JP2004203020A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing density unevenness of an image and improving quality of the image. <P>SOLUTION: An LED array controlling part 34 for driving and controlling an LED print head 7 is composed of a characteristic data storing part 35, a driving electric current correcting data operating part 39, an image signal processing part 42, a control signal generating part 43 and an image data correcting and operating part 44. The characteristic data storing part 35 stores a plurality of characteristic data measured in advance in relation to an individual LED element constituting an LED array 31. The driving electric current correcting data operating part 39 reads out the characteristic data stored in the characteristic data storing part 35 and calculates driving electric current correcting data P. The image data correcting and operating part 44 uses the driving electric current correcting data P outputted from the driving electric current correcting data operating part 39 and corrects the image data outputted from the image signal processing part 42, and the corrected image data are outputted to the LED print head 7. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an LED print head as exposure means for an electrophotographic printer, a facsimile, a copying machine, or the like.

  2. Description of the Related Art In recent years, an electrophotographic image forming apparatus using an LED array as an optical writing unit has attracted attention in order to reduce the size and simplify the apparatus. In this electrophotographic image forming apparatus, the LED print head used for exposing the photoreceptor has an LED array formed by arranging a plurality of LED elements in a line, and controls each LED element based on image data. Light is selectively emitted individually.

  However, since it is impossible to manufacture the plurality of LED elements forming the LED array so that the light emission characteristics are all uniform, a current of the same magnitude is applied to all the LED elements. Also, the light amount differs for each LED element, and the light amount varies for each LED element. Therefore, the image density becomes uneven.

Therefore, an LED print head has been proposed in which the above-described variation in the light amount is suppressed and the light amount of each LED element is corrected to be uniform. For example, the light emission output of the LED printer is made uniform and the printing quality is improved. For this purpose, a technique has been proposed in which trimming by laser light is performed and the current supplied to each LED element is controlled by adjusting the resistance value so as to make the light amount constant (for example, see Patent Document 1). . In addition, in order to eliminate the need for adjustment work when assembling a head with a variation in the amount of light into a product or replacing an LED print head, correction data for keeping the amount of light emitted from each LED element constant is required. There has been proposed an LED print head which has been obtained in advance and has a ROM in which the correction data is stored, and which turns on each LED element using the correction data at the time of printing (for example, see Patent Document 2).
JP-A-5-4376 (page 3-4, FIG. 6-8) JP-A-5-50653 (page 3-4, FIG. 1)

  However, since optical image data emitted from each LED element is formed on a photosensitive member through a lens array, a latent image is formed on the photoreceptor. Due to variations in the optical characteristics of the lens array, the diameter of the formed dots also differs for each LED element, and it cannot be said that it is impossible to equalize the light amount distribution of all the dots. As a result, vertical stripes appear on the image. The inconvenience of doing so occurred. For example, as shown in FIG. 10, in the LED element a ′ and the LED element b ′, even if the light amounts of both LED elements are the same, the dot diameters Sa ′ and Sb ′ of both LED elements at the development threshold are different. For this reason (Sa '<Sb'), the latent image dot is larger in the LED element b 'having a larger dot diameter at the development threshold, and is expressed densely on the image.

  Further, the LED elements constituting the LED array can be ranked according to the amount of light when the LED elements are turned on with the same drive current. However, LED elements having different ranks are assigned to the same LED array (or the same LED array). When arranged in a chip), even if the drive current for each LED element is corrected as in the above-described related art, there is a possibility that dots that cannot be properly corrected due to the above-described variation in rank may be generated.

  Here, in order to avoid such inconveniences, it is sufficient to use only LED elements having the same rank, but when mass-producing LED elements, LED elements other than a certain rank are used because they are distributed in a plurality of ranks. There is a disadvantage that it cannot be performed, resulting in an increase in cost during mass production.

  In addition, when using LED elements having similar ranks in the same LED array (or the same LED chip), it is possible to avoid the inconvenience that a dot that cannot be properly corrected due to a variation in rank occurs. Since the average light amount varies about the number of ranks of the LED elements, the average light amount varies for each LED array (that is, the average exposure amount for each LED print head). As a result, in the output image of the image forming apparatus, However, there is a problem that the image density varies. In particular, since a plurality of LED print heads mounted on a tandem type color printer or the like have different average exposure amounts for each color, there is a problem that the color tone of an output image differs for each printer. .

  Further, when LED elements having different ranks are arranged in the same LED array (or the same LED chip), the drive time is corrected for each LED element after the drive current for each LED element is corrected. This makes it possible to eliminate the above-described variation in the average light amount, but in this case, it is necessary to set the drive time for each LED element, which complicates the configuration when performing control. There was a problem.

  SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide an image forming apparatus capable of suppressing image density unevenness and improving image quality.

  In order to achieve the above object, the image forming apparatus according to claim 1 includes an LED array including a plurality of LED elements whose lighting is controlled according to image data, and a driving unit that drives the plurality of LED elements. In an image forming apparatus having an LED print head composed of: and an LED array control unit for driving and controlling the LED print head, the LED array control unit stores characteristic data for storing a plurality of characteristic data for each of the plurality of LED elements. Storage means, and drive current correction data calculation means for reading the characteristic data from the characteristic data storage means and calculating drive current correction data for each of the plurality of LED elements based on the characteristic data. .

  An image forming apparatus according to claim 2, wherein an LED array including a plurality of LED elements whose lighting is controlled in accordance with image data, and a driving unit for driving the plurality of LED elements. In an image forming apparatus having a head and an LED array control unit for driving and controlling an LED print head, the LED array control unit includes a characteristic data storage unit configured to store a plurality of characteristic data items for each of the plurality of LED elements; Reading the characteristic data from the storage means and calculating the driving current correction data for each of the plurality of LED elements based on the characteristic data; and reading the driving current correction data from the driving current correction data calculating means. And a drive current correction data storage means for storing drive current correction data. And wherein the are.

  In the image forming apparatus according to the third aspect, the characteristic data storage unit stores data relating to the average light amount of the LED array as characteristic data, and the LED array control unit stores the data corresponding to the average light amount. A drive time data table storage means which is stored in advance and stores a drive time data table for driving all of the plurality of LED elements constituting the LED array at the same time; data on average light quantity and data on drive time A driving time control means for reading out the table and determining the driving time based on the data table on the average light quantity and the driving time is provided.

  According to a fourth aspect of the present invention, in the image forming apparatus, the data relating to the average light amount is obtained based on the exposure amount of the LED print head, and is stored in advance in the characteristic data storage unit.

  An image forming apparatus according to a fifth aspect is a tandem-type image forming apparatus including a plurality of LED print heads, and the driving time control unit includes a plurality of LED print heads each forming an LED array. The driving time is determined for each LED element.

  According to a sixth aspect of the present invention, in the image forming apparatus, the characteristic data storage unit stores light amount data relating to each of the plurality of LED elements as characteristic data.

  According to a seventh aspect of the present invention, in the image forming apparatus, the characteristic data storage unit stores data relating to beams emitted from each of the plurality of LED elements as characteristic data.

  Further, the image forming apparatus according to the present invention is characterized in that the characteristic data storage means stores resolution data relating to each of the plurality of LED elements as characteristic data.

  According to a ninth aspect of the present invention, in the image forming apparatus, the driving unit drives all of the plurality of LED elements simultaneously by static driving.

  An image forming apparatus according to a tenth aspect is characterized in that the LED array is divided into a plurality of blocks, and the driving unit sequentially drives the plurality of LED elements for each block by dynamic driving.

  ADVANTAGE OF THE INVENTION According to this invention, the density difference of the display density between the some LED element which comprises an LED array can be eliminated accurately, and the density unevenness of an image can be suppressed. Further, the occurrence of vertical stripes on an image can be efficiently reduced.

  Further, according to the present invention, even when it takes a long time to calculate the drive current correction data by the drive current correction data calculation means, the drive current correction data calculated in advance is stored in the drive current correction data storage means. Therefore, the correction of the image data can be performed at higher speed.

  Further, according to the present invention, it is possible to accurately eliminate the difference in gray level of the display density between the respective LED elements, and to equalize the exposure amounts between the LED print heads having different average exposure amounts. Therefore, not only the variation in density between the LED elements but also the variation in density between the LED print heads can be suppressed. As a result, it is possible to suppress variations in image density in an output image of the image forming apparatus.

  Further, according to the present invention, in particular, in each LED print head mounted on a tandem type color printer or the like, each color has the same average exposure amount, so that the color tone of the output image differs for each printer. The inconvenience of doing so can be avoided.

  Further, according to the present invention, since the driving time for driving all the LED elements constituting the LED array in the same time is determined, the driving time is set for each LED element. In comparison, the driving time can be controlled with a simple configuration.

  Further, according to the present invention, even if the LED elements having different ranks are arranged in the same LED array and the average exposure amount varies from one LED print head to another, it is possible to suppress the density variation between the LED print heads. Therefore, even if the LED elements are mass-produced and a plurality of ranks are distributed, the LED elements of all ranks can be used, and as a result, the cost can be reduced during mass production.

  According to the present invention, the average light amount of the LED array is obtained by measuring the exposure amount of each of the LED print heads in advance, and the average light amount is stored in advance in the average light amount data storage unit as characteristic data. With the configuration, even if the calculation of the average light amount originally takes a long time, the drive time control unit can quickly read out the average light amount, and as a result, the drive time control unit can determine the drive time more quickly. It can be performed at high speed.

  Further, according to the present invention, light amount data relating to each of the plurality of LED elements, data relating to a beam emitted from each of the plurality of LED elements (for example, beam diameter and beam area), and resolution data relating to each of the plurality of LED elements are characterized. Since the characteristic data is stored in the characteristic data storage means, a plurality of these characteristic data can be used in combination, and a more accurate driving current can be supplied to each LED element constituting the LED array. Correction data can be created.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram illustrating an entire configuration of an image forming apparatus according to a first embodiment of the present invention. In the image forming apparatus shown in FIG. 1, 1 is a tandem-type color printer as an example of the image forming apparatus, 2 is a housing, 3B, 3Y, 3C, and 3M are images for black, yellow, cyan, and magenta, respectively. In the forming section, 10B, 10Y, 10C, and 10M are toner hoppers for the respective colors. Reference numeral 12 denotes a paper feed cassette for storing paper 14, 13 denotes a paper feed guide, 11a and 11b denote conveyance belt driving rollers, 8 denotes a conveyance belt, 9 denotes a transfer roller, 17 denotes a fixing unit, 15 denotes a paper ejection guide, Denotes a paper discharge unit. Each of the image forming units 3B, 3Y, 3C, and 3M for each color includes a developing unit 4, a photoconductor 5, a main charger 6, an LED print head 7, a cleaning unit 20, and the like.

  In the color printer 1, an electrostatic latent image is formed by the LED print head 7 on the photoconductor 5 charged by the main charger 6, and is developed by the developing device 4 to form a visible image. Such a process is performed for each of the black, yellow, cyan, and magenta colors. The paper 14 sent from the paper feed cassette 12 is guided by the paper feed guide 13 and is attracted to the upper surface of the conveyor belt 8 rotating counterclockwise, so that the image forming units 3B, 3Y, 3C, The image of each color is sequentially transferred to the paper 14 by the transfer roller 9 when passing immediately below 3M. As described above, the four color toners that have formed the full-color image on the paper 14 are fixed when the paper 14 passes through the fixing unit 17. Thereafter, the paper 14 is guided to be discharged to the paper discharge unit 16 by the paper discharge guide 15.

  Next, the LED print head 7 provided in the above-described color printer 1 will be described with reference to FIG. FIG. 2 is a schematic diagram illustrating a schematic configuration of the LED array print head in the image forming apparatus according to the first embodiment of the present invention. As described above, each of the image forming units 3B, 3Y, 3C, and 3M for each color has the LED print head 7, and the color printer 1 includes the plurality of LED print heads 7. The LED print heads 7 are arranged in a row on a substrate 30 having wiring, and are arranged above the LED array 31 with an LED array 31 composed of a plurality of LED elements whose lighting is controlled according to image data. The LED array 31 includes a lens array 32 that forms an erect image of the same magnification and a drive circuit 33 that drives a plurality of LED elements that constitute the LED array 31. Here, the above-described substrate 30, the lens array 32, and the like are held by a holding member (not shown). Further, an LED array control unit 34 for driving and controlling the LED print head 7 is provided outside. The LED array 31 may be configured by dividing the LED array 31 into a plurality of blocks and arranging a plurality of chips (LED chips) on which a plurality of LED elements are arranged.

  FIG. 3 is a schematic diagram when the LED print head 7 is incorporated in an image forming apparatus. In FIG. 3, reference numeral 5 denotes a photosensitive member having a drum shape, and a dashed line indicates that the lens array 32 receives the light emitted from the LED light emitting element, refracts and transmits the light, and forms an image on the drum surface.

  As described above, each LED element is driven in response to an image signal transmitted from an external PC (not shown) or the like to the color printer 1 of FIG. Via 32, an image is formed as a dot on the surface of the photoconductor 5. Note that the image forming apparatus of the present embodiment is formed so that pixels having higher exposure energy (or LED element emission energy) on the photoreceptor 5 have a higher density, and the exposure energy (or LED element emission) is higher. Energy) is represented by light emission intensity (= drive current) × light emission time (= drive current supply time) of the LED element.

  Next, an operation of the LED array control unit and an operation of the driving circuit of the LED print head will be described with reference to FIGS. FIG. 4 is a block diagram showing a configuration of an LED array control unit in the image forming apparatus according to the first embodiment of the present invention, and FIG. 5 is an LED print head in the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration of a driving circuit of FIG.

  The LED array control unit 34 controls the driving of the LED print head 7, and includes a characteristic data storage unit 35, a drive current correction data calculation unit 39, an image signal processing unit 42, a control signal generation unit 43, and an image data correction calculation unit. 44.

  The image signal processing unit 42 appropriately performs image processing such as gradation processing on the image signal 41 sent from an external device, for example, a frame memory or a scanner to the LED array control unit 34, and converts the image signal 41 into an image. It is a means to convert to data. This image data is data for indicating pixel densities separated for each of the black, yellow, cyan, and magenta colors, and indicates a drive current (light emission intensity) and a light emission time (drive current supply time) of the LED element. This is m-bit digital data. The image data processed by the image signal processing unit 42 is output to the image data correction calculation unit 44.

  The characteristic data storage unit 35 is means for storing a plurality of characteristic data measured in advance for each of the plurality of LED elements constituting the LED array 31. For example, as shown in FIG. Light amount data storage unit 36 for storing light amount data relating to light emitted from each LED element, for example, a beam data storage unit 37 for storing data relating to a beam diameter and a beam area as characteristic data, and resolution relating to each LED element. , For example, MTF (Modulation Transfer Function) data as characteristic data. The characteristic data storage unit 35 is constituted by, for example, a ROM (Read Only Memory). However, in order to cope with the characteristic change of each LED element, a rewritable PROM (for example, data Or an EEPROM that electrically erases data).

  The drive current correction data calculation unit 39 is connected to the characteristic data storage unit 35. The drive current correction data calculation unit 39 reads out each characteristic data stored in the light amount data storage unit 36, the beam data storage unit 37, and the resolution data storage unit 38 provided in the above-described characteristic data storage unit 35, This is for calculating the drive current correction data P for each of the plurality of LED elements constituting the LED array 31 based on the characteristic data according to a predetermined arithmetic expression. The drive current correction data P calculated by the drive current correction data calculation unit 39 is output to the image data correction calculation unit 44.

The drive current correction data P is data used when changing the exposure intensity of each LED element by changing the drive current of each LED element constituting the LED array 31, as described later. for example, in the case of correcting the drive current of the dot 1 (No.1 of LED elements), the drive current correction data P ₁ is used, in case of correcting the drive current dot n (No.n of LED elements) Uses the drive current correction data _Pn .

  The image data correction calculation unit 44 corrects the image data output by the image signal processing unit 42 using the drive current correction data P output by the drive current correction data calculation unit 39. That is, the image data correction operation unit 44 is configured to output the image data output from the image signal processing unit 42 to each of the LED arrays 31 according to the drive current correction data P output from the drive current correction data operation unit 39. The m-bit digital data indicating the drive current for the LED element is corrected. The corrected image data is output to the LED print head 7, as shown in FIG.

  As shown in FIG. 5, the drive circuit 33 of the LED print head 7 includes a CLK counter 50 for counting the clock signal CLK, an SCLK counter 51 for counting the strobe clock signal SCLK, and a corrected image data indicating the pixel density. It has a storage unit 52 for temporarily storing, a gate unit 53 that opens and closes according to the logic of the output time control signal STROBE, and a constant current generation unit 54 that generates a drive current for the LED array 31.

  The driving circuit 33 of the LED print head 7 having the above configuration is initialized by the falling of the horizontal synchronization signal HSYNC input from the control signal generation unit 43, and also receives the clock signal CLK input from the control signal generation unit 43, The reception of the corrected image data input in synchronization with the clock signal CLK is started.

  The storage unit 52 has a shift register and a latch circuit, and temporarily stores data necessary for light emission of the LED array 31 in order to convert input corrected image data. Here, the driving method of each of the LED elements constituting the LED array 31 by the driving circuit 33 includes a static driving method in which the turning on / off control of all the LED elements is performed simultaneously (that is, all of the plurality of LED elements are simultaneously driven). There is a dynamic drive system in which the LED array 31 is divided into a plurality of blocks, and lighting control is performed for each block (that is, for each chip) (that is, a plurality of LED elements are sequentially driven for each block). When the method is adopted, the data is temporarily stored for all the LED elements, and when the dynamic driving method is adopted, the data for one block is temporarily stored.

  The CLK counter 50 determines whether or not the temporary storage of the image data in the storage unit 52 is completed based on the count number of the clock signal CLK. It outputs the timing control signal STREQ to the control signal generator 43.

  When the output time control signal STROBE is set to the active level (low level) by the control signal generation unit 43 that has received the light emission timing control signal STREQ, and the strobe clock signal SCLK starts to be input, the SCLK counter 51 counts the strobe clock signal SCLK. Starting, the gate 53 is opened. Therefore, a drive current based on the drive current correction data P stored in the storage unit 52 is applied to each LED element included in the LED array 31 for a light emission time based on the image data stored in the storage unit 52, and the photosensitive element is exposed to light. The exposure of the body drum 5 is performed.

  FIG. 6 is a flowchart illustrating a procedure of lighting control of the LED element. In this control procedure, first, n = 1 is set to target the first line out of the total line number N (step S1). Next, the characteristic data of each LED element is read from the characteristic data storage unit 35 (step S2), and the drive current correction data calculation unit 39 calculates the drive current correction data P for each LED element (step S3). Next, the calculated drive current correction data P is output to the image data correction calculation unit 44 (Step S4), and the image data correction calculation unit 44 corrects the image data (Step S5). Next, the corrected image data is output to the LED print head 7 (Step 6), and each LED element is turned on according to the corrected image data (Step S7). Further, in order to target the next line n, n is incremented by +1 (step S8), and it is checked whether or not n exceeds the total number N of lines to be printed (step S9). For example, the above process is repeated for line n in the same manner (steps S2 to S9).

  In the above-described embodiment, the drive current correction data P is calculated by the drive current correction data calculation unit 39 and then output directly to the image data correction calculation unit 44. However, as shown in FIG. A drive current correction data storage section 40 for storing the drive current correction data P calculated by the drive current correction data calculation section 39 is provided separately. It may be configured to be connected to the data correction operation unit 44.

  In this case, the drive current correction data storage unit 40 reads the drive current correction data P from the drive current correction data calculation unit 39, stores the drive current correction data P, and sends the read drive current correction data P to the image data correction calculation unit 44. Output data P. In order to cope with a change in the drive current correction data P based on a change in the characteristics of each LED element, the drive current correction data storage unit 40 includes, for example, a rewritable PROM (for example, data is erased by ultraviolet light). For example, an EPROM for performing data erasing and an EEPROM for electrically erasing data are used.

  With such a configuration, even when the calculation of the drive current correction data P takes a long time, the drive current correction data P calculated in advance is stored in the drive current correction data storage unit 40. The drive current correction data P can be quickly read out by the data correction calculation unit 44, and as a result, the image data correction by the image data correction calculation unit 44 can be performed at higher speed.

  In this case, the lighting control procedure of the LED element is performed according to the flowchart shown in FIG. That is, first, n = 1 is set to target the first line out of the total number N of lines (step S100). Next, the characteristic data of each LED element is read from the characteristic data storage section 35 (step S101), and the drive current correction data calculation section 39 calculates the drive current correction data P for each LED element (step S102). Next, the calculated drive current correction data P is stored in the drive current correction data storage unit 40 (step 103). Further, in order to target the next line n, n is incremented by +1 (step S104), and it is checked whether or not the number n exceeds the total number N of lines to be printed (step S105). For example, the above processing is repeated for line n in the same manner, and the drive current correction data storage unit 40 stores the drive current correction data P for all lines (steps S101 to S105).

  Next, in order to target the first line out of the total number N of lines, n = 1 is set again (step S106). Next, the drive current correction data P stored in the drive current correction data storage unit 40 is output to the image data correction calculation unit 44 (Step S107), and the image data correction calculation unit 44 corrects the image data (Step S107). S108). Next, the corrected image data is output to the LED print head 7 (Step 109), and each LED element is turned on according to the corrected image data (Step S110). Further, in order to target the next line n, n is incremented by +1 (step S111), and it is checked whether or not the number n exceeds the total number N of lines to be printed (step S112). For example, the above processing is repeated for line n in the same manner (steps S107 to S112).

FIG. 9 shows the relationship between the exposure intensity of the LED element and the beam diameter of the development threshold. Here, FIG. 9A shows the relationship between the exposure intensity of the LED element and the beam diameter of the development threshold before the image data is corrected, and FIG. 9B shows the relationship after the image data is corrected. 3 shows the relationship between the exposure intensity of the LED element and the beam diameter of the development threshold. As shown in FIG. 9A, in the LED element a and the LED element b, the light emission amount (peak area in the figure) is almost the same in both the high-density part and the low-density part. (This beam diameter is generally specified in a range of 13.5% of the peak light amount). That is, the high density portion, in either case of the low density portion, the beam diameter of the light-emitting element b is larger than the beam diameter of the light-emitting element _{a (D b> D a,} d b> d a).

However, as shown in FIG. 9 (a), in the high density portion, dot diameter S _b at the development threshold of the LED element b is, although larger than the dot diameter S _a of the LED elements a, low density part in the contrary to the case of the high density portion, dot diameter S _a at the development threshold of the LED element a is larger than the dot diameter S _b of the LED element b. That is, the size relationship between the dot diameters at the development threshold of the LED element a and the LED element b does not depend on the size relationship of the beam diameter, but depends on the display density of the LED element. Therefore, in this state, in the high density portion, the LED element b having the larger dot diameter at the development threshold is lower, and in the lower density portion, the LED element a having the larger dot diameter at the development threshold is smaller than the latent image dot. Becomes large, and is expressed darkly on the image.

  In view of this, the beam diameter of each display density portion of the LED element a and the LED element b is stored in advance as characteristic data, and correction data of the drive current is created using the characteristic data relating to the beam diameter. The difference in display density between the LED element a and the LED element b is eliminated.

  That is, as shown in FIG. 9B, in the high density portion, the driving current of the LED element b having a large beam diameter (large dot diameter) is reduced, and the LED element having a small beam diameter (small dot diameter) is reduced. Drive current correction data is created using the characteristic data related to the beam diameter so as to increase the drive current of a, and in the low density portion, the drive current of the LED element b having a large beam diameter (small dot diameter) is increased. Then, the drive current correction data is created using the characteristic data related to the beam diameter so as to reduce the drive current of the LED element a having the small beam diameter (the large dot diameter). Since the dot diameters of the LED element a and the LED element b are the same, it is necessary to eliminate the difference in display density between the LED element a and the LED element b in each display density section. It will be possible.

  Note that FIG. 9 shows a case where the drive current correction data is created using the beam diameter as the characteristic data of the LED elements. However, as described above, the light quantity data and the data on the beam area for each LED element and the MTF Driving current correction data can also be created by using data indicating resolution such as data individually or a combination of a plurality of data as characteristic data.

  As described above, in the present embodiment, the characteristic data storage unit 35 for storing a plurality of previously measured characteristic data is provided for the individual LED elements constituting the LED array 31, and the characteristic data storage unit 35 is provided in the characteristic data storage unit 35. A driving current correction data calculation unit 39 for reading out the obtained characteristic data and calculating driving current correction data P for each of the LED elements constituting the LED array 31 is provided, and the driving current based on the driving current correction data P controls the LED array 31. Since it is configured to flow through each of the constituent LED elements, it is possible to accurately eliminate the difference in display density between the LED elements, and to suppress unevenness in the density of an image. As a result, it is possible to efficiently reduce the occurrence of vertical stripes on the image.

  Further, in the present embodiment, a rewritable PROM can be used for the characteristic data storage unit 35. Therefore, even if the characteristic of each LED element changes, the characteristic data of each LED element can be stored. Rewriting can be performed smoothly. Therefore, when the drive current correction data P is calculated, the drive current correction data for each LED element can be calculated with high accuracy, and as a result, the image data can be corrected with high accuracy. Become.

  Next, a second embodiment of the present invention will be described in detail with reference to the drawings. FIG. 11 is a block diagram illustrating a configuration of the LED array control unit in the image forming apparatus according to the second embodiment of the present invention.

  In the present embodiment, in the LED array control unit 34 (see FIG. 4) described in the first embodiment, a drive time control unit that controls the drive time (light emission time) of a plurality of LED elements constituting the LED array 31. 60, an average light amount data storage unit 61 that stores the average light amount of the LED array 31 (hereinafter, sometimes referred to as an average exposure amount of the LED print head 7) as characteristic data, and a driving time based on the average exposure amount. The configuration is exactly the same as that of the above-described first embodiment except that a driving time data table storage unit 62 that stores a data table is provided. Therefore, since other operations and configurations are the same as those of the above-described first embodiment, the same members are denoted by the same reference numerals, and detailed description thereof will be omitted. In addition, the overall configuration of the image forming apparatus, the schematic configuration of the LED array exposure apparatus, the configuration of the driving circuit of the LED print head, and the like in the present embodiment are the same as those in the first embodiment. Description is omitted.

  Here, the LED elements constituting the LED array 31 can be ranked according to the amount of light when the LED elements are lit with the same drive current. However, LED elements having different ranks are assigned to the same LED array 31 (or When arranged in the same LED chip), even if the drive current for each LED element is corrected, there is a possibility that dots that cannot be properly corrected due to the above-described variation in rank may occur. Therefore, in order to avoid such inconveniences, it is sufficient to use only LED elements having the same rank.However, when mass-producing LED elements, since LED elements are distributed in a plurality of ranks, LED elements other than a certain rank can be used. It is no longer appropriate from the viewpoint of mass production. Therefore, in the same LED array 31 (or the same LED chip), LED elements of similar rank are often used. In this case, even if the driving current for each LED element is corrected, Since the average light amount varies about the number of ranks of the LED elements, the average light amount varies for each LED array 31 (that is, the average exposure amount for each LED print head 7). There is a problem that the image density varies in the image. In particular, since a plurality of LED print heads mounted on a tandem type color printer or the like have different average exposure amounts for each color, there is a problem that the color tone of an output image differs for each printer. .

  Therefore, in the present embodiment, the variation of the average exposure amount for each of the plurality of LED print heads mounted on the tandem type color printer shown in FIG. 1 is corrected, and the difference in the display density between the LED print heads is corrected. The driving time control unit 60, the average light amount data storage unit 61, and the driving time data table storage unit 62 are provided to reduce the above. Hereinafter, these will be described in detail.

  As shown in FIG. 11, the characteristic data storage unit 35 includes the above-described light amount data storage unit 36, beam data storage unit 37, resolution data storage unit 38, and an average light amount that stores the average light amount of the LED array 31 as characteristic data. It is composed of a data storage unit 61. Here, the average light amount of the LED array 31 refers to the average value of the light amounts of all the LED elements constituting the LED array 31, and more specifically, the energy amount per second when the LED elements are constantly turned on. Say The characteristic data relating to the average light amount is obtained by measuring in advance the exposure amount of each of the LED print heads 7 provided in the image forming units 3B, 3Y, 3C, and 3M for black, yellow, cyan, and magenta. It is obtained based on the amount, and is stored in advance in the above-described characteristic data storage unit 35 (that is, the average light amount data storage unit 61).

  Further, as shown in FIG. 11, a driving time control unit 60 is connected to the characteristic data storage unit 35. The drive time control unit 60 controls each of the characteristics stored in the light amount data storage unit 36, the beam data storage unit 37, the resolution data storage unit 38, and the average light amount data storage unit 61 provided in the above-described characteristic data storage unit 35. Among the data, the driving time for reading out the average light amount data stored in the average light amount data storage unit 61 and driving all the LED elements constituting the LED array 31 at the same time based on the average light amount data. It is for determining.

  The LED array control unit 34 is provided with a drive time data table storage unit 62 in which a data table (see FIG. 14 described later) relating to a drive time set in advance corresponding to a predetermined average light amount is stored. The driving time data table storage unit 62 is connected to the driving time control unit 60. This data table is created from the relationship between the exposure amount during light emission (or the exposure amount during pulse lighting) and the driving time for a plurality of LED arrays 31 having different average light amounts. Hereinafter, this point will be described in detail. The light emission exposure amount is determined by the EV characteristic of the photoconductor 5, and the value does not change if the photoconductor 5 is the same.

  FIG. 12 is a diagram showing the relationship between the exposure amount during light emission and the drive time at a predetermined average light amount. Here, Qa, Qb, and Qc indicate the average light amount of the LED array 31 (or the average exposure amount of the LED print head 7), and Qa> Qb> Qc (for example, Qa is 2.50 μW and Qb is 2.30 μW). , Qc have a relationship of 2.10 μW).

  As can be seen from FIG. 12, when the driving time is the same, as the average light amount of the LED array 31 (that is, the average exposure amount of the LED print head 7) increases, the light exposure amount also increases. That is, the light emission exposure amount in the LED print head having the average exposure amount of Qa is the largest, and the light emission exposure amount in the LED print head having the average exposure amount of Qc is the smallest. This difference in the exposure amount at the time of light emission causes variation in the image density in the output image.

  Therefore, in the present embodiment, by correcting the drive current described in the above-described first embodiment (that is, the drive current based on the drive current correction data P created using the characteristic data of each LED element). Is applied to each LED element), and a driving time for driving all of the plurality of LED elements constituting the LED array 31 at the same time based on the average light amount while suppressing the density variation between the LED elements. Is determined, the variation in density between the LED print heads 7 is also suppressed.

  That is, for example, when the light emission exposure amount is Q, as shown in FIG. 12, the driving time is set to Ta for the LED print head 7 having the average exposure amount Qa, and similarly, the average exposure amount is Qb. The driving time is set to Tb for the LED print head 7 of which is described above, and the driving time is set to Tc for the LED print head 7 whose average exposure amount is Qc. Based on the driving time data obtained in this way, the driving time is set in advance corresponding to each average light amount, thereby creating a data table relating to the driving time shown in FIG. It is stored in the driving time data table storage unit 62.

  The drive time control unit 60 reads out the average light amount data stored in the average light amount data storage unit 61, reads the drive time data table stored in the drive time data table storage unit 62, The drive time for obtaining the exposure amount Q is determined based on the drive time data table. That is, the drive time control unit 60 determines a drive time for driving all the LED elements constituting the LED array 31 in the same time based on the average light amount data and the drive time data table. For example, when the average light amount of the LED array 31 constituting the LED print head 7 provided in the black image forming unit 3B is 2.30 μW, the drive time is determined to be 2.34 μsec, and the yellow image forming unit 3Y is determined. When the average light amount of the LED array 31 constituting the provided LED print head 7 is 2.10 μW, the drive time is determined to be 2.50 μsec (see FIG. 14). Then, the driving times of the LED elements are similarly determined for the cyan and magenta image forming units 3C and 3M. In this embodiment, as described above, in the tandem-type color printer 1 including the plurality of LED print heads 7, the drive time control unit 60 controls the plurality of LED arrays 31 included in each of the plurality of LED print heads 7. The drive time is determined for each LED element. Thereafter, data (drive time data) regarding the drive time determined for each LED print head 7 is output from the drive time control unit 60 to the control signal generation unit 43.

  The control signal generator 43 that has received the drive time data generates an output time control signal STROBE corresponding to the drive time data, and the STROBE is output to the LED print head 7. Also, as shown in FIG. 11, similarly to the first embodiment, the corrected image data in which the drive current has been corrected is output to the LED print head 7. Then, the same control as in the case of the first embodiment described with reference to FIGS. 4 and 5 is performed. Therefore, in the present embodiment, the LED elements constituting the LED array 31 provided in each of the image forming units 3B, 3Y, 3C, and 3M are driven based on the driving current correction data P stored in the storage unit 52. The current flows for the drive time (or the light emission time) based on the drive time data output by the drive time control unit 60, and the photosensitive drum 5 is exposed.

  As shown in FIG. 13, the inclination of the straight line of each average light quantity Qa, Qb, Qc shown in FIG. 12 and the magnitude of each average light quantity Qa, Qb, Qc have a linear relationship (proportional relationship). 13, for example, another average light amount Qd shown in FIG. 12 (where Qd has a relationship of Qa> Qd> Qb, for example, Qa is 2.50 μW and Qd is 2.40 μW , Qb is 2.30 μW) and Qe (where Qe has a relationship of Qb> Qe> Qc, for example, Qb is 2.30 μW, Qe is 2.20 μW, and Qc is 2.10 μW). Can be obtained. Therefore, by using FIG. 12, it is possible to obtain the driving times Td and Te for the LED print head 7 having these average exposure amounts Qd and Qe when the exposure amount during light emission is Q. Therefore, it is possible to obtain the relationship between the exposure amount at the time of light emission and the drive time at an arbitrary average light amount. By adding these data, a more detailed drive time data table can be created, and as a result, As a result, the driving time can be determined with higher accuracy.

  Further, in the driving method of each LED element constituting the LED array 31, as in the first embodiment, the turning on / off control of all the LED elements is performed simultaneously (that is, all of the plurality of LED elements are simultaneously driven). 3) Either a static driving method or a dynamic driving method in which the LED array 31 is divided into a plurality of blocks and lighting / light-out control is performed for each block (that is, for each chip) (that is, a plurality of LED elements are sequentially driven for each block). May be adopted.

  FIG. 15 is a flowchart illustrating a procedure of lighting control of the LED element. In this control procedure, first, in the LED array control unit 34, the drive time control unit 60 reads out the average light amount data stored in the average light amount data storage unit 61 (step S51). Next, the drive time control unit 60 reads the drive time data table stored in the drive time data table storage unit 62 (step S52), and determines the drive time for obtaining the light emission exposure amount based on the average light amount. It is determined (step S53). Next, data relating to the determined drive time (drive time data) is output from the drive time controller 60 to the control signal generator 43 (step S54), and the control signal generator 43 corresponds to the drive time data. An output time control signal STROBE is generated (step S55), and the STROBE is output to the LED print head 7 (step S56). Next, the corrected image data in which the drive current has been corrected is output to the LED print head 7 (step S57), and each LED element is lit for the determined drive time according to the corrected image data (step S58). ).

  In this embodiment, as described above, the drive time control unit 60, the average light amount data storage unit 61, and the drive time data table storage unit are added to the LED array control unit 34 described in FIG. 4 of the first embodiment. However, as a modification of the present embodiment, the LED array control unit 34 (that is, the drive current correction data calculated by the drive current correction data calculation unit 39) described in FIG. An LED array control unit 34 provided with a drive current correction data storage unit 40 for storing P separately provided with a drive time control unit 60, an average light amount data storage unit 61, and a drive time data table storage unit 62. Good (see FIG. 16).

  As described above, in the present embodiment, the drive current correction data calculation unit 39 for calculating the drive current correction data P for each of the LED elements forming the LED array 31 based on the characteristic data described in the first embodiment is described. In addition, in the characteristic data storage unit 35, an average light amount data storage unit 61 that stores the average light amount of the LED array 31 as characteristic data is provided, and a driving time data table storage unit 62 that stores a driving time data table is provided. The time control unit 60 reads the average light amount data stored in the average light amount data storage unit 61, reads the drive time data table stored in the drive time data table storage unit 62, and reads the average light amount data and the drive time data table. All the LED elements constituting the LED array 31 are set to the same It has a configuration that determines the driving time to drive. Therefore, it is possible to accurately eliminate the difference in display density between the LED elements, and to determine the exposure amount between the LED print heads 7 in the color printer 1 including the plurality of LED print heads 7 having different average exposure amounts. Therefore, it is possible to suppress not only the density variation between the LED elements but also the density variation between the LED print heads. As a result, it is possible to suppress variations in image density in an output image of the image forming apparatus. In particular, in each LED print head mounted on a tandem type color printer, etc., each color has the same average exposure amount, so that the inconvenience that the color of the output image is different for each printer is avoided. Can be.

  Further, in the present embodiment, since the driving time for driving all of the plurality of LED elements constituting the LED array 31 at the same time is determined, the driving time is set for each LED element. It is possible to control the driving time with a simple configuration as compared with the case in which the driving is performed.

  Further, in the present embodiment, even when the LED elements having different ranks are arranged in the same LED array 31 (or the same LED chip) and the average exposure amount varies for each LED print head 7, Since the density variation between the print heads 7 can be suppressed, LED elements can be mass-produced, and even if a plurality of ranks are distributed, LED elements of all ranks can be used. As a result, costs can be reduced during mass production. Can be achieved.

  Furthermore, in the present embodiment, the average light amount of each LED array 31 is the exposure amount of each of the LED print heads 7 provided in the image forming units 3B, 3Y, 3C, and 3M for black, yellow, cyan, and magenta. The average light amount is obtained by measuring in advance, and the average light amount is stored in advance in the average light amount data storage unit 61 as characteristic data. Therefore, even when the calculation of the average light amount originally takes a long time, the drive time control unit 60 can quickly read out the average light amount. As a result, the drive time control unit 60 can determine the drive time more quickly. It is possible to do.

  It should be noted that the present invention is not limited to the above embodiment, and it is possible to appropriately change the structure and the like of each part based on the gist of the present invention, and they are not excluded from the scope of the present invention. .

  For example, in the above-described embodiment, the photosensitive member has a drum shape. However, the present invention is not limited to the drum shape. For example, a belt-like photosensitive member may be used.

  In the above embodiment, a color image is obtained by using black, yellow, cyan, and magenta toner images. However, the present invention is also applicable to a color image forming apparatus using two or more different color toners. can do.

  As an application example of the present invention, an image forming apparatus such as a copying machine or a printer using an LED print head having an LED array composed of a plurality of LED elements as a light source, in particular, a plurality of LED print heads And an image forming apparatus such as a tandem type color printer.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to a first embodiment of the present invention. FIG. 1 is a schematic diagram illustrating a schematic configuration of an LED array exposure apparatus in an image forming apparatus according to a first embodiment of the present invention. FIG. 3 is a schematic diagram when the LED array exposure apparatus is incorporated in an image forming apparatus. FIG. 2 is a block diagram illustrating a configuration of an LED array control unit in the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration of a drive circuit of the LED print head in the image forming apparatus according to the first embodiment of the present invention. 5 is a flowchart illustrating a procedure of lighting control of an LED element in the image forming apparatus according to the first embodiment of the present invention. FIG. 4 is a block diagram illustrating a configuration of an LED array control unit in a modification of the image forming apparatus according to the first embodiment of the present invention. 8 is a flowchart illustrating a procedure of lighting control of an LED element in a modification of the image forming apparatus according to the first embodiment of the present invention. FIG. 3 is a diagram illustrating a relationship between an exposure intensity of an LED element and a beam diameter of a development threshold in the image processing apparatus according to the first embodiment of the present invention. FIG. 3 is a diagram showing the relationship between the density of an LED element and the beam diameter of a development threshold in a conventional image processing apparatus. FIG. 9 is a block diagram illustrating a configuration of an LED array control unit in an image forming apparatus according to a second embodiment of the present invention. FIG. 3 is a diagram showing a relationship between a light emission exposure amount and a driving time at a predetermined average light amount. FIG. 13 is a diagram showing a relationship between the inclination of a straight line of each average light quantity shown in FIG. 12 and the magnitude of each average light quantity. FIG. 5 is a diagram showing an example of a data table relating to a drive time set in advance corresponding to a predetermined average light amount. 9 is a flowchart illustrating a procedure of lighting control of an LED element in the image forming apparatus according to the second embodiment of the present invention. FIG. 9 is a block diagram illustrating a configuration of an LED array control unit in a modification of the image forming apparatus according to the second embodiment of the present invention.

Explanation of reference numerals

REFERENCE SIGNS LIST 1 color printer 2 housing 3B, 3C, 3M, 3Y image forming unit 4 developing device 5 photoreceptor 6 main charger 7 LED print head 8 transport belt 9 transfer roller 10B, 10C, 10M, 10Y toner hopper 11a, 11b transport belt Drive roller,
REFERENCE SIGNS LIST 12 paper feed cassette 13 paper feed guide 14 paper 15 paper discharge guide 16 paper discharge unit 17 fixing unit 20 cleaning unit 30 substrate 31 LED array 32 lens array 33 drive circuit 34 LED array control unit 35 characteristic data storage unit 39 drive current correction data Calculation unit 40 Drive current correction data storage unit 41 Image signal 42 Image signal processing unit 43 Control signal generation unit 44 Image data correction calculation unit 50 CLK counter 51 SCLK counter 52 Storage unit 53 Gate unit 54 Constant current generation unit 60 Driving time control unit 61 Average light amount data storage unit 62 Drive time data table storage unit

Claims (10)

LED print head including an LED array including a plurality of LED elements whose lighting is controlled in accordance with image data and driving means for driving the plurality of LED elements, and an LED array for driving and controlling the LED print head In an image forming apparatus having control means,
The LED array control unit includes: a characteristic data storage unit configured to store a plurality of characteristic data relating to each of the plurality of LED elements; reading the characteristic data from the characteristic data storage unit; An image forming apparatus, comprising: a driving current correction data calculating means for calculating driving current correction data for each of the LED elements. LED print head including an LED array including a plurality of LED elements whose lighting is controlled in accordance with image data and driving means for driving the plurality of LED elements, and an LED array for driving and controlling the LED print head In an image forming apparatus having control means,
The LED array control unit includes: a characteristic data storage unit configured to store a plurality of characteristic data relating to each of the plurality of LED elements; reading the characteristic data from the characteristic data storage unit; Drive current correction data calculating means for calculating drive current correction data for each of the LED elements, and driving current correction data for reading the drive current correction data from the drive current correction data calculation means and storing the drive current correction data An image forming apparatus comprising storage means.   The characteristic data storage means stores data relating to the average light amount of the LED array as the characteristic data, and the LED array control means presets the LED array in accordance with the average light amount, and stores the LED array in the LED array control means. A drive time data table storage means in which a data table relating to a drive time for driving all of the plurality of LED elements to be driven at the same time is stored; and 3. The image forming apparatus according to claim 1, further comprising a driving time control unit that determines the driving time based on the data on the average light amount and the data table on the driving time. .   4. The image forming apparatus according to claim 3, wherein the data regarding the average light amount is obtained based on an exposure amount of the LED print head, and is stored in the characteristic data storage unit in advance.   The image forming apparatus is a tandem-type image forming apparatus including a plurality of the LED print heads, and the driving time control unit includes the plurality of LED elements included in the LED array included in each of the plurality of LED print heads. The image forming apparatus according to claim 3, wherein the driving time is determined for each of the images.   The image forming apparatus according to claim 1, wherein the characteristic data storage unit stores light amount data regarding each of the plurality of LED elements as the characteristic data.   3. The image forming apparatus according to claim 1, wherein the characteristic data storage unit stores data on a beam emitted by each of the plurality of LED elements as the characteristic data. 4.   The image forming apparatus according to claim 1, wherein the characteristic data storage unit stores resolution data regarding each of the plurality of LED elements as the characteristic data.   4. The image forming apparatus according to claim 1, wherein the driving unit drives all of the plurality of LED elements simultaneously by static driving. 5.   4. The LED array is divided into a plurality of blocks, and the driving unit sequentially drives the plurality of LED elements for each of the blocks by dynamic driving. An image forming apparatus according to claim 1.

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