Magnetic drilling stand with holding force monitoring

1. A magnetic drilling stand comprising:

a base;

a drilling unit received on said base;

an electromagnet received on said base for fixing said magnetic drilling stand on a component, said electromagnet having a rated current I N ;

an controller for controlling operation of said electromagnet and of said drilling unit;

a voltage source controlled by said controller and coupled to said electromagnet;

a sensor for monitoring a current through said electromagnet and for generating a current signal I indicative of a current flowing through said electromagnet and for outputting said current signal to said controller;

wherein said controller first powers said electromagnet for a certain test phase of a duration T, before operating said drilling unit and generates either an OK signal indicative for a sufficient magnetic holding force or a fault F signal indicative for insufficient magnetic holding force, depending on the current level signals at different times within said test phase;

wherein said controller generates said OK signal when, after 30% of the duration T of said test phase has elapsed, a current level of said electromagnet of at most 85% of said rated current I N is reached, and after 43% of the duration T of said test phase has elapsed said current level reaches at most 95% of said rated current I N .

2. The magnetic drilling stand of claim 1 , wherein said test phase has a duration of 700 to 800 milliseconds.

3. The magnetic drilling stand of claim 1 , wherein prior to said test phase said electromagnet is at least partially demagnetized in a demagnetization phase, before a DC voltage is applied to said electromagnet within said test phase.

4. The magnetic drilling stand of claim 1 , wherein said controller produces a fault signal indicative of a fault state, if the current level falls below a predetermined threshold value I min in a working phase following said test phase.

5. The magnetic drilling stand of claim 4 , wherein said controller produces said fault signal, if the current level in said working phase falls below 50% of said rated current I N of said electromagnet.

6. A magnetic drilling stand comprising:

a base;

a drilling unit received on said base;

an electromagnet received on said base for fixing said magnetic drilling stand on a component;

an controller for controlling operation of said electromagnet and of said drilling unit;

a voltage source controlled by said controller and coupled to said electromagnet;

a sensor for monitoring a current through said electromagnet and for generating a current signal I indicative of a current flowing through said electromagnet and for outputting said current signal to said controller;

wherein said controller first powers said electromagnet for a certain test phase, before operating said drilling unit and generates either an OK signal indicative for a sufficient magnetic holding force or a fault F signal indicative for insufficient magnetic holding force, depending on the current level signals at different times within said test phase;

wherein said controller generates said OK signal when, within said test phase, a current level of said electromagnet is below predetermined threshold values I 1 <I 1G and I 2 <I 2G at at least two predetermined times t 1 and t 2 after starting said test phase.

7. The magnetic drilling stand of claim 6 , further comprising a signalling means for signaling a fault state to a user, if said controller generates said F signal.

8. The magnetic drilling stand of claim 6 , wherein said controller allows activation of said drilling unit only when an OK signal is generated.

9. The magnetic drilling stand of claim 6 , wherein prior to said test phase said electromagnet is at least partially demagnetized in a demagnetization phase, before a DC voltage is applied to said electromagnet within said test phase.

10. The magnetic drilling stand of claim 9 , wherein within said demagnetization phase a DC voltage of alternating polarity or an AC voltage is applied to said electromagnet for demagnetizing said electromagnet.

11. The magnetic drilling stand of claim 6 , wherein, if the current level is above a predetermined threshold value at at least one of the predetermined times within said test phase, said controller produces an OK signal indicative of a sufficient magnetic holding force if the current level of the electromagnet is below predetermined threshold values I n <I nG and I n+1 <I n+1G at each of at least two later times within said test phase.

12. The magnetic drilling stand of claim 11 , wherein said controller generates an OK signal indicative of a sufficient magnetic holding force, if the current level of the electromagnet is below predetermined threshold values I n <I nG and I n+1 <I n+1G at each of at least two successive, later times within the test phase.

13. The magnetic drilling stand of claim 6 , wherein said controller produces a fault signal indicative of a fault state, if the current level falls below a predetermined threshold value I min in a working phase following said test phase.

14. The magnetic drilling stand of claim 13 , wherein said electromagnet has a certain rated current I N , and wherein said controller produces said fault signal, if the current level in said working phase falls below said predetermined threshold value I min which corresponds to 50% of said rated current I N of said electromagnet.

15. The magnetic drilling stand of claim 6 , wherein said test phase has a duration of 700 to 800 milliseconds.

16. The magnetic drilling stand of claim 6 , wherein said test phase has a duration of 720 to 750 milliseconds.

17. The magnetic drilling stand of claim 6 , wherein said test phase is preceded by a demagnetization phase with a duration of 700 to 1000 milliseconds.

18. The magnetic drilling stand of claim 6 , wherein said test phase is preceded by a demagnetization phase with a duration of 800 to 900 milliseconds.

19. A magnetic drilling stand comprising:

a base;

a drilling unit received on said base;

an electromagnet received on said base for fixing said magnetic drilling stand on a component;

an controller for controlling operation of said electromagnet and of said drilling unit;

a voltage source controlled by said controller and coupled to said electromagnet;

a sensor for monitoring a current through said electromagnet and for generating a current signal I indicative of a current flowing through said electromagnet and for outputting said current signal to said controller;

wherein said controller first at least partially demagnetizes said electromagnet in a demagnetization phase;

wherein said controller thereafter powers said electromagnet with a DC voltage for a certain test phase, before operating said drilling unit and generates either an OK signal indicative for a sufficient magnetic holding force or a fault F signal indicative for insufficient magnetic holding force, depending on the current level signals at different times within said test phase;

wherein said controller generates said OK signal when, within said test phase, if a current level of said electromagnet is below predetermined threshold values I 1 <I 1G and I 2 <I 2G at at least two predetermined times t 1 and t 2 after starting said test phase;

wherein, if the current level is above said predetermined threshold value at at least one of the predetermined times within said test phase, said controller produces an OK signal indicative of a sufficient magnetic holding force, if the current level of the electromagnet is below predetermined threshold values I n <I nG and I n+1 <I n+1G at each of at least two later times within said test phase; and

wherein said controller allows activation of said drilling unit only when an OK signal is generated.

20. The magnetic drilling stand of claim 19 , wherein said controller produces a fault signal indicative of a fault state, if the current level falls below a predetermined threshold value I min in a working phase following said test phase.