GB2062124A - Fluid driven oscillator and hammer device - Google Patents

Abstract

In a fluid driven oscillator and hammer device the position of the piston 3 relative to the pressure cylinder 2 is detected by an array of discrete position sensing units 14, the array extending in the direction of travel of the piston rod, and each sensing unit being capable of providing sensory data in the form of digital electrical signal. Electronic processing means 15 analyses the electrical signal output from the sensing unit and provides electrical signal inputs to control valve means 11 governing the supply of driving fluid to the oscillator. Conveniently the position sensing units are carried by the pressure cylinder and the piston rod carries means which co-operate with the sensing units to provide an indication to each unit in turn of the position of the rod along its travel. The position sensing units may be light emitting diodes, each with a phototransistor to receive light from reflecting regions on the piston rod. Alternatively the sensing units may be proximity sensing switches or micro- switches which may be mechanically triggered by trips carried by the piston rod. <IMAGE>

Description

SPECIFICATION Fluid driven oscillator and hammer device Oscillators driven by fluid especially hydraulic means find widespread use in manufacturing and engineering processes, for example in the forging of metal parts, in stamping and punching out articles from plate metal and in pile driving. In all of these circumstances the equipment operates as a hammer and is subject to a high level of vibration and mechanical stress. It is therefore desirable that these oscillators be constructed in the most rugged form practicable and that any associated control equipment is likewise as robust as it reasonably can be.

A hydraulic or pneumatic oscillator can be provided with a control system which operates to control the rate and force of striking of the oscillator. Hydraulic (or pneumatic) control systems are robust but are cumbersome and slow acting and cannot readily be adapted to suit changing demands. Also fluid control systems, as such, cannot in general easily be pre-programmed to respond to a given situation arising or to automatically proceed through a given sequence of operations. For such purposes, and also to make the control system less cumbersome and more responsive it is appropriate to use instead an electrical control system.However, electrical control systems which have been utilized heretofore are not sufficiently robust to give satisfactory service in heavy duty and harsh environments and require relatively sophisticated repair facilities and skilled repair personnel both of which are unlikely to be readily available in such situations.

Such prior art electrical control systems have utilized analogue measurements of the position and velocity of the moving (oscillating) piston but the apparatus for making these measurements is somewhat delicate. Typically it comprises an arm which is connected at one end to the oscillator piston rod and which forms at its other end a sliding contact with a specially designed potentiometer attached to the oscillator hydraulic cylinder to produce a voltage output which is proportional to the movement of the piston rod out of the oscillator hydraulic cylinder. The rate of change of the voltage gives a measure of the velocity of the piston.The data output from such an analogue measuring device has been directed to an electronic processing unit which controls the operation of an analogue type electrohydraulic servo-valve which itself controls the flow of the working fluid to the appropriate faces of the oscillating piston. In this system both the analogue measuring equipment and the electro-hydraulic servo-valve are rather expensive and sophisticated items requiring a high level of skilled maintenance.

For these reasons such systems are most unsuitable for use on civil engineering equipment and on heavy duty equipment in general.

The present invention has as an object the mitigation or elimination of these various disadvantages of the prior art fluid operated oscillator control systems and accordingly provides, in its broadest aspect, a fluid operated oscillator comprising a pressure cylinder; a piston slideable within said cylinder and dividing the space within said cylinder into two chambers; a piston rod attached to said piston and extending outside of said cylinder through one of said chambers; means for providing fluid flow in and out of at least one of said chambers; valve means for controlling said fluid flow;; means for detecting the position of the piston comprising an array of discrete position sensing units extending in the direction of travel of the piston rod and each sensing unit being capable of providing sensory data in the form of a digital electrical signal, and electronic processing means adapted to analyse electrical signal output from said detecting means and to exercise control of said valve means by providing electrical signal inputs thereto, said valve means being controllable by said electrical signal inputs.

Preferably the piston is biased towards one end of the cylinder by a constant high fluid pressure acting within one of the said chambers and bearing on the smaller face thereof i.e. the face towards the piston rod. In this case the larger face of the piston is alternately exposed to a lower pressure or to an equal high pressure to that bearing on the smaller face, i.e. the valve means is operating to effect a switch from low to high and from high to low pressure in succession in the chamber fronting the larger face of the piston. This causes the piston to oscillate to and fro in the cylinder at a frequency and with a free stroke length determined by the relative pressures on the piston faces and the frequency at which pressure switching takes place.In practice the time taken to effect the switching is also a factor but it is desirable to minimise the switching time and to achieve as "clean" an operation of the pressure switching as possible.

The working stroke can be either that in which the piston rod moves into the cylinder or that in which the piston rod moves out of the cylinder.

The working stroke will generally be that in which the piston rod moves out of the cylinder, when the oscillator is used for example pile driving.

In order to achieve as "clean" a switching operation as possible and also because they are more robust than the proportional valves used heretofore, it is preferred to use as the valve means a simple on/off valve. Hydraulic on/off valves are available which operate sufficiently rapidly to give good dynamic control and since they are substantially always either fully open or fully closed, they are more economical in operation than are proportioned valves where there is a significant power loss due to the more continuous throttling effect.On/off valves are also cheaper at first instance than are proportional valves and are cheaper to maintain and finally, in the current circumstances, it will be appreciated that on/off valves are particularly appropriate since the output from the processor unit need be only a simple binary signal having only two possible conditions corresponding to the two states of the valve.

A particularly suitable form of on/off valve which may be used in the oscillator of this invention is the fast-acting valve which is the subject of UK patent application No 29512/75. In this valve switching is normally initiated by a -hydraulic signal. In this case (and in the case of other valves of similar type) the hydraulic signal may conveniently be generated by a miniature solenoid valve which uses an electrical input signal to operate a small solenoid to produce a binary pressure signal. This hydraulic signal then effects hydraulic switching of the on/off valve. An alternative but less preferred arrangement because it has a higher electrical power demand is to mount a larger solenoid in the main valve to effect the switching directly: in this case it would normally be necessary to amplify the electrical signal to the valve in order to energise the large solenoid.

The piston position detecting means preferably comprises an array of discrete position sensing units the array extending in the direction of travel of the piston rod normally outside the cylinder.

Conceivably the piston may carry the sensing units but they are normally mounted directly or indirectly on the cylinder. The piston rod may itself directly or indirectly carry means which co-operate with the sensing units to provide an indication to each unit in turn of the position of the rod along its travel. Thus for example the sensing units may be mechanically triggered by trips projecting from the piston rod. It is preferred, however, where the oscillator is being used in heavy duty situations that the sensing units be of a non-contacting type, i.e. that they should not in fact touch the piston rod at any point along its travel. This ensures that no mechanical shocks are transmitted to the sensing units, or at least not directly through the piston rod which will experience the major shocks in the equipment of which it is a part.Whilst making this provision however it should at the same time be pointed out that digital position sensing units are anyway in most cases considerably more robust than the analogue position sensing devices used heretofore. Thus by carefully mounting the units on the equipment in a manner such that secondary shock is minimized it will be found that the sensing units used in this invention have a longer lifetime and give more trouble-free service than do the relatively fragile prior art sensing systems.

Sensing units which are suitable for use in the apparatus of this invention include micro switches, magnetic proximity switches or a combination of light emitting diodes with phototransistors. Of these the latter two types of sensor will operate with a gap of about 1 mm between the sensing unit and the face of the piston rod, this being normally about the minimum clearance necessary to avoid any contact between the units and the piston rod. Units of these types are not especially expensive items and an array suitable for any given oscillator will generally be cheaper, and perhaps as little as only half the cost of, the equivalent analogue position sensing equipment.

The number of sensing units which may be used for controlling any given oscillator depends upon the size of the oscillator (or more specifically its stroke length) and upon the degree of exactitude of the positional measurement which is required of the detection system. However the units need not, and in practice generally will not, be equispaced, but can be arranged in close proximity over regions of the piston rod travel where accurate determination of the piston position is required and can be more widely spaced out in regions where there is no necessity to know the position of the piston with great accuracy. In general this will mean that the line density of the sensing units will be high towards the ends of the travel of the piston rod and in the vicinity of the switching points but will be lower outside these regions.Typically for an oscillator cylinder with a stroke length of 5 feet (1.5 m), 32 sensing units will be an appropriate number, but arrays of 1 6 and 64 sensing units may be more appropriate in certain instances.

The sensing units can be arranged so as to be movable along the line of travel of the piston rod and for this purpose it is for example convenient to mount the units on a beam which extends alongside the line of travel of the rod. In this way the linear arrangement of the units can be readily varied according to differing requirements and the number of sensing units in the array can also be readily altered if desired. The beam on which the sensing units are carried is preferably flexibly mounted on the oscillator equipment so as to reduce the mechanical shock which is imparted thereto.

The sensing units are operated to give a digital electrical signal output which may be a binary signal indicating for example, whether or not the piston is alongside the sensing unit or if, as may be the case different parts of the piston are arranged to co-operate in different ways with the sensing units, whether or not a specified part of the piston is opposite the sensing unit.

The processing means when suitably programmed is able, by detecting parallel inputs from the whole array of sensing units, to identify the position of the piston along its travel and to calculate its velocity. For a given type of work the processor may be programmed to operate the oscillator in a desired manner, for example to deliver blows at a certain rate each with a particular energy content and in these situations the processor will merely act to open and close the control hydraulic valve at the appropriate times to ensure that the desired work rate is maintained.

This type of simple programming is appropriate to a situation where the load factor (i.e. the desired energy of each blow) remains substantially constant e.g. in a repetitive forging or stamping process, but in some situations, for example in pile driving, the load factor may vary depending upon the ground conditions which the pile is experiencing at any time. It is then important that the programme for the processor should provide for some degree of automatic control of the oscillator in order to ensure that the oscillator does not either overrun due to delivery of too heavy a blow to the pile or, on the other hand, does not deliver such a weak blow that the pile is scarcely moved or even not moved at all.In these circumstances therefore the processor will be programmed to interpret the positional and velocity data input from the sensing units to determine e.g. the blow energy being delivered, and to automatically adjust the valve switching sequence to appropriately adjust the length of the power stroke so as to maintain the blow energy at the desired preset level. Clearly the longer the power stroke during which the valve has switched high pressure to the cylinder the greater will be the impulsive energy delivered at each stroke of the piston.

Where the control valve is an on/off valve, which as described previously is the preferred form of valve. the output from the processor should be in binary form corresponding simply to a signal to either open or close the valve. If the input to the processor is also binary, then the processor does not need to be an especially elaborate item and the functions required of it are appropriate to the use of a microprocessor unit which is relatively inexpensive compared to the more sophisticated analogue computer required by oscillators with analogue control equipment. It may however be convenient to use, in addition to a microprocessor, a parallel bit selection logic unit which can analyse the parallel inputs from the sensing units and detect the point along the array of sensing units which some indicator on the piston rod has reached and feed this information to the microprocessor.The addition of the selection logic unit frees some of the computing capacity of the microprocessor so that the latter is able to make more rapid calculations based on the positional data intput and so to ensure a quicker response from the feedback control system.

As regards the hydraulic circuitry of the oscillator of this invention this may be entirely conventional in nature and it will not be necessary to deal here in detail with features of design of the pressure cylinder, piston, piston rod and other mechanical working parts of the equipment as the design of these items is well understood by those skilled in the art. As pointed out previously it is preferred to keep the pressure between the piston and the wall of the cylinder through which the piston rod passes substantially constant and this can be done by connecting this volume permanently to a high pressure line (say 2000 psi) with a pressure accumulator in the line to even out fluctuations caused by movement of the piston to and fro in the cylinder. The volume enclosed between the piston and the opposite end of the cylinder is connected to the outlet side of the on/off valve.In this type of arrangement, when the valve is in one position a connection is made between the high pressure supply line to the valve and the outlet therefrom to the pressure cylinder, whilst in the other position of the valve, the connection is made from a low pressure line to the valve and thence through to the cylinder. In this latter state of the valve, the low pressure connection in fact acts as a drain so that hydraulic fluid is then exhausted from the cylinder volume and through the valve to the low pressure line. In the first position the piston is driven along the cylinder by virtue of the fact that although the pressures on either side of the piston are the same, the surface area of the piston on the valveconnected side thereof is greater than on the other side, where the piston rod covers some of the face of the piston.In the other setting of the valve pressure is released on the valve-connected side, and by appropriate calculation of the respective exposed areas on the piston, it can readily be arranged that the piston will be driven back along the cylinder because the product of (pressure x area) on the piston-rod side exceeds the same product on the other side of the piston.

Thus by switching the valve at the appropriate moments of travel of the piston along the cylinder, the piston can be driven back and forth in the cylinder.

Although the use of an on/off valve is generally preferred, in certain circumstances it may be desirable that either side of the piston should be connected to the low pressure line when the opposite side is connected to the high pressure line and in these cases it is preferred to use a simple solenoid-operated direction control valve.

With a valve of this type having two outlets, one of the outlets is connected to one side of the piston and the other outlet to the other side of the piston.

In operation the valve connects either one outlet to high pressure and the other to low or the one to low pressure and the other to high pressure. This type of valve can be readily controlled by a binary signal output from a microprocessor in the same way that is possible with an on/off valve.

Where the oscillator is to be used as a pile driver or forging hammer the piston rod will carry a hammer head at its end remote from the piston and the working stroke will normally be an outward movement of the piston rod from the cylinder. When used as a metal punching or stamping tool use of the reverse stroke as the working stroke may in some cases be more convenient.

The invention will now be further described with reference to the embodiment thereof which is illustrated in the accompanying drawings in which: Figure 1 is a somewhat schematic diagram of an oscillator showing the hydraulic and electrical circuitry including an on/off valve; and Figure 2 shows the hydraulic circuitry for an oscillator using a direction control valve; Figure 3A is a partial sectional view of the piston rod showing a single sensing unit of the L.E.D./phototransistor type of the oscillator of Figure 1; Figure 3B is view similar to Fig. 3A in which the sensing unit is of the proximity switch type; Figure 4 is a schematic diagram showing the general electrical circuit arrangement for an oscillator of the general type of Fig. 1 in which the sensors are inductive transistors; and Figure 5 shows a typical circuit for effecting digital sorting of the output from a series of position sensors.

In Figure 1 a hydraulic oscillator is shown generally at 1. It comprises a pressure cylinder 2 (e.g. of steel), within wihch is located a freely movable piston 3. The piston 3 is integral with a piston rod 4 and is made of toughened steel.

(Alternatively the piston and rod can be separate parts, firmly connected together). Rod 4 projects out of the cylinder and carries at its outer end a suitable tool (not shown). The opening in the end wall of the cylinder through which the piston rod passes is fitted with a suitable seal 5 to prevent fluid from leakiny out of the cylinder along the piston rod. A high pressure feed 6 opens into the cylinder 2 at this end and is permanently connected to the fluid line shown as H P in the diagram. The feed 6 opens at one point into an accumulator 7 which serves to keep the pressure in the feed 6 (and in the right hand part of the cylinder, i.e. in space 8) constant.

Space 9 in the cylinder (i.e. on the left hand side of piston 3 in the sense of Figure 1) communicates through line 10 with valve 11, which is itself connected through inlets 12, 13 to high and low pressure fluid lines H.P. and L.P.

respectively.

Alongside piston rod 4 is mounted an array of discrete position sensors 14. These provide sensory input in the form of binary (i.e. on/off) signals to a microprocessor unit 15, which processes the information and provides binarycoded signals output to a miniature solenoid valve 1 6. This valve is supplied with fluid at high and low pressure through feed lines 17, 18 respectively and provides a fluid pressure signal to the main on/off (switching) valve 11.

Figure 2 shows an alternative form of oscillator in which a direction control valve 21 is used. The valve is operated through solenoids 26, 261 which cause the valve spindle to move so as to provide either connections between lines 22 and 25 and 23 and 24 or between lines 22 and 24 and 23 and 25. Line 22 is the H.P. line as illustrated in Fig. 2 and line 23 the L.P. line and lines 24 and 25 go to the cylinder on the larger area and smaller area sides respectively of the piston. High and low pressure fluid is therefore switched alternately to the two faces of the piston as the direction control valve is switched in response to binary control signals 27 from a microprocessor unit (not shown in Fig. 2).

As shown in Figure 3A the discrete digital position sensors are in the form of light emitting diodes coupled with phototransistors. Each light emitting diode e.g. 31, is arranged to project a beam of light onto the surface of piston rod 4.

Where the rod is highly polished, light will be reflected from the rod 4 into the associated and suitably placed phototransistor e.g. 32 but where the rod is substantially non-reflecting no light will be received by the associated phototransistor. By therefore providing along the length of the rod alternately reflecting and non-reflecting regions the position of the piston itself can be followed by association with the movements of the reflecting/non-reflecting interfaces, which as they move will "switch on" successive position sensors.

The sensor units comprising e.g. L.E.D. 31 and phototransistor 32, are mounted together on a beam 33 by e.g. a clamping arrangement 34. In this way by unclamping a unit it can be moved to any desired position on the beams so as to alter the array arrangement.

In the alternative sensor unit arrangement shown in Figure 3B, the units 35 are of the proximity detector type disposed adjacent the surface of the piston 41, The piston itself is stepped e.g. at 36 and the dimensional change resulting from this stepping gives rise to a binary signal from each sensor unit the value of which will depend on whether the change in dimension has or has not passed that particular sensor unit.

As with the L.E.D./phototransistor units of Fig. 2A, the proximity detector type sensors are most conveniently moveably mounted on a beam 37 which is arranged to lie parallel to the line of travel of piston 41. If the sensors cannot be got close enough together it may be necessary to arrange them on two or more such beams disposed around the circumference of the piston.

In Figure 4 there is shown a series of inductive transducers 41 which may typically be mounted in line on a beam arranged parallel to the surface of the oscillator piston as described in connection with Figures 3A, B of the drawings. Inductive transducers exhibit a change in current output dependent on the presence or otherwise of metal, particularly but not necessarily ferrous metal.

Therefore when a prominent metal part carried by the piston lies opposite a given transducer it will show a different current output to when that part does not lie opposite that transducer. The current output from each transducer is detected by a current level detector 42 which switches positively from one state to another, specifically from high (current) state to low or low to high as metal is/is not detected by the associated transducer. Level detectors 42 thus each produce a binary output which pases to a multiplexor 43 which provides an output 46 to a microprocessor (not shown). The multiplexor is itself under the control of the microprocessor via input line 47.

Additionally the level detector binary outputs operate a light-emitting diode bar display 44 which gives a visual display of the movement of the oscillator piston and also control field effect transistor switches on a chain of voltage deriving resistors 45 in order to produce an analogue output 48. Diodes are associated with the resistors so as to block reverse voltages and give a higher prevailing output.

In one embodiment of the apparatus, 32 transducers are lined up alongside the line of travel of the piston and the multiplexor is a 32:16 line device which, under the control of the microprocessor selects alternately the greater and the lesser 1 6 bits of the input from the transducers and directs this to the microprocessor. In the case of an inwardly stepped portion of the piston face i.e. a groove or channel therein, the input to the microprocessor may take the form such as 1111100001111111, or if the piston face is stepped outwardly i.e. if it has a band of metal projecting from its main body, the input may be in the form 0000000001110000. In either case the microprocessor will be programmed to detect the change of digit i.e.O to 1 or 1 to 0, though which registers is dependent upon whether the leading or the trailing edge of the groove or projecting metal band is detected.

As an alternative to the digital sorting routine being effected within the microprocessor/controller unit, it can be effected by appropriate circuitry. Typical circuitry is shown in Figure 5 of the drawings, where part of a circuit having inputs A-F from only six level detectors is shown. Each input is fed to two nand gates of which six are shown, designated 51 to 56. One of these pairs of inputs is in each case inverted by an inverter, shown at 57 to 61. Each nand gate has an input from two adjacent level detectors, one being fed through one of the inverters, except for the last gate in line which has a logic 1 input to make up its pair of inputs, the other being from level detector A.

The nand gates can be replaced by nor gates in an otherwise similar circuit arrangement, except that the input to the last gate in line is then logic 0. In the case of a series of nand gates as shown in Fig. 5 however the output to the microprocessor will show a "1" in the significant change position, e.g. the output will be of the form 0000000001000000, whereas if nor gates are used the significant change position will be shown by a "0", e.g. the output will be 1111101111111111. Such significant changes can be encoded by other circuitry to be in the form of a digital number of the position of the change so obviating the need for a multiplexor and increasing the available resolution.

Claims (14)

1. A fluid driven oscillator comprising a pressure cylinder; a piston slideable within said cylinder and dividing the space within said cylinder into two chambers; a piston rod attached to said piston and extending outside of said cylinder through one of said chambers; means for providing fluid flow in and out of at least one of said chambers; valve means for controlling the said fluid flow, means for detecting the position of the piston comprising an array of discrete position sensing units, the array extending in the direction of travel of the piston rod and each sensing unit being capable of providing sensory data in the form of a digital electrical signal; and electronic processing means adapted to analyse electrical signal output from said detecting means and to exercise control of said valve means by providing electrical signal inputs thereto, said valve means being controllable by said electrical signal inputs.

2. A fluid driven oscillator according to claim 1 wherein the position sensing units are carried by the pressure cylinder and the piston rod carries means which co-operate with the said sensing units to provide an indication to each unit in turn of the position of the rod along its travel.

3. A fluid driven oscillator according to claim 2 wherein the sensing units do not contact the piston rod at any point along its travel.

4. A fluid driven oscillator according to claim 3 wherein each sensing unit comprises a light emitting diode and a phototransistor and the piston rod is provided with reflecting and less highly reflecting regions alternately disposed along the length of the piston rod.

5. A fluid driven oscillator according to claim 3 wherein the sensing units are in the form of proximity sensing switches.

6. A fluid driven oscillator according to claim 2 wherein the sensing units make contact with the piston rod.

7. A fluid driven oscillator according to claim 6 wherein the sensing units are in the form of microswitches mechanically triggered by trips carried by the piston rod.

8. A fluid driven oscillator according to any one preceding claim wherein the sensing units are movable longitudinally in the direction of travel of the piston rod.

9. A fluid driven oscillator according to any one preceding claim wherein the sensing units provide sensory data in the form of a binary electrical signal.

1 0. A fluid driven oscillator according to any one preceding claim wherein the piston is biased towards one end of the cylinder by a constant high fluid pressure acting within one of the said chambers and bearing on the face of the piston which is towards the piston rod.

11. A fluid driven oscillator according to any one preceding claim wherein the valve means is in the form of an on/off valve.

12. A fluid driven oscillator according to claim 11 wherein the valve means is actuable by a fluid pressure signal, the fluid pressure signal being generated by providing the said electrical signal inputs to a miniature solenoid valve.

1 3. A fluid driven oscillator according to any one of claims 1 to 10 wherein the valve means is in the form of a directional control valve.

14. A fluid driven hammer device incorporating a fluid driven oscillator according to any one preceding claim.

1 5. A fluid oscillator substantially as hereinbefore described with reference to the accompanying drawings.