US2435254A - Dynamic strain pickup - Google Patents

Description

Feb. 3, 1948. v w, RAMBERG l 2,435,254

DYNAMIC STRAIN PICK-UP Filed Sept. 25, 1945 www Waller Ramberg'.

f (Lw LW Patented Feb. 3, 13948 DYNAMIC STRAIN PICKUP Walter Bamberg, Chevy Chase, Md.

Application September 25, 1945, Serial No. 618,597

3 Claims. (Cl. 20L-52) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) My invention relates generally t apparatus f014 detecting vibrational displacements, and more particularly to the pick-up component therefor.

The principal advantage of this pick-up over presently available pick-ups is ,its exceptionally large voltage variations for small vibrational displacements. The output is ample to operate high frequency recording galvanometers directly without the complication of high frequency oscillators and amplifiers.

A useful application would be the recording of vibration on aircraft in flight. Another promising application is in resonance fatigue tests in which the output of a vibration pick-up mounted on the resonant specimen is used to hold the frequency of a driving motor at resonance; difficulties have been experienced with pick-ups in the past art because of their insufcient output.

For a more complete understanding of the invention and for other objects and advantages thereof, reference should now be had to the following descriptions in connection with the accompanying drawings, in which Fig. l is a half-sectional view of my invention for detecting vibrational displacements, connected into a Wheatstone bridge circuit;

Fig. 2 is a view taken along line 2-2 of Fig. 1; Fig. 3 is a view taken along line 3--3 of Fig. 1; and

` Fig. 4 is a view taken along line 4--4 of Fig. 1.

Numeral I indicates generally a rectangular cross-sectioned housing, closed at each end. Centrally of one side, and projecting inwardly of said housing, is provided a normally projecting cylindrical stub element 2. The opposite side is centrally apertured 3 across which are secured two tandem spaced flexible plates 4 and 5 which have a sufficiently high natural frequency to respond to vibrations of a high order. Said plates are centrally apertured to receive assembly screw 6 and are secured to the housing by sliding their end portions into horizontal receiving slots 1 and 8 and peening said ends secure in said slots.

A cylindrical thrust element 9 is provided consisting of cylindrical sections Ill, II, I2 and I3 which are centrally apertured to receive assembly screw 6. End section I 3 is threaded to threadedly engage said screw 6. An elongated abutment member I4 and a conducting leaf spring I5 are likewise centrally apertured to receive assembly screw 6. The above said elements are arranged, assembled and secured to the flexible plates by means of assembly screw 6 in the following order: assembly screw 6, section I0, leaf spring spring I 5, abutment member I4, section II, flexible plate 5, section I2, flexible plate 4, and threaded section I3. Section I3 threadedly engages screw 6 thereby' allowing the screw to draw and secure said assembled elements tightly together and be carried by said flexible plates. Spring I5 and its abutment I4 are positioned parallel to each other so as to be in juxtaposed relationship through all deflection of said spring.

Stub element 2 is diametrically bored to receive non-conducting rodular member I6 which is xed and supported thereby intermediate said rods ends. A ne resistance wire I'I is coiled around one end of said rodular member I6 in closely wound coils and is then connected into a Wheatstone bridge I8 as one arm thereof. Each individual turn of Wire is insulated from its companion turn. The other end of said rod functions as an abutment for a leaf spring element I9 about to be described. Conducting leaf spring I9 is centrally apertured and secured to the top of stub element 2, in a position parallel to the axis of coil I'I, by means of screw 20 and washer 2|. The stub element 2 projects beyond the received rodular element I6 a. distance equal to the thickness of coil I'I so that the leaf spring i9 secured in position will just overlay the resistance coil I'l tangentially. That part of leaf spring I9 that bears on said resistance coil is surfaced with a metal that has a small contact resistance at low contact pressures, thereby making excellent contact with coil I1.

Said leaf springs I5 and I9 are welded together at their ends 22, generally forming an elliptic spring, and provided with a particular configura-- tion such that an approximately linear relationship obtains between the displacement of thrust element 9 and the current or voltage in the indi cator 23 across the bridge I8. Said indicator 23 is responsive to electrical variations resulting from the association of leaf spring i9 and resistance coil Il, whereby said congured leaf spring changes the extent of its bearing contact on said resistance coil by a change of the configuration of said spring I 9.

In operation the thrust element 9 is held against any vibrating body to be investigated. The vibrational displacement cau-ses the springs I5 and I9 to deflect. As leaf spring I9 deects, it changes its configuration and increases-the extent of its bearing contact along coil I 1. Thus progressively more and more turns are shorted out of the bridge circuit by spring I9, and the bridge is correspondingly unbalanced. Hence, any departure from a pre-determined and initial reading or reference point o f the milliammeter 23 serves to detect a vibrational displacement. By suitable calibration, the milliammeter 23 is made .to indicate strain directly. When the direction of the vibration is reversed, and the .thrust element reverses its direction correspondingly, more and more coil windings are progressively "cut-in to the bridge circuit, and the bridge is correspondingly re-balanced.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to -be limited thereto, since many modifications may be made, and I, therefore. contemplate by the appended claims to cover any such modifications as fall within the true spirit and sc'ope of my invention.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. In a. dynamic strain pick-up a housing having an opening in one side thereof, a flexible means of high natural frequency mountedon the housing across the opening and adapted to respond to vibrations, a thrust membermounted on the flexible means, a resistance coil having a supporting core, mounted in the housing transversely of the thrust member, and an elliptic spring having an electrical conducting leaf and a non-conducting leaf, the latter being secured to the thrust member and the former bearing on the resistance coil and adapted to deilectably extend its bearing contact along the coil to vary the current passing therethrough as a function of the displacement of the thrust member.

2. In a dynamic strain pick-up a housing having an opening in one side thereof; a thrust member exibly mounted to operate through said opening and adapted to respond to vibrations:

' resistance coil means mounted in said housing:

and' conducting elliptic spring means having the bottom of said spring means secured to said thrust member and the top of said spring means securely bearing on said resistance' means and adapted to deflectably extend its bearing contact along said resistance in a linear relation to the displacement of said thrust member.

3. A dynamic strain pick-up including a housing having an opening in one side thereof, a exii REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,759,967 'I'homas May 27, 1930 1,760,092 Thomas May 27, 1930 2,071,256 Dobbs Feb. 16, 1937 2,305,267 Minor Dec. 15, 1942 2,359,245 Ritzmann Sept. 26, 1944 FOREIGN PATENTS Number Country Date 82,335 Switzerland Sept. 16, 1919

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