Title: Transfer humidity control device

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Claims: What is claimed is:

1. In an electrostatographic copying system wherein an image on an initial image support is transferred to a second image support by variable transfer means, which transfer is affected by variations in the conductivity of the second image support, wherein said transfer means includes a transfer corona generator means to which a first voltage is applied for applying transfer charges to said second image support, and wherein said transfer means includes an auxiliary transfer corona generator means to which a second voltage is applied for applying pre-transfer charges to said initial image support, the improvement comprising:

conductivity sensing means for sensing the conductivity of the second image support prior to said transfer;

and transfer control circuit means controlled by said conductivity sensing means for varying both said first and second voltages applied to said transfer corona generator means and to said auxiliary transfer corona generator means in response to variations in the conductivity of the second image support sensed by said conductivity sensing means.

2. The electrostatographic copying system of claim 1, wherein said second image support is an individual copy sheet,

and wherein said sensing means is adapted to measure the conductivity of said copy sheet for a predetermined substantial length thereof as said copy sheet is moved past said sensing means, and

wherein said transfer control circuit means includes integration means for integrating the output of said sensing means over said predetermined length of the copy sheet to provide an averaged conductivity measurement for said copy sheet.

3. The electrostatographic copying system of claim 1,

wherein said second image support is a copy sheet being moved toward said transfer means,

wherein said conductivity sensing means comprises an opposing pair of overlying conductive rollers positioned upstream of said transfer means in the direction of the copy sheet movement toward said transfer means,

wherein said conductive rollers are positioned to forcibly engage an intermediate portion of the copy sheet therebetween and roll along directly opposing areas of opposite sides of said copy sheet in pressure engagement therewith,

said copying system further including current means for passing current between said opposing conductive rollers through the copy sheet engaged therebetween,

and limiting means for limiting the period during which said current is passed through the copy sheet between said rollers to a pre-set period corresponding to a substantial predetermined length of the copy sheet being moved between said rollers towards said transfer means, and

averaging means for averaging the current passed through said copy sheet between said rollers during said pre-set period to provide an averaged conductivity measurement of said pre-determined length of the copy sheet.

4. The electrostatographic copying system of claim 1, wherein said transfer control circuit means is connected to change at least one of said first and second applied voltages to said transfer corona generator means and said auxiliary transfer corona generator means from a direct current to an alternating current in response to a predetermined substantial change in conductivity of the second image support sensed by said conductivity sensing means.

5. The electrostatographic copying system of claim 4, wherein said transfer control circuit means is further connected to change at least one of said first and second applied voltages between at least two substantially different direct current voltage levels in response to a difference in conductivity of the copy sheet sensed by said conductivity sensing means.

6. The electrostatographic copying system of claim 1, wherein said transfer control circuit means is adapted to apply a said first applied voltage to said transfer corona generator means selected from an alternating current voltage and at least two different levels of direct current voltages, with said selection being controlled by said conductivity sensing means.

7. The electrostatographic copying system of claim 6, wherein said transfer control circuit means is additionally adapted to simultaneously apply a said second voltage to said auxiliary transfer corona generator selected from a direct current voltage and an alternating current voltage and no voltage.

8. The electrostatographic copying system of claim 1,

wherein said transfer control circuit means comprises at least four selectively actuatable switching means actuated in response to at least four different levels of conductivity of said second image support sensed by said conductivity sensing means, and

wherein said switching means connects with said transfer means to apply at least four different selected combinations of first and second applied voltages to said transfer means to compensate for the conductivity of said second image support.

9. The electrostatographic copying system of claim 8, wherein said first and second applied voltages include alternating current voltages and different levels of direct current voltages applied in response to different levels of conductivity sensed by said conductivity sensing means.

10. In an electrostatographic copying method wherein an image on an initial image support is transferred to a second image support by variable electrostatic transfer means, which transfer is affected by variations in the conductivity of the second image support, wherein said transfer means includes a transfer corona generator means to which first voltage is applied for applying transfer charges to said second image support, and wherein said transfer means further includes an auxiliary transfer corona generator means to which a second voltage is applied for applying pre-transfer charges to said initial image support, the improvement comprising:

sensing the conductivity of the second image support prior to said transfer; and

varying both said first and second voltages applied to said transfer corona generator means and said auxiliary transfer corona generator means in response to variations in the conductivity of the second image support sensed by said conductivity sensing means to compensate for variations in the second image support.

11. The electrostatographic copying method of claim 10, wherein said second image support is an individual copy sheet,

wherein the copy sheet is moved past said conductivity sensing means into said transfer means, and

wherein the conductivity of the copy sheet is measured for a predetermined substantial length thereof as the copy sheet is moved past said sensing means, and

wherein the output of said sensing means is integrated over said predetermined length of the copy sheet moved past said sensing means to provide an averaged conductivity measurement for said copy sheet.

12. The electrostatographic copying method of claim 10, wherein at least one of said first and second applied voltages to said transfer corona generator means and said auxiliary transfer corona generator means is changed from a direct current to an alternating current in response to a predetermined substantial change in conductivity of the second image support sensed by said conductivity sensing means.

13. The electrostatographic copying method of claim 12, wherein at least one of said first and second applied voltages is changed between at least two substantially different direct current voltage levels in response to a difference in conductivity of said second image support sensed by said conductivity sensing means.

Other info:

Inventors: Watanabe, Toshio (Ebina, JP)

Application Number: 832032
Filing Date: 1977-09-09
Publication_date: 1979-01-09
Assignee: Rank Xerox Limited (London, GB2)
Primary Class(es): 361/235 399/311
Other Classes:
US Patent Ref:

3816756

Jun, 1974

Bresnick

361/235.

Other Refs: Other References: Eastman Kodak Research Disclosure, 1/75, pp. 16-17.