PROCEDE PERMETTANT DE MESURER L'AFFAISSEMENT D'UNE PLAQUE DE VERRE

METHOD FOR MEASURING THE SAGGING OF A GLASS PANEL

Abrégé français

L'invention concerne un procédé permettant de mesurer l'affaissement d'une plaque de verre (6) dans le processus de cintrage de la plaque de verre (6) sur un moule en couronne (4). Le procédé consiste à mesurer l'affaissement au niveau d'un point de mesurage d'une plaque de verre et à utiliser les données de mesurage afin de réguler l'avancement du processus de cintrage, notamment le chauffage de la plaque de verre (6) ou l'interruption du processus de cintrage. Un plan de référence (5a, 5b) fixe par rapport au moule en couronne (4) est établi, un indicateur de distance (7, 70) est utilisé pour mesurer une distance entre le plan de référence (5a, 5b) et l'indicateur de distance (7, 70), un indicateur de distance (7, 70) est utilisé pour mesurer une distance entre le point de mesurage de la plaque de verre (6) et l'indicateur de distance (7, 70). Pour déterminer l'affaissement de la plaque de verre (6), on compare la distance entre le plan de référence (5a, 5b) et l'indicateur de distance (7, 70) à la distance entre le point de mesurage de la plaque de verre (6) et l'indicateur de distance (7, 70).

Abrégé anglais

The present invention relates to a method for measuring the sagging of a glass
panel (6) in the process of bending the glass panel (6) on a ring mould (4).
The method comprises measuring the sagging at a glass panel's measuring point
and the measurement data is applied to control progress of the bending
process, especially heating of the glass panel (6) or abortion of the bending
process. A reference plane (5a, 5b) stationary with respect to the ring mould
(4) is established, a distance gauge (7, 70) is used for measuring a distance
between the reference plane (5a, 5b) and the distance gauge (7, 70), a
distance gauge (7, 70) is used for measuring a distance between the glass
panel's (6) measuring point and the distance gauge (7, 70). The glass panel's
(6) sagging is determined by comparing the distance between the reference
plane (5a, 5b) and the distance gauge (7, 70) to the distance between the
glass panel's (6) measuring point and the distance gauge (7, 70).

Revendications

7
Claims
1. A method for measuring the sagging of a glass panel (6) in the process of
bending the glass panel (6) on a ring mould (4), said method comprising
establishing a reference plane (5a, 5b) stationary or positionally fixed with
respect to the ring mould (4) and measuring the sagging at a glass panel's
measuring point and the measurement data being applied to control
progress of the bending process, especially heating of the glass panel (6) or
abortion of the bending process, characterized in that a distance gauge (7,
70), including a transmitter and a receiver for laser pulses, is used for
measuring a distance between the reference plane (5a, 5b) and the distance
gauge (7, 70) by determining the transmission time of a laser pulse (7a)
from transmitter to receiver, a distance gauge (7, 70) is used for measuring
a distance between the glass panels (6) measuring point and the distance
gauge (7, 70) by determing the transmission time of the laser pulse (7a)
from transmitter to receiver, and the glass panel's (6) sagging is determined
by comparing the distance between the reference plane (5a, 5b) and the
distance gauge (7, 70) to the distance between the glass panel's (6)
measuring point and the distance gauge (7, 70).
2. A method as set forth in claim 1, characterized in that the first distance
gauge (7) is used for measuring the sagging of a pre-bent glass panel (6)
prior to a final bending process and the second distance gauge (70) is used
for measuring the sagging of the glass panel (6) during a final bending
process.
3. A method as set forth in claim 1 or 2, characterized in that the glass
panel's (6) sagging is measured at several measuring points successive in the
glass panel's (6) advancing direction.
4. A method as set forth in any of the preceding claims 1-3, characterized
in that the glass panel (6) lies between two reference planes (5a, 5b) in the
glass panel's (6) advancing direction.

8
5. A method as set forth in any of the preceding claims 1-4, characterized
in that the reference plane (5a, 5b) and/or the measuring point are located
essentially on the ring mould's centre axis of symmetry.

Description

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Method for measuring the sagging of a glass panel
The present invention relates to a method for measuring the sagging of a
glass panel in the process of bending the glass panel on a ring mould, said
method comprising establishing a reference plane stationary or positionally
fixed with respect to the ring mould and measuring the sagging at a glass
panel's measuring point and the measurement data being applied to control
progress of the bending process, especially heating of the glass panel or
abortion of the bending process.
This type of method for measuring a glass panel's sagging is prior known
from Finnish patent application FI-912871. That comprises monitoring the
sagging with a measuring instrument for applying a laser beam to the
surface of a glass panel and a CCD camera is used for tracking the distance
of a confluence point between glass and laser beam from a reference plane.
This arrangement requires a lot of space and sets constraints regarding the
choice of a measuring point. An angle of reflection required for the laser
beam calls for two holes in the roof of an oven for each measuring point and
accuracy is not sufficient because of the angle of reflection.
Patent application WO 02/23124 discloses a method, in which a line camera
is used for tracking the angle of reflection of a light beam reflected from
glass. The angle of reflection is highly sensitive to a possible surface
defect in
glass and to a local curvature defect in glass, whereby the angle of
reflection
provides a defective measuring result. This method may also involve
measuring the distance of a reflection point from the camera by applying a
second light source and the triangulation principle.
In addition to the above, there are a host of prior known methods, disclosed
for example in publications FI 850120 and FI 98757, wherein light beams
reflected from an arched or arching glass panel are monitored in various
ways by means of a line or matrix camera or cameras. These methods are

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hampered by problems similar to those found in the method disclosed in
publication WO 02/23124.
It is an object of the present invention to eliminate or substantially
alleviate
the above drawbacks.
In order to achieve the above object, a method of the present invention is
characterized in that a distance gauge, including a transmitter and a receiver
for laser pulses, is used for measuring a distance between the reference
plane and the distance gauge by determining the transmission time of a laser
pulse from transmitter to receiver, a distance gauge is used for measuring a
distance between the glass panels measuring point and the distance gauge
by determing the transmission time of the laser pulse from transmitter to
receiver, and the glass panel's sagging is determined by comparing the
distance between the reference plane and the distance gauge to the distance
between the glass panel's measuring point and the distance gauge.
Preferred embodiments of the present invention are set forth in the
dependent claims.
The invention will now be described in more detail with reference to the
accompanying drawings, in which:
Fig. 1 shows schematically an apparatus of the invention in a side view,
and
Fig. 2 shows schematically an apparatus of the invention in a plan
view.
Thus, figs. 1 and 2 depict one embodiment for an apparatus applying a
method of the invention. There is shown a section of an oven 1 designed for
bending a glass panel 6. The oven 1 includes an elongated space defined by
walls la, which is divided by means of a floor lb or the like for two

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elongated spaces on top of each other. The upper of these spaces is divided
by the vertical walls of mould carriages 3 for successive preheating
compartments 2, followed by an actual bending compartment 2a for the
glass panel 6, in which the inventive method for measuring the glass panel's
6 sagging is actually applied. The glass panel is generally heated by means of
resistances 9 disposed in the heating compartments 2 and in the actual
bending compartment 2a. The section of an oven downstream of the
bending compartment includes usually a lift compartment (not shown),
whereby the bent glass panel 6 is conveyed into the lower space. The lower
space is divided by the vertical walls of mould carriages 3 for successive
cooling compartments 8 for performing a controlled cooling of the glass
panel.
The glass panel 6 is carried on the mould carriage 3 along a conveying track
provided in the oven 1 in a per se known manner from one compartment to
the next. The glass panel 6 is laid on a ring mould 4 attached to the mould
carriage 3. The advancing direction of an upper conveying track is indicated
by reference numeral Dl and the traveling direction of a lower conveying
track is indicated by reference numeral D2. The method comprises
preheating the glass 6 on top of the ring mould 4 in the compartments 2. In
the process of bending on the ring mould 4, the glass 6 is not supported at
all in its middle section, but only along its periphery. As the mould carriage
3,
and thereby also the glass panel 6, proceeds from the preheating
compartment 2 to the bending compartment, the glass panel 6 may already
be in a somewhat bent condition in its middle section. The actual bending,
i.e. providing the glass panel 6 with a desired sagging, is performed in the
bending compartment 2a.
In view of measuring the above sagging, between the preheating
compartment 2 and the bending compartment 2a, outside the compartments
2 and 2a, preferably on top of the oven 1, is disposed a first distance gauge
or sensor 7, which defines a first measuring point for the glass panel 6 in
the
proceeding direction of the track Dl. In addition to this, on top of the

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bending compartment 2a, preferably above the glass panel's 6 middle section
(with the glass panel immobilised in the bending compartment 2a), is
disposed a second distance gauge or sensor 70, which is preferably identical
in its design and function to the distance gauge 7 placed between the
compartments. The second distance gauge 70 defines a second measuring
point. This gauge 7 and 70, used for applying the method, comprises a
transmitter and a receiver. The transmitter applies to the glass panel's 6
middle section, the surface thereof, at desired intervals, a short laser pulse
7a which reflects from the glass panel's 6 surface to the receiver. The
distance can be determined on the basis of the laser pulse's 7a proceeding
time from transmitter to receiver. The gauges 7 and 70 measure this
proceeding time. The measurement can be performed at each measuring
point from a single hole in the oven's roof, the space demand being modest
and the measuring point or a plurality of measuring points being easy to
choose.
In order to obtain this measuring result, it is necessary to establish a
reference plane in conjunction with the glass panel 6 for comparing
therewith the result measured from the middle of the glass panel 6.
Therefor, the ring mould 4 or the mould carriage 3, preferably along the ring
mould's 4 centre axis of symmetry, is provided with markers 5a and 5b or
identification tags. Viewed in the proceeding direction Dl, the markers are
positioned in the carriage's leading and trailing sections in such a way that
the glass panel 6 is held therebetween in its advancing direction.
A first measurement is performed while conveying the carriage 3 from the
preheating compartment 2 to the bending compartment 2a. The first
measurement involves using the distance gauge 7 for measuring a distance
between the reference plane 5a and the distance gauge 7. Thus, it is
preferred that the marker 5a be provided with a reflective surface for a laser
pulse to reflect back to the distance gauge 7. A first fixed reference plane
is
thereby established for a second measurement. Next, the second
measurement involves using the distance gauge 7 for measuring a distance

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between the glass panel's 6 measuring point and the distance gauge 7. The
glass panel's 6 sagging is determined by comparing at least these two
measuring results to each other. The glass panel 6 may have its surface 6b
provided in the glass panel's 6 advancing direction even with a plurality of
5 successive measuring points or the measurement may proceed almost
continuously for providing a sagging profile in almost solid line.
As the mould carriage 3 proceeds further along its track Dl, the trailing
marker 5b will also pass by the discussed measuring point for providing a
second reference plane. Thus, the mould-specific reference data can be
readily obtained from two locations (a measurement of two reference planes
enables a more precise determination of the reference plane than a
measurement of just one reference plane), and also obtained is information
about possible sagging caused by preheating. This information can be
utilized, for example, in the process of determining or regulating beforehand
an on/off pattern or effects produced by the bending compartment's 2a
resistances 9 in preparation of bending the discussed glass panel 6. The
measurement data can also be used in the process of regulating the
preheating compartments' 2 heating effect for subsequent glass panels.
The actual sagging measurement, in other words a measurement for a
distance and variation of distance to the immobilised glass panel's 6 centre
(measuring point), is performed with the second distance gauge 70 during
the bending process as shown in fig. 1. In order to ensure a correct
measuring result, the second gauge 70 also needs a reference plane, which it
acquires by measuring a distance to the marker 5a carried along with the
mould 4 proceeding into the bending compartment 2a. The measuring result
obtained from the measuring point is compared to the reference plane
measured by the second gauge 70. In addition to or instead of this, it is
possible to effect a comparison with the reference planes measured by the
first gauge 7. With regard to the marker 5b, the only available measuring
result is the one provided by the first gauge 7. It is further possible to
perform a measurement of sagging and a process control during the bending

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process without the first measurement effected by the first gauge 7. By
tracking the measuring result or results, the heating process (resistances)
can be controlled for producing a desired sagging. Once a desired sagging is
achieved, the bending process can be stopped and the glass panel 6 carried
along on its track Dl for further processing.
The number of gauges 7, 70 can be one, two or more. A practical
implementation of the invention requires at least a gauge 70 present in the
bending compartment. The number of reference planes 5a, 5b can also be
one, two or more for each bending mould. Each reference plane 5a, 5b must
be immobile or positionally fixed relative to the mould 4.

Dessin représentatif