Charging apparatus for electro-photographic copying device

Abstract

The invention is a process for the production of electro-photographic positive prints from positive and for negative originals with one and the same developer. The photo-conductor is charged with a polarity according to the nature of the original. The apparatus used for photocopying is adapted so that the charging polarity can be selected in dependance upon the nature of the original being copied.

Parent Case Text

This is a division of application Ser. No. 163,283, filed July 16, 1971.

Description

The invention relates to a process and apparatus for the production of electro-photographic pictures, positive pictures being obtained both from positive and from negative originals.

The necessity of enabling the electro-photographic process to take place both on the positive-positive and on the negative-positive principle is felt particularly in connection with the re-enlargement of micro-films. For this purpose, methods are known in which the developer of the appratus is changed, in that a developer with a negatively or with a positively charged toner is used, according to the nature of the film.

The operation of changing the developer involves complicated manipulations, e.g. the dismantling of the developing apparatus, the unclamping and re-clamping of flexible tube connections and the cleaning of large portions of the interior of the apparatus, as the same developer is used in each case.

The purpose of the invention is to simplify the production of electro-photographic positive prints from positive and from negative originals.

OBJECT OF THE INVENTION

The object on which the invention is based is that of devising a process and an apparatus to enable the electro-photographic process to be adapted to the character of the original. SUMMARY OF THE INVENTION

The invention enables this object to be achieved by providing an electrophotographic apparatus for the production of positive prints from positive and from negative originals with the same developer; including:

A. means for providing actinic light from an original to be copied;

B. a photoconductor for receiving said actinic light;

C. charging means positioned near to the photoconductor, for charging the photoconductor;

D. electrical circuit means for providing said charging means with a charging potential, including a charge polarity reversing switch connected with the charging means to enable the photoconductor to be charged selectively with a first polarity when a positive original is to be copied and with the opposite polarity when a negative original is to be copied;

E. light adjusting means associated with said means for producing actinic light and coupled to said charge polarity reversing switch for adjusting said actinic light when said charge polarity is reversed by said reversing switch.

Alternatively, the invention enables the object to be achieved by providing an electrophotographic apparatus for the production of positive prints from positive and from negative originals with the same developer, including:

A. means for providing actinic light from an original to be copied;

B. a photoconductor for receiving said actinic light;

C. a charging electrode positioned near to the photoconductor, for charging the photoconductor;

d. electrical circuit means for providing said charging electrode with a charging potential, including a transformer having a primary winding connectable with an alternating voltage source, and a secondary winding connected with the charging electrode via a charge polarity reversing switch to enable the photoconductor to be charged selectively with a first polarity when a positive original is to be copied and with the opposite polarity when a negative original is to be copied, said primary winding having a tapping point thereon;

e. charge potential adjusting means including a switch actuable by said charge polarity reversing switch adapted to connect the alternating voltage source selectively across the whole winding or part of the winding via said tapping point for adjusting said charge potential when said charge polarity is reversed by said reversing switch.

Further alternatively, the invention enables this object to be achieved by providing an electrophotographic apparatus for the production of positive prints from positive and from negative originals with the same developer, including:

a. means for providing actinic light from an original to be copied;

b. a photoconductor for receiving said actinic light;

c. a charging electrode positioned near to the photoconductor, for charging the photoconductor;

d. electrical circuit means for providing said charging electrode with a charging potential, including a transformer having a primary winding connectable with an alternating voltage source, and a secondary winding connected with the charging electrode via a charge polarity reversing switch to enable the photoconductor to be charged selectively with a first polarity when a positive original is to be copied and with the opposite polarity when a negative original is to be copied;

e. charge potential adjusting means comprising a changeover switch connected between the secondary winding and the charging electrode actuable by said charge polarity reversing switch and a resistive element connectable between the secondary winding and the charging electrode by said change-over switch whereby said change-over switch effects connection of the secondary winding selectively with the charging electrode either directly or via the resistive element for adjusting said charge potential when said charge polarity is reversed by said reversing switch.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIG. 1: a device for reversing the charging polarity, with adaptable charging voltage.

FIG. 2: a device with a modifiable screening potential.

FIG. 3: a device with a modifiable operating voltage for the source of illumination.

FIG. 4: a device with a grey filter which can be pivoted into positon.

DESCRIPTION OF PREFERRED EMBODIMENT

According to FIG. 1, a charging electrode 1 for a selenium drum 2 is connected with a pole reversing switch 3 with a high tension transformer 4 has a primary winding (connectible with an alternating voltage source 15) and a secondary winding 16 connected to the pole reversing switch 3. The primary winding 14 is provided with a tapping point 17 to which the alternating current source can be connected by means of a switch 5, operatively coupled with the reversing switch 3 by way of a coupling shown diagramatically at 18.

In the embodiment shown in FIG. 2 a change-over switch is connected between the secondary winding 16 and the screen 8 of the charging electrode 1. The change-over switch is actuable by the polarity reversing switch 3 by way of a coupling shown diagramatically at 19.

A resistor 7 can be connected between the secondary winding 16 and the screen 8 of the charging electrode 1 by the change-over switch 6 whereby the change-over switch 6 effects connection of the secondary winding 16 and earth potential selectively with the screen 8 of the charging electrode 1 either directly or via the resistor 7.

In the embodiment shown in FIG. 3 an actinic light source 11 is connected to a source of supply potential U.sub.L and arranged to illuminate the original 20. A resistor 10 can be connected between the light source 11 and the source of potential supply U.sub.L by a change-over switch 9 which is operatively coupled with the polarity reversing switch 3 by way of a coupling shown diagramatically at 21. The change-over switch 9 selectively connects the light source 11 with the supply potential U.sub.L directly on via the resistor 10.

In the embodiment shown in FIG. 4 a grey filter 12 can be moved into and out of the path of the actinic light from the light source 11. The grey filter 12 is operatively coupled with the polarity reversing switch 3 by way of a coupling shown diagramatically at 22.

The method of operation is as follows:

The high-tension apparatus 1 generates a non-earthed high tension of, for example, 7.2 KV, of which the negative pole, when the selenium drum 2 is being charged negatively, is connected via the pole reversing switch 3 to the charging electrode 1, while the positive pole is earthed. By moving over the pole reversing switch 3 the positive pole of the high-tension apparatus can be connected to the charging electrode 1 and the negative pole to earthed potential. In this process the adjustment of the pole reversing switch 3 causes the switch 5 to connect the supply source 15 to the tapping point 17 which results in a reduction of the output voltage of the high-tension apparatus to 5.8 KV, for instance, owing to the reduction of its primary voltage. These different high tensions result in different charging currents, by which the influence of the polarity-governed charging characteristic of the selenium drum 2 is compensated and a constant initial voltage obtained.

If, in another selenium drum, the difference of the charging current required in the event of opposite charging polarity is smaller, then the operation, as shown in FIG. 2 is as follows, with the high tension when the selenium drum 2 is being charged negatively the current produced by the charging electrode is increased as a result of the fact that a potential intermediate between that of the corona wire and that of the selenium layer is supplied to the screen 8 via a resistor 7.

It is also possible for a selenium drum to have polarity-governed discharge characteristics in addition to the polarity-governed charging characteristics. The reduction of an initial potential in the selenium drum from 500 V to 100 V, for instance, is effected, with a positive charge, by an exposure of 22 lxs (lux-seconds), while in the event of a negative charge an exposure of 56 lxs is required. In order to take account of these requirements, the switch 9, which is shown in FIG. 3, is coupled with the pole reversing switch 3, and is the means by which, the event of charging the selenium drum positively, the resistor 10 is connected into the current circuit of the light source 11 in order to reduce the light flux.

According to FIG. 4, the exposure of the selenium drum 2 can also be reduced when the selenium drum is being charged positively by moving the grey filter 12 into the path of the exposure rays.

Claims

I claim:

1. An electrophotographic apparatus for the production of positive prints from positive and from negative originals with the same developer, including:

a. means for providing actinic light from an original to be copied;

b. a photoconductor for receiving said actinic light;

c. a charging electrode positioned near to the photocondutor, for charging the photoconductor;

d. electrical circuit means for providing said charging electrode with a charging potential, including a transformer having a primary winding connectable with an alternating voltage source, and a secondary winding connected with the charging electrode via a charge polarity reversing switch to enable the photoconductor to be charged selectively with a first polarity when a postive original is to be copied and with the opposite polarity when a negative original is to be copied, said primary winding having a tapping point thereon;

e. charge potential adjusting means including a switch actuable by said charge polarity reversing switch adapted to connect the alternating voltage source selectively across the whole winding or part of the winding via said tapping point for adjusting said charge potential when said charge polarity is reversed by said reversing switch.

2. An electrophotographic apparatus for the production of positive prints from positive and from negative originals with the same developer, including:

a. means for providing actinic light from an original to be copied;

b. a photoconductor for receiving said actinic light;

c. a charging electrode positioned near to the photoconductor, for charging the photoconductor;

d. electrical circuit means for providing said charging electrode with a charging potential, including a transformer having a primary winding connectable with an alternating voltage source, and a secondary winding connected with the charging electrode via a charge polarity reversing switch to enable the photoconductor to be charged selectively with a first polarity when a positive original is to be copied and with the opposite polarity when a negative original is to be copied;

e. charge potential adjusting means comprising a change-over switch connected between the secondary winding and the charging electrode actuable by said charge polarity reversing switch and a resistive element connectable between the secondary winding and the charging electrode by said change-over switch whereby said change-over switch effects connection of the secondary winding selectively with the charging electrode either directly or via the resistive element for adjusting said charge potential when said charge polarity is reversed by said reversing switch.

3. An electrophotographic apparatus for the production of positive prints from positive and from negative originals with the same developer, including:

a. means for providing actinic light from an original to be copied;

b. a photoconductor for receiving said actinic light;

c. charging means positioned near to the photoconductor, for charging the photoconductor;

d. electrical circuit means for providing said charging means with a charging potential, including a charge polarity reversing switch connected with the charging means to enable the photoconductor to be charged selectively with a first polarity when a positive original is to be copied and with the opposite polarity when a negative original is to be copied;

e. light adjusting means associated with said means for producing actinic light and coupled to said charge polarity reversing switch for adjusting said actinic light when said charge polarity is reversed by said reversing switch.

4. An apparatus according to claim 3, wherein the electrical circuit means includes a transformer having a primary winding connectible with an alternating voltage source and a secondary winding, said polarity reversing switch being connected with the secondary winding and said charging means comprising a charging electrode connected with the secondary winding via said polarity reversing switch.

5. An apparatus according to claim 3, wherein the light adjusting means comprises a Grey filter coupled with the polarity reversing switch and movable into and out of the path of actinic light by operation of said polarity reversing switch.

6. An apparatus according to claim 3, wherein said means for providing actinic light includes a light source connectible with a source of supply potential and arranged to illuminate the original, a resistive element connectible between the light source and said source of supply potential and a change over switch actuable by said polarity reversing switch and adapted to selectively connect the light source with the source of supply potential directly or via the resistive element whereby the intensity of illumination of the subject is changed to effect adjustment of actinic light.