Grid wire cleaning mechanism

A grid wire cleaning mechanism is provided to prevent a reduction in image quality due to the surface of the electrostatic latent image carrier not being uniformly charged as a result of corona products adhering unevenly to the surface of the grid wires to extend the life of the grid wires and grid wire contact member. A first abrading member 71 abrades grid wires 224. A movement device 73 moves the first abrading member 71 in the same direction as the direction of extension of the grid wires 224. A humidity measurement unit 741 measures the humidity near the grid wires 224. The operation control unit 743 operates the movement device 73 when cleaning the grid wires 224, but does not operate the movement device 73 when the humidity measured by the humidity measurement unit 741 exceeds a predetermined threshold value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2006-205918 filed on Jul. 28, 2007. The entire disclosure of Japanese Patent Application No. 2006-205918 is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a grid wire cleaning mechanism. More specifically, the present invention relates to a grid wire cleaning mechanism having a cleaning mechanism that cleans grid wires used in a charging device that charges the surface of an electrostatic latent image carrier of an image forming apparatus.

2. Background Information

An image forming apparatus includes an electrostatic latent image carrier, a developing device that supplies developer to the electrostatic latent image carrier, a charging device that charges the surface of the electrostatic latent image carrier, and an irradiation device that irradiates the surface of the electrostatic latent image carrier with laser light. In this image forming apparatus, first the surface of the electrostatic latent image carrier is charged by the charging device. The surface of the charged electrostatic latent image carrier is irradiated with laser light by the irradiation device based on image data, to form an electrostatic latent image on the electrostatic latent image carrier. Then, developer is supplied from the developing device to the electrostatic latent image carrier on which the electrostatic latent image is formed. In this way, a toner image is formed on the electrostatic latent image carrier.

Charging devices that charge the surface of electrostatic latent image carriers include scorotron charging devices. Scorotron charging devices include discharge wires, and grid wires disposed in opposition to the discharge wires and disposed along the electrostatic latent image carrier. A bias voltage is applied to the grid wires in this charging device. Thereafter the surface potential of the electrostatic latent image carrier is controlled to be constant by the grid wires. Corona products, specifically NOx, SOx, can adhere to the grid wires.

Some image forming apparatus include a wire cleaning mechanism to clean corona products adhering to the grid wires like that shown in Japanese Patent Application Laid-open No. H10-207191. This wire cleaning mechanism includes a discharge wire abrading member that can abrade the discharge wires, a grid wire abrading member that can abrade the grid wires, and a movement mechanism that moves the discharge wire abrading member and the grid wire abrading member in the direction that the wires are stretched. After, for example, a predetermined number of sheets has been printed, the discharge wire abrading member and the grid wire abrading member are moved in the direction that the wires are stretched by the movement mechanism, and the grid wire cleaning mechanism cleans both sets of wires.

In the grid wire cleaning mechanism in Japanese Patent Application Laid-open No. H10-207191, the wire cleaning operation is carried out after completion of printing a predetermined number of sheets, regardless of environment. If the humidity around the image forming apparatus is high, or specifically if the humidity near the grid wires is high, corona products (for example, NOx, SOx, and so on) are absorbed by moisture in the air, and liquefy on the surface of the grid wires. In other words, they become water droplets. The corona products have electrically insulating properties, but in the liquid state they are electrically conducting. Therefore, even if liquid corona products adhere to the surface of the grid wires, the electrical resistance of the grid wires does not increase.

If the grid wire cleaning device carries out the cleaning operation with liquid corona products adhering to the surface of the grid wires in this way, the liquid is spread over the surface of the grid wires as a whole. If the humidity drops, in other words if drying occurs, while the liquid is spread over the whole surface of the grid wires in this way, the corona products dissolved in the liquid solidify, so solid corona products adhere to the whole surface of the grid wires in an uneven manner. Here, the solid corona products have electrically insulating properties, so the electrical resistance of the parts of the grid wires where corona products adhere increases. This causes unevenness of charging the surface of the electrostatic latent image carrier, which causes faulty developing, such as uneven density in the images. In this case also the life of the grid wires is shortened. Corona products also adhere to the grid wire contact member, so the life of the grid wire contact member is also shortened.

SUMMARY OF THE INVENTION

It is an object of the present invention to prevent a reduction in image quality due to the surface of the electrostatic latent image carrier not being uniformly charged as a result of corona products adhering unevenly to the surface of the grid wires by preventing the corona products from being spread by the grid wire contact member, and to prevent shortening of the life of the grid wires and grid wire contact member.

A grid wire cleaning mechanism according to a first aspect of the present invention cleans the grid wire of a charging device that charges the surface of an electrostatic latent image carrier of an image forming apparatus. The grid wire cleaning mechanism has a first abrading member, a movement device, a humidity measurement device, and an operation control device. The first abrading member is configured to abrade the grid wire. The movement device moves the first abrading member along a direction that is the same as the direction in which the grid wire is stretched. The humidity measurement device measures the humidity near the grid wire. The operation control device operates the movement device when cleaning the grid wire. Further, when the humidity measured by the humidity measurement device exceeds a predetermined threshold, the movement device is not operated.

In this grid wire cleaning mechanism, the grid wire is cleaned by abrading the grid wire with the first abrading member using the movement device. In this way, corona products on the grid wire are removed. The humidity measurement device measures the humidity near the grid wire, and if the measurement result is greater than a threshold value, the movement device is not operated.

Here, when the humidity near the grid wire is higher than the threshold value, the movement device is not operated. Therefore, it is possible to prevent liquid that is formed from corona products dissolved in moisture in the air and that adheres to the surface of the grid wire from being spread by the first abrading member. Further, it is possible to prevent reduction in image quality, and it is possible to prevent the life of the grid wire from being shortened. Also, it is possible to prevent adherence of corona products so it is possible to prevent shortening of the life of the first abrading member.

A grid wire cleaning mechanism according to a second aspect of the present invention is the grid wire cleaning mechanism according to the first aspect, wherein the charging device further has discharge wire disposed parallel to the grid wire that charges the electrostatic latent image carrier. The grid wire cleaning mechanism further includes a second abrading member configured to abrade the discharge wire, and the movement device moves the second abrading member together with the first abrading member.

Here it is possible to clean the discharge wire with the second abrading member at the same time as the grid wire cleaning.

A grid wire cleaning mechanism according to a third aspect of the present invention is the grid wire cleaning mechanism according to the first aspect, wherein it is possible to select alternatively abrading the grid wire with the first abrading member or abrading the discharge wire with the second abrading member.

Here it is possible to clean alternatively the grid wire or the discharge wire.

A grid wire cleaning mechanism according to a fourth aspect of the present invention is the grid wire cleaning mechanism according to the first aspect, wherein the movement device has a shaft member and a tubular shaped member. The shaft member is disposed parallel to the grid wire and provided with a spiral shaped projection continuous with the surface. The tubular shaped member is mounted on the shaft member and configured to rotate relative to the shaft member, on which the first abrading member is provided. The shaft member has a spiral shaped groove on the inside surface that is configured to mesh with the spiral shaped projection.

Here by rotating the shaft member relative to the tubular shaped member, it is possible to move the tubular shaped member. Also, by providing a drive source such as a motor to the shaft member, it is possible to move automatically the tubular shaped member.

A grid wire cleaning mechanism according to a fifth aspect of the present invention is the grid wire cleaning mechanism according to the first aspect, further including a counting device that counts the number of image forming operations of the image forming apparatus, and the operation control device moves the movement device when the number counted by the counting device exceeds a predetermined number.

Here wire cleaning is carried out after every predetermined number of image forming operations. Thus, it is possible to prevent corona products from adhering on the grid wire.

A grid wire cleaning mechanism according to a sixth aspect of the present invention is the grid wire cleaning mechanism according to the first aspect, wherein when operation of the movement device is proscribed by the operation control device, and when the measurement result of the humidity measurement device is less than the predetermined threshold, the operation control unit removes the proscription on the operation of the movement device.

Here, when the humidity is less than a predetermined threshold, moisture on the surface of the grid wire evaporates, the corona products solidify, and the resistance increases. However, after the corona products have solidified on the grid wire, the corona products are removed from the grid wire. Thus, there is no unevenness in cleaning the grid wire, and the electrostatic latent image carrier is uniformly charged.

A grid wire cleaning mechanism according to a seventh aspect of the present invention is the grid wire cleaning mechanism according to the fifth aspect, wherein when operation of the movement device is proscribed by the operation control device, and when the measurement result of the humidity measurement device is less than the predetermined threshold, the operation control unit removes the proscription on the operation of the movement device.

A grid wire cleaning mechanism according to an eighth aspect of the present invention is the grid wire cleaning mechanism according to a first aspect, wherein the humidity measurement device includes a humidity sensor that measures the humidity near the grid wire, and a temperature sensor that measures the temperature near the grid wire, and the absolute humidity near the grid wire is determined from the humidity sensor and the temperature sensor.

Here, the absolute humidity is measured, so the criterion is more objective than if the relative humidity is measured.

A grid wire cleaning mechanism according to a ninth aspect of the present invention is the grid wire cleaning mechanism according to the seventh aspect, wherein the humidity measurement device includes a humidity sensor and a temperature sensor. The humidity sensor measures the humidity near the grid wire. Further, the temperature sensor measures the temperature near the grid wire. Moreover, the absolute humidity near the grid wire is determined from the humidity sensor and the temperature sensor.

A grid wire cleaning mechanism according to a tenth aspect of the present invention is the grid wire cleaning mechanism according to the first aspect, wherein the first abrading member is a grinding member with grinding particles adhering to the surface on the side facing towards the grid wire.

Here, it is easier to remove the corona products adhering to the grid wire.

A grid wire cleaning mechanism according to an eleventh aspect of the present invention is the grid wire cleaning mechanism according to the second aspect, wherein the second abrading member has a non-woven fabric on the part capable of abrading the discharge wire.

A grid wire cleaning mechanism according to a twelfth aspect of the present invention is the grid wire cleaning mechanism according to the fourth aspect, wherein the movement device further includes a motor that rotates the shaft member.

An image forming apparatus according to a thirteenth aspect of the present invention has an electrostatic latent image carrier, a charging device, a developing device, and a grid wire cleaning mechanism according to the first aspect. Electrostatic latent images are formed based on image information on the surface of the electrostatic latent image carrier. The charging device charges the surface of the electrostatic latent image carrier using grid wire. The developing device supplies developer to the electrostatic latent image carrier.

EFFECT OF THE INVENTION

In the present invention, it is possible to prevent a reduction in image quality due to the surface of the electrostatic latent image carrier not being uniformly charged as a result of corona products adhering unevenly to the surface of the grid wires, by preventing the corona products from being spread by the grid wire contact member. In the present invention, it is also possible to prevent shortening of the life of the grid wires and grid wire contact member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. Overall Configuration

FIG. 1is a view of a diagram showing the schematic structure of a color printer1. As seen inFIGS. 1 to 4, the color printer1has a grid wire cleaning mechanism7according to an embodiment of the present invention. The grid wire cleaning mechanism7cleans the grid wires224of a charging device22.

The color printer1includes mainly an image forming unit2, a fixing unit3, a sheet storage unit4, a sheet discharge unit5, a sheet transport unit6, and the grid wire cleaning mechanism7.

As shown inFIG. 1, the image forming unit2includes a photosensitive drum21, the charging device22, a rotary developing device23, a transfer device24, a cleaning device25, and a laser unit26. Also, the image forming unit2is the part that forms toner images based on image information, and is provided in approximately the center of the color printer1. The charging device22is described in detail below.

The photosensitive drum21is the member on whose surface the electrostatic latent image is formed. The photosensitive drum21can rotate about an axis of rotation that extends in a direction normal to the plane of the paper inFIG. 1. A humidity and temperature sensor741a(seeFIG. 1) is disposed near the position on the photosensitive drum21that is exposed to light by the laser unit26. More preferably, the humidity and temperature sensor741ais located between the charging device22and the rotary developing device23. The humidity and temperature sensor741ais preferably configured to measure the humidity and temperature surrounding the charging device22, and more preferably to measure the humidity and temperature of the charging device22.

The rotary developing device23is provided adjacent to the photosensitive drum21, and includes a plurality of developing devices23aand a frame23b. Each of the plurality of developing devices23acontains toner of a different color, and a developing roller to supply toner to the photosensitive drum21. The frame23bis a member that supports the plurality of developing devices23a, and includes a frame rotational shaft23cdisposed parallel to the axis of rotation of the photosensitive drum21. The frame23bincludes four plate shaped members extending from the rotational shaft23cat equal intervals. The developing devices23aare supported between adjacent plate shaped members.

The transfer device24transfers toner images on the photosensitive drum21onto sheets, and includes a transfer belt241, a primary transfer roller242, a pair of secondary transfer rollers243, and a tension adjustment roller244. Also, the transfer device24is disposed below the photosensitive drum21. The transfer belt241is an endless belt that is wound around the primary transfer roller242, the pair of secondary transfer rollers243, and the tension adjustment roller244. The primary transfer roller242transfers toner images onto the sheets. In order that toner images can be transferred from the transfer belt241to the sheets transported by the sheet transport unit6, the primary transfer roller242supports the transfer belt241so that a part of the transfer belt241is disposed on a side of the sheet transfer unit6. The pair of secondary transfer rollers243supports the transfer belt241so that a part of the transfer belt241is disposed adjacent to the photosensitive drum21in order to transfer toner images on the photosensitive drum21to the transfer belt241. The tension adjustment roller244is a member that adjusts the tension in the transfer belt241, and is disposed to the right side inFIG. 1.

The cleaning device25is a member that removes residual toner that is not transferred but remains on the photosensitive drum21. The cleaning device25is preferably a plate shaped member that contacts the surface of the photosensitive drum21.

The laser unit26is a device that irradiates the photosensitive drum21with laser light based on image data, and is disposed above the rotary developing device23. The solid line extending from the laser unit26inFIG. 1indicates the path of the laser light.

The fixing unit3fixes toner images onto the sheets, and includes a pressure roller31and a heating roller32.

The sheet storage unit4stores sheets on which toner images will be fixed, and is disposed in the lower part of the color printer1.

The sheet discharge unit5discharges sheets on which toner images have been fixed, and is disposed in the upper part of the color printer1.

The sheet transport unit6is the part that transports sheets from the sheet storage unit4to the sheet discharge unit5via the image forming unit2and the fixing unit3. The sheet transport unit6preferably includes a plurality of rollers.

Next the charging device22is described.

The charging device22charges the surface of the photosensitive drum21. As shown inFIGS. 2,3, and4, the charging device22includes a device case221, a power supply222, a pair of discharge wires223, a plurality of grid wires224, and the grid wire cleaning mechanism7. Also, the charging device22is disposed above the photosensitive drum21. The following is a detailed description of the grid wire cleaning mechanism7.

The device case221is a member that supports the grid wires224and the discharge wires223, and includes a grid support housing221aand a discharge wire support housing221b. The grid support housing221ais a member that supports the grid wires224, and is a plate shaped member extending in the direction that the grid wires224extends, i.e., the stretching direction. The discharge wire support housing221bis a member that supports the discharge wires223, and is provided in opposition to the grid support housing221a.

The power supply222is a device that supplies electrical power to the discharge wires223and the grid wires224. The power supply222applies a high voltage current to the discharge wires223, and a bias voltage to the grid wires224. Then, to charge the photosensitive drum21, the discharge wires223are made to discharge. The surface of the photosensitive drum21is uniformly charged, and excess discharge current flows to the grid wires224.

The discharge wires223charge the surface of the photosensitive drum21. Further, each discharge wire223is supported at both ends by the discharge wire support housing221b. Discharge occurs when a high voltage is applied by the power supply222. Also, the surface of the two discharge wires223is plated, and the two discharge wires223are disposed at a predetermined distance apart.

The grid wires224uniformly charge the surface of the photosensitive drum21, and are disposed at a predetermined distance from the surface of the photosensitive drum21. Also, the grid wires224are supported by the grid wire support housing221a, and is disposed between the discharge wires223and the photosensitive drum21.

The grid wire cleaning mechanism7is provided to clean the grid wires224, and includes a first abrading member71, a second abrading member72, a movement device73, and a control unit74(seeFIG. 4).

Referring toFIGS. 2 to 4, the first abrading member71is disposed to be able to abrade the grid wires224, and includes a grinding member with grinding powder adhering to the surface on the side facing towards the grid wires224.

The second abrading member72is a member disposed to be able to abrade the discharge wires223, and includes a non-woven fabric in the portion that can abrade the discharge wires223.

The movement device73is provided to move the first abrading member71and the second abrading member72, and includes a motor731, a movement rotation shaft732, a tubular shaped member733(tubular shaped unit), and a pair of support members734. The motor731is disposed at one end of the movement rotation shaft732, and rotates the movement rotation shaft732. The movement rotation shaft732is preferably disposed parallel to the grid wires224, and is a shaft preferably provided with a spiral shaped protrusion732a. The tubular shaped member733is mounted on the movement rotation shaft732so that the tubular shaped member733can move relative to the movement (rotation) of the rotation shaft732. A spiral shaped groove (not shown on the drawings) that can mesh with the spiral shaped protrusion732ais formed on the inside of the tubular shaped member733. Also, the tubular shaped member733is preferably provided with two pairs of projections that project in directions at right angles to the direction of extension of the movement rotation shaft732. The two support members734are provided to support the first abrading member71and the second abrading member72. The two support members734are slidably supported in the direction of extension of the movement rotation shaft732by the discharge wire support housing221a. The two support members734include a first support member734athat supports the first abrading member71, and a second support member734bthat supports the second abrading member72. The first support member734ahas two intermediate members734cthat extend in one direction. The intermediate members734cbecome gradually thinner at the end towards the tubular shaped member733. The ends are disposed between the two pairs of projections provided on the tubular shaped member733. Also, the two intermediate members734care disposed corresponding respectively to the two discharge wires223, and the first abrading member71is disposed on the other end. The second support member734bsupports the second abrading member72, and has a second abrading member support member734dthat is supported by the intermediate member734cof the first support member734a. The second abrading member support member734dis a member with an approximately U-shaped cross-section, disposed so as to sandwich the two intermediate members734c. Also, the second abrading member72is disposed on the grid wires224side (the side on which the photosensitive drum21is disposed) of the second abrading member support member734d. By changing the angle of the support member734, it is possible to select alternatively the first abrading member71to abrade the grid wires224, or the second abrading member72to abrade the discharge wires223.

The control unit74controls the movement device73, and includes a CPU, memory, and so on. The control unit74preferably functions as a humidity measurement unit741, a counting unit742, and an operation control unit743by executing programs in the CPU. The control unit74carries out control of all parts (the image forming unit, and so on).

The humidity measurement unit741measures the humidity and temperature near the grid wires224from the humidity and temperature sensor741a, and from the measured temperature and humidity determines the absolute humidity, preferably of the area around the charging device22, and more preferably of the charging device22.

The counting unit742counts the number of image forming operations.

When the number of image forming operations counted by the counting unit742is equal to or greater than a predetermined number, the operation control unit743controls the movement device73to move the first abrading member71and the second abrading member72to clean the grid wires224and the discharge wires223. Here, if the absolute humidity determined by the humidity measurement unit741is equal to or greater than a predetermined threshold, specifically 20.0 g/m3, the movement device73is not operated. In other words, the first abrading member71and the second abrading member72are not moved. Then, in this case when the absolute humidity drops below 20.0 g/m3after some time has passed, the movement device73is moved, in other words the first abrading member71and the second abrading member72are moved, and the grid wires224and the discharge wires223are cleaned.

The following is an explanation of the operation of the color printer1.

Referring toFIGS. 1 to 3, when image information is sent to the color printer1from an externally connected computer or the like, the surface of the photosensitive drum21is charged by the charging device22. Specifically, high voltage current is applied to the discharge wires223, and bias voltage is applied to the grid wires224. When the discharge wires223discharge, the surface of the photosensitive drum21is charged, the surface of the photosensitive drum21is uniformly charged by the grid wires224, and excess discharge current flows to the grid wires224. The charged surface of the photosensitive drum21is irradiated with laser light from the laser unit26, based on image information. When the electrostatic latent image is formed on the photosensitive drum21in this way, toner of the respective colors is supplied to the photosensitive drum21by the rotary developing device23. In this way, a toner image is formed on the photosensitive drum21. This toner image is transferred by the transfer device24to a sheet transported by the sheet transport unit6from the sheet storage unit4. The sheet onto which the toner image has been transferred is transported to the fixing unit3, and after the toner image is fixed in the fixing unit3, the sheet is discharged from the sheet discharge unit5.

Next, the operation of cleaning the grid wires224and the discharge wires223is explained with reference to the flowchart inFIG. 5.

When an image forming operation is carried out (S1), [1] is added to the image forming operation cumulative count. After the image forming operation, the cumulative count is read (S2). After the cumulative count is read, it is determined whether the cumulative count is equal to or greater than a predetermined number (S3). If the cumulative count is less than the predetermined number (S3: NO), the next image forming operation is carried out. If the cumulative count is equal to or greater than the predetermined number (S3: YES), the absolute humidity is measured by the humidity measurement unit741(S4). It is determined whether the absolute humidity is equal to or greater than the threshold value (S5). If the humidity is equal to or greater than the threshold value (S5: YES), the process goes on standby until the humidity is less than the threshold value (S7). If the humidity is less than the threshold value (S5: NO), or if the humidity falls below the threshold value during the standby state, the grid wires224and the discharge wires223are cleaned. In other words, the movement device73is operated, and the first abrading member71and the second abrading member72are moved. Specifically, on the outward path, the second abrading member72is moved while the second abrading member72is in contact with the discharge wires223, and on the return path the first abrading member71is moved while the first abrading member71is in contact with the grid wires224.

Here, if the humidity near the grid wires224is high, the grid wires224are not cleaned (standby). Therefore, spreading of liquefied corona products near the grid wires224is prevented. Further, discharge current uniformly flows from the discharge wires223to the grid wires224, so reduction in image quality caused by charging defects can be prevented. Also, both the first abrading member71and the second abrading member72are provided, so it is possible to clean both the discharge wires223and the grid wires224. Furthermore, the discharge wires223and grid wires224cleaning operation is carried out every predetermined number of image forming operations. Therefore it is possible to prevent more than a predetermined quantity of corona products from remaining. Further, it becomes difficult for corona products to hinder the flow of discharge current in the grid wires224.

5. Other Embodiments

(a) In the above embodiment, the color printer1was explained as an image forming apparatus. However, the present invention is not limited to this, and a photocopier, multi-function printer, or the like may also be used.

(b) Also, in the above embodiment, it was determined whether to operate the movement device73based on the absolute humidity. However, the present invention is not limited to this, and the determination may also be made based on the relative humidity.

GENERAL INTERPRETATION OF TERMS