QuadStretcher: A Forearm-Worn Skin Stretch Display for Bare-Hand Interaction in AR/VR

TL;DR

QuadStretcher introduces a forearm-worn skin-stretch display with four independently controlled units and counteracting tactors, enabling higher-DoF haptic feedback for bare-hand AR/VR. In a 20-participant study against the Squeezer baseline, QuadStretcher outperforms in expressing force direction and realism during 3-DoF tasks, with detailed psychophysical measurements (JNDs, discrimination accuracy) and qualitative interviews informing design guidelines. The work demonstrates the distinct advantages of skin-stretch over squeezing for dynamic hand-object interactions and offers actionable insights for wearable forearm-haptic systems. These findings advance immersive bare-hand experiences in AR/VR and guide future developments in compact, multi-DoF forearm haptics.

Abstract

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.

Figures (14)

• Figure 1: Previously proposed wrist/forearm haptic solutions to support bare-hand activities. (a) Moriyama et al. (2018) moriyama2018development, (b) Sarac et al. (2022) sarac2022perceived, and (c) Pezant et al. (2019) pezent2019tasbi
• Figure 2: (a) The QuadStretcher worn on the forearm. (b) The top view of the stretch module. (c) The diameter of the stretch tactor.
• Figure 3: The system pipeline of using QuadStretcher.
• Figure 4: (a) The environment for the skin displacement measurements. (b) The process of computing the center of the tactor's bottom plane in contact with the skin: calculating the center of the marker plane first, and translating it by 20.3 mm. This was done while ensuring the tactor plane was parallel to the marker plane with a 3D-printed rigid add-on structure.
• Figure 5: (a) The amount of tactor displacement under no load: $-11.0$, 0.0, and +11.0 mm shown by top, middle, and bottom images, respectively. (b) The measured correlation between the control signal, the tactor displacement under no load condition (mm), and the amount of actual skin displacement (mm). D, R, V, and L denote the dorsal, right, ventral, and left side of the forearm, respectively, while the suffix 'd' and 'p' denote the distal and proximal sides. For example, 'Dd' denotes the tactor in the dorsal forearm at a more distal location.