Multi-stage electromechanical actuator with upper and lower position locking

Abstract

This invention proposes a multi-stage electromechanical actuator with upper and lower position locking, which is highly efficient and has strong fault tolerance. The invention is achieved through the following technical solution: the main and auxiliary motors are driven by a gear train unit, and the splined sleeve transmission shaft engages with the main lead screw. Through the main lead screw nut with a first-stage upper and lower position locking device, the auxiliary lead screw is driven, forming a dual-redundant electrical channel with two motor drive paths. The thrust angular contact ball bearing ring, assembled in the hollow blind hole of the main lead screw nut, constrains the auxiliary lead screw. Through the auxiliary lead screw nut with a second-stage upper and lower position locking device, the secondary piston cylinder, isolated by the first-stage piston cylinder stop ring, is driven to perform telescopic movement within the first-stage piston cylinder. The first-stage piston cylinder then performs telescopic movement within the actuator's outer cylinder moving cavity, giving the entire electromechanical actuator system two-to-two electrical redundancy fault-tolerant channels. This invention can significantly reduce the length of the locking structure within a specified stroke, solving the problem of conventional multi-stage electromechanical actuators locking the motor shaft and being unable to withstand large loads.

Description

Technical Field

[0001] This invention relates to the field of aerospace electromechanical actuators with high safety and reliability requirements, and to a multi-stage electromechanical actuator with upper and lower double-end locking and a long-stroke retraction structure applied to electromechanical actuators. Background Technology

[0002] Electromechanical actuators (EMAs) are widely used not only in aerospace vehicles but also in the driving of large robotic arms, large engineering machinery, and active suspension systems in marine and other defense and civilian fields. EMAs have grown alongside the aerospace industry and are gradually permeating other fields. An EMA is a mechatronic device that converts the output command signals of a servo controller / driver into mechanical quantities such as speed, displacement, and load to drive the controlled object at speed, displacement, and load. As a linear motion actuator, an EMA is an energy conversion device used to achieve linear reciprocating motion or oscillating motion less than 360° of a working mechanism. Typically, an EMA consists of a driver, drive motor, reduction gearbox, ball screw, ball screw pair transmission components, detection feedback and load actuator outer cylinder assembly, piston rod assembly, self-locking assembly, detection feedback position detection element, and load. It indirectly or directly controls the target motion by controlling the operation of the actuator. Due to technological and material limitations, EMA (Electromechanical Actuator) has relatively low power. The driver is composed of analog electronic devices, the actuator mainly uses a brushed DC motor, and the transmission device uses a ball screw. Currently, electromechanical actuator transmission mechanisms suffer from a large number of rigid bodies and long transmission chains. As the load's rotational inertia increases, the dynamic load effect generated by the inertial load and its own transmission mechanism becomes significant. Existing electromechanical actuators typically have an actuator rod hinged to a lower support and rocker arm at one end, and a gear reducer at the other end. A permanent magnet synchronous motor's shaft passes through the gear reducer and connects to a locking device. The permanent magnet synchronous motor drives the ball screw pair in the electromechanical actuator through the gear reducer to achieve linear extension and retraction of the actuator rod. Its working principle is to apply control actions to the controlled object or system based on the controller's output signal, outputting force in the required manner to change the response of the controlled object or system. Due to the single-motor dual-redundancy working mode, for various reasons, one motor may completely fail to work, leaving only one motor to complete the task. In this case, the output torque is only 50% of the normal operating mode, the system performance deteriorates significantly, and the task cannot be completed. In fault-tolerant operation, the power output of the faulty channel in an EMA system must be shared by other normal channels, i.e., power redistribution occurs; for a torque-integrated system, this is torque redistribution. This redistribution leads to increased power losses in the motor and inverter, and can also affect mechanical devices. Existing electromechanical actuators with self-locking devices prevent erratic movement caused by external forces when stopped at a defined position. These are typically locked by a mechanical lock within the actuator cylinder. A common type of mechanical lock is a ball lock, which consists of a ball, a locking groove, a conical piston, and a spring.

[0003] In applications where installation space is limited or the working stroke is required to be long, such as aircraft landing gear retraction and extension, and cabin door retraction and extension, the commonly used single-stage electromechanical actuators cannot meet the limited installation space requirements due to their long overall dead structure length. Although a large working stroke retraction and extension can be achieved by using multi-stage electromechanical actuators, conventional multi-stage electromechanical actuators still use the method of locking the motor shaft with a brake to achieve mechanical locking, which has poor reliability and lower load-bearing capacity than mechanical locks, thus making them less practical. Summary of the Invention

[0004] This invention provides a multi-stage electromechanical actuator solution with upper and lower position locking, featuring a simple structure, small installation space, high overload capacity, high reliability and safety, high efficiency, strong fault tolerance, long service life, and the ability to achieve a large working stroke and reliably lock the piston rod. It effectively solves the problem of poor locking capability in conventional multi-stage electromechanical actuators.

[0005] The technical solution adopted by this invention to solve its technical problem is: a multi-stage electromechanical actuator with upper and lower locking, comprising: a gear drive unit that converts the rotational motion of the main motor 1 and auxiliary motor 20 symmetrically arranged on both radial sides of the actuator outer cylinder 3 into the mechanical energy of the main lead screw 4 and the splined sleeve transmission shaft 22 respectively linked by a reducer in the transmission cavity, and a first-stage piston cylinder 11 that performs telescopic motion in the cylinder body of the actuator outer cylinder 3, characterized in that: the two motors, the main motor 1 and the auxiliary motor 20, pass through the gear drive unit, the splined sleeve transmission shaft 22 engages with the main lead screw 4, and the main lead screw 4 is connected by a first-stage piston cylinder 11 that performs telescopic motion in the cylinder body of the actuator outer cylinder 3. The main screw nut 10 of the first-level upper and lower locking device drives the auxiliary screw 19 to form a dual-redundant electrical channel driven by two motor channels. The thrust angular contact ball bearing collar assembled in the hollow blind hole of the main screw nut 10 constrains the auxiliary screw 19. The auxiliary screw 19 drives the second-level piston cylinder 18, which is isolated by the stop ring of the first-level piston cylinder 11, to perform telescopic movement in the first-level piston cylinder 11 through the auxiliary screw nut 17 with the second-level upper and lower locking device. The first-level piston cylinder 11 performs telescopic movement in the moving cavity of the actuator outer cylinder 3, so that the entire electric actuator system has two-to-two electrical redundancy fault-tolerant channels.

[0006] Compared with the prior art, the present invention has the following advantages: This invention transforms the rotational motion of the main motor 1 and auxiliary motor 20, symmetrically arranged on both radial sides of the actuator outer cylinder 3, into a gear drive unit that drives the main lead screw 4 and the splined drive shaft 22, respectively, through a reducer in the transmission cavity, and the auxiliary lead screw 19 via a splined sleeve. It also includes a first-stage piston cylinder 11 that extends and retracts within the actuator outer cylinder 3. This reduces the actuator's volume and size, improving the adaptability of the locking-function electromechanical actuator to installation space. It not only requires less installation space and has high overload capacity, but also significantly improves load-bearing capacity and rigidity; it avoids the problems of numerous rigid bodies and long transmission chains in current electromechanical actuator transmission mechanisms. Since each dual-winding motor is driven by two sets of power circuits, an electrical double-redundancy structure is first formed. The two motors then convert the output command signals of the servo controller / driver into mechanical quantities such as speed, displacement, and load, which, after passing through the gear transmission system, also form a mechanical double-redundancy structure. This results in a two-to-two redundancy structure with four electrical channels and two motor channels in the entire system. Therefore, the electrical channels have fault tolerance capabilities of "fault-operation, fault-operation". Significant improvements have been made in dynamic and steady-state performance as well as anti-interference capabilities. Steady-state error has been reduced by over 70%, and displacement deviation during interference has been reduced by over 60%. The actuator can still complete the flight mission even if any one motor fails. All motors are operational in normal working mode. When the system is fault-free, all four electrical channels and two motors are operational, with each motor outputting half power. If one electrical channel of one motor fails, that motor operates in single-channel mode, while the other motor operates in dual-channel mode, resulting in a dual-motor, three-channel operating system. If both motors have one electrical channel failure, each motor operates in single-channel mode, resulting in a dual-motor, dual-channel operating system.

[0007] This invention employs two motors, a main motor 1 and an auxiliary motor 20, driven by a gear train. A splined drive shaft 22 engages with a main lead screw 4. The main lead screw 4, via a main lead screw nut 10 equipped with a first-stage upper and lower locking device, drives the auxiliary lead screw 19, forming a dual-redundant electrical channel with two mechanically driven motor pathways. Depending on the actual application environment, a non-similar redundant actuator design can be adopted, enabling various types of redundancy designs for control, drive, and feedback. A single servo motor drives multiple functional actions, achieving interlocking functionality between actions. This improves safety and reliability.

[0008] This invention incorporates a lockable, unlockable upper-level steel ball 5 and a lockable lower-level steel ball 9 mechanical lock between the actuator outer cylinder 3 and the first-stage piston cylinder 11. The main motor 1 can drive the first-stage piston cylinder 11 to lock at the upper and lower ends of the actuator outer cylinder 3 and reliably unlock it. Furthermore, a lockable, unlockable upper-level steel ball 12 and a lockable lower-level steel ball 16 mechanical lock are designed between the first-stage piston cylinder 11 and the second-stage piston cylinder 18. The auxiliary motor 20 can drive the second-stage piston cylinder 18 to lock at the upper and lower ends of the first-stage piston cylinder 11 and reliably unlock it. This mechanical locking mechanism secures the piston rod in both extended and retracted positions, enabling a large working stroke and reliable piston rod locking. The double-end locking and multi-stage long-stroke retraction structure on the two-stage upper and lower locking devices significantly reduces the length of the locking structure within a specified stroke, solving the problem that conventional multi-stage electromechanical actuators cannot withstand large loads due to the brake locking the motor shaft. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the piston rod retracted state structure of the multi-stage electromechanical actuator with upper and lower locking of the present invention; Figure 2 yes Figure 1 Schematic diagram of the piston rod in the extended state; Figure 3 yes Figure 1 A partial cross-sectional left view of the splined drive shaft meshing with the secondary lead screw spline; In the diagram: 1. Main motor; 2. Main transmission gear; 3. Actuator outer cylinder; 4. Main lead screw; 5. First-stage upper steel ball; 6. First-stage upper lock bushing; 7. First-stage locking spring; 8. First-stage lower lock bushing; 9. First-stage lower steel ball; 10. Main lead screw nut; 11. First-stage piston rod; 12. Second-stage upper steel ball; 13. Second-stage upper lock bushing; 14. Second-stage locking spring; 15. Second-stage lower lock bushing; 16. Second-stage lower steel ball; 17. Secondary lead screw nut; 18. Second-stage piston rod; 19. Secondary lead screw; 20. Secondary motor; 21. Secondary transmission gear; 22. Splined sleeve transmission shaft.

[0010] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this does not limit the invention to the scope of the described embodiments. All these concepts should be considered as the content disclosed in this technology and the scope of protection of this invention. Detailed Implementation

[0011] See Figures 1-3In the preferred embodiment described below, a multi-stage electromechanical actuator with upper and lower locking includes: a gear drive unit that converts the rotational motion of a main motor 1 and an auxiliary motor 20 symmetrically arranged on both radial sides of the actuator outer cylinder 3 into mechanical energy that is respectively linked by a reducer in a transmission cavity to a main lead screw 4 and a splined sleeve transmission shaft 22 engaging with an auxiliary lead screw 19; and a first-stage piston cylinder 11 that performs telescopic motion within the cylinder body of the actuator outer cylinder 3, wherein: the two motors, the main motor 1 and the auxiliary motor 20, pass through the gear drive unit, and the splined sleeve transmission shaft 22 engages with the main lead screw 4, and the main lead screw 4 is connected by a first-stage upper and lower locking mechanism. The main screw nut 10 of the locking device drives the auxiliary screw 19 to form a dual-redundant electrical channel driven by two motor channels. The thrust angular contact ball bearing collar assembled in the hollow blind hole of the main screw nut 10 constrains the auxiliary screw 19. The auxiliary screw 19 drives the secondary piston cylinder 18, which is isolated by the stop ring of the primary piston cylinder 11, to perform telescopic movement in the primary piston cylinder 11 through the auxiliary screw nut 17 with the second-stage upper and lower locking device. The primary piston cylinder 11 performs telescopic movement in the moving cavity of the actuator outer cylinder 3, so that the entire electric actuator system has two-to-two electrical redundancy fault-tolerant channels.

[0012] The main screw nut 10 is equipped with a first-level upper and lower locking device that controls the locking of a first-level upper steel ball 5, which is locked in the upper locking groove of the piston head of the first-level piston cylinder 11 and rolled in the locking ring groove of the inner wall of the outer cylinder bottom, and a first-level lower steel ball 9, which is locked in the lower locking groove and rolled along the locking ring groove of the end of the inner wall of the outer cylinder, to achieve locking and unlocking. The auxiliary screw nut 17 is equipped with a second-level upper steel ball 12, which controls the locking of a second-level upper steel ball 12, which is locked in the upper locking groove of the piston head of the second-level piston cylinder 18 and rolled in the locking ring groove of the inner wall of the second-level piston cylinder 18, and a second-level lower steel ball 16, which is locked in the lower locking groove and rolled along the locking ring groove of the end of the inner wall of the second-level upper steel ball 12, to achieve locking and unlocking. The two-level upper and lower locking devices drive the first-level piston cylinder 11 and the second-level piston cylinder 18 to perform two-to-two electrical redundancy fault-tolerant channel extension and retraction movements in the actuator outer cylinder 3 and the moving cavity of the first-level piston cylinder 11 under the drive of the main screw nut 10 and the auxiliary screw nut 17, respectively.

[0013] In an alternative embodiment, during operation, the main motor 1 drives the gear at the shaft end of the main screw 4 to rotate through the main transmission gear 2, thereby driving the main screw nut 10, which in turn drives the first-stage piston cylinder 11 to extend out along the motion cavity of the actuator outer cylinder 3, thereby driving the first-stage upper and lower locking device to push the first-stage upper locking bushing 6 to the right, and the first-stage upper steel ball 5 to disengage from the upper locking groove on the inner wall ring of the piston head of the actuator outer cylinder 3. The step on the right end face of the main screw nut 10 pushes the first-stage piston cylinder 11 out of the motion cavity of the actuator outer cylinder 3, thereby unlocking the mechanical lock of the first-stage piston cylinder 11. The auxiliary motor 20 drives the gear at the end of the splined sleeve transmission shaft 22 to rotate through the auxiliary transmission gear 21, which drives the auxiliary lead screw 19 to rotate synchronously. Through the engagement of the auxiliary lead screw 19 with the auxiliary lead screw nut 17, the secondary piston cylinder 18 extends out along the moving cavity of the primary piston cylinder 11, which pushes the secondary upper and lower locking device to drive the secondary upper lock bushing 13 to move to the right. The secondary upper steel ball 12 disengages from the upper lock groove on the inner wall ring of the secondary piston cylinder 18 and disengages. The right end face of the auxiliary lead screw nut 17 pushes the secondary piston cylinder 18 out of the moving cavity of the primary piston cylinder 11, thereby unlocking the mechanical lock of the secondary piston cylinder 18.

[0014] The gear drive unit includes: an endo-gear transmission system in which the output shaft of the main motor 1 extends into the transmission cavity of the actuator outer cylinder 3, where the gear meshes with the main drive gear 2 to rotate the main lead screw 4; and an endo-gear transmission system in which the output shaft gear of the auxiliary motor 20 meshes with the splined sleeve drive shaft 22 via the auxiliary drive gear 21. The transmission system has multiple gears that transmit power to multiple interconnected gear output ends.

[0015] The inner ring of the thrust angular contact ball bearing, installed in the hollow stepped hole of the actuator outer cylinder 3, is axially limited on the stepped shaft at the necking ring end of the main screw 4 and bears the load of the main screw 4.

[0016] The inner ring of the bidirectional thrust angular contact ball bearing, which is installed in the hollow stepped hole of the main lead screw nut 10, is axially limited on the upper stepped shaft of the auxiliary lead screw 19 and bears the load of the auxiliary lead screw 19.

[0017] The first-stage upper and lower locking device includes: a first-stage upper steel ball 5, which is mounted on the outer annular surface of the piston head of the first-stage piston cylinder 11 and locked in the upper steel ball guide hole and the guide lock hole of the outer annular surface of the actuator outer cylinder 3; a first-stage lower steel ball 9, which is locked in the guide lock hole of the outer annular surface of the piston head; and a first-stage upper locking bushing 6 and a first-stage lower upper locking bushing 8, which are closely attached to the hollow stepped hole wall of the piston head and symmetrically constrain the first-stage locking spring 7 to both ends of the necking groove of the main screw nut 10.

[0018] The second-stage upper and lower locking device includes: a secondary upper steel ball 13, which is mounted on the outer annular surface of the piston head of the secondary piston cylinder 18 and locked in the upper steel ball guide hole of the cylinder wall of the primary piston cylinder 11 and the guide lock hole of the outer annular surface of the piston head; a secondary lower steel ball 16, which is locked in the guide lock hole of the outer annular surface of the secondary piston head; and a secondary upper locking bushing 13 and a secondary lower locking bushing 15, which are closely attached to the hollow stepped hole wall of the secondary piston head and symmetrically facing each other to constrain the secondary locking spring 14 to the two ends of the necking groove of the auxiliary lead screw nut 17.

[0019] When the first-stage piston cylinder 11 moves to the limit position of the actuator outer cylinder 3, the first-stage lower steel ball 9 is opposite to the lower steel ball guide hole on the cylinder wall of the actuator outer cylinder 3. Under the action of the first-stage locking spring 7, the first-stage lower locking bushing 8 pushes the first-stage lower steel ball 9 to the first-stage lower guide locking hole, and locks it into the chamfered surface at the lower end of the first-stage lower locking bushing 8, restricting the movement of the first-stage lower steel ball 9, realizing the mechanical locking of the first-stage lower steel ball 9, thereby locking the first-stage piston cylinder 11.

[0020] When the secondary piston cylinder 18 moves to the lower limit position of the primary piston cylinder 11, the secondary lower steel ball 16 is aligned with the lower steel ball guide hole of the primary piston cylinder 11. Under the action of the secondary locking spring 14, the secondary lower locking bushing 15 pushes the secondary lower steel ball 16 to the secondary lower guide locking hole, and locks it into the lower chamfered surface of the secondary lower locking bushing 15, restricting the movement of the secondary lower steel ball 16 and realizing the mechanical locking of the secondary lower steel ball 16, thereby locking the secondary piston cylinder 18.

[0021] Although the present invention has been described in conjunction with some preferred embodiments, the invention is not limited to these embodiments. Rather, the invention is intended to encompass all alternatives, modifications, and equivalents, provided that such solutions are included. The core concept and protection scope of this invention are defined by the appended claims.

Claims

1. A multi-stage electromechanical actuator with upper and lower position locking, comprising: The gear drive unit converts the rotational motion of the main motor (1) and auxiliary motor (20) symmetrically arranged on both radial sides of the actuator outer cylinder (3) into the mechanical energy of the main screw (4), splined sleeve drive shaft (22), and splined sleeve auxiliary screw (19) respectively linked by the reducer in the transmission cavity, and the first-stage piston cylinder (11) that performs telescopic motion in the cylinder body of the actuator outer cylinder (3), characterized in that: the two motors, the main motor (1) and the auxiliary motor (20), pass through the gear drive unit, the splined sleeve drive shaft (22) engages the main screw (4), and the main screw (4) passes through the main screw with the first-stage upper and lower locking device. The lever nut (10) drives the auxiliary lead screw (19) to form a dual-redundant electrical channel driven by two motor channels in the mechanical system. The thrust angular contact ball bearing ring in the hollow blind hole of the main lead screw nut (10) constrains the auxiliary lead screw (19). Through the auxiliary lead screw nut (17) with the second-stage upper and lower locking device, the secondary piston cylinder (18) isolated by the stop ring of the first-stage piston cylinder (11) moves in the extension and retraction of the first-stage piston cylinder (11). The first-stage piston cylinder (11) moves in the motion cavity of the actuator outer cylinder (3), so that the entire electric actuator system has two-to-two electrical redundancy fault-tolerant channels. The first-stage upper and lower locking device includes: a first-stage upper steel ball (5) mounted on the outer annular surface of the piston head of the first-stage piston cylinder (11) and locked in the upper steel ball guide hole and the guide lock hole of the outer annular surface of the actuator outer cylinder (3) in the direction of the generatrix of the piston head; a first-stage lower steel ball (9) locked in the guide lock hole of the outer annular surface of the piston head; and a first-stage upper locking bushing (6) and a first-stage lower upper locking bushing (8) that are close to the hollow stepped hole wall of the piston head and symmetrically constrain the first-stage locking spring (7) to the two ends of the necking groove of the main screw nut (10). The second-stage upper and lower locking device includes: a secondary upper steel ball (13) mounted on the generatrix direction of the outer annular surface of the piston head of the secondary piston cylinder (18) and locked in the upper steel ball guide hole and the guide lock hole of the outer annular surface of the piston head of the primary piston cylinder (11); a secondary lower steel ball (16) locked in the guide lock hole of the outer annular surface of the secondary piston head; and a secondary upper locking bushing (13) and a secondary lower locking bushing (15) that are closely attached to the hollow stepped hole wall of the secondary piston head and symmetrically constrain the secondary locking spring (14) to the two ends of the necking groove of the auxiliary screw nut (17).

2. The multi-stage electromechanical actuator with upper and lower position locking as described in claim 1, characterized in that: During operation, the main motor (1) drives the main screw (4) to rotate through the main transmission gear (2), which in turn drives the main screw nut (10), causing the first-stage piston cylinder (11) to extend along the motion cavity of the actuator outer cylinder (3), which in turn drives the first-stage upper and lower locking device to push the first-stage upper locking bushing (6) to move to the right. The first-stage upper steel ball (5) disengages from the upper locking groove on the inner wall ring of the piston head of the actuator outer cylinder (3), and the step on the right end face of the main screw nut (10) pushes the first-stage piston cylinder (11) to extend out of the motion cavity of the actuator outer cylinder (3), thereby unlocking the mechanical lock of the first-stage piston cylinder (11).

3. The multi-stage electromechanical actuator with upper and lower position locking as described in claim 2, characterized in that: The auxiliary motor (20) drives the gear at the end of the spline sleeve transmission shaft (22) to rotate through the auxiliary transmission gear (21), which drives the auxiliary lead screw (19)(4) to rotate synchronously. Through the engagement of the auxiliary lead screw nut (17) by the auxiliary lead screw (19), the secondary piston cylinder (18) extends out along the motion cavity of the primary piston cylinder (11), which pushes the secondary upper and lower locking device to drive the secondary upper lock bushing (13) to move to the right. The secondary upper steel ball (12) disengages from the upper lock groove on the inner wall ring of the secondary piston cylinder (18) and the right end face of the auxiliary lead screw nut (17) pushes the secondary piston cylinder (18) to extend out of the motion cavity of the primary piston cylinder (11), thereby unlocking the mechanical lock of the secondary piston cylinder (18).

4. The multi-stage electromechanical actuator with upper and lower position locking as described in claim 1, characterized in that: The gear drive unit includes: an endo-gear transmission system in which the output shaft of the main motor (1) extends into the transmission cavity of the actuator outer cylinder (3) and meshes with the main drive gear (2) to rotate the main lead screw (4); and an endo-gear transmission system in which the output shaft gear of the auxiliary motor (20) meshes with the spline sleeve drive shaft (22) through the auxiliary drive gear (21); the transmission system has multiple gears that transmit to multiple interconnected gear output ends.

5. The multi-stage electromechanical actuator with upper and lower position locking as described in claim 1, characterized in that: The inner ring of the thrust angular contact ball bearing installed in the hollow stepped hole of the actuator outer cylinder (3) is axially limited on the stepped shaft at the necking ring end of the main screw (4) and bears the load of the main screw (4). The inner ring of the bidirectional thrust angular contact ball bearing installed in the hollow stepped hole of the main screw nut (10) is axially limited on the stepped shaft at the upper end of the auxiliary screw (19) and bears the load of the auxiliary screw (19).

6. The multi-stage electromechanical actuator with upper and lower position locking as described in claim 5, characterized in that: The main screw nut (10) is equipped with a first-level upper-level locking device that controls the locking of a primary upper steel ball (5) in the upper locking groove of the piston head of the primary piston cylinder (11) and rolls in the locking ring groove on the inner wall of the outer cylinder bottom, and a primary lower steel ball (9) in the lower locking groove and rolls along the locking ring groove at the end of the inner wall of the outer cylinder to achieve locking and unlocking; the auxiliary screw nut (17) is equipped with a second-level upper-level locking device that controls the locking of a primary upper steel ball (5) in the upper locking groove of the piston head of the secondary piston cylinder (18) and rolls in the locking ring groove on the inner wall of the secondary piston cylinder (18). The upper-level steel ball (12) and the lower-level steel ball (16) which is locked in the lower-level lock groove and rolls along the locking ring groove at the end of the inner wall of the upper-level steel ball (12) realize the second-level upper and lower-level locking device. The two-level upper and lower-level locking devices drive the first-level piston cylinder (11) and the second-level piston cylinder (18) to perform two-to-two electrical redundancy fault-tolerant channel extension and retraction movements in the actuator outer cylinder (3) and the first-level piston cylinder (11) moving cavity, respectively driven by the main screw nut (10) and the auxiliary screw nut (17).

7. The multi-stage electromechanical actuator with upper and lower position locking as described in claim 1, characterized in that: When the first-stage piston cylinder (11) moves to the limit position of the actuator outer cylinder (3), the first-stage lower steel ball (9) is opposite to the guide hole of the lower steel ball on the cylinder wall of the actuator outer cylinder (3). Under the action of the first-stage locking spring (7), the first-stage lower locking bushing (8) pushes the first-stage lower steel ball (9) to the first-stage lower guide locking hole, and locks into the chamfered surface at the lower end of the first-stage lower locking bushing (8), restricting the movement of the first-stage lower steel ball (9) and realizing the mechanical locking of the first-stage lower steel ball (9), thereby locking the first-stage piston cylinder (11).

8. The multi-stage electromechanical actuator with upper and lower position locking as described in claim 1, characterized in that: When the secondary piston cylinder (18) moves to the lower limit position of the primary piston cylinder (11), the secondary lower steel ball (16) is opposite to the guide hole of the lower steel ball on the cylinder wall of the primary piston cylinder (11). Under the action of the elastic force of the secondary locking spring (14), the secondary lower locking bushing (15) pushes the secondary lower steel ball (16) to the secondary lower guide locking hole, and locks it into the lower end chamfered surface of the secondary lower locking bushing (15), restricting the movement of the secondary lower steel ball (16) and realizing the mechanical locking of the secondary lower steel ball (16), thereby locking the secondary piston cylinder (18).

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