The working principle of RLG can be illustrated by the first practical MEMS gyroscope in the world.

MEMS resonant gyroscope is a kind of inertial sensor for measuring angular velocity. It has many advantages, such as small volume, light weight, low cost, easy integration and so on. Therefore, it has wide application prospects in many fields.

Working principle of MEMS resonant gyroscope

Vibratory gyroscope is to produce gyroscopic moment by changing the direction of the vibrating plane of the vibrating object. Its main body is a high-frequency micro amplitude vibration element. It uses the Coriolis effect produced by the mass of high-speed vibration when it is driven to rotate by the base to sense angular motion.

The working principle of RLG can be illustrated by the first practical MEMS gyroscope in the world.

The figure above shows a monocrystalline silicon dual mass tuning fork gyroscope developed by Draper Laboratory of the United States. It adopts the working principle of resonant gyroscope to measure the y-direction angular rate input Ω 0. The vibration masses M1 and M2, as sensitive units, can vibrate in X and Z directions. The vibration in X direction produces velocity, which interacts with the angular rate input Ω 0 to produce Coriolis acceleration in Z direction. The vibrating mass is forced to vibrate by coriolis inertial force in Z direction. The magnitude of vibration amplitude in Z direction represents the magnitude of Coriolis acceleration, and then the magnitude of angular rate input can be calculated according to a simple proportional relationship.

  

Working principle diagram of tuning fork gyroscope

There is also a typical ring gyroscope, which is similar to hemispherical resonator gyroscope, but the ring structure is used in MEMS gyroscope at present. After the ring vibrates, the ring deforms into an ellipse (dotted line in Figure 2). The vibration velocity of the antinode is the highest, and the radial coriolis inertial force FC is generated by the angular rate input in Z direction under the influence of Coriolis effect, which forces the ring to produce elliptical vibration in 45 ° direction. The intensity of Coriolis effect can be calculated by detecting the vibration amplitude in 45 ° direction, and the magnitude of angular rate input can be obtained in proportion.

  

Structure and working principle of Vibrating Ring Gyroscope

Technical status of MEMS resonator gyroscope

MEMS resonator gyroscope is characterized by low power consumption, small size, low cost and batch production. Consumer electronics will play this feature to the extreme. The mysterious high inertial instrument has stepped down the altar because of MEMS technology and integrated into our daily life. In mobile phones, cars, even in our watches and clothes, it serves us all the time.

The military market with the biggest demand of high precision and high reliability is also increasingly favored by such technical advantages. More and more small or micro aerospace, aviation and weapon platforms make the overall miniaturization and scale possible because of the miniaturization of instruments. Drones are the best example. When the gyro inertial unit can be purchased at a price of less than ¥ 100, the flight control system as the core of UAV can be completed at a price of less than ¥ 500, and consumer UAVs with a price of ¥ 2000 or even lower are blooming everywhere.

Since 2010, the structure design and front processing technology of MEMS inertial instruments have become more and more mature, and packaging technology has become a research hotspot in recent five years. With the development of packaging technology, the integration of consumer electronics is getting higher and higher. For example, Bosch uses stack packaging method to realize 1.5mm × 1mm three-axis accelerometer instrument and 2.6mm × 2mm three-axis integrated gyroscope.

In recent years, MEMS inertial units with high integration are widely used in consumer electronic products. High density packaging technology meets the stringent requirements of volume, cost and power consumption for consumer electronics. For example, ST company, Bosch Company and invensense company all realize the packaging of 3-axis gyroscope, 3-axis accelerometer and 3-axis magnetometer in a single chip.

The results show that the stress release method of gyroscope sensitive structure based on package can improve the accuracy of the instrument obviously. So after 2010, sensonor invested a lot of research efforts to focus on the stress-free packaging technology of instrument sensitive structure.

Let’s talk about quartz tuning fork gyroscope again. Although it is still controversial in academic circles whether quartz tuning fork gyroscope belongs to the scope of MEMS concept, it has to be said that quartz processing technology has a longer history and more mature and stable technology than silicon MEMS. Therefore, quartz tuning fork gyroscope faced the market earlier, was applied more widely, and performed more stably, making it prosperous in 50 years of history. As a kind of piezoelectric material, it is more stable than quartz itself.

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