JPH08305095A - Image forming device - Google Patents

Abstract

PURPOSE: To suppress the occurrence of density unevenness while keeping such constitution that attachment/detachment is easy by constituting so that developing density is controlled by detecting the displacement of an image forming unit. CONSTITUTION: The vibration or the fluctuation component of the image forming unit 1 is detected by a vibration detection means 7 and the vibration or the fluctuation thereof is transmitted to a density control means 8 as an analog vibration signal. Then, since the moving speed of the unit 1 in a direction shown by an arrow B is added to the surface moving speed of a photoreceptor 9 in a direction shown by an arrow A when the unit 1 is displaced downward, the image density is lowered as the result. In such a case, since an output transmitted to the power source circuit of an electrostatic charge roll by the detection means 7 becomes large, the DC level of a chopping wave signal rises and the pulse width of a switching pulse becomes narrow. Besides, an output high voltage is lowered. Therefore, the electrostatic charge potential of a photoreceptor 9 is lowered and potential difference between the electrostatic charge potential and a developing bias voltage becomes large. Besides the developing density is made high. Thus, the image density is maintained to be constant as a whole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus using a detachable image forming unit containing an image bearing member, and more particularly to density unevenness on an image due to a displacement of a mounting position of the image forming unit. The present invention relates to a device for suppressing the occurrence of

[0002]

2. Description of the Related Art For example, in an electrophotographic image forming apparatus, in order to facilitate repair and maintenance,
It is known to use a detachable image forming unit containing an image carrier and a developing device. In an electrophotographic image forming apparatus using such an image forming unit, the rotation of a motor provided on the main body side of the image forming apparatus is transmitted to an image carrier in the image forming unit via a drive device such as a gear. The image carrier is driven to rotate. An exposure device such as a laser scanner provided on the main body side of the image forming apparatus scans the surface of the image carrier previously charged to a constant potential at a predetermined pitch to form an electrostatic latent image on the image carrier. A toner image is obtained by developing this electrostatic latent image.

However, in an electrophotographic image forming apparatus using such an image forming unit, the image forming unit is provided between the image forming unit and a housing portion for housing the image forming unit with respect to the apparatus main body. Since a slight gap is formed to make it detachable, when the image carrier is driven, the image forming unit itself oscillates and vibrates to change the exposure scanning pitch, resulting in uneven density on the image. There was a problem that it occurred. In the case of the developing method in which toner adheres to the exposed portion, for example, if the image forming unit is displaced in the same direction as the moving direction of the surface of the image carrier when viewed at the exposure position, the peripheral speed of the image carrier is equivalently equivalent. Since the scanning speed becomes faster, the scanning pitch of the exposure becomes wider and the density becomes lower. When displaced in the opposite direction, the concentration increases. The image forming unit periodically oscillates in synchronism with the rotational driving of the image carrier, and since the photoconductor rotates, the toner image formed on the photoconductor has a moving direction of the photoconductor. A striped pattern in which the density changes periodically is generated. This striped pattern is not included in the original image to be output, and causes deterioration of the image quality of the output image.

Therefore, in order to solve such a problem, as shown in FIG. 8, the image forming unit 1 is fitted to a positioning mechanism 3 provided on the apparatus main body 2 side, and a pressing member 4 such as a spring is used. It is known that the image forming unit 1 is positioned with respect to the apparatus main body 2 by pressing the image forming unit 1 against the positioning mechanism 3.
However, even in this case, it is necessary to set a fitting gap to some extent so that the image forming unit 1 can be attached and detached, and it is difficult to completely position the image forming unit 1.

Further, as described in JP-A-6-194892, it has been proposed to devise a positioning arrangement so that the image forming unit 1 does not easily swing even when the image carrier is driven. . That is, the guide groove 5 is provided on the apparatus main body 2 side, and the shaft 6 of the image carrier is supported by the guide groove 5 to prevent the image forming unit from rocking even when the image carrier is driven. . However, even with such a device, the image forming unit 1 is not completely fixed to the image forming apparatus main body 2 <, and vibration occurs during driving, which causes uneven density.

Further, in order to effectively prevent the swinging of the unit by a device such as the conventional branching technique described above, the fitting / removing fitting gap is made smaller, and the mounting / detaching guide groove 5 is made longer. It has a drawback that it requires a configuration, and as a result, it is difficult to attach and detach.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and eliminates the above-mentioned drawbacks and suppresses the occurrence of density unevenness while leaving the structure easy to attach and detach. The purpose is to do.

[0008]

SUMMARY OF THE INVENTION According to the present invention, an image forming unit device having an image bearing member built therein is detachably attached to an apparatus main body, and the image bearing unit is attached to the image bearing unit by an exposure device provided in the apparatus main body. In an image forming apparatus for exposing, a vibration detecting unit for detecting a swing or a vibration of the image forming unit unit, and a density of an image formed on the image carrier using a vibration signal detected by the vibration detecting unit. And a density control means for controlling the occurrence of density unevenness on the image.

[0009]

The operation of the present invention will be described with reference to specific examples.

FIG. 1 is a schematic diagram showing the basic structure of the present invention. The image forming apparatus main body 2 is provided with a positioning mechanism 3, and the image forming unit 1 inserted in the image forming apparatus main body 2 is pressed against the positioning mechanism 3 by a biasing means (not shown). As a result, the image forming unit 1 is substantially positioned with respect to the image forming apparatus main body 2. Further, on the image forming apparatus main body 2 side, a vibration detecting unit 7 that contacts the image forming unit 1 inserted in the image forming apparatus main body 2 to detect the vibration of the image forming unit 1, and by the vibration detecting unit 7 A density control unit 8 is provided for controlling the density of image formation according to the obtained vibration signal.

When the image carrier included in the image forming unit 1 is rotationally driven, the image forming unit 1 also vibrates accordingly. This vibration is detected by the vibration detecting means 7,
The density of the image formation is controlled and controlled by the density control means 8 according to the detected vibration. For example, in the case of a reversal development method in which toner adheres to the exposed portion, the image forming unit 1
If it is displaced in the same direction as the moving direction of the surface of the image carrier 9 when viewed at the exposure position, the peripheral speed of the image carrier is equivalently increased, so that the exposure scanning pitch is widened and the density is reduced.
At this time, the density of image formation is controlled to be high,
A decrease in concentration is prevented. Further, when the image forming unit 1 is displaced in the opposite direction, the image forming unit 1 is controlled in the opposite manner to prevent the increase of the density.

[0012]

EXAMPLES The present invention will be described below based on examples.

FIG. 2 is a schematic view showing an embodiment of the image forming apparatus of the present invention. The image forming unit 1 is detachably attached to the image forming apparatus main body 2. The image forming unit 1 includes a drum-shaped photoconductor 9 that rotates in the direction of arrow A, a charging roll 10 that contacts the surface of the photoconductor 9 and charges the surface of the photoconductor 9 to a uniform potential, and a photoconductor 9
The developing device 11 and the like for developing the electrostatic latent image formed on the surface of the toner with toner is incorporated. The developing machine 11 includes a developing roll 11a arranged close to the photoconductor 9, and a predetermined negative bias voltage is applied to the developing roll 11a from a bias power source (not shown).

On the image forming apparatus main body 2 side, a positioning mechanism 3 for positioning the image forming unit 1, a pressing member 4 for pressing the image forming unit 1 against the positioning mechanism 3, and a uniform charging. A laser scanner 12 that forms an electrostatic latent image by irradiating the surface of the photoconductor 9 with a laser beam 12a while scanning the photoconductor 9 in the axial direction of the photoconductor 9 at a constant cycle, and a photoconductor incorporated in the image forming unit 1. A drive motor 13 and a gear train 14 that apply a rotational driving force to the body 9, a recording paper storage unit 15 that stores recording paper on which an image is to be formed, a paper feeding device 16 that sends the recording paper from the recording paper storage unit 15, and a recording paper. A paper feeding chute 17 that guides the recording paper sent from the storage unit 15 to the transfer unit of the image forming unit 1 and a toner image formed on the surface of the photoconductor 9 are supplied from the paper feeding chute 17. Transfer device for transferring the recording paper 1
8, a paper discharge chute 19 for guiding the recording paper after transfer, a fixing device 20 for fixing the toner image on the recording paper, and the like are provided. In addition, a part of the upper surface of the image forming apparatus main body 2 is inclined to form a paper discharge tray 2a.

Further, in this embodiment, the positioning mechanism 3
Using the vibration detection means 7 such as a piezoelectric element that is disposed near the image forming unit 1 and is in contact with the image forming unit 1 with the image forming unit 1 inserted in the image forming apparatus main body 2, and a signal sent from the vibration detecting means 7. A density control means 8 for keeping the development density constant is provided. In the present embodiment, the vibration detection unit 7 is supposed to increase its output when the image forming unit 1 is pressed by the vibration detection unit 7 or when the image formation unit 1 approaches.

FIG. 3 is a circuit diagram showing a concrete embodiment of the density control means 8 shown in FIG. In the example shown in FIG. 3, the power supply circuit 21 for the charging roll 10 of the image forming unit 1 functions as the density control means 8. FIG.
FIG. 6 is a waveform diagram for explaining the operation of the charging roll power supply circuit 21.

As shown in FIG. 4A, the triangular wave signal S1 having a predetermined period from the oscillation circuit 22 and the reference voltage generation circuit 23.
The reference voltage signal S2 is compared with the differential amplifier circuit 24, and from the differential amplifier circuit 24, a periodic switching pulse S3 having a pulse width according to the DC level of the triangular wave signal S1 (see FIG. 4B). ) Is generated. The switching pulse S3 is supplied to the output transistor 27 of the drive circuit 26 via the drive current control circuit 25, and the output transistor 27 is periodically turned on / off. Therefore,
The current flowing to the primary side of the step-up transformer 28 is intermittent, and the switching pulse S3 is applied to the secondary side of the step-up transformer 28.
A negative high voltage (see FIG. 4 (c)) corresponding to the pulse width is generated. For example, when the DC level of the triangular wave signal S1 is lowered, the pulse width of the switching pulse S3 is widened and the ON period of the output transistor 27 is lengthened.
The output high voltage (absolute value) rises.

A part of the high voltage is rectified and applied to the charging roll 10 in a state of being superposed on the AC high voltage. A part of the output of the step-up transformer 28 is fed back to the input side of the differential amplifier circuit 24 via the output voltage detection circuit 29, and a closed loop is formed so that the output voltage is maintained constant.

For example, when the output high voltage (absolute value) decreases, the negative input of the differential amplifier circuit 24 decreases and the pulse width of the switching pulse S3 increases, so that the charging roll power supply circuit 21 increases the output voltage. Is controlled to prevent the output high voltage from decreasing.

A charging ON / OFF signal for controlling ON / OFF of the charging operation is supplied to the drive current control circuit 25 via the output ON / OFF control circuit 30. The configuration of the charging roll power supply circuit 21 described so far is the same as that of the conventional charging roll power supply circuit for a charger.

In this embodiment, the signal from the vibration detecting means 7 is supplied to the input side of the differential amplifier circuit 24, and the high voltage applied to the charging roll 10 is controlled according to the vibration of the image forming unit 1. I am trying to do it.

Next, the density correction operation in the above-mentioned image forming apparatus will be described.

When the start of printing is instructed, the drive motor 13 starts rotating, and this rotation is transmitted to the photoconductor 9 via the gear train 14, and the photoconductor 9 rotates. The last gear of the gear train 14 and the driven gear provided on the rotation shaft of the photoconductor 9 can be brought into contact with and separated from each other.
Both gears are engaged with each other when mounted in the image forming apparatus main body 2. Since the image forming unit 1 is attached to the image forming apparatus main body 2 with a slight gap, when the rotational force is applied from the gear train 14 to the driven gear of the photoconductor 9, the image forming unit 1 Receives a force and swings or vibrates.

A component of vibration or swing of the image forming unit 1 in the unmarked direction is detected by the vibration detection means 7, and the swing or vibration is sent to the density control means 8 as an analog vibration signal.

Now, the developing system of the image forming unit 1 is
A xerographic method of negative charge reversal development as shown in FIG. 5, that is, the surface of the photoconductor 9 is negatively charged, the charge is discharged by exposure, and the density is changed according to the difference between the developing bias voltage and the exposure potential. It is assumed to be a developing method.

In FIG. 2, when the image forming unit 1 is displaced downward, the moving speed of the image forming unit 1 in the arrow B direction is added to the original surface moving speed of the photosensitive member 9 in the arrow A direction. Therefore, the rotation speed of the photoconductor 9 is increased. Therefore, the laser beam 12a from the laser scanner 12 widens the pitch of the scanning lines formed on the surface of the photoconductor 9, and the density is reduced.

When the image forming unit 1 is displaced downward, the output of the vibration detecting means 7 to the charging roll power supply circuit 21 becomes large, so that as shown in FIG. DC level rises, Fig. 4 (e)
As shown in FIG. 4, the pulse width of the switching pulse S3 becomes narrow, and the output high voltage decreases as shown in FIG. 4 (f). Therefore, the charging potential of the photoconductor decreases from the state shown by the broken line in FIG. 5 to the state shown by the solid line, the potential difference between the charging potential and the developing bias voltage increases, and the developing density increases.

As described above, when the image forming unit 1 is displaced downward, the density of the image is lowered unless any measures are taken, but in this embodiment, the charging roll power source is used. Since the development density is increased by controlling the circuit 21, the image density is maintained constant as a whole. As a result, uneven development density is eliminated and high quality prints can be obtained.

FIG. 6 is a circuit diagram showing another specific embodiment of the density control means 8 shown in FIG. In the example shown in FIG. 6, the laser light amount control circuit 32 connected to the laser drive circuit 31 that drives the laser scanner 12 functions as the density control means 8. FIG. 7 is a waveform diagram for explaining the operation of the laser light amount control circuit 32.

The output of the oscillation circuit 33 is the triangular wave generation circuit 34.
To the triangular wave signal S5 from the triangular wave generation circuit 34.
(See FIG. 7A) is supplied to the negative input of the comparator 35. Further, the output of the oscillation circuit 33 is supplied to the latch circuit 36 via the 1/2 frequency dividing circuit 34, and the latch circuit 36 causes the image data to be 2 times the oscillation cycle of the oscillation circuit 33.
It is latched at the double cycle timing. Latch circuit 36
Is supplied to the D / A conversion circuit 38 via the level conversion circuit 37 for converting the level from the TTL level to the ECL level, and is converted into an analog image signal according to the value of the image data. This analog image signal is supplied to the positive input of the differential amplifier circuit 39. The output signal S6 of the differential amplifier circuit 39 is supplied to the positive input of the comparator 35 and compared with the triangular wave signal S5 from the triangular wave generation circuit 34. The comparator 35 outputs a pulse having a pulse width corresponding to the magnitude of the analog image signal. The signal S7 (see FIG. 7B) is output. The pulse signal S7 from the comparator 35 is supplied to the laser drive circuit 31 via the level conversion circuit 40 that performs level conversion from the ECL level to the TTL level.

The configuration up to this point is the same as the conventional laser light amount control circuit except for the differential amplifier circuit 39. In the present embodiment, the signal from the vibration detection means 7 is supplied to the negative input side of the differential amplifier circuit 39, and the width of the pulse signal supplied to the laser drive circuit 31 is adjusted according to the vibration of the image forming unit 1. I'm trying to control.

Next, the laser light amount control circuit 3 shown in FIG.
The operation of No. 2 will be described.

As the value of the density data increases, that is, when the image approaches white, the output signal S6 of the differential amplifier circuit 39 increases (see FIG. 7C), so the pulse width of the pulse signal S7 is wide. Therefore, the exposure amount of the laser scanner 12 increases. Therefore, the concentration is increased.

When the image forming unit 1 is displaced, a signal corresponding to the amount of displacement is supplied to the negative input side of the differential amplifier circuit 39, and the density is also controlled by the amount of displacement of the image forming unit 1. .

When the image forming unit 1 is displaced downward, the output of the vibration detecting means 7 to the laser light amount control circuit 32 becomes large, so that the output of the differential amplifier circuit 39 decreases. That is, the image signal is corrected in the black direction. Therefore, the exposure amount on the photoconductor is increased and the development density is increased.

As described above, when the image forming unit 1 is displaced in the downward direction, the density of the image is lowered if no measures are taken, but in this embodiment, the laser light amount control is performed. Since the development density is increased by controlling the circuit 32, the image density is maintained constant as a whole. As a result, uneven development density is eliminated and high quality prints can be obtained.

In the above-described embodiment, a piezoelectric element type sensor is used as the vibration detecting means 7, but the invention is not limited to this, and a sensor using a resistance wire strain gauge may be used. . If the signal sent by the vibration detection means 7 exceeds a certain level, the control may be disabled, and an abnormality detection signal may be sent to prompt the operator to inspect the process cartridge.

[0038]

As described above, according to the present invention, in the electrophotographic image forming apparatus using the detachable image forming unit containing the image carrier, the displacement of the image forming unit is detected to determine the developing density. Since it is controlled, the following effects are achieved.

(1) High-quality printing can be performed by correcting density unevenness on a formed image due to vibration or swing of the image forming unit.

(2) Even if the vibration of the image forming unit is large, unevenness in density can be corrected, so that the unit and its attaching / detaching mechanism can be realized with a low-cost structure.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a basic configuration of the present invention.

FIG. 2 is a schematic view showing an embodiment of the image forming apparatus of the present invention.

FIG. 3 is a circuit diagram showing an example of a density control unit using a charging roll power supply circuit.

FIG. 4 is a waveform diagram for explaining the operation of the charging roll power supply circuit.

FIG. 5 is an explanatory diagram of negative charge reversal development.

FIG. 6 is a circuit diagram showing an example of density control means using a laser light amount control circuit.

FIG. 7 is a waveform diagram for explaining the operation of the laser light amount control circuit.

FIG. 8 is a schematic configuration diagram of a conventional unit vibration countermeasure.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image forming unit, 2 ... Image forming apparatus main body, 3 ... Positioning mechanism, 4 ... Pressing member, 5 ... Guide groove, 6 ... Shaft, 7 ...
Vibration detecting means, 8 ... Density control means, 9 ... Photoconductor, 10 ...
Charging roll, 11 ... Developing machine, 12 ... Laser scanner, 13 ... Drive motor, 14 ... Gear train, 15 ... Paper storage unit, 16 ... Paper feeding device, 17 ... Paper feeding chute, 18 ...
Transfer device, 19 ... Paper discharge chute, 20 ... Fixing device, 21
Charging roll power supply circuit, 22 Oscillation circuit, 23 Reference voltage generation circuit, 24 Differential amplifier circuit, 25 Drive current control circuit, 26 Drive circuit, 27 Output transistor, 28
... Step-up transformer, 29 ... Output voltage detection circuit, 30 ... Output on / off control circuit, 31 ... Laser drive circuit, 32 ...
Laser light amount control circuit, 33 ... Oscillation circuit, 34 ... 1/2
Frequency divider circuit, 35 ... Comparator, 36 ... Latch circuit, 3
7 ... Level conversion circuit, 38 ... D / A conversion circuit, 39 ... Differential amplifier circuit, 40 ... Level conversion circuit

Claims (3)

[Claims] 1. An image forming apparatus in which an image forming unit device including an image carrier is detachably attached to an apparatus body, and the image carrier is exposed by an exposure device provided in the apparatus body. Image forming unit A vibration detecting means for detecting a swing or vibration of the unit, and a density of an image formed on the image carrier by controlling a density of an image formed on the image carrier by using a vibration signal detected by the vibration detecting means. An image forming apparatus comprising: a density control unit that suppresses the occurrence of unevenness. 2. The image forming apparatus according to claim 1, wherein the density control means is a charging potential control device that controls the charging potential using the vibration signal. 3. The image forming apparatus according to claim 1, wherein the density control unit is an exposure light amount control device that controls the exposure light amount using the vibration signal.