Development Of Hexapod Biomimetic Robot And Research On Its Motion Planning Issue

With the increasingly rapid step of human exploration of nature, the demand for robots with autonomous mobility under complex environment has been getting broader and deeper in more and more application areas. Theoretically, legged robot offers more superior performance of dealing with complicated terrain conditions than that provided by wheeled robot and therefore has been given great concern, however up to now, for the reason of absence of adaptive walk control algorithm, legged locomotion means still could not be put into practice in many practical applications yet. While on the other hand, as the most successful moving creature on the earth, multi-legged insect has facilely managed to surmount various complex natural landforms and even to walk upside down on smooth surfaces by right of its sophisticated limb structure and dexterous locomotion control strategies. Accordingly, it contains great theoretical and practical significance for the research and application of legged mobile robotics to blend the behavioral research effort of multi-legged insect into the design and control of walking robot and furthermore to develop hexapod biomimetic robots with more superexcellent mobility.In this work, a thorough investigation of configuration design, theoretical modeling, motion planning and contriving of control system were made in terms of bionics, and moreover, an intensive experimental study on its application in complex environment was performed simultaneously.From the aspect of robot system design, the walking structure of multi-legged insect was modeled as a configuration with 3-DOF legs and ellipse distribution of limbs; a mechanical configuration capable of omni-directional locomotion was fabricated with rudder-driven and parallel four-bar linkage transmission; by taking segment proportion and orientation of coax axes as the independent variables, and locomotion ranges of the robot body in six dimensions under reference posture as the attributive variables, an objective estimation function of mobility was constructed and the structure parameters were optimized. Stratified hardware structure comprised of upper PC, embedded main controller, controller of signal acquisition, drive unit and modularized software structure comprised of gait control, limb control, joint motor, sensing unit, communication module of the control system were developed. The task of walking control was functionally and behaviorally decomposed combinedly, further, a distributed gait control structure based on function-behavior-integration and an overall walking control mode combined with control mode of free gait and that of leg-end reflex applied under complicated terrain conditions were presented.From the aspect of kinematics and dynamics analysis, the kinematic model of hexapod biomimetic robot was established on the basis of structural modeling of multi-legged insect, besides, kinematic equations of position, velocity and acceleration of single swinging leg and multiple supporting legs were deduced separately by means of theories of serial and parallel mechanics. The Lagrange dynamic model of the hexapod robot was established based on the alembert principle, and by converting the entire forces endured by the robot system onto the generalized coordinates by means of the influence coefficient method of theory of mechanics, the equilibrium equations were established, the dynamics calculation was performed and further the Lagrange dynamic equations were deduced; the issue of over-determined torque input was discussed, and the cooperating equations of entire inputted torques were deduced in the light of the law of conservation of energy and the influence coefficient method of theory of mechanics. Through the simulation experiments, validity of kinematics was testified and the simulation testing of the dynamics characters of the robot system was performed.From the aspect of trajectory planning, a trajectory planning strategy of free gait and that of leg-end reflex were put forward aiming at separately the situations of slightly irregular and badly irregular terrain conditions. For the former one, a uniform trajectory planning description of stance phase and swing phase was upbuilt, a buffer-area-based trajectory planning strategy of swing phase using combined polynomial curve was proposed, and the problem of parallel closed link was transformed into the one of serial open link according to the principle of relative locomotion. While as to the latter one, the artificial realization modes of elevator reflex and searching reflex mechanisms were established by adopting the leg-end trajectory of combined beelines with camber transition; and according to the demand of walking, the artificial reflex modes of single reflex, multiple reflex and combined reflex were put forward.From the aspect of gait planning, by means of analysis and abstraction of multi-legged insect gait, the mathematical relationship of walking velocity and gait pattern was deduced and the velocity modulation method of multi-legged walking was presented; moreover, a phase-clock-based description of inter-leg phase sequence was proposed, and a principle of free gait generation was presented based on the adjustment of inter-leg phase sequence. By ways of comprehensively considering the effect of acceleration factor, a stability determination method based on the Improved Energy Stability Margin was put forward, the mathematical relationship of stability margin and step length, walking acceleration of hexapod walking was deduced, and the region of gait parameters by which the statically stable walking was maintained was presented. According to the principle of free gait generation, a regulation strategy of inter-leg phase sequence and a set of local rules operating between adjacent legs were put forward, further, by means of a distributed network of local rules and based on the theory of Finite State Machine, a specialized and a generalized control algorithms of free gait generation were applied separately to adaptively regulate the fluctuation of inter-leg phase sequence and therefore generate statically stable free gait, besides, the algorithms were testified by the simulation experiments.With the walking experimental platform of hexapod biomimetic robot, walking experiments of fixed gait, leg-end reflex and free gait were executed separately, which not only testified the validity of the hexapod walking theories proposed but also exemplified the adaptive stable locomotion ability of the robot under complex terrain conditions.