JP4817770B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly, to an image forming apparatus that forms an image by scanning laser light using a polygon mirror, and an image forming method for these apparatuses.

  FIG. 8 to FIG. 9 are diagrams showing the basic configuration of an image forming unit that forms an image by exposing and scanning laser light onto a drum in accordance with a conventional electrophotographic system. FIG. 8 is a top view of the image forming unit, and FIG. 9 is a side view of the image forming unit. In addition, this configuration is associated with each component of color image data composed of four density components of yellow (Y), magenta (M), cyan (C), and black (K), and four sets of image forming units are used. An image forming apparatus is configured.

  FIG. 10 is a diagram showing the basic configuration of a conventional color image forming apparatus. With such a configuration, a color image is formed by superimposing yellow, magenta, cyan, and black toner images.

  First, a conventional image forming process will be described with reference to FIGS.

  The laser beam light, which is driven by a driving circuit (not shown) in accordance with the input image signal and is irradiated from the laser diode 17, is irradiated toward the four-sided rotary polygon mirror 15. The laser beam light is reflected by the laser scanner motor 16 as a deflected beam that continuously changes its angle on its reflecting surface as the rotating polygon mirror 15 rotating in the direction of the arrow rotates. This reflected light is subjected to correction of distortion and the like by a lens group (not shown), and scans on the photosensitive drum 10 in the direction of arrow M through the reflecting mirror 18. The arrow M direction is referred to as the main scanning direction.

  One surface of the rotary polygon mirror 15 corresponds to one line scan, and the laser beam light emitted from the laser diode 17 by the rotation of the rotary polygon mirror 15 scans the photosensitive drum 10 in the main scanning direction line by line. The photosensitive drum 10 is charged in advance by a charger 11 and sequentially exposed by scanning with a laser beam to form an electrostatic latent image.

  Further, the photosensitive drum 10 is rotated in the direction of arrow S, the formed electrostatic latent image is developed by the developing device 12, and the developed visible image is recorded by the transfer charger 13 in the direction of arrow P. It is transferred to paper (not shown). The recording sheet on which the visible image has been transferred is conveyed to the fixing device 14 and is discharged outside the apparatus after image fixing.

  Here, a BD sensor 19 is disposed in the vicinity of the scanning start position in the main scanning direction on the side portion of the photosensitive drum 10. The laser beam light reflected by each reflecting surface of the rotary polygon mirror 15 is detected by the BD sensor 19 prior to scanning each line. The BD signal generated by the BD sensor 19 by detecting the laser beam light is used as a scanning start reference signal in the main scanning direction, and the writing start position of each line in the main scanning direction is synchronized based on this signal. .

  Next, a color image forming process will be described with reference to FIG.

  As described above, the color image forming apparatus shown in FIG. 10 forms a color image using four sets of the image forming units shown in FIGS. In the apparatus shown in FIG. 10, there are four sets of the same constituent elements already described in FIGS. 8 and 9 corresponding to the color image components. Therefore, the same numbers as those used in FIGS. 8 and 9 are used for such components, and the letters Y, M, C, and K corresponding to the color components are added to the end, and the respective components are designated. refer. Also, common components are referred to using the same reference numbers as used in FIGS.

  In FIG. 10, the photosensitive drums 10Y, 10M, 10C, and 10K are rotated clockwise. First, the photosensitive surfaces on the photosensitive drum charged by the chargers 11Y, 11M, 11C, and 11K are exposed through the reflecting mirrors 18Y, 18M, 18C, and 18K by the scanned laser beam light, and the electrostatic latent image is formed. It is formed. Note that the laser beam light to the reflecting mirrors 18M and 18C reaches the intermediate reflecting mirrors 18A and 18B.

  Next, the electrostatic latent image is developed by the developing devices 12Y, 12M, 12C, and 12K to form a visible image. On the other hand, since the recording paper (not shown) is conveyed from the right to the left of the paper in the direction of arrow P, yellow, magenta, cyan, and black toner images are sequentially recorded by the transfer chargers 13Y, 13M, 13C, and 13K. It is transferred to paper. In this way, a color image is formed. The color image on the recording paper is fixed by the fixing device 14 (see, for example, Patent Document 1).

In recent color image forming apparatuses, high image quality is demanded by performing correction such as color misregistration correction and light amount correction. Furthermore, with the speeding up of image formation, an apparatus including a plurality of image processing ICs has appeared to perform a plurality of image processings simultaneously (see, for example, Patent Document 2).
JP 2005-172997 A JP 2002-283625 A

  However, in the above-described conventional example, as the image formation speed increases and the image quality becomes higher, the time given for data transfer between a plurality of image processing ICs that perform image processing is shortened, and it is difficult to perform accurate data transfer. It has become to.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus and an image forming method capable of accurately transferring data between a plurality of image processing ICs.

  In order to achieve the above object, the image forming apparatus of the present invention has the following characteristics.

  First, the image forming apparatus scans a photoconductor through a rotating polygon mirror with light beams generated by a laser driving circuit according to input image data, forms an electrostatic latent image on the photoconductor, and develops the image. And forming an image by transferring the visualized image to a recording medium. It comprises the following components of this device.

That is, before the light beam scans the photoconductor, a detection sensor that detects the light beam, an interface unit that inputs image data, and a first image that performs image processing on image data input by the interface unit. And a processing IC. In addition, a second image processing IC is provided that generates a drive signal for driving the laser drive circuit based on the image data that has been subjected to image processing and transferred by the first image processing IC. Furthermore, a CPU is provided that controls the operations of the first and second image processing ICs based on image formation control information that is input via the interface unit and controls image formation in units of one surface of the recording medium .

In such a configuration, the second image processing IC generates a synchronization signal that defines a position at which image formation is started on the photoconductor based on the beam light detection signal generated by the detection sensor. Transmit to the image processing IC. On the other hand, the first image processing IC DMA-transfers the image data subjected to image processing to the second image processing IC in response to this synchronization signal. When the image formation control information is changed, the CPU instructs the first image processing IC to stop DMA transfer, and the first image processing IC responds to the instruction to stop DMA transfer. After the transfer of the image data for one surface of the recording medium, the CPU generates an interrupt signal together with the notification of the transfer end, and the CPU uses the interrupt signal to change the changed image formation control information corresponding to the entire surface of the next recording medium. Is set in the DMA transfer register, the first image processing IC restarts the DMA transfer of the image data on the one side of the next recording medium, and then the interrupt signal is canceled, and the image formation control information is not changed. The first image processing IC continues the DMA transfer .

  The above basic configuration and characteristics are applied to color image formation.

  That is, the image data is color image density data including a black component, a cyan component, a magenta component, and a yellow component. In this case, the apparatus configuration includes four photoconductors, four laser drive circuits, and four second image processing ICs corresponding to each of the plurality of density components. Each of the four second image processing ICs generates the synchronization signal for image formation of each of the four color components based on the beam light detection signal.

  The image formation control information includes the size and resolution of the recording medium.

In addition, four laser drive circuits are driven by drive signals generated by the four second image processing ICs to emit four beam lights, and these four beam lights pass through one rotating polygon mirror , It reaches each of the four photoconductors. This rotary polygon mirror has four light beam reflecting surfaces.

  According to still another invention, an image forming method having the following characteristics is provided.

  In this image formation, the input image data is subjected to image processing by the first image processing IC and the second image processing IC, and the rotating polygon mirror is generated by the beam light generated by the laser drive circuit based on the image processed image data. The photosensitive member is scanned through the photosensitive member, and an electrostatic latent image is formed on the photosensitive member. Further, the electrostatic latent image is developed and visualized, and the visualized image is transferred to a recording medium.

  Given this process, this method has the following characteristics.

That is, prior to the light beam scanning the photoconductor, the light beam is detected by the detection sensor, and the image data input via the interface is subjected to image processing by the first image processing IC. Next, based on the beam light detection signal generated by the detection sensor, the second image processing IC generates a synchronization signal that defines a position at which image formation is started on the photosensitive member, and this is used as the first image processing. Send to IC. In response to this synchronization signal, the first image processing IC DMA-transfers the image processed image data to the second image processing IC. Then, a drive signal for driving the laser drive circuit is generated by the second image processing IC based on the image data subjected to the image processing transferred by DMA. At this time, if there is a change in the image formation control information that is input via the interface and controls image formation in units of one side of the recording medium , the CPU instructs the first image processing IC to stop DMA transfer, In response to an instruction to stop DMA transfer, the first image processing IC generates an interrupt signal together with the transfer completion notification to the CPU after the image data transfer for one surface of the recording medium is completed. To set the changed image formation control information corresponding to one surface of the next recording medium in the DMA transfer register, and cause the first image processing IC to resume the DMA transfer of the image data of the next recording medium, and then When the interrupt signal is canceled and no change occurs in the image formation control information, the first image processing IC continues the DMA transfer .

  Therefore, according to the present invention, image data is DMA-transferred in response to a synchronization signal that defines a position at which image formation is started on the photoconductor generated based on the beam light detection signal. In addition, when there is a change in the input image formation control information, the CPU executes release and resetting of DMA transfer between image formation on one recording medium and image formation on the next recording medium.

  Thus, since the CPU is involved only in the case of the DMA transfer control when the image formation control information is changed, the image data transfer is surely performed without increasing the CPU load, that is, the load of software for controlling the CPU. Can be realized.

  Hereinafter, preferred embodiments of the present invention will be described more specifically and in detail with reference to the accompanying drawings.

  FIG. 1 is a side sectional view showing a schematic configuration of an image forming apparatus for forming a color image according to an electrophotographic system which is a typical embodiment of the present invention. This image forming apparatus employs a configuration in which a plurality of image forming units are arranged in parallel along a recording paper conveyance path.

  The image forming apparatus forms and outputs an image based on the scanner unit 1S for optically reading an image original and image data output from the scanner unit 1S or image data input from an external device via an interface (not shown). And an image output unit 1P. The image output unit 1P is roughly divided into an image forming unit 100, a paper feed unit 200, an intermediate transfer unit 300, a fixing unit 400, and a control unit 500.

  The image forming unit 100 is configured as described below.

  Photosensitive drums 111a, 111b, 111c, and 111d as image carriers are pivotally supported at their centers and are driven to rotate in the direction of the arrow. The primary chargers 112a, 112b, 112c, 112d, the laser scanner unit 113, and the developing devices 114a, 114b, 114c, 114d are arranged in order in the rotation direction so as to face the outer peripheral surfaces of the photosensitive drums 111a to 111d. The primary chargers 112a to 112d respectively apply a uniform charge amount to the surfaces of the photosensitive drums 111a to 111d. Next, the laser scanner unit 113 irradiates the photosensitive drums 111a to 111d with laser beam light modulated according to the image signal, thereby forming electrostatic latent images on the photosensitive drums 111a to 111d, respectively. Details of the operation of the laser scanner unit 113 will be described later.

  Further, developing devices 114a to 114d that respectively store toners of four colors of yellow (Y), cyan (C), magenta (M), and black (K) visualize this electrostatic latent image. The visible images visualized by the respective toners are transferred to the intermediate transfer belt 131 in the image transfer areas Ta, Tb, Tc, and Td, respectively. For each of the image transfer regions Ta, Tb, Tc, and Td, cleaning devices 115a, 115b, 115c, and 115d are provided on the downstream side of the photosensitive drums 111a to 111d. By these cleaning devices, the toner remaining on the photosensitive drums 111a to 111d without being transferred to the intermediate transfer belt 31 is scraped off to clean the drum surface.

  By the process described above, image formation with each toner is sequentially performed.

  The paper feed unit 220 includes cassettes 221 a and 221 b for storing the recording material P, and a manual feed tray 227. The cassettes 221a, 221b and the manual feed tray 227 are provided with pickup rollers 222a, 222b, 226 for feeding the recording paper P one by one from the inside. The recording paper P delivered from the pickup rollers 222a, 222b, and 226 is provided with a pair of paper feed rollers 223a, 223b, and 223c and a paper feed guide 224 for transporting to the registration rollers 225a and 225b. Note that the registration rollers 225 a and 225 b are provided to send the recording paper P to the secondary transfer region Te in accordance with the image forming timing of the image forming unit 100.

  The intermediate transfer belt 331 is made of, for example, PET [polyethylene terephthalate] or PVdF [polyvinylidene fluoride]. The intermediate transfer belt 331 is moved to the secondary transfer region Te across the intermediate transfer belt 331 and the tension roller 33 and the intermediate transfer belt 331 that apply an appropriate tension to the intermediate transfer belt 331 by urging a driving roller 32 that transmits a driving force and a spring (not shown). It is wound around an opposing driven roller 334. Among these, a primary transfer plane A is formed between the drive roller 32 and the tension roller 33. The drive roller 32 is a metal roller whose surface is coated with rubber (urethane or chloroprene) having a thickness of several millimeters, and prevents slipping between the drive roller 32 and the intermediate transfer belt 31. The drive roller 32 is rotationally driven by a pulse motor (not shown).

  In the primary transfer regions Ta to Td where the photosensitive drums 111a to 111d and the intermediate transfer belt 331 face each other, primary transfer chargers 335a to 335d are disposed on the back side of the intermediate transfer belt 331. On the other hand, a secondary transfer roller 336 is disposed to face the driven roller 334, and a secondary transfer region Te is formed by a nip with the intermediate transfer belt 331. The secondary transfer roller 336 is pressed against the intermediate transfer belt 331 with an appropriate pressure.

  A brush roller (not shown) for cleaning the image forming surface of the intermediate transfer belt 331 and a waste toner box (not shown) for storing waste toner are disposed on the intermediate transfer belt 331 and downstream of the secondary transfer region Te. ) Is provided.

  The fixing unit 400 includes a fixing roller 441a having a heat source such as a halogen heater therein, and a fixing roller 441b to which pressure is applied to the fixing roller 441a (this roller may also have a heat source). Further, a guide 443 for guiding the recording paper P to the nip portion of the pair of fixing rollers 441a and 441b, and an inner paper discharge roller 444 for further guiding the recording paper P discharged from the fixing rollers 441a and 441b to the outside of the apparatus. And an outer paper discharge roller 445.

  The control unit 500 includes a control board and a motor drive board (not shown) for controlling the operation of each mechanism in the image output unit 1P.

  Next, the operation of the image output unit 1P will be described.

  When the image forming operation start signal is issued, the paper feeding operation is started from the paper feeding stage corresponding to the selected paper size or the like. As an example, paper feeding from the cassette 221a will be described. First, the recording paper P is sent out one by one from the cassette 221a by the pickup roller 222a. Then, the recording paper P is guided between the paper feed guides 224 by the paper feed roller pair 223c and conveyed to the registration rollers 225a and 225b. At that time, the registration rollers 225a and 225b are stopped, and the leading edge of the paper hits the nip portion. Thereafter, the registration rollers 225a and 225b start to rotate in accordance with the image formation start timing of the image forming unit 100. The timing of the rotation is set so that the recording paper P and the toner image primarily transferred from the image forming unit 100 onto the intermediate transfer belt 331 exactly coincide with each other in the secondary transfer region Te.

  On the other hand, the image forming unit 100 executes the following process in which an image forming operation start signal is issued. First, a toner image formed on the photosensitive drum 111d that is furthest upstream in the rotational direction of the intermediate transfer belt 331 is transferred to the intermediate transfer belt 331 in the primary transfer region Td by the primary transfer charger 335d to which a high voltage is applied. Primary transcription. The primarily transferred toner image is conveyed to the next primary transfer region Tc. In the primary transfer area Tc, image formation is delayed by the time required to convey the toner image from the primary transfer area Td to the primary transfer area Tc. The next toner is aligned with the resist on the previous image. The image is transferred. The same process is repeated in the primary transfer region Tb and the primary transfer region Ta, and finally, four color toner images are transferred onto the intermediate transfer belt 331.

  Thereafter, when the recording paper P enters the secondary transfer region Te and contacts the intermediate transfer belt 331, a high voltage is applied to the secondary transfer roller 336 in accordance with the passing timing of the recording paper P. Then, the four-color toner images formed on the intermediate transfer belt 331 by the above-described process are transferred onto the surface of the recording paper P.

  Thereafter, the recording paper P is accurately guided to the nip portions of the fixing rollers 441a and 441b by the conveyance guide 443. Then, the toner image is fixed on the surface of the recording paper P by the heat of the fixing rollers 441a and 441b and the pressure of the nip. Thereafter, the recording paper P is conveyed by the internal and external paper discharge rollers 444 and 445 and is discharged out of the apparatus.

  Here, the configuration of the laser scanner unit 113 will be described.

  FIG. 2 is a diagram showing the configuration of the laser scanner unit 113.

  The laser scanner unit 113 includes a rotary polygon mirror (polygon mirror) 201 and a laser scanner motor (polygon motor) 202 that rotationally drives the rotary polygon mirror 201. The number of surfaces of the rotary polygon mirror 201 is determined by parameters such as the image forming speed and resolution, but in this embodiment, the number is four. The laser drivers 203a to 203d are equipped with laser diodes that are light sources of the image forming unit 100 corresponding to the four color toners (Y, M, C, and K). Each laser diode is turned on or off according to an image signal or a control signal by a drive circuit (not shown). The laser beam light generated and modulated by each laser diode is irradiated toward the rotating polygonal mirror 201.

  The rotating polygonal mirror 201 rotates in the direction of the arrow, and the laser beam light generated by each laser diode becomes a deflected beam that continuously changes its angle on its reflecting surface as the rotating polygonal mirror 201 rotates. . This deflected beam is subjected to correction of distortion and the like by a lens group (not shown), and irradiates the photosensitive drums 111d, 111c, 111b, and 111a through the reflecting mirrors 204, 205, 206, and 207, respectively. One surface of the rotating polygon mirror 201 corresponds to one line scanning, and the laser beam generated by the laser diode is irradiated to the photosensitive drums 111a to 111d line by line by the rotation of the rotating polygon mirror 201, and the main scanning is performed. Scanned in the direction. The positions of the reflecting mirrors 204, 205, 206, and 207 can mechanically correct the registration magnification and the deviation in inclination by driving the pulse motors M <b> 1 to M <b> 8.

  Further, a BD sensor 212 is arranged to generate a scanning start position reference signal in the main scanning direction. Ideally, the BD sensor 212 is installed in the vicinity of the scanning start position (in the vicinity of the photosensitive drum), but actually, the BD sensor 212 is placed in the laser scanner unit 13 by using a folding mirror (not shown) or the like. Is arranged. In other words, the laser beam light reflected by each reflecting surface of the rotary polygon mirror 201 is detected by the BD sensor 212 prior to scanning each line. The BD sensor signal generated based on the laser beam light detected by the BD sensor 212 is used as a scanning start reference signal in the main scanning direction, and the writing start position of each line in the main scanning direction is synchronized based on this signal. Is taken. Further, the rotational speed control and phase control of the laser scanner motor 202 are performed using the BD sensor signal. Further, the surface of the rotary polygon mirror 201 is also detected by counting the intervals of the BD sensor signals.

  The arrangement order of the photosensitive drums 111a to 111d shown in FIG. 2 is merely an example, and the present invention is not limited to this. Further, regarding the arrangement position of the BD sensor 212, in this embodiment, the BD sensor 212 is arranged on the path of the laser beam from the laser driver 203d used for image formation with black (K) toner, but this is not restrictive.

  Next, image processing executed by the image forming process will be described.

  FIG. 3 is a block diagram showing the configuration of the laser drive pulse output unit.

  In FIG. 3, an external input I / F unit 1000 is an interface for inputting image data and control data transferred from a personal computer (personal computer), a scanner unit 1S, or the like. The external input I / F unit 1000 converts input control data into image formation control information such as paper size and resolution information, and transfers it to the CPU 1001. On the other hand, the external input I / F unit 1000 outputs input image data as 1-pixel 4-bit image data at a predetermined transfer rate with the image data generation unit 1002.

  The CPU 1001 controls the entire image forming apparatus. For example, the CPU 1001 performs a motor for carrying recording paper, high-pressure control for forming toner images, and the like. Further, the CPU 1001 starts an image forming operation based on the image forming control information input from the external input I / F unit 1000.

  The image data generation unit 1002 performs image processing on the image data from the external input I / F unit 1001 based on the image formation control information from the CPU 1001, and laser-drives 1-pixel 6-bit image data in synchronization with the image clock. The signal is output to a signal generation unit (PWM unit) 1003. Further, the image data generation unit 1002 also performs surface detection of the rotary polygon mirror 201. The image data generation unit 1002 generates an interrupt signal (hereinafter referred to as IRQ signal) to the CPU 1001. The CPU 1001 provides image formation control information according to the IRQ signal. In this way, information is exchanged between the CPU 1001 and the image data generation unit 1002 in the form of interrupts and interrupt responses. The image data generation unit 1002 is composed of one image processing IC.

  In this embodiment, one laser drive signal generation unit (PWM unit) 1003 is provided for each laser diode. The laser drive signal generation unit (PWM unit) 1003 is composed of one image processing IC. Therefore, this embodiment includes four PWM units. That is, four image processing ICs of the same type are mounted.

  The laser drive signal generation unit (PWM unit) 1003 refers to the pulse width table, generates a drive pulse signal having a pulse width that varies according to 6-bit image data, and outputs the drive pulse signal to the laser drive unit 1004. At this time, the image formation control information from the CPU 1001 and the surface detection information of the rotary polygon mirror 201 having four surfaces are also output together. The communication between the image data generation unit 1002 and the laser drive signal generation unit (PWM unit) 1003 is based on a normal communication mode and a synchronization (Sync) signal that determines the main scanning writing position generated on the basis of the BD signal. DMA communication mode starting at

  Accordingly, in this embodiment, DMA transfer is performed from one image processing IC to four image processing ICs based on four sync signals corresponding to each color component generated based on one BD signal. It has been realized.

  The laser driving unit 1004 generates laser beam light according to the laser driving pulse signal and irradiates the rotary polygon mirror 201. The BD signal from the BD sensor 212 is transferred to the laser scanner motor rotation control unit 1005, the image data generation unit 1002, and the PWM unit 1003.

  Next, an image forming process executed by the color image forming apparatus having the above configuration will be described.

  FIG. 4 is a flowchart showing the image forming process.

  After the color image forming apparatus is turned on, first, in step S1100, the above-described reset operation of the image processing IC is performed. After releasing the reset, in step S1101, a predetermined initial value is input to each image processing IC. Next, in step S1102, for example, an external apparatus such as a personal computer or the scanner unit 1S waits for a signal input via the external input I / F unit 1000, and when there is an input, the process proceeds to step S1103.

  In step S1103, rotation of the laser scanner motor (polygon motor) 202 is started. When the laser scanner motor 202 reaches a predetermined number of revolutions, the laser driving unit 1004 emits a laser beam, and in step S1104, the BD signal generated by the BD sensor 212 is converted into an image data generating unit 1002, a laser driving signal generating unit (PWM unit). ) 1003 etc. When the BD signal is input to the laser drive signal generation unit (PWM unit) 1003, in step S1105, a synchronization (Sync) signal is output to the image data generation unit 1002 after the set time has elapsed.

  In step S1106, the CPU 1001 sets image formation control information for the first line in the main scanning direction in the image data generation unit 1002 based on the image formation control information from the external input I / F unit 1000. In step S1107, the CPU 1001 sets communication between the image data generation unit 1002 and the laser drive signal generation unit (PWM unit) 1003 to the DMA transfer mode. Thereafter, a recording paper feeding operation is performed. In step S1108, an image request signal from the CPU 1001 to the external I / F unit 1000 is confirmed, and the process proceeds to step S1109 to start the image forming operation.

  In step S1109, the image data generation unit 1002 waits for an input of a synchronization (Sync) signal, and when the input is confirmed, the process proceeds to step S1110 and starts DMA transfer. Thereafter, the DMA transfer is repeated with the same setting until the image formation control information from the external input I / F unit 1000 is changed.

  If it is confirmed in step S1111 that the image formation control information has been changed, the process proceeds to step S1112, and the CPU 1001 cancels the DMA transfer mode up to the sheet immediately before the change instruction is given. The image data generation unit 1002 that has received the DMA transfer mode release instruction generates an IRQ signal to the CPU 1001 after completing the data transfer for one page of the recording paper. In step S1113, the image data generation unit 1002 notifies the CPU 1001 of the end of data transfer.

  In step S1114, the CPU 1001 sets the changed image formation control information. In step S1115, the image data generation unit 1002 is set again to the DMA transfer mode. In step S1116, the IRQ signal is canceled. In step S1117, it is checked whether the image formation is completed. If not, the process returns to step S1109, and the above-described operation is continued until the image formation is completed.

  Here, the processing described in steps S1111 to S1115 is an example in which the image formation control information is changed between the image formation on the Nth recording sheet and the image formation on the (N + 1) th recording sheet. Will be described in detail.

  FIG. 5 is a time chart showing the DMA transfer timing when the image formation control information is changed.

  When the CPU 1001 receives the change of the image formation control information from the external input I / F unit 1000, as indicated by an arrow 1200, the laser beam is scanning the last line of the image formation on the Nth recording paper before the change. Clear the DMA transfer mode. In response to the instruction to clear the DMA transfer mode, the image data generation unit 1002 outputs an IRQ signal to the CPU 1001 when the DMA transfer in progress is completed as indicated by arrows 1201 and 1202.

  Receiving the IRQ signal, the CPU 1001 changes the set value of the DMA transfer register to image data corresponding to the (N + 1) th recording sheet, as indicated by an arrow 1203. After the register change, the CPU 1001 resets the image data generation unit 1002 to the DMA transfer mode as indicated by the arrow 1204, and returns the IRQ signal to the original state (IRQ release) as indicated by the arrow 1205.

  In this way, the cancellation and resetting of the DMA transfer accompanying the change of the image formation control information are performed between the image formation on the Nth recording sheet and the image formation on the (N + 1) th recording sheet. Therefore, the resetting is accurately reflected from the top line of the (N + 1) th image data.

  Next, the validity of the DMA transfer data when receiving a DMA transfer mode clear instruction will be described in more detail.

  FIG. 6 is a diagram showing valid data of DMA transfer data.

  In the color image forming apparatus of this embodiment, a plurality of color lasers are driven using one laser scanner motor (polygon motor) and one BD signal for the purpose of cost reduction or the like. Specifically, as shown in FIG. 2, the BD sensor 212 generates a BD signal only for the laser beam light from the laser driver 203d. In such a color image forming apparatus, the synchronization (Sync) signal for determining the main scanning writing position is calculated from one BD signal based on the color misregistration information and the image size information, and the image formation corresponding to each color component is performed. It is output at a predetermined timing. That is, for the image formation of each color component, each of the four image processing ICs generates a respective synchronization signal based on one BD signal. The black component synchronization signal for image formation is indicated by BK_Sync, the cyan component image formation synchronization signal is indicated by C_Sync, the magenta component synchronization signal for image formation is indicated by M_Sync, and the yellow component synchronization signal for image formation is indicated by Y_Sync. .

  These synchronization signals are not necessarily generated at the same timing due to the above-described information, the lens of the laser scanner, and the mechanical variations that occur during assembly. For example, BK_Sync and C component C_Sync have variations 1301 and 1302 as shown in FIG. On the other hand, in order to simplify the apparatus configuration, DMA transfer is performed based on a sync signal of one color component.

  For example, consider a case where DMA transfer is started based on the BK_Sync signal.

  In FIG. 6, when the BK_Sync signal is on the left side of the variation 1301 and the C_Sync signal is on the right side of the variation 1302, when the DMA transfer is started based on the BK_Sync signal, the cyan component image data is treated as valid data from the right side of the variation 1302. . For this reason, the initial portion of the cyan component image data becomes defective in transfer.

  In order to solve this problem, in this embodiment, dummy data is DMA-transferred for a time considering these variations, and then valid data is transferred. By adopting such a transfer method, even if the synchronization signal varies, the image data can be reliably transferred without loss.

  FIG. 7 is a time chart showing how the dummy data is DMA transferred prior to the effective image data.

  According to FIG. 7, the C_Sync signal is transmitted behind the BK_Sync signal. However, since dummy data is transferred to the initial part of the DMA transfer data, there is no loss of image data. In response to the IRQ signal, the CPU 1001 sets the changed image formation control information, resets the DMA transfer mode, and executes the IRQ signal as in steps S1114 to S1116 described above.

  Therefore, according to the embodiment described above, the CPU 1001 intervenes and changes settings only when the image formation control information is changed, so that the CPU 1001, that is, the software load is changed. As a result, reliable data transfer can be realized without an increase in the data.

  Also, even if the timing of the synchronization signal used for image formation of each color component is determined in each of the four image processing ICs, loss of image data can be prevented by DMA transfer of the corresponding dummy data. Can do. In this way, it is possible to reliably transfer data between a plurality of image processing ICs.

1 is a side cross-sectional view illustrating a configuration of an image forming apparatus that forms a color image according to an electrophotographic system that is a representative embodiment of the present invention. 2 is a diagram showing a configuration of a laser scanner unit 113. FIG. It is a block diagram which shows the structure of a laser drive pulse output part. It is a flowchart which shows an image formation process. 5 is a timing chart of DMA transfer when changing image formation control information. It is a figure which shows the effective data of DMA transfer data. It is a time chart which shows a mode that dummy data is DMA-transferred ahead of effective image data. It is a top view which shows the fundamental structure of the image formation part which forms an image by exposing and scanning a laser beam with respect to a drum according to the conventional electrophotographic system. FIG. 10 is a side view showing the basic configuration of an image forming unit that forms an image by exposing and scanning laser light onto a drum in accordance with a conventional electrophotographic system. It is a figure which shows the fundamental structure of the conventional color image forming apparatus.

Explanation of symbols

100 Image forming units 111a to 111d Photosensitive drum 113 Laser scanner unit 201 Rotating polygon mirror (polygon mirror)
202 Laser scanner motor (polygon motor)
203a to 203d Laser drivers 204, 205, 206, and 207 Reflecting mirror 212 BD sensors M1 to M8 Pulse motor

Claims (6)

An electrostatic latent image is formed on the photosensitive member by developing the electrostatic latent image by scanning the photosensitive member with a light beam generated by a laser driving circuit according to input image data through a rotating polygon mirror. An image forming apparatus that forms an image by transferring the visualized image to a recording medium,
One detection sensor for detecting the light beam before the light beam scans the photoconductor;
An interface unit for inputting image data;
A first image processing IC that performs image processing on the image data input by the interface unit;
A second image processing IC for generating a drive signal for driving the laser drive circuit based on the image data transferred by image processing by the first image processing IC;
A CPU that controls the operations of the first and second image processing ICs based on image formation control information that is input via the interface unit and controls image formation in units of one surface of a recording medium ;
The second image processing IC generates a synchronization signal for defining a position at which image formation is started on the photoconductor based on a beam light detection signal generated by the detection sensor, and sends the synchronization signal to the first image processing IC. Send
The first image processing IC DMA-transfers the image data to the second image processing IC in response to the synchronization signal,
When a change occurs in the image formation control information,
The CPU instructs the first image processing IC to stop the DMA transfer;
In response to the DMA transfer stop instruction, the first image processing IC generates an interrupt signal together with the transfer end notification to the CPU after the image data transfer for one surface of the recording medium is completed.
In response to the interrupt signal, the CPU sets the changed image formation control information corresponding to the entire surface of the next recording medium in the DMA transfer register, and the image data of the entire surface of the next recording medium is stored in the first image processing IC. Resume the DMA transfer, and then cancel the interrupt signal,
If there is no change in the image formation control information,
The image forming apparatus, wherein the first image processing IC continues the DMA transfer . The image data is color image density data composed of a black component, a cyan component, a magenta component, and a yellow component,
Four photosensitive members, four laser drive circuits, and four second image processing ICs corresponding to each of the plurality of density components,
2. The four second image processing ICs each generate the synchronization signal for image formation of each of the four color components based on the beam light detection signal. Image forming apparatus.   The image forming apparatus according to claim 2, wherein the image formation control information includes a size and resolution of a recording medium. The four laser drive circuits are driven by drive signals generated by the four second image processing ICs to emit four light beams, and the four light beams emitted are one of the rotary polygon mirrors. through the image forming apparatus according to claim 2 or 3, characterized in that to reach the four photosensitive members, respectively. The image forming apparatus according to claim 4 , wherein the rotary polygon mirror has four light beam reflecting surfaces. The input image data is subjected to image processing by the first image processing IC and the second image processing IC, and the light beam generated by the laser driving circuit based on the image data processed through the rotating polygon mirror. An image that forms an electrostatic latent image on the photosensitive member by scanning the photosensitive member, develops and visualizes the electrostatic latent image, and transfers the visualized image to a recording medium. A forming method comprising:
Detecting the light beam by a detection sensor prior to the light beam scanning the photoconductor;
Applying image processing to the image data input via the interface by the first image processing IC;
Based on the light beam detection signal generated by the detection sensor, the second image processing IC generates a synchronization signal that defines a position at which image formation is started on the photosensitive member, and sends it to the first image processing IC. Sending, and
DMA transfer of the image processed image data triggered by the synchronization signal from the first image processing IC to the second image processing IC;
Generating a drive signal for driving the laser drive circuit by the second image processing IC based on the image processed image data transferred by the DMA,
When there is a change in the image formation control information that is input via the interface and controls image formation in units of one surface of the recording medium ,
The CPU instructs the first image processing IC to stop the DMA transfer,
In response to the DMA transfer stop instruction, the first image processing IC generates an interrupt signal together with the transfer end notification to the CPU after the image data transfer for one surface of the recording medium is completed.
In response to the interrupt signal, the CPU sets the changed image formation control information corresponding to the entire surface of the next recording medium in the DMA transfer register, and the image data of the entire surface of the next recording medium is stored in the first image processing IC. Resume the DMA transfer, and then cancel the interrupt signal,
If there is no change in the image formation control information,
The image forming method, wherein the first image processing IC continues the DMA transfer .

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