Fast-response closed-loop micro-thrust measurement method and equipment based on dynamic thrust inversion

Abstract

The invention relates to a fast-response closed-loop micro-thrust measurement method and device based on dynamic thrust inversion. The method comprises the following steps of obtaining kinetic equation parameters of a measurement system; in each control period, calculating a control quantity, and taking the control quantity as a standard force; in the current control period, based on displacement data obtained through measurement of the measurement system and the kinetic equation parameters, the resultant force of the previous control period is calculated through a kinetic inversion algorithm; on the basis of the difference between the standard force of the previous control period and the resultant force, the thrust to be measured of the previous control period is obtained through calculation; and performing low-pass filtering processing on the thrust to be measured to obtain a final result. Compared with the prior art, the method can improve the measurement response speed on the premise of not increasing the noise level.

Description

Technical Field

[0001] The invention belongs to the technical field of micro-nano satellites and relates to a micro-thrust measurement method, in particular to a fast-response closed-loop micro-thrust measurement method and equipment based on dynamic thrust inversion. Background Art

[0002] Micro-nano satellites are one of the technologies that have received much attention in the fields of space science and commercial aerospace in recent years. Compared with traditional large satellites, micro-nano satellites have the advantages of light weight, small size, high flexibility and short development cycle. They can also complete space missions of the same complexity at a lower cost than a single large satellite through a formation networking working mode. Limited by their own mass and volume, micro-nano satellites require a propulsion system with high specific impulse and high stability. Micro-thrusters that can generate micro-thrusts in the micro-newton to millinewton range are the core devices of micro-nano satellite propulsion systems. Ground testing of micro-thrusters to measure and evaluate their performance indicators is an indispensable step before the formal application of micro-thrusters.

[0003] The specific impulse and response time of micro-thrusters are important parameters that affect their dynamic performance. In-depth understanding and evaluation of these dynamic parameters are of great significance for the design and development of high-performance micro-thrusters. The response time of many micro-thrusters can reach tens of milliseconds or even several milliseconds. Therefore, in order to accurately measure the dynamic parameters such as the specific impulse and response time of micro-thrusters, the measurement method used should also have a faster response speed.

[0004] The torsion pendulum has the advantages of high precision and high resolution, and is a widely used micro-thrust measurement system. At present, there are two main ways to measure the dynamic performance of micro-thrusters through torsion pendulums: open-loop dynamic measurement and closed-loop measurement. Open-loop dynamic measurement solves the measured force that changes with time through the rotation angle of the torsion pendulum and the dynamic equation. Closed-loop measurement is through closed-loop control, using a standard force of known size and the force to be measured to form a torque balance, so that the torsion pendulum is kept at zero position, so that the size of the force to be measured is reflected by the size of the standard force, such as a micro-newton-level micro-thrust dynamic test bench and test method based on closed-loop control disclosed in patent application CN110413015A.

[0005] The principle of open-loop dynamic measurement of the torsion pendulum is simple and the response speed is fast. However, the measurement range is usually small due to the limitation of the rotation range of the torsion pendulum. When the rotation angle of the torsion pendulum is large, the nonlinear error will increase due to the influence of factors such as the cables and air pipes carried by the thruster.

[0006] In closed-loop measurement, the torsion pendulum is controlled at zero position, and a larger range can be obtained by increasing the range of the standard force, and the nonlinear error caused by factors such as cables and air pipes during measurement will be reduced. Therefore, closed-loop measurement is a better choice in scenarios that require high-precision measurement. However, traditional closed-loop measurement has the following disadvantages:

[0007] 1. The traditional closed-loop measurement has poor performance in measuring dynamic parameters such as response time. This is because if you want to measure the response time of tens of milliseconds, the control frequency and response time of the closed-loop measurement should be high. In this case, the closed-loop circuit will significantly amplify the impact of high-frequency measurement noise on the standard force, and its noise level will increase significantly. And due to the stability of the closed-loop system, low-pass filtering cannot effectively solve the problem of high-frequency noise. Therefore, when the noise level is the same, the response speed of closed-loop measurement is often slower than that of open-loop measurement.

[0008] 2. Traditional closed-loop measurement usually requires tedious design and adjustment of the controller. Because its measurement performance is greatly affected by the controller, the dynamic parameters of the measurement system will change every time the thruster under test is replaced. In order to obtain the ideal response speed and noise level, the controller should also change accordingly. Summary of the invention

[0009] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a fast-response closed-loop micro-thrust measurement method and device based on dynamic thrust inversion, which can improve the measurement response speed without increasing the noise level.

[0010] The purpose of the present invention can be achieved by the following technical solutions:

[0011] A fast response closed-loop micro-thrust measurement method based on dynamic thrust inversion comprises the following steps:

[0012] Obtaining the parameters of the dynamic equation of the measurement system;

[0013] In each control cycle, a control quantity is calculated and used as the standard force;

[0014] In the current control cycle, based on the displacement data measured by the measurement system and the parameters of the dynamic equation, a dynamic inversion algorithm is used to calculate the resultant force of the previous control cycle;

[0015] Based on the difference between the standard force of the previous control cycle and the resultant force, the thrust to be measured of the previous control cycle is calculated;

[0016] The thrust to be measured is subjected to low-pass filtering to obtain a final result.

[0017] Furthermore, the dynamic equation parameters of the measurement system are obtained by measurement or calibration.

[0018] Furthermore, the expression of the dynamic equation of the measurement system is:

[0019]

[0020] Where T is the thrust to be measured, θ is the angular displacement output by the measurement system, and are the corresponding second-order differential and first-order differential respectively, J is the system moment of inertia, c is the system damping coefficient, k is the system stiffness coefficient, L T is the length of the force arm acting on the thrust;

[0021] The dynamic equation includes the system moment of inertia J, the system damping coefficient c, the system stiffness coefficient k and the length of the force arm L of the thrust T .

[0022] Furthermore, the control algorithm for calculating and obtaining the control quantity includes a PID algorithm.

[0023] Furthermore, the calculation formula of the resultant force of the previous control cycle is:

[0024]

[0025] in, is the resultant force of the k-1th period, and are the second and first order differentials of the angular displacement with respect to time in the kth period.

[0026] Furthermore, the second-order differential and the first-order differential are obtained by using backward difference approximate differential solution.

[0027] Furthermore, according to the measurement instruction, the thrust to be measured in each control cycle is calculated cyclically until the measurement is completed.

[0028] The present invention also provides a fast response closed-loop micro-thrust measurement device based on dynamic thrust inversion, comprising:

[0029] A parameter acquisition module is used to obtain the parameters of the dynamic equation of the measurement system;

[0030] A control quantity calculation module is used to calculate a control quantity in each control cycle and use the control quantity as a standard force;

[0031] A dynamic inversion module, used to calculate the resultant force of the previous control cycle using a dynamic inversion algorithm based on the displacement data measured by the measurement system and the dynamic equation parameters in the current control cycle;

[0032] A thrust preliminary calculation module to be measured, used to calculate the thrust to be measured in the previous control cycle based on the difference between the standard force in the previous control cycle and the resultant force;

[0033] The low-pass filter module is used to perform low-pass filtering on the thrust to be measured to obtain a final result.

[0034] The present invention also provides a computer-readable storage medium, comprising one or more programs for execution by one or more processors of an electronic device, wherein the one or more programs include instructions for executing the fast-response closed-loop micro-thrust measurement method based on dynamic thrust inversion as described above.

[0035] The present invention also provides an electronic device, comprising one or more processors, a memory and one or more programs stored in the memory, wherein the one or more programs include instructions for executing the fast-response closed-loop micro-thrust measurement method based on dynamic thrust inversion as described above.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] Compared with traditional closed-loop measurement, the present invention compensates for the tracking error and noise influence contained in the standard force. The measurement response speed and noise level are independent of the standard force. Under the premise of system stability, they are no longer affected by the controller, but only related to the cutoff frequency of the low-pass filter during dynamic thrust inversion. Experimental verification shows that this method can maintain a lower noise level while achieving a higher response speed. In addition, the measurement results of the present invention are independent of the controller parameters as long as the stability of the system is ensured, so the design of the closed-loop controller is simplified.

[0038] Compared with the traditional open-loop dynamic thrust inversion, this method not only retains the advantages of large range and small nonlinearity of traditional closed-loop measurement, but also has the advantage of being insensitive to the distortion of dynamic parameters. This is because the measurement results of the present invention are composed of two parts: standard force and dynamic inversion results, of which the dynamic inversion results only account for a part of the measurement results. Therefore, when the dynamic parameters deviate from the true value, the final measurement error caused in the present invention will be smaller than the error caused in the open-loop dynamic measurement. This means that when the dynamic parameters are not accurately calibrated due to noise interference and other reasons, using this method for measurement can obtain higher measurement accuracy.

[0039] In general, compared with the prior art, the technical solution of the present invention includes the following advantages:

[0040] First, compared with traditional closed-loop measurement, the present invention eliminates the tracking error of the standard force on the measured force and the measurement noise amplified by the control loop in the traditional closed-loop measurement results, thereby improving the response speed of the closed-loop measurement without increasing the noise level.

[0041] Second, compared with traditional closed-loop measurement, under the premise of system stability, the measurement performance of the present invention is almost independent of the controller parameters, and can achieve near-optimal measurement performance under any control parameters that stabilize the system, thereby greatly simplifying the design of the controller.

[0042] Third, compared with traditional open-loop dynamic measurement, the present invention not only retains the advantages of low nonlinearity and high precision of traditional closed-loop measurement, but also has the advantage of more accurate measurement results when the dynamic parameters are distorted, and has stronger robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a schematic diagram of the principle of traditional closed-loop measurement;

[0044] Figure 2 It is a schematic diagram of the principle of the present invention;

[0045] Figure 3 It is the algorithm flow chart of the present invention;

[0046] Figure 4 The measurement results of the 20mN amplitude step thrust under different control parameters by the method of the present invention;

[0047] Figure 5 The measurement results of 20mN amplitude step thrust under different control parameters by traditional closed-loop measurement;

[0048] Figure 6 The measurement result of the 2mN step thrust by the method of the present invention when the dynamic parameters are distorted;

[0049] Figure 7 This is the measurement result of a 2mN step thrust in traditional open-loop dynamic measurement when the dynamic parameters are distorted. DETAILED DESCRIPTION

[0050] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0051] Before introducing the technical solution of the present invention, it is necessary to analyze the reasons why the dynamic measurement performance of the traditional closed loop is poor.

[0052] For Figure 1 In the closed-loop measurement system shown in the figure, C(s), G(s) and H(s) are the transfer functions of the controller (including the actuator), the torsion pendulum and the displacement sensor, respectively, where H(s) is usually 1. x is the actual displacement of the torsion pendulum, which is measured by the sensor after being contaminated by the measurement noise n. n represents the measured displacement. r is the expected displacement, which is generally equal to 0, and e is the product of r and x n T and F represent the force to be measured and the standard force respectively.

[0053] The goal of closed-loop control is to stabilize the displacement x at zero position, and the standard force F is equal to the force to be measured T. Based on the transfer functions of each module of the system, the error between the force to be measured T and the standard force F can be written as follows:

[0054]

[0055] Among them, S TF =1 / (1+CG), S nF =C / (1+CG), respectively called F err The sensitivity function of the measured force T and the measurement noise n. In formula (1), S TF T is the inherent F to T tracking error in closed-loop control, S nF n is the error caused by measurement noise.

[0056] In traditional closed-loop measurement, to improve the response speed, the tracking error of F to T should be reduced, that is, S TF should be reduced, then the controller gain C should be increased. But when C increases, on the one hand, as C increases, S nF will also increase and gradually approach G -1 , from the transfer function model of the torsion pendulum, we know that G -1 =(Js 2 +cs+k) / L T , the model consists of a first-order and second-order differentiator, which will greatly amplify the high-frequency measurement noise, so the error caused by the measurement noise will increase. On the other hand, the system open-loop gain becomes larger, the phase margin and gain margin will decrease, and the stability of the closed-loop system will deteriorate. This makes it difficult to add a low-pass filter in the closed-loop loop to deal with high-frequency noise, because the low-pass filter will introduce additional phase delay, and when its cut-off frequency is low, it will cause the performance of the controller to deteriorate and even the system to diverge.

[0057] Therefore, the higher the response speed of traditional closed-loop measurement, the worse the system stability will be and the greater the noise of the measurement result will be.

[0058] The present invention innovatively proposes to eliminate the two errors in formula (1) to eliminate the contradiction between the closed-loop measurement response speed and the system stability and the noise of the measurement result. In the closed-loop measurement, the thrust actually acting on the torsion pendulum is the resultant force F_r of the standard force and the force to be measured, that is, the inverse of the error between the standard force and the force to be measured, and the displacement of the torsion pendulum is caused by the resultant force. Therefore, as long as the resultant force is calculated by inversion of the displacement of the torsion pendulum and then subtracted from the standard force, the measurement result without the two errors in formula (1) can be obtained.

[0059] It should be noted that dynamic thrust inversion usually amplifies the high-frequency noise in the measured displacement. Therefore, a low-pass filter needs to be added to filter the result after inversion. When the low-pass filter cutoff frequency is selected to be lower, the suppression of high-frequency noise will be enhanced, but the response speed will be reduced, and when the cutoff frequency is selected to be higher, the response speed will increase, but the suppression effect of high-frequency noise will be reduced. It can be seen that, affected by the measurement noise, there is still a certain contradiction between the response speed and the noise level of the present invention. However, this contradiction is an inherent contradiction in almost all measurements disturbed by high-frequency noise. It is different from the cause of generation in traditional closed-loop measurement, and its impact on measurement performance is also much smaller than the latter.

[0060] Based on the above innovative research results, the present invention provides a fast-response closed-loop micro-thrust measurement method based on dynamic thrust inversion, the purpose of which is to improve the response speed of closed-loop measurement without increasing the noise level, so that the closed-loop measurement is more suitable for the measurement of dynamic parameters of micro-thrusters. The method includes the following steps:

[0061] Step 1: Obtain the parameters in the dynamic equation of the measurement system by measurement or calibration.

[0062] This method is applicable to the kinetic equation Or a similar form of measurement system, where T is the thrust to be measured, θ is the angular displacement output by the measurement system, J is the system moment of inertia, c is the system damping coefficient, k is the system stiffness coefficient, and L T is the length of the force arm acting on the thrust.

[0063] The kinetic equation parameters obtained in step 1 include J, c, k, L T .

[0064] Step 2: In the kth control cycle, a control quantity F(k) is calculated by any control algorithm (such as PID, proportional-integral-differential control algorithm), and this control quantity is the standard force.

[0065] Step 3: Calculate the resultant force of the standard force F(k-1) and the force to be measured T(k-1) in the k-1th cycle by using the measured displacement data and the dynamic inversion algorithm.

[0066]

[0067] in and is the second-order differential and first-order differential of the angular displacement with respect to time in the kth period. In a specific embodiment, there are many ways to find the differential of discrete data. The following is a solution method using backward difference to approximate the differential:

[0068]

[0069] Where T s is the sampling period.

[0070] In addition to the above-mentioned discrete data differentiation methods, other calculations can also be performed using methods such as forward difference, central difference, and Savitzky-Golay derivation.

[0071] Step 4: Subtract the calculated resultant force from the standard force F(k-1) of the k-1th cycle Thus, the force to be measured in the k-1th cycle is obtained:

[0072]

[0073] Step 5, Perform low-pass filtering to obtain the final result.

[0074] Repeat steps 2 to 5 above until the measurement is completed.

[0075] In order to verify the measurement advantage of the proposed method, based on a set of horizontal torsion pendulums, Figure 2 The schematic diagram shown is similar to Figure 3 The flowchart shown in the figure conducted two sets of experiments, and the PID control algorithm was used in the experiments. In the first set of experiments, a step thrust with an amplitude of about 20mN was measured by the method of the present invention and the traditional closed-loop measurement method, and the measurement was completed under three different control parameters to verify the improvement of the response speed of the method of the present invention compared with the traditional closed-loop and the advantages that the measurement performance is almost unaffected by the controller parameters. In the second set of experiments, a step thrust with an amplitude of about 2mN was measured by the method of the present invention and the traditional open-loop dynamic measurement method, and the moment of inertia J and the damping coefficient c in the dynamic parameters were deviated from the calibration results by 5%, 10% and 15% respectively during the measurement, to verify the advantages of the method of the present invention having strong robustness to the distortion of dynamic parameters.

[0076] Figure 4 It is the measurement result of step thrust under different control parameters (including control parameter 1, control parameter 2 and control parameter 3) of the method of the present invention. It can be seen that the measurement results under different control parameters are basically consistent. The time required for the measured value to reach the ±5% error band of 20mN for the first time is taken as the measurement response time. The response time of the method of the present invention is about 325ms. Figure 5It is the measurement result of step thrust under different control parameters by traditional closed-loop measurement. It can be seen that under different control parameters, the measurement results of traditional closed-loop measurement vary greatly. The result under control parameter 1 shows large overshoot and oscillation. This is because the controller gain under control parameter 1 is large, resulting in large open-loop gain of the system, small gain margin and phase margin, and poor system stability. The low-pass filter in the measurement process introduces additional phase delay, further reducing the system stability, thus causing overshoot and oscillation in the system. The shortest response time of traditional closed-loop measurement is about 990ms, which is significantly slower than the method of the present invention.

[0077] Figure 6 is the measurement result of the step thrust when the dynamic parameters are distorted by the method of the present invention, and Figure 7 It is the measurement result of the traditional open-loop dynamic measurement when the dynamic parameters are distorted. It can be found that when the dynamic parameters are distorted, the change in the measurement result of the method of the present invention is much smaller than that of the traditional open-loop dynamic measurement. When J and c are greater than 15% of the calibration results, the maximum error between the result of the open-loop dynamic measurement and the dynamic parameters is accurate is 0.2976mN, and the average error is 0.0453mN, while the maximum error of the measurement result of the method of the present invention is 0.0860mN, and the average error is 0.0149mN. The error of the method of the present invention when the dynamic parameters are distorted is significantly smaller than that of the traditional open-loop dynamic measurement, so the method of the present invention has stronger robustness.

[0078] In other embodiments, a fast response closed-loop micro-thrust measurement device based on dynamic thrust inversion is also provided, comprising:

[0079] A parameter acquisition module is used to obtain the parameters of the dynamic equation of the measurement system;

[0080] A control quantity calculation module is used to calculate a control quantity in each control cycle and use the control quantity as a standard force;

[0081] A dynamic inversion module, used to calculate the resultant force of the previous control cycle using a dynamic inversion algorithm based on the displacement data measured by the measurement system and the dynamic equation parameters in the current control cycle;

[0082] A thrust preliminary calculation module to be measured, used to calculate the thrust to be measured in the previous control cycle based on the difference between the standard force in the previous control cycle and the resultant force;

[0083] The low-pass filter module is used to perform low-pass filtering on the thrust to be measured to obtain a final result.

[0084] If the above method is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0085] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0086] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A fast response closed-loop micro-thrust measurement method based on dynamic thrust inversion, characterized in that: The following steps are involved: Obtaining the parameters of the dynamic equation of the measurement system; In each control cycle, a control quantity is calculated and used as the standard force; In the current control cycle, based on the displacement data measured by the measurement system and the parameters of the dynamic equation, a dynamic inversion algorithm is used to calculate the resultant force of the previous control cycle; Based on the difference between the standard force of the previous control cycle and the resultant force, the thrust to be measured of the previous control cycle is calculated; The thrust to be measured is subjected to low-pass filtering to obtain a final result.

2. The fast response closed-loop micro-thrust measurement method based on dynamic thrust inversion according to claim 1 is characterized in that: The parameters of the kinetic equation of the measurement system are obtained by measurement or calibration.

3. The fast response closed-loop micro-thrust measurement method based on dynamic thrust inversion according to claim 1 or 2, characterized in that: The expression of the dynamic equation of the measurement system is: Where T is the thrust to be measured, θ is the angular displacement output by the measurement system, and are the corresponding second-order differential and first-order differential respectively, J is the system moment of inertia, c is the system damping coefficient, k is the system stiffness coefficient, L T is the length of the force arm acting on the thrust; The dynamic equation includes the system moment of inertia j, the system damping coefficient c, the system stiffness coefficient k and the length of the force arm L of the thrust T .

4. The fast response closed-loop micro-thrust measurement method based on dynamic thrust inversion according to claim 1 is characterized in that: The control algorithm for calculating and obtaining the control variable includes a PID algorithm.

5. The fast response closed-loop micro-thrust measurement method based on dynamic thrust inversion according to claim 3 is characterized in that: The calculation formula of the resultant force of the previous control cycle is: in, is the resultant force of the k-1th period, and are the second and first order differentials of the angular displacement with respect to time in the kth period.

6. The fast response closed-loop micro-thrust measurement method based on dynamic thrust inversion according to claim 5 is characterized in that: The second-order differential and the first-order differential are obtained by using backward difference approximate differential solution.

7. The fast response closed-loop micro-thrust measurement method based on dynamic thrust inversion according to claim 1 is characterized in that: According to the measurement instruction, the thrust to be measured in each control cycle is calculated cyclically until the measurement is completed.

8. A fast response closed-loop micro-thrust measurement device based on dynamic thrust inversion, characterized in that: include: A parameter acquisition module is used to obtain the parameters of the dynamic equation of the measurement system; A control quantity calculation module is used to calculate a control quantity in each control cycle and use the control quantity as a standard force; A dynamic inversion module, used to calculate the resultant force of the previous control cycle using a dynamic inversion algorithm based on the displacement data measured by the measurement system and the dynamic equation parameters in the current control cycle; A thrust preliminary calculation module to be measured, used to calculate the thrust to be measured in the previous control cycle based on the difference between the standard force in the previous control cycle and the resultant force; The low-pass filter module is used to perform low-pass filtering on the thrust to be measured to obtain a final result.

9. A computer-readable storage medium, characterized in that: The method comprises one or more programs for execution by one or more processors of an electronic device, wherein the one or more programs comprise instructions for executing the fast-response closed-loop micro-thrust measurement method based on dynamic thrust inversion as claimed in any one of claims 1 to 7.

10. An electronic device, characterized in that: The invention comprises one or more processors, a memory and one or more programs stored in the memory, wherein the one or more programs include instructions for executing the fast-response closed-loop micro-thrust measurement method based on dynamic thrust inversion as claimed in any one of claims 1 to 7.

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