1. Field of the Invention
This invention relates to an image formation apparatus such as a copier or a printer and in particular to an improvement in an image formation apparatus of the type comprising a charger having a charging member in contact with or brought close to the top of a photoreceptor.
2. Description of the Related Art
In recent years, demands for miniaturizing a color image formation apparatus and devises thereof have been made as the demands of the market.
For example, a tandem image formation apparatus comprises a plurality of photoreceptors such as photoconductor drums and devices such as a charger and a developing device disposed on each of the photoreceptors. As the apparatus itself is miniaturized, a so-called cleanerless system wherein a cleaning device and a remaining toner collection device are not provided for each of photoreceptors is often adopted.
However, in this kind of cleanerless system, after transfer, remaining toner exists on a surface of the photoreceptor although a trace quantity of toner remains, and the remaining toner becomes xe2x80x9cmemoryxe2x80x9d at a next image formation time, to affect the image quality adversely.
Thus, in a related art, for example, an art has been proposed wherein a memory removal member (for example, a brush roll) is placed in an upstream of a charger member (for example, a charge brush) as a charger to disturb the remaining toner (for example, refer to JP-A-Hei.4-371975).
However, in this kind of image formation apparatus, for example, using a charger of a charging roll type, as shown in FIG. 11, a phenomenon in which random spots are produced at arbitrary points on paper or continuous points, for example, which are spots in correspondence with every rotation period of a charging roll or a photoconductor drum (P/R), are produced is observed. The spots are roughly classified into background spots (BKG spots) occurring in a background and image part spots occurring in an image part (for example, a halftone image).
Particularly, it is acknowledged that such a spot phenomenon appears noticeably at the initial use stage of first using an image formation apparatus.
Next, the production principle of such spots is estimated. For example, as shown in FIG. 12, when a foreign substance 502 such as an aggregate of a developer is deposited on a photoconductor drum 510 and enters a nip area between a charging roll 511 and the photoconductor drum 510, the foreign substance 502 portion shields an electric field and a tenting part is formed on a surface layer film portion of the charging roll 511 in which the foreign substance 502 intervenes to cause a charge failure to occur in the part corresponding to the photoconductor drum 510 portion.
At this time, if the charge failure part caused by the foreign substance 502 moves to downstream of the photoconductor drum 510 and an electrostatic latent image is formed in the charge failure part and is developed, a spot having a comparatively large diameter is produced.
On the other hand, if the foreign substance 502 is deposited, for example, on the charging roll 511 side, a continuous point is produced every rotation period of the charging roll 511.
Pursuing the production cause of such a spot phenomenon, the inventors have estimated that the main cause of producing a spot is the fact that since the developer in a developing device often coagulates particularly at the initial use stage of an image formation apparatus, the aggregate of the developer is easily deposited on a charging roll.
If the developing device is immediately used at the initial use stage of the image formation apparatus, shortage of the charge amount of the developer is prone to occur and accordingly foreign substances of an external additive, a coating agent, etc., of the developer are parted to be easily transferred to the photoreceptor side; it is estimated that this factor also becomes the cause of producing a spot.
The invention is intended for solving the above-described technical problems and it is an object of the invention to provide an image formation apparatus intended for effectively avoiding a spot phenomenon at the initial use time.
According to the invention, there is provided an image formation apparatus comprising: a photoreceptor; a charger having a charging member placed in contact with or close to the photoreceptor, the charger for charging the photoreceptor; a latent image write unit for writing an electrostatic latent image onto the photoreceptor charged by the charger; a developing device having an agitating and charging element of a developer, the developing device for rendering visible the electrostatic latent image written onto the photoreceptor with the developer; and a performance maintaining controller for executing a performance maintaining initial sequence for agitating and charging the developer uniformly to such a degree that aggregating of the developer in the developing device is at least eliminated under a condition that the image formation apparatus is first used, wherein in the performance maintaining initial sequence, a unit sequence is executed a predetermined number of times, the unit sequence comprising a charge-up mode for agitating and charging the developer in the developing device to raise the charge amount of the developer and a cleaning cycle for cleaning a foreign material of the developer transferred to the photoreceptor.
According to the invention, as shown in FIG. 1, there is provided an image formation apparatus comprising a photoreceptor 1, a charger 2 having a charging member 2a placed in contact with or close to the photoreceptor 1, the charger 2 for charging the photoreceptor 1, a latent image write unit 3 for writing an electrostatic latent image onto the photoreceptor 1 charged by the charger 2, a developing device 4 having an agitating and charging element 4a of a developer G to render visible the electrostatic latent image written onto the photoreceptor 1 with the developer G, and a performance maintaining controller 5 for executing a performance maintaining initial sequence A for agitating and charging the developer G uniformly to such a degree that aggregating of the developer G in the developing device 4 is at least eliminated under a condition that the image formation apparatus is first used.
In such technical means, the invention includes not only a form in which a single photoreceptor 1 is provided, of course, but also a tandem form in which a plurality of photoreceptors 1 are arranged and further includes various forms such as a form in which a record material transport body and an intermediate transfer body are placed to face the photoreceptor 1.
The charger 2 is required to have the charging member 2a placed in contact with or close to the photoreceptor 1.
Since it is taken into consideration that it is possible to charge by minute space discharge even in the form in which the charging member 2a is placed close to the photoreceptor 1, the form in which the charging member 2a is placed not to contact with the photoreceptor 1 is also included.
However, preferably the charging member 2a is placed in contact with the photoreceptor 1 because it is facilitated to position the charging member 2a relative to the photoreceptor 1 and the dimension accuracy of the charging member 2a need not be high.
Further, the charger 2 may basically comprise the charging member 2a, but is not necessarily be limited to this. For example, the charger 2 maybe provided with a removal member disposed in contact with the photoreceptor 1 in upstream of the charging member 2a, the removal member for removing the deposit on the photoreceptor 1.
The removal member may be of contact type for removing the deposit on the photoreceptor 1 or may temporarily remove the deposit on the photoreceptor 1; the removal member may serve as a functional member for eliminating a situation in which the deposit on the photoreceptor 1 arrives at the charging member 2a and holding a good charge property.
The developing device 4 is mainly intended for a developing device using a dual-component developer, but is not necessarily be limited to this.
In this case, the developer G, which is a spherical toner having a form factor of 130 or less, may be used from the viewpoint of easily providing high image quality and a cleanerless system.
Further, the agitating and charging element 4a of the developing device 4 may be any element for agitating and charging a developer and may be an agitating member such as so called an auger, a charge bias with an AC component superposed (in a developing area, the developer alternation-operates to be agitated and charged), etc.
An appropriate apparatus may be selected as the performance maintaining controller 5 if the apparatus can execute the performance maintaining initial sequence A.
The expression xe2x80x9csuch a degree that aggregating of the developer G in the developing device 4 is at least eliminatedxe2x80x9d means that aggregating of the developer G, which is the main cause of the spot phenomenon at the initial use time, may be eliminated by executing the performance maintaining initial sequence A.
The expression xe2x80x9cat leastxe2x80x9d is used to assume that ejecting (corresponding to a cleaning cycle) of a foreign substance of the developer, such as an external additive or a coating agent, which are another main cause of a spot phenomenon at the initial use time, or the like is also contained.
Further, the requirement xe2x80x9cagitating and charging the developer G uniformlyxe2x80x9d is based on the fact that not only charging, but also agitating is required to eliminate aggregating of the developer G.
A representative form of the performance maintaining initial sequence A executed by the performance maintaining controller 5 is to execute a predetermined number of times a unit sequence comprising a charge-up mode for agitating and charging the developer G in the developing device 4 to raise the charge amount of the developer G and a cleaning cycle for cleaning a foreign material of the developer G transferred to the photoreceptor 1.
In this case, mainly, the xe2x80x9ccharge-up modexe2x80x9d corresponds to agitating and charging the developer and the xe2x80x9ccleaning cyclexe2x80x9d corresponds to the ejecting of the foreign substances of the developer such as an external additive.
Particularly, in the form in which the developing bias with an AC component superposed is applied to the developing device 4 in an image formation mode, preferably the performance maintaining controller 5 applies at least a charge bias with an AC component superposed to the developing device 4 in the charge-up mode.
In this case, charging up the developer G is promoted by the charge bias with an AC component superposed and ejecting foreign substances in the developer G is also promoted.
The charge bias may be any charge bias so long as superposed an AC component and may be set the same as or different from the developing bias.
If the user opens interlock by mistake, for example, while the performance maintaining initial sequence A is executed, and the apparatus itself shuts down accordingly, a situation in which the performance maintaining initial sequence A is interrupted can occur.
As a preferred form in such a circumstance, the performance maintaining initial sequence A executed by the performance maintaining controller 5 may make it possible to store an incomplete sequence process if the performance maintaining initial sequence A is interrupted at a midpoint and restart the performance maintaining initial sequence A from the midpoint.
According to the form, fruitless repeating the performance maintaining initial sequence A can be avoided.
The performance maintaining controller 5 may be any as long as it executes the performance maintaining initial sequence A; it may also execute a performance maintaining sequence B in addition to the performance maintaining initial sequence A.
For example, in addition to the performance maintaining initial sequence A, the performance maintaining controller 5 may execute the performance maintaining sequence B for uniformly agitating and charging the developer G in the developing device 4 at least based on elapsed time since the immediately preceding image formation mode.
The performance maintaining sequence B is executed to improve a phenomenon in which the charge performance of the developer G is degraded in correspondence with leaving time, and to avoid degradation of the image quality.
In this case, as the performance maintaining sequence B, it is common practice to the unit sequence including a charge-up mode and a cleaning cycle a predetermined number of times, but the performance maintaining sequence B is not limited to this.
Further, a measuring unit for measuring xe2x80x9cthe elapsed time since the immediately preceding image formation modexe2x80x9d may be a unit for measuring based on the power on time, but preferably the measuring unit can continuously measure the elapsed time when the power is off from the viewpoint of more precisely measuring the elapsed time.
In the form, preferably the performance maintaining initial sequence A involves the charge-up mode degree distributed larger than that of the performance maintaining sequence B.
According to this form, the spot phenomenon can be avoided more reliably because the charge property of the developer G can be provided more reliably at the initial use time.
At this time, the expression xe2x80x9cthe charge-up mode degree distributed largerxe2x80x9d includes prolonging the charging time itself, enhancing the charging degree itself of the developer G, or a combination both.
A preferred form of the performance maintaining sequence B may be taken an environmental condition into consideration.
In this case, the performance maintaining sequence B may be to uniformly agitate and charge the developer G in the developing device 4 based on the elapsed time since the immediately preceding image formation mode and the environmental condition of the image formation apparatus.
The expression xe2x80x9cthe environmental condition of the image formation apparatusxe2x80x9d may be a humidity condition largely affecting the performance of the developer G, but is not limited to this. An ambient temperature condition, temperature and humidity conditions, etc., maybe selected whenever necessary.
As a representative determination technique as to xe2x80x9cthe condition that the image formation apparatus is first used,xe2x80x9d for example, in a form in which a process cartridge that can be attached to and detached from the main unit of the image formation apparatus is installed, an identifier indicating that the process cartridge is unused may be provided and the performance maintaining controller 5 may determine whether or not the image formation apparatus is first used based on the identifier information of the process cartridge to execute the performance maintaining initial sequence A.
The expression xe2x80x9cthe process cartridge is unusedxe2x80x9d means not only a new product, but also a product unused in a wide sense including a recycled product.
On the other hand, the identifier means an unused flag, etc., previously written into a monitor in the process cartridge, for example.