JP2006349938A - Charging device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging device capable of accurately detecting soil on a charging member in its longitudinal direction, and to provide an image forming apparatus. <P>SOLUTION: The charging device 105 includes a charging roller 1, and a sound collecting member 2 disposed in the vicinity of the charging roller 1. The charging roller 1 is disposed in parallel with a photoreceptor drum in its longitudinal direction (axial direction) and rotated at a predetermined speed by a drive mechanism such as a motor. The sound collecting member 2 collects sound emitted from the charging roller 1 and the peripheral devices thereof. On the basis of signals output from the sound collecting member 2, the frequencies of the various kinds of sounds are extracted by a frequency conversion section 4. Then, a frequency corresponding to the natural oscillation of the charging roller 1 is extracted from the frequencies. On the basis of the frequency, it is determined whether the charging roller 1 is soiled or not. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus and a charging device used therefor. More specifically, a charging device for charging the surface of an image carrier by contacting or approaching (non-contacting) the image carrier, and a charging device for accurately detecting the stain distribution in the longitudinal direction, and the same The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus uses a charging member such as a conductive roller or a conductive brush to charge a surface of an image carrier in contact with or close to a rotating image carrier. It has been put into practical use. These charging devices have the advantage that the amount of ozone generated is small and can be operated with a low applied voltage, compared to a corona discharge charger using corona discharge.

  However, these charging devices tend to take in toner and paper powder remaining on the surface of the image carrier. Further, the deposit such as toner has a resistance component and a capacitance component, resulting in uneven charging and insufficient charging. That is, when the deposits are concentrated on an unspecified part, a surface voltage drop occurs non-uniformly, resulting in surface potential unevenness. In addition, dot-like discharge occurs due to insufficient current supply, resulting in image noise.

In order to prevent this, a method of mechanically cleaning the charging member with a brush, pad, film, etc., or a method of changing the voltage applied to the charging member at a predetermined timing and cleaning it electrically are proposed. Has been. Further, as a method of detecting the contamination of the charging member, for example, as shown in Patent Document 1, a method of measuring the surface potential of the image carrier, a method of measuring the image density on the image carrier, There have been proposed a method for measuring reflectance and a method for estimating dirt based on a change in impedance of a charging member. In this image forming apparatus, it has also been proposed to arrange the detection means at two or more places without limiting the number of measurement places to one.
JP-A-6-250504

  However, the conventional stain detection method described above has the following problems. In other words, the deposit location of the deposit in the charging member varies depending on the print pattern and is not determined at a specific position. Therefore, even if dirt detecting means such as sensors are arranged at a plurality of places, the part for detecting dirt is limited to the detection range of the sensor, and dirt on the entire surface of the charging member cannot be detected. For this reason, there is a portion where no dirt is detected, and charging unevenness cannot be avoided reliably. In addition, it may be possible to arrange the sensors in the longitudinal direction without any gap, but an increase in cost is inevitable.

  The present invention has been made to solve the problems of the conventional charging device described above. That is, an object of the present invention is to provide a charging device and an image forming apparatus that can detect dirt in the longitudinal direction of the charging member with high accuracy.

  A charging device designed to solve this problem is a charging device including a charging member, which is adjacent to the charging member and collects sound in the vicinity of the charging member, and is collected by the sound collecting member. A frequency extraction unit that converts the generated sound into a frequency component and extracts a frequency corresponding to the natural vibration of the charging member, and determines whether the charging member is contaminated based on the frequency extracted by the frequency extraction unit It is characterized by.

  The charging device of the present invention has a roller-shaped or brush-shaped charging member, and includes a sound collecting member that collects sound in a predetermined frequency region in the vicinity of the charging member. In this sound collecting member, various sounds generated from the charging member and its peripheral devices (AC power supply sound of charging bias and developing bias, rotation sound of polygon mirror, natural vibration sound of vibrating member such as charging member, etc.) are detected. Then, the collected sound is converted into a frequency component by the frequency extraction unit. Specifically, the frequency of the sound pressure peak in a predetermined frequency band is extracted. Thereby, the frequency of various sounds can be acquired from the collected sounds. Then, a frequency corresponding to the natural vibration of the charging member is extracted from the extracted frequencies.

  The contamination of the charging member is determined based on the frequency corresponding to the natural vibration of the charging member. That is, if toner adheres to any surface of the charging member, the frequency of the natural vibration of the charging member changes. Therefore, it is possible to determine the contamination of the charging member based on the magnitude of the frequency change amount. The frequency of the natural vibration of the charging member is not obtained from a specific portion of the charging member, but is obtained from the entire charging member. Therefore, no matter where the toner adheres over the entire length in the longitudinal direction, it can be detected as dirt.

  Further, the charging device of the present invention is better if the charging member is cleaned when contamination of the charging member is detected. That is, by removing dirt, uneven charging and image noise can be avoided.

  According to the present invention, the frequency of the natural vibration of the charging member can be acquired, and contamination of the charging member can be determined based on the frequency. Therefore, it is possible to determine the presence or absence of dirt in the entire longitudinal direction of the charging member. Therefore, it is possible to accurately detect the contamination in the longitudinal direction of the charging member.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In the present embodiment, the present invention is applied to a contact charging device provided in an electrophotographic image forming apparatus.

  The image forming apparatus according to the present embodiment is an electrophotographic laser printer. As shown in FIG. 1, a laser oscillator 102, a polygon mirror 103, and a reflecting mirror 104 are arranged in an optical system, and a photoconductor is provided in an image processing unit. A drum 101, a charging device 105, a developing device 106, a transfer charger 107, and a cleaning blade 108 are arranged. Further, a paper feed roller 109, a paper discharge roller 115, a paper feed sensor 110, a paper discharge sensor 114, a fixing device 111, and the like are arranged in the transport unit.

  Next, the operation of the laser printer configured as described above will be briefly described. The photosensitive drum 101 rotates in the direction of the arrow in FIG. The charging device 105 is a contact type roller member, and contacts the photosensitive drum 101 to uniformly charge the surface of the photosensitive drum 101. Further, the laser light is modulated and emitted from the laser oscillator 102 based on the image signal. This laser beam is scanned in the main scanning direction by the polygon mirror 103, reflected by the reflection mirror 104, and incident on the photosensitive drum 101. Thereby, an electrostatic latent image is formed on the photosensitive drum 101. This electrostatic latent image is developed by the developing device 106 to become a toner image. The toner image is transferred onto the recording paper P fed by the paper feed roller 109 by a transfer charger 107 disposed opposite to the photosensitive drum 101. Thereafter, the recording paper P to which the toner image has been transferred is heated in the fixing device 111, and the toner image is melted and fixed on the recording paper P by the heat. After the image is fixed, the recording paper P is discharged out of the apparatus by a paper discharge roller 115. With the above operation, printing for one sheet is performed.

  Next, the configuration of the charging device 105 provided in the laser printer of this embodiment will be described. As shown in FIG. 2, the charging device 105 includes a charging roller 1 and a sound collecting member 2 adjacent to the charging roller 1. The charging roller 1 is arranged in parallel with the photosensitive drum 101 in the longitudinal direction (axial direction), and rotates in accordance with the rotation of the photosensitive drum 101.

  As shown in FIG. 3, the charging roller 1 has an elastic layer 12, a first covering layer 13, and a second covering layer 14 sequentially laminated on a conductive core 11. A SUS material having an outer diameter of about 6 mm is used for the core 11 as a support. In addition, the metal core 11 should just have electroconductivity and rust prevention property. For example, it is possible to use a nickel-plated steel bar.

The elastic layer 12 is made of EPDM (ethylene / propylene / gen / rubber) sponge having a thickness of 3 mm and a volume resistivity of 10 ⁶ Ωcm, in which conductive carbon black is dispersed and foam vulcanized. The elastic layer 12 only needs to have a predetermined hardness (for example, an Asker C hardness of 75 degrees or less). For example, urethane rubber, epichlorohydrin rubber, silicon rubber, etc. are applicable. Also, it may be solid or sponge. The thickness is usually in the range of 2 mm to 5 mm. Further, a conductive material such as carbon black, metal, or metal oxide is dispersed in the elastic layer 12. Thereby, the elastic layer 12 has conductivity.

The first coating layer 13 is made of hydrin rubber having a thickness of 250 μm, a volume resistivity of 10 ⁷ Ωcm, and conductive tin oxide dispersed therein. The second coating layer 14 is made of nylon resin having a thickness of 10 μm, a volume resistivity of 10 ⁸ Ωcm, and conductive carbon black dispersed therein. These coating layers are elastic for the purpose of suppressing the seepage of oil and the like from the elastic layer 12, making the electric resistance of the charging roller uniform, suppressing adhesion to the surface of the charging roller, and adjusting the hardness of the charging roller. Provided on layer 12. The coating layer may be a single layer or multiple layers as long as these purposes are achieved. For example, hydrin rubber, urethane rubber, nylon resin, etc. are applicable. The thickness is preferably in the range of 100 μm to 1000 μm. Furthermore, the volume resistivity is desirably in the range of 10 ⁵ Ωcm to 10 ⁹ Ωcm. Also, the electrical resistance is adjusted by dispersing conductive materials such as carbon black, metal, and metal oxide in the coating layer. Thereby, each coating layer also has conductivity.

  The sound collecting member 2 is arranged toward the charging roller 1 and samples the sound near the charging roller 1. As the sound collecting member 2, for example, there is a sound collecting microphone capable of sampling a sound of 100 Hz to 10000 Hz.

  Further, as shown in FIG. 2, in the charging device 105, the charging roller 1 is connected to the high voltage power source 3, and a predetermined bias is applied to the charging roller 1. Moreover, the frequency conversion part 4 is connected to the sound collection member 2, and the electric signal sent from the sound collection member 2 is converted into the sound pressure for every frequency. Further, the sound pressure is sampled by the control unit 5, and the presence or absence of contamination of the charging roller 1 is determined based on the sound pressure value.

  A cleaning member 6 is provided near the charging roller 1 for cleaning the charging roller 1 in contact with the charging roller 1 in the cleaning mode. As the cleaning member 6, for example, there is one in which a rayon woven in a brush shape is wound around a cored bar.

  Next, a process for detecting dirt on the charging roller 1 will be described. The stain detection process is performed during non-image formation. Non-image formation corresponds to, for example, immediately after the image forming apparatus is turned on, at the end of a print job, or during a return sequence after jam processing.

  First, rotation of the charging roller 1 is started. During the dirt detection process, the charging roller 1 continues to rotate at a constant speed. A predetermined voltage is applied to the charging roller 1. The applied voltage need only be equal to or higher than the discharge start voltage, and may be the same voltage as during image formation.

  Next, the sound collecting member 2 samples various sounds generated from the charging roller 1 and its peripheral devices. The sampled sound is converted into a sound pressure for each frequency by the frequency converter 4. Next, the frequency of the sound pressure peak in a predetermined frequency band is acquired. That is, the frequency of various sounds (AC power supply sound of charging bias and developing bias, rotation sound of polygon mirror 103, natural vibration sound of vibration member such as charging roller 1) is acquired. And the frequency regarding the natural vibration of the charging roller 1 is acquired from the inside.

  Next, the contamination of the charging roller 1 is determined based on the natural vibration frequency of the charging roller 1. That is, when toner or paper scraps adhere to the charging roller 1, the surface hardness of the charging roller 1 changes. Therefore, the frequency of the natural vibration of the charging roller 1 changes. Therefore, the frequency of the natural vibration of the charging roller 1 is acquired, and the presence / absence of contamination on the entire surface of the charging roller 1 is determined based on the frequency.

  As a determination method, for example, a reference frequency (reference value) is stored, and contamination is determined based on whether or not the deviation from the actual measurement value is within an allowable range. That is, if it is out of the allowable range, it is determined that contamination has occurred.

  The charging roller 1 is formed so that the surface hardness is uniform, but there is a slight variation. Furthermore, the frequency of natural vibration changes due to environmental changes (changes due to temperature and humidity). Therefore, by correcting these fluctuation factors, it is possible to improve the detection accuracy of the charging roller dirt.

  Specifically, regarding the variation of the initial natural vibration, when the charging device is set in the image forming apparatus, the natural vibration frequency of the charging roller 1 is measured in advance and stored in the control unit 5 as comparison data. Correction becomes possible. The environmental change can be corrected by data acquired by an environmental sensor (temperature sensor, humidity sensor, etc.) installed in the vicinity of the charging device 105.

  Next, determination of contamination of the charging roller 1 will be described. In FIG. 4, the charging device 105 is set in the image forming apparatus, the sound generated when one test print is performed is collected by the sound collecting member 2, and the sound is converted into a frequency component to remove noise. The example of a result is shown. The horizontal axis in FIG. 4 means the passage of time from the start to the end of printing. That is, from the graph of FIG. 4, the polygon mirror 103 reaches a predetermined rotational speed in about 2 seconds, image formation is performed in the 3rd to 7th seconds, and the polygon mirror 103 is stopped after the 8th second. You can see that

  FIG. 4 shows various sound frequencies. The sound detected in the vicinity of the charging roller 1 is mainly a charging sound (frequency n times the AC voltage applied to the charging roller 1: n = 2, 3, 4), and a sound generated from the exposure means (the polygon mirror 103). Rotation sound), sound generated from the developer 106 (AC power supply sound applied to the developing roller), and natural vibration sound of the vibrating member of the charging roller 1.

  As the vibrating member, in addition to the charging roller 1, for example, a photosensitive drum 101 and a housing are used. In FIG. 4, the frequency corresponding to the natural vibration of the surface of the charging roller 1 is expressed as “natural vibration”. The frequency of natural vibration at the time of this test print is set as a reference value.

  Next, after actually printing a predetermined number of sheets, one test print was performed. Then, the sound generated at that time was sampled by the sound collecting member 2 and the frequency corresponding to the natural vibration of the surface of the charging roller 1 was extracted. FIG. 5 shows the amount of deviation between the extracted frequency and the reference value. As shown in FIG. 5, the amount of deviation after printing in this experiment is about 30 Hz and is outside the allowable range (within ± 15 Hz). Therefore, it can be determined that the surface of the charging roller 1 is dirty.

  Since it was determined that the surface of the charging roller 1 was dirty, the charging device 105 was set to the cleaning mode and the charging roller 1 was cleaned. The amount of misalignment after cleaning was within the allowable range. Therefore, it can be determined that the contamination of the charging roller 1 has been removed.

  In this experiment, the amount of misalignment was within an allowable range after a single cleaning, and thus the cleaning mode was completed by a single cleaning. However, the cleaning may not be within the allowable range after a single cleaning. In that case, the cleaning and dirt detection processing are repeated until the allowable range is reached. However, if it does not fall within the allowable range even after repeating the predetermined number of times, it is determined that the charging roller 1 has reached the end of its life, and a notification to that effect is given to the operation panel and the dirt detection process and cleaning mode are completed.

  As described above in detail, the charging device 105 according to the embodiment includes the sound collecting member 2 in the vicinity of the charging roller 1. The sound collecting member 2 collects sound generated from the charging roller 1 and its peripheral devices. The frequency of the natural vibration of the charging roller 1 is obtained from the collected sound. Then, the acquired frequency is compared with a frequency serving as a reference value, and the presence / absence of contamination of the charging roller 1 is determined based on the comparison result. That is, since the presence or absence of dirt is determined based on the change in the natural vibration accompanying the surface deposit on the charging roller 1, the spot for detecting dirt is limited to a specific position as in the conventional dirt detection method. There is no. Therefore, a charging device and an image forming apparatus that can accurately detect contamination in the longitudinal direction of the charging member are realized.

  Further, in the conventional charging device, it is necessary to install a plurality of sensors in order to achieve high accuracy. However, in this embodiment, the contamination in the entire longitudinal direction of the charging roller 1 can be determined by one sound collecting member 2. High accuracy can be achieved with a small number of parts. Furthermore, since the sound collecting member 2 is not in contact with the charging roller 1, there is no deterioration of the sensor due to sliding contact. Therefore, long-term reliability is ensured.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, in the embodiment, the present invention is applied to a printer, but the present invention is not limited to this. That is, it can be applied to a copying machine or the like. It can be applied to a color machine or a monochrome machine. Further, the charging device may be a contact type or a non-contact type.

  Further, the charging member is not limited to a roller-like conductive member. That is, a brush-like conductive member may be used. In the case of a brush-like member, variations in initial natural vibration are large due to the density of the fibers. For this reason, it is preferable to perform a process for correcting initial variations in natural vibration.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment. It is a block diagram which shows schematic structure of a charging device. It is sectional drawing which shows schematic structure of a charging roller. It is a graph which shows an example of the reference value of a natural vibration frequency at the time of dirt detection processing. It is a graph which shows an example of the gap | deviation amount of the reference value and measured value of a frequency.

Explanation of symbols

1 Charging roller (charging member)
2 Sound collecting member (sound collecting member)
3 High voltage power supply 4 Frequency converter (frequency converter)
5 Control unit (control unit)
6 Cleaning member 100 Laser printer (image forming apparatus)
105 Charging device (charging device)

Claims (4)

In a charging device provided with a charging member,
A sound collecting member adjacent to the charging member and collecting sound in the vicinity of the charging member;
A frequency extraction unit that converts the sound collected by the sound collecting member into a frequency component and extracts a frequency corresponding to the natural vibration of the charging member;
A charging device characterized by determining whether the charging member is contaminated based on the frequency extracted by the frequency extraction unit. The charging device according to claim 1,
A charging device that cleans the charging member when contamination of the charging member is detected. In an image forming apparatus including a charging device that charges the surface of an image carrier with a charging member,
A sound collecting member adjacent to the charging member and collecting sound in the vicinity of the charging member;
A frequency extraction unit that converts a sound collected by the sound collecting member into a frequency component and extracts a frequency corresponding to the natural vibration of the charging member;
An image forming apparatus comprising: a control unit that determines whether the charging member is contaminated based on the frequency extracted by the frequency extraction unit. The image forming apparatus according to claim 3,
An image forming apparatus, wherein the charging member is cleaned when contamination of the charging member is detected.

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