STEM与日常科技·英语30篇（7）
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How Touchless Soap Dispensers Measure Hand Size Accurately
免触式洗手液分配器如何准确测量手掌尺寸
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Touchless soap dispensers use infrared time-of-flight sensors to estimate hand size before dispensing.
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They emit invisible light pulses and calculate distance based on how long light takes to bounce back.
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By scanning multiple points across the palm area, they build a rough 3D profile in under half a second.
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This prevents over-dispensing for small hands or under-dosing for larger ones.
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Algorithms adjust output volume depending on detected surface area and proximity.
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Some models even learn user habits after repeated use to refine future responses.
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The sensor must distinguish hands from other objects like bags or sleeves using motion context.
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Power efficiency matters, so systems activate only when motion enters a defined detection zone.
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Calibration occurs during manufacturing and rarely needs field adjustment due to stable optics.
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This precision reduces waste and improves hygiene in hospitals and schools alike.