JP2016197154A - Mass measuring device, image forming apparatus, and mass measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a QCM sensor that can accurately measure the mass of a toner.SOLUTION: A QCM sensor 120 comprises: a quartz piece 127 that oscillates at a predetermined oscillatory frequency; and a toner adhesion surface 121 and a toner non-adhesion surface 122 that are provided at positions across the quartz piece 127. A toner is adhered to divided areas 133b that have substantially the same mass detection sensitivity of the toner adhesion surface 121. The mass of the adhered toner is calculated from the oscillatory frequency of the quartz piece 127 before the toner is adhered and the oscillatory frequency of the quartz piece 127 after the toner is adhered.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a mass measuring device for measuring the mass of fine particles, an image forming apparatus equipped with the mass measuring device, and a method for measuring the mass of fine particles.

  2. Description of the Related Art Some image forming apparatuses such as copiers and multifunction peripherals are of an electrophotographic system in which a toner image, which is a visible image, is formed on a photoreceptor, and the image is formed by transferring the toner image onto a recording sheet. The image forming apparatus forms a toner image by forming an electrostatic latent image on a photoconductor and developing the electrostatic latent image using a developer contained in a developing device. When the developer is a two-component developer having a toner and a carrier, the toner adheres to the electrostatic latent image due to an electric field generated between the developing device and the photoreceptor. For this reason, the charge amount of the toner (the charge amount per unit mass) is an important factor that determines the quality of the image. For example, when the charge amount Q / M of the toner in the developing device decreases, the image density increases. On the other hand, when the charge amount Q / M of the toner in the developing device increases, the image density decreases.

  As factors that cause the toner charge amount Q / M to fluctuate, changes in environmental conditions such as temperature and humidity in the installation environment of the image forming apparatus and deterioration of the developer due to long-term use are known. In addition, the charge amount Q increases and the charge amount Q / M fluctuates due to the stirring operation in the developing device and the friction when passing through the regulating member in the developing device during development. In order to form an image having a desired density, it is necessary to accurately grasp the charge amount Q / M of the toner immediately before development and to control the image forming condition to a condition suitable for the charge amount.

  In Patent Document 1, toner is adsorbed to a QCM sensor including a piezoelectric crystal resonator (piezo element) and an electrode, and the mass M calculated based on the change in the oscillation frequency of the piezo element and the toner adsorbed to the QCM sensor. The toner charge amount (Q / M) is calculated based on the charge amount Q.

US 5,006,897

  In Patent Document 1, a plate-like electrode (surface to be attracted) of a QCM sensor is disposed so as to face a surface of a cylindrical developing roller carrying toner. Since the developing roller is cylindrical, the distance between the electrode surface and the developing roller is not constant. Therefore, the amount of toner adhering to the electrode surface becomes non-uniform. That is, the amount of toner adhering to the region closest to the surface of the developing roller on the surface of the electrode is larger than the amount of toner adhering to the region farthest from the surface of the developing roller on the surface of the electrode.

  When the measurement object adheres unevenly to the surface of the electrode, there is a possibility that the mass of the measurement object attached to the electrode cannot be measured with high accuracy. This is because a QCM sensor using an AT-cut crystal resonator has different detection sensitivity depending on the position where a measurement object (for example, toner) adheres to an electrode. For example, when there are more measurement objects attached to the center part of the electrode having high detection sensitivity than measurement objects attached to other parts having low detection sensitivity, the QCM sensor detects all measurement objects attached to the electrodes. There is a possibility of detecting a mass larger than the mass. Therefore, when measuring the mass of the measurement object attached to the electrode, the QCM sensor needs to uniformly attach the measurement object to the surface of the electrode.

  Therefore, an object of the present invention is to measure the mass of toner with high accuracy.

  A mass measuring device of the present invention that solves the above problems is a mass measuring device that measures the mass of toner, and includes a plate-like crystal resonator and a first electrode attached to the first surface of the crystal resonator. And a second electrode attached to a second surface opposite to the first surface of the crystal resonator, and a direction in which the first surface and the second surface of the crystal resonator face each other. In order to vibrate the crystal resonator so as to slide, voltage application means for applying an alternating voltage to the crystal resonator via the first electrode and the second electrode, and the first electrode attached to the first electrode A detecting means for detecting a resonance frequency of the crystal resonator that changes in accordance with the mass of the toner, and an AC voltage applied to the crystal resonator in the voltage applying means in a state where the toner is attached to the first electrode. The resonance frequency detected by the detection means A determination unit that determines the mass of the toner attached to the first electrode based on the acquired resonance frequency, and a cover member that is provided to overlap the first electrode and has an opening formed therein. The region of the first electrode exposed from the opening of the cover member has a substantially equal amplitude when the crystal resonator vibrates.

  According to the present invention, the mass of a measurement object (for example, toner) can be measured with high accuracy.

1 is a schematic configuration diagram of an image forming apparatus. (A), (b) is a perspective view of a QCM sensor. FIG. 2 is a schematic configuration diagram of a developing device. FIG. 4 is a diagram illustrating a change in the charge amount of toner in a developing device. (A)-(d) is explanatory drawing of distribution of mass detection sensitivity. (A) is a partially enlarged view of the developing sleeve and the QCM sensor, and (b) is a view of the QCM sensor as viewed from the toner adsorption surface side. (A), (b) is a figure explaining the method of calculating | requiring mass detection sensitivity. (A)-(f) is a figure explaining the method of calculating | requiring mass detection sensitivity. (A), (b) is a figure showing a mode that a toner is made to adhere only to a division area. FIG. The block diagram of a control apparatus. The circuit illustration figure of a Q / M measurement part. 7 is a flowchart illustrating a toner charge amount calculation process. The timing chart at the time of charge amount calculation. The flowchart showing the detailed process of step S1301. The flowchart showing the detailed process of step S1302. The flowchart showing the charge amount and mass measurement process used as a reference | standard. 6 is a flowchart illustrating processing for attaching toner to a toner attracting surface electrode. The figure showing the relationship between an image signal and image density. The flowchart showing the measurement process of reference | standard charge amount. The flowchart showing the process which correct | amends (gamma) LUT. The schematic diagram of the gradation characteristic fluctuation | variation according to charge amount. The structural example figure of a QCM sensor. The circuit illustration figure of a Q / M measurement part.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a schematic configuration diagram of an electrophotographic image forming apparatus. In FIG. 1, symbols (Y, M, C, K) added to the end of the number represent the color of the toner image. Y represents yellow, M represents magenta, C represents cyan, and K represents black. In addition, when it is not necessary to distinguish between colors, the code (Y, M, C, K) at the end of the number is omitted. This image forming apparatus forms a full-color image by transferring the toner images formed on the photosensitive drums 101Y, 101M, 101C, and 101K so as to overlap the intermediate transfer belt 115.

  A charger 102Y, an exposure device 103Y, a developing device 104Y, an optical sensor 607Y, a primary transfer roller 113Y, and a cleaner 106Y are provided around the photosensitive drum 101Y. The photosensitive drum 101Y is a photosensitive member and rotates in the direction of the arrow in the figure. The developing device 104Y includes a toner charge amount measuring unit 108Y that measures the toner charge amount Q / M.

  The surface of the photosensitive drum 101Y is charged to a predetermined potential by the charger 102. The exposure device 103Y irradiates the charged surface of the photosensitive drum 101Y with laser light 100Y modulated based on the image signal of the image to be formed. Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 101Y. The developing device 104Y measures the charge amount Q / M of the toner in the developer to be accommodated, and then attaches the toner to the photosensitive drum 101Y by an electric field generated between the photosensitive drum 101Y and the developing sleeve, thereby electrostatic latent image. Develop. As a result, a yellow toner image is formed on the photosensitive drum 101Y. Details of the measurement process of the toner charge amount Q / M will be described later. The toner density of the toner image is detected by the optical sensor 607Y. The photosensitive drums 101M, 101C, and 101K also have the same configuration in the periphery, and similarly, toner images of each color are formed.

  The intermediate transfer belt 115 is sandwiched between the photosensitive drums 101Y, 101M, 101C, and 101K and the primary transfer rollers 113Y, 113M, 113C, and 113K, and is driven to rotate by the drive roller 105. Further, the intermediate transfer belt 115 is stretched around the secondary transfer roller 114. The toner images formed on the photosensitive drums 101Y, 101M, 101C, and 101K are transferred to the intermediate transfer belt 115 by the primary transfer rollers 113Y, 113M, 113C, and 113K. In this way, a toner image in which the four colors overlap is formed on the intermediate transfer belt 115. The residual toner remaining on the photosensitive drums 101Y, 101M, 101C, and 101K after the toner image transfer is removed by the cleaners 106Y, 106M, 106C, and 106K.

  The recording paper P is stored in a paper feed cassette, picked up one by one by a paper feed roller 116, and conveyed to a contact portion with the intermediate transfer belt 115. The recording paper P is conveyed to the contact portion in accordance with the timing at which the toner image formed on the intermediate transfer belt 115 is conveyed to the contact portion. The toner image formed on the intermediate transfer belt 115 is transferred to the recording paper P by the secondary transfer roller 114 at the contact portion. The recording paper P on which the toner image is transferred is conveyed to the fixing device 107. The fixing device 107 thermally presses the toner image onto the recording paper P. The toner image is fixed on the recording paper P by the fixing device 107. The recording paper P is discharged to the paper discharge tray 117 after the toner image is fixed. With the configuration and operation as described above, the image forming apparatus forms an image on the recording paper P.

  The developing device 104 measures the mass M and the charge amount Q of the toner before development by the built-in toner charge amount measuring unit 108. The measured toner mass M and charge amount Q are used to control the laser beam 100 emitted from the exposure device 103 to adjust the toner density of the toner image formed on the photosensitive drum 101. The toner charge amount measuring unit 108 includes a QCM sensor as a mass measuring device for measuring the mass M of the toner. The toner charge amount measuring unit 108 calculates the toner charge amount Q / M from the toner mass M measured by the QCM sensor and the toner charge amount Q.

(QCM sensor)
The configuration of the QCM sensor will be described with reference to FIG. Since the measurement principle of the QCM sensor 120 is described in detail in, for example, Japanese Patent No. 3725195, only the outline is described here. The QCM sensor 120 uses a characteristic that crystal vibration is excited by a piezoelectric inverse effect caused by application of an alternating voltage to a crystal resonator (crystal piece 127), and is measured by being adsorbed on a probe (electrode) of the QCM sensor 120. Measure the mass of the object. Since the QCM sensor 120 changes the oscillation frequency (resonance frequency) of the crystal resonator according to the mass change of the measurement object attached to the electrode surface, the mass of the measurement object is detected based on the change amount of the oscillation frequency. it can.

  The relationship between the mass change amount ΔM of the measurement object and the oscillation frequency change amount Δf is expressed by the Sauerbrey equation shown in the following equation (1).

f0 is the fundamental oscillation frequency of the crystal unit, ρ is the density of the crystal (2.649 × 10 ³ kg / m ³ ), μ is the shear stress of the crystal (2.947 × 10 ¹⁰ kg ms), and A is the electrode surface area (cm ²⁾ ).

For example, in the case of a crystal resonator with f0 = 10 [MHz], the mass change corresponding to the change of Δf = 1 [MHz] is about 5 [ng / cm ² ]. Measurement that is adsorbed to the probe based on the difference between the oscillation frequency of the crystal unit when the probe is not adsorbing the measurement object and the oscillation frequency of the crystal unit when the probe is adsorbing the measurement object The mass of the object is calculated.

  The QCM sensor 120 of the present embodiment is provided on a plate-shaped crystal piece 127, a first electrode provided on the first surface of the crystal piece 127, and a second surface opposite to the first surface of the crystal piece 127. Second electrode. 2A is a perspective view of the first surface side of the QCM sensor 120, and FIG. 2B is a perspective view of the second surface side of the QCM sensor 120. On the first surface of the QCM sensor 120, a toner adhesion electrode 121 to which toner adheres and an electrode terminal 123 formed integrally with the toner adhesion electrode 121 are provided. The toner adsorption electrode 121 corresponds to the first electrode. The second surface of the QCM sensor 120 is provided with a toner non-adhering electrode 122 to which toner does not adhere and an electrode terminal 124 formed integrally with the toner non-adhering electrode 122. The toner non-adsorbing electrode 122 corresponds to the second electrode. The toner adhesion electrode 121, the toner non-adhesion electrode 122, the electrode terminal 123, and the electrode terminal 124 are formed of a conductor such as gold. The electrode terminal 123 and the electrode terminal 124 electrically connect the toner adhesion electrode 121 and the toner non-adhesion electrode 122. The crystal piece 127 is a crystal resonator formed of an AT-cut crystal thin plate. In the QCM sensor 120, the oscillation frequency of the crystal piece 127 changes in accordance with the mass of toner attached to the toner attachment electrode 121.

  The mass of the substance adhering to the region where no electrode is present at the opposite position across the crystal piece 127 is not measured. This is because, when a voltage is applied between electrodes facing each other with the crystal piece 127 interposed therebetween, thickness-shear vibration occurs. However, if there is no electrode at the opposed position, the crystal piece 127 even if a voltage is applied to the crystal piece 127. This is because 127 does not generate thickness shear vibration. In the QCM sensor 120, a toner non-adhesion electrode 122 is provided at a position facing the toner adhesion electrode 121 with the crystal piece 127 interposed therebetween in order to measure the mass of the toner adhering to the toner adhesion electrode 121. Further, the electrode terminal 123 and the electrode terminal 124 are not provided at positions facing each other with the crystal piece 127 interposed therebetween. Therefore, the QCM sensor 120 does not measure the mass even if the toner adheres to the electrode terminal 123. The surfaces of the electrode terminals 123 and 124 are covered with an insulating material in order to prevent the influence of electrical disturbance components.

(Developer)
FIG. 3 is a schematic configuration diagram of the developing device 104. Since the configurations of the developing devices 104Y, 104M, 104C, and 104K for the respective colors are the same, the individual descriptions are omitted. The developing device 104 contains a developer 110 composed of two components of a toner 161 and a carrier 162, and attaches it to the photosensitive drum 101 to develop the electrostatic latent image. The toner 161 is a charged particle and is charged by friction or the like. The developing device 104 includes a developing sleeve 111, a regulation blade 112, two stirring screws 118, and a toner charge amount measuring unit 108. The toner charge amount measuring unit 108 includes a QCM sensor 120.

  The two agitating screws 118 each rotate in the direction of the arrow in the drawing to convey the developer 110 to the vicinity of the developing sleeve 111. The two stirring screws 118 charge the toner 161 by friction generated by stirring the developer 110. The developing sleeve 111 is a rotatable non-magnetic cylindrical member, and includes a magnet 152 having magnetic force inside the cylinder. The developing sleeve 111 attracts the carrier 162 to the outer peripheral surface by the magnetic force of the magnet 152 and rotates it in the direction of arrow A to convey the developer 110 while attracting the developer 110.

  The regulating blade 112 is a regulating member for regulating the amount of the developer 110 conveyed by the developing sleeve 111. The developer 110 conveyed by the developing sleeve 111 is regulated so that the amount of the developer 110 per unit area on the developing sleeve 111 is constant when passing through the gap between the developing sleeve 111 and the regulating blade 112. The At the same time, the contact friction between the developer 110 and the regulating blade 112 is promoted, and the charge amount of the toner 161 is increased.

  The toner charge amount measuring unit 108 is disposed on the downstream side of the regulating blade 112 and upstream of the position where the toner 161 is supplied to the photosensitive drum 101 with respect to the rotation direction A of the developing sleeve 111. Further, the toner charge amount measuring unit 108 allows the toner adhesion electrode 121 of the QCM sensor 120 not to contact the developer 110 on the developing sleeve 111 and allows the toner 161 to adhere to the toner 161 from the developing sleeve 111. It is arranged with a distance to be opened. The toner charge amount measuring unit 108 is disposed so that the toner adhesion electrode 121 does not come into contact with the developer 110 on the developing sleeve 111, thereby preventing fluctuation of the measurement value during mass measurement.

(Toner charge amount)
FIG. 4 is a diagram illustrating a change in the charge amount Q / M of the toner 161 in the developing device 104. The horizontal axis represents time, and the vertical axis represents the charge amount Q / M. A solid line represents a change in the charge amount Q / M of the developer 110 that has not deteriorated, and a broken line represents a change in the charge amount Q / M of the developer 110 that has deteriorated. As described above, the toner 161 is charged up to the charge amount (Q / M) S while being conveyed by the stirring screw 118. The charging speed gradually decreases. The toner 161 is also charged when passing through the regulating blade 112. The toner 161 is charged to a charge amount (Q / M) b sufficient to move to the photosensitive drum 101 by the regulating blade 112.

  When the toner 161 is deteriorated, the toner 161 is not charged up to the charge amount (Q / M) b. If development is performed with the charge amount Q / M not sufficient, a difference occurs with the toner 161 that has not deteriorated in the toner amount attached to the electrostatic latent image, and the density and color of the image fluctuate. End up. In order to correct this accurately, the toner charge amount measuring unit 108 needs to accurately measure the toner charge amount Q / M. Therefore, as shown in FIG. 3, the toner charge amount measuring unit 108 is arranged at a position where the toner charge amount Q / M can be accurately measured between the regulating blade 112 and the development position.

  Factors that vary the charge amount Q / M of the toner 161 include changes in temperature and humidity in the installation environment of the image forming apparatus, aging of the carrier 162, changes in toner consumption, and toner supply amount. In addition, when left unused for a long time, the charge amount Q / M of the toner 161 in the developing device 104 decreases, so the charge amount Q / M is relatively abrupt immediately after the start-up of the developing device 104. To change. The charge amount Q / M gradually changes when it is caused by environmental fluctuations or aging deterioration, and the charge amount Q / M changes rapidly when it is caused by toner consumption or supply. In the case of a rapid change, for example, the charge amount Q / M may change during image formation for one page.

  When the charge amount Q / M changes, when the toner 161 is supplied from the developing sleeve 111 to the photosensitive drum 101 under the same conditions, a difference occurs in the mass M of the toner 161 even if the charge amount Q is the same. The density and color of the image will vary. For example, when developing with the toner 161 having a small charge amount Q / M, if the charge amount Q within a certain area of the developing sleeve 111 is the same, the mass M of the toner 161 used for development increases and the toner amount increases. . As a result, the image density increases. Conversely, when developing with the toner 161 having a large charge amount Q / M, if the charge amount Q is the same, the mass M of the toner 161 used for development becomes small and the toner amount decreases. For this reason, the image density is lowered.

  In this embodiment, the amount of toner attached to the photosensitive drum 101 is adjusted by changing the correction condition for correcting the document data (image data) based on the charge amount Q / M of the toner 161. Therefore, it is necessary to accurately measure the charge amount Q / M of the toner 161. When the correction condition is changed, the exposure device 103 irradiates the laser beam 100 based on the image data corrected according to the correction condition. By changing the correction condition, the time (pulse width) that the laser beam 100 exposes one pixel is changed. Note that the method of correcting the correction condition based on the charge amount Q / M has an advantage that the time required for feedback control is short. In the image forming apparatus, the pulse width of the laser beam 100 that exposes the photosensitive drum 101 is adjusted so that the amount of toner attached to the photosensitive drum 101 becomes a target amount suitable for the charge amount Q / M of the toner 161. The electrostatic latent image formed by the laser beam 100 having the adjusted pulse width is developed using toner, whereby the density fluctuation of the image due to the fluctuation of the charge amount Q / M of the toner 161 can be suppressed.

(Detection sensitivity of QCM sensor)
The QCM sensor 120 is known to have different mass detection sensitivity depending on the position on the toner adhesion electrode 121. FIG. 5 is a distribution diagram of mass detection sensitivity. A region where the mass of the QCM sensor 120 can be detected is substantially equal to a region where the toner adhesion electrode 121 and the toner non-adhesion electrode 122 are provided to face each other.

  In the QCM sensor 120, the amplitude distribution is a convex shape so that the amplitude distribution is optimized concentrically. Both the toner adhesion electrode 121 and the toner non-adhesion electrode 122 are circular, and the central portion of the toner adhesion electrode 121 has the largest vibration amplitude. Further, the vibration amplitude of the toner adhesion electrode 121 decreases as the distance from the center of the toner adhesion electrode 121 increases. Therefore, the central portion of the toner adhesion electrode 121 has the highest mass detection sensitivity, and the mass detection sensitivity decreases as the distance from the central portion increases.

  The magnitude of the vibration amplitude in the mass detection region of the QCM sensor 120 is indicated by the size of the arrow in FIG. FIG. 5A shows the X-axis direction and the Z′-axis direction of the AT-cut crystal piece 127 (the direction tilted by 35 ° 15 ′ with respect to the Z-axis in the YZ plane). The direction is the X-axis direction. FIGS. 5B and 5C show a mass detection sensitivity distribution 128. In either direction, the mass detection sensitivity at the center of the toner adhesion electrode 121 is the highest, and the mass detection sensitivity becomes lower as the edge of the toner adhesion electrode 121 is closer. FIG. 5D shows the mass detection sensitivity distribution 128 three-dimensionally.

  Thus, in the QCM sensor 120, the mass detection sensitivity has a distribution corresponding to the vibration amplitude. When the toner 161 uniformly adheres to the toner adhesion electrode 121, the mass of the toner 161 adhered from the oscillation frequency can be accurately obtained by (Equation 1).

  However, as shown in FIG. 3, the distance between the developing sleeve 111 in the developing device 104 and the toner adhesion electrode 121 of the QCM sensor 120 is not constant. Therefore, the toner 161 does not uniformly adhere to the toner adhesion electrode 121, and the mass of the toner 161 adsorbed on the toner adhesion electrode 121 cannot be measured with high accuracy. FIG. 6A is a partially enlarged view of the developing sleeve 111 and the QCM sensor 120.

  The developing sleeve 111 causes the toner 161 to adhere to the toner adhesion electrode 121 of the QCM sensor 120 by an electric field. Here, the developing sleeve 111 is cylindrical. In the present embodiment, the QCM sensor 120 is arranged so that the region of the toner adhesion electrode 121 closest to the developing sleeve 111 is substantially equal to the center of the toner adhesion electrode 121. That is, the distance between the developing sleeve 111 and the toner adhesion electrode 121 is closer to the center of the QCM sensor 120 and further to the edge. If the QCM sensor 120 is a convex shape, the center is closer and the edge is farther away. The amount of toner adhering to the toner adhering electrode 121 varies depending on the distance between the developing sleeve 111 and the QCM sensor 120. For example, as shown in FIG. 6A, the amount of toner attached to the central portion of the toner attachment electrode 121 is larger than the amount of toner attached to the edge portion of the toner attachment electrode 121.

  FIG. 6B is a diagram of the QCM sensor 120 as viewed from the developing sleeve 111 side of the toner 161. In FIG. 6B, the distribution of the amount of toner 161 adhering to the toner adhering electrode 121 is shown in light and shade. The greater the amount of adhesion, the darker the color. The mass detection sensitivity of the QCM sensor 120 corresponds to the size of the arrow indicating the vibration amplitude. The mass detection sensitivity increases toward the center of the toner adhesion electrode 121.

  In FIG. 6B, the vibration direction of the QCM sensor 120, that is, the X direction of the axis of the crystal piece 127 is arranged so as to be parallel to the rotation axis direction of the developing sleeve 111. Since the mass detection sensitivity distribution of the QCM sensor 120 is concentric, there is no significant change in the relationship between the toner adhesion amount distribution and the mass detection sensitivity distribution of the QCM sensor 120 regardless of the orientation. In the case of FIG. 6B, a large amount of toner 161 adheres to the central portion of the toner adhesion electrode 121 with high mass detection sensitivity, and a small amount of toner 161 adheres to the peripheral portion of the toner adhesion electrode 121 with low mass detection sensitivity. Therefore, the mass M of the toner 161 calculated from the change in the oscillation frequency obtained by (Equation 1) is larger than the total amount of toner that adheres. That is, in the QCM sensor 120 in which the mass detection sensitivity is not uniform but varies, it is assumed that the amount of toner 161 adhered varies as shown in FIG. 6B and the substance adheres uniformly. (Formula 1) does not hold. As a result, it was found that the mass of the toner 161 adhering to the toner adhering electrode 121 cannot be accurately detected from the change in the oscillation frequency.

(Correction of mass detection sensitivity)
In order to accurately detect the mass of the toner 161 when the amount of adhesion of the toner 161 adhering to the toner adhesion electrode 121 varies, for example, the variation in the mass detection sensitivity distribution in the mass measurement region of the QCM sensor 120 is eliminated. And make it uniform. By making the mass detection sensitivity uniform, accurate mass detection is possible even when the amount of toner 161 adhering varies.

  In other words, the mass detection sensitivity in the mass detection area of the QCM sensor 120 is constant and the mass is measured by adsorbing the measurement object to an area where the sensitivity is known, and the mass detection sensitivity is corrected to accurately measure the measurement object. Can be detected. The toner adhesion electrode 121 is divided into a plurality of concentric areas, and a uniform film is formed for each area. From the ratio of the area of each area in the toner adhesion electrode 121 and the mass of the film formed in each area The mass detection sensitivity can be obtained for each divided area. 7 and 8 are diagrams for explaining a method of determining the mass detection sensitivity of each region by dividing the mass detection region (toner adhesion electrode 121) of the QCM sensor 120 into a plurality of regions. The mass detection sensitivity distribution 128 of the disk-shaped QCM sensor 120 has a convex shape.

  FIG. 7A shows a state in which the toner adhesion electrode 121 is concentrically divided into a plurality of regions. The toner adhesion electrode 121 is divided into a plurality of concentric divided regions 133a to 133f. As shown in FIG. 7B, the divided regions 133a to 133f are substantially equal with less variation in mass detection sensitivity in the region as compared with the entire QCM sensor 120. In FIG. 7B, the mass detection sensitivity values of the divided regions 133a to 133f are represented by “Ka to Kf”. The region where the mass detection sensitivities are substantially equal is a range in which the variation in mass detection sensitivity is within a predetermined range and a result is obtained such that the measured mass falls within the allowable range.

  The mass detection sensitivity Ka of the divided region 133a located at the outermost periphery is a region having the lowest sensitivity, and thus has a value smaller than “1”. The mass detection sensitivity Kf of the divided region 133f located in the center is a region having the highest sensitivity, and thus has a value larger than “1”. Any of the mass detection sensitivities Kb to Ke of the divided areas 133b to 133e located between the divided areas 133a and 133f has a value closest to "1". When the mass is detected using the region where the mass detection sensitivity is closest to “1”, a value close to the actual mass can be obtained without correcting the mass detection sensitivity.

  FIG. 8 is a configuration diagram of the masks 134a to 134f corresponding to the divided regions 133a to 133f. With reference to FIG. 8, how to obtain the mass detection sensitivities Ka to Kf of the divided regions 133 a to 133 f will be described. The mask 134a shown in FIG. 8A has an opening 135a for exposing the divided region 133a. A mask 134b shown in FIG. 8B is a cover member having an opening 135b for exposing the divided region 133b. The mask 134c shown in FIG. 8C has an opening 135c for exposing the divided region 133c. The mask 134d shown in FIG. 8D has an opening 135d for exposing the divided region 133d. A mask 134e shown in FIG. 8E has an opening 135e for exposing the divided region 133e. The mask 134f shown in FIG. 8F has an opening 135f for exposing the divided region 133f. Each mask 134a-134f is formed with an insulating material.

  Each opening part 135a-135e has four connection paths for connecting an outer area and an inner area. For this reason, regions that are not used for measuring the mass detection sensitivity are formed in a substantially cross shape with respect to the concentric divided regions 133a to 133e (FIG. 7A). However, the area that is not used for the measurement of the mass detection sensitivity is a size that does not cause a problem in the measurement of the mass detection sensitivity as compared with the other areas.

  Distribution of mass detection sensitivity is obtained using such masks 134a to 134f. First, a uniform film is formed over the entire area of the toner adhesion electrode 121 under predetermined conditions, and the mass M0 of the film is calculated from the change in oscillation frequency at that time. Next, the toner adhesion electrode 121 is covered with a mask 134a, and a film is formed under the same conditions. As a result, a film corresponding to the opening 135 a is formed on the toner adhesion electrode 121. The film mass Ma corresponding to the opening 135a is calculated from the change in the oscillation frequency at this time. Similarly, the film masses Mb to Mf corresponding to the openings 135b to 135f are respectively calculated.

The mass detection sensitivities Ka to Kf of the divided regions 133a to 133f are calculated by (Equation 2) based on the areas Sa to Sf of the divided regions 133a to 133f and the area S0 of the toner adhesion electrode 121. In (Formula 2), the calculation formula of the mass detection sensitivity Ka is shown as an example.
Kn = Mn / (M0 × (Sn / S0)) (where n = a to f) (Formula 2)

  The denominator of (Expression 2) represents the mass of the substance (film) actually attached to the area Sn of the divided region 133n, and the numerator represents the mass of the substance (film) calculated from the change of the oscillation frequency. For example, in the case of the divided region 133a, this ratio becomes the mass detection sensitivity Ka of the divided region 133a. As shown in FIG. 7B, the mass detection sensitivities Ka to Kf of the divided regions 133a to 133f are approximately the median values of the respective regions of the detection sensitivity distribution 128. Further, the mass detection sensitivity Ka of the divided region 133a is a value smaller than “1”, and the mass detection sensitivity Kf of the divided region 133f is a value larger than “1”. Any of the mass detection sensitivities Kb to Ke of the divided regions 133b to 113e in the meantime becomes a value close to “1”.

  If the QCM sensors 120 have the same shape, the mass detection sensitivity distribution is also the same. Therefore, once the mass detection sensitivities Ka to Kf of the QCM sensor 120 are calculated, the same divided regions 133a to 133f and mass detection sensitivities Ka to Kf can be applied as long as the QCM sensor 120 having the same shape is used. it can.

  As shown in FIG. 7B, among the divided areas 133a to 133f, the smallest divided mass detection sensitivity is the divided area 133f at the center. However, the area of the divided region 133f is the smallest among the divided regions 133a to 133f, and the amount of adhered substances is small. Further, since the divided region 133f has a higher mass detection sensitivity Kf than the other divided regions 133a to 133e, a measurement error becomes large even when there is a slight variation in the adhesion amount of the substance. In order to avoid this, when the mass of the toner 161 is actually detected, it is desirable to use a region having a large area and low mass detection sensitivity in order to increase the amount of attached material. The division region 133e outside the central division region 133f, the division region 133d outside, and the division region outside the central division region 133f can reduce the influence due to the variation in the amount of adhered substances.

  Which divided region is used to minimize the error depends on the distribution shape of the entire mass detection sensitivity, the area of the divided region, and how the amount of adhered substances varies, so the optimal divided region is determined experimentally. It will be. In addition, if the mass detection sensitivity is close to “1”, it is not necessary to correct the mass detection sensitivity. Therefore, this division region may be used.

  In the following, the mass of the toner 161 is divided by the divided region 133b, which has a relatively large area and has a mass detection sensitivity close to “1” as compared to the edge and the center, and is considered to have a relatively small error due to variation in the amount of adhered substances. The case of detecting the will be described.

  FIG. 9 is a diagram illustrating a state in which the toner 161 is attached only to the divided region 133b. FIG. 10 is a schematic configuration diagram of the developing device 104. As shown in FIG. 10, the toner charge amount measuring unit 108 includes a mask 134b (see FIG. 8B) having an opening 135b between the QCM sensor 120 and the developing sleeve 111. As shown in FIG. 9B, the mask 134 b is arranged with a slight gap so as to cover the toner adhesion electrode 121 of the QCM sensor 120. By applying an electric field to the toner adhesion electrode 121 of the QCM sensor 120, the toner 161 adheres only to the divided area 133b of the toner adhesion electrode 121 through the opening 135b of the mask 134b as shown in FIG. Note that the mass detection sensitivity Kb of the divided region 133b is calculated in advance.

  By detecting the change of the oscillation frequency by attaching the toner 161 only to the divided region 133b where the mass detection sensitivity Kb is calculated, the mass of the attached toner 161 can be calculated by (Equation 1). By dividing the calculation result by (Equation 1) by the mass detection sensitivity Kb, the accurate mass M can be calculated. In this way, the mass M of the toner 161 immediately before development can be measured in the image forming apparatus.

(Control device)
After measuring the mass M of the toner 161, the image forming apparatus measures the charge amount Q of the toner 161 and calculates the charge amount Q / M of the toner 161. FIG. 11 is a configuration diagram of a control device that calculates the charge amount Q / M of the toner 161 and controls the image forming process. The control device controls all processes related to image formation performed by the image forming apparatus. Here, the control unit measures the charge amount Q / M of the toner 161 and adjusts the laser light according to the charge amount Q / M (gradation). Only the configuration for performing correction) is shown, and the configuration for other processing is omitted. In order to simplify the description, FIG. 11 shows a configuration in which a toner image is formed on one photosensitive drum 101.

  The control device includes a control unit 1107 and a Q / M measurement unit 1101. The control unit 1107 controls the exposure unit 103 so that an appropriate laser beam is applied to the photosensitive drum 101, and controls the QCM sensor 120 to detect the charge amount of the toner 161 carried on the developing sleeve 111. The Q / M measurement unit 1101 inputs the measurement results of the mass M and the charge amount Q of the toner 161 to the control unit 1107.

  A CPU 606 controls each unit of the image forming apparatus. The ROM 605 is a storage unit that stores preset data such as computer programs. The RAM 604 is a storage unit that stores rewritable data. The control unit 1107 includes a Q / M calculation unit 1106, an LUT (Look Up Table) 601, an LUT correction unit 602, and a laser driver 603.

  The Q / M calculation unit 1106 calculates the charge amount Q / M of the toner 161 according to the mass M and the charge amount Q of the toner 161 measured by the Q / M measurement unit 1101. The LUT 601 stores a table for correcting image data. The CPU 606 corrects the image data based on the table stored in the LUT 601 and transfers the corrected image data (image signal) to the laser driver 603. The laser driver 603 controls the pulse width of the laser light emitted from the exposure device 103 based on the image signal. The LUT correction unit 602 corrects the contents of the LUT 601 according to the charge amount Q / M of the toner 161 calculated by the Q / M calculation unit 1106. By correcting the LUT 601 based on the charge amount Q / M, the gradation characteristics of the image formed by the image forming apparatus are corrected. As a result, the electrostatic latent image formed on the photosensitive drum 101 by the laser light emitted from the exposure device 103 is formed with an exposure time suitable for the charge amount Q / M of the toner 161 attached during development. Concentration fluctuations due to the influence of fluctuations in the quantity Q / M are suppressed.

  The Q / M measurement unit 1101 includes a Q measurement circuit 1102, an M measurement circuit 1103, an electrode power source 1104, and a switch circuit 1105. The Q measurement circuit 1102 measures the charge amount Q of the toner 161 by the toner charge amount measurement unit 108. The M measurement circuit 1103 is a determination unit that measures the mass M of the toner 161 by the toner charge amount measurement unit 108. The electrode power source 1104 supplies a voltage for generating an electric field to the toner adhesion electrode 121 of the toner charge amount measuring unit 108. The switch circuit 1105 controls conduction and non-conduction between the toner charge amount measurement unit 108, the Q measurement circuit 1102, the M measurement circuit 1103, and the electrode power source 1104.

  The Q / M measurement unit 1101 will be described in detail. FIG. 12 is a specific circuit diagram of the Q / M measurement unit 1101.

  The Q measurement circuit 1102 calculates the charge amount Q according to the measurement value obtained by the Q measurement capacitor 1211 for measuring the charge amount Q, the electrometer 1231 for measuring the output potential of the Q measurement capacitor 1211, and the electrometer 1231. The charge amount calculation unit 1232 is provided. The Q measurement capacitor 1211 is also used as a charging element for charging a voltage for adsorbing the toner 161 to the toner adhesion electrode 121 (hereinafter referred to as “toner adhesion voltage”). The charge amount calculation unit 1232 calculates the charge amount Q from the difference (V1−V2) between the potential V1 before the toner 161 adheres to the toner adhesion electrode 121 and the potential V2 after the adhesion, which is measured by the electrometer 1231. To do.

  The M measurement circuit 1103 includes the first and second coupling capacitors 1212 and 1213, the oscillation circuit 1233, the frequency measurement unit 1234 that measures the oscillation frequency of the oscillation circuit 1233, and the mass that calculates the mass of the toner 161 according to the oscillation frequency. A calculation unit 1235 is provided. The first coupling capacitor 1212 is provided between the oscillation circuit 1233 and the switch circuit 1105, and inputs only a high-frequency oscillation signal to the toner adhesion electrode 121. The second coupling capacitor 1213 is provided between the oscillation circuit 1233 and the switch circuit 1105 and inputs only a high-frequency oscillation signal to the toner non-adhesion electrode 122. The oscillation circuit 1233 outputs an oscillation signal for causing the QCM sensor 120 to oscillate. In FIG. 12, the oscillation circuit 1233 includes a logic IC (Integrated Circuit), a resistor, and a capacitor, but may have other configurations. The mass calculation unit 1235 calculates (detects) the frequency measurement unit 1234 from the difference (f1-f2) between the oscillation frequency f1 before the toner 161 adheres to the toner adhesion electrode 121 and the oscillation frequency f2 after the adhesion. The mass M is calculated.

  The electrode power source 1104 includes first and second resistors 1221 and 1222 and a QCM power source 1236. The first resistor 1221 is connected to the toner adhesion electrode 121 via the switch circuit 1105, and the second resistor 1222 is connected to the toner non-adhesion electrode 122 via the switch circuit 1105. The first resistor 1221 and the second resistor 1222 prevent a short circuit between the QCM power supply 1236 and the toner adhesion electrode 121 and the toner non-adhesion electrode 122. The QCM power supply 1236 applies a voltage (hereinafter referred to as “toner peeling voltage”) and a ground voltage for peeling the toner 161 from the toner adhesion electrode 121 to the QCM sensor 120.

  The switch circuit 1105 includes five switches, a first switch SW1 to a fifth switch SW5. The first switch SW1 switches between the on state (conducting state) and the off state (blocking state) of the toner adhesion electrode 121 and the Q measurement circuit 1102. The second switch SW2 switches between the on state and the off state of the toner adhesion electrode 121 and the M measurement circuit 1103. The third switch SW3 switches between the ON state and the OFF state of the toner non-adhesion electrode 122 and the M measurement circuit 1103. The fourth switch SW4 switches between the on state and the off state of the toner adhesion electrode 121 and the electrode power source 1104. The fifth switch SW5 switches between the ON state and the OFF state of the toner non-adhering electrode 122 and the electrode power source 1104. The CPU 606 of the control unit 1107 controls each switch of the switch circuit 1105.

  The developing sleeve power source 1237 supplies the alternating voltage to the developing sleeve 111 because the developing efficiency is improved by reciprocating the toner 161 between the developing sleeve 111 and the photosensitive drum 101.

(Charge amount Q / M calculation)
FIG. 13 is a flowchart showing a calculation process of the charge amount Q / M of the toner 161 using such a control device.

  The Q / M measurement unit 1101 charges the Q measurement capacitor 1211 of the Q measurement circuit 1102 by the electrode power source 1104 (S1301). The Q measurement capacitor 1211 applies a voltage to the toner adhesion electrode 121 in order to generate an electric field for causing the toner 161 to adhere to the toner adhesion electrode 121 of the toner charge amount measurement unit 108. Therefore, the Q measurement capacitor 1211 is charged. In this embodiment, the toner adhesion voltage is not directly applied to the toner adhesion electrode 121 from the electrode power source 1104. This is to prevent the charge of the toner 161 attached to the toner attachment electrode 121 from moving to the electrode power source 1104 and changing the charge amount Q of the toner 161.

  After charging the Q measurement circuit 1102, the Q / M measurement unit 1101 removes the toner 161 attached to the toner attachment electrode 121 (S1302). The Q / M measuring unit 1101 removes the toner 161 by applying a toner stripping voltage for stripping the toner 161 from the electrode power source 1104 to the toner adhesion electrode 121. After the removal of the toner 161, the Q / M measurement unit 1101 measures the reference charge amount and mass before the toner 161 is attached to the toner attachment electrode 121 (S1303). The Q / M measurement unit 1101 measures the amount of charge using the Q measurement circuit 1102 and measures the mass using the M measurement circuit 1103.

  After measuring the reference charge amount Q and mass M, the Q / M measurement unit 1101 causes the toner 161 to adhere to the toner adhesion electrode 121 of the toner charge amount measurement unit 108 (S1304). The Q / M measurement unit 1101 applies a toner adhesion voltage to the toner adhesion electrode 121 by the Q measurement capacitor 1211 of the charged Q measurement circuit 1102. By applying the toner adhesion voltage, an electric field is generated between the QCM sensor 120 and the developing sleeve 111, and the toner 161 adheres to the toner adhesion electrode 121.

  When the toner 161 adheres to the toner adhesion electrode 121, the Q / M measurement unit 1101 measures the amount of charge after the toner 161 is adhered by the Q measurement circuit 1102, and measures the mass by the M measurement circuit 1103 (S1305). The measurement process of the charge amount and mass after the toner 161 is attached is the same as the process in step S1303. The Q / M measuring unit 1101 calculates the charge amount Q and the mass M of the attached toner 161 from the difference between the reference charge amount and mass and the measured charge amount and mass (S1306). The Q / M measurement unit 1101 transmits the calculated charge amount Q and mass M of the toner 161 to the control unit 1107.

  The control unit 1107 receives the charge amount Q and the mass M of the toner 161 from the Q / M measurement unit 1101, and the Q / M calculation unit 1106 causes the charge amount Q / of the toner 161 attached to the toner attachment electrode 121. M is calculated (S1307). The control device determines whether or not to continue to measure the charge amount Q / M. If the measurement is continued, the process returns to step S1301 (S1308: Y), and if the measurement is terminated, the process is performed as it is. End (S1308: N)

  The amount of toner 161 adhering to the toner adhering electrode 121 of the QCM sensor 120 is a very small amount of several micrograms to several tens of micrograms, and the toner 161 adhering to the toner adhering electrode 121 does not affect image formation. Absent. Therefore, it is possible to perform image formation while continuously performing the measurement process of the charge amount Q / M.

  FIG. 14 is a timing chart when calculating the charge amount Q / M. This timing chart shows waveforms of the potential 902 of the developing sleeve 111, the potential 901 of the toner adhesion electrode 121, the potential 903 of the Q measurement capacitor 1211 of the Q measurement circuit 1102, and the states of the first to fifth switches SW1 to SW5. Represent. In the present embodiment, the developing sleeve power source 1237 has, for example, a pulse period in which the voltage value periodically changes between +300 [V] and −1200 [V], and a blank period in which the voltage value is −450 [V]. Are applied to the developing sleeve 111. The voltage applied to the developing sleeve 111 by the developing sleeve power source 1237 is hereinafter referred to as “blank pulse”. The potential 902 of the developing sleeve 111 is determined by the developing bias voltage. The blank period is 1 pulse for the sake of simplicity. The number of pulses being processed is also set to 1 pulse or 2 pulses for the sake of simplicity.

  The process of step S1301 in FIG. 13 is performed between times t1 and t6. FIG. 15 is a flowchart showing detailed processing of step S1301 of FIG. In step S1301, the Q measurement capacitor 1211 is charged.

  The electrode power source 1104 outputs a charging voltage (+150 [V]) (S1311). The switch circuit 1105 turns on the first switch SW1, the fourth switch SW4, and the fifth switch SW5 to connect the electrode power supply 1104 and the Q measurement capacitor 1211 (S1312). As a result, a charging voltage is applied from the electrode power source 1104 to the Q measuring capacitor 1211, and charging of the Q measuring capacitor 1211 is started at time t1. Here, it is assumed that the Q measurement capacitor 1211 has a charge corresponding to, for example, −200 [V]. The toner adhesion electrode 121 is connected to the Q measurement capacitor 1211 through the first switch SW1, and there is almost no electrical resistance therebetween. However, since the toner adhesion electrode 121 and the electrode power source 1104 are connected via the fourth switch SW4 and the first resistor 1221, the electrical resistance becomes the resistance value of the first resistor 1221. Therefore, at time t1, the potential 901 of the toner adhesion electrode 121 becomes the same potential as the −200 [V] potential 903 of the Q measurement capacitor 1211 without electrical resistance. At this time, since the fifth switch SW5 is also on, the toner non-adhesion electrode 122 and the toner adhesion electrode 121 have the same potential.

  When charging of the Q measurement capacitor 1211 is started, the Q / M measurement unit 1101 charges the Q measurement capacitor 1211 with a charge corresponding to +150 [V], which is a toner adhesion voltage, as shown at times t1 to t6. It waits until it is done (S1313). The Q / M measurement unit 1101 waits for a predetermined time or waits until the potential of the Q measurement capacitor 1211 reaches a predetermined value. The charging time is determined by the charge remaining in the Q measurement capacitor 1211 and the time constant of the Q measurement capacitor 1211 and the first resistor 1221. During charging, a charging voltage is also applied to the toner adhesion electrode 121. At times t2 to t3 and t4 to t5, the potential 901 (+150 [V]) of the toner adhesion electrode 121 is 1350 [V] higher than the potential 902 (−1200 [V]) of the developing sleeve 111. The toner 161 adheres to the toner adhesion electrode 121. However, since the toner 161 is removed in step S1302 (see FIG. 13), there is no problem in operation even if the toner 161 adheres. Further, the charge of the toner 161 adhering during charging is discharged through the electrode power source 1104.

  When the charging of the Q measuring capacitor 1211 is completed, the switch circuit 1105 turns off the first switch SW1, the fourth switch SW4, and the fifth switch SW5 and ends the charging of the Q measuring capacitor 1211 (S1314). Since the first switch SW1 is turned off, the Q measurement capacitor 1211 holds the toner adhesion voltage (+150 [V]) so as to be output by the charge charged in the Q measurement capacitor 1211.

  In FIG. 13, when the charging process ends, the process of step S1302 is performed. The process of step S1302 in FIG. 13 is performed between times t6 and t11. FIG. 16 is a flowchart showing detailed processing of step S1302 of FIG. In step S1302, the toner 161 is removed from the toner adhesion electrode 121.

  In order to remove the toner 161 adhering to the toner adhering electrode 121, the electrode power source 1104 outputs a toner peeling voltage (−1050 [V]) (S1321). The switch circuit 1105 turns on the fourth switch SW4 and the fifth switch SW5 (S1322). When the fourth switch SW4 and the fifth switch SW5 are turned on, the toner peeling voltage is applied to the toner adhesion electrode 121 and the toner non-adhesion electrode 122. Since the fifth switch SW5 is turned on and the toner peeling voltage is also applied to the toner non-adhering electrode 122, the QCM sensor 120 (crystal piece 127) is prevented from being broken. If the fourth switch SW4 and the fifth switch SW5 are not turned off in step S1314 in FIG. 15, the process in step S1322 is not necessary. In this case, the toner peeling voltage is applied to the toner adhering electrode 121 and the toner non-adhering electrode 122 as soon as the electrode power source 1104 starts outputting.

  When the application of the toner separation voltage to the toner adhesion electrode 121 and the toner non-adhesion electrode 122 is started, the Q / M measurement unit 1101 stands by until all the toner 161 adhering to the toner adhesion electrode 121 is removed (S1323). In time t6 to t7 blank opening and time t8 to t9 in FIG. 14, the potential 901 of the toner adhesion electrode 121 is −1050 [V], whereas the potential 902 of the developing sleeve 111 is +300 [V] and 1350 [V]. V] High. The toner 161 attached to the toner attachment electrode 121 due to the potential difference between the potential 901 and the potential 902 is removed by returning to the developing sleeve 111. The standby time until all of the toner 161 is removed is determined in advance, and the Q / M measurement unit 1101 determines that all of the toner 161 on the toner adhesion electrode 121 has been removed when the predetermined standby time has elapsed. To do. When the standby time has elapsed, the Q / M measurement unit 1101 turns off the fourth switch SW4 and the fifth switch SW5 by the switch circuit 1105, and ends the toner 161 removal process (S1324). Since the first switch SW1 is always off during the removal of the toner 161, the Q measurement capacitor 1211 of the Q measurement circuit 1102 continues to hold the charged charge.

  In FIG. 13, when the removal of the toner 161 is completed, the reference charge amount and mass are measured in that state. FIG. 17 is a flowchart showing a measurement process of charge amount and mass as a reference. This process is performed between times t11 and t14.

  The electrode power source 1104 applies the same blank pulse as the developing bias voltage to the toner adhesion electrode 121 so that the toner 161 does not adhere to the toner adhesion electrode 121 during the measurement of the reference charge amount and mass. As a result, the toner adhesion electrode 121 and the developing sleeve 111 have the same potential, and the movement of the toner 161 from the developing sleeve 111 to the toner adhesion electrode 121 is prevented. Note that the blank pulse applied by the electrode power source 1104 may cause a potential difference with the developing bias voltage in a range where the toner 161 does not move from the developing sleeve 111 to the toner adhesion electrode 121. In FIG. 14, the potential 901 of the toner adhesion electrode 121 is +320 [V] to −1180 [V], which is 20 [V] higher than the developing bias voltage applied to the developing sleeve 111 by the blank pulse applied from the electrode power source 1104. Therefore, the blank time becomes −430 [V].

  Therefore, the electrode power source 1104 starts outputting a blank pulse at time t11 in FIG. 14 (S1331). After the electrode power source 1104 starts outputting the blank pulse, the switch circuit 1105 turns on the second to fifth switches SW2 to SW5 (S1332). The second switch SW2 and the third switch SW3 are turned on to connect the oscillation circuit 1233 to the toner charge amount measuring unit 108. At the same time, the fourth switch SW4 and the fifth switch SW5 are turned on to charge the electrode power source 1104 with toner. Connected to the quantity measuring unit 108. As a result, as shown at times t12 to t13, the waveform of the blank pulse is accompanied by oscillation. When this blank pulse is applied to the oscillation circuit 1233, the elements in the oscillation circuit 1233 are destroyed. For this purpose, the blank pulse is cut off by the first and second coupling capacitors 1212 and 1213. The first and second coupling capacitors 1212 and 1213 have a property of passing high-frequency signals but not direct current or low-frequency signals. When the oscillation frequency of the oscillation signal output from the oscillation circuit 1233 is 5 [MHz], the cycle is 0.2 [μS]. The change time of the blank pulse is longer than this period, for example, 2 [μS], the oscillation signal of 5 [MHz] is passed through the first and second coupling capacitors 1212 and 1213, and the change time is 2 [μS]. Blank pulse fluctuation shall be cut off. This prevents a high potential blank pulse from being applied to the oscillation circuit 1233.

  After the second to fifth switches SW2 to SW5 are turned on, the electrometer 1231 measures the potential 903 of the Q measurement capacitor 1211 between times t12 and t13, and the charge amount calculation unit 1232 displays the measurement result of the electrometer 1231. Is stored (S1333). In FIG. 14, since the potential 903 of the Q measurement capacitor 1211 is +150 [V], the charge amount calculation unit 1232 stores this as a reference for the charge amount. Between times t12 and t13, since the blank pulse does not change, it is not affected by electromagnetic waves radiated at the time of change. Therefore, the potential 903 of the Q measuring capacitor 1211 is measured at this timing.

  Between times t12 and t13, the frequency measurement unit 1234 measures the oscillation frequency of the oscillation circuit 1233 (S1334). The mass calculation unit 1235 stores the oscillation frequency measured by the frequency measurement unit 1234 as a mass reference. The measurement is performed between times t12 and t13 in order to avoid the influence of a minute potential change that cannot be completely removed by the first and second coupling capacitors 1212 and 1213. Note that the Q measurement circuit 1102 is electrically independent of other circuits because the first switch SW1 is off. Therefore, the process for measuring the reference charge amount (S1333) and the process for measuring the reference mass (S1334) can be performed in parallel.

  When the measurement of the reference charge amount and mass is completed, the second to fifth switches SW2 to SW5 are turned off and the process is terminated (S1335). By measuring the charge amount and mass a plurality of times and using the average as the reference charge amount and mass, the measurement time increases, but the measurement error can be reduced and the measurement accuracy is improved.

  In FIG. 13, when the measurement of the reference charge amount and mass is completed, the toner 161 is attached to the toner attachment electrode 121 of the QCM sensor 120. FIG. 18 is a flowchart showing a process for attaching the toner 161 to the toner attachment electrode 121. This process is performed between times t14 and t20.

  A toner adhesion voltage is applied to the toner adhesion electrode 121 by the Q measurement capacitor 1211 and the toner 161 adheres. At this time, in order to prevent destruction of the toner charge amount measuring unit 108, the electrode power supply 1104 is set to +150 [V, which is the same voltage as the toner adhesion voltage, so that the toner non-adhesion electrode 122 has the same potential as the toner adhesion electrode 121. ] Is applied to the toner non-adhering electrode 122. Therefore, the electrode power source 1104 outputs +150 [V], which is the same voltage as the toner adhesion voltage (S1341).

  When the electrode power source 1104 outputs the same voltage as the toner adhesion voltage, the switch circuit 1105 turns on the first switch SW1 and the fifth switch SW5 (S1342). When the first switch SW1 is turned on, the Q measurement capacitor 1211 and the toner adhesion electrode 121 are connected, and a toner adhesion voltage is applied from the Q measurement capacitor 1211 to the toner adhesion electrode 121. Further, since the fifth switch SW5 is turned on, the electrode power source 1104 applies the same voltage as the toner adhesion voltage to the toner non-adhesion electrode 122. In this state, the Q / M measurement unit 1101 stands by (S1343). The waiting time is determined in advance, for example, and the adhesion amount of the toner 161 is determined according to the waiting time. In this embodiment, it waits from time t14 to t20.

  From time t14 to t15, the potential 901 (+150 [V]) of the toner adhesion electrode 121 is 600 [V] higher than the potential 902 (−450 [V]) of the developing sleeve 111. The toner 161 adheres. The potential 901 of the toner adhesion electrode 121 changes in the negative direction due to the negative charge of the adhered toner 161. In the example of FIG. 14, the potential 901 of the toner adhesion electrode 121 drops to +10 [V] at time t15.

  From time t15 to t16, since the potential 902 (+300 [V]) of the developing sleeve 111 is 200 [V] higher than the potential 901 (+100 [V]) of the toner adhesion electrode 121, the toner 161 is It does not adhere to 121. Therefore, the potential 901 of the toner adhesion electrode 121 remains +100 [V].

  From time t16 to time t17, the potential 901 (+100 [V]) of the toner adhesion electrode 121 is 1300 [V] higher than the potential 902 (−1200 [V]) of the developing sleeve 111. The toner 161 adheres. Due to the negative charge of the adhered toner 161, the potential 901 of the toner adhesion electrode 121 decreases to −50 [V] at time t17.

  Since the potential 902 (+300 [V]) of the developing sleeve 111 is 350 [V] higher than the potential 901 (−50 [V]) of the toner adhesion electrode 121 from time t17 to t18, the toner 161 is It does not adhere to the toner adhesion electrode 121. Therefore, the potential 901 of the toner adhesion electrode 121 remains at −50 [V].

  From time t18 to t19, the potential 901 (−50 [V]) of the toner adhesion electrode 121 is 1150 [V] higher than the potential 902 (−1200 [V]) of the developing sleeve 111. Toner 161 adheres to the surface. Due to the negative charge of the adhered toner 161, the potential 901 of the toner adhesion electrode 121 drops to −200 [V] at time t19.

  From time t19 to t20, since the potential 901 (−200 [V]) of the toner adhesion electrode 121 is 250 [V] higher than the potential 902 (−450 [V]) of the developing sleeve 111, the toner adhesion electrode 121. A small amount of toner 161 adheres to the surface.

  The potential 901 of the Q measurement capacitor 1211 changes due to the charge of the toner 161 adhering to the toner adhesion electrode 121 during the standby time. From this change amount, the Q measurement circuit 1102 can measure the charge amount Q of the toner 161.

  When the standby time ends, the switch circuit 1105 turns off the first switch SW1 and the fifth switch SW5. Thereby, the adhesion processing of the toner 161 to the toner adhesion electrode 121 is completed. When the first switch SW1 is turned off, the potential of the Q measurement capacitor 1211 is held without being influenced by others.

  In FIG. 13, after the toner 161 is attached to the toner attachment electrode 121, the amount of charge and the mass after the toner 161 are measured. This process is performed between times t20 and t23, but since it is a blank pulse, actual measurement is performed between times t21 and t22. The charge amount and mass measurement process after the toner 161 is attached is the same as the process of FIG. The potential of the Q measurement capacitor 1211 measured in a state where the toner 161 is adhered to the toner adhesion electrode 121 is “V2”, and the oscillation frequency is “f2”.

The charge amount Q of the attached toner 161 is calculated from the potential V1 stored in the charge amount calculation unit 1232 as a reference charge amount and the potential V2 measured in a state where the toner 161 is attached to the toner attachment electrode 121. . The charge amount calculation unit 1232 calculates the charge amount Q of the attached toner 161 by (Equation 3), assuming that the capacitance of the Q measurement capacitor 1211 is “C”.
Q = C × (V1-V2) (Formula 3)

The mass M of the adhered toner 161 is calculated from the oscillation frequency f1 stored in the mass calculation unit 1235 as a reference mass and the oscillation frequency f2 measured in a state where the toner 161 is adhered to the toner adhesion electrode 121. The mass calculation unit 1235 calculates the mass M of the attached toner 161 using (Equation 4) using (Equation 1) and the mass detection sensitivity Kb of the divided region 133b to which the toner 161 is attached in the present embodiment.
M = − (f2−f1) × [A√ (μ × p)] / (2 × f0 ^ 2) / Kb (Formula 4)

The calculated charge amount Q and mass M of the toner 161 adhering to the toner adhesion electrode 121 are sent from the Q / M measurement unit 1101 to the control unit 1107. The control unit 1107 uses the Q / M calculation unit 1106 to calculate the charge amount Q / M of the toner 161 attached to the toner attachment electrode 121. This process is started immediately after the calculation of the charge amount Q and the mass M after time t22. The Q / M calculation unit 1106 calculates the charge amount Q / M by (Equation 5) using the received charge amount Q and mass M.
Q / M = (measured Q) / (measured M) (Formula 5)

  Through the above processing, the mass M and the charge amount Q of the toner 161 attached to the QCM sensor 120 can be accurately measured, and the charge amount Q / M of the toner 161 is accurately measured. The time required for one measurement of the charge amount Q / M shown in FIG. 14 is t23 = 3.5 [ms], which is sufficiently faster than the image formation time required for one sheet. Therefore, it is possible to measure the charge amount Q / M a plurality of times while performing the image forming process.

(Gradation correction)
The calculated charge amount Q / M can be used for gradation correction, for example. The image forming apparatus has unique gradation characteristics. FIG. 19 is a diagram illustrating the relationship between the image signal and the image density, and represents the gradation characteristics. The image signal is generated by the image data processed by the control unit 1107 such as gradation correction. In general, it is desirable that the gradation characteristic of an image forming apparatus has a linear density or brightness of a formed image with respect to input image data (target density). The image forming apparatus performs gradation correction using the LUT 601 in order to obtain predetermined gradation characteristics. The LUT 601 stores data obtained by inversely converting “actual gradation characteristics” indicated by broken lines. The LUT 601 is written, updated, deleted, and the like by the LUT correction unit 602. A one-dot broken line represents a gradation correction table obtained by inversely converting “actual gradation characteristics”, and is stored in the LUT 601. This gradation correction table is hereinafter referred to as “γLUT”. The target density is obtained by correcting the “actual gradation characteristics” using the gradation correction table.

  The γLUT detects the density of a toner image of a predetermined multi-tone test image formed on the photosensitive drum 101 by the optical sensor 607 (see FIG. 1), and the image data of the test image and the density of the detected toner image. Are created based on the gradation characteristics obtained from the above. The γLUT needs to form a multi-tone test image and is difficult to create in a short time. However, the γLUT may be shifted during image formation due to a change in the installation environment of the image forming apparatus or a material change, and a desired image density may not be obtained. For this reason, it is necessary to correct this with reference to the γLUT created based on the test image in a short time such as during image formation.

  In normal image forming processing, the control unit 1107 performs gradation correction by performing γ conversion using γLUT on the input image data. The correction of γLUT is performed as necessary. Halftone processing and PWM processing are performed on the corrected image data. The PWM processing is performed by comparing an image signal obtained by performing tone correction and halftone processing on image data with a triangular wave signal having a predetermined period. The image signal is pulse-width modulated by PWM processing and output from the control unit 1107 as a laser drive signal. The laser drive signal is sent to the exposure device 103. The exposure device 103 irradiates the photosensitive drum 101 with laser light in accordance with a laser drive signal to form an electrostatic latent image.

  The reference γLUT created according to the density of the toner image of a predetermined multi-tone test image is stored in a storage medium such as a nonvolatile memory. The γLUT may be stored in advance in a memory (for example, the RAM 604 provided in the control unit 1107). The γLUT is created when, for example, there is a possibility that the gradation is remarkably changed immediately after starting the image forming apparatus or after a certain number of image forming processes.

  The image forming apparatus measures the reference charge amount Q / Mref simultaneously with the creation of the γLUT. FIG. 20 is a flowchart showing the measurement process of the reference charge amount Q / Mref. The measurement of the reference charge amount Q / Mref is performed, for example, when the image forming apparatus is activated.

  When the image forming apparatus is activated, the two stirring screws 118 of the developing device 104 start to rotate before development and charge the toner 161 (S701). Next, the image forming apparatus forms a test image (S702), and the developing device 104 starts development processing (S703). When the developing device 104 starts development processing, the toner charge amount measuring unit 108 starts detecting the charge amount Q and the mass M of the toner 161.

  The Q / M measuring unit 1101 measures the charge amount Q and the mass M of the toner 161 from the detection result of the toner charge amount measuring unit 108 with time (S704). The control unit 1107 calculates the charge amount Q / M of the toner 161 according to the measurement result of the Q / M measurement unit 1101 (S705). The control unit 1107 holds the calculated charge amount Q / M in the RAM 604 (S706).

  When the development process is continued (S707: N), the Q / M measurement unit 1101 and the control unit 1107 repeat measurement of the charge amount Q, mass M, and time of the toner 161. When the development process ends (S707: Y), the control unit 1107 determines the highest charge amount among the charge amount Q / M at each time held in the RAM 604 as the reference charge amount Q / Mref (S708), and the RAM 604. Hold on. In this way, the reference charge amount Q / Mref is determined during the creation of the γLUT. The reference charge amount Q / Mref may be determined from the transition of the toner charge amount Q / M at each time, or may be measured in advance.

  After the γLUT is created, γ conversion using the γLUT is performed on the image data, so that the image to be formed has a desired density. However, if a deviation occurs in the γLUT during the image forming process, the image cannot be formed with a desired density. Therefore, the image forming apparatus (control unit 1107) corrects the γLUT according to the toner charge amount Q / M acquired during image formation. FIG. 21 is a flowchart showing processing for correcting the γLUT during image formation.

When the image forming process is started, image data is input to the control unit 1107 (S711). The developing device 104 starts development processing (S712). When the developing device 104 starts development processing, the toner charge amount measuring unit 108 starts detecting the charge amount Q and the mass M of the toner 161. The Q / M measuring unit 1101 measures the charge amount Q and the mass M of the toner 161 from the detection result of the toner charge amount measuring unit 108 with time (S713). The control unit 1107 calculates the charge amount Q / M of the toner 161 according to the measurement result of the Q / M measurement unit 1101 (S714). The control unit 1107 determines whether the difference (ΔQ / M) between the calculated charge amount Q / M and the reference charge amount Q / Mref held in the RAM 604 is greater than or equal to the threshold value α (S715). The threshold α differs depending on the reference charge amount Q / Mref that changes depending on the type of the toner 161, the ratio of the toner 161 and the carrier 162, and the like. For example, when the reference charge amount Q / Mref is −60 [μC / g], the threshold value α is set to 3 [μC / g]. The difference (ΔQ / M) is expressed by (Expression 6).
ΔQ / M = | Q / Mref−Q / M | (Formula 6)

  When ΔQ / M is less than the threshold value α (S715: N), the control unit 1107 determines whether or not the currently set γLUT is the reference γLUT (S719). When the currently set γLUT is the reference γLUT (S719: Y), the Q / M measurement unit 1101 and the control unit 1107 repeat the measurement of the toner charge amount Q, mass M, and time. When the currently set γLUT is not the reference γLUT (S719: N), the control unit 1107 changes the setting of the currently set γLUT to the reference γLUT (S720). After the setting change, the Q / M measurement unit 1101 and the control unit 1107 repeat measurement of the toner charge amount Q, mass M, and time.

When ΔQ / M is equal to or larger than the threshold α (S715: Y), the control unit 1107 corrects the γLUT according to ΔQ / M (S716). The control unit 1107 updates the LUT 601 with the corrected γLUT. FIG. 22 is a schematic diagram of gradation characteristic variation according to the toner charge amount Q / M. The gradation characteristic representing the density of the image with respect to the image signal varies according to the change in the toner charge amount Q / M. Therefore, the γLUT is corrected according to ΔQ / M. For example, the LUT correction unit 602 calculates the toner charge amount correction coefficient k, and multiplies the γLUT by the toner charge amount correction coefficient k to correct the γLUT. The toner charge amount correction coefficient is expressed by (Expression 7).
k = (Q / M) / (Q / Mref) (Formula 7)

  When the development processing is continued after the update of the LUT 601 (S718: N), the Q / M measurement unit 1101 and the control unit 1107 repeat the measurement of the toner charge amount Q, mass M, and time. When the development process is to be ended (S718: Y), the control unit 1107 changes the reference γLUT and ends the process (S721).

  As described above, in this embodiment, the charge amount Q / M of the toner 161 immediately before being used for the development processing is measured in the developing device 104. In order to measure the mass of the toner 161, the QCM sensor 120 is divided into a plurality of areas for each area where the mass detection sensitivity is substantially equal. A mask 134 is disposed on the side of the QCM sensor 120 facing the developing sleeve 111 so that the toner 161 adheres to only one of the divided areas. Since the toner 161 adheres only to a region where the mass detection sensitivity is substantially equal, the mass M of the toner 161 calculated from the change in the oscillation frequency and the mass detection sensitivity can be accurately measured. Therefore, even when the QCM sensor 120 having a flat surface on which the toner 161 adheres is disposed at a position facing the cylindrical developing sleeve 111, the mass of the toner 161 can be detected with high accuracy, and the charge amount Q / M can be accurately measured.

  Further, by measuring the charge amount Q / M of the toner 161 even during the image formation process, it is possible to appropriately set the image formation condition considering the variation of the charge amount Q / M. Therefore, the color stability is greatly improved, and it becomes possible to stably form a high-quality image.

[Second Embodiment]
FIG. 23 is a structural example diagram of the QCM sensor 120 of the second embodiment. Since the configuration and operation of the image forming apparatus and the operation for measuring the toner charge amount are the same as those in the first embodiment, description thereof will be omitted.

  The QCM sensor 120 of FIG. 23 has the same basic configuration as the disk-shaped QCM sensor of the first embodiment, and the mass detection sensitivity is the same distribution as that of the first embodiment. Therefore, regions having substantially the same mass detection sensitivity exist concentrically. Similarly to the first embodiment, for example, the toner 161 is attached only to the region 133b of the mass detection sensitivity Kb, and the mass M of the toner 161 is calculated from the change of the oscillation frequency (resonance frequency) and the mass detection sensitivity Kb.

  23 has a configuration in which an insulating layer 131, a toner adhesion electrode 129, and an electrode terminal 130 are added to the configuration of the QCM sensor 120 of the first embodiment. The insulating layer 131 is an insulator such as SiO 2 and is formed so as to cover the entire area of the toner adhesion electrode 121. The toner adhesion electrode 129 is formed of a conductor such as gold on the insulating layer 131 so as to overlap the region 133b. The electrode terminal 130 is formed integrally with the toner adhesion electrode 129. The QCM sensor 120 having such a configuration is arranged with the toner adhesion electrode 129 facing the developing sleeve 111 side. Since the toner adhesion electrode 129 is formed so as to overlap the region 133b, the mask 134b (see FIG. 10) of the first embodiment is not necessary. In the second embodiment, the mass and charge amount of the toner 161 attached to the toner attachment electrode 129 are measured. Since the toner 161 does not directly adhere to the toner adhesion electrode 121 by the insulating layer 131, the toner 161 adheres only to a portion corresponding to the region 133b. Since the toner adhesion electrode 129 can be formed by a process similar to the semiconductor manufacturing process, the mass and charge amount of the toner 161 can be measured more accurately than when the mask 134 is used.

  FIG. 24 is a circuit diagram of the Q / M measurement unit 1101. The Q / M measurement unit 1101 connects the Q measurement circuit 1102 and the electrode power source 1104 to the toner adhesion electrode 129 via the switch circuit 1105. Further, a sixth switch SW6 is provided between the toner adhesion electrode 121 and the toner non-adhesion electrode 122. When the sixth switch SW6 is turned on, the toner adhesion electrode 121 and the toner non-adhesion electrode 122 are short-circuited to have the same potential and have the same function.

  With such a configuration, the electrical control of the toner adhesion electrode 121 is performed in accordance with the developing bias voltage applied to the developing sleeve 111. The switch circuit 1105 operates so that the toner adhesion electrode 121 is connected to the M measurement circuit 1103 only when the mass M of the toner 161 is measured. That is, the sixth switch SW6 is turned off only when the mass M of the toner 161 is measured, and is turned on at other times. Since the mass M of the toner 161 is calculated by a change in the oscillation frequency of the QCM sensor 120, the second and third switches SW2 and SW3 are turned on, and the sixth switch SW6 is turned off.

  A voltage is applied to the toner adhesion electrode 129 when the toner 161 is adhered in the same manner as the toner adhesion electrode 121 of the first embodiment. The M measurement circuit 1103 measures the mass M of the toner 161 attached to the toner attachment electrode 129. The Q measurement circuit 1102 measures the charge amount Q of the toner 161 attached to the toner attachment electrode 129. That is, the charging voltage, the toner peeling voltage, and the toner adhesion voltage are applied to the toner adhesion electrode 129 at the same timing as the toner adhesion electrode 121 of the first embodiment (see FIGS. 13 and 14). Accordingly, the ON state and OFF state of the first, fourth, and fifth switches SW1, SW4, and SW5 are controlled at the same timing as in the first embodiment.

  In the second embodiment as described above, in order to measure the mass of the toner 161, the QCM sensor 120 is divided into a plurality for each region where the mass detection sensitivity is substantially equal. Since the toner adhesion electrode 129 is formed so as to overlap the region 133b, the charge amount Q / M of the toner 161 can be accurately measured without using the mask 134b of the first embodiment. Since the toner 161 adheres only to a region where the mass detection sensitivity is substantially equal, the mass M of the toner 161 calculated from the change in the oscillation frequency and the mass detection sensitivity can be accurately measured. Therefore, even when the QCM sensor 120 having a flat surface on which the toner 161 adheres is disposed at a position facing the cylindrical developing sleeve 111, the mass of the toner 161 can be detected with high accuracy, and the charge amount Q / M can be accurately measured. When the mask 134 is used, cleaning is required when the toner 161 enters the gap between the mask 134 and the QCM sensor 120, but this is not necessary in the second embodiment. In addition, it is not necessary to strictly adjust the gap between the mask 134 and the QCM sensor 120.

  DESCRIPTION OF SYMBOLS 101 ... Photosensitive drum, 102 ... Charging device, 103 ... Exposure device, 104 ... Developer, 108 ... Toner charge amount measuring unit, 110 ... Developer, 111 ... Developing sleeve, 112 ... Regulator blade, 118 ... Agitating screw, 120 ... QCM sensor, 121, 129... Toner attached electrode, 122 .. toner non-attached electrode, 123, 124, 130... Electrode terminal, 127... Crystal piece, 131 .. insulating layer, 161.

Claims (13)

A mass measuring device for measuring the mass of toner,
A plate-shaped crystal unit,
A first electrode attached to the first surface of the crystal unit;
A second electrode attached to a second surface opposite to the first surface of the crystal unit;
In order to vibrate the crystal resonator so that each of the first surface and the second surface of the crystal resonator slides in the opposite direction, the crystal is interposed via the first electrode and the second electrode. Voltage applying means for applying an alternating voltage to the vibrator;
Detecting means for detecting a resonance frequency of the crystal resonator that changes in accordance with a mass of the toner attached to the first electrode;
In a state where the toner is attached to the first electrode, the voltage application unit applies an AC voltage to the crystal resonator, acquires a resonance frequency detected by the detection unit, and sets the acquired resonance frequency to the acquired resonance frequency. A determination unit for determining a mass of the toner attached to the first electrode based on
A cover member provided to overlap the first electrode and having an opening formed thereon,
The region of the first electrode exposed from the opening of the cover member has substantially the same amplitude when the crystal resonator vibrates,
Mass measuring device. The determination unit causes the voltage application unit to apply an AC voltage to the crystal resonator and acquires the first resonance frequency detected by the detection unit before the toner adheres to the first electrode. In the state where the toner adheres to the first electrode, the voltage applying unit applies an AC voltage to the crystal resonator, and acquires the second resonance frequency detected by the detecting unit, The mass of the toner attached to the first electrode is determined based on a resonance frequency and the second resonance frequency,
The mass measuring device according to claim 1. A capacitor connected to the first electrode;
The capacitor is connected to the first electrode when the toner is attached to the first electrode.
The mass measuring device according to claim 1 or 2. An opening corresponding to the region of the first electrode is provided, and a mask is provided so as to cover the first electrode.
The mass measuring device according to claim 1. An adhesion electrode having a shape corresponding to the region is provided at a position corresponding to the region with an insulator sandwiched between the first electrode,
In the crystal resonator, the resonance frequency is changed by attaching the toner to the attached electrode instead of the first electrode.
The mass measuring device according to claim 1. The first electrode is circular and has the highest mass detection sensitivity in the central portion, and the mass detection sensitivity decreases toward the edge,
The region is one of the first electrodes divided into a plurality of concentric divided regions having substantially the same mass detection sensitivity,
The mass measuring apparatus of any one of Claims 1-5. The region is a divided region having a mass detection sensitivity closest to “1” among the plurality of divided regions,
The mass measuring device according to claim 6. The mass detection sensitivity includes the mass of the toner uniformly attached to the first electrode, the mass of the toner uniformly attached to the region of the first electrode, the area of the first electrode, and It is calculated based on the area of the region of the first electrode,
The mass measuring device according to claim 6 or 7. A photoreceptor,
An exposure device that exposes the photoreceptor to form an electrostatic latent image on the photoreceptor;
A developing device comprising the mass measuring device according to claim 1, and developing the electrostatic latent image by attaching the toner to the electrostatic latent image formed on the photoconductor.
Measuring means for measuring a mass of the toner adhering to the first electrode of the mass measuring device from a change in a resonance frequency of the crystal resonator before and after the toner adhering. Characterized by the
Image forming apparatus. The measuring means includes a charging element that applies an adhesion voltage for adhering the toner to the first electrode, and the amount of charge of the toner adhering to the first electrode is attached to the toner. Measured from the change in output potential of the charging element before and after adhering,
The image forming apparatus according to claim 9. Control means for calculating the charge amount of the toner adhering to the first electrode from the mass and charge amount of the toner measured by the measurement means,
The image forming apparatus according to claim 10. The control means adjusts light emitted from the exposure device for exposing the photoconductor according to the calculated charge amount,
The image forming apparatus according to claim 11. A plate-shaped crystal unit,
A first electrode attached to the first surface of the crystal unit;
A second electrode attached to a second surface opposite to the first surface of the crystal unit;
In order to vibrate the crystal resonator so that each of the first surface and the second surface of the crystal resonator slides in the opposite direction, the crystal is interposed via the first electrode and the second electrode. Voltage applying means for applying an alternating voltage to the vibrator;
Detecting means for detecting a resonance frequency of the crystal resonator that changes in accordance with the mass of the toner attached to the first electrode, and the mass of the toner attached to the first electrode by the mass measuring device. A method of measuring,
Measuring the first oscillation frequency of the crystal unit before the toner adheres;
Measuring a second oscillation frequency of the crystal unit when the toner adheres to a region where the mass detection sensitivity of the first electrode is substantially equal;
Calculating the mass of the toner adhering from the first oscillation frequency and the second oscillation frequency;
Mass measurement method.