JP2009292058A - Image forming apparatus, and method of controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus securing a linearity of overall concentration regions of an output light pulse, and improving reproducibility of a line width in line drawings, letters and the like, and a method of controlling the same. <P>SOLUTION: The image forming apparatus corrects a pulse width of a driving pulse of an exposure part for forming an electrostatic latent image so as to dissolve light-on retardation and light-off retardation of the exposure part in accordance with a pulse interval of an off-time period of the driving pulse. In addition, the image forming apparatus fixes the correction amount of one of rise and fall of the driving pulse, and adjusts the correction amount of the other when correcting the pulse width. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pulse driving method of an exposure unit in an image forming apparatus, and in particular, appropriately controls a pulse width of a driving signal in a target pixel according to a situation of an image data string of the target pixel and its neighboring pixels, and outputs a desired output. The present invention relates to an image forming apparatus that scans a light pulse onto a photoconductor to form an image, and a control method thereof.

  2. Description of the Related Art Conventionally, there has been known an image forming apparatus in which a laser beam output is stabilized against a temperature change when a latent image is formed by scanning a photosensitive member by raster scanning. For example, Patent Document 1 proposes a technique for pulse width correction in a laser exposure type image forming apparatus. In such an image forming apparatus, the laser beam output is detected once in one horizontal scan in the vicinity of the laser, the detection signal is fed back to the laser driving circuit, and the laser beam intensity is controlled to make the laser output always equal to the set value. It is controlled to become. Such control is called auto power control (APC).

  In addition, there are known APC circuits that feed back the detection signal of the light output detection circuit to the LED light emitting region current (bias current) of the laser and those that feed back to the laser light emitting region current (operating current).

  In the APC circuit, as shown in FIG. 9, it is possible to control the parallel shift of the current-light output curve due to the laser temperature change. FIG. 9 is a diagram showing the relationship between laser current and optical output. In the case of laser bias current control, the bias current value shifts from the LED light-emitting area to the laser light-emitting area due to the decrease in the current-light output slope of the laser light-emitting area due to the change in the laser temperature, and no recording signal is input. Recording on the recording medium is performed. For this reason, toner fogging of the copied image occurs. Therefore, a margin is provided in the setting value of the bias current so that the bias current value does not shift to the laser emission region even if the bias current is made variable according to the temperature change, and the difference between the bias current IBIAS and the laser emission threshold current Ith depends on the laser temperature. To change.

  Further, in the APC circuit, when feeding back to the laser operating current, the laser light emission area is shifted to the laser light emission area when the recording signal is turned on. Further, when the recording signal is turned off, the laser light emission region is passed to the LED light emission region. For this reason, the rise and fall times of the laser beam output become long.

  FIG. 10 is a diagram illustrating a laser emission control unit. In FIG. 10, reference numeral 2 denotes input image input data. Reference numeral 3 denotes an image data converter that outputs a drive pulse 8 based on image input data. Reference numeral 14 denotes a drive circuit that drives the laser 11 in accordance with the drive pulse 8 output from the image data converter 4. Reference numeral 10 denotes a laser driving block.

  FIG. 11 is a diagram showing a laser drive current pulse waveform and a laser emission pulse waveform. FIG. 11 shows a laser drive current pulse waveform supplied to the laser 11 by the drive circuit 14 in response to the recording signals ON and OFF output from the image data converter 4 shown in FIG. ing. As shown in FIG. 11, the laser emission pulse waveform substantially follows the laser drive current pulse waveform exceeding the emission threshold current. For this reason, when the characteristics such as the rise and fall of the drive current pulse corresponding to ON / OFF of the recording signal change, the emission pulse waveform also changes accordingly, and the laser beam intensity changes.

  There are also phenomena in the laser chip such as stimulated emission by injected carriers, light emission delay in the process leading to laser oscillation due to optical resonance, and turn-off delay in the process leading to laser oscillation stop due to stop of injection. Therefore, the pulse width is further reduced and time delayed.

  As described above, when the threshold current Ith changes due to the change in the laser temperature, the rise and fall delay characteristics of the laser drive current pulse waveform that contributes to the laser light emission change. Therefore, there is a problem that the beam intensity (light amplitude and light pulse width) modulated by the recording signal changes despite the APC. The light amount fluctuation (beam intensity fluctuation) is particularly noticeable when the laser driving pulse width is very short with respect to the recording signal frequency, and such an APC circuit is not suitable for high density and high gradation image recording. Become.

  The above is mainly a problem in a sufficiently isolated pulse, but when the image density is expressed by the PWM of the laser pulse, there is no need to consider in a pulse in a high density region, that is, a region in which the laser off time is small. However, problems arise in the interaction between pulses.

  FIG. 12 is a diagram showing a relationship between a laser drive signal and an output light pulse for one screen dot formed by one pixel or a plurality of continuous pixels. The driving pulse is set to a small width in the low density portion according to the image data, and is set to be large in accordance with the high density. As shown in FIG. 12, the output light pulse at a low concentration is narrowed by the mechanism described above. In contrast, in the high-concentration portion, as the current drive signal lighting timing becomes closer to the previous drive signal extinction timing, the output light with respect to the drive signal lighting timing is caused by the presence of residual active carriers inside the laser chip. The amount of delay of light emission (lighting) of the pulse decreases rapidly. For this reason, the previous output light pulse and the current output light pulse are closer to each other and eventually become continuous.

  FIG. 13 is a diagram showing the relationship between the pulse width and the laser light quantity. The horizontal axis indicates the pulse width of the drive pulse. The vertical axis represents the laser light quantity (beam intensity). FIG. 13 shows the width of the output light pulse or the integrated value of the pulse. Reference numeral 1301 denotes a cycle of one screen dot formed by one pixel or a plurality of continuous pixels. Reference numeral 1302 denotes a state in which, as described with reference to FIG. 12, when the drive pulse ratio becomes a certain value or more, the laser light output pulse is continuously emitted and is saturated to a certain value.

In order to solve such problems, conventionally, the pulse width of the drive signal is increased in the region where the pulse width is short in the low concentration portion (pulse narrowing region), and the region where the off pulse is buried in the high concentration portion (pulse thickening). In the region, correction for shortening the pulse width of the drive signal has been proposed. For example, as shown in FIG. 13, the pulse width of the drive signal for the input image data 00H is set to a portion where the laser light quantity starts to change linearly, and the pulse width of the drive signal for FFH is just before the laser light quantity is saturated. Set to. As a specific configuration example for realizing this, Patent Document 1 proposes a correction method for a PWM system by comparing a triangular wave reference signal and an analog voltage value corresponding to input image data.
Japanese Patent No. 3245205

  However, the conventional techniques have the following problems. For example, although the correction method as described above is effective in terms of gradation stability control in the image portion, the ability to write graphic objects such as thin lines and line widths of small-point characters according to image information is reduced. End up. That is, when laser driving is performed by correcting the pulse width by the correction method as described above with respect to the period of one screen dot formed by one pixel or a plurality of continuous pixels, about one pixel or screen dot period When a line drawing having a width of 1 is written, the line drawing is written with an output light pulse having a narrower width than the original width by pulse width correction.

  Further, as a method for solving the problems related to the pulse width as described above, a system that increases the resolution and reduces the number of PWM modulations for each pixel, for example, a 2400 dpi binary system is also conceivable. However, even in such a system, if the printing speed is increased, the drive time per pixel is reduced, and thus the influence of the above-described pulse thinning or pulse thickening occurs.

  FIG. 14A to FIG. 14E are diagrams showing a relationship among an original image, a driving pulse, and a light output when a line drawing is formed in the binary system. Reference numeral 1401 in FIG. 14A indicates image data in which the width of four main scanning pixels is continuously adjacent to each other with a vertical line of 12 pixels. Reference numeral 1402 denotes image data of one scan line in the image data 1401. Reference numeral 1403 denotes a generated drive pulse. Reference numeral 1404 denotes an output light pulse of the laser element driven by the drive pulse 1403.

  Here, the scanning time for one pixel is 2.5 ns. On the other hand, when a pulse for four pixels is generated and a signal is transmitted to the laser element, a light emission delay of about two pixels occurs due to a light emission delay of 5 ns. On the other hand, the turn-off delay of about one pixel occurs due to the turn-off delay of 2.5 ns. As a result, the pulse width is reduced by about 2.5 ns for one pixel (light emission delay−light-out delay). That is, in this state, a line having a width of 4 pixels is written on the drum more narrowly.

  On the other hand, in Patent Document 1, this line drawing can be corrected by using a PWM pulse width correction system in which 16 pixels are set to one pulse period. That is, considering the “maximum pulse width of pixels” on the horizontal axis in FIG. 13 as 16 pixels and the input image data as (4/16) * FFH, an output pulse width of 4 pixels can be obtained. . More specifically, as indicated by 1405, it is possible to generate pulses for the original four pixels indicated by 1406 by increasing the pulse width.

  FIG. 14B shows a case where the interval between line drawings is further smaller than in FIG. 14A. Reference numeral 1407 denotes image data in which a line with a width of 4 pixels is continuously arranged with 8 pixels in between. Reference numerals 1408 and 1409 denote drive pulses and output light pulses when the same amount of pulse width correction as in FIG. 14A is performed. In this case, since the basic period of the PWM system has changed from the previous 16 pixel period to 12 pixels, the correction system itself does not actually function effectively. For example, it is necessary to change to a PWM system based on a 12-pixel cycle only for that portion, and to switch to a PWM pulse correction value corresponding to that. In the case of an analog PWM system such as Patent Document 1, as shown in FIG. 15, a reference triangular wave corresponding to the period of the basic clock is generated, and after adjusting the gain and offset for the output, the reference comparison input of the comparator To do. On the other hand, a desired pulse is generated by using a value obtained by DA conversion of the value of the image data as the other comparator input. Therefore, in order to switch from the 16 pixels to the 12 pixel cycle, it is necessary to locally switch the reference clock from the 16 pixel cycle to the 12 image cycle. However, although it is not so difficult to prepare and switch multiple basic clocks, it is possible to generate a stable triangular wave in response to it, and to change the gain and offset instantaneously to an accurate and stable state as necessary. It is very difficult to generate.

  FIG. 14C shows a case where the distance between the lines is further reduced. Reference numeral 1410 denotes image data in which a line having a width of 4 pixels is continuously arranged with 4 pixels off. In this case, it is necessary to locally switch the reference clock cycle of the PWM system to an 8-pixel cycle. Further, since the off period is reduced, the light emission delay amount is changed from 5 ns (corresponding to 2 pixels) to 3.75 ns (corresponding to 1.5 pixels). Is overcorrected by the equivalent of 2.5 ns and 0.5 pixels. Reference numerals 1411 and 1412 denote drive pulses and output light pulses when pulse width correction of the same amount as in FIG. 14A is performed.

  14D and 14E show a case where the distance between the lines is further reduced. In FIG. 14D, since the light emission delay and the turn-off delay have the same value, if the same amount of pulse width correction as shown in FIG. 14A is performed as shown in 1414 and 1415, the output light pulse width increases to about 5 pixels. . Further, in FIG. 14E, the light emission delay is further reduced abruptly and becomes almost zero. If the same amount of pulse width correction as shown in FIG. 14A is performed as shown in 1417 and 1418, the light emission is almost continuous. End up.

  This corresponds to the region 1302 shown in FIG. 13 and is in a state where it has begun to enter a region where a large fluctuation in laser intensity is caused by a slight fluctuation of the input pulse. For this reason, the area 1302 is usually an area that is not used for gradation control of the image portion. To use the area 1302, more precise gain and offset adjustment amounts are required. Realization is very difficult.

  The present invention has been made in view of the above-described problems. An image forming apparatus capable of ensuring linearity in the entire density range of output light pulses and improving the reproducibility of line widths in line drawings, characters, and the like. An object is to provide a control method thereof.

  The present invention can be realized, for example, as an image forming apparatus including an image carrier and an exposure unit that exposes the image carrier to form an electrostatic latent image. The image forming apparatus includes an input unit that inputs image data to be imaged, a pulse generation unit that generates a driving pulse for driving the exposure unit according to the input image data, and the generated driving pulse. And a pulse width for correcting the pulse width of the drive pulse so as to eliminate the lighting delay and the extinguishing delay caused by the exposure means in accordance with the detected pulse interval. And a correcting means.

  In addition, the present invention can be realized as a control method for an image forming apparatus including an image carrier and an exposure unit that exposes the image carrier to form an electrostatic latent image. The control method includes an input step of inputting image data to be image-formed, a pulse generation step of generating a drive pulse for driving the exposure unit in accordance with the input image data, and the generated drive pulse A detection step for detecting a pulse interval that is an off period, and a pulse width correction that corrects the pulse width of the drive pulse so as to eliminate the lighting delay and the extinguishing delay caused by the exposure unit according to the detected pulse interval. And a step.

  The present invention can provide, for example, an image forming apparatus that secures linearity in the entire density range of output light pulses and improves the reproducibility of line widths in line drawings, characters, and the like, and a control method therefor.

  An embodiment of the present invention is shown below. The individual embodiments described below will help to understand various concepts, such as superordinate concepts, intermediate concepts and subordinate concepts of the present invention. Further, the technical scope of the present invention is determined by the scope of the claims, and is not limited by the following individual embodiments.

<First Embodiment>
Hereinafter, the first embodiment will be described with reference to FIGS. 1 to 5. FIG. 1 is a diagram illustrating a relationship between a drive pulse timing correction amount and a pulse interval according to the first embodiment.

  In FIG. 1, the horizontal axis indicates how far away the nearest pulse before the current pixel to be pulse-generated is turned off. That is, it shows the pulse interval from when the previous drive pulse falls to when the current drive pulse rises. Hereinafter, this interval is referred to as a driving pulse off-period or a pulse interval. The vertical axis shows how much correction should be made with respect to the standard drive pulse lighting timing and extinguishing timing for the pulse generation block. In the present embodiment, a table defining the relationship shown in FIG. 1 is stored in a pulse generation unit or storage unit described later.

  FIG. 2A is a diagram illustrating a configuration example of the image forming apparatus according to the first embodiment. Here, descriptions are mainly given of components related to the present invention. Accordingly, the present invention may be configured to include other components.

  The image forming apparatus 200 includes a control unit 201, an exposure unit 202, a photoconductor 203, a recording material cassette 204, a fixing device 205, and a storage unit 206. The control unit 201 comprehensively controls each component of the image forming apparatus 200. Details of the control unit 201 will be described later with reference to FIG. 2B. The exposure unit 202 exposes the photoconductor 203 that is an image carrier in accordance with the drive signal input from the control unit 201, and forms an electrostatic latent image of an image formed on the photoconductor 203. The electrostatic latent image formed on the photoconductor 203 is developed with toner and transferred to the recording material conveyed from the recording material cassette 204. Thereafter, the recording material onto which the toner image has been transferred is conveyed to the fixing device 205. The fixing device 205 fixes the toner image on the recording material by heating and pressurizing. Thereafter, the recording material is discharged out of the image forming apparatus 200. The storage unit 206 stores a program, a set value, and the like for the control unit 201 to control the image forming apparatus 200. Further, a table defining the relationship between the drive pulse correction amount and the pulse interval shown in FIG. 1 is stored.

  FIG. 2B is a diagram illustrating a configuration example of a control unit according to the first embodiment. Here, description is mainly given about the block regarding this invention. Therefore, the present invention may be configured to include other blocks.

  The control unit 201 includes a pulse generation unit 211, a pulse off period counter 212, an image data input unit 213, and an image clock generation unit 214 in order to implement the present invention.

  The image data input unit 213 inputs image data as an image formation target. For example, the image data input unit 213 inputs 2400 dpi binary image data to the pulse generation unit 211 and the pulse-off period counter 212 according to the image to be formed. The image clock generation unit 214 functions as a pulse generation unit, and inputs an image clock for adjusting the image writing timing to the pulse generation unit 211 and the pulse-off period counter 212. Here, for example, an image clock having a pixel period of 2.5 ns is employed. The pulse-off period counter 212 receives image data and an image clock, and inputs a pulse-off period to the pulse generator 211.

  The pulse generator 211 receives image data, an image clock, and a pulse off period (pulse interval) for determining a drive pulse timing correction amount for a target pixel for generating a pulse, and outputs a corrected pulse of the drive signal. Generate. Further, the pulse generation unit 211 acquires a correction amount corresponding to the pulse interval from the table defining the correction amount of the pulse width and the pulse interval stored in the storage unit 206, and corrects the pulse width of the drive pulse. Also good. Therefore, the pulse generation unit 211 is an example of a pulse width correction unit. The pulse generated by the pulse generator 211 is input to the exposure unit 202. The pulse generation unit 211 uses a synchronization clock obtained by multiplying an input image clock by a frequency of about 4 to 16 times by a PLL method or the like as a reference clock, and a pulse having a predetermined width based on image data. Is output. Thus, the pulse generator 211 in the present embodiment can be realized as a relatively simple configuration in a digital circuit.

  However, the pulse correction resolution is limited by the multiplied value. For example, in the case of a quadruple clock base, correction is performed in units of 1/4 of one pixel. In addition, when performing high-resolution correction, a plurality of delay edges are generated by a multi-stage delay device, etc., using an image clock or a clock obtained by multiplying the image clock by several times. An output device or the like may be applied.

  FIGS. 3A to 3E are diagrams illustrating the relationship between input image data, corrected drive pulses, and light output during line drawing formation in the binary system according to the first embodiment. Here, as described above, the input image data is binary of 2400 dpi, and one pixel cycle is 2.5 ns.

  Reference numeral 301 in FIG. 3A indicates image data in which a vertical line having a width of 4 pixels is continuously adjacent as an image input with a space of 12 pixels. Reference numeral 302 denotes image data of one scan line in the image data 301. Reference numeral 303 denotes a drive pulse generated by the pulse generator 211. Reference numeral 304 denotes an output light pulse from the exposure unit 202 driven by the drive pulse 303.

  In the present embodiment, when the pulse OFF period is 7 pixels (threshold) or more, the turn-on (light emission) delay of the output light pulse with respect to the isolated drive pulse is equivalent to 2 pixels (5 ns), and the turn-off delay is equivalent to 1 pixel (2 .5 ns). Therefore, the pulse generation unit 211 increases the pulse width of the drive pulse 303 by one pixel (2.5 ns) with respect to the input image data when the pulse off period is 7 pixels or more. Here, as a correction method for increasing the pulse width, the pulse generation unit 211 may perform correction to advance the turn-on timing of the drive pulse 303 or to turn off the turn-off timing. Moreover, you may perform the correction | amendment which combined them. Here, forward lighting timing refers to correction that delays the rise of a pulse. On the other hand, backward turning-off timing refers to correction for delaying the falling edge of the pulse.

  In the present embodiment, in the isolated pulse state, the correction flow rate of the lighting pulse timing is set to zero, and all the pulse thinning amounts (lighting delay time-lighting delay time) at that time are corrected by retrofitting the light-off pulse timing.

  Reference numeral 305 in FIG. 3B indicates image data in which a vertical line having a width of 4 pixels is continuously adjacent as an image input with a space of 8 pixels. Reference numeral 306 denotes a drive pulse generated by the pulse generator 211. Reference numeral 307 denotes an output light pulse from the exposure unit 202 driven by the drive pulse 306.

  In this case, since the pulse off period is still 7 pixels or more, each drive pulse 306 can be regarded as equivalent to an isolated pulse. Therefore, as in FIG. 3A, the lighting delay is estimated to be equivalent to 2 pixels (5 ns), and the turn-off delay is estimated to be equivalent to 1 pixel (2.5 ns). That is, pulse width correction corresponding to one pixel may be performed on the image data 305. In the present embodiment, the correction of the lighting pulse timing is set to zero, and the backward correction for one pixel is performed with respect to the extinguishing pulse timing.

  Reference numeral 308 in FIG. 3C indicates image data in which a vertical line having a width of 4 pixels is continuously adjacent as an image input with a space of 3 pixels. Reference numerals 309 and 311 denote drive pulses generated by the pulse generator 211. Reference numerals 310 and 312 denote output light pulses from the exposure unit 202 driven by the drive pulses 309 and 311.

  In this case, since the pulse off period is not more than 7 pixels, each drive pulse cannot be regarded as being equivalent to the isolated pulse, and the lighting delay amount is mainly reduced compared to the isolated state. Therefore, in the case of the drive pulse 309 corrected by the same method as in FIG. 3A, the output light pulse becomes 310, which is overcorrected by an amount equivalent to 0.5 pixels.

  Therefore, in the present embodiment, as shown in FIG. 1, the reduction of the lighting delay amount is equivalent to 0.5 pixels, so that the turn-off pulse timing is delayed by a predetermined time corresponding to one pixel like the drive pulse 311. On the other hand, the lighting pulse timing is delayed by a time corresponding to 0.5 pixels so as to eliminate the excessive correction of the extinguishing timing. As a result, the output light pulse 312 has a pulse width corresponding to four pixels, similarly to the input image data.

  Reference numeral 313 in FIG. 3D indicates image data in which a vertical line having a width of 4 pixels is continuously adjacent as an image input with a space of 2 pixels. Reference numeral 314 denotes a drive pulse generated by the pulse generator 211. Reference numeral 315 denotes an output light pulse from the exposure unit 202 driven by the drive pulse 313.

  In this case, as in FIG. 3C, each drive pulse 314 cannot be regarded as equivalent to an isolated pulse, and the lighting delay amount is further reduced as compared to the isolated state. In this embodiment, as shown in FIG. 1, the reduction in lighting delay amount is equivalent to one pixel. That is, in the case of FIG. 3C, the amount of the turn-on delay and the turn-off delay are equal, and the width of the drive pulse 314 and the width of the output light pulse 315 are the same. Accordingly, the turn-off pulse timing is delayed by a predetermined time corresponding to one pixel, while the turn-on pulse timing is delayed by a time corresponding to one pixel. As a result, the output light pulse 315 has a pulse width corresponding to four pixels, similarly to the input image data.

  Reference numeral 316 in FIG. 3E denotes image data that are continuously adjacent to each other with a space of 4 pixels as an image input. Reference numerals 317 and 319 denote drive pulses generated by the pulse generator 211. Reference numerals 318 and 320 denote output light pulses from the exposure unit 202 driven by the drive pulses 317 and 319.

  In this case, each drive pulse cannot be regarded as equivalent to an isolated pulse, and the lighting delay amount is further reduced more rapidly than in the isolated state. Therefore, in the case of the driving pulse 317 corrected by the same method as in FIG. 3A, the output light pulse becomes 318, and a continuous lighting state is obtained.

  Therefore, in this embodiment, as shown in FIG. 1, since the reduction of the lighting delay amount is equivalent to 1.5 pixels, the drive pulse 319 is set to 0.5 pixels as a difference from the one pixel of the extinguishing delay amount. Reduce the input image data. Thereby, the widths of the image data 316 and the output light pulse 320 are made the same. That is, the turn-off pulse timing is delayed by a time corresponding to a predetermined one pixel, while the turn-on pulse timing is delayed by a time corresponding to 1.5 pixels. As a result, the output light pulse 320 has a pulse width corresponding to four pixels, similarly to the input image data.

  In the case of continuous pixels, the correction for the turn-off timing actually acts on the last pixel. In the case of the above-described example, the correction for the turn-off timing occurs for the first to third pixels, but the subsequent pixels are also ON, so that they do not substantially work.

  As described above, in this embodiment, in order to correct the drive pulse, all of the light output thinning in the isolated pulse is returned to the extinction timing, and the correction for the lighting timing is started from zero. Further, even when the pulses come close to each other, the turn-off timing always maintains the turn-on delay time-light turn-off delay time, while performing a correction for gradually turning the turn-on timing backward according to the proximity amount. Since the turn-off delay amount is generally relatively independent of the pulse proximity amount, the right (turn-off side) edge is well aligned as an image. The left side (lighting side) is ideally aligned as the correction table is accurate.

  FIG. 4 is a diagram showing a modification of FIG. From the viewpoint of the configuration of the pulse generation unit 211, as shown in FIG. 4, the extinction timing is always set to the correction value zero, and the lighting timing is advanced or delayed from the standard timing by the extinguishing delay time−the lighting delay time in an isolated region. A method may be applied. In this case, as shown in FIG. 4, when the pulse interval (proximity amount) falls below a threshold value corresponding to the correction zero point (here, 2 pixels), the standard timing is delayed to narrow the pulse. On the other hand, when the pulse interval exceeds the threshold value, the standard timing is advanced to thicken the pulse. Also in this case, since the correction value for the turn-off timing is made constant, the right side becomes a relatively stable image, and the left side depends on the accuracy of the correction value.

  If only the width of the output light pulse is to be made constant, it is possible to act as the sum of the correction for the lighting pulse timing and the correction for the extinguishing pulse timing.

  However, in order to always maintain a constant phase relationship (positional relationship) with the input image, the position of the output light pulse should be constant with respect to the corrected lighting delay amount, the extinguishing delay amount, or both. It is desirable to correct the pulse width. The above-described configuration is premised on optical pulse switching characteristics (the sum of the characteristics of the pulse generator and the lighting element) such that the delay amount with respect to the extinguishing side is substantially constant with respect to the proximity amount. However, if the turn-off delay amount also varies according to the proximity amount, the correction amount may be moved to an appropriate value for both the turn-on timing and turn-off timing of the drive pulse.

  FIG. 5 is a block diagram illustrating a configuration example of the pulse generation unit according to the first embodiment. The pulse generation unit 211 includes a drive pulse interval detection unit 501, a pulse width LUT (lookup table) 502, and a modulator 503.

  The drive pulse interval detection unit 501 is a block that detects an image input data sequence and counts how many pixel spaces are present from the current pixel of interest. The drive pulse interval detection unit 501 according to the present embodiment outputs the processing result in 4 bits, and 5 bits are input to the pulse width LUT 502 together with the current target pixel data 1 bit. The pulse width LUT 502 converts the input 5 bits into 8 bit data having a pulse width of 4 bits and a pulse centroid of 4 bits. The modulator 503 receives the output 8 bits from the LUT and generates a desired pulse.

  As described above, the image forming apparatus according to the present embodiment determines the pulse width of the drive pulse of the exposure unit for forming the electrostatic latent image according to the pulse interval that is the off period of the drive pulse. Correction is made so as to eliminate the lighting delay and extinguishing delay of the exposure unit. Further, in the present image forming apparatus, when correcting the pulse width, it is desirable to fix one correction amount of the rising or falling of the drive pulse and adjust the other correction amount. By correcting in this way, it is possible to ensure linearity in the entire density region of the output light pulse and improve the reproducibility of the line width in line drawings, characters, and the like. In addition, since the correction amount of one of the rising edge and the falling edge of the drive pulse is fixed, the circuit for generating the drive pulse can be simplified.

<Second Embodiment>
Next, a second embodiment will be described with reference to FIG. In the first embodiment, binary data of 2400 dpi is assumed as input image data. However, multi-value data is assumed in the present embodiment.

  FIG. 6 is a block diagram illustrating a configuration example of a pulse generation unit according to the second embodiment. Here, the same number is attached | subjected about the structure similar to FIG. 5, and description is abbreviate | omitted. Further, here, multi-value image data is assumed, and specifically, a system of 600 dpi, a pulse width of 8 bits, and a pulse barycenter position of 2 bits is assumed. In this embodiment, it is assumed that the resolution is reduced and the image clock is relatively low as compared with the first embodiment, and the interaction between the drive pulse and the turn-on delay of the drive pulse and the turn-off delay is the previous pixel. It is generated only in relation to the timing of turning off the pulse.

  The pulse generator 600 according to the present embodiment includes a drive pulse interval detector 501, a correction arithmetic circuit 601, a pulse width / position LUT 602, and a modulator 503. The drive pulse interval detector 501 refers to the pulse data 8 + 2 bits of the previous pixel, and calculates the turn-off timing and the amount of space to the left end of the current pixel. A position 2 bits shown in FIG. 6 indicates that in this embodiment, the pulse is shifted to the left within the pixel, the center of gravity is centered, and the pulse is shifted to the right side. For example, when the previous pixel is left-justified and 128/255, there is a space of 255-128 = 127, and this value is output. When the center of gravity is 128/155, the space is (255-128) /2=63.5. However, in the case of a system that does not handle a decimal point, decimals are assigned to either the right side or the left side. . In the present embodiment, 64 spaces are assigned to the right side. If right-justified, the space is zero.

  The correction arithmetic circuit 601 generates corrected input image data based on the current image data 8 + 2 bits and the output from the drive pulse interval detector 501. If the current pixel is right-justified, the output itself from the drive pulse interval detector 501 is a space, and a pulse width correction value for the space amount is shown in a table (see FIG. 1 or FIG. 4) showing the relationship between the space amount and the correction amount. Multi-valued.) The obtained pulse width correction value is added to the pulse width 8 bits of the current input data.

  If the current pixel is centered or left justified, the space on the left side of the current pixel is calculated in the same manner, and the output from the drive pulse interval detector 501 is added to the space. Similarly, the correction amount is referred from the table and added to the current pixel width data. As described above, an appropriate pulse width can be obtained by applying the present invention even in a multi-value data system.

<Third Embodiment>
Next, a third embodiment will be described with reference to FIGS. In the present embodiment, it is assumed that the density gradation is expressed by a ratio of pulse widths of continuous pulses in the image portion, which is a multi-value data system. In this case, the pulse width correction further requires a gradation part and other cases.

  FIG. 7 is a diagram illustrating the relationship between the drive pulse width and the output light pulse width according to the third embodiment. The horizontal axis indicates the drive pulse width, and the vertical axis indicates the output light pulse width. FIG. 7 shows the relationship between the drive pulse width and the output light pulse width when gradation control is performed with the on-duty of continuous pulses in units of one pixel. While the drive pulse is small, there is almost no output light pulse due to the lighting delay. Thereafter, the pulse width begins to increase gradually, and a linear region is reached in which the increase in the drive pulse directly increases the output light pulse. Further, when the drive pulse width is increased, the pulses are close to each other, and the lighting delay is rapidly reduced. Therefore, the increase amount of the output light pulse width is larger than the increase amount of the drive pulse. Finally, although the drive pulse has a pulse-off period, the output light pulse is continuously lit.

  In such a case, in order to ensure the continuity of the output image density, pulse width correction is performed so that the input image data 00-FFH is assigned only to the linear region. However, when the line width is secured to some extent as in a line drawing or a character, if this correction is performed, the maximum output light pulse width of one pixel becomes shorter than the original one pixel length, Image writing that is faithful to the image cannot be performed.

  In this embodiment, in order to solve this problem, the gradation part (image part) and the other part are identified by the image area signal or the like, and the pulse width correction amount is switched. FIG. 8 is a block diagram illustrating a configuration example of a pulse generation unit according to the third embodiment. Here, the same components as those in FIG. 6 are denoted by the same reference numerals and description thereof is omitted.

  In the pulse generation unit 800, an image area determination unit 801 is added to the pulse generation unit 600 shown in FIG. The image area determination unit 801 determines whether the input image data is binary data or multi-value data, and uses the determination result as a 1-bit identification signal and the correction arithmetic circuit 601 and the pulse width / position LUT 602. Output to. Further, a configuration for self-determination based on input image data may be used. If the identification signal is a value indicating the gradation part, the function of the correction arithmetic circuit 601 is invalidated, and the LUT dedicated to the gradation part is referred to in the LUT. Reference is made to the LUT for performing pulse width correction such that the linearity portion is 00-FF in FIG. On the other hand, in the case other than the gradation part, the correction arithmetic circuit 601 is validated, and the LUT for other than the gradation part is referred to. Depending on the adjacent amount with the adjacent pulse, an LUT having a lighting characteristic as indicated by alternate long and short dash lines indicated by E, D, and AB shown in FIG. 7 is used. However, these are all characteristics of a simple parallel shift relationship. If one simple LUT with input = output is prepared, it can be realized only with the output of the correction arithmetic circuit 601.

  However, when there is a space interval equivalent to an isolated pulse, there is a portion with low linearity at the rising edge of the pulse, and therefore it is desirable to input an isolated pulse equivalent identification signal to the LUT. Therefore, more accurate correction is possible if a table showing a relationship such as “more detailed non-gradation part 00-FF pulse width AB” in FIG. 7 can be referred to separately.

  In some cases, the pulse width correction exceeds 255, but there is no problem if the subsequent modulator can reproduce this carry. However, if this is not the case, a separate logic for transmitting (adding) the carry width pulse width data to the next pixel is required. Further, even when the pulse is carried, if the image input signal is such that the next pixel overlaps with it, the entire output light pulse is not actually corrected.

It is a figure which shows the relationship between the drive pulse timing correction amount and pulse interval which concern on 1st Embodiment. 1 is a diagram illustrating a configuration example of an image forming apparatus according to a first embodiment. It is a figure which shows the structural example of the control part which concerns on 1st Embodiment. , , , , It is a figure which shows the relationship between the input image data at the time of line drawing formation in the binary system which concerns on 1st Embodiment, the drive pulse after correction | amendment, and an optical output. It is a figure which shows the modification of FIG. It is a block diagram which shows the structural example of the pulse generation part which concerns on 1st Embodiment. It is a block diagram which shows the structural example of the pulse generation part which concerns on 2nd Embodiment. It is a figure which shows the relationship between the drive pulse width and output light pulse width which concern on 3rd Embodiment. It is a block diagram which shows the structural example of the pulse generation part which concerns on 3rd Embodiment. It is a figure which shows the relationship between a laser current and optical output. It is a figure which shows a laser light emission control part. It is a figure which shows a laser drive current pulse waveform and a laser emission pulse waveform. It is a figure which shows the relationship between the laser drive signal and output light pulse with respect to one screen dot formed with one pixel or several continuous pixels. It is a figure which shows the relationship between a pulse width and a laser light quantity. , , , , It is a figure which shows the relationship between the original image at the time of line drawing formation in a binary system, a drive pulse, and an optical output. It is a figure which shows an analog type PWM modulation system.

Explanation of symbols

200: Image forming apparatus 201: Control unit 202: Exposure unit 203: Photoconductor 204: Recording material cassette 205: Fixing device 206: Storage unit 211: Pulse generation unit 212: Pulse off period counter 213: Image data input unit 214: Image clock Generator

Claims (7)

An image forming apparatus comprising: an image carrier; and an exposure unit that exposes the image carrier to form an electrostatic latent image.
An input means for inputting image data to be imaged;
Pulse generating means for generating a driving pulse for driving the exposure means in accordance with the input image data;
Detecting means for detecting a pulse interval that is an off period of the generated driving pulse;
An image forming apparatus comprising: a pulse width correcting unit configured to correct a pulse width of the drive pulse so as to eliminate a lighting delay and a light extinguishing delay caused by the exposure unit according to the detected pulse interval. The pulse width correcting means includes
The image forming apparatus according to claim 1, wherein the pulse width of the drive pulse is corrected by advancing or delaying at least one of a rising timing and a falling timing of the driving pulse. The pulse width correcting means includes
If the detected pulse interval is greater than a predetermined threshold, delay the falling timing of the drive pulse by a predetermined time;
When the detected pulse interval is smaller than a predetermined threshold value, the drive pulse falling timing is delayed by the predetermined time, and the delay generated by delaying the falling timing is generated. The image forming apparatus according to claim 1, wherein the delay for correction is eliminated by delaying the rising timing of the drive pulse. The pulse width correction means corrects the falling timing of the drive pulse,
When the detected pulse interval is smaller than a predetermined threshold, delay the rising timing of the drive pulse,
3. The image forming apparatus according to claim 1, wherein when the detected pulse interval is larger than a predetermined threshold, the rising timing of the drive pulse is advanced. Storage means for storing a table defining a relationship between the pulse interval and the correction amount of the pulse width;
The pulse width correcting means includes
5. The image forming apparatus according to claim 1, wherein a correction amount corresponding to the detected pulse interval is acquired from the table, and a pulse width of the drive pulse is corrected. 6. A discriminator for discriminating whether the image data is binary data or multi-value data;
The pulse width correction means includes
The image forming apparatus according to claim 1, wherein a pulse width of the drive pulse is corrected based on a determination result determined by the determination unit. An image forming apparatus comprising: an image carrier; and an exposure unit that exposes the image carrier to form an electrostatic latent image.
An input step for inputting image data to be imaged;
A pulse generating step for generating a driving pulse for driving the exposure means according to the input image data;
A detection step of detecting a pulse interval that is an off period of the generated drive pulse;
And a pulse width correcting step for correcting a pulse width of the drive pulse so as to eliminate a lighting delay and a light extinguishing delay caused by the exposure unit according to the detected pulse interval. Control method.

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