JPH05309183A - Motor control circuit for shaver - Google Patents

Abstract

PURPOSE:To efficiently shave the skin by increasing the steady state rotational speed of a motor only during high load operation. CONSTITUTION:A bridge circuit in a bridge servo circuit BSC has a motor M, and the circuit BSC is connected to an interconnecting point between a first bridge resistor RK in the bridge circuit and the motor M, and incorporates a resistance value change-over circuit RT for alternately selecting a high or small resistance value. A resistor RI is connected between the emitter of a current control transistor Tr in the circuit BSC, for changing the value of current Im running through the motor M, and the ground. Further, there is provided a rotational speed control means RC for comparing a voltage VI detected across the resistor RI with a reference voltage Vref so as to select the low resistance value of the change-over circuit RT if the detected voltage is lower than the reference voltage, but select the high resistance value thereof if the detected voltage is higher than the reference voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control circuit for an electric razor.

[0002]

2. Description of the Related Art FIG. 2 shows a bridge servo circuit which constitutes a motor control circuit for a conventional electric razor. The bridge circuit includes first to third bridge resistors RK, R1 and R2 and a motor M as a bridge resistor. Has been formed. The equivalent circuit of the motor M inserted in one side of this bridge circuit is
Equivalent DC resistance Rm that normally forms the DC resistance of the motor coil
And a voltage source (that is, counter electromotive force) Ea whose voltage rises in proportion to the number of revolutions. In addition, R in FIG.
t is a semi-fixed resistor for adjustment, I is a constant current circuit, COM is a comparator, and Tr is a current control transistor.

The input balance condition of the comparator COM of the conventional motor control circuit is the first and second bridge resistance R.
When the voltage between the interconnection point of K and R1 and the interconnection point of the motor M and the third bridge resistor R2 is V, it is given by the following equation. RK · Im + Rt · Iref = V · R1
/ R1 + R2 (In this formula, RK, R1, R2
Are the resistance values of the bridge resistors RK, R1, and R2, Rt is the resistance value of the semi-fixed resistor Rt, Im is the current passing through the motor M,
Iref is a constant current determined by the constant current circuit I. )
In other words, the comparator COM outputs the voltage (RK · Im) across the first bridge resistor RK to the resistor RK.
And a total voltage value obtained by adding the voltage (Rt · Iref) between the interconnection point of the motor M and the comparator COM, and
Voltage value across the bridge resistor R1 (V · R1 / R1
+ R2). By the way, the combined voltage value is used as a reference voltage (substantially proportional to the back electromotive force Ea of the motor M) of the comparator CO by the constant current circuit I.
Given to M. Further, the change in the rotation speed of the motor M and the change in the counter electromotive force Ea of the motor M are in a proportional relationship, and the current Im passing through the motor M should change according to the load conditions such as the beard darkness and strength. Is known.

Then, the comparator COM operates so as to maintain the input balance condition. That is, the second
When the voltage value between both ends of the bridge resistor R1 exceeds the reference voltage, the comparison output output from the comparator COM is applied to the base of the current control transistor Tr accordingly, and the current Im flowing through the motor M is reduced. The counter electromotive force Ea of the motor M is controlled to be constant.

[0005]

As described above, the conventional motor control circuit keeps the counter electromotive force Ea of the motor M constant by the servo operation of the motor control circuit so that the motor M rotates at a predetermined rotation speed (steady rotation speed). The steady rotation speed is usually determined according to the standard load size. Therefore, for example, when the load at the time of shaving is larger than the standard, such as when the beard is long and the amount thereof is large, the rotation speed of the motor M and the speed of the inner blade corresponding to the rotation speed tend to be insufficient.
There is a problem that shaving cannot be performed efficiently.

By the way, in consideration of such a situation in advance, it is conceivable to design a motor control circuit in which the steady rotation speed of the motor M is increased in accordance with a high load. However, in this case, since the rotation speed of the motor is high even under a standard load, driving noise, vibration, and power consumption are all increased. Therefore, it is not practical to raise the steady-state rotation speed of the motor indiscriminately as described above.

An object of the present invention is to obtain a motor control circuit for an electric razor capable of efficiently shaving by increasing the rotation speed of the motor only when the load is high.

[0008]

In order to achieve the above object, a motor control circuit of the present invention comprises a bridge circuit including first to third bridge resistors and a motor, the first bridge resistor and the motor. A resistance value switching circuit that has a plurality of resistors connected to an interconnection point with and selects and switches the magnitude of a combined resistance value of these resistors, the first bridge resistor input through the switching circuit, and the resistance value switching circuit. A first comparison circuit for comparing the voltage at the interconnection point with the motor and the voltage at the interconnection point for the second and third bridge resistors, and the magnitude of the current flowing through the motor at the comparison output of this comparison circuit. A bridge servo circuit having a current controlling transistor for changing the voltage, a resistor inserted between the emitter of the transistor and ground, and a detection voltage generated across the resistor are compared with a reference voltage. A second comparison circuit is provided, and a combined resistance value of the resistance value switching circuit is selected to be small by a comparison output when the detection voltage is smaller than the reference voltage, and when the detection voltage is larger than the reference voltage. And a rotation speed control means for selecting a large combined resistance value of the resistance value switching circuit based on the comparison output.

[0009]

In the above structure, the resistance value switching circuit of the bridge servo circuit determines the reference voltage of the first comparison circuit of the servo circuit, and when the resistance value is selected to be small by the switching, the reference value corresponding to the low load is applied. A voltage is set in the first comparison circuit, and when a large resistance value is selected, a reference voltage corresponding to a high load is set in the first comparison circuit. Then, the bridge servo circuit performs a servo operation for controlling the magnitude of the current flowing through the motor via the current control transistor with the comparison output from the first comparison circuit. As a result, the rotation speed of the motor included in the bridge circuit is maintained at the steady rotation speed corresponding to the low load and at the high rotation speed corresponding to the high load. Further, the resistor connected to the emitter of the transistor detects the current passing through the motor and generates a detection voltage according to the current across the current. The rotation speed control means compares the detected voltage input thereto with a reference voltage, and when the detected voltage is smaller than the reference voltage set in the second comparison circuit of the rotation speed control means, the rotation speed control means compares the detected voltage with the reference voltage. The control means selects the combined resistance value of the resistance value switching circuit to be small, and when the detected voltage is higher than the reference voltage set in the second comparison circuit of the rotation speed control means, the rotation speed control means causes the resistance value to change. Make the combined resistance of the value switching circuit large.

Therefore, this motor control circuit controls the motor to a steady rotation by reducing the reference voltage of the bridge servo circuit when the load associated with shaving is small, and when the load associated with shaving becomes larger than usual. , Increase the reference voltage of the bridge servo circuit to control the motor at high speed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a diagram showing the configuration of a motor control circuit for an electric shaver according to an embodiment of the present invention. In the figure, RK is the first
R1 is a second bridge resistor,
One end thereof is connected to one end of the bridge resistor RK,
R2 is a third bridge resistor, one end of which is connected to the other end of the bridge resistor R1. M is a motor as a bridge resistor having one end connected to the other end of the bridge resistor RK and the other end connected to the other end of the bridge resistor R2. A bridge circuit is formed by these, and the interconnection point of the bridge resistors PK and R1 of this circuit is connected to the positive power supply terminal (+ Vcc) of a secondary battery or the like not shown.

The equivalent circuit of the motor M inserted into one side of this bridge circuit is an equivalent DC resistance Rm that normally forms the DC resistance of the motor coil and a voltage source (that is, counter electromotive force) whose voltage rises in proportion to the number of revolutions. ) It is represented by a series circuit of Ea. The motor M is a power source for driving the inner blade of the electric razor.

The interconnection point between the bridge resistor PK of the bridge circuit and the motor M is connected to the inverting input terminal (-terminal) of the first comparison circuit COM1 via the resistance value switching circuit RT and the constant current circuit I in series. Has been done. Further, the interconnection point of the bridge resistors R1 and R2 is connected to the non-inverting input terminal (+ terminal) of the first comparison circuit COM1. In the first comparison circuit COM1, the bridge resistance RK and the motor M which are input through the resistance value switching circuit RT and the constant current circuit I.
The voltage at the interconnection point with is set as the reference voltage. The first comparison circuit COM1 has its reference voltage and bridge resistors R1 and R1 input to the non-inverting input terminal (+ terminal).
The voltages at the two interconnection points are compared and a comparison output corresponding to the voltage difference is applied to the base of the npn-type current control transistor Tr. The collector of the transistor Tr is the bridge resistor R2 of the bridge circuit and the motor M.
And the emitter is grounded.

The bridge circuit and the resistance value switching circuit R
A bridge servo circuit BSC is formed by T, the constant current circuit I, the first comparison circuit COM1, and the transistor Tr. The resistance value switching circuit RT includes a first resistor RT1 connected to an interconnection point between the bridge resistor PK and the motor M, a second resistor RT2 connected in series with the resistor RT1, and a first resistor RT1. Pnp type transistor Q
Third connected in parallel through the emitter and collector of
It is formed from the resistor RT3.

A resistor RI for detecting a current Im passing through the motor M is inserted between the emitter of the transistor Tr of the bridge servo circuit BSC and the ground. Further, the emitter of the transistor Tr is the second comparison circuit CO.
It is connected to the non-inverting input terminal (+ terminal) of M2 via a resistor R5. The inverting input terminal (-terminal) of the second comparison circuit COM2 is variable with the resistance R7 in the DC voltage dividing circuit including the resistance R6, the resistance R7, and the variable resistance VR connected between the positive power supply terminal (+ Vcc) and the ground. It is connected to the interconnection point with the resistor VR. The interconnection point of the resistors R6 and R7 is grounded via the diode D in the forward direction. This diode utilizes its forward voltage drop to generate a constant voltage.

The second comparison circuit COM2, the DC voltage dividing circuit, and the diode D form a rotation speed control means RC. The output terminal of the second comparison circuit COM2 is connected to the base of the transistor Q of the resistance value switching circuit RT.

In the bridge servo circuit of the motor control circuit having the above structure, when the voltage between the interconnection point of the bridge resistors RK and R1 and the interconnection point of the motor M and the bridge resistor R2 is V, this voltage V Is given by V = RK · Im + Rm · Im + Ea (1) Then, the input balance condition of the first comparison circuit COM1 of this servo circuit is given by the following equation. RK · Im + RT · Iref = V · R1 / (R1 + R2) (2) Therefore, if R1 / (R1 + R2) is set as a constant k, k (RK · Im + Rm · Im +) can be obtained by the above (1) and (2).
Ea) = RK · Im + RT · Iref, and k
If (RK + Rm) = RK, then RT · Iref = k · Ea …………………………………… (3).

Since k is a constant, the counter electromotive force Ea of the motor M is proportional to the resistance value of the resistance switching circuit RT. Further, between the counter electromotive force Ea of the motor M and the rotation speed N, Ea = K · N (K is the motor M
It is also known that there is a proportional relationship between the counter electromotive force Ea and the rotation speed N. In addition,
In the equations (1) to (3), RK, R1, and R2 are resistance values of the bridge resistors RK, R1 and R2, RT is a resistance value of the resistance value switching circuit RT, Im is a current passing through the motor M, and Iref is Constant current determined by constant current circuit I, Ea
Is the back electromotive force of the motor M.

The motor control circuit provided with the bridge servo circuit having the above relationship is the first comparison circuit COM1.
At the interconnection point (reference voltage) between the bridge resistor RK and the motor M input to the inverting input terminal through the resistance value switching circuit RT and the constant current circuit I, and the bridge input to the non-inverting input terminal. The voltages at the interconnection points of the resistors R1 and R2 are compared, and a comparison output according to the voltage difference is applied to the base of the current control transistor Tr. for that reason,
The current Im passing through the motor M is controlled by the transistor Tr, whereby the servo operation for stabilizing the counter electromotive force Ea of the motor M is performed.

In this servo operation, the current Im passing through the motor M is inserted between the emitter of the transistor Tr and the ground after passing between the collector and the emitter of the transistor Tr (in other words, in the drive current circuit of the motor M). Through (inserted) resistor RI. Therefore, a terminal voltage corresponding to the current Im, that is, a detection voltage VI is generated between both ends of the resistor RI, and this voltage VI passes through the resistor R5 and is not applied to the second comparison circuit COM2 of the rotation speed control means RC. Input to the inverting input terminal.

Then, the second comparison circuit COM2 is
The reference voltage Vref corresponding to the variable resistor VR of the DC voltage dividing circuit including the resistors R6 and R7 and the variable resistor VR is compared with the detection voltage VI. The output of the second comparison circuit COM2 has a low (L) potential when the detection voltage VI is lower than the reference voltage Vref, and conversely has a high (H) potential when the detection voltage VI is higher than the reference voltage Vref.

Therefore, when the shaving load is small and therefore the current Im passing through the motor M is small, the detection voltage VI is also small, so that the output of the second comparison circuit COM2 becomes the L potential by the above comparison. Therefore, the transistor Q of the resistance value switching circuit RT is turned on, and the third resistor RT3 is connected in parallel to the first resistor RT1 via the emitter and collector of the transistor Q. Then, the combined resistance of the first to third resistors RT1 to RT3 becomes the resistance value of the resistance value switching circuit RT, so that the resistance value is small. Then, the voltage corresponding to the small resistance value is set as the reference voltage of the first comparison circuit COM1, so that the bridge servo circuit accordingly follows the counter electromotive force Ea of the motor M.
Servo operation is performed so as to reduce. As a result, the rotation speed N of the motor M decreases and the motor M maintains a steady rotation. Since such steady rotation is lower than the rotation corresponding to the high load, the driving sound, vibration, and power consumption of the electric razor at that time are small.

Further, when the user's beard is long and the amount is large, the load on the inner blade driven by the motor M (in other words, the load on the motor M) is large, and accordingly, the current Im flowing through the motor M is correspondingly large. Will grow. Therefore,
The detection voltage VI detected by the resistor RI is also large. As a result, when the detected voltage V1 becomes higher than the reference voltage Vref, the output of the second comparison circuit COM2 becomes H potential.

Then, the transistor Q of the resistance value switching circuit RT is turned off, and the third resistor RT3 is disconnected from the series circuit of the first and second resistors RT1 and RT2.
Therefore, the resistance value of the resistance value switching circuit RT becomes a combined resistance of the first and second resistors RT1 and RT2 connected in series, and therefore the resistance value of the resistance value switching circuit RT is the resistance during the steady operation. It becomes larger than the value and is set as the reference voltage of the first comparison circuit COM1.

Therefore, the bridge servo circuit is operated by the motor M.
Since the servo operation is performed so as to increase the counter electromotive force Ea, the rotation speed N of the motor M is increased and the driving speed of the inner blade can be increased. Therefore, it is possible to efficiently shave a beard with a high load.

The control for increasing the rotation speed of the motor M only when the load is high as described above is, of course, maintained by the servo operation of the bridge servo circuit as long as the high load is continued, and the load is small. Then, the normal rotation is restored. Moreover, as described above, the current flowing through the motor that changes according to the size of the load is detected when it deviates from the servo system of the bridge servo circuit, and the resistance value of the resistance value switching circuit is selected based on that, and the bridge servo circuit By changing the reference voltage and increasing the target speed,
The response of the servo operation of the bridge servo circuit can be compensated for to respond quickly, and the decrease in rotation speed can be reduced.

The present invention is not limited to the above embodiment. For example, a plurality of resistance value switching circuits RT including the first to third resistors RT1 to RT3 and the transistor Q in the one embodiment are provided in series and the reference voltage Vr is provided.
By providing a plurality of rotation speed switching circuit means RC each having a different value of ef and controlling ON / OFF of the transistor Q of the corresponding resistance value switching circuit RT by these, the target of the motor M according to the degree of the load due to the whiskers. The control rotation speed may be performed in multiple stages.

[0028]

As described above in detail, in the motor control circuit of the present invention, when the load associated with the shaving is small, the reference voltage of the bridge servo circuit is reduced to control the motor to the steady rotation, and the shaving is associated with the shaving. Only when the load becomes excessive, the reference voltage of the bridge servo circuit is increased to control the motor at high speed.Therefore, increase the motor speed only when the load is high, such as when shaving a long dark beard. Thus, it is possible to efficiently perform the shaving, and it is possible to prevent the rotation of the motor from being lowered when the load is small and the driving noise, vibration, power consumption, and the like from increasing.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a motor control circuit of an electric shaver according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a motor control circuit of an electric shaver according to a conventional example.

[Explanation of symbols]

RK ... first bridge resistance, R1 ... second bridge resistance, R2 ... third bridge resistance, M ... motor, RT ... resistance value switching circuit, RT1 to RT3 ... resistance, Q ... transistor, COM1 ... first Comparison circuit, Tr ... Transistor, BSC ... Bridge servo circuit, RI ... Resistor, COM
2 ... 2nd comparison circuit, RC ... Rotation speed control means.

Claims (1)

[Claims] 1. A bridge circuit composed of first to third bridge resistors and a motor, and a combined resistor having a plurality of resistors connected to an interconnection point between the first bridge resistor and the motor. A resistance value switching circuit that selects and switches the magnitude of the value, a voltage at an interconnection point of the first bridge resistor and the motor, which is input via the switching circuit, and an interconnection of the second and third bridge resistors. A first comparison circuit that compares the voltage at a point, a bridge servo circuit that has a current control transistor that changes the magnitude of the current that flows in the motor with the comparison output of this comparison circuit, the emitter of the transistor, and ground A resistor inserted between the resistor and a second comparison circuit for comparing a detection voltage generated across the resistor with a reference voltage, and when the detection voltage is smaller than the reference voltage, Rotation speed control means for selecting the combined resistance value of the resistance value switching circuit to be small by comparison output and selecting the combined resistance value of the resistance value switching circuit to be large for comparison output when the detected voltage is larger than the reference voltage A motor control circuit for an electric razor, which comprises: