Cairfirme bahuhsjbsbssb | Thesis Electrical Engineering

Texas Instruments Innovation Challenge

India Design Contest 2017

Quarter Finals – Interim - Project Report

/ Technical Paper

Team ID : 131852

Team Leader Name : Gangumolu Lakshmi Sowjanya

Project Title : Stair Chair for Physically Challenged

People

Project Abstract:

According to a statistical report given by the United Nations, there is an exceptionally rapid pace

in the growth of elderly people who are above sixty years. It is observed that the number of older

persons in 2013 is 841 million which is four times higher compared to 202 million older people in

1950. It is estimated that this population would get tripled by 2050 and is expected to reach 2

billion. Furthermore, according to Census of India loco motor disability is among the five types of

disabilities and is up to 20% of the total disabled population in India. With sharply increasing of

elderly and disabled people at present, the work which focuses making life easier for those people

have been paid more attention. One of the major challenges faced by the elderly people and

physically challenged people is to climb stairs even while moving on a wheel chair. So, this project

aims at designing a new powered stair-climbing wheelchair which can work in two modes: stair-

case mode and flat surface mode. In stair case mode before climbing or descending the stairs we

should rotate the seat backrest system handle to maintain centre of gravity while moving on stairs

and the moment when one reaches flat surface, again the seat comes to the original position by

rotating the handle in anti-clockwise direction. Here conventional wheels would be replaced by tri-

star wheels which enable wheelchair to ascend and descend stairs and move freely on uneven

surfaces. A seat backrest adjustment system would be designed to adjust the centre of gravity

before climbing up and down the stairs.

Keywords: Stair climbing, wheelchair, Tri-star wheels, Center of gravity.

Proposed Design

A. Objective

The objectives of Stair Chair are:

 To develop a wheel chair that can-do stair negotiation (Climbing up and down the stairs)

 To use a back-rest adjustment mechanism to maintain the center of gravity that ensures the

safety of the user while climbing up or coming down the stairs

 To make the chair work efficiently on flat surfaces and on stairs by making use of Tri-Star

wheels.

 To make use of a joystick to control the movement of the chair on flat surfaces

B. Proposed Solution

The system level diagram of the proposed wheel chair is shown in Fig.1.

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Texas Instruments Innovation Challenge

India Design Contest 2017

Quarter Finals – Interim - Project Report

/ Technical Paper

Team ID : 131852

Team Leader Name : Gangumolu Lakshmi Sowjanya

Project Title : Stair Chair for Physically Challenged

People

Project Abstract: According to a statistical report given by the United Nations, there is an exceptionally rapid pace in the growth of elderly people who are above sixty years. It is observed that the number of older persons in 2013 is 841 million which is four times higher compared to 202 million older people in

It is estimated that this population would get tripled by 2050 and is expected to reach 2 billion. Furthermore, according to Census of India loco motor disability is among the five types of disabilities and is up to 20% of the total disabled population in India. With sharply increasing of elderly and disabled people at present, the work which focuses making life easier for those people have been paid more attention. One of the major challenges faced by the elderly people and physically challenged people is to climb stairs even while moving on a wheel chair. So, this project aims at designing a new powered stair-climbing wheelchair which can work in two modes: s tair- case mode and flat surface mode. In stair case mode before climbing or descending the stairs we should rotate the seat backrest system handle to maintain centre of gravity while moving on stairs and the moment when one reaches flat surface, again the seat comes to the original position by rotating the handle in anti-clockwise direction. Here conventional wheels would be replaced by tri- star wheels which enable wheelchair to ascend and descend stairs and move freely on uneven surfaces. A seat backrest adjustment system would be designed to adjust the centre of gravity before climbing up and down the stairs. Keywords: Stair climbing, wheelchair, Tri-star wheels, Center of gravity. Proposed Design A. Objective The objectives of Stair Chair are:  To develop a wheel chair that can-do stair negotiation (Climbing up and down the stairs)  To use a back-rest adjustment mechanism to maintain the center of gravity that ensures the safety of the user while climbing up or coming down the stairs  To make the chair work efficiently on flat surfaces and on stairs by making use of Tri-Star wheels.  To make use of a joystick to control the movement of the chair on flat surfaces B. Proposed Solution The system level diagram of the proposed wheel chair is shown in Fig. 1.

Fig. 1 : System Level Diagram As shown in Fig. 1 , the wheels in the conventional wheel chair would be replaced by Tri-Star wheels on the front and rear ends of the chair. The tri-star wheels would take care of climbing up and down the stairs. The tri-star wheels are connected to the shafts of dc motor which are controlled by a microcontroller. While moving on the flat surfaces, the movement of the wheel chair can be controlled by making use of a joy-stick placed on the arm rest of the chair.To maintain centre of gravity while climbing and descending the stairs Seat backrest adjusting system is used. One can control the seat inclination by controlling the handle placed on seat. The block diagram of the proposed wheel chair is shown in Fig. 2. The proposed Stair Climbing Chair works in two modes of operation: Flat Surface mode and Stair case mode. The flat surface mode enables the chair to work as any motorized wheel chair and ensure free movement on the roads with the help of the Joy-stick. During the staircase mode the signals from the joy stick are disabled and the central shaft connected to the tri-star wheel comes into action. Fig. 2 : Block Diagram of Proposed Stair Chair Tri-Star Wheels Back-rest Electronic Circuitry Joy Stick

(Here M1: Motor1; M2: Motor2) Fig. 3 : Flow Chart for Software Implementation of Stair Chair The stair chair switches its mode either from the mode selection switch or when an obstacle is detected. In the normal mode, chair runs according to the control actions given by the joy stick. In climbing mode after adjusting the back rest, the chair climbs the stairs. Hardware Implementation: Implementation of Joystick The joy-stick is connected to the microcontroller as per the circuit diagram shown in Fig. Automatic seat inclination Automatic seat inclination Changes seat inclination Changes seat inclination

Fig.4: Connection Circuit of Joy-Stick with the Micro-Controller As mention above, the Joy-Stick is used to control the motor movement to navigate the chair under normal mode. It is an analog switch and has four pins Vcc, GND and two analog pins. The two analog pins are connected to the analog ports of the microcontroller. TO test the functionality of the microcontroller, LEDS are connected to the digital ports of the microcontroller. By moving the joy-stick along the horizontal and vertical directions, the flashing ON and OFF of the LEDs are observed. Inertial Measurement Unit (IMU) The IMU detects the change in the position of the chair and imbalance in the chair with respect to the ground. The IMU Consists of 8 pins including Vcc and GND. The IMU is interfaced with the microcontroller using I2C communication protocol. The SCLK, SDA pins of the IMU are connected to the SCK and SDA pins of the microcontroller. The IMU’s position is varied in steps along the Horizontal, vertical directions and the values along the X-axis and Y-axis are observed and noted. Similarly, the angle of the IMU is varied in steps and the corresponding values are also noted down. The circuit diagram for interfacing the IMU with microcontroller is shown in Fig.5. Fig.5: Connection Circuit for Inertial Measurement Unit (IMU) Stepper Motor The MSP430G2553 is an ultra low power microcontroller and cannot drive a stepper motor directly. So, an external stepper motor driver is connected in between the microcontroller and the stepper motor. The Stepper motor used in this project is “Invento Nema 17” bipolar stepper motor. The motor has two windings A and B and are coded with colour coding for identifications. The direction of the motor and the steps per revolution are controlled by the microcontroller. Tri-Star Wheel Design The design of the Tri Star wheel as per the calculations is shown in Fig.6. The design considerations are very important for the implementation of the Stair chair. The most important parts that require proper care for the implementation are: Tri Star Wheels, selection of a proper motor, gearing mechanism and seat back rest adjustment system. The design consideration for all the said mechanisms is described below:

Fig.7: Tristar wheel parameters rmin = 6R+a(3b−√ 3 a) ( 3 −√ 3 )a−( 3 +√ 3 )b = 9.57cm (2) rmax = √ a^2 +b^2 2 = 22.56cm (3) tmax= ar( 3 −√ 3 )+br( 3 +√ 3 )+a(√ 3 a−3b) 6R =5cm (4) Fig.8: Free body diagrams From free body diagrams, considering the equilibrium equations We have, T1 = N1Rcosθ- f(r+Rsinθ) (5) T2= N2Rcosθ+ f(r+Rsinθ) (6) T1 + T2 =mgRcos𝜃 (7) Maximum value of essential static torques Tall = 2 (T1 +T2 )max = 2mgR = MgR (8) Assuming overall weight of prototype to be 70 kg, T=Tall= 709.8*( 18. 42 ∗ 10 −^2 ) = 126.36 N-m (9)

Considering 1:2 gear ratio, power required would be P= 2 πNT 60 = 1.98 kW (10) DC Motor The driving mechanism is powered by 2 DC motor that are coupled to the right and left side of the rear wheels respectively. Here, we use 450W, 24V DC motor. The wheel chair would be designed to have a maximum velocity of10 kmph. Since the mechanism consists of two separates motor, the load can be equally distributed to each motor. Two 12V, 45AH batteries are used to run the motors. Here, we use gear train mechanism to reduce the speed of the wheel chair. The maximum velocity of the wheelchair is 10 kmph. The diameter (D) of the tri-star wheel is 38 cm. From the relation in equation ( 1 2) the number of rotations N is determined approximately to be 300rpm V = π D N 60

Expected Outcome: Fig.9: Expected Outcome The picture of the proof of concept developed till now is shown in Fig.10. Fig.10: Stair Chair and Remote-Controlled Joy-Stick Tri-Star Wheels Back-rest Electronic Circuitry Joy Stick

Cairfirme bahuhsjbsbssb, Thesis of Electrical Engineering

Partial preview of the text

Download Cairfirme bahuhsjbsbssb and more Thesis Electrical Engineering in PDF only on Docsity!

Texas Instruments Innovation Challenge

India Design Contest 2017

Quarter Finals – Interim - Project Report

/ Technical Paper

Team ID : 131852

Team Leader Name : Gangumolu Lakshmi Sowjanya

Project Title : Stair Chair for Physically Challenged

People