Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-07-24
2003-08-05
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06601946
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus applied to a printing unit of a digital copying machine, a facsimile or the like as well as to a digital printer, a plotter or the like, for forming an image on a recording medium by jetting a developer.
2. Description of the Background Art
Recently, an image forming apparatus has been proposed which outputs image signals as a visible image on a recording medium such as a sheet of paper, as described, for example, in Japanese Patent Laying-Open No. 4-286662. In the apparatus, an electric field is exerted on charged particles so that the particles are jet out by electric force, and the charged particles reach and adhere to the recording medium, as a potential applied to a control electrode including a plurality of through holes arranged in the jet travel path is changed. In this manner, an image is directly formed on the recording medium. In addition, the control electrode is driven by a driver, and a developer removing electric field is formed in the through holes of the control electrode, whereby the developer left in the through holes of the control electrode is removed.
In the conventional image forming apparatus having the above described structure, means for controlling passage of charged particles through a gate is used. In such an image forming apparatus, whether charged particles (toner) are allowed to jet out or not is controlled by controlling an electric field generated between the gate and a tone carrier, and, by a strong electric field generated by an opposing electrode, the toner is attracted to reach the surface of the sheet, which is the recording medium.
In the above described image forming apparatus, the toner inevitably adheres on the control electrode. The toner adheres not only to the surface of the control electrode facing the carrier but also the inside of the gate through which toner passes and to that side of the control electrode which faces the opposing electrode. Adhesion of toner causes various problems.
For example, the potential to be applied to the control electrode is shielded by the toner. In addition, the potential of the control electrode varies because of the potential caused by the charges held by the toner. More specifically, the potential is changed to a state which does not allow jetting of toner, resulting in unsuccessful toner jetting. As jetting of the toner is not satisfactory, resulting dots may have their diameters varied, and density inappropriate, readily resulting in degraded image quality.
Further, in such a state, a desired electric field cannot be generated around the gate, and therefore the course of travel of the jetting toner considerably deviates from a satisfactory course, and therefore it becomes difficult to control the course of travel of the jetting toner. Under such condition, it is difficult to guide the toner to a prescribed position. As a result, scattering of the toner is apt to occur, degrading quality of resulting dots, and, as already mentioned above, the diameters and densities of the dots may vary.
In such a situation, image formation of desired halftone is difficult, and satisfactory color reproduction is difficult in a color image forming apparatus. Further, if adhesion of the toner to the control electrode takes place in the gate which is the passage for the toner, it hinders passage of the toner through the gate, so that a prescribed amount of toner cannot pass through the gate, resulting in the above described problems. Further, the course of travel of the jetting toner changes by contact between the passing toner and the toner adhered to the inside of the gate, or by an electric field generated by the charges held by the toner adhered inside the gate. Therefore, satisfactory control of the course of travel of the jetting toner becomes difficult as in the above, resulting in similar problems. In addition, excessive adhesion of the toner to the control electrode eventually causes clogging of the gate. This physically prevents passage of the toner, readily resulting in unsatisfactory image formation or blank.
If a portion of the sheet should contact the control electrode because of a wrinkle or curl of the sheet, the toner adhered on the control electrode on the opposing electrode side touches and stains the sheet. Further, it may tarnish the formed image.
Now that adhesion of the toner to the control electrode is unavoidable and the adhered toner causes various problems, it is necessary to clean the control electrode of the adhered toner. In the conventional image forming apparatus as represented by the one described above, an AC potential is applied to the control electrode to form a cleaning electric field, which is an AC electric field having a DC component between the control electrode and the opposing electrode or the carrier to remove the toner.
However, the toner contains not only the toner of a desired charge polarity but also toner having the charge polarity opposite to the desired polarity. It is possible by the method of cleaning toner represented by the above described prior art to remove the toner having a prescribed charge polarity (hereinafter referred to as positively charged toner). It is difficult, however, to remove the toner having charge polarity different from the positively charged toner (hereinafter referred to as negatively charged toner).
In order to remove the negatively charged toner, it is necessary to reverse the polarity of the DC component in the cleaning electric field, and, in that case, it becomes difficult to clean the positively charged toner. Accordingly, what is possible by the cleaning electric field is only to remove the toner of one polarity, and simultaneous cleaning of the toners having opposite polarities has been difficult. Therefore, toners of respective charge polarities have to be cleaned separately. If cleaning is done in an interval of paper feeding, the time required is twice as long as that necessary for cleaning toner having single polarity. This time requirement makes it difficult to shorten the interval between paper feeding, and hence hinders improvement in speed of printing.
SUMMARY OF THE INVENTION
The present invention was made to solve the above described problems, and its object is to provide an image forming apparatus capable of high speed printing.
Another object of the present invention is to provide an image forming apparatus capable of high speed printing ensuring highly effective cleaning and free of image degradation.
Another object of the present invention is to provide an image forming apparatus capable of high speed printing, reduction in number of parts, reduction in size and cost, and improvement in reliability.
The image forming apparatus in accordance with an aspect of the present invention includes a toner carrier for carrying toner, an opposing electrode arranged opposing to the toner carrier, a high voltage power source unit for supplying a voltage to generate potential difference between the toner carrier and the opposing electrode, a control electrode including a plurality of electrodes arranged between the toner carrier and the opposing electrode, and a control power source unit for implementing a plurality of potential states of respective electrodes of the control electrode, the control electrode including an insulating substrate, the aforementioned plurality of electrodes each having a passage portion for the toner provided on the insulating substrate, and a dielectric layer formed on the side of the opposing electrode such that attracting force Fc exerted on the toner adhered on that surface of the control electrode which faces the opposing electrode is made smaller than attracting force Fb exerted on the toner adhered on the opposing electrode, and the control power source unit including an image forming unit for applying prescribed potentials to respective ones of the plurality of electrodes to control passage of the toner through the passage portion for forming an image on a surface of a recording medi
Fujita Hirokazu
Nishio Yukihito
Takai Yasuhiro
Wakahara Shirou
Barlow John
Conlin David G.
Daley, Jr. William J.
Edwards & Angell LLP
Gordon Raquel Yvette
LandOfFree
Image forming apparatus in which toner is removed by... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image forming apparatus in which toner is removed by..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus in which toner is removed by... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3117294