Step-by-step analysis of graph

The following photos are taken from a video clip of one cycle of a packing job.  Each photo shows one of the four primary steps of the task, which involved picking up products from a pallet on the floor, then placing them in three shipping boxes.  The arrows show the corresponding section of the graph (the graph was generated from a full video clip; these photos are simply to help you see what the graphs depict.)

The full work cycle for this task took 23.5 seconds, as shown on the horizontal axes of the two graphs.  The loads on the arms and back are shown on the vertical axes, thus the higher the peak and the larger the area under the curve, the greater the strain.

Bending and lifting the product from the pallet (3.5 seconds) is very observable in the Back graph, as would be expected.  The peak loads are 707 lbs. for the back and

Carrying the products to the conveyor (2.5 seconds) places a relatively small load on the back since the employee is now erect.  The load on the arms increases somewhat because the products are large, causing the arms to be more extended than when bending and lifting.

Sliding the products along the conveyor is the next step (4.5 seconds).  Since the weight of the products now primarily rests on the conveyor, the loads on the body are reduced.

Packing the products in three boxes (10 seconds) results in three blips on the graphs, as the arms are extended with the weight of the product in order to put it into the box.

Walking back to the pallet to start another cycle is the final step (3 seconds).  No photo is shown of this step, but the absence of any load other than the weight of the upper torso is clearly depicted on the graph.

Time involved — Packing the boxes (the only value-added step) took 10 seconds.  The remaining 13.5 seconds (57% of the work cycle) were wasted activities like walking and carrying.

Comments

  1. The graph for the Back shows the issues most dramatically.  Clearly the strain on the back is associated with bending down to the pallet to lift the product. 

  2. Most people who are involved with ergonomics would understand this point without needing to conduct a study.  However, it can be helpful to show managers and engineers this type of graph because it is easy to understand and the problems sort of point themselves out.