Dead reckoning navigational system using accelerometer to measure foot impacts
AssigneePoint Research Corporation
InventorsRobert W. Levi, Thomas Judd
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Abstract
A microcomputer-assisted position finding system that integrates GPS data, dead reckoning sensors, and digital maps into a low-cost, self-contained navigation instrument is disclosed. A built-in radio frequency transponder allows individual positions to be monitored by a central coordinating facility. Unique dead reckoning sensors and features are disclosed for ground speed/distance measurement and computer-aided position fixes.
Claims15
A method of determining displacement of a user on foot, the method comprising the following steps:
- generating a set of accelerations corresponding to foot impacts of the user on a surface;
- determining a peak acceleration in the set of accelerations;
- comparing the peak acceleration to a predetermined minimum threshold value;
- comparing, if the peak acceleration is above the predetermined minimum threshold value, a period of time from a previously detected footstep to the determined peak acceleration;
- determining whether the period of time is greater than a predetermined minimum threshold period of time;
- storing the determined peak acceleration as a detected footstep, if the period of time is determined to be greater than the predetermined minimum threshold period of time;
- and
- multiplying stored detected footsteps by a scale factor to thereby determine the displacement of the user on foot.
A method of determining displacement of a user on foot by detecting a fundamental period of a set of impact accelerations of the user's body, the fundamental period of the set of impact accelerations of the user's body corresponding to a step frequency of the user, the method comprising the following steps:
- generating a set of impact accelerations over a period of time related to foot contacts with a ground surface;
- obtaining a frequency-domain representation of the set of vertical accelerations;
- determining a frequency in the frequency-domain representation that has a largest magnitude of all frequencies in the frequency-domain representation, the frequency in the frequency-domain representation with the largest magnitude being labeled the step frequency of the user on foot;
- and
- generating a scale factor to be used in determining the displacement of the user.
In a dead reckoning system that determines a distance travelled by a user on foot by multiplying a number of steps by a step size, a method of dynamically adjusting the step size of the user, the method comprising the following steps:
- (a) generating three default values of:
- (1) a default step size S0;
- (2) a default step frequency f0, which is a frequency at which there is no correction to S0;
- and
- (3) a slope m of a step-size versus step-frequency calibration curve;
- (b) detecting a plurality of steps of the user;
- (c) noting the time of each of the detected steps;
- (d) generating an average step period as an average time between at least two of the plurality of detected steps of the user;
- (e) taking a reciprocal of the average step period, to thereby generate a step frequency;
- and
- (f) determining a new step size by adding:
- (1) the default step size;
- and
- (2) a product of both the slope of the step-size versus step-frequency calibration curve and a difference between the default frequency and the generated step frequency.
Dependencies are inferred from the claim text.