Mechanism output torque control method based on electromechanical actuator

Abstract

The invention relates to a mechanism output torque control method based on an electromechanical actuator, and belongs to the technical field of servo control. Building an electromechanical actuator transmission system; the tail end of the transmission mechanism is driven to complete a complete movement process; the actuating distance of a push rod of the electromechanical actuator and the angle of the tail end of the transmission mechanism relative to the horizontal direction in the whole movement process are measured, and relation calibration is carried out; performing relation calibration on the thrust of the electromechanical actuator and the torque of the tail end of the corresponding transmission mechanism; performing relation calibration on the thrust of the electromechanical actuator and the input current data of the electromechanical actuator; semi-closed-loop control is realized by controlling the input current of the electromechanical actuator and the torque at the tail end of the transmission mechanism; according to the invention, a five-order polynomial model fitting mode is adopted, indirect detection of the load torque is realized, and the problem of accurate control of the output torque when no torque feedback exists is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of servo control and relates to a mechanism output torque control method based on an electromechanical actuator. Background Art

[0002] Based on the mechanism of electromechanical actuator for torque output, the output torque is usually measured directly as a feedback signal to correct the output force of the actuator. When the output torque cannot be measured directly due to certain factors, a semi-closed loop method is required, that is, by detecting the force signal of the transmission link, the output torque is indirectly detected, and compared with the input original command torque value, and the difference after comparison is used for control.

[0003] In the prior art, the semi-closed loop torque control of the electromechanical actuator is usually based on the kinematic and dynamic characteristics of the transmission mechanism itself, and is realized by calculating the analytical solution. Specifically involved is the patent: hydraulic rocker arm loading device and loading method thereof, CN106840723, the invention is equipped with a tension and pressure sensor at one end of the hydraulic linear actuator, the advantage is that it can realize the real-time tracking loading of the torque according to the action form of the servo connected to the rocker arm, the disadvantage is that the torque loaded by this method is calculated by the kinematic and dynamic characteristics of the designed triangular rocker arm, but when the actual shape and size of the triangular rocker arm are different from the design, such as when there are errors in processing and assembly, the torque actually output by the loading device will also have a large error with the target, affecting the accuracy of the torque loading, and can only output a fixed extension or retraction torque to the triangular rocker arm by judging whether the tension or pressure sensor is subjected to tension or pressure, and cannot output a real-time, arbitrary torque to the rocker arm. The patented six-bar knee joint with knee torque control device, CN 1150868, controls the size of the friction torque by controlling the position of the friction cone in the knee joint torque control device. The advantage is that the torque control can be performed without relying on sensors, and the structure is compact and flexible. The disadvantage is that this torque control method is completely open-loop, and the current output torque cannot be calculated directly or indirectly through the sensor, so it is impossible to output a given torque, let alone a specific torque curve. Summary of the invention

[0004] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art, to propose a method for controlling the output torque of a mechanism based on an electromechanical actuator, to achieve indirect detection of the load torque by fitting a fifth-order polynomial model, and to solve the problem of accurately controlling the output torque when there is no torque feedback.

[0005] The solution of the present invention is:

[0006] A method for controlling a mechanism output torque based on an electromechanical actuator, comprising:

[0007] Step 1: Build an electromechanical actuator transmission system, including an electromechanical actuator fixing seat, a tension and pressure sensor, an electromechanical actuator, an electromechanical actuator push rod, a transmission mechanism connecting rod structure, a connecting rod structure fixing seat, a transmission mechanism end, a first connecting rod and a second connecting rod; through the reciprocating motion of the electromechanical actuator, the electromechanical actuator push rod, the transmission mechanism connecting rod structure, the first connecting rod and the second connecting rod are sequentially driven to drive the transmission mechanism end to perform rotational motion;

[0008] Step 2: Drive the end of the transmission mechanism through the electromechanical actuator to complete a complete motion process; measure the actuation distance of the electromechanical actuator push rod and the angle of the end of the transmission mechanism relative to the horizontal direction during the entire motion process;

[0009] Step 3, calibrate the relationship between the actuation distance of the electromechanical actuator push rod and the angle of the transmission mechanism end relative to the horizontal direction during the entire motion process;

[0010] Step 4: According to the complete motion process of step 2, the thrust of the electromechanical actuator and the torque at the end of the transmission mechanism corresponding to the thrust are obtained, and the input current data of the electromechanical actuator is obtained;

[0011] Step 5: calibrate the relationship between the thrust of the electromechanical actuator in step 4 and the torque at the end of the corresponding transmission mechanism;

[0012] Step 6: Calibrate the relationship between the thrust of the electromechanical actuator and the input current data of the electromechanical actuator in step 4;

[0013] Step 7. According to the parameters calibrated in the above steps, the thrust current coefficient K of the electromechanical actuator is obtained. The relationship between the input current of the electromechanical actuator and the torque at the end of the transmission mechanism obtained in step 3 is obtained, and semi-closed loop control is achieved by controlling the input current of the electromechanical actuator and the torque at the end of the transmission mechanism.

[0014] In the above-mentioned method for controlling the output torque of a mechanism based on an electromechanical actuator, in step 1, the specific structure of the electromechanical actuator transmission system is:

[0015] One axial end of the electromechanical actuator is installed on the horizontal fixed platform through an electromechanical actuator fixing seat; the tension and pressure sensor is installed on the electromechanical actuator; the bottom of the transmission mechanism connecting rod structure is rotationally connected to the horizontal fixed platform through the connecting rod structure fixing seat; the other axial end of the electromechanical actuator is rotationally connected to the transmission mechanism connecting rod structure through the electromechanical actuator push rod; one end of the second connecting rod is connected to the edge of the horizontal fixed platform; the other end of the second connecting rod is installed with the end of the transmission mechanism; one end of the first connecting rod is rotationally connected to the transmission mechanism connecting rod structure; the other end of the first connecting rod is rotationally connected to the middle part of the second connecting rod; the rotation center of the end of the transmission mechanism is the connection point between the second connecting rod and the edge of the horizontal fixed platform.

[0016] In the above-mentioned method for controlling the output torque of a mechanism based on an electromechanical actuator, in step 2, the actuation distance of the electromechanical actuator push rod is obtained by calculating the lead of the electromechanical actuator screw and the motor angle; the angle of the end of the transmission mechanism relative to the horizontal direction is obtained by measuring an external inclination sensor installed at the end of the transmission mechanism.

[0017] In the above-mentioned method for controlling the output torque of a mechanism based on an electromechanical actuator, in step 3, the relationship between the actuation distance of the electromechanical actuator push rod and the angle of the transmission mechanism end relative to the horizontal direction during the entire motion process is:

[0018] q=c5x 5 +c4x 4 +c3x 3 +c2x 2 +c1x+c0

[0019] Where q is the angle of the end of the transmission mechanism relative to the horizontal direction;

[0020] x is the actuation distance of the electromechanical actuator push rod;

[0021] c0, c1, c2, c3, c4, and c5 are the unknown coefficients of the quintic polynomial respectively;

[0022] Assume x1, x2...x n is the actuation distance of n sets of electromechanical actuator push rods, q1, q2...q n is the angle of the end of the 5 transmission mechanism corresponding to n groups relative to the horizontal direction. The unknown coefficients of the quintic polynomial are calculated by the Vandermonde matrix polynomial fitting method, which is specifically expressed as:

[0023]

[0024] Thereby, a clear relationship between the actuation distance of the electromechanical actuator push rod and the angle relative to the horizontal direction during the entire motion process of the transmission mechanism end is obtained.

[0025] In the above-mentioned method for controlling the output torque of a mechanism based on an electromechanical actuator, in step four, the thrust of the electromechanical actuator is measured by a tension and pressure sensor; and the input current data of the electromechanical actuator is obtained by feedback from the driver of the electromechanical actuator.

[0026] In the above-mentioned method for controlling the output torque of a mechanism based on an electromechanical actuator, the torque data of the end of the transmission mechanism is obtained by hanging a weight with a standard mass of m at the end of the transmission mechanism and calculating the gravity torque τ of the weight; g is set as the gravity acceleration constant, l is the actual length from the end of the transmission mechanism to the rotation center of the end of the transmission mechanism obtained by measurement, and the calculation method of the torque τ at the end of the transmission mechanism is:

[0027] τ=mglcos(q)

[0028] The actual length from the end of the driving mechanism to the center of rotation of the end of the transmission mechanism is measured by a vernier caliper.

[0029] In the above-mentioned method for controlling the output torque of a mechanism based on an electromechanical actuator, in step 5, the method for calibrating the relationship between the thrust of the electromechanical actuator and the torque at the end of the corresponding transmission mechanism is:

[0030] The relationship between the thrust of the electromechanical actuator and the torque at the end of the transmission mechanism under the thrust is obtained by differentiating both sides of the quintic polynomial equation with known coefficients obtained in step 3 with respect to time:

[0031]

[0032] Assuming η is the transmission efficiency of the transmission mechanism, according to the law of conservation of energy, we have:

[0033]

[0034] The relationship equation between the thrust of the electromechanical actuator and the torque at the end of the transmission mechanism corresponding to the thrust is obtained as follows:

[0035]

[0036] Where, τ is the end torque of the transmission mechanism;

[0037] F is the thrust of the electromechanical actuator.

[0038] In the above-mentioned method for controlling the output torque of a mechanism based on an electromechanical actuator, the transmission efficiency η of the transmission mechanism is calculated by the thrust of the electromechanical actuator obtained in step 3 and the torque data at the end of the transmission mechanism corresponding to the thrust:

[0039]

[0040] In the above-mentioned method for controlling the output torque of a mechanism based on an electromechanical actuator, in step 6, the method for calibrating the relationship between the thrust of the electromechanical actuator and the input current data of the electromechanical actuator is:

[0041] Assume K is the thrust current coefficient of the electromechanical actuator; then the relationship between the thrust of the electromechanical actuator and the input current data of the electromechanical actuator is:

[0042] F=Ki

[0043] Where F is the thrust of the electromechanical actuator;

[0044] i is the input current data.

[0045] In the above-mentioned method for controlling the output torque of a mechanism based on an electromechanical actuator, in step seven, the relationship between the input current of the electromechanical actuator and the torque at the end of the transmission mechanism is expressed by the unknown coefficients c0, c1, c2, c3, c4, c5 of the calibrated quintic polynomial, the transmission efficiency η and the thrust current coefficient K of the electromechanical actuator:

[0046]

[0047] Where, τ is the end torque of the transmission mechanism;

[0048] η is the transmission efficiency of the transmission mechanism;

[0049] K is the thrust current coefficient of the electromechanical actuator;

[0050] i is the input current data.

[0051] The beneficial effects of the present invention compared with the prior art are:

[0052] (1) The present invention adopts a method of experimentally calibrating and fitting the relationship between the input current of the electromechanical actuator, the thrust of the push rod, and the torque output at the end of the transmission mechanism. By controlling the input current of the electromechanical actuator, the torque output at the end of the transmission mechanism is semi-closed-loop controlled, ignoring the intermediate links, and directly establishing the relationship between the input current and the final output torque of the torque control system, the influence of the shape and size errors of the mechanical structure is eliminated, and the accuracy of torque control is effectively improved;

[0053] (2) The present invention realizes real-time, arbitrary-size, and even specific-curve torque semi-closed-loop control by establishing a functional relationship between the input current of the electromechanical actuator and the torque output at the end of the transmission mechanism, which includes a fifth-order polynomial, thereby effectively improving the flexibility of the torque output;

[0054] (3) The present invention introduces the Vandermonde matrix to fit the polynomial, which has a smaller amount of calculation than machine learning and other methods and is simple and fast to implement, effectively reducing the computational consumption of the system;

[0055] (4) In the calibration experiment, the present invention uses an external inclination sensor and a weight to measure the end angle and output torque of the transmission mechanism respectively. After the calibration experiment is completed, the transmission mechanism can be disassembled. In actual work, there is no need to install the above-mentioned measuring device, which effectively reduces the overall volume and weight of the mechanism and makes the mechanism more concise.

[0056] (5) The present invention adopts a fifth-order polynomial model to study the relationship between the actuation distance of the electromechanical actuator push rod and the angle at the end of the transmission mechanism, as well as the relationship between the actuator thrust and the torque output at the end of the transmission mechanism. Compared with the traditional second-order system model, the present invention solves the problem of high-order system dynamics modeling and solution difficulties, and effectively improves the accuracy of torque control. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 This is a flow chart of the mechanism output torque control based on the electromechanical actuator of the present invention.

[0058] Figure 2 It is a schematic diagram of the transmission system of the electromechanical actuator of the present invention;

[0059] Figure 3 This is a flow chart of measurement data of the present invention. DETAILED DESCRIPTION

[0060] The present invention will be further described below in conjunction with the embodiments.

[0061] The present invention provides a method for controlling the output torque of a mechanism based on an electromechanical actuator, which adopts a fifth-order polynomial model fitting method to achieve indirect detection of the load torque and solve the problem of accurately controlling the output torque when there is no torque feedback.

[0062] The output torque control method of the mechanism based on electromechanical actuators, such as Figure 1 As shown, the specific steps include:

[0063] Step 1, build an electromechanical actuator transmission system, including an electromechanical actuator fixing seat 1, a tension and pressure sensor 2, an electromechanical actuator 3, an electromechanical actuator push rod 4, a transmission mechanism connecting rod structure 5, a connecting rod structure fixing seat 6, a transmission mechanism end 8, a first connecting rod 9 and a second connecting rod 10; through the reciprocating motion of the electromechanical actuator 3, the transmission mechanism end 8 is driven to rotate through the electromechanical actuator push rod 4, the transmission mechanism connecting rod structure 5, the first connecting rod 9, and the second connecting rod 10 in turn.

[0064] The specific structure of the electromechanical actuator transmission system is:

[0065] One axial end of the electromechanical actuator 3 is mounted on the horizontal fixed platform through the electromechanical actuator fixing seat 1; the tension and pressure sensor 2 is mounted on the electromechanical actuator 3; the bottom of the transmission mechanism connecting rod structure 5 is rotationally connected to the horizontal fixed platform through the connecting rod structure fixing seat 6; the other axial end of the electromechanical actuator 3 is rotationally connected to the transmission mechanism connecting rod structure 5 through the electromechanical actuator push rod 4; one end of the second connecting rod 10 is connected to the edge of the horizontal fixed platform; the other end of the second connecting rod 10 is installed with the transmission mechanism end 8; one end of the first connecting rod 9 is rotationally connected to the transmission mechanism connecting rod structure 5; the other end of the first connecting rod 9 is rotationally connected to the middle part of the second connecting rod 10; the rotation center of the transmission mechanism end 8 is the connection point between the second connecting rod 10 and the edge of the horizontal fixed platform, as shown in FIG. Figure 2 shown.

[0066] Step 2: Drive the transmission mechanism end 8 through the electromechanical actuator 3 to complete a complete motion process; measure the actuation distance of the electromechanical actuator push rod 4 and the angle of the transmission mechanism end 8 relative to the horizontal direction during the entire motion process, such as Figure 3 shown.

[0067] The actuation distance of the electromechanical actuator push rod 4 is calculated by the lead of the lead screw of the electromechanical actuator 3 and the motor rotation angle; the angle of the transmission mechanism end 8 relative to the horizontal direction is measured by an external inclination sensor installed at the transmission mechanism end 8.

[0068] Step 3: calibrate the relationship between the actuation distance of the electromechanical actuator push rod 4 and the angle of the transmission mechanism end 8 relative to the horizontal direction during the entire movement process.

[0069] The relationship between the actuation distance of the electromechanical actuator push rod 4 and the angle of the transmission mechanism end 8 relative to the horizontal direction during the entire movement process is:

[0070] q=c5x 5 +c4x 4 +c3x 3 +c2x 2 +c1x+c0

[0071] Where q is the angle of the transmission mechanism end 8 relative to the horizontal direction;

[0072] x is the actuation distance of the electromechanical actuator push rod 4;

[0073] c0, c1, c2, c3, c4, and c5 are the unknown coefficients of the quintic polynomial respectively;

[0074] Assume x1, x2...x n is the actuation distance of n sets of electromechanical actuators 3 push rods, q1, q2...q n is the angle of the end of the 5 transmission mechanism corresponding to n groups relative to the horizontal direction. The unknown coefficients of the quintic polynomial are calculated by the Vandermonde matrix polynomial fitting method, which is specifically expressed as:

[0075]

[0076] Thereby, a clear relationship between the actuation distance of the electromechanical actuator push rod 4 and the angle relative to the horizontal direction during the entire movement process of the transmission mechanism end 8 is obtained.

[0077] Step 4: According to the complete motion process of step 2, the thrust of the electromechanical actuator 3 and the torque of the transmission mechanism end 8 corresponding to the thrust are obtained, and the input current data of the electromechanical actuator 3 are obtained.

[0078] The thrust of the electromechanical actuator 3 is measured by the tension and pressure sensor 2 ; the input current data of the electromechanical actuator 3 is obtained through the driver feedback of the electromechanical actuator 3 .

[0079] The torque data of the transmission mechanism end 8 is obtained by hanging a weight with a standard mass m at the transmission mechanism end 8 and calculating the gravity torque τ of the weight; assuming g is the gravity acceleration constant, l is the actual length from the transmission mechanism end 8 to the transmission mechanism end rotation center 7 obtained by measurement, then the calculation method of the transmission mechanism end 8 torque τ is:

[0080] τ=mglcos(q)

[0081] The actual length of the center of rotation of the transmission mechanism end 8 to 7 is measured by a vernier caliper.

[0082] Step 5: Calibrate the relationship between the thrust of the electromechanical actuator 3 in step 4 and the torque of the corresponding transmission mechanism end 8.

[0083] The method for calibrating the relationship between the thrust of the electromechanical actuator 3 and the torque of the corresponding transmission mechanism end 8 is:

[0084] The relationship between the thrust of the electromechanical actuator 3 and the torque of the transmission mechanism end 8 corresponding to the thrust is obtained by taking the derivative of both sides of the fifth-order polynomial equation with known coefficients obtained in step 3 with respect to time:

[0085]

[0086] Assuming η is the transmission efficiency of the transmission mechanism, according to the law of conservation of energy, we have:

[0087]

[0088] The relationship equation between the thrust of the electromechanical actuator 3 and the torque of the transmission mechanism end 8 corresponding to the thrust is obtained as follows:

[0089]

[0090] Where, τ is the torque at the end of the transmission mechanism;

[0091] F is the thrust of the electromechanical actuator 3.

[0092] The transmission efficiency η of the transmission mechanism is calculated by the thrust of the electromechanical actuator 3 obtained in step 3 and the torque data of the transmission mechanism end 8 corresponding to the thrust:

[0093]

[0094] Step six: calibrate the relationship between the thrust of the electromechanical actuator 3 and the input current data of the electromechanical actuator 3 in step four.

[0095] The method for calibrating the relationship between the thrust of the electromechanical actuator 3 and the input current data of the electromechanical actuator 3 is:

[0096] Assume K is the thrust current coefficient of the electromechanical actuator 3; then the relationship between the thrust of the electromechanical actuator 3 and the input current data of the electromechanical actuator 3 is:

[0097] F=Ki

[0098] Where, F is the thrust of the electromechanical actuator 3;

[0099] i is the input current data.

[0100] Step 7. According to the parameters calibrated in the above steps, the thrust current coefficient K of the electromechanical actuator 3 is obtained. The relationship between the input current of the electromechanical actuator 3 and the torque of the transmission mechanism end 8 obtained in step 3 is obtained, and semi-closed loop control is achieved by controlling the input current of the electromechanical actuator 3 and the torque of the transmission mechanism end 8.

[0101] The relationship between the input current of the electromechanical actuator 3 and the torque of the transmission mechanism end 8 is expressed by the unknown coefficients c0, c1, c2, c3, c4, c5 of the calibrated quintic polynomial, the transmission efficiency η and the thrust current coefficient K of the electromechanical actuator 3:

[0102]

[0103] Where, τ is the torque at the end of the transmission mechanism;

[0104] η is the transmission efficiency of the transmission mechanism;

[0105] K is the thrust current coefficient of the electromechanical actuator 3;

[0106] i is the input current data.

[0107] The present invention adopts a method of experimentally calibrating and fitting the relationship between the input current of the electromechanical actuator, the thrust of the push rod, and the torque output at the end of the transmission mechanism. The torque output at the end of the transmission mechanism is semi-closed-loop controlled by controlling the input current of the electromechanical actuator, ignoring the intermediate links, and directly establishing the relationship between the input current and the final output torque of the torque control system, eliminating the influence of the shape and size errors of the mechanical structure, thereby effectively improving the accuracy of torque control.

[0108] The present invention realizes real-time, semi-closed-loop control of torque of any size or even a specific curve by establishing a functional relationship including a fifth-order polynomial between the input current of the electromechanical actuator and the torque output at the end of the transmission mechanism, thereby effectively improving the flexibility of the torque output.

[0109] The present invention introduces the Vandermonde matrix to fit the polynomial, which has a smaller amount of calculation than methods such as machine learning and is simple and quick to implement, effectively reducing the calculation consumption of the system.

[0110] In the calibration experiment, the present invention uses an external inclination sensor and a weight to respectively measure the end angle and the output torque of the transmission mechanism. After the calibration experiment is completed, the transmission mechanism can be disassembled. In actual work, there is no need to install the above-mentioned measuring device, which effectively reduces the overall volume and weight of the mechanism and makes the mechanism more concise.

[0111] The present invention adopts a fifth-order polynomial model to study the relationship between the actuation distance of the electromechanical actuator push rod and the angle at the end of the transmission mechanism, as well as the relationship between the actuator thrust and the torque output at the end of the transmission mechanism. Compared with the traditional second-order system model, it solves the problem of high-order system dynamics modeling and solution difficulties, and effectively improves the accuracy of torque control.

[0112] The present invention is aimed at a semi-closed-loop torque control system composed of an electromechanical actuator element and a transmission mechanism without torque feedback, and proposes a mechanism output torque control method based on an electromechanical actuator. By fitting with a fifth-order polynomial based on experimental measurement data, a mapping model between the input current of the electromechanical actuator and the output torque at the end of the transmission mechanism is directly established, thereby realizing dynamic prediction of the end load and solving the problem of precise torque control when there is no torque feedback.

[0113] In order to solve the problems of difficulty in obtaining analytical solutions to nonlinear systems and inaccurate prediction models, the present invention establishes a fifth-order polynomial model, introduces the Vandermonde matrix polynomial fitting method, and constructs a mapping model between the actuation distance of the electromechanical actuator and the end angle of the transmission mechanism, thereby achieving accurate state characterization of complex nonlinear systems and solving the nonlinear control problem caused by mechanical transmission errors.

[0114] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for controlling the output torque of a mechanism based on an electromechanical actuator, characterized in that: include: Step 1: construct an electromechanical actuator transmission system, including an electromechanical actuator fixing seat (1), a tension and pressure sensor (2), an electromechanical actuator (3), an electromechanical actuator push rod (4), a transmission mechanism connecting rod structure (5), a connecting rod structure fixing seat (6), a transmission mechanism end (8), a first connecting rod (9) and a second connecting rod (10); through the reciprocating motion of the electromechanical actuator (3), the electromechanical actuator push rod (4), the transmission mechanism connecting rod structure (5), the first connecting rod (9) and the second connecting rod (10) are sequentially driven to drive the transmission mechanism end (8) to perform rotational motion; Step 2: driving the transmission mechanism end (8) through the electromechanical actuator (3) to complete a complete motion process; measuring the actuation distance of the electromechanical actuator push rod (4) and the angle of the transmission mechanism end (8) relative to the horizontal direction during the entire motion process; Step 3, calibrate the relationship between the actuation distance of the electromechanical actuator push rod (4) and the angle of the transmission mechanism end (8) relative to the horizontal direction during the entire movement process; Step 4: According to the complete motion process of step 2, the thrust of the electromechanical actuator (3) and the torque of the transmission mechanism end (8) corresponding to the thrust are obtained, and the input current data of the electromechanical actuator (3) are obtained; Step 5: calibrate the relationship between the thrust of the electromechanical actuator (3) in step 4 and the torque of the corresponding transmission mechanism end (8); Step 6: Calibrate the relationship between the thrust of the electromechanical actuator (3) and the input current data of the electromechanical actuator (3) in step 4; Step 7. According to the parameters calibrated in the above steps, the thrust current coefficient K of the electromechanical actuator (3) is obtained by the relationship between the input current of the electromechanical actuator (3) and the torque of the transmission mechanism end (8) obtained in step 3, and semi-closed loop control is achieved by controlling the input current of the electromechanical actuator (3) and the torque of the transmission mechanism end (8).

2. The method for controlling the output torque of a mechanism based on an electromechanical actuator according to claim 1, characterized in that: In the step 1, the specific structure of the electromechanical actuator transmission system is: One axial end of the electromechanical actuator (3) is mounted on a horizontal fixed platform via an electromechanical actuator fixing seat (1); a tension and pressure sensor (2) is mounted on the electromechanical actuator (3); the bottom of the transmission mechanism connecting rod structure (5) is rotationally connected to the horizontal fixed platform via a connecting rod structure fixing seat (6); the other axial end of the electromechanical actuator (3) is rotationally connected to the transmission mechanism connecting rod structure (5) via an electromechanical actuator push rod (4); one end of the second connecting rod (10) is connected to the edge of the horizontal fixed platform; the other end of the second connecting rod (10) is mounted on the transmission mechanism end (8); one end of the first connecting rod (9) is rotationally connected to the transmission mechanism connecting rod structure (5); the other end of the first connecting rod (9) is rotationally connected to the middle of the second connecting rod (10); the rotation center of the transmission mechanism end (8) is the connection point between the second connecting rod (10) and the edge of the horizontal fixed platform.

3. The method for controlling the output torque of a mechanism based on an electromechanical actuator according to claim 2, characterized in that: In the second step, the actuation distance of the electromechanical actuator push rod (4) is obtained by calculating the lead of the lead screw of the electromechanical actuator (3) and the motor rotation angle; and the angle of the transmission mechanism end (8) relative to the horizontal direction is obtained by measuring an external inclination sensor installed at the transmission mechanism end (8).

4. The method for controlling the output torque of a mechanism based on an electromechanical actuator according to claim 3, characterized in that: In step 3, the relationship between the actuation distance of the electromechanical actuator push rod (4) and the angle of the transmission mechanism end (8) relative to the horizontal direction during the entire movement process is: q=c5x 5 +c4x 4 +c3x 3 +c2x 2 +c1x+c0 Where q is the angle of the transmission mechanism end (8) relative to the horizontal direction; x is the actuation distance of the electromechanical actuator push rod (4); c0, c1, c2, c3, c4, and c5 are the unknown coefficients of the quintic polynomial respectively; Assume x1, x2...x n is the actuation distance of the push rods of n sets of electromechanical actuators (3), q1, q2...q n is the angle of the end of the 5 transmission mechanism corresponding to n groups relative to the horizontal direction. The unknown coefficients of the quintic polynomial are calculated by the Vandermonde matrix polynomial fitting method, which is specifically expressed as: Thus, a clear relationship between the actuation distance of the electromechanical actuator push rod (4) and the angle of the transmission mechanism end (8) relative to the horizontal direction during the entire movement process is obtained.

5. The method for controlling the output torque of a mechanism based on an electromechanical actuator according to claim 4, characterized in that: In the step 4, the thrust of the electromechanical actuator (3) is measured by the tension and pressure sensor (2); and the input current data of the electromechanical actuator (3) is obtained through feedback from the driver of the electromechanical actuator (3).

6. The method for controlling the output torque of a mechanism based on an electromechanical actuator according to claim 5, characterized in that: The torque data of the transmission mechanism end (8) is obtained by hanging a weight with a standard mass m at the transmission mechanism end (8) and calculating the gravity torque τ of the weight; assuming g is the gravity acceleration constant, l is the actual length from the transmission mechanism end (8) to the rotation center of the transmission mechanism end obtained by measurement, then the calculation method of the torque τ of the transmission mechanism end (8) is: τ=mglcos(q) The actual length from the end of the driving mechanism (8) to the rotational motion center of the end of the driving mechanism 7 is measured by a vernier caliper.

7. The method for controlling the output torque of a mechanism based on an electromechanical actuator according to claim 4, characterized in that: In step 5, the method for calibrating the relationship between the thrust of the electromechanical actuator (3) and the torque of the corresponding transmission mechanism end (8) is: The relationship between the thrust of the electromechanical actuator (3) and the torque of the transmission mechanism end (8) corresponding to the thrust is obtained by taking the derivative of both sides of the fifth-order polynomial equation with known coefficients obtained in step 3 with respect to time: Assuming η is the transmission efficiency of the transmission mechanism, according to the law of conservation of energy, we have: The relationship equation between the thrust of the electromechanical actuator (3) and the torque of the transmission mechanism end (8) corresponding to the thrust is obtained as follows: Where, τ is the torque at the end of the transmission mechanism (8); F is the thrust of the electromechanical actuator (3).

8. The method for controlling the output torque of a mechanism based on an electromechanical actuator according to claim 7, characterized in that: The transmission efficiency η of the transmission mechanism is calculated by the thrust of the electromechanical actuator (3) obtained in step 3 and the torque data of the transmission mechanism end (8) corresponding to the thrust:

9. The method for controlling the output torque of a mechanism based on an electromechanical actuator according to claim 2, characterized in that: In step six, the method for calibrating the relationship between the thrust of the electromechanical actuator (3) and the input current data of the electromechanical actuator (3) is: Assuming K as the thrust current coefficient of the electromechanical actuator (3), the relationship between the thrust of the electromechanical actuator (3) and the input current data of the electromechanical actuator (3) is: Where F is the thrust of the electromechanical actuator (3); i is the input current data.

10. The method for controlling the output torque of a mechanism based on an electromechanical actuator according to claim 4, characterized in that: In step 7, the relationship between the input current of the electromechanical actuator (3) and the torque of the transmission mechanism end (8) is expressed by the unknown coefficients c0, c1, c2, c3, c4, c5 of the calibrated quintic polynomial, the transmission efficiency η and the thrust current coefficient K of the electromechanical actuator (3): Where, τ is the torque at the end of the transmission mechanism (8); η is the transmission efficiency of the transmission mechanism; K is the thrust current coefficient of the electromechanical actuator (3); i is the input current data.

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