MEMS-integrated inertial measurement units on a common substrate

#This invention relates to the simplification, size reduction and cost reduction of Inertial Measurement Units (IMUs)

#Inertial Measurement Units (IMUs) measure the motion of a body in six degrees of freedom using a set of gyroscopes and accelerometers. A typical IMU comprises three gyroscopes and three accelerometers, each a single degree of freedom instrument. They are aligned with respect to three orthogonal axes. They are assembled onto a common member that is sometimes referred to as a “stable member” because it retains the relative alignment and positions of the instruments and, in gimballed guidance and navigation systems applications, it is held aligned to an inertial reference. Typically the instruments are self contained units with their own packages and electronics. And, usually they are representative of different designs, fabrication technologies and materials. IMUs are complex, large and expensive.

#This invention relates to the simplification, size reduction and cost reduction of IMUs through MEMS integration. MEMS (Microelectromechanical Systems) is the technology for fabrication and the basis for planar design and design methodologies. MEMS enables the batch fabrication of devices in large quantities to reduce cost. As the technology matures, MEMS will also enable the fabrication of devices having predictable functionality and uniformity. Perhaps not as well appreciated is that MEMS integrates parts into a completed entity. Further assembly and alignment is not required. The advantage of integration is that the uncertainty that normally accompanies the design and fabrication and assembly of separate parts based on dimensioning and tolerancing is reduced.

#Other objects, features and advantages will occur to those skilled in the art from the following descriptions of the preferred embodiments, and the accompanying drawings, in which:

#FIG. 1a depicts an embodiment of a planar gyroscope with a drive (outer) member that is oscillated about an axis that is normal to the plane and a responsive member that senses rotation rate about an axis in the plane.

#FIG. 1b depicts an embodiment of a planar gyroscope with a drive (outer)member that is oscillated about an axis in the plane and a responsive member that senses rotation rate about an axis in the plane.

#The invention incorporates gyroscope and accelerometer instruments on a common substrate to form a MEMS-integrated IMU. The instruments benefit from a common mechanical oscillation that is provided by the common substrate (also termed a common gimbal). For planar instruments, there are two mechanical oscillations possible: about an axis in the plane and about an axis normal to the plane. For each of these motions, there are candidate planar gyroscopes and accelerometers that are applicable. Each of these inertial measurement instruments comprises a responsive member that is coupled to the planar gimbal by flexures.

#MEMS gyroscopes and accelerometers are planar devices comprised of members that are flexurally connected to each other and the assembly to the case. Gyroscopes generally require two moving members. One member is driven into oscillation and the second member reacts to rotation rate by oscillating at the same frequency as the driven member at an amplitude that is proportional to input amplitude. Simple flexured accelerometers are either proof mass or pendulous devices that require one moving member. Tuned Flexure Accelerometers (TFA) (U.S. Pat. No. 6,338,274 B1) add a gimbal to the simple designs that is used to dynamically tune the mechanical response. The TFA requires two moving members. In this invention the greater benefit is realized for IMUs based on the larger number of two-member instruments. The simple accelerometers do not require the drive oscillation but can be included on the common member without degradation to their performance.

#To illustrate IMUs embodiments, some candidate gyroscopes and accelerometers are first identified. Others are possible. This list comprises one set of candidates.