JPH0424794Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of application of the invention] The present invention is a speed control device for an electric motor, particularly a speed control device for an electric motor equipped with a frequency generator, which determines that an overload has occurred when the motor suffers from overload and the speed decreases. death,
This relates to a protection circuit that stops an electric motor, and is used, for example, to drive a copying machine.

[Prior Art] Fig. 3 shows an example of a conventional protection circuit for a motor speed control device, in which 1 is a mono multivibrator, 2 is a comparator amplifier, 3 is a first AND circuit, 4 is the second AND circuit, 5 is
OR circuit, 6 is a motor, 7 is a frequency generator, 8 is an input terminal for a start control signal, Q1 to Q3 are transistors, R1 to R3 are resistors, C is a capacitor,
Dz is a Zener diode, and D is a diode.

In FIG. 3, a current flows from another control circuit (not shown) to the base of a transistor Q3 connected to the motor 6, causing the motor 6 to rotate, and the output of a frequency generator 7 directly connected to the motor The speed of the electric motor is controlled to maintain the speed of the electric motor at a set value by feedback to the other control circuit.

On the other hand, the output of the frequency generator 7 is the transistor Q1
The voltage is input to the mono multivibrator 1 via the motor, which is converted into a voltage proportional to the rotational speed of the motor and input to the comparator amplifier 2.
The output of the comparison amplifier 2 and the output of the start control signal input terminal 8 are compared with the reference voltage set by Dz.
The inverted output via the NOT circuit 9 is connected to the first
input to the AND circuit 3, and input the output of the first AND circuit 3, one directly and the other to the resistor R2 and the capacitor.
C1 and the resistor R3 to the second AND circuit 4, the output of the second AND circuit 4 and the output of the activation control signal 8 are outputted via the OR circuit 5, and the output is transmitted to the transistor Q2. The transistor Q3 is inputted to the base of the transistor Q3 and is configured to further control the transistor Q3.

FIG. 2 is a timing chart showing the voltage levels of various parts of the protection circuit shown in FIG. 3, and the operation of the protection circuit will be explained with reference to this diagram.

In Fig. 3, the start control signal is shown, the start is L level and the stop is H level, is the output of NOT circuit 9, is the output of frequency generator, is the output of transistor Q1, is mono multivibrator 1 is the smoothed voltage proportional to the speed, is the output of comparison amplifier 2, and is the first AND
The output of circuit 3 is the output of second AND circuit 4,
is the output of OR circuit 5.

Now, to start the motor, the level of the start control circuit 8 is set to L, and by turning on the transistor Q3 via the OR circuit 5 and the transistor Q2, the motor 6 is supplied to the base of the transistor Q3 from another control circuit. Rotates according to the drive signal.

When the motor rotates, a voltage is generated from the frequency generator 7, and a voltage f proportional to the rotation speed is input to the comparator amplifier 2 by the monomultivibrator 1 and the smoothing circuit, where it is compared with the reference voltage v. When the output becomes >v, it becomes L level.

When the above output is at the L level, the output of the first AND circuit 3 is at the L level and no signal is transmitted to the second AND circuit 4, so the protection circuit does not operate and the motor rotates normally.

However, when the load increases abnormally while the motor is operating, the rotational speed set by the control device cannot be maintained and the speed decreases, causing the output voltage to become lower than v, the output of the comparator amplifier 2 becomes H level, and the first AND
Since the inputs of circuit 3 are both at H level, the circuit 3
The output of the first AND circuit 3 becomes H level, and the second AND circuit 4 receives the output of the first AND circuit 3, and one directly connects the resistor R2, capacitor C1, and resistor R3 to the other.
and the output of the AND circuit 4 is
After the output of the first AND circuit 3 becomes H level, it becomes H level with a delay of a time determined by resistor R2 and capacitor C1, and the output of OR circuit 5 becomes H level, and then passes through transistor Q3 through transistor Q2. is turned OFF and the electric motor 6 stops.

That is, if an overload occurs during operation, and the rotational speed falls below a certain reference value, and this state continues for a certain period of time, it is determined that the motor is overloaded, and operates to stop the motor, thus functioning as an overload protection circuit.

In the above circuit, the delay circuit composed of the resistor R2 and the capacitor C1 prevents the output of the second AND circuit 4 from reaching the H level during the time when the speed passes through a region lower than the reference speed during the process of increasing speed at startup. Since the time constant is set in , the speed increase process at startup is configured so as not to be determined as an overload.

However, in the conventional protection circuit shown in Fig. 3, after determining that an overload has occurred and stopping the motor, if the mechanical part to which the motor is connected is moved from the outside while leaving the circuit state as it is, the motor will rotate.
The output of the frequency generator 7 is converted to a voltage proportional to the speed via the mono multivibrator 1, and when this voltage exceeds the reference voltage v, the comparator amplifier 2 determines that the rotation is normal, and the output of the OR circuit 5 becomes L level. As a result, the transistor Q3 is turned ON via the transistor Q2, and the motor 6 continues to rotate, resulting in a malfunction.

[Purpose of the invention] The purpose of the invention is to solve the above-mentioned problems in the conventional technology, and even if the motor is rotated from the outside after it has been determined to be overloaded and stopped, it is incorrectly determined to be rotating normally. An object of the present invention is to obtain a protection circuit for a speed control device of an electric motor that does not cause malfunction that causes continued rotation.

[Summary of the invention] As shown in Fig. 1, the outline of the invention is that the output of the second AND circuit 4 of the protection circuit and the output obtained by inverting the output of the start control circuit 8 by the NOT circuit 9 are input to the NAND circuit 10. The configuration is such that the output of the NAND circuit 10 is input to the reset terminal of the mono multivibrator 1.

[Embodiment of the invention] As shown in FIG. 1, an embodiment of the invention includes a NAND circuit 10 in the protection circuit of the motor control device shown in FIG. It is characterized in that the output obtained by inverting the output from the NOT circuit 9 and the output of the second AND circuit 4 are inputted, and the output is inputted to the reset terminal of the mono multivibrator 1.

The operation of the embodiment of the present invention shown in FIG. 1 is such that when the motor is operating normally, the NAND circuit 10
The input is that the output b of the NOT circuit 9 is at H level, and the second
Since the output of the AND circuit 4 is at the L level, the output becomes the H level, the mono multivibrator 1 is turned on, and the motor continues to operate.

Next, when an overload occurs and the speed of the motor decreases, and the voltage proportional to the rotational speed drops below the reference value v, the output of the comparator amplifier 2 goes to H level, and the output of the first AND circuit 3 goes to H level, and the resistor R
After a delay of the time constant set by C1 and capacitor C1, the output of the second AND circuit becomes H level.
The output of the OR circuit 5 becomes H level, turning on the transistor Q2 and turning off the transistor Q3, stopping the motor 6 and operating as an overload protection circuit.

In this state, the output of the NAND circuit 10 becomes L level, the mono multivibrator 1 turns OFF, and it will no longer accept input, so even if the motor is rotated externally and the speed exceeds the reference value, the mono multivibrator 1 and subsequent The circuit does not operate, and therefore no malfunction occurs that incorrectly determines that the rotation is normal.

In addition, in order to cancel the protection state and restart the device, if the startup control signal 8 is set to H level, the output of the NAND circuit 10 becomes H level, and the mono multivibrator 1 is reset to accept the output of the frequency generator 7. It will return to normal operating condition.

In other words, this is also a safety device in that once the protection circuit is activated, the activation control circuit cannot be restarted unless it is once stopped (high level).

[Effects of the invention] Since the present invention has the above-mentioned configuration, it can be applied to the protection circuit of the motor speed control device according to the prior art.
With a simple configuration that adds a NAND circuit and a NOT circuit, after determining an overload and stopping the motor,
When the motor is rotated externally, the motor does not continue to rotate, which is a malfunction, and once the protection circuit is activated, the start control circuit must be stopped (H level) before it will restart, and the safety device will not be restarted. It also has a great effect.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a protection circuit for a motor speed control device according to the present invention, FIG. 3 is a circuit diagram of a protection circuit according to the prior art, and FIG. 2 is a timing chart for explaining the operation. Explanation of symbols, 1...Mono multivibrator,
2... Comparison amplifier, 3... First AND circuit, 4
...Second AND circuit, 5...OR circuit, 6...Electric motor, 7...Frequency generator, 8...Start control signal terminal, 9...NOT circuit, 10...NAND circuit.

Claims (1)

[Scope of utility model registration request] A speed control device for a motor 6 equipped with a frequency generator 7 converts the output of the frequency generator 7 into a voltage proportional to the speed via an F/V converter formed by a mono-multivibrator 1, and converts the output of the frequency generator 7 into a voltage proportional to the speed. The output of the comparison circuit 2 and the inverted output signal of the signal 8 of the start control circuit are input to the first AND circuit 3. The output is input directly to one input terminal of the second AND circuit 4, and is input to the other input terminal via a delay circuit including a resistor R ₂ and a capacitor C ₁ , and the output of the second AND circuit 4 and the above are input. The second AND circuit 4 is equipped with a protection circuit that inputs the signal 8 of the start control circuit to the OR circuit 5 and sends a stop signal to the control circuit of the electric motor 6 using the output of the OR circuit 5.
and the inverted output signal of the startup control circuit 8.
1. A protection circuit for a motor speed control device, characterized in that the protection circuit is configured to input a signal to a NAND circuit 10, and input the output of the NAND circuit 10 to a reset circuit of the mono-multivibrator 1.