JPH0488822A - Safety circuit - Google Patents

Abstract

PURPOSE:To detect a ground fault without being subject to the effect of unbalanced currents by turning a relay OFF on the basis of output signals from an adding circuit adding an output from a current detecting section and the current detecting section and an output signal from the adding circuit. CONSTITUTION:A signal proportional to output currents from a current detecting section 211 is input to a process control circuit 310 through an abnormal current detecting section 230, etc. The process control circuit 310 starts an AC circuit interrupting routine and a ground-fault detecting routine. The AC circuit interrupting routine compares a ground-fault monitor signal and a decision level, and decides whether or not the ground-fault monitor signal exceeding the decision level is continued only for a fixed time, thus controlling the opening and closing of a circuit, to which AC load 2 is connected. The ground-fault detecting routine compares an abnormal current monitor signal and the decision level, and decides whether or not the abnormal current monitor signal exceeding the decision level is continued for a fixed time, thus controlling the opening and closing of the circuit, to which the AC load 2 is connected.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a safety circuit that detects abnormal current and ground fault current in an AC line provided in a copying machine.

[Background of the invention]

The AC line in the copying machine is naturally connected to an AC power source that supplies AC power. The AC line is connected to a DC power source such as a low voltage power supply unit of approximately 5 V for driving a control circuit, an AC load such as a fixing lamp of a fixing device, an exposure lamp, and a driver for driving the AC load. In particular, loads that receive power directly from an AC line are at risk of abnormalities and ground faults due to winding load layer shorts, etc., and safety circuits are required to prevent such ground faults. It is necessary to provide A typical earth leakage cutoff circuit uses, for example, a zero-phase current transformer sensor (commonly known as
ZCT) is provided. ZCT has a coil wound around an AC line and a detection circuit including the coil. If there is a difference in the going and returning current values in the AC line, a potential is generated at both ends of the coil C due to the action of electromagnetic induction. 1. The current is detected via a detection circuit connected to the means. When the current level exceeds a determination level, it is cut off via a relay. Further, as a general circuit for breaking off abnormal current, a system is used in which a fuse, breaker, etc. is used to cut off one side of the AC line. However, when the process control circuit is started to drive an AC load and a DC load, an unbalanced current may be generated in the AC line of the copying machine when the load is started. A detection circuit connected to the current difference detection means momentarily detects a large current. As a result, there have been problems such as malfunction of the ground fault relay circuit, and problems such as the fuse or the like not being able to sufficiently detect and shut off the state of overcurrent flowing due to an abnormality in the AC load or the like.

【the purpose】

In view of the above-mentioned problems, an object of the present invention is to provide a safety circuit that can detect ground faults without being affected by unbalanced currents generated in AC lines, and can also detect abnormal conditions in real time even when excessive current occurs. It's about doing. [Means for Solving the Problems] This invention that achieves the above object is a safety circuit that turns off a relay provided in an AC line of a copying machine that supplies power from an AC power source to an AC load, A current detection section is provided near the output terminal and input terminal of the AC power supply, and an addition circuit that adds the outputs from the current detection section; The device is characterized in that it is equipped with a control circuit that turns off the relay to detect abnormal currents and ground fault currents, thereby configuring a safety circuit.

【Example】

Next, embodiments of the present invention will be described based on the accompanying drawings. FIG. 1 is a block circuit showing an embodiment of the safety circuit according to the present invention. The copying apparatus has an AC load 2 and a low voltage power supply unit 3 connected to an AC line 100, and a low voltage DC load 3301, a driver 320, a process control circuit 310, and a high voltage power supply unit 4 are connected to the low voltage power supply unit 3. A high voltage DC load 340 is connected to the high voltage power supply unit 4. The AC load 2 is configured to be connected and disconnected from the AC line 100 via relays 101 and 102. relay 1
01 and 102 are electromagnetic relays and the like. Here, the AC load 2 includes a fixing device, an exposure lamp, an AC motor, and the like. The low-voltage DC load 330 is a load driven by DC power, such as a DC booster and a solenoid, and the high-voltage DC load 340 includes a charger, a separator, a transfer device, a developer, and the like. Furthermore, the copying apparatus has a characteristic configuration including a current detection section 211.
212, ground fault current detection section 220 and abnormal current detection section. A safety circuit consisting of 230 is provided. The configuration of each part of the safety circuit of this embodiment will be explained below. The current detection unit 211 is a circuit that obtains a current proportional to the output current to the AC line 100, and is provided with a coil near the output terminal of the AC power supply 1. The current detection unit 212 is a circuit that obtains a current proportional to the return current from the AC line 100, and the coil is provided near the input terminal of the AC power supply l. The current detection units 211 and 212 send alternating currents of different polarities to the ground fault detection unit 220 depending on the winding direction of the coil. The ground fault current detection section 220 is a circuit that detects the difference between the output current from the AC power supply 1 and the return current based on the output currents from the current detection sections 211 and 212, and the addition circuit 2211
It consists of a rectifier amplifier circuit 222 and the like. The adding circuit 221 is a circuit that adds alternating currents of different polarities, and the alternating current corresponding to the difference between the output current and the return current is added to the rectifying amplifier circuit 22.
Output to 2. The rectifier amplifier circuit 222 converts the input signal into
A rectified and amplified square wave voltage (for convenience, this is referred to as a ground fault monitoring signal) is sent to the process control circuit 310. Note that the amplification in the rectifier amplifier circuit 221 is performed to match the processing level of the process control circuit. The abnormal current detection unit 230 detects the AC power supply 1 from the output current proportional to the return current from the current detection unit 211 to the AC power supply 1.
This circuit monitors the return current to the current detection unit 211.
The output current is I/V converted, and a rectified and amplified square wave voltage (for convenience, this is referred to as an abnormal current monitoring signal) is sent to the process control circuit 310. As a result, unbalanced current caused by load fluctuations in the AC line lOO is detected. The process control circuit 310 is a microprocessor that mainly drives the AC load 2, the low voltage DC load 330, and the high voltage DC load 340 via a driver 320 etc. to start an image forming routine to execute the image forming process. A relay 101 that connects and disconnects the AC load 2 from the AC line 100,
The RO is equipped with an AC circuit breaking routine for controlling the AC current value T rev and a ground fault current abnormality determination level S rev.
It has an internal memory of M or RAM. The process control circuit 310 activates the AC circuit cutoff routine and the ground fault detection routine to determine different determination levels T rev, S according to the process control timing.
Output rev. In this embodiment, the determination level S
As rev, 1! These are two data corresponding to llv+A and 40mA, and the judgment level T rev is four data corresponding to IA, 5A, 15A, and 100A. The AC circuit cutoff routine uses the ground fault monitoring signal and judgment level S.
This routine controls the opening and closing of the circuit to which the AC load 2 is connected by comparing the ground fault monitoring signal S rev and determining whether the ground fault monitoring signal exceeding the determination level S rev continues for a predetermined period of time. The ground fault detection routine detects the abnormal current monitoring signal at the judgment level T.
This routine controls the opening and closing of the circuit to which the AC load 2 is connected by comparing the abnormal current monitoring signal T rev and determining whether the abnormal current monitoring signal exceeding the determination level T rev continues for a predetermined period of time. The operation of the copying apparatus of this embodiment will be explained below with reference to FIGS. 1 to 3. FIG. 2 is a time chart showing the abnormal current monitoring signal from the abnormal current detection section, and FIG. 3 is a time chart showing the ground fault monitoring signal from the ground fault current detection section. The time charts in FIGS. 2 and 3 are shown with the time axes aligned. The ground fault monitoring signal is output with a slight time difference from the abnormal current detection signal. The main switch of the copier is 1. When the AC load 2, low-voltage power supply unit 3, and high-voltage power supply unit 4 are turned on, the AC load 2, low-voltage power supply unit 3, and high-voltage power supply unit 4 are activated. At this time, since the relay 101102 is in the on state, the AC load 2 is connected to the AC line 100. Thereby, AC power is supplied to the AC load 2. As shown in FIG. 2, approximately 100
The abnormal current monitoring signal corresponding to A is the process control circuit 31
Sent to 0. In addition, as shown in FIG. 3, the ground fault detection unit 220 sends a ground fault monitoring signal equivalent to about 150 mA to the process control circuit 310 due to transient unbalance in the forward and return currents due to the charging current of the Nindensa, etc. . In other words, a difference occurs in the current values detected by the current detection units 211 and 212 due to the nonparallel current from the abnormal current detection unit 230,
Approximately 150 mA momentarily from the ground fault detection unit 220 at time t.
This will output a ground fault current of . However, as described above, the process control circuit 310 is in the initializing operation at time t1 and has not activated the ground fault detection routine and the AC circuit cutoff routine, and therefore does not detect the ground fault monitoring signal and the abnormal current monitoring signal. On the other hand, the high voltage power supply unit 4 supplies power to the high voltage DC load 340 from time t1, and the low voltage power supply unit 3 supplies power from time t1.
1 supplies power to the process control circuit 310 and driver 320. As a result, the process control circuit 310
Start the initialization routine and set the time E! to exit the routine. Here, t1 to t2 is referred to as initialization time for convenience. The process control circuit 310 reads the judgment level data corresponding to 15w+A from the ROM corresponding to the judgment level generating means at the initialization time, and initializes the normal judgment levels S rev and T rev. The determination levels at this time are 15 mA and 15 A, respectively. Then, the process control circuit 310 starts the process control routine, the AC circuit cutoff routine, and the ground fault detection routine at the same time as the initialization routine ends, that is, at time t2. The process control circuit 31O drives the fixing lamp via the driver 320 at time t. At this time, the abnormal current monitoring signal from the abnormal current circuit 230 momentarily outputs a signal of 70 to 80 A due to the rush current when the lamp is turned on. The process control circuit 310 reads judgment level data corresponding to 40 A as the ground fault judgment level from the ROM at a timing immediately before outputting the fixing lamp ON signal, and sets this as the judgment level S rev. Further, determination level data corresponding to 100 A is read as the abnormal current determination level, and this is set as the determination level T rev. The ground fault detection unit 220 instantaneously outputs a ground fault monitoring signal corresponding to about 30 mA to the process control circuit 310 with a slight time difference from time t, as shown in FIG. However, since the process control circuit 310 changes the determination level S rev to 40@Ai::R as described above, the circuit to which the AC load 2 is connected is not disconnected from the AC line 100. The process control circuit 310 determines the determination level S r
When a predetermined period of time, for example 10 seconds+sec, has elapsed after changing ev, the normal judgment level data is read from the ROM and the normal judgment level S rev is reset. In other words, the normal determination level S rev is changed to 15 layer A. Similarly, the abnormal current judgment level is sequentially set to 10.
Each level of 0A→5A→15A-41A is switched as a determination level. Similarly, the process control circuit 310 includes an optical motor as a DC load, a main motor as an AC load,
The exposure lamp, paper feed motor, etc. are sequentially sent out starting signals at times t and ~t.
~L, the ground fault monitoring signals corresponding to about 30 A are instantaneously outputted to the process control circuit 310 with a slight time difference as shown in FIG. However, as described above, the process control circuit 310 uses the determination level S rev
Since the current is changed to 40 A, the circuit to which the AC load 2 is connected is not disconnected from the AC line 100. When a predetermined period of time, for example 10+sec, has elapsed since changing the determination level S rev, the process control circuit 310 reads the normal determination level data from the ROM and sets the normal determination level S
Reset rev. In other words, the normal judgment level S
rev is changed to 15@A. In this manner, the copying apparatus of this embodiment performs the image forming process without detecting instantaneous currents that are not caused by ground faults and preventing malfunctions. If a ground fault occurs in the AC line 100, the copying apparatus of this embodiment can detect the ground fault without being affected by the unbalanced current generated in the AC line, and can also detect the ground fault in real time even when an excessive current occurs. A process control circuit M 310 capable of detecting an abnormal state cuts off the AC load 2 via relays 101 and 102 and stops its operation. In addition, in this embodiment, there are 2 levels as S ray, and 2 levels as Trev.
4 levels have been created, but it is possible to have multiple levels, or in self-diagnosis mode, etc., to measure the actual value of S revlT rev, memorize it, and then calculate a certain calculated value to 5revsT r
It is also easy to set it as ev. [Effects of the Invention] As explained above, in a safety circuit of a copying machine that turns off a relay provided on an AC line that supplies power from an AC power source to an AC load, current flows near the output terminal and input terminal of the AC power source. By providing a detection section, an addition circuit that adds the output from the current detection section, and a control circuit that turns off the relay based on the output signal from the current detection section and the output signal from the addition circuit. It has been possible to provide a safety circuit for a copying machine that can detect ground faults without being affected by unbalanced currents generated in AC lines, and can also detect abnormal conditions in real time even when excessive currents occur.

[Brief explanation of drawings]

Fig. 1 is a block circuit showing an embodiment of the safety circuit according to the present invention, Fig. 2 is a time chart showing the output signal from the abnormal current detection section, and Fig. 3 is the output current from the ground fault current detection section. FIG. 1... AC power source 2... AC load 101.
102... Relay 211.212... Current detection section 213... Addition circuit 214.221... Rectification amplifier circuit 310... Process control circuit

Claims (1)

[Claims] In a safety circuit that turns off a relay provided in an AC line of a copying machine that supplies power from an AC power supply to an AC load, a current detection section is provided near the output terminal and input terminal of the AC power supply, and the current detection section A safety circuit comprising: an addition circuit that adds outputs; and a control circuit that turns off the relay based on an output signal from the current detection section and an output signal from the addition circuit.