JP2002225344A - Imaging method and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exposing system in which the quantity of incident light for one scanning line of a photosensitive body or the image density can be made substantially constant even if the environmental conditions are varied through a simple arrangement. SOLUTION: The imaging apparatus for forming an image by transferring an image on a photosensitive body, formed by laser light from a laser light source, to a transfer sheet comprises halftoning means 32 and 33 for converting a multilevel image signal into a false gray scale image signal, means 34 for regulating the width of a laser light generation pulse to cancel variation in the density of an image formed on the photosensitive body, and a print means 40 for generating laser light depending on the false gray scale image signal from the halftoning means using a pulse regulated by the pulse width converting means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and an image forming apparatus, and more particularly, to an image forming method and an image forming apparatus capable of canceling a change in density of an image formed on a photosensitive member. Related to control.

[0002]

2. Description of the Related Art In a digital image forming apparatus such as a digital copying machine or a printer, an image is formed by scanning and exposing a photosensitive member with a laser beam. FIG. 6 is a configuration diagram showing an example of the arrangement of the laser optical system.

A laser beam emitted from a laser element 1 composed of a semiconductor laser is collimated by a collimating lens 2 and then deflected by a rotary polygon mirror (polygon mirror) 4 through a slit and a cylindrical lens (cylindrical lens) 3. Then, the laser beam is imaged on the photoconductor (not shown) by the fθ lens 5 and the correcting cylindrical lens (cylindrical lens) 6, is subjected to main scanning exposure by the rotary polygon mirror 4, and is formed on the photoconductor (not shown). An image is formed by performing sub-scanning by rotation.

In the image forming apparatus having the above-described configuration, it is known that the light amount of the laser beam irradiated on the photoconductor changes as the scanning angle θ of the polygon mirror changes. Therefore, the incident light amount of the scanning line on the photosensitive member varies in the main scanning direction to such an extent that the image quality is adversely affected.

In order to solve such a problem of such a variation in the light amount, Japanese Patent Application No. 6-307846 discloses a method in which an incident light amount of one scanning line of a photosensitive member extends in a scanning direction in an area before a polygon mirror. There has been proposed a method of inserting a filter for dimming a laser beam so as to be substantially constant. As a result, it is possible to easily correct the variation in the light amount of the scanning line on the photoconductor corresponding to the scanning angle of the polygon mirror.

In Japanese Patent Application Laid-Open No. 64-28667, in an optical system not using an fθ lens, a drive current value of a laser diode when the optical output coincides with a preset minimum value and maximum value, respectively, is driven. It has been proposed to store the current as a minimum value and a maximum value and control the LD drive current within that range.

Japanese Patent Application Laid-Open No. 9-197316 discloses a configuration in which correction coefficients for a plurality of preset correction positions are stored, a correction coefficient for a scan position is obtained, and a drive current is corrected.

[0008]

However, according to the method described in Japanese Patent Application No. 6-307846, a filter for correction is inserted into an area in front of a polygon mirror. As a result, the laser beam is dimmed, and the amount of light incident on the photoreceptor is reduced. Therefore, a large current must be supplied to the light source, which causes a new problem of low efficiency.

Further, the required quantity of incident light also changes due to deterioration or replacement of the photoconductor, and a correction filter corresponding to the sensitivity of the photoconductor is required, which causes a problem that general versatility is lost.

According to the method described in Japanese Patent Application Laid-Open No. 64-28667, the value of the drive current of the laser diode when the light output coincides with the minimum value and the maximum value, respectively, is set to the minimum value of the drive current. And the maximum value, and the LD drive current is controlled within the range. Therefore, when the environmental condition is changed, the minimum value and the maximum value of the drive current must be stored again. Problems arise.

In the method described in Japanese Patent Application Laid-Open No. Hei 9-197316, a correction coefficient for a plurality of preset correction positions is stored, a correction coefficient for a scanning position is obtained, and a drive current is corrected. The circuit system for this is complicated, and a high-precision one is required.
A dedicated IC such as an SIC had to be manufactured, and there was a problem that the cost was high.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a simple configuration and is capable of making the incident light amount or image density of one scanning line of the photosensitive member substantially constant even when environmental conditions change. It is an object to provide a possible image forming method and an image forming apparatus.

[0013]

SUMMARY OF THE INVENTION The present invention for solving the above-mentioned problems is constituted as follows. (1) The invention according to claim 1 is an image forming method for forming an image by transferring an image on a photoreceptor formed by a laser beam from a laser light source to a transfer sheet, wherein the multi-valued image signal is pseudo-scaled. The pulse width for laser light generation is adjusted so as to cancel the fluctuation of the density of the image formed on the photoreceptor, and the adjusted pulse is used to generate a pseudo-gradation image signal. An image forming method, wherein a laser beam is generated in response to the request.

According to the present invention, the multi-valued image signal is converted into a pseudo-gradation image signal, and the width of the laser light generating pulse is adjusted so as to cancel the fluctuation in the density of the image formed on the photosensitive member. And a laser beam is generated in accordance with the pseudo-gradation image signal using the adjusted pulse.

That is, by expressing a gradation by converting a multi-valued image signal into a pseudo-gradation image signal, a change in density within one scanning line is suppressed by adjusting the width of a pulse for generating laser light. Like that.

As a result, the incident light amount and the image density of one scanning line of the photosensitive member can be kept constant without requiring a complicated circuit configuration and even when various environmental conditions change.

(2) The invention according to claim 2 is an image forming apparatus for forming an image by transferring an image on a photoreceptor formed by a laser beam from a laser light source to a transfer paper,
A gradation processing unit for converting a multi-valued image signal into a pseudo gradation image signal, a pulse width conversion unit for adjusting a pulse width of a laser beam for forming a pixel on a photoconductor, and a pulse width conversion unit for adjusting the pulse width. And a printing unit for generating a laser beam in accordance with the pseudo gradation image signal from the gradation processing unit using the generated pulse.

It is desirable that the pulse width conversion means adjusts the pulse width so as to cancel the fluctuation of the density of the image formed on the photosensitive member. Further, it is preferable that the pulse width conversion means adjusts the pulse width so that the maximum pulse width is obtained at a position where the density of an image formed on the photosensitive member is the lowest.

Further, it is desirable to adjust the pulse width by using the fluctuation of the density obtained from the image formed on the photosensitive member at the time of manufacturing the image forming apparatus. And an image forming apparatus provided with an image reading unit, wherein the image reading unit reads an image formed on the transfer paper in a state where the pulse width conversion unit has generated a constant pulse width, and changes the density of the image. It is also desirable to obtain the information of

According to the present invention, the multi-valued image signal is converted into a pseudo gradation image signal, the width of the pulse for generating laser light is adjusted, and the adjusted pulse is used to respond to the pseudo gradation image signal. To generate laser light.

That is, gradation is expressed by converting a multi-valued image signal into a pseudo gradation image signal, and a change in density within one scanning line is suppressed by adjusting the width of a pulse for generating laser light. be able to.

This makes it possible to keep the incident light amount and image density of one scanning line of the photosensitive member constant without requiring a complicated circuit configuration and even when various environmental conditions change.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings. <Structure of Image Forming Apparatus> FIG. 1 is a block diagram showing the structure of the first embodiment of the present invention. In FIG. 1, reference numeral 10 denotes a control unit as a control unit for controlling each unit of the image forming apparatus; 20, a scanner as an image reading unit;
Reference numeral 0 denotes an image processing unit as an image processing unit for executing various image processing, and reference numeral 40 denotes a printer unit as a printing unit for forming an image.

In the image processing section 30, a density change section 31 converts an input luminance signal from the scanner section 20 into a density signal, and an image memory 32 temporarily stores image data converted into the density signal. And 33, a density adjustment processing unit for adjusting the brightness of the image data by gamma conversion and converting a multi-valued image signal into a pseudo-gradation image signal by a dither method or an error diffusion method, and 34 is formed on a photoreceptor. A pulse width modulation unit as pulse width conversion means for adjusting the width of a pulse for generating a laser beam so as to cancel the density fluctuation of an image.

<Operation of Image Forming Apparatus> The operation (image forming method) of the image forming apparatus according to the present embodiment will be described below with reference to the drawings.

FIG. 2 shows a schematic configuration of a printer section 40 using a semiconductor laser (LD) 41. In this case, the amount of light on the photoconductor 43 when the image height is changed by scanning with the laser light is not constant, and density unevenness occurs at the center of the image and at the end of the image (see FIG. 3).

Therefore, the present embodiment has a function of performing pulse width modulation, and uses a recording medium (photosensitive member 43) with an image signal that has been binarized into two or more values by a dither method, an error diffusion method, or the like. ) The upper side is scanned to form a gradation image. The light amount characteristic of the light beam is detected in advance, and the light amount is controlled by changing the pulse width at the time of lighting in accordance with the output characteristic. The control is performed so that the light amount of one scanning line becomes substantially constant in the scanning direction.

As described above, the conventional correction method for the density unevenness at the center of the image and at the edge of the image has the various problems described above. In a method of forming a gradation image using an image signal in which a document image signal is pseudo-multi-valued into two or more values by a dither method, an error diffusion method, or the like, the control of the semiconductor laser is, for example, ON / OFF for binary output. The OFF control is performed. Therefore, the method of the present embodiment is to correct the light quantity at the time of light emission by changing the pulse width modulation data according to the scanning position.

Since it is necessary to correct density unevenness using pulse width modulation, the function of performing pulse width modulation in the pulse width conversion unit 34 is 6 bits (64 steps).
It is desirable that the above modulation data can be input.

In the printer section 40, the light amount characteristic on the photosensitive member 43 when the image height is changed by scanning with a laser beam is set in advance in the full lighting (maximum light emission amount) state during pulse width modulation at the time of assembling the image forming apparatus. The density characteristics are measured and normalized in (FIG. 3).

Further, from the pulse width modulation characteristic data of the semiconductor laser 41 (see FIG. 4), normalization at the time of full lighting is obtained for each pulse width. At the scanning position (the end of the photoconductor) of the minimum light amount value of the image height, the pulse width is set to the full lighting (maximum light emission),
At each scanning position, a value that is reduced from the normal ratio at the image height by a value substantially equal to the amount of decrease in the minimum amount of light (ΔD, see FIGS. 3 and 4) is determined from the pulse width modulation normalization characteristic. The width data is used (see FIG. 5). Here, FIGS. 4 and 5
In this example, the pulse width data is 8 bits (00 to FF).

As a specific example of the circuit configuration shown in FIG. 1, each pixel from the scanner unit 20 outputs a multi-valued image by error diffusion binarization in the image processing unit 30 and has a pulse width of It is assumed that a modulation 8-bit function is provided.

In this case, when assembling the image forming apparatus,
An image is formed in a pulse width modulation fully lit state (in this example, FF), the formed image is read by the scanner unit 20, and density characteristic data (scanning line light amount characteristic data) is obtained from the image read by the scanner unit 20. Are obtained by the control unit 10 as shown in FIG.

FIG. 4 shows a state where the pulse width modulation characteristic data is normalized at the time of full lighting. Here, as shown in FIG.
The pulses at the image heights -a and + a (the end of the photoconductor) having the minimum light amount Pmin are set as the FFs of all lighting, and the maximum light amount Pma
The pulse at the image height 0 (center of the photoconductor), which is x, is F0
And Then, the pulse data at each position between the maximum and the minimum is determined in proportion to the pulse data. In this way, the correction data for the pulse width adjustment is obtained and stored in a memory or a table inside or outside the control unit 10.

For the binary error diffusion signal generated by the image memory 32 and the density adjustment processing section 33, the pulse width conversion section 34 corrects the pulse width correction data corresponding to the scanning position (image height). Multiply. That is, the control unit 10 supplies the pulse width conversion unit 34 with the correction data corresponding to the scanning position.

That is, at the center of the photoconductor, the dots forming one pixel are small, and at the end of the photoconductor, the dots forming one pixel are slightly larger.
By generating the laser light while adjusting the pulse width for generating the laser light, the density unevenness is suppressed as a result. By performing a kind of pulse width modulation to suppress density unevenness in this manner, the amount of one scanning line on the recording medium becomes constant in the main scanning direction. The correction data may be held in the pulse width conversion unit 34, and the pulse width may be corrected based on the clock count and the index signal.

That is, the multi-valued image signal is converted into a pseudo-gradation image signal such as dither or error diffusion to express gradation, and the width of a pulse for generating laser light is adjusted to perform one scanning line. The density change in the inside is suppressed.
This makes it possible to keep the incident light amount and image density of one scanning line on the photosensitive member constant without requiring a complicated circuit configuration and even when various environmental conditions change. Further, according to this method, it is possible to form a good pseudo-tone image without density unevenness without requiring an expensive dedicated ASIC as in the conventional method.

<Other Embodiments> In the above-described embodiment, the case where the scanning line light amount characteristic uses the light amount characteristic data at the time of assembling the image forming apparatus has been described, but the present invention is not limited to this. Absent. That is, the scanner unit 20 may read the image formed when a certain number of images have been formed or when a certain time has elapsed, and create the scanning line light amount characteristic data.

Also, instead of using the scanner unit 20,
A plurality of sensors may be provided in the vicinity of the photoreceptor of the printer unit 40, and the scanning line light amount characteristic data may be obtained from the photoreceptor before transfer to the transfer paper.

Further, since the light amount characteristic or the density unevenness characteristic on the photoreceptor in the above-described embodiment is an example, correction may be performed in accordance with the characteristic of each device actually obtained by measurement.

[0041]

As described above, according to the present invention, the following effects can be obtained.

(1) In the image forming method according to the first aspect, a multi-level image signal is converted into a pseudo-gradation image signal so as to cancel the fluctuation of the density of the image formed on the photosensitive member. Then, the width of the laser light generation pulse is adjusted, and the adjusted pulse is used to generate the laser light in accordance with the pseudo gradation image signal. That is, the multi-level image signal is converted into a pseudo-gradation image signal to perform gradation expression, and the width of a laser light generation pulse is adjusted to suppress a density change in one scanning line. I have. This makes it possible to keep the incident light amount and image density of one scanning line of the photosensitive member constant without requiring a complicated circuit configuration and even when various environmental conditions change.

(2) In the image forming apparatus according to any one of claims 2 to 6, the multi-valued image signal is converted into a pseudo gradation image signal, and the width of the laser light generating pulse is adjusted. Then, a laser beam is generated according to the pseudo gradation image signal using the adjusted pulse.

That is, gradation expression is performed by converting a multi-level image signal into a pseudo gradation image signal, and a change in density within one scanning line is suppressed by adjusting the width of a pulse for generating a laser beam. be able to. As a result, even if various environmental conditions change without requiring a complicated circuit configuration,
It is possible to make the incident light amount and image density of one scanning line of the photoconductor constant.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a perspective view showing a main part of the optical system according to the embodiment of the present invention.

FIG. 3 is a characteristic diagram illustrating a state of an exposure amount on a photoconductor of the image forming apparatus.

FIG. 4 is a characteristic diagram showing pulse width conversion characteristic data according to the embodiment of the present invention.

FIG. 5 is a characteristic diagram illustrating an example of a relationship between a scanning position and pulse width data according to the embodiment of the present invention.

FIG. 6 is a perspective view illustrating an example of an optical system of the image forming apparatus.

[Explanation of symbols]

 Reference Signs List 10 control unit 20 scanner unit 30 image processing unit 31 density change unit 32 image memory 33 density adjustment unit 34 pulse width conversion unit 40 printer unit

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2C362 CA01 CA08 CA09 5C072 AA03 BA17 HA02 HA13 HB04 HB08 XA01 XA05 5C074 AA09 BB03 BB26 CC26 DD07 EE02 EE11 FF08 GG12 GG19 5C077 LL04 LL17 NN08 NN11 SS 03 NN17

Claims (6)

[Claims] 1. An image forming method for forming an image by transferring an image on a photoreceptor formed by a laser beam from a laser light source to a transfer sheet, wherein the multi-level image signal is converted into a pseudo gradation image signal. Adjust the pulse width of the laser light generation pulse so as to cancel the fluctuation of the density of the image formed on the photoconductor, and generate the laser light according to the pseudo gradation image signal using the adjusted pulse. An image forming method. 2. An image forming apparatus for forming an image by transferring an image on a photoreceptor formed by a laser beam from a laser light source to a transfer sheet, wherein the multi-level image signal is converted into a pseudo gradation image signal. Gradation processing means, pulse width conversion means for adjusting the width of a pulse of laser light for forming a pixel on the photoreceptor, and using the pulse adjusted by the pulse width conversion means, An image forming apparatus, comprising: printing means for generating a laser beam according to a pseudo gradation image signal. 3. The image forming apparatus according to claim 2, wherein the pulse width conversion unit adjusts a pulse width so as to cancel a change in density of an image formed on the photosensitive member. 4. The apparatus according to claim 3, wherein the pulse width conversion unit adjusts the pulse width so that the maximum pulse width is obtained at a position where the density of an image formed on the photosensitive member is the lowest. The image forming apparatus as described in the above. 5. The image forming apparatus according to claim 3, wherein the pulse width is adjusted by using a change in density obtained from an image formed on the photosensitive member at the time of manufacturing the image forming apparatus. 6. An image forming apparatus provided with image reading means, wherein an image formed on transfer paper is read by said image reading means in a state where said pulse width conversion means generates a constant pulse width, The image forming apparatus according to claim 3, wherein information on a change in density is obtained.