In this paper, aiming at the problem that the ideal modeling point of the foot end deviates from the actual contact point due to the rolling effect of the semi-cylindrical foot end in leg hydraulics drive system (LHDS), a novel and relatively simple kinematics and statics correction algorithm is proposed. This algorithm can effectively improve the accuracy of LHDS kinematics and statics, and it is still applicable when the body and the contact surface are at different angles. Firstly, this paper deduces the kinematics and statics when the foot end of LHDS is regarded as the point foot, analyzes and calculates the deviation under common working conditions. Secondly, in view of this phenomenon, a kinematics correction algorithm based on virtual DOF and a statics correction algorithm based on translation theorem of forces are proposed respectively. Finally, the proposed algorithm is verified by LHDS performance test platform under various working conditions. The results show that after applying the kinematics correction algorithm, the trajectory deviation reduction rate of the hip joint is over 65%; after applying the statics correction algorithm, the deviation reduction rate of foot end contact force is over 43%. The related research results can be applied to any similar foot end, which has engineering application value.
In this paper, for the phenomenon of self-excited oscillation caused by nonlinear factors in a large aircraft wheel brake control system, the nonlinear dynamic behavior of the pressure servo valve-controlled cylinder system (PSVCS) is studied,and the influence law of the key parameters on the nonlinear self-excitation behavior is obtained. On this basis, the stability of the PSVCS is analyzed both in time domain and frequency domain, and it is proved in principle that the PSVCS is a stable self-closed loop control system. Firstly, the nonlinear dynamics model of the PSVCS is established in this paper. Secondly, using the method of phase plane analysis, the nonlinear dynamic behavior of the PSVCS and the influence law of key parameters on the system are studied. Thirdly, the nonlinear system of the PSVCS is transformed into a segmented local linear system, and the stability of the prestage and the power stage are analyzed and studied respectively. Finally, through a performance test platform, which is used to simulate the load of PSVCS, the theoretical analysis results of this paper are verified experimentally under a variety of working conditions. The final experimental results show that both the nonlinear dynamic model established in this paper and the influence law of the key parameters obtained by the phase plane analysis on the nonlinear self-excited oscillation behavior are correct, and the relevant conclusions can provide a reference for the design of the braking system control system.
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