Thermosensitive elastomers for shape adaption of soft robotic systems

Abstract:
Recent advances in soft robotics demonstrate robust and versatile performance for dexterous grasping and manipulation. Due to their intrinsically mechanical compliance, soft robots passively adapt their shape to an object during contact. This results in large contact patches and damping of contact dynamics, which compensates for uncertainties in sensing, modeling, and actuation. Therefore, the behavior of soft robots is also determined by contact-based deformations. Building these kinds of compliant structures by using thermosensitive hybrid materials of polydimethylsiloxane and different thermoplastic filler particles as thermosensitive elastomers (TSE) the design could receive a higher versatility and extra functionality. Thermosensitive elastomers (TSE) consist of an addition curing RTV-2 silicone in which different thermoplastic filler particles are embedded. These thermoplastic particles are polycaprolactone (PCL), polyamide-6 (PA6) and polymethylmethacrylat (PMMA) with melting temperatures in the range of 58deg C to 215deg C. In certain examinations, soft magnetic carbonyl iron particles (CIP) are also included to prove the compatibility of the two particle types within the polydimethylsiloxane (PDMS) matrix and to utilize a possible symbiotic effect of the particle mixtures. By means of mechanical tests, the thermosensitive hybrid materials enable shape changes by applying both external heat and stress/force. With a low melting point in the range of 58 °C to 60 °C, PCL offers good application potential compared to the other thermoplastic filler particles. One of PCL most important and application-oriented phenomena is the shape memory effect, which results from internal stresses between elastomer molecular chains and PCL particles. Whereby the external shape arises from the equilibrium of all internal forces. Consequently, the material composites can be referred to as both TSE and shape memory polymers (SMP). By adding soft magnetic particles, an accelerated heat distribution within the samples was detected, which results in a faster occurrence of the corresponding effects. Micro computed tomography (μ-CT) and scanning electron microscopy (SEM) examinations indicate that a homogeneous distribution of PCL and CIP within the thermosensitive elastomer prevails. Moreover, the TSE additionally contain CIP can combine the benefits of temperature and magnetic field effects. Due to the material’s ability to imprint or adapt to any shape, thermosensitive elastomers as shape memory polymers represent a potential opportunity to modify pre-existing robotic components. Depending on the initial design and force application, the modified systems could adapt to almost any shape under the influence of temperature. This leads to their use in a variety of applications in adaptive sensors, smart actuators, and gripping elements in soft robotics.