The application of machine vision, a lot of object surface will have messy glare, which will have a very serious impact on visual inspection, in order to reduce or eliminate glare interference, in many cases, we will use polarized light to eliminate the object surface reflection, so as to make the image stabilization .
Theory of polarized light
Adjusting the polarized filter will change the direction of light to make the polarized light。
The classification of polarized light：
Linearly polarized light: The trajectory of the endpoint of the light vector is straight, that is, the light vector vibrates only along a certain direction, and its magnitude changes with phase, but the direction remains the same, which is called linearly polarized light.
Elliptically polarized light: The trajectory of the endpoint of the light vector is elliptical, that is, the light vector is constantly rotating, and its magnitude and direction change regularly with time
Circularly polarized light: The trajectory of the end points of the light vector is a circle, that is, the light vector is constantly rotating, its magnitude is unchanged, but the direction changes regularly with time.
Polarizer film：
It is made of a certain grain (sodium iodide sulfate) in a certain way, coated on a thin transparent film. It is strongly dichroic: light is only allowed to pass in one direction - the direction of polarization.
How to use polarized light：
The polarized light is used in combination with the polarizer filter and polarizer plate at the same time. By adjusting the polarizer filter, the appropriate position can be found to reduce the influence of glare on the picture.
Case 1：Food package character print inspection
Picture 1: Used high angle ring light on food package. It has reflective from ring light’s ball, that will interference the character recognition.
Picture 2: Clear character and no shadow from ring light’s ball, used by high angle ring light with polarized light
Workpiece
NG: there is LED beams interference on the surface
OK: Clear character and eliminate reflection of surface
Picture 1: The surface of capacitance has reflective by the vision light , and interference the character recognition. Used by the ring shadowless light.
Picture 2: Clear character and eliminate reflection on capacitance surface, used by ring shadowless light with polarized light.
Workpiece
NG: Strong reflective
OK: Clear character and eliminate reflection of surface
Picture 1: The surface of battery packing box has strong reflective and interference the character recognition, used by the high angle ring light without polarized light.
Picture 2: Battery packing box surface is eliminate reflective of surface and clear character used by High angle ring light with polarized light.
Workpiece
NG: Character recognition affect by the reflect
OK: Clear character and eliminate reflection of surface
