Patent Application
20070286618
Hereinafter, embodiments of the invention will be described with reference to the drawings.
As shown in
Besides, as shown in
The rotary developing device 8A includes a first developing part 8a for supplying yellow toner, a second developing part 8b for supplying cyan toner, and a third developing part 8c for supplying magenta toner.
An exposure device 4 as an image forming unit to form an electrostatic latent image on the photosensitive drum 2 is provided below the developing device 8B and the rotary developing device 8A.
The intermediate transfer belt 3 is wound around a first to a fourth rollers 3a to 3d by a specified tensile force, constitutes a transfer belt unit 35, and is pressed to the photosensitive drum 2 by a primary transfer roller 12. A belt cleaner 14 for cleaning the intermediate transfer belt 3 is in contact with a portion of the intermediate transfer belt 3 which is wound around the first roller 3a.
The manual sheet feeder 26 provided at the side lower part of the image forming apparatus body 1 includes a pickup roller 7 to take out sheets set thereon, a paper feed roller 15 and a separation roller 16 to separate the sheets taken out by the pickup roller 7 one by one and to feed it into the image forming apparatus body 1.
The sheet sent out from the manual sheet feeder 26 is transported to a register roller pair 17. The resister roller pair 17 once stops the transported sheet, corrects the inclination of the sheet with respect to the transport direction, and has a role of causing the leading end of the sheet to coincide with the leading end of the toner image on the intermediate transfer belt 3. A secondary transfer roller 11 for transferring the toner image transferred on the intermediate transfer belt 3 to the sheet is disposed at the downstream side of the register roller pair 17 in the sheet transport direction. Besides, a density detection part 202 capable of detecting the density of an image formed on a second surface as a back surface opposite to a first surface of a sheet on which a toner image is to be transferred by the secondary transfer roller 11 is provided in the vicinity of the downstream side of the register roller pair 17.
A fixing unit 13 to heat and fix the toner image transferred on the first surface of the sheet is disposed at the downstream side of the secondary transfer roller 11 in the sheet transport direction. The fixing unit 13 includes a heat roller 13a for heating the sheet on which the toner image is transferred, and a pressure roller 13b for pressing the sheet against the heat roller 13a. The heat roller 13a is provided with a peeling plate 34 to prevent the sheet from being wound around this. A temperature detection part 33 for detecting the surface temperature of the roller surface of the pressure roller 13b is provided in the vicinity of the roller surface of the pressure roller 13b.
Although the surface temperature of the pressure roller 13b varies according to the machine type of the image forming apparatus, as an example, the temperature becomes 120° C. at the time of Ready display (printable) from a cold start, reaches 140° C. about one minute after this, and then rises to 160° C., and becomes 170° C. during continuous printing.
A discharge roller pair 30 for discharging the sheet is provided at the downstream side of the fixing unit 13 in the sheet transport direction, and a paper discharge tray 31 to receive the sheet discharged is provided at the carrying-out side of the discharge roller pair 30.
As stated above, an image forming part 900 of the embodiment includes the photosensitive drum 2, the charger 5, the developing device 8B, the rotary developing device 8A, the intermediate transfer belt 3, the cleaner 6, the fixing unit 13 and the like, and forms the toner image on the sheet.
The density detection part 202 is constructed of, for example, a line sensor or the like. The density detection part 202 detects the image density of the back side (second surface) opposite to the surface (first surface) on which an image is not printed. Specifically, the density detection part 202 detects the density of the image based on “print ratio to area” of a specified range from the sheet transport direction leading end (sheet transport direction downstream side end) of the second surface of the sheet or “reflection density” in the specified range.
Incidentally, the “specified range from the sheet transport direction leading end” here is a range which can have an influence on the winding around the pressure roller 13b in the case where a toner image is formed on the sheet, and is, for example, a range from the sheet transport direction leading end to a position spaced therefrom by about 20 mm over the whole length of the sheet in the width direction. Incidentally, the range in which the density value is sensed by the density detection part 202 can be regulated based on, for example, an elapsed time since the leading end of the transported sheet passed through the detection position of the density detection part 202.
The sheet feed detection part 203 detects the paper feeding of the sheet from the manual sheet feeder 26. Although the detection of the paper feeding can be grasped based on, for example, the paper feeding instruction from the CPU 30, a sensor is provided at the carrying-in position to the transport path of the sheet of the manual sheet feeder 26, and the paper feeding of the sheet from the manual sheet feeder 26 can also be detected.
The operation input part 23 is constructed of, for example, a touch panel display or the like, and acquires the operation input of information relating to the presence/absence of formation of an image on the second surface of the sheet, and information relating to the image formation processing to the second surface of the sheet (for example, data of the image formed on the second surface of the sheet, information indicating that the sheet is double side printed, and the like).
The image judgment part 201 judges whether the image has already been formed on the second surface of the sheet.
Specifically, in the case where the image density detected by the density detection part 202 exceeds a specified density threshold (for example, the reflection density is an OD value of 1.0 or more), the image judgment part 201 judges that the image is formed on the second surface of the sheet.
In the case where the sheet feed detection part 203 detects that the sheet is fed from the manual sheet feeder 26, the image judgment part 201 can also judge that the image is formed on the second surface of the sheet. In general, in the case where a sheet is fed from the manual sheet feeder 26 and the image formation processing is performed, especially in the case where the image formation processing is f or a normal sheet size such as A4 size, the sheet is often the back side of paper. Thus, in this embodiment, as one measure to judge whether the image is formed on the second surface of the sheet, it is also possible to use the information as to whether the paper is fed from the manual sheet feeder.
Besides, in the case where the operation input part 23 receives the operation input indicating that an image is formed on the second surface of the sheet, the image judgment part 201 can judge that the image is formed on the second surface of the sheet. Besides, in the case where the processing information acquisition part 204 acquires the information indicating that an image is formed on the second surface of the sheet, the image judgment part 201 can judge that the image is formed on the second surface of the sheet.
In the case where the image judgment part 201 judges that the image is formed on the second surface of the sheet, the image forming part 900 forms a specified image in the vicinity of the leading end of the first surface of the sheet in the sheet transport direction. Specifically, the image forming part 900 forms the specified image in a range of about 20 mm from the downstream side end of the first surface of the sheet in the sheet transform direction. The “specified image” here can be made, for example, a band-like image in which the foregoing whole specified area is made an image without spaces.
Incidentally, the operation input part 23 can also receive the operation input of information relating to the color of the sheet, and the image forming part 900 specifies the color of the sheet based on the information relating to the color of the sheet (for example, the information to specify the color of a color paper) inputted by the operation input part 23, and forms the specified image by a color in which at least one of a luminance difference, a hue contrast and a saturation contrast relative to the color of the sheet is small (that is, a color unnoticeable relative to the color of the sheet). Specifically, as the color used for the print of the specified image, for example, yellow can be named relative to the white sheet.
The image forming part 900 forms the specified image only in the case where the temperature detected by the temperature detection part 33 is lower than a specified temperature threshold. The “specified temperature threshold” here is set to, for example, such a temperature that adhesion of the sheet occurs when the temperature of the surface of the pressure roller is lower than that (for example, 140° C. when the temperature of the heat roller at the time of the fixing processing is 180° C.).
Besides, as the density of the sheet detected by the density detection part 202 becomes high, the image forming part 900 raises the density of the specified image formed on the first surface of the sheet. For example, in the case where the image density of the leading end of the back surface has an OD value of 1.0 to 1.4 in a solid black, the image forming part 900 causes the density of the specified image formed on the first surface to have an OD value of 1.0 or more in a solid black.
The CPU 30 has a role of performing various processings in the image forming apparatus, and also has a role of realizing various functions by executing programs stored in the MEMORY 32.
The MEMORY 32 is constructed of, for example, a ROM, a RAM or the like, and has a role of storing various information and programs used in the image forming apparatus.
According to the structure as stated above, since a peeling member at the pressure roller side becomes unnecessary, the winding of a sheet around the pressure roller can be prevented without causing the damage of the pressure roller due to the peeling member or the disturbance of an image due to the adhesion of toner or paper powder to the peeling member.
First, a document is set on the document transport unit 22, and a copy button of the operation input part 23 is depressed. By this, the document is transported to the document table, and is optically read by a not-shown image read device (S100). At this time, the surface of the photosensitive drum 2 is uniformly charged by the charger 5, and in the manual sheet feeder 26, the pickup roller 7 takes out the set sheet.
Next, based on the read data, it is judged whether the image density printed in a range of 20 mm from the leading end of the image print surface has an OD value of 1.0 or more (S120). In the case of the OD value of 1.0 or more, a judgment of YES is made, and exposure is started (S130).
On the other hand, at S120, in the case of the OD value of less than 1.0, a judgment of No is made, the density detection part 202 detects the reflection density of the back surface leading end of the image print surface of the sheet taken out by the pickup roller 7 (S140), and it is judged whether the detected reflection density has an OD value of 1.0 or more (image judgment step) (S150). In the case of the OD value of less than 1.0, a judgment of No is made, and advance is made to step 130. In the case of the OD value of 1.0 or more, a judgment of Yes is made, and it is judged whether the surface temperature of the pressure roller 13b detected by the temperature detection part 33 is lower than the fixing temperature of the toner by 40° C. or more (S160).
That is, for example, in the case of the machine type in which the fixing temperature of toner is 180° C., it is judged whether the surface temperature of the pressure roller 13b is 140° C. or lower. In the case where the difference between the surface temperature of the pressure roller 13b and the fixing temperature is less than 40° C., a judgment of No is made, and advance is made to S130. On the other hand, in the case where the difference between the surface temperature of the pressure roller 13b and the fixing temperature is 40° C. or more, a judgment of Yes is made, the information indicating that a specified image is to be formed on the first surface of the sheet, together with the information of the color and image density of the image to be formed, is sent (S170), and advance is made to S130.
The color of the image specified at S170 is a color in which at least one of the luminance difference, hue contrast, and saturation contrast relative to the color of the sheet is small and is a color unnoticeable relative to the sheet. For example, in the case of a white sheet, yellow toner is selected. Besides, the image density is adjusted according to the reflection density detected by the density detection part 202.
In the case where the judgment of Yes is made at S120, or the judgment of No is made at S150 or 160, in the processing at S130, the exposure device 4 irradiates light corresponding to the information read by the read device 38 onto the charged photosensitive drum 2 and an electrostatic latent image is formed.
On the other hand, in the case where the judgment of No is made at S120 and the judgment of Yes is made at S150 and 160, the information indicating that an image is to be formed on the image print surface leading end portion added at S170, together with the information of the color and density of the image, is sent to S130, and a processing of forming an electrostatic latent image, together with the information of the image read by the image read device, is performed.
The electrostatic latent image formed on the photosensitive drum 2 is sent to the developing device 8B and the rotary developing device 8A by the rotation of the photosensitive drum 2, black toner is supplied from the developing device 8B, respective toners of cyan, magenta and yellow are supplied from the rotary developing device 8A, and the development is performed (S180). The developed toner image is sent onto the intermediate transfer belt 3 by the rotation of the photosensitive drum 2 and is primarily transferred by the primary transfer roller 12, and after the transfer, the photosensitive drum 2 is optically electricity-removed by a not-shown charge remover, and the toner remaining on the photosensitive drum 2 is cleaned by the cleaner 6.
In the manual sheet feeder 26, the sheet is fed into the image forming apparatus body 1 by the paper feed roller 15 and the separation roller 16, and is sent to between the intermediate transfer belt 3 and the secondary transfer roller 11. The toner image on the intermediate transfer belt 3 is secondarily transferred to this sheet. After this transfer, the sheet is peeled off from the intermediate transfer belt 3 and is sent to the fixing unit 13, and the toner image is heated by the fixing unit 13 and is pressurized and fixed (image forming step) (S190).
The respective steps in the processing of the image forming apparatus 1 are realized by causing the CPU 30 to execute the image formation program stored in the MEMORY 32.
In this embodiment, although the description has been made while using the case where the function to carry out the invention is previously recorded in the inside of the apparatus, the invention is not limited to this, and the same function may be downloaded from the network to the apparatus, or a recording medium storing the same function may be installed in the apparatus. As the recording medium, any form may be used as long as a program can be stored and the apparatus can read, such as a CD-ROM. Besides, the function previously obtained by installation or download may be such that the function is realized in cooperation with the OS (Operating System) or the like in the inside of the apparatus.
Although the invention has been described in detail with the specific mode, it would be apparent for one skilled in the art that various modifications and improvements can be made without departing from the spirit and scope of the invention.
As described above in detail, according to the invention, it is possible to provide the technique in which the sheet jam in the fixing unit can be prevented without adding a special part, and without causing the damage of the pressure roller and the disturbance of the image due to the adhesion of toner or paper powder to the peeling member.
