JP3165381B2 - Magnet protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnet protection device for protecting a magnet.

[0002]

2. Description of the Related Art Conventionally, magnets have been used as actuators in various fields. For example, it is used as an actuator for opening a drawer of a cash register, connecting and disconnecting an electromagnetic clutch, and displacing levers. As described above, the magnet used as an actuator may burn out or break down if the continuous energizing time is long.

[0003] Therefore, a fuse is provided between the magnet and the main power supply, and when an abnormal current flows through the magnet, the fuse is blown to cut off the power supply to the magnet or to detect the operating state of the magnet. However, it is known that when an abnormality occurs, the power supply to the magnet is cut off by microcomputer control.

[0004]

In the method of cutting off the current to the magnet by blowing the fuse, an overcurrent flows through the magnet until the fuse is blown, so that the magnet may be deteriorated and, in some cases, repaired. Have to do. Replacing fuses is troublesome. The method of shutting off the power supply to the magnet under the control of the microcomputer cannot protect the magnet if the software runs away.

[0005]

According to the present invention, there is provided a main power switch unit connected between a main power unit and a magnet,
A capacitor to which a control voltage is applied, a resistor connected to the capacitor, and an energization command control signal for driving the magnet are turned off during the period of being output to the main power supply unit, and the capacitor is maintained in a charged state. And a signal switch unit that is turned on when the energization command control signal is interrupted and allows the capacitor to discharge, and the voltage of the resistor increases according to the amount of electricity stored in the capacitor when the energization command control signal is output. And a time constant circuit for turning off the main power switch when the voltage reaches a reference voltage. Therefore, when the energization command control signal is output to the magnet, the signal switch section is turned off, so that the capacitor stores the amount of electricity. When the energization command control signal is interrupted, the signal switch section is turned on, so that discharge from the capacitor is allowed. . If the energization command control signal to the magnet is output for a certain period of time for some reason, the signal switch section continues to be kept in the off state, the amount of electricity stored in the capacitor increases, and the voltage of the resistor increases according to the amount of electricity I do. When the detected voltage reaches the reference voltage, the main power switch is turned off.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. Reference numeral 1 denotes a constant voltage circuit as a main power supply for driving a magnet (not shown).
Has a transistor 2 as a main power switch in the output system to the magnet.

Reference numeral 3 denotes a time constant circuit. This time constant circuit 3
Is a capacitor 6 connected to a control power supply 5 via a resistor 4, a resistor 7 connected to the capacitor 6, and a control signal A, B, C, D for energizing the magnet.
The signal switch section 8 which is turned off when the output signal is output to maintain the capacitor 6 in the charged state and turned on when the energization command control signals A, B, C, and D are interrupted, and permits the discharge of the contentor 6, and an energization command control signal A comparator that outputs an output for switching off the transistor 2 when a detection voltage of the resistor 7 that increases according to the amount of electricity stored in the capacitor 6 at the time of output of A, B, C, and D reaches a reference voltage. 9 is provided.

Here, the resistance value R ₁ of the resistor 4 is determined to be larger than the resistance value R ₂ of the resistor 7. The comparator 9
Is a resistance value R of the two resistors 10 and 11.
_3, is set by R _4. The comparator 9 is connected to the base of the transistor 2 via the transistor 12. The signal switch section 8 has two transistors 8a and 8b, and supplies the energization command control signals A and
B, C, and D are connected through the diode 13 to the transistor 8a.
, The transistor 8b is turned off because no voltage is applied from the power supply 5 to the base.
Energization command control signals A, B, C, D to transistor 8a
8b, the transistor 8b is connected to the power supply 5
Is turned on in response to the voltage of

Next, the operation will be described. Figure 2
Is a time chart of each output indicating a normal operation, and FIGS.
6 is a time chart of each output showing an operation when an abnormality occurs. 1 in FIG. 1 indicate the locations where each output in FIGS. 2 and 3 occurs. In the present embodiment, assuming that there are four magnets to be driven, an energization command control signal for designating a magnet to be energized is divided into A, B, C, and D corresponding to each magnet. . These signals are input to the constant voltage circuit 1 and the time constant circuit 3 in parallel.

Since the magnet is normally driven intermittently in a short time, the energization command control signals A, B, C and D do not continue during normal operation. The energization command control signals A, B, C and D are integrated by the diode 13 into a serial signal as an output. When any of the signal signals A, B, C, and D is present, the transistor 8b is kept off, so that the capacitor 6 connected to the power supply 5 stores an amount of electricity. gradually increases the value R _2, but the signal a, B, C, and D is interrupted transistor 8b permits the discharging operation of the capacitor 6 becomes oN. That is, current flows from the capacitor 6 through the resistor 7 to the transistor 8b. Is the output of the transistor 8b in this case, also, the change in the resistance value R ₂ of the resistor 7. At this time, the discharge time is shortened by maintaining the relationship of R ₁ > R ₂ . As described above, when the signals A, B, C, and D are normally output within a predetermined time, the output from the comparator 9 is at the L level, so that the transistor 2 of the constant voltage circuit 1 is turned on. Will be maintained. At this time, the output of driving the magnet from the constant voltage circuit 1 is 24V.

Next, the operation at the time of abnormality will be described. As shown in FIG. 3, when a certain signal (B in this example) is output over a certain period of time, the output given to transistor 8a is continuous, and accordingly, transistor 8b is maintained in the off state. Time is longer. During this time, the discharge of the capacitor 6 is prevented, so that the voltage of the resistor 7 increases (see FIG. 3). When the detection voltage detected by the resistor 7 reaches the reference voltage set by the resistance values R ₃ and R _{4 of} the resistors 10 and 11, the output of the comparator 9 becomes H level at this moment. The output turns on the transistor 12. The transistor 2 is turned off by receiving the output of the transistor 12 at the base, and the connection between the constant voltage circuit 1 and the magnet is cut off. At this time, the output from the constant voltage circuit 1 becomes 0V.

As described above, if any of the energization command control signals A to D is output for a certain period of time for some reason, the energization to the magnet can be cut off. As a result, the magnet is prevented from being burned or broken.

When a plurality of magnets are driven, if the time constant circuit 3 detects a change in any one of the energization command control signals A to D as in the present embodiment,
A single time constant circuit 3 can protect a plurality of magnets.

[0014]

According to the present invention, a capacitor to which a control voltage is applied, a resistor connected to the capacitor, and an energization command control signal for driving a magnet are turned off during a period in which the control signal is output to the main power supply unit. And a signal switch unit that is turned on when the energization command control signal is interrupted while maintaining the capacitor in the charged state and permits the discharge of the capacitor, and the amount of electricity stored in the capacitor when the energization command control signal is output. When the voltage of the resistor, which increases accordingly, reaches the reference voltage, a time constant circuit is provided to cut off the power supply from the main power supply unit to the magnet, so that the energization command control signal is output for a certain period of time for some reason. In this case, the power supply to the magnet can be cut off accurately and reliably. As a result, burning and failure of the magnet can be prevented.

[Brief description of the drawings]

FIG. 1 shows a constant voltage circuit and a time constant circuit according to an embodiment of the present invention.

FIG. 2 is a time chart of each output showing a normal operation.

FIG. 3 is a time chart of each output illustrating an operation when an abnormality occurs.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main power supply part 2 Main power switch part 3 Time constant circuit 6 Capacitor 7 Resistance 8 Signal switch part A-D Energization command control circuit

Claims (1)

(57) [Claims] A main power switch connected between the main power supply and the magnet; a capacitor to which a control voltage is applied; a resistor connected to the capacitor; and a power supply for driving the magnet. A signal switch unit that turns off during the period when the command control signal is output to the main power supply unit, maintains the capacitor in a charged state, and turns on when the energization command control signal is interrupted to allow discharging of the capacitor. And a time constant circuit for turning off the main power switch when the voltage of the resistor, which increases according to the amount of electricity stored in the capacitor when the energization command control signal is output, reaches a reference voltage. Magnet protection device.