Minyung Kim, et al. 

Interactive Haptics Technologies, KAIST (Spring 2023)

 Stress management is increasingly vital in modern society, with virtual environment (VR) being recognized as a potential solution. While most VR relaxation applications rely on audio-visual cues, incorporating haptic sensations, particularly gentle human touch, can enhance stress reduction's immersive experience and effectiveness. We introduce HaptoRelax, a wrist-worn device utilizing shape memory alloys (SMA) to provide soft and smooth tactile feedback of ‘grabbing’ on the skin.

  Our contributions are:

1. showing that SMA-actuated grabbing sensations can provide the relaxing experience in VR 

2. the structure of SMA springs rendering repetitive gentle grabbing

 We selected the Nitinol Spring for our device due to the quick actuation and sufficient contraction force, providing grabbing sensation. Our final design consists of a single long spring (50.0mm) with two shorter springs (20.0mm) connected at each end. The structure was chosen as it was capable of repetitive elongation and contraction of springs, leading to continuous grabbing and realising on the wrist. We supplied powers in order, so that when longer spring contracts, the shorter two springs elongates, and vice versa. 

   In pilot study, we got the absolute threshold with two-down and one-up staircase method to establish the minimum power required for users perception of grabbing. Then we carried out two user studies 1) without HMD and 2) with HMD.

  With HMD, participants rated the higher than without HMD. They also gave positive feedbacks for the gentle sensation, relaxation through VR and the devices’ warmth. However, negative factors such as testing setup (cooling fan presence, VR animation unmatched) and limitations in functionality (weaker grabbing) disrupted relaxation.