Printing – Print plate feeding or delivering
Reexamination Certificate
1999-10-25
2001-03-27
Eickholt, Eugene (Department: 2854)
Printing
Print plate feeding or delivering
C101S409000, C271S082000, C271S307000
Reexamination Certificate
active
06205924
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a sheet unloading apparatus for a rotary drum rotatable in one direction along with a sheet which is wound around a peripheral surface of the rotary drum.
Jpn. Pat. Appln. KOKAI Publication No. 10-138520 discloses a rotary drum ink-jet printer which can print a large number of pages in a short period of time. The rotary drum ink-jet printer comprises a rotary drum rotatable in one direction and a print head for printing an image on a paper sheet wound around the rotary drum and rotated along with the rotary drum. The print head has a plurality of ink-jet nozzles arranged in a line across a paper sheet in the axial direction of the rotary drum. The print head jets ink through the ink-jet nozzles to the paper sheet which moves relative to the print head as the rotary drum rotates. This structure allows high-speed print, since it does not require that the print head move across the paper sheet as in the conventional serial ink-jet printer.
In general, a paper sheet is held on the rotary drum by a combination of vacuum attraction, electrostatic attraction, mechanical engagement, etc. Jpn. Pat. Appln. KOKAI Publication No. 10-193719 discloses a technique of mechanically engaging the front and rear ends of an externally supplied paper sheet on the peripheral surface of a rotary drum to prevent positional deviation of the paper sheet. According to this technique, engagement grooves are formed in the peripheral surface of the rotary drum at positions corresponding to the front and rear ends of the paper sheet. The front and rear ends of the paper sheet are engaged in the engagement grooves by clamping claws. The technique of engaging the rear end of a paper sheet is also disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-329375.
In the rotary drum ink-jet printer, at the time of unloading the paper sheet, the front end of a paper sheet is separated from the drum by a separation pawl which is brought into contact with the rotary drum, and then guided to a pair of pinch rollers. These pinch rollers are disposed near the rotary drum to pinch the front end of the paper sheet in a state where the rear end thereof is engaged in the engagement groove, and rotate in one direction at the same circumferential speed as the circumferential speed of the rotary drum to feed out the pinched paper sheet.
However, since the shapes of the engagement grooves and the rigidity of the paper sheet are determined to gain sufficient sheet holding force, it is possible that the rear end of the paper sheet may not be removed from the engagement groove by the sheet pulling force of the pinch rollers. If the rotary drum is further rotated together with the paper sheet whose the rear end is engaged in the engagement groove, the paper sheet will be pulled out of the pinch rollers in the reverse direction and wound around the rotary drum inside out, causing a paper jam. This problem can be overcome by increasing the rotation speed of the pinch rollers. However, since the paper sheet is easily waved by shock resulting from a difference in circumferential speed between the rotary drum and the pinch rollers, it is necessary to change the circumferential speed of the pinch rollers after the rear end of the paper sheet passes by the print head for printing an image on the paper sheet. This change of speed requires a complicated structure for a pinch roller driving circuit, resulting in an increase in cost, restriction on the layout and an increase in power consumption. Further, it is not easy to determine the optimal speed of the pinch rollers, which provides sheet pulling force slightly greater than the sheet holding force on the rotary drum. If the shape of the engagement grooves, such as the depth or the slope angle, or the rigidity of the paper sheet is to be changed, the optimal speed must be reset in accordance with such a change.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a sheet unloading apparatus which can reliably unload a sheet from the rotary drum without being considerably affected by holding force for holding the sheet on the rotary drum.
According to the present invention, there is provided a sheet unloading apparatus for a rotary drum rotatable in one direction along with a sheet which is wound around a peripheral surface of the rotary drum and at rear end mechanically engaged in an engagement groove formed in the peripheral surface, comprising: a separation pawl for separating a front end of the sheet from the rotary drum by contacting the peripheral surface of the rotary drum while the rotary drum rotates in the one direction; and a pair of pinch rollers for rotating to pinch and feed out the sheet supplied according to rotation of the rotary drum in a state where the front end of the sheet is separated from the rotary drum by the separation pawl and the rear end of the sheet is engaged in the engagement groove, the sheet unloading apparatus further comprising a removal assisting mechanism for assisting the sheet to be pulled out from the engagement groove by bending the sheet spanning between the rotary drum and the pair of pinch rollers.
In the sheet unloading apparatus, the removal assisting mechanism assists the sheet to be pulled out from the engagement groove by bending the sheet spanning between the rotary drum and the pair of pinch rollers. In this case, the sheet pulling force can be increased without requiring an increase in the circumferential speed of the pinch rollers. Such sheet pulling force has less dependence on the sheet holding force of holding the sheet on the rotary drum than in the case where the circumferential speed of the pinch rollers is changed. Therefore, the sheet can be reliably separated from the rotary drum without being considerably affected by the sheet holding force.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: 1515791 (1924-11-01), Redner
patent: 4401382 (1983-08-01), Minejima et al.
patent: 5296874 (1994-03-01), Nagata et al.
patent: 5323699 (1994-06-01), Mutoe et al.
patent: 5553543 (1996-09-01), Takahashi et al.
patent: 5623871 (1997-04-01), Takahira
patent: 5802434 (1998-09-01), Takehara et al.
patent: 10-138520 (1998-05-01), None
patent: 10-186867 (1998-07-01), None
patent: 10-193719 (1998-07-01), None
patent: 10-329375 (1998-12-01), None
Eickholt Eugene
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Toshiba Tec Kabushiki Kaisha
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