A Mechanically Intelligent Crawling Robot Driven By SMA And A Compliant Bistable Mechanism

In the traditional concept,mechanical structures are considered as lifeless and coldness parts,which can only produce relative motion or force by obtaining commands from center controller.In recent years,with the continuous development of robotics,mechanical science and material science,a machine which can undertake the task of sensors and controllers has returned to the researcher's vision,therefore the mechanical intelligence technology has received extensive attention.This paper proposed a mechanical intelligent crawling robot which was controlled by its own motion logic utilizing the "intelligent" material Shape Memory Alloy springs as the actuators.The robot actuation system incorporates a compliant bistable mechanism to ensure the reliability of the robot's motion while regulating the energy of the moving process during the motion between two stable positions.The crawling speed of the robot can be changed by adjusting the applied current according to the application,noting that,the untethered crawling robot achieves basic movement within any electronic control elements,so the robot design is lightweight and integrated,which can greatly improve the field of using SMA as actuators in robot field.The full text has acquired the following achievement:(1)According to the mechanical intelligence method,this paper proposed and designed a crawling robot controlled by a mechanical logic switch system which can replace the function of the position sensors as well as logically control the antagonistic SMA actuators activation according to the position of the robot movement.This mechanism can also reduce the complexity of the control system,improve the reliability and decrease the weight of the robot which makes the structure compact and integrated.(2)Traditional constitutive model of SMA is complicated,which increases the design difficulty for the engineering application.In this paper,a static two-state model was applied to establish a force-deflection mathematical model of the SMA spring actuator in only 100% austenite state and martensite state.The model can be applied for designing SMA spring actuators without the requirement for thermomechanical models.Finally,the experimental results and the model are well verified.(3)In order to make the compliant bistable mechanism better matches with the antagonistic shape memory alloy actuators,the PRBM and Bi-BCM were used to simulate the dimension design of the pre-strain compliant bistable mechanism.The mathematical model corresponding to the bistable mechanism geometrical parameters was established.Finally,the force-displacement curve relationship of the bistable mechanism was obtained which can be adjusted by the geometrical parameters which can be used to guide the design of the robot in theory.(4)In this paper,the static analysis of the robot system was carried out and the static SMA model is verified by experiments.The relevant crawling experiments were carried out to verify the design concept and the displacement-time relationship of the robot under different activated currents was obtained.The experimental results show that the motion frequency and speed of the crawling robot can be adjusted by the applipied current.Finally,the proposed method can reduce the cost of the shape memory alloy under the condition of satisfying the actuating accuracy.In the meanwhile,the complexity generated by the control strategy is decreased,which brings a new design idea for the application of using shape memory alloy as actuators in the robot field.