ADJUSTABLE FORCE SAFETY BRAKES

Abstract

An adjustable force safety brake for use in an elevator system. The adjustable force safety brake includes a safety block, first and second braking elements housed in the safety block and an electromagnet. The safety block includes a channel arranged to receive a guide rail of an elevator system in use. The first braking element is configured to move from an initial position into a position of engagement with the guide rail received in the channel to create a braking force, and the second braking element is configured to create an additional braking force on the guide rail when the first braking element is in the position of engagement. The electromagnet is operable to selectively produce a magnetic force which acts on the second braking element in a sideways direction away from the channel so as to reduce the additional braking force on the guide rail.

Claims

1. An adjustable force safety brake (100) for use in an elevator system, the safety brake comprising: a safety block (180), first and second braking elements (160, 150) housed in the safety block (180), and an electromagnet (170); wherein the safety block (180) includes a channel (182) arranged to receive a guide rail (20;120;320) of an elevator system in use; wherein the first braking element (160) is arranged at a first side (184) of the channel (182) and the second braking element (150) is arranged at a second side (186) of the channel (182), opposite to the first side (184) in a sideways direction; wherein the first braking element (160) is configured to move from an initial position into a position of engagement with the guide rail (20;120;320) received in the channel (182) to create a braking force; wherein the second braking element (150) is configured to create an additional braking force on the guide rail (20;120;320) when the first braking element (160) is in the position of engagement; and wherein the electromagnet (170) is operable to selectively produce a magnetic force which acts on the second braking element (150) in the sideways direction away from the channel (182) so as to reduce the additional braking force on the guide rail (20;120;320).

2. The adjustable force safety brake (100) of claim 1, wherein the second braking element (150) comprises a ferromagnetic material.

3. The adjustable force safety brake (100) of claim 1, wherein the second braking element (150) is configured to exert a resilient bias force in the sideways direction towards the channel (182).

4. The adjustable force safety brake (100) of claim 3, wherein the electromagnet (170) is operable to produce a maximum magnetic force which is less than the resilient bias force such that the second braking element (150) tends to remain in physical contact with the guide rail (20;120;320) when the first braking element (160) is in the position of engagement.

5. The adjustable force safety brake (100) of claim 1, wherein the electromagnet (170) is operable to produce a variable magnetic force in a range from zero to a maximum magnetic force.

6. The adjustable force safety brake (100) of claim 1, wherein the electromagnet (170) is positioned in the safety block (180) behind the second braking element (150) in the sideways direction from the channel (182).

7. The adjustable force safety brake (100) of claim 1, wherein the electromagnet (170) is positioned at a distance (D1) behind the second braking element (150) when the first braking element (160) is in the position of engagement.

8. The adjustable force safety brake (100) of claim 1, wherein the second braking element (150) comprises a frictional surface (152) or shoe arranged to face the second side (186) of the channel (182) to provide frictional engagement with the guide rail (20;120;320).

9. An elevator system (10;300) comprising: a component (16;316) moving along a pair of guide rails (20;120;320); a pair of safety brakes (24) mounted to the component (16;316) to each apply a braking force to a respective one of the pair of guide rails (20;120;320) when activated, wherein at least one of the pair of safety brakes (24) is the adjustable force safety brake (100) of claim 1; a safety controller (400) operatively connected to the adjustable force safety brake (100); and at least one sensor (390) operatively connected to the safety controller (400), wherein the at least one sensor (390) is configured to detect the braking forces being applied by the pair of safety brakes (24), and wherein the safety controller (400) is configured, in response to detection of the braking forces, to selectively operate the electromagnet (170) of the adjustable force safety brake (100).

10. The elevator system of claim 9, wherein the safety controller (400) is configured to vary the magnetic force produced by the electromagnet (170), in a range from zero to a maximum magnetic force, dependent upon the level of the braking forces detected.

11. The elevator system of claim 9, wherein the adjustable force safety brakes (100) are mounted to the component (16;316) on opposite sides to receive a respective one of the pair of guide rails (20;120;320) in the channel (182) of each adjustable force safety brake (100).

12. The elevator system of claim 11, wherein the safety controller (400) is configured to independently vary the magnetic force produced by the electromagnet (170) of each of the pair of adjustable force safety brakes (100), in a range from zero to a maximum magnetic force, dependent upon the level of braking force respectively detected at opposite sides of the component (16;316).

13. The elevator system of claim 9, wherein the at least one sensor (390) comprises a pair of accelerometers mounted on opposite sides of the component (16;316) to detect excessive and/or uneven braking forces being applied between the pair of guide rails (20;120;320).

14. A method for adjusting braking forces in an elevator system (10, 300), the method comprising: detecting, using at least one sensor (390), the braking forces being applied by a pair of safety brakes (24;100) mounted to a component (16;316) moving along a pair of guide rails (20;120;320) in an elevator system (10, 300), wherein at least one of the pair of safety brakes (24;100) is an adjustable force safety brake (100); and selectively operating an electromagnet (170) in the adjustable force safety brake (100) to change its additional braking force on the guide rail (20;120;320).

15. The method of claim 14, further comprising: analysing the level of braking forces being applied by the pair of safety brakes (24;100); and varying the magnetic force produced by the electromagnet (170), in a range from zero to a maximum magnetic force, dependent upon the level of braking forces.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Certain examples of this disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0041] FIG. 1 shows a schematic diagram of an elevator system employing a mechanical governor;

[0042] FIG. 2 shows a 3D perspective view of a prior art safety brake without a guide rail;

[0043] FIG. 3 shows a cross sectional view of the prior art safety brake in use with a guide rail;

[0044] FIG. 4 shows a 3D perspective view of an adjustable force safety brake according to an example of the present disclosure;

[0045] FIG. 5 shows a cross sectional view of the adjustable force safety brake in use with a guide rail;

[0046] FIG. 6A shows a cross sectional view of the adjustable force safety brake before a braking operation;

[0047] FIG. 6B shows a cross sectional view of the adjustable force safety brake at the beginning of a braking operation;

[0048] FIG. 6C shows a cross sectional view of the adjustable force safety brake during a braking operation;

[0049] FIG. 7 shows a schematic diagram of an elevator car employing a pair of adjustable force safety brakes according to an example of the present disclosure; and

[0050] FIG. 8 shows a flow chart representing a method of controlling the adjustable force safety brake according to an example of the present disclosure.

DETAILED DESCRIPTION

[0051] FIG. 1 shows an elevator system, generally indicated at 10. The elevator system 10 includes cables or belts 12, a car frame 14, an elevator car 16, roller guides 18, guide rails 20, a governor 22, and a pair of safety brakes 24 mounted on the elevator car 16. The governor 22 is mechanically coupled to actuate the safety brakes 24 by linkages 26, levers 28, and lift rods 30. The governor 22 includes a governor sheave 32, rope loop 34, and a tensioning sheave 36. The cables 12 are connected to the car frame 14 and a counterweight (not shown in FIG. 1) inside a hoistway. The elevator car 16, which is attached to the car frame 14, moves up and down the hoistway by a force transmitted through the cables or belts 12 to the car frame 14 by an elevator drive (not shown) commonly located in a machine room at the top of the hoistway. The roller guides 18 are attached to the car frame 14 to guide the elevator car 16 up and down the hoistway along the guide rails 20. The governor sheave 32 is mounted at an upper end of the hoistway. The rope loop 34 is wrapped partially around the governor sheave 32 and partially around the tensioning sheave 36 (located in this example at a bottom end of the hoistway). The rope loop 34 is also connected to the elevator car 16 at the lever 28, ensuring that the angular velocity of the governor sheave 32 is directly related to the speed of the elevator car 16.

[0052] In the elevator system 10 shown in FIG. 1, the governor 22, a machine brake (not shown) located in the machine room, and the safety brakes 24 act to stop the elevator car 16 if it exceeds a set speed as it travels inside the hoistway. If the elevator car 16 reaches an over-speed condition, the governor 22 is triggered initially to engage a switch, which in turn cuts power to the elevator drive and drops the machine brake to arrest movement of the drive sheave (not shown) and thereby arrest movement of elevator car 16. If, however, the elevator car 16 continues to experience an overspeed condition, the governor 22 may then act to trigger the safety brakes 24 to arrest movement of the elevator car 16 (i.e. an emergency stop). In addition to engaging a switch to drop the machine brake, the governor 22 also releases a clutching device that grips the governor rope 34. The governor rope 34 is connected to the safety brakes 24 through mechanical linkages 26, levers 28, and lift rods 30. As the elevator car 16 continues its descent, the governor rope 34, which is now prevented from moving by the actuated governor 22, pulls on the operating levers 28. The operating levers 28 actuate the safety brakes 24 by moving the linkages 26 connected to the lift rods 30, and the lift rods 30 cause the safety brakes 24 to engage the guide rails 20 to bring the elevator car 16 to a stop.

[0053] FIG. 2 shows a prior art safety brake 24′ as is known from ES1057303, the contents of which are hereby incorporated by reference. The safety brake 24′ includes a safety block 80, a first braking element 60, and a second braking element 50 with a frictional surface 52. The braking elements 50, 60 are housed in the safety block 80 on either side of a channel 82 arranged to receive a guide rail of an elevator system in use. The first braking element 60 is arranged at a first side 84 of the channel 82 and the second braking element 50 is arranged at a second side 86 of the channel 82, opposite the first side 84 in a sideways direction.

[0054] FIG. 3 shows the safety brake 24′ with the guide rail 20 received in the channel 82, i.e. during use of the safety brake 24′.

[0055] The first braking element 60 is a locking element which moves up or down into an engagement position to wedge against the guide rail 20 and produce a braking force on guide rail 20 e.g. when the car is moving too rapidly.

[0056] The first braking element 60 is a roller which sits in the safety block 80 on the first side 84 of the channel 82. It can be seen from FIGS. 2 and 3 that the roller 60 has a smaller outer diameter so that it easily moves along a ramp surface 81 of the safety block 80, and a larger inner diameter with a knurled surface for engaging with the guide rail 20. The larger diameter of the roller 60 fits into a groove 83 (seen in FIG. 2) so as not to frictionally engage with the safety block 80 when the roller 60 is moving to its engagement position. The safety block 80 has a ramp surface 81 including two oppositely inclining ramps which act to guide the roller 60 in both directions depending on the direction of braking.

[0057] The second braking element 50 is arranged at the second side 86 of the channel 82 in the safety block 80 to provide a frictional surface 52 on the opposing side of the guide rail 20 to that of the first braking element 60. The second braking element 50 includes two elastic elements 55 and a frictional surface 52 designed to act directly on the guide rail 20. The second braking element 50 is configured to exert a resilient bias force in the sideways direction onto the guide rail 20 by means of the elastic elements 55. It is designed to have a large area for the frictional surface 52, which engages with the guide rail 20 when the roller 60 moves to a position of engagement. The physical configuration of the two elastic elements 55 and the way in which they are housed in the safety block 80 allows for flexion and hence sideways movement of the second braking element 50.

[0058] FIGS. 2 and 3 show the safety brake 24′ before a braking operation. When the first braking element 60 is activated, for example by the governor rope 34 and mechanical linkages 26, levers 28, and lift rods 30 described in relation to FIG. 1, the roller 60 slides along the ramp surface 81 until it comes into contact with the guide rail 20, and then continues along the ramp surface 81 to become locked in full engagement, when the guide rail 20 is in full frictional contact with both the roller 60 and the frictional surface 52 of the second braking element 50. The braking force applied by the roller 60 is then partially absorbed by the second braking element 50 and spread through the safety block 80. When the roller 60 is fully engaged with the guide rail 20, the resilient bias force exerted by the second braking element 50 creates an additional braking force on the opposite side of the guide rail 20. It will be appreciated that no external activation is required for the second braking element 50 to exert its resilient bias force on the guide rail 20.

[0059] FIG. 4 shows an example according to the present disclosure of an adjustable force safety brake 100 comprising a safety block 180, a first braking element 160, a second braking element 150, and an electromagnet 170. The braking elements 150, 160 are housed in the safety block 180 on either side of a channel 182 arranged to receive a guide rail of an elevator system in use. The first braking element 160 is arranged at a first side 184 of the channel 182, and the second braking element 150 is arranged at a second side 186 of the channel 182, opposite to the first side 184 in a sideways direction.

[0060] FIG. 5 shows the adjustable force safety brake 100 with a guide rail 120 received in the channel 182 during use.

[0061] With reference to both FIGS. 4 and 5, the adjustable force safety brake 100 is now described in more detail. The first braking element 160 is a locking element which is designed to move into a position to wedge against the guide rail 120 and produce a braking force against the guide rail 120. The first braking element 160 in this example is a roller 160. Whilst a roller 160 is shown in this example, a person skilled in the art will appreciate that any other suitable locking element such as a wedge may be used instead.

[0062] The first braking element 160 is a roller which sits in the safety block 180 on the first side 184 of the channel 182. The roller 160 has a smaller outer diameter so that it easily moves along a ramp surface 181 of the safety block 180. The roller 160 has a larger inner diameter with a knurled surface for engaging with the guide rail 120 that fits into a groove 183 (seen in FIG. 4) so as to move freely within the safety block 180. In this example, the safety block 180 has a ramp surface 181 including two oppositely inclining ramps which act to guide the roller 160 in both directions depending on the direction of braking.

[0063] The second braking element 150 is arranged at the second side 186 of the channel 182 in the safety block 180 to provide a frictional surface 152 on the opposite side of the guide rail 120 to that of the first braking element 160. The second braking element 150 is configured to exert a resilient bias force in the sideways direction towards the channel 182, with a frictional surface 152 designed to act directly on the guide rail 120 in this example. In another example the second braking element 150 may have a separate brake shoe which acts as the frictional surface 152. The frictional surface 152 may be made of a material chosen to provide a suitable level of frictional engagement with the guide rail 120 and/or the frictional surface 152 may be suitably treated or contoured (as shown schematically) to aid frictional engagement with the guide rail 120. In this example the second braking element 150 comprises two elastic elements 155 which are housed in the safety block 180 allowing for flexion and hence sideways movement of the second braking element 150. The second braking element 150 is therefore designed to have a natural resilience to press the frictional surface 152 against the guide rail 120 when the roller 160 moves into a position of engagement, as is described below with reference to FIGS. 6A-6C.

[0064] When the adjustable force safety brake 100 is operated, the roller 160 moves along the ramp surface 181 to engage with the guide rail 120 and push the guide rail 120 into engagement with the frictional surface 152 of the second braking element 150.

[0065] The electromagnet 170 is positioned relative to the second braking element 150 such that, when the electromagnet 170 is operated, there is a magnetic force acting on the second braking element 150 to pull the second braking element 150 away from the channel 182 in the sideways direction. When the adjustable force safety brake 100 is installed in an elevator system so that a guide rail 120 is received in the channel 182, the electromagnet 170 is operable to pull the second braking element 150 away from the guide rail 120 and reduce the resilient bias force being applied on the guide rail 120, and therefore reducing the additional braking force provided by the second braking element 150. In this example the electromagnet 170 is placed behind the second braking element 150 in the sideways direction from the channel 182, and when operated pulls the second braking element 150 towards the electromagnet 170 and away from the guide rail 120. It will be appreciated by a person skilled in the art that another position for the electromagnet 170 could achieve the same result, within the design constraints of an elevator safety brake.

[0066] For the electromagnet 170 to produce a magnetic force which acts on the second braking element 150, it will be understood that the second braking element 150 should be susceptible to the magnetic field of the electromagnet 170. In some examples the second braking element 150 at least partially comprises a magnetic or ferromagnetic material. In this example the second braking element 150 is made of steel.

[0067] Advantageously, because the electromagnet 170 is located behind the second braking element 150 in the housing 180, the electromagnet 170 can act as a rebound stopper and prevent the second braking element 150 from moving sideways away from engagement with the guide rail 120 when braking first occurs. This will allow for a smooth and sustained initial braking, increasing the safety of the component being braked. For example, if the adjustable force safety brake 100 is located on an elevator car the safety of the passengers is improved.

[0068] In this example the second braking element 150 has a large surface area for the frictional surface 152, which engages with the guide rail 120. The second braking element 150 is shaped to include a large solid block in the centre behind the frictional surface 152, with the two thinner elastic elements 155 either side designed to flex sideways. This allows for a negligible deformation in the frictional surface 152 when pulled away from the guide rail 120 by the electromagnet 170, keeping parallelism and maintaining a small gap between the second braking element 150 and the electromagnet 170 behind.

[0069] The adjustable force safety brake 100 is shown in the process of a braking operation in FIGS. 6A, 6B and 6C, where the braking operation acts to prevent further downward movement of an elevator component.

[0070] FIG. 6A shows the adjustable force safety brake 100 in an initial position before a braking operation has commenced, and as positioned during the normal operation of the elevator. When the safety mechanism (not shown) is actuated to prevent further movement of the elevator component downwards in the hoistway, the roller 160 moves upwards from its initial position, along the surface of the ramp 181 where the roller 160 begins to engage with the guide rail 120 as shown in FIG. 6B. The normal force created by the contact of the roller 160 on the guide rail 120 (shown by the sideways force arrow) creates an upwards force (as shown by the arrow) and the roller 160 ascends freely along the ramp surface 181. The process is the same as for the prior art safety brake 24′ of FIGS. 2-3 where, if the car with the safety brake 24′ attached moves downwards, the relative movement of the guide rail 120 is in an upwards direction. Due to the knurled surface of the roller 160, the friction between the guide rail 120 and the larger diameter of the roller 160 is higher than the friction between the smaller diameter of the roller 160 and the safety block 180, and so the roller 160 spins and moves upwards. The roller 160 continues to move upwards into a position of engagement with the guide rail 120 as shown in FIG. 6C. The movement of the roller 160 and the guide rail 120 moves the safety block 180 into a position where the second braking element 150 and the roller 160 are applying opposing normal forces (as shown by the sideways force arrows pointing into the guide rail 120) onto each side of the guide rail 120, creating a braking force on both sides of the guide rail 120 (as shown by the upwards arrows in FIG. 6C).

[0071] Whilst in this example braking is shown to prevent downwards motion, it will be appreciated by a person skilled in the art that the principle of operation is similar for braking to prevent upwards motion, with the roller 160 instead moving downwards into a position of engagement with the guide rail 120.

[0072] As shown in FIG. 6C, when the adjustable safety brake 100 is in operation, sideways forces are applied normal to the guide rail 120 by the first and second braking elements 160, 150, producing an overall braking force in opposition to the movement of the safety block 180. By operating the electromagnet 170, the additional braking force applied to the guide rail 120 by the second braking element 150 can be reduced.

[0073] When the electromagnet 170 is operated, even when the magnetic force is at a maximum, some contact remains between the second braking element 150 and the guide rail 120. The maximum magnetic force of the electromagnet 170 is less than the resilient bias force of the second braking element 150. The second braking element 150 remains in physical contact with the guide rail 120 when the roller 160 is in the position of engagement. This can further prevent any bouncing of the second braking element 150 against the guide rail 120 and prevent the guide rail 120 moving away from contact with the roller 160 which could case interrupted braking forces and cause the elevator component to drop suddenly.

[0074] In this example, the electromagnet 170 is positioned in the safety block 180 behind the second braking element 150 so that when the roller 160 is in the position of engagement there is a non-zero distance D1 between the electromagnet 170 and the second braking element 150. This allows the second braking element 150 to move or flex as the guide rail 120 comes into engagement and to take into account tolerances of the whole system e.g. guide rail thickness, variations in the braking elements 150, 160, wear during use etc. and, to allow for rebound protection. In this example, the distance D1 is about 0.5 mm.

[0075] In this example, when the electromagnet 170 is not operated the maximum braking force is applied to the guide rail 120. This acts as a fail-safe option so if power to the adjustable force safety brake 100 is lost the biasing of the second braking element 150 will ensure that the maximum braking force is exerted on the guide rail 120.

[0076] In an example the electromagnet 170 is operable to produce a variable magnetic force, to provide a fully variable braking force on the guide rail 120, which can adjust to different levels of excessive and/or uneven braking.

[0077] FIG. 7 shows an example of an elevator system 300 where two adjustable force safety brakes 100 are attached to an elevator car 316. Also shown in FIG. 7 are a plurality of guide rails 320, at least one sensor 390, a travelling cable 395, and a safety controller 400 located at a fixed position e.g. in the hoistway or in a machine room.

[0078] In this example, a pair of sensors 390 is shown mounted to the bottom of the elevator car 316. The sensors 390 are configured to detect excessive and/or uneven braking forces being applied by the pair of adjustable force safety brakes 100 on the elevator component, for example the elevator car 316. It will be appreciated by a person skilled in the art that various different types of sensors could be used, and various numbers of sensors could be used to detect excessive and/or uneven braking, for example a pair of accelerometers 390 located beneath the elevator car 316 to detect the movement of each side of the elevator car 316 as shown here.

[0079] In this example a pair of adjustable force safety brakes 100 are shown mounted to the elevator car 316. It will be appreciated that while a pair of safety brakes is usually required, it may be suitable to use a combination of an adjustable safety brake 100 and another design of safety brake known in the art, i.e. two different safety brakes.

[0080] The plurality of sensors 390 communicate with the safety controller 400 through the travelling cable 395, and the safety controller 400 communicates with the adjustable force safety brake 100 through the travelling cable 395. In this example the sensors 390 and the adjustable force safety brake 100 communicate through a separate safety controller 400 to the elevator system controller. In another example the safety controller 400 may be integrated into the main elevator system controller.

[0081] In this example the accelerometers 390 are located on each side of the elevator car 316. An unbalanced deceleration of the elevator car 316 can be detected and the safety controller 400 can decide automatically which adjustable force safety brake 100 should be instructed to operate the electromagnet 170 to reduce the braking force on the guide rail 320.

[0082] Whilst in this example the sensors 390 are only used to detect an excessive and/or uneven braking force, in another example the sensors 390 may also be used for other purposes within the elevator system 300, for example as part of a position reference system.

[0083] In the example where the electromagnet 170 of the adjustable force safety brake 100 is operable to produce a variable magnetic force, the safety controller 400 sends a signal to indicate how much current in the electromagnet 170 is required to restore balance to the elevator car 316.

[0084] The strength of the electromagnet 170 and/or its range of varying strengths can be designed with reference to the type of component to which the safety brake 100 will be mounted for braking. Some elevator systems 300 will have elevator cars 316 and counterweights of much larger sizes, and capable of big variations in load, whereas others will have far smaller and more regular loads. A large elevator car 316 designed to carry heavy goods, for example, may have very different braking requirements to that of a small number of people transporting elevator car 316.

[0085] FIG. 8 shows a flow chart of a method for adjusting the braking force of an adjustable force safety brake 100 in an elevator system 300. The adjustable force safety brake 100 is controlled by the safety controller 400. In step 801 braking forces are detected to see whether excessive and/or uneven braking forces are being applied by a pair of safety brakes 24 including at least one adjustable force safety brake 100 mounted to a component e.g. moving along a pair of guide rails 320 in an elevator system. A signal is sent to the safety controller 400, for example via the travelling cable 395.

[0086] In this example, where the electromagnet 170 is operable to produce a variable magnetic force, in step 802 the safety controller 400 analyses the braking forces from the at least one sensor 390, e.g. calculating a corrected braking force to reduce or remove the excessive and/or uneven braking.

[0087] In step 803, the safety controller 400 then instructs the adjustable force safety brake 100 to operate the electromagnet 170 in the adjustable force safety brake 100 to change the additional braking force on the guide rail 320. In this example, the electromagnet 170 can vary the magnetic force produced by the electromagnet 170 depending on the level of excessive and/or uneven braking forces.

[0088] The sensor(s) 390 may be configured to continuously monitor the braking of the elevator car 316, and the safety controller 400 may provide continuous instructions to the electromagnet 170 of the adjustable force safety brake 100 to prevent any excessive and/or uneven braking from occurring.

[0089] It will be appreciated by those skilled in the art that this disclosure has been illustrated by describing one or more specific examples thereof, but is not limited to these examples; many variations and modifications are possible, within the scope of the accompanying claims.