4.7 Ergonomics & Manual Handling

Ergonomics is not about comfort; it is about Yield. A fatigued operator introduces variability into the manufacturing process. When physical stress exceeds the body's recovery rate, fine motor control degrades, leading directly to solder defects, dropped components, and long-term musculoskeletal disorders (MSDs). Treat the human operator as a precision servo-mechanism that requires specific mechanical calibration to function within tolerance.

Workstation Geometry

The "One Size Fits All" approach is a statistical guarantee of failure. Workstations must be adjustable to align the tool with the operator, not force the operator to conform to the tool.

• If Task requires Microscope Inspection -> Then adjust ocular height to maintain a vertical cervical spine (Neck angle 0˚).
  • Constraint: If the operator must hunch forward > 20˚, the chair is too low or the scope is too short.
• If Task is PCBA Assembly -> Then define the Primary Work Zone (Reach < 40 cm).
  • Logic: All high-frequency tools (tweezers, iron, solder wire) must reside in this arc. Reaching beyond 40 cm introduces shoulder torque.
• If Seating is Static -> Then verify the chair has 5-point stability and adjustable lumbar support.
  • Rule: Feet must remain flat on the floor or a footrest. "Dangling" legs compress the femoral artery, reducing circulation and focus.

Pro-Tip: Tilt the component bin forward by 15˚ – 30˚. This reduces wrist flexion (bending) every time the operator reaches for a part, saving 2,000 bad wrist movements per shift.

Manual Handling (Load Mechanics)

Gravity is a constant force vector. Lifting imposes a torque load on the lumbar spine (L5-S1 vertebrae) defined by the formula: Torque = Weight × Distance from Body.

• If Load is > 23 kg -> Then Mechanical Lifting Aid (Hoist/Cart) is Mandatory.
  • No Exceptions: Do not rely on "team lifting." It coordinates poorly and doubles the risk exposure.
• If Lifting Any Load -> Then keep the Center of Gravity (CoG) within the "Power Zone" (between knees and shoulders).
  • Physics: Holding a 10 kg box at arm's length (50 cm) creates the same spinal torque as holding 50 kg against the chest. Reduce the lever arm.
• If Transporting Solder Dross / Heavy Metals -> Then use carts with > 100 mm casters.
  • Reason: Small wheels get stuck on floor joints, creating sudden inertial stops that cause back injury.

Repetitive Motion & Visual Fatigue

Static loading is as damaging as dynamic overload. Holding a soldering iron requires continuous muscle contraction (isometric load).

• If Cycle Time is < 30 seconds (High Repetition) -> Then implement Job Rotation every 2 hours.
  • Metric: Shift the load to different muscle groups to allow lactic acid flushing.
• If Task involves Fine Pitch Inspection -> Then monitor Lux Levels.
  • Standard: General Assembly = 500 Lux. Precision Inspection = 1,000 – 1,500 Lux. Dim light forces the eyes to strain, triggering headache and fatigue.

Final Checklist

Parameter	Metric / Rule	Critical State
Max Manual Lift	Weight Limit	≤ 23 kg
Primary Work Zone	Reach Radius	< 40 cm
Microscope Posture	Neck Angle	< 20˚ Deviation
Load Position	Lever Arm	Close to Body
Inspection Lighting	Intensity	> 1,000 Lux
Caster Size	Heavy Carts	≥ 100 mm