FR2564203A1 - ANGULAR SPEED SENSOR - Google Patents

Abstract

THE INVENTION RELATES TO AN ANGULAR SPEED SENSOR. THIS SENSOR MAKES ESSENTIALLY A RESONANT STRUCTURE 10 MADE OF QUARTZ WITH PIEZOELECTRIC PROPERTIES AND INCLUDING AT LEAST TWO VIBRATING TABS 11, 12, AN ELECTROMAGNETIC DEVICE 14 FOR VIBRATING THE TONGS AT AN ATTACK FREQUENCY 17, 18, AND ONE DEVICE. COLLECT AN ELECTRICAL SIGNAL REPRESENTING THE ANGULAR SPEED OF A MOVEMENT TO WHICH THE SENSOR IS SUBMITTED. THE INVENTION APPLIES IN PARTICULAR TO GUIDING SYSTEMS FOR AIRCRAFT, SPACE MACHINES, MISSILES, ETC.

Description

The present invention relates to a sensor of

angular velocity.

  The angular velocity of the motion of a machine is essential input information for all navigation and inertial guidance devices. These devices are commonly used in aircraft, spacecraft, ships or missiles. The detection of the angular velocity of the movement is

  currently using a gyroscope.

  However, gyroscopes have various disadvantages. They must be built with extremely high precision and may have fraction drift rates of one degree per hour. Because of the price of their realization, they are very expensive; they are physically bulky and heavy. They must be maintained frequently and accurately because critical moving parts such as bearings can change over time. They can also be damaged by shocks and vibrations even at a reduced level. It can also lead to an increase in the drift rate of a value

  unknown, appearing at unknown times.

  Since gyroscopes are sensitive to the effects of shock and vibration, they often include heavy mounting devices for

  protect, and that are also expensive.

  It is therefore obvious that it would be desirable to replace a gyroscope by any other less expensive device capable of measuring angular velocities.

  thus measuring the attitude of a vehicle or craft.

  The invention therefore relates to an angular velocity sensor which essentially comprises a resonant quartz structure having piezoelectric properties,

  this structure comprising at least two elements

  two tabs each consisting of two parallel tongues and a common rod, the tongues and the rod being arranged in a plane, the common rod acting as an output rod, this structure forming a balanced resonance sensor reacting only to angular movement around an axis parallel to the output rod producing torsional deformation of the output rod; an electromagnetic device coupled with the tabs for vibrating at a driving frequency; and a coupled output device. with the output rod to produce an electrical signal representing the angular velocity of movement about the axis at which the device

is submitted.

  This sensor is preferably a tuning fork. The tuning fork must be mechanically stable in temperature, with low internal friction and according to Hook's law. Preferably, but not

  necessarily, the tuning fork is made of quartz.

  But other piezoelectric materials can be used, such as synthetic crystals; for example, ethylene diamine tartrate (EDT), dipotassium tartrate (DKT) or dihydrogenated ammonium phosphate (ADP). Non-piezoelectric materials may be

  used with a piezoelectric attack.

  Preferably, the tuning fork is made of an insulating material such as quartz but it is also possible to use conductive materials in which case the tabs of the tuning fork must be excited electromagnetically; that is to say by fixed coils and a magnetic circuit on the

tongues.

  The range of agreement consists of two

  spacecraft arranged parallel to each other and able to vibrate. They are connected by an output rod or handle, from which the output signal can be produced. This output signal simply represents the angular input velocity of the motion to which the device is subjected, producing a right-angle deformation in the direction of the vibrations; an optical output signal or frequency modulated can also be

got.

  The output signal can be obtained by coupling four capacitors with the tabs or the output rod, or it can be obtained by piezoelectric effect, resistance or optically. Measurable input speeds of the order of 10 per hour of the sensor according to the invention are sufficiently low to be used as a magnetically corrected difference in direction and as a gravity corrected vertical attitude reference. If input speeds of 0, 1 per hour are measurable, the device is usable for inertial quality references,

  as in an autonomous system of inertia guidance.

  Other features and advantages of the invention will be better understood when reading the

  following description of several examples of

  and with reference to the accompanying drawings in which Fig. 1 shows a range of agreement for explaining the principles of the invention. Fig. 2 is a side view of the range.

  Figure 1, showing two pairs of electric

  FIG. 3 is a plan view of an embodiment of the invention, comprising two tuning forks, the case being removed,

  Figure 4 is a section of the mode of

  FIG. 5 is a section along the line -.5 of FIG. 3 and also shows the box as well as the capacitive output which can be used in a circuit in FIG. 3 and shows a box enclosing the tuning fork. FIG. 7 is an enlarged plan view of a portion of the sensor of FIG. 3, showing the electrodes of etching and of the electrodes of FIG. Figure 8 is a schematic diagram of the output circuits of the bridge circuit of Figure 7, Figure 9 is a similar schematic diagram.

  to that of Figure 8 but showing a piezo

  As can be obtained with the configuration of the electrodes of FIG. 13, FIG. 10 shows another angular velocity sensor consisting of two tuning forks arranged in a line and perpendicular to the output rod. FIG. schematically the tension developed on the output rod under the effect of the mechanical deformation,

  Figure 12 represents another embodiment of

  the angular velocity sensor according to the invention, comprising 4 tuning forks, the forks of each pair being aligned and the two pairs being arranged parallel to the output rod, FIG. 13 schematically and on a large scale shows an output of FIG. 12 and shows the driving electrodes and one of the output electrodes, and FIG. 14 represents another still embodiment of a sensor according to the invention, comprising 8 tuning forks including 4 are arranged on the same axis and the axes of the two groups of forks being arranged parallel to the axis of the output rod. The figures, and particularly Figures 1 and 2 represent a simple range of agreement,

  to explain the bases of the operation of the invention

  tion. As indicated above, the tuning fork 10 is made of a piezoelectric material such as certain synthetic crystals, and preferably quartz. Figures 1 and 2 thus show a tuning fork 10 comprising two tongues 11 and 12 and an outlet rod or handle 13. The tongues can be vibrated by applying an electric field to them as will be explained with reference to FIGS. 6. Two electrodes 14, which are spaced apart from the free ends of each of the tongues, as at 11, are shown in FIG.

  capacitive. The tabs are vibrated

  towards each other, as indicated by the arrows 15, and opposite each other during the next alternation as shown by the arrows 16. Consequently, the tuning fork represents a resonance circuit

  balanced because the tongues 11,12 are balanced.

  The electrical output can be obtained by another pair of electrodes 17, 18, which can be applied directly on the region between the tongues 11, 12 and the output rod 13. The two electrodes 17, 18

  adopt different polarities because of the distortion

  tion of the fork 10 caused by angular movement of the assembly. When an angular movement is produced, the time derivative, i.e. the angular velocity of the motion can be easily obtained. It will now be assumed in a range

  a distance of 5 mm between the center of the movement

  the end of the tongue 11 or a distance of

  2 mm for the part of the tongue covered by the electri-

  trode 14, a distance of 4 mm between the center of the

  and the center of the electrode 14, a width of

  each tongue of 0.5 mm, a thickness of each

  0.05 mm, while half of the amplitude of the vibrations is 0.0025 mm and the driving frequency kHz, while the specific gravity of quartz is 2.6 g / cm3. With these assumptions, the angular momentum H can be calculated as follows: H = 6.53 x 10-4 g / cm 2 / sec (1) Similarly, the torque T can be calculated as follows: T = 1, 89 x 10-7 g / cm (2) Finally, the deformation of the tabs is: Y = 1.62 x 107 cm (3) It appears that the effect of increasing the size of the range of agreement, but not its width, is N which varies with the fifth power of an increase in dimensions. The table below can therefore be calculated:

TABLE 1

N 1 2 3 4 5

N5 1 32 243 1024 3125

  YN 1,62x10 7 5,18x10-6 3,94x10-5 1,66x10 -4 3,13x10-4 (cm)

  Table 1 therefore shows that an increase in

  The size of the tuning fork results in a considerable increase in the deformation of the tongues. Figures 3 to 9, and particularly Figures 3 to 6 illustrate a preferred embodiment of the invention. This embodiment has two tuning forks, whose two axes are spaced apart and parallel to the central axis. Thus, the first tabs 20, 20 'of the two tuning forks are made of the same section 22. The section 22 is divided into two parts which constitute the two tuning forks 20 and 21, by a gap 23 which leaves however a small bridge 24 to connect the two parts, 21. The other section 22 'is exactly symmetrical to the region 22 and has the other tabs 20', 21 '

two forks agree.

  The two ends of each of the two sections 22 and 22 'are connected by a connecting portion, 25'. Part 25 is separated from the two sections 22 and 22 'by two gaps 26 and 26'. The other connecting part 25 'is also separated from the two sections 22

and 22 '.

  The two connecting parts 25 and 25 'form the output rod. They are also connected by a small bridge 27, 27 'to an outer frame 30, separated from the two sections 22 and 22'. As shown in Figure 4, the tuning fork can be enclosed in a housing 31. Thus, the parts 20, 20 'form a pair of tongues and the parts 21, 21' form the other

range of agreement.

  Figure 5 shows the electrodes that can be provided at the ends of the two tabs 20, 20 'of a tuning fork. The tongue 20 carries an electrode 32, 33 on its opposite faces. Similarly, the tab 20 'carries an electrode 34, 35. One of the inner surfaces of the housing 31 is provided with a similar electrode 36 while the other inner surface

opposite carries an electrode 37.

  An oscillator 38 is connected to both elec-

  inner trodes 36, 37 of the housing 31. A capacitor is formed between the electrodes 37 and 32. Another capacitor 41 is formed between the electrodes 33 and 36. A third capacitor 42 is formed between the electrodes 34, 37 and a fourth capacitor 43

  is formed between the electrodes 35 and 36.

  The output of the bridge circuit of Figure 6

  can be measured by the measuring apparatus 44.

  Figure 8 shows the output circuit of the

  capacity bridge of Figure 6. The frequency of the oscillation

  attack driver 46 can be multiplied by a multiplier

  47 to a higher frequency. The driving oscillator is connected to the sensor of FIG. 3. A bridge amplifier 48 may be used to amplify the signal of the measuring apparatus 44. This amplifier is followed by a phase detector 50 which uses a phase of measurement. reference from the multiplier 47 coupled with the driving oscillator 46. The phase detector

  is followed by a filter 51 and an analog converter

  A digital processor 52 that drives a microprocessor, a linearization circuit, a display driver, and a digital-to-analog converter 53. Thus, the output signal can be obtained from the driver of

  digital output 54 or on the analog output conductor

  logic 55 and it can be applied to a device

appropriate display.

  Reference is now made to Figure 7 which represents, on a larger scale, a

  part of the sensor of Figure 3 and its electrodes.

  Two driving electrodes 60 and 61 are arranged on the tongue 20. The two driving electrodes are respectively connected to conductors 62 and 63 which

  are connected in turn to the attack oscillator.

  The two electrodes are slightly spaced from each other to develop an electric field causing the vibrations of the tongue. On the other tab are also provided similar electrodes 60 'and 61' which are also connected to the output leads 62 'and 63', the leads 62 and 62 'being connected together. An output electrode 64 is connected to another output electrode 65 also disposed on the tab 20. The output electrodes 64 and 65 are connected to the conductor 66 and to the frame 30. The other

  tongue 20 'has similar output electrodes.

  Note that the output electrodes 64 and 64 'are arranged directly on the tongue to form a capacitive output as shown in Figure 6. It is understood that one of the drivers

  output like 62, 63 can be grounded.

  FIG. 9 represents a piezoelectric output circuit for the electrodes of FIG. 13. Here again, the driving oscillator 46 excites the sensor

  3 and 13 are balanced by conductors 94 and 91.

  In this case, a piezoelectric voltage appears at the electrodes 96 and at the corresponding concealed electrode, under the effect of the stress in the crystal resulting from the deformation of the tongue. A buffer amplifier 67 follows the sensor of FIGS. 3 and 13 and is in turn followed by a phase detector 50, a filter 51, a digital analog converter 52 and a digital-to-analog converter 53. This again makes it possible to obtain a

  digital signal or an analogue signal on the

  54, 55. It should be noted that the intervals 23, 26 of FIG.

  mass of the tabs and therefore to obtain a frequency

  quence of lower resonance. The resonance frequency of the tongue in the direction of the deviation of

  output may be equal to the frequency of the drive signal.

  Thus, the resonant frequencies depend on the mass of the tongues, such as the tongues 20, 21 and the dimensions of the intervals 23, 26. These values can

so be adjusted at will.

  Figures 10 and 11 illustrate another sensor configuration according to the invention. As is apparent from FIG. 10, the sensor comprises two tuning forks 70 and 71 arranged on a common axis

  at right angles to the outlet rod 72.

  The outlet rod 72 is preferably fixed between two walls 73, 74. Preferably also, the outlet rod 72 comprises two symmetrical rectangular openings 75, 75 ', mainly to reduce the weight of the outlet rod and also to reduce its weight. rigidity. As a result, the resonant frequency of the output rod 72 is reduced. Therefore, the output rod 72 can also serve as a pair of

forks of agreement.

  Figure 11 shows the polarity of the voltage

  output, represented on the curves 76, 77, that is,

  say on the opposite sides of the outlet rod 72.

  Figures 12 and 13 show another confi-

  guration of a sensor according to the invention, comprising two pairs of tuning forks. As shown in Fig. 12, this sensor has a first pair of tuning forks 83, 84 with a common axis and a second pair of tuning forks 85, 86 also with a common axis, the two axes being spaced apart from each other. output rod 87. The two pairs of tuning forks are connected to the output rod 87 by a

connecting piece 88.

  Fig. 13 shows by way of example how the tuning forks can be attacked. The input leads 90, 91 from the driving oscillator are connected so that the input lead 91 is connected to the tuning forks 83 and 84. At the same time, the upper box 94 is excited by the input lead 90, like the lower case 95, thereby producing an electric field between

  the housings 94, 95 and the tuning forks 83, 84.

  One of the output electrodes 96 may be disposed on the connecting portion 88. The other output electrode is behind the electrode 96 and is

not visible in Figure 13.

  The sensor of Figure 14 is characterized by two groups of 4 tuning forks each. Thus, a first group of tuning forks 100, 101, 102 and 103 has a common axis. The second group of 4 tuning forks 100 'to 103' also has a common axis, but it is spaced from that of the output rod 105. The output rod 105 may also have at each end a rectangular recess or notch 106 to reduce its weight and rigidity and consequently its resonant frequency. The tuning forks as at 103 are separated from the output rod by wide intervals 107, 108 and 110. The output rod can also be arranged between two walls

111 and 112.

  The output rod 105 may be pre-twisted to produce a phase shift, i.e., it may be preloaded to detect

  the direction of angular movement in addition to its speed.

  Thus, the output rod 105 may be used to produce an output frequency that may be greater than the drive frequency. The same is true for

  the outlet rod 72 of FIG.

  It should be noted that the electrodes are preferably made of gold plating. By means of a

  laser attack, the two tabs of each furnace

  chette okay can be balanced; in other words, the laser can remove an appropriate portion of the electrode from a tab. This increases the factor of

Q quality of the circuit.

  It thus appears that the invention relates to an angular velocity sensor comprising essentially a tuning fork excited by a driving oscillator. An angular movement of the assembly causes a deformation of the output rod, perpendicular to the direction of vibration. This deformation can be measured by a capacitive effect, a resistive effect or an electrical voltage produced by the piezoelectric effect. Moreover, a frequency modulated output signal can be obtained or an optical sensor can be used. Various configurations have been illustrated for a large number of tuning ranges. The preferred arrangement makes it possible to control the frequency of the output signal with respect to the vibration of the sensor. This angular velocity sensor can be manufactured by semiconductor techniques,

  at a much lower price than a conventional gyroscope

  nel. In addition to being less expensive to manufacture, its

  accuracy should be sufficient for most applications

  practical references, such as direction and attitude references with magnetically or gravity-corrected applications, and even for quality references to

  inertia in an autonomous system of inertia guidance.

  Of course, various modifications can be made by those skilled in the art to the embodiments described and illustrated as examples.

  in no way limiting without departing from the scope of the invention.

Claims (17)

  An angular velocity sensor, characterized in that it comprises a quartz resonant structure (10) having piezoelectric properties, said structure comprising at least two vibrating elements (11, 12) each consisting of two parallel tongues and a common rod ( 13), said tongues and said rod being disposed in a plane, said common rod serving as an output rod, said structure constituting a balanced resonance sensor responsive only to angular movement about an axis parallel to said output rod, causing a deformation in   twisting said output rod; an electrical device   tromagnet (14) coupled to said tongues for vibrating at a drive frequency, and an output device (17, 18) coupled with said   output rod for producing an electrical signal   sensing the angular velocity of a movement around said   axis, to which said device is subjected.   2. Sensor according to claim 1, characterized   characterized in that said vibrating elements (11,12) are arranged symmetrically and spaced parallel to said output rod.   3. Sensor according to claim 1, characterized   characterized in that the vibrating elements (70,71) are arranged symmetrically and perpendicular to said output shaft (72).   4. Sensor according to claim 3, characterized   characterized in that said vibrating elements (70,71) and the output shaft (72) constitute a quartz tuning fork having piezoelectric properties, said tuning fork constituting said sensor   balanced resonance reacting only to a movement   angularly about an axis parallel to said output rod, causing torsional deformation of   said output rod, said output device comprises   phase detector (50) for the electrical signal and a device (53) for producing a   output indicating the angular velocity of the movement.   5. Sensor according to claim 4, characterized   characterized in that said electromagnetic device includes a driving oscillator (46), a first electrode (32-35) connected to each tab and a fixed electrode (36) spaced apart at said first electrode,   said electrodes being connected to said oscillator.   The sensor of claim 5, characterized in that said output device has two output electrodes (32-35) for each tab on said output rod, to produce an electrical signal representing the deformation of said rod due to a angular movement, said two electrodes   output being coupled with said phase detector.   7. Sensor according to claim 6, characterized   characterized in that said output electrodes (32-35) are connected to said phase detector and said phase detector is connected to said oscillator   drive to produce said output signal.   8. Sensor according to any one of the   4 to 7, characterized in that two of said tuning forks (70, 71> are provided, said tuning forks being arranged perpendicular to said output rod (72), said output rod being   arranged between two fixed elements.   9. Sensor according to any one of the   4 to 7, characterized in that 4 of said tuning forks (83-86) are provided, each pair of said tuning forks being arranged along   common axis, each of said axes being arranged parallel   same as said output rod (87) and said rod of   outlet being disposed between two fixed elements.   10. Sensor according to claim 9, characterized   characterized in that said electromagnetic device comprises a drive electrode for the tongues of each tuning fork and a driving oscillator comprising an output lead for said driving electrodes, each of a pair of driving electrodes of tabs of a pair of tuning forks being connected to the opposite conductors of said driving oscillator and each of the driving electrodes of the other pair of tuning forks being connected to the drivers of said driving oscillator for vibrating in phase opposition compared to the first pair of chord forks.   11. Sensor according to any one of the   4 to 7, characterized in that 8 of said tuning forks (100103; 100'-103 ') are provided, four of said tuning forks having a first common axis, and the other four tuning forks having a second common axis, said first and second axes being arranged parallel and at the same distance from said common rod (105), said common rod having the same length and being parallel to said axes, said common rod being   arranged between two fixed elements.   12. angular velocity sensor, characterized in that it comprises a one-piece quartz element comprising two parallel sections (22,22 ') each of said sections comprising in its center a first gap (23) leaving a small trigger guard (24) between the two portions (20, 21) of each section, each portion forming a tab of a tuning fork; said sections (22, 22 ') being connected at each end by a connecting element (25, 25') forming an outlet rod, each of said elements being separated from its associated section by a second gap leaving a small bridge between each element and its associated section, said intervals determining the input inertia and the frequency of said sensor, such that the dimensions of said gaps and said portions, and the masses of said sections, parts and elements determine the resonant frequency of said tongues and the frequency an output signal indicating the angular velocity of the   motion to which said sensor is subjected.   Sensor according to claim 12, characterized   characterized in that it comprises a housing (31), two driving electrodes being provided on each of said tongues and output electrodes on each of said tongues to produce an electrical signal indicating the deformation of said tongues, said housing being spaced from said electrodes.   14. The sensor according to claim 13, characterized   characterized in that a pair of inner electrodes is provided on the inner surface of said housing for each of said tuning forks, said electrodes   are connected to an attack oscillator.   The sensor of claim 14, wherein   in that said housing is etched to receive said electrodes.   16. Sensor according to any one of   Claims 1 to 15, characterized in that the rod of   output undergoes a pre-portion to produce an output signal representing the direction of motion angular.   17. Sensor according to claim 16, characterized   characterized in that said output rod has at least one rectangular notch to reduce its weight and rigidity.