# Masking Effects in Combined Hardness and Stiffness Rendering Using an Encountered-Type Haptic Display

**Authors:** Naghmeh Zamani, Heather Culbertson  
**arXiv:** [2110.06982](https://arxiv.org/abs/2110.06982)  
**Date:** 2021-10-13  
**Summary page:** https://www.summarizepaper.com/en/paper/2110.06982v1/

## Key points

- The paper addresses the challenge of accurately rendering stable hard surfaces in haptics for various applications
- Current impedance devices lack the necessary force and stiffness to render a wall accurately
- High friction and inertia of admittance devices make it difficult to render free space
- Proposed solution combines haptic augmented reality, untethered haptic interaction, and an encountered-type haptic display
- Plate with desired hardness is attached to the end-effector of a kinesthetic device, which users can interact with using an untethered stylus
- Changing the hardness of the end-effector can mask the device's stiffness and impact user perception
- Human subject experiment conducted to assess users' ability to perceive changes in underlying stiffness when interacting with different materials
- Results indicate that when the end-effector is made of a hard material, users find it difficult to discern changes in rendered stiffness
- When the end-effector is made of a soft material, users can easily distinguish variations in stiffness
- Findings demonstrate promising potential for overcoming limitations associated with rendering hard surfaces using haptic devices

## Summary

The paper titled "Masking Effects in Combined Hardness and Stiffness Rendering Using an Encountered-Type Haptic Display" addresses the challenge of accurately rendering stable hard surfaces in haptics for various applications such as orthopedic surgery or dentistry training simulators. Current impedance devices lack the necessary force and stiffness to render a wall accurately, while the high friction and inertia of admittance devices make it difficult to render free space. To overcome these limitations, the authors propose a solution that combines haptic augmented reality, untethered haptic interaction, and an encountered-type haptic display. They attach a plate with the desired hardness on the end-effector of a kinesthetic device, which users can interact with using an untethered stylus. This approach enables direct adjustment of the end-effector's hardness based on the object being rendered. In this study, the authors evaluate how changing the hardness of the end-effector can mask the device's stiffness and impact user perception. They conducted a human subject experiment to assess users' ability to perceive changes in underlying stiffness when interacting with different materials. The results indicate that when the end-effector is made of a hard material, users find it difficult to discern changes in rendered stiffness. However, when the end-effector is made of a soft material, users can easily distinguish variations in stiffness. These findings demonstrate promising potential for overcoming limitations associated with rendering hard surfaces using haptic devices. By dynamically adjusting the hardness of the end-effector based on the rendered object, this approach enhances user perception and provides more accurate haptic feedback for tasks requiring interactions with stable hard surfaces.