Development of Automatic Wheelchair for all Physical Disabilities

ABSTRACT

The Development of an Automatic Wheelchair for all Physical Disability Types is a mechanical device designed and developed compatible with most physical disabilities that is self-mobile with the aid of the user’s command. This project will benefit the user especially the physically challenged who is suffering from paralysis by controlling the motion of the wheelchair with the elementary movement of their hand, feet, or head. The project is composed of four major control systems: the head gear control system, the armrest control system, the footrest control system, and the wireless control system. The headgear, which has a transmitter employing an accelerometer which is responsible for transmitting control signals to the motor driver following the movement of the head. This will be an advantage for the person who is paralyzed from the neck down. The armrest is set-upped with a joystick to control the motion and direction of the wheelchair. The armrest is also comprised of push-button switches which serve as a back-up control system if another control system may fail. This will be an advantage for the person who can only move his hand. The footrest is also integrated with joystick to control the movement and direction of the wheelchair using the foot. With the aid of an ultrasonic sensor placed in the footrest, the chance of for collision is eliminated. This will an advantage for the person who is paralyzed from the leg up. The wireless control system can be done by the use of a mobile application with Bluetooth connection to control the movement of the wheelchair.

INTRODUCTION

Quadriplegia, also known as Tetraplegia, is defined as the “four-limb paralysis” and is caused by illness or accident, or injury that has resulted to the total or partial loss of ability to use the torso and limbs. The common cause of this is spinal cord injury. [1] Spinal Cord Injury or SCI primarily occurs amongst young to middle-aged people who obtained a traumatic injury, or non-traumatic medical condition that resulted in a disability that carries lifetime consequences. Each year in New Zealand, roughly 80–130 people are diagnosed with a Spinal Cord Injury. Most of these cases lead to partial or full paralysis. [2]. The figure below shows the causes of paralysis by percentage. It can be seen that the major cause of paralysis is stroke followed by spinal cord injury.

Figure 1: Cause of Paralysis [3]

One of the existing systems for a wheelchair which uses the head movement is the movement through voice recognition. Through voice commands, the user can control the wheelchair such as saying “susume” to navigate forward the wheelchair. It means “run forward” in Japanese. This is a grammar-based recognition system the researcher named “Julian”. There were three types of commands that are given: short moving command, basic reaction command, and verification command. The speech recognition system was experimented and resulted in 98.3% successful recognition rate for the movement command and 97.0% successful recognition rate for the verification command. Figure 1 below shows the block diagram of the system while figure 2 below shows one of the running experiment that was carried out. [4]

Figure 2: Voice recognition block diagram

Figure 3: Running Scene using a laptop

Another existing system uses facial recognition to give the command to the wheelchair. The user – with the initial help of another person or caregiver – could assign as to what facial expression is linked to a specific wheelchair movement. This was made possible through the use of facial recognition software, and a mounted Intel 3D RealSense Depth Camera, The computer captures a 3D map of the face and makes use of AI algorithms to process data in real-time to navigate the wheelchair. The system not only works on bright light but also on a dim light, and is incompatible with most of the motorized wheelchairs available on the market. [5]

Figure 4: Facial Expression Recognition

A similar paper proposed a system that assists the person with a disability to control the motion of the wheelchair wirelessly through hand gestures. The proposed system may be mounted on the principal functioning body part – like the hand to control the wheelchair movement. The system consisted of a transmitter that acts as a wireless remote that was mounted on the hand. The transmitter end consisted of a microcontroller using MEMS accelerometer which senses the tilt of the platform it is mounted on such as the upper side of the hand. Figures 4 and 5 below show the hand movement that will determine the motion of the wheelchair and the sensor used in the project. [6]

Figure 5: Hand movement for controlling

Figure 6: Accelerometer Sensor

Bluetooth is a wireless technology that is primarily designed for communication over a short range of distance at about 10m or 30ft. Electronic devices that use this technology have built-in radio antennas called receivers and transmitters that can simultaneously send and receive wireless signals to other devices with Bluetooth. It is often used for transferring photos from a digital camera to a personal computer, connecting wireless mouse to a laptop, hands-free headset to a mobile phone especially on cars while driving. These devices automatically connect to one another and up to 8 devices and do not interfere with each other because each pair uses different channels out of the available 79 channels. [7] The figure below show Bluetooth device connectivity.

Figure 7: Bluetooth Device Connectivity

Another similar research was about controlling a robot using an android application with the aid of Bluetooth connection. The Android OS if not the largest, is one of the largest numbers of operating systems used in smartphones that is very rampant nowadays due to research, entertainment, and social media. The objective of this paper is to be able to devise an Android application or program than can control a robot powered by an Arduino microcontroller with the use of a Bluetooth module and motor driver. Since Arduino and Android are open sources, it is an advantage for this research to obtain information about the different aspects of programming involved in the project. The result of this project is a concoction of embedded programming and computing. It was concluded on this project that it is not hard to implement Arduino with Android. The following figures below show the system block diagram and the prototype of the robot. [8]

Figure 8: System Block Diagram

Figure 9: The Robot Prototype

The primary structure for supporting most external loads and maintaining the stiffness of the structure of the wheelchair is the frame. The frame can always be made stronger by increasing its size or adding reinforcements but the weight should also be considered and must be limited. This is to improve the moving performance of the wheelchair hence, must be reduced. For this reason, it is important to adopt light-weight materials for the making or designing of the wheelchair frame. Yet, the strength and stiffness should also be maintained. One study suggests using the fiber-reinforced composite material because of its high stiffness-to-weight and strength-to-weight ratios.

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Plastics matrix and reinforced fibers compose the reinforced fiber composite materials. Fatigue life and density are low, stiffness and strength are high, corrosion and wear-resistant, and environmentally stable are the advantages of this material over monolithic materials. These composite materials that are laminated reinforced fibers are usually made out of polyester/glass or epoxy/carbon that are broadly utilized in military, automotive, aerospace, aircraft, sports structures, and marine. With the use of these epoxy/carbon materials, the weight of the wheelchair can be effectively reduced. Figure 10 below shows the reinforced carbon-fiber (epoxy/carbon) composite laminates. The different color implies the regions of connection and tubular frames which are made of 26-ply and 16-ply, respectively. Each ply has a thickness of 0.2mm. To reduce stress concentration, thicker structures are used in connection regions.

Figure 10: wheelchair Frame System

The use of solid mechanics is a strong tool for designing a project. With the help of finite element and analytical calculations, stiffness, strength, and stress areas of the wheelchair structure can be easily predicted and identified and can instantly be modified to achieve an optimal design. Using these tools, the behavior of material for structural and design of wheels, frames, and impact-absorbing structure in the wheelchair have been analyzed. Figure 11 below shows the loading and boundary conditions of the wheelchair frame.

Figure 11: Subjected to Upward loading Test

Figures 12 to 14 below show the FEM model of the wheelchair frame used in the ANSYS software. Elastic property and static structural analysis were done on this FEM model. Using the thick shell theory to simulate this epoxy/carbon composite laminates, the SHELL91 that is 8-noded high-order shell elements with multi-plies were used. Furthermore, it is assumed in the finite element analysis that there is perfect bonding between plie. To deliberate the effects on the magnitude of stress, the directions of fiber for all plies may be changed. The boundary conditions were set on specific nodes for the finite element model. The external nodes on the frame are set to many nodes.

Figure 12: Finite Element Model         Figure 13: Finite Element Model

Figure 14: Finite Element Model

Figure 15 below shows the global deformation of the wheelchair frame system associated with [0/45₄/−45₄/90₄]_s under the upward loading test. For the same case, figure 16 below shows the distribution of the normal stress (σ₁) along the fiber direction on the outer surface of the tubular frame. The stress concentration can be noticed around the connection region. [7]

Figure 15: Displacement contour of Wheelchair frame system

Figure 16: Contour of normal stress (σ₁) along fiber direction on the outer surface.

Another study simulated four wheelchair frames using different materials. It was Aluminium 1060 alloy, Gray Cast Iron, Stainless Steel, Mild Steel, and numerical analysis was done on it through Solidworks. This simulation was done with 980N (Above average weight of a person). The stress analysis on Aluminum, Cast Iron, Stainless, Mild steel is shown in figures 17 to 20.

Figure 17: Aluminium

Figure 18: Cast Iron

Figure 19: Stainless Steel

Figure 20: Mild Steel

From the simulation result, it is showed that Mild steel can sustain higher stress and its Strain & displacement is very low than other material. Due to the good simulation result, low market cost and availability Mild steel have been selected for frame material.

Table 1: Stress, strain, displacement result by simulation

Table 2: Properties of Mild Steel

 Tables 1 and 2 above shows the overall results from the simulation in ANSYS for the four different materials and the properties of Mild Steel.

Von Mises stress analysis is used to find the yielding criteria of isotropic or ductile materials under complex load. According to Von Mises yield criterion, it is independent of first stress invariant. But the ductile materials will exceed yield point when the second deviatory stress invariant will reach a critical value. The stress analysis of the wheelchair frame is given in figure 21 below [9]

Figure 21: Stress analysis on a frame

PROBLEM STATEMENT

 A handicapped person with a locomotive disability needs a wheelchair in order to move around. One can do so manually by forcing the wheels by hand. However, types of physical disabilities vary from one handicapped to another. Hence, it is desirable to provide them with an automatic wheelchair that can be controlled by the head, hands, and feet that will be compatible for all types of physical disability – may it be a person cannot move his upper body but can move his head or the other way around. Since it is motorized and can move at a fair speed, it is important that it is able to avoid obstacles automatically at an instant. All this should be achieved at a cost that is reasonable. With these requirements in mind, the researchers propose an automatic wheelchair for all physical disability types.

OBJECTIVES

General:

• To design and fabricate an automatic wheelchair for all physical disability types.
• To integrate appropriate sensor and actuators and use contemporary software on the automatic wheelchair for all physical disability types.
• To define mechanical properties, mechatronics properties, and control system of the automatic wheelchair for all physical disability types.

Individual:

• To design and fabricate the headgear of the developed prototype of an automatic wheelchair and integrate wireless connection.
• To develop the program of the accelerometer and Bluetooth module to control the wheelchair through the headgear and mobile device.
• To analyze and determine the external and internal forces, moments, axial, shear, and bending stresses, modulus, and strain, and failures involve in the framing of the wheelchair and identify stress concentration areas using ANSYS.

SCOPE OF THE PROJECT

 This project is about the design and fabrication of an automatic wheelchair that will be suitable for all types of physical disability. This was made possible with the use of appropriate sensors, actuators, and microcontroller. This paper is focused more on two of the four control systems of the wheelchair which are the headgear and the Bluetooth module. The rest of the control systems are discussed on different papers. Also, this paper is focused more on the behavior of the wheelchair frame upon loading conditions apply. This has been done through simulation with the use of finite element analysis using the software ANSYS and some useful mathematical equations.

WORK BREAKDOWN STRUCTURE

 The figure below shows the Work Breakdown Structure for the Development of an Automatic Wheelchair for all Physical Disability Types. It shows the five main phases of the project and the sub-activities under each activity.

Figure 22: Work Breakdown Structure of the Project

METHODOLOGY

 The project was carried out through the use of sensors, actuators, and microcontroller. The project was divided into four control systems. The control system on the headgear, armrest, and footrest, and wireless control. The headgear is composed of an accelerometer sensor that will send voltage output signal that ranges from 2-3.6V, the input signal to the microcontroller, that allows the wheelchair to move forward if the headgear is tilted forward; move backward if the headgear is titled backward; and the same concept applies if the headgear is titled both left and right sideward.  The armrest is composed of a joystick module that allows the wheelchair to move on four directions along with its output signal. Pushbutton switches are also integrated into the armest – one for each direction – that will serve as a backup control if other sensors may fail. The footrest has also composed a joystick. Also, the footrest is integrated with an ultrasonic sensor that serves as a safety device that stops the vehicle if there is chance of collision.

 The figure below shows the block diagram for the whole system of the Automatic Wheelchair for all Physical Disability Types that is divided into four control systems but are connected together in 2 microcontrollers. Two microcontrollers were used for the reason that the ultrasonic sensor created errors on the system and needs to be isolated from other sensors.

Figure 23: Block Diagram of the Whole System

The figure below shows the flowchart of the control system of the headgear with the use of accelerometer. The 0.6V output signal from the accelerometer was set as the parameter that serves as the input signal for the microcontroller that determines the direction of the movement of the wheelchair. It was decided to be 0.6V output set that would allow the wheelchair to run smoothly after series of trials and test were done after sensitivity issues were observed.

Figure 24: Flowchart for the Accelerometer

 The figure below shows the flowchart of the wireless control system which is the mobile device that is connected to the wheelchair using Bluetooth connectivity. It uses a low cost and low power transmitters, with a range of 10-30 meters for class 2 devices that are common to mobile devices. Incoming Bytes declared in the codes are read by the module that signifies which command the Bluetooth module will follow that allows the wheelchair to move on a specific direction.

Figure 25: Flowchart for the Bluetooth Module

COMPONENTS

 The following figures below show the major hardware components that were used as discussed above.

Hardware:

Figure 26: Arduino Uno Microcontroller

Figure 27: MPU-6050 Accelerometer Sensor

Figure 28: HC-05 Bluetooth Module

Figure 29:  Joystick Module

Figure 30:  Rocker Switch Module

Figure 31: Push Button

Figure 32: HC-SR04 Ultrasonic Sensor Module

Figure 33: 50W Wiper Motor Motor

Figure 34: 12V 7.0Ah Sealed Lead Acid Battery

Figure 35: 12V Sealed Lead Acid Battery Charger

Figure 36: 25mm Mild Steel Square Tubes

Figure 37: 75mm Rear Nylon Castor Wheels

Figure 38: 50mm Front Nylon Castor Wheels

Software:

 The figures below show the software programs that were used for finite element analysis for the wheelchair frame and the designing of the finite element model. ANSYS student version was used in the simulation of the wheelchair frame while Solidworks was used in making the 3D STEP model for the wheelchair frame. On the other hand, Arduino IDE software was used in compiling the programming codes with the use of C language for the Arduino Uno microcontrollers while Proteus was used in making the schematic diagram for the components.

Figure 39: ANSYS for Simulation of Wheelchair Frame

Figure 40: Solidworks for 3D Step File of Wheelchair Frame

Figure 41: Arduino IDE for Programming using Embedded C Language

Figure 42: Proteus for Circuit Diagram of the Whole System

 The figure below shows the circuit diagram of the whole system. It shows how the components such as the sensors and the switches are being connected to the microcontrollers. Since the accelerometer sensor provides analog voltage outputs, the pins are connected to the analog pins of the Arduino Uno microcontroller. The SDA of the accelerometer is connected to the A4 pin while the SDL is connected to the A5 pin. Of course, Vcc is connected to the 5V pin and GND to GND pin. On the other hand, the Bluetooth module is connected to the digital pin as it provides digital input signals that are written and read by the microcontroller.  The RXD pin of the Bluetooth module is connected to PIN 0 while the TXD is connected to PIN 1. Vcc and GND are connected to their respective pins. Joysticks, similar with accelerometer, give input analog signals to analog the microcontroller. The joystick for armrest is connected to analog pins. VRx and VRy are connected to A0 and A1, respectively. Similar case with the joystick on the footrest, VRx, and Vry pins are connected to A2 and A3, respectively. Pushbutton Switches are just the simple cut in and out of the digital input voltages on their respective pins. Each button signifies specific direction. The forward button is connected to Pin 8, Backward to Pin 9, Left to Pin 12 and Right to Pin 13. It also shows how the ultrasonic sensor is isolated in a different microcontroller that can be turned on and off anytime. A rectifier is provided to lower down the 12V supply from the battery to power the 5V Arduino Uno microcontroller. An L293D motor driver is integrated to drive the motors and allow the forward and reverse movement.

Figure 43: Circuit Diagram of the Whole System of Automatic Wheelchair

 The figure below shows the Arduino code used for the Automatic Wheelchair for all Physical Disability types. Comments are provided for better understanding. Indentions are made for better construction. The programming language used is embedded C language. This code is only used of the first microcontroller which integrates all the sensors except the ultrasonic sensor. The code for ultrasonic sensor is discussed in a different paper.

Figure 44: Programming Code for the Automatic Wheelchair for all Physical Disability Types

TOTAL COST

Table 3: Overall Cost for the Completion of Project

 Table 3 above shows the high-level cost breakdown of the components and materials used in the process of fabricating the Automatic Wheelchair for all Physical Disability Types.

RESULTS AND DISCUSSION

 After a series of trials and tests, the group has come up with the prototype of the Development of an Automatic Wheelchair for all Physical Disability Types. Figure 45 below shows the prototype of the project with all the components installed. The prototype and all its components are in good working condition. All components are connected together in the main board located below the seat just at the back of the footrest as shown in Figure 46.

Figure 45: Automatic Wheelchair for all Physical Disability Types

Figure 46: Mainboard of Automatic Wheelchair for all Physical Disability Types

 The figure below shows the headgear which is only made of a plastic headband available on department stores where the MPU-6050 Accelerometer is attached on the uppermost flat surface of the headband. The reason for choosing the headband is for the comfort of the wearer of the headgear. The headgear should be parallel to the ground when attached to the wheelchair so that it would maintain on stop position.

Figure 47:  Headgear with the MPU-6050 Accelerometer Sensor

The figure below shows the wireless system of the project which is the HC-05 Bluetooth module that is responsible for giving input signal to the microcontroller to control the movement of the wheelchair. This Bluetooth module connects to the mobile device through Bluetooth connectivity. The connection can be made around a 30m radius as per Bluetooth class 2 devices which are common for all mobile phones. [10]

Figure 48:  Headgear with the MPU-6050 Accelerometer Sensor

 The figures below show the free android software available on Google Play that is used in connecting and controlling the Automatic Wheelchair for all Physical Disability Types. It can be used as a remote control by touching the arrows as shown in Figure 50, and also can be used as accelerometer as shown in Figure 52. The application is user-friendly and has setting options that can be easily understood as shown in Figure 51.

Figure 49: Bluetooth RC Controller [11]

Figure 50: Bluetooth RC Controller Interface

Figure 51: Bluetooth RC Controller Menu Options

Figure 52: Bluetooth RC Controller as Accelerometer

 The armrest is integrated with the joystick module and position switches with arrows indicating the direction as shown in Figures 53 and 54, respectively. This is to provide option to the user whether the user is comfortable with toggling a joystick or pushing a button. Not only that, one serves as a back-up system if the other fails.

Figure 53: Joystick Module on the right armrest

Figure 54: Push Button Switches on the left armrest

The figure below shows the footrest of the Automatic Wheelchair for all Physical DIability Types. It employs a Joystick which can easily be toggled by a foot which is placed on the center front of the footrest so that either foot can toggle the Joystick. Also, an HC-SR04 Ultrasonic sensor is integrated for added anti-collision feature which stops the wheelchair and activates the buzzer if there is an obstacle within a 50cm distance. The sensor is placed on the front of the footrest as to it usually be a blind spot area or beyond the line of sight for the user if the user is facing upfront straight.

Figure 55: Footrest with Joystick and Ultrasonic Sensor

ANALYSIS OF WHEELCHAIR FRAME

 The figures below show the static structural analysis boundary conditions set based on the actual conditions of the wheelchair upon the user sits on it. The software used for analysis the frame is ANSYS.

Figure 56 below shows the first condition where a remote force which is equal to the weight of the person sitting is distributed on the sitting support. The figure below shows that a 980N (100kgf) downward remote force which is the base weight of our test as per research and the average weight of a built adult person. The weight will vary later as series of trials will be done.

Figure 56: Boundary Condition 1

 Figure 57 below shows the second condition where a downward force is applied on each armrest support which is equal to the weight of the resting arms. The average weight of the arm is about 5.3% of the total body weight of the person.The load varies as the weight of the person varies from person to person. [12]

Figure 57: Boundary Condition 2

 Figure 58 below shows the third and last boundary condition where fixed support is applied to the support where the wheels are attached. Take note that the Nylon wheels can only stand up to 100kg based on manufacturers manual [13] but the focus here is solely on the frame.

Figure 58: Boundary Condition 3

 In choosing the suited material for the frame, an analysis on four different materials was done and results were compared that lead the group in choosing the suitable frame material. The figures 60 to 63 below are the analysis of frame in four different material given the standard conditions and determining the maximum principal stress. The figures show that Mild Steel can withstand higher stress compared to the other three materials.

Figure 60: Mild Steel    Figure 61: Aluminium Alloy

Figure 62: Cast Iron    Figure 63: Aluminium Alloy

Also, Maximum Principal strain and Total Deformation of each material were also evaluated to be part of the determining factor in choosing the suitable frame material. The figures 64 and 65 below show an example of Maximum Principal Strain and Total Deformation Analysis on the Mild Steel frame.

Figure 64: Maximum Principal Strain        Figure 65: Total Deformation

Table 4: Comparison of a simulation result of four different materials

 The table above shows the simulation results of four different materials based on their maximum principal stress, maximum principal strain, and total deformation. Comparing all the given material with the given results, Mild Steel can sustain higher stress, and its strain and deformation are lower compared to the other materials. Due to good simulation results, low market cost, and availability of the material in NZ market, Mild Steel frame has been chosen as the suitable material for the Automatic Wheelchair for all Physical Disability Types.

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 Further analysis of the wheelchair frame was done by varying the weight of the person. The figures below show the simulation results of the Mild Steel frame with the increase of 10kgs in six analysis. Von-Mises Stress Analysis was used to determine the yielding criteria of ductile or isotropic materials experiencing complex load. According to Von Mises yield criterion, ductile materials will exceed its yielding point even though it is independent of its 1^st stress invariant when the 2^nd stress invariant will achieve a critical result. [14]

     Figure 66: 100kg                  Figure 67: 110kg

     Figure 68: 120kg                  Figure 69: 130kg

      Figure 70: 140kg                  Figure 71: 150kg

  Table 5: Overall Summary of Simulation Results

 The table above shows the overall summary of simulation results done in the Mild steel Frame after increasing the load by 10kgs in six evaluations.

Table 6: Properties of Mild Steel

 The table above shows the properties of Structural Mild Steel used in the simulation of the wheelchair frame. All these parameters were considered by ANSYS software as to this table is from the library of the software.

 The figure below shows the relationship of the Von-Mises Stress or the equivalent stress with the weight of the frame. It clearly shows that the frame can still withstand a 150kg person sitting without considering the capacity of the wheel and size of the person that may fit on the sit. Also, it can be noticed given the simulation results that the failure will most likely to occur on the welded joints.

Figure 72: Von-Mises Equivalent Stress VS Person’s Weight

CONCLUSION AND RECOMMENDATION

The prototype of the developed automatic wheelchair was designed and fabricated that can carry an average weight of a person that is 100kg.  Appropriate sensors were integrated and contemporary software were used. This wheelchair will benefit most physically challenged people especially the quadriplegics. The program for accelerometer and Bluetooth module was developed and was able to control the movement of the developed project. Suitable material was selected and Maximum Stresses, equivalent stresses, Maximum principal strain, total deformation and failure areas were identified with the use of ANSYS in this project. The developed automatic wheelchair is cost-effective compared to high-end automatic wheelchairs yet bring about the same functions and results.

For future work improvements, it is recommended to consider the design for waterproofing for electrical components. The use of a bigger capacity microcontroller that can cater to various sensor and functions is also recommended. A manual mode may also be considered. Switch for each component is recommended for future improvements since the user may not choose to use the control systems altogether. Also, it depends upon the type of disability the user has on what control systems will be appropriate to use. Also, an LED or LCD display can be integrated to show the remaining of the battery.

REFERENCES

APPENDIX

Fabrication of Wheelchair Frame:

Back-up control if all components fail.

Programming and Setting-up of Components