GB2143947A - An inertial instrument with cup-shaped inertial mass - Google Patents

Abstract

An inertial instrument, which may be a gyroscope or an accelerometer, has a cup-shaped inertial mass element 38, which in the illustration is a rotor of a gyroscope driven by the shaft 24 of a motor. A restoring torque is applied to the rotor, by way of coils 56 acting on permanent magnets 44,48 and 52, when any tilt of the rotor is detected by one or more pick-offs 58. In an alternative use the element 38 acts as an accelerometer. <IMAGE>

Description

SPECIFICATION An inertial instrument with cup-shaped inertial mass The present invention relates to inertial instruments and, more particularly, to such an instrument having a flexible suspension interconnection between the inertial element and the reference structure.

It has been recognised that virtually the same component elements can be used to create a one or two-degree of freedom accelerometer as are used to create a dynamically turned, free rotor gyroscope having two degrees of freedom. The primary difference would be that the gyroscope rotates while the acceleratometer does not. With a simpler suspension permitting only one degree of freedom, the single degree of freedom accelerometer can be created from substantially the same components.

This family of instruments can share common sensing and control elements such as pick-offs and torquers, as well as other components such as magnets, housings covers and the like. The pickoffs signal and the deviation of the inertial mass element from a predetermined rest or reference plane. The torquers apply restoring forces to return the mass element to the rest plane.

The following patent publications disclose dynamically tuned free rotor gyros: U.S. 3,301,073, E. W. Howe; U.S. 3,318,160, H. F. Erdley, et al; U.S. 3,354,726 W. J. Krupick, et al; and U.S. 3,678,764 H. F. Erdley, et al; The following patent publications disclose flexures and gimbal systems for dynamically tuned free rotor gyros: U.S. 3,542,608, J. C. Stiles; U.S. 3,543,301, D. Barnett; U.S. 3,585,866, W. B Ensinger; U.S. 3,832,906, R. J. G. Craig; U.S. 3,943,778 S. F. Wyse; U.S. Re 30,290, R. J. G. Craig; and U.S. 3,143,451 R. J. G. Craig U.S. Patent Application Serial No. 822,884 now abandones in favour of US continuation Patent Application Serial No. 06/150742, R.

J. G. Craig, et al.

In recent years, considerable interest has been shown in what have come to be known as dynamically tuned free rotor gyroscopes ("gyros") in which the rotor and shaft are connected through some type of a flexible universal joint. Such gyroscopes have been described in detail. The preceding paragraph lists many patent publications which in turn include references to yet still additional prior art.

These instruments have been built so that a central shaft is connected through flexural pivots to a mass element which surrounds the shaft. In the case, electromagnetic pick-offs are provided to signal changes in attitude from the plane normal to the spin axis. The mass element is provided with a magnet structure that interacts with torquer coils that apply force to the mass element to restore it to the normal plane.

If the central shaft is connected to a motor so that the inertial mass element is rotated, then the instrument becomes a gyroscope. If, on the other hand, the central shaft is merely fastened to a support frame, then the device could, just as easily, and with the same pickoffs and torquers, function as an accelerometer if the centre of mass is displaced with respect to the suspension flexural pivot axes.

It has always been a desirable goal to provide smaller more compact inertial instruments having the performance characteristics of their larger counterparts. Certainly, for inertial navigation and/or guidance, size and weight are always factors.

A number of applications no exist for instruments in which the diameter is the most important dimension and length is not critical.

In some instances, the desired diameter is less than one inch (2.5 cm). For these applications, the present invention may provide the only practical way of achieving the goal.

For use in more sophisticated applications, reductions in size and weight, without loss of accuracy, stability or repeatability are highly prized goals.

As the size of the inertial instrument is reduced, the flexures connecting the inertial mass to the shaft must become smaller and smaller, creating fabricating problems. Further, in current, state-of-the-art inertial instruments, especially gyroscopes, expensive, segmented magnets are placed about the periphery of the mass element which then interact with torquer coils to maintain the normal plane of the mass element.

In designing inertial instruments, and especially dynamically tuned free rotor gyroscopes, a design goal has been to place a substantial part of a mass of the rotating element at a distance from the spin axis. Where size is not a critical factor, the suspension can easily be positioned between the shaft and the rotating element. Various suspensions have been disclosed in the patent publications referred to above.

Some known gyros include the further design feature of shaping the mass element into a toroidal shape with an opening between the inner and outermost wall and positioning, in the interior, stationary torquer coils which cooperate with permanent magnets that are mounted on an interior surface of the toroid.

To decrease the overall size of such a gyro would require a proportional decrease in size of all of the component elements. This would lead to severe problems in the fabrication of the suspension and also in the fabrication and assembly of the permanent magnets which are affixed to the mass element and which interact with the torquer coils.

In addressing the problem of creating a small inertial instrument having a diameter of less than one and a half inches, the several problems created by the size reduction can be considered. A change in the suspension to simplify the complexity of fabrication and reduce the cost can contribute to the achievement of such a design goal. Further, a change in the permanent magnet assemblies can increase efficiency and at the same time reduce the power requirements for the torquers.

According to the present invention, there is provided an inertial instrument comprising a cup shaped inertial mass element mounted for limited rotation about a first axis and means for sensing the degree of rotation of the mass element about the first axis.

Thus the invention provided a new inertial instrument which, in various embodiments, can be either a gyroscope or an accelerometer. A number of improvements have been evolved which can be used individually or in combination. By employing a wholly new inertial mass design, together with a novel suspension configuration, improved, more efficient and less expensive permanent magnet arrangements can be used, as well, which can work with conventional pick-off devices and torque applying means.

One of the keys to the improved family of inertial instrument of the present invention is the provision of an inertial mass element which is substantially cup-shaped. Preferably the mass element is a section of a hollow cylinder having a solid base, the open end having a flange. A suspension structure, such as is disclosed in U.S. Patents Nos.

3,832,906, RE 30,290 and 3,143,451 can be coupled to the flange so that the inertial element rests wholly in the interior of the suspension. When used as a gyroscope, the opposite end of the suspension can be coupled to a source of rotational motion. If used as an accelerometer, the opposite end of the suspension can be connected to the base of the instrument.

In another embodiment, part of the rotor extends out beyond the diameter of the suspension. This increases the angular momentum of the instrument but still allows most of the features of the preferred embodiment to be used.

As in prior devices, coils for applying torque can be arranged to extend into the interior of the cup to interact with permanent magnets located therein. In a preferred embodiment, disc magnets, stacked within the cup and polarised in an axial direction provide the permanent magnetic field.

In a preferred embodiment, a stack of three magnets is used. A primary, central disc magnet is placed between a pair of secondary, disc magnets which function as "bucking magnets." The "north" face of the main magnet is adjacent the north face of one bucking magnet which tends to direct the lines of flux in the radial direction. Similarly, the adjacent south faces of the main and secondary magnets also produces a radial return flux path.

The circumferential wall of the cup shaped inertial mass elements acts as a part of the flux path. Clearly, a single disc magnet can be employed, but without the same degree of efficiency in flux utilization. More than three magnets can also be used, if desired.

A "spreader" or pole piece element between adjacent magnets helps to concentrate and direct the flux path. The bucking magnets also tend to isolate the instrument from the effects of external magnetic fields. It appears that the available magnetic field can reduce the power requirements of the torquers.

Axial magnetisation of disc magnets results in a very efficient magnetic design since nearly all available flux passes through the torque applying coil windings. Axially magnetised rings or segments, for example, would not be as efficient since a considerable amount of flux is lost through leakage.

The use of the disc permanent magnets avoids the necessity of a plurality of carefully matched individual magnets which, in prior art designs, were adhered circumferentially to the walls of the mass element adjacent the torque applying coils.

A fundamental problem present in conventional strap down gyroscopes is overcome using the teachings of the present invention.

In prior art gyroscopes, in order to obtain efficient torquing, a plurality of permanent magnetic segments were preferable since it is difficult to generate enough flux inside a solid ring to magnetise it to the same level as a segment exposed to the same flux.

Using the segments in a rotor, however, creates "noise" in the torque applying coils.

For example, a ring of nine segments when rotated creates noise at a frequency that is nine times the spin frequency and also subharmonics. These "noise" effects can create problems in other parts of the system such as the caging electronics. Since the preferred embodiment does not use a segmented structure, this noise problem does not trouble that embodiment.

In the prior art instrument designs, a plurality of torque applying coils cooperated with permanent magnets that were polarised in the plane orthogonal to the axis of symmetry, which is gyroscope was the spin axis. In such an arrangement, all of the available flux does not interact with the torquer coils. This situation is somewhat improved in embodiments in which the inertial mass element is an open toroid. Here, rings of specially shaped magnet segments were on the facing inner walls of the toroidal element. The torque applying coils were then positioned between the magnet rings.

Any improvement in the efficiency of the torque applying coils can reduce the coil power requirements of the instrument. For example, an increase in the amount of magnetic flux available to interact with the torque applying coils can be achieved using stronger permanent magnets. However, size limittions and the problems of fabricating such more powerful magnetis in the required shapes can cause a disproportionate increase in costs.

In a preferred embodiment of this invention, the the torque applying coils and pick-off coils are mounted at an end of the gyroscope rather than the centre. The end surface of the gyroscope is a very convenient place to do all interconnect wiring and also allows a single inexpensive multi-pin header to replace many individual feed-throughs.

A conventional dry-tuned gyroscope uses feedthroughs which extend out radially from a diameter near its centre. This arrangement makes inter-connecting wiring more difficult and also increases the effective diameter of the gyroscope. For those situations where a small diameter is essential, such as some missile and borehole applications, the endmounted header allows a gyroscope with a larger diameter rotor and suspension to be used, since no diameter is wasted by use of radial feedthroughs.

The end-mounted header also allows direct attachment of either a mating plug or electronic circuits or both. If electronic circuits are used, the boards can be stacked on the feedthrough pins with selective electrical connections to the circuits as required. This arrangement results in a minimum volume, low cost package.

In yet another embodiment of an inertial instrument in accordance with the invention, the stack of disc magnets can be replaced with a single bar magnet polarised in a direction orthogonal to the cylindrical axis. A single multi-turn toroidal torque applying coil concentric with the cylindrical axis is provided to interact with the magnet. For gyroscope embodiments, impulses to the torque applying coils would have to be provided in predetermined synchronism with the rotation of the gyroscope so that the magnet and rotor would be oriented properly each time a restoring impulse is implied.

An advantage of this arrangement is that the full height of the mass element has magnetic flux present. The toroidal torque applying coil has more turns in the flux field than with the prior art arrangements. As a result, more torque can be applied to the mass element for less power.

A one axis accelerometer embodiment creates no special problems since the magnet can be accurately positioned with respect to the pivot axis of the gimbal. For the gyroscope application, since the bar rotates with the rotor, the application of torquing pulses must be accurately synchronised to the position of the magnet relative to the pivot axes.

A two axis accelerometer may require a second bar magnet and a second torquer coil.

A suspension system, which can be made according to the teachings of U.S. Patent Applications Serial No. 822884 and 06/150742 is provided with an inside diameter sufficient to accommodate the inertial mass element. In the gyroscope version, the suspension can be connected between a motor and the mass element. In the accelerometer version, the suspension can be fastened to a reference frame. The rotation axes of the flexures pass through the centre of mass of the gyroscope rotor; but in the accelerometer the rotation axes are displaced either axially or radially from the centre of mass to impart a moment.

In a preferred embodiment, the suspension and shaft are fabricated from a single piece of material and are permanently attached to each other. Besides the cost savings realised during fabrication, this arrangement improves the geometric relationship between the suspension and shaft and ensures that it remains fixed for the life of these items.

This fixed relationship and improved geometry increase performance and allow final tuning and balancing to be accomplished in a test fixture rather than in the actual instrument. Since this fixture can be designed specifically for tuning and balancing, it can be designed to provide better access and to have other features not available in the gyroscope itself. This one-piece suspension/shaft construction thus allows more efficient tuning and balancing.

In another embodiment, the shaft and suspension as well as the bearing inner races are constructed from a single piece of material and are all permanently attached together.

This embodiment improves the geometric relationship of the suspension to the shaft as well as to the bearings. This improved geometry should result in improved performance.

In a different embodiment, the centre of mass of the mass element is displaced radially from the centre of suspension along an axis orthogonal to the rotational axes of the suspension. This results in a single axis accelerometer with the sensing axis orthogonal to the sensing axes of the two-axis instrument. The advantage of this embodiment is that a one axis and two axis instrument can be placed end to end, a most convenient packing arrangement, to produce a device sensitive to accelerations along three, mutually orthogonal axes.

By increasing the overall size of the suspension structure, the flexures are more easily fabricated. Further, the separation cuts can be made by more conventional machining methods, other than EDM. When substantially smaller instruments are desired, the arrangement of the present invention avoids the problems attendant upon fabricating even smaller flexures in a suspension that couples a motor shaft to a substantially toroidal rotor.

The accessability of the suspension structure also permits direction adjustment of the suspension and mass combination for balance, tuning and 2N (twice spin frequency) effects, without the need for repeated disassembly, especially as applied to the gyroscope embodiment.

The flexure blades can be sandblasted to change the effective spring rate, or the blades can be etched either chemically, or by some other similar process to achieve the same result. Further, the gimbal itself can be drilled to reduce inertia or weights can be added to increase inertia.

As is known from the prior art, the spin frequency is a direct function of the spring rate of the flexures but is an inverse function of the suspension inertia. Since both parameters can be controlled and modified, the tuning process can be simplified and, for final tuning, the instrument need not be disassembled.

In some respects the construction of the instruments can be quite conventional, using known motors and pick-offs, and, in the preferred embodiments, torquer coils.

In an alternative embodiment, disc magnets are replaced with a single bar magnet, necessitating a change in the shape of the torquer coils. A single, multiturn circumferential coil can interact with the bar magnet.

Several advantages of the improved instrument of the present invention have been noted during the testing of experimental models. For example, the greater mass and inertial of suspension structure tends to damp bearing "noise." Even though such bearing noise is a "second order" effect, by minimizing such effects the performance of the instrument can be improved.

The improved magnetic coupling provided by the design of the present invention has resulted in an unexpected improvement in an operating parameter known as the "time con stant." This generally represents the time required for a rotor, which has been deflected out of the "rest" plane to return to the rest plane. Ideally, a rotor, once displaced out of a plane orthogonal to the spin axis should remain displaced in the absence of restoring forces. In a perfect gyroscope, the system includes no restoring forces. However, a comS mercially produced gyroscope will have various restoring forces arising, for example, from friction, stray fluxes and the like, so that, in any gyroscope a finite time constant can be measured.

In the design of a gyroscope, the time constant can be predicted based upon the performance of prior similar designs. A time constant was predicted for the gyroscope of the preferred embodiment based upon the design parameters. However, when tested, it was found that the actual time constant turned out to be approximately three times the preducted value, suggesting a most efficient magnetic design. It is believed that this result can be attributed to the novel magnetic design and the high efficiency resulting therefrom with very low leakage.

For a better understanding of the present invention, and to show it may be put into effect reference will now be made, by way of example, to the accompanying drawings, in which Figure 1 is a side sectional view of a gyroscope according to the present invention; Figure 2 is a top section view of the gyroscope of Fig. 1 taken along the lines 2-2 in the direction of the appended arrows; Figure 3 is a top section view of an alternative embodiment according to the present invention, but using conventional magnet structures; Figure 4 is a top section view of a second alternative embodiment according to the present invention in which a bar magnet is used with a circumferential torquer coil; Figure 5 is a side sectional view of a twoaxis accelerometer instrument of the present invention, having two degrees of freedom; and Figure 6 is a side section view of an alternative one-axis accelerometer version having one degree of freedom.

Turning first to Fiture 1, there is shown in cross section a dynamically tuned, free rotor gyroscope 10 according to the present invention. As seen the gyroscope 10 is a two axis device and may be miniaturised to dimensions approximating one inch (2.5 cm) in diameter or smaller. The gyroscope 10 includes a top cover 1 2 and a bottom cover 14. An upper housing 1 6 surrounds the operational portion of the gyroscope. The top cover 1 2 seats against the upper part of the upper housing 1 6 and the bottom cover 14 encloses a motor portion which is fastened to a motor housing 18 coupled to the upper housing 1 6.

Attached to the motor housing 18 is a stator element 20. The motor further includes a hysteresis ring 22 which is connected to a shaft 24 that is supported by bearings 26. A suspension element 28 is connected to the shaft 24 and rotates with it. The suspension element 28 comprises a base structure 30 which is firmly coupled to the shaft 24, a gimbal 32 which is connected to the base structure 30 by flexures 34 and to an upper portion 36 by flexures 34. The upper portion 36 is adapted to connect to a rotor 38. In the preferred embodiment, the shaft 24 and suspension 28 are fabricated from a single piece.

The upper portion 36 and rotor 38 tilt about a first gimbal axis which is orthogonal to the axis of the shaft 24. The gimbal 32 tilts about a second gimbal axis that is orthogonal to the first gimbal axis and is also orthogonal to the spin axis.

As shown in Fig. 1, the rotor 38 is a cupshaped member including a mounting flange 40 which extends over the upper portion 36 of the gimbal suspension and is fastened thereto. Arranged within the interior of the cup or rotor housing 42 is a first or lower bucking magnet 44. Resting on the lower bucking magnet 44 is a first spreader or pole piece 46 which supports a main magnet 48.

A second spreader or pole piece 50 separates the main magnet 48 from an upper bucking magnet 52. A third, upper spreader or pole piece 54 is placed over the upper bucking magnet 52 to channel flux and to enclose the magnetic field.

The rotor housing 42, as well as the pole piece/spreaders, 46, 50 and 54 are magnetic conductors which establish a substantially closed magnetic field. The magnets 44, 48 and 52 are discs which have been polarised in the axial direction. In the embodiment shown in Fig. 1 the main magnet 48 is arranged with its north pole facing the open end of the rotor housing 42 and its south pole facing the closed end. The lower bucking magnet 44 then has its south face adjacent the spreader-pole piece 36 and the upper bucking magnet 52 has its north face adjacent the second spreader-pole piece 50.

As in prior art designs, torquer coils 56 are wound substantially in an elongated round or race track shape. Four torque coils 56 are provided, two for each axis, provided by the flexures 34. The torquer coils 56 are arranged circumferentially and are positioned within the rotor housing 42, between the housing wall and the outer periphery of the magnet stack.

As shown, the coils are arranged so that the windings intercept the main flux paths generated by the main magnet and bucking magnets.

The wall of the rotor housing 42 is magnetically conductive. The magnetic flux moves in a substantially close path and is intercepted by the windings of the torquer coils 56.

Conventional pick-offs 58 (only one of which is shown) are employed and are positioned to detect the proximity of the flange 40 of the rotor 38. Two of the pick-offs 58 are aligned on opposite sides of the spin axis to detect rotation of the rotor in a first direction along the first gimbal pivot axis. A second pair of pick-offs 58 rotated 90 therefrom, detects rotation of the rotor 38 about a second gimbal pivot axis orthogonal to the first pivot axis.

As shown, a conventional, multi-lead header 60, such as would be commercially available from the semi-conductor or connector industry, can be used to establish electrical connections to the interior of the gyroscope 10. The upper housing 1 6 and the bottom cover 1 2.

Electrical interconnections can be made through the header without affecting the interior.

The entire suspension element 28 and rotor housing 42 is accessible for adjustment and turning before the upper housing 16 is sealed in place. For example, the flexures 34 can be tuned and the mass of the suspension element 28 structure can be modified.

Once tuned and adjusted, the gyroscope 10 operates in more or less conventional fashion.

The interaction of the hysteresis ring 22 with the electrically energised stator 20 causes the ring 22 and the shaft 24 to revolve, rotating the suspension element 28 and the rotor 38.

As long as the rotor 38 is not subjected to forces along its sensitive axes, it will continue to rotate in its rest plane and the pick-offs 58 will each be equally spaced from the flange 40 of the rotor 38.

If, however, the gyroscope is subjected to imput forces or torques which cause the rotor 38 to "tilt" on the flexures 34, the pick-offs 58 will detect the differential proximities of the rotor flange 40.

As in the prior art, appropriate feedback circuits then apply "restoring" currents to the torquer coils 56 which generate a magnetic field which, when interacting with the magnetic flux field created by the permanent magnets 44, 48 and 52 applies a restoring force to the rotor 38 until the pick-offs 58 are equally affected again. In this respect, the operation is identical to that of a more conventional, dynamically tuned, free rotor gyroscope, such as is disclosed in, for example, U.S. Patents Nos. 3,832,906, RE 30,290, 3,143,451, 3,318,160 and 3,678,764.

Turning next to Fig. 2, there is shown in top section view, the arrangement of the magnetic components of the gyroscope 10 of Fig. 1. Fig. 2 provides a better view of the relationship of the rotor 38 with the components located therein. The suspension element 28 as shown includes the base portion 30 and the floating gimbal 32. The rotor housing 42 is shown concentric with the suspension 28 and, within the rotor housing 42, can be seen the torquer coils 56 and the disc magnet 48.

As will be appreciated, as the suspension element 28 rotates carrying the rotor 38 with it, the magnet 48 rotates as well. The torquer coils 56 remain stationary relative to the rotation of the rotor 38.

Turning next to Fig. 3, wherein the same parts have been given the same reference numerals, there is shown an alternative embodiment of the present invention, in which a more conventional magnet structure is employed. Arranged within the rotor housing 42 are a plurality of shaped permanent magnet segments 62 which are polarised radially. The magnets segments surround a pole piece 63.

Torquer coils 56, as in Fig. 2, can be employed and the rotor body 42 forms a return path for the flux which path includes the rotor body itself and the pole piece 63.

While the embodiment of Fig. 3 is a less preferable alternative, it is a possible arrangement which can take advantage of the "inside out" structure of the inertial instrument of the present invention. While lacking the advantages of the vastly improved magnetic flux distribution of the preferred embodiment, it does take advantage of existing magnetic technology, and includes the added advantages of the exterior suspension for a gyroscope or other inertial instrument of substantially reduced overall diameter.

In Fig. 4, there is shown a second alternative embodiment according to the present invention. Here an inertial instrument is provided with a bar magnet 64 within the gyroscope rotor housing 42, or, more generally, as in the case of an accelerometer instrument, within the inertial mass element. A modified torquer coil 66 is positioned within the interior of the rotor housing 42 surrounding the bar magnet 64 and is a multi-turn concentric coil.

To make such an embodiment operable as an accelerometer with one degree of freedom, the magnet 64 must be lined up with its north/south axis arranged at right angles to the axis of rotation provided by the gimbal flexures. In the gyroscope embodiment, it is necessary to synchronise the application of torquing currents to the orientation of the bar magnet 64. The position of the bar magnet 64 relative to the pick-off 58 would have to be known at any time. Therefore, additional circuitry is required to generate the torquing signal at the proper time to correct any displacement of the rotor effectively.

In Fig. 5, there is illustrated an inertial instrument according to the present invention functioning as an accelerometer 110, similar in structure to the gyro of Figs. 1 and 2. The accelerometer 110 has a top cover 112, a bottom cover 114, which corresponds to the lower housing 14, and an upper housing 116.

A suspension element 1 28 can be anchored to the bottom cover 114. The suspension element 1 28 includes a base portion 1 30 which is coupled to a floating gimbal 1 32 by flexures 1 34.

As can be seen, the pivot axes Cs of the suspension element 1 28 is in a plane displaced substantially below the centre of gravity of the ineitial mass element which, for convenience, will be referred to as the "rotor" 1 38. An upper portion 1 36 of the suspension element 128 is joined to the floating gimbal 1 32 by flexures (not shown) and supports a flange 140 of the rotor 1 38. The combination functions in substantially the same fashion in the embodiment of Figs. 1 and 2 (gyroscope 10).

Within the rotor housing 142 is placed a lower bucking magnet 144 on top of which is placed a spreader or pole piece 146. A main magnet 148 is provided, above which is a second spreader or pole piece 150, followed by an upper bucking magnet 1 52. As in the gyroscope embodiment an upper spreader or pole piece 1 54 completes the magnetic structure. Further, as in the gyroscope embodiment, the magnets are discs polarised in the axial direction.

Torquer coils 156, as in the gyroscope embodiment, are located within the interior of the rotor 1 38 between the magnets and the wall of the rotor housing 142.

Pick-offs 1 58 can be identical to those used in the gyroscope 10. As in the gyroscope 10, a header 1 60 can be mounted on the structure supporting the torque coils 1 56 to provide electrical connection to the interior of the instrument.

Because the plane of the centre of suspension is below the centre of mass, the embodiment functions as a pendulous accelerometer.

As in the gyroscope 10, a tilt of the mass element or rotor 1 38 can be detected by the pick-offs 1 58. This results in a restoring current being applied to the torquer coils 156, which interact with the permanent magnets to return the rotor 1 38 to its normal, aligned Finally, in Fig. 6, there is shown a modified accelerometer which is designed to be sensitive to accelerations along a single axis which axis is parallel to the axis of symmetry.

An accelerometer 110', substantially identical to the accelerometer 110 in Fig. 5 is employed. The primary difference in structure is that the centre of suspension is made coincident with the centre of mass of the inertial element as in the typical gyroscope configuration. However, a mass element 1 70 is added to the suspension structure 128' to shift the centre of mass in the radial direction along one of the suspension axes. This modification then renders the instrument 110' sensitive to acceleration in the vertical direction as seen in Fig. 6. As modified, instrument 110' is considered to have only a single axis of sensitivity. The mass element 1 70 can also be fabricated as a part of suspension.

The accelerometer 110 of Fig. 5 can also be modified to have a single axis of sensitivity by eliminating one pair of flexures. In that modification, the inertial mass would then be free to rotate only about one axis and would therefore be sensitive only to acceleration in a direction orthogonal to the suspension axis.

Thus there has been disclosed a novel inertial instrument which can be fabricated as a very small gyroscope or accelerometer and which, in a preferred embodiment, has a vastly improved magnetic flux path for interaction with torquer coils to reduce the currents required to restore the inertial mass element to a predetermined orientation.

The novel instrument of the present invention lends itself to modifications in which a more conventional magnetic structure can be employed. Further, in an alternative embodiment, a different novel magnetic structure can be used employing a bar magnet, together with a concentric torquer coil, which, however, required appropriate timing circuits when used in the gyroscope mode.

Claims (50)

1. An inertial instrument comprising a cup-shaped inertial mass element mounted for limited rotation about a first axis and means for sensing the degree of rotation of the mass element about the first axis.

2. An inertial instrument as claimed in Claim 1, the instrument comprising means for applying torque to the mass element about the first axis.

3. An inertial instrument as claimed in Claim 2, wherein the torque applying means can apply torque in a sense to restore the mass element to a rest attitude.

4. An inertial instrument as claimed in Claim 2 or 3, wherein the torque applying means comprises a coil.

5. An inertial instrument as claimed in Claim 4, wherein the cup-shaped inertial mass element carries one or more permanent magnets within the cup aligned so as to generate magnetic flux in a path extending generally at right angles to an insensitive axis of the cupshaped inertial element, the torque applying means being capable of acting on the permanent magnet(s).

6. An inertial instrument as claimed in Claim 5, wherein a first disc magnet is concentrically mounted within the cup-shaped inertial mass element.

7. An inertial instrument as claimed in Claim 5, wherein the first disc magnet is polarised in the direction of the insensitive axis.

8. An inertial instrument as claimed in Claim 7, the instrument including second and third disc magnets, each polarised in a direction parallel to the insensitive axis and having a pole adjacent a similar pole of the first disc magnet, the flux being directed, in use, substantially orthogonal to the insensitive axis and through the torque applying means, which comprises a coil.

9. An inertial instrument as claimed in Claim 5, wherein a bar magnet is mounted within the cup-shaped inertial mass element.

10. An inertial instrument as claimed in any one of claims 5 to 10, wherein the torque applying means includes a circular coil concentric with the central axis extending into the cup shaped inertial mass element between the permanent magnet(s) and a wall of the element.

11. An inertial instrument as claimed in any one of Claims 1 to 10, wherein the cupshaped inertial element is externally mounted by way of suspension means.

1 2. An inertial instrument as claimed in Claim 11, wherein the inertial mass element extends beyond the suspension means.

1 3. An inertial instrument as claimed in Claim 11 or 12, the suspension means being coupled to a support structure by way of flexure means, which permit the limited rotation about the first axis.

14. An inertial instrument as claimed in Claim 13, wherein the flexure means are located outside the cup-shaped inertial mass element.

1 5. An inertial instrument as claimed in Claim 11 or 12, wherein the inertial mass element includes a skirt portion surrounding the suspension means to add inertia.

16. An inertial instrument as claimed in any one of Claims 1 to 15, wherein the sensing means comprise pick-off means adjacent the inertial mass element.

1 7. An inertial instrument as claimed in Claim 1 having an insensitive axis, at right angles to the first axis about which the cupshaped inertial mass element is aligned.

18. An inertial instrument as claimed in Claim 17, wherein the insensitive axis is a central axis.

19. An inertial instrument as claimed in claim 1 7 or 18, wherein the torque applying means is operable to keep motion of the mass element about the first axis.

20. An inertial instrument as claimed in Claim, wherein the inertial mass element is so mounted by means of flexural mounting means having a cylindrical opening adapted to receive a peripheral edge of the mass element.

21. An inertial instrument as claimed in Claim 20, wherein the flexural mounting means is accessible for balancing and adjusting with the instrument otherwise assembled and operable.

22. An inertial instrument as claimed in any one of Claims 1 to 21, wherein the centre of mass of the mass element does not lie in the same plane as the first axis.

23. An inertial instrument as claimed in any one of Claims 1 to 22, wherein the inertial mass element is mounted also for rotation about a second axis, orthogonal to the first axis.

24. An inertial instrument as claimed in Claim 23 when dependent on any one of Claims 2 to 1 0, the torque applying means including a first pair of coils positioned to apply a restoring torque about the first axis and a second pair of coils positioned to apply a restoring torque about the second axis.

25. An inertial instrument as claimed in any one of Claims 1 to 24, the instrument including a pendulous mass element coupled to the inertial mass element.

26. An inertial instrument as claimed in any one of Claims 1 to 25, the instrument including a frame.

27. An inertial instrument as claimed in any one of Claims 1 to 26, the instrument including a housing.

28. An inertial instrument as claimed in Claim 27 when dependent on Claim 11, wherein the housing and suspension means are fabricated from a single piece of material and are permanently attached to one another.

29. An inertial instrument as claimed in Claim 27, the instrument comprising a header mounted adjacent the inertial mass to feed electrical signals through the housing.

30. An inertial instrument as claimed in any one of Claims 1 to 29, which instrument is a gyroscope.

31. An inertial instrument as claimed in Claim 30, the instrument including a motor, coupled to a shaft, the motor being adapted to rotate the inertial mass about its central axis.

32. An inertial instrument as claimed in Claim 31, wherein the inertial mass is coaxially aligned with the shaft.

33. An inertial instrument as claimed in Claim 31 dependent on Claim 11, wherein the suspension means connects the inertial mass to the shaft.

34. An inertial instrument as claimed in Claim 33, wherein the shaft and suspension means are fabricated from a single piece of material and are permanently attached to one another.

35. An inertial instrument as claimed in Claim 33, wherein the shaft is coupled to the motor with bearings and where the bearing inner races and shaft are fabricated from a single piece of material and are permanently attached to one another.

36. An inertial instrument as claimed in any one of Claims 1 to 29, which instrument is an accelerometer.

37. An inertial instrument as claimed in Claim 36, when dependent on Claim 11, wherein the centre of mass of the inertial mass element is displaced from the centre of suspension.

38. An inertial instrument as claimed in Claim 37, wherein the displacement is axially along an insensitive axis.

39. An inertial instrument as claimed in claim 37, wherein the displacement is radially from an insensitive axis.

40. A gyroscope substantially as described with reference to Figs. 1 and 2 of the drawings.

41. A gyroscope substantially as described with reference to Fig. 3 of the accompanying drawings.

42. A gyroscope substantially as described with reference to Fig. 4 of the drawings.

43. An accelerometer substantially as described with reference to Fig. 5 of the drawings.

44. An accelerometer substantially as described with reference to Fig. 6 of the drawings.

45. An inertial instrument having a central axis and including; 1) an inertial mass element having a substantially cup-shape, coaxial with the central axis; 2) suspension means direct coupled to said mass element exterior to the outside of said cup-shape; 3) flexure means symmetrically coupling said suspension means to a support structure for permitting limited rotation of said inertial mass element about a first axis orthogonal to the central axis; 4) pick-off means adjacent said inertial mass element for detecting and signal rotational motion about said first axis; and 5) torquer means for imparting to said inertial element a rotational motion about said first axis.

46. In an improved accelerometer including a frame, and an insensitive axis, the combination comprising: a) a cup-shaped inertial mass element coaxially aligned with the insensitive axis; b) flexural mounting means having a cylindrical opening adapted to receive said inertial mass element at the peripheral edge of said mass element and permitting said mass element limited rotational movement about at least e first axis orthogonal to the insensitive axis; c) magnetic means disposed in the interior of the cup of said cup shaped mass element; and d) torquer coil means fixed to a reference frame but extending into the cup interior adjacent to said magnetic means and cooperable therewith for maintaining said mass element in a plane orthogonal to the insensitive axis, whereby said flexural mounting means is accessible for balancing and adjusting with the instrument otherwise assembled and operable.

47. An improved dynamically tuned gyroscope including a frame, motor means fixed to the frame and including a shaft, rotatable about a spin axis, the combination comprising: 1) an open interior cup-shaped rotor coaxially aligned with the rotatable shaft; 2) flexural mounting means attached at one end to the shaft and rotatable therewith, and having a cylindrical opening at the other end adapted to receive said rotor; 3) connecting means joining the peripheral edge of aid rotor to said other end of said mounting means permitting said rotor limited rotational movement about a first axis orthogonal to the spin axis; 4) magnetic means disposed in the interior of the cup of said shaped rotor; and 5) torquer coil means fixed to the frame but extending into the cup interior adjacent to said magnetic means and operable therewith for maintaining rotor rotation in a plane orthogonal to the spin axis, whereby said flexural mounting means is accessible for balancing and adjusting means with the instrument otherwise assembled and operable.

48. In an improved, dynamically tuned gyroscope including a housing, motor means fixed to the housing, a shaft coupled to the motor and rotatable about a spin axis, means for sensing attitude of a rotor and means for torquing a rotor; a) a cup shaped rotor coaxially aligned with the rotatable shaft; and b) suspension means external to said cupshaped rotor for symmetrically connecting said rotor to the shaft.

49. In an improved accelerometer including a housing, a means for sensing the attitude of an inertial mass element, means of torquing the inertial mass element, and a central axis: a) a cup-shaped inertial mass element coaxially aligned with the central axis of the accelerometer; and b) suspension means external to said cupshaped inertial mass element, and symmetrically connected thereto-for permitting rotation about an axis orthogonal to the central axis the centre of gravity of said inertial mass element being displaced axially from centre of said suspension means.

50. In an improved single axis accelerometer including a housing, a central axis, means for sensing the attitude of an inertial mass element and means for torquing an inertial mass element: a) a cup-shaped inertial mass element coaxially aligned with the central axis; and b) suspension means external to said cupshaped inertial mass element and symmetrically mounted thereto for enabling rotation about an axis orthogonal to the central axis, the centre of gravity of said inertial mass element being displaced radially from the centre of said suspension.