Injection Molding of Signal Generators for Hallsensor-Arrays

• Applicant: Professor Dr.-Ing. Dietmar Drummer
• Subject Area: Plastics Engineering
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 238855620

In this project, the effects of various process parameters on the pole pitch accuracy in the production of multipolar magnets by injection molding will be investigated. The pole pitch accuracy is very important for the accurate detection of the angle with so-called "Hall-effect sensor arrays" that can be used in rotary encoders for determining the rotation angle. The Hall-effect sensor arrays reach the position resolutions that previously were reserved for optical encoders. The prerequisite, how-ever, is a high accuracy of the pole width, since the accuracy of the angular determination with the "Hall-effect sensor arrays" strongly depends on the precision of the width of each pole. For example a pole width deviation of 0.1 mm in the hall array AS 5304 causes a measurement error of approximately 0.025 mm. For the so-called "Hall-effect sensor arrays" mainly magnetically isotropic, elastic magnetic tapes are used, which are magnetized in a complex process by means of special multipolar magnetization devices within an additional manufacturing step. But it would be also possible to use an ansisotropic pole-oriented magnetic rings which can be aligned multipolar directly in injection molding. This would allow very economical "off-tool" manufacturing of signal generator for the precise angle sensors. The injection molding process also provides the opportunity to combine these magnetic rings with other functional elements, such as bushings, shafts, gears, or magnetic sensors, that can be manufactured directly in the two shot injection molding or insert molding process.The magnetic filler orientation by injection molding takes place during the injection and holding pressure. In these phases, the filler particles are in motion, and the viscosity of the polymer matrix changes very dynamically. This can lead to inaccuracies in the formation of the multi-polar structure inside the magnet. A technical requirement for the use of the injection molding magnetized magnets, is the elaboration of the factors influencing the accuracy of the pole width to achieve the the most accurate pole as a target. Since the height of the peak flux density is not relevant for the accuracy of the angle determination, the variables that determine the flux densities at peak will be not investigated under this project.The aim of this research project is the systematic investigation of the influences of material, process (gating, process parameters) and geometry on the pole pitch as well as the modeling and simulation of the process behavior and derivation of design rules for the manufacturing of precise signal generators.

• DFG Programme: Research Grants
• Major Instrumentation: Multipolares Magnet-Spritzgießwerkzeug
• Instrumentation Group: 2210 Kunststoffpressen und -spritzgußgeräte