In lunar sampling missions,the slender and flexible configuration of the robotic arm results in significant nonlinear characteristics and uncertainty in the end-effector's pose.To support rapid and intelligent sampling operations,visual pose estimation technology is introduced to provide real-time and accurate decision-making support.However,the inherent depth perception limitations of monocular vision,compounded by image degradation caused by extreme lighting variations on the lunar surface,pose severe challenges to the accuracy and robustness of pose estimation.To address the aforementioned issues,this paper proposes the geometrically constrained pose estimation network(GCP-Net).By integrating a differentiable projection module,the network constructs the reprojection error and the contour algebraic error as additional loss terms,establishing a consistency constraint between image semantics and spatial pose,thereby effectively improving depth estimation accuracy.Simultaneously,to simulate image degradation caused by extreme occlusion and lighting changes in real lunar environments,this paper introduces stochastic noise injection and feature masking enhancement strategies based on GCP-Net,proposing an enhanced geometrically constrained pose estimation network(EGCP-Net).Simulation experiments demonstrate that the proposed method maintains good robustness even under conditions of partial feature loss.Validated by the publicly reported image data from Chang'e-6,the reprojection results of the pose estimated by the algorithm highly match the observed features,proving the reliability and feasibility of this method in aerospace engineering missions.
Under the deterministic assembly mode of aircraft structures,coaxiality deviations occur at the connecting holes of parts during assembly due to factors such as hole-making deviations and shape deviations.When these deviations are relatively large,they cause local assembly stress and weaken the mechanical properties of the structure.For the deterministic assembly of aircraft fuselage structures,this study combines the Jacobian-torsor method with the influence coefficient method to determine the matrix expressions of part shape deviations,final hole positioning deviations,and temporary fastener connections.It also proposes a coaxiality deviation calculation model that accounts for deviation accumulation and part deformation,while establishing an assembly experimental system for coaxiality deviation.By comparing the measured deviation data,the calculation results of the Jacobian-torsor model and those of the proposed model,it is found that the average error between the proposed model and the measured data is reduced by 8.89%.This improves the deviation calculation accuracy of the fuselage structure under the deterministic assembly mode and provides a more reliable theoretical basis for the optimization of assembly processes.
To investigate the vibration characteristics of a landing gear gear-driven nose wheel steering system under transmission clearance conditions,this paper first conducts a simplified theoretical analysis to reasonably design anti-sway damping.Subsequently,the landing gear vibration coupled rigid-flexible multi-body dynamics simulation model is validated using both theoretical analysis results and vibration test results.Then,nonlinear factors such as gear transmission clearance and torque arm axial and radial transmission clearance are simultaneously considered in the vibration dynamics analysis,achieving a coupled rigid-flexible nonlinear dynamics model for landing gear with transmission clearance.Based on this model,a multi-factor study on the differences in vibration response characteristics is conducted.The results reveal that gaps can cause the landing gear to oscillate with constant amplitude,with gear transmission clearance having a greater effect on wheel swing angle than torque arm clearance.Additionally,the gap size is approximately proportional to the wheel swing angle.Increasing vertical load helps suppress vibration,while taxi speed primarily affects the wheel swing frequency.These findings provide theoretical reference for the design of landing gear anti-sway systems.
To quantify the correlation between freeze-thaw resistance and its influencing factors in macroporous recycled concrete （MRC） and its mesoscopic constituents—recycled aggregate （RA）， new paste （NP）， and interfacial transition zone （ITZ）—saturated specimens of RA， NP， ITZ， MRC and paste-coated single aggregate were subjected to freeze-thaw tests in air. Multiple properties and parameters of each kind of specimen were measured under different numbers of freeze-thaw cycles， and grey relational analysis was employed to quantify the correlations among the test results. The relational degree rankings of influencing factors were identified as follows： For NP compressive strength， NP indentation elastic modulus > NP pore size distribution coefficient > NP average pore size； For ITZ shear strength， ITZ indentation elastic modulus > ITZ thickness； For old paste （OP） detachment rate， OP average pore size > ITZ thickness > OP pore size distribution coefficient > ITZ indentation elastic modulus > OP indentation elastic modulus； For MRC compressive strength， NP compressive strength ≈ ITZ shear strength > OP detachment rate. The relational degrees of all factors ranged from 0.503 to 0.955， indicating significant correlations. The strength of the NP and ITZ were strongly influenced by indentation elastic modulus， while the OP detachment rate was determined by weak points in the RA. When the porosity is around 25%， the influence of the material and the pore structure on the compressive strength of MRC reaches its peak and minimum， respectively.
The paper presents a configurational synthesis method for multi-mode parallel mechanisms based on planar closed-loop chains.Firstly,a planar closed-loop chain with two motion modes is introduced.This chain is incorporated into the realm of parallel mechanisms and serves as the moving platform of the parallel mechanism.By toggling its motion modes,the change in the degrees of freedom of the parallel mechanism can be achieved.Secondly,the definitions of the full configuration and sub-configurations in multi-mode parallel mechanisms are expounded.The screw theory is introduced into the configurational synthesis theory of multi-mode parallel mechanisms.Furthermore,the configurational synthesis principle of multi-mode parallel mechanisms based on the screw theory is put forward.Subsequently,based on the configurational synthesis principle of multi-mode parallel mechanisms and planar closed-loop chains,the configurational synthesis of a class of parallel mechanisms with two motion modes is conducted.Finally,the degrees of freedom of the synthesized multi-mode parallel mechanisms are analyzed by means of the screw theory.
