Abstract:
Suspension and coupling beams of oscillating masses in a device which serves, for example, as a gyro and that includes oscillating masses form a single continuous network that allows the device to have a compact design. Preferably, a junction beam surrounds the two masses.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The subject of the invention is an oscillating mass resonator. 
   2. Discussion of the Invention 
   This type of device is widely manufactured using micromechanical techniques and is used in accelerometers and more specifically in gyros. It is essentially made up of two oscillating masses linked to a substrate by an elastic structure as well as means for producing oscillation of the masses and means for measuring the oscillations. If masses oscillate in one direction and the object upon which the resonator is placed turns towards a second direction, Coriolis forces produce movement of the masses along a third principal direction which is perpendicular to the previous ones. This is the movement that is measured. Its amplitude is used to deduce the speed of the rotation that the resonator is subjected to. 
   Movements in the third direction are usually measured by means of changes in capacitance between electrodes placed beneath the oscillating masses and on the substrate. In the case which is preferred in practice of a pair of masses whose phase opposition oscillations, that is in opposite directions, are controlled, the movements in the direction of measurement and capacitance variations are opposite so that differential measurements can be used to sum the two variations in capacitance associated with each of the masses whilst overcoming certain measurement errors which arise, for example, from movement of the assembly of masses relative to the substrate. 
   The oscillating movement of the masses is made possible by fine structures known as beams, by which the masses are suspended from the substrate and which are capable of readily undergoing flexion in an elastic manner in the direction of oscillations. Some advanced resonators include further beams of an elastic manner in the direction of oscillations. Some advanced resonators include further beams of an analogous nature which are coupling beams and which connect the masses together and sometimes to the substrate. These coupling beams are arranged in such a way that they readily deform when the masses oscillate in the desired phase relationship, but exhibit a high degree of stiffness to oscillations in other phase relationships in order to encourage oscillations in the desired phase relationship and thus reduce the consequences of lack of oscillation synchronisation on measurements. 
   Document U.S. Pat. No. 5,635,638 A describes such a resonator. The means for producing oscillations are electrical vibrators placed behind the oscillating masses. The suspension beams are also arranged behind the oscillating masses and extend perpendicular to the principal direction of oscillation so as to facilitate flexion in this direction. Coupling beams are formed by beams in the form of an arc of a circle which join the front faces of the masses and which are connected at their middles to other beams joined at their ends to the substrate and which extend in the direction of oscillation. Phase opposition of the movement of the masses produces simple bending of the beams in the shape of an arc and beams connected to the substrate, whereas a movement in phase of the masses produces traction and compression almost without any movement of the beams linked to the substrate and bends in complex modes. The system of coupling beams is therefore much more rigid for in-phase oscillations and does not allow these to be easily produced. 
   Some drawbacks of the existing systems are due to the fact that beams form a complex pattern which is sensitive to manufacturing uncertainties and to other deformations, and are despite efforts to the contrary, subject to a fairly significant degree of deformation associated with undesirable phase relationships. It may also be remarked that significant oscillation movements require long beams which therefore extend far from the masses, in particular in the principal direction of oscillation, and which increase the size of the oscillator. 
   SUMMARY OF THE INVENTION 
   The purpose of the invention is to provide a resonator with a beam structure which is simpler, of smaller dimensions and in which the coupling between oscillations of masses is properly achieved for a unique and determined phase relationship. 
   The suspension beams are all connected to the masses through coupling beams. This implies that there is a path leading from each anchorage point of the beams on the substrate to each of the masses, following the network of beams whereas in the earlier design, the suspension beams proper are always separated from the coupling beams and generally lead directly to a single mass. The network of beams obtained in this way generally exhibits two axes of symmetry, in the principal direction of the oscillations and along a direction which is perpendicular to the previous direction, but also parallel to the substrate. 
   This is described in document U.S. Pat. No. 5,349,855. In the invention, however, the network of suspension beams and coupling beams is unique and continuous and includes beams for attachment to the substrate, beams for attachment to the masses, and in a more noteworthy manner a junction beam which extends along a closed line to which all attachment beams are connected. The elastic deformations produced on oscillation are essentially concentrated on the junction beam; it is favourably curved so as not to produce concentrations of stresses. In advantageous manufacturing options it is arranged around the two masses; if these have a half-moon shape with facing rectilinear sides and curved sides facing the junction beam, a highly compact resonator is obtained. This continuous junction beam arrangement which extends along a closed line without passing through any masses or any other rigid part or fixed point of the structure ensures that there is not only good coupling of masses in the desired phase relationship but also that there is good flexibility of suspension which gives large displacements and measurement sensitivities. 
   The attachment beams to the substrate may include anchorage beams which extend overall in the direction of alignment of the masses between two regions of attachment to the substrate, and link beams which are perpendicular to the anchorage beams and which are joined to the anchorage beams at mid-distance from the regions of attachment. This arrangement tends to reduce the oscillations produced in the direction which is perpendicular to the principal direction. 
   The elements which produce oscillation may be placed between the junction beam surrounding the masses and the masses themselves, which contributes to the degree of compactness which is being sought. 
   The substrate may include a decoupling frame which surrounds the masses, the means for producing oscillation and the beams, and which is fixed to an underlying portion of the substrate by two frame anchorage regions aligned along a principal direction of oscillation of the masses. If the attachment beams to the masses are then in alignment with the frame anchorage regions, the frame and the junction beam may be designed to form end-stops in front of the frame anchorage regions; and if the oscillating masses have facing sides designed to form a mutual end-stop, the oscillation movements of the masses may be limited in this way. 
   According to other advantageous options for manufacture, the masses extend between the elements for producing oscillation and possess opposite facing sides between them equipped with interlocking electric combs. It will be seen that this arrangement reinforces the stability of the oscillating movement. 
   According to other factors the masses may each be made up of two sub-masses place symmetrically along a principle direction of oscillation of the masses, and the coupling beams include for each mass a sub-assembly of beams which extends between the sub-masses and which include two beams respectively linked to the sub-masses and to an interconnection beam, with the beams connected to the sub-masses extending along a principal direction of oscillation of the masses. The sub-masses may then mutually oscillate in one direction, move perpendicularly to the principle oscillation direction and provide an accelerometer with two measurement axes. The coupling beams may advantageously extend along the rigid beams (at least in the range of frequencies considered) which each extend around a mass and which bear elements which produce oscillation of the masses. The rigid beams may advantageously extend along closed lines and possess facing portions equipped with interlocking electrostatic combs common to the two masses instead of the latter being placed around the masses themselves as in other, less compact, arrangements. 
   Measurement of oscillations in the second direction may be achieved with the capacitance measurement electrodes with the masses, with the electrodes being fixed to the substrate and arranged in housings for the masses and having an asymmetric shape in the direction of oscillation of the masses. The asymmetric shape reinforces the capacitance variation resulting from the oscillations. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described with reference to the following figures which illustrate certain specific preferred manufacturing options: 
       FIG. 1  is a view of one option for manufacture of the invention, 
       FIG. 2  illustrates the deformations for this manufacturing option when the masses oscillate, 
       FIGS. 3 ,  4 ,  5 ,  6  and  7  illustrate other manufacturing options for the invention, 
       FIG. 8  is an enlargement of a part of  FIG. 7 , 
     and  FIG. 9  illustrates another type of measurement electrode design. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  thus represents a particularly simple manufacturing mode where two masses  1  and  2  arranged next to each other are connected by anchorage points  3  to an underlying substrate  9 , not shown in detail, which extends beneath the entire device. The anchorage points  3  are arranged as a quadrilateral at the exterior corners of the masses  1  and  2  through a single network of beams which include two anchorage beams  4 , each of which is linked to two respective anchorage points  3  whilst extending parallel to the alignment of masses  1  and  2 , two short attachment beams  5 , perpendicular to the above and linked to their respective middles, a junction beam  6  in the form of a rectangle extending around masses  1  and  2  and anchorage points  3  and  4 , and two short attachment beams  7  to the masses which extend between the junction beam  6  and the masses  1  and  2 , whose direction is the same as that of the alignment of masses  1  and  2 . This network of beams both ensures that masses  1  and  2  are suspended from the substrate by the anchorage points  3  and that those masses  1  and  2  are coupled to each other: when masses  1  and  2  oscillate in the principal direction of oscillation (which is the same as the direction of alignment of the masses) and in phase opposition, when approaching or moving away from each other, the network of beams deforms as shown in  FIG. 2 : the rectangle of the junction beam deforms, with the two sides becoming convex and the other two concave, and the anchorage beams  4  effectively deform like the sides of the junction beam  6  which is parallel and adjacent to them. Attachment beams  5  and  7  undergo practically no deformation. This system is flexible for the deformations shown in phase opposition, but is much more rigid for in-phase movements of the masses in the same direction, as the movements of the junction beam assembly  6  which would be proposed in the direction of oscillation and rendered almost impossible at the junctions to the attachment beams  5 . 
   The beam network thus ensures coupling of masses  1  and  2  which encourages the desired oscillation phase relationship. 
   The rectangular shape of the junction beam  6  has angles in which concentrations of complex deformations or stresses may be produced. It is possible to prefer a curved junction beams for this, as shown in  FIG. 3 , which is arranged around the two masses  11  and  12  of a half-moon shape and which has a shape which is oval, or elliptical, or circular, as desired. The anchorage points  13 , the anchorage breams  14 , the attachment beams to the substrate  15 , attachment beams to the masses  17  are not modified relative to preceding manufacturing option. The anchorage beams  14  however here extend outside the junction beam  16 , which is therefore close to the masses  11  and  12  that are made in the form of half-moons to improve the compactness of the assembly. The anterior sides of the half-moon shapes, opposite one another, are flat and their rear sides, opposite the junction beam  16  and linked to the respective attachment beams  17 , are curved, and follow the profile of the junction beam  16  at a small distance from it. 
     FIG. 4  shows a manufacturing option similar to  FIG. 3 , except that one cannot really talk about anchorage points  13 , but rather a decoupling fame  18  which is connected to an underlying substrate  19  by opposite anchorage points  20  located in the alignment direction of the masses  11  and  12 , a short distance from the junction beam  16  and the attachment beams to the masses  17 . The masses  11  and  12  and the beams are housed in a hollow of the decoupling frame  18 . This structure has the advantage of a greater degree of decoupling between the substrate  19  and the oscillating system. 
   A different manufacturing variation is shown in  FIG. 5 . The junction beam  16  is replaced by a junction beam  26  arranged between the masses  21  and  22 , which may without difficulties be of parallelepiped shapes like the masses  1  and  2  encountered at the beginning. The same network of anchorage beams and attachment beams is found as previously, although here only the attachment beams to the masses, here  27 , are connected to the front side of the masses  21  and  22 . This system works well for high frequencies and low movement amplitudes. The junction beam  26  is rounded, oval, circular, elliptical etc. like the junction beam  16 . 
   A more complete description of a simple realisation of the invention is shown in  FIG. 6 . The characteristics of the manufacturing option in  FIG. 4  can be recognised, with, in particular, the decoupling frame  18 , the curved junction beam  16  and the masses in the shape of half-moons  11  and  12 . The means for producing oscillation are shown, which are formed in the conventional manner from combs with interlocking teeth or extensions  28  and  29 , or “interdigitised”, according to a term which is widely used in practice. These are the source of the electrical attraction forces. Certain of the teeth  28  are placed on the rear face of the masses with a half-moon shape  11  and  12 , and the additional teeth  29  are placed on the fixed elements  30  in the from of an arc extending between the two masses  11  and  12  and the junction beam  16 , up to the attachment beam to the masses  17  and which are retained on the substrate  19  by anchorage points  31 . This particular arrangement means that only a small additional volume is used for the elements used to produce oscillation, and that the compactness of the device is therefore not adversely affected. The masses  11  and  12  are equipped with other extensions in the form of interlocking teeth of a comb which are interlinked one into the other at their front faces. They have the reference  32 . The interlocking of these combs produces electrostatic stabilisation forces which oppose unwanted movements of the masses  11  and  12  perpendicular to the principal direction of oscillation x, in the vertical axis y of the figure. The masses  11  and  12  are precisely balanced so that their principal axis of inertia is along the central alignment line. Extensions  28  and  32  are in particular placed symmetrically on either side of this line. It is also recommended that for each mass  11  or  12 , extensions  32  of the front faces be extended from the extensions  28  of the rear sides; the sum of the masses of elements  28  and  17  extending over the rear side of the oscillating masses  11  and  12  gives the same mass as the total for extensions  32  located on the front side. 
   If these conditions are applied, it can be seen that the oscillating masses are much less likely to move perpendicularly to the direction of oscillation as a result of imperfections in manufacture and external or internal constraints. 
   The attachment beams  15  and  17  are here split into two parallel beam elements in order to offer improved resistance to torsion. It has already bean remarked that the attachment beams cannot undergo much deformation because of their short length, and is in addition desirable to avoid deforming them, in particular those found outside the plane of the diagram, in the third direction Z which can only produce additional oscillatory motions which have a deleterious effect on measurements. 
   End stops for limiting the movement of the masses  11  and  12  are provided by contact of the teeth  32  with the opposite mass and in the other direction by contact of the junction beam  16  deforming against the uncoupling frame  18  at the anchorage points  20 . The reaching of end-stops always involves components at the same electrical potential and therefore does not disturb the operation of the device. 
   Moving on now to the more complex realisation in  FIG. 7 , the monolithic masses  11  and  12  are here replaced by complex masses  41  and  42  in the overall shape of a half-moon. These oscillating elements however are here made up of sub-masses  43  in the shape of quarter-moons, two of which form each of masses  41  and  42 . Complex masses  41  and  42  are surrounded by support elements  44  which extend along a closed line made up of one diameter and one half-circumference of a circle. These beams include interlocking teeth  28  and  32  similar to those in the previous realisation. The attachment beams  17  extend and are connected to the support elements  44  and are now attached only indirectly to the masses  41  and  42 . The support elements  44  resemble closed contour beams and may be regarded as coupling beams, but are significantly thicker than the other beams to the extent that they almost no longer deform. 
   The support beams  44  therefore belong to the network of beams which connect oscillating masses  41  and  42  to the substrate. The network also includes beams which extend between the sub-masses  43  in the form of quarter-moons, more specifically: two flexing beams  45  the ends of each of which are connected to a respective sub-mass  43  and which extend along the principal direction of oscillation of masses  41  and  42 , a connecting beam  46  which joins two opposite points of the support element  44  and which is extends to prolong the attachment beams  17 , in the principal direction of oscillation between a pair of flexing beams  45 , and a short interconnection beam  47  which is aligned perpendicular to the principal direction of oscillation and which connects the pair of flexing beams  45  to the connecting beam  46 . 
   Such a system can be used as dual axis gyro. It includes the option provided by earlier realisations and in addition allows Coriolis force accelerations to be measured which act in the Y direction of the device and which produce bending of the flexible beams  45 . 
   The measurement device is made up of fixed electrodes  48  arranged in the housings of sub-masses  43 . The fixed electrodes  48  are used to measure electrical capacitances between themselves and the sub-masses  43 . When the sub-masses  43  move, the fixed electrodes  48  approach certain parts of their housing and move away from others; the total capacitance is modified depending on the movements of the sub-masses  43 . Sensitive measurements can be obtained if the fixed electrodes  48  are asymmetric, for example crenellated on one side and smooth on the other. In the present case the crenellated side is aligned in the direction perpendicular to the principal direction of oscillation in order to measure movements of the quarter-moons in this perpendicular direction. 
   The fixed electrodes  48  are arranged symmetrically at the centre of inertia of the quarter-moons relative to the two directions of oscillation. 
   The crenellations can be of various shapes and openings. Another mode of manufacture of the fixed electrodes would involve arranging two twinned flat electrodes  49  and  50  as shown in  FIG. 9 , whose capacitance relative to the housing  51  would be measured independently. The movement of the sub-mass  43  would cause a reduction in one of the capacitances and a correlative increase in the other. Measurement by subtraction of capacitances would provide a sensitive evaluation of the movement. 
   Here in more detail is the manner in which the complex realisation in  FIGS. 7 and 8  would be used. Apart from the usual detection of angular acceleration in direction Y, it lends itself well to the angular acceleration direction in the third direction Z, through oscillation of masses in direction X. It is therefore the movement of masses  41  and  42  in direction Y which is measured, in response to the Coriolis forces produced in this direction. For each of the masses  41  and  42 , the total variation in capacitances recorded at the fixed electrodes  48  of each of the total sub-masses  43  are measured and subtracted from each other to obtain a larger result and more precise measurement, because of the essentially equal movements (antisymmetric) of the sub-masses  43  combined with the symmetrical arrangement of the fixed electrodes  49  between the sub-masses  43  of each mass  41  or  42 . The measurement by subtraction also eliminates the effects of unwanted oscillation of the sub-masses  43  in the Y direction relative to each other. The measurements of each of the masses  41  and  42  must also give opposite results. It is possible to correlate them by another subtractive measurement to eliminate the effect of unwanted oscillations in the Y direction. 
   The combs encountered in this invention have tooth overlap lengths which are significantly larger than those which are normally used. The extra electrostatic forces between the combs maintain them in a centring position, against disturbances which the oscillating system may be subjected to. For oscillation amplitudes of 5 μm for example, teeth of 7 μm in length are normal. 
   Total lengths of about 97 μm, that is 90 μm more, and therefore an overlap length (92 μm) greater than the oscillation amplitude are proposed in this example which is in accordance with the invention. The larger volume of the combs is compensated for by a much greater freedom in the design of the beams, which no longer have to provide guidance in the oscillation direction through an assembly stiffness which is greater in the perpendicular direction. The network for these may therefore be much simplified. 
   These resonators may be manufactured using conventional techniques for deposition and engraving etc. normally used in micromechanical engineering, so that no description of this will be given here.