IEEE Robotics & Automation Magazine - September 2013 - 73

realization of the latest artificial hand, called the University of
Bologna Hand, version IV (UB Hand IV, see Figure 1), are
illustrated through a general overview of the main design
aspects and related technologies. This article aims at suggesting
some concrete solutions to the difficulties encountered so far.
Related Work and Possible
Directions for Improvement
Many anthropomorphic robot hands have already been
designed, often trying to replicate or enhance the specific
features of the human hand. With the exception of a few
direct-drive solutions, tendon transmissions are usually
preferred because of the technological problems in the integration of the driving system within the hand. For instance,
in the Utah/Massachusetts Institute of Technology robot
hand, two antagonistic tendons for each joint are used,
whereas in the Jet Propulsion Laboratories/Stanford hand,
an N + 1 tendon network was adopted to reduce the
amount of actuators. Later, the sheath-guided tendons were
adopted in the UB Hand III [4] and, recently, the
Deutschen Zentrums für Luft- und Raumfahrt (DLR)
developed a new tendon-driven robot hand with compliant
actuators [5]. It is also worth mentioning the Shadow Hand
as the only commercially available tendon-driven device. In
addition, during the last ten years, technological advancements have facilitated the development of modular hands
with integrated drive systems, such as the DLR Hand II [6]
or the Twendy-One Hand. This solution allows the minimization of space requirements and the potential installation of these hands as end-effectors in common industrial
arms. The great interest in the development of anthropomorphic robot hands is also due to their use as prostheses,
and several devices for this application have been developed, e.g., the Cyberhand [2] and the DLR/Harbin Institute
of Technology prosthetic hand [3].
There have been dozens of different design proposals,
which makes it difficult to compare and assess within this
wide field. Nonetheless, in the authors' opinions, the current design of robot hands is mainly based on methodologies inherited from conventional mechanics and robotics.
The current technology, in terms of materials, sensors, and
motors' dimensions and power, has somehow reached the
limits, as far as possible solutions that can be proposed following the conventional design approaches. A potential
direction of improvement is to seek alternative solutions
for the realization of the hand structure and the sensorimotor system that are simple and, possibly, reliable. In particular, the general goal of the design simplification and
optimization might be achieved through the following
driving issues:
● trying to reduce the assembly complexity by adopting
endoskeletal structures articulated by means of nonconventional joints, either sliding or compliant (see the section
"Design Solutions for the Finger Structure")
● actuating the joints by means of remotely located actuators,
with the tendon-based transmissions routed by sliding

Figure 1. The UB Hand IV prototype. (Photo courtesy of Gianluca
Palli at the Laboratory of Automation and Robotics of the
University of Bologna.)

(a)

(b)

(d)

(c)

Figure 2. The UB Hand study prototypes: (a) endoskeleton
principle (UB Hand III [4])-the outer layer hosts sensors and
interacts physically with the environment, (b) exoskeleton
principle (UB Hand II [7]), (c) finger with close-wound springs
CJs, and (d) fully integral finger. (Photo courtesy of Gianluca Palli
at the Laboratory of Automation and Robotics of the University of
Bologna.)

paths (sliding tendons) and integrated within the finger
structure (see the section "Tendons and Tendon Net")
september 2013

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