JP2005096112A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can suppress not only density deviation among LED elements but also density deviation among LED printing heads. <P>SOLUTION: An LED array controlling part 34 is provided with a driving time controlling part 60 for controlling driving times (light emitting times) of a plurality of the LED elements constituting an LED array 31, a mean quantity-of-light data storing part 61 for storing a mean quantity-of-light of the LED array 31 as a characteristic data, and a driving time data table storing part 62 for storing a driving time data table based on a mean light exposure amount. The driving time controlling part 60 reads out the mean quantity-of-light data stored in the mean light volume data storing part 61, and reads out the driving time data table stored in the driving time data table storing part 62. Based on the mean quantity-of-light data and the driving time data table, the driving time for driving all the LED elements constituting the LED array 31 at the same time is determined. <P>COPYRIGHT: (C)2005,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, an LED print head that has been corrected so as to suppress the variation in the amount of light and make the light amount of each LED element uniform has been proposed. 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, the LED elements constituting the LED array can be ranked according to the amount of light when the LED elements are lit with the same drive current, and the LED elements with different ranks can be classified into the same LED array (or the same LED chip). ), Even if the drive current for each LED element is corrected as in the above-described prior art, there is a possibility that dots that cannot be corrected appropriately due to the variation in rank are generated.

  Here, in order to avoid such inconvenience, it is sufficient to use only LED elements having the same rank. However, when LED elements are mass-produced, LED elements other than a certain rank are used because they are distributed in a plurality of ranks. The inconvenience that it becomes impossible occurs, and as a result, the cost increases 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 dots that cannot be corrected appropriately due to rank variation can be avoided. Since the average light amount varies by about the number of ranks of the LED elements, the average light amount varies for each LED array (that is, the average exposure amount varies for each LED print head). As a result, in the output image in the image forming apparatus There is a problem that the image density varies. In particular, a plurality of LED print heads mounted on a tandem color printer or the like has a different average exposure amount for each color, so that there is a problem that the color of an output image also 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 current is corrected for each LED element and the drive time is corrected for each LED element. Thus, it is possible to eliminate the above-described variation in the average light amount, but in this case, it is necessary to set the driving time for each LED element, and the configuration for performing the control is complicated. There was a problem.

  The present invention solves the above-described problems, eliminates the difference in display density between the LED elements with high accuracy, and provides an image forming apparatus including a plurality of LED print heads having different average exposure amounts. It is an object of the present invention to provide an image forming apparatus capable of suppressing not only the density variation between the LED elements but also the density variation between the LED print heads by making the exposure amounts equal.

  In order to achieve the above object, an image forming apparatus according to claim 1 includes: an LED array composed of a plurality of LED elements that are controlled to be turned on according to image data; and a drive unit that drives the plurality of LED elements. In an image forming apparatus having an LED print head configured and an LED array control unit that drives and controls the LED print head, the LED array control unit includes a drive current correction unit that corrects a drive current for each of the plurality of LED elements. , A light amount data storage means in which data relating to the average light amount of the LED array is stored, and a driving time for driving all of the plurality of LED elements that are set in advance corresponding to the average light amount and constitute the LED array in the same time Driving time data table storage means storing data table, data on average light quantity and driving time Reads the data table relating, on the basis of the data table relating data and the drive time for the average amount of light, wherein the drive time control means for determining the driving time is provided.

  The image forming apparatus according to claim 2 is characterized in that the data relating to the average light quantity is obtained based on the exposure amount of the LED print head and is stored in advance in the characteristic data storage means.

  The image forming apparatus according to claim 3 is a tandem type image forming apparatus including a plurality of LED print heads, and the driving time control means includes a plurality of LED arrays included in each of the plurality of LED print heads. The driving time is determined for each LED element.

  The image forming apparatus according to claim 4 is characterized in that the driving means drives all of the plurality of LED elements simultaneously by static driving.

  According to a fifth aspect of the present invention, the LED array is divided into a plurality of blocks, and the driving means sequentially drives the plurality of LED elements for each block by dynamic driving.

  According to the present invention, the difference in display density between the LED elements can be eliminated with high accuracy, and the exposure amounts between the LED print heads having different average exposure amounts can be made equal as a result. Moreover, not only the density variation among the LED elements but also the density variation between the LED print heads can be suppressed. As a result, it is possible to suppress variations in image density in the output image in the image forming apparatus.

  Further, according to the present invention, in particular, each LED print head mounted in a tandem color printer or the like has an equal average exposure amount for each color. It is possible to avoid the inconvenience of being lost.

  In addition, according to the present invention, since the drive time for driving all the LED elements constituting the LED array in the same time is determined, the drive 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 when 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, density variation between the LED print heads can be suppressed. Therefore, even when LED elements are mass-produced and a plurality of ranks are distributed, LED elements of all ranks can be used, and as a result, costs 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 LED print head in advance, and the average light amount is stored in advance in the average light amount data storage unit as characteristic data. Because it is configured, even if it takes a long time to calculate the average light amount, 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. It becomes possible to perform at high speed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the 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 tandem 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 unit, 10B, 10Y, 10C, and 10M are toner hoppers of the respective colors. Further, 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 by the LED print head 7 on the photoreceptor 5 charged by the main charger 6, and developed by the developer 4 to form a visible image. Such a 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. 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 a 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 and an LED array 31 composed of a plurality of LED elements whose lighting is controlled according to image data. The lens array 32 forms 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. The LED array 31 may be constituted by dividing a plurality of chips (LED chips) on which a plurality of LED elements are arranged by dividing into a plurality of blocks.

  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, with reference to FIG. 4 and FIG. 5, an example of drive current correction for each of the plurality of LED elements constituting the LED array 31 in the present embodiment will be described. FIG. 4 is a block diagram showing the configuration of the LED array control unit in the image forming apparatus according to the embodiment of the present invention. In particular, FIG. 5 is a block diagram for explaining correction of the drive current of the LED element. 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. The correction of the drive current for each of the plurality of LED elements constituting the LED array 31 described below is merely an example, and the correction is not limited to this, and the background art described above is not limited thereto. Any correction of the drive current may be used including the correction of the drive current described in.

  In FIG. 4, the LED array control unit 34 controls 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 The image data correction calculation unit 44 is configured. Of these, the drive current for correcting the drive current for each of the plurality of LED elements constituting the LED array 31 by the characteristic data storage unit 35, the drive current correction data calculation unit 39, and the image data correction calculation unit 44. A correction unit is configured.

  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 characteristic data measured in advance for each of the plurality of LED elements constituting the LED array 31. For example, as shown in FIG. A light amount data storage unit 36 that stores light amount data as characteristic data, a beam data storage unit 37 that stores data related to a beam emitted by each LED element, for example, data related to a beam diameter or a beam area, and a resolution that relates to each LED element For example, MTF (Modulation Transfer Function) data is stored in the resolution data storage unit 38 as 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 the drive current of dot 1 (LED element No. 1) is corrected, the drive current correction data P ₁ is used, and when the drive current of dot n (LED element No. n) is corrected. The 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 constituting the LED array 31 by the driving circuit 33 includes a static driving method in which lighting / extinguishing 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 method in which the LED array 31 is divided into a plurality of blocks, and the lighting control is performed for each block (that is, for each chip) (that is, the plurality of LED elements are sequentially driven for each block). When the 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 drum 5 is exposed.

  FIG. 6 is a flowchart showing the procedure for controlling the lighting of the LED elements when the drive current for each LED element is corrected. 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 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 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 unit includes a characteristic data storage unit 35, a drive current correction data calculation unit 39, an image data correction calculation unit 44, and a drive current correction data storage unit 40. The 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 outputs the drive current correction data P to the image data correction calculation unit 44. 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 data correction calculation unit 44 can quickly read out the drive current correction data P. As a result, the image data correction calculation unit 44 can correct the image data 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 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 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 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 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).

  As described above, with respect to the individual LED elements constituting the LED array 31, the characteristic data storage unit 35 for storing a plurality of characteristic data measured in advance is provided, and the characteristic data provided in the characteristic data storage unit 35 is read. The drive current correction data calculation unit 39 for calculating the drive current correction data P related to the individual LED elements constituting the LED array 31 is provided, and the drive current based on the drive current correction data P is applied to each LED element constituting the LED array 31. Since it is configured to flow, the difference in display density between the LED elements can be eliminated with high accuracy.

  However, simply correcting the drive current for each LED element causes the following inconvenience. That is, the LED elements constituting the LED array 31 can be ranked according to the amount of light when they are lit with the same drive current, but LED elements with different ranks can be ranked with the same LED array 31 (or the same If the LED chips are arranged in the LED chip), there is a possibility that dots that cannot be corrected properly due to the variation in the ranks may be generated only by correcting the drive current for each LED element. Therefore, in order to avoid such inconvenience, it is sufficient to use only LED elements having the same rank. However, when LED elements are mass-produced, LED elements other than a certain rank can be used because they are distributed in a plurality of ranks. This is inappropriate from the viewpoint of mass productivity. Therefore, in the same LED array 31 (or the same LED chip), LED elements having similar ranks are often used. In this case, even if the drive current for each LED element is corrected, the LED array 31 Since the average light amount varies by 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 varies for each LED print head 7). As a result, the output in the image forming apparatus There has been a problem that the image density varies in the image. In particular, a plurality of LED print heads mounted on a tandem color printer or the like has a different average exposure amount for each color, so that there is a problem that the color of an output image also differs for each printer. .

  Therefore, in this embodiment, the variation in the average exposure amount for each of the plurality of LED print heads mounted on the tandem color printer or the like shown in FIG. 1 is corrected, and the difference in display density between the LED print heads is corrected. By reducing the above, it was decided to eliminate the inconvenience described above. This point will be described in detail below.

  FIG. 9 is a block diagram showing the configuration of the LED array control unit in the image forming apparatus according to the embodiment of the present invention, and in particular, a block diagram for explaining correction of the driving time of the LED elements.

  In the block diagram shown in FIG. 9, the LED array control unit 34 described with reference to FIG. 4 constitutes means for correcting variations in the average exposure amount for each of the plurality of LED print heads 7, ie, the LED array 31. Drive time control unit 60 for controlling the drive time (light emission time) of the plurality of LED elements to be stored, and the average light amount of the LED array 31 (hereinafter, may be expressed as the average exposure amount of the LED print head 7) as characteristic data. The configuration is exactly the same except that an average light amount data storage unit 61 for performing the above and a drive time data table storage unit 62 for storing a data table relating to the drive time based on the average exposure amount are provided. Therefore, since other operations and configurations are the same as those in the case of FIG. 4 described above, the same members are denoted by the same reference numerals, and detailed description thereof is omitted here.

  First, as shown in FIG. 9, the LED array control unit 34 is provided with an average light amount data storage unit 61 that stores the average light amount of the LED array 31. Here, the average light amount of the LED array 31 means an 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 always lit. Say. The characteristic data relating to the average light quantity is obtained by measuring the exposure amounts of the LED print heads 7 provided in the image forming units 3B, 3Y, 3C, and 3M for black, yellow, cyan, and magenta in advance. It is calculated based on the amount and stored in advance in the above-mentioned average light amount data storage unit 61.

  As shown in FIG. 9, the LED array control unit 34 is provided with a drive time control unit 60, and the average light quantity data storage unit 61 is connected to the drive time control unit 60. The drive time control unit 60 reads the average light amount data stored in the average light amount data storage unit 61 and drives all LED elements constituting the LED array 31 in the same time based on the average light amount data. This is for determining the driving time.

  Further, the LED array control unit 34 is provided with a drive time data table storage unit 62 in which a data table (see FIG. 12 described later) relating to a drive time set in advance corresponding to a predetermined average light amount is stored. The drive time data table storage unit 62 is connected to the drive 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 drive time for a plurality of LED arrays 31 having different average light amounts. This point will be described in detail below. Note that the exposure amount at the time of light emission is determined by the EV characteristic of the photoconductor 5, and the value does not change if the photoconductor 5 is the same.

  FIG. 10 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 is 2.10 μW).

  As can be seen from FIG. 10, 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 exposure amount during light emission also increases. That is, the LED print head having the Qa average exposure dose has the largest light emission exposure amount, and the LED print head having the Qc average exposure dose has the smallest light emission exposure amount. This difference in the exposure amount during light emission causes variations in image density in the output image.

  Therefore, in the present embodiment, the correction of the drive current described in FIGS. 4 to 6 is performed on each LED element, thereby suppressing the density variation between the LED elements and based on the average light amount. By determining the drive time for driving all of the plurality of LED elements constituting the LED array 31 in the same time, density variation between the LED print heads 7 is also suppressed.

  That is, for example, when the exposure amount during light emission is Q, as shown in FIG. 10, 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 and the driving time is set to Tc for the LED print head 7 having the average exposure amount Qc. Then, based on the drive time data obtained in this way, the drive time is set in advance corresponding to each average light amount, thereby creating a data table relating to the drive time shown in FIG. The drive time data table is stored in the storage unit 62.

  The drive time control unit 60 reads the average light amount data stored in the average light amount data storage unit 61 and reads the drive time data table stored in the drive time data table storage unit 62. The driving time for obtaining the exposure amount Q is determined based on the driving time data table. That is, the drive time control unit 60 determines a drive time for driving all 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 driving time is determined to be 2.34 μsec, and the yellow image forming unit 3Y When the average light amount of the LED array 31 constituting the provided LED print head 7 is 2.10 μW, the driving time is determined to be 2.50 μsec (see FIG. 12). Similarly, the driving times of the LED elements are determined for the cyan and magenta image forming units 3C and 3M. In this embodiment, in this way, in the tandem type color printer 1 including a plurality of LED print heads 7, the drive time control unit 60 includes a plurality of LED arrays 31 included in each of the plurality of LED print heads 7. The driving time is determined for each LED element. Thereafter, data relating to the driving time determined for each LED print head 7 (driving time data) is output from the driving time control unit 60 to the control signal generation unit 43.

  The control signal generator 43 that has received the driving time data generates an output time control signal STROBE corresponding to the driving time data, and the STROBE is output to the LED print head 7. As shown in FIG. 9, the corrected image data in which the drive current is corrected is output to the LED print head 7 as in FIG. 4 described above. And the control similar to the case demonstrated in FIG. 4, FIG. 5 is performed. Accordingly, 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 drive current correction data P stored in the storage unit 52. The current is applied only for the drive time (or 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. 11, the slopes of the straight lines of the average light amounts Qa, Qb, and Qc shown in FIG. 10 and the magnitudes of the average light amounts Qa, Qb, and Qc are in a linear relationship (proportional relationship). 11, for example, the other average light quantity Qd shown in FIG. 10 (where Qd has a relationship of Qa> Qd> Qb, for example, Qa is 2.50 μW, 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, Qc is 2.10 μW) Slopes Ld and Le can be obtained. Therefore, by using FIG. 10, it is possible to obtain the drive 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, since it becomes possible to obtain the relationship between the exposure amount at the time of light emission at an arbitrary average light amount and the driving time, it is possible to create a more detailed driving time data table by adding these data. As a result, the driving time can be determined with higher accuracy.

  In addition, as described above, the driving method of each LED element constituting the LED array 31 is a static driving method in which all the LED elements are turned on and off simultaneously (that is, all the plurality of LED elements are driven simultaneously), and the LED Any of the dynamic drive systems in which the array 31 is divided into a plurality of blocks and the lighting control is performed for each block (that is, for each chip) (that is, the plurality of LED elements are sequentially driven for each block) may be employed.

  FIG. 13 is a flowchart showing the procedure for controlling the lighting of LED elements when correcting the driving current for each LED element and determining the driving time for each of a plurality of LED elements constituting the LED array of each LED print head. It is. It is a flowchart which shows the procedure of the lighting control of an 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 sets the drive time for obtaining the light exposure amount based on the average light amount. Determine (step S53). Next, data relating to the determined drive time (drive time data) is output from the drive time control unit 60 to the control signal generation unit 43 (step S54), and the control signal generation unit 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 is 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 the present embodiment, as described above, the LED array control unit 34 described with reference to FIG. 4 includes the drive time control unit 60, the average light amount data storage unit 61, and the drive time data table storage unit 62. However, as a modification of the present embodiment, the LED array control unit 34 described in FIG. 7 (that is, the drive current correction data storage unit 40 that stores the drive current correction data P calculated by the drive current correction data calculation unit 39) is provided. A drive time control unit 60, an average light amount data storage unit 61, and a drive time data table storage unit 62 may be provided in a separately provided LED array control unit 34) (see FIG. 14).

  As described above, in this embodiment, in addition to the correction of the drive current for the individual LED elements constituting the LED array 31 by the drive current correction unit, the average light amount data storage unit 61 that stores the average light amount of the LED array 31 is provided. The drive time data table storage unit 62 for storing the drive time data table is provided, and the drive time control unit 60 reads the average light amount data stored in the average light amount data storage unit 61 and also stores the drive time data table in the drive time data table storage unit 62. The stored driving time data table is read, and the driving time for driving all the LED elements constituting the LED array 31 in the same time is determined based on the average light amount data and the driving time data table. Accordingly, the difference in display density between the LED elements can be eliminated with high accuracy, and the exposure amount between the LED print heads 7 is obtained as a result in the color printer 1 having a plurality of LED print heads 7 having different average exposure amounts. Therefore, not only the density variation among the LED elements but also the density variation between the LED print heads can be suppressed. As a result, it is possible to suppress variations in image density in the output image in the image forming apparatus. In particular, each LED print head mounted in a tandem color printer or the like has the same average exposure amount for each color, so that the inconvenience that the hue of the output image differs for each printer is avoided. Can do.

  In the present embodiment, the driving time for driving all the plurality of LED elements constituting the LED array 31 in the same time is determined, so that the driving time is set for each LED element. Compared to the case, the driving time can be controlled with a simple configuration.

  In the present embodiment, even when 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 density variation between print heads 7 can be suppressed, LED elements can be mass-produced, and even when multiple ranks are distributed, LED elements of any rank can be used, resulting in cost reduction during mass production. Can be achieved.

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

  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-described embodiment, a color image is obtained using 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 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 color printer.

FIG. 1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. These are the schematic diagrams which show schematic structure of the LED array exposure apparatus in the image forming apparatus which concerns on embodiment of this invention. These are schematic diagrams when the LED array exposure apparatus is incorporated in an image forming apparatus. These are block diagrams which show the structure of the LED array control part in the image forming apparatus which concerns on embodiment of this invention, Comprising: It is a block diagram for demonstrating especially correction | amendment of the drive current of an LED element. These are block diagrams which show the structure of the drive circuit of the LED print head in the image forming apparatus which concerns on embodiment of this invention. These are the flowcharts which show the procedure of the lighting control of an LED element at the time of correcting the drive current with respect to each LED element in the image forming apparatus which concerns on embodiment of this invention. These are the block diagrams for demonstrating the modification of the LED array control part shown in FIG. These are the flowcharts which show the procedure of the lighting control of the LED element in the modification of the LED array control part shown in FIG. These are block diagrams which show the structure of the LED array control part in the image forming apparatus which concerns on embodiment of this invention, Comprising: It is a block diagram for demonstrating especially correction | amendment of the drive time of an LED element. These are the figures which showed the relationship between the exposure amount at the time of light emission, and drive time in the predetermined average light quantity. These are the figures which showed the relationship between the inclination of the straight line of each average light quantity shown in FIG. 10, and the magnitude | size of each average light quantity. These are figures which show an example of the data table regarding the drive time preset corresponding to the predetermined | prescribed average light quantity. The LED when correcting the driving current for each LED element in the image forming apparatus according to the embodiment of the present invention and determining the driving time for each of the plurality of LED elements constituting the LED array of each LED print head. It is a flowchart which shows the procedure of the lighting control of an element. FIG. 10 is a block diagram for explaining a modification of the LED array control unit shown in FIG. 9.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color printer 2 Case 3B, 3C, 3M, 3Y Image forming 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 Driving roller,
DESCRIPTION OF SYMBOLS 12 Paper 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 39 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 Drive time control unit 61 Average light quantity data storage unit 62 Drive time data table storage unit

Claims (5)

An LED print head composed of an LED array composed of a plurality of LED elements whose lighting is controlled in accordance with image data, and a drive means for driving the plurality of LED elements, and an LED array for controlling the driving of the LED print head In an image forming apparatus having a control unit,
The LED array control means corresponds to a drive current correction means for correcting a drive current for each of the plurality of LED elements, a light quantity data storage means for storing data relating to the average light quantity of the LED array, and the average light quantity. Driving time data table storage means for storing a data table relating to driving time for driving all of the plurality of LED elements constituting the LED array in the same time, and data relating to the average light quantity And a drive time control means for determining the drive time based on the data table related to the average light quantity and the data table related to the drive time. .   The image forming apparatus according to claim 1, wherein the data relating to the average light amount is obtained based on an exposure amount of the LED print head and is stored in advance in the light amount data storage unit.   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 constituting the LED array of each of the plurality of LED print heads. The image forming apparatus according to claim 1, wherein the driving time is determined every time.   The image forming apparatus according to claim 1, wherein the driving unit drives all of the plurality of LED elements simultaneously by static driving.   The image forming apparatus according to claim 1, wherein 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.

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