23-Ind-B6 Human Factor in Design · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Examinations, May 2013 — 98-Ind-B6, Workplace Design (3-hour closed-book exam, Casio/Sharp approved calculators only. The front page states any 5 of the 7 questions, each worth 20 marks, constitute a complete paper; all 7 are answered below.)
Reference texts: Sanders & McCormick, Human Factors in Engineering and Design (7th ed.) — controls and displays, anthropometry and workstation design, physical work and manual materials handling, and human-machine system arrangement; Niebel & Freivalds, Methods, Standards, and Work Design — workplace layout and posture.
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.
Human engineering (human factors/ergonomics) is applied wherever a person interacts with equipment, an environment, or a system, including: equipment and product design (control/display layout, hand-tool design, consumer-product usability); workplace and workstation design (layout, seating, lighting, reach envelopes — Q3–Q5, Q7); work-method and job design (task sequencing, manual-materials-handling limits, shift/rest scheduling to manage fatigue); environmental design (noise, vibration, thermal comfort, illumination); systems and software/interface design (control-room and vehicle-cockpit design, human-computer interaction); safety and accident prevention (error-tolerant design, guarding, warnings, and hazard-control per the hierarchy of controls); and training and selection, where task and workstation design determine the skill/strength/anthropometric requirements a hiring or training program must meet.
An open-loop system executes a control action based only on the input command, with no measurement of the actual output fed back to correct the action — a microwave oven timer runs for the set time regardless of whether the food has actually reached the intended temperature. A closed-loop (feedback) system continuously measures its own output, compares it against the desired setpoint, and uses the resulting error to correct the control action — a thermostatically controlled heating system measures room temperature and adjusts the heater accordingly. Because a closed-loop system self-corrects for disturbances and modelling error, it is generally far more accurate and robust than an open-loop system, but it is also more complex (it needs a sensor and a comparator) and can become unstable if the feedback is not properly designed (e.g., excessive delay or gain in the loop causing oscillation).
An automated system is characterized by four elements arranged in a loop: a comparator that computes the error between the desired setpoint and the measured output, a controller that decides what corrective action the error calls for, an actuator that physically executes that action on the process, and a sensor/feedback path that measures the process output and returns it to the comparator.
A concrete example is a thermostatically controlled HVAC system: the comparator compares the room's measured temperature to the setpoint; the controller decides whether, and how strongly, to call for heating or cooling; the actuator opens/closes the heating or cooling valve/compressor; and the temperature sensor closes the loop by reporting the resulting room temperature back to the comparator. Because this loop measures its own output and feeds it back to correct future action, an automated system of this kind is, by definition, a closed-loop system — the presence of the sensor/feedback path is precisely what makes it "automated" rather than a simple, unmonitored, open-loop timer or sequencer.
