Smart Cane: Instrumentation of a Quad Cane with Audio-feedback Monitoring System for Partial

Weight-Bearing Support Joseph Mercado*, Gemmilyn Chu, Erika Jane Imperial,

Kelvin George Monje, Rae Mart Pabustan, Angelito Silverio Electronics Engineering Department

University of Santo Tomas Manila, Philippines

jmercadoece@gmail.com

Abstract—Proper cane handling is one of the main goals of cane therapy in the field of physical rehabilitation. Toward that goal, a system has been developed to monitor the weight-bearing performance of the patient and provide an audio feedback to affect a patient’s weight application onto the cane. The smart cane is designed to read the force measurement, to compare the read-out force and to generate an alert message if the force applied by the patient is incorrect. The system includes a graphical user interface, which allows real-time graphing of the force measurements and keeps a database for offline comparative data analysis by the therapist. It employs a wireless connection between the microcontroller and the computer using Bluetooth technology, which increases mobility of the patient. This will help the patient to achieve optimum rehabilitation that can lead to an improved balance in walking and eventually cane independence. Keywords— Cane, Audio-feedback, Weight-bearing, Load cell, Bluetooth, Physical Therapy

I. INTRODUCTION Physical Therapists (PTs) have no quantitative means of assessing the progress of the patient using walking aids for rehabilitation [1-2]. When the patient leaves the hospital, there are no means to monitor if the patient correctly uses the cane for his therapy or not. For faster and optimum rehabilitation effectiveness, it is important that the prescribed partial weight bearing is applied to the cane to support the impaired leg. The PTs just assess qualitatively the movement kinesiology of the patient without having a measure of the actual force applied onto the cane. Embedding sensors and monitoring circuitry onto these ambulatory aids such as the cane can support the PTs patient progress evaluation [3-7]. Moreover, if equipped with feedback mechanism, the patient can now be informed whether or not he is applying the right partial weight bearing or not. The Smart Cane System aids in monitoring the progress of rehabilitation by determining if proper weight-bearing is applied to the cane. It has a force pre-set feature that allows

the therapist to adjust the weight-bearing percentage that must be applied to the cane for optimal rehabilitation. This usually ranges from 20 – 25% of the patient’s bodyweight [2],[6]. It monitors the applied force and correspondingly issues an alarm whenever the prescribed weight application has not been achieved. This alarm will tell the user to either increase or decrease the force being applied. The alarm is continuous until such time that the force applied by the patient is within the allowable range of force application. The system will also keep a log of the force measurements and their contact duration during each step. This will provide the therapist a quantitative data of rehabilitation using the cane. While the Smart cane system uses sound as feedback, other cane systems provide feedback by means of vibration or lights. There are also other biofeedback devices that use foot plantar pressure rather than an instrumented cane. Examples of these devices include; Pedar (Novelgmbh, Munich, Germany), F-Scan (Tekscan Inc., Boston, MA, USA), and SmartStep (An-dante Medical Devices, Beer Sheva, Israel) weight-monitoring systems, which are most notable for their portability and accuracy. One major disadvantage of these portable plantar pressure devices is the cost. The Smart Cane system offers a low-cost rehabilitative tool for clinical and in-home therapy.

Figure 1. Smart Cane prototype

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II. METHODOLOGY To incorporate an audio feedback on the quad cane to monitor the weight- bearing of the user, a force sensor is installed onto the handle of the cane to measure the force exerted on it and an accelerometer to detect cane swing. These sensors are calibrated first to ensure that they exhibit the characteristics needed. A microcontroller is used to read the force measurement, compare the readings to the clinically set weight-bearing percentage, and generate an alarm once the force is out of range. The alarm will notify the patient to either add or reduce the force exerted on the cane. Bluetooth technology is used so that data will be transferred from the computer to the cane and vice versa. A graphical user interface (GUI) is also used to input the weight of the user, show the instantaneous applied force and provide a record of the force measurement logs and graphs obtained from the Smart Cane. This shall be an added feature so that the physical therapist may have a quantitative measure on the progress of the user. The Smart Cane was tested on thirty normal subjects in a controlled environment. Measurements of the applied force using the system with and without audio feedback were obtained for analysis. The effectiveness of the cane was verified through the comparison of weight-bearing performance of the user with and without the audio-feedback. A statistical tool, such as Paired T-test, was used to determine whether or not there is a significant effect on using the audio feedback system.

The system consists of four major blocks namely: the sensors and signal conditioning circuits; the microcontroller with associated hardware and software; the Bluetooth interface for wireless data transmission; and the audio feedback amplifier. The system block diagram is shown in Fig. 2.

Figure 2. System block diagram

A patient applies a force on the instrumented cane and this is instantaneously recorded through the sensor read-out circuit.

This circuit converts the measured force into voltage and sends it to an A/D converter, then to thedata communication interface. The microcontroller will then compare the measured applied force to the weight bearing percentage set by the physical therapist. The microcontroller will issue an alert message through the speaker once the measured force is outside the pre-set weight bearing percentage. The microcontroller will also send the data gathered to a computer via Bluetooth transmission and keep a database, which allows physical therapists to better evaluate the rehabilitation progress and establish appropriate rehabilitation programs. One of the sensors used in this study is a load cell, which produces an output signal that is proportional to the applied force. The load cell consists of four strain gauges in a Wheatstone bridge configuration contained in a metal bar. It was implemented as the handle of the cane to measure the force applied by the user. One end of the load cell was mounted on a rigid structure which is the cane’s shaft while the other end receives the load or force being applied by the patient in the form of a cantilever. The load sensor was calibrated by applying increasing standard test weights with increments of 1 kg until it reaches 20 kg. The respective voltage readings for every load increment were recorded when the readings stabilize. This data served as the calibration curve and whose slope was implemented onto the microcontroller program. The calibration curve is shown in Fig. 4.

Figure 3. Force sensor mounted as handle of the cane

Figure 4. Load sensor calibration curve

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The result shows that the load sensor linear response. The output voltage is papplied force with a slope of about 0.25electrical signal output coming from the order of a few millivolts, it was amplifinstrumentation amplifier with a gain of 1diagram of this circuit is shown in Fig. 5.

Figure 5. Instrumentation Amplifier schematic diagram

cell is represented by a resistive wheatstone

The 3-axis analog accelerometer was uswing. It uses ADXL335 low cost 3-axis works on 1.8V to 3.6V power supply ivoltage of the 3-axis analog accelerometerand when it is tilted was recorded. Taccelerometer produces a voltage of 1.15V and a slight change in voltage when it wasvoltage of the 3-axis analog accelerometer serves as the basis of threshold to measurement of the microcontroller.

The smart cane uses an Arduino-basecalled Gizduino. It is an open source cobased on a simple I/O board and theprogramming language. The board is poweand consists of an Atmega 168 microcontrand a 16MHz crystal. The Gizduino is progIntegrated Development Environment (IDETX disable switch. .

A Bluetooth shield compatible with thwas used to establish a wireless limicrocontroller and a remote computerBluetooth device acts as the master and theBluetooth shield acts as slave. Both devicessame baud rate for successful connectioshield employs the EGBT-04 series lomodule. It simplifies Bluetooth integration bas a simple UART channel to its host. Sendata to and from another Bluetooth devicsimple task of reading and writing to the

exhibits an almost proportional to the 5mV/kg. Since the load cell is in the fied using AD620 00. The schematic

m. Note that the load e bridge.

used to detect cane accelerometer and nputs. The output r when it is steady The 3-axis analog when it was steady s tilted. The output when it was tilted

initiate the force

ed microcontroller omputing platform

e use of standard ered by 5V supply, oller, 20 I/O ports, grammed using the E) with serial RX –

he microcontroller ink between the . The computer’s e microcontroller’s s must be set to the on. The Bluetooth w cost Bluetooth by presenting itself

nding and receiving ce is reduced to a

equivalent UART

channel. All complex bluauthentication, encryption, tranare automatically performed anby the EGBT-04. This Bluetoo9600 bps (bits per second) by dset depending on the desired tra

Figure 6. Smar

Our system also incorporat(GUI)for the user, e.g. physicalthe pre-setting and data logresearchers utilized an open-souPro(Release 9.2 Version 4 Betimplementation. Thirty subjects were enrolsubject was first instructed contralaterally. Contralateral usis the usually preferred methoforces, reducing pressure on tmaintaining more normal aContralateral cane use also resuduring gait. The biofeedback cthat the handle would be at thgreater trochanter. Subjects wloading the cane within 15% using a bathroom scale for feeperformed walking trials of cadence using the cane withouwere simultaneously logged retrials this time with the audiosegments were truncated and distance. Paired t-test was donesignificant improvement in theaudio-feedback.

III. RE

Two data sets were obtainedand without the audio feedbackthe percentage of the correct fo

uetooth tasks involved – nsport, channel hopping, etc.,

nd hidden from the user’s view oth module has a baud rate of default, but can be changed and ansmission rate.

rt Cane main components

es a Graphical User Interface l therapist, to easily manipulate gging on the system. , The urce program called StampPlot ta of June 2011) for the GUI

led to test the system. Each on how to use the cane

e of the cane was selected as it od for relieving hip abductor the plantar foot surfaces, and

arm-leg motion during gait. ults in less frontal plane motion ane’s shaft can be adjusted so

he same height as the subject's were then asked to practice and 30% of their bodyweight edback [6]. The subjects then 10-meter distances with free

ut any audio alarm. Force data emotely. Then they re-do the o alarm. Starting and ending not included in the 10-meter

e to evaluate whether there was e patient’s cane loading with

ESULT d for each subject for trials with . With each trial, the hit-rate or

orce loading onto the cane was

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obtained for each subject. Then, the hit ratethe audio-feedback were compared. Test r18 of the 30 subjects (60% of total populaimprovements in their applied forces whsystem was used; 4 subjects (13.33%) performance; while 8 subjects (26.67%) hrates when audio-feedback was used. Thispie chart of Fig. 7.

Figure 7. Effect of audio-feedback to 30 respondents wcane for ambulatory aid

To test for the significant difference in theach subject, a paired T-Test was donesignificance. A p value less than 0.05 significant difference with and without thThe paired T-Test results are shown in Tabl

TABLE I. P-VALUES OBTAINED FROM PAIRSIGNIFICANCE LEVEL

Subject p value Subject p value

1 0.040473 11 0.025652 2 0.000281 12 0.216702 3 0.015695 13 0.755829 4 0.00000529 14 0.014964 5 0.040532 15 0.00000124 6 0.038926 16 0.004968 7 0.000472 17 0.98238 8 0.408103 18 0.042363 9 0.865554 19 0.00000126

10 0.576907 20 0.000215 Based from the results of the paired T-subjects have shown significant differenceforces on the cane. There is a strong correto those subjects who have improved pregard to hitting the right partial weight-bwhen the smart cane was used.

IV. CONCLUSIONS The implementation of an audio-feedbacachieved by integrating a microcontroller, accelerometer, and a buzzer onto the cdeveloped in this study could provide userweight-bearing through an audio feedback. system has demonstrated acceptable

es with and without results showed that ation) have relative hen audio-feedback

have unimproved have decreased hit s is detailed on the

who utilized the smart

he two data sets for e at 5% level of tells that there is

he audio feedback. le I.

RED T-TEST AT 5%

Subject pvalue

21 0.035532 22 0546189 23 0.003202 24 0.02973 25 0.010445 26 0.0000165 27 0.000102 28 0.799493 29 5.78E-08 30 0.415352

-Test, 22 of the 30 es in their applied lation of such data performances with bearing percentage

ck cane system was load sensor, 3-axis cane. The system r control for proper In subject tests, the

audio feedback

characteristics. Based on the testhat audio-feedback can help performance of the user of the this study can be made by minand the number of wires in interfacing the microcontrollerdevices. Further work with thisemploying larger populations toof audio feedback on cane loadi

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[1] L.C. Chen, H.C. Chen , M.K.

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[3] MajdAlwan, AlexandreLedoux,Cunjun Huang. “Basic walker-asforces and moments exerted onormal subjects” Medical EngineApr. 2007.

[4] H. Hurkmans. “Partial Weight Bin patients with a total hip arthroM.A. thesis, Erasmus Universitei

[5] L. Inverarity. “Your Guide http://www.walking-canes.net/ne2012].

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st results, it can be generalized improve the weight bearing

cane. Further developments in nimizing the components’ size the hardware design, and by r with other plantar pressure

s system should include studies o better characterize the effects ing.

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2014 IEEE International Symposium on Bioelectronics and Bioinformatics (IEEE ISBB 2014)

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