Haptic perception is generally organized into two main pillars: tactile sensations (texture, friction, pressure, etc.) and kinesthetic sensations (force feedback, weight, muscle effort, etc.). Contemporary consumer XR haptic devices --- from controllers to suits --- are almost exclusively vibratory, and can render (or approximate through sensory substitution) many high-value tactile sensations. However, these devices are incapable of rendering kinesthetic forces, leaving haptic experiences incomplete. 

In this work, we describe a new haptic suit capable of rendering both vibrotactile and kinesthetic effects. Our core hardware design uses a small array of computer-controlled, motorized reels coupled with a variety of string-based mechanisms, such as pulleys and capstans. These mechanisms can be used for different purposes: for example, to create a mechanical advantage that can better match human strength (without increasing motor size), or to reroute or distribute forces over larger areas of the body. This combined approach allows us to achieve numerous key design goals, including:

• Soft, flexible, and safe design

• Comparatively low-cost (~$400)

• Lightweight (<5kg)

• Quick and easy to wear (<30 seconds)

• Multi-hour runtime on battery power

• Full-body, independent limb, haptic actuation

• High-bandwidth vibrotactile effects (up to 200Hz)

• Strong kinesthetic effects (up to 120N)

As we will discuss more in related work, rigid exoskeletons can achieve a similar range of effects, but are generally heavy, cumbersome to wear, and cost many thousands of dollars. More similar to our work are soft kinesthetic exosuits, of which a handful exist. However, none have full-body coverage, nor were any designed or evaluated for haptic rendering or XR use cases, instead targeting rehabilitation, accessibility, and strength augmentation. In contrast, we exclusively focus on haptics and XR with a consumer-oriented mindset, giving this work a different design ethos, objective function, evaluation scope, and success metric. 

After detailing our design and implementation of Kinethreads, we enumerate a non-exhaustive list of expressive kinesthetic forces one might encounter in XR experiences (e.g., centripetal force, high gravity, object weight, body compression, explosions). We combine our system's expressive capabilities into a suite of demo scenes, which we use to convey the feasibility of our system, and which we evaluate in a user study. The latter dovetails with a performance evaluation to quantify our system. 

Citation

Vivian Shen, Chris Harrison, and Craig Shultz. 2024. Expressive, Scalable, Mid-air Haptics with Synthetic Jets. ACM Trans. Comput.-Hum. Interact. 31, 2, Article 14 (April 2024), 28 pages. https://doi.org/10.1145/3635150