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INDUSTRIAL ERGONOMICS. DR. SITI ZAWIAH MD. DAWAL DEPT. OF ENGINEERING DESIGN AND MANUFACTURE UNIVERSITY OF MALAYA. Anthropometry. Measurement of the human body
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INDUSTRIAL ERGONOMICS DR. SITI ZAWIAH MD. DAWAL DEPT. OF ENGINEERING DESIGN AND MANUFACTURE UNIVERSITY OF MALAYA
Anthropometry • Measurement of the human body • Anthropometric information describes the dimensions of the human body, usually through the use of bony landmarks to which height, breadths, depths, distances, circumferences and curvatures are measured.
Selection Vs Modification • Assume a heavy box is to be moved from point A to point B. • Realizing that people are vary, there are probably two basic strategy, - One alternative is to use selection, that is, from the population of workers select a strong persons. - This can be label as fit the person to the job
Another alternative is job modification – that is almost everyone can do it. • This can be labeled as fit the job to the person or fitting the job to you. • Given the decision to modify the job, one question is “ how much modification is necessary?”
Anthropometry and its used • Body size and proportion vary greatly between different population and racial groups-a fact which designers must never lose sight of when designing for an international market. • The importance of anthropometric considerations in design as follows: • If a piece of equipment was designed to fit 90% of the male U.S. population, it would fit roughly 90% of Germans, 80% of Frenchmen, 65% of Italians, 45% of Japanese, 25% of Thais and 10% of Vietnamese.
It is usually impracticable and expensive to design products individually to suit the requirements of every user. • Mass-produced and designed to fit a wide range of users-the custom tailor, dressmaker, and cobbler are perhaps the only remaining examples of truly user-oriented designers in western industrial societies.
Availability of Anthropometric Data • Anthropometry of military populations is usually well documented and is used in the design of everything from cockpits to ranges and sizes of boots and clothing. • Data are available for U.S., British, and other European groups, as well as Japanese citizens.
Pheasant (1986) provides a useful and well illustrated collection of anthropometric data and a method of estimating unknown anthropometric dimensions from data on stature. Problems with much of the anthropometric data from the United States and Europe are the age of the data and the lack of standardization across surveys.
Structural Anthropometric Data • Measurements of bodily dimensions of subject in fixed (static) position. • Measurements made from one clearly identifiable anatomical landmark to another or to a fixed point in space.
2. Functional Anthropometric Data • Data that describes the movement of a body part with respect to a fixed reference point. • Area swept out by movement of hand – “workspace envelopes”
Functional anthropometric data The figure shows the shapes of the reach envelopes and the allowable (a) and preferred (p) zones for the placement of controls in a workspace
Fewer functional than structural anthropometric data are available even though functional measures are more representative of actual human activity. • Existing functional anthropometric data are useful for designing workspace and positioning object within them.
Principles in the Application of Anthropometric Data • Design for Extreme Individuals In some circumstances a specific design dimension or feature is a limiting factor that might restrict the use of the facility for some people. That limiting factor can be dictate either a maximum or minimum value of the population variable or characteristics.
Designing for Adjustable Range Certain features of equipment or facilities can be designed so they can be adjusted to the individuals who use them, e.g. automobile seat, office chair, desk height etc. This method of design is a preferred method, of course it is not always possible.
Designing for Average There is no average individual. A person may be average on one or two body dimensions but it is impossible to find anyone who is average in many dimensions. Often designers design for the average as a cop-out to avoid complexity of anthropometric data.
Designing to Fit the Body • Results of anthropometrics surveys are described in statistical terms, • Most body data appear in normal distribution: • Mean, • Standard deviation, • Range.
Why Percentiles Important ? • To establish the portion of a user population that will be included in (or excluded) from a specific design solution, • Percentiles are easily used to select subjects for fit tests, example 5th or 60th percentile values in the critical dimensions can be employed for use test, • Any body dimension, design issue or score of a subject can be exactly located, • Helps in selection of persons to use a given product. Example select cockpit crews whose body measures are 5 – 95th percentile
The normal distribution Ninety percent of the measurements made on different people will fall in a range whose width is 1.64 standard deviations above and below the mean.
To Determine a Single Percentile Point • Select desired percentile value, • Determine the associated k value, • Calculate p value from:
Percentiles Two ways to determine percentile values: • To take distribution of data and determine from the graph critical percentile values, • Calculate percentile value by multiplying standard deviation SD by a factor k then add the product to the mean m:
Missing Data Ration scaling • Estimating data from known dimensions assumption – Though people vary greatly in size. They are likely to be similar in proportions. • Use only pairings of data that are related to each other with a coefficient of correlation of least 0.7 (0.72 = 0.49 ~ 50% variability of derived info determined by at least 50% variability of predictor), • If value of dimension in sample x (dx) and values of a reference dimension D in both sample x and y (Dx and Dy)
Scaling factor E Example: If shoulder height is to be estimated for sample y and is known in sample x then: • Shoulder height in y = E stature in y
Questions 1 • Calculate the surface height of a keyboard so that the sitting operator has the forearms and wrists horizontal.
Solution • Assumption: that having tops of the keyboard at sitting elbow height will allow the operator to keep the wrists straight, forearm horizontal and upper arms effortless hanging down. • Select the percentile Adjusting keyboard height for the 10th (5th) percentile female elbow clearance to 90th (95th) percentile male clearance will be appropriate.
Solution • Listed (example of American Anthropometry: elbow height above seat pan female – 220.5.mm SD-26.8, male – 230.6mm SD -27.2mm) • Use the multiplication factor to calculate for 10th (5th) and 90th (95th) given in the table below. (10th and 90th = 1.28 and 5th and 95th = 1.65)
Solution • (for 10th and 90th ) • 10 p the values are 186 mm female and 196 mm male. • 90p the values are 265mm for male and 255 mm female. • Therefore the height of the keyboard should be adjustable from 186mm to 265mm. Thus, the adjustable range is 79mm under given assumptions.
Question 2 • Calculate the surface height of a keyboard so that the sitting operator has the forearms and wrists horizontal. *Select the percentile for the 20th percentile female elbow clearance to 80th percentile male clearance.
Some product dimensions which are determined using anthropometric considerations
Common Anatomical and Anthropometric Landmarks(Webb Associates, 1978)
Example • Design a computer workstation to be used by a clerk in an office work environment. • Three essential phases should be emphasis for the solution: - identification of the target population - proposition of criteria - application of the method of limits
What is your target population? • Most clerks are female (although may change in the future) • Depends on organization Government - tend to be older Private - tend to be younger • Therefore, should base your design on the female data (Malaysian industrial workers)
Criteria? • Chair • Computer table
Where do we start? • Computer table ? • Adequate clearance must be provided beneath the desk: 1) knee height above the floor or 2) thigh thickness above the height of the seat
Table Heights • The undersides of tables should provide clearance of the thighs and knees. • The correct height for the table surface depends upon the task to be performed upon it.
Table Height • Determine what Percentile to use • Find the thigh thickness above the height of the seat + popliteal height • Adding the shoes dimension (45 mm) • The optimum height for a seat is said to be 25mm to 50mm below popliteal height • So the clearance required for the ??percentile female /male is Reference: Pheasant (1984)
STEPS IN DESIGN FOR FITTING CLOTHING, TOOLS, WORKSTATIONS, AND EQUIPMENT TO THE BODY(Kraemer, Kraemer, Kraemer-Elbert 1994) • Step 1: Select those anthropometric measures that directly relate to defined design dimensions. Examples are: hand length related to handle size; shoulder and hip breadth related to escape-hatch diameter; head length and breadth related to helmet size; eye height related to the heights of windows and displays; knee height and hip breadth related to the leg room in a console. • Step 2: For each of these pairings, determine whether the design must fit only one given percentile (minimal or maximal) of the body dimension. or a range along that body dimension. Examples are: the escape hatch must be big enough to accommodate the largest extreme value of shoulder breadth and hip breadth. considering clothing and equipment worn; the handle size of pliers is probably selected to fit a smallish hand; the leg room of a console must accommodate the tallest knee heights; the height of a seat should be adjustable to fit persons with short and with long lower legs.
Step 3: Combine all selected design values in a careful drawing, mock-up, or computer model to ascertain that they are compatible. For example, the required leg-room clearance height needed for sitting persons with long lower legs may be very close to the height of the working surface determined from elbow height. • Step 4: Determine whether one design will fit all users. If not, several sizes or adjustment must be provided to fit all users. Examples are one extra-large bed size fits all sleepers; gloves and shoes must come in different sizes; seat heights are adjustable.
Table 9.3 Guidelines for the Conversion of Standard Measuring Postures to Real Work Conditions Adapted from Kroemer. Kroemer. and Kroemer-EIben (1997).
DESIGNING FOR MOTION IS DONE IN THESE STEPS: • Step 1: Select the major body joints involved. • Step 2: Adjust body dimensions reported for standardized postures (e.g., Tables 9.4 through 9.9) to accommodate the real work conditions. Use Table 9.3 for guidance. • Step 3: Select appropriate motion ranges in the body joints. The range can be depicted as the area between two positions, such as knee angles ranging between 60 and 105 degrees; or as a motion envelope, such as circumscribed by combined hand-and-arm movements, or by the clearance envelope under (through, within, beyond) which body parts must fit. Use Table 9.12 for guidance.
Basic work space design faults should be avoided. These include: • 1. Avoid twisted body positions, especially of the trunk and neck. This results often from bad location of work objects, controls, and displays. • 2. Avoid forward bending of trunk, neck, and head. This is frequently provoked by improperly positioned controls and visual targets including working surfaces that are too low. • 3. Avoid postures that must be maintained for long periods of time, especially at the extreme limits of the range of motion. This is particularly important for the wrist and the back. • 4. Avoid holding the arms raised. This results commonly from locating controls or objects too high, higher than the elbow when the upper arm hangs down. The upper limit for regular manipulation tasks is about chest height.
