Reach zones, work height and tool layout

Why it matters

Bringing the tool closer to the worker often reduces unnecessary movement; however, not every reach that looks short on a ruler is suitable. If the tool blocks the view of the part, requires the hand to rotate at the wrist or falls into the work area when released, the layout creates a new problem. A reach zone should not be thought of merely as the area inside a circle. The worker's posture, the seated or standing work condition, the direction of the load and the precision of the task are considered together. In method study, if these conditions are not preserved while the material's location is changed, the time gain cannot be sustained. The aim is as much to make the job safely repeatable as to find the smallest distance.

Frequently reached parts and occasionally used tools do not need to be in the same position. The number of repetitions changes the effect of distance on total movement. A light part used in every cycle can be presented close; for a heavy tool, safe support and grip are needed as much as closeness. The empty space on the work surface also has a purpose: it leaves room for turning, checking and setting down the part properly. Piling everything close by can cause searching, collisions and mix-ups. In a layout decision it is necessary to measure not only the center of the box but the actual grip point. If this point changes as the box empties, the different fill states of the arrangement are examined too.

Work height is not a single number independent of the task. A precise job that requires vision and a job in which force is applied may not call for the same working condition. Also, the surface of the bench is not the same as the height of the point being worked on; the fixture and the part can raise this point. A layout fixed for an average user may cause different users to raise their shoulders or bend their trunks. Adjustability is an option for meeting this difference; making the adjustment safe, maintaining it and verifying it at the start of the job are also part of the design. The existence of an adjustment mechanism does not by itself prove that the user can actually bring it to a suitable position.

In this lesson the distance and repetition calculation makes the movement load of the layout visible. The result is not a health risk score, and a time gain is not derived from distance alone. A shorter path may require the part to be gripped more slowly; the new position of a cable or hose may make movement harder. The two layouts are tried under the same output condition and the time is observed separately. Users are shown with codes such as K01 and K02; no judgment about personal suitability is made from a single number. The decision document states under which product and user conditions the chosen design was tested. That way a trial that looks good does not turn into a general bench dimension for all jobs.

Formula