A proposal of a new rotational-compliant joint with oil-hydraulic McKibben artificial muscles

Abstract

Conventional hydraulic actuators can generate a strong force due to high pressure. However, most of them are heavy and hard because they are made of metal. It is difficult to use such actuators in robots required to be as light as possible. Moreover, the joint mechanisms of these actuators have problems with intrinsic safety and robustness because the compliance is acquired using delicate sensors and advanced controls. Therefore, we propose a new rotational-compliant mechanism that allows the coexistence of strong force and compliance. The proposed mechanism has compliance in an active rotational direction and in two directions orthogonal to it. To realize this mechanism, we have developed a Hydraulic Artificial Muscle (HAM), which is very lightweight and able to generate strong force. Furthermore, the HAM has compliance without any advanced control. By exploiting the characteristics of the HAM, the function of the proposed mechanism can be realized even in conditions of compact dimensions. In this paper, by constructing a simple experimental system that imitates the proposed mechanism, and by modeling it, we verify its compliance from both a theoretical and an experimental point of view. We demonstrate that the mechanism has compliance in the three rotational directions.

Keywords:

• Hydraulic artificial muscle
• hydraulic actuator
• antagonistic drive
• rotational compliant mechanism
• tough robotics

Acknowledgements

Hydraulic artificial muscles used in this research have been jointly developed in collaboration with the Bridgestone Corp. We would like to express the deepest appreciation to them.

Notes

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan).