Abstract:
An actuator has an output ram driven to extend and retract by a rotating lead screw. The lead screw is coupled with a rotating input shaft via a lost-motion drive sleeve connected with the input shaft by cooperating threads so that rotation of the drive shaft causes both axial and rotational movement of the drive sleeve. The ram is locked in its retracted position by several radially-extending locking keys, one end of which engage an extension sleeve fixed with the ram and the other end of which are engaged by a lock sleeve. Rotation of the input shaft causes the drive sleeve to move axially and engage the lock sleeve, thereby pulling it to one side and allowing the locking keys to move radially out and disengage the extension sleeve to allow it to extend.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to actuators. 
         [0002]    The invention is more particularly concerned with linear actuators that can be locked in position. 
         [0003]    Conventional linear actuators may be driven from a rotary source such as an electric, hydraulic or pneumatic motor. The actuator includes a mechanism to convert the rotary motion from the motor to a linear output motion to translate an external load. The actuator may have a lock mechanism to retain the output ram in a fixed position, usually a retracted position, until power is applied to extend the ram. The lock is sequentially actuated to an unlocked state before the torque necessary to deploy the ram is applied. This is typically accomplished by a solenoid or electric motor mechanically linked to the lock mechanism and is separate from the drive motor that actuates the load. The use of a separate lock driver actuator increases the cost and complexity of the actuator. Separate dedicated actuation commands and logic devices are needed to control the lock. Furthermore, electrical wiring, linkage or hydraulic tubing is required to transmit the commands to actuate the lock. An important disadvantage in aerospace applications is the weight associated with the independent lock actuation and the equipment required to support it. An example of a previous linear actuator is described in U.S. Pat. No. 5,960,626. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    It is an object of the present invention to provide an alternative actuator. 
         [0005]    According to one aspect of the present invention there is provided an actuator including a rotary input member, a linear output member and a mechanism for converting rotary motion of the input member to linear motion of the output member, the actuator including a lock member displaceable from a first position in locking engagement with the linear output member to a second position out of locking engagement, and the lock member being retained in the first position until there is rotary motion of the input member. 
         [0006]    The lock member is preferably displaceable radially. The lock member may be retained in the first position by a second member and the second member may be displaceable axially in response to rotation of the input member. The lock member and linear output member may have cooperating inclined surfaces such that linear movement of the output member applies a radial force to the lock member. The mechanism for converting rotary motion to linear motion includes a lead screw and nut mechanism. The rotary input member is preferably coupled with the lead screw by a lost-motion coaxial drive sleeve, and the drive sleeve preferably connects with the input member by cooperating threads on the input member and the drive sleeve such that rotation of the input member initially causes axial displacement of the drive sleeve before it causes rotation of the drive sleeve and of the lead screw. The drive sleeve may cooperate with a separate, axially-displaceable lock sleeve to effect axial displacement of the lock sleeve when the drive sleeve is displaced axially. The lock sleeve may have an inner surface arranged to engage one end of a radially-displaceable lock member such as to enable or prevent displacement of the lock member. 
         [0007]    According to another aspect of the present invention there is provided an actuator including a rotary input member, a linear output member and a mechanism for converting rotary motion of the input member to linear motion of the output member, the actuator being arranged to lock the linear output member in a fixed position until there is rotary motion of the input member. 
         [0008]    According to a further aspect of the present invention there is provided an actuator including a rotary input member, a linear output member and a mechanism for converting rotary motion of the input member to linear motion of the output member, the actuator being arranged to displace a lock mechanism from a locking to a release state when rotary motion is applied to the input member. 
         [0009]    A linear actuator, for use in aircraft actuation systems, according to the present invention will now be described, by way of example, with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a view of the exterior of the actuator in a locked, stowed state; 
           [0011]      FIG. 2  is a sectional side elevation view of a part of the actuator in a locked, stowed state, to a larger scale; 
           [0012]      FIG. 3  is a sectional side elevation view of the actuator when drive is applied initially to unlock the ram but prior to extension of the ram; 
           [0013]      FIGS. 4 and 4A  are sectional side elevation views of the actuator as the ram begins to be extended while the lock keys are driven outwardly, with  FIG. 4A  being an enlarged detail of  FIG. 4 ; 
           [0014]      FIGS. 5 and 5A  show the actuator more fully extended with the lock keys driven fully out as the ram continues to a fully deployed position, with  FIG. 5A  being an enlarged detail of  FIG. 5 ; 
           [0015]      FIGS. 6 ,  6 A and  6 B are a sectional side elevation views of the actuator with the ram extended and where drive is applied to stow the ram, with  FIGS. 6A and 6B  being enlarged views of different parts of  FIG. 6 ; and 
           [0016]      FIGS. 7 and 7A  are sectional side elevation views of the actuator as the ram arrives at the stowed position and the lock sleeve drives the lock keys inwardly into the ram groove, with  FIG. 7A  being an enlarged detail of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]    With reference first to  FIGS. 1 and 2 , the actuator has an outer casing  1  of generally cylindrical shape and is supported approximately midway along its length by two gimbals for pivoting movement about an axis at right angles to the length of the casing. At the left-hand end of the casing  1 , on one side, there is an input drive connection  5  in the form of a bevel gear mounted to the axial drive shaft  6 . A lead screw and nut mechanism indicated by the numeral  40  and  42  converts the rotary motion of the axial drive shaft  6  into linear motion of a generally cylindrical ram member  11  so that this is extended out of or retracted into the right-hand end of the casing  1 . The ram member  11  has an eye  12  at its far end to which a member to be displaced, such as a door or panel, is attached. When the ram member  11  is fully retracted into the casing  1  it is locked in the retracted position by the mechanism until a rotary drive is applied by via the bevel gear  5  to extend the ram. 
         [0018]    The bevel gear  5  is supported in the casing  1  by a bearing  24 . The bevel gear  5  has an internally-splined sleeve  25  extending coaxially around an externally splined region located midway along an axial drive shaft  6 . The right-hand end of the drive shaft  6  is enlarged radially, is hollow and open at its end, providing a cylindrical portion  27 . On its external surface, the cylindrical portion  27  is cut with an Acme, helical thread lead screw  28 . The Acme thread  28  is engaged by an internally-threaded collar  29  at the rear, left-hand end of a lost motion coaxial drive sleeve  30 . The forward, right-hand end of the drive sleeve  30  supports on its outside surface a radially-extending thrust bearing  33 , the purpose of which will be explained later. 
         [0019]    The forward, right-hand end of the drive sleeve  30  is also internally splined and engages splines  132  on the outside of the rear end of a tubular output shaft  32 . At its right-hand, forward end  34  the output shaft  32  has internal splines  35 , which engage external splines  36  towards the rear, left-hand end of a ball screw shaft  40 . It can be seen, therefore, that rotation of the first bevel gear  5  is transferred via the drive shaft  6 , the drive sleeve  30  and the output shaft  32  to cause rotation of the ball nut shaft  40 . 
         [0020]    The ball screw shaft  40  has an external thread  41  in which ball bearings are captured. This cooperates with a translating ball nut  42  incorporating an eight circuit internal ball return path. The nut  42  embraces the shaft  40  and is fixed in the rear, left-hand end of the ram member  11  so that rotation of the shaft is translated into linear, axial displacement of the nut and hence of the ram member. 
         [0021]    The mechanism includes a lock arrangement for positively retaining the ram  11  in the primary stow or retracted position, where the ram is at the left-hand end of its travel. The lock is located in the direct path of the torque as delivered from the bevel gearing  5  and incorporates a lost motion mechanism so that priority is given to locking or unlocking before drive is applied to the linear ball screw  40 . 
         [0022]    The mechanism includes a lock sleeve  50 , which is slidable along the inside of the casing  1  and is urged forwardly, to the right, by a helical spring  51  in compression between a fixed plate  52  projecting inwardly from the casing and an inwardly-projecting ledge  53  at the rear end of the lock sleeve. A shallow collar  54  with inclined ends projects inwardly of the lock sleeve  50  a short distance from the forward end of the sleeve. In the stowed, retracted position shown in  FIG. 2 , the collar  54  engages the outer end  55  of the lock keys  56  in the form of radially-extending bolts slidable in respective, radially-extending recesses  57  formed in a fixed cylindrical support housing  58 . Both the outer ends  55  and inner ends  59  of the lock keys  56  have bevelled or chamfered edges. Inward displacement of the lock keys  56  is limited by a follower  72  projecting forwardly under the lock key  56  as the locking extension sleeve  64  is driven to the right with the ball nut  42 . In the stowed position shown in  FIG. 2 , the inner end  59  of the lock keys  56  are located in a groove  63  extending around the outside of a locking extension sleeve  64  projecting rearwardly and fixed at the rear end of the ball screw nut  42 . The groove  63  has a flat floor, is wider (as viewed in the drawings, that is, in a direction parallel to the actuator axis) than the lock keys  56  and has inclined sides. It can be seen that, when the lock keys  56  are held in by the lock sleeve  50 , no movement of the ram member  11  is possible even when very high external tension or compression loads are applied to the forward end  12  of the ram. 
         [0023]    When the ram  11  is to be extended, as shown in  FIG. 3 , rotary drive is applied to the bevel gear  5  and to the drive shaft  6 . Because of the lower mechanical force needed, the first few input rotations cause the drive sleeve  30  to be displaced rearwardly, to the left, along the Acme screw  28  and hence pulls the thrust bearing  33  with it. The left-hand face of the thrust bearing  33  engages the right-hand face of the ledge  53  on the lock sleeve  50  and thereby pulls this to the left against the action of the spring  51 . It can be seen that this displaces the collar  54  away from the lock keys  56  and thereby opens a space above the lock keys. The lock sleeve  50  is, therefore, shifted axially by the lost motion drive sleeve  30  before the Acme ball screw  40  and nut  42  converts the rotary motion into linear motion of the ram  11 . 
         [0024]    Once the thrust bearing  33  has been driven fully along the Acme screw  28  it comes into contact with a thrust washer  70 , which acts as an axial stop. All input torque is now automatically applied to the spline connection of the drive sleeve  30  and the output shaft  32 , which drives the ball screw  40 , ball nut  42  and ram member  11  forwardly, to extend the ram to the right. 
         [0025]      FIGS. 4 and 4A  show that the locking extension sleeve  64  also moves forwardly, the inclined rear side  66  of the groove  63  engaging the bevelled rear edge of the lock keys  56  to drive them outwardly and disengage the lock mechanism. As the extension sleeve  64  moves forwardly it is followed by a follower  72  under the action of a helical spring  73 . The follower  72  has a short, forwardly-projecting cylindrical wall  74  indicated by a broken, hidden line. 
         [0026]    As the extension sleeve  64  moves to a more fully deployed position, as shown in  FIGS. 5 and 5A , the follower  72  moves to its fully extended position in contact with the support housing  58 , with the wall  74  projecting beyond the inner end of the lock keys  56  and thereby prevents them being displaced inwardly. 
         [0027]    When rotation is applied to the input in the opposite sense, to cause the ram member  11  to stow or retract, as shown in  FIGS. 6 ,  6 A and  6 B, this first causes the drive sleeve  30  and thrust bearing  33  to advance forwardly, to the right, along the Acme screw  28  to its full extent, as limited by engagement with a forward thrust washer  75 . The spring  51  can now push the lock sleeve  50  forwardly until the incline on the forward end of its collar  54  engages the rear-facing chamfer  60  on the lock keys  56 . This produces an inwardly-directed force vector acting on the lock keys  56  but their movement is prevented by the follower  72 , which is still in the forward position. 
         [0028]    Continued rotation of the drive shaft  30  and the output shaft  32  causes the ram member  11  to be pulled inwardly until its extension sleeve  64  displaces the follower  72  rearwardly, as shown in  FIGS. 7 and 7A , and its groove  63  moves into alignment with the lock keys  56 . This allows the force vector between the lock sleeve  50  and the keys  56  to push them inwardly into the groove  63  and thereby lock the ram  11  in its stowed position. 
         [0029]    The locking and unlocking processes are totally automatic and do not require any additional signals or devices. In the stowed position, the actuator is mechanically and positively locked. An optional proximity sensor can be used to sense the position of the lock sleeve  50  and provide a lock indication to the control logic circuit if desired. The lock keys cannot be disengaged by any external forces and allow uncontrolled movement of the actuator ram.