22-11-2012, 04:08 PM
UTHM HAND: Performance of Complete System of Dexterous Anthropomorphic Robotic Hand
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Abstract
This paper describes a new robotic hand system working under master slave configuration. The slave robotic hand is tele-operated by a
master glove that a human operator can wear. The wireless tele-operation is being done by using Bluetooth as the communication channel
between master and slave. The angle information of the operator’s hand is transferred via this Bluetooth channel by embedding
BendSensors in the glove. BendSensors act like a potentiometer strip and detects the movement of every joint present in the hand. The
slave robotic hand, on reception of this angle information mimics the movement of human operator. The UTHM robotic hand is a multi
fingered dexterous anthropomorphic hand. The hand comprises of five fingers (four fingers and one thumb), each having four degrees of
freedom (DOF), which can perform flexion, extension, abduction, adduction and also circumduction. For the actuation purpose,
pneumatic muscles and springs are used. The paper exemplifies the design for the robotic hand and provides the torque modelling and
torque produced at each finger joint of the robotic hand. It also discusses different robotic hands that have been developed before date.
Introduction
Robots have become an integral part of modern human life. With every passing year the population of robots is being
increased. The industry has replaced a large number of human workers with lesser number of robots on the grounds of economy and efficiency. A robot is a modern version of slave, which perform any task in its capacity satisfying the old
human instinct to rule. A robot follows the command as ordered by the human master. Therefore the humans can still enjoy
mastering a dumb but efficient slave under their supremacy.
The intelligence of humans has been linked to the hands. Aristotle and Anaxagoras had been discussing this association
hundreds of years ago [1]. Humans are the only specie that has been gifted with this kind of dexterous hands, where the
universe of full of various species. These hands are capable of doing so many tasks in our routine like dexterously handling
different things and even sensing. Therefore this has been discussed from long to be one of the reasons that humans are so
intelligent.
The human hand consists of fifty four bones whereas the complete body of an adult human contains two hundred and six
bones [2], which is around 26% of the total human bones. When discussing the robotic hands, the segments or parts that join
together to build the robotic hand are mostly less than this number. Even after reaching this number, it cannot compete with
the human hand in a broad range of tasks. The reason is the structure of human hand and the material used in human hand
that cannot be compared by the material available for robotic hands. The toolset and materials of Mother Nature is far
advance than any of the latest technology.
Literature Review
The research on robotic hands is being done for a long period of time. Looking back to the history of robotic hands, in
1961 Heinrich Ernst developed for the first time, the MH-1 a computer operated mechanical hand at MIT [4]. This hand was
a gripper that used two fingers to pick and hold some blocks using electric motors as actuators and touch sensors for the
object identification.
Grippers are mostly application specific robots and they do not tend to copy the complete properties and characteristics
of actual human hand. The finger count for the grippers ranges from two to three fingers, which results in a low DOF that
does not make the robot hand able to act dexterously. Theoretically the least number of DOF to achieve dexterity in a
robotic hand with rigid, hard-finger, non-rolling and non-sliding contacts, is nine [5]. The proof for this theory was the
development of Stanford/JPL hand.
Many research works had been done on grippers [6], [7], [8], [9], [10], [11], [12] and many companies started
production of grippers. Universities, automotive companies, other industries and even space programs for some countries
are the customers to these gripper companies. The concentrated research work for grippers was done in 1980s and early in
the decade of 1990 the idea for gripper was well established.
Master Glove
The control of the under discussion robotic hand is done by using tele-operation. For the actuation of anthropomorphic
and dexterous robotic hand, all the angles of finger joints of the human operator must be tracked. Tracking of angles is done
by a special glove, which is embedded by BendSensors and it is also capable of tracking the sideways movement of the joint
that connects the finger to the palm as well i.e. abduction and adduction. The BendSensors are embedded at different
locations in the glove to get the complete angle information. To control all the joints of the robotic hand independently, the
actual angle of all the joints of the operator’s hand should be known. The angles between thumb and palm, index finger and
palm and pinkie and palm are straight forward. But the angle values for middle and ring finger with palm require some
calculations. The details of calculations, the sensors location in the glove and the modeling for torque produced at all joints
can be seen in [27]. The operator wearing the specially designed master glove, by the authors, is shown in Figure 1.
Robotic Hand
The theme of UTHM hand is to develop a dexterous and anthropomorphic robotic hand, therefore the inspiration for the
look and feel has been taken from human hand. The look and feel as well as the size of all the fingers and palm is very much
comparable to human hand. The hand comprises of five fingers including the thumb. The structure for all the fingers
including the thumb is same while the difference is size, as the sizes varies among the fingers in normal human hand. We
have designed the hand capable of twenty DOF which does not include the wrist and arms. Twenty DOF is from the
summation of all the fingers as each finger exhibits four DOF. All the joints are pin joints using the dowel pins for
connecting the different segments of hand. The details of mechanical design and motion mechanism can be studied in [26].
The design and its kinematic structure are shown Figure 2 and Figure 3.
Conclusion
The overview of the dexterous anthropomorphic robotic hand system has been elaborated in this paper. The robotic hand
system is based on Tele-operation using Bluetooth as the communication channel between them. The design has been made
simpler and its demand for space has been reduced from previous designs of robotic hands by using combination of
pneumatic actuator and springs. The state of the art microcontroller has been used as the control and processing unit for both
the master glove and robotic hand. This robotic system has many applications for the developments of safe industrial
environments, whereas the robotic hand alone can also be used for different applications in industry as well as for
rehabilitation.