Engineering 1000 Chapter 4: Solution Formulation and Ergonomics

Engineering 1000Chapter 4: Solution Formulation and Ergonomics

R. Hornsey Solution 2

Outline In this chapter, we will look first at general techniques for

problem solving with some logical problems as examples

We remind ourselves about constraints, and re-interpret some issues as constraints

Then we will consider ergonomic design what is ergonomic design how do we tell a good one human dimensions and variability human vision

Example case study


Introduction In later chapters, we will develop techniques for generating

multiple solutions to a problem

But which options should we follow? to pursue each possibility in depth will be wasteful of resources, so it is

useful to be able to eliminate some of them very quickly All we can do is

know the starting point, know the end point and develop a strategy for getting from one to the other efficiently

present state(problem)

desired state(solution)


Designing a Search Strategy – Step 1 Eliminate impossible solution paths

to paraphrase Sherlock Holmes, “if we eliminate all impossible paths, then whatever is left, however improbable, is a potential solution”

of course, we often don’t know enough to be certain we can eliminate a path

Making note of certainties is also a critical part of logical problem solving

see next two problems plus the coin example in the book (§4.2.1, 4.2.2)

In less artificial problems, these two techniques illustrate the importance of obtaining as much information as possible prior to analysing solutions

research, constraints, reverse engineering, experiments


Logic Problem #1 You are the National Nail Inspector. It is your job to go around

to the nail factories and make sure that the nails being produced are up to standard, that is each nail weighs exactly 10 grams.

You go around to 10 factories and get 10 nails from each factory and take them back to your office.

Unfortunately your electric scales are almost out of batteries but you know that you have enough power left for ONE and only ONE weighing.

You also know that ONE and only ONE of the factories is producing nails that weigh 11 grams.

Given 10 nails from each of 10 different factories and using the scales to get one and only one reading (you cannot increment the scales to get multiple readings), determine which factory is producing nails that weigh 11 grams as opposed to the standard 10 grams.


Logic Problem #2 There are five houses in a row, each of a different colour, and inhabited

by 5 people of different nationalities, with different pets, favourite drinks, and favourite sports. Use the clues below to determine who owns the monkey and who drinks water.

1. The Englishman lives in the red house. 2. The Spaniard owns the dog. 3. Coffee is drunk in the green house. 4. The Russian drinks tea. 5. The green house is immediately to the right of the white house. 6. The hockey player owns hamsters. 7. The football player lives in the yellow house. 8. Milk is drunk in the middle house. 9. The American lives in the first house on the left. 10. The table tennis player lives in the house next to the man with the fox. 11. The football player lives next to the house where the horse is kept. 12. The basketball player drinks orange juice. 13. The Japanese likes baseball. 14. The American lives next to the blue house.


Designing a Search Strategy – Step 2 Extract the most information possible

or “kill two birds with one stone” see the second coin problem in the textbook (§4.2.2)

For example, in logic problem #2 here clue 9 tells us the American is in the leftmost house clue 14 says that the house next to the American is blue from clue 5, we know the American’s house is neither white nor green

Sometimes we will not have enough information to make the next step

this may call for an assumption; assume some information and see where it leads

if you reach an impossibility, revisit the assumption if you reach a solution, revisit the assumption try to limit the number of choices before you assume something; this

can save a lot of work


Designing a Search Strategy – Step 3 Evaluate the current state

again, obtain as much information as is appropriate try to ensure that new data collected is aimed at solving the problem structure data collection efficiently

Evaluate the final solution state which is what a good problem statement should have done already

Make sure that the problem you have solved is the one you set out to solve

when designing VLSI chips, schematic circuit diagrams are simulated extensively to ensure the design is correct

then the circuit is transferred into the design for the actual parts of the silicon chip

because this process may introduce errors and non-idealities, the schematic corresponding to the final silicon design is extracted from the layout and simulated again to check that the performance is similar to the original design


Subdividing the problem From our objectives tree, Kepner-Tregoe analysis etc. we have

broken down the design into a number of objectives each objective may contain several sub-problems

The goals fell into two broad categories specific goals general goals

Specific goals are related to the features of our particular problem

General goals may be present in varying degrees in all situations (see next slide)

Continuous re-evaluation of our goals is important to ensure that we do not stray from the original objectives of the project

it is inevitable that new objectives will appear as work progresses original objectives may be rendered irrelevant as new information

becomes available


General Constraints

Safety laminated glass for car windows flatter TV screens

child-proof caps on medicine bottles

Environment rechargeable batteries Big Mac ‘clam-shells’

stay-attached ring-pulls

Public acceptance Apple Newton and Palm Pilot Orbitz drink

Reliability cars electronics

Performance everything!

Ease of operation user shouldn’t be able to do anything catastrophically wrong

cd or LP MAC and PC

Durability everything!

Minimum maintenance cars again (spark plugs, time between servicing)

Standard parts multiple sourcing of components well-known properties cost

Minimum cost cell phones inkjet printers


Working with constraints We have discussed a lot about constraints

safety, legal, regulatory, economic, environmental We have also talked about items we treated as goals

ladders that are lightweight the optimum volume for beverage containers public transport that is comfortable masks to protect against paint fumes

These are really constraints in disguise since they represent practical limits on the design

there’s little point in a ladder that is too heavy for anyone to carry masks must be of a suitable design to fit the head and face of a wearer a beverage container holds enough volume to be thirst-quenching, but

not so much that a significant amount is un-drunk All these issues depend on the characteristics of the human

user …


Ergonomics (Human Factors)


The Human is Part of the System At some point, every machine system has an interface

with a human Hence the way in which the system is perceived by the

human is (or should be) an integral part of the machine’s design

a display must provide a visual experience that looks as realistic as possible to the viewer, and takes into account the way in which visual information is processed by the eyes and brain

similarly, a hammer must be designed to be wielded by a human seating must be designed to take the human form into account door handles should provide clues about which side of the door

to push or pull automatic office windows in new buildings on York campus

should not remain stuck open on a cold October day We will look at issues particularly related to physical

dimensions and vision


Is Ergonomic Design Really Necessary? “Don’t worry, the user will adapt to it”

the so-called Procrustean approach Procrustes, whose name means "he who stretches", was arguably the

most interesting of Theseus's challenges on the way to becoming a hero. He kept a house by the side of the road where he offered hospitality to passing strangers, who were invited in for a pleasant meal and a night's rest in his very special bed. Procrustes described it as having the unique property that its length exactly matched whomsoever lay down upon it. What Procrustes didn't volunteer was the method by which this "one-size-fits-all" was achieved, namely as soon as the guest lay down Procrustes went to work upon him, stretching him on the rack if he was too short for the bed and chopping off his legs if he was too long. Theseus turned the tables on Procrustes, fatally adjusting him to fit his own bed. (www.mythweb.com)

What other perceived barriers can you think of that might prevent designers from pursuing an ergonomic design?

http://www.mythweb.com/




Ergonomic Design Ergonomic design can be thought of in terms of a ‘principle of

user-centred design’ “If an object or a system or an environment is intended for human use,

then its design should be based on the physical and mental characteristics of its human users”

Is a design ergonomic? Try using it. Think forward to all of the ways and circumstances in

which you might use it. Does it fit your body size or could it be better? Can you see and hear all you need to see and hear? Is it hard to make it go wrong? Is it comfortable to use all the time (or only to start with)? Is it easy and convenient to use (or could it be improved)? Is it easy to learn to use? Are the instructions clear? Is it easy to clean and maintain? Do you feel relaxed after a period of use? If the answer to all of these is 'yes' then the product has probably been thought about with the user in mind.

Bodyspace: Anthropometry, Ergonomics and the Design of Work, S. Pheasant, Taylor and Francis


Anthropometry Anthropometry refers to measurements of the dimensions of

the human body but which body?

Humans vary in size as a function of: genetics nutrition age ethnicity occupation

So it is tough to achieve a design that ergonomically satisfies all potential users

so who do we satisfy?


Seating In class, have your neighbour measure the distance between

your elbows when they are at your side similar to measurement #17 plot a distribution of the results for the class

How does this compare with the width of a seat on a TTC subway car?

width = 430mm leg room = 330mm

What are the competing pressures determining the seat size and leg-room allocated for economy class aircraft passengers?

What fraction of the population should we accommodate? 50%, 90%, 99.99%?


Deep Vein Thrombosis What is deep vein thrombosis?

Deep vein thrombosis (DVT) refers to the formation of a thrombus (blood clot) within a deep vein, commonly in the thigh or calf. The blood clot can either partially or completely block the flow of blood in the vein.

What causes deep vein thrombosis and who is at risk? DVT occurs when the flow of blood is restricted in a vein, and a clot

forms. It can be caused by poor circulation because of problems such as heart disease, a recent heart attack or stroke, varicose veins, or from inactivity or prolonged bed rest. DVT may develop during a long flight and has been dubbed ‘economy class syndrome’ because the cheaper seats in a plane have less leg room, encouraging minimal movement. However, it is not confined to economy class or to long haul flights.

http://hcd2.bupa.co.uk/


Context For the TTC or plane seats, we might decide that designing for

99% of the population is sufficient what about the size of an escape hatch in an elevator?


Variability

Engineering by Design, G. Voland, Addison Wesley, 1999


The Human Dimension



Data for US AdultsAnthropometric estimates for US adults aged 19-65 years (all dimensions in mm, except body weight, given in kg)

Dimension Men Women%ile 5th 50th 95th SD 5th 50th 95th SD1. Stature 1640 1755 1870 71 1520 1625 1730 642. Eye height 1595 1710 1825 70 1420 1525 1630 633. Shoulder height 1330 1440 1550 67 1225 1325 1425 604. Elbow height 1020 1105 1190 53 945 1020 1095 475. Hip height 835 915 995 50 760 835 910 456. Knuckle height 700 765 830 41 670 730 790 377. Fingertip height 595 660 725 39 565 630 695 408. Sitting height 855 915 975 36 800 860 920 369. Sitting eye height 740 800 860 35 690 750 810 3510. Sitting shoulder height 545 600 655 32 510 565 620 3211. Sitting elbow height 195 245 295 31 185 235 285 2912. Thigh thickness 135 160 185 16 125 155 185 1713. Buttock-knee length 550 600 650 31 525 575 625 3114. Buttock-popliteal 445 500 555 33 440 490 540 31length15. Knee height 495 550 605 32 460 505 550 2816. Popliteal height 395 445 495 29 360 405 450 2817. Shoulder breadth(bideltoid)

425 470 515 28 360 400 440 25

18. Shoulder breadth(biacromial)

365 400 435 21 330 360 390 19

19. Hip breadth 310 360 410 30 310 375 440 3920. Chest (bust) depth 220 255 290 22 210 255 300 2821. Abdominal depth 220 275 330 32 210 260 310 3122. Shoulder-elbow length 330 365 400 21 305 335 365 1823. Elbow-fingertip length 445 480 515 21 400 435 470 2024. Upper limb length 730 790 850 36 655 715 775 3525. Shoulder-grip length 615 670 725 33 560 610 660 3026. Head length 180 195 210 8 165 180 195 827. Head breadth 145 155 165 6 135 145 155 628. Hand length 175 191 205 10 160 175 190 1029. Hand breadth 80 90 100 5 65 75 85 530. Foot length 240 265 290 14 220 240 260 1331. Foot breadth 90 100 110 6 80 90 100 632. Span 1670 1810 1950 84 1505 1625 1745 7333. Elbow span 875 955 1035 48 790 860 930 4434. Vertical gripreach(standing)

1950 2080 2210 80 1805 1925 2045 73

35. Vertical grip reach(sitting) 1155 1255 1355 61 1070 1160 1250 5536. Forward grip reach 725 785 845 35 655 710 765 32Body weight 55 78 102 14 41 65 89 15

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illumination

colour


Proof the Blind Spot Exists So how come you never see the blind spot when you look

around? essentially because the brain fills in the gap

Proof that the blind spot exists close your left eye focus on the cross with your right eye you should be aware of the spot, without looking directly at it as you move the page towards you, the spot will disappear at some

point

at the distance where the spot vanishes, you can look to the right and it will reappear

what’s also neat is that the brain fills in the space – with whatever colour the background has!

+ •


http://serendip.brynmawr.edu/bb/blindspot4.html


Colour Vision

Because the cones are concentrated in the fovea, your central vision is less sensitive to low light levels

to see dim stars, it is best to use your peripheral vision

where there are lots of rods

This colour response is the basis for designing the phosphors in TV screens

Computer Vision and Image Processing, S. Umbaugh, Prentice Hall 1998


Resolution of the Eye The eye sees finer detail at

higher ambient light levels which is one reason why

you see small dust particles in car headlights (~5µm)

also important for high performance displays, VR etc.

For TVs (where the brightness and colour information are treated separately) the human resolution is reduced

hence 600 lines is adequate1 cycle

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Sensitivity of the Eye

no adaptation

including adaptation

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Temporal Response Being a chemical system, the

eye cannot respond to rapid changes of illumination

which is why TV and movies look like continuous moving images

movies ~15 pictures/second TV ~ 30 pictures/second computer monitors are scanned

more rapidly (e.g. 75Hz) You can see faster changes at

higher light levels so your can see your LCD watch

flashing in bright sunlight

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Hearing Hearing is an important consideration

both for data transmission and safety Unlike vision, hearing is pervasive

you do not have to ‘hear at’ something the way you would have to ‘look at’ it

which makes it ideal for warning signals etc.

Background noise is, however, a critical issue

and an alert sound must be distinctive



Human Factors Is is now realised that human factors play a vital role in

interface design USAF determined that just doubling the size of a cockpit display

increased the ‘efficiency’ of pilots by 30% example from the textbook: reading 270° into an aircraft inertial

navigation system instead of the correct 027° led to the plane crashing due to lack of fuel, killing 12 people

are analog or digital displays better? Can you combine a calculator and a phone?

the key pads are reversed – which is which?


Feedback “There’s a little black button on the black console that lights

up blackly to show you pushed it” loosely from Hitch Hikers Guide to the Galaxy, Douglas Adams

Feedback is a vital component of the system that informs the user that their action has had some effect

e.g. the beep that tells the supermarket cashier that the item has been scanned

beeps on phone or bank machine buttons it could also be a positive ‘click’ that indicates a mouse button has been

depressed or a power light that indicates that a unit is switched on


Good Design Revisited To develop good user-centred designs, we need to:

determine the necessary interactions between the user and the machine

identify the machine operations that require user input, monitoring or control and ensure these are within human capabilities

ensure that the product performs well in the environment where it will be used

automate where possible and desirable in order to minimise the interaction needed


Other Interesting Information The Humane Interface by Jeff Raskin

discussions of interface design from one of the creators of the MAC www.baddesigns.com

lots of examples of what not to do The Joy of Visual Perception, Peter Kaiser

www.yorku.ca/eye good optical illusions and a background to human vision

www.apple.com/about/ergonomics/ common ergonomic issues related to computer use

http://www.baddesigns.com/

http://www.yorku.ca/eye



http://www.apple.com/about/ergonomics/


Summary We have seen how general problem-solving strategies can be

developed to select between multiple solutions to a problem eliminate impossible paths make the most of your data review both the problem statement and the present situation

Be prepared to revise your goals The importance of constraints The human being as a constrain – ergonomics


Homework Read and understand chapter 4 of the text Follow the case studies in Ch.4

especially the illustrative examples of general constraints Do problems 4.4, 4.5, 4.6


Exercise – Beverage Crates

Task Prior to Abatement (Description) Workers unload cases of soda cans and bottles from trucks, carting them to and

stacking them on a customer's premises. Task Prior to Abatement (Method Which Verified Hazard)

NIOSH recommended weight limit lifting criteria was exceeded for most lifting tasks.

Task Prior to Abatement (Method Which Identified Hazard) An injury and illness rate of 18.5 per 100 full-time workers put the industry among

the top 12 for injury frequency and top 5 for severity according to NIOSH studies. Ergonomic Risk Factor (Force)

An average lift of 34,000 pounds each day was performed by each worker. Lifting of up to 45,000 pounds a day might have been required for some workers

because of case content inequities. Ergonomic Risk Factor (Posture)

Extended reach is required by delivery workers to unload the trucks. How would you solve these issues, and what benefits would you

expect?

Engineering 1000 Chapter 4: Solution Formulation and Ergonomics

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