Electrostatic copying machine having flash-discharge-lamp fixing unit

A lamp of low ozone generation is used as the flash lamp, to minimize the amount of ozone reaching the machine exterior. A first cooling-air passage includes the space surrounding the flash lamp and its reflector and is provided downstream thereof with an activated-carbon filter, from which is discharged a quite hot first cooling-air stream of low volumetric flow rate. A second cooling-air stream emerging from the electronics compartment of the machine is much cooler and cleaner and of high volumetric flow rate. The first and second cooling-air streams are mixed together, to dilute and cool the first, prior to actual discharge to the machine exterior. The mixed air streams are discharged in downwards direction.

BACKGROUND OF THE INVENTION 
The present invention relates to electrostatic copying machines of the type 
provided with flash-lamp fixing units. The flash lamp of the fixing unit 
emits a brief intense flash of radiant energy which raises the toner of 
the toner image on the copying medium to melting temperature and causes 
the toner image to be fused. 
Copying machines of this type, provided with so-called flash-lamp fixing 
units, are disclosed for example in German allowed patent application No. 
1,063,029, German published patent application No. 1,597,898 and German 
published patent application No. 1,908,827. It has been found that the 
performance of a flash fixing operation requires the use of high-energy 
flashes of radiation. As a result, when a flash operation is performed, a 
very sizable quantity of ozone may be generated in the air surrounding the 
flash lamp. Also, the intensity of the flash irradiation can result in 
partial decomposition of the relatively complex plastics of which the 
toner powder may be comprised into constituent components which, 
particularly if they vaporize, can be dangerous to inhale. If the number 
of flash operations performed per unit time are increased beyond a certain 
limit, the amount and concentration of environmentally undesirable and 
health-injurious ozone and toner vapors discharged to the exterior of the 
machine can become very serious. 
SUMMARY OF THE INVENTION 
It is a general object of the invention to be able to provide a copying 
machine of the type having a flash-lamp fixing unit which does not thusly 
threaten the environment and health, even if flash operations are 
performed at high frequency. 
According to one concept of the invention, use is made of a flash lamp of 
low ozone generation. Furthermore, the space surrounding the reflector and 
flash lamp forms a cooling-air passage through which cooling-air is 
driven. In this passage, downstream of the flash lamp and reflector, there 
is provided a filter. Preferably, the flash lamp is an 
ultraviolet-filtered flash lamp, e.g., a flash lamp surrounded by a layer 
of UV-absorptive quartz, and the filter is an activated-carbon filter. 
With this arrangement, the generation of ozone in the vicinity of the flash 
lamp is minimized, even if flashes of very high energy are being produced. 
Any toner vapors which are generated as a consequence of the intense 
irradiation of the toner image are removed from the stream of cooling air, 
prior to the discharge of the cooling air to the machine exterior. 
According to a particularly advantageous concept of the invention, the flow 
of cooling air through the interior of the copying machine is divided into 
at least two parts, the first of which passes through the space 
surrounding the flash lamp and reflector, as just mentioned. The provision 
of an activated-carbon filter at the downstream end of the first 
cooling-air passage results in a cooling-air flow of low volumetric flow 
rate. In contrast, the volumetric flow rate of the second stream of 
cooling air is much higher. The two streams of cooling air, one of low the 
other of high volumetric flow rate, are continually mixed together, prior 
to their discharge to the machine exterior. Preferably, inclined discharge 
guide plates discharge the mixed cooling-air streams to the machine 
exterior with a slightly downwardly inclined direction. Advantageously, 
the second cooling-air stream passes through the interior of the 
electronics compartment of the copying machine. 
With this expedient, the relatively hot and relatively 
low-volumetric-flow-rate stream of cooling air discharged from the outlet 
side of the filter is not discharged directly to the machine exterior. If 
this were done, then because of its high temperature and its low flow 
speed, it would, as soon as it left the discharge slots of the machine 
housing, rise up as a more or less cohesive cloud of gases and vapors, and 
could be easily inhaled by persons standing nearby. If that were the case, 
then even the presence of quite low residual amounts of pollutants could 
lead to irritation of the respiratory systems of such persons. Therefore, 
according to the inventive concept, this low-volumetric-flow-rate stream 
of hot cooling air, before being discharged to the machine exterior, is 
continually mixed into the high-volumetric-flow-rate stream of much cooler 
and cleaner air coming from, for example, the electronics compartment of 
the copying machine. As a result, the first air stream is very 
considerably diluted by the second air stream, prior to discharge. 
It is furthermore contemplated that the thusly mixed cooling streams be 
discharged through a discharge grill comprised of downwardly inclined 
guide plates, so that the discharged air be discharged downwards, e.g., 
towards the floor where it cannot be directly inhaled. By the time such 
discharged cooling air rises to the level where it can be inhaled, it will 
be still further diluted by ambient air. When this is done, then even if 
quite considerable quantities of health-injurious gases or vapors are 
contained in the air discharged from the filter, the concentration of such 
pollutants in the air of the room containing the copying machine, 
particularly, at the level where such air can be inhaled, will be very 
low, and inhalable without the possibility of respiratory irritation. 
The reflector housing surrounding the flash lamp is so designed that the 
radiation emitted by the lamp is distributed very uniformly upon that 
surface portion of the copying medium whose toner image is to be fixed. 
This expedient, too, contributes to the possibility of safely increasing 
the speed of the fixing operation. Due to the avoidance of loading spikes, 
as a consequence of the uniform irradiation implemented by such a 
reflector, the total amount of flash energy applied to the toner image to 
be fixed can be increased, without increasing any of the problems 
discussed above. 
As flash lamp of low ozone generation preferably a gas discharge lamp, 
e.g., a Xenon lamp, is used which is surrounded by a filter absorbing all 
UV-light with a wave length smaller than 250 nm (nanometers).

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Numeral 1 denotes the housing of an electrostatic copying machine. A 
copying drum 2 is mounted in the housing for rotation in the direction of 
arrow A. An optical system projects the image of an original 8 onto the 
photoconductive surface of the drum 2, during the course of a copying 
operation. The optical system includes a stationary objective 6 and a 
stationary deflecting mirror 6a, as well as a deflecting mirror 3 and 
light sources 9 which travel in the direction B, and a pair of deflector 
mirrors 4, 5 which likewise travel in direction B. The optical system per 
se is conventional and not described in detail here, except to note that 
during the course of a copying operation, the travelling units 3, 9, 9 and 
4, 5 more leftward in the direction of arrow B, at different speeds, from 
the illustrated solid-line positions to the illustrated dash-dot-line 
positions, and then return to their solid-line positions for the copying 
of the next original 8. The original 8 to be copied rests on a transparent 
support plate 7. 
A corona-discharge unit 10 is located at the periphery of copying drum 2, 
upstream of the location where exposure light is incident upon the drum. 
Corona-discharge unit 10 serves to uniformly charge up the surface of the 
copying drum, preliminary to its exposure to copying light. A developer 
unit 11 is located downstream of the exposure sector of drum 2, and serves 
to apply toner to and develop the latent electrostatic image on the 
surface of the drum. Located beneath developer unit 11 is a supply stack 
12 of sheets of copying paper. A feeder 13 feeds these sheets one at a 
time into a pair of transport rollers 14. The transport rollers 14 
transport the sheet of copying paper through the space between the drum 2 
and a corona-discharge image-transfer unit 15. The latter transfers the 
toner image from the surface of the copying drum to the surface of the 
sheet of copying paper 31. Downstream of image-transfer unit 15, a 
corona-discharge take-off unit 16 cancels the electrostatic force of 
attraction between the drum surface and the sheet 31, which force develops 
during the image-transfer operation, so that the sheet can be removed from 
the copying drum and fed into a fixing unit. 
The fixing unit includes a flash lamp 17. The flash lamp 17 fixes the toner 
image by producing a series of brief high-energy flashes. The toner, due 
to its relatively dark color, is preferentially or selectively heated by 
absorption of the infrared radiation contained within these flashes. The 
toner may comprise, for example, thermosplastic synthetic plastic and 
carbon black. The flash-type fixing operation brings the toner up to its 
melting temperature, so that it fuses upon the sheet of copying paper 31. 
In contrast, the white copying-paper stock reflects radiation and 
therefore is heated relatively little. The limited heating of the copying 
paper stock reduces the danger of scorching, and significantly enlarges 
the range of copying-paper types from which one may choose. In particular, 
it becomes possible to use copying stock of greatly varying heat capacity, 
mainly determined by the thickness and moisture content of the stock, 
because the success of the flash fixing operation does not require that 
the copying stock itself be brought up to any particular temperature. 
Likewise, the color of the copying stock no longer plays an important 
role, so long as its absorption spectrum does not approach that of the 
toner. Instead of being limited to smooth, white copying stock, use can be 
made, for example, of rough brown or gray paper, such as wrapping paper, 
or even transparent material. Furthermore, because of the low degree to 
which the copying stock itself becomes heated, the fixing operation cannot 
result in warping, curling or other mutilation such as could make the 
stock useless for furter processing, e.g., if the copying stock is in the 
form of perforated cards, or the like. Likewise, if the copying stock is 
provided on its back with a self-adhesive layer or with an 
impression-transfer layer, these layers will not be raised to temperatures 
at which they could soften. 
The flash lamp 17 is surrounded from above by a reflector 27. Below the 
reflector 27, guide wires 18, 19, which do not absorb the emitted 
radiation, define the transport path for the copying sheet 31, as the 
latter travels through the fixing station. The reflector 27 itself forms 
part of a cooling-air channel 21 containing a fan 20. Fan 20 sucks in air 
from the exterior of the machine, draws the air through apertures in the 
reflector 27 and transmits this air to a filter 22 filled with active 
carbon. Downstream of the carbon filter 22, the air drawn through the 
flash-lamp compartment enters a mixing chamber 23, into which likewise 
opens a further cooling-air channel 24. The latter contains a fan 25 which 
draws air from the outside of the copying machine into and through a 
compartment 26. Compartment 26 is sealed off from the remainder of the 
interior of the copying machine and contains the control and safety 
circuitry of the machine. The cooling air drawn through electronics 
compartment 26 is heated by the electronic cirucuitry to a comparatively 
small extent, and does not pick up gases or vapors which are hazardous to 
health. This clean and only somewhat warmed cooling air can be discharged 
in unfiltered condition to the exterior of the copying machine. Thus, 
whereas the cooling air discharged from the flash-lamp compartment is 
slowed down in passing through carbon filter 20, that discharged from the 
electronics compartment 26 can be freely discharged at high speed through 
the discharge openings defined by inclined discharge guide plates 28. The 
guide plates 28 determine the direction in which the cooling air is 
discharged, and this direction is maintained even for a certain time after 
the cooling air has been discharged from the machine. 
The high-volumetric-flow-rate air stream discharged from electronics 
compartment 26 is mixed, in mixing chamber 23, with the much hotter 
low-volumetric-flow-rate air stream discharged from the outlet face of 
carbon filter 20, before both air streams are discharged to the machine 
exterior. This prevents undiluted air from the carbon filter 20 from being 
directly discharged to the machine exterior in undiluted condition, where 
it could rise up into the nostrils of an operator standing nearby. With 
the illustrated expedient, an operator who works near the machine will not 
be irritated by any small residues of pollutants which may be present in 
the relatively hot air discharged from the carbon filter 20, first because 
this hot and possibly somewhat polluted air is mixed with a much greater 
quantity of relatively cool and clean air prior to discharge, and second 
because the high-volumetric-flow-rate discharge of the mixture causes the 
mixture to become quickly mixed with, and diluted by, the ambient air. 
This is particularly the case when as illustrated, guide plates 28 
initially direct the discharged cooling air downward. 
When the copying sheet 31 emerges from the fixing station, it is engaged by 
outfeed transport rollers 29 and is deposited into an outfeed bin 30. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
particular type of electrostatic copying machine, it is not intended to be 
limited to the details shown, since various modifications and structural 
changes may be made without departing in any way from the spirit of the 
present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.