JP2008122505A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stabilizing image quality throughout the use period of a toner container by restraining image fogging resulting from the supply of a large quantity of toner, which occurs right after replacement of toner container. <P>SOLUTION: The quantity of toner remaining in the toner container 5 is estimated from the integrated number of revolutions of a toner supply motor 37. The threshold (output value at which toner is supplied) of a sensor 36 for detecting the quantity of toner is gradually changed toward the integrated number A of revolutions of the toner supply motor 37, at which the toner container becomes empty of toner. Thereby, the weight of toner in the developing device is gradually increased as compared with that assigned for a regular control period. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer that includes a developing device that develops an electrostatic latent image on an image carrier and a replaceable toner container that supplies toner to the developing device. The present invention relates to a toner replenishment control method from a toner container to a developing device.

  In an image forming apparatus using an electrophotographic system such as a copying machine, a printer, or a FAX, a powder developer (hereinafter referred to as toner) is mainly used, and an electrostatic image formed on an image carrier such as a photosensitive drum. In general, the latent image is visualized with toner in the developing device, and the toner image is transferred onto a recording medium, and then a fixing process is performed. In such an image forming apparatus, a toner container for replenishing toner according to toner consumption in the developing device is mounted.

  6 is a schematic perspective view showing the internal structure of a conventional toner container, FIG. 7 is a side sectional view of the toner container as seen from the direction of arrow X in FIG. 6, and FIG. 8 is a view of the toner container as seen from below. It is a perspective view. Here, a toner container that stores and supplies powder toner will be described. As shown in FIG. 6, the toner container 5 includes a casing (housing) 101, a stirring paddle 102, and a conveying screw 103. The casing 101 is a container for storing toner, and a stirring paddle 102 and a conveying screw 103 are arranged in parallel in the casing 101.

  The stirring paddle 102 has an arm portion 102b standing around a rotating shaft 102a, a flat stirring plate 105 formed with a conveyance sheet 104 whose tip can be bent in the rotation direction and a window portion through which toner passes. Are provided at the tip of the arm portion 102b at positions alternately arranged in the axial direction, and are rotatably supported by the casing 101. The arm portion 102b includes a plurality of columns 106 and a tip shaft 107 fixed to the tip of the column 106 in parallel with the rotation shaft 102a.

  As the stirring paddle 102 rotates in the direction of arrow Y in FIG. 7, the toner stored in the casing 101 is stirred and guided to the conveying screw 103. The conveying screw 103 has a configuration in which a spiral blade 103b is provided around a rotation shaft 103a, and a toner supply port provided on the bottom surface of the casing 101 shown in FIG. 8 by rotating in a predetermined direction. From 108, toner is supplied to a developing device (not shown).

  In such a toner container, it is necessary to know the remaining amount of toner in the toner container in order to supply the toner stably to the developing device and notify the user of the replacement timing of the toner container. A toner remaining amount sensor was provided in the container. However, in addition to an expensive toner remaining amount sensor, connecting parts, a substrate, and the like are also required. In particular, it has been difficult to employ a disposable toner cartridge due to high cost.

  Therefore, various methods for stabilizing the toner supply from the toner container without providing a toner remaining amount sensor in the toner container have been proposed. For example, Patent Document 1 discloses the number of rotations of the toner supply roller and the amount of toner in the developing device. A method is disclosed in which the toner remaining amount in the toner container (toner bottle) is estimated using the detection result of the toner density sensor, and the user is notified of the toner container replacement time. Specifically, as the remaining amount of toner in the toner container decreases, the number of rotations of the toner supply roller is increased, and even if the toner supply operation is repeated a predetermined number of times at the maximum number of rotations, It is determined that there is no remaining amount of toner when it is below the specified value.

  However, in the control method of Patent Document 1, it is determined whether or not toner container replacement (REPLACE) is necessary after the toner in the toner container is exhausted and toner supply to the developing device is stopped until toner replacement is displayed. The amount of toner in the developing device is reduced from the stable weight by the amount of toner consumed during the cumulative number of rotations (cumulative driving time) of the toner supply motor necessary for determination.

  Now, the cumulative rotation speed of the toner supply motor, which is expected to run out of toner in the toner container, is A, and the cumulative rotation speed of the toner supply motor that rotates within the time required for the toner container replacement determination is converted from B, the printing rate. Assuming that the average toner consumption per printed sheet is C, the number of printed sheets in the time required for toner container replacement determination is D, and the toner weight in the developing device during normal control is E, as shown in FIG. Since the toner supply from the toner container stops after the cumulative rotation speed of the toner supply motor reaches A, the development is performed when the cumulative rotation speed of the toner supply motor reaches A + B and the toner container replacement is notified. The toner weight in the apparatus is E−C × D, which is smaller than the toner weight E during normal control by the consumption (C × D) due to printing within the time required for the toner container replacement determination. The In order to compensate for this consumption, a large amount of toner is supplied into the developing device at once immediately after the replacement of the toner container.

  For this reason, it takes time until the residual toner in the developing device and the newly added uncharged toner are uniformly mixed. If printing is performed immediately after the toner container is replaced, the toner with poor charging is developed. There was a problem that fogging occurred. On the other hand, if there is not enough time to determine toner container replacement to suppress toner consumption after stopping toner supply, toner supply cannot catch up with toner consumption, such as when images with a high printing rate are continuously printed. Even if the output value of the toner density sensor does not recover, there is a possibility that it is erroneously determined that it is time to replace the toner container, and the determination accuracy of toner container replacement will be reduced.

Patent Documents 2 and 3 describe a method of calculating a toner usage amount by using an integrated value of image signals, and further estimating a toner remaining amount in the toner container from the toner usage amount to determine a replacement timing of the toner container. Is disclosed. However, in the methods of Patent Documents 2 and 3, the amount of toner used varies depending on the type of image actually printed, the degree of deterioration of toner in the developing device, the usage environment of the image forming apparatus, and the like. In this case, it is necessary to further correct the calculated remaining toner amount, and the control becomes complicated.
JP 2002-148925 A JP 2000-182124 A Japanese Patent Laid-Open No. 10-247012

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming apparatus that suppresses image fogging caused by supplying a large amount of toner that occurs immediately after replacement of a toner container and stabilizes image quality throughout a period of use. To do.

  To achieve the above object, the present invention provides a developing device for forming a toner image corresponding to an electrostatic latent image by attaching toner onto an image carrier by a toner carrier, and the toner weight or toner in the developer device. A toner amount detection sensor for detecting density, a replaceable toner container for storing toner supplied to the developing device, a toner supply motor for driving the toner container to supply toner to the developing device, and the toner In the image forming apparatus, comprising: a count unit that counts the number of rotations of the supply motor; and a control unit that controls toner supply from the toner container in accordance with an output value of the toner amount detection sensor. When the output value of the toner amount detection sensor falls below a predetermined threshold value, toner supply from the toner container is executed, and the toner supply motor is When the output value of the toner amount detection sensor does not return to the threshold value or more during the rotation of the number of times, the replacement of the toner container is notified, and according to the integrated count value of the counting means since the previous toner container replacement. Control that changes the threshold value of the toner amount detection sensor stepwise is performed.

According to the present invention, in the image forming apparatus configured as described above, the integrated count value R of the counting unit when starting to change the threshold value of the toner amount detection sensor satisfies the following conditional expression (1). .
0 ≦ R ≦ A-2B (1)
However,
A: The cumulative number of rotations of the toner supply motor that is predicted to run out of toner in the toner container,
B: Number of rotations of the toner supply motor that rotates within the time required for determination of toner container replacement,
It is.

In the image forming apparatus having the above-described configuration, the maximum change width of the threshold of the toner amount detection sensor is set so that the target toner weight P in the developing device satisfies the following conditional expression (2). It is characterized by.
P = C × D + E (2)
However,
C: average toner consumption per printed sheet calculated from the printing rate,
D: number of prints within the time required for determination of toner container replacement,
E: the toner weight in the developing device before the threshold change,
It is.

  According to the first configuration of the present invention, the amount of toner in the developing device increases stepwise, and when the toner in the toner container runs out, the developing device is in a state of being replenished with extra toner. Even when the printing is continuously performed within the time required for the toner container replacement determination, the toner amount in the developing device is not significantly reduced. Therefore, it is possible to effectively prevent fogging images that are generated by developing a poorly charged toner because a large amount of new toner is not replenished immediately after replacement of the toner container.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, the integrated count value of the count unit that starts changing the threshold value of the toner amount detection sensor satisfies the conditional expression (1). As a result, it is possible to prevent the occurrence of a fog image before replacement of the toner container due to a rapid increase in the toner weight in the developing device.

  According to the third configuration of the present invention, in the image forming apparatus having the first or second configuration, the toner amount detection sensor of the toner amount detection sensor is set so that the target toner weight P in the developing device satisfies the conditional expression (2). By setting the maximum change width of the threshold, it is possible to supply an appropriate amount of toner according to the amount of toner consumed within the time required for determination of toner container replacement.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an image forming apparatus (for example, a printer) 100 of the present invention using a developing device. The image forming apparatus 100 includes a photosensitive drum 1, a charging unit 2, an exposure unit (laser scan unit) 3, a developing device 4, a toner container 5, a transfer roller 6, a cleaning unit 7, a paper feed mechanism 10, a transport unit 11, The image forming apparatus includes a fixing device 12 and a paper discharge unit 13.

  The photosensitive drum 1 is formed, for example, by laminating a photosensitive layer on an aluminum drum, and the charging unit 2 charges the surface. Then, an electrostatic latent image with attenuated charging is formed on the surface that has received a laser beam from the exposure unit 3 described later. The photosensitive layer is not particularly limited, but for example, amorphous silicon (a-Si) or organic photosensitive layer (OPC) having excellent durability is preferable.

  The charging unit (charging charger) 2 charges the surface of the photosensitive drum 1 by discharging (for example, corona discharge). For example, the charging unit 2 has a thin wire or the like, and discharges when a high voltage is applied using this as an electrode. The exposure unit (LSU) 3 irradiates the photosensitive drum 1 with a light beam (for example, a laser beam) based on the image data, and forms an electrostatic latent image on the surface of the photosensitive drum 1. The image data is transmitted from a personal computer (not shown).

  The developing device 4 forms toner images by attaching toner to the electrostatic latent image on the photosensitive drum 1. Examples of the developer accommodated in the developing device 4 include a two-component developer composed of a toner component and a carrier and a one-component developer composed only of a toner component.

  The toner container 5 supplies toner to the developing device 4 when the toner in the developing device 4 becomes insufficient, and stores spare toner. The transfer roller 6 shifts (transfers) the toner image formed on the surface of the photosensitive drum 1 onto the conveyed sheet without disturbing the toner image.

  The cleaning unit 7 removes toner (residual toner) remaining on the surface of the photosensitive drum 1 after the toner image is transferred to the sheet. For example, a blade that makes line contact with the longitudinal direction of the photosensitive drum 1 It is composed of materials, rubbing rollers and the like. The paper feed mechanism 10 accommodates a sheet (paper, OHP, etc.) on which an image (toner image) is printed, and feeds the sheet to the transport unit 11 which is a sheet path from the paper feed mechanism 10 to the paper discharge unit 13. To be sent.

  The fixing device 12 converts the toner image transferred onto the sheet into a stable permanent image. For example, by applying energy such as heat and pressure using a heating roller and a pressure roller, the toner in a powder state A heat roller fixing method for fusing an image is used. The paper discharge unit 13 accommodates a sheet that has passed through the fixing device 12, that is, a sheet on which a permanent image is printed.

  Then, the exposure unit 3 emits a laser beam on the photosensitive drum 1 based on image data input in advance, thereby forming an electrostatic latent image based on the image data on the surface of the photosensitive drum 1. Thereafter, toner is attached to the electrostatic latent image by the developing device 4 (a toner image is formed), and the toner image is transferred onto the sheet by the transfer roller 6. Next, heat and pressure are applied to the sheet on which the toner image has been transferred by the fixing device 12 to form a permanent image.

  FIG. 2 is a block diagram showing a control path of the image forming apparatus of the present invention. Portions common to FIG. 1 are denoted by the same reference numerals and description thereof is omitted. The image forming apparatus 100 includes an image input unit 30, an AD conversion unit 31, an image forming unit 32, a control unit 33, a storage unit 34, an operation panel 35, a toner container 5, a paper feed mechanism 10, a fixing device 12, and a toner amount detection sensor. 36, a toner supply motor 37, a motor rotation number counter 38, and the like.

  When the image forming apparatus 100 is a copying machine, the image input unit 30 is a scanning optical system equipped with a scanner lamp that illuminates an original during copying and a mirror that changes the optical path of reflected light from the original, and reflected light from the original. The image forming apparatus 100 is a printer as shown in FIG. 1. The image forming apparatus 100 includes a condenser lens that collects and forms an image and a CCD that converts the imaged image light into an electrical signal. In this case, the reception unit receives image data transmitted from a personal computer or the like. The image signal read by the image input unit 30 is converted into a digital signal by the AD conversion unit 31 and then sent to an image memory 60 in the storage unit 34 described later.

  The image forming unit 32 includes the photosensitive drum 1, the charging unit 2, the exposure unit 3, the developing device 4, and the transfer roller 6. An electrostatic latent image is formed and developed into a toner image by the developing device 4, and then the toner image is transferred onto the sheet by the transfer roller 6.

  The storage unit 34 includes an image memory 60, a RAM 61, and a ROM 62. The image memory 60 stores an image signal input from the image input unit 30 and digitally converted by the AD conversion unit 31, and is stored in the control unit 33. Send it out. The RAM 61 and the ROM 62 store the processing program and processing contents of the control unit 33. The RAM 61 (or ROM 62) also stores a threshold change start timing, a change width, and the like used for threshold value change control of a toner amount detection sensor 36 described later.

  The operation panel 35 includes an operation unit including a plurality of operation keys, and a display unit (none of which is shown) that displays setting conditions, apparatus states, and the like, and the user sets printing conditions and the like. In addition, when the image forming apparatus 100 has a facsimile function, it is used for various settings such as registering a facsimile transmission destination in the storage unit 34 and further reading and rewriting the registered transmission destination.

  The toner amount detection sensor 36 detects the toner weight (or toner concentration) stored in the developing device 4, and for example, a piezoelectric sensor or a magnetic sensor is used. The toner supply motor 37 drives the conveying screw in the toner container 5 in accordance with a control signal from the control unit 33. The motor rotation number counter 38 counts the accumulated rotation number of the toner supply motor 37 after the toner container 5 is replaced.

  The control unit 33 generally controls the image input unit 30, the image forming unit 32, the paper feed mechanism 10, the fixing device 12 and a motor (not shown) for driving them according to the set program, and also the image input unit. The image signal input from 30 is converted into image data by scaling processing or gradation processing as necessary. The exposure unit 3 irradiates a laser beam based on the processed image data to form a latent image on the photosensitive drum 1.

  Further, the control unit 33 determines whether or not the toner container 5 needs to be replaced based on the output value of the toner amount detection sensor 36 and the integrated rotation number of the toner supply motor 37 counted by the motor rotation number counter 38 and determines the toner amount. The detection sensor 36 has a function of changing a threshold value (an output value at which toner is supplied).

  In the present invention, the remaining amount of toner in the toner container 5 is predicted from the accumulated number of revolutions of the toner supply motor 37, and the toner amount is detected toward the accumulated number of revolutions of the toner supply motor 37 that is estimated to be empty. It is characterized in that the threshold value of the sensor 36 is changed stepwise.

  As a result, the amount of toner in the developing device gradually increases from that during normal control, so even if printing is performed within the time required for the toner container replacement determination after the toner in the toner container 5 runs out. The amount of toner in the developing device does not decrease significantly. Therefore, it is not necessary to replenish a large amount of new toner when the toner container 5 is replaced, and it is possible to effectively prevent a fogging image generated by developing a toner with poor charging.

  FIG. 3 is a diagram illustrating a relationship between the cumulative number of rotations of the toner supply motor and the remaining amount of toner in the developing device when threshold value change control of the toner amount detection sensor is executed. Note that the definitions of A, B, C, D, and E in the figure are the same as in the case of FIG. 9 of the conventional example. The threshold change start timing and change range of the toner amount detection sensor 36 will be described with reference to FIG.

  The change in the threshold value of the toner amount detection sensor 36 needs to be started at least before the toner in the toner container 5 is emptied, that is, until the cumulative rotation number of the toner supply motor 37 reaches A. If the threshold value is changed immediately before the toner value is reached, the toner weight in the developing device must be suddenly increased, and a large amount of toner is replenished from the toner container 5 at one time, so that a poorly charged toner is used for development.

Therefore, it is preferable that the threshold change start timing be at the time when the integrated rotation speed of the toner supply motor 37 becomes A-2B at the latest, as shown in FIG. Further, as shown in FIG. 3B, the threshold value may be changed immediately after the toner container replacement. That is, if the cumulative number of rotations of the toner supply motor 37 that starts changing the threshold value of the toner amount detection sensor 36 is R, the conditional expression (1)
0 ≦ R ≦ A-2B (1)
R may be set to satisfy the above.

In addition, if the toner is consumed within the time required for the toner container replacement and the toner amount in the developing device is smaller than the toner amount during normal control when the toner container is replaced, a large amount of toner is immediately after the toner container replacement. Will be replenished. For this reason, it is necessary to replenish a predetermined amount of toner when the toner in the toner container 5 runs out. This replenishment amount is determined by the amount of toner consumed (C × D) is sufficient. Therefore, if the target toner weight in the developing device is P, P is an amount obtained by adding C × D to the toner weight E in the developing device during normal control (before changing the threshold value). Therefore, conditional expression (2)
P = C × D + E (2)
What is necessary is just to set the maximum change width of a threshold value so that it may satisfy | fill.

  The threshold value may be changed every time the toner supply motor 37 rotates once, or every several to several tens of rotations. For example, in the control of FIG. 3A, the toner increase amount (toner increase speed) in the developing device per one rotation of the toner supply motor from the start of threshold change until the cumulative rotation speed reaches A is (toner increase amount) / (Rotation speed required for toner increase) = C × D / {A− (A−2B)} = C × D / 2B, and therefore the threshold when the threshold of the toner amount detection sensor 36 is changed stepwise. The change width is set so that the toner increase speed due to the threshold change is C × D / 2B.

  In the control of FIG. 3B, the toner increase speed in the developing device per one rotation of the toner supply motor is represented by C × D / A. Therefore, the threshold change width depends on the threshold change of the toner amount detection sensor 36. The toner increase speed is set to be C × D / A.

  Next, a toner replenishment control operation when performing continuous printing using the image forming apparatus of the present invention will be described. FIG. 4 is a flowchart showing a toner replenishment control procedure of the image forming apparatus of the present invention. The procedure for changing the threshold value of the toner amount detection sensor 36 will be described with reference to FIGS. In FIG. 4, the control in FIG. 3A that starts changing the threshold value of the toner amount detection sensor 36 when the total number of rotations of the toner supply motor 37 reaches A-2B is taken as an example. It is assumed that the toner amount detection sensor 36 is used so that the sensor output value increases as the toner weight increases.

  When the toner container 5 is replaced by the user (step S1), the count value R of the motor rotation number counter 38 is reset to 0 (step S2). Then, as printing is executed (step S3), the toner in the developing device 4 is gradually consumed.

  Further, by determining whether or not the output value S of the toner amount detection sensor 36 is smaller than the threshold value α (step S4), it is continuously detected whether a predetermined amount or more of toner is stored in the developing device 4. As long as the output value S is equal to or greater than the threshold value α, printing is performed as it is. On the other hand, when the output value S becomes smaller than the threshold value α in step S4, the toner supply motor 37 is rotated (step S5) to replenish toner from the toner container 5 to the developing device 4. At the same time, the count value R of the motor rotation number counter 38 is added by the rotation number of the toner supply motor 37 (step S6).

  Next, it is determined whether or not the count value R is greater than or equal to A-2B (step S7). When R is smaller than A-2B, the threshold change timing has not been reached, so it is determined whether or not the sensor output value S after a predetermined time is equal to or greater than the threshold value α without changing the threshold value α ( Step S10). If the output value S is less than the threshold value α (NO in step S10), toner replenishment and addition of the rotation count value R are performed again (steps S5 to S6). On the other hand, when the output value S is equal to or greater than the threshold value α (YES in step S10), the process returns to step S3 to execute printing and detect the toner amount in the developing device 4, and supply toner according to the detection result. The rotation speed count value R is added (steps S3 to S6).

  If the count value R is greater than or equal to A-2B in step S7, it is next determined whether or not R is greater than or equal to A (step S8). When R is smaller than A, the threshold value α of the toner amount detection sensor 36 is increased by a predetermined amount (step S9). In step S10, toner replenishment and count value R are added until the sensor output value S becomes equal to or greater than the threshold value α. Thereafter, toner supply and change of the threshold value α are repeated in the same procedure (steps S3 to S10), and the toner weight in the developing device 4 is gradually increased.

  If the count value R is greater than or equal to A in step S8, the remaining amount of toner in the toner container 5 is empty, so it is determined whether or not R has reached A + B by stopping changing the threshold value α. (Step S11). Since it is not possible to determine whether the toner container 5 needs to be replaced until R reaches A + B, the process returns to step S3 and continues printing.

  At this time, when the output value S becomes smaller than the threshold value α in step S4, the toner supply motor 37 rotates (step S5). However, since the toner in the toner container 5 has already disappeared, the toner is not replenished and the count value is reached. Only R is added (step S6). Therefore, the toner weight in the developing device 4 gradually decreases. Thereafter, when R reaches A + B in step S11, it is determined whether or not the toner container 5 is to be replaced, and a notification for prompting the user to replace the toner container 5 is made (step S12), and the toner supply control is terminated.

  By executing the control shown in FIG. 4, when the remaining amount of toner in the toner container 5 becomes zero, the developing device 4 is replenished with toner more than during normal control. For this reason, when the replacement of the toner container 5 is notified, the toner weight in the developing device 4 is not significantly reduced, and the fog image caused by the replenishment of a large amount of toner immediately after replacement with a new toner container 5 occurs. Generation can be effectively prevented.

  Further, the change of the threshold value of the toner amount detection sensor 36 is caused by the rotation of the toner supply motor 37 required for the determination of toner container replacement rather than the rotation speed A of the toner supply motor 37 estimated that the toner remaining in the toner container 5 is exhausted. It starts from the front by twice the number B. Thereby, since the toner weight in the developing device 4 gradually increases, it is possible to prevent the occurrence of a fogging image due to a rapid increase in new toner replenished into the developing device 4. Although not described here, the control in FIG. 3B in which the threshold value is changed immediately after replacement of the toner container 5 can be described in exactly the same manner.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, the developer used may be a one-component developer or a two-component developer, and may be a magnetic method or a non-magnetic method. Also, various conventionally known sensors such as a magnetic permeability sensor and a piezoelectric sensor can be used depending on the developer used as the toner amount detection sensor.

  For example, in the case of a two-component developer composed of toner and a magnetic carrier, if the toner concentration is detected using a magnetic permeability sensor, the sensor output value decreases as the toner concentration increases. In such a case, the toner density (toner amount) in the developing device can be gradually increased by lowering the threshold value of the magnetic permeability sensor stepwise at a predetermined timing.

  The present invention is not limited to the monochrome printer as shown in FIG. 1, but can be applied to various image forming apparatuses using a detachable toner container such as monochrome and color copiers, color printers, and facsimiles. is there.

  The suppression effect of the fogged image when the image formation was performed using the toner replenishment control of the present invention was investigated. The number of rotations (A) of the toner supply motor that is expected to run out of toner in the toner container is set to 10,000 rotations, the rotation number (B) of the toner supply motor required for determination of toner container replacement is set to 100 rotations, and one sheet of printing is performed. Developing device for toner consumption (C) per unit (C) of 40 mg / sheet (print rate 4% conversion), number of printed sheets (D) within the time required for toner container replacement determination, 500 sheets, during normal control (before threshold change) When the toner weight (E) is 165 g, the rotation speed (R) of the toner supply motor that starts changing the threshold value of the toner amount detection sensor and the target toner weight (P) in the developing device are expressed by the above conditional expression ( When the conditions 1) and (2) are satisfied (Inventions 1 and 2), the threshold value is changed, but the conditional expressions (1) and (2) are not satisfied (Inventions 3 and 4), and the toner amount detection sensor Do not change threshold Comparing the case (Comparative Example 1). Detailed conditions of Inventions 1 to 4 and Comparative Example 1 are shown in Table 1.

  As an evaluation method, a test image having a printing rate of 4% is continuously printed in a normal temperature and humidity environment (20 ° C., 65% RH) while replenishing toner in the developing device under the control of the present invention 1 to 4 and Comparative Example 1. The toner weight in the developing device before and after the toner container replacement was measured. Further, the FD (Fog Density) value of 1,000 sheets before and after the toner container replacement was measured using a Macbeth reflection densitometer (RD914), and image characteristics were evaluated. The maximum value of the FD value was less than 0.010, ◯ (no fogging), 0.011 or more and less than 0.015 was Δ (some fogging), and 0.015 or more was x (significant fogging).

As test machine setting conditions, a positively charged single-layer OPC drum having an outer diameter of 30 mm was used as the photosensitive drum, the drum charging potential (bright potential) was 475 V, and the drum peripheral speed was 93 mm / sec. The charging unit was a scorotron charging system, and the exposure unit was a laser scanner with a laser wavelength of 780 nm and a laser exposure of 0.9 μJ / cm ² . The developing device is a magnetic jumping developing system, and the developing roller has a DC bias of 350 V, an AC bias of 1.6 kV, a frequency of 2.4 kHz, and a duty ratio of 50%. As the toner amount detection sensor, a magnetic permeability sensor having sensor sensitivity as shown in FIG. 5 was used.

  As other conditions, the distance between the drum and the developing roller is 0.32 mm, the peripheral speed ratio of the developing roller to the photosensitive drum is 1.4, and the peripheral speed ratio of the toner supply roller (mixer) to the developing roller is 0.48. It was. As the developer, a one-component developer containing 40% magnetic powder and 2% wax as an internal additive and 1% silica and 1.4% abrasive (titanium oxide) as an external additive is used. It was. The test results are shown in Table 2.

  As apparent from Table 2, the threshold value change is started immediately after the toner container replacement (R = 0) and after the rotation of the toner supply motor 9800 (R = A-2B), and the increase amount of the toner weight is set to 20 g, that is, the target toner. In both of the present inventions 1 and 2 in which the weight is set to 185 g (P = C × D + E), the toner weight in the developing device is almost the same as 160 g during normal control before and after the toner container replacement, and before and after the toner container replacement. No fogging image was observed.

  In the third aspect of the present invention, in which the threshold value change is started after the rotation of the toner supply motor 9850 (R> A-2B), the toner replenishment speed increases because the threshold value of the toner amount detection sensor is suddenly increased. The toner was developed and a slight fog image was generated. However, no fogging image was observed after the toner container was replaced. Further, in the fourth aspect of the present invention in which the toner weight increase width is set to 10 g, that is, the target toner weight is set to 175 g (P <C × D + E), a fogging image before the toner container replacement does not occur. The toner weight in the apparatus decreased by 10 g from 160 g at the time of normal control to 150 g, and 10 g of toner was replenished at once immediately after the replacement, so that a slight fog image was generated after the toner container replacement.

  On the other hand, in Comparative Example 1 in which the threshold of the toner amount detection sensor is not changed, the toner weight in the developing device is reduced by 20 g from 160 g in the normal control to 140 g before the toner container replacement, and 21 g of toner immediately after the replacement. Was replenished all at once, so that a noticeable fogging image occurred after the toner container was replaced.

  From the above, in the toner replenishment control according to the first to fourth aspects of the present invention, the toner weight in the developing device before and after replacement of the toner container is more stable than in Comparative Example 1, and fogging images are generated before and immediately after replacement of the toner container. It was confirmed that suppression was possible. In particular, the present invention 1 and 2 in which the rotation speed (R) of the toner supply motor that starts changing the threshold value of the toner amount detection sensor and the target toner weight (P) in the developing device satisfy the conditional expressions (1) and (2). The inhibitory effect was high. The above-described embodiment is merely an example, and it is known that the same result can be obtained even when, for example, the test conditions (setting of the testing machine, type of developer, etc.) are changed.

  The present invention relates to a developing device that forms a toner image corresponding to an electrostatic latent image by attaching toner onto an image carrier by a toner carrier, and a toner amount detection that detects the toner weight or toner density in the developing device. A sensor, a replaceable toner container that stores toner supplied to the developing device, a toner supply motor that drives the toner container to supply toner to the developing device, and a count that counts the number of rotations of the toner supply motor In the image forming apparatus including the control unit and the control unit for controlling the toner supply from the toner container according to the output value of the toner amount detection sensor, the control unit has an output value of the toner amount detection sensor equal to or less than a predetermined threshold value. In this case, toner supply from the toner container is executed, and the output value of the toner amount detection sensor exceeds the threshold value while the toner supply motor rotates a predetermined number of times. It notifies the exchange of the toner container when not null, performs stepwise control for changing the threshold value of the toner amount detecting sensor in accordance with the accumulated count value of the counting means from the previous toner container exchange.

  As a result, after the toner in the toner container is emptied, the amount of toner in the developing device is not significantly reduced even if printing is continued within the time required for replacement, and the toner container can be replaced. Provided is an image forming apparatus capable of effectively preventing a fogging image generated by developing a poorly charged toner because a large amount of new toner is not replenished immediately thereafter.

  In addition, since the start timing of changing the threshold value of the toner amount detection sensor is determined using the conditional expression (1), it is possible to prevent the occurrence of a fog image before the toner container replacement due to a rapid increase in the toner amount in the developing device. . Accordingly, there is provided an image forming apparatus capable of forming a high-quality image while maintaining a high quality toner image created by a developing device immediately after replacement of a toner container and immediately before replacement with a next toner container.

  In addition, since the target toner weight P in the developing device is determined using the conditional expression (2), and the maximum change width of the threshold of the toner amount detection sensor is set in accordance with the target toner weight P, the time within the time required for the toner container replacement determination is set. Since an appropriate amount of toner is replenished according to the amount of consumed toner, the image forming apparatus can reliably prevent the occurrence of insufficient toner replenishment and excessive replenishment.

FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus of the present invention. These are block diagrams showing a control mechanism of the image forming apparatus of the present invention. FIG. 4 is a graph showing a relationship between an accumulated rotation speed of a toner supply motor and a remaining amount of toner in a developing device in toner supply control used in the image forming apparatus of the present invention. These are flowcharts showing a toner replenishment control procedure used in the image forming apparatus of the present invention. These are graphs showing the relationship between the output value of the magnetic permeability sensor used in the example and the toner weight in the developing device. FIG. 3 is a perspective view showing an internal structure of a conventional toner container. FIG. 6 is a side sectional view of a conventional toner container. FIG. 3 is a perspective view of a conventional toner container as viewed from the bottom side. These are graphs showing the relationship between the cumulative number of rotations of the toner supply motor and the remaining amount of toner in the developing device in conventional toner replenishment control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging unit 3 Exposure unit 4 Developing apparatus 5 Toner container 6 Transfer roller 30 Image input part 31 AD conversion part 32 Image formation part 33 Control part (control means)
34 Storage Unit 36 Toner Amount Detection Sensor 37 Toner Supply Motor 38 Motor Revolution Counter (Counting Unit)
100 Image forming apparatus

Claims (3)

A developing device for forming a toner image corresponding to the electrostatic latent image by attaching toner onto the image carrier by the toner carrier;
A toner amount detection sensor for detecting the toner weight or toner concentration in the developing device;
A replaceable toner container for storing toner to be supplied to the developing device;
A toner supply motor for driving the toner container and supplying toner to the developing device;
Counting means for counting the number of rotations of the toner supply motor;
An image forming apparatus comprising: control means for controlling toner supply from the toner container according to an output value of the toner amount detection sensor;
The control means executes toner supply from the toner container when an output value of the toner amount detection sensor becomes a predetermined threshold value or less, and the toner amount detection sensor while the toner supply motor rotates a predetermined number of times. When the output value of the toner container does not return to the threshold value or more, the replacement of the toner container is notified, and the threshold value of the toner amount detection sensor is set stepwise according to the integrated count value of the counting means since the previous toner container replacement. An image forming apparatus that performs control to be changed. 2. The image forming apparatus according to claim 1, wherein an integrated count value R of the counting unit at the start of changing the threshold value of the toner amount detection sensor satisfies the following conditional expression (1).
0 ≦ R ≦ A-2B (1)
However,
A: The cumulative number of rotations of the toner supply motor that is predicted to run out of toner in the toner container,
B: Number of rotations of the toner supply motor that rotates within the time required for determination of toner container replacement,
It is. The maximum change width of the threshold of the toner amount detection sensor is set so that the target toner weight P in the developing device satisfies the following conditional expression (2). Image forming apparatus.
P = C × D + E (2)
However,
C: average toner consumption per printed sheet calculated from the printing rate,
D: number of prints within the time required for determination of toner container replacement,
E: the toner weight in the developing device before the threshold change,
It is.

Images