Manufacture of a force transducer flexure device

(24) Running day

PATENT AUTHORITY (62) Stamansokans number (86) International filing day

82-07-06

82-07-08 (86) Filing date for European patent application (30) Priority information

81-07-'14 US 283130

Application received as:

O Swedish patent application

O completed international patent application with number

Q converted European patent application with number (71) Sucking

Sundstrand Data Control Inc,

Redmond Wash US (72) Inventor K W. Atherton, Bellevue Wash (74) Representative Holmqvist L (54) Designation Procedure for Manufacturing a Flexible Power Supply Company (56) Published Publications: - (57) Summary:

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The necessity for rigorous control of process variables and the execution of physical measurements is eliminated in a method of manufacturing a flexible means for use in connecting a power sensing element to a mounting base in a power sensor. The method means that indicator portions (100, 102) are provided on a blank and material is removed uniformly from the blank comprising the indicator portions until the indicator portions disappear. This method can also be used to produce a flexible member based on a uniform piece of material such as molten quartz, wherein the blank is masked on each surface except the indicator portions and at least one other surface portion (96, 98), after which material is removed from the unmasked portions of the blank. .

DB 647289

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Figures in brackets indicate international identification code, INID code Letters in clamps indicate international document code

451 900

The present invention relates to the manufacture of flexible members used in power transmitters and more particularly relates to a method of manufacturing flexible members formed in a single piece of material, such as molten quartz.

In a power transducer, for example, an electromagnetic, servo-balanced accelerometer, the power sensor may comprise a unitary portion of molten quartz, glass or metal consisting of a movable element connected to a base by means of a flexible flexible portion.

An example of such a sensor is found in US Patents 3,702,187 and 4,250,757. Swedish Patent Application No. 8204218-5, which is parallel to this, discloses flexible means for a power transducer with conductors located on the surfaces mainly in the neutral bending plane of the flexible body. The present patent application relates to a process for manufacturing such a flexible member.

In the manufacture of such a sensor, it is desirable to control the thickness dimensions of the flexible member with a high accuracy as this largely controls the final biasing properties of the sensor and it is also highly desirable to achieve this accuracy in a simple and reliable way. To date, the manufacture of such flexible members has required rigorous process control combined with periodic measurements of the thickness of the flexible member.

The present invention achieves this desirable combination of manufacturing properties of the flexible member by using a specially adapted process element, namely, an indicator surface.

A feature of the present invention is that the method of manufacturing the flexible portion of the transducer comprises the steps of providing a tongue member for the transducer having a portion suitable for the manufacture of the flexible member, preferably having parallel surfaces generally at right angles to the sensitive axis of the movable member. the element of the sensor, and removing material from at least one indicator portion of a surface to a

451 900 desired depth.

An indicator surface is a surface formed on an indicator portion of the sensor's tongue, from which the flexible member is formed. The purpose of the indicator surface is to provide an indicative reference plane, which has a known relationship to the plan for surfaces provided on other parts of the subject. *

Another feature of the present invention is that the material may be removed from at least one other portion on at least one surface of the flexible portion simultaneously with or in a manner substantially identical to the removal of material from the indicator portion. Portions made from the surface of the transducer's tongue, which are used for the indicator portion, will have surfaces which are substantially plane parallel to the indicator surface.

Lots made from the opposite surface of the tongue will have surfaces having substantially the same respective relation to the surface from which they were made as the indicator surface has to the surface from which it was made.

Another feature of the invention is that the indicator portions can be made from opposing surfaces of the sensor's tongue so that they are substantially or partially aligned with each other.

When the indicator portion is treated in a manner substantially identical to the treatment of another portion on the same surface of the blank as the indicator portion, the relationship between the planes of the generated surfaces will be substantially constant. In this way, a predetermined relationship between the plan can be maintained. A special case is that surfaces that are plane parallel before a treatment step remain essentially plane parallel after the step.

When the indicator portion is treated in a manner that is substantially different from the treatment of another portion of the blank, an adjustment of the relationship between the planes of the surfaces will occur. In this way, a predetermined relationship between the plan can be established or canceled.

A further advantage of the method is that the sensing of the desired thickness dimensions of the flexible member and the desired resilience of the flexible member can be determined from the actual part during processing by appropriate fabrication of the indicator portions and subsequent observation of the indicator portions and termination of the treatment as portions of the indicator surface break through. or disappears. Such a process provides suitable dimensioning with a high accuracy in a manner which is substantially insensitive to unavoidable process variations and. $ does not require moving elements of a unitary tongue of the transducer to be free, thereby increasing the sensitivity of the flexible member to damage, to accurately obtain the desired resilience of the flexible member.

A further feature of the present invention is that it may include the step of observing or otherwise sensing when the indicator surfaces

451 900 breakthrough and then complete removal of material from the flexible portion.

A further feature of the invention is that the indicator portions, the indicator surfaces and other surfaces with planes flat with the indicator surfaces can be treated so that when the indicator areas are broken, the indicator surfaces and the surfaces which are parallel to them coincide, mainly with the neutral bending plane of the flexible part. This feature makes the process uniquely well-suited for the manufacture of the flexible bodies described in Swedish patent application no. 8204220-1.

It is a special and unique advantage of the indicator surface process described above that the plane parallelism of the surfaces of the flexible portions made from opposite surfaces of the blank can be easily determined to a high accuracy by simply observing the blank itself during the treatment. This is accomplished by using counterbalanced indicator portions and by sensing the plane parallelism of opposite surfaces by the absence of the indicator surfaces when encountered during the material removal process. This capability of the process eliminates the need for rigorous process controls or measurement of parts that would otherwise be required to obtain similar dimensional tolerances for such a design of the flexible member.

Another advantage is that transparent or opaque tongues for the sensor can be used interchangeably in the process.

The invention is described in more detail below with reference to the accompanying drawings. FIG. 1 is an exploded perspective view of a power-driven accelerometer showing a power supply with flexible means designed in accordance with the present invention. Figure 2 is an enlarged fragmentary perspective view of the flexible portion taken along line 2-2 of Figure 1. Figs. 3, 4 and 5 are fragmentary sectional views taken along line 3-3 of Fig. 2 through a portion of a donor blank in which the flexible member is formed and shows the successive steps in the manufacture of the flexible member.

Referring to Fig. 1, there is shown a power transducer in the form of a power-driven accelerometer 10, comprising a flexible member 12 of a type which can be manufactured in accordance with the present invention. The accelerometer 10 is of the type described in U.S. Pat. Nos. 3,702,073, 4,182,187, and 4,250,757, although the invention is also applicable to the manufacture of flexible members and other resilient elements used in other power transducers using angular motion or linear motion of a force sensing element.

The accelerometer 10 consists of a pair of cylindrical body elements 14a, 14b and an inertial mass assembly 16 arranged therebetween.

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The body elements 14a, 14b are essentially identical and only the body element 14a is described in detail. The body element 14a comprises one_r cylindrical body wall 17 which has an inwardly extending edge 18 constituting a magnetic pole piece and including a base portion 19. The pole piece 18 has a cylindrical inner wall 20 which forms a recess 22. A cylindrical * permanent magnet 24 is attached to the base portion 19 of the recess 22.

The permanent magnet 24 has an outer peripheral surface spaced from the inner cylindrical wall 20 to form an annular space 26 therebetween.

The inertia mass assembly 16 comprises a force-sensitive element or tongue 30 which is hingedly mounted by the flexible members 12 at a mounting base or ring 32.

In the accelerometer shown in the figures, the flexible member 12 allows the tongue 30 to move relative to the mounting ring 32. However, it will be appreciated that the flexible member 12 can be combined with various mounting devices and used in a sensor using linear motion of the sensing element along the axis of the sensor 10 .

A pair of force resetting coils or torque coils 42, 43 are attached to the upper and lower surface 40, 41 of the tongue 30. The torque coils 42, 43 are wound on bobbins which fit into the annular space 26 formed in each body member 14a, 14b. when the various parts of the accelerometer 10 are assembled.

On the upper surface 40 of the tongue 30 is applied a layer of conductive material 45. A similar layer of conductive material is located on the lower surface 41 of the tongue 30. These electrically conductive layers form a pair of capacitor plates which cooperate with a surface 21 of the pole piece 18 and a corresponding surface of the pole piece of the body element 14b in a manner described in more detail. below.

Three mounting pads 34 (one of which is not shown in the figure) are located on an upper surface 36 of the mounting ring 32. A further three mounting pads are located axially opposite the mounting pads 34 on a lower surface 38 of the ring 32.

The mounting ring 32 is secured between the body elements 14a, 14b such that an edge 23 of the cylindrical body wall 17 and a corresponding edge of the body element 14b abuts the mounting pads and torque coils 42, 43 .

A pair of variable capacitors 48, 49 is formed in the accelerometer 10, one of the capacitors consisting of the surface 21 and the coating on the lower surface 38 and the other capacitor consisting of a surface corresponding to the surface 21 of the pole piece.

451 900 of the body member 14b and the coating 45 on the upper surface 36 of the tongue 30.

The conductive layer on the upper surface 40 and the lower surface 41 and the torque coils 42, 43 are coupled to outer circuits by four conductive strips 47 extending to the ring 32 over the flexible member 12. Electrical connection with external circuits is provided from the ring 32 by means of four contact pins (not shown) located in the body wall of the body elements 14a, 14b.

When accelerometer 10 is subjected to acceleration along this axis, tongue 30 moves relative to ring 32 and body elements 14a, 14b, which in turn causes a change in capacitance of capacitors 48, 49. The change in capacitance is sensed by a feedback servo circuit (not shown). , which in turn couples a signal proportional to the change in capacitance to the torque coils 42, 43. The resulting magnetic field constructed by the torque coils 42, 43 cooperates with the magnetic field developed by the permanent magnets of the body 14a, 14b to counteract the displacement of the tongue 30. The current required by the torque coils 42, 43 to maintain the tongue 30 in a neutral position corresponds to the acceleration force to which the accelerometer was subjected.

For further description of the accelerometer 10, reference is made to U.S. Patent 3,702,073.

Referring to Fig. 2, an embodiment of the flexible member 12 which can be manufactured according to the present invention is shown.

The flexible member has a double-sided or bifilar, freestanding configuration consisting of a pair of flexible portions 60, 62 extending between the tongue 30 and the mounting ring 32. The portions 60 and 62 are separated by an intermediate opening 63 which also extends between the tongue 30. and mounting ring 32.

The flexible portions 60 and 62 are identical and therefore only the portion 60 is described. The portion 60 comprises an upper and a lower surface 64 and 66 which are substantially parallel to one another, and a pair of edges 68, 70.

The flexible portion 60 has a pair of channels 71, 73 extending into the portion 60 from the surfaces 64, 66, The channels 71, 73 have grooved surfaces 72, 74 which are substantially plane parallel to each other and to the central plane of the cross-section of the flexible portion. and substantially coincides with the neutral bending plane of the flexible portion 60.

The neutral bending plane is defined as the plane which is not subjected to any stretching or compression when the flexible member is bent into single bending. For a flexible member having a uniform rectangular cross-section consisting of two parallel surfaces and two edges such as that shown in Fig. 2, the neutral bending plane consists of all points located at equal

451 900 distances from the surfaces of the flexible portion, i.e. the plane located midway between the surfaces of the flexible portion. For the embodiment of the flexible member shown in Fig. 2, the main plane and thus the neutral bending plane of the flexible portion is slightly rotated with respect to planes 71, 72, 73 and 74, but the discrepancy is minimal and has no particular effect on the use of the invention as is described herein.

The tongue 30, mounting base 32, and flexible member 12 are preferably made of a uniform member of a stable homogeneous material such as molten quartz. A circular blank of uniform thickness with plane parallel surfaces is treated by selective removal of material to achieve the desired design. The discussion below relates in particular to the preferred method used to form the channels 71, 73 with the surfaces 72, 74 located mainly in the neutral bending plane of the flexible portion.

Preferably, the material is removed from the blank by etching with a suitable quartz solvent. The quartz blank has those surfaces where materials are to be removed masked with a material which prevents the availability of the solvent for the quartz surface. The masked substance is then immersed in the solvent. In a few minutes, several tenths of millimeters of the quartz material is etched away, the exact rate depending on the composition of the quartz, the concentration of the solvent and the temperature of the bath. Alternatively, material can be removed from the blank by gas plasma etching in an atmosphere that dissolves quartz, or by ion beam processing.

Fig. 3 is a cross-section through the portion of the quartz blank 80 from which one half of the bifilar flexible member 12 is formed. The blank 80 may have plane parallel surfaces 82, 84 and for the purpose of this example a thickness of the order of 0.762 mm. The dashed lines 86, 88 identify material to be removed in a first step of the treatment to form the opposite laterally spaced channels 71 ', 73' as shown in Fig. 5. The dashed lines 90, 92 identify materials that are simultaneously removed in the first stage of the treatment and form a pair of opposite surfaces, which throughout the process act as indicators for the plane of associated excavated surfaces, which should become the surfaces 72 'and 74' of FIG. .

The surface indicated by the clamp 94 should not be subjected to removal of material in the first stage of the treatment and is therefore masked as described above.

The blank 80 is immersed in the solvent for a period of time sufficient to form the intermediate channels 96, 98 and the intermediate indicator surfaces 100, 102, cf. Fig. 4, which has a depth which is substantially half of the total final intended thickness of the flexible member. .

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The dotted lines in Fig. 4 indicate the final outer contour of the flexible member and its relation to the surfaces formed in the first etching step.

The coating of masking material is removed from the surfaces 94 and the substance is returned to the solvent. Materials are then read from all surfaces of the flexible member at a uniform rate. As the material removal proceeds or proceeds at the same rate from both the upper and lower surfaces of the flexible member, the indicator surfaces 100, 102 will meet and disappear at the plane which is spaced at equal distances from the original surfaces of the blank, i.e. substantially coincident with the blank. neutral bending plane of the flexible member. At the same time, an equal amount or depth of material has been removed to form the channels 71 ', 73' so that the bottom surfaces 72 ', 74' of the channels are located in the same plane with each other and with the cross-sectional center plane of the flexible member and substantially coincide with the neutral bending plane. for the flexible body.

The disappearance of the quartz material between the indicator surfaces 100, 102 is sensed. When this occurs, the substance is absorbed from the etching bath and the removal of material is stopped. This procedure typically achieves that surfaces 72 'and 74' substantially coincide with the neutral bending plane of the flexible member with an accuracy independent of process variations and without the need for rigorous physical measurements of the thickness of the flexible member.

The blank is washed to remove any residual solvent and is then ready for continued treatment to achieve the desired quartz piece design for the inertial mass assembly 16. Thereafter, a suitable conductor 47 is applied to surfaces 72 ', 74' such as by vacuum coating or plating.

If the etching process is not completed just at the breakthrough of the indicator surfaces 100, 102, the channels 71 ', 73' will be deeper or shallower and the surfaces 72 ', 74' located on either side of the neutral plane and the thickness of the flexible member will deviate slightly from the the desired dimension. However, the distance of these surfaces from the neutral plane and the deviation of the thickness of the flexible member will be small compared to the thickness of the flexible member, which may be on the order of 0.0254 mm in this example and such errors do not significantly reduce the usefulness or efficiency of the flexible member. process.

The process can also be used to fabricate flexible members of a predetermined thickness by first removing material from an indicator surface to form a recess of a predetermined depth and then removing material from a flexible area while removing material from the excavated indicator surface. When the indicator surface breaks through the material, a flexible member of the predetermined thickness is obtained.

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