Research On Model And Experiment Of Foot-Ground Interaction Mechanics Of The Robot In Soft Geology

Legged robots have now made considerable progress in the path planning within the field of view,and can avoid and pass structured terrain.However,the detection,surveying,mapping,and rescue of legged robots need to be carried out in soft,potholes terrains.This kind of unstructured terrain is easy to make the robot's feet sink into relatively soft sand because the physical parameters and mechanical properties of the soil are unknown.And it cannot produce good adhesion during the contact with the ground,resulting in slipping.The study of foot-ground interaction mechanics provides a core solution for foot-type robots to deal with unstructured terrain.This paper combines ground mechanics and classical soil mechanics to establish a new foot-ground interaction mechanical model,and conducts experimental research and parameter identification of foot-ground force under soft geology.In order to establish a complete mechanical model of foot-ground interaction,the mechanism of the foundation subsidence process is first analyzed,and the previous model that only considered the compaction and shear phase was revised.Applying the bearing characteristics of ground mechanics and the ultimate bearing capacity theory of classical soil mechanics in the two stages of compaction,shearing and failure,respectively,a model of flat-bottomed foot-ground interaction mechanics is proposed.The semi-cylindrical foot and spherical foot are modeled by the ground mechanics stress integration method,and the applicable scope of the model is analyzed.Considering the influence of the bulldozing effect of different speed angles on the amount of subsidence when the robot is moving,a mechanical model of the flat foot-ground action considering the speed angle is derived.In order to meet the functional requirements of the robot foot normal intrusion into sand and soil with a certain speed angle,a single-foot test platform is designed and developed.The motion device system is designed to adjust various motion states of the robot foot.Develop a supporting power drive system,feedback and accurately adjust the speed and displacement of the horizontal and vertical motors.Develop a signal acquisition system to collect the six-dimensional force,velocity,displacement and other data during foot-ground action,and provide data support for subsequent analysis of the foot-ground interaction mechanics.In order to obtain accurate soil mechanics parameters,a segmented soil parameter identification method is proposed,which improves the problem of large fitting results of the overall fitting method in the existing parameter identification.The data processing method of weighted averaging and the fitting method of the least square error principle are used to obtain the pressure characteristic parameters of soft geology,which improves the accuracy of parameter identification.The direct shear test is designed to measure the internal friction angle of the soil,and the coefficient of ground bearing capacity related to Terzaghi theory can be calculated according to the internal friction angle obtained by the identification.Design experiments of round and square flat feet with different radio.The analysis shows that the curve collapses to the same master curve under each load.The dimensionless coefficient of the linear section is not affected by the area and shape of the sole;the depth of the theoretical boundary point is in good agreement with the experimental one,which verifies the correctness of the ultimate bearing capacity principle in the failure stage and the validity of the segmented flat foot-ground action mechanical model.The semi-cylindrical foot and spherical foot experiments are designed,and the average maximum error rate is within a reasonable range,which verifies the validity of the semi-cylindrical and spherical foot-ground interaction mechanical models.The experiments of flat feet under different speed angles are designed,identifying the scaling factor and linear segment coefficient of the pressure characteristics,and successfully predicting the relationship between the normal force and the subsidence of the large radius flat feet and the final subsidence when the speed angle is 45°.