JP5589773B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that prevents fatigue over time due to bending of an elastic sheet member that cleans a detection surface of a toner density sensor as much as possible and accurately controls toner density with a correct sensor output over a long period of time.

  Conventionally, there is an electrophotographic image forming apparatus. In this image forming apparatus, generally, a photosensitive drum is uniformly charged and initialized, an electrostatic latent image is formed on the photosensitive drum by optical writing, and the electrostatic latent image is converted into a toner image. Is directly or indirectly transferred onto a transfer material such as paper and fixed by a fixing device.

  Such electrophotographic image forming apparatuses include those using a one-component developer (toner) and those using a two-component developer. Since the method using a single component developer is relatively easy to handle and control, a single component toner has been dominant as a developer.

  In recent years, there has been a strong demand for speeding up printing (hereinafter also referred to as printing). A method using a two-component developer can cope with speeding up of the printing process better. For this reason, various developing devices using a two-component developer have been proposed.

  The above two-component developer is composed of toner and carrier. The carrier is mixed and agitated with the toner in the developing unit to give the toner a predetermined charge. The charged toner temporarily adheres to the surface of the carrier and coats the surface of the carrier.

  The carrier carries charged toner onto the photosensitive member, transfers the toner to the electrostatic latent image on the photosensitive member, and develops the toner image on the electrostatic latent image. The carrier from which the toner on the surface has been released remains on the developing roller, returns to the inside of the developing device, and is mixed and stirred again with new toner to be replenished to the developing device, charges the toner, and transports the toner onto the photoreceptor. , And so on.

  Toner is supplied to the developing device from a toner supply device. As a toner replenishment path from the toner supply device to the developing unit, a pipe having a built-in coil screw or a natural fall path due to toner gravity is used.

  The developing device incorporates a toner mixing and stirring mechanism. The toner mixing and stirring mechanism supplies (supplements) toner supplied from a toner supply device to a developing roller while mixing and stirring with a two-component developer having a reduced toner concentration (hereinafter simply referred to as developer).

  Here, if the toner concentration in the developer of the developing device is too high, background staining or the like occurs. Conversely, if the toner density is too low, a high density image cannot be obtained. Therefore, in order to obtain a high-quality image, it is necessary to control the toner concentration of the developer in the developing device within a certain range.

  Therefore, a developing device of an electrophotographic image forming apparatus that forms an image using such a developer is provided with a toner density sensor for measuring the amount of toner consumed by printing. When it is detected that the toner density is lower than a predetermined value, the developing device is replenished with toner.

  Generally, a sensor that detects magnetic permeability is used as the toner concentration sensor. There are several methods for detecting the magnetic permeability, such as a method using an inductance component of a coil, a frequency type, and a magnetic bridge type.

  In any case, the toner concentration sensor exposes a detection surface to a part of the inner wall surface of the developing device, and detects a change in magnetic permeability from the carrier in the developer around the detection surface. That is, when the toner concentration is high, the magnetic permeability decreases and the sensor output becomes weak. When the toner concentration is low, the magnetic permeability increases and the sensor output becomes strong.

  In such a toner concentration sensor, if the developer stays on the detection surface, it becomes impossible to detect the accurate toner concentration. If an accurate toner density cannot be detected, a malfunction may be caused in controlling the toner replenishment amount.

  Therefore, the elastic sheet material is fixed parallel to the shaft portion at a position facing the detection surface of the toner density sensor of the shaft portion of the conveying screw that conveys the developer in the developing device while stirring. A sensor that cleans the detection surface of a toner density sensor has been proposed. (For example, refer to Patent Document 1.)

JP 05-150650 A

  However, the elastic sheet material that is cleaned by rubbing the detection surface of the toner density sensor disposed in the developing device deteriorates in elasticity over a long period of use, and the stirring ability to replace the developer staying on the detection surface is reduced. .

  When the elastic sheet material to be cleaned deteriorates, the developer stays on the detection surface of the toner concentration sensor, and the toner concentration “T (toner) / D (developer)” detected by the toner concentration sensor changes from a normal value to an abnormal value. This causes the problem of fluctuations.

  When the elastic sheet material that has deteriorated in elasticity over a long period of use as described above is examined in detail, the elastic sheet material that should have been arranged in a flat form is deformed as if it had a curl. It was observed. Therefore, it is considered that the action of rubbing the detection surface of the toner density sensor is weakened.

  The present invention solves the above-described conventional problems, and prevents fatigue over time due to bending of the elastic sheet member that cleans the detection surface of the toner concentration sensor, and enables accurate toner concentration control with correct sensor output. An object of the present invention is to provide an image forming apparatus that can be used over a long period of time.

In order to solve the above-described problems, an image forming apparatus of the present invention includes a developing unit that performs development with a two-component developer, a stirring and conveying member that is disposed in the developing unit and stirs and conveys the two-component developer, A cleaning blade fixed to the rotating shaft of the agitating / conveying member and rotating, and a detection surface exposed in the developing device are arranged, and the detection surface is slid by the cleaning blade every rotation of the agitating / conveying member. It is friction, the toner concentration sensor during rubbing after rubbing outputs an output value at a higher value to output a small amplitude of the toner density detection signal having a predetermined period to output an output value at a lower value, the stirring A control device that detects an output value period of a small-amplitude toner density detection signal of the constant period during the agitating and transporting of the two-component developer by a transport member, and the control device comprises: And before When stopping the stirring and conveying member, based on the output value cycle control device detects, that controls to stop at the position of the timing of lower output values Ru is output, is configured as characterized in that The

  In this image forming apparatus, for example, the toner density detection sensor is provided to detect a toner supply threshold value for supplying toner to the developing unit, and the small density toner density detection signal having a constant period is: The toner density detection sensor is a signal generated by being superimposed on the toner density detection signal being detected in order to detect the toner replenishment threshold.

  According to the present invention, it is possible to prevent fatigue over time due to bending of the elastic sheet member that cleans the detection surface of the toner density sensor as much as possible, and to perform accurate toner density control with correct sensor output over a long period of time. An apparatus can be provided.

1 is a cross-sectional view illustrating an internal configuration of a full-color image forming apparatus (printer) according to Embodiment 1 of the invention. 1 is a circuit block diagram including a printer control device according to Embodiment 1. FIG. FIG. 3 is an enlarged cross-sectional view illustrating the developing device of the printer according to the first exemplary embodiment together with the photosensitive drum. FIG. 3 (a) shows the configuration of each part of the developing tank in order to show the arrangement relationship among the second stirring / conveying member, the cleaning blade, and each part of the toner density sensor in the developing tank of the developing device of the printer according to the first embodiment. (B) is an enlarged view of a portion surrounded by a broken line h in (a). 6 is a diagram illustrating an example of an output of a toner density sensor of the developing device of the printer according to the first embodiment. FIG. (a) is a figure which shows the pulse signal of the narrow period which appears superimposed on the output signal which should be the original output value of the toner density sensor of the printer concerning Example 1, (b) makes the shape of the pulse signal gentle. And it is a figure which expands and shows a period. 6 is a flowchart of a process for controlling a stop timing of the photosensitive drum of the developing device of the printer according to the first embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, a two-component developer composed of a toner and a carrier is used. In the following description, the two-component developer is simply referred to as a developer.

  FIG. 1 is a cross-sectional view illustrating an internal configuration of a full-color image forming apparatus (hereinafter simply referred to as a printer) according to Embodiment 1 of the present invention.

  An image forming apparatus 1 shown in FIG. 1 is an electrophotographic secondary transfer tandem color image forming apparatus, and includes an image forming unit 2, a transfer belt unit 3, a toner supply unit 4, a paper feeding unit 5, and a belt. It is composed of a type fixing unit 6.

  The image forming unit 2 is in contact with the lower running unit surface 8a of the transfer belt 8 of the transfer belt unit 3 and multi-stages four developing devices 9 (9y, 9m, 9c, 9k) from right to left in FIG. It consists of a side-by-side configuration. The image forming unit 2 is held by a frame of the main body of the image forming apparatus 1 so that it can be moved up and down from the printing execution position shown in FIG. 1 to a maintenance position below it.

  Of the four developing devices 9, three developing devices 9y, 9m, and 9c on the downstream side (right side in the figure) are yellow (Y), magenta (M), and cyan (C), which are subtractive three primary colors, respectively. A mono-color image is formed with the color toner, and the developing device 9k forms a monochrome image mainly with black (K) toner used for characters and dark portions of the image.

  Each of the developing devices 9 has the same configuration except for the color of the toner that develops the image. Therefore, the configuration of the developing device 9k for black (K) toner will be described below as an example.

  The developing device 9 includes a photosensitive drum 10 at the top. The photosensitive drum 10 has a peripheral surface made of, for example, an organic photoconductive material. A cleaner 11, a charging roller 12, an optical writing head 13, and a developing roller 15 of the developing device 14 are disposed around the periphery of the photosensitive drum 10.

  The developing device 14 includes a first stirring / conveying member 16 and a second stirring / conveying member 17 in two developing tanks located below the developing roller 15. Details of the first and second stirring and conveying members 16 and 17 will be described later.

  The transfer belt unit 3 has an endless transfer belt 8 that extends in the shape of a flat loop in the left-right direction in the figure at approximately the center of the main unit, and the transfer belt 8 is stretched over the transfer belt 8. A driving roller 18 and a driven roller 19 are provided to circulate and move counterclockwise as indicated by arrows a and b in the figure.

  The above-described transfer belt 8 is directly transferred to the surface of the belt that circulates below by a primary transfer roller 21 that is integrated with the unit and pressed against the photosensitive drum 10 via the transfer belt 8 (primary transfer). Then, the toner image is conveyed to the secondary transfer unit 23 to the paper for further transfer (secondary transfer) to the paper.

  In the transfer belt unit 3, the cleaning blade 25 of the belt cleaner 24 is disposed in contact with the surface of the belt 18 that is stretched around the driving roller 18. A waste toner collecting container 26 is detachably disposed below the belt cleaner 24.

  In the belt cleaner 24, the cleaning blade 25 abuts on the surface of the transfer belt 8 to scrape and remove the waste toner, and the waste toner is sent to a lower waste toner collection container 26 by a conveying member.

  The toner supply unit 4 includes four toner hoppers 27 (27y, 27m, 27c, and 27k) disposed above the upper running unit of the transfer belt 8. The four toner hoppers 27y, 27m, 27c, and 27k contain yellow (Y), magenta (M), cyan (C), and black (K) toners, respectively.

  The toner supply unit 4 includes yellow (Y), magenta (M), cyan (C), and black (Y) as indicated by Y, M, C, and K (hereinafter referred to as “YMCK”) in FIG. One of the toners K) is supplied to the developing device 14 of the developing device 9 through a toner supply path (not shown).

  The paper feed unit 5 includes one paper feed cassette 29. A paper take-out roller 31, a feed roller 32, a separating roller 33, and a standby conveyance roller pair 34 are disposed in the vicinity of the paper feed port (right side of the drawing) of the paper feed cassette 29.

  In the paper conveyance direction (vertical upward direction in the figure) of the standby conveyance roller pair 34, a secondary transfer roller 35 that is in pressure contact with the driven roller 19 via the transfer belt 8 is disposed, and the above-described secondary transfer onto the paper is performed. Part 23 is formed.

  A diffuse reflection type density sensor 36 is disposed in the vicinity of the lower running portion surface 8a of the transfer belt 8 at a substantially intermediate position between the secondary transfer portion 23 and the most downstream developing device 9m. A belt-type heat fixing unit 6 is disposed downstream (upward in the drawing) of the secondary transfer portion.

  Further downstream of the belt-type heat fixing unit 6, a pair of unillustrated unloading rollers for unloading the fixed sheet from the belt-type heat fixing unit 6 and a sheet discharge tray on which the unloaded paper is formed on the upper surface of the apparatus. A pair of paper discharge rollers (not shown) for discharging paper to 37 is disposed. An operation panel unit 38 is disposed at an upper end of the main body located to the right of the paper discharge tray 37 with a slight inclination.

  FIG. 2 is a circuit block diagram including the control device of the printer 1 described above. As shown in FIG. 2, the circuit block is centered on the printer controller 40. The printer controller unit 40 is connected to an I / F (interface) 43 and a head controller unit 44 of a network controller unit 42 via a plurality of buses 41.

  The operation panel unit 38 described above is connected to the I / F 43 of the network controller unit 42 via another bus 41. The I / F 43 receives a signal such as print data from a host device (not shown) such as a personal computer.

  The network controller unit 42 transmits print data input from the outside via the I / F 43 to the head controller unit 44, and transmits command data included in the print data and instruction data input from the operation panel unit 38 to the printer controller unit. 40.

  An EEPROM (electrically erasable programmable ROM) 45, a ROM (read only memory) 46, and a paper feed motor 47 are further connected to the printer controller unit 40 via a bus 41.

  The printer controller 40 reads out a control program stored in the ROM 46, and in accordance with the read-out control program, a diffuse reflection type sensor 36, a registration sensor 49, a DDS (developer drum set for each YMCK, in this example, the developing device 9 Each part is controlled according to the sensor output received from the new and old detection sensors 51 and the like.

  Also, the printer controller 40 monitors whether the sensor output signal received from the toner density sensor 62 (62y, 62m, 62c, 62k) for each YMCK exceeds the toner supply threshold, and exceeds the toner supply threshold. At this time, the toner replenishing devices 57, 58, 59, 61 corresponding to each YMCK are driven to replenish toner to the developing device 9.

  The printer controller 40 controls optical writing of the heads (optical writing heads 13) for each YMCK via the head controller 44 based on the print data received from the network controller 42.

  On the other hand, the printer controller 40 controls the paper feed motor 47 to transport the paper to the secondary transfer unit 23 based on the print data, and controls the high-pressure unit 52 to drive the drive unit 53 for each YMCK. , 54, 55, and 56, a bias voltage is applied to the charging roller 12, the developing roller 15, the primary transfer roller 21, the secondary transfer roller 35, and the like.

  In addition, the printer controller unit 40 temporarily stores the desired timing calculated from the pulse signal of the narrow cycle that appears superimposed on the output signal output for the toner density sensor 62 for each YMCK to detect the toner supply threshold value in the EEPROM 45. Then, the driving of the driving devices 53, 54, 55, 56 for each YMCK is stopped at the stored desired timing.

  FIG. 3 is an enlarged sectional view showing the developing unit 14 together with the photosensitive drum 10. As shown in FIG. 3, the developing device 14 includes two developing tanks 65 (65 a and 65 b) partitioned by an outer wall 63 and an inner partition wall 64.

  In the upper developing tank 65a, the developing roller 15 and the first stirring and conveying member 16 described above are disposed. A doctor blade 66 is in contact with the developing roller 15. The above-described second stirring / conveying member 17 is disposed in the lower developing tank 65a. In the developing tank 65a, a toner density sensor 62 is arranged with its detection surface 67 exposed in the tank.

  The first agitating and conveying member 16 includes a rotating shaft 68 and a helical fin 69 fixed to the rotating shaft 68 in a spiral shape. The second stirring / conveying member 17 includes a rotating shaft 71 and a spiral fin 72 fixed to the rotating shaft 71 in a spiral shape.

  The first agitating / conveying member 16 rotates counterclockwise in the figure as indicated by an arrow c, and the paper surface of the figure as indicated by an arrow e while stirring the developer in the developing tank 65a by the spiral fin 69. The developer is conveyed from the near side in the depth direction to the other side, and the developer is supplied to the developing roller 15.

  The developing roller 15 supplies only the developer toner to the photosensitive drum 10 to form (develop) the electrostatic latent image on the circumferential surface of the photosensitive drum 10 as a toner image. The carrier of the developer on the developing roller 15 from which only the toner has been taken up by the photosensitive drum 10 is mixed with the developer in the developing tank 65a, and enters the developing tank 65b at an outlet (not shown) on the other side in the depth direction of the drawing. Send it back.

  The second agitating and conveying member 17 in the developing tank 65b rotates counterclockwise in the figure as indicated by an arrow d, and the developer in the developing tank 65b is indicated by an arrow f while stirring the developer in the helical fin 72. In this way, the sheet is conveyed from the other side in the depth direction of the drawing to the near side.

  If the toner density of the developer is less than the specified level, the toner density sensor 62 detects a decrease in toner density. When a decrease in toner density is detected, toner is supplied from the toner hopper 27 corresponding to the developing device 14 of the toner supply unit 4 through the supply port.

  The second agitating and conveying member 17 feeds the developer to the developing tank 65a at a supply port (not shown) on the near side in the depth direction of the drawing while stirring and conveying the developer. In this way, the reflux of the developer and the replenishment of the toner are repeated, and the development with the toner proceeds sequentially.

  Since the detection surface 67 of the toner density sensor 62 is disposed so as to be exposed in the tank, the developer tends to stay on the detection surface 67. If the developer stays on the detection surface 67, the detection accuracy of the toner density sensor 62 is lowered.

  In order to prevent the detection accuracy of the toner density sensor 62 from deteriorating, the rotation shaft 71 of the second agitating / conveying member 17 in the developing tank 65b is positioned so as to rotate opposite the detection surface 67 of the toner density sensor 62. Further, a cleaning blade 75 including a blade holding portion 73 and an elastic sheet (blade) 74 held by the blade holding portion 73 is fixed.

  The cleaning blade 75 rotates together with the rotating shaft 71 of the agitating and conveying member 17, and rubs the detection surface 67 of the toner concentration sensor 62 with the elastic sheet 74 as shown in FIG. The developer to be retained is removed and replaced with the developer conveyed immediately thereafter.

  This prevents erroneous detection of the toner concentration that may be caused by the developer staying on the detection surface 67 of the toner concentration sensor 62.

  FIG. 4 (a) shows the configuration of each part in the developing tank 65b in order to easily show the positional relationship between the second stirring and conveying member 17, the cleaning blade 75, and the toner concentration sensor 62 in the developing tank 65b. FIG. 4 is a diagram viewed from the lateral direction indicated by an arrow g in FIG.

  FIG. 4B is an enlarged view of a portion surrounded by a broken line h in FIG. 4 (a) and 4 (b), the inclination of the spiral fin 72 of the second agitating and conveying member 17 is reversed. This is shown in FIG. 4 (b) in FIG. 4 (a). This is because the case is seen from the opposite side of the page.

  4 (a) and 4 (b), the same components as those shown in FIGS. 3 (a) and 3 (b) are assigned the same numbers as those in FIGS. 3 (a) and 3 (b). Show. As shown in FIG. 4A, the toner concentration sensor 62 is arranged with its detection surface 67 exposed so as to protrude slightly into the tank of the developing tank 65b in order to increase detection accuracy.

  However, the inner wall of the tank is gently formed with an inclination in the front, rear, left and right directions from the protruding corner of the detection surface 67 of the toner concentration sensor 62 so that the developer flows smoothly.

  FIG. 5 is a diagram showing an example of the output of the toner density sensor 62 described above. In FIG. 5, the horizontal axis indicates time (second (s)), and the vertical axis indicates the output average (voltage (V)) of the toner density sensor 62. Solid line graphs 76 (76a, 76b, 76c) indicate changes in the output value of the toner density sensor 62.

  Here, in order to explain the output of the toner density sensor 62, the two-component developer is again considered as being divided into carrier and toner. When there is a lot of toner, the magnetic permeability of the two-component developer is lowered and the output value of the magnetic permeability sensor, that is, the toner density sensor 62 is lowered.

  Conversely, when the amount of toner is small, the magnetic permeability of the two-component developer increases and the output value of the magnetic permeability sensor, that is, the toner density sensor 62 increases. For this reason, the output value of the toner density sensor 62 corresponding to the developer density to which the toner is to be replenished is set in advance in, for example, the EEPROM 45 as a replenishment threshold 77 (value indicated by the broken line in FIG. 5).

  Then, after starting printing at time t1 in FIG. 5, the amount of toner decreased at time t2 is detected by an increase in the output value of toner density sensor 62, and YMCK corresponding to the increase in output value of toner density sensor 62 is detected. The toner supply device of any of the developing devices 9 is driven to supply toner to the developing device 9.

  If the output value of the toner density sensor 62 satisfies the replenishment threshold value 77 at time t3, the driving of the toner replenishing device is stopped and toner replenishment is stopped.

  Although not shown in the figure, if the toner concentration falls below a predetermined value (see time t2) and the toner concentration does not increase within a predetermined time (see time t3) even if the toner replenishment operation is performed, the toner It is determined that there is no toner in the hopper 27, and the printing process is stopped.

  Incidentally, the output value of the toner density sensor 62 indicated by the solid line graph 76 (76a, 76b, 76c) in FIG. 5 indicates the average of the output values. Here, the average is to average the values of the pulse signals having a narrow period appearing superimposed on the solid line graph 76 (76a, 76b, 76c) which should be the original output value of the toner density sensor 62.

  FIG. 6A is a diagram showing a pulse signal with a narrow period that appears superimposed on the output signal that should be the original output value of the toner density sensor 62, and FIG. 6B shows the shape of the pulse signal gently. FIG.

  Here, the reason why the pulse signal having the above-described narrow period is generated by being superimposed on the original output value of the toner density sensor 62 will be described.

  As shown in FIG. 3B, the elastic sheet 74 of the cleaning blade 75 moves the detection surface 67 of the toner concentration sensor 62 at a constant period along with the rotation of the rotation shaft 71 of the second stirring and conveying member 17. Rub.

  While the elastic sheet 74 rubs against the detection surface 67, the elastic sheet 74 presses the developer against the detection surface 67, and the density of the developer on the detection surface 67 increases, and the toner density sensor 62 The output value rises slightly.

  Immediately after the sliding of the detection surface 67 by the elastic sheet 74 is completed, the elastic sheet 74 jumps off the developer in the vicinity of the detection surface 67, so that a gap is generated in the vicinity of the detection surface 67 and development on the detection surface 67 is performed. The density of the agent decreases, and the output value of the toner concentration sensor 62 slightly decreases.

  As described above, the detection output value of the toner density sensor 62 periodically changes in accordance with the cycle in which the elastic sheet 74 rubs the detection surface 67 during the stirring operation by the second stirring / conveying member 17. This is a pulse signal 78 having a narrow period shown in FIGS. 6 (a) and 6 (b).

  That is, the Max value 78 a of the pulse signal 78 indicates the timing at which the elastic sheet 74 of the cleaning blade 75 rubs against the detection surface 67 of the toner concentration sensor 62. The Min value 78 b of the pulse signal 78 indicates the timing at which the elastic sheet 74 is separated from the detection surface 67.

  As shown in FIG. 3B, while the elastic sheet 74 rubs the detection surface 67, the elastic sheet 74 is bent and rubs the detection surface 67. When the elastic sheet 74 is away from the detection surface 67 as shown in FIG. 3A, the elastic sheet 74 rotates in an original upright state.

  While the elastic sheet 74 is rubbing the detection surface 67 shown in FIG. 3 (b), the second agitating / conveying member 17 stops, that is, the developing device 14 stops development, that is, it is responsible for drive transmission mechanically. When the photosensitive drum 10 is stopped, the elastic sheet 74 is an elastic body, so that it is forced to be bent for a long period of time and deformed like a curl.

  If the elastic sheet 74 is deformed so as to be bent, the elasticity deteriorates, so that the developer staying on the detection surface 67 of the toner concentration sensor 62 is splattered and replaced with the subsequent developer. Decreases.

  When the rubbing ability of the elastic sheet 74 is lowered, erroneous detection occurs in the detection of the replenishment threshold 77 by the toner density sensor 62. If an erroneous detection occurs in the detection of the replenishment threshold 77, the toner density of the developing device 14 cannot be maintained properly, and the quality of the toner image formed on the photosensitive drum 10 is degraded.

  Therefore, it is necessary to replace the cleaning blade 75. However, it is technically difficult to replace only the cleaning blade 75 in order to maintain the balance with the peripheral members as before, and the second stirring and conveying member. All 17 need to be replaced. In some cases, the developer 14 itself must be replaced. This is uneconomical.

  Therefore, the inventor has proposed that the elastic sheet 74 is not bent and wrinkled. That is, the elastic sheet 74 is not forced to be bent for a long time while rubbing the detection surface 67.

  That is, the photosensitive drum 10 is not stopped when the elastic sheet 74 is in a position where the detection surface 67 is rubbed. In other words, when the photosensitive drum 10 is stopped, when the elastic sheet 74 is away from the detection surface 67, that is, at a timing when the pulse signal 78 indicates the Min value 78b. Is to stop.

  In this way, if the elastic sheet 74 is stopped from the detection surface 67 and the drive of the entire apparatus is stopped, the elastic sheet 74 will not be deformed as if it is bent, and the entire apparatus will not be deformed. The lifetime can be extended.

  FIG. 7 is a flowchart showing a control process performed by the printer controller 40 to stop the photosensitive drum 10 when the elastic sheet 74 is at a timing position where the elastic sheet 74 is away from the detection surface 67.

  In FIG. 7, the printer controller unit 40 (hereinafter simply referred to as the control unit 40) starts printing (step S1). Subsequently, the control unit 40 first reads the output value v of the toner density sensor 62 for each CMYK individually (step S2).

  Next, the control unit 40 calculates an average value (output average value V) of the output values v of the pulse signals 78 of the narrow cycle of the toner density sensor 62 for each CMYK individually read out in the process of step S2, and the calculation. It is determined whether the output average value V is equal to or less than the toner replenishment threshold 77 (step S3).

  If the output average value V of the toner density sensor 62 is equal to or less than the toner replenishment threshold 77 (Yes in S3), the control unit 40 performs a pulse with a narrow cycle of the toner density sensor 62 for each CMYK read in the process of step S2. The period of the output value v of the signal 78 is detected (step S4).

  Next, the control unit 40 determines whether or not printing is complete (no print data from the external host device or a stop instruction from the operation panel unit) (step S5). If the printing is not finished (No in S5), the process returns to step S2 to repeat the processes in steps S2 to S5.

  If the output average value V of the toner density sensor 62 exceeds the toner replenishment threshold 77 in the determination in step S3 (No in S3), the control unit 40 determines the color of the toner with the low toner concentration. Toner supply from one of the toner supply devices (57, 58, 59 or 61) corresponding to YMCK is executed (step S6), the process returns to step S3, and steps S3 and S6 are repeated.

  When the toner density is restored to an appropriate value (Yes in S3), the control unit 40 proceeds again to Steps S4 and S5. If the determination in S5 is No, Steps S2 to S5, or S2, The processes of S6 and S3 to S5 are repeated.

  Eventually, when it is determined in step S5 that printing has ended (YES in S5), the control unit 40 determines the stop position of the photosensitive drum 10 for each YMCK (step S7).

  This process is a process of calculating the timing t closest to the period in which the output value v of the pulse signal 78 of the narrow period of the output value of the toner density sensor 62 for each CMYK detected in step S4 becomes the output Min value 78b. is there.

  Then, the control unit 40 stops the photosensitive drum 10 at a timing when the output value v of the pulse signal 78 having a narrow cycle of the calculated output value of the toner density sensor 62 becomes the output Min value 78b (step S8). End the printing process.

  As described above, according to the present embodiment, the pulse signals having a narrow period superimposed on the output signal of the toner density sensor for detecting the toner replenishment threshold for each color are individually detected, and the sensor output is performed at the period of the pulse signal. The timing at which becomes the Min value is calculated.

  Since the position of the elastic sheet of the cleaning blade when the entire apparatus stops at the timing of the Min value is a position where the bent state is not forced, the entire apparatus is moved at the timing of the Min value every time printing is finished. Stop.

  As a result, the elastic sheet of the cleaning blade is prevented from being deformed as if it is bent, and the toner density can be accurately controlled over a long period of time based on the output of the correct toner density sensor.

  INDUSTRIAL APPLICABILITY The present invention can be used for a developing device used in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile using a two-component developer, a process cartridge including the developing device, and an image forming apparatus.

DESCRIPTION OF SYMBOLS 1 Full color image forming apparatus 2 Image forming part 3 Transfer belt unit 4 Toner supply part 5 Paper feeding part 6 Belt type fixing unit 8 Transfer belt 8a Lower running part surface 9 (9m, 9c, 9y, 9k) Developing device 10 Photosensitive drum DESCRIPTION OF SYMBOLS 11 Cleaner 12 Charging roller 13 Optical writing head 14 Developing device 15 Developing roller 16 1st stirring conveyance member 17 2nd stirring conveyance member 18 Drive roller 19 Followed roller 21 Primary transfer roller 23 Secondary transfer part 24 Belt cleaner 25 Cleaning Blade 26 Waste toner collection container 27 (27m, 27c, 27y, 27k) Toner hopper 29 Paper feed cassette 31 Paper take-out roller 32 Feeding roller 33 Rolling roller 34 Standby conveyance roller pair 35 Secondary transfer roller 36 Diffuse reflection type density sensor 37 Output tray 38 Operation panel 0 printer controller 41 bus 42 network controller 43 I / F (interface)
44 Head Controller 45 EEPROM (electrically erasable programable ROM)
46 ROM (read only memory)
47 Feeding motor 49 Registration sensor 51 DDS (developer drum set: development device) new and old detection sensor 52 High pressure unit 53 Y-drive device 54 M-drive device 55 C-drive device 56 K-drive device 57 Y toner replenishing device 58 M Toner replenishing device 59 C toner replenishing device 61 K toner replenishing device 62 Toner concentration sensor 62y Y toner concentration sensor 62m M toner concentration sensor 62c C toner concentration sensor 62k K toner concentration sensor 63 Outer wall 64 Internal partition wall 65 (65a, 65b) Developer tank 66 Doctor blade 67 Detection surface 68, 71 Rotating shaft 69, 72 Spiral fin 73 Blade holder 74 Elastic sheet (blade)
75 Cleaning blade 76 (76a, 76b, 76c) Average output of toner density sensor (V)
77 Supply threshold 78 Pulse signal 78a Pulse signal Max value 78b Pulse signal Min value

Claims (2)

A developing device for developing with a two-component developer;
An agitating and conveying member disposed in the developing device for agitating and conveying the two-component developer;
A cleaning blade that is fixed to the rotating shaft of the stirring and conveying member and rotates;
Wherein are arranged to expose the sensing surface into the developing device, the is rubbed by the cleaning blade the sensing surface for each revolution of the stirring conveying member, during rubbing outputs an output value at a higher value rubbed After that, a toner concentration detection sensor that outputs a low concentration toner concentration detection signal of a fixed period that outputs an output value at a lower value,
A control device for detecting an output value period of a small-amplitude toner concentration detection signal of the constant period of the toner concentration detection sensor during the agitation conveyance of the two-component developer by the agitation conveyance member;
Have
Wherein the control device further, in the case of stopping the stirring conveying member, based on the output value cycle control device detects, controls to stop at the position of the timing of lower output values Ru output The
An image forming apparatus comprising and this.   The toner density detection sensor is provided for detecting a toner supply threshold value for supplying toner to the developing unit, and the toner density detection signal of the small amplitude with a constant period is supplied by the toner density detection sensor. The image forming apparatus according to claim 1, wherein the image forming apparatus is a signal generated by being superimposed on a toner density detection signal being detected in order to detect a replenishment threshold.