In our last post we talked about the importance of wheel design in reducing friction. But why is that important? The answer is that any design element that decreases the force that must be exerted by the operator to manipulate a piece of equipment increases efficiency and decreases the risk of potential injury. The result is greater productivity. This is the goal of ergonomic design both in the design of equipment and the environment in which it will be used.
When a wheeled piece of equipment is used, the operator must first overcome inertia and friction. The initial force necessary to start an object in motion is far greater than the sustained force necessary to keep it moving. Once in motion, optimum sustained, or rolling, force is achieved when a steady, constant velocity is achieved. Any need to decrease or increase velocity requires increased force to combat inertia. This is particularly noticeable during turning and maneuvering when significant force must be applied to change direction. Stopping a piece of wheeled equipment requires the same high level of force as starting it. As when accelerating, the operator must overcome high levels of inertia and friction to decelerate.
The four physical elements required to move a piece of wheeled equipment — starting, rolling, turning and stopping — can place tremendous stress on the operator’s musculoskeletal system. If performing these tasks manually, workers frequently overexert and strain muscles while applying the necessary force to start or stop a piece of equipment. Turning and positioning equipment can cause operators to assume asymmetric body postures during exertion which can cause musculoskeletal injury.
Ergonomically designed carts and tugs seek to achieve the optimal wheel size, type, placement and composition to decrease the force an operator must exert to move a piece of equipment.