The invention relates to electromagnetic brakes, more particularly to solutions for supervising the condition of a brake .

Electromagnetic brakes are used e.g. in conveying systems to prevent movement of a motor and of a conveying apparatus .

Typically an electromagnetic brake comprises a frame part and an armature part that moves in relation to the frame part. A brake also comprises an activation means, e.g. a spring, which exerts a force between the frame part and the armature part, which force activates the brake by pressing the armature part into contact against the object to be braked. The brake opens when current is connected to the electromagnet of the brake and the magnet pulls the armature part away from the object to be braked.

Collision of the mechanical parts of a brake against each other when the brake is activated or opened may cause a disturbing noise. The noise problem is eliminated whenever possible by adding e.g. a damper to the air gap between the frame part and the armature part, which when the brake is open produces a small so-called hysteresis air gap between the frame part and the armature part. The damper in this case prevents direct contact between the metal surfaces of the frame part and of the armature part, at the same time damping the noise of the brake and also speeding up the action of the brake .

The damper can be made of an elastic material, such as rubber. A damper made of rubber, however, wears and generally becomes brittle as it ages. The damper wearing and/or becoming brittle may result in a progresseive reduction of the hysteresis air gap, in which case the metal surfaces of the frame part and of the armature part finally manage to strike against each other. The damper can also be made of e.g. paper and glue. In this case the glue can cake; paper, on the other hand, can tear or bend over time. As a consequence of these problems the hysteresis air gap between the frame part and the armature part might increase, which in turn reduces the force produced by the electromagnet, because the force produced by the electromagnet decreases as the air gap between the frame part and the armature part of the brake increases. In the worst case, the electromagnet is no longer able to keep the brake open after the hysteresis air gap has enlarged.

Owing to, among other things, the aforementioned drawbacks, an apparatus and a method for supervising the condition of a brake are presented as an invention.

In relation to the characteristic attributes of the invention, reference is made to the claims.

Some inventive embodiments are also discussed in the descriptive section of the present application. The inventive content of the application can also be defined differently than in the claims presented below. The inventive content may also consist of several separate inventions, especially if the invention is considered in the light of expressions or implicit sub-tasks or from the point of view of advantages or categories of advantages achieved. In this case, some of the attributes contained in the claims below may be superfluous from the point of view of separate inventive concepts.

By utilizing the invention the condition of a brake can be supervised during the lifetime of the brake such that e.g. wear and/or failure of the damping arrangement of the brake can be detected before the noise of the brake becomes disturbing or the brake is no longer able to open properly. Information about the possible servicing need of the brake can also in this case be notified in good time e.g. to the service center. The invention is very well suited for use e.g. in connection with elevator systems, escalator systems and travelator systems .

The first aspect of the invention relates to an apparatus for supervising the condition of a brake.

According to one or more embodiments of the invention, the brake comprises a frame part, an armature part supported by the frame part in a manner that allows movement, a spring or corresponding for activating the brake, and also a coil for opening the brake. The apparatus for supervising the condition of a brake comprises a brake control apparatus, for performing a brake control procedure, a movement determination part, for determining the starting situation of the armature part of the brake, a current determination part, for determining the magnitude of the current of the coil of the brake in the starting situation of the armature part of the brake, and also operating condition determination part, for determining the operating condition of the brake from the magnitude of the aforementioned current of the coil of the brake. The operating condition of the brake can in this case be determined from the magnitude of the current of the coil of the brake in the starting situation of the armature part of the brake, which improves the reliability of the brake control apparatus.

According to one or more embodiments of the invention, the brake comprises a damping arrangement for damping the noise of the brake. The aforementioned operating condition determination part is arranged to determine the operating condition of the damping arrangement of the brake from the magnitude of the current of the coil of the brake, which magnitude of the current of the coil of the brake is determined in the starting situation of the armature part of the brake, in connection with an activation procedure of the brake. Thus the reliability of the brake improves because malfunctioning and/or deterioration of the operating condition of the damping arrangement may result in an increase in the noise of the brake and/or a deterioration of the operational capability of the brake.

According to one or more embodiments of the invention, the aforementioned damping arrangement is fitted into the space in the brake between the frame part and the armature part . Wear and/or failure of the damping arrangement can in this case be detected e.g. from a change in the air gap between the frame part and the armature part, such that when the air gap changes the magnitude of the current of the coil of the brake in the starting situation of the armature part also changes.

According to one or more embodiments of the invention, the brake control apparatus comprises a memory, in which memory data about the magnitude of the current of the coil of the brake is recorded, and in which memory one or more limit values of permitted current are recorded. The operating condition determination part of the brake comprises a control for determining the operating condition of the brake from the aforementioned one or more limit values of the permitted current and also from the magnitude of the current of the coil of the brake.

According to one or more embodiments of the invention, the apparatus comprises an output for the signal indicating the operating condition of the brake. In this case e.g. information about wear or failure of the damping arrangement of the brake can be indicated, for instance for the performance of servicing procedures or for collecting reliability data.

According to one or more embodiments of the invention, the brake control apparatus comprises an electricity supply circuit, which electricity supply circuit comprises at least one controllable solid-state switch, for controlling the current of the coil of the brake with short pulses. In this case the current profile of the coil of the brake can be adjusted for controlling the operation of the brake.

According to one or more embodiments of the invention, the movement determination part comprises a position switch of the brake, for detecting movement of the armature part of the brake. In this case the starting situation of the armature part of the brake can be determined on the basis of the position data of the armature part indicated by the position switch.

According to one or more embodiments of the invention, the movement determination part comprises means for processing the determined current and/or supply voltage of the coil of the brake, for detecting movement of the armature part (4) of the brake. In this case the starting situation of the armature part can be determined also without a separate position switch of the brake.

The second aspect of the invention relates to a method for supervising the condition of a brake.

According to one or more embodiments of the invention, in the method a brake control procedure is performed, and movement of the armature part of the brake occurring as a response to the brake control procedure is detected, the magnitude of the current of the coil of the brake is determined in the starting situation of the armature part of the brake, and also the operating condition of the brake is determined from the magnitude of the current of the coil of the brake.

According to one or more embodiments of the invention, the magnitude of the current of the coil of the brake in the starting situation of the armature part of the brake is determined, in connection with an activation procedure of the brake, and also the operating condition of the damping arrangement of the brake is determined from the magnitude of the current of the coil of the brake.

According to one or more embodiments of the invention, a first range of permitted current is determined for the current of the coil of the brake by means of one or more first limit values, the determined current of the coil of the brake is compared to the first range of permitted current, and if the value of the current of the coil of the brake in this case differs from the first range of permitted current, it is concluded that the brake needs servicing.

According to one or more embodiments of the invention, a second range of permitted current is determined for the current of the coil of the brake by means of one or more second limit values, which second range of permitted current is fitted to be outside the first range of permitted current, the determined current of the coil of the brake is compared to the second range of permitted current, and if the value of the current of the coil of the brake in this case differs from both the first and the second range of permitted current, the next opening procedure of the brake is prevented.

According to one or more embodiments of the invention, information about the servicing need of the brake is sent to the service center.

According to one or more embodiments of the invention, at least one controllable switch of the electricity supply circuit of the brake is controlled as a brake control procedure, for supplying current to the coil of the brake and/or for disconnecting the flow of current.

According to one or more embodiments of the invention, the current of the coil of the brake is adjusted towards the current reference as a brake control procedure, by connecting at least one controllable switch of the electricity supply circuit of the brake with short pulses. According to one or more embodiments of the invention, movement of the armature part is detected with the position switch of the brake.

According to one or more embodiments of the invention, movement of the armature part is detected from the current and/or from the supply voltage of the coil of the brake.

According to one embodiment of the invention, the opening of the brake can if necessary be prevented on the basis of the supervision data of the condition of the brake, in which case drive of the object to be braked is prevented. According to one embodiment of the invention, information about the drive prevention can also be sent onwards to the control system of the object to be braked, such as e.g. of an elevator car, an escalator or a travelator.

Also presented as an invention is a determination of the condition of a brake activation means, such as of a spring or corresponding, from the magnitude of the current of the coil of a brake, which magnitude of the current of the coil of the brake is determined in the starting situation of the armature part of the brake, in connection with an opening procedure of the brake .

In the following, the invention will be described in more detail by the aid of some examples of its embodiments, which in themselves do not limit the scope of application of the invention, with reference to the attached drawings, wherein

Fig. 1 presents the principles of a brake according to the invention connected to an apparatus according to the invention for supervising the condition of the brake Fig. 2 presents a brake control apparatus according to the invention as a block diagram Fig. 3 illustrates the force produced by the electromagnet of a brake in connection with brake control procedures Fig. 4 presents the current references of the ^' coil of the brake in connection with a brake control procedure Fig. 5 presents the limit values of the permitted current of the coil of the brake

The drum brake 2 of the hoisting machine of an elevator presented in Fig. 1 comprises a frame part 3, which is fixed to the frame of the hoisting machine. The drum brake 2 also comprises an armature part 4 supported by the frame part 3 in a manner that allows movement, which armature part comprises a brake shoe 28. A damping arrangement 11, for damping the noise of the brake, is fitted into the space 12 in the brake drum 2 between the frame part 3 and the armature part 4. The damping arrangement 11 prevents direct contact between the metal surfaces of the frame part 3 and of the armature part 4, leaving between them a small hysteresis air gap when the brake is open.

The drum brake 1 also comprises two helical springs 5 as activation means, which exert a thrusting force between the frame part 3 and the armature part 4, which thrusting force endeavors to push the armature part 4 towards the brake drum

27 that is attached onto the rotating traction sheave of the hoisting machine. The armature part 4 comprises a brake pad 29, through which the brake shoe 28 connects mechanically to the brake drum 27 to brake the movement of the elevator when activating the drum brake 2. The drum brake opens when the current supplied to the coil 6 of the brake disposed in the frame part 3 achieves an electromagnetic force of attraction between the frame part 3 and the armature part 4 that is greater than the thrusting force achieved by the helical springs 5. In this case the armature part 4 starts to move towards the frame part 3. A force of attraction is produced, because both the frame part 3 and the armature part 4 comprise material that conducts magnetic flux, such as ferromagnetic iron, which together with the coil 6 of the brake forms a magnetic circuit. The magnetic flux produced by the current flowing in the coil 6 of the brake also flows between the frame part 3 and the armature part 4 over the air gap 37. The force of attraction brought about by the current of the coil 6 of the brake increases strongly when the air gap 37 between the frame part 3 and the armature part 4 decreases .

The supply conductors of the coil 6 of the brake are taken to the apparatus 1 for supervising the condition of the brake. With the apparatus 1 the operating condition of the ^• damping arrangement 11 of the brake is supervised in the situation when the brake is open and the damping arrangement 11 leaves a small hysteresis air gap between the frame part 3 and the armature part. Wear or failure of the damping arrangement 11, such as a rubber damping ring or a damping strip made of paper and glue, can be detected in that the hysteresis air gap either reduces or decreases in size to outside the normal operating range. When the hysteresis air gap changes, the force of attraction produced by the current of the coil 6 of the brake also changes. Since the thrusting force produced between the frame part 3 and the armature part 4 by the helical springs 5 can in this connection be assumed to be unchangeable, as a result of a change in the hysteresis air gap the current value at which the armature part 4 starts to move towards the brake drum 27 in connection with an activation procedure of the brake therefore changes. Thus in the starting situation of the armature part 4 the determined current of the coil 6 of the brake can also be used for supervising the operating condition of the damping arrangement 11 of the brake.

The apparatus 1 also comprises an output 16 for the signal indicating the operating condition of the brake. The signal is sent to the elevator control unit 26, which is connected to the apparatus 1 in a manner that enables data transfer. Information from the elevator control unit about the servicing need of the brake can be sent to the service center 22 according to need, e.g. via a wireless link.

In Fig. 1 a two-part position switch 19 of the brake is also fitted to the drum brake 2, the first part of which switch is fastened onto the frame part 3 and the second part onto the armature part 4. The switch contact of the position switch 19 opens and closes when the armature part 4 moves in relation to the frame part 3. With the position switch 19 a movement of the armature part 4 can be detected; on the other hand, movement of the armature part 4 can also be detected e.g. from changes in the current and/or voltage of the coil of the brake, in which case the position switch 19 is not necessarily needed .

The brake control apparatus 7 presented in Fig. 2 is suited for use e.g. in connection with the embodiment of Fig. 1. The brake control apparatus 7 comprises the electricity supply circuit 17 of the brake and also brake control electronics 30. The electricity supply circuit 17 of the brake comprises a controllable solid-state switch, such as a MOSFET transistor, IGBT transistor or corresponding, for controlling the current of the coil of the brake 2 with short pulses.

The brake control electronics 30 comprises a microprocessor 20, with which the operation of the brake control apparatus 7, such as the performing of brake control sequences, is managed. With the microprocessor 20 the operating condition of the brake 2 is also determined. The software of the microprocessor is saved in the memory 13; in addition, e.g. brake-specific parameters, such as the limit values of the permitted current of the coil 6 of the brake, are saved in the memory 13. The software comprises, in addition to brake control functions 38, a movement determination part 8, with which the starting situation of the armature part 4 of the brake is identified. The software also comprises a current determination .part 9, with which the magnitude of the current of the coil 6 of the brake in the starting situation of the armature part 4 of the brake is determined. The software further comprises an operating condition determination part 10, with which the operating condition of the brake is determined using for the determination the aforementioned determined current . of the coil 6 of the brake in the starting situation of the armature part 4 of the brake.

The current determination part 9 can determine the current of the coil 6 of the brake e.g. by reading the current data of the coil 6 of the brake formed by a current measurement 9 immediately it receives information from the movement determination part 8 that the armature part 4 of the brake has started to move. On the other hand, the current determination part 9 can also save in the memory 13 at regular intervals the current data of the coil of the brake formed by the current measurement 9. In this case the movement determination part 8 can together with the current determination part 9 resolve from the values of current saved in the memory the starting situation of the armature part 4 as well as the magnitude of the current of the coil 6 of the brake that corresponds to the starting situation, e.g. by interpolation or by comparing ranges .

The microprocessor 20 communicates e.g. with the electricity supply circuit 17 of the brake as well as with the other control units connected to the brake control apparatus 7 via a communication interface 21.

Fig. 3 illustrates how the force of attraction F produced by the current I of the coil 6 of the brake changes e.g. in connection with the brake control procedures referred to in the embodiments of Fig. 1 or 2. Initially the current I is zero, in which case the force F is zero and the brake is activated. After this the current I of the coil of the brake is started to be increased, in which case also the force F starts to increase. In the brake opening situation 31 the force of attraction F produced by the current I of the coil of the brake overcomes the thrusting force 34 produced between the frame part and the armature part by the activation means, and the armature part starts to move towards the frame part . When the armature part moves the air gap of the brake decreases, in which case the force of attraction F produced by the current I of the coil of the brake increases although the current here is kept as before during the movement . In the situation 32 the brake has opened, and the force of attraction F produced by the current I of the coil of the brake has considerably increased. When the brake is activated again after this, the current I of the coil of the brake must be reduced from the current according to the situation 32 until in the activation situation 33 of the brake the force of attraction produced by the current I of the coil of the brake falls below the thrusting force 34 between the frame part and the armature part, and the armature part starts to move controlled by the difference between the thrusting force 34 and the force of attraction F. The operating condition of the damping arrangement of the brake can be determined from the values of the current I of the coil of the brake that correspond to the activation situation 33; if the hysteresis air gap in this case starts to increase, the current I of the coil of the brake corresponding to the situation 33 starts to increase; when the hysteresis air gap decreases, the current I of the coil of the brake instead decreases. On the other hand, the operating condition of the activation means, such as a helical spring, of the brake can be determined in the opening situation 31, because as the spring loosens the current I, at which the brake starts to open, decreases. The changing of the current in the situation 31 as the spring loosens also affects the value of the current of the coil of the brake in the activation situation 33. Thus the limit values of the permitted current of the coil of the brake can be re- calibrated in the activation situation 33 on the basis of the change in the current of the opening situation 31.

The graph 24 of Fig. 4 presents the current of a brake e.g. in connection with an activation procedure of a brake according to one of the preceding embodiments. Correspondingly, the graph 25 presents the current of the brake in connection with an opening procedure of the brake. The current is decreased on a ramp-like curve according to graph 24 in connection with an activation procedure of the brake, e.g. by means of a ramp- like current reference or supply voltage reference of the coil of the brake. At the time 23 the armature part of the brake starts to move towards the object to be braked. Depending on, the control principle, the instantaneous transient that results from a change in the inductance of the magnetic circuit of the brake can be read from the current and/or supply voltage of the coil of the brake immediately after the starting moment of the armature part. The transient is marked in Fig. 4 with a dashed line 38. From this transient also the starting situation of the armature part of the brake can also be deduced. A corresponding type of transient 39 can be read from the current 25 and/or the supply voltage, when the armature part starts to move at the time 37 in connection with an opening procedure of the brake, and also this transient can be used to detect the starting of the armature part.

Fig. 5 presents the limit values 14, 15, 35, 36 of the permitted current of the coil of the brake, which determine the ranges of permitted current. The first limit values 14, 15 determine the first range of permitted current. The second limit values 35, 36 determine the second range of permitted current, which is situated outside the first range of permitted current. The current of the coil of the brake at the time of starting of the armature part is compared to the these ranges of permitted current, and if the value of the current of the coil of the brake in this case differs from the first range of permitted current but is still positioned within the second range of permitted current, it is concluded that the damping arrangement of brake has progressively worn or failed so that it needs servicing. If the value of the current of the coil of the brake in this case differs also from the second range of permitted current, it is deduced that wear/failure of the damping arrangement has progressed so far that the next opening procedure of the brake is prevented.

The apparatus 1 according to the invention can also be applied as a tool of a serviceman, which tool can be connected in contact with the brake in connection with a service and/or condition inspection.

The thrusting force between the ferromagnetic pieces in the magnetic circuit of the brake can be produced with many different activation means. In addition to a helical spring, the force effect can be achieved e.g. with a spring set, with a gas spring, or with a hydraulic means. In this case the number of components that produce the force effect can also differ.

The invention can be applied also to e.g. disc brakes, in addition to drum brakes.

It is obvious to the person skilled in the art that different embodiments of the invention are not limited to the examples described above, but that they may be varied within the scope of the claims presented below.