The magnetic field of a moving piston can be used for real-time estimation of its position. Piston position estimation is useful for a number of automation and performance improvement applications in hydraulic actuators, pneumatic cylinders, and I.C. engines. A significant challenge to magnetic field based position estimation comes from disturbances due to unexpected ferromagnetic objects coming close to the sensors.

This paper develops a new disturbance estimation method based on modeling the magnetic disturbance as a dipole with unknown location and magnitude. A Truncated Interval Unscented Kalman Filter (TIUKF) is used to estimate all the parameters of this unknown dipole. Experimental data from a pneumatic actuator is used to verify the performance of the developed estimator. Experimental results show that the developed estimator is significantly superior to a linear magnetic field model based disturbance estimator.

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