Parallel Helix Actuators for Soft Robotic Applications

Abstract

Fabrication of soft pneumatic bending actuators typically involves multiple steps to accommodate the formation of complex internal geometry and the alignment and bonding between soft and inextensible materials. The complexity of these processes intensifies when applied to multi-chamber and small-scale (∼10 mm diameter) designs, resulting in poor repeatability. Designs regularly rely on combining multiple prefabricated single chamber actuators or are limited to simple (fixed cross-section) internal chamber geometry, which can result in excessive ballooning and reduced bending efficiency, compelling the addition of constraining materials. In this work, we address existing limitations by presenting a single material molding technique that uses parallel cores with helical features. We demonstrate that through specific orientation and alignment of these internal structures, small diameter actuators may be fabricated with complex internal geometry in a single material-without-additional design-critical steps. The helix design produces wall profiles that restrict radial expansion while allowing compact designs through chamber interlocking, and simplified demolding. We present and evaluate three-chambered designs with varied helical features, demonstrating appreciable bending angles (>180 •), three-dimensional workspace coverage, and three-times bodyweight carrying capability. Through application and validation of the constant curvature assumption, forward kinematic models are presented for the actuator and calibrated to account for chamber-specific bending characteristics, resulting in a mean model tip error of 4.1 mm. This simple and inexpensive fabrication technique has potential to be scaled in size and chamber numbers, allowing for application-specific designs for soft, high-mobility actuators especially for surgical, or locomotion applications.

Evolutionary Inverse Material Identification: Bespoke Characterization of Soft Materials Using a Metaheuristic Algorithm

“…These robots offer many advantages over their rigid body counterparts, with the ability to traverse complex trajectories to reach previously inaccessible areas, deform both actively and passively in multiple directions, and interact safely within delicate environments (e.g., with biological tissues). Furthermore, they often represent simpler fabrication and assembly with respect to rigid robots with joints; being molded in monolithic material designs (Chandler et al, 2020), with embedded strain limiting materials (Mosadegh et al, 2014;Polygerinos et al, 2015) or with the addition of functional components (e.g., magnetic particles) (Kim et al, 2019;Lloyd et al, 2019). These advantages are afforded due to the highly compliant nature of the materials from which they are typically made, and have made soft robots (SRs) a popular choice for small-scale medical and surgical instrumentation (Cianchetti et al, 2014(Cianchetti et al, , 2018da Veiga et al, 2020); from common grasping tasks (Zhang et al, 2017b), endoscopic (Chauhan et al, 2021;Liu et al, 2021) and minimally invasive surgery (Edelmann et al, 2017;Oliver-Butler et al, 2017;Jeon et al, 2019) to microfluidic platforms in order to stimulate and sort cells (Zhang et al, 2017c;Onaizah et al, 2020).…”

An Origami-Based Soft Robotic Actuator for Upper Gastrointestinal Endoscopic Applications

“…A bending angle up to 140 o for a pressure of 0.1 bar was reported ( Elsayed et al, 2014 ) in a 25 mm diameter prototype, though this actuator relied on radial expansion. The parallel helix actuator ( Chandler et al, 2020 ) showed a minimum and maximum bending angle of 181 o to 222 o for 0.5 to 0.75 bar (for different prototypes) for a 9.6 mm actuator diameter. The results obtained for OA show improved performance, with low pressure actuation in a sub-cm diametrical size (i.e., = 8.5 mm).…”

“…The mounted end of the actuator was connected via three-way channel to three air supply tubes. Other components of this experimental setup comprised of, i) three 10 cc pneumatic syringes pressurized via controlled linear stages (actuated by a stepper motor) as detailed in ( Chandler et al, 2020 ), ii) a pressure regulator (ITV0010-3BL, SMC Pneumatics, United States), and iii) three equal-length pneumatic lines connected to each channel of the actuator.…”

“…In a previous study from the authors, we introduced the development of a mechanical continuum joystick for driving three individual corrugated bellows (configured at 120° angle around the central axis) ( Garbin et al, 2018b ). Later, we also introduced the possibility to generate an internal corrugated pattern with a smooth external design through the use of parallel helical cores ( Chandler et al, 2020 ). The parallel helical actuator reported the packing of three inflatable helical channels in an overall diameter of 9.54 mm.…”

Parallel Manipulation and Flexible Assembly of Micro-Spiral via Optoelectronic Tweezers

“…It has distinctive properties and advantages over the conventional spherical, rod, or lamellar particles ( Dong et al, 2022 ). Therefore, the spiral structure had a wide range of applications in various fields in recent years ( Berny et al, 2020 ; Chandler et al, 2020 ; Wu et al, 2021 ). For example, the spiral structure can be propelled by rotating itself around the long axis.…”