Grasp Quality Evaluation in Underactuated and Compliant Robotic Hands: New Indexes and New Challenges

The new trend in the design of robotic hands is to make them underactuated and compliant, so that they can safely interact with the enviroment, and adapt to the objects they have to grasp.
Evaluating the grasping capabilities of such type of hands is a challenging task because there is the need of an evaluation method that takes into account i) which forces can be actually controlled by the hand, depending on its actuation system, and ii) the parameters that characterize the contact points such as the friction coefficient and the maximum and minimum applicable contact forces.
To this aim, the work presented in [1] revisits some traditional quality measures developed for multi-fingered, fully actuated hands, and applies them to the case of underactuated hands. Measures based on the wrench space computation, namely the largest minimum resisted wrench, and measures of contact and grasp robustness, namely the Potential Grasp Robustness (PGR) and the Potential Contact Robustness (PCR), are compared through simulated examples. Both types of indexes are found to be suitable for evaluating underactuated grasps in a realistic and coherent way, because they can account for friction constraints and physically achievable contact forces.
Underactuated and compliant hands can adapt to the shape of the objects they have to grasp and tend to perform power grasps, rather than precision grasps. This consideration lead to the work described in [2], where authors demonstrate that the PGR can be applied not only to precision grasps, but also to power grasps.
The workshop entitled “Evaluation and benchmarking of underactuated and soft robotic hands” was held at IROS 2016 to discuss on the possibility of having a common benchmarking framework for assessing the quality of compliant and underactuated manipulation systems, and highlighted that in the community there is a clear need of comparability and reproducibility, not only for soft and underactuated hands, but for general robotic grasping systems.
The posters and the slides that were presented at the workshop are available here.



[1] M. Pozzi, A. M. Sundaram, M. Malvezzi, D. Prattichizzo, and M. A. Roa, “Grasp quality evaluation in underactuated robotic hands,” in Proceedings, IEEE/RSJ International Conference on Intelligent Robots and Systems, 2016. [PDF]

[2] M. Pozzi, M. Malvezzi, and D. Prattichizzo, “On grasp quality measures: Grasp robustness and contact force distribution in underactuated and compliant robotic hands,” IEEE Robotics and Automation Letters, vol. 2, 2017. [Link]

Thimbles, rings, armbands: a challenging road towards wearability in haptics at #WH2017

Thimbles, rings, armbands: a challenging road towards wearability in haptics is the ‘new’ title of my talk at the Workshop on Wearable Haptics in Munich on next Tuesday at the World Haptic Conference in Munich #WHC17 _DP #sirslab.

Francesco presenting his work at the Haptics Symposium in Philadelphia #haptics2016

Paper on “THE” Project published on Physics of Life Reviews

An article summarising the results of the four years EU project “The Hand Embodied – THE “ has been published on the prestigious journal Physics of Life Reviews. Here the link to the article. As University of Siena, we have contributed to the modelling of hand synergies and we have studied a systematic way to transfer human hand skills onto robotic hands. These results can be found here.

Abstract of the paper

The term ‘synergy’ – from the Greek synergia – means ‘working together’. The concept of multiple elements working together towards a common goal has been extensively used in neuroscience to develop theoretical frameworks, experimental approaches, and analytical techniques to understand neural control of movement, and for applications for neuro- rehabilitation. In the past decade, roboticists have successfully applied the framework of synergies to create novel design and control concepts for artificial hands, i.e., robotic hands and prostheses. At the same time, robotic research on the sensorimotor integration underlying the control and sensing of artificial hands has inspired new research approaches in neuroscience, and has provided useful instruments for novel experiments.

The ambitious goal of integrating expertise and research approaches in robotics and neuroscience to study the properties and applications of the concept of synergies is generating a number of multidisciplinary cooperative projects, among which the recently finished 4-year European project “The Hand Embodied” (THE). This paper reviews the main insights provided by this framework. Specifically, we provide an overview of neuroscientific bases of hand synergies and introduce how robotics has leveraged the insights from neuroscience for innovative design in hardware and controllers for biomedical engineering applications, including myoelectric hand prostheses, devices for haptics research, and wearable sensing of human hand kinematics. The review also emphasizes how this multidisciplinary collaboration has generated new ways to conceptualize a synergy-based approach for robotics, and provides guidelines and principles for analyzing human behavior and synthesizing artificial robotic systems based on a theory of synergies.

New paper published on Medical & Biological Engineering & Computing “Hand–tool–tissue interaction forces in neurosurgery for haptic rendering”

Haptics provides sensory stimuli that represent the interaction with a virtual or tele-manipulated object, and it is considered a valuable navigation and manipulation tool during tele-operated surgical procedures. Haptic feedback can be provided to the user via cutaneous information and kinesthetic feedback.


deviceSensory subtraction removes the kinesthetic component of the haptic feedback, having only the cutaneous component provided to the user. Such a technique guarantees a stable haptic feedback loop, while it keeps the transparency of the tele-operation system high, which means that the system faithfully replicates and render back the user’s directives.


figure1This work focuses on checking whether the interaction forces during a bench model neurosurgery operation can lie in the solely cutaneous perception of the human finger pads. If this assumption is found true, it would be possible to exploit sensory subtraction techniques for providing surgeons with feedback from neurosurgery. We measured the forces exerted to surgical tools by three neurosurgeons performing typical actions on a brain phantom, using contact force sensors, whilst the forces exerted by the tools to the phantom tissue were recorded using a load cell placed under the brain phantom box. The measured surgeon-tool contact forces were 0.01 – 3.49 N for the thumb and 0.01 – 6.6 N for index and middle finger, whereas the measured tool- tissue interaction forces were from six to eleven times smaller than the contact forces, i.e., 0.01 – 0.59 N.


Fingerprint_detail_on_male_finger_smallThe measurements for the contact forces fit the range of the cutaneous sensitivity for the human finger pad, thus, we can say that, in a tele-operated robotic neurosurgery scenario, it would possible to render forces at the fingertip level by conveying haptic cues solely through the cutaneous channel of the surgeon’s finger pads. This approach would allow high transparency and high stability of the haptic feedback loop in a tele-operation system.



M. Aggravi, E. De Momi, F. DiMeco, F. Cardinale, G. Casaceli, M. Riva, G. Ferrigno, D. Prattichizzo, D.
“Hand-Tool-Tissue Interaction Forces in Neurosurgery for Haptic Rendering.”
Medical & Biological Engineering and Computing, Springer, 2015.
DOI: 10.1007/s11517-015-1439-8

Silicon Valley 2016 – Intuitive Surgical Technology Research Grant Symposium

Silicon Valley 2016, Intuitive Surgical Technology Research Grant Symposium

12507134_10208629291997965_7814823607378336411_nHave a look to the photo album of the event.
– The idea we had in our lab #sirslab about using the cutaneous-only (no kinesthetic) haptic feedback in robot-assisted surgery, like the da Vinci system, was a great idea and it got the prestigious Intuitive Surgical Research Grant in 2015 (the only Italians) with a collaborative project with University of Pennsylvania (K.J. Kuchenbecker). Claudio Pacchierotti and I have been in California to present the results of the research based on our idea. We gave talks to surgeons and engineers of Intuitive Surgical in Santa Clara in the Silicon Vally and it was amazing. A lot of great conversations, ideas, and comments. We are coming back to Italy with more energy :-).

Screen Shot 2016-01-10 at 01.41.03
If you want to know more about the idea of cutaneous feedback in surgical robotics have a look to this paper

– L. Meli, C. Pacchierotti, D. Prattichizzo. Sensory subtraction in robot-assisted surgery: fingertip skin deformation feedback to ensure safety and improve transparency in bimanual haptic interaction. IEEE Transactions on Biomedical Engineering, 61(4):1318-1327, 2014

and to the paper where the idea has been implemented in the da Vinci System in

– C. Pacchierotti, D. Prattichizzo, K. J. Kuchenbecker. Cutaneous feedback of fingertip deformation and vibration for palpation in robotic surgery. IEEE Transactions on Biomedical Engineering. In Press, 2015




New paper published on IEEE Transactions on Haptics: “Digital Handwriting with a Finger or a Stylus: a Biomechanical Comparison”

The human hand is highly versatile and easily adaptable to a variety of manipulation tasks, exposing flexible solutions to the needs of control. In daily life, humans beings are, apparently without effort, able to generate complex and elegant movements of the hand and fingers, such as typing on keyboards, playing a musical instrument, or writing. 

In this paper we focus on the analysis of human hand movements during handwriting tasks, a subject which has been studied for many decades.

Screen shot 2015-12-15 at 1.04.49 PM

We present for the first time, at the best of our knowledge, a methodological approach based on the biomechanics of the human hand to compare two different input methods, i.e., the finger and the stylus, in digital handwriting tasks.

Performance of two input methods is evaluated and compared in terms of manipulability indexes in the task space, i.e., the ratio between a measure of performance (displacement, velocity, force in the task space) and a measure of effort in the input/joint space.

Screen shot 2015-12-15 at 1.14.02 PMBeside the mathematical analysis based on a biomechanical model of the hand, two experiments are presented, in which subjects were asked to write on a touchscreen using either their index finger, or a stylus.

The results (both analytical and experimental) assess that writing with the finger is more suitable for performing large, but not very accurate motions, while writing with the stylus leads to a higher precision and more isotropic motion performance.


D. Prattichizzo, L. Meli, and M. Malvezzi.
“Digital Handwriting with a Finger or a Stylus: a Biomechanical Comparison.”
IEEE Transactions on Haptics, 2015.
DOI: 10.1109/TOH.2015.2434812