Paper transfer system in a printer

A small printer is provided which comprises a housing, a rolled printing paper mounted in the housing, a platen along which a paper runs, a motor, and a carriage having a printing head for mosaic printing on a paper on the platen. The carriage travels along the whole width of the paper and is driven by the motor, and a paper transfer mechanism transfers the paper by one line for every traverse of the carriage. The paper transfer mechanism comprises an idler positioned beneath the path of the paper, the idler being swingable in the moving direction of the paper, and the idler having a first projection parallel to the path of the carriage at the left half of the idler and a second projection inclined to the path of the carriage at the right half thereof. The projections are engaged with the corresponding slots provided at the bottom of the carriage to ensure the swing movement of the idler is synchronized with the movement of the carriage. The idler has a substantially V-shaped friction member providing a large frictional force to the paper in the normal moving direction of the paper and a small frictional force to the paper in the opposite moving direction of the paper.

BACKGROUND OF THE INVENTION 
The present invention relates to the paper transfer system of a printer, in 
particular, relates to such a system which is small in size, simple in 
structure and is suitable for use in a simple small printer. 
The prior paper transfer system of a small printer rotates a gum roller by 
a motor or a ratchet means, and a paper which contacts with that gum 
roller is transferred by the friction with that gum roller. 
However, said prior paper transfer system has the disadvantages that the 
size is rather large since the diameter of the gum roller must be larger 
than a predetermined value, and a motor or a ratchet means must be 
utilized only for transferring a paper. Further, that prior system has the 
disadvantage that it is heavy, resulting in the high manufacturing cost. 
SUMMARY OF THE INVENTION 
It is an object, therefore, of the present invention to overcome the 
disadvantages and limitations of a prior paper transfer system by 
providing a new and improved paper transfer system for a printer. 
It is also an object of the present invention to provide a paper transfer 
system which is simple in structure and small in size, resulting in the 
low manufacturing cost. 
The above and other objects are attained by a paper transfer system 
comprising of a housing, a rolled printing paper mounted in the housing, a 
platen along which a paper runs, a motor, a carriage having a printing 
head for mosaic printing on a paper on the platen, said carriage 
travelling along the whole width of the paper driven by said motor, an 
idler being put beneath the path of the paper, said idler being swingable 
in the moving direction of the paper, said idler having the first 
projection parallel to the path of the carriage at the left half of the 
idler and the second projection inclined to the path of the carriage at 
the right half of the idler, those projections being engaged with the 
corresponding slots provided at the bottom of said carriage to ensure the 
swing movement of the idler synchronized with the movement of the 
carriage, said idler having a friction means providing a large friction to 
the paper in the normal moving direction of the paper and a small amount 
of friction to the same in the opposite moving direction of the paper.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows the plane view of the printer including the paper transfer 
system according to the present invention. In FIG. 1, the reference 
numeral 1 is a motor, 2a and 2b are gears engaged with each other and are 
rotated by said motor 1, 3 is a spindle having a screw slot in both the 
clockwise direction and the counterclockwise direction and said spindle 3 
is fixed to said gear 2b. The screw slot in the clockwise direction is 
coupled with the other screw slot of the counterclockwise direction at 
both the extreme ends of the spindle 3. The reference numeral 4 is a 
carriage for mounting a printer head 11, and said carriage 4 has a 
projection (not shown) which engages with one of the screw slots on said 
spindle 3, and said carriage 4 has also a pair of slots 4a and 4b at the 
bottom of the carriage. The former slot 4a is parallel to the spindle 3, 
and the latter slot 4b is inclined to said spindle 3. A printer head 
mounted on the carriage 4 may be a dot matrix printer for mosaic printing 
having a plurality of (for instance seven) dots which are selectively 
activated according to the desired pattern to be printed. The printer head 
disclosed in the U.S. Pat. No. 3,896,918 can be utilized as the printer 
head mounted on said carriage 4, alternatively, a thermal printer head 
which has a plurality of small thermal elements can be utilized as the 
printer head. In case of a thermal printer head, the printing paper is a 
treated thermal paper which is colored by heating the same by said thermal 
elements selectively. The reference numeral 5 is a guide shaft provided 
parallel to the spindle 3 for guiding the carriage 4 along the spindle 3. 
The reference numeral 6 is an idler, and said idler 6 is slidable in the 
perpendicular direction (the direction as shown by the arrow P in FIG. 1, 
FIG. 2 and FIG. 5) to the spindle 3. According to the preferred embodiment 
of the present invention, said idler 6 is a T-shaped plate as shown in 
FIG. 1, FIG. 5 and FIG. 6, having the first arm 6-1 parallel to the 
spindle 3, and the second arm 6-2 perpendicular to the spindle 3 (see FIG. 
5), and said idler 6 has the first projection 6a parallel to the spindle 3 
at the left half portion of the first arm 6-1, and the second projection 
6b which is inclined to the spindle 3 at the right half portion on the 
first arm 6-1. The inclined projection 6b is so inclined that the left 
extreme end of the same is close to the spindle 3 and the right extreme 
end of the same is far from the spindle 3 (see FIG. 1). Further, the 
inclined projection 6b is substantially parallel to the inclined slot 4b 
on the bottom of the carriage 4 so that projection 6b can engage with the 
slot 4b. The idler 6 has also a friction means 6c (see FIG. 5 and FIG. 6) 
near the end of the second arm 6-2. Preferably, the friction by said 
friction means 6c in one direction is different from that in the opposite 
direction due to the particular structure of the friction means 6c as 
mentioned later. 
The reference numeral 7 is a guide plate provided on the bottom of the 
housing 50 so that said guide plate 7 can be pivotable around the axis 8. 
The guide plate 7 has a pair of paper guides 7a projected perpendicular at 
both the extreme ends of the guide plate 7. Preferably, the guide plate 7 
has a T-shaped slot for receiving said T-shaped idler 6, and the idler 6 
is put in the slot of the guide plate so that the idler 6 can slide in the 
direction P in the slot of the guide plate 7. The guide plate 7 has a pair 
of friction means 7b and 7c as shown in FIG. 1, and preferably, the 
friction by said friction means 7b and 7c depend upon the direction. The 
reference numeral 8 is an axis for pivotably mounting said guide plate 7. 
The reference numeral 9 is a plate spring for urging the guide plate 7 in 
the upward direction, 10 is a rolled printing paper mounted in the housing 
50. The reference numeral 11 is a printer head for mosaic printing, 12 is 
a U-shaped paper guide fixed to the housing 50, and the thin paper path is 
provided between the paper guide 12 and said guide plate 7 (or the idler 
6) as shown in FIG. 2. The portion of the paper guide 12 confronting with 
the printer head 11 operates as a platen. Thus, the paper runs from the 
rolled paper 10 through that thin paper path between the paper guide 12 
and the guide plate 7 to outside of the printer, and when the paper runs 
in front of printer head 11 the printing operation is performed. Further, 
a friction means 6c on the idler 6 is projected in said paper path in 
order to transfer the paper by friction in every travel of the carriage. 
Now, the operation of the above apparatus is described. 
When the motor 1 rotates the first gear 2a, the second gear 2b which is 
engaged with the first gear 2a is rotated and the spindle 3 which is fixed 
to the second gear 2b is also rotated. The spindle 3 has a pair of screw 
slits 3a and 3b which are coupled with each other at both the ends 3-1 and 
3-2 of the spindle 3 as shown in FIG. 3. The projection (not shown) 
provided on the carriage 4 is engaged with that screw slit. Accordingly, 
when the spindle 3 rotates in one direction, the carriage 4 engaged with 
the slit of the spindle 3 is moved along the spindle 3 and the guide shaft 
5 in one direction (left or right), and when the carriage 4 reaches the 
extreme end of the spindle 3, the projection (not shown) of the carriage 4 
is engaged with the other screw slit and moves in the opposite direction. 
Thus, the carriage 4 moves in both the direction linearly guided by the 
guide 5 according to the rotation of the spindle 3. When the carriage 3 
moves from the left end to the right end, the printer head mounted on the 
carriage prints the desired pattern on the paper 10, and when the carriage 
4 moves from the right end to the left end, the paper 10 is transferred by 
one line. The operation for transferring paper is as follows. 
When the carriage 4 stands at the left end of the spindle as shown in FIG. 
1, the first slot 4a which is provided at the bottom of the carriage 4 
parallel to the spindle 3 is engaged with the first projection 6a which is 
parallel to the spindle 3. When the carriage 4 moves in the right 
direction and reaches the middle of the path, the slot 4a of the carriage 
4 does not engage with the projection 6a anymore, and instead, the second 
slot 4b which is substantially parallel to the second projection 6b is 
engaged with the second projection 6b which is also inclined to the 
spindle 3. When the carriage 4 moves further in the right direction, the 
projection 6b of the idler 6 is pushed by the slot 4b of the carriage 4 in 
the moving direction of the carriage 4. The force F of that push can be 
divided to the first component F.sub.A which is parallel to the slot 4b of 
the carriage 4, and the second component F.sub.B which is in the direction 
of the moving direction of a paper as shown in FIG. 4. In this case, it 
should be noted that the idler 6 is slidable on the guide plate 7 in the 
direction P of FIG. 5. Therefore, when the carriage 4 is moving from the 
middle of the path of the right end as shown by the arrow Q in FIG. 5, the 
idler 6 is pushed by the second component F.sub.B in the direction R of 
FIG. 5. That direction R is opposite to the normal moving direction of a 
paper. 
By the way, a paper touches with friction means 6c on the idler 6, and the 
friction means 7b and 7c on the guide plate 7. When the idler 6 moves in 
the direction R of FIG. 5, the friction between the friction means 6c and 
a paper is small, and so a paper does not follow to the movement of the 
idler 6 but remains stopped. The friction means 7b and 7c on the guide 
plate 7 prevent also the movement of a paper in the direction R when the 
idler moves in that direction. 
Next, when the carriage 4 is moving in the direction S of FIG. 6 from right 
to left, after the carriage reaches the extreme right end of the path, the 
projection 6b of the idler 6 is pushed by the slot 4b of the carriage 4 in 
the moving direction of the carriage 4. The force F' in this case is in 
the opposite direction of that of the force F of the case of FIG. 5, 
therefore, the idler 6 moves in the direction T of FIG. 6 when the 
carriage 4 moves in the direction S of FIG. 6. In this case, the friction 
means 6c on the idler 6 pushes a paper in the direction T by friction 
between said friction means 6c and a paper, when the idler 6 moves in the 
direction T. In this case, the friction by friction means 7b and 7c on the 
guide plate 7 is smaller than that by friction means 6c. Therefore, when 
the idler 6 moves in the direction T, a paper is moved also in the 
direction T by the length equal to the movement of the idler 6. 
In summarizing the above operation, when the carriage 4 moves in the 
direction of the printing line in both way, the idler 6 moves in the 
perpendicular direction to that printing line, or the moving direction of 
a paper. And, when the carriage 4 returns to the initial position, or the 
idler 6 moves in the direction T of FIG. 6, a paper is moved by the 
predetermined length or the length requested for the printing of one line. 
By repeating the above operation, a paper is moved by one line every time 
a carriage finishes each one line printing. 
When a paper 10 is not mounted, and a carriage 4 moves in both ways, the 
friction means 6c might contact directly with the bottom of the U-shaped 
member 12. In this case, the friction between the friction means and the 
member 12 might be very large, and that large friction would disturb the 
operation of the printer, or the movement of the idler 6. In order to 
solve that problem, the guide plate 7 is pivotably fixed to the axis 8 so 
that the guide plate 7 rotates against the spring 9 in the 
counterclockwise direction (see FIG. 2) when that friction is too large, 
that rotation of the guide plate 7 reduces the friction and facilitates 
the operation of the printer. 
Now, the structure of the friction means 6c, 7b and 7c will be described in 
accordance with FIGS. 7A, 7B, 7C and 7D. FIG. 7D is the perspective view 
of the friction means, which is in the cylindrical shape with a sector 
shaped slit 16. The friction means is made of material having a large 
amount of friction, like urethane gum or natural gum. The size of each 
friction means is small, and for instance, the length L is less than 5 mm, 
and the diameter is less than 3 mm, when the width of a paper is about 10 
cm. 
Due to the presence of the sector shaped slit 16, each friction means has a 
fixed portion 13, a spring portion 14 and a support portion 15 connecting 
both the fixed portion 15 connecting both the fixed portion 13 and the 
spring portion 14. The angle .alpha. of the sector shaped slit or the 
angle between the fixed portion 13 and the spring portion 14 can vary by 
pushing the spring portion 14 towards the fixed portion. Preferably, the 
spring portion 14 is divided in to a plurality of portions separated from 
one another by a thin slit 17. 
In FIGS. 7A through 7C, a paper 10 contacts with the friction means at the 
point A which is on the spring portion 14 near the edge of the same. 
When the friction means moves in the direction R as shown in FIG. 7B, the 
angle .alpha..sub.1 between the fixed portion 13 and the spring portion 14 
is smaller than the angle .alpha. of FIG. 7A in which the friction means 
stops, and therefore, the top point A on the spring portion 14 is lowered 
by the length .DELTA.P compared with the position when the friction means 
stops as shown in FIG. 7B. Accordingly, the friction between the friction 
means and a paper in the case of FIG. 7B is small, and a paper does not 
move in spite of the movement of the friction means in the direction R. 
On the other hand, when the friction means moves in the direction T as 
shown in FIG. 7C, the angle .alpha..sub.2 between the fixed portion and 
the spring portion becomes larger than that of the case of FIG. 7A because 
of the friction itself between the friction means and the paper. 
Therefore, the top point A on the spring portion 14 is raised by .DELTA.P' 
compared with the position of FIG. 7A where the friction means is stopped. 
Accordingly, the friction between the friction means and a paper in the 
case of FIG. 7C is large, and a paper moves following the movement of the 
friction means. 
Accordingly, it should be appreciated that the friction between the 
friction means and a paper depends upon the moving direction of the 
friction means and/or the paper due to the particular structure of the 
friction means shown in FIGS. 7A through 7D. 
Each friction means 6c, 7b and 7c are installed on the idler 6, and the 
guide plate 7 so that the upper portion or the spring portion 14 is at the 
upstream along the paper path, and the lower portion or the fixed portion 
13 is at the downstream along the paper path as shown in FIGS. 2, 5 and 6. 
Also, the height of three friction means 6c, 7b and 7c is supposed to be 
the same as one another to assure the contact with the paper at the same 
time. In those configurations, when the idler 6 moves in the direction T 
of FIG. 6, the relation between the friction means 6c and the paper is 
shown in FIG. 7C and the friction between the two is large, then, the 
paper is transferred in the direction T following the idler 6. In this 
case, the relation between the friction means 7b and 7c, and the paper is 
shown in FIG. 7B, and the friction between those friction means and the 
paper is small. Therefore, the friction by the friction means 6c is larger 
than that by the friction means 7b and 7c. 
On the other hand, when the idler 6 moves in the direction R of FIG. 5, the 
friction by the friction means 6c is small, and the friction by the 
friction means 7b and 7c is large. Therefore, the paper does not move. 
It should be appreciated that the structure of the friction means is not 
restricted to the shape as shown in FIGS. 7A through 7D, but a V-shaped 
friction material can be utilized for that purpose. Further, the friction 
means 7b and 7c do not necessarily depend upon the direction, but an 
ordinary friction means having the same friction in both the directions 
can be utilized for the friction means 7b and 7c. Further, the fixed 
friction means 7b and 7c can be mounted on the platen 12, instead of the 
guide plate 7. 
As described above in detail, according to the present invention, an idler 
swings synchronized with the round trip of a carriage, and a friction 
means mounted on the idler transfers a printing paper by one line whenever 
the carriage is in the return path. Accordingly, the structure of the 
present printer is simple, and the size of the printer is small. Further, 
no ratchet means, no motor nor gum roller for merely transferring a paper 
is necessary, thus, a printer with a light weight and low price can be 
obtained. 
From the foregoing it will now be apparent that a new and improved paper 
transfer system has been found. It should be understood of course that the 
embodiments disclosed are merely illustrative and are not intended to 
limit the scope of the invention. Reference should be made to the appended 
claims, therefore, rather than the specification as indicating the scope 
of the invention.