| Mobile manipulator has both mobile and operational capacity, and has larger operating space and better operational flexibility. It is a research focus in the robot 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. 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. The hexapod robot which is typically multi-legged is characterized by its climbing capability and fault-tolerance for walking on unstructured terrain. It is particularly suitable for tasks in complex environment where high reliability is essential. Thus the development of a hexapod robot capable of walking on unstructured terrain is of practical importance. In this paper, a novel hexapod robot HITCR suitable for walking on unstructured terrain is proposed, and also some advanced control strategy will be integrated to improve the ability of the robot.To improve the adaptation ability of hexapod robot, a thorough investigation of configuration design was made in terms of bionics. And structure parameters are optimized for improving dexterity of the robot; to equip the robot with perception of external environment and its internal states, the robot was characterized by high-integration and control with multi-sensors. As a typical MIMO system, a four-layer distributed hardware control system is developed. Also, the electrical system and the communication system were designed.Omni-directional motion planning is the foundation of implement unstructured terrain stable walking. It achieved the Omni-directional walk through establishing coordinationrules between legs and planning foot-end trajectories of the robot. Firstly, the forward and inverse kinematic model of hexapod biomimetic robot was established on the basis of theories of serial and parallel mechanics. Secondly, the adaptive foot-end trajectories generating strategy is presented using high order polynomial, which is of importance to the needs of leg movement and good movement characteristics of the robot. Finally, the coordinationrules between legs are integrated to produce the free gaits.Six-legged robot leg force control is an independent behavior, but the movement of the whole robot performance is critical, it is about leg movement in the process of state transition and foot end slip, accident cases on foot with the ground stability. Firstly, in order to meet the requirements of complex environment foot end force measurement, the three-dimensional force sensor is designed based on the principle of strain sensing, which has lots of advantages. Secondly, the foot end force measurement under different robot posture workspace is achieved through the space transformation of the foot end force sensor. Finally, the leg state controller based on events is developed, to improve the leg movement stability in the process of state transition of walking. The impact of in the of process leg state transition is effectively reduced, through integrating the foot end compliant force control strategy that bases on impedance model. Additionally, the adaptive adjustment of target damping is achieved through integrating independent adjustment of topography and stiffness and nonlinear gain compensation strategy.The hexapod robot is floating-base mechanism, whose posture is dependent on the supporting legs as well as the terrain shapes. The posture adjustment is to improve the stability of hexapod walking on unstructured terrain. Firstly, the original position of six-legged robot was planning; the walking benchmark is normalized, based on the kinematics and dynamics. Secondly, the LIT strategy was developed, to enable the robot distinguishautonomouslybetween mild rugged terrain and severe rugged terrains. Finally, the VSDM model is established to implement the posture control based on double loop integral sliding mode controller.Posture keeping strategy is used in the mild rugged terrain, while posture adjustment strategy is used in thesevere rugged terrains. The adjustment method for the center of gravity position is developed to improve the stability of the robot while walking.To test and verify the performance of the hexapod robot HITCR and the proposed control methods, four groups of experiments were carried out. Firstly, the stability of basic movement is tested through the comparison of different gait and movement patterns. Secondly, the walking ability on slope topographyand foot end force based center of gravity adjustment strategyare verified by the climbing experiment. In addition, the posture adjustment strategy under severe rugged terrains is also tested through stair climbing experiment.Finally,the omnidirectional motion experiment in complex terrain is designed to test the comprehensive motion ability of the robot and eventsbasedleg state controller. The adaptive stable locomotion ability of the robot under complex terrain conditions is exemplified by the comprehensive motionexperiment. |
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