JPS62114485A - Control circuit for speed of motor - Google Patents

Abstract

PURPOSE:To improve the precision of the speed of a motor, and to enlarge the variable range of the speed or revolution by changing charging currents from a sawtooth constant current source at a time when frequency is converted into voltage. CONSTITUTION:A power supply feeding charging currents to a capacitor C2 generating sawtooth waves in a sawtooth generating circuit 5 is used as a variahble constant current source 6. Consequently, voltage at both ends of the capacitor C2 rectilinearly rises. A variable range on the low speed side, the minimum number of revolution, can be lowered particularly, and the charging currents of sawtooth waves from the variable constant current source 6 are altered, thus extremely improving accuracy because the number of revolution is set previously.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a speed control circuit for a motor used in a power tool such as a cordless screwdriver.

[Background Art] FIG. 4 shows a specific circuit diagram of a conventional speed control device for a power tool, and FIG. 5 shows an operation waveform diagram of each part of FIG. 4. This device includes a waveform shaping circuit 21 that shapes a signal proportional to the number of rotations of the motor M from a function generator r7 (-) attached to the motor N1, and a signal from the waveform shaping circuit 21 into a square wave. A Schmitt circuit 22 that shapes the waveform, a one-shot multivibrator 23 that outputs a one-shot pulse based on the pulse signal from the Schmitt circuit 22, and an integrating circuit (sawtooth wave generation circuit) that integrates the one-shot pulse from the one-shot multivibrator 23. 24, a speed setting circuit 26 that continuously performs arbitrary speed settings, and an output comparator 2 that compares the output of the speed setting circuit 26 and the output of the integrating circuit 24.
5, and the output of this output humparator 25 causes the motor M
It is composed of a drive circuit 27 and the like that rotationally drives the.

Next, the operation will be explained based on FIGS. 4 and 5. still,
The waveform at point a-H in FIG. 5 shows the waveform at point a-H in FIG. First, a signal proportional to the rotational speed of the motor M is generated from the function generator FG attached to the motor M, as shown in FIG. 5(a). This signal is waveform-shaped by the Schmitt circuit 22 and is shown in FIG.
1)) It becomes a square wave as shown in (1)). Furthermore, this signal
The signal is input to the one-shot multivibrator 23, and a pulse as shown in FIG. 5(c) is generated. This trigger pulse turns on the discharge transistor Tr2 for a short time.

Further, the resistor 28 and capacitor 29 of this integrating circuit 24 are charged at a preset time constant.

The output of the integrating circuit 24 is input to the non-inverting input terminal of the operational amplifier 30 of the output comparator 25. The speed setting circuit 2G is composed of a capacitor 31, a Zener diode 32, a resistor 33, a volume Rv, etc., and a voltage continuously variable and set by the volume Rv is input to the inverting input terminal of the operational amplifier 30. ing. The polynium Rv is set to an arbitrary speed, and by changing the value of the volume Rv, a voltage corresponding to a certain speed is set. Now, assume that a certain speed is set by changing the volume Rv. The output comparator 25 compares the voltages from the speed setting circuit 26 and the integrating circuit 24, as shown in FIG. 5(d).
When the output voltage of the integrating circuit 24 is higher than the set voltage, an H level signal is output as shown in FIG. 5(e), and the pulse signal is inverted by the transistor Tr3 as shown in FIG. 5('). If the period of the pulse is faster (f), the frequency of the sawtooth wave will also be higher, and the frequency of the output waveform of the output comparator 25 will also be higher, and as shown in FIG. The energy to the integrating circuit decreases.Then, the amount of conduction of the transistor Tr decreases, suppressing the current of the power transistor Tr5 and lowering the rotation speed of the motor M.On the other hand, if the pulse period becomes slower, , is the opposite of the above operation and increases the rotation of the motor M. In this way, the speed setting circuit 26
The speed of the motor M can be continuously controlled by the voltage set by the voltage. In the case of the conventional example, the charging voltage of the capacitor 29 is input to the output comparator 30 and compared, so the speed variable range is narrow, the accuracy of the rotation speed is poor, and the response speed to sudden loads etc. The problem was that it was bad.

[Object of the invention] In view of the above-mentioned points, the present invention has the following propositions:
To provide a motor speed control circuit that improves the accuracy of motor speed and widens the variable range of rotational speed by changing the charging current from a sawtooth wave constant current source when converting frequency into voltage. The purpose is to be.

[Disclosure of the invention 1 Embodiments of the present invention will be described below with reference to the drawings.

For example, in electrical equipment that uses a motor, such as a power tool, it is very convenient to control the rotation speed of the motor.

Now, if we consider a rechargeable electric drill driver, when drilling a hole in an aluminum chassis, etc., it first carefully positions itself at low speed, then gradually increases the speed (rotation rfL) and drills the hole in a short time. You can finish the work. The present invention is for controlling the rotational speed of such a motor to a set speed. This will be explained in detail below.

FIG. 1 shows a specific circuit diagram of this device, and FIG. 3 shows its operating waveform diagram. This speed control exterior Fe includes an FG amplifier 1 that amplifies the output from the function generator F''G similar to the conventional one, and an F-V conversion means that converts the frequency of the output of the FG amplifier 1 into voltage via a hysteresis comparator 2. The sample-and-hold circuit 3 is compared with the sample-and-hold voltage output of the sample-and-hold circuit 3 and the output of the reference oscillator 9, and the PWM reference oscillator 9 for generating a reference clock is compared with the output of the reference oscillator 9 to generate a PWM for driving the motor M.
(Pulse W 1dth Modulation
n) Consists of an output comparator 7, which is a comparison means for generating the hull . The sample and hold circuit 3 performs frequency-voltage conversion, and includes a control pulse generation circuit 4, a sawtooth wave generation circuit 5, and a buffer 7B.
,, B2, a capacitor c y which is a hold circuit which switches the switch SW2 by a hold pulse from the control pulse generation circuit 4 and holds the sawtooth wave.
4J? It consists of The sawtooth wave generation circuit 5 is
The capacitor C2 for sawtooth wave generation is activated by the reset pulse from the control pulse generation circuit 4.
The capacitor C2 is composed of a variable constant current source 6 that charges the capacitor C2 with a constant current, a switch SW1 that charges and discharges the capacitor C2 using a reset pulse, and the like. Incidentally, FIG. 2 is an overall circuit diagram specifically showing the variable constant current T1.6, which is composed of a transistor TrHTr, a volume Rv, etc.

Next, the operation will be explained with reference to FIGS. 1 to 3.

The signal of the function generator FG, which generates a sine wave signal with a frequency proportional to the rotational speed of the motor M as shown in FIG. 3(a), is amplified by the FG amplifier 1.
In addition, as shown in the PtIJ3 diagram (b), the signal fluctuates around Vcc/2. Here, the resistances R1 and R1 on the input side of the operational amplifier OP of the FG amplifier 1 are R3=R,
The gain of FG amplifier 1 is set to R2/
It is determined by the ratio of R. The capacitor C1 is for cutting the DC component. Then, the FG 7 7'' 1 output is shaped into a square wave by the hysteresis comparator 2 as shown in FIG. 3(e). Using the square wave, the sample and hold circuit 3 performs frequency-voltage conversion. At this time, the variable constant current source 6 and the capacitor C2 form a linearly increasing sawtooth wave as shown in FIG. 3 (cl).The current value ro of the variable constant current source 6 is shown in FIG. The speed of the motor M can be set by making it variable using an external volume Rv.

The sawtooth wave generating circuit 5 generates a sawtooth wave as shown in FIG. 3(d), and the control pulse generating circuit 4 outputs a reset pulse and a sample pulse to hold the voltage charged in the capacitors C.

That is, the charge charged in the capacitor C1 is discharged by the reset pulse shown in FIG. 3(f), and the charging voltage of the capacitor C3 is sampled and held by the sample pulse shown in FIG. A DC signal proportional to the rotational speed as shown in (g) will be output.Then, the output of the sample hold circuit 3 and the inverting and non-inverting input terminals of the PWM reference reference oscillator 9 output output comparator 7 will be output. Each will be input.

The PWM reference generator 9 operates as follows. first,
Assume that the output of the operational amplifier OP2 has a positive saturation voltage ■1-. A charging current flows through the capacitor C2 through the resistor R3, and the voltage Vc at the e input terminal of the operational amplifier OP2
rises. ■The input terminal of operational amplifier OP2 has a resistor R.
6. Due to R,,R, the voltage Vc increases by (R)/(R8+R?)IVl-.

When the voltage Vc reaches the voltage given by the above equation, the output of the operational amplifier OP2 becomes a negative saturation value (=OV) V,-'.

Therefore, capacitor C4 is now! R7/(R6+R?>IVL"; is discharged until it becomes 0. This is repeated thereafter. The input terminal of the output comparator 7 is connected to the voltage from the sample and hold circuit 3 and the reference oscillator 11 as shown in FIG. 3(g). When the reference clock is input from the sample and hold circuit 3 and the voltage of the sample and hold circuit 3 is higher than the reference clock pulse, a pulse signal is outputted from the output comparator 7 as shown in FIG. The transistor Q1 is turned on via the output buffer 7, and the collector current of the output transistor Q is increased.
The flies are controlled. In other words, suppose that a certain speed is now set by changing the volume Rv,
If the period of the function generator FG is faster, the peak value of the sawtooth wave will be lower, so the output of the sample and hold circuit 3 will be lower than 9, the pulse width of the output converter 7 will be narrower, and the amount of conduction of the transistor Q will be reduced. Decrease the rotation speed of motor M. Conversely, if the period of the function generator FG becomes slower, the above operation is reversed and the rotation of the motor M is increased.

[Effect of the Invention 1] As described above, the present invention includes an F-V conversion means for converting a frequency signal proportional to the rotational speed of the motor into a voltage according to the frequency, and a reference clock pulse and the F-V conversion means. a control pulse generating circuit which receives the frequency signal and generates a predetermined timing pulse; The above-mentioned F- In the motor speed control circuit that constitutes the V conversion means, the voltage across the capacitor is Since the increase is linear, it is possible to lower the variable range, especially on the low speed side, that is, the minimum rotation speed.Also, by changing the sawtooth wave charging current from the variable constant current source, the rotation speed (speed) can be set. Because of this, the accuracy is very good, and it has the effect of widening the variable range of rotation speed.Furthermore, unlike the conventional model, there are fewer integration circuits, which means fewer capacitors. Therefore, the response speed is fast.

[Brief explanation of drawings]

FIG. 1 is a specific circuit diagram of an embodiment of the present invention, FIG. 2 is a more specific circuit diagram of the same as above, FIG. 3 is an operation waveform diagram of the same as above, and FIG.
The figure is a specific circuit diagram of a conventional example, and FIG. 5 is an operation waveform diagram of the same. 3 is a sample hold circuit, 4 is a control pulse generation circuit,
5 is a sawtooth wave generating circuit, 6 is a variable constant current source, C2 is a capacitor, and M is a motor.

Claims (3)

[Claims] (1) F-V conversion means for converting a frequency signal proportional to the rotation speed of the motor into a voltage according to the frequency; and comparison means for comparing a reference clock pulse with the voltage from the F-V conversion means; a control pulse generation circuit for generating a predetermined timing pulse in response to the frequency signal; and a control pulse generation circuit for generating a predetermined timing pulse in response to the frequency signal; A sawtooth wave generation circuit that generates a sawtooth wave and a hold circuit that holds the sawtooth wave voltage using the second timing pulse from the control pulse generation circuit can be
- A motor speed control circuit constituting a V conversion means, characterized in that the power supply for supplying charging current to a capacitor that generates a sawtooth wave of a sawtooth wave generation circuit is a variable constant current source. . (2) A speed control circuit for a motor according to claim 1, wherein the motor is a DC motor. (3) A speed control circuit for a motor according to claim 1, wherein the speed-controlled motor is used in a power tool.