Image forming apparatus and image forming method capable of detecting a resistance value of an intermediate transferring member

An image forming apparatus capable of detecting a resistance value of an intermediate transferring member at a stabilized sensitivity irrespective of the influences of environmental conditions, disturbing elements, etc. and contributing to the promotion of the image quality when forming images. The image forming apparatus is equipped with an electric potential controller to fix electric potential of the photosensitive surface of a photosensitive drum, a power source to supply a prescribed voltage or current to the photosensitive surface through the transferring surface of an intermediate transferring member, and a resistance detector to detect a current value flowing through the intermediate transferring member against a prescribed voltage supplied from the power source or a voltage value generated in an intermediate transferring member against a prescribed current and detect a resistance value of the intermediate transferring member based on the detected current value or voltage value.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from prior Japanese Application No. 2005-192922, filed on Jun. 30, 2005; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to an image forming apparatus and an image forming method.

In a so-called intermediate transferring type image forming apparatus which transfers toner images on sheets of paper using an intermediate transferring member, a construction to detect a resistance value of the intermediate transferring member and correct a primary transferring voltage output when forming images based on the detected resistance value so as to promote the stability of transferring (so-called primary transfer) efficiency of a toner image formed on an photosensitive surface of a photosensitive drum is so far known.

However, a resistance value of an intermediate transferring member fluctuates depending on environmental conditions such as ambient temperature, humidity, etc. and the influence of disturbing elements such as a printing operation and it is difficult to detect a resistance value of intermediate transferring members at stable sensitivity.

SUMMARY OF THE INVENTION

This invention is made in order for solving problems as mentioned above and it is an object to provide an image forming apparatus capable of detecting a resistance value of an intermediate transferring member at a stable sensitivity irrespective of influence of surrounding environmental disturbing elements and contributing to improvement of image quality at the time of image forming.

To solve the problem aforementioned, the present invention provides an image forming apparatus of an embodiment relating to the present invention, comprising an electric potential controller to fix a surface electric potential on a photosensitive surface of a photosensitive member to a prescribed value; a power source to supply prescribed voltage or current to the photosensitive surface through a transferring surface of an intermediate transferring member; and a resistance detector to detect a current value flowing through the intermediate transferring member against the prescribed voltage supplied from the power source or a voltage value generated in the intermediate transferring member against the prescribed current, and detect a resistance value of the intermediate transferring member based on the detected current value or voltage value.

Further, the present invention provides an image forming method of an embodiment relating to the present invention, comprising controlling a surface electric potential on a photosensitive surface of a photosensitive member to fix at a prescribed value; supplying a prescribed voltage or current to the photosensitive surface through a transferring surface of an intermediate transferring member; and detecting a current value flowing through the intermediate transferring member against the supplied prescribed voltage or a voltage value generated in the intermediate transferring member against the prescribed current, and detecting a resistance value of the intermediate transferring member based on the detected current value or the voltage value.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an embodiment of this invention will be explained with reference to the attached drawings.

FIG. 1is a schematic diagram for explaining the internal construction of an image forming apparatus in this embodiment. An image forming apparatus1in this embodiment is composed of, for example, a MFP (Multi Function Peripheral).

In image forming apparatus1, a paper supply cassette3is provided to supply paper P in the direction of an image forming unit2. Paper P is taken out of paper supply cassette3, conveyed along a conveying path3cand supplied in the direction of an aligning roller4. On the upper surface of image forming apparatus1, a scanner device5to read a document image and an automatic document feeder6are provided.

Image forming unit2is composed of a photosensitive drum7, a main charger8, an exposing portion9, a developing device10, a primary transferring stage11, a secondary transferring stage12and a cleaner13which are arranged along the rotating direction a of photosensitive drum7.

Primary transferring stage11is constructed with an intermediate transferring belt14pushed against photosensitive drum7with a primary transferring roller15. Intermediate transferring belt14is put over a driving roller16, a support roller17and a secondary transferring roller18. Intermediate transferring belt14is rotated in the arrow direction b by the rotation of driving roller16. Secondary transferring roller18is arranged opposing to an opposing roller19by way of intermediate transferring belt14, and secondary transferring stage12is composed of secondary transferring roller18, intermediate transferring belt14and opposing roller19.

At the downstream side of secondary transferring stage12, a fixing device20is arranged along conveying path3c. Fixing device20is composed of a heat roller21and a pressure roller22. Further, at the downstream side of fixing device20, an exit roller23is arranged along conveying path3c. Paper P with an image formed thereon and exits from exit roller23is piled up on a receiving tray24that is formed above image forming unit2.

An image on a document D conveyed on a platen glass6cby automatic document feeder6is read by scanner device5. The read image on document D is sent to exposing portion9as an image signal. A light image corresponding to the image signal sent from exposing portion9is irradiated on photosensitive drum7that is uniformly charged by main charger8and a latent image is formed on photosensitive drum7. This latent image is developed by developing device10and is converted to a toner image. This toner image is transferred on intermediate transferring belt14by the action of primary transferring roller15.

The toner image transferred on intermediate transferring belt14is transferred on paper P that is conveyed on conveying path3cby the action of secondary transferring roller18of the secondary transferring stage12. Paper P with the toner image transferred thereon is heated by the heat roller21of fixing device20and is fixed on paper P. Paper P with the fixed toner image is fed to receiving tray24by exit roller23.

After the toner image was transferred on intermediate transferring belt14, toner remaining on photosensitive drum7is removed by cleaner13.

Image forming apparatus1according to this embodiment further has an electric potential controller101, a resistance detector102, a power source103, an environment detector104, a photosensitive drum quantity consumed measure105, a CPU106, a MEMORY107and a coefficient memory108as shown inFIG. 2.

Electric potential controller101controls the electric potential of the photosensitive surface of photosensitive drum7so as to fix to a prescribed value.FIG. 3is a schematic diagram showing the construction around an intermediate transferring member A of the image forming apparatus1according to this embodiment. Electric potential controller101controls the surface potential of photosensitive drum7by controlling a grid bias potential shown inFIG. 3. That is, main charger8provided with a grid27is arranged in opposition to photosensitive drum7. There are a power source26to supply voltage to a wire25of the main charger8and a variable power source28to supply voltage to the grid27provided in the opening of main charger8. A grid bias potential is controlled by varying a voltage supplied from the variable power source28.

Power source103supplies a prescribed voltage (for example, a fixed value V1) or a prescribed current (for example, a fixed value A1) to the photosensitive surface of photosensitive drum7through the transferring surface of intermediate transferring belt14from primary transferring roller15as shown inFIG. 3. The toner image transferred on intermediate transferring belt14is transferred on paper P by secondary transferring roller18. Further, in this embodiment, the intermediate transferring member A refers to primary transferring roller15and intermediate transferring belt14.

Resistance detector102detects a current value flowing through intermediate transferring member A against a prescribed voltage supplied to photosensitive drum7from power source103or a voltage value or a current value generated against a prescribed current in intermediate transferring member A, and detects the resistance of intermediate transferring member A by computing a resistance value based on the detected current value or voltage value.

That is, in resistance detector102, a resistance value of intermediate transferring member A is detected by computing a resistance value based on the relation between voltage (V) and current (I).

Further, resistance detector102detects a resistance value of intermediate transferring member A in an area wherein no toner image is formed on the photosensitive surface of photosensitive drum7.

Environment detector104detects at least either one of the atmospheric temperature and humidity surrounding intermediate transferring member A as environmental data.

Photosensitive drum quantity consumed measure105measures a using volume of photosensitive drum7for the image forming in image forming apparatus1. For example, the number of sheets of paper P on which an image is formed using photosensitive drum7is counted. Here, the number of image forming paper to be counted denotes the number of sheets of paper P on which an image is to be formed from now on. Further, for example, the number of sheets of paper on which an image was already formed may be counted. Or the number of revolutions of photosensitive drum7may be measured. Furthermore, a driven time of photosensitive drum7may be measured. In any case, any method is usable provided that the using volume of photosensitive drum7can be measured.

CPU106executes various kinds of processes in image forming apparatus1. That is, various functions are realized by executing programs stored in MEMORY107. MEMORY107is composed of, for example, ROM, RAM, etc. and stores various data and programs that are used in the image forming apparatus1.

Further, electric potential controller101is capable of changing a prescribed value to fix the surface potential of the photosensitive drum7based on the environmental data detected by environment detector104or the number of papers P counted by photosensitive drum quantity consumed measure105.

A resistance value of intermediate transferring member A such as intermediate transferring belt14varies according to atmospheric temperature and humidity surrounding the intermediate transferring member A. That is, it is known that a resistance value becomes low in a high temperature and humid environment while it becomes high in a low temperature and humid environment.

FIG. 5is a graph showing the relation between a surface electric potential fixing the photosensitive surface of a photosensitive drum and a resistance value detected when the surface electric potential is fixed. As shown inFIG. 5, the detecting sensitivity of resistance values of intermediate transferring members is different depending on set values of surface potentials of photosensitive drums. That is, the detecting sensitivity was most high when the surface potential was fixed at 300V and was most low when the surface potential was fixed at 500V.

The relation of the characteristic of resistance value of intermediate transferring members with the surface potential and the detecting sensitivity is noted. That is, in an environment wherein resistance values become low, the surface potential of a photosensitive drum is set at a value at which the detecting sensitivity becomes high. On the contrary, in an environment wherein resistance values become high, the surface potential is set at a value at which the detecting sensitivity becomes low. Thus, by fixing surface potentials as shown above, the stabilized detection of resistance values of intermediate transferring members is achieved. In other words, by detecting resistance values at a sensitivity according to environments, it becomes possible to make the detection of resistance values at a sensitivity proper to the environment and the detection of resistance values at a proper sensitivity corresponding to the internal state (temperature, etc.) varying according to the number of print sheets in the image forming apparatus.

Further, image forming apparatus1in this embodiment is of such structure that power source103applies a voltage detected by resistance detector102and multiplied with a prescribed coefficient at the time when forming an image on the photosensitive surface of photosensitive drum7in the case when a prescribed current is supplied to the photosensitive surface by power source103(when a resistance value is detected according to a so-called constant-current system).

Prescribed coefficients are reserved in coefficient memory108as shown inFIG. 2. Power source103selects a proper prescribed coefficient corresponding to a voltage value received from resistance detector102through MEMORY107and multiplies the voltage value with a prescribed coefficient. That is, prescribed coefficients are reserved in coefficient memory108as “Coefficient Table” as shown inFIG. 6.

In the coefficient table shown inFIG. 6, a coefficient a is set for every color according to voltage (V1) detected in the monochromatic mode and the color mode. For example, the voltage (V1) detected in black (K) of the monochromatic mode is 1000V, the coefficient a will become 1.20. The output voltage V2in the image transferring at that time will become
V2=V1×a=1,000×1.20=1,200(V)
When the voltage V1detected in the magenta (M) of color mode is 600V, the coefficient a will become 1.55. The output voltage V2in the image transferring at that time will become
V2=V1×a=600×1.55=930(V)

Further, prescribed coefficients here are computed according to a prescribed computing formula that is set for every prescribed numerical range of voltage values detected by resistance detector102.FIGS. 7A to 7Eshow graphs of voltage values generated in intermediate transferring members detected by resistance detector102, having tilts that are set for every range of prescribed numerical values f the voltage values. Further, these graphs show tilts for every color in the monochromatic mode and the color mode.

FIG. 8shows one example of a formula to compute coefficient A according to detected voltage (V) in the monochromatic mode black (K). For example, when a detected voltage (V) is 1,000V to 1,500V, A=1.36−1.6×10−4×B, wherein A denotes coefficient and B denotes detected voltage, respectively.

Thus, by setting a voltage in the image forming apparatus1according to the detected voltage, it becomes possible to apply a proper voltage value with less error corresponding to detected voltage and make the transferring efficiency to an intermediate transferring member A of a toner image formed on the photosensitive surface of a photosensitive drum7suitable.

FIG. 9is a flowchart for explaining the process flow (the image forming method) in the image forming apparatus1according to this embodiment.

First, when setting the surface potential of the photosensitive drum7corresponding to temperature and humidity, at least either one of temperature and humidity is detected as an environmental data by environment detector104(Environmental Detection Step S101).

Electric potential controller101changes a prescribed value to fix the surface potential of the photosensitive drum7based on the environmental data detected in environmental detecting step S101(Electrical Potential Control Step S102).

On the other hand, to set the surface potential of the photosensitive drum7corresponding to accumulated number of sheets on which an image is to be formed instead of environmental data, accumulated number of sheets with an image formed is counted by photosensitive drum quantity consumed measure105(Count Step S103).

Electrical potential controller101changes a prescribed value to fix the surface potential of the photosensitive surface based on the number of sheets counted in the count step S103(Electrical Potential Control Step S104).

Then, electric potential controller101fixes the surface potential of the photosensitive surface of the photosensitive drum7at a prescribed value as described above (Electrical Potential Control Step S105).

In succession, power source103supplies a prescribed voltage or current to the photosensitive surface of the photosensitive drum7through the transferring surface of the intermediate transferring member A (Power Supply Step S106).

Resistance detector102detects a current value flowing through the intermediate transferring member A against the prescribed voltage supplied in the power supply step S106or a voltage value generated in the intermediate transferring member A against a prescribed current value and detects a resistance value of the intermediate transferring member A based on the detected current value or the voltage value (Resistance Detecting Step S107).

Then, in the case wherein a prescribed current is supplied to the photosensitive surface in the power supply step S106(the constant current system) (S108, YES), power source103applies a voltage multiplied with a prescribed coefficient selected from coefficient memory108to the voltage value detected in resistance detecting step S107to the primary transferring roller15at the time of image forming on the photosensitive surface (Step S109).

In the case of other than the (constant-current system) wherein prescribed current is supplied to the photosensitive surface (S108, NO) in the power supply step S106, a value of detected current multiplied with a prescribed coefficient is applied to primary transferring roller15at the time of the image forming (Step S110).

Further, in this embodiment, prescribed coefficients are set not only for every prescribed range of numerical numbers of detected voltage but also for every toner color (cyan, magenta, yellow) individually. As a charged amount of toner differs for colors, when voltage applied to the photosensitive drum is varied at the time of image forming, it becomes possible to form an image at a more suitable voltage value and contribute to the improvement of the image quality at the time of the image forming.

Each of the process steps in the image forming apparatus1described above is realized when an image forming program stored in MEMORY107is executed by CPU106.

This embodiment is explained above when the functions to execute the invention are pre-recorded in the apparatus; however, not restricted to this, similar functions may be downloaded in the apparatus through a network or recorded in a recording medium and installed in the apparatus. Recording media in any shapes, for example, CD-ROM capable of storing programs and readable by an apparatus are usable. Further, the functions that are obtained by installing or loading in advance may be those that can be realized in corporation with OS (Operating Systems), etc.

As described above, according to this embodiment, it is possible to detect a resistance value of a transferring member (an inherent resistance or an environmental change) with a high follow-up efficiency.

Further, in this embodiment, the structure to change a voltage value to fix the surface potential of a photosensitive drum based on temperature, humidity and counted value is shown but the structure is not restricted to this and can be in a structure, for example, to reset the surface potential for the second detection of a resistance value of intermediate transferring member based on the measured resistance obtained by the first detection of a resistance of the intermediate transferring member.

Further, in this embodiment, a surface potential value of the photosensitive drum is determined based on the result in either environment detection step S101or count step S103but the surface potential value of the photosensitive drum may be decided based on the results in both steps.

This invention is explained above in detail in a specific aspect but it is obvious that various changes and modifications may be made in the invention without departing from the spirit and scope thereof.

According to this invention as described above in detail, it is possible to provide a technology capable of detecting resistance values of intermediate transferring members at a stabilized sensitivity and contributing to the improvement of image quality in the image development irrespective of influence of environment and disturbance.