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Broken (Missing) Drill Detection

IP.com Disclosure Number: IPCOM000049556D
Original Publication Date: 1982-Jun-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Wray, TE: AUTHOR

Abstract

Disclosed herein is an arrangement for detecting broken (missing) drill bits in a multiple-bit drilling machine for printed circuit cards, by charging an electrical circuit as a result of an intact drill bit establishing and then breaking an electrical circuit to a conductive backing layer.

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Broken (Missing) Drill Detection

Disclosed herein is an arrangement for detecting broken (missing) drill bits in a multiple-bit drilling machine for printed circuit cards, by charging an electrical circuit as a result of an intact drill bit establishing and then breaking an electrical circuit to a conductive backing layer.

Assume, for example, a 3-bit multiple drill including drill bits 3, 5 and 7, as shown in the drawing. The bits are each electrically grounded via their collets or chucks and the metallic framework of the drill press, as indicated in the drawing. A circuit board to be drilled is indicated at 9. On the side of the circuit board furthest from the drills there is provided a backer 11 comprising a sandwich of insulator conductor insulator material. The conductive layer 13 is connected to an output terminal 15, and via a pull-up resistor 17 to a positive voltage terminal +V, the negative terminal being grounded. As shown by the waveform in the figure, the voltage at 15 will drop from +V to ground when a drill pierces the circuit board and the first layer of the backer and contacts the conductive layer. When the drill bit is retracted, the connection is broken and the voltage at 15 will return to the +V value.

By staggering the length of the drill bits, i.e., the spacing of the end of the bit from the board, a sequence of pulses can be produced as the ends of the drill bits successively contact the conductive layer.

Modifications include the provision...