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MPI 2006 Math Workshop          In cooperation with SIAM

Development of a quaternion-based algorithm to process data in robotics applications

Industrial Presenter: Jacqueline Ashmore, TIAX LLC

Reliable data about the orientation and location of a device is needed, and this information can be determined using measurements from inertial and magnetometer sensors, in combination with gyros. Typically a three axis accelerometer, a three-axis magnetometer, and a gyro will be employed for each physical component which is to be tracked. The readings from these sensors must be filtered and transformed to provide useful data. We are concerned here with transforming the readings from the moving sensor frame into the Earth’s frame. In general, it is useful for the transformations to be feasible for all orientations of the device, and for them to be achieved with computational efficiency.

A sensor attached to the device gives readings of the measured acceleration, angular rate, or magnetic field in the moving sensor frame from three axes which are not exactly orthogonal. An algorithm is required to

  1. calibrate the sensor readings;
  2. process data from the sensor to determine the readings in the Earth’s frame, accounting for both the nonorthogonality of the sensor axes and the necessary transformations from the sensor frame to the Earth’s frame;
  3. account for the presence of a gyro.

The MERLIN explorer, a mobile micro-robot which incorporates a 3-axis magnetometer and a gyroscope. This was developed in the Department of Cybernetics at the Czech Technical University. (Source: http://labe.felk.cvut.cz/~pelote/results/robots.htm)

This algorithm has been formulated using Euler angles, which have the advantage of relative simplicity but the disadvantage of the occurrence of singularities in the transformations, which limits the range of readings that can be processed accurately. Therefore a more useful algorithm is based on quaternions, which use complex four-dimensional vectors [1,2]. The advantages of quaternions are that no singularities occur in the transformations, i.e., all readings can be converted from the sensor to the Earth’s frame, and the manipulations are computationally less expensive. TIAX is asking for development of the necessary mathematical framework. We would also find it useful to have a Matlab code that implements the necessary calibrations and transformations. The code may use the robotics toolbox for Matlab that can be downloaded from the web [3]. This problem relates to motion control in robotics, as well as in other moving objects.

Useful References

  1. E.R. Bachmann, “Inertial and magnetic tracking of limb segment orientation for inserting humans into synthetic envirorments,” Ph.D. thesis, Naval Postgraduate School (2000).
  2. J.B. Schleppe, “Development of a real-time attitude system using a quaternion parameterization and non-dedicated GPS receivers,” Masters thesis, University of Calgary (1996).
  3. P. Corke, “A robotics toolbox for Matlab,” IEEE Robotics & Automation Magazine (1996). See also http://www.cat.csiro.au/ict/staff/pic/robot/
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