JP2005352094A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus improving image quality by suppressing unevenness in density of an image. <P>SOLUTION: An LED array control part 34 driving and controlling an LED print head 7 is provided with a property data storing part 35, a driving current current compensation data calculating part 39, an image signal processing part 42 and an image data compensation calculation part 44. A plurality of property data which are already measured regarding each LED element constituting the LED array 31 is stored by a data storing part 35. Driving current compensation data is calculated by reading the property data stored to the data storing part 35 by the data calculating part 39. Compensation is carried out of the image data outputted by the image signal processing part 42 by the compensation calculating part 44 by using the driving current compensation data outputted by the data calculating part 39 and the compensated image data is outputted to a print head 7. Developing bias potential and dark potential are set so that a ratio of the difference between a dark potential of a photoreceptor and a developing bias potential and the difference between a developing bias potential and the residue potential of the photoreceptor are always the same. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an LED print head as exposure means for an electrophotographic printer, facsimile, 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 been attracting attention in order to reduce the size and simplify the apparatus. In this electrophotographic image forming apparatus, an LED print head used for exposure of a photoreceptor has an LED array formed by arranging a plurality of LED elements in a line, and each LED element is arranged based on image data. The light is selectively emitted individually.

  However, since it is impossible to manufacture a plurality of LED elements forming this LED array so that their light emission characteristics are all uniform, a current of the same magnitude is applied to all the LED elements. However, the amount of light differs for each LED element, resulting in variations in the amount of light for each LED element. As a result, the image density becomes uneven.

Therefore, there has been proposed an LED print head which has been corrected so as to suppress the variation in the light amount and make the light amount of each LED element uniform. For example, the light emission output of the LED printer is made uniform and the print quality is increased. In order to achieve this, there has been proposed a technique in which trimming with a laser beam is performed and a current supplied to each LED element is controlled by adjusting a resistance value so that the amount of light is constant (for example, see Patent Document 1). . In addition, correction data that makes the light emission amount of each LED element constant is provided for the purpose of eliminating the need for adjustment work when a head with uneven light intensity is incorporated into the product or when the LED print head is replaced. It has been proposed that a ROM that stores the correction data in the LED print head in advance is provided, and each LED element is lit using the correction data at the time of printing (for example, see Patent Document 2).
Japanese Patent Laid-Open No. 5-4376 (pages 3-4 and 6-8) Japanese Patent Laid-Open No. 5-50653 (page 3-4, FIG. 1)

  However, since the optical image data emitted from each LED element forms a latent image on the photoreceptor through the lens array, in the image forming apparatus having the conventional LED print head, the light amount of each LED element is made constant. Due to variations in the optical characteristics of the lens array, the formed dot diameter varies depending on each LED element, and it can be said that it is impossible to make the light quantity distribution of all dots uniform, resulting in vertical streaks on the image. There was an inconvenience of doing so. For example, as shown in FIG. 15, in LED element a ′ and 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 LED element b ′ having a larger dot diameter at the development threshold has a larger latent image dot and is expressed darker on the image.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that solves the above problems and can improve image quality by suppressing density unevenness of an image.

  In order to achieve the above object, the present invention comprises an LED array composed of a plurality of LED elements that are controlled to be lit on a photoconductor according to image data, and a drive circuit that drives the plurality of LED elements. The image forming apparatus having the LED print head to be operated and the LED array control means for driving and controlling the LED print head has the following features.

  First, the LED array control means reads a plurality of characteristic data relating to each of the plurality of LED elements, reads the characteristic data from the characteristic data storage means, and based on the characteristic data Drive current correction data calculating means for calculating drive current correction data for each of the plurality of LED elements is provided. As a result, the drive current correction data for each LED element is calculated from the characteristic data such as the light quantity data for each LED element, the data relating to the beam of each LED element, and the resolution data for each LED element, which is the cause of the density unevenness of the image. Since each LED element is lit with the drive current corrected based on this, the difference in display density between the plurality of LED elements constituting the LED array can be eliminated with high accuracy, and the density unevenness of the image can be eliminated. Can be suppressed.

  Furthermore, the potential setting for setting the developing bias potential and the dark potential so that the ratio between the difference between the dark potential of the photosensitive member and the developing bias potential and the ratio between the developing bias potential and the residual potential of the photosensitive member is always the same. Means. Thereby, even if the density correction of the entire image is performed, the development threshold for the beam of each LED element can be maintained in a constant state.

  According to the image forming apparatus of the present invention, even if the density correction of the entire image is performed, the development threshold for the beam of each LED element can be maintained in a constant state. Correction can always be effectively used, and density unevenness of the image can be stably suppressed. As a result, the occurrence of vertical stripes on the image can always be efficiently reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. In the image forming apparatus shown in FIG. 1, 1 is a color printer as an example of the image forming apparatus, 2 is a housing, 3B, 3Y, 3C, and 3M are image forming sections for black, yellow, cyan, and magenta, respectively. Reference numerals 10B, 10Y, 10C, and 10M denote toner hoppers for the respective colors. Also, 12 is a paper feed cassette for storing paper 14, 13 is a paper feed guide, 11a and 11b are transport belt drive rollers, 8 is a transport belt, 9 is a transfer roller, 17 is a fixing unit, 15 is a paper discharge guide, 16 Is a paper discharge unit. The image forming units 3B, 3Y, 3C, and 3M for each color are each composed of a developing device 4, a photoreceptor 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 on the photosensitive member 5 charged by the main charger 6 by the LED print head 7, and the exposed electrostatic latent image is developed by the developing device 4. As a result, a visible image is formed. Such a reversal development process is performed for each color of black, yellow, cyan, and magenta. The paper 14 delivered from the paper feed cassette 12 is guided by the paper feed guide 13 and is attracted to the upper surface of the transport belt 8 rotating counterclockwise, so that the image forming units 3B, 3Y, 3C, When passing below 3M, the image of each color is sequentially transferred onto the paper 14 by the transfer roller 9. In this way, the four color toners that form a 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 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 showing a schematic configuration of the LED array print head in the image forming apparatus according to the embodiment of the present invention. In FIG. 2, the LED print heads 7 are arranged in a row on a substrate 30 having wiring, and an LED array 31 composed of a plurality of LEDs whose lighting is controlled according to image data, and above the LED array 31. The lens array 32 is arranged to form an erecting equal-magnification image, and a drive circuit 33 that drives a plurality of LED elements constituting the LED array 31. Here, the substrate 30 and the lens array 32 described above are held by a holding member (not shown). Further, an LED array control unit 34 that drives and controls the LED print head 7 is provided outside.

  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 drum-shaped photoconductor. 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 with a wavy line.

  As described above, each LED element is driven in response to an image signal transmitted to the color printer 1 of FIG. 1 from an external PC (not shown) or the like, and light emitted by each LED element is emitted from the lens array. An image is formed as a dot on the surface of the photoconductor 5 via the line 32. Note that the image forming apparatus according to the present embodiment is formed such that a pixel having a larger exposure energy (or LED element emission energy) on the photoconductor 5 has a higher density, and this exposure energy (or LED element emission) is formed. Energy) is expressed by the light emission intensity (= drive current) of the LED element × the light emission time (= drive current supply time).

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

  The LED array control unit 34 drives and controls 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 to the LED array control unit 34 from an external device such as a frame memory or a scanner, and converts the image signal 41 into an image. It is a means to convert to data. This image data is data for indicating the pixel density separated for each color of black, yellow, cyan and magenta, and indicates the drive current (light emission intensity) and the light emission time (drive current supply time) of the LED element. 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 a means for storing a plurality of pre-measured characteristic data for each of the plurality of LED elements constituting the LED array 31. As shown in FIG. A light amount data storage unit 36 that stores data as characteristic data, a beam data storage unit 37 that stores data related to a beam emitted from each LED element, for example, data related to a beam diameter or a beam area, and a resolution related to each LED element Data, for example, MTF (Modulation Transfer Function) data is configured by a resolution data storage unit 38 that stores characteristic data. The characteristic data storage unit 35 is composed of, for example, a ROM (read-only memory), but a rewritable PROM (for example, data erasure is performed by ultraviolet rays in order to cope with characteristic changes of individual LED elements. It is also possible to employ a configuration using an EPROM that is used in (1) or an EEPROM that electrically erases data.

  A 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 the 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 characteristic data storage unit 35, and 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 in accordance with 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 the individual LED elements by changing the drive current of the individual LED elements constituting the LED array 31, as will be described later. For example, when correcting the drive current of the first dot (LED element No. 1), the drive current correction data P ₁ is used, and the drive current of the nth dot (LED element No. n) is calculated. In the case of correction, drive current correction data P _n is used.

  The image data correction calculation unit 44 corrects the image data output from the image signal processing unit 42 using the drive current correction data P output from the drive current correction data calculation unit 39. That is, the image data correction calculation unit 44 is configured to display individual image data constituting the LED array 31 among the image data output from the image signal processing unit 42 according to the drive current correction data P output from the drive current correction data calculation unit 39. Correction of the m-bit digital data indicating the drive current relating to the LED element is performed. 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 receives the CLK counter 50 that counts the clock signal CLK, the SCLK counter 51 that counts the strobe clock signal SCLK, and the corrected image data indicating the pixel density. The storage unit 52 temporarily stores, the gate unit 53 that opens and closes according to the logic of the output time control signal STROBE, and the constant current generation unit 54 that generates the drive current of the LED array 31.

  The drive circuit 33 of the LED print head 7 having the above-described configuration is initialized by the fall 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. Reception of corrected image data input in synchronization with the clock signal CLK is started.

  The storage unit 52 includes a shift register and a latch circuit, and temporarily stores data necessary for light emission of the LED array 31 in order to convert the input corrected image data. Here, the driving method of each LED element that constitutes the LED print head includes a static drive system that performs turning on / off control of all LED elements at once, and a dynamic that performs turning on / off control for each block by dividing the LED into a plurality of blocks. There is a drive method, but when the static drive method is adopted, data for all LED elements is temporarily stored. When the dynamic drive method is adopted, 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 has been completed based on the count number of the clock signal CLK. The timing control signal STREQ is output to the control signal generator 43.

  When the control signal generator 43 receives the light emission timing control signal STREQ, the output time control signal STROBE is set to the active level (low level), and when the strobe clock signal SCLK starts to be input, the SCLK counter 51 counts the strobe clock signal SCLK. The gate part 53 is opened. Therefore, a drive current based on the drive current correction data P stored in the storage unit 52 is caused to flow through each LED element constituting the LED array 31 for a light emission time based on the image data stored in the storage unit 52, and the photosensitive element The body 5 is exposed.

  FIG. 6 is a flowchart showing the procedure of lighting control of the LED element. In this control procedure, first, n = 1 is set in order to target the first line out of the total number of lines N (step S1). Next, the characteristic data of each LED element is read from the characteristic data storage unit 35 (step S2), and the driving current correction data calculation unit 39 calculates the driving 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 S6), 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 the n exceeds the total number N of lines to be printed (step S9). For example, the above process is repeated in the same manner for line n (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 directly output to the image data correction calculation unit 44. However, as shown in FIG. The drive current correction data storage unit 40 for storing the drive current correction data P calculated by the drive current correction data calculation unit 39 is separately provided, and the drive current correction data storage unit 40 is used as the drive current correction data calculation unit 39 and the image. It may be configured to be connected to the data correction calculation 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 drive current correction data P to the image data correction calculation unit 44. Data P is output. In order to cope with the change of the drive current correction data P based on the characteristic change of each LED element, the drive current correction data storage unit 40 includes, for example, a rewritable PROM (for example, erasing data with ultraviolet rays). EPROM to be used, EEPROM to electrically erase data) or the like is used.

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

  In this case, the LED element lighting control procedure 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 unit 35 (step S101), and the drive current correction data calculation unit 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 S103). Further, in order to target the next line n, n is incremented by +1 (step S104), and it is checked whether or not the n exceeds the total number N of lines to be printed (step S105). For example, the above process is repeated in the same way for the line n, and the drive current correction data storage unit 40 stores the drive current correction data P for all the lines (steps S101 to S105).

  Next, in order to make the first line out of the total number of lines N, 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 S109), 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 n exceeds the total number N of lines to be printed (step S112). For example, the above process is repeated in the same manner for line n (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 before correcting the image data and the beam diameter of the development threshold, and FIG. 9B shows the state after correcting the image data. This 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 the same in both the high density part and the low density part, but the beam diameter (This beam diameter is generally defined in the range of 13.5% of the peak light amount). That is, in both the high density portion and 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 (Db> Da, db> da).

  However, as shown in FIG. 9A, in the high density part, the dot diameter Sb at the development threshold of the LED element b is larger than the dot diameter Sa of the LED element a, but in the low density part. Contrary to the case of the high density portion, the dot diameter sa at the development threshold of the LED element a is larger than the dot diameter sb of the LED element b. That is, the magnitude relationship between the dot diameters in the development threshold values of the LED element a and the LED element b does not depend on the magnitude relation between the beam diameters. Therefore, under this condition, the LED element b having a larger dot diameter at the development threshold is higher in the high density portion, and the LED element a having a larger dot diameter at the development threshold is lower in the low density portion. Becomes larger, and is expressed deeply on the image.

  Therefore, the beam diameter at each development threshold value of the LED element a and the LED element b is stored in advance as characteristic data, and correction data for the drive current is created using the characteristic data relating to the beam diameter, and the LED in each display density unit. The difference in display density between the element a and the LED element b is eliminated.

  That is, as shown in FIG. 9B, in the high density portion, the LED element b having a large beam diameter (large dot diameter) has a small driving current, and the LED element has a small beam diameter (small dot diameter). The drive current correction data is created using the characteristic data relating to the beam diameter so as to increase the drive current of a. On the other hand, in the low density portion, the driving current of the LED element b having a large beam diameter (small dot diameter) is increased, and the driving current of the LED element a having a small beam diameter (large dot diameter) is decreased. Current correction data is created using characteristic data relating to the beam diameter. Thereby, since the dot diameters of the LED element a and the LED element b at the development threshold value of each display density portion are the same, the difference in display density between the LED element a and the LED element b is eliminated in each display density portion. Will be able to.

  Although FIG. 9 shows the case where the drive current correction data is created using the beam diameter as the characteristic data of the LED element, as described above, the light amount data and the data regarding the beam area for each LED element, and the MTF. The drive current correction data can also be created 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, with respect to the individual LED elements constituting the LED array 31, the light amount data of each LED element and the data regarding the beam of each LED element, which are preliminarily measured and cause of uneven density of the image, In some cases, a characteristic data storage unit 35 for storing characteristic data including resolution data of each LED element is provided, and the characteristic data stored in the characteristic data storage unit 35 is read, and the individual LEDs constituting the LED array 31 are read. Since the drive current correction data calculation unit 39 for calculating the drive current correction data P related to the elements is provided and the drive current corrected based on the drive current correction data P flows to each LED element constituting the LED array 31, Differences in display density between LED elements can be eliminated with high accuracy, and uneven density in images can be eliminated. It can be obtained. As a result, it is possible to efficiently reduce the occurrence of vertical stripes on the image.

  In the present embodiment, since the rewritable PROM can be used for the characteristic data storage unit 35, the characteristic data of each LED element can be changed even when the characteristics of the individual LED elements change. Rewriting can be performed smoothly. Therefore, when calculating the drive current correction data P, it is possible to calculate the drive current correction data for each LED element with high accuracy. As a result, it is possible to correct the image data with high accuracy. Become.

By the way, the above-described correction of the drive current to each LED element is based on the precondition that the development threshold is in a constant state. However, in order to correct the density of the entire image, the development bias from the developing device 4 is simply used. When the adjustment is made by changing the potential V _DB , the development threshold value fluctuates following this, so that the correction of the drive current to each LED element subjected to the corner correction may become invalid. That is, as shown in FIG. 9B, the dot diameters Sa and Sb (or sa and sb) of the LED elements a and b made the same at a predetermined development threshold increase the development threshold (FIG. 9B). Sa> Sb (or sa> sb) as the development threshold value in the middle shifts upward), and conversely, Sb increases as the development threshold value decreases (the development threshold value in FIG. 9B translates downward). This is because> Sa (or sb> sa).

Therefore, in the present embodiment, in correcting the density of the entire image, the development position surface potential of the photosensitive member 5 charged by the main charger 6 together with the development bias potential V _DB , that is, the dark potential V ₀ is adjusted. In this case, the difference V ₁ (= V ₀ −V _DB ) between the dark potential V ₀ and the development bias potential V _{DB and} the difference V between the development bias potential V _DB and the surface potential after development position exposure, that is, the residual potential V _{L 2} (= V _DB -V _L) ratio of _{V 1 / V 2 (= (} V 0 -V DB) / (V DB -V L)) development bias so is always the same potential V _DB and dark potential By setting V ₀ , the development threshold for the beam of each LED element is maintained in a constant state.

The density correction method will be described with reference to FIGS. FIG. 10 is a schematic diagram showing the relationship between the developing bias potential V _DB , the dark potential V ₀ , and the residual potential V _L , and FIG. 11 shows the formation of a test pattern used for density correction of the entire image in the image forming apparatus of this embodiment. FIG. 12 is a side view of the main part, FIG. 13 is a diagram showing an example of the test pattern formation conditions, and FIG. 14 is a flowchart showing the density correction procedure.

As shown in FIG. 14, first, in step S200, a plurality of test patterns T (for example, patterns with a duty of 100%) are formed on the photoconductor 5 by the image forming unit 10B for density correction, for example, the image forming unit 10B for black. They are formed in order and transferred onto the conveyor belt 8 (see FIG. 11). Here, in forming each test pattern T, different conditions registered in advance, for example, five conditions shown in FIG. 13 are set. In particular, in the present embodiment, the development bias potential V _DB and the dark potential V _{0 under} each condition are the difference V ₁ between the dark potential V ₀ and the development bias potential V _DB , the development bias potential V _DB, and the residual potential V _L. The ratio V ₁ / V ₂ with respect to the difference V ₂ has a constant value (for example, 0.5 shown in FIG. 13). Note that the light emission time of each LED element is set to be increased in proportion to the increment of the contrast potential (V ₀ −V _L ) between the conditions.

  Next, in step S201, the amount (coverage) of each test pattern T on the conveyor belt 8 is sequentially detected by the reflective detection sensor 60 including a light emitting unit and a light receiving unit (see FIGS. 11 and 12). Subsequently, in step S202, each detected coverage is collated with a pre-registered target coverage. Here, together with the two detected coverage ratios between which the target coverage ratio exists, the test pattern forming condition at the detected coverage ratio is determined.

In step S203, the development bias potential corresponding to the target coverage is calculated from each development bias potential V _DB under the determined test pattern forming condition by proportional distribution with the distribution of the target coverage between the determined detected coverages. V _DB is calculated, and then the dark potential V ₀ is calculated from the calculated developing bias potential V _DB so as to satisfy the relationship of the ratio V ₁ / V ₂ . At the same time, from each light emission time under the determined test pattern formation conditions, a proportional calculation is made by the distribution of the target coverage between the detected coverages of the determination, and the light emission time corresponding to the target coverage is calculated. .

For example, as shown in FIG. 13, the detection coverage of the test pattern T formed under the second condition is 86%, and the detection coverage of the test pattern T formed under the third condition is 90%. When the target coverage ratio of 88% exists between the development bias potential V _DB of the second condition of 200 [V] and the development bias potential V _DB of the third condition of 220 [V], the target coverage ratio is reached. 210 [V] is calculated as the corresponding development bias potential V _DB . From this 210 [V], the dark potential 305 [V] corresponding to the target coverage is calculated so as to satisfy the relationship of 0.5, which is the ratio V ₁ / V ₂ . Incidentally, when the light emission time under the second condition is 2.7 [μs] and the light emission time under the third condition is 3.0 [μs], the light emission time corresponding to the target coverage is 2.85 [μs]. ] Is calculated.

Finally, in step S204, the calculated development bias potential V _DB and dark potential V ₀ are set as optimum conditions. However, such a series of processes is automatically performed under a command from the control unit. The dark potential V ₀ can be set, for example, by obtaining the relationship between the voltage applied to the main charger 6 and the dark potential V ₀ .

  This process is sequentially performed for the other yellow, cyan, and magenta image forming units 10Y, 10C, and 10M, thereby correcting the density of the entire image.

By performing this way entire image density correction, and dark potential V ₀ which the difference V ₁ of the developing bias potential V _DB, the ratio V ₁ / V of the developing bias potential V _DB the difference V ₂ of the residual potential V _{L Since} the development bias potential V _DB and the dark potential V ₀ are set so that ₂ is always the same, the development threshold for the beam of each LED element can be kept constant. Then, the correction of the drive current to each LED element can always be effectively used, and even if the density correction is performed, the density unevenness of the image can be suppressed.

  In addition, this invention is not limited to the said embodiment, Based on the meaning of this invention, it is possible to change suitably the structure of each part, etc., and they are not excluded from the scope of the present invention. .

  For example, in the above-described embodiment, the photoconductor is a drum shape. However, the photoconductor is not limited to the drum shape. For example, a belt-like photoconductor may be used.

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

  In addition, this invention is not limited to said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention.

  The present invention is useful for an image forming apparatus using an LED print head.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. It is a schematic diagram which shows schematic structure of the LED array exposure apparatus in the image forming apparatus which concerns on embodiment of this invention. It is a schematic diagram at the time of incorporating an LED array exposure apparatus in an image forming apparatus. It is a block diagram which shows the structure of the LED array control part in the image forming apparatus which concerns on embodiment of this invention. FIG. 2 is a block diagram illustrating a configuration of a drive circuit of an LED print head in the image forming apparatus according to the embodiment of the present invention. 4 is a flowchart illustrating a procedure for controlling lighting of LED elements in the image forming apparatus according to the embodiment of the present invention. It is a block diagram which shows the structure of the LED array control part in the image forming apparatus which concerns on other embodiment of this invention. It is a flowchart which shows the procedure of the lighting control of the LED element in the image forming apparatus which concerns on other embodiment of this invention. FIG. 4 is a diagram showing a relationship between exposure intensity of LED elements and a beam diameter of a development threshold value in the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a schematic diagram showing a relationship among a developing bias potential V _DB , a dark potential V ₀ , and a residual potential V _L. FIG. 5 is a perspective view of a principal part showing a formation / detection state of a test pattern used for density correction of the entire image in the image forming apparatus according to the embodiment of the present invention. FIG. 5 is a side view of a main part showing a test pattern formation / detection state used for density correction of the entire image in the image forming apparatus according to the embodiment of the present invention. FIG. 5 is a diagram illustrating an example of test pattern formation conditions used for density correction of the entire image in the image forming apparatus according to the embodiment of the present invention. 5 is a flowchart illustrating a density correction procedure in the image forming apparatus according to the embodiment of the present invention. It is the figure which showed the relationship between the light and shade of the LED element in the conventional image forming apparatus, and the beam diameter of a development threshold value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color printer 2 Case 3B, 3C, 3M, 3Y Image formation part 4 Developer 5 Photoconductor 6 Main charger 7 LED print head 8 Conveying belt 9 Transfer roller 10B, 10C, 10M, 10Y Toner hopper 11a, 11b Conveying belt Drive roller 12 Paper feed cassette 13 Paper feed guide 14 Paper 15 Paper discharge guide 16 Paper discharge part 17 Fixing part 20 Cleaning part 30 Substrate 31 LED array 32 Lens array 33 Drive circuit 34 LED array control part 35 Characteristic data storage part 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 Reflective type Detection sensor

Claims (1)

An LED print head composed of an LED array composed of a plurality of LED elements that are controlled to be lighted in accordance with image data with respect to the photoconductor, a drive circuit that drives the plurality of LED elements, and the LED print head. In an image forming apparatus having LED array control means for driving control,
The LED array control means reads characteristic data storage means for storing a plurality of characteristic data for each of the plurality of LED elements, reads the characteristic data from the characteristic data storage means, and sets the plurality of characteristics data based on the characteristic data. Drive current correction data calculating means for calculating drive current correction data for each of the LED elements, and
Further, there is provided a potential setting means for setting the developing bias potential and the dark potential so that the ratio between the difference between the dark potential of the photosensitive member and the developing bias potential and the ratio between the developing bias potential and the residual potential of the photosensitive member are always the same. An image forming apparatus.

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