WO1992022861A1

WO1992022861A1 - Improvements to vibrating materials handling and processing devices

Info

Publication number: WO1992022861A1
Application number: PCT/GB1992/001071
Authority: WO
Inventors: Paul Allan Marriott
Original assignee: Paul Allan Marriott
Priority date: 1991-06-15
Filing date: 1992-06-15
Publication date: 1992-12-23
Also published as: AU2019892A; GB9112973D0

Abstract

A resonance vibratory system for materials handling and processing comprises a surface resiliently mounted for vibration, means to measure the vibratory displacement of the surface, means to provide a signal to a driving device to maintain the resonant vibratory motion of the surface, means to measure the time period per stroke, means to measure the power required to maintain the vibration, and a control circuit for the various said means, wherein the control circuit includes signal processing means whereby a signal representative of vibratory displacement is capable of being compared with a signal derived directly or indirectly from the measurement of displacement and/or time period per stroke and/or maximum acceleration and/or maximum velocity of the vibrating surface and/or weight and/or mobility and/or movement and/or throughput of material upon the vibrating surface and/or with an external signal to provide an adjustment to the displacement or an override instruction to the normal vibratory motion control to alter the displacement and/or waveform and/or frequency and/or direction of vibration and/or to provide an output signal to influence an external device. The system permits improved control of resonance vibration to be attained.

Description

IMPROVEMENTS TO VIBRATING MATERIALS HANDLING AND PROCESSING DEVICES

This invention relates to materials handling and processing devices that embody a vibrating, shaking or pulsating action, hereinafter to be called a vibrating action. It relates more particularly to materials handling and separating devices such as vibrating screens, vibrating grizzlies, vibrating feeders and vibrating conveyors. The object of the invention is to improve the performance and/or offer improved methods of both manual and/or automatic control of such devices. The particular object is to provide such improvements without substantial additional cost of manufacture.

In international patent application published under No. WO 89/10197 there is described a vibratory separation device where the degree of vibration is automatically controlled so as continuously to maintain optimum performance. The core of the invention claimed in WO 89/10197 is the manner in which resonant vibration is produced and controlled and the present invention is concerned with both novel additions and variations to WO 89/10197 to provide an improved method for the production and control of vibration for a variety of vibrating devices and also improvements to the separation device particularly described in WO 89/10197, especially in order to optimise the advantages of power saving and reduced maintenance costs associated with a resonance vibratory system.

Presently manufactured vibratory materials handling, processing and separating devices exist in a wide range of sizes and configurations to perform a variety of different functions but at present most are caused to vibrate at a frequency that is determined in the design or is under a form of adjustment where exact resonant oscillatory motion is normally avoided. For the devices incorporating the improvements of the present invention, the operative vibrating surfaces are mounted for resonant oscillatory motion and the basic principles employed embody those essential common parts that are fundamental in a resonant vibratory system such as the separator described in WO 89/10197.

In order to provide a description which encompasses a variety of devices having different configurations of common essential component parts, it will in many cases be appropriate simply to show these on diagrams as numbered parts in an arrangement where the shapes and disposition of the parts shown may not necessarily bear direct resemblance to the shape or positions or attitude of those parts in perhaps a variety of different devices where nevertheless the description is applicable. Thus, for example, in practice the support for the vibrating surface in one case may be by suspension and in another case the support may be from underneath and in some cases vibrating surfaces may be horizontal and in others at some angle other than horizontal. In any event, throughout this specification and claims, the term "surface" is to be understood as referring to any component having an area or zone on which material may be handled or processed, irrespective of its particular orientation or configuration.

According to one aspect of the present invention, a resonance vibratory system comprises a surface resiliently mounted for vibration, means to measure the vibratory displacement of the surface, means to provide a signal to a driving device to maintain the resonant vibratory motion of the surface, means to measure the time period per stroke, means to measure the power required to maintain the vibration, and a control circuit for the various said means, wherein the control circuit includes signal processing means whereby a signal representative of vibratory displacement is capable of being compared with a signal derived directly or indirectly from the measurement of displacement and/or time period per stroke and/or maximum acceleration and/or maximum velocity of the vibrating surface and/or weight and/or mobility and/or movement and/or throughput of material upon the vibrating surface and/or with an external signal to provide an adjustment to the displacement or an override instruction to the normal vibratory motion control to alter the displacement and/or waveform and/or frequency and/or direction of vibration and/or to provide an output signal to influence an external device.

Embodiments of the invention will be further described with reference to the accompanying drawings, of which:

Figure 1 is a diagram showing the general arrangement of components in a resonance vibratory system to which the invention may be applied;

Figure 2 is a schematic representation of a circuit embodying all the various functions of the invention;

Figure 3 represents a vibratory feeder;

Figure 4 shows the output voltage from the displacement transducer of Figure 3 with the feeder in the loaded and unloaded conditions;

Figure 5 shows a circuit for averaging the voltage outputs of Figure 4;

Figure 6 illustrates a way of achieving maintenance of vibration in a horizontal plane with deflection in a vertical plane;

Figure 7 is a block diagram of a complete weight measuring arrangement;

Figure 8 shows a resonance assembly with a horizontal platform having a weight fixed thereon;

Figure 9 is a graph of apparent weight against true weight;

Figure 10 shows an assembly- similar to that of Figure 8 but with a movable "frictionlesε" weight on the platform;

Figure 11 shows an assembly similar to that of Figure 10, in which movement of the weight is subject to friction;

Figure 12 is a diagram representing a feeder with a replenishment hopper;

Figure 13 illustrates a particular aspect of operation of the feeder shown in Figure 12;

Figure 14 shows a two mass vibrating system; Figure 15 illustrates one timing sequence of electrical control signals to a vibratory system and sinusoidal motion produced;

Figure 16 illustrates another timing sequence of electrical control signals and the resulting vibratory motion waveform;

Figure 17 is a diagram representing a vibrating surface with a compression spring at each end thereof;

Figure 18 is a diagram showing the use of springs set at an angle to the motion of the vibrating surface;

Figure 19 is a diagram showing the use of vibratory drive devices which act in different directions;

Figure 20 shows another example of a multi-directional vibrating device;

Figure 21 shows a device similar to that of Figure 20 without rotating components; and

Figure 22 is a block diagram illustrating a controlled vibration starting system.

The essential components of all the devices that may benefit from the present invention are shown in Figure 1, in which an outer mounting on which the whole device is supported, whether this be an actual outer framework or suspension from some part of a building, hereinafter to be called the outer framework, is indicated as 1. Attached to the outer framework 1 are supports such as wires 2 that support the operative vibrating surface 3. A spring or springs (or components producing an effect similar to springs) 4 restrain the movement of the vibrating surface 3 and at the same time constitute, together with the mass of the vibrating surface 3, a natural resonant vibrating assembly whose movement is in the direction of the arrows shown. Other restraints or guides limiting the direction of movement of the vibrating surface will of course exist on many vibrating devices but are not necessarily included in the description which follows.

A displacement transducer 5, for instance of a proximity type, is attached to the outer framework 1 (except in certain circumstances to be described later) and provides an electrical signal output representative of the displacement of the vibrating surface 3, relative to the outer framework 1. Connected to the displacement transducer 5 are various detection circuits, for instance a detector of vibration stroke length 6. Also connected to the displacement transducer 5 is a device control circuit 7 which is required to provide pulses of electrical power to drive or control the driving device 8 to which it is connected. The power source is not shown. A driving device 8 may for example be an electromagnet or some other suitable device. The drive control circuit 7 is required to produce electrical pulse signals to control or activate the driving device 8 to provide pulling and/or thrusting motions to the vibrating surface 3 at the correct time and in the correct direction and of the correct strength to maintain the resonant vibratory motion. The alternating voltage signal from the displacement transducer 5 is also fed to the control circuit 7 to provide the timing means for the generation of such pulsed signals. An example of a simple fundamental complete working vibratory device follows. A required stroke length of resonant vibratory motion is achieved by providing an appropriate strength and/or duration of the electrical pulse signals from the control circuit 7 fed to the driving device 8. The control circuit 7 in this example is of the type where the control of strength and/or duration of the electrical pulse is itself governed by the amplitude of an input voltage. Such an input voltage is provided by a variable voltage control circuit 11 whose output voltage is caused to increase or decrease according to whether a control input voltage thereto is positive or negative. The input to this variable voltage control circuit 11 may come from a comparator 10 that compares an input from the stroke length detector 6 with an input from some source repersenting the stroke length that is required, namely ths signal source 9 representing a manual setting of a required stroke length. The comparator 10 thus compares the actual with the required stroke length and provides a positive or negative output dependent upon whether the actual stroke length is more or less than that set on the manual control 9. The signal from the comparator 10 thus controls the variable voltage control circuit 11 which in turn controls the drive control circuit 7 and thence the drive device 8 and accordingly adjusts the stroke length until the actual stroke length coincides with that of the manual setting. This source may be from signals generated within a particular device, as described hereinafter, or perhaps from some signal external to the machine.

The above represents the essential fundamental requirements of the simplest form of resonant stroke length controlled vibratory system but, in more complex devices, the displacement transducer 5 will also be connected to a circuit producing a signal representing the time period per stroke of vibration, hereinafter referred to as the stroke period detector 12. Further detection will be of the power required to produce the mechanical thrusts to move the vibrating surface 3 at the required stroke length. This is achieved by providing an output signal from the drive control circuit to a power measuring circuit 13 (see Figure 2) . Such detections of stroke period 12, power 13 and stroke length 6 have already been described in WO 89/10197 for the vibrating separator as providing some of the essential signals utilized in the automatic control of that and other vibratory separation devices. It is these signals which, together with others to be described hereinafter, are utilized in different ways to that described in WO 89/10197 to provide advantages enabling a resonant vibratory system to be utilized in further ways, as well as providing further improvements to separators as described in WO 89/10197.

The electronic control necessary to produce the wide range of improvements to be described could, for example, in practice be contained principally within a signal processing component 14 (see Figure 2) , different versions of which may be employed to cover a range of sizes and types of devices. An additional part of the processing component is a "plug in" program 15 to suit the type, size and special features of the device in question.

The description which now follows as to how various novel features are achieved in many cases describe mathematical processes such as addition, multiplication and squaring, as well as the production of timing signals. Most of such processes will be carried out in the processor 14 with the appropriate program component 15 to provide the necessary memory and command signals. For ease of description, some circuits including those previously described and shown in Figure 2 are shown as being outside the processor 14 whereas in practice most would be within that component. Likewise, some descriptions of circuits are shown external to the processor 14 for ease of description, but would in practice be within the processor. Descriptions of actions of circuits may be described in terms of voltages or other parameters whereas, in practice, no such voltage would necessarily exist in any way other than perhaps as a digital representation thereof. Many descriptions of circuits are limited; for example, many comparators might in practice be differential amplifiers and the necessary stabilisation of many closed loop systems has been ignored, but will be understood by the skilled person.

An essentially schematic representation of a circuit embodying all the various functions that are required in the present invention will now be explained with reference to Figure 2. It will be noted that the basic essential circuit of Figure 1 remains. The processor 14 is fed with signals from the stroke length detector 6, the stroke period detector 12, the displacement transducer 5 and the power detector circuit 13 and may also be fed with one or more input signals some of which may be manual input signals and/or from some external source 21. The principal essential output from the processor 14 is the input to the comparator 10 that controls stroke length. Another output 22 from the processor 14 connects to the control circuit 7 to override, optionally temporarily, the normal control of stroke length previously described, namely that from the voltage control circuit 11.

Additionally, a further output 23 from the processor 14 may be provided to the control circuit 7 to override, optionally temporarily, the timing of drive pulses affecting normal vibration to provide some other effects, to be described hereinafter. Other outputs 24 and 25 from the processor 14 may for instance be required to provide respectively warning/monitoring signals and signals to control external devices.

Certain vibratory devices embody movements of the vibrating surface 3 in more than one direction, for example additional movement at right angles to that depicted in Figure 1 and in the same horizontal plane, under such circumstances additional drive devices, displacement transducers and associated electrical and electronic controls would be required.

The objective of the improvements of the present invention is effect improved performance of various vibratory devices in one or a number of ways without substantial additional cost of manufacture. For instance such improvements may be that of carrying out an operation in a better or more efficient way and/or reducing manual effort by providing automated adjustment means and/or by saving power and/or by providing external signals of parameters to control other devices and/or of providing monitoring and warning signals.

The requirements for producing many of these improvements derive from the detection of parameters and the use of such data in logical and mathematical combinations to produce signals to alter the vibratory motion. For instance, a vital requirement in seeking automatic adjustment for optimum performance in many devices is to produce signals representing the quantity of and throughput rate of material as well as a signal representing how the material is behaving upon the vibrating surface. Some such signals, for example a signal representing the throughput of the device, may be utilized for comparison with an externally determined signal representing the required throughput rate to determine whether the former should be increased or decreased. Other signals, such as a signal representative of how material is behaving upon the vibrating surface, may be compared, for instance, with a signal representing the correct behaviour of material for the particular throughput rate, so as to enable automatic correction to maintain optimum performance at any throughput.

This specification therefore firstly describes the production and use of signals representing various parameters with the general ways in which these may be used and secondly describes ways in which vibration may be modified to produce certain advantageous results. Certain detection parameters were described in WO 89/10197; these and others described in this specification are required as the first part of achieving the improvements which are required.

There are many benefits to be gained on many devices, for example screens, feeders and conveyors, by having available a measurement of the parameter of weight of material being handled by the device, without appreciable additional manufacturing cost. Utilization of a signal representing weight of material upon the vibrating surface is essential to providing signals representing other parameters, for example in determining when the device is overloaded or empty so as to operate external warning and/or monitoring signals or to provide external signals required in integrated automated handling systems. Such a weight signal may also be used in a "weight loss" type of feeder where presently costly means such as strain gauges and associated amplifiers are required to obtain signals representing weight. Alternatively certain feeders presently with limited control of feed rate may incorporate an accurate "weight loss" control at little or no extra manufacturing cost.

One novel method of providing a signal representing weight, refered to for convenience as the "spring" method, will now be described with reference to a vibratory feeder of the type where the configuration is similar to presently manufactured devices and is as shown in Figure 3. A hopper for containing the material constitutes the vibratory surface 3 which is supported by the hinged supports 2 and restrained by the spring 4. An electromagnet driving device 8 provides the necessary pull and thrust force and a displacement transducer 5 is connected to measure displacement of the vibrating surface 3 relative to the outer framework 1. The direction of vibration in this type of device is that shown by the arrow. When vibrating, the displacement transducer 5 produces an alternating voltage due to the vibratory motion. This alternating voltage has a DC component dependent upon the weight upon the vibrating surface. Assumed in this example is an output from the displacement transducer of 1 volt per centimetre of movement and a vibratory stroke length (peak to peak) of 2cm. which will thus produce an alternating voltage output of 2 volts peak to peak. Under these circumstances, as is shown in Figure 4, the voltage output from the displacement transducer with no load in the hopper is a sine wave voltage having a peak voltage of 4 volts and a trough voltage of 2 volts, as shown at 28, and it is clear that the average voltage, namely the mean voltage of 3 volts, represents no weight in the hopper. With, for example, a 20 Kg. load in the hopper, the average depression of the hopper will result in a DC component of 5 volts as shown by waveform 29. An averaging circuit is therefore necessary and this is easily achieved by known means if the frequency is relatively high. If, however, the vibration frequency is relatively low and yet it is required to obtain an almost immediate signal representative of weight, then a fast averaging circuit is required to remove the alternating component due to the oscillatory motion. Such a fast averaging circuit is illustrated in Figure 5. The signal from the displacement transducer 5 is fed to a peak detection circuit 30 that detects and holds the peak voltage of each cycle until replaced by the next cycle. A similar detector 31 detects and holds the trough voltage. In the example of the loaded hopper waveform 29 (Fig. 4) , the peak voltage held will be 6 volts and the trough voltage will be 4 volts. In order to provide the necessary averaging, the trough voltage is subtracted from the peak voltage by the subtraction circuit 32 (Fig. 5) , providing a difference voltage between the two. This voltage is then halved for instance by a resistance divider 33 and the result added to the signal representing the trough voltage from detector 31 by the adding (summing) circuit 34. The result of this will be to produce a voltage of 5 volts equal to the average value, namely after removal of the AC component. In order to make use of this voltage for weight measurement, it is of course necessary to subtract from it, for instance by a subtracton circuit 35, a voltage representing zero weight in the hopper. This may be by a manually adjusted input 36 of 3 volts equivalent to zero weight in the hopper or from a voltage constantly held and modified in a memory device. This may be activated manually whenever zero adjustment is considered necessary or perhaps automatically where some external signal can provide information that the hopper is empt .

Being a spring controlled weighing device, it may of course occasionally be necessary to provide additional adjustments to compensate for spring ageing and this could, for instance, be achieved by modifying the signal from the displacement transducer 5, in order to alter the output voltage per given weight to the required new amount. The above values were chosen for clarity. In practice it is possible for instance that the zero weight setting of the device may be at 0 volts DC and be adjusted by an offset control on the displacement transducer.

Whilst for some devices the accuracy of weight measurement as above may be sufficient without further means to correct for errors, more accurate measurements are required for most applications and this may be achieved by providing various corrective means some or other of which may be employed according to the particular device in question. For example, in many devices the mechanical configuration is such that some inaccuracies in weight measurement will occur unless some correction means be employed. In the case of the vibrating feeder depicted in Figure 3, compression of the spring 4 will not be in direct proportion to the weight in the hopper since the hinged arrangement results in an arc movement of the hopper producing some non-linearity. However, in practice, such non-linearity may for example be corrected by an appropriately programmed correction circuit that corrects the output signal from the basic measuring circuit previously described. Correction is achieved by utilizing the uncorrected weight signal from the subtraction circuit 35 (see Figure 5) as a command signal to memory stored data to provide a correction signal appropriate to the signal from the subtraction circuit 35 to provide the necessary correction.

Another form of correction may be necessary if there is any inequality between the thrusting and pulling forces applied to the vibrating surface. It may of course be that pulling forces only are applied in some cases. Whichever system be employed, if the force applied in one direction exceeds that of the other, there will be some degree of movement of the average position of the vibrating surface in the direction of the major force which will, of course, result in an inaccurate weight measurement if no correction is applied. However, the pull and thrust may be equalized if necessary by alteration of the time duration and/or strength of the pulse of electrical energy applied in one direction to the drive device 8 so that it is different from that applied in the other in a manner that equalizes the two forces. This may be achieved for example by feeding the output from the displacement transducer 5 to a simple integrating circuit to detect rate of change which, in conjunction with a "sample and hold" circuit, will produce a signal representing the maximum velocity of the oscillatory motion. The "sample and hold" circuit is arranged to store a signal representing the maximum velocity for one half cycle and compare it in a comparator with a signal representing the maximum velocity for the other half cycle. The output from the comparator is then utilized to modify the strength and/or duration of the electrical energy pulse to the latter so that the maximum velocities and therefore the effective forces of each are equalized.

Where pull or thrust force is applied once per cycle, reasonably satisfactory correction may be achieved by utilizing the signal from the stroke length detector 6 as a command signal for a programmed correction. This method of correction can be reasonably accurate because, for example, if the drive device 8 (see Fig. 3) is of a type providing pulling force only, then the greater is the stroke length of vibration the greater will be the degree of the average vibratory motion in the direction of that pulling force. Without such correction, the result would be an indication of weight greater than was the actual weight; thus the correction would be a subtraction therefrom. The above description of circuitry involved all falls within that basic circuit of Figure 2 where the processor 14 fed from detection signals accomplishes all that has been described above, as well of course as all that is required in other respects for the device. The inventive feature in the detection of this parameter is that of utilizing displacement transducer 5 in conjunction with spring or springs 4 and of thus obtaining a steady and corrected signal representative of weight from such a vibrating device without the use of other expensive devices such as strain gauges.

It should be understood how the above "spring" type weight detection system is applicable only where additional weight upon the vibrating surface causes a difference in the mean vibrating position thereof. Thus, in some devices, for example where currently a suspension system for a vibrating surface has vertical wires as described in WO 89/10197, this weight measurement method could not be utilized without some modification. However, most such systems may easily be modified in one way or another; for example the mineral separator described in WO 89/10197 may easily be modified by arranging that the support wires are not vertical but at an angle, as shown by the dotted lines 38 in Figure 1 herein. Under these circumstances, the spring at the left hand side of the assembly would be supporting some weight with the result that different weights upon the vibrating surface would produce different average deflections of the vibratory surface, producing different average DC components to the voltage from the displacement transducer 5. For some devices, for example the separator described above, vibration in a line that is not horizontal produces no untoward effect and the use of costly strain gauges for such weight measurement is eliminated. Maintenance of vibration in a horizontal plane, but with deflection due to added weight in a vertical plane can also be achieved in other ways, for example as shown in Figure 6 where a hanging vibrating surface 3 has springs 39 connected to support wires 2 and the vibrating surface 3. The displacement transducer 5 is mounted at an angle on the outer frame 1 and faces a plate 40 mounted at an angle on the vibrating surface 3. Additional weight on the surface causes the average distance between displacement transducer 5 and plate 40 to be reduced, thus providing the necessary change in DC component to the output from the displacement transducer 5. An alteration of this type to the separator described in WO 89/10197 eliminates the requirement of a "master" separator embodying the expensive strain gauge arrangement and makes possible weight detection on every machine with the advantage that each machine is then independent and automated control is dependent only upon the parameters detected on each individual machine. Many other devices that are currently supported for and require vibratory movement in a horizontal plane can be provided with a modified support arrangement such that there is some degree of vertical movement when varying weights are applied and thus be applicable to weight measurement by this method. When no such vertical movement is possible on a device, an alternative method of producing a signal representative of weight may be used.

The alternative method of weight measurement may be employed in place of or in addition to that described above. It will be referred to for convenience as the "resonance" method. The reason for its possible use in addition to the "spring" method is that the method of producing this type of weight measurement in conjunction with the "spring" method enables the production of signals to represent other parameters the use of which will be explained hereinafter. The "resonance" method of producing a signal representing weight upon the vibrating surface does so by suitably processing the signal from the stroke period detector 12. If there were no friction or other losses in such a resonant vibratory arrangement, a signal representing weight could be obtained by suitably processing the signal from the stroke period detector 12. This processing would be according to the text book equation that relates spring force k, mass m and resonant stroke period T, namely m = T2 x k. However, such conditions without frictional losses do not occur in practice and to obtain accurate weight measurement by this method some correction for damping has to be effected.

However, it is because of the effects of damping that it is only in cases where movement of material upon the vibrating surface is relatively small and where such movement causes a relatively small frictional effect, that the production of a signal representative of weight of material upon the vibrating surface by the resonance method is possible. Accuracy in such cases may be made high enough for most practical purposes by applying a correction signal to the signal produced by squaring the stroke period signal. Correction is required principally to compensate for damping of the resonant oscillatory motion due to friction within the mechanical assembly which alters principally with the weight of material being processed, the length and period of stroke of vibration and the effect of eddy current and hysteresis losses in the drive component. The proportions of these various inputs and the manner of their use in providing correction depends upon the type and configuration of the particular device. Some inputs for such a correction arrangement are not necessarily used in a linear manner, for example frictional increase with frequency usually falls off at higher frequencies.

One way of achieving α complete weight measuring arrangement is shown in Figure 7, in which an output from the stroke period detector 12 is fed to a squaring circuit 43 the output of which is fed to a summing circuit 44 which is itself also fed with a correction signal output from the correction circuit 45. The output from the summing circuit 44 of course is required to have subtracted from it, by the subtraction circuit 46, an appropriate pre-set signal 47 representing the weight of the unloaded hopper. The correction circuit 45 requires inputs from the stroke length detector 5, the stroke period detector 12 and from the power detector circuit 13, the latter being a reasonable measure of the hysteresis and eddy current losses. A further input to the correction circuit 45 is required, namely the total weight, which signal is the output from the summing circuit 44. The output from subtraction circuit 46 provides a signal representing weight upon the vibrating surface achieved by the resonance method.

As already described, the resonance method of weight measurement is not suitable for cases where there is considerable movement of material upon the vibrating surface. It is in such cases that a measurement of parameters associated with such movement is desirable and possible. For example, a signal representing the mobility of material is possible - namely the degree of mobility for example by comparison of what might be termed "apparent weight" by resonance with that of the true weight obtained for instance by the "spring" method. The way in which such a comparison provides a signal is best described in a theoretical manner as follows.

Figure 8 shows a resonant assembly consisting of a horizontal vibrating platform 3 of weight 10 units restrained by springs 4 and supported on wheels 49; included but not shown is a driving means to maintain resonant vibration. Assuming the appropriate corrections for, for example friction, as previously explained, then Figure 9 shows a graph of weight as detected by "resonance" on the Y-axis against the actual weight detected by the "spring" method on the X-axis. With no weight upon the vibrating surface and an assumption that the vibrating platform weight is 10 units, the point 50 represents a signal showing equal weight representation by both systems. Additional fixed weights placed on the vibrating surface are then represented by the line 51.

If, however, as shown in Figure 10, movable weights 52 running on assumed frictionless bearings 53 be placed upon the surface instead of fixed weights, the addition of such movable weights has no effect upon the weight measurement by resonance which remains the same - namely 10 units- and the addition of such weights is represented by the horizontal line 54 in Figure 9. However, in practice friction is always present and accordingly Figure 11 shows unfixed (that is, sliding weights) resting upon the surface. With varying degrees of friction between sliding weight 52 and the surface 3, line 55 (Figure 9) might represent the graph of apparent weight against actual weight for a certain degree of such friction or mobility. In the case shown, a point 56 on line 55 of 20 additional units of actual weight W2 shows only 10 units on the Y-axis of additional "apparent weight" W3 as detected by resonance. A division of the apparent by the actual weight, namely W3/W2 or 10/20 = 0.5, may for example be utilized as a measure of mobility of material on the vibrating surface which will in future be termed the "mobility factor". Clearly, the nearer the mobility factor is to one, the closer will be the graph line to the line of fixed weight addition 51. Thus a signal may be produced, as shown in Figure 7, where, by dividing in the divider circuit 59 the output signal 60 from the subtraction circuit 46 by an input from that of a signal of actual weight measurement 61 as determined by the spring method, the signal of mobility factor 62 as described above will be produced.

There are many ways in which the signal representing the mobility factor may be utilized in controlling or assisting in the control of vibratory devices. In the case of the mineral separator described in WO 89/10197, a more precise control of the separation process may be achieved. In other devices such as vibrating feeders and screens, such a signal representing the mobility factor may, as shown in Figure 7, be compared in a comparator 63 with a signal 64 representing the ideal mobility factor for the particular situation. The result of such a comparison, namely signal 65, may be utilized to maintain the required mobility. Such "ideal" signals vary considerably for different types and configurations of devices and are not necessarily constant for all weights of material upon the surface. For example, on one type of feeder, it is found to be appropriate to effect a linear increase in the mobility factor with an increase in actual weight of material upon the vibrating surface as shown by an input to the ideal signal generator 64 from the actual weight of material signal 61. In cases of non linearity, appropriate generation of the ideal signal may be stored in memory and be available against a command signal from actual weight of material upon the vibrating surface. In other cases, some alternative parameters may be utilized to modify the mobility factor.

Another useful detection producing an improvement to various devices is that of detection when too much or all the material on a vibrating surface is immobile, for example material stuck to a vibrating surface or pegged or blinded upon a screen or grizzly. Such a condition may for example be detected if the mobility factor reaches too high a value, for example a mobility factor of 0.9 represented by the line 66 in Figure 9. In such cases, recognition of such a condition is achieved by a simple comparator arrangement as shown in Figure 7, where the mobility factor signal from the divider circuit 59 is compared in a comparator 67 with a preset signal 68 representing too low a mobility of material. The output of such a comparator may be utilized temporarily to bring into action one or other alterations to the vibration process to clear such sticking material, as described hereinafter. However, other methods of detection of material partly or wholly stuck or wedged on the vibrating surface are possible by methods that do not require measurement of mobility. For example, a signal representing the weight of material may indicate that a quantity of material upon the surface of a conveyor or feeder is not altering in the correct manner. This may be detected for example by a circuit which detects the rate of change of weight, which may indicate that the weight loss is too low or that the weight is not reducing at all. If this situation is taking place under conditions where the signal representing stroke length indicates a degree of vibration sufficient to produce a certain delivery of material, then appropriate logic circuits based upon the above can clearly provide an output signal which demands that curative action be taken with appropriate changes in stroke length.

Detection of mobility of material may, in certain cases, be difficult. For example, if most of the material on the vibrating surface is in a state of mobility higher than that normally required but part is stuck to it, then the former state may - with the previous detection means described - be masked by the latter. However, another detection process providing some discrimination between such effects described above and some others may be achieved by utilizing the signal representing mobility with that of the power being consumed in producing the vibrating process. Such a signal representing power is required to reflect the additional power required to provide the necessary vibration when the device is loaded compared with that when it is unloaded. The production of such a signal is relatively simple but the processes to attain same vary considerably according to the drive system employed. The factor that is significant in usage of the power signal is of course that such a signal can provide a fair representation of the additional frictional losses that occur due to various effects and loadings on the vibrating surfaces. Thus, for example, if material is all held solidly upon the vibrating surface, then no friction exists between the material and the surface or between particles of material. Under such circumstances the increase in power when the vibrating surface is loaded compared with that of the unloaded condition would be minimal. In the condition described previously, namely one where one incorrect condition masked another incorrect condition, a situation may exist where the mobility factor indicates that mobility is satisfactory but that, according to the signal representing weight being processed, the power signal should be higher for that mobility. Such a combination would, in this instance, only be possible if too much material were sticking to the vibrating surface. Thus a detection of such a condition becomes possible by circuitry performing the logic processes described above. Other discrimination of detection of effects involving somewhat similar means may be achieved where, for example, friction occurs both due to material moving upon a vibrating surface and of material being fed onto that surface by means, for example, of a self-replenishing feed system from a hopper above the vibrating surface as used in many devices. Useful additional data or enhancement of the detection previously described may also be achieved by arranging an occasional automated short term variation to the stroke and of the detection during that period of the relative changes to the signals of the mobility factor and power. Such measurements in some cases provide an indication of the relative contributions of effects, thereby providing a breakdown of the measurements thereof.

Another useful detection of a parameter is to provide a signal representing the maximum acceleration of vibration. This enables, for example, the production of a constant maximum acceleration of vibration to be maintained on a device if this is required. However, the use of a signal representing maximum acceleration is essential for other uses also. A signal representing the "g" value of maximum acceleration is achieved by a circuit performing a commutation of the

2 equation g = 0.01998 x A/T where A is the stroke length in centimetres and T is the stroke period in seconds. Therefore, with an appropriate division, squaring and multiplying circuit, a signal representing maximum acceleration will be produced without the employment of any additional components as are currently required on some devices where this parameter is measured. A comparator fed with one signal representing a required maximum acceleration and the other with a signal representing the actual maximum acceleration from such a detection arrangement will, for example, provide an output to control the stroke to maintain a required constant maximum acceleration of motion. However a signal representing maximum acceleration may be utilized in a novel way to produce signals representing other parameters. For example, production of a signal representing the rate of movement of material along a vibrating surface is useful for certain purposes. The distance that the material moves with each stroke of an angular movement of vibration such as is produced with a hopper replenished type feeder configuration shown in Figure 12 is dependent mainly upon the maximum acceleration of the forward and upward thrust and the angle of such thrust. On many devices, the amount of movement of material per cycle of vibration is also dependent upon other factors, for example the angle of tilt of the surface (if any) , the natural angle of repose of the material and the degree of friction of the material against the vibrating surface. The quantity of material upon a vibrating surface may also affect the effective maximum acceleration since, as shown in Figure 13, the distance of one part of the material 70 from the bottom of the support pivot 71 compared with that of, for instance, material at position 72 which is further away from the centre of support pivot 71 will result in a higher maximum acceleration for the material in the latter position. Finally of course a certain amount of acceleration is required before any movement takes place at all. Thus an equation to determine a signal representing rate of movement of material may differ from one device to another dependent upon the mechanical configurations thereof. Inputs to such a calculation circuit require to be principally that of the signal representing maximum acceleration and that of the signal representing the weight of material being processed since, as previously described, in many cases the maximum acceleration is partly dependent upon the quantity of material being processed, which quantity is of course measurable by weight. Thus in practice it becomes possible to produce a reasonably accurate signal representing the rate of forward movement of material upon a vibrating surface on many devices. Such a signal may be useful for an external indication or for example the signal may be utilized in a comparator circuit similar in effect to those previously described to provide a specific manually set rate of movement or an automatically adjusted movement rate of material along a conveyor.

From such a signal indicative of rate of movement of material along a vibrating surface, another valuable parameter may be achieved, namely a signal representing the delivery rate from a device. The first requirement for a signal representing delivery rate of material form a device is that of the weight of material upon the vibrating surface and this may, of course, be derived by the "spring" method of weight measurement previously described. In many cases, for example of feeders or conveyors, where the material is reasonably evenly distributed along the length of the vibrating surface, then clearly a signal representing the weight of material per unit length is itself readily determined. Thus with multiplication of the signal representing weight per unit length by that of the signal representing rate of movement of material, a signal representing the amount of material being delivered as an output product of the device in weight of material per unit of time is provided. Such a very valuable signal is presently available on various devices only by complex measuring means. In the case of this resonant vibratory system, such a signal is produced following a series of determinations of parameters, namely a signal representing maximum acceleration, a signal representing the movement of material along a vibrating surface, a signal representing the weight of material upon the vibrating surface, and signals representing cycle period and stroke, all of which originate from the one signal delivered by the displacement transducer 5. Such a very valuable signal of throughput of the device may of course be utilized in a variety of ways, for example in comparing it with a signal of desired delivery rate whether this be according to a manual or automatically controlled requirement, so as automatically to maintain the required delivery rate by control of the amplitude of vibration applied. Additionally such a signal may be valuable for providing controls in automated systems and/or external monitoring and/or of warning devices.

It should be appreciated that all the parameters previously described, which have their individual advantageous uses, are essential in combination to provide this signal of throughput which is novel, as is the production of signals representing the above additional parameters, to the extent that no detection means other than the displacement transducer 5 is required.

All the above feeder and conveyor type devices have been assumed to be of the type where the outer framework is fixed or stands upon the floor or are fixed to a relatively immobile part of a building or structure. However, in the case of some large vibrating devices such as conveyors and feeders, it is necessary to prevent or reduce vibration being transmitted to the building or structure supporting the device. To achieve this objective on many presently manufactured devices, the outer framework of the device may for example be supported underneath by heavy springs to a lower base upon which the whole device rests. In another example of presently manufactured devices, as shown in Figure 14, the vibrating component 3 and/or the drive device 88 is hung on wires 2 from the building, structure or hopper above. The drive device 88 is coupled to or embodies a heavy weight so as to utilize the inertia of the heavy weight against which the push and/or pull of the vibrating surface 3 acts. An essential feature of any such arrangement is that the weight of drive device 8, for example, which is typically a heavy electromagnet, be substantial and of the same order of weight as that of the vibrating component 3 when loaded. Additionally, a spring 4 between the drive device 8 and the vibrating surface 3 is usually incorporated in such an electromagnet drive component. Devices presently operating according to this method are currently known therefore as "two mass" versions of such devices. The only necessary additional components for converting presently manufactured "two mass" versions of such feeders or conveyors to resonant versions thereof are of a displacement transducer 5 positioned to detect displacement between the drive device 8 and the vibrating surface 3. The displacement transducer 5 is required in any event of course to provide the necessary feedback signal for the resonant vibratory system.

In cases of the use of the "two mass" type device of a configuration as shown in Figure 14, a signal representing the true weight by the "spring" method becomes possible with a hanging arrangement for the vibrating surface 3 and the electromagnetic drive 88, for example as shown by the dotted line support wires 75 in place of the wires 2. Such a support arrangement produces a change in the average spring, compression with change in weight on the vibrating surface 3. Such an arrangement in this case requires separate support wires for the electromagnetic drive device 8 and the vibrating surface 3 with positioning of the wires for example as shown, namely that they are not parallel. In the case of the example shown, the average compression to the spring will increase with increased weight upon the vibrating surface 3. Thus with such an arrangement, a signal representing true weight of material upon the vibrating surface will be available as previously described.

With any "two mass" type configuration, both the vibrating surface 3 and the counter weight, namely the drive device 8, will vibrate, the direction of one being 180° out of phase with the other. Under such circumstances the important stroke length of vibration, namely that of the vibrating component 3, will be part only of the total stroke as measured by the displacement transducer 5. A method of producing a signal representing the actual stroke of vibration of the vibrating surface 3 is of course required. Determination of such a signal first requires a signal representing the total weight of the combination of the vibrating component 3 and the mateial thereon which may be achieved as previously explained by the "spring" method. A signal representing the weight of the other contra-vibrating component, namely the drive component 8, is also required. This is of course a constant weight which can be represented by an appropriate signal. In order to produce a signal representing the stroke A2 of vibration of the vibrating surface 3, the weight Ml of the drive component 8 and the weight M2 of the loaded vibrating surface 3 may be applied to the equation

A2=A £

M1+M2

where A is the stroke length signal as measured by the displacement transducer 5. Thus there becomes readily available the stroke of vibration A2 of the loaded vibrating surface for this "two mass" type of configuration. A similar process may be employed on other "two mass" configurations of feeders and conveyors where similar or other support systems can be arranged to permit detection of weight determination signals by the "spring" method.

The above relatively complex way of measuring the vibration stroke on a "two mass" type device may of course be avoided if it is practical to position the displacement transducer between the vibrating surface and an outer stationary framework or part of the building.

Determination of a signal representing maximum acceleration of the vibrating surface with the "two mass" configuration is made possible through the normal equation involving cycle period and stroke of vibration of the vibrating surface as previously described. The detections of the cycle period of resonant oscillation and that of the stroke signal of the vibratory surface are utilized, the latter being produced as previously explained as a mass-dependent proportion of the signal representing the total amplitude of movement as measured by the displacement transducer 5. Determination of the signal representing maximum acceleration together with that representing stroke further enables determination of a signal representing rate of movement of material upon the vibrating surface of a "two mass" device as previously explained. Thus, with the signal representing the weight of material upon the vibrating surface also available, the final signal representing throughput of a "two mass" version of any of these devices becomes possible.

The objective of producing signals representing the various parameters previously described is of course principally to utilize these signals to effect changes to the vibratory motion of the devices in question to achieve the required results. In many cases, the alterations to vibratory motion consist merely of changes made to the stroke length of a generally sinusoidal oscillatory motion, and are generally effected via the output from the processor 14 to the stroke amplitude control circuit 11 and then to the drive control circuit 7. However, various other types of oscillatory motion, for example that of a non-sinusoidal type, are utilized on some presently manufactured devices and it is this type and other novel types of oscillatory motion that may be controlled by the detected parameters previously described and that are produced in a number of ways now to be described. Certain vibratory devices presently operate with a non-sinusoidal waveform of vibratory motion which is utilized in various devices principally to effect control of movement of material upon a vibrating surface. One example of such movement is that produced by cam action in mineral processing "shaking tables". Uses are also made of the system on some types of conveyor. Changes to stroke or waveform of vibration on such presently manufactured devices is not easily achieved since changes to drive belts and/or cams or adjustments thereof are usually necessary to do so. The method now to be described enables one or more of the signals representing the different parameters previously described to control changes in electrical signals which alone can produce alterations to stroke and/or waveform of motion and/or cycle period and/or even direction of motion without stopping the devices to do so. It was previously described how an input of a signal from a displacement transducer 5 to the drive control circuit 7 is required so as to ensure correctly timed pulse signals to produce correctly timed pulses of electrical energy to actuate the drive device 8 to maintain the vibratory motion. Such signals described were to provide sinusoidal vibratory motion and required relatively simple phasing determination. The method of providing non-sinusoidal motion requires more complex and variable phasing according to the type of waveform required. Such phase timings in this case are accomplished by modification to the signal input to the drive control circuit 7 from the processor 14 (see Figure 2) . An explanation will now be given for the timing of such pulse signals to the drive device 88. A sinusoidal motion is typically produced when the timing of the control electrical signals is as shown in Figure 15 where a typical alternating voltage output from the displacement transducer 5 representing the instantaneous position of the vibrating surface is shown by curve 76 and the electrical pulses to the drive device 8 are shown by the waveform 77 where the pulse timing, duration and/or amplitudes are identical for each cycle. Non sinusoidal waveforms are generated in various ways by arranging that the pulling and/or thrusting forces on the vibrating surface are dissimilar for each half cycle. For example, this may be achieved by arranging for different timings of switching on and switching off of the electrical pulses for the respective half cycles so as to produce different durations of force applied for the two half cycles as well as possibly providing strength of forces that are different to one another. Another example, see Figure 16, provides strong thrusting force pulses at positions 78 where the first part of the force is against that of the actual motion, causing a higher than normal deceleration of motion at position 79. Material on a vibrating surface under the decelerating conditions described above will move on such a horizontal vibrating surface in the direction shown by the arrow 80, namely against the direction of the decelerating force. Other pulsing arrangements to produce higher than normal accelerative or decelerative motion might also be employed.

Such methods will produce relatively small variations from a sinusoidal waveform of motion but are still sufficient for some purposes. A method of obtaining a substantial degree of non-sinusoidal vibratory motion for both transport of materials on a surface and to effect other advantageous movements may be achieved by an alteration to the spring arrangement of such resonant vibratory devices. On the devices previously described the spring arrangement is that typically shown in Figure 1 and is such that the action of the springs is linear and usually equal on each side of the central position of the vibratory motion. Production of non-sinusoidal vibratory motion may be brought into effect in the example shown in Figure 17, in which a compression spring 81 is located at one end such that, if there is sufficient amplitude of motion of the vibrating surface 3 in that direction, there will be contact between the vibrating surface 3 and the spring 81. If the spring 81 is of a far stiffer nature than the other springs employed, a new condition will arise where rapid deceleration of motion is caused to the vibratory surface 3 when that surface comes in contact with and compresses the spring 81. A substantially decreased stroke period may also ensue. The deceleration force with such an arrangement can be substantial.

A novel method of bringing such non-sinusoidal motion into action if it is not required continuously and/or of modifying the degree of non-sinusoidal waveform shape will now be described. It will be noted in this description that in addition to the compression spring

81 at one end there is a similar compression spring 82 at the other end. If such a horizontal vibrating surface 3 is caused to vibrate with a stroke that is insufficient for it to hit either of the compression springs 81 or 82 and the motion is of a generally sinusoidal form, no movement of material along the vibrating surface will take place. If, however, inequality of such thrusting forces is applied, the mean position of vibration can be caused to move towards one or other of the compression springs 81 or

82 according to the timing and strength of the pulses applied. Thrust pulses of equal amplitude and duration but in an opposite direction for each half cycle produce the sinusoidal waveform of motion as shown at 76 in Figure 15. However, as shown in Figure 16, if strong thrusting forces are applied in the direction as is shown by the thrusting force trace 78, the first part of the pulse of force provides a strong decelerative motion whilst a strong acceleration is caused in the second half. Under such circumstances the mean position of vibration will move in the direction of the acceleration providing force and the vibrating surface 3 will hit the spring 81 (see Figure 17) . This will cause very abrupt deceleration of the type that will move material upon the horizontal surface in the direction towards the spring 81. With a reversed phasing and direction of pulse forces, movement of material would of course be in the opposite direction.

Thus, by the simple process of changes to the timing and/or strength of the electrical signals to the drive control circuit 7, sinusoidal motion can be changed to no sinusoidal motion to provide a variety of affects. An example of this effect would be with a conveyor where material may be moved at an adjustable rate in either direction. An example of a more violent form of such vibration is on any vibrating device where it is required temporarily to cause violent agitation to clear material from the surface from which it is sticking, or in the cases of screens and/or grizzlies to clear the surface that has become blinded. Very heavy springs or rubber blocks may also be positioned in place of or in addition to and beyond the position at which the springs 81 and 82 are located. These would come into action with an even greater amplitude of movement to produce still higher degrees of deceleration. Additionally or alternatively, as shown in Figure 18, single or pairs of springs or groups of springs 83 may be set at an angle to that of normal motion of the vibrating surface 3. Sufficient motion of the vibrating surface 3 towards the right would cause the vibrating surface first to hit the lower spring and cause a violent upward motion, which motion would be quickly followed by a violent downward movement when the vibrating surface hit the upper spring if this was fitted. Such motion used for a short period will in many cases cause a satisfactory clearance of material that has become stuck or wedged to a vibrating surface.

Certain processing devices requiring or utilizing a vibratory motion in more than one direction can benefit from a resonant system and improvements previously explained. For example, certain types of screens and mineral processing devices benefit from an orbital or elliptical type of vibration. Such vibrations are often produced for these and other devices by rotating eccentric weight systems attached to the vibrating surface. Control of the amount of vibration on such systems is often limited and possible only by stopping the machine and effecting changes to the weights and/or position thereof. Use of the resonant vibration system makes possible changes to the amount of vibration as well as other advantageous effects while the machine is running. Multi-directional vibration can be achieved with the resonant system by arranging for the vibrating surface to be restrained by springs that permit movement in the required directions and maintained in vibratory motion by two or more drive components. For example, as shown in Figure 19 in purely schematic form, a horizontal vibrating surface 3 is suspended by wires 2 from the framework 1 and restrained by springs 4. Drive devices 96 and 97 are positioned so that each provides pulling and thrusting motions to the vibrating surface 3. Each driving device 96 and 97 is provided with an adjacent displacement transducer which is not shown but which provides the necessary signals to control, as previously explained, the required strength, timing and direction of forces to maintain the oscillatory motion. It will be clear that, for example with springs of equal characteristics and with equal pulling and thrusting forces from each of the drive devices but with a 90 phase difference in the timing of the force pulses, an orbital circular vibrative motion of the surface will be achieved. Numerous patterns of vibrating motion would, for example, be produced with changes to relative strength and/or the phase timing and/or spring forces, most of which changes can be achieved whilst running. The inclusion of additional springs as previously explained, to provide non-sinusoidal movement, can also be incorporated to produce violent decelerative and directional change of motion of the vibrating surface.

A further direction of vibrating motion can also be achieved on the above example with the addition of a drive device and associated displacement transducer to produce vertical movements. In practice each addition of a drive device and displacement transducer represents an addition to those parts, shown in Figure 2, which are on the left hand side of the dotted line, but in practice the respective control signals would be likely to be from the same processor 14.

Another example of multi-directional vibrating devices is that of certain vibrating screens employing a complex vibratory movement achieved, as shown in Figure 20, with a motor 98 driving a shaft 99 upon which are mounted eccentric weights 100 and 101 that may be set at different angles to one another to provide orbital and vertical vibrations to the screen bowl 102. The bearing assembly is spring mounted to an outer framework (not shown) to allow vibration to take place. Changes to amplitude or pattern of vibration requires stopping the motion and making mechanical adjustments to the positions of the weights. Elimination of rotating components and complete control for the pattern of vibratory motion is achieved for the resonant system with the arrangement shown in Figure 21 where a shaft 99 carries two weights 100 and 101 each supported by springs 103 attached to an outer framework which is not shown. Four drive devices 104 each provide pulses of pulling and thrusting forces and each is provided with a displacement transducer which is not shown. With appropriate phase timings and strengths of pulses of force from the drive devices, numerous patterns of vibration can be produced and the amplitude thereof can be controlled by changes to the electrical control signals alone.

It will be understood that, in the various embodiments of the invention described above, reference to "springs" and the like is to be taken as including resilient biassing means generally, to the extent that the context permits.

It will be understood from the foregoing that the resonant vibratory system according to the invention enables detection of various parameters and the production of various types and amplitudes of vibration which are, in most cases, under automated control. Such automation of control however usually necessitates the provision of automated measures to prevent a machine, for example, attempting to achieve the impossible, such as providing an excess of stroke length of vibration to cope with an excess of material fed to the machine. Such essential automated controls are now described together with novel improvements involving start up and idling conditions of devices in conjunction with reliability, savings in wear and tear and in power consumption.

In such a resonant vibratory system, a method is essential in some cases and highly desirable in others of assuring a gradual and controlled start to the vibratory motion under all possible conditions together with limiting excessive motion and ensuring minimum motion whilst the machine is unloaded. To achieve these objectives, as shown in Figure 22, the start up of vibration is preferably provided by a method that relies on lack of vibration rather than the effect of the switching on of power. An example of one such method utilizes a comparator 85 which is fed with a signal from the stroke detector 6 and from an appropriately programmed low voltage source 86. Under static conditions when, of course, the signal from the amplitude detector is zero and when the input to the comparator 85 from the low voltage source 86 thus exceeds that from the stroke detector 6, the comparator 85 provides an output signal to start a pulse generator 87 whose pulse frequency is arranged to be near to that of the natural resonant frequency of the device in question. The signal from the pulse generator 87 is fed into the drive control circuit 7 so as independently to cause output energy pulses to the drive device 8 and thus to produce a start to the vibratory motion of the device. Immediately there is a sufficient small amplitude of movement such that the voltage from the stroke detector 6 exceeds that of the low voltage source 86, these two signals are compared by the comparator 85, causing cessation of the pulse generator signal. However, at the same time as the comparator 85 starts the pulse generator 87, it also starts a voltage producing circuit 88, the output voltage of which is arranged to rise slowly. The voltage output from the circuit 88 is fed direct to the drive control circuit 7 to override the normal input from the stroke control circuit 11 with a low level input. However the slowly rising voltage of the circuit 88 allows a slow increase in the amplitude to occur. When the voltage of circuit 88 has reached a value of sufficient magnitude, the overriding of the signal from the stroke control circuit 11 ceases and this permits the normal control of stroke to be restored. Following the build up of vibration, prevention of possible overshoot causing excessive vibration at this or any other stage is preferable and is accomplished for example by the comparator 89 that compares a signal from the stroke detector 6 with that from a programmed voltage source signal 90 representing the maximum permissible stroke of vibration for the device. If the former exceeds the latter then the comparator 89 feeds a signal to the drive control circuit 7 to override the normal input form the stroke control circuit 11 and prevent the stroke of vibration exceeding the pre-set level.

Co-incidentally, at start up of any device, a detection can be made as to whether there is sufficient material upon the vibrating surface to warrant increasing the stroke of vibration to process the material. Such an improvement requires detection that there is no material or only a very small amount of material on the vibrating surface so as to limit the vibration to a low amplitude. One method of so doing requires use of the signal representing the weight of material on the vibrating surface, for instance as provided by the "spring" method. This actual weight signal 91 (see Figure 22) is fed to a comparator 92 that is additionally fed with a signal from a pre-set voltage source 93 representing an appropriate low weight of material remaining on the vibratory surface 3. When the signal representing the actual weight 91 is less than the pre-set voltage 93 representing a very small weight on the vibratory surface, the comparator 92 operates and is arranged to apply a stroke control signal to the drive control circuit 7 which signal represents a low amplitude of vibration. This stroke control signal overrides the normal stroke control signal fed from the circuit 11. When sufficient material again arrives upon the vibrating surface 3, and the signal representing weight 91 exceeds that of the pre-set voltage input 93, the comparator 92 removes the overriding control which allowed only a small stroke of vibration and the normal control of stroke by circuit 11 takes over. Such an arrangement also usefully results in saving of power and wear and tear whenever the machine is switched on but idling, namely awaiting further delivery of feed material.

The invention also includes a method of producing and controlling resonant vibratory motion of a vibrating surface in a resonance vibratory system as hereinbefore described, the method being defined in appended Claim 23.

SUBSTITUTE SHEET

Claims

1. A resonance vibratory system for materials handling and processing, the system comprising a surface resiliently mounted for vibration, means to measure the vibratory displacement of the surface, means to provide a signal to a driving device to maintain the resonant vibratory motion of the surface, means to measure the time period per stroke, means to measure the power required to maintain the vibration, and a control circuit for the various said means, wherein the control circuit includes signal processing means whereby a signal representative of vibratory displacement is capable of being compared with a signal derived directly or indirectly from the measurement of displacement and/or time period per stroke and/or maximum acceleration and/or maximum velocity of the vibrating surface and/or weight and/or mobility and/or movement and/or throughput of material upon the vibrating surface and/or with an external signal to provide an adjustment to the displacement or an override instruction to the normal vibratory motion control to alter the displacement and/or waveform and/or frequency and/or direction of vibration and/or to provide an output signal to influence an external device.

2. A resonance vibratory system according to Claim 1 for measurement of the weight of material on the vibrating surface, in which the means to measure the vibrating displacement comprises a displacement transducer, in which the transducer produces in use an alternating voltage having a direct current component representative of the weight of material on the surface, the system also including an averaging circuit.

3. A resonance vibratory system according to Claim 2, in which the averaging circuit is a fast averaging circuit for determining the mean voltage or direct current component when the vibration frequency is low.

4. A resonance vibratory system according to Claim 2 or Claim 3, in which the control circuit includes means to compensate for inaccuracies and/or ageing factors.

5. A resonance vibratory system according to Claim 1 for measurement of the apparent weight of material on the vibrating surface from the resonant frequency, the system comprising means for measurement and processing of the vibratory time period per stroke and means for correction of the processed signal to compensate for damping effects.

6. A resonance vibratory system according to any preceding claim for measurement of the mobility of material on the vibrating surface, the system comprising means for comparison of the apparent weight of the material with the true weight of the material and deriving a signal representative of mobility.

7. A resonance vibratory system according to Claim 6, for measurement of the extent to which material on the vibrating surface is rendered immobile, the system additionally comprising means for comparison of the derived mobility signal with a predetermined threshold signal representing the desired mobility, and means dependent on the resulting immobility signal for instituting a remedial action.

8. A resonance vibratory system according to Claim 6 or Claim 7, the system including means for combining and/or comparing the mobility signal with the power consumed in producing vibration of the surface, to effect separation to some degree of signals representing mobility, immobility and friction of and within material on the surface.

9. A resonance vibratory system according to Claim 8, further including means for utilization of the derived signals of mobility, immobility and friction to effect control or correction of the vibration.

10. A resonance vibratory system according to any of Claims 6 to 9, the system comprising means to effect an occasional automated short term variation to the stroke of the vibrating surface and for the detection during the said stroke variation of relative changes to the signals representative of mobility and power being consumed.

11. A resonance vibratory system according to any preceding claim, the system comprising means for determination of a signal representing maximum acceleration of vibration, the said means utilizing the displacement transducer for measurement of the vibrating displacement of the component in combination with a division, squaring and multiplying circuit.

12. A resonance vibratory system according to Claim

11, further including means to derive from the acceleration signal a signal representing rate of forward movement of material on the vibrating surface.

13. A resonance vibratory system according to Claim

12, further including means to measure delivery rate of material from the vibrating surface, the said means comprising respectively means to determine the forward movement of material upon the vibrating surface and the weight of material thereon, and means for processing the signals produced to derive a signal representing delivery rate.

14. A resonance vibratory system according to any preceding claim, the system being applied to a spring-coupled two mass resonant vibratory device.

15. A resonance vibratory system according to any preceding claim, the system being applied to a non-sinusoidal vibratory device to effect control of movement of material thereon by controlling the timing and/or amplitude and/or direction of pulses of force applied to the vibrating surface.

16. A resonance vibratory system according to Claim

15, the system including rebound spring means at one or each end of the vibrating surface, whereby to produce increased deceleration of motion in one or each direction and/or a decreased stroke period on contact of the vibrating surface with the or a spring, thereby creating enhanced non-sinusoidal vibration motion.

17. A resonance vibratory system according to Claim

16, in which the spring means are set at an angle to that of normal motion of the vibrating surface, to provide a variable degree of alteration to the direction of vibration.

18. A resonance vibratory system according to any preceding claim, the system including two or more drive components for elliptical, orbital or other vibration in two or more directions, the control circuitry being arranged to effect changes to the vibration parameters while the system is in operation.

19. A resonance vibratory system according to any preceding claim, including means for providing a gradual and controlled initiation of vibration, the said means being arranged to operate in response to lack of vibration.

20. A resonance vibratory system according to Claim 19, the initiation means comprising a stroke length detector and a low-voltage source, outputs from which are respectively fed to a comparator, the comparator output being connected firstly to a pulse generator the pulse frequency of which is arranged to be close to the natural resonance frequency of the vibrating surface, the pulse generator output being connected to the drive control circuit so as independently to cause output pulses to the drive device to initiate vibratory motion, and the comparator output being connected secondly to a voltage producing circuit the output of which is arranged to rise in a controlled manner and is fed to the drive control circuit to override the normal input from a stroke control circuit with a low level input.

21. A resonance vibratory system according to any preceding claim, including means to limit the maximum vibration displacement.

22. A resonance vibratory system according to any preceding claim, including means to reduce the vibration displacement when no material or only a small amount of material is present on the surface.

23. A method of producing and controlling resonant vibratory motion of a vibrating surface in a resonance vibratory system for materials handling and processing as claimed in any of Claims 1 to 22, the method comprising comparing a signal representative of vibratory displacement with a signal derived directly or indirectly from measurement of displacement and/or time period per stroke and/or maximum acceleration and/or maximum velocity of the vibrating surface and/or weight and/or mobility and/or movement and/or throughput of material upon the vibrating surface and/or with an external signal and applying the comparator output to a control circuit to adjust the displacement or to override the normal vibratory motion control to produce alteration of the displacement and/or waveform and/or frequency and/or direction of vibration and/or to provide an output signal to influence an external device.