Portable electrostatic photocopier

The development of a compact non-electrical mains supply based photocopier is described in which a piezo-electric crystal generator or a battery operated capacitor discharge circuit EHT supply is employed for generating the high voltage for charging the photoreceptive paper. The EHT supply for charging the paper is additionally used to provide the source of power for the light source (typically one or more fluorescent gas discharge tubes). The photocopier incorporates all the facilities to charge and subsequently apply toner and fix the latter in place, with a light-proof housing.

FIELD OF THE INVENTION 
This invention concerns electrostatic copying and apparatus therefor. 
BACKGROUND OF THE INVENTION 
The basic principle behind electrostatic photocopying processes is the fact 
that when a paper which is coated with a suitable material such as zinc 
oxide is subjected to an electric charge it will retain that charge unless 
exposed to light. By exposing the paper to light the charge is dissipated 
and this factor can be used to build up an electrostatic image in place of 
an optical image by forming an optical image of a document or scene onto 
the charged paper whereupon the charge will be dissipated in areas of the 
optical image which are brightly lit and will be less dissipated or not 
dissipated at all in areas which are less brightly lit or are dark. The 
paper containing the electrostatic charge pattern can then be placed in a 
solution of carbon black and dispersant or carbon powder can be cascaded 
over the paper and it is found that the carbon black will be attracted to 
those areas which are still charged. If employed the dispersant is then 
allowed to evaporate and the carbon is left on the paper or if a powder 
has been cascaded onto the paper is impregnated into the paper by being 
rolled between rollers which may be heated. 
By using suitable powders and microencapsulated inks, it has been possible 
to dispense with the heated rollers and simply cold roll the paper so as 
to impregnate the latter with the carbon. 
Depending on the way in which the optical image is formed, it may be 
necessary to provide for image reversal within such apparatus and this can 
either be achieved optically by using additional lenses or an intermediate 
plate may be used sometimes in the form of a drum on which the 
electrostatic image is formed and to which the carbon powder or carbon 
black is attracted and against which an ordinary plain piece of paper can 
then be pressed so as to transfer the carbon from the plate or drum to the 
plain paper. 
OBJECTS OF THE INVENTION 
With these points in mind it is an object of the present invention to 
provide a method and apparatus of photocopying which is of general 
application to all photocopiers but is of particular application to an 
apparatus incorporating the minimum of moving parts by which photocopies 
of flat documents can be obtained cheaply and easily. 
It is a secondary object of the invention to provide photocopying apparatus 
which is of a portable nature. 
THE INVENTION 
According to the broadest aspect of the present invention, in photocopying 
apparatus in which a plate (including a sheet of paper or a drum) is 
charged electrically and then exposed to light to form an electrostatic 
charge pattern corresponding to an image which is to be copied for 
attracting thereto powder or encapsulated ink or the like, the 
electrostatic charge to be applied to the plate is developed using a piezo 
electric crystal generator or a capacitor discharge circuit. 
A piezo electric crystal will produce a high voltage if compressed and an 
equal and opposite polarity high voltage when the pressure is released and 
the crystal is allowed to assume its undistorted condition. This dual 
polarity high voltage can be used to advantage by using one polarity to 
charge the plate (i.e. paper or drum etc.) and the other polarity to 
charge the carbon powder or carbon black usually referred to as toner. 
This dual charging action greatly enhances the attraction of the toner 
powder to the charged plate. To this end the apparatus preferably includes 
means for applying a compression force to the crystal and releasing same 
and synchronous means for diverting the charge of one polarity to the 
toner and the charge of the other polarity to the plate. Typically the 
synchronous means for diverting the charges of different polarity comprise 
diodes but alternatively mechanically operated switches operated in 
synchronism with the application and withdrawal of the compression force 
may in addition or alternatively be used. 
In order to produce a uniform charge over the plate whether it be a sheet 
of coated paper or a drum, the electrical output from the generator is 
applied either to a line of charge transmitting elements each operating on 
the so-called points discharge principle and located relative to the 
surface of the drum so that as the latter rotates the charge is 
transferred equally and evenly to the surface of the drum or in the case 
of a plain plate, the transmitter comprises a grid of conducting elements 
such as wires or thin strips of foil and the grid is located above the 
sheet at a distance therefrom such that whilst the electrical charge from 
the grid ionizes the air and transfers to the plate as required, at the 
same time does not produce an in-focus image of itself on the plate when 
the optical image is projected onto the plate after charging. 
Alternatively the charge can be produced from a single point discharge 
device. The use of an earthed frame produces a more even spread of charge, 
the frame comprising a ring of wire or conductive strip material which 
bounds the area over which the charge is to be applied. 
Where a flat plate is incorporated the grid used to charge the plate may 
alternatively be hingeable or slidable between two positions a first 
dormant position which the grid normally occupies (in which it does not 
protrude into the optical system which is incorporated to produce an 
optical image on the charged plate) and a second active position (in which 
the grid is spaced at an appropriate distance from the plate and lies 
fully in the optical system to allow charge to be transferred to the plate 
from the grid). In operation the apparatus is designed to move the grid 
from the dormant position to the active position just prior to the 
generation of the high voltage charge and after the charge has been 
transferred to the plate is adapted to move the grid back to its dormant 
position so that the plate is ready to have the optical image exposed 
thereto. 
The invention will now be described by way of example with reference to the 
accompanying drawings.

Apparatus for producing photocopies from transparencies so that no reversal 
of the image is required is shown in FIG. 1. This first apparatus 
comprises a flat bed of electrically insulating material 10 on which a 
sheet 12 of coated paper can be laid, a piezo electric crystal generator 
14 and a diode 16 and conductors 18 and discharge conductor 20 for 
transferring charge of one polarity from the generator 14 to the paper 12. 
An optical system including a lens 22 produces an image on the coated 
paper 12 after the latter has been charged. Rollers 24, 26 and a bath of 
toner 28 serve to apply a powder or ink to the paper to cause the powder 
or ink to be attracted to those areas of the paper which remain charged 
after exposure to the image and a second roller pair 30, 32 for crushing 
the powder or ink and causing it to become impregnated into the paper to 
fix the powder or ink image. 
The means for applying the powder or ink to the paper may comprise a bath 
through which the paper is drawn or a reservoir of powder or ink having a 
transfer roller for picking up powder or ink and transferring the latter 
to the surface of the paper as the latter is rolled thereover. 
The means rollers 30, 32 for fixing the powder or ink to the surface of the 
paper may be heated by heaters (not shown) or may be cold. Alternatively, 
not shown, an aerosol spray may be provided for forming a quick drying 
transparent film of cellulose or the like over the surface of the paper 
after the carbon or ink has been applied thereto and an image formed 
thereon. 
The document to be copied is laid face down on a glass plate 34 and covered 
by a flexible light-tight cover 36. The document 42 is illuminated by 
fluorescent tubes 38, 40. A reversed image of the document is formed by 
lens 44 on the sheet of charged paper 12. 
The paper 12 can be inserted through an opening 46 and is conveyed to and 
from its position on the plate 10 by transport rollers 48 and 50. 
FIGS. 2 and 3 illustrate a second apparatus which includes a frame 52 for 
holding a transparency and which can be slid into the apparatus to cause 
the transparency to be brought into contact with the sheet of paper 12 on 
which the image is to be formed so as to produce a so-called contact 
print. A number of fluorescent tube lights 54 provide a source of light 
for illuminating a transparency 56 to form an image thereof on the charged 
paper 12 so as to produce an electrical charge pattern required for the 
later stages of the process. 
Alternatively, not shown, the light source may comprise a translucent plate 
through which ordinary ambient lighting can pass. An optical condensing 
system (not shown) may be incorporated so as to produce substantially 
uniform illumination of the transparency from ambient light or from a 
light source incorporating one or more flashlamps or fluorescent tubes. 
My co-pending British Patent Application No. 54099/76 describes a light 
source incorporating a gas discharge tube which may be activated from a 
piezo electric crystal generator and such a light source may be 
incorporated in any of the embodiments herein described, so that a 
secondary source of electricity (either batteries or supply mains) is not 
required for the light source. In fact the same piezo electric crystal 
generator may be employed for charging the toner, the paper (or plate) and 
for energizing the light source. To this end each of the apparatus shown 
in FIGS. 1 to 3 is assumed to have such a source and a switch 58 is 
provided for directing the charge from the electrostatic generator 14 as 
appropriate to the different parts of the apparatus. 
FIG. 3 shows the plan layout within the apparatus of FIG. 2. The frame 52 
can be slid into and out of the housing 60 to locate the transparency 56, 
laid thereon, above the sheet 12. After exposure to the light the frame 52 
is withdrawn. 
A diode 62 (see FIG. 2) ensures that only the appropriate polarity charge 
reaches the tubes 54 and multiple flashes may be employed to increase the 
exposure. 
In FIG. 1 the exposed sheet 12 is then conveyed through the toner rollers 
24, 26 and fixing rollers 30, 32 to produce the photocopy. 
In the embodiment of FIG. 2 a roller or brush 64 loaded with toner is moved 
across the sheet 12 and back to its rest position. Thereafter a roller 66 
loaded with lacquer or simply pressing down on the sheet, is moved over 
the latter and back again to fix the remaining toner onto the sheet, which 
can then be removed as a finished photocopy from the housing 60 by drawing 
out the plate 10 by its handle 68. Handles 70 and 72 are provided on the 
rollers 64 and 66 respectively. 
Where reversal of the image is necessary this can be achieved optically 
using an intermediate lens as in FIG. 1 between the illuminated document 
and the sheet of charged paper. If no optical system is available (as in 
FIG. 2) an intermediate step in the process is required. This entails the 
use of an intermediate plate which may be disposable or comprise part of 
the FIG. 2 apparatus. 
Dealing first with the disposable type of plate, this may comprise a 
transparent or translucent sheet of plastics material or the like one 
surface of which is coated with a suitable material such as zinc oxide 
which can be charged and then exposed to a light image so as to produce an 
electric charge pattern thereon corresponding to the light image as 
previously described. By using a transparent medium to form a first 
photocopy of a reverse image with the coated surface being that which is 
exposed to the light, a transparency can be obtained which can then be 
used in a contact type process in the same apparatus using a sheet of 
ordinary coated paper as the new medium to which the contact light image 
is applied after charging. The sheet of ordinary coated paper after 
exposure is then subjected to toner and fixing as previously described to 
produce a print the correct way round. 
It will be appreciated that the sheet of transparent material may be used 
to produce other prints by the contact process without the need to produce 
one or more intermediate copies and the intermediate process is therefore 
most cost effective when a large number of copies of a single document are 
required. The transparent or translucent intermediate sheet is then 
discarded at the end of the run or can be stored if required for future 
use. 
Where the apparatus is to be used generally and in the main for single 
copies from different documents, the cost of the disposable intermediate 
sheets can be mitigated by using a semi-permanent intermediate sheet of 
suitable transparent or translucent material coated with the suitable 
medium such as zinc oxide and the image formed thereon as previously 
described with reference to the disposable sheet. The intermediate plate 
containing the reversed image is then exposed to the toner and a reversed 
print obtained on the coated surface of the intermediate plate and fixed 
in position using a fixing means which can be removed subsequently so as 
to remove all traces of the powder or ink so as to render the surface 
clean and reusable. To this end an aerosol spray or lacquer roller may be 
used to semi-permanently fix the toner in place so as to produce the 
reverse transparency needed for subsequent contact prints. 
The reverse transparency so produced is then used in conjunction with a 
sheet of coated paper in the same apparatus so as to expose the sheet of 
coated paper (after it has been charged) to an optical image of the 
reversed transparency which when exposed to toner and fixed produces a 
print the correct way round. 
After the appropriate number of copies have been obtained, the surface of 
the intermediate plate can be cleaned and rendered reusable. 
It is of course important that the apparatus previously described (and to 
be described) is contained within a light-tight housing such as 60 (see 
FIG. 2) so that after the coated paper or plate (sometimes referred to as 
a sensitized paper or plate) has been charged electrically, no light falls 
thereon except as provided by the exposure to the optical image of the 
document or transparency to be formed thereon. 
Where an intermediate plate is required and either a disposable or 
semi-permanent plate is used, the size of the latter can be reduced by not 
employing a contact process but by using a lens to form a reduced image of 
the document or scene to be copied and using a disposable or 
semi-permanent intermediate transparent plate of commensurate size with 
the reduced size image. One form of such apparatus is shown in FIG. 4. 
Having exposed the intermediate plate to the reduced size image and 
forming the reversed transparency thereon, the optics can be reversed so 
as to produce an enlarged image of the transparency on a sheet of ordinary 
coated (sensitized) paper which can then be processed to form a print in a 
manner as previously described. 
The apparatus of FIG. 4 comprises a light-tight housing 74 having a glass 
plate 34 and flexible cover 36 for locating a document 42 as in FIG. 1. 
Likewise fluorescent tube lights 38 and 40 are provided for illuminating 
the document and power therefor is obtained from a piezo electric source 
14 when switch 76 is in position (1). 
A lens 78 forms a reduced size image of the document on a small sensitized 
plate 80 carried on a movable support 82. 
A first roller/brush 84 from a toner bath 86 is slidable across the plate 
80 after exposure and a second roller 88 from a lacquer bath 90, for 
temporarily fixing the image on the plate. 
Below the support 82 is a condensing lens assembly 92 and further 
fluorescent tube source 94 and reflector 96. 
In position (2) switch 70 conveys charge from the source 14 to a charging 
conductor 20 and in position (3) switch 76 conveys charge to the tube 94. 
In use a reversed image transparency is first formed on the plate 80, from 
a document 42 located on glass plate 34 underneath flexible cover 36, 
which document is then removed. The switch is then put to position (3) and 
in darkness a sheet of charged sensitized paper is placed face down on the 
glass plate 34, so that when the source 14 is operated the light from 94 
forms an image of the transparency on the sensitized paper, which can then 
be processed through a toner bath and fixer (not shown) to produce a 
finished photocopy. 
The advantage of this particular method is that if a lens is to be employed 
to reverse an image so as to obtain a full size reversed image the spacing 
between the document to be copied and the plate or sheet of paper must be 
twice the focal length of the lens. Since a fairly long focal length lens 
will normally have to be employed, the apparatus is liable to become 
cumbersome in size if such a distance has to be employed and by adopting 
this alternative method, a smaller focal length lens may be used with no 
degradation of optical quality. 
In another method which may be based on the full sized contact reversal 
process previously described or may incorporate a reduced size 
intermediate plate as just described with reference to FIG. 4, the 
intermediate plate may be formed by exposing a charged surface to the 
light image, applying toner thereto but instead of fixing the toner in 
place, applying a sheet of transparent material having a suitable adhesive 
transparent backing onto the said surface (with the adhesive side in 
contact with the said surface) thereby to pick up the toner remaining on 
the charged areas of the surface. The transparent sheet can then be 
removed from the said surface and the toner adhering to the adhesive 
backed surface thereof fixed in place by means of a second sheet of 
transparent material which may or may not incorporate an adhesive surface 
but if it does the two sheets of transparent material are located so that 
the two adhesive backed surfaces are in contact. The toner adhering to the 
first adhesive surface is trapped between the two sheets of transparent 
material and a transparency is thereby formed which can then be used for 
projection purposes to form either a full sized contact print or where a 
reduced size image has been used, either to produce a reduced sized 
contact print or by suitable enlargement a full size or even enlarged size 
print on a sheet of coated paper. The surface which is charged may 
subsequently be cleaned as by a traversing roller or brush before being 
re-charged for subsequent exposures. 
Apparatus for performing the method just outlined is shown in FIGS. 5 and 
6. This apparatus is very similar to that shown in FIG. 4 and the same 
reference numerals have been used to depict items in common. The chief 
differences lie in the provision of 
(a) a cleaning roller/brush 98 in place of the lacquer roller 88, by which 
the surface of the sensitized plate 80 can be thoroughly cleaned of toner 
powder, 
(b) a roll 100 (see FIGS. 6 and 7) of adhesive backed transparent sheet 
(similar to Sellotape (Registered Trade Mark) with means (not shown) for 
drawing the tape over the plate 80 and lowering the tape with the adhesive 
side on the underside into contact with the toner marked charge pattern on 
the plate (after the latter has been exposed and toner applied thereto by 
toner roller 84). 
(c) a second roll 102 of non-adhesive backed transparent tape, 
(d) a pair of rollers 104, 106 forming a nip between which the two 
transparent sheets are squeezed, with the adhesive layer in contact with 
the upper side of the non-adhesive sheet, so that the two are stuck firmly 
together and the toner powder adhering to the underside of the first sheet 
is sandwiched firmly therebetween, and 
(e) a guillotine 108 (see FIG. 7) for severing the region of the sheet 
bearing the "transparency". 
By removing the plate support 82 and plate 80 and inserting in place the 
transparency and with switch 76 in position (3), a sheet of charged 
sensitized paper placed on glass plate 34 can be exposed to the 
transparency and subsequently processed through a toner bath and fixed as 
previously described. 
It is to be understood that this last aspect is not limited to the use of 
coated paper as the final medium for impressing the final image thereon 
but can also be used with a plain paper copier in which an intermediate 
member such as a plate or drum or the like is used. 
Where a full size reverse plate or a suitable master document is available 
so that it can be laid in contact with a sheet of sensitized paper in a 
reflex image forming technique the flat surface on which it is laid may 
comprise the light source and may comprise a translucent sheet with one or 
more point light sources behind it or may comprise a sheet of 
semi-conductor material which glows when a suitable potential is applied 
thereto. However it is to be understood that the invention is not limited 
to any particular form of light source or any particular form of producing 
uniform illumination of the said flat bed. 
The procedure for forming an image on a charged sheet by a reflex process 
is then as follows: 
1. The sheet of coated paper is laid on the flat bed and in complete 
darkness is charged electrically. 
2. Still in complete darkness the document which is to be copied is laid 
face down onto the charged surface with the printing or other material 
which is to be copied in contact with the charged surface. 
3. The reverse side of the coated or sensitized paper is then exposed to 
light for a prescribed interval of time. 
4. Again in the dark, the document is removed and toner powder applied 
thereto. 
5. The toner powder which adheres to the charged areas on the paper is then 
fixed in position either by being rolled so as to impregnate the paper or 
sprayed with a quick drying material which produces a transparent film 
over the entire surface of the paper and may for example comprise 
cellulose or an aerosol. 
6. Alternatively instead of fixing the toner powder on the sheet of paper, 
a sheet of adhesive backed transparent material such as a sheet of 
Sellotape (Registered Trade Mark) or the like is applied to the surface of 
the sensitized paper containing the toner image so that the toner 
remaining on the paper is picked up by the adhesive backed transparent 
medium. The picked-up toner can be fixed in position by peeling the 
adhesive backed material from the sensitized paper and sticking the 
adhesive backed surface onto another sheet of transparent material which 
may be plain or may itself have an adhesive surface which is laid in 
contact with the adhesive surface bearing the toner of the first 
transparent sheet material. 
The transparency so produced can then be used to produce positive prints by 
any convenient photocopying process including those described above, on 
suitable paper.