Lining method and apparatus for printers

In a method and apparatus for changing the line of a sheet to be printed, the sheet is set in a print starting position, in which a front end of the sheet is located in front of bail rollers which feed the sheet together with a platen, and a carriage with a print head and a sheet guide is moved to a predetermined guide position in which the sheet guide is located at or near the center of width of the sheet, prior to every change of line, until the front end of the sheet is held between the bail rollers and the platen.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method and apparatus for changing the 
line in a printer, in particular in a serial printer. 
The present invention can be applied to the printing of both cut sheets and 
continuous sheets with perforations on each side of the sheet. These 
continuous sheets will be referred to hereinafter as fanfold paper. 
In a serial printer which prints, for example, a cut sheet, after the cut 
sheet is loaded on a rear cover of the printer, the sheet is fed forward 
in accordance with a command to start printing from a line change drive 
control unit, so that a platen rotates to move the sheet with the help of 
pinch rollers. During the movement of the sheet, the sheet is sensed by a 
sensor, which is located on the passageway of the sheet to detect passing 
of the front end of the sheet. 
A further movement of the sheet is carried out through a predetermined 
displacement from the point of the detection to bring the sheet to a print 
starting position, at which the printing is commenced. The sheet set at 
the print starting position is printed by a printing head carried on a 
carriage which moves along the platen. The sheet is fed forward line by 
line by the rotation of the platen. 
2. Description of the Related Art 
Generally, when the sheet is located in the print starting position, the 
front end of the sheet is held between the platen and bail rollers which, 
together with the rotating platen, feed the sheet forward. 
Namely, there is a vacant space at the front end (leading end) of the 
sheet, corresponding to a distance L between the front edge of the sheet 
and the portion of the sheet that is located in front of the printing 
head. That is, when the sheet is located at the print starting position, 
the front edge of the sheet passes the printing head by the distance L. 
Therefore, when the printing is completed for one sheet, there is always a 
vacant space (non-printed area) corresponding to the distance L at the 
front end of the sheet. 
On the contrary, if the printing is commenced immediately the front edge of 
the sheet reaches the printing head, often the front end of the sheet is 
not held between the bail rollers and the platen when the front end of the 
sheet reaches the bail rollers during the forward movement of the sheet. 
This results in a paper jam. 
SUMMARY OF THE INVENTION 
The primary object of the present invention is to eliminate the drawbacks 
mentioned above and make it possible to carry out printing even on the 
front edge of the sheet, before the front edge of the sheet reaches the 
bail rollers, while ensuring that the front end of the sheet can be firmly 
held between the bail rollers and the platen when the front end reaches 
the bail rollers, without the possibility of a paper jam. 
In order to achieve the object mentioned above, according to the present 
invention, there is provided in a printer having a platen which rotates 
about its own axis to feed a sheet to be printed, a carriage which moves 
along the axis of the platen and which has a printing head and a sheet 
guide integral therewith to guide the movement of the sheet along the 
platen, and bail rollers which hold, between the bail rollers and the 
platen, the sheet when it has moved past the printing head, a method for 
changing the line of the sheet comprising setting the sheet in a print 
starting position, in which a front end of the sheet is located in front 
of the bail rollers, and moving the carriage to a predetermined guide 
position in which the sheet guide is located at or near the center of the 
width of the sheet, prior to every change of line, until the front end of 
the sheet is held between the bail rollers and the platen. 
According to another aspect of the invention, an apparatus for changing the 
line of the sheet comprises means for setting the sheet in a print 
starting position, in which a front end of the sheet is located in front 
of the bail rollers, and means for moving the carriage to a predetermined 
guide position in which the sheet guide is located at or near the center 
of the width of the sheet, prior to every change of line, until the front 
end of the sheet is held between the bail rollers and the platen. 
According to still another aspect of the invention, there is provided in a 
printer having a platen which rotates about its own axis to feed a sheet 
to be printed, a carriage which moves along the axis of the platen and 
which has a printing head and a sheet guide integral therewith to guide 
the movement of the sheet along the platen, bail rollers which hold, 
between the bail rollers and the platen, the sheet when it has moved past 
the printing head, and a sheet sensor which detects the presence of the 
sheet, said sheet being set in a print starting position in which the 
front end of the sheet is located in front of the bail rollers, an 
apparatus for changing the line of the sheet comprising means for counting 
accumulated number (M) of lines from the detection by said sensor, means 
for storing a set number (L) of lines, means for comparing the accumulated 
number (M) and the set number (L), means for storing a predetermined guide 
position (S) of the carriage in the direction of the movement thereof, 
means for determining whether the movement of the carriage is necessary or 
not, with reference to the result of a comparison at each command for 
change of a line, means for moving the carriage with the sheet guide to 
the guide position (S), in response to the determination of the 
determining means, and means for rotating the platen to feed the sheet by 
a predetermined amount of displacement when the carriage is moved to the 
guide position or when movement of the carriage is not necessary. 
With the arrangement of the invention mentioned above, the sheet to be 
printed is set in the print starting position, so that the front end 
thereof can be located in front of the printing head, upstream of the bail 
rollers, namely the front end does not reach the bail rollers at the 
beginning of printing. The carriage is always moved to a predetermined 
guide position in which the sheet guide on the carriage guides the 
movement of the sheet along the platen so as to feed the front end of the 
sheet between the bail rollers and the platen, prior to each change of a 
line of the sheet. Namely, when a line change command is given, the 
carriage is moved to the guide position in which the sheet guide is at or 
near the center of the width of the sheet, before the line change is 
carried out. 
This prior movement of the carriage takes place only until the front end of 
the sheet is located between the bail rollers and the platen. 
The movement of the sheet guide of the carriage to the guide position prior 
to each change of the line ensures that the front end of the sheet is fed 
between the bail rollers and the platen step by step. 
This results in the prevention of a paper jam which would otherwise take 
place because of a failure to squeeze the front end of the sheet into a 
slight gap between the bail rollers and the platen.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, the serial printer 1 has a printer body 11 on which a rear cover 
13 is detachably mounted. The rear cover 13 is provided with adjustable 
guides 15 which can be moved close to and away from each other to adjust 
the space therebetween in accordance with the width of a sheet 10 (FIG. 2) 
to be printed. A cylindrical platen 17, which is rotatably supported in the 
body 11, supports the sheet 10 while printing is carried out. The platen 17 
can be manually rotated by a platen knob 21 to manually feed the sheet, if 
necessary. The rear cover 13 is used to load cut sheets of paper and guide 
fanfold paper (continuous sheets). 
Sheet tractors (sprockets) 23 are rotatably supported in the body 11 holds 
and feed the fanfold paper. The sheet tractors 23 operate only when the 
fanfold paper is to be printed. The paper feed mode can be changed by a 
paper release lever 25 which can occupy two positions, i.e. a friction 
position in which pinch rollers 35 (FIG. 4) are pressed against the platen 
17 so as to feed cut sheets between the pinch rollers 35 and the platen 17 
and a release position in which the pinch rollers 35 are moved away from 
the platen, as designated by an imaginary line 35' in FIG. 4 and in which 
the sheet tractor 23 can rotate. 
A carriage 31 is mounted to the printer body 11 so as to move along the 
axis of the platen 17, namely in the direction perpendicular to the 
direction of feed of the sheet 10. The carriage 31 has a printing head 33 
which prints on the sheet 10. The gap between the printing head 33 and the 
platen 17 can be changed by a paper thickness level 37, in accordance with 
the thickness of the sheet 10. The sheet 10 printed by the printing head 
33 is held by bail roller units 39, each having a rotatable bail roller 41 
and a roller holder 42 (FIGS. 1 and 7), against the platen 17. Each bail 
roller unit 39 can move along and on a bail shaft 45 which extends 
parallel to the axis of the platen 17. 
The bail roller units 39 and the bail shaft 45 can be moved away from the 
platen 17 by a bail lever 43, as is well known. 
The numeral 50 designates a power switch of the printer 1. An operator 
panel 51 is provided with lamps, such as a power lamp 51a and an ON LINE 
lamp 51b (which lights when the printer is ON LINE with a host computer 
110), etc., and switches, such as an ON LINE switch 51c for setting an ON 
LINE or OFF LINE mode, and a sheet set switch (starter switch) 51d, etc. 
The illustrated mechanical construction of the serial printer per se is 
typical and is well known. Accordingly a further detailed explanation is 
omitted. 
In a conventional printer, as shown in FIGS. 7, 8, and 9, the cut sheet 10 
is loaded on the rear cover 13 and is inserted between the platen 17 and 
the pinch rollers 35. The insertion of the sheet 10 in the printer 1 
continues until the front end 10a of the sheet 10 is held between the 
platen 17 and the bail rollers 35. In other words, setting of the sheet at 
the print starting position is completed when the front end 10a of the 
sheet 10 is held between the bail rollers 35 and the platen 17, as shown 
in FIG. 7. After the sheet 10 is set in the print starting position in 
which the front end 10a of the sheet is held by the bail rollers 35 
against the platen 17, printing of the sheet can commence. As can be seen 
from the foregoing, when the sheet 10 is set in the print starting 
position, the front end 10a of the sheet 10 has moved past the printing 
head 33 by a distance L, which corresponds to the distance between the 
bail rollers 35 and the printing head 33 (exactly speaking, the print 
center of the printing head 33). Namely, the sheet 10 after printing 
always has a non-printed area (vacant space) defined by the distance L, at 
the top of the sheet 10, as shown in FIG. 8. This non-printed area 
decreases the printing density. 
On the other hand, if printing is commenced as soon as the front end 10a of 
the sheet 10 reaches the printing head 33, so that there is no vacant space 
at the top of the sheet, the front end 10a of the sheet 10 tends not to be 
inserted between the bail rollers 41 and the platen 17 when the front end 
10a reaches that point, thus resulting in the occurrence of paper jam, as 
designated by the numeral 20 in FIG. 9. This paper jam occurs particularly 
when the line change takes place when the carriage 31 with the sheet guide 
55 is far off the center 0 of the width of the sheet 10, as shown in FIG. 
9. 
In FIG. 7, S.sub.1 designates a sheet sensor which detects a passing of the 
front end 10a of the sheet 10 therethrough. 
The present invention aims at enabling the commencement of printing of the 
sheet 10 from the leading edge of the sheet 10 without producing an 
undesirable vacant space at the leading end 10a thereof, and without 
inviting a paper jam when the leading edge of the sheet 10 reaches the 
bail rollers 41. 
In summary, according to the present invention, printing of the sheet 10 
can be commenced, as soon as the front end 10a of the sheet reaches the 
printing head 33, as can be seen from FIG. 2, and the carriage 31 with the 
sheet guide 55 is always brought to a predetermined guide position on or 
near the center of the width of the sheet 10 before the line changing is 
carried out, until the front end 10a of the sheet 10 is held between the 
bail rollers 41 and the platen 17, as shown in FIG. 3. Since the line 
changing is always effected with the sheet guide located at the guide 
position, the front end 10a of the sheet 10 can be inserted between the 
bail rollers 41 and the platen 17 while being guided by the sheet guide 
55, without an occurrence of a paper jam. 
In FIG. 4, the numeral 3 designates a clutch which operates in response to 
the operation of the paper release lever 25 to rotate the sheet tractors 
23 when the continuous sheet 10' (fanfold paper) is loaded. As mentioned 
before, the pinch rollers 35 come away from the platen 17, so that the 
pinch rollers 35 do not interfere with the movement of the fanfold paper 
10', when the paper release lever 25 is operated. 
The sheet tractors 23 can be rotated by a first motor 5 referred to 
hereinafter as a line changing motor, through the clutch 3. The first 
motor 5 also rotates the platen 17 in accordance with line change commands 
from a control unit 100, which will be described hereinafter. A sensor 
S.sub.2 detects whether the paper release lever 25 is in the friction 
position or in the release position to detect whether the sheets are cut 
sheets 10 or fanfold paper 10'. The sheet tractors 23 do not rotate when 
the cut sheets 10 are loaded in the printer 1. The numeral 7 designates a 
second motor, referred to hereinafter as a space motor, which moves the 
carriage 31 and, accordingly, the printing head 33, in a direction 
parallel to the axis of the platen 17. 
The control unit 100 has a central processing unit (CPU) 101, a read only 
memory (ROM) 103 which stores programs, constants and the like, a random 
access memory (RAM) 105 which stores temporary data, and an input/output 
interface (I/O) 107 which is connected to the host computer 110, the 
sensors S.sub.1 and S.sub.2, the motors 5 and 7, the printing head 31, and 
the sheet set switch 51d, etc. 
In FIG. 6 which shows how the cut sheet 10 is set in the print starting 
position according to the present invention, 
B="0" shows the detection of the friction position of the paper release 
lever 25 by the second sensor S.sub.2 ; 
B="1" shows the detection of the release position of the lever 25 by the 
second sensor S.sub.2 ; 
C="0" shows the detection of the absence of the sheet 10 in front of the 
sensor S.sub.1, by the first sensor S.sub.1 ; and, 
C="1" shows the detection of the presence of the sheet 10 in front of the 
sensor S.sub.1 by the sensor S.sub.1. 
First, the cut sheet 10 is loaded on the rear cover 13 and the sheet set 
switch 51d is pressed, at step 601, and then whether the paper release 
lever 25 is in the friction position or in the release position is 
detected by the second sensor S.sub.2 (FIG. 4). 
The detection is confirmed in the control unit 100. 
When the friction position of the lever 25 is detected at step 603 (namely, 
B=0), the absence of the cut sheet 10 in front of the sensor S.sub.1 is 
then detected by the first sensor S.sub.1 at step 605. After the absence 
of the cut sheet 10 in front of the sensor S.sub.1 is detected (i.e. C=0), 
the carriage 31 is moved to the predetermined guide position at or near the 
center of the width of the cut sheet 10 to be printed, at step 607. This 
movement will be referred to hereinafter as "centering" of the carriage. 
When the centering of the carriage is finished, the line changing motor 5 
is reversed at step 609. The centering of the carriage 31 ensures that the 
sheet 10 can be guided by the sheet guide 55 integral with the carriage 31 
along the platen 17 and between the bail rollers 41 and the platen 17, 
which will be described in detail hereinafter. The reverse rotation of the 
line changing motor 5, which causes the reverse rotation of the platen 17, 
contributes to a correction of the posture of the sheet 10. Namely, even 
if the sheet is inclined with respect to the direction of the feed 
thereof, the inclination can be corrected by a slight reverse movement of 
the sheet 10 due to the reverse of the platen 17. Thus, the wrong posture 
of the sheet is corrected before it is fed between the pinch rollers 35 
and the platen 17. Note, step 609 can be dispensed with. The reverse 
rotation of the platen 17 continues until the amount N of reverse rotation 
is a predetermined value N1. When the amount N is detected to be N1, at 
step 611, the line changing motor 5 stops rotating to stop the platen 17, 
at step 613. The platen 17 remains stopped for a predetermined time 
T.sub.1. To this end, the time T.sub.1 is set in a timer T which is 
counted down by one at predetermined time intervals, at step 615. At step 
617, T is detected to be the set value T.sub.1, namely T.sub.1 .ltoreq.0. 
When T is zero or a minus value, the platen 17 is rotated in the forward 
direction again by the forward rotation of the line changing motor 5, at 
step 619. The forward rotation of the platen 17 continues for a 
predetermined amount of rotation. 
Namely, the rotation of the platen 17 continues until the amount N of 
rotation thereof after the detection of the passing of the front end 10a 
of the sheet 10 by the sensor S.sub.1 at step 621 is a predetermined value 
of N2. When the amount N is detected to be N2 at step 623, the line 
changing motor 5 is stopped to stop the rotation of the platen 17 at step 
625. At this stage, the sheet 10 is set in the print starting position. 
At step 603, if the sensor S.sub.2 detects the release position of the 
lever 25 (B=1), in which the pinch rollers 35 are away from the platen as 
shown by the imaginary line 35' in FIG. 4, and the sheet tractors 
(sprockets) 23 can be rotated by the line changing motor 5 through the 
clutch 3; namely, if the fanfold paper 10' is loaded in the printer 1, the 
flow chart goes to step 627, in which the first sensor S.sub.1 detects the 
absence of the sheet 10 in front of the sensor S.sub.1. 
After the absence of the sheet 10 in front of the sensor S.sub.1 is 
detected, the line changing motor 5 rotates to drive the platen 17 in the 
forward direction at step 629. When the platen 17 rotates, the sheet 
tractors 23 rotate together with the platen 17, so that the fanfold paper 
10' can be fed forward while being guided by the sheet guide 55. 
The rotation of the platen 17, and accordingly, the paper tractors 23, 
continues until the amount N of rotation thereof after the detection of 
passing of the front end of the sheet 10' by the sensor S.sub.1 at step 
631 is a predetermined value N3. When the sheet 10' is fed to the print 
starting position by the rotation of the line changing motor 5 by a value 
N3, the line changing motor 5 stops rotating at step 625. 
It should be noted that the roller holders 42 define a part of the 
passageway of the sheet 10 or 10'. Namely, the roller holders 42 prevent 
the portion of the sheet 10 that has passed the sheet guide 55 from coming 
out of the passageway. If the roller holders 42 are not provided, the sheet 
10 that has passed the sheet guide may not be brought between the bail 
rollers 41, and the platen 17. 
In the foregoing discussion the platen 17 is reversed once before the sheet 
10 is fed forward. Alternatively, it is also possible to repeat the forward 
and reverse rotation of the platen 17, so that the reversing of the platen 
17 takes place intermittently. This intermittent reverse motion is 
particularly useful for correcting inclination of the sheet 10 prior to 
the feed of the sheet 10 into the printing position, due to vibration by 
the intermittent reverse, where the inclination can not be corrected by 
only one reverse rotation of the platen 17, depending on the material, 
thickness or size of the sheet 10 to be loaded in the printer 1. The 
stopping of the platen 17 for a predetermined period between the forward 
rotation and the reverse rotation of the platen 17 (corresponding to steps 
615 and 617) can be dispensed with. Namely, the platen 17 can be rotated in 
the forward direction immediately after the stopping of the reverse motion 
of the platen 17, without a predetermined pause. 
At step 627, if the sensor S.sub.1 detects the presence of the sheet in 
front of the sensor S.sub.1 (i.e. C=1), setting of the sheet 10 is not 
necessary. 
After the sheet 10 is set in the print starting position as mentioned 
above, the carriage 31 is moved along the axis of the platen 17 by the 
spacing motor 7 and the printing head 33 is operated in accordance with 
printing programs from the host computer 110 to carry out the printing. 
During printing, the line change is effected by the operation of the line 
changing motor 5, similar to the conventional printing operation. 
In the print starting position, the front end 10a of the sheet 10 has not 
yet reached the bail rollers 41, in the present invention. 
FIG. 5 shows a flow chart of line changing steps before the front end 10a 
of the sheet 10 reaches the bail rollers 41, according to the present 
invention. 
In the present invention, the front end 10a of the sheet 10 is located 
directly in front of the printing head 33 upstream of the bail rollers 41, 
at the print starting position. 
In FIG. 5, when printing data is input to the printer from the host 
computer 110, at step 501, the printing starts at step 503. At step 501, 
if printing data is not received, printing does not start. Then, after the 
completion of printing of the first line is detected at step 505, the line 
changing is effected in accordance with line change commands. At step 507, 
whether or not a line change command has been sent is detected. When a line 
change command has not been sent, namely when a line change is not 
necessary, the printing is finished. When the line change command is 
detected at step 507, the accumulated number (M) of lines is compared with 
a predetermined number (L) of lines which is stored in ROM 103 in the 
control unit 100, to detect whether or not the sheet 10 should be guided 
by the sheet guide 55. When M.ltoreq.L is detected at step 509, namely, 
when the guiding of the sheet 10 by the sheet guide 55 is determined at 
step 509, the present position of the carriage 31, and accordingly, of the 
sheet guide 55 10 is calculated. Then, the present position Sc of the 
carriage 31 is compared with a predetermined guide position So of the 
carriage 31 stored in the ROM 103, at step 511. The guide position So is 
predetermined so that the sheet guide 55 is located on or near the center 
of the width of the sheet 10. This sheet guide position So generally 
correspords to the center of the platen 17 in the direction of the axis 
thereof but may be deviated therefrom, for example when the printing head 
33 is not positioned at the center of the sheet guide 55, that is the 
sheet guide 55 is offset from the center of the printing head 33 in the 
direction of the axis of the platen 17. 
If the carriage 31 happens to be in the guide position So (Sc=So), movement 
of the carriage is not necessary, and accordingly, line changing is 
immediately carried out at step 523. 
If the present position Sc of the carriage 31 is not in the guide position 
So at step 511 (Sc.noteq.So), whether the present position Sc is on the 
right or left of the guide position So is detected at step 513. 
In accordance with the detection of the present position at step 513, the 
carriage 31 is moved in either the left or right direction along the 
platen 17. 
For example, when the carriage 31 is offset from the guide position in the 
right direction, the carriage 31 is moved in the left direction until the 
carriage 31 comes to the guide position So, at step 515. 
On the other hand, when the carriage 31 is offset from the guide position 
in the left direction, the carriage 31 is moved in the right direction at 
step 517, until the carriage 31 comes to the guide position. 
The movement of the carriage 31 can be effected by the spacing motor 7 
(FIG. 4). When the carriage 31 reaches the guide position (i.e. Sc=So) at 
step 519 or 519', the carriage 31 is stopped, at step 521. After that, the 
line changing is carried out, at step 523. It will be appreciated that when 
the line changing is carried out, the carriage 31 is brought into the guide 
position prior to the movement of the carriage 31, so that the sheet guide 
55 is at or near the center of the width of the sheet 10, and accordingly, 
the sheet 10 can be guided by the sheet guide 55 during line changing. This 
prevents a paper jam which would otherwise take place, since the front end 
10a of the sheet 10 has not yet reached the bail rollers 41. 
After the line is changed, a programmed printing is carried out. 
The steps mentioned above are repeated until the printing is completely 
finished, which is detected at step 525. 
During further line changing, the accumulated number M of the lines exceeds 
the predetermined value L at step 509. When M&gt;L at step 509, the front end 
10a of the sheet 10 reaches the bail rollers 41 and is held by and between 
the bail rollers 41 and the platen 17 with the help of the sheet guide 55, 
as mentioned before. Namely, when the front end 10a of the sheet is held 
between the platen 17 and the bail rollers 41, centering of the carriage 
31 is not necessary, and accordingly, line changing can be immediately 
carried out, at step 523, without moving the carriage 31 to the guide 
position. That is, when M&gt;L at step 509, the process skips from step 509 
to step 523. This skip occurs also when the carriage 31 happens to be in 
the guide position at step 511, since centering of the carriage 31 is not 
necessary. After the accumulated number M becomes higher than the 
predetermined value L, the line changing is carried out without centering 
the carriage 31, similar to the prior art. 
As can be seen from the foregoing, according to the present invention, the 
carriage 31 is always brought to the sheet guide position prior to the 
change of line, until the front end 10a of the sheet 10 reaches the bail 
rollers 41, so that the sheet 10 can be guided by the sheet guide 55 
provided on the carriage 31 without a paper jam occurring. Accordingly, 
according to the present invention, printing can be made even at the top 
end of the sheet 10 without producing a vacant space thereat.