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

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

Anthropometry and design Workplace, Equipment, and Tool Design

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 1000 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

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

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 = 68.3 in, Stand. Deviation, σ = 2.71 in 50% 95th percentile male height = 68.3 + 1.645 x (2.71) = 72.76 in (≈185 cm) 5% 95% 5th percentile male height = 68.3 ‐ 1.645 x (2.71) = 63.84 in (≈162 cm) END 202 – Work analysis and design Workplace, Equipment, and Tool Design

Anthropometry Selected body dimensions END 202 – Work analysis and design Workplace, Equipment, and Tool Design

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Principles of workplace design Six basic seating postures END 202 – Work analysis and design Workplace, Equipment, and Tool Design

Principles of workplace design Properly adjusted workstation (pg 189) END 202 – Work analysis and design Workplace, Equipment, and Tool Design

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

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

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) END 202 – Work analysis and design Workplace, Equipment, and Tool Design

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

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

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

Principles of workplace design The principles of work design for workstations are summarized in Workstation Evaluation Checklist (Figure 5.16, pg 194: Course webpage) END 202 – Work analysis and design Workplace, Equipment, and Tool Design

Principles of machines and equipment design END 202 – Work analysis and design Workplace, Equipment, and Tool Design

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

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

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

Principles of machines and equipment design Examples of knob designs for three classes of use that are seldom confused by touch END 202 – Work analysis and design Workplace, Equipment, and Tool Design

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

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

Principles of machines and equipment design Relationship between C/R ratio and movement time END 202 – Work analysis and design Workplace, Equipment, and Tool Design

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

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) END 202 – Work analysis and design Workplace, Equipment, and Tool Design

Principles of tool design END 202 – Work analysis and design Workplace, Equipment, and Tool Design

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

Principles of tool design Types of grip END 202 – Work analysis and design Workplace, Equipment, and Tool Design

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

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

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

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

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

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

Principles of tool design 11. Design a 3‐in (7.6cm) grip span for two‐handled tools END 202 – Work analysis and design Workplace, Equipment, and Tool Design

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

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

Principles of tool design 17. Use the proper configuration and orientation of power tools END 202 – Work analysis and design Workplace, Equipment, and Tool Design

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) END 202 – Work analysis and design Workplace, Equipment, and Tool Design

Cumulative trauma disorders END 202 – Work analysis and design Workplace, Equipment, and Tool Design

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

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

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

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

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