Apparatus for selectively sealing a discrete dielectric sheet developer station

In an electrographic copier wherein discrete dielectric sheets are moved seriatim about a travel path having a portion in juxtaposition with a developer station for developing imagewise electrostatic charge patterns on such sheets with developer material, apparatus for selectively sealing developer material within such station and, during such sealing, guiding a moving sheet along such travel path portion out of developing relation with such developer material. The apparatus comprises a member selectively movable to a first position sealing developer material within the developer station and forming a sheet guide coincident with the sheet travel path portion, or a second position remote from such first position. In response to the lead edge of a discrete dielectric sheet moving away from the travel path portion, the member is moved to its second position leaving the sheet in developing relation to developer material in the developer station; and in response to the trail edge of such sheet moving into the travel path portion, the member is moved to its first position to seal developer material within such station and to guide such sheet along such travel path portion out of developing relation to developer material.

BACKGROUND OF THE INVENTION 
This invention relates generally to apparatus associated with a station for 
developing electrostatic charge patterns on discrete dielectric sheets 
with developer material and, more particularly, to apparatus for 
selectively sealing developer material within a developer station and, 
during sealing, guiding moving discrete dielectric sheet out of developing 
relation with such developer material. 
In U.S. Pat. No. 4,436,405 issued Mar. 13, 1984 in the name of Kindt, an 
electrographic copier is described which utilizes a plurality of discrete 
dielectric sheets respectively including a photoconductive layer. The 
discrete sheets are transported seriatim about a continuous path into 
operative relation with electrographic process stations to make 
information reproductions. In the reproduction process carried out at such 
process stations of the copier, a discrete dielectric sheet is uniformly 
charged and then exposed to an image of information to be reproduced 
(e.g., a document) to form an electrostatic charge pattern on such sheet 
corresponding image-wise to such information. The charge pattern is 
developed with pigmented thermoplastic electroscopic marking particles 
electrostatically attracted to the charge pattern to form a transferable 
image. The transferable image is then transferred from the sheet to a 
receiver member to form the information reproduction, and the sheet is 
cleaned for reuse. 
The development of the charge patterns on the discrete dielectric sheets is 
accomplished by a magnetic brush developer station. In a typical magnetic 
brush developer station, developer material including pigmented 
electroscopic marking particles adhering to magnetizable particles (or 
single component material where the pigmented particles are in themselves 
magnetizable) are brought into a magnetic field intercepting the path of a 
moving electrostatic charge pattern carrying member. The magnetizable 
particles align in the magnetic field to form a brush-like bristle nap of 
pigmented particles which contact such member. The pigmented particles are 
electrostatically attracted from the nap to the charge pattern and adhere 
to such pattern for development. However, when the charge pattern carrying 
member is a discrete sheet, there is a propensity for the leading edge of 
such sheet to plow through the bristle nap. This can lead to deposition of 
developer material on the back side of the sheet. Therefore, cleaning of 
the sheet is made more complex (i.e., the back side as well as the front 
side must also be cleaned). Moreover, contamination within the copier 
environment by airborne developer material, or non-transferred developer 
material carried out of the magnetic brush developer station by the sheet, 
is potentially increased. 
In the commonly assigned copending U.S. patent application Ser. No. 
633,564, filed July 23, 1984, in the name of Crandall, a mechanism is 
disclosed which prevents a moving discrete dielectric sheet from plowing 
through a bristle nap of a magnetic brush developer station. Such 
mechanism includes a movable belt in contact with the developer station 
and overlying the bristle nap to seal developer material of such nap 
within the developer station. The belt has an opening substantially 
congruent with the image (charge pattern bearing) area of a discrete 
dielectric sheet. The belt and sheet are moved in timed relation so that 
the image area of the sheet overlies the belt opening as a sheet is moved 
into developing relation with the nap. Thus, the marginal edges of the 
sheet are shielded by the belt and the image area is located so as to be 
developed by material from the nap. While this mechanism is successful in 
preventing the sheet from plowing through the magnet brush bristle nap, it 
requires accurate interrelated control of movement of the shielding belt 
with the sheet to ensure the alignment of the belt opening and the sheet 
image area during development. 
SUMMARY OF THE INVENTION 
This invention is directed to apparatus, in an electrographic copier 
wherein discrete dielectric sheets are moved seriatim about a travel path 
having a portion in juxtaposition with a developer station for developing 
imagewise electrostatic charge patterns on such discrete sheets with 
developer material, for selectively sealing developer material within such 
station and, during such sealing, guiding a moving sheet along such travel 
path portion out of developing relation with such developer material. The 
apparatus comprises a member selectively movable to a first position 
sealing developer material within the developer station and forming a 
sheet guide coincident with the sheet travel path portion, or a second 
position remote from such first position. In response to the lead edge of 
a discrete dielectric sheet moving away from the travel path portion, the 
member is moved to its second position leaving the sheet in developing 
relation to developer material in the developer station; and in response 
to the trail edge of such sheet moving into the travel path portion, the 
member is moved to its first position to seal developer material within 
such station and to guide such sheet along such travel path portion out of 
developing relation to developer material. 
The invention, and its objects and advantages, will become more apparent in 
the detailed description of the preferred embodiment presented below.

DESCRIPTION OF PREFERRED EMBODIMENT 
Referring now to the accompanying drawings, a magnetic brush developer 
station, designated generally by the numeral 10, is shown in FIG. 1. The 
developer station 10 includes a housing 12 forming a reservoir for 
particulate developer material T. The developer material T comprises, for 
example, a mixture of finely divided pigmented thermoplastic electroscopic 
marking particles (toner) held to the surface of ferromagnetic particles 
(carrier) by electrostatic charges created by triboelectrification. Of 
course, developer material of the type comprised solely of marking 
particles which exhibit magnetic properties (referred to as single 
component developer) is also suitable for use with this invention. 
The housing 12 of developer station 10 includes a top wall 12a having an 
opening 12b. The opening 12b is located in juxtaposition with a guide 
track assembly 14 of an electrographic copier utilizing moving discrete 
dielectric sheets, such as for example the aforementioned U.S. Pat. No. 
4,436,405. The guide track assembly of the copier of such patent supports 
marginal edges of discrete dielectric sheets and describes a path about 
which such sheets are transported seriatim and guided into operative 
relation with electrographic process stations. Of course, other guide 
assemblies for discrete dielectric sheets are suitable for use with this 
invention. The discrete dielectric sheets, which respectively include a 
photoconductive layer and an insulating layer, are uniformly charged and 
then exposed over an image-receiving area to a light image of information 
to be reproduced. Such exposure selectively alters the uniform charge to 
form electrostatic charge patterns on the sheets respectively 
corresponding image-wise to the light image. The charge patterns are 
developed by electroscopic marking particles to form transferable images 
on the sheets, and such images are then transferred from the sheets to 
receiver members to form the information reproductions. Of course, the 
developer station 10 is suitable for use in other discrete dielectric 
sheet copier apparatus, such as where the developed images are fixed 
directly on the sheet for example. 
An applicator 16, mounted in the housing 12 of the developer station 10, is 
adapted to transport developer material through the opening 12b into the 
discrete dielectric sheet travel path. The applicator 16 includes a 
rotatable hollow cylindrical shell 18 of non-magnetic material such as 
aluminum. The shell 18 is oriented such that its longitudinal axis spans 
the width of the guide track assembly and lies in a plane parallel to the 
plane of sheet travel through such assembly. A series of magnets 20 are 
supported within the shell. The particles of the developer material align 
in the fields of the magnets to establish a brush-like bristle nap 
extending substantially radially from the shell. As the shell rotates the 
bristles are moved through the opening 12b in the top wall 12a of the 
developer station housing and extend into the travel path of a discrete 
dielectric sheet. For a more detailed description of a typical magnetic 
brush developer station, see for example U.S. Pat. No. 3,457,900, issued 
July 29, 1969, in the name of Drexler et al. Of course, other magnetic 
brush developer stations (e.g., with plural applicators, or having a 
stationary shell with rotating magnets) establishing a path-intercepting 
developer material bristle nap are suitable for use with this invention. 
In order to prevent developer material T from escaping from the developer 
station 10 and discrete dielectric sheets from plowing through the 
developer material bristle nap as the sheets approach the station 10, 
apparatus 14a is provided to selectively seal developer material within 
the station and, during such sealing, guide a sheet along its travel path 
out of developing relation with such material. The apparatus 14a is 
configured as a pair of movable shoe members 22, 24. Since the shoes are 
mirror images of one another, only one is shown in detail in FIGS. 2a, 2b, 
2c. The shoes include portions 26, 28 interconnected by portion 38 and 
spaced to be respectively coincident with marginal edge supporting 
portions of the guide track assembly 14. The portions 26, 28 have a bottom 
surface 30 slidably received for reciprocation on the top wall 12a of the 
developer station housing 12. The top surfaces of portions 26, 28 have a 
first notch 32 forming an extension of guide track asembly 14 and a second 
notch 34 for receiving an extended tip 36 of the guide track assembly. The 
portion 38 has a bottom surface 40 adapted to seal the developer station 
opening 12b and an upper surface 42 adapted to guide a discrete dielectric 
sheet. 
In operation, the shoe members 22, 24 are initially in a first position in 
an end-to-end relationship (see FIG. 1). As such, the surfaces 40 of the 
abutting portions 38 form a contiguous seal covering the opening 12b of 
the developer station housing top 12a, and surfaces 42 form a sheet guide 
coincident with the portion of the sheet travel path adjacent to the 
developer station. Thus, developer material is substantially contained 
within the developer station housing 12 and prevented from contaminating 
the interior of the copier. During the reproduction process, a discrete 
dielectric sheet (e.g. sheet designated by letter "S" in FIGS. 3, 4, 5), 
bearing an image-wise electrostatic charge pattern to be developed is 
transported through the upstream portion of the guide track assembly 14 
toward the developer station 10 by driven nip roller pair 44. With the 
shoe members 22, 24 in the position of FIG. 1, extensions 36 of the guide 
track fit in notches 34 respectively. Therefore, the transported sheet is 
directed without interference into apparatus 14a and guided on the lower 
surfaces of notches 32, 34 and surface 42 of portion 38 to the downstream 
portion of the guide track assembly 14 (see FIG. 3) and into the driven 
nip roller pair 46. During such travel, such sheet is out of developing 
relation with the developer material. 
A detector D.sub.1, such as a photoelectric cell or mechanical switch for 
example, is located immediately upstream of the nip roller pair 46. 
Detector D.sub.1 senses the arrival of the lead edge of the charge pattern 
bearing sheet and, in response to such arrival, produces an appropriate 
control signal. Such control signal is used, at a predetermined time 
sufficient to enable such lead edge to enter the control of nip roller 
pair 46, to actuate an appropriate mechanism 48 as the lead edge exits the 
apparatus 14a. The mechanism 48 slides the shoe members 22, 24 apart to 
their positions shown in FIG. 4 (i.e., a second position remote from the 
opening 12b) leaving the sheet in developing relation with the developer 
material extending into opening 12b from applicator 16. 
A compliant back-up roller 50 is located adjacent to the applicator 16 on 
the opposite side of the sheet travel path. The longitudinal axis of the 
roller 50 extends substantially across the developer station and is 
parallel to the longitudinal axis of the applicator 16. The mechanism 48, 
on actuation, also moves the roller 50 to a position shown in FIG. 4 where 
the entire sheet is urged, element-by-element, through such developing 
relation to assure uniform development of the electrostatic charge pattern 
on such sheet. The surface of the roller 50 may be formed of a low 
friction material such as rayon for example. Such surface is in 
non-rolling contact with the moving discrete dielectric sheet to wipe the 
back surface of the sheet and clean such back surface. It should be noted 
that the distance between the point of tangency of the sheet with roller 
50 and the nip of roller pair 46 is less than the distance between the 
lead edge of a sheet and the adjacent marginal edge of its charge pattern 
bearing area. Thus, when the shoes are moved to their remote positions, 
the charge pattern bearing area of the sheet from such marginal edge will 
be in developing relation with the developer material for complete image 
development. 
As the trail edge of the sheet bearing the charge pattern being developed 
exits the control of nip roller pair 44, a detector D.sub.2 (similar to 
detector D.sub.1) senses such trail edge and produces an appropriate 
control signal. Such control signal, at a predetermined time, is used to 
actuate the mechanism 48 to move the back-up roller 50 to its remote 
position as shown in FIG. 5 and substantially simultaneously slide the 
shoe members 22, 24 together into their first position. Accordingly, the 
developer station 12 is resealed and remains resealed while the trail edge 
of the sheet is guided by the shoes to pass over the developer station 10 
out of developing relation with developer material. Similarly to the 
arrangement described above, the distance between the point of tangency of 
the sheet with the roller 50 and the nip of roller pair 44 is less than 
the distance between the trail edge of the sheet and the adjacent marginal 
edge of its charge pattern bearing area. Thus, development of the entire 
image area occurs before the shoes return to their first position. With 
the shoes in their first position, they are, of course, then ready for 
guiding the next discrete dielectric sheet directed along guide track 
assembly 14 toward developing relation with the station. 
The invention has been described in detail with particular reference to a 
preferred embodiment thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.