Note: Descriptions are shown in the official language in which they were submitted.
64'~
PHO 81.508 1 12.5.1982
"Printer comprising a guide device for a record carrier".
The invention relates to a printer comprising a guide
device for transporting a record carrier, by means of a transport
roller, to a strip-shaped, flat supporting surface which adjoins
the transport roller by way of one its long sides, viewed in the
5 transport direction of the record carrier, and along which a printing
head is displaceable, the record carrier heing pressed by a ruler frcm
the side of the printing head before it reaches the area of the printing
head. In a printer of this kind which is known, for example, from DE-OS
28 29 827, the record carrier should rest as flatly as possible on the
l0 supporting surface in order to keep the distance between the record
carrier and the printing head as constant as possible; this is important
notably when the printing head is an ir~ jet printing head. In the
printer which is known from said DE-OS 28 29 827, the supporting surface
tangentially adjoins the transport roller and the record carrier is press-
15 ed against the transport roller by means of a rule directly kefore theseparation from the transport roller. It has been found that the record
carrier does not rest flatly on the supporting surface in all circum-
stances in such a guide device.
It is the ohject of the invention to improve a printer OL the
20 kind set forth in order to ensure that the record carrier rests com-
pletely and perfectly flatly on the supporting surface. To this end,
the invention is characterized in that the supporting surface is situated
in a plane which segmentally intersects the path of the record carrier
around the transport roller, viewed in a cross-sectional view, thereof,
25 the ri`se of arc of the segment being smaller than half the radius -there-
of, the ruler pressing against the record carrier at the area of the
supporting surface without bringing the record carrier directly into
contact with the supForting surface. Thar~s to these steps, record
carrier becomes S-shaped at the passage from the transFort roller to
30 the supporting surface un~er influence of the forces acting on the
record carrier, the record carrier subsequently resting completely and
perfectly flatly on the supporting surface, so that always a constant
distance between this surface and the printing head is ensured.
.~
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P~7O 81.508 2 12 5.1982
A preferred embodiment of the printer in accordance with the
invention is characterized in that the transpor-t roller comprises
toroidal rings which are spaced apart in its longitudinal direction,
and which define the path of the record carrier around the transport
roller, the supporting surface comprising groove-shaped recesses at
its long side which faces the transport rol]er, said recesses corre-
sponding to the toroidal rings which project therein. The path of the
record carrier around the transport roller is thus determined by the
toroidal rings, because the record carrier rests only thereon. Because
o the toroidal ri.ngs project into the groove~shaped recesses in the
supporting surface, the supporting surface adjacent the toroidal rings
extends as far as the transpor-t roller, so that at these areas the sup~
porting surface is situated slightly helow the path oE the record carrier
at the passage from the transport roller to the supporting surface; this
lS has a favourable effect on the formation of a smooth S-curve in the
record carrier upon its passage to the supporting surface, so that the
flat positioning of the record carri.er on -the supporting surface is
fur-ther improved. It is to be noted that transport rollers comprising
toroidal rings which are spaced apart in its longitudinal direction are
known to ~e used in commercially available printers. In the akove context
however, the use of such a transport roller offers sai.d special advantage
that the passage of the rec.ord carrier -from the transport roller to the
supporting surface is ve.ry smooth.
In view of the simplicity of the constmction, the ruler is
preferahly form!ed by a bent end of a shell-like cover element which is
arranged around the transport roller at a distance therefrom.
The invention will be described in detail hereinafter with refer-
ence to the drawings which show two embodimen-ts in accordance with the
invention.
Figure 1 is a partly diagrammatic front view of the most
relevant parts of a printer comprisi.ng a transport roller with toroidal
rings.
Figure 2 is a cross~sectional view of the printer shown in
Figure 1.
Fi.gure 3 is a cross-sectional view of a further embodiment
comprising a transport roller whose circumferential surface defines the
path of a record carrier.
Figure 4 diagrammatically shows the plane of the supporting
P~-IO 81O508 3 12.5.1982
surface which seg~entally intersects the path of the record carrier
around the transport roller.
The reference numeral 1 in the Figures l and 2 denotes a
transport roller which serves for the transport or the line-wise
Eeeding of, for example, a sheet-like record carrier 2 which is shown
only in Figure 2. Viewed in the transport direction of the record
carrier (denoted by an arrow 3), the record carrier proceeds from a
guide surface 4 to the transport roller 1 and subsequently to a strip-
shaped flat supporting surface 5 along which a printing head 6, for
example, an ink yet printing head is displaceable. To this end, the
printing head 6 is mounted on a carrier 7 which is displaceable in the
line direction on two guide rods 8 and 9. The drive for such a dis-
placement of the printing head is not shown herein but may be realized
in a customar~r manner, for example, by means oE a motor with a drive
belt, a toothed belt or similar.
The transport roller 1 of this em~odiment comprises toroidal
rings 10 which are spaced apart in its longitudinal direction and which
are si-tuated in corresponding grooves; these rings are often also re-
ferred to as O-rings. Because the toroidal rings 10 project from the
circumferential surface of the transport roller 1, they define the path
of ~he record carrier around the transport roller. T~ pressure rollers
11 and 12 which are consecutively arranged along the path of the record
carrier around the transport roller co-operate with each each of the
toroidal rings 10, each of said pressure rollers being journalled on
25 U-shaped supports 13 and 1~ which themselves are mDunted on a shaft 15.
The shaft 15 is supported by two levers 16 and 17 which are pivotable
together about a stat~onary shaft 18, so that ~le pressure rollers can
be pivoted towards and away from the toroidal rings by displacement of
the levers 16 and 17. The pressure rollers 11 and 12 then pass through
corresponding openings 19 and 20, respectively, which are provided in
a shell-like cover element 21 which surrounds the transport roller at a
distance, thus forming a guide for the record carrier 2. When the
pressure rollers 11 and 12 are lifted off the toroidal rings 10, the
record carrier can be slid ~y hand from the guide surface 4 and around
the transport roller 1 until it reaches the supporting surface 5; it
can also ke pulled out of the printer by hand. However, when the
pressure rollers 11 and 1~ contact the toroidal rings 10, the record
carrier is transported further by rotation of the transport roller.
PHO 81.508 4 12.5.1982
To this end, the transport roller can be rotated either b~ means of
a handwheel 22 connected thereto or by means of a motor 23, via a
gearwheel drive with gearwheels 24 ar.d 25.
In a printer oE this kind it is very important that the record
carrier 2 rests flatly on the supporting surface 5 in order to ensure
that its distance from the printing head 6 is always -the same, regard-
less of the position of the head with respect to the record carrier,
because printing is correct only when this distance is the same. A
constant distance between the printing head and the record carrier is
required in several types of printing heads, for example, printing heads
of daisy-wheel printers, stylus prin-ters or ink jet printers. Notably
in the case of il~ je-t printers it is unportant that this req~lirement
is satisfied, ~ecause a comparatively small, constant distance between
the printing head and the record carrier is to be maintained, because
otherwise the print beco~les irre~ular and incor~?lete.
In order to ensure that the record carrier rests exactly flat
on the supporting surface 5, the supporting surface 5 is situated in
a plane which segmentally intersects the path of the record carrier 2
around the transport roller 1, viewed in a cross-sectional view; a ruler
26 presses the record carrier at the area of the supporting surface
without bringing the record carrier directly into contact with the
supporting surface 5. Thus, at the passaae of the record carrier from
the path around the transport roller to the supporting surface, the
record carrier ~ecomes S-shaped in order to ensure that the record
carrier is indeed completely flatly positioned on the surface 5 at the
area cf the printing ~ead~
The segmental intersecting of the path of the record carrier
around the transportroller by the plane of the supporting surface is
diagra~matically shown in Figure 4, the arc of circle 27 indicating the
path of the record carrier around the transport roller, whilst the
stroke/dot line 28 indicates the plane of the supporting surface. The
segment which is cut off is denoted by heavy lines. The position of
the ruler 26 is indicated by an angle. It is clearly shown that the
dimensions of the segment and the position of the ruler determine the
shape of the S-shape of the record carrier 2 at its passage from the
path around the transport roller to the plane of the supporting surface~
ExperimRnts have demonstrated that in order to ensure suitable flat
positioning of the record carrier on the supporting surface, the rise of
PMO 81.508 5 12.5.1982
h to ke one eighth of the radius rO The required position of the ruler
26 follows from the choice of the dimensions of the segment, because
the ruler must ke situated at such a distance from the plane 28 of the
supporting surface that the record carrier becomes (preferably lightly)
S-shaped, withcut being brought directly into contact with the sup-
porting surface; this is clearly shown in Eigure 4.
In the e~odiment shown in the Eigures 1 and 2, the ruler is
simply formed by the bending of the end 29 of the shell-like cover
element 21 which is situated near the supporting surface 5, the edge
thus bent over performing the function of the ruler. The distance between
the ruler 26 and the suppor~ing surface 5 can then be simply adjusted by
adjustment of the shell-llke cover element.
The Figures 1 and 2 also show that at the area of its long
side 30 which faces the transport roller 1 the supporting surface 5
comprises groo~e-like recesses 31 which correspond to the toroidal rings
10 and in which the toroidal rings project. The portions of the sup-
porting surface 5 adjacent the toroidc~l rings thus reach as far as the
transport roller 1, so that at these areas the surface is situated
slightly kelow the path of the record carrier at the passage frcm the
-transport roller to the surface. ~ kind of air cushion is thus formed
underneath the record carrier; it has keen found that this has a parti-
cularly favo~trable effect for a sm~oth S-shaped passage from the record
carrier to the supporting surface, so that the flat positioning of the
record carrier on the supporting surface is further enhanced.
The em~odiment shown in Figure 3 utilizes a transport roller 1
whose entire circumferential surface, ~or example, formed by a top
layer of an elastic material, is used for the transport of the record
carrier. Also provided are pressure rollers 11 and 12 which in this
case co-operate directly with the circumferential surface of the trans-
port roller 1 and which adjustable with respect thereto in the same
manner as in the emkodiment shown in the Figures 1 and 2. Similarly,
there is provided a shell-like cover element 21 which comprises openings
19 and 20 for the passage of the pressure rollers 11 and 12, respective-
ly~ rrhe supporting surface 5 whose long side 30 adjoins the circum~
ferential surface of the transport roller 1 again extends in a plane
which segm~etltally intersects the path of the record carrier around the
transport roller, said path keing defined by the circumferential surface
of the transport roller in said emkodiment. In said emkodimRnt a ruler 26
PI~O 81.508 6 12.5.1982
is provlded as a separate, strip-shaped component. The free end of the
r~]er again presses the record carrier at the area of the supporting
surface 5, ~ithout bringing the record carrier directly into contact
with the suppor-ting surface.
The choice of the dimensions of the segment cut off from the
path of the record carrier around the transport roller by the plane of
the suppcrting surface again determines the distance bet~een the free
end of the ruler 26 and the supporting surface 5 so thatuponits passage
from the transport roller to the supporting surface 5 the record carrier
~ecomes S-shaped as previously descri~ed ~ith reference to Figure 4.
The record carrier 2 is thus absolutely flatly positioned
against the supporting surface 5, so that it is ensured that the dis-
tance between -the printing head 6 and the record carrier is always
constant.
Obviously, the steps in accordance with the invention can also
be taken for printers having a record carrier transport device of a
type other than the descr:ibed type. For example, in the case of a
record carrier c~nprising edge perforations, a drive with so-called
tractors can be provided for this purpose. In suc~ a case the transport
roller itself may be formed as a so-called spiked roller.
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