835 research outputs found
Modeling and Control of a novel Variable Stiffness three DoF Wrist
This paper presents a novel design for a Variable Stiffness 3 DoF actuated
wrist to improve task adaptability and safety during interactions with people
and objects. The proposed design employs a hybrid serial-parallel configuration
to achieve a 3 DoF wrist joint which can actively and continuously vary its
overall stiffness thanks to the redundant elastic actuation system, using only
four motors. Its stiffness control principle is similar to human muscular
impedance regulation, with the shape of the stiffness ellipsoid mostly
depending on posture, while the elastic cocontraction modulates its overall
size. The employed mechanical configuration achieves a compact and lightweight
device that, thanks to its anthropomorphous characteristics, could be suitable
for prostheses and humanoid robots.
After introducing the design concept of the device, this work provides
methods to estimate the posture of the wrist by using joint angle measurements
and to modulate its stiffness. Thereafter, this paper describes the first
physical implementation of the presented design, detailing the mechanical
prototype and electronic hardware, the control architecture, and the associated
firmware. The reported experimental results show the potential of the proposed
device while highlighting some limitations. To conclude, we show the motion and
stiffness behavior of the device with some qualitative experiments.Comment: 13 pages + appendix (2 pages), 19 figures, submitted to IJR
Soft Robotics: Design for Simplicity, Performance, and Robustness of Robots for Interaction with Humans.
This thesis deals with the design possibilities concerning the next generation of advanced Robots. Aim of the work is to study, analyse and realise artificial systems that are essentially simple, performing and robust and can live and coexist with humans. The main design guideline followed in doing so is the Soft Robotics Approach, that implies the design of systems with intrinsic mechanical compliance in their architecture. The first part of the thesis addresses design of new soft robotics actuators, or robotic muscles. At the beginning are provided information about what a robotic muscle is and what is needed to realise it. A possible classification of these systems is analysed and some criteria useful for their comparison are explained. After, a set of functional specifications and parameters is identified and defined, to characterise a specific subset of this kind of actuators, called Variable Stiffness Actuators. The selected parameters converge in a data-sheet that easily defines performance and abilities of the robotic system. A complete strategy for the design and realisation of this kind of system is provided, which takes into account their me- chanical morphology and architecture. As consequence of this, some new actuators are developed, validated and employed in the execution of complex experimental tasks. In particular the actuator VSA-Cube and its add-on, a Variable Damper, are developed as the main com- ponents of a robotics low-cost platform, called VSA-CubeBot, that
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can be used as an exploratory platform for multi degrees of freedom experiments. Experimental validations and mathematical models of the system employed in multi degrees of freedom tasks (bimanual as- sembly and drawing on an uneven surface), are reported.
The second part of the thesis is about the design of multi fingered hands for robots. In this part of the work the Pisa-IIT SoftHand is introduced. It is a novel robot hand prototype designed with the purpose of being as easily usable, robust and simple as an industrial gripper, while exhibiting a level of grasping versatility and an aspect comparable to that of the human hand. In the thesis the main theo- retical tool used to enable such simplification, i.e. the neuroscience– based notion of soft synergies, are briefly reviewed. The approach proposed rests on ideas coming from underactuated hand design. A synthesis method to realize a desired set of soft synergies through the principled design of adaptive underactuated mechanisms, which is called the method of adaptive synergies, is discussed. This ap- proach leads to the design of hands accommodating in principle an arbitrary number of soft synergies, as demonstrated in grasping and manipulation simulations and experiments with a prototype. As a particular instance of application of the method of adaptive syner- gies, the Pisa–IIT SoftHand is then described in detail. The design and implementation of the prototype hand are shown and its effec- tiveness demonstrated through grasping experiments. Finally, control of the Pisa/IIT Hand is considered. Few different control strategies are adopted, including an experimental setup with the use of surface Electromyographic signals
A Novel Skin-Stretch Haptic Device for Intuitive Control of Robotic Prostheses and Avatars
Without proprioception, i.e., the intrinsic capability of a body to perceive its own limb position, completing daily life activities would require constant visual attention and it would be challenging or even impossible. This situation is similar to the one experienced after limb amputation and in robotic tele-operation, where the natural sensory-motor loop is broken. While some promising solutions based on skin stretch sensory substitution have been proposed to restore tactile properties in these conditions, there is still room for enhancing the intuitiveness of stimulus delivery and integration of haptic feedback devices within user's body. To contribute to this goal, here, we propose a wearable device based on skin stretch stimulation, the Stretch-Pro, which can provide proprioceptive information on artificial hand aperture. This system can be suitably integrated in a prosthetic socket or can be easily worn by a user controlling remote robots. The system can imitate the stretching of the skin that would naturally occur on the intact limb, when it is used to accomplish motor tasks. Two versions of the system are presented, with one and two actuators, respectively, which deliver the stretch stimulus in different ways. Experiments with able-bodied participants and a preliminary test with one prosthesis user are reported. Results suggest that Stretch-Pro could be a viable solution to convey proprioceptive cues to upper limb prosthesis users, opening promising perspectives for tele-robotics applications
Hap-Pro: a wearable haptic device for proprioceptive feedback
Objective: Myolectric hand prostheses have reached a considerable technological level and gained an increasing attention in assistive robotics. However, their abandonment rate remains high, with unintuitive control and lack of sensory feedback being major causes. Among the different types of sensory information, proprioception, e.g. information on hand aperture, is crucial to successfully perform everyday actions. Despite the many attempts in literature to restore and convey this type of feedback, much remains to be done to close the action-perception loop in prosthetic devices. Methods: With this as motivation, in this work we introduce HapPro, a wearable, non-invasive haptic device that can convey proprioceptive information for a prosthetic hand. The device was used with an under-actuated, simple to control anthropomorphic robotic hand, providing information on the level of hand aperture by mapping it to the position of a wheel that can run on the user's forearm. Tests with 43 able bodied subjects and one amputee subject were conducted in order to quantify the effectiveness of HapPro as a feedback device. Results: HapPro provided a good level of accuracy for item discrimination. Participants also reported the device to be intuitive and effective in conveying proprioceptive cues. Similar results were obtained in the proof-of-concept experiment with an amputee subject. Conclusions: Results show that HapPro is able to convey information on the opening of a prosthetic hand in a non-invasive way. Significance: Using this device for proprioceptive feedback could improve usability of myoelectric prostheses, potentially reducing abandonment and increasing quality of life for their users
Dexterity augmentation on a synergistic hand: the Pisa/IIT SoftHand+
Soft robotics and under-actuation were recently demonstrated as good approaches for the implementation of humanoid robotic hands. Nevertheless, it is often difficult to increase the number of degrees of actuation of heavily under-actuated hands without compromising their intrinsic simplicity. In this paper we analyze the Pisa/IIT SoftHand and its underlying logic of adaptive synergies, and propose a method to double its number of degree of actuation, with a very reduced impact on its mechanical complexity. This new design paradigm is based on constructive exploitation of friction phenomena. Based on this method, a novel prototype of under-actuated robot hand with two degrees of actuation is proposed, named Pisa/IIT SoftHand+. A preliminary validation of the prototype
follows, based on grasping and manipulation examples of some object
A synergy-driven approach to a myoelectric hand
In this paper, we present the Pisa/IIT SoftHand
with myoelectric control as a synergy-driven approach for
a prosthetic hand. Commercially available myoelectric hands
are more expensive, heavier, and less robust than their bodypowered
counterparts; however, they can offer greater freedom
of motion and a more aesthetically pleasing appearance. The
Pisa/IIT SoftHand is built on the motor control principle of
synergies through which the immense complexity of the hand
is simplified into distinct motor patterns. As the SoftHand
grasps, it follows a synergistic path with built-in flexibility to
allow grasping of a wide variety of objects with a single motor.
Here we test, as a proof-of-concept, 4 myoelectric controllers:
a standard controller in which the EMG signal is used only as
a position reference, an impedance controller that determines
both position and stiffness references from the EMG input, a
standard controller with vibrotactile force feedback, and finally
a combined vibrotactile-impedance (VI) controller. Four healthy
subjects tested the control algorithms by grasping various
objects. All controllers were sufficient for basic grasping,
however the impedance and vibrotactile controllers reduced
the physical and cognitive load on the user, while the combined
VI mode was the easiest to use of the four. While these results
need to be validated with amputees, they suggest a low-cost,
robust hand employing hardware-based synergies is a viable
alternative to traditional myoelectric prostheses
Design and realization of the CUFF - clenching upper-limb force feedback wearable device for distributed mechano-tactile stimulation of normal and tangential skin forces
Rendering forces to the user is one of the main goals of haptic technology. While most force-feedback interfaces are robotic manipulators, attached to a fixed frame and designed to exert forces on the users while being moved, more recent haptic research introduced two novel important ideas. On one side, cutaneous stimulation aims at rendering haptic stimuli at the level of the skin, with a distributed, rather than, concentrated approach. On the other side, wearable haptics focuses on highly portable and mobile devices, which can be carried and worn by the user as the haptic equivalent of an mp3 player. This paper presents a light and simple wearable device (CUFF) for the distributed mechano-tactile stimulation of the user's arm skin with pressure and stretch cues, related to normal and tangential forces, respectively. The working principle and the mechanical and control implementation of the CUFF device are presented. Then, after a basic functional validation, a first application of the device is shown, where it is used to render the grasping force of a robotic hand (the Pisa/IIT SoftHand). Preliminary results show that the device is capable to deliver in a reliable manner grasping force information, thus eliciting a good softness discrimination in users and enhancing the overall grasping experience
Teleimpedance Control of a Synergy-Driven Anthropomorphic Hand
In this paper, a novel synergy driven teleimpedance
controller for the Pisa–IIT SoftHand is presented. Towards
the development of an efficient, robust, and low-cost hand
prothesis, the Pisa–IIT SoftHand is built on the motor control
principle of synergies, through which the immense complexity
of the hand is simplified into distinct motor patterns. As the
SoftHand grasps, it follows a synergistic path with built-in
flexibility to allow grasping of objects of various shapes using
only a single motor. In this work, the hand grasping motion
is regulated with an impedance controller which incorporates
the user’s postural and stiffness synergy profiles in realtime.
In addition, a disturbance observer is realized which estimates
the grasping contact force. The estimated force is then fedback
to the user via a vibration motor. Grasp robustness and
transparency improvements were evaluated on two healthy
subjects while grasping different objects. Implementation of
the proposed teleimpedance controller led to the execution of
stable grasps by controlling the grasping forces, via modulation
of hand compliance. In addition, utilization of the vibrotactile
feedback resulted in reduced physical load on the user. While
these results need to be validated with amputees, they provide
evidence that a low-cost, robust hand employing hardwarebased
synergies is a viable alternative to traditional myoelectric
prostheses
An instrumented manipulandum for human grasping studies
This work presents a novel haptic device to study human grasp, which integrates different technological solutions thus enabling, for the first time, to achieve: (i) a complete grasp characterization in terms of contact forces and moments; (ii) an estimation of contact point location for varying-orientation contact surfaces; (iii) a compensation of force/torque offsets and estimation of the mass and center of mass of the device, for different orientations and configurations in the workspace; (iv) different stiffness properties for the contact points, i.e. rigid, compliant non-deformable and compliant deformable, thus allowing to study the effects of cutaneous cues in multi-finger grasps. In addition, given the modularity of the architecture and the simple mechanism to attach/detach the contact modules, this structure can be easily modified in order to analyze different multi-finger grasp configurations. The effectiveness of this device was experimentally demonstrated and applications to neuroscientific studies and state of the art of devices for similar investigations are discussed in depth within the text
Preliminary results toward a naturally controlled multi-synergistic prosthetic hand
Robotic hands embedding human motor control
principles in their mechanical design are getting increasing
interest thanks to their simplicity and robustness, combined
with good performance. Another key aspect of these hands
is that humans can use them very effectively thanks to the
similarity of their behavior with real hands. Nevertheless,
controlling more than one degree of actuation remains a
challenging task.
In this paper, we take advantage of these characteristics in
a multi-synergistic prosthesis. We propose an integrated setup
composed of Pisa/IIT SoftHand 2 and a control strategy which
simultaneously and proportionally maps the human hand movements
to the robotic hand. The control technique is based on
a combination of non-negative matrix factorization and linear
regression algorithms. It also features a real-time continuous
posture compensation of the electromyographic signals based
on an IMU. The algorithm is tested on five healthy subjects
through an experiment in a virtual environment. In a separate
experiment, the efficacy of the posture compensation strategy is
evaluated on five healthy subjects and, finally, the whole setup
is successfully tested in performing realistic daily life activities
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