# Integrated Haptic Feedback with Augmented Reality to Improve Pinching and Fine Moving of Objects
## 1 Introduction
Wireless vibrotactile displays were created to alert users about excessive strain on their body joints by delivering appropriate tactile stimuli and guiding the individuals toward safer physical movements through tactile stimuli. [PERSON] et al. [11] demonstrated the importance of vibrotactile feedback in improving spatial awareness by using a wristband to assist users in solving 2D puzzles. Their system analyzed the object's position and rotation concerning its target placement, delivering feedback to guide necessary adjustments. Another study in P. [PERSON] et al. [12] developed a haptics-based rehabilitation system using Novint Falcon gloves to enhance pinch skills and finger strength. They tracked the 3D positions of two devices,synchronized the data, and fed it into a game engine to create virtual balls. A force mechanics model calculated fingertip forces based on the spatial relationship with a target cube, generating precise haptic feedback for direction and strength. These haptic feedback technologies that integrated mixed reality were ballistically dependent on hand gesture recognition in the virtual environment. This is because humans often use their hands more frequently when communicating or interacting with their surroundings [13]. Despite the importance of hand gesture recognition with mixed reality, the long-term and large-scale gestures in mid-air seem to lead to muscle fatigue [14]. Other problems arise with rapid movement, where users may lose the interaction without notification when their hands disappear from the camera field of view of the head-mounted display (HMD). Another problem that a user may face in HMDs like HoloLens 2 (HL2) is related to near-interacting actions when the user's hand is really on the bounding box that surrounds the objects, but the contact is not recognized. However, there are many applications with haptic feedback for VR and robotics and only a few examples with AR. In particular for AR, perfect finger tracking would be required to offer the user a realistic visual interaction perception, which cannot be currently guaranteed with current AR devices like the HL2. In the case of a VR application, the virtual representation of the hand and fingers visually informs the user about their pose with the virtual objects to clearly understand their collisions and therefore the possibility of activating some gestures, such as pinching. This approach remains effective even if the tracking is not entirely accurate. Users can adjust the position of their hands and fingers to achieve the desired virtual pose, even if there is some misalignment between their actual pose and the virtual representation. The VR system only requires coherent tracking regarding the direction of movement (up-down, left-right, etc. ), and it can tolerate misalignment of up to several centimeters. In AR applications, errors that may happen during the tracking can lead to incorrect interactions with virtual objects. For example, a user may see their fingertips near an object but may fail to pinch it due to being below the required threshold distance. Haptic feedback helps notify users of gesture recognition and compensates for misalignment between visual perception and actual contact. For example, a user knows pinching is feasible after a haptic notification, even if fingers do not yet appear in contact with the object. Simple devices, such as vibrating bracelets, can be beneficial [11], while delivering haptic feedback directly to the fingers feels more natural and intuitive. Glove-like devices may interfere with hand and finger tracking, particularly with video-based tracking systems like those on the Microsoft HL2. Therefore, simpler devices that have less demanding wearability requirements may be a better option. For this reason, the goal of this paper is to compare simple vibrotactile rings with a full glove device, with their possibility for better recognition of a fundamental gesture like pinching, which leads to smoother and faster fine movement of objects with the Microsoft HL2.