Method and apparatus for guiding the paper in typewriters or similar office machines

A paper guiding device and operating method for use in an office writing machine, the device including a platen carried by a shaft and constituting a paper support, the platen shaft and platen being rotatable in a first direction for insertion of a paper sheet in the machine and in a second direction opposite to the first direction, a paper holding rail disposed adjacent the platen and carrying a plurality of pressure rollers which are pressed toward the platen, a rocker member supporting the rail and mounted to undergo pivotal movement about the axis of rotation of the platen shaft between a paper insertion position and a normal printing position; and a coupling member coupling the rocker member and platen such that rotation of the platen in the second direction effects pivotal movement of the rocker member into the paper insertion position for insertion of the leading edge of a paper sheet between the rollers and the platen and rotation of the platen in the first direction effects pivotal movement of the rocker member into the normal printing position, with simultaneous transport of the paper sheet, while the rollers maintain the sheet flat against the platen, the normal printing position being sufficiently remote from the printing line to assure that the printed characters will not be smeared upon contact with the rollers.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and an apparatus for guiding the 
record carrier, i.e. sheet of paper in typewriters or similar office 
machines. 
In office machines provided with an ink jet printer, it is necessary, in 
order to obtain a perfect recording, for the recording material to rest 
smoothly against the transporting element, e.g. the platen. For that 
reason, a special device is used to hold the recording material taut above 
the printing line. In such printers, paper pressing elements disposed 
after the printing location, when seen in the transporting direction of 
the platen, must be designed in such a manner that during the printing 
process they do not touch the paper during the time required for the ink 
to dry. Moreover, in such printers, which are designed for high operating 
speeds, the ink printing head is guided at a very close distance from the 
record carrier. The demands for accurate guidance of the record carrier in 
this region are therefore very high. 
In one proposed arrangement, smearing of the not yet dry ink is avoided in 
that the pressure rollers are provided in the form of pressure rings and 
are disposed on a drive shaft in such a manner that they drive the paper 
by contacting it in the spaces between the printed characters. This type 
of paper transport may be suitable for recordings in which the characters 
have a certain spacing between one another. But in facsimile and 
proportional script recordings smearing of the not quite dry ink cannot be 
avoided with this proposed arrangement. 
An arrangement disclosed in the IBM Disclosure Bulletin, Vol. 19, No. 3, 
August, 1976, page 754, includes an endless transporting belt for 
recording material printed by means of ink jet printers. This transporting 
belt is not made of a nonwettable or difficutly wettable material. 
Smearing of the not yet dry characters cannot be avoided here, either. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a paper guide apparatus 
for typewriters or similar office machines in which the paper pressing 
elements assure a constant spacing between the record carrier and the 
printing head in the region of the printing location and permit contact of 
the pressure rollers with the printed letters or characters only after the 
latter have dried, in order to thus avoid smearing of the printed 
characters. 
The above and other objects are achieved, according to the invention, by 
the provision of a novel paper guiding device for use in an office machine 
in which successive lines of characters are printed on a paper sheet and 
which machine includes a carriage supporting a printing head for movement 
along a printing line. The device comprises: a platen shaft arranged to be 
rotatably mounted in the machine; a platen carried by the shaft and 
constituting a paper support; the platen shaft and platen being rotatable 
in a first direction for insertion of a paper sheet in the machine and in 
a second direction opposite to the first direction; a paper guide trough 
surrounding a portion of the platen; a paper holding rail disposed 
adjacent the platen; a plurality of pressure rollers carried by the rail; 
spring means disposed for urging the rollers toward the platen; a rocker 
member supporting the rail and mounted to undergo pivotal movement about 
the axis of rotation of the platen shaft between a paper insertion 
position and a normal printing position; and coupling means coupling the 
rocker member and platen such that rotation of the platen in the second 
direction effects pivotal movement of the rocker member into the paper 
insertion position for insertion of the leading edge of a paper sheet 
between the rollers and the platen and rotation of the platen in the first 
direction effects pivotal movement of the rocker member into the normal 
printing position, with simultaneous transport of the paper sheet, while 
the rollers maintain the sheet flat against the platen, the normal 
printing position being sufficiently remote from the printing line to 
assure that the printed characters will not be smeared upon contact with 
the rollers. 
The objects according to the invention are further achieved by a method for 
inserting, transporting and ejecting sheets of paper in an office machine 
equipped with a paper guiding device as described above, and equipped with 
a control unit, a motor connected to rotate the platen, a keyboard having 
a paper insertion key and a paper ejection key, and a paper sensor 
disposed in the trough, which method includes the steps of: 
(a) inserting a sheet of paper between the platen and the trough while the 
rocker member is in the normal printing position, and actuating the paper 
insertion key for causing driving signals to be delivered to the platen 
under control of the control unit; 
(b) aligning the sheet by rotating the platen in the second direction while 
pivoting the rocker member from the normal printing position into the 
paper insertion position and automatically locking the rocker member in 
the paper insertion position; 
(c) rotating the platen in the first direction for transporting the sheet 
until it is sensed by the sensor and its leading edge is introduced 
between the rollers and the platen; 
(d) unlocking the rocker member and rotating the platen in the first 
direction while pivoting the rocker member in unison toward the normal 
printing position, and moving the carriage supporting the printing head 
into a printing position after the rocker member has reached an initial 
printing position between the paper insertion and normal printing 
positions; 
(e) further rotating the platen in the first direction while 
correspondingly pivoting the rocker member toward the normal printing 
position as lines of characters are printed until the rocker member is 
stopped at the normal printing position; 
(f) further rotating the platen in the first direction for advancing the 
sheet to its end, and then blocking further printing operations while 
holding the trailing end region of the sheet between the platen and the 
trough; and 
(g) actuating the paper ejection key to return the carriage to a rest 
position spaced from the platen, while transporting the sheet into a 
depository and halting rotation of the platen in response to the sensor no 
longer sensing the presence of the sheet. 
The apparatus according to the invention permits reliable insertion and 
transport of record carriers to be printed on, or provided with 
recordings, by means of ink jet printers, with clean script or facsimile 
recordings resulting even if slow drying inks are employed. The pivoting 
of the rocker carrying the pressure rollers about the platen axis from the 
paper insertion position into the initial printing position and then into 
the normal printing position assures reliable insertion of the paper and a 
constant distance between the surface of the sheet of paper and the 
printing head. The printing head which is outside the printing range when 
a sheet of paper is inserted is moved to the printing position only after 
the sheet of paper has been moved into the initial printing position. 
During this time, the pressure rollers are disposed directly above the 
printing head which is movable alongside the printing abutment. 
Certain preferred embodiments of the invention permit simple adjustment and 
arresting of the paper pressure rollers on the paper holding rail, while 
others make possible a simple method for inserting, transporting and 
ejecting sheets of paper. 
The invention will now be explained in greater detail with the aid of an 
embodiment which is illustrated in the drawing figures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 2 show a platen 1 which is rotatably mounted, via a platen 
shaft 3, in side walls 5 of the frame of a typewriter or similar office 
machine. A toothed wheel 9 can be fastened, by a set screw, to the free 
end of shaft 3. Wheel 9 can be driven by a stepping motor 17 via 
intermediate gear 11, 13 and 15. A rocker 19 is pivotally mounted on the 
platen shaft 3 and carries a paper holding rail 21 and paper holding 
rollers 23. Only one such roller is shown in FIGS. 1 and 2. Rocker 19 is 
provided with side members 25 designed to serve as bearing elements. 
One side member 25 is in a friction locking connection with a brake spring 
27 designed as a slide coupling, and additionally has an abutment arm 28 
which cooperates with fixed abutments 29 and 31 fixed to the machine 
frame. The abutments 29 and 31 may be made adjustable and serve to define 
two end positions for the movement of rocker 19. One end position of 
rocker 19 is defined by the abutment 31 and is the paper receiving 
position III, and the other end position is defined by abutment 29 and is 
the normal printing position setting I for the rocker 19. Spring 27 is 
fixed to the axial end surface of platen 1. 
The abutment arm 28 of the rocker 19, when in the paper receiving position 
III, can be latched by a detent 33 which is resiliently mounted, under the 
influence of a tension spring 39, on an arm 35 of a control lever 37 and 
is mounted to be rotatable about a bearing axis 41. The control lever 37 
is pivotal about an axis 43 fixed to the machine frame and is in operative 
connection with a control electromagnet 47 via a second arm 45. 
An abutment latch 49 having an abutment 51 is mounted for rotation about a 
bearing axis 52 at the second arm 45 and is used to arrest the rocker 19, 
when it is being pivoted from the normal printing position I, at an 
initial printing position II so that the pressure rollers 23 are disposed 
immediately above the printing head 53 which can be moved along the platen 
1. Arm 45 carries an abutment element 46 which cooperates with latch 49 to 
prevent that latch from pivoting counterclockwise from the position shown 
in FIG. 1 while permitting latch 49 to pivot clockwise, against the 
biassing force of spring 39, from the illustrated position. Latch 49 will 
be pivoted clockwise, when lever 37 is in the position shown in FIG. 1, by 
the action of arm 28 as rocker 19 pivots from position III toward position 
I. Similarly, detent 33 can pivot counterclockwise from the position shown 
in FIG. 1, but is prevented from clockwise pivoting by an abutment 48 
carried by arm 35 of lever 37. 
This stop is necessary when the sheet of paper is transported in a 
direction opposite to the paper insertion direction because the pressure 
rollers 23 could otherwise abut against the printing head 53 when it is 
still in the printing region and could then cause malfunctions. The 
abutment latch 49 blocks the rocker 19 only against rotation in a 
direction opposite the direction of paper insertion, i.e. against rotation 
in a clockwise direction in FIG. 1. When rocker 19 rotates in the paper 
insertion direction, i.e. from the paper receiving position III toward the 
normal printing position I, abutment arm 28 can resiliently deflect latch 
49 and escape therepast. Detent 33, however, when in the path of arm 28, 
prevents movement of arm 28 from the paper receiving position III; during 
movement of arm 28 toward the paper receiving position III, it can 
resiliently deflect detent 33 and moves therepast. 
Below the platen 1 there is a paper guide trough 55 with pressure rollers 
57 and 59 of which only two are shown in FIG. 1. Between the pressure 
rollers 57 and 59, the paper guide trough 55 has a recess 61 through which 
a sensor element 63 of a sensor switch 65 passes to sense the presence of 
a sheet of paper. The sensor switch 65 is, for example, a microswitch, but 
can also be a photoelectric element. 
The printing head 53 is an ink jet printing head which is disposed on a 
carriage 71 guided on shafts 67 and 69 along the platen 1, perpendicular 
to the plane of FIG. 1. The carriage 71 is moved by means of a 
conventional transporting device (not shown), e.g. a stepping motor. 
Referring to FIG. 3, each pressure roller 23 of the rocker 19 is rotatably 
mounted on a shaft 75 carried by a saddle-shaped roller mount 73 made of 
spring steel. The roller mount 73 is mounted to be pivotal about a bearing 
axis 18 in a guide member 79 which is supported by, and displaceable 
along, the paper holding rail, which rail has a profiled form, as shown. 
Moreover, the roller mount 73 carries a projecting resilient arm 83 which 
generates a force to clamp guide member 79 on the paper holding rail 21 
and to urge the pressure roller 23 against the platen 1. 
The paper holding rail 21 has a generally cylindrical shape but includes a 
flattened portion 89, while the guide member 79 which is displaceably 
mounted on rail 21 has a correspondingly designed bearing recess including 
a flattened portion 87 so that member 79 is pivotal within limits relative 
to rail 21. If the guide member 79 is urged by finger pressure in the 
direction of the arrow 85 as shown in FIG. 3, the clamping effect between 
paper holding rail 21 and bearing recess 87 is released in such a manner 
that the guide member 79 can easily be moved laterally and will 
automatically clamp itself onto rail 21 when the finger pressure is 
released. 
The procedure for inserting, transporting and ejecting sheets of papers 
will now be explained with the aid of the programming flow diagram of FIG. 
4 and the block circuit diagram of FIG. 5. When the machine is switched 
off and during periods when no printing is being performed, printing head 
53 and carriage 71 move outside the printing region. Only when carriage 71 
is in this position, can a paper insertion key 101 of a keyboard 105 give 
coded signals over a line 99 to a control unit 97, which may be a 
microprocessor or also a commercially available computer. 
The control unit 97 receives the data, makes certain calculations and 
transmits driving pulses via amplifiers 91 and 95 to the stepping motor 17 
for the platen 1 and to the control magnet 47 for the control lever 37. 
Actuation of the control magnet 47 pivots the control lever 37 clockwise, 
in the plane of FIG. 1, so that the abutment latch 49 is moved out of the 
path of movement of arm 28 and the detent 33 is brought into that path of 
movement. The stepping motor 17 is supplied with driving pulses by the 
control unit 97 in such a manner that the platen 1 is rotated opposite to 
the paper insertion direction, i.e. clockwise in FIG. 1, by ten steps, 
corresponding to ten printing lines. The platen 1 thereby moves the rocker 
19 and the paper holding rollers 23 clockwise, in the plane of FIG. 1, via 
the brake spring 27, from the normal printing position I into the paper 
receiving position III. The pivoting movement of the rocker 19 is limited 
by the abutment 31 causing the detent 33 to be arrested beneath the 
abutment arm 28 of the rocker 19. This prevents undesired counterclockwise 
return pivoting of the rocker 19. 
Then the stepping motor 17 is supplied with driving pulses for the opposite 
direction of rotation by the control element 97 in such a manner that the 
platen is rotated forward, i.e. counterclockwise, by 15 steps. During 
these 15 steps, the sensor switch 65 senses the presence of a sheet of 
paper 107 in the paper guide trough 55. If a sheet of paper 107 is 
present, the platen is shifted forward by an additional 10 steps until at 
least the leading edge of the sheet of paper 107 itself is disposed under 
the paper holding rollers 23. 
Then the control magnet 47 is switched off by the control element 97 and 
the platen 1 is advanced by four more steps in the forward direction until 
rocker 19 reaches the initial printing position II. In this position, a 
stepping motor 108 receives driving pulses for the carriage 71 equipped 
with the printing head 53. These signals come from the control element 97 
via an amplifier 93. Thus, the printing head 53 is brought into the 
printing position and is guided directly below the paper pressure rollers 
23 along the platen 1. The printing head 53 is disposed on carriage 71 
which is guided on shafts 67 and 69. The direction of movement of carriage 
71 is parallel to the platen 1, perpendicular to the plane of FIG. 1. 
After the printing head 53 reaches the printing position, the machine 
operator can begin putting in printing instructions. This is done in that 
the keyboard 105 delivers to unit 97, via line 99, signals which are coded 
to correspond to the characters to be printed, in response to which unit 
97, in a conventional manner, transmits corresponding ink ejection 
instructions to the printing head 53. During this printing process, the 
platen 1 is advanced counterclockwise in a known manner in the paper 
insertion direction, thus moving the rocker 19 in steps from the initial 
printing position II into the normal printing position I. 
After the rocker 19 has reached the normal printing position I, only the 
platen 1 continues to be advanced as further lines are printed. The normal 
printing position I is disposed far enough away from the printing location 
that the printed characters are already dry when they come into contact 
with the drive rollers 23. Smearing of the printed characters is avoided 
since the sheet of paper 107 is always held flat against the platen 1 in 
the printing region. 
Four steps before the end of the paper reaches the printing position, 
warning signals are emitted. When the end of the paper is reached, the 
keyboard is blocked, permitting the functions "reverse platen" and 
"backspace" still to be performed. In this position, the end of the sheet 
of paper 107 is still in the paper guide trough 55 so that it still rests 
flat against the platen 1 and thus cannot come closer to the ink jet 
printing head 53. The warning signals for the paper end are produced by 
sensor switch 65 which is located in the trough 55 more than four steps 
away from the printing head 53. 
To eject the sheet of paper, a paper ejection key 103 in the keyboard 105 
is actuated. This sends a coded signal to the control unit 97, causing 
driving pulses to be conducted via amplifier 93 to the stepping motor 108 
for the carriage 71. The carriage 71 with the printing head 53 are thus 
moved outside of the printing region. Then the stepping motor 17 receives 
driving pulses via amplifier 91, also from the control unit 97 to rotate 
the platen by 10 steps in the paper ejection direction, i.e. 
counterclockwise. After 10 further steps by the platen 1, the sensor 
switch 65 makes an interrogation. If no paper is present any longer, the 
stepping motor 17 receives enough driving pulses from the control unit 97 
to advance the platen 1 by 20 further steps. This assures that the 
completed sheet of paper 107 is reliably moved into a depository. This 
depository is located above the platen 1 in the frame of the typewriter 
and includes unitarily assoicated feed and receiving magazines in known 
manner as disclosed in U.S. Pat. No. 3,430,748. 
A new sheet of paper 10 is then pushed over a guide 109 into the insertion 
gap between the platen 1 and the paper guide trough 55, and the paper 
insertion key 101 can be actuated anew. The insertion of the new sheet of 
paper 107 takes place in the manner described above. By returning the 
platen 1 and pivoting back the rocker 19 from the normal printing position 
I to the paper receiving position III, the sheet of paper is aligned 
automatically. The apparatus according to the invention and the method 
according to the invention permit reliable insertion, transport and 
ejection of sheets of paper. 
The platen 1 can be designed as a hollow roller, its jacket being made of 
metal, e.g. aluminum. A heating element 2 is preferably disposed in the 
interior of the platen. This heating element may be an infrared lamp, a 
heating coil or some other heat radiator. The platen 1 preferably has a 
much greater diameter than prior art platens and thus effects reduced 
bending of the sheet of paper as a result of having been guided around the 
heated platen 1. The diameter of the platen 1 has an amount of 80,85 mm. 
The prior platens have a diameter of 40.5 mm. 
The lower right-handed side of FIG. 4 shows the sequence of operation 
during the ejection of sheets of paper. The left-handed side of FIG. 4 
contains the sequence of operation during the insertion of sheets of 
paper. When the ejection of a sheet of paper is finished then the 
insertion of a new sheet of paper takes place, as signified by the I near 
the top of FIG. 4. 
It will be understood that the above description of the present invention 
is susceptible to various modifications, changes and adaptations, and the 
same are intended to be comprehended within the meaning and range of 
equivalents of the appended claims.