Electrophotography – Control of electrophotography process – Responsive to number of copies or passage of time
Reexamination Certificate
1999-12-16
2001-04-17
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Responsive to number of copies or passage of time
C399S044000, C399S066000, C399S301000, C399S394000
Reexamination Certificate
active
06219496
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to an image-forming apparatus designed to form multi-colored images on a print sheet without any color shifts.
2. Background Art
Full color printers are known which are designed to form a multi-colored image by overlaying yellow, magenta, cyan, and block toner images in registration to a print sheet on a conveyer using a plurality of image-forming units placed in the direction of transport of the print sheet. In a printer of this type, misregistation between toner images will cause outlines off the toner images to be shifted from each other, resulting in reduction in image quality. In order to compensate for this shift, the printer prints the toner images on a conveyer belt and adjusts the interval between adjacent two of the image-forming units based on the images on the conveyer belt. It is, however, difficult to eliminate the shift between the toner images completely due to rises in temperature within the printer, of the conveyer belt itself, and of a belt drive shaft. Particularly, a fixing device usually generates a large quantity of heat, impinging upon the movement of the conveyer belt. Specifically, a print operation for a long time will cause the heat to be stored in a frame installed near the fixing device, thereby resulting in radiation of the heat to elevate the temperature of the conveyer belt and the belt drive shaft. When the print operation is turned off, the fixing device is placed in a standby mode so that the temperature thereof will be decreased. The on and off operations of the printer, thus, causes the temperature of the conveyer belt to be changed, which leads to a change in movement of the conveyer belt. The correction of a shift between toner images due to these thermal problems results in consumption of time in each print operation which will lead to a decrease in throughput.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide an image-forming apparatus designed to correct a belt speed for forming a multi-color image without any color shift and decrease in throughput.
According to one aspect of the invention, there is provided an image-forming apparatus which comprises: (a) a conveyer belt transporting a print sheet; (b) image-transferring units provided one for each of a plurality of primary colors, the image-transferring units being arrayed in a direction of transport of the print sheet to transfer primary-colored images to the print sheet on the conveyer belt, respectively; (c) a timer measuring an operating time of the apparatus; and (d) a control means for controlling positions where the images are formed by the image-transferring units on the print sheet conveyed by the conveyer belt based on the time measured by the timer.
According to the second aspect of the invention, there is provided an image-forming apparatus which comprises: (a) a conveyer belt transporting a print sheet; (b) image-transferring units provided one for each of a plurality of primary colors, the image-transferring units being arrayed in a direction of transport of the print sheet to transfer primary-colored images to the print sheet on the conveyer belt, respectively; (c) a timer measuring either or any more than two of an elapsed time from turning on of power or release of a sleep mode, a print-off time, and a print time; and (d) a control means for controlling a belt speed based on either or any more than two of the times measured by the timer.
According to the third aspect of the invention, there is provided an image-forming apparatus which comprises: (a) a conveyer belt transporting a print sheet; (b) image-transferring units provided one for each of a plurality of primary colors, the image-transferring units being arrayed in a direction of transport of the print sheet to transfer primary-colored images to the print sheet on the conveyer belt, respectively; (c) a timer measuring either or any more than two of an elapsed time from turning on of power or release of a sleep mode, a print-off time, and a print time; and (d) a control means for controlling an image-transferring cycle of each of the image-transferring units based on either or any more than two of the times measured by the timer.
In a tandem printer structure, the number of lines between the image-forming units (i.e., an interval between the image-forming units expressed in number of lines which can be drawn therebetween) is equal to a passage time between the image-transferring units/an image-transferring cycle (a time lag when each color image starts to be printed). The passage time between the image-transferring units is equal to an image-transferring unit-to-image-transferring unit interval/a belt speed. When a color shift is occurring, an apparent number of lines between the image-forming units is changed. Thus, the color shift may be corrected by changing any of the above terms.
According to the fourth aspect of the invention, there is provided an image-forming apparatus which comprises: (a) a conveyer belt transporting a print sheet; (b) image-transferring units provided one for each of a plurality of primary colors, the image-transferring units being arrayed in a direction of transport of the print sheet to transfer primary-colored images to the print sheet on the conveyer belt, respectively; (c) a timer measuring either or any more than two of an elapsed time from turning on of power or release of a sleep mode, a print-off time, and a print time; and (d) a control means for controlling intervals between the image-transferring units based on either or any more than two of the times measured by the timer.
According to the fifth aspect of the invention, there is provided an image-forming apparatus which comprises: (a) a conveyer belt transporting a print sheet; (b) image-transferring units provided one for each of a plurality of primary colors, the image-transferring units being arrayed in a direction of transport of the print sheet to transfer primary-colored images to the print sheet on the conveyer belt, respectively; (c) a timer measuring either or any more than two of an elapsed time from turning on of power or release of a sleep mode, a print-off time, and a print time; and (d) a control means for controlling an image transfer start timing of each of the image-transferring units based on either or any more than two of the times measured by the timer.
In the preferred mode of the invention, when a temperature of a fixing device is lower than a set temperature, the elapsed time from turning on of power or release of the sleep mode is set to zero (0), the print-off time is set to infinity, the previous print time is set to zero (0), and control of the controlling means is performed. The controlling means may also drive the conveyer belt for a constant period of time prior to a color shift detecting operation. The driving of the conveyer belt may be performed intermittently.
When the temperature of a fixing device is lower than the set temperature, a color shift detecting operation may be performed as is.
The timer has a clock circuit supported at least by a backup battery or a structure reading therein information on an external time. Based on this structure, after the power is turned on or the release of the sleep mode, the controlling means calculates the print-off time in a power-off condition from a final printing end time stored in a nonvolatile memory and performs each control.
According to the sixth aspect of the invention, there is provided an image-forming apparatus which comprises: (a) a conveyer belt transporting a print sheet; (b) image-transferring units provided one for each of a plurality of primary colors, the image-transferring units being arrayed in a direction of transport of the print sheet to transfer primary-colored images to the print sheet on the conveyer belt, respectively; (c) a timer measuring at least a print-off time and a print time; (d
Imado Susumu
Iwasaki Ryouhei
Kojima Takeo
Nakayasu Hirofumi
Armstrong Westerman Hattori McLeland & Naughton LLP
Chen Sophia S.
Fujitsu Limited
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