US3678383A

US3678383A - High impact withstanding taut band suspension instrument

Info

Publication number: US3678383A
Application number: US139513A
Authority: US
Inventors: Willem J L Boreas
Original assignee: Weston Instruments Inc
Current assignee: Weston Instruments Inc
Priority date: 1971-05-03
Filing date: 1971-05-03
Publication date: 1972-07-18
Anticipated expiration: 1989-07-18
Also published as: GB1382151A; DE7216466U

Abstract

In a taut band suspension instrument in which each taut band extends between two convex support surfaces and the end portions of the taut band are secured to the respective supports by fused metal connections at points spaced radially from the axis defined by the band, the support surface at the end of the band farther from the rotor is provided with a shallow groove, the bottom of the groove being continuous and uninterrupted and having a width at least twice the width of the taut band, the support surface at the other end of the band being smooth and unbroken for the full width thereof. The combination of the two support surfaces allows the taut band to shift laterally when the instrument is under shock, yet assures that the outer end of the taut band will be properly oriented when installed and thereafter.

Description

rite States Patent ii oreas 51 July 18, 1972 [72] Inventor: Willem J. L. Boreas, Sayreville, NJ. [73] Assignee: Weston Instruments, Inc., Newark, NJ.

[22] Filed: May 3, 1971 [21] App]. No.: 139,513

Related U.S. Application Data [63] Continuation-impart of Ser. No. 836,828, June 26,

1969, Pat. No. 3,624,505.

Primary Examiner-Alfred E. Smith Attorney-William R. Sherman, Jerry M. Presson' and Roylance, Abrams, Berdo & Kaul [57] ABSTRACT In a taut band suspension instrument in which each taut band extends between two convex support surfaces and the end portions of the taut band are secured to the respective supports by fused metal connections at points spaced radially from the axis defined by the band, the support surface at the end of the band farther from the rotor is provided with a shallow groove, the bottom of the groove being continuous and uninterrupted and having a width at least twice the width of the taut band, the support surface at the other end of the band being smooth and unbroken for the full width thereof. The combination of the two support surfaces allows the taut band to shift laterally when the instrument is under shock, yet assures that the outer end of the taut band will be properly oriented when installed and thereafter.

8 Claims, 12 Drawing Figures PATENTEU JUL 1 8 I972

sum

2 or 3 FIG. 6

FIG. 8

FIG. 11

FIG. 7

I820 85 82 IBIO INVENTOR WILLIAM J. L. BOREAS PATENTED JUL] 8

I972 sum

3 or 3 INVENTOR WILLIAM J. L. BOREAS HIGH IMPACT WITI'ISTANDING TAUT BAND SUSPENSION INSTRUMENT RELATED APPLICATION BACKGROUND OF THE INVENTION While taut band suspension instruments have long been known, such instruments have had relatively little capability of withstanding shock. This deficiency has been largely overcome by the construction disclosed in my application Ser. No. 836,828, in which the taut band has a limited freedom of lateral movement, relative to its supports, under conditions of impact. In that construction, the taut band is supported by an inner connector member, secured to the rotor, and an outer member, secured to a frame or like support, each connector member having a convex support surface so disposed that the axis of curvature thereof extends substantially at right angles to the axis of rotation of the rotor. The end portions of the taut band extend across the convex support surfaces and thence to a point of attachment spaced radially from the axis of rotation. The support surfaces are smooth and uninterrupted and of such width that the taut band can move through a significant distance laterally while still in contact with, or at least disposed for contact with, the support surfaces.

The construction further includes stop means so arranged as to limit movement of the rotor, and therefore the inner connector members carried thereby, axially relative to the frame and also to limit movement of the outer connector members axially away from the inner connector members, the stop means being such that the outer connector members are limited to an outward travel smaller than the axial distance through which the rotor is allowed to move. The inner connec tor members are in the form of stiff arms, and the outer connector members are resilient.

Connection of the taut bands to the inner connector members can be accomplished with the aid of a jig which assures that the band will extend substantially precisely across the center of the convex surface presented by the inner connector member. Connections of the bands to the outer connector members, however, must be made manually, without the use of a jig. Considering that the band is, advantageously, on the order of 0.005 in. wide and 0.0003-0.0004 in. thick, it will be understood that precise positioning of the band on the outer connector member is difficult to achieve manually. And the results of improper positioning of the band relative to the outer connector member can be significantly deleterious. For example, if the band is inadvertently offset from the center of the convex support surface presented by the outer connector member by several thousandths of an inch and the adjacent end portion of the band is, e.g., welded to the outer connector member with the inadvertent offset existing, the weld retains the end portion of the band in a normal position which is angularly offset by several degrees from the desired radial center of the outer connector member. Such angular offset not only improperly locates the taut band relative to the convex support surface but also causes an excessive stress concentration in the band at the weld, so that the ability of the taut band in the assembled instrument to withstand high impacts may be reduced.

OBJECTS OF THE INVENTION A general object of the invention is to provide a taut band suspension system, of the type described, in which precise centering of the band relative to the convex support surface of the outer connector member is achieved without loss of the capability of withstanding high impacts which stems from the freedom of lateral movement which the band is allowed.

Another object is to provide, in such a suspension system, lateral restrictions on movement of the taut band which are effective to assure proper positioning of the band during assembly and when the band is fully taut but which do not impede extreme lateral shifting of the band relative to the outer connector member under the slackened condition of the band encountered when the instrument is subjected to a high impact.

SUMMARY OF THE INVENTION Considered broadly, taut band suspension systems according to the invention include an outer connector member, advantageously in the form of a resilient arm, presenting the desired convex supporting surface for the taut band, the supporting surface being smooth and unbroken but being disposed between two raised portions which extend generally in the direction of the length of the band. Thus, the portion of the outer connector member which presents the convex supporting surface over which the band extends can be considered as having a shallow, relatively wide groove, with the supporting surface constituting the transversely fiat bottom of the groove and being at least twice as wide as is the band, the sides of the groove constituting raised portions having a height at least approximately equal to the thickness of the band. During assembly, the appropriate end portion of the band is manipulated manually to extend between the raised portions, along the length of the connector member, and through a locator notch and, with the band held in that position, the band is secured to the connector member by a fused metal joint, advantageously a spot weld, which is distant from the convex supporting surface and fixes a portion of the length of the band which is greater than the width of the band, so that the joint tends to constrain the band to its centered position on the convex support surface.

In order that the manner in which the foregoing and other objects are achieved according to the invention can be understood in detail, one particularly advantageous embodiment thereof will be described with reference to the accompanying drawings, which form a part of the original disclosure of this application, and wherein:

FIG. 1 is a front elevational view of an electrical meter according to the invention;

FIG. 2 is a longitudinal sectional view taken generally on line 2-2, FIG. 1, and being on larger scale than is FIG. 1;

FIGS. 3 and 4 are transverse sectional views taken generally on lines 3-3 and 4-4, respectively, FIG. 2;

FIG. 5 is a view, partly in longitudinal cross section and partly in side elevation, of a taut band and its associated connector members, forming part of the meter of FIGS. l4;

FIG. 5A is a fragmentary view showing the outer connector member of FIG. 5 with the taut band in a position resulting from high impact on the meter;

FIG. 6 is an end elevational view of the combination shown in FIG. 5;

FIG. 7 is a view taken generally on line 7-7, FIG. 5;

FIG. 8 is a transverse sectional view taken generally on line 8-8, FIG. 5;

FIG. 9 is a perspective view of the combination of elements shown in FIG. 5; and

FIGS. 10 and 11 are sectional views similar to FIG. 8 but showing the outer connector member in modified form.

Referring now to the drawings in detail, and particularly to FIGS. 1 and 2, there is shown an instrument in the form of a permanent magnet moving coil meter 1 which is provided with the improved taut band suspension arrangement of this invention. Meter 1 includes a stationary assembly in the form of a support frame 2, and a movable assembly in the form of a coil assembly 3 supported for pivotal movement by frame 2.

Frame assembly 2 includes a front frame element 4 and a rear frame element 5 which are secured to a magnetic structure 6 of the meter. The magnetic structure 6 includes a ring 7 of magnetic material and a cylindrical permanent magnet core 8 within the ring. The core is of a smaller diameter than the inside surface of the ring to provide the usual annular air gap 9 between the ring and the core.

Core 8 is maintained in concentric relation to the ring by spacer blocks 10 and 11 which are of nonmagnetic material and extend through air gap 9 in diametrically opposed relation to each other and are secured respectively to the core and the ring. The magnetic structure 6 is disposed between front frame element 4 and rear frame element 5 and the frame elements are securely clamped to the ring 7 of the magnetic structure by screws 13 which extend between the respective frame elements.

Coil assembly 3 includes a coil 14 having a plurality of turns of insulated coil wire wound on a rigid rectangular coil form 15. As shown at FIG. 2, the internal dimensions of the coil form 15 are only slightly greater than the external dimensions of core 8 and hence all the inside surfaces of the coil form are spaced slightly from the exterior surfaces of the core. The coil assembly is, of course, positioned on the core before the core is secured to ring 7.

The coil assembly 3 also includes a hub 16 secured to one side of coil form 15 and a hub 17 secured to the opposite side of coil form 15 and aligned with hub 16. Each hub has a threaded cylindrical tip 18 and the axes of the tips are aligned with each other and pass through the geometric center of coil form 15. Each hub also has a cylindrical portion 19, slightly larger than the tip, and with flat sides 20. Cylindrical portion 19 terminates at a transverse annular shoulder 21. Spaced inwardly of shoulder 21, in a direction toward coil 14, is a second shoulder 22. Between these shoulders is a cylindrical portion 23 which extends between the transverse surfaces of the shoulders Each hub has a central bore 24 and a transverse slot 25 which extends from the front of tip 18 to a location slightly inwardly of shoulder 22 to provide a flat outwardly facing surface 26.

Mounted on hub 16 is an inner connector member 28 which is ring-shaped and has a radially inwardly projecting arm 29 which extends through slot 25. The inside diameter of the ring-shaped portion of connector member 28 corresponds with the outside diameter of cylindrical portion 23 so the connector member is snugly received on cylindrical portion 23 of the hub and the inner face of the connector seats on shoulder 22. A pointer 30 is mounted on cylindrical portion 19 of hub 16. The pointer has an opening with flat sides that engage the flat sides 20 (FIG. 3) so the pointer is mounted on the hub against rotation. A nut 31, threaded onto tip 18, engages the front face of pointer 30 and holds the pointer against shoulder 21 of the hub. The thickness of connector member 28 is slightly greater than the distance between shoulders 21 and 22 so the connector member is held against axial movement relative to the hub.

Hub 17 is substantially identical to hub 16. Mounted on hub 17 is an inner connector member 32 identical to connector member 28. Connector member 32 has a ring-shaped body that extends around cylindrical portion 23 of hub 17 and a radially inwardly projecting arm 33 that extends through slot 25. The inner face of member 32 engages shoulder 22 of the hub. A counterweight 34 with an opening therein having flat sides corresponding to sides 20 of cylindrical portion 19 extends over the cylindrical portion and seats against shoulder 21 (FIG. 2). The flat sides prevent rotation of the counterweight relative to hub 19. A nut 35 identical to nut 31 is threaded onto tip 18 of hub 17 to hold the counterweight and connector member 32 against endwise movement.

Formed in front frame element 4 is a cylindrical bore 36. Extending through bore 36 is a molded bushing 37 formed from a semirigid thermoplastic material with good electrical insulating properties, such as polyethylene or polytetratluoroethylene. Bushing 37 has a frusto-conical inner end 38 which extends outwardly of cylindrical body 39 and terminates at a transverse shoulder 39'. Shoulder 39' engages the inner surface 40 of front frame element 4 to prevent movement of the bushing in a direction away from coil assembly 3.

End 38 is transversely split so it can be inserted through bore 36. Bushing 37 also has an enlarged head 41 with a transverse annular surface 41 that faces toward shoulder 39. The front face 42 of head 41 is cut at an angle along one side as at 42'. Formed in front face 42 is a rectangular slot 43 which extends from one side of the head to the other and follows the contour of face 42.

Mounted on cylindrical body 39 of bushing 37 is a zero setting or adjusting arm 44 having its outer surface in engagement with surface 41. Arm 44 is secured to the bushing, advantageously, with an epoxy cement, so the arm is fixed against movement relative to the bushing. Positioned on body 39 adjacent arm 44 is a flat washer 45. A Belleville type spring washer 46 is positioned on body 49 between outer surface 47 offront frame element 4 and the flat inner face ofa washer 45. It will be observed with references to FIG. 2 that the body 39 of bushing 37 is mounted for rotation in opening 36 of frame element 4 and that shoulder 39' of the bushing is biased into engagement with inner surface of the frame element by the action of the Belleville spring 46.

As shown at FIG. 4, a pair of spaced apart pins 48, formed integrally with bushing 37, project outwardly from the front face 42 of the bushing. An outer connector member 49 of generally U-shaped configuration, having a radially inwardly projecting arm 80, is provided with openings 51 (FIG. 4) to receive the pins 48. Connector member 49 is sandwiched between a front end member 52 and the front face 42 of bushing 37. As shown at FIGS. 1 and 4, the pins 48 project through openings in member 52 and extend beyond the front face 53 ofthe member. The member 52 and connector member 49 are connected to the bushing against rotational, as well as axial, movement by deforming the portions of the pins which extend through member 52 with a heated instrument so the tips of the pins are deformed as at 54, over front face 53.

Bushing 55 at the opposite end of the meter is identical to bushing 37 and extends through a cylindrical opening 56 in rear frame element 5. Bushing 55 has a transversely split tapered end 57 terminating at a transverse shoulder 58, which engages the inner surface 59 of the rear frame element 5. The head 60 of the bushing is identical to head 41, previously explained, and has a bevelled side 61, and a rectangular slot 62 formed in the end face 63 of the bushing. A Belleville type spring washer 64 is mounted on the bushing and engages the outside face 65 of frame element 5, and also engages one face ofa washer 66. A spacer washer 67 engages the transverse surface 68 of head 58. Secured to the outer end of the bushing is a second outer connector member 69 identical to connector member 49, and an end member 70 identical to end member 52. End member 70 and connector member 69 are secured to bushing 55 in the same manner as explained for end member 53 and connector member 49.

As seen in FIG. 3, connector member 28 has a flat ringshaped body 71, and arm 29 projects radially inwardly from the body. Body 71 is enlarged transversely, along the length of arm 29, to provide an outwardly extending lug 72. This outwardly extending lug 72 permits securing the taut band ele ment to connector member 28 at a location spaced substantially from the axis of rotation of coil 14, in a manner which will be explained in detail. As shown at FIG. 2, connector member 28 has a thickness which is substantially greater than the thickness of outer connector member 49 so the arm 29 is rigid. The inner end of rigid arm 29 is curved through an angle of approximately so it presents a convex surface 73 which merges smoothly into the transverse surface 74 along the length of arm 29.

Connector member 32 is identical to member 28, including arm 33, lug 75, and the rounded end on arm 33 which presents a convex surface 76, the rounded end of arm 33 being directed away from coil assembly 3 in the completed meter. Like connector member 28, member 32 is of relatively thick sheet metal so as to be essentially rigid with respect to forces applied to arm 33 by the taut band.

The body of connector member 49 is generally U-shaped, including supporting

legs

78 and 79 which lie flush against the front face 42 of bushing 37. Member 49 includes an arm 80 which is connected to

legs

78 and 79 via relatively thin portions 81 between the respective legs and the arm. Member 49 is formed from thin sheet spring material, such as phosphor bronze, so that arm 80 is resilient and, in the assembled device, can flex toward and away from the coil 14.

Arm 80 has a rounded tip 180, FIGS. 5-7, which curves through an angle of approximately 150 and, in the assembled device, extends toward coil 14. The side edges of tip 180 are deformed to provide raised

portions

181 and 182 which are of arcuate transverse cross section. Between raised

portions

181 and 182, tip 180 presents a convex surface 82 which merges smoothly with the transverse surface 83 presented by the outer face of arm 80. Convex surface 82 is transversely flat, so that raised

portions

181 and 182 coact with surface 82 to define a shallow groove with surface 82 forming the bottom of the groove. Raised

portions

181 and 182 are convex when viewed toward surface 182 and extend for most of the length of the curved tip 180. Raised

portions

181 and 182 have a maximum height midway between the ends of curved tip 180, Le, at the crest of convex surface 181, and taper to a zero height at each end of the raised portion.

Connecting portions 81 of member 49 extend circularly through an are which is concentric with the longitudinal axis of bushing 37. Arm 80 extends radially inwardly, its center line passing through the longitudinal axis of bushing 37. The length of arm 80 is such that, in the assembled device, the longitudinal axis of bushing 37 is substantially tangent to convex surface 82. Opposite tip 180, arm 80 is provided with a notch 183, FIGS. 4-7, which lies on the center line of arm 80.

Connector member 69 is identical to connector member 49, and includes a resilient arm 80' identical with arm 80 of member 49. Arm 80 is provided with raised portions corresponding precisely to raised

portions

181 and 182 of arm 80.

A first taut band suspension element 85 of elongated rectangular transverse cross section extends between outer connector member 49 and inner connector member 28. As shown at FIG. 5, suspension element 85 has a first portion 86 which extends along transverse surface 74 of connector member 29, and across convex surface 73 of that connector member. One wide face of the band engages these surfaces. Suspension element 85 also includes a second portion 87 which extends along transverse surface 83 of arm 80 and across the convex surface 82 of this arm. Extending between the

portions

86 and 87 is an intermediate portion 88. As seen in FIG. 3, portion 86 of band 85 is secured to connector element 28 at lug 72 by a relatively small spot weld 89. Similarly, as shown in FIGS. 4 and 6, portion 87 of band 85 is secured to arm 80 adjacent the outer end of the arm by a spot weld 90.

In a similar manner, a second taut band 91 (FIG. 2), identi cal to band 85, is connected between inner connector member 32 and outer connector member 69, at the rear of the meter.

As seen in FIG. 2, with connector member 29 positioned on hub 16, connector member 49 positioned on bushing 37, and with connector members 33 and 69 similarly positioned at the other end of the meter, coil assembly 3 is suspended by

taut bands

85 and 91 for pivotal movement about the axis determined by these bands. After

bands

85 and 91 are initially tensioned, they are maintained under sufficient tension by the resilient arms of

connector elements

49 and 69 so the axis of rotation of the coil assembly is essentially the same regardless of the orientation of the meter.

As previously explained, both bushing 37 and bushing 55 are free to rotate in the

respective frame elements

4 and 5. Such freedom of rotation permits adjusting the torsion in the

taut bands

85 and 90, after the meter is assembled, so the restoring force from the bands to return coil assembly 3 and pointer 30 to zero position can be set precisely by rotating bushing 37 and 55. After the initial adjustment of bushing 55, this bushing is secured to frame element 5 against rotation with a suitable cement. Thereafter, the zero set, for each use of the meter, can be provided by rotating bushing 37 via adjusting arm 44.

Nut 31 hub 16 extends into the central cylindrical opening 93 of bushing 13 and nut 31 of hub 17 extends into the bore 94 of bushing 55. It will be observed with reference to FIG. 2 that there is only a slight clearance between the external surface 95 of the nut on hub 16 and internal surface 93, and that, similarly, there is only a slight clearance between external surface 96 of the nut on hub 17 and internal surface 94.

Surfaces

93 and 95 function as stop surfaces to limit transverse movement of the coil assembly.

Axial movement of coil assembly 3, in the-event of impact, is limited in one direction by engagement of inside front surface 97 of coil form 15 with front surface 98 of core 8, and in the opposite direction by engagement of the rear inside surface 99 of the coil form 15 with rear surface 100 of the core.

As previously explained, arm of connector member 49 is resilient. As shown at FIG. 1, end member 52 has inwardly projecting tabs 101 which extend across the transverse surface 83 of the arm. As shown at FIG. 2, the inside surface 102 of tabs 101 is normally spaced slightly outwardly from arm 80. However, in the event of substantial shock or impact, surfaces 102 function as stop surfaces which are engaged by transverse surface 83 of the arm to limit the extent of deflection of arm 80 in a direction away from coil assembly 3. Stop surfaces 104, on the inner surface of the end member 70, similarly cooperate with arm 80' to limit its deflection in a direction away from the coil assembly 3, as a result of shock or impact. Advantageously, the stop surfaces 102 and 104 are so spaced from the arms that the maximum deflection of each arm away from the coil is less than the distance the coil assembly 3 can move axially from its normal position, before it engages one of the stop surfaces 98, 100 of the core.

The convex surface 73 of arm 29, while curved in front elevational as shown at FIG. 5, is substantially flat in a direction perpendicular to the side edge of portion 86 of the band and is substantially wider than the band. Hence, convex surface 73 takes the form of the surface generated by a straight line moved along the curvature of the surface in a direction perpendicular to the length of the line. While the convex surface does have some characteristics of a cylindrical surface, this convex surface need not be truly cylindrical. Since convex surface 73 includes any of a number of lines parallel to each other and perpendicular to the edge of portion 86 of the band, convex surface 73 will be termed transversely flat. Surface 73 extends completely to the edges of the tip of arm 29, this arm having no elements corresponding to raised

portions

181, 182 of arm 80.

The convex surface 82 of connector member 49 is similarly transversely flat and of a width substantially greater than the width of taut band 85. Like surface 73, convex surface 82 takes the form of a surface generated by a straight line moved perpendicular to its axis along the curvature of the convex surface.

Band is formed from a ribbon of a suitable alloy having a width from 8 to 12 times its thickness. While in the meter of this invention,

bands

85 and 91 are each 4 mils wide and 0.4 mils thick, bands 4 mils wide by 0.3 mils thick, as well as bands 4 mils wide by 0.5 mils thick can also be used to advantage. Since the band has substantial width as compared to its thickness, stresses are established in the side edges of the band as a result of attempting to pivot the band transversely about the weld spots 89 and 90. However, it has been found that the bands will curve elastically like a beam in response to a force applied to a side edge of the band, as when the band moves transversely and attempts to pivot about the weld point. Correspondingly, the

portion

86 and 87 of the bands which extend along the

respective arms

29 and 80 will curve along their length about a long radius if a band is displaced from its normal central position on the arms, without creating excessive stress in the band at the weld points 89 and 90. However, such elastic curvature with the absence of stress at the weld points can be obtained only if a substantial length of the band exlO I045 0447 tends along each arm. It has been found that remarkable resistance to breakage of the band in the event of severe impact is obtained if the convex surface, at the tangent point with the intermediate portion 88 of the band, is sufficiently wide that the band can move through an angle of l ll8 about the weld point where the band is fixed to the arm. It has also been found that a band 4 mils wide and 04 mils thick will curve elastically transversely of its length about the weld point, if the length of the band between the weld point and the tangent point with the convex surface is at least 50 mils and if the movement of the band from its neutral or central position does not exceed 6 in either direction when the band is in engagement with the

respective arm

29, 80.

In assembling the meter, the end of portion 86 of band 85 is secured to arm 29 by spot welding at 89 after assembling the band and member 28 in a jig (not shown) arranged to assure that end portion 86 extends along the center line of arm 29. Assembly is then continued until both member 28, with the band now welded thereto, and member 49 are in place. Manipulating the band 85 manually, as with tweezers, end portion 87 of the band is then stretched over the middle of the convex surface 82, thence over surface 83, and through notch 183. Presence of raised

portions

181, 182 allows the operator to properly position the band on surface 82 by eye, and use of notch 183 assures that the band portion 87 will extend along the center line of arm 80. Spot weld 90 is then established. Band 91 is installed in identical fashion.

Spot welds

89 and 90 are made with electrodes having a tip diameter which is significantly larger than the width of the band. Thus, with a band having a width of 0.004 in. the tip diameter of the welding electrode can be 0.01 in., so that the finished weld has a dimension, in the direction of the length of the band, 2.5 times the width of the band. With a significant portion of the length of the band thus rigidly fixed to the arm by the fused metal of the weld, the weld tends to constrain the band to a centered position relative to the arm, even when the band is not completely taut. In this connection, the elongated rectangular transverse cross section of the band tends to cause the band to behave as a beam, resisting bending in the direction of its width.

The width of surface 82 (and of the corresponding surface of arm 80') is from 1.5 to 4 times the width of the band. Typically, with band 85 having a width of 0.004 in., the lateral spacing between raised

portions

181 and 182 can be 0.008 in. With the width of surface 82 then being 0.008 in., and with the band 85 centered between raised

portions

181 and 182, the band can shift laterally over surface 82 through a distance of 0.002 in., or half of its width, in either direction. With the width of surface 82, as defined by the space between raised

portions

181 and 182, being 1.5 to 4 times the width of the band, the band is allowed to move laterally in either direction over the convex supporting surface of the outer connector member when engaged therewith, through a distance which is 25-150 percent ofthe width ofthe band.

Raised

portions

181 and 182 have a maximum height adequate to both visually define surface 82, for the operator who assembles the meter, and laterally restrain the band to surface 82 during assembly. Under conditions of extreme impact on the meter, however, the height of

portions

181 and 182 is adequately small, as seen in FIG. A, to allow the band, rendered slack by the impact, to move laterally without engaging the raised portions. Accordingly, raised

portions

181 and 182 can advantageously have a maximum height of l-l0 times the thickness ofthe band.

RESISTANCE OF THE SUSPENSION SYSTEM TO IMPACT What is believed to occur when meter 1 is subjected to impact, and What is believed to prevent breakage of the fragile bands when used in the taut band suspension system of this invention, will now be explained. First, consider what happens when the meter is dropped so it lands on a surface adjacent its end member 70 with the axis of rotation of the coil vertical. At the moment of impact, support assembly 2 will immediately stop, but coil assembly 15 will continue to move until its stop surface 97 engages the front face 98 of core 8. Such axial movement of coil assembly 3 is permitted by resilient arm of connector member 49. At the instant of impact, the arm 80, because of its mass, will deflect toward coil assembly 3. The arm 80, however, can deflect a greater distance toward coil as sembly 3, than coil assembly 3 can move axially before it engages the stop surface 98 of core 8. Hence, band is relaxed. At the opposite end of the meter, at the moment of impact, connector member 32 moves with the coil assembly toward end member 70. The resilient arm 80' of connector element 69 deflects in a direction away from the coil assembly 3, but its movement is limited by engagement with stop surface 104 and is less than the movement of the coil assembly. Hence. at the instant ofimpact, taut band 91 is also relaxed.

Immediately after impact, resilient arm 80 will spring back and tension band 85 to pull coil assembly 3 back to its properly suspended position. While there may be some vibration, the coil assembly will ultimately return to its normal suspended position between the

connector members

49 and 69. If the shock or impact is applied squarely to end member 70, there will be no transverse forces acting on either band, and hence, even though both

bands

85 and 91 were substantially relaxed at the instant of impact, the band will return to approximately a central position on the convex surfaces of the several connector elements, the fact that the band is of elongated rectangular transverse cross section and that the spot welds, being significantly elongated lengthwise of the bands, serving as a bias or constraint toward centered position.

Now consider the movement of the coil assembly and bands when the meter is dropped so its axis is horizontal. Assume for purposes of this explanation that arm 29 and arm 80 are in the same radial plane, as shown at FIG. 9, and that these arms are vertical at the instant of impact. At the instant of impact, frame assembly 2 will stop, but coil assembly 3 will continue to move in a direction perpendicular to its axis until the outside surface of the nut on hub 16 engages the inside stop surface 93 of bushing 37, and the outside surface 96 engages the inside surface 94 of bushing 55. At the instant ofimpact, the intermediate portion of band 85, because of its inertia, may deflect downwardly, but because of the smooth

convex surfaces

73 and 82, there is no stress concentration along the length of the band. Along

portions

86 and 87 of the band which extend around the convex surfaces and along the smooth transverse surfaces of the respective arms, it is believed that there is sufficient friction to prevent stress concentration in the bands at the weld points 89 and 90.

Now consider the action of the suspension system to resist breakage of the taut bands when the

arms

29 and 80 are radially aligned, the meter is dropped, and the arms are horizontal at the moment of impact. At the instant of impact, frame assembly 2 will stop instantly, but coil assembly 3 will continue to move until the

surfaces

95 and 96 of nuts 31 engage the respective stop surfaces 93 and 94 of bushings 37 and 55. The effect of such movement of the coil assembly is to displace member 28 from its normal position. Thus, there is some relative movement between connector member 28 and connector member 49, with the result that the tension in band 85 may increase slightly as a result of this movement. In addition, band 85, by virtue of its own inertia, will tend to continue to move. Because portion 86 of the band extends along the convex surface 73 and the smooth transverse surface 74 of connector member 28, and because the portion 86 of the band is sufficiently long that it can curve elastically along its length, the portion 86 will move laterally along convex surface 73 and transverse surface 74 to a gently curved position, but such movement will not create stress concentrations at weld point 89 sufficient to cause failure of the band. Likewise, portion 87 of the band will move along convex surface 82 and smooth transverse surface 83 of arm 80 and will also curve transversely, but will not break at weld point 90. As previously stated, a

convex surface on the arms of sufiicient width for the band to swing 1 l-l 8 relative to the weld point, where the length of the band extending around the convex surface and along the transverse surface of the arms is 50 mils long and has a width of 4 mils, exhibits excellent resistance to failure. As previously explained,

convex surfaces

73 and 82 are transversely fiat. Hence, any movement of band 85 transversely results in an increase in the length of the band with a corresponding increase in the tension in the band. As the tension in the band increases, a resisting force is developed which tends to return the band to its central position against the action of the forces I created by shock or impact. After the impact, the band will tend to return to its original centered position, but because of the friction between the length of

portions

86 and 87 of the band, and the corresponding surfaces of the

arms

29 and 80, the band may not return precisely to its original position. While a small displacement of the band may result, and may also occur with band 90, and will affect the accuracy of the instrument, because the axis of the coil assembly 3 is correspondingly displaced, it has been found that the extent of deviation in accuracy is less than 3 9% percent of full scale and that the bands did not fail when the meter was subjected to severe impact with decelerations on the order of 7,000 Gs. While ability to withstand very high impact forces is attained by increasing the length of the band between the weld point and the convex surface tangent point to, e.g., 50 mils, shorter lengths can be employed, with a corresponding decrease in impact resistance and increase in repeatability.

It will be appreciated that

connector arms

29 and 80 will not usually be radially aligned with each other at the instant of impact of the meter, because the relationship between these arms depends on the angular position of coil assembly 3. However, where the arms are aligned in a horizontal plane at the moment of impact, as explained with reference to FIG. 6, the most severe stresses that can be experienced are exerted on the bands at the weld points 89 and 90. Such impact tends to cause the bands to fail by bending at the edge of the weld. It will be appreciated, however, that the two arms which support a particular band may have virtually any angular relationship to each other and that the stresses in the bands at impact will be substantially less when the arms are displaced angularly than when the arms are aligned. It is also unlikely that the meter will ever be dropped so it lands with its axis precisely horizontal or with its axis precisely vertical as in the previously explained examples. Hence, the action of the suspension system in avoiding damage to the taut bands is believed to be the result of a combination of the actions explained above.

In considering lateral movement of the bands relative to their respective supporting arms, it is to be noted that raised

portions

181 and 182 are provided only on the

outer connector members

49 and 69 and not on the

inner connector members

28 and 32. Thus, the convex supporting surfaces presented by the arms of the inner connector members present no impediment to lateral movement of the taut bands and, therefore, allow a greater freedom of lateral movement of the bands than is allowed, under taut conditions, by the support surfaces and raised

portions

181, 182 of the outer connector members. In effect, presence of raised

portions

181 and 182 on the

outer members

49 and 69 is allowable because the taut bands can pivot generally in the plane of the lateral movement, so that the lateral excursion of the bands at the outer connector members need not be as great as that which is required at the inner ends of the bands to avoid breakage of the bands.

MODIFIED FORMS OF ARMS 80 AND 80' While the configuration of raised

portions

181 and 182, FIGS. 4-9, is particularly advantageous, the tips of

outer connector arms

80 and 80 can be modified considerably. Thus, as shown in FIG. 10, the edges of tip portion 180 can simply be turned up to provide raised portions 181a and 182:: generally in the nature of side flanges. Alternatively, tip portion 180 can Ill be kept completely flat throughout its width, and additional strips of material l8lb and 182b can be affixed along the edges thereof to provide the desired raised portions.

What is claimed is:

1. In a measuring instrument of the type comprising a rotor, support means, and taut band suspension means mounting the rotor on the support means, the suspension means comprising two inner connector members secured to the rotor, two outer connector members secured to the support means, each of the connector members presenting a convex support surface, and two thin resiliently flexible taut bands suspension elements each extending across the convex support surfaces of a different cooperating pair of the inner and outer connector members, the end portions of the suspension elements being secured at points radially spaced from the axis of rotary movement established by the suspension elements, the instrument further including cooperating stop means which limit outward movement of the outer connector members and axial movement of the rotor relative to the support with the outward movement of the outer connector members being held to less than the axial movement allowed the rotor, the improvement comprising two raised portions provided on the convex support surfaces of each of the outer connector members, said raised portions of each connector member extending generally in the direction of the length of the suspension element and being spaced apart, transversely of the suspension element, by distance at least about twice the width of the suspension element, the convex support surface of the respective connector member being smooth and uninterrupted between said raised portions; each suspension element extending outwardly across the convex support surface of the respective connector element in a location at least substantially centered between said raised portions and thence radially away from the axis of rotation established by said suspension elements along a line which at least approximately intersects the axis of rotation and being secured, at a point spaced radially from the axis of rotation, by a fused metal joint tending effectively to constrain the suspension element to its position between said raised portions, the convex support surfaces of said inner connector members being smooth and uninterrupted throughout the total extent of said elements in directions transverse to the axis of rotation. 2. A measuring instrument according to claim 1, wherein each of said outer connector members comprises a resilient arm formed of sheet stock and said raised portions are of rounded transverse cross section and convex as viewed from the side of said support surface engaged by the suspension element. 3. A measuring instrument according to claim 1 wherein each of said outer connector members comprises a resilient arm formed of sheet stock and said raised portions are upturned edge portions of the arm. 4. A measuring instrument according to claim 1, wherein the length of said raised portions does not substantially exceed the limits, in the direction of the length of the suspension element, of the respective convex support surface. 5. A measuring instrument according to claim 1, wherein the suspension elements are flat bands of elongated rectangular transverse cross section and the lateral space between said raised portions of each outer connector member is such'as to allow the band, when engaged with the respective convex support surface, to shift laterally in either direction, through a distance equal to 25-150 percent of the width of the band. 6. A measuring instrument according to claim 5, wherein the thickness of said bands is on the order of several ten thousandths of an inch and said raised portions project beyond the respective convex support surface by a distance equal to 1-10 times the thickness of the band in the area of the crest of the convex support surface.

7. A measuring instrument according to claim 2, wherein a locator notch is provided in each of said outer connector members at a point spaced from the convex support surface and the outer connector member includes a surface portion adjacent said notch, whereby in assembly the suspension element can be stretched across the convex support surface and thence along the connector member and through said notch, and a fused metal joint can then be established between the suspension element and said surface portion while the suspension element is held in said notch and in taut condition.

8. A measuring instrument according to claim 1, wherein the suspension elements are flat bands of elongated rectangular transverse cross section, the thickness of the bands being on the order of several ten thousandths of an inch and the width thereof being several times the thickness; and the bands are secured to the outer connector members by spot welds having a dimension, in the direction of the length of the band, significantly larger than the width of the band, the bands being biased by said spot welds to assume positions substantially centered between the respective raised portions even when the bands are slackened as a result of impact on the meter.

Claims

1. In a measuring instrument of the type comprising a rotor, support means, and taut band suspension means mounting the rotor on the support means, the suspension means comprising two inner connector members secured to the rotor, two outer connector members secured to the support means, each of the connector members presenting a convex support surface, and two thin resiliently flexible taut bands suspension Elements each extending across the convex support surfaces of a different cooperating pair of the inner and outer connector members, the end portions of the suspension elements being secured at points radially spaced from the axis of rotary movement established by the suspension elements, the instrument further including cooperating stop means which limit outward movement of the outer connector members and axial movement of the rotor relative to the support with the outward movement of the outer connector members being held to less than the axial movement allowed the rotor, the improvement comprising two raised portions provided on the convex support surfaces of each of the outer connector members, said raised portions of each connector member extending generally in the direction of the length of the suspension element and being spaced apart, transversely of the suspension element, by distance at least about twice the width of the suspension element, the convex support surface of the respective connector member being smooth and uninterrupted between said raised portions; each suspension element extending outwardly across the convex support surface of the respective connector element in a location at least substantially centered between said raised portions and thence radially away from the axis of rotation established by said suspension elements along a line which at least approximately intersects the axis of rotation and being secured, at a point spaced radially from the axis of rotation, by a fused metal joint tending effectively to constrain the suspension element to its position between said raised portions, the convex support surfaces of said inner connector members being smooth and uninterrupted throughout the total extent of said elements in directions transverse to the axis of rotation.

2. A measuring instrument according to claim 1, wherein each of said outer connector members comprises a resilient arm formed of sheet stock and said raised portions are of rounded transverse cross section and convex as viewed from the side of said support surface engaged by the suspension element.

3. A measuring instrument according to claim 1 wherein each of said outer connector members comprises a resilient arm formed of sheet stock and said raised portions are upturned edge portions of the arm.

4. A measuring instrument according to claim 1, wherein the length of said raised portions does not substantially exceed the limits, in the direction of the length of the suspension element, of the respective convex support surface.

5. A measuring instrument according to claim 1, wherein the suspension elements are flat bands of elongated rectangular transverse cross section and the lateral space between said raised portions of each outer connector member is such as to allow the band, when engaged with the respective convex support surface, to shift laterally in either direction, through a distance equal to 25-150 percent of the width of the band.

6. A measuring instrument according to claim 5, wherein the thickness of said bands is on the order of several ten thousandths of an inch and said raised portions project beyond the respective convex support surface by a distance equal to 1-10 times the thickness of the band in the area of the crest of the convex support surface.