1. Workplace, equipment, and tool design
Designing the workplace, tools, equipment, and work environment to fit the human operator is called ergonomics
Design the workplace, equipment and tools to increase production and efficiency of the operation and to decrease injury rates for the human operator
We will present some principles and appropriate checklists to facilitate the use of the design principles
Workplace, Equipment, and Tool Design

2. Content Anthropometry and design Principles of workplace design
Principles of machines and equipment design
Principles of tool design
Cumulative trauma disorders
Workplace, Equipment, and Tool Design

3. Anthropometry and design
Workplace, Equipment, and Tool Design

4. Anthropometry
The primary guideline is to design the workplace to accommodate most individuals with regard to structural size of the human body
Anthropometry is the science of measuring the human body (weight, length,..)
Anthropometric Source Book (Webb Associates, 1978): Close to different body dimensions for 100 different population types
CAESAR (Civilian American and European Surface Anthropometry Resource) project collected over 100 dimensions in 5000 civilians using three–dimensional body scans
Computerized human models: COMBIMAN, Jack, MannequinPro, Safeworks provide easy size adjustments, limitations and visibility as part of the computer aided design process
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

5. Probability distributions and percentiles
A kth percentile is the value such that k% of the data is below this value and 100‐k% of the data values are above this value
To form a standard normal distribution, approximate by z = (x‐µ)/σ with µ the mean value and σ the standard
deviation
50%
50th percentile = µ 5%
95%
Half of the males are shorter than 68.3 in (1.73 m) while other half are taller
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

6. Probability distributions and percentiles
For normal distribution
kth percentile = µ ± zσ
z values from Table on page 700:
kth percentile
10 or 90
5 or 95
z value
± 1.28
± 1.645
Mean value of male height, µ = in, Stand. Deviation, σ = 2.71 in
50%
95th percentile male height = x (2.71) = in (≈185 cm) 5%
95%
5th percentile male height = 68.3 ‐
1.645 x (2.71) = in (≈162 cm)
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

7. Anthropometry Selected body dimensions
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Workplace, Equipment, and Tool Design

8. Anthropometry END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

9. Anthropometry and design
Design for extremes
Design for adjustability
Design for the average
Practical considerations
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

10. Anthropometry and design
1. Design for extremes
A specific design feature is a limiting factor in determining either the maximum or minimum value of a population variable that will be accommodated
Doorway or an entry opening into a storage tank should be designed for the maximum individual: 95th percentile
male stature or shoulder width
However, this is not true in military aircraft or submarines since space is expensive!
Reaches to a brake pedal or control knob are designed for the minimum individual: 5th percentile female leg or arm length – 95% of all females and practically all males will have longer reach
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

11. Anthropometry and design
2. Design for adjustability
Typically used for equipment or facilities that can be adjusted to a wider range of individuals
Chairs, tables, desks, vehicle seats, steering columns are typically adjustable to accommodate the population ranging from 5th percentile females to 95th percentile males
It is the preferred method of design but there is a trade‐off with the cost of implementation
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

12. Anthropometry and design
3. Design for the average
Cheapest but least preferred approach
Adjustability can be impractical and too costly in
certain situations
Most industrial machines and tools are too large and too heavy to include height adjustability for the operator
If those machines are designed for 50% of the population, tall male or very short females may experience discomfort
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

13. Anthropometry and design
4. Practical considerations
Industrial designer should consider the legal rules or advices
Americans with Disabilities Act (1990): accommodate individuals with all abilities
Special accessibility guidelines (US Department of Justice, 1991): entryways into buildings, assembly area, ramps, elevators, doors, water fountains, lavatories, restaurants, alarms, telephones, etc.
Very useful to build a full‐scale mock‐up and ask the
end‐users to evaluate it before a mass production
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

14. Steps of a typical design problem
Determine the body dimensions critical for the design
Define the population being served: adult, child, male, female, etc.
Select a design principle and the percentage of the population to be accommodated
Find the appropriate anthropometric values from the given Table 5.1
Add allowances (shoes, hats, relaxed postures, etc.) and test
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

15. Designing seating in a large training room
Determine the body dimensions critical for the design: Sitting height, eye height
Define the population being served: Adult males and females
Select a design principle and the percentage of the population to be accommodated: Design for extremes and accommodate 95% of the population
Allow 5th percentile female sitting behind a 95th percentile male
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

16. Designing seating in a large training room
4. Find the appropriate anthropometric values from the given Table 5.1
5th percentile female eye height sitting is 26.6 in (67.5 cm)
95th percentile male sitting height is 38.1 in (96.7 cm)
A rise height of 11.5 in (29.2 cm) is necessary
– Too much and too steep it can be decreased
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

17. Principles of workplace design
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

18. Principles of workplace design
1. Determine work surface height by elbow height
Upper arms hanging down naturally
Elbows are flexed at 90⁰
Forearms are parallel to the ground
If work surface is too high → shoulder fatigue
If work surface is too low → back fatigue
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

19. Principles of workplace design
2. Adjust the work surface height based on the task being performed
Fine assembly → raise the work surface up to 8 in (20 cm) to bring the details closer to the optimal line of sight
Light, normal assembly
Rough assembly involving the lifting of heavy parts → lower the work surface up to 8 in (20 cm) to take advantage of the stronger trunk muscles
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

20. Principles of workplace design
3. Provide a comfortable chair for the seated operator
Seating posture reduces both the stress on the feet and the overall energy expenditure
Comfort is an individual response
Strict principles for good seating are difficult to define
Lumbar portion of the spine
While sitting
pelvis rotates backward
the pressure on the disks in the vertebral column increases
S shape to C shaped spine
Sitting Standing
Posture of the spine when standing and sitting
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

21. Principles of workplace design
4. Provide adjustability in the seat
Seat height is the most critical
Provide lumbar support
Increase body‐leg angle
Armrests for shoulders and arm support
Footrest for shorter individuals
Wheels assist in movement
Chair should be slightly contoured and slightly
cushioned
Use breathable fabric to prevent moisture
Adjustable chair recommended values on page 185
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

22. Principles of workplace design
Six basic seating postures
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Workplace, Equipment, and Tool Design

23. Principles of workplace design
Properly adjusted workstation (pg 189)
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Workplace, Equipment, and Tool Design

24. Principles of workplace design
5. Encourage postural flexibility
The work station height should be adjustable so that the work can be performed efficiently either standing or sitting
The human body is not designed for long periods of sitting
Provide a sit/stand stool so that the operator can change postures easily
Needs height adjustability
Large base of support
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

25. Principles of workplace design
6. Provide antifatigue mats for a standing operator
Standing for extending periods on a cement floor is fatiguing
The mats allow small muscle contractions in the legs, forcing the blood to move and keeping it from tending to pool in the lower extremities
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Workplace, Equipment, and Tool Design

26. Principles of workplace design
7. Locate all tools and materials within the normal working area
Normal and maximum working areas in the horizontal plane for women (for men, multiply by 1.09)
Normal and maximum working areas in the vertical plane for women (for men, multiply by 1.09)
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Workplace, Equipment, and Tool Design

27. Principles of workplace design
8. Fix locations for all tools and materials to permit the best sequence
Eliminates or minimizes the short hesitations required to search for and select the objects needed to do the work (S, SE: ineffective therbligs)
Tool balancers provide fixed locations for tools
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Workplace, Equipment, and Tool Design

28. Principles of workplace design
9. Use gravity bins and drop delivery to reduce reach and move times
Reach (RE) and move (M) are directly proportional to the distance that the hands must move
Gravity bins eliminates long reaches to get the supplies
Gravity chutes allow the disposal of completed parts within the normal area eliminating long moves
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

29. Principles of workplace design
10. Arrange tools, controls, and other components optimally to minimize motions
Optimum arrangement depends on many characteristics: human (strength, reach, sensory) and task (loads, repetition, orientation)
Locate the components relative to their importance and frequency‐of‐use
Once a general location is determined for a group of components, the functionality and sequence of use must be considered
Place the components or subassemblies in the order that they are assembled (to reduce wasteful motions)
Use Systematic Layout Planning (SLP) or other techniques to develop alternative layouts
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

30. Principles of workplace design
The principles of work design for workstations are summarized in Workstation Evaluation Checklist (Figure 5.16, pg 194: Course webpage)
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Workplace, Equipment, and Tool Design

31. Principles of machines and equipment design
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Workplace, Equipment, and Tool Design

32. Principles of machines and equipment design
1. Combine two or more tools in one
Advanced production planning for the most efficient manufacture includes combination of tools
2. Use a fixture instead of the hand as a holding device
Remember: Hold (H) is an ineffective therblig
A fixture can be designed to hold the work, thus allowing both hands to do useful work
Fixtures not only save time in processing parts but also permit better quality
Foot‐operated mechanisms can be used to allow both hands to perform productive work
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

33. Principles of machines and equipment design
3. Locate all control devices for best operator accessibility and strength capability
Frequently used controls should be positioned between elbow and shoulder height
Seated operators can apply maximum force to levers located at elbow level, standing operators at shoulder height
Handwheel and crank diameters depend on the torque to be expended and the position
The diameters of knobs should be increased as greater torques are needed
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Workplace, Equipment, and Tool Design

34. Principles of machines and equipment design
4. Use shape, texture, and size coding for controls
Shape coding, using 2‐ or 3‐dimensional geometric configurations permits both tactual and visual identification
It is especially useful under low light conditions
As the number of shapes and textures increases discrimination can be difficult and slow
If the operator wears gloves, it is possible to discriminate only 2‐4 shapes
Size coding is used principally where the controls cannot be seen by the operators
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Workplace, Equipment, and Tool Design

35. Principles of machines and equipment design
Examples of knob designs for three classes of use that are seldom confused by touch
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Workplace, Equipment, and Tool Design

36. Principles of machines and equipment design
5. Use proper control size, displacement, and resistance
The three parameters that have a major impact on performance:
Control size: A control that is either too small or too large cannot be activated efficiently. Tables 5.3, 5.4 and 5.5 provide min and max dimensions for various mechanism (pg 198)
Control response ratio (C/R): is the amount of movement in a control divided by amount of movement in the response. Low ratio indicates high sensitivity, high ratio means low sensitivity
Control resistance: Important for providing feedback to the operator. It can be displacement with no resistance, force with no displacement or incorporating features of both
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Workplace, Equipment, and Tool Design

37. Principles of machines and equipment design
Generalized illustrations of low and high control‐response ratios (C/R ratios) for lever and rotary controls. The C/R ratio is a function of the linkage between the control and the display.
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Workplace, Equipment, and Tool Design

38. Principles of machines and equipment design
Relationship between C/R ratio and movement time
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Workplace, Equipment, and Tool Design

39. Principles of machines and equipment design
6. Ensure proper compatibility between controls and displays
Compatibility is defined as the relationship between controls and displays that is consistent with human expectations
Affordance/Intuitive: the perceived property results in the desired action
A door with a handle to pull to open / a door with a plate to push to open
Mapping: the clear relationship between controls and responses
Controls on the stoves, clockwise movement to increase, pg 202
Feedback: so that the operator knows that the function is accomplished
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

40. Principles of machines and equipment design
The principles of work design for machines and equipment are summarized in the Machine Evaluation Checklist (Figure 5.21, pg 203: Course webpage)
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Workplace, Equipment, and Tool Design

41. Principles of tool design
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Workplace, Equipment, and Tool Design

42. Principles of tool design
1. Use a power grip for tasks requiring force and pinch grips for tasks requiring precision
In a power grip the handle of the tool, whose axis is more or less perpendicular to the forearm, is held by the partly flexed fingers and the palm. Opposing pressure is applied by the thumb, which slightly overlaps the middle finger.
The force parallel to forearm: sawing
The force at an angle to the forearm: hammering
The force acting on a moment arm: using a screwdriver
The pinch grip is used for control and precision. The item is held between the distal ends of one or more fingers and the opposing thumb.
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

43. Principles of tool design
Types of grip
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Workplace, Equipment, and Tool Design

44. Principles of tool design
2. Avoid prolonged static muscle loading
Tools held for extended periods results in fatigue, reduced work capacity, and soreness
3. Perform twisting motions with the elbows bent
When the elbow is extended (> 90⁰), tendons and muscles in the arm stretch out and provide low force capability
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Workplace, Equipment, and Tool Design

45. Principles of tool design
4. Maintain a straight wrist
As the wrist is moved from its neutral position a loss of grip strength occurs
Awkward hand positions may result in soreness of the wrist
Carpal tunnel syndrome
Grip strength as a function of wrist and forearm position
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Workplace, Equipment, and Tool Design

46. Principles of tool design
5. Avoid tissue compression
Considerable compressive force on the palm or the fingers obstructs blood flow to the tissues and may result in numbness and tingling of the fingers
Handles should be designed with large contact surfaces, to distribute the force over a larger area or to direct it to less sensitive areas
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

47. Principles of tool design
6. Design tools so that they can be used by either hand and by most individuals
Alternating hands allows reduction of the local muscle fatigue
90% of the population is right‐handed, 10% are left‐handed
Female grip strength typically ranges from 50 to 67% of male strength with a smaller grip span
The best solution is to provide a variety of tool sizes
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Workplace, Equipment, and Tool Design

48. Principles of tool design
7. Avoid repetitive finger action
Trigger forces should be kept low to reduce load on the index finger
Two or three finger‐operator controls are better
NIOSH found high rates of muscle‐tendon disorders in workers exceeding 10,000 motions per day
8. Use the strongest working fingers: the middle finger and the thumb
Index finger is usually the fastest but not the strongest
When a relatively heavy load is involved, use the middle finger, or a combination of middle finger and the index finger
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Workplace, Equipment, and Tool Design

49. Principles of tool design
9. Design 1.5‐in (3.8 cm) handle diameters for power grips
Power grips around an object should surround the circumference
The handle diameter for precision grips should be 0.5 in (1.3 cm)
10. Design handle lengths to be a minimum of 4‐in (10.2 cm)
For both handles and cutouts, there should be enough space to allow for all four fingers
5 in (12.7 cm) may be more comfortable
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Workplace, Equipment, and Tool Design

50. Principles of tool design
11. Design a 3‐in (7.6cm) grip span for two‐handled tools
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Workplace, Equipment, and Tool Design

51. Principles of tool design
12. Design appropriately shaped handles
Design for maximum surface contact to minimize unit pressure
For screwdriver type tools the handle end should be rounded to prevent pressure at the palm
T‐handles yield a much higher torque
13. Design grip surface to be compressible and nonconductive
Wood is usually the material of choice for tool handles
Since wooden handles can break and stain with grease and oil, there has recently been a shift to plastic and even metal
Increase friction
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Workplace, Equipment, and Tool Design

52. Principles of tool design
14. Keep the weight of the tool below 5 lb (2.3 kg)
The tool should be well balanced, with the center of gravity as close as possible to the center of gravity of the hand
15. Use gloves for safety and comfort
A trade‐off between increased safety and decreased performance with gloves must be considered
16. Use power tools instead of manual tools
Power tools perform work faster than manual tools and also do the work with considerably less operator fatigue
Power hand tools produce vibration which can cause health problems
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Workplace, Equipment, and Tool Design

53. Principles of tool design
17. Use the proper configuration and orientation of power tools
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Workplace, Equipment, and Tool Design

54. Principles of tool design
The principles of work design for tools are summarized in the Tool Evaluation Checklist (Figure 5.43, pg 221: Course webpage)
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Workplace, Equipment, and Tool Design

55. Cumulative trauma disorders
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Workplace, Equipment, and Tool Design

56. Cumulative trauma disorders
Cumulative trauma disorders (CTD) (repetitive motion injuries or work‐related musculoskeletal disorders) are injuries to the musculoskeletal system that develop gradually as a result of repeated microtrauma due to poor design and the excessive use of hand tools and other equipment
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

57. Cumulative trauma disorders
61% of all occupational illnesses are associated with repetitive motions
15 to 20% of workers in key industries are at potential risk for CTD
Because of the slow onset and relatively mild nature of the trauma, the condition is often ignored until the symptoms become chronic and more severe injury occurs
A collection of a variety of problems including repetitive motion disorders, carpal tunnel syndrome, tendinitis, ganglionitis, tenosynovitis, bursitis
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Workplace, Equipment, and Tool Design

58. Cumulative trauma disorders
Four major work related factors:
Excessive force
Awkward or extreme joint motions
High repetition
Duration of work
Most common symptoms associated with CTD:
Pain
Joint movement restriction
Soft tissue swelling
If the nerves are affected, sensory responses and motor control may be impaired
If left untreated, CTD can result in permanent disability
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Workplace, Equipment, and Tool Design

59. Content Anthropometry and design Principles of workplace design
Principles of machines and equipment design
Principles of tool design
Cumulative trauma disorders
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design

60. Workplace, equipment, and tool design
Key points:
Fit the workplace to the operator
Provide adjustability
Maintain neutral postures (joints in midrange)
Minimize repetitions
Use power grips when force is required
Use pinch grips for precision and not force
END 202 – Work analysis and design
Workplace, Equipment, and Tool Design