US3787758A

US3787758A - Apparatus including displacement-responsive inductive-transducers

Info

Publication number: US3787758A
Application number: US00220093A
Authority: US
Inventors: R Ashby; T Adams
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1972-01-24
Filing date: 1972-01-24
Publication date: 1974-01-22
Anticipated expiration: 1991-01-22

Abstract

A rate gyroscope includes an inductive pick-off that has, in addition to a main secondary winding providing an output in accordance with input rate to the gyroscope, a further secondary winding that provides a signal to back off undesired output from the main winding at zero input-rate. A thermistor is connected in series with the main winding to compensate the gyroscope scalefactor for ambient temperature variations, and at least a proportion of the signal supplied by the further winding is applied in series with a resistor across the thermistor to compensate for variation from one temperature to another in the zero-rate output. The thermistor may be connected between one end of the main winding and a tap on the further winding or between one end of the further winding and an output terminal of the gyroscope. The further winding may be provided as a secondary winding of a separate transformer that is energized in parallel with the pick-off, and where the thermistor is connected to a center-tap of this winding the two ends of the winding may be connected to one output terminal of the circuit by two resistors respectively.

Description

[ 1 ,Fan. 22, 1974 1 APPARATUS INCLUDING DISPLACEMENT-RESPONSIVE INDUCTIVE-TRANSDUCERS [75] Inventors: Robin Ashby, Stroud; Terence Ernest Adams, Cheltenham, both of England [73] Assignee: Smiths Industries Limited, London,

England 22 Filed: Jan. 24, 1972' 21 Appl. No.: 220,093

[52] US. Cl 323/51, 73/5.6, 323/61,

323/68 [51] Int. Cl G0lc 19/28 [58] Field of Search 323/48, 51, 57, 60, 61, 68, 323/90; 340/195, 199

Primary Examiner-A. D. Pellinen Attorney, Agent, or FirmWilliam D. Hall et al.

[5 7] ABSTRACT A rate gyroscope includes an inductive pick-off that has, in addition to a main secondary winding providing an output in accordance with input rate to the gyroscope, a further secondary winding that provides a signal to back off undesired output from the main winding at zero input-rate. A thermistor is connected in series with the main winding to compensate the gyroscope scale-factor for ambient temperature variations,

and at least a proportion of the signal supplied by the further winding is applied in series with a resistor across the thermistor to compensate for variation from one temperature to another in the zero-rate output. The thermistor may be connected between one end of the main winding and a tap on the further winding or between one end of the further winding and an output terminal of the gyroscope. The further winding may be provided as a secondary winding of a separate transformer that is energized in parallel with the pick-off, and where the thermistor is connected to a center-tap' of this winding the two ends of the winding may be connected to one output terminal of the circuit by two resistors respectively.

5 Claims, 4 Drawing Figures PATENTEWZ'QW 3787, 758

SHEET 2 OF 2 APPARATUS INCLUDING DISPLACEMENT-RESPONSIVE INDUCTIVE-TRANSDUCERS This invention relates to apparatus including displacement-responsive inductive-transducers.

The invention is particularly concerned with apparatus of the kind in which a di'splacemenbresponsive inductive-transducer has a primary winding and a secondary winding that are inductively coupled to one another to an extent dependent upon an applied displacement, and in which circuit means is coupled between said secondary winding and output terminals of the apparatus forsupplying to these output terminals a cyclically-varying electric signal derived from said secondary winding to have an amplitude dependent on said applied displacement.

Displacement-responsive inductive-transducers have found application in g yroscopes and other instruments for the purpose of deriving a signal-representation in accordance with an angular or linear displacement within the instrument. More particularly, such a transducer has been used in a rate gyroscope for deriving an output signal-representation of the extent to which the resiliently-restrained gimbal structure of the gyroscope is displaced angularly during'precession of the gyroscope rotor. In such an application, for which very small displacements are to be sensed accurately, difficulty has been experienced in ensuring that the output representation is not significantly affected by variations in ambient temperature. With this difficulty in mind it has been proposed where apparatus of the particular kind specified'in the preceding paragraph (referred to hereinafter as of the specified kind) is involved, to

- include a temperature-dependent impedance in the circuit means connected between the secondary winding of the transducer and the output terminalsof the apparatus.

The use of a temperature-dependent impedance included in the circuit means of apparatus of the specified kind, has been found to be generally effective to compensate for variations with temperaturein the scale factor of the apparatus, that is to say in the ratio to the maximum operational displacement, of the difference between the amplitudes of the outputsignal at the maximum and zero displacements. However, it is generally not effective to compensate adequately for variations that occur as between one temperature value and another in the amplitude of the output signal at a specific,

for example zero, displacement,

It is an object of the present invention to provide apparatus of the specified kind in which effective temperature compensation in the output signal can be achieved in the latter respect as well as in relation to the scale factor. I

According to the present invention apparatus of the specified kind includes means for deriving a further cyclically-varying signal and for applying this across a temperature-dependent impedance included in said circuit means, to modify the amplitude of the signal supplied to the output terminals in accordance with said further signal.

The said further signal may be derived from a further winding which is inductively coupled to the said primary winding of the transducer, or which is provided by a transformer that is separate from the transducer and is arranged to be energized synchronously with the transducer primary-winding. The temperaturedependentimpedance (which maybe a thermistor) may in either of these two cases be connected between one end of said secondary winding and a tap on said further winding, with electrical resistance connected between said one end of said secondary winding and one end of said further winding to shunt this impedance. Alternatively, one end of the temperature dependent impedance may be connected to one end of said further winding and via a first resistance to one end of said secondary winding. In the latter case, the other end of the said further winding may be connected to the other end of said temperature-dependent impedance via a second resistance.

The invention is especially applicable to temperature compensation in gyroscopes, and in this respect a rate gyroscope that includes apparatus in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a sectional side-elevation of the rate gyroscope;

FIG. 2 is a diagrammatic representation of a sectional view taken on the line IIII of FIG. 1, for the purposes of illustrating constructional features of a displacement-responsive inductive-transducer that forms part of the rate gyroscope;

FIG. 3 shows a temperature-compensating circuit that is coupled to the transducer of FIG. 2 in the rate gyroscope; and

FIG. 4 shows a form of temperature-compensating circuit that may be used in the rate gyroscope as an alternative to the circuit of FIG. 3.

Referring to FIG. I, a gimbal structure 1 of the rate gyroscope is rotatably mounted within a cylindrical casing 2 for angular displacement about the longitudinal axis 3 of the casing 2. The structure 1 is mounted by means of a bearing 4 at one end of the casing 2 and by means of a bearing 5 and a torsion bar 6 at the other end, the torsion bar 6 providing a resilient restraint opposing angular displacement of the structure 1 about the axis 3. An inductive transducer or pick-off 7 that comprises a ferromagnetic stator 8 carried by the casing 2 and a ferromagnetic rotor 9 carried by the structure 1, is arranged to be excited with alternating electric current so as to derive in the stator 8 a signal dependent upon any angular displacement of the structure 1 about the axis 3.

An electrically-driven rotor 10 of the rate gyroscope is carried by the gimbal structure 1, being rotatablymounted on a steel spindle 11 that is secured to the structure 1 with its longitudinal axis 12 perpendicular to the axis 3. The rotor 10 is in operation energized to cause it to rotate about the axis 12 (the spin axis of the gyroscope), and in these circumstances any angular movement of the casing 2 about an axis 13, which axis being perpendicular to the two axes 3 and 12 constitutes the input axis of the rate gyroscope, tends to precess the gimbal structure 1 about the axis 3 (the precession axis of the gyroscope). Precession in this way is restrained resiliently by the torsion bar 6 so that the resultant angular displacement of the gimbal structure 1 about the precession axis 3 is in accordance with the angular velocity or rate of the casing 2 about the input axis 13. The pick-off 7 derives an electric alternatingcurrent signal in accordance with the displacement, and this signal as applied to appear between

output terminals

14 and 15 mounted externally of the casing 2, provides a measure of the'input rate.

As shown in FIG. 2, the ferromagnetic, laminated stator 8 of the pick-off 7 has 12 equally-spaced and inwardly-directed-poles 20, and carries a primary winding 21 and a secondary winding 22. The primary winding 21 embraces the poles in pairs with the sense in which it is wound (indicated by arrows) alternating from one pole-pair to the next around the stator 8. The winding 22 is wound in the same way but with different pole-pairings so that the sense of inductive coupling between the two

windings

21 and 22 is reversed between consecutive poles 20.

The rotor 9 of the pick-off 7 is of a solid or laminated soft-iron construction, and has six equally-spaced and outwardly-directed poles 23 that serve to bridge the gaps between poles 20 of the stator 8. While the rotor 9 remains with its poles 23 symmetrically-positioned across the gaps the inductive coupling between the

windings

21 and 22 is nominally zero, there being substantially the same extent of coupling in one sense as in the other around the stator 8. Thus when an alternating-current supply source is coupled across the terminals 24 and 25 of the primary winding 21, the induced signal that in these balanced conditions appears between the

terminals

26 and 27 of the secondary winding 22, is of substantially zero amplitude. Angular displacement of the rotor 9 relative to the stator 8, however, brings about a condition of unbalance in which the signal amplitude across the

terminals

26 and 27 increases substantially linearly with increase in the displacement through the small angular range applicable to normal operation of the rate gyroscope. The phasing of the signal is dependent on the sense of the displacement from the symmetrical zero position.

To the extent that the rate gyroscope has so far been described it is of well-known form and although it is readily capable of sensing very low angular rates about the input axis 13, difficulty has been experienced in ensuring that the output signal appearing across the

terminals

14 and 15, and accordingly the representation of input rate provided, is not significantly affected by variations in ambient temperature. In particular difficulty has been experienced in achieving stability of the zero-rate output (that is to say, in the amplitude of the output signal when the input rate is zero) especially where large operational temperature-ranges (for example, as much as from -55C to +100C) are involved. One way in which zero-rate temperature stability can be improved is by submitting the gyrsocope to a temperature cycling process executed over somewhat more than the intended operational temperature range. In this way it is possible to reduce to a small degree those shifts in zero rate output which are of a permanent nature and which arise as a consequence of excursions of temperature during the operational life of the gyroscope.

The temperature cycling process usually results in an undesirably large amplitude of output signal at zero input rate, and it has been the practice to reduce this by a procedure involving angular adjustment of the pick-off stator 8 within the casing 2. The stator 8 is mounted within the casing 2 by screws 28 (of which only one is shown in FIG. 1) and according to the procedure these are first loosened to free the stator 8 for slight rotational adjustment with respect to the rotor 9. The angular location of the stator 8 is adjusted to achieve an acceptable zero-rate signal-amplitude, and the screws 28 are then re'tightened to hold the stator 8 fast within the casing 2 once again. Unfortunately this procedure usually has the disadvantage of producing new temperature dependent stresses. These stresses reintroduce the likelihood that subsequent temperature excursions will give rise to significant shifts in the zerorate output, and so make the temperature cycling process to a significant extent ineffective.

The necessity for mechanical adjustment of the pickoff stator 8, with its attendant disadvantage, may be avoided by backing off the standing zero-rate signal with an alternating-current signal that is derived as a fraction of the energizing signal supplied to the primary winding 21 of the pick-off 7. This signal may be derived using a separate transformer that is energized from the same source as the primary winding 21, but alternatively may be derived using a third winding on the pickoff stator 8. Where a third winding on the stator 8 is used, then this may be provided as illustrated in FIG. 2 as a second secondary winding 29 that is wound with the primary winding 21 so that the amplitude of in duced signal appearing across

terminals

30 and 31 of the winding 29 is independent of rotor displacement.

In addition to the above-discussed shifts in zero-rate output arising from temperature excursions, there are other temperature dependent effects that are of practical significance. Firstly there is variation with temperature in the scale factor of the gyroscope, that is to say, in the ratio to the value of the maximum operational input-rate, of the difference in output-signal amplitude between the maximum-operational and zero inputrates. Secondly there is variation in the zero-rate output-amplitude that takes place with variation in ambient temperature from one value to another. Compensation for the first of these effects can be obtained by connecting a temperature dependent impedance element, for example a thermistor, in series with the secondary winding 22 of the pick-off 7. A circuit which is illustrative of use of a thermistor in the latter respect and which also provides compensation for the second effect (namely variation in the zero-rate outputamplitude from one temperature to another) in the gyroscope of FIG. 1, is shown in FIG. 3.

Referring to FIG. 3, a thermistor 32 shunted by a resistor 33, is connected in series with the secondary winding 22 of the pick-off 7 to provide compensation for the variation in the scale factor throughout the operational temperature range of the gyroscope. The terminal 26 of the secondary winding 22 is connected via the shunt-connected thermistor 32 and resistor 33 to a centre-tap 34 (not shown in FIG. 2) of the second secondary winding 29. The signal induced in the winding 29 from the primary winding 21 is applied from the

terminals

30 and 31 across two serially-connected

resistors

35 and 36 to derive between the centre-tap 34 and the junction of the two

resistors

35 and 36, a signal in opposition to that supplied via the shunt-connected thermistor 32 and resistor 33. The resultant signaldifference is applied across a resistor 37 to the

output terminals

14 and 15 of the gyroscope.

Compensation for variation in the zero-rate output with variation in temperature from one value to another is provided from the signal induced in the winding 29. A fraction of this signal is tapped off and applied across the shunt'connected thermistor 32 and resistor 33, in opposition to the signal from the winding 22. To this end a resistor 38 is connected between the terminal 30 of the winding 29 and the terminal 26 of the winding 22; the resistor 38 may alternatively be connected to terminal 31 depending upon the phase of the signal required to achieve the compensatory effect. The value of the resistor 38 determines the amplitude of signal applied between the terminal 26 and the centre-tap 34, and can readily be adjusted as required, during assembly and testing of the gyroscope.

The values of the

resistors

35 and 36 are chosen to provide for zero output across the

terminals

14 and 15 for zero-rate input at a datum operational temperature (normally C). The value of the resistor 37, on the other hand, determines the scale factor applicable.

The quadrature component of the zero-rate output is reduced by means of a capacitor 39 connected from the terminal 31 to the terminal 27; it could equally well be connected from the terminal 31 to the terminal 26 or alternatively from terminal to either terminal 26 or 27.

All the components of the circuit of FIG. 3 are incorporated within the casing 2 of the gyroscope, but one main disadvantage of this circuit is the necessity of providing the centre-tap 34 on the winding 29. The need for a centre-tap can be avoided if the circuit of FIG. 4 is used instead.

Referring to FIG. 4, a resistor that is provided for sealing purposes is in this case connected between the terminal 26 of the secondary winding 22 and the terminal 31 of the second secondary winding 29. The terminal 31 is connected to the terminal 14 via a shuntconnected thermistor 41 and resistor 42 that serve to effect scale-factor temperature-compensation in the output signal. The other terminal, terminal 30 of the winding 29 is connected to the terminal 26 via a resistor 43 to back off across the resistor 40 the zero-rate signal that appears across the winding 22 at the datum temperature. A further resistor 44 is connected between the terminal 30 and the terminal 14 so as to apply across the shunt-connected thermistor 41 and re sistor 42 a signal providing compensation for the variation of the zero-rate output with variation in ambient temperature from one value to another,

In certain circumstances the quadrature component of the zero-rate output may be reduced with the circuit of FIG. 4, by connecting a capacitor between

terminals

30 and 26; this is indicated in FIG. 4 in broken line by the connection of a capacitor 45 in shunt with the resistor 43. The capacitor may alternatively be connected between the

terminals

30 and 27. On the other hand, there may be circumstances in which it is essential to reduce the number of components used and then it is possible to omit the resistor 43; its use is to be preferred however, wherever possible. The scaling resistor 40 may, as an additional alternative, be connected across the

terminals

14 and 15 instead of serially; the

terminals

26 and 31 of the two

windings

22 and 29 are in this case connected directly to one another.

The second secondary winding 29 as described above is wound on the stator 8 with the primary winding 211, and so the induction of voltage therein is influenced by substantially the same temperature-dependent variations as that of the signal in the winding 22. However, it is not essential that the winding 29 is provided on the stator 8 or even that the voltage it provides is temperature dependent. The winding 29, as an alternative, may be provided as the secondary winding of a separate transformer housed within the casing 2 and having a primary winding energized in parallel with the primary winding 21.

We claim:

l. in apparatus comprising a displacementresponsive transducer having a primary winding and a secondary winding inductively coupled to one another to an extent dependent on an applied displacement, output terminals, and circuit means coupled between said secondary winding and said output terminals for supplying to said output terminals a cyclically-varying electric signal derived from said secondary winding to have an amplitude dependent on the said applied displacement; the improvement wherein said circuit means comprises a further winding energized synchronously with said primary winding, said further winding having a tapping point between its two ends, a temperature-dependent impedance connected between a first of the two ends of said secondary winding and said tapping point, a resistance connected between said first end of said secondary winding and one of the two ends of said further winding, and two resistances interconnecting a first of said output terminals with the two ends respectively of said further winding, and means coupling the second end of said secondary winding to the second of said output terminals.

2. Apparatus according to claim 1 wherein said temperature-dependent impedance is a thermistor.

3. ln apparatus comprising a displacementresponsive transducer having a primary winding and a secondary winding inductively coupled to one another to an extent dependent on an applied displacement, output terminals, and circuit means coupled between said secondary winding and said output terminals for supplying to said output terminals a cyclically-varying electric signal derived from said secondary winding to have an amplitude dependent on the said applied displacement: the improvement wherein said circuit means includes a temperature-dependent impedance, means for deriving a further cylically-varying signal, and signal-applying means for applying the further signal across said temperature-dependent impedance to modify the amplitude of the signal supplied to the output terminals in accordance with said further signal, said means for deriving said further signal being a further winding energized synchronously with said primary winding, and said signal-applying means including connection means coupling a first of the two ends of said temperature dependent impedance to a first of the two ends of said further winding, first resistance means coupling said first end of said temperature-dependent impedance to one of the two ends of said secondary winding, and second resistance means coupling the second end of said further winding to the second end of said temperature-dependent impedance.

4. Apparatus according to claim 3 including third resistance means coupling said second end of said further winding to said one end of said secondary winding.

5. Apparatus according to claim 3 wherein said temperature-dependent impedance is a thermistor.

#i l l= l= l mg? UNITED STATES PATENT OFF'CE CERTIFICATE OF CORRECTION Patent No. 3,787,758 Dated January 22, 1974 Inventor (s) Robin Ashby and Terrence Ernest Adams 7 It is certified r1at error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: I v v Foreign Application Priority Data January 27, 1971 Great Britain. .7 .3310/71 Signed and sealed this 18th day of June 1974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR, V v c. MARSHALL DANN Attesting Officer a Commissioner of Patents zgz g UNITED STATES PATENT OFF'CE CERTIFICATE OF CORRECTION Dated January 22, 1974 Patent No. 3, 787 758 InVentOI(S) Robin Ashby and Terrence Ernest Adams It is certified hat error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Foreign Application Priority Data January 27, 1971 Great Britain. {3310/71 Signed and s eele d this 18th day of Jun e 1974'.

(SEAL) Attest: v

. C. MARSHALL DANN EDWARD M.FLETCHER,JR, t Attesting Officer Commissioner of Patents

Claims

1. In apparatus comprising a displacement-responsive transducer having a primary winding and a secondary winding inductively coupled to one another to an extent dependent on an applied displacement, output terminals, and circuit means coupled between said secondary winding and said output terminals for supplying to said output terminals a cyclically-varying electric signal derived from said secondary winding to have an amplitude dependent on the said applied displacement; the improvement wherein said circuit means comprises a further winding energized synchronously with said primary winding, said further winding having a tapping point between its two ends, a temperaturedependent impedance connected between a first of the two ends of said secondary winding and said tapping point, a resistance connected between said first end of said secondary winding and one of the two ends of said further winding, and two resistances interconnecting a first of said output terminals with the two ends respectively of said further winding, and means coupling the second end of said secondary winding to the second of said output terminals.

3. In apparatus comprising a displacement-responsive transducer having a primary winding and a secondary winding inductively coupled to one another to an extent dependent on an applied displacement, output terminals, and circuit means coupled between said secondary winding and said output terminals for supplying to said output terminals a cyclically-varying electric signal derived from said secondary winding to have an amplitude dependent on the said applied displacement: the improvement wherein said circuit means includes a temperature-dependent impedance, means for deriving a further cylically-varying signal, and signal-applying means for applying the further signal across said temperature-dependent impedance to modify the amplitude of the signal supplied to the output terminals in accordance with said further signal, said means for deriving said further signal being a further winding energized synchronously with said primary winding, and said signal-applying means including connection means coupling a first of the two ends of said temperature dependent impedance to a first of the two ends of said further winding, first resistance means coupling said first end of said temperature-dependent impedance to one of the two ends of said secondary winding, and second resistance means coupling the second end of said further winding to the second end of said temperature-dependent impedance.