JP2003079049A - Protection circuit for safety relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protection circuit which dissolves defects in a safety relay. SOLUTION: In the protection relay circuit, which, when a contact is melted and stuck, secures a safety function by a forced guide contact mechanism and controls an external device by the contact, a coil/contact is made free from magnetization, by raising an apparent restoration voltage by serially connecting a resistor R2 to a coil of the safety relay K3 and by suppressing heat generation inside the relay.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for a safety relay, and more particularly, to a protection circuit for a safety relay which secures a safety function at the time of contact welding by a forced guide contact mechanism. 2. Description of the Related Art A safety relay is an open / close relay called a forced guide relay in which safety is ensured even at the time of contact welding by a forced guide contact mechanism, unlike a general relay. Used in safety circuits to prevent runaway and ensure worker safety. FIG. 2 is a sectional view of a safety relay.
In FIG. 2, the safety relay has, for example, three relay contacts k11, k12, and k13, and the intervals between the contacts are ensured not only in the normal operation state but also 0.5 mm or more when a failure state occurs. Is required. For this reason, the safety relay is provided with a forcible guide, and when any of the normally closed (NC) contacts is welded, all the NC contacts are opened in a state where the coil is not energized.
A contact interval of 5 mm or more is secured, and even if one of the NC contacts is welded, all normally open (N
O) The contacts are not closed while maintaining a contact interval of 0.5 mm or more. FIG. 3 is a diagram showing an example of an internal circuit of the safety relay shown in FIG. 2 and an example of an external connection for directly opening and closing a power supply line of a motor. In FIG. 3, the safety relay has coils of three relays K1, K2, and K3, and relay contacts k1, k2, and k3 corresponding to the respective relay coils. Diodes D1, D2, and D3 are connected in parallel. Emergency stop switch EMO and electromagnetic switch MS outside the relay unit
1 and MS2. Electromagnetic switch MS1, MS
2 turns on and off the main circuit of the motor M. (1) First, in a state where all devices are normal and the emergency stop switch EMO is not pressed,
When the power of 24V DC is applied to the relay unit, the relay K3 is turned on, all the relay contacts k3 are closed,
A current flows through the coils of relays K1 and K2. Relay K
When a current flows through the coils 1 and K2, the NC contacts k1 and k2 connected to the coil of the relay K3 are opened, and the relay K3 is turned off. Since the relays K1 and K2 cannot hold themselves at the same time, a series circuit of a resistor R1 and a capacitor C1 is connected in parallel to the coil of the relay K3 as a delay element. [0006] Relays K1 and K2 are turned on, and K3 is turned off.
In this state, the electromagnetic switches MS1 and MS2 outside the relay unit are turned on, and power is supplied to the motor M. As described above, the relay K3 is turned on only once when the power is supplied to the relay unit in a normal state, and is immediately turned off. That is, the relay K3 operates as a relay for checking the initial operation state of the relays K1 and K2. (2) Next, when the emergency stop switch EMO is pressed while power is supplied to the motor M, the relay K
1 and K2 are turned off, the electromagnetic switches MS1 and MS2 outside the relay unit are turned off, and the power supply to the motor M is cut off. When the relays K1 and K2 and the electromagnetic switches MS1 and MS2 are turned off, the relay K3 is turned on. However, if the emergency stop switch EMO is kept pressed, the relays K1 and K2 are not turned on again. Power is not supplied. When the emergency stop switch EMO is released, the relays K1 and K2 are turned on and then the relay K3 is turned off, so that power is supplied to the motor M in the same manner as (1). (3) A case where the relay K1 or K2 is broken and does not operate will be described. When power is supplied to the relay unit in a state where the emergency stop switch EMO is not pressed, the relay K3 is turned on. Relay K3
Is turned on, all the NO contacts of the relay contact k3 are closed and the relays K1 and K2 are energized. However, if the relay K1 or K2 breaks and does not work,
The contact state of relays K1 and K2 does not change. As described above, since the contacts of the relays K1 and K2 do not operate, the electromagnetic switches MS1 and MS2 do not turn ON, and power is not supplied to the motor M. (4) Next, the operation when the contacts of the relay K1 or K2 are welded will be described. Since the relay K1 or K2 is a relay having a forced guide mechanism, if one of the contacts is welded, all the other contacts are opened. Therefore, the relay K1 or K2
If the normally closed contacts (contacts connected to the coil of the relay K3) are welded, the relay K3 remains ON and the electromagnetic switches MS1 and MS2 are turned ON.
No power is supplied to the motor M. When the NO contacts of the relays K1 and K2 are welded, the other NO contacts are open, so that the electromagnetic switches MS1 and MS2 are not turned on, and the motor M is not supplied with power. Not supplied. (5) When the relay K3 is broken and does not operate, in a state where the emergency stop switch EMO is not pressed,
Even if power is supplied to the relay unit, the relay K3
No, the relays K1 and K2 are not turned on. Therefore,
The electromagnetic switches MS1 and MS2 do not turn on,
No other power is supplied to the motor M. (6) In a state where the emergency stop switch EMO is not pressed, power is supplied to the unit and the relay K
Even if the coil No. 3 is energized, the relay K3 is open except for one welded point of the contact k3 of the relay K3, so that the relay K1 or K2 does not turn on. Therefore, the electromagnetic switches MS1 and MS2 are not turned on, and power is not supplied to the motor M. (7) When C1 and R1 of the relay K3 are broken, when the unit is powered on with the emergency stop switch not pressed, the relay K3 is turned on.
When the relay K3 is turned on, all NO contacts of the relay K3 are closed, and the relays K1 and K2 are turned on. When the relays K1 and K2 are turned on, the relay K3 is turned off. However, since the capacitor C1 or the resistor R1 is broken, the timing is simultaneous, and the relays K1 and K2 cannot be held by themselves, and are immediately turned off. Therefore, the electromagnetic switches MS1 and MS2 are not turned on, and the motor M
Is not powered. In an automatic device equipped with the safety relay unit as described above, when the emergency stop switch EMO is pressed to stop the device, the relays K1 and K2 are turned off and the relay K3 is turned off. Becomes ON state. The quiescent state was left for about half a day. After that, when the emergency stop switch EMO was released to operate, the relays K1 and K2 were turned on,
Although each contact is operating, relay K
3 did not turn off. Investigation of the relay K3 alone at this time revealed that, even though the return voltage was 2.4 V or higher in the manufacturer's catalog, it did not return even if the return voltage was lower than 1 V. At this time, when the relay main body is vibrated, it sometimes returns. From the above, it is assumed that the cause of the decrease in the return voltage of the relay K3 is that the ON / OFF for a long time is considered.
Mechanical failure due to use, the relay internal temperature rises due to the ON state for a long time (about half a day), the spring mechanism has deteriorated, and it is difficult to return because the capacitor C1 and the resistor R1 are connected between the relay coils, and it is difficult to return. ON (about half a day)
A possible cause is that the coil / contact is magnetized due to the continuation of the state. In particular, a small safety relay uses a permanent magnet in the coil portion, and is likely to be easily magnetized. Therefore, a main object of the present invention is to provide a protection circuit for a safety relay which can solve the above-mentioned problems. The present invention is a protection circuit for a safety relay which secures a safety function at the time of welding a contact by a forced guide contact mechanism, and controls an external device by the contact. It is characterized by connecting a resistor in series with the coil to increase the apparent return voltage. FIG. 1 is a circuit diagram of a protection circuit for a safety relay according to an embodiment of the present invention. In FIG. 1, in this embodiment, a resistor R2 is connected between a coil of a relay K3 and a ground line. Thus, the resistance R2
Is connected to the coil of the relay K3, not only can the voltage applied to the coil be reduced to suppress the heat generation inside the relay K3, but also the apparent reset voltage can be reduced by reducing the voltage applied to the coil by the resistor R2. Can be raised. As a result, it is possible to eliminate mechanical problems caused by long-time ON / OFF use, deterioration of a spring mechanism, and problems caused by magnetization of coils / contacts, which have occurred in conventional safety relays. The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. As described above, according to the present invention, a resistor is connected in series to the coil of the safety relay, and the voltage applied to the coil can be reduced to suppress heat generation inside the safety relay. Instead, the apparent return voltage can be increased by reducing the voltage applied to the coil by the resistance. As a result, it is possible to solve mechanical problems caused by long-time ON / OFF use, deterioration of a spring mechanism, and problems caused by magnetization of coils / contacts, which have occurred in conventional safety relays.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a protection circuit for a safety relay according to an embodiment of the present invention. FIG. 2 is a sectional view of a safety relay. 3 is a diagram illustrating an example of an internal circuit of the safety relay illustrated in FIG. 2 and an example of an external connection that directly opens and closes a power line of a motor. [Explanation of symbols] K1, K2, K3 relay, k1, k2, k3 relay contact, EMO emergency stop switch, MS1, MS2 electromagnetic switch, R1, R2 resistor, C1 capacitor.

Claims (1)

Claims: 1. A protection circuit for a safety relay in which a safety function is ensured at the time of contact welding by a forced guide contact mechanism, and an external device is controlled by the contact, the protection circuit being connected in series with a coil of the safety relay. Connect the resistor,
A safety relay protection circuit characterized by raising the apparent return voltage.