LabVIEW based control software for
Finger Force Sensor Instrumentation
Design
Jose Agraz
Robert Pozos
Bioengineering Department
University of California Los Angeles
Los Angeles, California 90095
Email: joseagraz@ucla.edu
Biology Department
San Diego State University
San Diego, California 92182
Email: bpozos@sciences.sdsu.edu
AbstractThis report describes National Instruments (NI) LabVIEW software for the control of finger force instrumentation for the
quantification of Repetitive Stress Injury (RSI),
Carpal Tunnel Syndrome (CTS), or other applications requiring automated data acquisition
of applied finger force using resistive type force
sensors. The quantification of finger force requires the precise data collection from resistive
force sensors for all five fingers and keyboard
key switches. This abstract describes how a
LabVIEW based software application allows for
the precise control over data force collection for
all fingers and key switches, while acquiring
human subjects study information, isometric
& datalogging finger force, and providing the
user with visual force measurements feedback.
The implementation of this software provides a
fast prototyping for evaluating finger force instrumentation. While no other LabVIEW based
software application is available to date for
this finger force data collection, our system
proved rugged and flexible enough to accommodate fine tuning changes on hardware and
software, with a minimum of dead time during
usage. The software is available for download
at www.joseagraz.com
KeywordsLabVIEW, Instrumentation, Finger, Carpal Tunnel Syndrome, Force, Control.
I.
I NTRODUCTION
Repetitive Stress Injury (RSI) is attributed
to a number of overlying biomedical factors. Repetitive activities performed at work
or leisure over an extended period of time,
constant excessive load and poor body mechanics are suggested as causes of RSI. In
978-1-4673-5683-1/13/$31.00 2013 IEEE
addition, medical conditions such as pregnancy, rheumatoid arthritis, and diabetes can
also contribute to RSI. LabVIEW, a high level
graphical programming language, brings software development speed and flexibility to programming data acquisition. In this application,
LabVIEW provides a natural intuitive manmachine interaction than text based languages
[1][2] at a much lower cost. In reviewing the
literature, no LabVIEW software applications
for finger force instrumentation has been published.
A. Carpal Tunnel Syndrome
The term given for the set of RSI symptoms
is carpal tunnel syndrome (CTS), which is the
narrowing of the anatomical tunnel formed by
the wrist (carpal) bones through which the
median nerve travels. The compression of the
median nerve influences its sensory and motor
innervations to the thumb, index, and middle
fingers causing tingling, numbness, burning
sensation, weakness and clumsiness [3]. The
U.S. Department of Labor (DoL) concluded
that CTS is the Chief occupational hazard of
the 90s, affecting around eight million Americans and accounting for 41% of all workrelated injuries. It is estimated that 25% of
all computer operators have CTS, and by the
year 2014 the DoL estimates over 50% of
the workforce may be affected. Approximately
20,000 medical procedures are performed every year to correct various aspects of CTS.
However, only 23% of all CTS patients are
able to return to their previous professions
after surgery. Women are twice as likely to
develop CTS as their male counterparts. Although they comprise 45% of the work force,
they experience 66% of all work related repetitive stress injuries [4].
Force Proles
Human subject
Questionnaire
Data
Recorder
Data
Plotting
Data
Reader
Force Test
Plotted
Force Test
Analog
FFSID System
Main Menu
<Please Select Option>
Quit
Ver 2.1
Copyright, 1999 J.L.Agraz
B. Why is CTS research important?
The Occupational Safety and Health Administration (OSHA) estimates that by the year
2014, cumulative trauma syndromes will account for 50 cents of each dollar spent on
medical care. The American Academy of Orthopedic Surgeons estimates that CTS cost 1
billion dollars annually in medial treatment.
Each worker compensation claim for repetitive
stress injuries can cost from $20-100K [5].
Computer keyboard usage exacerbates other
repetitive actions that are associated with CTS.
Furthermore, CTS and its associated pathologies, is common among persons who use keyboards or fretboards as well as flute and string
players.
(a)
Force Proles Diagram
Force
13pt Application Font
Human Subject Test.vi
Setting INI le Path.vi
error out
error in (no error)
Checking Data subdirectory.vi
STOP
Boolean Array To Number
Build Array
Wait Until Next ms Multiple
Quit
300
(b)
Fig. 1. LabVIEW finger force application. a) Front Panel
and b) diagram
B. Signal Acquisition
C. Developments in CTS research
At present there is no objective measurement
of the force that fingers can produce when
they are sequentially generating force on a
keyboard while controlling the wrist angle.
Although CTS is a major problem facing the
work force and recreational groups in the
United States, there is no reported method
that quantifies pre- and post-finger force values
after clinical intervention.
II.
M ETHODOLOGY
A. LabVIEW
The need for a real-time data collection program with a front end graphical user interface
(GUI), demanded an industry-standard data acquisition system. The software that displayed
the force profiles was developed using LabVIEW from National Instruments. The software ran on a generic personal computer (PC),
AMD 300MHz, 64Mbytes of RAM with a
Windows 98 operating system (OS)
The signals acquired in this project are; Finger
Force for all five right hand fingers and respective five Keyboard Key Switches. These signals
were acquired using a NI Data Acquisition
(DAQ) MIO E card, a jumperless, switchless
data acquisition board that uses the DAQ-STC
as the system timing control. DAQ-STC is the
backbone of the sensor system and the timing
control application specific integrated circuit
(ASIC). The DAQ-STC contains one 24-bit
counter and three 16-bit counters. The counters are divided into three groups: 1) Analog
Inputtwo 24-bit, two 16-bit counters, 2) Analog output, three 24-bit, one 16-bit counters
3) General purpose counter/timer functionstwo
24-bit counters. The board runs at a maximum speed of 250KHz and collects data using
ten analog channels, five force channels and
five switch channels. These channels operate
at a sampling frequency of 1KHz using a
non-referenced input setup to decrease noise
induced in the instrumentation cables. The
board is set up in the following data collection
mode: non-referenced single-ended (NRSE). A
channel configured in NRSE mode uses one
analog channel input line, which connects to
the positive input of the Programmable Gain
Instrumentation Amplifier (PGIA). The negative input of the PGIA connects to the analog
input sense (AISENSE) connection. Five analog channels were used to collect analog finger
force data, and five digital channels were used
to collect digital switch data from the keyboard
switches.
1) Finger Force: The force applied for
each finger was measured using five Tekscan
resistive-based technology force sensors (SSBT) placed on the surface of individual keys.
2) Keyboard Key Switches: The cherry
switches in the keyboard are set to high using
a pull-up resistor, then a NOT gate (7404),
which drives a Light Emitting Diode (LED)
and feeds the signal to the DAQ card.
C. Software Design
Software considerations for this project included; a) the need for visual feedback to the
subject (to insure that persons generated the
same amount of force each time they struck a
keyboard key) and b) isotonic force data was
recorded and stored. Based on other exercise
studies, 80% of the isometric force value was
taken as the target force value that each subject
had to generate for each depression. Hence
some form of visual feedback system of the
force generated by the subject was required for
the exercising of the subject. Another software
consideration was that each force profile was
to be visualized simultaneously in real-time
from the time of onset of key depression and
release. All force data would be saved and
a fitted curve to the data would be plotted.
Finally, an electronic record of each subject
would be gathered previous to the data collection process, and would be stored with the
force data (fig 1).
1) Software Structure: The software component of this system was programmed using
a graphical user interface (GUI) programming
language called LabVIEW. The short learning curve and the capability of providing an
exceptional user-friendly interface made this
program language the best choice. LabVIEW
Sub Virtual Instruments (VI), or procedures,
was used for programming which is similar to
text based programming languages such as C,
Assembly or Fortran [6]. The software goes
into a loop waiting for the user to click any
of the buttons on the screen. Once the subject
presses a button, the program executes the appropriate VIs. In addition, the data-collection
program uses an ini file that controls and stores
the parameters within the program. Data stored
includes;
1)
2)
3)
4)
5)
Sampling frequency
Calibration coefficients
Isometric parameters
Data file path
Initial sound and channel settings
The purpose of this feature is to decrease the
amount of time required for the development
of the system. When all the variables are
stored in a single easy-to-access file, changes
can easily be made to the program without
recompilation. The program will search for
the file force.ini containing the information
previously described. This force.ini file is
formatted according to Windows ini file
standard format such as labels (placed
within square brackets) and items that
follow immediately. The LabVIEW software
structure is divided in six different outcomes:
1) Human Subject Test, 2) Data Plottings,
3) Multiplot Chart, 4) Data logger, 5) Data
reader, 6) Quit (fig 2).
Human Subject Test.vi: The software collects
information about each human subject.
Human Subject Questionnaire: The software
questionnaire, approved by the Human Use
Committee, was used to maintain a permanent
record of the subjects voluntary participation
in this study. This electronic questionnaire
stored all the subjects information, increased
efficiency and reduced waste. Each set of user
information is attached to the force data-file
as a header.
Zero Force Input Calibration: The system
begins collecting data for one second at a
sampling frequency of 1KHz. Then, using
all the data collected, an average value is
calculated and stored in the force.ini file for
Welcome to the
Force Proles Test
Housekeeping
Please, use the mouse to select the appropiate answer to the following questions:
No
Button
Pressed
Yes
What's your gender?
Human
Subject Test
Data
Plotting
Multiplot
Chart
Data
Logger
Data
Reader
Questionnaire
Force or
Peak Prole
Plot Real
Time Force
Data
Collection
Plot
Force
Zero
Calibration
Calculate
Prole
Isometric
Calibration
Plot
Prole
Male
Female
Quit
What's your age?
0-20
Store
Data
20-30
30-50
Are you right handed?
50-70
Yes
No
Press
here to
Press
here
tocontinue
continue
Data
Collection
Copyright 1998 J. L. Agraz
Store
Data
Fig. 3. Human Subject Questionnaire front panel
No
Quit?
Yes
Pinky
Peak Detector Plotting & Curve Fitting
1.0 _
Pinky-Fit
0.9 _
0.8
0.7
0.6
Ring
Ring-Fit
Middle
Middle-Fit
Index
0.5 _
Index-Fit
0.4 _
Thumb
0.3 _
Thumb-Fit
0.2 _
Completed
Calculations
0.1 _
10
14
16
18
20
22
_
12
_
6
0.0 _
_
future references, and also becomes part of
the force data file header.
Isometric Parameter Setting: The program
will ask the human subject to use all five
fingers at the same time and press on the
keyboard keys as hard as possible; then, the
VI calculates the isometric target force by
using 80% (as stated in the force.ini file) of
the subjects maximum force value for each
finger.
Force Data: After the isometric parameters
have been established, data collection begins.
The force data is sampled at 1KHz, and
collected in small blocks of 50 samples.
These collected samples are stored in a 9K
bytes buffer for later retrieval. The number
of block samples collected at one time was
selected as a trade-off between accurate screen
refreshment and a reliable data collection,
without overflowing the buffer and crashing
the program. However, other sets of numbers
will work equally well, depending on the
computer hardware and speed (fig 3).
Data Plotting.vi: The data-plotting menu
displays a peak-force per repetition and a
linear fit curve is created to form a human
subject profile. The plotting of the force
profile for a single or all fingers is done by
Newtons (N)
Fig. 2. LabVIEW software structure
first stripping the human subject information
from the data file header. The binary data
stored in the data file is converted to an ASCII
format and plotted on the screen. The user
has the option of changing several parameters
of the plot such as: color, scales, line style,
point style, plot type, and interpolation. In
addition, the VI displays a set of markers that
shows when the switch closes and opens for
every key. The VI gives the user the option
of selecting a peak-force profile. This profile
is the result of the calculation of a peak force
for every key-strike (fig 4).
24
Time (sec)
Data Status
Zero Calibration Coe
Pinky:0.0000 N
Ring:0.0000 N
Middle:0.0000 N
Index:0.0000 N
Thumb:0.0000 N
File Name
Start Of Data
End Of Data
Block Size
13052
Start Time
10:16:22 PM
83528
12/10/2001
STOP
Copyright, 1999 J.L.Agraz
Fig. 4. Human Subject data reader peak detector
Multi-Plot Chart: This VI is used as a
troubleshooting tool to test each separate
channel of the data collection system. The
VI collects data in a real-time mode using
a sampling rate of 1KHz in blocks of 50
samples, and displays the data point for
each finger in separate plots. Its used mainly
for troubleshooting purposes because the
development of the system began using many
different force sensors. Also, this VI has the
feature of calibrating the output of the system
for zero input and storing the zero calibration
data in the force.ini file (fig 5).
Data Logger
Middle
Index
Thumb
Ring
Acquisition Information
Pinky
Start Date
4/4/1999
Start Time
4:35:24 PM
Scan Rate
STOP
1000
Number of Samples
30
Copyright, 1999 J.L.Agraz
Fig. 6. Human Subject Datalogger
1.0 _
Force Sensors
&
Switches
System Test
0.5 _
0.0 _
Thumb Force (N)
1.0 _
0.5 _
Time
10:16:22 PM
0.0 _
Index Force (N)
1.0 _
12/10/2001
0.5 _
0.0 _
Start Zero Calibration
EXIT
Middle Force (N)
1.0 _
0.5 _
0.0 _
Ring Force (N)
1.0 _
0.5 _
Copyright, 1999 J.L.Agraz
0.0 _
sets of data blocks. Each block is composed
of a number of data points that can be
controlled by the user through the Block Size
control. Also, the VIs graph contains a palette
that allows the user to zoom in and out of a
waveform and allows complete control over
the X and Y scales (fig 7).
Quit: Exit program.
Pinky Force (N)
Data Reader
0.3
Finger Force
Fig. 5. Human Subject multiple force plot
Kbd Switch
Kbd Switch On
Kbd Switch O
Data logger: This VI quickly begins data
collection without having to fill out an
electronic human subject questionnaire.
However, the VI uses isometric targets setup
in advance in the force.ini file. The purpose
of this VI is to provide the user with a fast
way to collect data from a human subject for
trial purposes. In addition, the VI displays the
date, time and sampling frequency being used
as well as the current force being exerted on
the keys by means of a set of blue color bars.
The recording of the data is at a sampling
rate of 1KHz in blocks of 40 samples that
update the force bars on the VIs front panel.
These parameters are also specified in the
force.ini file. The data is recorded in a binary
file named binary.dat and is stored in the
computers hard disk (fig 6).
Data reader: This VI displays the force
data recorded for all fingers by previous
VIs as the Data Logger.VI and the human
Subject Test.VI. The front panel displays all
the human subject information previously
recorded (if any), and allows the user to
navigate through the data file by means of
Newtons (N)
0.2
Finger Force
0.1
Recording Time in seconds
=X scale/[10*Scan rate]
0.0
20300000
20350000
20400000
20450000
20500000
20550000
20600000
20650000
20700000
20750000
20800000
20850000
20900000
20950000
Samples
What is your gender? Male
What is your age? 31-50
Are you right handed? Yes
Are you under the care of a [hysician for wrist injurise? No
Have you seen a physician about wrist pain in the last year? No
Do you experiance any wrist pain while typing? no
What is your occupation? RDOIJ
Approximately how many hours do you spend typing? 0.0
Have you ever played the piano? No
jose has a cradel for his forearm, index nger will be place on
20999000
11:40.1
Block Size
500
Must be less than the
amount of data in le
Start Date & Time
4:35:24 PM
4/4/1999
Time
NEXT
BLOCK
PREVIOUS
BLOCK
Scan Rate
1000
File Name
19.bin
STOP
Copyright, 1999 J.L.Agraz
Fig. 7. Human Subject data reader
III.
C ONCLUSIONS
The measurement of finger force was realized using a LabVIEW software method.
The experimental results indicated that finger
forces ranged from 300mN to 1.2N with 30mN
force necessary to close the key switch at
1,000 samples/sec. The force was greater for
the thumb, followed by middle finger, index,
ring and pinky fingers. Because of the systems
accuracy, reliability, flexibility and low cost
($2K in 2012), the instrument may have a large
impact in the diagnosis and quantification of
CTS injuries. Hardware information will be
published elsewhere while LabVIEW software
is available for download at NIs website free
of charge. In addition, hardware and thoroughly instrument testing will be published
elsewhere.
ACKNOWLEDGMENT
The authors would like to thank Robert
Pozos for his help and support in making this
work possible. In addition, Patricia Giarraputo,
Jesse Yonkovich, Kathleen Burgess, and Carol
Greentree for their scientific and editorial input.
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