Sensors 2015, 15, 10146-10165; doi:10.3390/s150510146 sensors
ISSN 1424-8220 www.mdpi.com/journal/sensors
A New MEMS Gyroscope Used for Single-Channel Damping
Zengping Zhang 1,*, Wei Zhang 2, Fuxue Zhang 2 and Biao Wang 1 1 School of Computer and Information Management, Inner Mongolia University of Finance and
Economics, Hohhot 010070, China; E-Mail: firstname.lastname@example.org 2 Sensing Technique Research Center, Beijing Information Science and Technology University,
Beijing 100101, China; E-Mails: email@example.com (W.Z.); firstname.lastname@example.org (F.Z.) * Author to whom correspondence should be addressed; E-Mail: email@example.com;
Tel.: +86-471-5300-499; Fax: +86-471-5300-500.
Academic Editor: Stefano Mariani
Received: 24 January 2015 / Accepted: 23 April 2015 / Published: 30 April 2015
Abstract: The silicon micromechanical gyroscope, which will be introduced in this paper, represents a novel MEMS gyroscope concept. It is used for the damping of a single-channel control system of rotating aircraft. It differs from common MEMS gyroscopes in that does not have a drive structure, itself, and only has a sense structure. It is installed on a rotating aircraft, and utilizes the aircraft spin to make its sensing element obtain angular momentum. When the aircraft is subjected to an angular rotation, a periodic
Coriolis force is induced in the direction orthogonal to both the angular momentum and the angular velocity input axis. This novel MEMS gyroscope can thus sense angular velocity inputs. The output sensing signal is exactly an amplitude-modulation signal. Its envelope is proportional to the input angular velocity, and the carrier frequency corresponds to the spin frequency of the rotating aircraft, so the MEMS gyroscope can not only sense the transverse angular rotation of an aircraft, but also automatically change the carrier frequency over the change of spin frequency, making it very suitable for the damping of a single-channel control system of a rotating aircraft. In this paper, the motion equation of the MEMS gyroscope has been derived. Then, an analysis has been carried to solve the motion equation and dynamic parameters. Finally, an experimental validation has been done based on a precision three axis rate table. The correlation coefficients between the tested data and the theoretical values are 0.9969, 0.9872 and 0.9842, respectively. These results demonstrate that both the design and sensing mechanism are correct.
Sensors 2015, 15 10147
Keywords: MEMS gyroscope; sensing element; motion equation; steady state solution 1. Introduction
For rotating aircraft, the attitude motion usually has three degrees-of-freedom (also called three channels) including pitch, yaw and rolling. According to the channel selection, the control systems of an aircraft can be divided into single-channel control systems and multi-channel control systems.
For some aircraft, which rotate around their longitudinal axis at high rate, a single-channel control system is a good choice [1–3], with many benefits such as less equipment, simple structure, light mass and a space saving layout. In the stable loop of a single-channel control system, the angular rate gyroscope is the key device. It is responsible for measuring the pitch and yaw of the rotating aircraft body, then it feeds the output signal back to the input end of the control system so that control system can adjust flight accuracy in time.
With the development of MEMS technology, MEMS gyroscopes are widely used in the areas of inertial navigation and guidance, since they many advantages including low cost, light mass, small volume and anti-shock properties, etc. [4–6]. Most MEMS gyroscopes are basically a vibratory gyroscope based on Coriolis force [7–10].
Common MEMS gyroscopes not only have sense structures, but also drive structures. In order to attain the maximum possible response gain and sensitivity, it is necessary to utilize resonance in both the drive and sense modes. This is mainly achieved by structure design or tuning the drive structure and sense structure resonant frequency to match . This paper will introduce a novel MEMS gyroscope, which has no drive structure, and only a sense structure [12,13]. It is mounted on a rotating aircraft, and can smartly determine the angular momentum by using the spin of the rotating aircraft, so it does not need a drive structure. Its proof-mass only has the detecting mode and its structure design is relatively simple, so its fabrication process is also not complex.
In addition, because of the high rate spin of rotating aircraft, a Magnus effect will exist. Generally, when we need to measure a transverse angular velocity input, two common MEMS gyroscopes will be orthogonally mounted on the rotating aircraft, and both the pitch channel and the yaw channel would produce coupling . In applications, it is found that the measured precision will be reduced and some form of compensation is usually necessary for common gyroscopes.
The non-driven MEMS gyroscope, which will be introduced in this paper, is installed on the rotating aircraft. When the aircraft is subjected to a transverse rotation, it can directly sense the transverse angular velocity input. In other words, it senses the resultant angular velocity of pitch and yaw. The amplitude of the output signal is proportional to the transverse angular velocity input. Then the output signal will be directly fed back to the input end of the control system, so the non-driven
MEMS gyroscope does not need to compensate for the influence of the Magnus effect. What is more, it can automatically change the carrier frequency of the output signal with the change of spin frequency of the rotating aircraft, making it very suitable for damping in the stable loop of a single-channel control system for a rotating aircraft.
Sensors 2015, 15 10148 2. The Sensing Mechanism
The sensing element of the MEMS gyroscope is fabricated using a bulk micromechanical process on a single-crystalline silicon wafer. Figure 1 is the structural diagram and the vibrating mode of the sensing element. 1