Department of Mechanical Engineering, Boston University, Boston, MA 02215, USA.
Department of Mechanical Engineering, Boğaziçi University, Istanbul, Turkey.
Soft Matter. 2023 Apr 5;19(14):2623-2636. doi: 10.1039/d2sm01390h.
Soft robots are well-suited for human-centric applications, but the compliance that gives soft robots this advantage must also be paired with adequate stiffness modulation such that soft robots can achieve more rigidity when needed. For this reason, variable stiffening mechanisms are often a necessary component of soft robot design. Many techniques have been explored to introduce variable stiffness structures into soft robots, such as pneumatically-controlled jamming and thermally-controlled phase change materials. Despite fast response time, jamming methods often require a bulkier pneumatic pressure line which limits portability; and while portable electronic control, thermally-induced methods require compatibility with high temperatures and often suffer from slow response time. In this paper, we present a magnetically-controlled stiffening approach that combines jamming-based stiffening principles with magnetorheological fluid to create a hybrid mechanical and materials approach. In doing so, we combine the advantages of fast response time from pneumatically-based jamming with the portability of thermally-induced phase change methods. We explore the influence of magnetic field strength on the stiffening of our magnetorheological jamming beam samples in two ways: by exploiting the increase in yield stress of magnetorheological fluid, and by additionally using the clamping force between permanent magnets to further stiffen the samples a clutch effect. We introduce an analytical model to predict the stiffness of our samples as a function of the magnetic field. Finally, we demonstrate electronic control of the stiffness using electropermanent magnets. In this way, we present an important step towards a new electronically-driven stiffening mechanism for soft robots that interact safely in close contact with humans, such as in wearable devices.
软体机器人非常适合以人为中心的应用，但赋予软体机器人这种优势的柔顺性也必须与足够的刚度调节相结合，以便在需要时使软体机器人能够获得更高的刚性。出于这个原因，可变刚度机构通常是软体机器人设计的必要组成部分。已经探索了许多技术来将可变刚度结构引入软体机器人中，例如气动控制的卡滞和热控的相变化材料。尽管响应时间很快，但卡滞方法通常需要更笨重的气动压力管路，这限制了其便携性；而虽然便携的电子控制、热诱导方法需要与高温兼容，并且常常受到响应时间慢的困扰。在本文中，我们提出了一种磁控增强方法，该方法将基于卡滞的增强原理与磁流变液相结合，创建了一种混合机械和材料方法。通过这种方式，我们结合了基于气动的卡滞的快速响应时间优势与热诱导相变化方法的便携性。我们通过两种方式探索了磁场强度对我们的磁流变卡滞梁样本增强的影响：利用磁流变液屈服应力的增加，以及通过使用永磁体之间的夹紧力进一步增强样本（离合器效应）。我们引入了一个分析模型来预测我们的样本的刚度作为磁场的函数。最后，我们展示了使用电永磁体对刚度的电子控制。通过这种方式，我们朝着用于与人类安全近距离交互的软体机器人的新型电子驱动增强机制迈出了重要一步，例如在可穿戴设备中。
