Micromachined rate and acceleration sensor

#The invention relates to an apparatus and methods for determining the acceleration and rate of angular rotation of a moving body, and in particular, one which is adapted to be formed, for example through micromachining, from a silicon substrate.

#The use of tactical grade inertia measuring units has been limited by their cost to high-priced systems such as military aircraft, missiles, and other special markets. The cost of inertia measuring units is dominated by the expensive discrete gyroscopes and discrete accelerometers and attendant electronics used to drive and convert these signals for use in computer systems.

#Other problems with inertial measuring units are high power consumption and large package size. The problems of high power consumption and large package size further limit applications to larger equipment boxes in equipment racks. For example, a hockey puck sized tactical grade navigator is not known in the prior art.

#Preferred embodiments of the invention are described below with reference to the following accompanying drawings.

#FIG. 1 is a top plan view of a unitary substrate out of which are formed a pair of accelerometers in accordance with a preferred aspect of the invention.

#FIG. 2 is an enlarged, fragmentary view of a portion of one of the FIG. 1 accelerometers, showing in particular, one force-sensing element configuration.

#Copending U.S. application Ser. No. 08/786,185, filed Jan. 20, 1997, incorporated herein by reference, describes and claims an apparatus and method for determining the rate of angular rotation of a moving body and, in particular, one which is adapted to be formed through micromachining of a silicon substrate.

#A basic sensor configuration is described in U.S. Pat. No. 5,241,861, issued Sep. 7, 1993, and U.S. Pat. No. 5,331,853, issued Jul. 26, 1994, commonly assigned and incorporated herein by reference. The described configuration includes two vibrating beam accelerometers fabricated in a dither structure from a monolithic silicon wafer. One limiting factor in rate bias accuracy is the modulation of the accelerometer due to coupling from the dither motion. This modulation can cause extreme phase angle sensitivity of the rate data. Also, external vibration of the package can couple into the rate channel due to this phase angle sensitivity. The invented sensor and methodologies through which it can be formed are directed to solving these and other problems.

#FIG. 1 shows a monolithic substrate for acceleration and angular rate sensing generally at 10. The substrate includes a support frame 12 including first and second posts 14, 16. The substrate further includes a first accelerometer 18 formed in the substrate. First accelerometer 18 has a proof mass 20 including first and second opposite edges 22, 24 respectively, and third and fourth opposite edges 26, 28 respectively. The proof mass includes first and second legs 30, 32 and a main body portion 34 connecting the legs and accommodating common movement of the legs relative to frame 12 in response to an acceleration force. First accelerometer 18 further includes a flexure 36 connecting first edge 22 of proof mass 20 to support frame 12. Flexure 36 defines a hinge axis HA.sub.1 for proof mass 20. Flexure 36 includes first and second spaced apart flexure portions 38, 40 respectively connecting the first and second legs 30, 32 to support frame 12. A portion of frame 12 which defines first post 14 extends intermediate first and second flexure portions 38, 40 and toward the second edge 24. More particularly, first post 14 is disposed between flexure portions 38, 40 and extends toward main body portion 34 and between legs 30, 32.