Printing device

Abstract

The present invention provides a printing device. The printing device comprises: a powder storage chamber for storing powder containing a color material and a carrier; a supply and conveying unit for conveying the powder while supplying the powder to a powder holder that holds the powder by forward rotation; a detection unit for detecting the amount of powder in the powder storage chamber at a position above a rotation axis of the supply and conveying unit, downstream in the conveying direction of the supply and conveying unit, and upstream in the conveying direction of a discharge portion that discharges excess powder; and a control unit for controlling at least one of the rotational direction and rotational speed of the supply and conveying unit based on the detection result of the detection unit.

Description

Technical Field

[0001] The present invention relates to a printing device. Background Art

[0002] A color image forming device is known, which is composed of a developing roller and a developer arranged below a photosensitive belt, wherein the developing roller has a magnetic roller on the inner side of a rotating sleeve, and the developer has a developer storage box, which is divided into a developer attachment chamber and a developer replenishing chamber by a developer scraper plate below the developing roller, and the developer is circulated between the two chambers by a stirring screw, wherein the color image forming device is constructed so that a non-magnetic area is formed on the opposite surface of the developer replenishing chamber side of the magnetic roller surface, and a developer discharge outlet is provided at the starting end of the developer replenishing chamber, and the stirring screw can be reversed when the developer is discharged (refer to Japanese Patent Gazette No. 4-37774).

[0003] Also known is an image forming device comprising: a developing device; a detection unit that detects information related to the colorant consumption of an output image; and a replenishing unit that replenishes the developer into a developing container based on the information related to the colorant consumption, wherein the developing device comprises: an image retaining member that forms an electrostatic latent image; a developing container that accommodates a two-component developer containing a colorant and a carrier; a developer retaining member that retains and conveys the two-component developer to convert the electrostatic latent image into a toner image; a developer conveying unit that is provided in the developing container and conveys and circulates the two-component developer accommodated in the developing container; and a discharge port that is provided in the developing container and is used to discharge the two-component developer accommodated in the developing container, wherein the image forming device comprises a control unit that controls so that, when the colorant consumption of one or more sheets detected by the detection unit exceeds a predetermined threshold value, the conveying speed of the developer conveying unit is faster than when the toner consumption does not exceed the predetermined threshold value (see Japanese Patent Application Laid-Open No. 2012-163628). Summary of the Invention

[0004] The purpose of the present invention is to stabilize the amount of powder containing color material and carrier in a powder supply device without reducing the productivity of image formation, compared to the case where the amount of powder containing color material and carrier is stabilized by performing action through pre-detection in a powder supply device having a powder discharge mechanism.

[0005] According to the first embodiment of the present invention, a printing device is provided, wherein the printing device comprises: a powder storage chamber for storing powder containing a color material and a carrier; a supply and conveying unit for conveying the powder while supplying the powder to a powder retaining body that retains the powder by forward rotation; a detection unit for detecting the amount of the powder in the powder storage chamber at an upper portion of the rotation axis of the supply and conveying unit, downstream in the conveying direction of the supply and conveying unit and upstream in the conveying direction of a discharge portion that discharges the remaining powder; and a control unit for controlling at least one of the rotation direction and the rotation speed of the supply and conveying unit based on the detection result of the detection unit.

[0006] According to the second aspect of the present invention, when the amount of the powder exceeds a predetermined threshold value, the control unit causes the supply and conveying unit to perform a reverse rotation operation and then a forward rotation operation at a faster rotation speed than normal.

[0007] According to the third embodiment of the present invention, when the amount of the powder becomes below a predetermined threshold value, the control unit causes the supply and conveying unit to perform a reverse action, and then to rotate forward at a speed faster than normal, and then causes the supply and conveying unit to rotate forward at the normal speed.

[0008] According to the fourth aspect of the present invention, the detection unit detects the height of the powder surface of the powder by measuring the magnetic permeability of the powder.

[0009] According to a fifth aspect of the present invention, the detection unit includes a piezoelectric element disposed in the powder storage chamber, and detects the height of the powder surface of the powder based on whether the powder is present on the piezoelectric element.

[0010] According to the sixth aspect of the present invention, the detection unit detects the height of the powder surface of the powder based on a change in a current value measured by applying a voltage between electrodes disposed opposite to each other vertically above the supply and conveyance unit.

[0011] According to the seventh embodiment of the present invention, the detection unit has an actuator that is displaced by contacting the powder surface of the powder vertically above the supply and conveying unit. When the powder surface of the powder contacts the actuator, the powder surface of the powder is detected by utilizing a light receiving portion to receive light emitted from a light emitting portion arranged outside the powder storage chamber. The light receiving portion is arranged at a position opposite to the light emitting portion.

[0012] (Effect)

[0013] According to the first aspect, the amount of powder including the color material and the carrier in the powder supply device having the powder discharge mechanism can be stabilized without reducing the productivity of image formation.

[0014] According to the second aspect, the supply and conveyance unit is reversed as needed, and thus a decrease in the productivity of image formation can be suppressed compared to a case where the supply and conveyance unit is reversed by predictive detection.

[0015] According to the third aspect, compared to the case where the supply and conveying unit is reversed by predictive detection, the amount of the powder containing the color material and the carrier does not need to be stabilized excessively, thereby suppressing a decrease in the productivity of image formation.

[0016] According to the fourth aspect, the powder surface of the powder containing the color material and the carrier can be reliably detected, and the amount of the powder containing the color material and the carrier can be stabilized when necessary.

[0017] According to the fifth aspect, the powder surface of the powder containing the color material and the carrier can be reliably detected, and the amount of the powder containing the color material and the carrier can be stabilized when necessary.

[0018] According to the sixth aspect, the amount of the powder containing the color material and the carrier can be detected at low cost without providing a detection unit, and the amount of the powder containing the color material and the carrier can be stabilized when necessary.

[0019] According to the seventh aspect, the detection unit can be prevented from being contaminated by the powder containing the color material and the carrier, and the powder surface of the powder containing the color material and the carrier can be reliably detected. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic cross-sectional view showing an example of a schematic structure of an image forming apparatus.

[0021] Figure 2 It is a schematic longitudinal sectional view showing a photoreceptor unit and a developing device.

[0022] Figure 3 This is to explain the conveyance of the developer in the developing device. Figure 2 Schematic diagram of the cross section of line ABC unfolded in the horizontal direction.

[0023] Figure 4 : is a functional block diagram showing the functional configuration of the image forming section.

[0024] Figure 5 This is a flowchart showing the operation flow of the developing device.

[0025] Figure 6 4 is a schematic cross-sectional view of a developing device equipped with a developer amount sensor according to Modification 1.

[0026] Figure 71 is a schematic cross-sectional view of the developing device for explaining detection of the developer amount by the developer amount sensor according to Modification 1. FIG.

[0027] Figure 8 4 is a schematic cross-sectional view of a developing device equipped with a developer amount sensor according to a second modification.

[0028] Figure 9 1 is a schematic cross-sectional view of the developing device for explaining detection of the developer amount by the developer amount sensor according to Modification 2.

[0029] Figure 10 4 is a schematic cross-sectional view of a developing device equipped with a developer amount sensor according to a third modification.

[0030] Figure 11 It is a perspective view showing an actuator of a developer amount sensor according to Modification 3.

[0031] Figure 12 1 is a schematic cross-sectional view of the developing device for explaining detection of the developer amount by the developer amount sensor according to Modification 3.

[0032] Figure 13 It is a schematic cross-sectional view for explaining the circulation state of the developer in the developing device.

[0033] Figure 14 This is a flowchart showing the flow of operations for controlling the amount of developer in the image forming apparatus of the comparative example. DETAILED DESCRIPTION

[0034] Next, the present invention will be described in further detail with reference to the accompanying drawings by way of examples and embodiments, but the present invention is not limited to these examples and embodiments.

[0035] In the description using the following drawings, it should be noted that the drawings are schematic and the ratios of dimensions and the like may differ from actual ones. For ease of understanding, illustration of components other than those necessary for the description is omitted as appropriate.

[0036] Implementation Method

[0037] (1) Overall structure and operation of image forming apparatus

[0038] (1.1) Overall Structure of Image Forming Apparatus

[0039] Figure 1 It is a schematic cross-sectional view showing an example of a schematic configuration of the image forming apparatus 1 according to the present embodiment.

[0040] The image forming apparatus 1 is configured to include: an image forming unit 10; a paper feed device 20 mounted below the image forming unit 10; a paper discharge unit 30 located at one end of the image forming unit 10 for discharging printed paper; an operation display unit 40; and an image processing unit 50 for generating image information based on print information transmitted from a higher-level device. The image forming apparatus 1 is an example of a printing device and may also be configured with other devices. For example, a powder coating device may be configured as an example of a printing device by using the developer described in each embodiment as a coating powder. Specifically, the developing device 14 described in each embodiment may be used as a powder coating head (an example of a powder supply device) in an electrostatic powder coating method, with a conductive sheet of medium being conveyed close to the powder coating head. By applying a bias voltage between the powder coating head and the conductive sheet of medium, charged coating powder (e.g., thermosetting toner) is applied to the sheet of medium. The surface of the sheet of medium can then be coated by heating the sheet of medium.

[0041] The image forming unit 10 is configured to include a system control device 11, an exposure device 12, a photoreceptor unit 13, a developing device 14, a transfer device 15, paper conveying devices 16a, 16b, 16c and a fixing device 17, and is used to form a colorant image on a recording medium fed from a paper feeding device 20.

[0042] The paper feeding device 20 supplies recording media to the image forming unit 10. Specifically, the paper feeding device 20 includes a plurality of paper loading sections 21 and 22 for storing recording media of different types (e.g., material, thickness, paper size, and paper texture), and supplies the image forming unit 10 with a recording medium fed from any of the plurality of paper loading sections 21 and 22.

[0043] The paper discharge unit 30 discharges the paper P after the image is output by the image forming unit 10 and the image is fixed by the fixing device 17. To this end, the paper discharge unit 30 includes a conveyance path 30a for conveying the fixed paper P and a paper storage unit T1 for discharging the fixed paper P. Furthermore, the paper discharge unit 30 includes a paper reversing unit 18, which reverses the front and back sides of the paper P when outputting images on both sides of the paper P and delivers the paper to the paper conveying device 18. Furthermore, the paper discharge unit 30 may also have a function for performing post-processing such as cutting or stapling (binding) on ​​the paper stack output from the image forming unit 10.

[0044] The operation display unit 40 is used for inputting various settings and instructions, and for displaying information. Specifically, it corresponds to a so-called user interface and is specifically constituted by assembling a liquid crystal display panel, various operation buttons, a touch panel, and the like.

[0045] (1.2) Structure and Operation of Image Forming Unit

[0046] In the image forming apparatus 1 having such a configuration, recording media fed from paper loading sections 21 and 22 designated for each sheet to be printed in a print job are fed into the image forming section 10 in accordance with the timing of image formation.

[0047] The photoconductor unit 13 includes a photoconductor drum 31 as a latent image holder that is rotatably driven. The photoconductor drum 31 is arranged below the exposure device 12. The charger 32, exposure device 12, developing device 14, primary transfer roller 52, and cleaning device 33 are arranged along the rotation direction of the photoconductor drum 31.

[0048] A developing roller 42 serving as a developer retainer is provided in the developing device 14 (an example of a powder supply device) and is arranged opposite to the photosensitive drum 31. Each developing device 14 has roughly the same structure except for the developer, and each developing roller 42 forms a colorant image of yellow (Y), magenta (M), cyan (C), and black (K) on the photosensitive drum 31.

[0049] Disposed above the developing device 14 are replaceable toner cartridges TC storing toner and a toner supply device 18 (not shown) that supplies toner and carrier from each toner cartridge TC to the developing device 14. Note that toner is an example of a colorant, and developer is an example of a powder containing a colorant and a carrier.

[0050] The surface of the rotating photosensitive drum 31 is charged by the charger 32, and an electrostatic latent image is formed by latent image forming light emitted from the exposure device 12. The electrostatic latent image formed on the photosensitive drum 31 is developed into a toner image by the developing roller 42.

[0051] The transfer device 15 is constructed to include an intermediate transfer belt 151 to which the colorant images of various colors formed by the photosensitive drums 131 of the photosensitive units 13 are multi-transferred, a primary transfer roller 52 that sequentially transfers (primary transfer) the colorant images of various colors formed by the photosensitive units 13 onto the intermediate transfer belt 51, and a secondary transfer roller 53 that transfers (secondary transfer) the colorant images of various colors transferred and overlapped on the intermediate transfer belt 51 together onto a sheet of paper P serving as a recording medium.

[0052] The color toner images formed on the photosensitive drum 31 of each photosensitive unit 13 are electrostatically transferred (primary transfer) in sequence to the intermediate transfer belt 51 by the primary transfer roller 52 to which a prescribed transfer voltage is applied, thereby forming an overlapping colorant image formed by overlapping color toners of each color. The prescribed transfer voltage is applied from a power supply device (not shown) controlled by the system control device 11.

[0053] The superimposed toner images on the intermediate transfer belt 51 are conveyed to the secondary transfer portion TR as the intermediate transfer belt 51 moves. In the secondary transfer portion TR, the secondary transfer roller 53 is arranged in pressure contact with the backup roller 65 with the intermediate transfer belt 51 interposed therebetween.

[0054] When the superimposed toner images are conveyed to the secondary transfer section TR, paper P is supplied to the secondary transfer section TR from the paper feed device 20 at that timing. Then, a predetermined secondary transfer voltage is applied from a power supply device (not shown) controlled by the system control device 11 to the backup roller 65 that faces the secondary transfer roller 53 with the intermediate transfer belt 51 interposed therebetween, thereby collectively transferring the multiple toner images on the intermediate transfer belt 151 onto the paper P.

[0055] The residual toner on the surface of the photosensitive drum 31 is removed by the cleaning device 33 and collected in a waste toner storage unit (not shown). The surface of the photosensitive drum 31 is charged again by the charger 32 .

[0056] The fixing device 17 includes: an endless fixing belt 17a that rotates in one direction; and a pressure roller 17b that contacts the peripheral surface of the fixing belt 17a and rotates in one direction, and a pressing portion (fixing area) is formed by the pressing area between the fixing belt 17a and the pressure roller 17b.

[0057] The paper P to which the toner image has been transferred in the transfer device 15 is conveyed to the fixing device 17 via the paper conveying device 16a without the toner image being fixed. The toner image on the paper P conveyed to the fixing device 17 is fixed by the heat and pressure of a pair of fixing belts 17a and a pressure roller 17b.

[0058] After the fixing process, the paper P is loaded into the paper discharge storage section T1. Furthermore, when outputting images on both sides of the paper P, the front and back sides of the paper P are reversed by the paper conveying device 16c and fed again to the secondary transfer section TR in the image forming section 10 via the paper conveying device 16b. After the toner image is transferred and the transferred image is fixed, the paper P is fed to the paper discharge section 30. As needed, the paper P fed to the paper discharge section 30 undergoes post-processing such as cutting or stapling.

[0059] (2) Main structure

[0060] Figure 2 is a schematic cross-sectional view showing the photoreceptor unit 13 and the developing device 14, Figure 3 The conveyance of the developer in the developing device 14 is described along Figure 2 Schematic diagram of the cross section of line ABC unfolded in the horizontal direction.

[0061] Hereinafter, the structure and operation of the developing device 14 will be described with reference to the drawings.

[0062] (2.1) Overall structure of the developing device

[0063] The developing device 14 includes: a developing housing 41 that stores a developer containing a colorant and a carrier, a developing roller 42 arranged to face the photosensitive drum 31, a stirring auger 43 that transports the developer while stirring the developer, and a supply auger 44 that is an example of a supply and transport unit that supplies the developer to the developing roller 42.

[0064] The developing roller 42 has a magnet inside and rotates by magnetically attracting the developer to its surface, thereby delivering the developer from the developing housing 41 to a developing position facing the photosensitive drum 31. At the developing position, the electrostatic latent image formed on the surface of the photosensitive drum 31 is developed. After development, the developer is returned to the developing housing 41 by the rotation of the developing roller 42.

[0065] (2.2) Developer circulation

[0066] Figure 3 This is to explain the transportation (movement) of the developer in the developing device 14. Figure 2 Schematic diagram of the cross section of the ABC line in the horizontal direction.

[0067] In the developer housing 41 , a partition wall 41 a is provided between the stirring auger 43 and the supply auger 44 , dividing the developer housing 41 into two developer storage sections 41A and 41B. Openings 45 and 46 are formed at both ends of the partition wall 41 a in the longitudinal direction.

[0068] The stirring screw conveyor 43 and the supply screw conveyor 44 are formed with spiral blades 43b and 44b around the rotating shafts 43a and 44a, and receive rotational force from a driving source (not shown) and rotate along the inner wall of the developer storage section 41A and 41B, thereby transporting the developer in a specified direction in the developer storage section 41A and 41B.

[0069] Specifically, the stirring auger 43 stirs the developer in the developer container 41A and conveys it in the direction of arrow (Y), and the supply auger 44 stirs the developer in the developer container 41B and conveys it in the direction of arrow (-Y). The developer conveyed in the direction of arrow (Y) moves from the opening 45 to the developer container 41B, and the developer conveyed in the direction of arrow (-Y) moves from the opening 46 to the developer container 41A.

[0070] Thus, the developer in the developing housing 41 circulates while being stirred by the two augers, namely the stirring auger 43 and the supply auger 44. This stirring of the developer charges the toner in the developer.

[0071] A receiving port 47 (at the top of one end of the developing housing 41) is provided for receiving the toner and carrier supplied from the toner cartridge TC. Figure 3 , schematically shown for functional purposes.) The toner received into the developing device 14 through the receiving port 47 is conveyed by the stirring auger 43, moved to the developer storage portion 41A of the developing housing 41, and mixed with the developer.

[0072] The toner supplied from the toner cartridge TC through the receiving port 47 is conveyed from the front side (outer side: -Y direction, hereinafter referred to as outer side) to the back side (inner side: Y direction, hereinafter referred to as inner side) while being stirred together with the carrier by the stirring auger 43, and then moves to the supply auger 44 on the back side (inner side: Y direction). The toner supplied from the supply auger 44 is then supplied to the developing roller 42.

[0073] The developing device 14 is provided with a toner concentration sensor SR1 that measures the ratio of toner to carrier (TC) in the developer circulating within the developing housing 41. In the image forming apparatus 1, the system control device 11 instructs replenishment of toner from the toner cartridge TC based on the value measured by the toner concentration sensor SR1, thereby maintaining the TC value of the developer at a predetermined value.

[0074] In this embodiment, since the developer is supplied to the developing roller 42 from the inside to the outside, the colorant supply amount decreases when the developer reaches the outside. Therefore, in order to accurately control the colorant supply amount, the colorant concentration sensor SR1 is set on the inside of the stirring auger 43.

[0075] Furthermore, a discharge port 48 is provided on the side portion of one end side (-Y direction: the front surface side of the device) of the developer housing 41. Since a reverse spiral blade 44c having a spiral direction opposite to that of the spiral blade 44b at other parts is provided between the developer housing 41 and the discharge port 48, most of the developer conveyed in the direction of the arrow (-Y) in the developer storage portion 41B of the developer housing 41 is guided to the opening 46 by the reverse spiral blade 44c and moves to the developer storage portion 41A, a portion of the developer passes over the reverse spiral blade 44c and is discharged from the discharge port 48 (at the end of the developer housing 41). Figure 3 , schematically shown for the purpose of explaining the function) is discharged to the outside of the developing device 14 as excess developer.

[0076] In order to stably discharge a portion of the developer circulating in this manner from the discharge port 48, a developer amount sensor SR2 as an example of a detection unit for detecting the amount of developer is provided on the upstream side of the discharge port 48 of the developer storage portion 41B of the developer housing 41 in the developer conveying direction. Figure 2 As shown, the developer amount sensor SR2 is arranged at a position above the rotating shaft 44d of the supply screw conveyor 44 in the vertical direction (refer to Z1 in the Z direction diagram) so as to be able to detect the amount of developer transported by the supply screw conveyor 44 in the developer storage section 41B.

[0077] (2.3) Control of developer quantity

[0078] Figure 4 is a functional block diagram showing the functional structure of the image forming unit 10, Figure 5 is a flowchart showing the operation flow of the developing device 14, Figure 13 is a schematic cross-sectional view for explaining the circulation state of the developer in the developing device 14. Figure 14 This is a flowchart showing the flow of operations for controlling the amount of developer in the image forming apparatus 100 according to a comparative example.

[0079] like Figure 13 As shown, within the developer storage section 41A of the developing device 14, the developer (indicated by halftone dots) is stirred and mixed with the toner and carrier supplied from the toner cartridge TC by the stirring auger 43, and is conveyed from the outside to the inside while maintaining a predetermined liquid level. Within the developer storage section 41B of the developing device 14, the developer flowing upward from the opening 45 is stirred by the supply auger 44 while being conveyed from the inside to the outside while maintaining a predetermined liquid level.

[0080] In this state, the toner in the developer is consumed as the image is formed, while the carrier is not. Therefore, prolonged agitation within the developer housing 41 may cause external additives or toner to adhere to the carrier surface, leading to so-called developer degradation. As a result, the carrier's charging force on the toner may decrease, potentially preventing the toner charge from being maintained at an appropriate level.

[0081] Furthermore, in a structure in which the developer remaining in the developing housing 41 is discharged to the outside of the developing device 14 through the discharge port 48, the following problem may occur: when the developer deteriorates, the fluidity of the developer decreases, the developer cannot be fully discharged from the discharge port 48, and the amount of developer in the developing housing fluctuates significantly.

[0082] In the image forming apparatus 100 of the comparative example, Figure 14 The operation flow shown in the flowchart suppresses discharge failure of degraded developer.

[0083] In an image forming device 100 of a comparative example that does not have a developer amount sensor SR2 for detecting the developer amount in the developer housing 41, the number of printed sheets is counted (S201). When the number of printed sheets P0 exceeds a threshold value Pth which is a predetermined number of printed sheets (S202: "Yes"), the total image pixels of the print job are measured using the image processing unit 50, and the image density AC of the print job is calculated (S203).

[0084] If the image density AC is higher than the predetermined threshold value ACth (S204: YES), the supply auger 44 is reversed for a predetermined time (S205), and then forwardly rotated at a faster speed than usual for a predetermined time (S206).

[0085] This can be expected to suppress discharge defects of degraded developer. However, since the supply auger 44 is temporarily reversed and then rotated forward based on prediction, regardless of the developer amount in the developer housing 41, there is a problem that fluctuations in the developer amount cannot be suppressed with high accuracy. Furthermore, since the supply auger 44 is reversed and then rotated forward for a predetermined period of time based on prediction, there is also a problem that the image forming productivity of the image forming apparatus 100 is reduced.

[0086] The image forming apparatus 1 of this embodiment includes a developer amount sensor SR2. The developer amount sensor SR2 is located above the rotation shaft 44d of the supply auger 44, downstream in the developer conveying direction of the supply auger 44, and upstream in the developer conveying direction of the discharge port 48 for discharging excess developer. The developer amount sensor SR2 detects the amount of developer in the developer housing 41. Figure 4 As shown in the functional block diagram of FIG, the system control device 11 as an example of a control unit controls at least one of the rotation direction and the rotation speed of the supply auger 44 based on the detection result of the developer amount sensor SR2.

[0087] In this embodiment, a magnetic permeability sensor can be used as the developer amount sensor SR2. The magnetic permeability sensor detects the magnetic permeability of the two-component developer composed of toner and carrier within the developer housing 41. The developer liquid level can then be detected based on the output value of the magnetic permeability sensor.

[0088] like Figure 5As shown in the flowchart, the image forming apparatus 1 obtains the output value A of the developer amount sensor SR2 (S101) and determines whether the output value A is greater than a predetermined threshold value Ath (S102). If the output value A is greater than the threshold value Ath (S102: "YES"), the supply auger 44 is reversed by a predetermined number of revolutions N1 (S103), and then the supply auger 44 is rotated forward by a predetermined number of revolutions N2 at a speed faster than normal (S104).

[0089] Then, it is determined whether the output value A of the developer amount sensor SR2 is greater than the threshold value Ath (S105). If the output value A is less than the threshold value Ath (S105: "No"), the supply screw conveyor 44 is reversed by a specified number of revolutions N1 (S106), and then the supply screw conveyor 44 is rotated forward by a specified number of revolutions N2 at a speed faster than normal (S107), and then rotated forward at the normal speed.

[0090] This makes it possible to reliably detect the developer liquid level in the developer storage section 41B of the developer housing 41, thereby stabilizing the developer amount. Furthermore, by detecting the developer liquid level in the developer storage section 41B and controlling the rotation of the supply auger 44 (reverse rotation and high-speed forward rotation) only when the liquid level exceeds a predetermined height, it is possible to suppress a decrease in image formation productivity.

[0091] Modification 1

[0092] Figure 6 FIG. 1 is a schematic cross-sectional view of a developing device 14 equipped with a developer amount sensor SR2A according to a first modification. Figure 7 1 is a schematic cross-sectional view of the developing device 14 for explaining detection of the developer amount by the developer amount sensor SR2A. Figure 6 As shown in FIG. 1 , the developer amount sensor SR2A may be a sensor including a piezoelectric element.

[0093] like Figure 7 As shown in (a), when the developer is located on the piezoelectric element of the developer amount sensor SR2A, the system control device 11 determines that the amount of developer stored in the developer storage portion 41B of the developer housing 41 is above a predetermined value, thereby reversing the supply screw conveyor 44 by a predetermined number of revolutions N1 (S103), and then rotating the supply screw conveyor 44 forward by a predetermined number of revolutions N2 at a speed faster than normal (S104).

[0094] On the other hand, Figure 7As shown in (b) of FIG. 1 , when developer is not present on the piezoelectric element of the developer amount sensor SR2A, the system control device 11 determines that the amount of developer contained in the developer storage portion 41B of the developer housing 41 is less than a predetermined value, and thus does not control the rotation (reverse rotation and high-speed forward rotation) of the supply auger 44. In this way, the piezoelectric element can reliably detect the liquid level of developer in the developer storage portion 41B of the developer housing 41, thereby stabilizing the developer amount.

[0095] Modification 2

[0096] Figure 8 FIG. 1 is a schematic cross-sectional view of a developing device 14 equipped with a developer amount sensor SR2B according to a second modification. Figure 9 1 is a schematic cross-sectional view of the developing device 14 for explaining detection of the developer amount by the developer amount sensor SR2B.

[0097] like Figure 8 As shown, the developer amount sensor SR2B may also be composed of electrodes P1 and P2 disposed opposite each other vertically above the supply auger 44 in the developer storage portion 41B of the developer housing 41. The system control device 11 detects the developer liquid level based on changes in the current value measured by applying a voltage between the electrodes P1 and P2.

[0098] like Figure 9 As shown in (a), when the developer is located between the electrodes P1 and P2 of the developer amount sensor SR2B, the system control device 11 determines that the amount of developer contained in the developer storage portion 41B of the developer housing 41 is greater than a predetermined value, thereby reversing the supply screw conveyor 44 by a predetermined number of revolutions N1 (S103), and then rotating the supply screw conveyor 44 forward by a predetermined number of revolutions N2 at a speed faster than normal (S104).

[0099] On the other hand, Figure 9 As shown in (b), when developer is not between electrodes P1 and P2 of developer amount sensor SR2B, the system control device 11 determines that the amount of developer stored in the developer storage section 41B of the developer housing 41 is less than a predetermined value, and thus does not control the rotation (reverse rotation and high-speed forward rotation) of the supply auger 44. In this way, by applying voltage to electrodes P1 and P2 arranged opposite each other vertically above the supply auger 44 and measuring the current flowing therethrough, the developer liquid level in the developer storage section 41B of the developer housing 41 can be reliably detected, thereby stabilizing the developer amount.

[0100] Modification 3

[0101] Figure 10FIG. 1 is a schematic cross-sectional view of a developing device 14 equipped with a developer amount sensor SR2C according to a third modification. Figure 11 1 is a perspective view showing an actuator of the developer amount sensor SR2C according to Modification 3, Figure 12 1 is a schematic cross-sectional view of the developing device 14 for explaining detection of the developer amount by the developer amount sensor SR2C.

[0102] The developer amount sensor SR2C of variant example 3 has an actuator 49, which is displaced by contacting the liquid surface of the developer vertically above the supply screw conveyor 44. When the liquid surface of the developer contacts the actuator 49, the liquid surface of the developer is detected by receiving light emitted from the light-emitting portion L1 arranged outside the developer housing 41 by the light-receiving portion L2. The light-receiving portion L2 is arranged at a position opposite to the light-emitting portion L1.

[0103] like Figure 11 As shown, the actuator 49 is composed of a contact portion 49a that contacts the liquid surface of the developer, an arm portion 49b, a detection portion 49c that blocks the light emitted from the light-emitting portion L1, and a rotating fulcrum 49d. Through the rotating fulcrum 49d, the actuator 49 is supported on the wall of the developer housing 41 in a rotatable manner.

[0104] In the developer amount sensor SR2C thus constructed, as shown in FIG. Figure 12 As shown in (a), when the liquid level of the developer in the developer storage portion 41B of the developer housing 41 is low, the contact portion 49a does not contact the developer, and the detection portion 49c does not block the light emitted from the light emitting portion L1.

[0105] On the other hand, Figure 12 As shown in (b), when the liquid level of the developer in the developer storage section 41B of the developer housing 41 becomes higher and the developer contacts the contact portion 49a, the actuator 49 rotates with the rotation fulcrum 49d as the rotation center, and the detection portion 49c blocks the light emitted from the light emitting portion L1.

[0106] As a result, the system control device 11 determines that the amount of developer stored in the developer storage section 41B of the developer housing 41 is greater than a predetermined value, and then reverses the supply auger 44 by a predetermined number of revolutions N1 (S103). Then, the supply auger 44 is rotated forward by a predetermined number of revolutions N2 at a speed faster than normal (S104). In this way, the actuator 49 can reliably detect the liquid level of the developer in the developer storage section 41B of the developer housing 41, thereby stabilizing the amount of developer.

Claims

1. A printing device comprising: a developer storage chamber for storing developer; a supply conveying unit that conveys the developer while supplying the developer to a developer holding member that holds the developer by forward rotation; a detection unit that detects the amount of the developer in the developer storage chamber above a rotation axis of the supply and conveying unit, downstream in the conveying direction of the supply and conveying unit, and upstream in the conveying direction of a discharge portion that discharges excess developer; and A control unit controls, when the amount of the developer detected by the detection unit exceeds a predetermined threshold value, the supply and conveyance unit to perform a reverse rotation operation and then a forward rotation operation at a rotation speed faster than a normal rotation operation.

2. The printing device according to claim 1, wherein The detection unit detects the height of the liquid level of the developer by measuring the magnetic permeability of the developer.

3. The printing device according to claim 1, wherein The detection unit includes a piezoelectric element disposed in the developer storage chamber, and detects the height of the developer liquid level based on whether the developer is present on the piezoelectric element. The printing device according to claim 1 , wherein: The detection unit detects the height of the developer liquid level based on a change in a current value measured by applying a voltage between electrodes disposed opposite to each other vertically above the supply and conveyance unit.

5. The printing device according to claim 1, wherein The detection unit has an actuator that shifts when it contacts the liquid surface of the developer vertically above the supply and conveying unit. When the liquid surface of the developer contacts the actuator, the liquid surface of the developer is detected by utilizing a light receiving portion to receive light emitted from a light emitting portion arranged outside the developer storage chamber. The light receiving portion is arranged at a position opposite to the light emitting portion.

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