US3004389A - Device for varying the frequency of a vibration exciter - Google Patents

Description

Oct. 17, 1961 MULLER 3,004,389

DEVICE FOR VARYING THE FREQUENCY OF A VIBRATION EXCITER Filed April 14, 1960 Jnyenfor: Zoo/we HULLER 191-10 vvers 3,004,389 DEVICE FOR VARYING THE FREQUENCY OF A VIBRATION EXCITER Ludwig Miiller, Heinrich-Heine Strasse 41, Marburg an der Lahn, Germany Filed Apr. 14, 1960, Ser. No. 22,230 Claims priority, application Germany Apr. 25, 1959 6 Claims. (Cl. 60-53) The present invention relates to a device for varying the frequency of a vibration exciter for pile driving devices using vibrations, and also for tuning the frequency to the natural frequency of the member to be driven by regulating the rate of rotation of the drive means of the exciter, generally hydraulic drive means.

There are known hydraulically driven vibrators which are controlled by means of an oscillating piston and in which the frequency of the vibrator can be adapted to the natural frequency of the working tool. As is well known optimal efficiency is obtained when the vibrator is in resonance with the working tool.

It has also been suggested in installations in which the working tool is a pile driver to conform the frequency of the exciter to the natural frequency of the member to be driven. This member, together with the ground in which it is held, constitutes a system capable of oscillating. It has further been suggested to provide an electromagnetic oscillation exciter for pile driving equipment using oscillations and to make adjustable the frequency of such exciter. The purpose of such arrangement is to facilitate in particular the lifting of a pile structure by tuning to resonance the frequency of the exciter and the natural frequency of the pile structure.

The present invention is concerned with oscillatory driving devices in which the oscillations are generated by rotary masses and in which the rotary masses, generally provided in pairs, are driven by hydraulic motors. Hydraulically operated exciters of this kind have the advantage when used in connection with oscillatory driving equipment that the hydraulic drive supplies a high torque at a low rate of rotation whereby the control of the drive is comparatively simple and inexpensive. D.-C. motors, due to the required rectifying equipment, and three-phase commutator motors, due to their sensitivity to stresses caused by oscillations, have been found to be unsuitable for oscillatory pile driving equipment.

According to another invention of the present inventor disclosed in other pending patent applications, the vibratory effect of a pile driver is supplemented by applying to the member to be driven a static pretension in the form of a pull load, that is, a load directed in the driving direction.

The required magnitude of such pretension is generally a function of the resistance .to penetration which the member to bedriven, for instance a pile or a sheet pile, encounters. Normally the penetration resistance is practically zero at the beginning of a driving operation, that is, when the pile member passes through the uppermost loose soil strata and increases with increasing depth of penetration. As is evident, the pretension always must, or at least always should be adjusted in accordance with resistance .to penetration encountered at a given stage of the driving operation.

At the beginnng of a driving operation, when the member to be driven is suspended freely from the frame structure of the driving device or just sits loosely on the ground or penetrates slightly into the ground due to its own weight, it is desirable that the vibrations are slow and readily controllable as otherwise the entire drive equipment will tend to become pendulous or whip back and forth- As the driving operation progresses, the resistance encountered by the leading tip of the driven 3,004,389 Patented Oct. 17, 1961 2 member increases, and the power required for the, driving operation can now be considerably reduced by increasing the pretension.

Accordingly, it is the broad object of the invention to provide a device which changes the frequency of the oscillations of the exciter in accordance with changes in the applied pretensions I A more specific object of the invention is to provide a device of the general kind above referred to in which the frequency of the oscillations is increased proportionately with the pretension, which in turn in increased with the increasing resistance encountered by the tip of the driven member as the member reaches greater depths. Such increase in the rate of the oscillations or vibrations affords the advantage that the ground surrounding the driven member is continuously shaken whereby the friction betwen the driven member and the adjacent ground is reduced. Furthermore it has been found that the use of higher vibration frequencies assists the tip of the driven member to chisel its way through the hard ground strata such as hardpan. Working with high frequency oscillations has also the advantage that it reduces wear and tear on the driven member in comparison with the wear and tear of the driven member when pile drivers operating by impact are used. Splitting and twisting of the driven member are avoided and wooden piles do not tend to crack or splinter.

When the frequency of the oscillation is near the natural frequency of the ground, the power take-up of the oscillation exciter is at its lowest. When now driving operations are carried out near building structures, ob

, v y P ions shouldbemaderthatrsuchmtructmes are not damaged by oscillations travelling through the ground. Oscillations dangerous to :guilding structures close to the location of the ramming operation will travel at a maximum when the frequency of such oscillations coincides with the natural frequency of the ground.

Accordingly, it is a further obect of the invention to provide a device of the general kind above referred to, in which the oscillation frequency of the exciter can be varied independent of the static pretension applied to the driven member so that the driving operation can be carried out selectively either in resonance with the natural frequency of the ground or above or below the natural frequency.

It is also an obcct of the invention to provide a device of the general kind above referred to, which can be so adusted for the aforementioned conditions that optimal operation of a pile driving device is effected.

In order to attain the aforementioned objects, features and advantages of the invention and other objects, features and advantages which will be pointed out hereinafter, the device of the invention provides for agradual variation of the rate of rotation of an exciter using rotary masses so that the rate of rotation of the rotary masses is low when the static load applied to the driven member is low and increases as the static load is increased.-

The device of the invention further provides for control-of the rate of rotation of the rotary masses ,inde-' pendent of changes in the static load to permit operation of 'the driving device selectively either in resonance or not in resonance with the natural frequency of. the ground. a i

More specifically the invention resides in providing a device by means of which the rate of rotation of a hydraulic motor driving the rotary masses of the exciter can be gradually regulated by correspondingly gradually varying the volume of pressure fluid fed from a con: stant speed, rotary pump to the hydraulic motor.

The device of the invention also provides that the control of the rotation of the exciter, in accordance with the applied static load which in turn is controlled by the resistance to driving of the pile member, is effected automatically. For this purpose a servo motor control systemis provided in which the position of a plungerin a cylindercontrols the position of a control lever for controlling the pressure fluid delivered by the pump.

In order to effect control of the rate of rotation of the exciter independent of the applied static loads, the control lever can be detached from the servo control system so that the pumped volume of pressure fluid can be regulated by adjusting the control lever by hand.

In the single figure of the accompanying drawing an elevational view of a pile driving installation according tothe inventionis shown. To simplify the illustration only those parts of the installation are shown which are essential for the understanding of the invention.

Referring, now to the figure in detail, there is shown a member 1 to be driven such as a pile structure or a sheet'pile which is clamped in a suitable clamping device 2 on the lower part of a vibration exciter 3. The exciter includes a pair of rotary masses 4a and 4b rotated by hydraulic motors 5a and 5b indicated only by dotted lines since the structure of the motors should be visualized as being conventional. The motors are connected by pipes 6 and 6' to a feed pump 7 for supplying a pressure fluid to the motors. Pump 7 is driven at a constant rate of speed by a motor 8. The volume or the pressure of pressure fluid delivered by the pump can be gradually and selectively varied by changing the angular position of a controlled lever 9. Lever 9 is shown as being linked to a servo control system which will be more fully explained hereinafter, but it should be understood that the lever is detachable from the control system and can then be freely tilted for adjusting the delivered volume and with it the rotary speed of the hydraulic motors thereby adjusting the vibration frequency independent of the control system which in turn is controlled as pre viously mentioned by a static load applied to pile structure 1.

In order to effect an automatic control of the hydraulic motors and with it of the vibrations applied by the exciter to pile structure 1, a control system is provided which basically comprises a detecting assembly and a regulating assembly. The detecting assembly comprises a yoke 10' mounting at its ends two pulleys 11 over which is guided a chain Or rope 16' indicated by dotted lines. The aforementioned static load acts upon chain or rope 10 in the direction indicated by the arrows and hence exercises a downwardly directed pull upon yoke 10. Changes in the static load may be effected by exerting pull upon ropes 10' by means of a pulley which may be turned more or less, adjustable springs and similar arrangements. Such arrangements are well known and the specific construction thereof does not constitute part of the invention. Yoke 10 is supported by means of suitably powerful compression springs 13- upon a block 15. This block also supports vibration exciter 3 by means of spring suspension 15' and is, in turn, slidably guided along a suitable frame structure which is not shown as it is not essential for the understanding of the invention. Block 15 is formed with a recess in which yoke 10 is slidably guided by suitable means such as guides 14.

The block 15 and the frame structure on which it is guided, should be visualized as having a mass so heavy that they will not vibrate for all practical purposes.

As is evident, the position of yoke 10 in reference to block 15 is a function of the down load acting upon chain or rope 10'. The position of the yoke is detected by means of a control cylinder 16 suspended from yoke 10 and a plunger 17 slidable within cylinder 16 and mounted on a plunger rod pivotally linked at 17' to block 15. The control asembly 16, '17 constitutes a pilot for a controlledor follower assembly including a cylinder 19and a plunger 2%). Cylinder 16 is connected with cylinder 19. by pipes18vand18' in aclosed pressure system. Plunger 20 is linked by connecting member 21 to lever 9. Both the connector 21 and the lever 9 are preferably provided with longitudinally spaced holes 21a and 9a respectively through which bolts or pins are fitted for linking lever 9 and connector 21 by selecting appropriate holes. 7

The operation of the device as heretofore described, is as follows:

Let it be assumed that the pull load applied to chain or rope 10' is increased, then the 'yoke It} will be pulled closer to block 15 and plunger 17 will slide deeper into cylinder 16. As a result, plunger 20 of follower cylinder 1 will move correspondingly, that is, outwardly or toward the right and lever 9, will be turned clockwise. Assuming that the illustrated angular position of lever 9 is a position of a low delivery of pressure fluid, such delivery will be correspondingly increased. If the downward pull upon yoke 10 is reduced, the aforedescribed cycle will be reversed, so that lever 9 will be turned toward counterclockwise.

As is now evident, pump 7 will be automaticallyregulated so that the exciter rotates at a high speed when a high driving resistance is encountered as such high driving resistance entails a correspondingly high static load upon yoke 10, and at a low rotational speed when the driving resistance is low.

As is further evident, the automatic regulation is effected within a given range of rotation which is determined by the effective lengths of lever 9 and connector 21. If it be desired to shift the range of control, this can be readily effectedby changing the respective holes through which lever 9 and connector 21 are linked. It;

is also possible either to increase or to decrease the width of the range of regulation. Obviously-the width. of the range is controlled by the effective length of lever 9 since the lever will turn through a wider or narrower angle for a given displacement of connector 21 depending upon the length of lever 9. Hence to effect a change in the width of the range, all that is necessary is to connect lever 9 through another hole from that shown.

While the invention has been described in detail with respect to a certain now preferred example and embodiment of the invention it will be understood by those skilled in the art after understanding the invention, that various changes and modifications may be made without depart.- ing from the spirit and scope of the invention, and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A device for varying the frequency of a vibration exciter for use with a vibration actuated pile driving device and for tuning said frequency to the natural frequency of a pile member to be driven or lifted, said device comprising a vibratory exciter including a rotary mass and a rotary hydraulic motor for driving said mass, a rotary, constant speed pump, conduit means connecting the pump with said motor for feeding pressure fluid to the motor, the feed of pressure fluid controlling the rotational speed of the motor, and control means for gradually regulating the feed of the pressure fluid to the motor.

2. A device according to claim 1 wherein said control means include a manually adjustable control lever, the position of said lever controlling the feed of pressure fluid to the motor.

3. A device for varying the frequency of a vibration exciter for use with a vibration actuated pile driving device and for tuning said frequency to the natural frequency of a pile member to be driven or lifted, said device comprising a vibratory exciter including a rotary mass and a rotary hydraulic motor for driving said mass, a rotary,

constant speed pump, conduit means connecting the pump with said motor for feeding pressure fluid to the motor,

the feed of pressure fluid controlling the rotational speed:

of the motor, and control means automatically and grad:

ually regulating the feed of pressure fluid to the motor, said control means including detecting means detecting and responsive to variations in the magnitude of a static load applied to the driven member, and adjustable regulating means regulating the pressure fluid flow and controlled by said detecting means to increase the fluid flow with an increasing load acting upon the detecting means and vice versa.

4. A device according to claim 3 wherein said detecting means comprises a detecting member detecting the static load, spring means yieldably supporting said detecting member on said vibration exciter, the position of said detecting member in reference to the exciter being indicative of the load detected by said detecting member, and wherein said regulating means comprise a first cylinder, a first plunger sl-idable in said cylinder and a movable control member controlling by its position the flow of pressure fluid delivered by said pump, said control member being linked to said plunger for control of the control member position by the position of the plunger in the cylinder, a second control cylinder, a second plunger slidable in the second cylinder, said second cylinder-plunger assembly being interposed between said detecting member and said exciter in engagement therewith so that the position of the second plunger in the second cylinder is controlled by the position of the detecting member in reference to the exciter, and conduit means connecting said second cylinder and said first cylinder in a closed circulation system whereby the first plunger will follow a displacement of the second plunger, said displacement effecting a corresponding change in the position of the control member.

5. A device according to claim 4 and further comprising adjustable means for linking said control member and said second plunger to vary the effective length of the dontrol member.

6. A device according to claim 5 and further comprising a connector member supporting said second plunger, and adjustable means for linking the control member to said connector member to vary the eifective length of the connector member.

References Cited in the file of this patent UNITED STATES PATENTS 1,829,655 Huguenin Oct. 27, 1931 2,391,996 Muller Jan. 1, 1946 2,743,585 Berthet et a1 May 1, 1956 2,744,385 Hohenner May 8, 1956 2,942,427 Berthet et a1 June 28, 1960

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