Week 4 – NavShoe
The paper highlights the problems faced by modern day navigation and tracking systems. They then introduce NavShoe a device that provides accurate tracking as well as orientation feedback. The major hurdle faced by such trackers is to maintain the accuracy with both orientation and position. Position tracking is based on inertial sensing but it is impossible to track a position for more than a few second based only on the inertial sensing. The main problem caused is due to the drift which causes a slowly growing tilt error. This is cubically related to position error which brings up the point that even a slight tilt error varies cubically for position. NavShoe works on the principle which brings down this cubic relation to a linear one. NavShoe decreases the sampling time and uses zero velocity updates to achieve this functionality. The authors propose several new methods. In one of their methods they talk about making use of commercial grade MEMS (microelectronic mechanical system) gyros and carefully calibrated and modeled solid state magnetic compass to achieve high accuracy results. They also state that the method is also cost effective one when compared to others. They further discuss on the implementation of NavShoe. The hardware basically consists of an inertia cube in the foot wired to a mounted antenna on a baseball cap; this was also one of the basic hurdles of NavShoe. It was overcome by getting rid of the cables and making use of RF transceivers. NavShoe uses standard strapdown INS (inertial navigation system). The IMU (Inertial Measurement Unit) reports the changes in velocity and position which are then used to update velocity and position states of the INS. After this a drift correction is performed. After each estimation cycle, filter delivers error estimates to the INS and clears the error vectors back to 0. Despite being fairly accurate NavShoe still came up with errors due the metal component present in the shoes. To overcome this compass calibration was performed once NavShoe was installed and it remained accurate till it was not removed from the shoe. The authors then show their test results which confirm the accuracy of NavShoe. The tests were performed both indoors and outdoors. The error indoors was found to be 0.06% while outdoor it was 0.3%.
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