Abstract:
A mechanical linear actuator having a tubular member that is defined by a housing for rotatably and axially supporting a circular nut, a lead screw is mated to the circular nut so that it can move axially in and out of the tubular member. A torsion spring clutch brake is wound about the circular nut to normally brake the nut and thus prevent the lead screw from moving into or out of the tubular member. An unlocking mechanism can remotely unwind the torsion spring clutch brake to sufficiently release the circular nut and thus allow the lead screw to pass in and out of the tubular member. An adjustable stop is provided for adjusting the stroke of the actuator.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention generally relates to the field of mechanical actuators and more specifically to a mechanical actuator assembly that can replace a hydraulic actuator as used, for example, in connection with a reclining seat apparatus. 
       BACKGROUND OF THE INVENTION 
       [0002]    Reclining chair apparatus are commonly known, such as those presently used in the airline industry. Typically, seat adjustment or positioning mechanisms that are used in these apparatus include a hydraulic cylinder that provides a number of features including those that enable the seatback to be dynamically adjusted between an upright position and an infinite number of reclined positions. 
         [0003]    It is has become desirable to provide a relatively less complex mechanical lock assembly that includes similar features as those that are presently found in hydraulic counterparts. These features may include unlimited position locking, infinite travel adjustment, and a manual override while providing for a smooth and controlled motion of the seat back. 
       SUMMARY OF THE INVENTION 
       [0004]    Therefore and according to one version of the invention, there is provided a mechanical linear actuator comprising an elongated tubular member which is defined by an end housing having an axial through opening. An elongated lead screw is slidably contained within the opening having a male threaded section upon an outer surface thereof. A cylindrical drive nut is mounted for rotation within said housing that contains a female thread that mates with the male threaded portion on the lead screw so that the lead screw moves axially as the nut rotates within the housing. A spring loaded clutch brake engages the nut and acts to normally hold the nut in a first braked position wherein the nut is restrained from rotating in said housing and a second released position wherein the nut is free to rotate within said housing. A control mechanism is provided for manually moving the clutch brake between the first braked position and a second released position. 
         [0005]    In one version of the invention, a manual override is provided that enables a reclined seat back on the chair to be brought to an upright position by someone who is not seated in the chair pushing the back rest toward the upright position. 
         [0006]    In one version of the invention, the clutch brake is urged into a braked condition by a wrap spring and is moved to a release position by a remote push button mechanism that acts through a control cable to reposition a lever arm that is in contact with the wrap spring. 
         [0007]    These and other features of the invention will become readily apparent from the following Detailed Description of the invention which is to be read in association with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a partial side view with portions broken away of a reclining chair that contains a linear actuator that embodies the teachings of the present invention; 
           [0009]      FIG. 2  is an enlarged perspective view of the linear actuator that is shown in  FIG. 1 ; 
           [0010]      FIG. 3  is a further enlarged perspective view of a drive system subassembly utilized in the present actuator; and 
           [0011]      FIG. 4  is a side view in section of the present actuator. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring initially to  FIG. 1 , there is illustrated a mechanical actuator, generally referenced  10 , that is attached to a reclining chair  12  such as found on aircraft, buses, theater and the like wherein the positioning of which is controlled by a person that is seated in the chair. The chair typically contains a stationary seat  13  and an adjustable back rest  15  that is movably connected to the seat by means of a hinged linkage assembly  16 . The linkage includes a back frame  17  that is rotatably coupled to the seat by means of a pivot pin  18 . One end of the back frame is secured to the back rest while the opposite end of the back frame is pivotably connected to a first clevis  20  that is mounted at one end of the actuator  10 . The opposing end of the actuator is also equipped with a second clevis  21  which in turn is pivotably coupled to the seat by a clevis pin  23 . As will be explained in greater detail below, the actuator is capable of being stroked between a fully extended configuration wherein the back rest is in an upright position and a fully compressed position wherein the back rest is in a fully inclined position. The inclined position is shown in phantom outline in  FIG. 1 . 
         [0013]    Turning now more specifically to  FIGS. 2-4 , the mechanical actuator  10 , which embodies the teachings of the present invention, is shown in greater detail. The actuator includes an elongated tubular member  25  that has a housing  26  supported at one end thereof. The tubing contains a blind hole  27  that is aligned along the axis  28  of the actuator and which extends substantially along the length of the tube  25 . The blind hole opens into a radially expanded cylindrical chamber  30  within the housing which is coaxially aligned with the blind hole. The chamber, in turn, opens to the surrounding ambient through the outer end face  31  of the housing. 
         [0014]    As best seen in  FIG. 4 , a cylindric drive nut  32  is contained within the chamber  30  so that it can freely rotate about axis  28  of the actuator. The outer surface of the nut is supported within the chamber by a pair of spaced apart circular bearings  33 - 33  that are fitted into the chamber  30  and which restrict the lateral movement of the drive nut. Washers  34  and  35  are also mounted within the housing chamber which, in turn, restrict the axial movement of the nut. 
         [0015]    With further reference to  FIG. 3 , the cylindrical drive nut contains an internal female thread  37  that is arranged to mate with a male thread  38  that surrounds a major portion of the actuator lead screw  40 . A torsional wrap spring  41  is wound about the outer surface of the cylindrical drive nut and serves as part of the clutch brake unit  39  in the assembly. 
         [0016]    The wrap spring contains an axially extended tab  42  on the final turn at one end of the spring and a radially extended tab  43  that is contained on the final turn of the spring at the opposite end thereof. As shown in  FIG. 2 , the housing  26  is provided with an axially disposed cutout  44  that is arranged to capture the end tab  42  of the wrap spring to prevent the tab from moving in a circumferential direction. The opposing end tab  43  is contained within a circumferential opening  45  that is formed in the housing and which permits the tab to move circularly within the opening. A collar  46  encircling the housing contains a raised lever arm  48  against which tab  43  rides in contact. The collar is held in the assembly within a circular groove  47  formed in the underside of a bracket  49  that is mounted upon the housing. Lever arm  48  is located adjacent to the bracket  49 . The bracket contains a flexible hollow cable  50  which passes upwardly through the arm rest  51  of the chair  12  ( FIG. 1 ). The cable slidably contains a length of control wire  53 , one end of which is connected to a control button  54  which is mounted on the inside of the chair arm rest  51 . The opposite end  55  of the cable is attached to the lever arm  48 . When the control button is actuated, the lever arm is pulled in a clockwise direction by the cable which, in turn, causes the tab  43  to rotate in the same direction. This action releases the cylindrical drive nut  32  allowing the nut to rotate freely within the housing. 
         [0017]    The cable contains a hex head nut  56  that is rotatably supported within the bracket  49  upon a circular pivot  57 . The nut further contains an internal thread that mates with a threaded shank  58  mounted upon the end of the cable. Accordingly by turning the hex head nut  56 , the position of the hollow cable  50  can be preset to limit the movement of the control wire  53 . A lock nut  59  is also mounted upon the threaded shank  58  which prevents the adjusting screw from rotating once the control wire has been selectively positioned within the bracket. 
         [0018]    As noted above with reference to  FIG. 1 , compressing the axial length of the actuator will cause the back rest of the chair to be tilted back about pivot  18  from its home or upright position. Accordingly, the back rest can be brought to an infinite number of positions within the stroke limit of the actuator. The stroke limit is dictated by how far the lead screw  40  can travel into the blind hole  27  that is contained within the aligned tubular member  25 . The tubular member contains a pair of opposed linear slots  63  that are formed in the sidewall of the tube. Each slot is axially aligned with the axis  28  of the actuator and extends along the tube to substantially the same length. The left hand end of the lead screw as viewed in  FIG. 4  has a reduced section  66  into which a pin  65  is press fitted. The pin, in assembly, passes through both of the slots in the tubular member and is seated in arresting contact with the end face  64  of the housing  26  when the lead screw is in its fully extended position (see  FIG. 2 ). The outer surface of the tubular member contains a male thread  67  that is coextensive with the slots  63  and a circular stop nut  69  is threadably mounted thereon. The stop nut thus can be moved to an infinite number of positions along the threaded section of the tubular member  26 . The pin  65  has a length such that it extends outwardly through both slots so that it will arrest against the stop nut as the lead screw moves into the tubular member. As should be now evident, the axial distance between the end face  64  of the housing  26  and the location of the stop determines the compressive limit of the actuator and thus the amount of incline afforded the back rest of the chair. At least one set screw  70  is threaded into the stop nut which serves to lock the stop nut against the tubular member when the nut is placed in a desired location. 
         [0019]    A helically wound compression spring  72  encircles the exposed length of the lead screw. The spring is adapted to act between the raised flange  73  on clevis  21  and the end face  31  of housing  26 . As can be seen, the spring becomes compressed as the lead screw moves into the tubular member and thus provides a force that urges the actuator to its fully extended home position. 
         [0020]    In operation, a person seated in the chair simply has to activate the control button which unwraps the wrap spring, which frees the circular nut so it can rotate freely within the housing on the tubular member section of the actuator. A slight rearward pressure by the occupant upon the back rest causes the lead screw to move axially through the nut into the tubular member. At this time the lead screw acts as a driver to turn the nut in place as it moves through the housing. When a desired tilt position is reached, the control button is released and the wrap spring locks the drive nut in place preventing further movement of the back rest. To return the back rest to its home or upright position, the chair occupant has only to reactuate the control button releasing the holding pressure of the clutch brake and allow the compression return spring to return the back rest to the home position. The stop nut arrangement on the tubular member further limits the stroke of the actuator and can be quickly and easily adjusted. Accordingly, chairs equipped with the present actuator can be readily adapted for placement within a wide range of location having varied space limitations. By the same token, the control button mechanism can also be easily adjusted to unwrap the wrap spring and thus release the drive nut. Accordingly, the actuator can be rapidly and conveniently set up and installed either in the factory or in the field without need of special tools or the like. 
         [0021]    The present actuator is also provided with a manual override feature that permits the unit to be returned to a fully extended position when the clutch brake is holding the unit in a compressed position. The drive nut is arranged to rotate in a counter-clockwise direction as the lead screw advances axially to compress the unit. The torsional wrap spring of the clutch brake is wound about the drive nut so that it will strengthen its hold upon the nut as the lead screw places a torque upon the drive nut that wants to drive the drive nut in a counter-clockwise direction. By the same token, the lead screw will turn the drive nut in the opposite or clockwise direction as the unit is extended. This, in turn, causes the wrap spring of the clutch brake to want to partially unwrap and release the drive nut. The amount of press-fit between the wrap spring and the drive nut determines how much rotational force will be required to unwrap the wrap spring and release the drive nut. This rotational force along with the lead screw pitch determines the axial force required to extend the unit. When the present actuator is employed in a reclining chair embodiment, the actuator override release force is generally set at about 20 pounds greater than the maximum output force of the compression spring. This amount of force can be easily generated through the chair linage by an average size person (flight attendant or the like) with little exertion by simply pushing a reclined seat back forward toward its upright position. 
         [0022]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof to adapt to particular situations without departing from the scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope and spirit of the appended claims.