ELECTRONIC SAFETY ACTUATOR AND METHOD OF CONDITION OR STATE DETECTION

Abstract

An electronic safety actuator (1) for an elevator safety brake, includes a first solenoid (2), a magnet (3), movable by the first solenoid (2) between a first position proximate to the first solenoid (2) and a second position distal from the first solenoid (2) a second solenoid (6) and a detector (8). The detector (8) is arranged to apply an electrical signal to one of the first solenoid (2) and the second solenoid (6), and to detect an electrical signal induced in the other of the first solenoid (2) and the second solenoid (6) as a result of the applied electrical signal. There is also provided a method of detecting a condition or state of the first solenoid (2) or the magnet (3).

Claims

1. An electronic safety actuator (1) for an elevator safety brake, comprising: a first solenoid (2); a magnet (3), movable by the first solenoid (2) between a first position proximate to the first solenoid (2) and a second position distal from the first solenoid (2); a second solenoid (6); and a detector (8) arranged to apply an electrical signal to one of the first solenoid (2) and the second solenoid (6), and to detect an electrical signal induced in the other of the first solenoid (2) and the second solenoid (6) as a result of the applied electrical signal.

2. The electronic safety actuator (1) of claim 1, wherein the detector (8) is further arranged to determine a condition or state of the first solenoid (2) or the magnet (3) by comparing the detected electrical signal to at least one reference value.

3. The electronic safety actuator (1) of claim 1, wherein the induced electrical signal is insufficient to move the magnet between the first position and the second position.

4. The electronic safety actuator (1) of claim 1, wherein the detector is arranged to detect a voltage across the first solenoid or the second solenoid.

5. The electronic safety actuator (1) of claim 4, wherein the detector is arranged to apply the electrical signal to the second solenoid (6) and measure the voltage induced in the first solenoid (2).

6. The electronic safety actuator (1) of claim 1, wherein a number of turns of the second solenoid (6) is less than half of a number of turns of the first solenoid (2).

7. The electronic safety actuator (1) of claim 1, wherein a number of turns of the second solenoid (6) is less than 20 turns.

8. The electronic safety actuator (1) of claim 1, wherein the detector is arranged to detect a current in the first solenoid or the second solenoid.

9. The electronic safety actuator (1) of claim 8, wherein the detector (8) is arranged to apply the electrical signal to the first solenoid (2) and measure the current induced in the second solenoid (6).

10. The electronic safety actuator (1) of claim 1, wherein the first solenoid (2) and the second solenoid (6) are coaxial.

11. A method of detecting a condition or state of a first solenoid (2) or a magnet (3) of an electronic safety actuator (1) for an elevator safety brake, the magnet (3) being movable by the first solenoid (2) between a first position proximate to the first solenoid (2) and a second position distal from the first solenoid (2), comprising: applying an electrical signal to the first solenoid (2) or a second solenoid (6); detecting an electrical signal induced in the other of the first solenoid (2) and the second solenoid (6) as a result of the applied electrical signal; and determining the condition or state based on the detected electrical signal.

12. The method of claim 11, comprising determining a position of the magnet (3).

13. The method of claim 11, comprising detecting whether the magnet is in an intermediate position, between the first position and the second position.

14. The method of claim 11, comprising determining that the magnet (3) is in the first position when the detected electrical signal is different to a first reference value; optionally wherein the first reference value is at least 80% of an electrical signal expected from an undamaged coil.

15. The method of claim 11, wherein determining the condition or state based on the detected electrical signal comprises detecting wear in the first solenoid (2).

Description

DRAWING DESCRIPTION

[0028] Certain preferred examples of this disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0029] FIG. 1 schematically shows a safety actuator with its magnet in a first “reset” position, proximate to the first solenoid;

[0030] FIG. 2 schematically shows a safety actuator with its magnet in a second “trigger” position, distal from the first solenoid;

[0031] FIG. 3 is a perspective view showing a first solenoid and a second solenoid according to an example of the present disclosure, connected to a safety actuator board;

[0032] FIG. 4 shows two graphs representing respectively an example of an electrical signal applied to the second solenoid and the corresponding voltage detected in the first solenoid according to an example of the present disclosure; and

[0033] FIG. 5 is a flow chart representing a method according to an aspect of the present disclosure.

DETAILED DESCRIPTION

[0034] FIG. 1 shows an electronic safety actuator 1 for an elevator car. The safety actuator 1 has a first solenoid 2 wound around a first core 7 e.g. a steel core, to form an electromagnet to which a magnet 3 e.g. a permanent magnet is selectively attached. The magnet 3 is contained by a second core 9 or block e.g. a second steel core. In this figure, the magnet 3 is in a first position, proximate to the first solenoid 2 i.e. the air gap 5a between the first core 7 and the second core 9 is small or non-existent.

[0035] In this example the magnet 3 is magnetically attached to the first core 7 by virtue of its own magnetic field. The first solenoid 2 is not supplied with any electrical current during normal use. Alternatively, the first solenoid 2 could be powered during normal use and the safety activated when the power supply to the first solenoid 2 is removed, as described above. In the configuration of FIG. 1 the magnet 3 is distanced from the guiderail 4 and is not in contact therewith. A mechanical lever (not shown) attached to the magnet 3 connects to an elevator safety brake (not shown) and when driven parallel to the guide rail 4 causes the safety brake to engage with the guide rail 4 (e.g. via a wedge or roller brake mechanism) so as to bring the elevator car to a stop. In some examples the magnet 3 could be the actual safety brake.

[0036] The electronic safety actuator 1 of FIG. 1 also includes a second solenoid 6, and a detector 8, which creates a magnetic circuit 10a, as described below.

[0037] FIG. 2 shows the same equipment as in FIG. 1, but with the magnet 3 in a second position, distal from the first solenoid 2, such that the first core 7 and the second core 9 are separated by a relatively large air gap 5b. In this position the magnet 3 is magnetically attached to the guide rail 4. In this position, friction between the guide rail 4 and the magnet 3 causes the lever (not shown) to be driven parallel to the guide rail 4 so as to engage the safety brake and stop the elevator car. The electronic safety actuator 1 of FIG. 2 also includes a second solenoid 6, and a detector 8, which creates a magnetic circuit 10b, as described below.

[0038] The magnet 3 is moved from the first position of FIG. 1, also referred to as the “reset” position, into the second position (the “trigger” position) of FIG. 2 by a current being applied to the first solenoid 2 so as to create a magnetic field strong enough to repel the magnet 3 away from the solenoid 2 and into magnetic engagement with the guide rail 4. In other examples the current may be removed from the solenoid to remove or reduce an attractive force holding the magnet 3 in place. The magnet 3 may move into an intermediate position (not shown) between the first position and the second position, in the event that its movement between the first and second positions is obstructed in some way, for example by the presence of a foreign object in the path of movement.

[0039] In use, an elevator car would typically have two safety brakes and two electronic actuators, each electronic actuator being as shown in FIGS. 1 and 2. In other examples there may be only one safety brake, or more than two safety brakes (and corresponding numbers of electronic actuators). A control unit (not shown) is capable of actuating both safety brakes. When an event (e.g. an overspeed event or overacceleration event) occurs that requires engagement of the safety brakes, a control unit operates switches of a safety actuation board 38 (seen in FIG. 3) that cause the first solenoid 2 to trip, or trigger, the magnet 3 into the rail-engaged (“trigger”) position of FIG. 2, thereby lifting the lever (not shown) that connects to the wedges or rollers of the corresponding safety brake.

[0040] The electronic safety actuator 1 according to the present disclosure also includes a second solenoid 6, also referred to as a control coil or a monitoring coil, as seen in FIGS. 1, 2 and 3. In the example of the Figures, this second solenoid 6 has a small number of turns, for example one single turn or a few turns. The first solenoid 2 and second solenoid 6 are shown in FIG. 3. As is seen in FIG. 3, the second solenoid 6 just has a few turns, far fewer than the first solenoid 2, and is arranged coaxially with the first solenoid 2 and wound around the same spool (and around the same first core 7).

[0041] As seen in FIG. 3, the first solenoid 2 has a first end 30 and a second end 32, which form connectors for each end of the first solenoid 2 through which a current can be driven. The second solenoid 6 also has a first end 34 and a second end 36, which form connectors for each end of the second solenoid 6 through which a current can be driven. Each of the ends are connected separately to the safety actuator board (SAB) 38.

[0042] According to the present disclosure, there is also provided a detector 8, seen in FIGS. 1, 2 and 3. An electric signal (for example as seen in FIG. 4) is introduced into either the first solenoid 2 or the second solenoid 6, through their respective connectors 30, 32, or 34, 36 by the detector 8. This creates a magnetic circuit 10a, 10b in the electronic safety actuator 1, as seen respectively in FIGS. 1 and 2, which in turn induces a current in the other of the two coils 2, 6, which can then be detected e.g. as a current or voltage.

[0043] The magnetic circuit 10a, 10b is a closed loop path containing a magnetic flux. The flux is generated by either the first solenoid 2 or second solenoid 6 (whichever the electrical signal is applied to). The flux is confined to the path by the cores 7 and 9 and the magnet 3.

[0044] In the case of FIG. 1, there is a minimal air gap 5a between the cores 7, 9, such that the closed loop path of the magnetic flux 10a effectively does not contain an air gap. As a result the magnetic circuit 10a has a low reluctance and the induced current approximates the behaviour of a transformer, in which the ratio of the voltages in the two coils is proportional to the number of coils in each solenoid, as represented by the below relationship.

[00001]$\frac{V_1}{V_2}=\frac{N_1}{N_2}$

[0045] This known relationship can be used to determine a reference value e.g. to predict theoretically an expected value for a voltage induced in the first or second solenoid 2, 6, based on an electrical signal applied to the other solenoid, when the magnet 3 is in the first position, shown in FIG. 1. Alternatively, or additionally, test measurements can be made to determine the reference value. The reference value may also be obtained from the applied signal, either directly or via an amplifier or voltage or current divider so as to scale it appropriately for comparison.

[0046] The detector 8 detects an induced electrical signal on one of the solenoids 2, 6, based on the electrical signal applied to the other solenoid 2, 6. This detected induced signal can then be compared to the reference value to determine a state or condition of parts of the elevator safety actuator as described below.

[0047] In FIG. 2, the magnet 3 is in the second position, i.e. the trigger position. In this position there is a large air gap 5b between the cores 7, 9. As a result the closed loop path of the magnetic flux includes the air gap 5b. This significantly increases the reluctance of the magnetic circuit 10b and accordingly reduces the electrical signal induced in one solenoid 2, 6 by an electrical signal applied to the other. In this case the detected induced signal can also be compared to the reference value. The significant drop in signal compared to the reference value (or expected value), can be used to determine that the magnet 3 is in the second, trigger position of FIG. 2, as described further below. Similarly where the magnet is in an intermediate position a substantial air gap (smaller than the air gap present when the magnet 3 is in the second position) will be included in the closed loop of the magnetic circuit. This will alter the relationship governing an induced electrical signal in one of the coils, resulting in a change in the detected induced signal compared to the value when the magnet is in the first position. In some examples reference values may be acquired with the magnet at a series of intermediate positions (and optionally also in the first position and/or the second position).

[0048] FIG. 4 shows an example electrical signal 40, in the upper graph, applied by the detector 8 to the second solenoid 6. Since the ratio of number of turns in the first solenoid 2 to the number of turns in the second solenoid 6 is high, the signal e.g. voltage induced in the first solenoid 2 as a result of the electrical signal applied to the second solenoid 6 will be high, as represented in the lower graph, which shows the induced electrical signal 42. This allows a small voltage to be applied to the second solenoid 6 whilst still inducing a voltage in the first solenoid 2 which is sufficiently large to be measured reliably and with high sensitivity. For example, if the first solenoid 2 has 800 turns and the second solenoid 6 (the monitoring coil) has 10 turns, then the turns ratio is 80:1 and a voltage of 10 mV applied to the second solenoid 6 will induce a voltage of approximately 0.8 V in the first solenoid 2.

[0049] This relationship is inverse for current i.e. a small current applied to the first solenoid 2 induces a larger current in the second solenoid 6, so that in examples where the electrical signal to be measured is current, and it is measured in the second solenoid 6, only a small current need be applied to the first solenoid 2. This improves the life of the first and second solenoids 2, 6 since they endure lower voltages and currents.

[0050] It will be appreciated that in other examples it is also viable to use a large voltage applied to the first solenoid 2 to produce a small voltage to be detected in the second solenoid 6, or to apply a large current to the second solenoid 6 in order to produce a small current to be detected in the first solenoid 2. Although these arrangements are less desirable from a sensitivity perspective, there may be other operational reasons for using such arrangements.

[0051] The relationship laid out above allows an expected value for an induced electrical signal (current or voltage) to be calculated e.g. for the position of the magnet 3 shown in FIG. 1.

[0052] The induced electrical signal may differ from the expected value. For example, as described above, when the magnet 3 is in the second, trigger position of FIG. 2, the closed loop 10b of the magnetic flux includes the air gap 5b. This causes the induced electrical signal to be much lower than the expected reference value based on the ideal ratio relationship described above. When the magnet 3 is in the second position, as shown in FIG. 2, the value of an induced electrical signal e.g. current or voltage, may, for example, be 80% or more lower than the expected value. Where the induced value is so much lower than the expected or predicted value this allows the determination that the magnet 3 must be in the second position. Such a large loss of signal cannot reasonably be attributed to wear in the first solenoid 2 (which would typically be expected to result in a loss of only a few percent of signal) and therefore such determination can be separately made alongside the wear monitoring using the same detector.

[0053] Similarly, where the magnet 3 is in an intermediate position, the closed loop will still include an air gap (albeit smaller than the air gap 5b). The amount by which the induced electrical signal is lower than the expected reference value will depend on the size of this air gap (i.e. on the distance of the magnet 3 from the first solenoid 2), such that the induced electrical signal can be used to determine whether the magnet is in an intermediate position. The dependency may be a simple linear dependency or may be more complex. It may be determined by measuring a series of test values at different intermediate positions.

[0054] As noted, the induced electrical signal may also be lower than the expected induced electrical signal as a result of wear occurring in the first solenoid 2. For example, if the first solenoid 2 is heated above a certain temperature, a coating on the conductor that forms the coil e.g. a resin coating on copper wire, will begin to soften or melt. This may cause contact between adjacent coils of the first solenoid 2, effectively reducing the number of turns in the solenoid 2. This will lead to the induced electrical signal being lower than expected based on the ratio relationship, but not by such a large amount as where the magnet 3 is in the second position. For example, the induced electrical signal may be within 40%, 20% or even 10% of the expected value. In many cases, the loss of only a small number of turns will result in less than 5% deviation from the expected signal.

[0055] Thus, comparison of the induced electrical signal, detected by the detector 8, to a predicted or expected value can be used to determine the position of the magnet 3 and also to detect wear in the first solenoid 2.

[0056] As noted above, in alternative arrangements, depending on the turns ratio and the choice of first/second solenoid as detector and the choice of voltage/current as measurement characteristic, the signals may be greater than the expected or predicted value instead of lower than it.

[0057] Thus, there is also disclosed a method of detecting a condition or state of a first solenoid 2 or a magnet 3 of an electronic safety actuator 1 for an elevator safety brake, as shown in the flow diagram of FIG. 5.

[0058] In a first step 50, the detector 8 is used to apply an electrical signal 40 to the first solenoid 2 or a second solenoid 6. Next, in step 52 the detector 8 detects the electrical signal 42 which is induced in the other of the first solenoid 2 and the second solenoid 6 as a result of the electrical signal applied in step 50. Then, in step 54, the detected electrical signal is compared to a reference value.

[0059] The reference value may be calculated or predicted using the known relationship described above, or it may be determined or measured in tests, for example by measuring the induced voltage in a test run immediately after installation, where the position of the magnet 3 is known.

[0060] Where the value of the induced electrical signal is close to or even equal to the reference value it is determined, in step 56, that the magnet 3 is in the first position, as shown in FIG. 1. This may be the case, for example, when the detected electrical signal is within 20% of the reference value (or more generally within a given range of the reference value). In this case a wear value may then be calculated e.g. by subtracting the detected induced signal from the reference value, in a step 58. This wear value may represent a severity of wear within the first solenoid 2.

[0061] Alternatively, it may be determined, in step 60, that the induced electrical signal is far from the reference value e.g. when the detected electrical system is 50% or 80% or more lower than the reference value. In this case a difference this large must be a result of an air gap e.g. the air gap 5b shown in FIG. 2, and therefore a determination will be made that the magnet 3 is in an intermediate position, or in the second position i.e. that the magnet 3 is not in the first position.

[0062] Then, at step 62 the comparison between the induced electrical signal and the reference value may be used to determine a particular position of the permanent magnet 3, for example that the magnet 3 is in the second position, or in an intermediate position between the first position and the second position. If the magnet 3 is determined to be in an intermediate position, step 62 may also comprise determining an approximate distance of the magnet 3 from the first position i.e. which particular intermediate position the magnet 3 is at. This may, for example, be done by comparing the detected electrical signal to measured or predicted values for a series of intermediate positions, and determining the magnet 3 to be at the intermediate position giving a value closest to the detected electrical signal.