JP5289106B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method having a function of changing an image forming speed by skipping a surface of a rotary polygon mirror, and relates to formation of additional dots for adding information to an input image.

  In recent years, the performance of image forming apparatuses such as color printers and color copying machines has improved, and high-quality images can be formed on paper. Under such circumstances, securities such as banknotes may be used for counterfeiting, and various counterfeit tracking techniques are being considered. For example, there is an example as shown in FIG. FIG. 14 is a diagram showing a conventional additional dot pattern. Conventionally, an image forming device such as the machine number of the image forming device is specified in a color image to be printed using a pattern (additional dot pattern) composed of fine dots in which part of the image is replaced with white or solid. There is a configuration for adding information to be added (see, for example, Patent Document 1). Such a dot pattern is formed by superimposing white dots (hereinafter, white dots) and solid dots (hereinafter, solid dots) as additional signals on the halftone processed image signal. The A conventional method of adding an additional signal is a method of superimposing an additional signal on an image signal in synchronization with a horizontal synchronizing signal (hereinafter referred to as a BD signal) output when the sensor detects the start of main scanning of the exposure beam. I'm taking it.

  On the other hand, recent color printers perform image formation by changing the printing process speed in response to changes in paper conditions. At this time, a mode is known in which the printing process speed is reduced by changing the sub-scanning speed of the printer to a half speed or a third speed without changing the main scanning speed of the laser scanner. At this time, image formation and additional dot pattern formation are performed as follows. That is, BD signals are thinned out at a certain number interval according to the sub-scanning speed, and image formation and additional dot pattern formation are performed in synchronization with the thinned BD signals. At this time, since the BD signal is thinned out, the laser beam is incident on the polygon mirror by skipping the surface. The main scanning speed is a scanning speed when the laser scanner scans the laser beam in a direction perpendicular to the rotation direction of the photosensitive drum as an image carrier. Further, the sub-scanning speed can be expressed by the rotational speed of the photosensitive drum (image carrier) and may be expressed by the surface moving speed of the photosensitive drum.

  In a color printer, a configuration in which a controller unit that performs image processing and an engine unit that performs image formation are separated is well known. The engine unit performs control based on a BD signal detected by a sensor existing inside, and the controller unit performs image output control according to the BD signal output from the engine. In addition, when performing surface skip control of the polygon mirror, the engine unit outputs the BD signal output in response to the light beam detection to the controller unit as it is, and performs thinning-out processing of the BD signal by each of the engine unit and the controller unit. It has a configuration. Here, the reason why the BD signal thinned out by the engine unit is not output to the controller unit is that there is jitter in the BD signal thinned out by the engine unit, and the jitter is the accuracy of the image writing position of the controller unit. It is because there exists a possibility of reducing.

JP-A-10-304179

  However, in the case where image formation is performed at a reduced sub-scanning speed by performing surface skipping control of the polygon mirror by performing thinning processing of the BD signal, the following problems occur. That is, if there is a difference in the timing of thinning between the BD signal thinned out by the controller and the BD signal thinned out by the engine, the image signal output by the controller and the additional signal output by the engine will not overlap.

  FIG. 15 shows a timing chart of the image signal and the additional signal in the case where such a timing shift occurs. Reference numeral 1021 denotes a BD signal, reference numeral 1022 denotes a BD signal thinned out by the controller (hereinafter referred to as controller thinning-out BD signal), and reference numeral 1023 denotes an image signal synchronized with the controller thinning-out BD signal 1022. Also, 1024 is a BD signal thinned out by the engine (hereinafter referred to as an engine thinned BD signal), 1025 is a white dot addition signal synchronized with the engine thinned BD signal 1024, and 1026 is a solid dot synchronized with the engine thinned BD signal 1024. It is an additional signal. When the output timing of the image signal 1023 synchronized with the controller thinning BD signal 1022 and the output timing of the white dot addition signal 1025 and the solid dot addition signal 1026 synchronized with the engine thinning BD signal 1024 are not aligned, as follows Problems arise. That is, in the conventional configuration, the white dot addition signal is not superimposed on the post-addition image signal 1027. Therefore, as in the example shown in FIG. 16, there is a possibility that white dots may not appear on the formed image, and there is a concern that the detection rate of the additional dot pattern may be reduced in that case.

  Here, if a signal line that synchronizes the thinning timing between the controller and the engine is added to solve the problem, it becomes necessary to prepare a dedicated signal line, for example. Alternatively, it is necessary to prepare a circuit for transmitting / receiving the synchronization signal, a circuit for changing the thinning timing in accordance with the received synchronization signal, and the like in the controller or the engine.

  The present invention has been made under such circumstances, and an object thereof is to provide an image forming apparatus and an image forming method for forming additional dots that can be accurately detected with a simple hardware configuration.

In order to solve the above problems, the present invention comprises the following arrangement.
(1) An image carrier, a rotating polygon mirror that rotates at a first predetermined rotation speed and deflects the laser beam emitted by the light emitting means, and a detection means that detects the deflected laser beam in a non-image area; And an electrostatic latent image is formed on the image carrier that rotates at a second predetermined rotation speed by scanning the laser beam based on the detection timing of the laser beam by the detection means, and is formed on the image carrier. A print engine that forms an image based on the electrostatic latent image, and a controller that has an image output unit that outputs an image signal to the print engine in accordance with the detection timing of the laser beam, and the image output unit detects the detection An image is output every time the laser beam is detected N times by the means, and the rotation speed of the image carrier is set to M (N of the second predetermined rotation speed). M) is an image forming apparatus capable of executing a low-speed mode in which image formation is performed, wherein the controller is configured to perform N times starting from any one of the detection timings of the laser beam in the low-speed mode. the outputs an image signal by the image output unit each time the laser beam is detected, the print engine is in the low speed mode, as the tracking information for each of the laser beam is detected by said detecting means, and the white dots It outputs a signal for adding, as a starting point any timing of the detection timing of the laser beam, as the tracking information for each of the laser beam N times is detected, adding one or more colored dots a control means for outputting a signal for an image signal output by the controller, the white disconnect A signal for adding a dot, and a signal for adding said colored dot, on the basis of an image forming apparatus and forming an image in which the white dot and the color dot is added.

  According to the present invention, it is possible to form additional dots that can be accurately detected with a simple hardware configuration.

1 is a diagram illustrating a configuration of a color image forming apparatus according to Embodiment 1. FIG. 1 is a diagram illustrating a configuration of an image exposure unit of a color image forming apparatus according to Embodiment 1. 1 is a diagram illustrating a configuration of a signal processing unit of a color image forming apparatus according to Embodiment 1. The figure which shows the structure of the dot pattern addition process part which concerns on Example 1. FIG. Timing chart of image signal and additional signal when sub-scanning speed is normal speed according to embodiment 1 Timing chart of image signal and additional signal when sub-scanning speed is 1/3 speed according to embodiment 1 The figure which shows the dot pattern formed on the image by the additional signal in case the subscanning speed which concerns on Example 1 is 1/3 speed. FIG. 6 is a diagram illustrating a configuration of a signal processing unit of a color image forming apparatus according to Embodiment 2. The figure which shows the structure of the dot pattern addition process part which concerns on Example 2. FIG. FIG. 5 is a diagram illustrating a configuration of a color image forming apparatus according to a third embodiment. FIG. 10 is a diagram illustrating a configuration of a signal processing unit of a color image forming apparatus according to Embodiment 3. Timing chart of image signal and additional signal when sub-scanning speed is 1/4 speed and the number of thinnings is corrected according to the third embodiment FIG. 10 is a diagram showing a dot pattern formed on an image by an additional signal when the sub-scanning speed is ¼ speed and the number of thinnings is corrected according to the third embodiment. The figure which shows the example of the additional dot pattern which concerns on a prior art example Timing chart showing deviation between image signal and additional signal generated during thinning control of BD signal according to conventional example The figure which shows the example of the abnormal dot pattern formed on the image by the additional signal which concerns on a prior art example

  Embodiments according to the present invention will be described below in detail with reference to the drawings. However, the components described in this embodiment are merely examples, and the scope of the present invention is not intended to be limited only to them unless otherwise specified.

[Configuration of color image forming apparatus]
FIG. 1 shows an electrophotographic color image forming apparatus in this embodiment. For example, each of the image forming units UY, UM, UC, and UBK for toners of yellow, magenta, cyan, and black disposed along the flat portion of the intermediate transfer belt 105 as an intermediate transfer member that is an image receiving member, The basic configuration is the same. For this reason, the following description of the image forming unit will be made only for the yellow image forming unit UY. In addition, a code | symbol shows yellow, m is magenta, c is cyan, and bk is black.

  In FIG. 1, a photosensitive drum 101y, which is a cylindrical photosensitive member as an image carrier, is rotated and moved at a predetermined rotational speed in the direction of arrow a. In this embodiment, the photosensitive drum 101y is configured to be rotatable at a plurality of speeds.

  The surface of the photosensitive drum 101y is uniformly charged by a contact-type charger 102y as charging means. The image exposure unit 103y serving as a latent image forming unit exposes the photosensitive drum 101y rotating at a predetermined rotation speed to form an electrostatic latent image. A developing unit 104y as developing means causes toner to fly onto the photosensitive drum 101y by applying a bias, develops and visualizes the electrostatic latent image, and forms a toner image.

  The toner image on the photosensitive drum 101y visualized by the developing unit 104y is conveyed to a primary transfer portion formed between the intermediate transfer belt 105 as an intermediate transfer member and the photosensitive drum 101y according to the rotation of the photosensitive drum 101y. . The intermediate transfer belt 105 is driven in the direction of arrow C in contact with the photosensitive drum 101y. The toner image that has reached the primary transfer portion is applied with a predetermined bias from a high-voltage power supply (HV) 114 to a primary transfer roller 108y, which is a primary transfer unit that is in pressure contact with the intermediate transfer belt 105. The image is transferred to the surface of the intermediate transfer belt 105. A conductive roller is used as the primary transfer roller 108y.

  The intermediate transfer belt 105 is stretched and driven by a drive roller 106 and support rollers 107a and 107b. Similarly to the image forming unit UY, the toner images formed by the other image forming units UM, UC, UBK are sequentially superimposed on the intermediate transfer belt 105 to form a full-color toner image.

  When the full-color toner image on the intermediate transfer belt 105 reaches the secondary transfer portion formed by the secondary transfer roller 109 and the intermediate transfer belt 105, the transfer paper P is supplied by the paper supply portion 110. Then, the full color toner image formed on the intermediate transfer belt 105 is transferred onto the transfer paper P by the action of a secondary transfer bias from a power source (not shown).

  The transfer paper P to which the full-color toner image has been transferred is separated from the intermediate transfer belt 105 by the curvature with the support roller 107b, then conveyed to the fixing device 111, and fixed on the transfer paper P by the action of heat and pressure.

  On the other hand, toner is removed from the photosensitive drums 101y, 101m, 101c, and 101bk after the primary transfer by the photosensitive drum cleaners 113y, 113m, 113c, and 113bk. Thereafter, the surface potentials of the photosensitive drums 101y, 101m, 101c, and 101bk are uniformly discharged by the pre-exposure lamps 124y, 124m, 124c, and 124bk, and are again used for image formation. The intermediate transfer belt 105 that has finished supplying the transfer paper P to the fixing device 111 is cleaned again by the intermediate transfer belt cleaner 112 and used again as an intermediate transfer member.

  In addition, the image forming apparatus according to the present exemplary embodiment can execute a low speed mode in which each member related to image formation is operated at a low speed to perform image formation. The rotational speeds of the photosensitive drums 101y, 101m, 101c, and 101bk, which are image carriers, are variable to low speeds. Further, when the rotational speed of the photosensitive drums 101y, 101m, 101c, and 101bk (hereinafter may be simply referred to as 101) is changed, the other image forming members also change the rotational speed. For example, the roller rotation speed of the paper feeding unit 110 and the rotation speed of the drive roller 106 are variable. Further, the rotation speed of the primary transfer rollers 108y, 108m, 108c, and 108bk, the rotation speed of the secondary transfer roller 109, and the roller rotation speed of the fixing device 111 are also variable. Then, the CPU 3030 of the engine 303 in FIG. 3 to be described later controls the rotation speed of each member described above based on the condition of the transfer paper P. Although detailed description is omitted here, various process conditions such as charging, exposure, development, transfer, and fixing are controlled in accordance with the type of transfer paper P in accordance with the change in the rotation speed. As a result, optimal image formation according to the type of transfer paper P can be performed.

  This low-speed mode will be described with a specific example. For example, each rotating member described in FIG. 1 that needs to be driven at the time of image formation including the photosensitive drum 101 is set to N minutes of a predetermined rotation speed in the normal mode. Change to 1 and drive. However, in this example, the rotational speed of the rotary polygon mirror is the same in both the normal mode and the low speed mode. When the photosensitive drum 101 operates at a rotational speed of 1 / N and the rotary polygon mirror operates at the same rotational speed as in the normal mode, every time the BD signal is output from the controller 302 N times, An image signal is output, and a laser beam based on the output is emitted.

  Alternatively, as another example, for example, the rotating members described in FIG. 1 including the photosensitive drum 101 that need to be driven during image formation are changed to M / N times the predetermined rotation speed in the normal mode. To do. For example, N = 3 and M = 2. The rotating polygon mirror is rotated at a rotation speed M times that in the normal mode (N and M are integers of 1 or more), and every time the BD signal is output N times from the controller 302, the image signal transmission unit 307 outputs an image. A signal is output, and a laser beam based on the output is emitted. Note that changing the rotational speed of the photosensitive drum to M for N when performing one or more image outputs every time the laser beam is detected N times by the BD sensor 202 may be as follows. . That is, it means that when the laser beam is incident on the polygon mirror and the image is formed by skipping the surface, the rotational speed of the photosensitive drum is changed so that normal image formation can be performed accordingly. Therefore, even if M is not strictly N, it may be approximately N for N within a range where normal image formation can be performed.

[Image exposure section]
Next, the image exposure unit is shown in FIG. The image exposure units 103y, 103m, 103c, and 103bk in FIG. 1 have the same configuration as the image exposure unit 103 in FIG. The image exposure unit 103 has the following configuration. First, a semiconductor laser 201, a polygon mirror 203 that is a rotary polygon mirror that deflects laser light (laser beam) output from the semiconductor laser 201, and a BD sensor 202 that detects irradiation of the laser light deflected by the polygon mirror 203 are provided. Have. Here, the BD sensor 202 detects the irradiation of the laser light deflected by the polygon mirror 203 in a non-image region that is outside the region where image formation is performed on the transfer material P later. The image exposure unit 103 includes an fθ lens 204 that corrects the laser light to scan the photosensitive drum 101 (photosensitive drums 101y, 101m, 101c, and 101bk in FIG. 1) at a constant speed. Further, the image exposure unit 103 includes a reflection mirror 205 that reflects the laser beam that has passed through the fθ lens 204 and has been speed-corrected to the photosensitive drum 101. The image exposure unit 103 also includes a laser driving unit 207 that receives a PWM signal (laser PWM signal) and controls the light emission of the semiconductor laser 201, and a scanner motor driving unit 208 that controls the rotational speed of the polygon mirror 203. Further, it has a scanner control unit 206 for transmitting a light emission command by a laser drive signal and a motor acceleration / deceleration command by a scanner motor drive signal to the laser drive unit 207 and the scanner motor drive unit 208.

  When the BD sensor 202 detects the irradiation of the laser beam, the BD sensor 202 transmits a BD signal to the scanner control unit 206. The scanner control unit 206 transmits a scanner motor drive signal to the scanner motor drive unit 208 so that the output cycle (that is, the rotation speed) of the BD signal becomes a predetermined cycle, and adjusts the speed of the scanner motor via the scanner motor drive unit 208. . The laser beam deflected by the polygon mirror 203 is corrected to a constant scanning speed by the fθ lens 204, reflected by the reflection mirror 205, and then incident on the photosensitive drum 101. In this way, an electrostatic latent image is formed on the photosensitive drum 101.

[Configuration of signal processing unit of color image forming apparatus]
FIG. 3 is a diagram showing a flow relating to signal processing of the present embodiment. The host 301 is an apparatus such as a PC (personal computer) used on the user side, and the controller 302 and the engine (print engine) 303 are image forming apparatuses described in this embodiment.

  Here, the CPU 301 exists in the host 301, the CPU 3020 exists in the controller 302, and the CPU 3030 exists in the engine 303. The controller 302 and the engine 303 are independently controlled by clocks having different frequencies, and communication is performed between devices via a communication bus.

  In addition to the communication bus, a signal line for the engine 303 to transmit a BD signal to the controller 302 exists between them. Since the controller 302 handles image signals, the operation clock CLK2 of the controller 302 usually has a higher operation frequency than the operation clock CLK3 of the engine 303. When the BD signal detected and output by the BD sensor 312 is thinned out by the engine 303, if the frequency of CLK3 is expressed as f3, a jitter of 1 / f3 at maximum occurs in the processed BD signal. . Since high accuracy is required for the BD signal that determines the main scanning writing position of the controller 302, it is not preferable to transmit the BD signal including such jitter to the controller 302 particularly for a normal image that is not an additional dot. . Therefore, the BD signal detected and output by the BD sensor 312 of the engine 303 is transmitted to the controller 302 without being processed, and the controller 302 and the engine 303 individually process the BD signal. Note that handling of an image signal by the controller 302 indicates processing by the color conversion processing unit 304, the γ correction unit 305, the halftone processing unit 306, and the image signal transmission unit 307 in FIG.

  In the present embodiment, the BD sensor 312 of the engine 303 detects a laser beam (laser light) and outputs a BD signal, and the controller BD signal thinning processing unit 308 and the engine BD signal thinning processing unit 313 individually output BD signals. Thin out. Since the thinning-out synchronization is not performed for both BD signals, the two thinning-out BD signals described above may have different thinning phases.

  The host 301 is controlled by the CPU 3010 with the operation clock CLK1, and the CPU 3010 outputs image data to the controller 302 as RGB image signals (RGB signals).

  The controller 302 includes a CPU 3020, a color conversion processing unit 304, a γ correction unit 305, a halftone processing unit 306, an image signal sending unit 307, and a controller BD signal thinning processing unit 308. Each block in the controller 302 is driven by the operation clock CLK2.

  The color conversion processing unit 304 of the controller 302 converts RGB signals, which are image data signals input from the host 301, into yellow (Y), magenta (M), cyan (C), and black (BK) image signals. Convert. The color conversion processing unit 304 outputs the converted image signal to the γ correction unit 305.

  Next, the γ correction unit 305 corrects the image signal output from the color conversion processing unit 304 so that the output density curve is linear, and outputs it to the halftone processing unit 306. On the other hand, in parallel with this, the CPU 3010 of the host 301 outputs a halftone instruction signal to the halftone processing unit 306 via the CPU 3020 of the controller 302. The halftone processing unit 306 performs halftone processing on the image signal output from the γ correction unit 305 in accordance with the halftone instruction signal instructed from the host 301 via the CPU 3020.

  The BD sensor 312 of the engine 303 detects a laser beam and outputs a BD signal to the controller 302. The controller BD signal decimation processing unit 308 of the controller 302 generates an BD signal by performing decimation processing from the BD signal according to the printing speed instructed by the CPU 3020, and outputs an image to the engine 303. 307.

  In the image signal transmission unit 307, the Y, M, C, and BK image signals (CYMK signal) processed by the halftone processing unit 306 are synchronized with the decimation BD signal output from the controller BD signal decimation processing unit 308. Output to the engine 303.

  The engine 303 includes a CPU 3030, an EEPROM 3031, a dot pattern addition processing unit 309, a PWM processing unit 310, a laser driving unit 311, a BD sensor 312, and an engine BD signal thinning processing unit 313. Here, the BD sensor 312 corresponds to the BD sensor 202 in FIG. 2, and the laser driving unit 311 corresponds to the laser driving unit 207 in FIG. The BD sensor 312 operates without depending on the operation clock CLK3 of the engine 303.

  The BD sensor 312 outputs a BD signal to the previous controller BD signal thinning processing unit 308, and also outputs a BD signal to the dot pattern addition processing unit 309 and the engine BD signal thinning processing unit 313. The engine BD signal decimation processing unit 313 generates a decimation BD signal obtained by performing decimation processing from the BD signal according to the printing speed instructed by the CPU 3030, and outputs the decimation BD signal to the dot pattern addition processing unit 309. In this embodiment, the decimation BD signal generated here may have a decimation phase different from the decimation BD signal generated by the controller BD signal decimation processing unit 308 of the controller 302 as described above.

  The dot pattern addition processing unit 309 adds a dot pattern as tracking information to the image signal input from the controller 302 using the dot pattern parameter output from the CPU 3030, the BD signal output from the BD sensor 312 and the thinned BD signal. . Note that the dot here refers to a dot image formed by laser irradiation for a plurality of spots, not by one laser spot. A detailed addition method will be described with the configuration of the dot pattern addition processing unit 309.

  The dot pattern addition processing unit 309 outputs the image signal to which the dot pattern, which is the tracking information described above, is added to the PWM processing unit 310, and the PWM processing unit 310 performs PWM processing according to the halftone instruction signal input from the controller 302. Do. The PWM processing unit 310 outputs the modulated PWM signal to the laser driving unit 311. The laser driving unit 311 performs light emission control of the laser 201 in accordance with the PWM signal, and the printing operation described with reference to FIGS. 1 and 2 is performed. .

[Detailed configuration of the dot pattern addition processing unit]
Next, the operation of the dot pattern addition processing unit 309 will be described. In this embodiment, the density level of each color image signal is expressed by 8 bits, and a dot pattern is added only to the yellow image signal. This is based on the fact that, among the colors, the yellow image is most difficult to be identified by human eyes. Thus, even if a dot pattern is added and printed, the image quality is not substantially degraded from the original image. For example, information for specifying the image forming apparatus is assigned to the dot pattern.

  FIG. 4 is an internal block diagram of the dot pattern addition processing unit 309. Hereinafter, the operation of the block will be described in order.

  The main scanning counter 404 performs a counting operation according to the clock signal (CLK) based on the detection timing of the laser beam by the BD sensor 312, that is, the output timing of the BD signal, and transmits the count value to the dot pattern generation circuit 406. The main scanning counter 404 is reset every time a BD signal is output from the BD sensor 312. Here, the time from the detection of the laser beam by the BD sensor 312 to the output of the BD signal is very short, and the detection timing of the laser beam by the BD sensor 312 is almost the same as the output timing of the BD signal. it can.

  The sub-scanning counter 405 performs a counting operation according to the thinned BD signal transmitted by the engine BD signal thinning processing unit 313 and transmits the count value to the dot pattern generation circuit 406.

  In accordance with each counter value, the dot pattern generation circuit 406 calculates the type of additional dot to be added to the image signal, that is, whether the additional dot to be added is a white dot (blank dot) or a solid dot. (Identify. The dot pattern generation circuit 406 receives dot pattern parameters stored in the ROM 401 in the CPU 3030. This dot pattern parameter expresses what value (position) the additional dots are added when the count values of the main scanning counter 404 and the sub-scanning counter 405 indicate. Parameter. The BY signal is an image signal for adding solid yellow dots. The WH signal is an image signal for adding blank dots.

  The dot pattern generation circuit 406 calculates (specifies) the type of additional dots to be added using the count values of the main scanning counter 404 and the sub-scanning counter 405 and the above-described dot pattern parameters. When the additional dot is a solid dot, a BY signal is output, and when the additional dot is a white dot, a WH signal is output. In neither of the above cases, neither the BY signal nor the WH signal is output.

  The dot pattern addition circuit 407 is an image signal if the yellow image signal input from the controller 302 is on the main scanning line where the BY signal is on (ON) and the thinned BD signal is output. Is converted to 0xFF (solid (yellow)). On the other hand, if the WH signal is ON, the image signal is converted to 0x00 (outlined) and output to the PWM processing unit 310. The dot pattern addition circuit 407 outputs the input image signal to the PWM processing unit 310 as it is when both the BY signal and WH signal output from the dot pattern generation circuit 406 are OFF. The present invention is not limited to 0xFF solid coating or 0x00 white outline, and may be substantially solid 0xFE or substantially white 0x01. In other words, the analysis device that analyzes the additional dot pattern that is the tracking information can analyze the colored dots and the white dots with a distinction, and the density of the colored dots is more than a certain level so that it can be easily distinguished from a normal image. I need it. In the description of the present embodiment, the description will be made using the term “solid dot”. This solid dot means a colored dot as just described.

[Timing chart during image formation]
~ When the sub-scan speed is normal speed (normal mode) ~
FIG. 5 shows a timing chart when the sub-scanning speed is a normal speed (when the engine 303 and the controller 302 do not thin out the BD signal). The normal speed is, for example, the rotation speed of each member in the image forming apparatus when printing on plain paper. The rotation speed of the photosensitive drum 101 at this time is a predetermined rotation speed. At this time, the rotational speed of each of the other members such as the polygon mirror is another predetermined rotational speed. In order to distinguish the rotational speed of each member, the first predetermined rotational speed, the second predetermined rotational speed, ..Described as the nth predetermined rotation speed.

  Hereinafter, FIG. 5 will be described in detail. A BD signal 501 is a BD signal input from the BD sensor 312 to the dot pattern addition processing unit 309. Further, it is also a BD signal input from the engine BD signal decimation processing unit 313 to the dot pattern addition processing unit 309. In the normal mode, the engine BD signal decimation processing unit 313 also has a function of outputting the BD signal input from the BD sensor 312 without processing.

  An image signal 502 is an image signal that the controller 302 outputs to the dot pattern addition processing unit 309 in synchronization with the output timing of the BD signal 501. The white dot addition signal 503 and the solid dot addition signal 504 are signals (WH signal and BY signal) output from the dot pattern generation circuit 406 in synchronization with the output timing of the BD signal 501. The post-addition image signal 505 is a composite signal obtained by combining the image signal output from the controller 302 with the dot pattern generated by the dot pattern generation circuit 406. Note that reference numerals 501 to 505 in FIG. 5 are shown in FIG. 4 described above.

  Here, a hatched portion of the image signal 502 indicates an image signal that has been subjected to halftone processing by the halftone processing unit 306. A white portion in the post-addition image signal 505 indicates a portion where the dot pattern addition circuit 407 has converted the image signal to 0x00 by the white dot addition signal 503. A black portion in the post-addition image signal 505 indicates a portion where the dot pattern addition circuit 407 has converted the image signal to 0xFF by the solid dot addition signal 504. The dot pattern addition circuit 407 outputs the post-addition image signal 505.

  As described above, in the case of FIG. 5, the BD signal output from the BD sensor 312 is not thinned out by either the controller 302 or the engine 303. Therefore, the image signal output timing of the controller 302 and the additional dot signal generation timing are shifted. Does not occur.

~ When sub-scan speed is 1/3 (1/3) (in low-speed mode) ~
Next, FIG. 6 shows a timing chart when the sub-scanning speed is 1/3, which is an example of the low-speed mode (when the engine 303 and the controller 302 thin out the BD signal twice every three times). Every time the BD signal is output N (N is an integer) times, an image signal is output from the controller 302, the rotation speed of the polygon mirror 203 is set to a normal M (M is an integer), and the rotation speed of the photosensitive drum 101 is set to M / If N (N> M), this FIG. 6 corresponds to the case where N = 3 and M = 1. The rotational speed of the photosensitive drum 101 at this time is 1/3 of the normal rotational speed of the photosensitive drum 101 described in FIG.

  First, in synchronization with the BD signal for which the controller BD signal thinning-out processing unit 308 has performed thinning-out processing on the BD signal, the image signal sending unit 307 outputs the image signal to the engine 303 only once for every three BD signals. . Here, regarding the thinning process, the controller BD signal thinning processing unit 308 performs a process of thinning out any two of the three BD signals. At this time, the image signal sending unit 307 outputs an image signal every time three laser beams are detected, starting from one of the detection timings of the laser beams detected by the BD sensor 312. . This is shown in the image signal 606, the image signal 609, and the image signal 612 in FIG.

  The dot pattern generation circuit 406 outputs the solid dot addition signal 604 only once for every three BD signals in synchronization with the BD signal that the engine BD signal thinning processing unit 313 has performed the thinning process. At this time, the dot pattern generation circuit 406 starts one solid dot every time three laser beams are detected, starting from one of the detection timings of the laser beam detected by the BD sensor 312. Output. This is shown in the solid dot addition signal 604 in FIG.

  On the other hand, the dot pattern generation circuit 406 outputs a white dot addition signal 603 every time the BD sensor 312 detects a laser beam. Here, the dot pattern generation circuit 406 outputs white dots in synchronization with all the BD signals, but no white dots that are not superimposed on the image signal remain, so that the BD signal 3 is apparently displayed on the image signal. It is output only once per time.

  Here, as the white dot addition signal 603 to be output, the same signal is repeatedly output three times with the circled numerals 1 ', 2' and 3 'in FIG. Further, in the next circled numerals 1 "to 3", a white dot addition signal 603 to be output on the next line is output according to the dot pattern parameter instructed from the CPU 3030. As described above, the white dot addition signal 603 is changed to a white dot at an appropriate image position every time it is output three times in order to add an accurate white dot. In the low-speed mode in which an image is output every time N times of laser beams are detected by the BD sensor 312, the next dot is output N times at the same main scanning position based on the dot pattern parameter, The white dot at the main scanning position is output N times again. That is, the CPU 3030 changes the output of white dots every N times.

  Here, the controller BD signal thinning-out processing unit 308 of the controller 302 performs the thinning-out BD signal as a controller thinning-out BD signal, and the engine BD signal thinning-out processing unit 313 of the engine 303 performs the thinning-out processing of the BD signal. Signal. In this embodiment, since the controller 302 and the engine 303 thin out the BD signal 601 at independent timings, there are three cases of the timing 605, 608, and 611 that the controller thinning BD signal can take with respect to the engine thinning out BD signal 602. To do. (A) shows a controller thinning BD signal 605 when the controller 302 and the engine 303 perform thinning at the same timing. (B) and (C) show controller thinning BD signals 608 and 611 when the controller 302 and the engine 303 perform thinning at different timings. As a result, the additional signals (603, 604) are superimposed on the image signals 606, 609, 612, and after the three types of additional processing shown in 607 (in the case of A), 610 (in the case of B), and 613 (in the case of C). One of the image signals is output from the dot pattern addition circuit 407 as an image signal. Note that reference numerals 601 to 613 in FIG. 6 are shown in FIG. 4 described above.

[Specific example of dot pattern]
FIG. 7 shows dot patterns formed on the image with respect to the post-addition image signals of 607, 610, and 613 described above. Reference numeral 701 denotes an example of a dot pattern on an image at the time of BD signal thinning-out control. In this embodiment, since the dot is added only to the yellow image signal, the solid dot signal (BY signal: see FIG. 4) is formed as a yellow dot on the image. That is, the hatched portion 702 in FIG. 7 represents a yellow background image, the black portion 703 represents an added yellow dot, and the white portion 704 represents an added white dot.

  705, 706, and 707 show the state in which the image is formed line by line with respect to the post-addition processed image signals 607, 610, and 613 in FIG. 7 correspond to the circled character numbers 1-3, 1′-3 ′, 1 ″ -3 ″ on the BD signal 601 in FIG. 6, respectively. ing. Actually, since the sub-scanning speed is 1/3, the images formed on the transfer material P are 708, 709, and 710 in which the positions of 705, 706, and 707 in the sub-scanning direction are compressed to 1/3. Become one of the images. By compressing the position in the sub-scanning direction, a background image is formed on the transfer material P without a gap, and yellow dots (solid dots) and white dots are also formed on the background image. In this way, no matter what timing the BD signal 601 is thinned out by the controller 302 and the engine 303, additional dots are formed on the background image.

  Here, depending on the transmission timing of the image signal, the positions of the yellow dots indicated by 705, 706, and 707 are relatively different from the white dots superimposed on the image signal. However, in the case of the present embodiment, it is assumed that the position error of the yellow dots 709 and 710 with respect to the white dots is within an allowable range in analyzing the additional pattern (tracking information).

  In the description of this embodiment, the color image forming apparatus uses an in-line method having a plurality of image carriers. Instead, a four-pass method in which a single image carrier is used and the developing machine is rotated is used. It may be used.

  Further, image forming apparatus control and dot pattern addition using BD signal thinning in this embodiment are not limited to the case where the sub-scanning speed is 1/3 speed. That is, it can be similarly performed at other sub-scanning speeds such as 1 / N (1 / N) speed that can be realized by thinning out BD signals such as 1 / 2-speed and 1 / 4-speed.

  As described above, according to this embodiment, it is not necessary to synchronize the transmission timing of the image signal and the transmission timing of the additional signal. Therefore, it is possible to form an additional dot pattern that can be accurately detected with a simple hardware configuration without using a dedicated signal line, a thinning timing correction circuit, or the like.

  In the second embodiment, another embodiment of the dot pattern addition processing unit 309 will be described. The configuration of the color image forming apparatus of this embodiment and the configuration of the image exposure unit are the same as those shown in FIGS. The rotational speed of the polygon mirror 203, the rotational speed of the photosensitive drum 101, and the number of thinnings are the same as in the first embodiment.

[Configuration of signal processing unit of color image forming apparatus]
FIG. 8 is a diagram showing a flow relating to signal processing of the present embodiment. The image signal transmission unit 307 in the present embodiment synchronizes with the decimation BD signal output from the controller BD signal decimation processing unit 308, and outputs the image signal (CYMK signal) processed by the halftone processing unit 306 to the PWM of the engine 303. Output directly to the processing unit 310.

  The PWM processing unit 310 of the engine 303 outputs a PWM signal processed based on the input image signal, a BY signal and a WH signal, which will be described later, to the laser driving unit 311. The laser driving unit 311 emits the laser 201 according to the PWM signal. Take control. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

[Detailed configuration of the dot pattern addition processing unit]
The operation of the dot pattern addition processing unit 309 according to the present embodiment will be described. Also in this embodiment, the density level of the image signal of each color is expressed by 8 bits, and a dot pattern is added only to the yellow image signal. Shall be assigned.

  FIG. 9 is an internal block diagram of the dot pattern addition processing unit 309. The main scanning counter 404 and the sub scanning counter 405 operate in the same manner as in the first embodiment, and a description thereof is omitted.

  In this embodiment, the image signal sending unit 307 of the controller 302 outputs the image signal (Y) directly to the PWM processing unit 310.

  In accordance with each counter value, the dot pattern generation circuit 406 calculates the type of additional dot to be added to the image signal, that is, whether the additional dot to be added is a white dot (blank dot) or a solid dot. (Identify. The dot pattern generation circuit 406 receives dot pattern parameters stored in the ROM 401 in the CPU 3030. This dot pattern parameter expresses what value (position) the additional dots are added when the count values of the main scanning counter 404 and the sub-scanning counter 405 indicate. Parameter.

  The dot pattern generation circuit 406 calculates the type of additional dots to be added using the count values of the main scanning counter 404 and the sub scanning counter 405 and the above-described dot pattern parameters. When the additional dot is a solid dot, a BY signal is output, and when the additional dot is a white dot, a WH signal is output. In neither of the above cases, neither the BY signal nor the WH signal is output.

  The dot pattern addition circuit 407 outputs a BY signal if the BY signal is on (ON) and is on the main scanning line from which the thinned BD signal is output, and a WH signal if the WH signal is ON. Each is output to the PWM processing unit 310. The dot pattern addition circuit 407 outputs nothing to the PWM processing unit 310 when the BY signal and the WH signal from the dot pattern generation circuit 406 are both OFF.

  When the BY signal and the WH signal are not off, the PWM processing unit 310 directly converts the PWM signal subjected to the dot pattern and processed based on the image signal (Y), the BY signal, and the WH signal to the laser driving unit. 311 is output. On the other hand, when nothing is output from the dot pattern addition circuit 407, a PWM signal obtained by modulating only the image signal (Y) is output to the laser driving unit 311.

  As described above, in this embodiment, the image signal and each dot addition signal are combined by the dot pattern addition circuit 407 to generate the post-addition image signal as in the first embodiment, but the PWM processing unit 310 does not generate the image signal. The PWM signal is directly shaped by the dot addition signal. Even in the case of such a configuration, the same effect as in the first embodiment can be obtained. That is, in the dot pattern addition process in the present embodiment, any one of the images 708, 709, and 710 in FIG. 7 shown in the first embodiment is formed on the transfer material P.

  As described above, according to this embodiment, it is not necessary to synchronize the transmission timing of the image signal and the transmission timing of the additional signal. Therefore, it is possible to form an additional dot pattern that can be detected with a simple hardware configuration without using a dedicated signal line, a thinning timing correction circuit, or the like.

  In the third embodiment, a configuration for adjusting the size of a solid dot to be added according to the surrounding environment and the type of printing paper will be described.

[Configuration of Color Image Forming Apparatus and Configuration of Signal Processing Unit]
FIG. 10 shows the configuration of the color image forming apparatus of this embodiment, and FIG. 11 shows the configuration of the signal processing section of this embodiment. Below, it demonstrates centering around the difference with respect to FIG. 3 of Example 1. FIG. In addition to the configuration of the signal processing unit according to the first exemplary embodiment, the image forming apparatus of the present exemplary embodiment detects an environmental sensor 801 that digitizes image forming conditions such as ambient temperature and humidity, the thickness of the printing paper, the surface condition, and the like. A condition detection sensor such as a media sensor 802 that detects and digitizes the image forming conditions. Detection results from the environment sensor 801 and the media sensor 802 are input to the CPU 3030.

  Based on the information input from the environment sensor 801 and / or the media sensor 802, the CPU 3030 calculates a thinning number, that is, an additional number, with respect to the number of times of detection of the laser beam so that the solid dot has an appropriate size.

  Table 1 shows the calculation rules by the CPU 3030 at this time. The information shown in Table 1 is stored in the EEPROM 3031 and is appropriately referred to by the CPU 3030 when the CPU 3030 calculates the number of additions described above.

  The CPU 3030 specifies the thinning-out number with respect to the number of times of laser beam detection based on the type of medium indicated by the information detected by the media sensor 802 based on the information in (a) of Table 1. Compared to commonly used plain paper, gloss paper or OHT paper (transfer material for overhead projector) has a smooth surface on the printing paper, so dots are formed darker. Therefore, the number of thinning-outs is greater when the information detected by the media sensor 802 is glossy paper or OHT paper than when it is plain paper.

  Further, the CPU 3030 specifies the thinning-out number for the laser beam detection circuit according to what kind of environment the information detected by the environment sensor 801 indicates based on the information in (b) of Table 1. In a high temperature and high humidity environment, dots are formed darker than in a low temperature and low humidity environment. Therefore, the number of thinning out is higher in the case of high temperature and humidity than in the case of low temperature and low humidity. The engine BD signal decimation processing unit 313 corrects the decimation number of the BD signal based on the calculation result of the decimation number sent from the CPU 3030.

[Timing chart during image formation]
FIG. 12 is a timing chart relating to the additional signal and the image signal when thinning is performed once every four times among the thinning methods of the BD signal. In other words, FIG. 12 is a timing chart related to the additional signal and the image signal when the solid dot addition signal is output by the dot pattern addition circuit 407 three times for the four times of laser beam detection by the BD sensor 202. Show. The description regarding the hatched portion, the white portion, and the black portion is the same as that in FIG.

  With respect to the BD signal 1001 detected by the BD sensor 312, the controller thinning-out BD signal 1002 is thinned out three times every four times, and the engine thinning-out BD signal 1003 is thinned out once every four times. As in the first embodiment, the image signal 1004 is synchronized with the controller thinning BD signal 1002, the solid dot addition signal 1006 is synchronized with the engine thinning BD signal 1003, and the white dot addition signal 1005 is synchronized with the entire BD signal 1001. Respectively. In other words, in this embodiment, a solid dot is added three times each time four laser beams are detected, starting from one of the detection timings of the laser beam detected by the BD sensor 312. Here, the solid dot addition signal 1006 is the same signal three times in the circled numerals 1 ′, 2 ′, 3 ′, 4 ′ (in the present embodiment, the rounded numerals 1 ′, 2 ′, 3 ′). (3 times) Output repeatedly. The white dot addition signal 1005 repeatedly outputs the same signal four times with the circled numerals 1 ', 2', 3 'and 4'. The post-addition processing image signal 1007 is an example of the post-addition processing image signal in this embodiment, and there are four types of post-addition processing image signals in the same manner as in the first embodiment, depending on the thinned BD signal timing of the controller 302 and the engine 303 To do.

[Specific example of dot pattern]
FIG. 13 shows four types of dot patterns formed on the image by the post-addition image signal. The description regarding the hatched portion, the white portion, and the black portion is the same as that in FIG. 1101 (in the case of (E)), 1102 (in the case of (F)), and 1103 (in the case of (G)) that the image signal after the additional processing is formed line by line with reference to the falling edge of the BD signal 1001 1104 (in the case of (H)). The circled character numbers 1, 2, 3, and 4 in FIG. 13 correspond to the circled character numbers 1, 2, 3, and 4 on the BD signal 1001 in FIG. As in the first embodiment, since the sub-scanning speed is 1/4, the formed image actually formed on the transfer material P has a position of 1101, 1102, 1103, 1104 in the sub-scanning direction of 1/4. One of the compressed images 1105, 1106, 1107, and 1108 is obtained. Since the solid dot addition signal is added to the same main scanning position for three consecutive times, the exposure amount for the yellow dot latent image formed on the photosensitive drum 101 is tripled, and the yellow dots formed on the image are sub-scanned. Longer in the direction. That is, the length of the yellow dots in the sub-scanning direction can be finely adjusted as compared with the conventional configuration. If the size of the solid dots can be finely adjusted, even if the solid dots are formed small depending on the environment and paper type and it becomes difficult to identify, it is difficult to identify yellow dots with a stable size. Easy to form.

  Further, the image forming apparatus control and the dot pattern addition using the thinning of the BD signal in this embodiment can be similarly performed at other sub-scanning speeds such as 1 / N (1 / N) speed. it can. When the sub-scanning speed is 1 / N speed, every time N laser beams are detected starting from one of the detection timings of the laser beam detected by the BD sensor 312 (N− 1) One or more times of solid dots are added.

  In addition, it is good also as a structure further equipped with the environment sensor 801 and the media sensor 802 of a present Example in the structure provided with the dot pattern addition process part as demonstrated in Example 2. FIG.

  As described above, according to the present exemplary embodiment, it is possible to form solid coated dots on an image that can be reliably detected even when the image forming condition changes due to a change in environment or paper type.

406 Dot pattern generation circuit 407 Dot pattern addition circuit

Claims (10)

An image carrier, a rotating polygon mirror that deflects a laser beam that is rotated at a first predetermined rotation speed and is emitted by a light emitting unit, and a detection unit that detects the deflected laser beam in a non-image area. Then, an electrostatic latent image is formed on the image carrier rotating at a second predetermined rotational speed by scanning the laser beam based on the detection timing of the laser beam by the detecting means, and the electrostatic latent image formed on the image carrier A print engine that forms an image based on a latent image; and a controller that has an image output unit that outputs an image signal to the print engine in accordance with the detection timing of the laser beam. An image is output every time the laser beam is detected, and the rotation speed of the image carrier is set to M of N (N> M) of the second predetermined rotation speed. Changes to an image forming apparatus capable of executing a low-speed mode for forming an image,
In the low-speed mode, the controller outputs an image signal by the image output means every time the laser beam is detected N times, starting from any one of the detection timings of the laser beam.
The print engine outputs a signal for adding a white dot as tracking information every time the laser beam is detected by the detection means in the low-speed mode, and one of the detection timings of the laser beam. starting from the timing, as the tracking information for each of the laser beam N times is detected, a control means for outputting a signal for adding one or more times a colored dot,
Based on the image signal output by the controller, the signal for adding the white dots , and the signal for adding the colored dots , the image with the white dots and the colored dots added is obtained. image forming apparatus and forming. The control means changes an output of a signal for adding the white dots every N times in order to change a position where the white dots are added in the main scanning direction. The image forming apparatus according to claim 1.   3. The image forming apparatus according to claim 1, wherein in the low-speed mode, a rotation speed of the rotary polygon mirror is M times the first predetermined rotation (M is an integer of 1 or more). Equipped with condition detection means for detecting image forming conditions;
The said control means changes the frequency | count of adding the said colored dot with respect to the frequency | count of detection of the said laser beam based on the detection result by the said condition detection means, The any one of Claim 1 thru | or 3 characterized by the above-mentioned. Image forming apparatus.   The image forming apparatus according to claim 4, wherein the image forming condition is a condition regarding an environment of the image forming apparatus or a condition regarding a paper type. An image carrier, a rotating polygon mirror that deflects a laser beam that is rotated at a first predetermined rotation speed and is emitted by a light emitting unit, and a detection unit that detects the deflected laser beam in a non-image area. Then, an electrostatic latent image is formed on the image carrier rotating at a second predetermined rotational speed by scanning the laser beam based on the detection timing of the laser beam by the detecting means, and the electrostatic latent image formed on the image carrier A print engine that forms an image based on a latent image; and a controller that has an image output unit that outputs an image signal to the print engine in accordance with the detection timing of the laser beam. An image is output every time the laser beam is detected, and the rotation speed of the image carrier is set to M of N (N> M) of the second predetermined rotation speed. Changes to an image forming method for executing an image forming apparatus slow mode for forming an image,
The controller outputs an image signal by the image output means every time the laser beam is detected N times starting from any one of the detection timings of the laser beam in the low speed mode;
The print engine outputs a signal for adding white dots as tracking information each time the laser beam is detected by the detection means in the low speed mode, and one of the detection timings of the laser beam. starting from the timing and control step of the laser beam N times as the tracking information for each detected, and outputs a signal for adding one or more colored dots,
With
Based on the image signal output by the controller, the signal for adding the white dots , and the signal for adding the colored dots , the image with the white dots and the colored dots added is obtained. image forming method and forming. In the control step, in order to change a position where the white dot is added in the main scanning direction, an output of a signal for adding the white dot is changed every N times. The image forming method according to claim 6.   8. The image forming method according to claim 6, wherein in the low-speed mode, a rotation speed of the rotary polygon mirror is M times the first predetermined rotation (M is an integer of 1 or more). A condition detection process for detecting image forming conditions is provided.
9. The control process according to claim 6, wherein in the control step, the number of times the colored dots are added to the number of detection times of the laser beam is changed based on a detection result in the condition detection step. Image forming method.   The image forming method according to claim 9, wherein the image forming condition detected in the condition detecting step is a condition related to an environment of the image forming apparatus or a condition related to a paper type.

Images