Space manipulator kinetic parameter identification method based on suspension type gravity unloading device

Abstract

The invention belongs to the technical field of space manipulator kinetic parameter identification, and particularly relates to a space manipulator kinetic parameter identification method based on a suspension type gravity unloading device, which comprises a mass parameter, a mass center position parameter and a rotational inertia parameter of each arm lever of a space manipulator. The method specifically comprises the following steps: S1, establishing a single rigid body kinetic equation of a space manipulator system, and separating to-be-identified parameters; s2, the overall kinetic parameters of the space manipulator are solved through a least square method; s3, a first motion joint of the space manipulator is unlocked, and a kinetic equation of a two-body system is established; s4, constructing a target optimization function of the equivalent two-body system of the space manipulator about the kinetic parameters; s5, kinetic parameter identification of each of the two bodies is completed by using a nonlinear optimization algorithm; and S6, the steps S3 to S5 are repeated, all joints are unlocked in sequence, and inertial parameter identification of each individual of the space manipulator is completed. The invention provides a space manipulator parameter identification method based on the momentum theorem on the basis of a suspension type gravity unloading device. According to the method, the number of optimized parameters is simplified through an identification strategy of first integration and second division, parameter identification of the space manipulator system is completed, and a reliable basis can be provided for various dynamics tests on the ground, gravity unloading on the ground, accurate control and the like of the space manipulator system.

Description

Technical Field

[0001] The present invention belongs to the technical field of dynamic parameter identification of space manipulators, and particularly relates to a method for identifying dynamic parameters of a space manipulator based on a suspended gravity unloading device. Background Technique

[0002] At present, space technology is in a stage of rapid development. In the face of many space missions, it poses challenges for astronauts to work outside the cabin. Space manipulators have unique advantages. They have the ability to replace humans to perform various complex tasks, such as capturing, releasing, monitoring, and retrieving satellites, etc. The Japanese satellite ETS-VII can achieve space satellite rendezvous, docking and other tasks; the Canadian space shuttle SRMS is the world's first space manipulator manufactured and used, which plays a huge role in the space station service system; the extravehicular free-moving robot EMR developed by the Space Robot Research Center of our country can successfully perform high-precision tasks such as capturing floating objects.

[0003] A space manipulator is a typical multi-rigid-body system. Space manipulators rely on accurate dynamic parameters in aspects such as dynamic control, path planning, attitude control, and ground gravity unloading simulation experiments, including the mass, center of mass, and moment of inertia parameters of each body. To ensure the successful completion of its space missions, it is important to test its dynamic performance on the ground, and it is necessary to carry out research on parameter identification of space manipulators on the ground.

[0004] When identifying parameters of a space manipulator on the ground, a slightly low-gravity environment needs to be provided. For example, for parameter identification of a space manipulator based on the air-floating method, the air-floating system provides an unloading force for identification. However, since the air-floating method can only provide two-dimensional planar motion, and the air-floating system will introduce additional torques, reducing the identification efficiency; other unloading methods, such as the parabolic flight method, the water-floating method, etc., reduce the identification efficiency and accuracy due to the too short experimental time provided or the too large resistance applied. Summary of the Invention

[0005] Based on a suspended gravity unloading device, the present invention proposes a method for identifying dynamic parameters of a space manipulator, which can solve the identification of the mass, center of mass position, and moment of inertia parameters of space manipulators with different configurations and different numbers of arm rods. Existing suspended gravity unloading devices include a follow-up subsystem and a constant-tension subsystem. The follow-up subsystem ensures that the sling always remains vertical, and the constant-tension subsystem ensures that the sling tension is always equal to the preset unloading force. The suspended unloading device can provide rich motions for the space manipulator in three-dimensional space, so that three-dimensional motion information of the space manipulator can be obtained. Compared with existing identification methods, it can identify inertial parameters more quickly and efficiently, improving the identification accuracy and efficiency.

[0006] The present invention includes three main steps: In the first step, all joints of the space manipulator composed of multiple rigid bodies are locked to transform it into a single rigid body. The dynamic equation of the single rigid body is established and the parameters to be identified are separated. The mass, centroid position, and moment of inertia parameters of this single rigid body are identified (including S1 to S2); in the second step, a certain moving joint of the space manipulator is unlocked to transform it into a two-rigid-body system. The motion of the unlocked joint is planned, and an optimization function regarding the parameters to be identified is established through the momentum theorem. The inertial parameters of the overall space manipulator that have been identified are used as prior information, and the number of parameters is simplified using the mass theorem, centroid theorem, and parallel axis theorem to identify the mass, centroid, and moment of inertia parameters of each body in the two-body system (including S3 to S5); in the third step, each joint of the space manipulator is unlocked in sequence to complete the identification of the dynamic parameters of each part of the space manipulator (S6).

[0007] Through the identification strategy of first overall and then partial, the identification of the dynamic parameters of the space manipulator system is completed, which can provide a reliable basis for various dynamic tests, ground gravity unloading, precise control, etc. of the space manipulator on the ground.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for identifying the parameters of a space manipulator based on a suspended gravity unloading device includes the following steps:

[0010] S1. Establish the dynamic equation of the single rigid body of the space manipulator system and separate the parameters to be identified;

[0011] S2. Use the least squares method to solve the dynamic parameters of the overall space manipulator;

[0012] S3. Unlock the first moving joint of the space manipulator and establish the dynamic equation of the two-body system;

[0013] S4. Construct the objective optimization function regarding the dynamic parameters of the equivalent two-body system of the space manipulator;

[0014] S5. Use the nonlinear optimization algorithm to complete the identification of the dynamic parameters;

[0015] S6. Repeat steps S3 to S5, unlock all joints in sequence, and complete the identification of the dynamic parameters of each body of the space manipulator.

[0016] The establishment of the dynamic equation of the single rigid body of the space manipulator system described in step S1 is as follows: Using the Newton-Euler method, the dynamic equation of the sling and the space manipulator system regarding its body coordinates is established as follows:

[0017]

[0018] Among them, the origin of the body coordinate system is OB , f and τ are the resultant force and resultant moment exerted by the sling at the origin of the body coordinate system, M is the total mass of the space manipulator, i is the sling serial number, N is the number of slings, ω B is the angular velocity of the single rigid body of the space manipulator system, is the angular acceleration of the single rigid body of the space manipulator system, is the linear acceleration of the origin of the body coordinate system relative to the world coordinate system, B r C is the position vector of the centroid C of the single rigid body relative to the origin of the body coordinate system. I eq is the inertia tensor at the centroid of the single rigid body, and the inertia tensor at the body coordinate system B I eq has the following relationship:

[0019]

[0020] where, is the rotation matrix from the centroid coordinate system to the body coordinate system, and E is the identity matrix.

[0021] The parameters to be identified for the single rigid body system of the space manipulator (in the body coordinate system) are as follows:

[0022] M, B r C = B r x B r y B r z T

[0023] where, B I xx , B I yy , B I zz are respectively the three moments of inertia of the single rigid body system along the x, y, and z axes of the body coordinate system, B I xy , B I xz , B I yz are respectively the three products of inertia of the single rigid body system, B r x , B r y , B r z are respectively the expressions of the centroid position of the single rigid body system in the body coordinate system.

[0024] Linearize the dynamic equation and separate the parameters to be identified: ​

[0025]

[0026] Among them, the two symbolic operations are respectively defined as:

[0027] a = [a1 a2 a3] T

[0028]

[0029] ω in the formula x , ω y , ω z are respectively the expressions of the three components of the angular velocity vector ω along the xyz axes of the world coordinate system.

[0030] Let:

[0031]

[0032] P = [M M B r x M B r y M B r z B I xx B I xy B I xz B I yy B I yz B I zz T

[0033] Then the dynamic equation of the equivalent single rigid body is:

[0034] F = AP

[0035] The dynamic parameters of the overall space manipulator solved by the least squares method in step S2 are: using a suspended gravity unloading device, suspending the overall space manipulator with slings (three or more) and releasing it from different initial positions and postures, recording the motion data, and using the dynamic equation after separating the parameters to be identified listed in step S1, and solving the dynamic parameters of the overall space manipulator by the least squares method, including its mass, center of mass position, and moment of inertia parameters.

[0036] Specifically, it includes the following steps:

[0037] ​T1. Use slings (three or more) to suspend the entire space manipulator in the air, record the positions of the upper and lower sling attachment points, and only turn on the measurement system of the unloading device. The follow-up subsystem and the constant force subsystem are turned off. At this time, the unloading device is equivalent to a fixed rack with slings.

[0038] T2. Release the space manipulator single-rigid body system from different initial positions and attitudes to let it swing freely. Measure the data through the inertial sensor IMU, and deduce the linear acceleration and angular velocity at the origin of the overall body coordinate system of the space manipulator. Obtain the angular acceleration through the angular velocity differential method.

[0039] The calculation relationship between the linear velocity at the IMU installation point (velocity measurement point) and the linear velocity at the origin of the body coordinate system is as follows:

[0040]

[0041] Differentiate both sides to obtain the relationship of linear acceleration:

[0042]

[0043] Among them, v Q represents the linear velocity at the IMU installation point, is the linear velocity of the origin of the body coordinate system relative to the world coordinate system, is the linear acceleration of the origin of the body coordinate system relative to the world coordinate system, ω B is the angular velocity of the space manipulator single-rigid body measured by the IMU, is the angular acceleration of the space manipulator single-rigid body calculated by differentiation, I r Q is the representation of the IMU sensor installation point in the body coordinate system in the world coordinate system.

[0044] T3. At the same time, use the tension sensor and laser sensor of the unloading device to record the sling tension and direction.

[0045] T4. Use the dynamic equation after separating the parameters to be identified listed in step S1 and the motion data recorded in the above steps T1 - T3, and solve for the dynamic parameters of the entire space manipulator through the least squares method. The formula is as follows:

[0046] P=(A T A) -1 A T F

[0047] Among them, the parameter matrix P contains ten parameters of the mass, center of mass position, and moment of inertia of the space manipulator single-rigid body system.

[0048] Unlock the first moving joint of the space manipulator described in step S3, and establish the dynamic equation of the two-body system as follows: After unlocking the first joint, the first arm rod is regarded as Body1 (body one), and the remaining second to nth arm rods are regarded as Body2 (body two), and establish the dynamic equation of the equivalent two-body based on the momentum theorem; The expressions of the linear momentum and angular momentum of the equivalent two-body system are:

[0049]

[0050] Among them, P is the total linear momentum of the system, H is the total angular momentum of the system, m0 is the mass of body one, m1 is the mass of body two, v0 is the linear velocity at the center of mass of body one, v1 is the linear velocity at the center of mass of body two, 0 I0 is the moment of inertia at the center of mass of body one, 1 I1 is the moment of inertia at the center of mass of body two, I R0 is the rotation matrix from the body one coordinate system to the world coordinate system, I R1 is the rotation matrix from the body two coordinate system to the world coordinate system, I r0 is the expression of the position of the center of mass of body one in the world coordinate system, I r1 is the expression of the position of the center of mass of body two in the world coordinate system.

[0051] Due to the unloading force error of the suspended gravity unloading device, the entire space manipulator system will be disturbed by external forces and external torques. According to the momentum theorem in the discrete form of the particle system, the following equation can be listed:

[0052]

[0053] Among them, F is the resultant external force caused by the unloading force error, N is the resultant external torque, Δt is the time interval, and P0, H0 and P1, H1 represent the linear momentum and angular momentum at two different times respectively.

[0054] According to the force condition of the space manipulator, the expressions of the resultant external force and resultant external torque received by the manipulator can be listed as follows:

[0055]

[0056] Then, within a period of time, the momentum theorem of the equivalent two-body can be expressed as:

[0057]

[0058] Among them, f1 is the sling force received by body one, I r Ti is the expression of the position vector of the suspension point of the sling on body one in the world coordinate system, and g is the acceleration due to gravity.

[0059] The objective optimization function of the equivalent two-body system of the space manipulator with respect to the dynamic parameters described in step S4 is as follows: By using the dynamic equations of momentum theorem for the equivalent two bodies listed in step S3, the objective optimization function of the equivalent two-body system of the space manipulator with respect to the dynamic parameters is constructed.

[0060] Specifically, it includes the following steps:

[0061] U1. Using the dynamic parameters of the overall space manipulator obtained in steps S1 and S2, through the three equations of mass theorem, centroid theorem, and parallel axis theorem, express the parameters in Body2 of the equivalent two bodies in step S3 in terms of the parameters in Body1:

[0062]

[0063] Among them, 0 a0 is the position vector of the centroid of Body1 in the body coordinate system of Body1, 1 a1 is the position vector of the centroid of Body2 in the body coordinate system of Body2, 0 R1 is the rotation matrix from the body coordinate system of Body2 to the body coordinate system of Body1, 0 I eq is the overall moment of inertia of the manipulator when in the initial position and aligned with the body-one coordinate system, r C is the position vector of the centroid of the overall manipulator in the body coordinate system of Body1, 0 l0 is the position vector from the origin of the body coordinate system of Body1 to the origin of the body coordinate system of Body2, 0 c0 is the representation of the position vector from the centroid of Body1 to the instantaneous centroid of the overall manipulator in the body coordinate system of Body1, 0 c1 is the representation of the position vector from the centroid of Body2 to the instantaneous centroid of the overall manipulator in the body coordinate system of Body1.

[0064] U2. Using the dynamics of the equivalent two-body system based on the momentum theorem established in step S3 and the dynamic parameters of Body1 expressed in terms of the parameters of the other body in step U1, construct an optimization function for the dynamic parameters of Body1:

[0065]

[0066] Among them,, I r Ti is the expression of the position vector of the suspension point of the sling on body one in the world coordinate system. r0 can be represented by a0 and I r Ti represents (r i represents the position of the suspension point of any sling hanging on this body, which can be derived from the kinematics of the suspended gravity unloading device),

[0067]

[0068] Then, the objective function for identifying the inertial parameters of the equivalent two-body system is defined as:

[0069]

[0070] where g x 、g y 、g z represent the function values of the first optimization function, h x 、h y 、h z represent the function values of the second optimization function, c I represents the first optimization function, and c II represents the second optimization function.

[0071] Step S5 uses a non-linear optimization algorithm to complete the identification of dynamic parameters as follows: Turn on the follow-up subsystem, constant-tension subsystem, and measurement system of the unloading device. Use the gravity unloading device to provide a slightly low-gravity environment for the space manipulator. Unlock a certain joint for experiments. Use a non-linear optimization algorithm to optimize the objective function to obtain the mass, centroid position, and moment of inertia parameters of Body 1 and Body 2 respectively.

[0072] Specifically, it includes the following steps:

[0073] E1 The suspended gravity unloading system adopted by the present invention includes a horizontal follow-up part and a vertical constant-tension part. The initial parameters of the mass, centroid, and moment of inertia of each arm of the object to be unloaded required by the unloading system are given by the nominal parameters of the space manipulator (CAD model parameters). The space manipulator is suspended by multiple slings, and a slightly low-gravity environment is provided through the unloading system.

[0074] E2. Unlock the first joint, plan the joint movement using cubic spline curves, and record the IMU data, sling tension, and swing angle simultaneously.

[0075] E3. Using the data collected in E2 and the objective optimization function established in S4, use a non-linear optimization algorithm to optimize the objective function to obtain the required parameters.

[0076] In step S6, unlock each joint in sequence, repeat the steps of S3 to S5 to complete the identification of the parameters of each body of the space manipulator. For a space manipulator with different configurations and multiple arms, unlock each joint in sequence and lock the other joints to ensure that only one joint moves during each solution. The formula remains unchanged, record the data of the movement of different arms, and complete the identification of the dynamic parameters of each arm.

[0077] The beneficial effects of the present invention are that

[0078] 1. The present invention is based on a suspended gravity unloading device, realizing the inertial parameter identification of a space manipulator in three-dimensional space. Compared with existing identification methods, the suspension method can provide richer motions of the space manipulator in three-dimensional space, improving the identification efficiency and saving costs.

[0079] 2. By using the strategy of first globally identifying and then locally identifying, the parameters of the entire space manipulator are first identified and used as prior knowledge, simplifying the number of optimized parameters and improving the solution efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] The accompanying drawings here are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0081] Figure 1 is the working principle diagram of the suspended gravity unloading device;

[0082] Figure 2 is the schematic diagram of the suspended gravity unloading device;

[0083] Figure 3 is the flow chart of the dynamic parameter identification of the space manipulator;

[0084] Figure 4 is the schematic diagram of the structure of the two-arm space manipulator prototype;

[0085] Figure 5 is the schematic diagram of the dynamic analysis of the equivalent single rigid body of the space manipulator;

[0086] Figure 6 is the schematic diagram of the dynamic analysis of the equivalent two-body of the space manipulator. SPECIFIC IMPLEMENTATION METHOD

[0088] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following will further elaborate on the present invention in detail with reference to the drawings of the specification and specific examples, but it shall not be construed as a limitation to the present invention.

[0089] A method for ground identification of the parameters of a space manipulator based on a suspended gravity unloading device is used to realize the dynamic parameter identification of each part of the space manipulator in a ground environment, providing a basis for subsequent ground dynamic tests and gravity unloading experiments of the space manipulator. The working principle of the suspended gravity unloading device is as Figure 1 shown, including an unloading system, a data measurement system, and the object to be unloaded. The schematic diagram of the structure of the unloading device is as Figure 2 shown, including a follow-up subsystem and a constant-tension subsystem. The follow-up subsystem ensures that the suspension cable always remains vertical, and the constant-tension subsystem ensures that the tension of the suspension cable is always equal to the preset unloading force.

[0090] The identification process is asFigure 3 As shown in the figure, first identify the mass, center of mass, and moment of inertia parameters of the equivalent single rigid body when all joints of the space manipulator are locked, then sequentially unlock each joint to identify the parameters of the equivalent two-body, and finally calculate the mass, center of mass, and moment of inertia parameters of each part through the parameter relationship between the part and the whole.

[0091] The structure of the space manipulator adopted in this example is as Figure 4 shown, which consists of two identical space manipulators. Its designed structural parameters are shown in Table 1, and its dynamic parameter reference point is the center of mass and is aligned with the body coordinate system.

[0092] Table 1 Dynamic parameters of the arm rod

[0093]

[0094] The specific implementation method of this example is as follows:

[0095] Step S1, establish the single rigid body dynamics equation of the space manipulator system and separate the parameters to be identified

[0096] When the joints of the space manipulator are locked in the normal position (90°), it can be equivalent to a single rigid body. Select the position and direction of the single rigid body coordinate system. The specific illustration is as Figure 5 shown. Select the suspension points and set the initial value of the unloading force through its nominal parameters, and hang two suspension cables on each arm rod. Select the origin of the manipulator body coordinate system on the axis of the leftmost rotating shaft of the manipulator, and the y-axis is along the rotating axis of the manipulator. Establish the coordinate system according to the right-hand rule. Establish the single rigid body dynamics equations of the system and the suspension cables according to the above S1 step, and separate ten parameters to be identified (including the center of mass positions xyz, mass m, moment of inertia I xx 、I xy 、I xz 、I yy 、I yz 、I zz ).

[0097]

[0098]

[0099] Step S2, use the least squares method to solve the dynamic parameters of the whole space manipulator

[0100] Turn on the data acquisition system of the gravity unloading device. At this time, the unloading device is equivalent to a fixed rack with a sling, and has sensors for measuring the tension and direction of the sling. Release the spatial manipulator single-rigid body system from different initial positions and postures to let it swing freely, and measure the linear acceleration and angular velocity of the overall spatial manipulator through the inertial sensor IMU. The initial experimental conditions are shown in Table 2, where the posture and position are set in the single-rigid body coordinate system relative to the world coordinate system.

[0101] Table 2 Initial experimental conditions

[0102]

[0103] During the experiment, measure the linear acceleration and angular velocity of the overall spatial manipulator through the inertial sensor IMU, and at the same time use the tension sensor and laser sensor to record the sling tension and direction. Among them, the linear acceleration at the origin of the body coordinate system is derived through the installation position (speed measurement point) of the IMU, and the angular acceleration is obtained by the angular velocity differential method. According to the dynamic equation established in step S1, the equation inputs are the sling tension, torque, angular velocity, angular acceleration, and linear acceleration of the unloaded object, and the data are all sensor measurement data; the equation output is the required dynamic parameters. Use the least squares method to identify the overall parameters of the spatial manipulator system (equivalent single-rigid body), and the identification results are shown in Table 3.

[0104] Table 3 Identification results of the overall dynamic parameters of the spatial manipulator

[0105]

[0106] Step S3, unlock the first moving joint of the spatial manipulator and establish the dynamic equation of the two-body system

[0107] In this example, the spatial manipulator is composed of two arm rods. Unlock the rotating joint among them and establish the dynamic equation of the two-body system based on the momentum theorem. The specific illustration is as Figure 6 shown. After the joint is unlocked, the first arm rod is used as Body1 (body one), and the second arm rod is used as Body2 (body two). The expressions of the linear momentum and angular momentum of the two-body system are:

[0108]

[0109] Step S4, construct the objective optimization function of the spatial manipulator equivalent two-body system with respect to the dynamic parameters

[0110] Considering that there is an unloading force error in the gravity unloading device, take it as the resultant external force received by the spatial manipulator system, and establish the momentum equation of the spatial manipulator system within a certain time period through the relationship between momentum and impulse.

[0111]

[0112] Using the dynamic parameters of the overall space manipulator obtained in steps S1 and S2, through three equations of the mass theorem, the centroid theorem, and the parallel axis theorem, express the parameters in Body2 of the two-body system in step S3 in terms of the parameters in Body1:

[0113]

[0114] By substituting the above two sets of equations into the momentum equation established in S2, establish the target optimization function of the dynamic parameters of the two-body system as follows:

[0115]

[0116] Step S5, complete the identification of dynamic parameters using the nonlinear optimization algorithm

[0117] This example uses the SolidWorks-Simulink co-simulation. Unload the initial parameters of the suspended object required by the system, which are given by the nominal parameters of the space manipulator (SW model parameters). Suspend the space manipulator with multiple slings to provide a microgravity environment through the unloading system.

[0118] By unlocking the first joint and driving the arm from the starting position (0°) to +30° and -30°, and then back to the starting position, Table 4 lists the motion nodes. Use cubic spline curves to plan the joint motion with a time interval of 0.1 s, and record the IMU data, sling tension, and swing angle simultaneously.

[0119] Table 4 Joint motion nodes

[0120]

[0121] In this example, the particle swarm optimization algorithm is selected to optimize the objective function in step S4. Use the particle swarm algorithm in the Matlab optimization toolbox, set the initial values and the population size to 200, and perform optimization to obtain the parameters to be identified. The identified dynamic parameters of Body1 are shown in Table 5.

[0122] Table 5 Identification results of the dynamic parameters of Body1

[0123]

[0124] Step S6, unlock each joint in turn, repeat the steps of S3 - S5 to complete the identification of the parameters of each body of the space manipulator

[0125] This example has only one joint. By using the overall dynamic parameters of the space manipulator and the dynamic parameters of the first arm (Body1) obtained through steps S1 to S5, and applying the mass theorem, the centroid theorem, and the parallel axis theorem of the inertia tensor, the dynamic parameters of the other arm (Body2) can be obtained, as shown in Table 6.

[0126] Table 6 Identification Results of Dynamic Parameters of Body2

[0127]

[0128] As can be seen from the above table, the parameter identification method of the space manipulator based on the suspended gravity unloading device proposed by the present invention can effectively and accurately identify that the mass, centroid, and moment of inertia parameter errors of each body of the space manipulator are below 1%. The identified dynamic parameters of the mass, centroid position, and moment of inertia of the space manipulator play a key role in aspects such as its dynamic control, path planning, attitude control, and ground gravity unloading simulation experiments.

[0129] For space manipulators with different configurations and multiple arm rods, unlock each joint in sequence and lock the other joints to ensure that only one joint moves during each solution. The formula remains unchanged, and record the data of the movement of different arm rods to complete the identification of the dynamic parameters of each arm rod.

[0130] The theory of the present invention is simple and easy to implement. The identification results of the present invention are basically consistent with the actual space manipulator model parameters, providing clear and effective guidance for quickly obtaining the dynamic parameters of the space manipulator on the ground. The above description shows and describes the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other examples. It can be applied to various other space manipulator configurations and can be modified within the scope of the inventive concept described herein through the above teachings or related technologies or knowledge. Any modifications and changes made by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for identifying dynamic parameters of a space manipulator based on a suspended gravity unloading device, wherein, The existing suspension gravity unloading device includes a follower subsystem and a constant tension subsystem. The follower subsystem ensures that the sling always remains vertical, and the constant tension subsystem ensures that the sling tension is always equal to the preset unloading force. It is characterized by the following steps: S1. Establish the single-rigid-body dynamics equation of the space manipulator system and separate the parameters to be identified; S2. Solve the dynamics parameters of the entire space manipulator using the least squares method; S3. Unlock the first moving joint of the space manipulator and establish the dynamics equation of the two-body system; S4. Construct the objective optimization function of the equivalent two-body system of the space manipulator with respect to the dynamics parameters; S5. Use the nonlinear optimization algorithm to complete the identification of the dynamics parameters; S6. Repeat steps S3 to S5, unlock all joints in sequence, and complete the identification of the dynamics parameters of each body of the space manipulator.

2. The method according to claim 1, wherein: In step S1, using the Newton-Euler method, establish the single-rigid-body dynamics equation of the sling and the space manipulator system with respect to its body coordinate system as follows: Among them, the origin of the body coordinate system is O B , f and τ are the resultant force and resultant moment exerted by the sling at the origin of the body coordinate system, M is the total mass of the space manipulator, i is the sling serial number, N is the number of slings, ω B is the angular velocity of the single rigid body of the space manipulator system, is the angular acceleration of the single rigid body of the space manipulator system, is the linear acceleration at the origin of the body coordinate system, B r C is the position vector of the centroid C of the single rigid body relative to the origin of the body coordinate system, B I eq is the representation of the inertia tensor at the centroid of the single rigid body in the body coordinate system.

3. The method according to claim 2, wherein: In step S2, the solution of the dynamics parameters includes the following steps: T1. Hang the entire space manipulator in the air using no less than three slings, record the positions of the upper and lower suspension points of the sling, only turn on the measurement system of the unloading device, and turn off the follower subsystem and the constant force subsystem. T2. Release the space manipulator system from different initial positions and postures, let it swing freely, measure the data through the inertial sensor IMU, deduce the linear acceleration and angular velocity at the origin of the body coordinate system of the entire space manipulator, and obtain the angular acceleration by the angular velocity differential method; T3. Use the tension sensor and the laser sensor to record the sling tension and direction; T4. Use the dynamics equation after separating the parameters to be identified and the motion data recorded in the above steps T1 to T3, and solve the dynamics parameters of the entire space manipulator by the least squares method.

4. The method according to claim 1, characterized in that: In step S3, unlock the first moving joint of the space manipulator and establish the dynamics equation of the two-body system: According to the momentum theorem in the discrete form of the particle system, the following equation can be listed: Where, P is the total linear momentum of the system, H is the total angular momentum of the system, m0 is the mass of body 1, m1 is the mass of body 2, v0 is the linear velocity at the centroid of body 1, v1 is the linear velocity at the centroid of body 2, I r0 is the expression of the centroid position of body 1 in the world coordinate system, I r1 is the expression of the centroid position of body 2 in the world coordinate system, 0 I0 is the moment of inertia at the centroid of body 1, 1 I1 is the moment of inertia at the centroid of body 2, I R0 is the rotation matrix from the body 1 coordinate system to the world coordinate system, I R1 is the rotation matrix from the body 2 coordinate system to the world coordinate system. F is the resultant external force caused by the unloading force error, N is the resultant external torque, I r Ti is the expression of the position vector of the suspension point in the world coordinate system, Δt is the time interval, P0, H0 and P1, H1 respectively represent the linear momentum and angular momentum at two different times.

5. The method according to claim 1, characterized in that: In step S4, it includes the following steps: U1. Using the dynamics parameters of the entire space manipulator obtained in steps S1 and S2, through the three equations of the mass theorem, the centroid theorem, and the parallel axis theorem, express the parameters in the second body of the equivalent two-body in step S3 in terms of the parameters in the first body. Among them, 0 a0 is the position vector of the centroid of Body1 in the body coordinate system of Body1, 1 a1 is the position vector of the centroid of Body2 in the body coordinate system of Body2, 0 R1 is the rotation matrix from the body coordinate system of Body2 to the body coordinate system of Body1, 0 I eq is the overall moment of inertia of the robotic arm at the initial position and aligned with the body-one coordinate system, r B is the position vector of the centroid of the overall robotic arm at the initial position in the body coordinate system of Body1, 0 l0 is the position vector from the origin of the body coordinate system of Body1 to the origin of the body coordinate system of Body2, 0 c0 is the representation in the body coordinate system of Body1 of the position vector from the centroid of Body1 to the instantaneous centroid of the overall robotic arm, 0 c1 is the representation in the body coordinate system of Body1 of the position vector between the centroid of Body2 and the instantaneous centroid of the overall robotic arm. U2. Using the dynamics of the equivalent two-body system based on the momentum theorem established in step S3 and the dynamics parameters of the first body expressed by the parameters of the other body in step U1, construct the optimization function of the dynamics parameters of the first body. Among them, f1 is the sling force received by the body one, I r Ti is the expression of the position vector of the suspension point in the world coordinate system, g is the acceleration due to gravity, g x 、g y 、g z represents the function value of the optimization function one, h x 、h y 、h z represents the function value of the optimization function two, c I represents the optimization function one, c II represents the optimization function two.

6. The method according to claim 1, wherein: In step S5, it includes the following steps: E1. The existing suspension gravity unloading device includes a horizontal follower part and a vertical constant tension part. The initial parameters of the mass, centroid, and moment of inertia of each arm of the object to be unloaded required by the unloading device are given by the nominal parameters of the space manipulator. Hang the space manipulator with multiple slings and provide a slightly low gravity environment through the unloading device; E2. By unlocking the first joint and using cubic spline curve to plan the joint motion, record the IMU data, sling tension and swing angle at the same time; E3. Using the data collected by E2 and the target optimization function established by S4, the target function is optimized by a non - linear optimization algorithm to obtain the required parameters.

7. The method according to claim 1, wherein: The parameters to be identified are as follows: Among them, B I xx 、 B I yy 、 B I zz are respectively the three moments of inertia of the single rigid body system along the xyz axes of the body coordinate system, B I xy 、 B I xz 、 B I yz are respectively the three products of inertia of the single rigid body system, B r x 、 B r y 、 B r z are respectively the expressions of the position of the center of mass of the single rigid body system in the body coordinate system.

8. The method according to claim 3, wherein: In step T2, the calculation relationship between the linear velocity of the IMU installation point and the linear velocity at the origin of the body coordinate system is as follows: Taking the derivative of both sides to obtain the relationship of linear acceleration: where v Q is the linear velocity representation of the IMU installation point, is the linear velocity at the origin of the body coordinate system, is the linear acceleration at the origin of the body coordinate system, ω B is the angular velocity of the single rigid body of the space manipulator measured by the IMU, is the angular acceleration of the single rigid body of the space manipulator calculated by differentiation, I r Q is the representation of the IMU sensor installation point in the body coordinate system in the world coordinate system.

9. The method according to claim 3, characterized in that: In step T4, the dynamic parameters of the overall space manipulator are obtained by solving with the least - squares method, and the formula is as follows: P = (A T A) -1 A T F Among them, the parameter matrix P includes ten parameters of the mass, center - of - mass position, and moment of inertia of the single - rigid - body system of the space manipulator.

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