JPH0132738B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a circuit for protecting a locked state of a DC motor.

[Prior art and its problems]

If the motor is overloaded beyond a certain level,
It becomes impossible to generate an output torque sufficient to follow or balance this load, and rotation stops or substantially stops, resulting in a so-called locked state. In such a state, an excessive amount of current flows through the motor, which is dangerous, so it is necessary to immediately cut off the power supply to the motor.

In the locked state, the electric motor appears to stop rotating or is in a state close to it. Therefore, conventional lock protection circuits detect when the rotational speed of the motor falls below a predetermined value. However, since the motor is at or close to stopping before or immediately after starting, it is possible to determine whether the stopped state of the motor is "normal" before starting or immediately after starting, or whether it is "abnormal" due to overload, etc. The structure was complicated because it had to be determined whether the

[Purpose of the invention]

An object of the present invention is to provide a lock protection circuit for a DC motor whose speed is controlled by a phase control method, which can provide reliable protection when the DC motor enters a locked state with a simple circuit configuration. shall be.

[Key points of the invention]

The lock protection circuit according to the present invention is adapted to a system that controls the speed of a DC motor using a phase control method, and employs a method of monitoring the back electromotive force of the motor as a detection method for rotation stoppage. The device is characterized in that a timer method is used to determine whether the stoppage is in a locked state or not, depending on whether the back electromotive force remains at OV or close to it for a predetermined period of time.

[Embodiments of the invention]

Examples will be described below with reference to the drawings.

FIG. 4 is a block diagram of a phase control type speed control system for a DC motor to which a lock protection circuit 6 according to the present invention is added. 1 is a rectifier circuit that rectifies commercial power to create a full-wave or half-wave rectified wave. 2
is a phase circuit that usually uses switching elements such as thyristors and transistors. Naturally, if a thyristor is used, the rectifier circuit 1 will be included in the phase circuit 2. 3 is a DC motor, 4 is a control circuit for controlling the phase of the phase circuit 2, and 2 and 4 constitute a phase control section of the motor. 5 detects the back electromotive force of the DC motor in 3 and
This is a back electromotive voltage detection circuit that provides feedback to the control circuit. The above is the configuration of a simple DC motor control system that is commonly used. The lock protection circuit according to the present invention can be used by being added to the position indicated by reference numeral 6 and receiving a back electromotive voltage signal from the back electromotive voltage detection circuit 5.

That is, one feature of the present invention is that it is possible to know from the magnitude of the back electromotive force that the motor has stopped. When the motor is phase controlled as shown in Figure 4, the period when no power supply voltage is applied to the motor (Figure 5 shows the voltage waveform between the motor terminals when a full-wave rectified wave is applied to the motor through the phase circuit 2). (The period between a and b in the figure is the period when no power supply voltage is applied, and the shaded area indicates the back electromotive force.)
In this case, a back electromotive force (induced voltage) is generated in the armature of the motor as shown in FIG. Since the back electromotive voltage follows the rotation of the motor, it does not occur when the motor speed v is zero. Therefore, by monitoring the magnitude of the back electromotive force, it is possible to know whether the motor is rotating or stopped.

However, what must be considered here is that
This means that as long as the motor is stopped, no back electromotive force is generated. For example, if we consider the situation immediately after turning on the switch that rotates the electric motor,
Since the motor had been stopped until then, no back electromotive force was generated (it cannot suddenly increase). If this is the case, if a lock protection circuit is constructed using only the above-mentioned detection means, it will operate at the same time as the switch is turned on, cutting off the power to the motor. Therefore, it becomes necessary to determine whether the stopped state of the motor is due to normal operation or a locked state caused by an abnormality such as overload. In order to understand what kind of stop state is the locked state of an electric motor, let's reconsider the normal stop state. The basic normal stop state is when the switch for rotating the motor is turned off. On the other hand, if the motor continues to stop even though the switch for rotating the motor is in the ON state, this can be considered to be an abnormal stopped state. If this abnormal stopped state is regarded as a locked state, it can be safely assumed that if the motor does not rotate for a certain period of time when power is supplied to the motor from the line, it is in a locked state.

Figure 1 is one example of a concrete circuit that summarizes the above ideas. First, so that this protection circuit can confirm that power is being supplied to the motor, a fourth
Connect it to the power line D located after the start switch in the control section 2 or 4 in the figure. Next, a back electromotive voltage signal from the back electromotive force detection circuit shown in FIG. 4 is input to the base terminal of the transistor Tr1. A command signal from this protection circuit, that is, a signal to cut off the power to the motor in the case of a lock state, is directly connected to the switching element in the phase circuit 2 shown in FIG.
It can be used by connecting it to an appropriate place in the phase control circuit.

Next, the detailed operation of this protection circuit will be explained. When power is supplied to this protection circuit (that is, the motor is supplied with power from the line and is in a normal rotating state), the transistor
The back electromotive voltage detection circuit 5 shown in Fig. 4 is installed at the base of Tr1.
A back electromotive voltage signal that is further fed back is added. When the motor is rotating, a back electromotive voltage is applied to the transistor Tr1, so that it is in the ON state. Therefore, the programmable union transistor PUT (hereinafter referred to as PUT) shown in Fig.
The anode voltage V _A of (denoted as ) is approximately OV, and the capacitor C1 is not charged. PUT gate potential
V _G is biased to an appropriate value by resistors R2 and R3. Capacitor C2 is a capacitor for preventing PUT from malfunctioning due to fluctuations in the power supply line. PUT is in the OFF state when V _G > V _A. In other words, it is OFF while the electric motor is rotating normally.

If we consider a case where the motor is not rotating even though power is being supplied to it, no back electromotive force is generated because it is not rotating. Therefore, the back electromotive voltage signal applied to the base of Tr1 becomes zero, and Tr1 becomes OFF.
Then, capacitor C1 starts charging via resistor R1. C1 is supposed to be charged to the power supply voltage, but because of PUT, it is actually charged until V _A = V _G. When V _A = V _G
PUT becomes ON, a voltage is generated in the resistor R4, and the transistor Tr2 becomes conductive. That is, the electric motor was stopped continuously for a certain period of time t until C1 was charged and V _A =V _B. This proves that this stop is an abnormal stop state, that is, a locked state, so PUT is turned on from the OFF state.
This means that the protection circuit has determined that this stoppage is a locked state.
When PUT is in the OFF state, no current flows into the base of Tr2, so the collector potential V _C of Tr2 has a certain positive potential. When PTU turns on, Tr2
Since it is turned on, the collector potential V _C becomes zero potential. This switching signal of Tr2 may be used as a control signal to cut off the power supply to the motor.

For example, if the switching element in the phase circuit 2 of FIG. 4 is an NPN transistor, the output terminal of this control signal may be connected to the base of the transistor. In addition, if a thyristor is used, the gate potential can be reduced to zero by connecting it to the gate terminal of the thyristor, so the next time the anode potential reaches zero potential (between a and c in Figure 5) When the time elapses from point c to point c), the power can be turned off. If the speed control circuit of the motor is configured with a hybrid IC or the like and this protection circuit cannot be directly connected, connect it to a suitable location within the phase control circuit 4 in Figure 4 (such as a power line). It can be used if it is connected to a location where, if the potential is zero, the operation of the phase control circuit 4 is stopped, that is, the switching element of the phase circuit 2 is turned off.

The block diagram of FIG. 4 will now be explained using the specific circuit diagram of FIG. 2. FIG. 2 is a circuit configuration diagram shown in FIG. 1 of Japanese Patent Application No. 136668/1983, which was filed simultaneously with the present invention. First, commercial power supply 1
A rectifier circuit 1 for full-wave rectification of 1 is provided, and its output current and voltage are input to a DC motor 3. Further, in order to control the speed, a transistor Tr4, which is a phase circuit 2 whose conduction angle is controlled, is connected in series to the motor 3.
Further, in order to detect the back electromotive force, a voltage dividing circuit including resistors R7 and R8 is connected in parallel with the motor 3, and the voltage dividing point thereof is connected to the base of the transistor Tr5. The emitter of the transistor Tr5 is connected to the DC voltage side via a current control resistor R9, and the collector is connected to the DC voltage side via a diode D2 and a resistor R/O. The conduction angle control circuit 4 of the transistor Tr4 is a Zener diode connected through a resistor R11 for control power supply.
A synchronization circuit 7 for synchronizing with the ZD commercial power supply, a sawtooth wave generation circuit 8 that generates sawtooth teeth in synchronization with the commercial power supply, and determining the conduction angle of the transistor Tr4 by comparing the back electromotive force and the sawtooth wave. It consists of a comparison switching circuit 9 for

Next, to explain the operation, first, when a commercial power supply voltage is applied, a trapezoidal wave V2 is generated in the Zener diode ZD, and using this as a power source, a sawtooth wave V4 synchronized with this trapezoidal wave is generated in the sawtooth wave generation circuit. Generated by 8. Here, if a back electromotive voltage V7 is generated, this sawtooth wave and the back electromotive force are compared, and the period in which the sawtooth wave is higher than the back electromotive voltage becomes the base signal V5 of the transistor Tr4. The conduction angle of is determined. moreover,
By varying the slope of the sawtooth wave with the setting device 10, the period during which the sawtooth wave is higher than the back electromotive voltage becomes longer or shorter, and the conduction angle of the transistor Tr4 is varied, allowing the speed of the DC motor 3 to be controlled.

Next, regarding the detection of the back electromotive force of the motor 3, if a back electromotive voltage V1 is generated across the motor 3 during the period when the transistor Tr4 is off, this back electromotive voltage flows through the resistors R7 and R8. , the back electromotive voltage divided by the resistor R7 becomes the bias voltage of the transistor Tr5.
to drive. Transistor Tr5 is a transistor
Using the full-wave rectified DC voltage during the off-period of Tr4 as a power source, a current i1 corresponding to this bias voltage is caused to flow. Further, the current i1 is biased by the diode D1 during the period when the transistor Tr4 is turned on. Therefore, only the current i1 corresponding to the back electromotive voltage is taken out during the period when the back electromotive force is generated in the motor 3, and in order to reduce ripples, the current i1 is smoothed by the diode D2 and the capacitor C3 and converted into voltage, thereby obtaining an appropriate amount of back electromotive voltage. The back electromotive force obtained in this way is input to the comparison switching circuit 9 and compared with the sawtooth wave to determine the conduction angle of the transistor Tr4. As the electromotive voltage decreases, the transistor
When the conduction angle of the transistor Tr4 increases, and conversely, the speed increases and the back electromotive force increases, the conduction angle of the transistor Tr4 is narrowed and controlled so as to reach the set speed.

When adding the lock protection circuit shown in FIG. 1 of the present invention to this circuit, the base of the transistor Tr1 is connected to the connection point A between the diode D2 and the capacitor C3, and the diode is connected from the base of the transistor Tr4 through the diode D3. Collector of transistor Tr2 and resistor R5 to cathode side B of D3
It is only necessary to connect the connection points of and also connect the power supply C of the protection circuit to the power supply line D. The diode D3 is inserted here because the resistor R5 forms an open collector, so when the transistor Tr2 is off, current flows to the base of the transistor Tr4 through the resistor R5 to prevent the transistor Tr4 from malfunctioning. It's for a reason.

Next, the switching element in the phase circuit shown in Figure 4 is
In the case of a PNP transistor, the protection circuit shown in Figure 1 cannot be connected. At that time, transistor Tr2
Another stage NPN transistor on the collector line of
If the circuit shown in FIG. 3a is made with Tr3 connected, the switching of Tr3 will be opposite to that of Tr2, so its output can be connected to the base of the PNP transistor. Also, like Tr2' in Figure 3b, PNP
If transistors are used, resistors R4', R5', R
By appropriately selecting the value of 6', it is possible to achieve the same operation as the circuit shown in FIG. 3a. This can be used as a switching element in the phase circuit 2 in Figure 4.
If you are using an NPN transistor, you can stop the transistor's operation by setting the base potential to zero, but if you are using a PNP transistor, the transistor will turn on when the base potential is zero. To connect and use the protection circuit, invert the control signal once.
This is because a signal indicating that it is OFF must be sent.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to know that the motor has stopped by using the back electromotive force used as a feedback signal for phase control of the motor, and to determine whether the stoppage is due to a lock state due to overload or the like by checking the capacitor. By making a judgment based on the applied timer, the protection circuit can be ensured without the need to add a new circuit to detect whether the motor is in a locked state (for example, a circuit to detect the motor's current or temperature). can be operated. Therefore, the circuit configuration is extremely simple and can be manufactured at low cost. Furthermore, it is versatile in that it can be easily added to almost any device that uses a circuit system that controls the speed of a DC motor using phase control. Especially sewing machines using small DC motors,
Since home appliances such as pumps and mixers are often handled directly by hand, adding such a lock protection circuit is very effective from a safety standpoint.

In addition to the system in which speed control is performed by feedback of back electromotive force, this invention can also be applied to cases in which a tachometer generator (rotational speed meter generator) is used for speed detection and phase control is performed by the output signal of the tachometer generator. It is possible. This is because when the DC motor is in a locked state, the output signal of the tachogenerator is 0, so by inputting this output signal to the lock protection circuit, the same operation can be achieved.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing one embodiment of the lock protection circuit of the present invention, FIG. 2 is a circuit configuration diagram of a DC motor control device to which the lock protection circuit of the present invention is connected, and FIGS. b is a circuit configuration diagram showing another embodiment of the present invention, FIG. 4 is a block diagram of a phase control type motor speed control device with the lock protection circuit of the present invention added, and FIG. 5 is a diagram of a motor during phase control. It is a terminal voltage waveform diagram. Tr1...Transistor for detecting back electromotive force, R1,
C1...Time constant circuit, PUT...Programmable union transistor, Tr2,
Tr3, Tr2'...Output transistor.

Claims (1)

[Scope of Claims] 1. In a circuit intended to protect a DC motor whose speed is controlled by a phase control method in a locked state due to an overload, a switching operation is performed when the back electromotive voltage of the DC motor decreases to at least a predetermined level or less. A detection circuit consisting of a switching element, and a detection signal from this detection circuit starts charging a capacitor via a power supply line, and when the detection signal continues for a predetermined time or more, the charging voltage of the capacitor increases to a predetermined voltage value. A DC motor lock protection circuit consisting of a timer circuit that generates a command signal to stop power supply to the DC motor when the DC motor exceeds the specified limit.