1. Field of the Invention
The present invention relates to an angular rate sensor used for, for example, shaking detection in a video camera, motion detection in a virtual reality apparatus, or direction detection in a car navigation system and, more specifically, relates to a small vibrating gyroscopic sensor including a cantilever vibrator and a method of adjusting the same.
2. Description of the Related Art
As a known commercial angular rate sensor, a vibrating gyroscopic sensor that is configured to detect angular rate by vibrating a cantilever vibrator at a predetermined resonance frequency and detecting the Coriolis force that is generated due to the angular speed with a piezoelectric device is widely used.
A known vibrating gyroscopic sensor is advantageous in that it has a simple mechanism, a short start-up time, and a low production cost. Such a known vibrating gyroscopic sensor is mounted on an electronic device, such as a video camera, a virtual reality apparatus, or a car navigation system, so as to function as a shaking detection sensor, a motion detection sensor, or a direction detection sensor, respectively.
A known vibrating gyroscopic sensor is produced by constructing a vibrator having a predetermined shape by using a machine to cut out a piezoelectric material. As the size and weight of components mounted on a known vibrating gyroscopic sensor have been reduced and the functions and performance of the components have been improved, size reduction and performance improvement of vibrating gyroscopic sensors have been required. However, it is difficult to produce a small and highly accurate vibrator due to a limit of the processing accuracy of machining.
Therefore, recently, a vibrating gyroscopic sensor including a cantilever vibrating element by employing thin film technology used in a semiconductor process so as to form a pair of electrode layers sandwiching a piezoelectric thin film on a silicon substrate has been proposed (for example, refer to Japanese Unexamined Patent Application Publication No. 7-113643). By reducing the size and thickness, such a vibrating gyroscopic sensor can be combined with other sensors used for other purposes to produce a complex and advanced system.
The vibrator of a vibrating gyroscopic sensor is often shaped as a prism, but it is difficult to produce a completely symmetric vibrator through a machining process or a thin film formation process. Therefore, the produced vibrator will be asymmetric with respect to the center line. When an asymmetric vibrator is vibrated, the vibration direction of the vibrator will be tilted with respect to the center line of the vibrator and will not be perpendicular to the support substrate. When the vibration direction of the vibrator is tilted, the magnitudes of the signals generated at the pair of detection electrodes that are symmetrically provided on the vibrator will differ. As a result, the characteristics of the vibrator will be unstable.
Accordingly, for a known vibrating gyroscopic sensor, the surface of an asymmetric vibrator is ground to adjust the mass balance of the vibrator (refer to Japanese Unexamined Patent Application Publication No. 2000-65579) or the vibration characteristics of the vibrator are adjusted at the positions where the vibrator is fixed to the support substrate (refer to Japanese Unexamined Patent Application Publication No. 2001-330440).