Abstract: The invention comprises a velocity sensor (10, 30, 50, 60, 70, 110) that measures velocity in only one degree of freedom and is insensitive to the other five degrees of freedom. The velocity sensor uses differential flux splitting, and by sensing changes in flux, common mode effects are removed. In practising the invention, a permanent magnet (17, 33, 55, 65, 71, 131) is used to create a flux field, and multiple return paths are used to split the flux. A plurality of pole pieces (20-21, 39-40, 58-59, 66-67, 72-73, 111-112) simultaneously move an equal amount in relation to the return paths for differentially varying the amount of flux carried by each return path (13-14, 34-36, 52-53, 63-64, 73A-C and 75A-C, to thereby induce a differential voltage in secondary coils (15-16, 37-38, 56-57, 68-69, 80-83 and 90-93, 140-143 and 150-153). Detection means (not shown) is used to sense the change in voltage and provide an indication of the sensed velocity.

Abstract: A sensor (10) for measuring angular rate and linear acceleration of a body, in which first and second rotors (30, 31), each carrying a plurality of accelerometers (44, 49), are mounted for counter-rotating dithering motion on opposite sides of a base plate (11). A single permanent magnet (70) is mounted centrally of the base plate, with one pole (71) disposed adjacent the first rotor and the other pole (72) disposed adjacent the second rotor. First and second X-shaped pole pieces (80, 81) are mounted at the respective opposite poles of the magnet, and a plurality of velocity sensing pick-off coils (86) are mounted on the arms (82, 83, 84 and 85) of the pole pieces for cooperation with flux splitting protrusions (34, 35 and 36) on the rotors. The arms of the pole pieces are associated with the flux splitting protrusions so that differential flux splitting is obtained as the rotors are rotated in opposite directions.

Abstract: Apparatus and method for counting frequency of a signal with improved resolution. Frequency counters (10, 60, and 100) accumulate clock cycles from a reference oscillator (20) during a sample interval. In the simplest form of the frequency counter, the reference clock signal is inverted and both the noninverted and inverted clock cycles are accumulated in separate counters (40 and 44). The accumulated counts are totaled in a summing circuit (48) and divided by two to determine their average, thereby doubling the resolution of the frequency counter. A more complex embodiment of the invention corrects a raw count of cycles of an input signal (12) that are accumulated during an extended sample interval defined by successive rising edges of a sample signal (114).

Abstract: A dual-edge frequency counter and method for minimizing the effects of duty cycle modulation. In its simplest form, a dual-edge counter (50) includes a first counter (52) that accumulates reference clock pulses between successive rising edges of an input signal. An input signal is also applied to an inverter (54), which inverts the square wave signal prior to applying it to a second counter (56) that also accumulates reference clock cycles between successive rising edges of the inverted sensor signal. A summation junction (60) totals the accumulated counts from the first and second counters so that they can be averaged by a divider (62), which divides the total count by two. The technique is also employed in connection with a frequency counter that includes an integer counter (72) for totaling the number of cycles of the sensor signal occurring during a sample time defined by successive gate signals.

Abstract: A torque motor for rotatably driving a rate sensor (10, 100) which includes a permanent magnet (30) that is magnetically coupled to an upper rotor (18, 106) and a lower rotor (44, 110). At three sites, the upper rotor includes an upper tab (60), which is centered between two electromagnetic coils (56, 58). Similarly, at each site, the lower rotor includes two lower tabs (62) that extend adjacent opposite faces of the electromagnetic coils. With no electrical current flowing through the electromagnetic coils, flexures (46) that connect the upper and lower rotors to a base (12) provide a spring bias force sufficient to maintain the upper tab centered in a slot (66) and thus, equidistant between each of the two lower tabs. As the electric current flows through the electromagnetic coils, distribution of the magnetic flux produced by the permanent magnet changes so that the upper tab is attracted toward one of the electromagnetic coils and repelled from the other.

Abstract: A transformer and method for sensing displacement, A linear variable displacement transformer (LVDT) 50, 100, 150, 200, and 250) is disclosed with respect to several embodiment,s each including a core (52, 102, 152, 202, and 252) having a primary leg (56, 104, 154, 204, and 254), and two secondary legs (58 and 60, 106 and 108, 158 and 160, 206 and 208, and 258 and 260). A primary coil (54, 110, 156, 210, and 264) is disposed on the primary leg, and secondary coils (62 and 64, 112 and 114, 162 and 164, 212 and 214, and 266 and 268) are disposed on the secondary legs. Pole pieces (70 and 72, 120 and 122, 170 and 172, 222 and 224, and 274 and 276) are disposed in gaps between the primary leg and each secondary leg, so that they control the reluctance to a magnetic flux produced by an electric current flowing thorugh the primary coil.

Abstract: A compact torque motor providing bi-directional, limited angle reactionless torque to opposed structures. A motor (10, 150) includes an X-shaped core (12), and first and second pole pieces (14 and 16), which are disposed at opposite sides of the core. Two opposed legs on the X-shaped core (12) comprise a first core section (18), which is transverse to a similar second core section (20). A first electromagnetic coil (22) is formed on the first core section and a second electromagnetic coil (24) on the second core section. When the first and second electromagnetic coils are alternately energized, tabs (38, 40, 44, and 46) disposed approximate the ends of the first and second pole pieces are attracted to the resulting magnetic poles (26 and 28, 30 and 32), causing the pole pieces to counter-rotate back and forth about a central axis (48). Magnetic flux developed by the first and second electromagnetic coils is conveyed through the tabs and the first and second pole pieces between the opposite magnetic poles.

Abstract: Apparatus and method for establishing a level plane and with respect to the level plane, vertically aligning an acceleration sensitive axis of a gravity measurement device (10). The gravity measurement device includes an accelerometer (68), which is rotatably mounted on a gimbal shaft (62) within a gimbal frame (54). The gimbal frame is also rotatable about a longitudinal axis that is preferably oriented at a right angle to the longitudinal axis of the gimbal shaft. A stepping motor (20) is connected through an antibacklash gear (30), an idler gear (32) and an antibacklash gear (48) to a drive shaft (50). Rotation of this drive shaft causes the accelerometer to rotate about the gimbal shaft. In a similar fashion, a stepping motor (22) is drivingly connected to a drive shaft (56), used to rotate the gimbal frame.

Abstract: A technique is described for tailoring the configuration of electrodes on a piezoelectric beam such that the tendency of the beam to vibrate in a predetermined flexure mode is enhanced. The mode has a predetermined longitudinal strain versus longitudinal position profile. At least two electrodes are mounted on the beam, and the configuration of at least one electrode varies as a function of longitudinal position, such that when a voltage difference is applied between the electrodes, the longitudinal force produced by the electrodes, as a function of longitudinal position, approximates the longitudinal strain versus longitudinal position profile. The configuration may be varied by varying the width of the electrode or the position of the electrode on the underlying beam surface.

Abstract: 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.

Abstract: A Coriolis rate sensor for determining both angular rate and linear acceleration with respect to three orthogonal axes. A first embodiment of the rate sensor (10) includes three pairs of accelerometers (26, 28, and 30) mounted on counter-rotating frame members (20, 22). The accelerometers are mounted with their sensitive axes antiparallel with each other, forming an acute angle with the common axis (40) about which the upper and lower frame members are counter-rotated back and forth in a dither motion. The upper and lower frame members are connected to a baseplate (12) by flex links (32), which are aligned radially about the axis. The flex links provide a relatively rigid support (in compression) between the frame members and the centrally disposed baseplate, yet readily permit counter-rotation of the two frame members. A link (56) prevents all but relative rotational movement between the frame members and baseplate.

Abstract: Disclosed is a borehole survey system that utilizes strapdown intertial navigation techniques for mapping a borehole while the system probe (10) is continuously moved along a borehole (12) by means of a cable (14) that is wound on a cable reel (16). Signals representative of the acceleration of the probe (10) relative to the three axes of a probe body coordinate system (34)) and signals representative of angular rotation of the probe (10) about the three axes of the probe body coordinate system are processed within a signal processor (24) to obtain signals that represent probe velocity and probe position in a level coordinate system (36) that is fixed in orientation relative to the geographic location of the borehole (12).

Abstract: A device and method for measuring the frequency of an input signal by measuring the number of cycles of the input signal that occur in a sample interval between successive sampling times t.sub.n. An integer counter determines an estimated integer number of input signal cycles, and fraction counters determine fractional counts by counting cycles of a clock signal during time intervals between a first measurement time before the sampling time and a second measurement time after the sampling time. A correction circuit refines the fractional counts by determining the phase relationships between the clock and input signals at each measurement time. The correction circuit includes a constant current source, a capacitor, a first switch connected between the constant current source and a reference potential, a second switch connected between the constant current source and the capacitor, and a control circuit for the switches.

Abstract: A borehole survey instrument has a probe with a polarized light system for transmitting a signal representing the angular orientation of the probe to the surface. Light from a source in the probe is directed through a polarized filter with an axis of polarization orthogonal to the longitudinal axis of the probe. The polarized light beam is transmitted to the surface through an optical fiber light conduit. The angle of polarization is detected with a rotating polarizing filter and provides a measure of the probe orientation. In surveying a borehole, azimuth is determined from inclinometer measurements. The probe orientation in vertical sections of the borehole is measured by the polarized light system. Two measures of borehole azimuth are combined, providing an improved measure of azimuth in boreholes near vertical and near horizontal.

Abstract: A borehole survey instrument has a probe with a polarized light system for transmitting a signal representing the angular orientation of the probe to the surface. Light from a source in the probe is directed through a polarizing filter with an axis of polarization orthogonal to the longitudinal axis of the probe. The polarized light beam is transmitted to the surface through an optical fiber light conduit. The angle of polarization is detected with a rotating polarizing filter and provides a measure of the probe orientation. In surveying a borehole, azimuth is determined from inclinometer measurements. The probe orientation in vertical sections of the borehole is measured by the polarized light system. Two measures of borehole azimuth are combined, providing an improved measure of azimuth in boreholes near vertical and near horizontal.

Abstract: A transducer for sensing the angular position or rate of change of displacement of a housing of a borehole survey instrument with respect to a reference position includes a rotor magnetically suspended within a stator which is in turn secured to the housing. The rotor is constrained by the magnetic suspension to rotate about a single axis relative to the stator. A frame of reference is established for the transducer, against which subsequent measurements are compared. Optical sensing means are included for sensing the movement of the rotor about the axis of motion to develop an indication of the angular position or rate of change of position of the housing.

Abstract: A borehole survey instrument has a probe with a polarized light system for transmitting a signal representing the angular orientation of the probe to the surface. Light from a source in the probe is directed through a polarizing filter with an axis of polarization orthogonal to the longitudinal axis of the probe. The polarized light beam is transmitted to the surface through an optical fiber light conduit. The angle of polarization is detected with a rotating polarizing filter and provides a measure of the probe orientation. In surveying a borehole, azimuth is determined from inclinometer measurements. The probe orientation in vertical sections of the borehole is measured by the polarized light system. Two measures of borehole azimuth are combined, providing an improved measure of azimuth in boreholes near vertical and near horizontal.

Abstract: An improved mounting between a cylindrical package, containing a sensitive instrument, and a protective cylindrical housing disposed thereabout. Plugs at opposite ends of the housing each have a conical recess opening toward the other plug and between which the package is confined. O-rings at each end of the package engage the tapered wall of the adjacent recess and absorb longitudinal and radial shock and center the package within the housing. To restrain relative rotational movement between the housing and instrument package, a plurality of coil springs are disposed within aligned bores in an end of the package and the adjacent plug.

Abstract: To provide for accurate determination of azimuth in a borehole survey apparatus, a downhole probe is provided with two or more sections connected by torsionally rigid, flexible joint assemblies with provisions for generating signals that represent the relative inclination and azimuth of one probe section from another. These signals are combined with inclination signals obtained from a set of accelerometers in one of the probe sections in a signal processing unit to generate signals that represent the direction and depth of the borehole.

Abstract: An improved capacitive pick-off circuit is provided by utilizing a reference current generator to apply a square wave to a pick-off capacitor and the resulting voltage across the capacitor is then applied to a fixed capacitor. The resulting fixed capacitor current then provides a measure of the capacitance of the pick-off capacitor. A differential capacitive pick-off circuit is provided by applying the reference current to each pick-off capacitor and providing a fixed capacitor for each of the pick-off capacitors. The resulting fixed capacitor currents are combined and the resulting differential current is used as a measure of the difference in capacitance or the difference in the gaps between the plates of the capacitors.