3D PRINTED HUMANOID HAND

Abstract

An original design of a humanoid hand created by a 3D printer is presented. A concept for directly printing the fingers of the hand as one connection which reduces the time for the assembly operations and improves the repairability. The hand is controlled by a sensor glove. The mechanical and also the control systems of the hand are presented. 3d Printed Humanoid Hand can be applied for student's education.

Full text

ISSN 1310-3946 Proceedings of the International Conference“Robotics & Mechatronics and Social Implementations”2018
107
3D PRINTED HUMANOID HAND
Ivan CHAVDAROV1, Pancho DACHKINOV1, Georgi ELENCHEV1, Radoslav ILIEV2,Ivelin
STOYANOV2,Stefani MINCHEVA2, Aleksandar KRASTEV1
1)Institute of Robotics, Bulgarian Academy of Sciences, Acad. G. Bonchev str., bl.1, Sofia, Bulgaria
2)National Professional High School of Computing and Technology Systems, str.4, Perusha,
Pravets, Bulgaria
Abstract: An original design of a humanoid hand created by a 3D printer is presented. A concept for directly printing the
fingers of the hand as one connection which reduces the time for the assembly operations and improves the repairability.
The hand is controlled by a sensor glove. The mechanical and also the control systems of the hand are presented. 3d
Printed Humanoid Hand can be applied for student’s education.
Key words: Humanoid Hand, 3D Printing, Education.
1. INTRODUCTION
A lot of the robots are made to manipulate with
different types of objects and for this reason they also have
various types of end effectors. One of the gripping
problems is the flexibility according to different objects
which has unique shape, geometry and are made from
specific material. The end effector should adapt itself
about the position and orientation of the object [1].
Movement in nature are based on a mechanical system
which is made from links with complicated 3D space
shape – bones which are driven by elastic elements
muscles. The development of the 3D printing technologies
increases the interest of research and creating of humanoid
robotic hands which are closer to the biological
analogues[2-5].An electrical system is used to driven da
hands and the muscles and tendons are represented by
wires [6,7]. Experiments with various shapes and types of
joints for fingers of the hands are made and also 3D
printed elastic elements are used [2,3].Some researchers
are focused on different methods of grip and manipulation
with objects and finger configurations [8].Some of the
developed hands find application for prosthesis[3] and
rehabilitation [9].Another are used by the humanoid
robots. Different achieves are used in a way to simplify
the design of the models[10].The development of the
control systems allows the usage of the myoelectric
control for some prosthesis[9].For the remote control
cases the humanoid hands are using both some algorithmic
programs and also sensor gloves for movement
realizationя [10].
From the analysis mentioned above, the following
problems are still unsolved:
-One of the fundamental problems in the design of the
hand is the realization of many degrees of freedom in
small volume (about 500 cm3) and also consideration with
the requirements for low mass. The development of the
technologies, connected with the driven systems allows
the fabrication of small size components but still
it is very hard so many mechanisms to be put in such small
volume which is the hand. Furthermore, a system
with a lot of electro motors becomes complicated for
control. It is required for the sources of energy to be with
small sizes and high reliability.
- The diversity of the movements humans could do
with their hands are also hard to be represented by a
mechanical designed system.
- A great part of the gestures are connected with
complex precisely coordinated movements of the fingers.
In this case, it is necessary the trajectories to be described
or velocity control to be done. A precise servomotors and
specific algorithms for control are used.
-There are also some problems with control system,
including: an appropriate microcontroller which could
control a lot of servomotors, has a suitable interface for
computer communication and is reliable enough.
- Important point is the compactness of the control
board which is usually pasted nearby the humanoid
robotics hand.
- Issues with the reliability of the components: The
mechanical system is often very complicated and consists
a lot of detail in order to satisfy the requirements of the
difficult three dimensional space movements of the hand
which decreases the reliability. For movements transfer in
higher distances, often are used wires or, fibers and elastic
elements [6], which could change their properties and
quality in time.
In this paper the realization of an idea of 3D printed
hand is discussed. Different options for control and
application of the hand are also shown [11].
The dimensions of the human fingers are individual
and could vary, see the average values at Fig. 1.
The opportunity for creating customized object with
complicated geometry is a reason for using 3D printing as
an appropriate method for building a humanoid hand.

Proceedings of the Int.Conf.“Robotics&Mechatronics and Social Implementations” ISSN 1310-3946/Year XXVI, Volume 4/225, August 2018
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Fig.1.Dimenssions of a human finger [3].
2. DESIGN OF THE HAND
An original idea of 3D printed humanoid hand which
fingers are directly printed as one assemvly is presented
[13].On the base 1 are are located the servomotors 2
(MIRCO SERVO, Model No. HD-1581HB, Reduction
ratio 1/522). On the shafts of the servomotors 2 are
assembled the rolls 3(Fig.2).
The tendons 4 are connected to the rollers 3 and goes
through holes in the fingers 5. The other end of the tendons
is static captured to the last links 6 of the fingers.
Fingers 5 are connected with the base 1 with screw
connection 7. The shape of the joints for each finger
consists of two cylindrical parts 8 and one spherical part
in the middle 9, as it is shown at Fig. 3. The innovation of
the proposed model is that the fingers (parts 6,8 and 9) are
printed whole.
The 3D printed elastic element 10 is constrained in its
one end with the external joint 6 of the fingers 5. The other
end of the elastic element is connected through the base 1
with the screws 7.
Fig. 2.Basic components of the hand.
The elastic component 10 is disposed on the outside of
the fingers.
Fig.3. 3D modelof a finger
The joints of each finger have minimum clearances
between the cylindrical 8 and spherical 9 surfaces and in
this way they are directly printed as one assembly. In the
external link 6 of each finger 5 exists a screw connection
mechanism 11 for controlling the tensile force of the
tendon 4.
The control of the motors is realized by a computer
which sends signals to the drivers 12. The communication
could be done wireless or via cable. The energy source for
the motors and also for drivers comes from the power
supply 13
The elastic element 10 is printed from a special
material – Filaflex for 3D printer. The most appropriate
elastic properties of the elastic element 10 are
experimentally defined by changing its width and
thickness. The tensile of the fibers is controlled by the
screw mechanisms 11 (Fig.4).

Proceedings of the Int.Conf.“Robotics&Mechatronics and Social Implementations” ISSN 1310-3946/Year XXVI, Volume 4/225, August 2018
109
Fig.4.Structure of the hand’s fingers.
On Fig. 5 is shown a prototype of the 3D printed hand.
Fig. 5.General view of the 3D printed hand.
Each finger of this hand has one joint and one link less
than the real human hand because of the small stroke of
the servomotors and also the limited volume of the palm.
Fig. 6. Location and orientation for printing of a finger.
Link 21 is rotated according to link 20 on angle 0 ≤
𝛼1≤90[𝑑𝑒𝑔], and 22 referred to 21 on angle 0 ≤ 𝛼2≤
90[𝑑𝑒𝑔].
For fabrication the hand is used FDM 3D printing
technology. For the correct fabrication of the finger, it is
recommended to be located parallel to the working plane
(bed’s plane) XY and the links 20, 21 and 22 should be
located half bended one to anotherFig.6. The clearances in
the joints are defined experimentally.The fingers, created
this way have good agility in the joints.
Fig. 7.Stages in the fingers movement and location of the
forces.
The driven moment from the servomotors creates
tensile force 𝐹
𝑚in the fibber (Fig.7). This force is
counterbalanced with the force of the 3D printed spring:
ee LkF 
. (1)
where
k
is the elastic coefficient of the 3D printed
spring and
e
L
is the length of the working area of the
spring. Depending from the distances
1
R
and
2
R
on which
the forces
1
F
and
2
F
acts, it is possible one of the elements
21 or 22 of the fingerto be driven. In the case when
21 RR 
, first 21 is rotated on 90 [deg], and then 22
rotates.
2
F
is less than
1
F
because there are more friction
loses. The length L is time variable and depends from the
joint restrictions.
3. CONTROL OF THE HAND
The microprocessor electric drive is carried out by
means of Arduino Nano based on the microcontroller
ATMEGA328 with embedded USB interface for servo
drivers control.

Proceedings of the Int.Conf.“Robotics&Mechatronics and Social Implementations” ISSN 1310-3946/Year XXVI, Volume 4/225, August 2018
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Because of the high energy consumption it is necessary
to use external power supply. The electrical scheme of the
microprocessor’s electrical motion is given at Fig.8.
For generating control signals a sensor glove is used.
The electrical scheme of the glove is shown on Fig. 9.
Fig. 8.An electrical scheme of the microprocessor’s
electrical motion
The glove is used as a control device. It could define
the movements all five fingers by tensor resistors and
communicates via USB and UART interface.
Fig.9.An electrical scheme of the glove.
As a programming language for development is used
Python in the programming environment PyCharm. The
library for developing the graphic user interface is tkiner.
This allows the application to be used on several platforms
and also to work on different operational systems.
It is a low cost development and it is easily available.
Because all of the fingers are driven independently, it is
easy a lot of finger combinations to be realized. In this way
some gestures as counting could be represented. The hand
is driven from six motors and two of them are used to drive
the thumb. This allows realization of more complicated
gesturers, for example contact between the thumb and
some of the other fingers.
Fig.10.Application of the hand.
The configurations and set up settings are specific,
depending from the application.
This research is made in cooperation with high school
students from a specialized computer technologies school
(Fig.10). In this application the students demonstrate their
knowledge and skills in the field of software and hardware
technologies.
4. CONCLUSIONS
An original mechanical construction of a humanoid
robotic hand is designed. A 3D printed prototype is
created, too.
An original conception for directly printing the fingers
as one assembly is used. The advantages are: modularity,
reduces assembly operations, improves reliabilityand the
robotic hand is easily repaired. It is experimented with
several different designs for the fingers of the hand.
The control system, realized by a sensor glove has the
advantage of remote control as well as to make records of
the hand movements sequence.
This model could be used for some applications
connected with the language of gestures – as an
independently working system or part of a humanoid
robot.
The prototype is appropriate for usage for high school
education in the field of computer technologies and
programming. In the development of the hand high school
students are taking part working on the hardware and on
the software as well.
ACKNOWLEDGMENT
These research findings are supported by the National
Scientific Research Fund, Project N ДН17/10 -
12.12.2017

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