Abstract
Inaccuracies in modeling of the geometric shape of PAMs has long been cited as a probable source of error in modeling and design efforts. The geometric shape and volume of PAMs is commonly approximated using a cylindrical shape profile, even though its shape is non-cylindrical. Correction factors—based on qualitative observations of the PAM’s general shape—are often implemented to compensate for error in this cylindrical shape approximation. However, there is little evidence or consensus on the accuracy and form of these correction factors. Approximations of the shape profile are also used to calculate the internal volume of PAMs, as experimental measurements of the internal volume require intrusive testing methods and specialized equipment. This research presents a photogrammetric method for measuring the shape profile and internal volume of PAMs. A test setup, method of image data acquisition, and a preliminary analysis of the image data, is presented in this research. A 22.2 mm (7/8 in) diameter PAM is used to demonstrate the photogrammetric procedure and test its accuracy. Analysis of the tested PAM characterizes trends of the shape profile with respect to pressure and contraction. The common method of estimating the diameter—through the use of the cylindrical approximation and initial geometry of the PAM—is tested by comparison to the measured shape profile data. Finally, a simple method of calculating the internal volume using the measured shape profile data is developed. The presented method of acquiring photogrammetric measurements of PAM shape produces an accurate characterization of its shape profile, thereby mitigating uncertainty in PAM shape in analysis and other efforts.
Highlights
Pneumatic Artificial Muscles (PAMs) are a form of soft actuator that is applied to an expanding number of applications for their unique characteristics such as their low weight and simple construction, inherent compliance, and high specific force and specific work capabilities
It is worth noting that since the scale was found to be uniform along the entire length of the PAM, there was no compensation of scaling due to image distortion used for this test
This research presents an approach for characterizing the shape profile of PAMs through photogrammetric measurement
Summary
Pneumatic Artificial Muscles (PAMs) are a form of soft actuator that is applied to an expanding number of applications for their unique characteristics such as their low weight and simple construction, inherent compliance, and high specific force and specific work capabilities. Actuator design requirements typically include force and stroke values, while common actuator design constraints include actuator size, energy efficiency, and storage requirements. Models have been developed which address each of these design constraints and requirements for PAMs, but many of those models lack the accuracy required for their use in a world of increasingly tight design spaces, and improvements to those models has remained stagnant for years. While continual improvements have been made in modeling the force response of PAMs, there has been little recent progress in the development of methods for characterizing the size and overall shape profile of PAMs during operation, parameters commonly used for calculating efficiency, fluid storage, and flow rate requirements. The PAM’s shape profile (Figure 1) has long been approximated through visual observations, and has often
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