Magnetic Actuator with Programmable Force Distribution and Self‐Sensing for Bidirectional Deformation Control

Abstract

Thus, various types of soft actuators have been developed to realize bidirectional deformation. Currently, most soft actuators, for example, shape memory material [6][7][8] and liquid metal, [9][10][11] are developed on the basis of transition between two different states, which complicate the control of overall movement. However, in order to realize more precise bionic movement, the whole process of bidirectional deformation can be controlled to achieve better actuating speed and body control, which is still a challenge for the development of soft actuators.The current actuating principles of soft actuators can be mainly summarized into three categories. [12] The first type is based on the principle of phase transition. The deformation function is realized by the change of the microstructure and macroscopic state of the material under external stimuli. [13] The reciprocal transition of materials between solid, liquid, and gaseous phases is the most prevalent phase change occurrence. The intermolecular interaction between the components causes the entire material to undergo a sequence of property changes or deformations during the phase change process. [14,15] The second type is based on the strain mismatch of different components of the composite structural system. [16] Subjected to the external excitation, the uncoordinated strain between the components creates internal stress at the interface, which in turn lead to the structure's reaction, such as bending deformation, [17] due to the varying mechanical characteristics of each part. The third type is based on the principle of mechanical instability, [18,19] which includes both microscopic and macroscopic structural instability levels. At the microstructural level, the material is considered to be a composite composed of many phases. Instability is manifested as a rapid transition to a position of low potential energy by skipping uniform changes between different phases of the material. At the macroscopic structure level, mechanical instability is usually manifested as buckling, torsion, wrinkling, and so on. [20][21][22][23][24] These large deformations lead to the mode conversion of the structure. The above soft actuators are difficult to control through the whole process of bidirectional deformation since the discontinuity of the switching between the two states.The magnetic actuator is not limited to switching between the two states. [25,26] It can be continuously controlled by the action of magnetic particles through the magnetic field. The

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