U.S. patent application number 10/057797 was filed with the patent office on 2003-02-27 for printing system with vacuum table.
This patent application is currently assigned to VUTEK, INC.. Invention is credited to Cleary, Arthur L., Duncanson, Paul, Lahut, Joseph A., Rall, Rainer.
Application Number | 20030038420 10/057797 |
Document ID | / |
Family ID | 26736895 |
Filed Date | 2003-02-27 |
United States Patent
Application |
20030038420 |
Kind Code |
A1 |
Cleary, Arthur L. ; et
al. |
February 27, 2003 |
Printing system with vacuum table
Abstract
An apparatus for transporting a substrate in a printing system
includes a transport belt provided with a plurality of holes which
extend through a thickness of the belt, and a vacuum table which
generates a vacuum, and is positioned on one side of the transport
belt. A porous sheet is positioned between the belt and the vacuum
table, while the vacuum table, the porous sheet, and the transport
belt are in fluid communication. The vacuum generated by the vacuum
table creates a suction on the substrate placed on the transport
belt, and the porous sheet restricts fluid flow between the table
and the transport belt to maintain a desired vacuum as an area of
the transport belt covered by the substrate varies as the substrate
is transported through the printing system.
Inventors: |
Cleary, Arthur L.; (Center
Harbor, NH) ; Lahut, Joseph A.; (Center Habor,
NH) ; Rall, Rainer; (Belmont, NH) ; Duncanson,
Paul; (Franklin, NH) |
Correspondence
Address: |
HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
530 VIRGINIA ROAD
P.O. BOX 9133
CONCORD
MA
01742-9133
US
|
Assignee: |
VUTEK, INC.
Meredith
NH
|
Family ID: |
26736895 |
Appl. No.: |
10/057797 |
Filed: |
October 29, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60244303 |
Oct 30, 2000 |
|
|
|
Current U.S.
Class: |
271/197 |
Current CPC
Class: |
B65H 2515/342 20130101;
B65H 11/005 20130101; B65H 2220/01 20130101; B65H 2406/322
20130101; B65H 2515/342 20130101; B41J 11/0085 20130101; B41J
11/007 20130101 |
Class at
Publication: |
271/197 |
International
Class: |
B65H 029/32; B65H
005/02 |
Claims
What is claimed is:
1. An apparatus, comprising: a transport belt provided with a
plurality of holes which extend through a thickness of the belt; a
vacuum table which generates a vacuum, the vacuum table being
positioned on one side of the transport belt; and a porous sheet
positioned between the belt and the vacuum table, the vacuum table,
the porous sheet, and the transport belt being in fluid
communication, the vacuum generated by the vacuum table creating a
suction on a substrate placed on the transport belt, the porous
sheet restricting fluid flow between the table and the transport
belt to maintain a desired vacuum as an area of the transport belt
covered by the substrate varies as the substrate is transported
through the printing system.
2. The apparatus of claim 1, wherein the desired vacuum is
maintained in the range from about -0.05 psi to about -0.3 psi.
3. The apparatus of claim 1, wherein the vacuum table is coupled to
a motor which generates a vacuum.
4. The apparatus of claim 3, wherein the motor is coupled to a CPU
which instructs the motor as to the amount of vacuum to
generate.
5. The apparatus of claim 3, wherein the vacuum table is coupled to
a vacuum sensor which detects the vacuum provided by the vacuum
table.
6. The apparatus of claim 5, wherein the vacuum sensor and the
motor are coupled to a CPU which receives vacuum information from
the sensor and sends instructions to the motor.
7. The apparatus of claim 1, wherein the transport belt is made
from woven polyester.
8. The apparatus of claim 7, wherein the woven polyester is a
reinforced polyurethane.
9. The apparatus of claim 7, wherein the transport belt has a
thickness of about 0.09 inch.
10. The apparatus of claim 1, wherein the holes of the transport
belt are spaced apart by about 1 inch.
11. The apparatus of claim 1, wherein the holes of the transport
belt have a diameter of about 0.1 inch.
12. The apparatus of claim 1, wherein the transport belt is made
from stainless steel.
13. The apparatus of claim 12, wherein the thickness of the
transport belt is about 0.008 inch.
14. The apparatus of claim 1, wherein the porous sheet is made of
sintered, porous polyethylene.
15. The apparatus of claim 14, wherein the porous sheet has a
thickness of about 0.5 inch.
16. A method for transporting a substrate in a printing system,
comprising: generating a vacuum with a vacuum table for holding the
substrate on a transport belt; and maintaining the vacuum at a
desired level as the area of the transport belt covered by the
substrate varies as the substrate is transported though the
printing system.
17. The method of claim 16, wherein the desired level of vacuum is
maintained from about -0.05 psi to about -0.3 psi.
18. The method of claim 16, wherein maintaining includes using a
porous sheet to maintain the vacuum at the desired level.
19. The method of claim 18, wherein the porous sheet acts as a flow
restrictor.
20. The method of claim 18, wherein the porous sheet distributes
the vacuum over a region of the transport belt.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/244,303, filed on Oct. 30, 2000. The entire
teachings of the above application are incorporated herein by
reference.
BACKGROUND
[0002] Certain types of printing systems are adapted for printing
images on large-scale substrates, such as museum displays,
billboards, sails, bus boards, and banners. Some of these systems
use so-called drop on demand ink jet printing. In these systems, a
piezoelectric vibrator applies pressure to an ink reservoir of the
print head to force the ink out through the nozzle orifices
positioned on the underside of the print heads. A particular image
is created by controlling the order at which ink is ejected from
the various nozzle orifices.
[0003] In some of these systems, a carriage which holds a set of
print heads scans across the width of a flexible substrate while
the print heads deposit ink as the substrate moves. In another type
of system, a solid, non-flexible substrate is supported on a table.
The carriage holding the print heads has two degrees of motion so
that it is able to move along the length as well as the width of
the substrate as the print heads deposit ink onto the substrate.
And in yet another arrangement, a solid, non-flexible substrate is
held to a table as the entire table and substrate move together s
along one axis of the substrate under the print heads as the
carriage holding the print heads traverses in a direction normal to
that axis while the print heads deposit ink to create a desired
image.
SUMMARY
[0004] A transport belt is typically used to move substrates
through the printing system. In some systems, a vacuum table is
positioned beneath the belt, and the belt has holes through which
the vacuum table draws a vacuum to create a suction between the
belt and the substrate. The amount of vacuum that has to be
generated by the vacuum table can significantly vary depending upon
how much of the table is covered by the substrate. Thus some
systems use a vacuum table divided into several manifolds such that
when certain portions of the table are not covered by the
substrate, the vacuum generated by the manifolds in those portions
of the table is reduced. It is desirable, therefore, to provide a
vacuum system that draws a vacuum without varying the vacuum while
the substrate covers varying portions of the belt positioned above
the table.
[0005] In one aspect of the invention, an apparatus for
transporting a substrate in a printing system includes a transport
belt provided with a plurality of holes which extend through a
thickness of the belt, and a vacuum table which generates a vacuum,
and is positioned on one side of the transport belt. A porous sheet
is positioned between the belt and the vacuum table, while the
vacuum table, the porous sheet, and the transport belt are in fluid
communication. The vacuum generated by the vacuum table creates a
suction on the substrate placed on the transport belt, and the
porous sheet restricts fluid flow between the table and the
transport belt to maintain a desired vacuum as an area of the
transport belt covered by the substrate varies as the substrate is
transported through the printing system.
[0006] Embodiments of this aspect can include one or more of the
following features. The desired vacuum is maintained in the range
from about -0.05 psi to about -0.3 psi. In some embodiments the
vacuum table is coupled to a motor which generates a vacuum. The
motor can be coupled to a CPU which instructs the motor as to the
amount of vacuum to generate. The vacuum table can also be coupled
to a vacuum sensor which detects the vacuum provided by the vacuum
table, and the sensor can be coupled to the CPU which receives
information from the sensor.
[0007] In some embodiments, transport belt is made from woven
polyester such as, for example, a reinforced polyurethane. The
transport belt can have a thickness of about 0.09 inch, and the
holes of the transport belt can be spaced apart by about 1 inch,
and have a diameter of about 0.1 inch.
[0008] In other embodiments, the transport belt is made from
stainless steel which can have a thickness of about 0.008 inch. The
porous sheet can be made of sintered, porous polyethelene, and have
a thickness of about 0.5 inch.
[0009] In a related aspect of the invention, a method for
transporting a substrate in a printing system includes generating a
vacuum with a vacuum table for holding the substrate on a transport
belt, and maintaining the vacuum at a desired level as the area of
the transport belt covered by the substrate varies as the substrate
is transported though the printing system.
[0010] In some embodiments, the desired level of vacuum is
maintained from about -0.05 psi to about -0.3 psi. In certain
embodiments, a porous sheet which acts as a flow restrictor is used
to distribute the vacuum over a region of the transport belt.
[0011] Among other advantages, the vacuum table is able to generate
a vacuum that need not be varied as the substrate covers varying
portions of the belt. The porous sheet facilitates drawing a
continuous vacuum with the vacuum table, while making no further
adjustment to the vacuum level as one or more substrates are
transmitted through the printing system during the print process.
This feature is applicable to both continuous substrates, for
example, those supplied from a roll, as well as non-continuous
substrates such as a flexible or a rigid sheet supplied
individually.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of preferred embodiments of the invention, as
illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention.
[0013] FIG. 1 is an perspective view of a printing system in
accordance with the present invention.
[0014] FIG. 2A is a cross-sectional and block diagram view of the
printing system of FIG. 1.
[0015] FIG. 2B is a top view of a transport belt of the printing
system of FIG. 1.
[0016] FIG. 3A is an isolated view of a thickness indicator roller
of the printing system of FIG. 1.
[0017] FIG. 3B is a side view of the thickness roller along the
line 3B-3B of FIG. 3A.
[0018] FIG. 4A is an isometric view of a part of a rail system for
supporting a carriage of the printing system of FIG. 1.
[0019] FIG. 4B is a cross-sectional view of the rail system of FIG.
4A shown mounted to a support beam.
[0020] FIG. 4C is a cross-sectional view of the rail system of FIG.
4A shown with the carriage of the printing system.
DETAILED DESCRIPTION OF THE INVENTION
[0021] A description of preferred embodiments of the invention
follows.
[0022] Referring to FIG. 1, there is shown a printing system 10
that prints on both flexible and non-flexible substrates. Further,
the printing system 10 is able to accommodate substrates with
various thickness automatically during the printing process.
[0023] The printing system 10 includes a base 12, a rail system 14
attached to the base 12, a transport belt 18 which moves a
substrate though the system, and a substrate thickness indicator
roller 20. A carriage 16 holding a set of print heads 17 (shown in
phantom) is supported by and traverses along the rail system
14.
[0024] Referring further to FIG. 2, the set of print heads 17 which
are typically positioned from about 0.04 inch to about 0.08 inch
from a substrate 32 as the substrate moves through the system by
the transport belt 18. A carriage motor 48 such as, for example, a
servo motor or any other suitable drive mechanism, of the carriage
16 is connected to a feedback device 50 and a carriage motor
controller 52. The motor controller 52 as well as the feedback
device 50 transmit signals to a controller such as a central CPU
44.
[0025] As mentioned above, the printing system 10 is able to
automatically accommodate changes in the thickness of the
substrate. For example, if the thickness of the substrate increases
or if the substrate is thicker than the previous substrate, as the
substrate moves through the system, the indicator roller 20 which
sits on top of the substrate rises. The increased thickness is
detected in turn by a dial indicator 29 that is attached to the
indicator roller 20. This increased thickness information is
transmitted from the dial indicator 29 to the CPU 44. The CPU 44
then transmits a signal to the controller 52 to instruct the
carriage motor 48 to move carriage 16 and hence the print heads 17
upwards away from the substrate. Meanwhile, the position of the
carriage is relayed to the feedback device 50 and in turn to the
CPU 44 which then determines if further finer adjustments are
needed to position print heads 17 at the proper height. Thus
regardless of the thickness and/or stiffness of the substrate, the
printing system 10 maintains a precise desired gap between the
print heads 17 and the substrate 32. The printing system 10 is able
to automatically accommodate a change in thickness of the substrate
in about five seconds. In sum, the printing system 10 is capable of
handling flexible substrates as well as solid non-flexing
substrates with various thicknesses "on the fly" with minimal or no
intervention from an operator.
[0026] To prevent the substrate from slipping on the transport belt
18, the printing system 10 also includes a vacuum table 22 provided
with a set of holes 21. A vacuum motor 42 supplies the vacuum to
the vacuum table 22, and the vacuum is detected by a vacuum sensor
40. Both the vacuum sensor 40 and the vacuum motor 42 are connected
to and under the direction of the CPU 44 which receives and
transmits the appropriate signals to maintain the desired vacuum.
In the illustrated embodiment, the vacuum provided by the vacuum
table 22 is approximately in the range -0.05 psi to -0.3 psi.
[0027] The transport belt 18 is provided with holes 100 (FIG. 2B)
that extend through the thickness of the belt, each having a
diameter of about 0.1 inch, which are spaced apart from one another
by about one inch. The belt 18 is a woven polyester made from
reinforced polyurethane, and has a thickness of about 0.09 inch.
The woven polyester minimizes stretching of the belt 18 and thus
provides high stepping accuracy and uniform vacuum distribution.
Alternatively, the belt can be made from stainless steel having a
thickness of about 0.008 inch.
[0028] A porous sheet 43 having a thickness of about 0.5 inch sits
between the vacuum table 22 and the transport belt 18. The porous
sheet is made from a sintered, porous polyethylene, or any other
suitable material. The holes in the belt 18, and the porous sheet
43 assure that a suction is applied to a substrate when a vacuum is
provided by the vacuum table 22. In essence, the porous sheet 43
acts as a flow resistor. Thus when the substrate covers only a
portion of belt 18, the vacuum provided by the vacuum table 22 does
not have to be significantly readjusted, if at all, even as the
area over the belt covered by the substrate varies. In sum, with
the porous sheet 43, a continuous vacuum can be provided by the
vacuum table 22, and no further adjustment to the vacuum level
needs to be made as one or more substrates are transmitted through
the printing system during the print process. This feature is
applicable to both continuous substrates, for example, those
supplied from a roll, as well as non-continuous substrates such as
a flexible or a rigid sheet supplied individually.
[0029] Turning now to the drive mechanism of the printing system
10, the transport belt 18 wraps around a drive roller 24 and an
idler roller 26, while an optical encoder wheel 28 and the
thickness indicator roller 20 sits on top the belt 18. The idler
roller 26 is able to move in the x-direction and through a dynamic
tensioning device 29 keeps the belt 18 under a constant tension
during the printing process.
[0030] A drive motor 36 rotates the drive roller 24 which causes
the belt 18 to move in the direction of arrow A, and is connected
along with the encoder wheel 28 to a drive controller 38. The
encoder wheel 28 detects the precise distance that the substrate
moves. This information is relayed to the drive controller 38 and
in turn to the CPU 44. The CPU 44 transmits a signal back to the
controller 38 which controls the speed of the drive motor 36 so
that the distance the substrate moves is precisely controlled. Thus
the feedback position signals from the optical encoder 28
compensates for belt thickness variations, seams in the belt, and
variations in the diameter of the rollers over time.
[0031] In some embodiments, the feed wheel 30 supplies a flexible
substrate 32, which wraps underneath a dancer roller 34, to the
printing system. The feed wheel 30 is rotated by a feed motor 53
which is controlled by a feed controller 54. Both the feed
controller 54 and the dancer 34 are connected to a position sensor
55, and located above and below the dancer 34 is a top limit switch
56a and a bottom limit switch 56b, respectively.
[0032] If during the printing process a jam occurs, the dancer 34
will rise and trigger the top switch 56a to send a signal to the
central CPU 44 which then directs the printing system 10 to
terminate the printing process because a problem has been detected.
And if the feed roll 30 becomes depleted of the substrate material
32 during the printing process, the dancer 34 will drop down and
trigger the bottom switch 56b to transmit a signal to the CPU 44 to
shut the printing process off since there is no longer any
substrate material.
[0033] During the printing process, as the substrate 32 is fed by
the feed wheel 30, the position sensor 55 detects the height of the
dancer 34. This height information is transmitted to the feed
controller 54 which in turn adjusts the power to the feed motor 53
to increase or reduce the feed speed, or to reverse the feed
direction of feed wheel 30 such that a constant tension is
maintained in the substrate. A constant tension is desired to
maintain positional accuracy of the substrate and to remove any
wrinkles in the substrate while it moves through the printing
system.
[0034] The printing system 10 can detect thickness variations of
the substrate regardless of the width of the substrate or the
position of the substrate relative to the width of belt 18. This
capability is illustrated in FIGS. 3A and 3B. As shown, the
thickness indicator roller 20 rotates freely about a bar 21 that is
supported by a pair of ratchet/gear mechanisms 57, each of which
includes a gear 58 engaged with a rachet 59. Thus when a substrate
causes the height of indicator roller 20 to vary, both of the gears
58 rotate so that the indicator roller 20 is at the same height,
"h", along the width, "w.sub.1,", of the belt 18 regardless of the
width, "w.sub.2", of the substrate 32 that is fed to the printer
system. Note that the vertical position, "y", of the dancer 34
(FIG. 2) is also controlled by a similar ratchet/gear mechanism.
Alternatively, a laser triangulation device is used to determine
the thickness of the substrate.
[0035] Referring now to FIGS. 4A and 4B, the rail system 14
includes a top rail 60 and a bottom rail 62. These rails are
attached to a set of spacer support plates 64 by a set of screws 65
along a bottom and a top machined V-groove 66a and 66b,
respectively. These grooves 66 provide a two-point contact with
each of the rails 60 and 62. This two-point contact is maintained
along the entire length of the rails 60 and 62. The set of support
plates 64 is attached to a support beam 67 of the base 12 by a
series of set screws 68. The horizontal displacement, "x", of the
support plates 64 with respect to the support beam 66 is adjusted
by a set of horizontal jack screws 70. Each horizontal jack screw
70 is associated with a bellvile washer 71 that pushes the support
plates 64 away from the support beam 66 to assure that the
horizontal jack screws 70 are always under tension. The vertical
position, "y", of the support plates 64 is adjusted by a set of
vertical jack screws 72. The vertical jack screws 72 are threaded
into a block 74 that is attached to the support beam 67. The
machined V-grooves 66, and the jack screws 70 and 72 enable an
operator to adjust the position of the rails 60 and 62 so that the
rails remain parallel in a plane and parallel to one another to
within a tolerance of about .+-.0.0005 inch which ensures the
precise positioning of the print heads 17 relative to
substrate.
[0036] Also shown in FIGS. 4B and 4C is a pulley 76 and a carriage
belt 78 that is attached to the carriage 16. The pulley 76 and
another similar pulley, one of which is connected to a motor, are
located on either end of the rail system 14. Referring in
particular to FIG. 4C, the carriage 16 is provided with a set of
sleeve bushings 80 to enable the carriage to slide along rails 60
and 62. Accordingly, as the motor drives the pulley, the carriage
16 traverses partially or fully along the length of the rails 60
and 62.
[0037] In use, an operator activates the printer system 10 and
places the substrate 32 onto the belt 18. As mentioned above, the
vacuum sensor 40 detects the vacuum of the vacuum table 22 as
applied to the substrate 32. This information is fed to the CPU 44
which controls the vacuum motor 42 to maintain the desired vacuum.
Because porous sheet 43 acts as a flow resistor, large variations
in the applied vacuum are not required. In fact, little or no
variations in the applied vacuum are required in a typical printing
process.
[0038] The drive motor 36 rotates the drive roller 24 to move the
transport belt 18 and hence the substrate 32 under the print heads
17. Meanwhile, the dynamic tensioning device 29 of the idler roller
26 maintains a constant tension in the belt 18 during the printing
operation. The translational movement of the substrate 32
underneath the print heads 17 is monitored by the encoder wheel 28
to ensure that this movement is precisely controlled.
[0039] As the substrate moves under the carriage 16 and hence the
print heads 17, the carriage 16 traverses back and forth (that is,
in and out of the page when referring to FIG. 2A) along the width
of the substrate as instructed by the CPU 44, while the print heads
17 deposit ink onto the substrate to create the desired image. The
ink can be, for example, solvent pigment inks, UV resistant inks,
or water inks. The through put of printing system 10 ranges from
about 0.5 ft/min to about 10 ft/min.
[0040] As discussed above, changes in the thickness of the
substrate are automatically detected by the system. Thus, if a
thin, flexible substrate is followed by a thicker, non-flexible
substrate, the system automatically without the intervention of the
operator adjusts the height of carriage 16 such that the proper gap
is maintained between the print heads 17 and the substrate.
[0041] While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
* * * * *