US Patent 9,881,277 B2 tracks a warehouse worker's hand by RF time-of-flight and adds haptic feedback plus gesture sensing

US 9,881,277 B2, titled "Wrist band haptic feedback system," was filed by Amazon Technologies, Inc. on 2016-03-28 and granted 2018-01-30 (per the patent's own front matter: "Patent Number: US9881277B2 ... Assignee: Amazon Technologies Inc ... Filing Date: March 28, 2016 ... Publication/Grant Date: January 30, 2018"). Its full abstract, confirmed verbatim in a single clean extraction pass: "Inventory management systems and related methods employ radio frequency based tracking of a worker's hands to monitor performance of inventory tasks. An inventory management system includes inventory bins, a user-wearable unit configured to be worn in proximity to a user's hand, fixed RF antennas configured to transmit at least one RF interrogation signal and receive at least one RF response signal, a RF transceiver operatively coupled with the fixed RF antennas, and a management module operatively coupled with the RF transceiver." Location is computed from "time of flight of interrogation signals from and back to respective RF antennas" — a distinct method from the time-of-arrival scheme in the ultrasonic sibling patent. The same wearable carries a haptic feedback mechanism "to communicate a haptic feedback to the user indicating whether the identified inventory bin matches a designated inventory bin," plus "a motion detection unit configured to generate data that can be processed to track orientation" for recognizing hand-gesture commands — a capability not present in the ultrasonic patent.

This is the radio-frequency half of the mechanism split first reported by NPR (2018) and synthesized in claim-amazon-2018-worker-tracking-wristband-patents; its ultrasonic sibling, filed the same day, is claim-us-9881276-ultrasonic-wristband-patent-mechanism. Like that patent, it is a hardware-era ancestor of Inertia-1's wearable-accelerometer lineage.