US Patent 9,881,276 B2 tracks a warehouse worker's hand by ultrasonic time-of-arrival and feeds back through the same wristband

US 9,881,276 B2, titled "Ultrasonic bracelet and receiver for detecting position in 2D plane," was filed by Amazon Technologies, Inc. on 2016-03-28 and granted 2018-01-30 (per the patent's own front matter: "Patent Number: US9881276B2 ... Assignee: Amazon Technologies Inc ... Filing Date: March 28, 2016 ... Grant Date: January 30, 2018"). Its mechanism is ultrasonic time-of-arrival localization: a worker-worn ultrasonic unit periodically emits pulses, which fixed transducers mounted near inventory bins detect. Per the description, "[u]ltrasonic transducers are arranged relative to inventory bins and generate signals that are processed to track the location of the ultrasonic pulse emitting units relative to the inventory bins." The management module compares arrival times across transducers to compute the unit's — and so the hand's — position. The same wearable also carries "a haptic feedback mechanism that is controlled to provide suitable haptic feedback to the worker," so tracking and correction live in one device.

This is the ultrasonic half of the mechanism split first reported by NPR (2018) and synthesized in claim-amazon-2018-worker-tracking-wristband-patents; its radio-frequency sibling, filed the same day, is claim-us-9881277-rf-wristband-patent-mechanism. As a wearable instrument of hand motion, it is a digital-era descendant of the Gilbreth chronocyclegraph and a hardware-era ancestor of Inertia-1's accelerometer corpus.