JPH05346712A - Electronic image forming device - Google Patents

Abstract

PURPOSE:To obtain an electronic image forming device where carrier rise or fogging is prevented from occurring by changing the timing of starting the rotation of a photosensitive body and starting impressing developing bias. CONSTITUTION:In the electronic image forming device, the carrier rise or the fogging is prevented from occurring, especially, it is prevented from occurring after turning off the power source of the device. A real time clock 9 is provided in the device so as to measure a power source turnoff time. When the power source is turned on again, a PCU 8 changes the timing of starting the rotation of the photosensitive drum 1 and starting impressing the developing bias potential by a grid 2 according to the length of the measured time. A different process where the developing bias is impressed after starting a drum motor, or the drum motor is started after impressing the developing bias is performed according to the time before or after potential difference causing the adhesion of the carrier, that is, the surface potential of the photosensitive body 1 becomes <=-350V by dark attenuation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic image forming apparatus for forming images, characters, etc. on paper.

[0002]

2. Description of the Related Art In an image forming apparatus of a reversal developing system, particularly a laser printer, a sequence of a copying process is usually such that a bias is applied before the surface potential is raised to a carrier when a drum is rotated. This prevented fogging.

[0003]

However, if the power supply to the apparatus is cut off during copying, carrier rise and fogging occur. The generation process of this phenomenon will be described with reference to the drawings.

FIG. 4 shows the correlation with the dark decay time of the surface potential of the photoconductor. Surface potential remains in the development area,
Since only a gentle potential drop occurs due to dark decay, the potential stays for a long time. When the potential is supplied again in this state, if the conventional image forming process is performed in the above sequence, the carrier may rise before the developing bias is applied, and the developer may fall into the machine such as the transport path. is there. If the carrier adheres to the drum, the drum may be damaged, resulting in fatal damage. Also, if the drum is rotated after applying the developing bias uniformly, fogging occurs when the surface potential is lowered,
It causes deterioration of image quality and unnecessary toner consumption. The process of occurrence of these problems is shown in FIG.

An object of the present invention is to provide an electronic image forming apparatus which eliminates these drawbacks.

[0006]

During the image forming operation of the present invention, the surface of the photoconductor is charged to a predetermined potential by the main charger, and the surface of the photoconductor is exposed by the laser beam emitted from the exposure device and is static. An image forming apparatus, in which an electrostatic latent image is formed, an electrostatic latent image is developed by a developing device to form a toner image, and the toner image is transferred to a transfer sheet by a transfer device, does not require power-off time of the image forming apparatus. It has a timer for measuring, and means for changing the timing of starting the rotation of the photoconductor and applying the developing bias according to the amount of time measured by the timer when the power is turned on.

[0007]

The electronic image forming apparatus of the present invention has a timer for measuring the power-off time of the apparatus and means for changing the timing of starting the rotation of the photosensitive member and applying the developing bias when the power is turned on.

The above timing is changed depending on whether the time measured by the timer is smaller or larger than a predetermined value.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a side view showing an example of the overall structure of a copying machine, which is an image forming apparatus equipped with the potential control device according to the present invention. As shown in the figure, the digital copying machine of this embodiment
The scanner unit 30 includes a scanner unit 31, a laser printer unit 32, a multi-stage paper feeding unit 33, and a sorter 34.

The scanner unit 31 is composed of a document placing table 35 made of transparent glass, a double-sided automatic document feeder (RDF) 36, and a scanner unit 40. Scanner unit 31
Is a unit for scanning the document placed on the document table 35, and the scanner unit 40 is a mechanism unit for exposing the document at the time of scanning the document.

The multi-stage paper feeding unit 33 includes cassettes 51, 52,
53 and a cassette 55 that can be added by selection.
The multi-stage paper feeding unit 33 is a paper feeding unit, and the RDF 36 is a unit for automatically feeding a plurality of originals one by one to the scanner unit 40.

The image data obtained by reading the original image with the scanner unit 40 is once stored in the memory of the image processing unit, and the image is formed on the paper by the laser printer unit 32. The laser writing unit 46 is a unit that emits laser light.

The electrophotographic process section 47 includes a photosensitive drum 48.
A charging device, a developing device, a transfer device, a peeling device, a cleaning device, a static eliminator, and a fixing device 49 are arranged around the area.

A transport path 50 is provided downstream of the fixing device 49 in the transport direction of the sheet on which an image is to be formed.
50 is a transport path 57 leading to the sorter 34 and a multi-stage paper feeding unit
It is branched to the conveyance path 58 leading to 33.

A toner image formed by an electrostatic latent image on the surface of the photosensitive drum 48, which is made to scan with a laser beam by the laser writing unit 46 and visualized with toner, is conveyed from the multi-stage paper feeding unit 33. It is electrostatically transferred and fixed on the surface of the paper.

In the electronic image forming apparatus having the above-described overall structure, FIG. 1 is a diagram in which functional blocks around the electrophotographic process section (47 in FIG. 2) and the control section according to the present invention are extracted and illustrated. Is.

The image forming unit in FIG. 1 includes a photoconductor 1 and a grid 2.
, Developing unit 4, transfer unit 6, high voltage power supply 7, PCU (process control unit) 8, clock 9 and power supply
Consists of 10. The power source output which is the output terminal of the high-voltage power source 7 is connected to the charger wire 2a, the grid bias output GB to the grid 2, and the developing bias output BIAS to the developing device 4 by connecting lines 12, 13, and 14, respectively.
The PCU 8 is connected to the high voltage power supply 7 by a grid control line 15 and a bias control line 16, and is connected to the power supply 10 by a power OFF signal line 17 in addition to the drive power supply line + 5V.

In the image forming section, the surface potential of the photosensitive member 1 is applied by the grid 2 and the developing bias is applied by the developing device 4. These applied voltages are supplied from the high-voltage power supply 7 via the connection lines 12 to 14.

The PCU 8 is a section for controlling the process operation of the image forming apparatus, and obtains time data required for control from the clock 9. The clock 9 is a real-time clock, has a backup battery (not shown), and operates even when the power supply 10 of the image forming apparatus is turned off.

When the power source 10 of the image forming apparatus shown in FIG. 2 is cut off during the copying operation, the potential of the photosensitive member 1 is attenuated with time as shown in FIG. 4, and the power source 10 is turned on again as shown in FIG. It is roughly divided into two cases, that is, when the electric potential of the photosensitive member 1 of a) remains and when the electric potential of FIG.

It is empirically known that, with respect to the above two states, if the potential difference between the photoconductor 1 and the developing device 4 is 350 V or more, the carrier goes up, and if it drops down, fogging occurs. There is. As shown in FIG. 4, the predetermined time until the surface potential on the drum reaches less than −350 V due to dark decay changes depending on various conditions such as temperature and humidity.
Assuming that, the following explanation will be given.

The PCU 8 of FIG. 1 receives a power OFF signal for turning off the power supply 10 from the power supply 10 via the connection line 17. The PCU8 detects the time signal at this point and uses the backup battery to operate the clock IC even when the power is off.
Measure the time with (real time clock).

With the analysis of the above problems and the hardware configuration of FIG. 1 corresponding to them, the problems can be solved by the following procedure.

In step S1, the power SW of the image forming apparatus is turned off.
FF. A power OFF signal is transmitted from the power supply 10 of FIG. 1 to the PCU 8 via the signal line 17. P in step S2
CU8 receives and stores time data (T1) from clock 9. In step S3, the power SW of the image forming apparatus is turned on. In step S4, the PCU 8 receives the time data (T2) at power-on from the clock 9 and stores it. In step S5, the power-off time (T2-T1) is calculated and compared with the specified value t1. Condition T2-T1
When> t1 is satisfied, the process B of step S6 is executed, and when the condition T2-T1≤t1 is satisfied, the process A of step S7 is executed and the process ends.

Process A in steps S6 and S7
The contents of Process B are shown below. Process A is a process in the case of (a) in FIG. 6 in which the power-off time is the specified time t1 or less and the surface potential of the photoconductor 1 is still high. In the process A, a developing bias is applied to the developing device 4 and the motor of the photoconductor 1 is driven after the lapse of the specified time tA.

In the process B, the power-off time is longer than the specified time t1 and the surface potential of the photoconductor 1 is lowered sufficiently.
This is the process in the case of (b). In the process B, the motor of the photoconductor 1 is driven to apply the developing bias to the developing device 4 after the lapse of the specified time tB.

Specified times t1 and t in the above processing steps
A and tB are determined by the following procedure. Time t1 is
This is the time when the surface potential of the photoreceptor 1 becomes −350 V or less due to dark decay. Time after power-off of image forming apparatus and photoconductor 1
The surface potential relationship of is shown in FIG. 5, and the specific values are advantageously determined on the basis of experimental data. The prescribed times tA and tB are also determined based on experimental data.

In the embodiment, the power failure time is measured by the PCU.
Although it is decided that 8 will do, it is also effective to do at clock 9.

[0029]

The electronic image forming apparatus of the present invention prevents carrier adhesion and fogging. Carrier adhesion and fogging are the causes of damage to the photoconductor drum, deterioration of image quality, unnecessary toner consumption, etc. According to the present invention, these troubles are prevented from occurring even when the power supply to the apparatus is cut off. can do.

[Brief description of drawings]

FIG. 1 is a functional block diagram of an image forming unit according to an embodiment of the present invention.

FIG. 2 is a side view showing an example of the overall configuration of an electronic image forming apparatus according to the present invention.

FIG. 3 is a flowchart of an example.

FIG. 4 is a timing diagram of processing A and processing B of FIG.

FIG. 5 is a diagram showing a dark decay characteristic of a photoreceptor surface potential.

FIG. 6 is a timing diagram showing a process in which a problem occurs in an electronic image forming apparatus based on a conventional technique.

[Explanation of symbols]

 1 Photoconductor 2 Grid 2a Charger wire 4 Developing device 6 Transfer part 7 High voltage power supply 8 Process control unit (PCU) 9 Clock 10 Power supply

Claims (1)

[Claims] 1. A surface of a photoconductor is charged to a predetermined potential by a main charger during an image forming operation, and the surface of the photoconductor is exposed by a laser beam emitted from an exposure device to form an electrostatic latent image. An image forming apparatus in which the electrostatic latent image is developed by a developing device to form a toner image, and the toner image is transferred to a transfer sheet by a transfer device, and the time for powering off the image forming apparatus is measured. An electronic image forming apparatus comprising: a timer for turning on the power source; and means for changing the timing of starting the rotation of the photoconductor and applying the developing bias according to the amount of time measured by the timer when the power is turned on.