JPH09197920A - Image printing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the safer protection possible, while maintaining a low cost. SOLUTION: When spark leakage or the like occurs by abnormal electrostatic discharge in a separating electrifier 9, an AC overcurrent protection circuit 6 is allowed, to detect that an abnormal AC eddy current flows, and to control voltage application by two high voltage applying parts. Namely, the voltage application on the separating electrifier 9 is stopped, by stopping a high voltage AC transformer L1 and a high voltage DC transformer L3 from actuating. Moreover, since the overcurrent is made to flow on the DC current, the DC overcurrent protection circuit 7 is operated, and the high voltage AC transformer L1 and the high voltage DC transformer L3 is similarly stopped from actuating, the voltage application is stopped as a result. In this manner, by monitoring and executing the protective operation not only for the AC current but also for the DC current, the power of abnormal electric discharge is restricted when the overcurrent is made to flow, and overlapping output of the high voltage DC transformer L3 can be restricted, therefore safer protection can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image printing apparatus such as an electrophotographic copying machine or printer using corona discharge.

[0002]

2. Description of the Related Art Generally, in an image printing apparatus such as an electrophotographic copying machine or a printer, a primary charging device for uniformly charging a photoconductor or a transfer charging for transferring a latent image formed on the photoconductor onto a sheet. Various high voltage corona chargers are needed, such as a container, a separator charger that separates the paper from the photoreceptor.

Further, the image printing apparatus as described above is provided with a protective device for limiting the high voltage output to the charging device, and when some abnormality occurs in the charging device and spark discharge occurs, the paper and peripheral parts are Overcurrent is detected and high voltage output is limited so as not to ignite or smoke.

FIG. 3 shows an example of a conventional image printing apparatus including such a corona charger and a protection device.

The conventional image printing apparatus shown in FIG. 3 has a high-voltage AC transformer L1 for generating an AC high voltage and an AC drive circuit section 3 connected to the high-voltage AC transformer L1 for driving the high-voltage AC transformer L1.
2, a high-voltage DC transformer L3, and a high-voltage DC generator 33 that generates a high-voltage direct current.
DC drive circuit unit 34 for driving the transformer L3 and high voltage D
A control circuit 35 that controls the C transformer L3 with a constant current, an overcurrent protection circuit 36 that detects that an abnormal overcurrent has flown from the high voltage AC transformer L1 and limits the drive of the high voltage AC transformer L1, and a latent electrostatic charge on the surface. The photosensitive drum 38 for forming an image and the separation charger 39 connected to the secondary winding side of the high-voltage AC transformer L1 are provided.

Here, the AC drive circuit section 32 includes two transistors Q21 and Q22 which are complementary connected and a backflow prevention diode D which is connected in parallel to each of these transistors.
21 and D22, and filters R21 and C1 provided in the input part of the primary winding of the high-voltage AC transformer L1. Further, the outputs from the pulse generation circuit 21 are applied to the base terminals of the transistors Q21 and Q22, respectively. It is configured to be. As a result, the AC drive circuit unit 32 is configured to generate the AC high voltage as a whole so that the high voltage AC transformer L1 is generated.
Is to be driven.

The DC high voltage generator 33 has a diode D31 and a resistor R31 connected to the primary winding side of the high voltage DC transformer L3, and the secondary winding side of the high voltage DC transformer L3 is connected via the diode D31. It is connected in series to the high voltage AC transformer L1.

The DC drive circuit section 34 includes a pulse generation circuit 4
1, a transistor Q having a base terminal connected to the output side of the pulse generation circuit 41 and a collector terminal connected to one of the primary windings of the high-voltage DC transformer L3.
41, and a capacitor C41 and a diode D41 connected in parallel to the transistor Q41.
In addition, the input power source Vcc of the DC drive circuit unit 34 is the resistor R4.
High voltage DC transformer L3 through the filter section of 1 and C2
Is connected to the other side of the primary winding of
The DC drive circuit unit 4 is configured to drive the high voltage DC transformer L3 so as to generate a DC high voltage as a whole.

The control circuit 35 has its output terminal connected to the pulse generating circuit 41 and its inverting input terminal connected to the reference power source E51.
And an operational amplifier 50 connected to the control circuit 3
Reference numeral 5 denotes a capacitor C52 and a resistor R5 which are feedback-connected between the output side terminal of the operational amplifier 50 and the inverting input terminal.
2 is provided. Further, the control circuit 35 includes the operational amplifier 5
0 non-inverting input terminal and a capacitor C51 and a resistor R connected in series to one end of the secondary winding of the high voltage DC transformer L3
It has 51.

The output terminal of the overcurrent protection circuit 36 is connected to the pulse generation circuit 21 via the diode D1.
The non-inverting input terminal has an operational amplifier 60 connected to the reference power source E61 via a resistor R63, and the overcurrent protection circuit 36 further includes an inverting input terminal of the operational amplifier 60 and a secondary winding of the high voltage DC transformer L3. Resistor R connected in series between
62, a diode D61 and a capacitor C61. Further, the overcurrent protection circuit 36 includes a capacitor C6.
2, C63 and resistor R61. One end of each of these is grounded, a capacitor C62 is connected between a diode D61 and a capacitor C61, and a resistor R
62 and a capacitor C63 between the diode D61,
The resistor R61 is connected.

In an image printing apparatus having such a structure,
Separate charging, post charging, etc. from 10 KVpp to 12 KV
An AC high voltage of about pp is applied to the charger 39, and a DC high voltage of about 500V to 1000V is superimposed and applied in series with the high voltage AC transformer L1 in order to control the DC current to an appropriate value. Is taking.

Further, normally, when an overcurrent flows, the overcurrent protection circuit 36 operates to stop the driving of the high-voltage AC transformer L1 having a large output, but when the current value falls below a predetermined value, the driving is restarted. Then, even if the wire of the charger 39 is broken or the like, the overcurrent flows again even if the driving is restarted, and the overcurrent protection circuit 36 operates to stop and restart the output for several tens of meters.
It becomes an intermittent operation that is repeated every sec. This limits the power of abnormal discharge and protects the abnormal discharge part from ignition or smoke even if foreign matter such as copy paper is caught.

[0013]

However, in the conventional image printing apparatus as described above, overcurrent protection is provided only for the high-voltage AC transformer L1 having a large output, and the high-voltage D
No protection circuit was provided for the C transformer L3. This is because the output of the high-voltage DC transformer L3 is often smaller than that of the high-voltage AC transformer L1, and the safety is high even if the protection circuit is not provided. However, protection with higher safety is performed. There is a need.

Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image printing apparatus which enables protection with higher safety at low cost.

[0015]

In order to solve the above-mentioned problems, an image printing apparatus according to the present invention is an image printing apparatus for printing an image by an electrophotographic method utilizing corona discharge, in which a high voltage is applied to the image printing apparatus. A charger that generates a corona discharge, an AC high voltage generator that applies an AC high voltage to this charger, and a DC high voltage that is connected in series to the AC high voltage generator and is superimposed on the AC high voltage. A direct current high voltage generator, an overcurrent detector that detects an overcurrent of the two high voltage generators, and a voltage application by the two high voltage generators is controlled according to a detection result of the overcurrent detector. And a control means.

At this time, the overcurrent detecting means includes a first overcurrent detecting means for detecting an overcurrent of the AC high voltage generating section and a second overcurrent detecting section for detecting an overcurrent of the DC high voltage applying section. An overcurrent detection unit, the control unit controlling the voltage application by the two high voltage generation units according to the detection result of the first overcurrent detection unit; The second control means may control the voltage application by the two high voltage generators according to the detection result of the second overcurrent detection means.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First Embodiment) First, a first embodiment of the present invention will be described.

FIG. 1 is a block diagram showing the outline of an image printing apparatus according to the present invention, mainly showing the high voltage power source section thereof. In the following, since there is a part overlapping with the example of the prior art shown in FIG. 3, the part will be omitted.

This apparatus is an image printing apparatus for printing an image by an electrophotographic method using corona discharge, and is a high voltage AC
An AC high voltage generating section including a transformer L1 and an AC drive circuit section 2 for driving the high voltage AC transformer L1, and a high voltage D
A DC high voltage generating unit including a C transformer L3 for generating a DC high voltage and a DC driving circuit unit 4 for driving the high voltage DC transformer L3; and a high voltage connected to the DC high voltage generating unit. A constant current circuit 5 for controlling a constant current of the DC transformer L3, and an A connected to the AC high voltage generator.
The C overcurrent protection circuit 6, the DC overcurrent protection circuit 7 connected to the DC high voltage generator, the photosensitive drum 8 that produces static electricity on the surface due to corona discharge, and the high voltage AC transformer L1.
It has a separate charger 9 connected to the next winding side.

The high-voltage AC transformer L1 is driven by the AC drive circuit section 2, and its secondary winding is connected to the separation charger 9 to apply an AC high voltage.

The high voltage DC transformer L3 is a DC drive circuit unit 4
The AC high voltage generator is connected in series with the high voltage AC transformer L1 to superimpose the DC high voltage on the AC high voltage and apply the DC high voltage.

Operational amplifier 60 of AC overcurrent protection circuit 6
Has its output terminal connected to the pulse generation circuits 21 and 41 of the drive circuit units 2 and 4 via the diode D1.

Further, the AC overcurrent protection circuit 6 is connected to the high-voltage AC transformer L1 so that an abnormal A
C has a function as a first overcurrent detection means for detecting that an overcurrent has flowed, and further has pulse generation circuits 21, 4
It also has a function as a first control unit that is connected to No. 1 and controls the voltage application by the two high voltage generators according to the detection result of the AC overcurrent. Further, the AC overcurrent protection circuit 6 includes a time constant circuit that holds the detection result of the AC overcurrent for a predetermined time.

The DC overcurrent protection circuit 7 has an operational amplifier 70 whose inverting input terminal is connected to the reference power source E71, and further has a secondary winding of the high voltage DC transformer L3 and a non-inverting input terminal of the operational amplifier 70. Resistor R7 connected between
1. A feedback resistor R72 is connected between the non-inverting input terminal and the output side terminal in a feedback manner.

The DC overcurrent protection circuit 7 is a high voltage DC
The pulse generator circuit 21 is connected to the transformer L3 and has a function as a second overcurrent detection unit that detects that an abnormal DC overcurrent flows from the DC high voltage generation unit.
It also has a function as a second control unit that is connected to 41 and controls the voltage application by the two high voltage applying sections according to the detection result of the DC overcurrent. Further, the DC overcurrent protection circuit 7 includes a time constant circuit that holds the detection result of the DC overcurrent for a predetermined time.

The separation charger 9 is capable of separating the copy paper from the photosensitive drum 8 by applying a high voltage to generate corona discharge.

Next, the operation of the image printing apparatus having the above structure will be described.

First, the two overcurrent protection circuits 6 and 7 drive the high voltage transformers L1 and 3 of AC and DC for several tens of msec by the time constant circuit which holds the detection result for a predetermined time and its hysteresis operation. The intermittent operation of stopping and restarting the operation is repeated, and the protective operation is performed to prevent the copy paper from being ignited.

When a spark leak or the like occurs in the separation charger 9 due to an abnormal discharge, the AC overcurrent protection circuit 6 detects that an abnormal AC overcurrent has flowed, and the two high voltage applying sections apply a voltage. To control. That is, the driving of the high-voltage AC transformer L1 and the high-voltage DC transformer L3 is stopped, and the voltage application to the separation charger 9 is stopped.

Further, at this time, since the overcurrent due to the DC current is also flowing, the DC overcurrent protection circuit 7 operates, and like the AC overcurrent protection circuit 6, the high voltage AC transformer L1 and the high voltage DC are supplied.
The driving of the transformer L3 is stopped, and as a result, the voltage application is stopped.

Such an operation is performed unless the abnormality of the separation charging device 9 is removed, and a protection operation is performed so that the copy paper or the like is not ignited.

In this way, each overcurrent protection circuit 6, 7
Monitors not only AC current but also DC current, and AC, D
C By protecting both transformers, it is possible to limit the power of abnormal discharge and also limit the output of DC high voltage that is superposed when an overcurrent flows, enabling higher safety protection. Becomes

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG.

The image printing apparatus according to the second embodiment has substantially the same block configuration as the image printing apparatus according to the first embodiment, but two overcurrent protection circuits 6 and 7 are provided. In the first embodiment, the pulse generator circuits 21 and 22 of the AC and DC drive circuit units 2 and 4 are connected, but in the present embodiment, the input power source Vc is connected.
It is connected to the c side. That is, in the present embodiment, the drive circuit sections 2 and 4 each have a transistor Q23 and a transistor Q42 connected to the input power source Vcc side, and the output terminal of the operational amplifier circuit 60 further includes a transistor Q23 and a transistor Q23 via a diode D1. Transistor Q4
2 is connected to the base terminal of the transistor Q23, and the output terminal of the operational amplifier circuit 70 is also connected to the transistor Q23 via the diode D2.
And a structure connected to the base terminal of the transistor Q42.

As a result, the overcurrent protection circuit 6 becomes
It is configured to detect that an abnormal AC overcurrent has flown from the C transformer L1 and limit the input power supply voltage to the high voltage AC transformer L1 and the high voltage DC transformer L3. Further, the overcurrent protection circuit 7 is also configured to limit the input power supply voltage similarly to this.

According to the present apparatus having such a configuration, first,
Each of the overcurrent protection circuits 6 and 7 has a time constant circuit that holds the detection result for a predetermined time and a hysteresis operation, which makes it possible to perform several tens of ms.
During c, the intermittent operation of stopping the input of the input power supply voltage to the AC and DC high voltage transformers L1 and L3 and restarting the operation is repeated, and the protection operation is performed so that the copy paper or the like is not ignited.

When a spark leak or the like occurs in the separation charger 9 due to an abnormal discharge, the AC overcurrent protection circuit 6 operates to cut off the input of the input power supply voltage to the high voltage AC transformer L1 and the high voltage DC transformer L3. The application of voltage to the separation charger 9 is stopped.

At this time, since an overcurrent due to the DC current is also flowing, the DC overcurrent protection circuit 7 operates and similarly cuts off the input of the input power supply voltage to the high voltage AC transformer L1 and the high voltage DC transformer L3.

Such an operation is carried out unless the abnormality of the separation charger 9 is removed, and a protection operation is carried out so that the copy paper or the like will not be ignited.

In this way, each overcurrent protection circuit monitors not only the protection AC current but also the DC current, and the AC, DC
By performing the protection operation of cutting off the input of the input power supply voltage to both transformers, the power of abnormal discharge can be limited, and higher safety protection can be performed.

In the first and second embodiments described above, a display unit is provided to display the occurrence of any abnormality in the device, and the overcurrent detection means indicates an overcurrent to this display unit. You may make it display that it was detected. By the display by this display unit, an abnormal state of the device including the occurrence of overcurrent can be immediately known, and it can be used as an auxiliary means for performing protection with higher safety.

The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above, A
Each of the C and DC overcurrent protection circuits 6 and 7 controlled the voltage application to both the AC and DC high voltage applying sections, but the DC overcurrent protection circuit 7 controls only the DC high voltage applying section and the AC overcurrent protection section. The current protection circuit may control only one of the AC high voltage applying units, such as controlling only one of them.

[0044]

As described above, according to the present invention, an overcurrent is detected not only in the AC high voltage applying section but also in the DC high voltage applying section, and the voltage generated by the two high voltage applying sections is detected according to the detection result. Since the application is controlled, it is possible to provide an image printing apparatus which is low in cost, limits the power of abnormal discharge, and enables protection with higher safety.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration block diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a conventional example.

[Explanation of symbols]

 1 High-voltage AC transformer 2 AC drive circuit section 3 High-voltage DC transformer 4 DC drive circuit section 6 AC overcurrent protection circuit 7 DC overcurrent protection circuit

Claims (4)

[Claims] 1. An image printing apparatus for printing an image by an electrophotographic method using corona discharge, wherein a charger is applied with a high voltage to generate the corona discharge, and an AC high voltage is applied to the charger. A high voltage generator, a direct current high voltage generator connected in series to the alternating high voltage generator and applying a direct current high voltage to the alternating high voltage, and detecting an overcurrent of the two high voltage generators. An image printing apparatus comprising: an overcurrent detection unit; and a control unit for controlling voltage application by the two high voltage generation units according to a detection result of the overcurrent detection unit. 2. The overcurrent detection means includes a first overcurrent detection means for detecting an overcurrent in the AC high voltage generating section, and a second overcurrent for detecting an overcurrent in the DC high voltage generating section. And a second control unit configured to control voltage application by the two high voltage generation units according to a detection result of the first overcurrent detection unit. The image printing apparatus according to claim 1, further comprising a second control unit that controls voltage application by the two high voltage application units according to a detection result of the current detection unit. 3. The control means controls the two high voltage generators so as to stop the generation of the voltage when the overcurrent detecting means detects an overcurrent. The image printing apparatus according to 1 or 2. 4. A display unit for displaying an abnormality of the device when the abnormality occurs, and the display unit displays that the overcurrent detection unit has detected an overcurrent. The image printing apparatus described in 1, 2, or 3.