Curl correction apparatus

This invention relates to a curl correction apparatus comprising holder means for holding a rolled sheet material; transport means for transporting the sheet material housed in said holder means; a curl correction member positioned between said holder means and said transport means and adapted to guide said sheet material in a curved state for correction of the curl thereof; a guide member contacting a face of said sheet material opposite to the face guided by said curl correction member and serving to guide said sheet material to said curl correction member; and moving means for moving at least one of said curl correction member and said guide member according to the amount of said sheet material remaining in said holder means.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a curl correcting apparatus for correcting 
curling of a rolled sheet material. 
2. Related Background Art 
The recording system of various office equipment such as a facsimile or 
printer generally employs a continuous web-shaped recording sheet wound in 
a roll form. 
Because of the rolled form, the sheet material tends to show curling. For 
this reason there have been proposed technologies for removing or reducing 
said curling. 
As an example of said technologies, FIG. 23 illustrates a curl eliminating 
apparatus, in which a main body 1 and a cover 2 are mutually articulated 
movably by a pin 3. In the main body 1 there are provided a roll holder 4, 
a platen roller 5, a cutter 6 and a guide member 7a constituting the curl 
eliminating device, while the cover 2 holds a recording head 8 and a guide 
member 7b constituting the curl eliminating device in cooperation with the 
guide member 7a. Said roll holder 4 supports a roll 9a of the sheet 
material 9. 
The sheet material 9 fed from said roll 9a is transported by the platen 
roller 5, and the curl is removed in passing an acute angled path formed 
by the guide members 7a, 7b. Then the sheet is subjected to image 
formation by the recording head 8, cut by the cutter 6 and discharged from 
the apparatus. 
In the conventional structure shown in FIG. 23, the sheet material 9 
remains bent between the guide members 7a, 7b in the stand-by state of the 
apparatus. Thus the sheet material 9 between said guide members 7a, 7b 
generates curling in a direction opposite to that generated by winding, 
and such curling may give rise to troubles such as sheet jamming. Also the 
guide members 7a, 7b of fixed angle may be unable to adequately remove the 
curling which varies according to the diameter of the roll 9a . 
FIG. 24 illustrates another example of the already proposed curl removing 
apparatus. The clockwise rotation of the platen roller 5 is transmitted, 
through a frictional clutch, to a guide shaft 10 and arms 11 provided on 
both ends of said shaft 10. At the outer end of the arms 11, there is 
rotatably supported a curl correction shaft 12. In predetermined positions 
of the main body 1, there are fixed stoppers 13, 14 for limiting the 
movement of the arms 11, which is constantly biased toward the stopper 13 
by means of a spring. 
The sheet material 9 is transported by the platen roller 5, of which 
rotation is transmitted to the guide shaft 10 thereby rotating the arms 11 
clockwise. When the arms 11 impinge on the stopper 14, the rotation of the 
arms 11 is stopped by the slippage of the frictional clutch. The sheet 
material 9 is bent in acute angle in a path from the roll 9a, through the 
guide shaft 10, to the curl correction shaft 12 for curl correction, and 
is then transported to the platen roller 5. 
When the rotation of the platen roller 5 is terminated, the arms 11 rotate 
anticlockwise by the biasing force of the spring and returns to the 
position in contact with the stopper 13. 
In this conventional structure, the curling on the sheet material 9 is 
removed by the guide shaft 10 and the curl correction shaft 12 mounted on 
the arms 11 rotated by the transportation of the sheet material 9. 
In the conventional structure shown in FIG. 24, in loading a new roll 9a in 
the roll holder 4, the leading end of the sheet material 9 has to be 
threaded between the guide shaft 10 and the curl correction shaft 12, so 
that a cumbersome some operation is required. Also the sheet material 9 
subjected to curl correction by the shaft 12 shows a large wrapping angle 
on the platen roller 5, thus eventually developing curl again. Also in the 
standby state of the apparatus, the sheet material 9 hangs down between 
the platen roller 5 and the roll 9a, thereby curl opposite to the curl of 
rolling. Also the main body 1 has to be made larger in order to 
accommodate the rotation of the arms 11 about the guide shaft 10 for curl 
correction of the sheet material 9. 
Also the curl correction apparatus disclosed in the Japanese Patent 
Laid-open No. 55-15381 is associated with a drawback of curl generation 
opposite to the curl by rolling, since the sheet material remains bent for 
curl correction in the stand-by state of the apparatus. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a curl correction 
mechanism capable of adequately correcting the curl of a sheet material 
varying according to the diameter of roll, and a recording apparatus 
equipped with such mechanism. 
The above-mentioned object can be achieved, according to the present 
invention, by a curl correction mechanism provided with transport means 
for transporting a sheet material; a guide member for guiding said sheet 
material; a curl correction member for guiding said sheet material through 
a bent path; moving means for moving at least one of said guide member and 
said curl correction member; and biasing means for biasing said moving 
means in such a direction as to increase the bend of the sheet material. 
In another structure, there are provided transport means for transporting 
the sheet material; a curl correction member positioned in the upstream 
side of said transport means in the transport direction of the sheet 
material for guiding said sheet material; and a guide member positioned in 
the upstream side of said curl correction member in the transport 
direction of the sheet material, for guiding said sheet material which is 
moved by interaction of the tension on said sheet material and the power 
transmitted thereto. 
Also there is preferably provided retracting means composed of a rotatable 
member supporting the curl correction member or a moving member for moving 
said curl correction member in relation to the opening motion of the 
cover. 
The above-mentioned recording apparatus is featured by recording means for 
forming an image, in response to image signal, on a sheet material 
transported by the transport means, and said curl correction mechanism 
positioned in the upstream side of said recording means in the transport 
direction of the sheet material. 
In the above-explained structure, the curl correction member is positioned 
in the upstream side of the transport means, for transporting the sheet 
material, in the transport direction thereof and the guide member is 
positioned in the upstream side of said curl correction member and is 
rendered movable by the interaction of the tension on said sheet material 
and the power for moving said guide member, so that the curling of the 
sheet material can be corrected according to the tension acting on said 
sheet material. 
The curl developed in a rolled sheet material generally depends on the 
diameter of roll, becoming stronger as the roll diameter decreases. 
On the other hand, the tension on the sheet material depends on the contact 
friction between the rolled sheet material and the holder supporting said 
roll. For a larger roll diameter, the tension is higher because of the 
larger roll weight, and the tension is smaller for a smaller roll 
diameter. 
While the sheet material is transported by said transport means, the power 
of the drive means is transmitted to the guide member, which is therefore 
moved and brought into contact with the transported sheet material. The 
guide member continues to move after contacting the sheet material, and 
stops at a position where the moving force for the guide member balances 
with the synthesized tension on the sheet material. Consequently the 
amount of movement of the guide member varies according to the tension 
applied to the sheet material. 
When the guide member stops as explained above, the sheet material is wound 
around the guide member and the curl correction member, in a direction 
same as the direction of curling around the guide member and opposite to 
the direction of curling around the curl correction member, so that the 
curling of the sheet material is corrected by wrapping around said curl 
correction member. 
The amount of wrapping of said sheet material around the curl correction 
member varies according to the amount of movement of the guide member. 
More specifically, when the sheet material is under a higher tension, the 
guide member moves less and the wrapping amount of the sheet material on 
the curl correction member becomes less, so that the corrective action on 
the sheet material is reduced. On the other hand, when the sheet material 
is under a lower tension, the guide member moves more to increase the 
wrapping amount of the sheet material on the curl correction member, 
thereby increasing the corrective action on the sheet material. 
If the curl correction member is made retractable from the working position 
by the opening of the cover, even when the guide member and the curl 
correction member are involved in the sheet jamming developed in the 
course of curl correction, the disposal of such sheet jamming can be 
easily made by retracting the curl correction member by opening the cover. 
Also the loading of the roll is facilitated since the curl correction 
member is retractable from the working position by the opening of the 
cover and the threading of the leading end of the sheet material through 
the curl correction member is not necessary. 
Furthermore it is rendered possible to correct the curling of the sheet 
material in a recording apparatus by incorporating said curl correction 
mechanism in the apparatus, and to reduce the possibility of troubles such 
as sheet jamming, resulting from the curling of the sheet material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, the present invention will be clarified in detail by embodiments 
thereof applied in a recording apparatus. 
FIG. 1 is a schematic perspective view of a recording apparatus; FIGS. 2A 
and 2B are views showing the principle of curl correction; FIGS. 3A and 3B 
are partial magnified views thereof; FIG. 4 is a schematic view of curling 
of a sheet material; and FIG. 5 is a chart showing experimental results. 
At first there will be briefly explained the structure of the recording 
apparatus. 
A cover 2 is rotatably articulated by a shaft 3 on a main body 1, and is 
made engageable with the main body 1 by a click mechanism (not shown). In 
a rear part of the main body 1 there is provided a roll holder 4, in which 
a roll 9a of sheet material 9 such as plain paper or thermal recording 
paper is loaded. The sheet material 9 extracted from the roll 9a goes 
around a guide shaft 21 constituting the guide member and a curl 
correction shaft 22 constituting the curl 10 correction member, and is 
transported by a platen roller 5. A recording head 8, mounted on the cover 
2 by means of a compression spring 8a, is maintained in pressure contact 
with said platen roller 5. An image is formed on the sheet material 9 by 
driving the recording head 8 according to image signals supplied from a 
control unit (not shown) while the sheet material 9 is transported by the 
platen roller 5. After said image formation, the sheet material 9 is cut 
by a cutter 6 and discharged from the apparatus. 
In the above-explained structure, the curl of the sheet material 9 is 
corrected by the wrapping thereof around the curl correction shaft 22. The 
amount of movement of the guide shaft 21 varies according to the weight of 
the roll 9a loaded in the roll holder 4, thereby varying the angle .theta. 
of the sheet 9 around the curl correction shaft 22. If said angle .theta. 
is larger, or the wrapping amount of the sheet 9 on the curl correction 
shaft 22 is larger, the curl correcting effect becomes smaller, and vice 
versa. 
In the following there will be explained various parts of the apparatus. 
The roll holder 4 is shaped as a polygon open on the top, and is positioned 
in the rear part of the main body 1. A part of the wall of said roll 
holder 4 at the side of platen roller 5 is folded to constitute a stopper 
4a for an arm 27 to be explained later. The roll 9a is loaded in the roll 
holder 4, and a frictional resistance is generated by the contact between 
the external periphery of said roll 9a and the internal wall of said roll 
holder 4. Said frictional resistance is large when the roll 9a is large in 
diameter and heavy, but decreases as the roll 9a becomes lighter. 
Said stopper 4a is constructed in such a manner that, when in contact with 
a contactor 27b of the arm 27, the angle .theta. of the sheet material 9 
around the curl correction shaft 22 becomes about 30.degree. by the 
function of a guide shaft 21 mounted on said arm 27. 
The platen roller 5 is driven by a motor 23 such as a stepping motor. The 
rotation of said motor 23 is transmitted, from a gear 23a mounted thereon, 
to a gear 25 mounted on the platen roller 5 through an intermediate gear 
24. The recording head 8 is maintained in pressure contact with the platen 
roller 5 across the sheet material 9, which is transported by said platen 
roller 5. 
Said motor 23 is controlled by a control unit to rotate the platen roller 
in a direction a or b. In the image formation on the sheet material 9, the 
platen roller 5 is rotated in the direction a to advance the sheet 
material 9 in a direction c. After the sheet cutting by the cutter 6 
subsequent to the image formation, the platen roller 5 is rotated in a 
direction b to return the leading end of the sheet material 9 to a 
predetermined stand-by position. 
The cutter 6 is composed of a pair of blades 6a, 6b. The blade 6a is fixed 
to the main body, while the blade 6b is rotatable about a shaft 6b1 and is 
driven by drive means (not shown). In response to a cutting signal from 
the control unit, the blade 6b rotates in shearing motion with respect to 
the blade 6a thereby cutting the sheet material 9. 
Said cutter 6 may be so constructed as to be driven by the motor 23, or by 
other drive means. Between said cutter 6 and platen roller 5, there are 
provided paired cutter guide members 6c, 6d for guiding the sheet material 
9. 
The recording head 8, to be driven by image signals from the control unit 
for forming an image on the sheet material 9, is supported on the cover 2 
through a compression spring 8a and is made rotatable about a shaft 8b at 
an end. 
In the present embodiment, the recording head 8 is composed of so-called 
thermal head having a plurality of heat-generating elements arranged on a 
face in contact with the sheet material, along the transversal direction 
thereof. In the image formation, the heat-generating elements 8c are 
selectively energized according to the image signals, and the image is 
formed on the sheet material 9 by the heat thus generated. 
The sheet material 9 is composed for example of plain paper or thermal 
recording paper, of the appropriate characteristics matching the property 
of the recording means. In the present embodiment employing a thermal head 
8, the sheet material 9 is composed of thermal recording paper wound on a 
core 9b as a roll 9a. 
Because of said rolled form, the sheet material 9 develops curling, of 
which level depends on the diameter of the roll 9a. The curl developed at 
a large roll diameter has a small height H as shown in FIG. 4A, but the 
curl height H increases as the roll diameter decreases, eventually 
reaching a rounded curl state as shown in FIG. 4B. For this reason, there 
is required a curl correction mechanism functioning depending on the 
diameter of the roll 9a, for achieving effective curl correction. 
The guide shaft 21, constituting the guide member, serves to correct the 
curl developed in the sheet material 9, in cooperation with the curl 
correction shaft 22 to be explained later. 
Said guide shaft is rotatably mounted on an arm 27 which is rotatable about 
a shaft 26. Said shaft 26 is rotatably supported by the main body 1, and 
receives the power of the motor 23, through a slip clutch (frictional 
joint means) 28. Thus the power of the motor 23 is transmitted, through 
the gear 23a fixed to the motor 23, intermediate gear 24, gear 25 fixed to 
the platen roller 25 and an intermediate gear 29, to a gear 28a 
constituting the slip-clutch 28. 
The transmission system from the motor 23 to the platen roller 5 and the 
transmission system from the motor 23 to the arm 27 are preferably so 
constructed that the rotating speed of the arm 27 is equal to or slightly 
faster than the rotating speed of the platen roller 5 or the advancing 
speed of the sheet material 9. The power transmitted from said motor 23 to 
the shaft 26 rotates said shaft 26 in the same direction as that of the 
platen roller 5. 
The arm 27 need not necessarily be driven by the motor 23 for driving the 
platen roller 5, but can be driven by another motor. 
The slip clutch 28 is composed of a clutch plate 28b fixed to the shaft 26, 
a friction member 28c in face contact with said clutch plate 28b, and a 
compression spring 28d mounted on an end of the shaft 26. The gear 28a is 
pressed to the clutch plate 28 across the friction member 28c by means of 
the compression spring 28d, and the power of the motor 23 is transmitted 
to the shaft 26 by the friction of contact. Consequently the power 
transmitted to the shaft 26 is determined by the frictional coefficient 
between the clutch plate 28b and the friction member 28c, and the biasing 
force of the compression spring 28d. Therefore, the biasing force of the 
spring 28d is preferably made adjustable, by a nut engaging on a screw 
thread formed on the end portion of the shaft 26. 
A pair of arms 27 are fixed, at the approximate center thereof, to end 
portions of the shaft 26. The guide shaft 21 is rotatably supported on an 
end 27a of said arms 27 close to the roll 9a. The other end of the arms 27 
constitute a contactor 27b for contacting the stopper 4a formed in a part 
of the roll holder 4 or a stopper 32 provided on a mounting member 30 to 
be explained later. 
Said arms 27 are so shaped that, when rotated in a direction e, the guide 
shaft 21 is accommodated in a space defined above a wall of the roll 
holder 4 opposed to the platen roller 5 and below a guide plate 34. 
The curl correction shaft 22 is rotatably mounted on a rotatable member 
(retracting means) 31, which is rotatably mounted on a mounting member 30 
fixed to the cover 2. 
Said mounting member 30 is composed of a guide portion 30a serving as a 
guide member for the sheet material 9 and as a stopper for limiting the 
rotary motion of the recording head 8 when the cover 2 is opened, brackets 
30b extending downwards from both sides of said guide portion 30a, a 
stopper 30c for the rotatable member 31, formed at the upstream side of 
the guide portion 30a with respect to the advancing direction of the sheet 
material 9, a stopper 30d for the rotatable member 31, formed at the 
downstream side, and brackets 30e extending upwards from both sides of the 
guide portion 30a. 
At the end of said brackets 30b there are provided stoppers 32 for 
contacting the contactors 27b of the arms 27 thereby limiting the 
rotatable range thereof. The brackets 30e rotatably supports the rotatable 
member 31 by means of a shaft 33. 
Said rotatable member 31 is composed of axe-shaped plates rotatably 
mounted, in a direction f or g, on both ends portions of the shaft 33. The 
curl correction shaft 22 is rotatably mounted in the axe-shaped protruding 
part of said rotatable member 31. Consequently the rotatable member 31 
always suspends vertically, by the weight thereof and the weight of the 
shaft 22, regardless of the opened angle of the cover 2. 
The rotatable range of the member 31 is limited as an upper face 31a 
impinges on the stopper 30c of the mounting member 30 and a lateral face 
31b impinges on the stopper 30d. Also a lower face 31c of the rotatable 
member 31 impinges on the shaft 26 when the cover 2 is closed. When the 
cover 2 is closed, the rotatable member 31 can assume, as shown in FIGS. 
3A and 3B, a position in which the upper face 31a is in contact with the 
stopper 30c but the lower face 31c is separated from the shaft 26, or a 
position in which the upper face 31a is separated from the stopper 30c but 
the lower face 31c is in contact with the shaft 26. 
When the cover 2 is opened, the upper face 31a of the rotatable member 31 
is separated from the stopper 30c of the mounting member 30 by said 
opening, or is already separated from the stopper 30c even prior to said 
opening, and the lower face 31c of the rotatable member 31 moves in a 
direction g along the shaft 26. When the cover 2 is closed, said lower 
face 31c moves in a direction f along the shaft 26, whereby the position 
of the rotatable member 31 is limited by the stopper 30c and the shaft 26. 
Consequently, when the cover 2 is closed as shown in FIG. 2A, 2B or 9, the 
rotatable member 31 is either in a position in which the upper face 31a is 
in contact with the stopper 30c and the lower face 31c is separated from 
the shaft 26, or in a position in which the upper face 31a is separated 
from the stopper 30c and the lower face 31c is in contact with the shaft 
26. 
The curl correction shaft 22 is provided at a position at the upstream side 
of the platen roller 5 with respect to the advancing direction of the 
sheet material 9 and not providing an excessively large introduction angle 
of the sheet material 9 into the platen roller 5. 
The guide plate opposed to the shaft 22 extends at an end close to the 
platen roller 5 and at the other end close to the upright wall of the 
roller holder 4, and serves to guide the sheet material 9 from the roll 9a 
to the platen roller 5. 
In the following there will be explained the principle of curl correction 
in the above-explained recording apparatus. FIG. 2A shows the curl 
correction in case the roll diameter is large, and FIG. 2B shows that in 
case of small roll diameter. 
The motor 23 rotates the platen roller 5 in a direction a, thereby 
advancing the sheet material 9 in a direction c. At the same time the 
power of the motor 23 is transmitted to the slip clutch 28, thereby 
rotating the arms 27, fixed on the shaft 26, in a direction d and bringing 
the guide shaft 21 into contact with the sheet material 9. Thus the 
transport path of the sheet material 9 is defined by the roll 9a, guide 
shaft 21, curl correction shaft 22 and platen roller 5, wherein the sheet 
material 9 wrappes the shaft 21 in the same direction as the winding 
direction of the roll 9a but the shaft 22 in the opposite direction. The 
curl of the sheet material 9 is corrected by the wrapping on the curl 
correction shaft 22. 
By the contact friction between the roll holder 4 and the roll 9a loaded 
therein, the sheet material 9 is subjected to a tension F, proportional to 
the weight of the roll 9a. 
In FIG. 2A, the sheet material 9 is subjected to a tension F.sub.1, 
corresponding to the weight G.sub.1 of the roll 9a, before and after the 
guide shaft 21 and the curl correction shaft 22. When the shaft 21 is 
positioned in a direction d, the upper face 31a of the rotatable member 31 
is brought into contact with the stopper 30c by the synthesized tensions 
F.sub.1 before and after the curl correction shaft 22, thereby defining 
the position of said shaft 22. At the same time the wrapping amount of the 
sheet material 9 on the guide shaft 21, whereby the resistance by said 
synthesized tension F.sub.1 to the rotating force of the arms 27 (torque 
transmitted by the slip clutch 28) increases. Thus the rotation of said 
arms 27 is stopped at a position where the rotating force thereof balances 
with said synthesized force. In this state slippage is generated between 
the clutch plate 28b and the friction member 28c of the slip clutch 28. 
When the rotating force on the arms 27 balances with the tension F.sub.1 on 
the sheet material 9, said sheet material 9 moves from the shaft 21 to 22 
with an angle .theta.1, and then proceeds to the platen roller 5. 
When the roll 9a is reduced in diameter, with a weight G.sub.2 smaller than 
G1, as shown in FIG. 2B, the tension F.sub.2 on the sheet becomes smaller 
than F.sub.1. Consequently, the resistance on the guide shaft 21 by said 
tension is reduced, and the arms 27 further rotates in the direction d, 
from the position under the tension F.sub.1. The arms 27 are stopped 
either at a position where the rotating force therefor balances with said 
resistance, or at a position where the contactors 27b engages with the 
stopper 4a if the rotating force is larger. The curl correction shaft 22 
is lifted by the tension of the sheet material 9, and is stopped where the 
upper face 31a of the rotatable member 31 engages with the stopper 30c. In 
this state the angle .theta.2 of the sheet material 9 before and after the 
shaft 22 is smaller than .theta.1. Consequently, the wrapping amount of 
the sheet 9 on the curl correction shaft 22 is small for a large roll 
diameter, and increases as the roll diameter decreases. 
FIGS. 4A and 4B show the curl developed in the sheet material 9, wherein H 
indicates the curl height. FIG. 5 shows the curl height H of the sheet 
material 9 of a predetermined length, cut from the roll 9a with and 
without curl correction. 
In the present experiment, the sheet material 9 was composed of thermal 
recording paper of a width of 210 mm (corresponding to A4 size) and a 
length of 100 m, wound as a roll 9a on a core 9b of a diameter of 1 inch 
(25.4 mm). The initial roll diameter was 96 mm. The rotating force of the 
arms 27 was selected as 1 kg, and the diameter of the curl correction 
shaft 22 was 4 mm. The angle .theta. of the sheet material 9 before and 
after the shaft 22 was selected as 130.degree.-30.degree.. The sheet 
material 9 was cut at a length of 297 mm corresponding to A4 size. 
In FIG. 5, white triangles indicate sheets without curl correction, showing 
curl as indicated in FIG. 4A. White circles indicate those with curl 
correction, showing curl as indicated in FIG. 4A. Black triangles indicate 
sheets without curl correction, showing curl as illustrated in FIG. 4B. 
As will be apparent from FIG. 5, the height H of the curl developed in the 
sheet material 9 becomes smaller as the diameter of the roll 9a increases, 
and vice versa. A fully rounded curl is observed in the sheet material 9 
when the diameter of the roll 9a becomes smaller than about 40 mm. 
On the other hand, the sheet material 9 corrected by the curl correction 
mechanism of the present embodiment is almost free from curl development, 
and the measured curl height H is almost constant. This fact indicates 
that appropriate correction was applied to the sheet materials 9 of 
different curl heights H depending on the roll diameter. 
As explained in the foregoing, the curl correction mechanism of the present 
embodiment defines the transport path of the sheet material 9 by the guide 
shaft 21 mounting the arms 27, depending on the balance between the 
tension F on the sheet 9 and the rotating force on said arms 27, thereby 
varying the angle of the sheet material 9 before and after the curl 
correction shaft 22 and correcting the curl of said sheet material 9 
according to the tension F applied thereon. 
After the image recording of a page and the cutting of the sheet material 9 
with the cutter 6 in the above-explained mechanism, the motor 23 is 
activated to rotate the platen roller 5 in a direction b in order to bring 
back the leading end of the remaining sheet material 9 toward the 
recording position of the recording head 8, whereby the power of the motor 
23 is at the same time transmitted, through the slip clutch 28, to the 
shaft 26, thereby rotating the arms 27 in a direction e, until the 
contactor 27b impinge on the stopper 32. In this state, the guide shaft 21 
is positioned on the extention of the guide plate 34 as shown in FIGS. 6A 
and 6B, closing a space 35 defined by the roll holder 4 and the roll 9a. 
Also the slip clutch 28 shows slippage between 10 the clutch plate 28b and 
the friction member 28c. 
Also since the curl correction shaft 22 is disengaged from the sheet 
material 9, the rotatable member 31 descends by the weight thereof to a 
position where the lower face 31c of the rotatable member 31 is contact 
with the shaft 26. 
The rotation of the arms 27 in the direction e releases the guide shaft 21 
from the contact with the sheet material, whereby the guide shaft 21 no 
longer defines the transport path of the sheet material 9, thus generating 
a slack in the sheet material 9 between the roll 9a and the platen roller 
5. Said slack portion of the sheet material 9 extends along the guide 
plate 34 positioned opposite to the shaft 22, and is supported by the 
shaft 21 positioned on the extention of the guide plate 34. Consequently, 
the sheet material 9 does not enter the space 35, but is accommodated in a 
space between the roll 9a and the cover 2, showing a mild curve as 
illustrated. Thus the sheet material does not develop local folds. 
When the diameter of the roll 9a decreases as shown in FIG. 2B, the guide 
shaft 21 moves to above the curl correction shaft 22 by the rotation of 
the arms 27 in a direction d. The shafts 21, 22 mutually interfere if the 
cover 2 is opened in this state, for example for removing the sheet 
jamming developed in the apparatus. 
In the present embodiment, the cover 2 can be easily opened even when the 
guide shaft 21 and the curl correction shaft 22 mutually interfere, 
because the shaft 22 is mounted on the rotatable member 31 which is 
rotatably mounted on the mounting member 30 and can be retracted at the 
opening of the cover 2. 
When the cover 2 is closed, the position of the rotatable member 31 is 
limited as the upper face 31a thereof is in contact with the stopper 30c 
as explained before. When the cover 2 is opened, the upper face 31a or the 
rotatable member 31 is released from the stopper 30c, whereby the lower 
face 31c rotates along the shaft 26. Then, when the cover 2 is further 
opened as shown in FIG. 7, the lower face 31c of the rotatable member 31 
is released from the shaft 26, whereby the rotatable member 31 is rendered 
rotatable in a direction f or g about the shaft 33, in a range from a 
position where the upper face 31a is in contact with the stopper 30c to a 
position where the lateral face 31b is in contact with the stopper 30c. 
Consequently, when the cover 2 is opened in a state of mutual interference 
of the guide shaft 21 and the curl correction shaft 22 as shown in FIG. 
2B, the rotatable member 31 rotates, as shown in FIG. 7, in a direction g, 
keeping the lower face 31c in contact with the shaft 26, by means of the 
weight of said member 31 and that of the shaft 22. Said rotation of the 
rotatable member 31 in the direction g eliminates the mutual interference 
of the shafts 21 and 22, thereby enabling easy opening of the cover 2. 
On the other hand, when the cover 2 is closed with the arms 27 in a 
position shown in FIG. 7, the rotatable member 31 rotates with respect to 
the cover 2 by means of the weight of said member 31 and that of the curl 
correction shaft 22, but the lower face 31c of the rotatable member 31 is 
positioned above the shaft 26 while the upper face 31a is positioned below 
the guide shaft 21, because the lateral face 31b of said member 31 is in 
contact with the stopper 30d as shown in FIG. 7. When the cover 2 is 
further closed, the lower face 31c of the rotatable member 31 is brought 
into contact with the shaft 26 and rotates along said shaft 26, so that 
the cover 2 can be closed without the interference of the rotatable member 
31 and the guide shaft 21. 
In the following there will be explained the image forming operation on the 
sheet material 9 by the recording apparatus equipped with the 
above-explained curl correction mechanism. 
At first the roll 9a is loaded in the roll holder 4 by opening the cover 2 
as shown in FIG. 8. Due to the opening of the cover 2, the contactors 27b 
of the arms 27 are released from the stopper 32, whereby the arms 27 are 
no longer limited in rotation in the direction e. In this state as shown 
in FIG. 8, the arms 27 maintain a position indicated by a double-dotted 
chain line. If the roll 9a touches the guide shaft 21 at the loading, said 
shaft 21 is rotated in the direction e, by the weight of the roll 9a, to a 
gap between the roll holder 4 and the guide plate 34. Consequently, the 
guide shaft 21 does not unfavorably affect the loading of the roll 9a, 
whereby the entire apparatus can be made compact. 
Then the sheet material 9 is pulled out from the roll 9a, and is threaded 
through the platen roller 5 and between the cutter guides 6c, 6d. Then the 
cover 2 is closed as shown in FIG. 9 whereby the stopper 32 is brought 
into contact with the contactors 27b, thus rotating the arms 27 from said 
chain-lined position in the direction d to the initial stand-by position. 
Also the rotatable member 31 is brought to the initial position in which 
the lower face 31c is in contact with the shaft 26, so that a gap is 
maintained between the upper face 31a and the stopper 30c. Said gap is 
provided for ensuring an over-stroke of the cover 2 in engaging the same 
with the main body 1. 
As explained in the foregoing, the present embodiment allows to dispense 
with the threading of the sheet material under the curl correction shaft, 
whereby the setting of the sheet material is facilitated and the entire 
apparatus can be compactized. 
When the recording signal is sent from the control unit (not shown), the 
motor 23 is activated to rotate the platen roller 5 in the direction a as 
shown in FIGS. 2A and 2B, thereby advancing the sheet material 9 in the 
direction c. At the same time the arms 27 rotate in the direction d, and 
stops at a position balanced with the tension F on the sheet material 9. 
Also the rotatable member 31 rotates in the direction f, and stops at a 
position where the upper face 31a thereof is in contact with the stopper 
30c. In this state, the transport path of the sheet material 9 is defined 
by the guide shaft 21 and the curl correction shaft 22. Thus the sheet 
material 9 wraps the shaft 22 with an angle corresponding to the tension F 
on said sheet material, whereby the curl is corrected. 
On the other hand, the recording head 8 is given image signals in 
synchronization with the transportation of the sheet material 9 to 
activate the heat-generating elements 8c, thereby forming an image on the 
sheet material 9. 
After image formation, the sheet material 9 continues to be advanced in the 
direction c. When the rear end of the image formed on the sheet material 9 
reaches the cutter 6, said cutter 6 is energized to cut the sheet material 
9. The cut sheet 9 is then discharged from the main body 1. 
After said cutting, the platen roller 5 is rotated in the direction b by 
the motor 23 as shown in FIGS. 6A and 6B, and the arms 27 simultaneously 
rotate in the direction e. Since the rotating speed of the arms 27 is 
equal to or faster than the transporting speed of the sheet material 9 by 
the platen roller 5, the guide shaft 21 is released from the sheet 
material 9 and is retracted to the initial position where the contactors 
27b of the arms 27 are in contact with the stopper 32. Also the rotatable 
member 31 descends by the weight thereof, and stops at the initial 
position where the lower face 31c is in contact with the shaft 26. The 
sheet material 9 is pulled back by the rotation of the platen roller 5 in 
the direction b, and the motor 23 is stopped and enters the stand-by state 
when the leading end of the sheet material 9 reaches a predetermined 
stand-by position. 
When the next recording signal is sent from the control unit in said 
stand-by state, the motor 23 rotates the platen roller 5 in the direction 
a as shown in FIGS. 2A and 2B, and the arms 27 rotate simultaneously in 
the direction d. Also the rotatable member 31 rotates and stops at a 
position where the upper face 31a is in contact with the stopper 30c. In 
this operation, at first transported is the slack of the sheet material 9 
pulled back by the rotation of the platen roller 5 in the direction b 
after the preceding image recording. While said slack is transported, the 
arms 27 rotate to limit the transport path of the sheet material 9, 
whereby the curl thereof can be appropriately corrected. 
FIG. 10 shows another embodiment of the curl correction mechanism in which 
the curl correction shaft 22 can be moved by the opening and closing 
motion of the cover 2. In FIG. 10, same or equivalent components as those 
in the foregoing first embodiment are represented by same numbers, and 
will not be explained further. 
On both sides of the main body 1, there are fixed rail members 40. The curl 
correction shaft 22 is supported at both ends by said rail members 40, and 
is made movable along said rail members 40. Tension springs 42 are 
provided between both ends of the shaft 22 and a pin 41 provided in the 
main body 1. Also on each end of the shaft 22 there is fixed a wire 43 
which goes around pins 44a-44c provided in the main body 1 and is 
connected at an end to the cover 2. 
Consequently, the curl correction shaft 22 is constantly biased, by the 
tension springs 42, in a direction h along the rail members 40, and is 
maintained in contact with the end of said rail members 40 when the cover 
2 is closed. When the cover 2 is opened, the wires 43 are pulled in a 
direction j, whereby the shaft 22 moves in a direction i along the rail 
members 40. 
In the present embodiment, as explained above, the curl correction shaft 22 
is movable from the initial position along the rail members 40, by opening 
of the cover 2. Consequently, even when the cover 2 is opened in a state 
of mutual interference of the guide shaft 21 and the curl correction shaft 
22 as indicated by solid lines in FIG. 10, the shaft 22 can be retracted 
from the initial position, so that the cover 2 can be easily opened 
without interference of said shaft 22 with the guide shaft 21. 
In the above-explained structure, the curl correction for the sheet 
material 9 can be achieved as in the first embodiment explained above. 
In the following there will be explained still another embodiment with 
reference to FIG. 11 which is a schematic perspective view of a recording 
apparatus, and FIGS. 12 and 13 which are views showing the principle of 
curl correction, and FIGS. 14 and 15 which are views for explaining curl 
of the sheet and result of the experiment, wherein same components as 
those in the foregoing embodiments are represented by same numbers and 
will not be explained further. 
On the cover 2, a recording head 61 is mounted by means of a compression 
spring 61a, in a position opposed to the platen roller 5. Also in a 
predetermined position of the cover 2, there is detachably mounted a 
cartridge 63 housing an ink sheet 62 constituting a transfer medium, by 
means of engaging means (not shown). On said cartridge 63 there is 
rotatably mounted the curl correction shaft 22. 
Said recording head 61 is maintained in pressure contact with the platen 
roller 5, across the recording sheet 9 and the ink sheet 62, and an image 
is formed on the recording sheet 9 by driving the recording head 61 
according to image signals from a control unit (not shown), while the 
recording sheet 9 is advanced by the platen roller 5. After image 
formation, the recording sheet 9 is cut by the cutter 6 and discharged 
from the apparatus. 
In the present embodiment, the recording sheet 9 is advanced by pinching 
said sheet 9 and the ink sheet 62 between said platen roller and the 
recording head 61. Said recording head 61 is composed of so-called thermal 
head having a plurality of heat-generating elements (not shown) arranged 
on a face in contact with the ink sheet 62, along the transversal 
direction thereof. At the image formation, the heat-generating elements 
are selectively activated according to the image signals to generate heat, 
whereby the ink coated on the ink sheet 62 is transferred, by fusion or 
sublimation, to the recording sheet 9 to form an image thereon. 
The recording sheet 9 is composed of continuous plain paper or plastic film 
of an appropriate quality matching the structure of the recording means. 
In the present embodiment employing the thermal head 61, the recording 
sheet 9 is composed of plain paper wound as a roll 9a on a core 9b. 
Ends of arms 27 constitute contactors 27b for contacting stoppers 65, 66 
provided on the main body 1. 
The curl correction shaft 22 is rotatably mounted on mounting members 64 
protruding from the cartridge 63. When the cover 2 is closed, said shaft 
22 is maintained in a constant position in the main body 1, since it is 
mounted on the mounting members 64 protruding from the cartridge 63. 
The ink sheet 62 constituting the transfer medium is formed by coating a 
substrate such as a polyethylene terephthalate film with heat-fusible ink. 
The cartridge 63 is mounted detachably on the cover 2 by engaging means 
(not shown), and houses the ink sheet 62 extended between a feed roll 63a 
and a take-up roll 63b. The cartridge 63 is provided, in a position 
opposed to the platen roller 5, with a window 63c in which the ink sheet 
62 is exposed. When the cover 2 is closed, the recording head 61 is 
maintained in contact with the platen roller 5 through said window 63c. 
On the lower face of said cartridge 63, and at the upstream side of the 
platen roller 5 with respect to the transport direction of the recording 
sheet 9, there are formed protruding mount members 64 rotatably supporting 
the curl correction shaft 22. Opposed to the shaft 22 there is provided a 
guide plate 34, of which an end extends close to the platen roller 5 while 
the other end extends close to a vertical wall of the roll holder 4. Said 
guide plate 34 serves to guide the recording sheet 9 from the roll 9a to 
the platen roller 5. 
In the following there will be explained the image formation on the 
recording sheet 9 by the above-explained recording apparatus. 
At first, in loading the roll 9a in the main body 1, the cover 2 is opened 
and the roll 9a is loaded in the roll holder 4. At the same time the 
recording sheet 9 is pulled out from the roll 9a and is threaded over the 
platen roller 5 and between the cutter guides 6c and 6d. 
The curl correction shaft 22 moves with the cover 2, as it is mounted on 
the cartridge 63 on the cover 2. Consequently the roll holder 4, guide 
shaft 21, guide plate 34 and platen roller 5 provided in the main body 1 
are exposed, and it is not necessary to thread the recording sheet 9 under 
the curl correction shaft. Thus the roll 9a can be easily set. 
When a recording signal is sent from the control unit (not shown), the 
motor 23 rotates the platen roller 5 in a direction a, thereby advancing 
the recording sheet 9 and the ink sheet 62 in a direction c. 
Simultaneously, the arms 27 rotate in a direction d and stop at a position 
balanced with the tension F on the recording sheet 9. In this state, the 
transport path of the recording sheet 9 is defined by the guide shaft 21 
and the curl correction shaft 22, and the recording sheet wraps the shaft 
22 with an angle .theta. corresponding to the tension F on said recording 
sheet 9, and is subjected to curl correction. 
The recording head 61 receives the image signals in synchronization with 
the transportation of the recording sheet 9 to heat the ink sheet 62 by 
heat generated by the heat-generating elements, whereby the ink coated on 
the ink sheet 62 is transferred, by fusion or sublimation, to the 
recording sheet 9 to form an image thereon. 
After the image formation, the recording sheet 9 continues to be advanced 
in the direction c, and, when the rear end of the image formed on said 
sheet 9 reaches the cutter 6, said cutter 6 is energized to cut the 
recording sheet 9 which is subsequently discharged from the main body 1. 
After said cutting, the platen roller 5 is rotated in the direction b by 
the motor, and the arms 27 are simultaneously rotated in the direction e. 
Since the rotating speed of the arms 27 is equal to or larger than the 
transport speed of the recording sheet 9 by the platen roller 5, the guide 
shaft 21 is rapidly released from the recording sheet 9 and is retracted 
into the initial position in a space 67. When the leading end of the 
recording sheet 9 pulled back from the cutter 6 by the rotation of the 
platen roller 5 in the direction b, the motor 23 is stopped and enters the 
stand-by state. 
When a next recording signal is sent from the control unit in said stand-by 
state, the platen roller 5 is rotated in the direction a by the motor 23, 
and the arms 27 are simultaneously rotated in the direction d. In this 
operation, at first transported is the slack of the recording sheet 9 
pulled back by the rotation of the platen roller 5 in the direction b 
after the preceding recording. During the transportation of said slack, 
the arms 27 rotate to define the transport path of the recording sheet 9, 
whereby the curl of the recording sheet 9 can be appropriately corrected. 
In the foregoing embodiments, the rolled sheet material is placed on the 
roll holder, but the present invention is likewise applicable to a rolled 
sheet material rotatably supported by a shaft inserted into the center of 
said roll, if the sheet pulling resistance decreases with the decrease of 
the sheet material. 
Also in the foregoing embodiment the curl correction is achieved by a curl 
correction shaft and a guide shaft of both cylindrical shape, but either 
or both may be replaced by a guide plate or guide plates. 
In the following there will be explained still another embodiment of the 
present invention applied to a facsimile apparatus, with reference to 
FIGS. 14 and 15 which are perspective views of a recording system of the 
facsimile apparatus and FIG. 16 which is a cross-sectional view of the 
entire facsimile apparatus. 
As shown in FIG. 16, the facsimile apparatus is composed of a recording 
system B equipped with a curl correction mechanism, and an original 
reading system C. 
Referring to FIG. 16, the recording system B has a main body 100 and a 
cover 102 articulated thereto by a shaft 103, wherein said cover 102 can 
engage with the main body 100 by a clock mechanism (not shown). In a roll 
holder 104 formed in the rear part of the recording system, there is 
loaded a roll 105a of a thermal recording sheet 105. Said sheet material 
105 is advanced by the rotation of a platen roller 106a constituting 
transport means, and is subjected to curl correction by being bent, in 
passing the curl correction mechanism A, in a direction opposite to the 
direction of curl. 
After curl correction, the sheet material 105 is subjected to image 
formation by recording means 106, and the sheet material 105 after image 
formation is cut by a cutter 107 and discharged by discharge rollers 108 
onto a discharge stacker 109. 
In the original reading system C, plural original documents 111 are set on 
an original stacker 110 formed on the upper face of said cover 102. In the 
reading operation, several lowermost sheets of said plural originals 111 
are advanced by a preliminary transport roller 111a and a pressure member 
112b, and then are separated and advanced one by one by a separating 
roller 113a and a pressure member 113b in contact therewith. The separated 
original 111 is illuminated by a light source 116 while it is transported 
by paired transport rollers 114a, 114b; 115a, 115b, and the reflected 
light is introduced, through a mirror 117 and a lens 118, into a 
photoelectric converting device 119 such as a CCD for conversion into 
electrical signals. Said signals are transmitted to the recording system B 
in case of the copy mode, or transmitted to the recording system of 
another apparatus in the facsimile mode. 
In the following explained is the structure of the recording system B 
equipped with the curl correction mechanism A. 
The roll holder 104 is open on the stop and is positioned in the rear part 
of the main body 100 of the recording system. The sheet roll 105a is 
loaded in said roll holder 104, and frictional resistance is generated by 
the contact of the external periphery of said roll 105a with the internal 
wall of the holder 104. Said frictional resistance is large when the roll 
105a is large in diameter and heavy, but decreases as the roll 105a 
becomes lighter in weight by the consumption of the sheet 105. The tension 
on the sheet material 105 varies proportionally with said frictional 
resistance. 
Recording means 106, for recording an image on said sheet material 105, is 
composed of a platen roller 106a and a recording head 106b. The platen 
roller 106a is composed of a material of a high frictional coefficient, 
such as hard rubber, formed as a roller, and is rotatably supported in the 
main body 100 and driven by a motor 120. As shown in FIG. 14, the rotation 
of the motor 120 is transmitted from a gear 121a fixed to the motor shaft, 
through an intermediate gear 121b, to a gear 121c fixed on the shaft of 
the platen roller 106a, thereby rotating the platen roller 106a. Said 
platen roller 106a serves also as transport means for the sheet material 
105. 
The recording head 106b heats the sheet material 105 according to the image 
signals to form an image on said sheet material 105, and is pressed to the 
platen roller 106a across said sheet material 105. More specifically said 
head is rotatably mounted about a shaft 106c on the cover 102, and is 
pressed to the platen roller 106a by a compression spring 106d when the 
cover 102 is closed. Consequently the sheet material 105 is advanced by 
the rotation of the platen roller 106a while said sheet 105 is sandwiched 
between the platen roller 106a and the recording head 106b. 
The recording head 106b in the present embodiment is composed of so-called 
line thermal head having a plurality of heat-generating elements 
106b.sub.1 arranged on a face in contact with the sheet material 105 along 
the transversal direction of the sheet material 105, and the energization 
of said heat-generating elements 106b.sub.1 according to the image signals 
selectively heats the sheet material 105, thereby developing a color on 
the thermal recording sheet 105. 
The cutter 107 in the present embodiment is composed of a rotary cutter 
consisting of a fixed blade 107a and a driven blade 107b. More 
specifically the fixed blade 107a is fixed on the main body 1, while the 
driven blade 107b is rotatable about a shaft 107c and, when rotated by 
drive means, cuts the sheet material 105 in cooperation with the fixed 
blade 107a. Said driven blade 107b may be driven by the motor 120 for 
driving the platen roller 106a, or by another independent motor. 
The sheet material 105 cut by said cutter 107 is discharged to a stacker 
109 by discharge rollers 108 driven by drive means (not shown). The sheet 
material 105 used in the recording is curled when pulled out from the roll 
105a, because of winding around the core 105b, the level of said curling 
depends on the diameter of the roll 105a. 
As shown in FIGS. 14 and 15, a curl correction shaft 122 is rotatably 
mounted on a mounting member 124 fixed on the cover 102. Said mounting 
member 124 is composed of a flat plate 124a serving as a guide for the 
sheet material 105, and brackets 124b standing on both ends of said flat 
plate 124a, wherein the distance of said brackets 124b is larger than the 
width of the sheet material 105 but smaller than the distance of arms 
supporting the both ends of the guide shaft 123 to be explained later. 
Said brackets 124b rotatably support the curl correction shaft 122. 
As shown in FIGS. 17 and 18, said shaft 122 is always maintained in a 
constant position in the main body 100 when the cover 102 is closed, said 
position being at the upstream side of the platen roller 106a in the 
transport direction of the sheet material 105, so as not to excessively 
increase the introduction angle of the sheet material 105 into the platen 
roller 106a. 
Opposed to said curl correction shaft 122, there is provided a guide plate 
104, for guiding the sheet material 105 pulled out from the roll 105a to 
the platen roller 106a. Said guide 104a is extended at an end thereof to 
the vicinity of the platen roller 106a, and is integrally united, at the 
other end, with the roll holder 104. 
The guide shaft 123 is rendered movable by moving means, with respect to 
the curl correction shaft. 122. As shown in the perspective view in FIG. 
19 and the cross-sectional view in FIG. 20, said moving means is composed 
of a shaft 125 mounted in the main body 100 and two arms 126 fixed to said 
shaft 125 and rotatably supporting the guide shaft 123, whereby the 
rotation of the shaft 125 causes integral displacement of the arms 126 
thereby moving the guide shaft 123 with respect to the curl correction 
shaft 122. 
Said shaft is rotatably supported by bearings 127 mounted on the main body 
100, and is provided, at an end thereof, with a clutch flange 128, a 
clutch gear 129 and a spring clutch 130 for transmitting the one 
directional rotating force to the shaft 125. Said clutch flange 128 is 
composed of a cylindrical portion 128a and a flange portion 128b and 
integrally rotates with said shaft 125 by means of an engaging pin 131. 
The clutch gear 129 is composed of a cylindrical portion 129a and a gear 
portion 129b, and has a central hole slightly larger than the diameter of 
the shaft 125, whereby said gear 129 is rotatably fitted on said shaft 
125. 
The spring clutch 130 is composed of a coil of a steel wire, a steel belt 
or a plastic wire, wound over the cylindrical portions 128a, 129a of the 
clutch flange 128 and clutch gear 129, and engages with the flange portion 
128b of the clutch flange 128 at an end. The other end is bent outward to 
constitute an engaging portion 130. 
Said spring clutch 130 transmits the rotation of the clutch gear 129, only 
in one direction, to the clutch flange 128. More specifically, when the 
clutch gear 129 rotates in the direction a shown in FIG. 19, the spring 
clutch 130 becomes slack and the rotation is not transmitted to the clutch 
flange 128. On the other hand, when the clutch gear 129 rotates in the 
opposite direction a' (hereinafter the sign ' indicates opposite 
direction), the spring clutch 130 is tightened over the cylindrical 
portions 128a, 129a to maintain these portions in a locked state, whereby 
the rotation is transmitted to the clutch flange 128 thereby moving the 
guide shaft 122 in the direction b. 
Said clutch gear 129 is driven by the motor 120 used for driving the platen 
roller 106a. As shown in FIG. 14, the power of the motor 120 is 
transmitted to the platen roller 106a through the gears 121a-121c as 
explained before, and the gear 121c on the platen roller shaft meshes with 
the gear portion 129b of the clutch gear 129 through an intermediate gear 
121d. 
Consequently the forward rotation, in the direction c of the motor 120 as 
shown in FIG. 14 causes the rotation of the platen roller 106a in the 
direction d, thereby rotating the clutch gear 129 in the direction a. 
Thus, when the platen roller 106a rotates for advancing the sheet material 
105 in the direction e, the spring clutch 130 is in the non-transmitting 
free state. 
When the motor 120 rotates in the opposite direction c', the platen roller 
106a so rotates as to reverse the sheet material 105, and the clutch gear 
129 rotates in the direction a' to maintain the spring clutch 130 in the 
locked state, thereby rotating the guide shaft 123 in the direction b 
shown in FIG. 19. 
In the following, there will be explained the structure of means for 
biasing said guide shaft 123 so as to balance with the tension of the 
sheet material 105. 
As shown in FIGS. 19 and 20, a pulley 133 is fixed, by a pin 132, to the 
other end of the shaft 125. The periphery of said pulley 133 is provided 
with a groove 133a and a hook 134a at a predetermined position. A tension 
spring 135 is provided, under a tension, between said hook 134a and a hook 
134b (FIG. 15) provided in the main body 100, whereby the pulley 133 is 
constantly biased in a direction f in FIG. 19 (direction for increasing 
the curl correction effect by the guide shaft 123). 
Also in the main body 100, there are provided stoppers 136 in the rotating 
range of said arms 126. Said stopper 136 engages with the arm 126 when it 
rotates in the direction b' in FIG. 19, thereby limiting the rotation in 
said direction, thus defining the maximum wrapping amount of the sheet 
material 105 on the curl correction shaft 122. 
Further as shown in FIGS. 19 and 21, a stopper 137 is provided in the main 
body 100, in the rotating range of the engaging portion 130a of the spring 
clutch 130. Said stopper 137 serves to limit the rotation of the spring 
clutch 130 rotating with the gear 129 in the locked state in response to 
the rotation of the clutch gear 129 in the direction a', thereby limiting 
the rotation of the arms 126. More specifically, if the clutch gear 129 
rotates in said direction a' while the engaging portion 130a is in contact 
with the stopper 137, the spring clutch 130 is loosened whereby the 
rotation is not transmitted to the clutch flange 128 and the rotation of 
the arms 126 in the direction b is limited. Consequently, the arms 126 
rotate within the range defined by the stoppers 136, 137. 
In the following there will be explained the recording operation with the 
recording system B equipped with the above-explained curl correction 
mechanism, with emphasis on the curl correcting function for a large roll 
diameter shown in FIG. 17 and a small roll diameter shown in FIG. 18. 
At first the cover 102 is opened, then the sheet roll 105a is loaded in the 
roll holder 104 and the leading end of the sheet is pulled out to the 
platen roller 106a. Since the curl correction shaft 122 is mounted on the 
cover 102 while the guide shaft 123 is mounted in the main body 100, said 
shafts 122, 123 are separated by the opening of the cover 102 as shown in 
FIGS. 14 and 15 to facilitate the setting of the sheet material 105. 
When a recording start signal is entered after the closing of the cover 
102, the motor 120 rotates in the forward direction to rotate the platen 
roller 106a in the direction d, thereby advancing the sheet material 105 
in the direction e. In synchronization the heat-generating elements 
106b.sub.1 of the recording head 106b are selectively energized to form a 
record on the sheet material 105. In the course of transportation of said 
sheet material 105, the curl thereof is corrected by the function of the 
curl correction mechanism A. The forward rotation of the motor 120 is 
transmitted to the clutch gear 129, but not to the clutch flange 128 
because of the above-explained free state of the spring clutch 130. 
On the other hand, the shaft 125 is biased in the direction f by the 
tension spring 135 as shown in FIG. 19, whereby the guide shaft 123 moves 
by the rotation of the arms 126 in the direction b' and stops at a 
position balanced with the tension on the sheet material 105. 
Thus the sheet material 105, in the transport path thereof, wraps the guide 
shaft 123 in the direction of curl of the sheet roll 105a, and the curl 
correction shaft 122 in the opposite direction. The curl correction is 
achieved by said wrapping of the sheet material 105 on the shaft 122. 
The tension on the sheet material 105 is determined by the contact friction 
between the roll holder 104 and the roll 105a loaded therein. As shown in 
FIG. 17, the sheet 105 before and after the guide shaft 123 is subjected 
to a tension F1, corresponding to the weight G1 of the roll 105a. When the 
guide shaft 123 moves in the direction b', the wrapping amount of the 
sheet material 105 on the shaft 123 increases whereby the rotating power 
of the arm 126 (torque of the pulley 133 by the tension spring 135) 
increases against the synthesized tension F1. Thus the arms 126 stop at a 
position where said rotating force of the arms 126 balances with said 
synthesized tension. 
When the roll diameter is large as shown in FIG. 17, the sheet material 105 
shows an angle .theta.1 before and after the curl correction shaft 122 
when the tension F1 of the sheet 105 balances with the rotating force of 
the arms 126. 
When the roll diameter is reduced as shown in FIG. 18, the roll weight is 
reduced to G2 (&lt;G1) so that the tension on the sheet material 105 is also 
reduced to F2 (&lt;F1). Thus the arms 126 rotate further in the direction b' 
than in the case of larger roll diameter, and stop at a position where the 
rotating force thereof balances with the afore-mentioned resistance, or in 
contact with the stopper 136 if the rotating force is larger. In this case 
the angle .theta.2 of the sheet material 105 before and after the curl 
correction shaft 122 is smaller than the angle .theta.1 corresponding to 
the larger roll diameter. 
Consequently, the wrapping amount of the sheet material on the shaft 122 is 
small for a large roll diameter, but increases as the curl becomes 
stronger for a smaller roll diameter. The curl correcting effect becomes 
stronger as said wrapping amount increases because the sheet material 105 
is more strongly bent opposite to the direction of curl. Thus the curl 
correcting effect appears stronger at a smaller roll diameter where the 
curling becomes stronger. 
As explained in the foregoing, the curl correction mechanism A is capable 
of appropriate curl correction, by varying the correcting effect according 
to the level of curling, utilizing the balance of the tension on the sheet 
material 105 and the rotating force on the arms 126. 
The arms 126 are biased by the tension spring 135, and the rotation of the 
motor 120 in the direction c is transmitted to the platen roller 106a but 
not to the arms 126. Consequently, the precision of sheet transportation 
can be improved to achieve a high quality recording, as the power for 
moving the arms 126 is not required for the motor 120 at the image 
recording. 
The sheet material 105 thus subjected to curl correction is then subjected 
to image recording, then cut with the cutter 107 and discharged by the 
discharge rollers 108. 
On the other hand, the sheet material 105 remaining in the apparatus is 
transported backward by a distance l corresponding to the distance between 
the position of the cutter 107 to the recording means 106, in order to 
avoid formation of an empty space in the leading end part of the sheet 105 
at the next recording. For this purpose the motor 120 is reversed by a 
predetermined amount, whereby the power thereof is transmitted not only to 
the platen roller 106a but also to the clutch flange 128 through the 
spring clutch 130 in the locked state as explained before, thus generating 
a force to rotate the arms 126 in the direction b. 
In this state the tension spring 135 exerts a force against said rotation, 
as shown in FIGS. 19 and 21. For this reason, the reversing power of the 
motor 120 in the present embodiment is selected larger than the arm 
rotating force of the tension spring 135. Therefore, when the motor 120 is 
reversed for reversing the sheet material 105, the arms 126 are rotated in 
the direction b and separated from the sheet material 105. At the same 
time the engaging member 130a of the spring clutch 130 rotates 
substantially integrally with the arms 126 (FIG. 21 A.fwdarw.B.fwdarw.C), 
and the spring clutch 130 becomes loose when the clutch gear 129 rotates 
while the engaging member 130a is in contact with the stopper 137 as shown 
in FIG. 21C. Thus the clutch gear 129 slips with respect to the clutch 
flange 128, and the arms 126 returns to the initial position. 
Said initial position is defined in such a manner that the guide shaft 123 
does not close the aperture of the roll holder 104, and the guide shaft 
123 does not interfere with the curl correction shaft 122 at the opening 
of the cover 102. More specifically, the engaging member 130a of the 
spring clutch 130 is in contact with the stopper 137 as shown in FIG. 21C. 
In this state, since the guide shaft 123 is separated from the sheet 
material 105, a curling of opposite direction is not generated even in a 
prolonged stand-by state. 
The motor 120 stops after the reversing of the sheet material 105 by said 
amount l, and the arms 126 are in a biased state by the tension spring 
135. As shown in FIG. 19, said tension tends to rotate the pulley 133 in 
the direction f, whereby the spring clutch 130 is locked and biases the 
clutch gear 129 in the direction a, thereby giving a torque to the motor 
120 through the gears 121a-121d. 
In the recording apparatus of the present embodiment, the arms 126 in the 
stand-by state are maintained in the initial position, represented by 
double-dotted chain lines in FIGS. 17 and 18. Consequently, in opening the 
cover 102 for example for loading the roll 105a, the guide shaft 123 does 
not interfere with the curl correction shaft 122, and the cover 102 can be 
smoothly opened. 
The apparatus of the present embodiment of the above-explained structure is 
not only capable of curl correction according to the level of curling, but 
also precise sheet transportation since the motor 120 is only required to 
rotate the platen roller 106a at the recording. Furthermore the 
replacement of the roll 105a can be easily achieved. 
In the foregoing embodiment, the guide shaft 123 is rendered movable with 
respect to the curl correction shaft 122. Now, FIG. 22 illustrates another 
embodiment in which the guide shaft 123 is rendered movable with respect 
to the curl correction shaft 122. In FIG. 22, same or equivalent 
components as those in FIGS. 14 to 19 are represented by same numbers and 
will not be explained further. 
Referring to FIG. 22, the guide shaft 23 is rotatably supported by support 
members 38 of the main body 1. The curl correction shaft 22 is rotatably 
mounted on arms 40 fixed to a shaft 39 which is rotatably mounted on the 
cover 2, and effects curl correction for the sheet material 5 when the 
arms 40 are rotated in a direction g, but are released from said curl 
correction when the arms 40 are rotated in a direction g'. 
On an end of said shaft 39 there is rotatably mounted a clutch gear 42 
fixed to a solenoid clutch 41, which, in response to a signal from a 
control unit (not shown), transmits or does not transmit the rotation of 
said clutch gear 42 to the shaft 39. Said clutch gear 42 meshes with a 
gear 44 mounted on a motor 43, whereby the rotation of said motor 43 is 
transmitted to said clutch gear 42. 
On the other end of said shaft 39 there is fixed a pulley 45 as in the 
foregoing embodiment, and a tension spring 47 is provided between a 
projection formed on the periphery of said pulley and a hook 46 provided 
in a predetermined position on the cover 2, thereby biasing the arms 40 
constantly in the direction g. 
Also in the rotating range of the arms 40 on the cover 2 there is provided 
a microswitch 48 which is actuated by the arms 40 upon arriving at the 
initial position by rotation in the direction g', whereby the motor 43 is 
stopped by a signal from said microswitch 48. 
In the above-explained structure, the solenoid clutch 41 is energized in 
the stand-by state, whereby the arms 40 are maintained in the 
double-dotted chain line position by the self-holding force of the motor 
43. Consequently, the curl correction shaft 122 and the guide shaft 23 do 
not interfer each other at the opening of the cover 2, so that the 
replacement of the roll 5a can be easily achieved. 
At the image recording, the cover 2 is closed, and the motor 20 is 
activated to rotate the platen roller 6a, thereby advancing the sheet 
material 5 in the direction e. At the same time the recording head 6b is 
activated according to the image signals to form an image on the sheet 
material 5. Simultaneous with the activation of the motor 20, the solenoid 
clutch 41 is turned off whereby the arms 40 rotate in the direction g by 
the tension spring 47, and the curl correction shaft 22 is brought into 
contact with the sheet material 5 as represented by solid lines in FIG. 
22. The position of said shaft 22 is determined by the balance of the 
biasing force of the tension spring 47 and the tension of the sheet 
material 5 as in the foregoing embodiment, and the curl correction of the 
sheet material 5 is achieved by bending with the shaft 22 opposite to the 
direction of curling. 
After the recording, the motor 20 is reversed to move the leading end of 
the sheet material 5 from the cutter 7 to the platen roller 6a. At the 
same time the solenoid clutch 41 is energized and the motor 43 is reversed 
by a predetermined amount to rotate the arms 40 in the direction g'. When 
the arms 40 are retracted to the initial position, the microswitch 48 is 
actuated to stop the motor 43, whereby the curl correction shaft 22 is 
retained in the initial position. 
The returning of the arms 40 to the initial position can be detected not 
only by the microswitch 48, but also any other means capable of detecting 
the position of the arms 40, such as a photointerruptor. 
The movable curl correction shaft 22 explained above provides the same 
effects as in the foregoing embodiments. 
As still other embodiments, it is also possible to move the guide shaft 23 
or the curl correction shaft 22 in parallel manner along racks or rails, 
or to move said shaft by a cam. Also the shaft 22 or 23 may be fixed to 
the mounting members 24 or arms 26, or may be composed of a metal plate or 
the like suitably formed to have a predetermined radius of curvature. It 
is furthermore possible to construct both of the shafts 122 and 123 
movable. Furthermore, the spring clutch 130 or the solenoid clutch 41 
employed for selectively transmitting the power of the motor to the shaft 
22 or 23 may be replaced by other devices, such as a needle clutch of 
roller type. 
Also the guide shaft 23 is moved by the motor 20 used for driving the 
platen roller 6a, but they may naturally be driven by separate motors. 
Also the driving force need not necessarily supplied by a motor but by 
other means such as a plunger. 
Also in the foregoing embodiment, a tension spring is employed for biasing 
the curl correction shaft 22 or the guide shaft 23 in a direction toward 
stronger curl correcting function, but there may be employed other means, 
for example, various springs such as torsion coil spirng, compression 
spring or spiral spring, cylinders such as air cylinder or oil cylinder, 
or a solenoid.