The art of applying video image analysis to drill bit inspection is well known for those familiar in the art of image analysis, and several earlier patents cover different systems and applications. The application of a computer video image analysis system to a high speed drilling machine of the type used in manufacture of printed circuit boards to detect drill bit breakage, quality, set height and size between each drill stroke is a novelty for those familiar with this type of usually high speed multiple-spindle drilling machines, typically used for the manufacture of printed circuit boards.

Other existing systems are available to detect drill breakage, employing microwave detection of drill chips, laser beams, ultrasonic analysis of drill chips, etc. These existing competing systems are disposed to false triggering, do not give accurate setting heights of drill bit and do not detect partial breaks and/or wear, i.e. drill bit quality and drill size. The industry has therefore looked for a better system, which this invention set out to provide.

To cost-competitively work at the high drill stroke frequencies (hit rate, for those familiar with printed circuit board drilling machines) normally employed and not reduce machine capacity, interpretation have to work with the image of a high speed continuously rotating drill bit, requiring a fast and effective analysis method. Typically drill speeds range from 16,000 rpm to 100,000 rpm and hit rates are typically 150 hits per minute and can be over 400 hits per minute.

The drill bit is examined at its top position during the delay time occurring during repositioning of table and/or drill spindle. The physical embodiment of the invention involves a video camera attached to a drill spindle so that a right angle to drill axis view of the tip part of a drill bit illuminated from behind is obtained. Mechanical designs, involving special mountings ,lenses and/or fiber optics is not the scope of the patent. The method utilises back ighting of a rotating drill bit that lends itself to high speed computer evaluation when certain conditions are fulfilled: If an analogue camera is used, the response time of the photo sensitive materials in the picture plane should typically be several times longer than slowest drill bit rotation period and shorter than 2-3 frames(complete pictures) or use a mechanical shutter to avoid delay time until picture has stabilized.

The here preferred method involves a digital video camera with external light integration (exposure) time setting and no mechanical shutter, reducing weight, wear and cost. The exposure time for each light sensitive pixel in the digital video camera is selected longer than the slowest rotation period for the drill bit. If light integration period is similar to rotation period, integration time should be close to integer multiples of rotation speed for correct averaging, or integration times should be selected many times larger than the rotating time to obtain required accuracy. The resulting image - if black & white -displayed on a video monitor consists of white background, homogeneous gray areas where the spirals and cutting edges of the drill bit intermittently block the back light, while the core of the drill bit appears black. Drill bits with chipped or rounded cutting- edge(s) can be separated from good drill bits in dedicated software, which also can evaluate drill tip height and drill diameter measures and stopped bits. Utilizing different light integration times, rotation speed can also be measured. Typically drill bits from 6 mm to 0.1 mm can be evaluated with the system.

The introduction of a real time drill wear management system using actual wear instead of expected drill life time is a development of basic system, capable of reducing drill bit cost at any given required drill quality.

The use of a video camera sensitive in the infra red spectrum gives the added advantage of detecting tip temperature as an indication of wear, although image analysis software need to be modified to incorporate the added variable with minimum losses of geometrical accuracy.