JPH0588097A - Image forming device - Google Patents

Abstract

PURPOSE:To correct the positional deviation of the exposure of a vertical direction on a photosensitive drum caused by an optical path even when it occurs and to obtain a high-quality image without causing the irregularity of a pitch to the output image. CONSTITUTION:By a vertical synchronization detector 22, beam light 2 is detected before the photosensitive drum 5 is exposed by the light 2. By an arithmetic part 24, the positional deviation quantity of the exposure of the vertical direction of the light 2 is calculated by detecting the exposure position of the vertical direction of the light 2 with respect to the drum 5 by the output signal of the detector 22 and comparing it with a reference exposure position which is previously set. By a control part 29, the exposure position of the vertical direction of the light 2 with respect to the drum 5 is controlled by controlling the reflecting angle of a mirror for serveo 23 used for guiding the beam light from a laser generator 25 to a polygon mirror based on the deviation quantity calculated by the arithmetic part 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer type image forming apparatus such as a laser printer or a digital copying machine.

[0002]

2. Description of the Related Art For example, in a transfer type image forming apparatus such as a laser printer, a photosensitive drum serving as an image bearing member is rotated, and the photosensitive drum is scanned and exposed with a beam of light so as to be statically exposed. An electrostatic latent image is formed, the formed electrostatic latent image is developed into a toner image, the developed toner image is transferred onto a sheet as a transfer material, and the toner image on the sheet is thermally fixed. ..

In such an image forming apparatus, recently, a higher speed and higher definition is required. In order to achieve high speed, it is necessary to increase the process speed, and in order to achieve high definition, it is necessary to improve the process accuracy. However, there are still various problems in rendering an image accurately at high speed.

For example, when a latent image is formed by exposing a beam of light onto a photosensitive drum, the beam of light is reflected from a polygon mirror as a rotary polygon mirror that scans the latent image onto the photosensitive drum. Have an optical path through. This polygon mirror has, for example, eight mirror surfaces,
The eight mirror surfaces are mirrors each having a certain variation. Further, the reflection mirror that guides the exposure onto the photosensitive drum is often oscillated by the vibration transmitted from other places of the apparatus itself. For this reason, there is a problem that a vertical exposure position shift occurs on the photoconductor drum, pitch unevenness occurs in the output image, and a high-definition image cannot be obtained.

Regarding these problems concerning the optical path, conventionally, a method of improving the precision of each mirror surface in a polygon mirror and a method of taking a vibration proof in a reflecting mirror have been taken. However, according to these methods, if the device changes, the degree of the countermeasures also changes, and it cannot be said that the countermeasures are efficient.

Further, the rotation of the photosensitive drum on which the latent image is formed (movement of the image carrier) must be performed at higher speed and with higher precision, but again, the drive motor is rotated. The rotation unevenness of the photosensitive drum occurs due to the rotation unevenness, the meshing variation of the gears in the transmission drive system, and the like. This rotation fluctuation of the photosensitive drum results in uneven pitch in the image, as in the case of the problem in the above optical path.

To solve this problem, conventionally, a method has been adopted in which a flyhole is mainly attached to the photosensitive drum to increase the inertia to suppress the uneven rotation. But,
This method makes the equipment very heavy, and
This has included problems such as an increase in the starting torque of the photosensitive drum.

[0008]

As described above, when the vertical exposure position deviation on the image carrier due to the optical path occurs or the moving state of the image carrier fluctuates, the output image There is a problem in that pitch unevenness occurs and a high-definition image cannot be obtained.

Therefore, according to the present invention, even if the exposure position shift in the vertical direction on the image carrier due to the optical path occurs, it can be corrected and a high-definition image can be obtained without causing uneven pitch in the output image. An object of the present invention is to provide an image forming apparatus capable of performing the above.

Further, according to the present invention, even if the exposure position shift in the vertical direction on the image carrier due to the fluctuation of the optical path and the moving state of the image carrier occurs, it can be corrected and uneven pitch is caused in the output image. It is an object of the present invention to provide an image forming apparatus that can obtain a high-definition image.

[0011]

An image forming apparatus according to a first aspect of the present invention includes image forming means for forming an image on an image bearing member by scanning and exposing the image bearing member which is moved by a light beam. Prior to exposure of the light beam onto the image carrier, detection means for detecting the exposure position of the light beam in the direction perpendicular to the image carrier, and the exposure position detected by this detection means and a reference exposure position set in advance By comparing with, the shift amount calculating means for calculating the shift amount of the vertical exposure position of the light beam, and the vertical direction of the light beam with respect to the image carrier based on the shift amount calculated by the shift amount calculating means. Vertical exposure position control means for controlling the exposure position in the direction.

An image forming apparatus according to a second aspect of the present invention includes image forming means for forming an image on the image carrier by scanning and exposing the image carrier which is moved by the light beam, and an image forming means for forming an image on the image carrier. Beam light detecting means for detecting the beam light before the exposure of the light beam, and vertical exposure position detecting means for detecting the exposure position of the light beam in the vertical direction with respect to the image carrier based on the output signal of the light beam detecting means. By comparing the exposure position detected by the vertical exposure position detection means with a preset reference exposure position,
A deviation amount calculation means for calculating a deviation amount of the exposure position of the light beam in the vertical direction, and a vertical exposure position of the light beam with respect to the image carrier based on the deviation amount calculated by the deviation amount calculation means. It comprises vertical exposure position control means and horizontal exposure start time control means for controlling the horizontal exposure start time of the light beam on the image carrier based on the output signal of the light beam detection means.

In the image forming apparatus according to the third aspect of the invention, an image forming means for forming an image on the image carrier by scanning and exposing the image carrier which is moved by the light beam, and an image forming means on the image carrier. Prior to the exposure of the light beam, a first detection unit for detecting the exposure position of the light beam in the vertical direction with respect to the image carrier, an exposure position detected by the first detection unit, and a preset reference exposure position are provided. By comparison, a shift amount calculating means for calculating the shift amount of the exposure position of the light beam in the vertical direction, a second detecting means for detecting the moving state of the image carrier, and a second detecting means for detecting the shift state. And a vertical exposure position control means for controlling the exposure position of the light beam in the vertical direction with respect to the image carrier based on the movement state of the image carrier and the deviation amount calculated by the deviation amount calculation means.

[0014]

According to the first invention, the exposure position of the light beam in the vertical direction with respect to the image carrier is detected, the shift amount of the exposure position is calculated, and the shift amount of the light beam in the vertical direction is calculated based on the calculated shift amount. By controlling the exposure position, even if the vertical exposure position shift on the image carrier due to the optical path occurs, it can be corrected, and the beam light is always exposed on the image carrier at a predetermined position where there is no position shift. To be done.

According to the second invention, like the first invention,
By detecting the exposure position of the light beam in the vertical direction with respect to the image carrier, calculating the amount of deviation of the exposure position, and controlling the vertical exposure position of the light beam based on the calculated amount of deviation Even if a vertical exposure positional deviation occurs on the image carrier, it can be corrected, and the beam light is always exposed on the image carrier at a predetermined position without positional deviation.

Further, the exposure signal of the light beam in the vertical direction with respect to the image carrier is detected and the horizontal exposure start time of the light beam with respect to the image carrier is controlled by the output signal of the single light beam detecting means. Therefore, it is not necessary to provide a detection means for each of them, so that the configuration can be simplified and the cost can be reduced.

According to the third aspect of the invention, the exposure position of the light beam in the vertical direction with respect to the image carrier is detected to calculate the shift amount of the exposure position, and the movement state of the image carrier is also detected. By controlling the vertical exposure position of the light beam based on the moving state of the image carrier and the calculated shift amount, the vertical direction on the image carrier caused by the fluctuation of the optical path and the moving state of the image carrier. Even if the exposure position shift occurs, it can be corrected, and the beam light is always exposed on the image carrier at a predetermined position where there is no position shift.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 schematically shows the internal structure of a laser printer as an example of the image forming apparatus according to the present invention. This laser printer is composed of a laser optical system and an image forming section in which an electrophotographic system capable of forming an image on a transfer material is combined. That is, the semiconductor laser oscillator is driven according to a print signal sent from a print control unit (not shown) in accordance with image data sent from an external device or the like, and laser beam light is output. The output beam light is shaped by a beam shaping optical system including, for example, a cylindrical lens, and is deflected by a polygon mirror 1 as a rotary polygon mirror that is rotationally driven by a high speed rotation motor.

The deflected beam light 2 is reflected by the reflection mirror 4 through the fθ lens 3 and forms a spot image having a required resolution at the exposure position point 6 on the photosensitive drum 5 as an image carrier. An electrostatic latent image is formed on the photosensitive drum 5 by being scanned and exposed. Further, the deflected light beam 2 is detected by a beam detector composed of a photodiode, so that the main scanning direction (horizontal direction) is synchronized.

Around the photosensitive drum 5, a charger 7 for charging the surface of the photosensitive drum 5 and the photosensitive drum 5 are provided.
A developing device 8 for developing the electrostatic latent image on the top, a transfer charger 9 for transferring the toner image on the photoconductor drum 5 onto a sheet, a charge removing charger 10 for removing the charge on the surface of the photoconductor drum 5, a surface of the photoconductor drum 5. A cleaner 11 for cleaning the above and a charge eliminating lamp 12 for keeping the surface potential of the photosensitive drum 5 constant are provided.

The photosensitive drum 5 is rotationally driven at a peripheral speed of Vo by a drive motor (not shown), and the surface thereof is charged by a charging charger 7 having a grid electrode. The surface of the photoconductor drum 5 is formed of an organic photoconductor. This photoconductor usually has a high resistance, but it has the property of changing the specific resistance of the light irradiation portion when light is irradiated.

Then, the surface of the charged photosensitive drum 5 is scanned and exposed by the beam light 2 corresponding to the image data, so that an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum 5. It The electrostatic latent image is an image formed on the surface of the photoconductor drum 5 by charging, and the irradiation of the beam light 2 reduces the specific resistance of the irradiation surface of the photoconductor, so that the charged charges flow and the beam light is emitted. 2 is formed by remaining electric charge in the portion not irradiated with 2 (negative latent image).

In this way, the light beam 2 is spot-imaged on the charged photosensitive drum 5 at the exposure position 6 and the electrostatic latent image is formed on the photosensitive drum 5. The electrostatic latent image on the photosensitive drum 5 is developed by the developing device 8 to become a visible toner image at this position.

In the developing device 8, a toner containing a dye and formed of resin and a magnetic material (carrier) are mixed. The toner is frictionally charged by being agitated in the developing device 8, and has a charge of the same polarity as the electrostatic charge charged on the photosensitive drum 5. As the surface of the photosensitive drum 5 passes through the developing device 8, the toner electrostatically adheres only to the electrostatic latent image portion where the charge is removed, and the electrostatic latent image is developed by the toner. (Reverse development).

The photosensitive drum 5 on which the toner image is formed is
Subsequently, the transfer charger 9 rotates at the speed of Vo, and at the transfer position, the transfer charger 9 transfers the transfer material onto the paper as the transfer material supplied at a timing by the paper feeding system.

The paper feeding system comprises a pickup roller 13, a feed roller 14, and a registration roller 15. The paper picked up by the pickup roller 13 from the paper feed cassette 16 is conveyed to the registration roller 15 by the feed roller 14, and the registration roller 15 corrects the posture of the paper and then sends the paper to the transfer position.

The toner image in contact with the paper at the transfer position is separated from the photosensitive drum 5 by the transfer charger 9 and transferred onto the paper. As a result, a toner image based on the image data is formed on the paper.

The sheet on which the toner image has been transferred adheres to the surface of the photoconductor drum 5 due to static electricity, and is peeled off from the surface of the photoconductor drum 5 by the peeling charger 17 and sent to the fixing device 18. .. The fixing device 18 is composed of a heat roller having a heater incorporated therein, and heats a toner image only on the sheet by an electric charge to melt the toner and permanently fix the toner on the sheet.
The paper on which the fixing is completed is carried out to the paper discharge tray 20 by the sending roller 19.

On the other hand, the photosensitive drum 5 which has passed the transfer position
Is rotatably driven at the outer peripheral speed VO as it is, the surface of the surface is discharged by the discharging charger 10, the residual toner and paper dust are cleaned by the cleaner 11, and the surface potential of the discharging lamp 12 is adjusted to a constant level. The series of processes from the charger 7 is again entered.

FIG. 1 shows in detail the essential parts of a laser printer using the correction means according to the first embodiment. In the figure, the horizontal synchronization detector 21 is composed of, for example, a photodiode, and is arranged on the upstream side in the scanning direction of the light beam 2. The light beam 2 once emits light from before the horizontal sync detector 21 and scans on the horizontal sync detector 21 to set the horizontal position writing position (horizontal exposure start time) on the photosensitive drum 5. decide. That is, the light beam 2 scanning the horizontal synchronization detector 21 is detected, and the exposure on the photoconductor drum 5 is started each time after a certain time has passed, so that the static light formed on the photoconductor drum 5 is detected. The positions of the electric latent images in the main scanning direction with respect to the sub scanning direction are aligned.

Conventionally, only the horizontal synchronization detector 21 was used to correct the position in the main scanning direction, but not to correct it in the sub scanning direction. However, in reality, as described above, the exposure position of the light beam 2 on the photoconductor drum 5 in the sub-scanning direction (vertical direction) varies due to the surface tilt of the polygon mirror 1 and the vibration of the reflection mirror 4. This occurs, and this causes unevenness in the pitch of the image, which is one of the causes of image deterioration.

Therefore, in the present embodiment, the vertical sync detector 2
2 and an arithmetic unit 2 for calculating the amount of deviation of the vertical exposure position of the light beam 2 based on the output signal of the vertical synchronization detector 22.
4, the servo mirror 23 for controlling the vertical exposure position of the light beam 2, and the servo mirror 23 for calculating the servo mirror 23.
A control unit 29 is provided for controlling the output based on the output of FIG.

The vertical sync detector 22 is, for example, a reduced type C.
Horizontal sync detector 2 consisting of CD linear image sensor
1 is arranged on the upstream side in the scanning direction of the light beam 2,
Further, it is arranged on the upstream side of the horizontal synchronization detector 21.
In this embodiment, as a reduction type CCD linear image sensor, for example, TCD106C manufactured by Toshiba Corporation is used.
(Pixel size 7 × 7 μm) is used.

Here, a basic description of the CCD linear image sensor will be given. As shown in FIG. 3, the basic structure of a CCD is a MOS capacitor in which electrodes are provided on an insulating film on the surface of a semiconductor substrate. When a voltage is applied to the electrode, a depletion layer is formed in the vicinity of the interface between the insulating film and the semiconductor substrate, and this becomes a voltage depression having a low energy level with respect to minority carriers (this is called a potential well). If you inject the signal charge generated by light incidence into the well of this potential,
These are temporarily accumulated and stored as analog quantities.

Next, the operation principle of the CCD analog shift register (charge transfer) will be described. As an example, the case of three-phase drive is shown in FIG. In the CCD analog shift register, a plurality of units of MOS capacitors are arranged close to each other as shown in the figure, and a signal charge is transferred from one MOS capacitor to an adjacent MOS capacitor to transfer the charges. First, at time t1, the signal charge accumulated under the electrode of φ1 partially moves under the electrode of φ2 by applying a positive voltage to the electrode of φ2 (time t2).
Further, by lowering the positive voltage of the φ1 electrode (time t3), all the signal charges move to below the electrode of φ2 (time t4). By sequentially performing this operation, transfer of charges is realized.

Actually, the CCD linear image sensor is composed of a photosensitive section composed of a pn photodiode and a transfer section called a CCD analog shift register. The photodiode, which has received the charge injection in the photosensitive section, moves the photo-accumulated charges of all bits to the analog shift register at once by the shift pulse signal. Then, while the photosensitive unit is injecting the next charge, the image signal of one pixel is transferred and taken out from the analog shift register in accordance with the transfer clock pulse in each cycle of the transfer clock pulse.

The vertical exposure position of the light beam 2 is detected as follows. First, the initial value is shown in FIG.
As shown in (a), the CCD linear image sensor (vertical synchronization detector 22) is set so that a predetermined threshold of the signal charge of the light beam is incident on the bit position N1 of the CCD linear image. The bit position N1 in the sensor is stored in the calculation unit 24 as the reference exposure position. Then, when the exposure position is displaced as shown in FIG. 5B, the displacement amount in the CCD linear image sensor is detected by counting the transfer clock pulse in the arithmetic unit 24.

That is, the threshold of the signal charge accumulated as a predetermined analog amount is compared with the extracted image signal of each pixel, and the transfer clock pulse when the condition is satisfied is the bit in this CCD linear image sensor. The position is N2. The difference (N2-N1) in the number of bits between the read position N2 and the bit position N1 is sent to the control unit 29. With respect to this bit shift number (N2-N1), the control unit 29 determines that the beam width of the light beam 2 is
The deviation amount of the exposure position of is derived as (N2−N1) × 7 μm. The control unit 29 further determines the correction angle of the servo mirror 23 based on each of the optical characteristic values given in advance on the basis of the positional deviation amount.

In this way, the vertical synchronizing signal is generated from the output signal of the CCD linear image sensor, that is, the vertical synchronizing detector 22. Actually, the CCD linear image sensor used needs to read the odd bits and the even bits separately, and also needs a reset pulse, but the detailed description is omitted here. FIG. 6 shows a schematic example of this read timing chart.

On the other hand, the optical system which is the scanning unit of the beam light,
A semiconductor laser oscillator 25 driven and controlled by the print control unit 35, a shaping optical system 26 including a cylindrical lens for shaping the laser beam light output from the semiconductor laser oscillator 25, and a beam light after being shaped by the shaping optical system 26. And a polygon mirror 1 for scanning the light beam from the servo mirror 23 toward the reflection mirror 4, and an fθ lens 3 provided between the polygon mirror 1 and the reflection mirror 4. To be done.

The servo mirror 23 has a support shaft 27 that can rotate about an axis parallel to the rotation axis of the photosensitive drum 5, and a mirror correction actuator 28 that causes a minute rotation around the support shaft 27 is provided. Has been. In this embodiment, the mirror correction actuator 28 uses a piezoelectric element that causes a minute displacement when a voltage is applied.

The shift amount of the vertical exposure position of the light beam 2 on the photosensitive drum 5 calculated by the calculation unit 24 based on the output signal from the vertical synchronization detector 22 is determined by the control unit 2.
At 9, the amount of change in the reflection angle of the servo mirror 23 is converted and output to the mirror correction actuator 28 via the actuator drive unit 30. The mirror correction actuator 28 controls the reflection angle of the servo mirror 23 based on this value, and corrects the vertical exposure position of the light beam 2.

The vertical exposure position of the light beam 2 is corrected on each surface of the polygon mirror 1 that scans the light beam 2, and the vertical synchronization detector 22 is scanned with the light beam 2 to detect the photosensitive member. This is performed until the exposure on the drum 5 is started, and the beam light 2 exposes an accurate position on the photosensitive drum 5.

As described above, according to the first embodiment, the exposure position of the light beam 2 on the photosensitive drum 5 in the vertical direction is deviated due to, for example, the surface tilt of the polygon mirror 1 or the vibration of the reflection mirror 4. Even if occurs, since the exposure position deviation is corrected by calculating the exposure position deviation amount before the actual exposure on the photosensitive drum 5, the vertical exposure position deviation on the photosensitive drum 5 does not occur. Disappear. Therefore, it is possible to prevent pitch unevenness from occurring in the output image, and it is possible to obtain a high-definition image.

FIG. 7 and FIG. 8 show in detail the main parts of the laser printer using the correction means according to the second embodiment. In the second embodiment, the servo mirror 23 as in the first embodiment is not provided, but instead the reflection angle of the reflection mirror 4 is controlled to correct the vertical exposure position of the light beam 2. It was done.

That is, the reflection mirror 4 is provided with a support shaft 2 which is rotatable about an axis parallel to the rotation axis of the photosensitive drum 5.
A mirror correction actuator 28, which has 7 and causes a minute rotation around the support shaft 27, is provided. Also in this second embodiment, the mirror correction actuator 2
As the element 8, a piezoelectric element that causes a minute displacement when a voltage is applied is used.

When the mirror correction actuator 28 is driven, the reflection angle of the reflection mirror 4 changes, so that the beam light 2
Of the light beam 2 on the photoconductor drum 5 by changing the optical path of
The exposure position can be changed in the rotation direction of the photoconductor drum 5, that is, in the vertical direction. The process and means for calculating the vertical exposure position shift amount of the light beam 2 and converting it into the movement amount of the mirror correction actuator 28 for output are the same as in the case of the first embodiment. ,
It is performed by the arithmetic unit 24, the control unit 29, and the actuator driving unit 30. In this way, the beam light 2 reflected by the reflection mirror 4 whose reflection angle is controlled exposes an accurate position on the photosensitive drum 5.

According to the second embodiment described above, the same effect as that of the first embodiment can be expected, and since the servo mirror as in the first embodiment can be omitted, the structure is simplified and the cost is reduced. Can be lowered.

FIG. 9 shows in detail the essential parts of a laser printer using the correcting means according to the third embodiment. In the third embodiment, the vertical sync detector 22 is also used as a horizontal sync detector.

That is, the output signal of the vertical sync detector 22 is sent to the arithmetic section 24, where the horizontal sync signal and the vertical sync signal are generated. As explained above, CCD
In a linear image sensor, first, a photosensitive part made up of a photodiode generates signal charge by light incidence,
These are temporarily accumulated and stored as analog quantities. This is moved to a transfer unit called a CCD analog shift register at once by a shift pulse, and a transfer clock pulse is applied to take out an image signal of each pixel. That is, the threshold of the signal charge accumulated as an analog amount is determined in advance, and this is compared with the extracted image signal of each pixel, and when the condition is satisfied, the horizontal synchronization time may be set.

This horizontal synchronizing time is counted by the timer in the arithmetic unit 24. That is, the timer measures the time T from when an image signal satisfying the threshold condition is obtained to when an image signal satisfying the next threshold condition is obtained. However, when the vertical exposure position of the light beam 2 is deviated, the time of the horizontal synchronizing signal becomes longer or shorter.

Therefore, the number N of transfer clock pulses when an image signal satisfying the threshold condition is obtained,
The time F of the transfer clock pulse is multiplied and the time subtracted from the horizontal sync time T is used as the horizontal sync reference time To. That is, the relationship of (horizontal synchronization reference time TO) = (horizontal synchronization time T)-(transfer clock pulse number N) * (transfer clock pulse time F) is established.

As a result, even if the vertical exposure position of the light beam 2 is deviated, the start time of the horizontal writing position (horizontal exposure position) is corrected,
You can always start writing from a fixed position. The vertical exposure position of the light beam 2 is detected in the same manner as in the first embodiment.

According to the third embodiment described above, the same operational effect as that of the first embodiment can be expected, and since the vertical sync detector also serves as the horizontal sync detector, there is only one sync detector. Only, the structure can be simplified and the cost can be reduced.

FIG. 10 shows in detail the essential parts of a laser printer using the correcting means according to the fourth embodiment. In the fourth embodiment, as in the second embodiment, the servo mirror 23 is omitted and the reflection angle of the reflection mirror 4 is controlled in the same manner as in the second embodiment, so that the vertical direction of the light beam 2 is changed. The exposure position is corrected.

According to the above-described fourth embodiment, the same effect as that of the third embodiment can be expected, and since the servo mirror can be omitted, the structure can be further simplified and the cost can be reduced.

FIG. 11 shows in detail the essential parts of a laser printer using the correction means according to the fifth embodiment. In the fifth embodiment, the vertical synchronization detector 22 is arranged at a position equivalent to that on the surface of the photosensitive drum 5 in the third embodiment. Even in this case, the same effect as that of the third embodiment can be expected.

FIG. 12 shows in detail the essential parts of a laser printer using the correcting means according to the sixth embodiment. In the sixth embodiment, as in the fourth embodiment, the servo mirror 23 is omitted and the reflection angle of the reflection mirror 4 is controlled in the same manner as in the fourth embodiment, so that the beam light 2 in the vertical direction is changed. The exposure position is corrected. Even in this case, the same effect as that of the fourth embodiment can be expected.

FIG. 13 shows in detail the essential parts of a laser printer using the correction means according to the seventh embodiment. This seventh embodiment differs from the first embodiment in that the photosensitive drum 5
The exposure position of the light beam 2 in the vertical direction is corrected in consideration of the rotational fluctuation of the light.

That is, the photosensitive drum rotation fluctuation detector 3
1 is, for example, a high-precision rotary encoder,
It is mounted on the rotary shaft of the photosensitive drum 5. The photosensitive drum rotation fluctuation detector 31 generates an encode pulse according to the rotation of the photosensitive drum 5 and inputs it to the arithmetic unit 33. The calculation unit 33 compares the output pulse of the photosensitive drum rotation fluctuation detector 31 with the reference pulse from the reference pulse oscillator 32 to calculate the amount of deviation of the actually rotated photosensitive drum 5 from the reference position. , To the control unit 29.

The control unit 29 adds, for example, the shift amount of the exposure position of the light beam 2 calculated by the output of the calculation unit 24 and the shift amount of the photosensitive drum 5 calculated by the calculation unit 33, and the addition is performed. The result is converted into a reflection angle change amount of the servo mirror 23, and the servo mirror 23 is controlled via the actuator drive unit 30.

According to the seventh embodiment described above, for example,
Even if the vertical exposure position of the light beam 2 on the photosensitive drum 5 is deviated due to the surface tilt of the polygon mirror 1, the vibration of the reflection mirror 4, the rotational fluctuation of the photosensitive drum 5, or the like. Before exposure on the photoconductor drum 5 of
Since the exposure position deviation is corrected by calculating the exposure position deviation amount, the vertical exposure position deviation on the photosensitive drum 5 is eliminated. Therefore, it is possible to prevent pitch unevenness from occurring in the output image, and it is possible to obtain a high-definition image.

FIG. 14 shows in detail the essential parts of a laser printer using the correcting means according to the eighth embodiment. In the eighth embodiment, as in the second embodiment, the servo mirror 23 is omitted and the reflection angle of the reflection mirror 4 is controlled in the same manner as in the second embodiment, so that the vertical direction of the beam 2 is changed. The exposure position is corrected.

According to the above-described eighth embodiment, the same operational effect as that of the seventh embodiment can be expected, and since the servo mirror can be omitted, the structure can be further simplified and the cost can be reduced.

[0066]

As described above in detail, according to the present invention, even if the exposure position shift in the vertical direction on the image carrier due to the optical path occurs, it can be corrected and the pitch unevenness in the output image can be caused. Therefore, it is possible to provide an image forming apparatus capable of obtaining a high-definition image.

Further, according to the present invention, even if the exposure position shift in the vertical direction on the image carrier due to the fluctuation of the optical path and the moving state of the image carrier occurs, it can be corrected, and the pitch unevenness in the output image can be corrected. It is possible to provide an image forming apparatus that can obtain a high-definition image without raising it.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing in detail a main part of a laser printer using a correction unit according to a first embodiment.

FIG. 2 is a configuration diagram schematically showing an internal structure of a laser printer.

FIG. 3 is a basic structure diagram of a CCD.

FIG. 4 is a diagram showing the operating principle of a CCD analog shift register.

FIG. 5 is a state diagram of a vertical sync detector.

FIG. 6 is a read timing chart of the CCD linear image sensor.

FIG. 7 is a configuration diagram showing in detail a main part of a laser printer using a correction unit according to a second embodiment.

FIG. 8 is a side view of the main part of the second embodiment.

FIG. 9 is a configuration diagram showing in detail a main part of a laser printer using a correction means according to a third embodiment.

FIG. 10 is a configuration diagram showing in detail a main part of a laser printer using a correction means according to a fourth embodiment.

FIG. 11 is a configuration diagram showing in detail a main part of a laser printer using a correction means according to a fifth embodiment.

FIG. 12 is a configuration diagram showing in detail a main part of a laser printer using a correction means according to a sixth embodiment.

FIG. 13 is a configuration diagram showing in detail a main part of a laser printer using a correction means according to a seventh embodiment.

FIG. 14 is a configuration diagram showing in detail a main part of a laser printer using a correction means according to an eighth embodiment.

[Explanation of symbols]

1 ... Polygon mirror (rotating polygonal mirror), 2 ... beam light, 4 ... reflection mirror, 5 ... photosensitive drum (image carrier), 8 ... developing device, 16 ... paper feed cassette, 18 ......
Fixing device, 21 ... Horizontal sync detector, 22 ... Vertical sync detector, 23 ... Servo mirror, 24 ... Arithmetic unit, 25
...... Semiconductor laser oscillator, 27 ...... Support shaft, 28 ...... Mirror correction actuator, 29 ...... Control section, 30 ...... Actuator drive section, 31 ...... Photosensitive drum rotation fluctuation detector, 32 ...... Reference pulse oscillator, 33 ... Calculation unit, 3
5: Print control unit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location H04N 1/23 103 Z 9186-5C (72) Inventor Masao Yamaguchi 70 Yanagicho, Kawasaki-shi, Kanagawa Prefecture Toshiba Yanagimachi Plant (72) Inventor Koichi Watanabe 70 Yanagicho, Sachi-ku, Kawasaki-shi, Kanagawa Toshiba Yanagimachi Plant

Claims (3)

[Claims] 1. An image forming unit for forming an image on an image carrier by scanning and exposing the image carrier moving by the beam light, and the beam before the exposure of the light beam to the image carrier. By detecting the exposure position of the light in the vertical direction with respect to the image carrier and the exposure position detected by the detection device and a preset reference exposure position, the vertical exposure of the light beam is performed. A displacement amount calculation unit that calculates the displacement amount of the position, and a vertical exposure position control unit that controls the exposure position of the light beam in the vertical direction with respect to the image carrier based on the displacement amount calculated by the displacement amount calculation unit. An image forming apparatus characterized by the above. 2. An image forming unit for forming an image on the image carrier by scanning and exposing the image carrier moving by the beam light, and the beam before the exposure of the light beam to the image carrier. A beam light detecting means for detecting light, a vertical exposure position detecting means for detecting an exposure position of the light beam in a vertical direction with respect to an image carrier based on an output signal of the beam light detecting means, and this vertical exposure position detecting means A displacement amount calculating means for calculating a displacement amount of the exposure position in the vertical direction of the light beam by comparing the detected exposure position with a preset reference exposure position, and a displacement amount calculating means for calculating the displacement amount. Vertical exposure position control means for controlling the exposure position of the light beam in the vertical direction with respect to the image carrier based on the shift amount; and the light beam based on the output signal of the light beam detection means. An image forming apparatus characterized by including a horizontal exposure start time control means for controlling the horizontal direction of the exposure start time for the image bearing member. 3. An image forming means for forming an image on the image carrier by scanning and exposing the image carrier moving by the beam light, and the beam before the exposure of the light beam on the image carrier. By comparing the exposure position detected by the first detection means for detecting the exposure position of the light in the vertical direction with respect to the image carrier and the preset reference exposure position, A deviation amount calculating means for calculating a deviation amount of the exposure position in the vertical direction, a second detecting means for detecting a moving state of the image carrier, a moving state of the image carrier detected by the second detecting means, and An image forming apparatus comprising: a vertical exposure position control unit that controls an exposure position of the light beam in a vertical direction with respect to the image carrier based on the displacement amount calculated by the displacement amount calculation unit.