Note: Descriptions are shown in the official language in which they were submitted.
2 0 ~ 9
METHOD FOR THE INSPECTION OF THE VOLUME
OF A PLASTIC BOTTLE AND BOTTLE INSPECTION MACHINE
FOR PERFORMING THE METHOD
The invention relates to a method for inspecting
a returnable plastics bottle, in particular a PET bottle,
in respect of its volume. The invention also relates to a
bottle inspection machine for performing the method.
It is a known procedure to inspect returnable
plastics bottles, which are known mainly in the form of
PET (polyethylene terephthalate) bottles, upon each
return. In the course of the inspection the bottles are
checked for cleanness and absence of damage.
It would be desirable to extend the inspection
to include a simple volume check, as PET bottles in
particular are not volume-stable; it is quite possible for
a PET bottle to deviate substantially from its nominal
volume before completing its return-cycle life
(approximately 25 fills), which may cause problems,
especially upon filling. The problem is to perform the
desired inspection-step easily and quickly and with
sufficient accuracy. Modern bottle inspection machines
have a targeted inspection capacity of approximately ~00
bottles per minute, which of course should not be lowered
by the volume check.
The problem is solved according to the invention
by determinin~ at least one linear dimension of the
2 ~
bottle.
Surprisingly, it has been shown that for
plastics bottles and for PET bottles in particular the
volume of the bottle can be determined with adequate
accuracy by detecting one linear dimension of the bottle.
Detection of one linear dimension can very easily be
performed, even on bottles which are being conveyed at
high speed in an inspection machine.
Preferably the height of the bottle is detected.
PET bottles have been found to be particularly susceptible
to loss of height, and this is the main cause of reduction
in volume. The height dimension is moreover particularly
easy to detect, as will presently be explained.
The bottle inspection machine according to the
invention is equipped with a measuring arrangement for the
linear dimension.
An embodiment will now be explained in detail by
way of example and with reference to the drawings, in
which the single figure shows a diagrammatic
representation of the measuring arrangement for measuring
the height of a bottle.
In Fig. 1 only the top part 2 of a PET bottle 1
is shown. A transmitter 4 transmits a laser beam 5 in the
form of a vertically extended strip or ribbon which is
received at a receiver 6. Suitable transmittingJreceiving
systems with associated receiving amplifier are
manufactured eg. by the firm of Keyence, Osa~a, Japan
under the type designation LX2. The receiving amplifier
2 ~
may give the amount by which the quantity of laser light
received exceeds or falls below a specific limit value, or
alternatively it can output an analogue voltage which is
proportional to the quantity of light received and can be
subjected to further processin~.
In the illustrated arrangement the quantity of
light received is governed by the height of the bottle, as
the top of the bottle 3 interrupts the strip-like laser
light beam from the bottom edge. The taller the bottle,
the further it projects into the strip of light, and the
smaller the quantity of light transmitted to the receiver.
The shorter the bottle, the less it projects into the
light strip, and the larger the quantity of light
transmitted. In this way, the height of the bottle can be
determined with an accuracy of approximately 0.1 mm. As
there is a very close correlation between the height and
volume of PET bottles of a given shape, so that the volume
of the bottle can be inferred with reasonable accuracy
from its height, the height measurement which has been
described offers a quick and simple method for volume
inspection. It will usually only be necessary to detect
bottles with a height which falls below a predetermined
lower limit (corresponding to an upper limit for the
quantity of light received), as the inspection is usually
only concerned with finding bottles which are undersize.
In some cases, instead of the height of the
bottle, another linear dimension correlatiny sufficiently
accurately with the volume for the type of bottle under
2 0 9 ~
test may be detected. For example, the height of the
collar 3 may be detected, or the diameter of the bottle if
this is a suitable yardstick for the change in volume for
a particular bottle type.
For the height measurement described above it
has been assumed that the bottle is standing upright on,
and is being conveyed on, a base whose distance from the
measuring arrangement 4,5,6 is known and fixed. This will
usually be the case on a conveyor in an inspection
machine, eg. a carousel or belt conveyor. If the
measurement is performed while the position of the bottle
is not so well defined, then eg. two measuring
arrangements can be provided, one to detect the top of the
bottle as shown in Fig. l, and the other to detect the
bottom. The height of the bottle and its conformity with
the nominal volume can then be determined from the two
received light quantities and/or output signals of the
measuring arrangements.
This detection of a linear dimension of the
bottle is preferably performed in an inspection machine.
The measuring arrangement can be arranged alongside the
conveyor path in a variety of ways. It is also possible
to provi~e several measuring arrangements to allow several
bottles to be inspected independently at the same time.
2S Where bottle height measurement is already provided with
sufficient accuracy in an inspection machine for reasons
other than determination of volume, the measurements
obtained can be used for the volume inspection according
~09~
to the invention.
Detection of the linear dimension, can, however,
also be performed separately from an inspection machine,
along a bottle conveyor path, eg. at a bottling station.
S A rejector device is preferably installed
downstream of the height/volume detection unit, to respond
to the reading obtained and to reject from the conveyor
path, and hence from circulation, any bottle detected as
having become undersize.
