Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2001-12-26
2003-10-28
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S232000, C347S243000, C349S045000
Reexamination Certificate
active
06639616
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine and a printer. More specifically, the present invention relates to an image forming method that is applied to the apparatus and relates to an apparatus for performing image formation by converting light to scanning light using a reflective polyhedron.
2. Description of the Related Art
Conventionally, there have been known two methods as an image forming method for obtaining a color image on a sheet material by superimposing toner images of a plurality of colors. One is a method of forming electrostatic latent images on an image bearing member, sequentially developing them by toner to transfer them to a sheet material each time they are developed and superimposing toner images of a plurality of colors on the sheet material (hereinafter referred to as multiple transfer method). The other is a method of superimposing toner images of a plurality of colors on an image bearing member or an intermediate transfer member and transferring the superimposed toner images of a plurality of colors collectively to a sheet material (hereinafter referred to intermediate transfer method).
Among them, the former method is put to practical use with structures described in DE2607727, Japanese Patent Application Laid-open No. Sho 50-50935 and the like.
On the other hand, the latter method is a technology having advantages such as a simple structure and currently drawing attention, although it has problems of color mixture at the time of development and image deterioration at the time of re-transfer.
Moreover, in recent years, a so-called tandem type multiple transfer method, which is capable of forming a full color image using one path by providing process units such as a photosensitive member and a developing device independently for each color, begins to draw attention in terms of high-speed productivity.
In any of the methods, toner images T of a plurality of colors formed and superimposed on a sheet material
103
are finally heated and fixed by a fixing device that uses a roller or a belt as shown in FIG.
8
. As a result, toner images of each color are mixed and a full color image can be obtained.
FIG. 8
is a schematic view of a fixing device that is used in the conventional image forming apparatus.
An example of a fixing device of this type by a heat roller method will be hereinafter described with reference to FIG.
8
. In
FIG. 8
, a fixing roller
101
is for melting to fix the toner T on the sheet material
103
by heating and application of pressure. A pressure roller
102
, which is disposed opposing the fixing roller
101
, is for applying pressure to the fixing roller
101
.
Usually, the fixing roller
101
often has a structure to be heated by a heater
104
such as a halogen lamp from the inside of the roller.
Therefore, it is a general practice to monitor a surface temperature of the fixing roller
101
by a temperature sensing element
114
such as a thermistor to on/off control the heater
104
, thereby performing temperature control.
In addition, as the toner T, toner of four colors of yellow, cyan, magenta and black is generally used.
In this case, silicone oil
106
or the like is applied to the surface of the fixing roller
101
by a blade
105
via a drawing roller
116
and an applying roller
115
in order to prevent offset. Alternatively, toner originally containing wax or oil component is used to prevent offset.
In addition, the surface of the fixing roller
101
may be cleaned by a cleaning web
107
or the like, if necessary.
Incidentally, in the case in which a transparent film for an over-head projector (hereinafter referred to as OHP (over-head projector) sheet), a sheet for realizing high gloss (hereinafter referred to as high gloss paper or high gloss sheet) or the like is used, a method of giving it a heat quantity larger than that required for fixing an image on a normal transfer sheet to perform fixing and realizing desired transparency and glossiness is often used.
As a method for this purpose, for example, it is possible to increase a heat value of the heater
104
incorporated in the fixing roller
101
. However, with this method, a sufficient heat quantity is not obtained in many cases and it takes long to make a temperature of the fixing roller
101
follow. Thus, this method cannot always be effective.
As another method, there is a method of reducing a fixing speed by the fixing roller
101
to give a sufficient heat quantity to a sheet. With this method, a desired heat quantity is easily obtained and, at the same time, it is possible to execute fixing immediately without providing a waiting time because it is unnecessary to change a temperature setting of the fixing roller
101
itself.
However, if reduction in a fixing speed is attempted as described above, a sheet exists on a transfer portion and a fixing portion simultaneously unless a distance between the transfer unit and the fixing unit is sufficiently large as compared with a maximum sheet length of a sheet to be used (in case of an intermediate transfer member, unless a distance between a primary transfer unit and a secondary transfer unit is sufficiently large as compared with the maximum sheet length) in case of the above-mentioned multiple transfer method.
Consequently, a fixing speed cannot be reduced after toner images of final colors are formed on a photosensitive member until all toner images are transferred to the sheet.
That is, it has become necessary to additionally rotate a transfer drum or an intermediate transfer member. In this case, a printing time is substantially extended
Moreover, in recent years, a so-called quadruple multiple transfer method using photosensitive members for four colors draws attention as a high-speed full color printing method. In this method, decelerated fixing cannot be performed with a machine in which a distance between portions for transferring and fixing final color is shorter than a maximum sheet length unless the machine is put in a decelerated state in advance from the time when an image is formed on a photosensitive member. (It is needless to mention that, in the above-mentioned multiple transfer or intermediate transfer member method, it is also possible to perform the same method as described below instead of rotating the transfer drum or the intermediate transfer member additionally.)
That is, in an image forming apparatus with a short distance between a transfer unit and a fixing unit, it becomes necessary to perform image formation in a decelerated state in advance in order to avoid shock caused by reducing a fixing speed during image formation.
Nevertheless, the applicants and the like found, as a result of examining a laser printer of a method of deflecting a laser beam irradiated from a light source by a reflective polyhedron (e.g., polygon mirror) to scan a member to be scanned such as a photosensitive member by the deflected laser beam, that a laser beam quantity became excessive and deficiencies such as tendency of image block-up and defective middle tones were caused if image formation is performed in a decelerated state (e.g., at a half speed of a standard speed) in the laser printer.
Thus, it became necessary to reduce a laser beam quantity in the decelerated state. However, it was difficult to steadily realize a significant change of a light amount such as reducing it to half or one third as in this example using a laser beam emitting circuit.
In addition, it took long to change a speed of a polygon mirror and a process speed could not be changed promptly.
There is known a method of making predetermined surface unused among all surfaces of a polygon mirror instead of reduction of a laser beam quantity.
This method is a so-called thinning-out scanning for thinning out the number of surfaces to be used of a polygon mirror to use them and substantially reducing a laser beam quantity, which is recognized as a publicly-known technology. Further, thinning out one surface of reflective surfaces of a p
Enomoto Naoki
Takeuchi Akihiko
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Pendegrass Joan
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