JP2009202604A - Image forming apparatus and method of controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce shift in image forming position which depends on the light quantity of a light beam. <P>SOLUTION: In an image forming apparatus where the light quantity of a light beam being used for forming a latent image is switched depending on the difference of resolution, lasers 101 to 104 emit a light beam for forming a latent image on a photosensitive drum 203. A light beam thus emitted is used for scanning by a polygon mirror 105 and the scanned light beam is detected by a BD sensor 106. When controlling the emission timing of the lasers 101 to 104 depending on the timing the light beam is detected, a timing control section 204 selects a suitable emission timing from a table in a storage 205 depending on the light quantity of the light beam or the resolution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming technique for forming an image using a light beam such as a laser beam.

  2. Description of the Related Art Conventionally, there is known an image forming apparatus capable of forming a high resolution (for example, 1200 dpi) image and a low resolution (for example, 600 dpi) image by switching resolution.

  When the rotation speed of the polygon mirror is the same when forming an image of 600 dpi and when forming an image of 1200 dpi, the rotational speed of the photosensitive drum is set to ½ at 1200 dpi compared to 600 dpi. To do. Further, in order to make the integrated light amount of the laser scanned on the photosensitive drum equal in both cases, the laser light amount is set to ½ at 1200 dpi as compared to 600 dpi, and further, an image clock for driving the laser. Needs to be doubled. By controlling in this way, an image of 1200 dpi is formed on both the main scanning line and the sub-scanning line.

  By the way, when forming an image, it is necessary to always form an image from the same position, and for that purpose, horizontal synchronization and vertical synchronization must be obtained. If horizontal synchronization cannot be obtained correctly, the image will be displaced in the horizontal direction.

  To obtain this horizontal synchronization, when a light beam is detected by a photodetector provided near the end of the photosensitive drum when the light beam is scanned onto the photosensitive drum by a polygon mirror, a horizontal synchronization signal is generated. There is a way to output.

  However, as described above, if the amount of light beam is switched in accordance with the resolution, the output timing of the horizontal synchronization signal is shifted. This is because the horizontal synchronization signal is output when the integrated light quantity of the light beam applied to the photodetector reaches a predetermined value. That is, the horizontal synchronization signal is output relatively early when the light amount is large, and the horizontal synchronization signal is output relatively late when the light amount is small.

  In order to solve this problem, when scanning on the photosensitive drum, the amount of light beam is set in accordance with the resolution, while on the other hand, when the light beam scans on a photodetector provided at the end of the photosensitive drum. Has proposed a technique for controlling the amount of light so that the amount of light beam is always constant regardless of the resolution (Patent Document 1). That is, the amount of light is switched not only when the resolution is switched but also during one scan.

JP-A-8-304723 JP 2004-058492 A

  Incidentally, some color image forming apparatuses include a plurality of lasers, and each laser is assigned to each color material such as cyan, magenta, yellow, and black. Moreover, there are cases where these lasers are scanned in different directions for reasons such as reducing the number of polygon mirrors (Patent Document 2). For example, when the yellow laser scans in the right direction, the magenta laser scans in the left direction. In such a case, the image writing position shift caused by the above-described difference in resolution (that is, the difference in light amount) is in the opposite direction, so that the shift amount is doubled. Moreover, since this shift appears as a color shift, the quality of the formed image is greatly deteriorated.

  There is a possibility that this problem can be solved by applying the method described in Patent Document 1 described above. However, since a circuit for setting the amount of light when scanning on the photosensitive drum and a circuit for setting the amount of light when scanning on the photodetector are required, the circuit scale increases and cost increase can be avoided. There is a problem that there is no.

  Therefore, an object of the present invention is to solve these and other problems. Other issues can be understood throughout the specification.

  In order to solve the above-described problems, the present invention provides suitable light emission according to the difference in the light amount or resolution of the light beam when controlling the light emission timing of the light emitting means according to the detection timing of the light beam detected by the detector. The timing was selected.

  As described above, in the present invention, since a suitable light emission timing is selected according to the difference in the light amount or resolution of the light beam, the light beam is scanned on the photosensitive drum and the light detector is scanned. It is possible to omit the control of changing the amount of light depending on the time. Further, the cost can be reduced while reducing the deviation of the image writing position.

FIG. 1 is a diagram showing an example of an optical scanning device of a color image forming apparatus to which the invention according to this embodiment can be applied. FIG. 2 is a diagram illustrating an example of an optical scanning device and a timing control unit according to the present embodiment. FIG. 3 is an exemplary flowchart regarding the process of controlling the light emission timing according to the present embodiment. FIG. 4 is a diagram showing the relationship among each light quantity, BD signal, and image signal. FIG. 5 is a diagram showing the relationship among each light quantity, BD signal, and image signal related to the conventional example. FIG. 6 is a diagram illustrating a formed image shift caused by a write timing shift. FIG. 7 is a diagram illustrating a shift in the formed image accompanying a shift in the writing timing regarding the color image. FIG. 8 is a diagram illustrating an example of an image forming apparatus according to the present embodiment. FIG. 9 is a diagram showing a plurality of recording sheets on which calculation patterns are formed using different amounts of light. FIG. 10 is a diagram illustrating an example of a correction value table according to the present embodiment. FIG. 11 is a diagram illustrating a relationship between the correction value according to the present embodiment and the light emission timing at each light quantity. FIG. 12 is an exemplary flowchart for the calculation processing of the light emission timing for each light quantity according to the present embodiment. FIG. 13 is a diagram showing an example of a table showing the relationship between the light amount setting value and the light emission timing data according to the present embodiment. FIG. 14 is a diagram showing a reference timing determination principle according to the present embodiment.

  In the following, an embodiment useful for understanding the high-level concept, middle-level concept, and low-level concept of the present invention will be described. Note that not all of the concepts included in the following embodiments are described in the claims. However, it should be understood that this is not intentionally excluded from the technical scope of the patented invention, but is not described in the scope of claims because it is equivalent to the patented invention.

[First Embodiment]
FIG. 1 is a diagram showing an example of an optical scanning device of a color image forming apparatus to which the invention according to this embodiment can be applied. Yellow image forming semiconductor laser (hereinafter referred to as yellow laser) 101, magenta image forming semiconductor laser (hereinafter referred to as magenta laser) 102, cyan image forming semiconductor laser (hereinafter referred to as cyan laser). .) 103 and a black image forming semiconductor laser (hereinafter referred to as a black laser) 104, each laser beam is condensed into a parallel light beam by each collimator lens (not shown) and is rotated at a constant rotational speed. By being reflected by the rotating polygon mirror 105, scanning is performed at an equiangular velocity.

  Each laser beam reflected by the polygon mirror 105 passes through each fθ lens (not shown) and is reflected by a reflecting mirror 111 for a yellow laser, a reflecting mirror 112 for a magenta laser, and a reflecting mirror for a cyan laser. 113 is reflected by the reflecting mirror 114 for the laser for black, and irradiated to a photosensitive drum (not shown).

  The image forming position on the photosensitive drum surface is determined by BD signals output from BD (beam detect) sensors 106 and 107. The yellow / magenta BD sensor 106 detects yellow laser light in order to determine the write start timing of the yellow laser 101 and the magenta laser 102. Then, after a certain time from the timing at which the yellow laser beam is irradiated, the writing start timing for yellow and magenta is set. On the other hand, similarly, the black laser 104 and the cyan laser 103 each have a writing start timing after a certain time from the timing when the black laser beam is irradiated onto the black / cyan BD sensor 107.

  In such a configuration, when the amount of light is changed by switching the resolution, the shift direction is reversed, so the shift amount is relatively doubled, and the color shift in the main scanning direction is likely to be remarkable. Therefore, the improvement effect when the present invention is applied is great. However, the present invention is not limited to such a configuration, and can be applied to an image forming apparatus that uses only one laser or an image forming apparatus that uses a plurality of lasers and has the same scanning direction. can do.

  FIG. 2 is a diagram illustrating an example of an optical scanning device and a timing control unit according to the present embodiment. This figure shows one of a plurality of lasers in a simplified manner. Reference numeral 201 denotes the collimator lens described above. Reference numeral 202 denotes the fθ lens described above. Reference numeral 203 denotes the above-described photosensitive drum. Laser light emitted from each of the lasers 101 to 104 passes through the collimator lens 201, is condensed into a parallel light beam, and is reflected by the polygon mirror 105 that rotates at a constant speed, thereby being scanned at an equiangular speed. Further, the laser light that has passed through the fθ lens 202 is irradiated onto the surface of the photosensitive drum 203 at a constant speed, thereby forming an electrostatic latent image.

  A timing control unit 204 controls the light emission timing of each of the lasers 101 to 104. Reference numeral 205 denotes a storage device that stores light emission timing data corresponding to the light amount setting signal. The main control unit 206 is a control device such as a printer controller that executes image processing and an engine control unit that controls an image forming engine. The main control unit 206 outputs a corresponding light amount setting signal in accordance with the resolution instruction input from the host device or the operation unit. When the timing control unit 204 receives the BD signal output from the BD sensors 106 and 107, the timing control unit 204 is based on a light amount setting signal (may be resolution identification information) input from the main control unit 206. Select the corresponding light emission timing. For example, the timing control unit 204 reads the light emission timing data corresponding to the light amount setting signal from the storage device 205, and determines the light emission start timing based on the read light emission timing data and the rising timing of the BD signal. Light emission is instructed according to the light emission timing. In the light emission timing data, when the light amount is A, the light is emitted after t1 seconds from when the BD signal is received (that is, when the rising edge of the pulse of the BD signal is detected), and when the light amount is B, the light emission timing data is t2 from when the BD signal is received. Data such as light emission after 2 seconds is included.

  FIG. 3 is an exemplary flowchart regarding the process of controlling the light emission timing according to the present embodiment.

  In step S301, the main control unit 206 sets the resolution according to an instruction input from the host device or the operation unit.

  In step S302, the main control unit 206 selects a light amount according to the set resolution. For example, a table indicating the relationship between the resolution and the light amount is stored in advance in a memory (not shown) provided in the main control unit 206, and the light amount corresponding to the set resolution is read out. The main control unit 206 outputs a light amount setting signal indicating the selected light amount to the timing control unit 204.

  In step S303, the timing control unit 204 selects a light emission timing corresponding to the above-described light amount setting signal. For example, light emission timing data corresponding to the input light amount setting signal is read from a table indicating the relationship between the light amount setting signal and the light emission timing data stored in the storage device 205.

  In step S304, the timing control unit 204 determines whether or not a BD signal has been received from the BD sensors 106 and 107. When the BD signal is received, the waiting loop is exited. The BD signal is output when the BD sensors 106 and 107 are irradiated with laser light.

  In step S <b> 305, the timing control unit 204 waits for the elapse of time as indicated by the light emission timing data with reference to the BD signal. This time is measured by a counter built in the control unit 204. When the image writing timing comes, the process proceeds to the next step.

  In step S306, the timing control unit 204 controls the light emission of the lasers 101 to 104 based on the image data and the light amount setting signal.

  FIG. 4 is a diagram showing the relationship among each light quantity, BD signal, and image signal. In this example, when the light amount is A, the time after t1 from the rising timing of the BD signal is used as the writing start timing, and when the light amount is B, the image writing timing is set after t2 from the rising timing of the BD signal. Even in this case, as a result, it is shown that images can be formed at the same timing. It is assumed that the storage device 205 stores light amounts A and t1 in association with each other, and stores light amounts B and t2 in association with each other.

  Hereinafter, in order to explain the effect of the present invention, a conventional example and the present invention will be compared.

  FIG. 5 is a diagram showing the relationship among each light quantity, BD signal, and image signal related to the conventional example. According to the prior art, the write timing is shifted between the light amount A and the light amount B because the write timing is the time when a certain time t has elapsed from the detection timing of the BD signal, even though the light amount has changed. . Here, it is assumed that the relationship of light quantity A> light quantity B is established.

  FIG. 6 is a diagram illustrating a formed image shift caused by a write timing shift. Compared to the image formed with the light amount A, the image formed with the light amount B has a write position shifted in the main scanning direction (horizontal direction) by a position corresponding to the shift of the write timing.

  FIG. 7 is a diagram illustrating a shift in the formed image accompanying a shift in the writing timing regarding the color image. In particular, in the color image forming apparatus as shown in FIG. 1, the scanning direction of laser light is reversed between some lasers and other lasers. For this reason, it can be understood that a deviation in the writing timing causes a color deviation and significantly deteriorates the quality of the formed image.

  According to the invention according to the present embodiment, by switching the light emission timing according to the laser light quantity setting value, it is possible to form an image at a stable position regardless of the laser light quantity. In particular, a color image forming apparatus that forms a color image by superimposing a plurality of images of different colors, and when the scanning direction of laser light differs between an image of one color and an image of another color Can reduce color misregistration occurring in the main scanning direction.

  Further, unlike the technique described in Patent Document 1, the amount of light when scanning on the photosensitive drum and the amount of light when scanning on the photodetector are not switched. It may be eliminated and the circuit scale may be reduced. That is, unless the resolution is changed, the light amount of the laser light is not intentionally changed, so that the control of the light amount of the laser light is simplified.

[Second Embodiment]
In the present embodiment, a calculation example of suitable light emission timing data for each light amount will be described.

  FIG. 8 is a diagram illustrating an example of an image forming apparatus according to the present embodiment. The same components as those already described are denoted by the same reference numerals and the description thereof is omitted.

  The printer controller 801 is an image processing apparatus that performs arbitrary image processing on image data input from the host device or the optical sensor controller 806. The engine control unit 802 is a control device that controls the image forming engine 803 based on the image signal output from the printer controller 801. The image forming engine 803 includes lasers 101 to 104, a photosensitive drum 203, a fixing device (not shown), a recording paper conveyance mechanism, and the like. The engine control unit 802 includes the timing control unit 204 and the storage device 205 described above.

  The calculation pattern data ROM 804 stores pattern data used for calculating the light emission timing data. The optical sensor 805 is a detection device that optically detects a pattern formed on the recording paper. If the image forming apparatus is a copying machine, an optical sensor 805 may be substituted for a reader that reads a document. Otherwise, the optical sensor 805 is disposed in the recording paper conveyance path downstream of the fixing device in the recording paper conveyance path of the image forming apparatus. The optical sensor controller 806 is a processing circuit that creates image data based on data input from the optical sensor 805. The light emission timing calculation unit 807 forms a calculation pattern on the recording paper for each of a plurality of light amounts, and compares the formed patterns to detect positional “deviation” and corresponding temporal timing. This is an arithmetic circuit that calculates the deviation of the light and finally calculates the light emission timing for each light quantity. The calculated light emission timing is stored in the storage device 205.

  FIG. 9 is a diagram showing a plurality of recording sheets on which calculation patterns are formed using different amounts of light. The recording paper 810A has a pattern formed using the light amount A. The recording paper 810B has a pattern formed using the light quantity B. In the calculation, in both cases of the light amount A and the light amount B, an image is formed after the lapse of the same time is counted after receiving the BD signal. That is, the invention according to the first embodiment is not applied.

  According to the example shown in FIG. 9, it can be seen that the pattern 901 formed by the light amount B is deviated by a distance d on the right side as compared with the pattern 901 formed by the light amount A. That is, this distance d corresponds to the deviation of the writing position described above. The trajectory when the optical sensor 805 passes over the recording paper is a straight line with a distance ds from the left end of the recording paper. Further, as shown in the figure, it is assumed that the distance from the left end of the recording paper to the upper end of the “<” shape is dA for the recording paper 810A and dB for the recording paper 810B. In this example, ds = dA. Then, the distance d representing the deviation is d = dB−dA. The correction value t3 is determined in accordance with a correction value table representing the relationship between the deviation amount d and the correction value t3. Note that dB or dA may be calculated by the light emission timing calculation unit 807 from image data read by the optical sensor 805. For example, it can be obtained as t3 = k1 · d. Here, k1 is a coefficient representing the relationship between t3 and d. Note that the function representing the relationship between the two is not necessarily a linear function, and may be a higher order function.

  Alternatively, the light emission timing calculation unit 807 may count the time from when the optical sensor 805 detects the upper “/” in the character “<” to the lower “\”. As a result, it is assumed that the detection time of the recording paper 810A is tA and the detection time of the recording paper 810B is tB. Further, when the angle of the “<” is 2θ and the conveyance speed of the recording paper is v, the above-described deviation amount d = (tA−tB) · v / tan θ. The deviation amount d calculated in this way may be used.

  Furthermore, the above-described correction value t3 may be calculated using dt (however, dt = tA−tB), which is a measurement time difference between tA and tB. For example, it can be obtained as t3 = k2 · dt. Here, k2 is a coefficient representing the relationship between t3 and dt. Of course, depending on the characteristics of the image forming apparatus, the relationship between t3 and dt may be expressed by a higher-order function.

  FIG. 10 is a diagram illustrating an example of a correction value table according to the present embodiment. In this example, it is assumed that the relationship between the measurement time difference dt and the correction value t3 is t3 = k2 · dt.

  FIG. 11 is a diagram illustrating a relationship between the correction value according to the present embodiment and the light emission timing at each light quantity. In this example, when the time from the rise of the BD signal to the light emission start timing is t1 for the light amount A and the correction value is t3, the time t2 between the rise of the BD signal and the light emission start timing for the light amount B is t2 = t1. -T3. Here, if t1 is equivalent to the light emission timing (t) when the recording paper 810A and the recording paper 810B are created, it can be obtained as t2 = t−t3. That is, if the recording paper 810A and the recording paper 810B are formed at the same light emission timing (t), a shift corresponding to t3 occurs, so the light emission timing for one light quantity is corrected by the correction value t3. By doing so, the deviation is offset.

  FIG. 12 is an exemplary flowchart for the calculation processing of the light emission timing for each light quantity according to the present embodiment.

  In step S1201, when the calculation process of the light emission timing is started, the timing control unit 204 sets the light emission timing to t. Note that this step may be omitted when the default light emission timing is used.

  In step S1202, the main control unit 206 (controller 801 or engine control unit 802) sets the i-th light amount in the timing control unit 204 using the light amount setting signal. Note that the initial value of i is 1.

  In step S <b> 1203, the controller 801 in the main control unit 206 reads image data of the calculation pattern from the ROM 804.

  In step S1204, the controller 801 generates an image signal for the read pattern image and sends it to the engine control unit 802. The engine control unit 802 drives and controls the image forming engine 803 to form an image according to the image signal using the set light amount. In this way, a calculation pattern corresponding to the i-th light amount is formed on the i-th recording paper.

  In step S1205, the optical sensor 805 reads the calculation pattern formed on the i-th recording paper. The read data is converted into image data by the optical sensor controller 806. The light emission timing calculation unit 807 calculates the recording position of the character “<” for the i-th pattern based on the image data. Alternatively, the time difference from the detection of the upper side “/” of the character “ku” to the detection of the lower side “\” is detected.

  In step S1206, the main control unit 206 determines whether the calculation processing for the pattern formation position or the pattern detection time difference has been completed for all types of light amounts. If completed, the process proceeds to step S1207.

  In step S1207, the light emission timing calculation unit 807 substitutes each pattern formation position or the detection time difference of each pattern into the above-described arithmetic expression for each of the second and subsequent recording papers with the first recording paper as a reference. The correction value is calculated. The recording paper other than the first one may be used as a reference, or data stored in the storage device 205 in advance may be used as a reference. If the data actually read from the recording paper is used, there is an advantage that the storage capacity can be reduced rather than storing the reference data in advance.

  In step S1208, the light emission timing calculation unit 807 calculates the light emission timing based on the respective correction values of the respective light amounts. When the calculation is completed, the light emission timing calculation unit 807 creates a light emission timing table so that each light quantity corresponds to each light emission timing, and stores the light emission timing table in the storage device 205.

  As described above, in the image forming apparatus according to the present embodiment, the mechanism for optimizing the light emission timing is mounted in the image forming apparatus. It will be possible to respond dynamically.

[Third Embodiment]
In the present embodiment, an example of a specific method for determining the light emission timing is shown. FIG. 13 is a diagram showing an example of a table showing the relationship between the light amount setting value and the light emission timing data according to the present embodiment. The horizontal axis indicates the light amount setting value, and the vertical axis indicates the light emission timing. In the example of the figure, the light emission timing data is determined as t1 seconds when the light amount is A and t2 seconds when the light amount is B. These light emission timing data t1, t2 indicate the light emission start time of the laser light with reference to the rising time of each BD signal.

  By referring to the table in this way, the light emission timing can be uniquely determined by the set light amount. The table can be stored in the storage device 205. The storage device 205 outputs light emission timing data corresponding to the light amount setting signal output from the main control unit 206 to the timing control unit 204. Alternatively, the timing control unit 204 reads light emission timing data corresponding to the light amount setting signal output from the main control unit 206 from the table of the storage device 205. The timing control unit 204 controls the light emission timing of the lasers 101 to 104 based on the light emission timing data.

  According to the present embodiment, a calculation sequence for calculating light emission timing data, correction values, and the like can be omitted. Therefore, it is possible to reduce the deviation in the light emission timing caused by the difference in the light amount without reducing the throughput of the image forming apparatus. That is, a stable light emission timing can be obtained without depending on the amount of light.

[Fourth Embodiment]
In the above-described embodiment, the light emission start time is controlled from the rise time of the signals output from the BD sensors 106 and 107 as a reference. That is, the time from the start-up to the start of light emission is suitably changed according to the light amount so that light can be emitted at substantially the same timing even if the light amount changes.

  In the present embodiment, the time after the above-described rising time and before the falling time is set as the reference time. That is, the light emission timing is determined based on a division point that divides the pulse width of the BD signal output from the BD sensors 106 and 107 functioning as detection means at a predetermined ratio. That is, in the present embodiment, the above-mentioned “deviation” can be absorbed by changing the reference time in each BD signal in accordance with the difference in the amount of light. For this reason, even if the amount of light changes, the time interval from the reference time to the start of light emission can be made substantially the same value.

  FIG. 14 is a diagram showing a reference timing determination principle according to the present embodiment. Specifically, for each of the light amounts A and B, outputs (BD signals) from the BD sensors 106 and 107 and a reference time regarding the light emission timing are shown.

  It has been experimentally known that the amount of change at the rise of the BD signal and the amount of change at the fall of the BD signal accompanying the change in the amount of light are approximately linear. For example, in the case of a BD sensor having a light quantity dependency as shown in FIG. 14, the division point that divides the pulse width of the BD signal by 1 to 2 is used as the reference time for counting the light emission timing. The dependent light emission timing shift can be reduced.

  Note that the division ratio of 1: 2 is merely an example, and in practice, a suitable ratio may be employed according to the characteristics of the BD sensor employed in the image forming apparatus. That is, the division ratio can be m: n (where m and n are natural numbers).

  Further, the time interval t from the reference time thus determined to the light emission start time may be changed according to the difference in the light amount, or may be the same without depending on the light amount. This is because in any case, the time interval t and the reference time (division ratio) may be appropriately determined so that the light emission timing is finally synchronized. Further, the division ratio may be different for each light quantity, or may be the same without depending on the light quantity. In this case, the time interval t from the reference time to the light emission time may be determined so that the final light emission timing is synchronized. If the same division ratio is used, there is an advantage that the storage capacity required for holding the division ratio in the storage device can be saved as compared with the case of using a plurality of division ratios. This corresponds to image formation with a large number of resolutions. As a result, in an image forming apparatus that uses various amounts of light, the effect of saving storage capacity is increased.

  Note that these parameters may be calculated at the time of design and stored in the storage device 205, and the timing control unit 204 may read and use them. Alternatively, a control unit such as the timing control unit 204 may dynamically calculate these parameters during operation. In the former case, there is an advantage that the calculation sequence can be omitted, and in the latter case, there is an advantage that it is possible to appropriately cope with variations in component accuracy, aging, etc. for each image forming apparatus.

  As described above, according to the present embodiment, since the reference time for defining the light emission timing can be a point other than the rising edge in the BD signal, there is an advantage that the degree of freedom in design is increased. Of course, similarly to the above-described embodiment, it is possible to reduce the deviation of the light emission timing due to the light amount dependency.

[Other Embodiments]
In the above-described embodiment, the light emission timing is determined according to the set light amount. However, the light emission timing may be determined corresponding to data other than the set light amount. For example, if the set resolution and the laser light quantity have a one-to-one correspondence, the light emission timing can be controlled by the set resolution data from a printer controller or the like.

  Further, the light amount may be measured by the BD sensors 106 and 107 or the photodiodes in the lasers 101 to 104, and the write timing may be actively controlled according to the measured light amount. That is, the timing control unit 204 selects a suitable light emission timing using the measured light quantity instead of the above-described light quantity setting signal.

  In the second embodiment, the “<” character pattern is used when calculating the correction value of the light emission timing, but other patterns may be used as long as the pattern conforms to the “<” character. Here, the pattern conforming to the character “ku” means a geometric pattern effective in calculating the correction value and the light emission timing. For example, “A”, “∠”, “○”, and so on, if there is any relationship between the horizontal displacement and the vertical displacement (eg, proportional, inversely proportional), what geometric pattern is used. May be. This is because in any case, it is a figure that can be numerically converted and a correction value and light emission timing can be calculated.

  Note that the selection of the light emission timing is not only to select a suitable light emission timing from a plurality of light emission timings, but also to calculate a suitable light emission timing, to read out data of a suitable light emission timing from the storage device, etc. Also means.

  Although various embodiments have been described in detail above, the present invention may be applied to a system constituted by a plurality of devices, or may be applied to an apparatus constituted by one device. For example, there are a scanner, a printer, a scanner, a PC, a copier, a multifunction machine, and a facsimile machine.

  Note that the present invention supplies a software program (in this embodiment, a program corresponding to the flowcharts shown in FIGS. 3 and 12) for realizing each function of the above-described embodiment directly or remotely to a system or apparatus, This can also be achieved by a computer included in the system or apparatus reading and executing the supplied program code.

  Accordingly, since the functions and processes of the present invention are implemented by a computer, the program code itself installed in the computer also implements the present invention. That is, the computer program itself for realizing the functions and processes is also one aspect of the present invention.

  In this case, the program may be in any form as long as it has a program function, such as an object code, a program executed by an interpreter, or script data supplied to the OS.

  As a recording medium for supplying the program, for example, flexible disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD-R).

  As another program supply method, a client computer browser is used to connect to an Internet homepage, and the computer program of the present invention itself or a compressed file including an automatic installation function is downloaded from the homepage to a recording medium such as a hard disk. Can also be supplied. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer may be a constituent requirement of the present invention.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. It is also possible to execute the encrypted program by using the key information and install the program on a computer.

  In addition to the functions of the above-described embodiments being realized by the computer executing the read program, the OS running on the computer based on the instruction of the program is a part of the actual processing. Alternatively, the functions of the above-described embodiment can be realized by performing all of them and performing the processing.

  Furthermore, after the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion board or The CPU or the like provided in the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

Claims (2)

An image forming apparatus in which the amount of light beam used for latent image formation can be switched according to the difference in resolution,
A light emitting means for emitting a light beam for forming a latent image on the photosensitive drum;
Scanning means for scanning the emitted light beam;
Detecting means for detecting the scanned light beam;
Selection means for selecting the light emission timing according to the light amount or the resolution of the light beam when controlling the light emission timing of the light emission means according to the detected timing of the light beam;
Control means for controlling the light emission timing of the light emission means according to the selected light emission timing,
The selection means includes
An image forming apparatus, comprising: a light emission timing determining unit that determines the light emission timing based on a division point that divides a pulse width of a signal output from the detection unit at a predetermined ratio. A method of controlling an image forming apparatus in which the amount of light beam used for latent image formation changes according to the difference in resolution,
Emitting a light beam for forming a latent image on a photosensitive drum of the image forming apparatus;
Scanning the emitted light beam;
Detecting the scanned light beam;
When controlling the light emission timing of the light beam according to the detected timing of the light beam, selecting a light emission timing according to the light amount of the light beam or the resolution;
Controlling the light emission timing of the light beam according to the selected light emission timing,
The selection step includes:
A method for controlling an image forming apparatus, further comprising: determining the light emission timing based on a division point when a pulse width of a signal output in response to detection of the light beam is divided at a predetermined ratio. .

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