Pick and place machine with component placement inspection

Abstract

Improved component placement inspection and verification is performed by a pick and place machine. Improvements include stereovision imaging of the intended placement location; enhanced illumination to facilitate the provision of relatively high-power illumination in the restricted space near the placement nozzle(s); optics to allow image acquisition device to view the placement location from an angle relative to a plane of the placement location, thereby reducing the possibility of such images being obstructed by the component; techniques for rapidly acquiring images with commercially available CCD arrays such that acquisition of before and after images does not substantially impact system throughput; and image processing techniques to provide component inspection and verification information.

1 . A method of processing a plurality of images of an intended placement location in a pick and place machine to verify component placement, the method comprising: 
 acquiring before-placement and after-placement images of an intended placement location;    selecting a region of interest in the before-placement and after-placement images;    generating a difference image based upon differences between the before-image and the after-image;    thresholding the difference image to produce a binary difference image;    performing connectivity analysis on the binary difference image to obtain an image metric; and    comparing the image metric with expected object metric to provide component placement verification.    
     
     
         2 . The method of  claim 1 , and further comprising masking at least one area known to change in the before and after images.  
     
     
         3 . The method of  claim 2 , wherein the area includes a nozzle of the pick and place machine.  
     
     
         4 . The method of  claim 1 , and further comprising masking at least one area not within an expected envelope of the component.  
     
     
         5 . The method of  claim 1 , and further comprising: 
 aligning the before-image with the after-image before obtaining the difference image.    
     
     
         6 . The method of  claim 5 , wherein the step of aligning includes applying a correlation.  
     
     
         7 . The method of  claim 1 , and further comprising: 
 performing a morphological erosion operation on the binary difference image.    
     
     
         8 . The method of  claim 7 , wherein the morphological erosion operation is repeated.  
     
     
         9 . The method of  claim 1 , and further comprising performing a morphological dilation operation on the binary difference image.  
     
     
         10 . The method of  claim 9 , wherein the morphological dilation operation is repeated.  
     
     
         11 . The method of  claim 1 , wherein the metric includes object centroid.  
     
     
         12 . The method of  claim 1 , wherein the metric includes object length.  
     
     
         13 . The method of  claim 1 , wherein the metric includes object width.  
     
     
         14 . The method of  claim 1 , wherein the metric includes object area.  
     
     
         15 . The method of  claim 1 , wherein the metric includes object rotation.  
     
     
         16 . The method of  claim 1 , wherein the method is performed within an image acquisition device.  
     
     
         17 . A method of processing a plurality of images of an intended placement location in a pick and place machine to verify component placement, the method comprising: 
 acquiring before-placement and after-placement images of an intended placement location;    selecting a region of interest in the before-placement and after-placement images;    generating a difference image based upon differences between the before-image and the after-image;    thresholding the difference image to produce a binary difference image;    calculate pixel change count of the intended placement location;    calculate total pixel count; and    comparing the pixel change count of the intended placement location with the total pixel count to provide component placement verification.    
     
     
         18 . A method of processing a plurality of images of an intended placement location in a pick and place machine to verify component placement, the method comprising: 
 acquiring before-placement and after-placement images of an intended placement location;    selecting a region of interest in the before-placement and after-placement images;    generating a difference image based upon differences between the before-image and the after-image;    calculate difference intensity sum of the intended placement location;    calculate total pixel difference intensity sum; and    comparing the pixel difference intensity sum of the intended placement location with the total pixel difference intensity sum to provide component placement verification.