveform, is constructed by dividing a resistor using the output voltage of the motor and making a part of the reference triangular wave higher than the F-V converted signal voltage. A motor speed control circuit characterized by: