Читать книгу Whole-Angle MEMS Gyroscopes - Doruk Senkal, Andrei M. Shkel - Страница 16

Nondegenerate mode CVGs are currently being used in a variety of commercial applications due to ease of fabrication and lower cost. Most common implementations utilize two to four vibratory modes for sensing angular velocity along one to three axes. This is commonly achieved by forcing a proof mass structure into oscillation in a so‐called “drive” mode and sensing the oscillation on one or more “sense” modes. For example, the ‐axis of the gyroscope in Figure 1.1, can be instrumented as a drive mode and the ‐axis can be instrumented as a sense mode. When a nonzero angular velocity is exerted (i.e. along the ‐axis in Figure 1.1), the resultant Coriolis force causes the sense mode (i.e. the mode along the ‐axis in Figure 1.1) to oscillate at the drive frequency at an amplitude proportional to input angular velocity.

Resonance frequency of sense modes are typically designed to be several hundreds to a few thousand hertzs away from the drive frequency. The existence of this so‐called drive‐sense separation () makes nondegenerate mode gyroscopes robust to fabrication imperfections. However, a trade‐off between bandwidth and transducer sensitivity exists since smaller drive‐sense separation frequency leads to higher transducer sensitivity, while the mechanical bandwidth of the sensor is typically limited by drive‐sense separation ().

Nondegenerate mode gyroscopes are typically operated using open‐loop mechanization. In open‐loop mechanization, “drive” mode oscillation is sustained via a positive feedback loop. The amplitidue of “drive” mode oscillations are controlled via the so‐called Amplitude Gain Control (AGC) loop. No feedback loop is employed on the “sense” mode, which leaves “sense” mode proof mass free to oscillate in response to the angular rate input.