Patent Grant
8238768
The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2008-261561 filed in Japan on Oct. 8, 2008.
1. Field of the Invention
The present invention relates to an image forming apparatus that uses a developing unit having a structure in which developer, conveyed along a certain circulation channel, is held on a moving surface of a developer holding body to contribute to a development process, and then returned from the surface of the developer holding body to the circulation channel.
2. Description of the Related Art
Japanese Patent Application Laid-open No. H9-160364 discloses a developing apparatus that is a known example of this kind of developing unit. This developing apparatus is shown in
The developing roller 910 is arranged at the short-length lateral side of the second developer container 903. The developing roller 910 includes a developing sleeve having a non-magnetic pipe that is driven to rotate, and a magnet roller, not shown, that is held inside the developing sleeve in an unrotatable manner. The developer in the second developer container 903 is carried on the surface of the rotating developing sleeve by way of the magnetic force from the magnet roller, and conveyed to a developing area where the developing sleeve faces a photoconductor not shown. After the surface of the sleeve is developed with the developer, the developer on the surface of the sleeve is collected to the second developer container 903. The concentration of the toner in the developer becomes reduced after the toner contributed to the development process. A controlling unit not shown calculates the number of pixels in an image based on image information thereof, predicts how much toner is consumed for developing the image based on the calculation result, and drives a toner supplying unit, not shown, for a length of time corresponding thereto. Toner is then added to the developer in the first developer container 901 through a toner supplying opening 915 provided near the end of the first developer container 901 at the upstream of the conveyed developer. In this manner, the toner concentration of the developer is recovered. According to such a toner supplying structure, the toner concentration can be recovered more quickly in comparison to a structure where the toner is added after a toner concentration sensor detects a decrease in toner concentration.
However, in the development process, the toner is not necessarily consumed in the amount that is predicted based on the number of pixels in the image. It is possible for the amount of toner consumption to fall below or exceed the prediction, depending on factors such as environmental variation. If the toner is kept being added based on the prediction having such an error with respect to the actual toner consumption, the toner concentration in the developer cannot be maintained appropriately.
It is an object of the present invention to at least partially solve the problems in the conventional technology.
According to one aspect of the present invention, there is provided an image forming apparatus including: a latent image carrier that holds a latent image; an image information obtaining unit that obtains image information; a latent image forming unit that forms a latent image on the latent image carrier based on the image information; a developing unit that conveys developer-containing toner and carrier along a predetermined circulation channel to a developing area that is an area where a developer holding body faces the latent image carrier by holding the developer on a moving surface of the developer holding body in a supply area that is an area of the circulation channel facing the developer holding body, that develops a latent image on the latent image carrier by attaching the toner in the developer thereto in the developing area, and returns the developer contributed to the development in the developing area to the supply area of the circulation channel along with the movement of the surface of the developer holding body; a toner supplying unit that supplies toner to a non-supply area that is not the supply area in the circulation channel through a toner supplying opening arranged at a predetermined position in the non-supply area; and a controlling unit that determines a driving amount of the toner supplying unit based on the image information. A toner concentration detecting unit is provided at a position downstream of the toner supplying opening in the non-supply area and upstream of the supply area to detect toner concentration in the developer. The controlling unit is structured to recognize an excess or a shortage in an amount of supplied toner correspondingly to a detection result of the toner concentration detecting unit, and to correct a determined value of the driving amount determined based on the image information correspondingly to the excess or the shortage that has been recognized.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
An Embodiment of the present invention applied to an electrophotographic printer (hereinafter, simply referred to as “printer”) that is an image forming apparatus will now be explained.
To begin with, a basic structure of a printer according to the embodiment will be explained.
The photoconductor unit 2Y includes a drum-shaped photoconductor 3Y that is a latent image carrier, a drum cleaning unit 4Y, a neutralizing unit not shown, and a charging unit 5Y. The charging unit 5Y as a charging means uniformly charges the surface of the photoconductor 3Y that is driven to rotate by a driving unit, not shown, in the clockwise direction in
The second conveyor screw 11Y in the second developer container 14Y is driven to rotate by a driving unit, not shown, toward the rear side in
In
The optical writing unit 20 is provided under the processing units 1Y, 1C, 1M, and 1K in
A first paper feeding cassette 31 and a second paper feeding cassette 32 are arranged under the optical writing unit 20, stacked on top of each other in the portrait direction. Recording paper sheets P, each of which is a recording medium, are held in each of the paper feeding cassettes as in a bundle of stacked recording papers. A first paper feeding roller 31a and a second paper feeding roller 32a are in contact with the recording paper sheets P placed at a top of the bundle. When the first paper feeding roller 31a is driven to rotate in the counter-clockwise direction in
A transferring unit 40 is arranged above the processing units 1Y, 1C, 1M, and 1K in
The secondary transfer backup roller 46 nips the intermediate transfer belt 41 with a secondary transfer roller 50 arranged outside of the loop of the intermediate transfer belt 41, forming a secondary transferring nip. The resist roller pair 35, explained earlier, sends the recording paper sheet P, nipped therebetween, into the secondary transferring nip at a timing synchronized with the arrival of the four-colored toner image on the intermediate transfer belt 41. The four-colored toner image on the intermediate transfer belt 41 is secondarily transferred onto the recording paper sheet P altogether at the secondary transferring nip by way of nipping pressure and a secondary transfer electrical field generated between the secondary transfer roller 50 and the secondary transfer backup roller 46 to which a secondary transfer bias is applied. Along with the white color of the recording paper sheet P, a full-colored toner image is obtained.
Residual toner, not transferred onto the recording paper sheet P, remains attached on the intermediate transfer belt 41 even after going through the transfer process at the secondary transferring nip. The belt cleaning unit cleans this residual toner. The belt cleaning unit includes a cleaning blade that is held in contact with the front surface of the intermediate transfer belt 41, and removes the residual toner by wiping the residual toner therewith.
The first bracket in the transferring unit 40 slides in a predetermined rotation angle around the rotation axis of the auxiliary roller when the driving of a solenoid, not shown, is turned ON and OFF. Upon forming a monochromatic image, the printer according to the embodiment drives the solenoid to cause the first bracket to rotate slightly in the counter-clockwise direction in
A fixing unit 60 as a fixing means is provided above the secondary transferring nip in
Outside of the loop of the fixing belt 64, a temperature sensor, not shown, is arranged facing the front surface of the fixing belt 64 with a predetermined gap therewith to detect the temperature at the surface of the fixing belt 64 right before going into the fixing nip. The result of this detection is sent to a fixer power circuit that is not shown. The fixer power circuit controls ON and OFF of the power to be supplied to the heat source included in the heating roller 63 or one included in the pressing and heating roller 61, based on the detection result of the temperature sensor. In this manner, the temperature at the surface of the fixing belt 64 is maintained at approximately 140 Celsius degrees. The recording paper sheet P, having gone through the secondary transferring nip and removed from the intermediate transfer belt 41, is sent into the fixing unit 60. While the recording paper sheet P is conveyed from the bottom to the top of
The recording paper sheet P, thus applied with the fixing process, is ejected outside of the printer after being passed through the rollers of a pair of paper ejecting rollers 67. A stacking unit 68 is provided on the top surface of the chassis of the printer. The recording paper sheet P, ejected by the pair of paper ejecting rollers 67, is stacked sequentially on the stacking unit 68.
Above the transferring unit 40, four containers for toner, toner bottles 72Y, 72C, 72M, and 72K, are provided. These toner bottles 72Y, 72C, 72M, and 72K store therein Y toner, C toner, M toner, and K toner, respectively. The toner of each of the colors, contained in each of the toner bottles 72Y, 72C, 72M, and 72K, is supplied to the developing units 7Y, 7C, 7M, and 7K, included in the processing units 1Y, 10, 1M, and 1K, respectively, by way of the toner supplying unit 70. The toner bottles 72Y, 72C, 72M, and 72K can be removed from and attached to the printer independently from the processing units 1Y, 10, 1M, and 1K.
As already shown in
A gear, not shown, is formed on each of the outer circumference of the tip of bottle units 73K, 73Y, 73C, and 73M in the toner bottles 72Y, 72C, 72M, and 72K. These gears are covered by the holder units 74K, 74Y, 74C, and 74M. To expose a gear partially, a cutout, not shown, is formed on a part of the circumference of the holder units 74K, 74Y, 74C, and 74M. In this manner, a part of the gear is exposed therefrom. When the holder units 74K, 74Y, 74C, and 74M of the toner bottles 72K, 72Y, 72C, and 72M are engaged with the bottle driving unit 96, K, Y, C, and M bottle driving gears, not shown, provided on the bottle driving unit 96 are engaged with the gears on the bottle unit 73K, 73Y, 73C, and 73M, respectively, through the cutouts. The K, Y, C, and M bottle driving gears on the bottle driving unit 96 are driven to rotate by a driving system not shown, further to drive the bottle units 73K, 73Y, 73C, and 73M to rotate in the holder units 74K, 74Y, 74C, and 74M.
In
A lateral conveying pipe 79Y is connected to the bottom of the hopper 76Y. The Y toner in the hopper 76Y slides along a taper formed thereon by way of its own weight, dropping into the lateral conveying pipe 79Y. A toner supplying screw 80Y is provided in the lateral conveying pipe 79Y, and along the driving rotation thereof, the Y toner is conveyed laterally along the longitudinal direction of the lateral conveying pipe 79Y.
A drop guiding pipe 81Y is connected to a longitudinal end of the lateral conveying pipe 79Y, in an extending manner along the portrait direction. The bottom end of the drop guiding pipe 81Y is connected to the toner supplying opening 17Y, provided on the first developer container 9Y of the developing unit 7Y. When the toner supplying screw 80Y, installed in the lateral conveying pipe 79Y, is rotated, the Y toner, conveyed to the longitudinal end of the lateral conveying pipe 79Y, is dropped into the first developer container 9Y in the developing unit 7Y through the drop guiding pipe 81Y and the toner supplying opening 17Y. In this manner, the Y toner is supplied to the first developer container 9Y. Moreover, the toners of the other colors (C, M, and K) are supplied in the same manner.
According to the structure where the toner is supplied by way of the driving rotation of the toner supplying screw 80Y as described above, a supply resolution is not very high.
In response to this issue, in the printer according to the embodiment, a lower limit B is set to the length of time the toner supplying unit is driven, and the driving of the toner supplying unit is turned ON or OFF following a condition for ensuring the driven time to be longer than the lower limit B. By supplying toner in this manner, the variations in the amount of supplied toner in a supply operation can be suppressed. A specific method of setting the lower limit B will be explained later in detail.
In the printer according to the embodiment, the toner supplying unit is driven at a constant speed regardless how much toner needs to be supplied in each time unit. The amount of supplied toner per time unit is adjusted by controlling the frequency of setting the drive ON and OFF. During the time a relatively large amount of toner supply is required in a time unit, the drive is turned ON and OFF frequently. On the contrary, during the time a relatively small amount of supply is required in a time unit, the drive is turned ON and OFF less frequently. If images with a high image-area ratio are successively output during the time such ON and OFF control is performed, the toner supplying unit may be kept driven for a certain length of time, as shown in an upper area of
In response to this issue, in the printer according to the embodiment, an upper limit E is set to the time the supply operation is allowed to be kept running as shown in the lower diagram of
A method of controlling the toner supply in a conventional image forming apparatus will now be explained.
A characterizing structure of the printer according to the embodiment will now be explained.
For each page to be output, a supply controlling unit 102, included in the printer, creates a drive controlling pattern for the toner supplying unit 70, based on the image-area ratio of the output page. At this time, such a pattern is created so that the variation of toner concentration, occurring every time the page is output (the expected change in toner concentration in the developer passed through the second developer container 14Y as the supply area), is offset by changing the amount of supplied toner. To create such a drive controlling pattern, a preparatory experiment is run to actually measure a waveform of toner concentration variation that occurs when a flat-black image, having an image-area ratio of 100(%), is output, using a toner concentration sensor (such a waveform is hereinafter referred to as “reference consumption waveform”). If toner is supplied in an amount corresponding to a waveform having a phase opposite to the reference consumption waveform (hereinafter, “reference offsetting waveform”), the toner concentration variation, occurring when a flat-black image with an image-area ratio of 100(%) is output, can be completely offset. Thus, if a flat-black image having an image-area ratio of 100(%) is output, the toner concentration variation, occurring in such an output, can be completely offset by supplying the toner variably in an amount corresponding to the reference offsetting waveform. If the image-area ratio is 80%, the toner concentration variation can be offset by changing the amount of supplied toner according to a waveform having the same phase as the reference offsetting waveform, but 80% of its amplitude. To achieve this goal, an active noise control (ANC) filter circuit is prepared to convert the amplitude of the reference offsetting waveform to a height corresponding to the image-area ratio of an output image, to obtain an offsetting waveform for the image-area ratio.
The reference consumption waveform corresponds to a flat-black image output onto a sheet of an A4-sized paper, such as one shown in
As shown in
A drive controlling pattern is made of a plurality of rectangular-shaped pulse signals arranged one after another. If a plurality of drive controlling patterns is simply superimposed over one another, the amplitude of the rectangular-shaped pulse signal becomes increased. However, in the printer according to the embodiment, the amount of the toner supply is not adjusted by controlling the driven speed, and the driven speed is kept constant. Thus, the control cannot be performed to reflect the increase in the amplitude of a rectangular-shaped pulse signal. In response to this problem, if rectangular-shaped pulse signals are to become superimposed over one another upon synthesizing the drive controlling pattern of the next page to that of the previous page, the positions of the rectangular pulse signals in one of the drive controlling patterns are shifted with respect to those in the other so as to avoid such superimposition.
Instead of synthesizing the drive controlling pattern of the next page to the unexecuted portion of the drive controlling pattern of the previous page to control driving of the toner supplying unit, the ANC filter circuit may be structured as follows. If a simulated impulse signal corresponding to the next page is received, the ANC filter corrects an unexecuted portion of the offsetting waveform, created based on a simulated impulse signal corresponding to the previous page, by synthesizing the offsetting waveform created based on the next simulated impulse signal thereto. In other words, the ANC filter may be structured to output the synthesized waveform shown in
In the explanation above, it is assumed that the size or the conveyed direction of the recording paper to be used remains constant; however, in reality, the size or the conveyed direction of the recording paper changes. For example, an A4-sized recording paper is sometimes conveyed laterally along the short-length direction, and some other time, an A4-sized recording paper is vertically conveyed along the longitudinal direction. A recording paper of a completely different size may also be conveyed laterally.
Thus, the printer according to the embodiment includes a plurality of ANC filter circuits each corresponding to each of a plurality of standard sizes of recording papers and the conveyed directions thereof. While a page is being output, a simulated impulse signal, corresponding to the image area of the output page, is output to the ANC filter circuit corresponding to the size and the conveyed direction of the output page. For example, it is assumed herein that a size A is output on the first page, and a size B is output on the second page. As shown in
Upon completing the output of the last page when an image forming operation is continuously executed, or upon completing the output of a single page when an image forming operation is executed for a single page, an idle operation is run for a predetermined length of time, and each of the units is stopped driving. At this time, no problem will occur if an entire drive controlling pattern for the toner supplying unit is completely executed; however, when the toner concentration variation, due to toner consumption for the previous page, persists for a quite large number of pages, the entire drive controlling pattern may not be completely executed. In this situation, if the idle operation is kept running until the entire drive controlling pattern is executed completely, the idle operation might prevent a print job to be ended quickly. In addition, generally upon starting a print job, an idle operation is also run for a predetermined length of time before starting an image formation. Thus, even if the supply controlling unit 102 stops driving each of the units before completely executing a portion of a drive controlling pattern when a print job is ended, that portion can be executed during the idle operation performed upon starting a print job. Therefore, in the printer according to the embodiment, the supply controlling unit 102 is structured to store an incomplete portion of the drive controlling pattern, if any, in a data storage unit upon ending a print job, and to perform a control to drive the toner supplying unit based on that portion of the pattern upon starting the next print job. For example, it is assumed herein that, if the entire scheduled drive controlling pattern is to be executed upon ending a print job, the control will be performed in the manner as shown in the timing chart in
If the ANC filter circuit is structured to correct the output waveform so as to output the synthesized waveform shown in
The printer according to the embodiment is switched between two printing speed modes (a high-speed print mode and a low-speed print mode) according to an instruction issued by a user. If the printing speed, that is, a linear processing speed is changed, the rotation speed of the conveying screw in the developing unit also changes, thus resulting in a different reference consumption waveform or offsetting waveform. The drive controlling pattern will also be different. However, a drive controlling pattern at one linear processing speed can be converted into a drive controlling pattern at the other linear processing speed based on the difference in the linear speed. For example, it is assumed herein the drive controlling pattern at the low-speed printing mode is as shown in
When the ANC filter circuit is structured to correct the waveform output therefrom so as to output the synthesized waveform shown in
If an average of the image-area ratio in the output image changes while an image forming operation is continuously executed, the toner supply capability of the toner supplying unit will also change.
In response to this problem, during the continuous image forming operations, the printer according to the embodiment obtains a moving average of the image-area ratio of the output image, and, based on the result, corrects the amount of toner supplied per unit image-area ratio.
A data table is stored in the data storage unit beforehand for determining a correction coefficient. Then, with reference to the data table, a correction coefficient α corresponding to the moving average of the image-area ratio is determined (S3). An example of the data table is shown in Table 1.
The higher the moving average of the image-area ratios is, the smaller correction coefficient α is selected, based on the fact that the higher the moving average is, the higher the toner supply capability of the toner supplying unit becomes. Alternatively, this data table may be those shown in Table 2 or 3, as long as the smaller correction coefficient α is selected when the moving average becomes higher.
An amplitude (height) Xa(k) of the simulated impulse signal is then calculated (S4). At this time, a formula “Amplitude Xa(k)=image-area ratio X(i)/100×β×α” is used. In this formula, β denotes to an amplitude with the image-area ratio X(i) of 100(%). α denotes to the correction coefficient. If the characteristic shown in
As an example with specific numbers, when images of the image-area ratio 80 (%) are continuously output, the moving average of the image-area ratio will be 80(%). Based on the data table shown in Table 1, the correction coefficient α is determined to be 0.85. Assuming that the amplitude β with the image-area ratio X(i) of 100(%) is 1, the amplitude Xa of the simulated impulse signal will be 0.68, based on the calculation “Amplitude of Simulated Impulse signal Xa(k)=0.8×1×0.85”. By adopting the amplitude Xa, the amount of toner supplied per an image-area ratio unit is corrected. In this manner, the amount of supplied toner can be prevented from becoming inappropriate, due to the change in toner supply capability caused by a change in the average image-area ratio.
The supply controlling unit 102 also performs a toner supply control based on a difference between an output voltage (Vt) from the toner concentration sensor and a target voltage Vtref that is a control target of the toner concentration, in parallel with the toner supply control performed in the above-described manner based on the image-area ratio. More specifically, the supply controlling unit 102 samples the output voltage Vt from the toner concentration sensor (for example, 10Y) at a predetermined sampling cycle, and obtains an average of Vt over a predetermined time period, every time the predetermined time elapses. If the average of the Vt is higher than the target voltage Vtref, that is, if the toner concentration in the developer in the first developer container is lower than a target value, the drive controlling pattern, created based on the image-area ratio, is corrected according to the amount of supplied toner required to resolve the difference between the Vt average and the target voltage Vtref. In this manner, by recognizing an excess or a shortage of supplied toner based on the detected result of the toner concentration, the supply controlling unit 102 corrects the length of time the toner supply unit is driven, determined based on the image information, based on the excess or shortage in the amount of the supplied toner. By way of this correction, the supply controlling unit 102 eliminates an error between a theoretical amount of supplied toner based on the image-area ratio, and the amount of toner actually needed to be supplied. In this manner, it is possible to avoid a development performance degradation that might have occurred if such an erroneous toner supply were to be continued.
Other embodiments in which the printer according to the embodiment is provided with additional characterizing structures will be now explained. Otherwise specified herein, the structure of the printer according to these embodiments will be the same as the one according to the embodiment described above.
The supply controlling unit 102 in the printer according to a first embodiment of the present invention obtains a Vt average that is an average of the detection results detected by a toner concentration sensor, for each of the colors K, C, M, and Y. The supply controlling unit 102 then obtains an additional drive controlling pattern required for bringing the Vt average to a predetermined target, that is, for bringing the Vt average to the target voltage Vtref, for the toner supplying unit. The drive controlling pattern, created based on the image-area ratio, is corrected by synthesizing this additional drive controlling pattern thereto.
In
The Smith compensator 102d will now be explained in further detail.
When, instead of correcting the drive controlling pattern upon occurrence of the next page output, the ANC filter circuit is structured to correct the waveform output therefrom so as to output the synthesized waveform, as shown in
The supply controlling unit 102 in the printer according to a second embodiment of the present invention obtains a Vt average that is an average of the detection results of a toner concentration sensor, for each of the colors K, C, M, and Y. The supply controlling unit 102 then obtains a correction scale factor for the amount of the toner required to be supplied per image-area ratio to bring the Vt average to a predetermined target, that is, to bring the Vt average to the target voltage Vtref. To describe more in detail, the supply controlling unit 102 obtains how many times the amplitude of the offsetting waveform should be multiplied to bring the Vt average to the target voltage Vtref, and uses the result as a correction scale factor. The drive controlling pattern, created based on the image-area ratio, is corrected based on the correction scale factor. More specifically, the drive controlling pattern is corrected so that each of the rectangular pulse signals to be included in the drive controlling pattern is generated in a frequency multiplied by the correction scale factor with respect to the frequency in the original drive controlling pattern. Preferably, the offsetting waveform is maintained, and an applicable portion of thereof is converted sequentially, as required, to an ON and OFF pattern of rectangular pulse signals, instead of maintaining the ON and OFF pattern of the rectangular pulse signals itself as a drive controlling pattern. In this manner, as shown in
According to a third embodiment of the present invention, the drive controlling pattern is corrected by a method in which the correction method according to the first embodiment is combined with that according to the second embodiment.
Each variation of the printer according to the embodiment will now be explained. Unless otherwise specified, the structure of the printer according to each of the variations is the same as one according to the embodiment.
First Variation
A printer according to a first variation of the present invention is the same as one according to the embodiment excluding a point described below. As show in
Second Variation
A printer according to a second variation of the present invention develops a color image using a revolver developing apparatus. More specifically, the printer includes a drum-shaped revolver developing apparatus with its axial direction arranged horizontally. The revolver developing apparatus holds the C, M, and Y developing units with a rotating supporting body. Every time the rotating supporting body is rotated for 90 degrees, a developing unit of a different color is moved to a position facing a photoconductor. In this manner, the developing units are switched according to the rotation angle of the rotating supporting body in the revolver developing apparatus, to sequentially develop the K, C, M, and Y latent images, sequentially formed on the photoconductor, into the K, C, M, and Y toner images. These K, C, M, and Y toner images are overlapped one another, and transferred onto the intermediate transfer body.
The revolver developing unit holds the K, C, M, and Y toner cartridges in removable and attachable manner. These toner cartridges are rotated around the rotation of the rotating supporting body, rotating around a rotation axis thereof. Taking advantage of the rotation, the toner is ejected from each of the toner cartridges, temporarily stored in a temporary toner storage. By way of the driving rotation of the rotating member, the toner is supplied from the temporary toner storage into the developing unit. In such a structure, if the development of a predetermined color is continued for a long time, with the revolver developing unit kept stopped at a predetermined rotation angle, the amount of toner stored in the temporary toner storage of the color will gradually decrease. If a monochromatic image having a high image-area ratio is continuously printed under this condition, the larger amount of toner will become supplied from the developing unit from the temporary toner storage, in comparison to the amount supplied from the toner cartridge to the temporary toner storage, supplied by the rotation of the revolver developing apparatus. In this manner, a space is created in the temporary toner storage. If the toner density in the temporary toner storage decreases in this manner, the less amount of toner is supplied in a time unit. In other words, the higher the average image-area ratio is, the lower the toner supply capability of the toner supplying unit becomes.
Table 4 indicates an example of a data table used for determining the correction coefficient in the printer.
The higher the moving average is, the higher correction coefficient α is selected, considering the fact that the higher the average image-area ratio is, the lower the toner supply capability of the toner supplying unit becomes. Data tables shown in Tables 5 and 6 may also be used, as long as a higher correction coefficient α is selected correspondingly to the increase in the moving average.
Third Variation
A controlling unit 100 in a printer according to a third variation of the present invention performs an imaging performance adjusting process immediately after turning on the printer, upon starting a print job after waiting for a long time for a print command from a user, and every time a predetermined number of paper sheets are printed.
After calibrating the optical sensor, a predetermined patch pattern is formed (S2). More specifically, a plurality of patch-like latent images, each having a predetermined shape, is formed on the photoconductor, each with a different writing light intensity, and the electric potentials of these patch-like latent images are detected by an electric potential sensor. These patch-like latent images are developed with different developing biases (voltages applied to the developing roller) to form a patch pattern including a plurality of predetermined patch toner images.
When such a patch pattern is formed, the amount of light reflected on the surface of each of the patch toner images, included in the patch pattern, is detected by the optical sensor (S3). The detection results are sequentially converted into data of the amount of attached toner per an area unit (S4). Out of the patch toner images of K, C, M, and Y, for K, only an intensity of a specular reflection is detected. For C, M, and Y, both intensities of a specular reflection and of a diffuse reflection are detected.
After obtaining the amount of toner attached to each of the patch toner images, a development γ (development performance) is obtained based on the results (S5). More specifically, a development potential that is the difference between the electric potential of the latent image and the developing bias is calculated for each of the patch toner images. Then, a linear approximation of the relationship between the development potential and the amount of toner attached to the corresponding patch toner image is obtained by least squares (the inclination is called to be the development γ, and a segment x is called to be a development initiating voltage). Instead of the linear approximation, a secondary approximate curve may also be obtained. If the secondary approximate curve is to be obtained, the development γ will be a differential at the point where a target amount of attached toner is obtained.
Then, a potential required to obtain a target amount of attached toner is determined in the linear approximation, and a developing bias for realizing the development potential is calculated (S6). More specifically, the developing bias is calculated based on a formula “Developing Bias [−V]=Development Potential-Latent Image Potential [V]”. Because the latent image potential is approximately −50[V], the developing bias will be a value of the latent image potential subtracted from the development potential with the plus or the minus sign reversed.
Once the developing bias is calculated, the uniformly-charged potential of the photoconductor and the optical writing intensity of the optical writing unit are calculated (S7). For the calculation of the uniformly-charged potential, a formula “Uniformly-Charged Potential [V]=Developing Bias [−V]−200 [V]” is used. The value −200 [V] is a background potential for preventing the background from becoming smeared. The background potential is offset from the developing bias toward the polarity of the charged toner by a predetermined degree. The optical writing intensity is obtained in the range from 80 to 120(%) based on a predetermined conversion formula that executes a conversion according to the uniformly-charged potential of the photoconductor. For a print job thereafter, a combination of the calculated developing bias, the uniformly-charged potential, and the optical writing intensity is used.
Then, the target voltage Vtref that is a control target for the toner concentration is corrected (S8). More specifically, the development γ calculated based on the amount of attached toner (hereinafter, referred to as “imaging development γ”) is compared with a target development γ. If the imaging development γ is higher than the target development γ, the target voltage Vtref is corrected to a greater value (to lower the toner concentration target). If the imaging development γ is higher than the target development γ, it means that the imaging has been performed with the development γ that is higher than the target development γ. In such a situation, the development γ will be lowered, in comparison to the one used up to that point in time, for the next print job and thereafter, and the target value of the toner concentration must be also lowered. On the contrary, if the imaging development γ is lower than the target development γ, the target voltage Vtref is corrected to a smaller value (to raise the toner concentration target).
If the target voltage Vtref is corrected according to the imaging performance adjusting process described above, the difference between the output voltage Vt and the target voltage Vtref will be relatively great immediately after the correction. Such a difference will gradually become smaller, and become almost none as the drive controlling pattern is corrected based on the difference between the Vt average and the target voltage Vtref, while several tens of paper sheets are being printed thereafter. However, during the period, the images will be temporarily output in a lighter or darker density than the target. Therefore, it is preferable to raise or lower the output voltage Vt to the target voltage Vtref as quickly as possible, immediately after correcting the target voltage Vtref. If the amplitude of the simulated impulse signal is corrected based on the difference between the Vt average and the target voltage Vtref, in the manner described in the second embodiment, the output voltage Vt might be caused to overshoot temporarily after gradually bringing the output voltage Vt closer to the target voltage Vtref, after performing the correction of the target voltage Vtref, as shown in
Therefore, the supply controlling unit 102 is structured to temporarily change the amount of toner supplied per image-area ratio unit after correcting the target voltage Vtref, until the output voltage Vt rises or drops to the corrected target voltage Vtref or its approximation. The supply controlling unit 102 temporarily changes the amount of toner supplied per image-area ratio in a manner described below. In other words, the amplitude of the simulated impulse signal is changed temporarily. Table 7 indicates the relationship between the imaging development γ, the correction of the Vtref, and the correction scale factor for the simulated impulse signal, used for temporarily changing the amount of supplied toner (hereinafter, referred to as “supply correction scale factor”).
As shown in Table 7, if the imaging development γ is higher than the target, the target voltage Vtref is corrected to a higher value (the target toner concentration is lowered), and the amplitude of the simulated impulse signal is temporarily made less than one time thereof, so that the toner is temporarily supplied in an amount less than one time thereof per image-area ratio unit (supply correction scale factor). In this manner, the amount of toner supply is temporarily reduced, so that the output voltage Vt that is lower than the target voltage Vtref is immediately raised to the target voltage Vtref. On the contrary, if the imaging development γ is lower than the target, the target voltage Vtref is corrected to a smaller value (the target toner concentration is brought up). At the same time, the amplitude of the simulated impulse signal is temporarily made higher than one time thereof, so that the toner is supplied in an amount greater than one time thereof per image-area ratio unit. In this manner, the amount of supplied toner is temporarily increased, so that the output voltage Vt that is higher than the target voltage Vtref is immediately brought down to the target voltage Vtref.
By temporarily changing the amount of toner supplied per image-area ratio after correcting the target voltage Vtref in the manner described above, the output voltage Vt, after correcting the target voltage Vtref, is immediately caused to reach the target voltage Vt as shown in
Fourth Variation
A printer according to a fourth variation of the present invention is the same as that according to the third variation, excluding the method of correcting the target voltage Vtref.
The printer according to the fourth variation forms a toner patch image in a corresponding inter-paper space on the intermediate transfer belt when image forming operations are continuously executed. A corresponding inter-paper space on the intermediate transfer belt means an area of the surface of the intermediate transfer belt, located between the area brought in contact with the current recording paper sheet by way of the secondary transferring nip, and the area brought in contact with the next recording paper sheet, as shown in
In the third embodiment, the development γ is measured as an index indicating the development capability. On the contrary, in the printer according to the second embodiment, the amount of toner attached on the patch toner image, formed on the corresponding inter-paper space, (hereinafter, referred to as the “amount of toner attached on the inter-paper patch”) is measured as the index of the development capability. As shown in the graph in
Table 8 indicates the relationship between the amount of attached toner on the inter-paper patch, a correction of Vtref, and the supply correction scale factor.
As shown in Table 8, if the amount of toner attached on the inter-paper patch is higher than the target, the target voltage Vtref is corrected to a greater value (the target toner concentration is lowered). At the same time, the amplitude of the simulated impulse signal is temporarily made less than one time thereof, so that the toner is temporarily supplied in an amount less than one time thereof per image-area ratio unit (the supply correction scale factor). In this manner, the amount of supplied toner is temporarily reduced, so that the output voltage Vt that is lower than the target voltage Vtref is immediately raised to the target voltage Vtref. On the contrary, if the amount of toner attached on the inter-paper patch is less than the target, the target voltage Vtref is corrected to a smaller value (the target toner concentration is raised). At the same time, the amplitude of the simulated impulse signal is temporarily made higher than one time thereof, so that the toner is temporarily supplied in an amount greater than one time thereof per image-area ratio unit. In this manner, the amount of toner supply is temporarily increased, so that the output voltage Vt that is higher than the target voltage Vtref is immediately dropped to the target voltage Vtref.
By temporarily changing the amount of toner supplied per image-area ratio in the manner described above after correcting the target voltage Vtref, the output voltage Vt, after correcting the target voltage Vtref, is immediately caused to reach the target voltage Vt as shown in the lower graph of
According to the present invention, a toner concentration detecting unit is arranged downstream of a toner supplying opening in the direction in which developer is conveyed. The toner concentration detecting unit detects toner concentration of the developer after toner is added thereto through the toner supplying opening in a non-supply area of a circulation channel. If the toner concentration of the developer is lower than a target value, it is considered that the amount of supplied toner is less than the actual toner consumption (a shortage in the supply). If the toner concentration of the developer is higher than the target value, it is considered that the amount of supplied toner is greater than the actual toner consumption (an excess in the supply). In this manner, the controlling unit recognizes an excess or a shortage in the amount of supplied toner based on the detection result of the toner concentration, and corrects a determined value in the length of time the toner supplying unit is driven, determined based on the image information, based on the excess or the shortage. By way of this correction, the amount of supplied toner is adjusted to an amount appropriate for the actual toner consumption. Therefore, it is possible to avoid a development performance deterioration that might have occurred if the toner is kept supplied in an erroneous amount with respect to the actual toner consumption.
Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
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