Flywheel unloading method in position protection period based on electric push mechanical arm

Abstract

The invention provides a flywheel unloading method based on an electric pushing mechanical arm in a position protection period. The flywheel unloading method comprises the steps that a joint corner combination is selected when the thrust direction is in a position protection allowable range; the control torque under the joint rotation angle combination of each mechanical arm is determined, and an initial table look-up matrix is established; determining an optimal torque and a torque error allowable range; according to the control torque, the optimal torque and the torque error allowable range, grade division is conducted on the joint corner combination; constructing a cost function according to the optimal torque and the control torque; on the basis of grade division, the smaller the cost function is, the higher the priority of the joint corner combination is; selecting a joint corner combination with the highest priority from the initial look-up table matrix, performing permutation and combination of joint corners around the joint corner combination in a fine step length manner, determining a corresponding control moment, forming a second-order look-up table matrix, and selecting a joint corner combination with the highest priority; and circularly selecting the joint corner combination with the highest priority to obtain a final joint corner combination.

Description

Technical Field

[0001] The present invention belongs to the technical field of the control of the guidance, navigation and control (GNC) subsystem of spacecraft, and particularly relates to a method for unloading a flywheel during the on-orbit position keeping (orbital position maintenance) of a service target at the end of its life using a robotic arm and an electric thruster at the end of the robotic arm. Background Art

[0002] In recent years, with the development and maturity of space technology, the rendezvous and docking of on-orbit spacecraft have become a conventional space operation means. After a satellite rendezvouses with and captures a cooperative or non-cooperative target, a double-satellite combination will be formed to complete subsequent tasks.

[0003] In addition, with the consumption of on-orbit fuel, there are more and more satellites at the end of their lives, and the demand for orbit life extension vehicles increases accordingly. The assisted satellite is usually a communication satellite, which operates in the geostationary orbit and maintains the attitude towards the earth through flywheel control for earth communication. After the life extension vehicle docks with the assisted vehicle, it mainly provides east-west and north-south position keeping for the assisted vehicle, extends the on-orbit working time of the vehicle, and provides higher economic value.

[0004] As the operating time of the satellite increases, after the fuel is consumed, the satellite loses its jet control ability. Due to the influence of the space disturbance torque, the flywheel of the satellite will gradually become saturated. Therefore, the life extension vehicle also needs to provide the function of unloading the flywheel to ensure the attitude stability of the assisted vehicle.

[0005] For this reason, the present invention provides a method for unloading a flywheel during position keeping based on an electric propulsion robotic arm, using the robotic arm + electric thruster at the end of the robotic arm to provide multi-directional thrust to achieve the purpose of unloading the flywheel during position keeping. Summary of the Invention

[0006] In order to overcome the deficiencies in the prior art, the inventor of the present invention has conducted intensive research and provided a method for unloading a flywheel during position keeping based on an electric propulsion robotic arm, using only an actuator of a robotic arm + an electric thruster at the end to perform position keeping orbit control and unload the flywheel of the target satellite at the same time.

[0007] The technical solution provided by the present invention is as follows:

[0008] In a first aspect, a method for unloading a flywheel during position keeping based on an electric propulsion robotic arm includes:

[0009] Arrange and combine the rotation angles of the robotic arm joints on the double-satellite combination with a first step size, and select the combination of joint rotation angles whose thrust direction is within the allowable range of position keeping;

[0010] According to the centroid of the combined body, the ignition position, the thrust direction, and the nominal thrust of the electric thruster in the target star layout coordinate system, determine the control torque under each combination of robotic arm joint angles, and establish an initial look-up table matrix based on the joint angle combination and the corresponding control torque;

[0011] According to the flywheel speed before orbit control jet, the flywheel moment of inertia, and the set jet duration, determine the optimal torque and the allowable range of torque error;

[0012] Compare the optimal torque with the control torques under each combination of robotic arm joint angles, and classify the joint angle combinations based on the allowable range of torque error as the grading basis;

[0013] Construct a cost function based on the optimal torque and the control torques under each combination of robotic arm joint angles; on the basis of the classification, the smaller the cost function, the higher the priority of the joint angle combination;

[0014] Select the joint angle combination with the highest priority from the initial look-up table matrix. Around this group of joint angle combinations, perform permutations and combinations of joint angles with the second step size, determine the control torque of each group of robotic arm angles, form a second-order look-up table matrix, and select the joint angle combination with the highest priority; among them, the second step size is smaller than the first step size;

[0015] Repeat the step of selecting the joint angle combination with the highest priority multiple times to obtain the final joint angle combination.

[0016] In a second aspect, a flywheel unloading control device for position maintenance during electric propulsion robotic arm operation includes:

[0017] One or more processors;

[0018] A storage device for storing one or more programs,

[0019] When the one or more programs are executed by the one or more processors, the one or more processors implement the flywheel unloading method for position maintenance during electric propulsion robotic arm operation described in the first aspect.

[0020] In a third aspect, a readable storage medium stores a computer program, and when the program is executed by a processor, it implements the flywheel unloading method for position maintenance during electric propulsion robotic arm operation described in the first aspect.

[0021] In a fourth aspect, a computer program product includes: a computer program (which can also be called code or instruction), and when the computer program is run, it executes the flywheel unloading method for position maintenance during electric propulsion robotic arm operation described in the first aspect.

[0022] A flywheel unloading method during position maintenance based on an electric propulsion robotic arm provided by the present invention has the following beneficial effects:

[0023] (1) A flywheel unloading method during position maintenance based on an electric propulsion robotic arm provided by the present invention includes: selecting joint angle combinations when the thrust direction is within the allowable range of position maintenance; determining the control torques under each robotic arm joint angle combination, and establishing an initial look-up table matrix; determining the optimal torque and the allowable range of torque error; classifying the joint angle combinations according to the control torque, the optimal torque, and the allowable range of torque error; constructing a cost function according to the optimal torque and the control torque; on the basis of the classification, the smaller the cost function, the higher the priority of the joint angle combination; selecting the joint angle combination with the highest priority from the initial look-up table matrix, arranging and combining the joint angles around this joint angle combination with a fine step size and determining the corresponding control torques to form a second-order look-up table matrix, and then selecting the joint angle combination with the highest priority; repeating the step of selecting the joint angle combination with the highest priority to obtain the final joint angle combination. The method of the present invention performs unloading control on the target star flywheel while performing position maintenance control, without the need for an additional process.

[0024] (2) A flywheel unloading method during position maintenance based on an electric propulsion robotic arm provided by the present invention does not involve complex inverse kinematic inverse solutions of the robotic arm, does not require the robotic arm to reach any arbitrary pose in space, and there will be no unsolvable situation; and this method can add constraints more conveniently and is more suitable for complex on-orbit situations.

[0025] (3) A flywheel unloading method during position maintenance based on an electric propulsion robotic arm provided by the present invention can find a local optimal solution by changing the number of times of the step of repeatedly selecting the joint angle combination with the highest priority, with a controllable calculation amount and a controllable accuracy.

[0026] (4) A flywheel unloading method during position maintenance based on an electric propulsion robotic arm provided by the present invention only requires one robotic arm and one electric thruster, with a simple actuator and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flowchart of the flywheel unloading method during position maintenance based on an electric propulsion robotic arm of the present invention;

[0028] Figure 2 is a schematic diagram of the combined body layout;

[0029] Figure 3 is the change in the flywheel speed during unloading control of the present invention;

[0030] Figure 4 is the change in the geographical accuracy during seven-day position maintenance + unloading control of the present invention;

[0031] Figure 5For the seven-day position maintenance + unloading control in the present invention, the rotational speed of the target flywheel changes. Detailed implementation manners

[0032] The present invention will be described in detail below, and the features and advantages of the present invention will become clearer and more definite along with these descriptions.

[0033] The special term "exemplary" here means "serving as an example, embodiment or illustration". Any embodiment described as "exemplary" here does not have to be construed as superior to or better than other embodiments.

[0034] As Figure 1 shown, the present invention provides a flywheel unloading method during position maintenance based on an electric-push robotic arm. During the position maintenance of the target satellite, only one robotic arm and one electric thruster at the end of the robotic arm are used for flywheel unloading, which specifically includes the following steps:

[0035] Step 1, determine the input parameters and output parameters of the unloading method

[0036] Input parameters:

[0037] The centroid c of the combined body in the layout coordinate system of the target satellite = [X Y Z];

[0038] The desired rotational speeds of the three axes of the flywheel S (the rotational speeds of the three axes of the flywheel before orbit control jetting);

[0039] The moment of inertia J of the flywheel;

[0040] The jetting duration t (given by the orbit control strategy);

[0041] The range of the electric-push thrust direction F (given by the orbit control strategy);

[0042] The nominal thrust f of the electric thruster;

[0043] The rotational ranges of the N joints of the robotic arm.

[0044] Output ammunition number:

[0045] The joint rotation angles of the robotic arm.

[0046] Step 2, determine the conversion relationship between the coordinate systems on the double-satellite combined body and align the coordinate systems

[0047] As Figure 2 shown, there are multiple coordinate systems and coordinate origins involved in the unloading method. First, unify them to the layout coordinate system of the target satellite to facilitate the subsequent work.

[0048] (2.1) The main coordinate systems include:

[0049] The layout coordinate system F of the extended-life vehicle DT (O DTX DT Y DT Z DT ),origin O DT is located on the life-extension vehicle, and the directions of the X DT , Y DT , Z DT axes are established according to engineering examples in practical applications.

[0050] Target star layout coordinate system F T (O T X T Y T Z T ), origin O T is located on the target star, and the directions of the X T , Y T , Z T axes are established according to engineering examples in practical applications.

[0051] Manipulator base coordinate system F0(O0X0Y0Z0), origin O0 is located on the manipulator base, and the directions of the X0, Y0, Z0 axes are established according to engineering examples in practical applications.

[0052] (2.2) Coordinate transformation relationship:

[0053] The coordinate transformation matrix from the life-extension vehicle layout coordinate system F DT to the manipulator base coordinate system F0 is A 0DT ;

[0054] The coordinate transformation matrix from the target star layout coordinate system F T to the life-extension vehicle layout coordinate system F DT is A DTT or the attitude quaternion q DTT ;

[0055] The three axes of the target star layout system F T and the centroid body system F b point in the same direction, that is, A bT is the identity matrix.

[0056] (2.3) Coordinate origin transformation relationship:

[0057] The coordinate of the origin O0 of the manipulator base system in the life-extension vehicle layout system F DT is r DT0

[0058] The coordinate of the origin O DT of the life-extension vehicle layout system in the target star layout system F T is r TDT

[0059] The position of the origin O0 of the manipulator base system in the target star layout system F can be calculated from the above two equations T is r T0 = r TDT + A TDT r DT0 .

[0060] Step 3: Determine the ignition position and ignition direction of the electric thruster at the end of the manipulator

[0061] According to the DH (Denavit - Hartenberg) model of the manipulator, determine that the transformation matrix from the end of the manipulator to the manipulator base coordinate system is C 0←n .

[0062] The ignition position is expressed in the manipulator base coordinate system as:

[0063] P0 = [C 0←n (1,4) C 0←n (2,4) C 0←n (3,4)] T

[0064] The thrust direction is expressed in the manipulator base coordinate system as:

[0065] D0 = -[C 0←n (1,1) C 0←n (2,1) C 0←n (3,1)] T

[0066] Furthermore, the ignition position is expressed in the target star layout coordinate system as:

[0067] P T = r T0 + A DTT T A 0DT T P0

[0068] The thrust direction is determined by the joint angles of the manipulator. The thrust direction is expressed in the target star layout coordinate system as:

[0069] D T = A DTT T A 0DT T D0.

[0070] Step 4: Arrange and combine the joint angles of the N joints of the manipulator with a relatively coarse step size, select the joint angle combinations when the thrust direction is within the range allowed by position and attitude maintenance, and determine the control torque T for each joint angle combination of the manipulator according to the centroid c of the combined mass, ignition position, thrust direction, and nominal thrust f of the electric thruster in the target star layout coordinate systemc , an initial look-up table matrix is established according to the above joint angle combinations and corresponding control torques.

[0071] The control torque T c is expressed in the target star layout coordinate system as:

[0072] T c = (P T - c) × (D T · f)

[0073] Step 5: Determine the optimal torque T opt according to the flywheel, flywheel moment of inertia, and set jet duration and rotational speed before attitude maintenance (before orbit control jetting). err .

[0074]

[0075] where S is the desired three-axis rotational speed of the flywheel to be unloaded (the three-axis rotational speed of the flywheel before orbit control jetting), J is the flywheel moment of inertia; t is the jet duration.

[0076] Step 6: Construct a cost function H according to the optimal torque T opt and the control torque magnitudes T c generated by each robotic arm joint angle combination:

[0077] H = a1(T opt (1) - T c (1)) 2 + a2(T opt (2) - T c (2)) 2 + a3(T opt (3) - T c (3)) 2

[0078] where a1, a2, and a3 are adjustable weight coefficients for the three axes, T opt (1), T opt (2), T opt (3) are the optimal torques for the X, Y, and Z axes respectively, and T c (1), T c (2), T c (3) are the control torques for the X, Y, and Z axes respectively.

[0079] Design a selection logic: If the three-axis errors between T c and T opt are all within the range of T err , such rotation angles are type I rotation angles, and calculate the cost function H; if the two-axis errors between T c and T opt are both within the range of Terr within a range and a one-axis T that does not meet the requirements c is the same as T opt in the same polarity, and |T c (i)| < 2|T opt (i)|, such a rotation angle is a type-II rotation angle, and the cost function H is calculated; all three axes meet T c is the same as T opt in the same polarity, and |T c | < 2|T opt |, such a rotation angle is a type-III rotation angle, and the cost function H is calculated; if none of the above conditions are met, it is a type-IV rotation angle. The priority of type-I rotation angle > type-II > type-III > type-IV, and on this basis, the smaller the cost function H, the higher the priority.

[0080] Step 7: Select the group of rotation angles with the highest priority in the initial look-up table matrix through the selection logic in Step 6. Around this group of rotation angles, perform permutations and combinations of rotation angles with a finer step size to determine the control torque of each group of robotic arm rotation angles, forming a second-order look-up table matrix; use the method in Step 6 to select the group of rotation angles with the highest priority.

[0081] Step 8: Loop the methods in Steps 6-7 multiple times, such as 4 times, to obtain a group of rotation angles with sufficiently high accuracy.

[0082] Step 9: If it is necessary to change the constraints for determining the joint rotation angle combination (such as the rotation angle range of each joint of the robotic arm), the constraints can be increased or decreased in Step 4; if it is necessary to increase or decrease the rotation angle accuracy, the number of loops can be increased or decreased in Step 8.

[0083] Figure 3 In the simulation results, it is assumed that the flywheel speeds at the start of position protection are -1000 rpm for the X-axis, 1000 rpm for the Y-axis, and 1000 rpm for the Z-axis, the position protection jet duration is 3000 s, and position protection control is performed using the rotation angles of each joint of the robotic arm calculated by the above algorithm. After the position protection ends, the flywheel speeds of all three axes drop below 200 rpm.

[0084] Figure 4 、 Figure 5 is the seven-day position protection simulation diagram using the above algorithm, with position protection control performed twice at the ascending and descending nodes every day. Figure 4 is the position protection accuracy curve, and the position protection accuracy is better than 0.02°; Figure 5 is the flywheel speed curve of the combined body for seven days. The flywheel speeds of the X and Z axes are maintained within 50 rpm, and the Y axis is disturbed by the periodic light pressure torque and maintained within 1500 rpm.

[0085] The present invention also provides a flywheel unloading device during position protection for an electric propulsion robotic arm, including:

[0086] one or more processors;

[0087] A storage device for storing one or more programs,

[0088] When the one or more programs are executed by the one or more processors, the one or more processors implement the above-mentioned flywheel unloading method during the position holding period of the electric propulsion robotic arm.

[0089] The present invention also provides a readable storage medium, on which a computer program is stored, and when the program is executed by a processor, the above-mentioned flywheel unloading method during the position holding period of the electric propulsion robotic arm is implemented.

[0090] The readable storage medium includes, but is not limited to: various media such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs that can store program codes.

[0091] The present invention also provides a computer program product, which includes: a computer program (which can also be referred to as code or instructions), and when the computer program is run, it executes the above-mentioned flywheel unloading method during the position holding period of the electric propulsion robotic arm.

[0092] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer instructions are loaded and executed on a computer, the processes or functions described in the embodiments of the present application are generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium.

[0093] Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. A professional technician can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present application.

[0094] The present invention has been described in detail in conjunction with specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications, or improvements can be made to the technical solutions and their implementation manners of the present invention, and all of these fall within the scope of the present invention. The protection scope of the present invention shall be subject to the appended claims.

[0095] The content not detailed in the specification of the present invention belongs to the well-known technology of those skilled in the art.

Claims

1. A flywheel unloading method during position-holding based on an electric propulsion manipulator, characterized in that: include: The first step is to arrange and combine the rotation angles of the robot arm joints on the binary satellite assembly, and select the joint rotation angle combination whose thrust direction is within the allowable range of position preservation; According to the center of mass of the assembly, ignition position, thrust direction and nominal thrust of the electric thruster in the target satellite layout coordinate system, the control torque under each manipulator joint angle combination is determined, and the initial lookup matrix is ​​established according to the joint angle combination and the corresponding control torque; Determine the optimal torque and the allowable range of torque error according to the flywheel speed, flywheel rotational inertia and set jet duration before orbital control jet injection; Compare the optimal torque with the control torque under each robot joint angle combination, and classify the joint angle combinations based on the allowable range of torque error; According to the optimal torque and the control torque under each robot joint angle combination, a cost function is constructed; based on the level division, the smaller the cost function, the higher the priority of the joint angle combination; The joint angle combination with the highest priority is selected in the initial lookup matrix, and the joint angles are arranged and combined around this group of joint angle combinations with a second step length to determine the control torque under each group of robot joint angle combinations, to form a second-order lookup matrix, and the joint angle combination with the highest priority is selected; wherein the second step length is smaller than the first step length; The steps of selecting the joint rotation combination with the highest priority are repeated multiple times to obtain the final joint rotation combination.

2. The flywheel unloading method during position-holding based on an electric propulsion manipulator according to claim 1 is characterized in that: In the step of determining the control torque under each mechanical arm joint angle combination according to the center of mass of the assembly, the ignition position, the thrust direction and the nominal thrust of the electric thruster in the target star layout coordinate system, the ignition position is expressed as: P T =r T0 +A DTT T A 0DT T P0 The thrust direction is expressed in the target satellite layout coordinate system as: D T =A DTT T A 0DT T D0 The control torque is expressed in the target star layout coordinate system as: T c =(P T -c)×(D T ·f) Where P T and D T are the ignition position and thrust direction in the target satellite layout coordinate system; T c is the control torque; r T0 A is the position of the origin of the robot base system in the target constellation system; DTT A is the coordinate transformation matrix from the target satellite layout coordinate system to the life extension vehicle layout coordinate system; 0DT is the coordinate transformation matrix from the life extension vehicle layout coordinate system to the manipulator base coordinate system; P0 and D0 are the ignition position and thrust direction in the manipulator base coordinate system, respectively; c is the representation of the center of mass position of the assembly in the target satellite layout system; f is the nominal thrust of the electric thruster.

3. The flywheel unloading method during position-holding based on an electric propulsion manipulator according to claim 1, characterized in that: In the step of determining the optimal torque and the allowable range of torque error according to the flywheel speed, flywheel rotational inertia and set jet duration before orbital control jetting, the optimal torque is: The allowable range of torque error is: Where, T opt is the optimal torque, T err is the allowable range of torque error, S is the three-axis speed of the flywheel expected to be unloaded, J is the moment of inertia of the flywheel; t is the jet duration.

4. The flywheel unloading method during position-holding based on an electric propulsion manipulator according to claim 1, characterized in that: In the step of classifying the joint angle combinations, the classification logic is: If the control torque T c With the optimal torque T opt The three-axis errors are all within T err Within the range, this type of corner is a Class I corner; if T c With T opt The error of both axes is T err Within the range, and does not meet the one axis T c With T opt The polarity is the same, and |T c (i)|<2|T opt (i)|, this type of rotation is a type II rotation; all three axes meet T c With T opt The polarity is the same, and |T c |<2|T opt |, this type of corner is a Class III corner; if none of the above conditions are met, it is a Class IV corner; the corner priority is Class I>Class II>Class III>Class IV.

5. The flywheel unloading method during position-holding based on an electric propulsion manipulator according to claim 1, characterized in that: In the step of constructing the cost function H according to the optimal torque and the control torque under the combination of the joint angles of each robot arm, the cost function H is: H=a1(T opt (1)-T c (1)) 2 +a2(T opt (2)-T c (2)) 2 +a3(T opt (3)-T c (3)) 2 In the formula, a1, a2, and a3 are the weight coefficients of the three adjustable axes, T opt (1) T opt (2) T opt (3) are the optimal moments of X, Y, and Z axes, T c (1) T c (2) T c (3) are the control torques of the X, Y, and Z axes, respectively.

6. The flywheel unloading method during position-holding based on an electric propulsion manipulator according to claim 1, characterized in that: The method also includes: increasing or decreasing the accuracy of the joint angle combination by changing the number of times the step of cyclically selecting the joint angle combination with the highest priority is performed.

7. The flywheel unloading method during position-holding based on an electric propulsion manipulator according to claim 1, characterized in that: The method also includes: screening the joint angle combinations by changing the constraint conditions of the joint angle combinations, wherein the constraint conditions include the angle ranges of the joints of the robotic arm.

8. A flywheel unloading control device during position protection based on an electric propulsion manipulator, characterized in that: include: one or more processors; a storage device for storing one or more programs, When the one or more programs are executed by the one or more processors, the one or more processors implement the flywheel unloading method during position retention based on an electric propulsion manipulator as described in one of claims 1 to 7.

9. A readable storage medium, characterized in that: A computer program is stored thereon, and when the program is executed by a processor, the flywheel unloading method during position retention based on an electric propulsion manipulator as described in one of claims 1 to 7 is implemented.

10. A computer program product, characterized in that The computer program product comprises: a computer program, which, when being executed, executes the flywheel unloading method during position retention based on an electric propulsion manipulator as claimed in any one of claims 1 to 7.

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