Patent Grant
7251420
This application claims priority to Japanese patent application nos. 2004-194857 filed on Jun. 30, 2004 and 2005-054815 filed on Feb. 28, 2005, the entire contents of each of which are hereby incorporated by reference herein.
1. Field of the Invention
This patent specification relates to an image forming method and apparatus capable of reducing downtime of an image forming apparatus while maintaining toner density stability.
2. Description of the Related Art
In a background image forming apparatus such as a copier and a printer, image forming conditions need to be controlled to maintain toner density of images formed by the background image forming apparatus at a desirable level. The image forming conditions are controlled to appropriately adjust a toner amount by, for example, forming test toner patterns on a non-image area of a toner-image carrying member and detecting an amount of toner adhered to the test toner patterns. Particularly in a full-color image forming apparatus, such detection needs to cover a wide range from relatively high-density parts to relatively low-density parts of an image to maintain density gradation and color reproductivity of the image at desirable levels.
To obtain a toner gradation sequence, a plurality of toner image patterns need to be formed for detection of a wide range from relatively high-density parts to relatively low-density parts of an image. Generally, a plurality of toner image patterns are formed by applying different development bias voltages, different exposure energies, and so forth to a surface of an image carrying member in a rotation direction thereof. Then, the plurality of toner image patterns sequentially reach a detecting position of a toner density sensor, and the toner density sensor sequentially detects toner density values of the respective toner image patterns. In this case, the detection takes a relatively long time and thus may not be performed frequently. Therefore, the detection is performed after printing a predetermined number of sheets or at predetermined time intervals, for example.
According to a two-component development system, toner is mainly consumed as an image forming operation continues to be performed. Therefore, toner is replenished in a development device and is charged by friction together with carrier by using a conveying screw or the like. Then, the toner is conveyed onto a surface of a magnet roller (i.e., a development roller), and toner images are developed thereon. In a small-size image forming apparatus using this system, however, an amount of carrier is limited. As a result, if toner is replenished in the development device in a relatively short time, concentration distribution of toner supplied onto the surface of the magnet roller may temporarily become uneven.
Therefore, in the background image forming apparatus, toner image patterns are formed after having equalized a concentration distribution of toner by rotating a conveying screw provided at an upstream side of a magnet roller to mix and convey the toner and carrier.
For example, if a development device is replenished with its maximum replenishment amount of toner, and if a predetermined time period is set as a time period required for equalizing the concentration distribution of toner, toner image patterns are formed always after the conveying screw has been rotated for the predetermined time period. An amount of toner replenished, however, corresponds to an amount of toner consumed, which relates to a pixel count of images formed on a printed page, for example. Therefore, the amount of toner replenished is not necessarily the maximum replenishment amount. As a result, if the amount of toner replenished in a toner replenishment is smaller than the maximum replenishment amount, the time required for equalizing the concentration distribution of toner which was made uneven by the toner replenishment may be shorter than the above predetermined time period. As in this case, if the time period required for equalizing the concentration distribution of toner is set at a predetermined value, unnecessary downtime of the image forming apparatus results.
To attempt to resolve this problem, there is a technique using a video counter for counting and summing up image data values of images developed by a plurality of development devices, and a developer density detection device for summing up the image data values and detecting information of toner consumption in the developer. In this technique, toner is replenished in accordance with a toner replenishment signal which is based on a signal output from the developer density detection device, and a speed of driving the mixing member can be varied according to a value of the video counter. This technique, however, is to simply optimize the speed of driving the mixing member and is not based on an idea to reduce the downtime of the image forming apparatus while maintaining toner density detection stability.
This patent specification describes an image forming apparatus. In one example, an image forming apparatus includes an image forming mechanism and a control device. The image forming mechanism is configured to perform an image forming operation under predetermined image forming conditions. The image forming mechanism includes an image carrying member, a development device, and a transfer device. The image carrying member is configured to form an electrostatic latent image thereon. The development device is configured to develop the electrostatic latent image into a toner image. The transfer device is configured to transfer the toner image to a recording medium. The control device is configured to control an amount of toner replenished to the development device, to set a developer mixing time for evenly mixing developer in the development device, to cause the development device to mix the developer for the set developer mixing time, to cause the image forming mechanism to form toner image patterns, to detect the toner image patterns, and to determine the predetermined image forming conditions based on the detection of the toner image patterns.
This patent specification further describes another image forming apparatus. In one example, this image forming apparatus includes an image forming mechanism and a control device. The image forming mechanism includes an image carrying member, a charging device, an exposure device, a development device, a transfer device, and a toner replenishing device. The charging device is configured to charge the image carrying member. The exposure device is configured to expose the image carrying member to form an electrostatic latent image thereon. The development device is configured to develop the electrostatic latent image into a toner image. The development device includes a mixing and conveying device configured to mix and convey developer including carrier and toner, and a development roller configured to carry and supply the mixed and conveyed developer to the image carrying member. The transfer device is configured to transfer the toner image to a recording medium. The toner replenishing device is configured to replenish toner in the development device. The control device is configured to control an amount of toner replenished to the development device, to set a developer mixing time for evenly mixing the developer in the development device, to cause the development device to mix the developer for the set developer mixing time, to cause the image forming mechanism to form toner image patterns, to detect the toner image patterns, and to determine predetermined image forming conditions based on the detection of the toner image patterns.
In the image forming apparatus, the control device may set the developer mixing time based on a state of the development device.
In the image forming apparatus, the control device may calculate, prior to a process control starting point at which a process of determining the image forming conditions starts, a time required for mixing the developer and resolving insufficient toner dispersion caused by a change in a toner amount in the development device, and set the time obtained from the calculation at the process control starting point as the developer mixing time which starts after the process control starting point and finishes before formation of the toner image patterns.
In the image forming apparatus, the control device may calculate, in every printing operation during a time required for mixing the developer and resolving insufficient toner dispersion caused by a maximum change in the toner amount in the development device until the process control starting point, a time required for sufficiently dispersing toner in the developer according to a change in the toner amount, and set the time obtained from the calculation at the process control starting point as the developer mixing time which starts after the process control starting point and finishes before formation of the toner image patterns.
In the image forming apparatus, the control device may calculate the developer mixing time based on a toner replenishment amount in the development device.
In the image forming apparatus, the control device may calculate the developer mixing time based on an image area.
In the image forming apparatus, the control device may calculate the developer mixing time based on a developer use history.
This patent specification further describes an image forming method. In one example, an image forming method includes appropriately controlling an amount of toner replenished, setting a developer mixing time for evenly mixing developer, mixing the developer for the developer mixing time, forming toner image patterns, detecting the toner image patterns, and determining predetermined image forming conditions based on the detection of the toner image patterns.
This patent specification further describes another image forming method. In one example, this image forming method includes: providing an image forming mechanism configured to perform an image forming operation under predetermined image forming conditions, and a control device; providing the image forming mechanism with an image carrying member, a charging device, an exposure device, a development device, a transfer device, and a toner replenishing device; and causing the control device to control an amount of toner replenished to the development device, set a developer mixing time for evenly mixing the developer in the development device, cause the development device to mix the developer for the set developer mixing time, cause the image forming mechanism to form toner image patterns, detect the toner image patterns, and determine predetermined image forming conditions based on the detection of the toner image patterns.
The image forming method may further include causing the control device to set the developer mixing time based on a state of the development device.
The image forming method may further include: calculating, prior to a process control starting point at which a process of determining the image forming conditions starts, a time required for mixing the developer and resolving insufficient toner dispersion caused by a change setting the time obtained from the calculation at the process control starting point as the developer mixing time which starts after the process control starting point and finishes before formation of the toner image patterns.
The image forming method may further include: calculating, in every printing operation during a time required for mixing the developer and resolving insufficient toner dispersion caused by a maximum change in the toner amount in the development device until the process control starting point, a time required for sufficiently dispersing toner in the developer according to a change in the toner amount; and setting the time obtained from the calculation at the process control starting point as the developer mixing time which starts after the process control starting point and finishes before formation of the toner image patterns.
The image forming method may further include calculating the developer mixing time based on a toner replenishment amount in the development device.
The image forming method may further include calculating the developer mixing time based on an image area.
The image forming method may further include calculating the developer mixing time based on a developer use history.
A more complete appreciation of the invention and many of the advantages thereof are obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing the embodiments illustrated in the drawings, specific terminology is employed for the purpose of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so used, and it is to be understood that substitutions for each specific element can include any technical equivalents that operate in a similar manner.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, particularly to
The image forming apparatus 100 illustrated in
In the image forming apparatus 100, the transfer belt 1 is provided in the transfer belt device 10, and the photoconductor drums 20K, 20Y, 20C, and 20M which serve as image carrying members are included in respective four image forming stations.
As illustrated in
With reference to
A sheet of the recording medium 2 stored in one of the sheet-feeding cassette 3, the sheet-feeding cassette 4, or the hand-feed tray 15 is sent out by the corresponding sheet-feeding roller 5. When a leading end of the recording medium 2 reaches the registration roller pair 6, a sensor (not illustrated) detects arrival of the recording medium 2. The registration roller pair 6 conveys the recording medium 2 to a nip formed by the transfer belt 1 and each of the transfer rollers 7K, 7Y, 7C, and 7M at an appropriate timing according to a detection signal output from the sensor. The transfer rollers 7K, 7Y, 7C, and 7M, which are examples of transfer devices, transfer developed toner images to the recording medium 2.
The photoconductor drums 20K, 20Y, 20C, and 20M are uniformly charged by the corresponding charging devices 30K, 30Y, 30C, and 30M and then exposed and scanned by respective scanning light beams L applied by the optical writing device 8 which exposes the photoconductor drums 20K, 20Y, 20C, and 20M. As a result, electrostatic latent images are formed on the photoconductor drums 20K, 20Y, 20C, and 20M, respectively.
The electrostatic latent images thus formed on the photoconductor drums 20K, 20Y, 20C, and 20M are then developed by corresponding development rollers 54K, 54Y, 54C, and 54M which are included in the development devices 50K, 50Y, 50C, and 50M, respectively. As a result, toner images of respective colors, i.e., black, yellow, cyan, and magenta, are formed on surfaces of the photoconductor drums 20K, 20Y, 20C, and 20M, respectively.
The transfer rollers 7K, 7Y, 7C, and 7M are applied with voltages, and the toner images formed on the surfaces of the photoconductor drums 20K, 20Y, 20C, and 20M are sequentially transferred onto the recording medium 2 which is conveyed by the transfer belt 1. The respective toner images are formed on the surfaces of the photoconductor drums 20K, 20Y, 20C, and 20M at different times such that the toner images are aligned at the same position on the recording medium 2 conveyed on the transfer belt 1.
When the recording medium 2 passes the photoconductor drum 20K, which is the last photoconductor drum in the transfer process, the toner images of the respective colors have been printed on the recording medium 2. The recording medium 2 on which the toner images of the respective colors are transferred is then separated from the transfer belt 1 due to a curvature of the support roller 56 supporting the transfer belt 1. The recording medium 2 is conveyed into the fixing device 90, and the toner images are fixed by heat to the recording medium 2. Thereafter, the recording medium 2 is conveyed by the ejection roller pair 12 into the ejection tray 13 to be stored therein. Alternatively, the recording medium 2 may be differently directed by a direction-switching claw 22 and sent to a finisher (not illustrated) to be subjected to a post-process such as stapling and punching. Still alternatively, the recording medium 2 may be differently directed by a direction-switching claw 23 and sent to another sheet-receiving tray such as a 4-bin print post (not illustrated).
After the toner images are transferred from the photoconductor drums 20K, 20Y, 20C, and 20M to the recording medium 2, toner remaining on the photoconductor drums 20K, 20Y, 20C, and 20M is cleaned by the cleaning devices 40K, 40Y, 40C, and 40M in preparation for a next image forming operation. Toner remaining on the transfer belt 1 is cleaned by the transfer belt cleaning device 14 in preparation for the next image forming operation.
The image forming apparatus 100 is capable of two-side printing. In the two-side printing, after toner images are fixed on one side of the recording medium 2, the direction-switching claw 22 guides the recording medium 2 into the reversing unit 16 to reverse the recording medium 2. The recording medium 2 thus reversed is conveyed into the reversal conveyance unit 17 and sent back to the registration roller pair 6. Thereafter, toner images are formed on the other side of the recording medium 2 according to the image forming procedure described above. Accordingly, toner images are formed on both sides of the recording medium 2.
The optical writing device 8 is described with reference to
The transfer belt 1 is described with reference to
The development devices 50K, 50Y, 50C, and 50M are described with reference to
The development device 50M includes a casing 51M, a left conveying screw 52M, a right conveying screw 53M, the development roller 54M, a T sensor (toner density sensor) 58M, and a partition 530.
A dry two-component magnetic brush development system is used in the development device 50M to respond to a relatively high photocopying speed. In the casing 51M, the left conveying screw 52M and the right conveying screw 53M extend in a direction of piercing
As illustrated in
As described above, each of the development devices 50K, 50Y, 50C and 50M is provided with a mixing and conveying part which mixes the developer including carrier and toner and conveys the developer to a development position, and a corresponding one of the development rollers 54K, 54Y, 54C, and 54M which carries and supplies the developer to a corresponding one of the image carrying members (i.e., the photoconductor drums 20K, 20Y, 20C, and 20M). In the development devices 50K, 50Y, 50C and 50M according to the present embodiment, mixing and conveyance of the developer are simultaneously performed. Therefore, such expressions as “mixing and conveyance” and “mixing and conveyance time” may be also understood as “mixing” and “mixing time” throughout the present specification.
A mechanism of toner replenishment to the development devices 50K, 50Y, 50C and 50M is described with reference to
The toner replenishing device 800 illustrated in
The toner replenishing device 800 supplies toner from the toner cartridges 60K, 60Y, 60C, and 60M to the corresponding development devices 50K, 50Y, 50C, and 50M. The toner cartridges 60K, 60Y, 60C, and 60M contain black toner, yellow toner, cyan toner, and magenta toner, respectively, and are detachably provided in the image forming apparatus 100. The following description is made on a system of replenishing the magenta toner to the development device 50M, as an example. The following description therefore applies also to systems of supplying the black toner, the yellow toner, and the cyan toner to the corresponding development devices 50K, 50Y, and 50C.
The magenta toner is conveyed from the toner cartridge 60M to the development device 50M by using the air pump 600 which is also shared by the other toner cartridges 60K, 60Y, and 60C, and by using the toner powder conveying pump 9M. The black toner, the yellow toner, and the cyan toner are conveyed by the air pump 600 and by the respective toner powder conveying pumps (mohno pumps) 9K, 9Y, and 9C.
The toner cartridge 60M has a toner supply port (not illustrated) provided with a sponge valve (not illustrated) which prevents toner from dropping from the toner replenishing port in replacing the toner cartridge 60M with a new toner cartridge. When the toner cartridge 60M is attached to the image forming apparatus 100, a valve of a toner replenishing port of the image forming apparatus 100 opens, and toner drips from the toner cartridge 60M and is sent by the toner powder conveying pump 9M to the development device 50M. The toner is replenished at a position on one side of the casing 51M in the development device 50M. The position is indicated by an arrow 601 in
In this toner replenishing process, the toner contained in the toner cartridge 60M is stirred by force of air sent from the air pump 600. The air supplied by the air pump 600 is controlled by closing and opening air supply valves 605K, 605Y, 605C, and 605M provided for the respective toner colors. Air is supplied into the respective toner cartridges 60K, 60Y, 60C, and 60M according to toner density control of toner contained in each of the toner cartridges 60K, 60Y, 60C, and 60M.
The toner is suctioned from the toner cartridge 60M by the toner powder conveying pump 9M through the toner conveying pipe 607M, so that the toner flows in an order of arrows 602, 603, 604, and 601 shown in
As described above, the toner replenishing device 800 includes the mechanical members and the toner replenishment amount controlling device which controls the toner replenishment amount. The control device 700 illustrated in
The control device 700 illustrated in
A process in which the image forming condition setting device sets the image forming conditions is described below.
Processes from setting of the developer mixing time to controlling of the toner density are first described. A process control of setting the image forming conditions is performed in such circumstances as at a start-up of the image forming apparatus 100, at an end of a job, at a start of an interrupt printing operation (i.e., at a start of an exposure process), and in a stand-by state of the image forming apparatus 100. In this process control, a CPU (central processing unit) provided in the image forming apparatus 100 controls the image forming operation of forming the toner image patterns on the image carrying members (i.e., the photoconductor drums 20K, 20Y, 20C, and 20M), and sets the image forming conditions such as a development bias voltage and a transfer bias voltage based on a result of detection of the toner image patterns.
Prior to the process control, if the amount of toner contained in each of the development devices 50K, 50Y, 50C, and 50M has changed due to consumption or replenishment of toner, and if the time required for sufficiently mixing the developer has not yet elapsed, the concentration distribution of the toner in the development device is uneven. This unevenness of the toner concentration distribution may be resolved over time by driving the development devices 50K, 50Y, 50C, and 50M to mix and convey the developer. If toner image patterns are formed in a state in which the developers are insufficiently mixed, unevenness of the toner density is observed both temporally and spatially. For example, unevenness of the toner density may be observed between a toner image pattern formed at a given time point and a toner image pattern formed later than the time point. Further, unevenness of the toner density may be observed within a single toner image pattern. Therefore, toner density of toner transferred onto the development rollers 54K, 54Y, 54C, and 54M also becomes uneven. For example, substantially dark toner image patterns or substantially light toner image patterns may be obtained, compared with a case in which the unevenness of the toner density has been resolved over time. If the image forming conditions are set based on the thus formed toner image patterns, the image forming conditions are inappropriately set.
At the start of the process control, therefore, the developer contained in the development devices 50K, 50Y, 50C, and 50M may be sufficiently mixed and conveyed before forming the toner image patterns. If a relatively sufficient and fixed time period is used as the developer mixing time, however, the developer mixing time is wasted and the downtime of the image forming apparatus 100 is increased in such circumstances as when an the replenishment toner amount is relatively small and when a sufficient time has passed since the toner replenishment until the start of the process control and thus mixing of the developer can be completed in a relatively short time.
Accordingly, in an embodiment described below, the developer mixing time actually required is set in consideration of such factors as variation of the toner amount in each of the development devices 50K, 50Y, 50C, and 50M and time elapsed since a change in the toner amount until the start of the process control, so that the toner image patterns are formed after the toner has been mixed and conveyed for the developer mixing time thus set. In the present embodiment, a desirable developer mixing time is determined based on an area of an image to be formed (hereinafter referred to as image area) and a required toner replenishment amount. The toner image patterns are formed after having mixed the developer for the developer mixing time thus determined, and the image forming conditions are set based on detection of the toner image patterns.
An execution procedure of calculating the image area and the toner replenishment amount is described with reference to a flowchart of
At Step S101 of the flowchart in
At Step S102, a group of motors is driven. When the printing operation starts, the polygon motor 606 is turned on. Then, after the polygon motor 606 has entered into a steady state, the photoconductor drive motors driving the photoconductor drums 20K, 20Y, 20C, and 20M, the development motors driving the development rollers 54K, 54Y, 54C, and 54M, and the transfer belt drive motor driving the transfer belt 1 are turned on. Further, the charging devices 30K, 30Y, 30C, and 30M are applied with a charging bias voltage by a charging bias voltage applying device (not illustrated). Spaces formed between the development rollers 54K, 54Y, 54C, and 54M and their opposed photoconductor drums 20K, 20Y, 20C, and 20M are applied with a development bias voltage by a development bias voltage applying device (not illustrated). The transfer rollers 7K, 7Y, 7C, and 7M are applied with a transfer bias voltage by a transfer bias voltage applying device (not illustrated).
At Step S103, a sub-scanning gate signal FGATE is detected as being ON. When the respective photoconductor drums 20K, 20Y, 20C, and 20M are rotated, charged by the charging devices 30K, 30Y, 30C, and 30M, and prepared for exposure, the sub-scanning gate signal FGATE serving as a reference signal (i.e., a synchronization signal) for starting the printing operation turns ON and rises.
At Step S104, an output voltage output from the T sensor is read in each of the development devices 50K, 50Y, 50C, and 50M. In
At Step S105, the sub-scanning gate signal FGATE is detected as being OFF. When an exposure operation to an image area of a first page is completed, the sub-scanning gate signal FGATE falls and turns OFF, as illustrated in
At Step S106, a pixel count of the image area is read, and it is determined if the pixel count is completed. The LD control part drives and controls the laser diodes provided in the optical writing device 8 and exposes an image, and the number of pixels included in the exposed image area is counted.
At Step S107, pixel density of the exposed image is determined. Resolution of the exposed image is determined to find whether the pixel count of the exposed image is 600*600 dpi (dots per inch) or 1200*1200 dpi.
At Step S108, an image area of the exposed image is calculated from an equation of IA=PC/PD, wherein IA is an image area, PC is a pixel count, and PD is pixel density. If the pixel count of the exposed image is 600*600 dpi, for example, the image area of the exposed image is 6002/2.542.
At Step S109, the toner replenishment amount is calculated for each of the four kinds of toner by using one of the following four equations of TRA=IA*PTA*α(Vt−Vref)+β(Vt−Vref), TRA=IA*PTA*α, TRA=IA*PTA+β(Vt−Vref), and TRA=β, wherein TRA is a toner replenishment amount, IA is an image area (cm2), PTA is a per-unit-area toner amount (mg/cm2), Vt is an output voltage actually output from the T sensor, Vref is a target output voltage expected to be output from the T sensor, α is a correction coefficient for such errors as an error in a drive time of each of toner replenishing clutches (i.e., a drive time of each of toner powder conveying pump 9K, 9Y, 9C, or 9M) and an error in rotation of each of the left conveying screw 52M and the right conveying screw 53M, β is a correction value for other factors than the image area, such as an amount of toner adhered to non-image areas on the surface of the transfer belt 1, for example. Values of Vref, α, and β, for example, are stored in advance in the CPU as data.
At Step S110, data of the image areas, the output voltages output from the T sensors, the toner replenishment amounts, and so forth are stored in a nonvolatile memory of the CPU.
At Step S111, it is determined whether the printing operation has completed. If it is determined that the printing operation has completed, operation of the group of motors is stopped. If it is determined that the printing operation has not yet completed, on the other hand, toner is replenished in a printing operation to a next page (i.e., the second page) according to a procedure described below, and the Steps S103 through S110 are repeated. In the present embodiment, as illustrated in
At Step S112, operation of the group of motors is stopped. When the Step S111 has finished, the charging bias voltage applying devices, the development bias voltage applying devices, and the transfer bias voltage applying devices are turned off. Further, the polygon motor 606, the photoconductor drive motors, the development motors, and the transfer belt drive motor are turned off.
An execution procedure of replenishing toner is described with reference to a flowchart of
At Step S201, it is determined if a printing operation starts. When the start button of the image forming apparatus 100 is pressed, or when print data sent from the computer connected to the image forming apparatus 100 is received, the printing operation starts.
At Step S202, the group of motors are driven. When the printing operation starts, the polygon motor 606 is turned on. After the polygon motor 606 has entered into the steady state, the photoconductor drive motors driving the photoconductor drums 20K, 20Y, 20C, and 20M, the development motors driving the development rollers 54K, 54Y, 54C, and 54M, and the transfer belt drive motor driving the transfer belt 1 are turned on. Further, the charging bias voltage applying devices apply charging bias voltages to the respective charging devices 30K, 30Y, 30C, and 30M. The development bias voltage applying devices apply development bias voltages to the spaces formed between the respective development rollers 54K, 54Y, 54C, and 54M and their opposed photoconductor drums 20K, 20Y, 20C, and 20M. The transfer bias voltage applying devices apply transfer bias voltages to the respective transfer rollers 7K, 7Y, 7C, and 7M.
At Step S203, the sub-scanning gate signal FGATE is detected as being ON. When the respective photoconductor drums 20K, 20Y, 20C, and 20M are rotated, charged by the charging devices 30K, 30Y, 30C, and 30M, and prepared for exposure, the sub-scanning gate signal FGATE serving as the reference signal (i.e., the synchronization signal) for starting the printing operation turns ON and rises.
At Step S204, data of the toner replenishment amount stored in the nonvolatile memory at Step S110 shown in the flowchart of
At Step S205, a time period in which the toner replenishing clutch should be kept in an ON state (hereafter referred to as ON-time of the toner replenishing clutch) is calculated for each of the toner replenishing clutches. That is, an ON-time is calculated for each of the toner powder conveying pumps 9K, 9Y, 9C, and 9M. The ON-time of each of the toner replenishing clutches can be obtained from an equation of ON=TRA/RC, wherein ON is the ON-time (sec) of toner replenishing clutch, TRA is a toner replenishment amount (mg), and RC is per-unit-time toner replenishing capacity (mg/sec) of the toner replenishing clutch.
At Step S206, the toner replenishing clutches are turned on. The toner replenishing clutches are turned on based on respective ON-times of the toner replenishing clutches obtained at Step S205, and the toner powder pumps 9K, 9Y, 9C, and 9M are driven.
At Step S207, the toner replenishing clutches are kept in the ON state (i.e., the toner powder conveying pumps 9K, 9Y, 9C, and 9M are driven) for the respective ON-times obtained at Step S205, i.e., until the ON-time elapses. The toner is replenished in the respective development devices 50K, 50Y, 50C, and 50M by the corresponding toner powder conveying pumps 9K, 9Y, 9C, and 9M. As illustrated in
At Step S209, it is determined whether the printing operation has completed. If it is determined that the printing operation has completed, operation of the group of motors is stopped in Step S210. If it is determined that the printing operation has not yet completed, the Steps S103 through S110 are repeated in a next printing operation.
At Step S210, the operation of the group of motors is stopped. When Step S209 has finished, the charging bias voltage applying devices, the development bias voltage applying devices, and the transfer bias voltage applying devices are turned off. Further, the polygon motor 606, the photoconductor drive motors, the development motors, and the transfer belt drive motor are turned off.
An execution procedure of controlling the toner density is described with reference to a flowchart of
At Step S301, the group of motors are driven. An operation of controlling the toner density is executed under such circumstances as at power-on of the image forming apparatus 100 and after printing a predetermined number of recording medium 2. When the operation of controlling the toner density starts, the polygon motor 606 is turned on. After the polygon motor 606 has entered into the steady state, the photoconductor drive motors, the development motors, and the transfer belt drive motor are turned on. Further, the charging bias voltage applying devices apply charging bias voltages to the respective charging devices 30K, 30Y, 30C, and 30M. The development bias voltage applying devices apply development bias voltages to the spaces formed between the respective development rollers 54K, 54Y, 54C, and 54M and their opposed photoconductor drums 20K, 20Y, 20C, and 20M. The transfer bias voltage applying devices apply transfer bias voltages to the respective transfer rollers 7K, 7Y, 7C, and 7M.
At Step S302, data of the toner replenishment amount, which is stored in the non-volatile memory according to the procedure of Step S110 shown in
At Step S303, data of the image area, which is stored in the non-volatile memory according to the procedure of Step S110 shown in
At Step S304, the developer mixing time is calculated. The toner replenishment amount or a toner density stability time constant for the image area is calculated in advance based on results of experiments. The developer mixing time required for evenly mixing the developer is calculated from an approximation formula, for example, by using the toner replenishment amount read at Step S302 and the image area read at Step S303.
An example of the calculation of the developer mixing timer is described with reference to a graph of
It was also discovered from the experiments that the time constant increases as the developer deteriorates. There is a tendency that, as the developer is used for a longer time period, a longer time is taken for stabilizing the toner density. This tendency is observed in a graph of
The developer mixing time is appropriately obtained based on results of the experiments. The time taken since the toner replenishment until stabilization of the toner density is proportional to the developer mixing time. The developer mixing time is, therefore, obtained by multiplying the toner replenishment amount by a stabilization coefficient. For example, if the stabilization coefficient is set to be 0.2, and if the toner replenishment amount is 100 milligrams, the developer mixing time is twenty seconds.
As described above, the time constant increases as a developer use history (i.e., the number of pages printed with a developer) increases. Therefore, the developer mixing time may be alternatively obtained by taking the developer use history into consideration, i.e., by using an equation of MT=TRA*VT*ST, wherein MT is the developer mixing time, TRA is a toner replenishment amount, VT is a value obtained from a developer use history look-up table, and ST is a stabilization coefficient. The developer use history look-up table provides values predetermined for respective numbers of printed pages, which may be determined in advance based on the results of experiments. For example, the developer use history look-up table may be set to provide a value 1.0 for the printed page number of 0 and a value 1.1 for the printed page number of 10000.
As illustrated in the graphs of
Alternatively, the image area may be used as a parameter. For example, in the vicinity of the development roller 54M, the toner density of the developer changes, i.e., toner moves from the development roller 54M to the photoconductor drum 20M in the development process and thus the toner density of the developer around the development roller 54M temporarily decreases. As a result, if the image area is used as a parameter, relationships between the changes in the toner density and the times required for stabilizing the toner density with respect to toner consumption amounts are represented by waveforms shown in
Either one of the developer mixing time obtained through the calculation using the toner replenishment amount and the developer mixing time obtained through the calculation using the image area can be used as the developer mixing time actually used. Alternatively, either one of the above two developer mixing times may be obtained by calculation and used as the developer mixing time actually used. Still alternatively, both of the above two developer mixing times may be obtained by calculation so that either a longer time or a shorter time of the two developer mixing times is used as the developer mixing time actually used. Generally, a longer developer mixing time is more preferable to a shorter developer mixing time.
Furthermore, the developer mixing time may be set in consideration of the developer use history as well as either one or both of the toner replenishment amount and the image area.
With the developer use history taken into consideration, relationships between the changes in the toner density and the times required for stabilizing the toner density with respect to developer use histories are represented by waveforms shown in
At Step S305, the development motors are turned on. Referring to
At Step S306, it is determined whether the developer mixing time calculated at Step S304 (i.e., time in which the development motor operates) has elapsed. If it is determined that the developer mixing time has elapsed, the procedure advances to Step S307.
At Step S307, an operation of forming the toner image patterns starts for detecting the toner density. As illustrated in
At Step S308, whether the toner image patterns have reached the P sensor 57 is determined. As illustrated in
At Step S309, the output voltage output from the P sensor is read. When the toner image pattern group TP reaches the position at which the toner image patterns included in the toner image pattern group TP are detected by the P sensor 57, the toner image patterns are detected for their toner density values. Surface roughness (i.e., regular reflectance) is different between non-image areas on the transfer belt 1 and the toner image patterns formed on the transfer belt 1, and the surface roughness of the toner image patterns correlates with and changes with the toner density of the toner image patterns. Therefore, the toner density is obtained for each of the toner image patterns as an analogous value by using the above-described characteristics of the surface roughness.
At Step S310, the image forming conditions are determined. After the toner density values of the toner image patterns are obtained as analogous values, the image forming conditions are determined to appropriately adjust the actual toner density, i.e., to match the obtained analogous values with a target value. For example, when the toner image patterns are formed, toner image patterns of different densities are formed by applying different development bias voltages. Accordingly, a formula representing a relationship between the development bias voltage and the toner density is obtained.
A development bias voltage value with which the target toner density value can be obtained is calculated from the above formula, and the obtained development bias voltage is used as an image forming condition. Further, toner image patterns of different densities are formed by changing such factors as an exposure condition to appropriately maintain toner density of a halftone area and a highlighted area. Accordingly, the exposure condition is determined such that the halftone area and the highlighted area have respective target toner density values. Alternatively, a toner density target level may be controlled to appropriately maintain a development γ (gamma), which is a gradient representing a relationship between the toner density and the development bias voltage. After the image forming conditions have been determined, the image forming conditions are set.
At Step S311, operation of the group of motors is stopped. After the image forming conditions have been set, the charging bias voltage applying devices, the development bias voltage applying devices, and the transfer bias voltage applying devices are turned off. Further, the polygon motor 606, the photoconductor drive motors, the development motors, and the transfer belt drive motor are turned off.
In the above-described process of forming the toner image patterns for determining the image forming conditions, before the process of determining the image forming conditions starts (i.e., before a starting point of the process control), the image forming condition setting device calculates the developer mixing time required for resolving insufficient toner dispersion of the developer caused by a change in the toner amount in a development device (i.e., time required for evenly mixing the developer in the development device and stabilizing the toner density of the developer). The image forming condition setting device calculates this developer mixing time by taking into consideration a state of the development device, which is indicated by toner amount changing factors such as the toner replenishment amount and the image area, and the developer mixing and conveying time in which the development device is driven to operate, for example. Then, a developer mixing operation is executed for the calculated developer mixing time after the start of the process control until the start of an operation of forming the toner image patterns. Upon completion of the developer mixing operation, the toner image patterns are formed.
As described above, the developer mixing time is individually set depending on a degree of the insufficient toner dispersion, and then the developer is mixed for the developer mixing time thus set. Therefore, the downtime of the image forming apparatus 100 can be reduced, compared with in a case in which the developer mixing time is set at a fixed and relatively large value for safety. Further, according to the present embodiment, the toner image patterns are formed after the developer has been mixed for the thus set developer mixing time, and the image forming conditions are determined based on a result of detection of the thus formed toner image patterns. Thereafter, the image forming operation is performed. Accordingly, image quality of images formed according to the above procedure can be improved due to the image forming conditions appropriately set. Since the developer mixing time is thus appropriately set, the downtime of the image forming apparatus 100 can be reduced to an appropriate value, i.e., the minimum value, which is shorter than in a case in which the above-described control is not performed. Further, according to the present embodiment, a total operating time of the image forming apparatus 100 is also reduced. Therefore, lifetimes of the image forming apparatus 100 and the developer can be extended.
The image forming condition setting device individually sets the developer mixing time based on such factors as the toner replenishment amount and the image area at every start of the process control before starting the operation of forming the toner image patterns used for setting the image forming conditions. Further, the image forming condition setting device sets the developer mixing time in consideration of the use history of the developer or the development device. Then, the developer is mixed for the thus set developer mixing time, and the toner image patterns are formed. Accordingly, the developer mixing time can be appropriately set. Further, toner density detection stability can be improved and the downtime of the image forming apparatus 100 can be reduced in the present embodiment, compared with a case in which the developer mixing time is set not based on the use history of the developer or the development device. Furthermore, since a total operating time of the image forming apparatus 100 is reduced, the lifetimes of the image forming apparatus 100 and the developer can be extended.
In the above embodiment, the developer mixing time for a development device is set based on the state of the development device at the time of printing a page immediately before the process control starting point.
In another embodiment described below, the developer mixing time for a development device is set according to states of the development device during a developer mixing time required for resolving insufficient toner dispersion caused by a maximum change in the toner amount in the development device until the process control starting point. As illustrated in a time chart of
Therefore, when the maximum change in the toner amount, which causes the worst possible insufficient toner dispersion occurring in the development device, happens, changes in the toner density of the developer caused by the maximum change in the toner amount settle and the insufficient toner dispersion resolves in twenty seconds after the maximum change in the toner amount. Accordingly, when the process control is performed, changes in the toner amount should be monitored for the twenty seconds preceding the process control starting point, and then the developer mixing time should be set at a necessary value based on the monitoring.
In
In the following five example cases illustrated in
In a first case, the maximum toner replenishment amount VSmax (300 milligrams) of toner is replenished in synchronization with a rise of the sub-scanning gate signal FGATE in response to exposure of the previous fourth page, and thereafter a toner replenishment amount VS (50 milligrams) of toner is replenished at every rise of the sub-scanning gate signal FGATE in response to exposure of each of the subsequent pages, i.e., the previous third page, the previous second page, and the previous first page. In this case, a toner replenishment time t2 is three seconds when the maximum toner replenishment amount VSmax (300 milligrams) of toner is replenished, and a developer mixing time t3 required for settling the changes in the toner density caused by the toner replenishment is twenty seconds. Further, the toner replenishment time t2 is 0.5 seconds when the toner replenishment amount VS (50 milligrams) of toner is replenished, and the developer mixing time t3 required for settling the changes in the toner density caused by the toner replenishment is four seconds.
At the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous fourth page, the maximum toner replenishment amount VSmax (300 milligrams) of toner is replenished, and thus twenty seconds are required as the developer mixing time t3.
After the per-page exposure time t1 (five seconds) has elapsed since the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous fourth page, the sub-scanning gate signal FGATE rises in response to exposure of the previous third page. At this rise of the sub-scanning gate signal FGATE in response to the exposure of the previous third page, a remaining developer mixing time required in response to the toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner is fifteen seconds (i.e., 20−5=15). That is, fifteen seconds are required for the developer mixing time at this stage. Further, four seconds are required as the developer mixing time t3 in response to the toner replenishment of the toner replenishment amount VS (50 milligrams) of toner. This developer mixing time t3 (four seconds) is, however, shorter than the remaining developer mixing time (fifteen seconds) in response to the toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner. Therefore, this developer mixing time t3 (four seconds) can be left out of consideration. Accordingly, the developer mixing time required at the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous third page is fifteen seconds.
After the per-page exposure time t1 (five seconds) has elapsed since the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous third page, the sub-scanning gate signal FGATE rises in response to exposure of the previous second page. At this rise of the sub-scanning gate signal FGATE in response to the exposure of the previous second page, a remaining developer mixing time required in response to the toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner is ten seconds (i.e., 15−5=10). That is, ten seconds are required for the developer mixing time at this stage. Further, four seconds are required as the developer mixing time t3 in response to the toner replenishment of the toner replenishment amount VS (fifty milligrams) of toner. This developer mixing time t3 (four seconds) is shorter than the remaining developer mixing time (ten seconds) in response to the toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner. Therefore, this developer mixing time t3 (four seconds) can be left out of consideration. Accordingly, the developer should be mixed for ten more seconds.
After the per-page exposure time t1 (five seconds) has elapsed since the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous second page, the sub-scanning gate signal FGATE rises in response to exposure of the previous first page. At this rise of the sub-scanning gate signal FGATE in response to the exposure of the previous first page, a remaining developer mixing time required in response to the toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner is five seconds (i.e., 10−5=5). That is, five seconds are required for the developer mixing time at this stage. Further, four seconds are required as the developer mixing time t3 in response to the toner replenishment of the toner replenishment amount VS (50 milligrams) of toner. Since this developer mixing time t3 (four seconds) is shorter than the remaining developer mixing time (five seconds) in response to the toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner, this developer mixing time t3 (four seconds) can be left out of consideration. Accordingly, the developer should be mixed for five more seconds.
The process control starting point TP is set to be a time point at which t1 (five seconds) has elapsed since the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous first page. Therefore, the changes in the toner density caused by the changes in the toner amount have settled and the insufficient toner dispersion has been resolved before the process control starting point. Therefore, a developer mixing time tx required after the start of the process control starting point and before the start of formation of the toner image patterns is zero seconds. Accordingly, formation of the toner image patterns starts as the process control starts.
In a second case, the maximum toner replenishment amount VSmax (300 milligrams) of toner is replenished in synchronization with every rise of the sub-scanning gate signal FGATE in response to exposure of each of the four pages.
At the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous fourth page, the maximum toner replenishment amount VSmax (300 milligrams) of toner is replenished, and thus twenty seconds are required as the developer mixing time t2.
After the per-page exposure time t1 (five seconds) has elapsed since the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous fourth page, the sub-scanning gate signal FGATE rises in response to the exposure of the previous third page. At this rise of the sub-scanning gate signal FGATE in response to the exposure of the previous third page, a remaining developer mixing time required in response to the previous toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner is fifteen seconds (i.e., 20−5=15). That is, fifteen seconds are required for the developer mixing time at this stage. Further, twenty seconds are required as the developer mixing time in response to the toner replenishment of this time, i.e., the toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner. Therefore, the above two developer mixing times (fifteen seconds and twenty seconds) are compared with each other and the larger time (twenty seconds) is required as the developer mixing time actually used.
After the per-page exposure time t1 (five seconds) has elapsed since the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous third page, the sub-scanning gate signal FGATE rises in response to the exposure of the previous second page. At this rise of the sub-scanning gate signal FGATE in response to the exposure of the previous second page, a remaining developer mixing time required in response to the previous toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner is fifteen seconds (i.e., 20−5=15). Further, twenty seconds are required as the developer mixing time in response to the toner replenishment of this time, i.e., the toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner. Therefore, the developer mixing time required at this stage is twenty seconds, which is the larger one of the above two developer mixing times (fifteen seconds and twenty seconds).
After the per-page exposure time t1 (five seconds) has elapsed since the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous second page, the sub-scanning gate signal FGATE rises in response to the exposure of the previous first page. At this rise of the sub-scanning gate signal FGATE in response to the exposure of the previous first page, a remaining developer mixing time required in response to the previous toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner is fifteen seconds (i.e., 20−5=15). Further, twenty seconds are required as the developer mixing time in response to the toner replenishment of this time, i.e., the toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner. Therefore, the developer mixing time required at the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous first page is twenty seconds, which is the larger one of the above two developer mixing times (fifteen seconds and twenty seconds).
The process control starting point TP is set to be the time point at which t1 (five seconds) has elapsed since the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous first page. Therefore, the developer mixing time tx required after the start of the process control and before the start of formation of the toner image patterns is 15 seconds (20−5=15). Accordingly, formation of the toner image patterns should be started after elapse of the developer mixing time tx (fifteen seconds) since the start of the process control.
In a third case, the toner replenishment amount VS (50 milligrams) of toner is replenished in synchronization with every rise of the sub-scanning gate signal FGATE in response to exposure of each of the previous fourth page, the previous third page, and the previous second page, and thereafter the maximum toner replenishment amount VSmax (300 milligrams) of toner is replenished in synchronization with the rise of the sub-scanning gate signal FGATE in response to exposure of the previous first page.
Similarly to the above first and second cases, the developer mixing time required at the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous first page is twenty seconds, which is the time required for mixing the developer in response to the toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams).
The process control starting point TP is set to be the time point at which t1 (five seconds) has elapsed since the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous first page. Therefore, the developer mixing time tx required after the start of the process control and before the start of formation of the toner image patterns is fifteen seconds (i.e., 20−5=15). Accordingly, formation of the toner image patterns should be started after elapse of the developer mixing time tx (fifteen seconds) since the start of the process control.
In a fourth case, the toner replenishment amount VS (50 milligrams) of toner is replenished in synchronization with the rise of the sub-scanning gate signal FGATE in response to exposure of the previous fourth page, and the maximum toner replenishment amount VSmax (300 milligrams) of toner is replenished in synchronization with the rise of the sub-scanning gate signal FGATE in response to exposure of the previous third page. Further, the toner replenishment amount VS (50 milligrams) of toner is replenished in synchronization with the rise of the sub-scanning gate signal FGATE in response to exposure of each of the previous second page and the previous first page.
At the rise of the sub-scanning gate signal FGATE in response to the previous first page, a remaining developer mixing time required in response to the toner replenishment of the toner replenishment of the maximum toner replenishment amount VSmax (300 milligrams) of toner performed at the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous third page is ten seconds (i.e., 20−10=10). Further, four seconds are required as the developer mixing time t3 in response to the toner replenishment of this time, i.e., the toner replenishment of the toner replenishment amount VS (50 milligrams) of toner. Therefore, similarly to the above first to third cases, the developer mixing time required at the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous first page is ten seconds, which is the larger one of the above two developer mixing times (ten seconds and four seconds).
The process control starting point TP is set to be the time point at which t1 (five seconds) has elapsed since the rise of the sub-scanning gate signal FGATE in response to the exposure of the previous first page. Therefore, the developer mixing time tx required after the start of the process control and before the start of formation of the toner image patterns is five seconds (i.e., 10−5=5). Accordingly, formation of the toner image patterns should be started after elapse of the developer mixing time tx (five seconds) since the start of the process control.
In a fifth case, the toner replenishment amount VS (50 milligrams) of toner is replenished in synchronization with every rise of the sub-scanning gate signal FGATE in response to exposure of each of the four pages. In this case, the developer mixing time t3 required in response to exposure of each of the four pages is four seconds, which is shorter than the per-page exposure time t1 (five seconds). Therefore, the developer mixing time tx required after the start of the process control and before the start of formation of the toner image patterns is zero seconds. Accordingly, formation of the toner image patterns starts as the process control starts.
As described above, the image forming condition setting device calculates the time required for mixing the developer and sufficiently dispersing toner in the developer according to the changes in the toner amount. This time is calculated, in every printing operation, when the sub-scanning gate signal FGATE rises and the exposure operation starts. The calculation continues during the developer mixing time t3 required for resolving the insufficient toner dispersion caused by the toner replenishment of the maximum toner replenishment amount VSmax of toner in a development device until the process control starting point TO. Then, the developer mixing time required at the process control starting point TO is set as the developer mixing time tx required after the process control starting point TO and before the start of formation of the toner image patterns. Accordingly, the minimum developer mixing time required for evenly mixing the developer can be set according to the states of the development device. As a result, the toner image patterns can be formed in a state in which the toner density is stabilized.
The developer mixing time can be controlled by comparing, at every rise of the sub-scanning gate signal FGATE, the developer mixing time required in response to the change in the toner density caused by a past toner replenishment, for example, and the developer mixing time required in response to the change in the toner density caused by a present toner replenishment, for example, and updating the larger one of the two developer mixing times in the memory. The developer mixing time thus updated in the memory at each rise of the sub-scanning gate signal FGATE is used as the developer mixing time required at the rise time of the sub-scanning gate signal FGATE.
The above-described embodiments are illustrative, and numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative and exemplary embodiments herein may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-194857 | Jun 2004 | JP | national |
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