@conference {2655, title = {Reflex Control of the Pisa/IIT SoftHand during Object Slippage}, booktitle = {IEEE International Conference of Robotics and Automation (ICRA2016)}, year = {2016}, pages = {1972 - 1979}, publisher = {IEEE}, organization = {IEEE}, address = {Stockholm, Sweden}, abstract = {

In this work, to guarantee the Pisa/IIT SoftHand{\textquoteright}s

grasp robustness against slippage, three reflex control modes,

namely Current, Pose and Impedance, are implemented and

experimentally evaluated. Towards this objective, ThimbleSense

fingertip sensors are designed and integrated into the thumb

and middle fingers of the SoftHand for real-time detection and

control of the slippage. Current reflex regulates the restoring

grasp forces of the hand by modulating the motor{\textquoteright}s current

profile according to an update law. Pose and Impedance reflex

modes instead replicate this behaviour by implementing an

impedance control scheme. The difference between the two

latter is that the stiffness gain in Impedance reflex mode is

being varied in addition to the hand pose, as a function of

the slippage on the fingertips. Experimental setup also includes

a seven degrees-of-freedom robotic arm to realize consistent

trajectories (e.g. lifting) among three control modes for the sake

of comparison. Different test objects are considered to evaluate

the efficacy of the proposed reflex modes in our experimental

setup. Results suggest that task-appropriate restoring forces

can be achieved using Impedance reflex due to its capability

in demonstrating instantaneous and rather smooth reflexive

behaviour during slippage. Preliminary experiments on five

healthy human subjects provide evidence on the similarity of the

control concepts exploited by the humans and the one realized

by the Impedance reflex, highlighting its potential in prosthetic

applications.

}, keywords = {Haptics, Robotics}, doi = {10.1109/ICRA.2016.7487344}, url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=\&arnumber=7487344}, author = {A. Ajoudani and E. Hocaoglu and Altobelli, A and M. Rossi and E. Battaglia and N G Tsagarakis and A. Bicchi} } @article {2544, title = {ThimbleSense: a fingertip-wearable tactile sensor for grasp analysis}, journal = {IEEE Transactions on Haptics}, volume = {9}, year = {2016}, note = {
This work was partially supported by the European Community funded projects WEARHAP, PACMAN and SOMA (contracts 601165, 600918 and 645599 respectively), by the ERC Advanced Grant no. 291166 SoftHands
}, month = {03/2016}, pages = {121-133}, abstract = {

Accurate measurement of contact forces between hand and grasped objects is crucial to study sensorimotor control during grasp and manipulation. In this work we introduce ThimbleSense, a prototype of individual-digit wearable force/torque sensor based on the principle of intrinsic tactile sensing. By exploiting the integration of this approach with an active marker-based motion capture system, the proposed device simultaneously measures absolute position and orientation of the fingertip, which in turn yields measurements of contacts and force components expressed in a global reference frame. The main advantage of this approach with respect to more conventional solutions is its versatility. Specifically, ThimbleSense can be used to study grasping and manipulation of a wide variety of objects, while still retaining complete force/torque measurements. Nevertheless, validation of the proposed device is a necessary step before it can be used for experimental purposes. In this work we present the results of a series of experiments designed to validate the accuracy of ThimbleSense measurements and evaluate the effects of distortion of tactile afferent inputs caused by the device{\textquoteright}s rigid shells on grasp forces.

}, keywords = {Haptics, Robotics}, issn = {1939-1412}, doi = {10.1109/TOH.2015.2482478}, url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=\&arnumber=7294702}, author = {E. Battaglia and M. Bianchi and Altobelli, A and G. Grioli and M. G. Catalano and A. Serio and M. Santello and A. Bicchi} } @conference {2538, title = {Effect of Homogenous Object Stiffness on Tri-digit Grasp Properties}, booktitle = {37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC2015)}, year = {2015}, note = {
This work is supported in part by the European Research Council under the Advanced Grant SoftHands {\textquotedblleft}A Theory of Soft Synergies for a New Generation of Artificial Hands{\textquotedblright} no. ERC-291166 and under the EU FP7 project WEARHAP {\textquotedblleft}WEARable HAPtics for Humans and Robots{\textquotedblright} no. 601165.
}, pages = {6704 - 6707}, publisher = {IEEE}, organization = {IEEE}, address = { Milano, Italy, August 25th-29th, 2015}, abstract = {
This paper presents experimental findings on how humans modulate their muscle activity while grasping objects of varying levels of compliance. We hypothesize that one of the key abilities that allows humans to successfully cope with uncertainties while grasping compliant objects is the ability to modulate muscle activity to control both grasp force and stiffness in a way that is coherent with the task. To that end, subjects were recruited to perform a grasp and lift task with a tripod-grasp device with contact surfaces of variable compliance. Subjects performed the task under four different compliance conditions while surface EMG from the main finger flexor and extensor muscles was recorded along with force and torque data at the contact points. Significant increases in the extensor muscle (the antagonist in the task) and co-contraction levels were found with increasing compliance at the contact points. These results suggest that the motor system may employ a strategy of increasing cocontraction, and thereby stiffness, to counteract the decreased stability in grasping compliant objects. Future experiments will examine the extent to which this phenomenon is also related to specific task features, such as precision versus power grasp and object weight.
}, keywords = {Haptics, Robotics}, doi = {10.1109/EMBC.2015.7319931}, url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=\&arnumber=7319931}, author = {S. B. Godfrey and Altobelli, A and M. Rossi and A. Bicchi} } @conference {2398, title = {Electromyographic Mapping of Finger Stiffness in Tripod Grasp: a Proof of Concept}, booktitle = {International Conference on Rehabilitation Robotics (ICORR), 2015}, year = {2015}, note = {

softhands, wearhap

}, pages = {181-186}, publisher = {IEEE}, organization = {IEEE}, address = {Singapore, 11 {\textendash} 14 August 2015}, abstract = {

Effective execution of a manipulation task using prosthetic or robotic hands requires that the motion and the impedance profiles of the\ fingers\ be appropriately commanded. This, however, brings some design and control challenges regarding the individual planning and realization of the\ finger\ motion and\ stiffnesstrajectories. It appears that the central nervous system solves for this complexity in an effective and coordinated manner which has been well-recognized under the\ concept\ of hand synergies. While the exploitation of this\ concept\ in kinematic coordinates has lead to the development of several successful robotic designs and control strategies, its extension to dynamic coordinates, such as coordinated stiffening of the\ fingers, remains to be investigated. Indeed, in this study we provide preliminary evidence on the existence of such coordinated stiffening patterns in human\ fingers\ and establish initial steps towards a real-time and effective modelling of the\ fingerstiffness\ in a\ tripodgrasp. To achieve this goal, the endpoint\ stiffness\ of the thumb, index and middle\ fingers\ of five healthy subjects are experimentally identified and correlated with the electromyography (EMG) signals recorded from a dominant antagonistic pair of the forearm muscles. Our findings suggest that: i) the magnitude of thestiffness\ ellipses at the fingertips grows in a coordinated way, subsequent to the co-contraction of the forearm muscles; ii) the length of the ellipses{\textquoteright} axes appears to have a nearly linear relationship with the co-contraction level of the antagonistic muscle pair.

}, keywords = {Haptics, Robotics}, doi = {10.1109/ICORR.2015.7281196}, url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=\&arnumber=7281196}, author = {M. Rossi and Altobelli, A and S. B. Godfrey and A. Ajoudani and A. Bicchi} } @conference {2621, title = {An instrumented manipulandum for human grasping studies}, booktitle = {14th IEEE/RAS-EMBS International Conference on Rehabilitation Robotics, ICORR 2015}, year = {2015}, pages = {169-174}, publisher = {IEEE}, organization = {IEEE}, address = {Singapore, 11-14 Aug. 2015}, doi = {10.1109/ICORR.2015.7281194}, url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=\&arnumber=7281194}, author = {Altobelli, A and M. Bianchi and M. G. Catalano and A. Serio and Baud-Bovy, G and A. Bicchi} } @conference {2307, title = { Three-digit grasp haptic device with variable contact stiffness for rehabilitation and human grasping studies}, booktitle = {22nd Mediterranean Conference of Control and Automation (MED) 2014 }, year = {2014}, pages = {346 - 350}, publisher = {IEEE}, organization = {IEEE}, address = {Palermo, Italy, 16-19 June 2014 }, abstract = {

This paper describes an haptic system designed to vary the stiffness of three contact points in an independent and controllable fashion, by suitably regulating the inner pressure of three pneumatic tactile displays. At the same time, the contact forces exerted by the user are measured by six degree-of-freedom force sensors placed under each finger. This device might be profitably used in hand rehabilitation and human grasping studies. We report and discuss preliminary results on device validation as well as some illustrative measurement examples.

}, keywords = {Haptics, Robotics}, doi = {10.1109/MED.2014.6961395}, url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=\&arnumber=6961395}, author = {Altobelli, A and M. Bianchi and A. Serio and Baud-Bovy, G and M Gabiccini and A. Bicchi} }