JP2015087645A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device exposing an image carrier with a plurality of light sources, which corrects an amount of light of each light source with high accuracy.SOLUTION: The image formation device has control means for performing a correction operation for correcting a preset value which is an amount of light emitted by a laser independently for each laser so that a difference between VL141 (potential after exposure) and Vd143 (charging potential) is a specified value, based on a measurement result obtained from a surface potential sensor 113 when a photosensitive drum 111 is exposed by a laser (two-beam semiconductor laser 123). When the photosensitive drum 111 is exposed by one laser, the control means reduces the revolution speed of the photosensitive drum 111 than that when an image is formed so as to uniformize a surface potential of the photosensitive drum 111.

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer having a function of forming an image on a recording material such as a sheet.

The contrast of the latent image formed on the photosensitive drum is determined by the potential difference between the charged and exposed photosensitive drum potential (hereinafter referred to as VL) and the developing bias (hereinafter referred to as Vdc). Since this contrast varies depending on the environment, the film thickness of the photosensitive drum, etc., correction is necessary.
In recent years, in an electrophotographic image forming apparatus such as a digital copying machine or a laser beam printer, the use of a multi-beam method as a light source is increasing with an increase in process speed (image forming speed).
In an image forming apparatus including at least one system in which light emitted from a light source exposes a photosensitive drum, a desired contrast is obtained by correcting the light amount of the light source in accordance with the contrast variation obtained through VL detection. The configuration is disclosed in Patent Document 1, for example.

JP-A-4-52665

  However, in the multi-beam method, it has been difficult to appropriately detect the light quantity of each multi-beam. Therefore, there has been a demand for a method for obtaining a desired contrast by correcting the light quantity of the multi-beam with high accuracy with respect to the change in contrast of the photosensitive drum.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to perform light amount correction of each light source with high accuracy in an image forming apparatus that exposes an image carrier with a plurality of light sources.

In order to achieve the above object, the present invention provides:
An image carrier;
A plurality of light sources that respectively expose different positions in the sub-scanning direction on the surface of the image carrier;
With
In the image forming apparatus that forms a latent image on the image carrier by exposing the uniformly charged surface of the image carrier with the plurality of light sources, and developing the latent image to form an image.
Measuring means for measuring the magnitude of the potential of the surface of the image carrier;
Based on the measurement result of the measuring means when the image carrier is exposed by the light source, the magnitude of the surface potential of the image carrier after the exposure and the magnitude of the charged potential of the image carrier before the exposure Control means capable of independently performing a correction operation for each light source so as to correct a set value, which is the magnitude of the amount of light emitted from the light source, so that a difference between the light source and the light source is a predetermined value;
With
The control means, when exposing the image carrier with one light source, makes the rotation speed of the image carrier slower than that during image formation so that the surface potential of the image carrier becomes uniform. It is characterized by.

An image carrier;
A plurality of light sources that respectively expose different positions in the sub-scanning direction on the surface of the image carrier;
With
In the image forming apparatus that forms a latent image on the image carrier by exposing the uniformly charged surface of the image carrier with the plurality of light sources, and developing the latent image to form an image.
Measuring means for measuring the magnitude of the potential of the surface of the image carrier;
Based on the measurement result of the measuring means when the image carrier is exposed by the light source, the magnitude of the surface potential of the image carrier after the exposure and the magnitude of the charged potential of the image carrier before the exposure Control means capable of independently performing a correction operation for each light source so as to correct a set value, which is the magnitude of the amount of light emitted from the light source, so that a difference between the light source and the light source is a predetermined value;
With
When the image carrier is exposed by one light source, the control means causes the light spot diameter when the light source exposes the image carrier so that the surface potential of the image carrier is uniform. The size in the sub-scanning direction is larger than that during image formation.

An image carrier;
A plurality of light sources that respectively expose different positions in the sub-scanning direction on the surface of the image carrier;
With
In the image forming apparatus that forms a latent image on the image carrier by exposing the uniformly charged surface of the image carrier with the plurality of light sources, and developing the latent image to form an image.
Measuring means for measuring the magnitude of the potential of the surface of the image carrier;
Based on the measurement results of the measuring means when the image carrier is exposed with a plurality of different amounts of light by one light source, the amount of light emitted by the light source and the image carrier Derivation means for deriving a relationship between the magnitude of the surface potential;
Using the relationship derived by the deriving means from the target value, the target value of the surface potential of the image carrier after exposure is determined from the magnitude of the charged potential of the image carrier before exposure, A correction operation that obtains a target value of the amount of light to be emitted by the light source and corrects a setting value that is a magnitude of the amount of light emitted by the light source according to the target value of the amount of light is independent for each light source. Control means that can be executed,
It is characterized by providing.

  According to the present invention, in an image forming apparatus that exposes an image carrier with a plurality of light sources, the light amount of each light source can be corrected with high accuracy.

FIG. 3 is a block diagram for explaining control of the image forming apparatus according to the first embodiment. Sectional drawing which shows schematic structure of the principal part of the image forming apparatus of Example 1. FIG. 1 is a diagram illustrating a schematic configuration of a main part of an image forming apparatus according to a first embodiment. The figure explaining the state transition of the surface potential of the photosensitive drum at the time of printing operation 1 is an external view showing a schematic configuration of a two-beam semiconductor laser module of Example 1. FIG. Enlarged view illustrating the configuration of the two-beam semiconductor laser of Example 1 and its periphery Circuit block diagram and peripheral circuit diagram in laser driver of embodiment 1 The figure for demonstrating the state of VL (post-exposure potential) 141 in FIG. The figure which shows the flowchart for description of the light quantity correction control of Example 1. FIG. The figure which shows the flowchart for description of the light quantity correction control of Example 3.

  DETAILED DESCRIPTION Exemplary embodiments for carrying out the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

[Example 1]
Example 1 will be described below.
FIG. 1 is a block diagram for explaining control of a laser beam printer 100 as an image forming apparatus according to the present embodiment.
As shown in FIG. 1, the host PC 101 sends the status of the laser beam printer 100 from the image controller 102 (the presence / absence and type of an error, the presence / absence of a recording material in a feeding tray (not shown), the toner in a toner cartridge (not shown)). Information about the remaining amount). Then, the host PC 101 sends a print instruction command and image data to the image controller 102.

  The image controller 102 obtains information on the status of the printer engine (the presence or absence and type of an error, the presence or absence of a recording material in the feeding tray, the remaining amount of toner in the toner cartridge, etc.) from the CPU 139 in the engine control unit 103 as a control unit. To do. Then, the image controller 102 sends image data and the like developed for the printer engine to an ASIC (not shown) in the engine control unit 103 such as a print instruction command to the CPU 139.

Upon receiving the print instruction command, the CPU 139 performs the following control after confirming that the printer engine has no error and is in a printable state. That is, heating of the fixing device (not shown) is started by supplying power to the fixing device temperature control unit 109. A motor (not shown) of the recording material conveyance control unit 104, a scanner motor (not shown) of the optical system control unit 107, and a motor (not shown) for rotating the photosensitive drum 111 of the photosensitive drum rotation control unit 105 at a constant speed. to start. Here, the photosensitive drum 111 corresponds to an image carrier.
Then, after the feeding is enabled, the recording material in the feeding tray is picked up by turning on a feeding clutch (not shown) of the recording material conveyance control unit 104. Alternatively, the engine control unit 103 instructs the feeding option control unit 110 to feed the recording material, and transports the recording material into the printer engine.

FIG. 2 is a diagram for explaining a main part 138 of the control unit shown in FIG. 1, and shows a main part of the laser beam printer 100 when a cross section perpendicular to the axial direction of the rotation axis of the photosensitive drum 111 is taken. It is a figure which shows schematic structure. FIG. 2 shows in detail the internal configuration of the optical system control unit 107 and the high voltage control unit 106, and also shows a connection between the main part 138 and the engine control unit 103 that controls the main part 138 as a block diagram. ing.
When the leading edge of the fed recording material is detected by a TOP sensor (not shown) of the sensor input unit 108, a charging roller as a charging unit is generated with a high voltage generated by the charging bias application circuit 116 of the high voltage control unit 106. The surface of the photosensitive drum 111 is uniformly charged by 112. As a result, the surface of the photosensitive drum 111 is charged to Vd 143 (potential after charging, charging potential, drum potential before exposure).

The two-beam semiconductor laser module 120 of the optical system control unit 107 irradiates (exposes) the front light beam 124 from the two-beam semiconductor laser 123 to the photosensitive drum 111 according to the image data sent from the engine control unit 103. As a result, the portion (image portion) on the surface of the photosensitive drum 111 irradiated with the front light beam 124 is discharged to VL141 (post-exposure potential), and a latent image (electrostatic latent image, electrostatic latent image image) is formed. The Rukoto. To the latent image irradiated with the front light beam 124 on the photosensitive drum 111, toner (developer) is supplied from the developing sleeve 114 to which Vdc 142 (developing bias) is applied. As a result, the latent image on the photosensitive drum 111 is developed with toner, and a toner image is formed on the photosensitive drum 111. Here, the two-beam semiconductor laser 123 includes two lasers (hereinafter referred to as LD1_1) as a plurality of light sources.
93, LD2_194), and the front luminous flux 124 (with respect to the photosensitive drum 111).
An LD1 front beam 124a and an LD2 front beam 124b, which will be described later, are irradiated.

  Then, the high voltage generated by the transfer bias applying circuit 118 of the high voltage control unit 106 is applied to the recording material to be conveyed and the photosensitive drum 111 so that the toner image on the photosensitive drum 111 is transferred to the recording material. Is done. The recording material to which the toner image has been transferred is fixed by being pressurized and heated by the fixing device temperature control unit 109 and discharged to a discharge tray (not shown).

FIG. 4 is a diagram for explaining the state transition of the surface potential of the photosensitive drum 111 in FIG. 2 during the printing operation (during printing and image formation). Hereinafter, the magnitude relationship between the potentials on the surface of the photosensitive drum 111 described with reference to FIG. 2 will be described with reference to FIG.
The photosensitive drum 111 with non-uniform surface potential after the toner image is transferred is charged by the charging roller 112 so as to be uniform at −600 V (= Vd 143). Thereafter, the portion irradiated by irradiation with the front light flux 124 is neutralized to -200 V (= VL 141), and becomes a latent image.

Thereafter, the portion where the potential on the surface of the photosensitive drum 111 becomes VL141 is opposed to the developing sleeve 114 to which −400 V (= Vdc142) is applied. At this time, due to a potential difference of 200 V (contrast 144) between VL141 and Vdc142, the toner adheres to the portion where the potential of the surface of the photosensitive drum 111 is VL141. Further, due to the potential difference of 200 V (back contrast 145) between Vd143 and Vdc142, the toner does not adhere to the portion where the surface potential of the photosensitive drum 111 is Vd143.
By stabilizing the contrast 144 and the back contrast 145, it is possible to stably maintain a high quality image after transfer and fixing to a recording material.

FIG. 3 is a diagram for explaining a main part 138 of the control unit shown in FIG. 1, when the configuration in which optical system components are added to the configuration shown in FIG. 2 is viewed from above the laser beam printer 100. FIG.
2 is a view as seen from the direction of the rotation axis of the photosensitive drum 111, whereas FIG. 3 is an upper view as seen from above of optical system components such as lenses and mirrors. Also in FIG. 3, the connection between the main part 138 and the engine control unit 103 that controls the main part 138 is shown as a block diagram.

  The front light beam 124 is irradiated from a two-beam semiconductor laser 123 and passes through a collimator lens 130 for making parallel light and a cylindrical lens 131 for correcting the tilt of the optical path with respect to the scanning surface, and is rotated by a polygon mirror 132 that rotates at a constant speed. Scanned. Light having a constant angular velocity (light beam) scanned by the polygon mirror 132 as a rotating polygon mirror passes through the fθ lens 133 and is scanned on the photosensitive drum 111 at a constant velocity. In the following description, a direction in which light is deflected and scanned by the polygon mirror 132 is referred to as a main scanning direction, which is a direction substantially perpendicular to the main scanning direction and substantially parallel to the rotation axis of the polygon mirror 132. Is called the sub-scanning direction. Further, depending on the configuration of the laser beam printer 100 and the arrangement of optical components, a folding mirror 134 may be provided. Further, the movable lens 137 shown in FIG. 3 as an optical member is not used in this embodiment, but is used in Embodiment 2 described later. In this embodiment, the movable lens 137 is located outside the optical path of the front light beam 124. ing.

A horizontal synchronization signal (not shown) generated by the light incident on the horizontal synchronization signal IC 135 is sent to the CPU 139, and the CPU 139 synchronizes with the horizontal synchronization signal (not shown) to generate image data (details will be described later in the description of FIG. 7). Is sent to the laser driver 119.
The laser driver 119 controls the blinking of the two-beam semiconductor laser 123 according to the image data, thereby forming a horizontal synchronized latent image on the photosensitive drum 111.

In general, in a semiconductor laser, the current necessary for maintaining a constant light amount varies depending not only on the environmental temperature but also on heat including self-heating and life. Therefore, in order to keep the light amount of the spot imaged on the photosensitive drum 111 from the front light beam 124 within the desired range, it is necessary to continue the light amount adjustment (hereinafter, APC) within a specified time.
Specifically, the APC causes the laser to emit light, and the amount of light of the front light beam 124 is kept constant by adjusting the current injected into the semiconductor laser so that the current generated in the photodiode 121 by the back light beam 122 is kept constant. That is. Here, the photodiode 121 corresponds to a light receiving unit (light receiving element) that receives the back light beam 122 (a part of light emitted from the laser).
Therefore, in order for the photodiode 121 to perform APC of one two-beam semiconductor laser 123, it is necessary to perform APC for each beam. When two beams are irradiated at the same time, it is not possible to measure (detect) individual light quantity differences with a single photodiode, and to measure the total light quantity of the two beams. There is a concern that the amount of light cannot be adjusted with high accuracy.

FIG. 5 is an external view showing a schematic configuration of the two-beam semiconductor laser module 120 constituting the optical system control unit 107 shown in FIGS.
The metal laser case can 150 includes four metal terminals 151, 152, 153, and 154, and window portions that irradiate the LD1 front light beam 124a and the LD2 front light beam 124b. The four metal terminals 151, 152, 153, and 154 are mounted on the same printed circuit board as the laser driver 119 of FIG. 2 by soldering, and are electrically connected to the laser driver 119.

FIG. 6 is an enlarged view for explaining the configuration of the two-beam semiconductor laser 123 in the two-beam semiconductor laser module 120 shown in FIG.
The two-beam semiconductor laser 123 includes a power supply terminal 151, a laser connection terminal 1_152, FIG.
A wire is connected to the laser connection terminal 2_153, and current is supplied from the laser driver 119 to emit light. Two light emitting points (LD1 front light emitting point 157a and LD2 front light emitting point 157b) are formed at a front end portion of the two-beam semiconductor laser 123 with high accuracy by a semiconductor process with an interval 155 of several μm to several 100 μm. Has been. Also, a waveguide 159 is formed inside the two-beam semiconductor laser 123, and an LD1 back light emission point 158a and an LD2 back light emission point 158b are formed at the rear end. Then, the light quantity ratio between the front light beams 124a and 124b radiated forward and the back light beams 122a and 122b radiated rearward is determined by the reflection films provided on the front and rear end faces of the two-beam semiconductor laser 123.
The light beams emitted from the LD1 back light emission point 158a and the LD2 back light emission point 158b are irradiated onto one photodiode 121. The photodiode 121 is wire-connected to the PD terminal 154 (not shown), and the current generated by the laser driver 119 is monitored. The LD1 front light emission point 157a and the LD1 back light emission point 158a are defined as LD1_
193, and the LD2 front light emission point 157b and the LD2 back light emission point 158b constitute LD2_194.

FIG. 7 is a circuit block diagram and a peripheral circuit diagram in the laser driver 119 constituting the optical system control unit 107 shown in FIGS.
The CPU 139 receives the LD1_193 or LD from the logic unit 183 of the laser driver 119 via the drive current source 179 or 180 and the laser switching unit 186 or 187.
Light emission is started by injecting current 184 or 185 into 2_194.
The current from the photodiode 121 that flows to the laser driver 119 via the PD terminal 154 described in FIG. 5 is converted to a voltage by flowing to the resistor 176 or 177 via the PD monitor 170. The converted voltage increases the light amount by increasing the current 184 or 185, and finally adjusts the current, that is, the light amount so that the reference voltage Vref178 is stably obtained. The current at this time is converted into a voltage and charged into a capacitor 173 or 174 connected to the sample and hold circuit 171 or 172 and stored.
This series of operations is specific APC control, and light emission for performing APC is called APC light emission. At the time of printing, APC light emission is performed at the timing of irradiating the non-image area 140, and blinking control is performed on the basis of the image data 190 and 191 in FIG. Form an image. Here, the image area 136 is an area where a latent image can be formed on the surface of the photosensitive drum 111 in the rotational axis direction of the photosensitive drum 111, and the non-image area 140 is a photosensitive drum in the rotational axis direction of the photosensitive drum 111. It is an area other than the image area 136 in the 111 surface.

Here, the surface potential sensor 113 as a measuring means will be described.
When the surface potential sensor 113 is disposed in the non-image area 140, the surface potential of the photosensitive drum 111 can be measured (detected) during the printing operation. However, when there is no need to measure the surface potential during printing, the installation position of the surface potential sensor 113 may be within the image area 136. In such a case, by disposing the surface potential sensor 113 in the image region 136, it is possible to suppress the length of the photosensitive drum 111 in the rotation axis direction from being increased. Alternatively, the surface potential may be measured based on the discharge current flowing from the photosensitive drum 111 to the charging roller 112 or the transfer roller 115 without using the dedicated surface potential sensor 113.
In the case where VL141 can be measured by the surface potential sensor 113, in this embodiment, based on the measured value, a correction operation for correcting the light amount of the LD1 front light beam 124a to a light amount for obtaining a desired contrast 144 (hereinafter, referred to as the light amount). The light amount correction) can be executed. In other words, based on the measurement result of the surface potential sensor 113, the set value, which is the amount of light of the LD1 front light beam 124a, is corrected so that the difference between VL141 and Vd143 becomes a predetermined value (400 V in this embodiment). As a result, a desired contrast 144 is obtained.

FIG. 8 is a diagram for explaining the state of the VL 141 in FIG.
The 1 dot spot diameter on the photosensitive drum 111 when the LD1 front light beam 124a and the LD2 front light beam 124b are irradiated is circular or elliptical, and a horizontal line-like latent image is formed by continuous irradiation. At this time, the LD1 front light beam 124a and the LD2 front light beam 124b are configured to irradiate (expose) different positions on the surface of the photosensitive drum 111 in the sub-scanning direction.

In FIG. 8A, the LD1 front light beam 124a and the LD2 front light beam 124b are simultaneously irradiated while the photosensitive drum 111 is rotated by the photosensitive drum rotation control unit 105 at the same speed as that during printing (hereinafter, full speed rotation). The latent image formed when it continues doing is shown.
In this case, since the surface of the photosensitive drum 111 is uniformly exposed over the entire surface, a latent image having a uniform potential (VL141) is formed on the surface of the photosensitive drum 111 without any gap.
Here, in FIG. 8, the portion of the potential VL141 on the photosensitive drum 111 is shown in black (solid image), and the portion of Vd143 is shown in white (outlined image).

FIG. 8B is a diagram when irradiation is continued with only the LD1 front light beam 124a. In such a case, a horizontal stripe-like latent image in which VL141 portions and Vd143 portions are alternately formed is obtained. .
As described above, when a portion having a potential of VL141 and a portion of Vd143 are periodically formed on the photosensitive drum 111 to form a horizontal stripe-like latent image, the VL141 cannot be accurately measured, and the light amount There is a concern that it cannot be corrected.

Therefore, in this embodiment, when the light amount correction for obtaining the desired contrast 144 is performed by irradiating only the LD1 front light beam 124a, the rotational speed of the photosensitive drum 111 is set so that the surface potential of the photosensitive drum 111 becomes uniform. Decelerate to a speed slower than full speed rotation.
That is, in this embodiment, as shown in FIG. 8C, the LD1 front light beam 124a is irradiated while only ALD is emitted from the LD1_193, and the photosensitive drum 111 is rotated at a speed approximately half that of the full speed rotation. In addition, the photosensitive drum rotation control unit 105 controls.
As a result, a latent image having a uniform potential (VL141) can be formed on the photosensitive drum 111 without any gap, and the surface potential sensor 113 can measure the uniform VL141. Therefore, it is possible to perform light amount correction of the LD1 front light beam 124a for obtaining a desired contrast 144.
In the same way, the light amount correction is also performed for the LD2 front light beam 124b. As described above, by executing the light amount correction described above independently for each laser (each light source), it is possible to obtain a desired contrast 144 and back contrast 145 during printing.

FIG. 9 is a flowchart showing a specific light amount correction sequence executed by the CPU 139 in this embodiment.
First, the CPU 139 uses the optical system control unit 107 once in the past to increase the value of the optical system control unit 107 based on information in an EEPROM (not shown) as storage means for storing the light amount setting and the like provided in the laser beam printer 100 in step (hereinafter, S) 302. It is determined whether or not the light amount correction has been performed with accuracy. Here, the EEPROM may be an electrically rewritable and non-volatile memory.
In the case of negative determination in S302, the process proceeds to S312 and, as described above, the light quantity is obtained by rotating the photosensitive drum 111 at about half the speed at full speed rotation while performing APC emission independently for each laser as described above. Make corrections. Then, the result of the light quantity correction and the conditions for the light quantity correction are stored in the EEPROM. The conditions at the time of light quantity correction include, for example, the number of prints, the accumulated rotation amount of the photosensitive drum 111, the environment (temperature, humidity, etc.), the accumulated emission time of each of LD1_193 and LD2_194, the values of currents 184 and 185 injected to each laser, PD These are current-voltage conversion results in the monitor 170 and the like.

  On the other hand, if it is determined in S302 that the light amount correction has been performed in the past, the process proceeds to S303. In S303, the accumulated light emission time of each of LD1_193 and LD2_194 after the previous light amount correction is confirmed from the storage means, and it is determined whether or not a longer time than specified has elapsed. If it is determined that a longer time than specified has elapsed, it is determined that there is a possibility that the threshold current (laser emission start current) and the differential efficiency (light intensity / current gradient) may have changed due to secular change, and S312. Then, the light quantity correction of each of LD1_193 and LD2_194 is performed.

  If the accumulated light emission time is within the specified time in S303, the process proceeds to S304. In S304, it is determined whether or not the factor that increases the relative difference between the light amounts of LD1_193 and LD2_194 due to factors other than S302 and 303 is within the specified range. As an increase factor, for example, it is conceivable that the accumulated rotational speed of the polygon mirror 132 reaches a longer time than specified, and minute dust sucked from the outside changes the transmittance of an optical system such as a lens or a diaphragm.

Next, if the enlargement factor is within the specified range, the process proceeds to S305. In S305, the CPU 139 measures the environment by the sensor input unit 108 provided in the laser beam printer 100, and determines whether the amount of change in the environment is within the specified range. To do. If the change amount of the environment is not within the specified range, the process proceeds to S313. In step S313, during the period during which the photosensitive drum 111 (image area 136) is scanned, forced light emission is performed simultaneously with LD1_193 and LD2_194. In the period when the photosensitive drum 111 (image area 136) is not scanned, APC is performed for each scan or once every several scans in the LD1_193 and LD2_194. By performing APC at such a short interval, the amount of light is held so that the electric charges of the capacitors 173 and 174 that have been subjected to thermal droop or sample and hold do not change more than prescribed due to leakage.
Here, the forced light emission means that the LD1_193 or the LD2_194 is forcibly emitted with the value stored in the capacitor 173 or 174 by the APC without using the current flowing through the photodiode 121. Therefore, the LD1_193 and the LD2_194 can emit light without any problem.

  If the environmental change is within the specified range in step S305, the process proceeds to step S306. In step S306, the photosensitive drum 111 is based on information from a storage unit (not shown) such as an EEPROM provided in a cartridge (not shown) that holds the photosensitive drum 111. Determine if it is new. If it is determined that it is a new product, the process proceeds to S313, where the photosensitive drum 111 is irradiated by forcibly emitting light simultaneously at LD1_193 and LD2_194, and the VL141 is measured. Then, a light amount change ratio necessary for obtaining the desired contrast 144 is calculated, and the light amount is corrected at a fixed ratio in which the light amounts of the LD1_193 and LD2_194 are calculated. As a method of correcting the amount of light, for example, there is a method of transforming the voltage sampled and held (by the sample hold circuit 171 or 172) for all the light sources at a constant rate using a PWM signal or a DA converter (not shown). .

  If it is determined in S306 that the photosensitive drum 111 is not new (used), the process proceeds to S307. In S307, the accumulated rotation amount of the photosensitive drum 111 is confirmed from the storage means provided in the cartridge that holds the photosensitive drum 111, and it is determined whether or not the accumulated rotation amount is within a specified range. If it is determined that the integrated rotation amount is not within the specified range (has reached a longer time than specified), it is determined that there is a possibility that the film pressure of the photosensitive drum 111 has decreased and the photosensitive characteristic has changed, and the process proceeds to S313 and LD1_193 is reached. , LD2_194 performs light quantity correction by performing forced light emission at the same time. Similarly, the CPU 139 stores the results and conditions in the storage unit included in the cartridge that holds the photosensitive drum 111 even after the light intensity correction is performed simultaneously by LD1_193 and LD2_194.

When the light quantity correction is completed and the process proceeds to step S308 where the light quantity can be printed, and other functions are also printable, when the CPU 139 receives a print instruction from the image controller 102 in step S309, the process proceeds to step S310 and the printing operation is performed. To start.
Thereafter, the process proceeds to S311. If there is one print job, the process proceeds to S315, and this sequence is terminated and the process returns to START 301. If there are a plurality of print jobs, the process proceeds to S314. If a predetermined number or more of the print jobs are continuously printed, the print job is temporarily interrupted, the sequence is terminated, and the process returns to start 301. Then, after performing the light amount correction again, the desired contrast 144 can be maintained by restarting the print job.

Here, in S313, it is not necessary to forcibly emit light simultaneously with LD1_193 and LD2_194, and the light quantity correction of LD1_193 and LD2_194 may be performed as follows.
First, the light quantity of the LD1_193 is corrected by rotating the photosensitive drum 111 at about half the speed during printing while performing APC light emission only on the LD1_193. Thereafter, the current light amount correction result of LD1_193 and the past light amount correction result are compared, and the desired light amount of LD2_194 is calculated from the ratio of the PD currents stored in LD1_193 and LD2_194. Here, the PD current is a current from the photodiode 121 that flows to the laser driver 119 via the PD terminal 154. LD2_194 corresponds to a light source other than the light source on which the light amount correction (correction operation) is performed.
Such light amount correction may be performed until a predetermined condition is satisfied (negative determination in any of S302 to S304). When a predetermined condition is met, light amount correction is performed with high accuracy for all lasers.

As described above, according to the present embodiment, the light quantity correction of each of LD1_193 and LD2_194 can be performed independently and with higher accuracy. Thereby, a more stable contrast 144 can be obtained.
Further, in the process of assembling and manufacturing the laser scanner unit 146 including a lens system such as the optical system controller 107, the polygon mirror 132, and the fθ lens 133, LD1_193, L
It is not necessary to adjust the light amount with high accuracy for each of D2_194. Thereby, the effect that the manufacturing cost for the amount of light adjusted with high accuracy can be reduced is also obtained.
Further, the light amount correction can be automatically performed by executing the above-described sequence. As a result, even when the laser scanner unit 146 is replaced due to a failure or the like, the amount of light is automatically adjusted after replacement, and the maintenance can be simplified.

In the present embodiment, the two-beam semiconductor laser module 120 including the two-beam semiconductor laser 123 and one photodiode 121 has been described. However, the present invention can be preferably applied to any configuration provided with a plurality of light sources that respectively expose different positions in the sub-scanning direction on the surface of the photosensitive drum 111. In a configuration including a plurality of light sources, light amount correction is performed for each light source, and at this time, the rotational speed of the photosensitive drum 111 is made slower than that during image formation so that the surface potential of the photosensitive drum 111 becomes uniform. As a result, the light amount correction of each light source can be performed with high accuracy.
In particular, as a semiconductor laser module (light source unit, exposure means) having a plurality of light sources, at least m irradiation lights and n light receiving elements (light quantity monitoring elements) smaller than m for monitoring the irradiation light, It is good to be comprised from. That is, any semiconductor laser module having an m-beam semiconductor laser and n photodiodes may be used. For example, even a semiconductor laser module having two photodiodes and 32 multi-beam semiconductor lasers with irradiation light. Good.

  Further, in the configuration provided with the two-beam semiconductor laser 123 of this embodiment, when the light amount correction is performed while performing APC emission for each laser, the photosensitive drum 111 rotates at a speed that is approximately ½ of the full-speed rotation. Was to control. On the other hand, in the case of a configuration provided with an m-beam semiconductor laser, at a speed of approximately 1 / m (rotation speed at the time of printing divided by the number of lasers (light source, light flux)) at full speed rotation, Control may be made so that the photosensitive drum 111 rotates. For example, when the laser beam printer 100 includes a four-beam laser, the photosensitive drum 111 is rotated at a speed that is approximately ¼ of the full-speed rotation. The light quantity can be corrected.

[Example 2]
Example 2 will be described below. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
In Example 1, the VL 141 is made uniform by slowing the rotation speed of the photosensitive drum 111. However, the laser beam printer 100 may not be provided with means for reducing the rotational speed of the photosensitive drum 111. In addition, the rotational speed of the photosensitive drum 111 that should be set at the time of light amount correction may be lower than the decelerable range of the photosensitive drum rotation control unit 105.

On the other hand, in this embodiment, when the light amount correction is performed, the spot diameter is printed as shown in FIG. 8D by moving the movable lens 137 on the optical path of the front light beam 124 as shown in FIG. It is characterized in that it is enlarged in the rotation direction of the photosensitive drum 111 than the time. here,
The lens 137 is movably supported by a moving means (moving mechanism) controlled by the CPU 139, and is positioned outside the optical path during printing. In addition, when performing light amount correction in this embodiment, in FIG. 9, when performing light amount correction by APC light emission for each light source in S <b> 312, or performing light amount correction by APC light emission for one light source in S <b> 313. Corresponding to
In the case of providing two-beam lasers LD1_193 and LD2_194, the spot diameter is approximately doubled in the rotation direction (sub-scanning direction) of the photosensitive drum 111, and scanning is performed while performing APC emission for only one laser, thereby correcting the amount of light. I do. At this time, the rotation speed of the photosensitive drum 111 is not decelerated, and is rotated at the same speed as that during printing. Thereby, a uniform latent image can be obtained as in the first embodiment.
Thus, also in the present embodiment, the same effects as those of the first embodiment can be obtained.

Here, regarding the main scanning direction on the photosensitive drum 111, the continuously irradiated LD1_193 is obtained.
Alternatively, since scanning is performed by the LD2_194, the scanned range (region) is not based on the spot diameter. Therefore, the main scanning direction width of the spot diameter transmitted through the movable lens 137 may be enlarged or reduced, and is arbitrary.
Further, in FIG. 3, a movable lens 137 is arranged between the cylindrical lens 131 and the polygon mirror 132 to enlarge the spot diameter. However, the arrangement of the lens for enlarging the spot diameter is within the optical path. It is optional if it exists.
Further, the spot diameter may be enlarged by changing the optical path length by changing the position of the folding mirror 134 instead of the lens, or by switching to a mirror having a different curvature.
Further, in the configuration provided with the two-beam semiconductor laser 123 of the present embodiment, the spot diameter is increased approximately twice in the rotation direction of the photosensitive drum 111 when the light amount correction is performed for each laser. On the other hand, in the case of a configuration including an m-beam semiconductor laser, the spot diameter may be increased by approximately m (a value obtained by multiplying the size at the time of printing by the number of lasers) in the rotation direction of the photosensitive drum 111. .

  When the movable lens 137 is moved on the optical path, an error may occur due to the transmittance of the lens, and when the folding mirror 134 is switched, an error may occur. If this transmission or reflectance error is known and stable, the amount of light necessary to obtain the desired contrast 144 may be derived by calculation. If the transmission or reflectance error is not known or stable, the following may be used. That is, the transmittance or reflectance is measured in the assembly / manufacturing process, or an optical attenuator having a transmittance error equivalent to the movable lens 137 or a reflectance error equivalent to the folding mirror 134 is provided and switched. To correct.

[Example 3]
Example 3 will be described below. In this embodiment, the same components as those in Embodiments 1 and 2 are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 10 is a flowchart illustrating the light amount correction control according to the present embodiment.
In this embodiment, the rotational speed of the photosensitive drum 111 is not reduced, and the spot diameter is not enlarged, and the VL 141 and Vd 143 are periodically repeated in a horizontal stripe pattern as shown in FIG. 8B. A latent image is formed by APC emission of only LD1_193.
At this time, in the surface potential sensor 113, the sensor unit (measuring unit) for measuring the surface potential of the photosensitive drum 111 has a sufficiently large area (the length of the photosensitive drum 111 in the rotation direction) to stabilize the potential measurement result. Is sufficiently long).

Since the difference between the average potential obtained by measuring the non-uniform latent image and the charging potential Vd 143 is a two-beam semiconductor laser 123 in the case of a system proportional to the amount of light, the result doubled as shown in Equation 1 is VL 141- Vd143 is equal to or within an allowable range. VL141 described here is
A desired value (Vd143) such that VL141-Vd143 becomes a desired potential difference (predetermined value).
Target value).
Formula 1: VL141−Vd143 = (Measured average potential−Vd143) × 2
In the case of such a system, the desired contrast 144 is obtained by correcting the light amounts of the LD1_193 and LD2_194 so that the respective potentials measured by the surface potential sensor 113 are (VL141 + Vd143) / 2. be able to.
In this case, the light amount can be corrected according to the sequence flowchart of FIG.

However, depending on the charging characteristics or photosensitive characteristics of the photosensitive drum 111 and the characteristics of the surface potential sensor 113, there are systems that cannot be calculated using a simple expression such as Expression 1. For example, in the case of a system that does not have a proportional relationship but can be approximated by a linear function having an intercept, the relationship between VL141-Vd143 and the light amount Pvl for forming the (desired) VL141 is as follows. An approximate expression (relational expression) can be obtained.
That is, an approximate expression can be obtained by performing APC light emission with at least two types of light amounts of different sizes and measuring the VL 141 formed with each light amount.

This point will be specifically described below.
Assuming that the measurement result of the post-exposure potential formed with the small light amount Psmall is VLsall, and the measurement result of the post-exposure potential formed with the large light amount Pbig is VLbig, the relationship between the desired VL141 and the light amount Pvl is expressed by Equation 2. be able to. Therefore, in order to obtain a desired VL 141 such that VL 141 -Vd 143 becomes a predetermined value, the light quantity Pv is obtained using Equation 2.
l (target value of the light amount) can be obtained. Then, in accordance with the value of the light quantity Pvl, the light quantity correction is performed by correcting the set value that is the magnitude of the light quantity emitted by the LD1_193.
Formula 2: VL141-Vd143
= [{(VLbig−Vd143) − (VLsmall−Vd143)} / (Pbig−Psmall)] × 2 × (Pvl−Pbig) + (VLbig−Vd143)

  Furthermore, when it cannot be expressed by a linear function expression and is expressed by a quadratic or higher order function, APC light emission is performed with two or more kinds of light quantities of different sizes, and based on the results, The desired amount of light can be calculated by deriving an approximate expression in the same manner as the derivation method of Expression 2.

  In the case of a system with small variations and small fluctuations, the coefficients of the approximate expression can be obtained in advance at the time of design and set (stored) in advance. On the other hand, in a system with large variations or fluctuations, the light quantity correction for obtaining a desired contrast can be performed by deriving the coefficients of the approximate expression in the sequence as shown in FIG.

Hereinafter, the light amount correction control of this embodiment will be described with reference to FIG.
The sequence of FIG. 10 is executed by the CPU 139 that controls each control of the engine control unit 103, as in FIG. In FIG. 10, steps similar to those in FIG. Here, the CPU 139 (engine control unit 103) corresponds to derivation means.
As shown in FIG. 10, when a negative determination is made in any of S302 to S304, the process proceeds to S316.
In S316, it is determined whether an approximate expression (for example, Expression 2) for performing light amount correction is not set in advance, has not been derived in the past, or needs to be recalculated and derived again. If the determination is affirmative, the process proceeds to S317. Here, the unknown approximate expression means, for example, an unused state after assembly / manufacture of the laser scanner unit 146 or a state when the laser scanner unit 146 is replaced during maintenance. Further, the need for recalculation means a state in which it is necessary to recalculate, for example, when the cumulative number of printed sheets has increased by more than a specified value and the durability of the photosensitive drum has progressed.

In S317, light quantity correction is performed by deriving an approximate expression while performing APC emission for each laser. At this time, the APC emission of one laser (for example, LD1_193) is performed with two kinds of light amounts having different sizes, and the average potential is measured with respect to each light amount by the surface potential sensor, whereby an approximate expression is derived. Then, the derived approximate expression, the result of the light amount correction, and the conditions for the light amount correction are stored in the EEPROM, and the process proceeds to S308. The conditions at the time of light quantity correction include, for example, the number of prints, the accumulated rotation amount of the photosensitive drum 111, the environment (temperature, humidity, etc.), the accumulated emission time of each of LD1_193 and LD2_194, the values of currents 184 and 185 injected to each laser, PD These are current-voltage conversion results in the monitor 170 and the like.

If it is determined in S316 that the approximate expression has been set in advance and it is not necessary to derive the expression again by recalculation, the process proceeds to S313.
In S313, as described in the first embodiment, the light amount correction is performed by simultaneously performing light emission of LD1_193 and LD2_194. However, the light amount correction of LD1_193 and LD2_194 may be performed as follows.
First, the light quantity of the LD1_193 is corrected by deriving the approximate expression as described above while performing APC light emission only on the LD1_193. Thereafter, the current light amount correction result of LD1_193 and the past light amount correction result are compared, and the desired light amount of LD2_194 is calculated from the ratio of the PD currents stored in LD1_193 and LD2_194.

As described above, also in the present embodiment, the same effects as those of the first embodiment can be obtained.
In the present embodiment, the surface potential sensor 113 has a sufficiently large area to stabilize the potential measurement result, but is not limited to this. When the surface potential sensor 113 cannot secure a sufficiently large area so that the measurement value is stabilized in a short time measurement, the surface potential of the photosensitive drum 111 is measured as follows. Also good. That is, a value obtained by performing arithmetic processing on a value measured a plurality of times, for example, an average value obtained by performing measurement 100 times at a sampling rate of 5 msec period is used as a measurement result measured by the surface potential sensor 113. Also good. Even if this result is used, light quantity correction can be suitably performed.

  DESCRIPTION OF SYMBOLS 100 ... Laser beam printer, 103 ... Engine control part, 111 ... Photosensitive drum, 113 ... Surface potential sensor, 139 ... CPU, 193 ... Laser LD1, 194 ... Laser LD2

Claims (10)

An image carrier;
A plurality of light sources that respectively expose different positions in the sub-scanning direction on the surface of the image carrier;
With
In the image forming apparatus that forms a latent image on the image carrier by exposing the uniformly charged surface of the image carrier with the plurality of light sources, and developing the latent image to form an image.
Measuring means for measuring the magnitude of the potential of the surface of the image carrier;
Based on the measurement result of the measuring means when the image carrier is exposed by the light source, the magnitude of the surface potential of the image carrier after the exposure and the magnitude of the charged potential of the image carrier before the exposure Control means capable of independently performing a correction operation for each light source so as to correct a set value, which is the magnitude of the amount of light emitted from the light source, so that a difference between the light source and the light source is a predetermined value;
With
The control means, when exposing the image carrier with one light source, makes the rotation speed of the image carrier slower than that during image formation so that the surface potential of the image carrier becomes uniform. An image forming apparatus.   The rotation speed of the image carrier controlled to be slower than that at the time of image formation is set to a value obtained by dividing the rotation speed at the time of image formation by the number of the light sources. The image forming apparatus described. An image carrier;
A plurality of light sources that respectively expose different positions in the sub-scanning direction on the surface of the image carrier;
With
In the image forming apparatus that forms a latent image on the image carrier by exposing the uniformly charged surface of the image carrier with the plurality of light sources, and developing the latent image to form an image.
Measuring means for measuring the magnitude of the potential of the surface of the image carrier;
Based on the measurement result of the measuring means when the image carrier is exposed by the light source, the magnitude of the surface potential of the image carrier after the exposure and the magnitude of the charged potential of the image carrier before the exposure Control means capable of independently performing a correction operation for each light source so as to correct a set value, which is the magnitude of the amount of light emitted from the light source, so that a difference between the light source and the light source is a predetermined value;
With
When the image carrier is exposed by one light source, the control means causes the light spot diameter when the light source exposes the image carrier so that the surface potential of the image carrier is uniform. An image forming apparatus characterized in that the size in the sub-scanning direction is larger than that during image formation. An optical member is provided movably for making the size of the spot diameter of light when the light source exposes the image carrier in the sub-scanning direction larger than that during image formation,
The optical member is located outside an optical path of light emitted from the light source during image formation,
The image forming apparatus according to claim 3, wherein the control unit positions the optical member on the optical path when the image carrier is exposed by the light source.   The size in the sub-scanning direction of the spot diameter controlled to be larger than that at the time of image formation is set to a value obtained by multiplying the size at the time of image formation by the number of light sources. Item 5. The image forming apparatus according to Item 3 or 4. An image carrier;
A plurality of light sources that respectively expose different positions in the sub-scanning direction on the surface of the image carrier;
With
In the image forming apparatus that forms a latent image on the image carrier by exposing the uniformly charged surface of the image carrier with the plurality of light sources, and developing the latent image to form an image.
Measuring means for measuring the magnitude of the potential of the surface of the image carrier;
Based on the measurement results of the measuring means when the image carrier is exposed with a plurality of different amounts of light by one light source, the amount of light emitted by the light source and the image carrier Derivation means for deriving a relationship between the magnitude of the surface potential;
Using the relationship derived by the deriving means from the target value, the target value of the surface potential of the image carrier after exposure is determined from the magnitude of the charged potential of the image carrier before exposure, A correction operation that obtains a target value of the amount of light to be emitted by the light source and corrects a setting value that is a magnitude of the amount of light emitted by the light source according to the target value of the amount of light is independent for each light source. Control means that can be executed,
An image forming apparatus comprising:   The measurement means is a measurement in which the length in the rotation direction of the image carrier is set to such a length that the measurement result obtained when the image carrier is exposed by one light source is stabilized. The image forming apparatus according to claim 6, further comprising a unit.   When the measurement is performed when the image carrier is exposed by one light source, the measurement unit performs measurement a plurality of times, and uses the result obtained by calculating each value as a measurement result. The image forming apparatus according to claim 6. A light receiving unit that is provided in fewer than the number of the light sources and receives a part of the light emitted from the light sources;
Adjusting means for adjusting the magnitude of the amount of light emitted by the light source to be the set value based on the magnitude of the amount of light received by the light receiving unit;
The image forming apparatus according to claim 1, further comprising: Storage means for storing the information of the setting value corrected by executing the correction operation for each light source;
The control means includes
When the predetermined conditions are met, the correction operation is executed for all the light sources,
In a case where the setting value is corrected after the information of each setting value corrected by the correction operation being performed on all the light sources by the storage unit is stored in the storage unit, the predetermined value Until the condition of
For one light source, the set value is corrected by executing the correction operation,
For a light source other than the light source for which the correction operation has been performed, the setting value is corrected from the setting value corrected by the correction operation and information on each setting value stored in the storage unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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