Method of and apparatus for drying running webs of photographic material

A moist web of exposed and developed photographic film or photographic paper is continuously advanced through a drying unit wherein selected areas of the path for the web are monitored by devices which generate signals denoting the heat absorptivity of monitored portions of the web. Such signals are processed and utilized to regulate the intensity of heat which is emitted by batteries of heating elements at both sides of the path for the running web. This ensures that the less developed portions of the web are subjected to sufficient heating action and that the more developed portions of the web are not overheated. The monitoring can involve ascertaining the intensity of heat which has penetrated through successive portions of the running web and/or ascertaining the intensity of heat which is reflected by successive portions of the running web and issues from heating elements designed to emit heat of known intensity.

BACKGROUND OF THE INVENTION 
The invention relates to the treatment of running webs of photographic 
material, such as exposed and developed photographic films or exposed and 
developed strips or sheets of photographic paper. More particularly, the 
invention relates to improvements in methods of and in apparatus for 
drying moist or wet webs which contain photographic material. As used 
herein, the term "web" or "webs" is intended to embrace elongated strips 
as well as discrete sheets of photographic material. 
Commonly owned U.S. Pat. No. 4,485,565 granted Dec. 4, 1984 to Franz Ertl 
et al. discloses an apparatus for drying running strips or sheets of 
photographic material. In accordance with a feature of the patented 
invention, the intensity of heat which is radiated by a plurality of 
heating elements against a running strip or sheet can be varied depending 
upon the characteristics of the material to be dried. The intensity of 
radiated heat is selected in advance and remains unchanged in the course 
of the drying operation. A drawback of such proposal is that the patented 
apparatus is not ideally suited for the drying of webs of photographic 
material wherein randomly distributed portions exhibit widely different 
heat absorptivities due to pronounced differences of opacity. Thus, if a 
running web includes randomly distributed portions having widely different 
heat transmissivities, any advance adjustment of the intensity of heat 
which is directed against and is supposed to reduce the moisture content 
of a running web is highly unlikely to ensure a desirable uniform drying 
of the web. The reason is that the less exposed portion of an exposed and 
developed web is lighter and thus absorbs less heat than a darker portion, 
i.e., a portion which was exposed to a larger amount of light and is more 
opaque than the less exposed portion. If a fixed intensity of heat is 
selected in advance of transport of a web through the drying station, the 
less exposed portions of the web are likely to be adequately dried and/or 
the more exposed portions are likely to be damaged as a result of 
overheating. 
The situation is analogous with certain other types of webs (sheets or 
strips) of photographic material which are to be dried by exposure to 
radiated heat. 
OBJECTS OF THE INVENTION 
An object of the invention is to provide a method which renders it possible 
to reduce the moisture content of running webs of photographic material 
regardless of random distribution of more and less exposed portions in the 
running web. 
Another object of the invention is to provide a method which renders it 
possible to subject a freshly developed web of photographic material to an 
accurately predictable drying action. 
A further object of the invention is to provide a method which renders it 
possible to avoid insufficient drying of less exposed portions and/or 
overheating of more exposed portions of a running moist or wet web of 
photographic material. 
An additional object of the invention is to provide a simple and 
inexpensive method which ensures automatic adjustment of the drying action 
and does not require any advance adjustments of the intensity of heat 
which is to be directed against a running web of photographic material. 
Still another object of the invention is to provide a novel and improved 
apparatus for the practice of the above outlined method. 
A further object of the invention is to provide an apparatus which can 
automatically regulate the intensity of heat that is used to reduce the 
moisture content of a running web of photographic material. 
Another object of the invention is to provide an apparatus which can 
uniformly dry a running web of photographic material regardless of the 
exact distribution of more and less exposed portions in the running web. 
An additional object of the invention is to provide the apparatus with 
novel and improved means for adjusting the intensity of heat which is 
being directed against a running web of photographic material. 
Still another object of the invention is to provide an apparatus which can 
be installed in existing developing machines for webs of photographic 
material. 
SUMMARY OF THE INVENTION 
One feature of the present invention resides in the provision of a method 
drying a moist or wet web which contains photographic material and 
comprises randomly distributed portions having different heat 
absorptivities. The improved method comprises the steps of advancing the 
web in a predetermined direction along a predetermined path, directing 
heat of variable intensity against the advancing web in at least one 
predetermined section of the path whereby the randomly distributed 
portions having different heat absorptivities absorb different quantities 
of heat, monitoring the absorptivity of the randomly distributed portions 
in the at least one section of the path and generating signals which 
denote the monitored absorptivities, and utilizing the signals to vary the 
intensity of directed heat. 
The monitoring step can include ascertaining the amounts of heat which 
penetrate through the randomly distributed portions of the advancing web 
and/or ascertaining the amounts of heat which is reflected by the randomly 
distributed portions of the advancing web. 
The method can further comprise the steps of monitoring the intensity of 
heat prior to impingement upon the advancing web in the at least one 
section of the path and generating second signals which denote the 
monitored intensity, and comparing the second signals with signals 
denoting the monitored absorptivity. The utilizing step of such method 
preferably comprises varying the intensity of directed heat as a function 
of differences between the compared signals. 
The heat directing step can include directing heat against both sides of 
the advancing web in the at least one section of the path. 
The advancing step can include transporting the web along the at least one 
section of the path in a predetermined plane, and the heat directing step 
of such method can include directing heat of variable intensity against at 
least one side of the advancing web at least substantially at right angles 
to the predetermined plane. The heat directing step of such method can 
comprise directing heat from a plurality of sources forming at least one 
row disposed at the at least one side of the predetermined plane and being 
at least substantially equidistant from the plane. The row preferably 
extends transversely of the predetermined direction. 
Another feature of the present invention resides in the provision of an 
apparatus for drying a moist (wet) web which contains photographic 
material and comprises randomly distributed portions having different heat 
absorptivities and is advanced in a predetermined direction along a 
predetermined path. The improved apparatus comprises adjustable means for 
directing heat of variable intensity against the advancing web in at least 
one predetermined section of the path whereby the randomly distributed 
portions of the web absorb different quantities of heat, means for 
monitoring the absorptivity of the randomly distributed portions of the 
advancing web in the at least one section of the path including means for 
generating signals which denote the monitored absorptivity, and means for 
adjusting the directing means as a function of variations of the signals. 
The heat directing means can comprise at least one array of adjustable 
heating elements extending transversely of the predetermined direction at 
least at one side of the predetermined path. 
The monitoring means can include means for monitoring the transmissivity of 
heat by the randomly distributed portions of the advancing web. 
The apparatus can further comprise means for limiting the range of the 
monitoring means. Such limiting means can comprise means for confining the 
monitoring means to monitoring of a predetermined part of the web in the 
at least one section of the path. 
The apparatus can further comprise means for directly monitoring the 
intensity of heat prior to impingement of directed heat upon the web in 
the at least one section of the path including means for generating second 
signals which denote the monitored intensity of heat. The adjusting means 
of such apparatus preferably includes means for adjusting the directing 
means as a function of the second signals. 
The heat directing means can include a battery of adjustable heating 
elements at each side of the web in the at least one section of the path. 
If the heat directing means includes a plurality of adjustable heating 
elements, the means for monitoring the absorptivity of randomly 
distributed portions of the running web can include a discrete monitoring 
device (e.g., a photodiode) for each adjustable heating element. 
Analogously, the means for directly monitoring the intensity of heat 
directed by the heating elements can also comprise a discrete intensity 
monitoring device for each adjustable heating element. 
The novel features which are considered as characteristic of the invention 
are set forth in particular in the appended claims. The improved apparatus 
itself, however, both as to its construction and its mode of operation, 
together with additional features and advantages thereof, will be best 
understood upon perusal of the following detailed description of certain 
presently preferred specific embodiments with reference to the 
accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 illustrates an exposed and developed web 1 of photographic material 
(e.g., a customer film) which is advanced in the direction of arrow T in a 
vertical plane by customary advancing rolls (not shown) of the type 
employed in developing machines of photographic laboratories. Reference 
may be had to the commonly owned U.S. Pat. No. 4,485,565 to Ertl et al. 
The illustrated part of the film 1 is in the process of advancing through 
a drying apparatus or unit D which is the last unit in a standard 
developing machine and wherein the film is relieved of excess moisture, 
such as a rinsing liquid through which the film 1 was caused to advance 
subsequent to advancement through a developing bath and thereupon through 
a fixing bath. 
The drying unit D comprises two arrays of heating elements 2, one at each 
side of the vertical plane for the advancing web 1. Each array is in the 
form of a row which extends transversely of the direction indicated by the 
arrow T and wherein the heating elements 2 may but need not be equidistant 
from each other. The heating elements 2 of each array can be and 
preferably are disposed at the same distance from the respective side of 
the advancing web 1. The drying unit D further comprises two 
concavo-convex mirrors 3, one at each side of the web 1, which serve to 
direct heat issuing from the respective array of heating elements 2 
against the corresponding side of the web. 
Each mirror 3 is provided with a window 4 for each of the respective array 
of heating elements 2. For the sake of simplicity, the drawing merely 
shows two windows 4 for two monitoring devices 5 having signals 
transmitting outputs connected to the corresponding inputs of a control 
circuit 8. Each monitoring device 5 monitors a selected part of the path 
for the advancing web 1; in the illustrated embodiment, the windows 4 are 
designed in such a way that each device 5 monitors a rectangular part of 
the path for the web 1. The purpose of each monitoring device 5 is to 
generate and transmit a signal denoting the intensity of heat which issues 
from a heating element 2 at the other side of the path of the web 1, i.e., 
to ascertain the intensity of heat which has penetrated through the web 1 
and thereupon through the respective window 4 in the mirror 3 at the 
left-hand side of the vertical plane of the illustrated portion of the 
web. The windows 4 limit the range of the corresponding monitoring devices 
5. 
A second monitoring device 7 (called reference sensor) is disposed at the 
right-hand side of the path for the web 1, i.e., at the side opposite that 
which confronts the illustrated monitoring devices 5. The purpose of the 
monitoring device or reference sensor 7 is to transmit to the 
corresponding input of the control circuit 8 second signals which denote 
the intensity of heat issuing from one or more heating elements 2 at the 
right-hand side of the path for the web 1 prior to impingement of such 
heat upon the advancing web. 
The control circuit 8 evaluates and processes the signals from the 
monitoring devices 5, 7 and adjusts the intensity of heat issuing from one 
or both arrays of heating elements 2 in dependency upon variations of 
characteristics (such as intensities) of the evaluated signals. Evaluation 
of signals from the monitoring devices 5 and 7 enables the control circuit 
8 to ascertain the transmissivity of those portions of the advancing web 1 
which are then in register with the areas 6 monitored by the devices 5. An 
advantage of employing two or more monitoring devices 5, each of which 
monitors a different zone 6 of the path for the film 1, is that the 
control circuit 8 can ascertain an average transmissivity of the monitored 
film, namely the average transmissivity of that length of the advancing 
web 1 which happens to be located in the drying unit D. The transmissivity 
is indicative of the extent to which various randomly distributed portions 
of the advancing web or film 1 can absorb heat. If the absorptivity is 
pronounced, the transmissivity is low and vice versa. Signals from the 
control circuit 8 are used, in a manner well known per se, to 
automatically adjust the intensity of heat issuing from the heating 
elements 2 in the one and/or the other array. 
As the web 1 advances in the direction of arrow T, successive portions of 
such web move into register with the areas 6 and are monitored by the 
devices 5 which transmit corresponding signals to the control circuit 8. 
This ensures that the intensity of heat issuing from the heating elements 
2 is varied (when necessary) at the rate at which the heat transmissivity 
of successive web portions moving into register with the areas 6 changes. 
It has been found that the improved apparatus can react (when necessary) 
to randomly distributed changes of heat transmissivity of successively 
monitored portions of the advancing web 1 so that the drying action of the 
unit D is much more satisfactory than that of conventional drying units. 
Thus, the less developed portions of the web are adequately dried and the 
more developed portions of the film are not damaged as a result of 
overheating. 
In accordance with a modification, the monitoring devices 5 can be designed 
to constitute means for generating signals denoting the intensity of heat 
which is reflected by heating elements 2 at the same side of the advancing 
web 1. The ability of the web to absorb heat can be ascertained on the 
basis of monitored heat reflectivity. Thus, all that is necessary is to 
employ heating elements 2 which are designed to emit heat of known 
intensity and to ascertain the intensity of heat which is reflected by 
such heating elements. This enables the monitoring devices and/or the 
control circuit 8 to continuously transmit signals denoting the heat 
absorptivity of momentarily monitored portions of the advancing web and to 
adjust the heating elements 2 accordingly. 
An important advantage of the improved method and apparatus is their 
simplicity. Thus, all that is necessary is to continuously monitor the 
heat absorptivity of the running web of photographic material and to 
regulate the intensity of heat which is being directed against the web in 
dependency on changes of intensity and/or other characteristics of signals 
which are generated to denote the ascertained absorptivity. Such 
regulation of heating action ensures that the advancing web is subjected 
to an optimal drying action regardless of the random distribution of more 
and less exposed web portions. Consequently, less exposed portions are 
subjected to more intensive drying than in heretofore known drying units 
wherein the intensity of heat is selected in advance and remains unchanged 
in the course of drying, and the more exposed portions are not overheated 
and hence not damaged on their way through the drying unit, e.g., on their 
way into a copying unit wherein successive or selected frames of an 
exposed, developed and dried customer film are imaged onto photographic 
paper. 
FIG. 2 illustrates a portion of one presently preferred control circuit 8 
which serves as a means for adjusting the heating elements 2 in response 
to variations of intensities and/or other characteristics of signals from 
the monitoring devices 5 and/or 7. This control circuit evaluates the 
first signals (from 5) denoting the intensity of radiation passing through 
those portions of the web 1 which are located in the path section between 
the mirrors 3 and adjusts the heating action of the elements 2 
accordingly. It is presently preferred to provide a discrete monitoring 
device 5 and a discrete monitoring device 7 for each heating element 2, or 
at least for each heating element 2 at one side of the path for the web 1. 
The monitoring device 5 which is shown in FIG. 2 comprises a photodiode 
which transmits photocurrent or photovoltage through a conduit 5a to the 
corresponding input of an integrator 9 wherein the signals are integrated 
with a suitable time constant and transmitted to the memory of a computer 
(CPU) 11 through an analog-digital converter 10. The other monitoring 
device 7 (reference sensor) of FIG. 2 transmits second signals through a 
conductor 7a to the corresponding input of the integrator 9 where the 
signals are integrated with the same time constant as that selected in 
connection with integration of signals from the monitoring device 5. The 
integrated second signals are also stored in the memory of the computer 11 
which receives such signals through the analog-digital converter 10. The 
computer 11 ascertains the quotient of the integrated first and second 
signals, and such quotient is indicative of average density or opacity of 
monitored portions of the running web 1. The quotient is used to 
ascertain, in a comparison table or chart (LUT) 12, a required or optimum 
value of heating action of the corresponding heating element 2. A signal 
denoting the thus ascertained optimum value is transmitted from the output 
of the computer 11 to a control panel 14 which, in turn, transmits 
appropriate signals via conductor 2a to the respective heating element 2 
so that the latter is adjusted accordingly. 
The character 13 denotes in FIG. 2 a computer input which is connected with 
the output of a further system 113, for example, the developing machine 
which treats successive webs 2 prior to entry of such webs into the drying 
unit D. 
The drying unit D can employ heating elements 2 of many kinds. Presently 
preferred adjustable heating elements 2 are infrared heaters of the type 
also known as heating rods. Suitable heating rods are shown and described 
in the aforementioned commonly owned U.S. Pat. No. 4,465,565 to Ertl et 
al. to which reference may be had if necessary. 
The monitoring devices 5 and 7 in a drying unit which employs heating 
elements in the form of adjustable infrared heaters can constitute 
commercially available infrared radiation detectors which are capable of 
measuring the intensity of heat radiated by the heating elements 2. 
Suitable monitoring devices are photodiodes known as Type LD 274 
distributed by Siemens. Such photodiodes are highly sensitive to infrared 
radiation. However, it is also possible to employ other types of 
monitoring devices, depending for example upon the absorptivity of webs to 
be dried. For example, the aforediscussed photodiodes can be replaced with 
wide-band diodes, e.g., silicon diodes. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic and specific aspects of our contribution to 
the art and, therefore, such adaptations should and are intended to be 
comprehended within the meaning and range of equivalence of the appended 
claims.