JP2000350493A - Drive device for dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a drive device for a DC motor that can perform operation, stop, forward rotation, and backward rotation, and prevent overcurrent. SOLUTION: A switching element 22 and a current detection resistor R are provided between a DC power supply V and contact switches 12 and 14, and a current limiting circuit 24 is provided. The current limiting circuit 24 turns off the switching element 22 when a current value being detected by the current detection resistor R exceeds a prescribed value and turns on the switching element 22 again, after a prescribed amount of time passes or when a current value goes below a specific value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for a DC motor that performs operation, stop, forward rotation, and reverse rotation.

[0002]

2. Description of the Related Art Electric linear actuators are used in nursing beds and the like. In order to expand and contract this linear actuator, it is operated with a remote control,
Running, stopping, forward rotation, and reverse rotation of the DC motor.

Conventionally, a circuit as shown in FIG. 5 is used as a drive device for operating, stopping, rotating forward and rotating the DC motor.

A DC motor M is connected to a DC power supply V, and a relay switch 110 for normal rotation and a relay switch 112 for reverse rotation are arranged on the way. This forward rotation relay switch 110 is a remote control switch 1 provided on a remote controller.
14 and the relay switch 112 for reverse rotation is
It is also operated by a remote control switch 116 provided on the remote control.

[0005]

However, in the driving device described above, an excessive motor current flows when the motor is started or when the motor is overloaded, and the relay switch 11
There is a problem that the contacts 0, 112 and the like are deteriorated and the life is remarkably shortened.

To prevent this overcurrent, a method of limiting the current on the DC power supply side is conceivable. However, the circuit configuration becomes complicated, and it is difficult to increase the response speed of the current limiting operation. there were.

Accordingly, the present invention has been made in view of the above problems, and provides a DC motor drive device having a configuration capable of running, stopping, normal rotation, and reverse rotation, and capable of preventing overcurrent.

[0008]

A DC motor driving apparatus according to the present invention uses a contact switch such as a relay switch provided between a DC power supply and a DC motor to operate, stop, forward and reverse the DC motor. In the switching device for a DC motor to be switched, a switching element and a current detection resistor are provided between the DC power supply and the contact switch, and when the current value detected by the current detection resistor exceeds a predetermined value, the switching element is switched. In the OFF state, the overcurrent is prevented from flowing to the contact switch and the DC motor side.
A current limiting circuit is provided for returning the switching element to the ON state after a predetermined time from the F state or when the current value becomes equal to or less than the predetermined value.

With this DC motor drive device, when an overcurrent flows when the motor is started or when the motor is overloaded, the overcurrent is detected by a current detection resistor, and the current limiting circuit switches. The element is turned off.

Thus, it is possible to prevent an overcurrent from flowing to the contact switch and the DC motor.

Further, after a predetermined time from the OFF state or when the value of the overcurrent has become equal to or less than a predetermined value, the switching element is returned to the ON state, so that the DC motor can be continuously operated. Become.

[0012]

(Embodiment 1) Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS.

FIG. 1 is a circuit diagram of a DC motor driving apparatus 10 according to a first embodiment, in which a DC motor M is rotated forward or backward by a DC power supply V.

The details are as follows.

C-contact type relay switches 12 and 14
Is provided, and c of the pair of relay switches 12 and 14 is provided.
A DC motor M is connected between the points. The + side of the DC power supply V is connected to the point a of the relay switches 12 and 14,
The point b side of the relay switches 12 and 14 is connected respectively. Then, the relay coil 1 of the relay switch 12
3 and an operation switch 16 are connected in series, and the operation switch 16 is provided on a remote controller provided outside the driving device 10. Relay coil 1 of relay switch 14
5 and an operation switch 18 are connected in series, and the operation switch 18 is also provided on a remote controller.

A flywheel diode 20 is provided in parallel with the relay switches 12 and 14, and the direction of the diode 20 is opposite to the DC power supply V.

The reason why the diode 20 is provided is that when the current flowing through the current detection resistor R exceeds a predetermined value, a current limiting operation for turning off the switching element 22 is performed.
Since a back electromotive force is generated due to the inductance L of the motor M and an overvoltage is applied to the switching element 22 to cause destruction, the diode 20 is provided to short-circuit the DC motor M to prevent the breakdown. It is.

A switching element 22 composed of a semiconductor such as an FET and a current detecting resistor R are connected in series between the point b of the relay switches 12 and 14 and the negative side of the DC power supply V. When the switching element 22 is turned off, the power supply to the DC motor M is stopped.

A current limiting circuit 24 for turning on / off the switching element 22 is provided. The current limiting circuit 24 calculates a current value (voltage) flowing through the current detection resistor R.
Is detected, and when it exceeds a predetermined value, the switching element 22 is turned off.

The structure of the current limiting circuit 24 will be described in detail with reference to FIG.

The output terminal of the comparator 26 is connected to the switching element 22 described above.
Is connected to one end of the current detection resistor R. On the other hand, the non-inverting terminal of the comparator 26 has a resistor R
1, and a DC power supply V1 is connected to the resistor R1. A feedback resistor R2 is provided between the output terminal and the non-inverting terminal of the comparator 26.

An operation state of the DC motor driving device 10 having the above configuration will be described.

When both the points c of the relay switches 12 and 14 are connected to the point a, no current flows to the DC motor M and the DC motor M is stopped. Similarly, when the point c is connected to the point b, no current flows and the state is stopped.

When only the operation switch 16 of the remote controller is turned on and the operation switch 18 is turned off, the contact of the relay switch 12 is moved to the point a, and the contact of the relay switch 14 is held at the point b. Then, a current flows through the DC motor M, and the DC motor M rotates forward.

Conversely, when only the operation switch 18 is turned on and the operation switch 16 is turned off, the relay switches 12 and 14 operate in the opposite direction, and the DC motor M rotates in the reverse direction.

If an excessive motor current flows when the motor is started or the motor is overloaded, this current also flows to the current detecting resistor R. Therefore, when this current value becomes larger than a predetermined current value I0 determined by the DC power supply V1 and the resistor R1, the comparator 26 turns off the switching element 22. As a result, overcurrent does not flow through the relay switches 12 and 14. When the current value becomes equal to or less than the predetermined value, the switching element 22 is turned on by the output from the comparator 26, so that the current flows again.

By doing so, the relay switch 1
The current flowing through the relay switches 12 and 14 can be limited to a predetermined value or less, and the life of the relay switches 12 and 14 can be extended.

Since the current flowing through the DC motor M can be limited at the same time, the motor heat generation at the time of overload can be suppressed low.

Since the switching element 22 can be turned off instantaneously in the event of an overcurrent, high-speed and reliable current limiting can be performed.

Even when an overcurrent occurs, when the current value becomes equal to or less than the predetermined value, the switching element 22 returns again to be in the ON state, so that the DC motor M can be continuously operated.

(Embodiment 2) The difference between this embodiment and Embodiment 1 is in the structure of the current limiting circuit 24.

That is, in the second embodiment, as shown in FIG. 3, a monostable multivibrator MM is connected to the output terminal of the comparator 26.

By connecting this monostable multivibrator MM, when the current value detected by the current detection resistor R exceeds a predetermined value, the switching element 22 is turned off.
Set to F state and turn on switching element 22 after a predetermined time
State. The predetermined time can be determined based on the characteristics of the monostable multivibrator MM. For example, 10 ms can be considered.

(Embodiment 3) The difference between the present embodiment and the first embodiment is that the arrangement of the current limiting circuit 24, the current detection resistor R and the switching element 22 is different.

That is, in the first embodiment, a circuit such as the current limiting circuit 24 is provided on the negative side of the DC power supply V, but in this embodiment, it is provided on the + side of the DC power supply V.

The operation and effects are the same as in the first embodiment.

[0037]

As described above, according to the DC motor driving apparatus of the present invention, the current value can be limited by instantaneously turning OFF the contact switch and the DC motor when an overcurrent flows through the DC motor. In addition, the life of the contact switch can be prolonged, and heat generation of the motor at the time of overload can be suppressed low. Even if an overcurrent flows, the switching element is turned on again after a predetermined time or when the current value becomes equal to or less than a predetermined value, so that the DC motor can be continuously operated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a driving device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a current limiting circuit.

FIG. 3 is a circuit diagram of a current limiting circuit according to a second embodiment.

FIG. 4 is a circuit diagram of a driving device according to a third embodiment.

FIG. 5 is a circuit diagram of a conventional driving device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 Drive device 12 Relay switch 14 Relay switch 16 Operation switch 18 Operation switch 20 Diode 22 Switching element 24 Current limiting circuit 26 Comparator R Current detection resistor M DC motor

Claims (1)

[Claims] 1. A driving device for a DC motor which switches between operation, stop, forward rotation, and reverse rotation of the DC motor by a contact switch such as a relay switch provided between the DC power supply and the DC motor. A switching element and a current detection resistor are provided between the switch and the switch. When the current value detected by the current detection resistor exceeds a predetermined value, the switching element is turned off and an overcurrent is applied to the contact switch and the DC motor. And a current limiting circuit for returning the switching element to the ON state after a predetermined time from the OFF state or when the current value becomes equal to or less than the predetermined value. Motor drive.