JP2020109433A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can optimize an amount of charge on a surface of a photoreceptor even when a range for using an amount of light emitted from a light emitting element is relatively large.SOLUTION: An image forming apparatus 100 comprises: a photoreceptor 1; charging means 2; light irradiation means 31 having a light emitting element 107 including a first light emitting unit 107A and a second light emitting unit 107B, and scanning means 133; developing means 4; and control means 101. In first scanning of light from the light emitting element 107 performed by the scanning means 133, the control means 101 can perform control of causing the first light emitting unit 107A to normally emit light with a normal light emission amount for irradiating an image part with light and to minutely emit light with a minute light emission amount for irradiating the image part with light and smaller than the normal light emission amount, and not causing the second light emission unit to minutely emit light with a minute light emission amount for irradiating a non-image part with light and smaller than the normal light emission amount.SELECTED DRAWING: Figure 13

Description

The present invention relates to an electrophotographic image forming apparatus such as a laser printer, a copying machine, and a facsimile.

In the image forming apparatus using the electrophotographic method, further downsizing of the apparatus is required. Patent Documents 1 and 2 propose a configuration in which a voltage is applied from a single high-voltage power source to the developing means and charging means of a plurality of image forming units for the purpose of downsizing the apparatus.

If the high-voltage power supply is shared in this way, there are the following problems. That is, in a so-called tandem type image forming apparatus in which a plurality of image forming units each include a photosensitive drum, the sensitivity characteristic (photosensitive characteristic, EV characteristic, EV curve) of each photosensitive drum may change due to various factors. At this time, for example, if a high-voltage power supply that applies a voltage to the charging unit of each image forming unit is shared, the charging voltage in each image forming unit cannot be controlled independently, so that the charging potential is appropriately adjusted for each photosensitive drum. Cannot be set to. In this case, if the control of the developing potential in each image forming section is insufficient, the relationship between the charging potential and the developing potential becomes unsatisfactory, and the toner is apt to be transferred to the non-image area to cause fogging. This problem is more remarkable when a high-voltage power source that applies a voltage to the developing unit of each image forming unit is shared, or when a high-voltage power source that applies a voltage to a plurality of developing units and a plurality of charging units is shared. Becomes Even if the high-voltage power supplies are not shared, similar problems are assumed when the power supply control capability (voltage conversion capability) of each high-voltage power supply is insufficient or when independent power supply control is not performed. It

Therefore, Patent Documents 1 and 2 propose a method of optimizing the charge amount (surface potential) of the surface of each photosensitive drum by exposing the photosensitive drum by causing the laser element to emit a small amount of light. ing. Further, Patent Document 2 proposes to turn off some light sources of a plurality of light sources included in a laser element for the purpose of reducing both the normal light emission amount and the minute light emission amount.

JP2012-189886A JP, 2014-13373, A

As described in Patent Documents 1 and 2, when the laser device is used with a normal light emission amount and a minute light emission amount, the usage range of the chip surface light amount (light emission luminance, light emission intensity, light emission amount, light emission level) of the laser device Grows. It should be noted that the normal light emission amount is a light emission amount for making the surface of the photosensitive drum a charge amount to which toner adheres, that is, a light emission (normal exposure) for exposing the photosensitive drum at an exposure amount having such a charge amount ( It is the amount of light emitted during normal light emission). In addition, the minute light emission amount is a light emission amount for making the surface of the photosensitive drum a charge amount that toner does not adhere, that is, light emission for exposing the photosensitive drum at a light exposure amount (micro exposure) (micro exposure) ( It is the amount of light emitted when a slight amount of light is emitted.

In addition, the optimum normal light emission amount and minute light emission amount change depending on the film thickness, material, and life of the photosensitive drum. In recent years, the normal light emission amount and the minute light emission amount have been used in accordance with the extension of the life of the photosensitive drum. The range tends to be expanded further.

Furthermore, the optical efficiency of the laser scanner also changes the amount of light on the chip surface of the laser element required to normally expose the surface of the photosensitive drum and the amount of light on the chip surface of the laser element required to slightly expose the surface of the photosensitive drum. To do.

Therefore, depending on the conditions such as the film thickness and material of the photosensitive drum, the service life, or the optical efficiency of the laser scanner, the minimum value of the usage range of the minute light emission amount may be lower than the lower limit guaranteed value of the light amount on the chip surface of the laser element. .. In that case, the amount of charge (surface potential) on the surface of the photosensitive drum cannot be optimized.

Therefore, an object of the present invention is to provide an image forming apparatus capable of optimizing the amount of charge on the surface of the photoconductor even when the usage range of the amount of light emitted from the light emitting element is relatively large.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention includes a photoconductor, a charging unit that charges the photoconductor, an image portion to which toner is attached by irradiating the charged photoconductor with light, and a non-image portion to which toner is not attached. Light emitting means for forming an electrostatic image containing the light on the photoconductor, the light emitting device having a first light emitting part and a second light emitting part, and a predetermined light on the photoconductor by deflecting light from the light emitting device. Scanning means for scanning in the direction of, a light irradiation means included therein, a developing means for supplying toner to the electrostatic image formed on the photoconductor to form a toner image, and a control means for controlling the light irradiation means. And the control unit causes the first light emitting unit to normally emit light at a normal light emission amount for irradiating the image unit in one scan of the light from the light emitting element by the scanning unit. A minute amount of light for irradiating the non-image portion, which is smaller than the normal amount of light emission, and a small amount of light for irradiating the second light emitting part to the image portion. The image forming apparatus is characterized in that it is possible to perform control so as not to perform the minute light emission with the minute light emission amount for irradiating the non-image portion which is smaller than the normal light emission amount.

According to the present invention, it is possible to optimize the charge amount on the surface of the photoconductor even when the light emission amount of the light emitting element is used in a relatively large range.

FIG. 3 is a schematic cross-sectional view of the image forming apparatus. FIG. 3 is a schematic cross-sectional view for explaining the layer structure of the photosensitive drum. FIG. 6 is a graph for explaining a change in sensitivity characteristic of a photosensitive drum. It is a schematic diagram for explaining a charging/developing high-voltage power supply. It is a schematic perspective view of an exposure apparatus. It is a schematic diagram for demonstrating the spot diameter of a beam spot. It is explanatory drawing for demonstrating the measuring method of a spot diameter. It is a schematic diagram for demonstrating the schematic structure of a laser drive system circuit. It is a schematic diagram for demonstrating the schematic structure of a laser drive system circuit. It is explanatory drawing for demonstrating correction|amendment of a minute light emission amount. It is a flowchart figure for demonstrating the basic process of correction|amendment of the light emission amount. FIG. 6 is a schematic diagram showing an example of a table showing the relationship between the usage state of the photosensitive drum and the setting of the light emission amount. FIG. 6 is a timing chart diagram for explaining laser drive control in the first embodiment. 5 is a schematic diagram showing a relationship between a 1-dot width and a spot diameter in the case where a small amount of light emission thinning is not performed and in a case where it is performed in Example 1. FIG. FIG. 6 is a flowchart for explaining the process of correcting the light emission amount according to the first embodiment. It is a schematic diagram which shows the other example of the table which shows the use condition of a photosensitive drum, and the relationship of light emission amount setting. FIG. 9 is a schematic diagram showing a relationship between a 1-dot width and a spot diameter in the case where a small amount of light emission thinning is not performed and in a case where it is performed in Example 2.

Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[Example 1]
1. Schematic Configuration of Image Forming Apparatus FIG. 1 is a schematic sectional view of an image forming apparatus 100 according to the present exemplary embodiment. The configuration and operation of the image forming apparatus 100 of this embodiment will be described with reference to FIG.

The image forming apparatus 100 includes first to fourth (a to d) image forming stations (image forming units) Ua to Ud. Here, the first is yellow (hereinafter referred to as Y), the second is magenta (hereinafter referred to as M), the third is cyan (hereinafter referred to as C), and the fourth is black (hereinafter referred to as Bk). Is. The symbols a to d are omitted as appropriate unless it is necessary to describe each color. In this embodiment, the image forming station U is configured to include a photosensitive drum 1, a charging roller 2, an exposure device 31, a developing device 4, a primary transfer roller 14, a drum cleaner 5 and the like, which will be described later. Further, each image forming station U is provided with a storage member (memory tag) 17 for storing the cumulative number of rotations of the photosensitive drum 1 as information regarding the remaining life of the photosensitive drum 1. Further, at least a part of the elements forming each image forming station U is replaceable with respect to the main body of the image forming apparatus 100. Note that the replaceable elements in each image forming station U need only include at least the photosensitive drum 1, and there is no particular limitation as to which members can be replaced.

In the following, the operation of the first (Y) image forming station Ua will be described as an example of each image forming station U. The image forming station Ua includes a photosensitive drum 1a as a photoconductor, and the photosensitive drum 1a is rotationally driven in a direction indicated by an arrow at a predetermined peripheral speed (hereinafter, referred to as a process speed). The peripheral speed (moving speed of the surface) of the photosensitive drum 1a is substantially equal to the moving speed of the surface of the intermediate transfer belt 10, and can be rephrased as a transfer speed or the like. In addition, the peripheral speed of the secondary transfer roller 20 and the moving speed of the recording material (recording medium, sheet) P can also be referred to. During this rotation process, the photosensitive drum 1a is uniformly charged to a charging potential Vd having a predetermined polarity by the charging roller 2a as a charging unit. Next, the laser beam 6a of the exposure device 31a as the light irradiation means (exposure means) is scanned based on the image data (image signal) supplied from the outside. As a result, the image portion on the surface of the photosensitive drum 1a is exposed (normal exposure) with the exposure amount E [μJ/cm ² ] to remove the electric charge, and the exposure potential Vl is formed on the surface of the photosensitive drum 1a. The exposure device 31a exposes the non-image portion on the surface of the photosensitive drum 1a with the exposure amount Ebg [μJ/cm ² ] (Ebg<E) by scanning with the laser beam 6a (micro exposure), and after micro exposure ( The corrected potential Vd_bg is formed. As a result, an electrostatic image (electrostatic latent image) including an image portion to which toner is attached and a non-image portion to which toner is not attached is formed on the photosensitive drum 1. Next, the toner adheres to the exposure potential Vl portion which is the image portion due to the potential difference between the development potential Vdc applied to the developing device (yellow developing device) 4a as the developing means and the exposure potential Vl, and the toner is developed (visualized). It The portion of the potential Vd_bg, which is the non-image portion, has a potential at which the toner does not easily adhere (a potential at which normal fog or reverse fog does not easily occur) because of the relationship with the development potential Vdc, and therefore toner does not adhere. Specifically, the charging potential Vd is set to about -700V to -600V, the charging potential Vd_bg after slight exposure is set to about -550V to -400V, the developing potential Vdc is set to about -350V, and the exposure potential Vl is set to about -150V. The image forming apparatus 100 according to the present exemplary embodiment is a reversal development type image forming apparatus that performs image exposure by the exposure device 31a and develops toner on the exposed portion.

The intermediate transfer belt 10, which is an endless belt as an intermediate transfer member, is stretched by stretching members 11, 12, and 13 and is in contact with the photosensitive drum 1a. The intermediate transfer belt 10 is rotationally driven so as to rotate at the contact position in the same direction as the photosensitive drum 1a and at substantially the same peripheral speed. The yellow toner image formed on the photosensitive drum 1a is transferred as follows. That is, the yellow toner image passes through the contact portion between the photosensitive drum 1a and the intermediate transfer belt 10 (hereinafter referred to as the primary transfer nip portion). In this process, the yellow toner image is transferred (primary transfer) onto the intermediate transfer belt 10 by the primary transfer voltage applied from the primary transfer power supply 15a to the primary transfer roller 14a as the primary transfer means. The primary transfer residual toner remaining on the surface of the photosensitive drum 1a is cleaned and removed by a drum cleaner 5a as a cleaning unit. After that, the above-described charging and subsequent image forming processes are repeatedly performed. Similarly, a magenta toner image (M) of the second color, a cyan toner image (C) of the third color, and a black toner image (Bk) of the fourth color are formed and transferred in sequence on the intermediate transfer belt 10. A composite color image is obtained.

During the process in which the four color toner images on the intermediate transfer belt 10 pass through the contact portion between the intermediate transfer belt 10 and the secondary transfer roller 20 (hereinafter referred to as the secondary transfer nip portion), the secondary transfer power source 21 A secondary transfer voltage is applied to the secondary transfer roller 20 as a secondary transfer unit. As a result, the four-color toner images on the intermediate transfer belt 10 are collectively transferred (secondarily transferred) onto the surface of the recording material P such as paper fed by the paper feed roller 50. After that, the recording material P carrying the toner images of four colors is introduced into a fixing device 30 as a fixing means, and heated and pressed there, whereby the toners of four colors are melt-mixed and fixed to the recording material P. .. With the above operation, a full-color toner image is formed on the recording medium. The secondary transfer residual toner remaining on the surface of the intermediate transfer belt 10 is cleaned and removed by the intermediate transfer belt cleaning device 16 as a cleaning unit.

2. Sectional Structure of Photosensitive Drum FIG. 2 shows an example of a section of the photosensitive drum 1a. The photosensitive drum 1a is configured by laminating a charge generation layer 23a and a charge transport layer 24a on a conductive support base 22a. The conductive support base 22a is, for example, an aluminum cylinder having an outer diameter of 30 mm and a thickness of 1 mm. The charge generation layer 23a is, for example, a phthalocyanine-based pigment having a thickness of 0.2 μm. The charge transport layer 24a has a thickness of, for example, 20 μm, is made of polycarbonate as a binder resin, and is blended with an amine compound as a charge transport material. Of course, FIG. 2 is an example of the photosensitive drum 1a, and the dimensions and materials are not limited to those described here.

3. Sensitivity Characteristic of Photosensitive Drum FIG. 3 is an example of the sensitivity characteristic of the photosensitive drum (photosensitive characteristic, EV characteristic, EV curve). The surface of the photosensitive drum after being charged to V is exposed on the surface of the photosensitive drum. The potential decay is shown when the laser light exposure is performed so that the amount becomes E [μJ/cm ² ]. This sensitivity characteristic shows that a larger potential attenuation can be obtained by increasing the exposure amount E. Further, in the high-potential portion, the environment is a strong electric field, and recombination of charge carriers (electron-hole pairs) generated by exposure is hard to occur, so that large potential attenuation is exhibited even with a small exposure amount. On the other hand, in the low potential portion, the generated carriers are likely to be recombined, so that there is a phenomenon that the potential attenuation is small even with the exposure of a large exposure amount. Further, in the same figure, the sensitivity characteristic at the initial stage when the photosensitive drum is started to be used and the sensitivity characteristic when the photosensitive drum is continuously used and is approaching the end of its life are respectively shown. In FIG. 3, the broken line curve is the sensitivity characteristic when the photosensitive drum is approaching the end of its life. The sensitivity characteristic of the photosensitive drum shown in FIG. 3 is an example, and application of photosensitive drums having various sensitivity characteristics is assumed in this embodiment.

4. Charging/Developing High Voltage Power Supply FIGS. 4A and 4B show an example of the charging/developing high voltage power supply. In the example of FIG. 4A, the charging rollers 2 a to 2 d corresponding to each of a plurality of colors and the developing rollers 43 a to 43 d corresponding to each of a plurality of colors are connected to the charging/developing high voltage power source 52. The charging/developing high-voltage power supply 52 supplies the charging voltage Vcdc (power supply voltage) output from one transformer to the charging rollers 2a to 2d, and the developing voltage Vdc divided by two resistance elements to the developing rollers 43a to 43d. 43d. In the power supply circuit of FIG. 4A, since the power supply system is simplified, it is possible to collectively adjust the voltage input (applied) to each roller while maintaining a predetermined relationship. On the other hand, individual adjustment (individual control) independent between colors cannot be performed. Similarly, individual adjustment (individual control) cannot be performed on the voltage input (applied) to the charging roller 2 and the developing roller 43. In this embodiment, the charging/developing high-voltage power supply 52 is feedback-controlled by the CPU of the engine controller 101 described later so that the charging voltage Vcdc becomes -1100V and the developing voltage Vdc becomes -350V. Under this control, the charging rollers 2a to 2d uniformly charge the surfaces of the photosensitive drums 1a to 1d to the charging potential Vd.

Further, FIG. 4B shows another example of the charging/developing high voltage power source. In the example of FIG. 4B, at least two power sources are used, such as a charging/developing high voltage power source 90 for YMC color image forming stations Ua to Uc and a charging/developing high voltage power source 91 for Bk color image forming station Ud. Divided. Then, when the image is formed in the full color mode, the charging/developing high voltage power sources 90 and 91 are turned on. On the other hand, when the image is formed in the mono-color mode, the charging/developing high-voltage power source 90 for the YMC color image forming stations Ua to Uc does not operate (OFF), while the Bk color image forming station Ud. The charging/developing high-voltage power supply 91 for use is turned on. In the case of the example of FIG. 4B, the same applies to the charging/developing high-voltage power supply 90 for the YMC color image forming stations Ua to Uc as in the example of FIG. 4A.

As described above, according to the charging/developing high-voltage power supply shown in FIGS. 3A and 3B, the high-voltage power supply is commonly used for the plurality of charging rollers and the developing rollers, and the apparatus can be further downsized. it can. Further, the cost can be reduced as compared with the case where a transformer whose output voltage is variable for each color is provided and the input voltage to each charging roller and each developing roller is individually controlled. In addition, the cost is higher than the case where a DC-DC converter (variable regulator) is provided for each charging roller and each developing roller and the output from one transformer is individually controlled for each charging roller and each developing roller. Can be suppressed.

In the present invention, the voltage is supplied from the power source common to the charging rollers 2 of the plurality of image forming units U, in addition to the configuration in which the voltage is supplied from the common power source to the charging rollers 2 and the developing rollers 43a of the plurality of image forming units U. Is also particularly effective when it is configured to be supplied.

5. Schematic Configuration of Exposure Apparatus Next, the schematic configuration of the exposure apparatus 31 in this embodiment will be described. Here, one image forming station U will be described as a representative, but in this embodiment, the configuration of the exposure device 31 is substantially the same in all the image forming stations U.

FIG. 5 is a schematic perspective view of the main part of the exposure device (optical scanning device, optical device, laser scanner) 31 in this embodiment. The exposure device 31 has a laser diode 107 (hereinafter, referred to as LD 107) as a light emitting element (light emitting unit, light source). In the present embodiment, the LD 107 is a two-beam semiconductor laser diode having two light emitting units 107A and 107B built therein as a plurality of light emitting units capable of emitting light independently. Each of the two light emitting units 107A and 107B is composed of a laser diode as a light emitting element (light emitting unit, light source), and each of them is provided with a first light emitting unit 107A (or LD 107A) and a second light emitting unit 107B (or LD 107B). ). The laser drive system circuit (LD driver) 130 is a circuit for supplying a drive current to each of the first and second light emitting units 107A and 107B of the LD 107. The first and second light emitting units 107A and 107B of the LD 107 emit laser light with light emission amounts (light emission brightness, light emission intensity, light emission level, chip surface light amount) corresponding to their drive currents. The laser drive system circuit 130 is electrically connected to an engine controller 101 and a video controller 102 described later.

The laser light emitted from the LD 107 is shaped into a parallel beam by the collimator lens 134 and is made into a parallel beam. The parallel beam is shaped by the cylindrical lens 135 so as to form an image on the polygon surface (scanning surface) 133-1 of the polygon mirror (rotating polygonal mirror) 133 as the scanning means. The laser light shaped by the cylindrical lens 135 is imaged on the polygon surface 133-1 of the polygon mirror 133 after the width of the laser light is limited by the aperture 136. Then, the laser light is exposed (scanned) to the fθ lens 132 by the rotating polygon mirror 133. The exposed (scanned) laser light passes through the fθ lens 132 and is imaged as a dot-shaped beam spot having a predetermined spot diameter, which will be described later, on the surface of the photosensitive drum 1 rotating in the direction of arrow R in the figure. Further, the photosensitive drum 1 is exposed (scanned) in the horizontal direction (rotational axis direction). At this time, the direction in which the polygon mirror 133 deflects and scans the laser light is referred to as the main scanning direction, and the direction orthogonal to the main scanning direction and parallel to the rotation axis of the polygon mirror 133 is referred to as the sub scanning direction.

FIG. 6 shows an example of the beam spot. The spot diameter of the beam spot imaged on the surface of the photosensitive drum 1 is determined by the shape of the aperture 136. In this embodiment, as shown in FIG. 6, the width of the beam spot in the main scanning direction (spot diameter) is 80 μm, and the width in the sub scanning direction (spot diameter) is 90 μm. Here, a method for measuring the spot diameter of the beam spot will be described. FIG. 7 is a schematic graph for explaining the method of measuring the spot diameter. When the peak intensity is A, the spot diameter of the beam spot is represented by the width of the portion until the intensity decreases to A×1/e ² . The intensity distribution includes Gaussian distribution, Lorentz distribution, and the like. Further, the spot diameter was measured at 9 points where the image forming area was divided into 8 in the longitudinal direction, and the average value of the 9 points was defined as the spot diameter [μm]. Further, in general, the shape of the beam spot is often elliptical. Here, the spot diameter at each measurement point is the minimum value of the spot diameter D1 in the longitudinal direction (sub scanning direction in this embodiment) and the spot diameter D2 in the lateral direction (main scanning direction in this embodiment). The spot diameter D1 and the spot diameter D2 can be measured by using, for example, a beam analyzer manufactured by Melles Griot Co., Ltd.

On the other hand, a reflection mirror 131 is provided corresponding to an exposure (scanning) position on one end side of the photosensitive drum 1 in the rotation axis direction, and a laser beam projected at the exposure (scanning) start position is detected by a BD detection element (synchronization signal detection element). ) It is reflected toward 121. Then, the start timing of exposure (scanning) of the laser light is determined based on the output (scanning synchronization signal, BD signal) of the BD detection element 121. As will be described later, based on the output of the BD detection element 121, APC (Auto Power Control), which is automatic light amount control that makes the laser light amount a desired light amount, is performed to adjust the laser emission level. To be done.

6. Laser Driving System Circuit Next, a method of using the laser driving system circuit 130 to cause the LD 107 to emit a normal light emission amount and a minute light emission amount will be described. In this embodiment, this method is the same as that described in Patent Document 2, so an outline will be described below. Here, one image forming station U will be described as a representative, but in this embodiment, this method is substantially the same for all image forming stations U, and the light emission amount is controlled independently for each image forming station U. Is possible.

FIG. 8 is a schematic diagram showing a circuit for causing the LD 107 to emit light with a normal light emission amount and a minute light emission amount. Here, in order to facilitate understanding, a circuit for causing one light emitting unit 107A of the LD 107 to emit light will be described first. FIG. 9 shows a circuit for causing the two light emitting units 107A and 107B of the LD 107 to emit light, which will be described later. Further, in FIG. 8, the LD 107A will be described as the LD 107 for convenience. In FIG. 8, a portion surrounded by a dotted line 130 frame corresponds to the laser drive system circuit 130 shown in FIG.

The laser drive system circuit 130 includes a first light intensity adjusting unit 103 as a first current adjusting unit, a second light intensity adjusting unit 104 as a second current adjusting unit, first and second switching circuits 105 and 106, and a current voltage. It includes a conversion circuit 109, an image signal supply unit 124, and the like. The normal light emission amount (first light emission amount) and the minute light emission amount (second light emission amount) are independent by the first light intensity adjusting unit 103 and the second light intensity adjusting unit 104 as adjusting means for adjusting the respective light emitting amounts. Controllable.

The engine controller 101 as a control unit has an ASIC, a CPU, a RAM as a storage unit, an EEPROM, and the like. Further, the engine controller 101 performs not only control of the printer engine (mechanism portion for forming an image described with reference to FIG. 1) but also communication control with the video controller 102. The engine controller 101 inputs the reference voltage Vref11 to the first light intensity adjusting unit 103. Here, although not shown, the reference voltage Vref11 is determined by the pulse width of the signal of the PWM signal PWM1 and is controlled by the engine controller 101. The engine controller 101 also inputs the reference voltage Vref21 to the second light intensity adjusting unit 104. Although not shown here, the reference voltage Vref21 is determined by the pulse width of the signal of the PWM signal PWM2 and is controlled by the engine controller 101. Note that the reference voltages Vref11 and Vref21 may be directly output without instructing the PWM signal from the engine controller 101.

The Ldrv signal of the engine controller 101 and the VIDEO signal from the video controller 102 are input to the image signal supply unit 124, and the Data signal is output to the first switching circuit 105. The VIDEO signal is a signal based on print data sent from an external device such as a reader scanner or a host computer connected to the outside. The VIDEO signal is driven by image data of a multi-valued signal (0 to 255) of 8 bits (=256 gradations), for example, and is a signal for determining the laser emission time. Note that the case where the image data for controlling the LD 107 is 8 bits (=256 gradations) is an example, and the image data is, for example, 4 bits (=16 gradations) or 2 bits (4th gradation) after halftone processing. Key) may be used. The image data after the halftone process may be a binarized signal.

The reference voltage Vref11 is set as a target voltage for causing the LD 107 to emit light with a normal light emission amount. Further, the reference voltage Vref21 is set as a target voltage for the minute light emission amount. The first switching circuit 105 is turned on/off by a Data signal which is a pulse modulated data signal. The second switching circuit 106 is turned on/off by an input signal Base from the engine controller 101. The first and second switching circuits 105 and 106 are connected to the LD 107, and supply the drive currents Idrv and Ib from the first and second light intensity adjusting units 103 and 104, respectively, to the LD 107. A photodiode 108 (hereinafter, referred to as PD 108) that monitors the light amount of the LD 107 is connected to a current-voltage conversion circuit 109, and a monitor current Im according to the amount of received light is passed to the current-voltage conversion circuit 109. As a result, the current-voltage conversion circuit 109 converts the monitor current Im into the monitor voltage Vm. The monitor voltage Vm is input to the first and second light intensity adjusting units 103 and 104.

Although the engine controller 101 and the video controller 102 are shown separately in FIG. 8, the invention is not limited to this. For example, some or all of the engine controller 101 and the video controller 102 may be constructed by the same controller. Further, the laser drive system circuit 130 surrounded by a dotted frame in the figure may be partially or entirely incorporated in the engine controller 101, for example.

The engine controller 101 sets the second light intensity adjusting unit 104 to the non-sampling state and turns the second switching circuit 106 to the off operation state by the input signal Base. Further, the engine controller 101 sets the first light intensity adjusting unit 103 to the sampling state, turns on the first switching circuit 105 by the Data signal, and sets the LD 107 to the normal light emitting state. The period during which the first light intensity adjusting unit 103 is in the sampling state corresponds to the APC operation with the normal light emission amount. In this state, when the LD 107 is in the full-emission state, the current-voltage conversion circuit 109 converts the monitor current Im1 into the monitor voltage Vm1. Further, the first light intensity adjusting unit 103 controls the drive current Idrv so that the monitor voltage Vm1 matches the first reference voltage Vref11 that is the target value. During non-APC operation, that is, during normal image formation (time during which an image signal is sent), the first light intensity adjusting unit 103 is in a non-sampling state, and the first switching circuit 105 is turned on according to the Data signal. -Off operation is performed and pulse width modulation is applied to the drive current Idrv.

On the other hand, the engine controller 101 sets the first light intensity adjusting unit 103 to the non-sampling state and turns the first switching circuit 105 to the off operation state by the Data signal. Further, the engine controller 101 sets the second light intensity adjusting unit 104 in the sampling state, turns on the second switching circuit 106 by the input signal Base, and sets the LD 107 in the minute light emitting state. The period during which the second light intensity adjusting unit 104 is in the sampling state corresponds to the APC operation with the minute light emission amount. In this state, when the LD 107 is in the weak light emission state (lighting maintenance state) in the state where the light amount is weak, the current-voltage conversion circuit 109 converts the monitor current Im2 (Im1>Im2) into the monitor voltage Vm2. Further, the second light intensity adjusting unit 104 controls the drive current Ib so that the monitor voltage Vm2 matches the second reference voltage Vref21 that is the target value. Then, during non-APC operation, that is, during normal image formation (time during which an image signal is being sent), the second light intensity adjusting unit 104 is in a non-sampling state, and the entire surface is in a weak light emission state with a weak light amount. Is maintained.

The drive current Ib in the entire weak light emission state is set to be the small light emission amount P(Ib). The minute light emission amount P(Ib) is a light emission amount at which the toner does not substantially adhere to the photosensitive drum 1 even when laser irradiation is performed at that light emission amount, and is a light emission amount for improving the toner fog state. .. That is, the minute light emission amount P(Ib) is LD107 for forming the charging potential Vd_bg after the minute exposure by slightly exposing the non-image portion on the surface of the photosensitive drum 1 with the exposure amount Ebg [μJ/cm ² ]. [W] (amount of light emitted per unit time). The minute light emission amount P(Ib) is assumed to be the light emission amount of the LD 107 emitting laser light. If the minute light emission amount P(Ib) is the light emission amount of the LED light emission less than the laser light emission, the wavelength distribution of the spectrum is broadened, and the wavelength distribution is wider than the rated wavelength of the laser. Therefore, the sensitivity of the photosensitive drum is disturbed and the surface potential becomes unstable. Therefore, the minute light emission amount P(Ib) needs to be the light emission amount of the LD 107 that emits laser light.

On the other hand, the drive current Idrv+Ib during normal image formation is set to be the normal light emission amount P(Idrv+Ib). Note that the normal light emission amount P(Idrv+Ib) is a light emission amount at which the toner adhesion to the photosensitive drum 1 becomes saturated when laser irradiation is performed at that light emission amount. That is, the normal light emission amount P(Idrv+Ib) is the light emission amount [W] of the LD 107 for forming the exposure potential Vl by exposing the image portion on the surface of the photosensitive drum 1 with the exposure amount E [μJ/cm ² ]. (Amount of light emitted per unit time).

Here, the charging voltage Vcdc described with reference to FIG. 4 is variably set depending on the environment, deterioration of the photosensitive drum 1 (usage condition), and the like. From the viewpoint of maintaining the image quality, it is necessary to variably set the target minute light emission amount P(Ib). For example, if the value of Vdcd becomes large, the minute light emission amount also becomes large, while if the value of Vdcd becomes small, the minute light emission amount also becomes small. Then, when the LD 107 is caused to emit light at the normal light emission amount, the circuit of FIG. 8 is operated as follows. That is, the second light intensity adjusting unit 104 is set to the non-sampling state, the second switching circuit 106 is turned on, the first light intensity adjusting unit 103 is set to the non-sampling state, and the first switching circuit 105 is turned on. Make it work. As a result, the drive current Idrv+Ib is supplied to the LD 107. Further, the drive current Ib can be supplied to the LD 107 by turning off the first switching circuit 105. As described above, the normal light emission amount P(Idrv+Ib) is a light emission amount obtained by superposing the PWM light emission amount (added light emission amount) P(Idrv) by pulse width modulation on the minute light emission amount P(Ib). As a result, two levels of light emission are possible between the drive current Ib and Idrv+Ib, that is, the light emission amount between P(Ib) and P(Idrv+Ib). Further, at the normal light emission amount P(Idrv+Ib), the laser light emission at the time according to the pulse duty is performed based on the minute light emission amount P(Ib).

The circuit for causing one light emitting unit 107A of the LD 107 to emit light has been described above with reference to FIG. In this embodiment, the LD 107 has a so-called multi-beam structure including two light emitting units 107A and 107B. FIG. 9 shows a circuit for causing the two light emitting units 107A and 107B of the LD 107 to emit light. Elements having the same or corresponding functions as those in FIG. 8 are designated by the same reference numerals (the reference numerals of the elements for the first light emitting portion 107A are A, and the reference numerals of the elements for the second light emitting portion 107B). Is attached to B). The circuit shown in FIG. 9 basically has a configuration in which one portion surrounded by a dotted line frame 130 in FIG. 8 is provided for each of the first and second light emitting units 107A and 107B. However, the PD 108 and the current-voltage conversion circuit 109 are common. In FIG. 9, the portions surrounded by the dotted lines 130A and 130B correspond to the laser driving system circuits for the first and second light emitting units 107A and 107B, respectively. Therefore, the operations of the circuits surrounded by the dotted lines 130A and 130B in FIG. 9 for the first and second light emitting units 107A and 107B are the same as those described with reference to FIG.

7. Necessity of correction of LD light emission amount When the usage amount of the photosensitive drum is increased, the surface of the photosensitive drum is deteriorated by the discharge of the charging means, and the surface of the photosensitive drum is scraped by rubbing with the cleaning means, and the film thickness of the surface layer thereof. (The thickness of the charge transport layer in this example) becomes thin. At this time, if photosensitive drums having different usage states (for example, cumulative number of rotations) are mixed, the film thickness of each photosensitive drum varies. In this state, when a constant charging voltage Vcdc is applied to the plurality of photosensitive drums by the common high-voltage power supply as illustrated in FIG. 4, the potential difference generated in the air gap between the charging roller and the photosensitive drums is different, so that the charging is performed. The potential Vd varies. Specifically, since the photosensitive drum having a small number of times of image formation has a large film thickness and the potential difference generated in the air gap between the charging roller and the photosensitive drum is small, the absolute value of the charging potential Vd becomes small. On the other hand, since the photosensitive drum having a large cumulative number of rotations has a small film thickness and the potential difference generated in the air gap between the charging roller and the photosensitive drum is large, the absolute value of the charging potential Vd becomes large.

Then, for example, in a thick photosensitive drum, when the developing potential Vdc and the charging potential Vd are set so that the back contrast Vback (=Vd−Vdc) which is the contrast between the developing potential Vdc and the charging potential Vd becomes a desired state, There is such a problem. That is, as shown in FIG. 10A, in an image forming station having a thin photosensitive drum, the absolute value of the charging potential Vd becomes large and the back contrast Vback becomes large. When the back contrast Vback becomes large, the toner that cannot be charged to the normal polarity (in the case of reversal development as in this embodiment, toner that is not negative and is positive to 0) is discharged from the developing roller onto the photosensitive drum. Transferred to the non-image area and fogging occurred. Further, in the image forming station where the film thickness of the photosensitive drum is thin, the charging potential Vd rises, so that the exposure potential Vl also rises in the configuration where the exposure amount (exposure intensity) is constant. Therefore, the development contrast Vcont (=Vdc-Vl), which is the difference value between the development potential Vdc and the exposure potential Vl, becomes small, and the toner can be electrostatically sufficiently transferred from the developing roller to the image portion on the photosensitive drum. However, the density of the solid black image is likely to be low.

On the other hand, when the developing voltage and the charging voltage are fixed and the exposure amount is changed from E1 to E2 as shown in FIG. 10B, it is a difference value between the developing potential Vdc and the exposure potential Vl by the individual control of each exposure amount. The development contrast Vcont can be controlled to be substantially constant. Therefore, the concentration can be kept constant. However, the back contrast Vback, which is the contrast between the developing potential Vdc and the charging potential Vd, spreads, and the problem of fog remains as described above.

Therefore, in the present embodiment, as shown in FIG. 10C, the minute light emission amount and the normal light emission amount of each LD 107a to 107d are corrected by changing them in association with the remaining life of each photosensitive drum 1a to 1d. .. As a result, the minute exposure amount Ebg1 is corrected to the minute exposure amount Ebg2, and the normal exposure amount E1 is corrected to the normal exposure amount E2. As a result, even when the power source configuration illustrated in FIG. 4 is used, the charge amount (Vd_bg) of the non-image portion and the charge amount (Vl) of the image portion of each of the photosensitive drums 1a to 1d can be appropriately adjusted with a simple configuration. It is possible to control, and it is possible to suppress the occurrence of fogging and low density.

8. Correction of Light Emission Amount of LD Next, a process of correcting the light emission amount of the LD 107 will be described with reference to the flowchart of FIG. The process shown in FIG. 11 is executed by the CPU of the engine controller 101. Here, in order to describe the basic operation of correcting the light emission amount of the LD 107, it is assumed that the minute light emission thinning control described later is not performed.

First, in step (hereinafter, referred to as S) 101, the engine controller 101 reads information on the cumulative number of revolutions of the photosensitive drum 1 from the storage member 17 of each image forming station U as information on the remaining life of the photosensitive drum 1. .. In this embodiment, the storage member 17 of each image forming station U is a memory tag provided in each image forming station Ua to Ud. The information storage means may be, for example, a RAM or an EEPROM in the engine controller 101 as long as it can store necessary information.

Here, the information about the remaining life of the photosensitive drum 1 can be rephrased as the information about the usage status (usage amount) of how much the photosensitive drum 1 is rotated or used. Therefore, as the information regarding the remaining life of the photosensitive drum 1, typically, the cumulative number of rotations of the photosensitive drum 1 can be mentioned. Further, the information on the remaining life of the photosensitive drum 1 can be called the information on the sensitivity characteristic of the photosensitive drum 1 (FIG. 3). Further, as a modification of the information regarding the remaining life of the photosensitive drum 1, information regarding the film thickness of the photosensitive drum 1 can be given. The information about the film thickness of the photosensitive drum 1 includes, for example, the number of rotations of the intermediate transfer belt 10, the number of rotations of the charging roller 2, and the number of prints in consideration of the paper size, in addition to the cumulative number of rotations of the photosensitive drum 1. be able to. Further, a means for directly detecting the film thickness of the photosensitive drum 1 may be provided corresponding to each photosensitive drum 1, and the detection result may be used as information regarding the remaining life of each photosensitive drum 1. Further, the value of the charging current flowing through the charging roller 2, the motor driving time of the motor driving the photosensitive drum 1, the driving time of the motor driving the charging roller 2, and the like may be used as the information regarding the remaining life of the photosensitive drum 1.

In S102, the engine controller 101 refers to a table as shown in FIG. 12, in which the correspondence relationship between the cumulative number of revolutions of the photosensitive drum 1 (usage condition of the photosensitive drum 1) and the parameter of the normal exposure amount is determined. The table of FIG. 12 will be further described later. The information acquired in S101 may differ for each photosensitive drum 1. Therefore, the engine controller 101 refers to the table of FIG. 12 for each photosensitive drum 1. Then, the engine controller 101 sets the above-mentioned reference voltage Vref11 corresponding to the normal light emission amount (mW) as a parameter of the normal exposure amount of the LDs 107a to 107d based on the information on the integrated rotation speed acquired in S101. Through the processing of S102, the engine controller 101 sets the normal light emission amount for setting the exposure potential Vl of each photosensitive drum 1 to a target potential or a potential within an allowable range regardless of the sensitivity characteristic of each photosensitive drum 1. get. Then, by causing the LDs 107a to 107d to normally emit light with this acquired setting, it is possible to at least reduce the variation in the exposure potential Vl after the normal exposure in each of the plurality of photosensitive drums 1, and to realize a desired potential. Although the target exposure potential (corresponding to Vref11) of each photosensitive drum 1 is typically substantially the same, it may be set individually according to the characteristics of each photosensitive drum 1 in some cases.

The operation by the engine controller 101 in S102 will be described in more detail. First, the engine controller 101 sets the light emission amount (mW) corresponding to the acquired information on the integrated rotation speed of each photosensitive drum 1 as Vref11a to Vref11d according to the PWM signal instruction. Note that although the light emission amount (mW) is shown in FIG. 12 for the sake of explanation, the engine controller 101 actually outputs a voltage value/signal corresponding to this light emission amount (mW) by Vref11a to Vref11d according to the PWM signal instruction. Set as. Further, the engine controller 101 sets the PWM value for normal exposure when the image density is 0% to PW _MIN, and sets the PWM value for normal exposure when the image density is 100% to PW ₂₅₅ . Then, the engine controller 101 sets a pulse width for image data of an arbitrary gradation value n (=0 to 255) by the following equation (1).
_{PW n = n × (PW 255} -PW MIN) / 255 + PW MIN ··· formula (1)

According to equation _{(1), PW 0 = PW} MIN next with n = 0, the _{PW 255} at n = 255. Then, when the engine controller 101 is externally instructed to emit light with image data having an arbitrary gradation value n, the engine controller 101 outputs a voltage value/signal corresponding to the corresponding pulse width (PW _n ) set here. , VIDEO signal a. The same applies to the VIDEO signals b to d.

Explaining the next step, in S103, the engine controller 101 uses the above-mentioned reference voltage Vref21 corresponding to the minute light emission amount (mW) as a parameter of the minute exposure amount based on the integrated rotation speed of the photosensitive drum 1. To set. Also in this S103, the engine controller 101 refers to the table of FIG. 12 for each photosensitive drum 1. More specifically, the engine controller 101 reads out the Vref21 value (PWM value) corresponding to the information of the integrated rotation speed acquired in S101 for each photosensitive drum 1, and sets it to Vref21a to Vref21d. Through the processing of S103, the engine controller 101 sets the charging potential Vd of each photosensitive drum 1 to the target potential (value of the corrected charging potential Vd_bg) or the allowable range potential regardless of the sensitivity characteristic of the photosensitive drum. It is possible to acquire the setting of the minute light emission amount of. Then, the laser drive system circuit 130 performs APC with the acquired settings and, under the control thereof, causes the LDs 107a to 107d to slightly emit light, thereby correcting the background portion (non-image portion) of each of the plurality of photosensitive drums 1. It is possible to at least reduce the variation in the post-charge potential. The target minute exposure potential (corresponding to the Vref21 value) of each photosensitive drum 1 is typically substantially the same, but may be individually set according to the characteristics of each photosensitive drum 1 in some cases.

As described above, by performing the processing of S102 and S103, the minute light emission amount for the minute exposure and the normal light emission amount for the normal exposure are appropriately set in relation to the remaining life of each photosensitive drum 1. It is possible to appropriately set the exposure amounts of the non-image portion and the image portion of the.

Note that, in S102 and S103, the engine controller 101 has been described as referring to the table in FIG. 12, but the present invention is not limited to that form. For example, the CPU in the engine controller 101 may be configured to calculate a calculation formula. That is, the CPU may perform the calculation to obtain a desired set value (Vref11a to Vref11d or Vref21a to Vref21d) from the parameter (for example, the integrated rotation speed of the photosensitive drum) regarding the remaining life of the photosensitive drum 1. Alternatively, for example, all the values calculated by the equation (1) may be stored in a table in advance and the table may be referred to by the engine controller 101 each time. Further, the storage member 17 may store and hold a plurality of types of sensitivity characteristics corresponding to each usage state of the photosensitive drum 1 as shown in FIG. In this case, the engine controller 101 specifies the sensitivity characteristic according to the acquired information regarding the usage status of the photosensitive drum 1, and further, the required exposure amount [μJ/ cm ² ] is calculated. Then, the engine controller 101 sets the parameters of the light emission amount corresponding to those set in S102 and S103, from the exposure amount [μJ/cm ² ] obtained each time.

Returning to the description of FIG. 11, in S104, each member executes the series of image forming operations and control described in FIG. 1 under the control instruction of the engine controller 101. Further, in S105, the engine controller 101 measures the number of rotations of each of the photosensitive drums 1a to 1d rotated in a series of image formation. The measurement process is performed to update the usage status of the photosensitive drum 1. In addition, this S105 is actually performed in parallel with the process of S104.

The engine controller 101 determines in S106 whether or not the image formation is completed. If it is determined in S106 that the image formation is completed, the engine controller 101 shifts the processing to S107. In S107, the engine controller 101 adds the measurement result of each photosensitive drum 1 measured in S105 to the corresponding cumulative rotation speed, and in S108, the updated cumulative rotation speed of each image forming station U. It is stored in the non-volatile storage member 17. By the processing of S108, the information regarding the remaining life of the photosensitive drum 1 is updated. Note that the storage destination here may be a storage unit other than the storage member 17 as described in S101.

Here, the correction table of FIG. 12 will be further described. FIG. 12 is a diagram showing an example of a table that the engine controller 101 refers to in S102 and S103 of FIG. The table in FIG. 12 is a table in which information regarding the remaining life of the photosensitive drum 1 (in the figure, the cumulative number of revolutions of the photosensitive drum 1) is associated with the setting of the minute light emission amount and the normal light emission amount. In FIG. 12, the light emission amount (mW) is shown as a setting of the light emission amount for convenience, but as described above, the reference voltages Vref11a to Vref11d corresponding to this light emission amount (mW) or this reference voltage is designated. The PWM value may be set. Further, the light emission amount in FIG. 12 is a minute exposure amount [μJ/cm ² ] required to obtain the desired charge amount on the surface of the photosensitive drum 1 based on the sensitivity characteristics illustrated in FIG. It is preset according to [μJ/cm ² ]. In FIG. 12, the minute light emission amount and the normal light emission amount indicate the light emission amount necessary for the entire LD 107 (that is, both the first and second light emitting units 107A and 107B). In this embodiment, it is assumed that the light emission amount obtained by dividing the light emission amount shown in FIG. 12 into two equal amounts is required for the first and second light emitting units 107A and 107B, respectively, unless the minute light emission thinning described later in detail is performed. Further, in FIG. 12, the normal light emission amount indicates a value obtained by adding the light emission amount (additional light emission amount) to be superimposed on the minute light emission amount. Actually, the setting corresponding to the added light emission amount for causing the LD 107 to emit light at the light emission amount during normal exposure is set to Vref11 or the PWM value corresponding thereto. By referring to the table as shown in FIG. 12 by the engine controller 101, it is possible to eliminate or at least reduce the variation in the surface potential of the background portion of each of the plurality of photosensitive drums 1 after charging. Further, it is possible to eliminate or at least reduce the variation of the exposure potential Vl in each of the plurality of photosensitive drums 1 after the normal exposure. Information of the table as shown in FIG. 12 is preset and stored in the EEPROM of the engine controller 101.

In the table illustrated in FIG. 12, both the minute light emission amount and the normal light emission amount change. By referring to the table in FIG. 12, the engine controller 101 can appropriately set not only the minute light emission amount but also the normal light emission amount in association with the cumulative rotation speed of the photosensitive drum 1. The minute light emission amount and the normal light emission amount may be increased linearly or non-linearly according to the integrated rotation speed of the photosensitive drum 1 in consideration of the characteristics of the photosensitive drum 1.

9. Slight emission thinning control As described above, when the laser element is used at the normal emission amount and the minute emission amount, the use range of the chip surface light amount (emission brightness, emission intensity, emission amount, emission level) of the laser device becomes large. .. Then, depending on the conditions such as the film thickness and material of the photosensitive drum 1, the life, or the optical efficiency of the laser scanner, the minimum value of the usage range of the minute light emission amount may fall below the lower limit guaranteed value of the light amount on the chip surface of the laser element. is there. In that case, the amount of charge on the surface of the photosensitive drum 1 cannot be optimized.

Therefore, in the present embodiment, when each light emitting portion of the two-beam semiconductor laser diode emits a small amount of light, it is necessary to use less than the lower limit guaranteed value of the chip surface light amount of each light emitting portion. Fine light emission is thinned out for each arbitrary light emitting portion of the laser diode. This makes it possible to optimize the amount of charge on the surface of the photosensitive drum 1.

An example of the minute light emission thinning control when the resolution in image formation is 600 dpi×600 dpi will be described. At this time, the 1 dot width (in the main scanning direction and the sub scanning direction) in image formation is 42.3 μm, and the spot diameter of the laser spot is as shown in FIG. 6 (80 μm in the main scanning direction, 90 μm in the sub scanning direction). There is.

FIG. 13 is an example of a timing chart of laser scanning by the exposure device 31 when the thin light emission thinning is performed in the image forming apparatus 100 of the present embodiment. In FIG. 13, the horizontal axis represents time (t) and the vertical axis represents the light emission amount (chip surface light amount) of the first light emitting unit 107A and the second light emitting unit 107B.

The image area in FIG. 13 is the timing (area) at which the surface of the photosensitive drum 1 can be exposed to the laser light with which the polygon surface 133-1 of the polygon mirror 133 is exposed with the normal light emission amount. Further, the minute light emission area in FIG. 13 is the timing (area) at which the surface of the photosensitive drum 1 can be exposed to the laser light with which the polygon surface 133-1 of the polygon mirror 133 is exposed with a small amount of light emission. is there.

In FIG. 13, times t0 to t1 and t10 to t11 are APC timings for normal light emission in the first light emitting unit 107A. Further, times t1 to t3 and t11 to t13 are APC timings for normal light emission in the second light emitting unit 107B.

Further, in FIG. 13, times t2 to t3 and t12 to t13 are BD signal detection timings. At this time, one scan is performed from the BD detection timing from time t2 to t3 to the BD detection timing from time t12 to t13. More specifically, one scan is performed from time t2 to t12 or time t3 to t13.

Further, in FIG. 13, times t3 to t4 are APC timings for minute light emission in the first light emitting unit 107A. Further, times t9 to t10 are the minute light emission APC timing in the second light emitting unit 107B.

Further, in FIG. 13, times t4 to t5 and t8 to t9 are non-emission timings (non-emission areas). Further, the times t5 to t8 are the minute light emission timing (minute light emission area). Further, the times t6 to t7 are normal light emission timings (image areas).

Then, each operation (region) in one scan described above is repeatedly performed until image formation is completed.

In the main scanning direction, the small light emitting area is wider than the image area, and the image area is inside the small light emitting area. Further, in the present embodiment, in the main scanning direction, the minute light emitting area is wider than the area corresponding to the edge portion of the recording material P, and the area between the edge portions of the recording material P is within the minute light emitting area. .. Further, in the present embodiment, the width of the minute light emitting area in the main scanning direction is equal to the photosensitive area (effective area) of the photosensitive drum 1 in the main scanning direction. Further, in the present embodiment, APC is performed in a region outside the minute light emitting region, particularly in a region opposite to the minute light emitting region with the non-light emitting region sandwiched therebetween. In addition, in the present embodiment, the light emission unit (the first light emission unit 107A or the second light emission unit 107A or the second light emission unit 107A or the second light emission unit that turns off the light in the region corresponding to the non-image region in the image emission region and in the image emission region by the minute emission emission thinning control. The APC for minute light emission is also performed on the light emitting unit 107B). This is to stabilize the normal light emission amount because the normal light emission amount is obtained by superimposing the added light emission amount on the minute light emission amount in this embodiment. At this time, the APC for minute light emission of the light emitting unit (the first light emitting unit 107A or the second light emitting unit 107B) that is turned off by the minute light emission thinning control is a light emission amount larger than the lower limit guaranteed value of the chip surface light amount (typically, a minute light emission. The light emission amount is the same as that of the light emitting unit which is not turned off by the thinning control.

Note that the execution frequency of APC can be set as follows independently for each of the first and second light emitting units 107A and 107B for normal light emission and for minute light emission. That is, it may be performed for each laser scan, for each page (only the first one scan of the page), or for each predetermined number (two or more) of laser scans. However, in particular, by performing APC for minute light emission a plurality of times in one job, the charging potential Vd can be more appropriately maintained throughout one job, and reversal fog and positive fog can be suppressed more effectively.

Here, in the control of the light emission amount of the LD 107 described with reference to FIG. 11, for example, the laser drive control is performed by setting the normal light emission amount of the entire LD 107 to 8.0 [mW] and the minute light emission amount to 0.30 [mW]. It is assumed that it is necessary to do so. In this embodiment, the lower limit guaranteed value of the light amount on the chip surface of each of the first and second light emitting units 107A and 107B of the LD 107, which is a two-beam semiconductor laser diode, is 0.20 [mW]. As described above, in this embodiment, when the minute light emission thinning is not performed, the light emission amount obtained by dividing the light emission amount of the LD 107 obtained by referring to the table of FIG. , Respectively required for the first and second light emitting units 107A and 107B. Therefore, in the case of this example, the first and second light emitting units 107A and 107B of the LD 107 need to perform laser drive control with a normal light emission amount of 4.0 [mW] and a minute light emission amount of 0.15 [mW], respectively. There is. In the case of this example, as described above, the lower limit guaranteed value of the light amount on the chip surface of each of the first and second light emitting units 107A and 107B of the LD 107 is 0.20 [mW]. Therefore, in the case of this example, with the obtained value, the first and second light emitting portions 107A and 107B of the LD 107 are used below the lower limit guaranteed value of the light amount on the chip surface at the time of slight light emission.

The light amount on the chip surface is the light amount on the end face of the laser element that emits laser light. Here, the light emission amount of the laser element means the light amount on the chip surface. The lower limit guaranteed value of the light amount on the chip surface is the lower limit value (smallest light amount value) of the light amount of the laser light that can be emitted by the laser element (or each light emitting unit) that emits the laser light. Typically, the lower limit of the light emission amount guaranteed by the manufacturer is applicable. As can be seen from the table of FIG. 12, in the present embodiment, in the initial stage of use of the photosensitive drum 1, the amount of light obtained by halving the total amount of minute light emission required for slightly emitting the LD 107 is 0.15 [mW]. Becomes Therefore, in this embodiment, the light emission amount of each of the light emitting units 107A and 107B becomes less than the guaranteed lower limit value of the light amount on the chip surface in the initial use of the photosensitive drum 1. The lower limit guaranteed value of the light amount on the chip surface of each light emitting unit is typically substantially the same, but may be different depending on the characteristics of each light emitting unit in some cases. In that case, it is possible not to use below the lower limit guaranteed value for each light emitting unit, or to use below the largest lower limit guaranteed value among a plurality of different lower limit guaranteed values.

Therefore, in the present embodiment, in the case of the above example, as shown in FIG. 13, with respect to the first light emitting portion 107A, the minute light emission amount is set to 0.30 [mW], and the LD 107 as a whole is set as described above. The required minute light emission amount is divided into two equal parts and is twice the minute light emission amount 1.50 [mW]. Then, with respect to the second light emitting unit 107B, the laser drive control is performed such that the minute light emission is not performed (thin light emission is thinned out) in the minute light emission region from time t5 to t8. On the other hand, the normal light emission amount is set to 4.0 [mW] for both the first and second light emitting units 107A and 107B. That is, the second light emitting unit 107B does not perform the minute light emission in the region outside the image emitting region and the minute light emitting region, and does not perform the minute light emitting in the region corresponding to the non-image portion in the image region. As a result, the minute light emission amount of the entire LD 107 in the minute light emission region becomes 0.30 [mW], and the average minute light emission amount for each scanning is the minute amount required by the entire LD 107 obtained as described above. It is the same as the light emission amount. That is, while the LD 107 emits light at a light emission amount that is equal to or higher than the lower limit guaranteed value of the chip surface light amount of each light emitting unit 107A, 107B, the average minute light emission amount for each scan is the required minute light emission amount obtained as described above. A light emission amount substantially equal to is obtained. Therefore, the charge amount (surface potential) of the surface of the photosensitive drum 1 can be set to the optimum charge amount. As described above, the APC for minute light emission is also performed on the second light emitting unit 107B that stops the minute light emission in the minute light emitting region.

As described above, when the minute light emission thinning is performed, the minute light emission amount of the first light emitting unit 107A that slightly emits light in the minute light emitting region is equal to or more than the lower limit guaranteed value of the chip surface light amount, and when the minute light emission thinning is not performed. Greater than a small amount of light emission. In addition, the amount of minute light emission in the entire LD 107 is substantially equal when the thin light emission thinning is not performed and when the minute light emission thinning is performed. In particular, in this embodiment, since the LD 107 has two light emitting units 107A and 107B, when performing thin light emission thinning, the minute light emission amount of the light emitting unit that slightly emits light in the small light emitting area is the thin light emission thinning. The light emission amount is doubled, which is an integral multiple of the minute light emission amount when not performed.

FIGS. 14A and 14B are schematic diagrams of beam spots formed on the photoconductor when the small light emission thinning is not performed and when it is performed. The horizontal axis direction in FIGS. 14A and 14B corresponds to the main scanning direction, and the vertical axis direction corresponds to the sub scanning direction. FIG. 14A shows the relationship between the 1-dot width and the spot diameter when the minute light emission thinning is not performed. Further, FIG. 14B shows the relationship between the 1 dot width and the spot diameter in the case of performing the thinning out of the small amount of light. In this embodiment, the 1 dot width (1 line width) in the sub-scanning direction is 42.3 μm. Further, in this embodiment, the width (spot diameter) of the beam spot on the photosensitive drum 1 in the sub-scanning direction is 90 μm. Therefore, even when the second light emitting unit 107B does not emit the minute light emission in the minute light emission region, the beam spots due to the adjacent minute light emission in the sub-scanning direction partially overlap each other. Accordingly, even when performing thin emission thinning, it is possible to reduce unevenness of the minute exposure amount in the rotation direction (sub-scanning direction) of the photosensitive drum 1 and increase the uniformity of the charge amount on the surface of the photosensitive drum 1 due to the minute exposure. You can

FIG. 15 is a flowchart of a process of correcting the light emission amount of the LD 107 including the minute light emission thinning control in the present embodiment. In the process shown in FIG. 15, the same operation (process) as the basic operation of the process for correcting the light emission amount of the LD 107 described with reference to FIG. Detailed explanation is omitted. The process shown in FIG. 15 is executed by the CPU of the engine controller 101.

After acquiring the setting of the minute light emission amount by the process of S103, the engine controller 101 determines that the minute light emission amount of each light emitting unit 107A, 107B of the LD 107 is the lower limit guaranteed value of the chip surface light amount of each light emitting unit 107 in the obtained setting. It is determined whether or not the above (S201). At this time, in the present embodiment, as described above, in the table of FIG. 12, the setting of the minute light emission amount is set as the minute light emission amount of the entire LD 107. Therefore, the minute light emission amount required for each of the light emitting units 107A and 107B obtained by dividing the minute light emission amount into two equal parts is compared with the lower limit guaranteed value of the chip surface light amount. Information regarding the lower limit guaranteed value is stored in advance in the EEPROM of the engine controller 101.

If the engine controller 101 determines in S201 that the value is equal to or higher than the lower limit guarantee value, the process proceeds to S104, and thereafter, the same process as described with reference to FIG. 11 is performed without performing the thin light emission thinning. To do.

On the other hand, when the engine controller 101 determines in S201 that the value is less than the guaranteed lower limit value, it determines to perform the thin light emission thinning (S202). Further, at this time, the engine controller 101 determines a light emitting unit that stops the minute light emission in the minute light emitting region and a minute light emitting amount in the light emitting unit that emits the minute light emitting in the minute light emitting region. In this embodiment, the light emitting portion that stops the minute light emission in the minute light emitting region is the second light emitting portion 107B. Further, in the present embodiment, the small amount of light emitted from the light emitting unit that emits a small amount of light in the small light emitting region is twice the amount of small amount of light emission required for each of the light emitting units 107A and 107B compared with the lower limit guaranteed value in S201, that is, in S103. It is assumed that the obtained LD 107 has a necessary minimum amount of light emission. After that, the engine controller 101 thins out a small amount of light emission and performs the same processing as described with reference to FIG.

In the present embodiment, whether or not to perform the thin light emission thinning is determined by obtaining the minute light emission amounts necessary for the light emitting units 107A and 107B of the LD 107 and comparing the minute light emission amounts with the lower limit guaranteed value. The minute light emission amount of the light emitting portion that emits a minute light in the minute light emitting region was determined. However, the present invention is not limited to such an aspect. For example, the relationship between the information about the remaining life (usage status) of the photosensitive drum 1 as shown in FIG. 16 and the setting of the minute light emission amount and the normal light emission amount of each of the light emitting units 107A and 107B of the LD 107 in consideration of the thin light emission thinning are shown. Each light emission amount may be determined with reference to the table shown.

Further, in the present embodiment, the image forming apparatus 100 changes the normal light emission amount and the minute light emission amount according to the information regarding the remaining life (usage status) of the photosensitive drum 1 (information correlated with the film thickness of the photosensitive drum 1). It is configured to let. Then, in this embodiment, in such a configuration, only when it is necessary to use the light emitting portions 107A and 107B of the LD 107 at less than the lower limit guaranteed value of the chip surface light amount in the minute light emission according to the remaining life of the photosensitive drum 1. , Thin emission was thinned out. However, the present invention is not limited to such an aspect. For example, although it is desired to increase the total amount of light emission by using a plurality of light emitting units, when a plurality of light emitting units are used, the use range of the minute light emitting amount of each light emitting unit is irrespective of factors such as the usage status of the photosensitive drum. A configuration in which the minimum value falls below the lower limit guaranteed value of the amount of light on the chip surface can be considered. In such a configuration, regardless of factors such as the usage status of the photosensitive drum, the same minute emission thinning as in the present embodiment may be performed to control the laser drive.

As described above, in the present embodiment, the control unit 101 normally sets the normal light emission amount for irradiating the first light emitting unit 107A to the image unit in one scan of the light from the light emitting element 107 by the scanning unit 133. While emitting light, a small amount of light for irradiating a non-image portion smaller than the normal amount of light is made to emit a small amount of light, and the second light emitting part 107B is made to emit a normal amount of light for irradiating the image part, It is possible to perform control (fine emission thinning control) that does not perform minute emission with a small emission amount for irradiating a non-image portion smaller than the normal emission amount. In this embodiment, the control unit 101 emits the second light emission when both the first light emission unit 107A and the second light emission unit 107B emit light in order to obtain the light emission amount of the light emission element 107 for irradiating the non-image portion. The light emission amount of the portion 107B is obtained. Then, the control unit 101 performs the minute light emission thinning control when the light emission amount is less than the predetermined light emission amount. At this time, the minute light emission amount of the first light emitting unit 107A in the case of performing the minute light emission thinning control is larger than the above-obtained light emission amount of the second light emitting unit 107B. In other words, in this embodiment, the control unit 101 divides the light emission amount of the light emitting element 107 for irradiating the non-image portion by the number of light emitting portions included in the light emitting element 107 so that the light emission amount is less than the predetermined light emission amount. In this case, the minute light emission thinning control is performed. At this time, the minute light emission amount of the first light emitting unit 107A in the case of performing the minute light emission thinning control is larger than the above equally divided light emission amount. Further, in the present embodiment, the predetermined light emission amount is the lower limit guaranteed value of each light emitting unit included in the light emitting element 107. In addition, in the present embodiment, when performing the slight emission thinning control, the spots of the light irradiating the non-image portion that are adjacent to each other in the direction (sub scanning direction) orthogonal to the predetermined direction (main scanning direction) are , Some overlap. Further, in this embodiment, the image forming apparatus 100 has an acquisition unit 17 that acquires information regarding the remaining life of the photoconductor 1. Then, the control unit 101 can change the light emission amount of the light emitting element 107 for irradiating the non-image portion based on the acquisition result of the acquisition unit. In other words, the image forming apparatus 100 may include an acquisition unit that acquires information regarding the film thickness of the surface layer of the photoconductor 1. Then, the control unit 101 may be able to change the light emission amount of the light emitting element 107 for irradiating the non-image portion based on the acquisition result of the acquisition unit. Further, in the present embodiment, the image forming apparatus 100 includes a plurality of image forming units U each including the photoconductor 1, the charging unit 2, the light irradiation unit 31, and the developing unit 4. .. In this case, a voltage may be supplied from a common power source to the charging unit 2 of the plurality of image forming units U, or the charging unit 2 and the developing unit 4 of the plurality of image forming units U. In this case, the control unit 101 can independently control the light irradiation units 31 of the plurality of image forming units U.

As described above, according to this embodiment, the light emitting portions 107A and 107b of the two-beam semiconductor laser diode 107 can be driven with the chip surface light amount equal to or higher than the lower limit guaranteed value of the chip surface light amount. Therefore, the amount of charge on the surface of the photosensitive drum 1 can be set to an optimum value.

[Example 2]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, in the image forming apparatus according to the present exemplary embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus according to the first exemplary embodiment will be denoted by the same reference numerals as those in the first exemplary embodiment, and detailed description thereof will be omitted. ..

In the first embodiment, the LD 107, which is the laser element of the exposure apparatus 31, has the two light emitting units 107A and 107B, but the number of light emitting units included in the laser element is not limited to two. The number of light emitting units included in the laser element may be three or more.

FIG. 17 shows a case where the LD 107 has three light emitting portions, that is, the first, second, and third light emitting portions 107A, 107B, and 107C, on the photoconductor with and without fine light emission thinning. It is a schematic diagram of the beam spot imaged on. FIG. 17A shows the relationship between the 1-dot width and the spot diameter when the minute light emission thinning is not performed. Further, FIG. 17B shows the relationship between the 1 dot width and the spot diameter in the case of performing the thin light emission thinning. Here, a case is shown in which the second light emitting unit 107B of the first, second, and third light emitting units 107A, 107B, and 107C stops the minute light emission in the slight light emission thinning control. The 1 dot width and the spot diameter in this embodiment are the same as those in the first embodiment.

Also in this case, the minute light emission amounts of the first and third light emitting units 107A and 107C, which emit a small amount of light in the minute light emitting region when performing the thin light emission thinning, are equal to or higher than the lower limit guaranteed value of the light amount on the chip surface, and are small. It is larger than the minute light emission amount when light emission thinning is not performed. In addition, the amount of minute light emission in the entire LD 107 is substantially equal when the thin light emission thinning is not performed and when the minute light emission thinning is performed. In the case where there are a plurality of light emitting portions that emit a small amount of light in the minute light emitting region when performing the thin light emitting thinning, typically, the minute light emitting amounts of the plurality of light emitting portions are substantially the same, but they may be different according to need. Good.

Also in this case, the minute light emission of the central second light emitting unit 107B in the sub-scanning direction is stopped so that the beam spots due to the adjacent minute light emission in the sub-scanning direction partially overlap each other. Accordingly, even when performing thin emission thinning, it is possible to reduce unevenness of the minute exposure amount in the rotation direction (sub-scanning direction) of the photosensitive drum 1 and increase the uniformity of the charge amount on the surface of the photosensitive drum 1 due to the minute exposure. You can Whether or not to perform the minute light emission of each light emitting portion in the thin light emission thinning can be determined according to the spot diameter of the beam spot on the photosensitive drum 1 and the one-line width in the sub-scanning direction calculated from the number of pixels. it can.

As described above, according to the present embodiment, even in the configuration in which the laser element has the three light emitting units 107A, 107B, and 107C, the same minute light emission thinning control as in the first embodiment is performed, and thus the same as in the first embodiment. The effect of can be obtained.

[Other]
Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above embodiments.

For example, in the above-described embodiments, the present invention is applied to a so-called tandem type color image forming apparatus. The present invention provides a tandem type color image forming apparatus, for example, a voltage is supplied from a common power source to a charging unit of a plurality of image forming units or a charging unit and a developing unit, and the charge amount of a photoconductor is changed in each image forming unit. This can be said to be particularly effective when individual control cannot be performed. However, the present invention can also be applied to a monochrome image forming apparatus having only one photoconductor, for example, when using a light irradiation unit having a light emitting element having a plurality of light emitting units. This makes it possible to appropriately control the charge amount of the photoconductor by appropriate exposure control regardless of the control capability of the power supply that supplies the voltage to the charging unit and the developing unit.

Further, in the above-described embodiment, the light emission amount is set to 0 by stopping the light emission of the light emitting portion which does not perform the minute light emission in the minute light emission region in the minute light emission thinning control. However, depending on, for example, the configuration of the light emitting element or the driving circuit, the light emission amount of the light emitting portion that does not perform the minute light emission in the minute light emission region in the minute light emission thinning control is not completely 0, and an appropriate minute exposure is required. There may be a case where a slight amount of light that is less than the required amount is emitted. This case also includes not performing the minute light emission in the minute light emission region in the minute light emission thinning control.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 4 Developing device 31 Exposure device 100 Image forming device 101 Engine controller 107 Two-beam semiconductor laser diode 130 Laser drive system circuit 133 Polygon mirror

Claims (10)

A photoconductor,
Charging means for charging the photoreceptor,
Light emitting means for irradiating the charged photosensitive member with light to form an electrostatic image on the photosensitive member including an image portion to which toner is attached and a non-image portion to which toner is not attached, the first light emitting portion A light emitting element having a second light emitting portion; a scanning means for deflecting light from the light emitting element to scan the photosensitive member in a predetermined direction;
Developing means for supplying toner to the electrostatic image formed on the photoconductor to form a toner image;
Control means for controlling the light irradiation means,
Have
The control unit causes the first light emitting unit to normally emit light at a normal emission amount for irradiating the image unit in one scan of the light from the light emitting element by the scanning unit, and the normal emission amount. A small amount of light is emitted to irradiate the non-image area, which is smaller than the normal light emission amount, and the second light emitting unit is normally emitted to emit a normal light amount to irradiate the image portion. An image forming apparatus capable of performing control so as not to perform a minute light emission with a minute light emission amount for irradiating a small non-image portion. The control means emits light from the second light emitting portion when both the first light emitting portion and the second light emitting portion emit light in order to obtain the light emission amount of the light emitting element for irradiating the non-image portion. The amount of light is obtained, and when the amount of light emission is less than a predetermined amount of light emission, the control is performed so as not to perform minute light emission with a small amount of light emission for irradiating the non-image part of the second light emitting part The image forming apparatus according to claim 1. The minute light emission amount of the first light emitting unit when the control is performed so as not to perform the minute light emission with the minute light emission amount for irradiating the non-image portion of the second light emitting unit, The image forming apparatus according to claim 2, wherein the light emitting amount is larger than the two light emitting units. The control unit controls the second light emission when the light emission amount obtained by equally dividing the light emission amount of the light emitting element for irradiating the non-image portion with the number of light emitting units included in the light emitting element is less than a predetermined light emission amount. The image forming apparatus according to claim 1, wherein the control is performed so as not to perform the minute light emission with the minute light emission amount for irradiating the non-image portion of the image portion. The minute light emission amount of the first light emitting unit in the case of performing the control not to perform the minute light emission with the minute light emission amount for irradiating the non-image portion of the second light emitting unit is the equally divided light emission amount. The image forming apparatus according to claim 4, wherein the image forming apparatus is larger than the above. The image forming apparatus according to claim 2, wherein the predetermined amount of light emission is a lower limit guaranteed value of each light emitting unit included in the light emitting element. In the case of performing the control not to perform the minute light emission with the minute light emission amount for irradiating the non-image portion of the second light emitting portion, the non-image portion adjacent to the non-image portion in the direction orthogonal to the predetermined direction is The image forming apparatus according to claim 1, wherein the irradiated light spots partially overlap each other. Having an acquisition means for acquiring information about the remaining life of the photoconductor,
8. The control unit is capable of changing a light emission amount of the light emitting element for irradiating the non-image portion based on an acquisition result of the acquisition unit. The image forming apparatus according to item 1. Having an acquisition means for acquiring information about the film thickness of the surface layer of the photoreceptor,
8. The control unit is capable of changing a light emission amount of the light emitting element for irradiating the non-image portion based on an acquisition result of the acquisition unit. The image forming apparatus according to item 1. A plurality of image forming units, each of which includes the photoconductor, the charging unit, the light irradiation unit, and the developing unit,
A voltage is supplied from a common power source to the charging unit of the plurality of image forming units, or the charging unit and the developing unit of the plurality of image forming units,
The image forming apparatus according to claim 1, wherein the control unit is capable of independently controlling the light irradiation units of the plurality of image forming units.

Images