A Pneumatic Generator Based on Gas-Liquid Reversible Transition for Soft Robots

Abstract

The soft robots actuated by pressure, cables, thermal, electrosorption, combustion and smart materials are usually faced with the problems of poor portability, noise, weak load capacity, small deformation and high driving voltages. In this paper, a novel pneumatic generator for soft robots based on the gas-liquid reversible transition is proposed, which has the advantages of large output force, easy deformation, strong load capacity and high flexibility. The pressure of the pneumatic generator surges or drops flexibly through the reversible transformation between liquid and gas phase, making the soft actuator stretch or contract regularly, without external motors, compressors and pressure-regulating components. The gas-liquid reversible-transition actuation process is modeled to analyze its working mechanism and characteristics. The pressure during the pressurization stage increases linearly with a rate regulated by the heating power and gas volume. It decreases exponentially with the exponential term as a quadratic function of time at the fast depressurization stage, while with the exponential term as a linear function of time at the slow depressurization stage. The drop rate can be adjusted by changing the gas volume and cooling conditions. Furthermore, effectiveness has been verified through experiments of the prototype. The pressure reaches 25 bar with a rising rate of +3.935 bar/s when 5 mL weak electrolyte solution is heated at 800 W, and the maximum depressurization rate in air cooling is –3.796 bar/s. The soft finger actuated by the pneumatic generator can bend with an angular displacement of 67.5°. The proposed pneumatic generator shows great potential to be used for the structure, driving and sensing integration of artificial muscles.

Decade of bio-inspired soft robots: a review

“…Its applications can be further extended by enhancing its energy efficiency and utilization or by using other liquid hydrocarbon fuels like liquid butane possessing higher energy density. Despite much progress on pressure, combustion, or thermal powered soft robots there still occurs the problem of noise, poor load capacity, and portability, and to address this problem a pneumatic generated which used liquid-gas reversible transition was proposed in [132]. It has offered the advantage of greater output force with easily achieved deformation due to higher flexibility as shown in figure 15(c).…”

3D Printing Bio‐Inspired Micro Soft Robot with Programming Magnetic Elastic Composites

“…[37][38][39] Control systems for gas-liquid phase change robots are relatively complex because the control of gas-liquid phase change requires precise temperature, pressure, and flow control. [40][41][42] In contrast, magnetic actuation enables simple wireless non-contact control and has a unique advantage in controlling soft robots inside enclosed spaces. Hu et al used Ecoflex and NdFeB hybrid mold casting to create a millimeter-scale soft robot that can move reversibly between different liquid and solid terrains, [43] but it requires a complex external magnetic field device to realize the motion of the soft robot.…”

Wireless Micro Soft Actuator without Payloads Using 3D Helical Coils

“…On the other hand, the micro thermopneumatic actuator operates with thermal expansion caused by heating the air when the electric current is supplied to the Joule heater inside the actuator [ 13 ]. The thermopneumatic mechanism is a promising alternative to the configuration of a portable system because it can replace the external power supplies needed for operating actuators with small batteries [ 14 ]. Additionally, an actuator without a battery, which is the heaviest payload for driving a heater, can be realized by introducing wireless power transfer.…”

“…Moreover, because the air pressure for deformation of the thermopneumatic actuator requires a significant energy supply, actuators based on the liquid–gas phase change of substances with low boiling points have been developed [ 14 , 19 ]. Compared to typical thermopneumatic actuators those heat the interior enclosed air, the actuators based on the liquid–gas phase change operate with less power because these are only needed to provide power to heat a temperature above the low boiling point of the liquid.…”