Monitoring of brake

1. A method for monitoring a brake that comprises:

first and second braking surfaces, and

magnetizing means arranged to move the braking surfaces to an open state, in which the braking surfaces are separated from each other, and to a closed state, in which the braking surfaces are connected to each other, the method comprising:

measuring the time that elapses from the change in the magnetic field caused by the magnetizing means to the shift of the braking surfaces from one state to another;

determining a strength of the brake's magnetic field; and

determining a malfunction of the brake when the magnetizing means generate a magnetic field in the closed state of the braking surfaces.

2. A method as claimed in claim 1 , further comprising:

performing several measurements on the time that elapses from the change in the magnetic field caused by the magnetizing means to the shift of the braking surfaces from one state to another; and

determining the condition of the brake on the basis of the change in the times.

3. A method as claimed in claim 1 , comprising:

performing several measurements on the time that elapses from the increase in the magnetic field and the shift of the braking surfaces from the closed state to the open state; and

determining the decrease in the condition of the brake when the measured times are increasing.

4. A method as claimed in claim 1 , comprising:

performing several measurements on the time from the decrease in the magnetic field of the brake and the shift of the braking surfaces from the open state to the closed state; and

determining the decrease in the condition of the brake when the measured times are decreasing.

5. A method as claimed in claim 1 , comprising:

determining a threshold value for the time that elapses from the change in the magnetic field caused by the magnetizing means to the shift of the braking surfaces from one state to another; and

determining a malfunction of the brake when the measured time exceeds the defined threshold value.

6. A method as claimed in claim 1 , comprising:

determining the strength of the brake's magnetic field in the open state of the braking surfaces; and

determining a malfunction of the brake, when the magnetic field generated by the magnetizing means is smaller than the determined magnetic field of the brake in the open state of the braking surfaces.

7. A method as claimed in claim 1 , wherein the monitored brake comprises a braking surface that is arranged to rotate with the device to be decelerated, the method comprising:

determining a malfunction of the brake when, on the braking surface that is arranged to rotate with the device to be decelerated, an angular velocity deviating from zero is measured and the strength of the magnetic field generated by the magnetizing means is essentially zero.

8. A method as claimed in claim 1 , comprising:

advising a service centre of the change in the condition level and/or a malfunction of the brake; and

performing an emergency stop if the brake has a malfunction.

9. A computer program embodied on a non-transitory distribution medium, having program instructions which, when loaded into an apparatus will cause execution of steps of a method as claimed in claim 1 when downloaded into the device.

10. A device for monitoring an electromagnetic brake, the brake comprising first and second braking surfaces being movable between an open state opened by means of a magnetic field of the brake, where the braking surfaces are not connected to each other, and a closed state, where the braking surfaces are connected to each other, the device comprising:

receiving means for receiving energy from the magnetic field of the brake, and the device being arranged:

to measure time from the change in the magnetic field caused by the magnetizing means to the shift of the braking surfaces from one state to another; and

determine a malfunction of the brake when the magnetizing means generate a magnetic field in the closed state of the braking surfaces.

11. A device as claimed in claim 10 , the device being arranged:

to perform several measurements on the time that elapses from the change in the magnetic field caused by the magnetizing means to the shift of the braking surfaces from one state to another; and

to determine the condition of the brake on the basis of the change in the times.

12. A device as claimed in claim 10 , the device being arranged:

to perform several measurements on the time that elapses from the increase in the magnetic field of the brake and the shift of the braking surfaces from the closed state to the open state; and

to determine the decrease in the condition of the brake when the measured times are increasing.

13. A device as claimed in claim 10 , the device being arranged:

to perform several measurements on the time from the decrease in the magnetic field of the brake and the shift of the braking surfaces from the open state to the closed state; and

to determine the decrease in the condition of the brake when the measured times are decreasing.

14. A device as claimed in claim 10 , the device being arranged:

to determine a threshold value for the time that elapses from the change in the magnetic field caused by the magnetizing means to the shift of the braking surfaces from one state to another; and

to determine a malfunction of the brake when the measured time exceeds the determined threshold value.

15. A device as claimed in claim 10 , the device being arranged:

to define the strength of the brake's magnetic field in the open state of the braking surfaces; and

to determine a malfunction of the brake, when the magnetic field generated by the magnetizing means is smaller than the determined strength of the brake's magnetic field in the open state of the braking surfaces.

16. A device as claimed in claim 10 , wherein the monitored brake comprises a braking surface that is arranged to rotate with the device to be decelerated, the device being arranged:

to determine a malfunction of the brake when, on the braking surface that is arranged to rotate with the device to be decelerated, an angular velocity deviating from zero is measured and the strength of the magnetic field generated by the magnetizing means is essentially zero.

17. A device as claimed in claim 10 , wherein the receiving means for receiving energy from the magnetic field of the brake comprise a coil or a Hall sensor.

18. A device as claimed in claim 10 , wherein the device comprises a pulse sensor or a biaxial acceleration transducer for determining the angular velocity of at least one braking surface.

19. A device as claimed in claim 10 , wherein the device comprises an acceleration transducer to determine the shift of the braking surfaces from one state to the other.

20. A device as claimed in claim 10 , wherein the condition of the brake comprises the condition of any braking surface.

21. An electromagnetic brake that comprises a device as claimed in claim 10 .

22. An electromagnetic brake as claimed in claim 21 and comprising a housing with a recess, into which recess a device for monitoring an electromagnetic brake is installed, the brake comprising first and second braking surfaces being movable between an open state opened by means of a magnetic field of the brake, where the braking surfaces are not connected to each other, and a closed state, where the braking surfaces are connected to each other, the device comprising:

receiving means for receiving energy from the magnetic field of the brake, and the device being arranged:

to measure time from the change in the magnetic field caused by the magnetizing means to the shift of the braking surfaces from one state to another; and

determine a malfunction of the brake when the magnetizing means generate a magnetic field in the closed state of the braking surfaces.

23. A hoisting device that comprises the electromagnetic brake as claimed in claim 22 .

24. A hoisting device as claimed in claim 23 and comprising a rope drum that is functionally connected to at least one braking surface of said electromagnetic brake, whereby both are arranged to rotate when load is lifted or lowered, and a multiaxis acceleration transducer that is arranged at the rope drum to measure the angular velocity of the rope drum.

25. A hoisting device as claimed in claim 24 and comprising at least one of the following: quay crane and bridge crane.

26. A method for upgrading a hoisting device, the device comprising an electromagnetic brake with first and second braking surfaces being movable between an open state opened by means of a magnetic field of the brake, where the braking surfaces are not connected to each other, and a closed state, where the braking surfaces are connected to each other, the method comprising:

installing the device of claim 10 in connection with an electromagnetic brake.

27. A device for executing a method for monitoring a brake that comprises:

first and second braking surfaces, and

magnetizing means arranged to move the braking surfaces to an open state, in which the braking surfaces are separated from each other, and to a closed state, in which the braking surfaces are connected to each other, the device comprising:

means for measuring the time that elapses from the change in the magnetic field caused by the magnetizing means to the shift of the braking surfaces from one state to another;

means for determining a strength of the brake's magnetic field; and

means for determining a malfunction of the brake when the magnetizing means generate a magnetic field in the closed state of the braking surfaces.