Proceedings of the 2009 IEEE Systems and Information
Engineering Design Symposium, University of Virginia,
Charlottesville, VA, USA, April 24, 2009
FPM2HF.Health.2
A Virtual Reality Interface to Provide Point Interaction
and Constriction to the Finger
Kimberly A. Everett, Rachael E. Exon, Sylvia H. Rosales, and Gregory J. Gerling, Member, IEEE
Abstract—
Virtual reality (VR) simulation of tube
thoracostomy may improve the procedural training for medical
and nursing students. Current VR simulators, however, do not
provide tactile feedback, which is essential for enabling certain
tasks (e.g., surface palpation to identify rib location, blunt
dissection for access to pleural space surrounding the lungs,
and finger sweep to confirm location in the pleural space). This
work develops a physical apparatus that provides users with
point feedback at the fingertip when palpating an external
surface and a sensation of constriction around the finger during
insertion into a body. The physical apparatus is composed of
two components that separately control the constriction on the
tip and middle of the finger. Each constriction component is
made of two nylon casings coated with a silicone-elastomer that
enclose about the top and bottom of the finger. DC gearhead
motors control the magnitude of pressure in proportion to
feedback from force transducers embedded in the siliconeelastomer. The device is intended to communicate with a
virtual environment (written in H3D). The apparatus augments
traditional stick-based force feedback and should enhance the
learning of tactile tasks in tube thoracostomy.
T
I. INTRODUCTION
thoracostomy (chest tube insertion) is a medical
procedure in which a tube is inserted into the pleural
space to drain excess fluid, blood, or air, thereby relieving
pressure from the lungs [1]. All medical and nursing
students must learn to insert chest tubes. At present, the
procedure has a complication rate of 30% [2]. As a
supplement to current training materials, virtual reality
simulation can provide an environment for repeated practice
and for learning the overall cognitive steps. A preliminary
computer simulation of chest tube insertion coupled with a
haptic device has been developed [3], [4]. However, key
tasks in the cognitive sequence cannot be performed at
present because the simulator cannot adequately render
tactile forces to the bare finger. The primary goal of this
work is to develop the functionality to enable tasks involving
tactile palpation. For instance, during chest tube insertion,
the clinician must locate the correct location for the incision
UBE
Manuscript received April 6, 2009.
K. A. Everett is a fourth year student in Systems and Information
Engineering (SIE) and Biomedical Engineering at the University of
Virginia, Charlottesville, 22904 (phone: 434-924-0533, e-mail:
[email protected]).
R. E. Exon is a fourth year student in SIE at the University of Virginia,
Charlottesville, 22904 (e-mail: [email protected]).
S. H. Rosales is a fourth year student in SIE at the University of
Virginia, Charlottesville, 22904 (e-mail: [email protected]).
G. J. Gerling is an assistant professor in SIE at the University of
Virginia, Charlottesville, VA 22904 (e-mail: [email protected]).
1-4244-4532-5/©2009 IEEE
by feeling ribs through the skin. Another tactile task occurs
during blunt dissection, when the clinician places his index
finger into the incision hole to confirm the trajectory of the
path. Third, after the pleural space has been punctured, the
clinician performs a ‘finger sweep’ by pushing the tip of his
index finger into the pleural space and rotating his bent
finger to ensure placement [1], [5], [6]. The virtual reality
apparatus designed and built in this work seeks to enable the
performance of these tactile steps.
A. Prior Art in Virtual Reality Simulation in Medicine
Virtual reality (VR) simulation has been employed to
teach other types of surgery and is increasingly popular as a
training tool. VR simulation can provide students with
graduated levels of difficulty, train students for rare but
dangerous events, and also provide objective feedback [7],
[8]. VR training has been most frequently employed for
laparoscopic surgeries, as they necessitate the use of videogame-like controls in the procedure itself. Preliminary
studies have found that surgeons who practice laparoscopic
cholecystectomy on VR devices make fewer mistakes in
actual surgery [9]. VR tools have also been developed for
training basic surgical skills, in addition to their usage in
training bone surgery, cataract surgery, and cardiac
catheterization, among others [10].
B. Prior Art in Bare Finger Interface Devices
One mechanism developed to constrict the bare finger was
developed by Inaba and Fujita. The user places his finger in
between two contact plates that are connected by a loop of
Velcro. A driving motor rotates a shaft, which tightens the
contact belt. The two contact plates are pulled together,
creating constriction [11].
Kramer developed an interface that transmits force,
texture, temperature, and pressure to the entire arm. This
invention includes a glove that can sense position and
dynamically change the force exerted on each finger through
a feedback control loop. The pressure applied to the hand is
generated by a motor or pneumatic/hydraulic fluid [12].
While these types of devices constrict a user’s finger, none
were built to mimic the sensation of being inside the human
body nor are simple enough to incorporate with a SensAble
OMNI or the H3D Software Virtual Environment.
II. METHODS
A motor-controlled constriction device with forcefeedback capabilities was designed and built to enable tactile
and palpation tasks of chest tube insertion. The device is
203
composed of two motor-driven components that control
constriction of the tip and middle of the finger to achieve
different sensations depending on the task. The levels of
constriction are achieved through feedback from the device.
ensuring that there are no organs adherent, and that the tube
can be inserted safely [1], [5], [6].
B. Requirements
The device was built to meet a set of requirements
specific to the three palpation tasks and to the overall
usability of the device.
1) Task Requirements:
Req. 1: The device shall provide point interaction on the
user’s fingertip within the palpation task.
Req. 2: The device shall constrict and release to reach the
appropriate pressure on the finger, which is defined in
each task, and do so within two seconds.
Req. 3: The device shall allow for individual control of the
two components that encase the finger.
Fig. 1. The University of Virginia Chest Tube Insertion Simulator
A. Task Analysis
The physical VR interface will add tactile and palpation
feedback to address three tasks that require interaction via
the forefinger: surface palpation of the ribs before incision,
blunt dissection, and finger sweep. A task analysis with
physicians was done to better understand the goals and subtasks that underlie each task and the typical errors of novice
learners.
1) Surface Palpation: To identify the correct site for
incision, the physician must palpate the fifth intercostal
space (the space between the fifth and sixth rib) [13].
Interviews with resident physicians identified that positional
errors are commonly made by making too low an incision,
resulting in a tube inserted in the abdomen [5]. During the
surface palpation task, the clinician feels point interaction on
his fingertip with a change in resistance depending on
whether the finger is moved over a rib or muscle. There are
no constrictive forces on the finger.
2) Blunt Dissection: After making an incision, the
physician uses a Kelly clamp to bluntly dissect a tract
toward the lungs. We observed that clinicians switch
between using the Kelly clamps and using their index finger
during the blunt dissection step and emphasized that students
should do the same. The forefinger plays a large role in
confirming the location of the tract. During blunt dissection
the clinician feels the resistance of moving through, over, or
around different types of tissue. When the finger enters the
body the clinician feels constrictive forces on the tip of his
finger, but not upon the middle of the finger. When the
finger is completely inside the body, the clinician feels
constrictive forces along the length of the finger.
3) Finger Sweep: After dissecting the tissue and muscle
between the ribs, the physician punctures the pleural space.
The physician then inserts his finger into the pleural cavity
and performs a sweep of the space with his fingertip,
1-4244-4532-5/©2009 IEEE
2) General Requirements:
Req. 4: Once inserted, one’s finger shall be aligned with and
close to the stereo plug of the haptic device to minimize
discrepancy between how the user perceives his finger in
the physical and virtual worlds.
Req. 5: The device shall accurately mimic the feeling of
tissue on a user’s finger when interacting with the virtual
body.
Req. 6: Appropriate safety controls shall ensure that any
constriction will stop before injuring a user’s finger.
Req. 7: The placement of one’s finger in the device shall be
intuitive and easy.
Req. 8: The device shall be lightweight to allow the user to
easily move one’s hand in space.
Req. 9: The device shall fit in a 16 cm by 10 cm by 12 cm
space in order to fit easily on the table.
Req. 10: The device shall not impede the range of motion of
the force feedback device, which allows a range of motion
of a hand pivoting at the wrist.
Req. 11: The device shall attach to a SensAble PHANTOM
Omni haptic device.
Req. 12: The device shall accommodate various finger
lengths and diameters.
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Fig. 2. Task Flow Diagram
C. System Overview and Base Functionality
The physical apparatus was designed to be mounted on
the stereo plug of a SensAble PHANTOM Omni (Fig. 1).
The apparatus provides users with both point feedback and
constriction, and consists of two components that separately
control the constriction on the tip and middle of the finger.
Basically, the device is designed to react to the change in
location in the virtual body.
During the surface palpation task, both constriction
components will tighten equally until there is very slight
pressure on the user’s finger (Fig. 2). This will ensure
contact so that point interaction feedback will be transferred.
During blunt dissection, both motors will constrict to a
higher level of pressure. As the user moves his finger into
the pleural space, the fingertip component will relax,
allowing the user to perform a sweep.
D. Hardware Design
1) Finger Casings: The device’s main structure consists
of two constricting components, one for the tip of the finger
and one for the middle of the finger (Fig. 3 and Fig. 4, Label
c). Both components have an upper and lower casing made
of Nylon 6-6. The inner surfaces of both casings are coated
in a solid silicone-elastomer (5005 BJB Enterprises with
50% C), with a thin layer on the flat interior surface and a
thicker layer on the inside of the half-cylinders (Fig. 4, l)
(Implementation Element 1). The silicone provides for the
feeling of tissue during constriction of the finger. A force
sensor (Flexiforce 0-1 lb, Tekscan, South Boston, MA) is
embedded in the silicone of the lower casings (Fig. 3 and
Fig. 4, d).
Control of the casings is achieved by driving the lower
casings, which glide upon aluminum rods, towards the fixed
upper casings (Fig. 3 and Fig. 4, b). Various finger sizes are
accommodated by the size of the cylinders cut in each casing
and the adjustable distance between the top and bottom
casings (Implementation Element 2). The stereo jack
attaches the device to the existing PHANTOM Omni
(Implementation Element 3), and does not impede the range
of motion that already exists. Point-interaction was fulfilled
by aligning the fingertip nylon casing with the stereo jack
(Fig. 3, k), and by creating a silicone wall at the end of the
fingertip casing (Implementation Element 4).
2) Drive Mechanism: Two DC gearhead motors are used
to drive the lower casings towards the upper casings, one for
each constriction component (Fig. 4, p). When constriction
of a component is desired, the motor turns, which screws a
bolt through the horizontal aluminum plate (Fig. 4, m). A
flexible 24-inch socket extender (Implementation Element 5)
is used to separate the heavy motors from the device.
As the user’s finger is compressed, the force generated on
the pressure sensor, embedded in the silicone-elastomer,
controls the duration for which the motor turns (Fig. 3 and
Fig. 4, d). Thus, the communication between the flexi-force
sensors, STAMP code, and the motors (Implementation
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205
Fig. 3. Side-view of the device. (a) ¼” Aluminum nuts (b)
Aluminum bolts threaded at each end (c) Nylon finger casings
(d) Flexi-Force Sensor (e) Aluminum plates (f) Flexible socket
extension (g) Steel bracket (h) Rivets (i) 3/16” Aluminum nuts (j)
Nylon block (k) Radio jack
Fig. 4. Straight-on view of the device. (a)
¼” Aluminum nuts (b) Aluminum bolts
threaded at each end (c) Nylon finger
casings (d) Flexi-Force Sensor (e)
Aluminum plates (f) Flexible socket
extension (h) Rivets (l) Silicon lining (m)
Square head screw (n) Set screw (o) Nylon
rod (p) Motor
Fig. 5. Electronic Component Schematic for One Motor
Table I. Results Matching Requirements to Implementation Elements
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206
Element 6) allows for the adjustable constriction of the
finger based on the current pressure. This helps adjust for
different finger sizes, as the running time for the motor may
change with different users, but the resulting pressure is the
same. Implementation Elements 2 and 6 also allow for the
constriction of different parts of the finger depending on the
task.
E. Electrical Component Design
A Basic STAMP microcontroller is used to control the
two motors and to read the pressure exerted at the interior of
the silicone casings. The analog signals from both force
transducers are amplified by INA114 instrumentation
amplifiers and converted from analog to digital with an
ADC0831 (Fig. 5). The resulting signal is input into the
microcontroller program. The two motors are wired in Hbridge circuits, which allow them to be turned in either
direction. Each H-bridge is composed of two NPN
transistors (TIP120) and two PNP transistors (TIP125).
When one NPN and one PNP transistor are connected to
opposite sides of the motor and turned on, the motor turns in
one direction. The transistors are connected to the
microcontroller output by opto-couplers, which protect the
microcontroller from the rest of the circuit.
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III. RESULTS AND DISCUSSION
The design of the VR finger interface is able to fulfill both
the task and general requirements (Table I). The immediate
next steps are to design a safety mechanism to protect
against injury and to perform usability studies with potential
users. The interface will then be integrated with the virtual
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The development of point interaction and constriction
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ACKNOWLEDGMENTS
The authors would like to thank Jacob Scanlon for his
guidance. We would also like to thank Professor Reba
Moyer Childress of the University of Virginia School of
Nursing, and Dr. Marcus L. Martin of the University of
Virginia School of Medicine for their clinical advice related
to teaching and performing the tube thoracostomy
procedure.
1-4244-4532-5/©2009 IEEE
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