Patent Application
20080008485
In the following, embodiments of the present invention are described with reference to the accompanying drawings.
The image formation apparatus 1 includes a photoconductor 2 that is shaped like a drum, is rotated, and serves as the image supporting object. Around the photoconductor 2, the following units are sequentially arranged in a direction of an arrow for performing an image formation process; namely, an electrification unit 3, a writing unit 4, a developing unit 5, a transfer unit 6, and a cleaning unit 7. Further, an eraser 8 is arranged for reducing background optical density before development so that background dirt may be reduced, and an electrification removing unit 9 is arranged for removing residual charge (electrification) of the photoconductor 2.
The electrification unit 3 is a non-contacting type electrification unit such as a corona charger. The writing unit 4 is configured such that an electrostatic latent image may be formed by an exposure light irradiated to the photo conductor 2 through a lens and two or more mirrors, which exposure light is obtained by irradiating the laser light onto the manuscript placed on a manuscript placing table 4A.
Further, the developing unit 5 uses a two-component developer made of the toner and a carrier. The developing unit 5 includes a stir-mixing roller 5A that is rotated such that the toner that is friction-charged may be adhered to the carrier to constitute the developer. The developing unit 5 further includes a development sleeve 5B that counters the photoconductor 2 for supplying the toner/developer to the photoconductor 2 so that the electrostatic latent image on the photoconductor 2 may be developed to be visible.
The transfer unit 6 includes a transfer belt 6A that counters and contacts the photo conductor 2, and a transfer roller 6B that counters the photo conductor 2 for providing transfer bias.
According to the image formation apparatus 1 as described above, the electrostatic latent image is formed by the writing unit 4 on the photoconductor 2 that is uniformly charged (electrified) by the electrification unit 3, and the electrostatic latent image is developed by the toner of the developer supplied by the developing unit 5. The developing unit 5 includes a toner supply unit 103, and supply of the toner is controlled by the control unit 100 as described below.
The toner image that has been made visible is transferred to a recording medium S such as a sheet of paper that is fed by a feeding apparatus (not illustrated) using the transfer bias provided by the transfer roller 6B of the transfer unit 6. After the toner image is transferred, the toner image is thermally fixed to the recording medium S by a fixing apparatus 10.
Further, the image formation apparatus 1 includes an image density detection sensor (P sensor) 101, which is an optical sensor for detecting the density of the image formed on the photoconductor 2, and a toner density sensor (T sensor) 102 for detecting the density of the toner held in the developing unit 5 using a permeability detection method. The P sensor and the T sensor are connected to the input side of the control unit 100 as shown in
The control unit 100 controls detection of image density of the patch image having a reference density, which patch image is formed separately from an image to be printed. In order to obtain proper image density according to a detection result, the control unit 100 controls operations of the toner supply unit 103 of the developing unit 5. Accordingly, the toner supply unit 103 is connected to the output side of the control unit 100. A specific target of the toner supply unit 103 to be controlled may be a driving source of a member that supplies the toner held in a toner storage tank.
Next, operations of the control unit 100 are described.
Operation (1): The generating interval of the patch image (that has the reference density) is adjusted according to the image density value (Vp=Vsp/Vsg) detected by the image density detection sensor 101.
Operation (2): Specifically, if the image density value is not equal to a target value, the generating interval of the patch image is reduced (shortened).
Operation (3): If the image density value (Vp=Vsp/Vsg) is out of a predetermined range, and if a greater number of sheets than a predetermined value is processed, the patch image is formed even if an image is being formed.
The operations of the control unit 100 are further described.
Generally, toner density control is for adjusting the toner density reference value (Vtref) that serves as the target toner density according to the image density detection result of the patch image, and for controlling supply of the toner so that the toner density may be in agreement with the adjusted toner density reference value.
Although the embodiment of the present invention employs this approach, the embodiment further provides a solution for the problem wherein the amount of electrification of the developer is low, the same image density value is continuously used, and proper image density cannot be maintained.
Specifically, concerning the operation (1) above, it is considered that a fluctuation of the amount of electrification occurs when starting the image formation apparatus, and when a predetermined number of sheets have been processed. If at least one of these conditions is met, the image density detection sensor 101 detects the density of the patch image. If the image density value (Vp) detected is out of a predetermined range, e.g., between 0.08 and 0.12, the generating interval of the patch image is changed, and the changed generating interval is stored in a storage unit.
Further, the toner density of the developing unit 5 is detected, the compensation value (ΔVtref) for obtaining the target toner density value is computed based on the toner density value (Vt) and the image density value (Vp) at the present time, and the compensation value (ΔVtref) is updated from the previous compensation value to the computed compensation value. Here, the toner density reference value (Vtref) has been acquired through experiments, and the like, and is stored in the control unit 100 as mapped data.
When an image density value (Vp) that serves as the target of the image density sensor 101 is determined, supply conditions of the toner are arranged in a direction that cancels the difference between the toner density reference value (Vtref) and the tone density value (Vt) detected by the toner density sensor 102 for every one copy. Then, the toner supply unit 103 operates under the supply conditions.
By the operations as described above, the generating interval of the patch image can be adjusted according to the fluctuation of the amount of electrification, that is, the compensation of the toner density is performed following the fluctuation of the amount of electrification. This is in addition to the control shown in
Next, the operation (2) is described.
The generating interval of the patch image is reduced if the image density value (Vp) acquired at the present time is out of the predetermined range, e.g., between 0.08 and 0.12.
Next, the operation (3) is described.
In contrast to the operations (1) and (2) described above, according to the operation (3), the generating interval of the patch image is reduced while continuously processing a great number of sheets so that the density compensation can be carried out and the image density in the beginning and in the last part may be the same.
That is, the control unit 100 performs the compensation control of the toner density so that the toner density reference value (Vtref) may be adjusted based on the toner density value (Vt) and the image density value (Vp) at the present time, and so that the toner density value (Vt) may be in agreement with the updated toner density reference value (Vtref) In addition to this, according to the operation (3), the patch image is formed if the image density value (Vp) becomes different from the target value before the number of times of image formation processes exceeds the predetermined value if the number of times of image formation processes is greater than a predetermined value.
In this way, regardless of the number of the image formation processes, the density control is performed during the image formation processes based on comparison of the image density value with the target value so that the image density is made uniform from the beginning to the last when the great number of sheets is processed.
In addition, the patch image may be formed not only when the image density value (Vp) becomes different from the target value, but also every time a desired predetermined number of sheets is processed.
Then, the computed image density value (Vp) is compared with the target (ST3). If the Vp is out of the predetermined range, the generating interval of the patch image is adjusted, and information about the updated generating interval is stored in the storage unit (ST4). The generating interval is adjusted according to the magnitude of the difference from the predetermined range as shown in
Whether the generating interval of the patch image is changed or not, the toner density sensor 102 detects the toner density in addition to the image density. The toner density value (Vt) is acquired. The compensation value (ΔVtref) for the toner density value that serves as the target is obtained from the previous detection values (Vp and Vt) and the present detection values (Vp and Vt), and the toner density value (Vtref) is updated with the compensation value (ΔVtref). Then, the updated Vtref is stored in the storage unit (ST5 through ST7).
The control unit 100 performs drive control of the toner supply unit 103 for controlling the supply of the toner such that the toner density value may be in agreement with the target toner density value determined at step ST7. If the image density value (Vp=Vsp/Vsg) of the patch image obtained by the image density detection sensor 101 falls within the predetermined range, the generating interval of the patch image is returned to the initial value (10 in this example) (ST4A).
If it is determined that the selected number exceeds the predetermined number of sheets at step ST8, steps ST1 through ST3 (the same as shown in
The toner density when forming the patch image at step ST9 is detected by the toner density sensor 102 and a toner density value (Vt) is acquired (ST5). Then, the same process as steps ST6 and ST7 shown in
Further, the present invention is not limited to these embodiments, but variations and modifications may be made without departing from the scope of the present invention.
The present application is based on Japanese Priority Application No. 186814 filed on Jul. 6, 2006 with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-186814 | Jul 2006 | JP | national |
