# Integrated Haptic Feedback with Augmented Reality to Improve Pinching and Fine Moving of Objects
## 2 Materials and Methods
### Haptic Feedback  
Two haptic devices were used in this experiment. The first was a full vibrotactile glove developed by the company bHaptics, provided with full black gloves with a yellow cover to improve the hand trekking, and the gloves are combined with 6 vibrotactile motors (5 on the user tips and one on the wrist) (see Figure 3a). The vibration patterns can be customized through the company's portal website. Connecting the gloves to the HL2 involves two steps: first, installing the bHaptics package from the Unity Store into the Unity application, and second, downloading their companion application on an Android device. This application communicates with the HL2 over the same Wi-Fi network and sends events to the gloves via Bluetooth, enabling them to vibrate in the desired pattern [20]. The second device features a pair of vibrotactile rings designed by the team at the University of Pisa, which has an electronic board (ESP8266), manufactured by Espressif Systems, Shanghai, China with custom code written through Arduino IDE, while the vibration motors are (FIT0774), from DFRobot, Shanghai, China (see Figure 3b).  
This device is integrated with the HL2 through UDP sender/receiver packets. The device includes a receiver for the UDP packets, allowing the HL2 to send messages with the desired vibration patterns directly to the device via Wi-Fi, without the need for communication with a PC, mobile device, or any additional hardware. Both devices are designed to offer fast response times and extremely low latency. They also offered a variety of vibration  
Figure 2: Object distribution over the X-axis in the view scene, where users can choose the desired mode from the button matrix.  
patterns tailored to different user actions. Three distinct patterns were selected for the bHaptics glove, each corresponding to different gesture intensities as follows:  
* Low intensity on a finger, 30% of the provided intensity: vibration on the index or on the thumb, used during simple touch of an object to notify about the identification of a collision but without the detection of pinching.
* Medium intensity on both fingers 40% of the provided intensity: vibration on both the index finger and thumb, triggered during a pinching action. This vibration is maintained until the pinching is active.
* High intensity 80% of the provided intensity: Full-glove vibration, including all fingers and the wrist, is used to signal task completion and indicate that no further interaction is needed. The task is considered completed when the distance error becomes lower than 1 mm.  
The vibrotactile rings developed by the University of Pisa offer safe vibration patterns with a high degree of customization. Vibration patterns can be tailored by adjusting two key variables: frequency, which affects the intensity of the vibrations, and pulse-width modulation (PWM). The PWM operates at a frequency of 5 KHz, which controls the duration of each pulse within a cycle by rapidly turning the vibration motor on and off. This allows for the creation of various customized patterns for both continuous and discrete vibration effects. We set these intensities to match the user's perception with that of the bHaptic glove:  
* Low intensity on a finger 20% of PWM cycle.
* Medium intensity on both fingers 35% of PWM cycle.
* High intensity: applied to both fingers when the task is completed and further interaction is unnecessary 50% of the PWM cycle.  
The only difference between the haptic patterns is to signal the task completion: full glove vibration for the bHaptics glove vs. index and thumb vibration for the rings.