JPH0429517A - Safety circuit for copy machine - Google Patents

Abstract

PURPOSE:To detect ground fault in distributed AC lines and to prevent secondary trouble by detecting the current difference between AC lines, comparing an amplified current difference with a predetermined current and then turning an AC line relay ON/OFF. CONSTITUTION:When there is a difference between incoming and outgoing currents of an AC line 100, a potential is produced across a coil in a current difference detecting circuit 10 and a current is obtained through a magnetic circuit 20. A rectifying/amplifying circuit 30 then rectifies/amplifies the AC current to produce a DC current. A comparing circuit 40 compares an output voltage from the rectifying/amplifying circuit 30 with a reference current value to produce a binary signal. When High level sustains for a predetermined time at the output of the comparing circuit 40, a timer circuit 50 produces a ground signal. Upon receiving the ground signal, a control circuit 5 opens relays 101, 102 thus opening a circuit for connecting the AC line 100 with an AC load 5.

Description

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

The present invention relates to a safety circuit for a copying machine, and more particularly to a safety circuit for detecting a ground fault in an AC line provided in a copying machine.

[Conventional technology]

Since a copying apparatus is equipped with a plurality of AC loads, a large number of movable members are driven by attaching a plurality of AC wirings. There is a risk of ground faults occurring in AC lines that supply power to these AC loads, and there is a desire to prevent secondary disasters due to ground faults. If a ground fault were to occur, (1) the entire copying machine would be at the potential of one end of the AC power supply, so if a user comes into contact with a conductive member, such as a metal part, on the exterior of the copying machine, there is a risk of electric shock. Furthermore, if a ground fault occurs under unstable conditions, there is a danger that an arc will occur between the electric wire of the AC line and the case of the copying machine, resulting in smoke, fire, etc. According to experiments, secondary disasters occur when there is a resin member near an AC load through which ground current flows. For example, when a ground current of 4 to 5 A flows from an AC line, smoke is generated, and when a ground current of 6 to 7 A flows, it results in ignition. Therefore, as a measure to prevent secondary disasters caused by the above-mentioned ground fault accident, instructions should be provided by grounding the case by connecting a ground wire from the case of the copying machine (for example, a service person or instruction manual, etc.)
It is stated in the manual etc. ). In addition, various measures have been taken, such as making resin members often used in copying machines flame-retardant, reconsidering AC lines to prevent ground faults, and adding fuses to AC lines. Furthermore, it has been proposed to install household earth leakage breakers on AC lines.

[Problems to be solved by the invention]

However, all of the above measures for preventing ground faults in copying machines are incomplete. Despite the above-mentioned guidance regarding the grounding of the case, in offices and the like where copying machines are installed, the case is not completely grounded due to various reasons. Other countermeasures cannot be implemented due to various reasons, such as cost. In particular, when the above-mentioned breaker is installed in the AC line of a copying machine, it is for a large current of about 15A, so it is large, goes against the recent trend of downsizing of equipment, and is also expensive. There is a problem. In view of the above-mentioned problems, it is an object of the present invention to provide a safety circuit for a copying machine that is capable of detecting ground faults in AC lines that are distributed in a copying machine and preventing secondary disasters caused by ground fault accidents. Our goal is to provide the following.

[Means to solve the problem]

The present invention, which achieves the above object, is a safety circuit for a copying machine including a relay that connects and disconnects an AC line that supplies power from an AC tW to an AC load, the current difference detecting the current difference between the AC lines. a detection means, a rectification amplifier circuit that rectifies and amplifies the output signal from the current difference detection means, a comparison circuit that compares the output current from the rectification amplifier circuit and a predetermined current, and an ON signal from the comparison circuit. The present invention is characterized in that it includes a timer circuit that detects that the relay continues for a predetermined period of time, and a control circuit that turns on and off the relay based on a signal from the timer 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 of a copying machine according to the present invention. Prior to explaining the safety circuit of the copying apparatus of this embodiment, the AC line to which the safety circuit is applied will be explained. The copying apparatus of this embodiment has an AC line 1 connected to an AC power supply l.
A DC power supply 2, an AC load 3, and a driver 4 for driving the AC load 3 are connected to the DC power supply 2, and a control circuit 5 is connected to the DC power supply 2. Here, the AC load 3 includes a fixing device, a pre-exposure static eliminator, a high-voltage power supply unit, and the like. The control circuit 5 is driven by DC power from the DC power supply 2,
By driving the driver 4, the operation of the AC load 5 is controlled and various DC loads are driven. Here, the DC load is a load driven by DC power, such as a DC motor and a solenoid. Note that the control circuit 5 has other functions, which will be described later. The safety circuit of this embodiment monitors the difference between the forward current and the return current flowing through the AC line 100, and when the difference exceeds a predetermined value for a predetermined period of time or more, a switch is sent to the relay with an off signal from the control circuit 5. This is a circuit that opens and closes the AC circuit connected to the AC load 3 via 101 and 102, and the current difference detection circuit lO
1 magnetic circuit 20, rectifier amplifier circuit 30, comparator circuit 40, timer circuit 50, relay +01102, and control circuit 5. The current difference detection circuit 10 is, for example, a zero-phase current transformer sensor (commonly referred to as zCT), and has a coil C wound around the AC line 100 and a magnetic circuit including the coil C. If there is a difference between the going and returning current values, a potential is generated across the coil C due to the action of electromagnetic induction, and a current is obtained through the magnetic circuit 20. The rectifier amplifier circuit 30 is a circuit that rectifies the alternating current obtained from the magnetic circuit 20 and outputs the amplified direct current. The comparison circuit 40 is a circuit that outputs a value signal as a result of comparing the output voltage from the rectifier amplifier circuit 30 with a reference current value, for example, 30 μA. Here, a high level signal indicates that the reference current value has been exceeded, and a low level signal indicates that the reference current value has been exceeded.
This indicates that the reference current will not be exceeded. The timer circuit 50 sends out a ground fault signal when the output signal from the comparison circuit 40 continues to be at a high level for a predetermined period of time. Here, the predetermined time is a signal in the /X level state. Note that if the high level signal does not continue for a predetermined period of time, a low level ground fault signal is sent out. The control circuit 5 controls a relay 101102 that connects and disconnects the AC load 5 to the AC line 100, and controls the timer circuit 50.
When receiving a high level ground fault signal from
1, 102 opens the circuit connected from the AC line 100 to the AC load 5. relay 1
01.102 may be, for example, a triac, which, once conductive for -degrees, maintains the conductive state until the next trigger occurs. The operation of the safety circuit of this embodiment will be explained below. FIGS. 2(a) to 2(e) are time charts showing the operation of the safety circuit. In the figure, (a) shows the output current from the magnetic circuit 20, (b) shows the output current from the rectifier amplifier circuit 30, and (c) shows the output signal from the comparison circuit. , (d) show the output signal from the timer circuit 50. When the main switch of the copying machine is turned on, AC line 10
An alternating current is conducted to the DC power supply 2, and power is supplied to the DC power supply 2. DC power supply 2 supplies power to control circuit 5 . Control circuit 5
After a predetermined time t0 has elapsed, the relays 101 and 102 are closed to connect the AC load 3 and driver 4 to the AC line 100. A fuser as an AC load is driven. As a result, a surge current caused by load fluctuation is conducted through the AC line 100, although it is instantaneous. Due to the surge current, a large current is instantaneously conducted through the magnetic circuit 20 as shown in FIG. 2(a). This large current is obtained as the output current from the rectifier amplifier circuit 30 as shown in FIG. 2(b), and the output current from the comparator circuit 40 is also instantaneous as shown in FIG. 2(C), but gradually Becomes a high level. However, the ground fault signal from the timer circuit 50 is 30μ
Since the current of A or more does not continue for a specified time (for example, 1 m5ec), it remains at a low level. On the other hand, as shown in FIG. 2(a), the magnetic circuit 20 is operated for a predetermined period of time 1. After the lapse of time, an alternating current of 30 μA or more is conducted more than before t1. As a result, the output current from the rectifier amplifier circuit 30 is also obtained in the rectifier amplifier circuit 30 as shown in FIG. 2(b), and the output current from the comparator circuit 40 is also obtained as shown in FIG. 2(C). 1m of non-low level time
It will continue for more than 5 ec. The timer circuit 50 makes the ground fault signal high level as shown in FIG. 2(e). When the control circuit 5 detects a high-level ground fault signal, it opens the relays 101 and 102 and disconnects the AC load 3 and driver 4.
The circuit connected to the AC line 100 will be opened from the AC line 100. With the above-described configuration, the safety circuit of this embodiment is a safety circuit for a copying machine that includes a relay 100 that connects and disconnects an AC line 100 that supplies power from an AC power source 1 to an AC load 3. a current difference detection means 10 for detecting the current difference, a rectification amplifier circuit 30 for rectifying and amplifying the output signal from the current conversion means IO, and a comparison circuit for comparing the output signal from the rectification amplifier circuit 30 with a predetermined voltage. 4
0, a timer circuit 50 detects that the ON signal from the comparison circuit 40 continues for 1 m5ec, and the relay 101%1 based on the output signal from the timer circuit 50.
By providing a control circuit 5 that turns on and off 02,
It is possible to detect a ground fault in the AC line 100, which is distributed in the copying machine, and to cut off the AC load 3, etc. other than the DC power supply 2 of the control circuit 5 from the AC line 100, thereby preventing a ground fault from occurring. We were able to prevent secondary disasters. [Effects of the Invention] As explained above, the present invention detects the current difference between the AC lines in a safety circuit of a copying machine that includes a relay that connects and disconnects an AC line that supplies power from an AC power source to an AC load. a current difference detection circuit; a rectification amplifier circuit that rectifies and amplifies the output signal from the current difference detection circuit; a comparison circuit that compares the output voltage from the rectification amplifier circuit with a predetermined voltage; By providing a timer circuit that detects that an on signal continues for a predetermined period of time, and a control circuit that turns on and off the relay based on the output signal from the timer circuit, the relay can be distributed in a distributed manner within the copying machine. We have been able to detect ground faults in AC lines, prevent secondary disasters caused by ground fault accidents, and provide an inexpensive safety circuit for copying machines. Note that the DCPS, which is a type of AC load, is placed in a part where there is no risk of ground fault due to the placement of the AC line, such as not being placed near movable members. Furthermore, with regard to secondary circuits such as the control section, fuses and the like are installed in the power supply line, so there will be no occurrence of secondary disasters due to underground passages.

[Brief explanation of drawings]

FIG. 1 is a block circuit showing an embodiment of the safety circuit of a copying machine according to the present invention, and FIGS. 2(a) to 2(e) are time charts showing the operation of the safety circuit. 1... AC power supply 3... AC load 5...
Control circuit 10... Current difference detection means 30... Rectification amplifier circuit 40... Comparison circuit 50... Timer circuit

Claims (1)

[Claims] In a safety circuit of a copying machine equipped with a relay that connects and disconnects an AC line that supplies power from an AC power source to an AC load,
Comparing current difference detection means for detecting a current difference between the AC lines, a rectification amplifier circuit for rectifying and amplifying the output signal from the current difference detection means, and the output current from the rectification amplifier circuit and a predetermined current. a timer circuit that detects that an ON signal from the comparison circuit continues for a predetermined period of time; and a control circuit that turns on and off the relay based on the signal from the timer circuit. safety circuits for copying machines.