JPH02219073A - Digital image recorder - Google Patents

Abstract

PURPOSE:To obtain a clear copied picture with a proper gamma characteristic and without fog by displaying optimum grid voltage value on a drum cartridge and making it possible that the optimum grid voltage value is inputted to a device main body when the drum cartridge is loaded. CONSTITUTION:An image forming body 10 is of cartridge type and removable from the device main body. The drum cartridge 10 displays the optimum grid voltage value by a bar code or by showing the presence or absence of the connection among plural electric terminals. Every time a new drum cartridge 10 is loaded, its optimum grid voltage value is inputted to the device main body. Thereby, the charge potential at the time of developing the image forming body is maintained at the prescribed optimum value and the image forming body always holds the fixed gamma character. Therefore the satisfactory copied picture free from from fog is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic digital image recording apparatus, particularly a digital monochrome reversal type digital image recording apparatus.

[Background of the invention]

As is well known, an image recording device, for example, an electrophotographic copying machine for monochrome images, includes an image forming body having a photoreceptor layer on its surface, and a charger after the charge is removed by a pre-charging exposure lamp (hereinafter referred to as PCL). The image forming apparatus includes a latent image forming means for forming an electrostatic latent image of a document on the image forming body uniformly charged. 2. Description of the Related Art Digital devices using semiconductor lasers as writing means for forming latent images in printers are often used.

An electrostatic latent image is formed by irradiating the image forming body with a laser beam modulated by image information obtained by reading an image of the original, and this electrostatic latent image is developed by a developing means. The monochrome toner image on the image forming body, which has been developed and becomes a visible image, is transferred onto recording paper, and this is fixed by applying pressure and/or heat by a fixing means, thereby completing a copy of the original document.

Recently, in addition to monochrome binary images, there are also copy images.
In order to express halftones, the image information is multivalued, and the laser beam is modulated with the image data to form an electrostatic latent image with multiple levels of potential, making it possible to obtain copies with gradation. It looks like this.

In the digital image recording device that uses the laser beam mentioned above, the digital image recording method uses reversal development in which toner is attached to the part of the image forming body that is irradiated with the laser beam, which reduces the usage time of the laser light source. is commonly used because it can increase the copying speed (especially when the original is a document).

In addition, in recent years, organic photoconductors (hereinafter referred to as OPC) have been increasingly used as photoreceptors for image forming bodies, as they are less toxic than Se, etc., and are easier to form photoreceptor layers to reduce manufacturing costs. It became so.

However, in the case of OPC, unevenness in layer thickness is likely to occur during the manufacturing process, and therefore, uniform charging cannot be achieved with a charger using a corotron discharger. So O
In the case of PC, a scorotron type charger is used which can control the charging potential of the photoreceptor by its grid.

There are two types of OPC, one with positive charge polarity and the other with negative charge polarity, but the OPC generally used at present is negative OPC, and in the case of reversal development, negatively charged toner is used. Therefore, the toner image formed on the image forming body is transferred onto recording paper by a transfer device to which a high positive voltage is applied, and this recording paper is separated from the image forming body by a separator to which a high negative voltage is applied. Ru.

The laser beam used in the writing means of a general digital image recording device has a spot diameter of about one pixel (dot) of the image, so the MTF (Modulation) of the latent image formed on the image forming body is Trans
-fer Function) is limited. So,
When the spatial frequency of an image signal becomes high, sufficient gradation cannot be expressed by pulse width modulation in which the unit period is one pixel width.

Therefore, in order to express gradation, it is necessary to perform modulation based on a period of approximately two pixel width.

However, if the unit of modulation cycle is a cycle with a width of two pixels or more, there is no problem with things that require gradation such as photographs, but in the case of text (line drawings), for example, thin lines Since the recording quality deteriorates due to skipping, the modulation period is set to about one pixel width.

[Problem to be solved by the invention]

When multi-leveling is performed using the pulse width modulation method, the pulse width is set to be shorter than the light emission time of one pixel width even if the unit period is two to three pixel widths. When modulating with this short pulse width, the peak value of the optical energy distribution for the short pulse decreases, resulting in a behavior similar to optical intensity modulation. Because of these properties, the potential distribution of a latent image obtained by exposure with a pulse width modulated laser beam is as shown in FIG.

FIG. 9 is a diagram showing an example of the light energy distribution according to various pulse widths as a latent image potential distribution when the laser spot diameter on the image forming body is made approximately equal to the pixel width. The vertical axis in the figure represents the surface potential (V) of the image forming body, and the horizontal axis represents the length in units of pixel width.

Due to the above properties, an example of the relationship between the copy density of an image obtained by exposure with a pulse width modulated laser beam and the pulse width of the laser beam is shown in FIG. The vertical axis of the figure shows the copy density, and the horizontal axis shows the duty ratio (%) of the pulse width, and the charged potential on the surface of the photoreceptor is used as a parameter. As shown in the figure, as the duty ratio decreases, the gamma gradually increases, and the average value of the gamma varies depending on the charging potential (VH), resulting in different gradations.

Furthermore, Se-based photoreceptors have little variation in chargeability from lot to lot, and a stable charging potential can be obtained even with a corotron-type charger.However, OPC has large lot-to-lot variation in chargeability, and a suflotron is used. Even if a charger is used, the charging potential will not be constant and will affect the copy image quality. In particular, in reversal development, there is a problem in that charging properties are poor and when the charging potential approaches the development bias voltage, toner scatters and adheres to unexposed areas of the image forming body, resulting in blurring, which is easily noticeable and makes the copied image unclear. There is a point.

Therefore, in image forming bodies using OPC, it was necessary to apply the optimum grid voltage to each image forming body to a charger, but conventional devices do not have such a system.
The above problems were not resolved.

The present invention solves these problems and provides a digital image recording device that can apply an optimal grid voltage to each image forming body, have an appropriate gamma, and obtain clear copy images without fog. The purpose is to provide the following.

[Means to solve the problem]

The above object is to provide a digital image recording device that is composed of a drum cartridge type image forming body using an organic photoconductor as a photoreceptor and a scorotron type charger, and performs reversal development, by providing the optimum image forming apparatus for each of the drum cartridges. This is achieved by a digital image recording apparatus characterized in that the grid voltage value is displayed and the optimum grid voltage value can be input into the main body of the apparatus when the drum cartridge is loaded.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of a digital image recording apparatus which is an embodiment of the present invention. This digital image recording apparatus is a digital copying machine consisting of a scanner section IA, an image processing section IB, and a printer section 1G.

In the scanner part IA of FIG. 1, when a copy button provided on the digital copying machine is turned on, the original on the original platen 81 is optically scanned by the optical system.

This optical system is composed of a carriage 84 provided with a light source 85 and a reflecting mirror 86, and mirrors 88 and 89. A halogen lamp is used as the light source 85. It is also possible to use a commercially available green fluorescent lamp in place of the halogen lamp, and in this case, it is lit with a high frequency power source of about 40 KHz to prevent flickering. In addition, in order to maintain a constant temperature of the tube wall or promote warming up, it is necessary to keep the tube wall warm with a heater using a POSISTOR.

A standard white plate 97 is provided on the upper surface side of the left end of the document table 81 . This is because the image signal obtained by optically scanning the standard white plate 97 is used as a standard white signal, and thereby the image signal obtained thereafter is normalized.

The carriage 84 and the V-mirrors 88 and 89 are caused to run on slide rails (not shown) in a predetermined direction at predetermined speeds by a stepping motor 90. 2, this allows the lens 12 to be lowered from the reading image surface.
The distance is kept constant.

A light source 85 illuminates the document, and the reflected light is reflected by a reflecting mirror 87. (2) Guided to the optical information conversion unit 11 via mirrors 88 and 89. The optical information conversion unit 11 includes a lens 12 and a CCD 13 on which an optical image is formed, and the optical image is converted into an image (electrical) signal.

The image signal is subjected to various image processing in the image processing sl s, and then outputted to the image exposure means 5, which is a writing means of the printer section 1C, which will be described later.

As the deflector 55A of the image exposure means 5, in addition to a galvanometer mirror or a rotatable mirror, an optical deflector made of a crystal or the like may be used. The laser beam modulated by the image signal is deflected and scanned by this deflector 55A. When deflection scanning is started, the beam scanning is detected by a laser beam index sensor (not shown), and laser beam modulation using an image signal is started. As the image signal, the image information (copy data) of the document described above and the print data supplied from the outside can be selectively used.

Pa. The pulse width modulated laser beam is made to scan over the image forming member (photosensitive drum) 10 which has been charged with a negative charge by a charger 21 after being neutralized by the PCL 20 .

Here, an electrostatic latent image corresponding to the image signal is formed on the image forming body 10 by the main scanning by the laser beam and the sub scanning by the rotation of the image forming body 10.

This electrostatic latent image is formed by a developing roller 24 containing black toner.
Developed by a developing device 23 to which a predetermined developing bias voltage is applied from a high-voltage power supply, a monochrome toner image is formed.

On the other hand, the recording paper P sent out from the paper feeding device 41 via the sending roller 42 and the timing roller 43 is conveyed to the surface of the image forming body 10 in a state in which the timing is synchronized with the rotation of the image forming body 10. . The black toner image is transferred onto the recording paper P by a transfer device 30 to which a high voltage is applied from a high voltage power source, and separated by a separator 31.

The separated recording paper P is conveyed to the fixing device 32 and subjected to a fixing process using heat and/or pressure to obtain a monochrome image.

The image forming body IO after the transfer is cleaned by the cleaning device 26 and is prepared for the next image forming process.

The corotron type charger 21 used here is the third one.
It consists of a scorotron type discharge device having a cross section as shown in the figure, and 211 is a discharge wire made of a thin tungsten wire, and 212 is a discharge wire made of a plurality of thin tungsten wires, which is stretched between the discharge wire 211 and the image forming body 10. The grid 213 is an elongated frame-shaped shield member made of a conductive material such as sheet metal. This charger 21 is a discharge wire 211
The charging on the surface of the image forming body 10 can be freely controlled by the bias voltage applied to the grid 212 (hereinafter referred to as grid voltage) while a high voltage is applied to the grid 212, and various charging can be performed. .

For example, if a negative high voltage of several KV to 10 KV is applied to the discharge wire 211 and the grid voltage is -600V, the charged potential on the surface of the image forming member 10 will be -600 V, and if the grid voltage is Ov, the surface of the image forming member 10 will be becomes Ov, and static electricity can be removed.

The cleaning device 26 includes a blade 27 made of urethane rubber or the like that is pressed against the image forming body 1O to clean residual toner, and a predetermined DC voltage is applied to the cleaning device 26 to facilitate recovery of the toner cleaned by the blade 27, thereby forming an image. A metal roller 28, an auxiliary cleaning roller 29, etc. are provided which are disposed in a non-contact manner on the surface of the body 1O. The auxiliary cleaning roller 29 is arranged so as to rotate and press in the opposite direction to the rotation of the image forming body 1O in order to remove unnecessary toner that is left behind when the blade 27 is released from pressure after cleaning.

FIG. 2 is a plan view showing a main part of a deflection scanning system using a semiconductor laser of the image exposure means 5 of FIG. 1.

A laser beam modulated by the image signal from the image processing section IB is emitted from the semiconductor laser 51. This laser beam enters a polygon 55, which is, for example, an octahedral rotating polygon mirror, via mirrors 52 and 53. The laser beam deflected by the polygon 55 is irradiated onto the surface of the image forming body 10 through the fθ lens 54, so that the surface of the image forming body 10 is scanned at a constant speed in a predetermined direction a. 56.57 is a cylindrical lens for tilt angle correction,
58 is a laser beam index sensor that detects scanning of the laser beam.

Due to the laser beam scanning number as described above, an electrostatic latent image is formed on the negatively charged image forming body 10.

This electrostatic latent image is made into a visible toner image by reversal development as described below.

FIG. 4 shows potential changes on the surface of the image forming body during reversal development when a stationary OPC is used as the photoreceptor of the image forming body IO. FIG. 5 is a diagram showing a model of two-component developer particles used in this developing device 23. In the figure, V
H is the potential of the unexposed portion of the image area on the surface of the image forming member 10 that is uniformly charged, VB is the development bias voltage applied to the developing roller 24 of the developing device 23, and VL is the potential of the well where the charge is removed by laser light. The potential of the exposed portion PH whose absolute value has decreased as shown in FIG.

Referring to FIG. 4, the image area of the image forming body 10 is uniformly charged by the charger 21 and has a predetermined negative surface potential VH (1).

Exposure portion PH given image exposure by laser beam
The potential increases (the absolute value of the potential decreases) (2). In this case, since the pulse width modulated laser beam exhibits the properties shown in FIG. 8, the brightness modulation appears to be superimposed, and the potential of the exposed portion PH changes depending on the duty ratio of the pulse width.

The electrostatic latent image thus formed is developed by the developing roller 24 to which a negative bias voltage VB is applied.

The bias voltage VB for development is set to be VH) VB) VL in absolute value, an edible OPC is used as the photoreceptor, and an example in which the image signal is binary is VH#-. 60
0V, VB"; -480V, VL"t -100V
It is set so that

The developer is stirred in the developing device 23, and as shown in FIG. 5, the carrier C is positively charged and the toner T is negatively charged.
The toner T adheres to the surface and is transported to the development area by the development roller 24 to which the development bias voltage VB is applied.

Therefore, toner T has a relatively high potential (low absolute value)
The toner image is formed by flying toward the exposed portion PH and developing. The area where this toner image is formed has an absolute potential value of DP due to the adhesion of the negatively charged toner T.
Although the potential increases by U, it usually does not reach the same potential as the unexposed area (3).

The toner image developed as described above is transferred to recording paper P, and then separated and fixed to form a copy image.

In the digital image recording apparatus of the present invention, the image forming body 1O is of a cartridge type and is removable from the apparatus main body, and is referred to as a drum cartridge. The drum cartridge 10 displays the optimum grid voltage value, and also displays the optimum grid voltage value. (A code is provided that indicates the presence or absence of a connection between a plurality of electrical terminals.)

Next, a method of setting the grid voltage vG applied to the grid 211 of the charger 21 will be explained.

FIG. 6 is a system diagram showing an example of manually setting the optimum grid voltage value. In the figure, 100 is a CPU of the main body control unit, 101 is a cartridge sensor located on the apparatus main body side and detects whether the drum cartridge IO, which is an image forming body, is loaded or unloaded, and 105 is a memory that stores the optimum grid voltage value and other information. 110 is a numeric keypad provided on an operation panel (not shown); 215 is a main switch; and 215 is a high-voltage power supply circuit that supplies high voltage and grid voltage to the discharge wire 211 of the charger 21 and the grid 212. When loading or replacing the drum cartridge 10 for the first time, first press the main switch i while simultaneously pressing two specific keys on the numeric keypad 110.
By pressing ll or the like, a signal is sent to the CPU 100 to set the optimal grid voltage value. Then, when the previous drum cartridge IO is pulled out, the cartridge sensor 101 detects this and c p U 100
, the CPU 100 clears the previous optimum grid voltage value stored in the memory 105. Next, use the numeric keypad 110 to insert a new drum cartridge 1.
Enter the optimal grid voltage value shown at 0. Then, c p u ioo stores the value in memory 105 .

Finally, when the CPU 100 is returned to its normal state by inputting a specific hidden number using the numeric keypad 110, the high-voltage power supply circuit is set to apply the optimum grid voltage to the grid 212 of the charger 21 for subsequent copies. 215. It goes without saying that the memory 105 is backed up by a lithium battery or a secondary battery that is charged while the main switch Ill is turned on.

FIG. 7 is a system diagram showing another example of manually setting the optimum grid voltage value.

In the figure, the same parts as in FIG. 6 are represented by the same symbols. 112 is a digital switch. An assembly worker or service person installs a new drum cartridge lO1.
When loading the drum cartridge 10, the optimum grid voltage value displayed on the drum cartridge IO is set on the digital switch 112. Then, during the subsequent image forming operation, the CPU
100 confirms that the drum cartridge IO is correctly loaded by the signal from the cartridge sensor LO, reads the optimum grid voltage value from the digital switch 112 every time a copying operation is performed, and reads the optimum grid voltage value from the charger 21.
A predetermined high voltage is applied to the discharge wire 211 of the grid 21.
The high-voltage power supply circuit 215 is controlled so as to apply the above-mentioned optimum grid voltage to the grid voltage. Such a method has the advantage of not requiring memory 105 or a backup battery.

Next, a method for automatically setting the optimum grid voltage value will be explained.

FIG. 8 is a system diagram showing an example of automatically setting the optimum grid voltage value. In the figure, reference numeral 102 is a code reader provided in the main body of the apparatus, facing a code representing the optimum grid voltage value provided in the drum cartridge IO, and reading the code. Other parts that are the same as those in FIG. 6 are denoted by the same reference numerals, and details thereof will be omitted.

When the drum cartridge 10 is loaded, the code is placed so as to face the code reader 102, so during the image forming operation, the CPU 100 uses the cartridge sensor 101 to check whether the drum cartridge 10 is correctly loaded. The optimum grid voltage value is read from the code of the drum cartridge IO every time a copy operation is performed, and the discharge wire 211 of the charger 21 is
The high voltage power supply circuit 215 is controlled so as to apply a predetermined high voltage to the grid 212 and the above-mentioned optimum grid voltage to the grid 212 .

〔Effect of the invention〕

According to the present invention, in a digital image recording apparatus that performs reversal development as described above, the optimum grid voltage value is displayed on the drum cartridge type image forming member, and each time a new drum cartridge is loaded, the Since the optimum grid voltage value is input into the main body, the charging potential of the image forming member during development is maintained at a predetermined optimum value.

Therefore, the image forming body always maintains constant gamma characteristics,
It is possible to provide a digital image recording device that can obtain a copy image of good image quality without fogging.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a schematic configuration of an embodiment of the present invention, Fig. 2 is a plan view showing the main parts of a deflection scanning system using a semiconductor laser, and Fig. 3 is a sectional view showing a scorotron-type charger. , FIG. 4 is a diagram showing the change in potential on the surface of the image forming body during reversal development, FIG. 5 is a diagram showing a model of two-component developer particles, and FIGS.
Figure 8 is a system diagram showing an example of setting the optimum grid voltage value in the main body of the device, Figure 9 is a diagram showing the potential distribution of a latent image obtained by pulse width modulated laser beam exposure, and Figure 10 is a pulse FIG. 3 is a diagram showing the relationship between the copy density of an image obtained by width-modulated laser beam exposure and the pulse width of the laser beam. IA...Scanner part IB...Image processing section IC・
... Printer section 5 ... Image exposure means 10 ... Image forming body (drum cartridge) 21 ... Charger
23...Developer 30...Transfer device 31.
...Separator 100...CPU 101...Cartridge sensor 102...Code reader 105...Memory 110...Numeric keypad 1
11... Main switch 112... Digital switch 211... Discharge wire 212... Grid 21
5...High voltage power supply circuit VG...Grid voltage

Claims (2)

[Claims] (1) Consisting of a drum cartridge type image forming body using an organic photoconductor as a photoreceptor and a scorotron type charger,
In a digital image recording device that performs reversal development, an optimal grid voltage value is displayed on each of the drum cartridges, and when the drum cartridge is loaded, the optimal grid voltage value can be input into the device main body. A digital image recording device featuring: (2) The drum cartridge is provided with a code representing the optimum grid voltage value, and when forming an electrostatic latent image on the image forming body, the grid of the charger is provided with a code indicating the optimum grid voltage value read from the code. 2. The digital image recording apparatus according to claim 1, wherein the grid voltage is automatically applied.