Centrifugal electromechanical actuator

Abstract

Electromechanical actuator comprising: a motor (3); a shaft driven by the motor; a piston (5) movable in an axial direction between a low position and a high position; an upper tulip (8) slidably mounted on the shaft below the piston; a lower tulip (7) fixed on the shaft; arms (9) extending radially, fixed on the shaft (4) between the tulips (7) and (8); weights (10) of elongated shape in the axial direction, slidably mounted on said arms; lower ramps (11) and upper ramps (12) in contact with the axial ends of the weights, each ramp starting from one of the tulips (7) and (8) and moving away from the shaft in the direction of the other tulip, the weights thus being interposed between two ramps in order to keep the tulips separated from each other; an electromagnet (14) for holding the piston in the high position. Figure for the abstract: Fig. 2

Description

Title of the invention: Centrifugal electromechanical actuator Technical field

[0001] The present application relates to a centrifugal electromechanical actuator, in particular an actuator for a safety brake for lifting equipment. State of the art

[0002] A lifting device of the crane, overhead crane, etc. type, usually comprises a line provided with a drum around which suspension cables are wound to which the load to be lifted is attached. Such a lifting device can be used to lift extremely heavy loads, for example weighing from 50 to 500 tonnes.

[0003] The lifting machine needs to be equipped with brakes for several functions, including: slowing down and then stopping the load when approaching a stop position (service brake); blocking the lifting machine when it is in its stop position, i.e. when the load is at the desired height (parking brake); stopping and blocking the lifting machine in the event of an electrical failure or, more generally, in the event of an emergency of any nature (safety brake, also called an emergency brake or "failsafe brake" in English).

[0004] A safety brake is configured to be triggered when it is no longer supplied with electricity (in the event of a power failure): this is called a lack brake or negative brake. Disc brakes have been used for this purpose since the 1960s, in particular because their heating poses little or no problems.

[0005] A safety disc brake generally comprises:

[0006] - a disc secured to the line to be braked,

[0007] - a clamp, comprising two jaws or plates capable of pinching and clamping the disc, which jaws are generally provided with friction pads,

[0008] - for each jaw or for one of the two jaws only, a reserve energy in the form of a spring, for example a washer spring or a helical spring, configured to impose a pressure force on said jaw in the direction of closing the brake, that is to say so as to push and maintain under pressure the jaws against the disc and thus tighten the clamp,

[0009] - an electrically controlled actuator comprising a piston which, when deployed, pushes a plate on which the end of the spring rests, the extended piston thus compressing the spring in the direction of opening the brake; thus when the actuator is under tension, it can be activated to move the plate to a high position in which the spring is compressed, which opens the clamp and releases the disc (and therefore the line) in rotation. Alternatively, the piston is configured to act, not on the spring, but on the jaws (directly or through a mechanism) in the direction of opening the brake.

[0010] Some older installations still have drum safety brakes. These installations comprise a pulley secured to the line to be braked, a clamp comprising two curved shoes lined with a friction material, capable of pinching and tightening the pulley, as well as an energy reserve and an actuator as previously described for disc brakes.

[0011] Regardless of the type of safety brake considered (disc or drum), in the event of an electrical failure, the actuator suddenly becomes inoperative, releasing the spring or the jaws (or curved shoes), which causes the brake to close and the load to stop.

[0012] The constraints which determine the technical specifications of the actuators of the safety brakes for lifting equipment are in particular: the working environment of the brake in terms of temperature, humidity, access, available space, etc.; the travel of the brake; the braking force imposed by the spring, which the actuator must counteract to open the brake, the spring itself being sized according to the loads to be lifted; the opening time; the response time of the brake (in the closing direction) in the event of a cut in the electrical power supply to the actuator; the possibility of closing the brake gradually to slow the descent of a load.

[0013] The actuator used for opening a brake can be electrohydraulic, electromagnetic or electromechanical.

[0014] Electrohydraulic actuators present risks of fluid leakage. In the event of a leak, the actuator may become inoperative, resulting in a production shutdown to repair and / or replace the actuator. To ensure that the oil circuit is closed and the oil (fluid) is contained, electrohydraulic actuators are equipped with a number of hermetic seals, which are all wear parts that require regular replacement, resulting in unwanted production shutdowns and significant maintenance costs.

[0015] Furthermore, when the brake is intended to be used in a very hot environment, for example in a steelworks, the fluid of the electrohydraulic actuator must be an oil that is stable at high temperatures. Above a certain temperature, the oils of known actuators all present risks of flammability; the consequences of an oil leak can then be dramatic. Conversely, in very cold environments, it may be necessary to equip the actuator with a fluid heating system, which increases the weight and cost of the actuator and increases the risks of breakdown. In addition, oils are generally environmental contaminants. Certainly, there are oils that are not very flammable and / or biodegradable, but they are generally more expensive and less effective.

[0016] Without an oil circuit, electromagnetic or electromechanical actuators (ball or screw for example) do not have the aforementioned drawbacks. But they generally suffer from a response time (on closing, in the event of a power failure) which is longer, or even too long.

[0017] The centrifugal electromechanical actuator disclosed by GB687222 is also known. This actuator comprises: - an actuating rod mounted to slide in an axial direction, the sliding of the actuating rod towards the outside of the actuator causing the brake to close while its sliding towards the inside causes the brake to open, - a helical spring which, under compression, tends to move the actuating rod towards the inside of the actuator (closing the brake), - an electric motor, - a square section shaft driven in rotation by the electric motor, - two lower arms whose proximal ends are rigidly fixed to the shaft at a lower attachment point thereof, - a tulip mounted sliding on the shaft between a low rest position located above the attachment point of the lower arms and a high position which depends on the speed of rotation of the shaft, which tulip tends to compress the spring and to move the actuating rod outwards when it moves away from its low position under the effect of the rotation of the shaft, - two upper radial connecting rods articulated on the tulip by their proximal end, - two mass connection elements connecting, on each side of the shaft, the distal ends of one of the lower arms and one of the upper connecting rods.

[0018] When the engine is stopped, the tulip is in the lower position and the upper connecting rods are folded against the shaft. Rotation of the shaft causes the upper connecting rods to extend, driven by the mass connecting elements propelled radially outwards by centrifugal force, which causes the tulip to move upwards, compress the spring and subsequently open the brake. The final compression of the spring depends on the stroke of the tulip and therefore, among other things, on the rotational speed of the engine.

[0019] This brake has the advantage of not having an oil circuit but, given its architecture, it has a short stroke which limits its possibilities of use. Presentation of the invention

[0020] The invention aims to overcome at least one of the aforementioned drawbacks by proposing a centrifugal electromechanical actuator having a stroke greater than the actuators known electromechanical devices so that they can be used in a safety brake of a lifting machine capable of lifting very heavy loads, for example 50 to 500 tonnes. The invention also aims to provide an actuator with a considerably reduced response time.

[0021] In particular, an objective of the invention is to provide an electromechanical actuator having a stroke of up to 60mm and a response time of less than 300ms in the event of an electrical failure.

[0022] To do this, the invention proposes an electromechanical actuator comprising: - an engine, - a shaft driven in rotation by the motor, - a piston, which can be moved in an axial direction between a low position and a high position, - an upper tulip, which is slidably mounted on the shaft and comes to rest on the piston when the shaft is rotated.

[0023] The electromechanical actuator according to the invention is characterized in that it comprises: - a lower tulip fixed on the tree, - one or more (preferably at least two) radially extending arms, fixed on the shaft between the lower and upper tulips, - for each of said arms, a weight having an elongated shape in the axial direction, said weight being slidably mounted on said arm, - for each of said weights, a lower ramp and an upper ramp in contact with the axial ends of the weight, which lower and upper ramps follow curves starting respectively from the lower and upper tulips and moving away from the shaft in the direction of the other tulip, each of the weights thus being interposed between two ramps in order to keep the tulips separated from each other, - an electromagnet to hold the piston in the high position.

[0024] According to particular embodiments of the invention, the electromechanical actuator further meets the following characteristics, implemented individually or in any technically possible and operational combination.

[0025] In some embodiments, the electromagnet comprises a frame containing a coil, incorporated in the housing of the actuator, for example on an upper wall of said housing, and the piston comprises an armature configured to be attracted by said coil.

[0026] In certain embodiments, each weight has a wheel at each of its axial ends, configured to cooperate with a rail provided in the corresponding ramp.

[0027] In some embodiments, each of the upper and lower ramps has a stop at its free end, preventing the axial end of the associated weight from becoming detached from said ramp.

[0028] In certain embodiments, there are three arms, arranged at 120° to each other around the shaft, as are the weights, the lower ramps (starting from the lower tulip) and the upper ramps (starting from the upper tulip). The forces to which the shaft is subjected via the ramps and tulips under the effect of the radial movement of the weights are thus perfectly balanced, which allows the upper tulip to slide along the shaft with limited friction and without risk of jamming and also ultimately avoids any bending of the shaft.

[0029] The invention extends to a negative brake equipped with an actuator according to the invention. More particularly, the invention extends to a negative brake, comprising: - a disc, - a clamp comprising two jaws surrounding the disc, - a spring configured to impose a pressure force on at least one of said jaws in the direction of closing the clamp, - an actuator configured to counteract the action of the spring and allow the opening of the clamp, characterized in that the actuator is an actuator according to the invention, that is to say as described previously.

[0030] In some embodiments, the spring and the actuator are separate and arranged in parallel with each other, the actuator piston not acting directly on the spring.

[0031] In certain embodiments: - the axial direction of the actuator and the spring axis are vertical, while the direction of movement of the brake shoes is horizontal, - the brake comprises an upper balance pivotally mounted around a horizontal axis, and connected to the jaws by a mechanism configured to transform a pivoting movement of the balance upwards, respectively downwards, into a horizontal force on the jaws in the direction of opening, respectively closing, of said jaws, - the spring has an upper end connected to the balance wheel so as to pull it downwards (i.e. in the direction of closing the brake), - the actuator piston comprises an actuating rod extending projecting from a housing of the actuator, which actuating rod is connected to the rocker (104) so as to push the latter upwards (in the direction of opening the brake) when the piston - and therefore the actuating rod - is moved upwards Brief description of the drawings

[0032] The invention, according to an exemplary embodiment, will be well understood and its advantages will appear better on reading the detailed description which follows, given for information purposes and in no way limiting, with reference to the appended drawings in which:

[0033] [Fig-1] [Fig.l] represents an example of embodiment of an actuator according to the invention, seen in perspective with part of its casing torn away, the piston and the upper tulip of the actuator being in the low position;

[0034] [Fig.2] [Fig.2] shows the actuator of [Fig.l], still in perspective but with the piston and the upper tulip in an intermediate position;

[0035] [Fig.3] [Fig.3] shows the actuator of figures 1 and 2, still in perspective but with the piston and the upper tulip in the high position;

[0036] [Fig.4] [Fig.4] shows the actuator of figures 1 to 3, in perspective and with the piston held in the high position while the upper tulip is lowered to the low position;

[0037] [Fig.5] [Fig.5] is a perspective view of a disc brake incorporating an actuator according to the invention, which may be that of Figures 1 to 4.

[0038] [Fig.6] [Fig.6] represents the disc brake of [Fig.5], seen in perspective from another point of view,

[0039] [Fig.7] [Fig.7] is a perspective view of a drum brake incorporating an actuator according to the invention, which may be that of Figures 1 to 4.

[0040] Identical elements shown in the above-mentioned figures are identified by identical numerical references. Detailed description

[0041] Figures 1 to 4 represent an actuator 1 according to the invention. This comprises:

[0042] - a casing 2, shown partly transparent and part of which is torn away on the figures to show the different parts that make up the actuator;

[0043] - an electric motor 3 arranged in the lower part of the actuator; for example, the motor 3 can be a standard three-phase asynchronous motor, supplied with 400V,

[0044] - a shaft 4, which extends in an axial direction Ai of the actuator and is driven in rotation by the motor 3; in use, in particular when it is associated with a safety brake of a lifting device, the actuator 1 is arranged so that its axial direction Ai is vertical,

[0045] - a piston 5 mounted sliding on the shaft 4, provided with an armature configured to be attracted by the electromagnet 14 described below, and provided with an actuating rod 6 which protrudes from an upper wall 20 of the casing 2;

[0046] - a lower tulip 7, fixed on the shaft 5 at a low point thereof, that is to say at proximity to engine 3;

[0047] - an upper tulip 8 slidably mounted on the shaft 5 above the lower tulip lower 7;

[0048] - three arms 9 which extend radially, which arms are arranged at 120° to each other others and fixed on the shaft 4 between the lower and upper tulips;

[0049] - three weights 10, each weight being slidably mounted on one of the arms 9; to this end, each weight has a central hole through which it is threaded onto the arm 9;

[0050] - an electromagnet 14, represented here very schematically, the reference 14 pointing at a carcass incorporating a coil (not shown).

[0051] The weights have a dimension in the axial direction which corresponds substantially to the desired stroke for the actuator. This dimension is advantageously of the order of 60 mm.

[0052] For each arm 9, the actuator 1 comprises a lower ramp 11 formed in the extension of the lower tulip 7. When the motor is stopped ([Fig.l]), the lower ramp 11 extends from the lower tulip 7 to the distal end 90 of the arm. The lower ramp 11 follows a curve inscribed in a longitudinal (vertical) plane comprising the axis of the shaft 4 and the axis of said arm 9; this curve starts from the lower tulip 7 and moves radially away from the shaft 4 in the direction of the upper tulip 8 (i.e. upwards in the attached figures).

[0053] Similarly, for each arm 9, the actuator 1 comprises an upper ramp 12 formed in the extension of the upper tulip 8. When the motor is stopped ([Fig.l]), the upper ramp 12 extends from the upper tulip 8 to the distal end 90 of the arm. The upper ramp 12 thus follows a curve inscribed in the longitudinal plane which comprises the axis of the shaft 4 and the axis of said arm 9; this curve starts from the upper tulip 8 and moves radially away from the shaft 4 in the direction of the lower tulip 7 (downwards in the figures).

[0054] Each weight 10 is also essentially inscribed in the longitudinal plane which comprises the axis of the shaft 4 and the axis of the arm 9 on which the weight is slidably mounted. The weight 10 is embedded between the lower 11 and upper 12 ramps associated with said arm. It has an elongated shape in the axial direction. The length (dimension in the axial direction) of the weight 10 defines the distance which separates the upper and lower tulips when the actuator is at rest (engine stopped, [Fig.l]). As will be understood later, the length of the weight also defines the maximum possible stroke of the actuator. The length of the weight also and above all makes it possible to increase the mass of the weight and thus the force of the actuator. In operation, the actual stroke of the actuating rod 6 depends on the radial distance traveled by the weights 10 on the arms 9.

[0055] At each of its axial ends, the weight 10 comprises a bearing 13 engaged in a rail (not visible) provided in the ramp 11 or 12 against which said axial end of the weight rests.

[0056] When the engine is at rest, the flyweights 10 are pressed against the shaft 4. When the engine is running and the shaft 4 is rotating, the flyweights 10 are propelled radially outwards by centrifugal force. They then push on the upper 12 and lower 11 ramps with which they are respectively associated, moving the upper tulip 8 (sliding) away from the lower tulip 7 (fixed), which causes the piston 5 to move upwards as can be seen in [Fig.2] and 3.

[0057] [Fig. 3] illustrates the extreme position of the weights 10, when the radial ends of the weights reach the ends of the ramps 11 and 12. The piston 5 is then in a high position, in which its armature is pressed against the upper wall 20 of the casing 2 or rather against the frame of the electromagnet 14, and the actuating rod 6 is in the maximum extension position. The opening of the brake, that is to say the movement of the piston from its low position ([Fig. 1]) to its high position ([Fig. 3]) takes about 200 ms.

[0058] In the event of an electrical failure while the actuator is in the configuration of [Fig. 3], the motor 3 and the shaft 4 stop and the electromagnet 14 is deactivated. No longer subject to centrifugal force, the weights 10 return to their initial position against the shaft 4 under the effect of their own weight and that of the upper tulip 8. The upper tulip 8 and the piston 5 are in the low position, the actuating rod then being in its retracted position, as illustrated in [Fig. 1]. The descent of the piston and the upper tulip 8, slightly slowed down by the weights 10, can take up to 300 ms.

[0059] If the motor 3 is stopped while the piston 5 is in the high position and the electromagnet 14 is active, again, no longer being subjected to centrifugal force, the weights 10 return to their initial position against the shaft 4, under the effect of their weight and that of the upper tulip 8. The actuator may also comprise a small spring above the upper tulip 8 (this spring can be seen in [Fig.4]) allowing the upper tulip 8 and the weights 10 to descend a little more quickly. This spring makes it possible to overcome the inertia of the mechanism at the start of the downward movement of the tulip and the weights.

[0060] Thus, if the motor is stopped and the electromagnet 14 is activated, the upper tulip 8 is in the low position while the piston 5, retained by the electromagnet 14, remains in the high position as illustrated in [Fig.4]. The electromagnet therefore makes it possible to cut the motor while maintaining the actuator force, which prevents the motor from overheating and failing. The electromagnet thus improves the reliability and robustness of the actuator and extends its service life.

[0061] In the event of an electrical failure while the actuator is in the configuration of [Fig.4], the electromagnet 14 is instantly deactivated and the piston 5 falls under the effect of its weight. Not being braked by the upper tulip 8 and the weights 10, the piston 5 returns to its low position in a time (called response time) of the order of 100 ms. If the actuator is associated with a safety brake of a lifting machine, the fall of the load carried by the lifting machine is thus instantly stopped. The electromagnet 14 therefore also makes it possible to considerably reduce the response time of the actuator and the associated brake.

[0062] If the brake is required to close during normal operation, i.e. in the absence of an electrical fault, it is possible to obtain a less abrupt (or even progressive) closing of the brake by deactivating the electromagnet 14 while initially maintaining the piston 5 in the high position using the motor 3 and then stopping the motor. Decelerating the motor (before it comes to a complete stop) can even make it possible to manage the descent of the load.

[0063] [Fig.5] and 6 show the actuator of [Fig.l] to 4 integrated in a disc brake 100. This brake comprises:

[0064] - a disc 101, intended to be mounted on a braking line (not shown),

[0065] - on either side of the disc 101, jaws 102 parallel to the front faces of the disc 101 and forming a clamp which clamps the disc 101,

[0066] - a spring 103, for example a helical spring as illustrated in [Fig.6], configured to push one or both shoes in the direction of brake closure (i.e., toward each other),

[0067] - actuator 1.

[0068] In the example illustrated, the spring 103 is substantially parallel to the axial direction of the actuator, this being orthogonal to the working direction A2 of the jaws (i.e. to the axis of the disc 101). It will be easily understood that this architecture makes it possible to obtain a particularly compact brake, of limited dimension in the vertical direction.

[0069] Therefore, the brake further comprises a balance 104 and a mechanism capable of transforming a pivoting movement of this balance upwards and downwards into a movement of the jaws 102 in the direction of opening and closing the brake respectively. This mechanism is not shown in detail, the person skilled in the art being able to design it using his general knowledge.

[0070] The lower end of the casing 2 of the actuator is fixed to a base 105 of the brake. Similarly, the lower end of the spring 103 is fixed to said base 105.

[0071] The actuating rod 6 of the actuator is connected to the rocker 104 so that the extension of this rod causes the rocker to pivot upwards, i.e. imposes on the jaws 102 a force tending to open the brake. Conversely, the end upper part of the spring is connected to the balance 104 so that the spring (which, in the example illustrated, works in traction) causes the balance to pivot downwards, that is to say imposes on the jaws 102 a force tending to close the brake.

[0072] The stroke of the actuator 1 makes it possible to counter the action of the spring 103 and detach the jaws 102 from the disc 101 to open the brake.

[0073] Note that the compression of the spring depends on the movement of the actuating rod 6 of the actuator, therefore on the actuator force, the latter depending not only on the rotation speed of the motor 3 but also on the stroke of the tulip itself (the closer the tulip approaches the high position, the greater the centrifugal force will be and therefore the greater the actuator force will be). Thus, even if the motor is at a stabilized speed, the force continues to increase with the stroke of the tulip. However, in an actuator according to the invention, the tulip can have a greater stroke than in a prior art actuator such as that of GB687222. With an equal motor, the actuator according to the invention can therefore develop a greater force than prior actuators.

[0074] [Fig. 7] shows a drum brake 200. This brake usually comprises two shoes 202 (similar to the claimed jaws) forming a clamp which grips a drum (not shown), and it is remarkable in that it comprises an actuator 1 according to the invention. It will not be described in more detail here, the person skilled in the art being able to design the mechanism 203 making it possible to transform the vertical movements of the actuating rod 6 of the actuator into forces of the shoes 202 against the drum.

[0075] Since the actuator 1 has no oil circuit, it can be used in very hot environments without risk of fire and in very cold environments without risk of solidification of the oil.

[0076] Furthermore, its stroke being relatively long, it can develop a significant force allowing its use in a safety brake of a lifting machine intended to lift loads of up to 500 tonnes or more. The use of the electromagnet 14 of the actuator makes it possible to keep the brake open without using the motor 3 and to obtain instantaneous closing (in less than 100ms) of the brake in the event of a power cut.

Claims

Claims

1. Electromechanical actuator (1) comprising: - a motor (3), - a shaft (4) driven in rotation by the motor, - a piston (5), which can be moved in an axial direction (Ai) between a low position and a high position, - an upper tulip (8), which is slidably mounted on the shaft (4) and comes to bear on the piston (5) when the shaft is driven in rotation, characterized in that it comprises: - a lower tulip (7) fixed on the shaft, - one or more arms (9) extending radially, fixed on the shaft (4) between the lower (7) and upper (8) tulips, - for each of said arms (9), a weight (10) having an elongated shape in the axial direction, said weight being slidably mounted on said arm, - for each of said weights (10), a lower ramp (11) and an upper ramp (12) in contact with the axial ends of the weight,which lower and upper ramps follow curves starting respectively from the lower (7) and upper (8) tulips and moving away from the shaft towards the other tulip, each of the weights being thus interposed between two ramps in order to keep the tulips apart from each other, - an electromagnet (14) for keeping the piston (5) in the high position.,

2. Electromechanical actuator (1) according to claim 1, wherein the electromagnet (14) comprises a carcass containing a coil, incorporated in a casing (2) of the actuator, and the piston (5) comprises an armature configured to be attracted by said coil.

3. Electromechanical actuator (1) according to one of claims 1 or 2, in which each weight (10) has a bearing (13) at each of its axial ends, configured to cooperate with a rail provided in the corresponding upper or lower ramp (11, 12).

4. Electromechanical actuator (1) according to one of claims 1 to 3, in which each of the upper and lower ramps (11, 12) has a stop at its free end, preventing the axial end of the associated weight (10) from becoming detached from said ramp.

5. Electromechanical actuator (1) according to one of claims 1 to 4, in which the arms (9) are three in number, arranged at 120° to each other.

6.

7.

8. others around the shaft (4), as well as the weights (10), the lower ramps (11) and the upper ramps (12). Negative brake (100; 200), comprising: - a disc (101) or a drum, - a clamp comprising two jaws (102; 202) surrounding the disc or drum, - a spring (103) configured to impose a pressure force on at least one of said jaws (102; 202) in the direction of closing the clamp, - an actuator (1) configured to counteract the action of the spring and allow the opening of the clamp, characterized in that the actuator (1) is in accordance with one of the preceding claims. Negative brake according to claim 6, wherein the spring (103) and the actuator (1) are separate and arranged in parallel with each other, the piston (5) of the actuator not acting directly on the spring. Negative brake according to one of claims 6 or 7, in which: - the axial direction (Ai) of the actuator (1) and the axis of the spring (103) are vertical, while the direction (A2) of movement of the jaws (102) is horizontal, - the brake comprises an upper balance (104) pivotally mounted around a horizontal axis, and connected to the jaws (102) by a mechanism configured to transform a pivoting movement of the balance upwards, respectively downwards, into a horizontal force on the jaws in the direction of opening, respectively closing, of said jaws, - the spring (103) has an upper end connected to the balance (104) so as to pull the latter downwards, - the piston (5) of the actuator comprises an actuating rod (6) extending projecting from a housing (2) of the actuator, which actuating rod (6) is connected to the rocker (104) so as to push the latter upwards when the piston is moved upwards.

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