Патент USA US2411401код для вставки
42,411,401 _ SrTEs PATENT Fisici: 2,411,401 ACCELEROMETEB William r. welch, Arlington, va., ssngnor'» to Westinghouse Electric Corporation, East Pitts burgh, Pa., a corporation of Pennsylvania _ Application July 28, 1942, Serial No. 452,576 4 claims. (on. 1v1-209) l , This invention relates to a device for use in determining ’ the characteristics of motion im Referring to the drawing, the numeral I desig nates as a Whole a device for producing a measur parted to a body upon being subjected to a shock able impulse ln response‘to movement of a body 2 as caused by the application thereto of a shock The possibility of failure of apparatus when it ci ing force. The device l comprises a housing 3 ing force. ` y _ is subjected to an instantaneous or rapidly ap ' adapted to be rigidly attached to the body 2 and pliediorce in the nature of a shock is well known. -to this end the housing 3 is provided with a Apparatus which is apt to be subjected to shock threaded opening t for engagement with a ing forces in this manner is frequently tested for threaded end 5 of a member 6. The member lìy its ability to stand up under shock prior to being 10 preferably is formed ‘from a single piece of ma placed in actual use. To the best of my knowl terial having a hexagonal middle section and` edge, no device has been heretofore devised which will indicate or measure the motion whichv is im threaded ends band l. The other end 'l of the ' member S is threaded into a nut 5 welded to the parted' to a body upon being subjected to a shock body 2 for the purpose of securing the housing 3 ing force. Obviously, an instrument that will 15 to the body 2. y I measure the motion of a body subjected to shock A pair of quartz crystals 9 and l@ are mounted is desirable in that it will provide an aid in den within the housing l for generating a charge or ' termining the nature of a shock and explaining electrical impulse in response to smovement'. of why apparatus breaks when shocked. One of the principal objects ot this invention the casing 3 and body 2 by a shocking force ap plied to the body 2. -`'I'he crystals 8 and l0 are _. cylindrical in shape and are cut with their elec trical axis parallel to their cylindrical axis. A is to provide a device for producing a. measurable impulse proportional to the movement of a body subjected to a shocking force. copper electrode Il is positioned ,` 'between the A further object of this invention is to provide facing end surfaces of the crystals 9 and lll. The a device whichmay be readily attached to a. 25 other end surface of the crystal 9 is adapted to body to be subjected to a shocking force, and seat on a surface l2 formed in the housing 3. . which will generate an electrical impulse proper-_ The other end surface'of the crystal l@ is adapted tional to the movement of the body in response _to seat on surface ill provided by a member l5. to a shock from which the frequency and ac The member l5 is provided with a bias for celeration. of movement of the body may be de 30 maintaining the crystals 9 and l0 in position be- _ termined. _ tween the surfaces l2 and it. To this end the A further object is to provide a device for de _ member l5 is resiliently mounted within the Éecting the movement of a’body under a shock housing ßvby annular disk springs l 8 and I'l. The outer edges of the springs l@ and il' are anchored A further object is> to provide a device for rigid 35 to the housing t by an annular element I3 adapt attachment to a. body to be subjected to shock ed to seat against the housing 3 as at i9, an an orce. with charge generating means comprising a piezo-electric quartz crystal which will generate an impulse in response to movement of the body under shock from` which the acceleration and .40 frequency of movement imparted to the body _may be readily determined. ‘ ‘ nular spacer element 2b, and an annular adjust ing member 2l having threaded engagement with the housing 3. Upon positioning the spring I6 between the members it and 20 and the spring ll between the members 2@ and 2l as shown, the outer ends of the springs 'it and il will be Other objects and advantages of the invention ' anchored with respect to the casing 3. . will become apparent from a study of the follow» _ The inner ends of the springs I6 and Il are ing description, _taken in connection with the ac 45 anchored to the 'member i5 by an annular spacing companying drawing in which: Figure 1 is a-sectional view of a charge gen erating device constructed in accordance with the principles of this invention; - member 22- and an internally threaded member 23 adapted to have threaded engagement with ‘ the _member l5. Upon positioning the inner edge ,_ ' _ of the spring l5 between the annular surface 24 Fig. 2 is a schematic view showing the device 50 and the member 22 and the inner end of the ` oi' Fig. 1, with apparatus for measuring the ex _ tent and nature ofthe impulse produced by move ment in response to a. shocking force; and; Fig. 3 is a modification for use in connection with the device shown in Fig. 1. _ . spring I1 between the members 22 and 23, such inner `edges will be anchored in position with re spect to the member l5. ‘ Thr-:__ anchoring parts :for the springs I6 and Il « 65 are so designed that upon assembly of the parts 2,411,401 4 as viewed in Fig. 1, a compression of the crystals 9 and I0 will be had due to the mass of the mem ber I5 tending to remain at rest by reason of its inertia. The piezo-electric property of the crys tals 9 and I9 causes a charge to be produced pro portional to the force exerted by the accelerated as shown in_Flg. 1, the springs I6 and I1 will be flexed in a direction to provide a resilient bias maintaining the member i5 in engagement with the `crystal I 9. To adjust the deñection of the springs IE and I'I and thus the resilient bias on the member I5, removable shims 25 are provided between the outer edges of the springs I6 and the seating member I8. If the bias is to be increased, mass thereon. The crystals 9 and I9 are so ar ranged that their inner facing surfaces will be of it is merely necessary to remove one or more of like polarity. The charge produced by the crys mounted on armor-plated structure when it is struck by a projectile. The measurement of the faces of theucrystals 9 and I0. It frequently hap the shims 25 and thereafter operate the member 10 tals 9 and I0 is taken 01T as an electric impulse through the terminal 28 which is electrically con 2I to move the outer edges of the springs I6 and nected to the electrode II. The impulse flowing I1 inwardly with respect to the inner edges there through the electrode 28 is employed in a manner , of, the position of the inner edges being ñxed by to be described to indicate or measure the char the 4‘position of the member I5 as determined by acteristics of the motion imparted to the casing the crystals 9 and I0. 3 by the shocked body 2. When a body is struck a shocking force, it is The end surfaces of the crystals 9 and III, to subjected to large and rapidly applied accelera gether with the seating surfaces I2 and I4, are tions and consequently vlbrates at extremely high so formed that pressure applied to the crystals 9 frequencies. Such vibrations and accelerations are encountered, for example, by apparatus 20 and l0 will be distributed uniformly over the sur pens that adjacent surfaces will be formed withl high spots which may cause a concentration of the force applied thereto in a manner likely to bration, as made possible by the device I, pro vides knowledge which is helpful in theldesign of 25 cause crystal breakage. Such concentration of force may likewisevbe cau-sed by a particle of dirt apparatus to be used on an armor-plated struc- . 4being lodged between the surfaces I2 and I4 and ture such as a naval vessel which apparatus must the end surfaces of the crystals. In order to function even though the vessel be struck by a amount of acceleration andthe frequency of vi- , projectile. _ ` prevent such concentration of force due to high ' spots or dirt particles, a thin strip of relatively In order to prevent movement of the surface soft conducting material 21 such yas tin-foil, the thickness thereof being exaggerated in the draw I4 out of engagement with the crystal IIJ,A the bias on the member I5 must be suiiicient to withstand ing for the purpose of illustration, is inserted between the crystals and their seating surfaces By keeping down the mass of the member i5 and 35 on the casing 3 and the member I5. Thesoftness of the >conducting material enables the high spots ' Aemploying stiff springs i6 and I'I a bias may or deposited dirt‘particles to embed in the con readily be provided for maintaining the crystals extremely large accelerations tending to move ` the member I5 to the right a-s viewed in Fig. i. _9 and I0 in position suñlcient for accelerations ducting material andthe force is thereby dis-- tributed uniformly over the surfaces of the crys However, in this respect, -it »is necessary that the conducting material or tin-foil be thin tremely high frequencies and such `frequencies in order that a cushioning effect which would will be found to have a range up to 5,000 cycles otherwise interfere with the natural frequency per second or greater. For an indicatorto have will not be had. a response proportional to acceleration, its nat In the schematic showing of Fig. 2, the essen ural frequency must be greater than twice the 45 tial parts shown in~ Fig. 1 are indicated by like -frequency of the acceleration being measured. numerals. In this showing, it will be noted that The natural frequency of a device is a function the element 29 `is substituted for the springs I6 of its spring constant and its mass. In the case. and I‘I. The electrical impulse or chargek gen ' of the device I, the spring constant is approxi mately the elastic stiffness of the crystals 9 and 50 erated by the crystals 9 and I0 is taken of! through a conduit 30' which is connected to one I0 in an axial direction. By maintaining the side of a condenser 3l, the other side of the con mas-s of the member I5 small, the natural fre- f denser 3I being grounded tothelcasing 3. The quency of the device I will be found to, be very l charge which goes into the condenser 3l pro high and in the nature of from about 10,000 to duces a voltage which is proportional to the about 20,000 cycles per second. By increasing force supplied to the crystals 9 and I0 and is the weight of the mass I5, the sensitivity -of the measurable. A resistance 32 is shunted across . device I will ibe increased at the expense of a the condenser 3| and it is necessary ythat this 'decrease in the natural frequency thereof. Such resistance be sufñciently high to allow .the volt increase in sensitivity accordingly lowers the fre quency of vibration whichthe device I is capable 00 age across the condenser 3l to be proportional to the charge for the lowest frequency to be of measuring. However, the increase in sensi measured. The voltage across the condenser '3l tivity i-s frequently desirable for measuring is fed into an amplifier 33 of a type having a smaller accelerations. In this' respect, it will be y high input impedance. The output of the am noted that crystals 9 and I9 function> in the dual capacity of a piezo-electric generator and a ine-_ 65 pliñer 33 is fed into a cathode ray type oscillo up to about 8,000 times gravity. ‘ _ Bodies subjected to shock will vibrate at ex 40 tals. scope 35 capable of following frequencies of the type encountered. A tuned fllter 34 is located in the output circuit and is tuned to correspond on the body subjected to the shocking force in with the natural frequency of the device I. By the manner explained above. Upon a shock being applied to the body 2, the device I will be vibrated 70 this means transient impulses due to the natural frequency vibrations of the member I5 on the back and forth with the body 2 and a similar elastic stiffness of the crystals 9 and I9 are sup acceleration will be imparted to the casing 3 and is imparted to the body 2 by the shocking force. I pressed. chanical spring of high stillness. In operation, the detector device I isfmounted The electron beam of the oscilloscope is thus housing 3 is assumed in a direction to the richt 75 deflected by an amount proportional to the ac _ If the instantaneous acceleration imparted to the v2,4.1 1,401 5 6 , celeration of the casing 3. Thefbeam is at the in response to shock comprising a piezo-electric ì same time moved with a constant velocity in a crystal seated within said housing, a mass having a surface engageable with said crystal, resilient means for biasing said mass into engagement with direction perpendicular to the aforementioned deflection by means of a suitable sweep circuit (not shown). The trace of the beam is pho said crystal and forming therewith a vibratory tographed by the camera to produce arecord of _ system of 'a natural frequency higher than that of the shock movements to be detected, and re ternative to the use of a sweep circuit, the camera silient means disposed between said mass and ñlm may be moved with a constant velocity in a said housing for permitting said mass to remain direction transverse _to the beam ~deflection. 10 substantially at rest when the device is subï'ected From the photographic record -the acceleration to shock. and the frequency of vibration imparted to the 2. A device for detecting the movement of a i casing 3 may be readily determined. _ _ body under a shock force comprising a housing From the foregoing, it will be apparent vthat for rigid attachment to said body, charge gen the piezo-electric properties of the crystals 9` and erating means for producing an electric impulse the motion imparted to the casing 3. As fan al ill,` together with their mounting withinv the in response to movement of said body comprising a pair of piezo-electrical elements arranged for opposite polarity, Asaid housing having a surface engaging an end surface of one of said elements.' housing 3 provide a novel _and efñcient detector device for producing a measurable impulse from which the characteristics of the motion imparted to a body in response to the application thereto of a force of shock proportions may be deter mined. l The device I has the’advantage of being light in weight and small in size. It will thus a mass having a surface engaging an end surface of said other element, an electrode positioned be tween said elements and engaged by the other ‘end surfaces of said elements, and means'resil be apparent that its size and weight limitations `ientlilv mounting said mass within said housing do not interfere with its attachment to the body 25 and providing a biasing force applied axially of to be studied. Moreover, the apparatus for said elements. ` _ measuring the impulse generated in response to 3. A device for detecting the movement of a shock may be located'at a distance from the de- . body under a shock force comprising a housing vice, the impulse from the terminal 28 being for rigid attachment to said body, charge gener transmittable by cable to such apparatus. ating means for producing an electric impulse Referring to Fig. 3, there is shown a modified 30 in response to movement of said body comprising form of the member ISa for use in the device I a pair of piezo-electrical elements arranged for to enable such device to be employed as a force y opposite polarity, said housing having a surface meter. _In this showing, the numeral 38 desig natesthe threaded portion adapted to have en 35 engaging an Yend-surface of one of said elements. a mass having a surface engaging an end surface gagement with the element 23 as shown in Fig. 1. _ of said other element, an electrode positioned be The difference in_theconstruction of the- mem tween said elements and engaged byfthe other Y ber I5a lies in the provision' of the -additional end surfaces of said elements, and resilient means threaded portion 31. The portion 31 is adapted f_or engagement with anotherv part of a struc 40 vdisposed between said mass and .said housing for permitting said mass to remain substantially at ture (not shown) similar to the part 2. Relative ’ rest when the device is subjected lto shock so that ‘movement between such vDarts will vthus cause said generating means andv mass,- when under relative' movement between the part lia and the housing 3. vthelatter movement being representa . shock, form a vibratory system whose elastic de tive of :a force due to loading causing a deflec-- 45 terminant is substantially given by the axial elas- _ ticity of> said crystals. . tion of the structure being`> examined. This 4. A device for detecting the movement of a movement will cause a compression or change in body under a shock force comprising a `housing pressure onthe crystals 9 and I0 and a corre - for rigid attachment to said body, charge gener spondingchange in the charge or electric im ating means for producing an electric impulse in . pulse therefrom. -In using the device I as a force meter, it will be noted that the crystals 9 and 50 response to‘ movement of said body comprising a pair 'of piezo-electrical elements arranged for op- \ I0 are mounted between the- relatively movable ’ posite polarity, said housing having a surface en housing'3 and member I5a and that crystals 9 and I0 will indicate the amount of relative move gaging an end surface of one lof said elements, a mass having a surfaceengaging an end _sur ment as a measure of the force applied. Since certain changes may be made in thev 55 face oi!1 said` >other element, an electrode posi-` , tioned between said elements and engaged by the _above described construction> Í'andl diii'erent em other‘end surfaces of said elements. and means bodiments of the invention' may be made without departing from the scope thereof, it is intended ' resiliently mounting said mass within ~said hous ing and providing a biasing force applied axially that all matter contained in the above descrip tion or shown in the accompanying drawing shall ‘ 60 of said elements, said mass and said crystals be interpreted as illustrative and not in a limit ing sense. - ` I claim as my invention: _ Y _ i , _ . . 1. A device for detecting the movement of a 'forming together a vibratory system oi' a natural j frequency higher than that of the shock move ment to be detected and. said resilient biasing. means havinga stiffness relative to said mass‘so 'body under a shock‘ force comprising a housing 65 as to permit said mass to remain substantiallyat rest when shock is applied to said housing. to saidbody, charge gen Y for rigid attachment erating meansfor producing an electric impulse , - ». - WIIZLIAM P. WELCH.