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Abstract

A method for controlling a resonance enhanced rotary drill comprising a rotary drill bit and an oscillator for applying axial oscillatory loading to the rotary drill bit, the method comprising:

controlling frequency (f) of the oscillator in the resonance enhanced rotary drill whereby the frequency (f) is maintained in the range(D2 Us/(8000 πAm))1/2≦f≦Sf(D2 Us/(8000 πAm))1/2 where D is diameter of the rotary drill bit, Us is compressive strength of material being drilled, A is amplitude of vibration, m is vibrating mass, and Sf is a scaling factor greater than 1; andcontrolling dynamic force (Fd) of the oscillator in the resonance enhanced rotary drill whereby the dynamic force (Fd) is maintained in the range[(π/4)D2effUs]≦Fd≦SFd[(π/4)D2effUs]where Deff is an effective diameter of the rotary drill bit, Us is a compressive strength of material being drilled, and SFd is a scaling factor greater than 1,wherein the frequency (f) and the dynamic force (Fd) of the oscillator are controlled by monitoring signals representing the compressive strength (Us) of the material being drilled and adjusting the frequency (f) and the dynamic force (Fd) of the oscillator using a closed loop real-time feedback mechanism according to changes in the compressive strength (Us) of the material being drilled.

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First Claim