Method and apparatus for real time detection of faults in industrial objects

• US 4,433,385 A
• Filed: 01/13/1981
• Issued: 02/21/1984
• Est. Priority Date: 01/14/1980
• Status: Expired due to Fees

• Current Assignee: Tasco SPA
• Original Assignee: Tasco SPA
• Inventors: Racciu, Antonio, De Gasperi, Mario M., Nari, Dario
• Primary Examiner(s): Chin, Gary
• Application Number:
  US06/224,665
• Time in Patent Office: 1,134 Days
• Field of Search: 364/552, 364/554, 364/507, 364/468, 364/469, 364/812, 358/101, 358/106, 358/107, 358/93, 356/392-394, 250/572
• US Class Current: 382/149
• CPC Class Codes: G01N 21/88 Investigating the presence of flaws or contamination
• CPC Class Codes: G06T 2207/30164 Workpiece; Machine component
• CPC Class Codes: G06T 7/001 using an image reference approach

Abstract

Method and apparatus for the detection of faults in industrial objects and signalling such faults to handling apparatuses. According to the invention, the image is taken of a sample object by a television camera or other sensing device; the image is digitized and stored in a frame memory. The digitized sample (standard) image is then divided into small areas, for each of which the square root of variance (standard deviation) for the luminance levels of dots belonging to each area is calculated and stored. The same operations and elaborations are followed for each object to be checked and the obtained values are compared with those of the sample. When the differences thereof are above predetermined thresholds, an output signal is generated for distinguishing the fault and generally the faulty object and for controlling a handling apparatus for the objects.

Claims

1. A method for detection of object faults, in real time, and comprising the steps of:

scanning an object to be checked and detecting luminance levels of each of a finite number of dots thereof to provide analog image signals corresponding to each dot and indicative of said luminance levels;

converting said analog signals to corresponding digital signals according to a luminance level scale and storing said digital signals in a memory to provide a digitized object image;

dividing said digitized object image into a predetermined number of areas having a predetermined number of said dots;

calculating standard deviations for digitized luminance values of the dots of each area into which the digitized object image has been divided according to the formula;

##EQU5## wherein;

x₁ =luminance value of the individual dots pertaining to an area, and

n=number of dots in the area;

storing said standard deviations of said areas;

providing digitized reference standard deviation values corresponding to each of said areas;

comparing each of said standard deviations with said corresponding digitized reference standard deviation values; and

providing a fault signal when a threshold is exceeded during said comparing.

2. A method as in claim 1, wherein said digitized standard deviation reference values are obtained by performing the steps prior to said comparing step on a sample object.

3. A method according to claim 2, wherein each of said digitized standard deviation reference values are multiplied by a predetermined factor prior to said comparing.

4. A method as in claim 2, wherein each of said digitized standard deviation reference values are added to a predetermined factor prior to said comparing.

5. A method as in claim 2, and further comprising the step of:

defining basic color components of said objects and repeating the above sequence of steps, in parallel, for each of said basic color components.

6. A method as in claim 2, and further comprising the step of:

defining basic color components of said objects and repeating the above sequence of steps, in series, for each of said basic color components.

7. An apparatus for detection of object faults in real time, and comprising:

means for scanning an object to be checked and detecting luminance levels of each of a finite number of dots thereof to provide analog image signals corresponding to each dot and indicative of said luminance levels;

means for converting said analog signals to corresponding digital signals according to a luminance level scale and storing said digital signals in a memory to provide a digitized object image;

means for dividing said digitized object image into a predetermined number of areas having a predetermined number of said dots;

means for calculating standard deviations for digitized luminance values of the dots of each area into which the digitized object image has been divided according to the formula;

##EQU6## wherein;

x₁ =digitized luminance value of the individual dots pertaining to an area, and

n=number of dots in the area;

means for storing said standard deviations of said areas;

means for providing digitized reference standard deviation values corresponding to each of said areas;

means for comparing each of said standard deviations with said corresponding digitized reference standard deviation values; and

means for providing a fault signal when a threshold is exceeded during said comparing.

8. An apparatus as in claim 7, and further comprising:

means for multiplying each of said digitized standard deviation reference values by a predetermined factor prior to said comparing.

9. An apparatus as in claim 7, and further comprising:

means for adding a predetermined factor to each of said digitized standard deviation reference values prior to said comparing.

10. An apparatus as in claim 7, and further comprising:

means for multiplying each digitized luminance value of a particular predetermined area by itself to obtain a squared digitized luminance value, summing said squared digitized luminance values of said particular predetermined area to provide a sum of squares, and dividing said sum of squares by a total number of dots in said particular predetermined area to provide a first factor;

means for summing said digitized luminance values of the dots of said particular predetermined area to provide a sum of digitized luminance values, squaring said sum of digitized values and dividing a result thereof by the square of a total number of dots in said predetermined area to obtain a second factor, and operating on said second factor to provide a one'"'"'s complement thereof;

means for summing said first factor and said one'"'"'s complement of said second factor to provide a variance;

means for taking the square root of said variance to provide said standard deviation; and

means for providing said fault signal to a controller when a threshold is exceeded such that faulty objects may be sorted from objects which are not faulty.

11. An apparatus as in claim 7, and further comprising:

means for resolving said object into fundamental chromatic components and performing said fault detection according to said fundamental components.