Note: Descriptions are shown in the official language in which they were submitted.
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Method for treating an item
The invention relates to a method of altering the properties, at least in a
part-region, of and/or for
treating an item as defined by the characterising features of claim 1, and a
system for altering the
properties, at least in a part-region, of and/or for treating an item by
irradiation as defined in
claim 40.
Processing products of the most varied of species by irradiation using the
most varied of sources,
e.g. 'y or electron radiation, is a method which has become increasingly
commonplace in recent
years. By using high-energy radiation, this method can also be used as a means
of sterilising pro-
duce. However, in addition to flushing with toxins such as methyl bromide or
ethylene oxide,
irradiation to date has involved the use of radioactive isotopes such as
cobalt 60 or caesium 137
primarily as a means of achieving an increase in quality. Although methods of
this type are ef
fective in killing microbes, bacteria and germs to a high degree, it must
always be borne in mind
that the beam source is constantly activated and can not be "simply" switched
off, so that the
maintenance inspections required in these systems present a constant potential
risk to mainte-
nance personnel. Furthermore, irradiation techniques of this type are not
without controversy, at
least in the media world, making it very difficult to market produce treated
in this way. Moreo-
ver, essential vitamins, minerals and nutrients are lost. An irradiation
system of this type is
known from US 3,564, 241 A, for example. This document discloses a plant in
which produce of
all types is loaded in baskets mounted on overhead rails, in readiness for
sterilisation. The bas-
kets are fed on these rails into the interior of a radiation chamber, where
they are irradiated from
both the front and the rear with cobalt 60, depending on the selected layout
of the guide rails.
In order to avoid the above problems, the irradiation method was improved so
that heated cath-
odes were used as the beam source instead of radioactive material. The
electrons emitted from
the cathode are accelerated towards the anode and focussed, before being
finally deflected on to
the products to be sterilised. Practice has shown that the products can be
sterilised to a degree
comparable with that achieved using a radioactive irradiation process. A
system of this type is
known from WO 94/22162 A. Apart from the nature of the beam source, this
system is compara-
ble with that disclosed in the above-mentioned US-A system in terms of
structure. Here too, the
produce is loaded into baskets guided on a rail and conveyed through the
processing chamber.
The disadvantage of using this system to convey the products is that, due to
the selected con-
CA 02319344 2000-08-04
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veyor system, specific parts of the conveyor baskets which are repeatedly
subjected to constant
irradiation have a higher tendency to wear.
The underlying objective of the present invention is to propose a method and a
system for irradi-
ating an object, which enables objects to be treated and/or their properties
to be altered at least in
a part-region, by irradiation, in order to produce uniform exposure to
electrons across as large a
volume as possible.
This objective is achieved by the invention due to the characterising features
of claim 1. The
first advantage of using this type of method is that produce of the most
varied of types, for exam-
ple foodstuffs such as spices, water or similar, substances such as plastics,
ceramics, metals or
similar, can be irradiated in such a way that a significant improvement in
quality is obtained. An-
other advantage is the fact that the electron radiation can be pulsed at a pre-
definable frequency,
which assists in distributing the dose uniformly in the object to be
irradiated.
Another advantageous embodiment is defined in claim 2, enabling high-energy
electrons to be
accelerated in a simple manner.
The embodiment defined in claim 3 provides a capacity in which the
electromagnetic waves gen-
erated can be propagated in the form of a stationary wave.
Claims 4 and 5 outline advantageous embodiments whereby a simple and safe
operating technol-
ogy can be used to accelerate the electrons on the one hand and amplify the
effect of acceleration
on the other.
Claim 6 defines an advantageous embodiment designed to further enhance the
uniformity of the
dose distributed in the object to be irradiated.
Also of advantage is an embodiment defined in claim 7, since it provides
electrons with an en-
ergy which further enhances safety whilst producing the desired effect in the
object to be irradi-
ated.
The embodiments defined in claims 8 and 9 advantageously allows the required
radiation dose to
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be adapted to the object to be irradiated and does so specifically on the
basis of its dimensions.
A radiation system defined in claim 10 and/or 11 is advantageous since
irradiation of the objects
does not have any adverse effects on the parts of the system used to irradiate
the objects.
En embodiment defined in claim 12 advantageously shortens the irradiation
process, thereby
achieving a higher turnaround of the objects.
Due to the embodiments outlined in claims 13 and/or 14, it is advantageously
possible to adapt
the dose administered to suit the respective properties of the objects to be
irradiated whilst oper-
ating at a high production rate.
With the variant of the method defined in claim 15, the dose administered
during irradiation can
be radio-chromatically stored for subsequent evaluation and this data can be
accessed later for
control purposes.
The advantageous embodiments defined in claims 16 and 17 enable the
irradiation process to be
automated to a high degree.
Also of advantage is an embodiment outlined in claim 18 since it provides an
additional control
and monitoring routine.
The advantage of the embodiment defined in claim 19 is that the method can be
universally ap-
plied to objects of the most varied nature.
In accordance with an embodiment outlined in claim 20, simple means enable the
objects to be
irradiated individually so that the irradiation process can be finished off in
a simple manner at a
later stage.
The advantage of the embodiment defined in claim 21 is that a dosimeter used
to control the ra-
diation dose administered can be specifically assigned to the object to which
the dosimeter was
attached, thereby ensuring a high degree of safety.
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Productivity can be increased by means of the advantageous embodiments
outlined in claims 22
and 23.
The embodiment described in claim 24 advantageously improves the capacity
utilisation of the
accelerator unit.
The embodiment defined in claim 25 advantageously delivers the objects to the
accelerator
chamber depending on the degree to which they have already been processed.
The embodiment outlined in claim 26 has an advantage because it increases the
degree of auto-
mation in the production process still further.
Other embodiments described in claims 27 and 28 allow an object to be
irradiated several times,
which means that the operating parameters of the accelerator unit can be
retained at a high level,
enabling it to be run without interruption for a long period.
The embodiment defined in claim 29 provides simple means of monitoring the
objects as they
are fed in and out.
The embodiment defined in claim 30 provides a simple means of allowing the
irradiation process
to be integrated in the production line of a manufacturing process for
objects.
With the embodiment outlined in claim 31, when the objects have been
irradiated, they can be
fed away to a despatch area.
The embodiment outlined in claim 32 provides an effective means of defining
the dose adminis-
tered to the object.
The advantage of the embodiment described in claim 33 is that the minimum
radiation dose to be
applied can be directed across significant points in or on the object so that
the parameters used in
the production process itself can be selected to ensure that the object is
best prepared for the irra-
diction process.
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Also of advantage is an embodiment defined in claim 34, whereby the process
parameters can be
set, regulated and controlled depending on the radiation dose to be
administered.
Claim 35 defines an advantageous embodiment whereby a means is provided which
allows a re-
peated check to be made on the stability of the radiation process.
With the embodiment outlined in claim 36, the stability of the radiation
process can be controlled
individually and randomly.
The embodiment of the method described in claim 37 is of practical advantage
because the ra-
diation process can be checked at a glance by means of a display on a screen,
for example.
The advantage of the embodiments described in claims 38 and/or 39 is that the
process parame-
ters can be automatically optimised and adapted to the respective object to be
treated.
The task set by the invention is also solved by the features set out in claim
40. These offer ad-
vantages because the limit on the specific maximum size of the object is
considerably higher than
is the case with conventional systems and in addition, the electron flow does
not go to waste due
to intermediate spaces between the individual objects, nor does the electron
flow have to be in-
terrupted.
The advantage of another embodiment defined in claim 41 is that special
precautions usually
needed for the infeed and outfeed, such as gating systems, can be dispensed
with.
Claim 42 offers a cost-effective variant of a system as proposed by the
invention.
By using the embodiment defined in claim 43, a system of the type proposed by
the invention can
be readily integrated in an overall plant for a production process.
Furthermore, this embodiment
also offers a simple means of providing facilities to ensure that the finished
goods are despatched
quickly and safely, by means of a truck, for example.
Another embodiment, defined in claim 44 is of advantage because the objects to
be irradiated can
be fed past the accelerator unit at a pre-definable angle, as a result of
which the dose applied to
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the objects is unlikely to be unevenly distributed.
With an embodiment as defined in claims 45 and 46, contamination of the
irradiated goods can
advantageously be largely ruled out.
A high degree of safety can be guaranteed for the personnel operating the
plant if using the em-
bodiments described in claims 47 to 49.
The embodiment defined in claim 50 also has advantages since it is possible to
dimension the
system proposed by the invention to meet the essential requirements of the
conveyor system.
By virtue of another embodiment defined in claim 51, electrons can be
accelerated to a high
speed by simple means, thereby ensuring an adequate deposit of high-energy
electrons.
With the embodiments outlined in claims 52 and 53, the electron beam is able
to cover a large
part of the surface area of the objects to be irradiated.
By dint of the embodiment described in claim 54, the objects to be irradiated
can be processed
from start to finish in a single pass. At the same time, this type of electron-
emitting device can be
used to accelerate the electrons.
The advantageous embodiment set out in claim 55 obviates the need for any
awkward handling
of the goods, in particular unpacking and re-packing.
Also of advantage is the embodiment defined in claim 56, since it allows
larger objects to be ir-
radiated without any detriment to the irradiation quality.
The embodiments outlined in claims 57 and 58 offer an advantage in that an
electron beam can
be provided whose energy and output reliably ensure that the desired effect is
produced in the
irradiated object.
The advantage of the embodiments defined in claims 59 and 60 is that there is
no need for a
complicated system to move the objects to be irradiated.
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Advantageously, the embodiments set out in claims 61 and 62 ensure that the
radiation dose is
uniformly distributed.
By accelerating the electrons with electromagnetic waves as described in claim
63, a high energy
level can be imparted.
The advantage of the embodiments defined in claims 64 and 65 is that in order
to produce elec-
tromagnetic waves to accelerate the electrons, a capacity is provided in which
stationary waves
can be propagated.
The embodiments defined in claims 66 to 67 offer advantages because the energy
imparted to the
electrons is so high that under-irradiation of the objects is virtually out of
the question.
The embodiment defined in claim 68 ensures that moving system components are
handled so as
to be subjected to the least damage possible.
The advantage of the embodiments outlined in claims 69 to 72 is the high
product turnaround
and hence shorter production time.
Also of advantage is another embodiment described in claim 73, whereby the
object to be irradi-
ated can be passed across the electron-emitting device again in such a way
that double exposure
of individual surfaces of the object can be ruled out.
In accordance with the embodiments outlined in claims 74 and 75, the dose
applied to the object
is largely guaranteed to remain uniform if constant operating parameters are
set for the accelera-
for umt.
Claim 76 proposes an embodiment whereby the conveyor system can be assembled
using inex-
pensive and low maintenance individual components.
By splitting the overall conveyor system up into individual parts, as
described in claim 77, an ad-
vantage is to be had since these parts can be set up depending on the
respective beam load from
the electron accelerator.
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Claims 78 to 80 describe advantageous embodiments whereby the objects can be
individually
handled, thereby providing an effective quality management system.
The embodiments described in claims 81 and 82 advantageously enable the
individuality of the
objects to be detected automatically.
In accordance with the embodiments proposed in claims 83 and 84, any
interruption in the flow
of goods due to fluctuations in the input region can be ruled out as far as
possible.
The embodiment set out in claim 85 has proved to be of advantage because by
using an operating
device of this type for a stop, a low-maintenance system can be provided which
is stable in op-
eration over long periods.
The embodiment described in claim 86 offers the advantageous and simple
possibility of smooth
operation of the conveyor system and the respective forward feed speeds
required can be finely
tuned to suit the properties of the object to be irradiated.
In accordance with the embodiments described in claims 87 and 88, an advantage
is obtained be-
cause the degree of treatment which needs to be applied to the goods can be
determined in a sim-
ple manner and the efficiency of the entire system improved accordingly.
By providing an Emergency-Stop switch in the region of the conveyor system as
defined in claim
89, the safety of the plant can be further enhanced in the event of faults.
Claim 90 provides an advantageous embodiment whereby the objects to be
irradiated are trans-
ported more safely by means of the conveyor system.
By using a wire mesh belt for the process conveyor, as with the embodiment
outlined in claim
91, the operating safety of the process conveyor can be increased.
Another embodiment such as that described in claim 92 is possible, whereby the
environment
can be protected by improving the primary resources to generate heat.
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Finally, the embodiment outlined in claim 93 is of advantage because the
atmospheric conditions
inside the system are maintained so as to be compatible with human presence.
The invention will be described in more detail below with reference to the
embodiments illus-
trated in the drawings.
Of these:
Fig. 1 is a block diagram showing the basic modules used for a system as
proposed by the
invention;
Fig. 2 is a system as proposed by the invention, seen from a plan view;
Fig. 3 shows the dose distribution in irradiated objects depending on the
penetration depth;
Fig. 4 illustrates another embodiment of the system proposed by the invention,
in a plan
view;
Fig. 5 illustrates an embodiment of the electron-emitting device;
Fig. 6 is a simplified illustration of an embodiment of a part of the conveyor
system, seen
from a side view;
Fig. 7 is another simplified illustration of an embodiment of the process
conveyor, seen
from a plan view;
Fig. 8a-8e provide a schematic illustration of the timing with which the
objects are conveyed in
the region of the transverse conveyor in order to irradiate the objects from
several
sides.
Firstly, it should be pointed out that in the different embodiments described,
the same parts are
shown by the same reference numbers and referred to by the same component
names and the dis-
closures made throughout the description can be transposed in terms of meaning
to components
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bearing the same reference numbers or the same component names. Similarly, the
description of
positions chosen in the description, e.g. top, bottom, side, etc. relate
directly to the drawing being
described and can be transposed in terms of meaning when a different position
is being de-
scribed. Furthermore, the individual features or combinations of features from
the different em-
bodiments described and illustrated may be regarded as independent, inventive
solutions or solu-
tions of the invention in their own right.
Fig. 1 is a schematic block diagram showing the basic modules contained in a
system 1 of the
type proposed by the invention. In a linear accelerator 2, electrons are
released from a heated in-
candescent cathode 3, which are then accelerated across the length of the
linear accelerator and
focused by means of quadrupole magnets 4. Instead of the linear accelerator 2,
it would, of
course, also be possible to use all other types of accelerators, such as ring
accelerators for exam-
ple.
The system 1 proposed by the invention preferably has a beam output of between
5 kW and 30
kW, in particular 15 kW.
The energy of the electrons required to alter the properties of objects 5, for
example to sterilise
them, is preferably between 5 MeV and 30 MeV, in particular 10 MeV. Due to the
fact that it is
not possible to use an acceleration system with electrostatic fields such as
conventionally used in
cathode ray tubes, for example, with an energy of ca. 30 kV because of these
high energy levels,
it is preferable if the electrons are accelerated by means of electromagnetic
waves.
Cavity resonators 6 may be used, for example, known as wave guides, to
generate these electro-
magnetic waves along the acceleration path. Inside these cavity resonators 6,
which may be made
from metals such as copper, alloys thereof such as bronze and brass, or from
steel, ceramic, plas-
tics or similar, a stationary wave is formed, whose field distribution is
determined by the geome-
try of the cavity resonators 6 and the frequency of the microwave energy fed
in.
The stationary wave in the accelerator unit is preferably excited by pulsed
microwaves, which are
generated by an oscillator 7, for example, with an RF-driver, and amplified by
a microwave am-
plifier 8, for example a klystron. The energy required for this purpose is
supplied by a high-
voltage modulator 9, which is supplied from a primary energy source 10, for
example the public
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power grid.
The frequency of the pulsed microwaves lies within the GHz range, whilst the
electrons emitted
by the linear accelerator 2 may have a pulse frequency of approximately 300
pulses per second.
Accelerated and focused in this manner, the electrons are applied to the
objects 5, provided a
shutter 11 is open, in a defined, predetermined path, assisted by deflector
magnets 12. As will be
explained in more detail below, the objects 5 are moved with the aid of a
conveyor system 13
past an electron-emitting device 14, for example a scan horn, from which the
electron beam is
emitted via a window made from a metal film, for example. The dimensions of
the electron-
emitting device 14 are preferably selected so that a scan height of up to 100
cm, preferably 60
cm, can be achieved. Accordingly, the electron beam will strike objects 5 up
to the selected scan-
ning height. For large, in particular bulky objects, whose height falls
outside this range, the di-
mensions of a system 1 proposed by the invention can be adapted to suit
requirements accord-
ingly. In order to achieve the requisite dimensions, the height of the
electron-emitting device 14,
in particular, can be adjusted as well as the units co-operating with the
electron-emitting device
14 which deflect the electron beam, for example electric coils. For safety
reasons, a beam stop
15, for example an aluminium plate, may be provided behind the objects 5 in
the emission direc-
tion of the linear accelerator 2, preferably mounted on a boundary of an
irradiating chamber 16,
so that electrons potentially passing through can be decelerated, thereby
giving rise to soft 'y-
radiation only. Since humans need to be able to enter the irradiation chamber
16 for maintenance
purposes, at least one venting device 17, for example a ventilator, may be
provided in order to
maintain a compatible atmosphere in the irradiation chamber 16.
At this stage, it should be pointed out that any other methods known from the
prior art could be
used to accelerate the electrons. Above all, the embodiment of a system 1
proposed by the inven-
tion is not restricted to the use of microwaves as an accelerating medium
which is also amplified
by a klystron.
Fig. 2 is a simple, schematic illustration of the system proposed by the
invention, seen from a
plant view. The linear accelerator 2 is located in the irradiation chamber 16,
which is surrounded
by walls 18 to 22. The walls 18 to 22 are preferably designed so that they
prevent any electrons
from escaping and, since this is ionising radiation, any reaction products in
the atmosphere of the
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irradiation chamber 16, for example ozone. By preference, the walls 18 to 22
as well as a floor
plate 23 and the cover plate, not illustrated in Fig. 2, forming the bottom
and top seal of the irra-
diation chamber 16, are made from steel-reinforced concrete. However it would
also be conceiv-
able to use other materials capable of fulfilling the requirements listed
above, e.g. walls with
cladding made from metals with a high electron catchment cross section. The
thickness of these
walls 18 to 22 will depend on the respective regulations in force in the
country governing protec-
tion against irradiation ,but in any case should be such that they will
guarantee the safety of the
system 1. By preference, the wall 20 will be four metres thick and the walls
19 and 21 will each
be three metres thick. The walls 18 and 22 may be of a thinner design although
they should make
up three metres in total. The wall 20 is thicker than the other walls 18, 19,
21, 22 due to the fact
that the electron beam emitted from the linear accelerator 2 is directed onto
this wall 20.
As may be seen from Fig. 2, the objects 5 to be treated are delivered to and
fed back out of the
irradiation chamber 16 by the conveyor system 13 via a labyrinthine entrance.
Designing the en-
trance to the irradiation chamber 16 in this manner has an advantage in that
no additional facili-
ties have to be provided for transporting the objects 5 in and out, for
example special gating sys-
tems, since any ionising radiation and reaction products of the above-
mentioned type are pre-
vented from escaping as far as possible. Although, in theory, it will still be
possible to measure a
specific residual dose, this will be kept within the permissible legal limits
due to the selected de-
sign of the screening system,. In addition, the atmosphere is not dangerous to
a human because of
the venting device 17 (not illustrated in Fig. 2) mentioned above.
Fig. 2 also illustrates the preferred embodiment of the conveyor system 13. It
is preferably made
up of continuous conveyors, e.g. a roller track, a bar conveyor, a chain
conveyor, a chute, a belt
conveyor or similar, and is used to transport objects S of differing sizes. By
preference, the con-
veyor system 13 is divided up into a feed track, a delivery track, a process
track, a buffer roller
conveyor, a rising conveyor, at least one transverse conveyor, at least one
corner-turning mecha-
nism, a discharge track and the relevant equipment. However, it would also be
conceivable to use
different conveyor systems, at least for parts of the conveyor system 13, such
as belt conveyors,
vibrating conveyors or similar. The conveyor system 13 may preferably comprise
two separate
regions, one of which will be an unclean feed region 24 separated by a barrier
device 25, such as
a grating, a dividing wall, etc., from a clean discharge region 26.
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The objects 5 may be transferred manually from transport containers 27, such
as pallets, to a feed
track 28, for example, on which a control console 29 with an Emergency-Off
switch 30 is placed.
In the region of the driven feed track 28, the objects 5 may be fed alongside
a marker device 31,
such as a label dispenser, a device for attaching microchips, an ink jet
printer or similar, for ex-
ample, so that they can be simultaneously identified. So that the objects 5
can be identified and
the detected data forwarded to an EDP system, where it will preferably be
processed, a scanner
32, for example a reading head, is mounted on the feed track 28 before a stop
33. If microchips
are used to tag the objects, it is also possible to fit them with a
transmitter, for example an IR
transmitter, from which data specific to the object can be transferred to a
receiver unit, which is
preferably mounted in the region of the conveyor system 13.
From the roller track of the feed track 28 and the stop 33, the objects 5 are
transferred to a deliv-
ery track 34, which is preferably also a roller track. The delivery track 34
conveys the objects 5
into the irradiation chamber 16. A stop 33 may be mounted on the delivery
track 34 before every
change of direction in the conveyor system. The stop 33 will preferably be
provided in the form
of a valve coil, two reed switches and a driver roller. Clearly, it would also
be conceivable to use
other embodiments, such as light sensors, mechanical switches, magnetic pulse
transmitters or
similar.
From the roller track of the delivery track 34, the objects are transferred to
the irradiation cham-
ber 16 on a conveyor 35, which is preferably designed as a chain conveyor. If
opting for a chain
conveyor, account will need to be taken of the fact that the conveyor system
13 overall should be
maintenance-free for as long as possible, particularly as regards ionising
radiation.
At the corners of the irradiation chamber 16, the objects are fed along by
means of corner units,
which are also preferably chain conveyors. Once the centre of gravity of the
objects 5 has been
pushed across the centre point of the roller, the object 5 is transferred onto
a transverse conveyor
36 on a slightly lower level, for example a transverse chain belt conveyor,
the speed of which is
preferably faster than that of the conveyor 35. During this process, the
object is rotated by more
or less 90° around a corner stop (not illustrated in Fig. 2) and is
simultaneously oriented at the
inner side boundary of the chain guide, for example a stop made from metal,
plastics or similar.
The object 5, i.e. the surfaces to be irradiated, is oriented so that it can
bed fed past the electron
beam at a defined angle relative to the electron-emitting device 14,
preferably 90°. Clearly, how-
CA 02319344 2000-08-04
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ever, it would also be possible to feed the objects 5 in any position relative
to the electron-
emitting device 14, e.g. at an angle, transversely, upright, etc..
Since all the techniques used to turn corners on conveyors require a large
distance between the
items being conveyed, thereby preventing the system 1 from being used to its
optimum effi-
ciency, the objects 5 are transferred from the transverse conveyor 36 onto a
buffer conveyor 37 in
order to keep the distance between objects 5 as small as possible, thereby
enabling the electron
accelerator to be operated economically. The buffer conveyor 37 preferably
consists of freely
rotating rollers, which are mounted on a chain at either end. The objects 5
are then preferably fed
onto a process conveyor 38 without any gaps in between, which is preferably a
wire mesh belt
and on which the objets 5 are fed past the electron-emitting device 14 of the
linear accelerator 2.
The speed at which the objects 5 are transferred can be determined by means of
adjustable drive
devices, e.g. motors, from the control system so that as the gaps close
between the objects 5, the
objects 5 which are already on the process conveyor 38 are not pushed.
Once the objects 5 have been irradiated, they are fed by means of a conveyor
39, e.g. a chain
conveyor, to a rising conveyor 40, which is also a chain conveyor, for
example, from where they
are preferably conveyed across a driven roller track 41, preferably arranged
above the delivery
track 34, out of the irradiation chamber 16.
In the delivery region, the objects 5 are preferably fed along on two levels,
it being possible for
the objects 5 to be optionally fed in and out both in the top and in the
bottom level. If necessary,
however, these two parts of the conveyor system 13 may be fed alongside one
another, in order to
be able to transport larger objects 5. This dual-level system has an advantage
in that the size of
the labyrinthine entrance to the irradiation chamber 16 can be kept relatively
small, thereby in-
creasing the safety of the system 1.
A counting station, for example a scanner 32, may be positioned in the region
of the roller track
41, by means of which the degree to which the objects 5 have been processed
can be detected. By
preference, three sensors co-operate with the counting station. Located after
the scanner 32 is an-
other stop 33 ahead of a transverse conveyor 42. Using this transverse
conveyor 42, the objects 5
can be transferred back to the feed track 28, preferably being rotated by
180° in the process, to be
fed back through the irradiation process.
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So as to be able to ascertain at any one time how many objects 5 on the
conveyor system 13 have
not been treated or have been treated on one side only, two additional
counting stations, each
with three sensors, are preferably installed adjacent to the counting station
ahead of the trans-
verse conveyor 42, to carry out reciprocal checks. By preference, an
additional counting station is
provided in the vicinity of the electron-emitting device 14 and another
counting station on the
feed track 28 in the region of the control console 29.
A discharge track 43 forms the end of the conveyor system 13 at which the
objects are removed
from the processing area. An Emergency-Stop switch 30 may also be mounted in
the region of
the discharge track 43 for safety reasons.
The objects may be picked up from the discharge track 43 in the discharge
region 26 manually
and transferred onto a transport container 27, for example a pallet. If
necessary, the loaded con-
tainer units 27 ready for despatch can be shrink-wrapped in a winder.
The individual parts of the conveyor system 13 are preferably driven by servo
motors. However,
they could also be driven by any other appropriate drive mechanisms known from
the state of the
art. In any event, a drive device 44 of the transport system 13 should be such
that the object 5 can
be moved through the electron beam at a specific, defined speed. Preferably,
feed rates in the
range of 1 mm/s to 400 mm/s, preferably Smm/s to 200 mm/s are used, the
displacement speed
being set to suit the dose of radiation to be administered. The number of
drive devices 44 used
will preferably be selected on the basis of the length and the number of
individual conveyors.
The object 5 is preferably irradiated (as may be seen from Fig. 2)
horizontally, perpendicular to
the direction in which the object 5 is conveyed. However, it would also be
possible for the object
to be irradiated from all other directions, for example from above, from
underneath, etc., so
that the object 5 can be simultaneously and alternately irradiated from
several sides. If only one
electron accelerator is used, it would also be conceivable to split the
electron beam in front of
the outlet of the electron-emitting device 14 into at least two parts, by
means of deflector mag-
nets for example, one part-beam being alternately directed onto the object 5
other than from the
main direction of irradiation, for example from above. In this situation, the
use of a wire mesh
belt has proved to be a particularly effective process conveyor 38 since, as a
rule, it can be used
for long periods without problems, even if subjected to increased radiation
from above.
CA 02319344 2000-08-04
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Depending on the acceleration method used, a pulsed electron beam may be used
to cover the
surface of the object 5. This being the case, it has been found to be
particularly advantageous if
there is at least a 50% overlap of the pulses, which produces a uniform
distribution of the dose in
the object 5. Clearly, the speed at which the conveyor system 7 is fed,
particularly the process
conveyor 38, will need to be adjusted to the dose to be administered and to
the frequency timing
of the electron beam.
The maximum possible forward speed of the process conveyor 38 is determined in
particular by
the pulse rate, the pulse duration, the scanning frequency and the number of
pulses.
If the system 1 proposed by the invention is used to scan the objects 5, it
has proved to be of par-
ticular advantage compared with the systems known from the prior art if the
objects 5 are fed
past the electron-emitting device 14, for example the scan horn, without any
intermediate spaces.
This increases the efficiency of the system 1 significantly because, compared
with conventional
systems, the electron beam is constantly directed at the surface of an object
5 to be irradiated. To
increase the efficiency of the system 1 still further, a sensor may be
provided in the region of the
process conveyor 38, for example an optical sensor, which detects the end of
or an interruption in
a flow of objects and passes this information on to a control device for the
electron beam accel-
erator so that it can adjust the operating parameters of the accelerator unit
and the accelerator unit
can be switched to stand-by mode only.
The purpose of the shutter 11 is primarily to serve as a protective device for
the sensitive internal
parts of the electron accelerator so that in the event of breakage or damage
to the electron outlet
window in the region of the electron-emitting device 14, said parts of the
electron accelerator can
be protected from potential damage.
In order to increase the operating safety of the system 1 proposed by the
invention still further,
another protective device 45 may be provided where the conveyor system 13
enters the irradia-
tion chamber 16, which might take the form of a dividing wall, an appropriate
grating arrange-
ment or similar, for example, with a door 46 mounted therein. This will
largely prevent unau-
thorised access to the irradiation chamber 16. Additional measures might also
be taken and an
electronic lock system could be provided on a door 46 mounted in the
protective device, for ex-
ample, to prevent access to the irradiation chamber 16 if the electron-
emitting device 14 is emit-
CA 02319344 2000-08-04
-17-
ting electrons at that point in time. By preference, an Emergency-Stop switch
30 can be provided
on the door 46.
However, it would also be possible to set up the control system of the
accelerator unit so that an
appropriate sensor, for example an electrical contact, an optical sensor or
similar, in the frame of
the door 46 of the linear accelerator 2 could be automatically interrupted
when the door 46 is
opened, thereby ruling out virtually 100% any potential risk to persons due to
electron emis-
sions. As an additional safety feature, a cable pull switch 47 can be provided
along the conveyor
system 13, for example. This would enable personnel who had inadvertently
entered the irradia-
tion chamber 16 when the accelerator unit was activated to halt the
irradiation process and, pro-
vided the control and drive unit were set up accordingly for the accelerator
unit, to indicate to the
control and drive device unit via the cable pull switch 47, by sounding an
optional acoustic
warning signal, that the electron accelerator should not be switched to
operating mode. In addi-
tion, it would also be possible to provide electrical contacts, for example,
in a door mat behind
the door 46 or in the labyrinthine entrance in order to detect when persons
are entering the irra-
diation chamber 16 whilst the accelerator unit is in operation. This will
naturally mean that the
dimensions of the door mat must be selected so that it will not be possible to
step over it.
Clearly, light sensor units could also be mounted at specific points around
the system 1, for ex-
ample in the vicinity of the door 46, in order to monitor access to the
irradiation chamber 16.
Other standard sensors and warning devices such as motion sensors, rotating
mirrors, alarm
horns, could, of course, also be positioned at any point in the system 1.
It has also proved to be particularly effective if, as mentioned above,
observation cameras 48 are
placed at nodal points around the system 1, by means of which the irradiation
chamber 16 as well
the individual parts of the labyrinthine access system and the conveyor system
13 can be moni-
toyed.
All the data, in particular the data picked up by sensors, can advantageously
be transmitted by
optical fibres, thereby avoiding any interference from the accelerator unit
during data transmis-
sion.
CA 02319344 2000-08-04
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As an additional protective measure in the region of the beam path of the
linear accelerator 2, a
beam interrupter may be provided, which will automatically cut in in the event
of any operating
faults in the system 1, so that electrons can not be discharged from the
linear accelerator 2, in
particular the electron-emitting device 14.
By preference, the heat built up during processing is recycled in a manner
known from the prior
art by means of an appropriate heat exchanger and fed back into the process
system.
Fig. 3 illustrates the reach distribution, plotted from experimental data, the
penetration depth in
the object 5 to be irradiated being plotted in centimetres on the x-axis and
the dose transferred
being plotted in KGy on the y-axis. In order to plot this curve, a test
product with a density of
0.1 g/cm3 was used. This was irradiated with electrons having an energy of 10
MeV and a beam
output of 15 kW.
The electrons penetrate the objects 5 to be irradiated, which may be packaged
under certain cir-
cumstances, and start to alter the substance to be irradiated after only a few
centimetres. This is
determined not least by the high active cross section of the electrons and a
density of approxi-
mately 1 g/cm3 of the objects 5 to be irradiated. For this reason, it is
usually necessary to apply
radiation to the objects 5 from both sides. The conveyor system 13 is
therefore designed so that
objects 5 which have already been treated can be fed back through the
irradiation process, pref-
erably rotated by 180°.
Typical medical products generally have a density of 0.05 g/cm3 to 0.3 g/cm3
and may therefore
be treated in their original packaging.
As may be seen from Fig. 3, the dose applied to the irradiated test product of
said density travels
up to a distance of approximately 30 cm and the distance across the product is
more or less ir-
relevant. With the selected parameters, objects 5 of a thickness up to 60 cm
can be irradiated
from both sides without any loss of quality. The thickness of the product is
therefore correlated
with the flow line of the linear accelerator 2. In order to irradiate objects
5 of larger dimensions,
the parameter settings can be adjusted accordingly.
Fig. 4 is a schematic diagram of another embodiment of a system 1 as proposed
by the invention,
CA 02319344 2000-08-04
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seen in a plan view. The individual components of this embodiment are
essentially the same as
those of the embodiment described above. The only difference is that separate
labyrinths are used
to feed the objects 5 in and out. As a result, the unclean feed region 24 is
separated from the dis-
charge region 26 by the irradiation chamber 16. Consequently, this system 1
can be readily inte-
grated in a manufacturing process for objects 5, particularly as regards the
design of the conveyor
system 13, and the semi-finished objects 5 can be fully automatically
delivered to the feed region
24 (not illustrated in Fig. 4), passed through the irradiation process and
discharged from the op-
posite end in the discharge region 26. Clearly, in the embodiment described,
it will only be pos-
sible to feed through objects 5 whose dimensions and thickness are such that
only one irradiation
pass is required in order to produce the desired effect.
However, if this is not the case, it is nevertheless still possible, as
illustrated in the top part of
Fig. 4, to transfer the objects 5 via a transverse conveyor 42 after the first
pass through the irra-
diation process and onto a return conveyor 49. Due to the fact that none of
its components are
exposed to radiation at any time, the return conveyor 49 may be made from
simple and inexpen-
sive materials, for example an endless rubber belt. If there are several
changes of direction in the
return conveyor 49, as is the case in the diagram of Fig. 4, it may be divided
up accordingly using
elements known from the prior art, for example corner-turning devices, roller
conveyors with a
90° turn or similar.
As may be seen from the right-hand part of Fig. 4, the objects 5 fed back are
again transferred via
a transverse conveyor 42 of the delivery track 34 of the conveyor system 13
and passed through
the irradiation process again.
Clearly, instead of providing an additional transverse conveyor 42 in the left-
hand part of Fig. 4,
it would also be possible to feed the objects 5 back round to the return
conveyor 49 by means of
an additional corner-turning device 50 (shown by broken lines in Fig. 4). In
this case, the clean
discharge region 26 is on the same side of the irradiation chamber 16 as the
unclean feed region
24. This being the case, the unclean region can be separated from the clean
region by means of
the barner device 25 mentioned above.
Fig. 5 is a schematic illustration of a different embodiment of an electron-
emitting device 14. In-
stead of the scan horn mounted at the front end of the linear accelerator 2,
it essentially consists
CA 02319344 2000-08-04
L
-20-
of a ring 51 with several deflector devices 52 mounted around its periphery,
for example coils,
magnets or similar. As a result, the electrons located on a peripheral track
inside the ring 51 are
emitted through windows 53, for example a metal film, positioned opposite the
deflector devices
52, and can then penetrate the objects 5. The object 5 to be irradiated is
conveyed through the
ring 51 by the conveyor system 13. Beam stops 15 are mounted outside the ring
51 above the de-
flector devices 52 in such a way that any electrons passing through the
oppositely lying windows
will be captured.
Using this embodiment of an electron-emitting device 14, any number of
deflector devices 52,
windows 53 and beam stops 15 may be provided around the periphery of the ring
51. However,
care must be taken to ensure that the linear accelerator is itself not exposed
to irradiation due to
ill-considered positioning of the windows 53.
Advantageously, with a system 1 of the type proposed by the invention, objects
of the most var-
ied type can be treated and their properties altered in part-regions. A whole
variety of products
may be sterilised. These might include, amongst others, OP equipment, OP
cladding, bonding
substances, OP waste, pharmaceutical raw materials, pharmaceutical packaging,
containers made
from plastics and/or glass, test containers and laboratory equipment for the
biotechnology sector,
the sterilisation of liquids, recycled materials and refuse in the
environmental technology sector,
the removal of germs from plastics, the sterilisation of and removal of germs
from spices, raw
materials, products, beverages, seals and the sterilisation of packaging,
containers or receptacles
in packaging technology.
However, apart from sterilisation, there is a whole range of possible
applications for a system 1
of the type proposed by the invention. These might include the treatment of
surfaces, for example
by curing, curing and cross-linking plastics, setting and cross-linking
varnishes. By selecting an
appropriate transport system, for example in the form of bottles, even
liquids, e.g. beer, water or
similar, and gases can be irradiated in this manner. Bulk commodities and
granulates of the most
varied type can also be irradiated using the system 1 proposed by the
invention.
Fig. 6 illustrates a different embodiment of a conveyor system 13, which also
offers the option of
irradiating long items in the system 1 proposed by the invention. Given that
it is especially diffi-
cult to rotate long objects by a 90° turn in regions where space is
tight, the embodiment illus-
CA 02319344 2000-08-04
-21-
trated in Fig. 6 allows long objects to be conveyed upright. The only
restriction in terms of the
length of the objects 5 will be the height of the labyrinth and irradiation
chamber. As most parts
of the conveyor system 13 are essentially identical to those of the
embodiments described above,
only those parts that are different will be described.
Because of the restriction of the radiation height (scan height) due to the
electron-emitting device
14 (not illustrated in Fig. 6), for example the scan horn, objects 5, which
are fed through the irra-
diation chamber standing upright, for example long objects, are brought to a
position in front of
the electron-emitting device 14 in which the entire surface area of the object
5 can be covered.
As a result, as illustrated in the left-hand part of Fig. 6, a contact 54 can
be provided on the proc-
ess conveyor 38 on the intake side of the conveyor system 13, for example an
electrical contact,
which reacts to pressure and is linked via a line 55 with an actuator 56, for
example a lever made
from metal, plastics or similar. The contact 54 can be equipped so as to
prepare the object 5, for
example by applying a foam coating.
As the object 5 is fed by the conveyor 39 to the contact 54 and when pressure
is applied thereto,
an electric signal is transmitted across the line 55 to the actuator 56 so
that the actuator 56, which
is mounted so as to rotate at a point 57, is displaced upwards in the
direction of arrow 58 so that
the object 5 is guided in a rotary movement as indicated by arrow 59. As a
result, the object 5
will be moved from an upright position on the conveyor 39 to a position lying
flat on the process
conveyor 38. In this laid flat position, the object 5 is then fed past the
electron-emitting device 14
(not illustrated in Fig. 6) and its surface directed towards the electron-
emitting device 14 is si-
multaneously exposed to the electron beam. The object 5 is then tipped from
the processor con-
veyor 38, which is preferably arranged on a higher level, onto the conveyor 39
at a tipping point
60 as soon as the centre of gravity of the object 5 has moved beyond the
tipping point 60. When
an end face 61 of the object 5 comes into contact with a stop 62 of an
actuator 63, which can be
rotatably mounted at a point 64, the object 5 will be re-aligned as the
process conveyor 38 moves
forward and returned to an upright position so that the object 5 can be
transported back out of the
irradiation chamber standing upright again. The actuator 63 automatically
returns to its initial
position as soon as the stop 62 is released by the object 5. Preferably, the
latter is spring-
mounted.
In order to guarantee the lateral stability of the objects 5, a guide device
65 can be mounted along
CA 02319344 2000-08-04
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the entire length of the conveyor system 13. By preference, this will consist
of two height- and
width-adjustable rails enabling objects 5 of different widths and heights to
be conveyed through
the irradiation chamber.
Various measures known from the state of the art may be used to prevent long
objects from tip-
ping over in a direction parallel with the conveyor 39 if the standing surface
is too small.
Clearly, it would also be possible to arrange the process conveyor 38 on a
lower level than the
conveyor 39, although this would have the disadvantage of an additional height
restriction. This
being the case, the actuators 56, 63 would have to be adapted accordingly. In
particular, the ac-
tuator 63 would have to be positioned at the start of the process conveyor 38
(in the left-hand part
of Fig. 6) in order to be able to place long objects into an upright position
as they slide off. The
actuator 56, which is then placed at the end of the process conveyor, can then
assume charge of
transferring the long objects to the next conveyor 39 after irradiation.
The conveyor 39 and the process conveyor 38 may be designed as continuous
conveyors, as
mentioned above.
Fig. 7 is a schematic illustration of a conveyor system 13, seen from a plan
view, by means of
which the objects 5 can be irradiated from several sides during a single
circuit. To this end, the
process conveyor 38 to which the objects 5 are delivered by the conveyor 39,
is interrupted by a
rotary device 66.This rotary device 66 is preferably positioned before the
electron-emitting de-
vice 14 of the accelerator unit. As objects 5 are carried from the process
conveyor 38 on to the
rotary device 66, which may be a turn-table, the latter may be detected by an
observation device
67 for example, which might be provided in the form of a sensor. The
conveyance process will
then be interrupted, causing the rotary device 66 to be rotated, preferably by
180° to 360°. A sen-
sor, not illustrated in Fig. 7, may detect when the rotary movement is
complete, re-activating the
drive device 44 of the process conveyor 38 followed by all other drive devices
44 of the conveyor
system 13 with the exception of the rotary device 66, so that an object 5
behind pushes the object
located on the rotary device 66 in the direction of the second part of the
process conveyor 38,
which is then conveyed via the other parts of the conveyor system 13 out of
the irradiation cham-
ber.
CA 02319344 2000-08-04
-23-
In order to prevent objects 5 from mutually hampering one another on the
process conveyor 38
and the rotary device 66, the rotary device could be displaced out of the
plane of the process con-
veyor 38 once an object 5 has been placed on it, e.g. by raising or lowering
it. In addition, to fa-
cilitate transport of the objects 5 on the rotary device 66, other conveyor
devices, e.g. roller con-
veyors with or without a drive or similar, may be provided so that an object 5
can be automati-
cally centred on the rotary device 66 as soon as a sensor detects that an
object 5 has been moved
onto the rotary device 66.
Figs. 8a to 8e provide schematic illustrations of a detail of the transverse
conveyor 42 of the con-
veyor system 13 of the system 1 in order to provide a clearer illustration of
how objects 5 are
transported in this region and how the conveyor system is timed to expose the
objects 5 to radia-
tion from two sides.
Fig. 8a shows objects 5 being conveyed on the feed track 28, the objects 5
being unpacked or in
appropriate packaging, e.g. cardboard boxes. In a region 68, the objects 5 lie
close together, i.e.
without any intermediate spaces, and are fed as indicated by arrow 69 in the
direction of the irra-
diation chamber 16, which is not illustrated, and the linear accelerator 2,
also not illustrated. A
sensor 70, which may be an optical sensor such as a light sensor for example,
detects the pres-
ence of objects 5 in its region and activates the stop 33 in response to the
data picked up. This
stop 33 may be a rail made from the most varied of materials such as metal or
plastics or similar
and has a non-operating position underneath the feed track 28 whilst a part of
its surface projects
beyond the feed track 28 when operated so that objects 5 can be held back
instead of being car-
ried farther along. The stop 33 may be operated in conjunction with any type
of actuator known
from the prior art, for example pneumatic, electric, hydraulic, etc.. However,
before the stop 33 is
activated, care must be taken to ensure that no objects 5 are present on the
feed track 28 along a
length 71, so as to prevent the goods 5 inadvertently being lifted off the
feed track 28. In order to
keep this length 71 free, the objets 5 fed across the region 68 are briefly
halted and objects 5 al-
ready at a region 72 are continuously forwarded along. The advantage of this
is that there will
now be the required space between the individual objects 5 and the objects 5
can be fed round the
corner. As described above, the intermediate spaces are subsequently reduced
as far as possible
again by the buffer conveyor 37 farther on, not illustrated in Fig. 8, so as
to optimise the capacity
of the linear accelerator 2.
CA 02319344 2000-08-04
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Fig. 8b shows the timing used for objects 5 which have to be irradiated twice,
at a point at which
untreated objects 5 are fed to the irradiation chamber 16 in the direction of
arrow 69 and at which
objects 5 which have already been irradiated once, i.e. on one surface, are
despatched from the
irradiation chamber 16 by the discharge track 42 in the direction of arrow 73.
Another sensor 70
in the region of the discharge track 43 can detect the presence of objects 5
on the discharge track
43, for example by means of a control and drive unit such as an EDP unit, not
illustrated, in the
region of the transverse conveyor 36.
Then, as illustrated in Fig. 8c, objects 5 in the region 68 of the feed track
28 are buffered in front
of the stop 33 (indicated by circles 74 in Fig. 8c) and the object 5 which is
located on the trans-
verse conveyor 42 in the region of the discharge track 43 is moved as
indicated by arrow 75 in
the direction of the feed track 28. This movement is initiated on the basis of
the data picked up
by the sensor 70 located in the region of the discharge track 43 and may be
operated by using the
most varied of positioning technologies known from the prior art. For example,
the object 5
could be pushed onto the region of the transverse conveyor 42 of the feed
track 28 by means of a
displacement device 76, for example a ram 77 and a rod linkage 78.
Alternatively, this displace-
ment device 76 may be pneumatically operated, in which case the object 5 will
be displaced in
said direction by a blast of air. However, it would also be possible to
construct at least a part of
the transverse conveyor 42 as a roller track so that a short pulse could be
applied to the object 5
by means of an appropriate displacement device 76 in order to achieve the
desired displacement
in the direction required.
Clearly, however, it would also be possible for at least parts of the
transverse conveyor 42 to be
provided with drive devices 44, for example a servo motor, as illustrated in
Fig. 8c.
As illustrated in Fig. 8d, the objects 5 leaving the irradiation chamber 16
are transferred back to
the feed track 28 in the region 72. Since the feed track 28 is preferably
driven by means of a drive
device 44, for example a servo motor, in the region 72, the objects 5 which
have been irradiated
once are buffered in the region 68, again in the direction of arrow 69. The
objects 5 are prefera-
bly buffered until the first object 5 which has been irradiated twice, i.e. on
opposing surface,
reaches the corresponding sensor 70 in this region on the discharge track 43.
As a result, the sensors 70 detects, via a control and drive device, not
illustrated, the treatment
CA 02319344 2000-08-04
- 25 -
status of the objects 5, in particular the fact that the objects 5 have been
irradiated twice, by
means of the marking applied to the objects 5 as described above and moves the
stop 33 into its
non-operating position so that no part of the stop 33 is projecting above the
surface of the feed
track 28. Consequently, as illustrated in Fig. 8e, the buffered objects 5 can
be directed as indi-
cated by arrow 69 towards the radiation process whilst objects 5 which have
completed the ra-
diation process can be removed from the irradiation process via the discharge
track 43 as indi-
Gated by arrow 73.
With a conveyor system of this design, the objects 5 are not rotated on the
transverse conveyor
42 but are fed in a horizontal displacement only and are positioned on the
feed track 28 so that
they can be directed back round the circuit in the irradiation chamber 16
rotated by almost 180°
about their vertical axis.
At this point, it should be reiterated that Figs. 8a to 8e provide a schematic
illustration of the
conveyor system 13 in the region of the transverse conveyor 42 and that any
drive devices 44 and
sensors 70 can be mounted in the requisite positions in order to ensure that
the objects 5 are con-
veyed along on the conveyor system 13 smoothly.
The method described below has proved to be particularly effective as a means
of irradiating the
objects 5, although this approach does not necessarily have to be used and can
be modified as
required.
The object 5 to be irradiated is fed across the unclean feed region 24 to the
conveyor system 13.
This may be done manually by picking up the objects 5 from transport
containers 27, for example
pallets.
In order to identify the objects 5 individually, they are fed past a marker
device 31, for example a
label dispenser. Having been applied in this manner, these markings, which may
be a bar code
for example, are detected by a downstream scanner 32 and this data is fed to a
control and/or
drive device, for example an EDP system. A first stop 33 co-operates with the
scanner 32, in
front of which objects 5 from the feed region 24 are buffered. The stop 33
passes the objects onto
the delivery track 34 at intervals calculated on the basis of the
sterilisation status.
CA 02319344 2000-08-04
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The objects 5 are then fed across the individual parts of the conveyor system
13 into the irradia-
tion chamber 16. In order to determine the dose of radiation energy to be
applied to the objects 5,
it is important that the feed rate of the process conveyor 38, amongst other
things, is adapted to
the cyclical frequency of the linear accelerator 2. Since the electrons are
accelerated by electro-
magnetic waves pulsed at a predefined frequency, present as stationary waves
in cavity resona-
tors 6, and excited by a pulsed microwave generated by an oscillator 7 and
amplified by a klys-
tron, it has proved advantageous if the pulses of the electron beam overlap by
at least 30%, pref-
erably 50%. Accordingly, a dose can be uniformly distributed in the object 5.
It is of advantage to use an accelerator system in which a beam energy in the
region of 5 MeV to
30 MeV, preferably 10 MeV, is applied and a mean beam output in the region of
5 kW to 30 kW,
preferably 15 kW.
The feed rate of the process conveyor 38 should be between 1 mm/s and 400
mm/s, preferably 5
mm/s and 200 m/s and in any event adjusted to the dose to be administered.
The object 5 is preferably irradiated horizontally and vertically relative to
the direction of dis-
placement of the object 5 and irradiation may be applied from all sides,
especially if several
electron accelerators are used. In the latter case, the object 5 may be
irradiated from all sides on
an alternating basis or simultaneously, preferably in a vertical and
horizontal direction relative to
the conveyor system 13. Once irradiated, the object 5 is transported through
the labyrinthine ac-
cess out of the irradiation chamber 16 and on past an identification system,
for example a scanner
32, in particular a reading head. The data picked up may also be applied to an
EDP system,
which will therefore be able to ascertain the degree to which the object 5 has
been treated. If it is
necessary to irradiate the object 5 more than once, this data will be applied
to a stop 33, which, in
conjunction with the transverse conveyor 42, will cause the objects 5 on the
delivery track 34 to
be held back, by moving out a metal and/or plastic batten, instead of being
transported on into
the irradiation chamber 16. Consequently, objects 5 that have already been
irradiated can be re-
turned via the transverse conveyor 442 to the delivery track 34 and fed back
into the irradiation
process. The objects 5 located on the feed track 28 can be held back by means
of the first stop 33
and buffered until the first object 5 that has been irradiated twice reaches
the transverse conveyor
42 again. The fact that irradiation has been applied twice will be detected by
the scanner 32.
CA 02319344 2000-08-04
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-27-
By controlling the system in this way, the capacity of the resources available
can advantageously
be used to good effect. Optionally, in addition to the first stop 33, other
stops 33 could be
mounted across the length of the conveyor system 13. Preferably, these would
be positioned be-
fore each change of direction in the transport system. As a result, the
objects 5 would be buffered
so that any disruption to the flow of goods before the electron-emitting
device 14 is prevented as
far as possible. The objects 5 are released from each of the stops 33 at
defined intervals, timed to
coincide with the dose of radiation to be applied to the objects 5, i.e. they
are fed past the elec-
tron beam several times by parts of the conveyor system 13, in particular the
process conveyor
38, in order to achieve the required radiation dose.
Usually, the objects 5 are fed into and out of the irradiation chamber 16 from
one side of the irra-
diation chamber 16. However, it would also be possible for the objects 5 to be
fed in and out of
the irradiation chamber 16 from different sides of the irradiation chamber 16.
To determine the dose required for individual objects 5, dosimeters, for
example radio-chromium
film meters, could be mounted on individual objects 5 at significant points
and these objects ex-
posed to the radiation process. These significant points might be those points
at which a higher or
lower dose is needed. This is likely to be the case with the interior, but
also the corner regions of
the objects 5, especially if the objects 5 are irradiated in packaging, for
example their original
packaging, so that the dosimeters used can preferably be placed at these
points.
Radio-chromium film meters are excellent because their colour changes
depending on the irra-
diction time and the dose to be administered. This colour change can therefore
be measured by
means of a spectral photometer by measuring the drop in intensity of a light
beam passing
through or its reflection. The resultant values can be used to work out the
exact speed at which
the process conveyor 38 needs to be fed along at a constant beam output.
Alanine transfer do-
simeters have proved to be of particular advantage in determining the
calibration curve for evalu-
ating the films. Clearly, however, any other methods could be used for
calibration purposes.
In addition to radio-chromium film dosimeters, other dose meters could be used
to enhance
safety, preferably calorimetric dose meters.
To improve safety still further, additional film dosimeters could be attached
to objects 5 at de-
CA 02319344 2000-08-04
- 28 -
fined intervals along the route of the production process, preferably
dosimeters carrying the same
marker or identification as that used for the objects 5. This would prevent
the individual film
dose meters from being mixed up later. The objects 5 fitted with the
additional dosimeters can be
recognised by means of a control and/or drive device by means of a scanner 32,
for example.
For the purposes of subsequent processing and in order to control the
stability of the process, the
data obtained from the dosimeters could be applied to a data processing
system, by which it
could be archived.
Clearly, however, it would also be possible for the data picked up from the
dosimeters to be used
for the purposes of a DESIRED/ACTUAL comparison in order to control the
parameter settings
of the accelerator system and the drive speeds of the individual parts of the
conveyor system. To
this end, the DESIRED values could be stored in said data processing system.
Finally, it should be pointed out that in order to provide a clearer
understanding of the solutions
proposed by the invention, examples of embodiments and their individual
components are illus-
trated to a certain extent out of scale and/or on an enlarged and/or reduced
scale. Furthermore,
individual parts of the combination of features described above may be used in
combination with
other individual features from other examples of embodiments to provide an
independent solu-
tion or a solution of the invention.
In particular, the individual embodiments illustrated in Figs. l, 2; 3; 4; 5;
6; 7; 8a to 8e may form
the subject-matter of independent solutions to the invention in their own
right. The tasks set and
solutions proposed by the invention are to be found in the detailed
descriptions of these draw-
mgs.
CA 02319344 2000-08-04
-29-
List of reference numbers
1 System
2 Linear accelerator
3 Incandescentcathode
4 Quadrupole magnet
Object
6 Cavity resonator
7 Oscillator
8 Microwave amplifier
9 High-voltage modulator
Energy source
11 Shutter
12 Deflector magnet
13 Conveyor system
14 Electron-emitting
device
Beam stop
16 Irradiation chamber
17 Beam stop
18 Wall
19 Wall
Wall
21 Wall
22 W all
23 Floor plate
24 Feed region
Barrier device
26 Discharge region
27 Conveyor unit
28 Feed track
29 Control console
Emergency Stop
switch
CA 02319344 2000-08-04
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31 Marker device
32 Scanner
33 Stop
34 Delivery track
35 Conveyor
36 Transverse conveyor
37 Buffer conveyor
38 Process conveyor
39 Conveyor
40 Rising conveyor
41 Roller track
42 Transverse conveyor
43 Discharge track
44 Drive device
45 Protective device
46 Door
47 Cable pull switch
48 Observation camera
49 Return conveyor
50 Corner-turning
device
51 Ring
52 Deflector device
53 Window
54 Contact
55 Line
56 Actuator
57 Point
58 Arrow
59 Arrow
60 Tipping point
61 End face
62 Stop
63 Actuator
CA 02319344 2000-08-04
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64 Point
65 Guide device
66 Rotary device
67 Observation device
68 Region
69 Arrow
70 Sensor
71 Length
72 Region
73 Arrow
74 Circle
75 Arrow
76 Direction of displacement
77 Ram
78 Rod linkage
