Abstract
Inflatables are safe and lightweight structures even at the human scale. Inflatable robots are expected to be applied to physical human-robot interaction (pHRI). Although active joint mechanisms are essential for developing inflatable robots, the existing mechanisms are complex in structure and it is difficult to integrate actuators, which diminish the advantages of inflatables. This study proposes blower-powered soft inflatable joints that are easy to fabricate and contain enough space for an actuation inside. The joints are driven by tendon wires pulled by linear actuators. We derived a theoretical model for both unilateral and bilateral joints and demonstrated a hugging robot with multiple joints as an application of the proposed joint mechanism. The novelty of the proposed joint mechanism and the inflatable robot is that rigid parts have been thoroughly eliminated and the tendons for actuation have been successfully hidden inside. Moreover, the active control of the internal pressure makes inflatables resistant to punctures. We expect that the contact safety of inflatable robots will facilitate advancement of the pHRI field.
Highlights
Inflatable structures are used in a variety of products such as rubber boats, mattresses, advertising columns, and temporary architectures
There are no sensors mounted on the surface of the hug robot, a single pressure sensor is installed for feedback control of the internal pressure by the blower
The results showed that even during active stabilization of the internal pressure, human contact was noticeable as a change in the internal pressure
Summary
Inflatable structures are used in a variety of products such as rubber boats, mattresses, advertising columns, and temporary architectures. Their lightweight, cost-effectiveness, safety, and portability enhance the potential of inflatable robots. An early application of inflatable structures in robots was an attempt to replace the links of a space robot arm with inflatable cylinders (Koren and Weinstein, 1991). In this case, the joints and grippers were rigid mechanical parts. For fabric-based inflatables, a spherical robotic arm that combines two rotational degrees of freedom (DoF) in a single joint with a triplet actuator has been reported (Hofer and D’Andrea, 2020)
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