Assisted damage closure and healing in soft robots by shape memory alloy wires

Abstract

Self-healing soft robots show enormous potential to recover functional performance after healing the damages. However, healing in these systems is limited by the recontact of the fracture surfaces. This paper presents for the first time a shape memory alloy (SMA) wire-reinforced soft bending actuator made out of a castor oil-based self-healing polymer, with the incorporated ability to recover from large incisions via shape memory assisted healing. The integrated SMA wires serve three major purposes; (i) Large incisions are closed by contraction of the current-activated SMA wires that are integrated into the chamber. These pull the fracture surfaces into contact, enabling the healing. (ii) The heat generated during the activation of the SMA wires is synergistically exploited for accelerating the healing. (iii) Lastly, during pneumatic actuation, the wires constrain radial expansion and one-side longitudinal extension of the soft chamber, effectuating the desired actuator bending motion. This novel approach of healing is studied via mechanical and ultrasound tests on the specimen level, as well as via bending characterization of the pneumatic robot in multiple damage healing cycles. This technology allows soft robots to become more independent in terms of their self-healing capabilities from human intervention.

Towards high performance and durable soft tactile actuators

“…Among the various stimuli options, heat is commonly used to trigger self-healing and Joule heating has emerged as a popular choice due to its localized heating capability and portability. Joule heating can be achieved by introducing conductive agents such as CNTs, 306,313 liquid metal, 314 and shape memory alloy wires 315 into self-healing actuators. These conductive components can also provide additional functionality to self-healing actuators; for example, Tabrizian et al embedded shape memory alloy wires into a self-healable pneumatic actuator.…”

Mechanisms boosting material embodied intelligence to realize self-healing soft robots

“…(a) An embedded healable heater in a PneuNet bending actuator that provides stimulus for healing, detects the damage and monitor the health of the robot [15]. (b) Embedded shape memory alloy wires to make an SMA wirereinforced bending actuator with the ability of damage closure and providing stimulus for healing [16]. information about its occurrence, however not its location.…”

“…In self-healing soft robots, in case of a puncture or a small damage, closure may happen by the elastic response of the material, whereas large damage need to be closed by external forces. In figure 1.b, an SMA wire-reinforced self-healing soft bending actuator is shown [16]. The embedded SMA wires are pre-strained and able to recover their permanent shape if heated above their transition temperature [17].…”

“…Furthermore, the produced Joule heating that activates the wires will also transfer to the chamber and heat it up simultaneously. As such, the wires can not only close the damage, but also provide the stimulus for heating and healing of the actuator [16]. Upon cooling, the wires can be re-elongated by the elastic forces of the chamber or upon actuation of the robot, making the damage closure possible for multiple cycles.…”

“…Upon cooling, the wires can be re-elongated by the elastic forces of the chamber or upon actuation of the robot, making the damage closure possible for multiple cycles. Based on the length of the wires and the amount of pre-strain, they can close gaps as large as 2 mm [16]. For healing, usually the material is heated for a few minutes.…”