JP5039589B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer, and more particularly, a toner along an electrostatic latent image formed in advance on the surface of an image carrier by supplying toner toward the image carrier. The present invention relates to an image forming apparatus including a developing device that forms an image.

  For example, an image forming apparatus disclosed in Patent Document 1 is known. In this image forming apparatus, toner is supplied to an image carrier provided in the image forming apparatus to form a toner image along the electrostatic latent image formed in advance on the surface of the image carrier. I have a device.

  Such a developing device includes a developing unit having a toner carrier having a peripheral surface opposed to the surface of the image carrier, and a toner container for supplying toner to the developing unit. The development unit is provided with a sensor for detecting the amount of toner in the development unit. As a sensor for detecting the amount of toner, an optical sensor or a magnetic sensor is usually used, and these sensors can detect the amount of toner remaining in the developing unit by directly measuring the light or magnetic field in the developing unit. .

As described above, the amount of toner in the developing unit is monitored by the sensor, and when the amount of toner in the developing unit is consumed and reduced for forming a toner image on the surface of the image carrier, the amount of toner is reduced by the sensor. Detect that. Then, toner is replenished from the toner container toward the developing unit based on the detection result by the sensor. By repeating such toner replenishment, the developing unit can perform development processing on the image carrier until the toner container is empty.
Japanese Patent Laid-Open No. 1-142765

  However, providing a sensor such as an optical sensor or a magnetic sensor for detecting the toner amount in the developing unit causes an increase in the size of the developing unit, and it is difficult to realize space saving of the developing device. This is a very serious obstacle to downsizing the image forming apparatus.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of downsizing a developing device and detecting the amount of toner in the developing device.

  In order to achieve the above object, an image forming apparatus according to one aspect of the present invention forms a developing roller carrying toner on a surface, a voltage applying unit that applies a developing bias voltage to the developing roller, and an electrostatic latent image. And the voltage application unit applies a developing bias voltage to the developing roller, whereby the electrostatic latent image formed on the image bearing member is carried by the developing roller. An image forming apparatus comprising a developing device for supplying toner to form a toner image, a density sensor for detecting a density of a toner image on the image carrier, and the image carrier detected by the density sensor A developing unit that detects the amount of toner in the developing device based on the density of the toner image on the upper side, and the developing bias voltage applied to the developing roller by the voltage applying unit is a direct current bias voltage. A bias voltage with a predetermined duty superimposed on the bias voltage, and when the detection unit detects the amount of toner in the developing device, the voltage application unit applies a development bias voltage to the development roller. And the developing device forms an electrostatic latent image including a solid pattern and a blank paper pattern on the image carrier, and the detection unit Detects whether the density between the toner images corresponding to each of the solid pattern and the blank paper pattern on the image carrier is reversed before and after the duty of the developing bias voltage or the DC bias voltage is decreased. Then, it is detected that the toner amount in the developing device is less than a predetermined toner amount based on the detection result that the density is reversed.

  In the image forming apparatus described above, when detecting the toner amount in the developing device, the static bias including the blank paper pattern and the solid pattern with the duty of the developing bias voltage applied to the developing roller or the DC bias voltage lowered. An electrostatic latent image is formed, and each image density is detected. Then, before and after the development bias voltage duty or DC bias voltage is lowered, it is detected whether or not the density between the toner images corresponding to each of the solid pattern and the blank paper pattern is reversed, and the development is performed when the density is reversed. It is assumed that the toner amount in the apparatus is less than a predetermined toner amount. For this reason, in the past, the toner remaining amount was directly measured by using an optical sensor, a magnetic sensor or the like in the developing device. However, in the image forming apparatus described above, the optical sensor or the like is no longer necessary. Space saving. Therefore, it is possible to reduce the size of the image forming apparatus including such a developing device.

  The toner image is further transferred from the image carrier, and further includes an intermediate transfer member that transfers the transferred toner image onto a recording medium. The density sensor is disposed on the intermediate transfer member from the image carrier. It is preferable to detect the density of the transferred toner image.

  In this case, since the density of the toner image can be detected by using a density sensor arranged near an intermediate transfer member such as a transfer belt for calibration of the color difference of the toner image, the grounding of a new density sensor is possible. Is not required, and the cost of the image forming apparatus is not increased.

  Preferably, the developing device determines that the toner amount in the developing device is empty based on a detection result that the toner amount in the developing device is less than the predetermined toner amount.

  In this case, even when the developing device determines that the toner amount is empty, a predetermined amount of toner remains in the developing device, and there is no occurrence of an image defect such as no density or fading. . In addition, the remaining toner in the developing device can be discharged, or new toner can be replenished to reset the developing device to its initial state. Quality is maintained.

  According to the present invention, it is possible to provide an image forming apparatus capable of downsizing the developing device and detecting the amount of toner in the developing device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected about the same element and description may be abbreviate | omitted.

(Embodiment 1)
FIG. 1 is a perspective view of an external appearance of an image forming apparatus according to Embodiment 1 of the present invention. FIG. 1 (A) shows a state where a maintenance lid is closed, and FIG. 1 (B) shows a maintenance lid. FIG. 1C shows a state where the maintenance lid is opened and the toner container is removed. In FIG. 1, the XX direction is referred to as the left-right direction, and the YY direction is referred to as the front-rear direction. In particular, the -X direction is referred to as the left, the + X direction is referred to as the right, the -Y direction is referred to as the front, and the + Y direction is referred to as the rear.

  As shown in FIG. 1, an image forming apparatus 10 according to the present embodiment is configured to be capable of color printing, and will be described later in a main body 11 as a casing having a substantially cubic shape in appearance. It is configured by mounting various devices. The main body 11 has a rounded shape as a whole, and is designed so as to be visually friendly and give a compact impression to the user. The main body 11 is provided with a paper discharge tray 161 on the upper surface, a maintenance lid 112 is provided on the upper part of the front surface facing the user, and a detachable paper cassette 121 is provided below the maintenance lid 112, thereby improving usability. It is extremely easy to use in consideration.

  The paper discharge tray 161 receives the paper P that has been subjected to the printing process, and forwards the paper P so that it can receive the paper P discharged from the paper discharge port 162 formed facing the front at the rear of the upper surface of the main body 11. It is formed by an inclined surface that is arcuate and inclined upward.

  The maintenance lid 112 is normally closed as shown in FIG. 1A, and is opened as shown in FIGS. 1B and 1C when a toner container (replenisher) 30 described later is replaced. The The maintenance lid 112 is pivotally supported around a support shaft 122a installed slightly above the sheet cassette 121 between the front positions of the pair of side plates 111 of the main body 11, and is rotated forward and backward around the support shaft 122a. Thus, a closed posture Q1 (FIG. 1A) in which the front opening 110 of the main body 11 is closed, and an open posture Q2 (FIGS. 1B and 1C) in which the front opening 110 of the main body 11 is opened. The posture can be changed between.

  The maintenance lid 112 is provided with a manual feed tray 122 that is pivotally supported around the support shaft 122a. The manual feed tray 122 is used when manually supplying the printing paper P to the image forming apparatus 10, and the maintenance lid 112 is set to the closed posture Q1 (indicated by a solid line in FIG. 1A). By being rotated clockwise around the support shaft 122a in this state, it is pulled out from the maintenance lid 112 as shown by a two-dot chain line in FIG.

  The toner container 30 includes black container 30K filled with black toner, cyan container 30C filled with cyan toner, magenta container 30M filled with magenta toner, and yellow container 30Y filled with yellow toner. Types are adopted. The black to yellow containers 30K, 30C, 30M, and 30Y face the front opening 110 in the main body 11 from the left to the right, and the black container 30K, the cyan container 30C, the magenta container 30M, and the yellow container 30Y. Are arranged side by side.

  Accordingly, by opening the maintenance lid 112, the user faces the black to yellow containers 30K, 30C, 30M, and 30Y as shown in FIG. When the black to yellow containers 30K, 30C, 30M, and 30Y are removed from the main body 11 for replacement in this state, the state shown in FIG.

  In the present embodiment, a non-magnetic one-component toner can be used as the toner. Alternatively, magnetic one-component toner may be employed.

  The paper cassette 121 is for storing printing paper P and is detachably attached to the main body 11. In the example shown in FIG. 1, the paper cassette 121 is provided in two stages, but it may be one stage or three or more stages.

  FIG. 2 is an explanatory view of a side sectional view of the internal structure of the image forming apparatus 10 shown in FIG. In addition, the direction display by Y in FIG. 2 is the same as that in FIG. 1 (−Y: forward, + Y: backward). As shown in FIG. 2, the image forming apparatus 10 includes a paper feeding unit 12 that feeds the paper P to an image forming unit 13 described later, and a toner image on the paper P while conveying the paper P sent from the paper feeding unit 12. The image forming unit 13 to be transferred, the fixing unit 14 that performs a fixing process on the toner image transferred to the paper P by the image forming unit 13, and the discharge for switching the discharge destination of the paper P that has been subjected to the fixing process by the fixing unit 14 The destination switching unit 15 and the paper discharge unit 16 that discharges the paper P that has been printed are mounted on the main body 11.

  The paper feeding unit 12 includes a paper cassette 121 that can store a plurality of paper P that is detachably attached to the lower part of the main body 11, and a manual feed tray 122 that is used when manually feeding the paper P. I have.

  A pickup roller 123 is provided at an upper position on the front side of each paper cassette 121, and the paper P stored in the paper cassette 121 is picked up one by one by driving the pickup roller 123 and sent out toward the image forming unit 13. .

  The image forming unit 13 is rotatable about an axis extending in the left-right direction (a direction perpendicular to the paper surface of FIG. 2) in which an electrostatic latent image and a toner image are formed along the electrostatic latent image on the peripheral surface. A photosensitive drum (image carrier) 131, a charging roller 132 that forms a uniform charge on the peripheral surface of the photosensitive drum 131 by charging the peripheral surface of the photosensitive drum 131, and a uniform charge generated by the charging roller 132. An exposure device 133 that forms an electrostatic latent image on the peripheral surface by irradiating the peripheral surface of the applied photosensitive drum 131 with laser light based on image information, and the photosensitive drum on which the electrostatic latent image is formed. The developing device 10a that forms a toner image on the peripheral surface by supplying toner to the peripheral surface of 131, a transfer belt 134 to which the toner image formed on the peripheral surface of the photosensitive drum 131 is transferred, and the photosensitive drum The toner image on 131 A primary transfer roller 135 that is electrically peeled off and transferred onto the surface of the transfer belt 134, and a secondary that is electrostatically peeled off and transferred to the paper P fed from the paper feeding unit 12. A transfer roller 136, a drum cleaning device 137 that cleans the peripheral surface of the photosensitive drum 131 after being transferred to the transfer belt 134, and a belt cleaning that cleans the surface of the transfer belt 134 that has been transferred to the paper P. A density for detecting the density of the toner image on the transfer belt 134 in order to adjust the characteristics of the image forming unit 13 to unify the colors by correcting the color difference between the toner image on the apparatus 138 and the transfer belt 134. And a sensor 139.

  The charging roller 132 is configured such that a charge having a predetermined polarity is formed on the peripheral surface by a high voltage applied from a power source (not shown). Since the peripheral surface of the charging roller 132 is in contact with the peripheral surface of the photosensitive drum 131, uniform charges are formed on the peripheral surface of the photosensitive drum 131.

  The exposure device 133 irradiates the peripheral surface of the photosensitive drum 131 uniformly charged by the charging roller 132 with laser light based on image data input from a computer (not shown). An electrostatic latent image is formed on the peripheral surface of the photosensitive drum 131 by irradiation. By supplying the toner from the developing device 10a to the electrostatic latent image, a toner image is formed on the peripheral surface of the photosensitive drum 131, and the toner image is transferred to the rotating transfer belt 134.

  The developing device 10 a includes a rotary developing device (developing unit) 20 that supplies toner to the photoconductive drum 131 in a state adjacent to the photoconductive drum 131, and the main body 11 to supply toner to the rotary developing device 20. And a toner container (replenisher) 30 that is detachably mounted.

  The rotary developing device 20 includes a rotating frame body 21 formed in a circular shape when viewed from the side (as viewed from a direction perpendicular to the paper surface in FIG. 2), and four rotating frame bodies 21 mounted on the rotating frame body 21 at equal pitches in the circumferential direction. The unit developing unit 22 is provided. The rotary frame 21 is pivotally supported at a position behind the photoconductive drum 131 so as to be rotatable around a frame shaft 211 arranged in parallel with the axis of the photoconductive drum 131 and at substantially the same height level. Yes. The rotating frame body 21 is equally divided into four sections in the circumferential direction by four partition plates 212 protruding in the radial direction from the frame body axis 211, and a unit developing device 22 is mounted in each section. .

  The unit developing unit 22 includes a black unit developing unit 22K filled with black toner, a cyan unit developing unit 22C filled with cyan toner, a magenta unit developing unit 22M filled with magenta toner, and a yellow toner. There are four types of unit developing units 22Y for yellow filled with. When forming a toner image with yellow toner on the peripheral surface of the photosensitive drum 131, the yellow unit developer 22 </ b> Y is opposed to the photosensitive drum 131 by the rotation of the rotating frame 21 around the frame axis 211. The position is set, and in this state, the photosensitive drum 131 makes a round, and a yellow toner image is formed on the circumferential surface. This yellow toner image is immediately transferred to the rotating transfer belt 134.

  The magenta, cyan, and black toner images are formed on the peripheral surface of the photosensitive drum 131 in the same manner as in the case of yellow, and the unit developer 22 filled with the target color toner is arranged around the photosensitive drum 131. The toner image of the next color is sequentially transferred to the peripheral surface of the photosensitive drum 131 that is opposed to the surface and has the toner image disappeared by the transfer process to the transfer belt 134.

  A color image is formed on the surface of the transfer belt 134 by appropriately synchronizing the rotation of the transfer belt 134 and the toner image forming operation of the photosensitive drum 131. The color image is transferred to the paper P fed from the paper feeding unit 12 by the action of the secondary transfer roller 136, whereby color printing is performed on the paper P.

  A registration roller pair 124 (FIG. 2) is provided at a position immediately upstream of the secondary transfer roller 136, and the paper P sent from the paper feeding unit 12 to the image forming unit 13 is conveyed by the registration roller pair 124. The timing is adjusted. The color image on the transfer belt 134 is transferred to an appropriate position on the paper P by adjusting the conveyance timing by the registration roller pair 124.

  3A and 3B are diagrams showing the configuration of the unit developing unit 22, FIG. 3A is a perspective view, and FIG. 3B is an enlarged sectional view taken along line IIIB-IIIB in FIG. 3A. The direction display by X and Y in FIG. 3 is the same as in FIG. 1 (X is the left-right direction (-X: leftward, + X: rightward), Y is the front-back direction (-Y: forward, + Y: backward)). It is.

  As shown in FIG. 3, the unit developer 22 includes a pair of front and rear fan-shaped side plates 221 having a central angle set to 90 ° in a side view, and a toner storage container 222 sandwiched between the pair of fan-shaped side plates 221. 3A, the developing roller 223 provided between the pair of fan-shaped side plates 221 in the lower part of the toner storage container 222, and the pair of fan-shaped side plates 221 in the lower part of the toner storage container 222 in FIG. And a stirring / conveying member 224 installed in parallel with the developing roller 223.

  The agitating and conveying member 224 includes a screw feeder 224a provided at the left corner of FIG. 3B and a relay roller 224b interposed between the screw feeder 224a and the developing roller 223. A partition plate 226 extending from the arc top plate 222b of the toner storage container 222 is provided between the screw feeder 224a and the relay roller 224b, and the inside of the toner storage container 222 is separated by the partition plate 226 from the screw feeder 224a. The first chamber 222c on the side and the second chamber 222d on the relay roller 224b side are divided into two.

  A pair of communication openings 226a at least in the front-rear direction is provided at appropriate positions on the partition plate 226. The screw feeder 224a and the relay roller 224b are driven and rotated around the shaft center by driving of a drive motor (not shown), thereby the toner storage container 222. The toner replenished inside circulates between the first chamber 222c and the second chamber 222d through these communication openings 226a.

  The toner introduced into the second chamber 222d and being carried toward the developing roller 223 by the peripheral surface of the relay roller 224b extends from the arc top plate 222b toward the peripheral surface of the developing roller 223. The toner of the predetermined layer thickness is supplied to the peripheral surface of the photosensitive drum 131 from the peripheral surface of the developing roller 223, and electrostatically is applied to the peripheral surface of the photosensitive drum 131. A toner image is formed along the latent image. A voltage application unit 60 is connected to the developing roller 223. The voltage applying unit 60 applies a developing bias voltage obtained by superimposing the AC bias voltage Vpp to the DC bias voltage Vdc to the developing roller 223, and generates a potential difference with the photosensitive drum 131. Due to this potential difference, toner is supplied from the peripheral surface of the developing roller 223 to the peripheral surface of the photosensitive drum 131.

  A toner introduction opening 222 a for introducing toner into the unit developing device 22 is formed at an appropriate position on the circumferential surface of curvature of the toner storage container 222. The toner introduction opening 222a is provided with a sheet-like cover 225 made of an elastic material such as rubber for closing the toner introduction opening 222a. A slit 225a for inserting a tip of a toner transfer mechanism 50 described later is provided at a substantially central position of the sheet-like lid 225. As the toner transfer mechanism 50 is inserted into the slit 225 a, the toner from the toner container 30 is loaded into the toner storage container 222.

  Returning to FIG. 2, the transfer belt 134 includes a primary transfer roller 135, an idle roller 134 c provided slightly behind the primary transfer roller 135, and an unillustrated illustration provided slightly below the photosensitive drum 131. It is wound around a driving roller 134a that is driven and rotated by driving of a driving motor, and a driven roller 134b that is disposed opposite to the driving roller 134a at a front position below the photosensitive drum 131.

  The driven roller 134b is urged toward the direction away from the drive roller 134a by the urging force of the urging member 134d such as a coil spring, so that the tension state of the transfer belt 134 is maintained. The secondary transfer roller 136 is disposed opposite to the drive roller 134a via the transfer belt 134 at a position directly below the drive roller 134a.

  A bias voltage for electrostatically peeling off the toner image on the transfer belt 134 is applied to the secondary transfer roller 136 from a power source (not shown). Therefore, the toner image on the transfer belt 134 is transferred onto the paper P passing between the transfer belt 134 and the secondary transfer roller 136.

  Between the driving roller 134a and the idle roller 134c, a belt cleaning device 138 for cleaning the surface of the transfer belt 134 after the transfer processing on the paper P is provided, and the cleaning processing is performed by the belt cleaning device 138. The transfer belt 134 goes to the photosensitive drum 131 to receive the next transfer process.

  A density sensor 139 is provided between the driven roller 134b and the driving roller 134a. The density sensor 139 detects the density of the toner image on the transfer belt 134 and adjusts the characteristics of the image forming unit 13 based on the detection result. For example, the color difference of the toner image on the transfer belt 134 is corrected and color unification is performed.

  The fixing unit 14 performs a fixing process on the transfer image transferred to the paper P by the image forming unit 13. The fixing unit 14 is disposed opposite to the fixing roller 141 heated by the energization heating element and the fixing roller 141, and has a peripheral surface. And a pressure roller 142 that is pressed against and contacted with the peripheral surface of the fixing roller 141.

  Then, the paper P that has been transferred by the transfer belt 134 in the image forming unit 13 is guided to the circumference of the transfer belt 134 while being sandwiched between the transfer belt 134 and the secondary transfer roller 136, and is transferred to the fixing unit 14. The toner image is fixed on the paper P by heating when it is introduced and passes between the fixing roller 141 and the pressure roller 142.

  The paper P after the fixing process is led to the paper discharge conveyance path 101 by driving the first discharge roller pair 143, and the paper discharge conveyance path 101 is raised by the forward drive of the second discharge roller pair 102, and the paper discharge outlet 162. And is discharged to a paper discharge tray 161 provided at the top of the main body 11.

  The discharge destination switching unit 15 is used when double-sided printing is performed on the paper P. The paper P once sent from the fixing unit 14 to the paper discharge conveyance path 101 after the one-side fixing process is completed. The image is returned to the image forming unit 13 again with the front and back reversed. The discharge destination switching unit 15 includes a return roller 151 disposed opposite to a lower end portion of the discharge conveyance path 101 so that a peripheral surface thereof is in contact with a lower portion of the first discharge roller pair 143, and a lower portion of the return roller 151. And a return conveyance path 152 extending to the upstream side (the right side in FIG. 2) of the registration roller pair 124 from below the fixing unit 14.

  When performing double-sided printing on the paper P, the paper P after the fixing process for which single-sided printing has been completed is led out to the paper discharge conveyance path 101 until the trailing edge passes through the first discharge roller pair 143, and the second printing is continued. The discharge roller pair 102 is reversely driven. In this way, the paper P on which single-sided printing has been completed is guided by the drive of the return roller 151 and is sent back to the return conveyance path 152, and is directed to the registration roller pair 124 with the front and back being reversed through the return conveyance path 152. Therefore, after that, the image forming unit 13 performs a printing process on the back side of the paper P.

  The toner container 30 supplies toner of each color to the black unit developer 22K, the cyan unit developer 22C, the magenta unit developer 22M, and the yellow unit developer 22Y of the rotary developing unit 20. Each color toner is stored, and four units are adopted corresponding to the black to yellow unit developing units 22K, 22C, 22M, and 22Y.

  As shown in FIGS. 1B and 1C, these four toner containers 30 are attached to and detached from a pedestal 40 provided so as to extend in the left-right direction at a substantially middle position in front of the main body 11. It is installed as possible. Between each toner container 30 and the rotary developing device 20, a toner transfer mechanism 50 for sending the toner in the toner container 30 to each unit developing device 22 is provided. On the pedestal 40, a black container 30K, a cyan container 30C, a magenta container 30M, and a yellow container 30Y are mounted in parallel from left to right.

  Four toner transfer mechanisms 50 are arranged in parallel in the left-right direction so as to correspond to the respective sheet-like lids 225 of the black to yellow unit developing units 22K, 22C, 22M, and 22Y above the rotary developing unit 20. Has been. Then, the toner transferred in the toner transfer mechanism 50 in a state where a part of the toner transfer mechanism 50 penetrates the slit 225 a of the sheet-like lid 225 and enters the unit developer 22, enters the unit developer 22. Supplied.

  In the image forming apparatus 10 according to the present embodiment, any one of the four unit developing units 22 is set in a posture opposite to the photosensitive drum, and the unit developing unit 22 When the amount of toner in the second chamber 222d becomes less than the minimum amount of toner necessary for normal image formation processing on the peripheral surface of the photosensitive drum 131, the inside of the second chamber 222d is empty. Control is performed so as to be detected. Hereinafter, this control will be described.

  Here, the necessary minimum toner amount (hereinafter referred to as “required minimum toner amount”) will be described. The necessary minimum toner amount is an amount in which the image density in the axial direction of the developing roller 223 in the second chamber 222d cannot be maintained uniformly, or deteriorated toner in the second chamber 222d increases, and an image is generated under normal developing bias conditions. This is the amount when the concentration cannot be maintained.

  Whether the toner amount is less than the minimum necessary toner amount can be determined by detecting the density of the toner image using a density sensor 139 that detects the density of the toner image on the transfer belt 134. Specifically, the duty bias voltage condition (hereinafter referred to as “toner amount detection condition”) set to be smaller than the normal development bias voltage condition (hereinafter referred to as “normal condition”) at a predetermined timing. ), A 100% solid pattern image and a blank paper pattern image are formed on the transfer belt 134, the respective image densities are detected, and the light and shade between the 100% solid pattern image and the blank paper pattern image are normal conditions. On the other hand, it is determined that the necessary minimum toner amount has been reached when the toner is reversed.

  For example, if the duty is 40%, the ratio of the positive direction is 40% when the electric field direction in which the toner moves from the developing roller 223 onto the photosensitive drum 131 is the positive direction. The reverse direction is an AC bias voltage of 60%. When the duty is reduced to 15%, for example, the time for applying the electric field for the toner to move from the developing roller 223 toward the photosensitive drum 131 is shortened, and the time for returning to the developing roller 223 side is lengthened.

  This decrease in Duty is due to the prolonged application time of the electric field for moving the reversely charged toner from the developing roller 223 to the photosensitive drum 131 when the deteriorated toner in the second chamber 222d is reversely charged and the amount thereof is increasing. As a result, the density of the blank pattern image increases and the density of the 100% solid pattern image decreases. That is, as described above, when the density when the duty is reduced is reverse to that in the normal condition, the ratio of the reversely charged toner in the toner in the second chamber 222d increases. It can be determined that the possibility of exceeding 50% is high. Therefore, it can be determined that it is difficult to maintain the concentration under normal conditions.

  In order to perform such control, a control unit 70 and a voltage application condition management unit 80 are provided at appropriate positions in the main body 11. FIG. 4 is a block diagram for explaining control by the control unit 70 and the voltage application condition management unit 80. As shown in FIG. 4, the control unit 70 includes a CPU (central processing unit) 71 that is an arithmetic processing unit, a read-only ROM (read only memory) 72 attached to the CPU 71, and a readable / writable RAM (random). access memory) 73.

  The ROM 72 stores a program for executing this control, and the program is read into the CPU 71 each time the image forming apparatus 10 is powered on. Thereafter, the empty state in the second chamber 222d is based on this program. The control for detecting is executed. On the other hand, the RAM 73 is used as an area for temporarily writing and reading various data used temporarily when the above control is executed.

  The CPU 71 acquires the density of the toner image on the transfer belt 134 detected by the density sensor 139, and detects whether or not the second chamber 222d is empty based on the detection result; In executing the above control, an output unit 712 is provided that outputs a control signal to various locations in the image forming apparatus 10.

  As shown in FIG. 4, the voltage application condition management unit 80 includes a setting unit 81 that sets a developing bias voltage to be applied to the developing roller 223 with respect to the voltage applying unit 60 of the image forming unit 13, and the setting unit 81 includes a voltage applying unit. And a readable / writable RAM 82 in which development bias voltage conditions set to 60 are stored.

  The setting unit 81 changes the development bias condition set in the voltage application unit 60 based on the control signal from the output unit 712. Specifically, when the control signal from the output unit 712 is input, the setting unit 81 acquires the development bias condition according to the control signal from the RAM 82 and sets it in the voltage application unit 60.

  The RAM 82 stores a plurality of development bias voltage conditions set by the setting unit 81 in the voltage application unit 60. The development bias voltage conditions stored in the RAM 82 include the above-described normal conditions and toner amount detection conditions.

  The operation of the control unit 70 and the voltage application unit management unit 80 will be described. The detection unit 711 starts an operation of detecting an empty state in the second chamber 222d of the unit developer 22 at a predetermined timing. When the detection unit 711 outputs that the operation is started to the output unit 712, the output unit 712 that has received the notification causes the paper feeding unit 12 and the fixing unit 14 to temporarily stop the paper feeding operation and the fixing operation. A control signal is output to the paper feeding unit 12 and the fixing unit 14.

  The output unit 712 outputs a control signal for causing the image forming unit 13 to form an image pattern for detecting the toner amount (hereinafter referred to as “toner amount detection pattern”). Further, the output unit 712 outputs a control signal for causing the voltage application condition management unit 80 to set the above-described toner amount detection condition in the voltage application unit 60 of the image forming unit 13, and receives the control signal. The management unit 80 sets the toner amount detection condition for the voltage application 60.

  In the image forming unit 13, based on a control signal from the voltage application condition management unit 80, the voltage application unit 60 gives the development roller 223 a development bias voltage in accordance with the toner amount detection condition, and the development roller 223 and the photosensitive drum. A potential difference is generated with respect to 131. At the same time, based on a control signal from the output unit 712, the exposure device 133 irradiates the peripheral surface of the photosensitive drum 131 with laser light along the toner amount detection pattern to form an electrostatic latent image on the peripheral surface.

  When the developing device 10a supplies toner to the peripheral surface of the photosensitive drum 131 on which the electrostatic latent image is formed and forms a toner image on the peripheral surface, the toner image is formed on the peripheral surface of the photosensitive drum 131. The toner image is transferred to the transfer belt 134. The density of the toner image on the transfer belt 134 is detected by the density sensor 139, and the detected density is output to the detection unit 711.

  The detection unit 711 detects whether or not the second chamber 222d of the unit developer 22 is empty based on the density of the toner image on the transfer belt 134 detected by the density sensor 139. Hereinafter, the detection operation by the detection unit 711 will be specifically described with reference to FIGS. FIG. 5 is a specific example of the developing bias voltage condition set in the voltage application unit 60. FIG. 5A corresponds to the normal condition described above, and FIG. 5B illustrates the toner amount detection described above. Corresponds to the conditions.

  5A, the DC bias voltage Vdc is 60 V, the AC bias voltage Vpp is 1100 V, the frequency f is 4 kHz, and the duty is 40%. Specifically, under this normal condition, the developing bias voltage is obtained by superimposing the AC bias voltage Vpp of 1100 V on the DC bias voltage Vdc of 60 V, and the direction in which the toner moves from the developing roller 223 onto the photosensitive drum 131. The voltage in the direction of pulling the toner back from the photosensitive drum 131 to the developing roller 223 is −490 V. The application time of 610 V in one cycle is set to 40% and the application time of −490 V is set to 60%. The developing bias voltage is applied to the developing roller 223 at a frequency f of 4 kHz.

  On the other hand, in the above toner amount detection condition shown in FIG. 5B, the DC bias voltage Vdc is 60 V, the AC bias voltage Vpp is 1100 V, the frequency f is 4 kHz, and the duty is 15%. Specifically, in this toner amount detection condition, a developing bias voltage in which an AC bias voltage Vpp of 1100 V is superimposed on a DC bias voltage Vdc of 60 V, and toner is transferred from the developing roller 223 onto the photosensitive drum 131. The voltage in the moving direction is 610 V, the voltage in the direction of returning the toner from the photosensitive drum 131 to the developing roller 223 is −490 V, 610 V in one cycle is 15% application time, and −490 V application time is 85%. The developing bias voltage set to 1 is applied to the developing roller 223 at a frequency f of 4 kHz.

  FIG. 6 is a specific example of the toner amount detection pattern. The toner amount detection pattern shown in FIG. 6 is an image pattern in which a thin 100% solid pattern image exists in a blank paper pattern image.

  FIG. 7 shows a toner image on the transfer belt 134 detected by the density sensor 139. First, a case where the toner amount in the second chamber 222d is full will be described. In this case, since the amount of deteriorated toner in the second chamber 222d is small, the toner amount detection pattern shown in FIG. 6 is formed with the development bias voltage under the normal conditions shown in FIG. Then, as shown in FIG. 7, an image according to the pattern of FIG. 6 is formed. Further, even when the developing bias voltage of the toner amount detection condition of FIG. 5B is applied, the density of the 100% solid pattern image is lowered, but as shown in FIG. 7, the pattern of FIG. An image according to the above is formed.

  On the other hand, when the amount of toner in the second chamber 222d is empty, an image different from the above full image is formed. That is, when the toner amount in the second chamber 222d is empty, the deteriorated toner that is reversely charged in the second chamber 222d increases. For this reason, in the state where the development bias voltage of the normal condition of FIG. 5A is applied, an image according to the pattern of FIG. 6 is formed as shown in FIG. 7, but FIG. In the state where the developing bias voltage of the toner amount detection condition is applied, inversion occurs in the density between the 100% solid pattern image and the blank pattern image. As described above, this reverse rotation occurs in the case of the developing bias voltage in the toner amount detection condition shown in FIG. 5B in the electric field where the reversely charged toner moves from the developing roller 223 to the photosensitive drum 131 side. This is because the application time increases, and as a result, the density of the blank pattern image increases and the density of the 100% solid pattern image decreases. Therefore, it can be determined that the amount of toner in the second chamber 222d is empty based on the occurrence of this light / dark reversal.

  As described above, the detection unit 711 forms an image of the toner amount detection pattern of FIG. 6 in a state where the developing bias voltage of the toner amount detection condition of FIG. 5B is applied to the developing roller 223. Based on the density of the image, it is possible to detect whether or not the second chamber 222d of the unit developer 22 is empty.

  As described above, according to the image formation in the present embodiment, the blank pattern image and the 100% solid pattern image are formed in a state where the duty of the developing bias voltage applied to the developing roller 223 is reduced. By detecting each image density, it is possible to detect whether or not the inside of the second chamber 222d of the unit developer 22 is empty.

  In the present embodiment, an image pattern in which a thin 100% solid pattern image exists in the blank paper pattern image shown in FIG. 6 is used as the toner amount detection pattern. However, the present invention is not limited to this pattern. It is not something that can be done. In short, it is sufficient that two images of a blank paper pattern image and a 100% solid pattern image exist. For example, an image pattern in which a thin blank pattern image exists in a 100% solid pattern image may be used.

  In this embodiment, the density of the toner image on the transfer belt 134 is detected. However, the density of the toner image on the photosensitive drum 131 may be detected.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. The toner amount detection condition of the first embodiment reduces the duty of the developing bias voltage, shortens the voltage application time in the direction in which the toner moves from the developing roller 223 onto the photosensitive drum 131, and performs photosensitive The voltage application time in the direction in which the toner is pulled back from the body drum 131 to the developing roller 223 is increased. In contrast, the toner amount detection condition of the present embodiment is to reduce the DC bias voltage Vdc instead of reducing the duty of the developing bias voltage. Others are the same as in the first embodiment, and description thereof will not be repeated here.

  FIG. 8 is another specific example of the developing bias voltage condition set in the voltage application unit 60. FIG. 8A corresponds to the above normal condition, and FIG. 8B illustrates the above toner amount. This corresponds to the detection condition.

  In the normal conditions shown in FIG. 8A, the DC bias voltage Vdc is 60V, the AC bias voltage Vpp is 1100V, the frequency f is 4 kHz, and the duty is 40%. Specifically, under this normal condition, the developing bias voltage is obtained by superimposing the AC bias voltage Vpp of 1100 V on the DC bias voltage Vdc of 60 V, and the direction in which the toner moves from the developing roller 223 onto the photosensitive drum 131. The voltage in the direction of pulling the toner back from the photosensitive drum 131 to the developing roller 223 is −490 V. The application time of 610 V in one cycle is set to 40% and the application time of −490 V is set to 60%. The developing bias voltage is applied to the developing roller 223 at a frequency f of 4 kHz.

  On the other hand, in the above toner amount detection condition shown in FIG. 8B, the DC bias voltage Vdc is 30 V, the AC bias voltage Vpp is 1100 V, the frequency f is 4 kHz, and the duty is 40%. Specifically, in this toner amount detection condition, a developing bias voltage in which an AC bias voltage Vpp of 1100 V is superimposed on a DC bias voltage Vdc of 30 V, and toner is transferred from the developing roller 223 onto the photosensitive drum 131. The voltage in the moving direction is 580 V, the voltage in the direction to pull the toner from the photosensitive drum 131 back to the developing roller 223 is −520 V, 580 V in one cycle is 40% application time, and −520 V application time is 60%. The developing bias voltage set to 1 is applied to the developing roller 223 at a frequency f of 4 kHz.

  In the present embodiment, when the toner amount detection pattern of FIG. 6 is formed in a state where the developing bias voltage of the toner amount detection condition of FIG. As in the case, the contrast between the 100% solid pattern image and the blank pattern image is reversed. This reversal occurs in the case of the developing bias voltage under the toner amount detection condition shown in FIG. 8B because the voltage in the direction of pulling back the toner from the photosensitive drum 131 to the developing roller 223 increases. This is because the electric field in which the charged toner moves from the developing roller 223 to the photosensitive drum 131 increases, and as a result, the density of the blank pattern image increases and the density of the 100% solid pattern image decreases.

  In the present embodiment, the detection unit 711 forms an image of the toner amount detection pattern of FIG. 6 in a state where the developing bias voltage of the toner amount detection condition of FIG. 8B is applied to the developing roller 223. It is possible to detect whether or not the second chamber 222d of the unit developer 22 is empty based on the density of the image.

  The present invention is not limited to the first and second embodiments described above, and includes the following contents.

  (1) In the first and second embodiments, the printer 10 has been described as an example of the image forming apparatus to which the developing device according to the invention is applied. The present invention is also applicable to copying machines and facsimile machines.

  (2) In the first and second embodiments described above, the rotary developing device 20 for color printing comprising a plurality of unit developing devices 22 is adopted as the developing device. However, in the present invention, the developing device is for monochrome printing. In addition to the rotary developing device 20, the so-called tandem developing device in which unit developing devices for each color are arranged in parallel in the horizontal direction may be used. It may be.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an external appearance of an image forming apparatus according to Embodiment 1 of the present invention, in which (A) shows a state in which a maintenance lid is closed, and (B) shows a state in which the maintenance lid is opened. FIG. 4C is a diagram illustrating a state where the maintenance lid is opened and the toner container is removed. FIG. 2 is an explanatory view of a side sectional view of an internal structure of the image forming apparatus shown in FIG. 1. 3A and 3B are diagrams illustrating a configuration of a unit developing device, in which FIG. 3A is a perspective view, and FIG. 3B is an enlarged cross-sectional view taken along line IIIB-IIIB in FIG. It is a block diagram for demonstrating control by a control part. It is a figure which shows the specific example of the developing bias voltage condition set to a voltage application part, (A) is a figure equivalent to a normal condition, (B) is a figure equivalent to the condition for toner amount detection. FIG. 6 is a diagram illustrating a specific example of a toner amount detection pattern. FIG. 6 is a diagram for explaining a toner image on a transfer belt detected by a density sensor. It is a figure which shows the other specific example of the developing bias voltage condition set to a voltage application part, (A) is a figure equivalent to a normal condition, (B) is a figure equivalent to the toner amount detection conditions. .

Explanation of symbols

10 Printer (image forming device)
DESCRIPTION OF SYMBOLS 10a Development apparatus 11 Main body 12 Paper feed part 13 Image forming part 14 Fixing part 15 Discharge destination switching part 16 Paper discharge part 20 Rotary developing device (development part)
21 Rotating Frame 22 Unit Developer 22K Black Unit Developer 22C Cyan Unit Developer 22M Magenta Unit Developer 22Y Yellow Unit Developer 30 Toner Container (Supply Unit)
30K Black container 30C Cyan container 30M Magenta container 30Y Yellow container 40 Base 50 Toner transfer mechanism 60 Voltage application unit 70 Control unit 71 CPU
72 ROM
73 RAM
80 Voltage application condition management unit 81 Setting unit 82 RAM
DESCRIPTION OF SYMBOLS 101 Discharge conveyance path 102 Discharge roller pair 110 Front opening 111 Side plate 112 Maintenance lid 121 Paper cassette 122 Tray 122a Support shaft 123 Pickup roller 124 Registration roller pair 131 Photosensitive drum (image carrier)
132 charging roller 133 exposure device 134 transfer belt 134a drive roller 134b driven roller 134c idle roller 134d biasing member 135 primary transfer roller 136 secondary transfer roller 137 drum cleaning device 138 belt cleaning device 139 density sensor 141 fixing roller 142 pressure roller 143 Discharge roller pair 151 Return roller 152 Return conveyance path 161 Discharge tray 162 Discharge port 211 Frame shaft 212 Partition plate 221 Fan-shaped side plate 222 Toner storage container 222a Toner introduction opening 222b Arc top plate 222c First chamber 222d Second chamber 223 Development Roller 224 Agitating and conveying member 224a Screw feeder 224b Relay roller 225 Sheet-like lid 225a Slit 226 Partition plate 226a Communication opening 227 Blade 711 Detector 712 Radical 19

Claims (3)

A developing roller for carrying toner on the surface; a voltage applying unit for applying a developing bias voltage to the developing roller; and an image carrier on which an electrostatic latent image is formed, the voltage applying unit being the developing roller An image forming apparatus including a developing device that forms a toner image by supplying a toner carried by the developing roller to an electrostatic latent image formed on the image carrier by applying a developing bias voltage to the electrostatic latent image. There,
A density sensor for detecting the density of the toner image on the image carrier;
A detection unit that detects a toner amount in the developing device based on a density of the toner image on the image carrier detected by the density sensor;
The developing bias voltage applied to the developing roller by the voltage application unit is a bias voltage having a predetermined duty in which an AC bias voltage is superimposed on a DC bias voltage,
In the case where the detection unit detects the amount of toner in the developing device,
The voltage application unit lowers the duty or DC bias voltage of the developing bias voltage applied to the developing roller as compared with that during normal image formation, and the developing device has a solid pattern and a blank pattern on the image carrier. Forming an electrostatic latent image containing
The detection unit determines whether or not the density between the toner images corresponding to each of the solid pattern and the blank sheet pattern on the image carrier is reversed before and after the duty of the developing bias voltage or the DC bias voltage is decreased. And detecting that the amount of toner in the developing device is less than a predetermined amount of toner based on a detection result that the contrast has been reversed. Further comprising an intermediate transfer body to which the toner image is transferred from the image bearing member and transferring the transferred toner image to a recording medium;
The image forming apparatus according to claim 1, wherein the density sensor detects a density of the toner image transferred from the image carrier to the intermediate transfer member.   The developing device determines that the toner amount in the developing device is empty based on a detection result that the toner amount in the developing device is less than the predetermined toner amount. The image forming apparatus according to 1 or 2.

Images