JPH01227622A - Motor lock protective-device - Google Patents

Abstract

PURPOSE:To enable lock current to be interrupted an arbitrary time later, by charging a capacitor via a resistor, and by comparing its charged voltage and a set value with each other. CONSTITUTION:At the time of locking, the speed signal of a speed signal line 37 is fixed on a level H, and potential VC is heightened, and when the potential VC is made greater than VB, then the output of a comparator 5 comes to a level L, and the base potential of a current amplifying transistor 23 is lowered, and the transistor 23 is turned OFF. When the transistor 23 is turned OFF, then a power transistor 20 is turned OFF, and current flowing to a motor is interrupted. Then, the locking is released, and the speed signal comes to the level L, and this state is kept till the potential VC is made less than the VB.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a motor lock protection device for a DC motor that is equipped with a speed detector and that is used to drive a copying machine or the like and is driven by a pulse width modulation method.

2. Description of the Related Art A conventional lock protection method for a DC motor is, for example, by using a current fuse as shown in FIG.

A conventional motor rotor protection device will be explained below with reference to FIG.

The current fuse 43 is connected in series with the DC motor 18,
It is connected in parallel with one flywheel diode and in series with the power transistor 20. The base of this power transistor 20 is connected to the midpoint of resistor 21.22.

The emitter of the power transistor 20 and the resistor 21 are connected to the power supply 2
5. The rotation speed of the motor 18 is detected by the speed detector 26 and is applied to the control circuit 29 together with the rotation speed setting section 300 reference value via the waveform shaping circuit 27 . The control circuit 29 supplies a voltage corresponding to the deviation between the value of the speed detector 26 and the reference value to the pulse width modulation section 28, and the pulse width modulation section 28 modulates the duty according to the voltage supplied from the control circuit 29. The pulsed base voltage of transistor 2
3 and 1 to the power transistor 20 to control the on/off of the DC motor 18. Note that the output side of the pulse width modulation section 28 is connected to a power source via a resistor 24. Next, the operation when the DC motor 18 is locked will be explained.

When the motor 18 is locked, the deviation between the speed detector value and the reference value of the rotation speed setting section 300 becomes maximum, and in response to this maximum value, the pulse width modulation section 28 adjusts the base voltage such that the duty ratio is 1. is applied to the current amplifying transistor 23. Therefore, the power transistor 20 continues to be in an on state, and the lock current continues to flow through the motor 18 and the current fuse 43. When the lock current flows, the current fuse 37 blows out after a period of time according to its fusing characteristics to cut off the lock current and protect the motor 18 from heat generation and burnout due to the lock current.

Problems to be Solved by the Invention However, since the conventional configuration described above uses a current fuse, (1) the cut-off time cannot be arbitrarily set;

(2) There are large variations in cut-off time.

(3) Once blown, the fuse must be replaced, which is uneconomical.

It has the following problems.

The present invention solves the above-mentioned conventional problems, and aims to provide a motor lock protection device that can arbitrarily set the lock current cutoff time, has little variation, and can be used repeatedly.

Means for Solving the Problems To achieve this object, the motor lock protection device of the present invention operates only when the pulse signal of the speed detector and the run/stop signal for running/stopping the motor are in a specific state. A switching circuit, a time setting resistor and a capacitor connected to the switching circuit, and a comparator that compares the charging voltage charged in the capacitor with a set value and uses its output to cut off the base voltage of the power transistor. has been done.

Operation: With this configuration, the lock current of the motor can be cut off accurately at any desired time.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

Note that the same parts as in the conventional configuration are given the same reference numerals as in the conventional example, and the explanation thereof will be omitted. □Figure 1 shows a wiring diagram of a motor lock protection device in a first embodiment of the present invention. In FIG. 1, the base of an NPN transistor 1 whose emitter is grounded is connected to the same emitter □ via a resistor 8.
The collector is connected to the start/stop signal line 38 via the resistor 7, and the collector thereof is connected to the speed signal line 3'7. The base of the NPN transistor 2, whose emitter is grounded, is connected to the emitter through a 1° resistor, and is also connected to the speed signal line 37 through a resistor 9.
The collector is connected to the base of a PNP transistor 3 via a resistor 12, and the collector is connected to a resistor 11.
It is connected to the power supply line 39 via. The base of the transistor 3-5 = is connected to the power supply line 39 via the resistor 13, and the emitter thereof is also connected to the power supply line 39. These transistors 1, 2.3 and resistors? ,'8,9゜10.1j,12
These constitute a switching circuit 41 that operates only when the speed signal and run/stop signal are in a specific state.

'The collector of the transistor 3 is grounded across a capacitor 4 connected in series with a resistor. The capacitor 4 and the resistor 14 constitute a time limit setting circuit 42, and the opposite side of the capacitor 4 is connected to the speed signal line 37 via the resistor 17 and the diode 6, and the capacitor 4 is connected to the speed signal line 37 via the resistor 17 and the diode 6. The anti-ground side of 4 is also connected to the output input of comparator 5.

Resistors 15 and 16 are connected between the ground and the three power supply lines, and the voltage dividing point of the resistors 15 and 16 is connected to the non-inverting input of the comparator 5. The resistor 5a is connected to the output of the comparator. It is connected to the line 40 and the power supply line 39.The operation of the motor lock protection device 36' of the recommended example configured as above will be described below with reference to the waveform diagram of the timing chart in FIG. explain.

First, when both the speed signal and the run/stop signal are at H level, or when the speed signal is at L level and the run/stop signal is at H level, transistor 1 is turned on, lowering the base potential of transistor 2, and transistor 2 is turned off. Become. When transistor 2 is turned off, the base potential of transistor 3 rises and transistor 3 is turned off. Also, since transistor 1 is ON, capacitor 4 is connected to diode-1.
The capacitor 4 is discharged through the capacitor 6, and the potential VC of the capacitor 4 decreases. When the potential VB resulting from the voltage division between the resistors 15 and 16 is higher than VC, the output of the comparator becomes H level.

Next, when the speed signal and the run/stop signal are both at L level, transistors 1 and 2 are both OFF, transistor 3 is also OFF, and VC is low and the output VA of the comparator is at H level. Next, when the speed signal is at H level and the run/stop signal is at L level, transistor 1 is turned off.
F, and transistor 2 is turned on. When transistor 2 is turned on, the base potential of transistor 3 is lowered and transistor 3 is turned on. When transistor 3 is turned on, current flows to capacitor 4 via transistor 3 and resistor 14, and VC increases. The relationship between VC and time t is expressed by the following equation.

VC: (VCC-VCE3XI-e R”°04)・
- (1) When the speed signal is at H level and the run/stop signal is at L level, and VC becomes larger than VB, VA
becomes L level.

FIG. 3 shows the motor lock protection device according to the embodiment of the present invention shown in FIG. 1 applied to a DC motor equipped with a pulse width modulation and control circuit.

In FIG. 3, the same components as those of the embodiment of the present invention shown in FIG. 1 are designated with the same numbers. FIG. 3 will be explained below.

In the figure, 31 is a resistor provided between the power source and the run/stop signal line. The run/stop signal line is connected to the base of a transistor 33 via a resistor 32, and is further connected to the motor lock protection device 36 described above. A resistor 34 is provided between the base and emitter of the transistor 33, and the collector of the transistor 33 is connected to the output side of the pulse width modulation section 28. These resistors 31.
32゜34 and transistor 33 make up the operation/stop circuit 3
5. The speed signal and run/stop signal are output by an open collector, and the speed signal is configured to be at H level when the motor is locked. During normal operation, the run/stop signal is always at L level, the speed signal has a pulse waveform of H9L, and VC rises only when the speed signal is at H level. However, since it is a pulse waveform, when it is at L level, capacitor 4 is discharged and VC decreases. If VB is set to a value larger than VC obtained from equation (1), where t is the 1/2 period of the speed signal, the output of the comparator becomes H at this time, and the motor lock device does not operate. Next, when locking, the speed signal is fixed at H level, the potential of VC rises, and when VC becomes greater than V[+, the output of the comparator becomes L.
level, lowering the base potential of the current amplifying transistor 23 and turning off the transistor 23. When the transistor 23 turns off, the power transistor 20 turns off.
becomes F, cutting off the current flowing to the motor. This state is maintained until the lock is released, the speed signal goes to L level, and VC becomes smaller than VB.

Effects of the Invention As described above, according to the present invention, by charging a capacitor through a resistor and comparing the charging voltage with a set value, the lock current can be cut off after an arbitrary time. , lock protection is possible for motors of various capacities. Also, because it is separated from the motor side power supply, the voltage is lower and the size is smaller.

Furthermore, it is also possible to configure it inside the control IC.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a motor lock protection device in an embodiment of the present invention, Fig. 2 is a timing chart waveform diagram of a motor lock protection device in an embodiment of the invention, and Fig. 3 is a circuit diagram of a motor lock protection device in an embodiment of the invention. FIG. 4 is a circuit diagram of a motor lock protection device applied to a DC motor equipped with a pulse width modulation and control circuit. FIG. 4 is a circuit diagram of a conventional motor lock protection device. 1.2.3...Transistor, 4...
Capacitor, 5...Comparator, 5a, 7, 8, 9
,10,11゜12.13.14,15.16.17・
...Resistance, 6...Diode, 36...
...Motor lock protection device, 37...Speed signal line, 38...Run/stop signal line, 41...
...Switching circuit, 42...Time limit setting circuit.

Claims (1)

[Claims] A pulsed speed signal obtained by waveform shaping the output signal of a speed detector connected to a motor equipped with a drive circuit, and a run/stop signal input to run/stop the motor are in a specific state. A switching circuit that operates only at certain times, a capacitor that charges and discharges depending on whether the switching circuit is conductive or non-conductive, a resistor that determines the charging time of this capacitor, and a charging voltage of the capacitor that is compared with a set value. A motor lock protection device that is equipped with a comparator for the purpose of locking the motor and uses the output of the comparator to release the locked state of the motor.