Quote Product Code S338

Razor Blade Geometry Measuring System.

THE BRIEF:

A leading manufacturer of shaving blades approached us to develop a non-contact method of measuring the angle and protrusion of twin and single blades encased in a plastic cassette. The angle of the blade is very important in producing an effective cutting action of the hair base and is about 20 degrees. The protrusion must be large enough to cut the hair but short enough to avoid penetrating the skin.

Razor blade

THE METHOD:

The standard method is to project a visible line onto the cassette and view the line from an angle. The angles and position of the subsequent profile are proportional to the angles and position of the blades. Analysing this profile reveals the effective shaving angle and protrusion of each blade.

There are a variety of ways of projecting a line onto a surface. The instinctive solution would be to use a "laser diode line projector" (this consists of a laser and rod lens producing a fan of light). However, the specular and granular nature of the materials in the cassette produced "hot spots" caused by direct reflections of the laser beam into the viewing device. Interference effects, due to the coherent laser light, exacerbated this problem.

The solution was to cast a shadow onto the cassette. This way, the specular surface made no difference since there was no light at the points of interest.

Razor blade

A camera placed at right angles to the shadow generator (shown on left below), with the cassette placed at 45º between the two produces an image of the profile (shown on right below)

Shadow generator

Profile image

The IQ150 digitises six strategic areas to calculate: The position of the cap The two blades and the base The angles of the two blades

Digitised image

The IQ150 produces a repeatability of 1 degree on angle measurement and 12 microns for protrusion, ten times greater than the required specification.

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