The paradigm of bare-hand interaction has become increasingly prevalent in Augmented Reality (AR) and Virtual Reality (VR) environments, propelled by advancements in hand tracking technology. However, a significant challenge arises in delivering haptic feedback to users' hands, due to the necessity for the hands to remain bare. In response to this challenge, recent research has proposed an indirect solution of providing haptic feedback to the forearm. In this work, we present QuadStretcher, a skin stretch display featuring four independently controlled stretching units surrounding the forearm. While achieving rich haptic expression, our device also eliminates the need for a grounding base on the forearm by using a pair of counteracting tactors, thereby reducing bulkiness. To assess the effectiveness of QuadStretcher in facilitating immersive bare-hand experiences, we conducted a comparative user evaluation (n = 20) with a baseline solution, Squeezer. The results confirmed that QuadStretcher outperformed Squeezer in terms of expressing force direction and heightening the sense of realism, particularly in 3-DoF VR interactions such as pulling a rubber band, hooking a fishing rod, and swinging a tennis racket. We further discuss the design insights gained from qualitative user interviews, presenting key takeaways for future forearm-haptic systems aimed at advancing AR/VR bare-hand experiences.

翻译：在手部追踪技术进步的推动下，裸手交互范式在增强现实（AR）和虚拟现实（VR）环境中日益普及。然而，由于手部必须保持裸露状态，向用户手部提供触觉反馈成为一个重大挑战。针对这一挑战，近期研究提出了一种间接解决方案，即向前臂提供触觉反馈。本文中，我们介绍了QuadStretcher，这是一种皮肤拉伸显示器，其特点是在前臂周围配置了四个独立控制的拉伸单元。在实现丰富触觉表达的同时，我们的设备通过使用一对反向作用的触觉执行器，消除了前臂上对固定基座的需求，从而减少了体积。为评估QuadStretcher在促进沉浸式裸手体验方面的有效性，我们与基线解决方案Squeezer进行了对比用户评估（n = 20）。结果证实，在表达力的方向和增强真实感方面，QuadStretcher优于Squeezer，特别是在三维自由度（3-DoF）的VR交互中，如拉伸橡皮筋、挥动钓鱼竿和摆动网球拍。我们进一步讨论了从定性用户访谈中获得的设计见解，为未来旨在提升AR/VR裸手体验的前臂触觉系统提出了关键启示。