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Measurement Automation in Anechoic Chamber | Akash Bansal, Gaurav Kumar, Manjeet Kasotiya

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B-Tech Project

Final Report

Department of Mechanical Engineering

Measurement Automation in

Anechoic Chamber

Group No. – 18 Group Members: Project Adviser:

Akash Bansal 10051 Dr. Nachiketa Tiwari

Gaurav Kumar 10262 Professor

Manjeet Kasotiya 10387 IIT Kanpur


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ACKNOWLEDGMENT

We would like to express profound gratitude to our guide Prof. Nachiketa Tiwari

for his invaluable support, supervision and useful suggestions throughout the

project work. His technical support and continuous guidance enabled us to

complete our work successfully.

We are grateful for the cooperation and constant encouragement from the

members of the BTP evaluation committee, whose suggestions have been

instrumental in the making of this project.

We would like to express our appreciation to the staff of the workshop, who have

helped us every time whenever we faced difficulty in manufacturing and assembly.

We also appreciate the timely support of some of our course-mates, who were

always available for help in the electronic and coding part of the project.

Last but not the least, we thank each other for coming together and working on this

project relentlessly to make it a success.


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CERTIFICATE

It is certified that the work contained in this report titled “Specifications and Guidelines for

Preparation of Bachelor of Technology Project Reports" is the original work done by Akash

Bansal (10051), Gaurav Kumar (10262), Manjeet Kasotiya (10387) has been carried out under

our supervision.

Nachiketa Tiwari

Project Supervisor

Department of Mechanical Engineering

Indian Institute of Technology

Kanpur 208016

13 April 2014


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1. Introduction

1.1 Definition:

Anechoic Chamber: An anechoic chamber is a room designed to completely absorb

reflections of either sound or electromagnetic waves. They are also insulated from exterior

sources of noise. The combination of both aspects means they simulate a quiet open-space

of infinite dimension, which is useful when exterior influences would otherwise give false

results.

The measurements of the sound power level, sound intensity and the directional

characteristics of the electroacoustic transducers are usually performed in anechoic room.

Measurements of the sound power level, sound absorption coefficient and sound scattering

coefficient are carried out in a reverberation room.

1.2 Design Challenge:

We have come up with an anechoic chamber within our campus. In order to carry out

various measurements for source acoustic signature determination, we need to measure the

sound intensity at various locations within the chamber. The current challenges are that in

order to accomplish this task we need a lot of time as of now and the data points thus

obtained are not dense and accurate enough to help map the signature. Manual positioning

is time consuming and tedious as it requires a precise positioning of the measuring

microphone (e.g. on a stand) at many measurement points.

1.3 Design Requirements:

In order to conduct acoustic measurements for the identification of sound sources requires

an accurate positioning of the measuring microphone in the acoustic chamber. An

automatic measurement system has to be designed, fabricated and assembled. Automated

mechanical positioning would ensure the possibility of very accurate directional

characteristics measurement of the sound sources. So the problems on which we have to

work are as following.

i. To position elements of an acoustic measurement system at desirable locations in the space

within an anechoic chamber

ii. To determine the spatial coordinates of the measuring probe corresponding to every

acoustic measurement


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2. Conceptual Solution

2.1 Technical Challenges:

i. To design a 3 degree of freedom system assembly to be able to span the required

measurement space of the chamber

ii. Automated Movement and measurement of the acoustic sensor probe(microphone) in sync

with the user’s command

iii. Accurate determination of the physical coordinates of the sensor probe for every

measurement

iv. Minimal surface area of the assembly to avoid any active sound reflections and

reverberations caused by assembly

2.2 Sensor/Receiver Movement

The construction of the mechanical part of the device has to be done keeping in mind in

order to achieve 3-degree of freedom. It should be spanning the measurement span within

the chamber. The movement must be controllable using Computer User Interface. The

different motions can be realized independently

2.2.1 Rotational Movement:-

We need not go around the source to measure the directional properties, in order to avoid

the motion of the whole device set-up. However, we mount our source on a turntable and

rotate the turntable to realize all the possible relative directions w.r.t. the source.

Turntable hosting the sound generating source would rotate on its axis to give required

relative angle with source element

The calibrated rotation would be achieved using a servo/stepper motor control with the

specified step motion

2.2.2 Radial Movement:-

We support a horizontal beam above the turntable. The beam supports a sprocket chain

mechanism which will be powered by another stepper motor. By powering the stepper

motor, we can use a trolley holding the sensor to travel horizontally.

The beam is supported by another vertical support.


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2.2.3 Vertical Movement:-

The trolley mounted on the chains along the horizontal will hold a spool which would

support the sensor which goes up and down by the control of the rotation of the spool by

the stepper motor.


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3. Assembly:


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3.1 Sub-Assembly – 1

3.2 Sub-Assembly – 2


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4. Parts List:

PART

NO.

PART MATERIAL QUANTITY FABRICATION

/

PURCHASE

FROM

CALCULATION

1 CHAIN 2.5 m PURCHASE NO

2 HORIZONTAL

BEAM

STRUCTURE

STEEL

1 FABRICATION YES

3 STEPPER MOTOR 3 PURCHASE YES

4 VERTICAL BEAM STRUCTURAL

STEEL

1 FABRICATION YES

5 BASE PLATE STEEL 1 FABRICATION NO

6 CORNER

SUPPORT

ANGLES

STEEL 1 FABRICATION NO

7 BASE SUPPORT

ANGLES


8 SPROCKET

WHEELS

2 PURCHASE NO

9 TURNTABLE TOP ALUMINIUM 1 FABRICATION YES

10 TURNTABLE

RING

STEEL 1 FABRICATION YES

11 TURNTABLE

BASE


12 BASE RING STEEL 1 FABRICATION YES

13 BALLS STEEL 8 PURCHASE NO

14 MOTOR STAND WOODEN 1 FABRICATED NO

15 BASE STAND STEEL 4 FABRICATED NO


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5. Simulation 1: Horizontal Beam

5.1 Material Properties

Model Reference Properties Components

Name: AISI 1020 Model type: Linear Elastic Isotropic Default failure

criterion: Max von Mises Stress

Yield strength: 3.51571e+008 N/m^2 Tensile strength: 4.20507e+008 N/m^2 Elastic modulus: 2e+011 N/m^2 Poisson's ratio: 0.29 Mass density: 7900 kg/m^3 Shear modulus: 7.7e+010 N/m^2 Thermal expansion

coefficient: 1.5e-005 /Kelvin

SolidBody

1(Boss-

Extrude1)(Part5)

Loads and Fixtures

Load name Load Image Load Details

Force-1

Entities: 1 face(s)

Type: Apply normal force

Value: 50 N

5.2 Resultant Forces

Selection set Units Sum X Sum Y Sum Z Resultant

Reaction Forces N 49.9848 -0.0382462 -0.0081749 49.9848

Reaction Moments N·m 0 0 0 0


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5.3 Results

Name Type Min Max

Stress1 VON: von Mises Stress 26.3549 N/m^2

Node: 15086

2.50034e+006 N/m^2

Node: 15796

Part5-Study 1-Stress-Stress1

Name Type Min Max

Displacement1 URES: Resultant Displacement 0 mm

Node: 1

0.220241 mm

Node: 508

1

STRESS STUDY

DISPLACEMENT STUDY


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Name Type Min Max

Strain1 ESTRN: Equivalent Strain 4.02004e-011

Element: 8350

9.98646e-006

Element: 5623

Part5-Study 1-Strain-Strain1

STRAIN STUDY


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6. Simulation Sub-Assembly – 2

Model name: disc1

Current Configuration: Default

Solid Bodies

Document Name and

Reference Treated As Volumetric Properties Document Path/Date Modified

Cut-Extrude3

Solid Body

Mass:14.6398 kg

Volume:0.00185313 m^3

Density:7900 kg/m^3

Weight:143.47 N

C:\Users\VAIO\Desktop\DESIGN\disc1.SLDPRT

Nov 13 01:32:09 2013

6.1 Resultant Forces

6.1.1

Selection

set Units Sum X

Sum Y Sum Z Resultant

Reaction

Forces

N 0.0214097 0.0446741 399.984 399.984

Reaction

Moments

N·m 0 0 0 0

6.1.2 Simulation Results:


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Name Type Min Max

Stress1 VON: von Mises Stress 353.838 N/m^2

Node: 14183

673640 N/m^2

Node: 16648

Strain1 ESTRN: Equivalent Strain 4.00689e-009

Element: 7746

2.36511e-006

Element: 5303


Node: 5

0.00323814 mm

Node: 1363


Node: 5

0.00323814 mm

Node: 1363


Node: 5

0.00323814 mm

Node: 1363


Node: 5

0.00323814 mm

Node: 1363

disc1-Study 2-Displacement-Displacement1

DISPLACEMENT STUDY


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6.2

STRESS STUDY

STRAIN STUDY


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7. Manufacturing:

Manufacturing started in the 2nd Semester. It took about 3 months to complete the manufacturing

and assembly of the parts. Following is the final product after assembly.

1. TURN TABLE


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1.1 TURN TABLE BASE

1.2 TURN TABLE TOP


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2. STAND


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2.1 MOTOR SUPPORT

2.2 MOTOR SUPPORT


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8. Calculations

8.1 Torque required by the motor:

Volume of Aluminum disk 𝑉𝐴1 = 𝜋𝑟2ℎ

= π × 0.252 × 0.5 × 10-2

=9.81 × 10-4 m3

Mass of Aluminum disk 𝑀𝐴1 = 𝜌𝑎𝜋𝑟2ℎ

= (2700 kg/m3) × 9.81 × 10-4 m3

= 2.65 kg

Volume of Steel ring = 𝜋𝑟22ℎ − 𝜋𝑟1

2ℎ

= 𝜋ℎ(𝑟22 − 𝑟1

2)

=1.005 × 10-4 m3

Mass of steel ring 𝑀𝑠 = 𝜌 𝑉𝑠

= (8000 × 1.005 ×10-4) kg

= 0.804 kg

Maximum Payload = 30 kg

Total Mass = 33.5 kg

Total frictional force =𝜇 × 𝑚 × 𝑔

𝜇 = 0.2-0.6 (Steel Surface Contact)

Max Frictional Force = 0.6 × 33.5 × 9.81

= 197 N

Torque Required = 200 × 0.2 = 40 N-m

fr

fr

w

w(angular

velocity)

fr (friction)


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9. Assumptions in the Design

The source would be located on the existing TurnTable.

The working space would take the form of a cylinder with the height of H = 2000 mm and

the diameter of D = 2000 mm.

In the working space, the microphone would be suspended with small diameter ropes to

minimize the interference of the free field.

The accuracy of the positioning for a linear displacement of the microphone will be less

than 1 mm

The axis of the measuring microphone can be reoriented relative to the sound source.

All the simulations provide the results in the case of maximum loads and stresses possible.

10. Design Specifications

Degree of Freedom: 3 Meters

Vertical Span: 2 Meters

Horizontal Span (Radial): 2.5 m

Permeable Turntable Rotation: 360°

Circular Step-size: (10°-15°)

Linear Step-size: (5 cm – 10 cm)

Hardware interface: ATMEGA USB

Control Software: computer interface (GUI)

Turntable Payload Capacity: Max 30 Kg

Holder Payload: Standard Microphone


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11. References:

Testing of a Device for Positioning Measuring Microphones in Anechoic and

Reverberation Chambers by Jozef FELIS, Artur FLACH, Tadeusz

KAMISIŃSKI,AGH University of Science and Technology

SYSTEM FOR AUTOMATED ACOUSTIC MEASUREMENTS IN THE ANECHOIC

CHAMBER by Andrzej ZBROWSKI, Jordan MĘŻYK, Tomasz GIESKO Institute for

Sustainable Technologies – National Research Institute, Radom, Poland

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