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The design of this innovative robotic hand, inspired to the human hand model, abandons design concepts based on exoskeletal structures, previously adopted by most of the existing robot hands, in favor of the adoption of the endoskeletal model. This goal requires the design of

  • an internal articulated framework (the "skeleton");
  • transmission elements routed along its surface (the tendons);
  • an external compliant cover (the ``soft tissues'') that hosts the sensory equipment and plays a crucial role in the interaction with the manipulated objects.
Different kinds of articulations may be considered for the design of an endoskeleton, and simplified structures based on compliant hinges have be investigated.
By a proper choice of materials and processes compliant hinges may be integrated into the rigid links, thus obtaining one-piece articulated structures that are compact, light, easy to be manufactured, simple to be integrated with external sensors and compliant covers
Last prototype of the UB Hand III.
UB Hand III endo-skeleton.

The finger is made of rigid elements (the phalanges) connected through elastic hinges that allow relative motion due to self-bending. This structure presents four joints:

  • proximal allows adduction-abduction (yaw) motion;
  • the intermediate and the distal ones allow finger bending.

Each joint is actuated by forces exerted on the phalanges by remotely actuated tendons, that slide inside routing paths along the finger structure and pass through the hinges along their bending axis. After early attempts to develop monolithic fingers with hinges and tendons integrated into a single item, this new version adopts different materials for the hinges, the phalanges structure
and the tendons. The way to route the tendon paths inside the finger has been considerably improved.

The inner structure of each finger is a continuous framework
obtained by plastic moulding with inclusion of the elastic
elements that form the hinges and work, at the same time, as routing paths of the tendons. In the present implementation hinges are made of steel spiral coils that are used also as sheath for tendon routing. This solution allows to avoid assembly operations and obtains a simplified structure with a reduced number of parts,
easy to be manufactured, cheap, yet fully efficient and compatible with the required functions. The distal hinge is not crossed by any tendon, while the hinges placed up-stream progressively see an increasing number of
crossing tendons. The result of such a design provides a reduced cross section, very suitable to be covered with a thick external compliant layer to reproduce the soft tissue of the human hand.



The proposed design shows great versatility and allows the
development of many alternative hand configurations with the the following important features:

  • Modularity. The hand is obtained repeating a modular finger built by low cost moulding process. The complexity of the system can be customized according to the needs of the application. For
    example, a three fingered device could be enough for easy grasping tasks, while in tele-operated space applications the use of five fingers could allow a good reproduction of the human hand dexterity.
  • Possibility to change the actual number of d.o.f. without changing the finger structure. The adopted kinematical configuration is suitable for a reduction of the number of d.o.f. by coupling some
    of the joints. This strategy, for example, may be applied to connect the distal and medial bending motion to mimic the human finger behavior. Furthermore, by adopting elastic coupling devices
    between the linked joints it is possible to obtain self-adapting grasping procedures. This configuration could be very interesting for prosthetic applications, that are strictly conditioned by low bulk and weight requirements and do not admit a large number of
  • Compatibility with any kind of linear actuation. The adopted finger design is not dependent on a particular kind of actuation and it is compatible with future availability of new actuators, e.g. artificial muscles.
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