D
Computer Technology and Application 4 (2013) 569-574
DAVID
PUBLISHING
Remote-Controlled Ambidextrous Robot Hand Concept
Emre Akyürek, Alexandre Dilly, Fabrice Jourdan, Zhu Liu, Souraneel Chattoraj, Itziar Berruezo Juandeaburre,
Michel Heinrich, Leonid Paramonov, Peter Turner, Stelarc and Tatiana Kalganova
School of Engineering and Design, Brunel University, Uxbridge, Middlesex UB8 3PH, UK
Received: October 08, 2013 / Accepted: October 25, 2013 / Published: November 25, 2013.
Abstract: In the development of robotic limbs, the side of members is of importance to define the shape of artificial limbs and the range
of movements. It is mainly significant for biomedical applications concerning patients suffering arms or legs injuries. In this paper, the
concept of an ambidextrous design for robot hands is introduced. The fingers can curl in one way or another, to imitate either a right
hand or a left hand. The advantages and inconveniences of different models have been investigated to optimise the range and the
maximum force applied by fingers. Besides, a remote control interface is integrated to the system, allowing both to send commands
through internet and to display a video streaming of the ambidextrous hand as feedback. Therefore, a robotic prosthesis could be used
for the first time in telerehabilitation. The main application areas targeted are physiotherapy after strokes or management of phantom
pains for amputees by learning to control the ambidextrous hand. A client application is also accessible on Facebook social network,
making the robotic limb easily reachable for the patients. Additionally the ambidextrous hand can be used for robotics research as well
as artistic performances.
Key words: Robot hand, pneumatic muscles, remote platform, video streaming, telerehabilitation, hand recognition.
1. Introduction
The aim of the project is to design an
anthropomorphic ambidextrous robotic hand, actuated
by PAMs (pneumatic artificial muscles) and
controllable via a remote platform over internet using
hand gesture recognition through a webcam (Fig. 1).
Although a number of dexterous robot hands have
been developed over last decade, none of them
considered the possibility of an ambidextrous design,
with fingers performing both in “left hand” and “right
hand” behaviour, bending in one way or another to
have both a left and a right hand in a single
architecture. Consequently, the design allows
significant reduction of the required resources for its
application areas, such as rehabilitation and
physiotherapy after strokes. Phantom limb pain after
amputation could also be eased interacting with the
ambidextrous hand, as the movements may be
Corresponding author: Emre Akyürek, Ph.D. student,
research field: electronic and computer engineering. E-mail:
emre.akyurek@brunel.ac.uk.
interpreted as those of the missing limb. The
ambidextrous hand is also accessible from Facebook
social network to facilitate its access for the patients.
The objectives of the project included both the
design of ambidextrous fingers and the creation of a
remote control interface. Both of them are introduced
in this paper. The content of which is organized as
follow: Section 2 discusses different finger prototypes
tested and presents experimental data collected for
each phalange. Section 3 introduces the control theory
used to control the ambidextrous hand movements.
Section 4 describes the implementation of the remote
control platform and the video streaming of the robot
hand. Section 5 gives a conclusion. Finally, Section 6
presents applications under development.
Fig. 1
System architecture.
Remote-Controlled Ambidextrous Robot Hand Concept
570
2. Prototypes of Ambidextrous Fingers
change for the ambidextrous design, all the tests have
been focused on flexion/extension over a first phase.
2.1 Outline of the Research
Human fingers can make two kinds of antagonist
movements: flexion and extension, or abduction and
adduction. Flexion and extension control the angular
displacement of the three phalanges of a finger, which
means as many DOF (degrees of freedom). Abduction
and adduction imply lateral rotations of a whole finger
and constitute another DOF, which makes a total of
four distinct DOFs per finger [1]. These four DOFs
must be reproduced to obtain a robotic model as close
as possible to a human hand. As abduction and
adduction are not essential for a number of
applications, many dexterous hands have been
developed without taking them into account [2], [3].
Limiting the number of DOFs allows both easing the
control of the structure and reducing the number of
needed actuators. According to the first investigations,
the abduction/adduction of the whole hand can be
simulated with two PAMs spreading the five fingers or
bringing them closer at the same time. In addition to
these movements, using four PAMs to control the
flexion/extension of each finger would make a total of
22 PAMs for a robot hand of 16 DOFs and for which
the range is twice bigger than the one of a human hand
[4]. As showed in Table 1, it is current for dexterous
hands to use even more PAMs to imitate human
gestures.
Given
that
the
main
difference
with
the
ambidextrous hand is the range of fingers, the ability to
2.2 Results Obtained with Different Models
The tests have been made with standard PAMs, used
to control classic robot hand designs. As human distal
and middle phalanges do not move independently, a
first pair of antagonist PAMs is used to drive them
together while a second pair is connected to the
proximal phalanges. The tests are done with 150 mm
PAMs for the distal phalanges and 122 mm PAMs for
the proximal phalange, contracting with compressed
air at a maximum pressure of 3.5 bars.
Several designs have been investigated to maximise
the phalanges range and reach an ambidextrous
behaviour. Design A, shown in Fig. 2, consists in
coupling two pulleys of different diameters at joint
levels. Therefore, for the rotation of the first pulley
around a distance 𝑑0 with a force 𝐹0 , the second
pulley rotates around a distance 𝑑1 applying a force
𝐹1 on the following tendon, theoretically increasing
the range by the ratio 𝑑1 /𝑑0. Design B, also illustrated
in Fig. 2, consists in wrapping the tendons around the
pulley of the second joint, to prevent any looseness of
tendons during the rotation of the phalanges.
The performances of designs A and B are gathered in
Table 2, which indicates the maximum angles reached
by the metacarpo-phalangeal joint (MCP), the
proximal interphalangeal joint (PIP), and the distal
interphalangeal joints (DIP), as well as the maximum
forces applicable by their respective phalanges, both
cover such a large angle is the main point investigated
in this paper. As the
abduction/adduction does not
Table 1 Comparison between PAMs and DOFs of several
robot hands.
Robotic hands
J. Sancho-Bru et al, 2001[5]
D. Wilkinson et al, 2003 [6]
Y. Honda et al, 2010[7]
Festo, 2012 [8]
Shadow Robot, 2013 [9]
Number of
PAMs
25
31
25
26
40
Number of
DOFs
20
N/A ~ 20
17
N/A ~ 20
24
(a)
(b)
Fig. 2
Tendon routings of ambidextrous fingers
prototypes, where (a) is Design A and (b) is Design B.
Remote-Controlled Ambidextrous Robot Hand Concept
571
Table 2 Experimental data obtained with designs A and B.
Models
Design A
Design B
Joints
MCP
PIP
DIP
MCP
PIP
DIP
Max. angles
reached (°)
Left
Right
85
80
80
85
40
43
84
82
70
71
52
55
Max. forces
applied (N)
Left
Right
52
47
9
10
3
3
51
49
12
13
0
0
for their left and right positions (the maximum forces
have been collected applying pressure on the phalanges
until their maximum angles decrease of 10°).
As it can be observed, both of these designs reach
correct left and right positions. However, none of them
apply enough force on the distal phalange to allow a
proper control of the finger or to grab a light object. For
the Design A, it is due to the loss of force caused by the
coupled pulleys. Indeed, because of the range increase,
the force provided by the PIP joint is 𝐹1 = 𝐹0 ∗ 𝑑0 /𝑑1.
Other tests have been done also coupling the pulleys at
the DIP joint, but the force was so weak it even
decreased the maximum angles reached. Design B has
the same inconvenience because of the friction force of
the wrapped tendons.
To overcome these defects, the Design C, illustrated
in Fig. 3, includes intermediate pulleys which, as it is
for Design B, avoid the tendons to get loose, but this
time preserving most of the tendon force. The
movements of middle and distal phalanges are
synchronised because of torsion springs put under the
PIP and DIP joints. The same experiments are repeated
with Design C, using different size of pulleys at the
joints levels. The data collection is provided in Table 3.
The better pulley configuration to optimise the
angle/force ratio is 15.34 mm for the MCP joint and
7.71/2.95 mm for the PIP/DIP joints. It is seen that the
maximum angles can be increased using smaller
pulleys, but then the loss force becomes too significant.
As a conclusion, even though the experiments are
done with the standard PAMs, the ambidextrous design
reaches ranges quite close to other models. The ranges
reached for right hand behaviour are indicated in
(a)
(b)
Fig. 3 Tendon routing of Design C, (a) is a left position and
(b) is a right position.
Table 3 Experimental data obtained with different pulleys
configuration of Design C.
Joints
Pulleys’
diameter (mm)
MCP
MCP
MCP
PIP/DIP
PIP/DIP
PIP/DIP
PIP/DIP
23.81
15.34
7.71
23.81/15.34
15.34/15.34
7.71/2.95
2.95/2.95
Max. angles
reached (°)
Left
Right
58
54
85
80
90
90
54/10 60/19
73/29 77/36
75/51 80/55
88/68 90/72
Max. forces
applied (N)
Left
Right
91
86
53
49
38
31
59/4 62/11
30/18 35/22
21/10 23/13
12/3
15/4
Table 4 Comparison of joints maximum angles (°).
Joints Ambi-hand
MCP
80
PIP
80
DIP
55
Shadow Hand [10]
90
90
90
ACT Hand[11]
90
110
70
Table 4 for each joint, including comparisons with the
Shadow Hand and the ACT Hand, both known as
belonging to the most advanced robot hands in the
world.
It is noted that the ambidextrous hand can reach
better performance using more suitable PAMs.
However, the range was large enough to proceed with
first tests using control theory.
3. Control of the Hand
The use of PAMs instead of motors allows more
flexibility to the overall behaviour of the system.
Contracting or relaxing according to the amount of
compressed air getting in or out, their lengths variation
is used to interact with the endoskeleton of the hand,
such as real human muscles. However PAMs are rarely
used to control robotic structures because of the
572
Remote-Controlled Ambidextrous Robot Hand Concept
non-linearity existing between the inflation of the PAM
and the force provided [12], [13].
The airflow is controlled from valves opening or
closing for a specific time depending on the input
voltage they receive. Voltages’ switching is
commanded by a PIC microcontroller that converts the
control functions into analog signals. The delays
between these signals define the different contraction
rates of PAMs. Specific gestures of the ambidextrous
hand are calculated according to the parallel form of a
PID (proportional integrative derivative) control, for
which the equation is:
𝑡
𝑑
𝑢(𝑡) = 𝐾𝑝 𝑒(𝑡) + 𝐾𝑖 ∫ 𝑒(𝜏)𝑑𝜏 + 𝐾𝑑 𝑒(𝑡)
𝑑𝑡
0
The error 𝑒(𝑡) is determined according to the
difference between the target value and the current
data feedback. The output 𝑢(𝑡) is sent to valves,
making the PAMs react to reduce the error 𝑒(𝑡) until
the sensors return the target values. Appropriate
constants 𝐾𝑝 , 𝐾𝑖 and 𝐾𝑑 allow the system to reach
the target in a faster way, minimizing the overshoots
and the number of oscillations.
The PID control allows dealing with several
parameters of the system such as the joints’ angles, the
force at the fingertips or the PAMs’ pressure.
As the commands must be received from internet,
the control functions are recorded on the server that
runs on the host computer. The hand movements can be
watched online because of the video feedback
integrated in the remote control platform.
formats. The more suitable video format to implement
is MJPEG, because it is compatible with all web
browsers and can be streamed, with an appropriate
configuration, at a maximum of 10 Mbps of bandwidth,
which is available in most of internet connections.
The stream is sent using a HTTP server that deals
with HTTP requests, sending back the appropriate
HTTP headers and XML messages.
All these communication processes are integrated in
the server, the architecture of which is shown in Fig. 4.
It allows the server to communicate with its two
different clients. The first one is a Web application,
easily accessible from the ambidextrous robot hand’s
website or from its Facebook application. The video
control options are stored in XML files, got and parsed
with Java script.
Fig. 4 Server architecture.
4. Remote Control Platform
The video streaming and the communication
between the robotic limb and its operator are made
possible by the development of a client-server interface
on a Linux platform. The video is collected from an
embedded webcam using the USB Video Class (UVC)
protocol and the Linux UVC driver [14], which have an
interface for the Video For Linux (V4L) library [15].
The V4L library communicates with all input devices
and allows the operating system to decode some video
Fig. 5 Finger design driven by 2 passive and 3 active tendons.
Remote-Controlled Ambidextrous Robot Hand Concept
The second one is software developed on the
cross-platform library Qt4 [16], which would allow
communicating with the robot hand using other
hardware devices, such as EMG signals. It includes a
webcam control interface, webcam’s images renderer
and the robot hand control interface. Both of these
applications are based on TCP/IP protocol. Specific
commands can be selected from their respective
graphical user interfaces and sent to the server as XML
Http Request objects either from Java script or from Qt
software.
5. Conclusions
The testing of first prototypes has proved that an
ambidextrous behaviour is possible for a robot hand.
However, because of the range’s limitations and the
weak grasp of current designs, it has been decided to
use longer PAMs, able to inflate at a pressure up to
eight bars, to have a more accurate control of the hand.
As for the remote control platform, its functioning has
been proved by controlling ambidextrous prototypes
from a distance.
6. Future Plan
Independent prototypes are still tested and modified
recognition. Using previous research in this area [17],
the head region is currently recognized with the help of
the cascade classifier algorithm from OpenCV [18]. A
histogram of colours to repartition is created from this
region and used to find skin of the same colour to
identify the hand. This application has been integrated
in a browser plugin downloadable from the
ambidextrous hand website. Contrary to Flash and Java
applications, its use implies native code for every
operating system, which avoids respectively a low
power consumption for image processing and
interpretation tasks through Java Virtual Machine.
Developed with the NPAPI routines [19], the plugin
uses a dynamic library which allows it to deploy very
fast. However, the fingers tracking part has not finished
being developed yet. Once done, the patient’s
movements would then be imitated on the robotic
model as a hand of the same side or on the opposite
one, to allow mirroring movements.
Acknowledgments
This research was partially assisted by Shadow
Robot Company Ltd (London, UK), which provided a
number of pneumatic and electronic devices, as well as
hardware to control the first prototypes.
according to their kinematic performances. To reduce
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