Image forming apparatus

Abstract

To provide an image forming apparatus that can quickly and accurately detect the concentration of toner in developer even if the amount of developer in a developer tank increases or decreases with respect to a proper amount.SOLUTION: An image forming apparatus comprises: a developer tank 21 that stores developer D including toner T and carrier C; and a toner concentration detection unit 120 that detects the concentration of toner in the developer D in the developer tank 21, and the image forming apparatus adjusts the concentration of toner in the developer D in the developer tank 21 based on an output value from the toner concentration detection unit 120. The image forming apparatus sets in advance a developer weight correction value CV for an increase or decrease in the weight of the developer D in the developer tank 21, and corrects the output value from the toner concentration detection unit 120 based on the developer weight correction value CV.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present disclosure relates to image forming apparatuses such as copiers, multifunction peripherals, printers, and facsimile machines. Background Art

[0002] In an image forming apparatus, when a developer containing toner and a carrier is stored in a developing tank, the image forming apparatus is typically provided with a toner concentration detection unit that detects the toner concentration of the developer in the developing tank, and adjusts the toner concentration of the developer in the developing tank based on an output value from the toner concentration detection unit. That is, when the image forming apparatus detects, based on the output value detected by the toner concentration detection unit, that the toner concentration of the developer is lower than a reference toner concentration serving as a reference, the image forming apparatus increases the toner concentration; when it detects that the toner concentration is higher than the reference toner concentration, the image forming apparatus decreases the toner concentration, thereby adjusting the toner concentration to reach the reference toner concentration.

[0003] In such an image forming apparatus, when the amount of the developer in the developing tank is appropriate, the toner concentration of the developer can be properly detected based on the output value of the toner concentration detection unit. However, when the amount of the developer in the developing tank increases or decreases from the appropriate amount, the original toner concentration cannot be detected with high accuracy. As a result, problems arise where toner is excessively supplied when toner supply to the developing tank should be stopped, leading to an excessively high toner concentration, or toner is not supplied when toner should be supplied to the developing tank, leading to an excessively low toner concentration.

[0004] That is, even if the toner concentration of the developer in the developing tank is the same, when the amount of the developer in the developing tank increases or decreases from the appropriate amount, the output value of the toner concentration detection unit changes. This may cause the toner concentration detection unit to detect that the toner concentration is higher than the reference toner concentration, resulting in the actual toner concentration becoming lower than the original toner concentration, or detect that the toner concentration is lower than the reference toner concentration, resulting in the actual toner concentration becoming higher than the original toner concentration. Prior Art Documents Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-219615 [Overview of the project] [Problems that the invention aims to solve]

[0006] In this regard, Patent Document 1 discloses a configuration in which the permeability of the developer is detected by a permeability sensor attached to a developing container (developing tank) that contains the developer supplied from the developer supply unit, a comparison value indicating the amplitude of the output waveforms to be compared is obtained, the difference between a reference value indicating the amplitude of a reference output waveform and the comparison value is calculated, and if the difference is within a predetermined range, the developer is not supplied to the developer supply unit, and if the difference is outside the predetermined range, the developer is supplied to the developer supply unit.

[0007] However, in the configuration described in Patent Document 1, the toner concentration of the developer is detected when the amount of developer in the developing tank is adjusted to the appropriate level by checking whether or not the developing tank is replenished. Therefore, it takes time for the amount of developer in the developing tank to reach the appropriate level, and during that time, the toner concentration of the developer cannot be detected accurately.

[0008] Therefore, the present disclosure aims to provide an image forming apparatus that can quickly and accurately detect the toner concentration of the developer even when the amount of developer in the developing tank increases or decreases from the appropriate amount. [Means for solving the problem]

[0009] To solve the aforementioned problems, the following first and second embodiments of an image forming apparatus are provided. (1) Image forming apparatus according to the first embodiment An image forming apparatus according to the first embodiment of the present disclosure comprises a developing tank for containing a developer including toner and a carrier, and a toner concentration detection unit for detecting the toner concentration of the developer in the developing tank, wherein the toner concentration of the developer in the developing tank is adjusted based on the output value of the toner concentration detection unit, and further comprises an amplitude detection unit for detecting the amplitude of the output value of the toner concentration detection unit, wherein a developer weight correction value for weight increase or decrease of the developer in the developing tank is set in advance, the developer weight correction value includes an output fluctuation correction value set in advance according to the amplitude, the output fluctuation correction value is set so that the output value of the toner concentration detection unit increases as the amplitude is larger, and decreases as the amplitude is smaller, the weight of the developer is adjusted according to the correction value of the output fluctuation correction value that corresponds to the amplitude detected by the amplitude detection unit, and if the amplitude detected by the amplitude detection unit deviates from a predetermined judgment range, an alarm is issued prompting the replacement of the developer in the developing tank. (2) Image forming apparatus according to the first embodiment An image forming apparatus according to a second embodiment of the present disclosure comprises a developing tank for containing a developer including toner and a carrier, and a toner concentration detection unit for detecting the toner concentration of the developer in the developing tank, wherein the toner concentration of the developer in the developing tank is adjusted based on the output value of the toner concentration detection unit, and further comprises an amplitude detection unit for detecting the amplitude of the output value of the toner concentration detection unit, and a unit for the developer in the developing tank that controls the toner and Biki The device further comprises a supply means for supplying the carrier and a discharge means for discharging the developer, and is characterized in that, if the amplitude detected by the amplitude detection unit deviates from a predetermined determination range, an alarm is issued prompting the replacement of the developer in the developing tank. [Effects of the Invention]

[0010] According to this disclosure, even if the amount of developer in the developing tank increases or decreases from the appropriate amount, it becomes possible to quickly and accurately detect the toner concentration of the developer. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view of the image forming apparatus according to this embodiment, viewed from the front. [Figure 2] Figure 1 is a perspective view of the developing apparatus in the image forming apparatus, taken from the rear side, diagonally above. [Figure 3] This is a cross-sectional view showing a developing apparatus. [Figure 4] This is a cross-sectional view of the developing apparatus along line AA shown in Figure 2. [Figure 5] This is a cross-sectional view of the developing apparatus along the BB line shown in Figure 4. [Figure 6] This is an enlarged cross-sectional view showing one end of the developing apparatus in the longitudinal direction, as shown in Figure 4. [Figure 7] Figure 1 is a system block diagram of the control system, primarily focusing on toner density control, in the image forming apparatus shown. [Figure 8A] Figure 5 is an enlarged cross-sectional view showing a magnified view of the toner concentration detection section of the developing device. [Figure 8B] This is a schematic diagram showing the state of toner and carrier in the developer contained in the developing tank. [Figure 9] This figure shows the first developer weight correction table, which stores job condition correction values ​​as developer weight correction values. [Figure 10A] This graph schematically shows the temporal change in the output value of the toner concentration detection unit when the amount of developer in the developing tank is correct. [Figure 10B] This graph schematically shows the temporal change in the output value of the toner concentration detection unit when the amount of developer in the developing tank exceeds the appropriate amount. [Figure 10C] This graph schematically shows the temporal change in the output value of the toner concentration detection unit when the amount of developer in the developing tank falls below the appropriate level. [Figure 11] This diagram shows a second developer weight correction table, which stores a correction value for output variation as a developer weight correction value. [Figure 12]It is a flowchart showing an example flow of correction control for output values of a toner density detection unit according to the second to fourth embodiments. [Figure 13] It is a flowchart showing the flow of another example of the correction control shown in FIG. 12. MODE FOR CARRYING OUT THE INVENTION

[0012] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[0013] [Image forming apparatus] FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to the present embodiment as viewed from the front. In the drawing, reference sign X represents the left-right direction, reference sign Y represents the depth direction (front-rear direction), and reference sign Z represents the up-down direction (vertical direction).

[0014] The image forming apparatus 100 according to the present embodiment is a color image forming apparatus that forms multicolor and monochromatic images on a recording sheet P such as paper. The image forming apparatus 100 performs image forming processing in accordance with image data read by an image reading device 90 or image data transmitted from the outside. Note that the image forming apparatus 100 may be a color image forming apparatus of another form. Further, the image forming apparatus 100 may be a monochrome image forming apparatus.

[0015] The image forming apparatus 100 includes an image reading device 90 and an image forming apparatus main body 101. The image forming apparatus main body 101 is provided with an image forming unit 102 and a sheet conveyance system 103.

[0016] The image reading device 90 is located on the upper part of the image forming apparatus main body 101. The image reading device 90 reads images from a document (not shown) and comprises a document transport unit 90a and a document reading unit 90b. The image reading device 90 either transports the document in the document transport unit 90a while reading the image of the document in the document reading unit 90b, or scans and reads the document placed on the document tray of the document reading unit 90b. The image of the document read by the image reading device 90 is sent to the image forming apparatus main body 101 as image data.

[0017] The image forming unit 102 includes an exposure device 1 (exposure unit), multiple developing devices 2-2 (developing units), multiple photoreceptor drums 3-3 acting as image carriers, multiple photoreceptor cleaning devices 4-4 (cleaning units), multiple charging devices 5-5, an intermediate transfer belt device 6 (primary transfer device), a secondary transfer device 10 (transfer device), a belt cleaning device 4T (cleaning unit), multiple toner cartridges 15-15, and a fuser device 7 (fusing unit). The sheet transport system 103 includes a paper feed tray 81, an output roller 31, and an output tray 14. The intermediate transfer belt device 6 includes multiple intermediate transfer rollers 65-65 and an intermediate transfer belt 61. The intermediate transfer rollers 65-65 are located inside the intermediate transfer belt 61. The intermediate transfer belt 61 moves circumferentially in a predetermined circumferential movement direction M. The intermediate transfer rollers 65-65 transfer the toner images of each color formed on the surface of the photoreceptor drums 3-3 onto the intermediate transfer belt 61, while rotating in conjunction with the circumferential movement of the intermediate transfer belt 61.

[0018] The photoreceptor cleaning device 4-4 removes toner (waste toner) that remains on the photoreceptor drum 3-3 without being transferred to the intermediate transfer belt 61 using the intermediate transfer rollers 65-65.

[0019] The toner image, which has been transferred from the photoreceptor drums 3 to 3 onto the intermediate transfer belt 61 by the intermediate transfer rollers 65 to 65, is then transferred by the secondary transfer device 10 onto the recording sheet P fed from the paper tray 81.

[0020] The belt cleaning device 4T removes toner (waste toner) that remains on the intermediate transfer belt 61 and was not transferred to the recording sheet P by the secondary transfer device 10.

[0021] The image forming apparatus body 101 is provided with a sheet transport path W1. The sheet supply unit 11a supplies the recording sheet P contained in the paper feed tray 81 to the sheet transport path W1. The sheet transport path W1 guides the recording sheet P to the discharge tray 14 via the transfer roller 10a of the secondary transfer device 10 and the fuser device 7. The fuser device 7 heat-fixes the toner image formed on the recording sheet P by the secondary transfer device 10 to the recording sheet P. The sheet supply unit 11a, a plurality of transport rollers 12a to 12a, a register roller 13, a transfer roller 10a, a fuser roller 71 and a pressure roller 72 in the fuser device 7, and a discharge roller 31 are arranged near the sheet transport path W1.

[0022] In the image forming apparatus 100, sheets are transported from the paper feed tray 81 by the sheet supply unit 11a. The recording sheet P supplied to path W1 is transported via transport rollers 12a to 12a to the register roller 13. Next, the recording sheet P is transported to the transfer roller 10a at the timing when the register roller 13 aligns the recording sheet P with the toner image on the intermediate transfer belt 61, and the toner image is transferred onto the recording sheet P by the transfer roller 10a. After that, the recording sheet P passes through the fixing roller 71 and pressure roller 72 in the fixing device 7, and is discharged onto the discharge tray 14 via transport rollers 12a, 12a and discharge roller 31. If image formation is to be performed on the back surface of the recording sheet P as well as the front surface, the recording sheet P is transported in the reverse direction from the discharge roller 31 to the inverted sheet transport path W2. The recording sheet P is then inverted via inverted transport rollers 12b to 12b and guided back to the register roller 13. Then, the recording sheet P is discharged toward the discharge tray 14 after the toner image is formed and fixed on the back surface in the same way as on the front surface.

[0023] The developing units 2-2 develop the electrostatic latent image on the photoreceptor drums 3-3 using a two-component developer (developer) mainly composed of toner and carrier. The developing units 2-2 supply the non-magnetic toner contained in the two-component developer to the surface of the photoreceptor drums 3-3 by the developing electric field formed between them and the photoreceptor drums 3-3. In this example, the developing units 2-2 are trickle developing units that replace deteriorated carriers with new carriers. The toner cartridges 15-15 contain carriers mixed with toner at a fixed ratio (a ratio smaller than the ratio of toner). The developing units 2-2 replenish toner from the toner cartridges 15-15 along with new carriers into the developing tanks 21-21, while discharging the developer (waste developer) containing deteriorated carriers from the developing tanks 21-21 into a collection container (not shown).

[0024] [Developing equipment] Figure 2 is a perspective view of the developing apparatus 2 in the image forming apparatus 100 shown in Figure 1, viewed from diagonally above the rear side. Figure 3 is a cross-sectional view of the developing apparatus 2. Note that since the multiple developing apparatuses 2-2 all have substantially the same configuration, Figures 2 and 3 show a single developing apparatus 2 as representative.

[0025] The developing apparatus 2 includes a developing tank 21 that contains a developer including toner and a carrier. The developing tank 21 extends in the longitudinal direction (depth direction Y), and has an opening in the developing tank 21 at a position facing the photoreceptor drum 3. The photoreceptor drum 3 is positioned and mounted on a mounting portion 21b (see Figure 2) provided at one end of the developing tank 21 in the longitudinal direction (Y).

[0026] The developing apparatus 2 comprises a developing tank 21, a developing roller 22, a first transport member 23 (first transport screw), and a second transport member 24 (second transport screw).

[0027] The developing roller 22 is a magnetic roller that functions as a developer carrier and is positioned along an opening in the developing tank 21 facing the photoreceptor drum 3. The developing roller 22 comprises a non-magnetic cylindrical sleeve portion (not shown) that is rotatable around a rotation axis α, and a cylindrical magnetic, non-rotatable magnetic roll portion located inside the sleeve portion. Multiple magnetic poles, each with a single polarity, are formed on the circumferential surface of the developing roller 22 by the magnetism of the magnetic roll portion. The developing roller 22 is supported in the developing tank 21 at a position facing the photoreceptor drum 3, with a predetermined distance between it and the photoreceptor drum 3. The developing roller 22 carries developer on its surface, and the sleeve portion rotates in the rotation direction R3 (counterclockwise in Figure 3) around a rotation axis α arranged along the longitudinal direction (Y).

[0028] The developer supported on the surface of the developing roller 22 is restricted to a predetermined thickness by a regulating blade 21a provided in the developing tank 21, and rotates in the rotational direction R4 (clockwise in Figure 3) around the rotational axis β. The photoreceptor drum 3 is rotated and transported to the surface of the photoreceptor drum 3. In the developing region where the photoreceptor drum 3 and the developing roller 22 face each other, the electrostatic latent image formed on the surface of the photoreceptor drum 3 is developed by the toner in the developer.

[0029] The developing tank 21 is provided with a first chamber 21c and a second chamber 21d as circulation chambers. The first chamber 21c and the second chamber 21d are located on one side X1 and the other side X2 in the left-right direction X of the developing tank 21, respectively, and contain the developer. The first chamber 21c and the second chamber 21d form a long space along the longitudinal direction (Y) that contains the developer. The first chamber 21c is provided with a first conveying member 23 that conveys and agitates the developer to one side Y1 (front side) in the longitudinal direction (Y), which is the axial direction of the developing roller 22. The second chamber 21d is provided with a second conveying member 24 that conveys and agitates the developer to the other side Y2 (rear side) in the longitudinal direction (Y). As a result, the first transport member 23 can transport the developer to one side Y1 while agitating it in the first chamber 21c, and the second transport member 24 can transport the developer to the other side Y2, opposite to the transport direction of the first transport member 23, while agitating it in the second chamber 21d.

[0030] As shown in Figure 2, the developing apparatus 2 is equipped with a drive transmission mechanism 26. The drive transmission mechanism 26 comprises a first timing pulley 26a and a second timing pulley 26b, a timing belt 26c, and a drive gear 26d. The first timing pulley 26a and the second timing pulley 26b are fixed to the other end Y2 in the longitudinal direction (Y) of the rotation axes 23a and 24a of the first conveying member 23 and the second conveying member 24, respectively. The timing belt 26c is wrapped around the first timing pulley 26a and the second timing pulley 26b. The drive gear 26d is fixed to the outside in the longitudinal direction (Y) of the second timing pulley 26b, which is provided on the rotation axis 24a of the second conveying member 24. As a result, the second conveying member 24 is rotationally driven via the drive gear 26d, causing the first conveying member 23 to rotate in the opposite direction to the second conveying member 24.

[0031] As shown in Figure 3, the image forming apparatus 100 includes a replenishment unit 40 that supplies toner and carrier contained in the toner cartridge 15 to the developing tank 21. The replenishment unit 40 is in communication with the toner cartridge 15 (see Figure 1) so that toner and carrier flow in from the toner cartridge 15. The replenishment unit 40 includes a storage unit 41 (storage case) and a replenishment roller 42. The storage unit 41 stores the toner and carrier that have flowed in from the toner cartridge 15. An opening 41a is provided at the bottom of the storage unit 41, and a replenishment roller 42 is provided above the opening 41a. The replenishment roller 42 has a roller portion 42b made of a porous material around a rotating shaft 42a. A drive gear 42c is fixed to the other end Y2 in the longitudinal direction (Y) of the rotating shaft 42a. As a result, the supply roller 42 is rotationally driven via a drive gear 42c fixed to the rotating shaft 42a, thereby supplying the toner and carrier stored in the storage section 41 to the developing tank 21.

[0032] Figure 4 is a cross-sectional view of the developing apparatus 2 along line AA shown in Figure 2. Figure 5 is a cross-sectional view of the developing apparatus 2 along line BB shown in Figure 4.

[0033] As shown in Figure 4, the developing tank 21 has a first chamber 21c and a second chamber 21d adjacent to each other, and they are connected to each other via connecting passages 211 and 212 at both ends in the longitudinal direction (Y). That is, a partition wall 21g is provided inside the developing tank 21 that separates the first chamber 21c and the second chamber 21d, and connecting passages 211 and 212 are formed on both sides of the partition wall 21g in the longitudinal direction (Y).

[0034] In the developing apparatus 2 configured in this way, the developer contained in the first chamber 21c is transported in the first transport direction E1 while being agitated by the first transport member 23, passes through the connecting passage 211 provided on one side Y1, and reaches the second chamber 21d from the first chamber 21c. The developer is agitated by the second transport member 24 and transported in the second transport direction E2, passing through the connecting passage 212 provided on the other side Y2, and reaching the first chamber 21c. In this way, the developer is transported in a circulating manner between the first chamber 21c and the second chamber 21d.

[0035] Furthermore, a discharge section 25 is provided at one end Y1 of the first chamber 21c, and a discharge chamber 21f is provided in the discharge section 25. The discharge chamber 21f of the discharge section 25 is in communication with one end Y1 of the first chamber 21c.

[0036] As shown in Figure 5, the discharge section 25 is located at the downstream end of the first chamber 21c in the developer transport direction (first transport direction E1). As shown in Figures 2 and 5, a discharge section cover 251 is provided on the outside of the discharge section 25.

[0037] The discharge section 25 of the developing tank 21 is provided with a discharge port 25a (trickle port) for discharging developer from the developing tank 21 as toner and carrier are replenished. A recovery container (not shown) is connected to the discharge port 25a. The developer contained in the first chamber 21c is gradually discharged from the discharge chamber 21f of the discharge section 25 through the discharge port 25a to the recovery container.

[0038] As shown in Figure 4, the second transport member 24, which is located in the second chamber 21d, comprises a rotating shaft 24a and a helical blade 241. The helical blade 241 is formed in a spiral shape around the rotating shaft 24a. The helical blade 241 rotates together with the rotating shaft 24a to transport the developer in the second chamber 21d in the second transport direction E2.

[0039] In contrast, the first conveying member 23, which is arranged in the first chamber 21c, comprises a rotating shaft 23a extending in the longitudinal direction (Y), a first positive helical blade (first positive blade) 231, a reverse helical blade (reverse blade) 232, and a second positive helical blade (third positive blade) 233. The first positive helical blade 231, the reverse helical blade 232, and the second positive helical blade 233 are formed spirally around the rotating shaft 23a. The reverse helical blade 232 is provided between the first positive helical blade 231 and the second positive helical blade 233, and has a spiral shape that is reversed (reverse wound) in the opposite direction to the first positive helical blade 231, with a smaller pitch than the first positive helical blade 231. The second positive spiral blade 233 has a smaller pitch than the first positive spiral blade 231 and has a spiral shape in the same direction (same winding) as the first positive spiral blade 231. The first positive spiral blade 231, the reverse spiral blade 232, and the second positive spiral blade 233 are all integrally formed with the rotating shaft 23a. The reverse spiral blade 232 provided on the first transport member 23 transports the developer within the reverse spiral blade 232 in a direction that pushes back the developer being sent by the first positive spiral blade 231, thereby reducing the amount of developer sent to the second positive spiral blade 233 that transports the developer to the discharge port 25a. In other words, of the developer that was pushed back by the reverse spiral blade 232, some of the developer that could not be pushed back is discharged little by little from the discharge port 25a. In other words, the developer circulating between the first chamber 21c and the second chamber 21d by the first transport member 23 and the second transport member 24 is discharged at a constant rate from the outlet 25a in small amounts regulated by the reverse spiral vane 232. Meanwhile, a predetermined amount of carrier is supplied from the replenishment unit 40, so the amount of carrier in the developing tank 21 is controlled to remain constant. Therefore, after a predetermined time has elapsed, the carrier in the developing tank 21 is replaced, preventing image defects caused by carrier deterioration.

[0040] From this point onward, we will describe the detailed structure for discharging a certain amount of developer from this outlet 25a.

[0041] Figure 6 is an enlarged cross-sectional view showing an enlarged view of one end Y1 in the longitudinal direction (Y) of the developing apparatus 2 shown in Figure 4.

[0042] The first transport member 23 includes a first forward transport section 2310, a reverse transport section 2320, and a second forward transport section 2 It comprises 330 and a boundary portion 2340.

[0043] The first forward transport section 2310, the reverse transport section 2320, the boundary section 2340, and the second forward transport section 2330 are provided in this order toward one side Y1 in the longitudinal direction (Y) on one side X1 in the left-right direction X of the developing tank 21.

[0044] In addition to the first chamber 21c, the developing tank 21 is also equipped with a reverse transport chamber 21e and a discharge chamber 21f.

[0045] The first forward conveying section 2310 consists of a first chamber 21c and a first forward helical blade 231. The first forward helical blade 231 is located in the first chamber 21c. The reverse conveying section 2320 consists of a reverse conveying chamber 21e and a reverse helical blade 232. The reverse helical blade 232 is located in the reverse conveying chamber 21e. The reverse conveying chamber 21e is located at one end of the first chamber 21c in the longitudinal direction (Y) and communicates with the first chamber 21c. The second forward conveying section 2330 consists of a discharge chamber 21f and a second forward helical blade 233. The second forward helical blade 233 is located in the discharge chamber 21f. The discharge chamber 21f is located at one end of the reverse conveying chamber 21e in the longitudinal direction (Y) and communicates with the reverse conveying chamber 21e. Furthermore, the boundary portion 2340 is a space consisting only of the rotating shaft 23a, which does not have spiral blades.

[0046] The first forward transport unit 2310 transports the developer in the first chamber 21c toward the reverse transport unit 2320 in the first transport direction E1 (one side Y1) using the first forward spiral blade 231. The reverse transport unit 2320 applies a transport force to the developer in the reverse transport chamber 21e between the first chamber 21c and the discharge chamber 21f using the reverse spiral blade 232 toward the first forward transport unit 2310 in the second transport direction E2 (the other side Y2), which is opposite to the first transport direction E1. The second forward transport unit 2330 transports the developer in the discharge chamber 21f toward the discharge port 25a in the first transport direction E1 (one side Y1) using the second forward spiral blade 233.

[0047] The first forward spiral blade 231, the second forward spiral blade 233, and the reverse spiral blade 232 have fewer spiral strands in this order. The developer enters between these spiral blades, and the spiral blades form the flow of the developer. Therefore, the more spiral strands there are, the greater the transport force of the developer can be.

[0048] Furthermore, the inverted helical blade 232 has a small-diameter portion 2321 on the side of the first positive conveying section 2310 and a large-diameter portion 2322 on the side of the boundary portion 2340. The small-diameter portion 2321 has a first outer diameter. The large-diameter portion 2322 has a second outer diameter that is larger than the first outer diameter of the small-diameter portion 2321. That is, the inverted helical blade 2322 has the small-diameter portion 2321 provided on the upstream side of the conveying direction of the developer from the first positive conveying section 2310 (first conveying direction E1), and the large-diameter portion 2322 is provided connected to the downstream side of the small-diameter portion 2321. Moreover, the first outer diameter of the small-diameter portion 2321 is smaller than the outer diameter of the first positive helical blade 231, and the second outer diameter of the large-diameter portion 2322 is larger than the outer diameter of the first positive helical blade 231.

[0049] Furthermore, a gap G is provided between the inverted spiral blades 232 and the developing tank 21. This allows the developer to pass through the inverted spiral blades 232 and flow into the discharge chamber 21f via the boundary portion 2340.

[0050] The outer diameter of the second positive helical blade 233 is smaller than the outer diameter of the first positive helical blade 231 and the reverse helical blade 232. In the first conveying member 23, the difference between the outer diameters of the first positive helical blade 231, the reverse helical blade 232 and the second positive helical blade 233 and the outer diameter (shaft diameter) of the rotating shaft 23a is related to the area of ​​the first positive helical blade 231, the reverse helical blade 232 and the second positive helical blade 233. Therefore, the larger the outer diameters of the first positive helical blade 231, the reverse helical blade 232 and the second positive helical blade 233, the better the development. The transport capacity of the agent increases.

[0051] <Developer development process> In the developing apparatus 2 described above, when performing the developer development operation (trickle development operation), the first transport member 23 and the second transport member 24 are rotated in the forward rotation direction R1 (R11, R12). As a result, the developer is transported in the first transport direction E1 by the first forward spiral blade 231 in the first forward transport section 2310 of the first transport member 23 in the first chamber 21c, reaches the communication passage 212, and circulates between the first chamber 21c and the second chamber 21d. In this state, in the developing area where the photoreceptor drum 3 and the developing roller 22 face each other, the electrostatic latent image formed on the surface of the photoreceptor drum 3 is developed by the toner in the developer. When toner is consumed by this development operation and the toner density falls below the reference toner, toner and carrier are replenished. In addition, a portion of the developer that reaches the reverse transport section 2320 is transported in the first transport direction E1 by the first forward spiral blade 231 and flows into the reverse transport chamber 21e. The developer that flows into the reverse transport chamber 21e passes through the gap G against the transport force in the second transport direction E2 acting on the developer by the reverse spiral blades 232 in the reverse transport section 2320 in the reverse transport chamber 21e, and enters the discharge chamber 21f of the second forward transport section 2330 in the first transport direction E1. The developer that enters the discharge chamber 21f is transported in the first transport direction E1 by the second forward spiral blades 233 in the second forward transport section 2330 of the first transport member 23 in the discharge chamber 21f, and is discharged from the discharge port 25a. In this way, a certain amount of developer can be discharged from the discharge port 25a of the discharge chamber 21f in conjunction with the replenishment of toner and carrier. Thus, the developer development operation is performed.

[0052] <Developer discharge operation> Furthermore, the developing device 2 can perform a forced discharge operation of the developer. In this case, the first transport member 23 and the second transport member 24 are rotated in the reverse direction R2 (R21, R22). As a result, the developer is transported in the first transport direction E1 by the spiral blades 241 of the second transport member 24 in the second chamber 21d and reaches the connecting passage 212. A portion of the developer that reaches the connecting passage 212 moves to the reverse transport chamber 21e, where a transport force in the first transport direction E1 is applied by the reverse spiral blades 2320 of the reverse transport section 2320 as the developer moves to the boundary section 2340, where the developer accumulates. When a predetermined amount of developer has accumulated in the boundary section 2340, the rotation of the first transport member 23 and the second transport member 24 is stopped and they are rotated in the forward direction R1 (R11, R12). As a result, the developer accumulated in the boundary section 2340 is transported in the discharge chamber 21f in the first transport direction E1 by the second positive helical blade 233 in the second positive transport section 2330 of the first transport member 23, and discharged from the discharge port 25a. By repeating this series of operations, the desired amount of developer can be discharged from the developing tank 21. Thus, the developer discharge operation is performed. Here, the discharge section 25 is composed of a reverse transport section 2320, a second positive transport section 2330, and a boundary section 2340.

[0053] (Embodiment) Figure 7 is a system block diagram of the control system, primarily focusing on toner density control, in the image forming apparatus 100 shown in Figure 1.

[0054] The image forming apparatus 100 includes a control unit 110, a toner density detection unit 120 (sensor), a first drive unit 130, and a second drive unit 140.

[0055] The control unit 110 is responsible for controlling the entire image forming apparatus 100. The control unit 110 has a processing unit 111 and a storage unit 112. The processing unit 111 consists of a microcomputer such as a CPU. The storage unit 112 includes non-volatile memory such as ROM and volatile memory such as RAM. The control unit 110 controls the operation of various components by loading a control program, which is pre-stored in the ROM of the storage unit 112, onto the RAM of the storage unit 112 and executing it.

[0056] The toner concentration detection unit 120 detects the toner concentration of the developer in the developing tank 21. Specifically, the toner concentration detection unit 120 detects the toner concentration in the developing tank 21 while the developer is being agitated.

[0057] Figure 8A is an enlarged cross-sectional view showing the toner density detection unit 120 portion of the developing apparatus 2 shown in Figure 5. Figure 8B is a schematic diagram showing the state of toner T and carrier C in the developer D contained in the developing tank 21.

[0058] As shown in Figure 8A, the toner density detection unit 120 is located on the bottom surface 21h of the developing tank 21 (in this example, on the side of the discharge port 25a (Y1) in the longitudinal direction (Y) of the position corresponding to the first transport member 23 in the first chamber 21c).

[0059] As shown in Figure 8B, the developer D contains toner T and carrier C. Here, the toner concentration can be exemplified by the ratio of the weight of toner T to the weight of developer D (so-called T / D). The standard toner concentration is not limited to this, but can be, for example, around 6% to 8%.

[0060] As shown in Figure 7, the toner density detection unit 120 is electrically connected to the input system of the control unit 110 and transmits a toner density signal related to the toner density of the toner density detection unit 120 to the control unit 110. As a result, the control unit 110 can detect the toner density from the output value of the toner density detection unit 120.

[0061] The rotational drive shaft of the first drive unit 130 (drive motor) is connected to a drive gear 42c fixed to the rotational shaft 42a of the replenishment roller 42 in the replenishment unit 40. This allows the first drive unit 130 to rotate the replenishment roller 42. The first drive unit 130 is electrically connected to the output system of the control unit 110 and receives instruction signals from the control unit 110. This allows the control unit 110 to control the operation of the first drive unit 130. Therefore, the control unit 110 can perform toner and carrier replenishment operations.

[0062] The rotational drive shaft of the second drive unit 140 (drive motor) is connected to a drive gear 26d fixed to the rotational shaft 24a of the second transport member 24 in the developing tank 21. As a result, the second drive unit 140 rotates the second transport member 24, and, in conjunction with the rotation of the second transport member 24, rotates the first transport member 23 in the opposite direction to the second transport member 24 via the drive transmission mechanism 26. That is, when the second drive unit 140 is driven to rotate in the forward rotation direction R1, it rotates the first transport member 23 and the second transport member 24 in the forward rotation directions R11 and R12, respectively, and when it is driven to rotate in the reverse rotation direction R2, it rotates the first transport member 23 and the second transport member 24 in the reverse rotation directions R21 and R22, respectively. The second drive unit 140 is electrically connected to the output system of the control unit 110 and receives instruction signals from the control unit 110. As a result, the control unit 110 can control the operation of the second drive unit 140. Therefore, the control unit 110 can perform trickle development of the developer D and forced discharge of the developer D.

[0063] The control unit 110 adjusts the toner concentration of the developer D in the developing tank 21 using the replenishment unit 40 based on the output value of the toner concentration detection unit 120.

[0064] In other words, based on the output value detected by the toner density detection unit 120, the control unit 110 increases the toner density if it detects that the toner density of the developer D is lower than the standard toner density (e.g., 7%), and decreases the toner density if it detects that it is higher than the standard toner density (e.g., 7%), adjusting the toner density so that it becomes the standard toner density.

[0065] In this example, the toner density detection unit 120 is a permeability sensor that detects the permeability of the developer D. Specifically, as the carrier density in the developer D increases, the output value (output voltage) of the toner density detection unit 120 increases. Conversely, as the carrier density in the developer D decreases, the output value (output voltage) of the toner density detection unit 120 decreases.

[0066] Specifically, when the control unit 110 detects that the output value (output voltage) of the toner concentration detection unit 120 during the stirring operation of the developer D is higher than a reference output value (reference output voltage), it recognizes that the toner concentration of the developer D is lower than the reference toner concentration and drives the first drive unit 130 to replenish toner T and carrier C to the developing tank via the replenishment unit 40. On the other hand, when the control unit 110 detects that the output value of the toner concentration detection unit 120 is lower than the reference output value, it recognizes that the toner concentration of the developer D is higher than the reference toner concentration and stops driving the first drive unit 130 to stop the replenishment of toner T and carrier C to the developing tank via the replenishment unit 40. In this state, the toner concentration can be adjusted to the reference toner concentration by consuming toner T through the printing operation.

[0067] Incidentally, in the image forming apparatus 100, if the amount of developer D in the developing tank 21 is appropriate (for example, about 200g), the control unit 110 can appropriately detect the toner concentration of the developer D (for example, 7%) based on the output value of the toner concentration detection unit 120. However, even if the amount of toner T in the developer D in the developing tank 21 is the same, if the amount of carrier C in the developing tank 21 increases or decreases relative to the appropriate amount [for example, if the fluidity of the developer D deteriorates over time or for some reason, a predetermined amount of developer D will no longer be discharged from the discharge port 25a, causing the amount of developer D in the developing tank 21 (especially the amount of carrier C) to increase or decrease relative to the appropriate amount], even if the control unit 110 attempts to replenish the toner to bring the toner concentration of the developer D in the developing tank 21 to an appropriate value based on the output value of the toner concentration detection unit 120, it may not be able to correct the toner concentration to the appropriate value, resulting in image defects.

[0068] In other words, when the amount of developer D in the developing tank 21 increases or decreases from the appropriate amount (for example, to about 250g or 150g), the control unit 110 is unable to accurately detect the original toner concentration. As a result, when the supply of toner T to the developing tank 21 should be stopped, toner T is excessively supplied, resulting in a high toner concentration, or when toner T should be supplied to the developing tank 21, toner T is not supplied, resulting in a low toner concentration.

[0069] In this embodiment, the memory unit 112 has a developer weight correction value CV pre-set (stored) for changes in the weight of the developer D in the developing tank 21. Here, the developer weight correction value CV is a value used to correct the value detected by the toner density detection unit 120 when the amount of developer D in the developing tank 21 differs from the appropriate amount, and can be determined in advance through experiments or other means.

[0070] The control unit 110 corrects the output value of the toner density detection unit 120 based on the developer weight correction value CV set in the storage unit 112. Then, the control unit 110 adjusts the toner density based on the corrected output value.

[0071] According to this embodiment, the output value of the toner concentration detection unit 120 is corrected based on the developer weight correction value CV, and the toner concentration is adjusted based on the corrected output value. This effectively prevents the developer D containing toner T from being excessively supplied to the developing tank 21, causing the amount of developer D in the developing tank 21 to exceed the appropriate amount, or prevents the amount of developer D containing toner T from being insufficiently supplied to the developing tank 21, causing the amount of developer D in the developing tank 21 to be less than the appropriate amount.

[0072] (First Embodiment) Depending on the job conditions for image formation, the weight of the developer D in the developing tank 21 is likely to increase or decrease. Examples of such job conditions include process speed, operating environment (specifically ambient humidity), average print yield, and developer life. Job conditions can be a combination of one or more of the following (all of them in this example): process speed, operating environment (specifically ambient humidity), average print yield, and developer life. Here, the process speed can be exemplified by the number of copies per minute (CPM) of a predetermined size (e.g., A4 size) printed per unit time. The average print yield PR can be calculated by dividing the toner print area [i.e., the average print area per page obtained by dividing the total print area of ​​all jobs printed in the past (e.g., the area calculated from the pixel count) by the current total number of printed pages (e.g., A4 equivalent)] Sb by the area Sa of the recording sheet used for printing (Pr = Sb / Sa × 100 [%]). Furthermore, the developer life DL can be exemplified by the developer usage rate (=PN / AL × 100[%]) calculated by dividing the current number of printed pages PN (count value) since the initial printing or the last time developer D was replaced by the number of pages AL (lifetime) of developer D.

[0073] In this embodiment, the control unit 110 includes a job condition detection unit P1. The job condition detection unit P1 detects predetermined job conditions. The developer weight correction value CV includes a preset job condition correction value CV1 according to the job conditions. Here, the predetermined job conditions are job conditions that are likely to cause an increase or decrease in the weight of the developer D, and include, for example, the process speed, operating environment, average print density, and developer life mentioned above. Furthermore, the job condition correction value CV1 is determined in advance by experimenting with various process speeds and / or operating environments (specifically ambient humidity), and determining a correction value such that when the toner density is set to a standard toner density (e.g., 7%), the output value of the toner density detection unit 120 becomes the standard output value at various developer lives and / or average print densities. The job condition correction value CV1 includes 0 (no correction), positive values, and negative values.

[0074] The image reading device 90 is electrically connected to the input system of the control unit 110 and transmits image data corresponding to the read image to the control unit 110. This allows the control unit 110 to perform predetermined image processing on the image data read by the document reading unit 90b.

[0075] Furthermore, the image forming apparatus 100 is equipped with various transport detection units 50 (transport sensors) provided in the sheet transport system 103, and a humidity detection unit 60 (humidity sensor) that detects the ambient humidity of the image forming apparatus 100.

[0076] The transport detection unit 50 is electrically connected to the input system of the control unit 110 and transmits a transport status signal to the control unit 110 regarding whether or not the detected recording sheet P has been transported. This allows the control unit 110 to detect whether or not the recording sheet P has been transported to the sheet transport system 103 or the transport timing of the recording sheet P. The humidity detection unit 60 is electrically connected to the input system of the control unit 110 and transmits a humidity signal to the control unit 110 regarding the detected ambient humidity. This allows the control unit 110 to detect the ambient humidity of the image forming apparatus 100.

[0077] Figure 9 is a diagram showing the first developer weight correction table TB1, in which the job condition correction value CV1 is stored as the developer weight correction value CV.

[0078] As shown in Figure 9, the control unit 110 corrects the output value of the toner density detection unit 120 based on the correction value corresponding to the job condition detected by the job condition detection unit P1 from among the job condition correction values ​​CV1.

[0079] For example, in the job conditions detected by the job condition detection unit P1, the process speed PS is low (L), ambient humidity RH is standard (M), average print density PR is low (1), and developer life DL. If the latter half (2) is the case, the control unit 110 reads the correction value LM12 from the job condition correction value CV1 and adds the correction value LM12 to the output value of the toner density detection unit 120.

[0080] Furthermore, if the job conditions detected by the job condition detection unit P1 are high speed PS (H), low ambient humidity RH (L), medium average print density PR (2), and initial developer life DL (0), the control unit 110 reads the correction value HL2 from the job condition correction value CV1 and adds the correction value HL2 to the output value of the toner density detection unit 120.

[0081] The control unit 110 then adjusts the toner density (executes the operation) based on the corrected output value (the measured value plus the corrected value).

[0082] In this way, even if the job conditions change, the output value of the toner density detection unit 120 is corrected based on the correction value corresponding to the job conditions detected by the job condition detection unit P1 among the job condition correction values ​​CV1. Therefore, even if the amount of developer D in the developing tank 21 increases or decreases from the appropriate amount, the toner density of the developer D can be detected quickly and with greater accuracy.

[0083] In the example in Figure 9, all combinations of process speed PS, ambient humidity RH, average print density PR, and developer life DL are shown, but one or at least two of these combinations may be used.

[0084] By the way, in this embodiment, when the developer D is discharged from the outlet 25a of the discharge section 25 of the developing tank 21, the internal pressure inside the developing tank 21 changes according to the process speed PS. That is, the faster the process speed PS, the easier it is for the internal pressure inside the developing tank 21 to rise, so the developer D is more easily discharged from the outlet 25a of the developing tank 21. As a result, the amount of developer D in the developing tank 21 tends to decrease more than the appropriate amount, and as a result, the output value of the toner density detection unit 120 tends to decrease. On the other hand, the slower the process speed PS, the harder it is for the internal pressure inside the developing tank 21 to rise, so it is more difficult to discharge the developer D from the developing tank 21. As a result, the amount of developer D in the developing tank 21 tends to increase more than the appropriate amount, and as a result, the output value of the toner density detection unit 120 tends to increase.

[0085] In this embodiment, the job condition detection unit P1 detects job conditions including the process speed PS. For example, the job condition detection unit P1 can store the process speed PS in the storage unit 112 beforehand and detect the process speed PS by reading the process speed PS stored in the storage unit 112. Alternatively, the job condition detection unit P1 may detect the process speed PS by having the transport timing of the transported record sheet P detected by the transport detection unit 50.

[0086] Here, in the process speed PS shown in Figure 9, although not limited to these, examples of low speed (L) ranges include less than 40 CPM for A4 size, medium speed (M) ranges include 40 CPM or more and less than 70 CPM for A4 size, and high speed (H) ranges include 70 CPM or more for A4 size.

[0087] The job condition correction value CV1 is set so that the output value of the toner density detection unit 120 increases as the process speed PS increases, and decreases as the process speed PS decreases. Specifically, the job condition correction value CV1 is set to 0 when the process speed PS is the reference process speed. The job condition correction value CV1 is set to a positive value that increases as the process speed PS is faster than the reference process speed. This correction allows the output value of the toner density detection unit 120 to increase as the process speed PS is faster than the reference process speed. Also, the absolute value of the job condition correction value CV1 increases as the process speed PS is slower than the reference process speed. It is set to a negative value. This correction allows the output value of the toner density detection unit 120 to be reduced as the process speed PS slows down compared to the reference process speed.

[0088] By doing so, even if the developer D in the developing tank 21 decreases more easily than the appropriate amount when the process speed PS is fast, a decrease in the output value of the toner concentration detection unit 120 can be effectively prevented, and therefore the value can be maintained at the appropriate level, thereby improving the detection accuracy of the toner concentration of the developer D. On the other hand, even if the developer D in the developing tank 21 increases more easily than the appropriate amount when the process speed PS is slow, an increase in the output value of the toner concentration detection unit 120 can be effectively prevented, and therefore the value can be maintained at the appropriate level, thereby improving the detection accuracy of the toner concentration of the developer D.

[0089] Furthermore, the fluidity of the developer D changes depending on the ambient humidity RH (ambient environment) of the image forming apparatus 100. As a result, the weight of the developer D in the developing tank 21 changes. Specifically, the lower the ambient humidity RH, the higher the fluidity of the developer D, making it easier for the developer D to be discharged from the outlet 25a of the developing tank 21. Consequently, the amount of developer D in the developing tank 21 tends to decrease more than the appropriate amount, and as a result, the output value of the toner density detection unit 120 tends to decrease. On the other hand, the higher the ambient humidity RH, the lower the fluidity of the developer D, making it difficult to discharge the developer D from the developing tank 21. Consequently, the amount of developer D in the developing tank 21 tends to increase more than the appropriate amount, and as a result, the output value of the toner density detection unit 120 tends to increase.

[0090] In this embodiment, the job condition detection unit P1 detects job conditions including ambient humidity RH. For example, the job condition detection unit P1 can detect the ambient humidity RH of the image forming apparatus 100 by detecting the ambient humidity RH of the image forming apparatus 100 using the humidity detection unit 60.

[0091] Here, in the ambient humidity RH shown in Figure 9, examples of low humidity (L) ranges include less than 35%, standard (M) ranges include 35% or more and less than 60%, and high humidity (H) ranges include 60° or more.

[0092] The job condition correction value CV1 is set so that the output value of the toner concentration detection unit 120 increases as the ambient humidity RH decreases, and decreases as the ambient humidity RH increases. Specifically, the job condition correction value CV1 is set to 0 when the ambient humidity RH is the reference ambient humidity. The job condition correction value CV1 is set to a positive value that increases as the ambient humidity RH is lower than the reference ambient humidity. This correction allows the output value of the toner concentration detection unit 120 to increase as the ambient humidity RH is lower than the reference ambient humidity. Also, the job condition correction value CV1 is set to a negative value that increases in absolute value as the ambient humidity RH is higher than the reference ambient humidity. This correction allows the output value of the toner concentration detection unit 120 to decrease as the ambient humidity RH is higher than the reference ambient humidity.

[0093] By doing so, even if the amount of developer D in the developing tank 21 decreases more easily than the appropriate amount when the ambient humidity RH is low, a decrease in the output value of the toner concentration detection unit 120 can be effectively prevented, and therefore the value can be maintained at the appropriate level, thereby improving the detection accuracy of the toner concentration of the developer D. On the other hand, even if the amount of developer D in the developing tank 21 increases more easily than the appropriate amount when the ambient humidity RH is high, an increase in the output value of the toner concentration detection unit 120 can be effectively prevented, and therefore the value can be maintained at the appropriate level, thereby improving the detection accuracy of the toner concentration of the developer D.

[0094] Furthermore, the fluidity of the developer D changes according to the average print density PR of the image formed by the image forming apparatus 100. In other words, the higher the average print density PR, the more frequently the toner is replaced. Because the developer D has high fluidity, it is easily discharged from the discharge port 25a of the developing tank 21. As a result, the amount of developer D in the developing tank 21 tends to decrease below the appropriate level, and consequently, the output value of the toner density detection unit 120 tends to decrease. On the other hand, the lower the average print density PR, the more easily the carrier deteriorates, and the less fluid the developer D becomes, making it difficult to discharge the developer D from the developing tank 21. As a result, the amount of developer D in the developing tank 21 tends to increase above the appropriate level, and consequently, the output value of the toner density detection unit 120 tends to increase.

[0095] In this embodiment, the job condition detection unit P1 detects job conditions including the average print rate PR. For example, the job condition detection unit P1 constantly updates (stores) the average print rate PR calculated based on the image data read by the image reading device 90 in the storage unit 112, and can detect the average print rate PR by reading the average print rate PR stored in the storage unit 112. In other words, since the average print rate of images formed in the past is stored, the current state of the developer in the developing tank 21 can be predicted from there.

[0096] In the average print coverage ratio PR shown in Figure 9, examples of low (1) ranges include less than 3%, medium (2) ranges include 3% or more and less than 10%, and high (3) ranges include 10% or more.

[0097] The job condition correction value CV1 is set so that the output value of the toner density detection unit 120 increases as the average print density PR increases, and decreases as the average print density PR decreases. Specifically, the job condition correction value CV1 is set to 0 when the average print density PR is the reference average print density. The job condition correction value CV1 is set to a positive value that increases as the average print density PR is higher than the reference average print density. This correction allows the output value of the toner density detection unit 120 to increase as the average print density PR is higher than the reference average print density. Also, the job condition correction value CV1 is set to a negative value that increases in absolute value as the average print density PR is lower than the reference average print density. This correction allows the output value of the toner density detection unit 120 to decrease as the average print density PR is lower than the reference average print density.

[0098] By doing this, even if the developer D in the developing tank 21 decreases more easily than the appropriate amount when the average print density PR is high, a decrease in the output value of the toner density detection unit 120 can be effectively prevented, and therefore the value can be maintained at the appropriate level, thereby improving the detection accuracy of the toner density of the developer D. On the other hand, even if the developer D in the developing tank 21 increases more easily than the appropriate amount when the average print density PR is low, an increase in the output value of the toner density detection unit 120 can be effectively prevented, and therefore the value can be maintained at the appropriate level, thereby improving the detection accuracy of the toner density of the developer D.

[0099] Furthermore, in the first developer weight correction table TB1, each correction value may be further subdivided according to the average print density PR. This can further improve the accuracy of the correction.

[0100] Furthermore, the fluidity of the developer D changes according to the developer life DL of the image forming apparatus 100. As a result, the weight of the developer D in the developing tank 21 changes. Specifically, the smaller the developer life DL, the less the carrier deteriorates and the higher the fluidity of the developer D, making it easier for the developer D to be discharged from the outlet 25a of the developing tank 21. Consequently, the amount of developer D in the developing tank 21 tends to decrease more than the appropriate amount, and as a result, the output value of the toner density detection unit 120 tends to decrease. On the other hand, the larger the developer life DL, the more the carrier deteriorates and the lower the fluidity of the developer D, making it difficult to discharge the developer D from the developing tank 21. Consequently, the amount of developer D in the developing tank 21 tends to increase more than the appropriate amount, and as a result, the output value of the toner density detection unit 120 tends to increase.

[0101] In this embodiment, the job condition detection unit P1 detects job conditions including developer life DL. For example, the job condition detection unit P1 calculates the developer life DL of the transported record sheet P from the current number of printed sheets PN and the number of durable sheets AL of the developer D, which were detected by the transport detection unit 50 at the time of initial printing or replacement of the developer D. The calculated developer life DL is constantly updated (stored) in the storage unit 112, and the developer life DL can be detected by reading the developer life DL stored in the storage unit 112.

[0102] Here, in the developer life DL shown in Figure 9, although not limited to these, examples include the initial (0) range being less than 30%, the middle (1) range being 30% or more and less than 60%, and the later (3) range being 60% or more.

[0103] The job condition correction value CV1 is set so that the output value of the toner density detection unit 120 increases as the developer life DL decreases, and decreases as the developer life DL increases. Specifically, the job condition correction value CV1 is set to 0 when the developer life DL is the standard developer life. The job condition correction value CV1 is set to a positive value that increases as the developer life DL is smaller than the standard developer life. This correction allows the output value of the toner density detection unit 120 to increase as the developer life DL is smaller than the standard developer life. Also, the job condition correction value CV1 is set to a negative value that increases in absolute value as the developer life DL is larger than the standard developer life. This correction allows the output value of the toner density detection unit 120 to decrease as the developer life DL is larger than the standard developer life.

[0104] By doing this, the smaller the developer life DL, the more easily the amount of developer D in the developing tank 21 decreases below the appropriate amount, but the decrease in the output value of the toner concentration detection unit 120 can be effectively prevented, and therefore the value can be maintained at the appropriate level, thereby improving the detection accuracy of the toner concentration of the developer D. On the other hand, the larger the developer life DL, the more easily the amount of developer D in the developing tank 21 increases below the appropriate amount, but the increase in the output value of the toner concentration detection unit 120 can be effectively prevented, and therefore the value can be maintained at the appropriate level, thereby improving the detection accuracy of the toner concentration of the developer D.

[0105] Furthermore, in the first developer weight correction table TB1, each correction value may be further subdivided according to the developer life DL, similar to the average print density PR. This can further improve the accuracy of the correction.

[0106] (Second Embodiment) Figures 10A to 10C are schematic graphs showing the temporal change in the output value of the toner density detection unit 120 when the amount of developer D in the developing tank 21 is appropriate, when the amount of developer D in the developing tank 21 is greater than appropriate, and when the amount of developer D in the developing tank 21 is less than appropriate, respectively. The horizontal axis represents time, and the vertical axis represents the output value of the toner density detection unit 120, which fluctuates over time. This is because the toner density detection unit 120 detects the density of carrier C in the developer D, and outputs a higher value the higher the density of carrier C. However, when the outer circumference of the first spiral blade 231 of the first transport member 23 approaches the toner density detection unit 120, the amount of developer D in the region facing the toner density detection unit 120 becomes the smallest (the amount of carrier C also becomes the smallest), resulting in the lowest value. When the first transport member 23 rotates and the region facing the toner density detection unit 120 is between the first spiral blades 231, the amount of developer D becomes the largest (the amount of carrier C also becomes the largest), resulting in the highest value. In other words, the output value of the toner density detection unit 120 fluctuates according to the longitudinal pitch (spacing) of the first spiral blade 231 of the first transport member 23. Normally, an average value is calculated to cancel out this fluctuation, and the calculated value is set to a preset value (as mentioned above). When the output value of the toner density detection unit 120 exceeds the reference output value, the control unit 110 drives the second drive unit 140 to supply toner to the developing tank 21. When the output value of the toner density detection unit 120 falls below a preset value (the aforementioned reference output value), the control unit 110 stops the second drive unit 140 and stops supplying toner to the developing tank 21, thereby performing toner replenishment control.

[0107] As shown in FIG. 10B, as the amount of developer D in the developing tank 21 increases beyond an appropriate amount (for example, 200 g) (see FIG. 10A) (for example, when it reaches 250 g), the amount of carrier increases. Therefore, the average value Va of the output values (voltage values) of the toner density detection unit 120 is higher than the average value Vs of the output values when the amount of developer D is appropriate (see FIG. 10B) (Va>Vs), and the amplitude value Wa (W) of the output value of the toner density detection unit 120 is smaller than the reference amplitude value Ws that serves as a reference when the amount of developer D is appropriate (see FIG. 10B) (Wa<Ws). That is, as the amount of developer D in the developing tank 21 increases beyond the appropriate amount, the amplitude degree of the output value of the toner density detection unit 120 decreases.

[0108] On the other hand, as shown in FIG. 10C, as the amount of developer D in the developing tank 21 decreases below the appropriate amount (for example, 200 g) (see FIG. 10A) (for example, when it reaches 150 g), the amount of carrier decreases. Therefore, the average value Vb of the output values (voltage values) of the toner density detection unit 120 is lower than the average value Vs of the output values when the amount of developer D is appropriate (see FIG. 10B) (Vb<Vs), and the amplitude value Wb (W) of the output value of the toner density detection unit 120 is larger than the reference amplitude value Ws when the amount of developer D is appropriate (see FIG. 10B) (Wb>Ws). That is, as the amount of developer D in the developing tank 21 decreases below the appropriate amount, the amplitude degree of the output value of the toner density detection unit 120 increases. In other words, by focusing on the amplitude degree of the detection value of the toner density detection unit 120, the amount of developer D in the developing tank 21 can be estimated (determined).

[0109] Therefore, in the present embodiment, the output value of the toner density detection unit 120 is corrected by using the amplitude degree of the output value of the toner density detection unit 120. As described above, whether to perform toner supply is determined based on a preset value (reference output value). Therefore, in order to achieve appropriate toner supply timing with respect to this preset value, the output value of the toner density detection unit 120 is corrected according to the amount of developer D in the developing tank 21 (the output value itself before averaging is corrected, and adjustment is performed so that the reference output value corresponds to appropriate timing).

[0110] More specifically, the image forming apparatus 100 includes an amplitude detection unit P2 that detects the amplitude of the output value of the toner density detection unit 120. The amplitude detection unit P2 detects the amplitude of the output value of the toner density detection unit 120 when toner density is detected, and detects the ratio of this amplitude to a reference amplitude value Ws, which is the amplitude of the output value of the toner density detection unit 120 when the developer D is in the correct amount, as the amplitude.

[0111] The developer weight correction value CV includes a preset output variation correction value CV2, which is set according to the amplitude.

[0112] Figure 11 is a diagram showing the second developer weight correction table TB2, in which the output variation correction value CV2 is stored as the developer weight correction value CV.

[0113] As shown in Figure 11, the control unit 110 corrects the output value of the toner density detection unit 120 based on the correction value corresponding to the amplitude detected by the amplitude detection unit P2 among the output fluctuation correction values ​​CV2. In Figure 11, the output fluctuation correction values ​​CV2 are all negative values ​​when the weight of developer D increases, and the negative correction values ​​increase in absolute value as the weight of developer D increases, that is, as the amplitude decreases (|A1|<|A2|<|A3|). Also, the output fluctuation correction values ​​CV2 are all positive values ​​when the weight of developer D decreases, and the positive correction values ​​increase as the weight of developer D decreases, that is, as the amplitude increases ( B1 <B2<B3)である。

[0114] For example, if the amplitude detection unit P2 detects an amplitude of 75%, the control unit 110 reads a correction value A2 (a negative value) from the output fluctuation correction value CV2 and adds the correction value A2 (a negative value) to the output value of the toner density detection unit 120.

[0115] Furthermore, if the amplitude detected by the amplitude detection unit P2 is 160%, the control unit 110 reads a correction value B3 (positive value) from the output fluctuation correction value CV2 and adds the correction value B3 (positive value) to the output value of the toner density detection unit 120.

[0116] The control unit 110 then adjusts the toner density based on the corrected output value (the measured value plus the corrected value).

[0117] According to this embodiment, the output value of the toner concentration detection unit 120 is corrected based on a correction value corresponding to the amplitude degree detected by the amplitude degree detection unit P2 among the amplitude degrees of the output value of the output fluctuation correction value CV2. In other words, the output value of the toner concentration detection unit 120 is corrected while correctly recognizing the amount of developer D in the developing tank 21. This effectively prevents the amount of developer D in the developing tank 21 from exceeding the appropriate amount due to excessive supply of developer D including toner T to the developing tank 21, or from being not supplied with developer D including toner T to the developing tank 21, resulting in a lower amount of developer D in the developing tank 21. Moreover, since the output value of the toner concentration detection unit 120 is directly detected and corrected, the detection accuracy of the toner concentration of the developer D can be further improved.

[0118] In this embodiment, the output fluctuation correction value CV2 is set so that the output value of the toner density detection unit 120 increases as the amplitude is larger, and decreases as the amplitude is smaller. Specifically, the output fluctuation correction value CV2 is set to 0 when the amplitude is at the reference amplitude. The output fluctuation correction value CV2 is set to a positive value that increases as the amplitude is greater than the reference amplitude (as the weight of developer D decreases). This correction allows the output value of the toner density detection unit 120 to increase as the amplitude is greater than the reference amplitude. Also, the output fluctuation correction value CV2 is set to a negative value that increases in absolute value as the amplitude is smaller than the reference amplitude (as the weight of developer D increases). This correction allows the output value of the toner density detection unit 120 to decrease as the amplitude is smaller than the reference amplitude.

[0119] By doing this, the larger the amplitude, the more effectively it is possible to prevent a decrease in the output value of the toner concentration detection unit 120 even if the amount of developer D in the developing tank 21 is less than the appropriate amount, and therefore it can be maintained at the appropriate value, thereby improving the detection accuracy of the toner concentration of the developer D. On the other hand, the smaller the amplitude, the more effectively it is possible to prevent an increase in the output value of the toner concentration detection unit 120 even if the amount of developer D in the developing tank 21 is more than the appropriate amount, and therefore it can be maintained at the appropriate value, thereby improving the detection accuracy of the toner concentration of the developer D.

[0120] In this embodiment, the amplitude detection unit P2 detects the amplitude degree based on the amplitude ratio Rp (=W / Ws × 100 [%]) (PP ratio) between the amplitude value W (Peak-Peak) of the output value of the toner density detection unit 120 and the reference amplitude value Ws (reference peak-peak). The reference amplitude value Ws is the amplitude value of the output value of the toner density detection unit 120 when the amount of developer D in the developing tank 21 is appropriate (initial state of a new developer). The reference amplitude value Ws when the amount of developer D in the developing tank 21 is appropriate (initial state of a new developer) is stored in advance in the storage unit 112.

[0121] This allows for reliable detection of amplitude using a simple configuration, such as calculating the amplitude ratio Rp.

[0122] Incidentally, the control unit 110 can detect that the amount of developer D in the developing tank 21 is less than the appropriate amount when the amplitude (amplitude ratio Rp) is large, and can detect that the amount of developer D in the developing tank 21 is more than the appropriate amount when the amplitude (amplitude ratio Rp) is small.

[0123] In this embodiment, the control unit 110 adjusts the weight of the developer D according to the correction value corresponding to the amplitude detected by the amplitude detection unit P2 among the output fluctuation correction values ​​CV2.

[0124] In this way, the control unit 110 can adjust the weight of the developer D according to a correction value corresponding to the amplitude detected by the amplitude detection unit P2, thereby forcibly increasing or decreasing the amount of developer D in the developing tank 21 and returning the amount of developer D to the appropriate level. Here, the toner density detection unit 120 constantly monitors the toner density. Therefore, the control unit 110 can detect the fluctuation in the weight of the developer adjusted according to the correction value, which in turn causes a fluctuation in the amplitude (amplitude ratio Rp), and then perform feedback control to ensure that the weight of the developer returns to the appropriate level. This ensures that the weight of the developer is reliably maintained at the appropriate level, and therefore, the toner density of the developer D can be accurately detected without correcting the output value of the toner density detection unit 120 (corrected with a correction value of 0).

[0125] In this embodiment, the developing tank 21 is provided with a discharge section 25 for discharging the developer D. The control unit 110 performs a developer D discharge operation, discharging the developer D from the discharge section 25 (discharge port 25a). Furthermore, if the control unit 110 needs to reduce the weight of the developer D in the developing tank 21, it forcibly performs the developer D discharge operation.

[0126] This allows the developer D in the developing tank 21 to be discharged from the discharge unit 25. As a result, if the amount of developer D in the developing tank 21 exceeds the appropriate amount, the discharge operation of the developer D can quickly reduce the amount of excess developer D in the developing tank 21 to the appropriate amount or close to the appropriate amount. This allows the control unit 110 to accurately detect the toner concentration of the developer D in the developing tank 21 when the amount of developer D in the developing tank 21 is at or close to the appropriate amount.

[0127] (Third embodiment) In this embodiment, the image forming apparatus 100 includes a supply unit 40 for supplying toner and carrier to the developing tank 21. The control unit 110 performs a toner and carrier supply operation to supply toner and carrier from the supply unit 40 to the developing tank 21. Furthermore, if the weight of the developer D in the developing tank 21 is to be increased, the control unit 110 forcibly performs the toner and carrier supply operation.

[0128] This allows the developer D in the developing tank 21 to be replenished from the replenishment unit 40. As a result, if the amount of developer D in the developing tank 21 falls below the appropriate level, the amount of developer D in the developing tank 21 can be quickly increased by the toner and carrier replenishment operation to bring it to the appropriate level or close to the appropriate level. This allows the control unit 110 to accurately detect the toner concentration of the developer D in the developing tank 21 when the amount of developer D is at or close to the appropriate level.

[0129] (Fourth Embodiment) By the way, if the control unit 110 reduces the weight of the developer D in the developing tank 21, Even if the developer D is forcibly discharged, or if the weight of the developer D in the developing tank 21 is increased, or if the toner and carrier are forcibly replenished, if the amplitude detected by the amplitude detection unit P2 deviates from a predetermined judgment range, there is a high possibility that the developer D in the developing tank 21 is deteriorating.

[0130] In this embodiment, the control unit 110 issues an alarm (developer replacement alert) prompting the user to replace the developer D in the developing tank 21 if the amplitude detected by the amplitude detection unit P2 deviates from a predetermined judgment range. For example, a message such as "Please replace the developer." can be displayed on the display unit and / or an audio message can be generated from the voice generation unit.

[0131] (Control example 1 of this embodiment) Figure 12 is a flowchart showing an example of the flow of correction control of the output value of the toner concentration detection unit 120 according to the second to fourth embodiments.

[0132] In the control example shown in Figure 12, the control unit 110 detects the amplitude value of the output value of the toner density detection unit 120 (S1), and calculates the amplitude ratio Rp (amplitude degree) by dividing the amplitude value of the output value of the toner density detection unit 120 by the reference amplitude value of the output value of the toner density detection unit 120 (S2).

[0133] Next, if the amplitude ratio Rp is 60% or less (S3a), the control unit 110 refers to a correction value corresponding to the amplitude ratio Rp in the output fluctuation correction value CV2 (S4a) and performs a correction (weight correction) of the output value of the toner density detection unit 120 (S5a).

[0134] If the amplitude ratio Rp is greater than 60% and less than or equal to 95% (S3b), the control unit 110 refers to a correction value corresponding to the amplitude ratio Rp in the output fluctuation correction value CV2 (S4b) and performs weight correction of the output value of the toner density detection unit 120 (S5b).

[0135] If the amplitude ratio Rp is greater than 95% and less than or equal to 105% (S3c), the control unit 110 either performs weight correction on the output value of the toner density detection unit 120 with a correction value of 0, or does not perform weight correction on the output value of the toner density detection unit 120 (S5c).

[0136] If the amplitude ratio Rp exceeds 105% and is 150% or less (S3d), the control unit 110 refers to a correction value corresponding to the amplitude ratio Rp in the output fluctuation correction value CV2 (S4d) and performs weight correction of the output value of the toner density detection unit 120 (S5d).

[0137] Furthermore, if the amplitude ratio Rp exceeds 150% (S3e), the control unit 110 refers to a correction value corresponding to the amplitude ratio Rp in the output fluctuation correction value CV2 (S4e) and performs weight correction of the output value of the toner density detection unit 120 (S5e).

[0138] Then, the control unit 110 adjusts the toner density based on the corrected output value of the toner density detection unit 120 (S6).

[0139] (Control example 2 of this embodiment) Figure 13 is a flowchart showing another example of the correction control shown in Figure 12. In the flowchart shown in Figure 13, the same reference numerals are used for processes that are the same as those in the flowchart shown in Figure 12, and the explanation will focus on the differences from the processes in the flowchart shown in Figure 12.

[0140] In the control example shown in Figure 13, the control unit 110 performs an discharge operation for a specified time (S7a) if the amplitude ratio Rp is 60% or less (S3a), and determines whether the amplitude ratio Rp is above a predetermined lower limit amplitude ratio (S8a). If (S8a:No), a developer replacement alert is issued (S9a), and the system proceeds to S6. However, if the amplitude ratio Rp is greater than or equal to a predetermined minimum amplitude ratio (S8a:Yes), the system proceeds to S4a.

[0141] If the amplitude ratio Rp is greater than 60% but less than or equal to 95% (S3b), the control unit 110 performs the discharge operation for a specified time (S7b) and then proceeds to S4b.

[0142] If the amplitude ratio Rp is greater than 105% but less than or equal to 150% (S3d), the control unit 110 performs a replenishment operation for a specified time (S7d) and then proceeds to S4d.

[0143] If the amplitude ratio Rp exceeds 150% (S3e), the control unit 110 performs a replenishment operation for a specified time (S7e) and determines whether the amplitude ratio Rp is below a predetermined upper limit amplitude ratio (S8e). If the amplitude ratio Rp exceeds the predetermined upper limit amplitude ratio (S8e: No), the control unit 110 issues a developer replacement alert (S9e) and proceeds to S6. On the other hand, if the amplitude ratio Rp is below a predetermined maximum amplitude ratio (S8e: Yes), it proceeds to S4e.

[0144] This disclosure is not limited to the embodiments described above, and can be implemented in a variety of other ways. Therefore, these embodiments are merely illustrative in all respects and should not be constrained. The scope of this disclosure is defined by the claims and is not restricted by the text of the specification. Furthermore, any variations or modifications falling within the equivalent scope of the claims are all within the scope of this disclosure. [Explanation of symbols]

[0145] 100 Image forming apparatus 110 Control Unit 111 Processing Unit 112 Storage section 120 Toner density detection unit 130 First drive unit 140 Second drive unit 2. Developing device 21 Developer tank 23 First conveying member 231 First spiral blade 2310 First forward conveying section 232 Reverse spiral feather 2320 Reverse Conveying Section 233 Second spiral blade 2330 Second forward transport section 2340 Boundary 23a Rotation axis 24 Second conveying member 241 Spiral Feather 24a Rotation axis 25 Discharge section 25a Outlet 26 Drive transmission mechanism 40 Supply Department 41 Storage Unit 41a aperture 42 Supply Roller 50 Transport detection unit 60 Humidity detection unit 90 Image reading device C Career CV developer weight correction value CV1 Correction values ​​for job conditions CV2 Correction value for output fluctuation D Developer DL Developer Life E1 First conveying direction E2 Second transport direction P1 Job Condition Detection Unit P2 Amplitude detection unit PN Print Count PR average printing rate PS process speed R1 Forward rotation direction R2 reverse rotation direction RH Ambient humidity Rp amplitude ratio T Toner TB1 First Developer Weight Correction Table TB2 Second Developer Weight Correction Table W Amplitude Value Wa Amplitude Value Wb Amplitude Value Ws Reference Amplitude Value X Left / right direction Y (depth direction) Z vertical direction α rotation axis β Rotation axis

Claims

1. An image forming apparatus comprising a developing tank for containing a developer including toner and a carrier, and a toner concentration detection unit for detecting the toner concentration of the developer in the developing tank, wherein the toner concentration of the developer in the developing tank is adjusted based on the output value of the toner concentration detection unit, The toner concentration detection unit is equipped with an amplitude detection unit that detects the amplitude of the output value of the toner concentration detection unit, A developer weight correction value for changes in the weight of the developer in the developing tank is set in advance. The developer weight correction value includes a preset output variation correction value according to the amplitude degree. The output fluctuation correction value is set such that the output value of the toner concentration detection unit increases as the amplitude is larger, and decreases as the amplitude is smaller. The weight of the developer is adjusted according to the correction value corresponding to the amplitude degree detected by the amplitude degree detection unit among the output fluctuation correction values. An image forming apparatus characterized in that, if the amplitude detected by the amplitude detection unit deviates from a predetermined judgment range, an alarm is issued prompting the replacement of the developer in the developing tank.

2. An image forming apparatus according to claim 1, The image forming apparatus is characterized in that the amplitude detection unit detects the amplitude degree based on the amplitude ratio between the amplitude value of the output value of the toner concentration detection unit and a reference amplitude value.

3. An image forming apparatus comprising a developing tank for containing a developer including toner and a carrier, and a toner concentration detection unit for detecting the toner concentration of the developer in the developing tank, wherein the toner concentration of the developer in the developing tank is adjusted based on the output value of the toner concentration detection unit, An amplitude detection unit for detecting the amplitude of the output value of the toner concentration detection unit, The developing tank further comprises a supplying means for supplying toner and carrier to the developer, and a discharge means for discharging the developer, An image forming apparatus characterized in that, if the amplitude detected by the amplitude detection unit deviates from a predetermined judgment range, an alarm is issued prompting the replacement of the developer in the developing tank.

4. An image forming apparatus according to claim 3, A developer weight correction value for changes in the weight of the developer in the developing tank is set in advance. The developer weight correction value includes a preset output variation correction value according to the amplitude degree. An image forming apparatus characterized by adjusting the weight of the developer according to a correction value corresponding to the amplitude degree detected by the amplitude degree detection unit among the output fluctuation correction values.

5. An image forming apparatus according to claim 3, If the amplitude detected by the amplitude detection unit deviates from a predetermined determination range, as control to return the state of the developer in the developing tank to the determination range, a replenishment operation by the replenishment means and / or a discharge operation by the discharge means are performed according to predetermined conditions, and after the execution of the replenishment operation and / or the discharge operation, the amplitude is detected again. An image forming apparatus characterized by providing an alarm prompting the replacement of the developer in the developing tank if the amplitude continues to deviate from the determination range.

6. An image forming apparatus according to claim 5, An image forming apparatus characterized in that, when increasing the weight of the developer in the developing tank, the replenishment operation of the toner and the carrier is forcibly performed.

7. An image forming apparatus according to claim 5, An image forming apparatus characterized in that, when the weight of the developer in the developing tank is reduced, the discharge operation of the developer is forcibly performed.

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