Small-Strain Deployable Mechanisms

Soft robot has strong flexibility and adaptability to the complex working environments, and therefore becomes a hot research topic in recent years. However, soft robots based on pure soft materials also have some intrinsic drawbacks such as low load capacity, difficult to fabricate and control, etc., the rigid-flexible coupling design is an ideal solution to these problems. This chapter proposes the design approach for the rigid-flexible coupling small-strain deployable mechanisms based on traditional rigid mechanisms and soft origami, which can improve the load capacity of the system while maintaining the flexibility of the soft robots. This chapter first presents the design and control of a worm-like soft origami-based robot, which is designed from the waterbomb origami and driven by a 3-D Helmholtz coils magnetic system. The whole robot adopts soft materials and is manufactured by Stereo Lithography Apparatus technology. NdFeB cylindrical magnets with opposite magnetization directions are glued to the front and rear of the robot, and the different friction forces on the head and tail of the robot are used to realize the worm-like gait movement. Based on the principle of magnetic field superposition and the magnetic dipole model, the robot can be positioned in real-time with dual magnetic targets, and the robot’s automatic navigation movement is realized through closed-loop feedback. This chapter also presents the design of a rigid-flexible coupling origami gripper. The mechanism of the gripper is designed from the waterbomb origami, and the stiffness of the gripper is increased by attaching rigid steel sheets to the facets of the soft origami gripper. Then the gripper realizes the adaptivity of soft grippers and the high load capacity of rigid grippers. The structural design of the rigid-flexible coupling mechanism is first presented. Based on the DH parameter method and symmetrical folding hypothesis, the kinematics model of waterbomb is deduced. The shape adaptability experiment, load capacity experiment, and object recognition experiment are carried out to verify the performance of the proposed gripper. In this chapter, a rigid deployable mechanism with mobility bifurcation is also presented, in which the bifurcation will cause the deployment vibration. The revolute joints that introduce mobility bifurcation are analyzed, which shows that they can be replaced by the small-strain elastic joints without changing their mobility, the detailed design procedure for this type of elastic joint is discussed, and the main parameters of the elastic joints can then be determined based on the mobility and motion range of the deployable mechanism. The deployment experiments of both mechanisms are conducted to show the improvement of the latter mechanism.