JPH0923675A - Failure detection device for motor drive circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] In a device for detecting a failure state of a motor drive circuit, a disconnection or short circuit of a motor or a switching element for applying a forward / reverse voltage to the motor is reliably detected. A failure detection device for detecting a failure of a motor drive circuit composed of a motor 1 and four switching elements 2 bridge-connected to the motor 1 for applying forward and reverse voltages to the motor 1. Photo-couplers 11 and 12 which are respectively connected in parallel to the motor and detect the terminal voltage of the motor when a positive voltage or a reverse voltage is applied to the motor, and a flip-flop that is set or reset by the output of each photo-coupler. Circuit 13 and a retrigger type multivibrator 14 to which the output of the flip-flop circuit 13 is input. The output of the multivibrator 14 detects a failure state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure detection device for detecting a failure in a motor drive circuit. The motor drive circuit is, for example, a drive for switching and driving a rotor or a spool of a directional control valve that controls the flow direction of fluid when supplying fluid to a hydraulic actuator that repeatedly performs operations such as controlling the control surface of an aircraft. Used as a device.

[0002]

2. Description of the Related Art As shown in FIG. 4, a motor drive circuit described above includes a motor 1 and four switching elements 2a, 2b, 2c, 2 bridge-connected to the motor 1.
and a DC power supply voltage is supplied to the motor drive circuit to turn on the switching elements 2a and 2d, a positive voltage is applied to the motor 1, and the motor 1 is turned on by turning on the switching elements 2b and 2c. The reverse voltage is applied, and the current value is determined by the ratio of the voltage alternately applied to the motor 1 during one cycle (drive by the PWM method). In such a motor drive circuit, the current value flowing to the motor 1 is controlled by providing the current detection resistor 3 between the ground and the current detection resistor 4 connected in series to the motor 1. Is being done.

Conventionally, when such a failure of the motor drive circuit is detected, an amplifier 5 is connected to both ends of a current detection resistor 4 connected in series with the motor 1, and the current value is measured via this amplifier 5. By detecting, a failure of the motor drive circuit has been detected. Further, an amplifier (not shown) is provided at both ends of the current detection resistor 3 connected between the motor drive circuit and the ground, and the failure of the motor drive circuit can be detected by detecting the current value through this amplifier. Is also being done.

[0004]

However, according to the above-mentioned failure detecting device, when the current flowing through the motor 1 is controlled in the vicinity of 0, the voltage generated across the current detecting resistors 3 and 4 has a very small value. Therefore, the switching element 2
There is a problem that it is difficult to determine whether or not the wire is broken (in this case, the voltage across the current detection resistors 3 and 4 becomes 0).

Further, when the motor 1 is short-circuited, the current detection resistors 3 and 4 serve as loads to control the current.
There is a problem that the short circuit state cannot be detected. Also,
When detecting a failure with the current detection resistor 4, the current detection resistor 4
Since a high voltage is applied to the amplifier 5 connected to, it is necessary to use a high voltage amplifier, and there is a problem that the failure detection device becomes expensive.

Further, when the PWM drive is carried out, the ON / OFF signal to each switching element is carried out in a short time, so that the detection time in case of a failure is shortened, so that the failure can be surely detected. There was a problem that it was difficult.

The present invention has been made in view of the above circumstances, and in a motor drive circuit including a motor and four switching elements bridge-connected to the motor for applying forward and reverse voltages to the motor, Alternatively, it is an object of the present invention to provide a failure detection device capable of reliably detecting disconnection or short circuit of a switching element.

[0008]

To achieve the above object, the present invention provides a motor drive circuit comprising a motor and four switching elements bridge-connected to the motor for applying forward and reverse voltages to the motor. A failure detection device for detecting a failure of (1) is characterized by including the following configuration. First photo coupler. The first photocoupler is connected in parallel with the motor and detects the terminal voltage of the motor when a positive voltage is applied to the motor. Second photo coupler. The second photocoupler is connected in parallel to the motor and detects the terminal voltage of the motor when a reverse voltage is applied to the motor. Flip-flop circuit. This flip-flop circuit is set by the output of the first photocoupler and reset by the output of the second photocoupler. Detection means. The detection means inputs the output of the flip-flop circuit and detects a failure state of the motor drive circuit.

According to the present invention, the terminal voltage can be detected by the photocoupler connected in parallel to the motor, and the failure state of the motor drive circuit can be detected based on this voltage.

Further, when a disconnection occurs in the switching element, no voltage is applied to the motor and the terminal voltage becomes 0, so that the disconnection can be detected as a failure. Further, when the motor is short-circuited, the potential difference between both ends of the motor disappears and the terminal voltage becomes 0, so that the short-circuit can be detected as a failure.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a failure detecting device according to the present invention will be described with reference to FIG. The failure detection device 10 is a first device connected in parallel to the motor 1.
Photocoupler 11, second photocoupler 12, and flip-flop circuit 1 to which the output of each photocoupler is input
3 and a multivibrator 14 that outputs a failure signal.

The first photocoupler 11 is for detecting the presence or absence of a terminal voltage of the motor 1 when a positive voltage is applied to the motor 1. In addition, the second photo coupler 12 is
When a reverse voltage is applied to the motor 1, the presence or absence of the terminal voltage of the motor 1 is detected. Each of the photocouplers 11 and 12 has a light emitting portion configured of a light emitting diode or the like for converting an electric signal into an optical signal, and a light receiving portion configured of a phototransistor or the like for converting the optical signal into an electric signal, When a voltage difference occurs between the motors 1, a current flows through the light emitting diode to output an “H” signal, and when no current flows through the light emitting diode, an “L” signal is output.

The output of the first photocoupler 11 is connected to one input terminal (S) of the flip-flop circuit 13, and the output of the second photocoupler 12 is connected to the other input terminal (R). It is connected. Therefore, the output terminal (Q) of the flip-flop circuit 13 is set by the “H” output signal of the first photocoupler 11 to be “H”.
And is reset to "L" by the "H" output signal of the second photocoupler 12.

The output terminal of the flip-flop circuit 13 is
It is connected to a retrigger type multivibrator 14 which constitutes a detecting means. The retrigger type multivibrator 14 is of “H” (or “L”, which signal is to be output is determined in advance) when the “H” and “L” signals are input within a fixed period. Operates to continue signal output. Therefore, it can be detected from the output signal of the multivibrator 14 whether the output of the flip-flop circuit 13 is "H" or "L" periodically.

Next, the detection of a failure in the motor drive circuit by the failure detection device 10 having the above configuration will be described. FIG.
It shows a motor drive circuit to which the failure detection device 10 is connected, and the same components as those in FIG. 4 are designated by the same reference numerals. In addition, the retrigger type multivibrator 14 is provided when the “H” and “L” signals are input within a fixed period, that is, when the motor drive circuit operates normally.
When the failure signal from the multivibrator 14 is set to "H", the motor drive circuit is determined to be operating normally, and the failure signal is "L". , It is determined that a failure has occurred in the motor drive circuit.

When forward and reverse voltages are alternately applied to both ends of the motor by the on / off control of the switching element 2 (in the figure,
The solid line represents the current flow when the switching elements 2a and 2d are turned on, and the dotted line represents the current flow when the switching elements 2b and 2c are turned on. ), When the motor drive circuit is normal, the terminal voltage of the motor 1 is detected by the first photocoupler 11 and the second photocoupler 12,
The flip-flop circuit 13 is driven. In this case, the output terminal (Q) of the flip-flop circuit 13 periodically becomes "H" and "L" according to the application of the forward and reverse voltages, and the output (fault signal) of the multivibrator 14 holds the "H" state. .

When the motor 1 is in a short circuit state, the motor 1
The voltage across the two becomes equal. Therefore, there is no output from the first photocoupler 11 and the second photocoupler 12, and the output terminal (Q) of the flip-flop circuit 13 remains "H" or "L", and the multivibrator 1
The output of 4 (fault signal) is inverted to "L".

A case where any one of the switching elements 2 is short-circuited, for example, as shown in FIG. 3, the switching element 2b is short-circuited will be described. Switching element 2b, 2c is turned on, switching element 2
When a and 2d are turned off, the switching element 2b
Is in a short-circuit state, but since the switching element 2c is normal, current control is performed by the switching element 2c, and the motor drive circuit is in a normal operating state. Switching element 2a, 2d is turned on, switching element 2
When b and 2c are turned off, the switching element 2b
Is short-circuited, the current from the power supply flows through the switching element 2b and the switching element 2d, and the motor 1
Does not flow to Therefore, the voltage applied to the motor 1 is either forward or reverse, and the input to the flip-flop circuit 13 is also only on one side, so its output terminal (Q) is "H".
Alternatively, the output (failure signal) of the multivibrator 14 is inverted to "L" without changing as "L".

Therefore, according to the above embodiment, the photocouplers 11 and 12 connected in parallel to the motor 1 are connected.
Thus, the terminal voltage can be detected, and the failure state of the motor drive circuit can be detected based on this voltage. Further, since the photocouplers 11 and 12 are used, it is possible to reliably detect the presence or absence of the terminal voltage of the motor 1, and when the PWM drive is performed, the ON / OFF signal to each switching element is transmitted. Even in a short time, it is possible to reliably detect the failure.

When the switching element 2 is disconnected, the voltage is not applied to the motor 1 and the terminal voltage becomes 0. Therefore, the failure signal of the multivibrator 14 becomes "L" and the disconnection is detected as a failure. can do. Further, when the motor 1 is short-circuited, the potential difference between the both ends of the motor disappears and the terminal voltage becomes 0. Therefore, the failure signal of the multivibrator 14 becomes "L" and the short-circuit can be detected as a failure.

In the above embodiment, the multivibrator 14 is used.
Is set to continue outputting the "H" signal when the "H" and "L" signals are input within the fixed period (when the motor drive circuit operates normally). The output may be set to continue. In this case, when the failure signal from the multivibrator 14 is "L", it is determined that the motor drive circuit is operating normally, and the failure signal is "H".
At this time, it is determined that a failure has occurred in the motor drive circuit.

[0022]

According to the present invention, in a motor drive circuit comprising a motor and four switching elements bridge-connected to the motor for applying forward and reverse voltages to the motor, the motor drive circuit is connected in parallel to the motor. Since the terminal voltage is detected by each connected photocoupler and the failure state of the motor drive circuit is detected based on this voltage, disconnection or short circuit of the motor or the switching element can be reliably detected.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of a failure detection device for a motor drive circuit according to the present invention.

FIG. 2 is an equivalent circuit diagram showing the entire motor drive circuit failure detection device of the present invention.

FIG. 3 is an equivalent circuit diagram of a failure detection device for explaining a case where a switching element is short-circuited.

FIG. 4 is an equivalent circuit diagram of a conventional motor drive circuit failure detection device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Motor, 2 ... Switching element, 10 ... Failure detection device, 11, 12 ... Photocoupler, 13 ... Flip-flop circuit, 14 ... Multivibrator

Claims (1)

[Claims] 1. A failure detection device for detecting a failure of a motor drive circuit comprising a motor and four switching elements bridge-connected to the motor for applying forward and reverse voltages to the motor. A first photocoupler that is connected in parallel to the motor and detects the terminal voltage of the motor when a positive voltage is applied to the motor; and a first photocoupler that is connected in parallel to the motor and a reverse voltage is applied to the motor. A second photocoupler that sometimes detects the terminal voltage of the motor, and a second photocoupler that is set by the output of the first photocoupler.
A failure detection device for a motor drive circuit, comprising: a flip-flop circuit that is reset by the output of the photocoupler; and a detection unit that receives the output of the flip-flop circuit and detects a failure state of the motor drive circuit.