Position Tracking based on Linear Acceleration Measurements Only

Position tracking based on pure linear acceleration measurements is a difficult problem. To result in actual position values, linear acceleration (i.e. data from an accelerometer minus gravity) needs to be integrated twice. If there is only a minimal bias on the data of one of the tracked axes, the resulting position values will rapidly drift off.

Although it is well possible to increase the performance of such positioning information by sensor fusion with external reference signals (optical system, barometric pressure etc.), in many cases direct forward calculation of position from linear acceleration is required.

Lately we have been working on gradually improving our linear acceleration measurements in accuracy and tried to tune these measurements with various filters in order to gain relatively reliable displacement information.

The video below shows an exmaple of displacement tracking on the vertical axis using an LPMS-B device. Except for the sensor’s gyroscope, accelerometer and magnetometer, no external references have been used.

LpGlass and Head Tracking Revisited

We had the opportunity to try out one of the new augmented reality glasses AiRScouter produced by the Japanese company Brother. We first tried one at a Brother product exhibition here in Tokyo. Although the glasses are a little heavier than normal glasses, they fit quite well and the overlay image is well visible.

LP-Glass

We experimented with the glasses a bit and set-up a prototype application for augmented reality using our LPMS-B sensor for head tracking, codename: LpGlass. The video below shows a demo of our LPMS-B IMU attached to the AiRScouter.

Similar to the Google glasses there seem to be a huge number of applications, especially for augmenting task environments for medical procedures, industrial assembly, education etc.

Introducing LpTracker6D

We have created a first demo of our latest development, LpTracker6D. LpTracker6D is a system that allows the simultaneous tracking of position and orientation of a single point. Our system does not require any markers. Orientation readings are accurate to < 2° under dynamic and < 0.5° under static conditions.

Field Distortion Compensation Algorithm

If the LPMS is operated in an environment with a partially distorted (non-homogeneous) earth magnetic field, there is the possibility of the orientation readings becoming inaccurate due to invalid data from the magnetometer unit. To prevent this we have extended our sensor fusion algorithm to detect such field distortion and automatically switch to operation without magnetometer. The switching between the two states happens seamlessly (without orientation jump) and, if the exposure to the distorted magnetic field happens for a limited amount of time, without any major orientation drift.

Please see the video below for a demonstration of the improved filter. An iron plate is used to distort the magnetic field. As soon as the sensor gets close to the metal surface the magnetic field vector starts changing direction deliberately. The color of the cube on the monitor turns red in case of the detection of a distorted magnetic field.

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