Typewriting machines – Sheet or web – Including friction-feed means
Reexamination Certificate
1999-12-29
2002-04-02
Hilten, John S. (Department: 2854)
Typewriting machines
Sheet or web
Including friction-feed means
C400S636300
Reexamination Certificate
active
06364554
ABSTRACT:
FIELD OF INVENTION
This invention relates to a print feed mechanism for use in a printer. In particular, the invention relates to an apparatus for feeding print media in a controlled manner to a printing zone of a printer.
BACKGROUND
An ink-jet printer, or any printer using wet ink, typically includes a pen, also called a printhead, a print zone located adjacent the printhead, a feed mechanism for feeding print media through the print zone, and a platen positioned adjacent the print zone. The platen has a generally flat surface which guides and supports the print medium in the print zone. During printing, ink is placed on the print medium by dropping or ejecting the ink from ink nozzles in the printhead. These features of an wet ink printer are described, for example, in U.S. Pat. No. 5,356,229, assigned to Hewlett-Packard Company, and entitled ‘Print Medium Handling System To Control Pen-to-Print Medium Spacing During Printing’.
FIGS. 1 and 2
illustrate the functional elements of a printing mechanism of a known printer, for example the model HP 2500 printer available from Hewlett-Packard Company, USA. The printing mechanism includes a platen
110
with a flat print medium contacting surface
115
, and a feed mechanism
140
positioned adjacent the platen. The flat expanse of the platen
110
is positioned below a printhead
120
such that the platen
110
supports the print medium
130
throughout a print zone defined between the printhead
120
and the platen
110
. The print medium
130
is moved through the print zone in the direction indicated by the arrow A in
FIGS. 1 and 2
. At the same time, the printhead
120
performs a series of swath-like printing scans across the width of the print medium, in a direction perpendicular to the media motion direction, as indicated by arrow B in FIG.
2
.
The feed mechanism
140
is ideally arranged so as to feed the print medium
130
at a downward angle onto the platen
110
such that the print medium presents a flat profile to the scanning printhead
120
. Ink nozzles or pens
125
contained in the printhead are thus positioned at a uniform distance from the print medium. This constant pen-to-print medium spacing ensures optimum print quality in the printer.
In the HP 2500 printer, the feed mechanism
140
comprises four drive rollers
150
which are supported on a common axle
155
, and four complementary print media guides
160
. The common axle
155
is in turn supported by a chassis of the printer and is coupled via a gear mechanism to a drive motor. Each print media guide
160
includes a freely rotating pinch roller
165
which is biased against a respective drive roller
150
, and a deflector plate
170
which helps to deflect the print media
130
downwards. The pinch rollers
165
operate to ensure that the print medium remains in contact with and is properly fed by the drive roller
150
. The pinch rollers
165
are biased against the drive rollers at a point circumferentially displaced from the apex of the drive rollers. This displacement is indicated in
FIG. 1
as an angular displacement &agr;, and results in the print media
130
being directed downwards in co-operation with the downward deflection produced by the deflector plate
170
. The combination of the pinch roller
165
and the deflector plate
170
ensures that the print medium is fed at an appropriate dive angle to the platen
110
.
FIGS. 3 and 4
are detailed sectional views showing one of the drive rollers
150
and one of the print media guides
160
of the printer feed mechanism
140
, together with a support frame
310
also forming part of the printer feed mechanism. The support frame
310
is secured to a chassis of the printer and supports all four of the print media guides
160
. The support frame
310
includes two slot guides
315
(one of which is not shown in
FIGS. 3 and 4
) which are designed to receive respective end portions of a rod
175
of the print media guide
160
. The slot guides
315
prevent movement of the print media guide
160
, and hence the pinch roller
165
and deflector plate
170
, in the print media motion direction (arrow A in FIGS.
1
and
2
). When the rod
175
is received in the slot guides
315
, a raised portion
180
of the print media guide
160
abuts the lower surface of the support frame. A torsion spring which is coupled between the rod and the support frame biases the rear section of the print media guide towards the support frame as indicated by arrow C in FIG.
4
. In this arrangement, the print media guide pivots about the abutting point between the raised portion
180
and the lower surface of the support frame and biases the pinch roller in contact with the surface of the drive roller
150
.
It is important that the printer feed mechanism
140
is configured correctly, in order that the print medium
130
is directed at an appropriate angle onto the platen
110
,. The applicant has found that during production of the HP 2500 printer, the relative positions of the print media guides
160
and the drive rollers
150
can vary, resulting in the print medium
130
being directed at inappropriate angles onto the platen
110
. These inappropriate angles lead to variations in the pen-to-print medium spacing which degrades the printing quality of the printer output.
The variation of the relative positions of the print media guides
160
and the drive rollers
150
is caused by tolerances in the printer structure. These tolerances can combine to produce larger errors in the positions of the printer elements. For example, there are positional errors associated with the coupling of the print medium guide
160
to the support frame
310
, the attachment of the metal frame to the printer chassis, the supporting of the drive axle
155
by the printer chassis, as well as stress-associated positional errors in the individual printer elements. These errors or variations are accentuated in wide-format printers such as the HP 2500 printer that are capable of printing onto A3 size paper.
The problem of variations in the relative positions of the print media guides
160
and the drive rollers
150
has been resolved by the applicant by producing a series of print medium guides. These series of print medium guides can be systematically and selectively attached to the support frame
310
during production until an appropriate dive angle is produced. The series of print medium guides are graded according to the protrusion distance of the deflector plate
170
. Thus, each print medium guide in the series has a slightly different deflection property when coupled to the printer feed mechanism. However, this solution to the problem of variations has its drawbacks. Firstly, the solution requires there to be overproduction of the print medium guides to ensure there are sufficient quantities to form the series. Secondly, for a particular printer there may not be any one print medium guide from the series which is suitable. Thirdly, the process of systematically attaching the print medium guides and then testing the performance of the printer slows the overall production process.
In an alternative print mechanism used in the HP 2000 model printer, the platen can be raised or lowered relative to the print feed mechanism, to a position in which the print medium presents a flat profile to the scanning printhead. This print mechanism is more suited to narrow-format printers that are designed for printing onto A
4
size paper. The print mechanism is difficult to implement in wide-format printers in which the platen is correspondingly wider and requires more support.
SUMMARY OF THE INVENTION
The present invention provides for a print mechanism in which the print guide is adjustable relative to the drive roller so that the direction at which the print media is fed onto a platen can be varied to optimize printing quality in the printer.
According to the present invention there is provided a print feed mechanism for feeding print media in a controlled manner to a printing zone of a printer, the mechanism comprising a drive roller located ad
Huang Pui Wen
Lim Kong Hock
Sivanandam Sathiyamoorthy T.
Cone Davis N.
Hewlett--Packard Company
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