Vehicle windshield scanning system

The windshield scanning system of the present invention includes a windshield scanner apparatus, a general purpose digital computer and an output device. The windshield scanner apparatus further includes a scanner which is adapted to crawl across a large portion of a windshield surface. The general purpose computer is programmed to receive scanner image data and analyze representative samples of the scanner image data to determine either the general surface condition of the windshield or the surface condition given by the worst sample. The computer output device is used to display the results of the analysis.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus and method for measuring the 
surface damage of a vehicle windshield using a digital imaging device. 
2. Description of the Prior Art 
Pitting and scratching of vehicle windshields has long been a problem that 
causes interference with operator vision and driving safety. "Direct 
Measurement of Windscreen Surface Wear and the Consequences of Road 
Safety" presented by A. Timmermann at the Conference on Vision in 
Vehicles, Nottingham, UK, 9-13 September 1985, presents an apparatus for 
measuring the light scatter of a localized beam of light as it passes 
through a vehicle windshield. It comprises a means for directing a 
parallel beam to a first light detector. A second light detector 
surrounding the first light detector at the focus point detects stray 
light that is diverted by the windshield surface damage. With Timmerman's 
device the ratio of stray light to direct light provides a measure of 
windshield damage. Timmermann's device yields exact measurements for 
localized windshield damage but requires expensive, specialized equipment. 
Further, significant time and effort is required in the use of 
Timmermann's device to assess the surface quality of a windshield. 
Our investigations have shown that pitting varies widely across a 
windshield surface. Consequently, what is needed is a means for assessing 
pitting or surface damage over a large area of a windshield. We have found 
that a pattern of sample zones taken from a large area is an efficient and 
reliable means for assessing pitting or surface damage over a large area 
of a windshield. Further, we have found that values for pitting in pixels 
per square inch either on a worst case or on an average bases can be 
determined which correspond to a windshield having a unacceptable degree 
of surface damage or pitting. 
Our investigations have also revealed that the peripheral glare produced by 
surface pitting in areas of the windshield opposite an operator's eye 
point can produce significant visual interference. A method and apparatus 
is needed to quickly assess windshield surface quality in windshield areas 
opposite the operator's eye point. Accordingly, what is needed is a method 
and apparatus for assessing windshield surface quality over large portions 
of a windshield surface and consequently what is also needed is a method 
and apparatus for assessing windshield surface quality in a windshield 
area opposite an operator's eye point. 
SUMMARY OF THE INVENTION 
The present invention satisfies these needs by providing a new apparatus 
and method for scanning a vehicle windshield and determining the amount of 
surface damage present in the surface of a vehicle windshield. The 
windshield scanning system of the present invention includes a windshield 
scanner apparatus, a general purpose digital computer, and an output 
device such as a screen or a printer. In a first embodiment, the 
windshield scanner apparatus and method further includes a scanner which 
is adapted to crawl across a large portion of a windshield surface. The 
general purpose digital computer is programmed to receive scanner image 
data and analyze representative samples of the scanner image data to 
determine either the general surface condition of the windshield or the 
surface condition found in the worst sample. A computer printer or screen 
is used to output the results of the analysis. In a second embodiment, the 
windshield scanner apparatus and method includes a digital imaging device 
having a two dimensional array of photo-detectors adapted to rapidly 
produce a set of image data containing values corresponding to the output 
of each of the photo-detectors. The general purpose digital computer is 
programmed to receive the set of image data and analyze that image data to 
determine the condition of the windshield surface. 
In this way, the apparatus and method of the present invention provides a 
means for efficiently measuring surface damage over a large portion of a 
windshield surface. Values for surface damage can be gathered in terms of 
highly reflective, low transmissibility pixels per square inch for a 
number of sample zones and compared against a predetermined range or scale 
of values which represent a range from zero to that of a surface having an 
unacceptable degree of surface damage. Accordingly, the apparatus and 
method of the present invention can be employed to quickly assess the 
surface condition of a vehicle windshield either in a selected zone or 
across a large area of the windshield.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a vehicle windshield scanning system 10 in relation to a 
vehicle windshield 5. The vehicle windshield scanning systems includes a 
windshield scanning apparatus 20, a general purpose digital computer 80, 
and a printer 90. Scanning apparatus 20 further includes a scanner 
assembly 30, a scanner track 50, and a black mask 75. 
As can be seen in FIG. 2, scanner assembly 30 includes a scanner 32, a 
protective case 34, surrounding scanner 32 and track wheels 40. Scanner 32 
can be a Logitec PageScan.TM. color scanner having a sight source (not 
shown), charge coupled device (CCD) digital photo-detectors, a drive means 
for driving scanner 32 across vehicle windshield 5 and a contact sensor 
33. The scanner drive means propels scanner 32 and scanner assembly across 
the windshield surface as long as contact sensor 33 senses contact. 
Contact sensor 33 turns scanner 32 off if it is not in contact with 
windshield 5. A power and data transfer line 36 connects scanner 32 to 
general purpose digital computer 80. Wheels 40 are generally a pair of 
wheels adapted to roll in a direction parallel to the length of windshield 
5 and are mounted to protective case 34 sot hat they can be adjusted at 
sliding joint 42 towards and away from windshield 5 and pivoted about 
pivot joint 44 to change their angle with respect to windshield 5. 
As can be further seen in FIG. 2, scanner track 50 includes a first flange 
55, a second flange 60, and suction cups 70. First flange 55 is oriented 
generally parallel to the windshield surface 5 while second flange 60 is 
continuous with and generally normal to first flange 55. Suction cups 70 
are evenly spaced along the length of first flange 55 temporarily fasten 
scanner track 50 to windshield 5 which is adapted for receiving track 
wheels 40. Scanner track 50 can be made from almost any flexible material 
capable of conforming to the shapes of various vehicle windshields. 
As can also be seen in FIG. 2, track wheels 40 ride in track wheel groove 
57 of track 50. Track wheels 40 can be adjusted normally and pivotably to 
insure that they ride smoothly in track wheel groove 57. After scanner 
assembly 20 is manually placed so that flat track wheels 40 are positioned 
at one end of track wheel groove 57, it is activated by general purpose 
digital computer 80. After being activated, scanner 32 crawls across 
windshield 5 as track wheels 40 roll in track wheel groove 57 thereby 
guiding the path of scanner 32. As scanner 32 crawls across windshield 5, 
it shines light on windshield 5. Most of that light passes through 
windshield 5 without any interference, is absorbed by flat black mask 75 
and is registered as black digital pixel elements by the CCD detector 
inside scanner 32. Scanner light which strikes a pit (not shown) in 
windshield 5 is scattered within the pit and is reflected back to the CCD 
detector within scanner 32 as one or more non-black pixel elements. The 
CCD detector continuously transmits image data as a series of pixel 
elements through power and data line 36 to general purpose digital 
computer 80. When track wheels 40 reach the end of track wheel groove 57, 
they lift in a direction away from the surface of windshield 5 thereby 
lifting scanner 32 from the surface of windshield 5. As scanner 32 is 
lifted from the surface of windshield 5, contact sensor 33 stops sensing 
contact and signals scanner 32 to stop. Scanner 32 then stops moving and 
transmitting image data to general purpose computer 80. 
It should be appreciated that CCD detector within scanner 32 is a digital 
imaging device having a linear array of closely spaced photo-detectors. 
When light from a light source within scanner 32 strikes windshield 5 it 
passes through windshield 5 where windshield 5 is smooth. Where windshield 
5 is not smooth, but pitted, the light is brightly reflected. 
Because of this, the linear array of closely spaced photo-detectors within 
scanner 32 produces a set of discrete values where each of the values 
correspond to the intensity of light reflected at a discrete location on 
windshield 5. These discrete values having discrete locations may be 
called "pixels". As scanner 32 moves across windshield 5, it produces at 
set of discrete values corresponding to the amount of light reflected at a 
corresponding set of locations on the windshield surface. Discrete 
locations having surface damage are detected when discrete values fall 
into a predetermined high range indicating increased reflectivity and 
decreased transmissibility. A pixel having such a value falling into such 
a predetermined high range might be described as a "non-black" pixel. A 
value falling into a predetermined low range might be described as a 
"black" pixel. The program steps executed by the general purpose computer 
organize the set of discrete values so that each value is assigned a pair 
pixel coordinates in relation to the width of the linear array of 
photo-detectors in pixels and the length of scanner 32 travel in pixels so 
that the physical location associated with each discrete value can be 
known and used. 
FIG. 3 is a flow chart illustrating the program steps executed by general 
purpose computer 80 when activating scanner 32 (see FIG. 2), receiving 
image data from scanner 32 and analyzing image data from scanner 32. In 
step 100, the 30 test is begun and in step 110 customer data such as 
customer name, address, make of car and number of miles on the windshield 
are manually entered. In step 120 instructions are displayed for setting 
up the windshield scanner apparatus 20. In step 130, the scanner 32 is 
activated and run until it is de-activated. As shown in step 130, a gray 
scale TIF image file is collected and given the file name SCAN.TIF. A 
progress bar could be displayed on the screen of general purpose computer 
80 (see FIG. 1), while SCAN.TIF is being collected. 
The remaining steps 140 to 280, shown in FIG. 3 are devoted to analyzing 
the image data collected in the form of the image file SCAN.TIF. The 
purpose of the method of these steps is to perform a statistically 
accurate analysis of the image data without analysing all of the image 
data. To do this discrete square zones are analysed. First, in step 150, 
the width of the image file is found and named "iwidth". Since scanner 32, 
in this example has a scan width of 8.4 inches and has a setting of 200 
pixels per inch, the "iwidth" value should is 1680. In a TIF file, the 
file width is given at a predetermined location in the file. In step 160, 
datapointer, which is also at a 10 predetermined location in the TIF file 
gives the location in the TIF file where the pixel records begin. In step 
170, k, the number of non-black pixels is set at 0, www, the highest 
number of non-black pixels in a square is set at 0, ss, start point is set 
at value equal to data pointer added to a selected number of N time 
"iwidth" which is further added in this example to 150 (or 0.75 inches). 
Turning to FIG. 4, the location in the file given by ss is in first square 
A at point B. Also in step 170, s1 is initially set at ss, m, the 
horizontal counter is set at 0, and v, the vertical counter is set at 0. 
As can be seen in FIG. 3, step 180 begins a loop where t, the square number 
ranges from 1 to 45. In step 190, j the vertical pixel row counter ranges 
from 1 to 200. In step 200, i, the pixel position across a given square 
ranges from ss to ss+200. In step 210, k the non-black pixel counter is 
increased by 1 if the record in SCAN.TIF at a position corresponding to i 
is 0 or not black. After, step 210, if i equals ss+200, then step 230 is 
performed where ss is changed to a new value which corresponds to moving 
ahead in SCAN.TIF by "iwidth" which effectively moves i to the next line 
of pixels in a given square. At this point, the computer returns to step 
190, adds one to j and performs steps 200 through 230 until j equals 200 
at which point a given square is finished. In step 230 www, the value for 
the largest number of non-black pixels in a square is increased to the 
existing value for k if that value is larger than the old www. In step 
240, m the horizontal position is increased by one. Step 250 is executed 
if m does not equal 5. In step 250, ss is set to a new position equivalent 
to moving across 1.5 inches to the staring point of a new square in the 
same row. Step 260 is executed if m equals 5. In step 260, m, the 
horizontal position is reset at 0, one is added to v as ss is reset to a 
position equivalent to moving down 4 inches. In step 270, the last step is 
executed if t, the square counter is equal to 45, or the last square. The 
last square is square E in FIG. 4. In step 270, www which by now is the 
number of non-black pixels in the square having the most non-black pixels 
is printed out or displayed on a screen. 
It should be easily appreciated by those skilled in the art, that in step 
230 above, a record could be created giving a value of k (number of 
non-black pixels) for each value of t (square number 1 to 45). In this 
way, further statistical analysis could be performed wherein the average 
number of non-black pixels present in all of the square sample areas, the 
standard deviation, the best and worst values could all be determined. It 
should be further appreciated by those skilled in the art that values for 
ss could be varied within the entire SCAN.TIF file in a random manner so 
that random zones of a predetermined size could be chosen to provide 
random sampling. The analysis method of the above example employs sample 
squares to significantly reduce computation time. This method, however can 
also be used to map out the degree of damage across the windshield 
surface. It should also be easily appreciated by those skilled in the art, 
that after a worst square has been identified, a separate image file could 
be extracted from SCAN.TIF in accordance with the position of the worst 
square and displayed so that the most pitted sample square can be 
visualized. It should also be appreciated that the steps of the above 
described method could be simplified to accomplish simple random sampling 
or systematic sampling of one of every ten, twenty or even one hundred 
records or pixels in an image file to obtain a statistically accurate 
assessment of windshield quality over a large surface area. The advantage 
of employing such a method is that an accurate assessment of a windshield 
could be performed with relatively simple steps in much less time. 
FIG. 5 illustrates an alternate system measuring peripheral glare producing 
windshield surface damage. The inventors have discovered that windshield 
surface damage directly in front of the driver's eyepoint is less 
influential in causing vision loss due to glare than windshield surface 
damage in zones more distant from an operator's eyepoint. More 
particularly, as shown in FIG. 5, windshield 310 has a zone 320 that is 
located at about 25% of the windshield width and 25% of the windshield 
height from the corner opposite operator's eye point 330. Zone 320 of 
windshield 310 is the region of the windshield that produces the largest 
amount of scattered light producing vision loss due to glare. This is true 
because scattered light from zone 320 impacts more severely the peripheral 
light receptors of the operator's eyes than scattered light from any other 
region of the windshield. Consequently, a surface damage assessment from 
zone 320, a region that is approximately 25% up and 25% across from the 
far corner of the windshield opposite the operator's eye point will very 
quickly provide an assessment of the degree to which windshield 310 will 
contribute to vision loss due to glare. 
FIG. 5 also shows a hand held CCD imaging device 350 which has a light 
source and an array of photo-detectors capable of acquiring a 200 dpi 
image over an area that is two by four inches. Hand held imaging device 
350 also has a handle 352 and hood 354. An operator can hold imaging 
device 350 by handle 352 while placing hood 354 substantially flat against 
windshield 310 in region 320. Hand held imaging device 350 could employ a 
light source adapted to produce light that illuminates pits and scratches 
in the surface of windshield 310 while not illuminating dirt on the back 
of the windshield or objects inside the car. The image taken by hand held 
imaging device 350 could cover an area of for example two by four inches 
and contain 320,000 pixels. The image file having a set of values and 
associated pixel coordinates would be transmitted by logical communication 
protocol through a data transmitting means such as cable 355 as a 
formatted image data file to a general purpose digital computer 360. 
General purpose digital computer 360 receives the image file from hand 
held imaging device 350 and executes instructions whereby the number of 
non-black pixels is determined as described above and windshield surface 
damage is determined as a proportion of surface area that returns 
reflected light characteristic of pits and scratches. The results of these 
calculations are displayed on a screen 368 so that comparisons with new, 
undamaged windshields or windshields having acceptable levels of damage 
can be made. Using this alternate system, glare producing windshield 
surface damage can be very quickly measured and assessed. 
The skilled reader, in view of this specification may envision numerous 
modifications and variations of the above disclosed preferred embodiment. 
Accordingly, the reader should understand that these modifications and 
variations, and the equivalents thereof, are within the spirit and scope 
of this invention and the scope of the claims.