Brake monitoring

1. A method for monitoring a brake that comprises:

first and second braking surfaces, and

magnetizing means which, in response to an electric current supplied to the magnetizing means, are configured to generate a magnetic field that moves the braking surfaces from a closed state, in which the braking surfaces are connected to each other, to an open state, in which the braking surfaces are separated from each other; the method comprising:

generating the magnetic field by the magnetizing means to move the braking surfaces from the closed state, in which the braking surfaces are connected to each other, to the open state, in which the braking surfaces are separated from each other;

determining the electric current of the magnetizing means as the braking surfaces begin to move from the closed state to the open state,

determining a maximum electric current of the magnetizing means of the brake in the open state;

determining a condition of the brake as a current ratio from the electric current measured as the braking surfaces start to move to said maximum electric current.

2. The method as claimed in claim 1 , wherein, for a calculation of the current ratio, the maximum electric current of the magnetizing means is determined at a time instant of a local minimum of a time derivative of the brake current or at a time preceding the local minimum.

3. The method as claimed in claim 1 , wherein an adequacy of the electric current supplied to the brake is determined on the basis of said current ratio.

4. The method as claimed in claim 1 , wherein an air gap between the braking surfaces is determined on the basis of said current ratio.

5. The method as claimed in claim 1 , wherein the current ratio is determined once or several times; and

the condition of the brake is determined on the basis of one or more determined current ratios.

6. The method as claimed in claim 1 , wherein a disturbance in the power supply of the brake is determined on the basis of the change in the current ratios determined from several consecutive brake releases.

7. The method as claimed in claim 1 , wherein the condition of the brake is determined, when the current ratio of the brake exceeds a threshold value set for the current ratio.

8. The method as claimed in claim 1 , wherein the condition of the brake is determined on the basis of said current ratio and a current ratio threshold value defined for several brakes that differ in their electric and/or magnetic properties.

9. The method as claimed in claim 1 , wherein several brakes are monitored by using a same current ratio threshold value.

10. The method as claimed in claim 1 , wherein a service life of the brake is calculated on the basis of one or more current ratios, and the service life comprises a number of decelerations, date, number of days or combination thereof.

11. The method as claimed in claim 1 , wherein a service life of the brake is calculated on the basis of one or more current ratios and the service life is displayed on a display.

12. The method as claimed in claim 1 , wherein a warning or alert is given, when an increase in the deviation of the electric current measured as the braking surfaces start to move from the closed state to the open state in consecutive or closely consecutive measurings exceeds a given limit.

13. A device for monitoring an electromagnetic brake comprising first and second braking surfaces and magnetizing means which, in response to an electric current supplied to the magnetizing means, are configured to generate a magnetic field that moves the braking surfaces from a closed state, in which the braking surfaces are connected to each other, to an open state, in which the braking surfaces are separated from each other, the device being configured to:

determine the electric current of the magnetizing means as the braking surfaces begin to move from the closed state to the open state, wherein the device is configured to

determine a maximum electric current of the magnetizing means of the brake in the open state;

determine a condition of the brake as a current ratio from the electric current measured as the braking surfaces start to move to the maximum electric current.

14. The device as claimed in claim 13 , wherein, for a calculation of the current ratio, the maximum electric current of the magnetizing means is determined at a time instant of a local minimum of a time derivative of the brake current or at a time preceding the local minimum.

15. The device as claimed in claim 13 , wherein the device is configured to determine an adequacy of the current supplied to the brake on the basis of said current ratio.

16. The device as claimed in claim 13 , wherein the device is configured to determine an air gap between the braking surfaces on the basis of said current ratio.

17. The device as claimed in claim 13 , wherein the device is configured to determine a current ratio that is measured once or several times; and

to determine the condition of the brake on the basis of the one or more determined current ratios.

18. The device as claimed in claim 13 , wherein the device is configured to determine a disturbance in the power supply of the brake on the basis of a change in current ratios determined from several consecutive brake releases.

19. The device as claimed in claim 13 , wherein the device is configured to determine the condition of the brake, when the current ratio of the brake exceeds a threshold value set for the current ratio.

20. The device as claimed in claim 13 , wherein the device is configured to determine the condition of the brake on the basis of said current ratio and a threshold value determined for several brakes that differ in their electric and/or magnetic properties.

21. The device as claimed in claim 13 , wherein the device is configured to monitor several brakes by using a same threshold value of the current ratio.

22. The device as claimed in claim 13 , wherein a service life of the brake is calculated on the basis of one or more current ratios, and the service life comprises a number of decelerations, date, number of dates, or combination thereof.

23. The device as claimed in claim 13 , wherein a service life of the brake is calculated on the basis of one or more current ratios, and the service life is displayed on a display.

24. The device as claimed in claim 13 , wherein the device is configured to give a warning or alert, when an increase in the deviation in the electric current measured as the braking surfaces start to move from the closed state to the open state in consecutive measurings or in immediately consecutive measurings exceeds a given limit.

25. A computer program product comprising a non-transitory computer-readable storage medium having program instructions that when downloaded into a device cause the device to execute a method for monitoring a brake that comprises:

first and second braking surfaces, and

magnetizing means which, in response to an electric current supplied to the magnetizing means, are configured to generate a magnetic field that moves the braking surfaces from a closed state, in which the braking surfaces are connected to each other, to an open state, in which the braking surfaces are separated from each other;

the method comprising:

determining the electric current of the brake as the braking surfaces begin to move from the closed state to the open state;

determining a maximum electric current of the magnetizing means of the brake in the open state;

determining a condition of the brake as a current ratio from the electric current measured as the braking surfaces start to move to said maximum electric current.

26. A device comprising means for carrying out a method

for monitoring a brake that comprises:

first and second braking surfaces, and

magnetizing means which, in response to an electric current supplied to the magnetizing means, are configured to generate a magnetic field that moves the braking surfaces from a closed state, in which the braking surfaces are connected to each other, to an open state, in which the braking surfaces are separated from each other;

the method comprising:

determining the electric current of the magnetizing means as the braking surfaces begin to move from the closed state to the open state;

determining a maximum electric current of the magnetizing means of the brake in the open state;

determining a condition of the brake as a current ratio from the electric current measured as the braking surfaces start to move to said maximum electric current.

27. An arrangement comprising a device for monitoring an electromagnetic brake comprising first and second braking surfaces and magnetizing means which, in response to an electric current supplied to the magnetizing means, are configured to generate a magnetic field that moves the braking surfaces from a closed state, in which the braking surfaces are connected to each other, to an open state, in which the braking surfaces are separated from each other, the device being configured to:

determine the electric current of the magnetizing means as the braking surfaces begin to move from the closed state to the open state, wherein the device is configured to

determine a maximum electric current of the magnetizing means of the brake in the open state;

determine a condition of the brake as a current ratio from the electric current measured as the braking surfaces start to move to the maximum electric current.

28. The arrangement as claimed in claim 27 , wherein the arrangement comprises one or more electromagnetic brakes or hoisting devices, or a combination thereof.

29. An arrangement comprising a device comprising means for carrying out a method

for monitoring a brake that comprises:

first and second braking surfaces, and

magnetizing means which, in response to an electric current supplied to the magnetizing means, are configured to generate a magnetic field that moves the braking surfaces from a closed state, in which the braking surfaces are connected to each other, to an open state, in which the braking surfaces are separated from each other;

the method comprising:

determining the electric current of the magnetizing means as the braking surfaces begin to move from the closed state to the open state;

determining a maximum electric current of the magnetizing means of the brake in the open state;

determining a condition of the brake as a current ratio from the electric current measured as the braking surfaces start to move to said maximum electric current.

30. The arrangement as claimed in claim 29 , wherein the arrangement comprises one or more electromagnetic brakes or hoisting devices, or a combination thereof.

31. A method for upgrading a hoisting device with a monitoring function, wherein the hoisting device comprises an electromagnetic brake comprising first and second braking surfaces and magnetizing means which, in response to an electric current supplied to the magnetizing means, are configured to generate a magnetic field that moves the braking surfaces from a closed state, in which the braking surfaces are connected to each other, to an open state, in which the braking surfaces are separated from each other, the method comprising:

installing, in connection with an electromagnetic brake, a computer program product that comprises program instructions configured to cause the hoisting device to:

determine the electric current of the magnetizing means as the braking surfaces begin to move from the closed state to the open state;

determine a maximum electric current of the magnetizing means of the brake in the open state;

determine a condition of the brake as a current ratio from the electric current measured as the braking surfaces start to move to said maximum electric current.

32. A method for upgrading a hoisting device with a monitoring function, wherein the hoisting device comprises an electromagnetic brake comprising first and second braking surfaces and magnetizing means which, in response to an electric current supplied to the magnetizing means, are configured to generate a magnetic field that moves the braking surfaces from a closed state, in which the braking surfaces are connected to each other, to an open state, in which the braking surfaces are separated from each other, the method comprising:

installing, in connection with an electromagnetic brake, a device comprising means for:

determining the electric current of the magnetizing means as the braking surfaces begin to move from the closed state to the open state;

determining a maximum electric current of the magnetizing means of the brake in the open state;

determining a condition of the brake as a current ratio from the electric current measured as the braking surfaces start to move to said maximum electric current.

33. A method for upgrading a hoisting device with a monitoring function, wherein the hoisting device comprises an electromagnetic brake comprising first and second braking surfaces and magnetizing means which, in response to an electric current supplied to the magnetizing means, are configured to generate a magnetic field that moves the braking surfaces from a closed state, in which the braking surfaces are connected to each other, to an open state, in which the braking surfaces are separated from each other, the method comprising:

installing, in connection with an electromagnetic brake, a device being configured to:

determine the electric current of the magnetizing means as the braking surfaces begin to move from the closed state to the open state, wherein the device is configured to

determine a maximum electric current of the magnetizing means of the brake in the open state;

determine a condition of the brake as a current ratio from the electric current measured as the braking surfaces start to move to the maximum electric current.