PENDULOUS ASSEMBLY

Abstract: A pendulous assembly for use in an accelerometer or other such device which senses forces acting on the device in a particular direction is disclosed herein. This assembly includes a proofmass, an arrangement including a frame supporting one end of the proofmass for back and forth pivotal movement about a given axis to a resting plane which entirely contains the proofmass when the latter is at rest, and specifically configured mounting pads connecting the frame and proofmass to main support forming part of the overall force sensing device.

Description: The present invention relates generally to a pendulous assembly for use in an accelerometer or other such force sensing device, and more particularly to specifically configured mounting pads which serve to connect the pendulous assembly to a main support forming part of the device. The present invention relates more particularly to a force sensing device of the type disclosed in published European Patent Application EP-A-0268351, filed August 25, 1986 and in the Applicant's continuation-in-part U.S. application Serial No. 221,116, filed July 19, 1988, and entitled A PENDULOUS ASSEMBLY FOR USE IN AN ACCELEROMETER OR SIMILAR DEVICE which was unpublished on the priority date of this application. In the above recited patent applications, there is disclosed a prior art pendulous or proofmass assembly for use in an accelerometer or other such force sensing device. That prior art assembly has been reproduced in Figure 1 of the present application and is generally designated by the reference numeral 10. The pendulous assembly 10 is shown including a flat, generally rectangular proofmass 12 and a support arrangement including a flat frame 14 and flexures 16 supporting the proofmass for back and forth pivotal movement about a given axis through a horizontal resting plane which contains the proofmass, frame and flexures when the proofmass is at rest. The overall assembly may include other components such as pickoff plates and torque coils, as described in European patent application EP-A-0268351. In addition, the assembly includes one pair of top and bottom mounting pads 18 on one section 14A of frame 14, on one side of the proofmass, and a second pair of top and bottom mounting pads on an opposite section 14B of the frame, on opposite side of the proofmass. As best illustrated in Figure 2, the top one of the mounting pads 18 (designated at 18A) is disposed on the top side of frame section 14A while the bottom mounting pad 18 (designated 18B) is mounted on the underside of frame section 18A and is intended to be in vertical alignment with mounting pad 18A. The mounting pads 20 are positioned in a similar way on frame section 14B. Still referring to Figure 2 in conjunction with Figure 1, the purpose for the mounting pads is to mount the entire pendulous assembly to a main support by means of opposing clamps indicated by means of dotted line at 22. Note that the clamps engage the outwardly facing surfaces of the mounting pads 18A and B on opposite sides of frame section 14A and, while not shown, they engage the outer surfaces of mounting pads 20 on opposite sides of frame section 14B. This is well known in the art and, hence, will not be described in further detail. Suffice it to say that the entire pendulous assembly is supported by clamps 22 so that the proofmass is free to pivot or deflect back and forth relative to frame 14, the clamps and the outside world (e.g., the main support to which the frame is connected by means of the clamps). As discussed in detail in Applicant's previous applications recited above, it is extremely critical to the operation of the overall force sensing device that the proofmass, flexures and frame be as free as possible of random and uncontrollable stresses and strains. One particular situation which induces undesired and uncontrolled strains into frame 14 is when the top and bottom mounting pads are not truly aligned along their edges, as exemplified diagrammatically in Figure 3. As seen there, the front edge 24A of mounting pad 18A, that is, the edge furthest away from flexure 16, is not in direct vertical alignment with the front edge 24B of mounting pad 18B. This is also true for the back edges 26A and 26B. As a result, when clamping forces Fc are applied to the mounting pads as a result of clamps 22, the misalignment between two pads tends to produce a torque or twisting in the frame adjacent the pads, as diagrammatically illustrated by arrows 28. Such torque or twisting forces, in turn, produce undesired strains in the frame. These forces are especially troublesome to the back edges of the mounting pads since they are closest to the flexures, whereas the front edges of the pads have little effect and, hence, the back edges primarily determine any adverse affects on the way in which the proofmass pivots back and forth during operation of the overall force sensing device. In any event, as will be described hereinafter, it is desirable to keep such stresses on either ends of the mounting pads or, for that matter, on their sides, to a minimum. This can be accomplished by ensuring that each pair of top and bottom mounting pads are indeed in vertical alignment with one another. In the case of proofmass assembly 10, it is considerably easier to ensure that the side edges of each pair of mounting pads are in alignment if they are the full width of the frame and if they are co-extensive with the side edges of their respective frame section. However, it is more difficult to ensure that the end edges are in alignment since they are not co-extensive with any edges of the frame of proofmass assembly 10. In view of the foregoing, it is an object of the present invention to provide pendulous assembly of the general type described above, and specifically an assembly which is designed to ensure alignment between cooperating top and bottom mounting pads. A more particular object of the present invention is to provide a pendulous assembly which is designed to ensure that at least the end edges of each pair of mounting pads are in vertical alignment with one another. Another specific object of the present invention is to provide a proofmass assembly which is designed so as to ensure that both the end edges and the side edges of each pair of mounting pads are in vertical alignment with one another. The present invention provides a pendulous assembly for use in an accelerometer or other such force sensing device, having a flat proofmass (32), means including a flat frame (34) supporting said proofmass for back and forth pivotal movement about an axis (38) through a resting plane, and a pair of mounting pads (40A, 40B) on opposite sides of the frame for mounting the frame to a support, with each of the mounting pads having an edge (56A, 56B) extending in a direction parallel to the axis, characterized by a slit (60) extending through the frame-adjacent to the edges (56A, 56B) of the pads, with a side wall of the slit forming a continuous flat surface (62) with the edges (56A, 56B) and thereby ensuring accurate alignment of the pads along said edges. The present invention also provides a pendulous assembly for use in an accelerometer or other such force sensing device, having a flat proofmass (32), means including a flat frame (66) supporting said proofmass for back and forth pivotal movement about an axis (38) through a resting plane, and a mounting pad (68) for mounting the frame to a support, characterized in that the mounting pad (68) is offset laterally of the frame (66) and has accurately aligned coplanar edge portions parallel to the axis (38) on opposite sides of the frame (66). As will be seen hereinafter, the pendulous assembly disclosed herein includes at least one pair of vertically aligned top and bottom, generally rectangular mounting pads connected with the top side and bottom side of its frame, respectively, for mounting the frame and its associated proofmass to a main support forming part of the force sensing device. The top and bottom mounting pads have vertically aligned side and end pad to pad edges. In one embodiment disclosed herein the pads may not be the full width of the frame and a through-slit is provided in the frame adjacent each end edge so as to define single vertically continuous edges to ensure that the end edges of the mounting pads are, indeed, vertically aligned. In a second embodiment, the entire mounting pad including its end edges is connected to the frame in an outboard manner so that the end edges are exposed without the necessity for slits. In a third embodiment, a longitudinal through-slit is provided in the frame adjacent the inboard side edges of the mounting pads, whereby to ensure that most of the length of those edges are vertically aligned. Other embodiments will also be disclosed. The overall pendulous assembly and the various mounting pad embodiments will be described in more detail hereinafter in conjunction with the drawings, wherein: FIGURE 1 is a plan view of part of a pendulous assembly designed in accordance with the prior art; FIGURE 2 is a side sectional view of the assembly of Figure 1, taken generally alone line 2-2 in Figure 1; FIGURE 3 diagrammatically illustrates a possible structural drawback to the prior art pendulous assembly of the type illustrated in Figure 1 and 2; FIGURE 4 is a plan view of a pendulous assembly designed in accordance with the present invention; FIGURE 5 is a sectional view of a portion of the assembly of Figure 4, taken generally along line 5-5 in Figure 4, specifically illustrating a particular mounting pad arrangement designed in accordance with the present invention; and FIGURES 6-8 respectively illustrate mounting pad arrangements designed in accordance with three different embodiments of the present invention. Turning now to the drawings, wherein like components are designated by like reference numerals, attention is immediately directed to Figures 4 and 5 since Figures 1-3 have been discussed previously. Figure 4 illustrates a pendulous assembly 30 corresponding in function to assembly 10 and those described in Applicant's co-pending applications recited above. To that end, the pendulous assembly shown in Figure 4 includes a flat proofmass 32 and a support arrangement including a flat frame 34 and a flat flexure network generally indicated at 36 supporting the proofmass for back and forth pivotal movement about a given axis 38 through a horizontal resting plane (in the plane of the paper), which contains the proofmass, frame and flexure network when the proofmass is at rest. Like proofmass assembly 10, assembly 30 may include other components which are not pertinent to the present invention. The particular flexure network 36 is one which has certain novel features described in one of Applicant's parent applications. It is to be understood, however, that the present invention is not limited to any particular flexure network, as will be apparent hereinafter. The proofmass assembly 30 also includes two pairs of vertically aligned mounting pads 40 and 42. Like mounting pads 18 and 20 forming part of previously described assembly 10, the mounting pads 40 are located on the top and bottom of one side section 34A of frame 34 and mounting pads 42 are located on the top and bottom of an opposite frame section 34B. Both frame sections 34A and 34B extend normal to axis 38, as seen in Figure 4. As also seen in this figure, the frame sections 34A and 34B are disposed on opposite sides of proofmass 32. The frame section 34A includes a longitudinally extending outboard side edge 44 and a longitudinally extending inboard edge 46, the latter being closer to proofmass 32. In a similar manner, frame section 34B includes a longitudinally extending outboard edge 48 and a longitudinally extending inboard edge 50. Referring to Figure 5, the mounting pads 40 are shown in section. The upper pad is indicated at 40A and the lower pad is indicated at 40B. Returning to Figure 4, it can be seen that the outboard and inboard side edges 52 and 54, respectively, of upper and lower mounting pads 40A and 40B are co-extensive with the outboard and inboard edges 44 and 46 of frame section 34. As a result, all of these edges are exposed therefore, and, it can be readily visually seen whether they are in vertical alignment with one another and thereby define vertically aligned common pad to pad edges. In fact, the specific way in which the proofmass assembly is to be made, a preferred embodiment, ensures that all of these side edges are in vertical alignment with one another. More specifically, in this preferred embodiment, the proofmass 32, frame 34, flexure network 36 and the mounting pads 40 and 42 are integrally formed as a single unit from a quartz wafer. The proofmass 32, flexure network 36 and frame 34, except for sections corresponding to the mounting pads, are chemically etched thinner than the mounting pads so that the latter are raised relative to the other components. As illustrated in Figure 5, the vertical edges 52 and 54 are not exposed to etching since they are actually cut initially and, thus are well defined, whereas the liner where the etching process takes place leaves an edge which is not well defined. From the procedure just described, it should be apparent that the side edges 52 and 54 of pad 40 are automatically aligned with one another since they are cut that way. This is also true for mounting pads 42. However, it is not true for the end edges of either pair of mounting pads. The end edges of mounting pad 40A are shown at 56A and 58A in Figure 5, and the end edges of mounting pad 40B are shown at 56B and 58B in the same figure. The etching process described above does not ensure that end edge 56A vertically aligns up with end edge 56B or that end edge 58A vertically aligns up with end edge 56B because of the frame section therebetween. Therefore, in accordance with the present invention, through slits 60 are provided (cut) in frame section 34A adjacent the end edges of pads 40. In one case of, for example, edges 56A and 56B, the presence of through-slit 60 results in each of the end edges defining a single vertically continuous, exposed pad to pad edge 62 along substantially the entire extent of the slit. In the case of end edges 58A and 58B, slit 60 results in a similar vertically continuously exposed edge 64. These vertically continuous edges ensure that the end edges are vertically aligned with one another in the intended manner. This is also true for mounting pad 42. In actual practice, the slits 60 are provided in the quartz wafer after the latter is etched. In that way, the end edges of the mounting pads automatically line up with one another in the same manner as the lateral or side edges of the mounting pads. It may also be desirable to provide similar side slits so that it is not necessary to rely on the alignment of inboard and outboard side edges 52 and 54. Corresponding side slits 63 are shown along and through pad 42 by means of dotted lines. In this case, the side edges of pads 42 are spaced inward of the side edges of frame section 34B, as also indicated by dotted line. Similar side slits could be provided in pads 40. Figure 6 illustrates a frame section 66 corresponding in function to, for example, frame section 34 of assembly 30. However, in this embodiment, rather than having mounting pads on top and bottom of the frame section, the vertically aligned upper and lower mounting pads 68 are provided outboard of the outboard longitudinal edge 70 of frame section 66. As illustrated in Figure 6, the end edges and the outboard side edge of mounting pad 66 are laterally offset or outward of frame section 66. In that way, the end edges and the outboard edges of mounting pad 66 define vertically continuous exposed edges. In a preferred embodiment, the mounting pads 68, like previously described mounting pads 40 and 42, are formed integrally with the frame section 66 and the latter is etched thinner than the pads. Figure 7 illustrates an embodiment identical to the one shown in Figure 6 but includes a longitudinally extending through-slit extensive with the inboard side edges of outboard mounting pads 68. This provides the same advantage as previously recited slit 60, that is, slit 72 results in a single vertically continuous exposed edge along the inboard side edges of aligned mounting pads 68. The mounting pad arrangement shown in Figure 8 results from separating frame section 66 into two separate and distinct segments 70′ and 70″ which are respectively connected to opposite inboard ends of a pair of vertically aligned outboard mounting pads 74. As in the previous embodiments, mounting pad 74 can be integrally formed with frame segments 70′ and 70″ except that the latter are etched thinner than the mounting pads. In all of the embodiments described in Figures 6-8, similar mounting pads will most likely be provided on opposite sides of the frame, as in the case of assembly 30. Moreover, it is to be understood that while these mounting pad embodiments preferably form an integral unit with the frame and from a quartz wafer, the present invention is not limited to this particular approach. For example, it may be that the mounting pads are separate from the frame. In this case, the slits in the frame (where used) would serve to align cooperating pads. Alignment pins through the slits may be necessary to achieve proper alignment between cooperating pads. Moreover, it is to be understood that the mounting pads of the present invention are not limited to pendulous type accelerometers but may be incorporated into translational devices or other types of transducers.

Claims: A pendulous assembly for use in an accelerometer or other such force sensing device, having a flat proofmass (32), means including a flat frame (34) supporting said proofmass for back and forth pivotal movement about an axis (38) through a resting plane, and a pair of mounting pads (40A, 40B) on opposite sides of the frame for mounting the frame to a support, with each of the mounting pads having an edge (56A, 56B) extending in a direction parallel to the axis, characterised by a slit (60) extending through the frame adjacent to the edges (56A, 56B) of the pads, with a side wall of the slit forming a continuous flat surface (62) with the edges (56A, 56B) and thereby ensuring accurate alignment of the pads along said edges. A pendulous assembly as defined by Claim 1, further characterized by a second slit (60) extending through the frame (34) adjacent to second edges (58A, 58B) of the pads (40A, 40B), with a side wall of the second slit forming a continuous flat surface (64) with the second edges (58A, 58B) and thereby ensuring accurate alignment of the pads along the second edges. A pendulous assembly as defined by Claim 2 further characterized in that the second edges (58A, 58B) are parallel to the first named edges (56A, 56B). A pendulous assembly as defined by Claim 2 further characterized in that the second edges are perpendicular to the first named edges (56A, 56B). A pendulous assembly as defined by any of the preceding claims, further characterized in that the frame 34 includes a pair of frame sections (43A, 34B) which extend in a direction normal to the axis (38) on opposite sides of the proofmass (32), and mounting pads (40, 42) with edges aligned through slits (60) are provided for each of the frame sections. A pendulous assembly as defined in any one of the preceding claims, further characterized in that side edges (52, 54) of the pads (40A, 40B) are coextensive with a side edge (44, 46) of the frame (34). A pendulous assembly as defined by any of the preceding claims, further characterized in that the proofmass (32), frame (34), and mounting pads (40, 42) are integrally formed from a single sheet of material. A pendulous assembly for use in an accelerometer or other such force sensing device, having a flat proofmass (32), means including a flat frame (66) supporting said proofmass for back and forth pivotal movement about an axis (38) through a resting plane, and a mounting pad (68) for mounting the frame to a support, characterized in that the mounting pad (68) is offset laterally of the frame (66) and has accurately aligned coplanar edge portions parallel to the axis (38) on opposite sides of the frame (66). A pendulous assembly as defined by Claim 8 further characterized in that the pad (68) has inboard side edge portions aligned with an outboard side edge (70) of the frame. A pendulous assembly as defined by Claim 9 further characterized by a slit (72) extending through a frame adjacent to the side edge portions of the pad, with a side wall of the slit forming a continuous flat surface with the side edge portions. A pendulous assembly as defined by Claim 9, further characterized in that the frame is formed in two spaced apart sections (70′, 70″), and the mounting pad (74) is connected to the two frame sections toward opposite ends of the pad, with the pad (74) having accurately aligned coplanar edge portions along the inboard and outboard sides thereof and on opposite sides of the frame. A pendulous assembly as defined by Claim 9, further characterized in that the mounting pad (74) has inboard and outboard side edges located outboard of an outboard edge of the frame (70′, 70″). A pendulous assembly as defined by any of Claims 9 to 12, further characterized in that the proofmass (32), frame (66, 70′, 70″), and mounting pads (40, 42) are integrally formed form a single sheet of material.

Inventors: HANSON, RICHARD A.
Applicants: HANSON, RICHARD A.
Application year: 1989
Main classification: G01P15
IPC codes: G01P15