Tactile Weight Rendering: A Review for Researchers and Developers

TL;DR

The paper provides a structured review of tactile weight rendering, categorizing approaches into asymmetric vibrations and skin stretch, and further subdividing skin-stretch devices by actuation mechanism. It systematically compares devices across physical, mechanical, and perceptual criteria, highlighting belt-based skin stretch and 3 DoF tactile actuation as particularly promising for realistic weight rendering in VR, teleoperation, and rehabilitation contexts. The authors emphasize the need for standardization, per-user calibration, and broader grasp configurations to advance practical adoption, and call for strategies to achieve more realistic, multisensory object property rendering. Overall, the work guides researchers and developers toward selecting appropriate tactile weight rendering solutions and identifies key gaps that future research should address to enhance naturalistic object interaction in virtual environments.

Abstract

Haptic rendering of weight plays an essential role in naturalistic object interaction in virtual environments. While kinesthetic devices have traditionally been used for this aim by applying forces on the limbs, tactile interfaces acting on the skin have recently offered potential solutions to enhance or substitute kinesthetic ones. Here, we aim to provide an in-depth overview and comparison of existing tactile weight rendering approaches. We categorized these approaches based on their type of stimulation into asymmetric vibration and skin stretch, further divided according to the working mechanism of the devices. Then, we compared these approaches using various criteria, including physical, mechanical, and perceptual characteristics of the reported devices and their potential applications. We found that asymmetric vibration devices have the smallest form factor, while skin stretch devices relying on the motion of flat surfaces, belts, or tactors present numerous mechanical and perceptual advantages for scenarios requiring more accurate weight rendering. Finally, we discussed the selection of the proposed categorization of devices and their application scopes, together with the limitations and opportunities for future research. We hope this study guides the development and use of tactile interfaces to achieve a more naturalistic object interaction and manipulation in virtual environments.

Figures (3)

• Figure 1: Schematic representation of holding an object in the air through precision grasp. Here, the object is stabilized between the thumb and index finger. The gravity, $g$, acting on the object mass, $m$, creates a downward force, $F_{weight}$. This force is stabilized by friction forces on the thumb, $F_{friction_t}$, and index fingers, $F_{friction_i}$, controlled by corresponding grip forces, $F_{grip_t}$ and $F_{grip_i}$.
• Figure 2: An illustration of weight rendering through asymmetric vibrations. A vibrotactile actuator moving on the vertical axis is held between the thumb and index finger. The actuator's input current, with negative values causing a downward acceleration, is designed to create an asymmetric acceleration pattern, stronger in a downward direction, leading to the perception of an illusionary downward force. The current profile is adapted from culbertson_modeling_2016.
• Figure 3: Illustration of weight rendering approaches through skin stretch. Here, the users grip virtual objects via precision grasp with their thumb and index fingers by wearing or holding the devices. (a) Skin stretch via flat surface motion. e.g., kurita_weight_2011. The object weight is simulated by controlling the displacement of the flat surfaces contacted with fingers, creating a shear force toward gravity. (b) Skin stretch through belt motion, e.g., minamizawa_gravity_2007. When the motors of a belt rotate in opposite directions and at the same rate, it deforms the corresponding finger only in the normal direction, simulating the normal stress due to grip. When they rotate in the same direction and rate, they deform the fingerpad only in the tangential direction, simulating the shear stress based on the desired weight of the virtual object. They can simultaneously deform the fingertip in normal and shear directions by rotating at different rates. (c) Skin stretch through a tactor actuated in planar/tangential movement, e.g., girard_haptip_2016. Each fingerpad rests on the base of the device and contacts the tactor through an aperture at the center. The displacement of the tactor creates a shear force, simulating the weight of an object. (d) Skin stretch via a tactor actuated in 3 DoF translational movement, e.g., schorr_three-dimensional_2017. The object weight is simulated by controlling the displacement of a tactor placed on a 3 DoF, kinematic delta structure, providing both shear and normal stress on the skin.