JPH0559676B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a motor speed control device that can prevent overspeeding when a position rotational speed signal is no longer input while voltage is being supplied to a motor.

(Prior Art) As a conventional motor speed control device used in a copying machine or the like, there is one shown in FIG. 1, for example. This speed control device has a first power supply (e.g. 5V) that supplies the control circuit and a second power supply (e.g. 5V) that supplies the direct current (DC) motor 1 for driving the scanning mechanism.
24V), a pulse generator 3 that is directly connected to the motor 1 and generates a pulse signal according to the rotation speed, and an amplifier circuit 4 that amplifies the output signal of the pulse generator 3. A waveform shaping circuit 5 that shapes the waveform of a signal, a phase comparator 6 that compares the pulse signal b output from the waveform shaping circuit 5 with a reference clock a, and outputs a phase difference signal c; Every time pulse signal b is output,
The one-shot multivibrator 7 generates a signal with a constant width as the speed gain setting signal d in synchronization with the rising edge, and the output signal of the waveform shaping circuit 5 and the output signal of the one-shot multivibrator 7 are added, and the output is further integrated. An addition and integration circuit 8 that generates a signal e, a triangular wave generating circuit 9 that outputs a triangular wave signal f serving as a reference signal, and a triangular wave generating circuit 9
a comparison circuit 10 that compares the output signal of the adding and integrating circuit 8 with the output signal of the addition and integration circuit 8 and outputs a pulse width conversion signal g.
and power transistors 11a (Q1), 11b (Q2), 11c (Q3), 1 arranged in a bridge shape, two of which are energized when the motor 1 rotates in the forward direction and two when the motor 1 rotates in the reverse direction.
1d (Q4) and power transistors 11a to 1
1d based on the output signal of the comparator circuit 10, and a mode setting circuit 12 which controls based on forward/reverse rotation commands and start/stop commands.

In the above configuration, its operation will be explained according to the time chart in FIG.
The phase comparator 6 compares the output signal (speed signal) of the pulse generator 3 which is output according to the current actual rotational speed with the signal b obtained by waveform processing, and obtains the signal c (θ1, θ2, θ3 is the phase difference).
On the other hand, the one-shot multivibrator 7 detects the rising edge of the signal b, which is the speed signal, and outputs the timer signal c for a time t1 according to the set value.
This signal c and signal d are added, and this added value is integrated to obtain an integral signal e. Furthermore, the comparison circuit 10 compares the triangular wave signal f and the integral signal e to obtain a pulse width converted signal g. The speed of the motor 1 is controlled according to the average value of this signal g for each predetermined unit time. The mode setting circuit 12 controls the direction of rotation by turning on power transistors 11a and 11d during forward rotation, and turning on power transistors 11b and 11c during reverse rotation, thereby reversing the direction of current flowing through motor 1.

However, according to the conventional motor speed control device,
If the generating element and light receiving element of the pulse generator 3, which is directly connected to the motor, are connected to the board via a lead wire and a connector, the signal supply to the amplifier 4 will be interrupted if the connector comes off or the lead wire breaks. may be cut off. In this case, the actual number of rotations is considered to be 0, and the comparator circuit 10 outputs a command to rotate at full speed. If the motor 1 is driven at full speed, there is a risk of damaging the device.

Therefore, in order to prevent full-speed operation from occurring when the speed signal that is output according to the motor's rotational speed is no longer input, the power supply to the motor is stopped when the signal is not input for a predetermined period of time. It has been proposed to control the process so that it is stopped.

However, if the rotation direction is reversed while the motor is rotating, a state in which no speed signal is input continues for a predetermined period of time, and there is a possibility that power supply to the motor may be stopped. In other words, there is a time limit of 30 to 50 milliseconds in which encoder pulses are not generated during reverse rotation, so there is a risk that a situation may occur in which the power is cut off after this time is counted.

(Object and structure of the invention) The present invention has been made in view of the above,
In order to prevent full-speed operation from occurring when the speed signal that is output according to the motor's rotational speed is no longer input, the power supply to the motor is stopped when the signal is not input for a predetermined period of time. In addition, the present invention provides a motor speed control device that resets the timer based on a reversal signal that reverses the rotational direction of the motor while the motor is rotating, in order to prevent malfunctions during reversal.

(Example) Hereinafter, a motor speed control device according to the present invention will be explained in detail.

FIG. 3 shows an embodiment of the present invention, and parts that are the same as those in FIG. A pulse signal extinction detection circuit 20 is provided which changes the print start command to the mode setting circuit 12 to a stop command when the print start command does not reach the circuit board side. The print start command (START) and the print stop command () are output to the mode setting circuit 12 via an AND circuit 21 which performs an AND operation with the pulse width conversion signal g and the output signal k of the pulse signal extinction detection circuit 20. In addition, the pulse signal extinction detection circuit 20
The output terminal of is connected to the output terminal of a comparison circuit 10 (configured with a comparator 10a and an inverter 10b).

The pulse signal extinction detection circuit 20 includes a differential capacitor 20 to which the output signal of the pulse generator 3 is applied.
a, resistors 20b and 20c that form a pair with the differential capacitor 20a to form a differential circuit, and a resistor 2
A transistor 20d whose base is connected to the connection point of 0b and 20c and whose emitter is grounded, a resistor 20e connected between the 5V power supply and the collector of the transistor 20d, and a differential capacitor to which the START command and the command are applied. 20f, resistors 20g and 20h that form a pair with the differential capacitor 20f to form a differential circuit, and resistors 20g and 20h.
The transistor 20i has its base connected to the connection point of the transistor 20d, its emitter is grounded, and its collector is connected to the collector of the transistor 20d, and the resistor 20e is connected between the collector of the transistor 20d and the ground. and a transistor 20k whose base is connected to the collector of the transistor 20d.
, a resistor 20l connected between the transistor 20k and the power supply 5V line, and a transistor 20k
A Zener diode 20m whose cathode is connected to the emitter of the zener diode 20m, a resistor 20m connected between the anode of the diode 20m and the ground, and a base connected to the anode of the Zener diode 20m,
A transistor 20p whose emitter is grounded and whose collector is connected to the output terminal of the comparison circuit 10
, a differential capacitor 20q to which the command and the REVERSE command are applied, and a resistor 2 that forms a pair with the differential capacitor 20q to form a differential circuit.
0r and 20s, and a transistor 20t whose base is connected to the connection point between the resistors 20r and 20s and whose emitter is grounded.

In the above configuration, the rotational speed control of the motor, etc. is as described above, so the explanation will be omitted, but when the power is turned on, 5V power is supplied to each circuit, and the power transistors 11a to 11d
is supplied with 24V power. When a print start (START) command is issued, a pulse width conversion signal g is output to maintain the set speed. The pulse width conversion signal g is processed by the AND circuit 21.
A logical product with the START command is taken, and a signal having the same shape as the pulse width conversion signal g is applied to the mode setting circuit 12. This signal first makes the power transistors Q1 and Q4 conductive, and the motor 1 becomes normal. Rotate in the direction. In this case, if there is no abnormality in the path from the pulse generator 3 to the circuit board, a pulse signal is applied to the amplifier circuit 4 at intervals corresponding to the rotation speed, and the pulse signal is applied to the pulse signal extinction detection circuit 20. be done.

As shown in FIG. 4, the pulse signal h output from the pulse generator 3 is applied to the capacitor 20a,
Every time a signal is input in the order of capacitor 20a → resistor 20b → resistor 20c at each rising timing of signal h, a current flows instantaneously, and each time this current flows, the voltage generated across resistor 20c causes transistor 20d to It becomes conductive and its collector potential becomes almost 0 level. As a result, transistor 2
The charge in the capacitor 20j that was being charged through the resistor 20e when 0d is non-conductive is discharged in a sawtooth waveform as shown in FIG. transistor 2
0k is the base-emitter voltage V _BE1 , the Zener voltage of 20m Zener diode is V _Z ,
The base-emitter voltage of transistor 20p is
V _BE2 and the voltage between the terminals of capacitor 20j.
When Vc is established, a conductive state is established when _Vc (V _BE1 +V _Z +V _BE2 ) is established. Therefore, the pulse interval generated by the pulse generator 3 at the lowest speed of the motor 1 is sufficiently longer (for example, 50 m).
sec), the transistors 20k and 20p will not become conductive as long as the pulse signal is input within the set time.

By the way, if the light-emitting element or the light-receiving element of the pulse generator 3 breaks down, or if the light-receiving element fails, the connector 15
If a disconnection occurs at time t1 in the circuit leading to the motor, the pulse signal from the pulse generator 3 is not applied to the amplifier circuit 4, and the motor is 1's rotational speed increases. However, as the pulse signal is no longer applied to the capacitor 20a, the base voltage of the transistor 20d disappears, and the transistor 20d becomes non-conductive (at this time, the START command i remains output, but the signal does not change. (The transistor 20i is in a non-conducting state, and the signal l remains at 0 level, so the transistor 20t is in a non-conducting state.) The capacitor 20j is gradually charged through the resistor 20e, and finally at a time t2 (50 m from t1). sec) at (V _BE1 +V _Z +
reaches a voltage exceeding V _BE2 ). As a result, the transistor 20k becomes conductive, and the resistor 20l → transistor 20k → Zener diode 20m → resistor 20
A current flows in the forward path of n, and a voltage drop occurs across the resistor 20n. This voltage makes the transistor 20p conductive and the output terminal of the comparator circuit 10 is forcibly brought down to the ground level, so that the output signal of the comparator circuit 10 is not applied to the AND circuit 21. Therefore,
The output terminal of the AND circuit 21 becomes 0 level,
The same condition as when the STOP command is applied to the mode setting circuit 12 occurs, and the power transistors Q1 to Q
4 is not driven, and the power to the motor 1 is cut off. After this, when a REVERSE command is generated at time t3, the transistor 20t momentarily becomes conductive, and the charge in the capacitor 20j that is in the charged state is discharged all at once. As a result, transistor 20k
and 20p turn non-conductive, and the pulse width conversion signal g output from the comparator circuit 10 is output to the mode setting circuit 12 via the AND circuit 21, and power is supplied to the motor 1, which was in the power-off state, at time t3. and the rotation speed is controlled.

However, if the signal h is interrupted at time t4 and the transistor k becomes conductive at time t5, the power is cut off in the same way. Also, the START command is at time t6
, transistor k becomes non-conducting,
Power is supplied to motor 1 at time t6.

In the embodiment shown in FIG. 3, the output signal of the pulse signal extinction detection circuit 20 and the output signal of the comparator circuit 10 are paralleled to perform stop control of the motor 1, but as shown in FIG. It can also be configured independently. That is, power transistor Q3,
A transistor Q whose collector is connected to each base of Q4 and whose emitter is grounded.
5 and Q6, and the output signal of the pulse signal disappearance detection circuit 20 is applied to the base of the transistor. As a result, protection means can be provided without using the mode setting circuit 12.

In addition, in FIG. 5, the bases of power transistors Q3 and Q4 are connected to the pulse signal extinction detection circuit 2.
Although an example has been shown in which the base potential is forcibly set to the 0 level by the power transistors Q1 and Q4, the transistors Q5 and Q6 may be connected to the bases of the power transistors Q1 and Q4. In addition, in the embodiment, a timer circuit was illustrated as a timing means for timing the input interval of the speed signal, but
The present invention is not limited to a timer circuit as long as it is a means for timing the input interval of speed signals.

(Effects of the Invention) As explained above, according to the motor speed control device of the present invention, the power supply for the motor is cut off when the output of the pulse generator (motor rotational speed signal) stops for a certain period of time or more. , it is possible to suppress an abnormal increase in the rotational speed of the motor and prevent damage to the device. Further, since the time measurement of the time measurement means is reset based on a reversal signal that reverses the rotation direction of the motor while it is rotating, malfunctions can be accurately prevented.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional motor speed control device.
2 is an operation time chart of each part of the device shown in FIG. 1, FIG. 3 is a circuit diagram of an embodiment of the present invention, and FIG. 4 is an operation time chart of each part of the pulse signal extinction detection circuit 20 according to the present invention. FIG. 5 is a circuit diagram showing another embodiment of the present invention. Explanation of symbols 1...Motor, 2...Power supply section, 3...Pulse generator, 4...Amplification circuit, 5...Waveform shaping circuit,
6... Phase comparator, 7... One-shot multivibrator, 8... Addition/integration circuit, 9... Triangular wave generation circuit, 10... Comparison circuit, 11a to 11d... Power transistor, 12... Mode setting circuit, 20... Pulse signal extinction detection circuit , 20a, 20f, 20j,
20q...Capacitor, 20b, 20c, 20e,
20g, 20h, 20l, 20n, 20r, 20
s...Resistance, 20d, 20i, 20k, 20p, 2
0t...transistor, 20m...zener diode, 21...AND circuit.

Claims (1)

[Scope of Claims] 1. A motor speed control device that controls the rotational speed of the motor based on a comparison signal that compares a speed signal corresponding to the rotational speed of the motor with a reference signal of a predetermined speed, comprising: an input interval of the speed signal; means for outputting a motor stop signal when the speed signal is not input for a predetermined time period; and means for cutting off power to the motor based on the motor stop signal; 1. A motor speed control device comprising: means for outputting a reversal signal for reversing the direction of rotation during rotation of the motor; and reset means for resetting the time of the timer based on the reversal signal.