Soft Tensegrity Robot Driven by Thin Artificial Muscles for the Exploration of Unknown Spatial Configurations

Abstract

The primary role of a robot exploring an unknown space is to investigate the state and the spatial shape of the environment. We have designed a soft robot that aims to move forward in an unknown space as it recognizes and adapts to the spatial shape of the environment. We previously reported that soft tensegrity and recurrent neural network can be used to realize tensegrity structure shape recognition. In this study, a tensegrity robot was designed to actively generate propulsive force as it presses its body against a wall in its surrounding environment. This robot design includes a novel artificial muscle arrangement called "4/3 muscle winding," which induces large deformation in the tensegrity structure. The application of this new artificial muscle arrangement allows two types of large deformations to be induced in the tensegrity structure, which results in displacements of 20% to 40% in the axial and radial directions. We have demonstrated that the robot, which was created by connecting the tensegrity structures, is lightweight and possesses passive shape adaptability in a three-dimensional environment. This tensegrity robot could enter an unknown space, such as a cave, and recognize the spatial shape of the surrounding environment by recognizing the tensegrity structure shape.

Advances in artificial muscles: A brief literature and patent review

“…In the last 2 years, the performance metrics of artificial muscles have been upgraded and have continued to gain new applications in the field of soft robotics. We can see the refinement of artificial muscle powered insect-sized robots ( Wang Z et al, 2021 ; Kim D et al, 2022 ), the improvement of artificial muscle driven water-walking robots ( Zhou X et al, 2021 ; Kim S et al, 2022 ), soft tension robots for exploring unknown spaces ( Kobayashi et al, 2022 ; Zhou et al, 2022a ), the enhancement of artificial muscle driven soft crawling robots ( Liu et al, 2021 ; Wu et al, 2022 ), the realization of rehabilitation assistance training robot based on pneumatic artificial muscles ( Wang and Xu, 2021 ; Chu et al, 2022 ; Tsai and Chiang, 2022 ), control optimization and modeling of artificial muscle-actuated endo-exoskeleton robots ( Chen et al, 2022 ; Lin et al, 2021 ; Liu H et al, 2022 ; Yang et al, 2022 ), and the application of SNA in soft wearable robots ( Jeong et al, 2022 ).…”

Large Torsion Thin Artificial Muscles Tensegrity Structure for Twist Manipulation

“…Therefore, in addition to conventional tensegrity analysis [27], [28], it is necessary to consider the force characteristics of the artificial muscle. The kinematics and statics of deforming a tensegrity structure in the z-axis and radial directions using artificial muscles are described in [8]. However, [8] only considered the case of extension and contraction in the z-axis direction, and it was not possible to analyze the mechanics considering torsional deformation around the z-axis direction.…”

“…In recent years, in addition to these excellent properties, the environmental adaptability derived from the softness of the soft tensegrity has been focused, and tensegrity robots were developed in the field of robotics [4], [5], [6]. Tensegrity robots are expected to play an active role not only in cooperative work with humans [7], which has been done by conventional robots, but also in dangerous work in unknown spaces such as caves [8] and outer space [9], owing to their environmental adaptability, scalability, and high durability. To realize high functionality of soft tensegrity robots in such environments, modularization is effective in terms of versatility [10], [11], and it is desirable to be able to perform various deformations in Manuscript received: AUGUST, 26, 2022; Revised NOVEMBER, 9, 2022; Accepted JANUARY, 7, 2023.…”

“…1). Previously, we developed an inchworm-type robot that moves with large deformations of its tensegrity structure to explore unknown spaces [8]. This robot used six-bar tensegrity and thin McKibben muscles [18], and was comprised of a tensegrity module with displacements of 20%-40% in the axial and radial directions.…”

“…Additionally, in [11], we produced a robotic hand with large bending deformations by combining a hand-type structure with a tensegrity module and thin McKibben muscles. The use of thin McKibben muscles retains the light weight of normal McKibben muscles [19], but also allows for deformation without losing the characteristics of the soft tensegrity structure, because of its flexibility to be driven even in a bent state [8], [11], [20]. By adding torsional motion which is important for proper manipulation and rotational operation to the above mentioned approach, all basic deformation modes of the module can be realized, and the development of a versatile tensegrity robot with even greater applicability is expected.…”