JP2008209795A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which has a simple configuration without employing a pattern density sensor and a supply means sensor, detects improper replacement of a toner supply means, then, prevents toner deterioration resulting from improper replacement of the toner supply means. <P>SOLUTION: The image forming apparatus includes: the replaceable toner supply means which supplies a toner to a developing means; and a developing means sensor which detects an amount of toner in the developing means and outputs an output voltage according to the amount of toner. The image forming apparatus is characterized in that immediately after the replacement of the toner supply means, replacement detection toner is supplied from the toner supply means to the developing means so that the developing means sensor detects the replacement of the toner supply means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having a toner sensor for adjusting a toner amount in a developing unit.

As an image forming apparatus such as a copying machine or a printer, an apparatus having a structure in which toner is replenished in the developing means can be exemplified. Since the image forming apparatus having such a structure consumes toner as the image is formed, a toner replenishing unit (toner cartridge) that can be attached or detached by a user or a maintenance worker when the remaining toner is low. The toner is replenished by replacement.
Further, in such an image forming apparatus, in order to keep the toner amount in the developing unit within a certain range, a toner sensor (hereinafter referred to as a developing unit sensor) that measures the toner amount in the developing unit is provided. Is also known.

However, if uncharged toner or reversely charged toner is generated due to a change in the environment in the developing unit, the density of the image may change. In that case, there arises a problem that the density of the image is not constant even when the toner amount is constant.
In view of the problem, for example, Patent Document 1 below discloses an image forming apparatus provided with a pattern density sensor in addition to a developing unit sensor.
This pattern density sensor is for creating a reference pattern every time an output operation of a predetermined number or more is completed, and detecting the toner amount (density) of the toner image portion of the reference pattern. By providing the pattern density sensor, the toner amount (density) in the developer can be controlled so that an image with a constant density can be formed.

However, the image forming apparatus disclosed in Patent Document 1 has a problem that the structure becomes complicated because the pattern density sensor is provided.
In addition, since the image forming apparatus disclosed in Patent Document 1 adjusts the toner density so that the image density is constant by the pattern density sensor, an image may be formed in a state where the toner density is low. In such a case, the toner is stressed and the toner is likely to be deteriorated.
In particular, since the toner concentration in the developer is lower than that in the steady state (the state where the toner concentration is kept constant) immediately before the replacement of the toner replenishing means, the stress on the toner becomes larger than in the steady state, and the toner further increases. It becomes easy to deteriorate. When new toner is replenished rapidly in such a state, uncharged toner and reversely charged toner are more likely to be generated than in a steady state due to contact with deteriorated toner. As a result, a phenomenon (hereinafter referred to as replenishment fogging) occurs in which the toner adheres to the non-image portion that should originally be white and the density increases.

Further, in the image forming apparatus described in Patent Document 1, since the developing unit sensor is in the developing unit, it takes a certain period of time from when toner is actually supplied until it is detected that the toner has been supplied. More specifically, if the time until toner detection is made too short, it will be determined that the toner has run out even if the amount of toner does not increase due to deterioration of the initial toner drop or the like. It is necessary to provide time. Therefore, even if the toner replenishing means (toner cartridge) is forgotten to be attached or not firmly attached and the toner replenishing means has not been properly replaced, a certain amount of time is required to detect the toner. An image is formed at. In such a case, there is a problem that toner is not sufficiently replenished, toner deterioration proceeds, and eventually an image cannot be partially formed due to running out of toner, resulting in further deterioration of toner. . Further, even if image formation is not performed for a certain time required for detecting the toner, it is necessary to drive the developing unit to stir and convey the toner, so that the developer in the developing unit is stressed and the toner is Will deteriorate.
Further, in some users, in order to use up the toner in the toner replenishing means, the old toner replenishing means may be shaken and used again. At this time, if no toner remains in the old toner replenishing means, the toner deteriorates due to running out of toner as in the case where the toner replenishing means is not properly installed.

In addition to the developing unit sensor for measuring the toner amount in the developing unit, a toner sensor (hereinafter referred to as a replenishing unit sensor) for measuring the toner amount in the toner replenishing unit is separately provided, thereby providing toner. It is also possible to detect that the toner in the replenishing means has become low. As a result, it is possible to detect whether toner remains in the replaced new toner supply means.
However, there may be a case where the presence or absence of toner cannot be immediately determined depending on the mounting position of the replenishing unit sensor, the size of the toner replenishing unit, and the like. In particular, it is difficult to determine the presence or absence of toner, for example, when the amount of toner that has been reduced is offset. If the toner is agitated in the toner replenishing means, the deviation of the toner can be prevented, but the toner is deteriorated by the agitation. Further, as in the case of the pattern density sensor, since it is necessary to provide a replenishing unit sensor separately from the developing unit sensor, there is a problem that the structure becomes complicated.

Japanese Patent Laid-Open No. 10-186830

The present invention has been made in view of the above problems, and has a simple configuration that does not use a pattern density sensor or a sensor for replenishing means, and detects that the toner replenishing means has not been properly replaced. Another object of the present invention is to provide an image forming apparatus capable of preventing the deterioration of toner that occurs because the toner replenishing means is not properly replaced.
It is another object of the present invention to provide an image forming apparatus capable of suppressing the deterioration of toner immediately after replacement of the toner replenishing means and suppressing the occurrence of replenishment fog.

  The invention according to claim 1 is a replaceable toner replenishing means for replenishing toner to the developing means, and a sensor for developing means for detecting the toner amount in the developing means and outputting an output voltage corresponding to the toner amount. An image forming apparatus comprising: a replacement detection toner for causing the developing unit sensor to detect from the toner supply unit that the toner supply unit has been replaced immediately after the toner supply unit is replaced. The present invention relates to an image forming apparatus that is supplied to a developing unit.

  According to a second aspect of the present invention, there is provided control means for controlling a toner replenishment amount from the toner replenishment means so that an output voltage output from the developing means sensor is substantially equal to a reference target voltage. 2. The image forming apparatus according to claim 1, wherein the control unit reduces the target voltage to the same level as the output voltage immediately before the replacement of the toner supply unit immediately after the replacement of the toner supply unit.

  The invention according to claim 3 relates to the image forming apparatus according to claim 2, wherein after the developing unit sensor detects the supply of the replacement detection toner, the target voltage is gradually raised to a steady state. .

  According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the third aspect, wherein a replenishment speed of toner replenished by raising the target voltage to a steady state is greater than a maximum consumption speed of the toner.

  According to the first aspect of the present invention, immediately after the replacement of the toner replenishing means, the toner for replacement is detected from the toner replenishing means so that the developing sensor detects that the toner replenishing means has been replaced. It is possible to confirm whether the toner replenishing means has been properly replaced so that the toner can be properly replenished. Thereby, it is possible to prevent the toner from being deteriorated because the toner replenishing means is not properly replaced.

  According to the invention of claim 2, a large amount of toner is replenished when the toner replenishing means is replaced by reducing the target voltage to the same level as the output voltage immediately before the toner replenishing means is replaced immediately after the toner replenishing means is replaced. The toner can be prevented from being deteriorated due to generation of uncharged toner and reversely charged toner. As a result, the image density can be prevented from changing without using a pattern density sensor, and an image forming apparatus having a simple configuration can be provided. Further, since it is possible to prevent a large amount of toner from being replenished when the toner replenishing means is replaced, it is possible to suppress replenishment fog when the toner replenishing means is replaced.

  According to the third aspect of the invention, after the developing means sensor detects the supply of the replacement detection toner, the target voltage is stepped up to the steady state step by step, thereby not only immediately after the replacement of the toner replenishing means but also the toner amount. Generation of uncharged toner and reversely charged toner is suppressed until the image is kept constant, and the image density can be maintained more reliably without providing a pattern density sensor. . In addition, the occurrence of replenishment fog can be prevented more reliably.

  According to the fourth aspect of the present invention, the amount of toner in the developer is reduced because the replenishment speed of the toner replenished by raising the target voltage to the steady state is larger than the maximum consumption speed of the toner, so-called It is possible to prevent white spots from occurring.

Hereinafter, an image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an image forming apparatus 100 according to an embodiment of the present invention.
The image forming apparatus 100 includes a charging unit 2, an exposure unit 3, a developing unit 4, a transfer unit 5, a conveying unit 6, a fixing unit 7, a cleaning unit 8, and a toner replenishing unit (toner cartridge) 9 around the photoreceptor 1. is doing.

First, the overall configuration of the image forming apparatus 100 will be described with reference to FIG.
The photoconductor 1 serves as a drum-shaped image carrier and rotates in the direction of arrow A. Examples of the photoreceptor 1 include an a-Si photoreceptor.
The charging means 2 is for charging the surface of the photoreceptor 1 to a predetermined potential. The charging unit 2 includes an ionic charging roller 2a mainly composed of epichlorohydrin. In addition, by providing the charging unit 2 with a brush cleaner for removing paper dust and the like attached to the surface of the charging roller, the life of the charging unit 2 can be extended.

  The exposure means 3 is for irradiating the photosensitive member 1 with laser light L based on image information to be actually formed to form an electrostatic latent image. More specifically, when the photosensitive member 1 charged to a predetermined potential by the charging unit 2 is irradiated with the laser beam L generated from the exposure unit 3, the resistance of the portion irradiated with the laser beam decreases. And the part where this resistance fell becomes a latent image.

The developing means 4 has a developer containing toner therein and supplies charged toner to the surface of the photoreceptor 1. Since toner adheres electrostatically to the electrostatic latent image formed on the surface of the photoreceptor 1, the toner image corresponding to the electrostatic latent image is developed.
The toner in the developer decreases with image formation, but the reduced toner is replenished by a toner replenishing means (toner cartridge) 9.

The transfer unit 5 transfers the toner image developed by the developing unit 4 onto transfer paper.
The transport mechanism 6 transports the transfer paper onto which the toner image has been transferred to the fixing unit 7. After the toner image is fixed on the paper surface by the fixing unit 7, the transport mechanism 6 is discharged outside the apparatus.
The cleaning unit 8 is for removing toner remaining on the photoreceptor 1 after the fixing process.

Next, the developing unit 4 will be described in more detail.
FIG. 2 is an enlarged view of the periphery of the developing unit 4 and the toner replenishing unit 9 in FIG. 1, and FIG. 3 is a plan view showing the inside of the developing unit 4.
As described above, the developing unit 4 has a developer containing toner inside. Further, as shown in FIG. 2 or 3, the developing means 4 is provided with a stirrer 4a, a developing means sensor 4b, and a mag roller 4c. Further, the image forming apparatus 100 is also provided with a control means (not shown) for controlling the toner replenishment amount. In FIG. 2, 9a denotes a toner replenishing means mounting portion, and a toner replenishing means 9 (not shown in FIG. 2) is attached to the toner replenishing means mounting portion 9a.

  Examples of the developer in the developing unit 4 include a one-component developer that does not require a carrier and includes only toner, and a two-component developer that includes two components of a carrier and a toner.

  The stirrer 4a is for stirring the developer in the developing means 4. By having the stirrer 4a, the concentration of the developer becomes substantially uniform, and the formed image also has a constant concentration.

The developing means sensor 4b is for detecting the amount of toner in the developing means. Specifically, in the case of a one-component developer, the toner amount is directly detected, and in the case of a two-component developer, the toner amount is detected by detecting the toner concentration in the developer.
Further, the developing unit sensor 4b outputs an output voltage corresponding to the detected toner amount.
Further, since the developer is stirred by the stirrer 4a, the overall concentration becomes substantially constant, and the output voltage from the developing unit sensor 4b is also stabilized.
Examples of the developing unit sensor 4b include a sensor that uses the electromagnetic characteristics of a carrier such as a magnetic permeability sensor, a sensor that uses the fluidity of a developer, and a sensor that detects a change in development amount.
FIG. 4 is a diagram showing the relationship between the toner amount (toner weight) and the output voltage in an example of the developing unit sensor, where the horizontal axis indicates the toner amount (g) and the vertical axis indicates the output voltage (V). As shown in FIG. 4, as the toner amount (toner weight) increases, the output voltage also increases.

  The control means plays a role of adjusting the replenishment amount of new toner so that the toner amount in the developing means 4 falls within an appropriate range. Specifically, a target voltage corresponding to a desired toner amount is stored in advance in the memory of the control unit, and the target voltage is compared with the output voltage from the developing unit sensor 4b attached to the developing unit 4. To do. Then, the toner replenishing operation is controlled so that the output voltage of the developing unit sensor 4b is approximately equal to the target voltage. Specifically, if the output voltage is lower than the target voltage, the conveying member in the toner replenishing means 9 is rotated to replenish the toner. If the output voltage is higher than the target voltage, the conveying member in the toner replenishing means 9 is rotated. To stop toner supply.

The control means performs a specific operation when the toner replenishing means 9 is replaced. Hereinafter, the operation at the time of replacement of the toner replenishing means 9 will be described.
FIG. 5 is a diagram showing an operation flow when the toner replenishing means 9 is replaced.

When it becomes necessary for the user or maintenance worker to replace the toner replenishing means 9, the old toner replenishing means 9 is removed. At this time, the control means sets so as to store the output voltage (hereinafter referred to as Vb) immediately before the replacement of the toner replenishing means 9 (step a). When the toner replenishing means 9 is replaced, the amount of toner in the developing means 4 is lower than in the steady state, and the output voltage Vb is also lower than the steady state output voltage.
Then, the user or the maintenance worker replaces the toner replenishing means 9 by attaching a new toner replenishing means instead of the old toner replenishing means (step b).
As the replacement time of the toner replenishing means 9, when the output voltage detected by the developing means sensor 4b becomes smaller than a predetermined value, it is notified by a lamp or the like that it is time to replace the toner replenishing means 9. It can also be done.

  Immediately after the replacement of the toner replenishing means 9, the control means once corrects the target voltage to Vb (step c). As a result, the difference between the target voltage and the actual output voltage becomes small, and even if the toner is replaced with a new toner replenishing means 9, the toner is hardly replenished. Therefore, it is possible to prevent a large amount of toner from being replenished when the toner replenishing means 9 is replaced, causing the toner to deteriorate and causing replenishment fog.

After the target voltage is set to Vb, a certain amount of toner (hereinafter referred to as replacement detection toner) for notifying that the toner replenishing means 9 has been replaced is supplied (step d).
The supplied replacement detection toner is detected by the developing unit sensor 4b. Thereby, it can be confirmed that the toner replenishing means 9 is properly replaced and the toner can be replenished. In other words, if the toner replenishing means 9 is not completely attached or if the toner replenishing means 9 (old toner replenishing means) containing no toner is attached, the replacement detection toner is not supplied. It turns out that is in the state which cannot be replenished.
Further, when the toner replenishing means 9 containing no toner is attached, this can be detected, so that the developing means sensor 4b of the replenishing means sensor 4b for measuring the toner amount in the toner replenishing means 9 can be detected. It will also play a role. Therefore, it is not necessary to provide a sensor for replenishing means, and an image forming apparatus having a simple structure can be obtained.

If the replacement detection toner cannot be detected, the process does not proceed to the next step. For this reason, it is possible to prevent the so-called white spot phenomenon from occurring due to the toner being deteriorated after the image formation is continued in a state where the toner is not replenished.
At this time, it is preferable that the supply amount of the replacement detection toner is an amount that causes a potential difference higher than a voltage (noise level) output by noise of the developing unit sensor 4b. Thereby, even if noise occurs, it is not mistaken that the replacement detection toner has been supplied. The supply amount of the replacement detection toner is preferably set to an amount that does not cause replenishment fog from the viewpoint of suppressing replenishment fog.
If the replacement detection toner supply is not recognized, the user is informed that the toner replenishing means 9 has not been properly replaced, for example, by continuously turning on a lamp for notifying the replacement of the toner replenishing means 9. That's fine.

  The reason why the target voltage can be lowered to Vb when the toner replenishing means 9 is replaced is that the replacement detection toner is supplied. In other words, if the replacement detection toner is not supplied, it is not known that the replacement of the toner replenishing means 9 has been completed, so the target voltage must be set higher than Vb. In such a setting, a large amount of toner is replenished, and there is a high possibility that replenishment fog will occur.

After detecting that the replacement detection toner is supplied by the developing means sensor, the toner supply is actually started (steps e and f).
At this time, since the target voltage is approximately the same as the output voltage Vb immediately before the replacement of the toner replenishing means 9, the toner is hardly replenished in this state. Therefore, the toner is replenished by stepping up the target voltage (step e). By pulling up in stages, the amount of toner replenishment can be adjusted, so that a large amount of toner is not replenished, and contact between new toner and old toner prevents uncharged toner and reversely charged toner from being generated. be able to. Thereby, the occurrence of replenishment fog can be prevented.
Furthermore, since the generation of uncharged toner and reversely charged toner is suppressed, the image density can be kept constant without providing a pattern density sensor.
Further, the target voltage is raised so that the replenishment speed of the toner replenished by raising the target voltage does not fall below the maximum toner consumption speed. This is because if the speed is below the maximum consumption speed, the amount of toner decreases, and so-called white spots may occur.
The maximum toner consumption speed may be, for example, a consumption speed when forming a so-called solid image in which one side of the paper is filled, or a maximum consumption speed corresponding to an actual print amount is measured in advance. The maximum consumption speed may be set according to the actual printing amount.

  The toner is replenished while gradually raising the target voltage, and finally the target voltage is raised to a steady state voltage (steady voltage) (step f). By setting the target voltage to a steady voltage, the toner amount can be kept constant (in a steady state).

  In the above description, toner supply is controlled using the target voltage. However, an image forming apparatus that performs toner supply without using the target voltage is also included in the present invention. Such an image forming apparatus is superior to the conventional image forming apparatus because it provides an effect that it is possible to confirm whether the replacement of the toner replenishing means 9 is properly performed by replenishing the replacement detection toner. In this case, since the output voltage only has to play a role of notifying the presence or absence of toner, it is not necessary to increase the output voltage as the amount of toner increases as shown in FIG. It is only necessary to detect whether or not the amount is greater than or equal to a certain amount and to output a constant output voltage if the amount is equal to or greater than a certain amount.

(Test example)
Hereinafter, the effects of the present invention will be made clearer by showing test examples of the present invention.

First, an image forming apparatus (see FIG. 1) for performing this test example will be described.
As the image forming apparatus in this test example, an apparatus employing a one-component jumping development method was used. Further, an a-Si photosensitive member was used as the photosensitive member 1 and rotated at a peripheral speed of 307 mm / s. The charging means 2 was constituted by an ionic charging roller mainly composed of epichlorohydrin. In addition, a brush cleaner was provided to extend the service life. Further, the charging unit 2 is charged by applying an AC bias in which alternating current (AC) is superimposed on direct current (DC). Further, a styrene acrylic ground toner was used as the toner, and titanium oxide as a surface polishing agent for the photoreceptor 1 and a plurality of silica as charge control agents were externally added. In addition, a magnetic permeability sensor was used as the developing means sensor.
As the transfer means 5, a roller transfer system was adopted. The material of the roller was EPDM, and the electric resistance was 10 ⁷ to 10 ^7.5 Ω. As the fixing means 7, a heat roller fixing method is adopted. The heat roller is a 0.7 mm thick aluminum cylinder coated with 30 μm PFA (tetrafluoroethylene-perfluoropropyl vinyl ether copolymer), and the pressure roller is a PFA tube. A silicon rubber roller coated with In addition, a non-contact thermistor was provided in the center of the paper passing area, and a contact thermistor was provided in the non-paper passing area to control the temperature. As the cleaning means 8, a blade cleaning method was adopted.
The toner weight in the steady state developer was 250 g, and the toner weight when the toner replenishing means 9 was replaced was 100 g.

  As Test Example 1 using the above-described image forming apparatus, the target voltage is lowered when the toner replenishing means 9 is replaced, and replenishment fogging is likely to occur. High temperature environment (room temperature 28 ° C.), low density pattern (printing rate 1%) The intermittent durability evaluation was performed. Further, as Comparative Example 1, intermittent durability evaluation was performed in the same high temperature environment and low density pattern as in Test Example 1 without lowering the target voltage of the developing unit sensor.

As a result, in Test Example 1, the replenishment fog immediately after the cartridge replacement did not occur, and the durability of 300,000 sheets could be confirmed with a stable image density.
However, in Comparative Example 1, replenishment fog occurred from the end portion corresponding to the new toner circulation after about 50 sheets immediately after replacement of the first toner replenishing means 9, and finally the entire surface was fogged.

  From the above results, it can be seen that the image forming apparatus according to the present invention can prevent the toner from being deteriorated after the replacement of the toner replenishing means 9 and suppress the replenishment fog.

FIG. 6 is a graph showing the relationship between the rotation time of the image forming apparatus and the output voltage immediately after the toner supply means 9 is replaced in the image forming apparatuses of Test Example 1 and Comparative Example 1 according to the present invention. A solid line 61 indicates Test Example 1 and a broken line 62 indicates Comparative Example 1. Further, the horizontal axis indicates the rotation time (minutes), and the vertical axis indicates the output voltage (V).
As shown by the broken line 62 in FIG. 6, in Comparative Example 1, the output voltage suddenly increases immediately after the replacement of the toner replenishing means 9, and becomes a steady voltage in about 20 minutes. That is, it can be seen that a large amount of toner is replenished immediately after replacement, and in such a case, replenishment fog occurs.
On the other hand, as shown by the solid line 61 in FIG. 5, in Test Example 1 of the present invention, the output voltage is suppressed to about 0.8 V even after 100 minutes. That is, it can be seen that a large amount of toner is not replenished in a short time, and in such a case, replenishment fog does not occur.
That is, FIG. 6 also shows that the image forming apparatus of the present invention can satisfactorily suppress the occurrence of replenishment fog.

  Further, as Test Example 2, image formation was performed using the same image forming apparatus as in Test Example 1 in a state in which the toner replenishing unit 9 was forgotten to be mounted or erroneously mounted. Further, as Comparative Example 2, when the toner replenishing means 9 is replaced, the target voltage of the developing means sensor is lowered. However, the replacement detection toner is not supplied or detected, and the toner replenishing means 9 is forgotten to be installed or incorrectly installed. Image formation was performed in the generated state.

  As a result, in Test Example 2, when the toner replenishment means 9 was forgotten to be mounted, the subsequent toner replenishment was not performed and no image was formed. However, in Comparative Example 2, an image was formed even though the toner was not replenished. For this reason, the output voltage of the developing unit sensor, that is, the toner amount in the developer is further reduced, and a white spot phenomenon occurs in which a part of the image disappears.

  Thus, it can be seen that the image forming apparatus of the present invention can effectively prevent forgetting to mount the toner replenishing means 9 or erroneous mounting by supplying the replacement detection toner.

  The image forming apparatus according to the present invention can be suitably used for a copying machine, a printer, and the like.

1 is a schematic configuration diagram of an image forming apparatus of the present invention. FIG. 2 is an enlarged view of a periphery of a developing unit and a toner supply unit in FIG. It is a top view which shows the inside of a developing means. FIG. 6 is a diagram illustrating a relationship between toner weight (proportional to toner density) and output voltage in a developing unit sensor. FIG. 6 is a diagram illustrating an operation flow when a toner supply unit is replaced. FIG. 6 is a diagram illustrating a relationship between a rotation time of an image forming apparatus and an output voltage immediately after replacing a toner supply unit.

Explanation of symbols

4b Sensor for developing means 9 Toner replenishing means

Claims (4)

Replaceable toner replenishing means for replenishing toner to the developing means;
An image forming apparatus having a developing unit sensor that detects a toner amount in the developing unit and outputs an output voltage corresponding to the toner amount,
Immediately after the replacement of the toner replenishing means, the toner replenishing means supplies the developing means with replacement detection toner for causing the developing means sensor to detect that the toner replenishing means has been replaced. Image forming apparatus. Control means for controlling the amount of toner replenished from the toner replenishing means so that the output voltage output from the developing means sensor is approximately the same as a target voltage serving as a reference;
2. The image forming apparatus according to claim 1, wherein the control unit lowers the target voltage to the same level as the output voltage immediately before the replacement of the toner supply unit immediately after the replacement of the toner supply unit.   3. The image forming apparatus according to claim 2, wherein after the developing unit sensor detects supply of the replacement detection toner, the target voltage is stepped up to a steady state step by step.   4. The image forming apparatus according to claim 3, wherein a replenishment speed of toner replenished by raising the target voltage to a steady state is higher than a maximum consumption speed of toner.

Images