A layout optimization method for the landing gear system of an unmanned aerial vehicle

Abstract

The present invention discloses a layout optimization method for an unmanned aerial vehicle landing gear system, which specifically includes the following steps: S1: Simplify the landing gear system and confirm the connection pair categories of the landing gear system; S2: Obtain the point coordinates, performance limitations of the landing gear system, and operating conditions required for constructing the landing gear system model; S3: Confirm the design variables based on the point coordinates of the landing gear system and generate a parametric model; S4: Apply the ground load, gravity, and hatch retraction and extension loads of the landing gear, and set the effective conditions of each load; S5: Construct corresponding relevant constraint functions according to the retraction and extension stroke, landing gear retraction and extension angle limitations, and the installation cabin space limitations of the landing gear system; S6: Confirm the objective function based on the fuselage cross-link load, retraction and extension load, and retraction and extension efficiency; S7: Optimize the objective function, that is, optimize the installation points of the landing gear and the installation points of the retraction and extension actuators, and finally obtain the optimal overall layout of the landing gear system.

Description

Technical Field

[0001] The present invention relates to the field of aviation technology, and relates to a layout optimization method for an undercarriage system of an unmanned aerial vehicle (UAV). Background Art

[0002] Due to the characteristics of the UAV itself, such as light weight, good fuel economy, short re-deployment time, and good maintainability, with the use of UAVs at home and abroad in various fields, the demand for UAVs is increasing day by day. There is room for customized spatial layout for various UAVs, which means that the undercarriage system of the UAV also needs to be designed individually according to the spatial layout.

[0003] The undercarriage system of the UAV mainly consists of an undercarriage and a retraction actuator, and the undercarriage system is usually installed in the limited cabin of the UAV, and the spatial layout is greatly restricted. The spatial layout of the undercarriage system not only needs to consider that there is no interference with other components in the cabin during the retraction and extension process, but also needs to consider that during the entire retraction and extension process, the retraction and extension stroke, retraction and extension load, etc. meet the design requirements, which is a difficult problem for the design layout of the undercarriage system.

[0004] Conventional spatial layouts of undercarriage systems mostly establish associated motions for three-dimensional digital models to preferentially meet the non-interference requirements, and then repeatedly adjust to make the retraction and extension stroke, retraction and extension load, etc. reach an acceptable range. However, such a design method is time-consuming and laborious, and it is impossible to comprehensively consider all constraint factors in a short time. Sometimes, after the design is completed, one of the key constraint conditions or design requirements cannot be met, and then the design needs to be iterated repeatedly. When one or more design requirements change, the design iteration of the spatial layout even more needs to adjust the digital model to confirm whether the design requirements are met, which is not conducive to the rapid update of the spatial layout. Summary of the Invention

[0005] Aiming at the technical problem of high time consumption in the layout design of the undercarriage system of the UAV in the prior art, the present invention proposes a layout optimization method for the undercarriage system of the UAV.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A layout optimization method for an undercarriage system of an unmanned aerial vehicle, specifically comprising the following steps:

[0008] S1: Simplify the undercarriage system and confirm the connection pair categories of the undercarriage system;

[0009] S2: Obtain the point coordinates, performance limitations of the undercarriage system, and operating conditions required for constructing the undercarriage system model;

[0010] S3: Confirm the design variables according to the point coordinates of the undercarriage system and generate a parametric model;

[0011] S4: Apply the landing gear ground load, gravity, and door retraction / extension load, and set the effective conditions of each load.

[0012] S5: Construct corresponding relevant constraint functions according to the retraction / extension stroke, the landing gear retraction / extension angle limit, and the space limit of the landing gear system installation compartment.

[0013] S6: Confirm the objective function based on the fuselage cross-link load, retraction / extension load, and retraction / extension efficiency.

[0014] S7: Optimize the objective function, that is, optimize the installation points of the landing gear and the installation points of the retraction / extension actuating cylinder, and finally obtain the optimal overall layout of the landing gear system.

[0015] Preferably, in the S1, the simplifying assumptions for the landing gear system include:

[0016] Assumption 1: The shapes of all components in the UAV landing gear system are replaced by point-line models, ignoring fits and clearances.

[0017] Assumption 2: The coordinate points of the connection pairs of all components in the UAV landing gear system are taken as the center points of the connection areas.

[0018] Assumption 3: The loads applied to the UAV landing gear system are all applied as concentrated forces or torques.

[0019] Assumption 4: The lowered states and lowered angles of the nose landing gear and main landing gear in the UAV landing gear system are determined.

[0020] Assumption 5: The door retraction / extension mechanism of the UAV is linked with the landing gear, and the load applied by the door retraction / extension mechanism to the landing gear is determined.

[0021] Assumption 6: The three-sided layout of the landing gear system in the lowered state is determined.

[0022] Preferably, in the S1, the connection pair categories of the landing gear system include spherical pairs, prismatic pairs, and revolute pairs.

[0023] The landing gear system includes a landing gear (1), a retraction / extension actuating cylinder piston rod (2), and a retraction / extension actuating cylinder outer cylinder (3); among them, the retraction / extension actuating cylinder outer cylinder (3) is connected to the fuselage by a spherical pair, the retraction / extension actuating cylinder piston rod (2) is connected to the landing gear by a spherical pair, the retraction / extension actuating cylinder outer cylinder (3) is connected to the retraction / extension actuating cylinder piston rod (2) by a prismatic pair, and the landing gear (1) is connected to the fuselage by a left revolute pair and a right revolute pair.

[0024] Preferably, the S2 includes:

[0025] S2-1: Establish the Cartesian coordinate system of the UAV landing gear system: The positive direction of the X-axis is from the tail to the nose of the UAV, and the positive direction of the Y-axis is perpendicular to the X-axis and lies in the same horizontal plane; the positive direction of the Z-axis is towards the sky;

[0026] S2-2: After assembling the landing gear system into the correct Cartesian coordinate system, identify the connection pairs of the landing gear system, and confirm the required number of points according to the category and point overlap; then measure and record the coordinates of each required point to form the original point coordinate matrix X:

[0027]

[0028] In formula (1), x 1 represents the x-axis coordinate of the first point; y 1 represents the y-axis coordinate of the first point; z 1 represents the z-axis coordinate of the first point; x n represents the x-axis coordinate of the nth point; y n represents the y-axis coordinate of the nth point; z n represents the z-axis coordinate of the nth point.

[0029] Preferably, in S2-2, the required number of points is: 1 point for spherical pair demand, 2 points for rotational pair demand, 2 points for translational pair demand, 1 point for single-load application demand, and 1 point for single-component centroid demand; 2 points for constructing a single cylindrical component, 3 points for constructing a single triangular prism component, and 2 points for constructing a single rectangular component.

[0030] Preferably, S3 includes:

[0031] S3-1: Parametrize the original point coordinate matrix to determine the design variables;

[0032] S3-2: Establish a parametric model according to the design variables.

[0033] Preferably, S3-1 includes:

[0034] S3-1-1: Identify the related points and then perform parametrization to determine the design variables;

[0035] The related points include symmetry relationship, coplanarity relationship, and collinearity relationship; the design variables include the first design variable DV1, the second design variable DV2, the third design variable DV3, and the fourth design variable DV4;

[0036] S3-1-2: Set the valid value range for the design variables:

[0037] The point coordinates should satisfy that there is an avoidance space in the cabin space during the entire movement process of the landing gear system. By using the set point coordinates to draw regular shapes, a simplified model of the landing gear system is established.

[0038] Preferably, in the step S4, the gravity is applied at the center of gravity of the landing gear.

[0039] The ground load includes the vertical load F y , the heading load F x and the lateral load F z . The vertical load F y and the heading load F x are applied at the center of the wheel axle of the landing gear, and the lateral load F z is applied at the ground contact point of the landing gear tire.

[0040] The hatch retraction and extension load includes single-sided hatch retraction and extension and double-sided hatch retraction and extension. Among them, single-sided hatch retraction and extension means that only one side of the hatch of the landing gear system opens and closes, and the application point of force is the center point of the connection pair between the hatch mechanism and the landing gear; double-sided hatch retraction and extension means that both sides of the hatch of the landing gear system open and close, and the application points of force are the center points of the connection pairs between the hatch mechanisms on both sides and the landing gear respectively.

[0041] Preferably, the step S5 includes:

[0042] S4-1: Construct the length constraint function of the retraction and extension actuator:

[0043]

[0044] In formula (2), L min represents the minimum allowable length of the retraction and extension actuator; the first design variable DV1, the second design variable DV2, the third design variable DV3, the fourth design variable DV4; S represents the contraction displacement.

[0045] S4-2: Construct the angle limit constraint function for the retraction and extension of the landing gear:

[0046] g 2 (X) = Sc min -r wheel -Sc(X) t＝ts ≤0 (3)

[0047] In formula (3), g 2 (X) represents the angle limit constraint function for the retraction and extension of the landing gear; Sc min represents the minimum distance between the wheel center of the landing gear and the hatch when the landing gear is fully retracted; r wheel represents the maximum radius of the tire; ts is the time when the landing gear is fully retracted; Sc(X) t＝ts represents the distance between the wheel center of the landing gear and the hatch when the landing gear is fully retracted.

[0048] S4-3: Construct the point position space limit constraint function:

[0049]

[0050] In formula (4), g 3 (X) represents the point position space limit constraint function; CONTACT(X) i represents the i-th contact force; n represents the number of contact forces;

[0051] S4-4: Construct the relative position constraint function of each component of the landing gear system:

[0052] PO = z 1 -z 2 -5 ≥ 0 (5)

[0053] In formula (5), PO represents the position constraint between two points; z 1 represents the z-direction distance of the first point; z 2 represents the z-direction distance of the second point;

[0054] It is deduced from the above content that:

[0055]

[0056] In formula (6), g 4 (X) represents the relative position constraint function of each component of the landing gear system; PO(X) i represents the position constraint of the i-th point; m represents the number of point relative position constraints.

[0057] Preferably, in S6, the objective function is the fuselage load, the retraction and extension load, and the retraction and extension efficiency;

[0058] The fuselage load is divided into the resultant load of the connections between the fuselage and each component of the takeoff and landing system:

[0059]

[0060] In formula (7), F 1 represents the fuselage load; n represents the total number of connections, K i are the penalty factors of each objective function respectively, and their magnitudes and values need to be adjusted according to the actual working conditions, F 1,i is the resultant load of each connection;

[0061] The retraction and extension load F 2 is the same as the magnitude of the resultant load of the fuselage at the connection with the retraction and extension actuator;

[0062] Assume that the retraction and extension actuator is in the maximum extended state in the initial state, and the maximum contraction displacement is S max, the retraction and extension efficiency is as follows:

[0063]

[0064] In formula (8), η represents the retraction and extension efficiency; S max represents the maximum contraction displacement; represents the maximum resultant force on the fuselage at the connection of the retraction and extension actuator;

[0065] To simplify the calculation, the multi-objective optimization of the objective function is transformed into a single-objective optimization problem:

[0066] Q = α 1 F 1 + α 2 F 2 + α 3 η (9)

[0067] In formula (9), α 1 , α 2 , α 3 are the penalty factors of each objective function respectively.

[0068] In summary, due to the adoption of the above technical solutions, compared with the prior art, the present invention has at least the following beneficial effects:

[0069] The present invention saves the time and calculation cost of the initial layout design of the landing gear system, provides guarantee for the rapid iteration of the landing gear system layout, and simplifies the load analysis and motion state analysis of the landing gear system. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 It is a schematic diagram of a layout optimization method for an unmanned aerial vehicle landing gear system according to an exemplary embodiment of the present invention.

[0071] Figure 2 It is a schematic diagram of a connection pair of the landing gear system according to an exemplary embodiment of the present invention.

[0072] Figure 3 It is a schematic diagram of a parametric model of the landing gear system according to an exemplary embodiment of the present invention.

[0073] Figure 4 It is a schematic diagram of importing a model of cabin space limitation according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0074] The present invention will be further described in detail below in conjunction with embodiments and specific implementation manners. However, this should not be understood as limiting the scope of the above-mentioned subject matter of the present invention to the following embodiments. Any technology implemented based on the content of the present invention belongs to the scope of the present invention.

[0075] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0076] As Figure 1 shown, the present invention provides a layout optimization method for an unmanned aerial vehicle landing gear system, which specifically includes the following steps:

[0077] S1: Simplify and assume the unmanned aerial vehicle landing gear system, and confirm the types of connecting pairs of the landing gear system.

[0078] In this embodiment, the simplification and assumption of the unmanned aerial vehicle landing gear system include:

[0079] Assumption 1: The shapes of all components in the unmanned aerial vehicle landing gear system are replaced by point-line models, and irrelevant parameters such as fits and clearances are ignored;

[0080] Assumption 2: The coordinate points of the connecting pairs of all components in the unmanned aerial vehicle landing gear system are taken as the center points of the connecting areas;

[0081] Assumption 3: The loads applied to the unmanned aerial vehicle landing gear system are all applied as concentrated forces or torques;

[0082] Assumption 4: The lowered states and lowered angles of the nose landing gear and main landing gear of the unmanned aerial vehicle landing gear system are determined;

[0083] Assumption 5: The hatch retraction mechanism of the unmanned aerial vehicle is linked with the landing gear, and the load applied by the hatch retraction mechanism to the landing gear is determined;

[0084] Assumption 6: The three-sided layout of the landing gear system in the lowered state is determined.

[0085] In this embodiment, the types of connecting pairs of the landing gear system include spherical pairs, prismatic pairs, and revolute pairs.

[0086] As Figure 2 shown, a set of actuator direct-push type landing gear system includes landing gear 1, retraction actuator piston rod 2, and retraction actuator outer cylinder 3; the landing gear system needs to be left-right symmetric on the XY plane of the unmanned aerial vehicle. Among them, the connection between the actuator outer cylinder 3 and the fuselage, and between the actuator piston rod 2 and the landing gear is a spherical pair, the connection between the actuator outer cylinder 3 and the piston rod 2 is a prismatic pair, and the connection between the landing gear 1 and the fuselage is a left revolute pair and a right revolute pair.

[0087] S2: Obtain the point coordinates of the landing gear system, the relevant performance limitations of the landing gear system, and the operating conditions (including loads and working states), and establish the original point coordinate matrix.

[0088] In this embodiment, a Cartesian coordinate system of the UAV landing gear system is established: from the tail of the UAV to the nose is the positive direction of the X-axis, and the direction perpendicular to the X-axis and in the same horizontal plane is the positive direction of the Y-axis; the skyward direction is the positive direction of the Z-axis.

[0089] In this embodiment, after assembling the landing gear system into the correct rectangular coordinate system, the connection pairs of the landing gear system are identified by category, and the number of point requirements is confirmed by the category and the point overlap degree (reusable points, thus reducing the number of point settings).

[0090] In this embodiment, two spherical pairs and one translational pair can share two points to be established, and two rotational pairs can be determined by two shared points. Therefore, the number of point requirements is: 1 point is required for the spherical pair, 2 points are required for the rotational pair, 2 points are required for the translational pair, 1 point is required for the single-load application requirement, and 1 point is required for the centroid of a single component; 2 points are constructed for a single cylindrical component, 3 points are constructed for a single triangular prism component, and 2 points are constructed for a single rectangular component.

[0091] Then, measure and record the coordinates of each required point. As shown in Table 1, form the original point coordinate matrix X:

[0092]

[0093] In formula (1), x 1 represents the x-axis coordinate of the first point; y 1 represents the y-axis coordinate of the first point; z 1 represents the z-axis coordinate of the first point; x n represents the x-axis coordinate of the nth point; y n represents the y-axis coordinate of the nth point; z n represents the z-axis coordinate of the nth point.

[0094] Table 1. Point coordinates

[0095]

[0096]

[0097] S3: Confirm the design variables according to the original point coordinate matrix and establish a parametric model.

[0098] S3-1: Parametrize the original point coordinate matrix to determine the design variables.

[0099] S3-1-1: Identify the related points, then parameterize them to determine the design variables.

[0100] In this embodiment, the related points include points with relationships such as symmetry, coplanarity, collinearity, etc. These points need to be identified in advance before parameterization to simplify the number of variables for parameterization.

[0101] In this embodiment, by parameterizing the point coordinates in Table 1, the first design variable DV1, the second design variable DV2, the third design variable DV3, and the fourth design variable DV4 can be obtained, as shown in Table 2.

[0102] Table 2. Determination of design variables

[0103]

[0104]

[0105] S3-1-2: Set the valid value ranges for the design variables.

[0106] According to the landing gear system structure and rapid update and iteration, the following settings are made for the valid value ranges of the design variables: The point coordinates need to satisfy that there is a certain avoidance space in the cabin space during the entire movement process of the landing gear system. Use the set point drawing rules to draw regular shapes such as cuboids, triangular prisms, cylinders, etc. to simplify the modeling of the landing gear system.

[0107] In this embodiment, based on Table 2, the valid value ranges of the first design variable DV1, the second design variable DV2, the third design variable DV3, and the fourth design variable DV4 can be set:

[0108] -270≥DV1≥-330, 210≥DV2≥170, -530≥DV3≥-555, -255≥DV4≥-315.

[0109] S3-2: Establish a parametric model according to the design variables.

[0110] Use the design variables of the set points to draw regular shapes such as cuboids, triangular prisms, cylinders, etc. to perform parametric modeling on the landing gear system as Figure 3 shown. For example, the retraction and extension actuator can be replaced by two cylinders and a cuboid. The two cylinders represent the piston rod and the outer cylinder respectively, and the cuboid represents the motor assembly; the connection pairs between the components are set at the center points of the connections of the components.

[0111] S4: Apply the landing gear ground load, gravity, and hatch retraction and extension load, and set the effective conditions of each load.

[0112] In this embodiment, apply the celestial load F at the center point of the wheel axley 、Vertical load F x , apply a lateral load F to the tire contact point z , apply a gravity load to the centroid of the landing gear retraction actuator, and apply a door mechanism load to the connection of the upper door mechanism of the landing gear. The model is as Figure 3 shown.

[0113] Among them, the gravity is applied at the center of gravity of the landing gear; the ground loads are divided into vertical load F y 、vertical load F x and lateral load F Z . The vertical load and the vertical load are applied at the center of the landing gear axle, and the lateral load is applied at the tire contact point of the landing gear; the door retraction loads are divided into two cases: single-side door retraction and both-side door retraction. For single-side door retraction, only one side of the landing gear system has the door opening and closing, so only the door retraction load of one side of the door needs to be established, and the force application point is the center point of the connection pair between the door mechanism and the landing gear. Both-side door retraction means that both sides of the landing gear system have the door opening and closing, so the door retraction loads of both sides of the door need to be established, and the force application points are the center points of the connection pairs between the door mechanisms on both sides and the landing gear respectively.

[0114] In this embodiment, the following settings are made for the load effectiveness:

[0115] Integrate the static load analysis and the retraction load analysis of the landing gear system, and transform it into an optimization model in which the working state of the landing gear system changes with time. When the optimization proceeds to the static load analysis section of the landing gear system, the landing gear system is locked in the lowered state, and the landing gear ground load and the fixed angle load of the door are applied; when the optimization proceeds to the system retraction load analysis, the landing gear system retracts, and the gravity and the door retraction load are applied. Specifically as follows:

[0116] The static load analysis mainly analyzes the situation when the landing gear is subjected to static loads. At this time, the actuator is locked in the fully extended state. Since the calculation of the landing gear ground load already includes gravity, the gravity load is not applied during the static load analysis of the landing gear system.

[0117] The static loads of the landing gear system are divided into loads under various working conditions. After analyzing the static load working conditions, they are programmed into a function of load and time to realize the simulation of all static load working conditions within a certain time; the door retraction load changes with the opening and closing angle of the door, and the opening and closing angle of the door changes with the rotation angle of the landing gear. The door retraction load is set as a load that changes with the rotation angle of the landing gear, and the door retraction load is simulated; the gravity can be represented as a force with the fixed direction of the negative Y-axis upward at the centroid.

[0118] When performing a static load analysis on the landing gear system, the static load is valid, and the landing gear system is locked in the down position. At this time, the actuator is locked in the fully extended position. Since the ground load calculation of the landing gear already includes gravity, gravity load is not applied during the static load analysis of the landing gear system.

[0119] When performing a landing gear retraction / extension load analysis on the landing gear system, the door retraction / extension load and gravity are valid, and the landing gear system retracts / extends while the static load is invalid. The door retraction / extension load varies with the opening / closing angle of the door, and the opening / closing angle of the door varies with the rotation angle of the landing gear. The door retraction / extension load is set as a load that varies with the rotation angle of the landing gear, and the door retraction / extension load is simulated. Gravity can be represented as a force with a fixed direction of the negative Y-axis at the center of mass, and its magnitude is mg.

[0120] That is, assuming the static load simulation duration is t1, the load application situation is as follows:

[0121] If t ≤ t1, the static load is valid, and the door retraction / extension load and gravity are 0;

[0122] If t > t1, the door retraction / extension load and gravity are valid, and the static load is 0.

[0123] S5: According to the retraction / extension stroke, the landing gear retraction / extension angle limit, and the installation bay space limit of the landing gear system, construct the corresponding relevant constraint functions.

[0124] S5-1: Construct the length constraint function of the retraction / extension actuator.

[0125] In this embodiment, the retraction / extension stroke is affected by the structural characteristics of the retraction / extension actuator and has a minimum length limit, that is:

[0126]

[0127] In formula (2), L min represents the minimum allowable length of the retraction / extension actuator; the first design variable DV1, the second design variable DV2, the third design variable DV3, the fourth design variable DV4; S represents the contraction displacement.

[0128] S5-2: Construct the landing gear retraction / extension angle limit constraint function.

[0129] In this embodiment, to ensure that the landing gear can be fully retracted into the landing gear system bay and maintain a clearance distance from the door area when the landing gear is retracted, the minimum retraction / extension angle of the landing gear is constrained, and the constraint function is transformed into the minimum distance Sc between the wheel center of the landing gear and the door when the landing gear is fully retracted min Constraint:

[0130] g 2 (X) = Sc min -r wheel -Sc(X)t＝ts ≤0 (3)

[0131] In formula (3), g 2 (X) represents the landing gear retraction angle limit constraint function; Sc min represents the minimum distance between the wheel center of the landing gear and the hatch when the landing gear is fully retracted; r wheel represents the maximum radius of the tire; ts is the time when the landing gear is fully retracted; Sc(X) t＝ts represents the distance between the wheel center and the hatch when the landing gear is fully retracted.

[0132] S5-3: Construct the point position space limit constraint function.

[0133] In this embodiment, the layout of the landing gear system is restricted by the point position space. During the entire retraction and extension process, it is required not to interfere with the point position space and maintain a certain clearance distance. Therefore, the transformation of the point position space constraint is carried out: the point position space is reduced so that the reduced point position space maintains the clearance distance requirement everywhere with the original point position space. Contact is established between the reduced point position space and each component of the landing gear system. Then the final constraint function is:

[0134]

[0135] In formula (4), g 3 (X) represents the point position space limit constraint function; represents the i-th contact force; n represents the number of contact forces.

[0136] For example, import the cabin space limit into the model. As Figure 4 shown, establish the mutual contact forces CONTACT1, CONTACT2, and CONTACT3 between the cabin space and the landing gear, the cabin space and the retraction / extension actuator, and the retraction / extension actuator and the landing gear respectively, and establish the point position space limit function:

[0137] CONTACT1 + CONTACT2 + CONTACT3 ≤ 0.

[0138] S5-4: Construct the relative position constraint function of each component of the landing gear system.

[0139] In this embodiment, to ensure that the relative positions of each component of the landing gear system meet the design requirements, the relative positions of each component are constrained and transformed into constructing the relationship between the point positions of each component: for example, point 1 is required to always be above point 2, and the z-direction distance shall not be less than 5 mm. Then the position constraint between point 1 and point 2 is:

[0140] PO = z 1 -z 2 -5 ≥ 0 (5)

[0141] In formula (5), PO represents the position constraint between two points; z 1 represents the z-direction distance of the first point; z 2 represents the z-direction distance of the second point;

[0142] It can be deduced from the above that:

[0143]

[0144] In formula (6), g 4 (X) represents the relative position constraint function of each component of the landing gear system; PO(X) i represents the position constraint of the i-th point; m represents the number of relative position constraints of the points.

[0145] S6: Confirm the objective function according to the fuselage cross-link load, retraction load, and retraction efficiency.

[0146] Among them, the fuselage load (i.e., the fuselage cross-link load) is divided into the resultant force F 1,1 of the fuselage load at the left rotation axis of the landing gear, the resultant force F 1,2 of the fuselage load at the right rotation axis of the landing gear, and the resultant force F 1,3 of the fuselage load at the connection of the retraction actuator. Then the fuselage load is:

[0147]

[0148] In formula (7), F 1 represents the fuselage load; n represents the total number of connections; K i are the penalty factors of each objective function respectively, and their magnitudes and values need to be adjusted according to the actual working conditions; F 1,i is the resultant load of each connection. For example, F 1,1 represents the resultant force of the fuselage load at the left rotation axis of the landing gear; F 1,2 represents the resultant force of the fuselage load at the right rotation axis of the landing gear; F 1,3 represents the resultant force of the fuselage load at the connection of the retraction actuator.

[0149] In this embodiment, the retraction load refers to the driving force required for the retraction actuator to drive the landing gear to retract or lower, denoted as F 2 ; if the retraction load F 2 is the same as the resultant force of the fuselage load at the connection of the retraction actuator, it does not need to be applied separately.

[0150] In this embodiment, it is assumed that the retraction actuator is in the maximum extension state in the initial state, and the contraction displacement is S. Then:

[0151]

[0152] In formula (8), η represents the retraction efficiency; S maxDenote the maximum contraction displacement; Denote the maximum resultant force on the fuselage at the connection of the retracting and extending actuator;

[0153] In this embodiment, to simplify the calculation, the multi-objective (fuselage load, retracting and extending load, retracting and extending efficiency) optimization of the objective function is transformed into a single-objective optimization problem, that is, the objective function:

[0154] Q = α 1 F 1 + α 2 F 2 + α 3 η (9)

[0155] In formula (9), α 1 , α 2 , α 3 are respectively the penalty factors of each objective function; F 1 denotes the fuselage load; F 2 denotes the retracting and extending load; η denotes the retracting and extending efficiency.

[0156] S7: Use existing analysis software (ADAMS / ANSYS MOTION / LMS VIRTUAL LAB / NASTRAN / ABAQUS) to optimize the objective function, that is, optimize the installation points of the landing gear and the installation points of the retracting and extending actuator, and finally obtain the optimal overall layout of the landing gear system.

[0157] Those of ordinary skill in the art can understand that the above embodiments are specific embodiments for implementing the present invention, and in practical applications, various changes can be made in form and details without departing from the spirit and scope of the present invention.

Claims

1. A layout optimization method for a UAV landing gear system, characterized in that: The specific steps include: S1: Simplify the landing gear system and confirm the landing gear system connection sub-category; S2: Obtain the point coordinates, landing gear system performance limitations and operating conditions required to build a landing gear system model; S3: According to the point coordinates of the landing gear system, confirm the design variables and generate a parameterized model; S4: Apply landing gear ground load, gravity and door retraction load, and set the effectiveness of each load; S5: Construct corresponding related constraint functions according to the retraction and extension stroke, the landing gear retraction and extension angle limit, and the landing gear system installation compartment space limit; S6: Confirm the objective function based on the fuselage cross-linking load, stowage load, and stowage efficiency; S7: Optimize the objective function, that is, optimize the installation points of the landing gear and the installation points of the retractable actuator, and finally obtain the optimal overall layout of the landing gear system.

2. The layout optimization method of a UAV landing gear system according to claim 1, characterized in that: In S1, simplified assumptions are made for the landing gear system including: Assumption 1: The shapes of all components in the UAV landing gear system are replaced by point-line models, ignoring fit and clearance; Assumption 2: The coordinates of the connection points of all components in the UAV landing gear system are taken as the center point of the connection area; Assumption 3: The loads applied to the UAV landing gear system are all concentrated forces or moments; Assumption 4: The lowering status and lowering angle of the front landing gear and main landing gear of the UAV landing gear system have been determined; Assumption 5: The UAV's door retracting mechanism is linked to the landing gear, and the load applied by the door retracting mechanism to the landing gear has been determined; Assumption 6: The three-side layout of the landing gear system in the extended state has been determined.

3. The layout optimization method of a UAV landing gear system according to claim 1, characterized in that: In S1, the landing gear system connection pair categories include ball joints, translation joints and rotation joints; The landing gear system comprises a landing gear (1), a retractable actuator cylinder piston rod (2) and a retractable actuator cylinder outer cylinder (3); wherein the retractable actuator cylinder outer cylinder (3) and the fuselage, the retractable actuator cylinder piston rod (2) and the landing gear are connected by a ball pair, the retractable actuator cylinder outer cylinder (3) and the retractable actuator cylinder piston rod (2) are connected by a moving pair, and the landing gear (1) and the fuselage are connected by a left rotation pair and a right rotation pair.

4. The layout optimization method of a UAV landing gear system according to claim 1, characterized in that: The S2 includes: S2-1: Establish the Cartesian coordinate system of the drone landing gear system: the positive direction of the X axis is from the tail to the nose of the drone, the positive direction of the Y axis is perpendicular to the X axis and located in the same horizontal plane; the positive direction of the Z axis is the sky direction; S2-2: After assembling the landing gear system to the correct Cartesian coordinate system, the connection pairs of the landing gear system are identified by category, and the number of points required is confirmed by category and point overlap; then the coordinates of each required point are measured and recorded to form the original point coordinate matrix X: In formula (1), x1 represents the x-axis coordinate of the first point; y1 represents the y-axis coordinate of the first point; z1 represents the z-axis coordinate of the first point; n Indicates the x-axis coordinate of the nth point; y n Indicates the y-axis coordinate of the nth point; z n Indicates the z-axis coordinate of the nth point.

5. The layout optimization method of a UAV landing gear system according to claim 4, characterized in that: In S2-2, the number of points required is: 1 point required for the ball joint, 2 points required for the rotation joint, 2 points required for the translation joint, 1 point required for the application of a single load, and 1 point required for the center of mass of a single component; 2 points are required to construct a single cylindrical component, 3 points are required to construct a single triangular prism component, and 2 points are required to construct a single rectangular component.

6. The method for optimizing the layout of a UAV landing gear system according to claim 1, characterized in that: The S3 includes: S3-1: Parameterize the original point coordinate matrix and determine the design variables; S3-2: Establish a parametric model based on design variables.

7. A method for optimizing the layout of a UAV landing gear system as claimed in claim 6, characterized in that: The S3-1 includes: S3-1-1: Identify the relevant points, then parameterize and determine the design variables; The related points include symmetrical relationships, coplanar relationships, and colinear relationships; the design variables include a first design variable DV1, a second design variable DV2, a third design variable DV3, and a fourth design variable DV4; S3-1-2: Set the valid value range for the design variables: The point coordinates must ensure that the landing gear system can maintain avoidance space in the cabin space during the entire movement process. Regular shapes are drawn using the set points to simplify the modeling of the landing gear system.

8. The method for optimizing the landing gear system of a UAV according to claim 1, characterized in that: In S4, the gravity is applied to the center of gravity of the landing gear; The ground load includes the apical load F y , heading load F x and the lateral load F z , axial load F y , heading load F x Applied at the center of the landing gear axle, the lateral load F z Applied to the landing gear tire contact point; The door retraction and extension load includes single-side door retraction and extension and double-side door retraction and extension; among them, single-side door retraction means that only one side of the door of the landing gear system opens and closes, and the force application point is the center point of the connection pair between the door mechanism and the landing gear; double-side door retraction means that the landing gear system has double-side doors opening and closing, and the force application points are respectively the center points of the connection pairs between the door mechanisms on both sides and the landing gear.

9. The method for optimizing the layout of a UAV landing gear system according to claim 1, characterized in that: The S5 includes: S4-1: Construct the length constraint function of the retractable actuator: In formula (2), L min Indicates the minimum length allowed for the retractable actuator; the first design variable DV1, the second design variable DV2, the third design variable DV3, the fourth design variable DV4; S indicates the retracted displacement; S4-2: Construct the landing gear retraction angle limit constraint function: g2(X)=Sc min -r wheel -Sc(X) t＝ts ≤0 (3) In formula (3), g2(X) represents the landing gear retraction angle limit constraint function; Sc min Indicates the minimum distance between the wheel center and the door when the landing gear is fully retracted; r wheel Indicates the maximum radius of the tire; ts is the time when the landing gear is fully retracted; Sc(X) t＝ts Indicates the distance between the wheel center and the door when the landing gear is fully retracted; S4-3: Construct point space restriction constraint function: In formula (4), g3(X) represents the point space constraint function; CONTACT(X) i represents the i-th contact force; n represents the number of contact forces; S4-4: Construct the relative position constraint function of each component of the landing gear system: PO=z1-z2-5≥0 (5) In formula (5), PO represents the position constraint between two points; z1 represents the z-direction distance of the first point; z2 represents the z-direction distance of the second point; Based on the above, we can infer: In formula (6), g4(X) represents the relative position constraint function of each component of the landing gear system; PO(X) i represents the position constraint of the i-th point; m represents the number of relative position constraints of the points.

10. The method for optimizing the layout of a UAV landing gear system according to claim 1, characterized in that: In S6, the objective function is the fuselage load, the stowage load and the stowage efficiency; The fuselage load is divided into the combined force of the load at the connection between the fuselage and the components of the take-off and landing system: In formula (7), F1 represents the load on the fuselage; n represents the total number of connections, K i are the penalty factors of each objective function, and their magnitude and value need to be adjusted according to the actual working conditions. 1,i is the resultant load at each connection; The magnitude of the retracting load F2 is the same as the resultant force on the fuselage at the connection of the retracting actuator; Assume that the retractable actuator is in the maximum extension state in the initial state, and the maximum contraction displacement is S max , then the retractable efficiency is: In formula (8), η represents the retraction efficiency; S max represents the maximum contraction displacement; Indicates the maximum combined force on the fuselage at the connection point of the retracting and extending actuator; To simplify the calculation, the objective function is transformed from multi-objective optimization to a single-objective optimization problem: Q=α1F1+α2F2+α3η (9) In formula (9), α1, α2, and α3 are the penalty factors of each objective function.

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