This invention relates to a cross-mixer for a developer system of a photocopier, particularly one with a two component development system, which mixes the developer mixture (1) to assure uniform lateral distribution of the toner, (2) to assure uniform concentration of the toner mixture and (3) to triboelectrically charge the developer mixture. Adjacently offset rows of V-shaped baffles successively divide and intermix the developer mixture. Angled lifting plates interposed between successive rows of baffles scoop and lift the mixture so as to triboelectrically charge the same.

BACKGROUND OF INVENTION 
The present invention relates to a mixer for use in the development housing 
of a photocopying machine, serving to lift, and mix the developer mixture, 
and to level the concentration of the mixture with a single element. 
It is well known in the prior art that electrophotographic copying machines 
employ a two component brush developer to produce an image on an imaging 
surface by selectively developing toner particles from a mixture of 
carrier and toner. The quality of the resulting image depends upon the 
toner charge (tribo) and the toner concentration which is brought into 
contact with the imaging surface from the development unit. 
Triboelectric charging of the toner is effected by mixing or tumbling the 
toner and the carrier within the development unit. Indeed, it is necessary 
to stir, mix, lift, and drop the toner/carrier mixture in order to create 
the triboelectric charge required for the development process. It is well 
known in the prior art to provide such a means in a development unit. 
One consequence of image development onto the imaging surface is the 
removal of toner from the developer housing within the development unit 
thereby reducing the concentration of toner within the carrier. In order 
to maintain the toner concentration required for good and consistent image 
quality from the photocopying process, it is necessary to add toner to the 
development housing to replace that which is removed by the imaging 
surface. Toner, which is typically in powder form, is usually added 
uniformly along the entire length of the development unit--the length of 
the development unit usually being approximately equal to the maximum 
width of the copy media used by the photocopy apparatus. However, due to 
the spatial variations of the photocopied image (for example, most common 
applications may have more dark portions toward the center than around the 
edges of the image), toner is selectively removed at different rates 
across the width of the development housing. This selective removal of 
toner combined with the uniform addition of toner presents a problem in 
that the local toner concentration varies along the length of the 
developer system. This problem is particularly severe in long developer 
housings such as those used by engineering or architectural drawing copy 
machines. 
The prior art has attempted to remedy this deficiency by various means such 
as the use of twin oppositely feeding augers, a paddle wheel in 
conjunction with one or more augers, and hollow paddle wheels containing 
screw shaped baffle systems. These prior art devices are deficient in that 
they are unnecessarily complicated, and therefore are failure prone. 
Furthermore, these devices may reduce the developer usable lifespan and 
may still not result in uniform or complete mixing over the full length of 
the development system. 
It is therefore an object of this invention to provide an apparatus which 
will uniformly mix the developer mixture in a development system in a 
photocopier notwithstanding the non-uniform depletion of the toner in the 
developer system. 
It is a further object of this invention to provide an apparatus which will 
agitate the developer mixture in a photocopier so as to triboelectrically 
charge the mixture. 
It is a still further object of this invention to provide an apparatus 
which will not reduce the usable life of the developer mixture. 
A still further object of this invention to provide the aforementioned 
objects with a simple, single unit. 
SUMMARY OF INVENTION 
The above and other beneficial objects and advantages are attained in 
accordance with the present invention by providing a long hollow 
cylindrical mixer which is rotatable about its longitudinal axis. The 
mixer includes multiple, angular lifting plates that lift and dump the 
developer mixture as the mixer rotates. These angular lifting plates are 
spaced to allow the developer mixture to flow between adjacent plates into 
the center regions of the assembly. The angular lifting plates scoop, lift 
and drop the developer mixture so as to triboelectrically charge the same. 
A series of rows of alternately oriented flow directing baffles is 
interposed between the angular lifting plates in the center region. Each 
of these baffles is arranged to perform the function of dividing developer 
mixture into two parts and directing the material flow in laterally 
opposed directions as the mixer is rotated within the developer housing. 
By the use of a plurality of rows of baffles, the rotation of the mixer 
causes repeated cross-mixing to occur resulting in effective mixing of the 
developer and a uniform distribution of the toner therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings in detail wherein like numerals indicate like 
elements throughout the several views, FIG. 1 discloses a front plan view 
of apparatus 10. Apparatus 10 is roughly cylindrical in shape with two 
ends 12,13 and axles 14,15 extending from ends 12,13 along the 
longitudinal axis of apparatus 10. A lower row 16 of baffles 18 extends 
along the bottom of apparatus 10. An upper row 20 of baffles 18 is shown 
in phantom along the top of apparatus 10. Baffles 18 have the 
cross-sectional shape of a truncated V. The spacing interval of these 
baffles will be referred to as a "mixing-unit length" 22. An intermediate 
row 24 of baffles 18 is shown on the front of apparatus 10. Further, a 
second intermediate row 32 (see FIG. 2) of baffles 18 is on the rear of 
apparatus 10, directly behind row 24 and positioned between rows 16 and 
20. The position of baffles 18 in intermediate row 24 is offset by one 
half mixing-unit length 22 from the position of the baffles in rows 16 and 
20. This offset is necessary in order to provide a thorough mixing of the 
developer mixture without any net lateral displacement of the mixture. 
This necessity for an offset is illustrated graphically in FIG. 3. 
There are two kinds of flow directing baffles 18, each with identical 
mixing-unit lengths, but offset by one half mixing-unit length between 
adjacent rows 16, 20, 24, 32 (see FIG. 2 for element 32) of baffles 18. 
These types of flow directing baffles 18 will be referred to as "A" type 
and "B" type. To prevent any net lateral displacement of developer 
mixture, these flow directing baffles must occur in offset pairs. A 
minimum of one pair of rows (one "A" type and one "B" type) is required. 
More pairs, such as the two pairs shown in FIG. 1 may be advantageous to 
the efficacy of the design. In FIG. 1, rows 16 and 20 would be of one type 
chosen from "A" and "B", while row 24 and the rear row 32 (see FIG. 2) 
would be the other type. 
Angled lifting plates 26 are positioned between adjacent rows 16, 20, 24, 
32 (see FIG. 2 for element 32). The purpose of angled lifting plates 26 is 
to scoop, lift and drop the developer mixture as apparatus 10 rotates 
thereby effecting the triboelectric charging of the developer mixture. 
Apparatus 10 may optionally include a toner concentration sensor brush 28 
attached to apparatus 10 by a screw 30 or similar means. This brush 28 is 
used to wipe or flick stagnant or accumulated developer material away from 
a toner concentration sensor (not shown) in the development housing as 
apparatus 10 rotates. This brush is described in more detail in the 
commonly assigned application, "Toner Concentration Sensor Wiper for 
Photocopying Machines" Ser. No. 306,991, filed Feb. 6,1989, now abandoned. 
FIG. 2 discloses a side plan view of apparatus 10. There are a total of 
four lifting plates 26, positioned between rows 16, 20, 24, 32 of flow 
directing baffles 18. Mixing plates 26 have an outwardly pointing L-shaped 
cross section so as to provide a scooping means used for the triboelectric 
charging of the developer mixture as apparatus 10 rotates. 
FIG. 3 illustrates the cross-mixing function of the flow directing baffles 
18. The four rows 16, 20, 24, 32 of baffles 18 are shown in a linear 
rather than cylindrical shape. The alternating of rows of the "A" and "B" 
types of baffles 18 with an offset of one-half mixing-unit length 22 
between adjacent rows is shown. 
The baffles 18 are arranged to perform the function of dividing developer 
mixture into two parts and directing the material flow in opposite 
longitudinal directions as the apparatus 10 is turned within the developer 
housing (not shown). This takes the mixture in one mixing-unit length and 
deposits half of it in each of the two adjacent mixing-units located at 
the next rotational position of the device. These two rotationally 
disposed mixing-units are laterally displace by on half of a mixing-unit 
from the mixing-unit that supplied the developer material. This action is 
repeated along the entire length of the device with multiple mixing-units. 
When the assembly rotates sufficiently far to bring yet another lifting 
plate 26 (see FIGS. 4a and 4b) into position, half of the developer from 
each of the previous two laterally adjacent mixing-units is directed into 
a centrally located mixing-unit while all of the remaining developer 
mixture from each of the two mixing-units is split into the two laterally 
adjacent mixing-units nearest to the central mixing-units, all three 
mixing-units being rotationally displaced from the previous two 
mixing-units. Therefore, developer mixture is intermixed thereby 
correcting non-uniformities in toner concentration without causing any net 
longitudinal displacement of toner. The rotational version of the 
apparatus 10 is achieved by wrapping the elements of FIG. 3 into a 
cylinder. 
FIGS. 4a and 4b supplement FIG. 3 by illustrating the scooping and pouring 
of developer mixture by angled lifting plates 26. This occurs between the 
time that developer mixture engages adjacent rows 16, 20, 24, 32 of 
baffles 18 thereby further correcting non-uniformities in toner 
concentration in the developer. 
FIG. 5 shows how rotation of the angled lifting plates 26 also scoops, 
lifts and drops the developer mixture thereby assuring proper 
triboelectric charge for the developer. 
Thus, in accordance with the above, the aforementioned objects are 
effectively attained.