Flexible connection load transfer function identification method based on active frequency sweep excitation

Abstract

The invention relates to a flexible connection load transfer function identification method based on active frequency sweep excitation, and relates to the field of spacecraft attitude control, and the method comprises the following steps: a plurality of three-super platform actuators sequentially output sine frequency sweep excitation moments of a load in three rotation directions, and a high-bandwidth fiber-optic gyroscope simultaneously measures the triaxial angular velocity of the load; the obtained time domain result is converted into a frequency domain result, and then load transfer function model identification is carried out; and adjusting controller parameters in the three-super platform control unit based on the identification model so as to increase the control bandwidth and improve the secondary control capability on the basis of ensuring the stability margin of the controller in the three-super platform control unit. And a technical basis is provided for ultrahigh-precision pointing, ultrahigh-stability control and high-quality imaging of optical loads of spacecrafts in the future.

Description

Technical Field

[0001] This invention relates to the field of spacecraft attitude control technology, and in particular to a method for identifying the transfer function of flexible connection loads based on active frequency sweep excitation. Background Technology

[0002] Currently, large high-resolution optical remote sensing satellites have extremely high control performance requirements. These satellites are large inertial satellites with multiple large flexible attachments, low and dense modal frequencies, and severe coupling between rigid, flexible and fluid components. The contradiction between the agile maneuvering "fast start and fast stop" and the ultra-high resolution imaging "fast and stable, ultra-precise and ultra-stable" control is prominent. Traditional control methods that rely solely on the satellite platform level are insufficient to meet the extremely high performance requirements. Therefore, a three-super platform with rapid pointing adjustment, disturbance compensation and vibration isolation was designed between the satellite platform and the payload. Various on-board interferences are eliminated centrally at the payload mounting point to improve the "fast, stable and accurate" performance indicators.

[0003] To achieve extremely high precision control performance indicators, the three-dimensional platform needs to adopt high-bandwidth control at the second level. However, directly increasing the bandwidth by blindly adjusting or trial and error may cause the control system to oscillate or even become unstable.

[0004] Therefore, to address the above shortcomings, a method for identifying the load transfer function of flexible connections based on active frequency sweep excitation is needed. Summary of the Invention

[0005] (a) Technical problems to be solved The technical problem to be solved by this invention is to solve the problem of oscillation or even divergence in the control system caused by blindly adjusting parameters or by trial and error.

[0006] (II) Technical Solution To address the aforementioned technical problems, this invention provides a method for identifying the transfer function of a flexible connection load based on active frequency sweep excitation. The method utilizes a structure where a load is connected to a satellite platform by several sets of triple-platform actuators. Each set of triple-platform actuators includes a spring-damped passive element, a voice coil motor active element, and an eddy current sensor. A high-bandwidth fiber optic gyroscope and a triple-platform control unit are mounted on the load. The method includes the following steps: I. Several triple-platform actuators sequentially output sinusoidal sweep frequency excitation torques in three rotational directions of the load, while high-bandwidth fiber optic gyroscopes simultaneously measure the three-axis angular velocities of the load; II. Convert the obtained time-domain results to frequency-domain results, and then perform load transfer function model identification, specifically as follows: in, , , To identify the load triaxial direction transfer function; , , To identify the order of the obtained load triaxial direction transfer function; , , To identify the first of the obtained load triaxial direction transfer functions Amplitude value; , , To identify the first of the obtained load triaxial direction transfer functions First frequency; , , To identify the first of the obtained load triaxial direction transfer functions Damping ratio; III. Based on the identification model, adjust the controller parameters in the control unit of the super platform to increase the control bandwidth and improve the secondary control capability while ensuring the stability margin of the controller in the control unit of the super platform.

[0007] As a further explanation of the present invention, preferably, the sinusoidal sweep frequency excitation torque of the load in the three rotational directions is expressed as: in, These correspond to the load along the X, Y, and Z axes, respectively. Specifically: The torque amplitude output at the initial moment of the frequency sweep excitation; The torque amplitude output at the end of the frequency sweep excitation; For time; This represents the total sweep time for a single axis. Specifically: This is the start frequency for the frequency sweep; This is the sweep termination frequency.

[0008] As a further explanation of the present invention, preferably, the outputs of the plurality of triple-platform actuators are represented as follows: in, This refers to the output force vector of the voice coil motor inside the actuator of the three-dimensional platform. The number of actuators on the three-dimensional platform; This is the symbol for the transpose matrix; Specifically: Let be the Jacobian matrix from the load pose space to the actuator motion space; for The generalized inverse matrix.

[0009] As a further explanation of the present invention, preferably, the formula for converting the time-domain result into the frequency-domain result is as follows: in, , , This represents the frequency domain representation of the load triaxial transfer function obtained through time-domain data transformation. Represented as Fast Fourier Transform; , , These are the angular velocity measurement results of the load in the three axes.

[0010] (III) Beneficial Effects The above-described technical solution of the present invention has the following advantages: This invention, without adding any additional devices, can obtain an object model through the output of a triple-actuator and the measurement results of a high-bandwidth gyroscope. This model can then be used for controller stability analysis and control parameter optimization design. It solves the problem of control system oscillation or even divergence caused by blindly adjusting parameters or by trial and error, and improves the overall performance of the triple-actuator control system. This enables ultra-high precision, ultra-high stability, and ultra-high agility control performance of the load. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the system structure of the present invention; Figure 2 This is a flowchart of the method of the present invention; Figure 3 This is a graph showing the measurement results of the load of the present invention sweeping frequency excitation output in the X-axis direction and the high-bandwidth fiber optic gyroscope; Figure 4This is a graph showing the measurement results of the load of the present invention sweeping frequency excitation output in the Y-axis direction and the high-bandwidth fiber optic gyroscope; Figure 5 This is a graph showing the measurement results of the load of the present invention sweeping frequency excitation output in the Z-axis direction and the high-bandwidth fiber optic gyroscope; Figure 6 This is a diagram showing the measurement and identification results of the load transfer function in the X-axis direction according to the present invention; Figure 7 This is a diagram showing the measurement and identification results of the load transfer function in the Y-axis direction according to the present invention; Figure 8 This is a diagram showing the measurement and identification results of the load transfer function in the Z-axis direction according to the present invention; Figure 9 This is a diagram showing the stability analysis and control parameter optimization results of the load in the X-axis direction according to the present invention; Figure 10 This is a diagram showing the stability analysis and control parameter optimization results of the load in the Y-axis direction according to the present invention; Figure 11 This is a diagram showing the stability analysis and control parameter optimization results of the load in the Z-axis direction according to the present invention; Figure 12 This is a diagram showing the step response of the load in the X-axis direction and the optimization results of the control parameters according to the present invention; Figure 13 This is a diagram showing the step response of the load in the Y-axis direction and the optimization results of the control parameters according to the present invention; Figure 14 This is a diagram showing the step response of the load in the Z-axis direction and the optimization results of the control parameters according to the present invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0013] A method for identifying the load transfer function of flexible connections based on active frequency sweep excitation, such as... Figure 1As shown, the structure comprises a payload, a three-axis super-platform actuator, a high-bandwidth fiber optic gyroscope, and a three-axis super-platform control unit. The payload is typically an optical system used for high-quality target imaging. The high-bandwidth fiber optic gyroscope is mounted on the payload to measure its three-axis angular velocities. The three-axis super-platform control unit is mounted on the payload for high-bandwidth fiber optic gyroscope measurement and acquisition, control algorithm calculation, and three-axis super-platform actuator drive output. Each three-axis super-platform actuator consists of three parts mounted in parallel: a spring-damped passive element, a voice coil motor active element, and an eddy current measurement sensor. The voice coil motor actively controls the actuator's axial movement, and the eddy current measurement sensor measures the actuator's axial displacement. Several three-axis super-platform actuators connect the payload to the satellite platform, and the combined voice coil motors of these actuators enable attitude movement of the payload in all three axes.

[0014] like Figure 2 As shown, the specific steps of this method include: Ⅰ.① Several triple-platform actuators sequentially output sinusoidal sweep frequency excitation torques in three rotational directions of the load, specifically as follows: in, These correspond to the load along the X, Y, and Z axes, respectively. Specifically: The torque amplitude output at the initial moment of the frequency sweep excitation is preferably 5 Nm; The torque amplitude output at the end of the frequency sweep excitation is preferably 25 Nm; The current moment; The total sweep time for a single axis is preferably 60 seconds. Specifically: The sweep start frequency is preferably 0.1Hz; The sweep termination frequency is preferably 100Hz; It is the logarithm to the base e.

[0015] By employing a logarithmic sweep frequency method with increased amplitude, the signal-to-noise ratio of mid-to-high frequency signal measurements can be improved, thereby enhancing identification accuracy.

[0016] ②The frequency sweep excitation torque is then converted into multiple actuator outputs, specifically: in, This refers to the output force vector of the voice coil motor inside the actuator of the three-dimensional platform. The preferred number of actuators for the three-dimensional platform is 8; This is the symbol for the transpose matrix; Specifically: Let be the Jacobian matrix from the load pose space to the actuator motion space; for The generalized inverse matrix is ​​as follows: -0.0956 0.4621 0.1768 -0.1264 0.1264 -0.0926 0.3127 -0.2450 0.1768 -0.1264 0.1264 0.0926 0.3127 0.2450 0.1768 0.1264 0.1264 -0.0926 -0.0956 -0.4621 0.1768 0.1264 0.1264 0.0926 0.0956 -0.4621 0.1768 0.1264 -0.1264 -0.0926 -0.3127 0.2450 0.1768 0.1264 -0.1264 0.0926 -0.3127 -0.2450 0.1768 -0.1264 -0.1264 -0.0926 0.0956 0.4621 0.1768 -0.1264 -0.1264 0.0926] The sweep frequency output of each actuator, calculated based on the above formula, is executed through the output of the three-super control unit and the actuator voice coil.

[0017] ③ Simultaneously with the actuator voice coil output, the three-axis angular velocities of the load were measured using a high-bandwidth fiber optic gyroscope: in , , These are the angular velocity measurement results of the load in the three axes.

[0018] Based on the above parameters, the load triaxial sweep frequency excitation output and the high-bandwidth fiber optic gyroscope measurement results are as follows: Figures 3-5 As shown.

[0019] II. ① Convert the time-domain results obtained in step I into frequency-domain results, specifically as follows: in, , , This represents the frequency domain representation of the load triaxial transfer function obtained through time-domain data transformation. Represented as Fast Fourier Transform, obtained through Fourier Transform , , Then, the modulus and argument can be obtained. , , The amplitude and phase frequency results.

[0020] ② The following multiplication form of multiple sets of second-order linear systems is used to... , , Identify the frequency domain results: in, , , To identify the load triaxial direction transfer function; , , To identify the order of the obtained load triaxial direction transfer function; , , To identify the first of the obtained load triaxial direction transfer functions Amplitude value; , , To identify the first of the obtained load triaxial direction transfer functions First frequency; , , To identify the first of the obtained load triaxial direction transfer functions Damping ratio; This is the multiplication operator.

[0021] The load triaxial direction transfer function measurement and identification result curves are as follows: Figures 6-8 As shown, the identification model parameters are listed in Table 1-3, where the transfer function obtained above is the torque-to-angular velocity transfer function. To obtain... Figures 6-8 As shown in Table 1-3, the torque-to-angle transfer function requires multiplying the amplitude at each frequency point by the amplitude of the torque-to-angular velocity transfer function. (in For each corresponding frequency value): Table 1. X-axis identification results Table 2 Y-axis identification results Table 3 Z-axis identification results III. Based on the identification model in step II, adjust the controller parameters in the super-ultra-platform control unit to increase the control bandwidth and enhance the secondary control capability while ensuring the stability margin of the controller in the super-ultra-platform control unit: Figures 9-11 The stability analysis Nichols curves before and after optimizing the control parameters are presented. From the figure, it can be concluded that the control system has sufficient stability margin based on the identification model and optimized control parameters.

[0022] Figures 12-14 The unit step response curves before and after optimizing the control parameters are presented. By optimizing the control parameters, the dynamic characteristics of the control system are improved while ensuring sufficient stability margin, thereby enhancing the two-level control capability of the three-dimensional platform.

[0023] In summary, the identification method provided by this invention actively outputs force through the secondary control of a three-dimensional platform, and then identifies the transfer functions of the load in three directions of the secondary controlled object by measuring and acquiring results through a high-bandwidth fiber optic gyroscope. Based on this model, control parameters are optimized to achieve high control performance while ensuring sufficient stability margin in the secondary control system, thereby achieving higher control capabilities for the load. This provides a technical foundation for high-precision pointing, high-stability control, and rapid stabilization control of loads in next-generation spacecraft.

[0024] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flexible connection load transfer function identification method based on active frequency sweeping excitation, based on the structure connected by several groups of three ultra-platform actuators, wherein each group of three ultra-platform actuators includes a spring-damping passive link, a voice coil motor active link and an eddy current sensor, a high-bandwidth fiber-optic gyroscope and a three ultra-platform control unit are installed on the load, characterized in that: Includes the following steps: ​ I. Several triple-platform actuators sequentially output sinusoidal sweep frequency excitation torques in three rotational directions of the load, while high-bandwidth fiber optic gyroscopes simultaneously measure the three-axis angular velocities of the load; II. Convert the obtained time-domain results to frequency-domain results, and then perform load transfer function model identification, specifically as follows: in, , , is a triaxial direction transfer function of the identified load; , , is the order of the identified load triaxial direction transfer function; , , To identify the first of the obtained load triaxial direction transfer functions Amplitude value; , , To identify the first of the obtained load triaxial direction transfer functions First frequency; , , To identify the first of the obtained load triaxial direction transfer functions Damping ratio; III. Based on the identification model, adjust the controller parameters in the control unit of the super platform to increase the control bandwidth and improve the secondary control capability while ensuring the stability margin of the controller in the control unit of the super platform.

2. The method for identifying the load transfer function of a flexible connection based on active frequency sweeping excitation according to claim 1, characterized in that: The sinusoidal sweep frequency excitation torque of the load in the three rotational directions is expressed as: in, These correspond to the load along the X, Y, and Z axes, respectively. Specifically: The torque amplitude output at the initial moment of the frequency sweep excitation; The torque amplitude output at the end of the frequency sweep excitation; For time; This represents the total sweep time for a single axis. Specifically: This is the start frequency for the frequency sweep; This is the sweep termination frequency.

3. The method for identifying the load transfer function of a flexible connection based on active frequency sweeping excitation according to claim 2, characterized in that: The outputs of multiple triple-platform actuators are represented as follows: in, This refers to the output force vector of the voice coil motor inside the actuator of the three-dimensional platform. The number of actuators on the three-dimensional platform; This is the symbol for the transpose matrix; Specifically: Let be the Jacobian matrix from the load pose space to the actuator motion space; for The generalized inverse matrix.

4. The method for identifying the load transfer function of a flexible connection based on active frequency sweeping excitation according to claim 3, characterized in that: The formula for converting time-domain results to frequency-domain results is as follows: in, , , This represents the frequency domain representation of the load triaxial transfer function obtained through time-domain data transformation. Represented as Fast Fourier Transform; , , The figures show the angular velocities of the load in the three axes.

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