Typewriting machines – Carriage or carriage-moving or movement-regulating mechanism – Carriage – per se – or guideway therefor
Reexamination Certificate
2001-04-06
2002-10-29
Colilla, Daniel J. (Department: 2854)
Typewriting machines
Carriage or carriage-moving or movement-regulating mechanism
Carriage, per se, or guideway therefor
C400S354000, C347S037000
Reexamination Certificate
active
06471427
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates to a printhead carrier in an ink jet printer, and, more particularly, to a linear motion transmission device for a printhead carrier in an inkjet printer.
2. Description of the Related Art.
With inkjet printer products, a printing mechanism containing one or more printheads
10
(
FIG. 1
) must be traversed across the printing surface
12
. The printing mechanism is supported and slides along two smooth, round support shafts
14
, only one of which is shown. The force F needed to propel the printing mechanism is applied with a toothed belt
16
attached to the printing mechanism. Toothed belt
16
is then wrapped on a pulley
18
connected to a motor that applies torque. Disadvantages of this printing mechanism system include sensitivity to the belt attachment point, uneven drive force from the motor and belt system, and high friction printing mechanism supports.
Due to the small length of an inkjet printhead, the printhead
10
must be moved in some fashion over the entire width of a piece of media
12
. This is usually accomplished by traversing printhead
10
across the width of the media
12
, moving the media
12
lengthwise and repeating the process until the entire piece of media
12
has been covered by printhead
10
. Other methods exist, but the same principle applies.
In order for the printhead
10
or, in a color printer, group of printheads
10
to traverse, a force F must be applied to printheads
10
. These printheads
10
may be contained in a carrier
20
. In most inkjet printers today, belt
16
is attached to carrier
20
and applies a force F causing it to traverse. Other techniques include the use of a leadscrew, toothed rack and pinion, or linear stepper motor.
The attachment point of belt
16
should be located at the center of gravity of the carrier mechanism to prevent any undesired rotational moment forces in carrier
20
. Moment forces in carrier
20
will cause the carrier mechanism to rotate, changing the relationship between the printheads
10
and media
12
. This change will cause print quality defects and increase friction in the carrier supports
14
to counteract the moment forces.
Printheads
10
are directly attached to an ink tank on carrier
20
. As printing operations are conducted, the amount of ink present on carrier
20
is reduced. The change of ink mass causes the center of gravity to change. Since the center of gravity changes and the belt attach remains fixed, a moment force will begin to appear as the volume of ink in the tank is reduced during printing.
One known method to counteract this moment force is to create tighter supports
14
for carrier
20
. Constraining carrier supports
14
could protect carrier
20
from undesired moment forces by only allowing motion along the axis of carrier supports
14
. Unfortunately, tighter supports
14
result in a higher level of friction. More force will be required to move carrier
20
, and accurate motion will not be achieved due to the increased static and kinetic coefficients of friction.
To apply accurate force quickly to obtain fast carrier accelerations, a toothed belt
16
is typically used. The tooth belt
16
introduces error into the system due to the belt teeth engaging and disengaging on drive pulleys
18
. This added cyclical error often results in print quality defects.
To improve on the stated limitations and problems with the belt drive system, a leadscrew assembly could be used to provide a traverse force on the carrier. The leadscrew assembly consists of a machined screw and a nut that encompasses a portion of the screw. As the screw rotates, the rotationally constrained nut moves along the screw. As the screw is rotated, the nut slides along the screw threads, but suffers from drag due to friction. Accuracy is limited to the screw profile. Another problem is that accurate leadscrews are typically cost prohibitive.
What is needed in the art is an inexpensive and accurate linear motion transmission device for a printhead carrier of an ink jet printer.
SUMMARY OF THE INVENTION
The present invention provides a continuous linear motion transmission device that can smoothly, accurately, and inexpensively traverse a printhead carrier using roller bearings that engage and are angled relative to the carrier support shaft.
The invention comprises, in one form thereof, a printhead carrier assembly in an ink jet printer. The assembly includes a carrier moving along a linear path. At least one rotatable bearing is attached to the carrier. The at least one rotatable bearing has at least one axis of rotation. A rotatable shaft has a surface in contact with the at least one bearing such that the shaft is nonparallel to the at least one axis of rotation of the at least one rotatable bearing. The shaft is substantially parallel to the linear path of the carrier. Rotation of the shaft causes the at least one rotatable bearing to roll along a helical path on the surface of the shaft to thereby carry the carrier along the linear path.
A continuous linear motion transmission device (CLMTD) is applied to transport the printing mechanism across the printing surface. This device provides smooth and even actuation force to the printing mechanism and acts as a pure rolling support for the printing mechanism. The CLMTD attaches to one of the smooth support shafts and converts rotary motion of the smooth support shaft to linear motion of the printing mechanism.
An advantage of the present invention is that it provides very smooth and accurate linear motion due to the rolling support, low friction, and the ability to limit the force applied to the printing mechanism.
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patent: 11321012 (1999-11-01), None
Boyatt, III Richard Gordon
Pickett Peter Brown
Colilla Daniel J.
Lexmark International Inc.
Taylor & Aust PC
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