Abstract:
An apparatus for measuring gobs of viscous liquid in free-fall, comprises a video camera adapted to be focused on the path of the gobs so that the gobs fall through the field of view thereof. The video camera is equipped with an electronic shutter for capturing successive two-dimensional, high resolution, frozen video images of the path of the gobs; a digitizer for digitizing the successive images to produce n×n pixel arrays; and an image analyzer for identifying usable gobs in the arrays and analyzing the image in the vicinity of said gobs on a line-by-line basis to locate the edges thereof.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an apparatus for measuring gobs of viscous liquid in free fall, particularly gobs of glass falling from the orifice of a glass feeder. 
     In the manufacture of glass articles, molten glass is first supplied to a gob feeder. This comprises a plunger which forces a molten stream of glass through an orifice where the gobs are separated with shears prior to falling into the hopper of a glass forming machine. In order to control the manufacture of the glass articles, it is important to monitor the weight and shape of the gobs of glass as they fall into the hopper. 
     One such method is described in U.S. Pat. No. 4,205,973. In this method the gobs fall through laser beams that activate perpendicularly arranged line cameras. These line cameras take successive scans as the gobs fall through their field of view. The successive scans are combined to determine the outline of the falling gob. The system requires careful synchronization of the camera scanning speed with the motion of the gob to ensure that a complete scan is obtained for each passage. A slight variation in the speed of the gobs will cause an error in the measured size since the difference between scanning lines on the image, for a given scanning rate, depends on the velocity of the gob. Furthermore, a separate camera is required for each gob position. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an improved apparatus that is not dependent for its accuracy on the constancy of the velocity of the gobs. 
     Accordingly, the present invention provides an apparatus for measuring gobs of viscous liquid in free-fall, comprising: a video camera adapted to be focused on the path of the gobs so that the gobs fall through the field of view thereof, said video camera being equipped with an electronic shutter for capturing successive two-dimensional, high resolution, frozen video images of the path of the gobs; a digitizer for digitizing said successive images to produce n×n pixel arrays; and an image analyzer for identifying usable gobs in said arrays and analyzing said image in the vicinity of said gobs on a line-by-line basis to locate the edges thereof. 
     In accordance with the invention, a succession of digitized frozen images are analyzed. A preliminary analysis is carried out to determine whether a particular image contains usable gobs. If so, the image is then further analyzed to determine the outline of the gobs. Unlike the prior art, each useful image obtained from a single camera contains all the information pertaining to a gob, and preferably two or three gobs. 
     From the outline of the gob, the weight can be determined in accordance with the following formula. ##EQU1## where G dens  =Density of glass 
     K=Calibration constant 
     Width(y)=Width of gob at vertical position y 
     In effect, to obtain the weight of the gob, which is of course proportional to its volume, it is merely necessary to measure the width at each line and multiply the squares of the widths by a constant incorporating a calibration constant and the density of the glass. 
     The image is preferably a gray scale image, in which case the accuracy of the measurement can be increased by determining the values of the pixels in the vicinity of the edge and interpolating to find the precise location of the edge as a fraction of a pixel. 
     When a gray scale image is used, the intensities of the pixels can also be mapped to colors so that the relative temperatures of the different parts of the gob can be displayed, with the colder areas showing up as blue and the hotter areas showing up as red. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is an elevational view of a gob feeder showing the camera of the apparatus according to the invention; 
     FIG. 2 is a block diagram of the gob measuring apparatus in accordance with the invention; and 
     FIG. 3 is a digitized image showing the presence of detected gobs. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, gobs 1 fall from the orifice ring 20 of gob feeder 2 after being severed by shears 3. Although one orifice is shown, the gob feeder generally has several orifices arranged side by side. As the gobs fall into glass forming apparatus 4, they pass through the field of view of video camera 5 forming part of the apparatus according to the invention. This takes a succession of images frozen in time of the gobs 1 in free fall (FIG. 3). 
     Turning now to FIG. 2, the video camera 5 is a standard charge-coupled-device (CCD) two-dimensional video camera equipped with an electronic shutter. The camera 5 has a lens system suitable for focusing on the path of the gobs, and in the preferred embodiment this is a 75 mm. manual zoom lens with a two times extender. 
     The video camera 5 with electronic shutter 6 forms a succession of images of the path of the gobs 1. The scanning speed and the speed of the shutter is selected such that each image effectively freezes the motion of the gobs to create a stationary image. The output of the camera 5 is connected to a video digitizer 7, which for each successive image produces an n by n pixel array, which in the preferred embodiment is 512×512 pixels. While the computer captures a 512×512 interlaced frame, this is separated into two 512×256 fields, which are then analyzed as separate images. Alternatively, a camera with a frame activated shutter could be employed, in which case the image could be analyzed on a frame by frame basis. 
     This image is displayed on monitor 8. It is also fed to an IBM 33 MHz 486 computer 9 connected to monitor 10 and keyboard 11 for further processing. The computer 9 carries out the following operations on the digitized image: 
     1) The high resolution image is sub-sampled by extracting every 16th pixel horizontally and vertically to produce a low resolution 32×32 version of the image that is capable of rapid analysis. 
     2) Each pixel of the low resolution image is analyzed to determine whether it falls above or below a predetermined threshold value. All values above a pre-determined threshold are given a high value and all values below the threshold are given a low value. Thus, a bi-level low resolution image is created. 
     3) A low resolution, bi-value image is scanned to locate groups of adjacent pixels. Pixel groups within a certain size range are assumed to be valid gobs. 
     4) If tile number of gobs identified in step 3 meets the predetermined criteria, and none of the gobs touch the edges of the image, the computer 9 proceeds to carry out a full analysis on the high resolution image. If these criteria are not met, the system returns to step 1. 
     5) Assuming criteria are met, the locations of the gobs in the lower resolution image are stored, and these locations used to determine their corresponding locations in the high resolution version of the image. The image is then scanned in the vicinity of the gobs and the location of the edges determined on a line by line basis. 
     As the glass is hot, the edge of each gob is actually smeared over several pixels. The edge is determined empirically to lie at a certain point where the intensity has a particular gray scale value. By measuring the values of pixels at several adjacent locations, the precise position of the edge can be determined by linear interpolation as a fraction of pixel pitch as follows: ##EQU2## where x is the horizontal position below the threshold and x+1 is the horizontal position above the threshold. This is the equation for determining the location of the left edge. A similar equation is used to determine the of location the right edge. 
     6) At each scanning line, the width of the gob is determined from the distance between the detected edges. 
     7) Once the edges of the gob have been located, the weights of the gob are calculated from the following formula: ##EQU3## where G dens  =Density of glass 
     K=Calibration constant 
     Width(y)=Width of gob at vertical position y 
     The theoretical weight of the gob is actually given by the integral: ##EQU4## 
     A more accurate approximation to the integral can be obtained by using Simpson&#39;s rule for numerical integration if desired. 
     Since the vertical spacing of the pixels is constant, the mass of the gob is determined by summing the squares of the widths and multiplying by a constant, which can be determined by calibration of the equipment. It is not necessary to measure the width in perpendicular directions, as was done in the prior art, because it is a reasonable assumption that the gobs are symmetrical about the longitudinal axis due to the physical forces acting on them as they fall into the hopper. 
     Computer 9 outputs the signal representing the weights to digital-to-analog converter 12, which in turn is connected to a controller 13 controlling the gob feeder 2. The controller 13 can be set at a desired set point by the operator. 
     The shape of the gobs can be displayed on monitor 10, and furthermore, if desired the weight scale intensities of the pixels can be mapped to colors. In this way, a false colored image of the gobs will show the relative temperature of the various parts. Normally the colder areas are mapped to blue and the hotter areas are mapped to red. 
     By way of example, a suitable pseudo code for measuring three gobs is as follows: 
     
         ______________________________________LOOP:capture image 512x512vmin &lt;---- 255vmax &lt;---- 0for x &lt;---- 0 to 31for y &lt;---- 0 to 31image [x,y] &lt;---- digitizer [x/16, y/161]if (image [x,y] &lt; vmin) vmin &lt;---- image ]x,yl]if (image [x,y] &gt; vmax) vmax &lt;---- image [x,y]endforendforif (vmax - vmin &lt; 50)goto LOOPthreshold &lt;---- (vmin + vmax)/2for x &lt;---- 0 to 31for y &lt;---- 0 to 31if (image [x,yl] &gt;= threshold)  image [x,y] &lt;---- 255else  image [x,y] &lt;---- 0endforendfor gobcount &lt;---- 0for x &lt;---- 0 to 31for y &lt;---- 0 to 31if ( image [x,y] = 255)flood fill position x,yfloodsize &lt;---- # pixels in flooded regionminx &lt;---- minimum x value of flood regionmaxx &lt;---- maximum x value of flood regionminy &lt;---- minimum y value of flood regionmaxy &lt;---- maximum y value of flood regionif ( floodsize &lt; 150 or floodsize &gt; 300)  goto LOOPif ( minx &lt;= 1 or maxx &gt;= 30)  goto LOOPif ( miny &lt;= 1 or maxy &gt;= 30)  goto LOOPwindow.sub.-- minx [gobcount] = 16 * minxwindow.sub.-- maxx [gobcount] = 16 * maxxwindow.sub.-- miny [gobcount] = 16 * minywindow.sub.-- maxy [gobcount] = 16 * maxygobcount &lt;---- gobcount + 1endifendfor endforif (gobcount ! = 3) goto LOOPfor gob &lt;---- 0 to 2minx &lt;---- window.sub.-- minx (gob]maxx &lt;---- window.sub.-- maxx (gob)miny &lt;---- window.sub.-- miny [gob]maxy &lt;---- window.sub.-- maxy [gob]image &lt;---- digitizer image from minx,miny to maxx,maxyvolume &lt;---- 0for y &lt;---- 0 to (maxy - miny + 1)vmin &lt;---- 255vmax &lt;---- 0for x &lt;---- 0 to (maxx - minx + 1)if (image [x,y] &lt;  vmin) vmin &lt;---- image [x,y]if (image [x,y] &gt; vmax) vmax &lt;---- image [x,y]endforthreshold &lt;---- (vmin + vmax)/2left &lt;---- 0while (image [left,y] &lt; threshold)left &lt;---- left + 1right &lt;---- vmaxx - vminx + 1while (image [right,y] &lt; threshold)right &lt;---- right - 1left &lt;---- (threshold - image[left-1,y])/(image[left,y] image[left-1,y]) + left - 1right &lt;---- (threshold - image[right,y])/(image[right+1,y] - image[right,y]) + rightvolume &lt;---- volume + (PI/4) * (right - left) 2weight [pos] &lt;---- calibration.sub.-- const * volumeendforoutput average of weight[0], weight[1], weight[2] to D/Aendfor______________________________________ 
    
     A more complete example of a suitable program to implement the invention is given in the following appendix.