3D printed linear soft multi-mode actuators expanding robotic applications

Soft robotic actuators have played a fundamental role in the current shifts in task and workplace priorities. Unlike traditional hard robotic systems, soft robotic systems comprise complex control schemes and sensory mechanisms needed to provide the necessary task flexibility, compliance and safety. Producing intrinsically soft devices has emerged as a promising approach for integrating safety and compliance measures into established systems. Among them, soft pneumatic actuators are an attractive new technology featuring rapid response, high force-to-mass ratio and a versatile range of motions while offering intrinsic compliance.

Newer soft pneumatic actuators have been engineered to overcome the deficiencies of the earlier designs, like pneumatic artificial muscles, by increasing the degrees of freedom and achievable structural deformation. Pneu-Flex actuators and pneumatic networks, mostly developed by exploring the compliant nature of elastomers, are some of the common topologies of the new designs. Nevertheless, most of the existing soft pneumatic actuators are mainly suitable for creating bending motions, with very few used to either produce linear movements or strains in multiple directions.

Although linear soft pneumatic actuators function like biological muscles and are suitable replacements for rigid and heavy piston mechanisms, the linear operation of these actuators requires very high pressure to produce desirable strokes. 3D printing, specifically the digital light projection (DLP) method, is a promising technique for producing complex elastomeric parts commonly used in producing soft actuators. However, the lack of suitable materials is currently the biggest limitation to developing soft actuators through DLP.

Recently, a newly developed soft elastomeric resin, known as ElastAMBER, has proved effective for DLP printing of soft and flexible parts owing to its low stiffness, high elastic strains and low hysteresis properties. ElastAMBER was successfully used to produce Linear Soft Multi-Mode Actuators (LSOMMAs), capable of producing bidirectional actuation and achieving remarkable extensile and contractile forces under positive and negative pressures, respectively. It exhibited significant advantages over other soft actuators.

Inspired by the recent developments, Australian researchers: Dr. Ryan Drury, Dr. Vitor Sencadas and led by Professor Gursel Alici from University of Wollongong produced a novel 3D printed pneumatic device named LSOMMA. In their approach, the new elastomeric resin was designed to be used on DLP 3D printers. The characteristics and functional capabilities of LSOMMA were evaluated, including contraction and extension under differential pressures. Finally, the applications of these actuators in soft robotics were demonstrated. Their research work is currently published in the journal, Soft Matter.

The research team demonstrated the scalability of the presented LSOMMA as well as its ability to provide stable responses over 410,000 cycles. Such soft pneumatic actuators require low operating pressure to achieve meaningful strains at pressures way below that of most pneumatic devices. Thus, in correspondence to the actuator strains of up to 37% and -50%, LSOMMA was successfully operated at low pressures to realize full expansion and contraction at gauge pressures of 75 kPa and -25 kPa, respectively. Further, all actuators examined recorded a rise time of less than 250 ms.

Two mobile robots were constructed and analyzed to demonstrate the applicability and benefits of the multi-mode LSOMMA actuators in soft robotics. The peristaltic crawler robot could rapidly traverse vertical, horizontal and bent pipe sections while adapting to the pipe diameter changes. The ground locomotion robot could turn 361°C min^-1 and move up to 652 mm min^-1. An untethered version of the ground robot could transverse multiple surfaces materials like carpet. Furthermore, the lower operating pressures of LSOMMA allowed the utilization of lighter and smaller pumps and other control components, perming more opportunities for creating mobile devices.

In summary, soft pneumatic actuators based on 3D printed elastomeric resin, and their application in soft robotics were reported. Achieving multiple mode operations is beneficial in producing pulling and pushing forces using only a single actuator. All the demonstrated robotic applications performed significantly better in many categories than most reported in the literature. In a statement to Advances in Engineering, senior Professor Gursel Alici who is also the executive Dean of Faculty of Engineering and Information Sciences said ” We continuously aim to reduce the footprint of robotic technologies such that the mechanical structure, for example, seamlessly houses actuation and sensing elements and other important elements such as energy source (e.g., battery pack) to bring robotic systems one step closer to the operation and functions of biological systems. This work is a significant step towards this goal, pushing the limits for minimum foot-print robotic systems to widen their application prospects in the field of soft robotics”.