Method for calculating personal dead-reckoning data using gait characteristics

Abstract

Raw dead reckoning data is obtained from an inertial measurement unit (IMU) worn by a user. Drift in the raw data is compensated for by detecting a gait of the user and phase of that gait, and constraining the position of the IMU to lie within corresponding bounds as the IMU moves. The bounds depend on the bodily geometry of the user and the detected gait phase. The raw orientation data of the IMU may be also corrected for drift in a similar way. Gait and gait phase may be detected by sensors in an energy harvester worn around the knee, for example. Drift in the IMU measurements can be compensated for without depending on a GPS signal or on the earth's magnetic field.

1 . A method for outputting dead reckoned data for a user undergoing locomotion comprising:
 attaching an inertial measurement unit (IMU) to the user;   defining a first point at which the IMU is located;   detecting a phase of a gait of the user using one or more sensors;   defining bounds for displacement of the IMU during said phase of the gait;   obtaining raw positional data from the IMU for a second point, to which the IMU is displaced by the locomotion of the user; and   either determining, by a processor, that the raw positional data lies within said bounds and then outputting, from the processor, the raw positional data as dead reckoned data for the second point, or, in the alternative, determining, by the processor, that the raw positional data lies outside of said bounds and then compensating the raw positional data to result in compensated positional data that is within said bounds and outputting, from the processor, the compensated positional data as the dead reckoned data for the second point.   
     
     
         2 . The method of  claim 1 , wherein the user is a human. 
     
     
         3 . The method of  claim 1 , further comprising:
 defining a first orientation for the IMU at the first point;   defining further bounds for orientation of the IMU during said phase of the gait;   obtaining raw orientational data from the IMU for the second point;   either determining, by a processor, that the raw orientational data lies within said further bounds and then outputting, from the processor, the raw orientational data as further dead reckoned data for the second point, or, in the alternative, determining, by the processor, that the raw orientational data lies outside of said further bounds and then compensating the raw orientational data to result in compensated orientational data that is within said further bounds and outputting, from the processor, the compensated orientational data as the further dead reckoned data for the second point.   
     
     
         4 . The method of  claim 1 , wherein the IMU is attached to a lower leg. 
     
     
         5 . The method of  claim 4 , wherein the phase of the gait starts with a heel strike of the lower leg. 
     
     
         6 . The method of  claim 1 , wherein the phase of the gait starts with a heel strike. 
     
     
         7 . The method of  claim 6 , wherein the phase of the gait ends with either:
 a lift of said heel; or   a lift of a foot having said heel.   
     
     
         8 . The method of  claim 1 , wherein the compensated positional data is on a surface of the bounds at a point that is a shortest distance from the raw positional data to the bounds. 
     
     
         9 . The method of  claim 1 , wherein the bounds move as the user progresses through the gait. 
     
     
         10 . The method of  claim 1 , wherein said one or more sensors include one or both of a knee angle sensor and a knee angular velocity sensor. 
     
     
         11 . The method of  claim 1 , further comprising attaching a further IMU to the user and performing one or both of:
 further defining the bounds to lie within a predetermined distance from the further IMU; and   defining additional bounds for the further IMU such that the additional bounds lie within a predetermined distance from the bounds.   
     
     
         12 . The method of  claim 1 , wherein detecting the phase of the gait of the user comprises selecting a gait model from a library of gait models. 
     
     
         13 . The method of  claim 1 , wherein defining the bounds is based on:
 one or more dimensions of the user; and   one or more ranges of motion of one or more body parts of the user.   
     
     
         14 . The method of  claim 1 , wherein said outputting is to one or both of a data store and a monitoring computer. 
     
     
         15 . The method of  claim 1 , further comprising converting the dead reckoned data for the second point to dead reckoned data for the user.