A mechanism that allows a robotic arm to quickly grip various forms of objects at disaster sites will enhance the\nmobility of rescue robots by keeping their bodies stable and maintaining manipulability for target objects, such as\ndebris. Such a mechanism requires the ability to quickly and omnidirectionally change arm postures toward the target\nand hold it in a stable manner. Continuum robots are expected to provide this functionality. Conventional continuum\nrobots realize the function of changing arm postures and grasping objects by controlling pneumatic actuators with\nmultiple air chambers arranged in parallel. However, conventional robots cannot be applied to potential disaster\nsites filled with flammable gases, gasoline, or high radiation levels because they require electronic components (e.g.,\nsolenoid valves, and sensors) to control air pressures. This study proposes a unique approach to realize reflexive omnidirectional\nbending motion using only mechanical components without any electrical devices. The proposed system\nrealizes a reflexive motion to bend the arm in the targetââ?¬â?¢s direction by detecting a contact location using a mechanical\nreactive system. The proposed simple mechanism has the advantages of high durability and easy implementation.\nThis paper aims to confirm the proposed concept by prototyping a drive mechanism coupled with contact detection\nand bending motion using mechanical port valves. We report the design concept and development of this prototype.\nThe fundamental characteristics and feasibility of the proposed mechanism are experimentally confirmed. First, a\nprototype is developed using a mathematical model. Its performance in the bending and omnidirectional motions is\nevaluated. The results show that the model has a margin of âË?â??4.9% error in the bending angle and âË?â??7.4% error in the\ncentral curvature compared with the experimental values. We also confirm that using a higher pressure could realize a\nsmaller radius of curvature and reduce an unnecessary twisting motion. We also tested a second prototype to confirm\nthe grasping motion and force by changing the applied pressures. The influence of the bending direction was then\nevaluated. We confirm that a higher pressure generated a larger grasping force. The prototype can omnidirectionally\nproduce approximately the same forces although the generated forces depend on the number of air chambers\nexcited by the contact pads. Subsequently, we experimentally confirm the influence of gravity. The test shows\nthat the effect of own weight greatly influences the posture after the object is in contact. This effect should not be\nignored. Furthermore, the curve became sufficiently large when its contact pad is pressed. This result experimentally\nproved that self-holding is possible. The experimental results show the potential of the proposed mechanism.
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