Engineering 1000 Chapter 4: Solution Formulation and Ergonomics Outline In this chapter, we will look first at general techniques for problem solving We remind ourselves about constraints, and re-interpret some issues as constraints Then we will consider ergonomic design with some logical problems as examples what is ergonomic design how do we tell a good one human dimensions and variability human vision Example case study R. Hornsey Solution 2 Introduction
In later chapters, we will develop techniques for generating multiple solutions to a problem present state (problem) But which options should we follow? desired state (solution) 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 R. Hornsey Solution 3 Designing a Search Strategy Step 1 Eliminate impossible solution paths
Making note of certainties is also a critical part of logical problem solving to paraphrase Sherlock Holmes, if we eliminate all impossible paths, then whatever is left, however improbable, is a potential solution of course, we often dont know enough to be certain we can eliminate a path 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 R. Hornsey Solution 4 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. R. Hornsey Solution 5 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. R. Hornsey Solution 6 Designing a Search Strategy Step 2 Extract the most information possible For example, in logic problem #2 here or kill two birds with one stone see the second coin problem in the textbook (4.2.2) 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 Americans 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 R. Hornsey Solution 7 Designing a Search Strategy Step 3 Evaluate the current state Evaluate the final solution 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 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 R. Hornsey Solution 8 Subdividing the problem From our objectives tree, Kepner-Tregoe analysis etc. we have broken down the design into a number of objectives The goals fell into two broad categories each objective may contain several sub-problems
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 R. Hornsey Solution 9 General Constraints Safety laminated glass for car windows flatter TV screens child-proof caps on medicine bottles stay-attached ring-pulls rechargeable batteries Big Mac clam-shells
Public acceptance Apple Newton and Palm Pilot Orbitz drink Reliability cars electronics Performance everything! Ease of operation user shouldnt be able to do anything catastrophically wrong cd or LP MAC and PC
Environment Durability everything! Minimum maintenance cars again (spark plugs, time between servicing) Standard parts multiple sourcing of components Minimum cost R. Hornsey cell phones well-known properties cost
inkjet printers Solution 10 Working with constraints We have discussed a lot about constraints 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 safety, legal, regulatory, economic, environmental theres 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 R. Hornsey Solution 11 Ergonomics (Human Factors) R. Hornsey Solution 12 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 machines 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 R. Hornsey Solution 13 Is Ergonomic Design Really Necessary? Dont 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? R. Hornsey Solution 14
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 R. Hornsey Solution 15 Anthropometry Anthropometry refers to measurements of the dimensions of the human body
Humans vary in size as a function of: but which body? genetics nutrition age ethnicity occupation So it is tough to achieve a design that ergonomically satisfies all potential users so who do we satisfy? R. Hornsey Solution 16 Seating In class, have your neighbour measure the distance between your elbows when they are at your side How does this compare with the width of a seat on a TTC subway car?
similar to measurement #17 plot a distribution of the results for the class 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%? R. Hornsey Solution 17 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/ R. Hornsey Solution 18 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? R. Hornsey Solution 19 Variability Engineering by Design, G. Voland, Addison Wesley, 1999 R. Hornsey Solution 20 The Human Dimension R. Hornsey Bodyspace: Anthropometry, Ergonomics and the Design of Work, S. Pheasant, Taylor and Francis
20 35 30 8 6 10 5 13 6 73 44 73 1355 845 102 61 35 14 1070 655 41 1160 710 65 1250 765 89 55 32 15 Bodyspace: Anthropometry, Ergonomics and the Design of Work, S. Pheasant, Taylor and Francis Anthropometric estimates for US adults aged 19-65 years (all dimensions in mm, except body weight, given in kg)
Solution 22 Ethnic Variability Bodyspace: Anthropometry, Ergonomics and the Design of Work, S. Pheasant, Taylor and Francis R. Hornsey Solution 23 illumination colour R. Hornsey Computer Vision and Image Processing, S. Umbaugh, Prentice Hall 1998 Vision Solution 24 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 whats also neat is that the brain fills in the space with whatever colour the background has! R. Hornsey Solution 25 http://serendip.brynmawr.edu/bb/blindspot4.html R. Hornsey Solution 26 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 R. Hornsey Solution 27 The eye sees finer detail at higher ambient light levels Computer Vision and Image Processing, S. Umbaugh, Prentice Hall 1998 Resolution of the Eye which is one reason why you see small dust particles in car headlights (~5m) 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 adequate 1 cycle R. Hornsey Solution 28 including adaptation no adaptation Computer Vision and Image Processing, S. Umbaugh, Prentice Hall 1998 Sensitivity of the Eye Engineering by Design, G. Voland, Addison Wesley, 1999 R. Hornsey Solution 29 Temporal Response Being a chemical system, the eye cannot respond to rapid changes of illumination Computer Vision and Image Processing, S. Umbaugh, Prentice Hall 1998
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 R. Hornsey Solution 30 Hearing Hearing is an important consideration Unlike vision, hearing is pervasive both for data transmission and safety 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 Engineering by Design, G. Voland, Addison Wesley, 1999 R. Hornsey Solution 31 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? R. Hornsey
Solution 32 Feedback Theres 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 R. Hornsey Solution 33 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 R. Hornsey Solution 34 Other Interesting Information The Humane Interface by Jeff Raskin www.baddesigns.com lots of examples of what not to do The Joy of Visual Perception, Peter Kaiser discussions of interface design from one of the creators of the MAC
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 R. Hornsey Solution 35 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 R. Hornsey Solution 36 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 R. Hornsey Solution 37 Exercise Beverage Crates Task Prior to Abatement (Description) Task Prior to Abatement (Method Which Verified Hazard) 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)
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) NIOSH recommended weight limit lifting criteria was exceeded for most lifting tasks. Task Prior to Abatement (Method Which Identified Hazard) Workers unload cases of soda cans and bottles from trucks, carting them to and stacking them on a customer's premises. Extended reach is required by delivery workers to unload the trucks. How would you solve these issues, and what benefits would you expect? R. Hornsey Solution 38
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