Abstract
Their dexterity, compliance, energy efficiency, compactness, and lightweight structural architecture, have made Shape Memory Alloy (SMA)-based soft robotic grippers with variable stiffness an attractive alternative to their rigid and soft counterparts. However, they are limited by their slow response time due to slow heat dissipation from the heated embedded SMA. This study is aimed at performing a time response analysis of an SMA-based soft robotic gripper with variable stiffness, focusing more on the reduction of the cooling time, which will subsequently result in an improved response time. Finite Element Analysis (FEA) was conducted to investigate the effect of a heat sink comprising a silicone housing, and an ethylene glycol thermal compound, on the response time. A 3D model of the cylindrical cross-section of the gripper’s finger was generated. Using Ansys workbench, numerical analysis was conducted. A NiTi shape memory alloy of 15 mm diameter was heated and let to cool by natural convection in ambient conditions while observing its cooling time through a series of trials. A proposed heat sink was then incorporated and the cooling time in ambient conditions was measured. A reduction in cooling time was observed while the heat sink was incorporated.
From the numerical results, a response time of 37 s was observed while the SMA was not coupled with a heat sink. On the other hand, a response time of 24 s was observed while the heat sink was incorporated. This equates to an average response time of 30.5 s, leading to a percentage difference of 42 % in response time observed with and without the heat sink, which then translates to a 42 % improvement in response time. The comparative study indicates that in practical applications, this can be regarded as a significant improvement. A close association is observed from the experimental results, consistent with the numerical and comparative results. The implications of this being that the proposed heat sink, while maintaining a practical, cost effective, simplistic, compact, and lightweight structural design of the system, does so without compromising the system’s functionality, through improvement in response time by the proposed heat sink mechanism.
Additionally, it was found that most shape memory materials do not exist in the FEA platforms' material libraries, making it difficult to simulate them using current FEM tools. In the literature, there hasn't been much discussion of simulation of shape memory materials, especially NiTi SMAs, particularly regarding the analysis of the time response. The numerical modelling, simulation, and analysis of NiTi SMAs performed in this study, has demonstrated
that while it might occasionally be challenging to obtain these materials, it is possible to still be able to study them and gain an understanding of their behavioural characteristics.