JP7735144B2 - Image forming device - Google Patents

Description

In the past, in order to stabilize image quality, image forming devices have measured the surface potential of the photosensitive drum using a potential sensor or the like, and based on the measurement results, have adjusted the output of the charging voltage, developing voltage, and exposure intensity during image formation.

Figure 2 shows a block diagram of a surface potential measurement system for a photosensitive drum in a conventional image forming apparatus. In Figure 2, reference numeral 1' denotes the photosensitive drum, reference numeral 8' denotes a potential sensor for measuring the surface potential of the photosensitive drum, reference numeral 107 denotes a potential sensor control unit 107 for controlling the potential sensor 8', and reference numeral 111 denotes a controller 111 for controlling the entire apparatus body.

The operation of Figure 2 will be explained using Figure 3. In Figure 3, when the remote signal input from the controller 111 is turned ON, the operation of the potential sensor 8' and potential sensor control unit 107 begins. First, the drive signal Drv is input to the potential sensor 8 by the drive circuit 8h. This causes the tuning fork vibrator 8e to begin vibrating, with its tip vibrating in the directions of the arrows 8c and 8d on the left and right, respectively.

Meanwhile, as the tuning fork vibrator 8e vibrates, the capacitance between the measurement electrode 8f and the photosensitive drum 1' changes periodically C(t), which changes the amount of charge on the measurement electrode 8f. This change in charge is converted into voltage by the detection resistor RS in the detection circuit 8g, obtaining an AC voltage signal proportional to the potential difference between the photosensitive drum 1' and the measurement electrode 8f. This signal is then amplified and output to the potential sensor control unit 107. Note that the potential sensor 8' operates using the output of the high-voltage power supply 107b as its reference potential.

The potential sensor control unit 107 controls the output of the high-voltage power supply 107b based on the AC detection signal output from the detection circuit 8g so that the amplitude of this AC detection signal becomes zero. Here, the state where the amplitude of the AC detection signal is zero means that the tuning fork vibrator 8e is vibrating and the electrostatic capacitance between the measurement electrode 8f and the photosensitive drum 1' is periodically changing, but the amount of charge on the measurement electrode 8f does not change. This state means that the surface potential of the photosensitive drum 1' and the potential of the measurement electrode 8f, i.e., the surface potential of the photosensitive drum 1' and the output of the high-voltage generation unit 107b, are at the same potential. This makes it possible to obtain the surface potential of the photosensitive drum 1'. (Zero Method)
The potential sensor control unit 107 converts the output of the high voltage generation unit 107b at this time in a detection output signal generation unit (not shown) according to the relationship shown in Fig. 4, for example, and outputs the converted value to the controller 111. Fig. 4 shows the relationship between the detection value, which is the output of the potential sensor control unit 107, and the surface potential of the photosensitive drum 1. In the case of Fig. 4, when the measurement result of the potential sensor control unit 107 is 50V, the output of the detection output signal generation unit 107c is 0V, and when it is -900V, the output of the detection output signal generation unit 107c is 2.85V, so there is a linear relationship between the measurement result and the detection value.

The controller 111 can therefore obtain surface potential information for the photosensitive drum 1' by converting the signal input from the potential sensor control unit 107 based on the relationship shown in Figure 4. Based on this information, it then sets the output values for the charging voltage and developing voltage during image formation, as well as the exposure intensity required to achieve a specified density.

In addition, in image forming devices that use potential sensors like those mentioned above, a non-contact corona charger 2' is used to charge the photosensitive drum 1'. When charging the photosensitive drum 1' using the corona charger 2', an atmospheric discharge occurs, generating ozone. Ozone can cause image defects. For this reason, many image forming devices use a configuration that removes ozone using a fan and exhaust duct.

When miniaturizing an image forming device with this configuration, the exhaust duct is placed between the corona charger and the developer, close to each other. If the developer and exhaust duct are placed close to each other, there is a risk that toner scattered near the developer will be sucked in by the exhaust duct. For this reason, the exhaust duct's intake port is oriented toward the corona charger, which allows ozone to be exhausted while suppressing scattered toner.

In the image forming apparatus described above, it has been proposed that the potential sensor be attached to the ozone exhaust duct due to space constraints and cost reduction reasons.

JP 2011-39450 A

The potential of the above-mentioned potential sensor is roughly the same as the drum potential, and as shown in Figure 4, is approximately 0 to -900 V. Therefore, the exhaust duct must be floated from the housing (GND potential) of the image forming device. For this reason, a resin member is used to float the potential sensor attachment part of the exhaust duct from the GND potential of the image forming device. A resin member that is floated from the GND of the image forming device will have an unstable potential relative to the GND of the image forming device.

When the resin part of the exhaust duct is located near the tuning fork and detection electrode of the potential sensor, in addition to the capacitance C(t) between the detection electrode 8f and the photosensitive drum 1 as described in Figure 3, it is also affected by the capacitance Cd(t) between the detection electrode 8f and the resin part 150e of the exhaust duct near the potential sensor. This capacitance Cd(t) can affect the results of the photosensitive drum potential measurement by the potential sensor, which is an issue.

The image forming apparatus according to the present invention includes a photosensitive member that rotates around a rotation axis, a corona charger that charges the photosensitive member by corona discharge, a developing unit that develops an electrostatic latent image formed on the photosensitive member with toner, a duct that has an opening facing the corona charger, and a potential sensor that is attached to the duct and measures the potential of the photosensitive member, wherein the corona charger, the duct, and the developing unit are arranged in this order from upstream to downstream in the rotation direction of the photosensitive member, and the duct has a first surface that faces the photosensitive member, a second surface that faces the corona charger in the rotation direction and has the opening, and a developing unit that faces the developing unit in the rotation direction. and a third surface on which the potential sensor is attached, the first surface of the duct facing the photosensitive member includes a first portion corresponding to the position where the potential sensor is attached in the direction along the rotation axis, and a second portion at a position different from the first portion in the direction along the rotation axis, a first distance between the first portion and the photosensitive member is longer than a second distance between the second portion and the photosensitive member, the potential sensor protrudes from the first portion of the first surface of the duct toward the photosensitive member, and a third distance between the potential sensor and the photosensitive member is shorter than the first distance and the second distance .

According to this invention, by cutting out the portion of the exhaust duct where the potential sensor is attached near the detection electrode of the potential sensor and the tuning fork, it is possible to reduce the effect of the capacitance that occurs between the exhaust duct resin material and the detection electrode and tuning fork of the potential sensor. This makes it possible to improve the accuracy with which the potential sensor detects the photosensitive drum potential.

FIG. 1 is a diagram illustrating an example of a schematic configuration of an image forming apparatus. FIG. 1 is a block diagram of a surface potential measurement system for a photosensitive drum in a conventional image forming apparatus. 10A and 10B are diagrams illustrating an overview of a potential sensor and a control unit of the potential sensor in a conventional image forming apparatus. 10 is a diagram illustrating the characteristics of a detection output signal generating unit of a potential sensor control unit. FIG. 2 is a schematic diagram of the periphery of a photosensitive drum of the image forming apparatus according to the present embodiment. 10A and 10B are diagrams illustrating the shape of a portion of a conventional exhaust duct in the vicinity of where a potential sensor is attached. 4A and 4B are diagrams illustrating the shape of a portion of the exhaust duct in the vicinity of where the potential sensor is attached according to the present embodiment. 6A and 6B are diagrams illustrating the detection results of the potential sensor and the distance relationship between the potential sensor and the photosensitive drum.

Embodiments of the present invention will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the following embodiments may be modified as appropriate depending on the configuration and various conditions of the device to which the present invention is applied, and are not intended to limit the scope of the present invention to these alone.

Example 1
The image forming apparatus of this embodiment has a schematic configuration as shown in Figure 1. This apparatus is an electrophotographic image forming apparatus. In Figure 1, reference numerals 1a to 1d indicate photosensitive members, 2a to 2d indicate primary chargers, 8a to 8d indicate potential sensors, 3a to 3d indicate exposure units, 4a to 4d indicate developers, 53a to 53d indicate primary transfer units, and 6a to 6d indicate cleaners. Also, reference numeral 51 indicates an intermediate transfer belt, 55 indicates an intermediate transfer belt cleaner, and 56 and 57 indicate secondary transfer units.

After the photoconductor is uniformly charged by the primary charger, an exposure unit applies exposure according to an image signal, forming an electrostatic latent image on the photoconductor. Potential sensors 8a-8d are installed between the exposure and development stages to measure the potential of the electrostatic latent image.

The electrostatic latent image is then developed into a toner image by the developing unit, and the toner images on the four photosensitive drums are multi-transferred to the intermediate transfer belt by the transfer unit, and then transferred to the recording material P by the secondary transfer unit. Residual toner remaining on the photosensitive drums is collected by a cleaner, and residual toner remaining on the intermediate transfer belt is collected by the intermediate transfer belt cleaner 55. The toner image transferred to the recording material P is fixed by the fixing unit 7 to produce a color image.

As shown in Figure 5, the corona charger 2 has a shield plate 2e as the corona charger's housing, a discharge wire 2f, and a grid 2g, and is charged by corona discharge with the photosensitive drum 1. The discharge wire 2f is a tungsten wire with a diameter of approximately 50 μm. Note that the discharge wire may also be made of other conductive materials (which may have an anti-oxidation layer on their surface). It may also be in the shape of a needle electrode, sawtooth electrode, or other similar shape. The grid 2g is made of a metal conductive material edged with a specific pattern such as a mesh. In this embodiment, the charger 2 charges the surface of the photosensitive drum 1 to approximately -850 V. A discharge phenomenon occurs when a current is passed through the discharge wire 2f, generating ozone.

Next, we will explain the air flow around the corona charger. The intake fan 160 attached to the main body sends intake air A from outside the main body to the corona charger 2.

This intake air A is blown into the corona charger 2 through an opening at the top. An exhaust duct 150 is located downstream of the corona charger 2 in the direction of rotation of the photosensitive drum 1 (arrow). This exhaust duct 150 exhausts ozone generated by the discharge wire 2f to the outside of the main body.

As can be seen from Figure 5, the shield 2e of the corona charger 2 has different gaps between itself and the photosensitive drum 1 on the upstream and downstream sides in the direction of rotation of the photosensitive drum 1.

In this way, ozone is sent by intake air A from the opening at the bottom of the corona charger 2 to the exhaust duct 150 downstream in the direction of rotation of the photosensitive drum 1. The exhaust air B sent to the exhaust duct 150 passes through an ozone filter (not shown) at the rear of the main body and is exhausted outside the image forming apparatus.

The exhaust duct 150 also has an opening 150a for exhausting air on the side facing the corona charger. By providing the opening 150a on the side of the exhaust duct 150 in this way, the exhaust duct is prevented from attracting developer that has scattered near the sleeve 4e, which is the developer carrier of the developing unit 4.

If developer is exhausted through the exhaust duct 150 from the opening 150a, there is a possibility that developer may spread throughout the main body or leak outside the machine, so it is desirable to locate the opening 150a as far away from the developer unit 4 as possible.

Most of the intake air A containing ozone is collected in the exhaust duct 150. However, since it is a gas (fluid), it is not possible to collect all of the gas in the exhaust duct 150. In particular, as the photosensitive drum 1 rotates, the exhaust air C that is not collected in the exhaust duct 150 flows into the gap between the exhaust duct 150 and the photosensitive drum 1 shown in Figure 5.

This exhaust air C also contains ozone. Therefore, when the exhaust air C flows into the gap, ozone becomes suspended in the gap between the exhaust duct 150 and the photosensitive drum 1, and in the vicinity of the developing unit, which is downstream from that position in the direction of rotation of the photosensitive drum.

When ozone adheres to the photosensitive drum, it causes a loss of sensitivity in the photosensitive drum, resulting in an image defect known as image deletion, in which the formed image appears white. For this reason, it is desirable to position the exhaust duct opening 150a as close as possible to the photosensitive drum to reduce the amount of exhaust air C.

Figure 6 is a diagram illustrating the shape of the area of a conventional exhaust duct where a potential sensor is attached. Figure 6(a) is a view of the photosensitive drum 1 and exhaust duct 150 from the corona charger 2 side. The potential sensor 8 is attached to the center of the exhaust duct 150 when viewed in the axial direction of the photosensitive drum 1.

The potential sensor 8 is attached to the developer side of the exhaust duct 150. The dotted line in Figure 6(a) indicates the portion that is not visible when the exhaust duct 150 is viewed from the corona charger 2 side, and the solid line indicates the visible portion. Area 8i of the potential sensor 8 is where the detection electrode 8f and tuning fork 8e are located.

As such, in the conventional configuration, the area 8i of the potential sensor 8, where the detection electrode 8f and tuning fork 8e are located, is close to the exhaust duct. As a result, the capacitance between the resin part of the exhaust duct and the detection electrode 8f and tuning fork 8e described above has a significant impact on the drum potential measurement results of the potential sensor.

The exhaust duct opening 150a has a generally rectangular shape that extends along the rotational axis of the photosensitive drum. The opening 150a is located on the opposite side of the rotational direction of the photosensitive drum 1 from the part where the potential sensor 8 is attached.

Figure 6(b) is an enlarged view of the area near the exhaust duct in Figure 5. In this image forming device, the distance D between the photosensitive drum 1 and the potential sensor is 2 mm, and the distance E between the exhaust duct 150 and the drum is 4.8 mm.

Figure 7 is a diagram illustrating the shape of the exhaust duct near the location where the potential sensor is attached in this embodiment. Figure 7(a) is a view of the photosensitive drum 1 and exhaust duct 150 from the corona charger 2 side. The potential sensor 8 is attached to the center of the exhaust duct 150 when viewed in the axial direction of the photosensitive drum 1.

The potential sensor 8 is attached to the developer side of the exhaust duct 150. The dotted line in Figure 7(a) indicates the portion that is not visible when the exhaust duct 150 is viewed from the corona charger 2 side, and the solid line indicates the portion that is visible. Thus, in this embodiment, the potential sensor 8 also protrudes from the exhaust duct 150 toward the photosensitive drum 1 side.

Area 8i of the potential sensor 8 is where the detection electrode 8f and tuning fork 8e are located. In this embodiment, the portion of the exhaust duct 150 where the potential sensor 8 is attached, near the detection electrode 8f of the potential sensor and the tuning fork 8e, is shaped (cut out) as shown in Figure 7(a). This makes it possible to reduce the effect of the capacitance generated between the exhaust duct resin material and the detection electrode and tuning fork of the potential sensor, thereby improving the detection accuracy of the photosensitive drum potential by the potential sensor.

The opening of the exhaust duct 150 has a straight section 150a, where the distance from the photosensitive drum remains the same as in the conventional configuration, a section 150b where the distance from the photosensitive drum changes in a sloped manner, and an inclined section 150c where the distance from the photosensitive drum is longer than in the conventional configuration.

Figure 7(b) is an enlarged view of the vicinity of the exhaust duct in Figure 5. The dotted line portion of the exhaust duct 150 is the portion other than the vicinity where the potential sensor 8 is attached, and exhaust air B1 is exhausted from opening 150a. The solid line portion of the exhaust duct 150 is the vicinity where the potential sensor 8 is attached, and exhaust air B2 is exhausted from opening 150c.

In this embodiment, the distance D between the photosensitive drum 1 and the potential sensor is 2 mm, the distance E between the exhaust duct 150 at opening 150a and the drum is 4.8 mm, and the distance F between the exhaust duct 150 at opening 150c and the drum is 9.2 mm, but other dimensions are also acceptable. In other words, the distance between the photosensitive drum 1 and the part of the duct 150 facing the photosensitive drum 1 where the potential sensor 8 is attached is longer than the distance between the other parts and the photosensitive drum 1.

Figure 8 shows the relationship between the potential sensor detection results and the distance between the potential sensor and the photosensitive drum. The drum potential in Figure 8 is -900V. The horizontal axis of Figure 8 shows the distance between the potential sensor and the photosensitive drum, and the vertical axis shows the difference between the actual drum potential and the potential sensor detection results (equivalent drum potential value) (the value obtained by subtracting the actual drum potential from the potential sensor detection results).

The triangular points in Figure 8 represent the results when a potential sensor 8 is attached to a conventional exhaust duct 150, while the circular points represent the results when a potential sensor 8 is attached to the exhaust duct 150 of this embodiment.

When the distance between the potential sensor 8 and the photosensitive drum 1 is greater or less than 2 mm, a discrepancy occurs between the drum potential and the detection result of the potential sensor 8. However, as shown in Figure 8, in both cases, the detection result of this embodiment shows a smaller discrepancy in the measured drum potential compared to the conventional example, making it possible to improve the detection accuracy of the photosensitive drum potential by the potential sensor 8.

As described above, in this embodiment, by cutting out the portion of the exhaust duct where the potential sensor is attached near the detection electrode of the potential sensor and the tuning fork, it is possible to reduce the effect of the capacitance that occurs between the exhaust duct resin material and the detection electrode and tuning fork of the potential sensor. This makes it possible to improve the detection accuracy of the photosensitive drum potential by the potential sensor.

In addition, in this embodiment, the exhaust duct is cut out only in a limited area around the potential sensor. This minimizes the amount of ozone that flows between the photosensitive drum and the exhaust duct toward the developer, making it less likely that image defects (image deletion) will occur due to ozone adhering to the drum.

REFERENCE SIGNS LIST 1 Photosensitive drum 2 Corona charger 4 Developer 8 Potential sensor 150 Exhaust duct

Claims (5)

a photoreceptor that rotates around a rotation axis;
a corona charger that charges the photosensitive member by corona discharge;
a developing device that develops the electrostatic latent image formed on the photosensitive member with toner;
a duct having an opening for the corona charger;
a potential sensor attached to the duct for measuring a potential of the photosensitive member;
the corona charger, the duct, and the developing unit are arranged in this order from upstream to downstream in the rotation direction of the photosensitive member,
the duct has a first surface facing the photosensitive member, a second surface facing the corona charger in the rotation direction and having the opening, and a third surface facing the developing unit in the rotation direction and having the potential sensor attached thereto;
the first surface of the duct facing the photosensitive member includes a first portion corresponding to a position where the potential sensor is attached in a direction along the rotation axis, and a second portion at a position different from the first portion in a direction along the rotation axis;
a first distance between the first portion and the photosensitive member is greater than a second distance between the second portion and the photosensitive member;
the potential sensor protrudes from the first portion of the first surface of the duct toward the photoreceptor;
a third distance between the potential sensor and the photosensitive member is shorter than the first distance and the second distance;
An image forming apparatus characterized by: an edge of the opening on the side of the photosensitive member has a linear portion extending along the rotation axis and an inclined portion inclined relative to the linear portion;
2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. the potential sensor is attached at a position including a center of the duct in a direction along the rotation axis ;
3. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. the duct draws in air containing ozone generated by the corona discharge through the opening.
4. The image forming apparatus according to claim 1, wherein the first and second ink cartridges are arranged on the first and second ink cartridges. Further provided with an ozone filter,
The air drawn into the duct from the opening passes through the ozone filter and is discharged to the outside.
5. The image forming apparatus according to claim 4 .