STIFFNESS OF AN EVA GLOVE: OBJECTIVE EVALUATION
EVALUATION AND TESTING
PROCEDURES
1,2)
Mehdi Mousavi(1,2)
, Silvia Appendino(1), Alessandro Battezzato(1), Fai Chen Chen(1), Alain Favetto(1),
Francesco Pescarmona(1)
(1)
Center for Space Human Robotics, Istituto Italiano di Tecnologia, Corso Trento 21, 10129, Turin, Italy
(2)
Department of Mechanics, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129, Turin, Italy
ABSTRACT
Hand fatigue is one of the major problems of
astronauts during Extravehicular Activity (EVA),
due to the stiffness of the space suit, in particular
of the glove. In order to evaluate the stiffness of
EVA gloves, different methods have been
proposed in the past, mainly focused on the
effects of wearing an EVA glove on hand
performance when executing test protocols. In
this paper, an objective method for the evaluation
of the stiffness of EVA gloves is proposed, by
means of a tendon-actuated finger probe. The
finger probe is equipped with accelerometers, to
measure the angles of its phalanges. These are
actuated by applying different torques using the
finger probe tendons. The EVA glove is tested in
both pressurized and non pressurized conditions,
thanks to a hypobaric glove box. An Orlan-DM
EVA glove is tested and stiffness results are
presented. This setup can be used for different
kinds of gloves, not necessarily for EVA
application, and allows direct, numerical
measurement of their stiffness.
KEYWORDS
EVA Glove, Extravehicular Activity, Astronaut
Glove, Stiffness Measurement
1.
INTRODUCTION
The number of human space missions has increased
significantly in the last decades. In many missions,
extravehicular activity (EVA) is foreseen. Activities
defined as EVA are performed outside the spacecraft,
thus astronauts have to wear spacesuits to be protected
from the hazardous conditions of space.
Since hands are the major tool that astronauts have, the
EVA glove is one of the most important parts of the
spacesuit. However, due to its pressurization and to its
multilayer structure, the EVA glove is also a very
critical part. Hand fatigue, dexterity reduction of the
fingers and consequently decrease of possible EVA
hours are some of the most common problems which
arise [1-4].
Different solutions are being attempted, on one side the
development of novel EVA gloves with lower stiffness,
on the other the design of exoskeletons or other external
devices to overcome the stiffness [5-11]. In both cases, a
deeper knowledge on the gloves’ stiffness and a
standard method for its measurement are very useful. In
particular, standard measurement is necessary for
comparison between different gloves. Furthermore,
knowing the exact stiffness of the EVA glove is a prime
requirement to realize an external device such as a hand
exoskeleton, e.g. for the design of the structure and the
choice of appropriate actuation.
Several studies have been conducted to determine the
influence of the EVA glove on manual capabilities. Six
basic hand characteristics have been identified [12]:
range of motion, strength, tactility, dexterity, fatigue and
comfort. These aspects have been studied in several
papers [12-19] following different methods. However,
the effects of the glove on hand performances do not
supply numerical data regarding torques that EVA glove
apply to the joints of the astronaut’s fingers.
A study performed by the University of Maryland in
2000, presents a test apparatus used to measure the
mechanical characteristics of EVA gloves [20]. It
consists in a vacuum chamber and an actuated and
instrumented silicone hand, which is inserted in the
tested glove. The force necessary for the flexion of each
finger is measured. However, the test apparatus was not
suitable to measure the torque required to flex each joint
of the fingers separately. Also [21] proposes a solution
to measure the mechanical characteristics of EVA
gloves, by means of a finger exoskeleton. This is
positioned on the back of the glove finger and imposes
flexion, thus measuring the necessary force. As for the
previous case, this one degree of freedom exoskeleton
cannot evaluate the torque required to flex each finger
phalanx separately.
In this paper, a new method for measuring the stiffness
of the EVA gloves is presented. Contrarily to the
previous methods, the effects of the EVA glove on the
hand performance is not considered here; moreover, the
amount of torque that the EVA glove applies on each
finger joint is directly measured. A finger probe is
designed, realized and equipped with sensors to measure
the torques that the EVA glove applies to Distal
Interphalangeal (DIP), Proximal Interphalangeal (PIP)
and Metacarpophalangeal (MCP) joints of the human
index finger.
In order to perform tests in the same differential
pressure conditions of the pressurized EVA glove in
space, a hypobaric glove box is designed and realized.
This work describes the developed equipment, the used
methodology and finally results regarding the stiffness
of an Orlan – DM EVA glove.
2. MATERIALS AND METHOD
A mechanical finger probe has been designed to be
inserted in the finger of an EVA glove to test the
stiffness of each joint. For each phalanx, a known torque
is applied and, when the equilibrium between the active
torque and the one deriving from the stiffness of the
glove is reached, the angle is recorded. The finger probe
allows only flexion and extension movements, whereas
adduction and abduction are not possible. Thus only
stiffness in the sagittal plane is defined.
A hypobaric chamber has been realized to perform tests
in pressurized conditions. Fig. 1 shows the finger probe
in front of the glove box containing the EVA glove
under test.
Figure 2: Height and width of the finger probe
In order to measure the torque applied by the EVA
glove to the phalanges separately, each phalange has to
be actuated independently. Phalanges are actuated by
means of laboratory calibrated weights, connected via
Dyneema® strings, which are lightweight and have high
strength. Small holes are designed on the distal, middle
and proximal phalanges of the finger probe in order to
fix the end of each string. Furthermore, an appropriate
empty space inside the finger probe allows the passing
of the strings and the placement of the sensors and their
wires.
Figure 1: The measurement setup
2.1 Design and realization of the finger probe
The finger probe is designed to be inserted inside the
EVA glove instead of the human finger in order to
perform the tests, thus its dimensions have to be as
similar as possible to those of a human finger. The
average dimensions of human fingers can be found in
literature. However, since recent EVA gloves are
custom-made, the finger probe is designed to perfectly
fit inside the Orlan-DM EVA glove under test [22].
Nevertheless, the same approach is applicable to any
other EVA glove.
Based on the dimensions of this EVA glove, the lengths
of the distal, middle and proximal phalanges of the
finger probe are considered to be 25, 20 and 50 mm
respectively. Fig. 2depicts the main dimensions of the
finger probe.
Figure 3: A cross section view of the finger probe, with
tendon passing points.
As can be seen in Fig. 2 and 3, three coaxial pulleys are
positioned on the MCP joint. One of them is fixed to the
proximal phalange and rotates with it, while the other
two can rotate independently to guide the strings toward
the middle and distal phalanges. Similarly, one of the
two pulleys of the PIP joint is fixed to the middle
phalange whereas the other one can rotate independently
and is used to pass the related string toward the distal
phalange. Finally, there is just one pulley on the DIP
joint which is fixed to the distal phalange. A total of
three strings (proximal, middle and distal string) are
needed to actuate the three degrees of freedom of the
finger probe in the sagittal plane. As depicted in Fig.3,
the proximal string is fixed to the proximal phalanx after
passing over its fixed pulley through a small hole on the
wall of the proximal phalanx. The middle and distal
strings pass over the two independent pulleys of the
MCP joint towards the middle and distal phalanges. The
middle string is connected to the fixed pulley of the PIP
joint by means of a screw. Finally, the distal string is
fixed to the distal phalanx through an appropriate small
hole on its wall after passing over the independent
pulley of the PIP joint and fixed pulley of the DIP joint.
Moreover, small threaded holes are designed on the
walls of the phalanges at specific angles. These holes
are used to fix each phalanx at a certain angle related to
its adjacent phalanges by means of set screws. This
allows measuring of the torques required to flex each
phalanx when other phalanges are set at specific angles.
The proximal phalanx can be fixed at the angles of 0°,
30°, 60° and 90° and the middle phalanx can be fixed at
the angles of 0°, 40° and 80°.
2.3 Hypobaric glove box
As mentioned before, the spacesuit is internally
pressurized. Its air tightness is guaranteed by seals at
each joint and by the fact that it completely
encompasses the astronaut. Working with only a part of
it, such as the glove, makes the air tightness very
complicated to achieve. Therefore to create the same
differential pressure of space conditions in the
laboratory, depressurizing the outside of the EVA glove
is preferred rather than pressurizing its inside.
2.2 Sensorization
The angle of each phalanx is calculated by measuring its
orientation with respect to the gravitational acceleration.
In order to measure the direction of the gravitational
acceleration, a commercial accelerometer is used. The
accelerometer is available in a small and low profile
package (4mm × 4mm × 1.45mm), but its corresponding
commercial PCB is too large to be hosted inside the
finger probe. To overcome this issue, a mini-PCB
conditioning system prototype is designed and
fabricated. In the designed two-layer mini-PCB the top
layer maps all the components footprint and routes all
interconnections, while the uniform bottom layer is the
PCB ground plane. Using thin films of Kapton®, the
bottom of the mini-PCB is isolated from the metallic
phalanges of the finger probe to avoid short circuits and
Electro-Static Discharge (ESD). Fig. 4 shows the miniPCB installed on the appropriately designed place on the
distal finger, as well as the thin film of Kapton®.
a)
b)
Figure 5: The realized hypobaric glove box: picture and
details of the connection with the EVA glove
Figure 4: The mini-PCB installed on the distal phalanx
of the finger probe on a thin film of Kapton®
The PCB output channels are connected to the National
Instruments Data Acquisition system (NI-DAQ) to
acquire and process acceleration data based on a
LabView® software environment.
To achieve this, the hypobaric glove box depicted in
Fig.5a is designed and realized. It consists of a
430x440x630 mm aluminum parallelepiped, with 3
aluminum and 3 Plexiglas sides. One of these has an
opening which permits the insertion of the forearm in an
airtight flange. The flange ends with a joint that is
coupled with the forearm joint of the EVA glove. Thus,
different EVA gloves can be tested by substituting the
flange with another flange, custom-made for the
particular glove under test. Three sides of the box are
transparent in order to grant visual feedback. One side is
removable and kept closed by a set of screws. It may be
opened to insert or remove instrumentation from the
glove box when the vacuum pump is off. Air tightness is
guaranteed by gaskets along the perimeter.
The rear side hosts the pneumatic connections. The
pneumatic circuit consists of a vacuum pump, an
adjustable safety valve and a vacuum manometer.
Since the Orlan-DM EVA glove is used for the tests and
the inside pressure of this EVA glove in space condition
is about 40.7 kPa (0.4 bar / 5.9 PSI) [22], the hypobaric
glove box is designed so that it can provide at least 0.4
bar differential pressure.
2.4 Measurements
In order to evaluate the effects of differential pressure
on the EVA glove stiffness, tests are performed in three
different pressure conditions: differential pressure of 0
(unpressurized), 0.2 and 0.4 bar. The latter corresponds
to the real conditions the Orlan-DM glove is designed
for.
To apply force to each joint of the finger probe,
calibrated weights are hung to the tendon (string) of that
specific joint. When the force is applied to the proximal
string which is connected to the MCP joint, the other
two joints are free to rotate. However, when the
calibrated weights are hung to the middle string to
actuate the PIP joint the preceding joint (MCP) is fixed
at a certain angle (θP=0°, 40° or 80°). Similarly, when
the DIP joint is actuated the PIP and MCP joints are
fixed at certain angles, defining a series of couples of
defined angles (θP=0°, 40° or 80° and θM=0°, 30° or
60°). In each defined condition, a known force is
applied to the actuated joint and its angle is recorded.
The test is repeated for the entire set of torques,
acquiring data.
Figure 6 shows the finger probe inside the EVA glove in
the hypobaric glove box, ready to perform the tests.
arm of the applied forces, and consequently the torque
applied to each joint. In the following graphs, θP, θM
and θD represent the angle of the proximal, middle and
distal phalanges with respect to the phalanx before,
considering clockwise as the positive direction.
The data collected, both in pressurized and in
unpressurized testing conditions, have been interpolated.
For each joint and for specific values of the flexion of
the previous joints, an approximate law relates torque
and angle. In this way, a mathematical model of the
glove stiffness, in terms of polynomial laws, is obtained.
Unpressurized
Fig. 7. Torque vs. angle of the proximal (θP) and middle
(θM) phalanges in unpressurized tests
Fig. 8: Torque vs. angles of the proximal (θP) and
middle phalanges (θM) in pressurized tests (0.4 bar)
Figure 6: The realized finger probe in testing conditions
3. RESULTS AND DISCUSSION
The collected data are processed in order to correlate
joint angles with torques. Geometrical parameters are
used to calculate, for each phalanx at each condition, the
As examples, Figures 7 and 8 depict surfaces showing
the torques necessary to flex the middle phalange to a
specific angle for different values of the MCP joint
angle θP , in unpressurized (fig. 7) and pressurized (fig.
8) conditions respectively.
Moreover, executing tasks at different pressurization
conditions allows the evaluation of the effects of
pressurization. Figures 9-11 depict the important
consequences of pressurization on the compliance of the
EVA glove. This effect is most noticeable on the MCP
joint, where θP decreases to between half and one third
when the differential pressure is doubled (Figure 9).
The effect of pressure on the compliance of the PIP and
DIP joints of the EVA glove is evaluated while the
preceding phalanges are fixed at 0°.The results are
shown in Figures 10 and 11: it can be noticed how the
effect of pressurization is very similar for the PIP and
DIP joints.
Considering Figures 9 to 11, the MCP joint shows an
almost linear compliance in both tests (0.2 and 0.4 bar).
On the other hand, both the PIP and the DIP joints show
an initial overlapping, followed by a greater compliance
in the 0.2 bar test. In the final stages, the 0.4 bar curves
become less steep, both for the PIP and DIP joints. This
probably occurs due to the contact between different
parts of the glove which acts as a mechanical constraint
against the rotation of the phalanges and prevents them
from flexing more than a specific angle.
Fig. 9. Compliance behavior of the proximal phalanx
acquired in two different pressure conditions
Fig. 10. Compliance behavior of the middle phalanx
acquired in two different pressure conditions
Fig. 11. Compliance behavior of the distal phalanx
acquired in two different pressure conditions
4. CONCLUSION
The traditional methods of measuring the stiffness of the
EVA gloves evaluate their effects on hand performance.
The data achieved in these methods mostly presents the
percentage of reduction of the hand capabilities such as
power, dexterity, precision, etc. after wearing an EVA
glove. This data is used as a representative of the EVA
glove stiffness.
In this paper a new method of measuring the stiffness of
astronauts’ EVA glove is presented. Contrary to the
traditional methods, this new method gives numeric data
regarding the torque required to flex each finger
phalanx. A finger probe is realized to be used as an
alternative to the human index finger and is placed
inside an EVA glove. Using tendons and pulleys of the
finger probe, torque is applied on each finger phalanx
separately and the angle achieved is measured by means
of accelerometers which work as tilt sensors.
In order to simulate the operating pressure of the EVA
glove in space condition, a hypobaric glove box is also
designed and realized. Through a custom-made flange
sealing between the EVA glove and the glove box
connection is guaranteed. Then, the effect of
pressurization on the stiffness of the EVA glove is
explained.
The proposed test setup can be used to measure the
stiffness of different kinds of EVA gloves and allows
direct, numerical comparison of their stiffness. This
helps the EVA glove designers and manufacturers to
improve their products.
Furthermore, the outcome of this work is an essential
factor for designing hand exoskeletons to overcome the
EVA glove stiffness.
5. REFERENCES
[1] E.A. Benson, S.A. England, M. Mesloh, S.
Thompson, S. Rajulu, Use of traditional and novel
methods to evaluate the influence of an EVA glove
on hand performance, 40th International
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
Conference on Environmental Systems, 11-15 July
2010, Barcelona, Spain.
M.M.S Mousavi, E.P. Ambrosio, S. Appendino, F.
Chen Chen, A. Favetto, D. Manfredi, F.
Pescarmona, A. Somà, Spacesuits and EVA gloves
evolution and future trends of extravehicular
activity gloves, 41th International Conference on
Environmental Systems, Portland, Oregon, USA,
AIAA 2011-5147, July 2011.
M.H. Welsh, D.L. Akin, The effects of
extravehicular activity gloves on human hand
performance, 31st International Conference on
Environmental Systems, Orlando, FL, USA, July
2001, 2001-01-2164.
K. Tanaka, C. Abe, C. Iwata, K. Yamagata, N.
Murakami, M. Tanaka, N. Tanaka, H. Morita,
Mobility of a gas-pressurized elastic glove for
extravehicular activity, Acta Astronautica, 66
(2010) 1039–1043.
E. Matheson, G. Brooker, Augmented robotic
device for EVA hand manoeuvres, Acta
Astronautica, 81 (2012) 51–61
E.A. Sorenson, R.M. Sanner, C.U. Ranniger,
Experimental testing of a power-assisted space suit
glove joint, IEEE International Conference on
Systems, Man and Cybernetics, Computational
Cybernetics and Simulation, vol.3, 1997, 26192625.
Z.L. Sim, Development of a mechanical counter
pressure Bio-Suit System for planetary exploration,
Master's Degree Thesis, Massachusetts Institute of
Technology,
Dept.
of
Aeronautics
and
Astronautics,
2006,
URL:
http://hdl.handle.net/1721.1/35564, Last accessed:
12.12.2012.
K. Tanaka, J. Waldie, G. Steinbach, P. Webb, D.
Tourbier, J. Knudsen, C. Jarvis, A. Hargens, Skin
microvascular flow during hypobaric exposure
with and without a mechanical counter-pressure
space suit glove, Journal of Aviation space and
environmental medicine, 73 (11), November 2002,
pp. 1074-1078.
J.M.A. Waldie, Mechanical counter pressure space
suits: advantages, limitations and concepts for
martian exploration, The Mars Society, 2005,
URL:
http://quest.nasa.gov/projects/spacewardbound/aust
ralia2009/docs/Waldie%202005%20MCPPaper.pdf, Last accessed: 12.12.2012.
B.L. Shields, J.A. Main, S.W. Peterson, A.M.
Strauss, An anthropomorphic hand exoskeleton to
prevent
astronaut
hand
fatigue
during
extravehicular activities, IEEE Transactions on
Systems, Man and Cybernetics, Part A: Systems
and Humans, vol. 27, September 1997, 668-673.
M.C. Carrozza, L. Barboni, S. Roccella, F. Vecchi,
ADAH Project, Executive Summary, Document
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
Code:
ADAH-ES-SSSA-6,
URL:
http://esamultimedia.esa.int/docs/gsp/completed/co
mp_st_02_E32.pdf, Last accessed: 12.12.2012
L.M. O’Hara, M. Briganti, J. Cleland, D. Winfield,
Extravehicular Activities Limitations Study,
Volume II: Establishment of Physiological and
Performance Criteria for EVA Gloves-Final
Report, Report number AS-EVALS- FR-8701,
NASA Contract no NAS-9-17702, 1988.
D.C. Buhman, L. A. Cherry, L. Bronkema-Orr, R.
Bishu, Effects of glove, orientation, pressure, load,
and handle on submaximal grasp force,
International Journal of Industrial Ergonomics, vol.
25, 2000, pp. 247-256.
S. Appendino, E.P. Ambrosio, F. Chen Chen, A.
Favetto, D. Manfredi, Mehdi Mousavi, F,
Pescarmona, Effects of EVA glove on hand
performance, Proceedings of 41st International
Conference on Environmental Systems (ICES
2011), 17-21 July 2011, Portland, Oregon, USA,
Vol. 2, 1094-1103.
S. Thompson, M. Mesloh, S. England, E. Benson,
S. Rajulu, The Effects of Extravehicular Activity
(EVA) Glove Pressure on Tactility, 54th Annual
Meeting of the Human Factors and Ergonomics
Society, San Francisco, CA, September 2010.
S.L. Rajulu, G.K. Klute, A comparison of hand
grasp breakaway strengths and bare-handed grip
strengths of the astronauts, SML 3 test subjects,
and the subjects from the general population,
NASA Technical Paper 3286, Jan 1, 1993,
Document ID: 19930007430.
B. Wimer, T.W. McDowell, X.S. Xu, D.E.
Welcome, C. Warren, R.G. Dong. Effects of gloves
on the total grip strength applied to cylindrical
handles, International Journal of Industrial
Ergonomics 40 (2010) 574-583.
R.R. Bishu, G. Klute, The effects of Extra
Vehicular Activity (EVA) gloves on human
performance, International Journal of Industrial
Ergonomics vol. 16, 1995, pp.165-174.
F.A. Korona, D.L. Akin, Evaluation of a hybrid
elastic EVA glove, Society of Automotive
Engineers, 2002-01-2311.
Grant Ryan Lee, Development of a mechanical test
apparatus for spacesuit gloves, Master thesis,
Space Systems Laboratory of University of
Maryland, (2001), 10-50.
J.Y. Wang, Z.W. Xie, J.D. Zhao, H.G. Fang, M.H.
Jin, L Hong, An exoskeleton system for measuring
mechanical characteristics of extravehicular
activity glove joint, Proceedings of the
International Conference on Robotics and
Biomimetics, IEEE, Kunming, China, December
(2006), 1260-1265
A.I. Skoog, I.P. Abramov, The Soviet/Russian
spacesuit history, Part III, The European
connection, Acta Astronaut., Vol. 60, Issue 12, June
(2007), 1002-1014.