JP2016126297A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately control supply of toner to a developing unit.SOLUTION: A supply controller 110 comprises a band stop filter 113 and a first determination part 114. The band stop filter 113 reduces a long-period ripples that are generated according to a period of circulation of developer caused by screws 58 and 59 in the density of toner detected by a density sensor 20. The first determination part 114 determines a first supply amount R1n on the basis of the density of toner with a long-period ripples reduced by the band stop filter 113. This configuration can accurately control supply of toner to a developing unit 44.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus, and more particularly to replenishment control for maintaining a toner density in a developing device at a target density.

  A developing device that uses a two-component developer including toner and carrier detects the toner concentration with a sensor in order to maintain the toner concentration at a target concentration (Patent Document 1). When the toner is used for image formation, the toner is supplied from the toner tank to the developing device, and the toner and the carrier are stirred by the stirrer.

JP-A-8-110696

  In recent years, there has been a demand for downsizing and reducing the capacity of developing units. When the developing device is downsized, the amount of toner replenished per time with respect to the capacity of the developing device increases, and the toner and the carrier may not be sufficiently stirred. In particular, the toner density output from the sensor is likely to fluctuate immediately after the toner is replenished. This is particularly noticeable in a small developing device. The output value of the sensor converges to the actual toner density over time while repeating increase and decrease. Therefore, if the toner is replenished using the toner density acquired by the sensor when the toner and the carrier are not sufficiently stirred, the toner density cannot be controlled to the target density. Accordingly, an object of the present invention is to control toner replenishment to a developing device with high accuracy.

The present invention is, for example,
Latent image forming means for forming an electrostatic latent image corresponding to the image signal on the image carrier;
Developing means for developing the electrostatic latent image using a developer;
Stirring means for circulating the developer inside the developing means while stirring;
Detecting means for detecting the toner concentration of the developer present in the developing means;
Control means for controlling the replenishment amount of toner to the developing means so that the toner density detected by the detecting means approaches a target density;
Replenishing means for replenishing toner to the developing means according to the replenishment amount;
The control means includes
Filter means for reducing long-cycle ripples generated according to the developer circulation cycle by the stirring means at the toner concentration detected by the detection means;
An image forming apparatus comprising: a first determination unit configured to determine a first supply amount of the supply amount based on the toner density in which the ripple is reduced by the filter unit.

  According to the present invention, it is possible to control toner replenishment to the developing device with high accuracy.

The figure which shows an example of an image forming apparatus Schematic sectional view showing an example of developing device Block diagram showing an example of a replenishment controller Flow chart showing an example of replenishment control Diagram showing an example of the characteristics of the band stop filter A flowchart illustrating an example of a method for determining a replenishment amount based on toner consumption The figure explaining the effect of the averaging part Flow chart showing an example of averaging and mask processing The block diagram which shows the replenishment controller of the comparative example 1. The figure explaining the effect of an Example The figure explaining the effect of an Example

<About image forming apparatus>
The present embodiment can be applied to an image forming apparatus that forms an image on an image carrier using, for example, a photosensitive member or a dielectric by an electrophotographic method or an electrostatic recording method. The image forming apparatus forms a latent image corresponding to an image signal on an image carrier, and develops the latent image by a developing device using a two-component developer to form a visible image (toner image). The two-component developer contains toner particles and carrier particles as main components. The image forming apparatus transfers a visible image onto a transfer material such as paper and fixes the image on the transfer material with a fixing device. In addition, the image forming apparatus may be any product such as a printer, a copier, a multifunction machine, or a facsimile.

  In FIG. 1, an image of a document 31 to be copied is projected onto an image sensor 33 such as a CCD by a lens 32. The image sensor 33 decomposes the image of the document 31 into a large number of pixels and generates a photoelectric conversion signal corresponding to the density of each pixel. The analog image signal output from the image sensor 33 is sent to the image processing circuit 34. The image processing circuit 34 converts the analog image signal into a pixel image signal having an output level corresponding to the density of the pixel for each pixel, and sends it to the pulse width modulation circuit 35. For each input pixel image signal, the pulse width modulation circuit 35 forms and outputs a laser driving pulse having a width (time length) corresponding to the level. A wider driving pulse is generated for a high-density pixel image signal, and a narrower driving pulse is generated for a low-density pixel image signal. The laser driving pulse output from the pulse width modulation circuit 35 is supplied to a semiconductor laser 36 which is a latent image forming unit. The semiconductor laser 36 emits light for a time corresponding to the pulse width. Therefore, the semiconductor laser 36 is driven for a longer time with respect to the high density pixel and is driven with a shorter time for the low density pixel.

  The rotary polygon mirror 37 deflects and scans the laser beam 81 emitted from the semiconductor laser 36. A lens 38 such as an f / θ lens and a fixed mirror 39 spot-form a laser beam 81 on the photosensitive drum 40. Thus, the laser beam 81 scans the photosensitive drum 40 in a direction (main scanning direction) substantially parallel to the rotation axis of the photosensitive drum 40 to form an electrostatic latent image. In addition to the semiconductor laser 36 as in the present embodiment, some latent image forming means uses a light source such as an LED array, and the present invention is also suitably applied to these.

  The photosensitive drum 40 is an example of an image carrier. The photosensitive drum 40 has, for example, a photosensitive layer such as amorphous silicon, selenium, or OPC on its surface and rotates in the direction of the arrow. The photosensitive drum 40 is uniformly charged by the static eliminator 41 and then uniformly charged by the primary charger 42. Thereafter, exposure scanning is performed with a laser beam 81 modulated in accordance with the image signal. As a result, an electrostatic latent image corresponding to the image signal is formed. A developing unit 44 as developing means reversely develops the electrostatic latent image using a two-component developer (developer 43) in which toner particles and carrier particles are mixed to form a visible image (toner image). The reversal development is a development method in which a toner charged with the same polarity as the latent image is attached to a region exposed to the laser beam 81 on the surface of the photosensitive drum 40 to visualize the toner. The transfer charger 49 transfers the toner image to the transfer material 48 held on the carrier belt 47. The endless carrier belt 47 is stretched around the rollers 45 and 46 and driven in the direction of the arrow.

  For the sake of simplicity, only one image forming station (including the photosensitive drum 40, the static eliminator 41, the primary charger 42, the developing device 44, etc.) is illustrated. In the color image forming apparatus, for example, four image forming stations for cyan, magenta, yellow, and black colors are sequentially arranged on the carrier belt 47 along the moving direction thereof. An electrostatic latent image for each color obtained by color-separating the original image on the photosensitive drum of each image forming station is sequentially formed, developed by a developing device having a corresponding color toner, and held and conveyed by a carrier belt 47. The transfer material 48 is sequentially transferred. The transfer material 48 onto which the toner image has been transferred is separated from the carrier belt 47, conveyed to a fixing device (not shown), fixed, and converted into a permanent image. Residual toner remaining on the photosensitive drum 40 after the transfer is removed by the cleaner 50.

  FIG. 1 further shows an oscillator 65, an AND gate 64, and a counter 66 that generate clock pulses for estimating the amount of toner used for image formation. Also shown are a density sensor 20 for detecting the toner density in the developing device 44, an amplifier 21 and the like. The replenishment controller 110 includes a CPU 67 and a storage unit 68 and controls the amount of toner replenishment.

  An example of the developing device 44 will be described with reference to FIGS. 1 and 2. The developing device 44 is disposed so as to face the photosensitive drum 40, and the inside thereof is partitioned into a first chamber (developing chamber) 52 and a second chamber (stirring chamber) 53 by a partition wall 51 extending in the vertical direction. Yes. A nonmagnetic developing sleeve 54 that rotates in the direction of the arrow is disposed in the first chamber 52. The developing sleeve 54 functions as a conveying unit that conveys the developer to the image carrier. A magnet 55 is fixed in the developing sleeve 54. The developing sleeve 54 carries and conveys the two-component developer, and develops the electrostatic latent image by supplying the developer to the photosensitive drum 40 in a developing region facing the photosensitive drum 40. The thickness of the toner layer on the developing sleeve 54 is regulated by a blade 56. In order to improve the development efficiency, that is, the application rate of toner to the latent image, a development voltage obtained by superimposing a DC voltage on an AC voltage is applied to the development sleeve 54 from a power source 57.

  A screw 58 is provided in the first chamber 52. The screw 58 functions as a first circulation means for stirring the two-component developer present in the first chamber 52 and circulating the two-component developer between the first chamber 52 and the second chamber 52. The second chamber 53 is provided with a screw 59. The screw 59 stirs the developer 43 existing in the second chamber 53 and the toner 63 supplied from the toner replenishing tank 60, and removes the developer 43 between the first chamber 52 and the second chamber 53. It functions as a second circulation means for circulation. The screws 58 and 59 also function as a stirring unit that stirs the two-component developer inside the developing device 44. The conveyance screw 62 conveys the toner in the toner replenishing tank 60 while rotating, and supplies the toner from the toner discharge port 61 to the second chamber 53. The screw 59 agitates the toner 63 supplied from the toner replenishing tank 60 and the developer 43 already present in the developing device 44, so that the toner particle concentration (toner concentration) in the developer 43 becomes uniform. The partition wall 51 is formed with a passage (not shown) that allows the first chamber 52 and the second chamber 53 to communicate with each other at the front and back end portions in FIG. The developer 43 in the first chamber 52 consumes toner due to development, and the toner density decreases. The developer 43 in the first chamber 52 is moved from one passage into the second chamber 53 by the screw 58. The developer 43 whose toner concentration has been recovered in the second chamber 53 is moved into the first chamber 52 from the other passage by the screw 59.

  On the bottom wall of the first chamber (developing chamber) 52 of the developing device 44, a density sensor 20 as a toner concentration detecting means is installed. The density sensor 20 is a detecting unit that detects the toner density of the developer 43 existing in the first developing chamber 52 of the developing device 44. The density sensor 20 is an inductance sensor that detects the magnetic permeability of the developer 43. The density sensor 20 outputs a detection value corresponding to the toner density to the replenishment controller 110. The replenishment controller 110 functions as a control unit that controls the amount of toner replenished to the developing device 44 so that the toner density detected by the density sensor 20 approaches the target density.

  The counter 66 is a means for calculating consumed toner by the video count method, and counts the level of the output signal of the image processing circuit 34 for each pixel. An output signal of the pulse width modulation circuit 35 is supplied to one input of the AND gate 64, and a clock pulse from the oscillator 65 is supplied to the other input of the AND gate 64. Therefore, the AND gate 64 outputs a number of clock pulses corresponding to the pulse width of the laser driving pulse, that is, a number of clock pulses corresponding to the density of each pixel. The counter 66 calculates the video count value by accumulating the number of clock pulses for each image (original) (the maximum video count value for the A4 original is 3707 × 106). Thus, the pulse integration signal (video count value) for each image from the counter 66 corresponds to the amount of toner consumed by the developing device 44 in order to form one toner image of the document 31. The video counter such as the counter 66 is not limited to the one synchronized with the laser drive pulse, but various counters such as a counter that directly counts from image data, and any counter can be applied to the present invention.

  The replenishment controller 110 determines the replenishment amount of the toner 63 based on the output of the density sensor 20 and the video count value, and controls the motor 70 as toner replenishment means through the replenishment driver 69. The driving time and the number of driving times of the motor 70 are basically proportional to the replenishment amount. The driving force of the motor 70 is transmitted to the conveying screw 62 via the gear train 71. The conveying screw 62 conveys the toner 63 in the toner replenishing tank 60 and replenishes it to the developing device 44.

<About supply control>
FIG. 3 is a block diagram of the replenishment controller 110 of the embodiment. The supply controller 110 has a band stop filter 113 and a first determination unit 114, among others. The band stop filter 113 is an example of a filter unit that reduces a long-period ripple generated according to the developer circulation cycle by the screws 58 and 59 in the toner density detected by the density sensor 20. The first determination unit 114 is an example of a first determination unit that determines the first supply amount of the supply amount based on the toner density whose long-period ripple is reduced by the band stop filter 113. The other functions shown in FIG. 3 will be described with reference to FIG. The period of the ripple generated according to the developer circulation period is, for example, 30 sec or 60 sec. On the other hand, a short-cycle ripple occurs in the toner density according to the rotation cycle (stirring cycle) of the screws 58 and 59. The period of this ripple is, for example, about 0.1 sec or 0.2 sec. Short period ripples are reduced by the averaging unit 121.

  FIG. 4 is a flowchart showing the operation of the CPU 67. When power is supplied to the image forming apparatus from an external power source and the CPU 67 is activated, the CPU 67 reads out and executes the control program from the ROM of the storage unit 68, thereby realizing various functions as shown in FIG. Each function may be realized by hardware by a logic circuit.

  In step S201, the CPU 67 enters a standby state, and determines whether an image formation request has been received from the operation unit or an external computer. If there is no request for image formation, the process proceeds to S215. In S215, the CPU 67 determines whether or not a power-off instruction has been given from the operation unit. If power-off is not instructed, the process returns to S201. When instructed to turn off the power, the CPU 67 executes shutdown of the image forming apparatus. If there is a request for image formation in S201, the process proceeds to S202.

  In S202, the CPU 67 reads the previous delay calculation variable stored in the RAM of the storage unit 68 and instructs the developer controller 120 to rotate the screws 58 and 59. The developing device controller 120 causes the screw driver 122 to drive the motor 72. The motor 72 rotates the screws 58 and 59.

  In S203, the CPU 67 (difference unit 111) calculates and calculates the difference between the output value of the averaging unit 121 and the target value set by the target value determination unit 112. The averaging unit 121 has a function of smoothing the output of the density sensor 20. The averaging unit 121 functions as a reducing unit that reduces a short-cycle ripple that occurs in the toner density according to the stirring cycle.

In S204, the CPU 67 (band stop filter 113) performs a filter operation on the difference Xn output from the difference unit 111 using the following equation to obtain Yn.
Yn = b0 × Xn + P _n−1 (1)
Pn = b1 * Xn-a1 * Yn + Qn _-1 (2)
Qn = b2 * Xn-a2 * Yn (3)
Here, Xn is the current output value of the difference unit 111. Yn is the current output value of the band stop filter 113. Pn and Qn are the current delay calculation variables. P _n−1 and Q _n−1 are the previous delay calculation variables and are read from the storage unit 68. The CPU 67 stores the delay calculation variables Pn and Qn obtained in this calculation in the storage unit 68 and uses them in the next calculation. The coefficients a1, a2, b0, b1, and b2 are filter coefficients that are determined in advance when the image forming apparatus is designed or shipped from the factory. In this embodiment, Yn is calculated every 0.1 sec.

FIG. 5A is a Bode diagram showing the relationship between frequency and gain for the band stop filter 113. FIG. 5B is a Bode diagram showing the relationship between frequency and phase for the band stop filter 113. FIG. 5 (A) and FIG. 5 (B) show that the input ripple of 30 sec period is reduced. The coefficients for configuring the band stop filter 113 having such characteristics are as follows.
a1 = −1.97723 (4)
a2 = 0.977668 (5)
b0 = 0.990025 (6)
b1 = -1.97723 (7)
b2 = 0.987643 (8)
Thus, these coefficients are determined in advance according to the period of the ripple to be reduced.

  In S205, the CPU 67 (first determination unit 114) determines the first supply amount based on the output value Yn of the band stop filter 113. The first determination unit 114 is a PI controller (proportional / integration controller), and determines the first supply amount R1n by adding the current output value Yn and the accumulated value Tn of the output value up to the previous time.

R1n = g1 × Yn + g2 × Tn (9)
Tn = T _n-1 + Yn (10)
g1 and g2 are gains, which are coefficients set in advance.

In S <b> 206, the CPU 67 (second determination unit 116) inputs the video count value from the counter 66. In S207, the CPU 67 (second determination unit 116) determines the second supply amount R2n by applying a calculation described later to the video count value. In S208, the CPU 67 (summing unit 117) sums the first replenishing amount R1n and the second replenishing amount R2n to obtain a summed value Rn (Rn = R1n + R2n). In S209, the CPU 67 (arithmetic unit 118) adds the total value Rn to the replenishment amount buffer value Bn (Bn = Bn _-1 + Rn). The initial value of the buffer value Bn is, for example, zero.

  In S <b> 210, the CPU 67 determines whether or not an elapsed time after instructing the replenishment driver 69 to replenish last time exceeds a predetermined time. It is assumed that the CPU 67 measures the elapsed time since the replenishment is instructed using a timer or a counter. When the CPU 67 instructs replenishment, the timer is reset to zero. When replenishment is instructed, the replenishment driver 69 drives the motor 70 to rotate the screws 58 and 59 to replenish the toner 63 to the developing device 44. If the elapsed time does not exceed the predetermined time, the process proceeds to S211. If the elapsed time exceeds the predetermined time, the process proceeds to S213. The predetermined time is a time for making the toner density uniform in the developing device 44, and is determined in advance by experiments and simulations. If the next replenishment is executed in a state where the developer 43 and the toner 63 are not sufficiently stirred in the developing unit 44, a portion having a high toner density is locally formed in the developing unit 44. Therefore, the toner density is made uniform by continuing stirring for a predetermined time from the start of replenishment and then permitting replenishment.

  In S211, the CPU 67 (arithmetic unit 118) determines whether or not the buffer value Bn has reached a predetermined unit supply amount r or more. If the buffer value Bn is greater than or equal to the unit supply amount r, the process proceeds to S212. If the buffer value Bn is not equal to or greater than the unit supply amount r, the process proceeds to S213.

  In S212, the CPU 67 (arithmetic unit 118) instructs the supply driver 69 to supply, and subtracts the unit supply amount r from the buffer value Bn. The replenishment driver 69 drives the motor 70 according to the instruction to replenish the toner 63 to the developing device.

  In S213, the CPU 67 determines whether or not the stirring by the screws 58 and 59 is continued. For example, if the image formation according to the image formation request detected in S201 is continued, the CPU 67 determines that stirring should be continued. Further, the CPU 67 determines that stirring should be stopped when the image formation is completed. If stirring is to be continued, the process returns to S203, and the CPU 67 calculates the next difference. When stirring should be stopped, it progresses to S214. In S214, the CPU 67 stores various calculation values (eg, delay calculation variables Pn, Qn, Bn, etc.) in the storage unit 68. The buffer value Bn, the first supply amount R1n, the second supply amount R2n, etc. are reset to zero. Thereafter, the process returns to S201. In this way, a series of processing from S203 to S213 is performed, for example, every 0.1 sec. Therefore, the unit replenishment amount r corresponds to the toner amount replenished every 0.1 sec.

<Method for determining the second supply amount>
In this embodiment, the replenishment amount determination process for feeding back the output value of the concentration sensor 20 is executed at intervals of 0.1 sec during the operation of the screws 58 and 59. However, the video count value is an integrated value per image. If the integrated value is converted into the replenishment amount as it is, the replenishment amount every 0.1 sec becomes excessive. This is because the first supply amount R1n is determined based on the output value of the density sensor 20 output every 0.1 sec. Therefore, the second supply amount R2n determined based on the video count value is also set as the supply amount dispersed every 0.1 sec. Therefore, the second determination unit 116 divides the supply amount based on the video count value into a predetermined number of times and outputs it.

  FIG. 7 is a flowchart showing the operation of the CPU 67 (second determination unit 116). The second determination unit 116 starts calculating the replenishment amount at the same time as the screws 58 and 59 start rotating.

  In S301, the second determination unit 116 reads the previous calculation value from the storage unit 68. In S <b> 302, the second determination unit 116 inputs a video count value (integrated value) from the counter 66. S302 is performed every 0.1 sec while the screws 58 and 59 are rotating, but 0 is input as the video count value until the integration of the video count value per image is completed. When the integration is completed, the integrated value is input once.

  In S303, the second determination unit 116 determines whether the input video count value is zero. If the video count value is 0, the second determination unit 116 proceeds to S307 without changing the current second supply amount. If the video count value is not 0, the process proceeds to S305.

In S305, the second determination unit 116 determines the second supply amount U2k. The second supply amount U2k is determined by the following equation, for example.
U2k = g2 * (U2k _-1 * C + V) / D ... (11)
Here, U2k is the second supply amount determined this time. U2 _k-1 is the second supply amount determined last time. V is an input video count value (integrated value). D is the number of divisions. C is the current value of the division counter. The division counter C is an integer greater than or equal to 0, and the initial value is the division number D. The division counter C is decremented by 1 every 0.1 sec in S308 until it reaches zero.

U2k is updated every time S305 is executed. That is, U2k is not updated until S305 is executed or the count value C becomes zero, and is used as R2n. Incidentally, the next video count value may be input before the first video count value is input and the supply of the corresponding supply amount of toner is completed. That is, it is necessary to carry over the remaining amount of the total supply amount for the first video count value with respect to the supply amount for the next video count value. U2 _k-1 × C means the replenishment amount carried over. For example, if the next video count value is input immediately with respect to the first video count value, C is still a large value, and the majority of the supply amount corresponding to the first video count value is carried forward. It is. If C is zero, the supply amount corresponding to the first video count value is not carried over.

In this way, when the division counter C is not 0, the output of the division replenishment amount for the previous video count value is not completed. Therefore, as shown in the equation (11), the second determining unit 116 adds the remaining supply number (U2 _k−1 × C) and the newly input video count value V, thereby again providing the second supply. The quantity U2k is determined. When the division counter C is 0, the second determination unit 116 determines the second supply amount U2k from the current video count value V. The second supply amount determined here is thereafter used as the second supply amount R2n (R2n = U2k).

In S306, the second determination unit 116 sets the division number D in the division counter C.
C = D (12)
In S307, the second determination unit 116 determines whether the division counter C is zero. If the division counter C is not 0, the division replenishment based on the video count value V is not completed, and the process proceeds to S308. In S308, the second determination unit 116 subtracts 1 from the division counter C. On the other hand, if the division counter C is 0, the division replenishment is completed, and the process proceeds to S309. In S309, the second determination unit 116 sets the second supply amount R2n to 0.

  In S310, the second determination unit 116 outputs the second supply amount R2n to the summation unit 117. In S311, the second determination unit 116 determines whether or not stirring should be continued. The determination method of S311 is the same as that of S213. If stirring is to be continued, the process returns to S302. When stirring should be stopped, it progresses to S312. In S312, the second determination unit 116 causes the storage unit 68 to store the division counter C and the second supply amount R2n.

<Processing with the introduction of the band stop filter>
While the screw 58 is rotating, a ripple having a specific frequency is generated in the detection value of the concentration sensor 20. The frequency of the long period ripple is the reciprocal of the developer circulation period. The band stop filter 113 is provided to reduce the long-period ripple from the detection value of the density sensor 20. Furthermore, a short-cycle ripple corresponding to the stirring cycle (rotation cycle) of the screw 58 is also generated. The ripple period accompanying the developer circulation is about 30 sec, whereas the ripple period accompanying the rotation period is about 0.1 sec. The numerical values of these periods are merely examples. Therefore, means for reducing the short-cycle ripple is also required. While the screw 58 is rotating, the detection value of the concentration sensor 20 is acquired at a predetermined interval.

  FIG. 7A illustrates a detection value D1 of the density sensor 20, a moving average D2 of detection values, and an average value D3 with an initial mask. FIG. 7B is an enlarged view of a portion in FIG. 7A in which the initial mask is applied. 7A and 7B, the solid line indicates the detection value D1 of the density sensor 20. The broken line indicates the moving average D2 of the detected values. The alternate long and short dash line indicates the average value D3 with the initial mask.

  As indicated by the solid lines in FIGS. 7A and 7B, the detection value D1 of the concentration sensor 20 pulsates as the screw 58 rotates. This is because the toner density of the developer 43 detected by the density sensor 20 varies according to the rotation period of the screw 58. Therefore, the averaging unit 121 averages the detection value D1 according to the rotation period of the screw 58, and outputs the average value to the difference unit 111.

  When calculating the replenishment amount for each page, if the averaging is executed with a sufficient margin after the screw 58 starts to rotate, the short-cycle ripple is reduced. However, the band stop filter 113 requires the detection value of the density sensor 20 at a predetermined interval while the screw 58 is rotating. That is, the average value is required immediately after the screw 58 starts to rotate.

  As shown by the broken lines in FIGS. 7A and 7B, when the moving average D2 is simply obtained with respect to the detection value D1 of the density sensor 20, the moving average D2 is obtained at the beginning of the rotation of the screw 58. Does not converge. Therefore, the averaging unit 121 performs the averaging process according to the flow shown in FIG. In particular, the averaging unit 121 performs averaging by masking an unstable region generated over a predetermined period immediately after the rotation of the screw 58 is started. This also brings about an effect that the memory capacity required for the calculation can be reduced. As described above, the averaging unit 121 masks the toner density output from the density sensor 20 over a predetermined period after the operation of the screws 58 and 59 and does not reflect the toner density in the first supply amount R1n. It is.

  The averaging calculation executed by the averaging unit 121 will be described with reference to FIG. The averaging unit 121 starts the averaging calculation when the screws 58 and 59 start to rotate.

  In S <b> 401, the averaging unit 121 reads the last averaged output value (average value) stored when the screws 58 and 59 were stopped last time from the storage unit 68. In S402, the averaging unit 121 sets 0 to the mask counter Cm and the cumulative counter Ca. The mask counter Cm is a counter for managing the detection value D1 of the density sensor 20 that is to be masked. The accumulation counter Ca is a counter for counting how many times the detection value D1 is accumulated. In S403, the averaging unit 121 adds 1 to the cumulative counter Ca. In S404, the averaging unit 121 determines whether or not the mask counter Cm has reached a predetermined value Cmx. The predetermined value Cmx indicates the total number of masked average values. If the mask counter Cm is a predetermined value Cmx, the process proceeds to S406. If the mask counter Cm is not a predetermined value, the process proceeds to S405. In S405, the averaging unit 121 adds 1 to the mask counter Cm.

  In S406, the averaging unit 121 adds (accumulates) the current detection value D1 of the density sensor 20 to the accumulated value Da of the detection value D1. In S407, the averaging unit 121 determines whether or not the cumulative counter Ca has reached a predetermined value Cax. If the cumulative counter Ca has not reached the predetermined value Cax, S408 and S409 are skipped and the process proceeds to S410. The predetermined value Cax is a cumulative total of the detection values D1, and is determined in advance. If the cumulative counter Ca has reached the predetermined value Cax, the process proceeds to S408.

  In S408, the averaging unit 121 sets the cumulative counter Ca to zero. In step S409, it is determined whether the mask counter Cm has reached a predetermined value Cmx. The value of the predetermined value Cmx corresponds to the time from the timing at which the rotation of the screw 58 is started to the timing at which the moving average D2 converges to the final average value D3, as shown in FIG. 7B. If the mask counter Cm does not reach the predetermined value Cmx, an initial fluctuation component remains in the detection value D1, and it should be masked. Therefore, it progresses to S410. If the mask counter Cm has reached the predetermined value Cmx, no initial fluctuation component remains in the detection value D1, and therefore no mask is required. Therefore, it progresses to S411.

  In S410, the averaging unit 121 sets the previous average value D3 'stored in the storage unit 68 as the average value D3 output to the difference unit 111. In S411, the averaging unit 121 divides the accumulated value Da by the predetermined value Cax that is the accumulated number to obtain the average value D3. In S <b> 412, the averaging unit 121 outputs the average value D <b> 3 to the difference unit 111. In S413, the averaging unit 121 determines whether or not stirring should be continued. This is a determination process similar to S213 and S311. If stirring should be continued, the process returns to S403. If stirring should be stopped, the process proceeds to S414. In S414, the averaging unit 121 stores the last average value D3 in the storage unit 68.

  As described above, according to the present embodiment, by adopting the band stop filter 113, it is possible to reduce a long-period ripple generated in the toner density depending on the circulation cycle of the developer. Further, by adopting the averaging unit 121, it is possible to reduce a short period ripple generated in the toner density depending on the stirring period of the screws 58 and 59. Further, by masking the toner density acquired in a predetermined period after the rotation of the screws 58 and 59 from the detected value of the toner density, the influence of the fluctuation component at the initial rotation can be reduced. In addition, it becomes possible to prepare data required for the band stop filter 113 by using the average value D3 'of the past detection values in the predetermined period.

<About Comparative Example 1>
Comparative example 1 will be described in order to explain the effect of the example. In Comparative Example 1, the averaging unit 121 and the band stop filter 113 are omitted from the example.

FIG. 9 is a block diagram of the replenishment controller of the first comparative example. Since the averaging unit 121 is omitted, the difference unit 111 calculates a difference Xn between the detection value D1n from the density sensor 20 and the target value Dt determined by the target value determination unit 112. Since the band stop filter 113 is omitted, the first determination unit 114 is obtained by multiplying the current difference Xn by a predetermined gain g1 and by multiplying the accumulated value Tn of the previous difference by a predetermined gain g2. Is determined as the first supply amount R1n.
R1n = g1 × Xn + g2 × Tn (13)
Tn = T _n-1 + Xn (14)
The second supply amount R2n of Comparative Example 1 is the same as that of the example. The flowchart of the comparative example 1 is obtained by omitting the steps related to the averaging unit 121 and the band stop filter 113 from the flowchart of the embodiment. In other words, the omitted steps are the reading of the variable in S202 and the filter operation in S204.

<About Comparative Example 2>
In the second comparative example, the process of dividing the replenishment amount based on the video count value shown in FIG. That is, the replenishment amount converted from the video count value (integrated value per image) is reflected on the total value at a time. In Comparative Example 2, the other processes except for S207 of the example and the process shown in FIG. 6 are the same as those of the example. That is, the block diagram of Comparative Example 2 is the same as FIG. The mask process shown in FIG. 8 is also used. The second supply amount R2n is calculated by equation (15) when non-zero V is input. When V is zero, the second supply amount R2n is also zero. R2n = g2 × V (15)
<Description of Effect of Supply Control of Example>
The effect of the example will be described by comparing the example with comparative example 1 and comparative example 2. FIG. 10A shows the output value of the density sensor 20 in the embodiment. FIG. 10B shows the output value of the density sensor 20 of Comparative Example 1. Note that an equivalent feedback gain is set for each of the output value of the embodiment and the output value of the comparative example 1. FIG. 10C shows an output value when the gain of the comparative example 1 is lower than that of the example.

  Comparing FIG. 10 (A) and FIG. 10 (B), it can be seen that the embodiment can sufficiently reduce a plurality of ripples having different periods by the averaging process and the filter. That is, in the embodiment, the output value quickly converges to the target value. In Comparative Example 1, since a feedback gain equivalent to that of the embodiment is set, a large ripple occurs in the output value. This is because the toner cannot be sufficiently stirred due to the downsizing of the developing device 44. That is, in the first comparative example, the developer having a non-uniform toner density approaches the detection portion of the density sensor 20. The influence is fed back to the toner replenishment amount, and control oscillation occurs. In order to prevent this oscillation, it is conceivable to lower the feedback gain. However, when the feedback gain is lowered, as shown in FIG. 10C, the ability of the output value to return to the target value is lowered. Therefore, once the output value deviates from the target value due to disturbance, the deviated state continues for a long time.

  On the other hand, in the embodiment, the fluctuation of the output value of the density sensor 20 depending on the developer circulation cycle can be reduced by the band stop filter 113. Moreover, the fluctuation of the output value of the concentration sensor 20 according to the stirring cycle can be reduced by the averaging unit 121. Therefore, in the embodiment, the influence of fluctuation on the feedback control is reduced, and good followability to the target value and good convergence can be realized.

  In the embodiment, the calculation cycle of the band stop filter 113 may be synchronized with the operation of the screw. This means that the calculation cycle of the band stop filter 113 is not affected by the image size.

  FIG. 10D shows the output value of the density sensor of Comparative Example 2. When FIG. 10D is compared with FIG. 10A, in FIG. 10D, there are places where the ripple of the waveform is increased in some places. FIG. 11A shows the sum value output by the summing unit 117 of the embodiment. FIG. 11B shows the replenishment buffer value in the calculation unit 118 of the embodiment. FIG. 11C shows the sum value output by the summing unit 117 of the second comparative example. FIG. 11D shows the replenishment buffer value of the computing unit 118 of the second comparative example.

  In Comparative Example 2, the replenishment amount is calculated in fine steps in synchronism with the operation of the screw as in the embodiment. Therefore, as shown in FIG. 11C, the video count value that is discretely input may be a relatively large value. That is, in Comparative Example 2, an excessive supply amount may occur. This has caused the ripple shown in FIG.

  In contrast, in the embodiment, as shown in FIG. 11A, the video count values are distributed in a balanced manner and reflected in the replenishment amount. For this reason, in the embodiment, as shown in FIG. 10A, the output value of the density sensor 20 changes favorably.

<Summary>
According to the present embodiment, the replenishment controller 110 includes a band stop filter 113 and a first determination unit 114. The band stop filter 113 reduces a long-cycle ripple generated according to the developer circulation cycle by the screws 58 and 59 at the toner concentration detected by the density sensor 20. The first determining unit 114 determines the first supply amount R1n based on the toner density whose long-period ripple is reduced by the band stop filter 113. This makes it possible to control the replenishment of toner to the developing device 44 with high accuracy. In particular, when trying to reduce the size and capacity of the developing device 44, long-period ripples become conspicuous. Therefore, by reducing the long-cycle ripple, toner can be replenished to the developing device 44 with high accuracy. That is, it is possible to achieve both the high accuracy of replenishment, which has been difficult to achieve so far, and the downsizing and low capacity of the developing device 44.

  As described with reference to FIG. 4, the band stop filter 113 is configured to execute a filter operation at predetermined intervals while the screws 58 and 59 are operating, for example. As described with respect to S214 and the like, the replenishment controller 110 has the storage unit 68 that stores the calculation variables used by the band stop filter 113 when the screws 58 and 59 are stopped. As described with respect to S202 and S204, the band stop filter 113 is configured to execute a filter operation using the operation variables Pn and Qn read from the storage unit 68 when the screws 58 and 59 start operating. Yes. As a result, the ripple can be reduced with high accuracy by continuously using the previous calculation variables Pn and Qn.

  The replenishment controller 110 further includes an averaging unit 121 that masks the toner density output from the density sensor 20 over a predetermined period after the operation of the screws 58 and 59 and does not reflect the toner density in the first replenishment amount R1n. May be. As described with reference to FIG. 7, even if the moving average D2 is obtained for the detection value D1 of the density sensor 20, the moving average D2 does not converge to the actual value in a predetermined period after the screws 58 and 59 start operating. . Therefore, by masking the moving average D2 with respect to the detection value D1 for a predetermined period after the operation of the screws 58 and 59, it is possible to control toner supply to the developing device 44 with high accuracy. Become.

  In addition, the averaging unit 121 may function as a reduction unit that reduces a short-cycle ripple generated in the toner concentration according to the stirring cycle of the screws 58 and 59. As described above, the screws 58 and 59 are driven and rotated by the motor to convey the toner while stirring. Therefore, a short cycle ripple corresponding to the rotation cycle of the screws 58 and 59 is generated. Therefore, the averaging unit 121 can reduce the short-cycle ripple, thereby controlling the toner supply to the developing unit 44 with high accuracy.

  As described with reference to FIG. 8, the averaging unit 121 may hold the toner density (for example, the detection value D1 or the average value D3) when the screws 58 and 59 are stopped in the storage unit 68. The averaging unit 121 may reflect the toner concentration held in the storage unit 68 instead of the masked toner concentration in the first supply amount R1n for a predetermined period when the screws 58 and 59 resume operation. Good. The band stop filter 113 needs toner density data as soon as the screws 58 and 59 resume operation. However, no toner density is provided during the mask period. Therefore, the storage unit 68 stores the toner density when the screws 58 and 59 are stopped, and the averaging unit 121 reads and uses them when the rotation of the screws 58 and 59 is resumed. As a result, the toner density (average value) can be supplied to the band stop filter 113 as soon as the screws 58 and 59 resume operation. Since the toner 63 is not replenished while the screws 58 and 59 are stopped, the toner concentration of the developer 43 does not change. Therefore, even if the toner density at the previous replenishment is utilized as the toner density at the current replenishment, the calculation accuracy of the replenishment amount will not decrease so much.

  The averaging unit 121 may function as an averaging unit that calculates an average value of the toner density output from the density sensor 20. In this case, the replenishment controller 110 controls the replenishment amount using the average value of the toner density. The averaging unit 121 may obtain a moving average value of the toner density output from the density sensor 20. Since not so many toner density detection values are required to obtain the moving average value, the storage capacity for holding the toner density detection value can be reduced. Note that the number of samples (the number of detected toner density values) used to calculate the moving average value is set to a number that can reduce the short-cycle ripple.

  As described with reference to FIG. 3, the difference unit 111 may calculate the difference Xn between the toner density (average value) and the target density. In this case, the band stop filter 113 performs a filter operation on the difference Xn regarding the toner concentration to reduce the ripple frequency component among the frequency components included in the difference. The frequency pass characteristic of such a band stop filter 113 is a frequency pass characteristic that reduces the frequency component of the ripple, as shown in FIG. Thus, the coefficient required for the filter operation is determined depending on the ripple frequency.

  As described with reference to FIG. 3, by determining the replenishment amount in consideration of not only the toner density but also the toner consumption amount obtained from the image signal, the toner replenishment amount can be stably controlled. In this case, the counter 66 counts the amount of toner consumed for developing the electrostatic latent image based on the image signal. The second determination unit 116 determines the second supply amount R2n based on the count value of the counter 66. The summation unit 117 sums the first supply amount R1n determined by the first determination unit 114 and the second supply amount R2n determined by the second determination unit 116. The CPU 67, the developing device controller 120, and the toner replenishing tank 60 replenish toner to the developing device 44 based on the sum value of the summing unit 117. As a result, the toner replenishment amount can be stably controlled. The second determination unit 116 may determine the second supply amount R2n by dividing the supply amount obtained by converting the count value into a plurality of parts. The toner consumption per image is not known until the count is completed. If this toner consumption amount is reflected in the replenishment amount at once, the replenishment amount is not stable as described with reference to FIGS. 11C and 11D. This leads to an increase in ripple. Therefore, by dispersing the toner consumption amount per image and reflecting it in the replenishment amount, the replenishment amount is stabilized as described with reference to FIGS. 11A and 11B. That is, the toner density ripple is also reduced.

  Ripple may occur in the developing device 44 that is divided into a developing chamber and a stirring chamber. Therefore, by applying this embodiment, it is possible to control the toner supply to the developing device 44 with high accuracy.

  DESCRIPTION OF SYMBOLS 20 ... Density sensor, 44 ... Developing device, 60 ... Toner supply tank, 67 ... CPU, 68 ... Memory | storage part, 110 ... Supply controller, 113 ... Band stop filter, 114 ... 1st determination part, 116 ... 2nd determination part, 117 ... Summing unit, 121 ... Averaging unit

Claims (11)

Latent image forming means for forming an electrostatic latent image corresponding to the image signal on the image carrier;
Developing means for developing the electrostatic latent image using a developer;
Stirring means for circulating the developer inside the developing means while stirring;
Detecting means for detecting the toner concentration of the developer present in the developing means;
Control means for controlling the replenishment amount of toner to the developing means so that the toner density detected by the detecting means approaches a target density;
Replenishing means for replenishing toner to the developing means according to the replenishment amount;
The control means includes
Filter means for reducing long-cycle ripples generated according to the developer circulation cycle by the stirring means at the toner concentration detected by the detection means;
An image forming apparatus comprising: a first determining unit configured to determine a first supply amount of the supply amount based on the toner density in which the ripple is reduced by the filter unit. The filter means is configured to perform a filter operation at predetermined intervals during the operation of the stirring means,
The control means further includes a storage means for storing a calculation variable used by the filter means when the stirring means is stopped,
2. The image forming apparatus according to claim 1, wherein the filter unit is configured to perform a filter operation using an operation variable read from the storage unit when the agitation unit starts operating. 3. . The control means includes
3. The apparatus according to claim 1, further comprising a mask unit that masks the toner concentration output from the detection unit over a predetermined period after the stirring unit starts operating and does not reflect the toner concentration in the first supply amount. The image forming apparatus described in 1.   The mask means retains the toner concentration when the stirring means stops, and when the stirring means resumes operation, the mask means retains the toner density instead of the masked toner density for the predetermined period. 4. The image forming apparatus according to claim 3, wherein the toner density reflected is reflected in the first supply amount.   5. The image forming apparatus according to claim 1, further comprising a reduction unit configured to reduce a short-cycle ripple generated in the toner density in accordance with a stirring cycle of the stirring unit. The reduction means further includes an averaging means for obtaining an average value of the toner density output from the detection means,
The image forming apparatus according to claim 5, wherein the control unit controls the replenishment amount using an average value of the toner density.   The image forming apparatus according to claim 6, wherein the averaging unit obtains a moving average value of the toner density output from the detection unit. A difference means for calculating a difference between the toner density and the target density;
8. The filter according to claim 1, wherein the filter means performs a filter operation on the difference with respect to the toner density to reduce the long-period ripple included in the difference. The image forming apparatus described. Counting means for counting the amount of toner consumed to develop the electrostatic latent image based on the image signal;
Second determining means for determining a second supply amount based on the count value of the counting means;
A summing means for summing the first supply amount determined by the first determination means and the second supply amount determined by the second determination means;
The image forming apparatus according to claim 1, wherein the replenishing unit replenishes toner to the developing unit based on a sum value of the summing unit.   The image forming apparatus according to claim 9, wherein the second determination unit determines the second supply amount by dividing the supply amount obtained by converting the count value into a plurality of portions. The developing means includes
A first chamber having conveying means for conveying the developer to the image carrier;
A second chamber that communicates with the first chamber and is supplied with toner from the replenishing means;
The stirring means includes
A first circulation means provided in the first chamber for stirring the developer present in the first chamber and circulating the developer between the first chamber and the second chamber;
The developer provided in the second chamber is stirred between the developer present in the second chamber and the toner supplied by the replenishing means, and the developer is placed between the first chamber and the second chamber. 11. The image forming apparatus according to claim 1, further comprising a second circulation unit that circulates the liquid.

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