Sudden starts are a major source of discomfort
Aliases: abrupt motion onset · startup startle · motion surprise
What it is
Robot motion onset surprise is the startle, discomfort, or evasive response caused when a stationary robot begins moving without sufficient precursor. Suddenness depends on expectation, acceleration discontinuity, distance, and attention rather than peak speed alone; low final speed can still follow a disturbing near-field onset.
Why it happens
Stationarity establishes a short-term prediction of no motion. Abrupt onset violates that prediction and creates a salient motion transient. High initial jerk couples visible movement, motor sound, and structural vibration, capturing attention before direction is understood. Near-field and peripheral starts leave still less time for intent recognition.
Studying it
Stationary duration, preview, acceleration, jerk, distance, and visual-field position can be varied independently. Startle movement, physiological arousal, retreat, goal-recognition time, and discomfort distinguish responses. Peak speed must be held constant to isolate onset. Expected repeated starts underestimate surprise, so no-start trials or field observation are useful.
Where it stops holding
Rapid onset may be necessary to escape an imminent hazard, but needs a risk argument rather than an efficiency preference. Continuously operating machinery lacks the same stationary prior. Smooth onset cannot compensate for an intrusive path or inadequate stopping distance, and a quiet onset may be less detectable for blind pedestrians.
Applying it
- Insert a legible ready state between rest and motion, and constrain early jerk rather than only cruising speed.
- Use more conservative parameters near people, outside their view, and after long stationary periods; log emergency exceptions separately.
- Synchronise high-frame-rate video with motion logs to inspect cue, first displacement, and human retreat. Tune the profile using response margin and startle incidence.