Magnetic systems for position and orientation detection are typically based on the relative motion of a permanent magnet with respect to a magnetic field sensor. On one hand, features such as high resolution, contactless (and thus wear-free) measurement, low power consumption, robustness against temperature and contamination as well as low cost make them appealing for several industrial applications, especially in the automotive sector. On the other hand, a major challenge is represented by their sensitivity to fabrication tolerances.
In this work we present an implementation of the novel magnetic 3-axis joystick system, which realizes all degrees of freedom using only a single 3D sensor and a single magnet. The use of 3D printing technology for the device manufacture makes this implementation – referred to as “mini Drive” – highly cost-efficient. The system design ensures a unique magnetic output signal for every mechanical state (5 tilt states, continuous rotation).
In order to cope with the fabrication tolerances without resorting to a high-precision manufacture that would nullify the cost-efficiency of the mini Drive, we propose a novel calibration scheme based on analytical methods. This is done by using the analytical solution for the magnetic field – computed with the Magpylib package – and by applying a differential evolution algorithm, enabled by the fast analytical field computation, to solve a multivariate optimization problem including all relevant fabrication tolerances (as for instance the sensor position, the magnet position and magnetization, the maximum joystick’s rod tilt angles). The calibration procedure requires the measurement of only four points for each tilt with unknown rotational position, which makes it easy to apply for an end-user.
This novel scheme enables the calibration of more than 10 degrees of freedom within few seconds on conventional PCs and holds the potential to realize innovative, exotic and cost-efficient magnetic position systems.
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