Improvement of the reproduction accuracy of a defined pole length of injection molded encoder wheels

Abstract

Magnetically sensitive sensors are increasingly used in different applications for the measurement of physical values, such as angle, position or speed. Depending on the application certain requirements for a high measurement accuracy have to be achieved, such as a high pole length accuracy and repeatability for the signal transmitter. These signal transmitter can be produced economically in the injection molding process using compounds consisting of hard magnetic particles embedded in a polymer matrix, so-called polymer bonded magnets. By integrating a magnetic field inside the mold an orientation of the particles in the polymer melt as well as a partial magnetization can be conducted, such that the second magnetization step is not required. This paper deals with the influence of the cooling conditions on the orientation of the particles as well as the final magnetic properties, such as the resulting pole length accuracy. The cooling conditions are varied by using different materials for the cavity wall. It can be shown that the cooling of the surface layer and resulting particle orientation has a major influence on the quality criteria of injection molded signal transmitter for sensor applications.Magnetically sensitive sensors are increasingly used in different applications for the measurement of physical values, such as angle, position or speed. Depending on the application certain requirements for a high measurement accuracy have to be achieved, such as a high pole length accuracy and repeatability for the signal transmitter. These signal transmitter can be produced economically in the injection molding process using compounds consisting of hard magnetic particles embedded in a polymer matrix, so-called polymer bonded magnets. By integrating a magnetic field inside the mold an orientation of the particles in the polymer melt as well as a partial magnetization can be conducted, such that the second magnetization step is not required. This paper deals with the influence of the cooling conditions on the orientation of the particles as well as the final magnetic properties, such as the resulting pole length accuracy. The cooling conditions are varied by using different materials for the cavity wall....