CA1332969C - Analog torque rebalance loop for a tuned rotor gyroscope - Google Patents
Analog torque rebalance loop for a tuned rotor gyroscopeInfo
- Publication number
- CA1332969C CA1332969C CA000615093A CA615093A CA1332969C CA 1332969 C CA1332969 C CA 1332969C CA 000615093 A CA000615093 A CA 000615093A CA 615093 A CA615093 A CA 615093A CA 1332969 C CA1332969 C CA 1332969C
- Authority
- CA
- Canada
- Prior art keywords
- signal
- axes
- circuit means
- loop
- rotor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/02—Rotary gyroscopes
- G01C19/04—Details
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/02—Rotary gyroscopes
- G01C19/04—Details
- G01C19/30—Erection devices, i.e. devices for restoring rotor axis to a desired position
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T74/00—Machine element or mechanism
- Y10T74/12—Gyroscopes
- Y10T74/1229—Gyroscope control
Abstract
A rebalance loop for controlling a dry tuned rotor gyroscope having a rotor moveable about two orthogonal axes, a first pickoff associated with one of the axes for producing an electrical error signal when a rate is applied to one of the axes, a second pickoff associated with the other of the axes for producing an electrical error signal when a rate is applied to that axis and a pair of torquer coil adapted to receive electrical control signals from the rebalance loop and apply torques to the rotor about the two axes for correcting errors detectedby the pickoffs, the rebalance loop comprising a first direct-axis loop adapted to receive an error signal produced by one of the pickoffs and produce a first amplified error signal, a second direct-axis loop adapted to receive an error signal produced by the other of the pickoffs and produce a second amplified error signal, a first cross-axis loop for amplifying the error signal produced by the one of the pickoffs and adapted to produce a first correction signal, a second cross-axis loop for amplifying the error signal produced by the other of the pickoffs and adapted to produce a second correction signal, a first summing junction for adding the first correction signal to the second amplified error signal for producing a first torque correction signal, and a second summing junction for adding the second correction signal to the first amplified error signal for producing a second torque correction signal.
Description
13329~9 The present invention relates, in general, to an electronic gy,oscope control circuit and, more spe~ fic~lly~ to an electronic rebalance loop for a two-degl~-of-freedom, dry tuned rotor gy,oscope in~Pn~e~l for strapdown applications.
S BACKGROUND OF THE INVENTION
Two-degree-of-freedom, dry tuned rotor gyroscopes are well known. In order to be put into pr~ l use, an electric~l control system, known as a "reb~l~nce loop", must be provided in order to control the gyn~s~opG over its dynamic range and provide a precise output measurement of angular rate of the gyrosco~e rotor about 10 each of the rotor axes. The dynamic range of such an instrument may vary from0.01 degree/hour to greater than 1 Mdian/second reauiring çlectric~l reb~l~nce .;u,lcnls rangin~ from several mi~ GlGs to several hundred milli~ .es. In addition, the dry tuned rotor gy~oscol)e is, by nature, an insl~ument which is susceptible or sensitive to angular acceleration. A re~ n~ loop must COIIIPG~
15 for angular acceleration if full gyr~scope pG,ro,.,.~n~e is to be re~li7ed. In typical dry tuned rotor gyroscopes, flexures are used to support the rotor. Flexures are small mPt~llic blades ~u~)polling the rotor and arranged belween the motor shaft and the rotor in such a way as to give the rotor freedom of angular motion in two orthogonal axes. In a strapdown arrangement, the gyros are secured to the body axes of the 20 vehicle and are rG(luilèd to sense the full range of dynamics of the vehicle. The strapdown arrangPment greatly reduces the IllP~nic~l compl~PYity and cost of thegy~oscope and the,erolG of the system, such as an inertial navigation system forPy~mple, with which it is used, but increases the electronic complPYity with respect to the rebalance electronics. The gyros are provided with a "pickoff" for each 25 degree of freedom or axis of the gyro for producing an e~Pctric~l signal in response to angular motion applied to that axis and a "torquer" associated with each such axis for applying a colllp~ting torque about that axis. The pickoff signals are amplified and delivered to the rebalance loop which processes the signal and produces a torquer current which is delivered to the torquer. This causes the torquer to apply a torque 30 to the rotor so as to ,..~in~i" the rotor in a "null" position. 12~Pb~l~nce loops ty-pically include a direct-axis loops or circuits which receive the signal from the pickoff 1~32~9
S BACKGROUND OF THE INVENTION
Two-degree-of-freedom, dry tuned rotor gyroscopes are well known. In order to be put into pr~ l use, an electric~l control system, known as a "reb~l~nce loop", must be provided in order to control the gyn~s~opG over its dynamic range and provide a precise output measurement of angular rate of the gyrosco~e rotor about 10 each of the rotor axes. The dynamic range of such an instrument may vary from0.01 degree/hour to greater than 1 Mdian/second reauiring çlectric~l reb~l~nce .;u,lcnls rangin~ from several mi~ GlGs to several hundred milli~ .es. In addition, the dry tuned rotor gy~oscol)e is, by nature, an insl~ument which is susceptible or sensitive to angular acceleration. A re~ n~ loop must COIIIPG~
15 for angular acceleration if full gyr~scope pG,ro,.,.~n~e is to be re~li7ed. In typical dry tuned rotor gyroscopes, flexures are used to support the rotor. Flexures are small mPt~llic blades ~u~)polling the rotor and arranged belween the motor shaft and the rotor in such a way as to give the rotor freedom of angular motion in two orthogonal axes. In a strapdown arrangement, the gyros are secured to the body axes of the 20 vehicle and are rG(luilèd to sense the full range of dynamics of the vehicle. The strapdown arrangPment greatly reduces the IllP~nic~l compl~PYity and cost of thegy~oscope and the,erolG of the system, such as an inertial navigation system forPy~mple, with which it is used, but increases the electronic complPYity with respect to the rebalance electronics. The gyros are provided with a "pickoff" for each 25 degree of freedom or axis of the gyro for producing an e~Pctric~l signal in response to angular motion applied to that axis and a "torquer" associated with each such axis for applying a colllp~ting torque about that axis. The pickoff signals are amplified and delivered to the rebalance loop which processes the signal and produces a torquer current which is delivered to the torquer. This causes the torquer to apply a torque 30 to the rotor so as to ,..~in~i" the rotor in a "null" position. 12~Pb~l~nce loops ty-pically include a direct-axis loops or circuits which receive the signal from the pickoff 1~32~9
- 2 -q.~ciqtPd with one axis and delivers a torquer current to the torquer qc~c;q~ with the other axis.
Sevelal ty-pes of ~ pdowll rebqlqn~e loops are known incll1-1ing pulsed loops, of either the binary or pulse width mod~ qte~l types, and analog loops. For lower S pelro~ qnce instruments and systems, any of these types of rebqlqnce loops can be used if suitably modified to suit the specific gyloscope of int_rest. High pelro....qnce, strapdown, inertial gyloscopes having a wide dynamic range and effects due to ~c-pler~qtion require modified rebqlqnce loop de-si~n~. Most, if not all, analog rebqlqn-~ loops use the same principle of operation to g~n~ldle rate infol,llalion from the torquing current and that is by allowing the torquing current to flow through a precision resistor to obtain a voltage signal that is pro~o,lional to the torque.
Usually, the precision resistor is in the "return" lead of the torquer coils so that one node of that resistor can be referenced to ground. A rebqlqnce loop is a type of servo control that is inherently unstable unless the loop contains phase co~ n~qtion or some form of control scllPme-. The most simple scheme of phase colll~ qtion is aphase lag in the direct-axis loop and is used in analog as well as digital rebqlqn~
loops. Another scheme of which the inventors are aware, although it is not known whether it is used in rebql-q-n~ loops of the type with which the present invention is considered, is the so-called "cross-coupled loop" which uses cross-axis circuits for the pul~ose of making the loop stable. The cross-coupled loop uses dirr~r~ntiators as cross-axis circuits only to stabilize nutation but do not provide co,l,~n~qtion for angular acceleration.
SUMMAI~Y OF THE INVENTION
The present invention provides a high resolution analog rebalance loop which is capable of providing a precise output measurement of angular rate of the gyloscope rotor about each of the rotor axes and which provides a more benign en~i,ull"~ent for the gy~uscope than a pulsed rebqlqn~ loop. More spe~ifi~-qlly~ the present invention provides a phase lag rebql-qnc~e loop having cross-axis circuits which are operable to remove torque ~;U[lGllt~!i caused by the transverse inertia of the gyro rotor from the precision resistor, the resistor from which the rate infollllalion is obtained. Known cross-coupled loops were neither intended nor are they capable of doing this because 1~3~969
Sevelal ty-pes of ~ pdowll rebqlqn~e loops are known incll1-1ing pulsed loops, of either the binary or pulse width mod~ qte~l types, and analog loops. For lower S pelro~ qnce instruments and systems, any of these types of rebqlqnce loops can be used if suitably modified to suit the specific gyloscope of int_rest. High pelro....qnce, strapdown, inertial gyloscopes having a wide dynamic range and effects due to ~c-pler~qtion require modified rebqlqnce loop de-si~n~. Most, if not all, analog rebqlqn-~ loops use the same principle of operation to g~n~ldle rate infol,llalion from the torquing current and that is by allowing the torquing current to flow through a precision resistor to obtain a voltage signal that is pro~o,lional to the torque.
Usually, the precision resistor is in the "return" lead of the torquer coils so that one node of that resistor can be referenced to ground. A rebqlqnce loop is a type of servo control that is inherently unstable unless the loop contains phase co~ n~qtion or some form of control scllPme-. The most simple scheme of phase colll~ qtion is aphase lag in the direct-axis loop and is used in analog as well as digital rebqlqn~
loops. Another scheme of which the inventors are aware, although it is not known whether it is used in rebql-q-n~ loops of the type with which the present invention is considered, is the so-called "cross-coupled loop" which uses cross-axis circuits for the pul~ose of making the loop stable. The cross-coupled loop uses dirr~r~ntiators as cross-axis circuits only to stabilize nutation but do not provide co,l,~n~qtion for angular acceleration.
SUMMAI~Y OF THE INVENTION
The present invention provides a high resolution analog rebalance loop which is capable of providing a precise output measurement of angular rate of the gyloscope rotor about each of the rotor axes and which provides a more benign en~i,ull"~ent for the gy~uscope than a pulsed rebqlqn~ loop. More spe~ifi~-qlly~ the present invention provides a phase lag rebql-qnc~e loop having cross-axis circuits which are operable to remove torque ~;U[lGllt~!i caused by the transverse inertia of the gyro rotor from the precision resistor, the resistor from which the rate infollllalion is obtained. Known cross-coupled loops were neither intended nor are they capable of doing this because 1~3~969
- 3 -the effective transverse inertia at the nutation frequency would be reversed twice, once from the phase lag introduced into the signal and a second time by the cross-coupled circuit itself. This would render the loop unstable. In order to function pr~ ly, the cross-axis circuit must be such as to acting only on frequencies in the 5 closed loop bandwidth of the system and the nutation stability must not be afr~c~d.
In accor~lce with the present invention, there is provided a reb~l~nc_ loop for controlling a dry tuned rotor gy,oscope having a rotor moveable about two orthogonal axes, a first pickoff ~csoci~tPd with one of the axes for producing an -PlPctri~l error signal when a rate is applied to one of the axes, a second pickoff 10 ~csoc:~ed with the other of the axes for producing an elPctri~l error signal when a rate is applied to that axis and torquer coils ~ rt~pcl to receive elP~tric~l control signals from the reb~l~nce loop and apply torques to the rotor for colr~cling errors detected by the pickoffs. The reb~l~n-~ loop compri.cPs a first direct-axis loopadapted to receive an error signal produced by one of the pickoffs and produce a first 15 amplified error signal, a second direct-axis loop adapted to receive an error signal produced by the other of the pickoffs and produce a second ~mrlifiPd error signal, a first cross-axis loop for amplifying the error signal produced by the one of the pickoffs and adapted to produce a first correction signal, a second cross-axis loop for amplifying the error signal produced by the other of the pickoffs and adapted to20 produce a second correction signal, a first s~ ing junction for adding the first correction signal to the second ~mplifiPd error signal for producing a first torque correction signal, and a second s~ ning junction for adding the second correction signal to the first amplified error signal for producing a second torque correction slgnal.
`~
13329~
BRIEF DESCRIPlION OF THE DRAWINGS
These and other reatu~s of the invention will become more app~t from the following description in which reference is made to the appended drawings, wherein:
FIGURE 1 is one is a partially broken p~ re view of a typical two-degree-of-S freedom, dry tuned rotor gy~oscope;
FIGURE 2 is a block li~r~m fepr~ n of the gy~osco~e dynamics and of an analog rebalance loop accor~ing one embodiment of the present invention;
FIGURE 3 is a more det~ d block rli~r~m leprese~,t;~ n of an reb~l~nce loop according one embodiment of the present invention;
FIGURE 4 is an electric~l s~henn~tiC of a synchronous de-m~ul~tor and low pass filter/integ-~tQr employed in the em~odiment of FIGVRE 3;
FIGURE 5 is an el~tri~l scl-em~ti~ of a spin notch filter and low-pass f~ter employed in the embo~limPnt of FIGURE 3;
FIGURE 6 is an e1~tri~l scl~ lldlic of a torquer driver employed in the embo~im-ont of FIGURE 3;
FIGURE 7a-c is an el~tric~l sche",atic of cross-axis ~mplifi.o.rs which may be employed in the embodiment of FIGURE 3; and FIGURE 8a and 8b are block di~r~m scl~ tic illustrating the operation of a portion of tPrmin~l portions of the cross-axis and direct-axis ~mplifiPrs.
_. _ 13329~9 DESCRIPTION OF THE ~REFF.RRF.O EMBODIMENTS
With reference to ~IGURE 1 of the drawings, a typical two-degree-of-freedom, dry tuned rotor gy~scope 10 compri~es a housing or body 12 in which a shaft 14 is secured for rotation in bP~ring~ 16 and 18. The drive shaft is driven by 5a motor 20 also secured within the housing. A rotor 22 is secured to one end 24 of the shaft by a flexure assembly, generally design~tPd by reference numeral 26, which in~lud~Ps a gimbal ring 28. A first pair of coaxial half-axles 30 PYtPnding perpendicularly of the drive shaft are rotatably secured in the rotor and gimbal ring as shown and define a first axis and degree of freedom of the rotor and a second pair 10of coaxial half-axles 32 eYtPn~ing perpPn~ ul~rly of the drive shaft and the first pair of half axles are rotatably secured in the gimbal ring and the drive shaft as shown and define a second axis and degree of freedom of the rotor. It is to be undPrstood that the illustration of axles 30 and 32 is intenll~Pd to be functional only. In reality, the axles are flexures which are an integral part of a gimbal ring and rotor and are free 15to flex in such an oriPnt~tion as to be the equivalent to the axles illustrated in ~IGURE 1. Thus both axles allow two degrees of fieedom for the rotor.
The rotor is formed with a ci~culllr~ lial slot 34 in which a perm~nPnt magnet ring is secured for rotation with the rotor and in which torquer coils 40 are disposed. A pair of pickoff coils 36 and 38 are secured to the housing, intPrme~i~tP~
20the housing and rotor, in orthogonal relation to one another and each is operable to sense angular rates applied to one of the input axes of the gyr~scope case and provide coll~nding error signals to a rebalance loop. As is well known to those skilled in this art, a pickoff coil is a device which produces an output signal, generally a voltage, as a function of the angular disp1 ^-PmP-nt of the rotor relative to the gyro 25case or body. The pickoff signals are amplified by sensitive amplifiers, not shown, and delivered to a rebalance loop as explained later.
A pair of torquer coils 40, one of which is shown in FIGIJRE 1, are adapted to receive torquer CU11GI ~s from the reb~l~nce loop and apply torques to the rotor so as to "l~ ;lin the rotor in a "null" position. As shown in ~IGURES 6 and 8, the 30 torquer CU11CIII~ are delivered to an output tP-rmin~l 40' and rcllll~d to an input lcll.linal 40". As is known to those skilled in this field, a torquer coil is a device which exerts torque on the rotor in l-sponsc to a command signal in;~;~tPd by the _ ~., pickoff coils. The amount of current rGluircd to ",~inl~in a null position is directly p~llional to the angular rate applied to the gy~Jscope.
In a strapdown arrangement, the gyros are secured to the body axes of the vehicle and are lG lUil~d to sense the full range of dynamics of the vehicle. This arr~ngPtnPnt greatly reduces the mP~h~ni~l compl~Yity and cost of an inertial navigation system but increases the electronic complexity of the reb~l~n-,~e electronics.
The linealily and stability of the gyr~scope/re~ nce loop combination are of pnt~mount illl~lt;~lce in achieving the desired pGlr~llllance from the instrument.
With particular l~ f~lcnce to ~IGURE 2, the left side of the figure is a T ~rl~eTransform lG~ I;on of the gyroscope and the right side of the figure is the reb~l~no~ loop. The "figure 8" loop formed by blocks 42, 44, 46, 48, 50 and S2 rel,l~nt the "gyro dynamics" or "Nutation Loop", where the natural frequency of un~mped osr~ ti~n is 2~r(H/I) Hz and the damping factor can be ~s~lmed to be zero.
"S" is the Laplace Tl~ rollll opeldlor, "H" is the angular mol~ " and "I" is thel~ svcl~e moment of inertia. Blocks 54 and S6 represent the illlcgl~ling action of pickoff coils 36 and 38. The input to these blocks is angular rate while the outputs thelcrl~,,ll is angular position. S~"l"i~g points S8 and 60 are an integral part of the pickoff coils since the pickoff coils are secured to gyroscope housing 12. Negative inputs to s ~"",i,.g points 58 and 60 result from motion of the housing. Positive inputs result from rotor reaction. The output of the rebal~nrR loop is a pair of torquer .;wlclll~ which, in FIGURE 2, are applied to sllmming points 46 and 52. The other inputs applied to s.l~ g points 46 and 52 are torque the gyro rotor applies on itself on one axis as a result of an angular rate of the other axis.
With rcfercncc to the right side of ~lGURE 2, the rebalance loop 70 will be seento be comprised of a pair of cross-axis loops 72 and 74 and a pair of direct-axis loops 76 and 78. In FIGURE 2, C is used to denote a cross-axis loop and D a direct-axis loop.
A cross-axis loop is one which derives its input from a pickoff coil which senses angular rate about one axis and delivers its output, a torquer current, to the torquer coil which applies a torque about the same axis. On the other hand, a direct-axis loop is one which derives its input from a pickoff coil which senses angular rate about one axis and delivers its output, a torquer current, to the torquer coil which applies a torque about the other axis. This a~ ge."r~,l is based on the rl~u~ e~ law of preces~ion of a g~roscopewhich is defined as a rotation (n~") of the spin axis produced by a torque ("T") applied 133~969 about an axis mutually perpendicNI~r to the spin axis and the axis of the resulting rotation. In other words, "x" precession is produced by "y" torque.
The signal from pickoff coil 36 is applied to the input of each of cross-axis loop 72 and direct-axis loop 7C via conductor 80 while the pickoff signal from pickoff coil 38 S is applied to the input of each of cross-axis loop 74 and direct-axis loop 78 via con~ ctor 82. The outputs of cross-axis loops 72 and 74 are signals propGIliollal to the angular acceleration of the rotor about the two gyroscope axes mPnti~nP~i earlier while the outputs of direct-axis loops 76 and 78 are signals propo.lional to angular rate of the rotor. The output of cross-axis loop 72 and of direct-axis loop 78 are applied to a ~ junction 10 84 which is electrically coupled to a torquer coil where it is trans~ d to a torque about one gyroscope axis. Similarly, the output of cross-axis loop 74 and of direct-axis loop 76 are applied to a s-~--..--in~ jun~ti~r~ 86 which is electrically coupled to a torquer coil where it is tr~n~l~tP~ to a torque about the other gyroscope axis.
FIGURE 3 diagr~ ;ç~lly illustrates the rebalance loop of the present invention 15 in more detail. Thus, with refe~llce to FIGURE 3, reb~l~nce loop 70 will be seen to be co~ lised of a first rebal~nce loop portion 100 ~l~lged to receive an "x" pickoff signal and deliver a "y" torquer current and a second rebal ~nce loop portion 102 arranged to receive a -y" pickoff signal and deliver an "x" torquer current. Both portions include collllllon front-end circuits 104 and 108, les~e~,lively, each of which inc~ Ps, in series 20 connection, a pickoff signal dPm-d~ r 110, a d~Pm-~dlll~tl~r low pass filter/int~ldlor 112 (lilGURE 4) and a spin notch fflter 114 (EIGURE 5). The output of filter 114 of each loop portion is then delivered to its own direct-axis circuit which incl~ld~Ps a ~
low-pass filter 116 and a transcon~ ct~nce amplifier 118 (~lGURE 6) and to the cross-axis circuit of the other loop which incl~ldes nutation notch filters 120 and a dirrerelllialor 25 122 (FIGURE 7). One mlt~tiQn notch filter is hlvt;,~illg, the other is non-in~ ling and, epe-n~ling upon the application, cross-axis circuits 73 and 75 may not be employed. The reb~l~nce loop also in~ des a phase adjust circuit 124.
With rerelcllce to FIGURE 4, synchrollous dem- d~ tQr 110 effectively multipliesthe pickoff signal by a square-wave (factor + 1 and -1) supplied by phase adjust circuit 30 124. The square wave from the phase adjust circuit "flips" the pickoff signal, ~Itern~tely, by switching means, between the two comple~.~r~ sine wave signals supplied by phase splitting ll~lsrOIllæ, 146 at the rate of the pickoff reference frequency. The result is a full-wave rectification. The simpler form of a full-wave rectifier with diodes, or an L `-1332~g absolute value conve,ler, would not work since the rectified signal must have a bipolar range. The gain of the demod~ tor is set to .25 volt DC/volt RMS of pickoff.
Demod~ or 110 is co~ ,iscd of an AC coupled amplifier 130, a full wave syncllrollous re.;tir,er 132 and a low pass filter/illt~g~ator 112.
Low pass filter/il,t~,ato- 112 not only smooths out the demodulated pickoff signal, but also provides almost half of the phase lag in the loop. The re~"~i"i--g part of the phase lag is produced by a nutation low-pass filter, ~i~c~l~se~l later. The phase lag is nrcess~ for nutation stability. The phase lag is produced in two steps so that the phase res~ollse is such that the phase shift at freq~lPnci~s in the closed loop bandwidth is smaller. This is desirable for higher bandwidth. The re~onse of the filter part of the circuit is that of a second order low-pass filter with a natural frequency of 198 Hz and a damping ratio of .6. The amount of phase lag required ~lepen~l~ on the gyro and the phase lag in the rest of the loop, and can be adjusted by adjusting the 16 Kn resistor.
The circuit is de-signed so that, by the proper selection of resi~t~nre of this resistor, the natural frequency can be adjusted without ~ignific~ntly affecting the d~ll~ing ratio, within certain limits. The inleg,~ling part of the circuit (112 in Figure 4) is a cal~ac;lo- (1 ,uF) placed in series with the fee~lbaclr resistor (55.6 Kn). The c~ ;lo- is a low leakage type (polyester). The cut-off frequency of the in~eg~ting resl)onse is about 3 Hz. The Laplace t~sro"" analysis for this circuit shows that the les~onse of this circuit is itlentir~l to the ,~ollse of a circuit in which the filter ru,l~tion and the i,.~g,~ling funrtion would be pe,ro"ned sepdl~lely. Using the same inlegla~d circuit to accomplish the two functions reduces the sources of DC instabilities. The DC drifts in subsequent circuits do not affect the pe,ru~ ces of the loop (except the dirrerelltialùr). The DC
drifts in the demodulator and in the low-pass filter/inlegralor input do not affect the pe,ru,---ance of the loop directly, but a drift on the nulling of the pickoff signal will cause a small torque on the rotor of the gyro because of the flexures.
The hlt~Ldting function is co...~il.ed with the low-pass filter funrtion of an LM
308 Operational Amplifier (OP-AMP) 137 in order that the DC stability of the demodulator would be affected by only one OP-AMP for ..~ -... DC stability. The30 illh~a~ing colllyollenl of the filter, which i,.~gl~les from DC to 3 Hz, makes the steady state stiffn~ss of the system infinite. This nulls the pickoff signal at any applied rate of the gyroscope so that that which sets the rate limit is the ..~ -- output current of the torquer driver rather than the limited range of the pickoff signal.
13323~
The phase res~onse of the circuit (filter 112) is such that, while leading to a total phase lag of about 180 in the whole direct-axis loop at the ~ ;ol~ frequency of the gyroscope (which is in this case 184 Hz), the phase lag is .-i~ d at freq~lenri~os near the gain crossover frequency (where the open loop gain is unity) so as to ensure the best possible stability margin.
Amplifier 130 has an input terminal 136 to which the pickoff signal, an al~l--d~il-g voltage signal, is applied. The signal is passed to the base of transistor 138 via a vo1tage divider or attenuator co~ iscd of resistors 140 and 142 and GAIN potentiometer 144.
The output of the transistor is applied to the plillla.~ of a phase splitting ~,~,sr~"",~r 146 via c~ Ar;l. r 148 which pfevenls a high DC current from reaching the t~ sroll.ler. As shown in FIGURE 4, the opposile terrnin~ls of the transformer seconda, ~ are connected to switches 150 and 152 which serve as a demod--lAtor for clem~ll-lAting the pickoff signal. The phase-splitting ~srollll~[ must have a s~lffirient self-in~l~lctAnre (51 mH, one termin~l to ground) to cause only a minimAl phase shift of the current limited signal from the l,~sislol. A l,~lsro""er is used in the S~ ,hl`OnC~US ~em-)dlllAtor for DC
stability and because it offers a good short to any DC offsets caused by 54 KHz`llA.~
from switches 150 and 1S2. Since there is always one of the two S~vil~ hes that is in the ON state, these DC offsets are effectively shorted to ground through the low resi~ e of the l~ sro""er and the ON switch.
Phase adjust circuit 124 shifts the phase of the pickoff rererence signal so that the phase of the PO signal may be zero relative to the phase of the PO reference signal.
These signals are sine waves, and for proper demodulation, they must be phased relative to each other so that their zero-crossing points occur at the same time. The phase shift is accomplished by an all-pass filter (IC1 in ~IGURE 4), and this shift is adjusted for a given gyro. The output of the phase adjust circuit is a square wave produced by the col"~ lor IC2 and fed to IC3c and IC3d.
Phase adjust circuit 124 inr1~ldes an all-pass filter in the form of an LM 318 OP-AMP 154, which phase-shifts a 54 kHz rere~Ace signal at terminal 156, and in-~l-lrles an open-collector colllpal alor 164 in the form of an LM 311 integrated circuit to convert the phase-shifted signal to a square wave, which is applied to the control input of each of analog switches 160 and 162. The phase adjust will accept a 54 KHz sine-wave signal, 5 to 6V RMS IIIA~Cillllllll, This is the reference signal which is used for the synchronous demodulation.
,~ ~
., ~, 1~3~
Switches 160 and 162 serve as a phase splitter and are connected in such a manner as to provide two comple~ square waves having coincid~Pnt transitions.
They are either both ON or both OFF and switch simlllt~nPQusly. The state of these switches is clele~ ...i..P~l by the output of co~ a~r 164. If the signal is high the s~ ,l.cs are ON and if it is low, the switches are OFF. Switches 150, 152, 160 and 162 are provided by a quad CMOS type 4066 i.~ ated circuit used as analog ~vil~l-es. The use of half of the quad switch as a compl~ y driver for the other half of the quad switch is justified by the need to have coil-cid~P-~~l switching times. This is a rellu~el.æ.l~ for good DC stability. The duty cycle need not be exactly 50%. The quad CMOS switch 4066 must be either voltage or current prole.,~d against pickoff overd.ive. The ll~u sis~r and phase-splitting l~ansful---er stage serves this purpose by the use of lei.iStOlS at the collector and emitter of the transistor. The ~ i---.-.-- pickoff input voltage is 9V RMS.
With lerelel ce to FIGURE 5, the output of filter/i..~g~alor 112 is applied to spin notch filter 114 the output of which is applied to the input of low pass filter 116 of direct-axis circuit 77 (or 79) as well as to the nutation notch filters 120 of cross-axis circuit 75 (or 73), as best shown in FIGURE 3. Circuit 114 is a modified version of the c1~sic~l "twin-tee" circuit. By tradition, the twin-tee circuit has sy-.l,--~lly and uses ..~ -d co---~one--l~. A Laplace ll~-sful--- analysis shows that an identir~l second order res~onse could be obtained with a circuit that has no Syl--~ y or m~tc~ling. Such a circuit is 20 employed because it is easier to adjust than the clq~sic~l version. The fimction of the spin notch filter is to remove a small pred~ P4 band of frequencies around the spin frequency (105 Hz) of the gyro, to elimin~te the spin noise of the gyro. This noise is a characteristic of this type of gyro and is caused by a dimensional error in the rotor. The d~.-~ing ratio of this filter is .3 and the voltage gain is unity outside of the notch 25 frequency, and -60 dB to -~ dB at the notch frequency.
The purpose of Nutation Low-Pass Filter 116 is mainly to produce phase lag.
It has a second order lesl,onse, with a natural frequency of 114 Hz and a damping ratio of .7. Within certain limits, the natural frequency and the phase lag can be adjusted by adjusting the 9.2 Kn resistor without ~ignific~ntly affecting the damping ratio. The phase 30 lag of this circuit must be the same as the phase lag of the cross-axis circuit (73 or 75 in Figure 3) so that the time delay of the direct-axis loop m~t-h~Ps the time delay of the cross-axis loop for frequencies below 60 Hz, and the sum of the phase lags must produce a phase shift of -180 at the nutation frequency in the direct-axis loop. A potPntiomP-tp~r - 11 1332g~
166 provides frequency control and a potentiometer 168 provides for notch depth adju~tm~nt With reference to ~lGURE 6, torquer driver circuit 118 is con-~,ised of an LM308 OP-AMP 170 and an h.~ g push-pull amplifier composed of various discrete S colll~l ellls inr~ ing d~linglon transistors 172 and 174. OP AMP 170 dll~ to ovelco~--e any difference in voltage belw~ points A and B because of its high gain and, acco,dil-gly, the voltage at point B can be ~s~lmed to be equal to the voltage at point A.
Thus, with the current in resistor 176 being virtually zero, the torquer current will be equal to the voltage at point B divided by the resict~ e of a precision resistor 180.
C~a~;lor 182 is required for stabilizing OP-AMP 170.
The purpose of Torquer Driver 118 is to produce the nec~ss~ry current range for the torquer coils which l~ec~ss;'~t~ 5 a large voltage range This adds-up to a signific~nt power and, accordillgly, the transistors Q3, Q4 (172), Q5 (174) and Q6 are mounted on a heat-sink The circuit is essenti~lly co-ll~)oscd of ope,~lional amplifier LM 308 (170) and an inverting push-pull amplifier which serves to "boost" the voltage and current capabilities of the operational amplifier It will be noted that the feedback line goes into the non-inverting input of the operational amplifier. This is not a drafting error, it is because the booster is i~lv~ling and this effectively ~v~Ijes the input polarities of the boosted operational amplifier. The torquer coil is com~ec~d into the circuit in such a way that the current in the resistor 180 is forced into the torquer coil. Thus, it is a transcon~luct~nre amplifier, as a variation of the torquer coil resistance will not affect the current or the voltage-to-current gain of the circuit That which ~le~e Illill~,~ the current in resistor 180 is the fact that the voltage gain of the circuit is unity at point B (the voltage at point B is equal to the voltage at point A) The current from the dirrerellliator is applied to the torquer coil by point B. This current flows into the torquer coil and not into resistor 180 as it can not affect the voltage at point B for a given voltage at point A, or with the system in open loop With reference to ~IGURE 7, cross-axis circuit 73 will be seen to include a nutation notch filter 120 and a dirrere--liator 122. One notch filter is non-i,lvt;,ling as shown in FIGURE 7a, the other is inverting as shown in ~IGURE 7b. The notch filter receives its input from a spin notch filter 114 and delivers its output to the dirrerel~ lor 122. It will be noted that the dirÇele--liator may not be required for some applications.
The notch filters serve to elimin~te an unstable zero-pole cancellation in the Laplace plane 1~2~
at the nutation frequency and this ensures a large degree of stability of the opel~lioll of the gyro-loop coll,bindlion without any signific~nt sacrifice of the acceleration error co...pçnch~;Qn. The dirfelc~ iat~r produces an acceleration propo,lional voltage by dirreræ~ g a rate prupollional voltage delivered by the nutation notch filter.
S The operation of the torquer driver and cross-axis loop may best be understood by rererellce to FIGURE 8 wherein it will be seen that the current propollional to the acceleration torque coll~ cl.l (Iay), where a means the time delivdlive of ~ and c.~ is the angular rate, from the cross-axis circuit is co...~i..ed with the current plopollional to the precession (rate-producing) torque collll)onelll (H~x) to form the torquer coil current 10 which is plopollional to Ty, where Ty= -Hcl~" + Icry; and wl~eleil~ it will be seen that this col--~il.dlion is pelrol---ed in such a way that only the part of the torquer coil current that is plupolliollal to H~x flows into current sensing resistor 180 where the rate inrolllld~ion is taken, which therefore gelleld~es a voltage signal propollional to rate and rate only.
Without the cross-axis circuit, the current that will flow into the current sensing resistor 15 will be a current propollional to Ty, which is still equal to -H~ + I~xy~ and the resulting rate illrol...alion will be co~ .h1r~ with the Ialy component.
As in-lic~tecl, the torquer driver circuit is essçnti~lly a boosted operational amplifier, is col.-~,osed of an opeld~ional amplifier int~g~d~ed circuit and an invelling booster stage, behaves as an operational amplifier and is ~langed to serve as a 20 ~ scon~l.lct~nce amplifier for the torquer coil output, and as a voltage follower for the rate output. Resistors R2 and R3 form a voltage divider to feed a small current into R4 that is equal to the bias current of IC7, the operational amplifier integrated circuit, so that the current in the fee~bac~ lead (from point B to the positive input of IC7) is zero. The hlvellillg input of the booster stage is the emitter of Q1. The positive input of that stage 25 is the base of Q1, which is comlec~d to ground through a DC bias produced by D6 and D7. That bias has a purpose of thermal stabilisation. The booster stage itself also behaves as an operational amplifier, its input resistor is R6 and its feedback resistor is R15. Q1 acts mainly as a current source DC level shifter. Q6 is a class A amplifier which purpose is to develop the full voltage range of the torquer driver. Q2 is a current 30 source that is the active load for Q6. Q4 and Q5 are darlington L~ lol s that form the current amplifier stage for Q6. D8 and D9 bias Q4 and QS just enough so that there is no dead zone (no cross-over distortion) when contl~ction goes from one l~allsi~r to the other. Note that Q4 and Q5 are not completely biased. A full bias for a d~lil~ n - 13- 1332~
transistor is 1.2 volt, only half that bias is provided in the circuit (.6 volt per d~linglo transistor). However, this is enough because base-emitter resistors (not show) are in-~h~ in the d~linglon pac~es, so that at low ~;u~ , such a darlington llansi~lor behaves like a standard transistor needing only .6 volt for ,.,i"i",~", conduction. Rec~llce 5 of this, stabilising emitter resisk)~s are not required and the circuit is more therm~lly reliable and more efficient. Transistors Q3 and Q7 serve to assist Q4 and QS in sharing the voltage and power di~ipation Rec~lse of Rll,R13,Dll,D12 R14 and R21, the voltage on the darlington transistor is divided equally. C5, C4,C7,C6 and L1 serve to s~prcss a high frequency instability (20 MHz) local to each transistor. The open loop amplitude and phase rcs~onse of this circuit is controlled by C1, C2,C3,R12,R23 and C8so that the closed loop response is stable. R5, R8 and R18 are used to limit the current within a safe level in case of tr~n~i~ntc or lln~Ypected saturations to protect the COlllpOII~ . R24 serves to protect the gyro in case the analog output (meter) get short-circuited. R10, D10, R20, D3, D4 and D5 are used to limit the l~AJ.illl~llll current to 15 protect the darlington transistors in case the torquer coil is short-circuited to ground. If the current in RlOis over .7 A,D10 steals current from Q2 which limits the current in Q4,Q3 and R10. If the current in R20is over .7 A,DS steals current from Ql whichlimits the current into Q6,QS,Q7 and R20.
The purpose of the torquer driver is to produce a current in the torquer coil that ispl~ollional to the input voltage (point A) and that is independent of the torquer coil resi~tAnce. From the point of view of the torquer coil, the circuit is a source of a COllSl~l current signal, that is, the current is ind~pçnd~ of the voltage on the torquer coil. It is standard technology to use a COllSl~ll current source to drive torquer coils because the resi~tAnce of such coils is not stable due to temperature. The output current 25 is controlled by the input voltage and the resistor 180, the voltage gain at point B with respect to point Ais unity. The meter output must be point B rather than point A, for an ac~;ulale reading free from any voltage drifts from the operation amplifier (170).
The gain of the cross-axis loops must be zero at the nutation frequency. To adjust the notch frequency, the two resistors in the band-pass filter portion of the nutation notch 30 filters must be adjusted without c~ ging their ratio to each other. The use of the cross-axis loops has little effect on the closed-loop response of the system around the nutation frequency. The p.ll~,ose of the cross-axis loops is to remove the "acceleration c~ n~", in the manner explained above, from the torquer current sensing Lesi~t~l~. These ~4, ~ .t~ ~
acceleration (,UllCIllS will exist as part of the torquer current, and are caused by the lsvc;~ie inertia of the gyro rotor during applied angular accelerations. Recqllce these acceleration ~;ullcnls are supplied by the cross-axis loops, they will not flow into sensing resistor 180. The insertion of the cross-axis loops will change the effective value of the S torquer current sensing resistor 180 from 15 ohms to (1/{[1/15]+[1/500]}) ohms. The voltage to current gain of the cross-axis circuit is to be adjusted to be equal to (S/2~Fn) ffmes the voltage to current gain of the direct-axis circuit.
It will be seen that the line~ily of the rebqlqnce loop of the present inventiondepe-n-l~ on only one component, precision resistor 180 and, accol-lingly, the lil~a,ily of the loop is ess~-ntiqlly the high li~lealily of the resistor. The circuit achieves high static stability because no current other than the torquer current flows through precision resistor 180. The circuit achieves high dynamic stability because the phase lag control is known to be very safe and stable and the use of notch filters in the cross-loops ensures high stability because of the complete ~p,ession of the unstable zero-pole cqn~Rllqti-)n. The conrlgulalion used for the cross-axis loop not only illl~JlO~reS the dynamic damping and the gain margin, its also completely removes the acceleration error, a feature not seen in previous loop designs.
In accor~lce with the present invention, there is provided a reb~l~nc_ loop for controlling a dry tuned rotor gy,oscope having a rotor moveable about two orthogonal axes, a first pickoff ~csoci~tPd with one of the axes for producing an -PlPctri~l error signal when a rate is applied to one of the axes, a second pickoff 10 ~csoc:~ed with the other of the axes for producing an elPctri~l error signal when a rate is applied to that axis and torquer coils ~ rt~pcl to receive elP~tric~l control signals from the reb~l~nce loop and apply torques to the rotor for colr~cling errors detected by the pickoffs. The reb~l~n-~ loop compri.cPs a first direct-axis loopadapted to receive an error signal produced by one of the pickoffs and produce a first 15 amplified error signal, a second direct-axis loop adapted to receive an error signal produced by the other of the pickoffs and produce a second ~mrlifiPd error signal, a first cross-axis loop for amplifying the error signal produced by the one of the pickoffs and adapted to produce a first correction signal, a second cross-axis loop for amplifying the error signal produced by the other of the pickoffs and adapted to20 produce a second correction signal, a first s~ ing junction for adding the first correction signal to the second ~mplifiPd error signal for producing a first torque correction signal, and a second s~ ning junction for adding the second correction signal to the first amplified error signal for producing a second torque correction slgnal.
`~
13329~
BRIEF DESCRIPlION OF THE DRAWINGS
These and other reatu~s of the invention will become more app~t from the following description in which reference is made to the appended drawings, wherein:
FIGURE 1 is one is a partially broken p~ re view of a typical two-degree-of-S freedom, dry tuned rotor gy~oscope;
FIGURE 2 is a block li~r~m fepr~ n of the gy~osco~e dynamics and of an analog rebalance loop accor~ing one embodiment of the present invention;
FIGURE 3 is a more det~ d block rli~r~m leprese~,t;~ n of an reb~l~nce loop according one embodiment of the present invention;
FIGURE 4 is an electric~l s~henn~tiC of a synchronous de-m~ul~tor and low pass filter/integ-~tQr employed in the em~odiment of FIGVRE 3;
FIGURE 5 is an el~tri~l scl-em~ti~ of a spin notch filter and low-pass f~ter employed in the embo~limPnt of FIGURE 3;
FIGURE 6 is an e1~tri~l scl~ lldlic of a torquer driver employed in the embo~im-ont of FIGURE 3;
FIGURE 7a-c is an el~tric~l sche",atic of cross-axis ~mplifi.o.rs which may be employed in the embodiment of FIGURE 3; and FIGURE 8a and 8b are block di~r~m scl~ tic illustrating the operation of a portion of tPrmin~l portions of the cross-axis and direct-axis ~mplifiPrs.
_. _ 13329~9 DESCRIPTION OF THE ~REFF.RRF.O EMBODIMENTS
With reference to ~IGURE 1 of the drawings, a typical two-degree-of-freedom, dry tuned rotor gy~scope 10 compri~es a housing or body 12 in which a shaft 14 is secured for rotation in bP~ring~ 16 and 18. The drive shaft is driven by 5a motor 20 also secured within the housing. A rotor 22 is secured to one end 24 of the shaft by a flexure assembly, generally design~tPd by reference numeral 26, which in~lud~Ps a gimbal ring 28. A first pair of coaxial half-axles 30 PYtPnding perpendicularly of the drive shaft are rotatably secured in the rotor and gimbal ring as shown and define a first axis and degree of freedom of the rotor and a second pair 10of coaxial half-axles 32 eYtPn~ing perpPn~ ul~rly of the drive shaft and the first pair of half axles are rotatably secured in the gimbal ring and the drive shaft as shown and define a second axis and degree of freedom of the rotor. It is to be undPrstood that the illustration of axles 30 and 32 is intenll~Pd to be functional only. In reality, the axles are flexures which are an integral part of a gimbal ring and rotor and are free 15to flex in such an oriPnt~tion as to be the equivalent to the axles illustrated in ~IGURE 1. Thus both axles allow two degrees of fieedom for the rotor.
The rotor is formed with a ci~culllr~ lial slot 34 in which a perm~nPnt magnet ring is secured for rotation with the rotor and in which torquer coils 40 are disposed. A pair of pickoff coils 36 and 38 are secured to the housing, intPrme~i~tP~
20the housing and rotor, in orthogonal relation to one another and each is operable to sense angular rates applied to one of the input axes of the gyr~scope case and provide coll~nding error signals to a rebalance loop. As is well known to those skilled in this art, a pickoff coil is a device which produces an output signal, generally a voltage, as a function of the angular disp1 ^-PmP-nt of the rotor relative to the gyro 25case or body. The pickoff signals are amplified by sensitive amplifiers, not shown, and delivered to a rebalance loop as explained later.
A pair of torquer coils 40, one of which is shown in FIGIJRE 1, are adapted to receive torquer CU11GI ~s from the reb~l~nce loop and apply torques to the rotor so as to "l~ ;lin the rotor in a "null" position. As shown in ~IGURES 6 and 8, the 30 torquer CU11CIII~ are delivered to an output tP-rmin~l 40' and rcllll~d to an input lcll.linal 40". As is known to those skilled in this field, a torquer coil is a device which exerts torque on the rotor in l-sponsc to a command signal in;~;~tPd by the _ ~., pickoff coils. The amount of current rGluircd to ",~inl~in a null position is directly p~llional to the angular rate applied to the gy~Jscope.
In a strapdown arrangement, the gyros are secured to the body axes of the vehicle and are lG lUil~d to sense the full range of dynamics of the vehicle. This arr~ngPtnPnt greatly reduces the mP~h~ni~l compl~Yity and cost of an inertial navigation system but increases the electronic complexity of the reb~l~n-,~e electronics.
The linealily and stability of the gyr~scope/re~ nce loop combination are of pnt~mount illl~lt;~lce in achieving the desired pGlr~llllance from the instrument.
With particular l~ f~lcnce to ~IGURE 2, the left side of the figure is a T ~rl~eTransform lG~ I;on of the gyroscope and the right side of the figure is the reb~l~no~ loop. The "figure 8" loop formed by blocks 42, 44, 46, 48, 50 and S2 rel,l~nt the "gyro dynamics" or "Nutation Loop", where the natural frequency of un~mped osr~ ti~n is 2~r(H/I) Hz and the damping factor can be ~s~lmed to be zero.
"S" is the Laplace Tl~ rollll opeldlor, "H" is the angular mol~ " and "I" is thel~ svcl~e moment of inertia. Blocks 54 and S6 represent the illlcgl~ling action of pickoff coils 36 and 38. The input to these blocks is angular rate while the outputs thelcrl~,,ll is angular position. S~"l"i~g points S8 and 60 are an integral part of the pickoff coils since the pickoff coils are secured to gyroscope housing 12. Negative inputs to s ~"",i,.g points 58 and 60 result from motion of the housing. Positive inputs result from rotor reaction. The output of the rebal~nrR loop is a pair of torquer .;wlclll~ which, in FIGURE 2, are applied to sllmming points 46 and 52. The other inputs applied to s.l~ g points 46 and 52 are torque the gyro rotor applies on itself on one axis as a result of an angular rate of the other axis.
With rcfercncc to the right side of ~lGURE 2, the rebalance loop 70 will be seento be comprised of a pair of cross-axis loops 72 and 74 and a pair of direct-axis loops 76 and 78. In FIGURE 2, C is used to denote a cross-axis loop and D a direct-axis loop.
A cross-axis loop is one which derives its input from a pickoff coil which senses angular rate about one axis and delivers its output, a torquer current, to the torquer coil which applies a torque about the same axis. On the other hand, a direct-axis loop is one which derives its input from a pickoff coil which senses angular rate about one axis and delivers its output, a torquer current, to the torquer coil which applies a torque about the other axis. This a~ ge."r~,l is based on the rl~u~ e~ law of preces~ion of a g~roscopewhich is defined as a rotation (n~") of the spin axis produced by a torque ("T") applied 133~969 about an axis mutually perpendicNI~r to the spin axis and the axis of the resulting rotation. In other words, "x" precession is produced by "y" torque.
The signal from pickoff coil 36 is applied to the input of each of cross-axis loop 72 and direct-axis loop 7C via conductor 80 while the pickoff signal from pickoff coil 38 S is applied to the input of each of cross-axis loop 74 and direct-axis loop 78 via con~ ctor 82. The outputs of cross-axis loops 72 and 74 are signals propGIliollal to the angular acceleration of the rotor about the two gyroscope axes mPnti~nP~i earlier while the outputs of direct-axis loops 76 and 78 are signals propo.lional to angular rate of the rotor. The output of cross-axis loop 72 and of direct-axis loop 78 are applied to a ~ junction 10 84 which is electrically coupled to a torquer coil where it is trans~ d to a torque about one gyroscope axis. Similarly, the output of cross-axis loop 74 and of direct-axis loop 76 are applied to a s-~--..--in~ jun~ti~r~ 86 which is electrically coupled to a torquer coil where it is tr~n~l~tP~ to a torque about the other gyroscope axis.
FIGURE 3 diagr~ ;ç~lly illustrates the rebalance loop of the present invention 15 in more detail. Thus, with refe~llce to FIGURE 3, reb~l~nce loop 70 will be seen to be co~ lised of a first rebal~nce loop portion 100 ~l~lged to receive an "x" pickoff signal and deliver a "y" torquer current and a second rebal ~nce loop portion 102 arranged to receive a -y" pickoff signal and deliver an "x" torquer current. Both portions include collllllon front-end circuits 104 and 108, les~e~,lively, each of which inc~ Ps, in series 20 connection, a pickoff signal dPm-d~ r 110, a d~Pm-~dlll~tl~r low pass filter/int~ldlor 112 (lilGURE 4) and a spin notch fflter 114 (EIGURE 5). The output of filter 114 of each loop portion is then delivered to its own direct-axis circuit which incl~ld~Ps a ~
low-pass filter 116 and a transcon~ ct~nce amplifier 118 (~lGURE 6) and to the cross-axis circuit of the other loop which incl~ldes nutation notch filters 120 and a dirrerelllialor 25 122 (FIGURE 7). One mlt~tiQn notch filter is hlvt;,~illg, the other is non-in~ ling and, epe-n~ling upon the application, cross-axis circuits 73 and 75 may not be employed. The reb~l~nce loop also in~ des a phase adjust circuit 124.
With rerelcllce to FIGURE 4, synchrollous dem- d~ tQr 110 effectively multipliesthe pickoff signal by a square-wave (factor + 1 and -1) supplied by phase adjust circuit 30 124. The square wave from the phase adjust circuit "flips" the pickoff signal, ~Itern~tely, by switching means, between the two comple~.~r~ sine wave signals supplied by phase splitting ll~lsrOIllæ, 146 at the rate of the pickoff reference frequency. The result is a full-wave rectification. The simpler form of a full-wave rectifier with diodes, or an L `-1332~g absolute value conve,ler, would not work since the rectified signal must have a bipolar range. The gain of the demod~ tor is set to .25 volt DC/volt RMS of pickoff.
Demod~ or 110 is co~ ,iscd of an AC coupled amplifier 130, a full wave syncllrollous re.;tir,er 132 and a low pass filter/illt~g~ator 112.
Low pass filter/il,t~,ato- 112 not only smooths out the demodulated pickoff signal, but also provides almost half of the phase lag in the loop. The re~"~i"i--g part of the phase lag is produced by a nutation low-pass filter, ~i~c~l~se~l later. The phase lag is nrcess~ for nutation stability. The phase lag is produced in two steps so that the phase res~ollse is such that the phase shift at freq~lPnci~s in the closed loop bandwidth is smaller. This is desirable for higher bandwidth. The re~onse of the filter part of the circuit is that of a second order low-pass filter with a natural frequency of 198 Hz and a damping ratio of .6. The amount of phase lag required ~lepen~l~ on the gyro and the phase lag in the rest of the loop, and can be adjusted by adjusting the 16 Kn resistor.
The circuit is de-signed so that, by the proper selection of resi~t~nre of this resistor, the natural frequency can be adjusted without ~ignific~ntly affecting the d~ll~ing ratio, within certain limits. The inleg,~ling part of the circuit (112 in Figure 4) is a cal~ac;lo- (1 ,uF) placed in series with the fee~lbaclr resistor (55.6 Kn). The c~ ;lo- is a low leakage type (polyester). The cut-off frequency of the in~eg~ting resl)onse is about 3 Hz. The Laplace t~sro"" analysis for this circuit shows that the les~onse of this circuit is itlentir~l to the ,~ollse of a circuit in which the filter ru,l~tion and the i,.~g,~ling funrtion would be pe,ro"ned sepdl~lely. Using the same inlegla~d circuit to accomplish the two functions reduces the sources of DC instabilities. The DC drifts in subsequent circuits do not affect the pe,ru~ ces of the loop (except the dirrerelltialùr). The DC
drifts in the demodulator and in the low-pass filter/inlegralor input do not affect the pe,ru,---ance of the loop directly, but a drift on the nulling of the pickoff signal will cause a small torque on the rotor of the gyro because of the flexures.
The hlt~Ldting function is co...~il.ed with the low-pass filter funrtion of an LM
308 Operational Amplifier (OP-AMP) 137 in order that the DC stability of the demodulator would be affected by only one OP-AMP for ..~ -... DC stability. The30 illh~a~ing colllyollenl of the filter, which i,.~gl~les from DC to 3 Hz, makes the steady state stiffn~ss of the system infinite. This nulls the pickoff signal at any applied rate of the gyroscope so that that which sets the rate limit is the ..~ -- output current of the torquer driver rather than the limited range of the pickoff signal.
13323~
The phase res~onse of the circuit (filter 112) is such that, while leading to a total phase lag of about 180 in the whole direct-axis loop at the ~ ;ol~ frequency of the gyroscope (which is in this case 184 Hz), the phase lag is .-i~ d at freq~lenri~os near the gain crossover frequency (where the open loop gain is unity) so as to ensure the best possible stability margin.
Amplifier 130 has an input terminal 136 to which the pickoff signal, an al~l--d~il-g voltage signal, is applied. The signal is passed to the base of transistor 138 via a vo1tage divider or attenuator co~ iscd of resistors 140 and 142 and GAIN potentiometer 144.
The output of the transistor is applied to the plillla.~ of a phase splitting ~,~,sr~"",~r 146 via c~ Ar;l. r 148 which pfevenls a high DC current from reaching the t~ sroll.ler. As shown in FIGURE 4, the opposile terrnin~ls of the transformer seconda, ~ are connected to switches 150 and 152 which serve as a demod--lAtor for clem~ll-lAting the pickoff signal. The phase-splitting ~srollll~[ must have a s~lffirient self-in~l~lctAnre (51 mH, one termin~l to ground) to cause only a minimAl phase shift of the current limited signal from the l,~sislol. A l,~lsro""er is used in the S~ ,hl`OnC~US ~em-)dlllAtor for DC
stability and because it offers a good short to any DC offsets caused by 54 KHz`llA.~
from switches 150 and 1S2. Since there is always one of the two S~vil~ hes that is in the ON state, these DC offsets are effectively shorted to ground through the low resi~ e of the l~ sro""er and the ON switch.
Phase adjust circuit 124 shifts the phase of the pickoff rererence signal so that the phase of the PO signal may be zero relative to the phase of the PO reference signal.
These signals are sine waves, and for proper demodulation, they must be phased relative to each other so that their zero-crossing points occur at the same time. The phase shift is accomplished by an all-pass filter (IC1 in ~IGURE 4), and this shift is adjusted for a given gyro. The output of the phase adjust circuit is a square wave produced by the col"~ lor IC2 and fed to IC3c and IC3d.
Phase adjust circuit 124 inr1~ldes an all-pass filter in the form of an LM 318 OP-AMP 154, which phase-shifts a 54 kHz rere~Ace signal at terminal 156, and in-~l-lrles an open-collector colllpal alor 164 in the form of an LM 311 integrated circuit to convert the phase-shifted signal to a square wave, which is applied to the control input of each of analog switches 160 and 162. The phase adjust will accept a 54 KHz sine-wave signal, 5 to 6V RMS IIIA~Cillllllll, This is the reference signal which is used for the synchronous demodulation.
,~ ~
., ~, 1~3~
Switches 160 and 162 serve as a phase splitter and are connected in such a manner as to provide two comple~ square waves having coincid~Pnt transitions.
They are either both ON or both OFF and switch simlllt~nPQusly. The state of these switches is clele~ ...i..P~l by the output of co~ a~r 164. If the signal is high the s~ ,l.cs are ON and if it is low, the switches are OFF. Switches 150, 152, 160 and 162 are provided by a quad CMOS type 4066 i.~ ated circuit used as analog ~vil~l-es. The use of half of the quad switch as a compl~ y driver for the other half of the quad switch is justified by the need to have coil-cid~P-~~l switching times. This is a rellu~el.æ.l~ for good DC stability. The duty cycle need not be exactly 50%. The quad CMOS switch 4066 must be either voltage or current prole.,~d against pickoff overd.ive. The ll~u sis~r and phase-splitting l~ansful---er stage serves this purpose by the use of lei.iStOlS at the collector and emitter of the transistor. The ~ i---.-.-- pickoff input voltage is 9V RMS.
With lerelel ce to FIGURE 5, the output of filter/i..~g~alor 112 is applied to spin notch filter 114 the output of which is applied to the input of low pass filter 116 of direct-axis circuit 77 (or 79) as well as to the nutation notch filters 120 of cross-axis circuit 75 (or 73), as best shown in FIGURE 3. Circuit 114 is a modified version of the c1~sic~l "twin-tee" circuit. By tradition, the twin-tee circuit has sy-.l,--~lly and uses ..~ -d co---~one--l~. A Laplace ll~-sful--- analysis shows that an identir~l second order res~onse could be obtained with a circuit that has no Syl--~ y or m~tc~ling. Such a circuit is 20 employed because it is easier to adjust than the clq~sic~l version. The fimction of the spin notch filter is to remove a small pred~ P4 band of frequencies around the spin frequency (105 Hz) of the gyro, to elimin~te the spin noise of the gyro. This noise is a characteristic of this type of gyro and is caused by a dimensional error in the rotor. The d~.-~ing ratio of this filter is .3 and the voltage gain is unity outside of the notch 25 frequency, and -60 dB to -~ dB at the notch frequency.
The purpose of Nutation Low-Pass Filter 116 is mainly to produce phase lag.
It has a second order lesl,onse, with a natural frequency of 114 Hz and a damping ratio of .7. Within certain limits, the natural frequency and the phase lag can be adjusted by adjusting the 9.2 Kn resistor without ~ignific~ntly affecting the damping ratio. The phase 30 lag of this circuit must be the same as the phase lag of the cross-axis circuit (73 or 75 in Figure 3) so that the time delay of the direct-axis loop m~t-h~Ps the time delay of the cross-axis loop for frequencies below 60 Hz, and the sum of the phase lags must produce a phase shift of -180 at the nutation frequency in the direct-axis loop. A potPntiomP-tp~r - 11 1332g~
166 provides frequency control and a potentiometer 168 provides for notch depth adju~tm~nt With reference to ~lGURE 6, torquer driver circuit 118 is con-~,ised of an LM308 OP-AMP 170 and an h.~ g push-pull amplifier composed of various discrete S colll~l ellls inr~ ing d~linglon transistors 172 and 174. OP AMP 170 dll~ to ovelco~--e any difference in voltage belw~ points A and B because of its high gain and, acco,dil-gly, the voltage at point B can be ~s~lmed to be equal to the voltage at point A.
Thus, with the current in resistor 176 being virtually zero, the torquer current will be equal to the voltage at point B divided by the resict~ e of a precision resistor 180.
C~a~;lor 182 is required for stabilizing OP-AMP 170.
The purpose of Torquer Driver 118 is to produce the nec~ss~ry current range for the torquer coils which l~ec~ss;'~t~ 5 a large voltage range This adds-up to a signific~nt power and, accordillgly, the transistors Q3, Q4 (172), Q5 (174) and Q6 are mounted on a heat-sink The circuit is essenti~lly co-ll~)oscd of ope,~lional amplifier LM 308 (170) and an inverting push-pull amplifier which serves to "boost" the voltage and current capabilities of the operational amplifier It will be noted that the feedback line goes into the non-inverting input of the operational amplifier. This is not a drafting error, it is because the booster is i~lv~ling and this effectively ~v~Ijes the input polarities of the boosted operational amplifier. The torquer coil is com~ec~d into the circuit in such a way that the current in the resistor 180 is forced into the torquer coil. Thus, it is a transcon~luct~nre amplifier, as a variation of the torquer coil resistance will not affect the current or the voltage-to-current gain of the circuit That which ~le~e Illill~,~ the current in resistor 180 is the fact that the voltage gain of the circuit is unity at point B (the voltage at point B is equal to the voltage at point A) The current from the dirrerellliator is applied to the torquer coil by point B. This current flows into the torquer coil and not into resistor 180 as it can not affect the voltage at point B for a given voltage at point A, or with the system in open loop With reference to ~IGURE 7, cross-axis circuit 73 will be seen to include a nutation notch filter 120 and a dirrere--liator 122. One notch filter is non-i,lvt;,ling as shown in FIGURE 7a, the other is inverting as shown in ~IGURE 7b. The notch filter receives its input from a spin notch filter 114 and delivers its output to the dirrerel~ lor 122. It will be noted that the dirÇele--liator may not be required for some applications.
The notch filters serve to elimin~te an unstable zero-pole cancellation in the Laplace plane 1~2~
at the nutation frequency and this ensures a large degree of stability of the opel~lioll of the gyro-loop coll,bindlion without any signific~nt sacrifice of the acceleration error co...pçnch~;Qn. The dirfelc~ iat~r produces an acceleration propo,lional voltage by dirreræ~ g a rate prupollional voltage delivered by the nutation notch filter.
S The operation of the torquer driver and cross-axis loop may best be understood by rererellce to FIGURE 8 wherein it will be seen that the current propollional to the acceleration torque coll~ cl.l (Iay), where a means the time delivdlive of ~ and c.~ is the angular rate, from the cross-axis circuit is co...~i..ed with the current plopollional to the precession (rate-producing) torque collll)onelll (H~x) to form the torquer coil current 10 which is plopollional to Ty, where Ty= -Hcl~" + Icry; and wl~eleil~ it will be seen that this col--~il.dlion is pelrol---ed in such a way that only the part of the torquer coil current that is plupolliollal to H~x flows into current sensing resistor 180 where the rate inrolllld~ion is taken, which therefore gelleld~es a voltage signal propollional to rate and rate only.
Without the cross-axis circuit, the current that will flow into the current sensing resistor 15 will be a current propollional to Ty, which is still equal to -H~ + I~xy~ and the resulting rate illrol...alion will be co~ .h1r~ with the Ialy component.
As in-lic~tecl, the torquer driver circuit is essçnti~lly a boosted operational amplifier, is col.-~,osed of an opeld~ional amplifier int~g~d~ed circuit and an invelling booster stage, behaves as an operational amplifier and is ~langed to serve as a 20 ~ scon~l.lct~nce amplifier for the torquer coil output, and as a voltage follower for the rate output. Resistors R2 and R3 form a voltage divider to feed a small current into R4 that is equal to the bias current of IC7, the operational amplifier integrated circuit, so that the current in the fee~bac~ lead (from point B to the positive input of IC7) is zero. The hlvellillg input of the booster stage is the emitter of Q1. The positive input of that stage 25 is the base of Q1, which is comlec~d to ground through a DC bias produced by D6 and D7. That bias has a purpose of thermal stabilisation. The booster stage itself also behaves as an operational amplifier, its input resistor is R6 and its feedback resistor is R15. Q1 acts mainly as a current source DC level shifter. Q6 is a class A amplifier which purpose is to develop the full voltage range of the torquer driver. Q2 is a current 30 source that is the active load for Q6. Q4 and Q5 are darlington L~ lol s that form the current amplifier stage for Q6. D8 and D9 bias Q4 and QS just enough so that there is no dead zone (no cross-over distortion) when contl~ction goes from one l~allsi~r to the other. Note that Q4 and Q5 are not completely biased. A full bias for a d~lil~ n - 13- 1332~
transistor is 1.2 volt, only half that bias is provided in the circuit (.6 volt per d~linglo transistor). However, this is enough because base-emitter resistors (not show) are in-~h~ in the d~linglon pac~es, so that at low ~;u~ , such a darlington llansi~lor behaves like a standard transistor needing only .6 volt for ,.,i"i",~", conduction. Rec~llce 5 of this, stabilising emitter resisk)~s are not required and the circuit is more therm~lly reliable and more efficient. Transistors Q3 and Q7 serve to assist Q4 and QS in sharing the voltage and power di~ipation Rec~lse of Rll,R13,Dll,D12 R14 and R21, the voltage on the darlington transistor is divided equally. C5, C4,C7,C6 and L1 serve to s~prcss a high frequency instability (20 MHz) local to each transistor. The open loop amplitude and phase rcs~onse of this circuit is controlled by C1, C2,C3,R12,R23 and C8so that the closed loop response is stable. R5, R8 and R18 are used to limit the current within a safe level in case of tr~n~i~ntc or lln~Ypected saturations to protect the COlllpOII~ . R24 serves to protect the gyro in case the analog output (meter) get short-circuited. R10, D10, R20, D3, D4 and D5 are used to limit the l~AJ.illl~llll current to 15 protect the darlington transistors in case the torquer coil is short-circuited to ground. If the current in RlOis over .7 A,D10 steals current from Q2 which limits the current in Q4,Q3 and R10. If the current in R20is over .7 A,DS steals current from Ql whichlimits the current into Q6,QS,Q7 and R20.
The purpose of the torquer driver is to produce a current in the torquer coil that ispl~ollional to the input voltage (point A) and that is independent of the torquer coil resi~tAnce. From the point of view of the torquer coil, the circuit is a source of a COllSl~l current signal, that is, the current is ind~pçnd~ of the voltage on the torquer coil. It is standard technology to use a COllSl~ll current source to drive torquer coils because the resi~tAnce of such coils is not stable due to temperature. The output current 25 is controlled by the input voltage and the resistor 180, the voltage gain at point B with respect to point Ais unity. The meter output must be point B rather than point A, for an ac~;ulale reading free from any voltage drifts from the operation amplifier (170).
The gain of the cross-axis loops must be zero at the nutation frequency. To adjust the notch frequency, the two resistors in the band-pass filter portion of the nutation notch 30 filters must be adjusted without c~ ging their ratio to each other. The use of the cross-axis loops has little effect on the closed-loop response of the system around the nutation frequency. The p.ll~,ose of the cross-axis loops is to remove the "acceleration c~ n~", in the manner explained above, from the torquer current sensing Lesi~t~l~. These ~4, ~ .t~ ~
acceleration (,UllCIllS will exist as part of the torquer current, and are caused by the lsvc;~ie inertia of the gyro rotor during applied angular accelerations. Recqllce these acceleration ~;ullcnls are supplied by the cross-axis loops, they will not flow into sensing resistor 180. The insertion of the cross-axis loops will change the effective value of the S torquer current sensing resistor 180 from 15 ohms to (1/{[1/15]+[1/500]}) ohms. The voltage to current gain of the cross-axis circuit is to be adjusted to be equal to (S/2~Fn) ffmes the voltage to current gain of the direct-axis circuit.
It will be seen that the line~ily of the rebqlqnce loop of the present inventiondepe-n-l~ on only one component, precision resistor 180 and, accol-lingly, the lil~a,ily of the loop is ess~-ntiqlly the high li~lealily of the resistor. The circuit achieves high static stability because no current other than the torquer current flows through precision resistor 180. The circuit achieves high dynamic stability because the phase lag control is known to be very safe and stable and the use of notch filters in the cross-loops ensures high stability because of the complete ~p,ession of the unstable zero-pole cqn~Rllqti-)n. The conrlgulalion used for the cross-axis loop not only illl~JlO~reS the dynamic damping and the gain margin, its also completely removes the acceleration error, a feature not seen in previous loop designs.
Claims (14)
PROPERTY OF PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A rebalance loop for a dry tuned rotor gyroscope having a rotor moveable about two orthogonal axes, means associated with one of said axes for producing an electrical error signal when a rate is applied to said one of said axes, means associated with the other of said axes for producing an electrical error signal when a rate is applied to said other of said axes, first means responsive to a first torque control signal for applying a torque to said rotor about one of said axes for restoring said rotor to a null position about said one of said axes and second means responsive to a second torque control signal for applying a torque to said rotor about the other of said axes for restoring said rotor to a null position about said other of said axes and said rebalance loop comprising:
first direct-axis circuit means responsive to one of said error signals for producing a first rate proportional torque signal and delivering said first rate proportional torque signal to said first means;
second direct-axis circuit means responsive to the other of said error signals for producing a second rate proportional torque signal and delivering said second rate proportional torque signal to said second means;
first cross-axis circuit means responsive to said one of said error signals for producing a first acceleration proportional torque signal and delivering said first acceleration proportional torque signal to said second means; and second cross-axis circuit means responsive to said other of said error signals for producing a second acceleration proportional torque signal and delivering said second acceleration proportional torque signal to said first means.
first direct-axis circuit means responsive to one of said error signals for producing a first rate proportional torque signal and delivering said first rate proportional torque signal to said first means;
second direct-axis circuit means responsive to the other of said error signals for producing a second rate proportional torque signal and delivering said second rate proportional torque signal to said second means;
first cross-axis circuit means responsive to said one of said error signals for producing a first acceleration proportional torque signal and delivering said first acceleration proportional torque signal to said second means; and second cross-axis circuit means responsive to said other of said error signals for producing a second acceleration proportional torque signal and delivering said second acceleration proportional torque signal to said first means.
2. A rebalance loop as defined in claim 1, each said direct-axis circuit means including a nutation low-pass filter means for introducing a phase lag into a filtered input signal and torquer driver means for receiving and amplifying the output of said filter means and said acceleration proportional torque signal and producing said torque control signal.
3. A rebalance loop as defined in claim 2, said torquer driver means including an operational amplifier and an inverting push-pull amplifier for amplifying the output of said operational amplifier, said operational amplifier being adapted to receive, at its inverting input, said output of said filter means and, at its non-inverting input, the signal received at a return line from said said means responsive to a first torque control signal and said acceleration proportional torque signal from its associated cross-axis circuit means.
4. A rebalance loop as defined in claim 1, each said cross-axis circuit means including a nutation notch filter and a differentiator for differentiating the output of said nutation notch filter and producing one of said acceleration proportional signals.
5. A rebalance loop as defined in claim 2, each said cross-axis circuit means including a nutation notch filter and a differentiator for differentiating the output of said nutation notch filter and producing one of said acceleration proportional signals.
6. A rebalance loop as defined in claim 1, further including:
a first front-end circuit means associated with said first direct-axis circuit means and said second cross-axis circuit means adapted to receive said one of said error signals and a second front-end circuit means associated with said second direct-axis circuit means and said first cross-axis circuit means adapted to receive said other of said error signals, each said front-end circuit means including an AC amplifier for amplifying one of said error signals, a demodulator for demodulating said error signal, a low pass filter for filtering said demodulated error signal, an integrator for integrating said output of said filter, and a spin notch filter for filtering the output of said integrator and delivering an input signal to its associated direct-axis circuit means and cross-axis circuit means.
a first front-end circuit means associated with said first direct-axis circuit means and said second cross-axis circuit means adapted to receive said one of said error signals and a second front-end circuit means associated with said second direct-axis circuit means and said first cross-axis circuit means adapted to receive said other of said error signals, each said front-end circuit means including an AC amplifier for amplifying one of said error signals, a demodulator for demodulating said error signal, a low pass filter for filtering said demodulated error signal, an integrator for integrating said output of said filter, and a spin notch filter for filtering the output of said integrator and delivering an input signal to its associated direct-axis circuit means and cross-axis circuit means.
7. A rebalance loop as defined in claim 6, said low pass filter being arranged to provide a minimized phase delay at frequencies near the gain crossover frequency where the open loop gain is unity and to provide a predetermined amount of phase lag at the nutation frequency of the gyroscope.
8. A rebalance loop as defined in claim 6, further including a phase splitting transformer for minimizing the DC offset and drift of said demodulator, said transformer having a primary winding connected to the output of said AC amplifier and a secondary connected to said demodulator.
9. A rebalance loop as defined in claim 6, further including means for applying a reference signal to said demodulator.
10. A rebalance loop as defined in claim 9, said reference signal being a sine wave, and said means being adapted to convert said sine wave signal to a square wave, further including means for splitting said square wave and applying two complementary square waves having coincident transitions to said demodulator.
11. A rebalance loop as defined in claim 6, wherein said integrator being adapted to integrate the filtered output of said demodulator from DC to 3 Hz so as to make the steady state stiffness of the system infinite.
12. A rebalance loop as defined in claim 5, said torquer driver means including an operational amplifier and four darlington transistors adapted to receive the output of said operational amplifier.
13. A rebalance loop for a dry tuned rotor gyroscope having a rotor moveable about two orthogonal axes, means associated with one of said axes for producing an electrical error signal when a rate is applied to said one of said axes, means associated with the other of said axes for producing an electrical error signal when a rate is applied to said other of said axes, a first torquer coil responsive to a first torque control signal for applying a torque to said rotor about one of said axes for restoring said rotor to a null position about said one of said axes and a second torquer coil responsive to a second torque control signal for applying a torque to said rotor about the other of said axes for restoring said rotor to a null position about said other of said axes, said rebalance loop comprising:
first front-end circuit means for demodulating one of said error signals, filtering any residual carrier signal and spin noise from said one error signal, introducing a first predetermined amount of phase lag into said one error signal, and integrating said one error signal whereby to produce a first filtered and integrated signal;
second front-end circuit means for demodulating the other of said error signals,filtering any residual carrier signal and spin noise from said other of said error signal, introducing a first predetermined amount of phase lag into said other error signal, and integrating said other error signal whereby to produce a second filtered and integrated signal;
first cross-axis circuit means for filtering from said second filtered and integrated signal a predetermined band of frequencies centered on the nutation frequency of said gyroscope and differentiating said signal whereby to produce a first acceleration proportional torque signal;
second cross-axis circuit means for filtering from said first filtered and integrated signal a predetermined band of frequencies centered on the nutation frequency of said gyroscope and differentiating said signal whereby to produce a second acceleration proportional torque signal;
first direct-axis circuit means responsive to said first filtered and integrated signal for adding thereto a second predetermined amount of phase lag by a first nutation low-pass filter whereby to produce a first rate proportional torque signal and responsive to said first acceleration proportional torque signal to combine said first rate proportional torque signal and said first acceleration proportional torque signal to produce a first torque control signal and convert said first torque control signal in a first torquer driver to a form capable of driving said first torquer coil;
second direct-axis circuit means responsive to said second filtered and integrated signal for adding thereto a second predetermined amount of phase lag by a secondnutation low-pass filter whereby to produce a second rate proportional torque signal and responsive to said second acceleration proportional torque signal to combine said second rate proportional torque signal and said second acceleration proportional torque signal to produce a second torque control signal and convert said second torque control signal in a second torquer driver to a form capable of driving said second torquer coil;
said first torquer driver including an operational amplifier and an inverting push-pull amplifier for amplifying the output of said operational amplifier, said operational amplifier being adapted to received, at its inverting input, an output of said first nutation low-pass filter and, at its non-inverting input, the signal received at a return line from an output terminal of said first torquer coil to which output a signal from the second cross-axis circuit means is applied; and said second torquer driver including a further operational amplifier and a further inverting push-pull amplifier for amplifying the output of said further operational amplifier, said further operational amplifier being adapted to receive, at its inverting input, an output of said second nutation low-pass filter and, at its non-inverting input, the signal received at a return line from an output terminal of said second torquer coil, to which output a signal from the first cross-axis circuit means is applied.
first front-end circuit means for demodulating one of said error signals, filtering any residual carrier signal and spin noise from said one error signal, introducing a first predetermined amount of phase lag into said one error signal, and integrating said one error signal whereby to produce a first filtered and integrated signal;
second front-end circuit means for demodulating the other of said error signals,filtering any residual carrier signal and spin noise from said other of said error signal, introducing a first predetermined amount of phase lag into said other error signal, and integrating said other error signal whereby to produce a second filtered and integrated signal;
first cross-axis circuit means for filtering from said second filtered and integrated signal a predetermined band of frequencies centered on the nutation frequency of said gyroscope and differentiating said signal whereby to produce a first acceleration proportional torque signal;
second cross-axis circuit means for filtering from said first filtered and integrated signal a predetermined band of frequencies centered on the nutation frequency of said gyroscope and differentiating said signal whereby to produce a second acceleration proportional torque signal;
first direct-axis circuit means responsive to said first filtered and integrated signal for adding thereto a second predetermined amount of phase lag by a first nutation low-pass filter whereby to produce a first rate proportional torque signal and responsive to said first acceleration proportional torque signal to combine said first rate proportional torque signal and said first acceleration proportional torque signal to produce a first torque control signal and convert said first torque control signal in a first torquer driver to a form capable of driving said first torquer coil;
second direct-axis circuit means responsive to said second filtered and integrated signal for adding thereto a second predetermined amount of phase lag by a secondnutation low-pass filter whereby to produce a second rate proportional torque signal and responsive to said second acceleration proportional torque signal to combine said second rate proportional torque signal and said second acceleration proportional torque signal to produce a second torque control signal and convert said second torque control signal in a second torquer driver to a form capable of driving said second torquer coil;
said first torquer driver including an operational amplifier and an inverting push-pull amplifier for amplifying the output of said operational amplifier, said operational amplifier being adapted to received, at its inverting input, an output of said first nutation low-pass filter and, at its non-inverting input, the signal received at a return line from an output terminal of said first torquer coil to which output a signal from the second cross-axis circuit means is applied; and said second torquer driver including a further operational amplifier and a further inverting push-pull amplifier for amplifying the output of said further operational amplifier, said further operational amplifier being adapted to receive, at its inverting input, an output of said second nutation low-pass filter and, at its non-inverting input, the signal received at a return line from an output terminal of said second torquer coil, to which output a signal from the first cross-axis circuit means is applied.
14. A rebalance loop as defined in claim 13, further including a first precision resistor connected between said output terminal of said first torquer coil and ground and wherein said signal thereat is a voltage and a second precision resistor connected between said output terminal of said second torquer coil and ground and wherein said signal thereat is a voltage.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000615093A CA1332969C (en) | 1989-09-29 | 1989-09-29 | Analog torque rebalance loop for a tuned rotor gyroscope |
| US07/589,533 US5138883A (en) | 1989-09-29 | 1990-09-28 | Analog torque rebalance loop for a tuned rotor gyroscope |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000615093A CA1332969C (en) | 1989-09-29 | 1989-09-29 | Analog torque rebalance loop for a tuned rotor gyroscope |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1332969C true CA1332969C (en) | 1994-11-08 |
Family
ID=4140873
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000615093A Expired - Fee Related CA1332969C (en) | 1989-09-29 | 1989-09-29 | Analog torque rebalance loop for a tuned rotor gyroscope |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US5138883A (en) |
| CA (1) | CA1332969C (en) |
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| US6823733B2 (en) * | 2002-11-04 | 2004-11-30 | Matsushita Electric Industrial Co., Ltd. | Z-axis vibration gyroscope |
| US8187902B2 (en) | 2008-07-09 | 2012-05-29 | The Charles Stark Draper Laboratory, Inc. | High performance sensors and methods for forming the same |
| US9575089B1 (en) * | 2013-01-08 | 2017-02-21 | Maxim Integrated Products, Inc. | Adaptive phase delay adjustment for MEMS sensors |
| US9581447B2 (en) * | 2014-07-08 | 2017-02-28 | Honeywell International Inc. | MEMS gyro motor loop filter |
| CN110382577B (en) | 2017-01-25 | 2023-04-04 | Si集团有限公司 | Compositions and methods for stabilizing phenol-formaldehyde resins comprising calixarenes |
| US10875953B2 (en) | 2017-01-25 | 2020-12-29 | Si Group, Inc. | Solubilized alkoxylated calixarene resins |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8821370D0 (en) * | 1988-09-12 | 1989-03-30 | British Aerospace | Gyroscope control systems |
-
1989
- 1989-09-29 CA CA000615093A patent/CA1332969C/en not_active Expired - Fee Related
-
1990
- 1990-09-28 US US07/589,533 patent/US5138883A/en not_active Expired - Fee Related
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| Publication number | Publication date |
|---|---|
| US5138883A (en) | 1992-08-18 |
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