US3546925A - Mechanical oscillator - Google Patents

Description

Dec. 15, HHU I v, BARTON 3,546,925

MECHANICAL OSCILLATOR Filed Aug. 30, 1967 3 Sheets-Sheet 1 Millard Burton INVENTOR.

BY 7M WW6 ATTORNEY I M. v. BARTON 3,546,925

MECHANICAL OSCILLATOR Dec. 15, 1970 Filed Aug. 50, 1967 3 Sheets-Sheet 2 Fig.3 F196 Millard V. Borron mvsmozz.

ATTORNEY Dec. 15, 1970 M. v. BARTON 3,546,925

MECHANICAL OSCILLATOR Filed Aug. 30, 1967 3 Sheets-Sheet 3 Millard V. Barton INVENTOR.

wwm

ATTORNEY United States Patent O ABSTRACT OF mscnosunn An improved mechanicalf oscillator to achieve demagnification of response relative to that of a conventional spring-mass system andv forjuse as a shock gage or dynamic absorber. The oscillator consists of single or multiple opposing tapered thin n'jetal tapes which are attached to a-roller such that the roller will roll up on one tape and unroll on the other tape, The variation of taper proportionately varies the berfiiding moment in the tapes. When the roller rolls away from the equilibrium position the change in bending mohient in the tapes creates a restoring torque acting to return the roller to center.

SUMMARY OF inn INVENTION Briefly this invention provides an apparatus which combines translational and rotational mechanical oscillators for low frequency responsef to motions of a wide range of amplitude. The apparatus comprises a rotatable mass and bias means attached to the mass and adapted to rotate the mass when the massjis displaced.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: 5

FIG. 1 is a perspective view of an embodiment of the present invention;

FIG. 2 is an end view of the cylinder portion of the invention.

FIG. 3 is an end view of one embodiment of the present invention.

FIG. 4 is a side view of the embodiment in FIG. 3.

FIG. 5 is a plan view of one embodiment of the metal tapes before being wrappe around the cylinder.

FIG. 6 is a side view the metal tapes illustrated in FIG. after the tapes are wrapped around the cylinder and anchored at the supporting wall.

FIG. 7 illustrates one embodiment of the means by which the tapes are anchored at the supporting wall.

FIG. 8 is an end view of the present invention on a curved surface.

FIG. 9a illustrates a translational oscillatory system.

FIG. 9b illustrates a translational-rotational oscillatory system.

FIG. 10 is a side view of one embodiment of the present invention.

BACKGROUND OF THE INVENTION Field of the invention An apparatus for responding mechanically to low frequency motions and more particularly a mechanical oscillator which combines translational and rotational oscillation.

Description of the prior art Response to motions at frequencies above two c.p.s.

., has been measured in the past using reed gages, a low and record many motions, such as ground motion created 3,546,925 Patented Dec. 15, 1970 by nuclear detonations and earthquakes. Subjected to such a motion, the low frequency simple oscillator undergoes a displacement approaching thatof the ground itself, a large displacement. Low frequency mechanical oscillators have also been used as dynamic absorbers to reduce the motion of oscillating equipment. Such oscillators need to be very large and have many practical design problems.

Patented oscillators do not combine translational and rotational motion as a means for achieving demagnification. Four such patents are: 2,586,307, Crede, Seismic Frame Structure; 2,739,250, Marsh, Electromechanical Oscillator; 2,901,703, Plunkett, Frictionless Suspension Means for Rotary Elements; 2,904,302, Cavanaugh et al., Vibration Isolating Assembly.

Crede uses conventional fiexural pivots for pivotal movement. Marsh provides an electromechanical oscillator which uses pendulum motion, instead of a purely mechanicaloscillator using rotational and translational motion. Plunkett uses beam springs for only rotary motion, Cavanaugh et al. uses conventional curved springs which do not produce translational and rotational motion.

This invention improves upon the prior art by providing an apparatus which combines translational and rotational mechanical oscillation to achieve considerable demagnification of response relative to. that of a conventional spring-mass system thereby making possible a smaller and more rugged device capable ofimeasuring low frequency motions of large amplitude. In a conventional spring-mass system the mounting fra'me displaced by a shock or vibration moves translationally relative to the mass and with respect to a fixed point in space. The mass tends to stay at rest which means that the mass will move translationally with respect to the frame, but will not move with respect to a fixed point in space. It is at the time when the frame has moved; through a certain distance that the conventional system and the device of this invention are distinguished. The restoring force in the conventional system produces some translation of the mass relative to the frame as the mass catches up with the frame. However, in the present-device the coupling produced at the mass immediately itends to return the mass to equilibrium position relative to the frame and therefore to simultaneously produce rotation of the mass and translation in relation to both a fixed point in space and the frame. It is this quick catch up characteristic which affords the demagnification factor of this device. According to the teachings of this invention for a given shock displacement of the frame the mass translates less distance with respect to the frame in a translation-rotation device as claimed than does a trauslation device. Consequently, a smaller device is possible to accommodate the mass displacement. In addition, with clamping elements added the oscillator is a dynamic absorber for low frequency oscillations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, FIG. 1 shows a preferred embodiment of the oscillator. The oscillator ineludes a supporting frame 10, a hollow cylinder 11, four tapered thin metal tapes 12, 13, 14, 15, a flywheel 16, a stylus 17 (FIG. 10), and a recording plate 18 (FIG. 10).

The cylinder 11 and flywheel 16 provide the mass and moment of inertia to the oscillator. Any other element providing mass and moment of inertia can be substituted for the cylinder 11, such as a solid roller. FIG. 2 shows a hollow cylinder 11. Stiffening of cylinder 11 and viscous damping are made possible by fitting fluid leakproof end caps 20 to the ends of the cylinder 11. A fluid may be injected into the cylinder 11 for viscous damping and variation of effective mass. Viscous damping can be varied 1 3 by providing a gate or port 19 through the end cap 20 whereby the fluid inside the cylinder can be increased or decreased. Fluid may also be used in the flywheel 16 rim 'for damping and variation of effective mass. Port 29 provides a means for increasing or decreasing the fluid inside the hollow or tubular rim of the flywheel 16.

The four thin metal tapes 12, 13, 14, are wrapped around the cylinder 11 in opposite directions and are led off tangentially from the bottom to anchor points 21 on the supporting frame 10. Each tape is tapered, the width moment of inertia of the tape cross section. The bending moments in tapes 13 and 15 and in tapes 12 and 14 appear as opposing couples applied to the cylinder 11, and these couples are equal when the cylinder is at rest in the equilibrium position.

Since the tapesare tapered, the area moment, I, and bending moment vary with position of the cylinder 11. Displacement of the cylinder 11 from the equilibrium position causes thejcylinder 11 to roll up on one set of tapes and unroll from the other set, thus creating an unbalanced couple. In the direction of displacement of the cylinder 11, the moment, I, of the tapes rolled up onwill increase as displacement increases and the moment, I, of the opposing set of unrolled tapes will decrease. A change in moment, I, will proportionately change the bending moment of the tapes. The unbalanced couple created by an unbalanced bending moment acts to return the cylinder 11 to equilibrium position. I

Any number of metal tapes or other bias means may be employed which will create opposing couples tending to return the cylinder 11 to an equilibrium position. FIGS. 3, 4 illustrate such an arrangement with two tapes, 22, 23.

Experience has shown alignment of tapes to require a sensitive adjustment. The load on each tape at the at.- tachment to cylinder 11 and alignment of each tape must be accurate. Tofacilitate adjustment of load distribution and alignment of tapes, the tapes 24, 25, 26 are made in a single unit 27 as illustrated in FIGS. 5, 6. Unit 27 is attached to cylinder 11 at points 28 between tape 24 and tapes 25, 26. Each tape is wrapped around cylinder 11, tape 24 being threaded through the space between tapes 25 and 26 and the end of each tape is fastened at an anchor point 21. Any number of tapes can be integrally formed and wrapped around cylinder 11 and fastened at their ends in like manner.

Experience also has shown that where high amplitude shocks are applied to the oscillator, the tapes are stretched or buckled, an undesirable condition. Where low or medium amplitude/shocks only will occur, the anchor points 21 of the oscillator may include any well known securing means. However, where high amplitude shocks are to be applied to the oscillator, the securing means illustrated in FIG. 7 is preferred because the tapes are protected from stretching or buckling. The end of each tape is clamped at clamp 30. Clamp 30 is adapted to slide on the frame 10 a small distance toward and away from the cylinder 11. Walls 31, 32 of frame 10 limit displacement of clamp 30 toward cylinder/11 and away from cylinder 11, respectivelyJA resilient material 33 or other spring means is positioned between frame 10 and both sides of clamp 30 to absorb the shock and return clamp 30 to its norm position after the shock.

The cylinder 11 may roll over a flat surface as in FIGS. 1 and 3 or over a curved surface. FIG. 8 shows cylinder 11 suspended on tapes 35, 36 which are adapted to cause cylinderll to roll over curved surface 37.

The cylinder 11 is freely supported on the tapes but may in the alternative roll on another supporting surface,

due to rolling contact between the cylinder 11 and tapes, air friction during displacement, and hysteresis strain in the tapes. These friction c'oefficients are very low in comparison with the friction resultant from contact of cylinder 11 with another surfacegfor example surface 37.

The hubs 38 of the end caps 20, FIG. 1,-may be externally fitted with small instr'iltnent bearings 40 (FIG. 2). Horizontal tracks 41 mounted on the supporting frame 10 and above bearings 40 provide hold-down forces .against motion in an undesired *direction in a shock situation. Horizontal tracks 42 are shown-below the lower ends of cylinder 11, but may be positioned below the bearings 40 in the alternative. The clearance between the bearings 40 and tracks 41, 42 or cylinder 11 and tracks 42 should be small. In the absence of motion causing contact of the cylinder 11 with the track"s,41, 42, the bearings, 40 and cylinder 11 ride free of contact and are supported on the lateral stiffness of the tapes. In the event of motion causing contact between thjebearings 40, cylinder 11 and tracks 41, 42, the bearings 40 provide a shock cushion and reduce. friction during contact. l

FIG. 9 shows the relationship between translational and rotational systems. FIG. 9a" shows a mass 45 connected to a supporting frame 46 by aspring 47 and adapted for translational displacement.- In- FIG. 9b the mass 48 having moment of inertia, I and radius R, is adapted for rotational displacement and: also is connected to a supporting frame 46 by a spring 47. An external shock will cause displacement of the supporting frame 46 and the mass. The original position of the supporting frame 46 represents a reference point and? is the magnitude of displacement from the reference ."-point due to the shock. The magnitudes of relative displacement of the masses, 45 and 48, are indicated by x, and x respectively. The spring force, F is equal to the spring stiffness coefficient, k, times the displacement, x,

F1: kx v The inertia force, F is equal to the mass, m, times the acceleration of the system (F =ma). However, the acceleration due to a shock isth'e sum of the second derivative of x and the second derivative of y,

z= +i l') Then for an undamped translational system iii- 1 "1 7 where w =k/ m. For the rotational system in FIG. 9B

J 1 mR where w =k/ (m-l-l/R For two systems having the same frequency, w, and input acceleration 17 Hence, from this approximation for translational and rotational systems, it is clear that x can be made much smaller than x by adjusting J, m and R This demagnification factor, M, which makes possible a relatively small linear displacement for a given input acceleration 17 is represented by the relationship 12nd is a principle upon which the subject invention is ased.

Applying the foregoing principle, the cylinder 11 is designed with the proper moment of inertia J, mass 'm, and radius R to give the desired demagnification factor, M. To provide capability of varying the demagnification factor with a given cylinder, a flywheel 16 is attached to the cylsuch as surface 37 .in FIG. 8. Friction is reduced by freely supporting the cylinder 11, there appearing only friction inder 11 with an identical axis of rotation. Flywheel 16 is constructed with a rim 50 connected ,to cylinderll by spokes 51 or by a light-disc between the hub cylinder 11 and rim 50. In the case where the flywheel provides viscous damping, the rim 50 is tubular and adapted to receive a fluid therein. The rotor combining flywheel 16 and cylinder 11?]138 different values of J, m and R? due to the addition of Ithe flywheel 16. Multiple flywheels-may attached to cylinder 11 to further vary the demagnification factor of th' loscillator or a different size flywheel substituted.

FIG. shows one possible apparatus for recording displacement of the oscillator. A stylus 17 is mounted on one end of the cylinder 11 and held againsta' record plate 18%;by a'very light spring 54. The plate 18 islmounted on a wall of frame 10 opposite cylinder 11 and fextends along thiej 'cylinder translational path. The small stiffness of the stylus spring 54 ensures minimum stylus friction.

o obtain a permanent record of the displacement of cylinder 11 relative to frame 10, a strip f tape 55 is smg'iked and applied to the record plate 1, 8 After each run: the tape is removed and sprayed with a clear coating ate produce a permanent record. Styliis 17 can be mounted at the center of the hub 3'8 of end cap on the axis of rotation of cylinder 11 or for. an amplified record can be offset from the center. The record plate 18 can be I adaptedto be removable for easy access "to the record adjustable after each recorded displacement-so morethan 011 displacement can be taken on a single record. Means can be providedfor marking the equilibrium position on record.

"Other recording means are readily adaptable to measure displacement of the cylinder 11 and this invention is not liniited to the means illustrated in FIG. 10.

he oscillator may be packaged in a box or container for}; transport or use in the field as for example burial at a tea? site. The container shouldprevent exposure of the osillator to dirt particles or other foreign; bodies. The coiitainer can'readily provide easy access without opening the container for changing record plate 18, for providing an equilibrium mark on the record plate 18, and foii; locking or unlockingthe position of the; cylinder 11. The locking means may be a pin58 extending through fraine 10 into end cap 20 to prevent movement of cylinder 11;; jrelative to frame 10, but the locking means may include ot fj'ier conventional means.

jlilyhile certain embodiments of the inventipn have been d "Iribed in detail herein and shown in the accompanying'fjdrawing, it will be evident. that various additional md difications are possible in the arrangement and construction of its components without departing from the scope of the invention.

What is claimed is:

A combined translational and rotational oscillator comprising:

a frame,

a rotatable mass, and

at least two spring tapes oppositely wound upon the mass and attached to the mass at one tape end and to opposite sides of the frame at the other tape ends so that the mass is supported upon the tapes and will unwind on at least one tape upon mass displacement relative to the frame while simultaneously winding onto the opposing, at least one tape, each tape tapered with increasing width from the point of attachment on the mass to the point of attachment on the frame thereby providing a restoring force to return the mass to the equilibrium position.

2. A device as in claim 1 wherein: the mass is a roller.

3. A device as in claim 2 and further comprising: at least one flywheel connected to the roller.

4. A device as in claim 2 wherein: the roller is a hollow cylinder having a sealable port for passing fluid therethrough.

5. A device as in claim 2 wherein:

the frame provides tracks thereon adjacent to the ends of the roller,

and further comprising:

bearing shock absorber means connected to the ends ofthe roller and adapted to be guided by the tracks on the frame so the roller is restricted wrapped around said roller.

'7. A device as in claim 2 and further comprising: re-

cording means fqj'recording displacement of said roller relative to the frame. l

8. A device as in, claim 5 and further comprising: locking means connecting the roller to the frame so said roller can be locked; in any position, incapable of displacement until unlocked.

9. A device asfi n claim 3 wherein: the rim of each flywheel is tubular,1sa id tubular rim having a sealableport for passing fluid therethrough. a.

10. A device as in claim 7 wherein the recording means comprises: y

a recording plate, and

a stylus attached to the roller at one end and at the other end contacting the recording plate.

11. A device afjsj'in claim 8 wherein the roller is a hollow cylinder or tube having a scalable port for passing fluid therethrough-gr and further comprising:

recording meansgconnected to the cylinder for recording displace ent of said cylinder relative tojthe frame.

12. A device as n claim 4 wherein:

the frame prosiids tracks thereon adjacent to the ends of the cylinder,

and further comprising:

bearing shock absorber means connected tothe ends of tfi'e cylinder and adapted to be guided by the tracks on the frame so the cylinder is? restricted. to move only in the direction off the tracks sa d bearing means normally not contacting said f fame and adapted so that upon contact the bea fig means absorb shock and minimize friction, 'nd 5 at least on gflywheel connected to the cylinde 13. A device as; in claim 12, and further comprising recording means for recording displacement of saidcylinder relative to flip frame.

14. A device as: in claim 13 and further comprising locking means connecting the cylinder to the frame so said cylinder can be locked in any position, incapable of displacement until unlocked.

15. A device as in claim 6 and further comprising recording means for recording displacement of said roller relative to the frame.

16. A device as in claim 15 wherein the recording means comprises:

a recording plate, and

a stylus attached to the roller at one end and at the other end contacting the recording plate.

17. A device as in claim 4 wherein:

the opposing spring tapes are formed integral in a single unit capable of being wrapped around said cylinder and having the ends of the tapes secured at the point of attachement on the frame, and

the frame provides tracks thereon adjacent to the ends of the cylinder,

and further comprising:

bearing shock absorber means connected to the ends of the cylinder and adapted to be guided by the tracks on the frame so the cylinder is restricted to move only in the direction of the tracks, saidbearing means normally not contacting said frame and adapted so that upon contact the bearing means absorb shock and minimize friction, and at least 'one flywheel connected to the circumferential surface of the cylinder, said flywheel having a tubular rim with a scalable port for passing fluid therethrough.

device as in claim 17 and further comprising 2,741,873 recojding means for recording displacement of said cyl- 3,003,357 indei relative to the frame. i 3,167,962

19 Q- A deviee as inclaim 18 and further comprising 1 locking means connecting the cylindee to the frame so said cylinder can be locked in any position, incapable of dis- 5 127,432

placement until unlocked.

References Cited UNITED STATES PATENTS 1-,s17 ,s6 7 8/1931 Karelitz 73- 11 1,998,136 4/1935 Iaenichen et al. 74--89.2

I I if 1' 4/1956 Erickson 46-?206 10/ 1961 Votta, Jr. V. 74: 8 9.2 2/1965 'Scotto 73 490 FOREIGN PATENTS 4/1960 U.S.S.R. 73 -11.1

RICHARDJC. QUEISSER, Primary Examiner J. P. BEAUCHAMP, Assistant Examiner

Images