pp.27-33
Yatish Upmanyu1,Sandhya Sharma2, Dr. Amit Singh3
1M.Tech Scholar, Suresh Gyan Vihar University, Jaipur, Rajasthan, India 2Associate Professor, E&C Department, Suresh Gyan Vihar University, Jaipur, Rajasthan, India 3Associate Professor, Mechanical Engg., MNIT, Jaipur, Rajasthan, India
Abstract– Flexiforce sensors are highly sensitive sensors as these are ultra-thin and flexible printed circuits. Due to their typical configurations they need to be handled with utmost care and precautions. For Instance, Load cells, known for high precisions also contributes to various drawbacks such as weight, size, and many contributing features. Generally, the effort is to reduce running injuries such as plantar fasciitis – inflammation in the bottom of the foot ,Achilles Tendinitis (Pain at the back of the leg – most common among the athletes) and the most important to prevent Foot Strike mainly. Despite of spending bulk of budget and highly vivid amount of money in minimizing running injuries and designing highly extravagant shoes, the ideal way is to prevent and deduct running injuries and perhaps easy way is to analyze the impact force and pressure attained at different parts of the foot such as forefoot, heels and joints for hip and flex muscles
Keywords – Accelerometer, DAQ(Data Acquisition), Flexiforce sensor, Foot Pressure Analysis, Foot Biomechanics, Foot Strike, LabView, and Strain Gauge.
INTRODUCTION
n the era of fast pace technology and state of art innovations the standard of clinical advancements had made it possible to remain fit and equally effective for the wholesome neuromuscular efficiency. In this regard the broad study of Gait analysis came into existence. Gait is generally repetitive strategic sequence of lower part of limbs or lower limb movement which ultimately leads to less wastage of energy expenditure among humans. This generally helps in explaining bone and muscle injuries from impact forces and physically applied pressure effects. Gait is generally the co-ordination between CNS (central nervous system) and neuromuscular system mechanisms.
The main objective is the wholesome study of kinematics and locomotion; further, other measurements include EMG (Electromyography), foot strike analysis approach and effect of strain gauge for pressure measurement and analysis. It was a necessity to design a perspective approach to measure the static and dynamic constraints of shear force, acceleration, pressure and strain. My first choice was to make analysis keeping in mind the foot functions and biomechanics related to it. My initial thought was to use accelerometer. It is the most common device and is easily available tool in our smartphones. The accelerometer is widely used to measure the motion and the vibration of the
structures, tolls, devices after being exposed to dynamic load. Dynamic load as in our case is Human activities: walking, running, and jumping. As accelerometers are easily available in any Smartphone had made my work more convenient and smooth as there is no need to do any additional programming on the cell phone.
The data Acquisition system also known as DAQ, plays a very vital role in measurement of plantar, motor and gait related sensory pressures. There has been wide variety of conceptual data’s for measurement of plantar pressures and the one caused by stimuli.
1.1 Pedobarography (PDB) – A Systematic Approach
Pedobarography is generally defined as the study of pressure fields which basically acts between the plantar surfaces of the foot. It is highly used primarily for biomechanical analysis. The analysis generally consists of gait and posture. This biomechanics’ oriented instrument most commonly used for variable analysis ‘peak pressure’ basically experienced over the duration of step or biomechanical behaviour change due to sudden stimuli.
1.2 A201 Flexiforce sensor
The A201 Flexiforce sensor is a thin and highly flexible piezoresistive force sensor and is available in various segments, lengths and diameters depending on the need and requirement of the project. These sensors are highly helpful in pressure measurement in various applications.
TECHNICAL & RESEARCH CHALLENGES
Flexiforce sensors are highly sensitive sensors as these are ultra-thin and flexible printed circuits. Due to their typical configurations they need to be handled with utmost care and precautions. For Instance, Load cells, known for high precisions also contributes to various drawbacks such as weight, size, and many contributing features. Like in this thesis while measuring the patient we wanted to have direct force measurement but due to its vivid application it measures the correlating strain of an assembly based on the applied load, this actually increased the complexity of our way of examining the setup.
2.1 Inevitable role of Data Acquisition
The data Acquisition system also known as DAQ, plays a very vital role in measurement of plantar, motor and gait related sensory pressures. There has been wide variety of conceptual data’s for measurement of plantar pressures and the one caused by stimuli. In this dissertation various National Instruments DAQ cards are used depending on the application of the system. However, Tekscan does produce flexiforce sensors of great tethering functionalities. Data Acquisition system works more like standard bridge transducer much in case of Flexible force sensors and linearized output. Data Acquisition actually helps in delivering high performance range up to 100 lbs. Data Acquisition basically is the process of sampling signals that actually measures physical conditions in real world and then converting samples into the digital numeric values which ids further characterized by computer. Data Acquisition comprises of sensors that converts the physical parameters to a justified electrical signals. While using DAQ device drivers the hardware usually interfaces between the various signals and PC. Various modules are checked during this process; from sensors based I/O Modules (IOM) to General purpose I/O modules all are characterized in order to meet measurement needs. Accelerometers, Strain gage, chassis, controllers and customized automated measurement system with NI Software helped in a fair amount of deal in analyzing, visualization and log of the data is kept under examination.
2.2 Why LabView
LabView is a very popular tool for the reliable data acquisition and signal conditioning. LabView is termed as (Laboratory Virtual Instrument Engineering Workbench). LabView includes extensive list and helpful tools in order to interface devices, instruments etc. In this dissertation I examined the hardware in detail and used native labview functions to control the devices and the bus system for signal conditioning. In order to get the reliable data I have used Compact RIO DAQ and also Virtual Instrument Software Architecture. LabView is used in order to control the acquisition of data with the help of various DAQ cards such as: NI 9234 (Flexiforce sensors), NI 9237 (Strain gauge measurement). These DAQ cards acts as the interface between computer bus system and the hardware. LabView provides a graphical programming platform in designing small to large systems. In this dissertation, the analysis depends on the front panel and the main program window also known as Block diagram to simulate the results for reliable and understandable application output.
The human foot has the typical characteristics of triple axial joint which helps in maintaining rotational movements & in adapting the foot generally in an uneven surface, unhealed road. Further, in the upright position, the neck plays a vital role; neck contains the femur which posteriorly opens the 20 degrees angle (approx). It was deduced by using the anatomical factors with reference to the frontal plane of the humanoid. In the same way hip joint corresponds to the inner/outer-malleolus. Similarly, there is logical connection between the ankle axis and the hip axis.
LabView is used to control and manage the acquisition of data with the help of DAQ cards (NI 9237). The input channel from the sensor is further passed via an amplifier to ADC (analog-to-digital converter). Here the processing takes further step to the processing and memory allocation of data in registers. The final and most important step is to create the loop so that the all the data be processed and simulated in a sequential order for the reliable and better performance. Various components and engineering tools of LabView altogether makes the system worth working and analytical data’s are outlined below with the help of two utmost important essential parts of LabView.
2.3 Kinematics and Locomotion Analysis of Human Foot
Biomechanics of running shoes is the essential relationship between limbs movements & forces used during running kinetics. Foot-strike patterns are variable & vary by multiple factors including speed, rigidity, footwear & surface. Foot-strike helps in examining the foot pressure distribution.
Foot Strike can be subdivided into following three types as
2.3.1 Heel Strike: It is the Pronation stage of foot Strike. Pronation is basically is to describe the rolling motion of the human foot and that too with the help of medial foot elongations. Pronation helps out in neutralizing the uneven terrains. Due to this nature the inner part of the foot when flattens acts as a shock absorber. The thing to keep in mind during this process is mainly deviating/unequal pronation which can cause vivid amount of foot injuries & this abnormal supination mainly forms when the foot is too strong.
2.3.2 Mid-foot strike: It is preferred on a wider scale. A mid-foot strike is basically when most of the force is handles by forefoot and have a slightest of contact with the ground. Even though according to skeletal system heel is the strongest bone o the human body but still it does not absorb the impact force. Gravitational forces also play a vital role in compressing the impact towards the skeleton. Mid foot runners do lands closer to their centre of the ball of the foot or to the centre of mass in comparison to the Hell strike sprinters. Also mid-foot mainly undergoes a moderate pressure in the human foot and thus the impact of force is on the medial part of the foot over the ground.
2.3.3 Forefoot Strike: It is the most essential component for as the most of the pressure is governed by forefoot strike only. Forefoot strike also known as Toe strike, which is considered as commendable form of running technique it occurs when an athlete lands on the ball of the foot towards the exact proportion of the toes. Forefoot affects more of muscle movements and usage as in this case the up and down bouncing is quiet low. Basically, while running to maintain the rhythm & momentum of the body the forefoot runner’s lands closer to their centre of mass comparatively to other runners.
Fig 1 Graphical Analysis of FootSrike
2.4 Clinical Examination of Human Foot
The foot is the main weight-bearing interface between the human body and the foot wears (shoes may be considered) for the purpose of all daily locomotion or stimulus any individual undergo. Generally, the weight of the body during stimulus is mainly transmitted across the heels, forefoot, mid foot, flex, brain stems and the sesamoid bones of first
and second MTH (metatarsal head).Therefore, plantar soft tissues which are mainly beneath the weightbearing humanoid. The function of the foot is mainly in running, jumping, sprinting and in changing directions too. The foot also acts as a very strong lever like to propel skeletal limbs either in forward or backward direction or either ways. The foot plays an essential role in acting as a shock absorber and helps in dissipating shear ground reaction forces.
2.5 Foot Biomechanics
The human foot has the typical characteristics of triple axial joint which helps in maintaining rotational movements & in adapting the foot generally in an uneven surface, unhealed road. Further, in the upright position, the neck plays a vital role; neck contains the femur which posteriorly opens the 20 degrees angle (approx). It was deduced by using the anatomical factors with reference to the frontal plane of the humanoid. In the same way hip joint corresponds to the inner/outer-malleolus. Similarly, there is logical connection between the ankle axis and the hip axis. Consequently, in upright position, there is an automatic rotation due to which the knee gets locked & when the human body walks the pelvis starts rotating approx 20 degrees inward in correspondence to upper limb/leg as soon as the flexion arises and thus, during the swinging state the foot takes up the straight position.
Fig 2 Graphical Comparison
2.6 Shoe Science
Shoe plays a vital role in kinematics of running and walking. Biomechanically, shoe is very important as acts as the interface between the ground & human foot. Shoe on the attachment of cushioned-heel completely transforms the roll over process & makes it compatible to act as a shock absorber. The height of the heel and thickness plays a great role in maintaining the locomotion itself. Shock absorber shoes are in great demand and keep the heel protected and thus, avoids negative effect on roll over process.
MATERIALS AND SENSOR BASED METHODOLGY
Heel 75%
Forefoot 1%
Mid foot 24% Foot Strike Analysis
0 20 40 60 80 100 Percentage
Finisher number
Heel
Midfoot
In order to produce a robust and applicable methodology it is examined & developed based on real case studies considering hands-on experience techniques implemented by using some simulations, optimizations, circuit designing and extensive use of sensors. My main emphasis is to adjudge various aspects of Flexiforce sensor and its vivid characteristics in various fields of applications. This work is purely based on Data processing & Data Acquisition of the simulations achieved after the keen examination of various design procedures implemented with the help of circuit design theory.
3.1 Flexiforce Sensor
environment. Flexiforce The Flexiforce sensor is highly commendable sensor due to its static and dynamic calibration constraints. The Flexiforce sensor is highly-thin and ultra flexible printed circuit mechanism. This sensor makes use of resistive based technology. Flexiforce sensor is a typically flexible in its own way, being having paper-thin construction. This type of construction makes Flexiforce sensor highly durable in measurement of force between any of the two surfaces & the durability is quiet wide under any circumstances or is highly versatile too; it has many advantageous properties such as: drift, temperature assessment, linearity, hysteresis curve nature and simply better force sensing properties. Being a resistive force sensor technology these sensors as a force range of mainly calibrated dynamically. These calibrations are for a wide way use an inertial force of a mass and acceleration can be measured by using accelerometer. Flexiforce sensor has force range of (0-110newton), also, the active sensing circumference is “0.37” dia circle at the one end of each sensor.
3.2 Accelerometer
It is defined as an electromechanical device which is mainly used in measuring acceleration forces. As we know that forces may or may not deviate and thus, are suggested as static or dynamic or may be continuous force to generally sense movement or vibrations. Acceleration is very vital as it is highly essential for the measurement of the change in velocity with respect to time.
3.3 Strain Gauge:
Strain Gauge is defined as simply the pattern of thin wires or foil. It is basically a device whose electrical resistance varies directly in proportion to the amount of the strain actually in the device. It principle states that when the wire is elongated or stretched or shortened it exhibits strain and this strain further leads to change in geometrical configuration and thus, changes electrical resistance of that wire. The strain gauge consists of grid lines, these grid lines or grid like pattern maximizes the quantity of metallic or foil subjects to strain in elongated parallel direction.
3.4 Gauge Factor
It is defined as the ratio of small change (fractional) in electrical resistance to the small (fractional) change in length. Generally, strain gauge sensitivity to strain is GF (gauge factor). Actually, sensitivity is synonym to the gauge factor to be precise.
Mathematically,
GF =1+ 2ʋ (Categorized as Piezoresistive Effect)
Table No. 1 General Examples of Strain Gauges
Material Type Gauge Factor(GF) Metallic Foiled Strain Gauge 2.0-5.0 Thick Material Film Resistor 100.0 Single Crystal Silicon Material -124.0 to +199~200 Polysilicon ±30
3.5 LabView Interfacing for Flexiforce Sensors:
LabView is abbreviated as (Laboratory Virtual Instrument Engineering Workbench). LabView is considered to be a graphical programming language that eventually uses icons instead of text formats to create applications more enhanced. The graphical language is named “G”. Labview is ideal software for any kind of measurements related to control system developed by NI (National Instruments) and is considered to be the heart of NI Design platform. LabView offers wide capacity for future innovation for prolonged productivity and faster analysis. It is highly integrated software with the hardware equally capitalizing on the latest computing technologies. The innovative part of LabView is its exclusive use of Data flow programming. G language is basically capable of high end parallel execution of various function nodes.
Fig 3 DAQ (Data Acquisition) setup for Flexiforce Sensor Conditioning
LabView data is basically interfaced with the DAQ card, for e.g. 9234, as the card for our dissertation to study FootSrike at different parts of human foot. I kept full care in connecting various channels Ai0,
Yatish Upmanyu1,Sandhya Sharma2, Dr. Amit Singh3 SGVU J Engg. & Techno., Vol. 2, Issue 1, pp. 27-33
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Ai1, Ai2 (1st part of the below mentioned figure) to get the output for Heel, Midfoot & Forefoot signals processing. This DAQ Card is further connected to the connector on which the card is hold (2nd part of the below mentioned figure) and thus, is finally adjoined to the Computer bus system in which the LabView is installed. In this way the LabView is build which is termed as “Building VI” and this illustration on the window command indicates that our data acquisition is successfully initialised.
Fig 4 LabView Interfacing Module setup
SIMULATION RESULT AND DISCUSSION
Foot Strike Analysis in shoe pressure measurement is a very inexpensive and is highly convenient way to display the various parts of human foot and which part undergoing how much pressure. It usually displays the pressure, maximum force and strain in various parts of human foot. In my dissertation data simulation is based on Flexiforce sensor & Strain gauge sensor with few references to accelerometer study too to make the concept clearer and efficient.
4.1 Preliminary Results
Using NI-DAQ driver software and LabView, we connect our prototype circuit PCB Layout to an SCXI Flexiforce sensor module and also the connector with the Bus system using DAQ card NI 9234. We created the block diagram for the Flexiforce sensor to test the prototype we had built for our convenience on NI Elvis also. On analyzing the pressure sensor in three different parts of human foot: heel, mid and forefoot we got the following results as:
Table No.2 Comparison of Various Types of Foot Strikes
Enhanced approach is used in terms of both software and hardware assessment and derived the conclusions based on the sensors.
Fig 5 Locomotion Variation due to Foot Strike
4.2 Accelerometer Software Approach:
Fig 6 Accelerometer Simulation in reference to LabView
It was a necessity to design a perspective approach to measure the static and dynamic constraints of shear force, acceleration, pressure and strain. My first choice was to make analysis keeping in mind the foot functions and biomechanics related to it. My initial thought was to use accelerometer. It is the most common device and is easily available tool in our smartphones. The accelerometer is widely used to measure the motion and the vibration of the structures, tolls, devices after being exposed to dynamic load. Dynamic load as in our case is Human activities: walking, running, and jumping. As accelerometers are easily available in any Smartphone had made my work more convenient and smooth as there is no need to do any additional programming on the cell phone. We can easily find out the force by using the relation as F=ma, here m = mass of human foot and a = acceleration. Acceleration is generally got by the sensor attached to the leg of human foot. But, certainly at a later stage I realized that I cannot study individual comparisons study of heel, midfoot or forefoot as accelerometer does can let me know the force but will not show if the force is coming from heel, midfoot or forefoot or any part of the foot.
Fig 7 Variation of human foot when undergo any stimuli how does the accelerometer behaves with the sensor
But, I do have analyzed the basic nature of Flexiforce sensor and showed the variation of human foot when undergo any stimuli how does the accelerometer behaves with the sensor. So, after a brief analysis I used LabView (Laboratory Virtual Instrument Engineering Workbench), with this software I analyzed that voltage signals waveform chart of yaxis is generally obtained& estimated on giving slight variation to the accelerometer device ADXL 335. For interfacing DAQ card is used. The Vcc, Ground and the Y-pin of accelerometer are connected to the DAQ card of National Instruments.
FINAL RESULT
LabView is used in order to control the acquisition of data with the help of various DAQ cards such as: NI 9234 (Flexiforce sensors), NI 9237 (Strain gauge measurement). These DAQ cards acts as the interface between computer bus system and the hardware. LabView provides a graphical programming platform in designing small to large systems. In this dissertation, the analysis depends on the front panel and the main program window also known as Block diagram to simulate the results for reliable and understandable application output.
5.1 Block Diagram (Programming Window):
PART I
Shunt Calibration and analysis of Wheatstone parameters also acquiring the data for the signal conditioning of these parameters.
Fig 8 Signal Conditioning and Shunt Calibration (PartI)
PART II
Final error output phase with reference to acquire output of the data:
Fig 9 Signal Conditioning and Shunt Calibration (Part II)
5.2 Front Panel Simulation (Control and Indicators):
Fig 10 Control and Indicators Setup
CONCLUSION
The main objective of my experimental analysis and simulation was to provide less expensive, a low-cost substitute for the foot pressure analysis and Foot strike measurement. We basically built a kind of in shoe pressure simulation measurement and Foot Strike analysis system to imprint of how the foot behaves as soon as it strikes on the ground. This dissertation also depicts the maximum pressure, stress and sensitivity parameters at different parts of human foot: Heel, Mid foot, Forefoot with the help of Gauge Factor. The peculiar aspect of this
experimental work is also to analyze the person correct way of running and how the foot behaves as soon as it lands in the ground. All these factors are analyzed while performing simulations.
With the required output we generated will help in extracting the foot functions, Gait analysis and in identification of the pressure and force range for extensive medical applications and Biomechanics, This study will also help on a large scale in Effective Footwear design, isolation of various foot related functions, foot screening, comparison study of footwear design and foot science technology attributes.
REFERENCES:
[1] C Lebosse, B.Bayle, M. de Mathelin, P.Renaud L GeCo, “Nonlinear modelling of low cost force sensors”,Robotics and Automation, 2008.ICRA 2008.IEEE, 2008/5/19.
[2]. A. Leon-Garcia, “Probability, Statistics, and Random Pro- cesses for Electrical Engineering”. Prentice Hall, 2008.
[3]. Vei Jye Thor and Jin Huat Low, “Designing an In-shoe Pressure and Shear Measuring System using NI LabView, DAQ and SCXI “, National University of Singapore.
[4]. Jacob.H.A.C, “Clinical Biomechanics 16 (2001)783-792[3]”, 2001
[5]. Zelun Zhang and Stefan Poslad, “Optimum use of Foot Force Sensors and mobile phone GPS for mobility Activity Recognition” Queen Mary University of London, 2014
[6]. Brand et al, “Biomechanics or Necromechanics”, the lowa journal, 2001.
[7]. Komi etal,”Biomechanics, Biology of Movements”, 2000.
[8]. Kalamdani abhinav, “Development and characterization of a high-spatial-temporalresolution Foot-sole-pressure measurement system”
The Robotics Institute Carnegie Mellon University Pittsburgh, PA 15213, August 2006.
[9]. Tara Sulewski, “Gait Retraining – A Smart Shoe” device to measure the ground reaction force primarily under the foot & provides a real-time feedback, for gait analysis.
[10]. Liu et al.199 E.L Teng, P Chou, H.H Hu, W N Cheng, B.N.Chiang, “Performance of a dementia screening test in relation to demographic Variables”.