JP2000131925A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent fog at a low temperature without providing an expensive surface-potential sensor by controlling the output of an electrostatic charger in the case the temperature of the surface of a photoreceptor is lower than a reference temperature, thereby compensating for a decrease in electrostatic charge potential. SOLUTION: When a main power source is turned on and printing is started, the temperature of the inside of the device is detected based on a detection signal from a temperature sensor 13. When the temperature T1 of the inside of the printer is lower than a specific reference temperature T0, a timer is started and a grid voltage Vg is set to a voltage value Vg1+A, which is higher than an ordinary grid voltage value Vg1, the time the timer expires. The set value is outputted to an electrostatic charging circuit 2c and consequently the circuit 2c applies a voltage of Vg1+A to a grid electrode 2b. Also, when the started timer expires, the grid voltage Vg is set to the ordinary grid voltage value Vg1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus. For example, an electrophotographic printer,
It relates to a copying machine, a facsimile, and the like.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, if the charge potential on the surface of a photoreceptor is lower than a certain predetermined value, a good image cannot be formed. For this reason, for example,
Japanese Patent No. 29504 describes a technique for controlling a bias voltage applied to a grid electrode of a scorotron charger, a developing bias voltage applied to a developing sleeve, and an exposure amount according to a usage time of a photoconductor. In addition, a technique for controlling the above parameters according to the detection result of the potential of the photoconductor surface is described.

In an electrophotographic image forming apparatus,
If the temperature of the photoreceptor surface is low, its charging ability is lowered and the charging potential is lowered, so that a good image cannot be formed. For this reason, a technique has been provided in which the exposure amount is controlled in accordance with the detection result of the temperature of the photoconductor to compensate for a decrease in the sensitivity of the photoconductor. In addition, a technique is provided in which a heater is provided inside the photoconductor drum to increase the temperature of the photoconductor surface. Further, there is provided a technique of detecting a potential on the surface of a photoreceptor by a surface potential sensor and controlling a bias voltage applied to a grid electrode of a scorotron charger in accordance with the detection result.

[0004]

It has been pointed out that fogging occurs in an electrophotographic image forming apparatus in a low-temperature environment such as the first in the morning. The reason is that the charging ability of the photoreceptor is low at a low temperature, so that the surface potential becomes low, and the fog margin (the difference between the surface potential and the developing bias) becomes smaller than usual. Particularly, in a model adopting the flash fixing method, the above problem is remarkable because there is no warm-up time unlike the heat roll fixing method. Further, in a model in which an amount of leakage light is generated in the exposure system, there is a problem that black stripe fog is easily generated due to the amount of leakage light.

The above-mentioned JP-B-61-29504 controls the parameters of the electrophotographic process in accordance with the usage time of the photosensitive member.
The technique described in Japanese Patent Application Laid-Open Publication No. H10-160555 is a measure against the fact that the charging ability of the photoconductor is reduced due to deterioration with time and the charging potential is gradually reduced. For this reason, it is not possible to cope with fog at a low temperature, which is unrelated to the deterioration with time of the photoconductor. In addition, the technique described in the publication that detects the surface potential of the photoconductor and controls the above parameters has a problem that an expensive sensor for detecting the surface potential is required.

The technique of controlling the exposure amount in accordance with the result of detecting the temperature of the photoreceptor controls the potential of an image-exposed portion by
Because this technology improves the adhesion of toner to the image area,
It cannot handle fog at low temperatures. Further, the technique of providing a heater inside the photosensitive drum has a problem that an expensive heater is required. Also, in the case of the technique of controlling the grid voltage of the scorotron charger by detecting the potential of the photoreceptor surface with a surface potential sensor, there is a problem that an expensive sensor for detecting the surface potential is required.

SUMMARY OF THE INVENTION It is an object of the present invention to reliably prevent fog at low temperatures without providing an expensive surface potential sensor in an electrophotographic image forming apparatus. Also,
It is an object to reliably prevent fog at low temperatures even when the image forming apparatus employs a flash fixing method. It is another object of the present invention to surely prevent black stripe fog even in the case of a model in which a leakage light amount occurs in an exposure system.

[0008]

According to a first aspect of the present invention, an electrostatic latent image is formed by charging a surface of a photoreceptor with a charger, and then performing exposure based on a document image, and forming the electrostatic latent image with toner. An electrophotographic image forming apparatus that develops, transfers and fixes on a sheet, a detection unit that detects a physical quantity related to a temperature of the photoconductor surface, and the detection unit that detects the physical amount based on a detection result of the detection unit. Determining means for determining whether or not the temperature of the photoconductor surface is lower than a predetermined reference temperature, and controlling the output of the charger when it is determined that the temperature of the photoconductor surface is lower than the reference temperature. An image forming apparatus comprising: a charger control unit that compensates for a decrease in the charged potential of the photoconductor surface.

According to a second aspect of the present invention, in the first aspect, the charger is a scorotron charger, and the charger control means controls a bias voltage applied to a grid electrode of the scorotron charger. An image forming apparatus characterized in that: According to a third aspect of the present invention, there is provided the image forming apparatus according to the first or second aspect, wherein the physical quantity is a temperature of the surface of the photoconductor or the vicinity of the photoconductor. According to a fourth aspect of the present invention, in the first or second aspect, the exposing is performed by a PLZT exposing device, the fixing is performed by a flash fixing device, and the physical quantity is a print time from the start of the image forming apparatus. An image forming apparatus characterized in that:

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration of the printer according to the embodiment, FIG. 2 is a block diagram showing a control system related to the surface potential of the photosensitive drum 1, and FIG. 5 is a flowchart showing a procedure for controlling the surface potential of the body drum 1.

The illustrated printer includes a PLZT print head 3 and a flash fixing device 10, and uses a polymerized toner having a small particle size (for example, about 8 μm) as a toner for the developing device 4. For this reason, it is possible to print an image such as a barcode that requires precision. In addition, since the flash fixing device 10 is used, even a label or the like that has adhesive or the like applied to the back surface and is affixed to the backing sheet can be printed without wrinkling or peeling off the backing sheet.

A charger 2 for charging the surface of the photosensitive drum 1 by corona discharge to the periphery of the photosensitive drum 1, and irradiating the surface of the photosensitive drum 1 charged by the charger 2 based on image data. Forming an electrostatic latent image by P
An LZT print head 3, a developing device 4 for developing an electrostatic latent image formed on the surface of the photosensitive drum 1 with toner, a temperature sensor 13 for measuring the temperature of the surface of the photosensitive drum 1, A transfer device 5 for electrostatically transferring the developed toner image onto paper (continuous paper) 12, a cleaner 6 for removing toner remaining on the surface of the photosensitive drum 1, and a residue on the surface of the photosensitive drum 1 A static eliminator 7 for removing charges is provided. Reference numeral 8 denotes a waste toner storage unit that stores the toner removed by the cleaner 6.

The paper (continuous paper) 12 is pulled out of the paper storage unit, sent to a transfer position (a position where the transfer unit 9 and the photosensitive drum 1 face each other) by the paper transport device 9, and is transferred onto the surface of the photosensitive drum 1. The carried toner image is electrostatically transferred. The paper 12 onto which the toner image has been transferred is sent to the flash fixing device 10 by the paper transport device 9 and subjected to flash fixing processing.
Is discharged onto the discharge tray 11.

As shown in FIG. 2, the charger 2 includes a charging wire 2
This is a scorotron charger that charges the surface of the photosensitive drum 1 by corona discharge a and controls the charging potential Vo to a desired value by a grid bias voltage Vg applied to the grid electrode 2b of the charger 2. The quality of the image is determined based on the charging potential Vo, the developing bias voltage Vb applied to the developing sleeve 4a of the developing device 4, and P
It is affected by the exposure of the LZT print head 3.
Further, the presence and degree of fog are influenced by the difference between the charging potential Vo and the developing bias voltage Vb.

The PLZT print head 3 is, for example, 40
The ON / OFF control of each of the PLZT elements arranged in an array at 0 dpi is controlled according to image data, thereby transmitting / blocking the light of a halogen lamp provided behind the element and guiding the light to the surface of the photoreceptor through a selfoc lens array. It is a member. Here, the PLZT element is an element obtained by adding a trace amount of lanthanum La to lead titanate zirconate ceramics (PbTiO ₂ -PbZrO ₂ ) and replacing Pb with La,
Expressed as PLZT9 / 65/35. This PLZT
By providing a polarizing plate so that the polarization plane is orthogonal to the front and back of the optical path of the element, by applying or not applying an electric field in a direction perpendicular to the optical path at an angle of 45 ° with the polarization plane of each polarizing plate, The light transmission / blocking of the PLZT element is controlled.

The flash fixing device 10 is a device for irradiating toner on a sheet with a xenon gas discharge tube to generate heat with light energy to fuse the sheet to the sheet. Since pressure is not applied as in the heat roll type fixing device, the toner is not crushed and the size of the toner particles is hard to change. Therefore, high-definition drawing is possible. Further, the paper is hardly damaged, and therefore, wrinkles are hardly generated, and it is possible to satisfactorily print on a label that has been coated with glue or the like on the back surface and affixed to the mount. Further, there is an advantage that a warm-up time is not required.

Next, the procedure for controlling the surface potential of the photosensitive drum 1 (the procedure for controlling the grid bias voltage Vg applied to the grid electrode 2b of the charger 2) will be described. As shown in FIG. 3, when the main power is turned on and printing is started (S1), the internal temperature is detected based on the detection signal of the temperature sensor 13 (S2). On the other hand, PL
Control of the ZT exposure device 3 (S7) and the flash fixing device 1
The control of 0 (S8) and the like are also started, but since these processes are not related to the process for controlling the surface potential, the description is omitted here.

If the internal temperature T1 of the printer is lower than a predetermined reference temperature T0 (eg, about 15 ° C.) (S3: YE
S), the timer is started (S4), and the grid voltage Vg is set to a voltage value “Vg1 + A” higher than the normal grid voltage value Vg1 until the timer ends (S5). This set value is output to the charger circuit 2c, whereby the charger circuit 2c
Is applied with a voltage of “Vg1 + A”.

When the timer started in step S4 ends, the grid voltage Vg is set to the normal grid voltage value Vg1 (S6). This set value is output to the charger circuit 2c, whereby the charger circuit 2c
Applies a normal voltage “Vg1” to the grid electrode 2b.

As described above, the grid electrode 2b of the charger 2
Is controlled. In addition, the detected inside temperature T
If 1 is equal to or higher than the predetermined reference temperature T0 (S3: NO),
The grid voltage Vg is set to the normal grid voltage value Vg1 (S6), and the set value is output to the charger circuit 2c, and the normal voltage "Vg1" is applied to the grid electrode 2b.

In the above description, the grid bias voltage applied to the grid electrode 2b of the charger 2 is controlled by detecting the temperature inside the apparatus. For example, in the case of an image forming apparatus using a flash fixing device, the start-up of the device is performed. The temperature rise inside the machine and the temperature inside the machine can be estimated based on the number of prints (fixation) or the printing time from the time.
The configuration may be such that the grid bias voltage applied to the grid electrode 2b of the charger 2 is controlled.

Further, in the above description, the case where the charger 2 is a scorotron charger is described as an example. However, the present invention can control the charging potential of the photosensitive drum by controlling the output of the charger. If applicable. For example, a contact type charger (brush charger) may be used.

[0023]

According to the present invention, the output of the charger is controlled in accordance with the temperature inside the machine or the number of prints or the printing time from the start of the apparatus. Fog can be reliably prevented. Further, even in the case of a flash fixing type apparatus which does not require a warm-up time, fog at low temperatures can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an overall configuration of a printer according to an embodiment.

FIG. 2 is a block diagram showing a control system related to the surface potential of the photosensitive drum 1.

FIG. 3 is a flowchart showing a control procedure of a surface potential of the photosensitive drum 1 executed by a control unit 20 of FIG. 2;

[Explanation of symbols]

 2 Charger (scorotron charger) 2b Grid electrode 3 PLZT exposure device 10 Flash fixing device

Claims (4)

[Claims] After charging the surface of a photoreceptor by a charger, exposure based on an original image is performed to form an electrostatic latent image, and the electrostatic latent image is developed with toner, transferred to a sheet, and fixed. An electrophotographic image forming apparatus, wherein: a detecting unit that detects a physical quantity related to a temperature of the surface of the photoconductor; and a temperature of the surface of the photoconductor becomes higher than a predetermined reference temperature based on a detection result of the detecting unit. Determining means for determining whether the temperature is low or not, and when it is determined that the temperature of the photoconductor surface is lower than the reference temperature, compensating for a decrease in the charging potential of the photoconductor surface by controlling the output of the charger. An image forming apparatus comprising: 2. An image according to claim 1, wherein said charger is a scorotron charger, and said charger control means controls a bias voltage applied to a grid electrode of said scorotron charger. Forming equipment. 3. The image forming apparatus according to claim 1, wherein the physical quantity is a temperature of a surface of the photoconductor or a temperature near the photoconductor. 4. The image forming apparatus according to claim 1, wherein the exposing is performed by a PLZT exposing device, the fixing is performed by a flash fixing device, and the physical quantity is a printing time from the start of the image forming apparatus. An image forming apparatus characterized in that: