JP4282257B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a facsimile, a copying machine, and a printer, and more specifically, development that develops an electrostatic latent image formed on an image carrier using a two-component developer composed of toner and a carrier. A developing device comprising: a developer carrying member; and a stirring and conveying member having a screw for stirring while carrying the developer from one end side to the other end side in the axial direction of the developer carrying member; A toner storage unit that stores toner to be replenished, a toner concentration sensor that detects the toner concentration of the developer of the developing device, a toner concentration sensor that detects the toner concentration of the developer of the developing device, and a toner concentration sensor Image forming apparatus comprising: a comparison unit that compares a detection result with a comparison reference value; and a replenishment control unit that controls toner replenishment from the toner container to the toner replenishing port of the developing device based on the comparison result of the comparison unit. It relates to location.
[0002]
[Prior art]
In recent years, there has been a demand for downsizing, space saving, and cost reduction of image forming apparatuses from the market, and it is necessary to reduce the size and cost of developing apparatuses while maintaining good images over a long period of time. There is. Therefore, the applicant firstly stirs the replenished toner and the developer sufficiently until they reach the developing roller without making the stirring mechanism very complicated, and eliminates uneven stirring and uneven charging of the agent. As a developing device that can secure the charge amount, a developing device disclosed in Japanese Patent Laid-Open No. 11-2949 has been disclosed. In the developing device according to this prior application, a two-component developer composed of toner and a carrier is used, and a developing roller for applying the developer to the surface of the image carrier, and from one end side to the other end side in the axial direction of the developing roller. And a stirring / conveying member having a blade portion for stirring the developer while being conveyed. By agitating and conveying the developer along the axial direction of the developing roller with the agitating and conveying member, the replenished toner and developer can be sufficiently agitated before reaching the developing roller, and the required charge amount Can be secured. Since the developer that has passed through the developing roller consumes toner due to development and the toner density is lower than usual, the toner is replenished based on the detection result of the toner density sensor. As this toner concentration sensor, a magnetic sensor of a system that detects a change in the magnetic permeability of the developer in a certain volume near the sensor by using the inductance of the coil is often used because of low cost and few false detections. Yes.
[0003]
As the toner density control using the toner density sensor, for example, in the developing device disclosed in Japanese Patent Laid-Open No. 11-2949, a new developer is set in the developing device when a new developer is introduced or replaced. When the initial material is set, when the magnetically saturated developer reaches the toner density sensor, the toner density sensor output is detected, and the value is stored as a control reference value in the memory of the control unit. As the control reference value, for example, immediately after the main switch of the image forming apparatus is turned on, a reference pattern as a reference image is formed in a predetermined area of the latent image carrier at a predetermined timing, and toner adhesion to the reference pattern is performed. There is also a method in which the amount is detected by a photo sensor and a control reference value is calculated from the detection result. In normal operation (when the image forming operation is performed with the target image density and image quality), the toner replenishment time is determined by comparing the output value of the toner density sensor at the start of the image forming operation with the control reference value. Control toner density. Specifically, for example, when the toner density sensor detects that the magnetic permeability of the developer in a certain volume has become larger than the control reference value, the controller determines that the toner density of the developer has decreased. The toner density is controlled based on a sequence in which the toner replenishment bottle drive motor is driven for a predetermined toner replenishment time (for example, 1 second) and the toner is replenished from the toner replenishment port.
[0004]
[Problems to be solved by the invention]
The toner concentration sensor detects a change in the magnetic permeability of the developer in a certain volume. Therefore, if there is a change in the bulk density of the developer due to neglect or environmental change, the toner density is the same. However, there is a problem that the magnetic permeability is determined to be different. In particular, if a toner concentration sensor is provided in the vicinity of the toner supply port, the above problem is likely to occur. In order to deal with this problem, this toner density sensor is usually arranged in the vicinity of the agitating and conveying member where the developer is stably circulating and flowing, and at a position away from the toner supply port.
[0005]
As described above, since the toner concentration sensor is arranged at a position away from the toner supply port, a time lag occurs until the toner supplied from the toner supply port reaches the toner concentration sensor position. In some cases, the control unit drives the bottle driving motor again based on the signal to replenish toner. Then, there is a possibility that the toner replenishment amount is excessive and the toner density is excessive.
For example, as shown in FIG. 9, immediately after the development operation is started, the analog output value Vta of the toner density sensor is A / D converted into a digital value Vtd by a sensor controller every 30 (msec) at a sampling time of 30 (msec). The digital value Vtd is output to the control unit. Then, for example, the control unit calculates an average value of the digital value Vtd for eight times to obtain the toner density, and compares the toner density with the control reference value Vtref, and when the toner density becomes equal to or higher than the control reference value Vtref. It is determined that the toner density is lowered, a control signal is output, and the bottle drive motor is turned on for a predetermined time. After the bottle drive motor is turned off, the toner density detection is resumed. However, in this case, since the toner density of the developer having a low toner density before the replenished toner reaches the toner density sensor is detected, the toner density calculated by the control unit sets the control reference value Vtref. Then, the bottle drive motor is turned ON again for a predetermined time (control signal of A part in the figure). Then, there is a possibility that the toner replenishment amount is excessive and the toner density is excessive.
[0006]
The present invention has been made in view of the above background, and an object of the present invention is to provide an image forming apparatus capable of preventing excessive toner concentration due to erroneous detection of the toner concentration sensor and maintaining a stable toner concentration. Is to provide.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is a developer carrier that develops an electrostatic latent image formed on an image carrier using a two-component developer comprising a toner and a carrier. An agent container for containing a developer; While transporting the developer from one end side to the other end side in the axial direction of the developer carrier A first conveying screw for supplying the developer to the developer carrying member; and a second conveying screw for conveying the developer in a direction opposite to the first conveying screw, the first conveying screw and the second conveying screw. The developer in the agent container is circulated while being stirred and conveyed by a screw. An image device, a toner container for storing toner to be replenished to the developing device, and a toner concentration sensor for detecting the toner concentration of the developer of the developing device; The Comparing means for comparing the detection result of the toner density sensor with a comparison reference value, and replenishment control means for controlling toner replenishment from the toner containing portion to the toner replenishing port of the developing device based on the comparison result of the comparing means In an image forming apparatus having The toner replenishing port is provided in a developer transport region by the second transport screw, and the toner concentration sensor is below the second transport screw and is transported by the developer of the second transport screw from the toner replenishment port. Provided downstream in the direction, The toner density sensor does not detect the toner concentration within a predetermined time after the toner is supplied from the toner supply port by the supply control means. The toner density detection by the toner density sensor is resumed when the predetermined time elapses, and the predetermined time is equal to or longer than the time until the toner supplied from the toner supply port reaches the toner density sensor, Less than the time until the replenished toner passes through the toner density sensor It is characterized by this.
[0008]
As described above, the toner concentration sensor may be erroneously detected due to the time lag until the toner replenished from the toner replenishing port reaches the toner concentration sensor position. In the image forming apparatus, the toner concentration sensor does not detect the toner concentration within a predetermined time after the toner is replenished from the toner replenishing port by the replenishment control means, and the replenished toner controls the toner concentration sensor. Since the toner density detection by the toner density sensor is resumed so as to detect the toner density when it first passes, erroneous detection of the toner density sensor due to the time lag can be prevented. As a result, the replenishment control means reliably recognizes that the toner has been actually replenished, prevents excessive toner concentration due to excessive toner replenishment, and maintains a stable toner concentration.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter simply referred to as a copying machine) will be described.
First, the basic configuration of this copier will be described. FIG. 1 is a schematic configuration diagram of a copying machine according to the present embodiment. As shown in the figure, this copying machine supplies a scanner unit 100 that reads image information of an original, an image forming unit 200 that forms an image on a transfer sheet P that is a recording member, and supplies the transfer sheet P to the image forming unit 200. And a sheet feeding unit 300 for performing the above. A control unit (not shown) for controlling the operation of each device in the copying machine is also provided.
[0010]
The scanner unit 100 reads image information of a document placed on a contact glass (not shown) by the light receiving device 101 and sends the read image information to the control unit.
[0011]
Based on the image information received from the scanner unit 100, the control unit controls a laser diode (not shown), a polygon mirror, and the like in the laser writing unit 200A of the image forming unit 200 to be directed to the photosensitive drum 206 of the process cartridge 200B. Then, the laser writing light L is irradiated. By this irradiation, an electrostatic latent image is formed on the surface of the photosensitive drum 206 as an image carrier, and this latent image is developed into a toner image via a predetermined development process.
[0012]
The image forming unit 200, which is a visible image forming unit and a reference image forming unit, is a fixing device 200D, a paper discharge device 200E, and a developing substance supply unit (not shown) in addition to the laser writing unit 200A and the process cartridge 200B. A toner supply device, a toner bottle 215, a transfer device 200C as a contact transfer unit, and the like are also provided. The laser writing unit 200A functions as an electrostatic latent image forming unit.
[0013]
The paper feed unit 300 includes four paper feed cassettes 301a, b, c, d, four paper feed rollers 302a, b, c, d, four paper transport roller pairs 303a, b, c, d, and the like. Yes. The paper transport roller pair 303a also serves as a registration roller pair.
[0014]
Each of the paper feed cassettes 301a, 301b, 301c, and 301d is for receiving and storing a transfer paper P as a recording member.
[0015]
The paper feed rollers 302a, b, c, d respectively eject only one transfer paper P stored in the paper feed cassettes 301a, b, c, d, and the transport roller pairs 303a, b, c, It is sent to the paper conveyance path constituted by d and the like.
[0016]
When the control unit receives the image information from the scanner unit 100, the control unit performs the laser writing and development process as described above to form a toner image on the photosensitive drum 206, and has a size corresponding to the image information. In order to feed the transfer paper P to the image forming unit 200, one of the four paper feed rollers 302a, b, c, d is operated. As a result, one sheet of transfer paper P is discharged from one of the paper feed cassettes 301a, b, c, and d, and conveyed to the paper conveyance roller pair 303a. Then, the paper transport roller pair 303a is fed to the transfer position between the process cartridge 200B and the transfer device 200C at an appropriate timing. At this transfer position, a transfer device 200C, which is a contact-type transfer means, is disposed, and a transfer roller 220 as a contact member is brought into contact with the photosensitive drum 206 to form a transfer nip. The transfer roller 220 is applied with a transfer bias controlled at a constant current by a constant current power source which is a constant current supply unit (not shown), thereby forming a transfer electric field in the transfer nip. The transfer device 200 </ b> C includes, in addition to the transfer roller 220, a static elimination needle for neutralizing the transfer paper P.
[0017]
The toner image developed on the photosensitive drum 206 is superposed on the transfer paper P sent at the timing in the transfer nip. Then, the toner image is transferred onto the transfer paper P under the influence of an electrostatic force received from the transfer electric field or a pressing force between the photosensitive drum 206 and the transfer roller 220.
[0018]
The transfer paper P onto which the toner image has been transferred in this manner is sent into the fixing device 200D, and is sandwiched between the pressure roller 222 and the heating roller 223 therein. The toner image is fixed by the synergistic action of the applied pressure and the heating force, and is discharged from the transfer device 200D. Then, the toner image is discharged to the outside through the pair of discharge rollers of the discharge device 200E. .
[0019]
Next, the development process in this copying machine will be described in detail.
FIG. 2 is a schematic configuration diagram showing a process cartridge of the copying machine. In the figure, the process cartridge 200B includes a latent image forming unit 201, a cleaning unit 202, and a developing unit 203.
[0020]
The latent image forming unit 201 receives a charging bias from a static elimination lamp 208 or a charging bias power source (not shown) as a voltage supply unit around the photosensitive drum 206 that is rotated counterclockwise in the drawing by a driving system (not shown). A charging roller 207 as a contact charging unit to be applied is provided. As the surface of the photosensitive drum 206 rotates, the surface of the photosensitive drum 206 is first neutralized by being irradiated with the neutralizing light from the neutralizing lamp 208. Then, it is rubbed against the charging roller 207 that is driven to rotate counterclockwise in the drawing by a drive system (not shown) and is uniformly charged to a potential of −700 [V]. Next, the laser writing light L described above is emitted from the laser writing unit 200A. Then, an electrostatic latent image of −100 [V] is carried by this irradiation. When the electrostatic latent image thus carried passes through a position (development position) opposite to a later-described agent carrying portion with the rotation of the photosensitive drum 206, toner as a developing substance is adhered to the toner image. Developed.
[0021]
In the copying machine of the present embodiment, a reversal development method is employed in which the latent image formation target portion of the photosensitive drum 206 is irradiated with laser light, but laser light is applied to a portion that is not the latent image formation target portion. Irradiating forward developing method may be adopted.
[0022]
The developing unit 203 includes an agent carrying unit 204 and an agent storage unit 205. The agent storage unit 205 includes a first transport screw 209, a second transport screw 210, a storage unit casing 211, a toner concentration sensor 212, and the like. The first conveying screw 209 and the second conveying screw 210 are arranged so as to maintain a positional relationship parallel to each other, and are driven to rotate clockwise or counterclockwise in the drawing by a driving system (not shown). Yes. A partition wall 211a configured integrally with the housing casing 211 is provided between the two conveying screws, and thereby a developer housing for housing a two-component developer (hereinafter referred to as a developer) composed of toner and a magnetic carrier. Space is reserved separately around both screws. However, the partition wall 211a is not provided in a region corresponding to the vicinity of both ends of the two conveying screws, and the two developer accommodating spaces communicate with each other here. In the unused state, the sealant is isolated by a seal member 221 provided between the agent carrying part 204 and the agent storage part 205.
[0023]
The developer accommodating space in which the second conveying screw 210 is accommodated is provided with a toner receiving port (not shown) to receive toner conveyed from a toner supply device (not shown). ing. The developer around the second conveying screw 210 takes in the toner received in this way, and then is mixed with the magnetic carrier by the rotation of the second conveying screw 210 and then from the near side to the far side in the figure. It is conveyed to. At this time, the toner and the magnetic carrier are rubbed against each other, and the toner is negatively charged.
[0024]
The developer transported to the far end in the figure by the second transport screw 210 is delivered to the developer accommodating space on the first transport screw 209 side via a communication space (not shown) at the far end. Then, by the rotation of the first conveying screw 209, it is conveyed from the back side to the near side in the figure. During this conveyance, charging of the toner in the developer is further promoted.
[0025]
The developer accommodating space on the first conveying screw 209 side opens toward the developing sleeve 213 of the agent carrying part 204. The developing sleeve 213 includes, for example, a magnet roller (not shown) having five magnetic poles extending in the depth direction in the drawing and a cylindrical nonmagnetic pipe covering the magnetic roller, and only the nonmagnetic pipe is driven by a driving system (not shown). In the figure, it is driven to rotate clockwise. The non-magnetic pipe carries the developer conveyed by the first conveying screw 209 by adsorbing the developer by the magnetic force generated by the magnet roller. The developer carried in this way is taken into the agent carrying part 204 as the nonmagnetic pipe rotates.
[0026]
In addition to the developing sleeve 213, the agent carrier 204 includes a flexible doctor blade 214 that contacts the developing sleeve 213, an opening that opens toward the photosensitive drum 206, and the like. A part of is exposed. When the developer taken in the agent carrying part 204 passes through a position facing the doctor blade 214, the layer thickness on the developing sleeve 213 is regulated. Then, the toner is conveyed through the opening to a developing position that is a position facing the photosensitive drum 206.
[0027]
A developing bias of −400 [V] is applied to the developing sleeve 213 by a power source (not shown), an electrostatic latent image having a charge of −100 [V] on the photosensitive drum 206, and −400 A developing electric field that exhibits a developing potential of +300 [V] is formed between the surface of the developing sleeve 213 having an electric field of [V] and a negatively charged toner. On the other hand, a negative charge is charged between the background portion having a charge of −700 [V] on the photosensitive drum 206 and the surface of the developing sleeve 213 having an electric field of −400 [V]. A developing electric field that develops a developing potential of −300 [V] is formed with respect to the charged toner.
[0028]
Here, the polarity of the developing potential indicates the direction of the electrostatic force applied to the toner by the developing electric field. When the developing potential is positive, the direction is the direction of the photosensitive drum 206. It becomes the sleeve 213 direction. Accordingly, the developer conveyed to the developing position by the rotation of the developing sleeve 213 causes the toner adhering to the magnetic carrier to adhere to the electrostatic latent image on the photosensitive drum 206 due to the positive development potential. Further, it does not adhere to the background portion on the photosensitive drum 206 due to the negative development potential. In this way, the electrostatic latent image is developed by attaching the toner only to the electrostatic latent image.
[0029]
The toner image developed on the photosensitive drum 206 is transported to the transfer nip and transferred onto the transfer paper P as the photosensitive drum 201 rotates. The transfer paper P onto which the toner image has been transferred is separated from the photosensitive drum 206 by the separation claw 216 and then conveyed to the fixing device 200D.
[0030]
The residual toner remaining on the surface of the photosensitive drum 206 after passing through the transfer nip is scraped off by the cleaning blade 217 when conveyed to a position facing the cleaning unit 202. Then, after being collected in the casing of the cleaning unit 202 to be collected toner, it is transported again to the agent storage unit 205 by the collection screw 218 or the like and reused or collected in a waste toner bottle.
[0031]
The cleaning unit 202 is provided with a photosensitive shutter 219 for covering the photosensitive drum 206. The photosensitive shutter 219 covers and protects the photosensitive drum 206 by rotating in the direction of arrow F in the figure when the process cartridge 200B is removed from the apparatus main body.
[0032]
Although not shown, a photo sensor (hereinafter referred to as “P sensor”) for detecting the amount of toner adhering to the photosensitive drum 206 is provided facing the photosensitive drum 206. The P sensor includes a light emitting element that irradiates light to the photosensitive drum 206 and a light receiving element that receives reflected light, and changes the output voltage in accordance with the light reflection amount of the toner image on the photosensitive drum 206. . Since the amount of reflected light varies depending on the toner adhesion amount M / A per unit area in the toner image, the P sensor changes the output voltage in accordance with the toner adhesion amount M / A. This output voltage is output as a digital signal to the control unit via an A / D converter (not shown). The copier according to the present embodiment uses the P sensor that decreases the output value Vsp as the toner adhesion amount M / A increases.
[0033]
The toner remaining on the surface of the developing sleeve 213 after passing through the developing position is taken into the agent carrying portion 204 again as the developing sleeve rotates. The developer thus taken in is taken in by the developer not carried on the developing sleeve 213 and conveyed to the front end in the figure by the first conveying screw 209. FIG. 3A is a configuration diagram of the developing unit 203, and FIG. 3B is a perspective view of the agent storage unit 205 for explaining the operation of the first and second conveying screws 209 and 210. In FIG. 3B, the developer transported to the front end by the first transport screw 209 is returned to the developer storage space on the second transport screw 210 side via the communication space at the front end. Since the developer returned in this manner contains a developer that has consumed toner by development, the toner concentration is lower than usual. For this reason, a toner replenishing device (not shown) supplies toner to the toner receiving port 225 (see FIG. 4) to recover the toner concentration of the developer.
[0034]
The toner concentration sensor 212 of the agent storage unit 205 includes, for example, a magnetic permeability sensor that detects the mixing ratio of toner and carrier magnetically (permeability), and the like in the developer storage space on the second conveying screw 210 side. The output voltage value is changed according to the toner concentration of the developer stored therein.
[0035]
Based on the output value from the toner concentration sensor 212, the control unit obtains the toner concentration of the developer stored in the developer storage space on the second conveying screw 210 side. Further, the control unit includes data storage means (not shown) constituted by a RAM or the like, and a control reference value VTref as a comparison reference value that is a target value of the output voltage of the toner density sensor 212 is stored in the data storage means. In addition, a P target value that is a target value of an output voltage of the P sensor (not shown) is stored. Then, after determining the rotational drive number (rotational drive time) of the toner bottle 215 shown in FIG. 1 based on the acquired toner density result, the toner bottle 215 is rotationally driven.
[0036]
The developing ability of the developing unit 203 depends not only on the toner concentration of the developer but also on the properties of the toner. Therefore, the toner image density may change even if the toner concentration is kept constant. Therefore, the control unit forms a reference pattern, which is a reference image, in a predetermined area of the photosensitive drum 206 at a predetermined timing, for example, immediately after a main switch of a copying machine (not shown) is turned on, and the toner adheres to the reference pattern. The control reference value VTref is corrected based on the amount M / A. Then, by correcting the control reference value VTref in this way, the developing ability of the developing unit 203 is stabilized. Specifically, first, the P target value is compared with the output voltage value from the P sensor (not shown) when the reference pattern is detected. By this comparison, the amount of toner adhesion M / A with respect to the reference pattern is indirectly determined. Next, based on the comparison result and the value of the output VT from the toner concentration sensor 212 for detecting the toner concentration of the developer in the developing unit 203, the control unit has used the control used so far. A correction amount ΔVTref with respect to the reference value VTref is determined. Then, the control reference value VTref is corrected by adding the correction amount ΔVTref. The control unit stabilizes the developing ability of the developing unit 203 by such correction.
[0037]
FIG. 4 is a schematic perspective view showing the relationship between the toner bottle 215 and the process cartridge 200B. FIG. 5 is an explanatory view of mounting the toner bottle 215 to the apparatus main body, and is a perspective view showing the relationship between the toner bottle 215 and the bottle drive motor 227. Immediately after starting the developing operation, the toner concentration sensor 212 detects the toner concentration of the developer stored in the agent storage unit 205. Specifically, for example, eight digital values Vtd obtained by converting the analog output value Vta of the toner density sensor 212 by an A / D converter (not shown) are averaged to obtain the toner density, and this toner density is stored in the memory of the control unit. When the toner density exceeds the control reference value Vtref, the controller turns on the bottle drive motor 227 shown in FIG. 5 to rotate the toner bottle 215. Then, as shown in FIG. 4, the toner accommodated in the toner bottle 215 is discharged from the bottle opening 215a, scraped up by the toner replenishment mylar 228, discharged from the discharge port 224, and the toner in the process cartridge 200B. The toner drops from the receiving port 225 to the inside, supplied from the toner supply port 226 into the agent storage unit 205, and dropped onto the second conveying screw 210. In this way, by supplying a necessary amount of toner into the agent container 205, the toner concentration of the developer in the agent container 205 is maintained almost constant.
[0038]
However, as described above, since the toner concentration sensor 212 is disposed at a position away from the toner supply port 226, a time lag occurs until the toner supplied from the toner supply port 226 reaches the toner concentration sensor position. During this time, the controller may replenish toner by driving the bottle drive motor 227 again based on the detection signal of the toner density sensor 212. Then, there is a possibility that the toner replenishment amount is excessive and the toner density is excessive.
[0039]
Therefore, the copying machine according to the present embodiment is configured to detect the toner density at the timing when the replenished toner first passes through the toner density sensor to prevent the toner density from becoming excessive.
[0040]
[Example 1]
FIG. 6 is a diagram showing the positional relationship between the toner supply port 226 and the toner density sensor 212. In FIG. 6, the distance L (mm) between the center of the toner supply port 226 and the center of the toner density sensor 212 is smaller than ½ of the entire length of the second conveying screw 210. As a result, the toner concentration sensor 212 is located at a position downstream of the toner supply port 226 in the developer transport direction and away from the center of the second transport screw 210 in the axial direction opposite to the toner supply port. Compared to the case where the toner density sensor 212 is disposed, the newly supplied toner is less likely to spread in the transport direction before reaching the position where the toner density sensor 212 is disposed. For this reason, the toner concentration of the developer that has reached the toner concentration sensor 212 is not so much lower than the toner concentration of the developer immediately after toner replenishment, and the output value of the toner concentration sensor 212 before and after toner replenishment. A large difference appears in the toner density sensor, and erroneous detection of the toner density sensor 212 can be prevented. On the other hand, if the distance L between the center of the toner supply port 226 and the center of the toner density sensor 212 is too small, the toner density sensor 212 may be erroneously detected due to a change in the bulk density of the developer. For this reason, it is desirable that the distance L is secured at least so that the bulk density fluctuation of the developer does not occur.
[0041]
In FIG. 6, when the rotation speed of the second conveying screw 210 is N (rpm) and the screw pitch is P (mm), the toner supply from the toner supply port 226 to the toner concentration sensor 212 is reached. The time t (sec) can be expressed by the following formula 1.
[Expression 1]
t = L / (P × N / 60)
[0042]
According to an experiment conducted by the present inventor, after the control unit outputs a control signal for turning on the bottle drive motor 227, the replenished toner reaches the toner concentration sensor 212 at the time t. It took about twice as long. This is because it takes time from the time when the bottle driving motor 227 is turned on by the control signal until the toner falls to the toner replenishing port 226, and the developer agitating and conveying by the second conveying screw 210 is calculated. However, it may be time consuming. Therefore, the time T (sec) for the toner density sensor 212 to resume the toner density detection after the control signal for turning on the bottle drive motor 227 is output from the control unit can be expressed by the following equation (2).
[Expression 2]
T ≧ 2 × L / (P × N / 60)
[0043]
By satisfying the relationship of the above formula 2, the concentration of the replenished toner can be detected by the toner concentration sensor 212, and erroneous detection of the toner concentration can be reliably prevented.
[0044]
More specifically, the distance L between the center of the toner supply port 226 and the center of the toner density sensor 212 is 62.9 (mm), the rotational speed N of the second conveying screw 210 is 312.6 (rpm), and the screw pitch. When P is 16 (mm), the time t from when the toner is replenished to the toner replenishing port 226 until reaching the toner density sensor 212 is 0.7545 (sec) according to the above equation (1). In consideration of the transport time from when the bottle drive motor 227 is turned on to when the toner falls to the toner replenishing port 226, a control signal for turning on the bottle drive motor 227 is output from the control unit according to Equation 2 above. After that, the time T until the replenished toner reaches the toner density sensor 212 is 1.509 (sec). Accordingly, the toner concentration sensor 212 is not detected at least before 1.509 (sec) after the control unit outputs a control signal for turning on the bottle drive motor 227, for example, 1.6 (sec). The toner density detection is resumed later. For example, A / D conversion by the sensor controller is not performed during 1.6 (sec).
[0045]
Here, in FIG. 7, the analog output value Vta of the toner density sensor 212 changes from about 1.75 (sec) after the control signal for turning on the bottle drive motor 227 is output from the control unit. In the toner density detection, the analog output value Vta of the toner density sensor 212 with a sampling time of 30 (msec) at 30 (msec) intervals is A / D converted into a digital value Vtd by a sensor controller (not shown), and the digital value Vtd is converted by the control unit. The average value for 8 times is calculated as the toner density. For this reason, it takes about 0.45 (sec) to detect the toner density. Specifically, the toner density is set to a substantially average value between 1.6 (sec) and 2.05 (sec) after a control signal for turning on the bottle drive motor 227 is output from the control unit. The toner density calculated by the control unit does not become the control reference value Vtref or less, and toner replenishment is not performed again, so that excessive toner replenishment can be prevented.
[0046]
If toner density detection is resumed at a timing after the supplied toner has completely passed through the toner density sensor 212, the supplied toner density cannot be detected. Therefore, it is desirable to restart the toner density detection before the elapsed time from when the replenished toner reaches the toner density sensor 212 until it completely passes. The time for which the replenished toner passes through the toner density sensor 212 is substantially equal to the time when the bottle drive motor 227 is turned on. If the time when the bottle drive motor 227 is turned on is tm (sec), It is desirable that the relationship 3 is satisfied.
[Equation 3]
t × 2 + tm ≧ T ≧ t × 2
[0047]
In addition, although the control signal for turning on the bottle drive motor 227 is output from the control unit, there is a case where the toner does not fall into the toner supply port 226 for some reason and the toner is not supplied. In this case, for example, if the result of toner density detection restarted after 1.6 (sec) is equal to or greater than the control reference value Vtref, a control signal for turning on the bottle drive motor 227 is output from the control unit, and the toner Supply is made. As a result, insufficient toner concentration can be prevented.
[0048]
[Example 2]
In the case of the configuration in which the driving force from the common driving motor is transmitted to the toner supply bottle using an electromagnetic clutch without providing a single bottle driving motor for rotating the toner supply bottle as in the first embodiment. In this case, there is a delay in driving transmission by the clutch. Then, as compared with the configuration of the first embodiment in which no clutch is provided, it takes time for the delay in clutch drive transmission until the supplied toner reaches the toner density sensor 212. FIG. 8 shows output characteristics in a state where the analog output value Vta of the toner density sensor changes after the bottle drive motor and the clutch are turned on simultaneously when the clutch is not provided (solid line) and when the clutch is provided (dotted line). It is a graph which shows. From this graph, it can be seen that there is a drive transmission delay time td due to the clutch. The clutch drive transmission delay time td is normally about 250 (msec). If the toner density detection is resumed without considering the drive transmission delay time td, the toner replenishment amount may be excessive and the toner density may be excessive for the reasons described above.
[0049]
Therefore, it is desirable to restart the detection of the toner density sensor in consideration of the delay time of the clutch drive transmission after the toner supply. Assuming that the clutch drive transmission delay time is td (sec), the time T2 (sec) at which the toner density sensor 212 restarts the toner density detection after the control signal for turning on the clutch is output from the control unit is the following. This can be expressed by the following formula 4. In Equation 4, L, P, and N mean the same variables as in Equation 1 above.
[Expression 4]
T2 ≧ {L / (P × N / 60)} × 2 + td
[0050]
As described above, when the clutch is used in the drive transmission system, the concentration of the replenished toner can be detected by the toner concentration sensor 212 by satisfying the relationship of the above formula 4, and erroneous detection of the toner concentration can be detected. It can be surely prevented.
[0051]
As described in the first embodiment, if toner density detection is restarted at a timing after the supplied toner has completely passed through the toner density sensor 212, the supplied toner density cannot be detected. . Therefore, it is desirable to restart the toner density detection before the elapsed time from when the replenished toner reaches the toner density sensor 212 until it completely passes. The time for which the replenished toner passes through the toner density sensor 212 is substantially equal to the time when the clutch is engaged. Therefore, if the time when the clutch is engaged is tm (sec), the relationship of the following formula 5 is satisfied. Is desirable.
[Equation 5]
{L / (P × N / 60)} × 2 + td + tm ≧ T2 ≧ {L / (P × N / 60)} × 2 + td
[0052]
As described above, in this embodiment, a developer carrier that develops an electrostatic latent image formed on the photosensitive drum 206 as an image carrier using a two-component developer composed of a toner and a carrier. A developing device including a developing sleeve 213 and a second conveying screw 210 as an agitating and conveying member having a screw for agitating while conveying the developer from one end side to the other end side in the axial direction of the developing sleeve 213 A developing unit 203, a toner bottle 215 as a toner containing unit for containing toner to be replenished to the developing unit 203, a toner concentration sensor 212 for detecting the toner concentration of the developer in the developing unit 203, and the toner concentration Comparison means for comparing the detection result of the sensor 212 with a control reference value Vtref as a comparison reference value, and based on the comparison result of the comparison means, -In an image forming apparatus having a control unit as a replenishment control unit for replenishing toner from the bottle 215 to the toner replenishing port 226 of the developing unit 203, a predetermined amount after the toner is replenished from the toner replenishing port 226 by the control unit. The toner concentration sensor 212 detects the toner concentration when the replenished toner first passes through the toner concentration sensor 212 without detecting the toner concentration during the time. Restart detection. Therefore, at the timing before the toner replenished from the toner replenishing port 226 first passes through the toner density sensor 212, the toner density is not detected, and the density of the replenished toner can be reliably detected. As a result, the controller can reliably recognize that the toner has been actually replenished, and can prevent a toner concentration from being excessive due to the excessive replenishment of toner, thereby maintaining a stable toner concentration. If the toner is not replenished for some reason despite the toner replenishing operation, the toner replenishing operation can be performed again to reliably replenish the toner. It is possible to prevent the image density from being lowered. As a result, it is possible to form a high-quality image without scumming or image density reduction.
Further, the toner replenishing port 226 is set to T [sec] after the control unit starts the toner replenishing operation from the toner bottle 215 to the toner replenishing port 226, and the toner concentration sensor 212 resumes the toner concentration detection. And the toner density sensor 212 is L [mm], the rotational speed of the second conveying screw 210 is N [rpm], and the screw pitch of the second conveying screw 210 is P [mm]. The relation of ≧ 2 × L / (P × N / 60) is satisfied. More specifically, a time T during which the control of the toner density sensor 212 is restarted after the control unit starts the toner supply operation from the toner bottle 215 to the toner supply port 226, is supplied from the toner bottle 215. In consideration of the transport time to the mouth 226 and the like, the transport time from the toner supply port 226 to the toner density sensor 212 is set to be twice or more. Therefore, erroneous detection of the toner concentration sensor 212 due to a time lag from when the control unit starts the toner supply operation from the toner bottle 215 to the toner supply port 226 until the toner concentration sensor 212 is reached. Can be prevented.
A toner replenishment mylar 228 as a conveying means for conveying toner from the toner bottle 215 to the toner replenishing port 226; a common drive motor as a drive source for applying a driving force to the toner replenishment mylar 228; Drive transmission means for transmitting the driving force of the common drive motor to the toner replenishment mylar 228 and the like, the drive transmission means including a clutch, and switching operation between fastening and non-fastening of the clutch. The control is performed by a control signal, and the time when the toner concentration sensor 212 restarts the toner concentration detection after the control unit outputs the control signal for engaging the clutch is T2 [sec]. When the drive transmission delay time is td [mm], the relationship of T2 ≧ 2 × L / (P × N / 60) + td is satisfied. Therefore, the toner concentration detection of the toner concentration sensor 212 can be restarted in consideration of the clutch drive transmission delay time, and erroneous detection of the toner concentration sensor 212 due to the delay time can be prevented.
[0053]
【The invention's effect】
According to the first aspect of the present invention, by setting the detection timing of the toner concentration sensor appropriately, it is possible to prevent excessive toner concentration due to excessive toner supply due to erroneous detection of the toner concentration sensor and to maintain a stable toner concentration. it can. Further, it is possible to prevent the image density from being lowered without toner replenishment. As a result, it is possible to form a high-quality image without scumming or image density reduction.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a copier according to an embodiment.
FIG. 2 is a schematic configuration diagram showing a process cartridge of the copying machine.
FIG. 3A is a configuration diagram of a developing unit.
(B) is a perspective view of the agent accommodating part 205 for demonstrating operation | movement of a 1st, 2nd conveyance screw.
FIG. 4 is a schematic perspective view showing a relationship between a toner bottle and a process cartridge.
FIG. 5 is an explanatory view of mounting the toner bottle on the apparatus main body, and is a perspective view showing the relationship between the toner bottle and the bottle drive motor.
FIG. 6 is a diagram illustrating a positional relationship between a toner supply port and a toner density sensor.
7 is a timing chart showing a relationship among an analog output value of a toner density sensor according to Embodiment 1, an A / D conversion value of a sensor controller, and a bottle drive motor control signal of a control unit. FIG.
FIG. 8 is an explanatory diagram of a clutch drive transmission delay time according to the second embodiment.
FIG. 9 is a timing chart showing a relationship among an analog output value of a toner density sensor according to a conventional example, an A / D conversion value of a sensor controller, and a bottle drive motor control signal of a control unit.
[Explanation of symbols]
100 Scanner section
101 Photodetector
200 Image forming unit
200A Laser writing unit
200B process cartridge
200C transfer device
200D fixing device
200E paper discharge device
201 Latent image forming unit
202 Cleaning section
203 Development Unit
204 Agent carrying part
205 Agent container
206 Photosensitive drum
207 Charging roller
208 Static elimination lamp
209 First conveying screw
210 Second conveying screw
211 Housing casing
212 Toner density sensor
213 Development sleeve
214 Doctor Blade
215 Toner bottle
225 Toner receiving port
226 Toner supply port
227 Bottle drive motor
300 Paper feeder
301 Paper cassette
302 Paper feed roller
303 Paper transport roller pair

Claims (3)

Using a two-component developer comprising a toner and a carrier, a developer carrier for developing an electrostatic latent image formed on the image carrier, a developer container for containing the developer, and a developer carrier A first conveying screw that supplies the developer to the developer carrying member while conveying the developer from one end side to the other end side in the axial direction, and a first conveying screw that conveys the developer in a direction opposite to the first conveying screw. and a second conveying screw, and the current image device for circulating while stirring, to convey the developer in the agent accommodating unit by the first transport screw and the second transport screw,
A toner containing portion for containing toner to be replenished to the developing device;
A toner concentration sensor for detecting the toner concentration of the developer of the developing device ;
Comparison means for comparing the comparison reference value and the detection result of the toner concentration sensor,
In an image forming apparatus having a replenishment control means for controlling toner replenishment from the toner container to a toner replenishment port of the developing device based on a comparison result of the comparison means,
The toner replenishing port is provided in a developer conveyance area by the second conveyance screw,
The toner density sensor is provided below the second transport screw and downstream of the toner supply port in the developer transport direction of the second transport screw.
The toner density sensor is not detected by the toner density sensor within a predetermined time after the toner is supplied from the toner supply port by the supply control means, and the toner density detection by the toner density sensor is resumed when the predetermined time elapses. Is,
The predetermined time is equal to or longer than the time until the toner replenished from the toner replenishing port reaches the toner density sensor, and is equal to or shorter than the time until the replenished toner passes through the toner density sensor. An image forming apparatus. The image forming apparatus according to claim 1.
After the replenishment control means starts the toner replenishment operation from the toner container to the toner replenishment port, the time when the toner concentration sensor restarts the toner concentration detection is T [sec], and the toner replenishment operation time is tm [sec. ], The distance between the toner supply port and the toner concentration sensor is L [mm],
When the rotation speed of the stirring and conveying member is N [rpm] and the screw pitch of the stirring and conveying member is P [mm],
2 × L / (P × N / 60) + tm ≧ T ≧ 2 × L / (P × N / 60)
An image forming apparatus satisfying the relationship: The image forming apparatus according to claim 1 or 2,
A conveying unit configured to convey toner from the toner container to the toner replenishing port; a driving source that applies a driving force to the conveying unit; and a drive transmission unit that transmits the driving force of the driving source to the conveying unit. And
The drive transmission means includes a clutch, and is configured to perform a switching operation between engagement and non-engagement of the clutch by a control signal of the replenishment control means,
The time when the toner concentration sensor restarts toner concentration detection after the replenishment control means outputs the control signal for engaging the clutch is T2 [sec],
The engagement time of the clutch is tm,
The distance between the toner supply port and the toner concentration sensor is L [mm],
The rotational speed of the stirring and conveying member is N [rpm],
The screw pitch of the stirring and conveying member is P [mm],
When the drive transmission delay time when the clutch is engaged is td,
2 × L / (P × N / 60) + td + tm ≧ T2 ≧ 2 × L / (P × N / 60) + td
An image forming apparatus satisfying the relationship:

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