Excess Developer Removal Apparatus

My invention relates to apparatus for removing excess liquid developer from the photoconductive surface of a plain paper electrophotographic copier.

It is necessary in plain paper electrophotographic copiers to remove most of the layer of liquid developer formed on the photoconductive surface during development, if damp or stained plain paper copies are to be voided. The removal must be performed without disturbing the delicate developed toner image on the photoconductive surface. Various techniques have been used in the prior art in attempts to accomplish this removal.

One system of the prior art includes a doctor blade in closely spaced relation to the photoconductor surface followed by a corona wire which generates an electrostatic field to provide a non-mechanical cleaning action. This arrangement has not proved satisfactory for that it does not reduce the liquid level sufficiently. As a result, high heat is required to dry the copies resulting in a high level of developer liquid carrier fumes in the region of the copier.

According to another technique of the prior art, an elongated high-velocity air jet is directed from an air knife to effect removal of the excess developer under the action of the air jet. Since this technique requires a relatively high-volume-velocity air stream, a considerable amount of developer liquid is vaporized. If pollution of the surrounding region is to be avoided, the resultant fumes must be collected and carried away by bulky supporting systems.

U.S. Pat. No. 3,907,423, issued to Hayashi et al, discloses an arrangement in which a closely spaced roller disposed across the photoconductive surface is rotated at a high speed in a direction opposite to that of the surface. While this technique is generally satisfactory, the multiplicity of moving parts makes the system undesirably complex.

One of the objects of my invention is to provide an apparatus for removing excess liquid developer which does not disturb the developed image.

Another object of my invention is to provide an apparatus for removing excess liquid developer which does not create an excess amount of fumes.

A further object of my invention is to provide an apparatus for removing excess liquid developer which does not require bulky auxiliary systems.

Still another object of my invention is to provide an apparatus for removing excess liquid developer which is mechanically simple.

Other and further objects will be apparent from the following description.

In general, my invention contemplates an apparatus for removing excess liquid developer from a photoconductive surface in which a mechanical barrier member formed with a narrow slot extending across the photoconductive surface is supported in closely spaced relationship to the surface with a gap between the barrier and the surface which is substantially less than the thickness of the developer layer. Low-pressure air supplied to the slot from inside the barrier forms a low-pressure air barrier which assists in effectively removing nearly all of the developer liquid without disturbing the toner image. Preferably, the barrier member is supported in this manner by suitably biasing rollers rotatably attached to the ends of the barrier member against the photoconductive surface. By so positioning the member relative to the photoconductive surface, substantially all of the developer layer can be removed using only a minimal amount of air pressure and with very little air volume. Vaporization of the liquid developer is only a small fraction of that produced by air knife assemblies of the prior art, and air pollution is thus substantially eliminated.

FIG. 1 is a side elevation of an electrophotographic copier, incorporating one embodiment of my apparatus.

FIG. 2 is a fragmentary view of the apparatus taken along line 2--2 of FIG. 1, with parts removed.

FIG. 3 is an enlarged section of the apparatus, taken along line 3--3 of FIG. 2.

FIG. 4 is an enlarged section of the apparatus shown in FIG. 1 in its inoperative position.

Referring to the drawings, an electrophotographic copier 10 incorporating my excess developer removal apparatus includes a drum 12 having a photoconductive surface 14 which is rotated in the direction shown past a plurality of processing stations. More particularly, the drum 12 rotates past a charging station 16 at which a corona charger 18 provides the drum surface 14 with a uniform electrostatic charge, an exposure station 20 at which the surface 14 is exposed to a light image of an original selectively to discharge the surface and form an electrostatic image, a developing station 22 at which a liquid developer is applied to the surface from a developing tank 24 to form a visible toner particle image on the surface 14, and a transfer station l26 at which the developed image is transferred to a sheet 28 of plain paper. Preferably, the copier 10 also includes a cleaning station (not shown) between the transfer station and the charging station 16, at which accumulated toner deposits are removed from the drum surface 14.

The excess developer removal apparatus, indicated generally by the reference numeral 30, is located on the drum periphery immediately following the developing tank 24 in the direction of movement of the drum 12. The apparatus 30 comprising a hollow, generally cylindrical member 32, the ends of which receive stub shafts 34 and 36. Shafts 34 and 36 rotatably support rollers 38 and 40 which engage the drum surface 14 near its lateral edges. Rollers 38 and 40 are formed with a slightly greater diameter than that of the member 32 to provide a gap between the member 32 and the drum surface 14 of about 0.002 inch. After passing through the developing station 22, the surface 14 typically carries a film of developer which is about 0.012 inch thick. Thus member 32 acts as a mechanical barrier to the passage of a film of this thickness. While member 32 provides a mechanical barrier to the passage of the relatively thick layer of developer liquid, I have discovered that some means must be provided for preventing wetting of the trailing portion of the member 32 following the point of closest proximity of the member 32 to the surface 14. If this is not done and the trailing portion is wet with developer liquid, large drops of liquid are left on the photoconductive surface 14 as the surface tension film of liquid developer along the trailing portion of the barrier member 32 and the surface 14 is broken loose.

I form the member 32 with an axially extending exit slit 42 communicating with the hollow interior of member 32. Preferably, the width of the exit slit 42 is five to ten times the gap between the member 32 and the drum surface 14, or about 0.02 inch. Tubing 46 feeds compressed air from a supply 48 to a bore 44 formed in the shaft 36 and leading into the interior of member 32. Preferably, the air supply 48 provides air at a pressure between 5 and 10 inches of water. The member 32 is preferably formed with axially extending grooves 60 and 62 on the outer surface adjacent to the edges of the slit 42 to provide a well-defined region of adjacency and to reduce turbulence.

The narrow spacing between the slit 42 and the surface 14 and the slight positive pressure in the region between the member 32 and the surface 14 cooperate to form an effective air barrier which breaks the surface tension of the liquid between drum 12 and member 32 to prevent wetting of the trailing portion of member 32. This is accomplished without disturbing the developed image. My arrangement requires only a low volume of air of from about 2 to about 4 cubic feet per minute.

A pair of pivot members 50 and 52, arms of which rotatably receive the stub shafts 34 and 36, support barrier member 32 in its operating position. Each of the pivot members 50 and 52 pivots upon a pivot shaft 54 and is suitably biased by means of a spring 56 attached between an arm of the pivot member and a fixed point 58. Springs 56 bias the rollers 38 and 40 against the drum 12 so that the barrier member 32 remains a fixed distance from the drum 12 despite any eccentricity or surface irregularity of the drum 12.

It will be appreciated that, in the course of an operating cycle, some wetting of member 32 in and adjacent to the area of the slit 42 occurs. To remove such developer and to prevent buildup of toner deposits in these areas, after each machine use period, I wipe the slit area of member 32 with an elongated spongy pad 64 carried by a supporting member 66 at a location spaced away from the drum surface 14. Preferably, an elongated perforated tubing 68 supplies the spongy pad 64 with developer liquid to keep it wet.

A rotary solenoid 70 mounted on pivot member 50 and coupled to stub shaft 34 is energized during a machine use period to maintain the member 32 in the position shown in FIG. 3, in which the exit slit 42 is adjacent to the drum surface 14. At the end of a machine use period, solenoid 70 is de-energized to permit the exit slit 42 of the member 32 to rotate counterclockwise past the sponge 42 to the downwardly facing position shown in FIG. 4. As the exit slit 42 moves past the pad 64, liquid developer is wiped off. At the beginning of the next machine use period, solenoid 70 is again energized to rotate the barrier member clockwise to its operative position with the exit slit 42 adjacent to the drum surface 14.

It will be seen that I have accomplished the objects of my invention. My apparatus removes excess liquid toner without disturbing the developed toner image. My apparatus does not create an excess amount of fumes, nor does it require bulky auxiliary support systems. Finally, it is mechanically simple.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.