Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Patent
1996-06-27
1997-12-02
Le, Hoa Van
Radiation imagery chemistry: process, composition, or product th
Including control feature responsive to a test or measurement
430428, G03C 5026
Patent
active
056934408
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to process verification in photographic processes and is more particularly concerned with the application of multivariate statistical process control methods to these processes.
BACKGROUND OF THE INVENTION
It is well-known to control a process so that it operates within specified boundaries. This can be achieved using statistical process control (SPC) techniques which involve constant monitoring of the process. Such techniques may be univariate wherein a single variable of the process is monitored or multivariate where more than one variable is monitored. Multivariate SPC techniques are particularly well suited to use with complex processes in which a large number of variables are monitored routinely to assess the status of a particular process. Some of the variables may not be independent and the degree to which they are correlated is often unknown, and such processes cannot be assessed adequately with conventional control techniques.
A single parameter known as Hotelling's T.sup.2 (Hotelling, H, (1931), The Generalisation of Student's Ratio, Ann. Math. Statist., 2, pages 360-378) can be used successfully as an indicator in multivariate SPC techniques to determine the current status of the process. The parameter utilises all the information contained in the monitored variables as well as accounting for any correlation between them. The state of a process is determined by the magnitude of T.sup.2, for example, if it exceeds the 95% limit, then the process is behaving in a significantly different way to that of the standard.
The underlying analysis required to deduce the T.sup.2 parameter provides a method of quickly identifying causes of process failure. Corrective action guidelines (CAG) can be developed to facilitate the operation of the system and to provide help for common control failure conditions.
This technique has been applied previously for monitoring a photographic product, namely, black-and-white film as described in JACKSON, J. E. (1991), A User's Guide to Principal Components, pages 123-141, Wiley, N.Y. However, in the example described therein, the optical densities of all fourteen steps representing a series of graduated exposures on a piece of film designed to represent the entire range of practical exposures are measured. The purpose of the analysis, in this case, was to assess the effects of variability on a continuous curve shape, namely, the D-Log E curve.
In another example, concerned with colour film, a similar exposure to that described above is used to monitor the film over the normal picture taking range, but unlike the previous example, densities for only a few exposure levels were used for control purposes. In the particular example therein, only three levels were used in each colour record. One of these steps was in the high density region of the curve, another in the low density region, and a third in the middle section of the curve.
The physical interpretation of the principal components allows a process to be monitored based largely on control charts of the principal components. It is the principal component control chart which is considered an improved way of monitoring process variability in this particular example. In particular, the use of generalised T.sup.2 statistics and the breakdown of T.sub.o.sup.2, the overall variability of a subgroup about an aim or grand mean, into T.sub.D.sup.2, a measure of the variability of the subgroup about its mean, and T.sub.m.sup.2, a measure of the distance of the subgroup mean from the target, as an indicator for individual observation and process variability, respectively, being out-of-control.
PROBLEM TO BE SOLVED BY THE INVENTION
Process control is commonly achieved by using the D-Log E curve and either assigning band limits into which the curve can fall or applying limits for each parameter in the process using univariate methods. This allows large changes in the D-Log E curve which produces unacceptable results, for example, high speed and low contrast. This produces a
REFERENCES:
patent: 5479340 (1995-12-01), Fox et al.
Photogrammetric Engineering and Remote Sensing, Nasu et al. vol.42, No. 6, 06/76, pp.777-788.
A User's Guide To Principal Component, J.E. Jackson, 1991, John Wiley & Son, N.Y. pp. 51-58 and 123-141.
Barbur Vicki Ann
Green Andrew
Eastman Kodak Company
Le Hoa Van
Noval William F.
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