Gap regulation for suspended rotating disks in microgyroscopes

Abstract

Microactuators (the power supply in small machines) play an important role in microelectromechanical systems (MEMS). Electrostatic combs, for example, provide linear motion. Magnetic actuators are particularly interesting because of their controllability. They have been studied for years. Yet the drive power of the typical planar-coil design1 in such devices is extremely limited. Moreover, the practical fabrication process is imperfect, giving rise to problems such as undesired bubbles or cavities inside a microsolenoid (looped structure) coil.2 To overcome the disadvantages of the traditional design, we propose an innovative pyramidal solenoid that performs the dual functions of actuator and sensor. The magnetic module is basically similar to a microscale linear variable differential transformer (LVDT), which actively adjusts the height of the rotating seismic disk used in a gyroscope. When the microgyroscope is subjected to an angular excitation (x or y axis) that is perpendicular to the principal spinning axis (z axis), the pitch angle (x or y axis) of the rotating disk responds accordingly. Because of the Coriolis effect (an artifact of the earth’s rotation), this induced pitched motion can be used to estimate the angular rate exerted. We designed a micromagnetic height adjuster (MMHA) for microgyroscopes that consists of four identical LVDT pairs, distributed evenly 90◦ apart in a circle.3, 4 Each pair contains two sets of LVDTs, one above and the other below the disk. Each LVDT set comprises three pyramids (see Figure 1) whose primary winding is located between two secondary windings. The rotating disk is sandwiched between four LVDT pairs (see Figure 2). The nominal gap between the rotating disk and the LVDT is set at 10μm. The key role of the primary winding is to regulate the gap change when it is perturbed by disk-mass eccentricity or Figure 1. Individual set of micromagnetic height adjusters (MMHAs).