A Novel Machine for Scanning Permanent Magnets Used in Magnetic Angle SensorsAuthors: Marjan Blagojevi (SENIS GmbH); Nenad Markovi (SENIS GmbH); Radivoje Popovi (SENIS GmbH); Dragan Mani (Faculty of Electronic Engineering University of Ni) Modern magnetic angle sensors consist of a combination of a rotating permanent magnet and a magnetic field sensor. The characteristics of the permanent magnets for such sensors must be carefully controlled. The characterization of the magnets includes scanning of the magnetic field by means of a magnetic field probe.General Hall effect system

This is a challenging task due to the following facts: (i) The crucial characteristic to be determined is the orientation of the magnetic field vector; therefore, at least two, but preferably all three components of the magnetic field must be measured at the same points, which raises the issues of the positioning and orthogonality of the magnetic sensors in the probe; (ii) the magnets of interest might be as small as a few millimeters in diameter, and therefore the magnetic fields might be very inhomogeneous; so the spatial resolution of the probe must be very high.We have pushed the limits in this field by building a magnetic scanning machine with several novel features. We applied a CMOS fully integrated 3-axis Hall probe with the magnetic sensitive volume of about 0.1mm x 0.1mm x 0.01mm. This meets the requirements of the measurements of all three components of a magnetic field with high spatial resolution. The other features of the Hall probe include: On-chip suppression of offset and 1/f noise Negligible planar Hall effect No parasitic inductive and capacitive coupling High DC field resolution: up to 5T at 20mTTilt is angle of rotation around y axis;Roll is angle of rotation around z axis;Pitch is angle of rotation around x axis. However, we found that the mutual orthogonality of the horizontal and vertical Hall elements integrated in the probe was not sufficient for the present task. In order to improve the magnetic angle measurement, we developed a software correction of the measured magnetic angle error. Briefly, we proceed as follows: We record the matrix of the magnetic vectors for a given position of the magnet under test. Then, we rotate the magnet for 90, and record again the matrix of the magnetic vectors. Ideally, the second matrix must be equal to the transposed matrix of the first one. If this is not the case, we apply an adequate Eulers transformations on the measured field components. In this way, self-consistent magnetic angle measurements were obtained, with the resolution of 0.1 degree. We also developed a novel procedure for the alignment of the rotating axis of the permanent magnet under test with the axis of the sensitive zone of the probe. We use a rotating platform with the permanent magnet placed out of the rotation axis of the platform. By successively rotating the platform and moving the Hall probe according to an algorithm, the alignment of the rotating axis and the probe is obtained in a few iterations. Procedure for Alignment of the Field Sensitive Volume with the Axis of Rotation (2D simulation)Start position for probe and magnetPosition of probe respect to rotation axis before and after applied procedure

Position where measured component By is maximal

Position of probe and magnet when component By change sign

Position of probe and magnet after rotation of 180

Position of probe and magnet after second change of sign of component ByPosition of probe in the middle between two changes of sign

Position where measured component Bx is maximal

Position of probe and magnet when component Bx change sign

Position of probe and magnet after rotation of 180

Position of probe and magnet after second change of sign of component Bx

Position of probe in the middle between two changes of sign

Ideal Probe alignmentEuler's transformations:The definition of the homogeneity:The tool for the precise aligning Definition of the Angular errors

The misalignment of the Probe relative to magnet