JPH11252979A - Load torque detection circuit for dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a load torque detection circuit capable of load torque positively from light load timing to locking timing, regardless of how a flywheel diode is connected. SOLUTION: An integrating capacitor C1 is charged by the voltage across a current detection resistor Ri, which detects armature current to obtain a load torque detection signal Vst across the capacitor C1 . To charge the integrating capacitor C1 only for a fixed period after the time when a transistor TR1 which on-off controls the armature current turns to in an on-condition, an integrating time limit circuit 10 which limits the charging time of the integrating capacitor C1 is provided. The charging time of the integrating capacitor C1 is set to a fixed, value which is smaller than the on-time of the transistor TR1 , when the on-duty ratio of the transistor TR1 is minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load torque detecting circuit for detecting a load torque of a DC motor whose armature current is on / off controlled.

[0002]

2. Description of the Related Art A circuit shown in FIG. 7 or FIG. 8 is known as a circuit for detecting a load torque of a DC motor. In these figures, Wa is an armature coil of the DC motor 1, and one end of the armature coil Wa is a PNP transistor TR.
1 and the emitter of the transistor TR1 is connected to the positive terminal of a DC power supply (not shown) that outputs a DC voltage VB. Ri is a current detection resistor Ri connected in series with the armature coil at the other end of the armature coil.
The terminal of the current detection resistor Ri on the side opposite to the armature coil is grounded together with the negative terminal of a DC power supply (not shown). Connect the resistor R1 to the non-ground side
Is connected, and an integrating capacitor C1 is connected between the other end of the resistor R1 and ground.

[0003] The base of the transistor TR1 is connected to the control unit 2, and an on / off command signal is given from the control unit 2 to the base of the transistor TR1. The on / off command signal generated by the control unit 2 is a signal in which an on command signal Von and an off command signal Voff are generated alternately. In this example, since the transistor TR1 is a PNP transistor, the off command signal Voff is a high-level signal,
The ON command signal Von is a signal of a zero level (ground level).

The control section 2 controls the on / off control of the transistor TR1 by changing the time width of the on command signal Von applied to the transistor TR1 according to a predetermined control condition (for example, a condition that the rotational speed is maintained at an indicated value). By controlling the average value of the armature current Ia, the rotation speed of the electric motor is controlled. The control unit 2 also decreases the on-duty ratio of the transistor TR1 to reduce the armature current when the motor load exceeds the limit value due to an excessive load on the motor or the rotor is locked. It has a current limiting function that controls to keep it below. The on-duty ratio is defined by the ratio of the on-time Ton to the sum of the on-time Ton of the transistor TR1 and the off-time Toff following the on-time [= Ton / (Ton + Toff)].

In the example shown in FIGS. 7 and 8, an armature current control switch which is turned on by the transistor TR1 and which supplies an armature current to the armature coil Wa only while the ON command signal Von is being supplied. The motor drive circuit is constituted by the armature current control switch 3, the control unit 2, and a DC power supply (not shown).

A resistor R1 as a current limiting element and an integrating capacitor C1 constitute an integrating circuit 4 ', and a resistor Ri for current detection and an integrating circuit 4' constitute a load torque detecting circuit 5 '.

Df is set so that the voltage induced in the armature coil Wa is applied in the forward direction when the transistor TR1 is turned off and the armature current Ia flowing through the armature coil Wa is cut off. A flywheel diode connected in parallel to the armature coil Wa. In the circuit shown in FIG. 7, the armature coil Wa and the current detecting resistor R
This flywheel diode Df is connected in parallel to both ends of a series circuit with i.

When the flywheel diode is connected in parallel to the armature coil Wa in this way, when the armature current control switch 3 is turned on and off to perform the PWM control of the armature current, the switch 3 is turned on. Since the armature current (flywheel current) can flow through the flywheel diode Df by the induced voltage of the armature coil even during the off state, the flywheel effect is generated by the flywheel current to smoothly rotate the motor. Can be

However, if a flywheel diode is connected to both ends of the series circuit of the armature coil Wa and the current detecting resistor Ri as shown in FIG. 7, a loss occurs when the flywheel current flows through the resistor Ri,
There is a problem that the amount of attenuation of the flywheel current is increased and the flywheel effect is reduced. In order to avoid such a problem, in the circuit shown in FIG. 8, the flywheel diode D is directly connected to both ends of the armature coil Wa.
f are connected in parallel.

In the circuits shown in FIGS. 7 and 8, the armature current Ia flows through the current detecting resistor Ri, and the resistor Ri
A voltage Vi proportional to the armature current Ia is generated at both ends of the armature.
In the DC motor, since the armature current Ia is proportional to the load torque, the load torque can be detected from the voltage Vi.

If the transistor TR1 is kept on when the DC motor is driven and the armature coil is continuously energized, the current flowing through the current detecting resistor Ri does not fluctuate finely. The voltage at both ends of Ri can be used as it is as a load torque detection signal, but the transistor TR1 is turned on / off (PWM control).
Control), the voltage across the resistor Ri fluctuates finely as the transistor TR1 turns on and off.
It is not appropriate to use the voltage between both ends of the resistor Ri as it is as the load torque detection signal.

In the load torque detecting circuit 5 'shown in FIGS. 7 and 8, the voltage Vi generated across the current detecting resistor Ri is applied to the integrating capacitor C1 through the resistor R1.
To obtain an integrated voltage indicating the average value of the armature current Ia at both ends of the integrating capacitor C1 and use the integrated voltage as a load torque detection signal Vst indicating the average load torque of the motor. Like that.

FIG. 9 shows the waveform of each part of the circuit shown in FIGS. 7 and 8 with respect to time t. In FIG.
Although the periods T1 to T3 are shown, in this example, the period T1
It is assumed that the motor load increases stepwise from 1 to T3, and in the period T3, the motor load becomes excessive or the rotor is locked, so that the control unit 2 It is assumed that a current limiting operation for limiting the current to the limit value or less is being performed.

FIG. 9A shows the on / off operation of the transistor TR1. The transistor TR1 is in the ON state during the period when the ON command signal Von is supplied (the period indicated as ON in the figure). , While the OFF command signal Voff is given (period indicated as OFF in the figure)
It turns off.

When the transistor TR1 is on, an armature current flows from a DC power supply (not shown) through the emitter-collector circuit of the transistor TR1, a series circuit of the armature coil Wa and the current detecting resistor Ri.
When the transistor TR1 is turned off, an induced voltage is generated in a direction in which the armature current that has been flowing to the armature coil Wa continues to flow. Since this induced voltage is applied to both ends of the flywheel diode Df in the forward direction, the flywheel diode Df
Current continues to flow through f, but this current decays over time.

In the example shown in FIG. 7, since the flywheel diode Df is connected in parallel to the armature coil Wa via the current detecting resistor Ri, the flywheel diode Df passes through the flywheel diode Df while the transistor TR1 is in the off state. The flowing armature current also flows through the current detection resistor Ri. Therefore, the waveform of the voltage Vi generated at both ends of the current detection resistor Ri is similar to the waveform of the armature current, and as shown in FIG. 9B, at a predetermined rate during the time when the transistor TR1 is in the ON state. Rise, transistor T
During the period when R1 is in the off state, the waveform falls at a predetermined rate. The load torque detection signal Vst obtained by integrating this voltage Vi by the integration circuit 4 'becomes a DC voltage having a predetermined level as shown in FIG. 9 (C), and this load torque detection signal (both ends of the integration capacitor C1). The level of the voltage (Vst) is proportional to the magnitude of the average load torque.

In the period T1 shown in FIG. 9, since the motor is rotating with a relatively small load, the load torque detection signal Vst (FIG. 9C) obtained from the load torque detection circuit shown in FIG. Indicates a relatively low level. In the period T2 in FIG. 9, the level of the load torque detection signal Vst is higher than the level in the period T1 because the motor is rotating with a larger load than in the period T1. In the period T3 in FIG. 9, the load on the electric motor becomes excessive or the rotor is locked, and the control unit 2 performs the current limiting operation. Is getting smaller. In this state, the maximum value of the voltage Vi at both ends of the current detection resistor Ri is kept near the set value VL corresponding to the limit value of the armature current. In the period T3, FIG.
The level of the load torque detection signal Vst (FIG. 9C) obtained from the load torque detection circuit shown in FIG. 9 is higher than the level in the period T2. Therefore, in the example shown in FIG. 7, by checking the level of the load torque detection signal Vst, it is possible to accurately detect the load torque of the motor in any state from the light load state to the locked state.

On the other hand, in the example shown in FIG. 8, since the flywheel diode Df is directly connected in parallel to both ends of the armature coil 1 without passing through the resistor Ri, the armature coil Df is turned off while the transistor TR1 is in the off state. The armature current flowing from Wa through the flywheel diode Df does not flow through the resistor Ri. Therefore, the current detection resistor Ri
The waveform of the voltage Vi obtained at both ends is as shown in FIG. 9D, and is an intermittent waveform like the ON command signal Von.
The load torque detection signal Vst obtained by integrating the voltage Vi by the integration circuit 4 'is as shown in FIG.

Also in the example shown in FIG. 8, the on-duty ratio of the armature current control switch 3 increases with an increase in load torque.
Since the level of the load torque detection signal Vst changes in proportion to the magnitude of the average load torque, the load torque detection signal Vst
The average load torque of the motor can be known from st. However, as shown in a period T3 in FIG. 9, when the load of the motor becomes excessive or the rotor is locked, and the controller 2 performs the current limiting operation for limiting the armature current, Although the peak value of the armature current Ia increases, the on-duty ratio of the armature current control switch 3 decreases, so that the level of the load torque detection signal Vst falls in the period T2.
, And the level of the load torque detection signal Vst does not reflect the magnitude of the load torque. In such a state, even if the electric motor is locked, the state cannot be detected, so that necessary protection measures cannot be taken.

[0020]

As described above, a conventional load which obtains a load torque detection signal by integrating the voltage between both ends of a current detection resistor connected in series to an armature coil. In the torque detection circuit, when the flywheel diode is directly connected in parallel to both ends of the armature coil, it is not possible to accurately detect the load torque of the motor, and it is not possible to detect that the motor is locked. Was.

It is an object of the present invention not only when a flywheel diode is connected in parallel to both ends of a series circuit of an armature coil and a current detecting resistor, but also when the flywheel diode is directly connected in parallel to both ends of an armature coil. It is therefore an object of the present invention to provide a motor load torque detection circuit capable of accurately detecting the load torque of the motor.

[0022]

According to the present invention, an armature current control switch is connected in series to an armature coil, and the armature current is controlled by turning on and off the armature current switch. The present invention relates to a load torque detection circuit for detecting a load torque of a controlled DC motor.

In the present invention, a current detecting resistor connected in series to an armature coil and a voltage across the current detecting resistor or a voltage obtained by amplifying the voltage are charged with a constant time constant. An integration circuit having an integration capacitor to generate a load torque detection signal at both ends of the integration capacitor; and charging the integration capacitor only during a certain integration time τo from the time when the armature current control switch is turned on. And an integration time limiting circuit for limiting the charging time of the integration capacitor, and setting the integration time τo to be equal to or less than the on-time of the armature current control switch when the on-duty ratio of the switch is minimum. I did it.

The integration time limiting circuit includes, for example, an integration time limiting switch that conducts when a drive signal is applied to discharge the charge stored in the integration capacitor and prevent the integration capacitor from being charged; An integration time determining capacitor charged with a constant time constant by
When the armature current control switch is turned on, a reset circuit that turns on for a short time to discharge the integration time determination capacitor and compares the voltage across the integration time determination capacitor with a reference voltage And a switch drive circuit for supplying a drive signal to the integration time limiting switch during a period when the voltage across the integration time determining capacitor exceeds the reference voltage. In this case, the charging time constant of the integration time determining capacitor and the reference voltage are set so that the time during which the voltage across the integration time determining capacitor is equal to or less than the reference voltage is equal to the integration time τo.

The integration time limiting circuit also includes an integration time determination capacitor that is charged with a constant time constant by the DC voltage, and a short-time ON state when the armature current control switch is turned ON to perform integration. A reset switch for discharging the capacitor for time determination, and conducting when the voltage at both ends of the capacitor for integration time determination exceeds a set value to discharge the electric charge accumulated in the integration capacitor and prevent charging of the integration capacitor; And a switch for limiting the integration time.

In this case, the time during which the voltage at both ends of the integration time determining capacitor is lower than the set value is determined by the integration time τ.
Set the charging time constant of the integration time determination capacitor to be equal to o.

The integration time limiting circuit has a switch in the output stage, and is triggered when the armature current control switch is turned on, so that the output stage is switched only for a set time equal to the integration time τo. It can also be constituted by a monostable multivibrator that keeps the switch off. In this case, the output stage switch of the monostable multivibrator is connected in parallel to the integrating capacitor.

As described above, the integration time limiting circuit is provided so that the time required to charge the integration capacitor of the integration circuit is fixed to be equal to or less than the ON time of the armature current control switch when the ON duty ratio of the switch is minimum. If the time is limited, the charging time of the integrating capacitor can be kept constant under all conditions from when the motor is lightly loaded to when it is locked, regardless of how the flywheel diode is connected. The level of the load torque detection signal obtained from the integration circuit can be increased as the load increases, and the level of the load torque detection signal can be maximized when the motor is locked. Therefore,
Regardless of how the flywheel diode is connected, the load torque of the motor can be accurately detected, and the lock of the motor can be reliably detected.

[0029]

FIG. 1 shows an example of the configuration of a load torque detection circuit according to the present invention together with the configuration of a motor drive circuit. In FIG. 1, the same components as those of the conventional circuit shown in FIG. The same parts as those in FIG. 8 are denoted by the same reference numerals.

In the example shown in FIG. 1, a current detecting resistor Ri is connected in series to the armature coil 1, and a flywheel diode Df is directly connected in parallel to both ends of the armature coil 1. One end of a resistor R2 is connected to the non-ground side terminal of the resistor Ri through a resistor R1, and an integrating capacitor C1 is connected between the other end of the resistor R2 and ground. A diode D1 whose cathode is directed toward the integrating capacitor C1 is connected to both ends of the resistor R2. An integrating circuit 4 is formed by the resistors R1 and R2, the diode D1, and the integrating capacitor C1. An output terminal 4a is drawn from a non-ground side terminal of the integrating capacitor C1, and a load torque detection signal Vst is obtained between the output terminal 4a and the ground. In the integrating circuit 4, the integrating capacitor C1 is charged by the voltage across the resistor Ri through the resistor R1 and the diode D1. Therefore, the charging time constant of the integrating capacitor is determined by the resistance value of the resistor R1 and the capacitance of the integrating capacitor C1. The resistor R2 is provided to have a time constant when discharging the integrating capacitor through a reset circuit described later, and the resistance value of the resistor R2 is set to be sufficiently large.

The collector of an NPN transistor TR2 whose emitter is grounded is connected to the connection point between the resistors R1 and R2, and the output terminal of the comparator CP1 is connected to the base of the transistor TR1. A resistor R3 is connected between the output terminal of the comparator CP1 and the positive output terminal of the DC power supply (not shown).
Is connected, and when the potential of the output terminal of the comparator CP1 is at a high level, the transistor TR is connected through the resistor R3.
2 is supplied with a base current to make the transistor conductive.

A voltage dividing circuit composed of a series circuit of resistors R4 and R5 is connected between the output terminals of a DC power supply (not shown) whose negative terminal is grounded, and a constant DC voltage obtained from the voltage dividing circuit is a reference voltage Vr. Is input to the inverting input terminal of the comparator CP1.

A capacitor C2 for determining the integration time is connected between the other end of the resistor R6, one end of which is connected to the positive terminal of a DC power supply (not shown), and the ground. It is designed to be charged at a constant. The voltage Vc2 across the integration time determining capacitor C2 is input to the non-inverting input terminal of the comparator CP1.
When the voltage Vc across the capacitor C2 exceeds the reference voltage Vr, the potential at the output terminal of the comparator CP1 changes from a low level to a high level.

The non-grounded terminal of the capacitor C2 is connected to the collector of an NPN transistor TR3 whose emitter is grounded. The base of the transistor TR3 is a signal obtained by inverting the output of the control unit 2 through a differential capacitor C3 and a resistor R7. Is entered. The signal supplied to the base of the transistor TR3 is a high-level signal Von 'obtained by inverting the zero-level ON command signal Von output from the control unit 2, and
A high-level off command signal Voff output from the control unit 2 is inverted to a zero-level signal Voff ', and the transistor TR3 for a short time until the charging of the differential capacitor C3 is completed at the rise of the signal Von'. Becomes conductive.
That is, the transistor TR3 is turned on for a short time when the armature current control switch 3 is turned on, and discharges the integration time determining capacitor C2.

In the example shown in FIG. 1, the integrating circuit 4 is constituted by the resistors R1 and R2, the diode D1, and the integrating capacitor C1.

The transistor TR2 constitutes an integration time limiting switch 6 which conducts when a drive signal is supplied and discharges the charge accumulated in the integration capacitor C1.

Further, the transistor TR3 and the capacitor C
3 and the resistor R7 constitute a reset circuit 7 which is turned on for a short time when the rising of the ON command signal Von is detected and discharges the integration time determining capacitor C2. A reference voltage generating circuit 8 for dividing a DC voltage and outputting a reference voltage Vr is provided.

The voltage at both ends of the integration time determining capacitor C2 is determined by the comparator CP1 and the resistor R3.
Compared with r, a switch drive circuit 9 for providing a drive signal to the integration time limiting switch 6 during a period in which the voltage across the integration time determining capacitor exceeds the reference voltage is provided.

The integration time limiting switch 10, the integration time determining capacitor C2, the reset circuit 7, the reference voltage generating circuit 8, and the switch driving circuit 9 constitute an integration time limiting circuit 10. . Other points are the same as those of the conventional circuit shown in FIG.

In the example shown in FIG. 1, the control section 2 supplies a rectangular wave on / off command signal including an on command signal Von and an off command signal Voff to the base of the transistor TR1. As a result, the transistor TR1 is turned on and off as shown in FIG. Since a current flows through the current detection resistor Ri only while the transistor TR1 is in the ON state, the waveform of the voltage Vi obtained at both ends of the resistor Ri is as shown in FIG. Since the voltage Vi is applied to the integrating capacitor C1 through the resistor R1 and the diode D1, the integrating capacitor C1 is charged with a constant time constant.

The ON command signal Von generated by the control unit 2
And a signal Von 'obtained by inverting the off command signal Voff.
And Voff ', the transistor TR3 is turned on as shown in FIG.
The transistor TR3 is turned on for a short time when the armature current control switch 3 is turned on as shown in FIG. Each time the transistor TR3 is turned on, the integration time determining capacitor C2 is discharged.

The integration time determining capacitor C2 is charged with a constant time constant through the resistor R6 at the output of a DC power supply (not shown), and is discharged through the transistor TR3 when the armature current control switch 3 conducts. A voltage Vc2 having a waveform as shown in FIG. 2D is obtained at both ends of the capacitor C2. While the voltage Vc2 is lower than the reference voltage Vr, the potential of the output terminal of the comparator CP1 is at a low level, and when the voltage Vc2 is higher than the reference voltage Vr, the potential of the output terminal of the comparator CP2 is at a high level. become.
Therefore, a rectangular wave signal Vcp as shown in FIG. 2E is obtained at the output terminal of the comparator CP2. This rectangular wave signal V
cp is a signal that maintains a state of zero level for a predetermined time τo from the time when the armature current control switch 3 is turned on, and maintains a state of high level during other periods. FIG.
As shown in (F), while the rectangular wave signal Vcp is at the low level, the transistor TR2 is held in the off state,
While the rectangular wave signal Vcp is at a high level, the transistor TR2 is kept on. Transistor TR
While the transistor TR2 is in the off state, the transistor TR2 does not affect the integration operation of the integrating circuit 4. However, while the transistor TR2 is in the on state, the charge supplied from the non-ground side terminal of the resistor Ri. Since the current is bypassed from the integrating capacitor C1 through the transistor TR2, the charging of the integrating capacitor C1 is performed only during the period .tau.o when the transistor TR2 is off. Integration capacitor C
The waveform of the voltage Vs applied to 1 is as shown in FIG. 2 (G), and the charging of the integrating capacitor C1 is always performed only for a fixed time .tau.o. In the present invention, the charging time .tau.o of the integrating capacitor C1 is determined by the armature current control switch 3.
Of the switch 3 when the on-duty ratio is the minimum (the minimum value of the signal width of the on-command signal).

As described above, according to the present invention, since the integration capacitor C1 is charged only for the fixed charging time τo set to be equal to or less than the minimum value of the signal width of the ON command signal, the voltage at both ends of the integration capacitor C1 is obtained. The level of the load torque detection signal Vst is not affected by the change in the on-duty ratio of the armature current control switch 3 and is always the resistance Ri.
Indicates a value substantially proportional to the average value of the current detection signal Vi (armature current) obtained at both ends of the current detection signal Vi. Since the average value of the armature current is proportional to the average load torque of the motor, the level of the load torque detection signal Vst is substantially proportional to the average load torque of the motor.

In the example shown in FIG. 2, as in the example shown in FIG. 9, an operation state in which the load of the motor increases stepwise from the period T1 to T3 is assumed. It is assumed that the control unit 2 is performing a current limiting operation of limiting the armature current to a limit value or less because the load becomes excessive or the rotor is locked.
In the period T1 shown in FIG. 2, since the load on the motor is relatively light and the average value of the armature current is small, the load torque detection signal Vst (FIG. 2H) obtained from the load torque detection circuit 5 shown in FIG. Indicates a relatively low level.
In the period T2 in FIG. 2, the load on the motor further increased than in the period T1, and the average value of the armature current increased.
The level of the load torque detection signal Vst is higher than the level in the period T1. Further, in the period T3 in FIG. 2 in which the control unit 2 performs the current limiting operation, the average value of the armature current Ia becomes larger than the average value of the armature current in the period T2.
The level of st becomes higher than the level in the period T2.

As described above, according to the present invention, since the integration capacitor is always charged for a fixed time τo from the light load state to the locked state, the flywheel diode is directly connected in parallel to both ends of the armature coil. In this case, the level of the load torque detection signal can be changed almost in proportion to the average load torque of the motor without being affected by the change in the on-duty ratio of the armature current control switch. The load torque can always be accurately detected.

FIG. 3 shows another example of the configuration of the load torque detecting circuit according to the present invention. In this example, the voltage between both ends of the integration time determining capacitor C2 directly constitutes the integration time determining switch 6. The voltage is applied between the base and the emitter of the transistor TR2. Other points are the same as those of the example shown in FIG. FIG. 4 shows signal waveforms indicating the operation of the load torque detection circuit shown in FIG.

In the load torque detecting circuit shown in FIG. 3, the on / off operations of the transistors TR1 and TR3 are as shown in FIGS. 4A and 4B, respectively. The transistor TR3 outputs signals Von 'and Voff obtained by inverting the on / off command signals Von and Voff output from the control unit 2.
And the transistor TR1 is turned on for a short time when the transistor TR1 is turned on. Transistor TR
3 while the capacitor C2
Is discharged. After the transistor TR3 is turned off, the capacitor C2 is charged with a constant time constant through the resistor R6, so that a voltage Vc2 as shown in FIG. 4C is obtained at both ends of the capacitor C2. This voltage V
c2 turns on the transistor TR2.
During this period, the transistor TR2 is kept off, so that the integration capacitor C1 is charged. Voltage V
c2 turns on the transistor TR2.
Then, the transistor TR2 is turned on to stop charging the integrating capacitor C1. The charging time constant of the capacitor C2 is set so that the time τo during which the transistor TR2 is in the off state (the charging time of the integrating capacitor) indicates a constant value equal to or less than the minimum value of the signal width of the on command signal.

In the above example, the integrating capacitor C1 is charged by the voltage Vi obtained at both ends of the current detection resistor Ri. However, the voltage obtained at both ends of the current detection resistor Ri is too low. If a large integrated voltage (load torque detection signal) cannot be obtained, as shown in FIG.
The integrating capacitor C1 may be charged through the resistor R1 with the voltage obtained by amplification by the step S1. In the example shown in FIG. 5, the amplifier 11 comprises an operational amplifier OP1 and a resistor R10.
And R11.

In the example shown in FIGS. 1 and 3, the integration time limiting circuit 10 changes the charging current of the integration capacitor from the integration capacitor for a certain period of time after the armature current control switch is turned on. Bypass, integrating circuit 4
A circuit having a function of limiting the time required to charge the integrating capacitor to a fixed time equal to or shorter than the on-time of the armature current control switch 3 when the on-duty ratio of the switch 3 is the minimum may be used. It is not limited to the example.

For example, a switch is provided in the output stage, and triggered by an ON command signal generated by the control unit 2 or a signal obtained by inverting the ON command signal, the output stage switch is turned off for a set time. A commercially available monostable multivibrator IC to be maintained may be used as the integration time limiting circuit 10, and a switch at the output stage of the monostable multivibrator may be connected in parallel to the integration capacitor C1.

In the above example, the on / off command signal generated by the control unit 2 is used as a trigger signal for the integration time limiting circuit 10, but the method of triggering the integration time limiting circuit 10 is not limited to this. For example, a configuration may be employed in which the rising edge of the voltage across the current detecting resistor R1 is detected and the integration time limiting circuit 10 is triggered.

In the above description, the flywheel diode Df is directly connected in parallel to both ends of the armature coil Wa, but the flywheel diode Df is connected in series with the armature coil Wa and the current detection resistor Ri. Of course, the present invention can be applied to a case where the circuit is connected in parallel to both ends of the circuit.

The DC motor to which the load torque detecting circuit according to the present invention is applied is not limited to a motor having a single armature coil. For example, as shown in FIG. 6, bridge-connected PNP transistors TRu, T
Rv, TRw and NPN transistors TRx, TRy,
TRz and feedback diodes Du, Dv, Dw and Dx, Dy, Dz connected in anti-parallel to these transistors.
By controlling the transistors of the drive circuit 21 on and off according to the rotational angle position of the rotor using the inverter type drive circuit 21 composed of the three-phase armature coil W
The load torque detection circuit of the present invention can be applied to a DC brushless motor 1 'in which a current is commutated to au to Waw to rotate a rotor. In this case, the current detection resistor Ri is connected to the power supply input terminal on the negative side of the drive circuit 21 (the transistors TRx to TR constituting the lower side of the bridge).
Connect between the common connection point of the emitter of y) and ground (negative terminal of DC power supply).

[0054]

As described above, according to the present invention, the integrating capacitor of the integrating circuit for outputting the load torque detection signal by integrating the voltage across the current detecting resistor or the voltage obtained by amplifying the voltage. An integration time limiting circuit that limits the charging time of the motor to a fixed time equal to or less than the on-time of the armature current control switch when the on-duty ratio of the switch is the minimum is provided. Under all circumstances, the charging time of the integrating capacitor can be kept constant, and the level of the load torque detection signal obtained from the integrating circuit increases with increasing load regardless of the connection of the flywheel diode. Can be raised. Therefore, regardless of how the flywheel diode is connected, the load torque of the motor can always be accurately detected, and the lock of the motor can be reliably detected.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration example of a load torque detection circuit according to the present invention together with a configuration example of a drive circuit of an electric motor.

FIG. 2 is a timing chart showing signal waveforms of various parts in FIG. 1 and on / off operations of transistors.

FIG. 3 is a circuit diagram showing another configuration example of the load torque detection circuit according to the present invention together with a configuration example of a drive circuit of an electric motor.

FIG. 4 is a timing chart showing signal waveforms of various parts in FIG. 3 and on / off operations of transistors.

FIG. 5 is a circuit diagram illustrating a main part of another configuration example of the load torque detection circuit according to the present invention, together with a configuration example of a drive circuit of an electric motor.

FIG. 6 is a circuit diagram showing an example of a winding configuration of a DC brushless motor to which the load torque detection circuit of the present invention can be applied and an example of a configuration of a main part of a driving circuit thereof.

FIG. 7 is a circuit diagram showing a conventional load torque detection circuit together with a drive circuit of an electric motor.

FIG. 8 is a circuit diagram showing a conventional load torque detection circuit together with another drive circuit of an electric motor.

FIG. 9 is a timing chart showing signal waveforms of respective parts in FIGS. 7 and 8 and on / off operations of transistors.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... DC motor, 2 ... Control part, 3 ... Armature current control switch, 4 ... Integration circuit, 5 ... Load torque detection circuit, 6 ...
Integration time limiting switch, 7: reset circuit, 8: reference voltage generation circuit, 9: switch driving circuit, 10: integration time limiting circuit, TR1: transistor forming a switch for armature current control, TR2: integration time limiting Transistor constituting switch, TR3: transistor, C1: integrating capacitor, C2: capacitor for determining integration time, C3
... Differential capacitor, CP1 ... Comparator.

Claims (4)

[Claims] 1. A load of a DC motor in which an armature current control switch is connected in series to an armature coil, and the armature current is controlled by turning on / off the armature current control switch. In a load torque detection circuit for detecting torque, a current detection resistor connected in series to the armature coil, and a voltage at both ends of the current detection resistor or a voltage obtained by amplifying the voltage. An integration circuit having an integration capacitor charged with a time constant and generating a load torque detection signal at both ends of the integration capacitor; and a fixed integration time τo from a time when the armature current control switch is turned on. An integration time limiting circuit for limiting the charging time of the integrating capacitor so that only the charging of the integrating capacitor is performed. DC motor for the load torque detection circuit, characterized in that the on-duty ratio of the child current control switch is set in the following on-time of the minimum said switch when the. 2. The integration time limiting circuit according to claim 1, wherein said integration time limiting circuit conducts when a drive signal is applied, discharges the charge stored in said integration capacitor, and prevents charging of said integration capacitor. An integration time determining capacitor charged with a constant time constant by a voltage; and a reset for discharging the integration time determining capacitor by turning on for a short time when the armature current control switch is turned on. Circuit, comparing the voltage across the integration time determining capacitor with a reference voltage, and applying a drive signal to the integration time limiting switch during a period in which the voltage across the integration time determining capacitor exceeds the reference voltage. And a switch drive circuit for providing the integration time τo during which the voltage at both ends of the integration time determination capacitor is equal to or lower than the reference voltage. DC motor for the load torque detection circuit of claim 1, characterized in that the charging time constant and the reference voltage is set for the integration time determination capacitor to be equal. 3. The integration time limit circuit is turned on for a short time when the armature current control switch is turned on when the integration time determination capacitor is charged with a constant time constant by a DC voltage. A reset switch for discharging the integration time determining capacitor, and conducting when the voltage at both ends of the integration time determining capacitor exceeds a set value to discharge the charge accumulated in the integration capacitor and to discharge the integration capacitor. An integration time limiting switch for preventing charging of the capacitor. The integration time determination capacitor is configured such that the time during which the voltage at both ends of the integration time determination capacitor is equal to or less than the set value is equal to the integration time τo. 2. The load torque detecting circuit for a DC motor according to claim 1, wherein the charging time constant is set as follows. 4. The integration time limiting circuit has a switch at an output stage, and is triggered when the armature current control switch is turned on for a set time equal to the integration time τo. 2. The DC motor load according to claim 1, further comprising a monostable multivibrator that keeps an output stage switch in an off state, wherein the output stage switch of the monostable multivibrator is connected in parallel to the integrating capacitor. Torque detection circuit.