Method And Apparatus For Producing Vibratory Motion

Abstract

A method and apparatus for producing vibratory movement comprises a work piston reciprocable in a work cylinder, a supply of fluid under pressure and a slide valve for controlling the supply of pressure fluid to reciprocate the pistons. In one form the slide valve has a cylindrical housing and a piston that is rotatable by a motor to supply pressure fluid intermittently to the work cylinder and is axially movable manually, mechanically, hydraulically, electrically or by other power equipment to control the area the valve ports are opened and hence the rate of movement of the work piston. In another form the slide valve has a housing and a valve piston that is reciprocable by a cam wheel to supply pressure fluid intermittently to the work cylinder and is rotatable manually, mechanically, hydraulically, electrically or by other power equipment to vary the opening of the valve ports and hence the rate of movement. Selective action of the slide valve is obtained by providing two cam wheels of different characteristics and air springs for biasing the valve slide toward one or the other cam wheel.

Description

The invention relates to a process and apparatus for the reciprocatory displacement of a work piston which is movable back and forth in a work cylinder by a pressure fluid. The process and apparatus in accordance with the invention can be used in many different fields where vibratory movement is required, for example, in the building manufacturing textile and machine tool industries, for screening, drilling, conveying, bagging, etc.

In prior apparatus, a work piston arranged in a cylinder and displaceable in the cylinder by a pressure medium has been vibrated by a special apparatus that produces vibrations and is connected with the work piston. The vibrations are thereby transmitted to the work piston. Such apparatus has been relatively complex and correspondingly expensive.

The present invention is based on the principle of vibrating the work piston through the pressure medium by which the work piston is displaced. In accordance with the invention, the piston is vibrated by being displaced in one direction by the prssure medium and in the opposite direction by a return force, for example by a force provided by a spring, or alternatively the piston is displaced alternately in opposite directions by the pressure medium. In the one case the piston is loaded or biased to move in one direction and the pressure fluid is intermittently admitted to the cylinder on one side of the piston to move the piston against the bias and then discharged from the cylinder to permit return of the piston by the biasing force. In the other case the piston is double-sided and pressure fluid is admitted to the cylinder alternately on opposite sides of the piston to move the piston back and forth. Vibration of the work piston is thereby produced in a very simple manner. It is particularly advantageous that the vibrations are linear with respect to the control.

Moreover, in accordance with the invention it is possible to obtain a progressive unidirectional displacement of the piston superimposed on reciprocatory vibration. In other words, a unidirectional static force is superimposed on the vibrational forces to move the piston progressively in one direction while it is being vibrated. This is achieved by admitting slightly more fluid to the cylinder to displace the piston in one direction than is discharged from the cylinder when the piston is displaced in the opposite direction either by a return force or by pressure fluid on the opposite side of the piston. In this manner the piston is moved slightly farther in one direction than in the other so that the cumulative effect of these minute increments of movement is a progressive unidirectional displacement of the piston superimposed on its vibratory motion.

The process in accordance with the present invention is carried out by apparatus which is characterized by the provision of a control unit which is interposed between the work cylinder and a source of the pressure medium and which in rapid succession alternately admits the pressure medium to the work cylinder and discharges it from the cylinder. The control unit preferably comprises a slide valve having a cylinder which is provided with a rotatable or oscillatable and simultaneously axially movable piston. The vibration of the work piston is effected by the rotary movement of the control piston. Any known medium, for example an electric motor or a fluid pressure motor can be used to produce the rotary movement of the control piston. By such rotation, a pulsation of the pressure medium and thereby a reciprocation of the work piston is effected by alternately connecting conduits leading to the work cylinder with supply and return conduits of the pressure medium in time with the frequency of rotation of the control piston. Through the axial displacement of the control piston, it is possible to vary the forward movement of the pressure medium through greater or lesser throttling of the inlet opening while maintaining the outlet opening for the return of the pressure medium constant and thereby obtain different velocities of foward displacement of the work cylinder superimposed on the reciprocatory movement.

It is not necessary to work only with a rotating control piston as the present invention also provides the very simple posibility of producing, by means of a single distributin slide valve, high frequency vibration in hydraulic apparatus and simultaneously a unidirectional driving force.

In accordance with one aspect of the invention, the supply of pressure fluid to the working cylinder is controlled by a distributing slide valve provided with an axially movable piston rod which is biased in one direction by the force of a spring and is movable in the opposite direction by a cam wheel. With this arrangement it is possible to attain a desired high frequency corresponding to the rate of rotation of the cam wheel provided that the force of the spring corresponds to the mass of the piston and piston rod so as to maintain the piston rod in engagement with the cam wheel. Preferably the cam wheel is provided with a plurality of cams. This has the advantage that a high vibration frequency of the work piston can be obtained with a low speed of rotation of the cam wheel. It is, moreover, advantageous for the flanks of the cams of the cam wheel to be unsymmetrical. In this manner it is possible to regulate the curve form of vibration amplitude in relation to time, which for many applications is significant. For example, in many cases of tamping railroad ties it is advantageous if the vibration amplitude curve is of somewhat rectangular or square wave form. The action of the slide valve is of interest when the cam form is selected to provide a gradual rise and an abrupt fall. As the cam runs by the piston rod, the piston rod is pushed solely through the force of the spring initially with a high velocity and upon greater tensioning of the spring with a decreased velocity so that full opening of the fluid passageway is effected in a very short period of time, while closing of the passageway is effected slowly.

It is advantageous when the spring is an air spring. It is also advantageous when the rise flanks of the cams are not as steep as the descent flanks. To control the rate of flow it is also advantageous if the control piston is not only axially movable but also rotatable and if the control cams are inclined to a plane perpendicular to the axis of movement. When no means is provided for fixing the rotatable cylinder at a particular angle so that it is still axially movable but not rotatable, the rate of flow can be ajusted to a particular predetermined value.

In many applications, for example in track construction, it is advantageous when the vibration amplitude or the vibration frequency can be changed at a selected point in the work process. In this case it is advantageous if the piston is provided on opposite sides with piston rods both of which are engageable with cam wheels each of which can be stopped in a selected position in which the piston rods are freed to move and two separately activatable air springs are provided to press the piston rod either against one or against the other cam wheel.

The nature and advantages of the invention will be more fully understood from the following description of preferred embodiments shown schematically by way of example in the following drawings in which:

FIG. 1 is a schematic illustration of apparatus in accordance with the invention with a working cylinder in which a piston is movable in one direction by spring force and in the opposite direction by fluid pressure.

FIG. 2 is a schematic axial section of a control unit for controlling the supply of pressure fluid to the working cylinder.

FIG. 3 is a longitudinal section corresponding to FIG. 2 but with the piston turned 180.degree. so as to show the discharge of the pressure fluid.

FIG. 4 is a cross section along the line IV--IV in FIG. 2.

FIG. 5 is a cross section along the line V--V in FIG. 3.

FIG. 6 is a schematic longitudinal section through the control unit shown in a central position.

FIG. 7 is a cross section along the line VII--VII in FIG. 6.

FIG. 8 is a schematic view showing flow of the pressure fluid through the control piston in a direction toward the working cylinder.

FIG. 9 is a schematic view showing flow of the pressure fluid through the control piston in a direction away from the pressure cylinder.

FIG. 10 is a cross section with the control cylinder shown in the position of FIG. 8.

FIG. 11 is a cross section with the control cylinder shown in the position of FIG. 9.

FIG. 12 is a schematic illustration of apparatus in accordance with the invention in which the piston is double-sided and is moved alternately in opposite directions by pressure fluid.

FIG. 13 is a schematic longitudinal section through the control valve unit of the apparatus shown in FIG. 12.

FIG. 14 is a schematic longitudinal section similar to FIG. 13 but showing pressure fluid supplied to the opposite side of the working piston.

FIG. 15 is a schematic section with a slide valve actuated by a rotating cam wheel, and

FIG. 16 is a schematic section through a slide valve with two air springs and two driving cam wheels.

The principle of the apparatus in accordance with the present invention is illustrated schematically in FIG. 1. A work piston K is reciprocably slidable in the work cylinder Z and has a piston rod R which extends out through an axial bore in one end of the cylinder Z and is connected to the implement or workpiece to which vibration is to be transmitted for example a tamper, screen or conveyor. A compression spring F acts between one end of the cylinder and one face of the piston K to exert a force on the piston tending to move it in one direction, namely toward the left as viewed in FIG. 1. A fluid pressure medium, for example, hydraulic oil, is admitted to the cylinder Z on the opposite side of the piston K to exert there a force on the piston in the opposite direction from force exerted by the spring F. The pressure fluid is supplied to the cylinder K from a reservoir SP through a conduit z, a pump P, a valve Vz, a throttle D, a control unit ST, and a conduit a connected with an inlet-outlet A of the cylinder Z located near the end of the cylinder opposite that through which the piston rod R extends. Under control of the control unit ST, pressure fluid can also be discharged from the cylinder Z through the conduit a, the control unit ST and a return conduit r provided with a valve Vr and discharging into the reservoir SP.

In accordance with the invention, the control unit ST, which will be described more fully below, connects the inlet-outlet port A of the cylinder Z alternately in rapid succession with the pressure fluid supply line z and with the return line r. When the pressure fluid from the supply line z enters the cylinder Z, it exerts a force on the piston K to move the piston in a direction against the force of the spring F, namely toward the right as viewed in FIG. 1. When the port A of the cylinder is, on the other hand, connected by the control ST with the return line r, the spring F moves the piston toward the left as viewed in FIG. 1 thereby discharging pressure fluid through the port A, conduit a, control unit ST and return conduit r to the reservoir SP. Hence the connection of the cylinder Z with the fluid pressure supply line and the return line alternately in rapid succession produces vibratory motion of the piston K and this motion is transmitted through the piston rod R to the implement or workpiece to be vibrated. The adjustable throttle valve D controls the rate of flow of the pressure fluid to the work cylinder and thereby the rate of movement of the piston by the pressure fluid. A separately adjustable throttle valve (not shown) may, if desired, also be provided in the return line r to regulate the rate of flow of fluid discharged from the cylinder and thereby the rate of movement of the piston K by the spring F. The speed of movement of the piston in each of the opposite directions can thereby be separately and selectively regulated. The frequency of vibration of the piston K is regulated by varying the speed of operation of the control unit ST and thus the frequency with which the cylinder is alternately connected with the pressure supply line and the return line of the pressure fluid. The amplitude of vibration of the piston K is a function of the frequency and the rate of movement of the piston alternately in opposite directions and hence depends on the pressure and viscosity of the pressure fluid, the setting of the throttle valve D in the supply line and any throttle valve if provided in the return line, the force of the spring F and the rate of operation of the control unit ST. If it is desired to superpose a progressive unidirectional movement on the vibratory motion of the piston K, the hydraulic fluid system is operated in such a manner that the amount of pressure fluid admitted to the cylinder Z in each cycle slightly exceeds the amount of pressure fluid discharged. Alternatively if progressive movement of the piston in the opposite direction is desired, the amount of pressure fluid admitted to the cylinder in each cycle is slightly less than the amount of fluid discharged. The valves Vz and Vr are normally open during operation of the apparatus and are closed when the apparatus is stopped. Alternatively the valves Vr and Vz can be partially opened during operation of the apparatus and used as throttle valves to control the rate of flow of the pressure fluid and the return fluid. Instead of a pump being provided in the supply line z as shown, the reservoir SP can be pressurized, for example with nitrogen or other gas, in which event means is provided for pressurizing the reservoir and for returning to the reservoir under pressure the fluid discharged from the working cylinder.

The control unit ST as shown schematically in FIGS. 2 to 11 comprises a pressure cylinder 1 and a piston 2 which is rotatable and also axially slidable in the cylinder. The cylinder 1 has an inlet 3 connected with the pressure fluid line z from the reservoir SP and an outlet 4 connected with the return line r leading to the reservoir. It further has a port 25 connected by the line a with the inlet-out port A of the working cylinder Z.

The piston 2 constitutes the moving element or slide of a slide valve of which the cylinder 1 is the housing and is provided with a plurality of grooves and passageways for connecting the port 25 leading to the working cylinder Z alternately and successively with the inlet port 3 and the discharge port 4. As shown by way of example in FIGS. 2 to 5, the piston 2 has an annular peripheral groove 5 which in all positions of the piston communicates with the pressure fluid inlet port 3. A bore 6 connects the groove 5 with an axially extending recess 7 which has an axial extent as shown in FIGS. 2 and 3 and a circumferential extent as shown in FIG. 5. Diametrically opposite the recess 7 there is an axially extending recess 10 which is connected by a bore 9 with an end face of the piston 2 opening into an end portion of the cylinder 1 communicating with the fluid return port 4. An over-pressure release valve is provided between the inlet port 3 and the outlet port 4 so as to relieve excessive fluid pressure.

The piston 2 is rotatable by a motor M which is shown as being located inside the control cylinder 1 but which can be outside the cylinder if desired. The motor M, which can conveniently be a hydraulic motor driven by pressure fluid, is connected with the piston 2 through a splined coupling C permitting axial movement of the piston 2 while driven rotationally by the motor M. The piston 2 is movable axially of the cylinder 1 by means of a lever 8 connected with a yoke on the stem portion of the piston which is coupled to the motor M.

When the rotary piston 2 is in the position shown in FIGS. 2 and 4, the control port 25 connected with the working cylinder Z (FIG. 1) by the line a communicates through the recess 7, the bore 6 and the annular groove 5 with the fluid pressure inlet 3 connected to the pressure line z so that pressure fluid is supplied to the cylinder Z to move the piston K toward the right as viewed in FIG. 1. When the rotary piston 2 has rotated 180.degree. to the position shown in FIGS. 3 and 5, the control port 25 is connected through the recess 10 and the bore 9 to the discharge outlet 4 connected with the return line r so that fluid is discharged from the working cylinder Z as the piston is moved by the spring F toward the left as viewed in FIG. 1. Hence as the rotary piston 2 of the control unit ST is rotated by the motor M, the working piston K is moved alternately toward the right and toward the left, thereby producing vibratory movement of the piston. The frequency of such vibratory movement depends on the speed of rotation of the motor M and can vary from one or several cycles per second to as high a frequency as is desired within the limits of construction of the apparatus. It will be understood that the frequency of vibration can readily be varied as desired by varying the speed of rotation of the motor M.

When the piston 2 of the control unit ST in the position shown in FIG. 2, it will be seen that the recess 7 overlaps approximately half the area of the control port 25. The same is true with respect to the recess 10 of the piston in the position shown in FIG. 3. If the piston 2 is moved toward the left as seen in FIG. 2 by means of the lever 8, the area of communication between the control port 25 and the recesses 7 and 10 is increased. Conversely if the piston 2 is moved toward the right, the area of communication of the recesses 7 and 10 with the control port 25 is decreased. In this manner the rate of flow of the pressure fluid into and out of the working cylinder Z can be readily controlled, thereby controlling the rate of movement of the working piston K and hence the amplitude of vibration, assuming that the frequency remains the same. While the means for moving the piston 2 axially to vary the port openings has been shown schematically as a manually operable lever 8, it will be understood that such movement can alternatively be effected mechanically, hydraulically, electrically or by other power equipment.

It will be understood that the control unit as shown in FIGS. 2 to 5 can be kinematically reversed so that the piston is stationary and the housing is rotatable or oscillatable and axially movable. The circumferential positions of the inlet and outlet openings of the housing 1 of the control unit ST can be varied as desired by providing between the control piston and the housing an adjustably rotatable bushing provided with corresponding circumferential grooves. The circumferential grooves can be made accessible to the outside of the housing.

FIGS. 6 to 11 illustrate schematically a control unit for apparatus in accordance with the present invention in which the working piston K is moved alternately in opposite directions by fluid pressure as illustrated in FIG. 12. At one end, the working cylinder Z is provided with an inlet-outlet port A1 connected by a line a1 with the control unit ST while at the opposite end a second inlet-outlet port A2 is connected with the control unit by a line a2. The control unit shown in FIGS. 6 to 11 has a control port 25a connected by the line a1 with the port A1 of the working cylinder Z and a second control port 25b connected by the line a2 with the port A2 at the opposite end of the working cylinder. The port 25b is spaced circumferentially 90.degree. from the port 25a and is also spaced axially. The slide valve piston 2 of the control unit rotated by the motor M has a central circumferential groove 5 connected with axially extending recesses 7a and 7b spaced diametrically opposite one another. At one end of the piston 2 there are diametrically opposite recesses 10a extending in from the end face of the piston while at the opposite end there are diametrically opposite recesses 10b likewise extending in from the end face of the piston. The housing 1 has an inlet port 3 connected with the fluid pressure supply line z and positioned so as to communicate with the central circumferential groove 5 of the piston. The housing 1 also has outlet ports 4a and 4b connected with the return line r and opening into the spaces at opposite ends of the piston 2 so as to communicate respectively with the recesses 10a and 10b. The control port 25a is positioned so as to communicate successively with the recesses 7a, 10a and 7b of the cylinder as the cylinder rotates and control port 25b is positioned as to communicate successively with the recesses 7a, 10b and 7b. With the piston in the position shown in FIGS. 6 and 8, the line a1 (FIG. 12) is connected with the fluid pressure supply line through recess 7a and circumferential groove 5 while the line a2 is connected to the fluid return line through the recess 10b of the piston 2. The working piston K is hence moved toward the right as viewed in FIG. 12. When the piston 2 of the control valve has rotated 90.degree. to the position shown in FIG. 9, the line a2 is connected to the fluid pressure supply line through the recess 7b and the circumferential groove 5 while the line a1 is connected to the fluid return line through one of the recesses 10a. The working piston K is thereupon moved toward the left as viewed in FIG. 12. With continued operation in like manner the working piston K will be reciprocated through two complete cycles for each revolution of the slide valve piston 2.

The control value unit shown schematically in FIGS. 13 and 14 is likewise for controlling movement of the working piston alternately in opposite directions by fluid pressure as illustrated in FIG. 12. The valve housing 11 has an inlet port connected with a fluid pressure supply line 13 and an outlet port connected with a fluid return line 14. A first control port 21 is connected by a line a1 with one end of the working cylinder Z (FIG. 12) while a second control port 22 is connected by a line a2 with the opposite end of the working cylinder. A rotatable and axially movable valve piston 12 has a circumferential groove 15 communicating with the fluid pressure supply line 13. A bore 16 connects the groove 15 with an axially extending recess 17 positioned so as to communicate successively with control ports 21 and 22 as the piston rotates. A bore 19 connects an axially extending recess 20 with the space at one end of the piston so as to be in communication with the return line 14. The recess 20 is diametrically opposite the recess 17 and likewise in position to communicate successively with the control ports 21 and 22 as the piston 12 rotates. The piston 12 is connected by a splined coupling C with a hydraulic motor M connected by lines 27 and 28 with the fluid pressure supply line 13 and return line 14 respectively.

With the piston 12 in the position shown in FIG. 13, the control port 21 and hence line a1 (FIG. 12) is connected through the recess 20 and bore 19 to the return line 14 while the control port 22 and hence line a2 are connected through recess 17, bore 16 and annular groove 15 with the fluid pressure supply line 13. The working piston K will thereby be moved toward the left as viewed in FIG. 12. When the control piston 12 has rotated 180.degree. to the position shown in FIG. 14, the control port 21 and hence line a1 are connected to the fluid pressure supply line 13 while the control port 22 and hence line a2 are connected through the recess 20 and bore 19 to the return line 14. The working piston 12 will thereupon be moved toward the right. Hence a complete reciprocation of the working piston 12 will be produced for each rotation of the slide valve piston 12. Except as otherwise described, the systems illustrated in FIGS. 1-14 operate in like manner.

In FIG. 15 there is shown schematically a slide valve unit for controlling the reciprocation of a working piston which is moved alternately in opposite directions by fluid pressure. A valve housing 31 is provided with central bore 42 to receive a slide and with a fluid pressure inlet 32 and a fluid discharge 33 connected with a fluid return line. It also has a control port connected by a line 34 with one end of a working cylinder 35 in which a piston 41 is reciprocable and a second control port connected by a line 36 to the opposite end of the working cylinder 35. A passage 43 connects opposite end portions of the central bore 42 with one another. A valve stem 37 carries two valve cylinders 38a and 38b which are axially spaced from one another and are slidable axially in the central bore 42 of the housing 31. A spring 39 biases the valve stem 37 axially toward the right as viewed in FIG. 15. A rotatable cam wheel 40 driven by a suitable motor (not shown) carries a plurality of cams 45 which are engageable with the valve stem 37 to move it toward the left against the action of the spring 39.

The slide valve shown in FIG. 15 operates in the following manner. When the valve stem 37 has been moved toward the left as viewed in FIG. 15 by one of the cams 41, the pressure supply line 32 is connected with the line 34 so as to supply pressure fluid to the left hand end of the cylinder 35. At the same time the line 36 at the opposite end of the cylinder 35 is connected with the fluid return line 33. The working piston 41 is thereby moved toward the right. When the valve stem 37 rises off of a cam 41, it is moved toward the right by the spring 39 so that the line 34 at the left hand end of the piston 35 is connected through passage 42 with the fluid return line 33 while the line 36 at the right hand end of the cylinder 35 is connected with the fluid pressure supply line 32 so as to move the working piston 41 toward the left. Hence as the cam wheel 40 rotates in a counterclockwise direction as viewed in FIG. 15, the valve stem 37 is reciprocated by the cooperation of the cams 41 and the spring 39 and thereby produces corresponding reciprocation of the working piston 41. The number of reciprocations produced by each rotation of the cam wheel 40 is equal to the number of cams 41 on the cam wheel. The opening and closing times of the valves as well as the forward and reverse movement are controlled by the curve form of the cams 41. In this manner the frequency of vibration, which depends moreover on the speed of rotation of the cam wheel 40, as well as the amplitude of vibration is determined. Moreover, the cam form determines the amount of hydraulic fluid supplied alternately to opposite ends of the cylinder. If in each cycle more oil is supplied to one side of the piston than to the other, a progressive rectilinear movement will be superimposed on the reciprocatory movement.

In FIG. 16 there is shown a slide valve similar to that of FIG. 15 but with air springs 39a and 39b and cam wheels 40a and 40b provided at each of the opposite ends of the valve. By means of passageways 44a and 44b provided with suitable valving the air cushions 39a and 39b can selectively be connected either to a compressed air supply or to the atmosphere so as to activate one or the other of the air springs. When the air spring 39a is supplied with pressure, the valve stem 7 is biased toward the cam wheel 40a and is accordingly reciprocally actuated by the cams on that cam wheel. Care must be taken that the cam wheel 40b is positioned so as not to interfere with the movement of the valve stem 37 by the cams on the cam wheel 40a. When the air spring 39b is pressurized, it biases the valve stem 37 toward the cam wheel 40b whereupon the valve stem is reciprocated by the cams on the cam wheel 40b in cooperation with the air spring 39b. The cam wheels 40a and 40b are provided with cams of different curvature and, if desired, with a different number of cams. In this manner the operating characteristics of the slide valve and hence of the working piston 41 can be changed during operation of the apparatus merely by selectively activating one or the other air springs 39a, 39b. With the valves of FIGS. 15 and 16 further control is provided by inclining the ends of the valve pistons 38a and 38b and providing means for turning the valve slide to different angles while it is reciprocated so as to vary the amount of opening of the valve ports and thereby vary the rate of movement of the work piston 41. Thus with the valves of FIGS. 15 and 16, cyclical operations of the work piston is effected by reciprocation of the valve member while the rate of movement of the work piston is regulated by the angle at which the valve slide is turned, it being understood that when turned to a selected angle the valve slide remains at that angle while continuing to reciprocate. A suitable arm or collar (not shown) is provided at one end of the valve stem to control its angular position. It will be understood that control of the angular position of the valve item to regulate the rate of movement of the work piston can be controlled manually, mechanically, hydraulically, electrically or by other power equipment.

While preferred embodiments of the invention have been illustrated in the drawings and are herein particularly described, it will be understood that the invention is in no way limited to these embodiments.

Claims

What I claim is:

1. A method of producing cyclical relative vibratory movement of a work piston in a work cylinder which comprises cyclically supplying fluid under pressure to one side of the piston to move the piston in one direction and alternately applying a restoring force for movement of the piston in the opposite direction while exhausting said pressure fluid, controlling the frequency and durations of the intervals during which said pressure fluid is supplied and the rate at which it is supplied to control the frequency, and amplitude of the vibratory movement of the work piston as well as its displacement/time curve and variably controlling the supply of pressure fluid to said work cylinder and the exhausting of said pressure fluid from said work cylinder so that the amount of said fluid exhausted in each cycle differs by a selected increment from the amount of said fluid supplied to said work cylinder in said cycle so that a progressive unidirectional movement of said work piston relative to said work cylinder is superposed on said cyclical vibratory movement.

2. A method according to claim 1, in which the amount of fluid supplied to said side of the piston in each cycle of vibratory movement slightly exceeds the amount of fluid exhausted in said cycle.

3. A method according to claim 1, in which said restoring force is applied by elastic means biasing said piston in a direction opposite to the direction of movement by said piston by said pressure fluid.

4. A method according to claim 1, in which fluid under pressure is applied alternately to opposite sides of said piston to move said piston alternately in opposite directions.

5. Apparatus for producing vibratory movement comprising a work cylinder, a work piston relatively reciprocable in said cylinder, means supplying fluid under pressure and means for connecting said supply means to said work cylinder including valve means and means for operating said valve means to supply pressure fluid intermittently to said work cylinder on one side of said work piston to move said work piston in one direction and to exhaust fluid from said work cylinder during return movement of said work piston, said valve means comprising a valve cylinder and a valve piston in said cylinder and having two modes of movement relative to said valve cylinder, namely rotary movement and axial movement, said valve cylinder and said valve piston having ports, said valve piston being continuously driven by said operating means in one of said modes of movement to bring ports of said valve piston cyclically into communication with ports of said valve cylinder to supply said pressure fluid cyclically to said work cylinder and alternately exhaust said pressure fluid from said work cylinder to produce vibratory movement of said work piston relative to said work cylinder, and means for controllably and non-cyclically moving said valve piston relative to said valve cylinder in the other of said modes of movement to variably control the amount of communication of said ports of said valve piston with said ports of said valve cylinder in each cycle of operation to thereby variably control the rate of supply and exhaust of said pressure fluid and thereby variable control the amplitude of vibratory movement of said work piston relative to said work cylinder.

6. Apparatus according to claim 5, in which said valve cylinder has ports connected respectively with a fluid pressure supply line from said supply means, a fluid return line to said supply means and a control line connected to said work cylinder and said valve piston has recess and passageways registrable with said ports to connect said control line alternately to said supply line and to said return line as said valve piston rotates.

7. Apparatus according to claim 6, in which said means for operating said valve means comprises a hydraulic motor coupled with said valve piston to rotate it.

8. Apparatus according to claim 6, in which means is provided for moving said valve piston axially to vary the area of registration of said passageways and recesses of said valve cylinder with said ports to regulate the rate of flow of fluid therethrough and thereby regulate the rate of movement of said work piston.

9. Apparatus according to claim 5, in which said work piston is double acting and in which said valve cylinder has a first control port connected with one end of said work cylinder, a second control port connected with the opposite end of said work cylinder, a supply port connected with said fluid pressure supply means and a return port connects with a return line to said supply means, said valve piston having passageways and recesses for connecting said control ports alternately with said supply and return ports as the valve piston rotates in said valve cylinders.

10. Apparatus according to claim 5 further comprising means for controlling the supply of pressure fluid to said work cylinder and the exhausting of said pressure fluid from said work cylinder so that the amount of said fluid exhausted in each cycle differs from the amount of said fluid supplied to said work cylinder in said cycle so that a progressive unidirectional movement of said work piston relative to said work cylinder is superposed on said cyclical vibratory movement.