GB2301437A

GB2301437A - Thermally compensating a rate gyro

Info

Publication number: GB2301437A
Application number: GB9000019A
Authority: GB
Inventors: Alain Raffy; Francois Haffner; Jean-Claude Card
Original assignee: Societe de Fabrication dInstruments de Mesure SFIM SA
Current assignee: Societe de Fabrication dInstruments de Mesure SFIM SA
Priority date: 1989-01-10
Filing date: 1990-01-02
Publication date: 1996-12-04
Anticipated expiration: 2010-01-02
Also published as: GB2301437B; DE4000559A1; GB9000019D0; FR2729752A1; FR2729752B1

Description

1 2301437 A METHOD AND APPARATUS FOR THERMALLY COMPENSATING A RATE GYRO

The invention relates to a method and an apparatus for thermally ccxnpensating a rate gyro.

BACKGROUND OF THE INVENTION

In conventional manner, as shown in the longitudinal section view of Figure la, a rate gyro includes a flywheel Vo which is usually mounted on a Cardan coupling Cd, the flywheel being driven by a torque motor Mc, with the ring of magnets of the torque motor Mc being referenced CA. The assembly is mounted on a fixed gyro body Ca and is driven by the drive shaft Ar of a drive motor Me. The flywheel Vo is rotatable about the shaft Ar, and the position of the flywheel Vo is detected by a position detector Dep fixed to the gyro body Co. A cover Ca protects the assembly.

In the above-described type of rate gyro, the torque motor Mc is of the galvanometric type. The force F exerted thereby is a function of the magnetic field generated by the ring of magnets and of the current Imc flowing through its windings. The magnetic field established in this way varies with the core temperature of the gyro, thereby varying the force F, and thus the scale factor of the gyro, which factor is directly related to the effective temperature of the moving parts constituted by the flywheel and the rings of magnets in the torque motor.

Because the above-mentioned parts are moving parts, it is not possible to measure their temperature since, during operation of the gyro, they are rotating rapidly at about 100 revolutions per second.

The rise in temperature of the above-mentioned moving parts is essentially due to the current Imc flowing through the windings of the torque motor, thus giving a dynamic and accumulative aspect to the variation in the scale factor of a rate gyro.

The method and the apparatus for thermally compensating a rate gyro seek to remedy the above-mentioned drawback by implementing a technique in which the temperature of the moving parts is not measured, but is estimated.

1 Another object of the present invention is to implement a method and apparatus for thermally compensating a rate gyro, which method and apparatus are specific to a given type of gyro.

Another object of the present invention is to implement a method and apparatus for thermally compensating a rate gyro, which method and apparatus are specific to the application or the utilization conditions of said gyro for a given type of gyro.

Another object of the present invention is also to Implement a method and an apparatus for thermally compensating a rate gyro whereby the accuracy of the thermal compensation can be rogranned and left merely to the initiative of the user for a given application.

SUMMARY OF THE INVENTION

The method and the apparatus of the invention for thermally compensating a rate gyro including a drive motor, a torque motor, and moving parts such as a flywheel and a ring of magnets, are remarkable in that in order to determine a scale factor coefficient of the gyro as a function of temperature in real time, the temperature Tm of a fixed element internal to the gyro is measured, the electrical power delivered to the gyro is measured, and the estimated temperature TP of the ring of magnets and of the flywheel is determined from a mathemat ical model or a conversion table. The scale factor coefficient KT of the gyro is established as a function of temperature in accordance with a polynomial relationship of the form:

n KT = KTo E Xp(T - To)P P=0 whiere KTo represents the scale factor of the gyro at a reference temperature To. The value of the parameter KTo is obtained by calibration at the above-mentioned refezence temperature To, n represents the degree of the polynomial relationship, and Xp represents a sequence of proportionality coefficients determined by calibration.

The method and apparatus of the invention are applicable to navigation or stabilization systems for aircraft or other mechanical assemblies.

3 BRIEF DESCRIPTION OF THE DRAWINGS

The method and apparatus of the invention for thermally compensating a rate gyro are described in greater detail below with reference to the accompanying drawings, in which:

Figure la is a section through a conventional type of rate gyro; Figure lb is a block diagram of the component parts of apparatus in accordance with the invention; Figure 2 shows a non-limiting embodiment of an element of the apparatus of the invention shown in Figure lb; Figure 3a is a flow chart for a subprogram for calculating the estimated temperature of the moving parts of the gyro; and Figure 3b is a flow chart of a subprogram for calculating the scale factor coefficient of the gyro on the basis of the previously calculated estimated temperature of the moving parts of the gyro.

DETAILED DESCRIPTION

The method of the invention for thermally compensating a rate gyro is initially described with reference to Figure lb.

As recalled above with reference to Figure la, the gyro may be constituted by a conventional type of rate gyro, essentially constituted by a drive motor Me, a torque motor Mc, and moving parts such as a flywheel Vo and a ring of magnets CA.

As shown in Figure lb, the method of the invention for thermally compensating a conventional type of gyro, such as that shown in Figure la, consists in measuring the temperature Tm of a fixed element internal to the gyro, and in measuring the electrical power delivered to the gyro. Naturally, the order in which the temperature Tm. and the electrical power delivered to the gyro are measured is not critical, and either of these parameters may be measured after the other or vice versa.

The method of the invention then consists in determining the estimated temperature T for the ring of magnets from a conversion table or a mathematical model, and then in establishing a scale factor coefficient for the gyro in real time, said scale factor coefficient being KT.

i 4 Preferably, in accordance with an advantageous aspect of the method of the invention, the gyro scale factor KT is expressed as a function of temperature using a polynomial relationship of the form:

n KT - KTo E \p(fr - T0)p (1) p=o In the above relationship: KTo represents the scale factor of the gyro under consideration at a reference temperature To, with the value of the parameter KTo being determined by calibration at the abovementioned temperature To, and the parameters Xp representing proportionality coefficients also determined by calibration; n represents the degree of the above-mentioned polyncminal relationship; and p is the index variable of the polynominal relationship.

Naturally, the parameters KTo and Xp are parameters given by the manufacturer of the gyro, with the parameters being obtained by calibration for a specific type of gyro.

Calibration may consist in such cases in measuring the scale factor while the gyro under consideration is placed in a thermal enclosure at the above-mentioned reference temperature To, said reference temperature constituting an equilibrium temperature for the gyro.

In accordance with a particularly advantageous aspect of the method of the invention, the conversion table or the mathematical model for the gyro of the type under consideration has the form:

aP(t) + P[dP/dt]t + XTm(t) + 8[dTm/dt]t + n[dt/dt]t (2) In this relationship, P(t) represents the instantaneous electrical power delivered to the gyro; [dP/dt]t represents the instantaneous value of the derivative of the electrical power delivered to the gyro; Tm(t) represents the instantaneous value of the measured temperature of the fixed internal element of the gyro; [dTm/dt]t represents the instantaneous value of the derivative of the measured temperature of the fixed internal element of the gyro; 1 1 --- - --- -- [dt/dtlt represents the instantaneous value of the derivative of the estimated temperature of the ring of magnets; and a, P, j, 6, and rl represent proportionality coefficients determined for a given type of gyro for a utilization under consideration.

It may also be observed that depending on the intended application, or at least depending on the gyro utilizations to which the method of the invention is applied, the measured temperature Tm(t) of the fixed element is replaced by the difference between said temperature and the surrounding temperature Te(t). This makes it possible, in particular, to take account of the thermal inertia of the gyro in a particular application under consideration relative to the surrounding temperature.

Naturally, for a given type of gyro, the parameters a, P, 6, and -9 are determined by calibration for the application under consideration.

it will naturally be understood that the measurement of the temperature Tm, and in particular the instantaneous temperature Tm(t), and the measurement of the electrical power P(t), and also of the surrounding temperature Te(t) is performed by periodic sampling, e.g. at a determined sampling frequency selected as a function of the application or the utilization of the gyro under consideration.

By way of non-limiting example and in accordance with an advantageous characteristic of the method of the invention, the electrical power P(t) delivexed to the gyro is determined by measuring the currents Imc and Ime as delivered respectively to the torque motor Mc and to the drive motor Me of the gyro.

Naturally, in accordance with this advantageous characteristic of the method of the invention, the temperature Tm(t) of a fixed internal eleinent of the gyro is measured by measuring the temperature of a fixed internal element of the gyro which is close to the moving parts whose temperature is to be estimated, i.e. the flywheel and the rings of magnets. The fixed element is preferably constituted by the flywheel i i 1 6 position detector Dep which is naturally fixed to the body Co of the gyro.

It will be observed that the method of the invention is paticularly advantageous insofar as the polynomial form of the scale factor coefficient KT and in particular the degree thereof can be optimized as a function of the desired accuracy, with the coefficients \p of the terms of degree 2 thus being capable of taking up zero values in order to obtain a variation relationship for the scale factor coefficient KT of the gyro under consideration which is the closest possible to the real relationship for the type of gyro under consideration.

As for the mathematical model or the conversion table and the form given thereto in above-mentioned relationship (2), it will naturally be observed, as described in greater detail below, that while calculating the first estimated temperature value of the ring of magnets t, the value of the derivative relative to time of said variable is arbitrarily selected as being equal to zero, which amounts to considering that the first calculated value of the estimated temperature t is taken as being equal to a notional earlier value in order to initialize the method of the invention. Naturally the value of the derivative of the estimated temperature t may then be updated and, in particular, it may be taken as being equal or proportional to the difference in the estimated temperature t following two successive samplings of the electrical power P(t) delivered to the gyro. The same applies to the measured temperature Tm(t) for the fixed internal element of the gyro, and even to the surrounding temperature Te(t).

In general, it is not necessary for the sampling frequencies at which the three above-mentioned parameters are measured to be identical.

There follows a more detailed description of apparatus for thermally compensating a rate gyro using the method of the invention, with the apparatus being described with reference to the same Figure lb.

As shown in said figure, the apparatus of the invention comprises means 1 for measuring the temperature Tm of a fixed i 7 internal element of the gyro, as described above, and means 2 for measuring the electrical power delivered to the gyro.

In addition, calculating means 3 are provided, said calculating means comprising at least one calculation central unit 30 and software means serving firstly to establish the estimated temperature t of the ring of magnets on the basis of a mathematical model or a conversion table, and secondly in real time, to establish a scale factor coefficient for the gyro using a polynomial relationship expressed in the form of abovementioned equation (1).

Naturally, as also shown in Figure lb, the calculation means 3 also include, in association with the central unit 30, at least one nonvolatile RCM type memory 31 and a working RAM type memory 32. The central unit is preferably constituted by a 16-bit microprocessor, or even by a 32-bit microprocessor, e.g. a Motorola 68000 microprocessor.

As also shown in Figure lb, the means 1 for measuring the tamperature Tm may be constituted by a temperature sensor placed on the position detector Dep as shown in Figure la, said temperature sensor being constituted, for example, by a temperature measuring probe sold by ANALOG DEVICE under the reference 590. It will also be observed, as shown in Figure lb, that the temperature measurement probe constituting the means for measuring the temperature Tm(t) and referenced 1 is connected to an analog-to-digital converter 10 which is connected via a bus type connection to the central unit 30 of the calculating means 3.

Similarly, a temperature measurement probe 4 is placed on the outside of the gyro cover in order to measure the surrounding temperature Te(t), this temperature probe 4 is likewise connected to an analog-to-digital converter 40 in turn connected to the central unit 30 of the calculating means 3.

Similarly, the stator circuit of the torque motor Mc is powered by current Imc via a control circuit 5 which is itself connected to the central unit 30 of the calculator means 3 via a bus type link.

1 1 Likewise, the drive motor Me is fed with current Ime via a control circuit 6, which is likewise connected to the central unit 30 of the calculator means 3.

It will be observed that the control circuit 5 for the torque motor Mc and the control circuit 6 for the drive motor Me are constituted by similar circuits which are shown and described in greater detail in Figure 2.

The control circuit 5 preferably controls the current delivered to the torque motor Mr. Thus, as shown in Figure 2, this control circuit comprises a digital-to-analog converter 50 directly connected via a bus connection to the central unit 30 of the calculator means 3, and a voltage/current amplifier 51, which amplifier may be constituted by any conventional type of voltage/current amplifier, and is therefore not described in greater detail herein.

In contrast, the control circuit 6 may be constituted in the same way by a digital-to-analog converter direc ly connected via a bus connection to the central unit 30 of the calculator means 3 together with a voltage amplifier, thereby amplifying the voltage delivered by the above-mentioned digital-to-analog converter so as to provide direct voltage control of the drive motor me.

It will naturally be understood that regardless of the way in which the torque motor Mc and the drive motor Me are controlled, i.e. by current or by voltage, all of the control signals delivered by the central unit to the digital-to-analog converter in the control circuit 5 or 6 are converted into voltages by the digital-to-analog converter circuits and the resulting voltage is then transformed either into a current or else into a voltage for controlling the torque motor Mc or the drive motor me respectively unambiguously as a function of the information delivered by the central unit 30 of the calculator means 3. In this way, the currents Imc and Ime delivered to the torque motor Mc and the drive motor Me are kxxym at each instant, and in particular at the sampling instants for the above- mentioned temperature values. There is thexefore no need to measure the values of the currents Imc and Ime directly in the physical sense.

There follows a more detailed description of the software means for implementing the method and the apparatus of the invention with reference to Figures 3a and 3b.

In general, the software means enabling the estimated temperature t of the ring of magnets CA to be estimated are advantageously constituted by a subprogram stored in the nonvolatile memory of the calculator means 3.

Similarly, the software means for establishing a scale factor coefficient KT of the gyro in real time may advantageously be constituted by a subprogram stored in the working memory of the calculator means.

As shown in Figure 3a, the subprogram for establishing the estimated temperature t of the ring of magnets CA may advantageously include a module for sampling and storing the temperature Tm(k) of the fixed internal element of the gyro and the surrounding temperature Te(k). Naturally, the currents delivered respectively to the torque motor Imc(k) and to the drive motor Ime(k) are determined as described above. The index k of the measured values or of the values determined by sampling actually represents the instantaneous value of the cozz spcnding parameter at the sampling instant under consideration. Naturally, the sampled values Tm(k), Imc(k), Ime(k), and Te(k) are stored, preferably in the RAM 32 of the calculator means 3.

In addition, the subprogram for determining the estimated temperature t of the ring of magnets CA also includes a module for calculating the derivative [dTm/dt]t of the measured temperature Tm. By definition, this derivative is proportional to the difference between two successive teniperature samples, which samples are written Tm(k) and Tm(k-1). The coefficient of proportionality is specified by Kl, and this coefficient may be determined by the successive increases of the successive sampled values Tm(k) and by corresponding averaging.

The above-mentioned subprogram also includes a module for calculating the instantaneous electrical power P(k) corresponding to the power delivered to the gyro at the sampling instants. This instantaneous electrical power is defined by the sum of the products of the power supply voltages and the currents Imc(k) and Ime(k) in the corresponding motors. Naturally the power supply voltages V for the corresponding motors may be determined in the same way as the currents, and as described 5 above.

As also shown in Figure 3a, the above-mentioned subprogram includes a module for calculating the derivative of the instantaneous electrical power delivered to the gyro [dP/dtlt. By definition, this derivative is proportional to the difference P(k) - P(k-1) of two successive calculated electrical powers. The coefficient of proportionality K2 may be determined in similar manner to the coefficient of proportionality Kl by the successive increases in the delivered electrical power.

As shown in Figure 3a, a read module is provided for reading the values of the above-described coefficients a, 8, and 71. Once the values of these coefficients have been acquired by the central unit 30, the above-mentioned subprogram further includes a module for calculating the instantaneous estimated temperature t(k) of the ring of magnets using the relationship given by the mathematical model or the conversion table. As mentioned above, the value of the derivative Edt/dtlt of this estimated temperature is defined as being proportional to the difference between the two closest successive temperature estimates t(k-1) - t(k-2). Naturally, as described above, the value of the derivative is initialized by arbitrarily attributing the value thereto. In the expression for the estimated temperature t(k) in the calculation module as shown in Figure 3a, the proportionality coefficients K3 and K4 are determined in the same way as the proportionality coefficients Kl and K2, thexeby enabling the values of the derivatives of the measured temperatures Tm(k) and t(k-1) to be calculated.

Finally, a module is provided for calculating the new value of the derivative of the temperature t proportional to t(k) - t(k- 1), said module serving to define said derivative as being proportional to the difference t(k) - t(k-1), which is 1 11 the difference of the two most recent successive values of the estimated temperature. The coefficient of proportionality is a coefficient K5 which is determined in similar manner to the above-mentioned coefficients Kl to M Naturally, and in advantageous but non-limiting manner, the new value of the derivative of the estimated temperature t may be reinjected into the module for calculating the estimated t(k) in order to perform a series of iterations, thereby increasing the accuracy with which the estimated temperature t(k) representing the instantaneous estimated temperature is calculated.

A more detailed description of the subprogram stored in the working memory 32 of the calculator mean 3 for calculating the instantaneous scale factor coefficient KT(k) of the gyro is described with reference to Figure 3b.

In the above-mentioned figure, the above-mentioned subprogram may advantageously include a module for reading the value of the parameter To at the reference temperature To and for reading the above-mentioned coefficients >,p. Naturally, the coefficients KT and \p relating to a determined type of gyro under consideration may advantageously be stored for the gyro in the non-volatile memory 31 of the calculator means 3.

In addition, the above-mentioned subprogram includes a module for calculating the instantaneous coefficient KT(k) of the instantaneous scale factor KT using the polynomial relationship under consideration. In the expression of the polynomial relationship shown in the above-mentioned calculation module, the variable t(k) is naturally the value of said variable as calculated in the calculation module of the preceding subprogram as shown in Figure 3a.

A method and an apparatus have been described for thermally compensating a rate gyro, whIch method and apparatus are particularly effective firstly insofar as the accuracy with which the instantaneous scale factor coefficient KT is calculated can be determined by selecting the degree of the polynominal relationship representative thereof.

Secondly, the method and the apparatus of the invention appear to be particularly effective insofar as for a determined 12 type of gyro, i.e. a gyro that does in fact correspond to a data series defined by a manufacturer, together with the parameters KTo and Xp which are determined and supplied by the manufacturer, it is possible in each application for said gyro under consideration to subsequently determine the parameters a, P, V, 6, and n of the mathematical model or conversion table that represent the particular utilization for the type of gyro under consideration. Naturally, the above-mentioned coefficients a, P, y, 8, and.9 may be determined, for example, while testing the gyro in the application under consideration with different electrical powers being delive to the above mentioned gyro. By sampling the temperature measurement values, either of the surroundings or else of the tenperature Tm, i.e.

the measured temperature of the fixed internal element of the gyro, and then by measuring the coefficient KT for each power value, it is possible to deduce the estimated temperature 'P and finally for each value of power under consideration. Then, the measurements of the measured Tm for the corresponding powers can be used for establishing a system of equations in a, P, V, 8, and TI and this system of equations can be solved without difficulty using the least squared method with optimum filtering applied thereto as is well known to the person skilled in the art of digital processing.

j_--- 1 --- - ------- 1 1 0 13

Claims

CLAIMS 1/ A method of thexmally compensating a rate gyro comprising a

drive motor, a torque motor, and moving parts such as a -flywheel and a ring of magnets, the method consisting in:

measuring the temperature Tm of a fixed internal element of the gyro; measuring the electrical power delivered to the gyro; determining the estimated temperature rr of the ring of magnets on the basis of a conversion. table or of a mathematical model; and establishing a scale factor coefficient KT of said gyro as a function of temperature and in real time using a polynomial relationship of the form: n KT = KTo E' Xp(tr - To)P P=0 in which:

KTo represents the scale factor of said gyro at a reference temperature To, the value of the parameter KTo being obtained by calibration at the above-mentioned reference temperature To, Xp represents proportionality coefficients detned by calibration, and n represents the degree of the above-mentioned polynomial relationship.

2/ A method according to claim 1, whierein said conversion table or mathematical model for a gyro of given type has the form: t = aP(t) + 0[dP/dt]t + yTm(t) + 8[dTm/dt]t + Edt/dtlt in which:

P(t) represents the instantaneous electrical power delive red to the gyro; [dP/dtIt represents the instantaneous value of the derivative of the electrical power delivered to the gyro; Tm(t) represents the instantaneous value of the measured temperature of the fixed internal element of the gyro; [dTm/dt]t represents the instantaneous value of the derivative of the measured temperature of the fixed internal element of the gyro; 14 [dt/dt]t represents the instantaneous value of the derivative of the estimated temperature of the ring of magnets; and a, p, V, 6, and TI represent proportionality coefficients determined for a given type of gyro for a utilization under consideration.

3/ A method according to claim 2, wherein the measured temperature Tm(t) of the fixed element is replaced by the difference between said temperature and a surrounding temperature Te(t).

4/ A method according to any one of claims 1 to 3, wherein the electrical power P delivered to the gyro is determined by measuring the electrical currents Imc and Ime delivered respectively to the torque motor and the gyro drive motor.

5/ A method according to any one of claims 1 to 4, wherein the temperature Tm of a fixed internal element of the gyro is measured by measuring the temperature of a fixed internal element of the gyro which is closest to the moving parts, the fixed element being constituted, for example, by the flywheel position detector.

6/ A method of thermally compensating a rate gyro substantially as herein described with referece to the accompanying drawings.

7/ Apparatus for thermally compensating a rate gyro, the gyro comprising a drive motor, a torque motor, and moving parts such as a flywheel and a ring of magnets, said apparatus comprising:

means for measuring the temperature Tm of an internal fixed element of the gyro; means for measuring the electrical power delivered to the gyro; and calculator means including at least am central calculation unit and software means serving to establish firstly the estimated temperature fr of the ring of magnets on i 1 the basis of a conversion table or of a mathematical model, and secondly, in real time, a scale factor coefficient of the gyro using a polynomial relationship of the form: n KT = KTo E p(,t - TOT p=o in which:

KTo represents the scale factor of said gyro at a refezence temperature To, the value of the parameter KTO being obtained by calibration at the above-mentioned reference temperature To, Xp represents proportionality coefficients determined by calibration, and n represents the degree of the above-mentioned polynomial relationship.

8/ Apparatus according to claim 7, further including means for measuring the temperature Te(t) surrounding the apparatus.

9/ Apparatus according to claim 7, wherein the software means for establishing the estimated t of the ring of magnets are constituted by a subprogram stored in non-volatile memory of said calculator means.

10/ Apparatus according to claim 7, 8, or 9, where-in said software means for establishing, in real time, a scale factor coefficient of the gyro are constituted by a subprogram stored in working memory of the calculator means.

11/ Apparatus according to claim 9, wherein said subprogram for establishing the estimated temperature T of the ring of magnets ccmprise:

a module for sampling and storing the temperature Tm(k) of the fixed internal element of the gyro and the surrounding temperature Te(k), together with the electrical currents Imc(k) and Ime(k) respectively delive to the torque motor and to the gyro drive motor; a module for calculating the derivative [dTm/dt]t, said derivative being proportional to the difference between two successive temperature samples Tw(k) Tw(k-1); 1 16 a module for calculating the electrical power P(k) delivered to the gyro, said electrical power being defined as the sum of the products of the power supply voltages and the currents Imc(k) and Ime(k) delivered to the corresponding motors; a module for calculating the derivative of the electrical power [dP/dtlt delivered to the gyro, said derivative being proportional to the difference P(k) - P(k-1) of two successively calculated electrical power; a module for reading the values of the coefficients a, P; 6, and -q; a module for calculating the estimated temperature t(k) of the ring of magnets an the basis of the relationship given by the conversion table or the mathematical model, with the value of the derivative [dlt/dt]t of said estimated temperature being defined as being proportional to the difference between the two most closest estimated temperatures Tr(k-1) - t(k-2); and a module for calculating the new value of the derivative proportional to t(k) - t(k-1), i.e. the difference between the two most recent successive values of the estimated temperature.

12/ Apparatus according to claim 10, wherein said subprogram stored in working memory of the calculator means comprises: a module for reading the value of the parameter KTo at the reference temperature To and for reading the coefficients >,p; and a module for calculating the instantaneous coefficient KT(k) of the scale factor KT in acoordan with the polynomial relationship under consideration.

13/ Apparatus for thermally compexisating a rate gyro substantially as herein described with referece to and as illustrated in the accompanying drawings.

1 Amendments to the claims have been filed as follows 1-7 CLAIMS 1/ A method of thermally compensating a rate gyro comprising a drive motor, a torque motor, and moving parts such as a flywheel and a ring of magnets, the method consisting in:

measuring the temperature Tm of a fixed internal element of the gyro; measuring the electrical power delivered to the gyro; determining the estimated temperature T of the ring of magnets on the basis of a conversion, table or of a mathematical model; and establishing a scale factor coefficient KT of said gyro as a function of temperature and in real time using a polynomial relationship of the form:

n KT - KTO E Xp(T - To)P P-O in which:

KTo represents the scale factor of said gyro at a reference temperature To, the value of the parameter KTo being obtained by calibration at the above-mentioned referexice tenature To, Xp represents proportionality coefficients determined by calibration, n represents the degree of the above-mentioned polynomial relationship, and p is the index variable of the polynomial relationship.

2/ A method according to claim 1, wherein said conversion table or mathtical model for a gyro of given type has the form: t - (%P(t) + P[dP/dt]t + VTm(t) + 6[dTrn/dt]t + [dt/dtlt in which:

P(t) represents the instantaneous electrical power delivered to the gyro; EdP/dtIt represents the instantaneous value of the derivative of the electrical power delivered to the gyro; Tm(t) represents the instantaneous value of the measured temperature of the fixed internal element of the gyro; [dTm/dt]t represents the instantaneous value of the derivative of the value Tm(t); h [dt/dtIt represents the instantaneous value of the derivative of the estimated temperature of the ring of magnets; and a, 0, y, 8, and n represent proportionality coefficients determined for a given type of gyro for a utilization under consideration.

3/ A me a=ozang to claim 1, WhWILtn said cxxslan table or mathwatical =dbl úCW & gy= of given t3" has the form: f a aP(t) + t3C4P/dtIt + ITZ(t) + 6(dtIt + ICC/dtIt In Which '.

PM V the Lnatmtwm Clact:1C41 power delivered to tm; EdPIdtIt rqpceaents tM lrummtara value of the Ivati,vm of the cle=leal pew Mlivered to tr gm, Ma(t) represents the d.tterance between the instantaneous value of the miaagured temperature. of the fixed internal element of eh^ gyro and the value of a mesured surrounding trature, Te(t).

EdIM/dt3t ra&Mtz tha. Inatwo value of the d6Civative of the value Ta(t); [dPr/dtlt rapresenta CW instantaneous value of the derivative of the estimated tratvze of the ring of magnets; and a, 6, &ld rl represent proportionality coefficients date=ined for a given type of for a utilization under consideration.

(0z 4/ A method according to any one of claims 1 to 3, wherein the electrical power P delivered to the gyro Is detexmined by measuring the electrical currents Imc and Ime delivered respectively to the torque motor and the gyro drive motor.

5/ A method according to any one of claims 1 to 4, wherein the temperature Tm of a fixed internal element of the gyro is measured by measuring the temperature of a fixed internal element of the gyro which is closest to the moving parts, the fixed element being constituted, for example, by the flywheel position detector.

6/ A method of thermally compensating a rate gyro substantially as herein described with referece to the accompanying drawings.

7/ Apparatus for thermally compensating a rate gyro, the gyro c=prising a drive motor, a torque motor, and moving parts such as a flywheel and a ring of magnets, said apparatus comprising: means for measuring the temperature Tm of an internal fixed element of the gyro; means for measuring the electrical power delivered to the gyro; and calculator means connected to said measuring means and including at least one central calculation unit and software means serving to establish firstly the estimated temperature T of the ring of magnets on the basis of a conversion table or of a mathematical model, and secondly, in real time, a scale factor coefficient of the gyro using a polynomial relationship of the form:

n KT = KTo E Xp(t - To)P P=0 in which:

1 KTo represents the scale factor of said gyro at a reference temperature To, the value of the parameter KTo being obtained by calibration at the above-mentioned reference teinperature To, Xp represents proportionality coefficients determined by calibration, n represents the degree of the above-mentioned polynomial relationship, and p is the index variable of the polynomial relationship. 8/ Apparatus a rding to claim 7, further including means for measuring the temperature Te(t) surrounding the apparatus.

9/ Apparatus a rding to claim 7, wherein the software means for establishing the estimated t of the ring of magnets are constituted by a subprogram stored in non-volatile memory of said calculator means.

10/ Apparatus according to claim 7, 8, or 9, wherein said software means for establishing, in real time, a scale factor cCef:fic:Lent of the gyro are constituted by a subprcxjram stored in working memory of the calculator means.

ll/ Apparatus according to claim 9, whexein said subprogram for establishing the estimated temperature Tr of the ring of magnets comprise:

a module for sampling and storing the temperature Tm(k) of the fixed internal element of the Tyro and the surrounding temperature Te(k), together with the electrical currents Imc(k) and Ime(k) respectively delivered to the torque motor and to the gyro drive motor; a module for calculating the derivative [dTtn/dtjt, said derivative being proportional to the difference between two successive temperature samples Tm(k) Tm(k-1); ZA a module for calculating the electrical power P(k) delivered to the gyro, said electrical power being defined as the sum of the products of the power supply voltages and the currents Imc(k) and Ime(k) delivered to the corresponding motors; a module for calculating the derivative of the electrical power [dP/dtjt delivered to the gyro, said derivative being proportional to the difference P(k) - P(k-1) of two successively calculated electrical power; a module for reading the values of the coefficients a, 0; 8, and -q; a module for calculating the estimated temperature t(k) of the ring of magnets on the basis of the relationship given by the conversion table or the mathematical model, with the value of the derivative [dt/dtjt of said estimated temperature being defined as being proportional to the difference between the two most closest estimated temperatures t(k-1) - t(k-2); and a module for calculating the new value of the derivative proportional to t(k) - t(k-1), i.e. the difference between the two most recent successive values of the estimated temperature.

12/ Apparatus according to claim 10, whexein said subprogram stored in working memory of the calculator means comprises: a module for reading the value of the parameter KTo at the I reference temperature To and for reading the coefficients),p; and a module for calculating the instantaneous coefficient KT(k) of the scale factor KT in accordance with the polynomial relationship under consideration.

13/ Apparatus for thermally compensating a rate gyro substantially as herein described with referece, to and as illustrated in the accompanying drawings.