Wrist Motion Sensor Timing via Factory Characterized RF Stop
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Solution Overview
Problem
Existing methods for athletes to time themselves over a premeasured distance require synchronization between a wrist-mounted motion sensor and a smartphone, which can lead to drift and require frequent recalibration due to non-linearities, making the process inconvenient.
Innovation Solution
A method using a single time base on the wrist-mounted motion sensor, where the smartphone generates a RF stop request after a video trigger, allowing for factory characterization of delays to subtract residual errors, eliminating the need for user recalibration and ensuring accurate timing without drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single time base on the wrist-mounted motion sensor is used, then timing accuracy and reliability are improved by eliminating drift, but the device complexity increases due to factory characterization requirements
Solution Approach 1:
The patent performs delay characterization during factory manufacturing before the device reaches the user. Multiple trials are conducted to establish the average RF request delay and standard deviation, which are then stored in the device. This preliminary action eliminates the need for user recalibration and ensures consistent timing accuracy throughout the device's lifetime.
2Ease of operation
If the smartphone generates a RF stop request after a video trigger, then the ease of operation is improved by allowing self-timing, but measurement precision deteriorates due to OS delay of 0-20 ms
Solution Approach 1:
The patent incorporates feedback by measuring the actual delay between video trigger and RF request transmission during factory characterization. The average delay value is then used to compensate for this systematic error in timing calculations, improving measurement precision while maintaining ease of operation.
Solution Approach 2:
The patent changes the timing parameter by subtracting the characterized average delay from the measured time. This parameter adjustment compensates for the OS delay and provides more accurate timing results while maintaining the simple self-timing operation.
3Ease of operation
If the slap-sync method is used for synchronization, then the ease of operation is improved by allowing user calibration, but the productivity deteriorates due to frequent recalibration requirements
Solution Approach 1:
The patent extracts the calibration process from the user environment and moves it to the factory environment. By performing all necessary delay characterization during manufacturing, the device is delivered ready-to-use without requiring users to perform calibration or synchronization procedures, thereby eliminating productivity losses from frequent recalibration.
Data Source
AI summary
An athlete measures sprint time by locating a smartphone having a camera and clock start button which is first activated at the finish line. The sprint end time is recorded by a photo stamp time app. This sprint end time activates a video trigger causing the smartphone to send a RF stop event signal to a wrist mounted motion sensor worn by the athlete. A sensor timer is started via the start event by track or self starting. In track starting, the athlete pushes a start button on the sensor to initiate a variable 2-5 second delayed sound READY-SET-GO series of beeps to start the sprint. In self starting, the sensor detects threshold motion parameters of the sprinter's start which activates the sensor's free running clock and saves the start time. The time base on the sensor is used to calculate run time.