GB2145824A

GB2145824A - Angular rate sensor utilizing parallel vibrating accelerators

Info

Publication number: GB2145824A
Application number: GB08422024A
Authority: GB
Inventors: Rex B Peters
Original assignee: Sundstrand Data Control Inc
Current assignee: Sundstrand Data Control Inc
Priority date: 1983-09-02
Filing date: 1984-08-31
Publication date: 1985-04-03
Also published as: GB8422024D0; HK20387A; AU2896484A; SE8404319L; FR2557978A1; IT8448741A0; NL8402552A; AU554302B2; JPS6066110A; FR2557978B1; GB2145824B; CH661358A5; SE8404319D0; IL72542A0; BE900483A; ZA846116B; CA1215245A; DE3431615A1; IL72542A; NO843472L

Abstract

Inertial measurement of the angular rotation and translational motion of a structure can be provided by a pair of vibrating accelerometers 10, 12 aligned in a side-by-side arrangement with their force sensing axes A<1>z, A<2>z in the same plane and vibrated to and away from each other in that plane along an axis normal to their force sensing axes. <IMAGE>

Description

SPECIFICATION N Angular rate sensor utilizing parallel vibrating accelerometers Related 'Patent Applications This application relates to co-pending U.S.

Patent Applications Serial No. R57,714, filed March 12, 1982, Serial No. 3 ',715, filed March 12, 1982 and Serial No. 528776, filed September 02, 1 983 which are directed to apparatus utilizing moving accelerometers to measure the specific force and angular rate of a moving body.

Technical Field The invention relates to the field of angular rate determination utilizing moving accelerometers and more particularly to angular rate detectors using paired accelerometers.

Background of the Invention In the above cited Patent Application Serial No. 357,714 as well as the article, a method and apparatus for measuring the specific force vector and angular rate vector of a moving body by means of a plurality of cyclically driven accelerometers is disclosed. The copending Patent Application Serial No.

357,715 cited above discloses similar techniques for measuring the specific force vector and angular rate vector of a moving body utilizing either a single or a pair of accelerometers vibrating at a constant frequency. In the embodiments of the paired accelerometer rate and force sensors disclosed in the above patent application, the masses of the accelerometers are balanced with respct to rectolinear translation. This means that the pairs of accelerometers can be attached to a mounting frame work without causing any vibrational translation of the center of mass. However, the accelerometer configurations disclosed in the above patent application will produce an gular vibration of any mass to which they are attached about the center of that mass.

As might be expected, it is important in many systems such as in inertial navigation systems to reduce to a minimum any vibration, be it linear or angular, that could affect the system. For example, in inertial navigation systems it is important to minimize the effects of one sensor on the performance of other sensors in the navigation system.

Summary of the Invention The invention provides an apparatus for generating a signal representing the angular rate of motion of a structure comprising: a first accelerometer for generating a first output signal representing acceleration along a first force sensing axis; a second accelerometer for generating a second output signal representing acceleration along a second force sensing axis; alignment means for aligning said first and second accelerometers in a side by side relationship with said first force sensing axis par allel to said second force sensing axis;; vibration means operatively connected to the structure and said alignment means for vibrating said first and said second accelerometers in opposite directions at a frequency a, along a vibration axis that is normal to said force sensing axes and in a plane defined by said force sensing axes; and signal processing means responsive to said first and second output signals for generating a rate signal representing the angular rate of motion of the structure about an axis perpendicular to the plane defined by said force sensing axes and said vibration axis.

By arranging the accelerometers as indicated above, it is possible substantially to eliminate torques resulting from the vibration of the accelerometes. The vibration means is preferably a vibrating mechanism for vibrating the accelerometers individually in a substantially linear direction along a vibration axis normal to the accelerometers force sensing axes at a frequency a,.

In a preferred embodiment, the invention provides an angular rate sensing accelerometer structure that includes a housing; a shaft mounted for rotation in the housing; a first accelerometer secured to a first support member; a first flexure for securing the first support member to the housing such that the first accelerometer can move in a substantially linear manner in a direction generally normal to the axis of the shaft and in a direction to and away from the shaft.The structure also includes a second support member securing a second accelerometer; a second flexure for securing the second support member to the housing such that the second accelerometer can move in a substantially linear manner in a direction generally normal to the axis of the shaft in a direction generally to and away from the shaft; a mechanism for rotationally vibrating the shaft; and a linkage arrangement connected to the shaft and the first and second support members effective to vibrate the accelerometers in the directions permitted by the flexures.

Brief Description of the Drawings Figure 1 is a simplified perspective diagram of a pair of accelerometers in a side by side arrangement with their force sensing axes aligned in the same direction; Figure 2 is a front view of a mechanism for implementing the paired accelerometer arrangement of Fig. 1; Figure 3 is a side view of the accelerometer arrangement of Fig. 2; and Figure 4 is a block diagram of an analog signal separating circuit for use with a pair of accelerometers.

Detailed Description of the Invention As shown in Fig. 1, a pair of accelerometers 10 and 1 2 are mounted in a side by side arrangement with their force sensing axes A1 and A2, aligned in the same directiion. In order to minimize any mass imbalances as well as torque imbalances that could be transmitted to a support structure (not shown), the accelerometers 10 and 12 are vibrated in opposite directions to and away from each other along the axes indicated by lines 1 4 and 1 6 which are normal to the sensitive axes Al and A2. As described in detail in the co-pending Merhav patent applications, the acceleration signals from the accelerometers 10 and 1 2 can be used to provide signals representing translation of the structure containing the accelerometers 10 and 1 2 along the axes A' and A2z along with signals representing angular rotation of the structure.

The preferred embodiment of an apparatus for mechanizing the paired accelerometer structure of Fig. 1 is illustrated in Figs. 2 and 3. In this apparatus, substantially linear translation of the accelerometers 10 and 1 2 along the axes 14 and 16 as shown in Fig. 1 is provided by a mechanism that includes a pair of support members 1 8 and 20 that hold the accelerometers 10 and 1 2 respectively. In turn, the support members 18 and 20 are secured to a housing 22 by means of a pair of flexures 24 and 26. A shaft 28 which is rotatably secured within the housing 22 by a pair of bearings 30 and 32, has secured to it a linkage member 34. Attached to the linkage member 34 are a pair of linkage pins 36 and 38 which are inserted into slots 40 and 42 configured into support members 1 8 and 20.

Also attached to the shaft 28 is a rotor 44 that, when combined with a stator 46 attached to the housing 22, will cause the shaft to vibrate back and forth through a small angle at a frequency . As can be seen from Figs. 2 and 3, the vibration of the shaft 28 will result in the linkage pins 36 and 38 forcing the support members 18 and 20 and hence the accelerometers 10 and 12 to move in a direction perpendicular to the shaft and to and away from each other. Since the accelerometers 10 and 12 will only move a very small distance, their direction of travel will be substantially linear with respect to the axis of the shaft 28.Signals representing the rotational motion of the shaft 28 can be obtained by means of the capacitor pick-off arrangement shown at 48: The angular capacitive detector 48 provides a means for angular motion feedback to be used in maintaining the driven motion of the shaft 28 constant over time.

A signal processor for separating the force signals F from the angular rate signals Q and the output signals of accelerometers 10 and 1 2 is provided in Fig. 4. A control pulse generator 50 generates signals on a line 52 as a function of the frequency a, that will cause a drive signal generator 54 to vibrate the accelerometers 10 and 1 2 at freqeuency a, as previously desribed. The output signals of the accelerometers 10 and 1 2 a) and a2, are transmitted over lines 56 and 58 to a preseparation processor 60.The preseparation processor 60 shown in Fig. 4 is appropriate for a paired accelerometer mechanization of the type shown 1(1 Fig. 1 where the force sensing axes A' and A2 are aligned in the same direction. The accelerometer output signals at lines 56 and 58 are summed in a summing junction 62 and differenced in a summing junction 64. A pair of scaling amplifiers 66 and 68 receive the summed and differenced signals from summing junctions 62 and 64 respectively over lines 70 and 72.

The principal force separation is the same as the one disclosed in the previously cited Merhav Application Serial No. 357,715 wherein the combined signal from amplifier 66 is provided over a line 74 to a force channel 76. The force channel 76 includes an integratiny circuit and a sample and hold circuit with signals from the control pulse generator 50 being applied over lines 78 and 80 to the integrating and sample and hold circuits. The combined acceleration signals on lines 74 are integrated over the time period T of the frequency a, to provide a force signal F7 on line 82 that represents the change in velocity along the axis Z of the structure or housing 22 holding the accelerometers 10 and 12.

Similarly, an angular rate channel processor 84 receives the differenced signals over line 86 and multipliers them by the zero mean periodic function sgncwt. As with the force channel, the resulting signal is integrated over a time period T through a sample and hold circuit to an output line 88. The signal S3 representing angular rate information is transmitted through a low pass filter 90 and output as a signal 5a0 on a line 92.

In the above manner signals from the accelerometer arrangement illustrated in Figs.

1-3 may be processed to produce force signals and angular rate signals.

Claims

1. An apparatus for generating a signal representing the angular rate of motion of a structure comprising: a first accelerometer for generating a first output signal representing acceleration along a first force sensing axis; a second acceit,orneter for generating a second output signal representing acceleration along a second force sensing axis; alignment means for aligning said first and second accelerometers in a side by side relationship with said first force sensing axis par allel to said second source sensing axis; vibration means operatively connected to the structure and to said alignment means for vibrating said first and said second accelerometers in opposite directions at a frequency e.

along a vibration axis that is normal to said force sensing axes and in a plane defined by said force sensing axes; and signal processing means responsive to said first and second output signals for generating a rate signal representing the angular rate of motion of the structure about an axis perpendicular to the plane defined by said force sensing axes and said vibration axis.

2. The apparatus of Claim 1 wherein said first and said second accelerometers are aligned in mutually opposite directions.

3. The apparatus of Claim 1 wherein said first and said second accelerometers are aligned in the same direction.

4. An angular rate sensing accelerometer structure comprising: a housing; a shaft rotatably mounted in said housing; a first support member; a first accelerometer secured to said first support member; a first flexure means for securing said first support member to said housing such that said first accelerometer can move in a substantially linear manner in a direction generally normal to the axis of said shaft and in a direction to and away from said shaft; a second support member; a second accelerometer secured to said second support member; a second flexure means for securing said second support member to said housing such that said second accelerometer can move in a substantially linear manner in a direction generally normal to the axis of said shaft and in a direction to and away from said shaft; vibrating means for rotationally vibrating said shaft; and linkage means connected to said shaft and first and second support members for vibrating said first and second accelerometers in the direction of movement permitted by said first and second flexure means.

5. The structure of Claim 4 wherein the force sensing axes of said first and said second accelerometers are aligned in the same direction.

6. The structure of Claim 4 wherein said vibrating means includes an electric motor having a rotor secured to said shaft and a stator secure to said housing.

7. The structure of Claim 4 wherein said linkage means includes first and second linkage members secured to said shaft and disposed to said first and second support members respectively.