Research On Control And Gait Planning For A Hydraulic Quadruped Robot

The four-legged mammals can walk around on almost every corner of the Earth land.They have a lot of advantages such as running speed, kinematic flexibility and dexterity,environment adaptation and load capacity. If quadruped robots have all these qualities, theyare expected to be employed for a variety of dangerous and insalubrious tasks such asmilitary and civilian material transportation, resource exploration, geographic expeditionand disaster rescue etc. Therefore, the research on the bionic quadruped robot attractattentions of domestic and overseas researchers.The research on quadruped robot covers various aspects including bionic body design,system modeling, gait planning and motion control etc. Therefor, a mature and completetheoretical system of quadruped robots is yet to be designed. So the common problems ofquadruped robots are still worthy of exploring and studying. The objective of thisdissertation is to make a significant contribution toward the development of a fast movingand highly dynamic quadruped robot. The main work focuses on the bionic structure designof the hydraulic quadruped robot, mathematical modeling, forward and inverse kinematicsand dynamics analysis, foot trajectory planning and gait generation. Details are as follows.Based on the analysis of dog’s bone structure and motion range, the mechanism with16active DOFs is determined. According to the result of joint torque upper limit estimation,the hydraulic cylinders’ attachment points are fixed. The mathematical model of thequadruped robot is the basis of gait analysis and control. The coordinates and joint variablesare defined and the forward and inverse kinematics are deduced in detail. To makepreparations for the foot trajectory planning and tracking, the workspace of one leg isanalyzed. The dynamitic analysis is presented and a simulation experiment is done toevaluate the effectiveness.To make the robot compact, a small and light electro-hydraulic servo valve controlledsingle rod cylinder is designed. One kind of the cylinder’s position signal is fed back by anLVDT which has two parts of nonlinear output ranges. So a line-element based nonlinearadaptive piecewise compensation correction algorithm is proposed which effectivelyextends the workspace of sensors and can reduce the cost of sensors and systems. Thereason for different dynamic characteristics of the cylinder in the stretch-out and draw-backmotions is derivate. And a fuzzy adaptive PID controller is designed to modify the characteristics. To make the leg active compliance, a force-feedback based active compliantposition control strategy is proposed.To generate the bionic gaits for the quadruped, the mammals gait characteristic isanalyzed. Then the basic concepts of quadruped robots are described. Aimed to eliminatethe impact during the leg swinging process, a zero impact foot trajectory planning methodis proposed. As a consequence, the influence from the contact with ground is reduced and astable walk is achieved. Considering the redundant degree of freedom (DOF) of a robot leg,pitch-hip joint constraint method and foot attitude angle constraint method are designed.According to the leg phases of trot gait, the quadruped robot completes trot running withgood performance. The derivation of stability criterion under the Zero Moment Point theoryin walk gait is given. Correspondingly, a stability margin maximizing in a suboptimaltriangle method was proposed. The experiments demonstrate the effectiveness of themethod under plain and slope terrain.Under the inspiration of animals’ rhythmic movement, the bionic gait planning schemeis studied in this paper. After the analysis and comparison of existing neuron models, theMatsuoka model is chosen to constitute an Central Pattern Generator (CPG) neural network.The relationship between the parameters and gait style, period, stride is analyzed. Fouroscillation units are used to control four legs of the robot. So it is crucial to expand thesingle output of an oscillation unit to at least three signals for one leg. The mappingfunctions are designed in the dissertation. By replacing the gait matrixes, the CPGcontroller can change gait smoothly and as a result, the walking speed of the robot can beadjusted easily.The prototype of the hydraulic driven quadruped robot is introduced at the end of thedissertation. A three-level control system is built to control the robot, which composes fourDSPs, a PC104computer and a PC. A series of experiments including foot trajectoryfollowing, mark time and trot gait walking, load test etc are carried out to give the directionto improve the system and accumulates a lot of data and experiences.