JPS6323737B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an overheat protection device for a motor.

(Objective) The object of the present invention is that it can be applied to a motor that is phase-controlled or pulse-width controlled by an AC power source or a DC power source, and that the temperature of the motor coil can be increased without providing a heat-sensitive part such as a temperature fuse or thermostat. By detecting the change in coil resistance caused by the motor during operation and activating the overheat protection circuit, detection sensitivity is good, and operation is ensured without detection delays and detection errors due to power fluctuations, etc. The purpose of the present invention is to provide an overheat protection device.

(Prior art) As a protection device to prevent the motor from overheating due to overload or abnormal use, resulting in a shortened lifespan or burnout, a temperature fuse or thermostat is used to control the motor power supply. cut off,
If necessary, a buzzer or other device is used to warn of these operations, but even if temperature fuses and thermostats are installed near the coil, which is the heat source, there may be a delay in operation due to heat conduction, or the temperature of the coil may decrease. There are problems such as not being detected faithfully. Particularly in small motors, installing temperature fuses, thermostats, etc. close to the coils poses problems such as space and insulation problems.

(Solution Means) The present invention controls the phase of the AC power supply voltage so that the voltage waveform supplied to the motor has a rest period, that is, a period in which no supply voltage is applied to the motor, and the length of the rest period, etc. In combination with a drive circuit that controls speed, the motor heating detection circuit can detect changes in coil resistance caused by a rise in the temperature of the motor coil without providing an additional heat-sensitive part to detect the rise in temperature of the motor coil. If the temperature rise exceeds a predetermined temperature by detecting it in the rest period, an overheat protection circuit is activated, such as by sounding a buzzer or displaying a lamp, or by cutting off the supply circuit as necessary.

(Embodiment) FIG. 1 is a control circuit diagram showing an embodiment of the present invention, where V is an AC commercial power supply, SW ₁ is a power switch,
M is the commutator motor, A is its armature, and ST is the field coil. SCR is a reverse blocking thyristor.
The speed of the motor M is controlled by half-wave phase control of the voltage supplied to the motor M. R ₁ is the gate circuit current limiting resistor of the thyristor SCR, R ₂ , R ₂ , R ₄ are the speed setting resistors,
C ₁ is a phase shift capacitor for expanding the phase control range, and SW ₂ , SW ₃ , SW ₄ , and SW ₅ are switches for high speed, medium speed, low speed, and stop in motor M operation. This is a lock release type push switch in which when one switch is pressed, the circuit is closed, the pressed state is locked, and the other switches are released. D ₁ is a rectifier diode, D ₂ is a thyristor protection diode,
_R5 and _C2 are a resistor and a capacitor, respectively, to prevent thyristor accidental firing. T is a control power transformer, the primary side of which receives an alternating current power supply V, and the secondary side connected to a full-wave rectifier stack RC. ZD ₁
is a Zener diode to make it a constant voltage as a control power supply, _R6 is a current limiting resistor of the Zener diode, _C3 is a smoothing capacitor, _R7 is a capacitor _C3 when the power is off, and a capacitor _C4 to be described later. This is a discharge resistor. FF is a flip-flop circuit, and the set terminal has a capacitor charged by receiving the positive side of the Zener diode _ZD1 , which is the control power supply, through a resistor _R8 .
It is receiving the charging voltage of _C4 . This is to temporarily set the setting terminal to a low level immediately after turning on the power switch _SW1 to initially set the flip-flop circuit, and thereafter set the negative output to a low level. D ₃ is a switch
This is a diode for discharging capacitor _C4 when _SW1 is off. Transistors Tr ₁ and Tr ₂ are the main elements of the motor overheat detection circuit.
The collector of the transistor Tr ₁ is connected to the base of Tr ₂ , and the emitter of the transistor Tr ₁ receives the potential divided by the Zener diode ZD ₁ by the semi-fixed resistor VR and the resistance of the field coil ST of the motor M. As long as field coil ST is below the set temperature and its resistance value is relatively low, its emitter current flows and does not supply base current to transistor _Tr2 . When the temperature rises and the resistance value rises, the divided voltage rises, and when it exceeds the set temperature, the emitter current is blocked and the base current is supplied to the transistor Tr ₂ , so that the transistor is activated. It's getting old. Note that even if there is a fluctuation in the AC commercial power supply V, there is no risk of an error in detecting the coil temperature because the control power supply is stabilized by the Zener diode _ZD1 . The semi-fixed resistor VR is used to set the operating temperature. R ₉ is the base resistance of the transistor Tr ₁ , and diodes D ₄ and D ₅ are the transistors from the voltage during operation of the motor M.
This is a diode for protecting Tr ₁ , Tr ₂ and a transistor Tr ₃ to be described later. The collector of the transistor Tr ₂ receives the positive potential of the Zener diode ZD ₁ via the load resistor R ₁₀ , and the collector serves as one input of the NAND circuit NA ₁ via the inverter IN, and the other input of the NAND circuit is It receives a voltage having the same phase as the anode side of the thyristor SCR from the secondary coil of the control power transformer T via the diode _D6 . The output of the NAND circuit serves as the reset input R of the flip-flop circuit FF, and resets the flip-flop circuit on condition that the anode of the thyristor SCR is at a positive potential and the transistor _Tr2 is activated. The negative side output is set to a high level, and at that time, the transistor Tr ₃ for activating the alarm circuit is activated. R ₁₁ is the base resistance of the transistor. BZ is an alarm buzzer, which issues an alarm by activation of transistor Tr ₃ . D ₇ is a buzzer
This is a BZ freewheel diode. _D8 is a light emitting diode, which forms a photocoupler together with the phototransistor _PTr1 , and when the transistor _Tr3 is activated, the phototransistor is activated and the thyristor is activated.
It is designed to short-circuit the gate potential of the SCR. R ₁₂ is the protection resistor of the light-emitting diode D ₈ .
Note that a warning lamp may be lit instead of the buzzer BZ.

The operation of the control circuit shown in FIG. 1 above will be explained below. When the power switch SW ₁ is turned on, the side of the Zener diode ZD ₁ connected to the resistor R ₆ becomes a constant positive potential. At the initial stage of turning on the power switch, the charging current of the capacitor _C4 causes a voltage drop across the resistor _R8 , causing the setting input of the flip-flop circuit FF to be at a low level.
Therefore, the negative side output is made low level. As a result, transistor Tr ₃ is inactive and the buzzer BZ,
Both phototransistors PTr ₁ are inactive. When charging of capacitor _C4 is completed, the setting input of flip-flop circuit FF becomes high level, but since the field coil of motor M is at room temperature before motor operation, the preset semi-fixed resistance
Since the potential of the emitter of the transistor Tr ₁ , which is divided by the resistance value of VR and the resistance value of the field coil ST, is a relatively low potential, the base current passing through the resistor R ₉ flows through the emitter. , so the transistor Tr ₂ is non-conductive and the collector of the transistor is at a high level, so the inverter IN
One input of the NAND circuit NA via the NAND circuit is set to a low level, the reset input of the flip-flop circuit FF is set to a high level, and its output remains at a low level. Switches SW ₂ , SW ₃ , for operating the motor M at specified speeds;
When either SW ₄ is pressed, the motor is operated at a specified speed, and when stop switch SW ₅ is pressed, the gate potential of the thyristor SCR is short-circuited to stop the motor M.

Next, to explain the case where motor M experiences an abnormal temperature rise due to overload, etc., Figure 2 shows the field coil
ST terminal voltage V _ST waveform diagram, when switch SW ₃ for specifying medium speed is pressed, the reverse blocking thyristor
This shows a state in which half-wave phase control is performed by SCR. The sine waveform shown by the dashed-double line, which includes a part of the solid line with respect to the time axis t, is a waveform when it is assumed that the thyristor SCR is short-circuited, but the actual terminal voltage V _ST is at time t ₁ as shown by the solid line. with thyristor
The SCR is fired, and as a result of the influence of the inductance of the motor M, the current lags behind the voltage, causing the terminal voltage to turn off at time _t2 , when the positive and negative sides are reversed, and the waveform is repeated. ,
Acts as motor operating voltage. Field coil ST
Also, the voltage obtained by dividing the voltage of the Zener diode ZD ₁ by the semi-fixed resistor VR and the resistance of the coil is
V _STR is applied, and to make it easier to understand, during the extinction period t ₂ to t ₄ of the thyristor SCR,
0 level 0 is exaggerated and shown larger. When the semi-fixed resistor VR is fixed, this divided voltage increases as the temperature of the field coil ST increases, in this case the resistance value increases based on the resistance temperature coefficient of the copper wire, and the voltage of the transistor Tr ₁ increases. Acts to reduce emitter current. V _STB indicated by a chain line is the upper limit voltage component preset by the semi-fixed resistor VR as the voltage component at the safe upper limit temperature of the field coil ST. ₅ and later, when the divided voltage V _STR matches the upper limit divided voltage V _STB , the base current of the transistor Tr ₁ is supplied as the base current of the transistor Tr ₂ , which is activated, and the NAND circuit NA ₁ is connected via the inverter IN. One input becomes high level. Then, after the time point _t6 when the secondary voltage of the transformer T becomes a positive level, when the other input of the NAND circuit via the diode _D6 becomes a high level, the NAND circuit becomes a low level and the flip-flop circuit FF is negated. Set the side output to a high level. Transistor Tr ₃
is activated, the buzzer BZ is activated, and the phototransistor PTr ₁ is activated, and the gate potential of the thyristor SCR is short-circuited, so that the thyristor, which was extinguished at time _t5 , will not be activated thereafter, and the motor The current in M is cut off to prevent further overheating. When the temperature of the field coil ST decreases due to the interruption of the current, the transistor Tr ₂ becomes inactive again, and the reset input of the flip-flop circuit FF goes to a high level, but since the set input is at a high level, its negative side The output remains at a high level, so the operation of the buzzer BZ and the current interruption of the motor M continue. Then, when the abnormality of the motor is detected by the alarm, the power switch SW ₁ is turned off, the abnormality is dealt with as necessary, and the motor M is turned on again, and the motor M returns to normal operation.

FIG. 3 is a control circuit diagram showing another embodiment, in which a bidirectional thyristor TRIAC is used to perform full-wave phase control of the voltage supplied to the motor M. Part 1 below
Elements common to those in the figures are represented by the same reference numerals, and their explanations are omitted, and only the different parts will be explained. DIAC
is a constant voltage discharge electron for ignition of thyristor TRIAC,
The thyristor TRIAC is actuated by the voltage across the capacitor _C5 when charging and discharging the capacitor C5 via resistors _R1 , _R2 , _R3 , etc., to fire the thyristor TRIAC. SW ₆ is a relay switch that is closed when the relay coil Ry is excited, and stops the motor M by the same action when the stop switch SW ₅ is closed. A capacitor _C5 is connected to both ends of the field coil ST via a resistor _R13 . And there are light emitting diodes on both ends of the capacitor.
_D9 is connected, and the connection side between field coil ST and armature A serves as its anode. Resistor R ₁₄ is for current limiting of the light emitting diode. The Zener diode ZD ₂ is for high voltage protection of the light emitting diode. PTr ₂ is a phototransistor that forms a photocoupler with a light emitting diode D ₉ , and a Zener diode ZD ₁ is connected to its collector via a resistor R ₁₅ .
When the phototransistor is inactive, the third input of the NAND circuit NA ₂ , which receives the first and second inputs similarly to the NAND circuit NA ₁ , is set to a high level. and is at a low level when activated. The output of the NAND circuit serves as an input for resetting the flip-flop circuit FF.

In the control circuit shown in FIG. 3, the operation will be described below when the temperature of the motor M increases abnormally due to overload or the like.

Figure 4 is a waveform diagram of the terminal voltage V _ST of the field coil ST, showing a state in which the switch SW ₃ for specifying medium speed is pressed and the full-wave phase is controlled by the bidirectional thyristor TRIAC. ing. A sine waveform shown by a dashed-two dotted line including a part of a solid line with respect to the time axis t is a waveform when it is assumed that the thyristor TRIAC is short-circuited. The actual terminal voltage V _ST is as shown by the solid line when the thyristor TRIAC fires at time t ₁ ′.
Under the influence of the inductance of the motor M, the current lags behind the voltage, so that the arc is extinguished at time t ₂ ' when the terminal voltage is inverted.
Thereafter, as in FIG. 2, a divided voltage V _STR is applied to the field coil ST, but this voltage is not used. and reverse firing at time t ₃ ′,
When the arc is extinguished at time _t4 ', a steep voltage is generated at the time of extinction. A similar phenomenon occurs at time t _{2 '} and in FIG. _V By generating a steep falling voltage. The subsequent voltage V _STR is then used for subsequent temperature detection. The main difference between Figure 3 and Figure 1 is that the NAND circuit NA ₂ is replaced by a light emitting diode D ₉
It is also possible to detect the operation of the That is, at the point of arc extinction
At t ₄ ′, without immediately turning off the light-emitting diode D ₉ , the electric charge of the capacitor C ₅ charged by the positive voltage is discharged through the light-emitting diode D ₉ over a short period of time to turn it on. When the divided voltage V _STR after the steep rise becomes stable, the light is turned off, the third input of the NAND circuit NA ₂ is set to high level, and the flip-flop circuit FF is reset, thereby dividing the steep rise voltage. This is done to prevent it from being mistakenly detected as voltage V _STR . Thereafter, temperature rise detection and overheat protection control are performed in the same manner as in FIGS. 1 and 2.

(Effects) As described above, the present invention can be applied to a motor that is phase-controlled or pulse-width controlled by an AC or DC power source, and is provided with an additional heat-sensitive section for detecting a temperature rise in a heat-generating section such as a motor coil. Because it directly senses the temperature rise of the coil, there is no problem with the connection space for the heat-sensing part or its insulation, there is no detection delay due to heat conduction, and there is no detection error due to power supply fluctuations. This is a useful invention, as it can be easily detected and controlled using electronic circuits.

[Brief explanation of the drawing]

1 and 3 are control circuit diagrams showing two different embodiments of the present invention, and FIGS. 2 and 4 are voltage waveform diagrams for explaining the operations of FIGS. 1 and 3, respectively. be. In the figure, M is the motor, NAND circuits NA ₁ and NA ₂ are the main elements of the temperature detection interval setting circuit, transistors Tr ₁ and Tr ₂ are the main elements of the temperature detection circuit, buzzer BZ, phototransistor PTr, and switch SW ₁
is the main element of the protection circuit.

Claims (1)

[Claims] 1. In a combination of a motor and a drive circuit in which the voltage waveform supplied to the motor has a section in which the supply is suspended, and the motor speed is varied by phase control or pulse width control based on a combination of the pause section and the supply section, a temperature detection interval setting circuit for detecting the rest interval; a stabilized DC power supply for supplying a minute DC current to the motor coil in the interval; An overheat protection device for a motor, comprising: a temperature detection circuit that generates a signal when the temperature exceeds the temperature of the motor; and a protection circuit that is activated by the detection signal of the detection circuit to prevent the motor from overheating.