DESIGN TRADE.docx

DESIGN TRADE-OFFS

Design Trade-offs

Starting up the design trade-offs, the designers consider the functionality that can satisfy the economic, functionality, and sustainability.

Based on the constraints articulated previously, the various decision criteria were derived. Using the model on trade-off strategies in engineering design presented by Otto and Antonsson (1991), the importance of each criterion (on a scale of 0 to 5, 5 with the highest importance was assigned and each design technology's ability to satisfy the criterion (on a scale from -5 to 5, 5 with the highest ability to satisfy the criterion) was likewise tabulated.

Below is the computation of ranking for ability to satisfy criterion of materials:


%difference= (Higher Value-Lower Value)Higher ValueEquation 4.1

Subordinate Rank=Governing Rank-%Difference x 10 Equation 4.2

The governing rank was the subjective option of the designers where in the value for the criterion's importance and its ability to satisfy the criterion would be chosen by the designers. Unlike subordinate ranking, governing rank does not require any calculating.

Three AutoCAD designs have been considered for the trade-offs to be used. The three schematic designs have a different capabilities of being the most acceptable and most efficient motion-based earthquake device alarm. Design 1 used Load cell, Design 2 used torque sensor and Design 3 used touch sensor. In order to find the best component, it was rated using the designers' criterion.Each design has been discussed previously.

After considering the design constraints, the designers came up with the initial rankings on the Motion-Based Earthquake Alarm Device. Table 4-1 shows designers raw ranking based on economic, environmental, and cost constraints.

Table 4-1 Designer Tabulation Form

Decision Criteria
Criterion's Importance
(On scale of 0 to 5)
Able to satisfy the criterion
(On scale from -5 to 5)


Design 1
(Iron Ball)
Design 2
(Swinging Ball)
Design 3
(Copper Plate)
Economics (Cost)

3
5
2
Functionality(Sensitivity)
3
5
3
4
Sustainability (Life Span)
4
4
5
3
Overall Rank
51
39
49
Reference: (Otto, 1991)
http://www.design.caltech.edu/Research/Publications/90e.pdf on March 11, 2013.

In determining the trade-offs for the designs, the designers assigned respective importance values for each criterion shown in Table 4-1. The economic constraints or the cost of the device was given importance by ranking it into the highest value, which were given a five since the device must be low-cost and was available to manufacture with less expenses. The designers had also taken into consideration the importance of functionality or the sensitivity of the device and it were considered to be second on the highest value. Sustainability or the life span of the materials used and it were considered to be the third on the highest value since the materials has its own capability to stay longer.

TRADE-OFF #1: Economical

Initial Cost Estimate for Design of Motion-Based Earthquake Alarm Device

Table 4-2 shows the over-all cost of the Design 1, 2 and 3. The ranking, stated in the tradeoff table would be based on the formula that is computed. The total cost for each specific component to be used was tabulated previously.

Table 4-2 Initial Cost of each component

Design Category
Total
Design 1
PHP8,250.00
Design 2
PHP 9,503.00
Design 3
PHP 2,710.00

Table 4-2 represents the price of the device in the industry and its quantities when manufactured. The equations mentioned above were considered to calculate for the values of the ability to satisfy the criterion.
Computation for Trade-Offs #1:

To compute the value of the ability to satisfy the criterion the designers need to determine the value of the subordinate rank. As for the Design 1 (USING IRON BALL):

%difference=Using Iron Ball-Using Copper Plate(Using Iron Ball)

To get the percent difference, subtract the value of the second design that consists of String to the value of the first design that consists of Iron Ball and divide it into the value of String.

%difference=8250-27108250

%difference=0.672

Subordinate Rank=Governing Rank-%difference x 10

Subordinate Rank=5-0.672x 10

Subordinate Rank=-1.72




Figure 4.1 Subordinate ranking of Iron Ball in economic cost

Figure 4.1 represents the subordinate ranking of the device, Iron Ball, to satisfy the criterion from Table 4-1. The value calculated signifies the importance of a device in a design project. As the Figure shows, Iron Ball has the significance of 3.68 which means that it was one of the main components of the device.

The value calculated from the subordinate rank would be tailing in the Table 4-1. To calculate the value of the criterion of Design 3 (Copper Plate), use equations 2.1 and 2.2:

%difference=Using String-Using Copper PlateUsing String

%difference=9,503-27109,503

%difference=0.715

Subordinate Rank=Governing Rank-%difference x 10

Subordinate Rank=5-0.715x 10

Subordinate Rank=-2.15



Figure 4.2 Subordinate ranking of Copper Plate in economic cost

Figure 4.2 represents the similarity to the Load cell, Torque sensor criterion was tailed under Table 3-2. This shows that Load cell has a higher criterion that it acquires during the calculations. This was due to the affordability of the device in the market. Considering the value of the Figure 4-1, it shows that in Figure 4-2, load cell has a higher importance than torque sensor having a value of 3.4 for the economic cost criterion.

TRADE-OFF #2: Manufacturability

Table 4-3 shows the estimated number of days in order to acquire the sensors used for the three designs. The table is used as the basis of the ranking on Trade-offs in accordance with the computations.

Table 4-3 Availability of the Materials

Design
Sensors
Days(s) to Acquire
Design 1
Load cell
1
Design 2
Torque sensor
7
Design 3
Touch sensor
5

As stated on the previous chapter, manufacturability was one of the most important design constraints because some of the components may not be available within the country and thus needed to be bought outside of the country. The estimated days to acquire the desired component are 1 day since the component is available within the country.


Computation for Trade-Offs #2:

Touch sensor has similarities to Torque sensor when it comes to the availability of the materials. Though the touch sensor can also be found outside the country, torque sensor is indeed hard to find compared to touch sensor.Using the equations 4.1 and 4.2, the value of manufacturability criterion can be calculated.

%difference=Torque sensor availability-Load cell availabilityTorque sensor availability

%difference=7-17

%difference=0.86

Subordinate Rank=Governing Rank- %difference x 10

Subordinate Rank=3- 0.86 x 10

Subordinate Rank=-5.6 -5











Figure 4.3 Subordinate ranking of Load cell sensor in manufacturability

Figure 4.3 shows the computed value acquired for the manufacturability of the Load cell sensor considering the time it takes to assemble the device on the prototype. From the calculated value, -1.30 represents the ratio of availability of the material to be used to complete the prototype.

Using the same equations, the value of the Touch Sensor can be calculated as follows:

%difference=Touch sensor availability-Load cell availabilityTouch sensor availability

%difference=5-15

%difference=0.8

Subordinate Rank=Governing Rank- %difference x 10

Subordinate Rank=3- 0.8 x 10

Subordinate Rank=-5












Figure 4.4 Subordinate ranking of Touch sensor in manufacturability

Using the same equation used to compute the value of manufacturability on load cell, Figure 4-4 represents the computed value for the touch sensor. Considering the value of 5, it represents the ratio of the availability of the device in the market.

TRADE-OFF #3: Sustainability

Table 4-4 shows the life span or sustainability of each component depending on their quality. The designers considered another method of computing the sustainability criterion. The criteria were ranked from 1 to 3 wherein 3 is the highest which means it was the best. 2 mean better and 1 means good. The ranking was based upon the sustainability of the materials that is being used on the design prototype. The basis of these criteria was taken based on the components accuracy, sensitivity, stability, time it would response, linearity and their life span.

Table 4-4 Sustainability of components

Criteria
Design 1 (Load Cell)
Design 2 (Torque Sensor)
Design 3 (Touch Sensor)
Accuracy
3
1
2
Sensitivity
2
1
3
Stability
3
2
1
Life Span
2
3
1
Fast Response Time
3
1
2
Linearity
2
3
1
Total
15
11
10

The designers chose the Load cell design to obtain the highest rank due to its availability and sustainability to be used in the prototype. To calculate the values of the ability to satisfy the sustainability criterion, it was required to determine the value of the subordinate rank.

Computation for Trade-Offs #3:

By using the same equations from before equations 2.1 and 2.2, the designers were able to compute the value needed for the said criterion.


%difference=Higher value-Lower valuehigher value

%difference=15-1015

%difference=0.33

Subordinate Rank=Governing Rank-%differencex 10

Subordinate Rank=4-0.33x 10

Subordinate Rank=0.70 0











Figure 4.5 Subordinate ranking of Load cell based on sustainability

Figure 4.5 shows the acquired values for the subordinate rank for load cell depending on the designers chosen device to work on the prototype. The calculated value of 0.70 represents the sustainability of the device according to the designers.

The same equations would be used to compute the said criterion for Touch sensor.

%difference=Higher value-Lower valuehigher value
%difference=15-1015
%difference=0.33

Subordinate Rank=Governing Rank-%differencex 10

Subordinate Rank=4-0.26x 10

Subordinate Rank=1.4 1












Figure 4.6 Subordinate ranking of Touch sensor based on sustainability

The calculation in Figure 4.6 shows that the load cell design takes advantage in terms of its sustainability. It has the quality that was needed for the prototype to be completed among other designs presents. The calculated value of 1.4 shows the sustainability of the touch sensor according to the desired of the designer.

Summary of Trade-Offs:

Based on the constraints articulated previously, the various decision criteria were derived. Using the model on trade-off strategies in engineering design presented by Otto and Antonsson (1991), the importance of each criterion (on a scale of 0 to 5, 5 with the highest importance was assigned and each design technology's ability to satisfy the criterion (on a scale from -5 to 5, 5 with the highest ability to satisfy the criterion) was likewise tabulated. Table 5-5 shows the tabulation of the criterion for the design project.

Table 4-5 Tabulation of Trade-offs

Decision Criteria
Criterion's Importance
(On scale of 0 to 5)
Able to satisfy the criterion
(On scale from -5 to 5)


Design 1
(Load Cell)
Design 2
(Torque Sensor)
Design 3
(Touch Sensor)
Economics (Cost)
5
4
2
5
Functionability
(Sensitivity)
3
5
3
4
Sustainability (Life Span)
4
4
5
3
Overall Rank
51
39
49

The designers ranking section depends on the importance of the constraints. The economic criterion was set to five (5) because the client wants it to be affordable. The sustainability was ranked as the second highest with the rank of four (4) because the client wants it to have a long life at the same time, the functionality of the sensors used is accurate, last was the manufacturability criterion which rank as three (3) because the designers wanted all the components to be available in the country and it also considers the time to process the prototype.

The Table 4-5 shows the values taken from the computation that the designers came up with in order to find the satisfying value for the trade-offs of each component. The one with the highest value would be chosen for the design. As seen in the Table 4-5, Design 1 using load cell has the highest overall value among the other two components based on the computations considering the cost, availability and its sustainability that was suited for the design.

The designers based the cost of each component depending on the prices of the sensors in the market. The Design 3 (touch sensor) obtained the highest value since it has the lowest price among others; it was then followed by Design 1 (load cell) and Design 2 (torque sensor). As for the sustainability of each sensor, Design 2 (torque sensor) obtained the highest value due to its sustainability while the rest of the sensor does not, however, even though Design 2 has the highest value of sustainability the designer still choose Design 1 due to other reasons such as availability. The designers also need to consider the time and availability of each sensor and based on the manufacturability criterion, Design 1 using Load Cell has obtained the highest value since the device was available within the country. And since Load Cell has second to the lowest value when it comes to cost, the designers preferred to use it due to how it fitted for the design.

Influence of Design Trade Offs in the Final Design

The constraints, trade-offs and standards contributed in the production of this design. In accordance with the multiple constraints that the designers stated, choosing the right component depends on the affordability of the materials; the numbers of years that the component may be used without being replaced; and the availability of the materials in order for the production of the design to meet the deadline. These constraints became the criteria for the tradeoff table where the comparisons for each sensor to be used were expressed.

The standards stated in the previous chapter have been considered when measurement for each specific component and process were taken. The standards stated previously become one of the contributing factors towards the success of the design.

Design Criterion 1: Economic (Cost)

The costs of each component have been taken into consideration in the development of the design. The designers anticipated the over-all cost based on the price of each component. The tradeoffs of the sensors were conducted through calculations to determine the right component to be used. As calculated from the previous chapter, Table 4-2 shows that touch sensor has the highest scale due to its low cost, however, even though the touch sensor has the lowest cost, load cell was still chosen for the completion of the prototype since it's available in the country.


Design Criterion 2: Manufacturability (Availability of Materials)

The availability of the material has been taken into consideration for the success of the design therefore the chosen component must be available to meet the deadline of the production. Table 4-3 shows the different availability of each component used for trade-offs. The use of load cell has the highest scale due to its availability within the country.

As calculated in the previous chapter, the load cell is more advisable to use compared to torque sensor and touch sensor. The designers have chosen load cell knowing that the cost is affordable, sustainable for the design project and since the device was available in the country. The standards have been the basis that needs to be considered upon the use of each specific component and process taken by the designers.

Design Criterion 3: Sustainability (Life Span)

The life span of the component was also taken into consideration to make the prototype last a long time. Table 4-4 shows the life span of each component. The component with the highest value was Design 2 which consists of Torque sensor and this was due to the fact that Torque sensor was more expensive and therefore has the quality to last longer than the rest. However, the chosen component to complete the prototype was Design 1 which consists of Load cell because of how affordable it was compared to torque sensor and due to its availability in the market. Also Design 1 (Load cell) was ranked second for lasting longer unlike touch sensor.