Patent Publication Number: US-2023151880-A1

Title: Electric actuator having hand-screw release device

Description:
FIELD 
     The disclosure belongs to the technical field of linear actuation technologies, and more particularly relates to an electric actuator having a hand-screw release device. 
     BACKGROUND 
     An electric actuator, also referred to as a linear actuator, is widely used in fields such as furniture, medical equipment, and solar power generation. The electric actuator mainly comprises: a drive motor, a drive worm, a worm gear, a screw rod, and a nut. The operating principle of electric actuators goes like this: the drive motor activates the drive worm to rotate; the drive worm which meshes with the worm gear actuates the worm gear to rotate; then rotation of the worm gear drives the screw rod to rotate, and rotation of the screw rod drives the nut to move axially; since the nut is usually attached to an inner tube, the axial movement of the nut results in extension and retraction motion of the inner tube. 
     Owing to application environments of the electric actuator, a clutch device is additionally provided mainly to disengage power transmission between the drive motor and the rotary screw rod when the electric actuator encounters drive motor failure or power-off or other circumstances which require power cutoff, whereby the rotary screw rod may be manually activated to realize reverse push. For example, the Chinese Patent Application No. CN201621013870.3 discloses a solution of additionally providing a clutch device to an electric actuator. 
     In addition, in order to generate a resistance upon retraction of the electric actuator, a self-locking device is usually provided on the electric actuator; the self-locking device generally comprises a friction sleeve and a self-locking torsion spring sleeved outside the friction sleeve, such that when the friction sleeve rotates reversely along with the rotary screw rod, the self-locking torsion spring retracts radially to embrace the friction sleeve, whereby to generate a self-locking resistance against the rotary screw rod. Such self-locking devices provided on an electric actuator have been well known. 
     However, conventional electric actuators are only provided with either a clutch device or a. self-locking device; even the clutch device and the self-locking device are both provided, the driving units for driving the two devices are usually provided standalone, such that in the case of need to control the clutch device and the self-locking device simultaneously, it would be very complex to manipulate the two devices independently and synchronously. 
     Moreover, conventional clutch devices or self-locking devices are substantially driven by a cable pulling a cable pulling lever; however, it is difficult to control the pulling strength or stroke of such a driving manner, resulting in operation clumsiness of the clutch device or self-locking device. Hand-screw release devices are already available in the market. For example, the Chinese Utility Patent No. CN201220326831.4 discloses a hand-screw release solution. However, such a hand-screw device is usually mounted on an end portion of the electric actuator, and if the installed stroke of the electric actuator is restricted, the mount space for the electric actuator with a hand-screw device would be affected. 
     SUMMARY 
     To overcome the above and other drawbacks in conventional technologies, the disclosure provides an electric actuator having a hand-screw release device, which enables control of two devices with one hand-screw release device and offers smoother, more convenient operation. 
     The present disclosure adopts the following technical solution. 
     An electric actuator having a hand-screw release device comprises: a housing, a drive motor, a transmission assembly, a rotary screw rod and a driving nut, the drive motor activating, via the transmission assembly, the rotary screw rod to rotate, rotation of the rotary screw rod driving the driving nut to move axially along the rotary screw rod; and the electric actuator further comprises: 
     a clutch device provided between the transmission assembly and the rotary screw rod, configured to engage or disengage power transmission between the transmission assembly and the rotary screw rod; 
     a self-locking device configured to produce a friction resistance against the rotary screw rod when the rotary screw rod rotates reversely, wherein the self-locking device comprises a release torsion spring for unlocking the self-locking device; and 
     a hand-screw release device provided on the housing, the hand-screw release device comprising a. first driving member, a second driving member, and a release rotary knob for activating the first driving member and the second driving member, the first driving member being connected to the clutch device, the second driving member being configured to connect the self-locking device, and the release rotary knob being turned to present an initial state and a completely released state, wherein in the course of switching from the initial state to the completely released state, the first driving member activates the clutch device to disengage power connection, and the second driving member activates the release torsion spring to release. 
     The present disclosure offers the following benefits: 
     The electric actuator according to the present disclosure is provided with both a clutch device and a self-locking device, which improves functional versatility of the electric actuator; moreover, the clutch device in combination with the self-locking device further offers an advantage that the rotary screw rod, which is substantially in a completely free rotation state after the clutch device disengages the power transmission, easily results in a very fast retraction speed of the electric actuator, while the self-locking device may provide certain resistance to prevent the rotary screw rod from retracting too fast. 
     Secondly, the self-locking device according to the disclosure is further provided with a release torsion spring, such that the self-locking device is unlockable by itself; when the release torsion spring is released, the self-locking device is in an unlocked state; now, irrespective of whether the electric actuator rotates forwardly or reversely, the self-locking device substantially produces no resistance against the rotary screw rod, which renders the electric actuator in a state of quick release, i.e., the electric actuator may retract quickly. 
     Additionally, the electric actuator according to the disclosure is further provided with a hand-screw release device in this embodiment. The hand-screw release device comprises a first driving member, a second driving member, and a release rotary knob configured to activate the first driving member and the second driving member, the first driving member and the second driving member being configured to drive the clutch device and the self-locking device, respectively, such that when it is needed to quickly release the electric actuator, an operator manipulates the hand-screw release device to be in a completely released state, which renders the clutch device in a disengaged state and meanwhile the self-locking device in an unlocked state; accordingly, the user may conveniently control the two devices by manipulating the hand-screw release device. 
     Finally, the hand-screw release device according to the present disclosure is released via the release rotary knob. Such rotational setting enables better control of the driving strokes of the first driving member and the second driving member, thereby mitigating the instantaneous over large driving stroke occurring to the first driving member and second driving member as much as possible, and thereby offering a smoother operation. Moreover, the hand-screw release device according to the present disclosure is disposed on the housing, rather than being disposed on an end portion of the electric actuator like a conventional hand-screw device, which eliminates a need of additionally increasing the axial retracted height of the electric actuator, without affecting the axial mount space. 
     Preferably, the hand-screw release device further comprises a pull lever axially movable along the rotary screw rod, a rack portion being provided on the pull lever, the release rotary knob being attached with a release gear which meshes with the rack portion. 
     Preferably, the electric actuator comprises an outer tube, and an inner tube extendable and retractable relative to the outer tube, a mount base being mounted on the outer tube, the release rotary knob being rotatably mounted on the mount base, the pull lever being at least partially slidably mounted on the mount base. 
     Preferably, a limit step is provided on the pull lever, a pull lever reset spring for resetting the pull lever is provided between the limit step and the mount base. 
     Preferably, the second driving member comprises a push block, the push block being provided on the pull lever or being provided integrated with the pull lever, the push block having a guiding face, the release torsion spring comprising a pin which extends radially, wherein when the pull lever moves axially, the guiding face on the push block abuts against the pin, resulting in outward expanding of the release torsion spring. 
     Preferably, the first driving member comprises a swing link rotatable relative to the housing, wherein axial movement of the pull lever brings the swing link to rotate, and swinging of the swing link axially pushes the clutch device. 
     Preferably, the transmission assembly comprises a drive worm and a drive worm gear, the drive worm being connected to the drive motor, the drive worm gear being sleeved outside the rotary screw rod, the clutch device being provided between the drive worm gear and the rotary screw rod. 
     Preferably, the clutch device comprises an adapter coupling, a toothed groove in transmission fit with the adapter coupling being provided on the drive worm gear, the adapter coupling being sleeved over the rotary screw rod and axially movable relative to the rotary screw rod. 
     Preferably, the self-locking device comprises a first friction sleeve and a second friction sleeve; the first friction sleeve and the second friction sleeve being sleeved over the rotary screw rod, respectively, an axial end face of the first friction sleeve abutting against an axial end face of the second friction sleeve, the first friction sleeve rotating synchronously with the rotary screw rod, the second friction sleeve rotating freely relative to the rotary screw rod, a self-locking torsion spring being sleeved over the first friction sleeve, and the release torsion spring being sleeved over the second friction sleeve; or, the self-locking device comprises a third friction sleeve, the third friction sleeve rotating synchronously with the rotary screw rod, the release torsion spring being sleeved over the third friction sleeve. 
     Preferably, in the course of the hand-screw release device&#39;s returning to the initial state from the completely released state, the second driving member is firstly disengaged from the release torsion spring on the self-locking device to generate a self-locking force, and after the release torsion spring returns to the initial state, the first driving member is correspondingly disengaged from the clutch device. 
     These characteristics and advantages of the disclosure will be disclosed in detail through the embodiments below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Hereinafter, the disclosure will be described in further detail with reference to the accompanying drawings, among which: 
         FIG.  1    is a first overall schematic view of an electric actuator according to a first embodiment of the disclosure; 
         FIG.  2    is a first exploded schematic view of the electric actuator according to the first embodiment of the disclosure; 
         FIG.  3    is second exploded schematic view of the electric actuator according to the first embodiment of the disclosure; 
         FIG.  4    is a local enlarged schematic view of the electric actuator according to the first embodiment of the disclosure; and 
         FIG.  5    is an exploded schematic view of internal parts in the electric actuator according to the first embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the technical solutions of the present disclosure will be explained and illustrated through embodiments with reference to the accompanying drawings. However, the embodiments are only some embodiments of the present disclosure, not all of them. Other embodiments obtained by those skilled in the art without exercise of inventive work based on the examples in the embodiments all fall within the protection scope of the present disclosure. 
     In the description of the present disclosure, it should be understood that the orientational or positional relationships indicated by the terms “inner,” “outer,” “upper,” “lower,” “left,” and “right,” etc. are orientational or positional relationships based on the drawings, which are intended merely for facilitating description of the present disclosure and simplifying; relevant illustrations, not for indicating or implying that the devices or elements compulsorily possess those specific orientations and are compulsorily configured and operated with those specific orientations; therefore, such terms should not be construed as limitations to the present disclosure. 
     First Embodiment 
     As illustrated in  FIGS.  1  to  5   , an electric actuator, also referred to as a linear actuator, is provided in this embodiment. The electric actuator comprises: a housing, an outer tube  13 , an inner tube  14 , a drive motor, a transmission assembly, a rotary screw rod  20 , and a driving nut  21 , wherein the drive motor activates, via the transmission assembly, the rotary screw rod  20  to rotate, and rotation of the rotary screw rod  20  brings the driving nut  21  to move axially along the rotary screw rod  20 ; since the driving nut  21  is securely connected to the inner tube  14 , axial movement of the driving nut  21  brings the inner tube  14  to move axially relative to the outer tube  13  and the housing; a to-be-driven object is connected to an outer end of the inner tube  14 . The electric actuator in this embodiment further comprises: 
     a clutch device provided between the transmission assembly and the rotary screw rod  20 , and configured to engage or disengage power transmission between the transmission assembly and the rotary screw rod  20 ; 
     a self-locking device configured to generate a friction resistance against the rotary screw rod  20  when the rotary screw rod  20  rotates reversely, wherein the self-locking device comprises a release torsion spring  43  for unlocking the self-locking device; and 
     a hand-screw release device provided on the housing, the housing comprising an upper housing  11  and a lower housing  12  in this embodiment; wherein the hand-screw release device comprises a first driving member, a second driving member, and a release rotary knob  55  configured to activate the first driving member and the second driving member, the first driving member being connected to the clutch device, the second driving member being configured to connect the self-locking device, the release rotary knob being turned to present an initial state and a completely released state, wherein in the course of switching from the initial state to the completely released state, the first driving member drives the clutch device to disengage power connection, and the second driving member activates the release torsion spring to release. 
     In this embodiment, the electric actuator is provided with both a clutch device and a self-locking device, which improves functional versatility of the electric actuator; moreover, the clutch device in combination with the self-locking device further offers an advantage that the rotary screw rod  20 , which is substantially in a completely free rotation state after the clutch device disengages the power transmission, easily results in a very fast retraction speed of the electric actuator, while the self-locking device may provide certain resistance to prevent the rotary screw rod  20  from rotating too fast, thereby preventing the driving unit  21  from retracting too fast. 
     Secondly, the self-locking device is further provided with a release torsion spring  43 , such that the self-locking device is unlockable by itself; when the release torsion spring is released, the self-locking device is in an unlocked state; now, irrespective of whether the electric actuator rotates forwardly or reversely, the self-locking device substantially produces no resistance against the rotary screw rod  20 , which renders the electric actuator in a state of quick release, i.e., the electric actuator may retract quickly. 
     Additionally, the electric actuator is further provided with a hand-screw release device in this embodiment. The hand-screw release device comprises a first driving member, a second driving member, and a release rotary knob  55  configured to activate the first driving member and the second driving member, the first driving member and the second driving member being configured to activate the clutch device and the self-locking device, respectively, such that when it is needed to quickly release the electric actuator, an operator manipulates the hand-screw release device to be in a completely released state, which renders the clutch device in a disengaged state and meanwhile the self-locking device in an unlocked state; accordingly, the user may conveniently control the two devices by manipulating the one hand-screw release device. 
     Finally, the hand-screw release device in the present disclosure is released via a release rotary knob  55 . Such rotational setting enables better control of the driving strokes of the first driving member and the second driving member, mitigating the instantaneous over large driving stroke occurring to the first driving member and second driving member as much as possible, thereby offering a smoother operation. Moreover, the hand-screw release device according to the present disclosure is disposed on the housing, rather than being disposed on an end portion of the electric actuator like a conventional hand-screw device, which eliminates a need of additionally increasing the axial retracted height of the electric actuator, without affecting the axial mount space. 
     In this embodiment, in order to improve manipulation precision of the release rotary knob  55  when being turned, the hand-screw release device further comprises a pull lever  51  which is axially movable along the rotary screw rod, a rack portion  511  being provided on the pull lever, wherein the rack portion  511  may be constructed integrally with or separately from the pull lever  51 ; the release rotary knob  55  is attached with a release gear  551  in mesh with the rack portion  511 , such that when the release rotary knob  55  is rotated, the release gear  551  is brought to rotate, while rotation of the release gear  551  drives the rack portion  511  to move axially along the rotary screw rod  20 , thereby driving the pull lever  51  to move axially; axial movement of the pull lever  51  brings the first driving member and the second driving member to move, thereby achieving the purpose of driving the clutch device and the self-locking device. 
     In order to install the pull lever  51  more securely, a mount base  6  is mounted on the outer tube in this embodiment, the release rotary knob  55  is rotatably mounted on the mount base  6 , and the pull lever  51  is at least partially slidably mounted on the mount base  6 . As illustrated in  FIGS.  1  and  2   , the mount base  6  is sleeved over the outer tube  13  in this example, the rack portion  511  of the pull lever  51  being disposed in the mount base  6 , a fraction of the pull lever  51  extending out of the mount base  6 ; a base cover plate  61  is provided over the mount base  6  to cover those parts including the release gear  551  and the rack portion  511 . 
     A limit step is provided on the pull lever in this embodiment, a pull lever resetting spring  56  for resetting the pull lever  51  being provided between the limit step and the mount base  6 . In this embodiment, the pull lever comprises a first pull lever and a second pull lever, the first pull lever being configured mainly to drive the first driving member and the second driving member, the corresponding rack portion  511  being provided on the second pull lever, wherein the first pull lever has a rectangular flat shape as a whole and the second pull lever is relative thin cable, thereby forming the limit step at a joint between the first pull lever and the second pull lever; while the pull lever reset spring  56  is disposed between the limit step and the mount base  6 , such that when the force applied upon the release rotary knob vanishes, the corresponding pull lever is reset to the initial position under the action of the pull lever reset spring  56 . 
     In this embodiment, the transmission assembly comprises a drive worm  35  and a drive worm gear  34 , wherein the drive worm  35  is connected to the drive motor, the drive worm gear  34  is sleeved outside the rotary screw rod  20  and coaxial with the rotary screw rod  20 , and the clutch device is disposed between the drive worm gear  34  and the rotary screw rod  20 . In this embodiment, the clutch device is mainly configured to disengage the power link between the drive worm gear  34  and the rotary screw rod  20 . 
     Hereinafter, specific constructions of the clutch device and the self-locking device are described below: 
       FIGS.  4  and  5    illustrate a specific construction of the clutch device in this embodiment. The clutch device comprises a ball bushing  31 , a spline sleeve  32 , and an adapter coupling  33 , wherein the ball bushing  31  is sleeved over the rotary screw rod  20  via a squared section and rotates synchronously with the rotary screw rod  20 ; a plurality of balls are provided on an outer periphery of one end of the ball bushing  31 , the spline sleeve  32  is sleeved outside the ball hushing  31 , and the spline sleeve  32  is constantly in mesh with the drive worm gear  34 , wherein the spline sleeve  32  and the ball set  31  are not directly connected, and the adapter coupling  33  is configured to engage or disengage the spline sleeve  32  with or from the ball bushing  31 , the adapter coupling  33  being axially movable relative to the rotary screw rod  20 . 
     As illustrated in  FIG.  5   , a spline slot fitted with the spline sleeve  32  is provided on an inner wall of the adapter coupling  33  in this embodiment, i.e., the adapter coupling  33  constantly rotates synchronously with the spline sleeve  32 ; a ball groove  332  fitted with balls of the ball bushing  31  is further provided on an inner wall of the adapter coupling  33 , such that when the adapter coupling  33  moves axially towards the balls on the ball bushing  31 , the balls are docked into the ball groove  332 , causing the adapter coupling  33  to be fitted and docked with the ball groove  332 , thereby implementing torque transmission between the adapter coupling  33  and the ball bushing  31 . Therefore, the adapter coupling now serves to couple the rotary screw rod  20  and the drive worm gear  34 . The state illustrated in  FIG.  4    is the state in which the adapter coupling  33  is docked with the ball bushing  31 . When the adapter coupling  33  moves away from the balls, the adapter coupling  33  is disengaged from the ball bushing  31 , whereby to disengage torque transmission between the adapter coupling  33  and the rotary screw rod  20 . 
     In this embodiment, the self-locking device comprises: a first friction sleeve  41 , a second friction sleeve  42 , a release torque spring  43 , and a self-locking torque spring  44 , wherein the second friction sleeve  42  is sleeved outside the first friction sleeve  41 , an outer end face of the first friction sleeve  41  abuts against an inner end face of the second friction sleeve  42 , and the first friction sleeve  41  and the rotary screw rod  20  are positioned via a squared section, i.e., in the circumferential direction, the first friction sleeve  41  and the rotary screw rod  20  rotate synchronously therebetween, while the second friction sleeve  42  rotates freely relative to the rotary screw rod  20 ; and in the axial direction, the outer end face of the first friction sleeve  41  abuts against the inner end face of the second friction sleeve  42 . Meanwhile, the release torque spring  43  is sleeved over the second friction sleeve  42 , the release torque spring  43  always embraces the second friction sleeve  42  in the initial state, and the self-locking torque spring  44  is sleeved over the first friction sleeve  41 . The self-locking device in this embodiment reduces the mount space, mainly the axial space, which facilitates reducing the overall size of the electric actuator. 
     When the inner tube  14  in the electric actuator extends out normally, the drive motor activates, via the clutch device, the rotary screw rod  20  to rotate forwardly; and after the inner tube  14  extends out till a predetermined position, the drive motor stops. At that position, when the inner tube  14  has a retraction tendency, an axial end face of the first friction sleeve  41  abuts against an axial end face of the second friction sleeve  42 ; since the self-locking torque spring  44  serves to embrace the first friction sleeve  41  to produce a resistance and meanwhile the second friction sleeve  42  is also embraced by the release torque spring  43  in a normal state, a friction resistance is produced when the end face of the first friction sleeve  41  abuts against the end face of the second friction sleeve  42 ; the friction resistance generates a resistance against the rotary screw rod  20  to prevent the rotary screw rod  20  from reverse rotation, thereby implementing self-locking. 
     In the case of normal retraction of the electric actuator, the drive motor drives, via the clutch device, the rotary screw rod  20  to rotate reversely; at this point, the rotating torque of the rotary screw rod  20  overcomes the self-locking force provided by the self-locking device, and the rotary screw rod  20  continues reverse rotation. 
     When the electric actuator needs to retract rapidly before extending out to the predetermined position, this embodiment enables unlocking of the self-locking device, thereby achieving the purpose of rapid release. In this embodiment, the unlocking is mainly implemented via the second driving member. The second driving member specifically comprises: a push block  52 , the push block  52  being preferably integrated with the pull lever, i.e., in this embodiment, the self-locking device and the clutch device share one pull lever  51 ; the push block  52  is provided with a guiding face  521 ; the release torque spring  43  comprises a pin  431  extending radially; wherein the guiding face  521  is disposed on a side face of the push block  52 , such that when the pull lever  51  is pulled to move, the guiding face  521  on the push block  52  abuts against the pin  431  to outwardly expand the release torque spring  43 ; when the release torque spring  43  is expanded outwardly, the resistance between the release torque spring  43  and the second friction sleeve  42  will be diminished correspondingly, In this state, when the end face of the first friction sleeve  41  abuts against the end face of the second friction sleeve  42 , the second friction sleeve  42  will rotate synchronously along with the first friction sleeve  41 ; as such, the first friction sleeve  41  does not produce a resistance against the rotary screw rod  20 , thereby achieving a resistance-free state of the rotary screw rod  20 . At this point, if the clutch device disengages the connection, the self-locking device will also be unlocked. Under this state, the rotary screw rod  20  is substantially in a freely idling state, which enables rapid retraction of the driving nut  21 . 
     Additionally, in this embodiment, by gradually pushing the release torque spring  43  via the guiding face  521 , the self-locking device is gradually diminished, such that the self-locking device will not vanish abruptly, thereby achieving an objective of stepless adjustment. 
     In view that the clutch device and the self-locking device are both provided in this embodiment, the axial force is transmitted in the following manner: 
     When the inner tube  14  of the electric actuator extends till a predetermined position and has a tendency of retraction, the axial force of the inner tube  14  is transmitted to the driving nut  21 ; the driving nut  21  transmits the axial force to the rotary screw rod  20 ; when the rotary screw rod  20  is subjected to the axial force, the ball bushing  31  abuts against the shoulder position of the rotary screw rod  20 , such that the axial force applied against the rotary screw rod  20  is first transmitted to the ball bushing  31 ; since the end face of the ball bushing  31  abuts against the end face of the first friction sleeve  41 , i.e., the ball bushing  31  and the first friction sleeve  41  are axially limited, the axial force is transmitted to the first friction sleeve  41 ; since the tail end face of the first friction sleeve  41  abuts against the inner end face of the second friction sleeve  42 , the axial force is transmitted to the second friction sleeve  42 ; and since a conical roller bearing  25  is provided between the tail end face and the tail pull head  15  of the second friction sleeve  42 , the axial force will be finally transmitted to the tail pull head  15  via the conical roller bearing  25 . 
     In this embodiment, the ball bushing  31 , the first friction sleeve  41 , and the second friction sleeve  42  jointly constitute an axial limit kit, wherein the rotary screw rod  20  transmits the axial force to the tail pull head  15  via the axial limit kit; from the perspective of the overall process of axial force transmission, the adapter coupling  33  in this embodiment is never subjected to the action of the axial force; therefore, it is also labor-saving to turn the adaptor coupling  33 . 
     Meanwhile, since the clutch device is not subjected to the axial force from the rotary screw rod  20 , the service life of the clutch device may be significantly improved. Of course, it is noted that, if the self-locking device is not provided in the electric actuator, a shaft sleeve-like construction may be additionally provided to the rotary screw rod  20 , serving as an axial limit kit. 
     In this embodiment, the first friction sleeve  41  preferably comprises a front sleeve and a rear sleeve, and a thrust bearing is provided to abut against the axial middle between the front sleeve and the rear sleeve; in an alternative embodiment, the first friction sleeve  41  may be an integral sleeve. 
     In this embodiment, the first driving member comprises: a swing link  53  connected to the pull lever  51 . In an actual installation, an upper end of the swing link  53  is rotatably connected to the pull lever  51 . Specifically, a notch is provided at the bottom of the pull lever  51 , the top of the swing link  53  is positioned in the notch; the middle of the swing link  53  is rotatably mounted on a swing link sleeve  531 ; a lower end of the swing link  53  is connected to the adapter coupling  33 , such that when the pull lever  51  is pulled to move, the swing link  53  swings to push the adapter coupling  33  to move axially. 
     In order to optimize manipulation of the clutch device and the self-locking device, the operation sequence of the clutch device and the self-locking device is optimized in this embodiment: 
     As illustrated in  FIG.  2    and  FIG.  3   , in the initial state, the guiding face  521  of the push block  52  needs to move a segment of stroke to be in contact with the pin  431  of the release torque spring  43 ; this segment of stroke may be understood as an idle stroke of the push block  52 ; during this idle stroke, the clutch device operates normally, such that the adapter coupling  33  is first turned; meanwhile, upon reset, the self-locking device is first self-locked, and then the clutch device performs power engagement, offering an advantage that after the self-locking device produces a self-locking force, the rotating speed of the rotary screw rod  20  decreases, such that when the adapter coupling  33  is engaged with the ball bushing  31 , no damages are caused to the adapter coupling  33  and the ball bushing  31 , thereby significantly extending their service life. 
     It is noted that the constructions of the self-locking device and the clutch device are not limited to those illustrated in this embodiment. An exemplary self-locking device may merely comprise one third friction sleeve, wherein the third friction sleeve rotates synchronously with the rotary screw rod  20 , and the release torque spring  43  is sleeved over the third friction sleeve; in the initial state, the release torque spring  43  embraces the third friction sleeve to produce a resistance against the rotary screw rod  20 ; in this case, the release torque spring  43  serves as the self-locking torque spring  44 ; after the release torque spring  43  is pushed to move by the push block  52 , the resistance from the release torque spring  43  against the third friction sleeve vanishes. An exemplary clutch device may be implemented by an alternative combination of the spline sleeve  32  and the spline. 
     What have been described above are merely embodiments of the present disclosure; however, the protection scope of the present disclosure is not limited thereto. A person skilled in the art should understand that the disclosure includes, but is not limited to, the contents described in the drawings and the embodiments. Any modifications without departing from the functions and structural principles of the disclosure will be included within the scope of the claims.