Winding – tensioning – or guiding – Tension control or brake – Supply controlled
Reexamination Certificate
2000-05-12
2002-08-20
Jillions, John M. (Department: 3653)
Winding, tensioning, or guiding
Tension control or brake
Supply controlled
C242S534000, C242S545000, C242S545100, C242S563000, C242S564400
Reexamination Certificate
active
06435446
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a roll sheet conveying device adapted for use in a recording apparatus or the like, such as a printer, a facsimile equipment or a copying machine, using a sheet, such as a roll of paper or a roll of film.
2. Description of Related Art
Known recording apparatuses arranged to record an image on a roll-shaped recording medium (sheet), such as recording paper or film, while conveying the roll-shaped recording medium are generally arranged as follows.
FIG. 12
shows a sheet conveying path of a recording apparatus of the above-stated kind. Roughly speaking, the recording apparatus is composed of a roll sheet holder
100
arranged to rotatably hold a roll sheet Pr so as to feed the paper of the roll sheet Pr for recording, a sheet conveying part
110
arranged to convey the roll sheet Pr to an image forming part
130
, the image forming part
130
arranged to form an image on the roll sheet Pr while holding the roll sheet Pr sent out from the sheet conveying part
110
, a sheet delivery part
140
arranged to deliver the sheet after image formation to the outside of the apparatus, and a manual-feed conveying part
120
arranged to feed and convey a manually-fed cut sheet to the image forming part
130
.
The roll sheet Pr is rotatably held within the roll sheet holder
100
through a spool
101
, and is set within the roll sheet holder
100
with the fore end part of the roll sheet Pr pinched or nipped between paper feed rollers
103
(the fore end of the roll sheet Pr being located at a position A).
A recording operation begins with a sending-out action on the roll sheet Pr. The paper feed rollers
103
first rotate to move the fore end (leader) part of the roll sheet Pr out from the roll sheet holder
100
. After that, upon arrival of the fore end part of the roll sheet Pr at the sheet conveying part
110
, the roll sheet Pr is conveyed to the image forming part
130
by the conveying force of conveying rollers
111
and the guide of a pair of guides
113
and another pair of guides
114
. The roll sheet Pr is then wrapped around the surface of a conveying roller
131
to be further conveyed. The conveying action on the roll sheet Pr comes to a stop a predetermined period of time after the fore end of the roll sheet Pr passes a sheet delivery roller
141
.
An image forming action next begins. An image is formed by an image recording head
135
on the roll sheet Pr with the sheet held on a platen
134
. Upon completion of the image forming action, the roll sheet Pr is cut by a cutter
142
when a part of the roll sheet Pr where the image is formed reaches a path part located on the lowerstream side of the cutter
142
. With the roll sheet Pr thus cut, the image-formed part of the roll sheet Pr (an image bearing sheet) is delivered to the outside of the recording apparatus, for example, by its own weight.
The recording apparatus of the kind mentioned above, however, has presented the following problems. In starting the next image forming process continuously after one image-formed portion of the roll sheet has been cut, the fore end margin of the next image becomes too wide as much as a length C as shown in FIG.
12
. Therefore, the roll sheet cannot be considered to be effectively used.
In order to avoid this, the roll sheet Pr must be pulled back to set its fore end near to a nipping part of the sheet delivery roller
141
. Further, in the event of an attempt to convey a cut sheet by manually inserting it after image recording on the roll sheet Pr, a portion of the roll sheet wrapped around the conveying roller
131
hinders this attempt. To avoid this, the roll sheet must be pulled back (rewound) at least to a position where its fore end is on the upperstream side of a point of confluence B of the roll sheet path and the manual-feed sheet path.
Further, to facilitate replacing work on the roll sheet, the apparatus of this kind generally has the roll sheet holder
100
arranged to be drawn out from the body of the apparatus. In that case, if the roll sheet holder
100
is drawn out while the roll sheet is in a state of having been moved out from the roll sheet holder
100
, the fore end of the roll sheet would remain inside of the apparatus. Under such a condition, the replacing work on the roll sheet would become very difficult.
Then, in order to avoid this trouble, the fore end of the roll sheet must be moved back to the position A within the roll sheet holder
100
before the roll sheet holder
100
is drawn out from the body of the apparatus.
For this purpose, the apparatus must be provided with a roll sheet pullback mechanism. The roll sheet pullback mechanism is arranged to drive and rotate the conveying rollers
103
,
111
and
131
in a direction reverse to the direction of sending out the roll sheet.
However, the pullback action of the roll sheet pullback mechanism necessitates a space for allowing a redundantly pulled-back portion of the roll sheet Pr to slacken within the roll sheet holder
100
, as indicated with a two-dot-chain line in FIG.
12
. That arrangement increases the size and weight of the roll sheet holder
100
, and thus increases the size of the apparatus.
It is conceivable to solve this problem by a method of driving the spool
101
concurrently with the pullback action to wind and take up the redundantly pulled-back portion of the roll sheet Pr onto the roll of sheet. The roll-sheet winding speed, however, varies with the roll (coil) diameter of the roll sheet. This problem may be solved by measuring the roll diameter and varying the spool driving speed according to the measured diameter to make the roll-sheet winding speed constant. However, this method necessitates use of a roll-diameter measuring mechanism, a discrete spool driving mechanism and a device for control over the spool driving speed. Such a method not only makes the structural arrangement of the apparatus complex but also causes an increase in cost.
According to another conceivable method which is simpler than the above-stated method, the amount of slack of the roll sheet is measured and the roll sheet is wound up for a predetermined period of time. However, that method also necessitates use of some additional detecting mechanism.
While these methods have the above-stated shortcoming, the problem can be simply solved by setting the spool driving speed at a relatively high speed and by arranging a slip mechanism, within a spool driving mechanism, to have a slip caused to take place by a tension developed when the roll sheet is stretched beyond a prescribed torque. However, it is difficult to set the prescribed torque, because of the following reasons.
When the roll sheet is pulled out from its roll by means of the conveying roller, the roll sheet is caused to obliquely travel even by a slight unevenness of the conveying force of the conveying roller in the direction of the width of the roll sheet and/or by a slight degree of discrepancy between the axis of the roll and that of the shaft of the conveying roller.
In order to prevent the oblique travel of the roll sheet, it is necessary to apply some rotation load (roll sheet brake) to the roll sheet. The greater the braking force, the larger the effect of preventing the oblique travel is. However, in rewinding the roll sheet, the spool must be driven while overcoming the rotation load, so that the setting value of the slip torque of the spool must be increased to greater than the rotation load.
Such an arrangement causes an increase in the driving load, and thus results in unsteadiness in speed and amount of transport of the roll sheet and also in increases in size and power consumption of the motor.
Further, a problem with the spool rewinding method lies in that, in the event of occurrence of a slip between the roll sheet and its roll core, an idle rotation of the roll core takes place to eventually bring about slacking of the sheet within the roll sheet holder.
This slip takes place in cases where the roll sheet is not firmly attached to the roll core wi
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