An Advantageous Array of Air Springs that Attenuates Aerial Inherent Nonlinearities for Force Sensing

Despite the inherent leakage issue, pneumatics is advantageous for device development in some respects. The use of air secures power transmission flexibility while it could alleviate structural complexity depending on the design objectives. Since air is compressible and can act as a spring, it is worth utilizing this for the development of a force sensing device. However, air's inherent nonlinearities cause a decreased linear relationship between the imposed force and deformation even at low frequencies. Those lead to irregular responses and eventually energy dissipation. We note that a serial deployment of two air springs can reduce the effect of aerial inherent nonlinearities since the arithmetic summation of the stiffnesses of the two air springs in the proposed deployment becomes linear over a wide range of displacement. In this study, we investigated the influences of the serial deployment of air springs in reducing the effect of aerial inherent nonlinearities. The Lyapunov exponent is employed to characterize the behaviors of air springs in response to external excitation. We found that the serial deployment efficiently promotes the linear relationship between the imposed force and deformation, indicated by a lower value of the Lyapunov exponent. These results suggest that the effect of aerial inherent nonlinearities is mitigated, in particular, at low frequencies where contacts with humans are considered to occur primarily. Experimental validation was performed.