244 – Analysis of Magnetic Field Intensity at Sensor Position

Application Note / Model Data

Overview

In controlling the position and speed of motors, actuators, etc., it is necessary to detect the position of moving parts and calculate command values based on those signals. Methods for sensing magnetic flux leakage generating from a target object as ways of detecting positions are widespread.
Sensing types range from those that use electromagnetic induction by pickup coil, to methods that use the Hall effect and magnetic resistance effect. Regardless of the frequency of the detection target, practical use of these latter methods has begun to advance in recent years because of the possibility to obtain signals corresponding to the magnitude of magnetic flux density.
In order to predict the signal that occurs at the sensor due to magnetic flux density that generates at the sensor position and to apply this to the varying position and speed control of moving parts, electromagnetic field analysis is effective in accurately calculating the magnetic flux density and magnetic field distribution that generates from the detection target.
In this example, the motor as the detection target, the TMR sensor as the detecting element, and the waveform of the detection signal obtained based on the magnetic field calculated by electromagnetic field analysis.

Magnetic field strength and TMR ratio at sensor position

Fig. 1 displays the magnetic field intensity radial direction component at the sensor position. Increasing the motor electric current value increases the TMR ratio and it can be confirmed that the rotor position that takes the maximum value shifts to the lower angle side.
Fig. 2 displays the sensor pin layer fixed in the radial direction and the TMR ratio when assuming that magnetization of the free layer completely follows the external magnet field (maximum value of the TMR ratio assumed to be 100 %). It can be confirmed that the TMR ratio shifts to the lower angle side when the electric current changes, and it is understood that the relationship between signal strength and motor position varies depending on electric current amplitude. It is necessary to grasp the relationship between output and the rotor position when the electric current value changes in order to accurately detect the rotor position.

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