Vibration transmission and isolation

1. An apparatus for testing or use in resonance enhanced rotary drilling, which apparatus comprises:

(a) a vibration damping and/or isolation unit; and

(b) a vibration enhancement and/or transmission unit,

wherein the vibration damping and/or isolation unit and the vibration enhancement and/or transmission unit comprise a spring system comprising two or more frusto-conical springs arranged in series,

wherein a frustoconical spring of the vibration damping and/or isolation unit satisfies the following equation:

ω/ω η1 ≧2.3

wherein ω represents an operational frequency of axial vibration of the resonance enhanced rotary drilling apparatus, and ω n1 represents the natural frequency of the frustoconical spring of the vibration damping and/or isolation unit; and

wherein the frustoconical spring of the vibration enhancement and/or transmission unit satisfies the following equation:

0.6≦ω/ω η2 ≦1.2

wherein ω n2 represents the natural frequency of the frustoconical spring of the vibration enhancement and/or transmission unit,

wherein the vibration damping and/or isolation unit, as situated above an oscillator in the resonance enhanced rotary drilling apparatus, dampens and/or isolates vibration from the oscillator, and

wherein the vibration enhancement and/or transmission unit, as situated below an oscillator in the resonance enhanced rotary drilling apparatus, enhances and/or transmits vibration from the oscillator.

2. An apparatus according to claim 1 , wherein the frustoconical spring is one such that the force, P, applied to the frustoconical spring can be determined according to the following equation:

P

=

1.1

⁢

E

⁢

⁢

δ

⁢

⁢

C

R

2

⁡

[

(

h

-

δ

)

⁢

(

h

-

δ

2

)

⁢

t

+

t

2

]

wherein t is the thickness of the frusto-conical spring, h is the height of the frustoconical spring, R is the radius of the frustoconical spring, δ is the displacement on the frustoconical spring caused by the force P, E is the Young modulus of the frustoconical spring, and C is the constant of the frustoconical spring.

3. An apparatus according to claim 2 , wherein the frustoconical spring comprises one or more Belleville springs.

4. An apparatus according to claim 1 , wherein the frustoconical spring is formed from a metal.

5. An apparatus according to claim 1 , which apparatus comprises:

(i) an upper load-cell for measuring static and dynamic axial loading;

(ii) an oscillator for applying axial oscillatory loading to the rotary drill bit;

(iii) a lower load-cell for measuring static and dynamic axial loading;

(iv) a drill-bit connector; and

(v) a drill-bit,

wherein the upper load-cell is positioned above the vibration damping and/or isolation unit and the lower load-cell is positioned between the vibration enhancement and/or transmission unit and the drill-bit, and wherein the upper and lower load-cells are connected to a controller in order to provide down-hole closed loop real time control of the oscillator.

6. An apparatus according to claim 5 , wherein the oscillator comprises a magneto-strictive oscillator.

7. An apparatus according to claim 5 , wherein the controller is configured to control the frequency (f) and the dynamic force (F d ) of the oscillator.

8. An apparatus according to claim 7 , wherein the frequency (f) and the dynamic force (F d ) of the oscillator provides according to load cell measurements representing changes in the compressive strength (U s ) of material being drilled.

9. An apparatus according to claim 5 , which apparatus further comprises an oscillator back mass.

10. An apparatus according to claim 1 , which apparatus comprises:

(i) an upper load-cell for measuring static loading;

(ii) an oscillator for applying axial oscillatory loading to the rotary drill bit;

(iii) a lower load-cell for measuring dynamic axial loading;

(iv) a drill-bit connector; and

(v) a drill-bit,

wherein the upper load-cell positioned above the vibration damping and/or isolation unit and the lower load-cell is positioned between the oscillator and the drill-bit wherein the upper and lower load-cells are connected to a controller in order to provide down-hole closed loop real time control of the oscillator.

11. An apparatus according to claim 10 , wherein the oscillator comprises an electrically driven mechanical actuator.

12. An apparatus according to claim 1 , which apparatus further comprises:

(i) a resonance enhanced rotary drilling module comprising an oscillator;

(ii) a fixed frame for fixing the apparatus to a base surface;

(iii) a movable frame for moving the rotary drilling module in an axial direction relative to a sample;

(iv) a means for generating relative rotary motion between the drilling module and a sample; and

(v) a torsion restraint unit for reducing the torsional loading on the oscillator.

13. An apparatus according to claim 12 , wherein an upper load-cell is positioned above the vibration damping and/or isolation unit and a lower load-cell is positioned between the vibration enhancement and/or transmission unit and a drill-bit, and wherein the upper and lower load-cells are connected to a controller in order to provide down-hole closed loop real time control of the oscillator.

14. A method of drilling comprising operating an apparatus as defined in claim 1 .

15. A method of drilling according to claim 14 , the method comprising controlling an operational frequency of axial vibration of the resonance enhanced rotary drilling apparatus such that the frustoconical spring system of the vibration damping and/or isolation unit satisfies the following equation:

ω/ω n ≧2.3

wherein ω represents an operational frequency of axial vibration of the resonance enhanced rotary drilling apparatus, and ω η represents the natural frequency of the frustoconical spring of the vibration isolation unit.

16. A method of drilling according to claim 14 , the method comprising controlling an operational frequency of axial vibration of the resonance enhanced rotary drilling apparatus such that the frustoconical spring of the vibration enhancement and/or transmission unit satisfies the following equation:

0.6≦ω/ω η ≦1.2

wherein ω represents an operational frequency of axial vibration of the resonance enhanced rotary drilling apparatus, and ω η represents the natural frequency of the frustoconical spring of the vibration transmission unit.

17. A method according to claim 14 , wherein the method further comprises controlling the amplitude of vibration of the oscillator to be maintained within the range 0.5 to 10 mm.

18. A method according to claim 14 , wherein the frequency (f) of the oscillator is controlled to be maintained in the range 100 Hz and above.

19. A method according to claim 14 , wherein the dynamic force (F d ) is controlled to be maintained within the range up to 1000 kN.

20. A vibration damping and/or isolation unit comprising a spring system comprising a frusto-conical springs, wherein the frustoconical spring satisfies the following equation:

ω/ω n ≧2.3

wherein ω represents an operational frequency of axial vibration, and ω n represents the natural frequency of the frustoconical spring of the unit and wherein the vibration dampening and/or isolation unit is situated above an oscillator and dampens and/or isolates vibration from the oscillator.

21. A vibration enhancement and/or transmission unit comprising a spring system comprising a frusto-conical springs, wherein the spring system satisfies the following equation:

0.6≦ω/ω η ≦1.2

wherein ω represents an operational frequency of axial vibration, and ω n represents the natural frequency of the frustoconical spring of the unit and wherein the vibration enhancement and/or transmission unit is situated below an oscillator and enhances and/or transmits vibration from the oscillator.

22. A method of using a spring system comprising a frusto-conical spring in a high-torsion environment, wherein the frustoconical spring is for vibration damping and/or isolation and satisfies the following equation:

ω/ω n ≧2.3

wherein ω represents an operational frequency of axial vibration, and ω n represents the natural frequency of the frustoconical spring of the unit and

wherein the spring system is situated above an oscillator and dampens and/or isolates vibration from the oscillator, or

wherein the frustoconical spring is for vibration enhancement and/or transmission and satisfies the following equation:

0.6≦ω/ω η ≦1.2

wherein ω η represents the natural frequency of the frustoconical spring and

wherein the spring system is situated below an oscillator and enhances and/or transmits vibration from the oscillator.

23. A method according to claim 22 , wherein the frustoconical spring is one such that the force, P, applied to the frustoconical spring can be determined according to the following equation:

P

=

1.1

⁢

E

⁢

⁢

δ

⁢

⁢

C

R

2

⁡

[

(

h

-

δ

)

⁢

(

h

-

δ

2

)

⁢

t

+

t

2

]

wherein t is the thickness of the frusto-conical springs, h is the height of the frustoconical spring, R is the radius of the frustoconical spring, δ is the displacement on the frustoconical spring caused by the force P, E is the Young modulus of the frustoconical spring, and C is the constant of the frustoconical spring.

24. The method according to claim 22 , wherein the frustoconical spring comprises one or more Belleville springs.

25. The method according to claim 22 , wherein the frustoconical spring is formed from a metal.

26. A unit according to claim 20 or claim 21 , wherein the frustoconical spring is one such that the force, P, applied to the frustoconical spring can be determined according to the following equation:

P

=

1.1

⁢

E

⁢

⁢

δ

⁢

⁢

C

R

2

⁡

[

(

h

-

δ

)

⁢

(

h

-

δ

2

)

⁢

t

+

t

2

]

wherein t is the thickness of the frusto-conical spring, h is the height of the frustoconical spring, R is the radius of the spring system, δ is the displacement on the frustoconical spring caused by the force P, E is the Young modulus of the frustoconical spring, and C is the constant of the frustoconical spring.

27. A unit according to claim 20 or 21 , wherein the frustoconical spring comprises one or more Belleville springs.

28. A unit according to any of claim 20 or 21 , wherein the frustoconical spring is formed from a metal.