Lower, arced decurling guide (1) is pivoted on pin (3) and biased upward by spring (7). Upper stop (11) prevents the lower guide from moving closer to upper decurling roller (15). Paper (9) is guided between these upper and lower guides and the lower guide is moved outward in proportion to the rigidity of the paper being decurled. This automatic adjustment provides good decurling for all papers within a broad range of rigidity.

TECHNICAL FIELD 
This invention relates to an apparatus to straighten paper which is curled. 
Paper can be decurled by bending it in a direction opposite from that of 
the curl and various apparatus exists to guide paper in a bent path for 
such a purpose. This invention relates to such apparatus having 
self-adjusting decurl based on the rigidity of the paper. 
BACKGROUND OF THE INVENTION 
Paper takes on a semi-permanent set or curl by being bent, especially under 
heat. Other factors, such as printing on one side of paper, may also cause 
curl. Electrophotographic imaging typically involves bonding toner to 
paper using heat as a final step in imaging, which results in significant 
curling. Where the paper is to be conveyed further, such as for duplex 
printing on the opposite side to the first printing, decurling typically 
is employed to assure that the paper will feed reliably during the second 
printing operation. 
U.S. Pat. No. 5,066,984 to Coombs teaches a decurler of the general kind in 
which this invention is employed. That patent employs a stationary guide 
in the form of in an arc spaced from and partially surrounding a rotating 
roller. The paper is fed between the guide and the roller, where it is 
bent around roughly 120 degrees of the roller. The roller is rotated in a 
direction which assists in paper feeding, but the contact with the roller 
is light because the space between the guide and the roller is more than 
the thickness of the paper. 
Japanese patent 60-97162 to T. Hashimoto, issued May 30, 1985, discloses a 
flat guide spaced from pinch rollers for decurling. 
The decurler of the foregoing patent 5,066,984 does not provide 
satisfactory results for papers of different rigidity. Configurations of 
the arc guide and the spaced roller may be satisfactory for one paper but 
produce under decurling or over decurling (curling in the direction 
opposite from the original curling) for other papers. This invention 
employs self-adjustment of the guide to achieve consistent and highly 
satisfactory results for papers within a wide range of rigidity. 
U.S. Pat. No. 2,531,619 to Gonia discloses a decurler in which decurling is 
by directing paper around a spring-mounted roller for which the pressure 
is mechanically adjusted to vary the degree of flexing. This adjustment is 
done by adjusting screws and is not automatic. 
DISCLOSURE OF THE INVENTION 
In accordance with this invention, it is recognized that light papers 
typically require a tighter bend than heavy papers to achieve 
straightening or sufficient decurl. This invention employs an internal 
guide surface and outer guide spaced from the internal guide formed in an 
arc partially around the internal surface. The internal guide may be a 
roller which is rotated to assist paper feed. The arced guide is pivotally 
mounted and biased toward the roller and is moved outward by heavier 
papers being decurled, but not moved or moved less by lighter papers. This 
movement in proportion to the rigidity of the paper being decurled 
automatically adjusts the outer guide to the rigidity of the paper being 
fed to provide good decurling for all papers within a broad range of 
rigidity.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to FIG. 1 the arced, decurl guide 1 is mounted on a pin 3 to 
pivot around pin 3. An arm 5 of guide 1 is connected through a spring 7 to 
the frame (a stationary point) of the decurler. Spring 7 biases guide 1 to 
move clockwise around pin 3. 
FIG. 1 shows guide 1 contacting a stationary, upper stop surface 11, which 
is the rest position and the position when the rigidity of a paper 9 being 
decurled is not sufficient to overcome the bias of spring 7. FIG. 2 shows 
in guide 1 contacting a stationary, lower stop surface 13, which is the 
position of guide 1 after the largest movement of guide 1 permitted by the 
mechanism. Roller 15 is located opposite the arced surface of guide 13, 
and stop 11 is located to leave a separation of more than the thickness of 
paper 9 between 15 and guide 13. 
The moment (torque characteristics) and other mechanical characteristics of 
guide 1 as pivoted on pin 3 and resilience and other mechanical 
characteristics of spring 7 are selected so that paper of number 16 weight 
(international measure: 60 gr./m.sup.2) does not move guide 1, and paper 
of number 24 weight (90 gr./m.sup.2) is just sufficient to move guide 1 
against lower stop 13. Pinch rollers 17 and 19 rotate to drive paper 9 
between guide 1 and roller 15. Roller 15 is always spaced from guide 1 
more than the thickness of any paper to be decurled, and pinch rollers 17 
and 19 are on the input side and are positioned close enough to guide 1 so 
that pinch rollers 17 and 19 are a significant moving force on paper 9 
while paper 9 passes between guide 1 and roller 15. Pinch rollers 21 and 
23 are on the output side located to grasp any paper 9 of length to be 
decurled (seven inches or longer in this specific embodiment) before 
leaving rollers 17 and 19 and pull paper 9 between guide 1 and roller 15. 
In this manner paper 9 being decurled is initially moved by rollers 17 and 
19. The paper 9 is guided to contact roller 15 opposite guide 1, and 
roller 15 is a urethane, high friction material rotated to assist the 
paper 9 movement. Before paper 9 exits rollers 17 and 19, it is in the nip 
of rollers 21 and 23, which turn to continue the movement of paper 9 
between guide 1 and roller 15. 
FIG. 3 shows a perspective view of the decurl guide structure of this 
specific embodiment. The upper stop 11 is implemented by being the outer 
surface of a low-friction bushing for a shaft 30 (shown on the right 
without the right bushing) which supports decurl roller 15. Lower stop 13 
is a pin mounted on the frame 32 which extends a limited distance to 
contact guide 1. Although shown on only one side in FIG. 3, upper stop 11 
and lower stop 13 are substantially identical on each side of decurl 
roller 15. 
Lower guide 34 extends across the decurler of a width of at least the width 
of the widest paper 9 to be decurled (almost 9 inches in this specific 
embodiment; since, when guide 34 is wider than the paper, a skewed paper 9 
can pass through without encountering frame 32, which is an advantage). 
Lower guide 34 is molded plastic and, as is conventional to reduce 
electrostatic charging, has a number of raised integral, thin guides 36 on 
which the paper primarily rests. Reference again to FIG. 1 and FIG. 2 
illustrates that guide 36 faces a upper guide 38. Upper guide 38 is 
pivoted on rod 40 by which in the clockwise position of guide 38 (not 
shown) paper 9 from rollers 17 and 19 is directed to bypass decurling. In 
the position shown in FIGS. 1 and 2 upper guide 38 directs paper 9 for 
decurling and is positioned opposite guides 36 and the lower edge of guide 
34 to direct paper 9 to contact decurl roller 15. Ideally, this contact is 
tangential to roller 15, but a more directed contact is acceptable. 
The force from pinch rollers 17 and 19 is not critical to the 
self-adjustment of this decurler since paper which is not stiff enough to 
overcome the force from spring 7 will be deflected by guide 1 even if the 
force from roller 17 and 19 is otherwise large. This stiffness 
characteristic of paper is sometimes termed beam strength. 
Roller 15 has a frictional surface and is driven in the paper feed 
direction. This facilitates paper movement. Movement of roller 15 is not 
considered critical to function since it is not the primary drive force 
during the decurling, and roller 15 ideally might be replaced with a 
shaped surface of very low drag to paper 9 having a surface complementary 
to the arc of guide 1. Alternatively, such a stationary surface might be 
used having significant friction but with feed of paper 11 being assisted 
by, for example, air jets. 
Other variations will be apparent or may be developed in the future which 
are within the spirit and scope of this invention, with particular 
reference to the accompanying claims.