Print medium conveying unit and printing apparatus using said conveying unit

A print medium conveying unit for conveying a print medium to a plurality of printing positions with a plurality of print heads disposed along a conveyance direction of the print medium includes rotary members provided over the print face of the print medium between print heads. The rotary members suppress displacement from the print face of the print medium.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a print medium conveying unit for 
conveying a print medium and a printing apparatus using said conveying 
unit, and more particularly to a print medium conveying unit for conveying 
a print medium through a plurality of printing positions satisfactorily, 
and a printing apparatus using said conveying unit. 
2. Related Background Art 
Conventionally, some recording apparatuses have been known in which a 
plurality of recording heads are arranged along a direction of conveying a 
recording sheet or the like, and the image recording is performed on the 
recording sheet by conveying the recording sheet to pass through a 
plurality of recording sites by the plurality of recording heads. 
In such recording apparatuses, after recording by a recording head on the 
upstream side in the direction of conveying the recording sheet, and when 
conveying the recording sheet to the next recording site by a recording 
head subsequently located downstream, the rising of the recording sheet 
off a platen surface might occur. This causes the recording sheet to be 
brought into a space within the recording head out of the normal conveying 
path, because of, for example, a rolling recording sheet, oblique running 
of recording sheet, or the effect which the recording sheet undergoes from 
the recording head in recording (pressure applied by the recording head in 
case of a recording head of contact recording type, or deformation of the 
recording sheet due to sticking of ink droplets in case of a recording 
head of non-contact recording type). Therefore, there was a risk that the 
normal recording at the recording site downstream might be hampered, or 
the conveyance stop might occur due to jamming of the recording sheet. 
To prevent such unfavorable conveyance of the recording sheet, an apparatus 
is known in which the recording sheet is adsorbed onto a platen by sucking 
the air from the back side of the platen through fine apertures punched on 
the platen supporting the recording sheet in a plurality of recording 
sites. Further, an apparatus is known in which the recording sheet is 
adsorbed onto the conveying surface of an endless conveying belt for 
conveying the recording sheet through a plurality of recording sites by 
means of static electricity or weak adhesives. 
However, such a recording apparatus may require a pump device for suction, 
an electric apparatus for charging or discharging the endless conveying 
belt or the recording sheet, or a device for applying adhesives to the 
endless conveying belt, resulting in larger recording apparatus as such, 
or more complex recording process, with higher costs. 
On the other hand, conventionally, there was a label sheet of the type in 
which a number of labels were successively bonded, easily releasably, on a 
lengthwise released paper called a separator as the recording sheet, but 
this label sheet was commonly in the form of having labels bonded on the 
separator, such labels made of thermal paper to effect thermal printing by 
means of a thermal head. Further, this separator was mostly formed like a 
roll and delivered to the recording apparatus. 
The above-described technical problem was significantly serious, 
considering that when using a label sheet as the recording sheet, there 
was a risk that the label sheet might not be conveyed normally to the 
downstream recording site, since the label sheet might rise up from a 
mount, due to the above-mentioned phenomenon, though the released paper 
itself as the mount could be conveyed normally. 
Furthermore, this problem is conceivably a very important subject, in that 
when using a recording apparatus of an ink jet system, as the recording 
system, in which a fixed gap is held contactless between the recording 
head and the recording sheet in recording, the label sheet may swell out 
to cause deformation like wrinkles or decrease the adhesive power of 
adhesives, due to sticking of ink droplets produced by the ink jet 
recording at a plurality of recording sites. This results is an abnormal 
condition of conveying the recording sheet as previously described, 
whereby it is expected that new problems may be possibly incurred, such as 
clogging of ink discharge ports with paper scraps produced by contact of 
the recording sheet with a member for guiding the recording sheet, false 
recording of image or clogging of ink discharge ports caused by contact of 
the recording sheet with the ink jet head disposed downstream, which was 
no problem in the case of the contact type recording system such as a 
thermal system or a thermal transfer system. 
SUMMARY OF THE INVENTION 
The present invention has been achieved in the light of aforementioned 
problem, and an object of the present invention is to provide a print 
medium conveying unit which can convey a print medium in good condition 
through a plurality of printing positions. 
It is another object of the invention to provide a printing apparatus which 
can make excellent image prints by conveying a print medium in good 
condition through a plurality of printing positions. 
It is a further object of the invention to provide a print medium conveying 
unit which can convey a print medium in good condition, while preventing a 
displacement beyond a predetermined amount off a print medium conveyance 
path between printing positions, in conveying the print medium through a 
plurality of printing positions, as well as a printing apparatus using 
said conveying unit. 
It is a still further object of the invention to provide a print medium 
conveying unit which can convey a print medium with a recording sheet in 
good condition through a plurality of printing positions, with the 
recording sheet held on a sheet substrate. 
It is another object of the invention to provide a printing apparatus which 
can make excellent image prints by conveying a print medium in good 
condition through a plurality of printing positions, with the recording 
sheet held on a sheet substrate. 
It is another object of the invention to provide a print medium conveying 
unit for conveying a print medium to a plurality of printing positions 
with a plurality of print heads disposed along a conveyance direction of 
said print medium, comprising rotary members provided over the print face 
of said print medium between print heads mutually, said rotary members 
suppressing displacement from the print face of said print medium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments of the present invention will be described below 
in detail with reference to the drawings. 
It is to be noted that the following embodiments use the print medium in 
the form of roll paper where labels are successively arranged on a 
released sheet, but may use other print media in various forms, kinds or 
materials in conformance to the printer used. For example, the print 
medium may be a cut sheet, or may be of film, cloth or others. Also, in 
this embodiment, an ink jet print head of full-line type which can exhibit 
the most remarkable effect of the present invention is used, but a serial 
type ink jet print head can be also used, or other recording systems, 
e.g., a thermal head, may be used to obtain desired effects. 
While this invention is described below with a label printer, it is of 
course possible that the printer of the present invention may take various 
forms in which the print medium is a scored continuous paper to be able to 
cut away, a calling card, other cards, or the form of a ticket vending 
machine. 
FIG. 1 is a perspective view showing the appearance of a label printer 
according to an embodiment of the present invention. 
The label printer of this embodiment uses a sheet in the form of roll paper 
in which labels are successively arranged on a released paper, and can be 
largely classified, in its arrangement or constitution, into three units, 
including a roll paper supply unit 101, a print head unit 102, and an ink 
cartridge accommodating unit 103. A cover 111 of roll paper supply unit 
101 is detachably mounted, thereby enabling a new roll paper to be set. 
The roll paper accommodated within the roll paper supply unit 101, which 
is conveyed by a sheet conveying mechanism constructed between the print 
head unit 102 and the ink cartridge accommodating unit 103, as will be 
described later in connection with FIG. 2, is printed on each label by a 
print head of print head unit 102, and then exhausted via an exhaust 
opening 114 out of the apparatus. It is to be noted that a device for 
releasing a label from the released paper which is exhausted through the 
sheet exhaust opening 114, or a device for winding the released paper to 
be exhausted together with bonded labels, may be connected to the label 
printer of this embodiment. 
The print head unit 102 is provided such that the whole head unit can be 
opened or closed around a support shaft at a back end portion in the 
cartridge accommodating unit 103, as will be described later in connection 
with FIG. 2, thereby allowing maintenance of a print head of print head 
unit 102, or a sheet conveying mechanism, or setting of the roll paper. At 
a front end portion of print head unit 102, there are provided a lamp or a 
liquid crystal display for informing various sorts of printer status, as 
well as an operation unit 112 equipped with operation keys. 
A front cover 113 of the ink cartridge accommodating unit 103 can be opened 
or closed around a rotational shaft at an end portion to the left in the 
figure, thereby allowing mounting or dismounting of an ink cartridge by 
opening this front cover 113 for the replacement of the ink cartridge. 
FIG. 2 is a perspective view of the label printer as shown in FIG. 1, in 
which the cover 111 of roll paper supply unit 101 is removed and the print 
head unit 102 is turned upward into an open state, and FIG. 3 is a 
perspective view showing the label printer in the state where the front 
cover 113 of ink cartridge unit 103 is opened. 
As shown in FIG. 2, a roll 126 around which the roll paper 124 accommodated 
within the roll paper supply unit 101 is wound is placed on two drive 
rollers 301 (one not shown) installed on the bottom of the unit 101, in 
which the external periphery of the roll 126 and the drive rollers are in 
contact owing to a pressure produced by its dead weight of the roll paper. 
In this state, by the above drive rollers 301 being rotated due to the 
motive power of a motor, not shown, the roll paper 124 is subjected to 
separation at the outermost turn from its inner roll paper and delivered 
therefrom. This supply of roll paper is performed, substantially 
independently of the conveyance by the roll paper conveying mechanism 104 
(its details not shown) between the printer head unit 102 and the 
cartridge accommodating unit 103. Accordingly, to regulate the conveyance 
between these two units, the supply of roll paper is controlled to form a 
loop (slack, not shown in FIG. 2) which serves as a buffer in the roll 
paper supply as above described. That is, if a loop sensor (not shown) 
does not sense any loop in the conveyance by the conveying mechanism 104, 
the roll paper supply is performed while forming a loop by driving the 
above drive rollers. 
A sheet guide 131 is slidably provided along a direction of the width of a 
roll 126 to be accommodated. That is, in accommodating the roll paper, the 
sheet guide 131 is slid beyond the width of roll paper 124 to place the 
roll 126 on the driving rollers, and then is slid up to the width of roll 
126, so that a part of sheet guide 131 can be abutted against a core 125 
of roll 126. Thereby, when the roll paper 124 is supplied, it is possible 
to regulate the roll paper 124, within a tolerance of minute deflection, 
from being swung widthwise upstream of the driving rollers in its supply 
direction. It is to be noted that the sheet guide 131 is provided with a 
stopper 316 for securing its slide position. 
In the roll paper conveyance path, as obliquely feeding unit 128 is 
provided near an entrance into the conveyance path for the conveying 
mechanism 104. The obliquely feeding unit 128 has two obliquely feeding 
rollers (not shown) contacting with the lower surface of roll paper 124, 
and obliquely feeding rolls 129, 130 contacting with the upper surface of 
roll paper 124 placed opposed to those rollers. Two obliquely feeding 
rollers consist of a driving roller disposed opposite an obliquely feeding 
roll 130, and driven by a driving force from the conveying mechanism 104, 
and a driven roller disposed opposite an obliquely feeding roll 129 and 
not driven by any driving force, each roller being mounted to be rotated 
obliquely relative to the direction of conveying the roll paper (the 
rotational shaft is inclined from a direction orthogonal to the conveyance 
direction). Also, the obliquely feeding rolls 129, 130 are also mounted 
obliquely relative to the conveyance direction, like the obliquely feeding 
rollers. With these obliquely feeding rollers and obliquely feeding rolls 
129, 130, the roll paper being conveyed is subjected to a conveying force 
obliquely directed, which acts to press the roll paper onto the predefined 
guide on the rear side in the figure. As a result, since the roll paper 
124 is subjected to a regulation force to perform the conveyance in a 
fixed direction, it can be conveyed satisfactorily without fluctuations in 
the conveyance direction. 
The roll paper conveying mechanism 104 provided between the print head unit 
102 and the cartridge accommodating unit 103 is comprised of a plurality 
of belts disposed under the roll paper 124 (or accordingly on the upper 
surface of cartridge accommodating unit 103) and extending in the 
conveyance direction, though they are omitted in FIG. 2, rollers for 
driving them, provided upstream and downstream in the conveying direction, 
and spurs 141 (shown in FIG. 4) disposed under the lower surface of print 
head unit 102, each spur getting a driving force via a predetermined belt 
among the above-mentioned belts. 
In FIG. 3, the ink cartridge accommodating unit 103 comprises four 
cartridge accommodating chambers 140Y, 140M, 140C, 14OBk, corresponding to 
four kinds of inks for use in the label printer in this embodiment, i.e., 
yellow (Y), magenta (M), cyan (C) and black (Bk). Near an entrance of each 
cartridge accommodating chamber, a shutter 142Y, 142M, 142C or 142Bk for 
substantially shuttering the inside of this accommodating chamber is 
provided. Those shutters have the upper portion supported rotatably, 
provided to protect the user from falsely putting a hand into the 
accommodating chamber and touching an ink supply needle. When inserting an 
ink cartridge, the cartridge itself forces a shutter to open to the rear 
side of accommodating chamber to achieve the insertion. 
FIG. 4 is a front view showing the constitution of a print head station 151 
(hereinafter referred to as PHS) which is a main mechanism of the print 
head unit 102. 
PHS 151 has an ink jet head (hereinafter referred to as a head) 155Y, 155M, 
155C, 155Bk which has discharge ports arranged over the entire width of 
the label in a width direction of roll paper to make prints on labels 
placed on the roll label 124. This head is one having elements for 
generating thermal energy for causing film boiling in the ink as the 
energy for use to discharge the ink from the ink discharge ports. Also, 
PHS 151 has withdrawal means of the ink which is discharged out of the ink 
discharge ports disposed on each head, a blade for wiping and removing 
remaining ink on the discharge port formation face near the ink discharge 
ports of head, and a recovery system unit 153 having a cap for preventing 
drying around the ink discharge ports. 
In PHS 151, there are provided a drive system unit for moving vertically a 
head holder unit 152 for supporting each head from the print position onto 
the roll paper 124, and moving the recovery system unit 153 horizontally 
along the roll paper conveyance direction a predetermined amount, and a 
cool unit for cooling the head. 
Also, beneath the PHS 151, spurs 141 are provided on both sides of each 
head, as above noted. 
While in the above description, the label printer was largely classified 
into three units, it is of course possible that each unit is not only 
provided with elements or mechanisms as described. Other relevant elements 
to those as described, or a control substrate, a driving motor, and an ink 
supply system, are appropriately disposed, wherein well-known elements can 
be used, except for each of elements or mechanisms as described below. 
Next, the conveying mechanism 104 as above will be described in detail. 
While in the following embodiment the print medium is conveyed by means of 
the conveying belt 401, it will be appreciated that the print medium may 
be directly conveyed on a flat platen (print medium supporting surface), 
instead of using the conveying belt 401. 
FIG. 5 is a perspective view showing the whole label printer including the 
conveying mechanism 104, FIG. 6 is a plan view of the conveying mechanism 
104, FIG. 7 is a side view of the conveying mechanism 104, and FIG. 8 is a 
front view of the conveying mechanism. 
The conveying mechanism 104 comprises a plurality of conveying belts 401 
forming the conveyance surface on the platen 400, a spur driving belt 402 
which is driven by the same driving source (omitted in the figure) as that 
for the plurality of conveying belts 401, and forms the drive plane on the 
platen 400 outside the roll paper 124 (as seen to the left and downward in 
FIG. 5) to be conveyed by the conveying belts 401, a plurality of spurs 
141 disposed in suspension a predetermined height above the plurality of 
conveying belts 401, and pulleys 404 for sharing the rotational shaft with 
the plurality of spurs 141, and transmitting a rotational driving force to 
the spurs 403 by abutting with the spur driving belt 402. 
The plurality of conveying belts 401 are stretched around the rotational 
shafts 405 and 406 disposed downstream and upstream of the platen 400, 
respectively. The provision of plural conveying belts 401 has the 
advantage that the use of a wide and expensive conveying belt can be 
avoided, and the assembling operation can be facilitated, compared to the 
wide conveying belt. It is needless to say that the thickness of the 
plural conveying belts 401 is all equal. 
At one end of the rotational shaft 405 (on the rear side in FIG. 5), a 
conveyance drive motor, not shown, is attached, this drive force being 
transmitted to the rotational shaft 406 via the plural drive belts 401. 
Therefore, even with the provision of plural conveying belts 401, there is 
no variation in the conveying speed between conveying belts, so that the 
occurrence of any inconvenience, such as oblique running of the roll paper 
124 to be conveyed, can be prevented. The other end of rotational shaft 
405 is connected via a round belt 409 with a rotational shaft 408 of a 
waste paper system for the roll paper 124, as shown in FIGS. 6 and 7. 
Also, the other end of rotational shaft 406 is connected via a round unit 
410 with the driving system of the obliquely running unit 128 as above. In 
either case, the connection via the round belt has the effect of improving 
the unevenness in conveyance. 
The spur driving belt 402 is stretched between the rotational shafts 405 
and 406, like the conveying belts 401. In this embodiment, the spur 
driving belt 402 is looped around the other end of each rotational shaft 
(on the fore side in FIG. 5). This position corresponds to the outside of 
the roll paper 124 to be conveyed by the plurality of conveying belts 401. 
Accordingly, the spur driving belt 402 is not directly involved in 
conveying the label sheet. 
This spur driving belt 402 is abutted by pulleys 404 which share the 
rotational shafts with the spurs 141. A driving force from the spur 
driving belt 402 is transmitted via the pulleys 404 to the plurality of 
spurs 141. 
These spurs 141 are provided on the lower portion of PHS 151, and set in 
suspended state a predetermined height above the roll paper 124 to be 
conveyed, when this PHS 151 is covered over the platen 400. Herein, the 
gap between the surface of roll paper 124 and the spurs 141 is normally 
set to 0.14 mm.+-.0.05 mm, but is not particularly limited as far as it is 
in the range where the roll paper is satisfactorily conveyed to the next 
print position. 
The height of spurs 141 above the platen 400 is adjusted so that the wall 
thickness of spur driving belt 402 is greater than that of the plurality 
of conveying belts 401 in this embodiment. With this method, it is 
possible to make the spurs 141 and the pulleys 404 of the same diameter, 
and render the peripheral speed of both equal. Of course, the 
above-mentioned height may be adjusted in such a way that the wall 
thickness of spur driving belt 402 is made equal to that of conveying 
belts 401, and the size of spurs 401 is made different from that of 
pulleys 404. 
Also, the spurs 141 are disposed on the PHS 151 under the platen 400 and 
near a TOP sensor 411 disposed at a position upstream of the conveyance 
path, as shown in FIG. 7. This TOP sensor 411 is to sense a TOF (Top of 
Form) mark as a trigger for print start attached on the back side of roll 
paper 124. When this roll paper 124 is rising up, the separation distance 
between the TOP sensor 411 and the TOF mark may vary, resulting in less 
sensing accuracy, but owing to the presence of spurs 141 near the TOF 
sensor 411, the variation of the above separation distance can be 
suppressed to the minimum, thereby making it possible to raise the sensing 
accuracy. 
Further, the plurality of spurs 141 are each equipped with a cleaner 412 
made of an absorbing material. This cleaner 412 abuts against the marginal 
portion of spur 141 owing to its dead weight or an urging member such as a 
leaf spring, thereby allowing removal of adhering matter such as ink 
discharged by each ink jet head 155 onto the roll paper 124 constantly. 
While in the above embodiment, the spur drive belt 402 was disposed to the 
fore side as shown in FIG. 5, it will be appreciated that the spur drive 
belt may be disposed to the rear side. When it is disposed to the rear 
side, the width of roll paper 124 to be conveyed is not limitative, but a 
wider roll paper 124 can be also conveyed and printed, with the advantage 
of having a higher degree of freedom for the applied sheet. In this case, 
pulleys 413 mounted at the end portion opposite pulleys 404 take over a 
rotational driving force transmission function to the spurs 141 which is a 
function of pulleys 404, while the pulleys 404 share a spacer function 
which is a function of the pulleys 413. For this purpose, the pulleys 413 
are of the same diameter as the spurs 141, and the pulleys 404 are needed 
to be replaced with those having a radius equal to the radius of spurs 141 
plus the thickness of spur drive belt 402. 
It should be noted that the ink jet recording apparatus as above described 
may be used as an image output terminal for an information processing 
equipment such as a computer, and additionally take the form of a copying 
machine in combination with a reader, and further a facsimile apparatus 
having the transmission and reception function. 
As above described, according to this embodiment, by providing spurs 
between a plurality of print heads, the print medium can be securely 
suppressed from rising up, even if it rises up during the conveyance, so 
that the contact between the discharge port face of print heads and the 
surface of print medium can be prevented. If the print head is of the ink 
jet print system, it is possible to make high quality prints on the print 
medium with the same method. 
Also, by providing spurs suspended over the surface of the print medium, 
they normally make no contact with the print medium surface being 
conveyed, so that the production of paper powder from the print medium can 
be prevented, and the increase in conveyance load of the print medium can 
be suppressed, and further, when the print medium rises up, its rising 
part can be suppressed to prevent contact with the print head firmly. 
Further, by rotating the spurs at the same speed as the conveying speed of 
print medium, even when the print medium rises up to make contact with 
spurs, the spurs will not impose any load on the conveyance, whereby it is 
possible to prevent oblique running of the print medium, and to perform 
the conveyance at a constant speed. 
Also, by driving the print medium via a plurality of conveying belts to be 
driven by the same drive source, it is possible to prevent oblique running 
of the print medium securely by eliminating the variations in the 
conveying speed between the plurality of conveyance belts. Also, owing to 
the provision of the plurality of conveyance belts, the use of a wider and 
expensive conveyance belt can be avoided, and the cost can be reduced. 
Further, by providing a spur drive belt to drive for rotation the spurs 
outside the print medium being conveyed, and making the spurs contacting 
with this spur drive belt and the pulleys sharing the rotational shaft 
with the spurs the same diameter, the peripheral speed of pulleys and 
spurs can be made equal to realize the conveyance at stable speed.