Broken drill bit detector

For use in detecting broken or missing drill bits in numerically controlled drilling machines the method of:

• A. generating light pulses at a predetermined frequency of pulses;
• B. directing said light pulses at a predetermined portion of a drill bit to be detected;
• C. detecting changes of light intensity occurring when the drill bit is broken or missing;
• D. providing control signals at said predetermined frequency indicative of the detected change in light intensity;
• E. selecting a predetermined time interval that said control signals must be present to accurately indicate the detected drill bit is broken or missing;
• F. timing the occurrence of said control signals;
• G. enabling the issuance of stop signal after said predetermined time interval has elapsed provided said control signal is still present;
• and
• H. generating said stop signals in response to said control signals for causing the numerically controlled drilling machine to be stopped in response thereto.

For use with a numerically controlled drilling machine broken or missing drill bit detector cpable of detecting drill bits of less than 30 mils diameter comprising:

• support means for mounting to the numberically controlled drilling machine in the vicinity of the drill bit to be detected;
• emitter means for emitting pulsed light at a predetermined frequency mounted to said support means, wherein said emitter means includes oscillator means for providing drive signals at a predetermined frequency, and infrared emitting diode means coupled to said oscillator means for providing light pulses at said predetermined frequency;
• first optical means coupled to said emitter means for focusing said pulsed light at a predetermined portion of the drill bit to be detected, wherein said first optical means includes fiber optical means having a first end coupled to said emitter means and a second end mounted in a predetermined relationship to the drill bit to be detected;
• second optical means in predetermined relationship to said first optical means for receiving light not blocked by the drill bit being detected, wherein said second optical means includes second fiber optic means having a first end coupled to said detector means and a second end mounted in axial alignment with said second end of said first fiber optic means;
• detector means coupled to said second optical means for detecting changes in light intensity occurring when the detected drill bit is not present in the path of said pulsed light, and including control signal generating means for generating first control signals when said drill bit is present and second control signals when said drill bit is missing in response to said sensed change in light intensity, said detector means mounted on said support means, wherein said detector means includes trigger circuit means for providing electrical signals at said predetermined frequency, the amplitude of said electrical signals being dependent upon the intensity of the light pulses detected, and phase lock loop means responsively coupled to said trigger circuit means and tuned to said predetermined frequency for generating said first control signals when the amplitude of said electrical signals is less than a predetermined threshold, and for providing said second control signals when the amplitude of said electrical signals is greater than said threshold value and at said predetermined frequency, thereby said second control signal indicating that the drill bit being sensed is missing;
• control signal conductor means for carrying said first and second control signals to control circuitry in the numerically controlled drilling machine;
• power conductor means coupled to said emitter means and said detector means for receiving power and applying it thereto;
• and
• timer means coupled to said phase lock loop means for enabing said second control signals to said control signal conductor means when said second control signal from said phase lock loop means has occurred for a predetermined time interval, whereby said second control signals occurring for less than said predetermined time interval are ignored as spurious and operation is not interrupted.

For use in a numerically controlled drilling machine having multiple drill spindles, control apparatus for positioning a work piece to be drilled and controlling the actuation of a drilling function in cycles, a drill bit detector comprising:

• a plurality of emitter means for directing a source of energy in the vicinity of each of the drill bits to be detected, each of said emitter means including signal source means for providing drive signals at a predetermined frequency different from the frequencies of all other signal source means, and light emitting means coupled to said signal source means for emitting pulses of light energy, said pulses occurring with a frequency substantially equivalent to the said predetermined frequency of said drive signals from the associated on of said signal source means;
• a plurality of detector means each oppositely disposed and responsively associated with a different one of said emitter means for receiving a first energy level when the drill bit to be detected is present and a second level of energy when said associated drill bit is absent, and wherein each of said detector means includes energy detecting circuit means for providing said second level signals at the frequency of said emitted energy pulses associated therewith when the drill bit is missing;
• and
• a plurality of control circuit means and coupled to one of said detector means for providing disable signals in response to said second energy level for disabling the control apparatus of said numerically controlled drilling machine for stopping operation immediately upon detection of the absent drill bit, wherein each of said control circuit means includes frequency responsive means responsively tuned to the frequency of said emitted energy pulses associated therewith for providing said disable signals in response to said second level signals from said detector means and for providing enabling signals in response to said first level signals, whereby said enabling signal allow said numerically controlled drilling machine to continue operation and said disabling signals are utilized to cause said numerically controlled drilling machine to stop operation each of said frequency responsive means includes phase lock loop means responsive to signals at an amplitude sufficient to be detected and occurring at said associated frequency for locking on and switching its output to provide said disable signal;
• tuning means for tuning each of said phase lock loop means to be responsive to signals detected by said detector means at said associated predetermined frequency;
• and
• timer means coupled to said frequency responsive means and responsive to said disable signals for passing said disable signals to the numerically controlled drilling machine control apparatus when said disable signals continuous occur for a predetermined threshold time interval, whereby said disable signals occurring for less than said threshold time are ignored as spurious and the operation of the numerically controlled drilling machine is not interrupted.