ELECTROPHOTOGRAPHY hester f. carlson Patented October 6, 1942 #2,297,691 A from Chester carl- sons patent application a feature of the present materials for photographic purposes. In its prefe form the invention involves the use of materials which are insulators in the dark but become partial conductors when illuminated. These materials 227 respond to light, being slightly conduc- again becoming insulating when the n be called pho- toconductive insulating materials Working in the patent departm at the P.R. Mallory Company in the 1930s, Carlson became frustrated try- 型和 ing to obtain copies of patent drawings nd specifications. Unlike others attempting chemical photographic methods, he used the principles of electrostatics to produce his first dry copy in 1938. A photoconductive plate connected to an electric charge wa exposed to the desired image. The plate retained the electric charge on the dark areas of the image and lost it on the white areas. Dusting the plate with a powder reproduced the image. Xerox Corporation negotiated rights to the process in 1947 and introduced its first office copier in 1968.( Copyright 1995, Dew Ray Products, Inc. Used with permission. The constitutive matrix C may be functions of space-time coordinates, thermodynamical and continuum- mechanical variables, or electromagnetic field strengths. According to the functional dependence of C, we can lassify the various media as(1)inhomogeneous if C is a function of space coordinates, (2)nonstationary if C is a function of time, (3)time-dispersive if Cis a function of time derivatives, (4)spatial-dispersive if C is a function of spatial derivatives, (5) nonlinear if C is a function of the electromagnetic field, and so forth. In he general case C may be a function of integral-differential operators and coupled to fundamental equations of other physical disciplines c 2000 by CRC Press LLC© 2000 by CRC Press LLC The constitutive matrix may be functions of space–time coordinates, thermodynamical and continuum￾mechanical variables, or electromagnetic field strengths. According to the functional dependence of , we can classify the various media as (1) inhomogeneous if is a function of space coordinates, (2) nonstationary if is a function of time, (3) time-dispersive if is a function of time derivatives, (4) spatial-dispersive if is a function of spatial derivatives, (5) nonlinear if is a function of the electromagnetic field, and so forth. In the general case may be a function of integral-differential operators and coupled to fundamental equations of other physical disciplines. C C C C C C C C ELECTROPHOTOGRAPHY Chester F. Carlson Patented October 6, 1942 #2,297,691 n excerpt from Chester Carl￾son’s patent application: A feature of the present invention resides in the use of photoelec￾tric or photoconductive materials for photographic purposes. In its preferred form the invention involves the use of materials which are insulators in the dark but become partial conductors when illuminated. These materials respond to light, being slightly conduc￾tive whenever they are illuminated and again becoming insulating when the light is cut off. They can be called pho￾toconductive insulating materials. Working in the patent department at the P.R. Mallory Company in the 1930s, Carlson became frustrated try￾ing to obtain copies of patent drawings and specifications. Unlike others attempting chemical photographic methods, he used the principles of electrostatics to produce his first dry copy in 1938. A photoconductive plate connected to an electric charge was exposed to the desired image. The plate retained the electric charge on the dark areas of the image and lost it on the white areas. Dusting the plate with a powder reproduced the image. Xerox Corporation negotiated rights to the process in 1947 and introduced its first office copier in 1968. (Copyright 1995, DewRay Products, Inc. Used with permission.) A