JP7155974B2 - Developing device and image forming apparatus having the same - Google Patents

Description

The present invention relates to a developing device used in image forming apparatuses such as copiers, printers, and facsimiles, and more particularly to a method for suppressing clogging of developer in a gap between a developing roller and a regulating blade.

Conventionally, as a developing method in an image forming apparatus using an electrophotographic process, a powder developer is mainly used. After the visible image (toner image) is transferred onto the recording medium, a process of fixing is generally performed.

Developers are roughly classified into two-component developers consisting of toner and magnetic carrier, and one-component developers consisting only of non-magnetic or magnetic toner. As a development method using a magnetic one-component developer, a fixed magnet body having a plurality of magnetic poles is arranged inside the developing roller, and the toner in the developing container is carried on the developing roller using magnetic carrying force. A so-called jumping one-component development system is known, in which a toner thin layer is formed by regulating the layer thickness using a regulating blade, and the toner is caused to fly onto the photosensitive drum at the development position.

In the magnetic one-component development system, sufficient magnetic force is required at the tip of the regulating blade in order to ensure the stability of the toner layer on the developing roller and to improve the performance of charging the toner. Therefore, conventionally, there is a technique of increasing the magnetic force at the tip of the regulating blade by attaching a blade magnet to the side surface of the regulating blade. However, when the blade magnet is attached, toner aggregates tend to occur around the blade magnet and around the tip of the blade in the developing device. As a result, the toner layer on the developing roller is disturbed, and image defects such as white streaks are likely to occur.

In view of this, Japanese Patent Laid-Open No. 2002-100001 discloses a method for suppressing the generation of aggregated toner by rotating a developer carrying member in the reverse direction within a predetermined range when a temperature detecting member for detecting the temperature of a regulating member detects a temperature equal to or higher than a predetermined value. is disclosed. Further, Japanese Patent Application Laid-Open No. 2002-100000 discloses that the image density can be improved by changing the arrangement angle of a magnetic field generating means having a plurality of magnetic poles arranged inside a developer bearing member according to the usage environment and usage conditions of the image forming apparatus. A method is disclosed to improve image quality degradation due to degradation and white background fogging.

JP 2006-268056 A JP 2005-49574 A

However, in the method of rotating the developing roller in reverse as in Patent Document 1, it is easy to collect the aggregated toner inside the regulating blade (around the blade magnet), but the aggregated toner at the tip of the regulating blade, which most likely affects the image, is removed. Since it is difficult to collect the toner, the effect of suppressing toner aggregation was not sufficient.

Further, in the technique of Patent Document 2, by slightly changing the positional relationship of the main pole facing the photosensitive drum during printing, the magnetic binding force of the toner in the developing area is changed so that the toner adheres to the photosensitive drum. It was intended to adjust the amount of toner, and it was difficult to suppress retention and blocking of the low-melting-point toner in the regulating portion.

In view of the above problems, the present invention provides a developing device capable of maintaining a high magnetic force at the tip of a regulating blade and suppressing the generation of developer aggregates around the blade magnet and at the tip of the blade, and an image forming apparatus equipped with the developing device. The purpose is to provide an apparatus.

In order to achieve the above object, a first configuration of the present invention includes a housing, a developer carrier, a regulating blade, a magnet member, and a blade magnet, and is formed on an image carrier. A developing device for developing an electrostatic latent image. The housing accommodates developer having magnetism. The developer carrier is rotatably supported by the housing and carries developer on its outer peripheral surface. The regulating blade is made of a magnetic material, is arranged at a predetermined distance from the developer carrier, and forms a regulating portion that regulates the layer thickness of the developer carried on the developer carrier. The magnet member has a shaft arranged inside the developer carrier, and a plurality of magnetic poles including an S pole and an N pole fixed to the outer peripheral surface of the shaft. A blade magnet is fixed to the regulating blade and induces a magnetic pole at the tip of the regulating blade. The magnet member has a first position where a magnetic pole having the same polarity as the opposing magnetic pole of the blade magnet facing the developer carrying member is arranged in the regulating portion, and a second position where a magnetic pole having a different polarity from the opposing magnetic pole is arranged in the regulating portion. position and can be moved to. The blade magnet has a reference position where the tip of the opposing magnetic pole is arranged radially outside the tip of the regulating blade on the developer carrier, and a reference position where the tip of the opposing magnetic pole is radially inside the developer carrier on the tip of the regulating blade. and a protruding position protruding to the upper side. The developing device rotates and regulates the developer carrier in the positive direction, which is the rotational direction during image formation, with the magnet member arranged at the second position and the blade magnet arranged at the reference position during non-image formation. a first developer removing mode for removing the developer accumulated in the portion, and a state in which the magnet member is arranged at the first position and the blade magnet is arranged at the projecting position, and the developer carrying member is moved in the forward direction and the opposite direction. It is possible to execute a developer removing mode including a second developer removing mode in which the blade magnet is rotated in a certain opposite direction to remove the developer staying between the blade magnet and the developer carrier.

According to the first configuration of the present invention, a first developer removing mode in which a repelling magnetic field is generated between the regulating blade and the developer carrier during non-image formation and then the developer carrier is rotated forward; By executing a developer removal mode including a second developer removal mode in which a repelling magnetic field is generated between the blade magnet and the developer carrier and then the developer carrier is reversely rotated, developer aggregates are formed. It is possible to effectively suppress the clogging of the regulating portion caused by the grain and the resulting image defects such as white streaks or gray vertical streaks. Furthermore, since the blade magnet is placed at the reference position when the first developer removal mode is executed, it becomes easier to remove developer aggregates adhering to the tip of the regulating blade. Further, since the blade magnet is arranged at the projecting position when the second developer removal mode is executed, it becomes easier to remove the developer aggregates remaining in the stepped portion between the regulating blade and the blade magnet.

Schematic cross-sectional view of an image forming apparatus 100 equipped with a developing device 4 according to an embodiment of the present invention. A plan view and a front view of the developing device 4 according to the first embodiment of the present invention. Side cross-sectional view of the developing device 4 of the first embodiment FIG. 4 is an enlarged view of the periphery of the developing roller 25 in the developing device 4 of the first embodiment; FIG. 5 is a cross-sectional view of the developing roller 25 in FIG. 4 as seen from a direction perpendicular to the axial direction; FIG. 2 is a block diagram showing an example of control paths used in the image forming apparatus 100; 3 is a flow chart showing an example of control of the developer removal mode in the developing device 4 of the first embodiment; FIG. 4 is an enlarged view of the developing roller 25 and its surroundings of the developing device 4, showing the state in which the N2 pole 27d of the fixed magnet body 27 is moved to a position facing the regulation blade 29; 8. A partially enlarged view showing the direction of the magnetic field around the restricting portion 30 in FIG. FIG. 10 is an enlarged view of the developing roller 25 and its surroundings of the developing device 4, showing a state in which the S2 pole 27c of the stationary magnet body 27 is moved to a position facing the regulating blade 29; FIG. 10 is a partially enlarged view showing the direction of the magnetic field around the restricting portion 30 in FIG. 10 FIG. 4 is an enlarged view of the development roller 25 and its surroundings of the development device 4, showing a state in which the fixed magnet 27 is rotated in the opposite direction to move the N1 pole 27b to a position facing the regulation blade 29; FIG. 10 is a partial enlarged view showing the orientation of the magnetic field around the restricting portion 30 when the fixed magnet 27 is rotated in the opposite direction, showing a state in which the N1 pole 27b approaches the restricting portion 30; FIG. 4 is a partial enlarged view showing the orientation of the magnetic field around the restricting portion 30 when the fixed magnet 27 is rotated in the opposite direction, and shows a state in which the N1 pole 27b has passed through the restricting portion 30; Graph showing the relationship between the development drive time T and the aggregation generation level in the regulation section 30 Graph showing temperature dependence of aggregation occurrence coefficient a_N Graph showing toner deterioration characteristics for each coverage rate FIG. 15 is a graph comparing the execution frequency of the developer removal mode when the toner deterioration degree is less than 1 and when it is 2. FIG. 10 is a flow chart showing an example of control of the developer removal mode in the developing device 4 according to the second embodiment of the present invention; FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 including a developing device 4 according to one embodiment of the invention. When the image forming apparatus (for example, a monochrome printer) 100 performs a printing operation, the image forming unit 9 in the image forming apparatus 100 receives an image from a host device (not shown) such as a personal computer (hereinafter referred to as a personal computer). An electrostatic latent image is formed based on the document image data, and toner is adhered to the electrostatic latent image by the developing device 4 to form a toner image. Toner is supplied to the developing device 4 from a toner container 5 . In the image forming apparatus 100, the image forming process for the photoreceptor drum 1 is executed while rotating the photoreceptor drum 1 clockwise in FIG.

The image forming unit 9 includes a charging device 2 , an exposure unit 3 , a developing device 4 , a transfer roller 6 , a cleaning device 7 , and a neutralizing device (not shown) along the rotation direction (clockwise direction) of the photosensitive drum 1 . ) are provided. The photosensitive drum 1 is, for example, an aluminum drum laminated with a photosensitive layer, and the charging device 2 uniformly charges the surface thereof. Then, an electrostatic latent image is formed on the surface receiving the light beam from the exposure unit 3, which will be described later, with the charge attenuated. Although the above photosensitive layer is not particularly limited, amorphous silicon (a-Si) or the like, which is excellent in durability, is preferable.

The charging device 2 uniformly charges the surface of the photosensitive drum 1 . As the charging device 2, for example, a corona discharge device that discharges electricity by applying a high voltage to thin wires or the like as electrodes is used. Instead of the corona discharge device, a contact-type charging device that applies a voltage while a charging member typified by a charging roller is in contact with the surface of the photosensitive drum 1 may be used. The exposure unit 3 irradiates the photosensitive drum 1 with a light beam (for example, a laser beam) based on image data to form an electrostatic latent image on the surface of the photosensitive drum 1 .

The developing device 4 adheres toner to the electrostatic latent image on the photosensitive drum 1 to form a toner image. In this embodiment, the developing device 4 contains magnetic one-component developer (hereinafter referred to as toner) made of magnetic toner. Details of the developing device 4 will be described later. The cleaning device 7 includes a cleaning roller, a cleaning blade, etc., which make line contact in the longitudinal direction of the photosensitive drum 1 (the direction perpendicular to the paper surface of FIG. 1). Toner remaining on the surface of the photosensitive drum 1 is removed.

A sheet of paper is conveyed from the sheet containing section 10 to the image forming section 9 at a predetermined timing through the sheet conveying path 11 and the pair of registration rollers 13 toward the photosensitive drum 1 on which the toner image is formed as described above. . The transfer roller 6 transfers (transfers) the toner image formed on the surface of the photosensitive drum 1 to a sheet conveyed along the sheet conveying path 11 without disturbing the toner image. After that, in preparation for subsequent formation of a new electrostatic latent image, the cleaning device 7 removes the residual toner on the surface of the photosensitive drum 1, and the static eliminator removes the residual charge.

The paper on which the toner image has been transferred is separated from the photosensitive drum 1, conveyed to the fixing device 8, and heated and pressurized to fix the toner image on the paper. After passing through the fixing device 8 , the paper passes through the pair of discharge rollers 14 and is discharged to the paper discharge section 15 .

2A and 2B are a plan view and a front view of the developing device 4 according to the first embodiment of the invention, and FIG. 3 is a side sectional view of the developing device 4 of the first embodiment. . For convenience, FIG. 2A shows a state in which the inside can be seen with the top cover removed. As shown in FIGS. 2 and 3, the interior of the housing 20 is divided into a first storage chamber 21 and a second storage chamber 22 by a partition wall 20a integrally formed with the housing 20. As shown in FIG. A first stirring screw 23 is provided in the first storage chamber 21 and a second stirring screw 24 is provided in the second storage chamber 22 .

The first stirring screw 23 and the second stirring screw 24 each have a structure in which spiral blades are provided around a support shaft (rotating shaft), and are rotatably supported by the housing 20 in parallel to each other. . In addition, as shown in FIG. 2( a ), there is no partition wall 20 a at both ends of the housing 20 in the longitudinal direction, which is the axial direction of the first stirring screw 23 and the second stirring screw 24 . 23, the transfer of toner between the second stirring screws 24 is possible. As a result, the first stirring screw 23 transports the toner in the first storage chamber 21 in the direction of the arrow P while stirring it to the second storage chamber 22, and the second stirring screw 24 moves the toner in the second storage chamber 22. The toner conveyed to 22 is conveyed in the direction of arrow Q while being agitated and supplied to developing roller 25 .

The developing roller 25 supplies toner to the photosensitive layer of the photosensitive drum 1 by rotating in accordance with the rotation of the photosensitive drum 1 (see FIG. 1). A stationary magnet body 27 made of a permanent magnet having a plurality of magnetic poles is fixed inside the developing roller 25 . A magnetic brush is formed by attaching (carrying) toner to the surface of the developing roller 25 by the magnetic force of the fixed magnet body 27 . The developing roller 25 is rotatably supported by the housing 20 in parallel with the first stirring screw 23 and the second stirring screw 24 .

The regulating blade 29 is formed so that its longitudinal direction (horizontal direction in FIG. 2) is larger than the maximum development width, and is arranged at a predetermined distance from the developing roller 25 to supply the photosensitive drum 1 with the developing roller 25 . A regulating portion 30 is formed to regulate the amount of toner (toner layer thickness). As a material of the regulating blade 29, a magnetic SUS (stainless steel) or the like is used.

A toner amount detection sensor (not shown) for detecting the amount of toner stored in the housing 20 is provided on the bottom surface of the second storage chamber 22 facing the second stirring screw 24 . The toner stored in the toner container 5 (see FIG. 1) is supplied into the housing 20 through the developer supply port 20b provided at the top of the housing 20 according to the detection result of the toner amount detection sensor.

DS rollers 31 a and 31 b are rotatably fitted around the rotation shaft of the developing roller 25 . The DS rollers 31 a and 31 b strictly regulate the distance between the developing roller 25 and the photoreceptor drum 1 by coming into contact with both ends of the outer peripheral surface of the photoreceptor drum 1 in the axial direction. The DS rollers 31a and 31b have bearings built therein, and rotate following the photosensitive drum 1 to prevent abrasion of the drum surface. Magnetic sealing members 33 a and 33 b are provided at both ends of the developing roller 25 in the axial direction to prevent leakage of toner from the gap between the housing 20 and the developing roller 25 .

FIG. 4 is an enlarged view around the developing roller 25 in the developing device 4 of the first embodiment. FIG. 5 is a cross-sectional view of the developing roller 25 in FIG. 4 as seen from a direction perpendicular to the axial direction. As shown in FIG. 4, the stationary magnet body 27 has four magnetic poles 27a to 27d consisting of an S1 pole 27a, an S2 pole 27c and an N1 pole 27b and an N2 pole 27d fixed to a metal shaft 27e.

As shown in FIG. 5, flange portions 25a and 25b are attached to both longitudinal ends of the developing roller 25, and a drive input shaft 25c is fixed to the flange portion 25a. One end (right end in FIG. 5) of the shaft 27e of the stationary magnet body 27 is fixed to the housing 20 (see FIG. 3), and bearings 26a and 26b are arranged between the flange portions 25a and 25b and the shaft 27e. It is When a rotational drive force is input to the drive input shaft 25c from the development drive motor 41 (see FIG. 6) through a drive input gear (not shown), the development roller 25 rotates together with the flange portions 25a and 25b, but is fixed. The magnet body 27 does not rotate.

A drive input gear 37 is fixed to one end of the shaft 27e, and a magnet drive motor 43 (see FIG. 6) is connected to the drive input gear 37. As shown in FIG.

Returning to FIG. 4 , a blade magnet 35 is attached near the tip of the regulation blade 29 . The blade magnet 35 is fixed to a magnet support stay 36, and the magnet support stay 36 is supported on the back side (right side in FIG. 4) of the regulation blade 29 so as to be vertically movable.

The upper surface of the magnet support stay 36 is provided with a shaft 36a passing through the upper surface of the regulating blade 29 and a pressed surface 36b having a larger diameter than the shaft 36a fixed to the upper end of the shaft 36a (see FIG. 9 for both). ing. A coil spring 38 is fitted around the shaft 36a, and the coil spring 38 is sandwiched between the upper surface of the regulating blade 29 and the pressed surface 36b.

An eccentric cam 39 is arranged above the regulating blade 29 . As the eccentric cam 39 rotates while contacting the surface 36b to be pressed, the pressing force of the eccentric cam 39 and the biasing force of the coil spring 38 move the blade magnet 35 up and down together with the magnet support stay 36 . A blade magnet moving motor 44 is connected to the eccentric cam 39 . The shaft 36a, the pressed surface 36b, the coil spring 38, and the eccentric cam 39 are provided at least at both ends of the regulating blade 29 in the longitudinal direction (the direction perpendicular to the plane of FIG. 4).

The blade magnet 35 is arranged at a reference position (position shown in FIG. 4) where the tip edge of the opposing magnetic pole 35a is located inside (diametrically outside of the developing roller 25) the tip of the regulating blade 29 during image formation.

As shown in FIG. 2, the blade magnet 35 is provided between the magnetic seal members 33a and 33b over substantially the entire length of the regulating blade 29 in the longitudinal direction (horizontal direction in FIG. 2). The blade magnet 35 contacts the regulating blade 29 with the S pole facing downward, and the N pole is induced at the tip of the regulating blade 29 . As a result, a magnetic field is generated between the fixed magnet body 27 and the S2 pole (regulating pole) 27c in a direction that attracts the regulating portion 30 . As shown in FIG. 4, the fixed magnet 27 is the first position of .

Due to this magnetic field, a magnetic brush of continuous toner particles is formed between the regulating blade 29 and the developing roller 25, and the magnetic brush passes through the regulating portion 30 to be regulated to a desired height. On the other hand, the toner not used for forming the magnetic brush stays along the upstream (right) side of the regulation blade 29 . Thereafter, when the developing roller 25 rotates counterclockwise and the magnetic brush moves to an area (developing area) facing the photosensitive drum 1, a magnetic field is applied by the N1 pole (main pole) 27b. contacts the surface of the photosensitive drum 1 to develop the electrostatic latent image.

When the developing roller 25 further rotates in the counterclockwise direction, the S1 pole (conveying pole) 27a applies a magnetic field in the direction along the outer peripheral surface of the developing roller 25, which is not used for forming the toner image together with the magnetic brush. The collected toner is collected on the developing roller 25 . Further, the magnetic brush separates from the developing roller 25 and falls into the housing 20 at the missing portion between the S1 pole 27a and the N2 pole 27d. After being stirred and conveyed by the second stirring screw 24, a magnetic brush is again formed on the developing roller 25 by the magnetic field of the N2 pole (drawing pole) 27d.

Magnetic sealing members 33a and 33b are arranged in the housing 20 surrounding both ends of the developing roller 25, respectively. Note that FIG. 4 shows only the magnetic seal member 33a. As shown in FIG. 4, the magnetic seal members 33a and 33b are not in contact with the developing roller 25, i.e., are separated from the outer peripheral surface of the developing roller 25 by a predetermined gap. is placed in The magnetic seal members 33a and 33b are arranged on the opposite side of the photosensitive drum 1 with the developing roller 25 interposed therebetween.

FIG. 6 is a block diagram showing an example of control paths used in the image forming apparatus 100. As shown in FIG. Since various parts of the apparatus are controlled when the image forming apparatus 100 is used, the overall control path of the image forming apparatus 100 is complicated. Therefore, here, the portion of the control path that is necessary for implementing the present invention will be mainly described.

The development drive unit 40 includes a development drive motor 41 , a development clutch 42 , a magnet drive motor 43 and a blade magnet movement motor 44 . The development driving motor 41 rotates the first stirring screw 23 , the second stirring screw 24 , and the developing roller 25 . The development clutch 42 turns ON/OFF the rotational drive force input from the development drive motor 41 to the first stirring screw 23 , the second stirring screw 24 , and the development roller 25 . The magnet drive motor 43 rotates the fixed magnet body 27 fixed to the shaft 27e by a predetermined angle by rotating the shaft 27e. The blade magnet moving motor 44 rotates the eccentric cam 39 to vertically move the blade magnet 35 together with the magnet support stay 36 .

The voltage control circuit 51 is connected to a charging voltage power supply 52 , a developing voltage power supply 53 and a transfer voltage power supply 54 , and operates these power supplies according to output signals from the control section 90 . These power sources are controlled by a control signal from the voltage control circuit 51, the charging voltage power source 52 to the wire in the charging device 2, the developing voltage power source 53 to the developing roller 25 in the developing device 4, and the transfer voltage power source 54 to the transfer roller. 6 is applied with a predetermined voltage.

The image input unit 60 is a receiving unit that receives image data transmitted from a personal computer or the like to the image forming apparatus 100 . The image signal input from the image input section 60 is converted into a digital signal and sent to the temporary storage section 94 .

The internal temperature and humidity sensor 61 detects the temperature and humidity inside the image forming apparatus 100 , particularly the temperature and humidity around the developing device 4 , and is arranged near the image forming section 9 .

The operation unit 70 is provided with a liquid crystal display unit 71 and LEDs 72 for indicating various states, such as to indicate the state of the image forming apparatus 100 and to display the image forming state and the number of print copies. Various settings of the image forming apparatus 100 are performed from the printer driver of the personal computer.

The control unit 90 includes a CPU (Central Processing Unit) 91 as a central processing unit, a read-only memory (ROM) 92, a readable/writable memory (RAM) (Random Access Memory) 93, a temporary A temporary storage unit 94 for temporarily storing image data, etc., a counter 95, a timer 97, and a plurality of units (here, 2) I/F (interface) 96 at least.

The ROM 92 stores a program for controlling the image forming apparatus 100 and data such as numerical values necessary for control that are not changed while the image forming apparatus 100 is in use. The RAM 93 stores necessary data generated during control of the image forming apparatus 100, data temporarily necessary for controlling the image forming apparatus 100, and the like. The RAM 93 (or ROM 92) also stores the relationship between the cumulative drive time T of the developing device 4 measured by a timer 97 (described later) and the aggregation occurrence level in the regulating section 30 (see FIG. 16), the cumulative drive time Tsum A table (see Table 1) defining the relationship between , aggregation occurrence coefficient, and toner deterioration coefficient is also stored.

The temporary storage unit 94 temporarily stores an image signal input from the image input unit 60 that receives image data transmitted from a personal computer or the like and converted into a digital signal. A counter 95 accumulates and counts the number of printed sheets. The timer 97 separately measures the cumulative drive time Tsum (first drive time) from the start of use of the developing device 4 and the cumulative drive time T (second drive time) from the most recent execution of the developer removal mode. .

Further, the control unit 90 transmits a control signal from the CPU 91 to each part and device in the image forming apparatus 100 through the I/F 96 . Signals and input signals indicating the state of each part and device are transmitted to the CPU 91 through the I/F 96 . The parts and devices controlled by the control section 90 include, for example, the fixing device 8, the image forming section 9, the development driving section 40, the voltage control circuit 51, the image input section 60, the operation section 70, and the like.

As described above, when continuous printing is performed in a high-temperature environment using a low-melting-point toner as a magnetic one-component developer, the toner remaining in the regulating portion 30 of the developing device 4 softens and causes blocking, resulting in clogging. Occur. Therefore, in the present embodiment, a developer removal mode for removing the toner (developer) remaining in the regulating portion 30 during non-image formation can be executed. The developer removal mode will be described in detail below.

FIG. 7 is a flow chart showing a control example of the developer removal mode in the developing device 4 of the first embodiment. The execution procedure of the developer removal mode will be described along the steps of FIG. 7 while referring to FIGS. 1 to 6 as necessary.

When a print command is input from a host device such as a personal computer and printing is started (step S1), the control section 90 (see FIG. 6) determines whether or not printing is continuing (step S2). If printing continues, it is then determined whether or not the number of printed sheets has reached a specified number (step S3). If the number of printed sheets has not reached the specified number (No in step S3), the process returns to step S2 to continue printing. If printing is completed before reaching the specified number of sheets (No in step S2), the process is terminated.

When the number of sheets to be printed reaches the prescribed number (Yes in step S3), the control signal from the control unit 90 stops the paper feeding from the paper container 10 (step S4). Further, the application of the developing bias from the developing voltage power supply 52 (see FIG. 6) to the developing roller 25 is stopped (step S5), and the developing clutch 42 (see FIG. 6) is turned off (step S6) to rotate the developing roller 25. to stop.

Then, a control signal is transmitted from the control unit 90 to the magnet drive motor 43 (see FIG. 6), and the fixed magnet body 27 is rotated in the direction of rotation of the developing roller 25 (forward direction, counterclockwise direction in FIG. 4) during image formation. By rotating it by a predetermined angle, the N2 pole (pumping pole) 27d is moved to a position facing the regulation blade 29 (step S7). A second position of the fixed magnet 27 is a state in which a magnetic pole opposite in polarity to the opposing magnetic pole 35a of the blade magnet 35 (here, the N2 pole 27d) is arranged at a position facing the regulating blade 29. FIG.

FIG. 8 is an enlarged view of the development roller 25 and its surroundings of the development device 4, showing a state in which the N2 pole 27d of the stationary magnet body 27 is moved to a position facing the regulation blade 29. As shown in FIG. FIG. 9 is a partially enlarged view showing the direction of the magnetic field around the restricting portion 30 in FIG. When the N2 pole 27d is arranged to face the regulating blade 29, as shown in FIG. 9, a line of magnetic force (indicated by a broken line in FIG. 9, a repelling magnetic field) is generated between the N pole induced at the tip of the regulating blade 29 and the N2 pole 27d. Occur. Next, in the state of FIG. 8, the developing clutch 42 (see FIG. 6) is turned ON (step S8), and the developing roller 25 is rotated in the forward direction (counterclockwise direction in FIG. 8) (step S9). Execute developer removal mode.

As a result, as shown in FIG. 9, a force in the rotational direction of the developing roller 25 acts on the toner aggregates G adhering to the tip of the regulating blade 29 . As a result, toner aggregates G are removed from the tip of regulation blade 29 . At this time, the blade magnet 35 is arranged at the reference position where the tip edge of the opposing magnetic pole 35 a is located inside the tip of the regulating blade 29 . Therefore, the toner aggregates G adhering to the tip of the regulating blade 29 can be easily removed.

Next, the stationary magnet 27 is rotated in the opposite direction (clockwise direction in FIG. 8) from the state shown in FIG. (Step S10). Further, a control signal is sent from the control unit 90 to the blade magnet moving motor 44 to rotate the eccentric cam 39 so that the large diameter portion of the eccentric cam 39 contacts the pressed surface 36b. As a result, the blade magnet 35 together with the magnet support stay 36 is arranged at a protruding position where the tip edge of the opposing magnetic pole 35a protrudes outward (inward in the radial direction of the developing roller 25) from the tip of the regulating blade 29 (step S11). Then, in this state, the developing roller 25 is rotated in the opposite direction (clockwise direction in FIG. 10) to that during image formation (step S12) to execute the second developer removing mode.

FIG. 10 is an enlarged view of the developing roller 25 and its surroundings of the developing device 4 showing a state in which the S2 pole 27c of the stationary magnet body 27 is moved to a position facing the regulating blade 29 in the developing device 4 of this embodiment, and FIG. 11 is a partially enlarged view showing the direction of the magnetic field around the restricting portion 30 in FIG. 10; FIG.

By arranging the S2 pole 27c having the same polarity as the opposing magnetic pole of the blade magnet 35 (different polarity from the magnetic pole induced at the tip of the regulating blade 29) at a position facing the regulating blade 29, the blade magnet 35 as shown in FIG. A repelling magnetic field is generated between 35 and the developing roller 25 . By rotating the developing roller 25 in the reverse direction in this state, a force in the rotational direction of the developing roller 25 acts on the toner aggregates G around the blade magnet 35 . As a result, toner aggregates G are removed from the tip of blade magnet 35 .

At this time, the blade magnet 35 is arranged at a protruding position where the tip edge of the opposing magnetic pole 35 a protrudes outside the tip of the regulating blade 29 . As a result, the toner aggregates G accumulated in the stepped portion between the regulating blade 29 and the blade magnet 35 are pushed out toward the developing roller 25, so that the toner aggregates G pushed out by the developing roller 25 rotating in the reverse direction can be easily removed.

After that, a control signal is transmitted from the control unit 90 to the blade magnet moving motor 44, and the eccentric cam 39 is rotated so that the small diameter portion of the eccentric cam 39 contacts the pressed surface 36b. As a result, the blade magnet 35 is moved again to the reference position (see FIG. 4) (step S13). The control unit 90 determines whether or not printing continues (step S14), and if printing continues (Yes in step S14), the process returns to step S1 to resume printing. If printing has ended (No in step S14), the process ends.

According to the control shown in FIG. 7, by generating a repulsive magnetic field between the regulation blade 29 and the developing roller 25 and rotating the developing roller 25 forward, the toner aggregates G attached to the tip of the regulation blade 29 are removed. It moves to the developing roller 25 side and adheres. The toner aggregates G adhering to the developing roller 25 rotate together with the developing roller 25 and move downward, and are collected from the lower end portion of the developing roller 25 into the housing 20 .

In particular, when a low melting point toner with a glass transition point (Tg) of 55° C. or less is used in a developing system with a linear speed (process speed) of 500 mm/sec or more for the developing roller 25, continuous printing is repeated in a high temperature environment. Even in this case, the toner aggregates G do not stay in the regulating portion 30, and blocking of the toner due to heat or mechanical stress is suppressed. Therefore, it is possible to effectively prevent the clogging of the toner at the regulation portion 30 and the resulting image defects such as white streaks or gray vertical streaks.

Further, by executing the second developer removal mode following the first developer removal mode, the toner aggregates G adhering to the tip of the regulating blade 29 and the toner aggregates G adhering to the tip of the blade magnet 35 are removed. Both can be effectively removed. Furthermore, by moving the blade magnet 35 from the reference position to the projecting position when the second developer removal mode is executed, the toner aggregates G staying at the stepped portion between the regulating blade 29 and the blade magnet 35 are pushed out by the blade magnet 35 . Thus, the toner aggregates G can be efficiently removed.

In the control example of FIG. 7, the fixed magnet 27 is rotated in the positive direction (counterclockwise direction in FIG. 8) when the first developer removal mode is executed, and the N2 pole 27d is arranged at a position facing the regulation blade 29. However, as shown in FIG. 12, the fixed magnet 27 may be rotated in the opposite direction (clockwise direction in FIG. 8) to arrange the N1 pole (main pole) 27b at a position facing the regulating blade 29. FIG.

13 and 14 are partially enlarged views showing the direction of the magnetic field around the regulating portion 30 when the fixed magnet 27 is rotated in the opposite direction. It is a figure which shows the state which passed 30. FIG. 12 to 14, the shaft 36a, pressed surface 36b, coil spring 38, and eccentric cam 39 are omitted.

When the N1 pole 27b approaches the regulating portion 30 from the opposite direction (left direction in FIG. 12), as shown in FIG. A line of magnetic force (repulsive magnetic field) directed toward the inside of (right direction in FIG. 13) is generated. Due to this repulsive magnetic field, the toner aggregates G adhering to the tip of the regulation blade 29 are once swung inside the developing device 4 .

When the fixed magnet 27 rotates in the opposite direction from the state of FIG. 13 and the N1 pole 27b passes through the restricting portion 30, the N pole and the N1 pole 27b induced at the tip of the restricting blade 29 as shown in FIG. The direction of the magnetic field between them is reversed, and a line of magnetic force (repulsive magnetic field) directed toward the outside of the developing device 4 (to the left in FIG. 14) is generated. This repulsive magnetic field causes the toner aggregates G to be shaken to the outside of the developing device 4 this time. Since the toner aggregate G vibrates in accordance with the change in the magnetic field in this manner, a loosening effect can be expected due to the vibration, and the toner aggregate G can be easily removed when the developing roller 25 rotates forward.

12, the fixed magnet 27 is rotated in the opposite direction (clockwise direction) so that the N1 pole (main pole) 27b is arranged at a position facing the regulation blade 29 when the first developer removal mode is executed. In this case, the fixed magnet 27 is rotated in the forward direction (counterclockwise direction) to arrange the S2 pole 27c at a position facing the regulation blade 29 when the second developer removal mode is executed.

At this time, since the S2 pole 27c approaches the opposing magnetic pole 35a (S pole) of the blade magnet 35 from the inside of the developing device 4, a repelling magnetic field toward the outside of the developing device 4 is generated between the opposing magnetic pole 35a and the S2 pole 27c. Occur. As a result, the toner aggregate G adhering to the tip of the blade magnet 35 is once swung outside the developing device 4 (to the left in FIG. 14). After that, when the S2 pole 27c passes through the blade magnet 35, the direction of the repelling magnetic field is reversed to the inside of the developing device 4 (to the right in FIG. 14), and the toner aggregate G is swung inside the developing device 4 this time. Therefore, since the loosening effect by vibration can be expected, the toner aggregate G can be easily removed when the developing roller 25 is reversely rotated.

Furthermore, the execution frequency of the first developer removal mode can be changed according to the detection result of the internal temperature and humidity sensor 61 . That is, by increasing the execution frequency (shortening the interval) of the first developer removal mode as the temperature inside the machine increases, it is possible to suppress toner aggregation and effectively prevent image defects.

Instead of the internal temperature/humidity sensor 61, an external temperature sensor for detecting the temperature outside the image forming apparatus 100 (external temperature) is provided. You may change the execution frequency of agent removal mode.

Next, a second embodiment of the invention will be described. FIG. 15 is a graph showing the relationship between the development driving time T and the aggregation generation level (layer formation rank) in the regulation section 30. As shown in FIG. As is clear from FIG. 15, the development driving time T and the aggregation generation level are correlated, and the longer the development driving time T, the higher the aggregation generation level. Further, as shown by the slope of the graph in FIG. 15, the degree of increase in the level of cohesion generation with respect to the development drive time T (hereinafter referred to as cohesion generation coefficient) changes with temperature, and the higher the temperature, the greater the slope.

Therefore, in this embodiment, the execution timing of the developer removal mode is determined based on the development driving time T. FIG. Specifically, it is determined whether or not the aggregation generation level has reached the first level (here, level 2) based on the development drive time T, and the developer removal mode is executed when the first level is reached. .

At this time, the development driving time T at each temperature is converted into the driving time Tst at the reference temperature S by the following equation (1), considering the temperature dependency of the cohesion generation coefficient.
Tst=T×(a_N/a_S) (1)
however,
a_S; aggregation occurrence coefficient at reference temperature S; a_N; aggregation occurrence coefficient at temperature N;

FIG. 16 is a graph showing the temperature dependence of the aggregation occurrence coefficient a_N. For example, if the reference temperature S is 35° C., and the development driving time T is 120 (min) at 40° C., from FIG. a_40)=1.0, Tst=120×(1.0/0.5)=240 (min) from the equation (1). From FIG. 15, when the development drive time T at 35° C. is 240 minutes, the aggregation occurrence level is level 2, so the developer removal mode is executed at intervals of 240 minutes as indicated by the dashed line in FIG.

By the way, when the toner in the developing device 4 deteriorates, the aggregation occurrence level increases. Therefore, it is preferable to determine the execution frequency of the developer removal mode in consideration of the degree of deterioration of the toner. Therefore, in this embodiment, the calculated driving time Tcal is calculated by the following equation (2) in consideration of the degree of toner deterioration.
Tcal=T×(a_N/a_S)×α (2)
however,
α: Toner deterioration coefficient.

The toner deterioration coefficient α is determined according to the printing rate and the accumulated driving time Tsum (first driving time) of the developing device 4 . In general, the lower the print rate and the longer the cumulative drive time Tsum, the greater the degree of toner deterioration. FIG. 17 shows a graph showing toner deterioration characteristics for each printing rate. In FIG. 17, the toner deterioration characteristics at printing ratios of 1%, 3.8%, 5%, 10% and 50% are indicated by a solid line, a dotted line, a broken line, a one-dot chain line and a two-dot chain line, respectively.

Table 1 shows the relationship between the degree of toner deterioration calculated from the graph of FIG.

From FIG. 17, the cumulative driving time Tsum is 50 minutes or more at the printing rate of 1% or less, the cumulative driving time Tsum is 66.6 minutes or more at the printing rate of 3.8% or less, and the cumulative driving time Tsum is 83.3 minutes at the printing rate of 5% or less. The degree of toner deterioration in the above case (the toner deterioration level is 15 or higher) is assumed to be 1, and as shown in Table 1, the toner deterioration coefficient α is assumed to be 1.5.

Similarly, the cumulative driving time Tsum is 117 min or more at a printing rate of 1% or less, the cumulative driving time Tsum is 200 min or more at a printing rate greater than 1% and 3.8% or less, and the printing rate is greater than 3.8% and 5 minutes. % or less and the accumulated driving time Tsum is 400 min or more (toner deterioration level 30 or more), the toner deterioration degree is 2, and the toner deterioration coefficient α is 2 as shown in Table 1. Also, the toner deterioration degree is set to 3 when the cumulative driving time Tsum is 183 minutes or more at the printing rate of 1% or less, and the cumulative driving time Tsum is 1283 minutes or more at the printing rate of 3.8% or less (the toner deterioration level is 45 or more). The toner deterioration coefficient α is set to 5 as shown in .

When the printing rate is greater than 3.8% and less than or equal to 5% (between the dotted line and the dashed line in FIG. 17), when the cumulative driving time Tsum reaches 400 minutes or more, the degree of deterioration progresses due to an increase in the cumulative driving time Tsum and printing The replacement of the toner is balanced, and the degree of toner deterioration does not change from 2 to 3. When the degree of toner deterioration is less than 1 and the printing rate exceeds 5%, the toner deterioration coefficient α is uniformly set to 1.

FIG. 18 is a graph comparing the execution frequency of the developer removal mode when the toner deterioration degree is less than 1 and when the toner deterioration degree is 2 in FIG. For example, when the toner deterioration degree is 2, the toner deterioration coefficient α is ×2, so the calculated drive time Tcal is doubled, and the aggregation occurrence level reaches level 2 when the drive time Tst=120 min. As a result, the developer removal mode is executed at intervals of 120 minutes as indicated by the dotted line in FIG. That is, the frequency of execution of the first developer removal mode increases (doubles) compared to when the degree of toner deterioration is less than 1 (indicated by the dashed line in FIG. 18).

FIG. 19 is a flow chart showing a control example of the developer removal mode in the developing device 4 according to the second embodiment of the invention. Referring to FIGS. 1 to 6 and 15 to 18 as necessary, the procedure for executing the developer removal mode will be described along the steps of FIG.

When a print command is input from a host device such as a personal computer and printing is started (step S1), the control section 90 (see FIG. 6) determines whether or not printing is continuing (step S2). If printing is not finished (No in step S2), printing is continued.

If printing is completed (Yes in step S2), the development drive time T measured by the timer 97 is detected (step S3). Further, the internal temperature is detected by the internal temperature and humidity sensor 61 (see FIG. 6) (step S4). Then, the cohesion generation coefficient a_N is determined from the detected development driving time T and the internal temperature of the machine (step S5).

Also, the development driving time T is converted into the driving time Tst at the reference temperature S (35° C.) using the formula (1) (step S6). Further, the toner deterioration coefficient α is determined based on the coverage rate and the cumulative drive time Tsum of the developing device 4 (step S7), and the calculated drive time Tcal is calculated using equation (2) (step S8).

The control unit 90 determines whether or not the calculated driving time Tcal is less than a threshold value (here, 240 minutes) (step S9). If the calculated drive time Tcal is less than 240 minutes (Yes in step S9), the process returns to step S1 to resume printing. If the calculated driving time Tcal is 240 minutes or more (No in step S9), the N2 pole 27d is moved to a position facing the regulation blade 29 (step S10), and the developing roller 25 is rotated in the forward direction (counterclockwise in FIG. 8). direction) (step S11), the first developer removal mode is executed.

Next, the S2 pole 27c is moved to a position facing the regulating blade 29 (step S12), the blade magnet 35 is moved to the projecting position (step S13), and the developing roller 25 is rotated in the opposite direction (clockwise direction in FIG. 8). ) (step S14), the second developer removal mode is executed. After that, the blade magnet 35 is moved to the reference position (step S15), the development driving time T is reset (step S16), and the process is finished.

According to the control of FIG. 19, the developer removal mode is executed in accordance with the development drive time T from the previous execution of the developer removal mode and the calculated drive time Tcal calculated based on the toner deterioration coefficient. That is, the developer removal mode is executed at an appropriate frequency according to the degree of toner deterioration. As a result, it is possible to effectively suppress toner clogging in the regulating portion 30 and the resulting vertical streak image.

When the development device 4 is driven for a certain period of time after the aggregation generation level reaches the second level (here, level 3) which is more advanced than the first level (level 2), the life of the development device 4 is displayed on the liquid crystal display 71. , or at least one of an indication prompting replacement of the developing device 4 is displayed. As a result, the developing device 4 is not used for a long period of time in a state where the toner has deteriorated, and it is possible to prevent toner from clogging the regulating portion 30 and occurrence of vertical streak images due to the deterioration of the toner.

In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention. For example, in each of the above-described embodiments, the fixed magnet body 27 has a quadrupole configuration having two N poles and two S poles, but the present invention applies the fixed magnet body 27 to a five-pole configuration or a three-pole configuration. is also applicable. Also, in each of the above embodiments, the second developer removal mode is executed after the first developer removal mode is executed, but the first developer removal mode may be executed after the second developer removal mode is executed. .

In each of the above-described embodiments, the blade magnet 35 is moved between the reference position and the projecting position by the coil spring 38, the eccentric cam 39, and the blade magnet moving motor 44. However, the mechanism for moving the blade magnet 35 is limited to this. Instead, a conventionally known mechanism such as a solenoid or a rack and pinion mechanism can be used.

INDUSTRIAL APPLICABILITY The present invention is applicable to a developing device using a magnetic one-component developer and a developer carrier used therein. By utilizing the present invention, it is possible to provide a developing device capable of suppressing toner clogging in the toner regulating portion even when continuous printing is performed in a high-temperature environment, and an image forming apparatus having the same.

4 developing device 9 image forming unit 20 housing
23 First stirring screw 24 Second stirring screw 25 Development roller (developer carrier)
27 fixed magnet body (magnet member)
27a S1 pole (transport pole)
27b N1 pole (main pole)
27c S2 pole (regulation pole)
27d N2 pole (pumping pole)
27e Shaft 29 Regulating Blade 30 Regulating Part 35 Blade Magnet 35a Opposing Magnetic Pole 61 Internal Temperature and Humidity Sensor (Temperature Detection Device)
71 liquid crystal display (display device)
90 control unit 97 timer (time counting unit)
100 Image forming apparatus G Toner aggregate

Claims (10)

a housing for containing a developer having magnetism;
a developer carrier that is rotatably supported by the housing and that carries the developer on its outer peripheral surface;
a regulating blade disposed at a predetermined distance from the developer carrier and formed of a magnetic material forming a regulating portion for regulating the layer thickness of the developer carried on the developer carrier;
a magnet member having a shaft arranged inside the developer carrying member and a plurality of magnetic poles including an S pole and an N pole fixed to the outer peripheral surface of the shaft;
a blade magnet that is fixed to the regulating blade and induces a magnetic pole at the tip of the regulating blade;
In a developing device for developing an electrostatic latent image formed on an image carrier,
The magnet member has a first position where a magnetic pole having the same polarity as the opposing magnetic pole of the blade magnet facing the developer carrier is arranged in the regulating portion, and a first position where the magnetic pole having the opposite polarity to the opposing magnetic pole is arranged in the regulating portion. a second position located at and movable to;
The blade magnet has a reference position where the tip of the opposing magnetic pole is arranged radially outside the tip of the regulating blade, and a reference position where the tip of the opposing magnetic pole is positioned radially outward of the tip of the regulating blade. and a protruding position protruding radially inward of the agent carrier,
With the magnet member positioned at the second position and the blade magnet positioned at the reference position during non-image formation, the developer carrier is rotated in the positive direction, which is the direction of rotation during image formation. a first developer removal mode for removing the developer remaining in the regulating portion;
With the magnet member arranged at the first position and the blade magnet arranged at the projecting position, the developer carrying member is rotated in the reverse direction opposite to the forward direction to rotate the blade magnet and the blade magnet. a second developer removal mode for removing the developer that has accumulated between itself and the developer carrier;
A developing device capable of executing a developer removing mode including: 2. The apparatus according to claim 1, wherein when the first developer removing mode is executed, the magnet member is rotated in the opposite direction to move the magnet member from the first position to the second position. development equipment. 2. The magnet member is rotated in the forward direction to move the magnet member from the second position to the first position when the second developer removal mode is executed. Item 3. The developing device according to item 2. 4. The developing device according to any one of claims 1 to 3, wherein the rotational speed of said developer carrier during image formation is 500 mm/sec or more. 5. The developing device according to claim 1, wherein the developer is a magnetic one-component developer consisting only of magnetic toner. An image forming apparatus comprising the developing device according to any one of claims 1 to 5. A first driving time Tsum, which is the cumulative driving time from the start of use of the developing device, and a second driving time T, which is the cumulative driving time from execution of the first developer removing mode immediately before, are separately measured. a time counting unit for
a control unit that controls the developing device;
with
The control section determines whether or not the level of occurrence of aggregation of the developer has reached a first level based on the second driving time T measured by the time counting section, and determines whether or not the level of developer aggregation has reached the first level. 7. The image forming apparatus according to claim 6, wherein the developer removing mode is executed when the developer is removed. A temperature detection device that detects the temperature inside or outside the image forming apparatus,
The control unit converts the second driving time T at the temperature N detected by the temperature detection device to a driving time Tst at the reference temperature S using the following equation (1), and converts the aggregation based on the driving time Tst. 8. The image forming apparatus according to claim 7, wherein it is determined whether or not the occurrence level has reached the first level.
Tst=T×(a_N/a_S) (1)
however,
a_S; aggregation occurrence coefficient at reference temperature S; a_N; aggregation occurrence coefficient at temperature N; The control unit calculates a calculated driving time Tcal considering the degree of deterioration of the developer according to the following equation (2), and determines whether the aggregation generation level has reached the first level based on the calculated driving time Tcal. 9. The image forming apparatus according to claim 8, wherein determination is made as to whether or not.
Tcal=T×(a_N/a_S)×α (2)
however,
α: Toner deterioration coefficient. a display device capable of displaying an indication of the life expectancy of the developing device predicted based on the aggregation occurrence level or an indication prompting replacement of the developing device;
When the control unit is driven for a predetermined period of time after the aggregation generation level reaches a second level advanced from the first level, the control unit uses the display device to display the end of life of the developing device. 10. The image forming apparatus according to any one of claims 7 to 9, wherein at least one of display prompting replacement is displayed.

Images