IEEE Robotics & Automation Magazine - September 2023 - 129

human spaces. The human-robot interaction (HRI) hand [32]
presents an anthropomorphic end effector as a research platform
for collaborative robotics that can be built for a lower
cost than acquiring a commercial gripper. A derivative version
of the adaptive anthropomorphic hand of OpenBionics [33]
aims to be capable of carrying out more dexterous manipulation
tasks with fingers that can also move in the abduction/
adduction direction. Human-like robot hands are also pivotal
to prosthesis hand development. Such hand designs are often
open sourced for affordability compared to commercially
available prostheses and provide a research platform for evaluating
control algorithms, human-machine interfaces, and
operation schemes in powered prosthetics. To achieve these
objectives, open prosthetic hand designs maintain a low complexity
of design so that the hands are easily reproducible. The
OpenBionics prosthetic hand [34] uses just a single actuator
with a lockable differential mechanism to permit locking different
fingers in position. Anthropomorphic hands such as the
Open Source Hand [35] can also be created with the aim of
serving as a testbed to implement different prosthetic control
strategies on a six-degree-of-freedom (6-DoF) hand. The PUT
hand [36] combines fully actuated and underactuated fingers
in its anthropomorphic design, with the goal of manipulating
elastic objects. Similarly, the Brunel hand [37] can be used as
a platform for researchers in prosthetics, grasping, manipulation,
and HRI. This hand is available for purchase from Open
Bionics Labs but can also be fabricated using the design files
provided by the developer.
Similar to prostheses, open source exoskeletons for arms and
hands serve to increase accessibility to wearable, assistive devices
for those who have lost some upper-limb functionality. The lowcost
ExoArm v2 [38] exoskeleton aims to assist elderly or disabled
individuals with lifting objects and with rehabilitation of arm
motion. Exoskeletons for hands or exogloves can restore grasping
capabilities and finger mobility in the hand [see Figure 2(c)]. The
exoglove in [39] can be either body powered or motor driven, and
Sparthan [40] features 3D-printed ring structures. These type of
hand exoskeletons are often tendon driven, but some have also
added pneumatic actuation for modulating stiffness and inflating
a telescoping thumb [25]. Linkage-based actuation is also
common in hand braces and orthoses, such as the purely passive
wrist-driven orthosis that was open sourced in [41] and inspired
the adapted motor-driven version [42]. Beyond assistive devices,
exogloves also have a lot of applications in virtual reality and haptics.
In [43] and [44], finger motions and pinch gestures are used to
manipulate objects in virtual reality and simulations. Exogolves
can be used to transmit haptic feedback to the wearer triggered
by a variety of sensors, such as underwater ultrasonic range data
indicated by micropumps varying pressure at the fingertips [45],
or spatial position observed through a camera translated to vibration
stimuli [46].
In comparison to robot hands, prostheses, and exogloves,
open source multi-DoF robot arms are less commonly shared,
likely due to the size and complexity of the whole arm design.
Larger arms capable of carrying heavier payloads would also
need components to be fabricated, using metal machining or
other manufacturing processes that may not be accessible to
many users. The Niryo One [26] [see Figure 2(d)], Thor robot
arm [47], and CM6-compliant arm [48] with six DoF attempt
to bridge the fabrication gap by requiring mostly 3D-printed
components. And other robot arms such as the OpenManipulator-X
[49] are made entirely from off-the-shelf components
from ROBOTIS. Neither of these robot arms have a payload of
more than 500-750 g. In comparison, the 3-DoF printed articulated
robotic arm (PARA) [50] and 5-DoF Dexter [51] robot
arms have higher payloads of 1-3 kg and use acrylic tubes and
carbon-fiber plates for structure, respectively. Still, larger 6- or
7-DoF robot arms are particularly absent from the open hardware
space. Although users might not be able to fabricate components
for heavier payload arms, open sourcing the design files
and releasing documentation still has the benefits of allowing
users to repair, modify, and upgrade the hardware, as outlined
previously in the " Characteristics of ORH " section.
SOCIAL ROBOTS
HRI is an active area of research in robotics, and social robot
platforms are a central apparatus that researchers have used
to test expressive gestures and behaviors in real-world experimental
settings. Commercially available products may not be
suitable to the type of empirical evidence researchers hope to
collect, and this could often require the researchers to develop
or adapt their own hardware. The MyKeepon project [52]
[see Figure 3(a)] modified an off-the-shelf toy product and
released a programmable, low-cost platform that could be
built and repaired by users, allowing even multiple instances
of MyKeepon robots to be deployed for comparative studies.
On the other hand, some HRI experiments may call for customized
and unique social robots.
The Open Source Social Robot Platform (OPSORO) [56]
allows the user to produce novel embodiments of social robots
from a set of modules atop a skeletal frame for an accelerated
design cycle. Users can incorporate different modules of the
platform to enact facial features and design distinct outer layers,
allowing for a wide variety of robots to be created with the
platform. In a similar vein, the Blossom social robot [53] can be
custom built with novel handcrafted exteriors and outfitted with
a range of crafted parts such that no two robots have to look
alike [see Figure 3(b)]. Both the internal and external structures
of Blossom are fabricated from soft materials to add compliance
in the natural motions of the robot. Soft actuators and compliant
mechanisms are also employed in the CASTOR social robot
[57]. CASTOR has a partially humanoid-like appearance and
is intended for use in therapy for children with autism spectrum
disorder. Humanoids deployed as social robots and beyond are
discussed in the next section in more detail. All of these open
social robot platforms can be constructed using inexpensive
materials and accessible components, and associated control
software and assembly instructions are made available for users
to implement the robots easily, such as the well-organized wiki
for CASTOR [58]. Social robots thus represent a model section
of the wider ORH community, where commercially available
products may not appropriately match the type of physical
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IEEE Robotics & Automation Magazine - September 2023

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