JP2013246344A - Image forming apparatus and density adjustment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize density adjustment of an image forming apparatus, improve accuracy and reliability of density adjustment under a density sensor method, and stabilize image density under a density sensor-less method.SOLUTION: An image forming apparatus, having a developer carrier, developer supply means and transfer means, further includes: calculation means 60a for calculating, based on print image information, a developer amount necessary for transferring a visible image on a recording medium at a target density in a predetermined period while the image forming apparatus operates; and supply amount detection means 60b for detecting a developer supply amount corresponding to a predetermined period of the developer supply means. Further, the apparatus performs adjustments so as to bring a visible density on the recording medium close to a target density by changing an image-forming condition including a visible image-forming condition or transfer condition on the basis of necessary developer amount calculated by the calculation means 60a and the developer supply amount detected by the supply amount detection means 60b.

Description

  The present invention relates to an image forming apparatus and a density adjustment method thereof.

  In an image forming apparatus using an electrophotographic system, image density adjustment control (process control) is performed in order to set an image density to a target density and maintain stable image quality. In this image density adjustment control, for example, a density sensor system described in Patent Document 1 (Japanese Patent Laid-Open No. 2005-49701) is known. In this density sensor system, a test pattern is formed on an image carrier (photosensitive drum, intermediate transfer belt, intermediate transfer drum, paper as a recording medium, etc.), and the test pattern is optically reflected on the image carrier. The detection result is reflected in the image forming conditions (development bias, charging bias, exposure energy, etc.). Further, in recent years, as a low-end image forming apparatus, the use of an additional toner replenishment method as a toner is increasing with the aim of reducing the cost per unit print (lowering CPP).

  However, in the density sensor method, a certain user waiting time is generated for creating and detecting a test pattern, and toner for the test pattern is also wasted. Further, the density sensor is expensive, and it is difficult to obtain a stable detection result due to deterioration with time, contamination, and the like of the LED that is the sensor light source and the photodiode that is the light receiving element. In order to stabilize the detection result of the sensor, it is necessary to periodically develop a predetermined standard image on the image carrier to calibrate the detection characteristics, and the waiting time becomes longer. Thus, the density sensor method has room for improvement in the accuracy and reliability of density adjustment and the user standby time.

  On the other hand, in recent image forming apparatuses, a density adjustment method in which test pattern creation and density sensor detection are not performed is employed to reduce cost and reduce density adjustment operation time (hereinafter referred to as a density sensorless method). In this density sensorless system, a table of image forming conditions (development bias, charging bias, exposure energy, etc.) is created in advance from the environment (temperature, humidity) and the durability of the developing device, and the table is based on the usage conditions in actual use. The method of quoting values and determining the imaging conditions has become the mainstream. However, such table reference type control predicts the developing capability of the toner from the environment, the durability of the developing device, etc., and does not monitor any parameters directly related to the toner density. In addition, since the step width of the control value is large, changing the developing bias or the like during image formation causes the image density to change suddenly, for example, from about ID = 1.0 to 1.9. It was difficult to adjust the concentration.

  Therefore, as an improved density sensorless method, an image forming method disclosed in Japanese Patent Application Laid-Open No. 2001-296706 has been proposed. This method is for the purpose of setting and maintaining the image density of an image forming apparatus using two-component toner at a target value, and for developing device operation time, toner density, toner consumption, toner replenishment amount, replenishment toner remaining amount, and detection. Reflecting the reflection density ratio by the optical sensor of the pattern, the temperature and humidity around the toner, and a plurality of information including at least one history information of these history information as input, comprehensively inferring the developing capability of the developing device, Based on this inference result, at least one of a latent image forming condition, a toner supply condition, a toner charging member, and a developing bias condition is selectively controlled.

  In one embodiment, the toner charge and the degree of toner deterioration are predicted from the temperature / humidity sensor and the operation time counter of the photosensitive member, respectively, and the toner density in the developing unit is predicted. Then, the difference between the target toner density in the developing device and the current predicted toner density is calculated, the toner density is set so as to cancel the difference, and replenishment control or the like is performed.

  However, even the improved density sensorless system does not monitor any parameters directly related to the toner density, so that there is a problem that the density variation range is large.

  SUMMARY OF THE INVENTION An object of the present invention is to improve the accuracy and reliability of density adjustment using a density sensor system and to stabilize image density using a density sensorless system in order to appropriately perform density adjustment in an image forming apparatus.

  In order to solve the above-described problems, the present invention provides a developer carrying body that visualizes and carries a developer based on print image information, a developer supply unit that supplies the developer to the developer carrying body, An image forming apparatus having transfer means for transferring a visible image on a developer bearing member to a recording medium at a predetermined target density; and the visible image is transferred to the target in a predetermined period while the image forming apparatus is operating. A calculating means for calculating a developer amount necessary for transferring the developer onto the recording medium at a density based on the print image information, and a supply amount for detecting the developer supply amount corresponding to the predetermined period of the developer supplying means. Detecting means, and changing the image forming condition including the visualization condition or the transfer condition based on the required developer amount by the calculating means and the developer supply amount by the supply amount detecting means, The image density on the medium. Serial is an image forming apparatus that is adjusted to approach the target concentration.

  According to the present invention, the developer supply amount from the necessary developer amount for a predetermined period required for visualization at a target density on the recording medium and the developer supply amount supplied to the developer carrier during the predetermined period. Therefore, it is possible to easily determine whether the visible image density on the recording medium is close to the target density by changing the image forming condition based on the determination.

  In addition, it is possible to easily determine whether or not density adjustment control is necessary by determining whether the developer supply amount is excessive or insufficient, so there is no need to use a density sensor, and it is easier, faster and more accurate to determine whether or not density adjustment is necessary. Can be done. Furthermore, it is possible to omit the density sensor type test pattern creation and detection thereof, thereby shortening the user waiting time and saving the test pattern toner.

1 is a schematic configuration diagram of a printer as an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged view of an image forming unit of the printer of FIG. 1. It is a block diagram of an image density control means. It is another control flow of density adjustment. It is still another control flow for density adjustment. FIG. 4B is a diagram illustrating a relationship among a target density, a necessary toner amount, and a supplied toner amount in the control flow of FIG. 4A. FIG. 4B is a diagram illustrating a relationship among a target density, a necessary toner amount, and a supplied toner amount in the control flow of FIG. 4B. It is a control flow which substitutes for a part of control flow of Drawing 4A and Drawing 4B.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, in each drawing for explaining the embodiment of the present invention, components such as members and components having the same function or shape are once described by giving the same reference numerals as much as possible. The description is omitted.

(Image forming device)
First, an overall configuration and operation of an image forming apparatus to which the present invention is applied will be described with reference to FIG.
The image forming apparatus shown in FIG. 1 is a color laser printer, and four process units 1Y, 1M, 1C, and 1Bk as image forming units are detachably mounted on the printer main body 100. Each process unit 1Y, 1M, 1C, 1Bk contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (Bk) corresponding to the color separation components of the color image. The configuration is the same except that. In this embodiment, a one-component developer made of toner is used as the developer.

  Specifically, each process unit 1Y, 1M, 1C, 1Bk includes a photosensitive drum 2 as a latent image carrier or a developer carrier, a charging roller 3 for charging the surface of the photosensitive drum 2, and the like. Cleaning provided with a charging device, a developing device 4 as a toner supply means (developer supply means) for supplying toner to the surface of the photosensitive drum 2, a cleaning blade 5a for cleaning the surface of the photosensitive drum 2, and the like. The apparatus 5 is configured. In FIG. 1, only the photosensitive drum 2, the charging roller 3, the developing device 4, and the cleaning blade 5 included in the black process unit 1 </ b> Bk are denoted by reference numerals, and the other process units 1 </ b> C, 1 </ b> M, and 1 </ b> Y are denoted by reference numerals. Is omitted.

  In FIG. 1, an exposure device 6 as an exposure means for exposing the surface of the photosensitive drum 2 is disposed above each process unit 1Y, 1M, 1C, 1Bk. The exposure device 6 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photosensitive drum 2 with laser light based on image data.

  A transfer device 7 is disposed below each process unit 1Y, 1M, 1C, 1Bk. The transfer device 7 has an intermediate transfer belt 8 constituted by an endless belt as a transfer body. The intermediate transfer belt 8 is stretched between a driving roller 9 as a support member and a driven roller 10 with a predetermined tension, and when the driving roller 9 rotates counterclockwise in the drawing, the intermediate transfer belt 8 is It is configured to run around (rotate) in the direction indicated by the arrow in the figure. A reflection sensor 25 is disposed in the vicinity of the driven roller 10 toward the surface of the intermediate transfer belt 8.

  Four primary transfer rollers 11 as primary transfer means are disposed at positions facing the four photosensitive drums 2. Each primary transfer roller 11 presses the inner peripheral surface of the intermediate transfer belt 8 at each position, and a primary transfer nip is formed at a location where the pressed portion of the intermediate transfer belt 8 and each photosensitive drum 2 come into contact with each other. Has been. Each primary transfer roller 11 is connected to a power source (not shown), and a predetermined direct current voltage (DC) and / or alternating current voltage (AC) is applied to the primary transfer roller 11.

  A secondary transfer roller 12 as a secondary transfer unit is disposed at a position facing the drive roller 9. The secondary transfer roller 12 presses the outer peripheral surface of the intermediate transfer belt 8, and a secondary transfer nip is formed at a location where the secondary transfer roller 12 and the intermediate transfer belt 8 are in contact with each other. Similar to the primary transfer roller 11, the secondary transfer roller 12 is connected to a power source (not shown) so that a predetermined direct current voltage (DC) and / or alternating current voltage (AC) is applied to the secondary transfer roller 12. It has become.

  A belt cleaning device 13 for cleaning the surface of the intermediate transfer belt 8 is disposed on the outer peripheral surface on the right end side of the intermediate transfer belt 8 in the drawing. This belt cleaning device 13 has a cleaning blade 13a, a conveying coil 13b, and a cleaning counter roller 13c. The toner on the intermediate transfer belt 8 scraped off by the cleaning blade 13a is extended from the conveying coil 13b and the belt cleaning device 13. The toner is sent to a waste toner container 14 disposed below the transfer device 7 via a waste toner transfer hose (not shown).

  A paper feed cassette 15 that accommodates a recording medium P such as paper or an OHP sheet is disposed below the printer main body 100. The paper feed cassette 15 is provided with a paper feed roller 16 for feeding out the stored recording medium P. On the other hand, a pair of paper discharge rollers 17 for discharging the recording medium to the outside and a paper discharge tray 18 for stocking the discharged recording medium are disposed on the upper portion of the printer main body 100.

  In the printer main body 100, a transport path R for transporting the recording medium P from the paper feed cassette 15 through the secondary transfer nip to the paper discharge tray 18 is disposed. In the transport path R, a pair of timing rollers 19 are disposed upstream of the position of the secondary transfer roller 12 in the recording medium transport direction. A fixing device 20 is disposed downstream of the position of the secondary transfer roller 12 in the recording medium conveyance direction.

(Operation of image forming apparatus)
The image forming apparatus operates as follows.
When the image forming operation is started, the photosensitive drums 2 of the process units 1Y, 1M, 1C, and 1Bk are rotated in the clockwise direction in FIG. Are uniformly charged. Based on the image information of the original read by a reading device (not shown), the exposure device 6 irradiates the charged surface of each photosensitive drum 2 with laser light to form an electrostatic latent image on the surface of each photosensitive drum 2. Is done. At this time, the image information to be exposed on each photosensitive drum 2 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. The electrostatic latent image formed on the photosensitive drum 2 in this manner is supplied with toner by each developing device 4, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  A drive roller 9 that is wound around one side of the intermediate transfer belt 8 with a predetermined tension is driven to rotate, causing the intermediate transfer belt 8 to run in the direction of the arrow in the figure. Further, a primary voltage between each primary transfer roller 11 and each photoconductive drum 2 is applied to each primary transfer roller 11 by applying a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner. A transfer electric field is formed at the nip. Then, the toner images of the respective colors on the respective photosensitive drums 2 are sequentially superimposed and transferred onto the intermediate transfer belt 8 by the transfer electric field formed in the primary transfer nip. Thus, the intermediate transfer belt 8 carries a full-color toner image on its surface. The toner on each photosensitive drum 2 that could not be transferred to the intermediate transfer belt 8 is removed by the cleaning blade 5.

  When the image forming operation is started, the paper feed roller 16 rotates and the recording medium P is carried out from the paper feed cassette 15. The unloaded recording medium P is timed by the timing roller 19 and sent to the secondary transfer nip between the secondary transfer roller 12 and the intermediate transfer belt 8. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 8 is applied to the secondary transfer roller 12, thereby forming a transfer electric field in the secondary transfer nip. Then, the toner image on the intermediate transfer belt 8 is collectively transferred onto the recording medium P by the transfer electric field formed in the secondary transfer nip. Thereafter, the recording medium P is sent to the fixing device 20 and the toner image is fixed on the recording medium P. Then, the recording medium P is discharged to the paper discharge tray 18 by the pair of paper discharge rollers 17.

  The above description is an image forming operation when a full-color image is formed on a recording medium. A single color image is formed using any one of the four process units 1Y, 1M, 1C, and 1Bk, and 2 Two or three process units can be used to form a two or three color image.

(Developing device and toner cartridge)
FIG. 2 is a schematic sectional view of the developing device 4 and the toner cartridge 50.
As shown in FIG. 2, the developing device 4 includes a developing housing 40 having a toner containing portion that contains toner, a developing roller 41 that supplies toner to the photosensitive drum 2, and a supply roller that supplies toner to the developing roller 41. 42, a regulating blade 43 as a regulating member for regulating the amount of toner carried on the developing roller 41, a first toner conveying member 44 such as a screw for conveying toner, a second toner conveying member 45, and the like. .

The developing roller 41 is composed of a metal core and conductive rubber disposed on the outer periphery of the core. In the present embodiment, the outer diameter of the core metal is set to φ6, the outer periphery of the conductive rubber is set to φ12, and the rubber hardness Hs75. The conductive rubber has a volume resistance adjusted to about 10 ⁵ to 10 ⁷ Ω. For example, conductive urethane rubber or silicone rubber can be used as the conductive rubber. The developing roller 41 rotates in the counterclockwise direction in FIG. 2 and conveys the toner held on the surface to a position facing the regulating blade 43 and the photosensitive drum 2.

  Generally, a sponge roller or the like is used as the supply roller 42. As the sponge roller, it is appropriate that the foamed polyurethane mixed with carbon and made semiconductive is attached to the outer periphery of a metal core. In this embodiment, the outer diameter of the metal core is set to φ6, and the outer diameter of the sponge portion is set to φ12. The supply roller 42 is in contact with the developing roller 41. The nip formed by the contact between the supply roller 42 and the developing roller 41 is usually set to about 1 mm to 3 mm. In the present embodiment, the nip portion is 2 mm. Further, the supply roller 42 rotates in the counter direction (counterclockwise in FIG. 2) with respect to the developing roller 41, so that the toner in the developing housing 40 can be efficiently supplied to the surface layer of the developing roller 41. In this embodiment, a good toner supply function is ensured by setting the rotation speed ratio between the developing roller 41 and the supply roller 42 to 1.

  The regulating blade 43 is made of, for example, a metal plate such as SUS having a thickness of about 0.1 mm. The regulating blade 43 is in contact with the surface of the developing roller 41 on the tip side thereof, and the toner supplied onto the developing roller 41 by the supply roller 42 passes through the nip portion between the developing roller 41 and the regulating blade 43. As a result, the thickness is regulated and at the same time frictional charging is performed. Since the control of the toner amount on the developing roller 41 is a very important parameter for stabilizing the developing characteristics and obtaining good image quality, the contact pressure of the regulating blade 43 with respect to the developing roller 41 is 20 in a normal product. About -60 N / m, the position of the nip portion is strictly controlled to about 0.5 ± 0.5 mm from the tip of the regulating blade 43. These parameters are appropriately determined according to the characteristics of the toner to be used, the developing roller, the supply roller, and the like. In this embodiment, the regulation blade 43 is made of a SUS material having a thickness of 0.1 mm, the contact pressure is 45 N / m, the position of the nip portion is 0.2 mm from the tip of the regulation blade 43, and the support end of the regulation blade 43 By setting the length (free length) from to the free end (tip) to 14 mm, a stable toner thin layer can be formed on the developing roller 41.

  In the developing housing 40, a toner sensor 46 is provided at a predetermined height position as a developer remaining amount detecting means. As this toner sensor, any type of sensor such as a light transmission sensor, a piezoelectric sensor, a mechanical sensor, etc. can be employed. In this embodiment, an optical sensor including a light emitting element and a light receiving element is used. When toner is supplied from the developing roller 41 to the photosensitive drum 2 so that the remaining amount of toner in the developing housing 40 becomes a predetermined amount or less, the draft surface of the toner passes from the detection tip of the toner sensor 46 downward from above. The toner sensor 46 detects this.

  Further, a toner cartridge 50 as a toner container for containing replenishing toner is detachably mounted on the upper portion of the developing housing 40. The developing device 4 and the toner cartridge 50 are configured as a process unit in which the developing device 4, the toner cartridge 50, the photosensitive drum 2 and the like are integrated, and the developing device 4 and the toner cartridge 50 are integrated to form a photosensitive drum. Various combinations, such as the structure which makes 2 separate, are possible.

  Replenishing ports 50 a and 40 a for replenishing toner in the toner cartridge 50 into the developing housing 40 are formed in the lower part of the toner cartridge 50 and the upper part of the developing housing 40, respectively. Further, in the toner cartridge 50, the third toner conveying member 51 by a screw or a coil for conveying the internal toner to the replenishing port 50a, and the fluidity of the toner in the toner cartridge 50 are secured, and this first An agitator 52 for bringing the internal toner toward the toner transporting member 51 side of the third is rotatably provided. The third toner transport member 51 is configured to be connectable to a main body drive unit (not shown), and the main body drive unit and the third toner transport member 51 can be controlled to be connected or disconnected by a known method such as a clutch. The replenishment drive can be freely configured. The toner replenishment amount can be controlled by the driving time and driving speed of the main body driving unit. For example, the driving time and driving speed are changed in accordance with the change in toner fluidity in a temperature and humidity environment. Control is also possible.

  The toner is replenished based on the detection result of the toner sensor 46 as the toner remaining amount detecting means. That is, when the draft surface of the toner passes from the top to the bottom of the detection tip of the toner sensor 46, the toner sensor 46 detects this, and it is detected that the remaining amount of toner in the developing housing 40 has become a predetermined amount or less. The Based on the detection result, the third toner conveying member 51 of the toner cartridge 50 is driven at a predetermined time and a predetermined speed (predetermined number of rotations).

  By driving the third toner conveying member 51 for a predetermined time and at a predetermined speed, a predetermined amount of toner is supplied from the toner cartridge 50 to the developing housing 40 through the supply ports 50a and 40a. As the toner is supplied in a fixed amount in this manner, the draft surface of the toner in the developing housing 40 rises above the detection tip of the toner sensor 46, and the detection tip is buried in the toner again. By repeating the toner replenishment operation described above, the maximum and minimum height positions of the toner draft surface in the developing housing 40 become substantially constant.

  Further, the interior of the developing housing 40 is divided into a first region A in which the replenishing port 40a is disposed by a partition member 48 having a communication port 48a, and a second region in which developing means such as the developing roller 41 and the regulating blade 43 are disposed. It is divided into the area B. By dividing the inside of the developing housing 40 by the partition member 48 in this manner, it is possible to suppress the toner powder pressure from being concentrated on the supply roller 42 and applying a large load. A first toner transport member 44 is disposed in the first area A, and a second toner transport member 45 is disposed in the second area B.

  A predetermined bias voltage difference is applied to the supply roller 42 and the developing roller 41 by an electric circuit (not shown). Due to this bias voltage difference, the toner in the second region B in the developing housing 40 is supplied from the supply roller 42 to the developing roller 41, and a thin toner layer is formed on the surface of the developing roller 41. The toner thus moved to the developing roller 41 is made uniform on the toner layer adhering to the surface of the developing roller by the regulating blade 43, and then the developing roller 41 is rotated at a position close to the photosensitive drum 2, whereby the photosensitive member. Due to the potential difference between the electrostatic latent image on the drum 2 and the toner on the developing roller 41 moves to the photosensitive drum 2, a toner image is formed on the surface of the photosensitive drum 2 based on the electrostatic latent image. (Visualization). Such a developing device is an example, and selection of magnetic toner or non-magnetic toner, selection of contact development method or non-contact development method, and the like are arbitrary.

  As described above, the toner that has moved to the photosensitive drum 2 and remains on the photosensitive drum 2 as a transfer residue is removed by the cleaning blade 5a of the cleaning means 5, and then the conveying coil 5b and a waste toner transfer hose (not shown). And is collected in a waste toner container 14 installed in the image forming printer main body 100. A constant voltage is applied to the cleaning blade 5a from an electric circuit (not shown), and the tip of the cleaning blade 5a comes into contact with the surface of the photosensitive drum 51 to remove residual toner and paper dust and erase the electrostatic latent image. . As a result, the surface of the photosensitive drum 51 is cleaned and continuous use is possible. As the cleaning means, other contact type or non-contact type using a cleaning roller or the like can be adopted, and a cleaningless system without using the cleaning means can be adopted.

(Density adjustment)
As described above, the toner images on the intermediate transfer belt 8 are collectively transferred onto the recording medium P. At this time, the image density (visible image density) on the recording medium P is the upstream developing roller 41. Visualization conditions including the toner amount above, the potential difference between the developing roller 41 and the photosensitive drum 2, and the transfer conditions from the photosensitive drum 2 to the intermediate transfer belt 8, and the intermediate transfer belt 8 to the recording medium P Varies depending on the transfer conditions. In this embodiment, image forming conditions (development bias, charging bias, exposure energy, etc.) including these visualization conditions and transfer conditions are controlled by the image density control means 60 of FIG. The image density control means 60 includes necessary toner amount calculating means (necessary developer amount calculating means) 60a, toner supply amount detecting means (developer supply amount detecting means) 60b, and image forming condition changing means 60c. For example, the control is performed as shown in the control flow of FIG. 4A or 4B.

  The necessary toner amount calculating means 60a is a toner necessary for transferring the toner visible image formed on the photosensitive drum 2 onto the recording medium P at a target density during a predetermined period while the printer main body 100 is operating. The amount is calculated based on the print image information. This print image information includes the dot arrangement and dot density of the visible image in addition to the print rate. In addition to the printing rate, the dot arrangement, the dot density, and the like are taken into the calculation to improve the calculation accuracy of the required toner amount.

  Further, the toner supply amount detection means 60b detects the toner supply amount supplied in the order of the supply roller 42 → the developing roller 41 → the photosensitive drum 2 corresponding to the predetermined period. Correspondingly, the amount of toner supplied to the toner housing 40 by the third toner conveying member 51 is detected by the supply amount detecting means 60b. The supply amount detection means 60b can detect the toner supply amount from the drive time and drive speed (rotation speed) of the third toner conveying member 51. This detection method has an advantage that the existing toner replenishment toner sensor 46 can be used as it is, but detection of the toner supply amount is not limited to this method. That is, the amount of toner that moves from the developing roller 41 to the photosensitive drum 2, the amount of toner that moves from the photosensitive drum 2 to the intermediate transfer belt 8, or the amount of toner that moves from the intermediate transfer belt 8 to the recording medium P, You may make it detect by arrange | positioning a suitable detection means to these movement paths.

  Next, the control flow of the image density control means 60 will be described. Here, the two control flows of FIGS. 4A and 4B are illustrated, and the relationship among the target density, the necessary toner amount, and the supplied toner amount referred to in these control flows is illustrated in FIGS. 5A and 5B.

  The control flow in FIG. 4A starts with the toner replenishment operation when the height of the water draft of the toner in the developing housing 40 falls below the detection tip of the toner sensor 46. Here, when the height of the waterline of the toner reaches the detection tip of the toner sensor 46, the remaining amount of toner in the development housing 40 is X1, and when the toner sensor 46 detects the waterline of the toner, “toner in development housing” Amount <X1 ”is determined (step A1), and then the toner replenishment operation is executed and the toner replenishment amount is calculated (step A2). If the toner amount in the developing housing is equal to or greater than X1, “END” is set and density adjustment is not performed.

  The toner replenishing operation in step A2 is performed by driving the third toner conveying member 51 of FIG. 2 for a predetermined time as described above (quantitative replenishment). When this replenishment is performed a plurality of times during the predetermined period, the toner replenishment amount (supply amount) is calculated as the integrated value of the plurality of times. Next, the required toner amount calculation means 60a calculates the required toner amount for the predetermined period (step A3), and then the toner supply amount detection means 60b detects the toner supply amount (step A4).

  For the calculation of the necessary toner amount in step A3, a conventionally known control technique for predicting the toner consumption amount from print image information such as dot arrangement, dot density, or print rate from the writing control system can be used. In this embodiment, the toner adhesion amount on the photosensitive drum 2 when the target density on the recording medium P is obtained is measured in advance, and the target density is used to determine the target density on the recording medium P during the predetermined period. The amount of toner consumed when the toner image is visualized can be calculated. The “toner supply amount” detected in step A4 basically uses the previous supply amount as it is as the “toner supply amount”. In other words, this “toner supply amount” is regarded as the actual toner consumption amount from the completion of the previous replenishment operation to the start of the current replenishment operation.

  Thereafter, an excess / deficiency amount D of toner (= | necessary toner amount−toner supply amount |) is calculated from the results of steps A3 and A4 (step A5). However, here, D is calculated as an absolute value in the following configuration of the control flow.

  If the excess / deficiency amount D is larger than the predetermined value B1, an error is displayed because there is a possibility that some abnormality (image blurring, toner spillage from the developing housing, etc.) has occurred (step A7). If the excess / deficiency amount D is less than the predetermined value B1, it is subsequently determined whether or not it exceeds the predetermined value B2 (step A8). If B2 <D <B1, density adjustment is started (step A9). If the amount D is less than or equal to the predetermined value B2, “END” is obtained and density adjustment is not performed.

  In the density adjustment (step A9), the image forming condition is adjusted so as to bring the visible image density on the recording medium P close to the target density. The image forming condition changing means 60c adjusts the image forming condition (development bias). In the case of changing the charging bias, exposure energy, etc., it is possible to change the image forming condition once (density adjustment) with a change amount (fixed value) fixed for each parameter of the plurality of image forming conditions. Control can be simplified by changing the imaging conditions with fixed values.

  Further, the target density achievement rate in a predetermined period can be calculated from the excess / deficiency amount D, and the image forming condition can be changed based on the target density achievement rate. In this case, it can also be performed with a plurality of change amounts set stepwise corresponding to the magnitude of the excess / deficiency amount D for each parameter of the plurality of image forming conditions. By changing the image forming conditions with a plurality of change amounts set stepwise in this way, the target density can be quickly adjusted.

  FIG. 4B shows another control flow in place of FIG. 4A. In this control flow, only the one-point toner remaining amount X1 is detected by the toner sensor 46 as shown in FIG. Instead, the control flow uses a toner sensor capable of detecting an arbitrary toner remaining amount from the maximum toner remaining amount to the minimum toner remaining amount. When such a toner sensor is used, toner replenishment control can be started when an arbitrary amount of toner remains, and the toner replenishment amount can be supplied in an appropriate amount necessary for the toner replenishment control.

  In the control flow of FIG. 4B, when the predetermined density adjustment operation execution determination timing is reached, the density adjustment execution determination flow is started (step B1). If the determination timing has not been reached, “END” is set and density adjustment is not performed. This density adjustment operation execution determination timing includes, for example, any one parameter such as the result of detecting the remaining amount of toner in the developing device, the number of prints of the recording medium P, the total number of rotations of the photosensitive drum 2 or the developing roller 41, or some It can be determined by combining parameters. The density adjustment execution determination flow can be started each time the parameter reaches a predetermined value. By reducing the “predetermined value” that the parameter reaches, it is possible to perform more accurate density adjustment with fine detection timing.

  When the density adjustment execution determination flow is started, a necessary toner amount is first calculated (step B2). The calculation of the necessary toner amount is the amount of toner necessary for transferring the visible toner image formed on the photosensitive drum 2 onto the recording medium P at a target density during a predetermined period while the printer main body 100 is operating. Is calculated based on the print image information. This print image information includes the dot arrangement of the visible image, the dot density, or the print rate.

  Subsequently, the remaining amount of toner in the developing housing 40 is detected and the amount of toner replenished is calculated (step B3). This “toner replenishment amount” is the toner replenishment amount after the previous replenishment operation is completed and before the start of the current replenishment operation. Then, the toner supply amount (consumption amount) in the predetermined period is detected by the toner supply amount detection means 60b (step B4). Subsequent steps B5 and subsequent steps are the same as steps A5 and subsequent steps in FIG. 4A.

  FIG. 5A shows a simplified relationship among the target density, the necessary toner amount, and the integrated supply toner amount in the density adjustment of the control flow (FIG. 4A). When the target density and the print image information are constant, the required toner amount increases with the operation time (or the number of printed sheets) of the printer. On the other hand, the cumulative amount of toner supplied increases stepwise as the toner is intermittently replenished each time the toner sensor 46 detects a decrease in the toner draft surface. The density adjustment this time is started following the detection of the toner draft by the toner sensor 46 and the subsequent toner supply operation. In this density adjustment, as described in the control flow of FIG. 4A, the (integrated) supply toner amount from the completion of the previous replenishment operation to the start of the current replenishment operation is compared with the necessary toner amount, and the (integrated) supply toner amount Based on the excess / deficiency D, the image forming condition is changed (current density adjustment).

  FIG. 5B shows a simplified relationship between the target density, the necessary toner amount, and the integrated supply toner amount in the density adjustment of the control flow (FIG. 4B). When the target density and the print image information are constant, the required toner amount increases with the operation time (or the number of printed sheets) of the printer. On the other hand, with respect to the cumulative supply toner amount, for example, an appropriate amount of toner is supplied from the toner cartridge 50 to the development housing 40 in a timely manner in order to optimize the toner amount in the development housing 40 in accordance with the operating status of the printer. Increase in steps. This time, the density adjustment is started following the timely toner supply operation. In this density adjustment, as described in the control flow of FIG. 4B, the (integrated) supply toner amount from the completion of the previous replenishment operation to the start of the current replenishment operation is compared with the necessary toner amount, and the (integrated) supply toner amount Based on the excess / deficiency D, the image forming condition is changed (current density adjustment).

  FIG. 6 shows a control flow that can be replaced with step A6 and subsequent steps in FIG. 4A and step B6 and subsequent steps in FIG. 4B to simplify the control flow. In this simplified control flow, the excess / deficiency amount D is calculated in a form including positive and negative instead of an absolute value, and whether the excess / deficiency amount D is positive or negative is determined (step C1). When the excess / deficiency amount D is 0 or more, the toner supply amount (actual consumption amount) is smaller than the necessary toner amount (target consumption amount), so it is estimated that the current image density is lower than the target density. . Therefore, in order to increase the image density, the image forming conditions such as developing bias, exposure energy, and fixing temperature are controlled to the density increasing side (step C2).

  Conversely, when the excess / deficiency amount D is 0 or less, the toner supply amount (actual consumption amount) is larger than the necessary toner amount (target consumption amount), so it is estimated that the current image density is higher than the target density. Is done. Therefore, in order to increase the image density, the image forming conditions such as the developing bias, exposure energy, and fixing temperature are controlled to the density lowering side (step C3).

  In the density control in step C2 or C3, the image forming condition change amount such as the developing bias, the charging bias, and the exposure energy is the image forming condition with a change amount (fixed value) fixed for each parameter of the plurality of image forming conditions. Can be changed once (density adjustment). In this case, the control can be simplified by changing the imaging condition with a fixed value.

  Further, in the density control in step C2 or C3, for the image forming condition change amount such as the developing bias, the charging bias, and the exposure energy, the target density achievement rate in a predetermined period is calculated from the excess / deficiency D, and the target density is calculated. The image forming conditions can be changed based on the achievement rate. In this case, it can also be performed with a plurality of change amounts set stepwise corresponding to the magnitude of the excess / deficiency amount D for each parameter of the plurality of image forming conditions. By changing the image forming conditions with a plurality of change amounts set stepwise in this way, the target density can be quickly adjusted.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above-described embodiment, a one-component developer composed of toner is used as the developer, but a two-component developer composed of toner and carrier may be used. In this case, the toner concentration in the development housing 40 is kept constant. To maintain it, toner density control means can be provided. Further, although a printer is exemplified as the image forming apparatus, the present invention can be applied to a copying machine other than the printer, a facsimile, or a complex machine of these.

JP 2005-49701 A Japanese Patent Laid-Open No. 2001-296706

1Y, 1M, 1C, 1Bk: process unit 2: photosensitive drum 4: developing device 40: developing housing 41: developing roller 42: supply roller 46: toner sensor 50: toner cartridge 51: third developer conveying member 60: Image density control means 60a: Necessary developer amount calculation means 60b: Developer supply amount detection means 60c: Image forming condition change means

Claims (14)

A developer carrying member that visualizes and carries the developer based on the print image information, developer supply means for supplying the developer to the developer carrying member, and a developed image on the developer carrying member; In an image forming apparatus having transfer means for transferring onto a recording medium at a target density,
A calculation means for calculating an amount of developer necessary for transferring the visible image on the recording medium at the target density in a predetermined period while the image forming apparatus is operating, based on the print image information;
A supply amount detection means for detecting a developer supply amount corresponding to the predetermined period of the developer supply means;
Based on the required developer amount by the calculation means and the developer supply amount by the supply amount detection means, the image density on the recording medium is changed by changing the image forming condition including the visualization condition or the transfer condition. An image forming apparatus that is adjusted so as to approach the target density.   A target density achievement rate in the predetermined period is calculated from a required developer amount by the calculation unit and a developer supply amount by the supply amount detection unit, and the image forming condition is changed based on the target density achievement rate. The image forming apparatus according to claim 1.   Adjusting the image density on the recording medium by changing the image forming condition based on the target density achievement rate when the difference between the required developer amount and the developer supply amount is within a predetermined range; The image forming apparatus according to claim 2, wherein an error is displayed when the predetermined range is exceeded.   The relationship between the required developer amount and the developer supply amount is determined. Based on the determination result, when the required developer amount is less than the developer supply amount, the visible image density on the recording medium is reduced and the required development is performed. 2. The image forming apparatus according to claim 1, wherein when the amount of the agent> the amount of the developer supplied, the visible image density on the recording medium is increased.   The image forming apparatus according to claim 1, wherein the adjustment of the visible image density is performed with a fixed change amount for each of a plurality of parameters included in the image forming conditions.   The adjustment of the visible image density is performed with a plurality of change amounts set stepwise corresponding to the difference between the required developer amount and the developer supply amount for each of a plurality of parameters included in the image forming conditions. The image forming apparatus according to claim 1, which is configured as described above.   The image forming apparatus according to claim 1, wherein the print image information includes a dot arrangement, a dot density, or a print rate of a visible image on the recording medium.   2. The image forming apparatus according to claim 1, wherein detection of the developer supply amount by the supply amount detection unit is detected based on a drive time and a drive speed of the developer supply unit.   The adjustment of the visible image density on the recording medium is performed each time the number of visible images transferred on the recording medium, the driving time of the developer supply means, or the rotation amount of the developer carrier reaches a predetermined value. The image forming apparatus according to claim 1. In the density adjustment method of the image forming apparatus, the developer is visualized on the surface of the developer carrier based on the print image information, and the developed image on the developer carrier is transferred to the recording medium with a predetermined target density.
A required amount of developer for transferring the visible image onto the recording medium at the target density in a predetermined period while the image forming apparatus is in operation, and supplying the developer to the developer carrier corresponding to the predetermined period An image in which the developed image density on the recording medium is adjusted to be close to the target density by changing the imaging condition including the visualization condition or the transfer condition based on the supplied developer supply amount. Density adjustment method for forming apparatus.   The density adjustment method according to claim 10, wherein a target density achievement rate in the predetermined period is calculated from the required developer amount and the developer supply amount, and the image forming condition is changed based on the target density achievement rate. .   When the difference between the required developer amount and the developer supply amount is within a predetermined range, the visible image density on the recording medium is adjusted by changing the imaging condition based on the target density achievement rate The density adjustment method according to claim 10, wherein an error is displayed when the predetermined range is exceeded.   The relationship between the required developer amount and the developer supply amount is determined. Based on the determination result, when the required developer amount is less than the developer supply amount, the visible image density on the recording medium is reduced and the required development is performed. 11. The density adjustment method according to claim 10, wherein when the amount of the agent> the developer supply amount, the visible image density on the recording medium is increased.   The adjustment of the visible image density on the recording medium is performed each time the number of visible images transferred on the recording medium, the driving time of the developer supply means, or the rotation amount of the developer carrier reaches a predetermined value. The density adjustment method according to claim 10.

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