Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1989-10-23
1991-12-24
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250239, 354298, G01N 2186
Patent
active
050755633
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to densitometry. It relates in particular to measuring optical densities of, for example, photographic materials.
In photographic processing apparatus, such as used for X-ray materials, it is necessary to monitor the activity of processing solutions and if necessary replenish such solutions. A well-known technique for performing such a monitoring operation is to produce a process control strip of photographic material on which a series of graduated exposures have been produced, known as step wedges. The densities of such wedges are the measured in a densitometer so as to provide an indication of the state of the processing solutions in which the strip has been processed, and hence an indication of the need for replenishment.
U.S. Pat. No. 3,623,418 shows a densitometer having a measuring light source and photocell accommodated in different housing portions between which a strip is moved from a supply spool to a take-up spool.
The arrangement shown in U.S. Pat. No. 3,623,418 requires that the strip be of sufficient length to enable the use of the spools. If, however, the strip were very short, for example about 15 cm long, it would not be possible to use such an arrangement.
Other densiometers are shown in U.S. Pat. Nos. 4,057,818, 4,293,226; and 4,370,558.
In accordance with the present invention there is provided a densitometer head comprising a base plate on which are mounted two housing portions, a wall section of one housing portion being spaced from a wall section of the other housing portion so as to form a gap therebetween and the base plate forming a bottom of said gap, there being provided in one of said housing portions a light source and in said one or the other of said housing portions light-sensitive means which cooperates with the light source in the measurement of optical properties of strip of material passed through said gap, said gap being effective to locate said strip for such measurement, and resilient means in said gap for positioning such a strip of material whilst it passes therethrough.
THE DRAWINGS
The present invention will now be described, by way of example, with reference to the single FIGURE of the accompanying drawing which is a perspective view of a densitometer head of the present invention, with a strip of material to be measured being indicated by broken lines.
DETAILED DESCRIPTION OF THE INVENTION
The following description is directed in particular to photographic material. It is emphasised, however, that the apparatus and method are also applicable to other suitable materials.
A densitometer head 2 is provided with a base plate 4 on which are mounted housing portions 6 and 8. The housing portions 6 and 8 are spaced from each other to form a gap 10 which has a tapered entry portion 12 at one end of the head 2. In housing portion 6 is provided a light source, such as one or more LED's (light-emitting diodes) or one or more incandescent lamps, which is shown in a representative manner by the numeral 14. In housing portion 8 is provided a light-sensitive device, such as one or more photodiodes, which is shown in a representative manner by the numeral 16. The light source 14 and light-sensitive device 16 are optically aligned with one another.
The light-sensitive device 16 is preferably resiliently urged by one or more springs (not shown) towards the light source 14. If desired, the light source 14 could be similarly resiliently urged. This has the effect of resiliently positioning a strip of material passing through the gap 10.
OPERATION
As an alternative to the light-sensitive device 16 and light source 14 being resiliently urged, they can be in fixed positions and plush provided along one or both opposing edges of the gap 10, so as to provide for resiliently positioning a strip of material passing through the gap 10.
In operation of the device a strip 18 of film to be measured is moved through the gap 10 in the direction of arrow A with its lower (as viewed in the FIGURE) longitudinal edge abutted against the upper (as viewed in the
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Allen S.
Childess G. Herman
Eastman Kodak Company
Nelms David C.
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