Question 7 of 7: Component Arrangement, Link Types, and Displays/Controls Workspace Guidelines

Question 7: Component Arrangement, Link Types, and Displays/Controls Workspace Guidelines (20 marks: i–6, ii–7, iii–7)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(i) Guiding Principles of Component Arrangement

Components (equipment, controls, displays, storage, people) in a workspace are arranged according to four guiding principles, applied roughly in the order given whenever they conflict. The importance principle places the components most critical to safety or task success in the most accessible, prominent positions, regardless of how often they are used. The frequency-of-use principle places the most frequently used components in the most convenient locations (closest reach, best sightline) for the operator. The function principle groups components that serve a related function together (all instruments for one subsystem clustered, all tools for one operation stored together), so the operator does not have to search across the workspace to complete one activity. The sequence-of-use principle arranges components used in a fixed order (a startup checklist, an assembly sequence) in that same physical order, typically left-to-right or top-to-bottom, matching the natural scan and reach pattern the task already follows. Where these conflict — a critical component that is rarely used, for instance — importance is generally given precedence over frequency, since the cost of a slow response to a rare but critical event outweighs the small convenience lost on routine use.

(ii) Types of Links Between Components

A "link" is a relationship between two components (a person and a piece of equipment, two people, or two items of equipment) that the arrangement should account for. The human-factors classification used in link analysis (Sanders & McCormick) has three types. Communication links carry information between components and are sub-classified by channel: visual (an operator reading a display or seeing another person), auditory — voice (talking with another operator), auditory — non-voice (an alarm or buzzer) and touch (a tactile signal). Control links are the operator acting on equipment to change its state, by touch (a push-button or switch) or by movement (a lever, handwheel or pedal) — they tie a person to the controls. Movement links are the operator moving some part of the body from one component to another in sequence: eye movements between displays, hand or foot movements between controls, and whole-body movements between locations. Communication and control links are often called functional links (they are how the job is done), whereas movement links are sequential (they are the path taken between elements). Each link is then given a value (frequency × importance) so that high-value links can be shortened in the arrangement.

At the scale of a whole facility or work cell the same idea is often expressed by what flows along the link. Process (material) links capture the physical movement of material, parts, or product between two stations — the heavier or more frequent this flow, the more strongly the layout should pull the two stations together. Personal (operator/movement) links capture the movement of people between components — an operator walking between a machine and a supply bin, or between two workstations they both tend — and are minimized by placing frequently-linked stations close together. Information/control links capture the flow of signals, instructions, or data between components (a supervisor's console and the machines it monitors, a sensor and its control panel) and do not necessarily require physical proximity if the information can be transmitted electronically, though a strong link still argues for locating them within sightline of each other where practical. Communication/coordination links capture verbal or visual coordination between people at different stations (a two-person task requiring frequent consultation) and behave similarly to personal links in favouring proximity. Classifying links this way lets a layout be optimized separately for material flow, operator travel, and supervisory/communication needs, rather than treating "closeness" as a single undifferentiated criterion.

(iii) General Guidelines for Workspaces Involving Displays and Controls

Sanders & McCormick state the general guidelines for an individual workplace containing displays and controls as an order of priority: (1) primary visual tasks are located first, in the operator’s normal line of sight (about 15° below the horizontal) and within the preferred viewing area; (2) primary controls that interact with those primary visual tasks are then placed within easy reach; (3) control-display relationships — each control is placed close to its associated display, with compatible movement relationships; (4) elements used in sequence are arranged together in their order of use; (5) frequently used elements are placed in convenient locations for reach and viewing; and (6) consistency — the layout is kept consistent with other layouts in the same system (and in similar systems) so that operators moving between workplaces do not face conflicting arrangements. This is the importance/frequency/function/sequence logic of part (i) applied to displays and controls, with one further, display-control-specific guideline layered on top: display-control compatibility — each control should be located near, and should move in a manner consistent with, the display it affects, so the operator does not have to search for or reason out the relationship between them (part of the spatial and movement compatibility already discussed in Question 1(i)). Applied in practice: the most safety-critical displays/controls occupy the most prominent positions regardless of use frequency; the most frequently used displays/controls occupy the positions requiring least reach and best sightline; displays/controls serving a common function are grouped into a common panel or cluster; controls and displays used in a fixed operating sequence are arranged in that order; and every control is placed and oriented consistently with its associated display. Where a workspace serves multiple operators or a range of statures, the anthropometric and reach-envelope principles from Question 6 are applied on top of this priority ordering, so that the highest-priority displays/controls also fall within the normal reach/view zone for the full intended user population.