Printer with variable ribbon shifting mechanism

A printer comprising printing head moving means, printing ribbon feeding means, ribbon printing position change means and printing control means, in which printing control means gives instruction signals to regulate the crosswise move of the ribbon or to change the number of shift instruction signals less at both the ends of the ribbon to make the usage frequency substantially uniform with the central region.

BACKGROUND OF THE INVENTION 
The present invention relates to a printer equipped with a mechanism for 
shifting across a printing head a printing ribbon that is broader than the 
printing head. 
This kind of a printer is known as disclosed, for example, in Japan 
Published Unexamined Patent Application No. 59-78882. Conventional 
printers of dot impact type are constructed so as to feed a printing 
ribbon broader than a printing head in a direction of printing lines and 
to shift the ribbon by a stepping motor or the like in a direction of 
ribbon width orthogonal to printing lines. 
Such shifting will be explained with reference to FIG. 7. A printing ribbon 
200 is fed in a direction shown by an arrow a, and, after one line is 
printed, the ribbon 200 is shifted in a direction of its width b or c by 
the amount of shift corresponding to a fixed number of pulses giving to a 
stepping motor in a shape of steps (n represents positions of steps). 
Oblong printing faces 201 which can be printed in case of impacting all 
printing wires of a printing head are shifted reciprocally within the area 
of 12 steps in a direction of the ribbon width. In this way, the printing 
ribbon 200 can be efficiently consumed. By shifting an amount of three 
steps, the ribbon 200 is shifted the longitudinal width of the printing 
face 201. 
The printer described in the above, however, has the following problems. 
The printing areas A, B through O are different in frequency of use by the 
printing head during one cycle of reciprocation of the printing face 201 
on the ribbon 200. In other words, the area A or O is used once, the area 
B or N thrice, the area C or M five times and the areas D through L are 
used six times per one cycle. For this reason, the printing faces 201 
strike more in the central region of the ribbon 200, while striking less 
in the top and bottom regions of the ribbon 200. The areas A, B, N and O 
where usage frequency is less than 3 times occupy 4/15 or 26.6% of the 
effective usage area of the ribbon in the direction of width. 
Accordingly, when the ribbon 200 is used repeatedly, the central region is 
used more than the top or bottom region. As a result, printing effects are 
dark and thick in the top and bottom regions while light and thin in the 
central region. 
In the top and bottom regions of the ribbon, which are not used frequently, 
the ink remaining nearby blots at the position where the ribbon is 
impacted by the printing wire, resulting in different shade of the ink of 
one character printed. 
SUMMARY OF THE INVENTION 
This invention is made to solve the above problems and for improvement of 
the usage efficiency of the ribbon as well as maintenance of high quality 
printing. 
In order to accomplish the above objects, the printer of the invention 
comprises; 
a printing head moving means M1 which moves a printing head H to print 
according to input data along printing lines of a printing sheet P: 
a printing ribbon shifting means M2 which shifts a ribbon R extending in a 
direction of printing lines between the head H and the sheet P in 
correspondence to instruction signals inputted and in a direction of the 
ribbon R having a broader width than the printing width of the printing 
head N in a direction of its height: 
a ribbon feeding means M3 which feeds the ribbon R in a direction of 
printing lines; and 
a control means M4 which outputs specified number of shift instruction 
signals to the ribbon shifting means after the movement of the printing 
head H by the head moving means M1, wherein the printer is provided with a 
shift amount change means M5 which changes smaller the number of shift 
instruction signals outputted at one time shift of the ribbon R when the 
printing position is within the specified region from the end portion of 
the ribbon R than the number when it is in the central region outside of 
the above end portion.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
One embodiment of the invention will now be described in detail with 
reference to drawings. 
In FIG. 2, a plate-like platen 5 is provided between a pair of frames (not 
shown) in a dot printer and a sheet of printing paper 7 is inserted to the 
platen. The printing paper 7 is fed in a fixed direction being driven by a 
paper feeding roller (not shown). Between these frames, a pair of carriage 
guides 9 are provided parallel to the platen 5. A carriage 11 is slidably 
supported in an axial direction of the carriage guides 9 thereon. To the 
carriage 11, a carriage driving motor 10 such as a stepping motor, a DC 
motor and others are connected, as shown in FIG. 4, via a timing belt (not 
shown) so that the carriage 11 may reciprocate parallel to the printing 
line being driven by the carriage driving motors 10. 
A printing head 13 of dot impact type is provided on the carriage 11, which 
selectively drives a number of electromagnetic devices (not shown) 
contained therein according to the printing data and actuates printing 
wires (not shown) corresponding to such devices, thus printing the 
printing data in a type of dot matrix. 
At the end portion of a nose 13b of the head 13, a ribbon guide 15 as a 
guide member is supported centering around a shaft 15a to move vertically 
crossing the printing lines. A broad printing ribbon 29 of black and red 
colors is supported in the ribbon guide 15 so as to run along the printing 
line. As shown in FIG. 3, the ribbon guide 15 is unitally formed of 
synthetic resin with a pair of guide bodies 17 shaped like a disk and a 
stopper 19 connecting these guide bodies 17 as well as regulating the 
movement of the ribbon guide 15 in a vertical direction by abutting the 
nose portion 13b of the head 13. On the rear end surface of surface 17b is 
formed substantially corresponding to the printing end surface of the head 
13. On both the rear end side surfaces of the guide body 17, ribbon guide 
members 21, 23 having guide passages 21a are unitally formed somewhat 
inclining ahead at the side of the printing head and extending in the 
printing line direction. Further, a gear 17c is provided at the front end 
side of the guide body 17, to which a ribbon shift motor 25 such as the 
stepping motor or others provided on the carriage 11 are connected via an 
idling gear 26. Being driven by the ribbon shift motor 25, the ribbon 
guide 15 swings vertically crossing the printing line and centering around 
the axis 15a via the gear 17c. Thus, the printing ribbon 29 inserted into 
the guide passage 21a is shifted. 
The ribbon 29 is formed in a shape of an endless loop and is contained in a 
ribbon cassette 27 interchangeably attached to the frame, the ribbon being 
folded in a direction of the width crossing the printing line. The ribbon 
is sent out by a ribbon feeding motor 39. 
Driving control of the printer is executed by an electronic control device 
41 as shown in FIG. 4. The electronic control device 41 takes in outside 
input signals such as detection signals of each sensor, output signals of 
each switch and others, which drive the carriage driving motor 10, the 
ribbon feeding motor 39 and the ribbon shift motor 29 via each driving 
circuit 43, 45 or 47 and send printing signals to the printing head 13 to 
execute printing. The electronic control devices 41 comprise known CPU 51, 
ROM 53, RAM 55, Input/Output interface 57. ROM 53 stores programs and data 
to execute processing as shown in flowcharts of FIG. 6, FIG. 7, and FIGS. 
10A and 10B. 
Before explaining the ribbon shift process shown in a flowchart of FIG. 6, 
the general concept of this invention will be described with reference to 
FIG. 5. 
FIG. 5 illustrates a printing ribbon 29 one inch wide, 3/4 inches of which 
are black zone 29B and 1/4 inches of which are red zone 29R. The ribbon 29 
is moved against the printing face 13a of the printing head 13 by pulse 
signals of 21 steps of the ribbon feeding motor 39. The positions of 21 
steps are represented by n (0, 1, 2, . . . 21 ). The step positions 0 
through 14 are used for the black zone 29B and only the bottom step 
position 21 is used for the red zone 29R. 
When the printer is actuated, the printing face 13astarts from the step 
position n=0 of the printing ribbon 29 for printing in black. First, at 
step position n=0, four printing lines are maintained. Then, it moves to 
step position n=2. After that, it moves downwards sequentially by one step 
for printing one line each. When it reaches step position n=14, it is 
maintained at that position four times for printing. According to this 
routine K1, the ribbon is shifted from the uppermost to the bottom of the 
black zone 29B. On the other hand, the routine K2 of shifting from step 
position n=14 to step position n=0 is that it moves to step position n=12 
and then moves upwards sequentially one step each, reaching step position 
n=0. This reciprocating move is repeated. 
When changing printing from black to red or vice versa, the ribbon is 
shifted in one motion K3 to step position n=21 of the red zone 29R, if the 
printing face 13a is within step positions n=6 through 14 of the black 
zone 29B. If it is within step positions n=0 through 5, the ribbon is 
shifted to step position n=21 in two motions K4 and K5. 
When shifting the ribbon from red to black, the process moves to step 
position n=14 of the black zone 29B, when the ribbon is shifted from step 
position n=21 of the red zone 29R by seven steps upwards. Furthermore, it 
moves to step position n=12 shifting in nine steps upward motion K6. 
Such ribbon shift routine is explained with reference to a flowchart of 
FIG. 6. In the following description, S represents a step of the routine, 
and the routine is based on the processes of K1 through K6 in FIG. 5. 
First, whether the current printing color is red or black is determined at 
S1. If the current printing color is black, the routine moves to S2, which 
determines whether the next printing color is red or black. If the next 
color is black, the routine moves to S3. In other words, when printing is 
continuously black, the routine moves from S1 to S2 to S3. S3 determines 
whether or not the printing face 13a is at step position n=0 of the ribbon 
29. When the printing face 13a is at step position n=0, the routine moves 
to S4, where flag F is set to 1. The flag F shows whether the ribbon 29 is 
controlled to shift downwards K1 (F=1) against the printing face 13a from 
the uppermost or to shift upwards K2 (F=-1). In this case, since step 
position n is 0 and the shift direction is only downwards, flag F is set 
to 1. At S5, a counter C counts up, and at S6, whether or not the counter 
C is 4 is determined. In the first process steps, since the counter C is 
0, a negative determination is made at S6 and the process steps end. In 
another routine, one line of printing is executed. 
Next, at S1 through S6, the counter C counts up while executing 4 lines of 
printing. When the counter C reaches 4, an affirmative determination is 
made at S6 and the process steps move to S7. At S7, the counter C is 
reset, and at S8, the value of n is increased by F*2, or 2 since F is 1. 
At S9, the ribbon 29 is shifted to step position n=2 set at S8. Thus, this 
routine ends and one line of printing is executed at this position. 
Next, a negative determination is made at S3 since n is 2, and the process 
moves to S10, which determines whether or not the step position n is 14; 
specifically, S10 determines whether the printing face 13a is at the 
bottom position of the black zone 29B. Since n is 2, the process steps go 
to S11, where n is increased by the number of F or 1. At S9, the printing 
ribbon 29 is shifted according to the value of n and this routine ends. 
Accordingly, by the repetition of S1 to S2, S3, S10 and S11, the printing 
face 13a is shifted one step each to step position n=14. When it is 
determined at S10 that n reaches 14, or the ribbon 29 reaches the bottom 
of the black zone 29B, the process steps go to S12 and sets flag F to -1. 
Next, at S1 through S6, the printing face 13a is maintained at step 
position n=14 by 4 printing lines and thereafter, at S7 through 9, the 
ribbon 29 is shifted to step position n= 12. By the repetition of S3 to 
S10, to S11, the printing face 13a is shifted in one step increments from 
step position n=12 to step position n=0. 
The change of printing color from black to red or from red to black is 
executed by the processes of S1, S2, S14 through S22. In other words, when 
S2 gives an instruction to change color from black to red, the process 
steps go to S14, resets the counter C, and, at S15, sets the flag F to -1. 
Setting of this flag F is a preliminary preparation for changing the shift 
direction to K2, when the next-time ribbon shift from red to black is 
executed. At S16, it is determined whether n is less than 5 or not, 
namely, whether step position n is within 0 through 5 or within 6 through 
14. When it is determined to be within 6 through 14 at S16, the process 
steps go to S17, set n to 21 and shift the ribbon to step position n=21 at 
S9 (K3). 
When it is determined at S16 that step position n is within 0 through 5, n 
is set to 11 at S18 and ribbon shift is executed at S19 (K4). At S20, a 
signal is output to the carriage drive motor 10 to move the carriage 11 by 
around 100 mm. At S17, n is set to 21, and at S9 the ribbon is shifted to 
step position n=21. 
When the printing color is red in succession, S1 to S21 is repeated. At 
S21, when printing is changed from red to black, n is set to 12 at S22 and 
the ribbon is shifted at S9. In other words, the ribbon is shifted by nine 
pulses upwards from step position n=21 within the red zone 29R to step 
position n=12 within the black zone 29B. 
In this embodiment, the printing face 13a is maintained four times at the 
both end portions n=0 and 14 of the black zone 29B of the ribbon 29, 
therefore the ribbon 29 being used at almost the same frequency as the 
intermediate portion where n=1 through 13. The printing duty ratio showing 
the usage frequency in the width direction of the ribbon 29 is 74 percent 
at the minimum and 119 percent at the maximum. Compared with the prior 
art, the usage frequency of the ribbon 29 becomes uniform. The 
non-uniformity of printing shade owing to different positions of the 
printing face 13a becomes imperceptible, thus improving the printing 
quality. 
When shifting the ribbon from black to red, if the distance is short, as 
when n=6 through 14, the shift is executed in one move. However, if the 
shift distance is long, as when n=0 through 5, the shift is executed in 
two moves. Since the ribbon is not shifted a long distance, it prevents 
the ribbon 29 from creasing. When shifting the ribbon extending over the 
black and red zones, the number of steps is different according to the 
shifting direction. Because the red zone 29R is narrow compared with the 
black zone 29B, when shifting from the narrow zone to the wide zone, the 
tensile force is large in the vicinity of the central portion. To secure 
shifting in opposition to this force, when shifting from red to black, 
more steps are taken. Namely, if going back from step position n=21 to 
step position n=14, it can be shifted to black, however, two steps are 
added, going back to step position n=12. Conventionally, the black zone 
29B is to be used theoretically by the width of 14 steps but only 12 
steps have been used to prevent the colors from mixing. By so 
differentiating the shift amount, the usage is expanded to 14 steps, thus 
the ribbon is effectively used. 
In this embodiment, the ribbon is one inch wide, 3/4 inches of which is for 
black and the rest is for red. Also when a one-inch black ribbon is used, 
the same effect as in the embodiment can be obtained. Also a 7 pin printer 
or 1/72 pin pitch for a one-inch ribbon may be used, but a different 
number of pins or a ribbon of different width can be used in the same way 
as in the first embodiment. 
Next, a second embodiment of this invention will be described below with 
reference to the drawings. 
As shown in FIG. 9, a carriage 102 having a printing head 101 at the front 
is supported movably in a lateral direction along a pair of front and rear 
guide shafts 104a, 104b disposed parallel to a platen 103 between a pair 
of right and left frames (not shown). A pair of front and rear guide pins 
105, 106 are erected respectively on both sides of the front of the 
carriage 102, to which a ribbon guide 107 is inserted slidably upwards and 
downwards. 
Further, a ribbon holder 109 is inserted into two guide pins 108 erected on 
both sides of the front end of the ribbon guide 107, by which a printing 
ribbon 110 one inch wide or broader than the width of a nose portion 101a 
of the printing head 101 in a direction of its height is guided and 
supported on the ribbon holder 109 to run in the front of the nose portion 
101a. 
As shown in FIG. 8, the ribbon 110 is shaped like an endless belt, which is 
accommodated in a cassette so that a part thereof is exposed outside 
between front openings 111b of ribbon guide arms 111a extending out to the 
front from the both sides of the ribbon cassette 111. 
From the ribbon guide 107, a pair of legs 107a on both sides extend out and 
downwards, the lower ends of which are engaged and supported slidably in a 
lateral direction by the guide rails 112 extending along guide shafts 
104a, 104b. On both ends of the guide rails 112, racks 113 are fixed and 
slots 114 are formed thereon. The guide pins 115 fixed on the frame are 
engaged with the slots. Further, engagement pins 116 provided on the upper 
ends of each rack 113 are supported going through the slots 117 formed on 
the printer frame, thus enabling the both racks 113 to move only in a 
vertical direction. 
The engagement pins 116 provided on the upper ends of each rack 113 are 
engaged with a recess 124 formed in the front end lower portion of the 
ribbon cassette 111. The engagement portion 125 formed at the rear portion 
of the ribbon cassette 111 is engaged and supported from the above by a 
horizontal fulcrum pin 126 fixed on the frame so as to be detachable and 
swingable. Gears 118 of the right and left racks 113 are engaged for 
interlocking with output gears 123 of ribbon shift motors 122 such as a 
stepping motor and others via pinion gears 119 and gears 120, 121 engaged 
therewith. In accordance with the reciprocal rotation of the ribbon shift 
motor 122, the racks 113 on both sides move vertically, then the guide 
rail 112 moves vertically and the ribbon guide 107 shifts against the nose 
portion 101a of the printing head 101 provided on the carriage 102. 
Simultaneously, the ribbon cassette 111 swings with a shaft center x of 
the fulcrum pin 126 as a center in a direction of y shown in the figure. 
Thus, the ribbon 110 is shifted in a vertical direction against the nose 
portion 101a of the printing head 101a of the printing head 101 or in a 
cross direction of the ribbon. 
The ribbon 110 is forwarded by a known ribbon feed motor 39 in a direction 
of the printing line. When power is put on, a ribbon shift motor 29 is 
actuated and the upper end portion of the ribbon 110 is compulsorily set 
at an initial position opposing to the nose portion 101a. The driving 
control of the printer is executed by the electronic control device 41 
shown in FIG. 4. 
When a two-pulse drive signal is input, a driving circuit 43 of the ribbon 
shift motor 29 shifts across the ribbon 110 by one unit amount or an 
amount of one step via the ribbon shift motor 29. By the shift of an 
amount of 14 steps, the ribbon 110 is shifted by the height of the 
characters which can be printed by all the printing wires. In other words, 
the shift of 14 step amount in the printer of this embodiment corresponds 
to the 3 step amount of the prior art shown in FIG. 7. 
A ribbon feed motor 39 is driven via a driving circuit 47 while a carriage 
drive motor 10 is driven. 
Next, the printing shift routine executed in this electronic control 
devices 41 is explained according to the flowcharts of FIGS. 10A and 10B. 
The printing shift routine as shown in FIGS. 10A and 10B is repeated each 
time when printing instruction signals are input. Through the initial 
processing, such as clearing of the internal register at the actuation of 
the electronic control devices 41, setting of initial value 16 at a 
position counter CP described later, setting of initial value 1 for the 
shift direction change flag FS and a ribbon upper end turn-down flag FU 
and others , this routine is executed. 
First, S105 determines from the setting status of the shift direction 
change flag FS whether or not the direction of the ribbon shift is 
forward, namely, the direction in which the ribbon 110 is shifted upwards 
and the printing position of the nose portion 101a descends relative to 
the ribbon width direction or the reverse direction in which the ribbon 
110 is shifted downwards and the printing position ascends relative to the 
ribbon width direction. 
This shift direction change flag FS is set to 1 when the printing position 
reaches the upper end turn-down position. When FS is 1, subsequent ribbon 
shift direction is forward. 
When it is determined FS is 1 at S105, the process moves to S115 and after 
the subsequent processes for shifting the ribbon 110 forwards. When FS is 
0, the process moves to S225 and the subsequent processes for shifting 
backwards. After it is determined FS is 1 at S105, the setting status of a 
ribbon upper end turn-down flag FU determines whether or not the printing 
position is the upper end turn-down position of the ribbon at S115. 
When it is determined that FU is 1 at S115, the ribbon upper end turn-down 
flag FU is set to 0 at S120, the printing head 101 and the carriage 102 
are driven according to the printing data to print one line at S130, thus 
ending this process steps. In other words, the first printing after power 
being put on is to execute the processes of S105, S115, S120 and S130 
since FS is 1 and FU is 1 in the initial process as described in the 
above. Ribbon shift of the ribbon 110 is not executed. At the ribbon upper 
end turn-down position, one-line printing is necessarily executed. 
When the next printing instruction signal is input, it is determined FU is 
0 at S115. It is determined at S135 whether or not the position counter CP 
is within less than 20. Whether or not the printing position is situated 
at the upper end portion within the specified region from the ribbon upper 
end turn-down position is determined by the CP value in order to shift the 
ribbon 110 forward. 
When one line printing is executed at the ribbon upper end turn-down 
position, it is determined affirmative at S135 since CP is 16 at the 
initial process described above. The position counter CP is increased by 2 
at S140. Then, a 2-pulse drive signal is outputted to the drive circuit 43 
to drive a ribbon shift motor 29 and to shift the ribbon 110 forward by 
one step amount at S150. Next, one line printing is executed at S130. 
Starting from CP being 16 and repeating twice each process step S140, S150, 
S130, the CP becomes 20. Accordingly, a negative determination is made at 
S135 and the process steps move to S165, where it is determined whether or 
not the printing position is situated in an upper region adjacent to the 
upper end portion at the central side of the ribbon according to whether 
or not the value set at the position counter CP is less than 40. 
Since the CP is 20 in this case, it is determined affirmative at S165 and 
the CP is increased by the value of 20 at S170, a twenty pulse drive 
signal is outputted to the drive circuit 43 and the ribbon 110 is shifted 
forward by the amount of ten steps at S180. Then, the process moves to 
S130, where one line printing is executed. 
Next, as the CP becomes 40, a negative determination is made at S165 and 
the process steps move to S185, where it is determined whether or not the 
printing position is situated in the central region of the ribbon, 
according to whether or not the value set at the position counter CP is 
less than 112. 
Since the CP is 40 in this case, an affirmative determination is made at 
S185, the position counter CP is increased by the value of 8 at S190, and 
an eight pulse drive signal is outputted to the drive circuit 43 to shift 
the ribbon 110 forward by an amount of four steps at S200. Then, the 
process steps move to S130, where one line printing is executed. 
Starting from the status where the CP is 40 and repeating the process steps 
S190, S200, S130 nine times, the CP becomes 112 and it is determined 
negative at S185. The process steps go to S205, where it is determined 
whether the printing position is situated in a lower region adjacent to 
the lower end portion within the specified range from the lower end 
turn-up position of the ribbon according to whether or not the value set 
at the position counter CP is less than 132. 
Since the CP is 112 in this case, an affirmative determination is made at 
S205 and the process steps move to S170, where the value of the position 
counter CP is increased by 20. Then, the ribbon 110 is shifted forward by 
an amount of ten steps at S180. Next, at S130, one line printing is 
executed. 
When the CP becomes 132, a negative determination is made at S205 and the 
process steps move to S215, where it is determined whether or not the 
printing position is situated at the lower end portion according to 
whether or not the value set at the position counter CP is less than 134. 
As the CP is 132, an affirmative determination is made at S215 and the 
process steps go to S140, where the value of the position counter CP is 
increased by 2 and, thereafter, S150 and S130 are executed. In other 
words, the forward shift of the printing ribbon 110 by an amount of one 
step and one line printing are sequentially executed. 
Next, the CP becomes 134 and a negative determination is made at S215. 
Then, the value of the shift direction change flag FS is set to 0 at S220 
to change the following ribbon shift direction to backward. The process 
steps go to S140, the value of CP is increased by 2, the ribbon 110 is 
shifted forward by one step amount, and one line printing is executed with 
the printing position at the turn-up position of the bottom end of the 
ribbon at S130. 
Since the shift direction change flag FS is 0 after the printing position 
reaches the turn-up position of the bottom end of the ribbon, a negative 
determination is made at S105 and the process steps after S225 are 
executed. 
Regarding the process steps after S225, the shift step amount against the 
printing position, execution of printing and others are the same as the 
case of forward shift except tee direction of the ribbon shift being 
backward or the direction which the printing position ascends crosswise of 
the ribbon. Accordingly, the following explanation is made omitting the 
same portions. 
After finishing the printing at the turn-up position of the bottom end of 
the ribbon, the CP is 136. An affirmative determination is made at S225, 
the value of the CP is decreased by 2 at S230, the ribbon 110 is shifted 
backward by one step amount at S240, and then S130 is executed to print 
one line. 
Thus, repeating twice the process steps S230 through S240 starting from CP 
being 136, CP becomes 132 and the process steps go to S245, where it is 
determined whether or not the printing position is situated in the lower 
adjacent region. 
Since the CP is 132 in this case, an affirmative determination is made at 
S245 and the CP is decreased by 20 at S250. The printing ribbon 110 is 
shifted backward by an amount of ten steps at S260 and the process steps 
move to S130. Next, since CP is 112, the process steps move to S265, where 
it is determined whether the printing position is situated in the central 
region of the ribbon. 
As the CP is 112, an affirmative determination is made at S265, the CP is 
decreased by 8 at S270, the ribbon 110 is shifted backward by an amount of 
four steps at S280, then the process steps go to S130. 
Repeating 9 times the process steps S270, S280 from when the CP is 112, the 
CP becomes 40. The process steps go to S285, where it is determined 
whether or not the printing position is situated at the upper adjacent 
region. 
As the CP is 40, an affirmative determination is made at S285 and the 
process steps go to S250, where the CP is decreased by 20 and the ribbon 
110 is shifted backward by an amount of ten steps, then one line printing 
is executed at S130. 
Thus, the CP is 20 and a negative determination is made at S285, the 
process steps move to S295, where it is determined whether the printing 
position is situated at the upper end region. An affirmative determination 
is made at S295 since the CP is 20, The process steps S230, S240 and S130 
are executed and the CP value is decreased by 2. Then, an amount of one 
step backward shift of the ribbon 110 and one line printing are executed. 
Since the CP is 18, the process steps go to S300, where the shift direction 
change flag FS is set to 1 in order to change the next direction of the 
ribbon shift to forward. Then the process steps go to S230, S240 and then 
S130, where the ribbon 110 is shifted an amount of one step backward. One 
line printing is executed at the turn-down position of the upper end of 
the ribbon. 
Next, the shift status of the printing position on the printing ribbon 110 
is explained starting from the actuation of the printer with reference to 
FIG. 11. In the figure, the CP represents the value of the position 
counter and n the step position. 
When the printing shift routine is executed, the printing ribbon 110 is 
shifted, as shown in FIG. 11, forward "b", backward "c" and in a printing 
direction "a" while the printing position 110A reciprocates across the 
width of the ribbon 110. The following table 1 shows each usage frequency 
of each printing region R1, R2, R3 through R29 during one reciprocation of 
the printing 110A on the printing ribbon 110 and each respective 
percentage occupying the area. 
TABLE 
______________________________________ 
Usage frequency 
(times) Printing regions 
Percentage 
______________________________________ 
1 R1, R29 2.70 
3 R2, R28 2.70 
4 R6, R7, R23, R24 
13.51 
5 R3, R27 27.02 
6 R5, R8, R10, R12, R14, 
R16, R18, R20, R22, R25 
29.74 
7 R4, R26 5.41 
8 R9, R11, R13, R15, R17, 
18.92 
R19, R21 
______________________________________ 
As shown in the above table, the usage frequency of R1, R2, R28 and R29 on 
both the ends of the ribbon 110 is 3 times or less and the percentage of 
R1, R2, R28 and R29 is only 5.4 in this embodiment. Accordingly, the area 
used substantially uniformly is broadened, thus improving the usage 
efficiency of the ribbon, making imperceptible nonuniform printing shades 
and maintaining better printing quality for a longer time. 
Moreover, the usage frequency of R3, R27 on the upper end portion and the 
lower end portion within the specified region from the turning position on 
both the end portions of the ribbon is high, thus making uniform the ink 
that remains within the printing region, averting the leakage to the 
impact position by the printing wire and diminishing the non-uniform shade 
of characters printed. 
Further, when the printing position is situated on the upper and lower 
adjacent regions to the upper and lower end regions at the central side of 
the ribbon 110, this embodiment is constituted to shift by the amount of 
ten steps, namely, an amount of less than fourteen steps corresponding to 
the height of the character which can be printed by all the printing wires 
of the printing head 101 and an amount of more than four steps in the 
central region of the ribbon 110. 
This constitution enables a more uniform usage frequency, an improved usage 
efficiency of the ribbon, and a stabilized printing quality of the uniform 
printing shade. 
This invention is not limited to the above embodiment but can be modified 
in various ways without departing from the scope and spirit of the 
invention. This invention is constituted such that the ribbon shift is 
executed corresponding to one line printing but can be constituted so as 
to do the shift each time when the ribbon 110 accommodated in the cassette 
111 makes one round. Further, if another one-line printing is executed 
again at the turning portions on both the ends of the ribbon after 
executing one line printing and feeding the ribbon only in the printing 
direction, the usage frequency at both the ends of the ribbon increases, 
thus decreasing ink run.