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HugBot: A so robot designed to
give human-like hugs
Hooman Hedayati∗
Srinjita Bhaduri∗
hooman.hedayati@colorado.edu
srinjita.bhaduri@colorado.edu
University of Colorado
Boulder, CO
Tamara Sumner
Daniel Szafir
Mark D Gross
sumner@colorado.edu
daniel.szafir@colorado.edu
mdgross@colorado.edu
University of Colorado
Boulder, CO
∗
Both authors contributed equally to this re-
search. ABSTRACT
As robots increasingly enter our daily lives, there is a need to understand how to design robots capable
of emotional interaction with humans, especially children, due to their sensitivity and vulnerability.
For example, robots that provide children with social and emotional support might be more eective
at also helping children develop cognitive abilities, rather than designing robots that focus solely on
helping children acquire cognitive skill. In this paper, we examine the design of robots that can provide
human-like hugs as a particular form of social and emotional support. We first discuss the need to
design robots that can interact emotionally with children. Then, we present the development of a
shirt augmented with pressure sensors used to collect data on how humans hug each other. Finally,
we detail the design of “Hugbot”, a so robot that could use this data to give human-like hugs, and
discuss our planned future work on this system.
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IDC ’19, June 12–15, 2019, Boise, ID, USA
©2019 Association for Computing Machinery.
ACM ISBN 978-1-4503-6690-8/19/06. . . $15.00
hps://doi.org/10.1145/3311927.3325332
556
HugBot: A so robot designed to give human-like hugs IDC ’19, June 12–15, 2019, Boise, ID, USA
CCS CONCEPTS
•Computer systems organization →Robotics
;
•Human-centered computing →
Interaction
design; Collaborative interaction.
KEYWORDS
So robots; Human-like hugs; Social robots; Child-robot interaction
ACM Reference Format:
Hooman Hedayati, Srinjita Bhaduri, Tamara Sumner, Daniel Szafir, and Mark D Gross. 2019. HugBot: A so
robot designed to give human-like hugs. In Interaction Design and Children (IDC ’19), June 12–15, 2019, Boise, ID,
USA. ACM, New York, NY, USA, 6 pages. hps://doi.org/10.1145/3311927.3325332
INTRODUCTION
The rise in technologies, especially in the area of robotics, is leading to a rise in aordable robots for
families, such as Roomba and Sphero robots. Moreover, there is a trend in developing social home
robots to assist children in a variety of tasks such as developing and improving motor skills, verbal
skills, creativity, etc. Most existing work involving social robots focusew only on the task e.g., ways to
help a child through storytelling [
9
], act as a companion to learn English as a second language [
8
], or
even as informants for young children [
3
]. These eorts are valuable by themselves but we believe
children may learn beer if they can emotionally connect to their tutor or companion. Research shows
that teachers with social-emotional skills have beer influence on their students’ learning [
7
] but
when there is still much to be explored on how robots with such skills impact children’s behavior or
learning. The lack of knowledge in this area is due to the relatively new body of research that looks at
ways to develop robots that can eectively provide social and emotional support. One such area is
the interaction of robots and humans through hugs.
Hugs are a natural and intuitive way of expressing aection and giving a hug is an expression that
comes almost instinctively for some people, while others feel uncomfortable in giving hugs because of
the complex series of interactions involved. First, a “good” hug involves proper positioning of the arms
and hands and torso, then one must be aware of the appropriate amount of force to use, and finally
understand when is the right moment to let go [
2
]. It is a two-way interaction between huggee and
hugger. Researchers have studied how robots could engage in giving hugs, from using a robot-like
design called the “Hug” to give “tele-hugs” [
5
], to acting as a companion inspired by animal therapy to
promote the overall health of an individual [
11
], or even using personal robots to give hugs to adults
for emotional support [
2
]. However, most previous research focuses on the robots instead of the users
i.e., the robot initiates the hugs and opens and closes its arms to give a hug, lacking a consideration of
when the user wants to let go or if the hug is suicient for providing emotional support. More research
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HugBot: A so robot designed to give human-like hugs IDC ’19, June 12–15, 2019, Boise, ID, USA
is needed to explore ways to train a robot to understand these challenges and provide emotional
support to children. Children are sensitive to hugs and by learning how to give a good hug they might
learn an important social skill from a robot and be more socially engaged with their parents and peers
[
12
]. Bearing in mind the process of a “good” hug, we designed HugBot: a so-robot that can give
human-like hugs to users, especially children. In this paper, we describe background research and our
approach for designing the HugBot. First, we lay out the steps to design a custom sensory t-shirt to
measure how humans hug each other, e.g., how to initiate hug, aachment-detachment time, etc.
Then, we discuss the design of HugBot (see Figure 1), and finally, we share our findings and elaborate
our future plans to collect data to train the HugBot to give human-like hugs.
Figure 1: A child geing hugged by the
HugBot
RELATED WORK
We designed the HugBot in consideration of prior work in two research areas: robots as social agents
and the need for designing so robots to provide more human-like interactions.
Robots as social agents
Research has shown that children tend to perceive robots as life-like characters and with extended
interaction the relationship evolves to the point that children see robots as their peers [
6
]. As a result,
researchers have suggested the need to create robots that are engaging and interact continuously
with humans. In the case of children, robots serve as tutors, therapeutic assistants, or toys [
6
]. In
exploring these use cases, researchers have developed robots that express emotions in a variety of
ways, for example through eye gaze or gestures [
3
]. Although dierent social-emotional interactions of
robots have been studied, comparatively less work has explored the impact of the robot on children’s
learning to actively engage in such interactions. Researchers have postulated that this could advance
the field of child-robot interaction [
1
]. In this work, we are interested in supporting children’s learning
of social and emotional skills, such as giving and receiving hugs, and ways to use this learning in
other aspects of day-to-day interactions.
Figure 2: Design of sensory shirt: contains
a shirt with 8 pressure sensors that uses
velostat to measure the pressure and alu-
minium foil to make the sensors conduc-
tive
So robots to support human-like interactions
Interactive robots are being used in providing physical, educational and therapeutic assistance in
schools, homes, and hospitals [
5
]. Robots with animal-like appearances, such as the robotic dog AIBO,
can be an important factor in providing tangible interactions and developing a sense of emotional
aachment [
13
]. PARO, a robotic baby harp seal, has been used to help reduce agitation and improve
mood states in people with dementia [
4
]. Others have designed so robots that react to touch, like
the Huggable [
11
], which can motivate children, or like the HuggieBot [
2
], which can engage adults in
aectionate behavior such as cuddling or hugging. Additionally, Disney plush toys or stued animals
are being used by researchers to study the amount of pressure children can exert while giving hugs,
558
HugBot: A so robot designed to give human-like hugs IDC ’19, June 12–15, 2019, Boise, ID, USA
in order to design interactive robots [
10
]. Our work contributes to this area through the design of a
human-size so robot that supports opportunities for social and emotional skill enhancement.
Figure 3: Prototype of a 3D printed arm
with 3 joints and a fixed part on which the
other joints rest
SYSTEM DESIGN
Our system consists of 3 components: 1) a sensory shirt to study hugs, 2) robotic arms to manipulate
the hug, and 3) a panda-like stued animal, which hosts all the sensors and actuators.
Design of a sensory shirt
To execute a realistic hug, it is necessary to study how people give and get hugs. It is also important
to describe a hug by features or aributes so that it can measured and emulated. We identify two
features to describe a hug. First, “engaged body parts”, a vector of n bits where n is the number of
sensors, and each bit represents whether the relevant sensor is sensing pressure. Second, “duration”, is
the total aachment-detachment time, starting when one of the sensors show a number more than
the threshold (e.g. in our application it is 0.12) and ending when all the “engaged body parts” vectors
are less than the same threshold. We designed a custom sensor shirt, consisting of 8 pressure sensors
(4 on the chest and 2 on each arm) that can record the amount of pressure exerted to dierent parts
of the chest and arm, the aachment-detachment time, and which parts of body are involved during
the hug (see Figure 2). A preliminary study with volunteers provided an initial understanding of the
data. We used these data to control and actuate the robotic arm to imitate a hug. In the future, we
plan to collaborate with local primary schools to complete a formal user study with children. We
used the gathered data in two ways, first for classifying the dierent type of hugs, and second for
reinforcement learning, to control the robot arm so that it can give realistic hugs.
Design of a so-robotic arm
To design a proof-of-concept arm, we used cardboard to develop arms with dierent degrees of
freedom (DOF) to determine a design that supports a flexible arm that can bend freely around an
object. These parts are still being developed and we need more data to accurately classify hugs.The
Figure 4: Design of HugBot’s arm using
foam sponge and strings
robotic arm should be able to completely grasp the chest and back with an adjustable pressure similar
to human arms when humans hug each other. Aer several iterations, we found that an arm with
3 joints provides a suitable trade-o between arm complexity and flexibility. Next, we 3D printed a
variety of joints for the arms to test possible shapes (see Figure 3). Through this process, we determined
that each joint should have a curvature of at least 30 degrees. From the 3D printed joints we observed
that for safety, it was essential to make the material for the arms soer, as we did not want HugBot
to exert an uncomfortable amount of pressure on the person it was hugging. In the final design, the
arms were made using foam sponge. As shown in Figure 4, it consisted of 6 identical pieces roughly
quarter-circle shape (15cm x 10cm x 5cm). Strings were used to keep the arms straight, with one end
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HugBot: A so robot designed to give human-like hugs IDC ’19, June 12–15, 2019, Boise, ID, USA
fixed to the end of the arm, while the other side was connected to a servo motor. Rubber bands were
Figure 5: The T-shape structure used for
making the backbone of HugBot
used to keep the arms open by default. The arms were aached to a T-shaped wooden structure,
which acted as a backbone for the robot (Figure 5). The actuation of the arms were such that the
entire arms bend on the pulling and releasing of two strings aached to a pulley that go all the way
through both the arms. To automate this process, a stepper motor was added to the T-shape structure
and it completed majority of the Hugbot design.
Figure 6: A panda shaped stued toy we
used for creating the HugBot
Choice of so robot
There are multiple challenges to choose the right robot body for this project. It is essential that the
appearance of the robot be acceptable to children. No maer how well the hugging part of the robot
works, if the robot itself is not appealing (e.g., scary, too big, etc.), children will not use it. We opted
for a zoomorphic appearance, rather than a humanoid morphology to avoid uncanny valley eects.
As we wanted to put the arm and actuators inside the body, the choice of using a stued animal
was promising. We decided to use a panda stued animal that is visually appealing and mimics the
common notion of a stued bear with which many children are familiar (Figure 6). As elementary
school children are the main target of this research, we decided to use a stued animal with 1 meter
height, roughly mimicking the height of the children.
DESIGN IMPLICATIONS AND FUTURE WORK
This paper presents ongoing work on HugBot, a hugging robot that gives human-like hugs. The aim
of designing such a robot is to teach social skills to children through emotional interactions like hugs.
To test the feasibility of our design we pilot tested it with dierent users. The sensor-shirt was tested
by members from our research group and we noted changes necessary in order to eectively collect
data, such as increasing the surface area of the 8 pressure points and making the pressure points
more continuous instead of separating them from one another. We presented our work at a research
expo where child visitors interacted with the HugBot (see Figure 1). From our observations we saw
that robots with zoomorphic appearance keep children more engaged, and that HugBot could be used
as a means to teach social skills to children. Our system design and initial tests suggest that there are
dierent types of hugs (e.g., between two friends, or between a parent and a child). To design a robust
system that mimics these types of human hugs, intensive user studies need to be conducted with
children to train the robot. As part of our future work, we will test the sensor-shirt and the robotic
arms with children and their parents and peers, and record types of hugs. Using these data, we plan
on implementing machine learning techniques to train the robot to give dierent hugs and enable
more social interaction with children. Thus, we envision all the parts of our system to be integrated
into a HugBot design that can help children learn about social skills like hugs and it comfortable for
them to interact with family and peers.
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HugBot: A so robot designed to give human-like hugs IDC ’19, June 12–15, 2019, Boise, ID, USA
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