JPH0429589A - Method of judging lock condition of dc motor - Google Patents

Abstract

PURPOSE:To dispense with a resistor for current detection and prevent the waste of power for detection of lock condition by detecting whether or not counterelectromotive voltage by rotation while the driving current to a motor is interrupted. CONSTITUTION:A microcomputer 13 outputs a pulse drive voltage Vd from an output port 13a to turn on a field effect transistor 2 and a drive a motor 1. The microcomputer 13 detects the voltage VD across a motor through a voltage controller 11 and an AND gate 12. When the current application to the motor 1 is broken, the terminal voltage of the motor 1 becomes lower than the application voltage by the amount of electromotive force. The microcomputer 13 detects the terminal voltage VD of the motor 1, after the current application to the motor is interrupted, so as to judge the lock condition of the motor 1. The abnormal heating, etc., of the motor 1 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for determining whether a DC motor is in a locked state.

(Prior art) If the DC motor is locked and does not perform the required rotational movement even though drive current is being supplied, an excessive current will flow through the armature of the DC motor, resulting in burnout of the armature. In addition, there is a risk that it may cause a serious fire in some cases. Therefore, various methods have been proposed for quickly detecting that the DC motor is in a locked state and stopping the supply of drive current. One method of this type is, for example, by inserting a resistor with a small resistance in series with the DC motor, and when the voltage level across the resistor exceeds a predetermined value, the DC motor There is a known method for determining whether the device is in the locked state.

(Problem to be solved by the invention) However, in this conventional method, a resistor is inserted in series with the DC motor, so power is constantly lost in the resistor, reducing efficiency. If an excessive current flows due to a short-circuit accident or other electrical failure in the motor drive circuit, it is impossible to distinguish this from a locked state of the motor, resulting in an erroneous determination.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide an improved method for determining the lock state of a DC motor, which can solve the above-mentioned problems in the prior art.

(!! Means for Solving Problem 1) The feature of the method of the present invention for solving the above problem is that a DC motor that is driven by intermittently applying a driving current with a pulse signal is in a locked state. In the method for determining whether or not the DC motor has become energized, the terminal voltage of the DC motor is detected while power to the DC motor is cut off, and if the detected terminal voltage does not fall below a predetermined level, the lock is activated. The point is that it is determined that the state is present.

(Function) When a pulse-driven DC motor is operating,
The terminal voltage of the DC motor after a certain period of time has passed since the current supply to the DC motor is cut off becomes lower than the applied voltage by the amount of electromotive force generated in the motor.

This is because after the power supply to the motor is cut off, the motor acts as a generator, and the terminal voltage of the motor is lower than the applied voltage by this electromotive force.

If the motor terminal voltage or the motor's electromotive force does not decrease after the power is turned off to the motor, the detected terminal voltage will not fall below a predetermined level, and this will indicate that the DC motor is in a locked state. It is determined that

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a motor control circuit that uses the method of the present invention to determine whether or not a DC motor is in a locked state. In FIG. 1, 1 is a DC motor, 2 is a field effect transistor for controlling the supply of drive current to the DC motor l, 3 is a field-effect transistor that turns on the supply of current to the DC motor 1,
A diode for absorbing the back electromotive force generated when the motor is turned off; 4 to 10 are resistors; 11 is a voltage comparator for comparing the terminal voltage of the DC motor 1 with a predetermined reference level;
2 is an ant gate, and 13 is a microcomputer.

Next, the operation of the motor control circuit shown in Fig. 1 will be explained in Fig. 2 (a).
) to FIG. 2(e) and FIG. 3, the explanation will be given below. The output port 13a of the microcomputer 13 outputs a pulse drive voltage Vd for pulse-driving the DC motor l according to a predetermined control program, and this pulse drive voltage Vd is divided by a resistor 9. A drive control pulse voltage v1 having a waveform shown in FIG. 2(a) is applied to the gate of the field effect transistor 2. In the illustrated embodiment, when the drive control pulse voltage 1 becomes high level, the field effect transistor 2 is turned on, and the DC motor 1 is turned on.
This is a configuration in which current flows for driving.

By pulse-driving the DC motor l as described above,
A voltage corresponding to the voltage generated across the DC motor l is taken out from the connection point of the resistor 4.5 as a detection voltage Vt, and applied to one input terminal of the voltage comparator 11.

As shown in FIG. 2(b), the level of the detection voltage Vt is approximately equal to the level of the drive pulse voltage 1 shown in FIG. During the low level period of the drive pulse voltage v1, which is between the drive current cutoffs M of 1, the drive pulse voltage v1 becomes high level.

Here, DC motor 1 or time 1 = 1. Since the DC motor 1 is at a low rotational speed for a while after being pulse driven by the drive control pulse voltage V1 at The terminal voltage of the DC motor 1 after a predetermined period of time to from the time of interruption is almost the same as the power supply voltage VS applied to the DC motor 1.

However, when a predetermined time T has elapsed from t ==t + and the steady operating state is reached, the level of the drive control pulse voltage V1 becomes a low level and the current supply to the DC motor l is cut off. Due to the back electromotive force generated by the rotation of the sensor, the level of the detection voltage Vt tends to decrease as shown in FIG. 2(b). This drop is most noticeable just before the next energization starts, and in order to detect this level drop state in the detection voltage Vt at an appropriate timing a little before this, the The potential Vr at the connection point of the resistor 6.7, which is determined in consideration of the decreasing tendency of the detection voltage Vt, is applied to the input terminal of the voltage comparator 11 as a reference level. The level of this potential Vr is shown by a dotted line in FIG. 2(b), and the level of the output voltage VO of the voltage comparator 11 is shown in FIG. 2(C).
will change as shown in .

The output voltage Vo is applied to the other input of the controller 1-12, to which the gate pulse GP output from another output port 13b of the microcomputer 13 is applied. The gate pulse GP is as shown in Fig. 2(d).
As shown in FIG. 2, the output signal is output after a predetermined time T has elapsed from the rotation start time t1 of the DC motor I, and is output every time ta elapses after each power cutoff.

This time ta is selected at an appropriate timing when the level of the output voltage VO is lower than the reference potential Vr for the above-mentioned reason if the DC motor l is rotating normally. During normal operation of the AND gate 12, a pulse signal corresponding to the gate pulse GP is obtained from the output of the AND gate 12, as shown in FIG. 2(e).

On the other hand, when the DC motor 1 is in a locked state, no back electromotive force is generated due to its rotation, so the voltage level across the DC motor 1 does not decrease when the current is cut off, and the power supply voltage +V
It is almost the same as s. In Fig. 2(b), the DC motor l
The state of change in the detection voltage Vt when in the locked state is shown by a dashed-dotted line. Therefore, when the DC motor 1 is in the locked state, the AND gate 12 will not output a pulse signal corresponding to the gate pulse GP shown in FIG. 2(e).

The output from AND gate 12 is microcomputer 1
The microcomputer 13 determines whether or not the DC motor 1 is in a locked state based on the level change state of the output of the AND gate 12.

For this determination, a determination program is stored in advance in the microcomputer 13, and according to this determination program, it is determined whether the DC motor 1 is in a locked state.

FIG. 3 shows a flowchart showing the discrimination program. This discrimination program 20 is activated at regular time intervals, and after activation, it is first determined in step 21 whether or not a flag F indicating that the motor is in a locked state is set. If F-rl, the execution of this program ends, and if F=rOJ, the program proceeds to step 22. In step 22, it is determined whether or not the DC motor 1 is being controlled, and if the DC motor 1 is not being controlled, the execution of this program ends.

If the motor is being controlled, the content of the counter TR1, which is preset to a predetermined value A, is decremented by 1 in step 23, and it is determined in step 24 whether TR1=0. If TRI≠0, this program ends, but if TR1=O, the process proceeds to step 25 and the voltage Vd
Based on the level of , it is determined whether or not the current supply to the DC motor l has been cut off. If the DC motor l is not energized or cut off, the execution of this program ends here.

When the DC motor l is energized or cut off, the contents of another counter TR2 are decremented by 1 in step 26, and it is determined in step 27 whether TR2=O or not. TR2≠
If it is 0, execution of this program ends. TR=
In the case of O, the value of the counter TR2 is set to a predetermined initial value B in step 28, and then, in step 29, it is determined whether the output of the AND gate 12 is in a low level state. If the DC motor 1 is operating normally, the output of the AND gate 12 becomes high level, and the execution of this program ends. If the output of the AND gate 12 is at a low level, a flag F is set in step 30, and an operation for controlling and stopping the DC motor 1 is executed (step 31). Furthermore, in step 32, a process for ensuring the safety of the DC motor 1 is executed, and the execution of this program 20 is completed.

That is, according to this program 20, control of the DC motor l is started in the state of F; [0], and the timer T is
When the preset value A corresponding to the time T of RI becomes zero, the timer TR2 starts decrementing, and the time ta
When the preset value B corresponding to becomes zero, it is determined whether the level of the output of the AND gate 12 is high or low (step 29). At this time, if the output level of the AND gate 12 is low, it is determined that the DC motor 1 is in a locked state, a flag F is set, and a predetermined process such as stopping the control of the DC motor 1 is performed. will be carried out.

As a result, without wasting power in the resistor,
It is possible to reliably detect that the DC motor 1 is in a locked state, distinguishing it from a short-circuit accident, etc., and reliably prevent abnormal heat generation, burnout, etc. of the DC motor 1.

(Effects of the Invention) According to the present invention, as described above, when the drive current is intermittently supplied to the motor using a pulse signal, the back electromotive force generated by the rotation of the motor is prevented while the drive current to the motor is cut off. Since whether the voltage is present or not is detected based on the level drop of the terminal voltage, there is no need for a resistor for current detection, and power is not wasted to detect the lock state. In addition, it has an excellent effect of being able to reliably distinguish between a short-circuit accident in a motor or the like and a locked state of the motor.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a motor control circuit that determines the locked state of a DC motor according to the present invention;
2(a) to 2(e) are waveform diagrams showing signal waveforms of each part of the circuit shown in FIG. 1, and FIG. 3 shows a discrimination program executed by the microcomputer shown in FIG. 1. It is a flowchart. 1... DC motor, 2... Field effect transistor,
11... Voltage comparator, I2... AND gate, 13
...Microcomputer, vl...Drive control pulse voltage, Vt...Detection voltage, vO...Output voltage, GP...
gate pulse.

Claims (1)

[Claims] 1. In a method for determining whether a DC motor driven by intermittently applying a drive current by a pulse signal is in a locked state, A method for determining a locked state of a DC motor, comprising: detecting a terminal voltage of a motor; and determining that the DC motor is in a locked state if the detected terminal voltage does not fall below a predetermined level.