Small printer

A printer of small overall size includes a plurality of typing wheels on the periphery of which are provided letters characters or symbols. At a printing position, a selection mechanism selects one of the plurality of letters, characters or symbols on each typing wheel. A printing mechanism prints the letter, character or symbols selected by the selection mechanism by applying a pressure thereto. A mechanism for feeding recording paper is arranged after the printing device in the feeding direction of the recording paper, and the printing mechanism moves in a direction opposite to the feeding direction of the recording paper after which pressure is applied to the printing device to effect printing.

BACKGROUND OF THE INVENTION 
This invention relates generally to a small printing device using a type 
wheel selection system and more particularly, to a small printing device 
in which typing wheels are set at a desired position by a selection 
device, a paper is printed and thereafter is passed to a take-up device. 
The typing wheels include a plurality of numerals, letters or characters 
symbols, or the like on the external peripheral surface. The printing 
device is used for point-of-sale and electronic cash register 
applications. 
Predominately, conventional printing devices having typing wheels are 
constructed in such a way as to frictionally drive the selected typing 
wheels and to effect aligned printing. Thus, conventional printing devices 
are unfit for ink roller type applications making it necessary to use an 
ink ribbon. This is a significant disadvantage, for example, in an 
electronic cash register which is subjected to heavy duty usage. Further, 
U.S. Pat. No. 2,770,188 discloses a construction wherein a ratchet and a 
ratchet wheel are engaged with each other and driven in a type wheel 
system. In this construction, however, there is the drawback that the 
electromagnetic actuation device must be energized until completion of the 
printing in order to maintain engagement between the ratchet and the 
ratchet wheel. Also, there is another significant drawback in that a 
ratchet wheel is required for each typing wheel. These factors increase 
the cost of the device and make it complex to manufacture. 
Furthermore, as disclosed, for example, in the U.S. Pat. No. 3,920,113, 
assigned to the present assignees, another conventional printing device is 
of a pressure type. The device includes a printing roller rotatably held 
by a bearing plate which is provided with a bearing portion of a circular 
slot configuration and which is fixed to a crank shaft which continuously 
rotates in one direction. This conventional system has a major advantage 
in that the printing roller is in contact with and rolls on the surface of 
a typing wheel having letters or characters thereon, so as to apply a 
pressure, thereby producing a high printing pressure with a low torque. 
Such a printer is capable of copying using carbonless duplicating paper. 
However, with such a construction, there is an inconvenience that the 
diameter of the locus of the outer periphery of the printing roller which 
rotates, must be increased as the surface of the typing wheel having 
letters or characters increases. Thus, the printing device having a 
characteristic feature that the letters or characters are of large size, 
has a major disadvantage in that the structure as a whole is large and 
much space is required. 
This system has another major disadvantage in that the printing roller is 
positioned a long distance away from the surface of the typing wheel 
having letters or characters and therefore a long distance from the 
printing paper, other than at the time of actual printing, thereby making 
it difficult to insert the printing paper to a desired preselected 
position. In addition, in this construction it is necessary to move the 
printing paper over a long distance immediately after completion of 
printing in order to confirm the quality of the printed letters or 
characters. Thus, there is also another drawback in that the distance 
between the printed lines must be increased. In addition, this system has 
another disadvantage in that the torque when pressure is applied and 
printing is effected, must be in proportion to the number of letters or 
characters to be printed. 
As a swinging system for pressure printing, there has conventionally been 
known a method whereby the same letter or character is pressed and printed 
twice within one reciprocating motion of a pressing member, or a following 
line is printed during a return motion. In this case, however, there is 
not only a serious disadvantage in that a shear in printing is caused when 
the same letter or character is pressed and printed twice within one 
reciprocating motion, but also another disadvantage in that the time 
required for the printing is twice as long as that usually required. 
Thereby, printing speed is decreased. When a new line is started within 
one reciprocating motion, the direction of movement relative to the 
printing paper reverses, and thus the space between the lines becomes 
irregular. This is also a serious disadvantage. 
Thus, for the reasons enumerated above, there are various types of serious 
disadvantages which are difficult to overcome in the conventional pressure 
printing constructions. 
What is needed is a small printer capable of printing letters or characters 
of large size, with regularly spaced and aligned lines, by pressure 
techniques. 
SUMMARY OF THE INVENTION 
Generally speaking, in accordance with the invention, a small printer 
especially suitable for electronic cash register and point of sales 
applications is provided. The printing device is of small overall size and 
includes a plurality of type wheels around which are provided a plurality 
of letters, characters and symbols. The printing device also includes 
selecting means for selecting one of the plurality of letters, characters 
and symbols on the typing wheels, printing means for printing the selected 
letter, character or symbol by applying a pressure thereto, and feeding 
means for feeding a recording paper to be printed by the printing means. 
The feeding means is arranged after the printing means in the feeding 
direction of the recording paper. Means are also provided for moving the 
printing means in a direction opposite to the feeding direction of the 
recording paper and to then apply a pressure to the printing means as it 
moves over the typing wheel to effect printing. The printing means 
includes a pair of bearing plates fixed to an oscillating swinging crank 
shaft and provided with substantially L-shaped bearing grooves. The 
L-shaped grooves are formed by connecting circular shaft bearing grooves 
of long and short radii respectively. A printing roller, which engages the 
bearing grooves of the bearing plates is rotatably held. The printing 
roller engages the rotation shaft bearing grooves of long radii in the 
bearing plates and are driven so as to rotate when the printing means 
moves forwardly in oscillating motion. The printing roller engages the 
rotation shaft bearing grooves of short radii when the bearing plates are 
driven so as to rotate when the printing means moves backwardly in the 
oscillating motion. Also, control means operate to detach the printing 
roller from the surface of the selected character of the typing wheel 
during the backward motion. 
Accordingly, it is an object of this invention to provide an improved 
printer of small size which is capable of printing letters or characters 
of large size as are required for a point of sale or an electronic cash 
register printer by the application of pressure, and wherein paper feeding 
is smoothly accomplished. 
Another object of this invention is to provide an improved printer which 
eliminates non-alignment of lines which is caused by non-alignment of the 
typing wheels when printing is effected. Elimination of such defects as 
missing, smudged and broken letters is also desirable. 
A further object of this invention is to provide an improved printer which 
is of small size, simple in construction low in cost and simple to 
assemble. 
Still another object of this invention is to provide an improved printer 
wherein the period of time for passing an electric current through an 
electromagnetic actuator is made short, thereby decreasing the consumption 
of electrical energy. 
Yet another object of this invention is to provide an improved printer 
having improved operational capabilities and ease of assembly and 
maintenance by providing a unitary printing selection device. 
Still other objects and advantages of the invention will in part be obvious 
and will in part be apparent from the specification. 
The invention accordingly comprises the features of construction, 
combination of elements and arrangement of parts which will be exemplified 
in the constructions hereinafter set forth, and the scope of the invention 
will be indicated in the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The printer in accordance with this invention provides a solution to the 
above-mentioned problems as explained in detail below. FIG. 1 is a 
perspective view of a printing device of small overall size constructed in 
accordance with the present invention. The printer includes a DC motor 1 
which drives a typing wheel shaft 2 which drives a plurality of typing 
wheels by means of gears, and further drives an ink roller shaft 7. A gear 
3 drives a pressure printing device and a gear 4 drives a paper feeding 
mechanism. A transmission gear 5 drives a take-up device and a detection 
device 6 detects a pulse which is generated in correspondence with the 
typing of a letter, character or the like by the printing wheel. 
FIG. 2 is a sectional view showing essential parts of the printer in 
accordance with the present invention. Visible in FIG. 2 are a typing 
wheel and typing wheel selector 200, a pressure printing device 300, a 
paper feeding device 400, an ink roller 70, printing paper 8 and a typing 
wheel control device 900. The paper feeding device 400 is located at a 
forward position in the paper feeding direction, indicated by the arror A, 
with respect to the pressure printing device 300. The pressure printing 
device 300 moves in a direction opposite to the paper feeding direction A 
to effect the pressure printing. 
Next, the major portions of the printer device in accordance with this 
invention are explained with reference to the various drawings. 
FIG. 3 is a sectional view of the typing wheel selector in accordance with 
this invention. A typing wheel shaft 210 is provided with a plurality of 
spline grooves 211 and is driven by a motor (not shown) so as to rotate in 
the direction indicated by the arrow B to execute a selection stroke. The 
selection stroke rotates and moves a typing surface 221 of a typing wheel 
220 to a predetermined printing position. Then, the typing wheel shaft 210 
comes to a standstill, and during that period, a printing roller 330 
rotates, moving along a locus C of rotation and presses the selected 
typing surface 221 at the printing position. Thus, printing is 
accomplished. 
It should be understood that a plurality of similar typing wheels 220 are 
mounted on the shaft 210 and operate in a similar manner to simultaneously 
print a line. Hereinafter, a description of the structure and operations 
relative to one typing wheel 220 is equally applicable to the other typing 
wheels. Further, similar components, performing similar functions are 
given the same reference numerals throughout the Figures. 
After completion of the printing operation, the typing wheel shaft 210 
again rotates in the direction indicated by the arrow B together with the 
typing wheel 220 which has finished printing. Thus, the shaft 210 is 
driven so as to rotate once and return the typing wheel 220 to the standby 
position as shown in the drawing. By having the speed in the returning 
portion after printing higher than that in the selection portion or 
stroke, the efficiency of the overall printing cycle is not lowered. 
A clutch pawl 230 and a clutch spring 240 are located on a side surface of 
the typing wheel 220. The clutch pawl 230 is always energized, that is, 
acted upon, by the clutch spring 240 in such a manner as to be biased 
toward engagement with the spline grooves 211 of the typing wheel shaft 
210 as explained more fully hereinafter. Around the outer periphery of the 
clutch pawl 230 and the clutch spring 240, a strip 250 is provided 
protruding from the side surface of the typing wheel 220. The protruding 
strip 250 is hereinafter referred to as a "detent guide" and the strip 250 
is partially cut away and partially recessed. An end or head portion 231 
of the clutch pawl 230 projects away from the cut-away portion of the 
detent guide 250. The ends 251,252, which define the cut-away portion of 
the detent guide 250, act as engaging surfaces of the clutch pawl 230 when 
in operation. That is, when the clutch pawl 230 is pivoted so as to engage 
the spline grooves 211 of the typing wheel shaft 210, the clutch pawl 230 
is prevented from being further pivoted when the head portion 231 of the 
clutch pawl 230 abuts the end 252 of the clutch guide 250. Thereby, a 
predetermined positional relationship is maintained between the detent 
guide 250 and the clutch pawl 230. 
As the typing wheel 220 is rotated to return its original position, the 
head portion 231 of the clutch pawl 230 contacts the bent portion 281 of a 
trigger spring 280 which disengages the pawl 230 from the spline groove 
211 on the rotating shaft 210. When the clutch pawl 230 is released from 
engagement with the spline groove 211 of the typing wheel shaft 210, the 
head portion 231 of the clutch pawl 230 contacts the end 251 of the 
cut-away portion of the detent guide 250. Thus, the typing wheel 220 is 
prevented from overrunning and rapidly comes to a standstill at a position 
where a detent spring 291 is inserted into a recessed portion 253 of the 
detent guide 250, that is, in the standby condition as shown in the 
drawing of FIG. 3. In the standby condition, that is, in the condition 
where the engagement between the spline 211 of the typing wheel shaft 210 
and the clutch pawl 230 is released, the typing wheel 220 does not freely 
rotate due to the detent spring 291 which provides a controlling force. 
The trigger spring 280 is arranged such that the bent portion 281 thereof 
contacts the outer surface of the detent guide 250 of the typing wheel 220 
by its own resiliency and also contacts the head portion 231 of the clutch 
pawl 230. One end of the trigger spring 280 and one end of the detent 
spring 291 are fixed by means of a screw 299 to one end of a draw plate 
holding member 290. The end of the trigger spring 280 engages the free end 
261 of a draw plate 260 which is an armature member of an electromagnetic 
actuation device. 
In the standby condition, the draw plate 260 is held away from a core 270 
of the electromagnetic actuation device, and an electromagnetic coil 271 
is wound around the core 270. When an electric current is passed through 
the electromagnetic coil 271, the draw plate 260 rotates about an end 214 
on a yoke 213 which serves as a pivoting surface. The yoke 213 constitutes 
one portion of a magnetic path for the electromagnetic actuation device. 
When the draw plate 260 rotates about the center of rotation at the end 
214, engagement between the bent portion 281 of the trigger spring 280 and 
the head portion 231 of the clutch pawl 230 is released. 
A plate 292 supports the electromagnetic coil 271. A typing wheel guide 212 
maintains the position of the typing wheel 220 in the transverse 
direction, that is, in the direction of the shaft 210. An ink roller 70 is 
forced to rotate such that the peripheral speed of the typing wheel 
surface 221, by rotation of the typing wheel shaft 210, coincides with the 
peripheral speed of the outer surface of the ink roller 70. 
In the embodiment in accordance with the present invention, as described 
above, when the typing wheel shaft 210 is to effect a selected rotation of 
the typing wheel 220 in accordance with input information, a short 
pulse-like signal is developed so as to instaneously energize the 
associated electromagnetic coil 271. Thus, the draw plate 260 is pulled 
and pivots against the spring 281. Then, the bent portion 281 of the 
trigger spring 280 is pushed away from the outer surface of the detent 
guide 250 so as to release its engagement with the head portion 231 of the 
clutch pawl 230. As a result, the clutch pawl 230 pivots counterclockwise, 
as seen in the drawing, as a result of the spring force applied by the 
clutch spring 240. Thus, the clutch pawl 230 engages a spline groove 211 
of the typing wheel shaft 210. By this engagement, the typing wheel 220 
and the typing wheel shaft 210 are coupled together and the clutch pawl 
230 comes into contact with the end 252 at the cut-away portion of the 
detent guide 250 on the typing wheel 220. This contact brings pivoting of 
the clutch pawl 230 to a halt. 
When energization of the electromagnetic coil 271 for a short time period 
has ceased, the trigger spring 280 moves the draw plate 260 away from the 
core 270 by its own resilience, and in the same time the bent portion 281 
of the spring 280 slides along the outer surface of the clutch pawl 230 
until it comes in contact with the outer peripheral surface of the detent 
guide 250. 
As the typing wheel shaft 210 rotates for a selection stroke from the 
reference position in the described manner, the same operation is 
acccomplished at the typing wheel portion of each column, and the typing 
wheels of 220 successively are coupled to the typing wheel shaft and start 
to rotate. Thus, when one rotation of the selection stroke has been 
completed and the typing wheel shaft 210 comes to a standstill, the typed 
letters or characters, in correspondence with the input information, are 
put into proper relative positions opposite to the printing roller 330. 
During the stationary period, the printing roller 330 moves along the 
locus of rotation so as to effect the printing operation. 
When the printing operation is ended, the typing wheel shaft 210 again 
starts to rotate with the typing wheels 220. As stated above, the bent 
portion 281 of the trigger spring 280 at this time already occupies a 
position in contact with the outer surface of the detent guide 250. The 
head portion 231 of the clutch pawl 230, which is rotated together with 
the typing wheel 220, comes into contact with the bent portion 281 of the 
trigger spring 280 and is pushed back until it reaches the end 251 of the 
cut-away portion of the detent guide 250. Therefore, the clutch pawl 230 
is pivoted clockwise so as to release engagement with the spline groove 
211 and free the typing wheel 220. At the same time, the end of the detent 
spring 291 falls into the recessed portion 253 of the detent guide 250. 
Thus, the typing wheel 220 soon comes to a standstill without moving 
freely, at a predetermined position due to the controlling force of the 
detent spring 291. Thereby, one cycle is complete. With each of the typing 
wheels 220 selected and rotated once, all of the typing surfaces 221 come 
into contact with the ink roller 70 during one rotation through the 
selection stroke and the returning stroke, thereby coating ink on each 
typing surface 221. 
FIG. 4 is a sectional view of a typing wheel control mechanism constructed 
in accordance with this invention. The typing wheel shaft 210, which 
includes the spline grooves 211, is shown together with a typing wheel 
shaft control cam 223. The shaft control cam 223 is integral and coaxial 
with the spline grooves 211. As stated, the typing wheel shaft 210 is 
selectively rotated once, comes to a standstill and is rotated to its 
standby position by means of a driving mechanism (not shown). The typing 
wheel 220 is arranged on the typing wheel shaft 210, and on the peripheral 
surface of the typing wheel 220, typing surfaces 221 and typing wheel 
control cam grooves 222 are provided alternately. 
The clutch pawl 230 is energized by the clutch spring 240 and mounted on 
the side surface of the typing wheel 220 as described above. A crank shaft 
310 is rotated by a driving device (not shown) and the printing roller 
330, which is eccentrically mounted to the crank shaft 310, moves along 
the locus C at the outer periphery of rotation. The crank shaft 310 is 
operated in synchronism with the typing wheel shaft 210 such that when the 
typing wheel shaft 210 is stationary, the selected typing surface 221 of 
the typing wheel 220 engages the printing roller 330 thereby effecting the 
pressure printing. 
A typing wheel aligning plate 980 is located between a pivot shaft 919 and 
an aligning plate driving cam 921. The typing wheel aligning plate 980 is 
biased in a clockwise direction by means of an aligning plate return 
spring 930. The typing wheel aligning plate 980 is provided with a typing 
wheel shaft operating portion 981 which engages and actuates a shaft 
control groove 24 on the typing wheel shaft control cam 223. The typing 
wheel aligning plate 980 is also provided with a typing wheel operating 
portion 982 which engages and actuates the typing wheel control cam groove 
222. 
When the typing wheel shaft 210 is stationary, the typing wheel aligning 
plate 980 is pivoted about the rotation shaft 919 as a center of rotation 
by the rotating push-in cam portion 921 of the aligning plate driving cam 
920. Then, first, the typing wheel shaft operating portion 981 engages and 
actuates the shaft control groove 224 in the typing wheel shaft control 
cam 223. After that, the typing wheel operating portion 982 engages and 
actuates the typing wheel control cam groove 222. The typing wheel 
aligning plate 980 is provided with an operating portion 983 for forcibly 
returning the plate 980. If not returned by means of the aligning plate 
return spring 930, engagement of the operating portion 983 with the 
forcibly returning cam portion 922 of the aligning plate driving cam 920 
causes the return operation of the aligning plate 980. 
When the trigger spring 280 is actuated during the selective rotation of 
the typing wheel shaft 210 in correspondence with an electric input pawl 
signal, the clutch pawl 230 engages the spline groove 211 so that the 
typing wheel 220 rotates in synchronism with the typing wheel shaft 210 as 
described above. Thus, when the typing wheel shaft 210 comes to a 
standstill together with the successively and selectively rotated typing 
wheels 220, the typing wheel aligning plate 980 is actuated at the same 
time by the push-in cam portion 921 of the aligning plate driving cam 920. 
Then, first of all, the typing wheel shaft operating portion 981 engages 
the shaft control groove 224 of the typing wheel shaft control cam 223 so 
as to slightly rotate, if misaligned, and control the typing wheel shaft 
210 in a correcting manner, that is, in an aligning manner. At the same 
time, the typing wheel 220 is also aligned. That is, the typing wheel 
operating portion 982 falls into the typing wheel control cam groove 222, 
thereby supplementally rotating the typing wheel 220 in an aligning and 
controlling operation. The typing wheels 220 and the typing wheel shaft 
210 are in the desired position. The actuated position of the typing wheel 
aligning plate 980 is shown with broken lines in FIG. 4. 
While the typing wheel 220 is constrained and aligned by the typing wheel 
aligning plate 980, the printing roller 330, which is driven by the crank 
shaft 310 as described above, presses and prints the selected typing 
surface 221. The typing wheel aligning plate 980, which has constrained 
and aligned the typing wheel 220 during the time that the printing roller 
is in contact with the typing surface, returns to the position indicated 
by the solid lines, by the force of the aligning plate return spring 930 
or the forcible action of the returning cam portion 922 of the aligning 
plate driving cam 920. This forcing action is effected if it is impossible 
to return the typing wheel 220 by the spring force immediately after the 
completion of printing, that is, immediately after the printing roller 330 
has separated from the typing surface 221. When the typing wheel aligning 
plate 980 returns to its standby position, the typing wheel shaft 210 
again rotates, as previously described, together with the typing wheel 
220, whereupon the return trigger spring 280 engages the clutch pawl 230. 
When the engagement between the clutch pawl 230 and the spline groove 211 
is released, the typing wheel 220 returns to the standby condition as 
indicated by the solid lines in the drawing. Thus, the typing wheels 220 
successively return to the standby condition and thereby a selective 
printing operation is completed. 
FIGS. 5 and 7 are sectional views of alternative embodiments of pressure 
printing mechanism in accordance with the present invention. The crank 
shaft 310 is driven in such a way so as to oscillatingly swing through a 
desired rotational angle .alpha. by means of a driving mechanism (not 
shown). Bearing plates 321,322, which are mounted on the crank shaft 310, 
are driven together in such a way as to swing oscillatingly with the shaft 
310. Each plate 321,322 includes a bearing portion 341 having a long 
radius of rotation, and a bearing portion 343 having a shorter radius of 
rotation about the crank shaft 310. The bearing portions 341,343 are 
connected so as to provide a substantially L-shaped bearing hole. The 
substantially L-shaped bearing holes in the bearing plates 321,322 are 
fixed to the crank shaft 310 with a phase difference .theta. (.theta.&gt;0). 
A printing roller 330 on a shaft 331 is provided between the bearing plates 
321,322. The shaft 331 of the printing roller 330 is rotatably supported 
by the bearing plates 321,322 in the substantially L-shaped bearing hole 
which includes the bearing portions 341,343 of the bearing plates 321,322. 
When the typing wheel 220 rotates so that the center of the selected typing 
surface 221 reaches a line defined between the centers of the crank shaft 
310 and the typing wheel 220, the typing wheel 220 comes to rest. At this 
moment, the typing surface 221 is pressed upon and typed on the printing 
paper 8 by means of the crank shaft 310 which is rotated counterclockwise. 
That is, the printer roller 330 which is held by the bearing plates 
321,322 passes over the selected typing surface 221. Then, the roller 330 
pivots back so as to return to the standby position. Thus, a selective two 
step oscillating rotation is effected. In this way, the printing roller 
330 when pressing is moved in a direction opposite to the paper feeding 
direction A, thereby effecting a pressure printing. 
Printing roller control springs 84,85 control the motion of the roller 330 
and also function as a paper guide. A square hole, not visible in the 
drawings, is formed at the portion of the control springs corresponding to 
the typing surface 221 of the typing wheel 220 which is to be printed. 
When pressure typing is effected, the printing roller 330 is adapted to 
directly push the printing paper 8 onto the typing surface 221 of the 
typing wheel through the square holes. The printing roller control springs 
84,85 are made of an elastic material. Both ends of the control springs 
are supported by a member 88 which is part of a frame (not shown). In 
addition, reference numeral 89 on the drawing represents a printing roller 
stopper, which is provided to stop the clockwise rotation of the crank 
shaft 310 and prevent the printing roller 330 from floating up and make it 
wait in the stable condition. 
In accordance with the present invention as described above, any selected 
typing wheel 220 is brought to a standstill with any selected typing 
surface 221 directed toward the center of the crank shaft 310. The printer 
is comprised of a plurality of typing wheels 220 mounted on the common 
shaft 210 so that when all the typing wheels 220 come to a standstill with 
a selecting typing surface 221 directed toward the center of the crank 
shaft 310, the crank 310 is rotated counterclockwise from the standby 
condition shown in solid lines. When the crank shaft 310 rotates, that is, 
the connected bearing plates 321,322 are rotated, the rotational shaft 331 
of the printing roller 330 enters the bearing portion 341 having the long 
rotation radius. Then the outer periphery of rotation of the printing 
roller 330 moves along the broken line 337 as indicated by the arrows. As 
the printing roller 330 moves, the printing roller control springs 84,85 
as well as the printing paper 8 which is held therebetween, approach the 
typing surface 221 of the typing wheel 220. When the crank shaft 310 is 
further rotated counterclockwise, the printing paper is completely pushed 
against the typing surface 221 for printing on the paper 8. 
When the centers of the crank shaft 310, the printing roller 330 and the 
typing wheel 220 are arranged on a straight line, the pushing force is a 
maximum. In accordance with the present invention, the center of the 
typing surface 221 of each typing wheel 220 lies precisely on a straight 
line connecting the center of the crank shaft 310 and the center of the 
typing wheel 220. Since the substantially L-shaped bearing grooves 341,343 
of the bearing plates 321,322 are positioned with a phase difference 
.theta., the moment when the centers of the typing wheel 220, the printing 
roller 330 and the crank shaft 310 are arranged on a straight line, that 
is, when the pushing force is a maximum, differs for each typing wheel 220 
by a small amount of time. Thus, the crank shaft 310 stops its 
counterclockwise rotation when the center of the letter or character on 
the typing surface 221 is passed on the last typing wheel 220 in the 
transverse row of typing wheels, and the printing roller 330 goes further 
and passes the end of the letter or character on the last typing surface 
221. Thereby, printing is accomplished. 
In this construction (FIG. 5) the printing roller 330 is subjected to a 
force which is directed upwards as seen in the drawings by the printing 
roller control springs 84,85. Thus, when the crank shaft 10 rotates back, 
that is, in a clockwise direction, the rotation shaft 331 of the printing 
roller 330 moves from the long radius rotation shaft bearing portion 342 
of the bearing plates 321,322 to the shorter radius rotation shaft bearing 
portion 344. This counterclockwise position, at the start of the clockwise 
motion, is shown with broken lines in FIG. 5. As the crank shaft 310 
rotates clockwise, the printing roller 330 moves horizontally (FIG. 5) as 
shown by the broken line 332 while being supported in this elevated 
position by the printing roller control spring 84. 
At this time, since the printing roller 330, the printing paper 8 and the 
typing surface 221 of the spring wheel 220 are held apart from each other 
by the printing control springs 84,85, the returning rotation of the 
typing wheel 210 to the standby condition is effected simultaneously with 
the returning rotation of the crank shaft 310 as described above. When the 
crank shaft 310 returns to the standby condition as shown by the solid 
lines in FIG. 5, the printing roller 330 also strikes against the printing 
roller stopper 89, stops and returns to the standby condition. Thus, the 
center of the printing roller 330 moves as shown by the broken line 332 
and the outer periphery of the printing roller moves to print as shown by 
the broken line 337 in response to a oscillatingly swinging motion of the 
crank shaft 310. The return portion of the broken line 337 is not shown in 
FIG. 5 but, as stated, the roller 330 is supported by the spring 84. 
FIG. 6 shows the relationship between the pressure printing load torque and 
the rotational angle .alpha. of the crank 310. The phase difference 
.theta. for the occurrence of the peak torque T.sub.1 for each typing 
wheel 220 is shown. The instantaneous total torque has a peak T.sub.N 
which is less than T.sub.1 .times.N, where N is the number of typing 
wheels. N is 3 in the illustration of FIG. 6. In other words, the peak 
torque T.sub.N is less than the sum of the individual peak torques T.sub.1 
if these individual peaks were to occur simultaneously. 
FIG. 7 shows an alternative embodiment of a pressure printing construction 
in accordance with this invention. In this construction, the printing 
roller 330 acts as the guide for the printing paper 8. This is not done in 
conventional printing systems. Additionally, a paper feeding roller 410 
and a paper holding roller 411 are positioned in the vicinity of the 
printing mechanism. Therefore, by using the roller 330 also as a guide, 
the path for the printing paper 8, which is a most serious problem in the 
design of a printer mechanism, is made short. Further, by such an 
arrangement, space may be provided for locating other mechanical parts 
such as the motor 1, thereby decreasing the size of the printing device as 
a whole, and a high degree of freedom is available for the layout of the 
overall printer system. 
FIGS. 8,9 and 10 are respectively a plan view, a side view and a 
perspective view of a take-up device 511 in accordance with the present 
invention. A transmission gear 5 transmits power from an external power 
source and a transmission shaft 520 supports the transmission gear 5. A 
take-up gear 530 is in engagement with the transmission gear 5, and a 
take-up flange plate 540 is integral with the take-up gear 530. A take-up 
shaft 550 is also integral with the take-up gear 530. A frame 560 is on 
the journal side and a recording paper 570 is taken up on the journal 
side. A recording paper 580 is being taken up. One portion 590 of the 
take-up shaft 550 engages a holding portion 510 of the frame 560 for 
holding the take-up unit 511. Thus, for supporting the take-up shaft 550, 
the take-up device utilizes a cantilever supporting system. The frame 560 
on the journal side and the take-up shaft 550 have an angle .delta. with 
respect to the direction perpendicular to the running path of the 
recording paper 580 as indicated by the arrow a. 
Having the take-up shaft 550 at an angle .delta. with respect to the 
direction perpendicular to the running path, in the direction indicated by 
the arrow a, of the recording paper produces the following effects. 
First, as a consequence of the angle for the take-up shaft 550, the 
recording paper 580 is in contact with the take-up shaft 550 only near the 
end of the take-up shaft 550. At this contact portion, a tensile force is 
generated in the recording paper 580. 
Secondly, inasmuch as the take-up shaft 550 has an angle with respect to 
the recording paper 580, and the recording paper 580 is under a tensile 
force at the end of the take-up shaft 550, the recording paper 580 is 
pushed against the take-up flange plate 540 due to a belt effect. 
In order to prevent meandering the coiled expansion, as well as to align 
the end surface of the recording paper 570 which is wound around the 
take-up shaft 550, it is required that the recording paper 580 be pushed 
against the take-up flange plate 540 and, at the same time, for the 
recording paper 570, which is taken up, to be fastened at the end of the 
take-up shaft 550. 
The take-up unit 511 is mounted with an inclination of an angle .beta. with 
respect to the vertical direction of the frame 560 (FIG. 9). Therefore, 
the recording paper is pushed towards the take-up flange plate and is thus 
taken up. As a result, the cantilever flange has the same function and 
effect as with a flange plate where both ends are supported. A perspective 
view of this take-up unit 511 is shown in FIG. 10. 
FIG. 11 is a sectional view of a paper feeding device in accordance with 
this invention including a paper feeding roller 410 and a paper holding 
roller 411. A ratchet gear 412 engages the paper feeding roller 410 as 
well as a one-way spring clutch (not shown) and the paper feeding driving 
gear 4 (FIG. 1). An electromagnetic device 420 effects the engagement and 
non-engagement operation of the paper feeding driving gear 4 with the 
paper feeding roller 410. The electromagnetic device 420 includes a coil 
421, a yoke 422, an engaging lever 424 and a bias spring 425. 
First, after completion of printing by the printing device, or when paper 
feeding is desired, the coil 421 is fed an electrical pulse of short 
duration so as to energize the yoke 422 and move the engaging lever 424 in 
the direction indicated by the arrow D against the force of the spring 
425. Then, engagement between the engaging lever 424 and the paper feeding 
ratchet gear 412 is released. Thereby, the ratchet gear 412 rotates by an 
amount corresponding to one tooth. Thereby, the paper feeding roller 410 
rotates by a predetermined amount and the paper feeding ratchet gear 412 
again engages the engaging lever 424 so as to stop rotation of the paper 
feeding roller 410. When the paper feeding roller 410 rotates in this way, 
a predetermined amount equivalent to at least one printed line of 
recording paper 8 is fed. 
A small printer constructed as described above, in accordance with this 
invention provides the following effects. Inasmuch as the spline grooves 
are integrally provided on the typing wheel shaft itself, the clutch pawl 
is arranged so as to approach the vicinity of the center of the typing 
wheel as closely as possible, thereby making it possible to provide a 
space to locate a detent guide on the outer periphery of the typing wheel. 
Furthermore, the outer surface of the detent guide is made the sliding 
surface of the armature member (draw plate) or any other member, for 
example, the trigger spring, which moves together with the armature 
member. Therefore, it is possible for the armature member to always be in 
a position to engage the clutch pawl. At the same time, it is possible to 
limit the movement when the clutch pawl pivots by the end of the cut-away 
portion of the detent guide. In addition, one portion of the detent guide 
is provided with a recess for controlling the detent, thereby completely 
preventing free movement of the typing wheel in the standby condition. 
Thus, signals which are required in one cycle of the printing motion are 
sufficient with only short pulse signals being inputted at required 
rotational positions of the typing wheel shaft. 
After having released engagement with the clutch pawl, the armature member 
(draw plate) which is driven by means of these short pulse signals, or any 
other member (trigger spring) which moves together with the armature 
member, comes into sliding contact with the outer surface of the detent 
guide as stated above so as to be in a position to disengage the clutch 
pawl. Thereby, actuation of the pawl is reliable. In addition, the detent 
guide is provided on the outer surface of the clutch pawl and clutch 
spring thereby preventing the clutch pawl and clutch spring from 
overtravel. Also, accummulation of dust is prevented. Thereby, free 
movement of the detent is prevented and engagement and release from 
engagement between the clutch pawl and the spline grooves is made 
reliable. Thereby, reliability is greatly enhanced and electric energy 
consumption is diminished. 
Also, because the spline grooves are provided on the typing wheel shaft 
itself, no ratchet wheel paired with the typing wheel shaft is necessary. 
Thereby, the number of parts is decreased at the same time as the number 
of steps required in assembly is reduced. Furthermore, the printing 
selection mechanism is completely and integrally unitary. Thereby, the 
number of steps needed in the manufacturing assembly is further decreased 
and the ease of handling during production, as well as in servicing and 
maintenance for the user, is improved. 
Also, since the position of the typing wheel shaft and the typing wheel 
itself is corrected at the moment of printing in such a manner that they 
are constrained and aligned by means of one member, that is, the typing 
wheel aligning plate, the connection between the printing system and the 
typing wheel selection system, which has been a problem in the past, is 
ended. 
Applicable fields for the printer in accordance with this invention are not 
limited to only a typing wheel selection system of one rotation clutch 
type, and to a printing system using a printer roller. In addition, the 
present invention is very advantageous in cost, quality and reliability. 
Furthermore, the bearing portion for the shaft of the printing roller is 
changed from the conventional circular to a substantially L-shape, and 
phase difference is provided for the different bearing portions of the 
typing wheels. 
Thus, pressure printing is performed using this invention with a simple 
structure in accordance with a oscillatingly swinging motion, through a 
rotation angle of several tens of degrees without continuously rotating 
the printing roller. Thereby, it is possible to readily accomplish 
pressure printing. In addition, there is a very advantageous effect in 
that the peak load torque of the pressure printing is also decreased. 
Furthermore, since the paper feeding device is arranged after the printing 
device in the feeding direction of the recording paper, the paper feeding 
ability is greatly improved and paper jamming is eliminated. Thus, the 
present invention is most advantageous as a printer for use in point of 
sale and electronic cash register applications. 
It will thus be seen that the objects set forth above, among those made 
apparent from the preceding description, are efficiently attained and, 
since certain changes may be made in the above constructions without 
departing from the spirit and scope of the invention, it is intended that 
all matter contained in the above description or shown in the accompanying 
drawings shall be interpreted as illustrative and not in a limiting sense. 
It is also to be understood that the following claims are intended to cover 
all of the generic and specific features of the invention herein described 
and all statements of the scope of the invention which, as a matter of 
language, might be said to fall therebetween.