Apparatus and method for detecting the presence of a discontinuity on a glass surface

The present invention is directed to an apparatus and method for detecting the presence or absence of a discontinuity on a glass surface. The apparatus includes a transmitting means for directing and receiving infrared electromagnetic radiation relative to the glass surface, a positioning means for positioning the transmitting means in a fixed angular and distance relation with respect to the glass surface, and a sensing means for determining the relative magnitude of the received radiation, the magnitude being indicative of the presence or absence of a discontinuity. The apparatus may be translated relative to the glass surface to detect discontinuities therealong.

TECHNICAL FIELD 
This invention relates generally to an apparatus and method for detecting 
the presence or absence of a discontinuity on a glass surface, and in 
particular an apparatus or method using a photoelectric sensor. 
BACKGROUND ART 
Automotive glass sheets such as front windows or back lights are generally 
adhesively secured within window frames of automotive vehicles. Prior to 
installation, a number of preparation steps are required to insure that 
the adhesive properly secures the glass within the frame. 
The first step is to chemically etch the marginal edge of the glass. This 
is accomplished by the application of a liquid primer which etches and 
cleans the glass surface. After applying this solution by brush, dobbing, 
spraying or other means, this primer is wiped away with a lint free 
substance to provide a clear, dry surface. 
The second step is to apply a black primer to the etched edge of the glass 
prior to the application of a urethane sealant. The black primer protects 
the urethane sealant from sunlight which causes deterioration in the 
sealant. The black primer is applied by means of a brush, spray or drip 
and is allowed to dry. Then the urethane sealant is applied prior to 
installation of the glass in the vehicle. 
A serious problem over the years has been to detect whether the primers, in 
particular the etching primer which is generally clear, ave been applied 
continuously along the marginal edges of the glass surface. If any primer, 
either the etching primer or the black primer, is not applied, the bonding 
of the urethane sealant may fail resulting in the glass coming free of the 
automotive vehicle. 
Various approaches, i.e., camera systems, thermal sensors, and flow sensors 
have been experimented with and capacitative probes have been inserted 
into a brush applying the primers all in an effort to determine whether 
the sealant has been or is being applied to the glass. None of these 
approaches has proven satisfactory. 
These means of detection of the primer coatings suffer from several 
disadvantages. First, typically a rather large quantity of primer must be 
present in order for these detection means to insure detection of their 
presence. A second problem is that these detection means generally 
indicate only whether a coating is present and do not readily quantify the 
amount present. Third, these means are not suitable to sense the presence 
of a coating on a glass surface as the sensing means moves relative to the 
glass surface. 
Previous attempts at directing electromagnetic radiation perpendicularly 
downward towards a glass surface and measuring the difference between the 
reflectivity of a wet surface and a dry surface has proven unsuccessful in 
determining the presence or absence of a coating of primer. 
DISCLOSURE OF INVENTION 
It has been discovered that there exists a difference in the relative 
reflectivity of incident infrared electromagnetic radiation upon a dry 
versus wet glass surface when the incident radiation is directed at an 
angle of 3.degree.-18.degree. from a line perpendicular to the glass 
surface. The present invention senses this difference in reflectivity to 
determine the presence or absence of liquid coating on a glass surface. 
Further, this invention may detect the presence of a crack on a glass 
surface due to the change in reflectivity of incident radiation upon the 
glass surface with a crack therein. 
The present invention includes an apparatus for detecting the presence or 
absence of a discontinuity on a glass surface. These discontinuities 
include a coating such a liquid primer or a crack located on a glass 
surface. The apparatus comprises a transmitting means for directing 
electromagnetic radiation in the infrared range toward a glass surface and 
for receiving infrared electromagnetic radiation reflected back from the 
glass surface. Also included is a sensing means for sensing the relative 
strength of the reflected radiation to determine the presence or absence 
of a discontinuity. The invention further includes a positioning means for 
positioning the transmitting means in a fixed angular and distance 
relation relative to the glass surface. The apparatus may be moved 
relative to the glass surface to sense the presence of a discontinuity 
over a continuous region of the glass surface. 
The present invention has several advantages over other detection apparatus 
and methods. First, the present invention is more sensitive to 
discontinuities than the apparatus and methods used in the past. Second, 
the present invention can be used to evaluate the presence of a 
discontinuity as the apparatus moves relative to the glass surface at a 
relatively high rate of speed. Finally, this invention can, to a degree, 
quantify the amount of material present on a glass surface. 
An important object of the present invention is to overcome the 
disadvantages and problems encountered with respect to prior methods of 
detecting discontinuities on a glass surface and in particular to 
detecting coatings on the surface. 
Another object is to provide a more sensitive method for detecting the 
presence or lack of presence of a discontinuity on a glass surface as 
compared to prior methods used. 
Yet another object is to provide an apparatus and a method wherein the 
sensing of a discontinuity as the sensing device moves relative to a glass 
surface is performed at a relatively high rate of speed. 
Other objects, features and advantages will become more readily apparent 
from the following description and accompanying sheet of drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
The present invention includes an apparatus and a method for detecting the 
presence or absence of a discontinuity on a glass surface. A description 
of the preferred embodiment of the apparatus and method follows. 
As shown in FIG. 4, an apparatus 12 for detecting the presence of 
discontinuities on a glass surface 14 includes a transmitting means 16 for 
directing incident upon and receiving from the glass surface reflected 
electromagnetic radiation in the infrared range of the spectrum, i.e. 880 
nanometers, a positioning means 18 for supporting and positioning 
transmitting means 16 in a fixed angular and distance relation from the 
glass surface 14, and a sensing means 20 for sensing the magnitude of the 
reflected radiation received by the transmitting means 16. Transmitting 
means 16 is optically connected to the sensing means 20. FIG. 9 shows that 
a portion of the incident radiation is reflected back to the transmitting 
means 20 as coincident radiation 15 and a portion scatters as 
noncoincident radiation 17. 
Transmitting means 16 is preferably a commercially available fiber optics 
light guide such as Model BF-C-36 sold by Tri-Tronics Company, Inc. This 
particular model has a bundle of fiber optics, approximately half of which 
transmit and direct emitting radiation towards the glass surface 14 and 
the other half which receive and transmit reflected radiation from the 
glass surface 14 or discontinuities 22 located thereon. The emitting and 
receiving fiber optics are parallel to one another and evenly dispersed 
throughout the bundle. The bundle of fiber optics is arranged 
rectangularly and the width of radiation scanning glass surface 14 is 
approximately 0.55 inch. 
Sensing means 20 is a photoelectric sensor such as a Smarteye Switching 
Model SAL sold by Tri-Tronics Company, Inc. The sensing means 20 is 
connected to the transmitting means 16 through an Optical Block model F1, 
also sold by Tri-Tronics Company, Inc. The sensing means 20, i.e. the 
Smarteye Switching Model SAL, both emits infrared radiation and senses the 
magnitude of the reflected infrared radiation which is input from the 
transmitting means 16. It is contemplated that a separate means for 
generating the infrared light could also be used and connected to the 
transmitting means 20. The sensing means 20 generates an analog output 
voltage proportional to the magnitude of reflected radiation input 
thereto. 
Positioning means 18 is a compliance device which adapts to the glass 
surface 14 and supports and positions the transmitting means 16 in a fixed 
angular and distance relation relative to the glass surface 14. An angle 
.alpha., as shown in FIG. 4, defines the angle between a line 
perpendicular to the glass surface 14 and the incident and reflected 
radiation transmitted through the transmitting means 16 and lies in a 
plane parallel to a longitudinal member which is also the plane of 
translation of the apparatus 12. The perpendicular distance between the 
glass surface 14 and the end of transmitting means 16 is defined by 
distance .delta.. .alpha. may range from 3.degree. to 18.degree., and the 
distance .delta. may range from 0.5 to 1.5 inches. 
For a particular type of glass surface and fretting (the marginal edge of 
the glass surface often comes with a black coating or fretting thereon 
from the glass manufacturer), the optimal angle .alpha. and distance 
.delta. are experimentally determined. A variety of .alpha. and .delta. 
combinations are investigated to establish which output of voltage from 
sensing means 20 for reflected radiation received from a dry surface is 
maximum relative to the output when receiving reflected radiation from a 
wet surface. 
Glass used by different automakers has proven to have different optimal 
combinations of .alpha. and .delta.. For a particular glass tested, at an 
.alpha. of 15.5 degrees and a .delta. of 0.500", the relative difference 
in reflectivity of the dry surface versus the wet surface has been 
established to be maximum. The voltage output from the sensing means 20 
for a wet surface is nearly zero while with a dry surface a voltage of 15 
volts is output. Consequently, the value of voltage output from sensing 
means 20 is determinative of the presence or absence of the primer coating 
on glass surface 14. In the event that streaking of the applied primer 
occurs, the degree of streaking is proportional to the voltage output from 
sensing means 20 and is somewhat indicative of the amount of liquid or 
primer present. 
As shown in FIG. 4, positioning means 18 includes longitudinal member 30 
having a leading end 32 and a trailing end 34. Pivotally connected to the 
leading end 32 is a rolling member 36 and at the trailing end is a similar 
pivotally connected rolling member 38, both of which are made of a 
wear-resistant material such as nylon. The rolling member 38, as shown in 
FIG. 6, serves as a pulley around which a felt ribbon 40 is driven. The 
felt ribbon 40 is made of polypropylene and/or polyester material, and is 
stored on a large rotatable spool 42. 
Positioning means 18 further includes a positioning bracket 46 connected to 
longitudinal member 30 and supports the end of the transmitting means 16. 
Preferably, the optimal .alpha. and .delta. for the particular glass 
surface 14 is experimentally determined as described above, with bracket 
46 then being fixedly secured to longitudinal member 30 such that .alpha. 
and .delta. are permanently fixed relative to the glass surface 14. This 
prevents accidental misalignment of .alpha. and .delta. while apparatus 12 
is operating. Alternatively, bracket 46 may be designed such that it is 
slidably and rotatably adjustable relative to longitudinal member 30 to 
fix the transmitting means 16 in various angular and distance relations 
relative to the glass surface 14. 
Longitudinal member 30 also supports a dispenser 48 having a brush 50 
attached thereto for applying primer. Primer is supplied to the dispenser 
48 by a supply tube 52. The brush 50 applies a coating of the primer ahead 
of the incident and reflected radiation. 
A pair of springs 54 provide biasing to ensure that rolling member 36 and 
felt ribbon 40 maintain contact with the glass surface 14. 
The apparatus 12 may be either stationary or moving relative to glass 
surface 14 when detecting discontinuities 22 on the glass surface 14. 
Preferably, a robotic linkage 56 supports apparatus 12 such that it is 
translated about the marginal edge of glass surface 14 with the 
positioning means 18 having rolling member 36 and the felt ribbon 40 
contacting the glass surface 14 while maintaining the relative positioning 
of transmitting means 16 with respect to glass surface 14. The 
translational movement of apparatus 12 is such that rolling member 36 will 
precede felt ribbon 40 across the glass surface 14. The rolling members 36 
and 38 are longitudinally spaced rather closely together so that the 
transmitting means 16 and the brush 50 maintain a relatively uniform 
distance .delta. from glass surface 14 as apparatus 12 translates about 
changing contours of glass surface 14. Using the transmitting and sensing 
equipment as described above, apparatus 12 may be translated at a rate of 
25"/sec while accurately detecting discontinuities 22. 
In operation, rolling member 36 and felt ribbon 40 are placed in contact 
with glass surface 14, with springs 54 biasing the positioning means 18 
such that the contours of the glass surface 14 are followed. The 
positioning bracket 46 is fixedly secured to longitudinal member 30 such 
that the distance .delta. and the angle .alpha. are permanently set to 
their desired parameters, which for a glass surface as described above 
would be preferably at an .alpha. of 16.5.degree. and at a .delta. of 
0.500". 
The dispenser 48 and associated brush 50 are also positioned such that the 
brush 50 contacts the glass surface 14. 
The sensing means 20 is then calibrated. If there is no interfering 
discontinuity 22, i.e. a dry or uncracked surface, located on the glass 
surface 14, a substantial portion of the emitted radiation from 
transmitting means 16 will reflect off the glass surface 14 and is 
received by transmitting means 16 which transmits the radiation to sensing 
means 20. The output of voltage from sensing means 20 is proportional to 
the magnitude of the reflected radiation and is adjusted such that a 
steady voltage, i.e. 15 volts, is output in response to emitted infrared 
radiation upon the clean, continuous glass surface 14. The output voltage 
relatively to a wetted surface should be very low. FIG. 9 shows 
schematically that some of incident radiation from transmitting means 20 
returns back thereto. 
As seen in FIG. 1, robotic linkage 56 supports and translates apparatus 12 
about the marginal edge of glass 14. Supply tube 52 supplies dispenser 48 
with primer and brush 50 applies a coating of the primer to glass surface 
14 as apparatus 12 is translated along the margin of the glass. 
When the coating completely covers the glass surface 14, very small amounts 
of radiation will be reflected back to the transmitting means 20, and 
accordingly very little voltage will be output from sensing means 20. If 
no coating is applied, the glass surface will remain fully reflective and 
a large magnitude of reflected radiation will be received and the 15 volts 
will be output by sensing means 20. In the event that streaking occurs as 
shown in FIG. 7, the increase in output voltage will be indicative of the 
severity of the streaking. 
If a sufficiently high voltage is output, i.e. 5.0 volts if the maximum 
output is 15 volt, a signal device (not shown) may be activated indicating 
that glass surface 14 is defective and appropriate corrective measures 
should be taken. 
Trailing the applied coating of primer is felt ribbon 40 which wipes and 
removes the primer from the glass surface 14. The rolling member 38, as 
shown in FIG. 6, is driven to rotate the felt rope 40 thereabout to ensure 
that all of the excess primer is removed. 
A black primer is applied thereafter, which is a prerequisite to applying a 
urethane sealant. A pivotally connected trailing rolling member (not 
shown) similar to rolling member 36 replaces rolling member 38 and is 
perpendicularly offset from longitudinal member 30 such that the black 
primer is left undisturbed on surface 14 and is allowed to dry without 
being crossed by the offset rolling member. The urethane sealant is then 
applied. 
FIG. 8 shows a marginal edge on the glass surface 14 which has a crack 
therein. The crack serves as a discontinuity 22' which adversely affects 
reflectivity of glass surface 14 and accordingly creates a spike in the 
voltage output from sensor means 20. The spike in voltage output may be 
used to signal that a crack is present in the glass surface and that 
appropriate corrective measures should again be taken. 
While the foregoing specification of this invention has been described in 
relation to certain preferred embodiments thereof, and many details have 
been set forth for the purpose of illustration, it will be apparent to 
those skilled in the art that the invention is susceptible to additional 
embodiments and that certain of the details described herein can vary 
considerably without departing from the basic principles of the invention.