Abstract:
A locking device for use in a rotor blade, said locking device comprising: a locking member that is arranged to be movable from an unlocked position to a locking position upon experiencing sufficiently fast rotation; and a selectively engagable retaining device arranged when engaged to retain the locking member in the unlocked position. The locking device will typically default to an unlocked position during normal rotation and will only be locked so as to prevent movement when the retaining device is de-activated. A method of locking an actuator is also disclosed. The locking device has applications in helicopter rotor blades and wind turbine blades amongst others.

Description:
FOREIGN PRIORITY 
       [0001]    This application claims priority to European Patent Application No. EP14182042.3 filed Aug. 22, 2014, the entire contents of which is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    This disclosure relates to actuator locks for use in rotational environments, particularly for use in rotary blade systems such as helicopter rotor blades or wind turbine rotor blades. 
       BACKGROUND 
       [0003]    Some advanced helicopter rotor systems have flaps on the rotor blades that act as secondary control surfaces and affect the aerodynamic characteristics of the blades. These are similar in nature to the flaps provided in fixed wing aircraft wings although they are generally smaller and more compact due to the smaller size of the rotor blades. These flaps can be used for improving the efficiency of the rotor blades by modifying the lift and by reducing the vibrations on the rotor. 
         [0004]    Each flap requires an actuator to control its movement. Movement may be controlled by the pilot either directly or via an electronic controller. In the case of anti-vibration system the latter is more likely, with rotor flaps being automatically controlled based on the outputs of various sensors. 
         [0005]    In certain circumstances it may be desirable to disable these flaps. This may be an intentional flight decision not to use them or it may be desirable to disable them in case of system failure. 
         [0006]    Flaps will generally be provided on each of several rotor blades and there may be more than one flap per blade. It may be desirable to disable all or only some of the flaps. 
       SUMMARY 
       [0007]    According to this disclosure there is provided a locking device for use in a rotor blade, said locking device comprising: a locking member that is arranged to be movable from an unlocked position to a locking position upon experiencing sufficiently fast rotation; and a selectively engageable retaining device arranged when engaged to retain the locking member in the unlocked position. 
         [0008]    This arrangement makes use of the rotation of the rotor to accomplish movement of the locking member towards the locked position When the rotor is rotating in normal operation, the default position of the locking member is in the unlocked position and the locking member is retained by the retaining device. The lock may be engaged by disengaging the retaining device so that the locking member is pulled by the g force into the locking position. In some preferred examples, by making the retaining device dependent on a power source to retain the locking member, a fault in the system will result in the locking device losing power and entering the locked state as a fail safe condition. 
         [0009]    The locking device may be arranged to move radially with respect to the rotor, i.e. substantially parallel to the length of the blade so that upon rotation of the rotor, the locking member experiences a g-force towards the tip of the blade. The locking position is thus radially outward of the unlocked position, i.e. the locking position is closer to the tip and the unlocked position is closer to the root of the blade. 
         [0010]    The retaining device may be arranged when engaged to provide a retaining force equivalent to more than 200 g. “g” here is the gravitational acceleration at the earth&#39;s surface, i.e. about 9.8 ms-2. The actual force that must be provided by the retaining device will depend on the mass of the locking member which can vary according to the design and in particular according to the size of the rotor and the rotor blades. Helicopter rotors typically maintain a fairly constant rotation speed (typically a few hundred rpm, again dependent on size and construction). The g-force experienced varies along the length of the rotor such that a locking member located towards the centre of the rotor (i.e. nearer the blade root) may experience 300 g or less while a locking member located towards the outside of the rotor (i.e. nearer to the blade tip) may experience 750 g or more. In order to accommodate this range, in some examples, the retaining device may be arranged when engaged to provide a retaining force equivalent to more than 500 g. In other examples, the retaining device is preferably capable of supplying enough force to counteract 850 g. 
         [0011]    The retaining device may be any mechanism that can selectively retain the locking member, i.e. it can be switched between a retaining state and a non-retaining state. In the retaining state, the locking member is held in the unlocked position against the g-force of the rotor rotation. In the non-retaining state, the locking member is allowed to move under the g-force and thus moves into the locked state in which it prevents movement of the actuator. However, a convenient implementation is where the selectively engageable retaining device is an electromechanical actuator, preferably a solenoid. A solenoid is capable of providing a retaining force upon engagement by providing power to create a magnetic field to create a force on an armature (the locking member) to counteract the g-force of the rotor. The solenoid may either act to hold the armature against the solenoid coil or force the armature away from it. Either way, the armature can be released simply by switching off the power to the coil, thus allowing the armature to move to the locked state under the rotor g-force. Such electromechanical arrangements are particularly advantageous because they can be small and involve few moving parts. The mounting space for such equipment inside a rotor blade is very limited and all parts experience a high-g environment, so reliability under extreme forces is an important consideration. 
         [0012]    In some examples, the solenoid may be small for the purpose of minimizing size and cost of components. The solenoid cannot then be used to disengage the lock while the rotor is spinning since the pulling capability of the solenoid falls off rapidly as the armature moves away from the coil. For example, in a typical implementation, when the armature is more than 0.5 mm from the solenoid, the solenoid provides insufficient attractive force to pull the armature back against the full speed spinning rotor g-force. For this reason, in such examples the unlocked position may not be restored during normal rotation (e.g. in flight in the case of helicopter blades) after a locking process has happened. Instead, to re-engage the lock it is necessary to slow down the rotor so that the armature can be moved back to the unlocked position. 
         [0013]    In normal operation, when the rotor is spinning at full speed, it is preferred that in the event of a fault, accidental or unwanted movement of the actuator is prevented. However it may also be preferred that when the rotor is stationary (or spinning down and at low speed), the default position be that the lock is disengaged. This facilitates repair and maintenance of the blades as the actuators are unlocked when the power is off, allowing correct movement to be checked and assessed. Therefore a resilient biasing device may be arranged to bias the locking member in the direction of the unlocked position. The biasing force provided by this biasing device must be less than the g-force experienced by the locking member under normal rotation. For example, the biasing device may provide a biasing force equivalent to about 200 g, i.e. less than the minimum 300 g that is experienced by a locking member mounted at a relatively inner position on a helicopter blade. It will be appreciated that other biasing values will apply in other circumstances. Again, the actual force to be provided by the biasing member will depend on the mass of the locking member which will vary with design and application. The biasing device may be a spring, e.g. a coil spring, although other biasing devices may equally well be used. 
         [0014]    A further advantage of the biasing device when used together with an electromechanical actuator such as a solenoid, is that it provides a force to move the locking member back to the unlocked position when the force provided by the electromechanical actuator is weak due to the separation of the locking member (armature) from the coil. Once the rotor speed has dropped sufficiently, the biasing device will ensure that the armature once again comes into sufficiently close contact with the coil that the retaining force provided by the retaining device is strong enough to hold the locking member against the g-force of full normal rotation speed. 
         [0015]    The way in which the locking device prevents movement of the relevant actuator may vary from one device to another, but in some preferred examples, in the locking position the locking member engages with a pin so as to prevent movement of the pin. In other examples, the locking member may engage with any other part of the moving actuator assembly, e.g. an actuator rod or a pivoting part such as a lever or cam. The locking member may simply engage frictionally with the pin (or other part) with sufficient force to prevent actuation. However, preferably the locking member blocks movement of the pin. The locking member may have a groove that engages with said pin. 
         [0016]    The engagement of the locking member with the pin (or other part) may simply prevent further movement, thus locking the pin in its current position at the time of engagement. However, in some examples, it is preferred that the pin (or other part) be held in a predetermined position in the locked position, e.g. in a neutral position. For example in the case of secondary movable blade surfaces (such as flaps) it may be preferred that they be held in line with the rest of the blade, i.e. in a non-deployed or neutral position. It may of course be held at any other predetermined position within its normal range of motion. To achieve this, the locking member may comprise a groove with sloped sides that are arranged to guide the pin (or other part) to a predetermined position. For example, when the locking member is released and moves radially outwardly, if the pin is in a position different from the predetermined position, one of the sloped sides will contact the pin and bias it towards the predetermined position as the locking member moves further in the radially outward direction. With this arrangement, in the locked state the pin will be moved to and held in the predetermined position and cannot move from that position until the locking member is disengaged. 
         [0017]    According to this disclosure there is also provided a rotor blade comprising one or more locking devices as described above, optionally including any of the optional or preferred features described above. In some examples the rotor blade may have one, two or three locking devices, e.g. corresponding to different control surfaces (flaps and/or slats) on the blade. A rotor may comprise two or more rotor blades, e.g. two, three, four or more blades. In one example a rotor of five blades, each with three locking devices is provided. 
         [0018]    Accordingly, this disclosure also provides a rotor blade comprising one or more adjustable blade surfaces each having an actuator and each having a locking device as described above arranged to lock said actuator. The actuators may be for controlling control surfaces such as flaps and/or slats on the blade. The adjustable surfaces may be part of an anti-vibration system. The control of actuators for such surfaces may be performed by an electronic controller. The blade may be a helicopter or wind turbine blade, although it will be appreciated that the disclosure may be applied to any rotor blade. 
         [0019]    According to another aspect, this disclosure provides a method of locking an actuator in a rotor blade, comprising: a locking member moving from an unlocked position to a locked position upon experiencing sufficiently fast rotation of the rotor blade; wherein in the locked position said locking member prevents movement of said actuator. 
         [0020]    The method may further comprise the step of: releasing a selectively engageable retaining mechanism so that it no longer retains the locking member in an unlocked position. The rotation speed of the rotor blade may be sufficient that the locking member experiences a g-force that overcomes the force of a biasing device arranged to bias the locking member towards an unlocked position. 
         [0021]    The preferred features described above in relation to the locking device all also apply to the method of locking. For example, the method of locking may include sloped surfaces of a groove on the locking member biasing a locking pin (or other part) into a predetermined position during movement from the unlocked position to the locking position. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0022]    One or more non-limiting examples will now be described, by way of example only, and with reference to the accompanying figures in which: 
           [0023]      FIG. 1  shows an actuator and locking mechanism; 
           [0024]      FIG. 2  shows the system of  FIG. 1  in cross-section; 
           [0025]      FIG. 3  shows a locking mechanism in more detail; 
           [0026]      FIGS. 4   a  and  4   b  show the locking mechanism in unlocked and locking positions respectively; and 
           [0027]      FIG. 5  illustrates an armature of the mechanism. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  shows an actuator system  100  for a movable surface on a helicopter rotor blade. System  100  includes an actuator  102  and rod  104  which pushes a lever  106  that is rotatable about pivot  108  leading to output motion as indicated by arrow  110 . 
         [0029]    A sensor  112  senses the position of lever  106 . The main function of the position sensor  112  is to provide an independent measurement of the position of the lever  106  in addition to the one derived from the position of the actuator  102 . It can be used for monitoring purposes. It is independent of the locking mechanism described below. 
         [0030]    Lever  106  has a pin  114  that moves as the lever  106  rotates about its pivot  108 . The locking mechanism  120  shown in  FIGS. 3 ,  4   a  and  4   b  acts on this pin  114  so as to be able to prevent movement of the pin  114  and thereby prevent movement of the lever  106  and actuator  102 . 
         [0031]    As can best be seen in  FIG. 2 , the locking mechanism  120  is mounted on a static support  116 . This support  116  is static with respect to the rotor blade in which it is mounted, i.e. the lever  106  rotates with respect to support  116 . Lever  106  is mounted to support  116  via pivot  108 . 
         [0032]    The locking mechanism  120  is shown in more detail in  FIG. 3  which is a cross-section through the mechanism  120  viewed from an angle 90 degrees to the viewing angle of  FIG. 1  so that  FIG. 3  shows the side of the generally cylindrical locking pin  114  rather than the end thereof which is shown in  FIG. 1 . The locking mechanism (locking device)  120  includes a solenoid body  122  with solenoid coils (not shown in  FIG. 3  but indicated by arrow  124 ) that can be selectively activated so as to create a magnetic attraction on armature  126 . In  FIG. 3 , the armature  126  is shown pulled tight against the solenoid body  122  which is the unlocked position and thus the armature  126  is disengaged from locking pin  114 . As the lever  106  rotates, locking pin  114  moves into and out of the paper as shown in  FIG. 3 . 
         [0033]    The operation of locking mechanism  120  will be described with reference to  FIGS. 4   a  and  4   b .  FIGS. 4   a  and  4   b  are cross-sections through the locking mechanism  120 , but taken in the same orientation as  FIGS. 1 and 2  (and thus at 90 degrees to  FIG. 3 ) so that they show the end of the generally cylindrical locking pin  114 .  FIG. 4   a  shows the unlocked state and  FIG. 4   b  shows the locking state 
         [0034]      FIG. 4   a  illustrates the situation where solenoid coils  124  are active and the solenoid attracts the armature  126  so that it abuts the solenoid body  122 . Locking pin  114  passes through a groove or hole  128  in the centre of armature  126 . The spatial relationship between armature  126  and locking pin  114  in  FIG. 4   a  is such that the locking pin  114  is free to move to a certain extent, i.e. the part of groove  128  that is aligned with pin  114  is wider than the diameter of pin  114  so that pin  114  can move within groove  128 . This in turn allows lever  106  to move by pivoting around pivot  108  and thus permits the actuator  102  to cause movement of the flap (or other mechanism) attached to the output end of lever  106 , thus operating the flap. 
         [0035]      FIG. 4   a  also illustrates the situation where the solenoid coils  124  are inactive and there is no magnetic attraction to pull armature  126  into abutment with solenoid body  122 . However a spring  130  housed in spring housing  132  also biases the armature  126  in the direction of the solenoid body  122  (i.e. towards the unlocked state). Spring  130  ensures that when the rotor is stationary (not rotating), the locking mechanism  120  is biased into the unlocked state. This provides a default state for a powered off/low rotor speed configuration, e.g. during inspection, maintenance or repair. In such situations it is desirable to have the system in the unlocked state so that correct movement of the flaps (or other mechanisms) can be checked without having to power on the solenoid  124 . 
         [0036]    Spring  130  provides a certain force on armature  126 , but that force will only be sufficient to counter the g-force up to a certain rotation speed of the rotor. Thus above a certain rotation speed the spring  130  will be compressed and, in the absence of activation of the solenoid  124 , armature  126  will move into the locked state of  FIG. 4   b . The strength of spring  130  is chosen to be strong enough that it reliably biases the armature  126  into the unlocked position when the rotor is stationary, but weak enough that it is overcome during normal operation of the rotor. 
         [0037]      FIG. 4   b  shows the locking state in which pin  114  is held in place, preventing movement of lever  106 . The spatial relationship between armature  126  and locking pin  114  in  FIG. 4   a  is such that the locking pin  114  is secured and cannot move, i.e. the part of groove  128  that is aligned with pin  114  is essentially the same size as the diameter of pin  114  so that pin  114  cannot move within groove  128 . This in turn prevents lever  106  from pivoting and moving and thus prevents actuator  102  from causing movement of the flap (or other mechanism) attached to the output end of lever  106 . 
         [0038]      FIG. 4   b  shows the state of the locking device when under normal rotation and when the solenoid  124  has released armature  126 , i.e. when the g-force due to rotation has overcome the biasing force of spring  130 . In this example, the solenoid  124  is not strong enough to pull the armature  126  back into a locked state against the g-force of normal rotation (even with the assistance of the spring). Therefore in this example once the locking device is locked it cannot be unlocked until the rotor is stopped or has been spun down to a sufficiently low speed. With this arrangement, the solenoid can be small which is important due to the space restrictions within the mounting environment. Therefore in normal operation, the solenoid  124  must be engaged so as to retain the armature  126  before the rotor is spun up or while it is still rotating at low speed. 
         [0039]    In larger or slower rotors (e.g. in large wind turbines), a solenoid may be made large enough to pull the armature  126  back against the g-force of normal rotation. The pin  114  can thus be released, allowing it to move by activating the solenoid  124  (i.e. by passing a current there through) so as to draw armature  126  into contact with solenoid body  122 , thus moving the wider part of groove  128  into alignment with pin  114  and permitting movement of the pin  114  and lever  106 . 
         [0040]    As can be seen in  FIGS. 4   a  and  4   b , the groove  128  has sloped sides such that the groove  128  narrows progressively from a wider region to a narrower region. The intermediate sloped sides serve to guide the locking pin  114  into a predetermined position as the armature  126  moves from the unlocked configuration ( FIG. 4   a ) to the locking configuration ( FIG. 4   b ). When the armature is in the unlocked position, the locking pin  114  may take a range of positions depending upon the current position of the actuator  102 . If the actuator  102  (and thus the rest of the actuator assembly  100  and the output apparatus (e.g. a movable flap) are not in their neutral (central) position when the solenoid  124  is switched off and the armature  126  released, the pin  114  will not be aligned with the narrow part of groove  128  and the first contact between armature  126  and pin  114  will be on one side of pin  114 . As the armature  114  progresses towards the locking position (under the g-force caused by rotor rotation), the sloped sides of groove  128  will force the pin  114  and thereby the lever  106 , connecting rod  104  and actuator  102  as well as the flap itself (or other output mechanism) to move towards the predetermined position that is defined by the narrow part of groove  128 . In this example, the predetermined position is a neutral, central position that will cause the connected flap to be aligned with the rest of the rotor blade so as to cause minimal alteration to the normal blade profile. However this need not be the case—the groove  128  may be asymmetrical, defining a locked position of the actuator system and output mechanism that is non-central. The predetermined position is determined by the point at which both sides of groove  128  contact pin  114 , thus clamping it and holding it in place. 
         [0041]      FIG. 5  shows the relationship between the armature  126  and the locking pin  114 . The arrow  140  shows the movement that locking pin  114  is permitted to undertake within groove  128  in the unlocked position. The dashed circle  142  shows the relative position of the pin  114  with respect to the armature  126  in the locked position where it is clamped by the narrow part of groove  128  and no movement can occur.