JP4535498B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device and a beam scanning type image forming apparatus using the optical scanning device (for example, a laser printer, a digital copying machine, a facsimile machine, etc.) And an image forming apparatus.

Conventionally, in an image forming apparatus such as a laser printer, a digital copying machine, and a facsimile machine, an image is written by a light beam scanning method. In this method, laser light is scanned in a main scanning direction on a scanned surface of a photoconductor to be image-written by scanning means such as a polygon mirror, and the scanned surface is moved in a sub-scanning direction on the photoconductor. In this method, an image is written line by line.
In such a beam scanning type writing system, laser light is deflected at a constant angular velocity by a polygon mirror. However, since the surface to be scanned is a flat surface, the scanning speed on the surface to be scanned is not constant. For this reason, the scanning speed on the surface to be scanned is made constant by using an fθ lens and an fθ mirror.
However, even if the scanning speed on the surface to be scanned is constant, the laser light intensity on the surface of the photoconductor is fluctuated depending on the image height. This is because the light utilization efficiency such as reflectance and transmittance of optical elements such as glass, lenses, and mirrors that pass from the time when the laser light is emitted from the laser diode to the surface of the photoreceptor varies depending on the incident angle of the laser light, fθ This is because the lens thickness varies depending on the image height. Since the intensity of the beam light intensity due to the image height (this is called “shading characteristics”) affects the density of the formed image, the image forming apparatus corrects the density fluctuation caused by the shading characteristics. Is required.

As a conventional technique related to a shading correction method, for example, the following Patent Document 1 can be cited. A beam scanning type image forming apparatus described in Patent Document 1 is provided in advance corresponding to a scanning position detection unit that detects a main scanning position of a laser beam and a main scanning position of the laser beam detected by the main scanning position detection unit. Storage means for storing the light quantity correction data of the light source, and control means for controlling the laser light quantity of the light source corresponding to the scanning position of the laser light based on the light quantity correction data stored in the storage means. It is a thing. In addition, this document prevents the beam intensity from changing suddenly due to the switching of the laser light amount at the main scanning position to prevent a step in the image density, and smoothes the step in the image density to improve the image quality. In addition, it has been proposed to include a low-pass filter (LPF) for smoothing the light amount setting signal based on the light amount correction data.
Further, as another conventional example of controlling the laser light quantity at a predetermined time (area) in the main scanning period, the following Patent Document 2 can be cited. The beam scanning image forming apparatus described in Patent Document 2 always maintains the temperature distribution inside the laser element in the temperature distribution of the image region, and the light output varies due to the temporal change of the element whose light emission amount changes depending on the temperature. In order to prevent the occurrence of such a problem, there has been proposed an apparatus provided with means for forcibly emitting light in a non-image area with a light amount higher than that of the image area.
Further, the laser light amount that can be detected by the photo IC used as means for detecting the reference position (synchronization signal) of the main scanning of the laser light may be different from the laser light amount used in the image area. However, it is necessary to control the laser light amount to a light amount suitable for the position of the photo IC and the image area in the main scanning period.
JP 2000-71510 A Japanese Patent Laid-Open No. 11-105338

By the way, as shown in the above prior art, in the beam scanning type image forming apparatus provided with means for controlling the laser light quantity at a predetermined time in the main scanning period, the step of the image density at which the laser light quantity at the main scanning position is switched. In order to smooth the noise and to remove noise of the light amount setting signal based on the light amount correction data such as shading, a smoothing means such as a low-pass filter (LPF) is added to the light amount setting signal, and the light amount setting signal Needs to be smoothed, a delay occurs depending on the added LPF. In particular, as described above, when there is a difference between the laser light amount of the image region and the light amount of the non-image region in order to perform temperature correction or detect the synchronization signal output from the photo IC, the image region Even if the light amount setting signal is switched at the start time of the image, the light amount at the start time of the image area becomes a value different from the target value due to a delay due to the LPF, and the light amount until the target value is stabilized. Fluctuates and eventually the density of the image to be formed changes (see FIG. 7).
There has been no proposal for a means for solving the problem caused by the delay due to the LPF, and it is an unsolved problem.
The problem to be solved by the present invention is to solve the above-mentioned unsolved problems. That is, the light quantity is stabilized at the target value when the light quantity setting signal is switched as described above, which occurs in an optical scanning apparatus employing a beam scanning type writing method in which an LPF for smoothing the light quantity setting signal based on the light quantity correction data is provided in the writing control unit. The object is to eliminate the influence of fluctuations in the amount of light that occurs in the meantime, so that a normal amount of light can be obtained in the writing area, and to improve the writing performance.

According to a first aspect of the present invention, there is provided a light source that generates a laser beam having a light amount corresponding to a drive signal, a light beam scanning unit that projects a laser beam generated from the light source onto a target surface as a scanning beam at a predetermined period, and the target Data signal generating means for generating a data signal for determining the lighting timing of the light source, and the target of the laser light for scanning one line, in order to cause the laser light projected as a scanning beam to carry a signal of the original data A light amount setting signal generating means for generating a light amount setting signal for setting the light amount of the laser light in accordance with a position in the main scanning direction, and noise generated at the time of switching the light amount setting signal in order to correct fluctuations in intensity on the surface. and smoothing means for smoothing to remove the light quantity setting signal the scanned laser beam through the smoothing means at the time reaches the target surface by the light beam scanning means The light source is set by a light amount setting signal switching timing setting means for setting the switching timing of the light amount setting signal in the light amount setting signal generating means so as to be a normal value, and a drive signal generated based on the light amount setting signal and the data signal. An optical scanning device having light source driving means for driving.
According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the light amount setting signal switching timing setting unit is a unit that enables the setting of the light amount setting signal switching timing to be changed. It is.

According to a third aspect of the present invention, there is provided a light source that generates laser light having a light amount corresponding to a drive signal, a light beam scanning unit that projects the laser light generated from the light source onto a target surface as a scanning beam at a predetermined period, and the target Data signal generating means for generating a data signal for determining the lighting timing of the light source and a laser beam scanning range are divided into a predetermined number of areas so that the laser beam projected as a scanning beam on the surface bears the original data signal. Area dividing means, light quantity setting signal generating means for generating a light quantity setting signal for setting the laser light quantity generated by the light source for each divided area, and smoothing the light quantity setting signal by removing noise generated at the time of switching. and smoothing means, the time the laser beam scanned by said light beam scanning means reaches the target surface, the light quantity setting signal divided areas through the smoothing means is a constant An optical scanning device having means for adjusting the divided area so as to be a value, and a light source driving means for driving the light source by a drive signal generated based on the light amount setting signal and the data signal generated for each divided area It is.

According to a fourth aspect of the present invention, in the optical scanning device according to any one of the first to third aspects, the light amount setting signal generating means is a means for generating a setting signal at a voltage corresponding to the set light amount. It is what.
According to a fifth aspect of the present invention, in the optical scanning device according to the fourth aspect, the light amount setting signal generating means for generating a setting signal at a voltage corresponding to the set light amount includes a digital / analog converter. that is also the in.
According to a sixth aspect of the present invention, in the optical scanning device according to the fourth aspect, the light amount setting signal generating means for generating a setting signal at a voltage corresponding to the set light amount includes a pulse width modulating means and the pulse width modulating means. Is provided with a low-pass filter that smoothes the output from.
According to a seventh aspect of the present invention, in the optical scanning device according to any one of the first to third aspects, the light amount setting signal generating means is a means for generating a setting signal with a current corresponding to the set light amount. It is what.

  The invention according to claim 8 is the optical scanning device according to any one of claims 1 to 7, wherein the original data to be carried by the laser beam generated from the light source is image data, and the optical beam scanning of the optical scanning device. An image forming apparatus including a photosensitive member having a target surface scanned by a unit and a unit that develops a latent image formed on the photosensitive member as a visualized image.

According to the first to seventh aspects of the present invention, by smoothing the light amount setting signal, the level difference between the switching of the laser light amount is smoothed, and noise generated when the light amount setting signal is switched based on the light amount correction data such as shading is removed. In addition, when the writing (target) surface is reached by the light quantity setting signal switching timing setting means, the fluctuation in the transition period that the smoothing means has as a side effect is stabilized, and a desired light quantity is obtained. It becomes possible to improve performance.
In addition, by making it possible to change the setting of the light amount setting signal switching timing, the write amount can be written regardless of the light amount difference between the writing surface and the non-writing surface, and the time constant of the smoothing means (LPF). It becomes possible to obtain a desired laser light amount when reaching the entry surface.
In addition, the laser beam scanning range is divided into a predetermined number of areas and can be applied to a method in which the amount of light can be set in each area, so that a desired configuration can be obtained when the shading correction function and writing surface are reached with a simple configuration. It is possible to realize a function of changing the amount of light (claim 3).
Further, since the light amount setting signal is generated by voltage or current, control such as automatic light amount adjustment can be easily performed, and the circuit configuration can be simplified.
In addition, since a digital / analog converter is used as a means for generating the light amount setting signal as a voltage, an effective means for simplifying the circuit configuration is provided, and the implementation is facilitated (claim 5).
In addition, as a means for generating the light amount setting signal as a voltage, a pulse width modulation means and a low-pass filter for smoothing the output from the pulse width modulation means are used, so that an effective means for simplifying the circuit configuration is reduced. It is provided at a cost and facilitates implementation (claim 6).
In addition, in the optical writing on the photosensitive member of the image forming apparatus, the effects of the first to seventh aspects of the present invention are realized, and the quality of the formed image can be improved (claim 8).

An optical scanning apparatus and an image forming apparatus according to the present invention will be described based on the following embodiments. In the embodiments described below, the present invention forms an optical scanner that performs LD (laser diode) optical writing in the main / sub-scan mode, and forms an image written on a photoconductor by this optical scanner on a paper medium as a visualized image. The present invention is applied to a color copying machine as an image forming apparatus.
FIG. 1 shows a schematic configuration of the optical scanning device of the present embodiment.
In the optical scanning device 21 shown in FIG. 1, when a synchronization signal from a synchronization sensor 61 (detecting a scanning beam at a reference position) that detects main scanning timing is input to the writing control unit 60, the detected synchronization signal is detected. A pixel clock generation circuit for determining a pixel position in the main scanning direction is generated by the pixel clock generation circuit. Further, the writing control unit 60 generates a lighting / extinguishing control signal and a light amount setting signal for controlling the light emission amount based on image data and light amount setting data from the outside (the internal configuration of the writing control unit 60, Details of the operation will be described later). When the lighting / extinguishing control signal and the light amount setting signal are input to the light source driving means 62, a driving signal is supplied to the light source unit 71 having a laser diode (LD) as a light source, and the lighting of the LD is controlled.
The laser light emitted from the LD is shaped through a collimating lens and an aperture in the light source unit 71, and after passing through the cylinder lens 66, the incident laser light is deflected and scanned by the polygon mirror 67 for rotationally deflecting the laser light. The The polygon mirror 67 is rotationally driven at a predetermined rotational speed by a polygon motor. The laser light reflected by the polygon mirror 67 passes through the fθ lens 68, passes through the barrel toroidal lens 74 for correcting the surface tilt of the polygon mirror 67, is reflected by the folding mirror 69, and further passes through the dust-proof glass. Thus, the light is focused on the writing (target) surface 15.

FIG. 2 shows a schematic configuration of the color copying machine of this embodiment in which the optical scanning device of FIG. 1 is mounted as an exposure device. FIG. 3 is an explanatory diagram showing a schematic configuration around the exposure apparatus in FIG. 2 and an optical path until an image is written on the photosensitive member while deflecting and scanning the light beam output from the LD.
As shown in FIG. 2, the color copying machine of this embodiment mainly includes a copying machine main body 100, a paper feed table 200, a scanner 300, and an automatic document feeder (ADF) 400.
An endless belt-like intermediate transfer member 10 is provided at the center of the copying machine main body 100. In this example, the intermediate transfer member 10 is wound around three support rollers 14, 15, and 16, and is rotated and conveyed clockwise as indicated by arrows in the drawing.
Among the three support rollers, four color components composed of black, cyan, magenta, and yellow are arranged on the intermediate transfer member 10 stretched between the first support roller 14 and the second support roller 15 along the conveyance direction. The so-called tandem-type image forming apparatus 20 is configured in which the image forming units 18 are arranged side by side and simultaneously enable image forming operations of four colors. Further, an exposure device 21 is provided above the tandem image forming apparatus 20.
Further, an intermediate transfer member cleaning device 17 for removing residual toner remaining on the intermediate transfer member 10 after image transfer is provided on the right side of the second support roller 15.

On the other hand, a secondary transfer device 22 is provided on the opposite side of the intermediate transfer member 10 from the tandem image forming device 20. The secondary transfer device 22 is configured such that a secondary transfer belt 24, which is an endless belt stretched between two rollers 23, is pressed against the third support roller 16 via the intermediate transfer body 10. The image on the intermediate transfer member 10 is transferred to a sheet supplied between the secondary transfer belt 24 and the intermediate transfer member 10.
A fixing device 25 for fixing the transfer image on the sheet by a thermocompression bonding method is provided on the downstream side of the secondary transfer device 22. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt.
In this example, as the secondary transfer device 22, a device having a sheet conveyance function for conveying the image-transferred sheet to the fixing device 25 is used. Of course, a non-contact charger may be arranged as the secondary transfer device 22, but in this case, it is necessary to provide this sheet conveying function separately.
Further, in the embodiment shown in FIG. 2, under the secondary transfer device 22 and the fixing device 25, the sheet inversion is performed to invert the sheet in order to record images on both sides of the sheet in parallel with the tandem image forming apparatus 20 described above. A device 28 is provided.

When copying a document using the color copying machine shown in FIG. 2, the document is set on the document table 30 of the automatic document feeder 400 or the automatic document feeder 400 is opened and the document is placed on the contact glass 32 of the scanner 300. , And a start switch (not shown) is pressed while the automatic document feeder 400 is closed and pressed. When a document is set on the automatic document feeder 400, the document is transported and moved onto the contact glass 32 (sheet-through reading mode). When a document is set on the contact glass 32, the scanner 300 immediately Driven to cause the first traveling body 33 and the second traveling body 34 to travel (book reading mode).
In any of the above-described reading modes, when the document surface is illuminated by the light source of the first traveling body 33, the reflected light from the document surface is reflected by the mirrors of the first traveling body 33 and the second traveling body 34, and is connected. The image is input to the reading sensor 36 through the image lens 35, and the image on the document surface is read.
When a start switch (not shown) is pressed, one of the support rollers 14, 15 and 16 is driven to rotate by a drive motor (not shown), and the other two support rollers are driven to rotate. 10 is rotated and conveyed. At the same time, the photoconductors 40 of the four-color image forming unit 18 are individually rotated to form black, yellow, magenta, and cyan monochrome images on the photoconductors 40, respectively. Then, the intermediate transfer member 10 is conveyed, and the monochrome image on each photoconductor 40 is sequentially transferred to form a composite color image on the intermediate transfer member 10.
An image is formed on each photoconductor 40 by the exposure device 21 using an LD light beam writing method. The exposure device 21 controls the LD driving unit 62 based on the image data of the document read by the reading sensor 36 and the like and the pixel clock generated and corrected by the pixel clock generation circuit described later, and the light whose lighting is controlled. By scanning the surface of the photoconductor 40 in the main scanning direction while deflecting the beam with a polygon mirror, an electrostatic latent image is formed on the surface of the photoconductor. The exposure apparatus 21 will be described in detail later with reference to FIG.

On the other hand, when a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated, and a desired paper feed cassette 44 provided in multiple stages in the paper bank 43 is selected. The sheet is fed out and fed one by one to the sheet feeding path 46 while being separated one by one by the separation roller 45, conveyed by the conveying roller 47, guided to the sheet feeding path 48 in the copying machine main body 100, and abutted against the registration roller 49 and stopped. Let In addition to the above paper feeding method, the paper feed roller 50 is rotated to feed out the sheets on the manual feed tray 51, and the paper is fed to the manual paper feed path 53 while being separated one by one by the separation roller 52. You may stop at 49.
After the sheet is stopped by the registration roller 49, the registration roller 49 is rotated in synchronization with the composite color image formed on the intermediate transfer body 10, and the sheet is placed between the intermediate transfer body 10 and the secondary transfer device 22. A color image is recorded on the sheet by feeding and transferring by the secondary transfer device 22.
The sheet after the image transfer is conveyed by the secondary transfer device 22 and sent to the fixing device 25, and heat and pressure are applied by the fixing device 25 to fix the transferred image, and then the sheet is switched by the switching claw 55 and discharged. The paper is discharged at 56 and stacked on the paper discharge tray 57. Alternatively, when the sheet is switched by the switching claw 55 and enters the sheet reversing device 28, the sheet is reversed and guided again to the transfer position, and an image is recorded on the back surface, and then discharged onto the discharge tray 57 by the discharge roller 56. The
On the other hand, the intermediate transfer member 10 after the image transfer is subjected to removal of residual toner remaining on the intermediate transfer member 10 after the image transfer by the intermediate transfer member cleaning device 17, so that the image forming device 20 by the tandem method can form an image again. Prepare.

Here, the configuration and operation of the exposure apparatus will be described in more detail with reference to FIG. 3 for explaining the optical path for writing an image on the photosensitive member while deflecting and scanning the light beam output from the laser diode.
As shown in FIG. 3, in order to detect the main scanning timing, a synchronization sensor 61 is arranged at a reference position on the scanning optical path of the beam from the LD 63. When the synchronization signal from the synchronization sensor 61 that detects the main scanning timing is input to the writing control unit 60, a pixel clock is generated based on the synchronization signal. Further, a signal for controlling the light source driving means 62 is generated based on image data input from the outside and light amount setting data for correcting shading and the like. The light source driving means 62 supplies a drive signal to the LD 63 as a light emission source based on this control signal, and controls the lighting of the LD 63 to perform image writing.
The laser beam emitted from the LD 63 is shaped through the collimator lens 64 and the aperture 65, passes through the cylinder lens 66, and then the incident laser beam is deflected and scanned by the polygon mirror 67 for rotational deflection. The polygon mirror 67 is rotationally driven at a predetermined rotational speed by a polygon motor (not shown). The laser light reflected by the polygon mirror 67 passes through the fθ lens 68, is reflected by the folding mirror 69, and further passes through the dust-proof glass 70 and is collected on the photoreceptor 40 as a recording medium.
For example, a photosensitive drum is used as the photosensitive member 40. The photosensitive drum 40 is rotationally driven in a direction opposite to the sub-scanning direction by a rotation driving unit (not shown), and is uniformly charged by a charger (not shown), and then a laser. By repeatedly scanning in the main scanning direction with light, an image is written and an electrostatic latent image is formed.
The electrostatic latent image formed on the photosensitive drum 40 is developed by a developing device (not shown) to become a toner image, is transferred to a recording sheet such as transfer paper through the above-described transfer process, and is fixed by a fixing device 25. It is fixed on the recording sheet.
In this way, the laser light emitted from the LD 63 is deflected at a constant angular velocity by the polygon mirror 67, and the polygon mirror 67 and the fθ lens 68 (or fθ) are used in order to make the scanning speed on the writing surface of the photoreceptor 40 constant. An optical element such as a mirror) or a folding mirror 69 is used.

However, as described above in the section “Background Art”, the use of these optical elements makes the scanning speed on the writing surface of the photoreceptor 40 constant, but the laser beam intensity on the writing surface. Depending on the height of the image, strength is generated. This is because the light utilization efficiency such as reflectance and transmittance of optical elements such as glass, lenses, and mirrors that pass from the time when the laser light is emitted from the laser diode to the surface of the photoreceptor varies depending on the incident angle of the laser light, fθ This is because the lens thickness varies depending on the image height. The intensity of the beam light intensity depending on the image height is called a shading characteristic. However, since this affects the density of the formed image, the shading characteristic is corrected by controlling the amount of laser light at a predetermined time in the main scanning period. .
FIG. 4 is a block diagram showing a basic configuration of a writing unit that can control the amount of laser light in the main scanning direction.
4 includes an LD 63, a light source driving unit 62 that drives the LD 63, and a writing control unit 60 that generates a light on / off control signal and a light amount setting signal that are input to the light source driving unit 62 as drive control signals. In the present embodiment, the turn-on / off control signal is generated by the data signal generation circuit 601 based on the image data. The light amount setting signal Vc is generated by the light amount setting signal generation circuit 603 based on the light amount setting data, and the generated light amount setting signal Vc is smoothed by the filter means 605 and output as a light amount setting signal.

When a synchronization signal from the synchronization sensor 61 that detects the main scanning timing is input to the writing control unit 60 during the writing operation, each pixel position in the writing (image) area in the scanning direction is determined based on the synchronization signal. A pixel clock is generated by a pixel clock generation circuit (not shown). On the basis of the image data input through the scanner 300 or the like, the data signal generation circuit 601 generates a lighting / extinguishing control signal synchronized with the pixel clock and inputs it to the DATA terminal of the light source driving means 62. . Further, when light amount setting data (for example, setting data for correcting shading or the like) set in advance by designating a position in the scanning direction (image region, pixel position, etc.) is input, a light amount setting signal generation circuit 603. Thus, the light quantity setting signal Vc is generated. The generated light quantity setting signal Vc is smoothed by the filter means 605 and input to the Vcont input terminal of the light source driving means 62 as a light quantity setting signal. The light source driving means 62 supplies a drive signal to the LD 63 as a light source based on the input lighting / extinguishing control signal and the light quantity setting signal, and the LD 63 is controlled to be turned on to write an image.
The light quantity setting signal Vc is an analog signal. By changing the light quantity setting signal Vc, the laser light quantity can be increased or decreased in accordance with the set quantity and controlled. In this control, as shown in FIG. 5, by using an LD driver IC having a proportional relationship between the light quantity setting signal Vc and the light emission power Po as the light source driving means 62, the light quantity control circuit configuration is also simplified. It is desirable.
Further, when the amount of light can be controlled according to the beam position in the main scanning direction as in the case of shading correction, the configuration includes an LPF 605 that smoothes the light amount setting signal Vc based on the light amount correction (setting) data. By switching the laser light amount at the main scanning position, it is possible to prevent the intensity of the beam light from changing suddenly and prevent a step in the writing result (image density), smooth the change, and avoid the generation of a step. It becomes.
In addition to the shading correction function, in other cases where the amount of light needs to be controlled according to the beam position in the main scanning direction, for example, the temperature distribution inside the laser element is always maintained at the temperature distribution in the image area, In order to prevent fluctuations in the light output due to changes over time, a function was provided to forcibly emit light with a higher light intensity than in the writing (image) area in the non-writing (image) area. It can be configured.
Even when the laser light amount detectable by the photo IC (synchronous sensor 61) used as means for detecting the reference position of the main scanning of the laser light is different from the laser light amount used in the image area, the main scanning is performed. It is necessary to control the increase / decrease in the amount of laser light inside.
As a means for realizing the functions as described above, a writing control unit 60 that controls the amount of light according to the beam position in the main scanning direction is used.

However, in the above light amount control, the step of the writing result (image density) generated by switching the laser light amount at the main scanning position is smoothed, and an LPF or the like added to remove noise generated in the light amount setting signal at the time of switching is used. As a side effect, the smoothing means 605 causes a delay until the smoothed light amount setting signal Vcont becomes a stable setting signal.
FIG. 6 is a timing chart showing signals generated during operation of the writing unit of FIG. In the figure, the change of each signal is shown by dividing one cycle of main scanning into a non-image (writing) area and an image (writing) area. As signals, a synchronization signal detected by the synchronization sensor 61, a light amount setting signal Vc, a smoothed light amount setting signal Vcont, input image data DATA, and a laser emission power Po are shown.
As shown in FIG. 6, when there is a difference between the laser light amount in the image area and the set light amount Vc in the non-image area, even if the light amount setting signal Vc is switched at the start time of the image area, the LPF 605 Since a delay occurs, the smoothed light amount setting signal Vcont deviates from the target value, and the light emission power Po at the start time of the image area also differs from the target. In this embodiment, in the non-image (writing) area, the light amount setting signal Vc is maintained at a high temperature setting and the setting is not switched. Therefore, as shown in FIG. A stable and high light emission power Po can be obtained according to the image data DATA.
FIG. 7 is a timing chart similar to that shown in FIG. 6 and shows a change in image density. In the figure showing the density change, the horizontal axis is the image height X (X = 0 is the center of the writing surface). As shown in FIG. 7, due to the delay caused by the LPF 605, the light emission power Po similarly fluctuates until the light amount setting signal Vcont becomes a stable setting signal in accordance with the smoothed light amount setting signal Vcont and deviates from the target. End up. As a result, the density of the written image becomes higher than the target set value at the start of the image area, and the density change occurs during the transition period ti until the target image is stabilized.

Therefore, in this embodiment, in order to solve such a problem, by changing the light amount setting signal at a time before reaching the image area, the influence of the change in the transition period is avoided, and at the start time of the image area. Set to the target setting value.
FIG. 8 is a block diagram showing the configuration of the writing unit of the present embodiment. In the configuration of FIG. 8, a Vc switching timing signal generation circuit 607 is provided as means for changing the setting of switching timing in the basic configuration shown in FIG. 4, and the light quantity setting signal is output at a time before reaching the image area. It is possible to set the switching timing. The configuration of the writing unit according to the present embodiment is the same as that shown in FIG. 4 except that the Vc switching timing signal generation circuit 607 is added. For other components, refer to the above description. The description is omitted here.
The Vc switching timing signal generation circuit 607 according to the present embodiment scans the light amount setting data input to the light amount setting signal generation circuit 603 in accordance with the light amount switching timing set in advance together with the light amount, that is, the scanning designated according to the set light amount. A signal for changing the position (region) in the direction for a necessary time is generated.

FIG. 9 is a timing chart showing signals generated during operation of the writing unit of FIG. As shown in FIG. 6, the synchronization signal detected by the synchronization sensor 61, the light amount setting signal Vc, and smoothing are divided into a non-image (writing) area and an image (writing) area corresponding to one main scanning period. The subsequent light quantity setting signal Vcont, input image data DATA, and laser emission power Po are shown.
In the embodiment shown in FIG. 9, the smoothed light amount setting signal Vcont is in a steady state, and the transition period is time t1, and the Vc switching timing signal generation circuit 607 reaches the time when the image area is reached in advance. Setting is made so that the switching timing of the set light amount is advanced by time t1. In this case, as shown in the timing chart of FIG. 9, by setting the switching time t1, the smoothed light amount setting signal Vcont is in a steady state and the light emission power Po is in a steady state at the start of the image area. Can be used at a place, and a desired light emission power can be obtained.
FIG. 10 is a timing chart similar to that shown in FIG. 9 and shows a change in image density. In the figure showing the density change, the horizontal axis is the image height X (X = 0 is the center of the writing surface). As shown in FIG. 10, due to the delay due to the LPF 605, the light emission power Po similarly varies with the light amount setting signal Vcont after smoothing until the light amount setting signal Vcont becomes a stable setting signal, but the time t1 After that, it becomes a steady state and becomes the target light emission power Po. As a result, the density of the written image can be set to the target density at the start of the image area.

Regarding the time t1 set when the switching timing is changed, that is, the time required for the smoothed light amount setting signal Vcont to be in a steady state, the time constant of the LPF 605 and the size of the image area and the non-image area It depends on the difference in light quantity.
In order to cope with such a variation factor, the setting of the switching timing in the Vc switching timing signal generation circuit 607 can be changed.
FIG. 11 is a timing chart showing signals generated during operation of the writing unit when the setting of the switching timing is changed. The timing chart of FIG. 11 shows an example in which the setting time t1 of the switching timing shown in FIG. 9 is changed to the setting time t2, and between the light amount setting signal Vc set in the image area and the non-image area. Even if the light amount difference or the time constant of the LPF 605 changes, it is possible to obtain a constant desired laser light amount at the start time of the image region by adjusting the switching timing setting time.

The conditions necessary for the light amount setting signal Vc in the writing unit shown in FIG. 8 will be described.
As described in the writing section shown in FIG. 4, the LD driver IC having the proportional relationship shown in FIG. 5 between the light quantity setting signal Vc and the laser light quantity (light emission power Po) is used as the light source driving means 62. It is desirable to do.
This condition is the same in FIG. 8, and the light amount setting signal Vc input to the light source driving means 62 needs to be an analog signal. Therefore, in this embodiment, the analog light quantity setting signal Vc is set as a voltage value.
By setting the light amount setting signal Vc to a voltage value that has a linear relationship with the laser light amount (light emission power Po), the light amount control can be easily performed with a simple configuration with respect to the light amount control.
Here, an embodiment in which the analog light quantity setting signal Vc is a voltage value is shown, but a current value may also be used.

The following embodiment shows an embodiment of a light amount setting signal generation circuit 603 that uses the above-described analog light amount setting signal Vc as a voltage value. This light quantity setting signal generation circuit 603 is an element constituting the writing control unit 60 of the writing unit (FIG. 8).
The light quantity setting signal generation circuit 603 according to the first embodiment uses a D / A (digital / analog) converter.
FIG. 12 is a block diagram showing an internal configuration of the light amount setting signal generation circuit according to the first embodiment.
In FIG. 12, the light amount setting data of the digital signal input to the light amount setting signal generation circuit 603 is converted into a voltage value having a linear relationship with the laser light amount by the D / A converter 611, and an analog light amount setting signal is obtained. Output as Vc.
In the light quantity setting signal generation circuit 603, the Vc switching timing signal generation circuit 613 advances the switching timing in the same manner as the writing control unit 60 shown in FIG. The laser light quantity can be set.
The light amount setting signal generation circuit 603 according to the second embodiment uses a pulse width modulation circuit and an LPF (low pass filter) circuit 625.
FIG. 13 is a block diagram showing an internal configuration of a light amount setting signal generation circuit according to the second embodiment.
In FIG. 13, the pulse width modulation circuit 621 generates a PWM (pulse width modulation) signal having a duty corresponding to the light amount from the light amount setting data of the digital signal input to the light amount setting signal generation circuit 603. The generated PWM signal is smoothed by the LPF 625, converted into a voltage value having a linear relationship with the laser light quantity, and output as an analog light quantity setting signal Vc.
Since the light quantity setting signal generation circuit 603 is configured by the pulse width modulation circuit 621 and the low-pass filter 625 as described above, the light quantity setting data can be converted into the light quantity setting signal with a simple and low-cost configuration for the light quantity control. It becomes.
Also in this light quantity setting signal generation circuit 603, the Vc switching timing signal generation circuit 623 advances the switching timing in the same manner as the writing control unit 60 shown in FIG. The laser light quantity can be set.

The following embodiment relates to a writing unit having a writing control unit 60 adapted to a method in which a laser light scanning width is divided into a predetermined number and a light amount setting signal can be set for each divided area.
FIG. 14 is a block diagram showing the configuration of the writing unit of the present embodiment. The configuration of FIG. 14 generates a light quantity setting signal as a means for dividing the laser beam scanning width into a predetermined number and enabling setting of a light quantity setting signal for each divided area in the basic configuration shown in FIG. By adding a divided area signal generation circuit 609 to the circuit 603, the light quantity setting signal generation function is expanded. The configuration of the writing unit of the present embodiment is the same as that of FIG. 4 except that the light amount setting signal generation circuit 602 is added to the light amount setting signal generation circuit 603 to configure the light amount setting signal generation means 602. The other components are referred to the above description, and the description is omitted here.
A divided area signal generation circuit 609 of the light amount setting signal generating means 602 generates a divided area signal based on input of divided area setting data for dividing the laser beam scanning width into a predetermined number. The divided area setting data is, for example, data indicating the number of divisions and a predetermined range of the scanning area (for example, the position of the head area in the scanning direction and the size of the area).
The light amount setting signal generation circuit 603 generates an analog light amount setting signal Vc based on the light amount setting signal set for each divided area and the divided area signal generated by the divided area signal generation circuit 609, and Output to the LPF 605.
FIG. 15 is a timing chart showing signals generated during operation of the writing unit capable of setting a light amount setting signal for each divided area shown in FIG. FIG. 15 illustrates an operation example in which a predetermined range of the scanning area is divided into eight and areas 1 to 8 are set.
In this case, the start time of the image area is set as the head position of area 1. Accordingly, in the area 1 at the start time of the image area, the light amount setting signal Vc is switched and Vc changes greatly. Therefore, as shown in FIG. 6, a delay due to the LPF 605 occurs, and the smoothed light amount setting signal Vcont. Deviates from the target value, and the light emission power Po at the start of the image area also differs from the target.

Therefore, in the present embodiment, the divided areas are adjusted so that the light amount setting signal Vcont after smoothing becomes a steady value when reaching the start time of the image area.
In this adjustment, for example, an area including a time ti (transition period) in which a delay due to the LPF 605 occurs (here, area 1) is assigned before the image region start time.
FIG. 16 is a timing chart showing signals generated during operation of the writing unit when the divided area is adjusted so that the light amount setting signal Vcont after smoothing becomes a steady value.
As shown in FIG. 16, the area 1 including the transition period ti is assigned before the start time of the image area, and the smoothed light amount setting signal Vcont is applied at the start time of the image area as in FIG. Since the steady state can be obtained, the light emission power Po can be used when the desired light emission power is stabilized.
Note that the time during which the light amount setting signal Vcont after smoothing takes a steady value varies depending on the characteristics of the LPF 605 and the light amount setting value to be set as described above. Therefore, when the area allocation method in the present embodiment is used, the smoothed light amount setting signal Vcont does not always become a steady value only in area 1 shown in FIG. In such a case, adjustment is performed by a method of adding an area to be allocated before the start time of the image area.

1 shows a schematic configuration of an optical scanning device according to an embodiment of the present invention. 1 shows a schematic configuration of a color copying machine according to an embodiment of the present invention. The optical path of writing on the photosensitive member by the light beam output from the LD is shown. It is a block diagram which shows the basic composition of the writing part which enabled control of the light quantity in the main scanning direction. The relationship between the light quantity setting signal Vc and the light emission power Po is shown. It is a timing chart showing the signal produced at the time of operation | movement of a writing part (FIG. 4). FIG. 7 is a timing chart in which image density as a writing result is added to FIG. It is a block diagram which shows the structure of the writing part which can change the switching timing of a light quantity setting signal. It is a timing chart showing the signal produced at the time of operation | movement of a writing part (FIG. 8). FIG. 10 is a timing chart in which image density as a writing result is added to FIG. It is a timing chart showing the signal which arises at the time of operation | movement of the writing part (FIG. 8) at the time of changing the setting of a switching timing. It is a block diagram which shows the internal structure of a light quantity setting signal generation circuit. It is a block diagram which shows the other example of the internal structure of a light quantity setting signal generation circuit. It is a block diagram which shows the structure of the writing part which can set a light quantity setting signal for every division area. It is a timing chart showing the signal which arises at the time of operation | movement of the writing part (FIG. 14) which made it possible to set a light quantity setting signal for every division area. It is a timing chart showing the signal produced at the time of operation | movement of the writing part (FIG. 14) which made the light quantity setting signal become a steady value in the division area provided in the non-image area.

Explanation of symbols

21 ... Exposure device 40 ... Photoconductor
60..Write controller 61..Synchronous sensor,
62 .. Light source driving means, 63 .. LD (laser diode),
67 .. Polygon mirror, 601 .. Data signal generation circuit,
603 .. Light quantity setting signal generation circuit 605 .. Filter means (LPF)
607 ..Vc switching timing signal generation circuit,
609 .. Divided area signal generation circuit.

Claims (8)

A light source that generates a laser beam having a light amount corresponding to the drive signal;
A light beam scanning means for projecting laser light generated from a light source onto a target surface as a scanning beam at a predetermined period;
Data signal generating means for generating a data signal for determining the lighting timing of the light source in order to carry the signal of the original data to the laser beam projected as a scanning beam on the target surface;
A light amount setting signal generating means for generating a light amount setting signal for setting the light amount of the laser light according to the position in the main scanning direction in order to correct the fluctuation of the intensity of the laser light scanning one line on the target surface ;
Smoothing means for removing and smoothing noise generated during the switching of the light amount setting signal;
It said light beam as the light quantity setting signal the scanned laser beam through the smoothing means at the time reaches the target surface by the scanning means reaches a steady value, set the switching timing of the light quantity setting signal in the light amount setting signal generating means A light quantity setting signal switching timing setting means to perform,
An optical scanning device comprising light source driving means for driving the light source by a drive signal generated based on the light quantity setting signal and the data signal.   The optical scanning device according to claim 1, wherein the light amount setting signal switching timing setting unit is a unit that enables the setting of the light amount setting signal switching timing to be changed. A light source that generates a laser beam having a light amount corresponding to the drive signal;
A light beam scanning means for projecting laser light generated from a light source onto a target surface as a scanning beam at a predetermined period;
Data signal generating means for generating a data signal for determining the lighting timing of the light source in order to carry the signal of the original data to the laser beam projected as a scanning beam on the target surface;
Area dividing means for dividing the laser beam scanning range into a predetermined number of areas;
A light amount setting signal generating means for generating a light amount setting signal for setting a laser light amount generated by the light source for each divided area;
Smoothing means for removing and smoothing noise generated during the switching of the light amount setting signal;
At the time the laser beam scanned by said light beam scanning means reaches the target surface, as the light quantity setting signal divided areas through the smoothing means reaches a steady value, and means for adjusting the divided area,
An optical scanning device comprising: a light source driving unit configured to drive the light source by a light amount setting signal generated for each of the divided areas and a drive signal generated based on the data signal.   4. The optical scanning device according to claim 1, wherein the light amount setting signal generating means is a means for generating a setting signal with a voltage corresponding to the set light amount. The optical scanning device according to claim 4, wherein the light quantity setting signal generating means for generating a set signal at a voltage corresponding to the set amount of light, the optical scanning device characterized in that it comprises a digital / analog converter.   5. The optical scanning device according to claim 4, wherein the light amount setting signal generating means for generating a setting signal with a voltage corresponding to the set light amount smoothes the pulse width modulating means and the output from the pulse width modulating means. An optical scanning device comprising a low-pass filter.   4. The optical scanning device according to claim 1, wherein the light quantity setting signal generating means is a means for generating a setting signal with a current corresponding to the set light quantity. The optical scanning device according to claim 1, wherein original data to be carried by the laser light generated from the light source is image data.
A photoreceptor having a target surface scanned by a light beam scanning means of the optical scanning device;
An image forming apparatus having means for developing a latent image formed on a photoreceptor as a visualized image.

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