GB2030731A - Vibratory Conveyors - Google Patents

Abstract

A vibratory conveyor, such as a bowl feeder, is provided with a drive to cause generally vertical and horizontal vibrations. The drives are preferably independently controllable in amplitude and of adjustable frequency. Control circuits are provided to produce vibrational amplitudes selected as appropriate to the load conveyed. An excess horizontal vibration amplitude is sensed for example via an electromagnetic transducer SC, providing a signal (FCin) for use with a reference signal (REF) to cause the supply of more load (FA, FG) to the conveyor for a prescribed time, enabling substantially constant load operation for consistent conveying. An excess vertical amplitude signal which may be derived from the drive energization, may be used similarly to maintain a selected vertical vibration by altering energisation (VUver) as load reduces, thereby providing efficient conveying conditions while emptying the bowl of the conveyor. The vertical signal is also usable to cause the supply of more load to the conveyor. <IMAGE>

Description

SPECIFICATION Vibratory Conveyors This invention relates to vibratory conveyors.

Vibratory conveyors for piece-parts are known in which a part-supporting platform is vibrated both up and down and to and fro. The movement can cause the parts to move up an inclined platform of the conveyor. The parts may then enter a guide all arranged in one sense only to be guided to a subsequent work station.

In one form such conveyors are bowls with a ledge on the inside of the bowl inclined up towards the rim of the bowl. Parts placed in the bowl are vibrated with the bowl to be fed onto and then up along the inclined ledge over or through the bowl rim and into a guide. In one known form of such conveyor the bowl is resiliently suspended and driven by a single actuator, e.g. a supply mains frequency impulser, against the resilience of the suspension to produce both the up and down and the to and fro vibratory movements. However in this arrangement the relation between the phase and amplitude of the two movements is fixed by the construction of the conveyor resilient support and cannot be altered easily, if at all, in use. Also the impulser operates at only one frequency and amplitude.In another form of such conveyors the bowl is driven by separate drive means, one for the up and down motion the other for the to and fro motion. In this way the relation between the motions can be adjusted in amplitude and phase.

The phase between the components of the drive frequency bringing about the two motions is altered to produce movement of the bowl in a closed loop by use of suitable phase shifting means. UKPS 1154042, and equivalent USPS 332793, describes such a form of conveyor.

However, despite the control of feed conditions produced by the last-described device there are still some shortcomings. The feed efficiency can very with the load on the conveyor and the vibration of the load can generate a great deal of noise.

Unless the quantity of parts on the conveyor is kept fairly close to a selected amount the speed of feed is impaired. To provide some degree of quantity control it is known to pivot a paddle over the bowl to be displaced as the bowl contents level changes. A microswitch operated by the paddle at a selected position brings about the supply of more piece parts as the bowl contents level decreases and stops the supply as the bowl contents level increases. However the paddle control is responsive only to the contents level at one position in the bowl, is fragile and not very sensitive, and is easily damaged or put out of adjustment. Conveyor operators generally prefer to control the supply of parts manually to achieve best results.To reduce noise the bowl is surrounded by heavy sound-absorbing covers and the bowl is often lined with felt but these techniques are of littie total effect as firstly apertures have to be left for piece part supply and secondly operators cannot check the action of the feeder without opening the covers.

There is therefore a need to improve the conventional bowl feeder to achieve higher, reliable, feed rates at a lower noise level.

It is an object of the invention to provide an improved vibratory conveyor in which feed efficiency is less dependent on load.

According to the invention there is provided a vibratory conveyor including a substantially imperforate load supporting platform, resilient mounting means for the platform permitting vibratory platform movement with reference to a desired direction of movement of load, driving means arranged to urge the plafform to vibrate to and fro and up and down in a closed loop motion, and further means responsive to the amplitude of the operational motion in at least one direction and responsive to a reference signal representing a selected value of this amplitude to control the amplitude in said at least one direction to conform to the selected value.

There may be first and second controllable driving means respectively for the first and second directions. The driving means may be controllable to produce motion amplitudes in the first and second directions independently of each other.

The motion amplitude may be reduced by causing an increase in the load on the conveyor or by reducing the drive means energisation. The conveyor may be operated to convey a reducing load to empty the conveyor under a substantially constant amplitude up and down vibratory motion set by the reference signal. The conveyor may be operated at substantially constant load by supplying load to the conveyor to result in a to and fro vibratory motion amplitude less than a selected maximum value at a selected energisation of the drive means.

The to and fro and up and down motions may differ. The motions may be set having regard to the natural vibrational frequency of the vibratory platform in at least one direction; The one direction may be the horizontal direction or the vertical direction. The drive means may have controls settable with reference to the behaviour of the loaded conveyor to establish the optimum operating conditions in terms of frequency, amplitude and phase and retain these as reference values.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a pian, partly in cut-away, of a vibratory bowl conveyor drive means, Figure 2 shows a cross-sectional view of the drive means of Figure 1, Figure 3 is a general view of a bowl conveyor, Figure 4 is-a circuit diagram of a bowl conveyor feed control, and Figures 5 and 6 show block schematic diagrams of vibration conveyor control circuits.

Referring initially to Figure 3, this shows a general view of a bowl conveyor or feeder. The conveyor is supported on a substantial plinth P which may be fabricated from steel plate and structural sections stiffened with suitable gusset plates. The top of the plinth provides a table T upon which the conveyor itself is mounted. A strong steel ring R is resiliently supported from the table T, as shown in more detail in Figures 1 and 2 referred to later, and from ring R a further strong stiff steel plate PL is resiliently supported.

The conveyor bowl B is attached to plate PL. The bowl B is of general conventional form but includes several features to improve its performance when compared with conventional bowls. The centre of the bowl has a bowl cone BC and around the inside of the bowl is an inclined platform Bl insulated from the bowl by a layer of acoustic insulating material INS. A suitablyshaped aperture in the bowl wall, not shown, permits piece parts moved up the inclined platform BI, and arranged in a selected sense if required, to emerge from the bowl into a peripheral chute CH. This chute is attached to the outside of the bowl for at least part of its length.

This chute conveys parts all arranged in the same sense to a subsequent work station. Parts may be fed to the bowl from time-to-time from a hopper H through a vibrated feed tray FT leading to a feed guide FG directed towards the bowl cone BC.

Various electromagnetic actuators are employed in the operation of the conveyor, as will be described later, and means are provided in the form of electronic circuitry to energise and control these actuators. Conveniently the circuitry is mounted on plinth P and is in two portions. A vibrator unit VU energises and controls the drive means for the bowl while a feed control unit FC energises and controls the feed tray FT to supply piece parts to the bowl.

Referring now to Figures 1 and 2, these show in more detail the drive means by which the bowl B is vibrated to and fro and up and down to convey the piece parts up the incline Bl towards chute CH. In the particular case illustrated of a bowl conveyor the to and fro motion is actually a rotary vibration. However if the invention is embodied in the form of a linear conveyor the to and fro motion would be longitudinal and the term to-and-fro and up-and-down include motion in straight and curved paths. Referring to Figure 2, which shows an embodiment suitable for a 670 mm (27") bowl, table T is a relatively massive steel plate some 1 3 mm thick, and 600 mm across. Ring R is some 610 mm in diameter and some 100 mm wide and formed from 6 mm thick steel.Ring R is attached to table T by three springs units one of which is indicated at reference HS. The units may be tilted slightly to give a twisting action to ring R. The spring units HS are spaced equally around the ring and are resilient in a horizontal direction to permit ring R to turn a small amount about its perpendicular axis of symmetry to execute the to and fro motion as a horizontal vibration. Each "horizontal" spring HS is of generally U-form each limb of the U being resilient and the bend of the U being rigid. In one form each horizontal spring HS is fabricated from leaf-spring limb elements and stiff link elements.

Each limb of the U is typically formed from four spaced-apart strips of some 20x4 mm cross section linked by a 20 mmxl 0 mm bar. One limb is bolted to table T and the other limb to ring R by a suitably massive angle bracket. In one embodiment the strips are of unannealed "gauge" plate to ensure consistent thickness. Clearly other steel material, e.g. spring steel, is suitable. Other materials are also suitable when prepared with the required stiffness and consistency, e.g. fibre glass or carbon fibre based composites.

There are three similar horizontal drive actuators, indicated at HA1, HA2 and HA3. Each actuator includes a E-shaped core of magnetic material, e.g. laminations supporting an energising winding and an associated but separate I-shaped armature completing the actuator magnetic circuit but not connected to the E-shaped portion. Each armature is attached to ring R. The E portions and the winding are securely mounted on the table T so that when the winding is suitably energised the armature is attracted and released in a controlled manner flexing the spring HS and causing the ring R to vibrate as described above. It should be noted that in addition to permitting this vibration the springs HS must also support the dead weight of plate PL and bowl B and other equipment.

A plate PL of at least as massive a construction as ring R is fitted in the aperture in ring R but spaced from the inner side of ring R. Plate PL is supported by and connected to ring R for vertical vibration by at least three similar "vertical" springs VS. Each vertical spring VS is of U-form and has limbs each of two lengths of 6 mmx2 mm steel bar joined by a stiff limb and securely bolted to ring Rand plate PL. Preferably three springs VS are spaced equally around the periphery of plate PL. Plate PL is caused to execute vertical vibrations by a vertical actuator VA of generally similar form to the three horizontal actuators HA, etc. The E-shaped core part of vertical actuator VA is secured to table T beneath the center of plate PL. The armature of vertical actuator VA, of I-shape, is connected to the centre of plate PL.

With the arrangement thus far described it can be seen that plate PL can be caused to execute vertical, up and down, motion and horizontal, to and fro, motion by suitable energisation of the vertical and horizontal actuators. The frequency and amplitude of the vibrations will be determined by the energisation of the actuators together with the characteristics of the vertical and horizontal springs. For an equipment dimensioned as described above, which is suitable for a cast aluminium bowl of some 670 mm diameter, the natural frequency of the suspension "horizontal" spring's HS is in the order 30 Hz and typically 26 Hz. For smaller bowls, say 520 mm (21"), the frequency is typically 29 Hz. Clearly other values and sizes are possible for example a lighter bowl, say of stainless steel, can operate at a natural frequency of some 35 Hz.The same amplitude of vibration being maintained the feed rate is appropriately higher. Preferably the springs are designed so that the natural frequencies of vibration in the horizontal and vertical directions are separated by a significant amount, that is at least 10 to 15%, so that distinct control can be achieved. Preferably the "vertical" frequency is some 12% higher. In operation the horizontal, to and fro, vibration is at substantially the natural frequency of the suspension. The vertical, up and down, vibration is usually at a frequency, the horizontal frequency, below the natural vertical frequency as a fixed phase relationship is needed.

A search coil SC is mounted on table T adjacent to one of the horizontal springs HS to detect the motion of the ring R by means of a magnetic coil core or ring R. The design of the search coil is not critical and will be readily apparent to those skilled in the art, as will what winding is required on the coil to provide an adequate output signal having regard to the size and motion of the ring R. Suitable terminals, SCT are provided so that connections can be made to the search coil for associated apparatus. Suitable terminals or connectors, not shown, are also provided for the actuators so that these can be energised from associated electrical equipment.

Reverting to Figure 3, this shows the general electrical layout of the equipment and controls and connections. Vibrator unit VU contains amplifiers and an oscillator, preferably of solidstate form, to produce suitable energising signals of different and controllable frequency, amplitude and phase for the vertical actuator VA and for the horizontal actuators HA, etc. The signal for the vertical actuator is identified by reference VUver and that for the horizontal actuators by reference VUhOr. Preferably these signals are pulses of d.c.

lasting between 3 and 30 ms at a rate of 20 to 30 pulses per second. Currents of some tens of milliamps at a few hundred volts d.c. may be used. In hazardous areas, or to ease insulation problems, low voltage (24v) and higher currents may be used, with appropriate modifications. The same output of search coil SC is supplied via terminals SCT both to the vibration unit VU and to the feed controller FC. The input to the vibration unit is indicated as VUIn and that to the feed controller as FC1n. Clearly in other embodiments of the invention it may be preferred to use part only of the search coil output for one or other of the inputs or to derive the inputs from separate search coils or other transducers, e.g. optical, electromagnetic or dectrostatic, on the drive circuits or actuators themselves.Such provisions will be readily apparent to those skilled in the art in any particular case.

The detailed circuitry of vibrator unit VU and feed control FC will not be described except where relevant to the present invention as suitable circuitry will be readily apparent to those skilled in the electronic art. However to assist in understanding the invention the performance of one embodiment of this circuitry will be outlined.

Considering first vibrator unit VU this is provided with five main controls. These are as follows: a clock control CK, a horizontal sync delay control HSD, a vertical phase control VP, a vertical energisation control VE, and a feed rate control FR. Other minor controls such as on/off switches etc. are provided. Briefly the operation of the vibration unit is as follows. The equipment is switched on and with the bowl empty but being vibrated in both the two and fro and up and down directions the clock control is adjusted to vary the horizontal excitation frequency from a value below the natural frequency of the horizontal suspension. This is easily detected by observing the horizontal vibration of the bowl which reaches a maximum at or near this natural frequency. The clock control is then locked.The horizontal sync delay and vertical phase controls are then adjusted to cause the bowl to execute a closed loop motion. This is most easily done by placing some parts of the type to be conveyed in the bowl and adjusting the controls to produce the forward and upward motion of the parts along the incline BI. It is to be noted that by adjusting these controls the parts can be made to move forward, stand still or go down the incline as desired. The vertical excitation and feed rate are then adjusted as desired. It is to be noted that the feed rate control is effectively a horizontal excitation control. In adjusting these controls the aim is to cause the bowl to vibrate only by that amount which is necessary to convey the parts so that the noise generated by the vibration is kept to the minimum and the power input is reduced as far as possible.

The conveyor is now ready for use to convey parts fed into the bowl from the hopper H towards the chute CH, all the parts entering the chute being aligned in the same sense. It has been found that the conveyor works more efficiently when initially filled to a selected level and the maintained filled to within + 10% of this level with the parts to be conveyed. Wider tolerances are possible, up to +20%, as are narrower tolerances if cost permits. The tolerance used can depend on the parts to be conveyed. The lower end of the range is usually more important in its effect on efficiency. In the past the level of filling has been maintained either by having an operator watch the bowl to feed parts by hand when required or by having an automatic feed controlled by a paddle suspended over the bowl so that when the parts fall below a set level the paddle operates a microswitch to cause parts to be fed automatically until the microswitch is released by the raising of the paddle on the fed parts accumulating in the bowl. The manual technique is unsatisfactory in that it ties the operator to a more or less continuous watch on the machine and can lead to overfilling or underfilling of the bowl if the operator is not diligent. The paddle controlled feed is erratic in its action as the paddle is not a very sensitive device and can only respond to the height of the parts at one point in the bowl.Although the paddle is not very sensitive it is a very fragile device and is liable to be broken or distorted in use.

In the illustrated embodiment the control of the supply of parts to the bowl conveyor is controlled by sensing the motion of the bowl rather than by sensing the level of the parts present in the bowl.

To this end a further signal is derived from the search coil SC, this signal is identified as FCjn, mentioned above. This signal is derived from the to and fro motion of the bowl and indicates the amplitude of this motion. The feed control circuit FC is responsive to the amplitude of this signal and a reference signal value indicative of the required amplitude of the to and fro motion of the bowl. When the actual motion exceeds the desired value the feed control FC is effective to cause more parts to be fed into the bowl.

The detailed operation of this feed control will now be described with reference to Figure 4 which shows in outline the circuit of the feed control FC. The feed control FC consists of seven different stages. A low pass filter, LPF receives the signal FC,, from the search coil. The output of the filter is supplied to a peak detector PD which supplies a signal representing the peak value of the vibration of the bowl to one input of a comparator COMP the other input of which is supplied with a reference signal from a reference circuit REF. The output of the comparator is supplied directly to one input of a logical OR circuit LOR and indirectly, via a monostable MS, to the other input of circuit LOR. The output of logic stage LOR is connected to a driver circuit DR.The driver circuit DR supplies an output signal FCaut of sufficient power to switch off and on a feed actuator controller FAC which controls the energisation of an actuator PA for feed tray FT.

Actuator FA is conveniently a mains-frequency vibrator. The action of feed control circuit FC is that when the amplitude of the horizontal vibration of the bowl exceeds the reference value set by circuit element REF the comparator COMP supplies an output directly to one input of the OR gate to cause the driver stage DR to supply signal Flout to energise the actuator FA to feed piece parts into the bowl B. The output of circuit element COMP also starts the timing action of monostable MS to ensure that the feed actuated by actuator FA is continued for at least the period timed by monostable MS.If at the end of this timed period insufficient parts have reached the bowl B so that the reference value REF is still exceeded the direct connection to the OR gate LOR ensures that piece part supply is continued until demand is satisfied. The provision of monostable MS reduces the possibility of hunting with the consequent frequent supply of small numbers of piece parts. Periods of between 5 and 60 seconds have been found generally suitable.

While the general range of the reference value REF can be predicted the exact value depends to a certain extent on the individual bowl and the nature of the piece parts being conveyed. To this end the circuit shown in detail in Figure 4 is provided with setting-up controls to enable an operator or a more-skilled machine setter to set the control arrangement for a particular use of the conveyor. A preset control BPS is associated with the low pass filter LPF to adjust the filter to match to the particular bowl installed in the conveyor.

This control does not need to be adjusted by an operator in normal use of the conveyor. The feed level adjustment control FLA sets the reference level for the comparator. Two light-emitting diodes Ii, 12 are provided to assist the operator in setting the feed level.

The circuit will not be described in detail as the component types and values will be apparent from Figure 4. It is observed that the low pass filter, peak detector and monostable are based on integrated circuits whereas discrete components are used for the comparator, the diode OR gate and the output stage DR. The comparator inputs are in opposite sense and arranged to respectively charge and discharge capacitor C, which capacitor is also steadily discharged by resistor R.

The monostable timing is controlled by capacitor T. The signal from the output stage is of relatively low power being required only to drive a contactor or like device which connects the supply means via connection FE to the actuator FA. A power supply unit PSU supplies smoothed DC for the signal-processing stages and raw DC for the driver stage DR.

The greater degree of control exercisable by the present embodiment on the horizontal and vertical energisation permits a more accurate matching of the bowl vibration to the parts to be conveyed and no more energy need be supplied than is required to cause the parts to execute the required trajectory in moving up the incline in the bowl. The reduction of power input and the consequent more precise matching of the vibration to the piece parts greatly reduces the noise level of the equipment thereby reducing operator fatigue and generally improving the factory environment. The heating of the actuator coils is also reduced, extending their life.

The bowl may be cast in aluminium with the casting designed so that there is no significant out of balance force due to a heavy concentration of metal at any one point. The incline track Bl is not attached directly to the bowl B but an insulating layer is interposed to reduce the noise due to the motion of the parts on the track. The track BI is prefeably of austenitic stainless steel and the insulator is a layer of rubber some 3 to 6 mm thick. The cone BC is also of stainless steel and may be supported on acoustically insulating material if required. The various measures taken to reduce the noise from the apparatus are successful in that whereas hitherto vibratory bowl conveyors have had to be fitted with acoustic shields and covers and have still been extremely noisy, the conveyor embodying the present invention is sufficiently quiet to be operated without such covers and still only produce a moderate and generally acceptable noise level.

The arrangement described so far thus produces a more efficient and more acceptable bowl conveyor in that operation is quieter and that the supply of piece parts is controlled automatically. In a typical application to the feeding of sparking plug piece parts to a welding machine conveying rates closely approaching 20,000 in an 8 hour shift have been attained during trials. The less-vigorous vibration and more controlled manner of operation greatly reduce the wear and tear on the machine and therefore longer reliable operation is achieved with less maintenance.

The technique of monitoring the degree of loading of the bowl by examining the motion of the bowl leads to other applications. It is very often desirable that all piece parts be emptied from a bowl conveyor, for example when the nature of the piece part to be conveyed is changed slightly. Hitherto the unalterable operating conditions have meant that as the load involved fell due to the disposal of piece parts the feed and conveyance became increasingly less efficient and reliable. So much so that it is probably necessary to empty the last few piece parts out by hand. Two further embodiments of the invention will now be described whose action is to control the motion of the bowl as the quantity of piece parts diminishes so that consistent operation is obtained while the piece parts are finally fed out of the bowl.

Figure 5 shows an arrangement based on search coil similar to that described above but now effective to monitor the vertical vibrations of the bowl. Figure 5 shows a block schematic diagram of an electronic circuit to utilise the output of such a search coil to control the amplitude of vertical vibration. The circuit has some elements similar to that described above with reference to Figure 4. Thus a low pass filter and peak detector are responsive to the output of the search coil to give a signal representing the amplitude of vertical oscillation. This signal is linearised in circuit element LIN and compared with the reference signal for the vertical vibration, Vref, to produce an error signal indicative of the change in the energisation of the bowl required to restore the vibration to the desired value.The action of this circuit is to control the bowl vibration so that piece parts in the bowl execute the same trajectory and therefore are fed and conveyed in the same manner regardless of the number of parts remaining in the bowl. In this way the feed rate from the bowl is maintained at an optimum level and the bowl can be caused to empty all the remaining piece parts in an efficient manner if this is desired.

Figure 6 shows another embodiment in which this time instead of sensing the movement of the bowl with a search coil the waveform of the drive current for the vertical actuator VA is derived from I energisation VUver. The current waveform indicates the motion of the bowl with respect to the actuator magnet and this in turn is an indication of the load in the bowl. By suitable processing filtering and peak detection, as shown by the block schematic in Figure 6, a control signal can be derived having regard to a reference value and this control signal used to control the energisation of the bowl so that, as in the embodiment just described, optimum feed rate and self-emptying for the bowl are obtained.

The circuit elements in the embodiments just described with reference to Figures 5 and 6 can be similar to those described with reference to Figure 4, with obvious modifications where appropriate for different frequencies or other parameters. Those circuits not shown in detail, such as the linearising and dividing circuit elements, can be any of those described in the standard textbooks on electronic circuit design.

Those skilled in the art will find no difficulty in making any minor adaptations required to a particular circumstance.

As mentioned above vibratory conveyors can be associated with another machine, or machines, to carry out manufacturing operations on the parts conveyed by the conveyor. In general a particular combination of conveyor and such machines will be set-up to operate at a feed rate appropriate to the operation carried out. The flexibility of controlled operation provided by the equipment described does however permit this feed rate to be adjusted to suit the operation. As the energisation of the conveyor is increased the feed rate increases and vice versa. The signals representing actual conveyor vibration can therefore be used in conjunction with a reference signal whose value is controlled by the associated machine to produce the appropriate feed rate.

Sensors on the machine can supply a reference signal value varying from time to time in response to, e.g. insufficient part supply or oversupply of parts to speed up or slow down the conveyor.

The invention has been described in terms of a bowl conveyor specifically designed to provide a suitable control signal and include drive control arrangements. However the invention can also be applied to modify and improve many existing types of vibratory conveyors by incorporating a suitable transducer, such as the coil and magnet mentioned above, and a drive control circuit. In this way the operation of the many vibratory conveyors already in use can be made more efficient without incurring the heavy cost of complete replacement.

The arrangements and techniques described above permit the improvement of vibratory conveyors, particularly those of the bowl feeder type, to both increase the efficiency with which piece parts are conveyed and fed and to reduce the noise and wear and tear due to the operation of the machines. An optimised feed rate can be maintained for longer periods without attention reducing the amount of time an operator must spend watching the machine so improving productivity and the use of resources.

Claims (11)

Claims

1. A vibratory conveyor including a substantially imperforate load supporting platform, resilient mounting means for the platform permitting vibratory platform movement with reference to a desired direction of movement of load, driving means arranged to urge the platform to vibrate to and fro and up and down in a closed loop motion, and further means responsive to the amplitude of the motion in at least one direction and responsive to a reference signal representing a selected value of this amplitude to control the amplitude in said at least one direction to conform to the selected value.

2. A conveyor according to Claim 1 in which the further, amplitude, control means is operable in response to an excessive amplitude to reduce the motion amplitude by causing at least one of an increase in the load on the conveyor and a reduction in the energisation of the drive means.

3. A conveyor according to Claim 1 in which the reference signal is derived from associated equipment supplied from the conveyor and indicates a required rate of supply, the amplitude of vibration in at least one direction being thereby controlled to achieve a required rate of supply.,

4. A conveyor according to Claim 1 or Claim 2 in which the further, amplitude, control means is responsive to a signal representing excessive motion amplitude in substantially that direction in which a load is to be conveyed and to the reference signal for this motion to actuate means to load the conveyor to increase the conveyor load to reduce the excessive motion signal value towards or below the reference signal value, whereby the conveyor is operated at substantially constant load for a given energisation.

5. A conveyor according to Claim 4 which is a bowl conveyor associated with a source of pieceparts to bs aligned and guided to a work station by the action of the conveyor, the conveyor including means responsive to the motion of the bowl substantially in the to and fro sense to generate a respective motion amplitude signal, and the source of piece parts including means selectively operable in response to a feed control signal to feed parts from the source to the conveyor, the further, amplitude, control means including a control arrangement responsive to the motion amplitude signal to filter said signal and derive the peak value thereof, means to generate a reference signal of a value of a desired peak value of the motion amplitude signal, means to compare the derived and generated signal values and produce a feed demand output when the derived signal value is deficient, a period timer started on the production of said output, logic means responsive to the feed demand output and the timer output provide a feed control input to a power stage of the control arrangement providing the feed control signal so long as either the period is being timed or the feed demand output is maintained, parts thereby being fed to the conveyor for at least a minimum time, said period, to maintain a motion amplitude generally below a selected maximum.

6. A conveyor according to any one of Claims 1 to 5 in which the means responsive to the amplitude of the conveyor motion is a transducer responsive to relative motion of platform parts on either side of a resilient support.

7. A conveyor according to Claim 1 or Claim 2 in which the further amplitude control means is responsive to a signal representing excessive motion amplitude in a direction substantially perpendicular to that in which a load is to be conveyed and to the reference signal for this motion to actuate means to reduce the energisation of the conveyor drive means to reduce the excessive motion signal value towards or below the reference signal value whereby the conveyor is operated at substantially constant vibration amplitude in said direction to permit a reduction of load conveyed from full load to zero without substantial change in the conveying conditions.

8. A conveyor according to Claim 7 which is a bowl conveyor arranged to align and guide piece parts loaded into the bowl individually to a work station by the action of the conveyor, the conveyor including means responsive to the motion of the bowl substantially in the up and down sense to generate a motion amplitude signal, the bowl drive means for this sense being graduable in operation in response to a drive control signal, the further, amplitude control means including a control arrangement responsive to the motion amplitude signal to filter said signal and derive the peak value thereof, linearise the derived signal, means to generate a reference signal of the value of a derived linearised peak value of the motion amplitude signal, means to generate an error signal from the derived and generated signal values and produce a bowl drive means control signal in accordance with the error signal to graduate the operation of the drive means to maintain a motion amplitude in said up and down direction substantially constant in accordance with the reference signal value when the load on the conveyor varies, in operation, from full load to zero, to empty the conveyor thereby while maintaining efficient conveying of parts.

9. A conveyor according to Claim 7 which is a bowl conveyor arranged to align and guide piece parts loaded into the bowl individually to a work station by the action of the conveyor, the conveyor including means to drive the bowl to vibrate substantially in the up and down sense, the drive means including means to sense the drive energisation and derive therefrom a signal representing bowl vibration amplitude in said sense, means to sample and filter the derived signal and to detect the peak value thereof, means to generate a reference signal for the desired peak value of the vibration amplitude signal, vertical drive control means responsive to the detected and reference values of the vibration signal to control the drive energisation to maintain a substantially constant amplitude of vibration in said up and down sense whereby, as the load on the conveyor varies, in operation, from full load to zero, to empty the conveyor while maintaining efficient conveying of parts.

10. A conveyor according to any one of the preceding claims including first and second controllable driving means arranged respectively to urge the platform to vibrate to and fro and up and down with the vibration amplitudes in the first and second directions controllable and independent of each other.

11. A conveyor including a vibration amplitude control arrangement substantially as herein described with reference to the accompanying drawings.