Abstract:
The invention concerns a vibrating gyro-scope comprising a vibrating cylinder ( 1 ) magnetically excited by an internal stator ( 9 ) and whereof the vibrations are detected by means of the same stator comprising field coils and separate or common or multiplexed detection coils. The resulting gyroscope is very accurate while being economical and simple to produce. The invention is useful for measuring angular speed

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a vibrating gyroscope for the accurate measurement of angular speed within a wide measurement range. This gyroscope has the advantage over techniques usually used of being simpler to use and therefore of being inexpensive while remaining accurate and requiring little space. 
     2. Description of the Prior Art 
     Vibrating gyroscopes are based on the action of the Coriolis forces caused by a rotation imposed on masses in motion. 
     Several embodiments have been proposed in the past for the production of a vibrating element sensitive to angular speed. 
     The method most frequently used consists in vibrating a cylindrical or hemispherical test piece perpendicularly to its axis, and in observing the vibration nodes when it is subjected to rotation about said axis. 
     The main difficulties stem from the means used to create and measure the vibration. 
     The solutions proposed to date for the creation of the vibration have mainly been of an electromagnetic, electrostatic or piezoelectric nature. 
     The main drawback of electrostatic solutions is that they require high electric voltages and, in order to be efficient, very small air gaps. To avoid arc ignition, the assembly must be in a vacuum which, in addition to the machining accuracy needed, is a very costly requirement. 
     The piezoelectric solutions use either a cylinder, entirely in piezoelectric material, or small piezoelectric elements mounted usually by bonding, onto a metal cylinder. 
     The use of small piezoelectric elements mounted onto a metal cylinder enables costs to be reduced somewhat, but hardly any improvement is made to performance due to the crossfeed caused by the masses of said ceramics located on particular points of the cylinder. 
     Another major difficulty with all these solutions resides in the fact that the detection signals are of very low electrical level and that it is very difficult to protect them from low-level excitation signals within the same frequency band. For this reason, the means for detecting and exciting the vibrations are usually of a different nature and, insofar as possible, far apart from one another. 
     U.S. Pat. No. 4,793,195 describes e.g. a vibrating cylinder gyroscope equipped with electrostatic detection and is magnetically excited at a frequency half that of its vibration frequency in order to reduce these effects. 
     French patent application No. 95/11211 describes a gyroscope with magnetic excitation and optical detection also well protected from the excitation signals. 
     OBJECT OF THE INVENTION 
     This invention introduces a simplification to this latter type of gyroscope by suppressing the optical detection means and by using the electromagnetic excitation device itself to perform detection. Separation of the excitation and detection signals is achieved, on the one hand, by using an excitation at half frequency and, on the other hand, by distributing the polarisations and directions of winding so as to cancel interaction between excitation and detection. Another embodiment using multiplexing enables this separation to be further enhanced. The accuracy of the gyroscope obtained depends solely on the precision of highly conventional and therefore inexpensive mechanical machining as well as on electronic parameters that are easily mastered. This solution thus has the advantage of being even more economical. 
     SUMMARY OF THE INVENTION 
     The invention thus relates to a vibrating gyroscope of the type comprising: 
     a thin vibrating element generated by revolution, 
     an excitation means enabling the generation of vibrations at at least one point of the vibrating element so as to cause to appear, on said vibrating element, a succession of vibration nodes and bulges susceptible of moving under the effects of an angular speed of rotation, and 
     a means for detecting said vibrations, disposed so as to be able to detect said nodes and/or said bulges, characterized in that said excitation and detection means are both electromagnetic and made from the same electromagnetic assembly common to both the excitation and detection functions. 
     Embodiments of the invention will now be described, by way of non-limiting examples, in reference to the appended drawings in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a skeleton diagram showing the operation of a vibrating gyroscope, 
     FIG. 2 is a sectional view of the vibrating gyroscope embodying the invention, 
     FIGS. 3 and 4 are top views of four embodiments of the magnetic circuit of the gyroscope in FIG. 2, 
     FIG. 5 is a skeleton diagram of the electronic and electric circuits of the vibrating gyroscope according to the invention in a version separating the excitation and detection functions within a same excitation/detection assembly, 
     FIG. 6 is a skeleton diagram of another embodiment of the electronic and electric circuits of FIG. 5, 
     FIG. 7 is a skeleton diagram of another embodiment of the electronic and electric circuits of FIG. 6, 
     FIG. 8 is a skeleton diagram of the electronic and electric circuits of the vibrating gyroscope according to the invention in the version with multiplexing of its detection and excitation functions, 
     FIG. 9 is a skeleton diagram of another embodiment of the electronic and electric circuits in FIG. 8 in which the polarisation is periodically reversed, and 
     FIG. 10 shows two further embodiments of the magnetic circuit of the vibrating gyroscope according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As previously mentioned, and as shown in FIG. 1, a vibrating gyroscope comprises a test piece  1 , having an axis of symmetry  6 , e.g. cylindrical (FIG. 1 a ), but which can be flat or of any other shape, and which is vibrationally excited (FIG. 1 b ) in two main directions  2  and  3  perpendicular to one another and to the axis of the test piece  1 , in such a way that four vibration nodes  4  and four vibration bulges  5  appear, the displacement of the parts situated on the vibration bulges being in opposition of phase for the two main directions of excitation  2  and  3 . 
     When the test piece  1  is subjected to a rotation about an axis perpendicular to the main directions of excitation  2  and  3 , the vibration nodes do not rotate with the test piece. They do not remain stationary in space either, but rotate at an angular speed which is a fraction of the angular speed of the test piece. The relation between the angular speeds of the test piece and of the vibration nodes depends on the geometry of the test piece. 
     The vibration nodes  4  are therefore not linked to the test piece  1  but move in relation to the latter at an angular speed proportional to the angular speed of the test piece itself. 
     It will thus be understood that, to produce a gyroscope capable of measuring angular speed, two problems will have to be solved: on the one hand, the vibrational excitation, and, on the other hand, the detection of the position of the vibration nodes in relation to a reference linked to the test piece. 
     FIG. 2 shows a sectional view of a preferred embodiment of the vibrating gyroscope according to the invention, capable of obviating these problems economically. 
     The gyroscope comprises: 
     a cylindrical exterior box  7 , 
     a test piece or vibrating cylinder  1 , 
     an excitation-detection support  8 , 
     a magnetic exciter detector or stator  9 , 
     an electronic circuit  10 , 
     securing, wiring and closing means. 
     The exterior box  7 , of open-ended cylindrical shape, comprises, at one of its ends, an extra thickness  11  in which are arranged securing holes  12  for the test piece  1 . 
     The other end of the exterior box comprises, on the inside, a part fitted with a bore  13  of diameter slightly greater than the inside diameter of the rest of the box, said bore being connected to the inside of the cylinder  7  by means of a circular countersinking  14 . This bore  13  is prolonged, at the box end side, by an internal screw thread  15 . 
     The test piece is made in the form of a thin-walled vibrating cylinder  1 , having an axis of symmetry  6 , open at one of its ends  16  and closed at its other end  17  by a wall preferably thicker than those of the cylinder itself and forming a bottom  18 . 
     Said bottom  18  is itself fixed at its centre, by a leg  19 , to a circular plate  20  comprising a centring countersinking  21  as well as securing holes  22  on its periphery. 
     The revolving excitation-detection support  8  comprises a first part  29  of diameter such that it can be centred and brought to bear against the countersinking  14  in the bore  13  in the exterior box  7  and a second part comprising two successive diameters  30  and  39  of decreasing size, of which the second is destined to serve as a support for the magnetic stator  9  on which the coils are placed. 
     This support  8  thus positions itself in the bore  13  of the box  7  and bears against the countersinking  14 . 
     It is dimensioned in such a way that the stator  9  finds itself centred in the open end  16  of the cylinder  1  while leaving as thin an air gap  28  as possible. 
     An outwardly threaded nut  40 , screwed into the internal screw thread  15 , tightens and secures the part  29  of the support  8  to the countersinking  14  in the box  7 . 
     The magnetic exciter is preferably produced by using (FIG. 3 a ) sheets of metal  24  of the type used for wound rotors in electric motors. Several such sheets of metal  24  are stacked to constitute a stator  9  of diameter slightly smaller than the inside diameter of the vibrating cylinder  1 . This stator comprises notches  25  separating teeth  26  around which electric windings are placed. The number of these teeth must be a multiple of four. In the case of four teeth, the latter must be angled apart by a multiple of 45 degrees, the first two teeth being separated by an angle which is an odd-numbered multiple of 45 degrees and the other two teeth also being angled apart by an odd-numbered multiple of 45 degrees. In the case of the embodiment using multiplexing, the number of teeth can be reduced to two teeth angled apart by an odd-numbered multiple of 45 degrees. In a preferred embodiment of the invention, the teeth  26  are eight in number, all spread 45 degrees apart. They are relatively narrow and prolonged by eight polar masses  27 . 
     The windings  23  are constituted (FIG. 3 b ) by at least four and preferably by eight coils  31  to  38  of insulated conducting wire, each surrounding one of the teeth  26  of the stator. 
     These coils  31  to  38  are used for excitation and detection. 
     In a first embodiment of the invention, the coils fulfil the following functions two-by-two: 
     excitation of the vibration, EXV, 
     detection of the vibration, DV, 
     detection of the position of the vibration nodes, DN, 
     automatic control of the position of the nodes, AN. 
     Functions EXV and DV are carried out by coils of same rank, e.g. even-numbered, functions DN and AN then being fulfilled by the coils of odd-numbered rank. 
     The two coils of same function can be placed at 90 or 180 degrees from one another. In order to minimize crossfeed between the excitation EXV and automatic control AN functions towards the detection functions DN and DV respectively, it is preferable to place the coils of same function at an angle of 180 degrees from one another in accordance with e.g. the distribution set forth in the table below. As the first coil of each pair,  31  to  34 , is by convention wound in the positive direction, the wiring direction of the second coil of each pair,  35  to  38 , is given on the third line of the table. 
     
       
         
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
             
             
               
                 Coil No. 
                 31 
                 32 
                 33 
                 34 
                 35 
                 36 
                 37 
                 38 
               
               
                 Positions 1 
                 DN 
                 DV 
                 AN 
                 EXV 
                 DN 
                 DV 
                 AN 
                 EXV 
               
               
                 Winding 
                 + 
                 + 
                 + 
                 + 
                 − 
                 − 
                 − 
                 − 
               
               
                 direction 
               
               
                   
               
             
          
         
       
     
     To complete this arrangement, four coils  41 ,  42 ,  45  and  46  are placed on the same teeth as the coils  31 ,  32 ,  33  and  36  respectively. These coils are connected in such a way that the current coming from a current source  49  (FIG. 5) circulates in the same direction for coils  41  and  46 , and in the opposite direction for coils  42  and  45 , so that e.g. north poles will appear on the teeth bearing coils  41  and  46  and south poles on the teeth bearing coils  42  and  45  (FIG. 3 b ). It should be noted that the residual polarisation of the four teeth bearing coils  33 ,  34 ,  37  and  38  can be suppressed by additional coils not represented in FIG. 3 b.    
     This arrangement creates considerable crossfeed between the excitation of the vibrations and the detection of said vibrations. This crossfeed could disrupt the electronics, which is why it is preferable to excite the vibrations by using a frequency half the natural frequency of the vibrating cylinder  1 . This type of excitation enables the crossfeed at half frequency to be filtered by demodulating the detection signals as a function of the natural frequency of the vibrating cylinder. The same process also provided, in the case of FIG. 3 b , for the automatic control of the nodes has the drawback of not being linear, and it is preferable to automatically control the nodes by using a modulation at the natural frequency of the cylinder. To this end, a polarisation must be introduced onto the corresponding teeth AN by means of two coils  43  and  47 , so as to have a south pole and a north pole appear there (FIG. 3 c ). 
     With this gyroscope is associated excitation and automatic control electronics of which the principles are well known. 
     FIG. 5 shows a first variation of the connections of the electronics in which the excitation and automatic control are carried out at a frequency half the natural frequency of the vibrating cylinder. It comprises an exciting circuit  50  and a servo-control circuit  51 . 
     The exciting circuit  50  comprises a phase looping oscillator followed by a divider dividing frequency by two. The signals  59  at half frequency coming from this divider, control the non-polarised EXV coils  34  and  38 . The cylinder is thus excited at the frequency of the oscillator. When this frequency is equal to the natural frequency of the cylinder, the latter vibrates and induces signals on the vibration detection coils  32  and  36 . These signals are retransmitted to the input of the oscillator of said exciting circuit  50  and serve, by way of a phase looping, to bind the frequency thereof to the natural frequency of the vibrating cylinder. 
     The servo-control circuit  51  receives the signals transmitted by the vibration node detection DN coils  31  and  35 , demodulates them and remodulates them at half frequency. The remodulated signals  59  control the node control AN coils  33  and  37  in order to oblige the position of said nodes to remain fixed at the level of the teeth bearing said coils  31 ,  33 ,  35  and  37 . The demodulated signal, after being subjected to a quadratic compensator, is transmitted to the output  52  and represents the angular speed measured by the gyroscope. 
     To avoid drifts caused by the hysteresis of materials, it is advantageous to periodically change the polarisation sign of the detection coils. To this end, as shown in FIG. 6, a sequencer  53  triggers, in the current source  49 , a periodic reversal of the current in the coils  41 ,  42 ,  45  and  46  and simultaneously controls a reversal of the looping phase in the oscillator of the exciting circuit  50  and a reversal of phase of the demodulation of the node detection signals in the servo-control circuit  51 . The frequency of the reversal is chosen to preferably be a sub-multiple of the frequency of the oscillator. The sequencer is thus in this case synchronised by the oscillator itself. 
     FIG. 7 shows another embodiment of the electronics of FIG. 6 adapted to the configuration of FIG. 3 c  and in which the servo-control circuit  51  remodulates the signal at the natural frequency of the vibrating cylinder. The teeth used for this automatic control are polarised by coils  43  and  47 , supplied by the cut source  49  and serialised with the coils  41 ,  42 ,  45  and  46 . In this case, the quadratic compensator is suppressed and the signal demodulated by the servo-control circuit  51  is sent directly to the output  52  to represent the angular speed of the gyroscope. 
     In a more sophisticated version of the electronics, and to avoid all problems of crossfeed between the excitation and the detection, a multiplexing technique is used (FIG.  8 ). 
     In this solution, the windings are successively used to excite, and then to detect the vibrations and the position of the nodes, The windings are then constituted (FIG. 4 a ) by eight pairs of coils  31  to  38  and  41  to  48 , each pair, e.g.  31  and  41 , surrounding one of the teeth  26  of the stator, said windings of each pair being superposed or placed side by side, 
     One of the coils of each pair, e.g.  41  to  48 , serves to polarise the stator. They are connected in such a way that the current coming from the source of current  29  (FIG. 7) circulates in the same direction for the coils of even-numbered rank and in the opposite direction for the coils of odd-numbered rank, so that alternated north and south poles appear at each of the polar masses  27  (FIG. 4 a ). 
     The coils  31  to  38  serve to detect and excite the vibrations of the vibrating cylinder. They are serially connected, four by four, the coils of even-numbered rank  32 ,  34 ,  36  and  38  together, and the coils of odd-numbered rank  31 ,  33 ,  35  and  37  together. The direction of connection of each coil will be such that the signals of two coils, situated at 90 degrees from one another, are subtracted from one another and that, therefore, the signals of two opposite coils are added up. 
     One of the ends of each of these sets of four coils is connected to an earth  60 , the two other ends  54  and  55  being sent to two reversers  56  and  57  controlled by the sequencer  53 . These reversers  56  and  57  switch said ends  54  and  55  alternately to the inputs and outputs respectively of the exciting circuit  50  and servo-control circuit  51 . The sequencer  53  controls the operation of these two circuits as a function of the position of said reversers  54  and  55 . 
     The operating frequency of the sequencer is a sub-multiple of the natural frequency of the vibration cylinder  1 . The cyclical ratio of the switching between the excitation period and the detection period can be 1:1. It can also advantageously be 1:2, 1:3, 1:4 or even less depending on the surge voltage of the vibrating cylinder. Switching from the excitation function to the detection function is preferably carried out at the instant the current in the coils  31  to  38  goes through zero. Switching from the detection function to the excitation function preferably takes place when the control sine wave of the current in said coils passes through zero. 
     In this solution, and also to avoid drifts due to the hysteresis of the materials, the current in the polarisation coils can be periodically reversed. In this case, the sequencer  53  (FIG. 9) controls, in the current generator  49 , the periodic reversal of the coils  41  to  48  and at the same time controls the demodulation and modulation phases of the automatic control circuit  51  as well as the looping phases of the oscillator and the excitation of the vibrations of the exciting circuit  50 . 
     Finally, a last embodiment of the invention (FIG. 4 b ) can be produced by replacing the sheets of metal of the stator by a material forming a permanent magnet and magnetised so as to show a same distribution of the north and south poles as that of FIG. 4 a . In this case, the coils  41  to  48  and the current supply circuit  49  are suppressed. 
     It should be noted that, in the multiplexed variations (FIGS. 4,  8  and  9 ), the stator can be reduced to four teeth or even two teeth provided at least two of these teeth form an angle of 45 degrees. 
     It should also be noted that, especially in the case of non-multiplexed electronics, the utilisation of a 16-tooth stator  62 , preferably having dissymmetrical polar masses  61 , as shown in FIG. 10 a , can enable crossfeed phenomena to be reduced without departing from the scope of the invention. Separation of the detection and excitation channels can be further accentuated by separating the  16  teeth into eight elementary magnetic circuits  63  (FIG. 10 b ). In both these cases, the  16  coils for polarisation, on the one hand, and for excitation or detection, on the other hand, can be placed on each of the  16  teeth, or better, separated themselves into two and placed two by two on each of the teeth. In this configuration, and in order to simplify the gyroscope, it is possible to use just one of the two elementary magnetic circuits in a variation with multiplexed electronics. Four elementary magnetic circuits are needed in the version using frequency division. 
     It should also be noted that, in all the embodiments of the invention described above, the coils placed serially can be placed in parallel or even used separately or in pairs in order to establish redundancies, for instance. 
     It should finally be noted that the excitation and detection device can be applied, by adapting its shape, to any other form of vibrating body, without departing from the scope of the invention.