3rd International Conference on Electronics, Biomedical Engineering and its Applications (ICEBEA'2013) January 26-27, 2013 Hong Kong (China)

Smartphone Accelerometer Controlled Automated Wheelchair Vigneshwar. Santhanam and Vignesh. Viswanathan

operating system[1], with more advanced computing capability and connectivity than a feature phone. Most smart phones contain accelerometers for user interface control; often the accelerometer is used to present landscape or portrait views of the device's screen, based on the way the device is being held. Also most smart phones have Bluetooth Wireless Technology IEEE 802.15.1 module inbuilt in the device for various small range wireless applications like headset, file transfer, wireless input devices etc. The proposed concept exploits these features of the Smartphone to use it as a transmitter and control device completely eliminating the need for a separate transmitter block.

Abstract—Wheelchair bound patients in many countries are still dependent on other people for movement. Though automated wheel chairs are available, they are tough to operate and are power consuming. This paper is a proposal of a simpler automated wheel chair that takes advantage of the 3 axis accelerometer present in most Smart phones and Bluetooth wireless technology enabling patients to move their wheelchairs by just tilting their Smartphone. The actuators for this concept are controlled by a microcontroller powering a basic servo motor for directional motion and a pair of DC motors for the wheels. The power supply can be achieved by rechargeable battery which is also charged using the alternator during the motion of the wheels. This concept is more economic than existing systems as it uses basic ready-to-use components that can be attached to any existing wheelchair.

Keywords—Accelerometer, Electric assistance, powered wheelchair, Bluetooth.

wheelchair,

B. Accelerometer An accelerometer is an electromechanical device that will measure acceleration forces. These forces may be static, like the constant force of gravity pulling at your feet, or they could be dynamic - caused by moving or vibrating the accelerometer. The Smartphone Accelerometer is a semiconductor IC that measures motion and its intensity in all 3 axes and directly can provide values to suitably designed application.

patient

I. INTRODUCTION

P

ATIENTS involved in physical injuries and disabilities with good mental strength struggle to get through places using the conventional hand powered wheelchair. This concept enables an economic assembly in any existing wheelchair that enables a smart system for automated motion which can be controlled by any Smartphone. The concept particularly mentions ‘Smartphone’ which covers devices like any Android powered mobile phone which have inbuilt 3 axis accelerometer and Bluetooth Wireless technology. The functionality can be extended to other mobile devices using a suitable application. The other end of the system has a microcontroller which drives the various actions of the servo motor for directional movement and powers the DC motor for linear motion of the wheelchair. The servomotor controls the front wheels for turning the wheelchair while the pair of DC motor connected to the rear wheels enable linear motion.

C. Functional Application for Smartphone Bluetooth modules inbuilt in the phone can be tapped suitably using protocol stacks in the application design environment of the mobile operating system. The operating system suggested for this application is Android OS because there are existing applications that can connect to any Bluetooth device and can read values from the inbuilt accelerometer and transmit the values needed for this application. D.An Example Application An example for such application is BlueBotsPro [2] by develectronics that is available for USD 1.65 in the Google Play application store. The application interfaces accelerometer to work with Bluetooth modules that is described in the receiver section below [3]. The application also has a secondary 2 axis touch controller as a backup for the accelerometer controller.

II. HUMAN INTERFACE - TRANSMITTER A. Smartphone A Smartphone is a mobile phone built on a mobile

III. RECEIVER

Vigneshwar. Santhanam is studying Electronics and Communication Engineering at Sri Venkateswara College of Engineering, Sriperumbudur – 602105, India. (Phone: +919094148335, email: [email protected]) Vignesh. Viswanathan is studying Electronics and Communication Engineering at Sri Venkateswara College of Engineering, Sriperumbudur – 602105, India. (Phone: +919789037874, email: [email protected])

A. Microcontroller A microcontroller is the heart of the automated wheelchair. A microcontroller is a programmable device that can be used 57

3rd International Conference on Electronics, Biomedical Engineering and its Applications (ICEBEA'2013) January 26-27, 2013 Hong Kong (China)

to perform any arithmetic and logic operations. The difference between a microcontroller and a microprocessor is the availability of internal memory to store the programme code and it can function as a standalone controller. The need for microcontroller in this concept design involves receiving data from the Smartphone via Bluetooth technology and control the working of servo and DC motors. There are several self sufficient microcontroller boards available of which Arduino is the best suited for the following functions. Arduino is an open-source single-board microcontroller [4], descendant of the open-source Wiring platform, designed to make the process of using electronics in multidisciplinary projects more accessible. The hardware consists of a simple open hardware design for the Arduino board with an Atmel AVR processor and on-board input/output support. The software consists of a standard programming language compiler and the boot loader that runs on the board. Arduino hardware is programmed using a Wiring-based language (syntax and libraries), similar to C++ with some slight simplifications and modifications, and a Processing-based integrated development environment. This is a simple controller which can be easily incorporated with the Bluetooth stick. It is programmed in such a way to control the servo and DC motors. This is done by using a simple coding technique similar to the C program coding. It is also the cheapest and most widely used controller. As we employ only simple operations this controller is sufficient. The controller takes the input from the Bluetooth card and controls the motion of the wheel chair. The main reason for employing this controller is its low power consumption and ease in the coding .The supply is drawn from the batteries which are used to run the motors. The output of the controller just indicates the motors that are to be activated are. The output ports are coupled to motors via the relays and based upon the controller output, the corresponding motor rotates to move the wheel chair in the desired direction. The wheel chair interacts with the smart phone app by means of this Arduino via Bluetooth. The Bluetooth receiver that can be interfaced to the Arduino board is EGBT-045MS Bluetooth module

Current: 40mA max.

Fig. 1 Pin Configuration of EGBT-045MS Bluetooth Module

Fig. 2 Interfacing EGBT-045MS Bluetooth Module to a Microcontroller

C. Motion Driver Components The main purpose for the usage of servo motor is to bring about the directional motion in the wheelchair. The motor, controlled by the microcontroller indicates the direction of motion (left/right). The motor is connected to a central axle for the front wheels. The microcontroller signals the degree of tilt from the Smartphone and the servo motor correspondingly turns the servo motor which rotates the axle. The servo motor picks the control signal from the controller and draws a supply from the battery provided. The wheelchair mostly is operated with a patient weighing more than 60 kilograms on an average, there is a need to make sure the motor can perform well under such loaded conditions and hence we move on for a more powerful servo motor which is characterized by its speed-torque curve, maximum torque. Another torque calculation critical for sizing the servo motor is RMS torque. To decelerate the load, often a reverse torque is required. The reverse torque during deceleration is not as high as the forward torque during acceleration, since friction also helps decelerate the load. The servo motor is connected to the axle of the front wheels which guides the diagonal direction. The axle is coupled with the motor by means of shaft assembly

B. Bluetooth Receiver Module Specification EGBT-045MS is a generic Bluetooth Modules loaded with SPP firmware for UART wireless cable replacement functions [5]. The EGBT-045MS can be configured by the user to work either as a master or slave Bluetooth device using a set of AT commands. SPECIFICATIONS EGBT-046S: Radio Chip: CSR BC417 Memory: External 8Mbit Flash Output Power: -4 to +6dbm Class 2 Sensitivity: -80dbm Typical Bit Rate: EDR, up to 3Mbps Interface: UART Antenna: Built-in Dimension: 27W x 13H mm Voltage: 3.1 to 4.2VDC 58

3rd International Conference on Electronics, Biomedical Engineering and its Applications (ICEBEA'2013) January 26-27, 2013 Hong Kong (China)

which helps in rotating the axle. Typical servo motor mechanism is not complex. The servo motor has control circuits and a potentiometer that is connected to the output shaft. The shaft, which is the output device, links to a potentiometer and control circuits that are located inside the servo. The potentiometer, coupled with signals from the control circuits, control the angle of the shaft – anywhere from 0 to 180 degrees, sometimes further. The potentiometer allows the control circuitry to monitor the current angle of the servo motor. If the shaft is at the correct angle, the servo motor idles until next positioning signal is received. The servo motor will rotate the correct direction until the angle is correct. Each servo motor works off of modulation known as Pulse Coded Modulation or PCM [6]. The motor has a control wire that is given a pulse application for a certain length of time. The angular degree of the shaft is determined by the length of the pulses, which the servo motor anticipates every couple seconds. A normal servo is mechanically not capable of rotating further due to a mechanical stop built into the main output gear. The amount of power applied to the motor is proportional to the distance it needs to travel. So if the shaft of the servo motor needs to turn a large distance, the servo motor will run at full speed. If the servo motor needs to rotate only a small amount, the motor will run at a slower speed. This is referred to as Proportional Control. The servo motor expects to see a pulse every 20 milliseconds (.02 seconds) and the length of each pulse will determine how far the servo motor will rotate.

Fig. 3 Triangular Operating Pattern of Servo Motor

2) Trapezoidal Operating Pattern Maximum Speed:

v0 =

X0 t0 − t A

(4)

Acceleration/Deceleration Time:

t A = to −

X0 vo

(5)

t0 = t A +

X0 vo

(6)

Total Travel Time:

Constant-Velocity travel time:

t B = to − 2 * t A

D.Formulas for Operating Patters of Servo Motor First the relationship between time and speed for each item that is being controlled is determined and then is converted to the operating pattern for these items into a servo motor shaft operating pattern [7].

(7)

Total Travel Distance:

X o = V0 (t 0 − t A )

(8)

Acceleration/Deceleration Travel Distance: 1) Triangular Operating Pattern

XA =

Maximum Speed:

X v0 = t A0 Xo vo

X B = v0 * t B

(1)

(10)

Where v 0 is the maximum speed in ms-1 X 0 is the maximum displacement in m X A is the acceleration/deceleration distance in m X B is the constant velocity travel distance in m t 0 is the total travel time in s t A is the acceleration/deceleration time in s t B is the constant-Velocity travel time.

(2)

Travel Distance:

X 0 = t A *v0

(9)

Constant-Velocity Travel Distance:

Acceleration/Deceleration Time:

tA =

(v 0 − t A ) 2

(3)

Where v 0 is the maximum speed in ms-1 X 0 is the maximum displacement in m t A is the acceleration/deceleration time in s.

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3rd International Conference on Electronics, Biomedical Engineering and its Applications (ICEBEA'2013) January 26-27, 2013 Hong Kong (China)

F. Interfacing with Wheelchair The servo motor is linked to a shaft in such a way that based on the command received from the Smartphone; it helps in turning the wheelchair in the desired direction. The servo motor is therefore specifically connected to the front wheels of the wheelchair. The pair of DC motor is connected to the rear wheels and connected to the battery through a relay which is being signaled/ triggered by the controller based on the command given to it by the transmitter. The Bluetooth chip is inserted to the microcontroller for the purpose of establishing the wireless command transfer. The chip receives the command from the Smartphone and instructs the controller to perform the required function. Thus the establishment of link between the phone and the wheelchair is done here. By this we interface the wheelchair with the Smartphone and control the motion of the chair by means of using the Smartphone.

Fig. 4 Trapezoidal Operating Pattern of Servo Motor

3) Speed – Slope Relationship Ascending Time:

tA =

vo − v1

α

(11)

Distance moved including Ascending time (tA):

X A = 0.5α * t A + v1 * t A 2

Speed after ascending:

v0 = v1 + α * t A

(12)

(13)

Speed Gradient:

α=

vg tg

(14) Fig. 6 Interfacing servo motor to the axle

IV. CONCLUSION A. Advantages • Provides easy movement for physically challenged people. • Easy to implement on any existing wheelchair and does not require sophisticated components. • Less expensive that completely built electric wheelchairs and many existing systems. B. Disadvantages • Requires Smartphone for operation as the system is completely dependent on the accelerometer in the Smartphone. • Batteries can be a complexity in both transmitter and receiver. The Smartphone batteries as well as battery to drive the motors have to be periodically recharged and maintained.

Fig. 5 Speed and Slope When Ascending Operating Pattern

E. DC Motor for Driving Linear Motion The DC motor is employed to help in the linear motion of the wheelchair. This motor is in turn controlled by the microcontroller. The type of motor generally employed is DC motors with higher RPM, torque and the one which can withstand higher capacity (weight). Any motor with higher performance can be used for this purpose. 60

3rd International Conference on Electronics, Biomedical Engineering and its Applications (ICEBEA'2013) January 26-27, 2013 Hong Kong (China)

C. Future Works • Automatically recharging the battery using alternator during movement of the wheelchair • Finding more power economic methods for implementing • Designing applications for other dominant Smartphone operating systems like iOS, Windows Phone and BlackBerry 10.

ACKNOWLEDGMENT Authors thank develectronics, an android app developer whose application BlueBotsPro has key functionality in this conference. Authors also expand their gratitude to www.hobbytronics.co.uk for providing basic support to interfacing Arduino board to the Bluetooth module mentioned in the concept. REFERENCES [1] [2] [3] [4] [5]

[6]

[7]

Wikipedia – Smartphone, http://en.wikipedia.org/wiki/Smartphone BlueBotsPro – Google Play , https://play.google.com/store/apps/details?id=blue.bots.matt&hl=en BlueBots, Bluetooth module, Arduino interfacing – HobbyTronics, http://www.hobbytronics.co.uk/magician-android-bluebots Wikipedia – Arduino, http://en.wikipedia.org/wiki/Arduino RAS Micro EGBT-045MS Bluetooth Module http://www.rasmicro.com/Bluetooth/EGBT-045MS046S%20Bluetooth%20Module%20Manual%20rev%201r0.pdf Servo Motor Guide – Anaheim Automation, http://www.anaheimautomation.com/manuals/forms/servo-motorguide.php Servo Motor Selection Guide, http://www.ia.omron.com/data_pdf/guide/14/servo_selection_tg_e_1_1_ 3-13%28further_info%29.pdf

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