Patent Grant
7215348
The present invention relates to an image forming apparatus and an image forming method which are directed to simplify the circuit structure and to speed up the light emitting control during exposure of pixels on an image carrier in multiple exposure manner capable of outputting gradation.
In conventional image forming apparatus in which a latent image is written on an image carrier, it is known to employ an LED (light emitting diode) array as writing means. In case of employing light emitting elements such as an LED, it is necessary to pay attention to the relation between the luminance (amount of light) and the life duration of each light emitting element. That is, the life duration can be increased by reducing the luminance of the light emitting element. In this case, however, there is a problem that the amount of light for exposure is insufficient to form image. When the luminance of the light emitting element is increased, enough amount of light for exposure for forming image is obtained. In this case, however, there is a problem that the life duration is shortened.
For this, the development of material for obtaining light emitting elements capable of providing large luminance and having long life duration has been encouraged. However, in the present state of affairs, it is too expensive to achieve the practical use. In this connection, a line head (optical head) of multiple exposure type in which each pixel is exposed by a plurality of light emitting elements has been developed. As an example (1) of such line heads of multiple exposure type, Japanese Patent Unexamined Publication No. S61-182966 discloses a recording array head on which light recording elements are aligned in a plurality of rows in the rotational direction of a photoreceptor drum. An image data is overlappingly recorded at the same pixel by shifting the light emitting recording elements in the direction of the rows with moving the photoreceptor drum. The example (1) has an advantage that higher speed image formation is achieved even using light recording elements with low light-emitting output.
Another example (2) is disclosed in Japanese Patent Unexamined Publication No. S64-26468 in which an EL element panel is composed of EL element group of 20 dots×640 dots (vertical×horizontal). The EL element group is driven at a speed same as the moving speed of a photoreceptor for every line. Accordingly, the amount of light irradiated on a single pixel is twentyfold the amount of light emitted from each EL element. This example also can cope with high speed of image formation because the amount of light of exposure per pixel is increased.
Another example (3) is disclosed in Japanese Patent Unexamined Publication No. H11-129541 and is a print head on which LEDs are aligned in a plurality of lines such that multiple exposure is made on each pixel by moving the print head in the main scanning direction. In this example, since the multiple exposure is conducted, variations in amount of light among the respective LEDs can be equalized, thereby improving the image quality. Still another example (4) is disclosed in Japanese Patent Unexamined Publication No. 2000-260411 and is an optical printer head on which plural lines of LED array chips are aligned. The gradation of each pixel can be changed among three levels by turning ON or OFF the LED array chips on each line.
The aforementioned examples (1) and (2) relate to a technology of monochrome image formation and therefore have a problem that gradation control for neutral density is impossible. The example (3) relates to a technology of a serial type in which the line head is driven and therefore has a problem of having a complex driving mechanism. The example (4) relates to a technology in which the LED array chips on each line are turned ON and OFF and therefore has a problem of complexity of the control circuit.
Since the number of light emitting elements in the line head of multiple exposure type are greater than that of a line head of normal exposure type and it is necessary to control the light emitting elements synchronously with the movement of the photoreceptor, there is a problem of complexity of the control circuit for conducting the data processing and it is therefore difficult to achieve higher speed light emitting control. Especially, in case that a line head (optical head) of multi-exposure type is employed for color image formation, the amount of data to be processed must be severalfold that in the case of ON-OFF control because the gradation control for each pixel is sometimes required. This makes the speeding up of emission control further difficult. In case of line head of multiple exposure type, it is required to send a large amount of data processed by a data processing unit to the line head, thus increasing the number of wires between the line head and the body of an image forming apparatus. Accordingly, it is necessary to employ an interface capable of supporting the high-speed processing, thus increasing the cost.
The present invention was made in view of the aforementioned problems of conventional techniques and the object of the present invention is to provide an image forming apparatus and an image forming method which are directed to simplify the circuit structure and to speed up the light emitting control during the exposure of pixels on an image carrier in multiple exposure manner capable of outputting gradation.
A first image forming apparatus of the present invention achieving the aforementioned object is an image forming apparatus in which a plurality of lines each having a plurality of light emitting elements are arranged to have rows in a sub scanning direction of an image carrier so that light emitting elements are arranged in a matrix in a plane, wherein pixels on said image carrier are exposed by the light emitting elements aligned in one line and exposed again by the light emitting elements aligned in the next line after the movement of said image carrier, and in the same manner, said pixels are sequentially exposed by the light emitting elements on another line after the movement of said image carrier so as to achieve multiple exposure of the pixels. The first image forming apparatus is characterized by comprising control means by which said light emitting elements on respective lines for exposing same pixels are driven by a TFT so as to emit a same amount of light, so that the pixels can be exposed according to gradation output formed by said control means.
The first image forming apparatus of the present invention is characterized by comprising storage means for storing image data formed by said control means and outputting said image data to said light emitting elements, wherein said storage means is composed of multiple shift resistors which are arranged to correspond to the lines of the light emitting elements arranged in the sub scanning direction, respectively and are designed to transport image data, hold the image data, and output the image data to the light emitting elements, wherein the image data supplied to the shift resistor on the first line is transmitted in the main scanning direction and is also transmitted in the sub scanning direction to the shift resistor on a next line, and, in this manner, the image data is sequentially transmitted in the sub scanning direction to the shift resistors on the respective lines so that the image data is outputted to the light emitting elements on each of lines corresponding to the shift resistors, respectively. The first image forming apparatus is further characterized in that there are lines of pixels to be exposed and lines of pixels not to be exposed on said image carrier, the light emitting elements on the respective lines are arranged to correspond to the lines of pixels to be exposed, respectively, said storage means are arranged to correspond to both the lines of pixels to be exposed and the lines of pixels not to be exposed, respectively, and the storage means corresponding to the lines of pixels not to be exposed do not output said image data.
Furthermore, the first image forming apparatus of the present invention has the following characteristics with regard to said light emitting elements: (1) the interval in the sub scanning direction between spot positions formed on the image carrier by the light emitting elements is an integral multiple of the pixel pitch in the sub scanning direction; (2) the light emitting elements are controlled by a driving circuit according to the active matrix method; (3) the amounts of light of the light emitting elements are controlled in the PWM method; (4) the amounts of light of the light emitting elements are controlled in the intensity modulation method; and (5) each of the light emitting elements comprises an organic EL.
The first image forming apparatus of the present invention is still further characterized in that the image forming apparatus is of a tandem type which comprises at least two image forming stations each having an image carrier and further having a charging means, an exposure head, a developing means, and a transfer means which are arranged around said image carrier and forms a color image by passing a transfer medium through the respective stations.
In the first image forming apparatus of the present invention, once the control means forms data for the first one line, the operations of all of light emitting elements in the line head can be controlled by storing the image data for the first one line in the storage means (shift resistors) and just transmitting the image data among the storage means. Therefore, the control means is not required to produce data for all light emitting elements of the line head, thereby simplifying the structure of circuit and achieving the high-speed data processing.
In the first image forming apparatus of the present invention, the storage means for pixel lines and the light emitting element lines can be arranged to correspond to each other. In this case, the timing for transmitting image data stored in a storage means to the next storage means and the timing for making light emitting elements in the line to emit light on the basis on the image data for a pixel line stored in the storage means can be synchronized, thereby simplifying the circuit structure and speeding up the operation of the light emitting element lines.
Further, in the first image forming apparatus of the present invention, the light emitting elements are controlled according to the active matrix method. Accordingly, the light emitting elements can be maintained to keep emitting light by means of condensers and transistors arranged around the light emitting elements. Therefore, the light emitting elements remain to emit light even during the transmission of image data from a storage means to the next storage means, thereby exposing pixels with high luminance.
In addition, in the first image forming apparatus of the present invention, the amount of light emitted from the light emitting elements is controlled in the PWM method. Since the amount of exposure can be changed by ON/OFF control of the light emitting elements, the circuit structure can be simplified. Moreover, in the first image forming apparatus of the present invention, the amount of light emitted from the light emitting elements is changed in the intensify modulation method. Therefore, it is not required to control the ON/OFF of the light emitting elements at a high speed. Even when the speed of response of the light emitting elements is slow, the amount of exposure can be changed at a high speed. In addition, in the first image forming apparatus of the present invention, the light emitting elements can be easily formed on a glass substrate, thereby achieving lower price.
A first image forming method of the present invention achieving the aforementioned object is an image forming method using a plurality of lines each of which has a plurality of light emitting elements to be controlled by a TFT and which are arranged to have rows in the sub scanning direction of an image carrier and using multiple shift resistors which are adapted to transport image data formed by control means, hold the image data, and output the image data to the light emitting elements, which are arranged to correspond to the lines of the light emitting elements, respectively. The first image forming method is characterized by comprising supplying image data to the shift resistor on a first row and transmitting the image data in the main scanning direction, actuating the light emitting elements on a first line to expose pixels on the image carrier to light according to the image data outputted from the shift resistor of the first line, moving the image carrier for a pixel pitch, transmitting the image data from the shift resistor on the first row to the shift resistor on the next row in the sub scanning direction synchronously with the movement of the image carrier in timing, actuating the light emitting elements on a next line to emit a same amount of light as that of the light emitting elements on the former line to repeatedly expose said pixels, and sequentially transmitting the image data in the sub scanning direction at the shift resistor for the respective lines with moving of the image carrier for the pixel pitch, so that said pixels are subjected to multiple exposure by the light emitting elements on the respective lines. The first image forming method is characterized by further comprising a step of actuating the light emitting elements according to the gradation output formed by said control means to expose the pixels.
A second image forming apparatus of the present invention achieving the aforementioned object is an image forming apparatus in which a plurality of lines each having a plurality of light emitting elements are arranged to have rows in the sub scanning direction of an image carrier so that light emitting elements are arranged in a matrix in a plane, wherein pixels on said image carrier are exposed by the light emitting elements aligned in one line and exposed again by the light emitting elements aligned in the next line after the movement of said image carrier, and in the same manner, said pixels are sequentially exposed by the light emitting elements on another line after the movement of said image carrier so as to achieve multiple exposure of the pixels. The second image forming apparatus is characterized by comprising storage means for storing information of misalignment of the mounted position of the line head relative to the apparatus, light emitting elements for adjusting the image position which are preliminarily arranged in respective lines of said line head, and control means for inserting blank data to the image data for every line of the light emitting elements corresponding to the misalignment so as to form image in normal position by correcting said misalignment of the mounted position of the line head according to the information of misalignment of the mounted position of the line head.
According to the second image forming apparatus, it is not required to mechanically correct the misalignment of image forming portions. That is, the misalignment in image formed by image forming portions can be corrected by controlling the positions where image data are written, thereby eliminating the mechanical adjustment. Therefore, the misalignment in image can be easily corrected in the line head for conducting multiple exposure.
A third image forming apparatus of the present invention achieving the aforementioned object is an image forming apparatus comprising line heads in which a plurality of light emitting elements are arranged in a matrix in a plane to form a plurality of unicolor images to be superposed on each other, storage means for storing information of misalignment of the mounted position of the line head relative to the apparatus, and control means for inserting blank data to the image data for every line of the light emitting elements corresponding to the misalignment so as to form image in normal position by correcting said misalignment of the mounted position of the line head according to said stored information of misalignment of the mounted position of the line head.
According to the third image forming apparatus of the present invention, even when the mounted position of one of line heads is shifted from the normal position in an image forming apparatus for forming a color image, the misalignment in image can be easily corrected without moving the position of the line head.
Further, the third image forming apparatus is characterized in that the image forming apparatus is of a tandem type which comprises at least two image forming stations each having an image carrier and further having a charging means, an exposure head, a developing means, and a transfer means which are arranged around said image carrier and forms a color image by passing a transfer medium through the respective stations. According to the third image forming apparatus of the present invention, in an image forming apparatus of a tandem type, the misalignment in image can be easily corrected.
A second image forming method of the present invention achieving the aforementioned object is an image forming method using a plurality of lines each of which has a plurality of light emitting elements and which are arranged to have rows in the sub scanning direction of an image carrier and using storage means, designed to transport image data formed by control means, hold the image data, and output the image data to the light emitting elements, which are arranged to correspond to the lines of the light emitting elements, respectively. The second image forming method is characterized by comprising a step of preliminarily arranging light emitting elements for adjusting the image position respective lines of said line head, a step of storing information of misalignment of the mounted position of the line head relative to the apparatus, a step of inserting blank data to the image data for every line of the light emitting elements corresponding to the misalignment so as to form image in normal position by correcting said misalignment of the mounted position of the line head according to said stored information of misalignment of the mounted position of the line head, a step of actuating the light emitting elements on the first line to expose pixels on the image carrier according to the image data outputted from the storage means, a step of moving the image carrier for a pixel pitch, a step of transmitting the image data to the storage means for the next line synchronously with the movement of the image carrier in timing, and a step of actuating the light emitting elements on the next line to emit the same amount of light as that of the light emitting elements on the former line to repeatedly expose said pixels. Further, the second image forming method is characterized by further comprising a step of actuating the light emitting elements according to the gradation output formed by said control means to expose the pixels.
A fourth image forming apparatus of the present invention achieving the aforementioned object is an image forming apparatus comprising a line head in which a plurality of lines each having a plurality of light emitting elements aligned in the main scanning direction are arranged to have rows in the sub scanning direction of an image carrier so that light emitting elements are arranged in a matrix in a plane, wherein pixels on said image carrier are exposed by the light emitting elements aligned in one line and exposed again by the light emitting elements aligned in the next line after the movement of said image carrier, and in the same manner, said pixels are sequentially exposed by the light emitting elements on another line after the movement of said image carrier so as to achieve multiple exposure of the pixels. The fourth image forming apparatus is characterized by comprising storage means for storing information of tilt of the line head relative to the main scanning direction, image data supplying means for supplying image data to the respective light emitting elements, delaying means for delaying the timing of supplying image data from said image data supplying means to the light emitting elements, and control means for conducting delay control to the image data to be supplied from said delaying means to light emitting elements according to said information of tilt in such a manner that the position of image formation corresponding to pixels on the image carrier is corrected from the tilt of the line head.
The fourth image forming apparatus is characterized in that the image forming apparatus is of a tandem type which comprises at least two image forming stations each having an image carrier and further having a charging means, an exposure head, a developing means, and a transfer means which are arranged around said image carrier and forms a color image by passing a transfer medium through the respective stations.
The fourth image forming apparatus conducts the following delay control in order to correct the tilt of the line head: (1) the light emitting elements are divided into a plurality of blocks and the delay control is conducted to image data to be supplied to said light emitting elements for every block; (2) a plurality of said line heads are arranged to correspond to different colors, respectively, and the light emitting elements of the line head which is tilted is subjected to said delay control during multiple exposure in which the respective colors are superposed on each other; and (3) among said plurality of light emitting element lines, the first light emitting element line is controlled with a delay control signal for correcting the tilt of said line head and the light emitting element lines including and after the second light emitting element line are controlled with signals formed by adding signal corresponding to the timing shift from the former light emitting element line to the aforementioned delay control signal for the front light emitting element line.
The storage means in the fourth image forming apparatus of the present invention has the following characteristics: (1) the storage means is disposed in the apparatus body; (2) the storage means is disposed in a cartridge in which the line head is arranged; (3) the storage means is disposed in the line head.
The light emitting elements in the fourth image forming apparatus of the present invention have the following characteristics: (1) said light emitting elements are controlled by a driving circuit according to the active matrix method; (2) the amounts of light of said light emitting elements are controlled in the PWM method; (3) the amounts of light of said light emitting elements are controlled in the intensity modulation method; and (4) each of said light emitting elements comprises an organic EL.
In the fourth image forming apparatus of the present invention, if the line heads are installed to the apparatus such that one or more of the line heads is tilted relative to the main scanning direction, the misalignment in image is corrected by controlling the positions where the image data are written, thereby eliminating the mechanical adjustment. Therefore, the misalignment in image can be easily corrected in the line head for conducting multiple exposure.
Further, in the fourth image forming apparatus, since the delay control is conducted for every block, the circuit structure can be simplified as compared to the case in which the delay control is conducted for every light emitting element. Since the delay control is conducted during multiple exposure, in case of forming an image formed by superposing a plurality of colors, the fourth image forming apparatus can form the image without color registration error. Since the light emitting element are controlled with signals formed by adding signal corresponding to the timing shift between the light emitting element lines, the control for light emitting elements can be simplified as compared to the case in which delay timings are set for all of the light emitting element lines.
In the fourth image forming apparatus of the present invention, since storage means for storing information of tilt of line head relative to the main scanning direction is disposed in the apparatus body, even when the line head is out of order for any reason, the tilt information of the line head can be securely maintained. Since the storage means is disposed in the cartridge to which the line head is mounted, the storage means can be replaced with a new storage means storing information corresponding to the tilt of new line heads automatically at the same time as the replacement of the cartridge. Since the storage means is disposed in the line head, after the replacement of the line head, the control for light emitting elements can be conducted according to the tilt information of a new line head.
Further, in the fourth image forming apparatus of the present invention, since the light emitting elements are controlled by a driving circuit according to the active matrix method, the light emitting elements can be maintained to keep emitting light by means of condensers and transistors arranged around the light emitting elements. Therefore, the light emitting elements remain to emit light even during the transmission of image data from a shift resistor to the next shift resistor, thereby exposing pixels with high luminance. In addition, the fourth image forming apparatus of the present invention is characterized in that the amounts of light emitted from the light emitting elements re controlled in the PWM method. Since the amount of exposure can be changed by ON/OFF control of the light emitting elements, the circuit structure can be simplified. Moreover, the amounts of light emitted from the light emitting elements are controlled in the intensify modulation method. Therefore, it is not required to control the ON/OFF of the light emitting elements at a high speed. Even when the speed of response of the light emitting elements is slow, the amount of exposure can be changed at a high speed. In addition, each of the light emitting elements comprises an organic EL. Therefore, the light emitting elements can be easily formed on a glass substrate, thereby achieving lower price.
Further, the fourth image forming apparatus is adopted to an image forming apparatus of a tandem type which comprises at least two image forming stations each having an image carrier and further having a charging means, an exposure head, a developing means, and a transfer means which are arranged around said image carrier and forms a color image by passing a transfer medium through the respective stations. Accordingly, in the image forming apparatus of a tandem type, the misalignment in image can be easily corrected.
A fifth image forming apparatus of the present invention is an image forming apparatus comprising a line head in which a plurality of lines each having a plurality of light emitting elements aligned in the main scanning direction are arranged to have rows in the sub scanning direction of an image carrier so that light emitting elements are arranged in a matrix in a plane, wherein pixels on said image carrier are exposed by the light emitting elements aligned in one line and exposed again by the light emitting elements aligned in the next line after the movement of said image carrier, and in the same manner, said pixels are sequentially exposed by the light emitting elements on another line after the movement of said image carrier so as to achieve multiple exposure of the pixels.
The fifth image forming apparatus being characterized by comprising storage means for storing information of tilt of the line head relative to the main scanning direction, and control means for controlling light emitting elements which protrude from the normal exposure line, among light emitting elements aligned in the sub scanning direction of said line head, to emit smaller amount of light and controlling the image data to be supplied to light emitting elements in such a manner that the position of image formation corresponding to the pixels on the image carrier is corrected from the tilt of the line head.
In the fifth image forming apparatus of the present invention, since the control means for controlling light emitting elements which protrude from the normal exposure line to emit smaller amount of light and controlling the image data to be supplied to light emitting elements in such a manner that the position of image formation corresponding to the pixels on the image carrier is corrected from the tilt of the line head is provided, outlines of pixels which are adjacent to each other in the main scanning direction can be clearly formed, thus preventing the deterioration of printing quality.
A third image forming method of the present invention achieving the aforementioned object is an image forming method using a line head in which a plurality of light emitting element lines each having a plurality of light emitting elements aligned in the main scanning direction are arranged in a matrix in a plane to have rows in the sub scanning direction of an image carrier so that pixels on the image carrier are repeatedly exposed by light emitting elements on the respective lines to achieve the multiple exposure. The third image forming method is characterized by comprising a step of storing the information of tilt of said line head relative to the main scanning direction and a step of controlling the image data to be supplied to light emitting elements by delaying the supply timing in such a manner that the position of image formation corresponding to the pixels on the image carrier is corrected from the tilt of the line head.
According to the third image forming method of the present invention, even when the line heads are installed to the apparatus such that one of the line heads is tilted to the main scanning direction, an image can be formed by multiple exposure without need of mechanical adjustment of the line head and with the printing quality prevented from deteriorating.
A fourth image forming method is an image forming method using a line head in which a plurality of light emitting element lines each having a plurality of light emitting elements aligned in the main scanning direction are arranged in a matrix in a plane to have rows in the sub scanning direction of an image carrier so that pixels on the image carrier are repeatedly exposed by light emitting elements on the respective lines to achieve the multiple exposure. The fourth image forming method is characterized by comprising a step of storing the information of tilt of said line head relative to the main scanning direction and a step of controlling light emitting elements which protrude from the normal exposure line to emit smaller amount of light, wherein the image data supplied to light emitting elements are controlled such that the position of image formation corresponding to the pixels on the image carrier is corrected from the tilt of the line head.
According to the fourth image forming method of the present invention, occurrence of misalignment in image due to the tilt of the line head can be prevented with simple control.
a)–9(c) are characteristic graphs of an example in which the light emitting elements are controlled by the PWM method;
The present invention will be described in the below with reference to the drawings.
The data processing means 23 carries out processes such as color separation, gradation treatment, bit-mapping of image data, and correction of color registration error. The data processing means 23 outputs image data for each line to each storage means 24–27. Each light-emitting element line head 28–31 has a plurality of light emitting element lines arranged therein and is structured to conduct multiple exposure in which light emitting elements on the respective lines emit light to a same pixel. Therefore, each storage means 24–27 outputs image data for plural lines to each light-emitting element line head 28–31.
Now, the operation of the block diagram shown in
The shift resistor 24b outputs the image data to the light emitting elements of the line 28b so that the light emitting elements work. Accordingly, the pixels previously exposed by the light emitting elements of the line 28a are exposed again by the light emitting elements of the line 28b with the equal amount of light. In this manner, the image data is sequentially transmitted from the previous shift resistor to the next shift resistor while the image carrier is moved in the direction of arrow X, whereby each same pixel is exposed again and again by light emitting elements in different lines. Consequently, in the example of
In case of gradation control for neutral density is conducted by the structure of
In the present invention, once the data processing means 23 of the image forming apparatus produces data only for the front one line, the image data for the first line is stored in the storage means (shift resistor) and are transmitted among the storage means, whereby the operations of all light emitting elements of the line head can be controlled. Since the data processing means is not required to produce data for all light emitting elements of the line head, the structure of circuit can be simplified and the data processing can be conducted at high speed.
In the example of
In the same manner, the movement of the image carrier, the transmission of the image data to the respective shift resistors, and the output of the image data to the light emitting elements are sequentially conducted, thereby achieving multiple exposure relative to same pixels. In this case, the gradation control for neutral density can be conducted on the basis of the data prepared by the data processing means 23. Though the lines of which pixels are exposed and the lines of which pixels are not exposed are arranged alternately every line in the example of
According to the present invention, even when the interval in the sub scanning direction between the spot positions where the light emitting elements emit light to the image carrier is an integral multiple of the pixel pitch in the sub scanning direction, the multiple exposure of each pixel can be achieved by arranging the respective shift resistors to correspond to the line with light emitting elements and line without light emitting elements as shown in
Description will now be made as regard to the operation of
Then, the image data in the shift resistor 24s is transmitted to the shift resistor 24t. In the same manner, the image data is sequentially transmitted from the shift resistor 24r to the shift resistor 24s, from the shift resistor 24q to the shift resistor 24r, and the shift resistor 24p to the shift resistor 24q. To the shift resistor 24p, image data is transmitted from the data processing means 23 through the signal line 35a. During this, the image carrier is moved for the pixel pitch. Since the light emitting elements at the light emitting parts Z remain to emit light because of the function of the active matrix, the light emitting elements do not lights out even during the transmission of image data between the shift resistors, thereby exposing pixels with high luminance. By repeating the outputting of image data from the shift resistor 24 to the light emitting elements, the transmission of the image data between the shift resistors, and the movement of the image carrier, the image data onto the image carrier can be consecutively written.
Description will now be made as regard to the operation of the circuit shown in
In the present invention, by controlling the light emitting elements in the pulse-width modulation (PWM) method, the control of the amount of emitting light is conducted. By the control according to the PWM method, the gradation control for the light emitting elements can be achieved. In the present invention, gradation data is formed by an 8-bit gradation data memory.
a)–9(c) are characteristic graphs showing a concrete example of the PWM control shown in the block diagram of
c) shows the waveform Dc of the signal outputted from the comparator, i.e. the operating characteristics of the switching TFT, when the gradation datum is the bit datum No. 6 (64 gradation level). In this case, the switching TFT is turned ON when the output of the counter is in a range from 0 to 63, and the switching TFT is turned OFF when the output of the counter is 64 and 255. In case of
In the example of
In the present invention, organic EL (organic electroluminescence element) arrays are employed in lines of light emitting elements for multiple exposure.
An anode 3 is formed on the reflection layer 2 by the spattering method. The anode 3 is made of a light-transmitting and conductive material. As an example of the material having such characteristics, ITO (indium tin oxide) having large working function may be used. Then, a hole transportation layer 4 is formed on the anode 3 by the inkjet method. After forming the hole transportation layer 4, ink composition is discharged into the hole (not shown) from a head of an ink-jet printing device, thereby achieving the patterning application on the emitting layer of the pixel. After the application, the solvent is removed and the applied ink composition is treated by heat, thereby forming a light-emitting layer 5.
The organic EL layer composed of the hole transportation layer 4 and the emitting layer 5 may be formed by other known method such as a spin coating method, a dipping method, and other liquid phase deposition method instead of applying ink compositions by inkjet method as the above. The material of the hole transportation layer 4 and the emitting layer 5 may be known EL materials listed in Japanese Patent Unexamined Publication No. H10-12377 and Japanese Patent Unexamined Publication No. 2000-323276, so description about details will be omitted. Then, a cathode 6 is formed by vapor deposition method. As the material of the cathode 6, for example, Al may be employed.
The organic EL array head 10 has thin layer portions 6a–6c formed at the cathodes 6 having a U-like section corresponding to light emitting parts 10x–10z. The thin layer portions 6a–6c are formed to have such a thickness in holes of a wall 9 as to allow light transmission. At the light emitting parts 10x–10z, semi-transparent reflection layers (dielectric mirrors) 7 composed of a plurality of dielectric multi-layered films are formed on the bottoms of the cathodes 6 by the spattering method. The semi-transparent reflection layers 7a–7c composed of dielectric multi-layered films may be formed of, for example, three pairs of layers made of SiO2 and TiO2. The semi-transparent reflection layers 7 formed of such dielectric multi-layered films according to the present invention has reflectance of about 0.9. In the embodiment of
By the way, a line head in which light emitting elements are aligned in a plurality of rows has a possible problem that the mounted position of the head to an apparatus is easily shifted due to a problem caused in the manufacturing process.
Even when the mounted position of the line head is shifted from the normal position as mentioned above, an embodiment of the present invention can maintain the image quality without complex alignment of the mounted positions of line heads.
In the line head 28 shown in
Now, the control example for correcting the misalignment as shown in
The line head in which light emitting elements are aligned in a plurality of rows has a possible problem that the mounted position of the head to an apparatus is easily tilted relative to the main scanning direction due to a problem caused in the manufacturing process.
Since the line head for magenta (M) is tilted relative to the main scanning direction Ya, however, the pixel line 33q is not neatly superposed on the pixel line 33p. Then, the paper sheet is fed in the direction W and a pixel line 33r is formed to be superposed on the pixel line 33p by the line head for cyan (C). The paper sheet is further fed in the direction W and a pixel line 33s is formed to be superposed on the pixel lines 33p, 33r by the line head for black (K). Therefore, in the example of
To prevent any one of the line heads for exposure of plural colors from being tilted like the above example, it is required to improve the accuracy in alignment of the entire printer, causing a problem of increasing the cost. In addition, it is necessary to conduct alignment of the respective line heads with test printing so that there is a problem that the alignment takes time and makes the operation complex.
That is, as taken from the paper feeding direction W, the operation timing for the pixel row Ra, of which the front light emitting element Zx protrudes from the main scanning direction Ya, is delayed for a predetermined period of time. It should be noted that, in the present invention, the array of light emitting elements in the main scanning direction is referred to as a light emitting element line and the array of light emitting elements in the paper feeding direction (sub scanning direction) is referred to as a light emitting element row. The pixel row Rn, of which the front light emitting element Zy does not protrude from the main scanning direction Ya, is set not to delay the operation timing. In the example shown in
The tilt information of the line head is obtained from the memory 50 and the delay circuit 40 sets the level of delay time for each light emitting element row according to the degree of tilt of the light emitting element lines relative to the main scanning direction. The output signal from the delay circuit 40 is given to the light emitting element line head 28 through the second shift resistor 24b. The second shift resistor 24b outputs signals through signal lines 38a–38n, thereby sequentially operating the light emitting elements of the light emitting element lines 28a–28c of
As mentioned above, in the control unit 22, the image data supplied from the delay circuit 40 to the light emitting elements are controlled to be delayed according to the tilt information of the line head stored in the memory 50 in such a manner as to correct image positions of pixels on an image carrier from tilting due to the tilt of the line head. The delay control for the timing of supplying image data to the light emitting elements can be carried out, for example, by providing a CPU, which is not shown in drawing, to the delay circuit. The aforementioned memory 50 may be arranged in the engine controller separately from the line head. In this case, even when the line head is out of order for any reason, the tilt information of the line head can be securely maintained. The memory 50 may be formed integrally with the line head 28. In this case, since tilt information of new line head is stored in a memory (storage means) during the replacement of the line head, the control for light emitting element rows can be conducted according to the tilt information. The storage means may be formed in a cartridge including exposure units as will be described later. In this case, the storage means can be replaced with a new storage means storing information corresponding to the tilt of new line heads at the same time as the replacement of the cartridge.
Instead of supplying delay signals to the light emitting element lines in
Though the line head for magenta (M) is installed to the apparatus in a state tilted relative to the main scanning direction Ya, the pixel line 33q formed by the line head for magenta (M) is parallel to the line of the main scanning direction Ya in the example of
In the example of
Accordingly, the light emitting element Zp and the light emitting element Zr protrude from the width of the exposure line. Therefore, the outlines of pixels which are adjacent to each other in the main scanning direction are superposed on each other, thus deteriorating the image quality as described with reference to
The example of
Suffixes “K”, “C”, “M”, and “Y” added to reference numerals indicate black, cyan, magenta, and yellow, respectively. That is, the photoreceptor drums designated by reference numerals with such suffixes are photoreceptor drums for black, cyan, magenta, and yellow, respectively. The same is true for other members. The photoreceptor drums 41K, 41C, 41M and 41Y are driven to rotate in the direction of arrows shown in
Also arranged around each photoreceptor drum 41 (K, C, M, Y) are a developing device 44 (K, C, M, Y) for applying toner as a developer to an electrostatic latent image formed by the organic EL array exposure head 1 (K, C, M, Y) so as to form a visible image (toner image), a primary transfer roller 45 (K, C, M, Y) serving as transfer means for sequentially transferring the toner image developed by the developing device 44 (K, C, M, Y) onto the intermediate transfer belt 50 as a primary transfer target, and a cleaning device 46 (K, C, M, Y) as cleaning means for removing the toner remaining on the surface of the photoreceptor drum 41 (K, C, M, Y) after the transfer of the toner image. Each organic EL array exposure head 1 (K, C, M, Y) is installed in such a manner that the array direction of the organic EL array exposure head 1 (K, C, M, Y) is parallel to the bus-bar of the photoreceptor drum 41 (K, C, M, Y). The emission energy peak wavelength of each organic EL array exposure head 1 (K, C, M, Y) and the sensitivity peak wavelength of the photoreceptor drum 41 (K, C, M, Y) are set to be approximately coincident with each other.
The developing device 44 (K, C, M, Y) uses anon-magnetic single-component toner as a developer, for example. The single-component developer is conveyed to a development roller through a supply roller, for example, and the thickness of the developer layer adhering to the development roller surface is regulated with a regulating blade. The development roller is brought into contact with or pressed against the photoreceptor drum 41 (K, C, M, Y) to allow the developer to adhere to the surface of the photoreceptor drum 41 (K, C, M, Y) according to the electric potential level thereof, thereby developing the electrostatic latent image into a toner image. Toner images of black, cyan, magenta and yellow formed by unicolor toner image forming stations for the four colors are sequentially primarily transferred onto the intermediate transfer belt 50 by a primary transfer bias voltage applied to the respective primary transfer rollers 45 (K, C, M, and Y), and sequentially superimposed on each other on the intermediate transfer belt 50 to form a full-color toner image, which is then secondarily transferred onto a recording medium “P” such as a paper at a secondary transfer roller 66. The transferred full-color toner image is fixed on the recording medium “P” by passing between a pair of fixing rollers 61 as a fixing device. Then, the recording medium “P” is discharged through a pair of sheet delivery rollers 62 onto an outfeed tray 68 formed on the top of the apparatus body.
In
Though the image forming apparatus and the image forming method of the present invention have been described with reference to the embodiments disclosed herein, the present invention is not limited thereto and various modifications may be made therein.
The present invention as described in the above can provide an image forming apparatus and an image forming method, which are directed to simplify the circuit structure and to speed up the light emitting control during the exposure of pixels on an image carrier in multiple exposure manner capable of outputting gradation, at low cost.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002-158865 | May 2002 | JP | national |
| 2003-126213 | May 2003 | JP | national |
| 2003-126214 | May 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP03/06655 | 5/28/2003 | WO | 00 | 5/21/2004 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO03/101743 | 12/11/2003 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5245355 | Morton | Sep 1993 | A |
| 5831657 | Sakaue et al. | Nov 1998 | A |
| 5978403 | Iwasa et al. | Nov 1999 | A |
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| Number | Date | Country | |
|---|---|---|---|
| 20050068355 A1 | Mar 2005 | US |
