Method for enabling the cutting to size of a continuously extruded weather strip with variable characteristics, particularly for motor vehicle bodies

A method for enabling the cutting to size of a continuous extruded weather strip including an anchoring profile provided with internal longitudinal retaining ribs and a tubular sealing profile co-extruded with the retaining profile and having variable characteristics. In order to cut the weather strip in predetermined zones related to the variations in the characteristics of the weather strip during extrusion, at least one of the internal longitudinal ribs is at least partially omitted in sections spaced from each other according to the length of the pieces of extrusion to be cut to size, and the omitted sections are detected to provide corresponding signals to enable cutting.

BACKGROUND OF THE INVENTION 
The present invention relates in general to the production of extruded 
weather strips. More specifically, the invention concerns a weather strip 
intended particularly for fitting to the edge of an aperture or closure 
element of the body of a motor vehicle, of the type comprising a 
U-sectioned anchoring profile of elastomeric material provided with 
internal longitudinal ribs for retaining the weather strip on the edge, 
and a tubular sealing profile also of elastomeric material and co-extruded 
with the retaining profile, and in which the tubular profile and/or the 
anchoring profile have variable characteristics. 
These variable characteristics may consist, for example, of a 
differentiated section of the wall of the tubular profile, a variable 
configuration of the anchoring profile, or even of variations in the shape 
or relative positioning thereof. 
In the production of such weather strips, there is the problem of cutting 
the continuously extruded element to size in order to obtain pieces of a 
length which is predetermined in dependence on the fitting requirements. 
The cutting zones are normally coordinated with the variations in the 
characteristics of the extrusion. The cutting must be effected 
automatically, in synchronisation with the advance of the weather strip 
output by the extrusion head and with maximum precision, that is, exactly 
in correspondence with the predetermined zones. However, since the speed 
of advance of the extrusion may be subject to variations during extrusion, 
control of the cutting action cannot be directly related to this advance. 
It is therefore necessary to provide references on the extruded weather 
strip for detection by suitable sensors for controlling the cutting. 
According to current techniques used by the Applicant, such references are 
constituted by additional parts in the form of appendages or projections 
formed on the weather strip directly during extrusion, in correspondence 
with the predetermined cutting zones, and cooperating, for example, with 
mechanical detectors operatively associated with the cutting unit. 
This solution involves considerable complications in the weather strip 
extrusion process, as well as additional costs due to the need to use 
auxiliary equipment for obtaining the reference projection and for 
compensating for pressure differences which are generated according to 
whether the additional part is present or not in a section of the 
extrusion. Moreover, this projection remains on the finished weather strip 
and is then visible from outside, with obvious aesthetic disadvantages 
when the weather strip is in the mounted condition. To avoid the latter 
problem, it is necessary to remove the reference projection after the 
weather strip has been cut, which involves further production tasks. 
SUMMARY OF THE INVENTION 
The object of the present invention is to avoid the above problems, by 
means of a method adapted to enable the precise cutting to size of 
extruded weather strips with variable characteristics of the type defined 
at the beginning, which enables the use of projections or similar 
reference elements visible from outside, or intended subsequently to be 
removed from the weather strip, to be avoided. 
The method according to the invention is characterised in that it consists 
of the at least partial omission during extrusion of the weather strip, of 
at least one of the internal longitudinal retaining ribs of the anchoring 
profile of the weather strip in sections which can be related to the 
predetermined cutting zones, and of the detection of the omitted sections 
and the provision of corresponding signals to enable cutting. 
The elimination of short portions of one or more of the internal ribs of 
the anchoring profile may be achieved by providing the extrusion head with 
simple devices for temporarily interrupting the flow of material destined 
to form the retaining rib or ribs from which the omission is to be 
effected. This interruption occurs for very short periods and the omitted 
sections are therefore of a size which has a negligible effect on the 
functioning of the ribs. In other words, the efficiency of the anchorage 
of the profile of the weather strip is not impaired and the aesthetic 
aspect of the weather strip is likewise unaltered, eliminating the need 
for further supplementary operations after cutting. 
According to the invention, the detection of the omitted sections of the 
rib or ribs and the generation of the relative signals for enabling 
cutting are preferably performed by means of an optical transducer.

DETAILED DESCRIPTION OF THE INVENTION 
Referring initially to FIGS. 1 and 2, a weather strip produced by means of 
continuous extrusion is generally indicated 1 and is intended, in 
particular, to be fitted to the edge of an aperture or closure element of 
a motor vehicle body. The weather strip 1 comprises a U-sectioned 
anchoring profile 2 of elastomeric material, to which is connected a 
sealing profile 3 co-extruded with the anchoring profile 2 and made, for 
example, of a cellular elastomeric material. The anchoring profile 2 has 
longitudinal retaining ribs 4 on the internal surfaces of the U for 
enabling the weather strip to be fitted to the edge of an aperture or 
closure element and for preventing its detachment. The anchoring profile 2 
is usually provided with a stiffening core, normally metallic, indicated 
5. 
FIG. 2 shows the weather strip in cross-section and fitted to a closure 
element C (for example, a door) of a motor car body. 
The weather strip 1 normally has variable characteristics produced directly 
during extrusion. These variable characteristics may consist, for example, 
of a longitudinally differentiated piece of the wall of the tubular 
sealing profile 3, of a different shape of the line of connection between 
the tubular profile 3 and the anchoring profile 2, of a differentiated 
configuration of the latter, or even of variations in the shape or 
dimensions of one or both of the profiles 2 and 3. 
As stated above, the weather strip 1 is produced continuously by means of 
an extrusion head and must then be cut to size transversely, so as to 
obtain pieces of predetermined length in dependence on the fitting 
requirements. Clearly, the cutting must be carried out very precisely, 
independently of the speed of advance of the weather strip 1 at the output 
of the extrusion head, since this speed may be subject to variations. 
Moreover, the cutting is normally carried out in correspondence with 
predetermined zones related to the variations in the characteristics of 
the weather strip. 
According to the invention, these cutting zones are identified by means of 
references constituted by interruptions in one or more of the internal 
longitudinal retaining ribs 4 of the anchoring profile 2, spaced from each 
other by a distance equal to the length of the pieces of the profile to be 
cut to size. 
With reference to FIG. 3, in the case of the example illustrated, short 
sections 4a of one of the ribs 4 adjacent the longitudinal edges of the 
profile 2 are omitted in correspondence with the predetermined cutting 
zones during the extrusion stage of the weather strip 1. This omission is 
obtained simply by the periodic interruption of the supply through the 
extrusion head of the elastomeric material destined to form the rib 4. The 
omitted sections 4a are detected downstream of the extrusion plant, during 
advance of the weather strip 1, by means of an optical transducer 6 facing 
the path of movement of the rib 4 in which the interruptions 4a are made. 
The optical transducer 6 may, for example, be constituted by the end of a 
double fibre optic receiver/transmitter with "reflex" operation. The 
electrical signals generated by the transducer 6 in correspondence with 
the omitted sections 4a of the rib 4 are sent to an electronic control 
unit 7 through which the equipment for cutting the weather strip is 
controlled by means of devices known to an expert in the art. 
It should be noted that the optical transducer 6 could be replaced by a 
different but functionally equivalent detection device, such as, for 
example, a mechanical or electromechanical feeler. 
It will be clear that the method according to the invention uses simply and 
economically produced references which, in particular, are situated inside 
the weather strip 1 and are thus invisible from outside in the fitted 
condition of use shown in FIG. 2. In this way, aesthetic alterations of 
the weather strip 1 are avoided without, however, any risk of prejudicing 
the functional characteristics of the weather strip. In fact, the removal 
of short sections 4a of one or more of the internal ribs 4 does not' alter 
the anchoring characteristics of the profile 2 relative to the support 
structure C.