Planer Blade Edge Quality Inspection.

The cutting edge of high quality carbide planer blade for wood working has to be sharp and without cracks.
To guarantee the quality of the edge a visual control is necessary, until now this control is done by human labor. Planer Blade image
A vision system can measure very accurate the sharpness of the tool and detect cracks or damages or imperfection as a result of grinding. The measured data is important to improve the current quality level an can be used for very fast process control which is not possible by human inspection.
Cracks with a minimal depth of 3 μm and a width of 3-6μm on the cutting edge have to be detected and classified. The sizes of the planer blades range from (length x width) 7 x 5 mm up to 80 x 15 mm. Measuring a crack of 3 x 3-6 μm with a certain accuracy requires a magnification of about 1 μm/pixel or better.

Here starts the microscopic domain.
It is necessary to do a profound investigation of the illumination, the optics and software algorithms to be sure that a crack of that size can be found.
Measurements in the micrometer world needs a 'micrometer mind set'. Keep in mind that the wavelength of light is close to a half pixel size.

To create a good image with a resolution of 1 μm, the focus depth range is in the order 100μm (+/- 50μm) or less.
The illumination has to be as homogeneous as possible. And preferable no movement or vibrations of the tool and or the camera with optics. Planer Blade Side view 01
In order to be able to determine the defect or crack, it is essential that the contrast of the defect is sufficiently large. The contrast determines whether a defect can be found.
Next step is measuring the size of the defect accurate, this is only possible using an accurate edge detection algorithm and good and smart mathematics.

Planer Blade Side view graph 01 This report describes in detail the result of two planer blades out of a large set of tools. The first planer blade contains a large damage, the second blade does have the smallest damage out of the planer blade set.
The second blade is also manually measured with a electronic microscope, with a field of view of 165 x 130 μm!
The cutting edge is measured in two directions, one direction is a side view using a back light. The other direction is a top view using a special illumination. Planer Blade Top view 01

Side view: The magnification of this camera is 1 μm/pixel for the side view and a working distance of 60 mm. Planer Blade Top view 02
The camera sensor (in binning mode) is 1296 x972 pixels and a pixel size of 4.4 μm. The magnification can be increased to 0,5 μm/pixel when the binning mode is switched off.

Top view: Planer Blade Top view graph 01 This camera (also in binning mode) is equipped with a microscopic objective with a magnification of 1,1 μm/pixel, short working distance. The magnification can be increased to 0,55 μm/pixel when the binning setting is not used.

For more detailed information please download the pdf:
Planer Blade Edge Quality Inspection.pdf