Introduction to Work Study and Ergonomics Analysis of the basic hand, arm, and body movements ofworkers as they perform work is called Motion Study. Frank Gilbreth – first to analyze and classify the basicmotion elements “Therblig”s – 17 basic motion elements

Spelled backward except for “th” Basic building blocks of virtually all manual work performed at asingle location (so the primary interest is the hand motions)

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The 17 Therbligs1. Transport empty (TE) – reach for an object with empty hand – today

we call it “reach”2. Grasp (G) – grasp an object by contacting and closing the fingers

until control has been achived3. Transport loaded (TL) – move an object with hand and arm – today

we call it “move”4. Hold (H) – hold an object with one hand5. Release load (RL) – release control of an object6. Use (U) – manipulate/use a tool7. Pre-position (PP) – position object for next operation8. Position (P) – position object in defined location9) Assemble (A) – join two parts10) Disassemble (DA) – seperate multiple parts that were previously

joined

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The 17 Therbligs (continued)11) Search (Sh) – attempt to find an object using eyes or hand12) Select (St) – choose among several objects in a group (hand-eye

coordination is involved)13) Plan (Pn) – decide on an action (a short pause or hesitation in the

motions)14) Inspect (I) – determine quality of object using the eyes15) Unavoidable delay (UD) – waiting due to factors beyond worker

control16. Avoidable delay (AD) – worker waiting17. Rest (R) – resting to overcome fatigue

Work Systems and the Methods, Measurement, and Management of Workby Mikell P. Groover, ISBN 0-13-140650-7.

©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Therbligs

Work Systems and the Methods, Measurement, and Management of Workby Mikell P. Groover, ISBN 0-13-140650-7.

©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Therbligs

Work Systems and the Methods, Measurement, and Management of Workby Mikell P. Groover, ISBN 0-13-140650-7.

©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Therbligs

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Example

Classification of TherbligsEffective therbligs:Physical Basic Motion Elements: Transport empty Grasp Transport loaded Release load Use Assemble DisassembleMental Basic Elements: InspectDelay Elements: Rest

Ineffective therbligs:Physical Basic Motion Elements: Hold Pre-positionPhysical and Mental Basic MotionElements: Position Search SelectMental Basic Elements: PlanDelay elements: Unavoidable delay Avoidable delay

Method study at the therblig level seeks to eliminate or reduce ineffective therbligs.

Time Study All the ways in which time is analyzed in work situations.Time is important, because; Most workers are paid for their time on the job The labor content (cost of labor time) is often a major

factor in the total cost of a product or service For any organization, it is important to know how much

time will be required to accomplish a given amount of work

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When Are Time Standards Beneficial? Characteristics of industrial situations in which time

standards would be beneficial:

Low productivity Repeat orders Long production runs Repetitive work cycles Short cycle times

Functions of Time Standards They define a “fair day’s work” They provide a means to convert workload into staffing and equipment needs They allow alternative methods to be compared objectively They provide a basis for wage incentives and evaluation of worker performance They provide time data for:

Production planning and scheduling Cost estimating Material requirements planning

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Average WorkerA worker who is representative of the persons who usually

perform tasks similar to the task being measured If the work is performed mostly by men, then the average

worker is male If the work is performed mostly by women, then the

average worker is female

Standard PerformanceA pace of working that can be maintained by an average

worker throughout an entire work shift without harmful effects on the worker’s health or physical well-being

The work shift includes periodic rest breaks and occasional interruptions are experienced by the worker

Benchmarks of standard performance(EX: Walking at 3 miles/hr on level flat ground Dealing four hands of cards from a 52 card deck in

exactly 30 sec)

Distribution of Worker PerformanceWorker performance is expressed in terms of daily output

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How a Standard Time is DefinedDistribution of worker performance, indicating how standard time is defined so that it can be readily achieved by most workers

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Allowances in Time Standards Normal time is adjusted by an allowance factor Apfd to

obtain the standard time Purpose of allowance factor is to compensate for lost

time due to work interruptions and other reasons Standard time:

Tstd = Tn(1 + Apfd)where pfd = Personal time, Fatigue, and Delays

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Rest Periods Common in industry

Paid for by the employer as regular work time Rest breaks usually included in allowance factor built

into the time standard Relatively short duration - 5 to 20 minutes Meal periods - not included

ErgonomicsErgonomics can be defined as the application of knowledge of human characteristics to the design of systems.

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Human Variability Differences in body dimensions exist among people

because of: Ethnicity and Nationality Heredity Diet Health Sex Age Living conditions

Static Dimensions of Human Body

Standing

Seated

Anthropometric Design Principles Design for extreme individuals Design for adjustability Design for the average user Design different sizes for different size users

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Design for Extreme Individuals Designing for the maximum

Doorway heights Automobile door openings Mattress sizes

Designing for the minimum Heights of kitchen cabinets Locations of levers and dials on equipment Weights of portable power tools

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Design for Adjustability To accommodate a wide range of users Examples:

Automobile driver seats Adjustable steering wheel in an automobile Office chairs Worktable heights Tilt angles of computer monitors Lawnmower handle heights Bicycle handlebars

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Adjustable Chair for Workplace

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Design for Average User For situations in which design for extreme individuals

and adjustability are not feasible Examples:

Stair heights Stadium seats Sofas Heights of checkout counters at supermarkets Lengths of shovel handles

Work Systems and the Methods, Measurement, and Management of Work.

Workplace Arrangement Normal and maximum working areas in the workplace

Design for average

user

Different Sizes for Different Size Users When the only way to accommodate user

population is to make the product in different sizes

Examples: Clothing Shoes Elementary school desks and chairs

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The Physical Work Environment1. The Visual Environment and Lighting2. The Auditory Environment and Noise3. Climate Control in the Work

Environment

Visual Environment and Lighting About 80% of the information input to the human

brain comes from visual stimuliRelative possibility of being seen under prevailing conditions of light, distance, and related factors Most important factor = level of illumination Other factors:

Visual angle - angle subtended at the eye by the smallest distinguishable detailv = 3438 h/dwhere v is measured in arc minutes

Brightness contrast - relative luminance between object and background Color

Lighting Systems Lamp - a single artificial source of light (e.g., an

incandescent lamp, fluorescent lamp) Luminaire - complete lighting unit, including

One or more lamps Reflectors and other apparatus to distribute the

light Means to connect to power supply

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Auditory Environment and Noise The second most important means by which humans

receive information Visual and auditory stimuli account for 95% or more of a

person's information input The auditory environment also includes:

Noise - defined as unwanted sound

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Effects of Noise on Humans Distraction Negative emotions such as annoyance,

frustration, anger, and fear Interference with conversation, thinking, and

other cognitive processes Interference with sleeping Temporary hearing loss Permanent hearing loss

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Climate Control Four primary variables that define climate:

1. Air temperature2. Humidity - usually relative humidity3. Air movement4. Radiation from surrounding objects, including the sun

Most comfortable working environment (called the comfort zone) Air temperature = 19 to 26C (66 to 79F) Relative humidity = 50% Slow air movement = 0.2 m/s (0.64 ft/sec)

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Heat Stress Occurs when body absorbs more heat than it gives off, raising the body core temperature Illnesses resulting from heat stress:

1. Heat rash - areas of skin erupt into red or white bumps due to inflammation of sweat glands2. Heat cramps - spasms of muscles in physical labor3. Heat exhaustion - muscle weakness, nausea, dizziness4. Heatstroke - fever, dry skin, convulsions, coma (in extreme cases: death)

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Cold Stress Drop in core body temperature below normal due to net

heat loss from combination of low temperature and air movement

Windchill factor - estimates cooling effect of moving air on exposed skin

Jobs where cold stress is a problem: Refrigerated warehouses Construction jobs in wintertime Aboard ships in extreme northern climates Research in Antarctica