Information
-
Patent Grant
-
6455810
-
Patent Number
6,455,810
-
Date Filed
Friday, May 4, 200123 years ago
-
Date Issued
Tuesday, September 24, 200222 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 219 216
- 219 469
- 432 60
- 432 228
- 399 279
- 399 286
- 430 353
- 430 354
-
International Classifications
- G03D1300
- G03G1510
- G03L1500
-
Abstract
Apparatus for processing heat processable media comprising: a rotatable heated drum for processing heat processable media having width and depth dimensions, and a plurality of rollers spaced around a portion of the periphery of said drum and in contact therewith, said rollers holding said media to said drum; wherein at least one of said drum and/or at least some of said plurality of rollers have a channel in a central region thereof, said channel having a width greater than said width dimension of said media and a depth less than said thickness dimension of said media.
Description
FIELD OF THE INVENTION
This invention relates in general to heat processable media imaging systems and more particularly to such systems that have reduced maintenance costs and more reliable image quality performance.
BACKGROUND OF THE INVENTION
One way of heat processing photothermographic media in a processor is to bring it in contact with a heated drum. To maintain good media contract with the drum a plurality of hold-down-rollers can be used to hold the media against the drum. During processing, some of the silver behenate in the media emulsion is converted to silver behenic acid. Some of the behenic acids and other byproducts of the processing reactions can leach through the media emulsion overcoat. These escaped chemicals are referred to as FAZ. At processing temperatures, the escaping FAZ is liquid. The FAZ ends up coating the drum surface where the media makes contact. After the media leaves the drum, the FAZ liquid left behind goes through changes. If the media hold-down-rollers contact the drum surface after the media has passed, some FAZ transfers to the contacting roller surfaces. Retained coating solvents and other light molecules in the FAZ quickly evaporated off the FAZ liquid surface. The remaining less volatile molecules can continue to slowly react with one another, with gasses diffusing in from the liquid/air surface and with the solid surfaces on which the FAZ clings. In some cases, FAZ reactions can form solid particles which can either remain in suspension in the FAZ liquid or deposit on the drum or rollers. FAZ, which is not attached to the surfaces as a solid deposit, is subsequently diluted by FAZ leaching from the next sheet of media processed. Some of this FAZ mixture leaves the drum as a surface deposit on the media overcoat. Ideally, the system would reach a steady state condition in which the quantity FAZ leaching out of the media equals the evaporation quantity plus the quantity exiting the processor on the surface of the sheet of media. This is often not the case and eventually some solid deposits form on the drum and/or roller surfaces.
In processors where media hold-down-rollers contact the FAZ coated part of the processing drum, the solid surface area with which FAZ interacts approximately triples. Consequently, the FAZ surface exposed to air also. Roller/drum contact also introduces mechanical working of the FAZ surface deposits. The contacting roller nips also serve to repeatedly force dust and other dirt particles brought into the processor on the media to be repeatedly pressed against the drum and roller surfaces, increasing their chance of sticking to one or the other and becoming nucleation sites for FAZ deposits. Small but frequent thermal cycling of FAZ is introduced as the FAZ on the heated drum and cooling rollers pass through their contact nips where heat is exchanged. FAZ on the rollers also sees much larger cooling cycles as media comes through, cooling the rollers significantly. All of these factors can serve to drive chemical reactions which might be absent in an undisturbed FAZ drum coating.
Although stepped drums or rollers have been used in reproduction systems (see: U.S. Pat. No. 5,465,146, issued Nov. 7, 1995, inventors Higashi et al.—Stepped Roller in a Fuser; U.S. Pat. No. 5,583,556, issued Dec. 10, 1996, inventor Kim—Stepped Drum in a Thermal Transfer Type Printer; U.S. Pat. No. 6,042,228, issued Mar. 28, 2000, inventors Yamada et al.—Stepped Rollers for Feeding Roll Sheets in an Image Forming Apparatus), none are suitable for solving any of these problems.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a solution to these problems. The frequency and time required for preventive maintenance of a photothermographic processor can be significantly reduced by the use of stepped rollers or of a stepped drum design. In such a system the rollers and drum surface are gapped and do not touch each other in the central zone where they make media contact during media transport. This prevents the media hold-down-rollers from touching the processing residue coating (FAZ) on the drum. In either of these designs, an undercut that is about ⅝ the thickness of the media to be transported is used either on the drum or on the rollers in the media contact area. During standby, while film is not being processed the drum and rollers are gapped and only make rolling contact on either side of the film path. As film is transported through such a processor, it lifts the rollers by about ⅜ the media thickness, providing the full clamping force of the rollers against the film to ensure contact of the media against the hot processing drum.
According to a feature of the present invention, there is provided an apparatus for processing heat processable media comprising: a rotatable heated drum for processing heat processable media, having width and depth dimensions; and a plurality of rollers spaced around a portion of the periphery of said drum and in contact therewith, said rollers holding said media to said drum; wherein at least one of said drum or at least some of said plurality of rollers have a channel in a central region thereof, said channel having a width greater than said width dimension of said media and a depth less than said thickness dimension of said media.
ADVANTAGEOUS EFFECT OF THE INVENTION
The invention has the following advantages.
1. Reduced maintenance time and costs.
2. More reliable image quality performance.
3. Increased life of system components.
4. Reduced need for strong chemical cleaners
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1-4
are diagrammatic views of one embodiment of the present invention.
FIGS. 5-8
are diagrammatic views of another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to
FIGS. 1-4
, there will be described one embodiment of the present invention. As shown in
FIGS. 1 and 2
, a processor
10
for processing heat processable media
12
(such as photothermographic sheets exposed to medical images) includes a heated drum
14
which rotates about axis
15
in direction
16
. Drum
14
preferably has an outer elastomeric layer for improved processing. A plurality of rollers
18
are spaced around a portion of the periphery of drum
14
to hold media
12
in contact with drum
14
. Rollers
18
are biased into contact with drum
14
by springs
20
bearing on axles
21
of roller
18
. According to the present invention roller
18
is stepped and includes annular channel
22
in the central region thereof and annular shoulders
24
,
26
on either end of channel
22
.
Channel
22
has a width which is greater than the width of the widest media processed by processor
10
. Channel
22
has a depth d which is less than the thickness of processed media (see: FIGS.
3
and
4
). Preferably, d equals ⅝ t.
The shaded region
28
(
FIG. 1
) is the media contact area.
In Operation, when media is not present, rollers
18
ride on drum
14
by means of shoulders
24
,
26
of roller
18
contacting drum
14
outside of the media contact area
28
of drum
14
. When media
12
is processed by drum
14
, the media
12
lifts roller shoulders
24
,
26
off of drum
14
until media
12
passes by the lifted roller.
It was found that the stepped roller configuration increased the number of media that can be processed before preventative maintenance was required by a substantial factor, thus substantially reducing the probability of drum damage by a like factor. FAZ and image artifacts were substantially reduced.
Referring now to
FIGS. 5-8
, there will be described another embodiment of the present invention. As shown, processor
100
for processing heat processable media
112
, includes a heated drum
114
rotatable about axis
115
in direction
116
. A plurality of rollers
118
are disposed about a portion of the periphery of drum
114
and are biased into contact with drum
114
by springs
120
bearing on axles
121
of roller
118
. Rollers
118
hold media
112
against heated drum
114
to effect heat processing of exposed media
112
.
According to the present invention, drum
114
has an annular channel
122
in the central region thereof with outer shoulders
124
,
126
of greater diameter than annular channel
122
. Channel
122
has a width that is greater than the widest media
112
processed by processor
100
and a depth d which is less than the thickness of media
112
. Preferably d=⅝ t. For example, for media thickness of 8 mils., the depth of channel
122
is preferably 5 mils. The depth should be great enough to compensate for any bowing of rollers
118
at the center thereof. As shown in
FIG. 7
, drum has an elastomeric coating
130
from which channel
122
is ground. If coating
130
has a thickness of 30 mils. at shoulder
124
, its thickness at channel
122
can be 25 mils.
The shaded area
132
is the media contact area.
In operation, when media
112
is not present (
FIG. 8
) roller
118
rides on shoulders
124
,
126
of drum
114
. When media
112
is processed by heated drum
114
, media
112
left rollers
188
off of drum
114
until media
112
passes by the lifted roller.
It was found that the stepped drum configuration increased the number of media that can be processed before preventative maintenance was required by a substantial factor, thus substantially reducing the probability of drum damage by a like factor. FAZ and image artifacts were substantially reduced.
It will be appreciated that it is within the scope of the present invention to combining a stepped drum with stepped rollers to accomplish the same advantages resulting form the use of one or the other alone. In such case, the combined depth of the drum and roller channels should be less than the thickness of the processed media.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
PARTS LIST
10
processor
12
media
14
heated drum
15
axis
16
direction
18
rollers
22
annular channel
24
,
26
annular shoulders
28
region
100
processor
112
media
114
heated drum
116
direction
118
rollers
120
springs
121
axles
122
annular channel
124
,
126
outer shoulders
130
elastomeric coating
132
shaded area
Claims
- 1. Apparatus for processing heat processable media comprising:a rotatable heated drum for processing heat processable media having width and depth dimensions; and a plurality of rollers spaced around a portion of the periphery of said drum and in contact therewith, said rollers holding said media to said drum; wherein at least one of said drum and/or at least some of said plurality of rollers have a channel in a central region thereof, said channel having a width greater than said width dimension of said media and a depth less than said thickness dimension of said media.
- 2. The apparatus of claim 1 wherein said drum has an annular channel in said central region thereof.
- 3. The apparatus of claim 1 wherein said at least some of said plurality of rollers have annular channels in said central regions thereof.
- 4. The apparatus of claim 1 wherein said channel has a depth sufficient to avoid contact between said rollers and said drum in said central region but to bowing of said rollers.
- 5. The apparatus of claim 1 wherein said drum and at least some of said plurality of rollers have complimentary annular channels in the central regions thereof.
US Referenced Citations (6)