JP2008151839A - Developing device and image forming apparatus having the same - Google Patents

Abstract

An object of the present invention is to provide a developing device in which both toner density controllability and toner presence / absence detectability are improved.
A developer agitating / conveying means for agitating and conveying a developer containing toner and a carrier, a containing means for containing the developer and the developer agitating / conveying means, and a toner concentration of the developer in the containing means are detected. And a developer agitating / conveying means for conveying the developer in the containing means, and a toner concentration detecting means and a developing means for supplying the developer in the containing means to the photosensitive member. By having a stirrer that prevents the bulk or bulk density of the developer from becoming high, the flow of the developer can be secured without the influence of the developer having a high bulk or bulk density, and the toner concentration controllability and Both toner presence / absence detectability can be improved.
[Selection] Figure 3

Description

  The present invention relates to a developing device used in a printer, a multifunction machine, and the like, and an image forming apparatus including the developing device.

  In conventional image forming apparatuses, developing apparatuses using a two-component developer containing toner and a carrier are widely used. The two-component developer is composed of a toner and a carrier, and the ratio of the toner in the developer is expressed as a toner concentration. Here, the carrier is a magnetic material, and the toner concentration sensor is obtained by measuring the magnetic permeability of the developer. That is, the toner density sensor represents the carrier filling state in the developer as a sensor output. When the toner density sensor output is equal to or higher than the reference voltage, the distance between the carriers is short, that is, the toner amount is smaller than the reference value, and the toner density sensor output is below the reference level from the toner container such as a toner bottle. Until the developer is replenished. This control makes it possible to keep the toner concentration in the developer in the developing device within a certain range.

  In order to accurately detect the toner density, the developer at the upper part of the toner density sensor is constantly replaced by being moved by the conveying means, and a new developer is continuously sent to the detection range of the toner density sensor continuously. It is necessary to obtain a sensor output corresponding to the toner density.

  Japanese Patent Application Laid-Open No. 2004-133867 discloses a developing device that appropriately performs the developer transport movement. The developing device disclosed in Patent Document 1 includes a screw shaft having spiral blades around it and a stirring member (stirring plate) provided between adjacent spiral blades in the upper part of the toner concentration sensor. ).

  According to this configuration, the developer is transported in the axial direction of the screw shaft by the rotation of the spiral blade by the rotation of the screw shaft, and the agitating member is also rotated in the rotational direction of the screw shaft. The developer staying around is forcibly stirred. As a result, new developer is always supplied around the upper portion of the toner density sensor, so that a change in the output of the toner density sensor with respect to the toner density can be stably obtained.

  On the other hand, if the remaining amount of toner in the toner storage unit that supplies toner to the transport unit is exhausted, it becomes difficult to control the toner density appropriately. Therefore, it is necessary to monitor the remaining amount of toner in the toner storage unit. For this purpose, it is possible to provide a dedicated sensor for detecting the remaining amount of toner. However, in order to reduce the cost, a sensor configured to be used also as a toner density sensor is known (see Patent Document 2). .

  This is to detect the presence or absence of toner in the toner accommodating portion based on a change in toner density when the toner supply mechanism is operated.

As described above, a configuration is also known in which toner density control is performed by the toner density sensor, and also the presence / absence detection of toner in the toner container is also used.
JP 2002-304050 A JP 10-123811 A

  However, this conventional technique has the following problems.

  In recent years, in printers and multi-function peripherals, in order to improve the productivity of the number of printed sheets per unit time, the speed is increasing. For this purpose, it is necessary to increase the rotation speed of the developing sleeve provided in the developing unit for supplying the developer to the photosensitive member in accordance with the speeding up of the device. For this purpose, the screw shaft for mixing and stirring the developer is required. By increasing the rotation speed, it is necessary to maintain the stirring property while improving the transportability of the developer.

  However, in the configuration described in Patent Document 1, when the rotational speed of the screw shaft is increased, a state in which the developer is sparse occurs after the stirring member that stirs the developer passes through the upper portion of the toner density sensor. This varies depending on the rotational speed of the screw shaft, and the sparse state is more strongly generated as the rotational speed of the screw shaft is higher.

  As described above, the higher the rotational speed of the screw shaft, the more sparse space is formed in the developer contained in the developing device, so the height of the developer layer from the bottom of the developing device to the surface of the developer is compared to the amount. (Below referred to as being bulky). When the volume of the developer increases, the average bulk density (developer weight per unit volume) decreases, but the developer is compressed under the influence of gravity, and near the toner concentration sensor detection surface located under the developer. The bulk density causes a phenomenon that becomes higher than the average bulk density.

  Further, the developer conveyed by the screw shaft and the spiral blade is blocked by the stirring member, and the developer passes over the stirring member and flows downward (developing device bottom). As a result, the developer is forcibly fed into the gap between the toner concentration sensor detection surface and the stirring member, and the developer bulk density near the toner concentration sensor detection surface is further increased.

  Here, as described above, the toner concentration sensor converts the magnetic permeability of the carrier in the developer into a read output. If the toner concentration is high, the number of carriers per unit volume decreases, so the sensor output decreases. Conversely, when the toner concentration is low, the number of carriers per unit volume increases and the sensor output increases. Accordingly, when the developer is compressed in the vicinity of the toner density sensor detection surface and the bulk density of the developer is increased, the number of carriers per unit volume is increased and the toner density sensor output is increased.

  For this reason, even when the toner density is the same, the bulk density of the developer increases, so that the number of carriers in the vicinity of the toner density sensor detection surface increases, and the toner density sensor erroneously detects that the toner density is low.

  That is, in Patent Document 1, the developer bulk density in the vicinity of the toner concentration sensor detection surface is affected by the bulk of the developer and the force of compressing the developer in the gap between the toner concentration sensor and the stirring member. It was difficult to control the toner density.

  Further, the developer after supplying the toner to the image portion of the photoreceptor forming the latent image consumes the toner and has a low toner density. On the other hand, the developer corresponding to the non-image portion is in the state of the reference toner density set initially because the toner is not consumed. In such a state, the developer is conveyed.

  Therefore, in the portion where the stirring member is located in the upper part of the toner density sensor, the image portion has a low developer volume, and conversely, the non-image portion has a high developer volume (initially set reference bulkiness). .

  In the area where the volume of the developer is low in the image area, the bulk density of the developer is almost uniform. However, in the non-image area, the volume of the developer is high, and therefore, in the vicinity of the toner density sensor detection surface. Bulk density increases due to compression by its own weight.

  For this reason, the toner density sensor erroneously detects that the toner density is low because the bulk density due to the compression of the developer in the non-image area is high, and the sensor output is high. As a result, the toner is replenished in spite of the non-image portion, and the toner is excessively replenished, resulting in a problem that the toner density increases.

  On the other hand, in order to use the toner density sensor also as a toner presence / absence detection sensor and monitor the remaining amount of toner in the toner storage unit, if the technique of Patent Document 2 is implemented with the configuration of the stirring member described in Patent Document 1, stirring is performed. Since the developer in the portion blocked by the member enters the space surrounded by the spiral blade and the stirring member, the developer cannot be replaced efficiently. For this reason, the toner replenished in a large amount temporarily by replenishing toner has a specific gravity lighter than that of the carrier, and thus flows along the surface of the developer with good flow. Further, since the toner dispersibility is poor even when agitated with the developer, the replenished toner is not uniformly dispersed in the developer. Therefore, a non-uniform toner density distribution is formed on the toner density sensor detection surface. Although it can be replaced after a certain amount of time, it cannot secure the reproducibility in a short time required for detecting the presence or absence of toner, so a large change in toner density sensor output cannot be obtained even if toner is replenished. It is difficult to use as toner remaining amount detection. This is a big problem for a developing device aiming at speeding up, and in this type of developing device, it is difficult to use the toner density sensor also as a toner presence / absence detecting sensor.

  The present invention has been made in view of such problems, and ensures the flow of the developer by providing a stirring unit that prevents the bulk or bulk density of the developer around the toner concentration detection unit from increasing. Another object of the present invention is to provide a developing device in which both toner density controllability and toner presence / absence detection properties are improved.

  The developing device according to the present invention includes a developer agitating / conveying means for agitating and conveying a developer including toner and a carrier, a containing means for containing the developer and the developer agitating / conveying means, and a toner concentration of the developer in the containing means A toner concentration detecting means for detecting the developer and a developing means for supplying the developer in the storage means to the photosensitive member. The developer agitation transport means includes a transport section for transporting the developer in the storage means, and a toner density detection And a stirrer for preventing an increase in the bulk or bulk density of the developer around the means.

  With this configuration, the present invention prevents the developer stirring / conveying means in the housing means from increasing the bulk and bulk density of the developer around the detection unit of the toner density detecting means, and the detection output of the toner density detecting means. Thus, stable toner density control can be performed.

  Further, the developing device of the present invention has a configuration in which the stirring unit is disposed over the entire detection surface of the toner concentration detection means.

  With this configuration, the present invention allows the developer on the entire upper surface of the detection surface of the toner density detection unit to be agitated and moved by the agitation unit, so that the developer can always be replaced without the developer staying, and the developer can be replaced. Therefore, it is possible to control the toner density with high accuracy.

  Further, in the developing device of the present invention, the transport unit includes a rotating shaft portion provided in the developer transport direction and a spiral blade provided on the outer periphery of the rotating shaft portion, and the stirring unit is adjacent to the rotating shaft portion. It has a configuration including a stirring plate provided between two spiral blades, and an opening formed in the spiral blade near the coupling portion between the stirring plate and the spiral blade.

  With this configuration, the present invention stirs in the stirrer, and the developer that is partially increased in bulk or bulk density moves over a certain bulk or bulk density from the opening, and develops in the stirrer. The bulk or bulk density of the agent can always be kept substantially constant, and the toner density can be controlled stably.

  Further, the developing device of the present invention has a configuration in which the stirring plate is disposed over the entire detection surface of the toner concentration detection means.

  With this configuration, the present invention allows the developer on the entire upper surface of the toner density detection unit to be agitated and moved by the agitation plate, so that the developer can always be replaced without the developer staying in place. Since a corresponding toner density sensor output can be obtained, the toner density can be controlled with high accuracy.

  The developing device of the present invention has a configuration in which the opening is formed in a spiral blade in a range of 15 ° to 80 ° when viewed from the axial direction of the rotating shaft.

  With this configuration, the present invention can sufficiently prevent the increase in the bulk of the developer or the increase in the bulk density while sufficiently performing the stirring function by the stirring section, and has high accuracy. It is possible to control the toner density and detect the presence / absence of the toner density with high accuracy.

  Further, the image forming apparatus of the present invention has a configuration provided with the above developing device.

  With this configuration, the present invention can obtain stable image output by stable toner density control corresponding to high speed.

  According to the present invention, it is possible to prevent an increase in the bulk or bulk density of the developer around the toner concentration detection unit, so that the developer mixed and agitated with toner is sequentially switched to the detection region around the toner concentration detection unit. Thus, stable toner density control and stable toner remaining amount detection can be performed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic diagram showing a schematic configuration of a color image forming apparatus according to Embodiment 1 of the present invention. In FIG. 1, an image forming apparatus according to the present embodiment includes an image forming unit 101 that forms an image on recording paper through processes of charging, exposure, development, transfer, and fixing, and a paper feed path A to the image forming unit 101. The sheet feeding unit 102 having a sheet feeding cassette for storing the recording sheets 103 sequentially fed through the recording medium 103 and the recording sheet 103 on which a required image is formed by the image forming unit 101 are discharged out of the apparatus via the sheet discharge path B. And a paper discharge unit 104 provided outside the apparatus.

  The image forming unit 101 includes a plurality of process units 111 to 114 that form toner images for respective color components of yellow (Y), magenta (M), cyan (C), and black (K), and the process units 111. ˜114, a laser scanning unit (hereinafter referred to as LSU) 116 that scans an image forming surface of each photosensitive drum (hereinafter referred to as “photosensitive member”) 111a to 114a, and each process. And an intermediate transfer belt 117 in which the toner images of the respective colors formed on the photoconductors 111a to 114a in the units 111 to 114 are sequentially transferred and synthesized, and the photoconductors 111a to 114a of the respective colors are intermediate. It has a tandem structure arranged along the transfer belt 117.

  In each of the process units 111 to 114, the electrostatic latent image is obtained by scanning the image forming surface of each of the photoconductors 111a to 114a uniformly charged by the chargers 111b to 114b from the LSU 116. The electrostatic latent images of the respective photoconductors 111a to 114a are developed with the toners of the respective colors supplied from the developing devices 111c to 114c, and single color toner images for the respective color components are formed on the respective photoconductors 111a to 114a. It is formed on the image forming surface.

  The intermediate transfer belt 117 is wound around and supported by a driving roller 121 and a driven roller 122. Inside the intermediate transfer belt 117, the intermediate transfer belt 117 is pressed to form toner images on the photoconductors 111a to 114a. Primary transfer rollers 124 to 127 for the respective colors to be transferred to the intermediate transfer belt 117 are provided. Further, a secondary transfer roller 128 for transferring the toner image on the intermediate transfer belt 117 to the recording paper 103 is disposed on the side of the end of the intermediate transfer belt 117. The recording paper 103 that has passed through the paper feeding path A is guided to the secondary transfer roller 128 by the guide plate 105.

  The recording paper 103 onto which the toner image has been transferred by the secondary transfer roller 128 is transported to the fixing device 119, and a process for fixing the toner image on the recording paper 103 by heat and pressure is performed. Thereafter, the recording paper 103 passes through the paper discharge path B and is discharged to the paper discharge unit 104 by the paper discharge roller 120.

  FIG. 2 is a configuration diagram schematically showing a developing device 111c (developing device 111c to developing device 114c will be described as a representative case because of the same structure) in the present embodiment.

  In FIG. 2, the developing device 111 c includes a replenishing toner container 201 that contains toner and has a toner replenishing port 200 below, a developing case (accommodating means) 203 as a stirring chamber that accommodates the developer 202, and a replenishing toner container 201. A first agitation screw 204 that mixes and agitates the replenished toner with the developer 202 in the developing case 203 and conveys the toner is provided. Further, the developing device 111c includes a toner concentration sensor 205 that is provided on the bottom surface of the developing case 203 below the first stirring screw 204 and detects the toner concentration of the developer 202 that has been mixed and stirred. The developing device 111c includes a second stirring screw 206 disposed in the developing case 203 in parallel with the first stirring screw 204 so that the developer 202 circulates in the developing case 203. Further, the developing device 111c supplies the developer 202 supplied by the second stirring screw 206 to the photosensitive member 111a, a developing sleeve (developing means) 209 having a mag roll 208 inside, and the developing supplied to the developing sleeve 209. And a doctor blade 210 that regulates the layer thickness of the agent 202.

  Further, the developing device 111c includes a CPU 211 that controls the amount of toner to be replenished from the replenishment toner container 201 based on the toner density detected by the toner density sensor 205, a RAM 212 that reads and writes various data under the control of the CPU 211, and a CPU 211. And a ROM 213 storing a program for operating the computer.

  The first stirring screw 204 has a screw shaft (rotating shaft portion) 214, a spiral blade 215 formed on the outer periphery thereof, and a stirring plate 216 provided between two adjacent spiral blades 215. The second stirring screw 206 includes a screw shaft (rotating shaft portion) 217 and a spiral blade 218 formed on the outer periphery thereof.

  When a latent image (not shown) is formed on the photosensitive member 111a in FIG. 2, the toner of the developer 202 layered on the developing sleeve 209 is developed on the latent image of the photosensitive member 111a by the rotation indicated by the arrow. Thereafter, the developer 202 is separated from the developing sleeve 209 and collected at a portion where the second stirring screw 206 is disposed. The developing case 203 is configured such that the developer circulates at both ends (the front and back portions in the figure) of the first stirring screw 204 and the second stirring screw 206, and the developer 202 collected from the developing sleeve 209 is configured. Is conveyed to the first stirring screw 204 by the second stirring screw 206 while mixing and stirring the developer in accordance with the rotation indicated by the arrow. The developer 202 conveyed to the first agitating screw 204 has a toner density detected by the toner density sensor 205, and when the CPU 211 determines that the output from the toner density sensor 205 is higher than the reference voltage, the toner amount is small and the distance between the carriers. Therefore, the toner is replenished from the replenishment toner container 201 under the control of the CPU 211. The replenished toner is conveyed while being mixed and agitated by the rotation of the first agitating screw 204 as indicated by an arrow, and is circulated to the second agitating screw 206.

  FIG. 3 is a configuration diagram showing the configuration of the first stirring screw 204 in the present embodiment. In FIG. 3, the first agitation screw 204 includes a screw shaft 214 and a spiral blade formed on the outer periphery of the screw shaft 214 for transporting the developer 202 in the direction of the solid line arrow as described with reference to FIG. 2. 215. The spiral blade 215 has a first transport surface 215a and a second transport surface 215b opposite to the first transport surface 215a, and the toner between the first transport surface 215a and the second transport surface 215b. A stirring plate 216 is provided above the concentration sensor 205. Further, the spiral blade 215 has an opening 301 formed by a notch in the vicinity of the coupling portion with the stirring plate 216, and the developer 202 whose flow is blocked by the stirring plate 216 is the opening 301. To the downstream side.

  In this embodiment, the opening 301 is formed by cutting out the entire spiral blade 215 in the vicinity of the joint with the stirring plate 216. However, the present invention is not limited to this, and an appropriate area of the opening 301 is provided. The same effect can be achieved by forming the spiral blade 215 by cutting away the outer peripheral portion while leaving the portion where the spiral blade 215 is connected to the screw shaft 214.

  In other words, in the present embodiment, the developer agitation and conveyance unit includes a conveyance unit including the screw shaft 214 and the spiral blade 215 and an agitation unit including the agitation plate 216 and the opening 301. Further, the screw shaft 214 includes a rib 302 on the downstream side of the stirring plate 216 where the developer 202 flows.

  FIG. 4 is an explanatory diagram of the notch angle 303 of the opening 301 at the joint between the stirring plate 216 and the spiral blade 215. A spiral blade 215 arranged on the outer periphery of the screw shaft 214 is a predetermined axis with the screw shaft 214 as a central axis when viewed from the upstream side of the screw shaft 214 (right side in the drawing) from the joint with the stirring plate 216. An opening 301 is formed by cutting out by the notch angle 303.

  In FIG. 3, the toner replenished from the replenishing toner container 201 in the direction of the dotted line arrow is constituted by the first conveying surface 215a and the second conveying surface 215b by the rotation of the screw shaft 214 while being mixed and stirred with the developer 202. In the concave portion 304, it is conveyed in the direction of the screw shaft 214 along the direction of the solid line arrow. The developer 202 conveyed to the upper part of the toner density sensor 205 is agitated in the rotational direction of the screw shaft 214 by the agitating plate 216, and the flow is temporarily inhibited, but the developer overflowed from the concave portion 304 is inhibited. 202 is discharged from the opening 301 located on the downstream side, so that a series of flow of the developer 202 in the direction of the screw shaft 214 is secured.

  That is, the developer 202 conveyed to the detection range of the toner density sensor 205 by the first agitation screw 204 is agitated by the agitation plate 216 that is located in front of the detection surface of the toner density sensor 205 and agitates and conveys the developer. In addition, since the flow in the direction of the screw shaft 214 along the concave portion 304 is hindered, the developer 202 temporarily stays and a part of the developer 202 is sparse by the stirring plate 216. The developer 202 tends to be bulky. However, the developer 202 exceeding the amount of the developer 202 that can be held by the stirring plate 216 by the stirring is discharged from the opening 301 located on the downstream side, and the bulk is prevented. The amount that the stirring plate 216 can hold the developer 202 is always the same according to the number of rotations of the first stirring screw 204, so that when the amount of the developer 202 conveyed from the upstream is large, the opening 301 is large in amount. If the amount of the developer 202 discharged from the upstream side and conveyed from the upstream is small, the amount discharged from the opening 301 is also small. Therefore, in the vicinity of the front surface portion of the detection surface of the toner density sensor 205, it is possible to prevent the developer 202 from staying between the detection surface and the stirring plate 216 and increasing the bulk density as in the past. In other words, in the present embodiment, the stirring unit composed of the stirring plate 216 and the opening 301 prevents the bulk or density of the developer 202 around the toner density sensor 205 from being increased by the action of the opening 301. ing.

  On the downstream side of the developer 202 discharged from the opening 301, the toner and the developer 202 are further mixed and stirred by the rib 302. This is to change the degree of mixing and stirring of the toner and the developer 202 before and after the detection region of the toner concentration sensor 205 to achieve both toner density controllability and toner presence / absence detectability.

    That is, if the replenishment toner and the developer are completely made uniform upstream of the detection range of the toner density sensor 205, a difference in sensor output voltage with respect to the replenishment toner amount cannot be obtained, and the toner presence / absence detection function is deteriorated. On the upstream side of the detection range of the toner density sensor 205, it is necessary to appropriately replenish the replenished toner to the developer. Thereafter, on the downstream side after passing through the detection range of the toner density sensor 205, the developer 202 positioned at the upper part in the developing case 203 and the developer 202 positioned at the lower part of the developing case 203 are positively mixed by the rib 302. Stir. As a result, after the toner and the developer 202 are sufficiently mixed, the developer 202 is conveyed to the second agitating screw 206 and development with a uniform developer is possible.

  As described above, in the present embodiment, the developer 202 conveyed by the first conveyance surface 215a is agitated by the agitation plate 216, and the flow is inhibited and temporarily accumulated, and then the developer 202 passes through the opening 301. Will be discharged. That is, the developer 202 conveyed from the upstream does not stay on the stirring plate 216 for a long time, and the bulk density does not increase as in the conventional case, and can be sequentially replaced with the upstream developer 202 in a short time. It becomes. Here, when the toner density sensor 205 detects the toner density of the developer 202 and the CPU 211 determines that the toner density is low, the toner is supplied from the supply toner container 201 to the developing case 203. The replenished toner is mixed and agitated with the developer 202 in the developing case 203 by the first agitating screw 204 and conveyed to the agitating plate 216 where the toner concentration sensor 205 is disposed. The developer having a high toner concentration mixed and stirred with the replenishing toner temporarily stays on the stirring plate 216, but is sequentially replaced with the upstream developer, so that the density around the detection surface of the toner concentration sensor 205 is not affected. It is possible to continuously detect the toner density with high accuracy.

  Here, the developer 202 in the image area, which is an area where the toner is consumed by developing on the latent image on the photoreceptor 111a, has a small amount of developer 202 conveyed to the stirring plate 216 portion. The amount discharged from the opening 301 is also small. On the other hand, the developer 202 in the non-image area where the toner is not developed has a large amount of developer conveyed to the stirring plate 216, so that the amount discharged from the opening 301 is also increased. An increase in the amount of developer 202 on the detection surface can be prevented. As a result, in the detection surface of the toner density sensor 205, the amount of the developer 202 in the image portion and the non-image portion on the stirring plate 216 becomes almost the same amount, thereby preventing the developer 202 from becoming bulky. Thus, the bulk can be kept substantially constant.

  If the bulk of the developer 202 corresponding to the image portion and the non-image portion is different from that of the conventional developing device and the bulk of the developer 202 corresponding to the image portion and the non-image portion is different, the developer 202 is compressed around the detection surface of the toner density sensor 205. Since the degrees are different, the toner density sensor output value is different even at the same toner density, and the toner density control accuracy is lowered. However, in this embodiment, the developer 202 is prevented from becoming bulky and is kept substantially constant, so that the degree of compression of the developer 202 around the surface of the toner density sensor 205 becomes approximately the same. Accordingly, it is possible to prevent the bulk density from being increased, and to measure the toner concentration of the developer 202 which is purely composed of the mixing ratio of the toner and the carrier without being affected by the bulk density.

  By the way, in the present embodiment, a sensor output value (initial set value) at the maximum toner concentration, which is a toner concentration immediately after toner is supplied from the supply toner container 201 to the developing case 203, and a sensor output value before toner supply. The CPU 211 monitors the difference between the output values before and after toner replenishment, and determines that the toner has been replenished if the difference between the output values before and after the replenishment of the toner is equal to or higher than a specified voltage. That is, when the voltage is lower than the specified voltage, it is possible to determine that there is no toner in the replenishment toner container 201 because the predetermined toner has not been replenished from the replenishment toner container 201. Further, since the toner density sensor output changes according to the amount of replenished toner, the remaining amount of toner in the replenished toner container 201 can be detected with high accuracy.

  Therefore, the toner concentration sensor 205 can be used as a sensor for accurately detecting the remaining amount of toner in the replenishing toner container 201, so that it is not necessary to attach a dedicated toner remaining amount sensor, thereby reducing costs. Become.

  Further, when making a product using the same developing device and increasing the productivity of copying, it is necessary for the developing device 111c to increase the rotation speed of the developing sleeve 209 in order to maintain the supply of toner to the photosensitive member 111a. is there. Accordingly, it is necessary to increase the rotation speeds of the first stirring screw 204 and the second stirring screw 206. In this way, even if the rotation speed increases due to the change in the rotation speed of the first stirring screw 204, other than the prescribed amount of the developer 202 that temporarily stays on the stirring plate 216, it is discharged from the opening 301 as described above. Therefore, the bulk of the developer 202 can be prevented from being increased by the stirring plate 216 as in the prior art, and the volume can be made substantially constant.

  FIG. 5 is a graph showing toner density controllability and toner presence / absence detectability with respect to the notch angle 303. The horizontal axis indicates the notch angle 303, the left vertical axis indicates the toner density controllability, and the right vertical axis indicates the toner presence / absence detectability.

  The toner density controllability represents a difference between the toner density of the developer after the toner replenished to the developing case 203 is stirred and conveyed by the developer stirring unit for a predetermined time and a predetermined uniform toner density. is there. Further, the toner presence / absence detectability represents the degree to which the amount of toner supplied to the developing case 203 is an appropriate amount. These vary depending on the size of the notch angle 303 of the opening 301 as shown in FIG. A method for measuring these characteristics will be described with reference to FIG.

FIG. 6 is a graph showing the notch angle 303, an index of toner density controllability and toner density presence / absence detectability,
The sensor output of the toner density sensor 205 is shown as a function of time. In the present embodiment, in FIG. 6, the developer 202 having a toner concentration of 8% is stirred for 4.5 minutes, and the average output voltage for the last one minute is set to “V1”. Thereafter, the toner is replenished 20 times from the replenishment toner container 201 at the toner replenishment timing every 5 seconds shown in FIG. V difference ". After supplying the toner 20 times, the sensor output is measured every 10 seconds while stirring is continued for 2 minutes, and each voltage is set to “Vi (i = 1 to 12)”. After measuring all “Vi”, once all the developer 202 is taken out from the developing case 203 and mixed, the developer 202 is returned to the developing case 203 again, and the stirring operation is further performed for 4.5 minutes. Let the average output voltage for the last minute be “V2”. Thus, “Vi” is the toner concentration measured 12 times every 10 seconds after the toner is replenished 20 times, and “V2” is after the developer is taken out and the toner is mixed uniformly. The toner density is stable. Therefore, as shown in Expression (1), the change rate of the difference between “Vi” and “V2” with respect to the root mean square (V1−V2) is “error rate” T, and the toner density controllability is shown.

すなわち、「誤差率」Ｔは、トナーを２０回補給した後の出力と、一旦現像剤を出し入れした後の出力の（Ｖ１−Ｖ２）に対する割合であって、トナーの２０回補給後の攪拌によってＶｉとＶ２との差がなくなる「０」が一番望ましい値である。これに対して、図６は出力ＶｉとＶ２との間に差「Ｖｚ」があることを示している。これは、現像剤の出し入れによるセンサー出力の方が低いため、トナー濃度センサー２０５周辺における現像剤２０２の入れ替えが良くないためと考えられる。つまり、トナー補給により現像剤２０２の平均トナー濃度は高くなるがトナー濃度センサー２０５上方部周辺の現像剤２０２だけが入れ替えが悪く、現像剤２０２の全体平均トナー濃度より低いトナー濃度の状態になっていると考えられる。

That is, the “error rate” T is a ratio of the output after the toner is replenished 20 times and the output after the developer is once taken in and out (V1−V2). “0” that eliminates the difference between Vi and V2 is the most desirable value. In contrast, FIG. 6 shows that there is a difference “Vz” between the outputs Vi and V2. This is presumably because the replacement of the developer 202 in the vicinity of the toner density sensor 205 is not good because the sensor output due to the loading and unloading of the developer is lower. That is, the toner replenishment increases the average toner density of the developer 202, but only the developer 202 around the upper portion of the toner density sensor 205 is poorly replaced, resulting in a toner density lower than the overall average toner density of the developer 202. It is thought that there is.

  Here, the variation in the current toner density fluctuation is “error rate” T = 0.3, which is about 1% in terms of toner density. In this case, since the reference toner density is 8%, it varies up to 9%. However, it is generally desirable for the developing device 111c to suppress the toner density variation to half or less of 0.5%. Therefore, in order to suppress the “error rate” to about 0.5% in terms of toner density, the critical value of the “error rate” T is about 0.2.

  As shown in FIG. 5, the “error rate” T is changed by changing the notch angle 303 of the opening 301, and in this embodiment, the cut of the opening 301 where the “error rate” T is 0.2 or less. The notch angle 303 ranges from 15 ° to 80 °, and there is a range in which the toner density control accuracy is kept high. It should be further desired to obtain an optimum range for obtaining the minimum value of the “error rate” T when the notch angle 303 is in the range of 30 ° to 60 °.

  The “V difference” is a change in the sensor output when the toner is replenished. The larger the value, the higher the sensitivity to toner replenishment, that is, the toner presence / absence detectability. As shown in FIG. 5, the “V difference” also changes depending on the notch angle 303 of the opening 301. FIG. 5 shows that the “V difference” decreases as the notch angle 303 increases. This is because when the notch angle 303 is “0”, the toner supplied from the supply toner container 201 is conveyed in the detection range of the toner density sensor 205 in an aggregated state, so that the “V difference” is the largest. Although it is large, as the notch angle 303 increases, the replenished toner is mixed and stirred with the developer 202, so the “V difference” is considered to be small. That is, the smaller the “V difference” is, the higher the mixing and stirring rate of the toner and the developer 202 is. From the viewpoint of toner presence / absence detectability, the greater the “V difference”, that is, the more the toner and developer 202 are not mixed and stirred, the higher the sensitivity, but the toner concentration control based on the mixing and stirring property of the toner and developer 202 Therefore, there is an optimum range of the notch angle 303 in consideration of the property.

   FIG. 7 is a graph showing the relationship between the copy speed (number of printed sheets per unit time) and the “error rate” T for the conventional example and this embodiment. In the conventional example indicated by the alternate long and short dash line 701, the “error rate” T increases as the copy speed increases, and the control accuracy of the toner density becomes “error rate” T = 0.2 (the variation in toner density is about 0.5%). However, according to the present embodiment indicated by the solid line 702, the “error rate” T can be reduced to 0.2 or less even when the copy speed is increased. As described above, in this embodiment, the toner density controllability can be stably maintained without depending on the copy speed.

  The relationship between the notch angle 303, the toner density controllability, and the toner presence / absence detectability is similar even when the reference toner density is other than 8%.

  From the above, the notch angle 303 that satisfies both conditions even if the copy speed is increased from the viewpoint of both “error rate” T and “V difference” is in the range of 15 ° to 80 °. The toner density control accuracy is high and the toner presence / absence detection accuracy condition can be obtained. Furthermore, it is desirable to obtain an optimum range for obtaining the minimum value of the “error rate” T when the notch angle 303 is in the range of 30 ° to 60 °.

  If the opening 301 is formed by cutting out the outer peripheral portion while leaving the portion where the spiral blade 215 is connected to the screw shaft 214, for example, the opening 301 is half the height of the spiral blade 215. When the opening 301 up to this point is formed, the notch angle 303 may be set to 10 ° to 90 °, for example, to ensure an appropriate area of the opening 301.

(Embodiment 2)
FIG. 8A is a configuration diagram showing a main part of the developing device according to the second embodiment of the present invention. In FIG. 8A, the position of the stirring plate 216 is positioned slightly upstream from the upper part of the toner density sensor 205. Other configurations are the same as those of the first embodiment.

  Also in the present embodiment, since the developer 202 around the toner density sensor 205 can be moved by the rotation of the stirring plate 216, the toner density of the new developer 202 flowing from the upstream can always be detected.

(Embodiment 3)
FIG. 8B is a configuration diagram showing a main part of the developing device according to the third embodiment of the present invention. In FIG. 8B, the position of the stirring plate 216 is positioned slightly downstream from the upper part of the toner density sensor 205. Other configurations are the same as those of the first embodiment.

  Also in the present embodiment, since the developer 202 around the toner density sensor 205 can be moved by the rotation of the stirring plate 216, the toner density of the new developer flowing from the upstream can always be detected.

  The developing device according to the present invention has a stirrer that prevents an increase in the bulk or bulk density of the developer around the toner concentration detection unit, so that the developer always stirred and mixed around the detection unit of the toner concentration sensor. Since the agent can be continuously supplied, the toner density controllability can be improved, and the accuracy with respect to toner presence / absence detection can be improved, which is useful for image forming apparatuses such as printers and copiers. .

1 is a schematic diagram of an image forming apparatus in which a developing device according to Embodiment 1 of the present invention is used. 1 is a configuration diagram of a developing device according to a first embodiment of the present invention. 1 is a configuration diagram illustrating a developer stirring and conveying unit of a developing device according to a first embodiment of the present invention. Explanatory drawing of the notch angle of the opening part of the developer stirring conveyance means which concerns on Embodiment 1 of this invention. 6 is a graph showing a relationship between a notch angle, toner density controllability, and toner density presence / absence detectability of the developing device according to the first embodiment of the present invention. 6 is a graph showing notch angles, indices of toner density controllability and toner density presence / absence detectability of the developing device according to Embodiment 1 of the present invention. Graph showing the relationship between copy speed and error rate according to Embodiment 1 of the present invention (A) Configuration diagram showing developer stirring and conveying means according to Embodiment 2 of the present invention (b) Configuration diagram showing developer stirring and conveying means according to Embodiment 3 of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Image forming apparatus 102 Paper feed part 103 Recording paper 104 Paper discharge part 111-114 Process unit 111a-114a Photoconductor 111b-114b Charger 111c-114c Developer 116 LSU
117 Intermediate transfer belt 119 Fixing device 120 Paper discharge roller 121 Drive roller 122 Driven roller 124-127 Primary transfer roller 128 Secondary transfer roller 200 Toner supply port 201 Supply toner container 202 Developer 203 Developing case 204 First stirring screw 205 Toner Concentration sensor 206 Second stirring screw 208 Magroll 209 Development sleeve 210 Doctor blade 211 CPU
212 RAM
213 ROM
214, 217 Screw shafts 215, 218 Spiral blades 215a First conveying surface 215b Second conveying surface 216 Stirring plate 301 Opening 302 Rib 303 Notch angle 304 Concavity

Claims (6)

A developer agitating / conveying means for agitating and conveying a developer including toner and a carrier; a housing means for accommodating the developer and the developer agitating / conveying means; and a toner for detecting a toner concentration of the developer in the accommodating means. And a developer agitating / conveying means for conveying the developer in the accommodating means, and a toner concentration detecting means. A developing device comprising: a stirring section for preventing the developer or the bulk density around the means from increasing. The developing device according to claim 1, wherein the agitation unit is disposed over the entire detection surface of the toner concentration detection unit. The conveyance unit includes a rotation shaft portion provided in the developer conveyance direction and a spiral blade provided on an outer periphery of the rotation shaft portion, and the stirring unit includes two adjacent spiral shapes. 2. A stirring plate provided between the blades, and an opening formed in the spiral blade in the vicinity of a joint portion between the stirring plate and the spiral blade. Development device. 4. The developing device according to claim 3, wherein the stirring plate is disposed over the entire detection surface of the toner concentration detection means.   The developing device according to claim 3, wherein the opening is formed in the spiral blade within a range of 15 ° to 80 ° when viewed from the axial direction of the rotating shaft. An image forming apparatus comprising the developing device according to claim 1.

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