enhanced hardware design of force platform - report

Monash University Malaysia Sunway Campus

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TRC3000MECHATRONICS

PROJECT 2

MULTIPLE FORCE PLATFORMS USING

ETHERNET DAQ DEVICE

Final Report

Multiple Force Platforms Using Ethernet DAQ Device Final Report

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Team Members

M. M. Danushka Ranjana Marasinghe 19778252

Mervin Chandrapal 19906110

Jeya Mithra Kumar 19206895

Tung Mun Hon 19906064

Yulius 19573294


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Abstract

The project was carried out as a requirement of the subject TRC3000 and also to upgrade and improve existing designs of previous students. Its goal is to fabricate and program two similar force platforms that can be interfaced to perform as one; to analyze the motion of a test subject.

The platforms consist of 5 layers. First layer is 3mm thick and consist of 144 with 20mm holes drilled through acrylic for each platform. It’s to provide the place of FSR sensors. Second layer is also 3mm and consisting of 144 holes, but the diameter for the holes is 10mm. The sensors will be placed on this layer and the sensor leg will be place through the holes. Third layer is Copper board, which is the connection of 144 sensors to 40 ways male connector as output. Fourth layer is a smooth rubber material. The purpose of this layer is to protect the connections of the copper board. And the final layer is to ensure the stability and rigidity of the platform. It’s 3mm thick acrylic material.

The data acquisition circuit is responsible for collecting data from sensors. Voltage divider is used to convert the FSR resistance values to voltage values. LM324 op-amps are used to amplify the voltage reading. The output voltage from each sensor is then multiplexed using CD4051B 8 channel multiplexer. For the convenience of troubleshooting six voltage outputs will multiplex into 1 output. The required digital inputs for the multiplexer are given by the LABJACK DAQ unit. After that all the data will be sent to computer in voltage form.


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Acknowledgements

Our gracious gratitude is extended to those who in one way or another aided and instructed us in the process of completing this monumental project. First and foremost to our lecturer Dr Arosha Senanayake who assisted us through out this project. Also not forgetting Mr. Darwin, the designer of the previous force platform and Mr. Khoo Boon How who helped us in difficulties faced while using LabVIEW.

Not forgetting also our dedicated lab technicians Mr. Paneer, Mr. Maniarasu and Mr. Khalid who readily provided us the necessary tools to complete the project successfully.

Last but not least we would like to thank all those who helped us throughout this project whose name we have failed to mention. Without the help of those concerned our project may never have been completed.


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Contents

Introduction ..................................................................................................................................................7

Background ...................................................................................................................................................9

Literature Review....................................................................................................................................10

Objective .....................................................................................................................................................11

Description of the Force platform ..............................................................................................................12

Background .........................................................................................................................................12

Preliminary designs.............................................................................................................................12

Platform: by Layers .............................................................................................................................13

Description of the Switching and multiplexing circuit. ...............................................................................20

Circuit Overview......................................................................................................................................20

Quadrant Selector...............................................................................................................................20

Row Selection......................................................................................................................................21

Column selector ..................................................................................................................................21

Complete Circuitry Overview..............................................................................................................22

Description of the PCB Layout ................................................................................................................23

THE PIN CONFIGURATION ........................................................................................................................24

Hardware of the circuit...........................................................................................................................25

Circuit 1 ...............................................................................................................................................25

Circuit 2 ...............................................................................................................................................26

Inter Connecting Circuit ......................................................................................................................26

Lab View Programming and Explanation ....................................................................................................27

Introduction to Lab View d ......................................................................................................................28

Summary and Block Diagrams of Program Design..................................................................................30

Summary of How the Program Works: .......................................................................................................30

Block Diagram .....................................................................................................................................31

Scanning Process.................................................................................................................................32

Replay Simulation ...............................................................................................................................33

Detail Explanation on the Program Design.............................................................................................33

Section 1: Run Simulation Menu Section............................................................................................34


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Section 2: User Input Section..............................................................................................................36

Section 3: Scanning and Force Conversion Processes Section............................................................39

Section 4: Force Summation and Specific Activity Parameters Computation Section .......................59

Section 5: Replay Simulation section..................................................................................................65

Graphical User Interface (GUI)............................................................................................................70

Components used during the project. ........................................................................................................80

Evaluation ...................................................................................................................................................86

Comparison with previous Designs Force Platform................................................................................86

Comparison with previous Designs Switching Circuit ............................................................................88

Problems faced .......................................................................................................................................90

Future improvements .................................................................................................................................92

Reference....................................................................................................................................................93

Appendix A - Description of Timelines

Appendix B – Work Distribution

Appendix C – 3D CAD Drawings Material properties table/chart. FSR Platform Top Layer Dimension Second layer Dimension Second Layer reverse dimensions Bottom layer Dimensions

Appendix D – PCB Design

Appendix E – Data Sheet FSR CD4051BCN LM324 IC7660 LabJack UE9 Quickstart Guide CB37 LabJack Extension datasheet


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Introduction

The subject of biomechanics on sports is growing as athletes going to improve their performance and also improve accuracy in sports. Many students and scientists are interested to learn about it and is also a good idea to appreciate forces involved and Newton’s laws. The force platforms are using to measure the magnitude and direction of force between an athlete or subject and the ground (force platforms). Force platforms consist hundreds of force detecting sensors that are used to detect the force applied on them.

Besides biomechanics, force platform is also used in various fields, such as gait analysis, engineering, medical research, orthopedics, rehabilitation evaluation, prosthetics and other general industrial uses. Common applications of force platform are such as:

To evaluate the movement pattern of a test subject and jumping performances of an athlete evaluation of ground reaction forces associated with dogs at a walk, trot and while jumping compare forces, before and after surgery Evaluate and compare between normal and abnormal gaits

In addition to force distribution density chart, the force platform has several common additional features, as follow:

Summation of forces applied on force platform Jumping in flight time Jumping take-off velocity

The purpose of this project is to design, build, and validate two similar force platforms. These two force platforms will be combined into one so that they will be able to provide a larger movement area for test subjects. The sensor which will be used in this project is force sensing resistor (FSR). As their name implies, force sensing resistors use the electrical property of resistance to measure the force (or pressure) applied to them.

The force platforms are divided into three main sections, the platform, the data acquisition circuit and the data acquisition software. The platforms are used to obtain the data for analysis of movements such


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as running, jumping and walking. The data acquisition circuit will do the reading, convert the data collected by sensors and send it to computer. And finally the data acquisition software is used to convert the data collect from sensors and display it as force, velocity etc.

The platforms consist of 5 layers. First layer is 3mm thick and consist of 144 with 20mm holes drilled through acrylic for each platform. It’s to provide the place of FSR sensors. Second layer is also 3mm and consisting of 144 holes, but the diameter for the holes is 10mm. The sensors will be placed on this layer and the sensor leg will be place through the holes. Third layer is Copper board, which is the connection of 144 sensors to 40 ways male connector as output. Fourth layer is a smooth rubber material. The purpose of this layer is to protect the connections of the copper board. And the final layer is to ensure the stability and rigidity of the platform. It’s 3mm thick acrylic material.

The data acquisition circuit is responsible for collecting data from sensors. Voltage divider is used to convert the FSR resistance values to voltage values. LM324 op-amps are used to amplify the voltage reading. The output voltage from each sensor is then multiplexed using CD4051B 8 channel multiplexer. For the convenience of troubleshooting six voltage outputs will multiplex into 1 output. The required digital inputs for the multiplexer are given by the LABJACK DAQ unit. After that all the data will be sent to computer in voltage form.

The data acquisition software will take the data and convert the voltage gain from data acquisition circuit to data and useful information wanted by using LABVIEW software.


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Background

The basic concept and function of force platforms are to obtain the force exerted between subject and the floor (platforms) while performing in sports activities, such as running, jumping, and walking. This data is important to improve the performance of athletes. It can also be used to research the suitabletype of floor for some kinds of sports.

In this force platforms constructed, there consist of 3 parts, platform, data acquisition circuit and data acquisition software. There are 2 platforms constructed, each platform contains 144 FSR sensors. It is used to take the data from walking, running and jumping on the sensors.

The data from sensors will be processed in data acquisition circuit by using LM324 op-amps to amplify the voltage reading. 8 channels multiplexer switching IC is used to multiplex 6 voltage output into 1 voltage output. After that the output will be sent to computer through Ethernet LABJACK DAQ device.

The data from LABJACK device will be processed in the computer using LABVIEW software. It will convert data from LABJACK in voltage form to useful information such as force, velocity and etc.


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Literature Review

Some of similar product has been available in the market. Among them which are used as reference as mention as below:

1. The Magic Carpet a

Magic Carpet is a prototype that uses a pair of Doppler radars to measure upper-body kinematics such as velocity, direction of motion and a grid of piezoelectric wires hidden under a carpet to monitor dynamic foot position and pressure. Magic carpet has been used in an audio installation, where users launch and modify complex musical sounds and sequences as they wander about the carpet.

2. Pressure Sensitive Floor b

This device is designed to help study of human step movement. By measuring the pressure of a user interacting with the system, the device is able to provide real-time knowledge about both the location of the performer on the floor as well as the amount and distribution of force being exerted on the floor. The device consists of numerous pressure sensor mats that are capable of gathering and transmitting pressure information to the computer.

3. The 'Smart' Floor c

This prototype is designed for identifying people based on their footstep force profiles. This floor system may be used to validate biometric user identification based on users’ footsteps. The 'Smart' floor consists of several load cells that is used to convert forces into electrical signals. The signals are hen converted from analog to digital via Ethernet data acquisition.


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Objective

The objective of this project is to build two multi-sensor force platforms consisting of hundreds of force sensitive sensors. The sensors are to measure force distribution, evaluate movement and jumping performance of athletes exerted on both platforms. These force platforms should be able to be combined into one. By combining two force platforms, they will be able to provide a larger movement area for test subjects. Substantial improvement over the current hardware design is essential.

The information from the sensors is to be transmitted to a computer. For data acquisition, a DAQ system is to be developed to integrate LabJack Ethernet device and the platform. The data acquisition device will be used to receive data signal from the force platform and transmit it to the computer. Performance of the LabJack device is to be evaluated as well as increasing the accuracy of the data acquisition. Overall device portability is designate to increase at the same time.


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Description of the Force platform

Background

The Force platform is designed to house the FSR sensors. Its build has to be sturdy and durable, plus it has to withstand large force and impulse due to jumping.

Many designs were considered and much research was put into designing a platform that would be able to meet these requirements.

Material selection was carried out and based on the previous designs and research on the various material properties (Appendix C) it was concluded that the best material that met both the stability requirements and the aesthetic requirements was acrylic.

Therefore the first task undertaken was to fabricate a prototype to test the material that was chosen, for elasticity, durability and crack resistance.

Once the prototype was fully tested and its functionality was proven then the actual board was fabricated.

Preliminary designsThe first design was to place the FSR sensors in a 3 mm groove (Appendix C) at the top most layer of

the platform this would minimize the thickness and the weight of the platform. However it was soon discovered that cutting a groove in acrylic wasn’t a feasible option since it could lead to cracks in the whole piece of acrylic. Therefore the other option was to place another 3mm thick piece on the top of the current layer and cut through holes, since this was much easier to fabricate.

The initial design also made use of individual wires to connect the sensors this was the method used in the previous board designs (generation 1 & 2).this caused the board to be extremely bulky and introduced unnecessary complications. The alternative chosen to overcome this difficulty was to replace the entire wiring of the sensors with a PCB. The PCB would have connections that would connect directly to the sensor “legs” at one end and to the connectors at the other end.

Lastly the platform need to be secured in place t was suggested that countersunk screws be used but the force of a jump or the impact of the landing may cause the screw holes to crack. Thus the use of bolts and nuts was adopted.


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Platform: by Layers

CAD designBefore the pieces could be fabricated they had to be first designed and tested by simulation to check for possible problems that might arise due to design or while assembly

For this purpose two softwares were used: SOLIDEDGE and SOLIDWORKS.

Solid EDGE

Solid Edge is 3D CAD parametric feature solid modeling software. It runs on Microsoft Windows and provides solid modeling, assembly modeling and drafting functionality[2] for mechanical engineers. Through third party applications it has links to many other Product Lifecycle Management (PLM) technologies.

Originally developed and release by Intergraph in 1996 using the ACIS geometric modeling kernel it later changed to using the Parasolid kernel. In 1998 it was purchased and further developed by UGS Corp (the purchase date correspond to the kernel swap). [3]

Solid Works

SolidWorks is a 3D mechanical CAD (computer-aided design) program that runs on Microsoft Windows and was developed by SolidWorks Corporation. SolidWorks is a parametric feature-based solid modeler, using the Parasolid geometric modeling kernel. SolidWorks was introduced in 1995 as a competitor to CAD programs such as Pro/ENGINEER, I-DEAS, Unigraphics, CATIA, and Autodesk Mechanical Desktop, and is currently one of the leading products in the "midrange" or "mainstream" mechanical CAD market.[4]

SolidWorks employs a parametric, feature-based approach to creating models and assemblies. Parameters refer to constraints or conditions whose values determine the size, shape, characteristics, and behavior of the model or assembly. Parameters can be either numeric, for example dimension values such as the diameter of a circle or the length of a line; or geometric, such as conditions like tangent, concentric, coincident, parallel, horizontal, and the like. Numeric parameters such as dimensions can easily be related to each other through equations to capture even the most complicated design intent. [5]

Top LayerThe top layer has to allow for an opening to enable the sensor heads (the sensitive part of the

sensor) to come into direct contact with the applied force. To this end there are 144; 20mm diameter holes drilled to allow contact to the FSR sensors. There are also 54; M4 countersunk screw holes spread evenly. These screws are of utmost importance to hinder the whole platform from sagging or bulging.


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The dimension of the entire board is 540 mm x 480mm. A 3mm thick piece of acrylic was used for the top player.

Figure 1 Top Layer

The final aspect that was to be considered is the interface or the junction when two or more boards are connected. Previously the junction would be an area which was insensitive to applied force. To overcome this problem the sides of the platform are spaced at half the normal distance between sensors, therefore when two boards are placed together there will be a seamless transition from one board to another.

After the top piece was designed the CAD drawings were used to fabricate the actual part. Forthe engineering drawings refer to drawing appendix (Appendix C)

Second LayerThe second layer of the platform is designed to house the FSR sensors. There are two parts to

consider when housing the sensor, firstly the FSR’s have to be in alignment with the holes in the layer above, secondly the FSR “leg” holes have to match with the copper clad board in the layer below. The original design was to embed the sensors in to the acrylic but this measure turned out to be impractical. Therefore the sensors were just placed on the layer and a 10mm diameter through hole was cut into the piece to allow the FSR “legs” to be connected to the copper clad board in the layer below .

The first diagram(Appendix C) shows the projected placement of the FSR’s from the top layer to the second layer. This view simplifies the estimation for the placement of the FSR “leg” holes.


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Figure 2 Second layer (Top view)

The second view (Appendix C) shows the actual holes (12mm diameter) that allow the FSR “legs” to connect to the copper clad board below via the double SIL connectors.

Figure 3 Second layer (Reverse View)

Third LayerThis layer deals with the connections that have to be made between the sensors and the

external interface. As mentioned above the previous generation’s design utilized wires to connect each individual sensor. This method although simple in theory was extremely error prone and painstakingly difficult to troubleshoot. Therefore it was propose to use a copper clad board to manage the wirings.

The required copper tracks are drawn on the board by means of an etch resist pen then the rest of the copper is etched away. Once the tracks have been etched and the SIL (Single In Line) connectors soldered onto the reverse side of the board the sensor can then be plugged into the connectors enabling ease of removal and replacement.

Each sensor needs to be connected to +5 V supply and the other lag will be connected as the output signal.


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Figure 4 Copper Tracks Wiring Design

To protect the sensitive circuitry a soft padding layer is sandwiched between the bottom layer and the copper tracks.

Fourth Layer The bottom layer i.e. the final layer functions as a cover to hold all the layers together. Its

fashioned from the same material as the top two layers that is a 3mm think 40cm x 54cm acrylic piece(Appendix C). On the bottom side nuts are fastened to the M4 bolts. There is also a soft padding layer attached to the bottom side to prevent the board from sliding and also to even out the force that the bolts will concentrate.

Figure 5 Bottom Layer


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Assembled CAD Model of platform

Figure 6 Isometric View of assembled platform

Actual PlatformThe design of the platform being completed the actual fabrication of the platform was

undertaken. Many problems were encountered during this task and suitable solutions were carried out.

Top Layer The top Layer was initially intended t have 144 20mm diameter holes but due to some

miscommunication the top board ended up having another row of holes i.e. 156 holes. This although unexpected did have its own advantage such as giving the impression that the platform was fully sensitive.

Figure 7 View of Top Layer (Assembled board)


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Second LayerThe second layer was fabricated as designed and there were no significant problems

encountered. The only concern that arose was the alignment

Figure 8 FSR Sensors on second layer

Third layer (Copper Clad Board)The Fabrication and the etching of the board was somewhat tedious since the etch pens that

were purchased weren’t reliable this caused the copper tracks to be etched away during the etching process. Etched tracks ha to be reconnected using solder a this led to uncertain connections. The surface of the copper tracks also oxidizes due to the reaction with the etch ink, this makes the soldering process more difficult since the solder does not stick to the copper.

Figure 9 Tracks drawn using Etch pen on copper board


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Figure 10 Completed Connections

The connections are then soldered by quadrant, to a 40 way cable which is then connected to a 40 way male connector. Each connector connects 36 sensors and one power line. This is the external interface to the platform.

Padding LayerA layer of padding was added to protect the circuitry and also absorb the impact of a test

subject.

Figure 11 Yellow padding Layer

Completed board

Figure 12 Completed Platform with connectors


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Description of the Switching and multiplexing circuit. The main purpose of the multiplexing circuit is to minimize the outputs of 144 sensors of a single platform to a compatible number of outputs for the DAQ device.

Circuit Overview A step down approach was implemented in order to minimize the number of outputs.

Quadrant Selector

Figure 13 Quadrant Selector

The 144 sensors on the platform have been divided into four quadrants of 36 sensors each. Each quadrant will provide one output to the Data Acquisition (DAQ) device. The sensors were arranged in a 6x6 matrix order. These will be multiplexed in two stages.

1 Quadrent - 1 Quadrent -

1 Quadrent - 1 Quadrent -

1st Quadrant 2nd Quadrant

3rd Quadrant 4th Quadrant

Output 1Output 2

Output 3 Output 4


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Row Selection The state one of the multiplexing is the row selection .In the 6x6 matrix arrangement a single multiplexer is assigned to control one row (6 sensors).

Figure 14 Row Selector

Two op-amps and 6 channels of a single multiplexer are used in the row selection process. There will be six outputs for 36 sensors (1 quadrant).

Column selector The state two is row selection. The 6 outputs from the row selection circuit are then multiplexed by using a single multiplexer. This acts as a column selector.

Figure 15 Column Selector

When a digital state is selected in this multiplexer it will correspond to the particular row of stage one.

1 Quadrant - 36 Sensors

Output

Multiplexer

Opamp

FSR sensor

1 Row – 6 Sensors


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Complete Circuitry Overview

Figure 16 Complete Circuitry Overview

The outputs from each quadrant will feed into the labjack. The Labjack will then transfer the relevant data to the PC through Ethernet port.

1st Quadrant 2nd Quadrant

3rd Quadrant 4th Quadrant

Output 1

Output 2

Output 3Output 4

LabJack PC

Ethernet

Row Selector

Column Selector


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Description of the PCB Layout

Figure 17- PCB Diagram of the Circuit for 1 quadrant

As illustrated in the above diagram the quadrant circuit consists of two parts. Namely circuit 1 and circuit 2.

CIRCUIT 1

The inputs of 36 sensors (one quadrant) are multiplexed in circuit 1. This is further divided into 6 similar sub circuits. Each of this corresponds to a single row of the quadrant containing 6 sensors.

Each sub circuit contains of two LM324 amplifiers and one multiplexer. The input signals from the sensors are fed into the LM324 op-amp after a voltage divider connection with a 10k resistor. The outputs from the op-amps are then fed into the multiplexer. The digital inputs for the multiplexers are obtained by the LabJack.

The digital ABC input for the multiplexer is shared within circuit 1

CIRCUIT 2

Circuit 2 contains the final multiplexer and connecting interface. The outputs from the six multiplexers in circuit 1 are fed into a final multiplexer that is situated in circuit 2. The output of this is used as the input to the DAQ device. The 40 way cable connecter is the signal line from the force platform to the switching circuit. The six 10 way connectors provide the signal line from circuit 1 to circuit 2.

The digital ABC input for the multiplexer is shared within circuit 1


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THE PIN CONFIGURATION

Pin configuration of the 10 way cable in main quadrant circuit (Circuit No1)Pin no Assigned to Node in Multiplexer 1 Multiplexer 72 Multiplexer 63 Multiplexer 54 Multiplexer 45 Not Used6 Multiplexer 37 Output from the multiplexer8 Not Used9 Multiplexer 210 -5V

Node Connection of the final multiplexer (Circuit No 2)Output from Node in final Multiplexer Sub – Circuit 1 2Sub – Circuit 2 3Sub – Circuit 3 4Sub – Circuit 4 5Sub – Circuit 5 6Sub – Circuit 6 7

Pin Configuration of 40 ways connector in circuit 2 (This configuration is for 1 quadrant consists of 36 FSR sensors)

Pin range of 40 way Connector number of the 10 way connector1 – 6 10 way cable no17 – 12 10 way cable no313 – 18 10 way cable no519 - 20 NOT CONNECTED21 – 26 10 way cable no227 – 32 10 way cable no433 - 38 10 way cable no639 NOT CONNECTED40 5V power

Figure 18 Numbering order of the 10 way and 40way connector

Figure 18 shows the numbering order of the 10 way (on the left) and 40 way (on the right) connecter.


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Hardware of the circuit

Circuit 1

Figure 19 Circuit 1 (Outer Loop)

Each circuit contains 2 Op-amps and 1 multiplexer. 10Way cables connect the sensor signals from 40 way cable in circuit 2 and the -5V for multiplexers. Also the 10 way cable send back the output of the multiplexers to the circuit 2 (Stage 2) multiplexer.

Resistor

10way Cable

Multiplexer

OP-Amp

Digital input to the multiplexer

5V


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Circuit 2The output signals for one quadrant of the platform are fed into the circuit using a 40way cable. The 40th

pin in the cable is connected to +5V input to power up the sensors on the platform. -5V input is given to power the multiplexers.

Figure 20 - Connections of the circuit 2 (Inner Loop)

Inter Connecting CircuitA simple linking circuit is made to link connections within circuit boards. The +5V to -5V conversion is done by the IC7660 IC.

40Way Cable

+5V to power the sensors on the platform

Single Output to the DAQ device after multiplexing 36 sensors

-5V input

Digital input from the multiplexer


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Figure 21 – Inter Connecting Circuit

All the circuits for one platform is placed in a box to improve mobility and durability. Each platform contains one box.

Figure 22 – Circuit Box

The box contains a switch, LED to indicate the functionality, power output and I/Os for Labjack.

Lab View Programming and Explanation

Digital inputs for circuit 1

Digital inputs for circuit 2

Power +5V

Power -5V

IC7660 ICOutput to DAQ

Ground


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Introduction to Lab View d

Lab View is an abbreviation Laboratory Virtual Instrumentation Engineering Workbench developed by National Instruments (NI). It is a graphical programming language that uses icons instead of lines of text to create applications. In contrast to text-based programming languages, where instructions determine program execution, Lab View uses dataflow programming, where the flow of data determines program execution. Lab View was first launched for the Apple Macintosh in the year 1986. Common applications of Lab View include data acquisition, industrial automation as well as instrumentation control.

Lab View programs are called virtual instruments, or VIs in short. This is because their appearance and operations imitate the real physical instruments used, such as oscilloscopes and multimeters. Every VI uses functions that manipulate input from the user interface or other sources and displays that information or moves it to other files.

In Lab View, the user interface is built by using a set of tools and objects. The user interface is known as the front panel, as shown in figure 23 below. The front panel is built with controls and indicators which are the interactive input and output terminals of the VI respectively. Examples of controls are such as push buttons, knobs and numeric controls while indicators are such as graphs and LEDs.

Figure 23 – Front Panel

The codes are then added using graphical representations of functions to control the front panel objects. The block diagram, as shown in figure 24 below contains these codes. In some ways, the block diagram resembles a flowchart of the program. Note that the front panel objects appear as terminals on


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the block diagram just like ‘Numeric’ and ‘Numeric2’ and ‘Output Indicator’ in figure 24. The blockdiagram contains functions and structures from built-in Lab View VI libraries. Virtual ‘wires’ then connect each of the nodes on the block diagram which includes controls, indicators, functions and structures.

Figure 24 – Block Diagram

From the example above, ‘Numeric’ and ‘Numeric2’ blocks are connected to the ‘addition’ icon to perform summation. The ‘Output Indicator’ block will then display the result of the summation in the front panel as shown in figure 1 above, which in this case it displays value ‘2’ since both ‘Numeric’ and ‘Numeric2’ blocks have input values of 1. In the case above, the blocks are connected by orange wires in which orange color represents double precision format

There are several advantages of using Lab View compared with other programming languages, such as C++ or Matlab. Beginners will be easier to learn and understand Lab View programming since it is a graphical programming tool. Besides that, it is easier to troubleshoot or debug Lab View programs since they are written in graphical representation. In addition, the simulation of the program can be run after finish wiring the blocks in the block diagram, without the need of compilation or linking processes.


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Summary and Block Diagrams of Program Design

The program codes designed for the force platforms perform three tasks sequentially when it is executed. The first task is to get the relevant data which from the data acquisition circuit via Lab Jack. The data of interest here is the voltage values when there are forces exerted on the force platform. The second task is to convert the voltages obtained to appropriate force values and finally the third task is to display the information of the forces on the front panel. The full program codes can be found in the Appendix Section.

Summary of How the Program Works:

1. Prompt the user to key in relevant information, such as mass and number of samples to be taken as well as choose a specific activity to obtain the desired outputs

2. Scan the force platforms and obtain the voltage data from Lab Jack. The voltages are then converted into force values

3. Determine the total force exerted on both platforms at any instant4. Compute instantaneous force information, such as maximum force, minimum force and

mean force exerted on both platforms5. Displays the force information in waveforms and intensity graphs for both platforms after

each successive session6. Stores the data obtained into a folder specified in a computer7. Compute the parameters of the specific activity based on the force data obtained. For

example, the hang time, take-off velocity for jumping activity8. Display the computed parameters on the front panel9. Replay simulation using the data stored earlier if the user wish to review back the simulation


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Block Diagram

General Block Diagram

WaveformsIntensity Graphs

Display Force information

Prompt User for input parameters

Scanning and Force Conversion Processes

Force SummingSave Force Information

Compute specific activity parameters

Display the computed

activity parameters

Replay Simulation

End

Start


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Scanning Process

No

Yes

End

Finish scanning

N samples?

Scan Row

Start

Scan Column

Store Values into

Shift Registers


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Replay Simulation

Detail Explanation on the Program DesignThe program codes are divided into 5 sections, which are:

Section 1: Run Simulation Menu Section

Yes

NoStop Simulation?

End of File?

No

End

Start

Prompt User to

Type File Name

File Name Found? No

Play Simulation?

Yes

Display Waveform and Intensity Graph

NoYes

Yes


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Section 2: User Input Section

Section 3: Scanning and Force Conversion Process Section

Section 4: Specific Activity Parameters Computation Section

Section 5: Replay Simulation section

The program is intended to be executed sequentially instead of simultaneously, starting from Section 1 to Section 5. This makes sense since the program needs data from Lab Jack first before it is able to convert them to force values and then finally compute the desired output parameters of the specific activity. The outer most of the program design consists of a while loop and a stacked sequence structure, as shown in figure 25

below:

Figure 25 – Outer mist structure for the program

The stacked sequence structure, as the name implies is used to force the execution of the functions sequentially. Hence whatever functions in page 0 of the stacked sequence structure will be executed first followed by the ones in page 1 and so on. On the other hand, the while loop is used to execute the entire program continuously until the user stops it at the Run Simulation Menu Section. Note that the stacked sequence is used only for Section 3 and Section 4 of the program.

Section 1: Run Simulation Menu Section

This is the section to prompt the user to choose the desired function. There are 3 functions, which are:


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1. Run Simulation2. Replay Simulation3. Exit

To do the run simulation menu section, the Prompt User and Case Structure functions, as shown in figure 4 below are used:

Figure 26 Prompt User function

Figure 26 show the simplified version of the program. The Prompt User VI has 3 input names which are Run Simulation, Replay Simulation and Exit. The Run Simulation input is connected to Case Structure 1 while the Replay Simulation input is connected to Case Structure 2. The Exit input, on the other hand connects to a STOP function and a red button. Note that the Prompt User function connects with other functions by using green wires which transmit Boolean values (FALSE or TRUE). The case structures receive the Boolean value and the functions inside it will execute based on the Boolean values it received (functions under ‘true’ tab will execute if the case structure receives TRUE value and otherwise). The STOP VI is used to stop the program when it receives a TRUE value.

When the program runs initially, the user will be asked to select one of the 3 inputs as shown in figure 27:


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Figure 27: Prompt user menu

From figure 27, if the user wishes to select Run Simulation, then the case structure 1 will receive true value and will initiate the simulation program whereby the program computes and display the specific activity parameters done on the platforms. However, if the user chooses Replay Simulation, the case structure 2 will receive true value and allows the user to replay the simulation obtained earlier.

Section 2: User Input Section

If the user selects Run Simulation in section 1, then the program will execute this section where it prompts the user to key in some input parameters, such as name, age, height and mass, as shown in figure 6:


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Figure 28: Prompt User for input profiles

From figure 28, the only relevant input parameter for the program is the name of the user because the name will be saved into a path specified for replay simulation purpose in section 5. This will be discussed later in section 3. Once the user has key in all the parameters, the user will be asked to specify number of samples to be taken and the activity to be performed on the force platforms. This is shown in figure 29 below:


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Figure 29: Prompt user to select specific activity and number of samples

After that the program will advance to Section 3 where scanning and force processes occur. The overall simplified version of the program for section 2 is shown in figure 30 below:

Figure 30: Simplified program version of Section 2

Once again Prompt User VI is used to prompt the user to key in the input parameters. The inputted parameters will be transmitted to the indicators respectively to be displayed in the front panel. Note that the value of mass inputted by the user will be multiplied by 9.81 to obtain the weight value. The purple color wire indicates that it contains string information which transmits from the Name input from the 1st Prompt User VI to the Name indicator. The string will then be transferred to case structure 1 for recording data purpose which will be explained in Section 3.

The Boolean values, with LSB to MSB starting from Static input to jumping inputs from Prompt User2 VI are then combined to form an array, with the first element at the top of the array using build array VI. The array is then converted to a number by using Boolean Array to Number VI. The purpose of converting the array to a number will be further explained in section 4 later.


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Section 3: Scanning and Force Conversion Processes Section

This is the section where scanning and force conversion processes take place. This is the most crucial section in the entire program because if the scanning process does not work properly, then the data obtained will not be accurate and thus computation of output parameters for section 4 will result in large error.

Before this section begins, the program needs to communicate with Lab Jack device and get a handle that the driver uses for further interaction. To communicate with Lab Jack, LJUD_OpenLabJackS subVI is used, as shown in figure 31:


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Figure 31: LJUD_OpenLabJackS.vi

The device type for the UE9 Lab Jack is ‘LJ_dtUE9’. There are two choices for connection type for the UE9, which are: ‘LJ_ctUSB’ and ‘LJ_ctETHERNET’. Since USB cable is used, therefore ‘LJ_ctUSB’ string is connected to the connection type parameter. For the FirstFound parameter, if it is true, then the address and connection type parameters are ignored and the driver opens the first Lab Jack found with specified device type. Referring to figure 9, a True Constant VI which gives a constant TRUE value is connected to the FirstFound parameter. The output parameter is a handle that interacts with other Lab Jack subVIs. Note that LJUD_OpenLabJackS only need to be initialized once, so it is placed outside the Case Structure 1 as shown in figure 31.


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Figure 32: 1st Part of Section 3 Programs

Figure 32 above shows the first part of Section 3 programming. Section 3 consists of an outer most stacked sequence structure, with a while loop nested between 2 for loops. The while loop is used to repeat the scanning process until N-sample has been reached. Figure 33 below shows the explanation of a For Loop VI:


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Figure 33: For Loop VI explanation

Since values of 6 are connected to both outer and inner for loops as shown in figure 32, therefore each loop will execute for 6 times.

The outer for loop is used for multiplexer switching while the inner one is for input switching. This is because the scanning process is done on the columns of the platforms first before scanning the rows. In other words, the columns scanning are to be done first in a full cycle of 6 before it scans the next row and repeat the same process. In total, there will be 6x6 = 36 loop iterations for one sample scanning process. Note that the inner for loop is a decremented loop with ‘i’ starting from 5 to 0. This is because the input switching 8:1 multiplexer selects the output from 111 first to 000.

To ensure that scanning of the columns and rows of the sensors in each quadrant is done properly, accuracy in timing is crucial. The timer needs to be fast enough for switching and be able to synchronize between the multiplexers and the program itself. To do that, Wait Until Next ms Multiple VI is used, as shown in figure 34. Referring back to figure 32, Wait Until Next ms Multiple is placed at the inner For loop and connected to ‘delay time’ Dial Input where the range is from 1 to 100. Hence, the user can slows down the sampling rate from 1 to 100ms.


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Figure 34: Wait Until Next Multiple VI

To accomplish the scanning process, The ADDbit to LJ subVI which is created by the programmer is used and it consists of the following codes shown in figure 35 below:

Figure 35: ADD bit to lab jack subVI


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Figure 36: ADDbit to LJ subVI codes

According to Figure 36, the ADDbit to LJ subVi consists of 3 LJUD_eGetS subVIs. The eGetS VI is designed for reading or writing values into the Lab Jack terminals, depending on the IOType parameter used. In this case LJ_ioPUT_DIGITAL_BIT is used for the IOType, which is used to write digital bits to the digital I/O of Lab Jack. The channel parameter specifies which of the terminals to be written. There are 23 digital I/O available in Lab Jack. They are:

0-7 FIO0 – FIO7 8-15 EIO0 – EIO7 16-19 CIO0 – CIO3 20-22 MIO0 – MIO2

The numbers on the left correspond to the particular digital I/O channel. So, if a 0 number is connected to the channel parameter, it means LJUD_eGetS is writing to FIO0 terminal and so on. Referring back to


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figure32, FIO5, FIO4 and FIO1 are to be written in the outer for loop while MIO0, MIO1 and MIO2 are to be written in the inner loop.

Before the digital I/Os are to be written, the number from the iteration terminal (i) in the for loop is to be converted to Boolean arrays by using Number To Boolean Array VI. The converted Boolean array is then fed into index array to extract out the bits with the LSB to MSB in descending order. The bits have to be converted to number by using Boolean to (0,1) VI (from green wire to blue wire) because LJUD_eGetS subVI only accepts numbers in long/double format for the value write parameter as shown in figure 36.

Before the scanning process is to be executed, a 6x6 array with elements ‘0’ is initialized using Initialize Array VI (figure 37). The array is passed into shift registers (refer back to figure 10) so that the array values will be passed and updated whenever the loops begin their next iteration. This array is used to store the force values for one quadrant after converting them from voltage values. Since there are total of 8 quadrants (4 quadrants for one platform), therefore 8 arrays are needed.

Figure 37: Initialized Array VI

Four 6x6 arrays (to represent one platform) are then fed into Voltage to Force subVI (figure 18) which is created by the programmer, where the voltage values obtained from all the quadrants from a platform are converted to Force values. The Voltage to Force subVI consists of the following codes, shown in figure 16:


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Figure 38 Voltage to Force subVI

Figure 39: Voltage to Force subVI codes

To get the voltages from the Lab Jack terminals, LJUD_eGets subVIs are used again but this time LJ_ioGET_AIN is used for the IOType parameter. LJ_ioGET_AIN command is used to read the analog


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voltage from the AIN terminals with the channel parameter specifying the particular AIN terminal. From figure 10, constants ‘1’,’4’,’5’ and ‘6’ are connected to the Voltage to Force subVI, therefore the voltage readings for the first platform will be taken from AIN1,AIN4,AIN5 and AIN6 terminals. As for second platform, voltage values from AIN terminals 8,9,10 and 11 are read.

The four voltage values will be transferred to the formula node where conversion to force takes place. For each voltage value, if it is less than 0.88, then the converted force value will be 0. Otherwise, the formula for the force will be given by:

F = (0.9907*V – 0.4836) N

The converted force values are then stored into the 6x6 arrays by using Replace Array Subset VI.

Once obtaining the force arrays after the for loops iterations, the arrays will be transferred to the Combine Matrix subVI, shown in figure 40 to form the overall force array for each platform. Once again, the Combine Matrix subVI is created designed by the programmer and it consists of the following codes as shown in figure 41:

Figure 40: Combine Array subVI


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Figure 41: Combine Matrix subVI codes

Referring to figure 41, Array 1 and Array 2 are to be combined first using Insert Into Array VI. The output array is then fed into the second Insert Into Array VI where it combines with Array 3 to form the next output array and finally the overall force array for one platform is produced when the second output array combines with array 4.


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Figure 42: 2nd part of Section 3 program

Figure 42 above shows the 2nd part of the Section 3 program. This is the part where instantaneous force values are to be determined.

Once the overall array for each platform is created from 1st part of section 3, the 3D intensity graphs for each platform can be plotted by using 3D surface VI (figure 42)


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Figure 43: 3D Surface VI

The Force values in the array are then added all together by using the Add Array Elements VI and the computed sum value is to be connected to Waveform Charts VI to plot the total forces exerted on each platform with respect to time. This is illustrated in figure 45:


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Figure 44: Add Array Element and Waveform Chart VIs

The instantaneous maximum force and its time for each platform can be found by using the Find Max Time subVI, shown in figure 45 and 46 respectively:

Figure 45: Find Max Time subVI


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Figure 46: Find Max Time subVI codes

To find the maximum value in an array along with the indexes for the value, Array Max and Min VI is used, as shown in figure 47.

Figure 47: Array Max and Min VI


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According to figure 47, the force array from each quadrant of a force platform is to be transferred to Array max and min 1,2,3,4 respectively to find their maximum values along with the indexes. The maximum value from each array will be combined to form a maximum values array through Build Array 1.

The maximum indexes (a 1D array in this case) for each array can be used to find the time for the maximum value to occur. The maximum indexes are first to be incremented first by 1 using Increment VI before transferred to Multiply Array Elements Vi to multiply the indexes. The result is then multiplied with the delay time in ms to find the time for the maximum value. For example, if the maximum value for the 1st Quadrant of a platform occurred at indexes [1 2] and the delay time is 1ms, then the time for the maximum value would be = [(1+1)x(2+1)] x 1m = 6ms. The time for each maximum value will also be combined to form an array through Build Array 2.

The appended array produced from Build Array 1 is fed to another Array Max and Min VI (labeled ‘array max’ in figure 47) to find the maximum values exerted on the platform. The maximum index is connected to Index Array VI labeled ‘Max time index array’ from figure 47 to select the time for the particular maximum value. The maximum impulse exerted on the platform can then be computed by multiplying the maximum value with the time for it to occur.

Referring back to figure 42, the instantaneous average force exerted on the platform can be determined by first finding the size of the overall force array for one platform. Hence, Array Size VI as shown in figure 48 is used. Note that the output array size is a 1D array. elements in the size array is then multiplied by using Multiply Array Elements VI to get the number of sensors in the platform (which is 144). Next the total force exerted on the platform is to be determined by summing up all the force values in the overall force array by using Add Array Elements VI. The average force can then be computed by using the following formula: (Total Force detected by 144 sensors)/144 sensors.


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Figure 48 24: Array Size VI

Finally, the force distribution of both platforms can be determined by combining the overall force arrays from 1st and 2nd platform by using Insert Into Array VI. The waveform as well as the intensity graph for the combined platforms can then be plotted using the same methods applied to each platform earlier. The total impulse force exerted on both platforms can be determined by summing up the forces in the combined platform force array and then multiplied by total time taken to obtain one sample (36 x delay time).

At the same time, the maximum force values from both platforms are to be combined to form a 1D array using Build Array VI. The time for both maximum values are also combined using Build Array VI. The appended maximum value array is then fed to Array Max and Min VI to compare the values and get the higher one to represent the maximum value exerted on the platforms at N-instant. The maximum index is fed to the Index Array VI, which its input is the appended maximum time array to select the time for occurrence of that maximum value.

To allow some of the data to be recorded, data logging method is used by using Write To Measurement File VI, shown in figure 49.


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Figure 49 : Write To Measurement File VI

The Write To Measurement File VI requires the input to be a dynamic data type. Therefore, Convert To Dynamic Data VI as shown in figure 50 is used.

Figure 50 : Convert To Dynamic Data VI

The configuration for the Write To Measurement File VI is shown in figure 51 below:


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Figure 51 : Configuration for Write To Measurement File VI

If the file name input for the Write To Measurement File VI is unwired, the path of the recorded data would be the one shown in figure 51 above which is C:\Documents and Settings\WinXP\My Documents\LabVIEW Data\test.lvm. However, in figure 42, the file name input is wired and hence the path for the filename would be the path name connected to it. The path name actually consists of combined strings that are converted into path data using String to Path VI as in figure 52 below.


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Figure 52 : String To Path VI

The combined strings are actually obtained from single strings that are concatenated together by using Concatenate Strings VI.

Figure 53 : Concatenate Strings VI

There are two Concatenate Strings VI used as shown in figure 42. The first one is used to concatenate the user’s name with ‘C:\Mervin\’ string. The output is then fed to the second Concatenate Strings VI to combine the output string with ‘.Ivm’ string. Hence the combined strings would be C:\Mervin\user’s name.Ivm. The file name would be user’s name.Ivm and it is stored into a folder named ‘Mervin’ in C drive.

The maximum force and the time for its occurrence, total force and impulse exerted on the platforms need to be stored before the next sample is to be taken. Hence, an empty 1D array is used as shown in figure 54 below:


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Figure 54 : Initialized empty 1D array

Note from figure 54 that 4 empty arrays are placed before the outer while loop which means the arrays are initialized before the program starts the scanning process. The shift registers are used to bring forward the updated arrays. The data are inserted into the arrays by using build Array VIs with the top element is connected to the 1D empty arrays and the element below it is the data to be inserted as shown in figure 55.

Figure 55 : Storing data into the empty array

So for N-samples, the arrays would have N of the data stored inside it and have array size of N. These arrays are to be carried forward to the next page of the stacked sequence structure where Section 4 programs are to be executed. For this purpose, sequence locals are used as shown in figure 56. Once all the samples, as specified by the user have been taken, the program will proceed to Section 4.


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Figure 56 : Sequence locals

Section 4: Force Summation and Specific Activity Parameters Computation Section

This is the section where the program computes the specific activity (as chosen by the user in Section 2) parameters. Referring back to figure 30 in Section 2, the purpose of converting the Boolean values from Prompt User for Input 2 to a number is for the program to determine which activity parameters to be computed. The converted number is connected to the inner case structure where it determines which page of the case structure to be executed. Since the number converted from the Boolean values can only be 1, 2, 4 or 8, therefore the program can only execute codes on either page 1, 2, 4 or 8 of the case structure.

Static ActivityThe program will compute the parameters for static activity when it executes page 1 of the case structure. Figure 33 below shows the program codes for static activity:


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Figure 57 : Static Activity program codes

From figure 57, the maximum static weight can be found by using Array Max and Min VI with the input array is the maximum force array. The maximum index is connected to Index array to get the time for the maximum static weight occurrence and is used to find the maximum impulse exerted on the platforms from all the samples obtained.

Besides that mean static weight and mean impulse can be determined by using Mean VI (figure 58) with the input array is total sum force and impulse array respectively.

Figure 58 : Mean VI


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The mean static mean found is to be divided by 9.81 to get the mean static mass of the user. The static LED indicator is connected to Constant True VI to indicate that static activity is performed on the platforms in the front panel.

Walking and Running ActivitiesFigure 59 and figure 60 show the codes for walking and running activities respectively. Note that walking or running activity parameters are computed if the program executes page 2 or 4 respectively.

Figure 59 : Walking activity codes


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Figure 60 : Running activity codes

As observed, the codes for both walking and running activities are very much similar to static activity mentioned previously and therefore the explanation on obtaining the outputs including the maximum force exerted and maximum impulse is the same as the static activity.

Jumping activityFigure 61 below shows the program codes for jumping activity. Note that the codes will only execute if page 8 is ‘true’

.


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Figure 61 : Jumping activity codes

The Maximum force, impulse and time for maximum impulse parameters are computed in the same manner as in the previous activities and will not be further discuss again. The hang time is defined as the time between two maximum forces exerted on the platforms (since the user exerts maximum forces on the platforms when he/she is about to jump and land on the platforms). To get the hang time(s) from the samples obtained, a For Loop is used with the number of iterations equal to the array size of the maximum force array. An empty array as well two constants ‘0’ are initialized with shift registers outside the For loop. The empty array is used to store the hang time value. Inside the For loop is a case structure which will executes based on the Boolean values received. By using Index Array VI, every elements in the maximum array is to be determined if it is equal to zero by using Equal to 0? VI as shown in Figure 62below:

Figure 62 : Equal to 0? VI

If the Maximum value is equal to zero, the constant zero at the bottom one will increment by 1 using Increment VI and the incremented results will then multiplied by time taken for one sample (36 x time delay). The multiplication result is then stored into the top shift register which previously have a value of 0. The hang time is basically equals to number of maximum force which have zero value times the time taken for one sample.

If however the maximum value is not equal to zero, then the false case structure will be executed. The incremented values at the bottom shift register will be reset back to zero and the whatever value in the top shift register will be stored into the empty array by using Build Array VI. The codes when the case structure receives a FALSE value are shown in figure 63 below:


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Figure 63: FALSE case codes

The maximum hang time can then be determined by using Max and Min Array VI with the input array is the stored hang time values array. To get the average hang time, the size of the hang time array and the total sum of the hang time are first to be determined by using Array Size VI and Add Array Elements VI respectively. The hang time array and its size value are then fed into a Math Node VI to determine if any of the element value in the hang time array is equal to zero. If it is, then the size of the array is decremented by 1 (the person is not jumping). The average hang time can then be computed by dividing the total sum hang time with the new array size value.

Once the hang time array has been obtained, the maximum velocity before jumping and maximum height can be computed by using the following motion equations and converts them into simple programming codes:

V = U + gt

Where V is the final velocity (velocity when maximum height is reached) which is equal to zero. The g is the gravitational acceleration value which is -9.81 m/s^2 downward direction (assuming vertical upwards is taken to be positive), t is the maximum hang time obtained and U is the initial velocity of interest. The equation above can then be simplified into:

U = 9.81t


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Hence, with the maximum hang time obtained from the hang time array, half of that value is then substituted into the t value to obtain the maximum initial velocity before jumping.

To get the maximum height reached, consider the following equation:

V2 = U2 + 2gS

Since the values of V, U and g are known, therefore the value of S which is the maximum height reached can be obtained easily.

The average height reached and average velocity before jumping can be obtained in a similar manner as mentioned above except that the average hang time value is used instead.

Section 5: Replay Simulation sectionThis is the section where the user can view back the force information obtained earlier during the run simulation. The program codes for replay simulation are as shown in figure 64 and figure 65 below.


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Figure 64 : top part of the program

Figure 65 : Bottom part of the program


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The top part of the program is to open the file name while the bottom part is to replay the force information from the file name. The program first begins by prompting the user for a file name using Prompt User Input VI.

Figure 66 : Prompting user for filename

Once the user has entered the file name (user’s name), the program will determine if such file (user’s name.Ivm) exist in the folder specified by the path, which in this case the folder path would be C:\Mervin\. To accomplish that, List Folder VI (figure 67) is first used to list the names of all files and folders in the path specified. The output would be an array which consists of the file names and it is connected to the Index Array VI inside the While loop at the bottom. The While loop will execute N times according to the array size. The size of the file names output can be determined by using Array Size VI


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Figure 67 : List Folder VI

As the While loop iterates from 0 to N, the Index Array VI will extract out the ith element of the array and compared with the required file name as specified by using the Equal? VI. If the strings match, then the Equal? VI will output a TRUE value and this is fed into an OR gate to terminate the loop. Otherwise, a FALSE value will be obtained and the loop will continue to execute until the OR gate receives a TRUE value from either the N iterations has been reached or the strings matched. All the Boolean values from the strings comparator are stored into Or Array Elements VI. The output from the Or Array Elements VI is inverted using Not gate and is then fed into Display Message to User VI, shown in figure 68..

Figure 68 : Display Message to User VI

The message to be display is as shown in figure 69 below:


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Figure 69 : Message to be displayed

Hence, if all the Boolean values in the Or Array Elements are 0, which means the file name does not exist, the Display Message to User VI will received a TRUE value and will displays the message shown in figure 69. Once the strings match, the program will proceed to the bottom part shown in figure 65.

As observed, the bottom part of the program consists of an outer while loop, 2 case structures with the Start/Pause button located in between the case structures. In the inner case structure, Read From Measurement File VI is used to read the data obtained from the file name which was written via Write To Measurement File VI in Section 3. Again, the Read From Measurement File VI requires a path name to specify the location of the file name. Therefore, String to Path VI is used to convert the concatenated strings from the top part of the program into path format. Convert from Dynamic Data VI (figure 70) is then used to convert the dynamic data signals into the force array of the combined platforms. The Waveform and Intensity graph can then be plotted from the force array by using the same method discussed earlier in Section 3.

Figure 70 : Convert from Dynamic Data VI


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The delay time control serves the same purpose as the one in Section 3, which is to slow down the simulation rate. The outer while loop will terminates if either EOF has been reached or the stop button is pressed. This is shown in figure 71:

Figure 71 : Terminating While Loop condition

Graphical User Interface (GUI)The user interface consists of 2 main tabs, which are Run Simulation and Replay Simulation. Figure 72below shows the Run Simulation tab:


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Figure 72 : Run Simulation tab

The user profile tab (not shown in figure 72) is to display the user’s input profile as he/she inputted during the Section 2 process. The force indicator is to show whether the scanning process (Section 3) is completed or not.

At the bottom tabs, there are Instantaneous Force Profile and Activity performed on the platform tabs. The Instantaneous Force Profile tab consists of the force information that were obtained during Section3 process, as shown in figure 73 below.


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Figure 73 : Instantaneous Force Profile tab

On the other hand, the Activity performed on the platform tab is to display the parameters computed in Section 4, as shown in figure 74,75,76,77 and 78.


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Figure 74 : Activity indicator tab – to indicate the activity performed on the platforms

Figure 75 : Static tab


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Figure 76 : Walking tab

Figure 77 : Running tab


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Figure 78 : Jumping tab

At the right side of the user interface is to display waveforms and intensity graphs for both platforms, as shown in figure 79,80, and 81


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Figure 79 : Waveform tab


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Figure 80 : Intensity Graphs tab


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Figure 81 : Combined waveform and intensity graph tab


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Figure 82 below shows the Replay Simulation tab:

Figure 82 : Replay Simulation tab


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Components used during the project.Following describes some of the main components used in building the force platform.

FSR (Force Sensing Resistor)The FSR sensor is the main component used in the design. Total number of sensors used for the project is 288 which are 144 per board. Considering the weight factor and the size the 12.7mm diameter FSR sensor developed by Interlink Electronics is used .The Data sheet is included in the appendix.

Figure 83 - FSR Sensor

The Force Vs Resistance relationship is used to do the analysis.

Figure 85 Force Vs resistance graph

According to the above graph there is a turn on threshold value “Break force” at around 100g this will create a sudden change in the resistance from 100kΩ to 10kΩ. the threshold value will change depending on the constant forces applied on the sensor by other layers like padding.

The sensor will also saturate after a force of 1000g (10kg). This means that the resistance will be zero. The average person weight is way above 10kg. So 144 sensors were used in the platform in order to distribute the force.

SIL Connector

Figure 84 - Dimensions


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UE9 LabJack and CB37 Terminal BoardLabjack is the USB/Ethernet based multifunction data acquisition and control device. The Labjack is used to sample the data from 288 sensors at a faster rate.

Figure 86 Labjack UE9 and Terminal Board

LabJack has 14 analog inputs (12- to 16-bit), 2 analog outputs (12-bit), 23 digital I/O, 2 counters, and 6 timers. 8 of the digital I/O can be configured on the fly as up to 6 timers and 2 counters.

Since the digital outputs and analog inputs in the UE9 device is not sufficient for our project the CB37 Expansion board is used.

The terminals FI01, FI04,FI05 MI00, MI01,MI02 is used as digital outputs to the multiplexer and AIN01-AIN09 are used as analog inputs from the sensors.

LM324 Op-Amp

Labjack UE9

CB37 Terminal Board


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The output of FSR sensors are a resistance value. This value will be converted to a readable voltage value using a voltage divider circuit.

Figure 87 - Voltage divider

The current through the FSR should be limited to less than 1 mA/square cm of applied force. The LM324 OP-amp is used because the low bias currents of this reduce the error due to the source impedance of the voltage divider.

Figure 88 – Pin Diagram of LM324

According to the above figures 88 and 89, Inverting inputs 2,6,13 and 9 will be connected with output pins 1, 7, 14 and 8 respectively. Non inverting inputs 3, 5, 12 and 10 will be connected to the voltage divider.

10kΩ ResistorA suitable resistor has to be chosen to use for the above explained voltage divider circuit. (Resistor RM in Figure 88).


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Figure 89 - Voltage Vs Force Relationship

The corresponding RM value is chosen by considering the Vout equation and the graph in Figure 90. For the project we have chosen to use the 10kΩ resistor as the RM.

CD4051 – Channel MultiplexerMultiplexing had to be used in order to minimize the 288 sensor outputs to the compatible number of outputs with the DAQ device. With regards to the force platform multiplexers used until it minimizes the number of 144 outputs to 4 outputs.

The most suitable component is the CD4051BCN 8 channel multiplexer. Bur for the convenience 6 channels are used in each multiplexer.

Figure 91 Pin Diagram of CD4051

Above two diagrams represent the pin configuration and the truth table that trigger each channel. In the project channels 7,6,5,4,3,2 were used as row selection and channels 2,3,4,5,6,7 were used as the column selector. This was explained further in the circuit description section.

IC7660 IC

Output Voltage:

VOUT = (V+) / [1 + RFSR/RM].

Figure 90 – Truth Table


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The multiplexers has to powered wit h both +5V and -5V supply. The power unit provides only a +5V power supply.

IC7660 IC is used to covert the +5V supply to -5V.

Figure 92 – Pin configuration and the Operation Configuration

Single in Line (SIL) ConnectorSIL connectors were used to connect the FSR sensor to the cooper board. This is illustrated in Figure 84above.

Figure 93 SIL Connector

By using SIL connector the FSR sensor can be removed without any trouble.

14 pin & 16 Pin IC SocketsIC sockets were soldered on the PCB board instead of soldering the ICs directly. This will prevent

damaging the IC of overheating and gives freedom to replace ICs without re-soldering.

3mm AcrylicThree layers of 3mm Acrylic sheets were used in fabricating the force platform. This material was used in order to increase the aesthetics and improve durability. The dimensions of the acrylic sheets are 480mm x 540mm x 3mm.

Power unit


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5V, 4A power unit is used to supply the voltage to the system. High ampere is used in order to prevent voltage drop throughout the circuit.

Figure 94 - Power Unit

Copper BoardEight A4 size and two 480mmx540mm copper boards were used in PCB designing. A4 size is used to design PCBs for switching circuits. The bigger boards were used to design the wire tracks in the force platform. These were illustrated in Diagram 96 and 97 below respectively.

Figure 95 -Switching Circuit PCB Figure 96 - Force platform PCB

6mm Rubber sheet.6mm Rubber sheet is used to even the bottom surface of the platform. The material is industrially used to manufacture slippers. The extending screw holes of the platform were covered by this hard rubber material.

10way 40way male/female connector and cable


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10 way connectors were used in the switching circuit to transmit signals from the column selecting circuit to row selecting circuit.

Figure 97 connection of 10Way cables and connectors.

40way cables and connectors were used provide connections from the force platform to the switching circuit.

Figure 98 - 40 connections used from circuits to platform

Evaluation

Comparison with previous Designs Force PlatformThe current force platform is the 3rd generation development. There are several improvements done compared to the previous two generations.


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Aesthetics Significant improvement from past designs, namely a more marketable appearance and an

increase in the reliability and durability of the material used. Previous material- wood: Tends to curve and sag over a period of time. This influences the

reading from the sensors. Also wood has a limited life-span and is susceptible to corruptive agents.

Bonding element changed from aluminum border around the Force Platform to M4 bolts. This improvement provides the same stability and holding capability while not sacrificing aesthetics.

Connectors to external circuit adapted instead of cables leading directly from the Force Platform, increases its portability.

Performance Sensors connectors, SIL (Single In Line) are used to enable the removal and the replacement of

damaged sensors. This possibility was non-existent until current Force Platform. More rigid contact (dense rubber) is used to transmit the force to the FSR sensors. The extra

thick circles that protrude on the surface of the Force Platform make sure that the force is concentrated only on the sensors and not on the platform.

The Force Platform was built with integration in mind. Three of its 4 corners can be seamlessly interfaced with the second platform while always maintaining the same surface sensitivity. This is because the three sides (excluding the side with the 40 way connectors) have half the normal spacing between the sensor and the edge.

Copper tracks ensure excellent connection that will not come apart with applied force a concern that was significant when wires were used.

Compatibility The current Force Platform was built following the similar design as the previous generation

therefore it can be run on the same software as that of the previous Force Platform. The above mentioned backward compatibility enables all 4 (2 previous and 2 current) platforms

to be use simultaneously.


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Comparison with previous Designs Switching CircuitFew improvements were made to the circuit in terms of aesthetics and functionality. Following images illustrate the 3 generations with respect to the circuits.

1st Generation 2nd Generation

Figure 99 - 1st Generation Figure 100 - 2nd Generation

3rd Generation

Figure 101 - 3rd t Generation


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1st Generation 2nd Generation 3rd Generation

Aesthetics

As illustrated in the above figure aesthetics are very minimum in the design

Aesthetically it is better than its previous design.

The component placement order and the wiring of cables are well organized compared to the previous two.

Design

Breadboard and wires used to design the circuits. This is very hard to troubleshoot and error ratio is significantly high.

PCB design is used. But one drawback is that the use of more jumper wires.

Designed to minimize the use of jumper wires and to use lesser components.

The Identical arrangement of the components made troubleshooting easy.

All the circuitry for one quadrant is integrated into one single A4 size PCB board.

Functionality

Functionality is almost same in all the three designs.

Portability

Since the circuits are not permanently fixed the portability is highly unlikely

Portability was increased by integrating all the switching circuits into a signal control box. One drawback is that the control box is bigger and the cables arepermanently fixed to the platform restricting movement.

Used the same theory as 2nd

generation, but consideration was given to reduce the size of the control box and increase portability by using removable cables between the platform and the control box.


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Problems faced

While the project was in phase, there were a few hurdles encountered and the proper solutions to overcome those difficulties were drawn out. Among the difficulties encountered were:

1. Program Timing Problem

After doing some troubleshooting, it is found that the sampling rate is very much slower, typically about 0.5s per sample. It is found that this may due to the lab Jack subVIs since it is the bottleneck of the program during the scanning process. The slow rate causes errors in computation in Section 4, especially for jumping activity. The profile performance and memory for the program when taking one sample is shown in figure 58 below:


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Figure 102 : The profile performance and memory for the program when taking one sample

As shown in figure 83, the LJUD_eGETs VI takes the longest time to finish its execution, about 46.9 ms for just one sample. Note that prompt User for Input2 VI is not taking into consideration since it does not play a part during the scanning process.

2. Aligning of the sensors on the platformThe sensors bulged after placing them onto the platform. This was totally out of expectation as the exact measurements and dimensioning were taken into consideration. The problem was due to the SIL connectors used to connect those sensors onto the PCB.

SOLUTIONReplacing those SIL connectors from another source was a direct fit and finish. No more bulging occurred.

3. Drilling problemDrilling was done individually on each acrylic surface one by one. When all 3 layers were put together, some of the holes were misaligned, affecting the sensors positioning and the holes of the screws.

SOLUTIONDrilled each holes through all 3 layers simultaneously.

4. ConnectorsInitially, the connections from the PCB utilize male connectors. Therefore female connectors were needed to connect it to one another.

SOLUTIONImplement direct connection to the cables by using male connectors instead of any female connectors.

5. ConnectionsLost of connectivity across the copper tracks

SolutionJumper wires were soldered across the copper track field to all lost connection points.


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Future improvements

FPGA

The implementation of a FPGA (Field Programmable Gate Array) will reduce the size of the conditioning circuitry since all of the multiplexing can be performed by the FPGA controller. If this method is implemented then a Flash ADC can also be used.

Multilayer PCB

The PCB design of the project involves many jumper wires. By using multilayer PCB layout the use of jumper wire can be eliminated and the circuit board size can be reduces significantly. This will increase mobility of the unit.

COMPONENTS

Micro electronic components can be used instead of conventional components such as resistors, multiplexers and integrated circuits. This will ensure minimizing the circuitry size.

Wireless Transmission

The project can be taken to a whole new level by using wireless connection instead of the current Ethernet connection. This will eliminate the use of cables to connect the platform to the computer thus increasing the ability of placing the platform anywhere to acquire data.

DAQ

The use of a DAQ device with higher sampling rate is suitable for this project as it will shorten the response time and real time updating is achievable.

JIGSAW PUZZLE COMBINATION

Brackets can be placed on all sides of the platform for the case of placing more than 1 platform across a playing field. With this bracket in place on all sides of the platforms, one can connect each and every platform to one another simply by fixing them together just like how jigsaw puzzles is fixed together.


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Reference

1. Literature Reviewa. http://web.media.mit.edu/~joep/SpectrumWeb/captions/Carpet.htmlb. http://ame2.asu.edu/projects/floorc. http://www.cc.gatech.edu/fce/pubs/floor-short.pdf

2. Article on Solid EDGE applicationhttp://en.wikipedia.org/wiki/Solid_Edge.

3. Explanation of Solid EDGE product and usagehttp://www.ugs.com/en_us/products/velocity/solidedge/

4. Article on Solid Works applicationhttp://en.wikipedia.org/wiki/SolidWorks

5. SolidWorks product explanation and advantageshttp://www.solidworks.com/pages/products/products.html

6. LabVIEWd. http://en.wikipedia.org/wiki/LabVIEW

7. TRC3000 Project Final Report 2006

8. LabJack www.labjack.com

9. Datasheetsa. FSR b. CD4051 multiplexerc. LM324 op-ampd. IC7660 Voltage inverting IC(-5V)e. LabJack datasheet

10. Information on the FSRhttp://www.interlinkelectronics.com/library/media/papers/pdf/fsrguide.pdf

http://web.media.mit.edu/~joep/SpectrumWeb/captions/Carpet.html

http://ame2.asu.edu/projects/floor

http://www.cc.gatech.edu/fce/pubs/floor-short.pdf

http://en.wikipedia.org/wiki/Solid_Edge

http://www.ugs.com/en_us/products/velocity/solidedge/

http://en.wikipedia.org/wiki/SolidWorks

http://www.solidworks.com/pages/products/products.html

http://en.wikipedia.org/wiki/LabVIEW

http://www.labjack.com/

http://www.interlinkelectronics.com/library/media/papers/pdf/fsrguide.pdf