JP5473276B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming equipment for forming an image by using a plurality of irradiation light emitted from the plurality of light sources.

  Conventionally, in an electrophotographic image forming apparatus that forms an image by optically scanning a photosensitive drum such as a laser beam printer, a scanning optical system that condenses laser light with a lens system and deflects and scans with a polygon mirror is often used. Has been.

  In an image forming apparatus having such a scanning optical system, a technique for forming an image by simultaneously scanning a plurality of beams by increasing the number of emitted lasers is proposed in order to cope with an increase in printing speed and resolution. Has been.

  Compared with the method of increasing the writing speed by increasing the speed of the polygon mirror, the method of increasing the number of lasers that emit light can increase the speed and resolution without increasing the rotational speed of the polygon mirror and the image clock. Therefore, it does not cause problems such as shortening the service life by increasing the speed of the polygon mirror, temperature rise and noise of the scanner, and it is not necessary to take measures to increase the speed of the laser drive circuit and transmission path by increasing the image clock speed. You can increase the speed.

  In particular, in a surface emitting laser (VCSEL), it is easy to array light emitting points, and many light emitting points can be arranged on one chip. In a scanning optical system using a surface emitting laser capable of arranging a plurality of light emission sources on one chip, a plurality of laser beams can be incident on a common lens system and a polygon mirror to perform optical scanning. For this reason, it is possible to increase the number of beams without changing the configuration of the optical system, compared to an optical system that scans a single beam.

  By the way, in an image forming apparatus that scans with laser light, a technique for performing light amount control (hereinafter referred to as APC: Automatic Power Control) is used in order to keep the light amount of a beam on a scanning surface constant during image formation. . As an APC method, the laser is turned on for a certain period, and the light emission amount of the laser light is detected by a PD (photodiode) that is built in or outside the laser, and performs laser detection according to the detected light amount. There is a method for feedback control of the drive current.

  Here, the PD outputs a current corresponding to the received light amount (incident light amount). This output current is converted into a voltage value by a current-voltage circuit, and is fed back to the laser drive current as a result of comparison between this voltage value and a reference value.

  As timing for performing APC, APC is performed in a non-image region period in which a beam (laser light) scans outside the image region on the photosensitive member. By performing in this period, the image formation is not affected. Further, by increasing the frequency of APC between scanning lines, fluctuations in the amount of light emitted from the laser element due to heat generation or the like can be suppressed.

  In a scanning optical system that scans a plurality of beams, it is difficult in terms of arrangement to have the same number of PDs corresponding to each beam as the number of laser elements. Even if it can be arranged, such a configuration leads to high costs. Therefore, a technique is used in which a plurality of beams are received by a single PD, a plurality of laser elements are sequentially turned on, and APC is performed to control the amount of light for each laser element.

  Particularly, in the surface emitting laser, since the beam emission direction is perpendicular to the semiconductor substrate, it is difficult to dispose the PD in the same package as in the edge emitting semiconductor laser. For this reason, a technique is used in which light emitted to the front surface is separated by a half mirror and incident on the PD.

  In Patent Document 1, light emitted from a surface emitting laser is converted into parallel light by a collimator lens, and the light beam after being narrowed by an aperture is separated into light traveling on a photoconductor and light traveling on a PD by a half mirror. A method of performing APC with a single PD is disclosed.

  In addition, as a method for performing APC of a plurality of beams, Patent Literature 2 selects each light source in order to independently control the light amounts of the plurality of light sources in a configuration having one PD for the plurality of light sources. A method of performing APC of each light source by sequentially turning on light sequentially is disclosed.

Patent Document 3 discloses a method of performing APC based on the total amount of light when all beams are turned on. In this method, the variation in the drive current-light quantity characteristics of a plurality of beams is adjusted in advance with a volume to adjust the balance of the quantity of light quantity variation between the beams, and the plurality of beams are turned on simultaneously during APC.
JP 2002-40350 A JP-A-7-235715 JP-A-8-264873

  However, when the conventional image forming apparatus performs APC with high accuracy for all the beams as the number of beams increases, there are the following problems.

  One of the problems is related to the frequency of APC. As the number of beams increases, when performing APC for each beam individually, it is necessary to secure an APC time for the number of beams. The non-image region period between lines is determined by conditions such as the size of optical system components and devices, the rotational speed of the polygon mirror, and it is difficult to increase or decrease the non-image region period according to the number of beams. For this reason, when the number of beams increases, it becomes difficult to have an APC time corresponding to the number of beams between lines. Therefore, APC is performed once for a plurality of lines for each beam.

  FIG. 11 is a timing chart showing an example of a conventional APC sequence. In this example, APC of four beams is sequentially performed between lines. In the first line, APC of LD1 to LD4 is performed, and APC of LD5 to LD8 is performed in the second line. As the number of beams increases, it becomes difficult to perform APC of all lasers between lines, and it is necessary to set an APC sequence so that APC is performed for each of a plurality of lines. For this reason, as the number of beams is increased, the frequency of APC decreases, and the output light of each beam tends to fluctuate. In order to stabilize the amount of light, it is necessary to increase the number of lasers that perform APC between lines and increase the frequency of APC.

  As a method of shortening the APC time and increasing the frequency of APC, there is a method of performing APC by simultaneously turning on a plurality of lasers as shown in Patent Document 3 described above. In order to maintain the frequency of APC, when APC is performed based on the sum of the light amounts of a plurality of beams, APC can be performed for all the beams at the same time, so that APC can be performed in a short time. However, the balance of the light emission quantity of each laser element is not always the same as the initial state due to the variation in the heat generation state of each laser element and the variation with time of the current-light quantity characteristic. For this reason, there has been a problem that a light amount difference is likely to occur between the beams depending on the temperature rising state on the chip surface.

  Another problem is the variation in the amount of light incident on the PD. In the surface emitting laser, when the method of separating the light with a half mirror and irradiating it on the PD has the following problems.

  In the optical system (see FIG. 3) that guides the laser light emitted to the PD using a half mirror, the light emitted from the surface emitting laser (101) is converted into parallel light by the collimator lens (203), and is reflected by the half mirror (204). Reflected to the PD side as part of the light traveling toward the photoreceptor.

  In order to increase the amount of light incident on the PD (102), the light reflected by the half mirror is condensed by the condenser lens (205), and light is irradiated onto the light receiving surface of the PD. As described above, in the method of condensing each laser beam on the PD, the amount of incident light on the PD can be increased without increasing the light receiving area of the PD, so that APC can be performed without impairing the response characteristics of the PD. It becomes. However, as the number of light emitting elements of the surface emitting laser increases, it becomes difficult to make all the beams uniformly incident on the light receiving surface of the PD.

  In the beam arrangement on the PD light receiving surface when the number of elements of the surface emitting laser is increased (see FIG. 4), the laser beams LD3 and LD4 in which light enters the center position of the PD light receiving surface and the end portions of the PD light receiving surface There is a difference in the amount of light incident on the PD between the laser beams LD1 and LD6 that enter the beam.

  Like the laser beams LD1 and LD6, the light amount of the beam irradiated to the end portion is low. Therefore, when performing APC with high accuracy, it is necessary to devise a method such as amplifying the detected light amount. For variations in the amount of light incident on the PD, for example, when an amplifier is provided for each laser light source, and the amount of light is detected at a constant level by adjusting the amplification factor, APC can be performed with high accuracy. However, in the method of switching the amplifiers individually, it takes time to start up the amplifiers.

  FIG. 12 is a timing chart showing light quantity detection when APC is performed sequentially by switching the light emission of each laser light source. Thus, in the APC of each laser beam, it is necessary to set the APC time longer by the amount corresponding to the rise time.

Accordingly, the present invention is, intended to provide the time of forming an image using the light emitted from the plurality of light sources, an image forming equipment which can increase the frequency of the light amount adjustment by shortening the time of light quantity adjustment To do. Further, the present invention is the amount of incident light is low light to the light receiving means of each irradiation light and even variations in the amount of incident light, the other object is to provide an image forming equipment which can perform stable light control And

In order to achieve the above object, an image forming apparatus of the present invention includes a plurality of light sources that emit a light beam, a detection unit that receives the light beam and generates a detection signal having a voltage corresponding to the received light amount, A setting means for setting a gain according to the light source; an amplification means for amplifying the voltage of the detection signal based on the gain set by the setting means; and a light beam from any one of the plurality of light sources. The detection signal voltage generated by the detection unit according to the received light quantity of the light beam and amplified by the amplification unit based on the gain set by the setting unit, and the plurality of light sources A light amount control for controlling the light amount of the light beam emitted by any one of the light sources based on a common reference voltage corresponding to the target light amount of the light beam. And means, and control means for executing the light amount control with respect to each of the plurality of light sources, the control means, the setting means for setting in accordance with the gain of the voltage by the amplifying means to the light source the provided, after performing the light amount control for a plurality of light sources corresponding to the first gain the setting means sets, for a plurality of light sources the setting means corresponding to the second gain to be set The light quantity control is executed, which is characterized in that

According to the present invention , when detecting a light amount by amplifying a signal corresponding to the amount of light incident on the light receiving means with a predetermined gain, the signal has a plurality of different gains (amplification factors). Therefore, even if the amount of incident light is low and the amount of incident light on the light receiving means varies for each light source, amplification suitable for each light source can be performed. Thereby, stable light quantity control can be performed. In addition, light sources that use the same amplification factor are grouped and the amount of light is adjusted for each group, so there is no need to switch the amplification factor within the group, and the output signal from the amplification means that occurs when the amplification factor is switched Can be shortened. Therefore, the light amount adjustment (APC) time can be set short. In this way, when an image is formed using irradiation light from a plurality of light sources, it is possible to shorten the light amount adjustment time and increase the frequency of light amount adjustment. That is, the light amount adjustment of each irradiation light can be performed with high accuracy in a short time.

According to the present invention , since the amplification factor is changed according to the amount of incident light on the light receiving means, even when the amount of incident light on the light receiving means changes due to environmental fluctuations, switching of the printing speed of the printer, etc. Selection is possible. Thereby, the precision of light quantity adjustment can be maintained.

According to the present invention , the order of the light sources for adjusting the light amount is determined in accordance with the amount of light incident on the light receiving means. That is, by adjusting the light amount in the order of the light source having the closest incident light amount to the light receiving means, the change in the output of the light receiving means when the light source is switched can be minimized. Therefore, the switching time until the next light amount adjustment can be shortened, and the light amount adjustment time can be shortened.

According to the present invention , when the light amount adjustment order is assigned to each group and the light amount adjustment is continuously performed within the same group, the light amount adjustment is performed for each group and / or in order of increasing or decreasing incident light amount within the group. Set the order of the light sources to be performed. Thereby, it is possible to effectively shorten the rise time of the output signal from the amplifying means that is generated when the amplification factor (gain) is switched.

According to the present invention , by having a plurality of voltage amplifiers having different amplification factors, stable light quantity control is possible by using a voltage amplifier suitable for each light source even if the amount of incident light on the light receiving means varies for each light source. become.

According to the present invention , the light amount can be easily adjusted by using the reference voltage.

It will be described with reference to the accompanying drawings, embodiments of an image forming equipment of the present invention. The image forming apparatus of the present embodiment, an image is formed by scanning light of the surface emitting laser having a plurality of light emitting points on a chip (laser light source) on the photoreceptor. In addition, this image forming apparatus separates a plurality of output lights from a surface emitting laser with a half mirror, irradiates the light receiving surface of a single light receiving element, detects the light quantity of each laser light, and detects the detected light quantity. Based on this, light quantity control (APC) of each laser beam is performed. As described above, in the APC, the amount of laser light emitted from each laser light source (light source) is adjusted.

[First Embodiment]
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to the first embodiment. The image forming apparatus mainly includes a printer unit 10 that outputs a document image on recording paper and a scanner unit 11 that reads data of the document image. An automatic document feeder 12 is provided above the scanner unit 11. The image forming apparatus can operate when the user sets a copy mode or the like via the operation unit 14.

  The printer unit 10 is provided with paper feed stages 34, 35, 36, and 37 in which recording paper is stored. The user freely assigns the recording paper to these paper feed stages 34, 35, 36, and 37 according to the paper size. A large capacity paper deck 15 can be connected to the outside of the printer unit 10. The recording paper is transported to the image forming unit by paper feed transport rollers 38, 39, 40, 41, and 42 driven by a motor (not shown).

  In the scanner unit 11, light is radiated from a light source 21 moving in the left-right direction in FIG. The irradiation light is reflected by the original, and the optical image is formed on the CCD 26 through the mirrors 22, 23, 24 and the lens 25. In the CCD 26, the imaged optical image is converted into an electrical signal and becomes digital image data. The image data is subjected to image conversion processing such as enlargement / reduction in response to a user request, and the image data after the image conversion processing is stored in an image memory (not shown).

  When outputting an image, the printer unit 10 calls the image data stored in the image memory, and reconverts the digital signal into an analog signal. The exposure control unit 50 provided in the printer unit 10 generates a laser beam (optical signal) from the analog signal and irradiates the photosensitive drum 31 via the scanner (polygon mirror) 28, the lens 29 and the mirror 30. Then, the photosensitive drum 31 is scanned.

  The photosensitive drum 31 has a photoconductive layer made of an organic photoconductor on its surface, and is driven to rotate at a constant speed during a copy job. The photosensitive drum 31 is attached with toner from a developing unit 33 filled with toner (not shown), and forms a visible image on the surface thereof.

  On the other hand, the recording paper is conveyed from the paper feed stages 34, 35, 36, and 37 through the paper conveyance path, and passes below the photosensitive drum 31 in accordance with the visible image. The visible image on the photosensitive drum 31 is copied (transferred) onto the recording paper by the transfer charger 48. A recording sheet on which an unfixed visible image is placed is introduced between the fixing roller 32 and the pressure roller 43. The unfixed toner image is welded by the fixing roller 32 and the pressure roller 43 and is discharged out of the printer unit 10.

  FIG. 2 is a diagram showing a configuration of an APC control circuit in the exposure control unit 50. As shown in FIG. An outline of light amount control (APC) in the present embodiment will be described. The APC control circuit includes an APC control unit 106, a voltage amplification unit 104, a comparator 105, a sample hold circuit 110, a current source 111, a surface emitting laser 101, a photodiode (PD) 102, a current / voltage conversion circuit 103, a CPU 112, and a memory. 113.

  A surface emitting laser (laser unit) 101 has a plurality of laser light sources 101a, 101b,..., 101c on a chip. Each laser light source (also simply referred to as a laser) emits light by an output current from a current source 111 (current sources 111a, 111b,..., 111c).

  Laser light output from each of the laser light sources 101a, 101b, and 101c is received by a PD (photodiode) 102, and the amount of light is detected. The detected incident light amount of the laser light is converted into a voltage value by the current-voltage conversion circuit 103 and then amplified by the voltage amplification unit 104. The voltage amplification unit 104 includes switch units 141 and 143 and a plurality of voltage amplifiers (voltage amplifiers A, B,..., F) 142.

  The APC control unit 106 includes an APC period setting unit 107, a gain selection unit 108, and a reference voltage setting unit 109. In the reference voltage setting unit 109, a reference voltage for each laser light source is set.

  The comparator 105 compares the reference voltage instructed from the reference voltage setting unit 109 for each laser light source with the output voltage from the voltage amplification unit 104. The output of the comparator 105 is input to the sample and hold circuit 110. The current source 111 sets a current value based on the voltage value sampled and held by the sample and hold circuit 110.

  The APC period setting unit 107 instructs ON / OFF of the sample hold circuit 110 corresponding to each laser light source, switching of the reference voltage in the reference voltage setting unit 109, and switching of the voltage amplifier 142 in the voltage amplification unit 104 in the APC period. .

  The CPU 112 reads out the target light amount value of each laser light source stored in the memory 113, instructs the reference voltage setting unit 109 to specify a reference voltage value corresponding to each laser light source, and corresponds to each laser light source to the voltage amplification unit 104. Indicates voltage amplifier 142.

  Here, the above-described target light amount value is a target value of the light amount for each laser light source incident on the PD 102. The target light amount value of each laser light source is set as follows. That is, at the time of manufacturing in the factory, each laser light source is caused to emit light so that the light amount of each beam is constant at the position corresponding to the image area, and the light amount value of each laser light source received by the PD at that time is stored as a target light amount value 113 is stored. The memory 113 has a ROM and a RAM.

  The reference voltage setting unit 109 generates a reference voltage corresponding to each laser light source, and outputs a reference voltage corresponding to the laser light source that performs APC in accordance with an instruction from the APC period setting unit 107. The gain selection unit 108 instructs the voltage amplification unit 104 to select the voltage amplifier 142 corresponding to the laser light source that performs APC in accordance with an instruction from the APC period setting unit 107.

  By sequentially performing such APC operation for each laser light source in the non-image region between the scanning lines, the output light (irradiation light) of each laser light source is controlled to be constant.

  FIG. 3 is a diagram showing the configuration of the optical system of the surface emitting laser 101. The output light (irradiation light) of the surface emitting laser 101 is output in the vertical direction from the chip surface. The output light is separated by the half mirror 204 into the direction of the photosensitive drum 31 and the direction of the PD 102. The light separated in the PD direction is condensed by the lens 205 and irradiated on the light receiving surface of the PD 102. Thus, at least a part of the irradiation light enters the PD 102.

  In the present embodiment, a plurality of laser beams are received by a single PD, and the irradiation position of the laser beam on the light receiving surface of the PD differs for each laser. In particular, when the number of elements of the laser light source is increased and the distance between the elements at these end portions is increased by mechanical arrangement, the irradiation positions of the respective laser beams on the PD are different as shown in FIG. For this reason, the amount of laser light received by the PD varies for each laser light source. FIG. 4 is a diagram showing the irradiation position of each laser beam on the PD.

  In the present embodiment, the voltage amplification unit 104 includes a plurality of voltage amplifiers (voltage amplifiers A, B,..., F) having different amplification factors. A selection is made. By selecting a voltage amplifier according to the level of the incident light amount, the light amount can be detected even if the incident light amount to the PD 102 varies from a low light amount to a relatively high light amount. The APC sequence of this embodiment is set so that laser light sources for which the same voltage amplifier is selected are grouped and APC is performed sequentially for each group.

  As shown in FIG. 4, in the present embodiment, the amount of light incident on the PD 102 differs between the laser beam disposed at the end and the laser beam disposed at the center at the irradiation position on the PD 102. That is, the relationship between the irradiation amounts of the laser beams LD1 to LD6 on the PD light receiving surface is expressed by Expression (1).

LD1, LD6 <LD2, LD5 <LD3, LD4 (1)
In the present embodiment, the gain selection unit 108 selects an amplifier during the APC period of each laser light source in accordance with the following rules. That is, the laser light with the laser beam LD5 or less applied to the PD light receiving surface is amplified by the amplifier 1 (for example, the voltage amplifier A), and the laser light having the laser beam LD3 or more is amplified by the amplifier 2 (for example, the voltage amplifier F). An amplifier selection is made to amplify.

  Specifically, the amplifier 1 is selected for the light amount detection of the laser beams LD1, LD6, LD2, and LD5. In addition, the amplifier 2 is selected for detecting the light amounts of the laser beams LD3 and LD4. In this case, the APC is continuously performed for the laser beams LD1, LD6, LD2, and LD5 that select the amplifier 1, and the APC is continuously performed for the laser beams LD3 and LD4 that select the amplifier 2. The sequence is set. The CPU 112 sets the APC period.

  FIG. 5 is a flowchart showing a procedure for setting an APC period for each group. This processing program is stored in the memory 113 and is executed by the CPU 112 when the power is turned on. After the power is turned on, the CPU 112 reads out the target light amount value that indicates the target light amount of each laser light source from the memory 113 (step S1).

  The CPU 112 writes the read target light amount value in a register corresponding to each laser light source in the reference voltage setting unit 109 (step S2). The CPU 112 uses the gain selection unit 108 to select the voltage amplifier 142 according to the target light amount value of each laser light source (step S3).

  Here, a voltage amplifier with a large gain (gain or amplification factor) is selected for a laser light source with a small amount of incident light on the PD 102, and an amplifier with a small gain for a laser light source with a large amount of incident light on the PD. Is selected. In the APC operation, feedback control is performed so that the incident light amount to the PD 102 is equal to the target light amount value, so that the target light amount value and the incident light amount are equal. Accordingly, it is possible to appropriately set the gain by uniquely selecting the gain of the voltage amplifier according to the level of the target light amount value.

  The CPU 112 groups the laser light sources using the same voltage amplifier with respect to the voltage amplifier selected for each laser light source in step S3 (step S4). Further, the CPU 112 determines the order of the laser light sources that perform APC in ascending order of the target light amount value among the grouped laser light sources (step S5).

  Then, the CPU 112 sets an APC period for each group and instructs the APC period setting unit 107 in order of APC (step S6). Thereafter, the CPU 112 ends this process.

  FIG. 6 is a time chart showing an APC sequence. In this example, the CPU 112 performs APC in ascending order of the amount of light incident on the PD 102. In addition, the CPU 112 switches from the amplifier 1 to the amplifier 2 between the APC of the laser beam LD5 and the APC of the laser beam LD3.

  An APC operation is performed for each laser light source in a predetermined APC time. During the light amount control (APC), only the laser light source that performs the APC operation is turned on. Further, after the APC is finished, the laser light source that has been performing the APC operation is turned off, and the next laser light source is turned on.

  The CPU 112 does not perform the APC operation until the light amount detection value in the PD is stabilized, and performs the APC operation of the next laser light source at a preset time interval after the lighting of the laser light source is switched.

  In addition, when switching on the laser light source, the OFF period is not provided, and the laser light source is turned off and the next laser light source is turned on at the same timing, so that the light quantity detection value of the next laser light is stabilized after the end of APC. The time until is shortened.

  When switching from APC of the laser beam LD5 to APC of the laser beam LD3, the amplifier is switched. When the amplifier is turned ON / OFF, it takes time until the output rises due to the slew rate of the amplifier. Therefore, when switching the amplifier, the time from the laser light emission to the start of APC is set longer than usual in consideration of the output rise time.

  As described above, in the present embodiment, the number of switching of the amplifier can be set to the minimum by continuously performing the light amount control (APC) on the laser light source that performs APC using the same amplifier. it can. Therefore, the APC time can be shortened.

  Next, the APC operation when changing the irradiation light amount will be described. When the environment changes or when the printing speed of the printer is switched, the light quantity control is performed so as to keep the image density constant by changing the irradiation light quantity. In this case, in the APC of this embodiment, the amount of incident light on the PD changes due to the change in the amount of irradiated light, so that the gain needs to be reset. Therefore, when the amount of light applied to the photoconductor is changed, the APC sequence is reset.

  FIG. 7 is a flowchart showing the procedure for setting the APC period for each group when the irradiation light quantity is changed. This processing program is stored in the memory 113 and is executed by the CPU 112 when the irradiation light quantity is changed. When instructed to change the irradiation light amount, the CPU 112 changes the target light amount value by multiplying the target light amount value of each laser light source read from the memory 113 by the change amount of the photosensitive member irradiation light amount (step S11). For example, when the light amount on the photosensitive member is increased by 30%, a value obtained by increasing the target light amount value of each laser light source by 30% is set as the target light amount value. Thereafter, the processing of steps S12 to S16 is the same as the processing of steps S2 to S6 when the power is turned on, and a description thereof will be omitted.

  FIG. 8 is a time chart showing an APC sequence when the irradiation light quantity is changed. The case where the irradiation light quantity was raised compared with before the light quantity change of FIG. 6 is shown. The amplifiers 1 and 2 are selected depending on whether the target light amount value is higher or lower than a certain threshold level. Here, since the target light amount value has increased due to the light amount change, the gain switching timing is reset. That is, in the example of FIG. 6, gain switching is performed between the APC timings of the laser beams LD5 and LD3, but in the example of FIG. 8, gain switching is performed between the APC timings of the laser beams LD6 and LD2. The gain setting and grouping are reset.

  According to the image forming apparatus of the first embodiment, since the amplification factor of the output signal is controlled in accordance with the amount of incident light on the PD, even if the amount of incident light is low and the amount of incident light on the PD varies, the laser Amplification suitable for each light source can be performed, and stable light quantity control (APC) becomes possible. Specifically, the order of the laser light sources for adjusting the light amount is determined according to the amount of light incident on the PD. That is, by adjusting the light amount in the order of the laser light source having the closest incident light amount to the PD, the change in the output of the PD when the light amount adjustment is switched can be minimized. Therefore, the switching time until the next light amount adjustment can be shortened, and the light amount adjustment time can be shortened.

  Further, by assigning an APC order to each group using the same voltage amplifier and further performing APC within the same group, it is not necessary to switch the amplification factor within the group. Therefore, it is possible to shorten the rise time of the output signal from the voltage amplifier that is generated when the amplification factor is switched. In this way, the number of amplifier switching is reduced, and the APC time is shortened.

  Further, by allocating the APC order for each group and / or within the group in ascending order of the target light amount value, the variation in the received light amount of the PD generated when switching the light emission of the laser light source can be minimized. Can be stabilized in a short time. In this way, the rise time of the output signal from the amplifier that is generated when the amplification factor (gain) is switched can be effectively shortened. Thereby, the time from the light emission switching of the laser light source to the start of APC can be shortened.

  Further, by having a plurality of voltage amplifiers having different amplification factors, even if the amount of incident light on the PD varies for each laser light source, it is possible to adjust the light amount stably by using a voltage amplifier suitable for each laser light source. Further, the light amount can be easily adjusted by using the reference voltage.

  As described above, when an image is formed on the photosensitive member by scanning a plurality of laser beams, the light amount of each irradiation light can be adjusted with high accuracy in a short time.

  In addition, since the amplification factor is changed in accordance with the incident light amount to the PD, the optimum amplification factor can be selected even when the incident light amount to the PD changes due to environmental changes, printer printing speed switching, or the like. Thereby, the precision of light quantity adjustment can be maintained.

  Further, by setting the APC sequence when the power is turned on and when the irradiation light quantity is changed, the same effect can be expected even if the irradiation light quantity changes. In the present embodiment, the APC order is assigned in ascending order of the target light amount value, but the same effect can be obtained even if the APC order is assigned in the order of increasing target light amount value.

[Second Embodiment]
Since the configuration of the image forming apparatus according to the second embodiment is the same as that of the first embodiment, only operations different from those of the first embodiment will be described here.

  FIG. 9 is a flowchart showing a procedure for setting an APC period for each group in the second embodiment. The same step number is assigned to the same step process as in the first embodiment. This processing program is stored in the memory 113 and is executed by the CPU 112 when the power is turned on. After the power is turned on, the CPU 112 reads out the target light amount value that indicates the target light amount of each laser light source from the memory 113 (step S1).

  The CPU 112 writes the read target light amount value in a register corresponding to each laser light source in the reference voltage setting unit 109 (step S2).

  The CPU 112 uses the gain selection unit 108 to select the voltage amplifier 142 according to the target light amount value of each laser light source (step S3). Here, the CPU 112 determines whether or not the gain setting range of each voltage amplifier has a gain corresponding to the target light amount value read from the memory 113, and determines the voltage amplifier to be selected in the APC of each laser light source. .

  The CPU 112 groups the laser light sources using the same voltage amplifier with respect to the voltage amplifier selected for each laser light source in step S3 (step S4).

  Then, the CPU 112 instructs (sets) the order of the APC periods for each group to the APC period setting unit 107 (step S6A). Thus, after setting the APC sequence, the CPU 112 ends this processing. In the present embodiment, the order of APCs in the group is not particularly set.

  FIG. 10 is a time chart showing the APC sequence. In the example of FIG. 10, the difference in the amount of incident light on the PD within the same group is small. For this reason, the APC switching time can be set short without determining the APC order in the group, and the operation of determining the APC order in the group by the CPU 112 may be omitted.

  In the image forming apparatus according to the second embodiment as well, as with the first embodiment, it is possible to shorten the time required for gain switching. Therefore, the APC time can be shortened.

  The present invention is not limited to the configuration of the above-described embodiment, and any configuration can be used as long as the functions shown in the claims or the functions of the configuration of the present embodiment can be achieved. Is also applicable.

  For example, in the above embodiment, in the grouping, only two groups are shown in the figure (see FIGS. 6 and 10), but it is needless to say that the grouping may be divided into three or more groups. Even in such a case, by assigning the order of the laser light sources that perform APC in order of increasing or decreasing target light amount value for each group and / or within the group, the received light amount of the PD generated at the time of switching the light emission of the laser light source Variations can be minimized.

  In the above embodiment, the case where a surface emitting laser having a plurality of light emitting points (laser light sources) on the chip is used as the light source is shown, but the present invention is the same even when other light sources such as an LED array are used. It is applicable to.

  In addition to the original printing apparatus, the image forming apparatus of the present invention may be a facsimile machine having a printing function, a multifunction machine (MFP) having a printing function, a copying function, a scanner function, etc. is there.

  The image forming apparatus of the present invention may be applied to an image forming apparatus that uses a photosensitive drum corresponding to each color of YMCK and sequentially transfers the toner images of each color carried on the photosensitive drum on a recording medium. . The image forming apparatus of the present invention uses an intermediate transfer member, and sequentially transfers the toner images of the respective colors onto the intermediate transfer member, and the toner images carried on the intermediate transfer member are collectively put on a recording medium. It may be an image forming apparatus for transferring.

  In addition, the shapes of the component parts described in the above embodiment, the relative arrangement thereof, and the like should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions, and the scope of the present invention is described above. It is not limited only to what is illustrated.

1 is a diagram illustrating a configuration of an image forming apparatus according to a first embodiment. 3 is a diagram showing a configuration of an APC control circuit in the exposure control unit 50. FIG. 2 is a diagram showing a configuration of an optical system of a surface emitting laser 101. FIG. It is a figure which shows the irradiation position of each laser beam on PD. It is a flowchart which shows the setting procedure of the APC period for every group. It is a time chart which shows an APC sequence. It is a flowchart which shows the setting procedure of the APC period for every group at the time of irradiation light quantity change. It is a time chart which shows the APC sequence at the time of irradiation light quantity change. It is a flowchart which shows the setting procedure of the APC period for every group in 2nd Embodiment. It is a time chart which shows an APC sequence. It is a timing chart which shows an example of the conventional APC sequence. It is a timing chart which shows the light quantity detection at the time of switching light emission of each laser light source, and performing APC sequentially.

Explanation of symbols

101 surface emitting laser 101a, 101b, 101c laser light source 102 photodiode (PD)
107 APC period setting unit 108 Gain selection unit 109 Reference voltage setting unit 112 CPU
113 Memory 142 Voltage Amplifier

Claims (7)

A plurality of light sources that emit light beams;
Detecting means for receiving the light beam and generating a detection signal of a voltage according to the received light amount;
Setting means for setting a gain according to the light source;
Amplifying means for amplifying the voltage of the detection signal based on the gain set by the setting means;
A light beam is emitted from any one of the plurality of light sources, generated by the detection unit according to the amount of light received by the light beam, and amplified by the amplification unit based on the gain set by the setting unit. Further, the light amount of the light beam emitted from any one of the light sources is controlled based on the voltage of the detection signal and a reference voltage corresponding to the target light amount of the light beam common to the plurality of light sources. Control means for executing light quantity control, comprising: a control means for executing the light quantity control for each of the plurality of light sources;
Wherein said control means comprises said setting means for setting in accordance with the gain of the voltage by the amplifying means to said light source, said light amount control for a plurality of light sources corresponding to the first gain the setting means sets after running, the image forming apparatus and executes the light amount control for a plurality of light sources the setting means corresponding to the second gain to be set.   The detection unit includes a light receiving element that receives the light beam, and the setting unit performs the light amount control on each of the plurality of light sources, and the plurality of light incident on the light receiving surface of the light receiving element. The image forming apparatus according to claim 1, wherein a gain based on a light receiving area of each light beam by the light receiving element is set. Wherein, a plurality of light sources after performing the light amount control for a plurality of light sources corresponding to the second gain, corresponding to the third gain to set said setting means in which the setting means sets The light amount control is executed for
The image forming apparatus according to claim 1, wherein the first gain is larger than the second gain, and the third gain is larger than the second gain. Wherein, a plurality of light sources after performing the light amount control for a plurality of light sources corresponding to the second gain, corresponding to the third gain to set said setting means in which the setting means sets The light amount control is executed for
The image forming apparatus according to claim 1, wherein the first gain is smaller than the second gain, and the third gain is smaller than the second gain. The detection means includes a light receiving element that receives the light beam and generates a current as the detection signal according to a received light amount, and a conversion circuit that converts the current into the voltage as the detection signal,
The amplification means includes: a first amplification circuit that amplifies the voltage based on the first gain; a second amplification circuit that amplifies the voltage based on the second gain; the conversion circuit; A first switch disposed between the first amplifier circuit and a second switch disposed between the conversion circuit and the second amplifier circuit;
When executing the light amount control of a plurality of light sources corresponding to the first gain, the control means applies a voltage output from the conversion circuit to the first amplifier circuit, and supplies the voltage to the second amplifier circuit. The first switch and the second switch are controlled not to be applied, and a plurality of voltages corresponding to the first gain are applied in a state where the voltage output from the conversion circuit is applied to the first amplifier circuit. The light beam is emitted sequentially from the light source,
When executing the light quantity control of a plurality of light sources corresponding to the second gain, the control means applies a voltage output from the conversion circuit to the second amplification circuit, and supplies the first amplification circuit to the first amplification circuit. The first switch and the second switch are controlled not to be applied, and a plurality of voltages corresponding to the second gain are applied in a state where the voltage output from the conversion circuit is applied to the second amplifier circuit. The image forming apparatus according to claim 1, wherein a light beam is sequentially emitted from the light source. The control means includes a comparator that compares a reference voltage corresponding to a target light amount of the light beam common to the plurality of light sources and a voltage of the detection signal from the amplification means,
The control means controls the light amount of a plurality of light sources corresponding to the first gain based on a comparison result between the voltage of the detection signal amplified by the first amplifier circuit by the comparator and the reference voltage. The light amount control of the plurality of light sources corresponding to the second gain is performed based on the comparison result between the voltage of the detection signal amplified by the second amplifier circuit by the comparator and the reference voltage. The image forming apparatus according to claim 5, wherein the image forming apparatus is executed. The control means includes a comparator that compares a reference voltage corresponding to a target light amount of the light beam common to the plurality of light sources and a voltage of the detection signal from the amplification means,
The amplifying unit includes a third switch disposed between the comparator and the first amplifier circuit, and a fourth switch disposed between the comparator and the second amplifier circuit. With
When executing the light amount control of a plurality of light sources corresponding to the first gain, the control unit is configured to apply the voltage output from the first amplifier circuit to the comparator. The switch is controlled to control the fourth switch so that the connection between the second amplifier circuit and the comparator is released, and the voltage output from the first amplifier circuit is supplied to the comparator. And sequentially emitting light beams from a plurality of light sources corresponding to the first gain in a state where the connection between the second amplifier circuit and the comparator is released,
When executing the light amount control of a plurality of light sources corresponding to the second gain, the control means is configured to apply the voltage output from the second amplifier circuit to the comparator so that the voltage output from the second amplifier circuit is applied. The switch is controlled to control the third switch so that the connection between the first amplifier circuit and the comparator is released, and the voltage output from the second amplifier circuit is supplied to the comparator. 6. The light beam is sequentially emitted from a plurality of light sources corresponding to the second gain in a state where the first amplifier circuit and the comparator are disconnected when applied. Image forming apparatus.

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