This paper presents the reconfigurable legged mobile lander (ReLML) with its modes from adjusting, landing, to roving. Based on the invented metamorphic variable-axis revolute hinge, the actuated link has three alternative phases of rotating around either of two orthogonal topological axes or locking itself to the base as a rigid body. This property enables the ReLML to switch among three modes and within two driving states (as the adjusting and roving modes are active mechanisms driven by motors, while the landing truss is regarded as a passive mechanism driven by the touchdown impact force exerted on footpad). The unified differential kinematics for the ReLML is established by the screw-based Jacobian modeling, unifying both active and passive operation phases throughout all modes. Afterward, the distributions of workspaces and singularity loci in three modes are discussed for the multi-solution sake, and the selection principle of the practicable solution pattern is proposed to obtain the actual workspace, singularity loci, and configurations. The results stemming from the Jacobian-matrix-based method and the Grassmann-geometry-based method give mutual authentication and match well. Finally, as prospects for promising applications, four bifurcated evolution routes and configuration transitions are figured out and compared.

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Passive overconstrained parallel mechanism has many advantages due to extra constraints to the platform. When applied to the force sensor field, it can increase the capability, stiffness and dynamic response of the sensor. In this study, an overconstrained [Formula: see text] platform is presented to measure the multi-dimensional landing impact force. Screw theory is used to obtain the concentrated inertia force. Then, by adding the inertial force into the VJM (Virtual Joint Method) stiffness model, the static analysis is extended to elastodynamics analysis. Natural frequency and modal are derived from the elastodynamics equation and show well agreement with the FEA result in Abaqus. Theoretical force measurement equation is deduced. The FEA simulation result proves the effectiveness of the theoretical equation. Experiments are also conducted to verify the feasibility of the platform.

The platforms of parallel mechanisms usually suffer vibration loads. In these cases, structure elastodynamic analysis and elastodynamic optimization of parallel mechanisms are important. A tube structure is very common for parallel mechanisms. This work establishes the model of a tube structure based on matrix structural analysis. The kinematic pair equivalent method is used to simulate the surface contact between the inner and outer tubes. The corresponding mass and stiffness matrices are derived through the strain energy minimization method. The reconfigurable legged lunar lander has been used as an example to verify the effectiveness of this method. By adding the mechanism configuration to the optimization process, the equivalent static load method and the desirability approach are combined and modified. A procedure for the multi-objective elastodynamic optimization of parallel mechanisms is proposed. The optimization procedure is implemented on the lander and the results show a reduction in mass and an increase in natural frequency.