Tag: wheeled carts

Human Factors Affect Push-Pull Equipment Design

Humans come in all shapes and sizes. And that’s the challenge in designing safe, effective ergonomic equipment. There is no such thing as “one size fits all” when you’re designing equipment that will be used by a diverse workforce. However, there are a number of specific human factors that affect a person’s ability to execute a pushing or pulling task. Ergonomics strives to incorporate these factors into equipment design to ensure that workers can safely and effectively complete required tasks.

  • Biomechanics use gender, body size (anthropometry), posture and push/pull force to calculate muscle force requirements and bone/joint compression forces. Biomechanics are useful in examining exertion, but generally fail to consider dynamics, repetition and duration of the task.
  • Physiology considers physical work capacity (a measurement of maximum aerobic capacity) and fatigue, particularly in tasks that are repetitive, fast paced or that require forceful exertion. Since each person is unique, his or her physical work capacity will be different. Factors considered include age, fitness, gender and maximum heart rate, as well as the energy demands and duration of the job. Physiology also factors in the necessary dissipation of body heat as affected by clothing, temperature, humidity and air movement. In designing equipment, ergonomic engineers consider the expected user population and generally design for the least physically capable individuals within that population.
  • Psychophysics takes human perception of the task into account. It evaluates the type, frequency, distance and hand height of the task, as well as the type of force required to execute the task. Also considered are the gender and characteristics of the average worker who will perform the task.

By considering these three types of human factors, ergonomic engineers strive to design an electric tug that can be safely and efficiently used by workers.

How Ergonomics Mitigates Force

Horizontal push force is a more significant factor than load weight in pushing and pulling tasks. In moving a wheeled piece of equipment or a load on a wheeled cart, three main forces come into play:

  • Starting or initial force is the effort required to initiate movement. It requires the greatest effort because it must overcome inertia.
  • Sustained or rolling force is the effort required to keep the load in motion and requires significantly less effort if a steady speed is maintained.
  • Turning force is the effort required to turn the load and can be significant as the load is moved into a new direction, often requiring asymmetric body postures and muscle exertion which carry a greater risk of injury.
  • Stopping or positioning force is the effort required to bring the load to a halt or position it in a specific place. Positioning can require significant, multidirectional force, exposing the worker to hazardous postures and muscle exertions.

Ergonomics mitigates these forces through design that seeks to minimize stress on the worker’s body and reduce wasted movement and effort. By reducing unnecessary movements and awkward postures, the force exerted by a worker is more efficiently utilized, thus reducing the amount of force necessary to move a load. This reduces both the time and effort needed to complete a task and the risk of worker injury. To ensure that equipment can be easily used by all members of the workforce, ergonomic design is often adjustable to fit a greater number of workers or is targeted to accommodate the weakest members of the workforce.

Ergonomics works to reduce inertial and dynamic forces, friction and physical interference to decrease the amount of force required to move a load. Considerations in ergonomic design generally include:

  • Floor materials, pitch and slope
  • Load weight, type and quantity per shift
  • Cart or equipment size, weight and design
  • Wheel or caster type, construction, materials, number and placement
  • Handhold type, height, width and placement
  • Control type and placement
  • Route, number of turns, obstacles and amount and type of maneuvering
  • Frequency, duration and repetition of task
  • Body postures required to operate equipment and perform tasks
  • Height, weight, strength and gender of typical worker