JP6825416B2 - Optical writing device and image forming device equipped with it - Google Patents

Description

The present invention relates to an optical writing device and an image forming device including the optical writing device.

In an electrophotographic image forming apparatus, an optical writing apparatus (printhead) that exposes a photoconductor is a line optical type (line light source type) that uses a light source in which light emitting elements are arranged in a line from an optical scanning type that deflects a laser beam. ) Is being switched.

As a line optical type optical writing device, there is an LED print head that uses a light emitting diode (LED) as a light emitting element. In the LED print head, the LED array and the substrate provided with the drive circuit for individually emitting the LEDs are separated. Therefore, it is difficult to reduce the cost.

Therefore, an OLED print head that uses an organic light-emitting diode (OLED) as a light emitting element has been proposed. In an OLED printhead, a thin film transistor (TFT) for driving can be formed on a substrate on which OLEDs are arranged. Therefore, it is easy to reduce the cost as compared with the LED print head.

By the way, the line optical type print head includes a rod lens array that collects the light from the light emitting element array onto the photoconductor. The rod lens array is housed in a housing together with a light source panel provided with a light emitting element array and integrated with the light emitting element array.

In the line optical printhead configured in this way, the coefficient of linear expansion differs between the light source panel and the rod lens array, so that the relative position of the light emitting element and the rod lens array in the plane direction of the light source panel is the temperature. It changes with the change of. Then, the amount of change is generally non-uniform between the light emitting elements.

When manufacturing a printhead, the relative position is determined so that the imaging efficiency of the lens is the best at a reference temperature (for example, 20 ° C.). Therefore, if the temperature at the time of use is different from the reference temperature, the imaging efficiency decreases according to the change in the relative position. Therefore, the amount of exposure in one line of light writing to the photoconductor becomes non-uniform within the line. That is, uneven exposure occurs and the print quality deteriorates.

As a prior art for reducing exposure unevenness due to a change in relative position due to a temperature change, there is a technique described in Patent Document 1. In Patent Document 1, an LED print head having a correction unit that corrects the amount of light emitted for each light emitting element using a correction value set for each light emitting element and a setting unit that sets the correction value according to the temperature is provided. It is disclosed.

Japanese Unexamined Patent Publication No. 2008-155458

According to the technique described in Patent Document 1, the exposure amount in the photoconductor can be made uniform. However, the change in the relative position between the light emitting element and the lens itself is not corrected. That is, so-called profile collapse, in which the conditions for condensing light between the light emitting element and the photoconductor are different from the conditions before the change in the relative position, remains to occur. Therefore, there is a problem that the deviation of the condensing position due to the profile collapse and the blurring of the condensing are not improved.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical writing device and an image forming device capable of correcting profile collapse in optical writing.

The optical writing device according to the embodiment of the present invention is an optical writing device that writes light to a photoconductor, and is a group of light emitting elements in which light emitting elements are arranged in two dimensions in a main scanning direction and a sub scanning direction. Of the light emitting element group, the light from the light emitting element group is focused on the photoconductor, and the relative position of the light emitting element group and the lens array is changed in the sub-scanning direction. The light emitting element selection unit that selects a part of the light emitting elements as the writing light source used for the light writing and the light emission timing of each of the selected writing light sources are set between the writing light sources arranged in the main scanning direction. It has a timing adjusting unit for adjusting so that the light collecting positions in the sub-scanning direction of the photoconductor are aligned.

According to the present invention, profile collapse in optical writing can be corrected.

It is a figure which shows the outline of the structure of the image forming apparatus provided with the printhead which concerns on one Embodiment of this invention. It is a figure which shows the outline of the structure of a print head. It is a figure which shows the structure of the OLED panel in a print head. It is a figure which shows the structure of a part of the circuit provided in the OLED panel. It is a figure which shows the example of the drive sequence of a light emitting element. It is a figure which shows typically the arrangement of the light emitting element in the TFT substrate. It is a figure which shows the functional structure of the main part related to the control of light emission in a print head. It is a figure which shows typically the example of selection of a light emitting element. It is a figure which shows the transfer timing of the write data. It is a figure which shows the other example of selection of a light emitting element schematically. It is a figure which shows another example of the functional structure of the main part related to the control of light emission in a printhead. It is a figure which shows the relationship between the position of a light emitting element, and the imaging efficiency of a rod lens array. It is a figure which shows each exposure amount before and after the change of a relative position.

FIG. 1 shows an outline of the configuration of an image forming apparatus 1 provided with a print head 13 according to an embodiment of the present invention.

The image forming apparatus 1 is an electrophotographic color printer, and includes a tandem type printer engine 1A, a paper feed cassette 1B, a control unit 1C, and a power supply 1D. The image forming apparatus 1 forms a color or monochrome image on the paper 5 according to a job input via a network (for example, LAN).

The printer engine 1A is mainly composed of four imaging stations 10k, 10m, 10c, and 10y.

The imaging station 10k forms a black (K) toner image. The imaging station 10k includes a tubular photoconductor 11, a charging charger 12, a print head 13, a developing device 14, a cleaner 15, and the like.

The imaging station 10m forms a magenta (M) toner image, the imaging station 10c forms a cyan (C) toner image, and the imaging station 10y forms a yellow (Y) toner image. The configurations of these imaging stations 10m, 10c, and 10y are the same as the configurations of the imaging stations 10k. That is, the printer engine 1A includes four print heads 13. The print head 13 is an OLED print head that uses an organic light emitting diode (OLED) as a light emitting element.

The photoconductor 11 is rotationally driven in the sub-scanning direction (clockwise in the figure). Of the peripheral surface of the photoconductor 11, the portion facing the charging charger 12 is uniformly charged. The print head 13 performs light writing on the charged photoconductor 11 in a pattern corresponding to the image. The charge on the exposed portion disappears, and an electrostatic latent image is formed on the photoconductor 11. The electrostatic latent image is developed by the developer 14 to become a toner image.

The toner image is first transferred from the photoconductor 11 to the transfer belt 16. In color printing, optical writing of each color of YMCK is performed at different timings so that the toner images of the four colors are correctly overlapped by this primary transfer.

The primary transferred toner image is secondarily transferred to the paper 5 drawn from the paper cassette 1B by the paper feed roller 19A and conveyed at the nip portion of the secondary transfer roller 19C. After the secondary transfer, the paper 5 is sent out to the upper output tray 18 through the inside of the fixing device 17. When passing through the fuser 17, the toner image is fixed on the paper 5 by heating and pressurizing.

The control unit 1C is in charge of overall control of the image forming apparatus 1. When executing the job, the control unit 1C generates write data D13 indicating the contents of optical writing of each color of YMCK based on the image data to be printed included in the job. The generated write data D13 is given to the printheads 13 of the corresponding color imaging stations 10k, 10m, 10c, 10y.

FIG. 2 shows an outline of the configuration of the print head 13, and FIG. 3 shows the configuration of the OLED panel 31 in the print head 13.

As shown in FIG. 2, the print head 13 includes an OLED panel 30, a rod lens array 32, a housing 34 that accommodates and supports them, and the like. The OLED panel 30 and the rod lens array 32 are covered with a holder (not shown) to prevent dust and the like from adhering to the OLED panel 30 and the rod lens array 32. Further, the print head 13 is provided with components necessary for the optical writing operation, including a cable for electrically connecting to other devices in the image forming apparatus 1 such as the control unit 1C and the power supply 1D.

The print head 13 is arranged in the vicinity of the photoconductor 11 so that the light emitting surface 322 of the rod lens array 32 faces the peripheral surface of the photoconductor 11. The light L emitted from the OLED panel 30 is incident on the rod lens array 32. The rod lens array 32 collects the incident light L on the photoconductor 11.

In FIG. 3, the configurations of the BB arrow cross section and the CC arrow cross section of the plan view are shown together with the configuration of the OLED panel 30 in a plan view.

The OLED panel 30 includes a TFT substrate 301, a sealing plate 302, a spacer 303, a source circuit chip 304, and the like.

The TFT substrate 301 is an elongated glass plate in which the light emitting element group 40 is arranged on one side. The TFT substrate 301 includes a light emitting element group 40, a drive circuit group that individually emits a large number of light emitting elements 41 constituting the light emitting element group 40, and a holding circuit group that holds the value of the brightness signal from the source circuit chip 304. Etc. are formed by a thin film process. Light L from the light emitting element group 40 is emitted from the surface 301S of the TFT substrate 301 opposite to the surface on which the light emitting element group 40 is arranged.

The sealing plate 302 is, for example, a glass plate, and faces the TFT substrate 301 via the spacer 303. The sealing plate 302 is elongated like the TFT substrate 301, but its length is shorter than that of the TFT substrate 301.

The spacer 303 is formed in a shape that surrounds the arrangement region of the light emitting element group 40 on the TFT substrate 301. The TFT substrate 301, the sealing plate 302, and the spacer 303 seal the arrangement region of the light emitting element group 40 so as not to come into contact with the outside air. The desiccant 305 is arranged in a closed internal space.

The source circuit chip 304 is an integrated circuit (IC) and is mounted on one end of the surface of the TFT substrate 301 on which the light emitting element group 40 is arranged, which does not face the sealing plate 302. Write data D13 (see FIG. 1) is input to the source circuit chip 304 from the data output unit 51 of the control unit 1C via the flexible cable 55 and the wiring pattern on the TFT substrate 301. The source circuit chip 304 includes a digital / analog converter (DAC) that converts digital write data D13 into an analog brightness signal, a shift register for sequentially inputting the brightness signal to a plurality of light emitting elements, and the like.

Further, the source circuit chip 304 has a built-in temperature sensor 350. The temperature detected value by the temperature sensor 350 can be used as the detected value of the environmental temperature of the light emitting element group 40.

The OLED panel 30 configured in this way is positioned so that its elongated direction is parallel to the rotation axis of the photoconductor 11. The long direction of the OLED panel 30 is the main scanning direction of optical writing by the print head 13, and the short direction is the sub-scanning direction.

FIG. 4 shows a configuration of a part of a circuit provided on the OLED panel 31, and FIG. 5 shows an example of a drive sequence of the light emitting element 41.

In FIG. 4, a drive circuit 45 and a holding circuit (S / H circuit) 46 are provided for each of the plurality of light emitting elements 41 arranged in the main scanning direction M1.

The holding circuit 46 has a memory unit 47 that stores the value of the luminance signal S13 from the source circuit chip 304, and a switch 48 that opens and closes the input path of the luminance signal S13 to the memory unit 47. The memory unit 47 has, for example, a capacitor as a memory element. When the switch 48 is in the closed state (ON), the capacitor is charged by the luminance signal S13, and an amount of electric charge corresponding to the voltage value of the luminance signal S13 is accumulated in the capacitor.

The drive circuit 45 causes a current corresponding to the voltage across the capacitor of the memory unit 47 to flow through the light emitting element 41. As a result, the light emitting element 41 emits light, and the amount of light emitted becomes the amount corresponding to the value of the luminance signal S13, that is, the value of the write data D13.

In the print head 13, the number N of light emitting elements 41 per row in the main scanning direction M1 is set to 14000 or more so that optical writing having an A3 size width (297 mm) is possible at a high resolution of, for example, 1200 dpi. .. If one DAC is provided for each of a large number of light emitting elements 41, the circuit scale of the source circuit chip 304 becomes large and the cost becomes high.

Therefore, a method is adopted in which a plurality of light emitting elements 41 are grouped and a DAC is provided for each group. Assuming that the light emitting elements 41 of each group are n, the number M of the required DACs 341a, 341b, ... 341m per row in the main scanning direction is 1 / n of the number N of the light emitting elements 41.

Writing (charging) by the luminance signal D13 to the N memory units 47 is performed by an active drive sequence (so-called rolling drive) in which n switches 48 are sequentially switched for each M group. The on / off of each switch 48 is controlled by the switching signal S48 from the shift register 340 of the source circuit chip 304.

As shown in FIG. 5, the value of the luminance signal S13 written in the charge period TC is held over the hold period TH until the next charge period TC after the main scanning period (Hsync) has elapsed. When the value of the luminance signal S13 is not a value indicating non-emission (for example, "0"), the light emitting element 41 continues to emit light for the hold period TH.

Not limited to the sequence of FIG. 5, for example, a light emitting period having a predetermined length is provided after the writing from the first to the nth is completed, and the light emitting elements 41 to be emitted may be made to emit light all at once during the light emitting period. Good. In that case, the light emitting elements 41 from the first to the (n-1) th are prohibited from emitting light from the end of the charge period TC to the start of the light emission period.

By the way, the print head 13 of the present embodiment responds to a change in the relative position between the light emitting element group 40 and the rod lens array 32 so that light writing of the same quality as before the change occurs can be performed. It has a function of changing the light emitting element 41 actually used for optical writing among 40. Hereinafter, the configuration and operation of the print head 13 will be further described with a focus on this function.

FIG. 6 schematically shows the arrangement of the light emitting elements 41 on the TFT substrate 301.

As shown in FIG. 6A, the light emitting element group 40 is formed by arranging light emitting elements 41 having the same light emitting surface in two dimensions in the main scanning direction M1 and the sub scanning direction M2. The number of sequences in the sub-scanning direction M2 is 7. That is, the light emitting element group 40 is composed of seven rows of light emitting element rows 401, 402, 403, 404, 405, 406, 407, each of which extends in the main scanning direction M1 and is arranged in parallel with each other. Each of the light emitting element rows 401 to 407 is composed of N light emitting elements 41. In the seven rows of light emitting element rows 401 to 407, the arrangement position of the light emitting element 41 in the main scanning direction M1 is the same. The geometric center of each light emitting element 41 in the light emitting element group 40 is the light emitting point.

The arrangement pitch (light emitting point interval) p1 of the light emitting elements 41 in the main scanning direction M1 is determined based on the specifications of the resolution of optical writing. For example, when the resolution is 1200 dpi, the array pitch p1 is about 21.17 μm.

The array pitch p2 of the light emitting elements 41 in the sub-scanning direction M2 is set to a smaller value within a range permitted by restrictions such as routing in the wiring. The smaller the array pitch p2, the higher the accuracy of correcting the profile collapse due to the change in the relative position with the rod lens array 32.

As shown in FIG. 6B, the TFT substrate 301 is provided with a plurality of light emitting blocks 42. Each light emitting block 42 has seven light emitting elements 41 arranged at the same position in the main scanning direction M1 of the TFT substrate 301, and the above-mentioned circuit (drive circuit 45) corresponding to each of these seven light emitting elements 41. And the holding circuit 46). The total number of light emitting blocks 42 is N.

As shown in FIG. 6C, the light emitting element group 40 faces the rod lens array 32. The rod lens array 32 is composed of a large number of columnar rod lenses that are arranged and integrated in a staggered pattern so as to extend straight in the main scanning direction M1. The diameter φ of each rod lens is, for example, about 60 μm.

In the example of FIG. 6C, the width w32 of the rod lens array 32 is smaller than the width w40 of the arrangement region of the light emitting element group 40, but the width w40 and the width w32 may be equal, and the width w32 may be the same. It may be larger than the width w40.

When manufacturing the printhead 13, the light emitting element group 40 and the rod lens array 32 are positioned so that the center lines in the sub-scanning direction M2 coincide with each other. Hereinafter, a state in which the center lines match or are close to each other in this way may be referred to as an "initial state". That is, for example, it is a state of a temperature set as a standard temperature or a reference temperature in the correction table 312T at the time of manufacturing or shipping.

Of the N × 7 light emitting elements 41 constituting the light emitting element group 40, N light emitting elements 41 having different arrangement positions in the main scanning direction M1 are used for optical writing by the print head 13.

In the initial state, the light emitting element row 401 in the center of the sub-scanning direction M2 of the seven rows of light emitting element rows 401 to 407 is used for optical writing. That is, in the setting at the time of manufacture, the N light emitting elements 41 constituting the light emitting element row 401 are defined as the writing light sources 41s used for optical writing.

The imaging efficiency (lens efficiency) of the rod lens array 32 is determined by the relative position between the rod lens array 32 and the light emitting element 41. Therefore, with respect to the light emitting element row 401 which is the writing light source group in the initial state, the light amount of each light emitting element 41 is adjusted so that the exposure amount of the photoconductor 11 is equal regardless of the relative position of the main scanning direction M1. .. That is, the source circuit chip 304 performs data correction such that the value of the luminance signal S13 given to the light emitting element 41 at the position where the imaging efficiency is low is increased.

For the remaining 6 rows of light emitting element rows 401 to 403 and 404 to 407, the light emitting amount of the light emitting element 41 having the same position in the main scanning direction M1 as each light emitting element 41 of the light emitting element row 401 is used as the light emitting element row. The amount of light is adjusted to be equal to the amount of light emitted from the light emitting element 41 of 401. That is, the source circuit chip 304 performs data correction such that the amount of light emitted from the seven light emitting elements 41 arranged in the sub-scanning direction M2 is aligned.

FIG. 7 shows the functional configuration of the main part related to the control of light emission in the print head 13.

The print head 13 includes a plurality of first changeover switches 43, a plurality of second changeover switches 44, a light emitting element selection unit 312, and a timing adjustment unit 314.

One first changeover switch 43 is provided for each of the N light emitting blocks 42. Similarly, one second changeover switch 44 is provided for each light emitting block 42. One or both of the first changeover switch 43 and the second changeover switch 44 may be provided in the vicinity of the light emitting block 42 corresponding thereto, or may be provided in the source circuit chip 304.

As shown in FIG. 7, each light emitting block 42 is composed of seven light emitting units 421. The seven light emitting units 421 correspond one-to-one with the seven light emitting element trains 401 to 407 shown in FIG. Each light emitting unit 421 includes one light emitting element 41, and a pair of one drive circuit 45 and one holding circuit 46 corresponding thereto.

The first changeover switch 43 connects any one of the seven light emitting units 421 to the power supply 1D according to the selection signal S42 from the light emitting element selection unit 312. Only the light emitting element 41 of the light emitting unit 421 connected to the power supply 1D can emit light by the current supplied from the power supply 1D.

The second changeover switch 44 connects any one of the seven light emitting units 421 to the timing adjusting unit 314 according to the selection signal S42 from the light emitting element selection unit 312. The luminance signal S13 described above is input from the timing adjustment unit 314 only to the light emitting unit 421 connected to the timing adjustment unit 314. By inputting the luminance signal S13, as described above, charging is performed according to the value of the luminance signal S13, and the amount of light emitted is determined.

A selection signal S42 having the same value is given to the first changeover switch 43 and the second changeover switch 44 corresponding to the same light emitting block 42. As a result, the light emitting unit 421 connected to the power supply 1D by the first changeover switch 43 is also connected to the timing adjustment unit 314 by the second changeover switch 44. Therefore, the light emitting element 41 of the light emitting unit 421 can emit light in response to the luminance signal S13.

The light emitting element selection unit 312 uses a part of the light emitting elements 41 of the light emitting element group 40 for optical writing according to a change in the relative position of the sub scanning direction M2 between the light emitting element group 40 and the rod lens array 32. Select as the writing light source 41S. The details are as follows.

Position change information D350 indicating a change in the relative position between the light emitting element group 40 and the rod lens array 32 is input to the light emitting element selection unit 312. The position change information D350 is, for example, a temperature detection value by the temperature sensor 350 built in the source circuit chip 304.

The light emitting element selection unit 312 refers to the table 312T. The table 312T is a lookup table that associates the value indicated by the position change information D350 with the identifier of the light emitting element 41 to be selected as the writing light source 41S, and is created in advance and stored in the non-volatile memory.

The contents of the table 312T are determined, for example, based on the results of experiments. In the experiment, for example, in each of a plurality of states having different temperatures, the light emitting element rows 401 to 407 are sequentially made to emit light, and the light emitting element 41 that obtains the best exposure result is selected for each of the N light emitting blocks 42.

Table 312T so that the positional relationship of the sub-scanning direction M2 between the writing light source 41s and the rod lens array 32 is close to the positional relationship in the initial state, that is, the exposure amount of the photoconductor 11 by the writing light source 41s is close to the initial exposure amount. The contents of are determined. The initial exposure amount is the exposure amount in the initial state.

The light emitting element selection unit 312 reads out the identifier of the light emitting element 41 to be selected according to the value indicated by the position change information D350 from the light emitting element 41 table 312T, and selects signals for each of the N light emitting blocks 42 according to the read identifier. The value of S42 is determined. Then, the selection signal S42 is output to each of the N light emitting blocks 42. As a result, the writing light source 42s is selected in each light emitting block 42.

The selection of the writing light source 42s is performed, for example, for each printing job, that is, each time the image formation is started. The writing light source 42s may be selected when the amount of temperature change, which is the difference between the measured environmental temperature and the initial set temperature (for example, 20 ° C.), is equal to or greater than the threshold value (10 ° C.). Alternatively, this may be performed when the amount of temperature change is estimated to be equal to or higher than the threshold value. For example, in a continuous printing job using a plurality of sheets of paper 5, when the number of times of optical writing exceeds a threshold value (for example, 50), the writing light source is reselected.

The timing adjusting unit 314 sets the timing of each emission of the selected N writing light sources 41 so that the focusing position of the sub-scanning direction M2 in the photoconductor 11 is set between the writing light sources 41s arranged in the main scanning direction M1. Adjust so that they are aligned. Specifically, as a process for adjusting the timing, the transfer of the write data D13 indicating the light emission amount of each of the N write light sources 41s is delayed according to the position of the sub-scanning direction M2 of the write light sources 41s. The delay can be performed, for example, in the process of data transfer in the source circuit chip 304 until the write data D13 input from the control unit 1C is input to the DACs 341a, 341b, ... 341m.

FIG. 8 schematically shows an example of selection of the light emitting element 41, and FIG. 9 shows the timing of transfer of the write data D13. In FIG. 8, the writing light source 41s is shaded to distinguish it from the other light emitting elements 41. Further, in FIGS. 8 and 9, the arrangement positions of the light emitting elements 41 in the main scanning direction M1 are indicated by the alphabets “A” to “Y”.

In FIG. 8A, the relative positions of the light emitting element group 40 and the rod lens array 32 are in the initial state. In the initial state, as described above, N light emitting elements 41 constituting the light emitting element row 404 are selected as the writing light source 41s. In this case, the write data D13 shown in FIG. 9A is transferred at the timing shown in FIG. 9B.

The timing of FIG. 9B transfers the write data D13 at the same position to the sub-scanning direction M2 all at once regardless of the positions (A to Y) of the main scanning direction M1.

In FIG. 8B, the rod lens array 32 is curved so as to be convex toward the downstream side in the sub-scanning direction M2 relative to the light emitting element group 40. The positional relationship shown in the illustration is an example, and there may be other positional relationships such as being curved in a wavy manner or being inclined with respect to the light emitting element group 40 while remaining substantially straight.

In the case of FIG. 8B, the light emitting element 41 of the light emitting element row 403 is selected as the writing light source 41s at the positions A to C and W to Y in the main scanning direction M1. Regarding the positions of D to J and O to V, the light emitting element 41 of the light emitting element row 404 is selected as the writing light source 41s as in the initial state. Then, for the positions K to N, the light emitting element 41 of the light emitting element row 405 is selected as the writing light source 41s.

That is, when the positional relationship between the light emitting element group 40 and the rod lens array 32 changes to a relationship different from the relationship in the initial state, the N light source 41s have different arrangement positions in the sub-scanning direction M2. Will be included.

Since the arrangement position of the sub-scanning direction M2 of the writing light source 41s is not uniform, if the writing data D13 is transferred at the timing of FIG. 9B and optical writing is performed, so-called BOW (distortion in which a straight line bends) is formed in the formed image. ) Occurs. Therefore, in order to perform correct optical writing that reproduces the image indicated by the writing data D13, it is necessary to adjust the transfer timing of the writing data D13.

In the case of FIG. 8B, the write data D13 is transferred at the timing shown in FIG. 9C. That is, the transfer of the other write light sources 41s is delayed with reference to the write light source 41s on the most downstream side in the sub-scanning direction M2 among the N write light sources 41s. Specifically, first, the data at the positions K to N is transferred, the data at the positions D to J and O to V are transferred with a delay of one transfer cycle, and then the data at the positions A to C and W to Y are further delayed by one transfer cycle. Transfer data.

Next, a case of performing optical writing of a multiple exposure method in which the amount of exposure indicated by the writing data D13 is divided into a plurality of times will be described.

FIG. 10 schematically shows another example of selection of the light emitting element 41. In FIG. 10, as in FIG. 8, the writing light source 41s is shaded to distinguish it from the other light emitting elements 41, and the arrangement positions of the main scanning directions M1 of each light emitting element 41 are arranged in the alphabets “A” to “Y”. It is shown by.

In FIGS. 10A and 10B, the light emitting element group 40b is composed of eight rows of light emitting element rows 401, 402, 403, 404, 405, 406, 407, 408. The light emitting element group 40b corresponds to the above-mentioned light emitting element group 40 to which the light emitting element row 408 is added. Similar to the other light emitting element rows 401 to 407, the light emitting element row 408 also has N light emitting elements 41 arranged in the main scanning direction M1.

Of the N × 8 light emitting elements 41 constituting the light emitting element group 40b, for example, N × 2 light emitting elements 41 are used to perform multiple exposure. That is, the exposure is performed twice on the same writing position of the photoconductor 11. At that time, for each of the positions A to Y in the main scanning direction M1, the light emitting elements 41 arranged adjacent to each other in the sub scanning direction M2 are used as the writing light source 41s.

As shown in FIG. 10A, in the initial state, the light emitting elements 41 constituting the light emitting element rows 404 and 405 near the center of the sub-scanning direction M2 of the light emitting element rows 401 to 408 are referred to as the writing light source 41s. Will be done.

In FIG. 10B, the rod lens array 32 is curved so as to be convex toward the downstream side in the sub-scanning direction M2 relative to the light emitting element group 40b. In this case, the light emitting elements 41 of the light emitting element rows 404 and 405 are selected as the writing light sources 41s for the positions A to F and T to Y in the main scanning direction M1. Regarding the positions of G to S, the light emitting element 41 of the light emitting element rows 405 and 406 is selected as the writing light source 41s.

FIG. 11 shows another example of the functional configuration of the main part related to the control of light emission in the print head 13b.

The print head 13b is provided in the image forming apparatus 1 instead of the print head 13 in the case of performing multiple exposure. The print head 13b includes a light emitting element selection unit 312b and a timing adjustment unit 314b. In the print head 13b, each of the N light emitting blocks 42b is composed of eight light emitting units 421.

A plurality of light emitting element selection units 312b are adjacent to the sub-scanning direction M2 based on the table 312Tb for each of the arrangement positions (A to Y) of the light emitting element 41 in the main scanning direction M1 according to the position change information D350. The light emitting element 41 of the above is selected as the writing light source 41s. Table 312Tb is a look-up table showing the light emitting elements 41 to be selected. The light emitting element selection unit 312b inputs a selection signal S42b indicating the position of the selected writing light source 41s in the sub-scanning direction M2 to the timing adjustment unit 314b.

The timing adjusting unit 314b adjusts the light emission timing of the writing light source 41s indicated by the selection signal S42b so that the multiple exposure type light writing is correctly performed. That is, by modifying the write data D13 indicating the light emission amount of the write light source 41s in the initial state according to the position of the sub-scanning direction M2 of the selected write light source 41s, the light emission of the selected write light source 41s A luminance signal S13 indicating the amount is created and output.

In multiple exposure, it is necessary to simultaneously emit light from a plurality of light emitting elements 41 adjacent to the sub-scanning direction M2. That is, instead of selecting one light emitting unit 421 for each light emitting block 42b, it is necessary to simultaneously perform light emission control for eight light emitting units 421. The light emission control referred to here is a control in which two of the eight pieces are made to emit light or all eight pieces are not made to emit light. For this control, the luminance signals S13 corresponding to each of the eight light emitting units 421 are simultaneously input. The timing adjusting unit 314b outputs the same number of 8 × 4 luminance signals S13 as the total number of the light emitting units 421 for each main scanning period Hsync.

FIG. 12 shows the relationship between the position of the light emitting element 41 and the imaging efficiency of the rod lens array 32, and FIG. 13 shows the exposure amounts before and after the change in the relative position.

In FIG. 12, the light emitting points α and β correspond to two light emitting elements 41 having the same position in the main scanning direction M1 and adjacent to the sub scanning direction M2. In the figure, the thick solid line K1 shows the relationship between the relative position before the relative position of the light emitting points α and β and the rod lens array 32 changes (initial state) and the imaging efficiency, and the broken line shows the relative position. It shows the relationship after the change.

Before the relative position changes, the imaging efficiency of the light from the light emitting point α is “100”, and the imaging efficiency of the light from the light emitting point β is “90”. On the other hand, after the relative position changes, the imaging efficiency of the light from the light emitting point α is “93”, and the imaging efficiency of the light from the light emitting point β is “97”.

First, as shown in FIG. 8, a case where one writing light source 41s is defined for each position (A to Y) in the main scanning direction M1 (a case where one light emitting point is set) will be described.

In the initial state, it is assumed that the emission amounts of the emission points α and β are both adjusted to “100”. Of the light emitting points α and β, the light emitting point α having excellent imaging efficiency is defined as the writing light source 41s. As shown in FIG. 13, the exposure amount of the photoconductor 11 is 100 × 1 = 100 from the light emission amount: 100 and the imaging efficiency: 100%.

The change in relative position reduces the imaging efficiency from 100 to 93. That is, profile collapse occurs. Therefore, in order to correct the profile collapse, the light emitting point β is set as the writing light source 41s instead of the light emitting point α. This increases the imaging efficiency from 93 to 97. That is, the profile collapse is improved. The exposure amount is 100 × 0.97 = 97, but such a decrease can be tolerated in terms of the influence on the image quality. It is also easy to adjust the amount of light emission so that the amount of exposure is 100, if necessary.

Next, as shown in FIG. 10, a case where two writing light sources 41s are defined for each position (A to Y) in the main scanning direction M1 (in the case of multiple exposure with two light emitting points) will be described.

In the initial state, it is assumed that the emission amounts of the emission points α and β are both adjusted to “50”. Both the light emitting points α and β are set as the writing light source 41s. As shown in FIG. 13, the exposure amount at the light emitting point α is 50 × 1 = 100 from the light emitting amount: 50 and the imaging efficiency: 100%. Further, the exposure amount at the light emitting point β is 50 × 90 = 45 from the light emitting amount: 50 and the imaging efficiency: 90%. Therefore, the total exposure amount is 50 + 45 = 95.

Even after the relative position changes, the light emitting points α and β are set as the writing light source 41s. As shown in FIG. 13, the exposure amount at the light emitting point α is 50 × 0.93 = 46.5 from the light emitting amount: 50 and the imaging efficiency: 93%. Further, the exposure amount at the light emitting point β is 50 × 0.97 = 48.5 from the light emitting amount: 50 and the imaging efficiency: 97%. Therefore, the total exposure amount is 46.5 + 48.5 = 95, which is equal to the exposure amount before the relative position changes.

As described above, in the multiple exposure, even if the imaging efficiency changes before and after the change, it is possible to keep the change in the exposure amount small. The plurality of light emitting elements 41 selected as the writing light source 41s do not necessarily have to be continuously arranged in the sub-scanning direction M2, and may be selected so that the exposure amounts are equal. However, if the deviation of the relative position in the sub-scanning direction M2 becomes large, the profile collapse becomes large, so it is desirable to select so that the deviation becomes as small as possible.

According to the above embodiment, it is possible to correct the profile collapse due to the change in the relative position of the light emitting element groups 40 and 40b and the rod lens array 32 in the sub-scanning direction M2. It is possible to reduce the deterioration of image quality by correcting the profile collapse in optical writing for image formation.

Since the light amount adjustment is performed in advance for the light emitting elements 41 of the light emitting blocks 42 and 42b in the light emitting element groups 40 and 40b so that the light emitting amounts are made equal to each other, any of these light emitting elements 41 can be selected as the writing light source 41s. The amount of light emitted does not change. As a result, the exposure amount when the relative position changes can be easily made equal to the exposure amount before the change.

In the embodiment described above, the position change information D350 is not limited to the detected value of the temperature. For example, a sensor such as a piezoelectric element is provided on the print heads 13 and 13b, and the result of measuring the distance d (see FIG. 2) between the reference surface of the housing 34 and the rod lens array 32 can be used as the position change information D350. In that case, it is preferable to provide sensors at a plurality of locations such as the central portion and both end portions of the main scanning direction M1. Further, as the position change information D350, information indicating a secular change such as the cumulative number of printed sheets and the date by the system clock can be used.

In the above-described embodiment, the writing light source 41s is selected based on the tables 312T and 312Tb whose contents are predetermined, but the writing light source 41s can be selected regardless of the tables 312T and 312Tb. .. For example, the writing light source 41s can be switched to periodically perform test printing for detecting density unevenness, and the writing light source 41S can be selected based on the result. That is, a combination of N light emitting elements 41 having the smallest density unevenness is obtained, and the N light emitting elements 41 are used as the writing light source 41S until the next test printing.

According to the method of selection based on the result of the test print, when a failure occurs in which the light emission of a part or all of the initial write light source 41s becomes defective for some reason, the light emitting element 41 other than the initial write light source is written. Normal optical writing can be performed by selecting the light source 41s. That is, the image forming apparatus 1 can be used continuously without replacing the print heads 13 and 13b.

In the embodiment described above, one or both of the light emitting element selection units 312 and 312b and the timing adjustment units 314 and 314b need not be fixedly provided on the OLED panel 30, and may be provided on another substrate or the like.

In the embodiment described above, multiple exposure may be performed in which the number of exposures to the same writing position of the photoconductor 11 is 3 or more.

In addition, the configuration of the entire image forming apparatus 1 and the print heads 13 and 13b, the content of processing, the order, the timing, and the like can be appropriately changed according to the gist of the present invention.

1 Image forming device 5 Paper 11 Photoreceptors 13, 13b Print head (optical writing device)
32 Rod lens array (lens array)
40, 40b Light emitting element group 41 Light emitting element 41s Writing light source 312, 312b Light emitting element selection unit 314, 314b Timing adjustment unit 370 Temperature sensor (temperature measurement unit)
D13 Write data M1 Main scanning direction M2 Sub scanning direction S13 Luminance signal (signal)

Claims (10)

An optical writing device that writes light to a photoconductor.
A group of light emitting elements in which light emitting elements are arranged two-dimensionally in the main scanning direction and the sub scanning direction, and
A lens array that collects light from the light emitting element group onto the photoconductor, and
A light emitting element selection unit that selects a part of the light emitting elements as a writing light source used for the light writing according to a change in the relative position of the light emitting element group and the lens array in the sub-scanning direction. When,
The timing of each emission of said selected write light source, have a, a timing adjustment unit which adjusts to the condensing position in the sub-scanning direction are aligned in the photosensitive member between the writing light source to each other aligned in the main scanning direction ,
The light emitting element selection unit selects the writing light source so that the positional relationship between the writing light source and the lens array in the sub-scanning direction is close to the initial positional relationship.
The light emitting element selection unit selects the writing light source so that the exposure amount of the photoconductor by the writing light source is close to the initial exposure amount.
An optical writing device characterized by the fact that. A plurality of light emitting elements arranged at the same position in the main scanning direction in the light emitting element group have the same amount of light emission.
The optical writing device according to claim 1 . As a process of adjusting the timing, the timing adjusting unit delays the transfer of write data indicating the amount of light emitted from the write light source according to the position of the write light source in the sub-scanning direction.
The optical writing device according to claim 1 or 2 . As a process of adjusting the timing, the timing adjusting unit receives write data indicating the amount of light emitted from the writing light source when the relative position is an initial value according to the position in the sub-scanning direction of the selected writing light source. By modifying, a signal indicating the amount of light emitted from the selected writing light source is generated.
The optical writing device according to claim 1 or 2 . The light emitting element selection unit selects a plurality of the light emitting elements arranged in the sub scanning direction as the writing light source for each of the arrangement positions of the light emitting element in the main scanning direction.
The timing adjusting unit adjusts the timing so as to perform multiple-exposure type optical writing in which the writing light sources having different positions in the sub-scanning direction are sequentially emitted.
The optical writing device according to any one of claims 1 to 4 . An image forming device that forms an image on paper.
Photoreceptor and
The photoconductor is provided with an optical writing device that performs optical writing that forms an electrostatic latent image corresponding to the image.
The optical writing device is
A group of light emitting elements in which light emitting elements are arranged two-dimensionally in the main scanning direction and the sub scanning direction, and
A lens array that collects light from the light emitting element group onto the photoconductor, and
A light emitting element selection unit that selects a part of the light emitting elements as a writing light source used for the light writing according to a change in the relative position of the light emitting element group and the lens array in the sub-scanning direction. When,
The timing of each emission of said selected write light source, have a, a timing adjustment unit which adjusts to the condensing position in the sub-scanning direction are aligned in the photosensitive member between the writing light source to each other aligned in the main scanning direction ,
The light emitting element selection unit selects the writing light source when the number of times of optical writing exceeds the threshold value in a continuous printing job using a plurality of sheets of the paper.
An image forming apparatus characterized in that. When the formation of the image is started, the light emitting element selection unit selects the writing light source, and the timing adjustment unit adjusts the timing.
The image forming apparatus according to claim 6 . An image forming device that forms an image on paper.
Photoreceptor and
The photoconductor is provided with an optical writing device that performs optical writing that forms an electrostatic latent image corresponding to the image.
The optical writing device is
A group of light emitting elements in which light emitting elements are arranged two-dimensionally in the main scanning direction and the sub scanning direction, and
A lens array that collects light from the light emitting element group onto the photoconductor, and
A light emitting element selection unit that selects a part of the light emitting elements as a writing light source used for the light writing according to a change in the relative position of the light emitting element group and the lens array in the sub-scanning direction. When,
It has a timing adjusting unit that adjusts the light emission timing of each of the selected writing light sources so that the focusing positions in the sub-scanning direction of the photoconductor are aligned between the writing light sources arranged in the main scanning direction. ,
It has a temperature measuring unit that measures the environmental temperature of the light emitting element group.
The light emitting element selection unit selects the writing light source when the amount of temperature change, which is the difference between the measured environmental temperature and the initially set temperature, is equal to or greater than the threshold value.
An image forming apparatus characterized in that . When the formation of the image is started, the light emitting element selection unit selects the writing light source, and the timing adjustment unit adjusts the timing.
The image forming apparatus according to claim 8. The light emitting element selection unit selects the writing light source when the number of times of optical writing exceeds the threshold value in a continuous printing job using a plurality of sheets of the paper.
The image forming apparatus according to claim 8 or 9.

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