Circular Hall Transducer for Accurate Contactless Angular Position Sensing 

Laurent Sache *, Serge Reymond**, Pavel Kejik**, Mikael Sjöholm*, Daniel Bommottet*, Volker Gass*,  Lionel Gaillard+ and Radjan S. Popovic **   Abstract Demands for robust, reliable and accurate angular position sensing of space mechanism are increasing  steadily. As a consequence, contactless sensors providing an alternative to triblogical drawbacks of the  current sliding potentiometers represent a key factor for the development of future space applications. In  the framework of the ESTEC activity [1] covering the selection of an angular position sensor (APS) based on MEMS technology and in collaboration with the EPFL-LMIS [2], RUAG is currently carrying out the qualification of a new contactless angular position sensor based on the Hall Effect. Providing the angle without need of a complex algorithm, it offers a more reliable, lighter, less sensitive to vibrations and cost  effective sensing solution.   Introduction

Current rotary sensors are either potentiometers or encoders. Be it in the case where those systems are  placed on the outside or on the inside of the satellite bus, the environmental conditions are typically very  harsh.    Potentiometers cover low accuracy application in a range down to 0.4°. They have the advantage of simplicity, size, ease of implementation and low cost. Rotor and stator (track) typically have to be installed independently but this process is not extremely sensitive with regards to the relative alignment of brushes to track. The electrical interface is typically a 0 - 5V analogue one. On the other hand potentiometer reliability suffers from the sliding contact of a metallic brush on a plastic film with implemented conductive materials (carbon, etc). Various combinations of materials with and without lubrication have been applied but sufficient reliability could not be proven so far specifically for long time application like telecom (12 to 15 years). An alternative to such simple device would be the most demanding application. 

Encoders are typically used when high resolution and reliability is required but suffer from their complexity of the mechanical integration and the electrical interface. Encoders have a higher mass and in case of high exposure to radiation they have to be additionally shielded by a metallic housing that adds weight. The electrical interface is digital (serial or parallel) and thus more complex to handle compared to the one  of a potentiometer. Additionally encoders are expensive and normally come along with long lead times.  The ideal replacement of a potentiometer and/or encoder would be a sensor that combines both positive  characteristics:  From the potentiometer:  /g131 simple electrical interface  /g131 simple mechanical interface (low sensitivity to misalignment)  /g131 radiation resistance  /g131 small and low weight  /g131 low cost  From the encoder:  /g131 high resolution  * RUAG Aerospace, Nyon, Switzerland   ** Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland  + European Space Research and Technology Centre (ESTEC), Noordwijk, The Netherlands

Proceedings of the 39th Aerospace Mechanisms Symposium, NASA Marshall Space Flight Center, May 7-9, 2008  171