Patent Publication Number: US-2022228654-A1

Title: Screw drive with self-locking mechanism

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application Ser. No. 63/139,574, filed on Jan. 20, 2021, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     Screw drive systems and more particularly screw drive systems with mechanical locking mechanisms. 
     BACKGROUND 
     Screw drive type linear actuators typically include a longitudinal screw and a nut that rides on the screw. As the screw is driven to rotate about its longitudinal axis, the nut translates axially. Rotating the screw drive in a first direction will cause the nut to extend and rotating the screw drive in a second direction will cause the nut to retract. In some applications, it is desirable to be able to mechanically fix the axial position of the nut on the shaft to prevent uncommanded motion of the nut. Fixing the axial position of the nut is particularly desirable when the nut is subject to external loads. 
     SUMMARY 
     The present disclosure provides a screw type linear actuator that includes a system for automatically fixing the nut in an axial position when it is retracted. In the depicted embodiment, when the system is commanded to operate the screw, the nut can automatically unlock. When the system screw is retracted fully, it automatically engages a mechanical lock. In the depicted embodiment, the lock does not require electrical power to remain engaged. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The following drawings are illustrative of particular embodiments of the present disclosure and therefore do not limit the scope of the present disclosure. The drawings are not to scale and are intended for use in conjunction with the explanations in the following detailed description. Embodiments of the present disclosure will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements. 
         FIG. 1  is a cross-section of an embodiment of the screw drive of the present disclosure in a first state; 
         FIG. 2  is a cross-section of the screw drive of  FIG. 1  in a second state; 
         FIG. 3  is a cross-section of the screw drive of  FIG. 1  in a third state; 
         FIG. 4  is a cross-section of the screw drive of  FIG. 1  in a fourth state; 
         FIG. 5  is a cross-section of the screw drive of  FIG. 1  in a fifth state; 
         FIG. 6  is a cross-section of the screw drive of  FIG. 1  in a sixth state; 
         FIG. 7  is a cross-section of the screw drive of  FIG. 1  in a seventh state; 
         FIG. 8  is a cross-section of an alternative embodiment of the screw drive of  FIG. 1  in a first state; 
         FIG. 9  is a cross-section of the screw drive of  FIG. 8  in a second state; 
         FIG. 10  is a cross-section of the screw drive of  FIG. 8  in a third state; 
         FIG. 11  is a cross-section of the screw drive of  FIG. 8  in a fourth state; 
         FIG. 12  is a cross-section of the screw drive of  FIG. 8  in a fifth state; 
         FIG. 13  is a cross-section of the screw drive of  FIG. 8  in a sixth state; and 
         FIG. 14  is a cross-section of an alternative embodiment of the screw drive of  FIG. 1 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of the present disclosure, examples of which are described herein and illustrated in the accompanying drawings. While the invention will be described in conjunction with embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     Referring to the figures, the actuator of the present disclosure is described herein in further detail. In the depicted embodiment, the linear actuator  10  includes a screw  12  including a first end portion  42  and a second end portion  14 . In the depicted embodiment, both the first end portion  42  and the second end portion  14  include cylindrical shaft portions that define a common longitudinal screw axis SA. In the depicted embodiment, the second end portion  14  includes a screw thread  16  defined on an exterior surface. It should be appreciated that many alternative configurations are possible. 
     In the depicted embodiment, the linear actuator  10  includes a nut  18  coaxially arranged on the second end portion  14  of the screw  12 . In the depicted embodiment, the nut  18  has an inner aperture that is configured to mate with the screw thread  16  of the second cylindrical portion of the screw  12 . In the depicted embodiment, the nut  18  is configured to axially translate along the second end portion  14  of the screw  12  from a retracted position to an extended position when the screw  12  is rotated relative to the nut  18 . It should be appreciated that many alternative configurations are possible. 
     In the depicted embodiment, the linear actuator  10  includes a torque transmitting screw drive member that is configured to transmit torque to the screw  12  to drive the rotation of the screw  12 . Referring more particularly to  FIGS. 1-7 , in one depicted embodiment of the actuator of the present disclosure, the torque transmitting screw drive member takes the form of a sliding drive gear  20  that includes a female gear  22  (e.g., a female spline gear) at a first end  24  and a cylindrical locking segment interface surface  26  at an opposed second end  28 . It should be appreciated that many other alternative configurations are possible. For example, referring more particularly to  FIGS. 8-13 , the torque transmitting screw drive member of the actuator  60  is a gear member  30  that has an inner aperture mated with a portion of the screw  12  and having a geared external cylindrical surface. This alternative configuration of the torque transmitting screw drive member will be described in further detail below with reference to the embodiment depicted in  FIGS. 8-13 . It should be appreciated that many other alternative configurations are also possible. 
     In the depicted embodiment, the linear actuator  10  includes a mechanical nut locking system configured to automatically lock the nut  18  when the nut  18  is retracted. In the depicted embodiment, the mechanical nut locking system is configured to automatically disengage the mechanical lock when the torque transmitting screw drive member is driven to transmit torque to the screw  12  in a direction that extends the nut  18 . In the depicted embodiment, the locking and unlocking of the nut  18  happens automatically as part of the normal operation of the actuator  10 . It should be appreciated that many alternative embodiments are possible including embodiments wherein the locking is less automatic or manual. 
     In the depicted embodiment, when the torque transmitting screw drive member is rotated in a direction to extend the nut  18  (e.g., clockwise), the torque transmitting screw drive member translates axially prior to transmitting substantial torque to the screw  12 . In the depicted embodiment, the axial translation of the torque transmitting screw drive member operates to disengage (unlock) the mechanical nut locking system. After the mechanical nut locking system is disengaged as a result of the translational movement of the torque transmitting screw drive member, additional rotation of the torque transmitting screw drive member causes the screw  12  to rotate thereby extending the nut  18 . It should be appreciated that many other alternative configurations are also possible. 
     In the depicted embodiment, when the torque transmitting screw drive member is driven to retract the nut  18  from an extended position, the screw drive member rotates the screw  12  to retract the nut  18 . After the nut  18  is retracted, the torque transmitting screw drive member subsequently translates axially without further rotating the screw  12  and this translation engages (locks) the mechanical nut locking system. In the depicted embodiment, the translational movement at both ends of the process is referred to as “loss motion” as there is rotation of the torque transmitting screw drive member that does not directly result in axial translation of the nut  18 . It should be appreciated that many other alternative configurations are also possible. 
     As discussed above, in one depicted embodiment, the torque transmitting screw drive member is a sliding drive gear  20  shown in  FIGS. 1-7 . In this depicted embodiment, the sliding drive gear  20  is generally cylindrical and includes a female gear  22  at a first end  24 . In the depicted embodiment, the sliding drive gear  20  includes an annular cavity that has a geared periphery which is configured to engage a geared drive gear/shaft. In the depicted embodiment, the sliding drive gear  20  includes a cylindrical locking segment interface surface  26  at a second end  28 . In the depicted embodiment, the cylindrical locking segment interface surface  26  selectively supports the locking segments. In the depicted embodiment, the sliding drive gear  20  includes a helical slot  32  that engages a pin  34  that extends inwardly from the first end portion  42  of the screw  12 . In the depicted embodiment, the helical slot  32  and pin  34  configuration enables the torque transmitting screw drive member to rotate without rotating the screw  12 . It should be appreciated that many alternative configurations are possible. 
     In the depicted embodiment, the mechanical nut locking system includes one or more locking members  36  that extend through a portion of the first end portion  42  of the screw  12 . In the depicted embodiment, the locking member  36  is a segmented ring. In the depicted embodiment, the locking members  36  are configured to selectively engage a retaining lip  38  of the nut  18 . The locking members  36  can be ball bearing structures, pin structures, spring loaded stops, a segmented ring, or any number of other structures. The segments in the depicted embodiment move radially based on the ramped geometry of the cylindrical locking segment interface surface  26 . In an alternative embodiment, the locking members  36  can be spring biased in a particular direction such as radially inwardly or outwardly. It should be appreciated that many alternative configurations are possible. 
     In the depicted embodiment, the mechanical nut locking system includes a locking member retention sleeve  40 . In the depicted embodiment, the locking member retention sleeve  40  is coaxial with the first end portion  42  of the screw  12  and is spring biased toward the second end portion  14  of the screw  12 . In the depicted embodiment, the locking member retention sleeve  40  includes a shoulder that slides on the first end portion  42  of the screw  12 . In the depicted embodiment, the locking member retention sleeve  40  rides against the nut  18  when the nut  18  is retracted and slides into place over the locking members  36  as the nut  18  begins to extend. The locking member retention sleeve  40  of the depicted embodiment prevents the locking members  36  from moving out of position. It should be appreciated that many other alternative retention configurations are possible. 
     In the depicted embodiment, the first end portion  42  of the screw  12  defines a cylindrical cavity  44  concentric about a longitudinal screw axis SA. In the depicted embodiment, the sliding drive gear  20  is positioned within the cavity  44 . In the depicted embodiment, a bearing  52  interfaces between the sliding drive gear  20  and the nut cavity. It should be appreciated that additional bearings could be incorporated or the existing bearings could be eliminated. Many alternative configurations are possible. 
     In the depicted embodiment, the nut  18  includes a first end portion that defines a cylindrical nut cavity  46  that is configured to receive a portion of the first end portion  42  of the screw  12 . In the depicted embodiment, the nut cavity  46  includes an inwardly radially extending retaining lip  38 . In the depicted embodiment, the sliding drive gear  20  is configured to translate axially which radially biases the locking members  36  into engagement with the retaining lip  38  of the nut cavity  46 . As discussed above, the sliding drive gear  20  is configured to rotate about the screw axis SA and translate axially without rotating the screw  12 . Since the screw  12  does not rotate during the axial translation of the sliding drive gear  20 , the nut  18  remains stationary during the locking and unlocking operations. In the depicted embodiment, the initial rotation of the sliding drive gear  20  in a first direction translates the sliding drive gear  20  without rotating the screw  12  and subsequent rotation of the sliding drive gear  20  in the first direction rotates the screw  12  and drives axial motion of the nut  18 . It should be appreciated that many alternative configurations are possible. 
     In the depicted embodiment, the actuator  10  includes a no-back system  54  arranged about the first end portion  42  of the screw  12 . No-back systems are useful to prevent back driving of the nut  18  when the nut  18  is extended or partially extended. No-back systems can be used with the actuator of the present disclosure. For additional information regarding no-back systems see U.S. Pat. No. 6,109,415 to Morgan et al. filed on May 29, 1998, which is hereby incorporated by reference in its entirety. 
     In the depicted embodiment, the actuator  10  comprises a locking member retention sleeve  40  coaxially arranged with the first end portion  42  of the screw  12 . In the depicted embodiment, the segment retention sleeve  40  is spring biased toward the second end portion  14  of the screw  12 . In the depicted embodiment, the locking member retention sleeve  40  includes a shoulder  58  that slides on the first end portion  42  of the screw  12  and a lip  50  that engages a portion of a housing to limit the axial translation of the locking member retention sleeve  40  in the second direction. In the depicted embodiment, the shoulder  58  in a first position retains the locking member  36  in the first end portion  42  of the screw  12 . It should be appreciated that many alternative configurations are possible. 
     Referring to  FIGS. 8-13 , an alternative embodiment of the actuator of the present disclosure is described in further detail. In the depicted embodiment, the linear actuator  60  includes a screw  62  having a first cylindrical portion  64  and a second cylindrical portion  66 . The first cylindrical portion  64  includes a first end and a second end. The first cylindrical portion  64  has a first hand screw lead (e.g., left hand lead) defined on an exterior surface. The second cylindrical portion  66  includes a first end and a second end. The second cylindrical portion  66  has a second hand screw lead (e.g., right hand lead) defined on an exterior surface. In the depicted embodiment, the actuator  60  includes a flange  68  located between the first cylindrical portion  64  and the second cylindrical portion  66 . In the depicted embodiment, the actuator  60  includes a mechanical stop  70  located at the first end of the first cylindrical portion  64  of the screw  62 . In the depicted embodiment, the mechanical stop  70  is also a flange. It should be appreciated that many alternative configurations are possible. For example, the flange  68  could be any mechanical stop. 
     In the depicted embodiment, the actuator  60  includes a nut  74  coaxially arranged on the second cylindrical portion  66  of the screw  62 . The nut  74  includes an inner aperture mated with the second hand screw lead of the second cylindrical portion  66 . It should be appreciated that many alternative embodiments are possible. 
     In the depicted embodiment, the actuator  60  includes a gear member  30  coaxially arranged on the first cylindrical portion  64  of the screw  62 . In the depicted embodiment, the gear member  30  has an inner aperture mated with the first hand screw lead of the first cylindrical portion  64  of the screw  62 . In the depicted embodiment, the gear member  30  defines a geared external cylindrical surface  72 . The geared external cylindrical surface  72  functions as a planetary gear. It should be appreciated that many alternative embodiments are possible. 
     In the depicted embodiment, the gear member  30  is configured such that when torque is applied to the gear member  30  in a first direction (counter clockwise) via the geared external cylindrical surface  72  the gear member  30  rotates about the screw  62  and translates axially away from the flange  68  until the gear member  30  applies an axial force against the mechanical stop  70  at which point the torque transmitted by the gear member  30  drives the screw  62  to rotate with the gear member  30  and thereby causes the nut  74  to translate axially towards the flange  68 . The gear member  30  can apply an axial force against the mechanical stop  70  via direct contact or via contacting other components that press up against the mechanical stop  70 . It should be appreciated that many alternative configurations are possible. 
     In the depicted embodiment, the gear member  30  is configured such that when torque is applied to the gear member  30  in a second direction (clockwise) via the geared external cylindrical surface  72  the gear member  30  rotates about the screw  62  and translates axially until the gear member  30  applies an axial force against the flange  68  at which point the torque drives the screw  62  to rotate with the gear member  30  and thereby causes the nut  74  to translate axially away from the flange  68 . The gear member  30  can apply the axial force against the flange  68  by abutting against the flange  68  or by abutting against components that are abutted against the flange  68 . It should be appreciated that many alternative configurations are possible. 
     In the depicted embodiment, the actuator  60  is configured such that when the gear member  30  applies an axial force on the flange  68  and the nut  74  is in a retracted position at least one axially extending flange pin  66  extends from the gear member  30  through the flange  68  into the nut  74  and thereby prevents relative rotation between the nut  74  and the screw  62 . It should be appreciated that many alternative configurations are possible. 
     In the depicted embodiment, the actuator  60  is configured such that when torque is applied to the gear member  30  in a second direction (clockwise) via the geared external cylindrical surface  72  the gear member  30  rotates and translates axially towards the mechanical stop  70 . In the depicted embodiment, when torque in the second direction is continued to be applied to the gear member  30  the screw  62  rotates with the gear member  30  which drives the nut  74  to translate axially towards the second end of the second portion of the screw  62 . In the depicted embodiment, the pins (pin  66 ) that lock the nut  74  from rotating relative to the screw  62  are retracted as the gear member  30  translates axially towards the mechanical stop  70 . It should be appreciated that many alternative configurations are possible. 
     Referring to  FIG. 14 , an alternative embodiment of the actuator of the present disclosure is described in further detail. In the depicted embodiment, the actuator  80  includes an axially translating locking sleeve  82  that extends over a flange  84 . In the depicted embodiment, the flange  84  includes a rim portion  86  that extends radially towards a nut  88 . In the depicted embodiment, the nut  88  includes a radial locking member recess  90  that receives a radially locking member  92 . In the depicted embodiment, the radially locking member  92  is held in engagement with the radial locking member recess  90  when the translating locking sleeve  82  is biased against the flange  84  by a gear member  94 . In the depicted embodiment, the translating locking sleeve  82  is spring biased towards the first end of the first cylindrical portion of the screw  96 . In the depicted embodiment, when the gear member  94  translates axially away from the flange  84  the translating locking sleeve  82  moves axially towards the first end of the first cylindrical portion thereby allowing the radially locking member  92  to move radially outwardly from the radial locking member recess  90 . 
     One aspect of the invention includes a linear actuator comprising: a screw including a first end portion and a second end portion, the first end portion defining a cylindrical cavity concentric about a longitudinal screw axis, the second end portion including a cylindrical shaft portion concentric about the longitudinal screw axis, the second end portion having an external thread; a nut coaxially arranged on the second cylindrical portion having an inner aperture having an inner thread engaged with the external thread of the second end portion of the screw, the nut including a first end portion that defines a cylindrical nut cavity that is configured to receive a portion of the first end portion of the screw, the nut cavity including an inwardly radially extending retaining lip; a locking member extending through a portion of the first end portion of the screw and configured to catch on the retaining lip of the nut cavity when in a first position; a sliding drive gear including a gear interface at a first end and a locking member interface at a second end, wherein the sliding drive gear is configured to extend and retract axially and thereby radially bias the locking member into engagement with the retaining lip of the nut cavity; and wherein initial rotation of the sliding drive gear in a first direction translates the sliding drive gear axially without rotating the screw and subsequent rotation of the sliding drive gear in the first direction rotates the screw and thereby drives axial motion of the nut. 
     Another aspect of the invention includes a linear actuator wherein the sliding drive gear includes a generally cylindrical body, a first end portion including an annular cavity having a gear periphery configured to engage a geared drive, and a second end portion having a cylindrical outer surface configured to selectively support the locking segments. 
     Another aspect of the invention includes a linear actuator wherein the axially sliding drive gear includes a helical slot that engages a pin that extends inwardly from the first end portion of the screw. 
     Another aspect of the invention includes a linear actuator that further comprises a bearing interfacing between the sliding drive gear and the nut cavity. 
     Another aspect of the invention includes a linear actuator that further comprises a no-back system arranged about the first end portion of the screw. 
     Another aspect of the invention includes a linear actuator that further comprises a locking member retention sleeve coaxial with the first end portion of the screw, the locking member retention sleeve is spring biased toward the second end portion of the screw. 
     Another aspect of the invention includes a linear actuator that further comprises a locking member retention sleeve coaxial with the first end portion of the screw and spring biased toward the second end portion of the screw, wherein the locking member retention sleeve includes a shoulder that slides on the first end portion of the screw and a lip that engages a portion of a housing to limit the translation of the locking member retention sleeve in the second direction, wherein the shoulder in a first position retains the locking segment in the first end portion of the screw. 
     Another aspect of the invention includes a linear actuator comprising: a screw including a first cylindrical portion and a second cylindrical portion, the first cylindrical portion including a first end and a second end, the first cylindrical portion having a first hand screw lead defined on an exterior surface, the second cylindrical portion including a first end and a second end, the second cylindrical portion having a second hand screw lead defined on an exterior surface; a flange located between the first cylindrical portion and the second cylindrical portion; a mechanical stop located at the first end of the first cylindrical portion of the screw; a gear member coaxially arranged on the first cylindrical portion of the screw, the gear member having an inner aperture mated with the first hand screw lead of the first cylindrical portion, the gear member defining a geared external cylindrical surface; a nut coaxially arranged on the second cylindrical portion having an inner aperture mated with the second hand screw lead of the second cylindrical portion; wherein when the gear member is configured such that when torque is applied to the gear member in a first direction via the geared external cylindrical surface, the gear member rotates about the screw and translates axially away from the flange until the gear member applies an axial force against the mechanical stop at which point the torque drives the screw to rotate with the gear member and thereby causes the nut to translate axially towards the flange; and wherein when the gear member is configured such that when torque is applied to the gear member in a second direction via the geared external cylindrical surface, the gear member rotates about the screw and translates axially until the gear member applies an axial force against the flange at which point the torque drives the screw to rotate with the gear member and thereby causes the nut to translate axially away from the flange. 
     Another aspect of the invention includes a linear actuator wherein the linear actuator is configured such that when the gear member applies an axial force on the flange and the nut is in a retracted position, flange pins extend from the gear member through the flange into the nut and thereby prevents relative rotation between the nut and the screw. 
     Another aspect of the invention includes a linear actuator wherein the gear member is configured such that when torque is applied to the gear member in a second direction (clockwise) via the geared external cylindrical surface, the gear member rotates and translates axially towards the mechanical stop, wherein when torque in the second direction is continued to be applied to the gear member the screw rotates with the gear member, wherein the nut translates axially towards the second end of the second portion of the screw when the screw rotates in the second direction; and wherein pins that lock the nut from rotating relative to the screw are retracted as the gear member translates towards the mechanical stop. 
     Another aspect of the invention includes a linear actuator wherein the linear actuator includes an axially translating locking sleeve that extends over the flange, wherein the flange includes a rim portion that extends towards the nut, wherein the nut includes a radial locking member recess that receives a radially locking member, wherein the radially locking member is held in engagement with the radial locking member recess when the translating locking sleeve is biased against the flange by the gear member, wherein the translating locking sleeve is spring biased towards the first end of the first cylindrical portion, wherein when the gear member translates axially away from the flange the translating locking sleeve moves axially towards the first end of the first cylindrical portion thereby allowing the radially locking member to move radially outwardly from the radial locking member recess. 
     The various embodiments described above are provided by way of illustration only and should not be construed to limit the claims attached hereto. Those skilled in the art will readily recognize various modifications and changes that may be made without following the example embodiments and applications illustrated and described herein, and without departing from the true spirit and scope of the following claims.