SPONGE: Open-Source Designs of Modular Articulated Soft Robots

TL;DR

SPONGE addresses reproducibility gaps in soft robotics by providing two open-source designs for modular articulated soft robots with antagonistic bellows. The semi-modular baseline and the fully modular variant integrate centralized pneumatic supply and serial communication to enable scalable multi-DoF systems. Experimental results demonstrate airtightness up to a central supply pressure, precise position tracking with mean errors around 2.6 degrees, and significantly improved longevity of cast bellows over printed ones. By releasing all hardware and software files, SPONGE offers a reusable benchmark platform for modeling, control, and comparison of soft robotic systems and supports development toward long snake robots.

Abstract

Soft-robot designs are manifold, but only a few are publicly available. Often, these are only briefly described in their publications. This complicates reproduction, and hinders the reproducibility and comparability of research results. If the designs were uniform and open source, validating researched methods on real benchmark systems would be possible. To address this, we present two variants of a soft pneumatic robot with antagonistic bellows as open source. Starting from a semi-modular design with multiple cables and tubes routed through the robot body, the transition to a fully modular robot with integrated microvalves and serial communication is highlighted. Modularity in terms of stackability, actuation, and communication is achieved, which is the crucial requirement for building soft robots with many degrees of freedom and high dexterity for real-world tasks. Both systems are compared regarding their respective advantages and disadvantages. The robots' functionality is demonstrated in experiments on airtightness, gravitational influence, position control with mean tracking errors of <3 deg, and long-term operation of cast and printed bellows. All soft- and hardware files required for reproduction are provided.

Figures (8)

• Figure 1: From semi-modular (a) to modular (b) ASRs with $n{=}3$ actuators. Blue lines indicate pneumatic connections and orange lines represent electronics. A scalable design is realized via central supply and communication.
• Figure 2: SPONGE designs: (a) The semi-modular actuator (diameter: $82m m$, height: $52m m$) consists of soft bellows, a discrete joint, and an encoder. (b) Fully modular design (diameter: $66m m$, height: $94m m$) with integrated microvalves and serial communication.
• Figure 3: (a) Sectional view with printed pneumatic channels inside the lower frame. Pressure supply $p_\mathrm{s}$ is directed to port 1 and inflates the bellows (port 2). The bellows is depressurized using port 3. (b) Design of each PCB mounted between adjacent actuators. (c) Modular test-bench architecture.
• Figure 4: Control architectures: (a) The semi-modular actuator is controlled by adjusting desired bellows pressures, which are set by the integrated pressure controllers of the external proportional valves. (b) The modular actuator consists of integrated binary valves and is controlled via PWM.
• Figure 5: (a) Molds for casting the bellows and (b) post-casting assembly for semi-modular design, ballooning of the cast bellows (c) without and (d) with a ring at $p_\mathrm{max}{=}0.5bar$ (semi-modular), (e) post-casting assembly and (f) expanded bellows at $p_\mathrm{max}{=}0.3bar$ (modular)