JP2009198809A - Toner density measuring apparatus, and toner density measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method capable of always measuring accurately a toner density in a developer. <P>SOLUTION: The toner density measuring apparatus is built in an image forming device including rotary members 13a, 13b for stirring the developer 2 in a stirring chamber 4 and measures the density of toner 3 in the developer 2 based on an output from a magnetic permeability sensor 14 for detecting a magnetic permeability of the developer 2. The measuring apparatus includes a control means 22 for controlling rotational speeds of the rotary members 13a, 13b, and the control means 22 is constituted to detect the magnetic permeability of the developer in the stirring chamber 4, by the magnetic permeability sensor 14, when making the rotational speeds of the rotary members 13a, 13b get lower than those when forming an image in the image forming device. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus and method for measuring the concentration of toner contained in a developer in an image forming apparatus, and more specifically, in an image forming apparatus that develops an image using a two-component developer, included in the two-component developer. The present invention relates to an apparatus and a method for measuring the concentration of toner.

  An image forming apparatus using an electrophotographic system such as a copying machine or a printer has a developing tank built therein. In the developing tank, the image transferred to the object is developed with a developer. As the developer, a two-component developer composed of a toner and a carrier is usually used. For the development in the developing tank, only the toner is used among the two-component developers held in the developing tank. For this reason, in order to always realize high-quality image formation, the concentration of the toner contained in the developer needs to remain within a certain range. That is, it is necessary to quickly replenish the toner to the developing tank according to the amount used for development.

  Here, if the concentration of the toner contained in the developer is out of a certain range, the following problem occurs. When the toner density falls below a certain value, the ratio of the toner contained in the developer becomes small, so that the total amount of toner conveyed to the developing area of the developing tank is lowered. At the same time, since the contact probability between the toner and the carrier increases, the charge amount of the toner increases. Further, in the development process, normally, the charged toner is deposited on the photoconductor so as to fill the potential difference generated on the photoconductor, so that a decrease in the total amount of toner and an increase in the amount of charged charge adhere to the photoconductor. Reduce toner amount. As a result, in a development process in which the toner density is required to be controlled within a certain range, appropriate developability cannot be maintained if the toner density is out of the certain range. In such a state, as a result, the density of the image formed on the object is extremely lowered. On the other hand, when the toner density exceeds a certain value, the contact probability between the toner and the carrier decreases, and the contact probability between the toners increases. In such a state, an uncharged toner having a low charge or a charge amount of almost zero, or a toner charged to a polarity opposite to the desired polarity is generated. These phenomena increase the amount of toner adhering to the photoreceptor in the normal configuration of the development process. As a result, the image density on the object is excessively increased, or toner adheres to an undesired portion, thereby causing background stain (toner fogging) on the object.

  As described above, the concentration of the toner contained in the developer is closely related to the amount of toner to be conveyed and the toner charge amount. Therefore, in the image forming process of the image forming apparatus, it is very important to accurately determine the toner density, the toner replenishment amount, and the toner replenishment timing.

  As a normal method for determining the toner replenishment amount, for example, a method of determining from a toner consumption amount obtained using a magnetic permeability sensor can be cited. The toner consumption amount is determined by the toner density before and after consuming the toner by the magnetic permeability sensor and by the difference between them. The magnetic permeability sensor is a sensor that detects the magnetic permeability of the developer, and detects the magnetic permeability at which carriers (particles) that are magnetic particles contained in the developer are generated. The relationship between the magnetic permeability of the developer and the concentration of toner contained in the developer will be described below with reference to FIG. FIG. 7 is a graph showing an example of the relationship between the output value from a normal magnetic permeability sensor and the concentration of toner contained in the developer. As shown in FIG. 7, as the output value from the permeability sensor changes (decreases), the concentration of toner contained in the developer increases linearly. That is, there is a proportional relationship between the output value from the magnetic permeability sensor and the concentration of toner contained in the developer.

  However, the output value from the magnetic permeability sensor and the concentration of toner contained in the developer do not always have the simple proportional relationship shown in FIG. It is well known that the output value from the magnetic permeability sensor varies greatly depending on factors other than the concentration of toner contained in the developer. The factor is a change in the bulk density of the developer due to, for example, the length of the stirring time or the standing time of the developer.

  When the image forming apparatus is in an operable state, for example, development including a toner (particle) having a positive or negative charge and a carrier (particle) which is a magnetic particle having a diameter of about 5 to 10 times that of the toner. The agent is stirred for a long time by various stirring members in the image forming apparatus. The bulk density of the developer being stirred is reduced (bulk is increased) by including air (biting) between the particles by stirring or by repulsive force acting between the particles due to the charge charged by the toner. That is, the decrease in the bulk density means a state in which a space is generated between the developer particles, and the decrease in the existence density of the carrier particles contained in the developer. For this reason, the magnetic permeability of the developer decreases due to the decrease in bulk density. As a result, the output value of the magnetic permeability sensor obtained from the developer having a low (high) bulk density is smaller than that of the developer having the same toner concentration and a high bulk density. Become.

  On the other hand, when the image forming apparatus is in a standby state or in a power-off state, and stirring of the developer is interrupted or stopped, the developer whose bulk density has once decreased by the stirring operation is The bulk density increases due to the dead weight of the developer and a decrease in repulsive force between the particles due to leakage of charges from the particles. For this reason, contrary to the above case, the output value of the magnetic permeability sensor obtained from the developer having a high bulk density is higher than that of the developer having the same toner concentration and a low bulk density. growing.

  As described above, the value output by the sensor in accordance with the magnetic permeability of the developer is the magnitude of the charge of the toner, the stirring time of the developer, or the density of the toner contained in the developer, It varies depending on the developer leaving time. That is, it is difficult to determine an accurate toner replenishment amount based on the toner density determined from the output value of the magnetic permeability sensor.

  As a technique for solving the above problem, Patent Document 1 discloses a developing tank in which a developing sleeve or a stirring rotor is driven at a lower speed than a normal rotational speed at the time of development at the initial stage of driving. The developing tank reduces the amount of developer conveyed to the toner density sensor side by rotating the developing sleeve or the agitation rotor at a low speed in the initial stage of driving. As a result, a large amount of the developer having an increased bulk density reaches the toner concentration sensor without being transported to the toner concentration sensor in large quantities. Therefore, the toner density sensor does not output an erroneous signal that the toner density is lowered. In addition, since the low-speed agitation at the initial stage of driving as described above allows air to be included (engaged) between particles in the developer having increased bulk density, the state of the developer is that the bulk density immediately before driving is From the state in which the increase is made, it becomes a stable state in which the bulk density during driving is lowered. As a result, erroneous detection by the toner concentration sensor (detecting the toner concentration of the developer having a high magnetic permeability as an incorrect value) can be avoided.

  Here, the relationship between the toner density of the developer in the developer tank and the output from the toner density sensor will be described with reference to FIG. As shown in FIG. 8, state A is a state in which the stirring mechanism is operating and the bulk density of the developer is stable. In the developing tank, the output of the toner density sensor in the state A is used as a toner density detection reference value. State B is a state where the bulk density of the developer is lowered by stopping stirring of the developer in state A and leaving it for a while. The state C is a developer state in which the stirring mechanism is operating and the toner concentration is higher than that in the state A.

  Based on the difference in the sensor output value between the state A during the operation of the stirring mechanism and the state B after being left, the developer in the state B is in the state C even though the toner density is the same. It is detected that there is. That is, the toner density sensor that detects the developer after being left and immediately after the start of stirring outputs a value larger than the correct value because the bulk density of the developer is reduced as described above. Thus, the erroneous determination is made that the developer in state B has a lower toner concentration than the developer in state A. In order to avoid erroneous detection of the toner density sensor at the initial stage of driving as described above, the developing tank rotates the developing sleeve or the stirring rotor at a low speed. For this reason, the developer in the state B reacts to the toner concentration sensor only by a smaller amount than in the normal stirring operation. Further, since the developer that has returned from the state B to the state A due to the stirring by the initial low-speed rotation is detected by the toner concentration sensor, it is possible to accurately measure the toner concentration.

  There are many known techniques for avoiding erroneous detection of the toner density that occurs during the development process operation, not only at the start of the development process after being left. As such a technique, there is a technique for detecting the toner concentration from information other than the magnetic permeability of the developer.

  As an example of this, there is a technique for detecting the toner density from a patch image developed using toner on a carrier carrying a developed image such as a photosensitive drum or an intermediate transfer member. In this technique, the density of a patch image is converted into a signal using a light source and a light receiving sensor for the reflected light provided opposite to the carrier. The signal output from the light receiving sensor is sampled, and the sampling information corresponding to the toner density and the information corresponding to the toner reference density are compared in a logic circuit. Based on the result of comparing the two pieces of information, the toner density of the current developer is estimated. This determines whether or not the developer needs to be replenished with toner and how much toner is replenished. Specifically, as a result of comparing the two pieces of information, if it is determined that the patch image density is higher than the reference density, toner supply is stopped until the toner density of the developer returns to the reference density. On the other hand, as a result of comparing the two pieces of information, if it is determined that the patch image density is lower than the reference density, toner supply is forcibly executed until the reference density is reached. Through the above processing, the toner density of the developer is maintained at a desired value.

  As another example, there is a video count method in which the toner replenishment amount is not determined based on the toner density, but the toner consumption amount due to development is calculated from image data representing the developed image. In the video count method, information regarding pixels that consume toner is extracted from image data. Based on the information about the pixel, the toner consumption amount due to development is calculated. In the video count method, if the toner supply mechanism simply supplies the toner corresponding to the calculated toner consumption amount to the developing tank, the toner density of the developer is maintained at a desired value.

  Here, a new problem that causes false detection of the toner density sensor as the developer particle size is reduced and the developing speed is increased will be described below. The new problem is a detection abnormality of the toner density sensor that occurs under a printing condition in which an image having an extremely low image ratio is formed on an object using a high-speed development process. The detection abnormality of the toner density sensor that occurs under the above printing conditions is considered to be caused by the change in the bulk density of the developer becoming larger as the image ratio is smaller. An example of such abnormal detection of the toner density sensor will be described below.

  Each of an image having an image ratio of 1% and an image having an image ratio of 10% is continuously formed on 1000 objects at a process speed of forming an image on 50 objects per minute, and Output. In order to detect the toner concentration, a magnetic permeability sensor having the properties shown in FIG. 7 was used. Then, based on the output value of the magnetic permeability sensor, the toner was supplied to the developer so as to maintain the initial toner density (here, 6% so that the numerical difference is easily understood). According to such a rule, after 1000 sheets of objects having two kinds of image ratios were output, the toner density of the actual developer was measured. After outputting 1000 objects having an image ratio of 1%, the toner density decreased from 6% to 3.8%. On the other hand, after outputting 1000 objects having an image ratio of 10%, the toner density decreased from 6% to 5.8%. As described above, when an object having an image ratio of 1% is output, the toner concentration of the actual developer is 3.8% from the initial 6% even though the toner is supplied while detecting the toner concentration. %.

  In the image formation with an image ratio of 1% as described above, the actual toner concentration is decreased because the magnetic permeability sensor erroneously detects the toner concentration due to a rapid change in the bulk density of the developer. . The rapid change in the bulk density of the developer is considered to be caused by a high-speed stirring operation and an increase in toner charge amount due to the high-speed stirring. The relationship between the change in the bulk density, the stirring operation and the increase in the toner charge amount will be described below.

  In image formation with an image ratio of 1%, the amount of toner consumed in development is extremely small. That is, since the amount of toner supplied to the developing tank is extremely small, the toner is hardly replaced in the developing tank. For this reason, if the developer is continuously stirred as the development process is performed, the contact frequency between the toner and the carrier increases, and the amount of charge charged by the toner increases. An increase in the charge amount of the toner increases the repulsive force between the toners, and as a result, the bulk density of the developer is greatly decreased (the bulk is greatly increased). Since the magnetic permeability sensor detects the developer having a high bulk density as a toner-rich state, in the image formation with an image ratio of 1%, the image formation is continued without toner replenishment. As a result, the actual toner concentration stirred in the developing tank is lowered. On the other hand, in the image formation with the image ratio of 10%, the toner amount is switched 10 times as compared with the image formation of 1%, so that the increase rate of the toner charge amount and the charge rising speed of the replenishment toner are balanced. As a result, the change in repulsive force acting between the toners becomes small, and it is considered that the bulk density did not change.

An image forming apparatus for solving the problems that occur in the formation of an image with a low image ratio as described above is disclosed in Patent Document 2. The image forming apparatus disclosed in Patent Document 2 includes a detection signal reference value correction unit that corrects a reference value to be compared with a detection signal (apparent toner density output value) based on a result of detecting magnetic permeability according to an image ratio to be formed. I have. The detection signal reference value correction means changes the degree of correction of the reference value according to the image ratio. For this reason, even in image formation with a low image ratio, the toner is replenished in accordance with the amount of consumed toner, so that a decrease in the bulk density of the developer can be suppressed.
Japanese Laid-Open Patent Publication No. 4-198971 (published July 20, 1992) JP 2004-85710 A (published March 18, 2004)

  However, each of the above four prior arts has unsolved problems. The unsolved problems in the four prior arts are described below.

  In the method of indirectly detecting the toner density from the patch image, there arises a problem of erroneous detection due to contamination of the optical system sensor, deterioration of the characteristics of the carrier, or change in the development density accompanying change in the toner charge amount. The change in the toner charge amount described above is caused by the deterioration of the developing tank over time and the environmental change. Due to the above three problems, it is difficult to always measure the exact toner density. Further, in the above method, a series of control sequences such as development of a patch image, detection of image density, and toner replenishment take time. For this reason, a certain amount of time is required from when the toner is consumed to when the toner is replenished. That is, the response after the toner supply is required is slow.

  In addition, in the method of calculating the toner consumption amount by the video count method, there is a possibility that a difference between the toner amount consumed in the actual development process and the calculated consumption amount may be difficult. This difference increases as the number of executions of the development process increases. Therefore, the method using the video count method is not reliable as a method for controlling the toner density of the developer in the medium to long term.

  Further, as described above, Patent Document 1 has a description of avoiding erroneous detection of the toner concentration at the initial stage of the stirring operation, but does not describe any detection of the toner concentration during the development process. . Therefore, it is not possible to solve the problems that occur during continuous output of images with a small image ratio due to the reduction in the particle size of the developer and the increase in the development speed.

  In Patent Document 2, as described above, the reference value of the detection signal is corrected according to the image ratio formed on the object. However, the fluctuation of the toner density detection signal is not necessarily caused only by the image ratio. For example, the detected value of the toner concentration varies depending on various factors such as the environment around the developer and the standing time, the resistance value of the developer and the change over time, or the deviation between the actual toner concentration and the detected value. Japanese Patent Application Laid-Open No. 2004-228561 does not consider the factors that change the detected value of the toner density. Therefore, even if the reference value of the detection signal is corrected with a preset value in accordance with the fluctuation of the detected value of the toner density expected from the image ratio, there is a possibility that it cannot be corrected accurately in accordance with the actual fluctuation. .

  From the above, in order to supply an appropriate amount of toner to the developer at an appropriate timing, it is most preferable to always accurately detect the actual toner density of the developer.

  Note that it is not so difficult to accurately detect the actual toner concentration using a magnetic permeability sensor. As a method for measuring the bulk density of the powder accurately and with good reproducibility, for example, “metal powder-tap density measuring method” of JIS standard JISZ2512 can be cited. The metal powder-tap density measuring method is a method of making the bulk density of the powder at the time of measurement a constant density with good reproducibility using taps (vibration). By tapping (vibrating) the powder, air that has entered between the powders can be removed, and the packing density of the powder can be settled in a desired state with good reproducibility. Therefore, according to the above method, when the concentration of the powder is measured, the powder always has a certain bulk density, so that the concentration of the powder can always be measured accurately.

  From the above, when the above method is used, the decrease in the developer bulk density (increased bulk) as a result of stirring of the developer by the air or the repulsive force due to the charge of the toner is extremely good. It will be resolved. For this reason, if necessary, the bulk density of the developer can be made constant with good reproducibility.

  Further, a method different from the metal powder-tap density measurement method may be employed to remove air that has entered between the powders (a space generated between the powders). For example, the fluidity measuring device FT-4 (Freeman technology) makes the bulk density of the powder constant and reproducible as required by slowly moving the rotating screw up and down in the powder. Can do.

  As described above, if the above method or apparatus is used, an accurate toner concentration can be measured. However, there is a need for an apparatus or method that can be easily combined with other apparatuses and can accurately measure the toner concentration, in addition to the above method or apparatus.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an apparatus and method that can always accurately measure the toner concentration of a developer.

In order to solve the above problems, the toner concentration measuring device of the present invention is:
Based on an output from a magnetic permeability sensor that is incorporated in an image forming apparatus including a rotating member that stirs the developer in the stirring chamber and detects the magnetic permeability of the developer, the concentration of toner contained in the developer is determined. A device for measuring,
Control means for controlling the rotational speed of the rotating member;
The magnetic permeability sensor detects the magnetic permeability of the developer in the agitation chamber when the control means is lowering the rotation speed of the rotating member than that during image formation by the image forming apparatus. Yes.

  The magnetic permeability of the developer is an apparent magnetic permeability that varies depending on the mixing ratio of the magnetic material (carrier) and the non-magnetic material (toner) contained in the developer. For this reason, if the developer contains a certain amount (number) of carriers, the change in the magnetic permeability of the developer according to the increase / decrease of the toner amount (according to the increase / decrease of the bulk of the developer). The toner density of the developer can be read.

  Here, when forming an image with a low image ratio, the developer in the stirring chamber is stirred by a rotating member that rotates at high speed. At this time, since the consumption amount of the toner contained in the developer is very small, the toner replenishment frequency is low. For this reason, the toner contained in the developer is vigorously stirred for a long time without much replacement. In other words, the frequency of contact between the carrier and the toner increases, and the charge carried by the toner becomes excessively large. If the charge carried by the toner increases, the repulsive force acting between the toners increases. At the same time, the increase in the stirring strength of the developer facilitates inclusion of air between the developer particles. As a result of these, the developer increases in bulk as stirring continues. That is, the developer kept stirring at high speed tends to increase in bulk regardless of the increase or decrease in the amount of toner. As described above, the magnetic permeability of the developer varies depending on the bulk of the developer. For this reason, an accurate value of the toner concentration contained in the developer cannot be obtained from the apparent magnetic permeability of the developer that is continuously stirred at a high speed.

  On the other hand, when the developer is left without stirring for a long time, the charged charge amount of the toner decreases for a while. For this reason, the electrostatic repulsive force (repulsive force) that acts between the toners also decreases with the passage of time. Further, as the time for which the toner is left is longer, the toner and the carrier are gradually clogged without a gap due to the weight of the developer. For this reason, the bulk of the developer becomes small even though the toner density is not changed. That is, an accurate value of the toner concentration contained in the developer cannot be obtained from the apparent magnetic permeability of the developer left for a long time.

  In the above configuration, when the toner concentration of the developer in the stirring chamber is measured based on the magnetic permeability of the developer, the rotation speed of the rotating member is lower than that during image formation by the control means. That is, when measuring the toner concentration, the developer in the stirring chamber is stirred more slowly than during image formation. In other words, the magnetic permeability sensor detects the magnetic permeability of the developer in a state where the developer hardly contains air. That is, with the above configuration, the magnetic permeability for measuring the toner concentration can be obtained from the developer that is not bulky or changed due to factors other than the increase or decrease of the toner amount.

  Furthermore, as described above, when measuring the toner concentration, the developer in the stirring chamber is stirred more slowly than during image formation. For this reason, it can be avoided that the bulk of the developer becomes extremely small. That is, according to the above configuration, the magnetic permeability for measuring the toner concentration can be obtained from the developer whose bulk is not changed due to factors other than the increase or decrease of the toner amount.

  Further, since the magnetic permeability is detected while stirring the developer slowly, the developer that has been vigorously stirred for a long time and has expanded is returned to the original state. Further, since the magnetic permeability is detected while stirring the developer slowly, the developer that has been left for a long time and has become less bulky returns to its original state. For this reason, it is possible to return the developer that has changed in bulk due to factors other than the amount of toner to the original state, and to detect an accurate magnetic permeability.

  In summary, by having the above configuration, the actual toner density of the developer can always be accurately measured. For this reason, it is possible to always grasp the amount of toner in the stirring chamber as an accurate value. Therefore, if the toner concentration measuring apparatus having the above configuration is used, the amount of toner to be replenished in the stirring chamber can be accurately determined.

In the toner concentration measuring apparatus of the present invention,
The magnetic permeability sensor preferably detects the magnetic permeability of the developer in the stirring chamber when the rotation speed of the rotating member is 50% or less during image formation in the image forming apparatus.

  The relationship between the rotation speed of the rotating member and the output value of the magnetic permeability sensor that measures the toner concentration will be described with reference to FIG. When the rotational speed of the rotating member is in the range of 150 rpm to 250 rpm, which is the rotational speed at the time of image formation, the output value of the magnetic permeability sensor tends to decrease as the rotational speed increases. As described above, this is a result of a reduction in carrier density due to repulsive force acting between the toners and air between the developer particles. On the other hand, when the rotation speed of the rotating member is 150 rpm or less, the output value of the magnetic permeability sensor (strictly speaking, the average value of the output values) changes between about 2.75 V and 2.85 V, and is almost constant. Being Calm. In order to keep the fluctuation of the output value of the permeability sensor with respect to the rotational speed of the rotating member from the value in the stationary state (rotational speed 0 rpm) to about 0.1 V, the toner density measuring device rotates at 250 rpm during image formation. The rotational speed of the rotating member must be reduced to about 150 rpm, strictly to 125 rpm or less. When the rotational speed exceeds 125 rpm, the repulsive force acting between the toners contained in the developer and air between the developer particles are likely to be contained due to the reasons described above. There is a risk that the sensor value may decrease. By detecting the magnetic permeability of the developer in the stirring chamber while rotating the rotating member at a rotation speed within the above range, it is possible to measure the toner concentration more accurately and more reliably.

In the toner concentration measuring apparatus of the present invention,
Calculating means for calculating the amount of toner consumed during the image formation;
Determination means for determining the magnitude of the toner consumption amount and a threshold value having a size equal to or greater than the maximum amount of toner consumed when forming one image;
Further comprising
When the determination unit determines that the toner consumption amount is greater than or equal to the threshold value, the control unit preferably reduces the rotation speed of the rotation member as compared to when the image is formed in the image forming apparatus. .

  In the above configuration, the maximum amount of toner consumed when forming one image is, for example, the amount of toner consumed when an image is formed on the entire surface of one printed matter with toner. Therefore, the determination unit does not determine that the toner consumption calculated by the calculation unit exceeds the threshold until an image is formed on at least one printed matter. Therefore, since the rotation speed of the rotating member does not decrease during image formation, the sufficiently stirred developer maintains a state suitable for image formation.

  On the other hand, if it is determined that the toner consumption amount is equal to or greater than the threshold value, the rotation speed of the rotating member decreases by the control means. That is, when the toner in the stirring chamber exceeds a certain amount, the developer is slowly stirred. Therefore, the developer returns to the original state. In this state, if the magnetic permeability is detected by the magnetic permeability sensor, the toner concentration of the developer can be accurately measured, and the amount of toner to be replenished in the stirring chamber can be accurately determined.

In the toner concentration measuring apparatus of the present invention,
The toner consumption calculated by the calculation means is preferably an integrated amount of toner consumption consumed when forming the plurality of images.

  By having the above configuration, for example, when it is determined that the toner consumption after forming an image on a plurality of printed materials is equal to or greater than a threshold value, the rotational speed of the rotating member is reduced for the first time. That is, the image formation can be continued until the toner needs to be replenished. Therefore, for example, processing that continues for a relatively long time, such as formation of an image with a low image ratio, can be completed without interruption.

In the toner concentration measuring apparatus of the present invention,
Preferably, the calculating means is a means for calculating a toner consumption amount during development based on pixel data representing a pixel desired to transfer toner in the image.

  In the above configuration, the control unit changes the rotation speed of the rotating member based on the toner consumption estimated from the pixel data without using the magnetic permeability of the developer. Therefore, it is possible to determine whether or not toner replenishment is necessary without stopping the image forming process.

  Even if the toner consumption calculated by the calculation unit is different from the amount of toner actually consumed in image formation, the toner concentration of the developer is measured later based on the detection result by the magnetic permeability sensor. The For this reason, the amount of toner actually supplied to the stirring chamber is corrected to an amount for maintaining the toner concentration of the developer.

  By having the above configuration, an appropriate amount of toner can always be replenished at an appropriate timing without hindering execution of the image forming process.

In the toner concentration measuring apparatus of the present invention,
The threshold value is preferably a value based on an allowable amount determined from the total amount of toner held in the stirring chamber.

  If the threshold value is set to a value that is too large with respect to the allowable amount of toner in the stirring chamber, the developer toner concentration may decrease until it becomes unsuitable for image formation. On the other hand, if the threshold value is set to a value that is too small with respect to the allowable amount of toner in the agitation chamber, the rotational speed of the rotating member is frequently decreased, which may lead to a decrease in image forming speed. These problems can be avoided by determining an appropriate threshold based on the amount of toner in the agitation chamber.

For example, the threshold value is preferably set within a range corresponding to a toner reduction amount of 0.07% to 12.5% with respect to the total amount of toner held in the stirring chamber. This range is determined for the following reasons. When the normally assumed printing conditions (conditions for printing toner on the paper at a density of 0.4 mg / cm ² and printing one A4 sheet at a printing rate of 5%) are selected as the printing conditions Will be described. At this time, the lower limit of the threshold value is obtained from the ratio of the weight of the consumed toner (0.012 g) to the maximum amount (18.4 g) occupied by the toner in the developer filled in the stirring chamber. Can do. That is, at least during the normally assumed printing operation of one A4 sheet, the toner consumption amount does not reach the threshold value for toner replenishment. On the other hand, the upper limit value of the threshold value is obtained from a value obtained by reducing 1% from the initial toner density condition (8%). This is the change amount of the toner density at which the development density change at the time of development starts to become apparent, and is equivalent to 2.3 g when replaced with the toner amount. This amount occupies 12.5% of the initial toner total amount (18.4 g). In other words, the upper limit value of the threshold value represents a value that should reach the threshold value for toner replenishment before consuming at least this toner amount so that the toner concentration in the stirring chamber does not decrease excessively. With the above configuration, unnecessary interruption of the image forming process can be avoided, and the toner density of the developer can always be maintained in a state suitable for image formation.

In the toner concentration measuring apparatus of the present invention,
It is preferable to further include output averaging means for averaging the output from the magnetic permeability sensor while the rotating member makes one or more rotations.

  It is assumed that the rotating member includes, for example, a cylindrical shaft and a blade that spirals around the shaft. Further, it is assumed that the spiral blade passes only once just above the magnetic permeability sensor during one rotation of the rotating member. At this time, in the detection of the magnetic permeability of the developer by the magnetic permeability sensor, the amount of the developer detected by the magnetic permeability sensor may vary depending on the position of the blade of the rotating member. For example, when the blade of the rotating member passes right above the magnetic permeability sensor, the developer just above the magnetic permeability sensor is pressed and solidified by the blade of the rotating member, The output value from the magnetic permeability sensor is maximized. Further, for example, when the blade of the rotating member is at the position farthest from the magnetic permeability sensor, most of the developer directly above the magnetic permeability sensor is lifted upward by the blade of the rotating member, and the density is increased. Is small, the output value from the magnetic permeability sensor is minimized. In this way, there is some variation in the output from the magnetic permeability sensor during one rotation of the rotating member.

  In the above configuration, the output averaging means averages the output from the magnetic permeability sensor during one rotation or more. For this reason, the averaged output can be used as the magnetic permeability of the developer. That is, by having the said structure, the dispersion | variation in the detected value by a magnetic permeability sensor accompanying rotation of a rotation member can be reduced.

In order to solve the above problems, the toner concentration measurement method of the present invention comprises:
In an image forming apparatus including a rotating member that stirs a developer in a stirring chamber, a method for measuring a concentration of toner contained in the developer based on an output from a magnetic permeability sensor that detects a magnetic permeability of the developer. Because
Including the step of controlling the rotational speed of the rotating member;
In the step of controlling the rotation speed of the rotating member, when the rotation speed of the rotating member is lower than that during image formation in the image forming apparatus, the magnetic permeability sensor has the permeability of the developer in the stirring chamber. It is characterized by detecting magnetic susceptibility.

  In the above configuration, when the toner concentration of the developer in the stirring chamber is measured based on the magnetic permeability of the developer, the rotation speed of the rotation member is greater than that during image formation in the step of controlling the rotation speed of the rotation member. Is also lowered. That is, when measuring the toner concentration, the developer in the stirring chamber is stirred more slowly than during image formation. In other words, the magnetic permeability sensor detects the magnetic permeability of the developer in a state where the developer hardly contains air and the repulsive force between the toners is not large. That is, according to the above configuration, the magnetic permeability for measuring the toner concentration can be obtained from the developer whose bulk is not changed due to factors other than the increase or decrease of the toner amount.

  Further, since the magnetic permeability is detected while stirring the developer slowly, the developer that has been vigorously stirred for a long time and has expanded is returned to the original state. Further, since the magnetic permeability is detected while stirring the developer slowly, the developer that has been left for a long time and has become less bulky returns to its original state. For this reason, it is possible to return the developer that has changed in bulk due to factors other than the amount of toner to the original state, and to detect an accurate magnetic permeability.

  Summarizing the above, by having the above-described configuration, the same effects as those of the above-described toner concentration measuring apparatus can be obtained.

  As described above, the toner concentration measuring device of the present invention stirs the developer slowly when measuring the magnetic permeability of the developer, so that the actual toner concentration of the developer is always accurately measured. Can do. As a result, there is an effect that the toner density of the developer can always be maintained in an appropriate state.

  Embodiments according to the present invention will be described with reference to FIGS. In the following description, the same members and components are denoted by the same reference numerals. The names and functions are also the same. Therefore, detailed description thereof will not be repeated.

(Image forming device)
An image forming apparatus according to an embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a plan view showing a main configuration of an image forming apparatus according to the present invention. FIG. 2 is a plan view showing the configuration of the developing tank according to the present invention. FIG. 3 is a cross-sectional view showing the main configuration of the image forming apparatus according to the present invention.

  As shown in FIG. 1, the image forming apparatus according to the present embodiment includes a plurality of developing tanks (stirring chambers) 4a to 4d, a frame 20 that fixes the plurality of developing layers 4a to 4d along the rail 21, and a plurality of developing tanks (stirring chambers). A toner concentration sensor (magnetic permeability sensor) 14 included in each of the developing tanks 4 a to 4 d and a microcomputer 22 electrically connected to the motor 19 are provided. Each of the plurality of developing layers 4a to 4d is a developing tank 4 that develops using any of black, magenta, cyan, and yellow toner. The toner concentration sensor 14 is electrically connected to the microcomputer 22 via a cable 15, a connector 17, a connector 18, wiring and an input / output (I / O) interface 23. The toner concentration sensor 14 is a magnetic permeability sensor that outputs a voltage based on the magnetic permeability of the developer in the developing tank 4 to the microcomputer 22. The motor 19 is electrically connected to the microcomputer 22 via wiring and an I / O interface 23. Further, the motor 19 is connected to stirring members (rotating members) 13a and 13b having stirring blades in the plurality of developing tanks 4a to 4d through gears. Inside the microcomputer 22, calculation based on the output from the toner density sensor 14 and control of the driving speed of the motor 19 are performed. The toner density measuring apparatus according to the present invention is built in the image forming apparatus as the toner density sensor 14 and the microcomputer 22. Further, on the left side of the developer carrier 5 on the paper surface, a photosensitive drum 1 (see FIG. 3) is disposed so as to face the developer carrier 5.

  The image forming apparatus according to the present embodiment having the above-described configuration is an apparatus that forms an image on an object by a so-called Carlson process. Here, an outline of an image forming process in the image forming apparatus according to the present embodiment will be described below.

  First, the photosensitive drum 1 (see FIG. 3), which is an image carrier, is uniformly charged by corona discharge of a charging means (not shown). The photosensitive drum 1 is irradiated with an exposure laser beam whose light intensity is modulated based on desired image information by an electrostatic latent image writing unit (not shown) having an exposure unit for irradiating a laser beam. Is done. As a result, an image based on the image information is written on the photosensitive drum 1. That is, the photosensitive drum 1 is in a state of holding an electrostatic latent image. The electrostatic latent image held on the photosensitive drum 1 becomes a visible image (developed) when the toner contained in the developer held on the surface of the developer carrier 5 adheres. In the developing tank 4, the developer is held on the surface of the developer carrier 5 by applying a development bias voltage to the developer carrier 5. The visible image formed on the photosensitive drum 1 is transferred to plain paper supplied from a paper feed unit (not shown) in a transfer unit (not shown). A visible image made of toner transferred onto plain paper is fused and fixed in a fixing unit (not shown) that fixes the toner by heating and pressurizing, and is discharged out of the image forming apparatus.

  On the other hand, the toner remaining on the photosensitive drum 1 without being transferred is removed by the cleaning means. The cleaned photosensitive drum 1 is irradiated with static elimination light from a static elimination lamp (not shown). As a result, residual charges that form an electrostatic latent image remaining on the surface of the photosensitive drum 1 are removed. That is, the photosensitive drum 1 is initialized in preparation for charging by the charging means described above.

  Next, details of the plurality of developing tanks 4a to 4d that stir the developer and hold the developer carrier 5 will be described below with reference to FIG.

(Developing tank 4)
As shown in FIG. 2, in the casing of the developing tank 4, a developer carrying member 5 carrying a two-component developer composed of a carrier and toner, stirring members 13a and 13b for stirring the developer, and the casing floor surface A toner concentration sensor 14 formed immediately below the stirring member 13b and a partition plate 16 provided between the stirring members 13a and 13b are provided. Each of the stirring members 13a and 13b is arranged in parallel to each other and has screw-like blades. The toner concentration sensor 14 is a sensor that detects the magnetic permeability of the developer. Underneath the developer carrier 5 is a doctor blade 12 (see FIG. 3) that keeps the amount of developer conveyed to the photosensitive drum 1 in contact with the developer carrier 5 constant. Is formed.

  As described above, the agitating members 13a and 13b are connected to the motor 19 via gears. Further, the gears of the stirring members 13a and 13b are engaged with each other. Therefore, as the motor 19 rotates, the stirring members 13a and 13b rotate in opposite directions. Therefore, the developer is sent by the screw-like blades of the stirring members 13a and 13b. And since the partition plate 16 exists between the stirring members 13a and 13b, in the developing tank 4, the developer is conveyed (circulated) in the direction of the arrow in the drawing while being stirred. The toner concentration sensor 14 outputs a voltage value to the microcomputer 22 based on the magnetic permeability of the developer circulating in the developing tank 4.

  Next, the concentration sensor 14 for measuring the toner concentration based on the magnetic permeability of the developer in the developing tank 4 will be described below with reference to FIG.

(Toner density sensor 14)
As described above, the toner concentration sensor 14 is a magnetic permeability sensor that outputs a voltage having a certain magnitude based on the magnetic permeability of the developer. The toner concentration sensor 14 outputs a voltage as shown in FIG. 7 according to the toner concentration of the developer in a state where the developer has a certain bulk density. That is, the toner density of the developer can be measured from the output of the toner density sensor 14. Further, the digital signal based on the output of the toner density sensor 14 may be used as it is in the arithmetic processing or the like in the microcomputer 22 without being replaced with the toner density.

  As shown in FIG. 3, the developer circulating in the developing tank 4 passes between the stirring member 13 b and the toner concentration sensor 14. At this time, the toner concentration sensor 14 outputs a voltage based on the magnetic permeability of the developer to the microcomputer 22. Here, when the toner concentration sensor 14 outputs a voltage based on the magnetic permeability of the developer, the rotational speed of the motor 19 is lower than that at the time of image formation in accordance with a signal from the control means inside the microcomputer 22. is there. The voltage is sent to the microcomputer 22 via the cable 15, connector 17, connector 18, wiring, and I / O interface 23. The voltage, which is an analog signal, is converted to a digital signal at an electrical interface and input to the microcomputer 22. In the microcomputer 22, it is determined based on the output of the toner concentration sensor 14 whether or not the toner concentration of the developer is below a desired value. When the microcomputer 22 determines “Yes” (the toner density is lower than the desired value), the toner is supplied to the developing tank 4.

  Next, the toner replenishing mechanism 6 will be described below with reference to FIG.

(Toner supply mechanism 6)
As shown in FIG. 3, the toner replenishing mechanism 6 includes a stirring blade and a rotating member 7. The toner replenishing mechanism 6 replenishes the toner 3 to the developing tank 4 by rotating the rotating member 7 using a driving unit (not shown). The rotating member 7 can send an amount of toner 3 corresponding to the number of rotations into a hole under the rotating member 7. The toner 3 fed into the hole falls into the developing tank 4. Therefore, the toner may be supplied by rotating the rotation member 7 by the number corresponding to the amount of toner 3 desired to be supplied. The amount of toner 3 to be replenished may be determined by the microcomputer 22 based on the output of the toner density sensor 14. The toner supply mechanism 6 having the above-described configuration uses a conventionally known toner supply method. Therefore, further detailed description is omitted.

(Developer 2)
The developer 2 of this embodiment is composed of toner particles and carrier particles. The toner particles are a polyester resin having a diameter of 6.5 μm. The carrier particles are particles having a diameter of 40 μm having a ferrite core as a core material and having a surface of the ferrite core coated with a silicone resin. The developing tank 4 is filled with 230 g of the developer 2. In the developer 2, which is a mixture of the two types of particles, the toner particles account for 8% by weight. Therefore, 18 g of toner particles are present in the developing tank 4. In the present embodiment, the reference value of the toner density is set to 8% by weight.

(Microcomputer 22)
The microcomputer 22 of this embodiment includes an arithmetic microprocessor (such as a CPU), a read memory, a read and write memory (such as a memory or a hard disk), and an I / O interface 23 (such as an external connection terminal). It has. The microcomputer 22 may be connected to another external device via the I / O interface 23. As described above, the microcomputer 22 detects the toner density based on the output from the toner density sensor 14, controls the rotation speed of the motor 19 based on the detected toner density, and determines the toner replenishment amount to the developing tank 4. It is carried out. Details of these processes will be described later in the section (Processing flow in the image forming apparatus). Further, the microcomputer 22 performs drive control of each component in the image forming process including charging, exposure, development, transfer, and fixing described in the section of (Image forming apparatus). Since the control in the image forming process performed by the microcomputer 22 employs a conventionally known control method, the details thereof are omitted.

(Processing flow in image forming apparatus)
An example of a processing flow from the start of image formation to the end of toner supply by the image forming apparatus according to the present embodiment will be described below with reference to FIG. FIG. 4 is a flowchart illustrating an example of a processing flow in the image forming apparatus according to the present embodiment. Note that the flowchart of FIG. 4 shows processing after the user instructs the image forming apparatus to form an image on n plain sheets. For this reason, in FIG. 4, the start of image formation is shown as the starting point of the process.

(Toner consumption comparison judgment)
As shown in FIG. 4, an image forming process for n plain sheets starts in accordance with an instruction from the user (S1). For the image forming process, reference may be made to (Image forming apparatus).

When the image forming process for the first plain paper is completed, the toner consumption T1 consumed for forming the image on the first plain paper is calculated by the calculation means inside the arithmetic microprocessor (S2). . More specifically, the calculation means is a value based on pixel data representing a pixel that consumes toner among the image data referred to by the electrostatic latent image writing means for writing on the photosensitive drum 1 (value of the video count number). To get. This toner consumption reference method based on pixel data is generally known as a video counting method. In order to write an electrostatic latent image on the photosensitive drum 1, a laser beam scanner subjected to pulse width modulation is used as an electrostatic latent image writing unit. The signal level input to the laser beam scanner is stored in the toner consumption map as the number of pulses for each pixel forming the electrostatic latent image. The integrated value of the number of pulses for forming a latent image corresponding to the image on the entire surface of the A4 paper is the video count of the entire A4 paper. For example, the maximum video count of one A4 sheet is 3884 × 10 ⁶ counts at 400 dpi and 256 gradations, and a black solid image is formed with the maximum video count. This count amount corresponds to a toner amount of 0.24 g consumed for solid development of one A4 sheet when the accumulation density of toner formed on the paper is 0.4 mg / cm ² . This video count is a value representing the image area and image density, and has a unique relationship with the amount of toner consumed during development. Data representing the relationship between the video count number and the amount of toner consumed during development is stored in a toner consumption map that is a read memory.

  That is, in S2, the video count number obtained from the image data is calculated, and then the toner consumption amount T1 corresponding to the calculated video count number is acquired from the toner consumption amount map which is a reading memory. The toner consumption amount T1 acquired by the calculation means is sent to the determination means inside the arithmetic microprocessor, and a logical determination sequence for toner supply is started.

  In the determination means, it is determined whether or not the toner consumption amount T1 exceeds the threshold value Ts (S3). When the toner consumption amount T1 is acquired, the determination unit acquires the threshold value Ts from the reading memory. Then, the determination unit determines the size between the toner consumption amount T1 and the threshold value Ts. When the determination unit determines “No” (toner consumption T1 is less than the threshold Ts), all the toner consumption stored in the reading and writing memory (integrated memory) is acquired. In this state, the toner consumption is not stored in the integration memory. Therefore, it is determined whether or not the sum of all the toner consumption amounts stored in the integration memory and the toner consumption amount newly sent to the determination means (the sum ΣTn of the toner consumption amounts) exceeds the threshold value Ts. The determination (S3 ′) process is cancelled. When S3 'is canceled, the toner consumption amount T1 is stored in the integration memory. Further, the determination unit instructs the image forming process control unit to resume the image forming process. That is, since the toner density detection operation flag is not raised, the toner replenishment logic determination sequence ends, and toner density detection and toner replenishment are not performed.

  When the image forming process for the second plain paper is completed, the toner consumption amount T2 consumed for forming the image on the second plain paper is calculated by the calculating unit, similar to S2. The toner consumption amount T2 is sent to the determination means, and the toner determination logic determination sequence is started again.

  As in S3, the determination unit determines whether the toner consumption amount T2 exceeds the threshold value Ts. When the determination unit determines “No” (toner consumption amount T2 is less than the threshold Ts), all of the toner consumption amounts (here, T1) stored in the integration memory are acquired. Next, the determination unit determines whether or not the sum ΣT2 of toner consumption (that is, T1 + T2) exceeds the threshold Ts (S3 ′). When the determination unit determines “No” (toner consumption T1 + T2 is less than the threshold Ts), the toner consumption T1 and T2 are stored in the integration memory. Further, the determination unit instructs the image forming process control unit to resume the image forming process. As described above, the determination unit compares the newly-consumed toner consumption amount with the threshold value Ts to determine the magnitude, and further determines the sum ΣTn of the toner consumption amounts calculated so far and the threshold value Ts. The size is determined by comparison.

  Here, even when the image forming process for the (n−1) th plain paper is completed, the determination means performs the comparison between Tn−1 and Ts and the comparison between the toner consumption amounts ΣTn−1 and Ts. In any case, it is assumed that “No” is determined.

  Next, when the image forming process for the nth plain paper is completed, the toner consumption amount Tn consumed for forming the image on the nth plain paper is calculated by the calculation unit, as in S2. The toner consumption amount Tn is sent to the determination means, and the toner determination logic determination sequence is started again.

  As in S3, the determination unit determines whether the toner consumption amount Tn exceeds the threshold value Ts. When the determination means determines “No” (toner consumption Tn is less than the threshold Ts), all of the toner consumption stored in the integration memory (here, T1 + T2 +... + Tn−1) is acquired. To do. Next, the determination unit determines whether or not the toner consumption amount ΣTn (that is, T1 + T2 +... + Tn−1 + Tn) exceeds the threshold Ts (S3 ′). When the determination unit determines Yes in S3 ', a toner concentration detection operation flag is set and toner concentration detection in the developing tank 4 is executed. Note that, when n = 1, the determination unit determines that the toner density in the developing tank 4 is “Yes” (toner consumption T1 exceeds the threshold Ts).

  Here, in the present embodiment, the threshold value Ts is set to 0.3 g. The reason for this will be described below.

In the developing tank 4 of the present embodiment, the amount of toner consumed for the image developed on the photosensitive drum 1 is 0.4 mg / cm ² . Therefore, the amount of toner consumed when a solid image is formed on the entire surface of the most typical A4 paper is calculated to be 0.24 g. That is, the maximum value of the amount of toner consumed in the image formation for one A4 sheet is 0.24 g. Therefore, if the threshold value Ts is set to less than 0.24 g, the solid image forming process on the entire surface of the A4 paper is interrupted. In order to avoid this problem, it is necessary to set the threshold value Ts to 0.24 g or more. In summary, the threshold value Ts needs to be appropriately changed according to the area of the object on which image formation is performed. Therefore, in the case of an image forming apparatus for an object having a smaller area (such as B5 paper), the minimum value of the threshold Ts may be less than 0.24 g.

  Further, as the threshold value Ts used for the comparison of the toner consumption amount is set to a smaller value, the fluctuation of the toner amount in the developing tank 4 in the image forming process can be reduced. This is because the toner density detection operation is performed more frequently as the threshold value Ts is smaller. However, the rotational speeds of the agitating members 13a and 13b are lower during the toner density detection operation than during the image forming process (see the section (Toner density sensor 14)). Therefore, the image forming process is interrupted. That is, when the threshold value Ts is extremely reduced, the interval of the toner density detection operation is extremely shortened. Therefore, when the image forming process for a large number of objects is continuously performed, the image forming process is frequently interrupted. The discharge speed of the object on which an image is formed per unit time is extremely reduced. Therefore, the threshold value Ts needs to be set small enough not to affect the change in toner density and large enough not to affect the discharge speed of the object.

  Although the threshold value Ts is set to 0.3 g in the present embodiment, the most preferable value may be selected as the value of the threshold value Ts based on the configuration and processing of the image forming apparatus. For example, when the total amount of the developer 2 that can be held in the developing tank 4 is twice that of the present embodiment, the threshold value Ts may be set to 6.0 g. This is because the ratio of the toner consumption to the developer 3 is ½ even if the toner consumption is the same. Therefore, the fluctuation of the toner amount in the developing tank 4 in the image forming process is reduced.

  In the image forming apparatus of this embodiment, 0.24 g of toner is 1.2% of the maximum amount of toner contained in the developer 3 that can be held in the developing tank 4. Further, 0.24 g of toner is an amount of toner that can form an image on 20 sheets of A4 paper in a normal image formation with an image ratio of 5%.

(Toner density detection and toner supply)
As described above, when the toner density detection operation flag is set, the toner density detection operation starts. At this time, since the density control process (toner density detection and toner supply) is out of the image forming process, the image forming operation is temporarily suspended.

  The toner density detection method of the present embodiment is as follows. During the image forming process, the stirring members 13a and 13b having screw-like blades are usually rotated at a rotational speed of 250 rpm. During the toner concentration detection operation, the motor 19 reduces the rotation speed of the stirring members 13a and 13b to 120 rpm in accordance with an instruction from the control means (S4). When the rotation speed is 120 rpm, the air contained in the developer 2 when the developer 2 is stirred at a high speed (250 rpm rotation speed) can be efficiently extracted in a short time. Therefore, the developer 2 can be in the same state as when tapped in a stationary state. That is, the bulk density that has been reduced by the air biting is restored to the original state, and the actual toner concentration contained in the developer can be accurately detected. As for how much the toner density can be accurately detected in practice, it is only necessary to refer to the section (the rotational speed of the stirring members 13a and 13b during the toner density detection operation) described later.

  When the toner density detection operation flag is set, the toner density sensor 14 determines the output density Vm corresponding to the toner density of the developer 2 with the toner density difference in a state where the rotation speed of the stirring members 13a and 13b is reduced to 120 rpm. Output to the means (S5). When the toner density difference determining means acquires the output value Vm, the output value (reference value Vref) of the toner density sensor 14 corresponding to the toner density reference value of 8% is acquired from the reading memory. The value of the reference value Vref is a reference value for determining whether or not the output value Vm of the toner density sensor is a value that requires toner replenishment. For example, assume that the reference value Vref is set to 2.7V. Here, when the output value Vm of the toner density sensor is larger than 2.7 V, it means that the toner density at the time of density measurement is less than 8% corresponding to the reference value Vref. On the other hand, when the output value Vm of the toner density sensor is smaller than 2.7 V, the toner density at the time of density measurement is increased by more than 8% corresponding to the reference value Vref, or supplied before that. This means that the toner is still sufficiently remaining.

  As described above, the toner density difference determining unit calculates the difference Vm−Vref between the output value Vm and the reference value Vref, and outputs the difference to the toner supply amount determining unit (S6). When the difference Vm−Vref is a negative value (Vm <Vref), it is determined that the toner density is maintained high enough not to require toner replenishment, and thus the density control process is terminated. The Upon completion of the density control process, the process returns to the image forming process, and the image forming process starts again.

  The toner replenishment amount determination means determines the toner replenishment amount Tm by comparing the calculated difference Vm−Vref with the toner replenishment amount map (S7). The toner replenishment amount map is a read-only memory that stores the relationship between the sensor output value and the toner density shown in FIG. Referring to the toner replenishment amount map, for example, a value of 1 V of the calculated difference Vm−Vref corresponds to a fluctuation of about 2% of the toner density. The toner having a density of about 2% corresponds to 4.6 g of toner. Therefore, when the difference Vm−Vref is 1V, the toner replenishment amount determining means determines that the toner replenishment amount Tm is 4.6 g.

  When the toner supply amount Tm is determined, the toner supply operation starts. Specifically, in accordance with the toner replenishment amount Tm, a motor that rotates the rotating member 7 that is a component of the toner replenishing mechanism 6 is driven (S8). The motor rotates the rotation member 7 by the number of rotations necessary for supplying the developing tank 4 with the toner supply amount Tm. The toner replenishment amount Tm corresponds to the number of rotations of the rotating member 7 having a sponge-like roller on the surface, which constitutes the toner replenishing mechanism 6 when the toner is replenished. The relationship between the toner replenishment amount Tm and the rotation speed of the rotating member 7 is, for example, that the rotating member 7 rotates once for a toner replenishing amount Tm of 200 mg. As a result, the toner consumed in the image forming process is replenished, and the toner density of the developer 2 returns to an appropriate range.

  The image forming process is resumed when the series of operations described above, that is, the logic determination sequence for toner supply, toner density detection, and toner supply operation is completed.

(Rotational speed of the agitating members 13a and 13b during the toner concentration detection operation)
During the toner density detection operation, the following relationship exists between the rotation speed of the stirring members 13a and 13b and the output value of the toner density sensor 14.

  In the toner concentration detection operation, the preferable rotation speed of the stirring members 13a and 13b is such that the amount of the developer 2 that can be held in the developing tank 4, the toner concentration, the fluidity of the developer 2, and the screw shape of the stirring members 13a and 13b. It is necessary to decide in consideration of conditions such as the shape of the blades. Therefore, it is difficult to uniquely determine a preferable speed in the toner density detection operation. However, normally, by rotating the stirring members 13a and 13b at a lower speed than during image formation, the air contained in the developer 2 can be efficiently removed in a short time by the high-speed stirring. Therefore, the developer 2 can be in the same state as when tapped in a stationary state.

  Here, FIGS. 5 and 6 show the difference in the output value of the toner density sensor 14 between when the developer 2 is tapped and when the developer 2 is slowly stirred (rotational speed of 120 rpm). This will be described below with reference. FIG. 5 is a graph showing the output value of the toner density sensor 14 during the image forming process and after the developing tank 4 is tapped. FIG. 6 is a graph showing the output value of the toner density sensor 14 during the image forming process and when the developer is slowly stirred. 5 and 6, the concentration of toner contained in the developer is always 8%. Further, during the image forming process, the rotation speed of the stirring members 13a and 13b is 250 rpm.

  As shown in FIG. 5, during the image forming process (area A), the output value of the toner density sensor 14 is about 2.30V. In the region A, the output value of the toner density sensor 14 changes due to various factors even if the toner density does not change. It is difficult to detect the actual toner concentration in the developer 2 from the output value of the toner concentration sensor 14 in the region A. Then, the developing tank 4 was tapped with the stirring members 13a and 13b stopped (broken line in the graph). As a result, the output value of the toner density sensor 14 gradually increases and shows 2.84 V (area B). The reason why the output value of the toner density sensor 14 changes between the area A and the area B is that the developer 2 is vibrated from the outside (the developing tank 4 is tapped). This is because the air contained in the developer 2 in the region A is released by the tapping of the developing tank 4 and the bulk density is restored to the original state. The output value of the toner density sensor obtained by tapping is hardly affected by the stirring state of the developer 2 or the development history. Furthermore, the output value can be obtained with good reproducibility by tapping. Therefore, measuring the toner density after tapping is very effective for the developer 2 to accurately detect the actual toner density of the developer 2. Note that the output value in the region A is 0.54 V higher than the output value in the region B even though the toner density has not changed. Therefore, it is determined that the toner density is excessive based on the output value of the toner density sensor 14 when rotating at 250 rpm.

  As shown in FIG. 6, during the image forming process (area A), the output value of the toner density sensor 14 is about 2.30V. When the agitating members 13a and 13b are rotated at a rotational speed of 120 rpm (region C), the output value of the toner density sensor 14 gradually increases and stabilizes in the vicinity of 2.90 V if an average is taken. The output value of 2.90 V is almost the same as the output value of the toner density sensor 14 in the region B of FIG. That is, it is close to the value obtained when the stirring is stopped and tapping is performed. The actual toner density of the developer 2 can be detected by rotating the stirring members 13a and 13b at a rotation speed of 120 rpm.

  As described above, the output value of the toner concentration sensor 14 decreases as the rotational speed of the stirring members 13a and 13b increases. This is because the developer swells due to the air bite (the bulk density decreases). On the other hand, when the rotation speed of the agitating members 13a and 13b is slowed, the degree of air biting in the developer is reduced (the bulk density is restored). For this reason, the output value of the toner density sensor 14 gradually increases and finally becomes equal to the output value of the toner density sensor 14 obtained at the time of tapping. That is, the rotational speeds of the stirring members 13a and 13b may be set so that a value equivalent to the output value obtained during tapping can be obtained.

  Further, the output value of the toner density sensor 14 when the rotation speed of the stirring members 13a and 13b is 120 rpm largely oscillates up and down depending on the position of the screw-like blade. This is because the amount of the developer 2 between the blade and the toner density sensor 14 varies depending on the position of the blade. For this reason, if the output value Vm of the toner density sensor 14 corresponding to the toner density is acquired only at a certain timing during the toner density detection operation, the output value Vm varies. In order to obtain a stable output value Vm at all times, a value obtained by averaging the output values during the time required for one rotation of the screw-like blades of the stirring members 13a and 13b should be obtained as the output value Vm. That's fine. As a method of averaging the output values, for example, there is a method of inserting a low-pass filter between the toner density sensor 14 and the I / O interface 23 that converts the acquired output from analog to digital and sends it to the microcomputer 22. . The low-pass filter may be composed of a resistor and a capacitor that remove vibration components. As another method, the vibration component of the output value of the toner density sensor 14 may be removed by calculation processing in the output averaging means inside the microcomputer 22 without using a low-pass filter.

(Other configurations)
The present invention can also be realized by the following configuration.

(First configuration)
In a toner concentration control method for a developer that is used in an image forming apparatus that uses a so-called two-component developer, and that performs toner concentration detection using a magnetic permeability sensor and determination of toner replenishment timing.
When the toner concentration in the developer is detected, the rotation speed of the stirring member that stirs the developer in the stirring chamber in which the magnetic permeability sensor is installed is lower than the rotation speed during the image forming process. A developer toner concentration control device configured to detect an output value from a magnetic sensor.

(Second configuration)
In using the toner concentration control device,
The timing of toner concentration detection and toner replenishment in the developer is
The amount of toner consumed for development is calculated based on the video count number obtained from the pixel information constituting the developed image, and the integrated value of the calculated amount is defined from the total amount of toner in the developer held in the developer tank. And a toner concentration control device according to a first configuration that executes toner density detection and a toner replenishment operation associated therewith only when it is determined that the reference value is exceeded.

(Third configuration)
In using the toner concentration control device,
The value referred to based on the output value from the magnetic permeability sensor is a first or second configuration in which a signal value averaged over a time period equal to or longer than the time required for one rotation of the stirring member is used as a reference value for toner density detection. A toner concentration control device according to the present invention.

  According to the present invention, the toner density of the developer can be maintained in a state suitable for image formation. Therefore, the present invention can be applied to an apparatus that forms an image on an object using a developer. In particular, it can be suitably used in an image forming apparatus using a two-component developer composed of toner and carrier.

1 is a plan view illustrating a configuration of a main part of an image forming apparatus according to the present invention. It is a top view which shows the structure of the developing tank which concerns on this invention. 1 is a cross-sectional view illustrating a main configuration of an image forming apparatus according to the present invention. 6 is a flowchart illustrating an example of processing in the image forming apparatus according to the present invention. 6 is a graph showing an output value of a toner density sensor during an image forming process and after tapping a developing tank. 6 is a graph showing an output value of a toner density sensor during an image forming process and when a developer is stirred at a speed of 120 rpm. It is a graph which shows the relationship between a toner density | concentration and an output value in a normal magnetic permeability sensor. It is a graph which shows the detection method of the toner density in a prior art. 6 is a graph showing a relationship between a rotation speed of a stirring member and an output value of a toner density sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Developer 3 Toner 4 Developer tank 4a-d Developer tank 5 Developer carrier 6 Toner supply mechanism 7 Rotating member 13a, b Stirring member (rotating member)
14 Toner concentration sensor (permeability sensor)
22 Microcomputer

Claims (8)

Based on an output from a magnetic permeability sensor that is incorporated in an image forming apparatus including a rotating member that stirs the developer in the stirring chamber and detects the magnetic permeability of the developer, the concentration of toner contained in the developer is determined. A device for measuring,
Control means for controlling the rotational speed of the rotating member;
The magnetic permeability sensor detects the magnetic permeability of the developer in the stirring chamber when the control means lowers the rotational speed of the rotating member than when the image forming apparatus forms an image. Toner concentration measuring device.   The magnetic permeability sensor detects the magnetic permeability of the developer in the stirring chamber when the rotation speed of the rotating member is 50% or less during image formation in the image forming apparatus. Item 2. The toner concentration measuring apparatus according to Item 1. Calculating means for calculating the amount of toner consumed during the image formation;
Determination means for determining the magnitude of the toner consumption amount and a threshold value having a size equal to or greater than the maximum amount of toner consumed when forming one image;
Further comprising
2. The magnetic permeability sensor detects the magnetic permeability of the developer in the agitation chamber when the determination means determines that the toner consumption amount is greater than or equal to the threshold value. 2. The toner concentration measuring apparatus according to 2.   4. The toner concentration measuring apparatus according to claim 3, wherein the toner consumption amount calculated by the calculating means is an integrated amount of toner consumption amounts consumed when forming the plurality of images.   5. The toner density according to claim 3, wherein the calculating means is a means for calculating a toner consumption amount at the time of development based on pixel data representing a pixel desired to transfer toner in the image. measuring device.   6. The toner concentration measuring apparatus according to claim 3, wherein the threshold value is a value based on an allowable amount determined from a total amount of toner held in the stirring chamber.   The toner density according to claim 1, further comprising output averaging means for averaging the output from the magnetic permeability sensor during one rotation or more of the rotating member. measuring device. In an image forming apparatus including a rotating member that stirs a developer in a stirring chamber, a method for measuring a concentration of toner contained in the developer based on an output from a magnetic permeability sensor that detects a magnetic permeability of the developer. Because
Including the step of controlling the rotational speed of the rotating member;
In the step of controlling the rotation speed of the rotating member, when the rotation speed of the rotating member is lower than that during image formation in the image forming apparatus, the magnetic permeability sensor has the permeability of the developer in the stirring chamber. A method for measuring toner concentration, comprising detecting magnetic susceptibility.

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