JPH04371860A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of an image caused by a breakage per light emitting element to extend the life of total light emitting elements. CONSTITUTION:An LED array 3 has an element density higher than the density of image data to be written. A plurality of LED elements are available for writing image data for one pixel. In addition, a light emitted from one LED element is adjusted by an image forming member 2 so that the area for a plurality of elements can be exposed to the light on a photosensitive body 1. Image data for one dot is recorded using a part of a plurality of LED elements, e.g. two of three elements. Light emitted from the LEDs is reflected by a spread mirror 5, and the intensity of the light is detected by a light emission detector 4. If abnormal elements exist, the elements are changed over to normal elements. Therefore, the array is improved in life, and the writing function as an array is not deteriorated even if a part of the elements is broken.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a digital copying machine or a printer that forms an image by exposing an image carrier to light using an exposure means based on input image data.

0002

2. Description of the Related Art: Processing is performed to create written image data based on image data taken in from an input device, and an electrostatic latent image is created by exposing a pre-charged photoreceptor to light based on the written image data. Some image forming apparatuses that form a visible image by attaching toner to the image forming apparatus use a light emitting diode element array as a means for exposing the photoreceptor. Compared to the method of scanning and writing with a single laser beam using a laser optical system, the method using a light emitting diode element array enables high-speed printing, facilitates wide printing, and saves the writing section. It has advantages such as being able to be made into a space.

On the other hand, a light emitting diode array consists of a large number of light emitting diode elements lined up in the width direction of the print, and if even one of these light emitting diode elements fails to emit light, that part will not be exposed and will become white. Streaks or black streaks occur and the entire array must be replaced. Furthermore, the lifespan of a light emitting diode is generally determined by its lighting time, and the lifespan of a light emitting diode array is determined by the lifespan of the light emitting diode element with the longest total lighting time. Therefore, in order to extend the life of the array, it is necessary to shorten the lighting time per element as much as possible. To this end, in the prior art, it has been proposed to move the light emitting diode array in the direction of the rotation axis of the photoreceptor. However, when this method is used, it is difficult to achieve positional accuracy for movement, and the structure of the machine becomes complicated.

0004

[Problems to be Solved by the Invention] The present invention solves the above-mentioned problems in the prior art, makes it easy to maintain positional accuracy without moving the light emitting elements arranged in an array, and prevents images due to damage as a unit of light emitting elements. An object of the present invention is to provide an image forming apparatus in which deterioration of the light emitting element is prevented and the life of the light emitting element as a whole is extended.

[0005]

[Means for Solving the Problems] In order to solve the above problems, the invention of claim 1 provides an image forming method in which an image is formed by exposing an image carrier to light using an exposure means based on input image data. In the apparatus, the exposure means includes light emitting elements arranged in an array in the main scanning direction, the light emitting elements are arranged at a higher density than the pixel density of the input image data, and a plurality of light emitting elements are arranged for one pixel of the input image data. The invention is characterized in that a light-emitting element is made to be capable of emitting light, and a part of the plurality of light-emitting elements is made to emit light, and in addition to the above, the invention is characterized in that when an abnormality occurs in the light-emitting element, It is characterized by comprising an abnormality detection means for detecting this, and a control means for controlling a light emitting element that is not emitting light among the plurality of light emitting elements to emit light when the abnormality detecting means detects an abnormality. shall be.

[0006]

According to the first aspect of the invention, the light emitting elements are arranged in an array in the main scanning direction at a density higher than the pixel density of the input image data, and a plurality of light emitting elements are arranged for one pixel of the input image data. Since some of them are enabled to emit light, the light emitting elements can be used alternately and the light emitting time per element can be shortened.

According to the second aspect of the invention, when the detection means detects an abnormality in the light emitting element, the control means controls the light emitting elements to emit light from among the plurality of light emitting elements that are not emitting light. Even if the light emitting element is damaged, the writing function of the light emitting element as a whole is not impaired.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of an exposure section of an image forming apparatus according to an embodiment of the present invention. Drum-shaped photoreceptor 1 as an image carrier
Scanning light emitted from an LED array 3 as a group of light emitting elements arranged in an array is imaged on the surface of the image forming member 2 via the imaging member 2 . The LED array 3 emits light in accordance with written image data processed based on image data captured from an input device (not shown). Note that photoreceptor 1
The upper part is charged in advance by a charging means (not shown).

An electrostatic latent image corresponding to the written image data is formed on the exposed photoreceptor 1, and then developed with toner and transferred by various devices (not shown) according to a normal image forming process. An image is formed through various steps such as transfer onto paper and fixing of the toner image.

In the exposure section of such an image forming apparatus, the LED array 3 used for writing has an element density greater than the density of image data to be written, and a plurality of LED arrays 3 are used for writing.
The D element can be used to write one pixel of image data. Furthermore, the light emitted from one LED element is directed to the imaging member 2 so as to expose an area corresponding to a plurality of elements on the photoreceptor.
is adjusted.

That is, one LED element is adjusted to expose a wider area in the axial direction of the photoreceptor than the size of each LED element constituting the LED array through the imaging member 2.

[0012] By doing this, it is possible to use a plurality of LED elements to write one pixel of image data and form an image by combining them. A portion of the element is used for writing to form an image. As a result, compared to the case where all the elements are used all the time, the lighting time per element is shortened and the life of the array is increased, and even if some elements are damaged, the writing function of the array is not impaired. Furthermore, by alternately switching the LED elements used, the lifespan of the LED elements can be extended on average.

FIG. 2 further shows an example of the configuration of the exposure section. Reference numeral 1 denotes a drum-shaped photoreceptor, 2 an imaging member for forming an image of light emitted from an LED on the photoreceptor, and 3 an LED array, which are also shown in FIG. Furthermore, 4 is a light emission detector, 5 is a spread mirror, and 6 is a member that images the light emitted from the LED on the light emission detector 4.

In this embodiment, a 1200 dpi LED array 3 is used to form an image with a data density of 400 dpi. Also, the density of the light receiving element of the light emission detector 4 is 1200 dp.
i, so that there is a one-to-one correspondence with the light emitting element of the LED. Since the data is 400 dpi compared to the writing density of 1200 dpi, one dot of image data is recorded with three LED elements each. The light emitted from the two adjacent elements passes through the imaging member 2 and is focused onto the photoreceptor 1. The beam diameter when the light is focused is approximately 63 μm in the axial direction of the photoreceptor and approximately 63 μm in the direction of rotation of the photoreceptor. It is approximately 20 μm.

Under normal operating conditions, two of the three adjacent elements
Exposure is performed using one. For this reason, the power of one LED element is adjusted so that the power of two LED elements is sufficient for image formation. The light emission state of the LED is detected by the light emission detector 4 and fed back to the switching section of the LED array. In this detection method, the light emitted from the LED is reflected by a spread mirror 5, and the light intensity is detected by a light emission detector 4. Based on the fed-back data, the switching section is controlled to perform exposure using only the LED elements that are normally emitting light.

FIG. 3 shows an example of the basic circuit configuration of the LED array 3. Image data is input from an image input device (not shown), passes through an image processing section (not shown), and is stored in the image memory 7.
is stored in The pixel clock is supplied to a counter 8 and a shift register 9.

The counter 8 receiving the clock performs a process of issuing a reset R signal in response to the input density data of the density of the image data and the density of the LED array 3 for writing. In this embodiment, the density of the LED array 3 is 1200d.
On pi, the density of the image data you are trying to write is 400d.
The case where pi is constant is shown. In this case, the counter 8 outputs a reset R signal to the image memory 7 every three clocks.

The image memory 7 updates the image data every time the reset R signal is received from the counter 8, and holds the output value at the previous state until the next reset signal is input. On the other hand, data is taken into the shift register 9 from the image memory 7 in accordance with the image clock, so that the same data is input for every three pixels.

When the input to the shift register 9 is completed, the output of the write data is started. A power supply current En corresponding to the lighting time is supplied to the current amplification section. The lighting time and the on/off timing of the power supply current are determined by a lighting time determining section (not shown) according to the density of image data.

FIG. 4 shows the switching section. An LED element that emits light is selected by turning on/off the current supplied to the rectifier. This selection is performed by the determination unit 10 as a control means. That is, the determining section 10 determines which element is defective in emitting light based on the signal from the light emitting detector 4 as an abnormality detecting means, and based on the determination, a normal element among the three elements is turned on. In this embodiment, L corresponding to one image data is
There are three ED elements, and these are A, B, and C. Under normal conditions, the setting is such that exposure is performed by two elements A and B, and if an abnormality is discovered in either element, the , A and B, whichever is normal, and C are used for exposure.

FIG. 5 is a timing chart showing the operation in this case. The density of writing LED array 3 is 12
At 00dpi, the density of the image data you are trying to write is 4.
This is the case of 00dpi. The pixel clock is counter 8
The counter 8 determines the timing for updating the image data. As shown in the figure, an update signal R is output to the pixel memory 7 after receiving the clock three times, and the image data is updated as shown. The shift register 9 stores M serial data and outputs parallel data.

When writing of M pieces of data to the shift register is completed, writing to the LED array 3 starts, and the LED array 3 is turned off by a signal S sent from a write timer (not shown). The write timer is set to write time equivalent to 400 dpi. That is, assuming the speed is constant, the lighting time is three times the writing time at 1200 dpi.

FIG. 6 shows the circuit configuration of another embodiment. In this embodiment, the LED element of the writing section has a density of 1200 dpi, and the density of image data is 300 dpi. Each LED element is operated as a group of four elements. The selector 11 receives the non-lighting signal from the non-lighting signal generating section 12 and the image signal from the image memory 7. Then, one of the two signals is selected and sent to the shift register 9 according to the signal inputted from the counting section 13. The shift register 9 and the light emitting elements have a one-to-one correspondence, and as a result, image data and a non-lighting signal are latched at two addresses in the shift register corresponding to the four elements. On the other hand, the signal output from the counting unit 13 follows the rules, and when selecting two elements from four LED elements capable of exposing one pixel of image data,
This is done so that the frequency of use of each element is averaged.

As to which of the four elements to use, there are methods such as interchanging every line in one frame of image, interchanging every frame, and interchanging every certain number of images. In the example, a method is used in which the sheets are mixed every set number of sheets.

[0025]

As described above, according to the present invention, in the invention of claim 1, the light emitting elements are arranged in an array in the main scanning direction at a density higher than the pixel density of the input image data. Since multiple light-emitting elements are made to correspond to each pixel so that some of them emit light, the light-emitting elements can be used alternately, and the amount of light emitted per element is reduced compared to when all the light-emitting elements are used all the time. It is possible to shorten the time and extend the life of the light emitting element as a whole.

In the invention of claim 2, when the detecting means detects an abnormality in the light emitting element, the control means controls the light emitting element to emit light from among the plurality of light emitting elements that are not emitting light. Even when the light emitting element is damaged, the write function of the entire light emitting element can be maintained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an exposure section of an image forming apparatus according to an embodiment.

FIG. 2 is an explanatory diagram of the above image writing section.

FIG. 3 is a circuit diagram showing an example of a light emitting circuit of an LED array.

FIG. 4 is a circuit diagram of a switching section of an LED array.

FIG. 5 is a timing chart showing the operation of the light emitting circuit of the LED array.

FIG. 6 is a light emitting circuit diagram of an LED array according to another embodiment.

[Explanation of symbols]

1 Photoreceptor (image carrier) 3 LED array (light emitting elements arranged in an array)
4 Light emission detector (abnormality detection hand) 8 Counter 9 Shift register 10 judgment section

Claims (2)

[Claims] 1. An image forming apparatus that forms an image by exposing an image carrier to light using an exposure unit based on input image data, wherein the exposure unit includes light emitting elements arranged in an array in a main scanning direction, The light emitting elements are arranged at a higher density than the pixel density of the input image data, and a plurality of light emitting elements correspond to one pixel of the input image data so as to be able to emit light;
An image forming apparatus characterized in that some of the plurality of light emitting elements emit light. 2. Abnormality detection means for detecting an abnormality when an abnormality occurs in the light emitting element; and when the abnormality detection means detects an abnormality, a light emitting element that is not emitting light among the plurality of light emitting elements is detected. The image forming apparatus according to claim 1, further comprising a control means for controlling the light to emit light.