Sheet turning device

A sheet turning device in a sheet transporting path for receiving a sheet transported in a predetermined direction turning the sheet and transporting the sheet in the predetermined direction. A pair of rollers are provided with a belt extending between the rollers for turning the sheet. A switch is provided for stopping the sheet transported onto the lower inner surface of the sheet turning belt. A driving shaft circulates the sheet turning belt to transport the sheet kept on the lower inner surface of the sheet turning belt in a direction orthogonal to the predetermined direction. A pressing member is provided for stopping and pressing the sheet on the upper inner surface of the sheet turning belt, and a sheet transporting roller for transporting the sheet pressed by the pressing member in the predetermined direction.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present imvention relates to a device for turning a sheet of paper and, 
more specifically, to such a device usable for copying on both sides of a 
sheet of paper in a copying machine. 
2. Disclosure of the Background Art 
An image formation apparatus, such as a copying machine or a laser printer, 
capable of forming an image on both sides of a sheet of paper is 
commercially available. In such an image formation apparatus, the sheet 
must be turned. For that purpose, a switchback type sheet turning device 
as shown in FIG. 6, for example, is commonly employed. The sheet turning 
apparatus is provided with a sheet transporting path 52, which makes a 
loop-shaped path with a printing unit 51 therein, to transport the sheet 
in the counterclockwise direction in the figure. The sheet is turned in 
the course of the circulation in the sheet transporting path 52 by rollers 
53 which rotates in both the forward and reverse directions. Specifically, 
after printed with an image on one side in the printing unit 51, the sheet 
is transported to the rolllers 53 and moved by the rollers 53 until the 
tail portion of the sheet is nipped by the rollers 53. Then, the sheet is 
stopped once and transported with its original tail portion first by 
reverse rotation of the rollers 53. Since the sheet is turned by the 
transportation through which the original tail portion of the sheet goes 
first, the other side of the sheet is then formed with an original image 
when the sheet is transported through the printing unit 51 again. After 
that, the sheet with two images on both sides is discharged onto a sheet 
receiver 54 by the forward rotation of the rollers 53. 
When a two-sided copy is carried out with the above device turning the 
sheet, the directions of the images on both sides of the sheet may be 
opposite to each other. For example, in the case where a direction of the 
sheet transportation is the same as that of the images, an image shown in 
a solid line in FIG. 7 is made on the first face of the sheet which is 
transported in the direction of an arrow A shown in FIG. 7. However, after 
the rollers 53 turns the sheet so that the tail of the sheet goes first, 
the sheet is transported in direction of an arrow B. Therefore, the 
direction of the image formed on a second face of the sheet is opposite to 
that of the image on the first face as can be seen from an illustration of 
a broken line in FIG. 7. 
In order to solve the above disadvantage, image information stored in 
memory can be read from the end of the information in, for example, a 
laser printer. In this manner, however, the control must be complicated. 
Transporting a sheet in a direction orthogonal to the transporting 
direction may come to turn the sheet as proposed in Japanese Examined 
Patent Publication No. 22787/1980. According to the description of the 
publication, first a sheet having an image on one side is turned so that 
the first character train in the image goes first, that is, the sheet is 
turned in a direction opposite to the predetermined direction when the 
image is automatically copied on both sides of the sheet through a copying 
machine. Second after the sheet goes through a fuser, the sheet is 
received by the sheet turning device. In the device, the sheet is 
transported in a direction orthogonal to the predetermined direction so 
that one side of the sheet goes first, and then the sheet is turned. 
Third, the sheet is transported in the predetermined direction so that the 
original head of the sheet goes first, and then the sheet is turned. 
Fourth, the sheet is transported in order to copy an image on the second 
face of the sheet. Fifth, the sheet having two images on both sides is 
received from the fuser by the sheet turning device and turned. After 
that, the sheet is transported to a sorter. 
SUMMARY OF THE INVENTION 
The present invention provides a sheet turning device in a sheet 
transporting path for receiving a sheet transported in a predetermined 
direction, turning the sheet and transporting the sheet in the direction, 
comprising a pair of rollers disposed on opposite sides of the sheet 
transporting path along the predetermined direction; a belt extending 
between the rollers for turning the sheet; means for stopping the sheet 
transported onto the lower inner surface of the belt; means for 
circulating the belt to transport the sheet kept on the lower inner 
surface of the belt in a direction orthogonal to the predetermined 
direction so that the sheet turns; a pressing member for stopping and 
pressing the sheet which is turning and moving, on the upper inner surface 
of the belt; and a sheet transporting roller for pressing the sheet 
against the pressing member to transport the sheet pressed by the pressing 
member in the predetermined direction in spite of pressing the sheet 
against the upper inner surface by the pressing member. 
Since the device according to the present invention has the pair of rollers 
and the sheet turning belt therebetween in the sheet transporting path, 
the transported sheet is moved upward by the inner surface of the belt in 
a direction orthogonal to the predetermined direction so that it is 
turned. The turning of the sheet is carried out not in a direction 
identical with the predetermined direction but in a direction orthogonal 
to the predetermined direction, so that the sheet can be turned without 
changing the head and tail of the sheet. 
When the sheet is turned, the sheet moves upward on the inner surface of 
the sheet turning belt, so that the sheet must be on the upper inner 
surface of the belt. In order to keep the sheet, the device according to 
the present invention has the pressing member for pressing the upper inner 
surface of the sheet turning belt. Since the pressing member is placed 
inside the sheet turning belt, the device can be miniaturized.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 5 is a schematic view showing a constitution of a main portion of a 
laser printed L having a sheet turning device which is an embodiment 
according to the present invention. 
The laser printer L comprises a printing unit 1, a sheet circulating unit 
2, a sheet turning unit (a sheet turning device) 3, a sheet tray 4 and a 
sheet receiver 5. 
The printing unit 1 includes a photoconductive drum 11 made of 
photosensitive substance and a processig unit provided on the peripheral 
portion of the drum 11 for producing an image. The printing unit 1 
produces an image on the upper side of a sheet fed from the sheet tray 4 
or the sheet circulating unit 2. An electrifying device 12 for uniformly 
establishing static electric charge on the surface of the photoconductive 
drum 11, a laser unit 13 for directing light to the charged 
photoconductive drum 11 to make a latent image thereon, a developing unit 
14 for depositing toner on the latent image and making it visible by 
development, a transferring unit 15 for transferring the image of toner to 
paper and a cleaner 17 for eliminating the toner remaining on the 
photoconductive drum 11 are disposed in that order, surrounding the 
photoconductive drum 11, to produce an image with toner on a sheet of 
paper. The image of toner is fused on the sheet by a fuser 16, and then 
the sheet is transported to the sheet circulating unit 2. 
The sheet circulating unit 2 receives the sheet from the fuser 16, 
transports the sheet in the counterclockwise direction so as to pass it 
under the printing unit 1 and further transports it through the sheet 
turning device 3 to the printing unit 1 again. The sheet circulating unit 
2 is provided with a flap 21 close to the fuser 16. The flap 21 sorts 
sheets fed from the fuser 16 upward and downward by virtue of a solenoid 
21a and a return spring 21b. A sheet guided upward is transported to the 
sheet receiver 5, and a sheet guided downward is transported to the 
printing unit 1 again through the sheet turning device 3. The sheet 
turning device turns the sheet. The sheet turning device has a microswitch 
22 serving as a sheet stopper and a feeding roller 23 in its inlet. 
FIGS. 1 to 3 are views showing a constitution of the sheet turning device 
3: FIG. 1 is a plan view, FIG. 2 is an elevational view and FIG. 3 is a 
side view seen from the right. 
Arrow C in those figures denotes a predetermined direction in which the 
sheet circulating unit 3 transports a sheet. Reference character D in FIG. 
1 denotes a sheet transporting path in the sheet circulating unit 3. 
A pair of rollers 31a, 31b are disposed on opposite sides of the sheet 
transporting path D in a direction corresponding to the predetermined 
direction C. The rollers 31a, 31b are connected to a driving system (not 
shown), such as a driving shaft of a photoconductive drum serving as belt 
driving means and rotated in the counterclockwise direction in FIG. 3. 
Belts, more specifically four sheet turning belts, 32a to 32d extend 
between the rollers 31a, 31b at an interval to each other. These belts 32a 
to 32d are rotated in the direction orthogonal to the predetermined 
direction C (namely, in the counterclockwise direction in FIG. 3) by the 
rotation of the rollers 31a, 31b. Between the belts 32b, 32c, a sheet 
transporting roller 33 is positioned. The sheet transporting roller 33 
(referred to simply as "transporting roller 33" below), which is rotated 
by a driving system not shown in the drawings, transports the sheet whose 
head and tail are reversed in the predetermined direction C. 
A pressed 34 is mounted close to and inside the upper extension of each of 
the belts 32a to 32d between the rollers 31a, 31b. The presser 34 may be a 
plate of resin such as acrylic and is pressed against the upper extension 
of each of the belts 32a to 32d from the inside by pressing members 
including springs 35. The sheet is sent in a space between the presser 34 
and the belts 32a to 32d by the rotation of the belts 32a to 32d. The 
transporting roller 33 rotates in contact with the upper surface of the 
presser 34 when the sheet is transported. The transporting roller 33 has 
semicircular pickup rollers 33a. Usually the transporting roller 33 does 
not come in contact with the presser 34, because each of the pickup 
rollers 33a is positioned with a straight part of its peripheral surface 
being opposite to the presser 34. However, in the case where the sheet 
sent to the presser 34 is transported in the predetermined direction C, 
the transporting roller 33 rotates, and a arc portion each of the pickup 
rollers 33a comes in contact with the presser 34. The sheet on the presser 
34 is transported in the predetermined direction C by friction force 
against the pressing force that the presser 34 produces by pressing the 
upper inside extension of each of the belts 32a to 32d. 
An end 34a of the pressser 34 is slightly bent down close to the roller 31a 
which comes in contact with the sheet and serves as a paper guide. Because 
of the end 34a, the sheet transported from the sheet turning device along 
the inner surface of each of the belts 32a to 32d is assuredly guided to a 
space between the presser 34 and the belts 32a to 32d without deviating 
from the presser 34. On the other hand, an end 34b of the presser 34 is 
bent up close to the roller 31b which does not come in contact with the 
sheet and serves as a guard. The end 34b stops the sheet sent through the 
space between the presser 34 and the belts 32a to 32d. A microswitch 36 is 
mounted close to the end 34b to sense the sheet kept at the end 34b. 
Further, a paper guide 37 is held slightly above the inner surface of the 
lower extension of each of the belts 32a to 32d along the predetermined 
direction C. The paper guide 37 prevents the belts 32a to 32d extending 
orthogonal to the predetermined direction C from catching the sheet from 
the sheet circulating unit 2. The sheet is sent along the paper guide 37. 
FIGS. 4(A) to 4(E) are views showing sequential steps of the operation of 
the sheet turning device. According to convenience of explanation, FIGS. 
4(A) and 4(E) are elevational views, and FIGS. 4(B) to 4(D) are side 
views. 
First, a sheet 40 printed with an image on one side is fed to the sheet 
turning device 3. The sheet 40 is sent in a direction corresponding to an 
arrow C along the paper guide 37 and is stopped on the inner surface of 
the lower extension of each of the belts 32a to 32d in accordance with a 
stop of the feeding roller 23 a predetermined period of time after the 
microswitch 22 turns off (the tail of the sheet passes the microswitch 
22). At this time, the sheet 40 has a face having the image positioned on 
the surface of each of the belts 32a to 32d (namely, the sheet 40 lies on 
the face having the image) (see FIG. 4(A)). 
When the rollers 31a, 31b are rotated in the counterclockwise direction, 
the sheet 40 begins to move along the inner surface of the extension of 
each of the belts 32a to 32d (FIG. 4(B)) and is sent to the space between 
the presser 34 and the belts 32a to 32d (FIG. 4(C)). The transportation of 
the sheet 40 is stopped by the end portion 34b of the presser 34, and 
simultaneously the microswitch 36 turns on (FIG. 4(D)). In accordance with 
the turning on of the microswitch 36, the rollers 31a, 31b are stopped. At 
this time, the sheet 40 has the face having no image positioned on the 
surface of the belts 32a to 32d, namely, the sheet 40 is turned compared 
to the original state shown in FIG. 4(A). 
Lastly, the feeding roller 33 rotates to move the sheet 40 on the presser 
34 in the predetermined direction C (FIG. 4(E)) to the printing unit 1 so 
that the sheet 40 lies on the face having no image therein. 
Thus, the sheet turning device 3 can turn a sheet in the above mentioned 
manner. In this sheet turning device 3, the head and tail of the sheet is 
kept unchanged, and therefore there is no need to rearrange an original 
image upside down. The sheet turning device 3 can be advantageously 
miniaturized because it does not require many trays and sheets are 
transported along and inside the sheet turning belts unlike a device 
disclosed in Japanese Examined Patent Publication No. 22787/1980. 
Although there are four of the sheet turning belts 32a to 32d extending 
between the rollers 31a, 31b in this embodiment, one belt may be 
substituted for them. An advantage of using a plurality of belts is that 
troubles such as a jam are easily settled. 
As has been described, the sheet turning device 3 turns a sheet without 
changing the head and tail of the sheet with regard to a predetermined 
direction in which sheets are transported, and therefore there is no 
possibility that an image is produced upside down when the sheet turning 
device 3 is employed in an imaging machine or the like. Additionally, 
there is another advantage that the sheet turning device can be 
miniaturized because the sheet is turned by transporting it along the 
inner surface of the belts extending between the rollers.