Mispuff Detector

Abstract

In an electrostatographic copying machine in which a developed image on the surface of a reproducing member is transferred to a transfer sheet in contact with said image, a device is provided for detecting the undesired continued presence of the transfer sheet on the reproducing surface after the image has been transferred, said device including a power source for providing a current flow between an electrode and the reproducing surface at a point beyond the image transfer area and a detecting circuit coupled to the electrode and power source for indicating a change in the current flow caused by the presence of the transfer sheet between the electrode and the surface, thereby indicating continued contact of the transfer sheet with the reproducing surface. The detecting circuit can be used to discontinue the operation of the machine.

Description

This invention relates to electrostatographic reproduction and more particularly to electrostatographic reproducing apparatus adapted to automatically detect any malfunction preventing timely removal of the transfer material from the surface of the reproducing member, hereinafter referred to as the reproducing surface.

The formation and development of the images employing photoconductive materials by electrostatic means is well known. The basic electrostatographic process, as taught by C. F. Carlson in U.S. Pat. No. 2,297,691, involves placing a uniform electrostatic charge on a photoconductive insulating layer, exposing the layer to a light-and-shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic material referred to in the art as "toner." The toner will normally be attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This powder image may then be transferred to a receiving surface such as paper. The transferred image may be subsequently permanently affixed to a support surface by heat. Instead of latent image formulation by uniformly charging the photoconductive layer and then exposing the layer to a light-and-shadow image, one may form the latent image by other means such as directly charging the layer in image configuration. Any other suitable fixing means such as solvent or overcoating treatment may be substituted for the foregoing heat fixing step.

Similarly other methods are known for applying the electroscopic particles to the electrostatic latent image to be developed. Included within this group are the "cascade" development technique disclosed by E. N. Wise in U.S. Pat. No. 2,618,552; the "powder cloud" technique disclosed by C. F. Carlson in U.S. Pat. No. 2,221,776 and the "magnetic brush" process disclosed, for example, in U.S. Pat. No. 2,874,063.

A difficulty often encountered in apparatus embodying such electrostatographic processes is that jamming can be caused by failure of the transfer material to be timely removed from the photoconductive surface, after transfer of the image. One solution has been to employ photodetection devices positioned at a point on the reproducing surface immediately past the position at which the transfer material is removed. Failure of the transfer material to be timely removed is thus optically detected and an appropriate signal generated for disconnecting the mechanism from the power source to prevent jamming. A disadvantage of photooptical devices, however, lies in their inherent unreliability in field use, their susceptibility to erroneous indications due to ambient light levels and build up of foreign matter interfering with the optical path, their expense, and the inconvenience of adding additional components to the mechanism. Another solution utilizes mechanical fingers which contact the drum and position sense the presence or absence of improperly positioned transfer material. However, this method can result in fatigue and physical damage of the reproducing member due to finger contact.

It is, therefore, a primary object of this invention to provide an improved means for detecting malfunction in a reproducing mechanism.

It is a further object of this invention to provide an arrangement for detecting malfunctions caused by jamming of transfer material in an electrostatographic device utilizing existing components within the electrostatographic device.

It is a still further object of the invention to provide a noncontacting arrangement for detecting failure of transfer material to be timely removed from a reproducing surface, which arrangement is reliable in operation and relatively inexpensive.

The foregoing objects are accomplished by providing a current flow between an electrode and the photoconductive surface at a position immediately past the point at which the transfer material is normally removed. The presence of transfer material on the reproducing surface will serve to alter the current flow between the electrode and the photoconductive surface. The electrode can be coupled to suitable electrical circuitry which will respond to the change in current flow level and thereby indicate the presence of transfer material past its point of proper removal. Such indication can be employed to disconnect the mechanism from its power source, and thus prevent jamming. In the electrostatographic device, the corona preclean unit may be employed as the current electrode.

The foregoing objects and brief description of the invention as well as further objects will become more apparent from the following detailed description of a preferred embodiment, with reference to the appended drawings wherein:

FIG. 1 is a schematic view of an electrostatographic reproducing apparatus in elevation;

FIG. 2 is a partial isometric view of the transfer station and photoconductive surface showing the use of the present invention;

FIG. 3 is a schematic representation of an arrangement for providing an indication of a change in current flow, caused by failure of removal of transfer material, in accordance with the invention; and

FIGS 4A and 4B are wave form diagrams illustrating the operation of the invention with respect to time.

Referring now to FIG. 1, a typical electrostatographic reproducing apparatus is shown.

For a general understanding of the processing system in which the present invention is incorporated, reference is had to FIGS. 1 and 2 wherein like numerals refer to like components in which the various system components are schematically illustrated. In the electrostatographic system shown, a light image of copy to be reproduced is projected onto the charged surface of an electrostatographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged electroscopic developing material to form a power image, corresponding to the latent image, on the plate surface. The powder image can then be electrostatically transferred to a web of suitable transfer material in sheet form to which it may be fused by a fusing device, whereby the powder image is caused permanently to adhere to said transfer sheet material.

In the system disclosed herein, documents to be reproduced are placed at the imaging station, generally designated by reference character 11, which includes a light projecting system, for the purpose of scanning. The illuminated data is projected downwardly by means of a mirror-lens imaging assembly 12 and through a slit aperture assembly 13 and onto the reproducing surface of an electrostatographic plate in the form of a drum 14.

The electrostatographic drum 14 includes a cylindrical member mounted in suitable bearings in the frame of the machine and is driven in a clockwise direction as viewed in FIG. 1 by a motor at a constant rate that is proportional to the scan rate whereby the peripheral rate of the drum surface is substantially identical to the rate of movement of the reflected light image. The drum surface comprises a layer of photoconductive material on a grounded conductive backing that is sensitized prior to exposure by means of a corona generating device 15.

The exposure of the drum surface of the light image discharges the photoconductive layer in the areas struck by light, whereby there remains on the drum a latent electrostatic image in image configuration corresponding to the light image projected. As the drum surface continues its movement, the electrostatic latent image passes through a developing station in which there is positioned a developer apparatus including a housing 16 for developing material. A suitable driving means is used to carry the developing material to the upper part of the developer housing where it is cascaded down over a hopper chute onto the electrostatographic image on the drum.

As the developing material is cascaded over the electrostatographic drum, toner particles are pulled away from the carrier component of the developing material and deposited on the drum to form powder images, while the partially denuded carrier particles pass off the drum into the developer housing sump.

Positioned next and adjacent to the developing station in a clockwise direction is an image transfer station which includes a sheet feeding mechanism adapted to feed sheets successively to the developed image on the drum at the transfer station. This sheet feeding mechanism, generally designated 18, includes a sheet source for a plurality of sheets of a suitable transfer material that is typically sheets of paper or the like, a separating roller adapted to feed the top sheet of the stack to feed belt and rollers 20 which direct the sheet material into contact with the rotating drum at a speed preferably slightly in excess of the rate of travel of the surface of the drum in coordination with the appearance of the developed image at the transfer station. In this manner, the sheet material is introduced between the feed rollers and is thereby brought into contact with the rotating drum at the correct time and position to register with the developed image. To effect proper registration of the sheet transfer material with the feed roller and to direct the sheet transfer material into contact with the drum, guides are positioned on opposite sides of the feed rollers.

The transfer of the powder image from the drum surface to the transfer material is effected by means of a corona transfer device 21 that is located at or immediately after the point of contact between the transfer material and the rotating drum. The corona transfer device 21 is substantially similar to the corona discharge device 15 in that it includes an array of one or more corona discharge electrodes that are energized from a suitable high potential source and extend transversely across the drum surface and are substantially enclosed within a shielding member.

In operation, the electrostatic field created by the corona transfer device is effective to tack the transfer material electrostatically to the drum surface, thus causing the transfer material to move synchronously with the drum while in contact therewith. Simultaneously with the tacking action, the electrostatic field is effective to attract a significant portion of the toner particles, forming the powder image, from the drum surface and cause them to adhere electrostatically to the surface of the transfer material.

Immediately subsequent to the image transfer station is positioned a transfer material stripping apparatus or paper pickoff mechanism, generally designated 22, for removing the transfer material from the drum surface. This device includes a plurality of small diameter, multiple outlet conduits 24 of a manifold that is supplied with pressurized aeriform fluid through the outlet conduits into contact with the surface of the drum slightly in advance of the sheet material to strip the leading edge of the sheet material from the drum surface and to direct it onto a horizontal conveyor 23. The sheet material is then carried to a fixing device in the form of a fuser assembly 25, whereby the developed and transferred powder image on the sheet material is permanently fixed thereto.

After fusing, the finished copy is preferably discharged from the apparatus at a suitable point 26 for external collection, in a copy collector positioned at a convenient place for copy removal by the machine operator.

The next and final station in the device is a drum cleaning station having positioned therein a corona precleaning device 27 similar to the corona charging device 15, to impose an electrostatic charge on the drum and residual powder adherent thereto to more readily permit removal of residual or untransferred toner. To aid in effecting removal of the powder a drum cleaning device 28, adapted to remove any powder remaining on the drum surface after transfer, is also provided as is a source of light 29 whereby the photoconductive drum is flooded with light to cause dissipation of any residual electrical charge remaining thereon.

In general, the electrostatic charging of the electrostatographic drum in preparation for the exposure step and the electrostatic charging of the support surface to effect transfer are accomplished by means of corona generating devices whereby electrostatic charge is applied to the respective surfaces in each instance. Although any one of a number of types of corona generating devices may be used, a corona charging device of the type disclosed in Vyverberg U.S. Pat. No. 2,836,725 is used for both the corona charging device 15, the corona transfer device 21, and the corona precleaning device 27, each of which is secured to suitable frame elements of the apparatus and connected to suitable power sources.

As will be evident from FIGS. 1 and 2, the paper pickoff mechanism 22 is positioned just past the image transfer station. Failure of the burst or puff of aeriform fluid to dislodge the transfer material from the drum 14 at that point will result in jamming of the reproducing apparatus by the sheet material. Such failure is commonly referred to as a "miss-puff."

Detection of the miss-puff or failure to remove transfer material is accomplished in accordance with the present invention through use of the corona precleaning device 27, in conjunction with the arrangement as shown in FIG. 3.

The principle of operation involves a discontinuity in the level of flow of current from the corona precleaning device 27 caused by alteration of the flow of current between the corona device and the reproducing surface of the drum 14. The alteration of current flow is that created by the miss-puff, i.e., the continued presence of the transfer material in contact with the drum surface.

As shown in FIG. 2, a power supply PS 33 provides energizing potential to the electrode 30 of the preclean device 27. A detector unit DET 35 is coupled to the power supply and electrode to detect the current differential and provide an indication of the current differential resulting from failure of removal of transfer material.

Referring to FIG. 3, a circuit for detecting the current discontinuity is shown. Using like reference numerals to represent like components, FIG. 3 shows a corona precleaning device 27 having at least one electrode 30. The drum 14 is connected to an electrical reference point 31 illustrated as ground, and includes a suitable photoconductive surface layer 32.

The corona precleaning device can be either positive, negative, (AC or in combinations), and as shown is AC biased with a negative potential by means of a power supply 33, which includes a DC voltage source 33B coupled through an AC voltage source 33A to the corona electrode 30. The detector unit 35 is connected between the DC source 33B and the electrical reference point, and can take the form of a half-wave diode rectifier including sensing resistor 36, smoothing capacitors 37 and 38, diode 39, current limiting resistance 40, and loading resistance 41.

As shown in FIG. 3, in operation, the potential of source 33 is designed such that under normal conditions, the potential E.sub.A at point A varies about a level which prevents any negative excursions. This condition is illustrated in FIG. 4A in time zone t.sub.0 -t.sub.1. As shown in FIG. 4B, no output voltage E.sub.B is present at point B under these conditions. Under mispuff conditions, the resulting unbalance results in a shift in operating voltage levels such that a portion of the potential at point A goes negative, thereby permitting a rectified output voltage E.sub.B to appear at point B as shown in FIG. 4B in the time zone t.sub.1 -t.sub.2. End of the condition at time t.sub.2 results in resumption of the original state. The voltage pulse at point B can be employed to energize a suitable relay unit 42 for shutting off the machine. An example of relay energizable machine stop sequences is shown by Osborne et al. in U.S. Pat. No. 3,301,126.

It is understood that other forms of detection devices can be employed to measure the electrical discontinuity caused by the presence of transfer material beneath the precleaning device, or past the image area and removal station, and that other aspects and alternatives within the scope of this invention will be apparent to those skilled in the art.

Claims

What is claimed is:

1. In an electrostatographic reproducing device wherein a developed image is transferred from an image transfer area on a reproducing surface to a transfer material in contact with said image, a device for detecting the continued presence of the transfer material on said reproducing surface after said image has been transferred, said device comprising a power source for providing a current flow between an electrode and said reproducing surface at a point beyond said image transfer area, a detecting unit coupled to said power source for detecting a change in said current flow caused by presence of said transfer material between said electrode and said surface, thereby indicating continued contact of said transfer material and said reproducing surface, and means coupled to said detecting unit for providing an indication of said change in current flow.

2. The combination of claim 1 wherein said power source includes a DC source series coupled through an AC source to said electrode, said detecting unit coupled between said DC source and a reference point.

3. The combination of claim 2 wherein said detecting unit is a half-wave rectifier.

4. In combination with an electrostatographic reproduction apparatus including a reproducing surface adapted to have formed thereon a powder image for transfer to a transfer material applied to said surface and pick-off means for removing said transfer material from said surface after transfer of said image thereto;

a device for detecting failure of removal of said transfer material from said surface after transfer of said image to said material, comprising:

energizing means for establishing a first current flow between an electrode and said surface at a position on said surface beyond said pick-off means in the absence of transfer material at said position, and a second current flow in the presence of transfer material at said position; and

detection means coupled to said energizing means and responsive to the change between said first and second current flows for providing an indication of said failure of said transfer material to be removed from said surface.

5. The combination of claim 4 wherein the electrode is a corona precleaning device for applying an electrostatic charge to said surface.

6. The combination of claim 4 wherein said power source includes a DC source series coupled through an AC source to said electrode, said detecting unit coupled between said DC source and a reference point.

7. The combination of claim 6 wherein said detecting unit is a half-wave rectifier.