Ergonomics of the Assembly Line

Ergonomics of the Assembly Line

By

Agapito Martinez

Ergonomics and Human Factors

TMGT 3355

Oct 17, 2011

Manufacturing and production settings such as assembly lines, warehousing, shipping & receiving facilities present a variety of ergonomic challenges. Employees often spend long periods standing, walking on hard surfaces, performing repetitive motions over the course of their shift. Ergonomic interventions significantly reduce the physical impact of these industrial tasks. Designing the industrial workstation from the bottom up decreases work-related repetitive stress injuries, increasing productivity and enhances worker motivation and job satisfaction.

First a job task analysis of the process has to be conducted to identify factors that have the potential to create ergonomic related injuries. Job tasks that involve activities such as repetitive and forceful exertions, excessive reaching, twisting, standing for extended periods, frequent heavy lifting, overhead lifts, awkward work positions/postures, or use vibrating equipment are most likely to contribute ergonomic injuries. A list by NIOSH on examples of these types of tasks is;

Meat packing Cleaning Metal tubs, shank trimming, removing lard and internal organs

Warehousing Lifting and carrying containers of assorted weights

Metal fabrication Cutting, threading, shaping bar stock, and coupling parts to form product

Electronics assembly Coil winding or trimming wire, circuit board wiring, fastening parts and packing products

Supermarket Express checkout operations

VDT office & clerical Sustained data entry and nonadjustable workstations

Clothing manufacture Sewing tasks

Glass products Decorating or etching glass

Plumbing fixtures Lifting and moving toilet bowls weighing 45 to 70 lb

Sheet metal products Riveting, seaming, assembly work

Plastic products Parts molding, trimming excess material, filing, and reaming and sanding to finish product

Logging Extended driving of log stackers or haulers over rough terrain

Film & paper products Repackaging larger bulk materials into smaller units for distribution

Day care Lifting and bending in tending to infant needs

Jewelry manufacturing Waxing, cutting, finishing tasks

Cabinetmaking Lifting and push-pull tasks

Auto products Lifting and handling parts weighing 36 to 78 lb

Tool and die making Grinding, polishing, deburring tasks

There are many factors that can contribute to ergonomic related injuries. The following is a short list and how they contribute to ergonomic related injuries;

Awkward Posture

Awkward postures affect joints and muscles that are used in repetitive tasks such as lifting. Also the amount of force or stresses that are generated or tolerated is affected by awkward posture. An example is the stress placed on the back when lifting or lowering objects with the back bent or twisted, compared with when the back is straight. Activities requiring frequent or prolonged work over shoulder height can be particularly stressful.

Forceful Exertions

Tasks that require forceful exertions place extra stresses on the muscles, tendons, ligaments, and joints. Repeated exposures of this type can give rise to feelings of fatigue but may also lead to musculoskeletal troubles when there is inadequate time for rest and recovery.

Repetitive Motions

When motions such as in an assembly line or meat packing line are repeated for prolonged work shifts, the possibility of fatigue and muscle-tendon strain is highly likely. Effects of repetitive motions from performing the same work activities are increased when awkward postures and forceful exertions are involved.

Duration

Duration refers to the length of time an employee is exposed to a risk factor in case a task requiring repetitive motion such as an automotive assembly line. Job tasks that require use of the same muscles or motions for extended periods of time increase the likelihood of both localized and general fatigue.

Contact Stresses

Steady contact with sharp objects such as non-rounded desk edges and narrow tool handles may create pressure on the arms or hands that can inhibit nerve function and blood flow.

Vibration

Exposure to vibration occurs when parts of the body such as the hands, arms and shoulders comes in contact with a vibrating equipment, such as a power hand tool. Whole-body exposure to vibration can occur when operating heavy-duty machinery such as a back-hoe.

Other Conditions

Workplace conditions can influence the presence and magnitude of the risk factors for ergonomic related injuries such as environmental conditions, lighting, noise, work-station floor surface, type of chair, tools, working surface and length of shift.

Once the ergonomics risk factors have been indentified, there is a variety of approaches that can help to control or eliminate these risk factors. The tried a true method is the three-tier hierarchy of controls in which is widely accepted as an intervention strategy for controlling workplace hazards, including ergonomic hazards.

The three tiers are as follows:

Engineering Controls

This is the preferred approach in preventing ergonomic related injuries. Engineering design and control strategies to reduce ergonomic risk factors such as;

* The strain of lifting of materials or finish goods is reduced by using mechanical devices.

* Changing the layout of the workstation, by using height-adjustable chairs, placement of tools or material to reduce reaching distances, improving lighting, and placing floor mats.

* Remove or reduce forceful exertions when assembling components to reduce stresses

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