Design And Static Analysis Of A Hybrid Continuum Robot

The intrinsic compliant body structure of continuum robots endows them with great environmental adaptability and safety,and thus,such robots have attracted increasing attention in recent years.However,the compliant structure may also lead to the lack of loading capacity and positioning accuracy.Considering this situation,a novel hybrid continuum robot is proposed to balance the requirements for flexibility,precision,and variable stiffness.The actuator of the robot incorporates a pneumatic muscle and an embedded elastic rod to maintain the system compactness.By employing the mode switching mechanism,the actuator can switch the drive mode between pneumatic mode and elastic rod mode to achieve largescale movement and precise positioning,during which the robot possesses variable stiffness.When performing large-scale movements,the pneumatic muscles provide most of displacement and force.Once the robot approaches the desired operational position,it will be driven by the linear motor through the elastic rod to achieve precise positioning,and the stiffness of the system is also improved.Based on the principle of force balance,the pressure-length model of the hybrid actuator is established.By comparing the simulated and experimental results,the dead zone of the actuator is found,and the model is then modified.The anti-hysteresis of robot is also verified.A three-dimensional static model of the robot is presented using an improved Kirchhoff rod theory,where elastic deformation of the robotic arm is accounted for from an optimal control point of view via minimal total potential energy principle.The static model and variable stiffness of the robot is validated by an experiment of applying external force to the robot tip under different configurations and drive modes.By recording the position of the robot tip,it is found that the positioning repeatability of the hybrid system is significantly increased in comparison to the pure pneumatic driving mode.Repeat positioning errors are decreased by an average of 62.8%.The results show that this design provides an effective way to enhance the positioning accuracy of the compliant continuum robot by using hybrid actuation with variable stiffness.