phloSAR: a Portable, High-Flow Pressure Supply and Regulator Enabling Untethered Operation of Large Pneumatic Soft Robots

Abstract

Pneumatic actuation benefits soft robotics by facilitating compliance, enabling large volume change, and concentrating actuator weight away from the end-effector. However, portability is compromised when pneumatic actuators are tethered to cumbersome air and power supplies. While there are existing options for portable pneumatic systems, they are limited in dynamic capabilities, constraining their applicability to low pressure and/or small-volume soft robots. In this work, we propose a portable, high-flow pressure supply and regulator (phloSAR) for use in untethered, weight-constrained, dynamic soft robot applications. PhloSAR leverages high-flow proportional valves, an integrated pressure reservoir, and Venturi vacuum generation to achieve portability and dynamic performance. We present a set of models that describe the system dynamics, experimentally validate them on physical hardware, and discuss the influence of design parameters on system operation. Lastly, we integrate a proof-of-concept prototype with a soft robot arm mounted on an aerial vehicle to demonstrate the system's applicability to mobile robotics. Our system enables new opportunities in mobile soft robotics by making untethered pneumatic supply and regulation available to a wider range of soft robots.

Figures (6)

• Figure 1: We present phloSAR, a portable high-flow pressure supply and regulator to enable untethered operation of large pneumatic soft robots. (a) PhloSAR prototype. (b) PhloSAR components and direction of airflow. (c) The prototype is integrated with an aerial vehicle and actuates a soft "vine" robot to demonstrate the phloSAR portability and that it can be used to realize mobile soft robots. (d) Mass distribution (chart values in kg). "Flow Control" includes the valves and Venturi pump, "Pneumatics" includes the reservoir and pneumatic connections, "Structure" includes the chassis and mounting hardware, and "Drone Integration" includes the vine robot and additional mounting hardware. The phloSAR mass is 0.84 kg. The total mass (phloSAR + soft robot) is 1.4 kg, which is within the drone payload capacity (approximately 1.5 kg).
• Figure 2: Qualitative comparison of existing pressure source and/or regulation solutions. Metrics are written around the circumference, and higher radii correspond with higher quality. Off-the-shelf regulators and custom regulators as is are not ready for untethered operation (they must be paired with a separate pressure source) and thus do not have quality values for "Air Supply" and "Renewability".
• Figure 3: Characterization of pressure reservoir discharge (singular trials) through a valve with constant flow resistance. We compare experimental data to the model presented in Sec. \ref{['sec:discharge-model']} for different initial reservoir pressures, reservoir sizes, and flow resistances. The tests shown represent the conditions with shortest and longest duration and one intermediate example.
• Figure 4: Comparing PhloSAR step response with the model (piecewise linear with an initial inflation speed given by Eq. \ref{['eq:fillup-rate']}). The pressure command, phloSAR reservoir pressure, and control volume size were varied (TC1, TC2, TC3) to yield different inflation speeds.
• Figure 5: Comparison of phloSAR closed-loop frequency response to the model presented in Sec. \ref{['sec:freq-response']}. Test condition TC4 is a phloSAR and control volume within expected operating conditions, and test condition TC5 is a more difficult condition (lower reservoir pressure, larger control volume, and higher-amplitude pressure command). The frequency response of a baseline (off-the-shelf pressure regulator) is overlaid. Baselines 1 and 2 correspond to TC4 and TC5, except the baseline regulator is supplied with its maximum recommended inlet pressure in both cases. Error bars represent 1 standard deviation, and bars not shown are within the bounds of the marker.