JP2000275914A - Image forming device and image adjusting method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect density with an image-density detector by forming a inspection image for image adjustment out of points each of which consists of laser dots. SOLUTION: An image-density adjusting operation is performed at a specific interval of time, etc., if necessary prior to an ordinary image-forming operation after warming up a machine or during an ordinary operation. In the image density adjustment, points each of which consists of laser dots are formed on a photoreceptor drum 42 at specific intervals by an exposure unit 44. In the exposure, the points are formed at specific intervals on the photoreceptor drum 42 by an ordinary laser output. Each point is formed, for example, of four laser dots, but the number of the dots is not limited thereto. The exposure for an inspection image consisting of such points is carried out on a specific inspection-area of the photoreceptor drum 42 by the exposure unit 44. After the formation of the latent image of the inspection image, the latent image is developed in an ordinary development condition by a developing unit 46. Then, the image density of the inspection image is detected by an image-density detector set in a cleaning unit 48.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image adjustment of an image forming apparatus, and more particularly to an image density adjustment method capable of detecting an accurate image density.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, an image is sometimes adjusted at the start of use or at predetermined time intervals in order to prevent image fluctuation. As a method of adjusting the image, a predetermined exposure is performed on the surface of the photoreceptor, the latent image is developed, and the density of the toner image is measured by a patch density sensor to adjust the image density.

When it is determined that the image density is high by this density adjustment method, the rotation speed of the developing sleeve is reduced, the developing bias is increased, or the charging voltage is lowered. If it is determined, the rotational speed of the developing sleeve is increased. However, in a so-called solid image in which toner was applied to the photosensitive drum at the highest density in image adjustment, the black was too strong and the difference in image density could not be determined.

Therefore, conventionally, a developing bias or the like is temporarily fluctuated to form a halftone, which is not the highest density, on the photosensitive drum, the image density is measured, and the maximum image density is estimated from the measured value to obtain an image. Adjustments were being made.

[0005]

However, when the maximum density is estimated from the halftone, an error is large and an accurate value cannot be obtained. In other words, the image density in the halftone and the reduction amount of the developing bias are not always directly proportional, and it is not possible to determine how much such a state is reduced from the maximum density,
It was impossible to estimate the maximum density from the amount of decrease in the developing bias. Also, the image with the developing bias reduced is not a normal image forming, but has a large error in the operation of forming a halftone, and from the reduced value, it is supposed that the developing bias value is not reduced. However, even if the image density is measured based on the estimated value, an original image serving as a reference for image adjustment cannot be accurately obtained.

[0006]

SUMMARY OF THE INVENTION The present invention has the following configuration in order to solve the above-mentioned problems and realize accurate image adjustment.

That is, the inspection image formed on the photosensitive drum is defined as a point formed by a plurality of laser light dots, the image density of the formed portion is measured, the original image density is estimated, and It was decided to adjust the density. The point to be formed may be a single point or a plurality of points at a predetermined density. By obtaining the densities of a plurality of points in advance, the image forming state of the image forming apparatus can be detected from the entire density.

In addition, an inspection image is formed by a plurality of lines, and the interval between these lines is set to a predetermined interval. The image density of a portion formed by such a plurality of lines is measured, and the measured image density is measured. Then, the original image density is estimated from the interval between the formed lines, and the density adjustment of the image forming means is performed.

Thus, the pixels formed by the laser can be formed with the dots under the same conditions as those in the normal use state and at the highest density, and the formed inspection image is a set of a plurality of pixels. The error is eliminated by averaging the density differences of the individual dots. Further, when the inspection image is formed by lines, each line is written at a predetermined interval, so that the entire image has a halftone, and an accurate image density of the image forming apparatus can be detected.

The pixels forming each line may be formed by a single dot or a set of a plurality of dots.
Further, the formed line is preferably inclined at 45 degrees with respect to the main scanning direction, but may be formed at another angle, vertical, or horizontal. The line interval is not particularly limited as long as the density of the formed image is a value that can be easily detected by the image density detector.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus according to the present invention will be described.

As shown in FIG. 1, the digital copying machine 2 includes a scanner section 20 for reading a document, a control section 22 for editing and processing an image, and an image forming section 24 for printing an image on a sheet.
, A paper feed unit 26 that supplies paper to the image forming unit 24, a fixing unit 28 that fixes an image on transfer paper, a sorter unit 30 that discharges a document, and the like.

The scanner unit 20 has a glass plate on the upper surface, and when an original is placed on the glass plate and the operation switch is turned on,
The reading lamp moves to read the original. The original is read as a digital signal, and the read image signal is sent to the control unit 22. In the case of copying, an image signal is sent from the control unit 22 to the image forming unit 24, the image is transferred to a transfer sheet from the sheet feeding unit 26, and the image is fixed by the fixing unit 28 and printing is performed.

The image forming section 24 is shown in FIG. As shown in FIG. 2, the image forming unit 24 includes a charger 41, a photosensitive drum 42, an exposure device 44, a developing device 46, and a transfer charger 43.
, A separation charger 45, a cleaning unit 48, and the like, and forms an image from the sent image signal, and forms a toner image on transfer paper from the paper supply unit 26.

The photosensitive drum 42 is formed by coating a photosensitive layer on the surface of a cylindrical base material made of, for example, aluminum having a diameter of 80 mm, and detects a drive motor for driving the photosensitive drum 42 and a rotation phase of the photosensitive drum 42. And the like (both not shown). The photosensitive layer has a thickness of 15 to 30 μm and a dielectric constant of 2.0 to 5.0, and the substrate is grounded. The photosensitive drum 42 is, for example, 280 mm /
It rotates at the speed of sec, and the rotation is measured by the encoder. After being uniformly charged by the charger 41 while rotating, it is exposed by the exposure unit 44 to form an electrostatic latent image on the surface.

The charger 41 is, for example, a scoroton charger, and uniformly charges the photosensitive drum 42 to a predetermined voltage, for example, -600 V prior to the latent image forming process.

The exposure unit 44 includes a laser, a polygon mirror, an optical system such as an f-θ lens (both not shown), and the like.
The light is reflected by a polygon mirror and is irradiated on the surface of the photosensitive drum 42 via an optical system such as an f-θ lens. The polygon mirror rotates at a constant rotation, and the main scanning of the laser beam is performed by the rotation, and the sub-scanning is performed by the rotation of the photosensitive drum 42. The formed electrostatic latent image is visualized by the toner in the developing device 46.

As shown in FIG. 2, the developing device 46 includes a magnet roller 14, a developing sleeve 16, and the like, and has a developer therein. The developer comprises a toner of a polyester material having an average particle size of 8.5 μm and a ferrite coating carrier having an average particle size of 60 μm, and the toner concentration is controlled to 4 to 6%. When the toner density decreases or the image density decreases, a toner supply motor (not shown) is operated to supply toner from the toner hopper to increase the toner density of the developer. .

A predetermined bias voltage (approximately −600 V) is applied to the developing sleeve 16 to maintain a voltage difference between the developing sleeve 16 and the charging voltage of the photosensitive drum 42 at a predetermined value. Form a brush. The exposed portion of the photosensitive drum 42 has a predetermined charging voltage difference from the toner, whereby the toner adheres to the exposed portion. Here, when the developing bias is changed, the photosensitive drum 42
Since the difference from the potential of the exposed portion fluctuates, the image density is appropriately changed. The attached toner is transferred to the transfer charger 43.
Then, the transfer paper on which the toner is transferred from the photosensitive drum 42 by the separation charger 45 is separated from the photosensitive drum 42 and is fixed by the fixing device 28.

The transfer charger 43 is disposed to face the photosensitive drum 42, and discharges electric charges from the back side of the transfer paper stacked on the photosensitive drum 42, which electrostatically carries the toner image, to transfer the transfer paper. To transfer the toner. The transfer charger 43 is preferably a scotron discharger, but may be a corotron charger, a charging roller, or the like.

The separation charger 45 includes a scotron discharger, a corotron charger, a charging roller, and the like, and removes electricity from the transfer paper adsorbed on the photosensitive drum 42 to separate the transfer paper from the photosensitive drum 42.

The paper feed unit 26 stores various sizes of paper so as to supply a predetermined size to the image forming unit 24 in accordance with an instruction from the control unit 22.

The toner remaining on the surface of the photosensitive drum 42 without being transferred to the transfer paper is removed and collected by the cleaning unit 48. The cleaning unit 48 is shown in FIG. The cleaning unit 48 includes a blade 49 that comes into contact with the photosensitive drum 42, and scrapes off toner, dust, and the like attached to the surface of the photosensitive drum 42, and stores the scraped toner and toner in the toner box.

Further, an image density detector 8 is provided in the cleaning unit 48. The image density detector 8
It is installed in front of the blade 49 and measures the density of a developed portion (hereinafter referred to as a patch) of an inspection image that has been exposed to the surface of the photosensitive drum 42 in a predetermined shape, and determines the state of toner adhesion to the photosensitive drum 42 and the like. To detect.

The fixing device 28 is a device for fixing the toner on the transfer paper, and applies a predetermined pressure and heat to the transfer paper on which the toner image has adhered. The sorter unit 30 is a discharge mechanism that discharges the printed transfer paper in a predetermined state. Note that a finishing unit may be provided to perform operations such as a stapling mechanism, a center folding mechanism, sorting, and grouping. The switch unit is provided on the upper surface of the digital copying machine 2, and can be used for inputting enlargement / reduction of a print image, designation of print paper, designation of the number of prints, and the like.

When the formation of one image is completed, the electrical history of the photosensitive drum 42 is erased by the pre-exposure lamp, and the next print cycle is started.

The control unit 22 controls the above mechanisms, detects the image density from the toner adhesion state measured in the inspection image in the image adjustment operation, and determines the developing bias or the charging voltage of the photosensitive drum 42 and the toner density. And so on so as to keep the image density constant.

Next, the image density adjusting operation of the image forming apparatus 2 will be described.

The image density adjusting operation is appropriately performed at a predetermined time interval after the image start switch is turned on from the stop state of the image forming apparatus 2 and before the normal image forming operation is performed after the warm-up is completed and during the normal operation. In the image density adjustment, first, a plurality of dots of the laser beam are formed on the photosensitive drum 42 at predetermined intervals as shown in FIG. In the exposure, a plurality of points are formed on the photosensitive drum 42 at predetermined intervals with a normal laser output. Each point is formed by four laser dots as shown in FIG. The number of dots is not limited to this. Exposure of the inspection image including a plurality of points is performed by the exposure device 44 on a specific portion of the photosensitive drum 42 for inspection. When the latent image of the inspection image is formed, the developing device 46 develops the latent image in a normal developing state. Then, the image density of the inspection image is detected by the image density detector 8 installed in the cleaning unit 48.

Next, the control unit 22 compares the detected image density value of the inspection image with a reference value to determine the image formation state of the image forming apparatus 2, and determines a difference between the two by a predetermined value or more. When it is determined that there is, the image density is adjusted by changing the developing bias, the charging voltage, the laser output, the toner density, and the like based on the detected value. The reference value differs depending on the inspection image. When a plurality of inspection image images can be selected, the reference value is stored for each image.

Next, another example of image density adjustment will be described.

In this example, a plurality of oblique straight lines as shown in FIG. 6 are formed on a specific portion of the photosensitive drum 42 for image inspection at predetermined intervals by laser light. Exposure is performed under ordinary conditions, and development is performed under ordinary conditions. The inspection image is formed in this manner, and the density of the inspection image is detected by the image density detector 8 to detect the image forming state of the image forming apparatus 2.

When an image for inspection is formed by a plurality of lines having a predetermined interval as described above, the image becomes a halftone as a whole, and image density detection by the image density detector 8 is easy.
In addition, it is possible to accurately grasp the state of adhesion of the toner to the photosensitive drum 42. The points that make up the line are:
Since there are a plurality of laser dots as shown in FIG. 7,
Fluctuations in the laser output are averaged. Further, since the lines are formed obliquely in the main scanning direction, it is possible to detect a change in image density in the main scanning direction.

Further, the density of the inspection image can be arbitrarily changed by adjusting the interval between the lines, and the density can be matched with the most sensitive density of the image density detector 8 to accurately detect the density. can do. Further, since the laser used for writing has a normal output, each pixel is formed with a normal density and does not need to be corrected, so that there is no error in the density.

Next, the image adjustment operation will be specifically described with reference to a flowchart shown in FIG.

When the image forming apparatus 2 is turned on (F-1), the warm-up operation is performed (F-2). When the warm-up operation is completed (F-3), the image density is first set before the normal operation. Adjustment is performed (F-4).

The image density adjustment will be described.

In the image density adjustment mode, first, an exposure signal for forming an inspection image is sent from the control unit 22 to the exposure unit 44. The exposing device 44 operates the laser to expose a pattern for inspection on the surface of the photosensitive drum 42 to a specific position for inspection (F-5). The pattern is a plurality of straight lines spaced at a predetermined interval. A straight line is written with pixels composed of four laser dots inclined at 45 degrees with respect to the main scanning direction. The exposed portion is developed in the developing device 46 (F-6). The development conditions are normal development conditions.

Then, the density of the image developed by the developing device 46 is detected by the image density detector 8 installed in the cleaning unit 48 (F-7). The detected value is compared with the reference value by the control unit 22 (F-8), and if it is within the reference value, the operation shifts to the normal operation (F-9). On the other hand, if the detected value is larger than the range of the reference value, it is determined that the image density is formed densely, and the density is reduced to adjust (F-11) so as to fall within the reference range. When the value falls below the range of the reference value, it is determined that the density is low, and the adjustment is performed in the direction of increasing the image density (F-1).
1).

After the adjustment is completed, the operation shifts to a steady operation (F
-9), when a copy start switch is input, predetermined operations such as image reading, transfer paper transfer, formation of a latent image on photosensitive drum 42, development, transfer of toner image to transfer paper, etc. Are sequentially executed. Start the steady operation, determine whether a predetermined time has elapsed, if the predetermined time has elapsed,
Returning to (F-4), the image density is adjusted again.

[0041]

According to the present invention, since the inspection image for image adjustment is made up of a plurality of laser dots, the difference in output for each laser dot is averaged, and the image is converted to a normal laser output. Therefore, no correction is required for the formation of the image, and since the inspection image is not solid black, the density detection by the image density detector can be reliably performed.

Also, since the inspection image is formed by lines spaced at a predetermined interval, an accurate halftone image can be formed, the fluctuation of the laser output can be averaged, and the density detection for density adjustment can be performed accurately. Thus, the reliability of the detected value can be improved.

Since an image for inspection is formed under the same conditions as in normal image formation, no error occurs in image formation.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating an image forming unit.

FIG. 3 is a diagram illustrating a cleaning unit.

FIG. 4 is a diagram illustrating an example of an inspection image.

FIG. 5 is a diagram illustrating an example of pixels forming an inspection image.

FIG. 6 is a diagram showing another example of the inspection image.

FIG. 7 is a diagram illustrating an example of pixels of an inspection image.

FIG. 8 is a flowchart showing an operation.

[Explanation of symbols]

 2 Image Forming Apparatus 8 Image Density Detector 14 Magnet Roller 16 Developing Sleeve 20 Reading Unit 22 Control Unit 24 Image Forming Unit 26 Fixing Unit 30 Discharge Unit 41 Charger 42 Photosensitive Drum 43 Charger 44 Exposure Device 45 Peeling Charger 46 Developing Device

Claims (7)

[Claims] 1. An exposure unit for forming a latent image by irradiating a photosensitive member with a laser beam, a developing unit for attaching and developing a toner to the latent image, and forming an image by attaching the toner to transfer paper. In an image forming apparatus including a transfer unit and a fixing unit for fixing the transferred toner image to transfer paper, a predetermined number of laser light dots are formed on the surface of the photoconductor by the exposure unit during an image density test. The points are exposed as an image for inspection, the developing unit develops the image for inspection under the same conditions as in normal image formation, and the image density of the developed image for inspection is detected by density detecting means. And adjusting the image of the image forming apparatus by comparing the detected image density value with a reference value. 2. The image adjusting method according to claim 1, wherein the inspection image is a plurality of lines spaced at a predetermined interval. 3. The image adjustment method according to claim 2, wherein the line is a straight line and has a predetermined angle with respect to a main scanning direction. 4. An exposure section for irradiating a laser beam to a photoreceptor to form a latent image, a developing section for applying toner to the latent image for development, and forming an image by attaching toner to transfer paper. An image forming apparatus comprising: a transfer unit; a fixing unit configured to fix the transferred toner image to transfer paper; and a density detection unit configured to detect an image density of an inspection image formed on the photoconductor for an image density inspection. In the apparatus, at the time of image inspection, the exposure unit exposes a point formed by a predetermined number of laser light dots as an inspection image, and the developing unit displays the inspection latent image formed by the exposure unit. An image forming apparatus which develops under normal conditions and detects the density of the inspection image by the detection means. 5. The image forming apparatus according to claim 4, wherein the inspection image is a plurality of lines having a predetermined interval. 6. The image forming apparatus according to claim 5, wherein the line is a straight line and has a predetermined angle with respect to a main scanning direction. 7. The image forming apparatus according to claim 4, wherein a developing bias of said developing unit is adjusted based on an image density value detected by said density detecting means.