Leg Structure Design Of The Hexapod Bio-robot And Research Of Its Compliance Control

With the development of human exploration of nature, the demand for robots which can move freely under complex environment has been getting broader in every area. Hexapod biorobot have strong abilities to adapt the terrain, and they can walk efficiently on rough environment. They have redundancy in the legs, so they can still do some work even if losing some legs. Therefore, the hexapod biorobot is suitable for the work with high requirements of reliability and autonomy to robots such as field reconnaissance, underwater search, and space exploration, etc.In this paper, a modular single leg structure with force sensing function of the hexapod biorobot is designed, and kinematics analysis and leg-end trajectory planning are done for the designed single leg. The compliance control strategy of the force applied on the leg end during the contacting process of the leg end and ground is studied, and the compliance control of the leg is realized.Firstly,an investigation of the legs of hexapod insects is conducted in terms of bionics. The structure and functional characters of the leg are analyzed, based on which a single-leg structure of hexapod biorobot was designed. A modularized joint is designed, with small size under the high-integrated requirements. Force and moment sensors are integrated on the leg structure, which include the design of three-dimensional force sensors at the foot-end and moment sensors at the joint. A passive compliant structure assembled at the single-leg tibia was designed, which combined with the force sensing function is the basis of the force compliance control of the single leg in the following text.Secondly, kinematics analysis of the designed single leg is conducted. The D-H coordination system of the single leg is built up, and the kinetic positive solution, negative solution and jacobian matrix of the robot single leg are solved out, which provided foundation for the whole movement and control of the robot in the following text. According to the gait character and control requirements of the hexapod biorobot, a trajectory planning for the leg-end is done, and the kinematics simulation for the generated leg-end trajectory is done.Thirdly, two impedance control strategies for the leg-end force are analyzed to solve the compliant control problem of the hexapod robots'leg-end force. In this paper, the impedance control strategy based on the leg-end position is adopted, and the influence of the impedance parameters on the force tracing is analyzed through formula derivation and system control simulation. In order to solve the problem of environmental parameters uncertainty, another impedance control strategy with online environmental parameter estimation is proposed and proved to be effectively in realizing force compliance of single leg through simulation.Finally, the combined simulation of Adams and Matlab is applied to prove the effectiveness of the impedance control algorithm.