Sundstrand Data Control, Inc.

Sundstrand Corporation

Alliedsignal Inc.

Sundstrand Data Control Group

Rex B Peters

Rand H Hulsing, Ii

Brian L Norling

Kurt E Steinke

Charles K Lee

Jeffrey F Tonn

Victor B Corey

Aleksandar M Gogic

Arnold Malametz

Richard A Hanson

James R Woodruff

Craig J Cornelius

Richard A Hilliker

Lalit Kumar

Edward A Urbach

An accelerometer, preferably made by silicon micromachining, includes a proof mass or pendulum connected to an isolator with a pair of flexures defining a hinge axis HA. The flexures enable the pendulum to rotate about the hinge axis HA relative to the isolator. In order to constrain movement of the pendulum, a pair of resonators are coupled between the pendulum and the isolator. The isolator is connected to a support by way of a pair of flexures which increases the compliance of the connection between the isolator and the support. The flexures connected between the isolator and the support have a relatively smaller cross section than the isolator and the support and, thus, reduce the transmission of stresses across the flexures. In addition, as the flexures become more compliant, the isolator deflects under acceleration which counteracts the deflection of the proof mass which results in the cross coupling error. By properly selecting the stiffness for the flexures used to connect the support and the isolator, cross coupling error can essentially be eliminated.

K.sub.ip cancellation in a pendulous silicon accelerometer

A servo accelerometer includes a proof mass suspended by way of a flat leaf flexure suspended between upper and lower excitation rings. Electrically conductive material forming pick-off capacitance plates is disposed on opposing sides of the proof mass to form capacitive elements with respect to the excitation rings which, in turn, forms a position detector. In response to a force or acceleration along a sensitive axis (i.e., generally normal to the plane of the proof mass), the proof mass is displaced relative to the excitation rings causing a change in the capacitance of the capacitive elements. A servo system, which includes one or more electromagnets, returns the proof mass to its null or at rest position. In order to compensate for the transverse bending of the flat leaf flexure which results in the proof mass having two degrees of freedom, the accelerometer is configured such that the two degrees of freedom respond like a single degree of freedom with respect to the servo system. In particular, the accelerometer is configured such that the centroid of the position detector is disposed as near as possible to the center of percussion, which minimizes the dynamic sensitivity of the accelerometer to the location of the center of force which, in turn, allows the center of force to be moved near the center of mass for optimized static performance. By moving the center of force close to the center of mass and, therefore, near the center of percussion, sensitivity of the accelerometer to production variations in the position of the centroid of the position detector is minimized.

Wide-band servo accelerometer with flat leaf flexure suspension

A method for selectively etching a semiconductor wafer in the presence of an electrochemical etchant wherein the electrical potential of the area that is selectively etched is automatically changed to a potential at which the etching is inhibited once the desired etching in the area is completed. The method is described with respect to making an electrode tip for a tunnel current sensing device.

Method of making an electrode tip for a tunnel current sensing device

A rate detection system (10) uses a balanced resonant sensor (12) having first and second tines (14,16) interconnected with a mounting pad (20). A sensing circuit (50) including a tunnel effect displacement sensor (38) having a first probe (40) connected to the mounting pad (20) and a second probe (42) connected to a reference pad (32) detects an output signal having a Coriolis component. A feedback circuit provides a compensation signal to the balanced resonant sensor (12).

Coliolis rate sensor using tunnel-effect displacement sensor

A viscously coupled dual beam accelerometer. An accelerometer (60) includes a first proof mass (32') and a second proof mass (42'), which are respectively connected by flexures (36' and 46') to a first base (34') and a second base (44'). The first and second bases are clamped between a top enclosure (62) and a bottom enclosure (64), between which is defined a cavity (66) in which the first and second proof masses are disposed. A quartz crystal resonator (38') extends between the first proof mass and the first base; similarly, a quartz crystal resonator (48') extends between the second proof mass and second base. The quartz crystal resonators experience tension/compression in a push-pull mode when the accelerometer is subjected to acceleration along an acceleration-sensitive axis (26') that extends transversely through the proof masses. A fluid within the cavity couples the first and second proof masses together through a 'squeeze film damping,' due to their closely-spaced relationship to each other. As a result of this dynamic mutual damping of out-of-phase motion of the first and second proof masses, tracking errors in the signals produced by the quartz crystal resonators are minimized when the accelerometer is subjected to vibration at a frequency close to the resonant frequency of the proof masses.

Viscously coupled dual beam accelerometer

An accelerometer comprising a monolithic crystalline substrate, the substrate comprising a support, a proof mass, and a force transducer. The proof mass is connected to the support by one or more proof mass flexures that permit the proof mass to rotate with respect to the support about a hinge axis. One end of the force transducer is connected to the support, and the other end is connected to the proof mass by a transducer flexure. The transducer flexure has a thickness substantially less than the thickness of the transducer, such that when the proof mass rotates, the transducer rotates with respect to the proof mass about a transducer axis that passes through the transducer flexure. Preferably, the transducer axis is offset from the hinge axis in a manner so as to cancel nonlinearities in the force transducer, and the length of the proof mass along the pendulous axis is less than half the length of the transducer. Damping plates are positioned above and below the proof mass, and provide shock stops and damping.

Monolithic accelerometer with flexurally mounted force transducer

A vibrating crystal transducer for measuring temperature is disclosed. The crystal includes a single elongated vibrating beam that has a torsional mode resonant frequency that is a function of the temperature of the crystal. The torsional moments of the crystal are reverse symmetric with respect to a nodal line on the beam. The beam is contained in a frame that is secured to a sensor frame member. The beam is attached to the frame by a pair of opposed mounting posts that are in line with the nodal line on the beam. The beam, the beam frame (16) and the mounting posts are formed out of an integral section of crystalline material. When the beam is vibrated, the reverse symmetrically opposed torsional moments along the beam cancel each other out and, consequently, no torsional energy is transmitted through the mounting posts to the beam frame or the sensor frame. Since the beam frame does not serve as a recipient for the torsional energy, torsional energy is not lost through the beam frame so that the beam has a relatively high quality factor and torsional vibration of the beam cannot cause the crystal to eventually work loose of the sensor frame at the beam frame.

Crystal temperature transducer

A method and apparatus for determining a change in velocity of a body following a power disruptive event. An accelerometer (10, 50) includes quartz crystals (16 and 18, 60 and 62), which produce output signals indicative of the acceleration to which a body connected to the accelerometer is subjected. The acceleration measured is directed along the sensitive axis of the accelerometer. The quartz crystals are selected to have different scale factors, K.sub.1 and K.sub.2, which define the change in frequency of the quartz crystal from its no-load resonant frequency as a force is applied to it. The quartz crystals are connected between a supporting case (14) and a proof mass (12) so that a given acceleration applied to the proof mass along its sensitive axis causes one of the crystals to experience a tension force and the other to experience a compression force. A processor (86) determines the change in velocity of the body as a function of the change in phase of the signals produced by the quartz crystals at a time, t.sub.1, and a subsequent time, t.sub. 2, and further in response to the scale factors, K.sub.1 and K.sub.2. Since the quartz crystals continue to oscillate during a brief interruption of their driving signal, the change in velocity of the body during a time interval from t.sub.1 to t.sub.2 can be determined after recovery from a brief power disruptive event that has occurred during that interval.

Method and apparatus for storing velocity data

A technique for reducing the effects of aliasing in a frequency output sensor system. The system includes a sensor for producing a sensor output signal at a frequency that varies within a modulation range as a function of an input parameter. The system also includes a processor for measuring the frequency of the sensor output signal at a sequence of sample times. The invention provides an analog filter for filtering the sensor output signal. In a first embodiment, the filter has an increasing phase lag versus frequency characteristic within the modulation range. In a second embodiment, the filter comprises a phase lock loop having frequency dividers in the input signal path and in the feedback path.

Anti-aliasing for frequency output sensors

A compact, low g range accelerometer comprising a support (22), a proof mass (20), flexures (24, 26) for mounting the proof mass to the support, and a force sensing element (40). The proof mass has a single rotational degree of freedom about a hinge axis (H) perpendicular to the accelerometer's sensitive axis (S). The force sensing element is positioned along a line that is normal to the hinge axis and that lies in a plane that is normal to the hinge axis and that passes through the center of gravity (46) of the proof mass. The perpendicular distance between the hinge axis and the force sensing element is less than the distance between the hinge axis and the center of the proof mass. The force sensing element may be parallel to the pendulous axis, to produce an extremely compact accelerometer, or may be oriented at an acute angle with respect to the pendulous axis, such that the line along which the force sensing element is positioned passes through the center of percussion of the proof mass.

Low profile accelerometer

A matched pair of vibrating beam force transducers for use in an instrument such as an accelerometer, to provide enhanced linearity and common mode tracking, while decreasing the possibility of lock in or cross-talk between the transducers. In a preferred embodiment, first and second transducers are provided, the transducers producing respective first and second output signals having respective first and second frequencies. The transducers are connected in an arrangement in which for a given acceleration, one frequency increases and the other frequency decreases. The first transducer comprises a pair of first beams, and the second transducer comprises a pair of second beams. The beam dimensions are selected such that the Euler buckling constants of the first and second transducers are substantially equal to one another, and such that the first and second frequencies are different from one another when the acceleration is zero and preferably are different from one another throughout the operating range of the accelerometer. In preferred arrangements, the transducer beams have a constant thickness, and the transducers have common axial stiffnesses.

Matched pairs of force transducers

An accelerometer comprising a body (10, 16, 12), a proof mass (18, 30, 32), a mounting strucutre comprising flexures (20, 22) for mounting the proof mass to the body, and force sensing elements (34, 38). The flexures permit translational motion of the proof mass with respect to the body along a sensitive axis SA and rotation of the proof mass with respect to the body about a hinge axis HA that is perpendicular to the sensitive axis. Acceleration of the accelerometer along the sensitive axis results in translational motion of the proof mass along the sensitive axis. The force sensing elements reacts to such translational motion by producing a signal indicative of acceleration along the sensitive axis. In a preferred embodiment, the mounting structure comprises a pair of fused quartz flexures that are oppositely directed with respect to one another, and the force sensing elements comprise a pair of vibrating beam force transducers that are connected to the proof mass on opposite sides of the hinge axis from one another. The described assembly method for accelerometers comprises forming bridges between the proof mass and body, the bridges being removed after attachment of the force sensing elements.

Translational accelerometer and accelerometer assembly method

A Coriolis rate sensor comprising first and second accelerometers mounted with their force sensing axes parallel to a common sensing axis. The accelerometers are vibrated along arcs in response to a periodic drive signal at a first frequency, each arc being tangent to a vibration axis normal to the sensing axis. The accelerometer output signals are demodulated to determine angular rate, as well as to detect the phase shift between the drive signal and the periodic compounds of the output signals. In one arrangement, the detected phase shifts are used to drive a phase servo that tends to reduce the bias error caused by interaction between the phase shifts and misalignments of the accelerometers with respect to the sensing axis. In another arrangement, the phase shifts are used to calculate a bias term for correcting the measured angular rate. A single accelerometer embodiment is also described.

Angular rate sensor with phase shift correction

A system and method for precisely and continuously estimating the path length between the entrance of a borehole and a probe (10) which is supported by an elastic cable (14) and carries a gyrocluster (42) and accelerometer cluster (40). The precise estimate of borehole path length is used to aid the inertial navigation performed within the survey system and is selectively determined by integration of either the rate at which the probe (10) moves along the borehole or a compensated cable feed rate that is based on the rate at which the cable (14) passes into or out of the borehole with correction being made for changes in temperature and gravity induced cable stretch. Selection of the rate to be integrated at any given time being determined by whether the rate at which probe (10) moves along the borehole exceeds the compensated cable feed rate by a predetermined amount.

Apparatus and method for determining the position of a tool in a borehole

Disclosed is an inertial navigation borehole survey system wherein the signals supplied by accelerometers (40) that are contained within the borehole survey system probe (10) are corrected for gravitational gradients encountered as the probe (10) travels through a borehole (12). The gravity correction is effected in the survey system signal processor (24) and is based on a gravity gradient signal that mathematically corresponds to: ##EQU1## where f represents the specific force due to gravity; f.sub.o represents the specific force of gravity at wellhead (20) of borehole (12); R.sub.o represents the average radius of the earth; .rho.(H) represents the local density of the geological formation penetrated by the borehole as a function of depth H; and .rho..sub.ave represents the means density of the earth. In utilizing the gravitational gradient to generate a gravity correction signal, the signal processor (24) effects a summation process that mathematically corresponds to: ##EQU2## where (.DELTA.H).sub.i represents the depth change between the 'ith' signal processing cycle and the nextmost antecedent processing cycle, and, the summation range extends from the first signal processing cycle performed during the borehole survey through the final signal processing cycle of the borehole survey operation.

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Woodinville, WA, United States of America

Rex B Peters