This document summarizes the design and evaluation of a novel two degree-of-freedom wearable tactile system that can simulate digit normal and shear forces. The system consists of two wearable devices for the index finger and thumb connected to a microcontroller and graphical user interface. Tests showed the device can exert different shear forces on the fingertips with errors under 0.3 N and forces perceptible to users. The system was also able to simulate realistic digit-object interactions comparable to real manipulation contexts. The device has potential for integration with virtual reality systems to enable multisensory feedback during human-machine interactions.

1. Contact Info: simone.toma@asu.edu, chinello@btech.au.dk, marco.santello@asu.edu
1. Pachierotti C, Sincalir S, Solazzi M, Frisoli A, Hayward V, and Prattichizzo D (2017) “Wearable haptic systems for the fingertip and the hand: Taxonomy, Review, and Perspectives” IEEE Transaction on Haptics.
2. Chinello F, Malvezzi M, Pacchierotti C, and Prattichizzo D (2015) “Design and development of a 3RRS wearable fingertip cutaneous device” IEEE/ASME International Conference on Advanced Intelligent Mechatronics
3. Shibata D, Toma S, Chinello F, Prattichizzo D, Santello M (2018). “Tactile and non-tactile signals are linearly integrated for the estimation of fingertip distance” 27th meeting of the Society for the Neural Control Movement
4. Shibata D, Kapper AML, Santello M (2014) “Digit forces bias sensorimotor transformations underlying control of fingertip position” Frontiers in Human Neuroscience
Design and Evaluation of a Novel Two Degrees of Freedom Wearable Tactile System
Simulating Digit Normal and Shear Forces
Simone Toma1*, Francesco Chinello2*, Magdalena P. Gajek1, Daisuke Shibata4, Domenico Praticchizzo5, Marco Santello1
1School of Biological and Health Systems Engineering, Arizona State University, Arizona, USA
2Department of Business Development and Technology, Aarhus University, Midtjylland, Denmark
4 Department of Health Exercise and Sports Sciences, University of New Mexico, New Mexico, USA
5 Department of Information Engineering, University of Siena, Italy
*equal contribution
We presented the working principle of a novel wearable haptic device capable of delivering consistent and distinguishable tactile stimulations on the users index and thumb finger
pads. Unlike most of the tactile technologies presented in literature, the current prototype is characterized by a closed-loop control that allows on-line monitoring of device
performance, hence enhancing reliability while rendering realistic haptic scenarios. Importantly, the current prototype allows the assessment of the user-device interaction by taking
into account both user (i.e., discrimination thresholds) and device (i.e., accuracy) datasets. Our tests revealed the ability of our tactile device to stimulate different shear forces on
users’ fingertip with an overall error that never exceed 0.3 N. Furthermore, psychophysical tests demonstrated the suitability of the device to exert range of forces perceivable by the
users. Importantly, we have shown that the simulation of digit-object interactions elicited perceptual and motor response comparable to those observed in real manipulation
contexts.3,4 We are currently working on the integration of the device within a virtual reality multisensory platform where visual, muscular and proprioceptive signals can be used
both as input and output for the haptic rendering. This set-up will allow investigation of what combinations of rendering features elicit stable, realistic user’s performance.
Technological advances have resulted in a multitude of devices designed to enable human-machine interaction,
virtual reality, and research applications. With regard to haptics, a number of approaches has been developed to
deliver haptic feedback to discrete areas of the hand, e.g., fingertips, in scenarios involving fine manipulation1. In this
work, we present a two-degrees-of-freedom wearable and portable haptic display capable of providing compression
( normal) and shear forces on the finger pad. The device set consists of two wearable devices for index finger and
thumb, a microcontroller, and a Graphical User Interface (GUI).
RATIONALE
This work was partially supported by a National Science Foundation BCS-1455866 grant.
Real & Simulated Manipulation
Normal force
Shear forces
Contact Point
Here we present the results of two sets of tests. While
the first set aimed at validating the accuracy and
precision of the forces exerted by the device (control
algorithm tests), the second set explored and quantified
the potential of this technology to simulate realistic
digit-object interactions (figure on the right).
Mechanics Device Accuracy and Precision during Force Exertion
DISCUSSION & PERSPECTIVES
RESULTSWORKING PRINCIPLE
Device simulation of real-like hand object interaction
Simulated Tactile
time time
Real Tactile
Matching
error
UU DD UD DU
A
B
C
D
E
F
A: linear gear B: stand for tracking C: normal servo motor D: finger
stand E: lateral servo motor F: lateral platform and piezo-resistive
sensor
Serial communication
Digital output (writing)
Analog input (reading)
NORMALForce
Upward
Downward
SHEARForce
Electronics
Graphical User InterfaceControl Algorithm
DeviceAccuracy(N)
UP DOWN
0
0.4
0.8
1.2
1.6
UP DOWN
DeviceResolution(N)
0
0.25
0.5
0.75
1
UP DOWN
PSE(N)
0.5
2.4
0
1.6
Reference Force
1.2
0.8
2
JND(N)
UP DOWN
0.25
0.75
1
0
0.5
Device Resolution
Users’ Detection and Discrimination of Exerted Shear Forces
P(CMP>STD)
0.25
0.5
0. 75
1
0
0 0.5 1.61.0 2.1 2.6 3.1
Shear Force (N)
UP
DOWN
-1.6 -0.5 0 0.5 1.61.0 2.1 2.6 3.1-3.1-2.6-2.1 -1
Shear Forces (N)
DOWNUP
DeviceError(N)
1
-0.5
0.5
-1
0
Reference Force (std)
Delta Force
𝑆𝐹𝑡 = 𝐹𝑁𝑡 ∙ 𝐿𝐷𝑡 ∙ 𝜔
𝑺𝑭 𝒕: shear force exerted at time t 𝑭𝑵 𝒕 : normal force exerted at time t 𝑳𝑫 𝒕: lateral platform displacement
𝝎: coefficient of elasticity2
Host PC MicroController Wearable device