A six-degree-of-freedom parallel mechanism active vibration reduction system

Abstract

The application relates to a six-degree-of-freedom parallel mechanism active damping system, which comprises an upper platform, a lower platform, six acceleration sensors, six controllers and six actuator rods driven by actuators, the six actuator rods are identical in structure, and the upper ends and the lower ends of the six actuator rods are hinged to the upper platform and the lower platform respectively; adjacent actuator rods are perpendicular to each other and meet at a point in the extension line direction; the signal input and output ends of each controller are electrically connected with the corresponding acceleration sensor and actuator respectively, the six acceleration sensors are installed on the upper platform on the upper side of the corresponding actuator rod to monitor the motion acceleration of the upper platform in real time and feed back to the corresponding controller to provide a control variable for the control of the controller; each controller controls the action of the corresponding actuator through an adaptive filtering algorithm based on an EPLL algorithm, so that active damping is realized. The system can realize fast and stable active damping control without the need of dynamic modeling of the six-degree-of-freedom parallel mechanism, and the system has strong universality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of satellite-borne motion accessory disturbance suppression, and particularly relates to a six-degree-of-freedom parallel mechanism active vibration reduction system. BACKGROUND

[0002] With the development of high-precision satellite remote sensing, space optical communication and other applications, the precision index of satellite-borne payloads is continuously improved, and the requirement for the stability of the working environment is more stringent. In view of the multi-degree-of-freedom characteristics of the micro-vibration on the satellite, a classic six-degree-of-freedom parallel mechanism is introduced as a connecting device between the precision payload and the satellite body, which can simultaneously realize the isolation and suppression of multi-degree-of-freedom vibration. When designing the controller of the traditional six-degree-of-freedom parallel mechanism, the dynamics modeling of the mechanism is needed to estimate the transfer function of the actuator.

[0003] The patent with the application number CN202211662413.7 discloses a two-dimensional pointing mechanism with bearing and vibration isolation capacity. In the static state, the high-static-low-action actuator has a large static stiffness, which can realize the static bearing of the two-dimensional pointing mechanism. When external disturbance acts on the lower platform, in the dynamic load transmission, the high-static-low-action actuator realizes the quasi-zero stiffness function, and isolates the high-frequency part of the dynamic load transmitted by the lower platform, thereby realizing the dynamic vibration isolation function. Although the patent provides a feasible pointing mechanism with bearing and vibration isolation capacity, the mechanism does not involve the control system, and does not truly realize active vibration isolation, so the precision is low and the stability is poor.

[0004] The prior art (Wang J M, Kong Y F, Huang H. Research on vibration isolation and vibration suppression collaborative control based on Stewart platform [J]. Vibration and shock, 2019, vol. 38 (7): 186-194) proposes a control method combining adaptive filtering and Skyhook, wherein the adaptive filtering control can realize isolation and vibration suppression collaborative control, and the Skyhook is introduced as an inner control loop to increase the active damping to ensure the stability of the system. Although the method has good stability, it still involves the dynamics modeling of the platform, which not only increases the complexity of the calculation, but also the system cannot maintain stability when the modeling error exceeds ±90°.

[0005] The prior art studies the six-degree-of-freedom parallel mechanism active vibration isolation system, and although certain achievements have been made in different research fields, the dynamics modeling of the six-degree-of-freedom parallel mechanism is still needed, and the modeling calculation process is complex, which requires a lot of solution time, and the system has poor universality and adaptability. SUMMARY

[0006] The present application aims to provide a six-degree-of-freedom parallel mechanism active vibration reduction system, which can realize rapid and stable active vibration reduction control without the need for dynamics modeling of the six-degree-of-freedom parallel mechanism, and has strong system universality.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: a six-degree-of-freedom parallel mechanism active vibration reduction system, comprising an upper platform, a lower platform, six acceleration sensors, six controllers, and six actuator rods driven by actuators. The six actuator rods have identical structures, and their upper and lower ends are respectively hinged to the upper and lower platforms; adjacent actuator rods are perpendicular to each other and intersect at a point in the direction of their extension lines; the signal input and output terminals of each controller are electrically connected to the corresponding acceleration sensors and actuators, respectively; the six acceleration sensors are respectively installed on the upper platform above the corresponding actuator rods to monitor the motion acceleration of the upper platform in real time and feed it back to the corresponding controllers, providing control variables for the controllers; each controller controls the corresponding actuator action through an adaptive filtering algorithm based on the EPLL algorithm, thereby achieving active vibration reduction.

[0008] Furthermore, the single actuator mainly consists of an actuator and ball joints fixed to the upper and lower ends of the actuator. The actuator is a voice coil motor, which is the power source for driving the actuator.

[0009] Furthermore, in the six-degree-of-freedom parallel mechanism active vibration reduction system, the six actuators are perpendicular to each other in the extension direction, so as to decouple the multi-input multi-output system into six single-input single-output subsystems, and adopt a distributed control strategy for system control;

[0010] Based on this, each controller uses an adaptive filtering algorithm based on the EPLL algorithm to perform single-input single-output control on a single actuator.

[0011] Furthermore, for a six-degree-of-freedom parallel mechanism operating under micro-vibration conditions, the estimated parameter space is set... A est (t), ω est (t), δ est (t) represents the estimated values ​​of the vibration amplitude, frequency, and phase angle of the disturbance, respectively; then the control force signal f of the actuator is... ai (t) The acceleration signal y transmitted to the upper platform through the actuator lever i (t) is:

[0012]

[0013] In the formula, f ai (t)=A est (t)sinφ est (t), estimate phase φ est (t)=ω est t+δ est (t); The transfer function of the control channel, i.e., the control force signal f of the actuator.ai (t) to a i (t) ; the total disturbance d i (t) ; e i (t) is the error signal, i.e. the rod acceleration a i (t), measured by an accelerometer mounted along the actuator rod axis; e i (t) = d i (t) - y i (t) ;

[0014] The adaptive filter algorithm based on the EPLL algorithm uses e i (t) to update the filter weight coefficients in real time, and further adjusts the output of the filter estimation parameter space to eliminate disturbances, so that the error signal e i (t) is minimized, i.e. the rod acceleration a i (t) is minimized; the corresponding adaptive filter parameter update equation is as follows:

[0015] A est (n+1) = A est (n) - μ1e i (n) x ai (n)

[0016] ω est (n+1) = ω est (n) - μ2e i (n) A est (n) x bi (n)

[0017] δ est (n+1) = δ est (n) - μ3e i (n) A est (n) x bi (n)

[0018] In the formula, u j (j = 1, 2, 3) is the step convergence factor, x ai (n) = sin (φ est (n) + α), x bi (n) = cos (φ est (n) + α), where n is the nth iteration, and α is the offset phase.

[0019] Further, the controller uses a phase compensation method to compensate for the secondary channel effect, specifically:

[0020] First, a small positive value is used to initialize the step size, in the early slow iteration process, select N samples, without updating the filter parameters, calculate the mean error signal energy and interference signal energy

[0021] Then, for another N samples, in the iteration process, update the adaptive filter parameters according to the EPLL algorithm, calculate the mean error signal energy κ e2 and interference signal energy

[0022] The ratio of κ e1 , The ratio of κ and κ e2 , The ratio of κ

[0023] If , it indicates that the residual signal power is increasing, the secondary channel influence algorithm is not iterating in the direction of convergence, at this time, the phase compensation is carried out, the acceleration signal phase is biased by 180°, the phase response of the secondary channel after phase bias moves to the convergence boundary of ±90°, the algorithm will continue to iterate in the direction of convergence, if , it indicates that the residual signal power is decreasing, the adaptive filter parameter update is not changed and continues to iterate.

[0024] Further, biasing the acceleration signal phase by 180° is equivalent to changing the positive and negative signs in front of the adaptive filter parameter update equation step size, which is convenient for operation.

[0025] Compared with the prior art, the present application has the following beneficial effects: the present application provides a six-degree-of-freedom parallel mechanism active vibration reduction system, which overcomes the problems of complex dynamics modeling, long solving time and the like in the prior art, controls the actuator to adjust the acceleration of the actuating rod through the adaptive filtering algorithm based on the EPLL algorithm, makes the disturbance acceleration tend to zero, realizes active vibration reduction of the six-degree-of-freedom parallel mechanism platform, has high control precision, rapid response and good control stability. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a structural diagram of the six-degree-of-freedom parallel mechanism in the embodiment of the present application;

[0027] Figure 2This is a control principle diagram of a single actuator in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram illustrating the implementation principle of the phase compensation method in this embodiment of the invention;

[0029] Figure 4 This is a schematic diagram illustrating the implementation principle of the adaptive filtering algorithm based on the EPLL algorithm in this embodiment of the invention. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0032] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] This embodiment provides a six-degree-of-freedom parallel mechanism active vibration reduction system, such as Figures 1-2 As shown, the system includes an upper platform 1, a lower platform 2, six acceleration sensors, six controllers, and six actuator rods 3 driven by actuators. The six actuator rods have identical structures, and their upper and lower ends are hinged to the upper and lower platforms, respectively. Adjacent actuator rods are perpendicular to each other and intersect at a point along their extended lines. The signal input and output terminals of each controller are electrically connected to the corresponding acceleration sensors and actuators. The six acceleration sensors are respectively installed on the upper platform above the corresponding actuator rod to monitor the motion acceleration of the upper platform in real time and feed it back to the corresponding controller, providing control variables for the controller's control. Each controller controls the corresponding actuator's action through an adaptive filtering algorithm based on the EPLL algorithm, thereby achieving active vibration reduction. The implementation principle of the adaptive filtering algorithm based on the EPLL algorithm is as follows: Figure 4 As shown.

[0034] In this embodiment, a single actuating rod mainly consists of an actuator and ball joints fixed to the upper and lower ends of the actuator. The actuator uses a voice coil motor, which is the power source for driving the actuating rod.

[0035] In the six-degree-of-freedom parallel mechanism active vibration reduction system provided by the application, six actuating rods are perpendicular to each other in the direction of the extension line, so as to decouple the multiple-input multiple-output system into six single-input single-output subsystems, and a decentralized control strategy is used for system control. On this basis, each controller uses an adaptive filtering algorithm based on the EPLL algorithm to perform single-input single-output control on a single actuating rod.

[0036] The control purpose of the system is that, in a micro-vibration environment, the acceleration of the upper end of the actuating rod in the rod direction is positively correlated with the acceleration of the upper platform, the controller adjusts the driving force of the voice coil motor, the acceleration response of the upper end of the actuating rod in the rod direction tends to zero, and then the acceleration of the upper platform also tends to zero.

[0037] Generally, sensors for measuring disturbance source signals cannot be installed at will inside a star-borne precision load, but the adaptive filtering feedback control based on the EPLL algorithm realized by the system can estimate and eliminate the disturbance without obtaining the disturbance information through additional sensors, so as to realize active vibration reduction of the six-degree-of-freedom parallel mechanism. Further details are described below.

[0038] When the six-degree-of-freedom parallel mechanism is in a micro-vibration environment, the estimated parameter space is A est (t), ω est (t), and δ est (t) are the corresponding estimated values of the vibration amplitude, frequency, and phase angle of the disturbance, respectively. The acceleration signal y ai (t) of the upper platform transmitted by the control force signal f i (t) of the driving actuator is:

[0039]

[0040] In the formula, f ai (t) = A est (t) sin φ est (t), the estimated phase φ est (t) = ω est t + δ est (t).

[0041] is the transfer function of the control channel, that is, the transfer function from the control force signal f ai (t) of the actuator to a i (t); the disturbance acceleration of the upper platform caused by the disturbance acceleration of the lower platform and the direct disturbance force is collectively referred to as the total disturbance d i (t); e i (t) is an error signal, that is, the rod direction acceleration a i (t) measured by the accelerometer installed in the axial direction of the actuating rod; ei (t) = d i (t) - y i (t).

[0042] The adaptive filtering algorithm based on the EPLL algorithm provided by the application utilizes e i (t) to update the weight coefficient of the filter in real time, and further adjusts the output of the filter estimation parameter space to eliminate disturbance, so that the error signal e i (t) is minimized, i.e., the rod acceleration a i (t) is minimized. The corresponding adaptive filtering parameter update equation is as follows:

[0043] A est (n+1) = A est (n) - μ1e i (n) x ai (n)

[0044] ω est (n+1) = ω est (n) - μ2e i (n) A est (n) x bi (n)

[0045] δ est (n+1) = δ est (n) - μ3e i (n) A est (n) x bi (n)

[0046] In the formula, u j (j = 1, 2, 3) is a step convergence factor, x ai (n) = sin (φ est (n) + α), x bi (n) = cos (φ est (n) + α), wherein n is the nth iteration, and α is a bias phase.

[0047] For the adaptive control described above, the unknown secondary channel will cause instability of the algorithm. In addition to the traditional estimation of the secondary channel through dynamic modeling, the application proposes a phase compensation method to compensate for the influence of the secondary channel, so that modeling of the secondary channel is not required. As shown in Figure 3 , the method specifically includes the following steps:

[0048] First, a small positive value is used to initialize the step, and in the slow iteration process in the early stage, N samples are selected, and the mean error signal energy and the interference signal energy

[0049]

[0050] Then, for the other N samples, the adaptive filter parameters are updated according to the EPLL algorithm during the iteration process, and the mean error signal energy κ is calculated. e2 and interference signal energy

[0051] Calculate κ e1 , ratio and κ e2 , ratio

[0052] like This indicates that the residual signal power is increasing, and the secondary channel is affecting the algorithm, preventing it from iterating towards convergence. In this case, phase compensation is performed on the algorithm, shifting the acceleration signal phase by 180°. For ease of computation, this operation can be equivalent to changing the sign of the step size in the adaptive filter parameter update equation. Based on the strictly positive real number property, the secondary channel phase response after phase shifting can be moved to within the ±90° convergence bound, and the algorithm will continue iterating towards convergence. If... This indicates that the residual signal power is decreasing. The adaptive filter parameters are updated without any changes and the iteration continues until the system reaches a stable convergence state, that is, the system vibration disturbance is eliminated.

[0053] Therefore, the controller in this system, through power monitoring and phase compensation strategies, does not need to model the secondary channel, thus avoiding the tedious step of estimating the transfer function of the actuator by performing dynamic modeling of the system.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, 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 scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A six-degree-of-freedom parallel mechanism active vibration reduction system, characterized in that, The six-degree-of-freedom parallel mechanism active vibration reduction system comprises an upper platform, a lower platform, six acceleration sensors, six controllers and six actuating rods driven by actuators, the six actuating rods are identical in structure, and the upper and lower ends of the actuating rods are hinged to the upper platform and the lower platform respectively; adjacent actuating rods are perpendicular to each other and meet at a point in the direction of extension; the signal input and output ends of each controller are electrically connected to the corresponding acceleration sensor and actuator respectively, the six acceleration sensors are installed on the upper platform on the upper side of the corresponding actuating rod to monitor the motion acceleration of the upper platform in real time and feed back to the corresponding controller to provide a control variable for the control of the controller; each controller controls the corresponding actuator to move through an adaptive filtering algorithm based on an EPLL algorithm, thereby achieving active vibration reduction. In the six-degree-of-freedom parallel mechanism active vibration reduction system, the six actuating rods are perpendicular to each other in the direction of extension, so as to decouple the multiple-input multiple-output system into six single-input single-output subsystems, and a decentralized control strategy is used for system control. On this basis, each controller uses an adaptive filtering algorithm based on an EPLL algorithm to control a single actuating rod in a single-input single-output manner. When the six-degree-of-freedom parallel mechanism is in a micro-vibration environment, the parameter estimation space is , , , The vibration amplitude, frequency, and phase angle of the disturbance are respectively estimated as corresponding estimated values; the control force signal of the driving actuator The acceleration signal transmitted to the upper platform through the actuator rod is : wherein , the estimated phase ; is the transfer function of the control channel, i.e. the control force signal to the transfer function; the disturbance acceleration of the lower plate, the disturbance acceleration of the upper plate caused by the direct disturbance force are collectively referred to as the total disturbance ; is the error signal, i.e. the rod acceleration measured by an accelerometer mounted along the axis of the actuator rod; ; The adaptive filtering algorithm based on the EPLL algorithm utilizes Real-time updating of the weight coefficients of the filter, and continuous adjustment of the output of the filter estimation parameter space to eliminate disturbances, so that the error signal is reduced to a minimum, i.e., the rod acceleration is reduced to a minimum; the corresponding adaptive filtering parameter update equation is as follows: In the formula, is a step convergence factor, , where is the nth iteration, is a bias phase.

2. The six-degree-of-freedom parallel mechanism active vibration reduction system according to claim 1, characterized in that, Each actuating rod mainly comprises an actuator and a spherical hinge fixed to the upper and lower ends of the actuator, the actuator is a voice coil motor, and the voice coil motor is a power source for driving the actuating rod.

3. The six-degree-of-freedom parallel mechanism active vibration reduction system according to claim 1, characterized in that, The controller uses a phase compensation method to compensate for the influence of the secondary channel, specifically as follows: First, a small positive value is used to initialize the step size, and in the slow iteration process in the early stage, N samples are selected, and the mean error signal energy is calculated without updating the filter parameters and the interference signal energy ; Then, for the other N samples, the adaptive filter parameters are updated according to the EPLL algorithm during the iteration process, and the mean error signal energy is calculated and the interference signal energy ; Computing , the ratio of and , the ratio of ; If , it indicates that the residual signal power is increasing, the secondary path influence algorithm is not iterating in the direction of convergence, at this time the phase compensation is carried out, the acceleration signal is biased by 180°; the phase response of the secondary path after phase biasing moves to the convergence boundary of ±90°, the algorithm will continue to iterate in the direction of convergence; if , it indicates that the residual signal power is decreasing, the adaptive filter parameter update does not make any change and continues to iterate.

4. The six-degree-of-freedom parallel mechanism active vibration reduction system according to claim 3, characterized in that, The phase offset of the acceleration signal by 180° is equivalent to changing the positive and negative signs in front of the step of the adaptive filtering parameter update equation.

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