GB2145584A - Electrically energised vibratory conveyors - Google Patents

Abstract

A linear vibratory conveyor drive circuit has electromagnetic actuator windings LA, LB. The windings are supplied from DC lines ST1, ST2 over a bridge circuit including diodes D1, D2 and transistors Q2, Q3 or thyristors. The transistors are turned on simultaneously by a control signal supplied to an FET Q1. When the transistors are turned off, the diodes provide a reverse path to the supply. <IMAGE>

Description

SPECIFICATION Electrically energised vibratory conveyors This invention relates to electrically energised vibratory conveyors which form a reactive load and areexcited ata selected frequency with controlled phase relationships.

Controlled phase vibratory conveyors,for example ofthe type disclosed in UKPS 1154042 provide a much better technique for conveying articles than simple vibratoryconveyors. As energisation ata selected frequency, which may need to be varied, and with a controlled phase relation between two energisation senses is required electrical power is a convenient form of energisation for such conveyors. However, there are still many factors in electrical energisation which give rise to problems. These include economy of power, to avoid undue heating of windings, control of ci rcuit voltages, to avoid damage to semiconductor devices, and control functions so that users can employ the conveyors without the need for extensive training in their use. It is also desirableto make the conveyors as compact as possible.A phenomenon affecting several of these factors is the voltage transient arising when a unidirectional current through an inductive load is interrupted. This occurs regularly because ofthe need to control amplitude and phase of energisation. These voltage transients can appear across the active semiconductor devices used to bring about the interruption and/or reversal of current and therefore the designer must use devices with voltage ratings significantly higher, at least two orthreetimes the voltage ofthe unidirectional supply.

This increases the cost of the devices and therefore the cost of the equipment.

It is an object ofthe invention to provide an improved electrically energised vibratory conveyor of the controlled phase type.

According to the invention there is provided a linear vibratory conveyor drive unit including a rigid base frame, resilient support members extending from the base frame, and an output member supported by the resilient members, the output memberto be capable of vibration in two directions substantially at right angles on the resilient support members, the unit also including first and second electromagnetic actuators on the base frame and respective first and second actuator armatures, the actuators to be energisable to act on the armatures to cause said vibration of the output member, together with electrical circuit panels mounted on the base frame to enclose the actuators and extend from the base to provide such enclosure, the electrical circuit panels supporting drive circuit elements, for applying a drive current to the actuators, andusercontrnl meansto enable the setting ofthe frequencyand/or amplitude and/or phase ofthe drive totheactuators together with power supply means for thecircuit panels whereby vibrations of controlled phase relation are produced.

There may be a subsidiary frame connected to the resilientsupportmembers,further resilient support members extending from the subsidiary frame and connected to the output member, andthefirst actuator armature connectecfto the subsidiary frame, and the second actuator armature connected to the outputmember,thesubsidiaryframeforming partof said enclosure ofthe actuators.

The drive circuit may include a reverse-conductivity path foractuator drive current.

In this way an alternating current flows in the load while energy is returned to the supply when the current control devices turn off, reducing the reverse voltage across the devices.

Convenientlythe current control devices are transis- tors, although SCR devices with associated commutation arrangements may be used. Advantageously the current control devices have a breakdown or like voltage rating of less than twice the supply voltage value.Asafety resistorof high ohmicvalue may be permanently connected across the output terminals.

Advantageously a complementary pair oftransistors, ie one n-p-n and one p-n-p, may be used as the current control devices each having its emitter connected to a supply terminal of appropriate polarity in the conductive sense of the respective forward biassed emitter base junction. Each said transistor may be of the "Darlington-pair" type.

According to a particular aspect of the invention there is provided a vibratory conveyor drive unit circuit arrangement for the energisation of a reactive load at a selected frequency with electrical energy from a unidirectional supply, the circuit arrangement including terminalsforthe connection of a unidirectional supply, an input terminal for the connection of a control signal and two outputterminalsfor the connection of a reactive load, the circuit arrangement including in a first series path across the supply terminals afirst polarised, active semiconductor current control device and afirst, oppositely poled, diode and in a second series path across the supply terminals in reverse order to the first path a second polarised, active semiconductor current control device and a second, oppositely poled diode, the polarity sense of both paths between the supply terminals being the same and the first and second paths each providing, at the connection between the respective device and diode, one ofthe output terminals, the circuit arrangementfurther including between the input terminal and respective control terminals of the current control devices a control circuit responsive to a control signal applied to the input terminal to cause the current control devices, in operation, to together control the current passing in series through them and a connected reactive load between on and off conditions, the diodes providing a reverse polarity conductive path to the supplyfor current in the reactive load on the turning off of current through the current control devices.

Desirablythe control circuit includes a phase splitter ofthedirectcoupledtype,although atransformer coupled type may be used, arranged to control transistor current control devices. A single field effect transistor may be used in such a direct coupled phase splitter.

According to a particular aspect of the invention the ;;ircuit arrangement for the energisation of a reactive load may have a control signal input of a frequency of a selected value or variable over range values to permit energisation of the load in operation respec tively at the selected frequency or at frequencies in the range of values.

According to a further aspect ofthe invention a combination of two circuit arrangements each as described above may each receive a control signal from a single frequency determining source over respective connections to the individual control signal inputterminal. One or both ofthese connections may include a phase shifting circuit, forexample a delay unit or units, to enable the relative phase of energisation from the two circuits to be controlled and/or adjusted.

Advantageously the combination of two circuit arrangements just described may be connected to energise a vibratory conveyor, one circuit providing energisation for substantially vertical vibration ofthe conveying surface the other for horizontal vibration of this surface.

The adjustment of relative phase of energisation permits the operation ofthe conveyor to be optimised for a particular working condition. Controls may also be provided forthe amplitude of energisation, e.g. the ratio of on to offtime ofthe current control devices, to permit the speed ofthe conveyorto be controlled. The frequency determining source may be the resilient suspension ofthe conveyorwhose motion is coupled to the input of the circuit arrangement via a search coil or other pick-up device.

Conveniently the combination of circuit arrangements and a suitable mains energised source of a unidirectional power supply may be mounted on the frame of a vibratory conveyor in a compact unit. The unit may be provided with a suitable damping mass and supported on resilient feet as a free standing stable equipment not requiring a rigid mounting plafform.

Embodiments ofthe invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a vibratory conveyor assembly according to the invention; Figure 2 is a diagram showing circuit arrangement according to the invention.

Figure 1 shows a vibratory conveyor according to the invention in which drive control ofthevibration actuators is by means of an electrical circuit arrangement. The illustrated conveyor is ofthe lineartype.

The construction ofthe vibratory conveyor in Figure 1 is arranged to have a compact rectangularform with all the electrical components housed inside the envelope ofthe conveyor. A rigid base plate BP is supported on fourfeet F (two only being shown) which are preferably adjustable to level the conveyorand may also be resilient, for example of rubber. The base plate has three electromagnetic actuators mounted on it (HA1, HA2 and VA) to drive a top plate TP and a mounting bar MB as now described.

Top plateTPissecuredto base plate BP byfoursets ofspring strips, one being indicated at HS, to permit movement ofthe top plate in a plane substantially parallel to the base plate. This movement is produced by the action ol the two actuators HA1 and HA2. Each actuator is conveniently of an E-form core carrying the energising winding and an I-form armature to cooperate with the flux from the openedge of theE-form core in known manner. The armatures are connected to the top plate TP and the cores to the base plate BP.

The spring strips are secured to the base plate and top plate by suitable fastenings, eg as shown.

A sub-top plate, STP, is positioned in a space in the top plate with a small clearance between the sub-top plate and top plate. The vertical actuatorVA is similar to the horizontal actuators, and of E- and I-form, but arranged to move the sub-top plate STP in the vertical direction. A mounting bar MB secures the sub-top plate STP to top plate TP via two further sets of spring strips VS.

The result of this construction is that mounting bar MB can be moved substantially parallel to base plate BP and at the same time moved towards and away from base plate BP in a regular manner. The amplitude speed and phase relation of these motions can be controlled and adjusted by an electrical circuit including elements as described above. The stiffness of the springs is also chosen having regard to operating conditions. The springs are conveniently of metal but other materials such as the general class of composites including those using or incorporating carbon fibre, glass fibre, KEVLAR (RTM) fibres and the like may be used instead. Otherforms of resilient member may be used, apart from those specifically illustrated.

For example a resilient memberthat can accommodate both the vertical and horizontal movements, eg a suitable coil spring, may be used to supportthe output member from the base plate. The armature arrangement shown would still be effective as these would still be within the field of influence of the respective actuator. The top plate and output member could then be one element.

The compact construction, the drive unit in Figure 1 is some 16 inches (400 mm) long and about 6 inches (150 mm) square, permits the ready incorporation of the unit into production equipment. Suitabletooling is readily fitted to the mounting barMBfor any specific use. An importantfeature of the unit is that the direction of conveying is readily reversed by a simple manipulation ofthe drive circuit controls.Thus in one application components to be placed in depressions in a surface are moved forward overthe surface, which is supported on the conveyor, until the depressions are filled, then surplus components returned to the starting point by reversing the drive and the filled surface then removed. Forfeeding applications the speed ofthe conveyor, iethe rate of feed, can be adjusted overwide limits by simple adjustments ofthe controls ofthe unit.

Additionally if required a rocking or sideways motion substantially in a horizontal plane can be produced simultaneously with the other motions by additional mechanical, electro-magnetic, pneumatic or other means.

The electrical circuit is conveniently mounted on circuit panels placed on the vertical faces of the conveyor construction. One panel, CP1 is shown in Figure 1 and in this embodiment one further panel, CP2 not shown, is fitted on the opposite, large, face of the construction. If required up to two more small panels can be fitted on the short faces.

The control panels CP1 and CP2 are conveniently metal plates with a lengthwise stiffening flange and are fitted by two bolts clamping the panels to brackets on base plate BP (as shown). Electrical components and printed circuit cards can be housed on the inside ofthe panel below the flange. Controls for operator use are fitted to the panels.

The circuit shown in Figure 2 and described in detail below is used with one modification to operate this conveyor in one embodiment. A sensor, such as an inductor and a movable core, is fitted between top plateTPand base plate BPto detect the motion of the top plate. This motion, including the initial movement on switching on the conveyor, generates a pulse which, shaped if needed, provides the inputfor circuits CC and PC. The electronic components ofthe units PC, CC, CC', EC, EC' and PSU and the sensor are arranged on the panels with the necessary heat sinks, connectors and the like to be electrically safe and efficient and not suffer mechanical damage in use of thevibratoryconveyor. Some components are indicated in outline in the figure. The actuators are connected to the outputterminals of circuits EC and EC'.Conveniently the horizontal actuators HA1, HA2 are connected in parallel directlyto the terminals of circuit EC and the vertical actuator directly to the terminals of circuit EC'. It will be noted that the actuatorwindings arethus directly connected to the unidirectional supply and not through a transformer.

In operation ofthe conveyor the motion of mounting beam MB is controlled by the controls for phase (in unit PC) and level ofenergisation (in units CC and CC').

Frequency of horizontal and vertical vibration is set by the feedback from the sensor to the input of units PC and CC to the natural frequency ofthe suspension of top plateTP by springs HS.

In conventional vibratory conveyors, energised by the a.c. mains supply frequency of 50 or 60 Hz as appropriate, the suspension springs are adjusted or chosen to produce vibration atthe supplyfrequency.

However it is not practical, and probably not possible, to produce vibratory conveyors for sale in quantity which are precisely set to the mains frequency for all loads. The mechanical springs generally available are not precise, consistent or stable enough forthis result.

It has also been found that a precision of +1% is desirable for the matching ofthe horizontal and vertical vibration frequencies to permit efficient conveyor operation. Such precision is beyond mechanical springs both initially and over some period of use.

However use of electronic drive and especially with feedback control permits such precision to be attained and maintained even over a wide operating temperature range. The energisation frequency is set by the conveyor and is not arbitrarily set by the local supply frequency therefore more efficient, quieter, faster operation is possible.

Figure 2 shows in detail a circuit arrangement according to the invention identified by outline EC.

The circuitof Figure 2 is for use on a nominally 32 vdc supply with ancillary units supplied at 12 vdc (stabil ized).

The circuit arrangement EC of Figure 2 includes a complementary pair of active semiconductor devices, specificallytransistors Q2 and 03 to control the current supplied in operation to a load such as LA connected to output terminals OPI, OP2. Each device is rated to withstand the full supply voltage andto control the full current to be supplied to the load, some 3A in this embodiment. Associated with the transistors are two diodes D2, D3with a similar current rating. Suitable devices are transistor types 2N6284 and 2N6285, a complementary pair of Darlington-pair devices, and conventional rectifier diodes of 6A rating, such as the "Radio-spares" type, or 1 N5402.

In this embodiment each transistor is connected in a respective series path with one diode directly across the 32 v supply terminals ST1, ST2. Each transistor is adjacent to one supply terminal so the devices are in reverse order in one path compared to the other.

Preferably the transistors are connected with their emitter basejunctionsadjacentto the respective supply terminals so that control signals can be applied between a supplyterminal and the base ofthe transistor. One of the output terminals OP1, OP2 is at the connection point of the diode and transistor in each path. A safety resistor R6 may be permanently connected across the otherwise open circuited output terminals and this resistor also assists testing. A suitable value is 105 ohms.

In operation it is required that both transistors Q2, 03 operate "in phrase". To control these transistors a direct coupled single transistor phase splitter is provided. The source and drain terminals of a small power field effect transistor Ol are connected into a series resistive path across the supply terminals formed by resistors R3, R4 and R5 as shown. Resistor R4 is conveniently 103 ohms and resistors R3 and R5 each 104 ohms. The gate terminal of transistor Q1 is connected to the input terminal IP1 of the circuit EC.

The resistors R3 and R5are included in the emitter base circuits of transistors Q2 and Q3 respectively as shown. In operation a suitable control signal applied to inputterminal IP1, using supply terminal ST2 as a common terminal, will turn transistor Q1 "on" so that currentflow in resistors R3, R5 will produce suitable emitter base potentials in transistors 02, Q3 to bring them into a conducting condition. Clearly when transistor Q1 is "off" the emitter base potentials of transistors Q2, will be too small to bring them into a conducting condition so these transistors also will be "off".

In operation it is the intention thattransistors Q2, Q3 will either be "off" orturned "on", to the saturated condition if possible, as this is a clearly defined condition and can be obtainedwithouttoo close control on device parameter tolerances and operating conditions. However, other modes of operation may be used eg controlling the emitter base potentials of devices 02, Q3to vary the current in the devices in the "linear" mode ratherthana"switching" mode as just described.

Operation in the "switching" mode with a connected reactive load LA will now be described. The reactive load in this case is an inductor, actuallythe winding of an electromagnetic actuator of a vibratory conveyor. This load is to be energised at a rate of a few tens of times a second, say 15 to 60 times. Accordingly a suitable control signal, such as a train of 10 volt pulses with a variable repetition rate in this range, is assumedto be connected to input terminal IP1 to causetransistor Q1 toturn on and off at this rate. The supply terminals are energised with a 32 v supply which is nominally direct current but can conveniently be rectified alternating (50 Hz) current only partially smoothed by the use of a single large electrolytic capacitor.Clearly care must be taken that the peak value of any supply variation does not exceed the voltage rating ofthetransistors.

On transistor 01 being switched "on" bythe input control signal transistors Q2, will in theirturn be switched on together and permit currentfrom the supplyto pass through the connected inductive load (LA). OntransistorQ1 being switched "off",eg bythe input control signal going to zero at the end of a pulse, currentwill cease to flow th rough transistors 02, Q3 asresistorsR3,R5actto holdoffthesetransistors.

However, energy will still remain in the inductance of the reactive load and will attemptto maintain the currentflow, in the well known manner. This attempt would usually produce excessive voltages at the transistor collectors which could breakdown the devices by exceeding their voltage rating. In known arrangements the transistors are therefore rated at two orthree times the supply voltage and protection diodes, snubber circuits and multiple windings are often connected between collectorandemitterofthe transistor.

In the circuit embodying the invention the production of excessive voltages on the switching off of load currentfrom the supply is avoided by the provision of diodes Dl, D2 connected in a particular relation with the load and the current control devices. On examin ingthe circuit diagram itwill be seen that if terminal OP2 rises to a potential only slightly (say 0.5 to 1.0 volt) more positive than the supply terminal ST1 diode D2 becomes conductive as does diode D1 ifterminal OP1 falls to a potential slightly more negative than supply terminal ST2. The effect of voltages induced by the switching off of current supply is therefore to connect the reactive load, in reverse, across the supply terminals. The effect can be regarded as discharging the energy in the load into the supply.

On transistor Q1 next being turned "on", by the next pulse ofthe input control signal, transistors Q2, 03 again permit currentto flowfrom the supply into the load, continuing the energisation ofthe electromagnetic actuator into the next cycle of operation.

Diodes D1, D2 are reverse biased firmly into the non-conductive condition once transistors Q2, Q3 are "on".

In addition to the above described control of induced voltages by diodes D1, D2 the circuit embodying the invention provides further advantages over other circuits to energise reactive loads at a variable frequency of some tens oftimes a second, or higher, up to saya few hundreds oftimes a second. If a simple diode clamp is used across a device such as a transistor the current decay rate after siwth off is much slower than the rate of current growth at switch on.

Accordingly instead ofthe current returning to zero between each "on" pulse itfalls onlyto an intermedi ate value. The resultisasignificantstanding current in theswitching device and the loadwhich wastes power, increases the load on the device and reduces the effectiveness of the load, such as a vibrator. The present invention overcomes this problem.

To improve the effectiveness of a vibratory actuator it is convenientto "tune"the circuits to the vibration frequency. However if this is done with a simple, single ended, current control arrangement additional components are needed to "tune", which reduces the range offrequencies for which the actuator is efficient and the highvoltage on switch off is required to improve the rundown of current after switch off.A double wourrd actuator drive circuit has been proposed, UKPA 2009177, bywhich energy can be returned to the supply from a secondary winding but this still requires devices rated at over twice the supplyvoltage and the leakage inductance between the windings can create transients which aggravate the load on the devices.

The present arrangement has the frequency indpendentfeature ofthe double wound arrangement to an even greater degree, avoidsth leakage inductance problems and overcomes the high voltage stress problem of all earliertechniques. The arrangement can also work with a single sided supply instead ofthe centre tapped types frequently proposed for semiconductor inverter duty. It has been found that the radiation of radio frequency interference (RFI) is also much reduced.

If required, the phase splittercan be ofthe transformer type or coupled to the base of the current control devices by a transformer to provide isolation from high voltages, eg 200 to 300 v or more, which may be used in the final stage when higher output powers are required. The reduced voltage stress on the devices permits the use of such high voltages with readily available devices and enables higher power levels to be reached at a given current and inductor construction, which generally depends on current rating not voltage atthesevalues.

Figure 2 also shows ancillary circuits which may be used with the energisation circuit. As mentioned above a source of pulses art a controllablyvariable frequency is used to operate the circuit EC. Means for controlling the amount of current supplied to the load may also be required. Suitable circuitelements are illustrated in Figure 2. Unit FG indicates a frequency generator. Two NANDgates (IC1 a, ICi b) of integrated circuit IC1 are cross connected to:forrn an oscillator whose frequency is setby resistors fS1. RIO and RH1 and capacitor C1.Adjustment of thegenerated fre- quency is by varying variable resitor RHI. The circuit is supplied with stabilised 12 vdc.

The output of frequency generator FG is a rectangularwave of approximately 1:1 mark/space ratio (typicallyfive unitsoftimeatthe-'high", greater than +6v, logic level and fourunits atthe "low", OV, logic level) witch a period controlled by resistorRH1. The output of:FG is supplied to an input of unit CC which is arranged to control the duration of the flow of current in circuit EC. Inunit(:Cthe output waveform of FG is differentiated in the network of capacitor C2, resistor R2 to produce a train of positive-going edges, one for each high level output ofthe frequency generator. The negative-going edges are clipped by the input circuit of IC1c. ICle is a NAND gate with one input permanently enabled by a connection to +12 vdc. The other inputreceivesthe positive-going edges from C2/R2 and is held in the "on" condition, output logic "low", onlyforas long astheedgeand itssubsequent decay exceed the logic threshold. This is only a small fraction of the wavelength of the rectangular wave.

The output of ICle is thus normally "high" and only "low" for a short time in each cycle from the frequency generator. The output of IC1c is connected via a diode D1 to the junction of a variable resistor RH2 and a capacitor C3 connected in series across the 12vsupply with the other end of the capacitorto the 0 v line.

When the output of lC1 c goes "low" the gate is "on" and quickly discharges the capacitors C3 via diode D1 and the current sinking capaicty ofthe "on" gate. The junction of RH2 and C3 is also connected to one input of a further NAND gate IC1 d. The other input ofthis gate is again permanently enabled by a connection to +12 vdc. The discharge of capacitor C3 is very rapid and the gate 1C1 d is thus rapidly put in the"off" condition and held there, even though gate ICi c has reverted to the "off" condition, until capacitor C3 has been charged through resistor RH2to the logic transition level of gate IC1d, diode D1 is in the blocking condition now.

The output of gate Cl d is applied to the input of the circuit EC described above. When gate lCl d is "on" the output is logic low and transistor Ol is off. When gate ICld is "off" the output is logic high and transister Ol is on, turning on transistors 02,03 to pass current from the 32 v supplythrough a connected load.Gate IC1 d is "off" from the discharge of capacitor C3 until it recharges to the logic transition level, about 6 v, and enables the connected input ICld to turn the gate "on" and thereby turn transistors Q2, off via transistors 01 .The length of time, in each cycle from frequency generator FG,forwhich transistors Q2, 03 are on is thus set bythe recharge time of capacitor C3 via variable resistor RH2 a higher setting of the resistor increasing the length of this on time. A fixed resistor may be included in series with RH2 to set the minimum on time while the maximum value of RH2, and and fixed resistor, may be chosen to set the maximum ontimeto less than awholecyclefrom FG.

The frequency at which the circuit EC is turned on is therefore set by resistor RHl and the proportion of timeforwhich circuit EC remains turned on is set by resistor RH2.

A power supply PSU provides suitable 12 v and 32 v supplies, with a common zero, from a 240 or 115 volts 50 or 60 Hz supply mains of required.

Other ancillary circuits are shown in Figure 2 to permit the control of another circuit EC', identical to circuit EC, to operate at the same frequency, set by resistor RH1, but at a different phase and to off ratio.

Circuit CC', identical to circuit CC, is operable in the same way as circuit CC to control the current in flow time in circuit EC'. Afurther circuit, PC, is provided for the control ofthe phase of current flow in circuit EC' with reference to that in circuit EC.

Circuit PC is the same as circuits CC and CC' except that the value of capacitor C3 is increased, typically being doubled to 0.47 microfarad. This increases the timetaken to charge the capacitorviathe variable resistor, RH2, and therefore increases the possible interval betweenthe positive-going edge at the output ofgeneratorFGandthefinal NAND gate in circuit PC being turned "off" to produce an output of a positivegoing edge to act on circuitCC' to turn on the current in circuit EC'.

The effect of this adjustable interval is to varythe phase of the operation ofcircuit EC' with respect to that of circuit EC. The circuit PC provides a delay of up to one cycle at the lowestfrequencyof FG and this affords a phase shift of up to 360" between the two circuits.

Circuits PC, CC' and EC' are shown in blockform; the only difference is the value of the timing capacitor in circuit PC, mentioned above. Values for components on Figure 2 are given on the accompanying list. IC1 is type 4011 and the bridge rectifier in unit PSU type KBPC 602. Clearly alternative values and devices are usable, or will be needed for different voltages, while gate turn off devices may be suitable alternatives for transistors Q2, Q3.

Resistors Capacitors Semi-conductors Rl 10K C1 0.22 F Ql VN1OKn R2 lOOK C2 O.OO1gF Q2 2N6285 R3 10K C3(CC) 0.22 F Q3 2N62S4 R4 1K C3(PC) 0.47 F D1 1N5402 R5 IOK C3(CC') 0.22 F D2 1N5402 R6 lOOK C10 O.1;F D 12 v zener R10 1M Cli 47SF Rll 560 Cii 4700 F As mentioned above the circuit arrangements can be used to drive a vibratory feeder.It has been found that with the low power level required to energise the feeder, because of the improved efficiency of the drive, the addition of a mass of material at the base of the feeder greatly reduces the vibration applied to the surface on which the feeder is placed. A mass of a few tens of pounds say 30 to 60 pounds attached to the base of a feeder ofthe size described above the permitsthefeederto be used as a free standing unit on almost any surface strong enough to supportthe unit. Hitherto it has been considered necessary to mount such feeders on rigid or heavy plinths or bases. The use of resilient feet, say of medium hard rubber, with the added mass has been found to produceafeederorconveyorunitwhich remains in position when free standing in operation atfull power. The unit is also very quiet in operation which will reduce "acoustic pollution" when the unit is in use in quantity in, say, an assembly line.

Claims (8)

1. Avibratory conveyor drive circuit arrangement fortheenergisation of a conveyor at a selected frequency with electrical energy from an un idirectional supply, the circuit arrangement including terminalsfortheconnection of an unidirectional supply, an inputterminalfortheconnection of a control signal and respective sets of output terminals fortheconnection of an actuatorofa conveyor, the circuit arrangement including two series paths across the supply terminals, each of a semiconductor current control device and a diode, the paths each providing, at the connection between the respective device and diode, one of said outputterminals,the circuit & angement further including between the input terminaland respective control terminals ofthe current control devices a control circuit responsive to a control signal applied to the inputterminal to cause the current control devices, in operation, to together control the current passing in series through them and a connected conveyor actuator reactive load between on and off conditions, the diodes providing a reverse polarity conductive path to the supply for current in the reactive load on the turning off of current through the current control devices.

2. A circuit arrangement according to Claim 1 including control means to provide a control signal of a frequency of a selected value or variable over range valuesto permit energisation of the conveyor in operation respectivelyatthe selected frequency orat frequencies in the range of values.

3. A circuit arrangement according to Claim 2 in which the frequency determining source includes means to generate a pulse at intervals at the selected frequency, meanstoform from each pulse a control signal of selected duration to control the passage of currentforsaid on condition.

4. Acircuitarrangementaccording to Claim 2 or Claim 3 in which the frequency determining source includes means to generate a rectangular wave of only approximately 1:1 marktspace ratio.

5. A circuit arrangement according to any preceding claim including two sets of drive circuit elements, each to receive a control signal from a single frequency determining source over respective connections to individual control signal inputterminals.

6. A circuit arrangement according to Claim 5 in which one or both of said connections includes a phase shifting circuit, such as a delay unit or units, to enable the relative phase of energisation from the two circuits to be controlled and/or adjusted.

7. Acircuitarrangement according to Claim 1 or Claim 2 including two sets of drive circuits elements one set providing energisation for substantially vertical vibration of a conveying surface the other for horizontal vibration ofthis surface.

8. A circuit arrangement substantially as herein described with reference to Figure 2 ofthe accompanying drawings.