This thesis is focused on the development of a precision servo accelerometer. Acceleration is a physical quantity, which gains increasing interests in many systems with regard to motion measurement, control, automation or other measurement applications. For motion measurement, it is essential to measure low-frequency acceleration with high accuracy. Servo accelerometers with servo feedback loop have been most commonly used for this purpose.
The servo accelerometers can be basically divided into two categories by manufacturing process and its size: (a) micromachining servo accelerometers and (b) electromechanical servo accelerometers. Micromachining servo accelerometers have generated great interests in recent years. The use of surface micromachining and/or bulk micromachining offers the possibility of producing smaller, lighter and potentially cheaper devices by a batch process. However these new devices do not yet have the sensitivity to be used in precision motion measurement applications such as inertial navigation and guidance instruments. The inertial navigation system (INS) applications need accelerometers of which performance is roughly characterised by a maximum working range of ±20 g (where g is the acceleration due to gravity) with a sensitivity threshold (DC resolution) of $10^{-4}g$. Since precision acceleration is measured, the stability of performance of accelerometers is also important. That is to say, these applications require more stable and more accurate accelerometers than currently developed micromachining servo accelerometers by several orders of magnitude. Therefore electromechanical servo accelerometers which have complicated structures and larger size than micromachining servo accelerometers are still widely used in INS applications and have been designed and developed by several researchers.
This paper is concerned in a design of an electromechanical servo accelerometer for INS applications. Special design considerations are made to guarantee low sensitivity threshold and high thermal stability.
In order to guarantee low sensitivity threshold while maintaining robustness against shock, the push-pull type long flexures are used in this paper. To improve thermal stability, this paper suggests electromagnets as a source of magnetic field and develops the silicon case together with the temperature compensator. The silicon pendulum assembly and the modified inductance type pick-up is also developed to reduce assembling procedure. After assembling the accelerometer, static tests are carried out. Static test show a sensitivity threshold of $4.6 \times 10^{-5}g$ and a maximum measurement range of ±24g. The push-pull type long flexures reduces spring constant considerably.
