JP2006208578A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stabilizing image quality by performing toner carriage in a developing apparatus in accordance with the toner consumption even in either case that an image to be printed is a letter image or a solid image. <P>SOLUTION: The image forming apparatus 100 is constituted of an image reading part 30, an AD conversion part 31, an image forming part 32, a control part 33, a storage part 34, an operation panel 35, a sheet storing part 51, a fixing part 53 and motors 36 to 39 for driving respective apparatus parts. The control part 33 has a function of calculating a printing rate and area information on an image concentrated with dots based on an image signal digital-converted by the AD conversion part 31 and switching a continuous printing mode and a recording operation stoppage mode, based on the calculated printing information, and a function of stopping the recording operation for a prescribed time for every operation of recording one sheet in the recording operation stoppage mode so as to recover the toner concentration. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like provided with a developing device of a lateral stirring method in which a developer inside the apparatus is stirred and conveyed in an axial direction and supplied to a developing roller. The present invention relates to a toner supply control method.

  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, and after the toner image is transferred onto a recording medium, a fixing process is performed.

  FIG. 6 shows a conventional image forming apparatus (for example, a printer) 100 using the developing device 21. The image forming apparatus 100 includes a photosensitive drum 41, a charging unit 42, an image writing unit (laser scanning unit) 43, a developing device 21, a toner container 44, a transfer unit 45, a cleaning unit 46, a sheet storage unit 51, and a conveyance unit. 52, a fixing unit 53, and a paper discharge unit 54.

  The photosensitive drum 41 is formed, for example, by laminating a photosensitive layer on an aluminum drum, and the charging unit 42 charges the surface. Then, an electrostatic latent image in which charging is attenuated is formed on the surface that has received a laser beam from an image writing unit 43 described later. The photosensitive layer is not particularly limited, but for example, amorphous silicon (a-Si) having excellent durability is preferable.

  The charging unit (charging charger) 42 charges the surface of the photosensitive drum 41 by discharging (for example, corona discharge). For example, the charging unit 42 has a thin wire or the like, and discharges when a high voltage is applied to the charging unit 42 as an electrode. The image writing unit (LSU) 43 irradiates the photosensitive drum 41 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 41. The image data is transmitted from a personal computer (PC) (not shown).

  The developing device 21 attaches toner to the electrostatic latent image on the photosensitive drum 41 to form a toner image. Examples of the developer accommodated in the developing device 21 include a two-component developer composed of a toner component and a carrier and a one-component developer composed only of a toner component. Details of the developing device 21 will be described later.

  The toner container 44 supplies toner to the developing device 21 and stores spare toner when the toner in the developing device 21 runs short. The transfer unit 45 transfers the toner image formed on the surface of the photosensitive drum 41 onto the conveyed sheet without disturbing the toner image.

  The cleaning unit 46 removes the toner (residual toner) remaining on the surface of the photosensitive drum 41 after the toner image has been transferred (transferred) to the sheet. It consists of a blade material, a rubbing roller, etc. that come into contact. The sheet storage unit 51 stores a sheet (paper, OHP, or the like) on which an image (toner image) is finally printed, and a conveyance unit 52 that is a sheet path from the sheet storage unit 51 to the paper discharge unit 54. The sheet is sent out.

  The fixing unit 53 converts the toner image transferred onto the sheet into a stable permanent image. For example, the fixing unit 53 melts the powder toner image by applying energy such as heat or pressure. The paper discharge unit 54 accommodates a sheet that has passed through the fixing unit 53, that is, a sheet on which a permanent image is printed.

  Then, the image writing unit 43 emits a laser beam (light beam) on the photosensitive drum 41 based on the preliminarily input image data, so that the electrostatic latent image based on the image data is formed on the surface of the photosensitive drum 41. Let it form. Thereafter, toner is attached to the electrostatic latent image by the developing device 21 (a toner image is formed), and the toner image is transferred onto the sheet by the transfer unit 45. Next, the fixing unit 53 applies heat or the like to the sheet on which the toner image is transferred to form a permanent image.

  FIG. 7 is a schematic perspective view of the developing device 21, FIG. 8A is a side sectional view, and FIG. 8B is a schematic plan view from above. 7 and 8B are expressed excluding the lid portion (cover portion) for the sake of convenience, and FIG. 8B expresses the vicinity of the first stirring screw 7 (described later) with emphasis. . As shown in FIGS. 7 and 8, the developing device 21 includes a casing (housing) 5, a cover (housing) 6, a first agitation screw (rotary conveyance unit) 7, and a second agitation screw (rotary conveyance unit) 8. The developing roller 11, the regulation blade 12, and a T sensor (detection means) 13 that detects the toner amount.

  The casing 5 stores toner, and the inside is divided by a partition plate 9 formed integrally with the casing 5, and a first storage chamber 15 and a second storage chamber 16 are formed. The first storage chamber 15 is provided with a first stirring screw 7, and the second storage chamber 16 is provided with a second stirring screw 8. The cover 6 seals the toner or the like accommodated in the casing 5 so as not to leak to the outside.

  The first stirring screw 7 conveys the toner and the like stored in the first storage chamber 15 in the direction of arrow P while stirring the toner, and guides it to the second storage chamber 16. The second stirring screw 8 2 The toner or the like conveyed to the storage chamber 16 is conveyed in the direction of arrow Q while being agitated and supplied to the developing roller 11. As shown in FIG. 8B, there is no partition plate 9 at both ends of the casing 5 in the longitudinal direction, and toner can be transferred (circulated) between the first stirring screw 7 and the second stirring screw 8. It has become. The first agitation screw 7 and the second agitation screw 8 have a structure in which the spiral shafts 7b and 8b are provided around the support shafts 7a and 8a, respectively, and the casing 5 is parallel to each other. It is pivotally supported so that it can rotate.

  The developing roller 11 supplies toner to the photosensitive layer of the photosensitive drum 41 by rotating according to the rotation of the photosensitive drum 41 (see FIG. 6). In the case of a developing device using a magnetic developer, a magnet roller having a magnetic field generating member (not shown) made of a permanent magnet fixed on the inner surface is used as the developing roller 11. A toner thin layer is formed by attaching (carrying) toner to the surface of the developing roller 11 by the magnetic force of the magnetic field generating member. On the other hand, in the case of a developing device using a non-magnetic developer, a rubber roller or the like is used as the developing roller 11. The developing roller 11 is rotatably supported on the casing 5 in a state parallel to the first stirring screw 7 and the second stirring screw 8. The first stirring screw 7, the second stirring screw 8, and the developing roller 11 are rotationally driven by driving means (not shown).

  The regulating blade 12 regulates the amount of toner supplied to the photosensitive drum 41, and in the case of a developing device using a magnetic developer, SUS (stainless steel) such as SUS430 is used. A magnetic field generating member provided opposite to the tip of the regulating blade 12 generates a magnetic field between the developing roller 11 and the regulating blade 12, and not only the distance between the regulating blade 12 and the developing roller 11 but also the magnetic field. The amount of toner adhering to the developing roller 11 is strictly regulated by the strength. This makes it possible to form a thin toner layer of several tens of microns.

  The T sensor 13 detects the amount of toner (or toner concentration or the like) stored in the casing 5, and for example, a piezoelectric sensor or a magnetic sensor is used. Piezoelectric sensors take advantage of the property of piezoelectric elements that generate a voltage proportional to the magnitude of an impact or vibration from the outside, taking out the impact or vibration as an electrical signal. Compact, lightweight, and highly sensitive It has the feature. The T sensor 13 is provided on the bottom surface of the second storage chamber 16 such that a detection surface 13a described later faces the second storage chamber 16 side, that is, the inner side.

  When the toner is sufficiently stored in the second storage chamber 16, the detection surface 13a of the T sensor 13 detects that the toner is sufficiently stored by being applied with a certain pressure by the toner. . On the other hand, when a sufficient amount of toner is not stored in the second storage chamber 16, the detection surface 13a is not subjected to a pressure exceeding a certain level by the toner. At this time, the T sensor 13 detects that the toner amount is not sufficient.

  In such an image forming apparatus, for example, when image forming processing is continuously performed, the toner supply amount from the toner container 44 may not catch up with the toner consumption amount, and the developed image density may become thin. In view of this, a method for maintaining good toner image quality by controlling the toner density in the developing device 21 has been proposed. There is disclosed a toner concentration control device that shifts to a consumption mode and pauses the recording operation for a predetermined time every time one recording is finished to recover the toner concentration.

  Patent Document 2 discloses an image in which the toner density in the developing device can be maintained constant regardless of the printing rate by changing the number of rotations of the toner conveying screw in the toner container according to the printing rate of the image. A forming apparatus is disclosed.

  Here, in the case of an image forming apparatus provided with a lateral stirring type developing device that circulates toner while being laterally stirred by the first stirring screw 7 and the second stirring screw 8 as shown in FIGS. Even if the printing rate of the entire image is low, if there is a portion where dots are concentrated (hereinafter referred to as a concentrated image), such as a solid image, in the printed image, the amount of toner consumption is partially high Therefore, even if the toner supply amount is sufficient for the entire image, the toner conveyance amount cannot keep up with the toner consumption amount on the developing roller 11 in the concentrated image portion, and the image quality may deteriorate.

However, since the method of Patent Document 1 is mainly intended to prevent the toner to be replenished in the developing device from being insufficient, when the printing rate is low and a concentrated image is included, the mode is shifted to the multi-consumption mode. In other words, the image density in the concentrated image is reduced or roughened, and the image quality is reduced. Also in the method of Patent Document 2, since the toner supply speed is changed based on the image printing rate information, the same problem occurs when a lateral stirring type developing device is used.
Patent No. 2914515 JP 2000-214672 A

  SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an image forming apparatus that stabilizes image quality by causing toner conveyance in the developing device to follow the amount of toner consumption, regardless of whether a printed image is a character image or a solid image. The purpose is to provide.

  In order to achieve the above object, the present invention has a developing roller, and a rotary conveying unit that agitates and conveys the developer in the apparatus in the axial direction and supplies the developer to the developing roller. An image forming unit for recording the toner image formed on the image carrier on a recording medium, the image forming unit including a developing device that forms a toner image corresponding to the electrostatic latent image And an image forming unit that switches between a continuous printing mode and a recording operation pause mode in which the recording operation is paused for a preset time at the end of each recording sheet. In the apparatus, the control unit switches to the recording operation pause mode when a printing rate of a formed image or a size of a concentrated image is a predetermined value or more.

  According to the present invention, in the image forming apparatus having the above-described configuration, the control unit is configured such that the vertical length of the concentrated image is equal to or longer than the image length corresponding to one rotation of the developing roller, or the horizontal length is Switching to the recording operation pause mode is performed when the toner transport distance per recording sheet in the rotary transport unit is equal to or longer than the toner transport distance.

  According to the present invention, in the image forming apparatus having the above configuration, when the printing rate is equal to or higher than a predetermined value, the control unit pauses the recording operation while continuing toner supply to the developing device, and the printing rate is a predetermined value. When the image is smaller and the size of the concentrated image is equal to or greater than a predetermined value, the toner supply to the developing device and the recording operation are suspended.

  According to the first configuration of the present invention, not only when the printing rate is high and the toner consumption is large, but also when the printing rate is low and an image including a concentrated image of a predetermined size is continuously printed. Since it automatically shifts to the recording operation pause mode, the amount of toner supplied to the developing device or the amount of toner transported in the developing device follows the amount of toner consumed regardless of whether the image to be printed is a character image or a solid image. Therefore, it is possible to effectively prevent image density from being lowered and rough.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, when the length of the concentrated image in the vertical direction is equal to or longer than the image length corresponding to one rotation of the developing roller, or in the horizontal direction. By switching to the recording operation pause mode when the length of the toner is equal to or longer than the toner transport distance per recording sheet in the rotary transport section, the toner supply amount on the developing roller can surely follow the toner consumption amount. Can do.

  According to the third configuration of the present invention, in the image forming apparatus having the first or second configuration, when the printing rate is equal to or higher than a predetermined value, the recording operation is performed while continuing the toner supply to the developing device. When the printing rate is lower than a predetermined value and the size of the concentrated image is equal to or larger than the predetermined value, the toner supply to the developing device and the recording operation are stopped, so that the toner corresponding to the toner consumption amount of the entire image is obtained. Replenishment is possible.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the image forming apparatus of the present invention. Portions common to FIG. 6 of the conventional example are denoted by the same reference numerals and description thereof is omitted. The image forming apparatus 100 includes an image reading 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 sheet storage unit 51, a fixing unit 53, and motors 36 to drive each unit of the apparatus. 39.

  The image reading unit 30 includes a scanner lamp that illuminates the document during copying, a scanning optical system equipped with a mirror that changes the optical path of reflected light from the document, and a condensing lens that focuses the reflected light from the document to form an image. , And a CCD that converts the imaged image light into an electrical signal. The image signal read by the image reading 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 a photosensitive drum 41, a charging unit 42, an image writing unit 43, a developing device 21, a toner container 44, and a transfer unit 45, and a photosensitive member based on the digital signal converted by the AD conversion unit 31. An electrostatic latent image is formed on the drum 41, developed into a toner image by the developing device 21, and then the toner image is transferred onto the sheet by the transfer unit 45.

  The storage unit 34 includes an image memory 60, a RAM 61, and a ROM 62. The image memory 60 stores an image signal read by the image reading 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. In addition, the RAM 61 also stores a reference print rate and reference area information of a concentrated image used for switching control between a continuous printing mode and a recording operation pause mode, which will be 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 main motor 36 drives the photosensitive drum 41, the transfer unit 45, and the fixing unit 53 in accordance with a control signal from the control unit 33. The toner stirring motor 37 drives the stirring screws 7 and 8 (see FIG. 7) in the developing device 21 in accordance with a control signal from the control unit 33. The toner replenishing motor 38 drives a replenishing screw in the toner container 44 in accordance with a control signal from the control unit 33. The paper feed motor 39 drives a paper feed roller in the sheet storage unit 51 in accordance with a control signal from the control unit 33. The driving force may be transmitted from the main motor 36 using a gear and a clutch instead of the toner agitation motor 37, the toner replenishment motor 38, and the paper feed motor 39.

  The control unit 33 generally controls the image reading unit 30, the image forming unit 32, the sheet storage unit 51, the fixing unit 53 and the motors 36 to 39 that drive them according to the set program. The read image signal is converted into image data by scaling processing or gradation processing as necessary. The image writing unit 43 irradiates a laser beam based on the processed image data, and forms a latent image on the photosensitive drum 41.

  Further, the control unit 33 has a function of switching between the continuous printing mode and the recording operation pause mode based on the printing information of the image signal digitally converted by the AD conversion unit 31, and in the recording operation pause mode, for each recording. It has a function to pause the recording operation for a predetermined time. In the recording operation pause mode, the driving of the main motor 36 is stopped for a predetermined time or the driving of the main motor 36 is not stopped and the writing of the latent image by the image writing unit 43 and the development by the developing device 21 are stopped. The image forming operation is paused, and the toner shortage in the developing device 21 is recovered in a short time.

  In the present invention, when image formation is continuously performed, switching between the continuous printing mode and the recording operation pause mode is performed in consideration of not only the printing rate information of the formed image but also the area information of the concentrated image in the image. It is characterized by performing. As a result, when continuously printing an image having a low printing rate and including a concentrated image of a predetermined size, the mode automatically shifts to the recording operation pause mode. Etc. can be effectively prevented.

  As the area information of the concentrated image used for this control, the length of the concentrated image in the vertical direction (drum rotation direction) and the horizontal direction (drum width direction) is used. That is, the switching from the continuous printing mode to the recording operation pause mode is performed when a concentrated image in which the length in either the vertical direction or the horizontal direction exceeds a predetermined threshold is present in the formed image.

  Next, a method for calculating the vertical and horizontal thresholds of the concentrated image will be described. FIG. 2 is a schematic plan view of a developing device used in the image forming apparatus of the present invention. Portions common to FIG. 8 of the conventional example are denoted by the same reference numerals and description thereof is omitted. Note that the description of the cover 6 is omitted as in FIG. In the present invention, the T sensor 13 for detecting the toner amount or the toner concentration is provided on the side surface of the first storage chamber 15 facing the first stirring screw 7.

  If the concentrated image continues for more than the length formed by one rotation of the developing roller 11, if the toner supply amount on the developing roller 11 does not catch up with the toner consumption amount, the image density is reduced or the image is reduced in the second rotation. Roughness is likely to occur. Therefore, it is preferable to use the image length formed by one rotation of the developing roller 11 as the vertical threshold value of the concentrated image. The threshold in the vertical direction is determined based on the diameter of the developing roller 11 and the peripheral speed ratio (hereinafter referred to as S / D ratio) of the developing roller 11 with respect to the photosensitive drum 41 (see FIG. 6).

  For example, when the diameter of the developing roller 11 is φ (mm) and the S / D ratio is x, the circumference of the developing roller 11 is represented by φ · π (mm) where the circumference ratio is π. Further, since the outer peripheral surface of the photosensitive drum 41 moves 1 / x mm while the outer peripheral surface of the developing roller 11 moves by 1 mm, the length of the image formed on the photosensitive drum 41 by one rotation of the developing roller 11 is reduced. If W1, W1 = φ · π / x (mm).

  On the other hand, when the horizontal length of the concentrated image is longer than the toner transport distance per recording sheet, a portion exceeding the toner movement distance if the toner supply amount on the developing roller 11 cannot catch up with the toner consumption amount. As a result, a decrease in image density and image roughness are likely to occur. Therefore, it is preferable to use the toner transport distance per recording sheet as the lateral threshold value of the concentrated image. The lateral threshold value is determined based on the toner conveyance speed in the developing device 21.

  For example, assuming that the distance from the toner replenishment position S to the T sensor 13 shown in FIG. 2 is d (mm) and the time from the toner replenishment until the sensor voltage of the T sensor 13 rises is t (sec), the toner conveyance speed. s1 is expressed as s1 = d / t (mm / sec) using d and t. In the case of an image forming apparatus that prints y sheets per minute, since the image printing speed s2 is y / 60 (sheets / sec), assuming that the toner transport distance per recording sheet is W2, W2 = s1 / s2 = 60 d / t · y (mm / sheet). That is, the toner transport distance W2 per recording sheet is inversely proportional to the image printing speed s2.

  Here, the image printing speed s2 varies depending on the size of the paper used in the conveyance direction. For example, when printing on B5 vertical size (257 mm) using an apparatus that prints Y sheets per minute in A4 vertical size (297 mm), assuming that y + α sheets can be printed per minute, image printing at this time The speed s2 is (y + α) / 60 (sheets / sec). As a result, the toner transport distance W2 per recording sheet is s1 / s2 = 60 d / t · (y + α) (mm / sheet), and y / y + α when A4 portrait size is printed. Accordingly, it is necessary to set the threshold value in the horizontal direction of the concentrated image to be smaller as the size of the used paper in the conveyance direction becomes smaller.

  Next, a toner density control operation when performing continuous printing using the image forming apparatus of the present invention will be described. FIG. 3 is a flowchart showing the image forming mode setting operation of the image forming apparatus of the present invention. A procedure for switching between the continuous printing mode and the recording operation pause mode will be described with reference to FIG. First, when image formation is started by the user, the image reading unit 30 reads a document image and converts it into an image signal (step S1). This image signal is converted into a digital signal by the AD converter 31 (step S2), and then output to the image memory 60.

  Next, it is determined whether or not continuous printing is set by the user (step S3). If continuous printing is set, the digital signal in the image memory 60 is read to the control unit 33, and the control unit 33 calculates the printing rate P and the area information Q of the concentrated image based on the digital signal (step S4).

  Next, it is determined whether or not the calculated printing rate P is greater than or equal to a preset reference printing rate Px (step S5). When the printing rate P is equal to or higher than the reference printing rate Px, the toner consumption amount of the entire image increases, so that a recording operation pause mode is set in which image formation is stopped for a predetermined time for each recording sheet (step S6).

  If the printing rate P is smaller than the reference printing rate Px in step S5, it is determined whether or not the area information Q of the concentrated image calculated in step S4 is greater than or equal to the preset reference area information Qx (step S5). S7). Specifically, it is determined whether at least one of the vertical and horizontal lengths of the concentrated image is greater than or equal to the vertical and horizontal thresholds determined by the above-described method.

  When the area information Q is equal to or greater than the reference area information Qx, a concentrated image having a predetermined size or more exists in the image, and the toner consumption is partially increased. Therefore, the print rate P is equal to or greater than the reference print rate Px. The recording operation pause mode is set in the same manner as in the case (step S6). On the other hand, if the area information Q is smaller than the reference area information Qx in step S7, a continuous printing mode in which image forming operations are continuously performed is set (step S8). Thereafter, image formation is started in each mode, and the image formation mode setting operation ends.

  If the continuous printing is not set in step S3, it is not necessary to set the recording operation pause mode or the continuous printing mode. Therefore, the print rate P and the area information Q of the concentrated image are not calculated, but based on the print data. Thus, normal image formation is performed.

  FIG. 4 is a flowchart illustrating another example of the image forming mode setting operation. The process from reading the original image to calculating the printing rate P and the area information Q of the concentrated image (steps S1 to S4) is the same as in FIG. In this example, the print rate P is greater than or equal to the reference print rate Px in step S5, and the concentrated image area information Q is greater than or equal to the reference area information Qx in step S7. The control is divided so that the operation is different.

  When the printing rate is high, the toner consumption amount as a whole image increases. However, when the printing rate is low and a concentrated image exists, the toner consumption amount as a whole image does not change. Therefore, as shown in FIG. 4, when it is determined in step S5 that the printing rate P is equal to or higher than the reference printing rate Px and the recording operation pause mode is set (step S61), the recording operation is paused while toner supply is continued. When the area information Q of the concentrated image is determined to be greater than or equal to the reference area information Qx in step S7 and the recording operation pause mode is set (step S63), both toner replenishment and recording operation are performed. It is more preferable to set the control to pause (step S64).

  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 time for stopping the recording operation may be changed according to the size of the recording medium and the amount of toner consumed per recording. Instead of stopping the recording operation, the image formation start time is delayed by a predetermined time. Also good. Further, the developer used in the image forming apparatus of the present invention is not particularly limited, and may be a one-component developer or a two-component developer, and also a magnetic method or a non-magnetic method. It doesn't matter.

  Here, the print rate P and the area information Q of the concentrated image are calculated based on the image signal for writing read by the image reading unit 30 and digitally converted by the AD conversion unit 31, and the mode setting is performed. However, the document may be pre-scanned in order to calculate the printing rate P and the area information Q of the concentrated image. In the case of a printer that does not have an image reading unit, the printing rate P and the concentrated image area information Q can be calculated based on image data transmitted from an external input unit such as a PC.

  The effect of suppressing image defects when continuous printing was performed using the image forming apparatus of the present invention was investigated. In this embodiment, the image processing speed is 200 mm / sec, the diameter of the developing roller 11 is 20 mm, the rotation speed is 350 mm / sec, the S / D ratio is 1.75, and the toner lateral agitation circulation speed (lateral transport speed) in the developing device 21. ) Is 30 mm / sheet as a tester, and the recording operation pause mode is set when the printing rate is 40% or more, or when the vertical direction includes a concentrated image of 36 mm or more or the horizontal direction of 35 mm or more. In the case (the present invention) and the case where the recording operation pause mode is set only when the printing rate is 40% or more (comparative example), 10 sample images each including concentrated images of various sizes and numbers are continuously displayed. It was printed and examined for the occurrence of image defects.

  The vertical threshold 36 mm of the concentrated image is calculated from the diameter of the developing roller 11 and the S / D ratio by 20 × 3.14 / 1.75≈36 mm, and the horizontal threshold 35 mm is per recording sheet. From the developer transport distance of 30 mm, it was set in consideration of variations in transport speed. Occurrence of an image defect was determined by measuring the density of a printed image using a reflection densitometer (RD918) manufactured by Macbeth Co., Ltd., and determining that the image density was defective when ID (image density) was 1.2 or less. . The test results are shown in FIG. In FIG. 5, for example, 30 mm images × 10 images represent sample images in which 10 concentrated 30 mm square images (solid images) are randomly arranged so as not to overlap in the vertical and horizontal directions, respectively. The printing rate at that time is 14%.

  As is apparent from FIG. 5, in the present invention in which the mode setting control is performed using the image information of the printing rate and the concentrated image, no image density defect occurs regardless of the printing rate, the size and the number of the concentrated images. It was. On the other hand, in the comparative example in which the mode setting control is performed using only the printing rate, if the printing rate is high, or the printing rate is low and the vertical and horizontal lengths of the concentrated image are smaller than the threshold value, the image density is poor. However, when the printing rate was low and the length of the concentrated image in the vertical or horizontal direction was equal to or greater than the threshold value, the occurrence of image density failure was recognized.

  The present invention includes a developing roller and a rotary conveying unit that stirs and conveys the developer in the apparatus in the axial direction and supplies the developer to the developing roller. An image forming unit that includes a developing device that forms a toner image corresponding to the image, records the toner image formed on the image carrier on a recording medium, and a control unit that controls a recording operation of the image forming unit. An image forming apparatus that uses a control unit to switch between a continuous printing mode and a recording operation pause mode in which a recording operation is paused for a preset time for each recording end. When the printing rate or the size of the concentrated image is greater than or equal to a predetermined value, switching to the recording operation pause mode is performed.

  As a result, not only when the printing rate is high and the toner consumption is large, but also when the printing rate is low and an image including a concentrated image of a predetermined size is continuously printed, the recording operation pause mode is automatically set. Therefore, regardless of whether the image to be printed is a character image, a solid image, or both, the amount of toner replenished to the developing device or the amount of toner transported in the developing device during continuous printing is determined. Provided is an image forming apparatus capable of following toner consumption, maintaining a high quality toner image formed by a developing device and continuously forming high quality images.

  Further, since the vertical threshold value of the concentrated image is the image length corresponding to one rotation of the developing roller and the horizontal threshold value is the toner conveyance distance per recording sheet in the rotary conveyance unit, the development is performed according to the specifications of the image forming apparatus. The amount of toner supplied onto the roller can reliably follow the amount of toner consumed.

  Further, when the printing rate is equal to or higher than a predetermined value, the recording operation is stopped while continuing toner supply to the developing device. When the printing rate is lower than the predetermined value and the size of the concentrated image is higher than the predetermined value, the developing device If the toner replenishment and the recording operation are stopped, the toner replenishment can be continued only at a high printing rate in which the toner consumption of the entire image is large, and the toner supply to the developing device is insufficient or excessively supplied. Preventing the occurrence of

1 is a block diagram showing a configuration of an image forming apparatus of the present invention. These are schematic plan views of a developing device used in the image forming apparatus of the present invention. These are flowcharts showing a recording operation pause mode setting procedure in the image forming apparatus of the present invention. These are the flowcharts which show the other example of a recording operation pause mode setting procedure. These are tables showing the effect of suppressing image defects when continuous printing is performed using the image forming apparatus of the present invention. FIG. 1 is a schematic diagram illustrating an overall configuration of a conventional image forming apparatus. These are schematic perspective views of a conventional developing device. These are a side sectional view of a conventional developing device (FIG. 8A) and a partial plan view from above (FIG. 8B).

Explanation of symbols

5 Casing (housing)
7 1st stirring screw (rotary conveyance part)
8 Second agitation screw (rotary conveyance part)
11 Developing roller 12 Regulating blade 13 T sensor (detection means)
13a Detection surface 21 Developing device 30 Image reading unit 31 AD conversion unit 32 Image forming unit 33 Control unit (control means)
41 Photosensitive drum (image carrier)
44 Toner container 100 Image forming apparatus S Toner supply position

Claims (3)

A developing roller, and a rotary conveying unit that stirs and conveys the developer in the apparatus in the axial direction and supplies the developer to the developing roller, and attaches toner onto the image carrier by the developing roller to form an electrostatic latent image. A developing device for forming a corresponding toner image, and an image forming unit for recording the toner image formed on the image carrier on a recording medium;
Control means for controlling the recording operation of the image forming unit,
In the image forming apparatus that switches between the continuous printing mode and the recording operation pause mode in which the recording operation is paused for a preset time for each recording end using the control unit,
The image forming apparatus according to claim 1, wherein the control unit switches to the recording operation pause mode when a printing rate of an image to be formed or a size of a concentrated image included in the image is a predetermined value or more.   The control means is configured such that when the length in the vertical direction of the concentrated image is equal to or longer than the image length corresponding to one rotation of the developing roller, or the length in the horizontal direction is a toner transport distance per recording sheet in the rotary transport unit. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus switches to the recording operation pause mode when the above is true.   When the printing rate is equal to or greater than a predetermined value, the control means pauses the recording operation while continuing toner supply to the developing device, the printing rate is smaller than the predetermined value, and the size of the concentrated image is equal to or larger than the predetermined value. 3. The image forming apparatus according to claim 1, wherein the toner replenishment and the recording operation to the developing device are suspended.

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