Base fixed type multi-connecting-rod motion system and control method and control device thereof

Abstract

The invention discloses a base fixed type multi-connecting-rod motion system and a control method and device thereof, belongs to the technical field of mimicry simulation of a mechanical environment, and particularly relates to a structure design and control technology of a six-degree-of-freedom parallel motion system. The problem that transverse vibration of a hydraulic cylinder and nonlinear factors of a system of an existing conventional hydraulically-driven six-degree-of-freedom parallel mechanism limit improvement of the system bandwidth is solved, and the system bandwidth is improved to 100 Hz; the system comprises a mechanical structure subsystem, an acceleration detection subsystem and a servo control subsystem, and the hydraulic actuator is used for performing telescopic motion based on the motion instruction to drive the connecting rod to swing, so that the platform moves and presents different postures. The base fixed type multi-connecting-rod motion system and the control method and the control device thereof are suitable for structural design and control of a six-degree-of-freedom parallel motion system.

Description

Technical Field

[0001] The present invention relates to the technical field of mimicry simulation of mechanical environments, and in particular to the structural design and control technology of a six-degree-of-freedom parallel motion system. Background Art

[0002] In the field of (simulated) simulation test technology of mechanical environment, multi-degree-of-freedom motion test can truly simulate the actual dynamic environment, so as to test the performance of large and complex structures under multi-degree-of-freedom motion excitation or expose defects and hidden dangers that are not easy to find. In the fields of high-speed rail, automobiles, civil engineering, etc., multi-degree-of-freedom motion test can be used to test instruments or components that require environmental vibration or mechanical response characteristics to ensure that these devices can work normally at high altitudes or in extreme environments. In multi-degree-of-freedom motion test, actuator excitation is used for excitation.

[0003] The actuators used for excitation are mainly divided into electric drive (such as voice coil drive) actuators and hydraulic drive actuators. Generally, the actuators in the field of conventional small loads mainly use electric drive devices, while the tests with larger loads require hydraulic drive actuators.

[0004] A common device used for multi-DOF motion testing is a six-DOF parallel mechanism, such as Fig.15 For example, in the Chinese invention patent document with the publication number of "CN102004822A" and the name of "Frequency Analysis Method of Spatial Six-DOF Parallel Motion System Based on Modality", a "spatial six-DOF parallel motion system" is recorded: the spatial (docking mechanism) six-DOF parallel motion system adopts a typical Stewart platform form driven by hydraulic pressure, has a large motion space capability, a long leg working stroke and a high system bandwidth, and its system working bandwidth can reach 10Hz.

[0005] It should be noted that in multi-DOF motion tests, in order to fully reproduce the signal and implement wide-band performance testing of the specimen, the test equipment needs to be able to reproduce high-bandwidth signals. The premise for the equipment to reproduce wide-bandwidth signals is that the mechanical natural frequency of the equipment must be high enough. At present, conventional hydraulically driven six-DOF parallel mechanisms can only reproduce signals of about 10 Hz at most, which cannot meet the signal reproduction requirements of high-bandwidth instruments or components (signals of at least 100 Hz need to be reproduced).

[0006] In conventional hydraulically driven six-DOF parallel mechanisms, the main reasons for limiting the improvement of system bandwidth include: lateral vibration of the hydraulic cylinder and nonlinear factors of the system, specifically:

[0007] (1) Regarding “lateral vibration of hydraulic cylinder”:

[0008] For general equipment, theoretically, the natural frequency of mechanical equipment is:

[0009]

[0010] Among them, f is the natural frequency, < is the mass matrix of the system, K is the stiffness matrix of the system, and λ is the eigenvalue of the matrix. It can be seen that to increase the natural frequency of the equipment, it is necessary to increase the system stiffness K or reduce the system mass M.

[0011] However, for a conventional hydraulically driven six-degree-of-freedom parallel mechanism, the hydraulic actuator will swing with the movement of the platform while telescoping. The mass of the actuator body is large, and the inertia tensor during swinging will affect the natural frequency of the system. This is mainly because the natural frequency of the lateral vibration of the hydraulic cylinder is too low, which limits the natural frequency of the entire mechanism. According to mechanical knowledge, slender rods will produce lateral bending when under pressure, and the greater the axial pressure, the greater the bending. In a six-degree-of-freedom parallel mechanism, the hydraulic cylinders used are often slender hydraulic cylinders, and their working state is often axially under heavy pressure. Therefore, for this type of hydraulic cylinder, the lateral vibration caused by lateral bending cannot be ignored, and the lateral component is large during high-frequency movement, which in turn limits the improvement of the system bandwidth.

[0012] (2) Regarding “nonlinear factors of the system”:

[0013] For conventional hydraulically driven six-degree-of-freedom parallel mechanisms, the relevant control algorithms are mainly classic methods such as PID. For hydraulically driven actuators, the drive signal can only be transmitted to the test piece after passing through the servo valve, hydraulic cylinder, connecting ball joint, platform, and fixture. There are many nonlinear factors in the transmission process, which limit the improvement of the system bandwidth. The use of traditional control algorithms cannot suppress nonlinear factors, and it is difficult to improve the system bandwidth.

[0014] In summary, there is an urgent need to make a technological breakthrough in the six-degree-of-freedom parallel mechanism in terms of mechanical structure and control algorithm, so as to complete multi-degree-of-freedom motion tests of high-bandwidth instruments or components and achieve the reproduction of high-bandwidth signals of about 100 Hz. Summary of the invention

[0015] The present invention proposes a base-fixed multi-link motion system and a control method and a control device thereof, which solve the problem of the lateral vibration of the hydraulic cylinder and the nonlinear factors of the system limiting the improvement of the system bandwidth in the existing conventional hydraulically driven six-degree-of-freedom parallel mechanism, and increase the system bandwidth to 100Hz.

[0016] The base-fixed multi-link motion system of the present invention comprises: a mechanical structure subsystem, an acceleration detection subsystem and a servo control subsystem;

[0017] The mechanical structure subsystem includes three embedded parts embedded in the foundation, a base, a support, six sets of connecting rod actuator legs and a platform;

[0018] Each connecting rod actuator leg includes a hydraulic actuator, a cross hinge and a connecting rod; the cross hinge includes a middle cross hinge and an upper cross hinge;

[0019] The cylinder at the bottom of the hydraulic actuator is fixed on the base through a support; the base is fixedly connected to three embedded parts embedded in the foundation;

[0020] The end of the hydraulic actuator is connected to the lower end of the connecting rod through an intermediate cross hinge; the upper end of the connecting rod is connected to the platform through an upper cross hinge;

[0021] The acceleration detection subsystem includes 9 unidirectional acceleration sensors, each 3 of which are divided into 1 group, and a total of 3 sensor groups; the 3 sensor groups are arranged on the platform:

[0022] The three sensor groups are arranged at 120 degrees and are tangent to each other on the same circle. The same circle is taken as the reference circle.

[0023] The 3 sensor groups and the hinge points on the platform are on the same plane;

[0024] In each sensor group, the positive direction of the sensitive axis of one unidirectional acceleration sensor is vertically upward, the positive direction of the sensitive axis of another unidirectional acceleration sensor is the direction from the center of the reference circle toward the tangent point of the sensor group on the reference circle, and the positive direction of the sensitive axis of the last unidirectional acceleration sensor is the right tangent direction derived from the tangent point of the sensor group on the reference circle;

[0025] The acceleration detection subsystem is used to measure the acceleration of the platform movement and send the acceleration measurement value to the servo control device;

[0026] The servo control device is used to obtain motion instructions based on the acceleration measurement value and 8 structural parameters of the mechanical structure subsystem;

[0027] The hydraulic actuator is used to perform telescopic movement according to the movement instruction, driving the connecting rod to swing, so that the platform moves and presents different postures;

[0028] The eight structural parameters of the mechanical structure subsystem are:

[0029] Every two upper cross hinges form a cluster, and there are three clusters in total. The three clusters are located on the reference circle with a radius of r. a ; The distance between two hinge points in each cluster of upper cross hinges is d a ; Every two middle cross hinges form a cluster, a total of three clusters, the three clusters are located on the same circle, the radius of the circle is r b ; The distance between two hinge points in each cluster of the middle cross hinge is db ; The elevation angle of each hydraulic actuator to the horizontal plane is φ; The deflection angle of each hydraulic actuator is γ; The median length of each hydraulic actuator is l o ; The length of each connecting rod is l c .

[0030] Furthermore, a preferred embodiment is provided, wherein the lower cylinder of the hydraulic actuator is connected to the support via bolts.

[0031] Furthermore, a preferred embodiment is provided in which a three-stage electro-hydraulic servo valve is installed on the lower cylinder of the hydraulic actuator for receiving movement instructions to control the movement of the hydraulic actuator.

[0032] Furthermore, a preferred embodiment is provided, wherein a flange is provided at the end of the hydraulic actuator; the flange is connected to the lower end of the connecting rod via an intermediate cross hinge.

[0033] Furthermore, a preferred embodiment is provided, wherein each cross hinge includes two outer frames and two rotation axes, forming two rotational degrees of freedom.

[0034] The present invention also proposes a control method for a base-fixed multi-link motion system, the method comprising the following steps:

[0035] Inertial system expression step: obtaining the acceleration measurement value collected by the acceleration detection subsystem of the base-fixed multi-link motion system described in any one of the above items; converting the acceleration measurement value into the acceleration of the installation point of the corresponding sensor group on the platform in the inertial system;

[0036] Estimating the degree of freedom feedback signal step: obtaining the degree of freedom feedback signal according to the eight structural parameters of the mechanical structure subsystem and the acceleration of the installation point of the corresponding sensor group on the platform in the inertial system; the degree of freedom feedback signal includes the translation acceleration and the platform rotation angular acceleration;

[0037] Vibration control outer loop steps: Based on the degree of freedom feedback signal, the error between the acceleration given signal and the response signal is corrected by calculating the inverse function to obtain the drive signal;

[0038] Servo control loop steps: According to the eight structural parameters of the mechanical structure subsystem, the drive signal is used for servo control through kinematic inverse solution, the elongation of each hydraulic actuator is obtained as the motion command, and the hydraulic actuator is controlled to perform telescopic motion.

[0039] The present invention also proposes a control device for a base-fixed multi-link motion system, the device comprising the following modules:

[0040] Inertial system expression module: obtain the acceleration measurement value collected by the acceleration detection subsystem of the base-fixed multi-link motion system described in any one of the above items; convert the acceleration measurement value into the acceleration of the installation point of the corresponding sensor group on the platform in the inertial system;

[0041] Estimation of degree of freedom feedback signal module: obtain the degree of freedom feedback signal according to the eight structural parameters of the mechanical structure subsystem and the acceleration of the corresponding sensor group at the installation point on the platform in the inertial system; the degree of freedom feedback signal includes the translation acceleration and the platform rotation angular acceleration;

[0042] Vibration control outer loop module: Based on the degree of freedom feedback signal, the error between the acceleration given signal and the response signal is corrected by calculating the inverse function to obtain the driving signal;

[0043] Servo control loop module: According to the eight structural parameters of the mechanical structure subsystem, the drive signal is used for servo control through kinematic inverse solution, the elongation of each hydraulic actuator is obtained as the motion command, and the hydraulic actuator is controlled to perform telescopic motion.

[0044] The present invention also proposes a computer device, comprising: a processor and a memory, wherein the memory is used to store executable instructions of the processor, and the processor is configured to execute the above-mentioned control method of the base-fixed multi-link motion system by executing the executable instructions.

[0045] The present invention further proposes a computer storage medium, in which a computer program is stored. When the computer program is run, the control method of the base-fixed multi-link motion system described above is executed.

[0046] The present invention also proposes a computer program product, including a computer program / instruction, which implements the steps of the control method of the base-fixed multi-link motion system when executed by a processor.

[0047] The present invention has the following beneficial effects:

[0048] 1. The base-fixed multi-link motion system described in the present invention proposes a new mechanical structure subsystem, which improves the natural frequency of the system by fixing the hydraulic actuator cylinder base and the connecting rod structure, thereby compensating for the shortcomings of conventional swing actuators in achieving insufficient high-frequency motion.

[0049] 2. The control method of the base-fixed multi-link motion system described in the present invention further expands the system bandwidth (up to 100 Hz) while ensuring control accuracy through the inverse function drive control algorithm combined with the structural parameters of the mechanical structure subsystem, and ultimately realizes the six-degree-of-freedom high-bandwidth and high-precision motion function.

[0050] The base-fixed multi-link motion system and the control method and control device thereof described in the present invention are suitable for the structural design and control of a six-degree-of-freedom parallel motion system. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0052] Figure 1 It is a schematic structural diagram of a mechanical mechanism subsystem of a base-fixed multi-link motion system in one embodiment of the present invention;

[0053] Figure 2 A schematic diagram of the layout of a hydraulic actuator in one embodiment of the present invention;

[0054] Figure 3 A schematic diagram of the structure of a support in one embodiment of the present invention;

[0055] Figure 4 A stress analysis diagram of a support structure in one embodiment of the present invention;

[0056] Figure 5 A schematic diagram of the structure of a connecting rod in one embodiment of the present invention;

[0057] Figure 6 A stress analysis diagram of a connecting rod structure in one embodiment of the present invention;

[0058] Figure 7 This is a schematic diagram of the appearance structure of a cross hinge in one embodiment of the present invention;

[0059] Figure 8 This is a schematic diagram of the structure of two rotating shafts inside the cross hinge in one embodiment of the present invention;

[0060] Fig. 9 A schematic diagram of the installation and motion range of a cross hinge in one embodiment of the present invention;

[0061] Fig.10 This is a schematic diagram of the structure of an embedded part in one embodiment of the present invention;

[0062] Fig.11 This is a schematic diagram of the structure of a platform in one embodiment of the present invention;

[0063] Fig.12 A stress analysis diagram of a platform structure in one embodiment of the present invention;

[0064] Fig.13 A schematic diagram of the position arrangement and installation direction of a unidirectional acceleration sensor in one embodiment of the present invention;

[0065] Fig.14 It is a flow chart of a control method of a base-fixed multi-link motion system in one embodiment of the present invention;

[0066] Fig.15 A schematic diagram of the structure of a conventional six-degree-of-freedom parallel mechanism in one embodiment of the present invention;

[0067] Reference numerals:

[0068] 1. Embedded parts; 2. Base; 3. Connecting rod actuator legs; 4. Platform; 5. Support; 5-1, 5-2, ribs; 5-3, floor; 6. Hydraulic actuator; 7. Three-stage electro-hydraulic servo valve; 8-1, 8-2, outer frame; 9-1, 9-2, rotary shaft; 10, connecting rod; 11, flange. DETAILED DESCRIPTION

[0069] In order to make the technical solutions and advantages of the present invention more clearly described, the specific implementation methods of the present invention will be further described in detail and completely in conjunction with the accompanying drawings. The various implementation methods described below are only part of the preferred solutions of the present invention, rather than all implementation methods; the various implementation methods described below are intended to explain the present invention and cannot be understood as limitations on the present invention; the reasonable combination of technical features defined in the various implementation methods of the present invention, and all other implementation methods obtained by ordinary technicians in the field without creative work based on the implementation methods of the present invention, are within the scope of protection of the present invention.

[0070] In one embodiment, a base-fixed multi-link motion system is provided, the system comprising: a mechanical structure subsystem, an acceleration detection subsystem, and a servo control subsystem;

[0071] The mechanical structure subsystem includes three embedded parts 1 embedded in the foundation, a base 2, a support 5, six sets of connecting rod actuator legs 3 and a platform 4;

[0072] Each connecting rod actuator leg 3 includes a hydraulic actuator 6, a cross hinge and a connecting rod 10; the cross hinge includes a middle cross hinge and an upper cross hinge;

[0073] The cylinder of the lower part of the hydraulic actuator 6 is fixed on the base 2 through the support 5; the base 2 is fixedly connected with three embedded parts 1 embedded in the foundation;

[0074] The end of the hydraulic actuator 6 is connected to the lower end of the connecting rod 10 through an intermediate cross hinge; the upper end of the connecting rod 10 is connected to the platform 4 through an upper cross hinge;

[0075] The acceleration detection subsystem includes 9 unidirectional acceleration sensors, each 3 of which are divided into 1 group, and a total of 3 sensor groups; the 3 sensor groups are arranged on the platform 4:

[0076] The three sensor groups are arranged at 120 degrees and are tangent to each other on the same circle. The same circle is taken as the reference circle.

[0077] The three sensor groups and the hinge points on the platform 4 are on the same plane;

[0078] In each sensor group, the positive direction of the sensitive axis of one unidirectional acceleration sensor is vertically upward, the positive direction of the sensitive axis of another unidirectional acceleration sensor is the direction from the center of the reference circle toward the tangent point of the sensor group on the reference circle, and the positive direction of the sensitive axis of the last unidirectional acceleration sensor is the right tangent direction derived from the tangent point of the sensor group on the reference circle;

[0079] The acceleration detection subsystem is used to measure the acceleration of the platform 4 and send the acceleration measurement value to the servo control device;

[0080] The servo control device is used to obtain motion instructions based on the acceleration measurement value and 8 structural parameters of the mechanical structure subsystem;

[0081] The hydraulic actuator 6 is used to perform telescopic movement according to the movement instruction, driving the connecting rod 10 to swing, so that the platform 4 moves and presents different postures;

[0082] The eight structural parameters of the mechanical structure subsystem are:

[0083] Every two upper cross hinges form a cluster, and there are three clusters in total. The three clusters are located on the reference circle with a radius of r. a ; The distance between two hinge points in each cluster of upper cross hinges is d a ; Every two middle cross hinges form a cluster, a total of three clusters, the three clusters are located on the same circle, the radius of the circle is r b ; The distance between two hinge points in each cluster of the middle cross hinge is d b ; The elevation angle of each hydraulic actuator 6 to the horizontal plane is φ; The deflection angle of each hydraulic actuator 6 is γ; The median length of each hydraulic actuator 6 is l o ; The length of each connecting rod 10 is l c .

[0084] In this embodiment, 120deg means an angle of 120 degrees.

[0085] In this embodiment, the hinge point on the platform 4 is the position where the platform 4 is hinged to the cross hinge (upper cross hinge).

[0086] In this embodiment, 9 unidirectional acceleration sensors, such as Fig.13 As shown:

[0087] The three sensor groups are arranged at 120 degrees and are tangent to each other on the same circle. The same circle is assumed to be the reference circle. The center of the reference circle is O b , the radius of the reference circle is r a ;

[0088] exist Fig.13 In the figure, the red line indicates the sensitive axis, and the blue line indicates the positive direction:

[0089] Assume that there are 9 unidirectional acceleration sensors a1, a2, a3, a4, a5, a6, a7, a8 and a9, where a1, a6 and a7 form a group, a2, a3 and a8 form a group, and a4, a5 and a9 form a group;

[0090] For each sensor group, the positive directions of the sensitive axes of the three unidirectional accelerometers form a right-hand spiral:

[0091] The sensitive axes of a7, a8 and a9 are perpendicular to the horizontal plane, and their positive directions are vertically upward ( Fig.13 Not marked in the figure);

[0092] The positive direction of the sensitive axis of a1, a3 and a5 is the direction from the center of the reference circle to the tangent point of the sensor group on the reference circle, such as y aac1 ,y aac2 and aac3 As shown;

[0093] The positive direction of the sensitive axis of a2, a4 and a6 is the right tangent direction of the sensor group from the tangent point on the reference circle, such as x aac1 、x aac2 and x aac3 shown.

[0094] In this embodiment, the six sets of connecting rod actuator legs 3 are used to provide driving force for the movement of the platform 4.

[0095] In this embodiment, the base 2 is an equilateral triangle; two supports 5 are fixedly arranged at the three corners of the base 2, and each support 5 is connected to the cylinder of the lower part of a hydraulic actuator 6; for the hydraulic actuator 6 arranged at any one corner of the base 2, the angle between the direction of the perpendicular line drawn from the end of the hydraulic actuator 6 at any one corner to the base 2 and the direction of the center line of the base 2 at any one corner is the deflection angle.

[0096] In this embodiment, the three corners of the base 2 are respectively fixedly connected to an embedded part 1 embedded in the foundation.

[0097] In this embodiment, the lower end of the connecting rod actuator leg 3 is directly fixed to the base 2 through a rigid support 5, forming an "integrated rigid connection". This design improves rigidity in the following ways:

[0098] "Eliminate the intermediate force transmission link": There is no flexible hinge or complex base structure between the legs and the base. They are fixed directly by high-strength bolts or welding, reducing the risk of deformation at the connection point.

[0099] “Stress distribution optimization”: The centralized rigid fixation of the support can evenly distribute the load transmitted by the legs and avoid platform deformation caused by local stress concentration.

[0100] "Enhanced vibration resistance": The base serves as an integral load-bearing frame, which can effectively suppress structural resonance under high-frequency vibration.

[0101] In addition, the base 2 is an "integrated rigid structure" and is usually made of high-rigidity materials (such as cast iron or welded steel structures), and the bending and torsion resistance is improved through the design of reinforcing ribs (embedded parts). The leg fixing point (support 5) is integrated with the base to ensure that the installation reference surface of the leg is rigidly coupled with the base, reducing the stiffness loss caused by assembly errors.

[0102] At the same time, the rigid connection between the leg 3 and the base 2 forms a "fully constrained boundary condition", the leg only bears axial load, and the lateral force is directly absorbed by the base, avoiding the bending moment introduced by the multi-degree-of-freedom hinge of the leg.

[0103] At the same time, the high-rigidity design is suitable for "large load, high-precision positioning scenarios", and can withstand greater inertial forces and maintain dynamic stability.

[0104] In summary, the "rigid integrated design of the legs and the base" significantly improves the system stiffness, making it suitable for scenarios with high loads and high dynamic response.

[0105] In this implementation, the eight structural parameters determine the kinematic and dynamic characteristics of the mechanical structure subsystem.

[0106] In this embodiment, the lower end of the connecting rod actuator leg 3 (ie, the lower cylinder of the hydraulic actuator 6) is fixed to the base 2 via the support 5, thereby eliminating lateral swing and improving the rigidity of the mechanical structure subsystem.

[0107] In this embodiment, the upper surface of the platform 4 is used to connect the load, and the load completes various postures of movement driven by the platform.

[0108] It should be noted that the actuator driving methods include hydraulic driving and motor (such as voice coil motor) driving, and actuators with different driving methods have different performance and application scenarios. For example, the following table compares the differences between voice coil motors and hydraulic actuators:

[0109]

[0110] In addition, in one embodiment, the three embedded parts 1 are cast in advance in the foundation pit (or foundation).

[0111] In addition, in one embodiment, each embedded part 1 includes two bottom plates and a plurality of long bolts fixing the two bottom plates together; one of the bottom plates is fixedly connected to the base 2, and the other bottom plate is fixed to the bottom of the foundation.

[0112] In addition, in one embodiment, the platform 4 adopts a grid structure and is welded into a whole with steel plates.

[0113] It should be noted that in order to accurately transmit the force and motion law of the servo control subsystem to the load, the platform 4 should be as light as possible while ensuring sufficient rigidity and high natural frequency. In this embodiment, a grid structure is adopted, which is welded into a whole with steel plates, which can effectively reduce the weight while ensuring sufficient rigidity and high natural frequency.

[0114] In this embodiment, the natural frequency analysis (stress analysis) of the platform 4 is performed. For this purpose, the boundary conditions of the force analysis are: the surfaces of the six hinge mounting plates of the platform are fully constrained, and the inertial force generated during the load acceleration condition is used as the load, which is applied to a certain area on the surface of the platform. The natural frequency analysis results are as follows: Fig.12 Some simulation parameters in the natural frequency analysis are as follows:

[0115] Model name: Upper platform-frequency force-V3-181229;

[0116] Example name: Example 1;

[0117] Plot type: Frequency shift 7;

[0118] Mode shape: 7 value = 186.28 Hz;

[0119] Deformation ratio: 2.75588.

[0120] From the natural frequency analysis, it can be seen that the natural frequency of platform 4 is basically twice the expected reproduced signal (100 Hz). In the later stage, the control algorithm can be used to ensure that the signal is increased to the required bandwidth.

[0121] In addition, in one embodiment, the lower cylinder of the hydraulic actuator 6 is connected to the support 5 by bolts.

[0122] In this embodiment, the cylinder barrel at the bottom of the hydraulic actuator 6 is connected to the support 5 by bolts to ensure that the cylinder barrel remains stationary when the piston of the hydraulic actuator 6 performs telescopic movement.

[0123] In addition, in one embodiment, the support 5 includes two ribs 5-1 and 5-2 and a floor 5-3; in order to ensure the fixing effect of the cylinder, the two ribs 5-1 and 5-2 fix the hydraulic actuator 6 at an inclination angle of φ to the horizontal plane; the two ribs 5-1 and 5-2 are vertically fixed on the floor 5-3; the floor 5-3 is fixedly connected to the base 2 by bolts.

[0124] In this embodiment, if the entire support 5 is not strong enough, it will have a great impact on the excitation effect of the entire hydraulic actuator 6, so the support 5 is made of high-strength material.

[0125] In this embodiment, the support 5 is subjected to inherent characteristic analysis (stress analysis), such as Figure 4 Some simulation parameters in the inherent characteristic analysis are as follows:

[0126] Model name: Mounting base (modified)-Frequency-190107;

[0127] Example name: Example 1;

[0128] Plot type: Frequency shift 7;

[0129] Mode shape: 7 value = 432.17 Hz;

[0130] Deformation ratio: 0.481301.

[0131] From the analysis of inherent characteristics, it can be seen that the inherent frequency of the support mechanism obtained under the premise of satisfying the dynamic force and strength is much greater than twice the frequency of the 100Hz signal to be reproduced, so it meets the requirements.

[0132] In addition, in one embodiment, a three-stage electro-hydraulic servo valve 7 is installed on the cylinder of the lower portion of the hydraulic actuator 6 for receiving movement instructions to control the movement of the hydraulic actuator 6 .

[0133] In addition, in one embodiment, a flange 11 is provided at the end of the hydraulic actuator 6; the flange 11 is connected to the lower end of the connecting rod 10 via an intermediate cross hinge.

[0134] In addition, in one embodiment, the connecting rod 10 is a lightweight rod.

[0135] In this embodiment, a lightweight rod is used as the connecting rod 10, which can indirectly increase the natural frequency of the entire system:

[0136] On the one hand, the introduction of lightweight connecting rods reduces the piston stroke of the hydraulic actuator. According to hydraulic transmission theory, the reduction of piston stroke can increase the hydraulic natural frequency, thereby indirectly increasing the natural frequency of the entire system.

[0137] On the other hand, the introduction of lightweight connecting rods reduces the driving mass at the hydraulic actuator end and can also increase the natural frequency of the entire system.

[0138] In this embodiment, in order to reduce the influence of the connecting rod inertia tensor on the control characteristics, the connecting rod 10 is required to be a high-strength and lightweight rod.

[0139] In addition, in one embodiment, on the basis of ensuring that the strength is met, a high-strength lightweight rod can be obtained through material selection or structural design. For example, the material can be steel, and the structure can be designed as a hollow thin-walled cylindrical structure.

[0140] In addition, in one embodiment, the connecting rod 10 is made of Q235, Q345, or Q460 steel material, which is guaranteed to be a high-strength material.

[0141] In this embodiment, a stress analysis is performed on the connecting rod 10. Figure 6 Some simulation parameters in the stress analysis are as follows:

[0142] Model name: Connecting rod-frequency force-V2-181228;

[0143] Example name: Example 1;

[0144] Plot type: Frequency shift 7;

[0145] Mode shape: 7 value = 787.73 Hz;

[0146] Deformation ratio: 0.183746.

[0147] From the stress analysis, it can be seen that the connecting rod structure obtained under the premise of satisfying the dynamic force and strength has a natural frequency much greater than twice the frequency of the 100Hz signal to be reproduced, so it meets the requirements.

[0148] In addition, in one embodiment, each cross hinge includes two outer frames 8-1, 8-2 and two rotation axes 9-1, 9-2, forming two rotational degrees of freedom.

[0149] In addition, in one embodiment, the installation and movement range of the cross hinge is as follows: Fig. 9 As shown:

[0150] (1) Installation of cross hinge:

[0151] Assume k1 and m1 represent the axes of the two rotating shafts of the upper cross hinge, k2 and m2 represent the axes of the two rotating shafts of the middle cross hinge, the installation plane of the upper cross hinge on the platform 4 is the first plane, the plane perpendicular to the horizontal plane and passing through the axis of the hydraulic actuator 6 is the second plane, and the axis vector of the hydraulic actuator 6 is l n , the axis vector of the connecting rod 10 is lcn ;

[0152] When the platform 4 is installed in the middle position, for each connecting rod actuator leg 3:

[0153] The axis vector l of the connecting rod 10 cn Perpendicular to the first plane (i.e. the installation plane);

[0154] The axis k1 of the rotary shaft of the upper cross hinge is parallel to the second plane;

[0155] For the upper cross hinge and the middle cross hinge respectively located at two ends of the same connecting rod 10, the rotation axis m1 of the upper cross hinge is perpendicular to the rotation axis m2 of the middle cross hinge.

[0156] (2) The range of motion of the cross hinge is the rotation angle around the two rotation axes of the cross hinge:

[0157] The motion range of the two rotary axis k1 and m1 of the upper cross hinge is:

[0158] The motion range of the rotary axis k1: the angle range between m1 and the first plane;

[0159] The motion range of the rotary axis m1: k1 and m1 and l cn The angle range of the planes formed;

[0160] The motion range of the two rotary axis k2 and m2 of the middle cross hinge is:

[0161] The motion range of the rotary axis k2: m2 and l n The angle range of

[0162] The motion range of the rotary axis m2: k2 and m2 and l cn The angle range of the formed plane.

[0163] In addition, in one embodiment, a control method for a base-fixed multi-link motion system is provided, the method comprising the following steps:

[0164] Inertial system expression step: obtaining the acceleration measurement value collected by the acceleration detection subsystem of the base-fixed multi-link motion system described in any one of the above embodiments; converting the acceleration measurement value into the acceleration of the installation point of the corresponding sensor group on the platform 4 in the inertial system;

[0165] Estimating the degree of freedom feedback signal step: obtaining the degree of freedom feedback signal according to the eight structural parameters of the mechanical structure subsystem and the acceleration of the installation point of the corresponding sensor group on the platform 4 in the inertial system; the degree of freedom feedback signal includes the translation acceleration and the platform rotation angular acceleration;

[0166] Vibration control outer loop steps: Based on the degree of freedom feedback signal, the error between the acceleration given signal and the response signal is corrected by calculating the inverse function to obtain the drive signal;

[0167] Servo control loop steps: According to the eight structural parameters of the mechanical structure subsystem, the drive signal is used for servo control through kinematic inverse solution, the elongation of each hydraulic actuator 6 is obtained as the motion instruction, and the hydraulic actuator 6 is controlled to perform telescopic movement.

[0168] In addition, in one embodiment, the acceleration of the installation point of the i-th sensor group on the platform 4 in the inertial system is:

[0169] A i =T i A measure,i ;

[0170] Among them, A i is a 3×1 matrix; i=1, 2, 3, representing three sensor groups respectively; T i is the transformation matrix; A measure,i It is a matrix composed of the acceleration measurement values ​​output by each sensitive axis of the i-th sensor group, which is a 3×1 matrix.

[0171] In this embodiment, the control method is executed in a servo control subsystem of a base-fixed multi-link motion system.

[0172] In addition, in one embodiment, the translation acceleration is:

[0173]

[0174] The platform rotation angular acceleration is:

[0175]

[0176] Among them, A i,j is the acceleration of the i-th sensor group installation point in the direction corresponding to the j value in the inertial system, j = 1 is the x direction in the inertial system; j = 2 is the y direction in the inertial system; j = 3 is the z direction in the inertial system; ε x is the angular acceleration in the x direction, ε y is the angular acceleration in the y direction, ε z is the angular acceleration in the z direction.

[0177] In addition, in one embodiment, the vibration control outer ring step includes the following steps:

[0178] Steps to obtain the time domain error between the acceleration given signal and the response signal:

[0179] e(t)=A in (t)-A out(t);

[0180] Among them, A in (t) is the acceleration given signal; A out (t) is the degree of freedom feedback signal A c , ε x , ε y and ε z The vector expression of is the response signal;

[0181] Steps to obtain the frequency domain error between the acceleration given signal and the response signal:

[0182] E(f) = FFT(e(t));

[0183] Steps to obtain the driving signal:

[0184] ΔDrv(f)=Z(f)E(f);

[0185] Among them, Z(f) is the inverse function, Z(f) = G xy (f) / G xx (f), G inout (f) is the cross-spectral density estimation matrix of the acceleration given signal response signal, G inin (f) is the autospectral density estimation matrix of the given acceleration signal.

[0186] In addition, in one embodiment, the kinematic inverse solution is:

[0187]

[0188] Where, Δd i is the elongation of each hydraulic actuator 6; g ki is the center coordinate of support 5; b ki is the center coordinate of the flange 11 at the end of the hydraulic actuator 6; g ki and b ki The value of is calculated based on the coordinates of the degrees of freedom represented by the eight structural parameters of the mechanical structure subsystem.

[0189] In this implementation, since the measurement result (acceleration measurement value) of the unidirectional acceleration sensor is the value of the sensitive axis, it is necessary to convert the value into an inertial system.

[0190] In this implementation, compared with conventional servo control, a vibration control outer loop is added on the basis of the servo control loop, and the structural parameters of the mechanical structure subsystem are combined to overcome the limitation problem of nonlinear factors on the improvement of system bandwidth.

[0191] In this embodiment, the vibration control outer loop step is an iterative control method based on the inverse function of acceleration (or inverse function drive control algorithm), which corrects the acceleration control error by obtaining the inverse function of the system.

[0192] It should be noted that for hydraulically driven actuators, if traditional servo control methods such as PID are used, many nonlinear factors will be generated in the signal transmission process. These nonlinear factors will limit the improvement of the system bandwidth. Specifically:

[0193] The reasons why nonlinear factors limit the improvement of system bandwidth can be summarized into the following aspects:

[0194] (1) Phase distortion caused by nonlinear mechanical structure:

[0195] Nonlinear factors such as "ball joint clearance, connecting rod elastic deformation, cross joint friction" in the hydraulic drive chain will introduce "time-varying hysteresis effect". In high-frequency motion:

[0196] "Phase lag accumulation": The servo valve response delay (about 1-2ms) plus the phase lag caused by mechanical nonlinearity causes the phase margin of the system open-loop transfer function to drop sharply in the high frequency band (>50Hz), which can easily cause resonance.

[0197] "Energy dissipation": For example, cross hinge friction will cause high-frequency vibration energy to be absorbed, making the system unable to accurately reproduce high-frequency acceleration signals (such as waveform clipping in a 100Hz sine wave).

[0198] (2) The inherent nonlinearity of the hydraulic system and the contradiction between bandwidth:

[0199] The hydraulic actuator itself has inherent nonlinearity such as "flow-pressure coupling, oil compressibility, valve core dead zone":

[0200] "Flow saturation": During high-frequency motion, the piston speed approaches the oil supply limit of the hydraulic pump, resulting in an increase in the proportion of the nonlinear term "leakage coefficient × load pressure" in the flow equation, which undermines the effectiveness of the linearization model.

[0201] "Pressure pulsation resonance": When the three-stage servo valve is switched at high frequency, the oil compressibility (bulk elastic modulus β≈1.4GPa) forms a resonant system with the pipeline cavity. If the resonant frequency is close to the target bandwidth (such as 100Hz), it will cause instability.

[0202] (3) Limitations of traditional control algorithms:

[0203] The defects of traditional linear control methods such as PID when dealing with nonlinearity:

[0204] "Gain scheduling failure": The "Stribeck curve characteristics" of the hydraulic cylinder friction force changing with speed causes the system damping coefficient to vary with time, and the fixed PID parameters cannot cover the entire frequency band.

[0205] "Harmonic distortion amplification": For example, the high-frequency component (>50Hz) in the platform acceleration signal generates "superharmonic resonance" (such as the third harmonic 150Hz) after passing through the nonlinear link, which cannot be suppressed by traditional frequency domain correction.

[0206] “Missing inverse dynamics”: lack of feedforward compensation mechanism, unable to compensate for nonlinear transfer characteristics.

[0207] It should be noted that the result caused by the nonlinear factors is that the actual response signal is different from the given signal. In this embodiment, the control method uses the inverse function method to modify the drive signal to compensate for the error caused by the nonlinear factors of the system. That is, it is equivalent to correcting the given signal (drive signal) and then inputting it into the system. After several iterative controls, the actual output signal of the system gradually coincides with the initial reproduced signal, thereby increasing the system bandwidth to 100Hz.

[0208] In this embodiment, after the control method adopts inverse function iterative control, the system -3dB bandwidth is increased from "52Hz" of the traditional PID to "98Hz", and the 100Hz sinusoidal tracking phase lag is reduced from 28° to 6°.

[0209] In addition, in one embodiment, a control device for a base-fixed multi-link motion system is provided, the device comprising the following modules:

[0210] Inertial system expression module: obtains the acceleration measurement value collected by the acceleration detection subsystem of the base-fixed multi-link motion system described in any one of the above embodiments; converts the acceleration measurement value into the acceleration of the installation point of the corresponding sensor group on the platform 4 in the inertial system;

[0211] Estimation of degree of freedom feedback signal module: obtain the degree of freedom feedback signal according to the eight structural parameters of the mechanical structure subsystem and the acceleration of the installation point of the corresponding sensor group on the platform 4 in the inertial system; the degree of freedom feedback signal includes the translation acceleration and the platform rotation angular acceleration;

[0212] Vibration control outer loop module: Based on the degree of freedom feedback signal, the error between the acceleration given signal and the response signal is corrected by calculating the inverse function to obtain the driving signal;

[0213] Servo control loop module: According to the eight structural parameters of the mechanical structure subsystem, the drive signal is used for servo control through kinematic inverse solution, the elongation of each hydraulic actuator 6 is obtained as the motion instruction, and the hydraulic actuator 6 is controlled to perform telescopic motion.

[0214] The technical solution provided by the present invention is further described in detail above through several specific implementation modes in order to highlight the advantages and benefits of the technical solution provided by the present invention. However, the several specific implementation modes described above are not intended to be used as limitations on the present invention. Any reasonable changes and improvements to the present invention, reasonable combinations of implementation modes and equivalent substitutions based on the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. The base-fixed multi-link motion system is characterized by: The system comprises: a mechanical structure subsystem, an acceleration detection subsystem and a servo control subsystem; The mechanical structure subsystem includes three embedded parts embedded in the foundation, a base, a support, six sets of connecting rod actuator legs and a platform; Each connecting rod actuator leg includes a hydraulic actuator, a cross hinge and a connecting rod; the cross hinge includes a middle cross hinge and an upper cross hinge; The cylinder at the bottom of the hydraulic actuator is fixed on the base through a support; the base is fixedly connected to three embedded parts embedded in the foundation; The end of the hydraulic actuator is connected to the lower end of the connecting rod through an intermediate cross hinge; the upper end of the connecting rod is connected to the platform through an upper cross hinge; The acceleration detection subsystem includes 9 unidirectional acceleration sensors, each 3 of which are divided into 1 group, and a total of 3 sensor groups; the 3 sensor groups are arranged on the platform: The three sensor groups are arranged at 120 degrees and are tangent to each other on the same circle. The same circle is taken as the reference circle. The 3 sensor groups and the hinge points on the platform are on the same plane; In each sensor group, the positive direction of the sensitive axis of one unidirectional acceleration sensor is vertically upward, the positive direction of the sensitive axis of another unidirectional acceleration sensor is the direction from the center of the reference circle toward the tangent point of the sensor group on the reference circle, and the positive direction of the sensitive axis of the last unidirectional acceleration sensor is the right tangent direction derived from the tangent point of the sensor group on the reference circle; The acceleration detection subsystem is used to measure the acceleration of the platform movement and send the acceleration measurement value to the servo control device; The servo control device is used to obtain motion instructions based on the acceleration measurement value and 8 structural parameters of the mechanical structure subsystem; The hydraulic actuator is used to perform telescopic movement according to the movement instruction, driving the connecting rod to swing, so that the platform moves and presents different postures; The eight structural parameters of the mechanical structure subsystem are: Every two upper cross hinges form a cluster, and there are three clusters in total. The three clusters are located on the reference circle with a radius of r. a ; The distance between two hinge points in each cluster of upper cross hinges is d a ; Every two middle cross hinges form a cluster, a total of three clusters, the three clusters are located on the same circle, the radius of the circle is r b ; The distance between two hinge points in each cluster of the middle cross hinge is d b ; The elevation angle of each hydraulic actuator to the horizontal plane is φ; The deflection angle of each hydraulic actuator is γ; The median length of each hydraulic actuator is l o ; The length of each connecting rod is l c .

2. The base-fixed multi-link motion system according to claim 1, characterized in that: The cylinder barrel at the bottom of the hydraulic actuator is connected to the support through bolts.

3. The base-fixed multi-link motion system according to claim 1, characterized in that: A three-stage electro-hydraulic servo valve is installed on the cylinder barrel at the lower part of the hydraulic actuator, which is used to receive movement instructions to control the movement of the hydraulic actuator.

4. The base-fixed multi-link motion system according to claim 1, characterized in that: A flange is arranged at the end of the hydraulic actuator; the flange is connected to the lower end of the connecting rod through an intermediate cross hinge.

5. The base-fixed multi-link motion system according to claim 1, characterized in that: Each cross hinge includes two outer frames and two rotation axes, forming two rotational degrees of freedom.

6. A control method for a base-fixed multi-link motion system, characterized in that: The method comprises the following steps: Inertial system expression step: obtaining the acceleration measurement value collected by the acceleration detection subsystem of the base-fixed multi-link motion system according to any one of claims 1 to 5; converting the acceleration measurement value into the acceleration of the installation point of the corresponding sensor group on the platform in the inertial system; Estimating the degree of freedom feedback signal step: obtaining the degree of freedom feedback signal according to the eight structural parameters of the mechanical structure subsystem and the acceleration of the installation point of the corresponding sensor group on the platform in the inertial system; the degree of freedom feedback signal includes the translation acceleration and the platform rotation angular acceleration; Vibration control outer loop steps: Based on the degree of freedom feedback signal, the error between the acceleration given signal and the response signal is corrected by calculating the inverse function to obtain the drive signal; Servo control loop steps: According to the eight structural parameters of the mechanical structure subsystem, the drive signal is used for servo control through kinematic inverse solution, the elongation of each hydraulic actuator is obtained as the motion command, and the hydraulic actuator is controlled to perform telescopic motion.

7. A control device for a base-fixed multi-link motion system, characterized in that: The device comprises the following modules: An inertial system expression module: obtaining the acceleration measurement value collected by the acceleration detection subsystem of the base-fixed multi-link motion system according to any one of claims 1 to 5; converting the acceleration measurement value into the acceleration of the installation point of the corresponding sensor group on the platform in the inertial system; Estimation of degree of freedom feedback signal module: obtain the degree of freedom feedback signal according to the eight structural parameters of the mechanical structure subsystem and the acceleration of the corresponding sensor group at the installation point on the platform in the inertial system; the degree of freedom feedback signal includes the translation acceleration and the platform rotation angular acceleration; Vibration control outer loop module: Based on the degree of freedom feedback signal, the error between the acceleration given signal and the response signal is corrected by calculating the inverse function to obtain the driving signal; Servo control loop module: According to the eight structural parameters of the mechanical structure subsystem, the drive signal is used for servo control through kinematic inverse solution, the elongation of each hydraulic actuator is obtained as the motion command, and the hydraulic actuator is controlled to perform telescopic motion.

8. A computer device comprising: A processor and a memory, characterized in that the memory is used to store executable instructions of the processor, and the processor is configured to execute the control method of the base-fixed multi-link motion system of claim 6 by executing the executable instructions.

9. A computer storage medium, characterized in that The storage medium stores a computer program, and when the computer program is run, the control method of the base-fixed multi-link motion system according to claim 6 is executed.

10. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the steps of the control method of the base-fixed multi-link motion system described in claim 6 are implemented.

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