Biomimetic Locomotion Control Theories And Methods Of Quadruped Robot

Compared with other kinds of robots, quadruped robot has more impressive flexibilityof locomotion and excellent adaptability to complex environment, which has made it aresearch hotspot in the field of walking robot. In recent years, developing a kind ofhigh-performance quadruped robot with high dynamics, high environmental adaptability,high locomotion stability, and high payload capacity has been a dominant research directionin the field of bionic robot. As a typical complex dynamic system with strong coupling andnonlinearity, related fundamental theories and key technologies of quadruped robot need tobe further investigated due to the complexity of its model structure and the numerousnumbers of connected factors. To enhance the environmental adaptability and locomotionstability of quadruped robot, this dissertation focuses on the biomimetic mechanism designof quadruped robot, biomimetic locomotion control theories and methods, and theconstruction of locomotion control system. The main work and contributions aresummarized as follows:(1) According to related biomimetic research results on the anatomical structure ofhorse, biomimetic laws for the mechanism design of quadruped robot were extracted.Relevant parameters of the kinematic mechanism of quadruped robot were determined.During the mechanism design process, Top-Down design method, modularization designidea and hierarchical assembly technology were utilized. After finishing the design of thequadruped robot, simulation analysis and performance evaluation of quadruped robots withdifferent joint configurations were carried out in terms of kinematic velocity, energyconsumption and terrain adaptability. Finally, the optimum joint configuration mode waspresented.(2) Considering the weaknesses of the model-based gait control method, such ascomplex modeling, single-period planning, being disadvantageous to adapt to unstructuredenvironment, the bionic control method of gait generation and gait transition for thequadruped robot was studied referring to the Central Pattern Generator (CPG) controlprinciple of animals. Aim at two major problems of traditional gait control strategies basedon CPG, one is that CPG models are only used for the implementation of inter-limbcoordination without the consideration of joints coordination within a single limb(intra-limb coordination), and the other one is that the stance phase and the swing phase share the same duration, a new multi-joint coordinated control method for both inter-limband intra-limb based on CPG was proposed. Based on Hopf oscillators, two kinds of CPGcontrol networks of quadruped robot which can realize the coordination among hip joints ofall limbs and the coordination between hip joint and knee joint within a limbsimultaneously were constructed. The CPG control networks integrate the control of kneejoints very well and can meet the control demands of rhythmic gaits with different dutyfactors. Moreover, the structure of the CPG control network is simpler and CPG parametersare easy to be adjusted, which greatly contribute to the real-time control of the robot. Inorder to solve the problem of unsmooth gait transition caused by the direct substitution ofdiscrete gait matrix at gait transition point, a new method to generate continuous andsmooth quadruped gait transition was proposed based on the presented CPG model. Byadjusting the relative phases among legs continuously, continuous and smooth transitionbetween any two kinds of gaits of quadruped robot can be realized. Using the co-simulationmethod of ADAMS and MATLAB, the correctness and effectiveness of the proposed gaitcontrol methods were verified.(3) On the basis of the fundamental gait control, the biomimetic control method forbetter terrain adaptability of quadruped robot was studied in the reference of biologicalreflex mechanisms. In this part, a modified vestibular reflex model was presented toguarantee the locomotion stability of quadruped robot when it walking on slope. Feedbackterm was introduced into the presented CPG model, and the fusion of the vestibular reflexmodel and the CPG model was realized by means of the feedback term. This modifiedvestibular reflex model can reduce the fluctuation of center of gravity (COG) when robotwalking on slope with the joint configuration of all inward-knee joints and improve thelocomotion stability effectively. To equip the quadruped robot with the ability of obstacleavoidance and obstacle navigation, flexor reflex models of the robot were established inaccordance to different time phases at the reflection point and different types of jointstructures. Moreover, a new method to determine parameters of the flexor reflex models byassigning maximal obstacle-navigation height was proposed which reveals the relationshipbetween parameters of flexor reflex model and the height of obstacle. In the process ofmodeling flexor reflex, the fusion of vestibular reflex model and flexor reflex model wasmade, which leads to the realization of obstacle navigation on slope. By means ofco-simulation of ADAMS and MATLAB, the correctness of both the vestibular reflexmodels and the flexor reflex models was verified. (4) On the basis of the basic gait control and terrain adaptive control and in the pursuitof higher dynamic stability that can resist external impact, dynamic stability control methodof quadruped robot under lateral impact was researched. A dynamic stability controlstrategy of quadruped robot in resistance of lateral impact based on CPG and side-stepreflection was proposed. A CPG control network which can realize not only the basic rhythmic movement but also the sideways movement of the robot was constructed, andside-step reflection mechanism was introduced into the robot by building hip-joint triggeroscillators for its lateral swing locomotion. The validity of the dynamic stability controlstrategy was verified by means of co-simulation of ADAMS and MATLAB.(5) Imitating the motor nerve control system of animals, a composite and bioniccontrol system scheme of quadruped robot which combines the hierarchical and thedistributed control architecture was presented. A kernel control framework synthesizingARM, FPGA and DSP technology was established and the function and systemcomposition of each submodule were planned. The design of gait generator was mainlydiscussed. The hardware circuit design of FPGA-based kernel PCB and expanded PCB, thesoftware design of Nios II-based soft core of the gait generator, CAN Bus and dual-portRAM communication program design were accomplished.(6) The principle prototype of the quadruped robot was developed, and severalexperiments were carried out, which include communication tests between gait generatorand actuator via CAN Bus, locomotion control tests of a single leg, and performance andpreliminary control tests of hydraulic driver unit. The results of these tests verified therationality of the mechanism design of the quadruped robot, the reliability and instantaneityof the CAN Bus communication protocol, and the correctness and validity of the gaitgenerator design and gait generation method.In conclusion, this dissertation is composed of ideas, theories, implementationmethods, simulation and experimental analysis. The research contents and resultsmentioned above have a certain reference function for the theoretical research andtechnological exploration of quadruped robot.