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		+	== Design for Environment (DFE) ==
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		+	Posting design for environment stuff

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Revision as of 16:46, 11 February 2012

Contents 1 Group Information 2 Project Executive Summary 3 Competitor Product Analysis 3.1 Product History 3.2 Product Functionality and Use 3.3 Preliminary Product User Study 3.4 Product Disassembly 3.5 Bill of Materials 3.6 Failure Mode Effects Analysis (FMEA) 3.7 Design for Environment (DFE)

Group Information

24-441 Spring 2012, Group 3

Resident Hawaiian: Kellen Chow

Live-saving Extraordinaire: Jacob Divone

Community Ass-Kicker (CA): KinHang Leung

International Covert Operative: Cecily Sunday

Project Executive Summary

A stethoscope is a medical device used for listening to internal body sounds. Our team is assessing the usability of a typical stethoscope used for medical applications. We will be studying the history of the stethoscope design to help determine how the product works. We will also be dissecting a stethoscope to study the construction and materials used in the assembly. We conducted a preliminary user study to develop ideas for improvement as well as features to consider during product dissection.

Competitor Product Analysis

Product History

The first stethoscope was invented in 1816 and it has been an essential tool in medical diagnostic methods ever since. René Laennec of France first came up with the idea of a stethoscope when he examined a patient using a stack of paper rolled into a cylinder. The first stethoscope was simply made of wood. In 1852, the design of a binaural stethoscope was introduced and the new prototype replaced wood with rubber making it more flexible and comfortable to use. In 1865, a more sophisticated stethoscope was designed with ivory, steel and wood. In 1870, the design of stethoscope became standardized as binaural and was manufactured with steel, rubber and cotton for quality and durability. In 1998, the modern binaural stethoscope was invented and manufactured using stainless steel, rubber, nylon and plastic.

WE NEED TO CITE THIS

Product Functionality and Use

Three main components allow the acoustic stethoscope to transmit sound: a chest piece, an air filled tube, and a headset. In this medical device, vibrations are used to create pressure waves which travel from the source to the listener via air trapped in a hollow tube. While several design variations of the stethoscope exist, the theory behind each model remains the same.

PICTUREs OF STEM

The chest piece is responsible for capturing vibrations on a surface. Most chest pieces consist of a diaphragm or a plastic disk that vibrates in response to the surface sound. As the diaphragm vibrates, an acoustic pressure wave is created in the hollow interior of the chest piece. This pressure wave then travels through an air filled tube to the ear buds at the end of the headset where the sound reaches the listener. Many stethoscopes also have a bell, or an inverted cup situated opposite of the diaphragm. In contrast to the diaphragm, the bell creates pressure waves from the vibrations of the skin itself. The diaphragm is used to transmit higher frequencies while the bell transmits lower ones.

The stethoscope depicted in Figure 1 has two diaphragms located on the chest piece as opposed to a diaphragm and a bell. However, the smaller diaphragm functions the same as the bell because it is used to hear lower frequencies. The front, clear plastic side of either diaphragm is meant to be placed on the surface while the backs are to be screw into the stem, or the metal component that connects the chest piece to the tubing (see Figure 2). Before using the stethoscope, the chest piece must be indexed, or turned appropriately so that airflow is directed through the correct path. Airflow is directed through a valve located in the stem.

PICTURES OF DIAPHRAGM AND STEM

The acoustics of the stethoscope will be affected if the path from the diaphragm to the headset is not airtight. Obstructions in its interior from dirt or related build-up will also affect the sounds quality of the stethoscope. For these reasons, frequent cleaning and maintenance is required to insure the stethoscope continues to function properly.

Preliminary Product User Study

Our group conducted a user study to determine the proper use of, problems with, and possible innovations for the stethoscope.

Observations from Preliminary User Study

(1) Hard to hear in loud environments

(2) Extra noise created if the chest piece slides along the surface

(3) Headphones are uncomfortable to wear

(4) Acoustics may be affected by loose parts or obstructions in the air path

(5) The quality of sound is likely to be affected by the following parameters: diameter, length, and material of tube, vibration medium (air vs. water), material and shape of the ear buds, single vs. double connecting tube

(6) Adding a visual representation of the frequency, input signal, etc. ?

Product Disassembly

show step-by-step product disassembly?

Bill of Materials

Part #	Part Name	QTY	Function	Manufacturing Process	Material	Weight (oz)	Image
1	Eartip	2	Ear Comfort	Molded	ABS<ref name="abs">Determined by deduction; it sinks in water (SG > 1.0), medium hardness, opaque, non-brittle, low-cost manufactured</ref>	0.05 (2)
2	Eartube Caps	2	Stabilize tubing	Molded	ABS<ref name="abs"/>	0.05 (2)
3	Binaural Eartube	2	Sound transmission	Extruded & bent	Stainless Steel	0.50
4	Triple-Leaf Spring	1	Stabilize and maintain tension in eartubes	Rolled sheet metal, stamped and bent	Stainless Steel	0.30
5	Tube Clamp	2	Keep rubber tubes together	Rolled sheet metal, stamped and bent	Stainless Steel	0.10
6	Rubber Tube	2	Sound transmission	Extruded	TPE	1.40
7	Low-freq Diaphragm Base	1	Connect diaphragm to chestpiece	Stamped and machined	Stainless Steel	0.30
8	Low-freq Diaphragm Ring	1	Holds diaphragm film	Stamped and machined	Stainless Steel	0.20
9	Low-freq Diaphragm Film	1	Acts as a sound resonator	Thermoformed	PE
10	High-freq Diaphragm Base	1	Connect diaphragm to chestpiece	Stamped and machined	Stainless Steel	0.70
11	High-freq Diaphragm Ring	1	Holds diaphragm film	Stamped and machined	Stainless Steel	0.40
12	High-freq Diaphragm Film	1	Acts as a sound resonator	Thermoformed	PE
13	Tube Pins	2	Connect rubber tubes to chestpiece	Casted and turned	Stainless Steel	0.10
14	Tube Split	1	Split sound into the binaurals	Casted and machined	Stainless Steel	1.00
15	Multi-head Chestpiece	1	Holds both diaphragms	Machined	Stainless Steel	0.80
16	Chestpiece Cap	1	Encloses screw inside the chestpiece	Stamped	Stainless Steel	0.10
17	1/8" Flat-head Screw	1	Secure the chestpiece and the tube split	Bought
18	Compression Spring	1	Holds chestpiece against the tube split during rotation	Bought
19	Washer	2		Bought
20	Punched Washer	1		Bought

Failure Mode Effects Analysis (FMEA)

This is the FMEA. It's going to rock.

Part	Part Function	Failure Mode	Failure Effects	Severity	Cause(s) of Failure	Occurence	Detection	RPN	Recommended Actions
Low Frequency Diaphragm	Changes pressure in stethoscope to detect sounds	Diaphragm is punctured	Loss of stethoscope functionality	5	Impact Fracture	3	3	45	Inspect stethoscope before each use
Low Frequency Diaphragm	Changes pressure in stethoscope to detect sounds	Diaphragm surface is scratched	Reduced sound quality and functionality	3	Surface fatigue wear	3	2	30	Inspect stethoscope before each use
Low Frequency Diaphragm	Changes pressure in stethoscope to detect sounds	Diaphragm surface is warped	Reduced sound quality and functionality	4	Thermal/surface fatigue	2	3	24	Inspect stethoscope before each use
High Frequency Diaphragm	Changes pressure in stethoscope to detect sounds	Diaphragm is punctured	Loss of stethoscope functionality	5	Impact Fracture	3	3	45	Inspect stethoscope before each use
High Frequency Diaphragm	Changes pressure in stethoscope to detect sounds	Diaphragm surface is scratched	Reduced sound quality and functionality	3	Surface fatigue wear	3	2	30	Inspect stethoscope before each use
High Frequency Diaphragm	Changes pressure in stethoscope to detect sounds	Diaphragm surface is warped	Reduced sound quality and functionality	4	Thermal/surface fatigue	2	3	24	Inspect stethoscope before each use
Binaural Eartube	Translates sound to eartips	Eartube bent	Reduced sound quality and functionality	2	Yielding	2	2	8	Inspect stethoscope before each use
Eartips	Sits in ear canal, translates sounds	Eartips are scratched or deformed	User discomfort	5	Surface fatigue wear	2	3	30	Inspect eartips before each use

Design for Environment (DFE)

Posting design for environment stuff