CN110989694A

CN110989694A - Electric actuating cylinder with negative feedback control system

Info

Publication number: CN110989694A
Application number: CN201911332141.2A
Authority: CN
Inventors: 邢文涛; 梁文涛; 任明辉; 罗巍
Original assignee: Sichuan Aviation Industry Chuanxi Machine Co ltd
Current assignee: Sichuan Aviation Industry Chuanxi Machine Co ltd
Priority date: 2019-12-21
Filing date: 2019-12-21
Publication date: 2020-04-10

Abstract

A control system of an electric actuating cylinder comprises a driving motor, a transmission gear set, a brake, a linear displacement sensor, a controller and an upper computer in communication connection with the controller; an output shaft of the driving motor and an output shaft of the brake are simultaneously connected to a first transmission shaft through a coupler, namely the driving motor and the brake are coaxially connected, and the first transmission shaft is in transmission connection with the ball screw through a transmission gear set; the screw rod nut is connected with the actuating rod; an inner-side micro switch and an outer-side micro switch which are respectively in communication connection with an upper computer are arranged in the actuator cylinder shell, and the installation positions of the two micro switches correspond to the set movement limit position of the screw nut; and the tail end of the ball screw is provided with a linear displacement sensor, a mandrel of the linear displacement sensor is directly or indirectly connected with the actuating rod, and the linear displacement sensor is in communication connection with an upper computer. The invention realizes real-time feedback of the motion position.

Description

Electric actuating cylinder with negative feedback control system

Technical Field

The invention belongs to the field of actuator control, and particularly relates to an electric actuator with a negative feedback control system.

Background

The actuator cylinder may be classified into a hydraulic actuator cylinder, an electric actuator cylinder, and the like. The electric actuating cylinder control system is mainly used for realizing the control of the electric actuating cylinder and is widely applied to various industries such as aviation, aerospace, weaponry, electronics, ships, nuclear industry and the like.

Hydraulic rams are widely used in hydraulic transmissions and rely on a continuous flow of oil, which is considered incompressible at normal pressures due to the very small amount of compression of the oil. The oil has the vibration absorption capacity, and a hydraulic buffer device can be arranged in the oil path, so that the vibration fastener is not impacted due to processing and assembling errors of a mechanical mechanism, the transmission is very stable, and frequent reversing is convenient to realize; therefore, it is widely used in machines requiring smooth transmission, such as grinding machines, which almost all use hydraulic transmission. Compared with the transmission modes of machinery, electric power and the like, the hydraulic transmission has the advantages that under the condition of outputting the same power, the volume and the mass can be greatly reduced, so that the inertia is small, and the action is sensitive; this is particularly important for hydraulic profiling, hydraulic automation and machines requiring reduced mass. The hydraulic transmission is easy to obtain large force and torque, so that the hydraulic transmission is widely applied to presses, tunnel boring machines, ten thousand ton ship steering engines, ten thousand ton hydraulic presses and the like.

The disadvantages of hydraulic rams are also evident, the high precision required for the manufacture of the hydraulic components, and the high technical requirements for the components and the difficulty of assembly, which make their use and maintenance more critical. Firstly, the fixed ratio transmission is difficult to realize: hydraulic transmission uses hydraulic oil as working medium, and inevitably leaks between surfaces moving relative to each other, and the oil is not absolutely incompressible. Therefore, it is not suitable for the application in the places with strict transmission ratio requirements, such as the transmission system of the thread and gear processing machine. Secondly, the power is not suitable for long-distance transmission: because the pressure oil is transmitted by adopting the oil pipe, the pressure loss is large, and the power is not suitable for being transmitted in a long distance. Air mixed in the oil easily affects the working performance. Thirdly, after air is mixed in the oil liquid, creeping, vibration and noise are easily caused, so that the working performance of the system is influenced. Fourthly, oil is easy to pollute: after the oil is polluted, the reliability of the system operation is influenced, and the fault is not easy to check and remove.

The electric actuating cylinder is widely applied due to the characteristics of simplicity, reliability, good manufacturability, convenience in use and maintenance and the like. Early in the second war, the U.S. C21 autopilot used an electric ram. The early actuating cylinder has small moment, slow response and relatively low control precision, and the development of the two key technologies is greatly promoted later. The novel rare earth permanent magnet material and the special driving module greatly improve the power-to-mass ratio and the reliability of the electric actuating cylinder. Secondly, the occurrence of a Digital Signal Processor (DSP) realizes the digitization of a DSP chip represented by TMS320 series, and greatly improves the real-time processing capability and the anti-interference performance. The brushless direct current motor, the alternating current motor, the DSP and the advanced control strategy are widely applied, so that the electric actuator cylinder technology is further developed, the size is compact, and the installation is convenient; the output torque is large, and the stability is good; simple control, convenient interface with a digital system and the like. The development of electric actuators can be summarized in three aspects: the performance is high in precision, efficiency, reliability and adaptability; the functions are miniaturized, lightened and multifunctional; systematized and compositely integrated on the level. The general trend of future development is to realize full digitalization, intellectualization and integration by adopting a motor technology mainly based on a rare earth permanent magnet brushless direct current motor, an alternating current motor and the like, a digital control technology based on a microprocessor and a control rule based on a modern control theory. The traditional control system has the following difficulties:

1) after the electric actuating cylinder acts in place, the stability of the final state of the electric actuating cylinder is not well maintained under the comprehensive action of external force, mechanism installation clearance, deformation and other factors;

2) in the motion process of the electric actuating cylinder, only stop position detection is carried out on the position of the stroke of the electric actuating cylinder, and no real-time position monitoring signal feedback exists in the motion process, so that the possibility of signal false alarm cannot be eliminated;

3) the current detection and control strategy is not deep, especially the output torque and the torque fluctuation are influenced, the dynamic response time is long, and the system reliability is not high.

Disclosure of Invention

The invention provides an electric actuator cylinder with a negative feedback control system for solving the problem that the prior art has no real-time position feedback in the motion process, and realizes the detection of real-time position information in the motion process by arranging a linear displacement sensor.

The specific implementation content of the invention is as follows:

an electric actuating cylinder with a negative feedback control system comprises an actuating cylinder shell, a telescopic execution mechanism, a driving motor, a transmission gear set, a brake, a linear displacement sensor, a controller and an upper computer in communication connection with the controller, wherein the controller is in communication connection with the driving motor and the brake; the telescopic actuating mechanism arranged in the actuating cylinder shell comprises a ball screw arranged in the actuating cylinder shell and a screw nut sleeved on the ball screw through a steel ball, and the screw nut is linearly and slidably connected with a long-strip key arranged in the actuating cylinder shell; an output shaft of the driving motor and an output shaft of the brake are simultaneously connected to a first transmission shaft through a coupler, namely the driving motor and the brake are coaxially connected, and the first transmission shaft is in transmission connection with the ball screw through a transmission gear set; the screw rod nut is connected with the actuating rod; an inner-side micro switch and an outer-side micro switch which are respectively in communication connection with an upper computer are arranged in the actuator cylinder shell, and the installation positions of the two micro switches correspond to the set movement limit position of the screw nut; moreover, a linear displacement sensor is mounted at the tail end of the ball screw, a mandrel of the linear displacement sensor is directly or indirectly connected with the actuating rod, and the linear displacement sensor is in communication connection with an upper computer;

the two sides of the screw nut are respectively provided with an inner disc spring group and an outer disc spring group through a sleeve sleeved outside the ball screw, and a convex part for limiting the linear movement limit positions of the inner disc spring group and the inner disc spring group is arranged in the actuator cylinder shell.

In order to better realize the invention, further, the transmission gear set comprises a second transmission shaft, a transmission gear Z1, a transmission gear Z2, a transmission gear Z3 and a transmission gear Z4;

the transmission gear Z1 is arranged on the first transmission shaft, and the transmission gear Z1 is meshed with the transmission gear Z2; the transmission gear Z2 and the transmission gear Z3 are arranged on the second transmission shaft side by side, and the transmission gear Z3 is meshed with the transmission gear Z4; the transmission gear Z4 is in meshing transmission with a ball screw which is rotatably arranged in the actuator cylinder shell.

In order to better realize the invention, further, the brake device also comprises a manual brake mechanism arranged on the actuating cylinder shell; the manual brake mechanism comprises a brake gear Z5, a brake gear Z6, an emergency pull ring and a brake gear shaft;

one end of the brake gear shaft extends out of the actuating cylinder shell and is transversely inserted into the emergency pull ring, and a brake gear Z5 is installed at one end of the brake gear shaft, which is positioned in the cavity of the actuating cylinder shell; the brake gear Z5 corresponds to the position of a brake gear Z6 arranged on the first transmission shaft; when the emergency pull ring is pulled out of the brake gear shaft, the brake gear Z5 and the brake gear Z6 can be meshed and then clamped.

In order to better implement the invention, further, the brake is a direct current electromagnetic actuator.

To better implement the present invention, further, the linear displacement sensor is an LVDT position sensor.

In order to better implement the present invention, further, the controller is a PI controller.

The invention also provides an electric actuating cylinder with a negative feedback control system, which comprises an actuating cylinder shell, a telescopic actuating mechanism, a driving motor, a transmission gear set, a brake, a linear displacement sensor and a controller, wherein the controller is in communication connection with the driving motor and the brake; the telescopic actuating mechanism arranged in the actuating cylinder shell comprises a ball screw arranged in the actuating cylinder shell and a screw nut sleeved on the ball screw through a steel ball, and the screw nut is linearly and slidably connected with a long-strip key arranged in the actuating cylinder shell; an output shaft of the driving motor and an output shaft of the brake are simultaneously connected to a first transmission shaft through a coupler, namely the driving motor and the brake are coaxially connected, and the first transmission shaft is in transmission connection with the ball screw through a transmission gear set; the screw rod nut is connected with the actuating rod; an inner-side micro switch and an outer-side micro switch which are respectively in communication connection with the controller are arranged in the actuator cylinder shell, and the installation positions of the two micro switches correspond to the set movement limit position of the screw nut; moreover, a linear displacement sensor is arranged at the tail end of the ball screw, a mandrel of the linear displacement sensor is directly or indirectly connected with the actuating rod, and the linear displacement sensor is in communication connection with the controller;

Compared with the prior art, the invention has the following advantages and beneficial effects:

1) a linear displacement sensor is added, so that the real-time monitoring of position information in the motion process is realized;

2) the PI controller is adopted, so that the detection and control of the system on the current are improved;

3) the direct-current electromagnetic magnetic actuator is arranged, so that the electric actuating cylinder can be automatically locked in time when a system fails, and the stability of the electric actuating cylinder is improved.

Drawings

FIG. 1 is a block diagram of an electric ram control system;

FIG. 2 is a schematic diagram of the operation of the electric actuator;

FIG. 3 is a schematic view of an electric actuator and a driving motor product;

FIG. 4 is a schematic view of the LVDT position sensor mounted to a ball screw and a ball screw actuator housing.

Wherein: 1. the brake device comprises an actuating cylinder shell, 2, a driving motor, 3, a transmission gear set, 4, a brake, 5, a linear displacement sensor, 6, a manual brake mechanism, 7, transmission gears Z1, 8, transmission gears Z2, 9, transmission gears Z3, 10, transmission gears Z4, 11, brake gears Z5, 12, brake gears Z6, 13, emergency pull rings, 14, brake gear shafts, 15, ball screws, 16, screw nuts, 17, an inner disc spring set, 18, an outer disc spring set, 19, a sleeve, 20, an inner microswitch, 21, an outer microswitch, 22 and a mandrel.

Detailed Description

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and therefore should not be considered as a limitation to the scope of protection. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "disposed," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Example 1:

an electric actuating cylinder with a negative feedback control system is shown in figures 1, 2, 3 and 4 and comprises an actuating cylinder shell 1, a telescopic execution mechanism, a driving motor 2, a transmission gear set 3, a brake 4, a linear displacement sensor 5, a controller and an upper computer in communication connection with the controller, wherein the controller is in communication connection with the driving motor 2 and the brake 4; the telescopic actuating mechanism arranged in the actuating cylinder shell 1 comprises a ball screw 15 arranged in the actuating cylinder shell 1 and a screw nut 16 sleeved on the ball screw 15 through steel balls, and the screw nut 16 is linearly and slidably connected with a long-strip key arranged in the actuating cylinder shell 1; the output shaft of the driving motor 2 and the output shaft of the brake 4 are simultaneously connected to a first transmission shaft through a coupler, namely the driving motor 2 and the brake 4 are coaxially connected, and the first transmission shaft is in transmission connection with the ball screw 15 through a transmission gear set 3; the screw nut 16 is connected with the actuating rod; an inner micro switch 20 and an outer micro switch 21 which are respectively in communication connection with an upper computer are arranged in the actuator cylinder shell 1, and the installation positions of the two micro switches correspond to the set movement limit position of the screw nut 16; moreover, the tail end of the ball screw 15 is provided with a linear displacement sensor 5, a mandrel 22 of the linear displacement sensor 5 is directly or indirectly connected with an actuating rod, and the linear displacement sensor 5 is in communication connection with an upper computer;

an inner disc spring group 17 and an outer disc spring group 18 are respectively arranged on two sides of the screw nut 16 through a sleeve 19 which is sleeved on the ball screw 15, and a convex part for limiting the linear movement limit positions of the inner disc spring group 17 and the inner disc spring group 17 is arranged in the actuating cylinder shell 1;

the transmission gear set 3 comprises a second transmission shaft, a transmission gear Z17, a transmission gear Z28, a transmission gear Z39 and a transmission gear Z410;

the transmission gear Z17 is arranged on the first transmission shaft, and the transmission gear Z17 is meshed with the transmission gear Z28; the transmission gear Z28 and the transmission gear Z39 are arranged on the second transmission shaft side by side, and the transmission gear Z39 is meshed with the transmission gear Z410; the transmission gear Z410 is in meshing transmission with a ball screw 15 which is rotatably arranged in the actuator cylinder shell 1;

the manual braking mechanism 6 is arranged on the actuating cylinder shell 1; the manual brake mechanism 6 comprises a brake gear Z511, a brake gear Z612, an emergency pull ring 13 and a brake gear shaft 14;

one end of the brake gear shaft 14 extends out of the actuator cylinder shell 1 and is transversely inserted into the emergency pull ring 13, and a brake gear Z511 is arranged at one end of the brake gear shaft 14, which is positioned in the cavity of the actuator cylinder shell 1; the brake gear Z511 corresponds to the brake gear Z612 arranged on the first transmission shaft in position; when the emergency pull ring 13 is pulled out from the brake gear shaft 14, the brake gear shaft 14 is pushed to enable the brake gear Z511 and the brake gear Z612 to be meshed and then clamped;

the brake 4 is a direct current electromagnetic actuator;

the linear displacement sensor 5 is an LVDT position sensor;

the controller is a PI controller.

The working principle is as follows: as shown in fig. 1, the upper computer, the power supply, the controller, the driver, the electric actuator cylinder and the linear displacement sensor 55 form a closed-loop control system, the upper computer gives a real-time control signal, the real-time control signal is received and set by the controller and amplified by the driver to generate a control logic to drive the electric actuator cylinder to act, the electric actuator cylinder outputs a rotating speed and a torque in real time according to a control rule, a rotating position quantity of the electric actuator cylinder is transmitted to the controller through the linear displacement sensor 5, and the given position quantity is compared with an actual position quantity to obtain an error so as to form a feedback loop. As shown in fig. 2, the driving motor 2 drives the first transmission rod to rotate, the first transmission rod drives the transmission gear Z17 to rotate, after the two-stage gear speed reduction and torque increase of the transmission gear Z28, the transmission gear Z39 and the transmission gear Z410, the transmission gear Z410 drives the ball screw 15 to rotate, the rotation of the ball screw 15 drives the rotation of the screw nut 16, but because the length-limiting key bar is arranged in the actuator cylinder box to limit the axial movement of the screw nut 16, the screw nut 16 can only move linearly, the sleeve 19 is fixed with the screw nut 16, the two ends of the sleeve 19 are provided with the disc spring sets, which can increase the stability in the movement process, and the inside and outside micro switches are arranged in the actuator cylinder box in a matching way, when the movement of the ball nut pair drives the inside disc spring set 17 to pass through the inside micro switch 20, the inside disc spring set 17 just rubs against the inside micro switch 20, the inner-side microswitch 20 is triggered to turn off the power supply, the direct-current electromagnetic brake 4 brakes the actuating cylinder to stop running after the power supply is turned off, and similarly, the outer-side disc spring group 18 touches the outer-side microswitch 21 when crossing the outer-side microswitch 21 to move inwards, so that the power supply is turned off, the brake 4 brakes to stop running, and finally the electric actuating cylinder is ensured to be stable under the action of external force after being in place and powered off, and the stability of the system is improved; the manual braking mechanism 6 is arranged, the braking gear Z612 is fixed above the braking gear Z511 through the emergency pull ring 13, and after the emergency pull ring 13 is manually taken down by a person, the braking gear Z612 falls into a gear gap of the braking gear Z511, so that the system can be immediately stopped from transmission, and the emergency braking effect is achieved; the LVDT position sensor works on the principle that a linear mechanical displacement of the mandrel 22 is converted into a voltage signal proportional to the linear mechanical displacement, and the sensor mainly comprises a stator and the mandrel 22. The shell of the stator is provided with an excitation winding (also called a primary winding) and an output winding (also called a secondary winding); the spindle 22 is a simple shaped magnetizer. After alternating current flows through an excitation winding of the LVDT, an alternating magnetic field is generated in a winding space. Because of the mutual inductance between the excitation and the output, an electrical signal is induced in the output winding that is proportional to the linear displacement of the moving core shaft 22. The two coils of the output winding are connected in opposition, either head-to-tail or tail-to-tail, so that when the moving core shaft 22 is in the middle of the two output coils, the induced voltages of the two output coils cancel each other out. If the movable core shaft 22 moves in one direction, the output voltage increases in proportion to the linear displacement of the movable core shaft 22; if the moving spindle 22 moves from the neutral position to the other direction, the output voltage still increases in proportion to the linear displacement of the moving spindle 22, but the phase is opposite; as shown in fig. 4, the core of the sensor is the mandrel 22, the mandrel 22 is in contact connection with one end of the ball screw, which is opposite to the ball screw nut pair, and along with the movement of the ball screw nut pair, the mandrel 22 also has corresponding displacement transformation, so that a controller connected with the LVDT position sensor can receive corresponding position transformation; the LVDT can monitor the stroke in real time, can feed back position signals in the motion process besides the stop position, and can effectively eliminate unpredictable risks brought by false alarm signals by mutual assistance of the LVDT and the stop position signals; in the current detection and control strategy, a PI controller is adopted to sample the current value of a motor in real time to realize current feedback, when the motor needs frequent forward and reverse rotation starting operation, the time of starting, braking and reverse rotation transition processes needs to be shortened as much as possible, the current in the transition process is increased and dynamic torque is increased to realize the current feedback, so that the dynamic response of a system is accelerated, the current is kept unchanged as the maximum value allowed by the system in the starting process time, the rotating speed required by the system is accelerated by the maximum torque, and the current is sharply reduced to the current value required by a load after the system reaches the steady rotating speed, so that the starting time of the motor is shortened, the overload capacity of the motor is fully utilized, and the fastest dynamic response speed is obtained. Meanwhile, the motor is protected to a certain extent, the maximum current value of the motor is limited, the motor is prevented from being damaged due to severe fluctuation of torque, and the power supply fluctuation and load disturbance resistance of the system is improved, so that the performance and reliability of the system are improved.

Example 2:

the invention also provides an electric actuating cylinder with a negative feedback control system, which comprises an actuating cylinder shell 1, a telescopic actuating mechanism, a driving motor 2, a transmission gear group 3, a brake 4, a linear displacement sensor 5 and a controller, wherein the controller is in communication connection with the driving motor 2 and the brake 4; the telescopic actuating mechanism arranged in the actuating cylinder shell 1 comprises a ball screw 15 arranged in the actuating cylinder shell 1 and a screw nut 16 sleeved on the ball screw 15 through steel balls, and the screw nut 16 is linearly and slidably connected with a long-strip key arranged in the actuating cylinder shell 1; the output shaft of the driving motor 2 and the output shaft of the brake 4 are simultaneously connected to a first transmission shaft through a coupler, namely the driving motor 2 and the brake 4 are coaxially connected, and the first transmission shaft is in transmission connection with the ball screw 15 through a transmission gear set 3; the screw nut 16 is connected with the actuating rod; an inner micro switch 20 and an outer micro switch 21 which are respectively in communication connection with a controller are arranged in the actuator cylinder shell 1, and the installation positions of the two micro switches correspond to the set movement limit position of the screw nut 16; moreover, the tail end of the ball screw 15 is provided with a linear displacement sensor 5, a mandrel 22 of the linear displacement sensor 5 is directly or indirectly connected with an actuating rod, and the linear displacement sensor 5 is in communication connection with a controller;

an inner disc spring set 17 and an outer disc spring set 18 are respectively installed on two sides of the screw nut 16 through a sleeve 19 externally sleeved on the ball screw 15, and a convex part for limiting the linear movement limit positions of the inner disc spring set 17 and the inner disc spring set 17 is arranged in the actuating cylinder shell 1.

Other parts of this embodiment are the same as those of embodiment 1, and thus are not described again.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications and equivalent variations of the above embodiments according to the technical spirit of the present invention are included in the scope of the present invention.

Claims

1. An electric actuator having a negative feedback control system, comprising: the linear displacement sensor comprises an actuating cylinder shell (1), a telescopic actuating mechanism, a driving motor (2), a transmission gear set (3), a brake (4), a linear displacement sensor (5), a controller and an upper computer in communication connection with the controller, wherein the controller is in communication connection with the driving motor (2) and the brake (4); the telescopic actuating mechanism arranged in the actuating cylinder shell (1) comprises a ball screw (15) arranged in the actuating cylinder shell (1) and a screw nut (16) sleeved on the ball screw (15) through steel balls, and the screw nut (16) is linearly and slidably connected with a long-strip key arranged in the actuating cylinder shell (1); an output shaft of the driving motor (2) and an output shaft of the brake (4) are simultaneously connected to a first transmission shaft through a coupler, namely the driving motor (2) and the brake (4) are coaxially connected, and the first transmission shaft is in transmission connection with a ball screw (15) through a transmission gear set (3); the screw rod nut (16) is connected with the actuating rod; an inner micro switch (20) and an outer micro switch (21) which are respectively in communication connection with an upper computer are arranged in the actuating cylinder shell (1), and the installation positions of the two micro switches correspond to the set movement limit position of the screw nut (16); moreover, a linear displacement sensor (5) is arranged at the tail end of the ball screw (15), a mandrel (22) of the linear displacement sensor (5) is directly or indirectly connected with the actuating rod, and the linear displacement sensor (5) is in communication connection with an upper computer;

an inner disc spring group (17) and an outer disc spring group (18) are respectively arranged on two sides of the screw nut (16) through a sleeve (19) sleeved outside the ball screw (15), and convex parts for limiting the linear movement limit positions of the inner disc spring group (17) and the inner disc spring group (17) are arranged in the actuator cylinder shell (1).

2. An electric ram with negative feedback control system according to claim 1 wherein the drive gear set (3) comprises a second drive shaft, drive gear Z1 (7), drive gear Z2 (8), drive gear Z3 (9), drive gear Z4 (10);

the transmission gear Z1 (7) is arranged on the first transmission shaft, and the transmission gear Z1 (7) is meshed with the transmission gear Z2 (8); the transmission gear Z2 (8) and the transmission gear Z3 (9) are arranged on the second transmission shaft side by side, and the transmission gear Z3 (9) is meshed with the transmission gear Z4 (10); the transmission gear Z4 (10) is in meshing transmission with a ball screw (15) which is rotatably arranged in the actuating cylinder shell (1).

3. An electric ram with a negative feedback control system according to claim 2 further comprising a manual brake mechanism (6) disposed on the ram housing (1); the manual brake mechanism (6) comprises a brake gear Z5 (11), a brake gear Z6 (12), an emergency pull ring (13) and a brake gear shaft (14);

one end of the braking gear shaft (14) extends out of the actuating cylinder shell (1) and is transversely inserted into the emergency pull ring (13), and one end, located in the inner cavity of the actuating cylinder shell (1), of the braking gear shaft (14) is provided with a braking gear Z5 (11); the brake gear Z5 (11) corresponds to the position of a brake gear Z6 (12) arranged on the first transmission shaft; when the emergency pull ring (13) is pulled out from the brake gear shaft (14), the brake gear shaft (14) is pushed to enable the brake gear Z5 (11) and the brake gear Z6 (12) to be meshed and then locked.

4. An electro-dynamic actuator with negative feedback control system according to any of claims 1 to 3 characterised in that the brake (4) is a dc electromagnetic actuator.

5. An electric actuator with negative feedback control system according to any of claims 1-3 wherein the linear displacement sensor (5) is an LVDT position sensor.

6. An electric actuator with negative feedback control system as claimed in any of claims 1-3 wherein said controller is a PI controller.

7. An electric actuator having a negative feedback control system, comprising: the linear displacement sensor comprises an actuating cylinder shell (1), a telescopic actuating mechanism, a driving motor (2), a transmission gear set (3), a brake (4), a linear displacement sensor (5) and a controller, wherein the controller is in communication connection with the driving motor (2) and the brake (4); the telescopic actuating mechanism arranged in the actuating cylinder shell (1) comprises a ball screw (15) arranged in the actuating cylinder shell (1) and a screw nut (16) sleeved on the ball screw (15) through steel balls, and the screw nut (16) is linearly and slidably connected with a long-strip key arranged in the actuating cylinder shell (1); an output shaft of the driving motor (2) and an output shaft of the brake (4) are simultaneously connected to a first transmission shaft through a coupler, namely the driving motor (2) and the brake (4) are coaxially connected, and the first transmission shaft is in transmission connection with a ball screw (15) through a transmission gear set (3); the screw rod nut (16) is connected with the actuating rod; an inner micro switch (20) and an outer micro switch (21) which are respectively in communication connection with a controller are arranged in the actuating cylinder shell (1), and the installation positions of the two micro switches correspond to the set movement limit position of the screw nut (16); moreover, a linear displacement sensor (5) is arranged at the tail end of the ball screw (15), a mandrel (22) of the linear displacement sensor (5) is directly or indirectly connected with the actuating rod, and the linear displacement sensor (5) is in communication connection with the controller;