Typewriting machines – Sheet or web – Including skew correction responsive to position of sheet or...
Reexamination Certificate
2000-12-19
2003-11-11
Hirshfeld, Andrew H. (Department: 2854)
Typewriting machines
Sheet or web
Including skew correction responsive to position of sheet or...
C400S582000, C400S586000, C400S596000, C400S600000, C400S630000, C400S631000, C400S625000, C400S636000, C400S637300, C400S637400, C271S227000, C271S228000, C271S236000, C271S240000, C271S242000, C271S225000, C271S243000, C271S902000
Reexamination Certificate
active
06644875
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a printing apparatus provided with a sheet conveyor mechanism, designed so that a sheet is held by means of conveyor roller pairs and delivered by means of frictional force, and a skew correcting mechanism for correcting a skew of the sheet fed skewed in the feeding direction.
BACKGROUND ART
Printing apparatuses frequently use sheet conveyor mechanisms, in which follower rollers are pressed against driving rollers so that a sheet is held between the driving rollers and the follower rollers as it is fed. The sheet conveyor mechanisms are designed to deliver the sheet by means of frictional force between the sheet and the rollers. The force for the delivery of the sheet is settled depending on the level of the force with which the follower rollers are pressed against the driving rollers.
According to one conventional printing apparatus, however, the type of sheets (standard sheets) to be normally used in the apparatus is supposed, and the level of the force of pressure contact is selected according to the sheet type. If a sheet that is thicker than standard ones is fed, the follower rollers are adapted to yield compressing shock absorbing springs. No special measures are taken to counter the use of sheets that are thinner than the standard ones.
On the other hand, many of the sheet conveyor mechanisms of the printing apparatuses are provided with stopper members for skew correction, which are located on the upper-stream side of a platen so that a skew of a sheet in the feeding direction can be adjusted by running the leading end edge of the sheet against them. This mechanism corrects the skew of the sheet by running the leading end edge of the sheet, skewed with slips between the rollers and the sheet, against the stopper members for skew correction and delivering the other side so that it runs against the stopper members with the delivery the impacted side (preceding side) stopped.
More specifically, the skew of the sheet is corrected by applying a turning moment to the sheet by means of sheet conveyor roller pairs. Primarily, however, a uniform holding force or uniform delivery force is applied to the sheet conveyor roller pairs so that the sheet can be delivered uniformly in the wide direction of the sheet. For skew correction, therefore, the holding force is adjusted so that greater slips are generated between the conveyor roller pairs and the sheet on the side where the sheet abuts against the stopper members for skew correction.
In a conventional sheet conveyor roller pair, however, one driving roller and one follower roller, which extend long in the width direction of a sheet conveyor path, are mounted on a driving shaft and a driven shaft, respectively, and the driving roller and the follower roller are opposed to each other. In consequence, the adjustment of the holding force is uniform in the width direction of the sheet, so that it is hard to obtain an appropriate holding force for adequate slips on one side and adequate feed on the other side. If the individual shafts are mounted so that they are situated at a distance of a value smaller than a set value from each other on one side and at a distance of a value greater than the set value on the other side, the sheet delivery force is greater on the shorter distance side. If the side on which the sheet delivery force is greater is coincident with the side to which adequate slips must be given, therefore, the slips are inadequate, so that there is a possibility of sheet jamming in positions for skew correction or of incomplete skew correction.
In order to correct a skew of a sheet, the sheet is expected to have a resistance high enough to stand the delivery force of the sheet conveyor roller pairs, which produce frictional force as they slide, without bending.
In the case of a sheet thinner than the standard ones or of a high-friction sheet, however, the delivery force of the sheet conveyor roller pairs is inevitably greater than the resistance of the sheet. In many cases, therefore, the sheet is bent or turned up during skew correction, so that the skew correction ends in failure. If the delivery force of the sheet conveyor roller pairs is reduced to fit the skew correction, in contrast with this, it is difficult normally to feed the sheet into a printing gap between the platen and a print head, since the resistance against the passage of the sheet in the printing gap is higher than in any other cases.
Disclosed in Japanese Utility Model Registration No. 2508855, therefore, is a printing apparatus in which soft auxiliary rollers
59
of sponge or the like are mounted individually on the respective outer peripheries of sheet feed rollers
51
(follower rollers) that are pressed against feed rollers
55
(driving rollers), as shown in FIG.
10
. In this printing apparatus, a sheet is transported with the sheet delivery force of the sheet conveyor roller pairs reduced by means of the auxiliary rollers before stoppers for skew correction are reached. Thereafter, the sheet feed rollers
51
are pressed strongly against the feed rollers
55
to squeeze the auxiliary rollers
59
so that the sheet can be transported with a great delivery force. In
FIG. 10
, numeral
52
denotes an openable cover;
53
, a shaft;
54
, a shank;
56
, a shaft;
57
, a guide;
59
, the auxiliary rollers; and
60
, sheet stopper members.
However, this arrangement can only reduce the sheet feeding force before the skew correction and restore the normal feeding force after the skew correction, and cannot be a solution when the type of the sheet and therefore the thickness of the sheet are changed or when the frictional force between the sheet and the sheet conveyor roller pairs (coefficient of friction of the sheet surface) is changed.
Many sheet conveyor mechanisms of printing apparatuses are provided with a skew correcting mechanism, which is located on the upper-stream side of the platen in the sheet feeding direction and is designed so that a skew of a sheet in the feeding direction is corrected by running the leading end edge of the sheet against stopper members of the mechanism. The stopper members are arranged so that they project above a sheet conveyor surface to intercept the sheet conveyor path only during skew correction and are evacuated from the sheet conveyor surface so that they do not hinder the transportation of the sheet in other cases.
According to a conventional skew correcting mechanism (e.g., Japanese Utility Model Registration No. 2508855, mentioned above), however, the stopper members are evacuated with a sheet held against them after the sheet is run against the stopper members to correct the skew. Therefore, the evacuation of the stopper members is incomplete, so that the transportation of the sheet after the skew correction sometimes may be hindered. This is because the sheet held against the stopper members is strongly pressed by means of the feeding force of the sheet conveyor roller pairs for feeding even in that state, the friction between the leading end of the sheet and the stopper members is great, and movable parts of a mechanism for pushing the stopper members in the feeding direction to evacuate the stopper members are subject to pinching. This trouble is liable to occur when a particularly stiff sheet or thick sheet is used.
According to the conventional mechanism, therefore, the evacuation of the stopper members requires a substantial driving force or undue operation, so that the leading end edge of the sheet may be damaged, in some cases.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a printing apparatus provided with a sheet conveyor mechanism, whereby skew correction and transportation of sheets into a printing gap can be normally performed even if the thickness and the coefficient of surface friction of the sheets varies depending on the type of the sheets. Another object is to provide a printing apparatus provided with a sheet conveyor mechanism, in which a sheet is given adequate slips on one side in the width direction ther
Kato Yoshiro
Kawasaki Makoto
Sakaino Tsuyoshi
Sato Katsuhiko
Citizen Watch Company Ltd.
Crenshaw Marvin P
Hirshfeld Andrew H.
Smith , Gambrell & Russell, LLP
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