JPH0611933A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent giving rise to a dark part at the edge of an image formed by presetting according to the result of detection by a light detection means the voltage applied to a charger, and causing the preset voltage to be output from the end of a document only for a certain period of time. CONSTITUTION:An amplifier 17 for amplifying output signals of a photo sensor 16 is connected to the photo sensor 16 and a CPU 18 is provided for controlling the voltage applied to a charger. The CPU 18 has an output port 20 and the charger for a charging unit 10 is connected to the output port 20. When scanning of a document is started the quantity of light at a predetermined position in front of the end of the document is detected by the sensor 16 and the voltage applied to the charger is set by the CPU 18 according to the quantity of light and is output from the end of the document only for a certain period of time. Therefore, the quantity of light is prevented from becoming insufficient due to a failure to turn on an exposure lamp at the optical end of the document resulting from a shortage of extra repeating time, and image deterioration can thereby be prevented.

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, and more particularly to an image forming apparatus capable of adjusting its charging voltage.

[0002]

2. Description of the Related Art An electrophotographic copying machine is a typical image forming apparatus. This copying machine optically reads an original placed on a contact glass with a scanner including an exposure lamp, an optical system, a traveling mechanism, and the like, and reads the read light on a photoreceptor (photoreceptor) whose surface is charged in advance by a charger. (Drum, photoconductor belt, etc.), the electrostatic latent image is developed with toner by a developing device to form a visible image, and the toner image is transferred to a transfer paper supplied at a timing. A fixing image is fixed on the paper by a fixing device to obtain a copied image.

[0003]

However, in the above-mentioned prior art, when the copying speed is increased and continuous copying is performed, the exposure lamp may not rise at the leading edge of the original, and as a result, the leading edge of the original may be lost. There is a problem that the area becomes dark and a black band is transferred. It is conceivable to continuously turn on the exposure lamp as a means for preventing the rise failure of the exposure lamp. However, when the exposure lamp is a halogen lamp, it has a short life, so it must be turned off when the exposure returns.

Incidentally, the technology relating to the field to which the present invention is applied includes, for example, JP-A-63-289570 and JP-A-60-215102.

It is an object of the present invention to provide an image forming apparatus capable of preventing image deterioration even when the exposure lamp does not rise.

[0006]

In order to achieve the above object, the present invention provides a light detecting means for detecting the light amount at a predetermined position before the leading edge of a document at the start of scanning, and a detection result of the light detecting means. Based on the above, the voltage applied to the charger is set, and a control means for outputting the set voltage from the leading edge of the document for a fixed time is provided.

Further, the light detecting means is adapted to detect the light amount of a standard white plate arranged at a predetermined position in front of the front end of the document.

[0008]

According to the above-mentioned means, the amount of light at a predetermined position in front of the leading edge of the original is detected at the start of scanning the original, and the applied voltage of the charging charger is set based on the detected light amount value. It is output from the department only for a certain period of time. Therefore, it is possible to eliminate a shortage of light amount at the leading end of the document due to insufficient margin of repeat time, and to prevent a dark portion (black band) from occurring at the leading end of the formed image.

When detecting the amount of light at a predetermined position in front of the leading edge of the document, a standard white plate is provided at that position to prevent variations in reflected light and prevent the timing of reading from deviating. It is possible to obtain an accurate exposure amount and always obtain a stable image.

[0010]

1 is a block diagram showing the construction of a control system in an embodiment of an image forming apparatus according to the present invention, and FIG. 2 is a schematic construction view showing a mechanical portion of the image forming apparatus. Here, a copying machine is shown as the image forming apparatus.

As shown in FIG. 2, a contact glass 3 on which an original 2 is set is installed on the upper surface of the main body 1. Below the contact glass 3, a halogen lamp 4 for illuminating the reading portion of the original 2 is provided, and a mirror 5 for horizontally reflecting the reflected light from the original due to the illumination is provided. A lens 6 is arranged on the reflected light path. Here, the halogen lamp 4, the mirror 5, and the lens 6 are integrally configured, and at the time of reading, the halogen lamp 4, the mirror 5, and the lens 6 move to the right in the figure at a constant speed, and when they reach a specified position, they return to home position. Furthermore, a mirror 7 for reflecting the incident light toward the exposure position is provided on the exit optical path of the lens 6 and below the end portion of the contact glass 3. A drum-shaped photosensitive member 8 is arranged on the reflected light path of the mirror 7.

A charging device 10 provided with a charging charger 9 is installed in the front stage of the exposure position of the photoconductor 8, and a developing device 11 is installed in the rear stage of the exposure position. Further, a transfer device 12 for transferring the toner image on the photoconductor 8 onto a transfer paper (not shown) and a separating device 13 for separating the transfer paper from the photoconductor 8 are provided in the subsequent stage of the developing device 11. . Further, in order to fix the toner image on the transfer paper from the separating device 13, a fixing device 14 including a fixing roller and a pressure roller is provided.

Around the photoconductor 8, a cleaning device for removing the toner remaining on the surface of the photoconductor 8 and a destaticizing device for destaticizing the surface of the photoconductor 8 before charging are installed. However, the illustration is omitted in FIG.
Further, on the reading start side of the contact glass 3, a standard white plate 15 used when measuring the light quantity is provided. Further, a light detection sensor 16 for detecting whether the lamp is turned on or off is provided near the halogen lamp 4.

When the original 2 is placed on the contact glass 3 and the size of the transfer paper, the number of copies, the reduction ratio, etc. are set and the start button is pressed, the scanner starts running,
Reading is started. Further, the photoconductor 8 starts rotating, and the photoconductor layer is charged by the charging device 10. At the same time, a transfer paper of a designated size is fed from a paper feed cassette (not shown) and conveyed to a registration position.

The light read by the scanner reaches the exposure position of the photoconductor 8 via each of the mirror 5, the lens 6 and the mirror 7, and an electrostatic latent image is formed. The electrostatic latent image reaches the developing position according to the rotation of the photoconductor 8, and the electrostatic latent image is subjected to toner development by the developing device 11. The transfer sheet is sent from the registration position to the transfer position at the same timing as the toner image reaches the transfer device 12.
By 2, the toner image is transferred onto the transfer paper. The transferred transfer paper is separated from the photoconductor 8 by the separating device 13 and is carried into the fixing device 14 by a transport roller (not shown). In the fixing device 14, the transfer paper inserted between the rollers is heated and pressed to melt and fix the toner image on the paper surface. This completes the copy operation.

Next, the configuration of FIG. 1 will be described.

An amplifier 17 for amplifying the output signal of the light detection sensor 16 is connected to the light detection sensor 16. Further, a CPU 18 is provided to control the voltage applied to the charger 9. The CPU 18 has a function of a small-scale microcomputer, has a function of converting an analog voltage output from the amplifier 17 into a digital signal, and has an AD port 19 as an input terminal thereof. Further, the CPU 18 is provided with an output port 20, a power circuit 21 for the charging device 10 is connected to the output port 20, and the charger 9 is connected to the power circuit 21.

FIG. 3 is a characteristic diagram showing the relationship between the amount of light and the developing bias value.

Here, the light quantity at the time of 100% rise of the halogen lamp 4 is L ₂ , and the set charging voltage at that time is VC
_Set to ₃ . If the light quantity is L ₁ or less, change the charging voltage value to VC
_If it is set to ₁ and the light intensity is determined to be L _{1 to} L ₂ ,
The charging voltage value is set to VC ₂ , and when the light quantity is L ₂ or more, the charging voltage value is set to VC ₃ . Such control is C
It is performed in the part of PU18, and specifically, the light detection sensor 1
The light amount value is calculated based on the output of No. 6, and this value is compared with the light amount set value set in the memory in advance, so that the process is executed according to the timing of FIG. 4 described below.

FIG. 4 is a timing chart showing the timing of reading the light quantity and setting the charging voltage.

Since the first copy has time to spare, the exposure lamp (halogen lamp 4) can be turned on faster than during repeat. After the exposure lamp is turned on, the scanner starts to move, and the amount of light (the reflected light from the standard white plate 15 is detected by the light detection sensor 16 at the position of the standard white plate 15 in front of the document leading edge (LE).
It is performed by detecting with). Since the first sheet has time to spare, it is assumed that the exposure lamp is up and the measured light amount value is set to the light amount L ₂ when the halogen lamp 4 rises to 100%. Then, the charging voltage of the first sheet becomes VC ₃ . As soon as the scanner starts returning, the exposure lamp is turned off and the second copy is started.
Since there is no time left after the second copy, the exposure lamp is turned on later than the first copy. The scanner starts moving, and the light amount is measured at the position of the standard white plate 15. This light quantity value is compared with the light quantity value of the first sheet, and the charging voltage value as shown in FIG. 3 is set based on the result. The charging voltage value set above is applied to the charging charger 9 from the document leading edge (LE) to a certain position. For the third and subsequent sheets, the above-described setting processing for the second and subsequent sheets is repeated. Incidentally, T ₁ in the figure is set so as to come to the position of the standard white plate 15, and T ₂ is set so as to have a time of about 20 mm at the leading end of the document.

[0022]

Since the present invention is configured as described above, it has the following effects.

According to another aspect of the image forming apparatus of the present invention, the light detecting means for detecting the light amount at a predetermined position in front of the leading edge of the document at the start of scanning, and the voltage applied to the charger based on the detection result of the light detecting means. Since the setting means and the control means for outputting the set voltage from the document leading edge for a certain period of time are provided, a shortage of light amount at the document leading edge due to insufficient margin of repeat time is eliminated and the leading edge of the formed image is eliminated. It is possible to prevent the occurrence of dark areas (black stripes).

According to another aspect of the image forming apparatus of the present invention, the light detecting means detects the light amount of the standard white plate arranged at a predetermined position in front of the front end of the document, so that the reflected light varies. It is possible to obtain a correct exposure amount even if the reading timing is deviated, and to always obtain a stable image.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a control system in an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram showing a mechanical section of the image forming apparatus.

FIG. 3 is a characteristic diagram showing a relationship between a light amount and a developing bias value.

FIG. 4 is a timing chart showing the timing of reading the amount of light and setting the charging voltage in the present invention.

[Explanation of symbols]

 1 Main Body 2 Original 3 Contact Glass 4 Halogen Lamp 5, 7 Mirror 6 Lens 8 Photosensitive Member 9 Charging Charger 10 Charging Device 11 Developing Device 12 Transfer Device 15 Standard White Plate 16 Optical Detection Sensor 17 Amplifier 18 CPU 19 AD Port 20 Output Port 21 Power Supply circuit

Claims (2)

[Claims] 1. A light detecting means for detecting a light amount at a predetermined position in front of the leading edge of the original at the start of scanning, and an applied voltage to a charging charger is set based on the detection result of the light detecting means. An image forming apparatus, comprising: a control unit that outputs a predetermined time from a tip portion. 2. The image forming apparatus according to claim 1, wherein the light detecting means detects the light amount of a standard white plate disposed at a predetermined position in front of the leading edge of the document.