CH633888A5 - SUPPORT DEVICE FOR TRANSDUCER. - Google Patents

Description

The present invention relates to the field of transducers such as accelerometers and similar devices, and it relates more particularly to the arrangement of a device for supporting an element with respect to a means for detecting the position inside the device. of support.

In the prior art, an example of a support is known in a seismic accelerometer device of the type claimed in United States patent No. 3,702,073, the transducer assembly, namely, in this case , an assembly seismi-15 that, being supported by a flexible articulation connected to an external annular support element which is maintained between the upper stator and the lower stator of the accelerometer. The seismic element comprises, in this particular example, a return coil and a curved capacitive sensing plate and it is connected by means of one or more flexible articulations to the external annular support element. In this instrument, the seismic assembly comprising the support ring and the flexible joints is arranged in the form of a single piece of molten quartz.

One of the objectives to be met when designing instruments and their associated bearing structure, as described in U.S. Patent No. 3,702,073, is to minimize the influence of stresses on the flexible joints ensuring the connection of the movable element or mass 30 with the external bearing structure. A deformation occurring in the flexible joints which support the seismic mass, under the effect of stresses generated in the bearing structure, can result in fairly large errors due to a deformation. In the example of US Pat. No. 3,702,073, which relates to a seismic assembly with a servo accelerometer, pick-up elements are used to produce signals indicating the position of the assembly at l inside the instrument, these signals being in turn used to produce a current in a booster coil fixed on the en-40 seems seismic in order to bring the seismic mass to a predetermined position inside the instrument. A stress exerted in the flexible joints in the servo position can result in an undesirable distortion of the output signal since the instrument tries to counterba-45 launch the forces generated in the flexible joints.

In the case of an open loop instrument, the stress exerted in the flexible joints can produce a movement of the sensor, that is to say generate an error due to distortion or deformation in the output signal. The 50 forces generated by stresses and which can be transmitted to the flexible joints depend on the method adopted to fix the load-bearing element on the stator elements of the assembly. Since the surface of the stator elements abutting against the carrier ring cannot in practice be provided with perfect flatness, the fixing of the carrier ring, which is also not perfectly plane, on the element stator generates, in most cases, forces exerted both in the external load-bearing element and in the flexible joints.

A method of reducing the stresses transmitted to the flexible joints in a transducer assembly has been described in U.S. Patent No. 3,702,073. The outer ring-shaped carrier is clamped between parts of stator, spacers or buffers being interposed between the faces of the stator parts and the carrier ring-65 tor. In this structure, three pairs of spacers are distributed approximately 120 ° around the carrier ring. However, even with this arrangement, undesirable forces due to stresses can be generated in

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the supporting ring and are transmitted to the flexible joints supporting the seismic mass.

A second method used to reduce the effect of stresses in the bearing structure has been described in US Patent No. 3,339,419. In this patent, a structure is claimed in which the bearing member is mounted cantilever and in turn supports a movable member cantilevered, essentially one half of the circular movable member and a circular sensor being placed on each side of the edge of the carrier element. This structure makes it possible to reduce the sensitivity to angular deformation due to the fact that essentially equal zones of the movable member and of the circular sensor are placed on each side of the support line of the support element.

However, it is usually not desirable, or practical, to use a circularly shaped catchment area. On the contrary, it is more efficient to concentrate the capture zone within a maximum radius starting from the pivot axis in a pendulum transducer, with a view to maximizing the angular capture gain.

The invention therefore aims to provide a support device for a transducer avoiding the aforementioned defects.

The transducer device according to the invention is defined by claim 1.

In cases where the catchment area is essentially circular, as in United States Patent No. 3,339,419, rotation around a line delimiting equal surfaces produces a marked decrease in the catchment sensitivity of this angular movement. However, in the field of precision transducers, attempts have been made to completely eliminate all these sources of error. Thus, the rotation of the carrier element around an axis passing through the center of gravity of the capture zone produces a maximum decrease in the sensitivity to an angular movement in cases where the capture zone is not circular and isn't even necessarily symmetrical.

If it were possible to place the center of gravity of the pick-up zone exactly on the axis of rotation of the carrier element, a pick-up transducer sensitive only to a linear movement would give rise to a zero error during a rotation of the carrier element around said axis. For example, it is theoretically possible to reduce the error caused by rotation by a proportion of 10/1 in a 25 mm diameter circular acceleration transducer of the type claimed in US Patent No. 3,702 073. The improvement obtained results from the positioning of the axis of rotation of the carrier element on the center of gravity of the curved catchment area, and not at the center of the circular catchment area, as described in the US Patent No. 3,339,419. The actual reduction of error is obviously a function in practice of the manufacturing tolerances involved in the making of the instrument.

The advantages and characteristics of the invention will be highlighted in the following description, given by way of nonlimiting example, with reference to the accompanying drawings in which FIG. 1 is an exploded view of an accelerometer comprising a support device of known type for supporting a mobile element in association with a collection means in the form of a seismic mass;

Fig. 2 is a plan view of a control mass assembly corresponding to the preferred embodiment of the invention and usable in an accelerometer;

Fig. 3 is a plan view of part of a control mass assembly which corresponds to another embodiment of the invention;

In Fig. 1, there is shown in exploded view a movable element associated with a collection means and being in the form of an acceleration transducer of the type claimed in the aforementioned American patent No. 3,702,073. In this embodiment, the accelerometer comprises an upper stator element 10 and a lower stator element 12. Each of the stator elements 10, 12 is provided with permanent magnets, as indicated for the magnet 14 incorporated in the lower stator element 12. In addition, the lower stator element includes supports for electrical wires, as indicated in 16 and 18. FIG. 1 also shows a mobile assembly being presented in the form of a control mass assembly, designated by 20 and of known type. An external annular support element 22 is provided in this control mass assembly which is supported between opposite planar surfaces 19 and 21 of the upper stator element 10 and of the lower stator element 15 12 by pairs of spacers or spacers 24 provided on the element 22. The lower buffer of each pair is not visible in the drawings. As shown in Fig. 1, each pair of buffers 24 is spaced approximately 120 ° from another pair on the periphery of the carrier ring 22. There is provided in the assembly 20 control mass 20 a movable flap or blade 26 extending radially inward from the outer support ring 22. An electrically conductive material 28 of curved profile has been deposited on each side of the flap 26, which serves as a capacitive capture zone or plate. The capacitive pick-up plates 25 provided on the upper and lower face of the flap 26 cooperate with the opposite surfaces 19 and 21 of the upper and lower stator elements 10, 12, to form a capacitive pick-up system.

There is provided on each side of the flap 26 a return coil 30 30. As is well known, the return coils 30 cooperate with the permanent magnets 14 to maintain the flap 26 in a predetermined position relative to the carrier ring 22 .

The flap 26, associated with the coils 30, is connected to the carrier ring 35 using two flexible articulation elements 32 and 34. The flexible articulations 32 and 34 allow the seismic element comprising the flap 26 and the coils 30 to move in a pendulum motion relative to the carrier ring 22. The flap 26 moves in response to forces exerted-40 ering along the axis of sensitivity 35 of the accelerometer. It is also provided on the carrier ring 22 and on the flexible joints 32 and 34 of the capture conductors 36 and 38 formed by thin films and which establish electrical connections with the capacitive plates 28 and the return coils 30. 45 As indicated above, the fixing of the support ring 22 on the stator elements 10 and 12 can produce an excessive stress in the external support ring 22 and it follows that a deformation can be transmitted to the flexible joints 32 and 34. This resulting deformation of so flexible joints 32 and 34 can cause current to flow through the booster coils of a servo accelerometer, thereby creating a significant error, due to deformation, in the accelerometer output signal .

There is shown in FIG. 2, a preferred embodiment 55 of the invention, in the form of a support device for a seismic assembly of circular profile of the type indicated in FIG. 1 by the reference 20, pairs of buffers or spacers being distributed on the carrier ring 22 so as to reduce the effects of stresses in the latter 60 when the upper and lower stator elements 10,12 are blocked together. It should be noted that the principle of the invention also applies to structures of non-circular shapes and, moreover, to support structures, both with continuous surface and with buffers. The principle of the invention also applies to transducers in which the external support element 22 is fixed to a single stator element, by blocking, by bonding or by other means. The invention also applies to other types of collection means, in particular types

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optics which may not require a pickup element such as the movable element shown in the figures.

According to the present invention, the major part of the carrier element is placed in overhang relative to the stator of the transducer so that the deformation resulting from this cantilever mounting occurs around an axis which passes through the center of gravity of the catchment area. The expression “center of gravity” is understood to mean the center of gravity of a body formed of a homogeneous material. In addition, the sensitivity to stresses exerted in the support part of the instrument is reduced by maximizing the spacing of the flexible joints connecting the mobile element to the support element relative to the point of door-to-door. false where the support constraint is exerted. This solution provides the additional advantage of not having to use a collection zone of symmetrical profile or of not having to center this collection zone on the movable element. It should be noted that most of the sensors are sensitive, not simply to the angle of rotation of the collection area, but also to the linear movement of the center of gravity of this collection area.

In Fig. 2, we have designated by 22,26,28,30, .32 and 34, elements similar to those described with reference to FIG. 1. In particular, a first pair of support pads 40 is provided, one of which is placed on the upper face and the other (not visible) on the lower face of the circular carrier element 22, each of the buffers 40,44, and preferably their edges, being essentially aligned with the center of gravity of the capture element 28, as indicated by line 42. The center of gravity of the capture element is designated by 41 on Fig. 2. When this capture element is planar and has a uniform thickness, being, for example, constituted by a thin layer of conductive metal denstined to form capacitive plates, the center of gravity 41 of the capture element is the center of gravity of the catchment area. With regard to the center of gravity of the collection zone 28 of FIG. 2, the product of the sensor surface located on one side of the axis 42 by the radius passing through the center of gravity of this surface is equal to the product of the same two values on the other side of said axis.

In addition, a second pair of support pads 44 is provided on the other side of the carrier ring 22 and in a condition essentially aligned with the axis 42. There is also provided a third pair of support pads 46 on the supporting ring 22 on a side opposite to the flexible joints 32 and 34. Although it is normally considered desirable to make the pads 40,44,46 as small as possible in order to reduce the stresses exerted in the 'carrier ring 22, there may be circumstances where it is desirable to join the pads 40, 44 and 46 in the form of a single element. Also in the case where separate support pads are used, as shown in FIG. 2, or else where a single curved support element is used extending from the position of the pad 40 to the position of the pad 44, it is considered to be very advantageous for the effective axis of rotation of the part cantilevered from the carrier ring 22 essentially coincides with a line or axis 42 passing through the center of gravity 41 of the capture element 28. By placing the support elements or buffers in this way, we decrease substantially the movement of the center of gravity 41 of the capture element 28 parallel to the sensitivity axis 35 of the instrument, as indicated in FIG. 1, under the effect of a stress generated in the carrier ring by the blocking of the stator elements 10, 12, one with the other. This is due to the fact that a rotation around the center of gravity of the bearing area produces equal pickup effects on both sides of the axis of rotation, so that pickup errors due to stresses exerted in flexible joints tend to cancel each other out.

Also, as shown in the embodiment of FIG. 2, it is desirable to place the hinge, materialized by the flexible joints 32 and 34, which supports the flap or mobile element 26, as far as possible from the axis 42, in order to minimize the deformation in the flexible joints 32 and 34. The capture plate 28 must be placed on the movable element 26 as far as possible from the flexible joints 32 and 34, so that they can make maximum use of the rotation of the flap 26. The sensitivity of the sensor is increased as a function of the distance from the collection zone relative to the point of rotation of the flap 26. Consequently, by giving the collection zone the curved profile in FIG. 2, the collecting zone of the flexible joints 32 and 34 can be moved as far as possible.

There is shown in FIG. 3 an embodiment of the invention in which additional flexible parts 48 and 50, formed by curved recesses formed in the annular support element 22, are preferably placed at a maximum distance from the support pads 40 and 44. These additional flexible joints 48 and 50 allow part of the support ring 22 to bend in a radial direction. Even when a continuous bearing surface is used between the pad 40 and the pad 44, this arrangement is advantageous. The combination of the flexible parts 48 and 50 with a maximum spacing of the flexible joints 32 and 34 relative to the axis of rotation 42 of the support ring 22 results in a reduction in the sensitivity to a radial deformation in the support ring 22, this deformation manifesting itself under the effect of a stress generated in the flexible joints 32 and 34.

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Claims (9)

633,888 2 1. Support device for a transducer comprising a stator (10,12), a carrier element (22) and a movable element (26) connected thereto, characterized in that the movable element (26) comprises at least a non-circular collection zone (28), a connecting means (32, 34, 70, 72) for connecting the mobile element (26) to the carrier element (22) allowing it at least a limited degree of movement , and at least one intermediate spacer element (40,44,46) between the stator (10,12) and the support element (22) and in that at least one edge of the spacer element is practically aligned with the center of gravity (41,63) of the collection zone (28, 66), in order to allow the part of the carrier element (22) which comprises said connecting means (32,34; 70 , 72) to rotate relative to the stator so that the axis of rotation (42, 64) passes essentially through the center of gravity (41, 63) of the collection zone. 2. Device according to claim 1, characterized in that the carrier element (22) has a circular configuration and comprises two bending parts (48,50) one of which is placed on one side of said connecting means (32 , 34), while the other is placed on the other side of said connecting means. 3. Device according to claim 1, characterized in that the carrier element (22) comprises a connecting means (32,34) intended to pendularly support said movable element (26) interposed between and supported by the first (10 ) and second (12) stator elements and at least one spacer element (40,44,46) interposed between at least one of the stator elements (10,12) and the support element (22) and in that the spacer is positioned to overhang a portion of the carrier (22) so that the axis of rotation (42) of the overhang passes by the center of gravity (41) of the collection zone (28). 4. Device according to claim 3, characterized in that said connecting means (32, 34) of the pendulum type is placed on the carrier element (22) at a maximum distance from said axis of rotation (42). 5. Device according to claim 3, characterized in that one of the spacing elements (40,44,46) is interposed between each stator element (10,12) and the carrier element (22) and in that these spacers are practically aligned with the center of gravity (41) of the collection zone (28). 6. Device according to claim 5, characterized in that an edge of each spacing element (40,44,46) is essentially aligned with the center of gravity (41) of the collection zone (28). 7. Device according to one of claims 3 to 6, characterized in that said carrier element (22) has a circular configuration and comprises two bending parts (48.50) allowing a radial bending of the carrier element (22 ). 8. Device according to claim 1, characterized in that it comprises a first (10) and a second (12) stator elements provided with opposite surfaces, in that the carrier element (22) is annular and concentric with the mobile element (26) which is connected to it by at least one flexible connection means (32,34), in that the annular support element (22) is placed between and supported by said opposite surfaces of said first and second elements of stator (10,12), several spacers (40,44,46) being interposed between the carrier element and said opposite surfaces of the stator elements (10,12), these spacers being essentially aligned with the center of gravity (41) of the collection zone (28) so as to form a cantilever support for the annular support element, such that the axis of rotation (42) of the door fastening - false passes through the center of gravity (41) of the collection zone. 9. Device according to claim 1, characterized in that the connecting means is constituted by at least two bending elements (70,72) placed on either side of the axis of rotation (64) and in that the carrier element (22) is provided with a slot (74) located essentially on the same side of said axis of rotation (64) as the spacers (40,44, 46).