Defect inspection system and method using an array of light sources
A defect inspection system is provided for inspection of defects in the surface of a sample. An array of light sources is used, with different light sources providing light to the sample from different directions. A main direction of illumination is defined with highest intensity, and this direction evolves over time. By providing varying directional illumination instead of blanket illumination, it becomes easier to detect defects.
1. A defect inspection system for visually inspecting surface defects in a sample, comprising:
a lighting system for illuminating the sample surface, comprising an array of light sources, wherein the array of light sources defines a range of illumination directions towards the sample within a plane of incidence, said range covering at least 90 degrees; and
a controller for controlling the light sources in the array to gradually vary output intensity of the light sources, wherein at respective points in time within a sequence each light source has a greater intensity than the others such that each point of the sample is illuminated, at the respective points in time within the sequence, with a light distribution having a maximum light source intensity in a single incident direction, and over time the direction in which the maximum light source intensity is provided changes to cover said range; and
a sample platform movable relative to the lighting system within said range of illumination directions defined by said array of light sources in a direction along a line perpendicular to said plane of incidence.
2. A defect inspection system for inspecting surface defects in a sample, comprising:
a lighting system for illuminating the sample surface, comprising an array of light sources, wherein the array of light sources defines a range of illumination directions towards the sample within a plane of incidence, said range covering at least 90 degrees; and
a controller for controlling the light sources in the array to gradually vary output intensity of the light sources, wherein at respective points in time within a sequence each light source has a greater intensity than the others such that each point of the sample is illuminated, at the respective points in time within the sequence, with a light distribution having a maximum light source intensity in a single incident direction, and over time the direction in which the maximum light source intensity is provided changes to cover said range;
a sample platform movable relative to the lighting system within said range of illumination directions defined by said array of light sources in a direction along a line perpendicular to said plane of incidence;
at least one camera;
a controller for controlling the camera to take successive images during the light source operation sequence; and
a processor for processing the images to derive at least one difference image, wherein the difference image highlights changes in shadow position caused by randomly located surface defects on an otherwise smooth surface, and to provide defect detection based on the difference image.
3. The system as claimed in claim 1 , wherein said range covers at least 135 degrees.
4. The system as claimed in claim 1 , wherein the controller is adapted to control the array to vary the output intensity of the light sources with sinusoidal intensity profiles, each profile having a same period and a different phase.
5. The system as claimed in claim 1 , wherein the array comprises a plurality of sub-arrays of light sources, each sub-array defining a range of illumination directions towards the sample within a respective plane of incidence, a normal direction of the respective plane of each sub-array being arranged along a same line.
6. The system as claimed in claim 1 , comprising a car body panel paintwork inspection system.
7. A method of providing lighting to a surface of a sample to enable visual inspection of defects in the sample, the method comprising:
illuminating the sample surface using an array of light sources, wherein the array of light sources defines a range of illumination directions towards the sample within a plane of incidence, said range covering at least 90 degrees;
controlling the light sources in the array to gradually vary output intensity of the light sources, wherein at respective points in time within a sequence each light source has a greater intensity than the others such that each point of the sample is illuminated, at the respective points in time within the sequence, with a light distribution having a maximum light source intensity in a single incident direction, and over time the direction in which the maximum light source intensity is provided changes to cover said range; and
moving the sample using a sample platform relative to the lighting system within said range of illumination directions defined by said array of light sources in a direction along a line perpendicular to said plane of incidence.
8. A method of providing lighting to a surface of a sample to enable inspection of defects in the sample, the method comprising:
illuminating the sample surface using an array of light sources, wherein the array of light sources defines a range of illumination directions towards the sample within a plane of incidence, said range covering at least 90 degrees; and
controlling the light sources in the array to gradually vary output intensity of the light sources, wherein at respective points in time within a sequence each light source has a greater intensity than the others such that each point of the sample is illuminated, at the respective points in time within the sequence, with a light distribution having a maximum light source intensity in a single incident direction, and over time the direction in which the maximum light source intensity is provided changes to cover said range;
moving the sample using a sample platform relative to the lighting system within said range of illumination directions defined by said array of light sources in a direction along a line perpendicular to said plane of incidence;
taking successive camera images during light source operation sequence;
processing the images to derive at least one difference image wherein the difference image highlights changes in shadow position caused by randomly located surface defects on an otherwise smooth surface; and
providing defect detection based on the difference image.
9. The method as claimed in claim 8 , comprising controlling the array to vary the output intensity of the light sources with sinusoidal intensity profiles, each profile having a same period and a different phase.
10. The method as claimed in claim 8 , comprising illuminating the sample using the array comprising a plurality of sub-arrays of light sources, each sub-array defining a range of illumination directions towards the sample within a respective plane of incidence, the respective planes of incidence for different sub-arrays being parallel to each other.
11. The method as claimed in claim 8 , comprising controlling the light sources of the sub-arrays of light sources to illuminate the sample such that a single incident direction of maximum light source intensity in a light distribution from each sub-array of light sources within each respective plane is different for different respective planes.
12. The system as claimed in claim 5 , wherein the controller is adapted to gradually vary the output intensity of the light sources from the sub-array within each respective plane of incidence in accordance with a respective sequence, wherein at respective points in time within the respective sequence, each light source from the sub-array has a greater intensity than the other light sources from the sub-array, and
wherein a single incident direction of maximum light source intensity in a light distribution from each sub-array of light sources within each respective plane of incidence is different for different respective planes.
13. The system as claimed in claim 1 , wherein said range covers at least 180 degrees.