WO2006003363A1

WO2006003363A1 - A metering arrangement and a method of monitoring a metering arrangement

Info

Publication number: WO2006003363A1
Application number: PCT/GB2005/002269
Authority: WO
Inventors: Laurence Richard Penn; Phillip Kenneth Thomson
Original assignee: Failsafe Metering International Limited
Priority date: 2004-07-07
Filing date: 2005-06-09
Publication date: 2006-01-12
Also published as: GB2415951A; GB2415951B; GB0415255D0

Abstract

A dispensing unit is provided for dispensing at least one liquid. The unit comprises two metering devices (33, 34) each configured to provide a plurality of sequential 'shots' of liquid. The 'shots' are passed to a mixing device (36) from which they are dispensed (38). Pressure sensors (41, 42) are associated with the output of each metering device and a control valve (44, 45) between the output of the metering device and an input to the mixer. A controller (43) closes each control valve and monitors the pressure sensed by the pressure sensors to determine if the dispensing unit is operating satisfactorily.

Description

A METERING ARRANGEMENT AND A METHOD OF MONITORING A METERING ARRANGEMENT

THE PRESENT INVENTION relates to a metering arrangement, and more particularly relates to a

reactive mixture.

There is frequently a need to dispense a multi-part reactive mixture, for example in the form of a two-part adhesive or sealant.

A two-part adhesive or sealant is formed by mixing together two liquid components which react together to provide the adhesive or sealant. The individual components may be stored over a long period of time without deteriorating significantly. When the two components are mixed together, the components react together and an adhesive or sealant having the appropriate properties is created. The adhesive or sealant may cure or set due to the chemical reaction between the two components over a relatively brief period of time.

In most cases it is critical that the components of the two liquid component adhesive or sealant are mixed together in a precisely predetermined ratio, so that the sealant or adhesive will have the desired properties. In order to achieve this end it has been proposed to utilise a dispensing unit which incorporates pumps to pump the two liquids to separate metering devices, which each meter one of the liquid components. The pumps help to ensure that the liquid is truly hydraulic and has a maximum density before the liquid is metered by the metering devices. The metering devices are operatively interconnected sot hat one metering device should fail, or should not work correctly both of the metering devices will stop so that no adhesive is dispensed which is incorrectly mixed.

A typical metering device proposed for use in this situation is a metering device of the type which includes a shuttle which is moveable within a chamber, the shuttle acting as a piston to seal the two ends of the chamber from each other. A valving arrangement is provided which, in one position, can supply liquid under pressure, from the pump, to one end of the chamber, whilst opening a flow path from the other end of the chamber to an appropriate outlet. Consequently the piston moves along the chamber pushing liquid located between the piston and the outlet out of the chamber forming a "shot" of liquid. When the piston completes its pre-set stroke, a signal is generated. Then the position of the valve is changed, so that the liquid supply is then connected to the end of the chamber adjacent the piston and the other end of the chamber is connected to the outlet. The piston then moves back along the chamber driving the liquid that was introduced during the first described stroke towards the outlet, thus forming another "shot" of liquid. Each shot of liquid is of a precisely predetermined volume.

It has been proposed to utilise two metering devices of this type, with the valve of each device being actuated in response to a signal from the other device confirming that the other device has successfully completed a stroke and thus delivered a "shot" of liquid to its outlet. Thus the metering devices work in anti-phase delivering successive shots of respective liquids to their respective outlets. In the dispensing unit the outlets of the two metering devices are connected to a mixer, which may be a static mixer. The liquids which are ejected from the metering devices are thus mixed to form a uniform homogenous mixture. The mixture has a precisely predetermined proportion of each of the two liquids, and consequently the adhesive or sealant has the desired properties. There is no risk that an incorrectly mixed, or "out-of-ratio", adhesive or sealant can be dispensed.

It is to be understood that if either of the two metering devices should fail to operate, so that the piston within the pump does not complete a stroke, then the dispensing unit will cease operation.

Should this event arise it is appropriate to check the condition of the dispensing unit before operation of the dispensing unit is recommenced.

It is envisaged that a dispensing unit of the type described above may be incorporated in a robotic dispensing station. Thus the described mixer and dispensing nozzle may be mounted on a robot arm, and the robot arm and the metering devices maybe computer-controlled so that the robotic dispensing station will execute a predetermined operational cycle. For example the arm may be programmed to lay down a bead of adhesive or sealant of a precisely predetermined form at a precisely predetermined location on a work-piece which is located at a known position relative to the robotic arm.

Should a dispensing unit in such a situation cease to operate due to a piston within a metering device not fully completing a stroke, the robotic dispensing station will cease operation, and any production line associated with the robotic dispensing station will also cease operation. It is therefore desirable that, in such a situation, the robotic dispensing station should begin to operate again as swiftly as possible. The present invention seeks to provide an improved dispensing unit and a method of monitoring a dispensing unit.

According to one aspect of this invention there is provided a dispensing unit for dispensing at least one liquid, the unit comprising at least metering device, the or each metering device being configured to provide a plurality of sequential "shots" of liquid, the or each metering device generating output signal when a "shot" of liquid is being dispensed, the or each metering device being connected to a controller controlling the dispensing unit and terminating the operation of the dispensing unit whenever a metering device fails to generate an output signal confirming that a "shot" of liquid has been dispensed, the output of the or each metering device being connected to a dispenser from which the liquid or liquids are dispensed, the unit further comprising a pressure sensor associated with the output of the or each metering device and a control valve between the output of the or each metering device and a corresponding input to the dispenser, the controller being arranged to close the or each control valve and to monitor the pressure sensed by the or each pressure sensors.

A preferred embodiment of the invention is a unit for dispensing a mixture of two liquids, the unit comprising two said metering devices, each metering device being configured to provide a plurality of sequential "shots" of liquid, each metering device generating an output signal when a "shot" of liquid has been dispensed, each metering device being connected to a said controller controlling the dispensing unit and terminating operation of the dispensing unit whenever one metering device fails to generate an output signal confirming that a "shot" of liquid has been dispensed, the outputs of the said metering devices being connected to a mixer from which the liquids are dispensed, the unit further comprising a said pressure sensor associated with the output of each metering device and a control valve between the output of each metering device and a corresponding input to the mixer, the controller being arranged to close the control valves and to monitor the pressure sensed by the pressure sensors.

Preferably the or each metering device is connected to a respective source of liquid under pressure, there being a control valve connected between the or each source of liquid under pressure and the corresponding input of the corresponding metering device, the controller being configured to actuate the or each control valve to disconnect the or each metering device from the respective source of liquid under pressure and being configured to monitor any subsequent pressure fall sensed by the or each sensor.

Conveniently the controller is programmed to determine if any pressure rise or any pressure fall sensed by the pressure sensors is within predetermined limits and to reactivate the or each metering device or to prohibit operation of the dispensing unit in dependence upon the determination.

Preferably each metering device incorporates an elongate chamber, there being a shuttle contained within the chamber, the shuttle having a portion which is a substantially sealing sliding fit within the chamber, the shuttle being moveable axially between an initial position and a second position within the chamber, each end of the chamber being provided with a liquid flow duct through which pressurised liquid may enter and leave the chamber, there being valve arrangement to control the flow of liquid to and from the chamber such that, during successive cycles of operation of the metering device, liquid is supplied to one end of the chamber causing the shuttle to move from the initial position at said one end of the chamber to the second position at the other end of the chamber, thus ejecting a pre- determined volume of liquid from the other end of the chamber, and subsequently liquid is supplied to said other end of the chamber causing the shuttle to move back from the second position to the initial position, ejecting a further pre-determined quantity of liquid from the said one end of the chamber, the valving means comprising a rotary valve rod contained within a valve bore, and a mechanism to rotate the valve rod, the liquid flow ducts from the chamber extending to the valve bore, at least one liquid inlet extending to the valve bore and at least one liquid outlet extending from the valve bore, the valve rod, in combination with the valve bore, defining liquid flow passages which, in one angular orientation of the valve rod, serve to interconnect a liquid flow inlet and the liquid flow duct extending to one end of the chamber whilst interconnecting the liquid flow duct extending to the other end of the chamber with an outlet and, in an alternate angular orientation, serving to interconnect the liquid flow inlet with the liquid flow duct extending to the other end of the bore whilst connecting the liquid flow duct extending to the said one end of the bore with an outlet.

Conveniently the shuttle is provided with two rods, each rod extending beyond the chamber, there being a contact of proximity sensor located adjacent the end of each rod to generate a signal when the shuttle reaches the initial position and the second position.

Preferably is incorporated in a robotic dispensing station, the dispensing station incorporated a robotically controlled arm, the mixer being carried by the arm, the metering devices being connected to the mixer by a hose.

Conveniently the station is provided with drums of liquid, each drum of liquid being provided with a transfer pump to pump the liquid.

According to another aspect of this invention there is provided a method of testing a dispensing unit which includes at least one metering device, for metering liquid under pressure, the outlet of the metering device being connected to a dispenser, the method comprising the steps of operating at least one valve to isolate the outlet of the or each metering device from the dispenser, and subsequently monitoring pressure at the outlet of the or each metering device to determine if the pressure at the or each outlet rises in a predetermined manner.

The invention provides a preferred method of testing a dispensing unit which includes two said metering devices, for metering liquid under pressure, the outlets of the metering devices being connected to a mixer, the method comprising the step of operating valves to isolate the outlets of the metering devices from the mixer, and subsequently monitoring pressure at the outlets of the metering devices to determine if the pressure at the outlets rises in a predetermined manner.

The method may further include the steps of operating the or each metering device to increase the pressure in the outlets of the device, terminating operation at the device and then monitoring pressure at the outlet of the or each device to determine if the pressure falls in a predetermined manner.

Advantageously the method further includes the step of re-commencing ordinary operation of the dispensing unit or prohibiting operation of the unit until the unit has been serviced in response to the determination.

According to a further aspect of this invention there is provided a dispensing unit for dispensing at least one liquid, the unit comprising at least metering device, the or each metering device being configured to provide a plurality of sequential "shots" of liquid, the or each metering device generating output signal when a "shot" of liquid is being dispensed, the or each metering device being connected to a controller controlling the dispensing unit and terminating the operation of the dispensing unit whenever a metering device fails to generate an output signal confirming that a "shot" of liquid has been dispensed, the output of the or each metering device being connected to a dispenser from which the liquid or liquids are dispensed, the unit further comprising a pressure sensor associated with the output of the or each metering device and a control valve between the output of the or each metering device and a corresponding input to the dispenser, the controller being arranged to close the or each control valve and to monitor the pressure sensed by the or each pressure sensors, the dispensing unit being for dispensing a mixture of two liquids, the unit comprising two said metering devices, each metering device being configured to provide a plurality of sequential "shots" of liquid, each metering device generating an output signal when a "shot" of liquid has been dispensed, each metering device being connected to a said controller controlling the dispensing unit and terminating operation of the dispensing unit whenever one metering device fails to generate an output signal confirming that a "shot" of liquid has been dispensed, the outputs of the said metering devices being connected to a mixer from which the liquids are dispensed, the unit further comprising a said pressure sensor associated with the output of each metering device and a control valve between the output of each metering device and a corresponding input to the mixer, the controller being arranged to close the control valves and to monitor the pressure sensed by the pressure sensors, wherein the or each metering device the or each metering device is connected to a respective source of liquid under pressure, there being a control valve connected between the or each source of liquid under pressure and the corresponding input of the corresponding metering device, the controller being configured to actuate the or each control valve to disconnect the or each metering device from the respective source of liquid under pressure and being configured to monitor any subsequent pressure fall sensed by the or each sensor, and wherein the controller is programmed to determine if any pressure rise or any pressure fall sensed by the pressure sensors is within predetermined limits and to reactivate the or each metering device or to prohibit operation of the dispensing unit in dependence upon the determination.

According to another aspect of this invention there is provided a method of testing a dispensing unit which includes at least one metering device, for metering liquid under pressure, the outlet of the metering device being connected to a dispenser, the method comprising the steps of operating at least one valve to isolate the outlet of the or each metering device from the dispenser, and subsequently monitoring pressure at the outlet of the or each metering device to determine if the pressure at the or each outlet rises in a predetermined manner, wherein the method is a method of testing a dispensing unit which includes two said metering devices, for metering liquid under pressure, the outlets of the metering devices being connected to a mixer, the method comprising the step of operating valves to isolate the outlets of the metering devices from the mixer, and subsequently monitoring pressure at the outlets of the metering devices to determine if the pressure at the outlets rises in a predetermined manner, the further steps of operating the or each metering device to increase the pressure in the outlets of the device, terminating operation at the device and then monitoring pressure at the outlet of the or each device to determine if the pressure falls in a predetermined manner, the method further including the step of including re-commencing ordinary operation of the dispensing unit or prohibiting operation of the unit until the unit has been serviced in response to the determination.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which:

FIGURE 1 is a partly cut-away view of one metering device for use in accordance with the invention, FIGURE 2 is a view of the rotary valve rod of the metering device of Figure 1 ,

FIGURE 3 is a diagrammatic sectional view illustrating one phase of operation of the metering device of Figures 1 and 2,

FIGURE 4 is a view corresponding to Figure 3 illustrating another phase of operation of the metering device of Figures 1 and 2,

FIGURE 5 is a diagrammatic view of a dispensing unit in accordance with the invention which incorporates two metering devices of the type shown in Figures 1 to 4, and

FIGURE 6 is a diagrammatic view of a robotic dispensing station incorporating a dispensing unit in accordance with the invention.

A metering device for use in accordance with the invention will initially be described with reference to Figures 1 to 4. The metering device incorporates a shuttle and, in operation, produces a plurality of discrete "shots" of liquid.

Referring initially to Figure 1 of the accompanying drawings a metering device for use in an embodiment of the invention comprises a housing 1 which defines a cylindrical chamber 2. Contained within the chamber 2 is a shuttle 3. The shuttle 3 is a unit or assembly which has a cylindrical central cylindrical portion 4 which is a sliding sealing fit with the chamber 2. The shuttle incorporates two rods 5,6 which extend axially from opposite sides of the cylindrical portion 4 and which pass, as a sliding sealing fit through apertures, with or without seals, formed in the end walls of the chamber 2, the rods 5,6 thus projecting beyond the housing. Mounted on the projecting portions of the rods 5,6 are adjustable collars 7,8, the position of which may be adjusted to alter the "stroke" of the metering device as will become clear from the following description. Located adjacent the ends of the rods 5,6 are sensors 9,10 which are responsive to the rods 5,6 each reaching a pre- determined position. The sensors may, ideally, be responsive to physical contact of the end of the rod with the sensor.

The central cylindrical portion 4 of the shuttle effectively divides the chamber 2 into two separate parts, one at the left-hand end of the chamber and the other at the right-hand end of the chamber. Respective liquid flow ducts 11 ,12 connect these end parts of the chamber 2 to spaced-apart points of a cylindrical valve bore 13 defined within the housing 1. Outlet and inlet ducting also communicate with the bore 13. Thus the housing defines a first outlet duct 14 offset from the duct 11 and second outlet duct 15 offset from the duct 12. The ducts 14 and 15 are off-set axially from the ducts 11 and 12, being closer to the ends of the valve bore 13, but one diametrically opposed to the ducts 11 ,12. A liquid inlet duct 16 is also defined located at a position between the two liquid flow ducts 11 ,12. Contained within the valve bore 13 is a rotary valve rod 17 which is driven rotationally by a stepping motor M in response to signals from the sensors 9,10.

The valve rod 17 has parts thereof cut away in the form of a channel or recess in the periphery of the rod and passages or bores through the rod so that the valve rod 17, when in the bore 13, may define liquid flow paths. The valve rod 17 is provided with a first through bore 18 which is inclined to the axis of the valve rod 17 and which, in one rotational position of the valve rod 17, when the valve rod 17 is present in the bore, serves to interconnect the liquid flow duct 11 and the outlet duct 14. A second corresponding bore 19 is provided, which is actually parallel with the first bore 18, which, as will be understood from Figure 2, in an alternate rotational position of the valve rod 17 serves to interconnect the liquid flow duct 12 and the outlet 15. Between the two bores 18, 19 there is an annular groove 20 formed in the exterior surface of the valve rod 17 which is in alignment with the inlet 16. The groove 20 is provided with two diametrically opposed axial extensions 21 ,22, which extend in opposite axial directions. It is to be appreciated that in one rotational position of the valve rod 17 the axial extension 21 will extend to the end of the flow passage 12 thus forming a liquid flow path from the inlet 16 to the right-hand end of the chamber 2, and, in an alternate position of the valve rod 17, groove 22 will establish communication with the liquid flow path 11.

Looking now at Figure 3, the shuttle 3 is shown, in a right-hand most position, with the end of the projecting shuttle rod 6 engaging the sensor 10. As the shuttle rod 6 contacts the sensor 10, so the stepping motor M rotates the valve rod 17 by 180°, thus moving the valve rod 17 to the position as shown in Figure 4. When the valve rod 17 is in the orientation or the position as shown in Figure 4 the groove 20 and the axial extension 21 serve to connect the inlet 16 to the liquid flow passage 12 which communicates with the right-hand end of the chamber 2, whereas the bore 18 serves to interconnect the liquid flow duct 11 (which, in turn, communicates with the left- hand end of the chamber 2), and the outlet 14. Pressured liquid may thus flow from the inlet 16 through the annular groove 20 and the axial extension 21, through the liquid flow duct 12 into the right-hand end of the chamber 2 thus serving to move the shuttle 3 towards the left. As the shuttle 3 moves towards the left, so liquid in the right-hand end of the chamber is discharged through the liquid flow duct 11 , and the bore 18 and through the outlet 14. The shuttle 3 thus continues to move towards the left until the shuttle rod 5 contacts sensor 9. When the sensor 9 is contacted, the shuttle 3 has completed its stroke and a pre-determined quantity of liquid in the form of a metered "shot" of liquid has been ejected through the outlet 14.

In response to a signal generated by the sensor 9 when touched by the shuttle rod 5, the stepping motor M again rotates the valve rod 17 by 180°, thus returning the valve rod 17 to the position or orientation shown in Figure 3. With the valve rod 17 in the position shown in Figure 3 liquid will flow from the inlet through the annular groove 20, the axial extension 22, and through the liquid flow duct 11 to the left-hand end of the chamber 2. The bore 19 in the valve rod 17 interconnects the liquid flow duct 12 and the outlet 15, allowing liquid from the right-hand end of the chamber to flow to the outlet 15. Thus the shuttle 3 will move towards the right until the shuttle rod 6 establishes a contact with the sensor 10. As the shuttle makes the movement to the right a pre-determined quantity of liquid, in the form of a metered "shot" of liquid, is ejected from the right-hand part of the chamber 6 through the outlet 15. When the shuttle rod 6 contacts the sensor 10 the motor M is actuated again. The cycle of operation may then repeat.

Since the stepping motor M only rotates the valve rod 17 on receipt of a signal from the sensor 9 or the sensor 10, should the shuttle not be able to complete its stroke, for example due to a lack of liquid, or insufficient liquid pressure, no signal will be given and the metering device will just stop. In this way it can be ensured that for each cycle of operation the metering device delivers an appropriate quantity of liquid, in the form of a correctly metered "shot", which can be of crucial importance if two liquids, which are components of, for example, a two-part adhesive or the like, are to be metered by two separate metering devices and mixed in a precisely pre-determined ratio.

It is to be appreciated that the position of the collars 7,8 on rods 5,6 may be adjusted and the position of the sensors 9,10 may be adjusted to increase or decrease the stroke of the shuttle, thus increasing or decreasing the quantity of liquid ejected on each stroke of the shuttle.

In an alternative arrangement the sensors 9,10 may be annular, with the rods 5,6 passing through the sensors 9,10. In such an embodiment the collars will engage with the sensors to cause the sensors to generate a signal. The sensors 9,10 in such an embodiment may be adjustably positioned.

As shown in Figures 3 and 4 the chamber 2 may be provided on either side of the cylindrical portion 4 of the shuttle 3, with air bleeds 23, 24. These may be opened to permit air to escape from the chamber 2, especially when the described metering device is first filled with the liquid to be metered, to ensure that all of the air is vented, so that hydraulic integrity can be established with no compressible air remaining in the chamber 2.

In the described embodiment the valve is a rotary valve rod, which facilitates manufacture and maintenance of the valve. In use, the valve rod may rotate almost uniformly, avoiding sudden changes of momentum as maybe experienced with a reciprocating valve.

Of course, the metering device as described may be "reversed", with pressurised liquid being supplied to the "outlets" 14,15, and with the "inlet" 16 actually acting as an outlet.

Whilst reference has been made to contact sensors responsive to physical contact with the shuttle rods, proximity sensors which respond when the shuttle rods reach predetermined positions may alternatively be used.

Turning now to Figure 5 a dispensing unit 30 is shown schematically. The apparatus, as illustrated, includes a source 31 of a first liquid under pressure and a source 32 of a second liquid under pressure. Each source of liquid may be a main supply pipe containing pressurised liquid to supply a plurality of units as described, or may be a drum of liquid with a transfer pump to pump liquid to the unit. The two liquids may be the two components of, for example, a two component adhesive which have to be mixed together in precisely predetermined relative quantities if the adhesive is to is to have the desired strength and stability.

The source of the first liquid 31 is connected to a metering device 33 of the type described above with reference to Figures 1 to 4. Similarly the source of the second liquid 32 is connected to an equivalent metering device

34. The metering device 33 has outlet 35 which extends to a mixer arrangement 36. Similarly the second metering device 34 has an outlet 37 which extends to the mixer 36. The mixer 36 may be a rotary mixer or may be a mixer which incorporates, as in the illustrated embodiment, a static mixer 38 of the type disclosed in EP 0105181.

A first controller 40 is provided. The controller 40 is connected to receive signals from each of the metering devices 33,34 to indicate when the shuttles of the two metering devices have reached the two respective end positions. The controller is connected to a motor associated with the first metering device 33 and the motor associated with the second metering device 34. The controller responds to a signal from one of the metering devices to operate the motor of the other of the metering devices. When the motor of the other metering device has been operated the shuttle of the other metering device will complete a stroke, and the controller will, in response to a signal confirming completion of the stroke of the shuttle, operate the motor of the first metering device. Thus the metering devices are operated in anti¬ phase generating successive "shots", of precisely predetermined volume, of the two liquids which pass through the outlets 35 and 37 to the mixer 36.

Alternatively a single motor may drive both of the devices, the motor only advancing when the shuttle of each of the devices has finished its stroke.

A first pressure gauge 41 is provided to sense the pressure in the outlet 35 and a second pressure gauge 42 is provided to sense the pressure in the outlet 37. Signals from the two pressure gauges pass to a second controller 43. The second controller 43 is connected to a first control valve 44 provided in the first outlet 35 adjacent the mixer 36 and also to a second control valve 45 in the outlet 37, again near the mixer 36. The controller 43 is connected to the controller 40. Indeed the controller 43 and the controller 40 may, in a practical embodiment of the invention, be fabricated as a single control unit.

The second controller 43 is also connected to control an inlet valve 46 located immediately adjacent the inlet to the metering device 33 which is connected to the first source 31 of liquid under pressure and also to a second inlet control valve 47 located immediately adjacent the inlet to the second metering device 34 which is to receive pressurised liquid from the second source 32 of pressurised liquid.

It is to be understood that in operation of the dispensing unit as described above, the metering devices 33 and 34 will operate until a shuttle, or piston, of one of the metering devices fails to complete a stroke, and thereby fails to generate the appropriate signal. Operation of the unit will then terminate.

When operation of the device terminates in this way, the controller 40 passes a signal to the second controller 43, and the second controller 43 will initiate a self-diagnostic sequence. The diagnostic sequence, which will now be described, is intended to verify the satisfactory operation and mechanical condition of the two metering devices.

Initially the controller 43 will ensure that the valves 44 and 45 are in the open position. As the metering devices 33 and 34 are not operating, and also because the outlets 35 and 37 of the metering devices 33 and 34 are in communication with the static mixer 38, the system, from the metering devices 33 and 34 to the outlet of the nozzle 38 will become hydraulically "relaxed", there being no effective pressure applied to the liquid within the outlets and the mixer.

The controller 43 will then close the valves 44 and 45 and, during a succeeding period of time, will monitor the pressure sensed by the pressure sensor 41 and 42. If the metering devices 33 and 34 are in good condition, the pressure should, within a predetermined period of time, not rise at all or rise only very slightly as a consequence of leakage of liquid under pressure, from the first liquid source 31 or the second liquid source 32, through the respective metering devices 33 and 34 to the outlets 35 and 37. If components of the metering devices have, for example, become worn, pressure will rise relatively swiftly, and this rise in pressure can be sensed by the pressure sensors 41 , 42.

If the pressure rises, during this part of the diagnostic routine, at an unacceptable rate or to an unacceptable level, the controller 43 will prohibit further operation of the dispensing unit before full servicing of the apparatus has been carried out.

If the pressure does not rise faster than the predetermined limit or does not rise above a predetermined level, the controller 43 will cause the metering devices 33 and 34 to be actuated, still with the valves 44 and 45 in the closed condition. The pressure within the outlets 35 and 37 will rise substantially, especially as a hydraulic liquid is effectively being pumped from the sources of pressurised liquid 31 ,32 through the metering devices 33 and 34 into a predetermined volume. Hydraulic liquid cannot be compressed, and consequently pressure will rise rapidly. If desired, at this stage the pressure of the pressured liquid supplied from the sources 31 ,32 may be increased above the normal level. The metering devices 33, 34 will continue to operate until the pressure within the outlets 35, 37 has reached a maximum, that maximum pressure being closely associated to the pressure at which the pressurised liquid is supplied to each metering device from the respective pressurised liquid source

31 or 32.

The valves 46, 47 are then operated by the control unit 43, to disconnect the inlets to the metering devices 33, 34 from the sources of liquid 31 , 32 and preferably exposing the inlets to the metering devices 33, 34 to atmospheric pressure. The pressure within the outlets 35, 37 is then monitored over a predetermined period of time by the pressure monitors 41 , 42. If the pressure should fall at a rate in excess of a predetermined rate, or if the pressure should fall below a predetermined threshold, then again the controller 43 will prohibit operation of the dispensing unit until a full service has been effected.

However, should the dispensing unit successfully complete the monitoring cycle as described above, ordinary operation of the device is allowed to recommence. The valves 44, 45 and 46, 47 are moved to the open position, and the metering devices 33, 34 are again operated in the "normal" way. However, should either of the metering devices 33, 34 of the dispensing unit fail again within a predetermined period of time, the dispensing unit will be disabled until a full service has been carried out.

It is to be appreciated, therefore, that in use of the dispensing unit described with reference to Figure 5, the two metering devices will meter two liquids in precisely known proportions, the liquids being mixed and dispensed. Should either metering device fail, the dispensing unit undergoes a self- diagnostic cycle, to determine the condition of the metering devices. On successful completion of the diagnostic cycle the metering devices are reactivated and the dispensing unit continues to dispense the mixed liquids. If the dispensing unit does not successfully complete the diagnostic cycle, then a full service has to be carried out before the dispensing unit can recommence work.

Figure 6 illustrates a robotic dispensing station incorporating a dispensing unit as shown in Figure 5.

Referring to Figure 6, a first source of liquid under pressure 31 is provided in the form of a drum 50 containing the first liquid, and a transfer pump 51 to pump the liquid.

Similarly a second source 32 of liquid under pressure is provided in the form of a drum 52, containing the second liquid and a transfer pump 53 to pump the liquid. Liquids from the drums 50, 52 are pumped to a housing 54 which contains two metering devices 33, 34 and the associated control arrangements 40, 43 as described above with reference to Figure 5. Two outlets 35, 37 from the housing 54 are connected to a two-bore hose 55 through which the two liquids flow to the mixer 36 provided with the static mixer 38.

A robot housing 56 is provided carrying an articulated arm 57 shown as comprising a first arm segment 58 and a second arm segment 59. Whilst the drums 50, 52 and the housing 54 are located adjacent robotic arrangement, the mixer 36 and dispensing nozzle 38 are provided on the free end of the second robot arm 59. The nozzle 38 is illustrated as being located immediately above a work-piece 60. The robot may be controlled in such a way that as the metering devices operate, and thus as liquid is dispensed through the static mixer 38, the arms 58, 59 of the robot are controlled so that the nozzle 38 executes a predetermined movement adjacent the work-piece 60. Thus a "bead" may be laid down, from the nozzle 38, on to the work- piece.

While the invention has been described with reference to an embodiment in which there are two metering devices metering two liquids that are mixed, in another, simple, embodiment only a single metering device is used to meter a single liquid. Such an arrangement may be used when it is desired to dispense a single liquid at a precisely pre-determined rate or in a pre¬ determined quantity.

When used in this Specification and Claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following Claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS:

1. A dispensing unit for dispensing at least one liquid, the unit comprising at least metering device, the or each metering device being configured to provide a plurality of sequential "shots" of liquid, the or each metering device generating output signal when a "shot" of liquid is being dispensed, the or each metering device being connected to a controller controlling the dispensing unit and terminating the operation of the dispensing unit whenever a metering device fails to generate an output signal confirming that a "shot" of liquid has been dispensed, the output of the or each metering device being connected to a dispenser from which the liquid or liquids are dispensed, the unit further comprising a pressure sensor associated with the output of the or each metering device and a control valve between the output of the or each metering device and a corresponding input to the dispenser, the controller being arranged to close the or each control valve and to monitor the pressure sensed by the or each pressure sensors.

2. A dispensing unit according to Claim 1 for dispensing a mixture of two liquids, the unit comprising two said metering devices, each metering device being configured to provide a plurality of sequential "shots" of liquid, each metering device generating an output signal when a "shot" of liquid has been dispensed, each metering device being connected to a said controller controlling the dispensing unit and terminating operation of the dispensing unit whenever one metering device fails to generate an output signal confirming that a "shot" of liquid has been dispensed, the outputs of the said metering devices being connected to a mixer from which the liquids are dispensed, the unit further comprising a said pressure sensor associated with the output of each metering device and a control valve between the output of each metering device and a corresponding input to the mixer, the controller being arranged to close the control valves and to monitor the pressure sensed by the pressure sensors.

3. A dispensing unit according to Claim 1 or 2 wherein the or each metering device is connected to a respective source of liquid under pressure, there being a control valve connected between the or each source of liquid under pressure and the corresponding input of the corresponding metering device, the controller being configured to actuate the or each control valve to disconnect the or each metering device from the respective source of liquid under pressure and being configured to monitor any subsequent pressure fall sensed by the or each sensor.

4. A dispensing unit according to Claim 1 , 2 or 3 wherein the controller is programmed to determine if any pressure rise or any pressure fall sensed by the pressure sensors is within predetermined limits and to reactivate the or each metering device or to prohibit operation of the dispensing unit in dependence upon the determination.

5. A dispensing unit according to any one the preceding Claims wherein each metering device incorporates an elongate chamber, there being a shuttle contained within the chamber, the shuttle having a portion which is a substantially sealing sliding fit within the chamber, the shuttle being moveable axially between an initial position and a second position within the chamber, each end of the chamber being provided with a liquid flow duct through which pressurised liquid may enter and leave the chamber, there being valve arrangement to control the flow of liquid to and from the chamber such that, during successive cycles of operation of the metering device, liquid is supplied to one end of the chamber causing the shuttle to move from the initial position at said one end of the chamber to the second position at the other end of the chamber, thus ejecting a pre-determined volume of liquid from the other end of the chamber, and subsequently liquid is supplied to said other end of the chamber causing the shuttle to move back from the second position to the initial position, ejecting a further pre-determined quantity of liquid from the said one end of the chamber, the valving means comprising a rotary valve rod contained within a valve bore, and a mechanism to rotate the valve rod, the liquid flow ducts from the chamber extending to the valve bore, at least one liquid inlet extending to the valve bore and at least one liquid outlet extending from the valve bore, the valve rod, in combination with the valve bore, defining liquid flow passages which, in one angular orientation of the valve rod, serve to interconnect a liquid flow inlet and the liquid flow duct extending to one end of the chamber whilst interconnecting the liquid flow duct extending to the other end of the chamber with an outlet and, in an alternate angular orientation, serving to interconnect the liquid flow inlet with the liquid flow duct extending to the other end of the bore whilst connecting the liquid flow duct extending to the said one end of the bore with an outlet.

6. A dispensing unit according to claim 5 wherein the shuttle is provided with two rods, each rod extending beyond the chamber, there being a contact of proximity sensor located adjacent the end of each rod to generate a signal when the shuttle reaches the initial position and the second position.

7. A dispensing unit according to Claim 2 or any Claim dependent thereon incorporated in a robotic dispensing station, the dispensing station incorporated a robotically controlled arm, the mixer being carried by the arm, the metering devices being connected to the mixer by a hose.

8. A dispensing unit according to Claim 7 wherein the station is provided with drums of liquid, each drum of liquid being provided with a transfer pump to pump the liquid.

9. A method of testing a dispensing unit which includes at least one metering device, for metering liquid under pressure, the outlet of the metering device being connected to a dispenser, the method comprising the steps of operating at least one valve to isolate the outlet of the or each metering device from the dispenser, and subsequently monitoring pressure at the outlet of the or each metering device to determine if the pressure at the or each outlet rises in a predetermined manner.

10. A method according to Claim 9 of testing a dispensing unit which includes two said metering devices, for metering liquid under pressure, the outlets of the metering devices being connected to a mixer, the method comprising the step of operating valves to isolate the outlets of the metering devices from the mixer, and subsequently monitoring pressure at the outlets of the metering devices to determine if the pressure at the outlets rises in a predetermined manner.

11. A method according to Claim 8 including the further steps of operating the or each metering device to increase the pressure in the outlets of the device, terminating operation at the device and then monitoring pressure at the outlet of the or each device to determine if the pressure falls in a predetermined manner.

12. A method according to Claim 9, 10 or 11 including the step of re¬ commencing ordinary operation of the dispensing unit or prohibiting operation of the unit until the unit has been serviced in response to the determination.

13. A dispensing unit for dispensing at least one liquid, the unit comprising at least metering device, the or each metering device being configured to provide a plurality of sequential "shots" of liquid, the or each metering device generating output signal when a "shot" of liquid is being dispensed, the or each metering device being connected to a controller controlling the dispensing unit and terminating the operation of the dispensing unit whenever a metering device fails to generate an output signal confirming that a "shot" of liquid has been dispensed, the output of the or each metering device being connected to a dispenser from which the liquid or liquids are dispensed, the unit further comprising a pressure sensor associated with the output of the or each metering device and a control valve between the output of the or each metering device and a corresponding input to the dispenser, the controller being arranged to close the or each control valve and to monitor the pressure sensed by the or each pressure sensors, the dispensing unit being for dispensing a mixture of two liquids, the unit comprising two said metering devices, each metering device being configured to provide a plurality of sequential "shots" of liquid, each metering device generating an output signal when a "shot" of liquid has been dispensed, each metering device being connected to a said controller controlling the dispensing unit and terminating operation of the dispensing unit whenever one metering device fails to generate an output signal confirming that a "shot" of liquid has been dispensed, the outputs of the said metering devices being connected to a mixer from which the liquids are dispensed, the unit further comprising a said pressure sensor associated with the output of each metering device and a control valve between the output of each metering device and a corresponding input to the mixer, the controller being arranged to close the control valves and to monitor the pressure sensed by the pressure sensors, wherein the or each metering device the or each metering device is connected to a respective source of liquid under pressure, there being a control valve connected between the or each source of liquid under pressure and the corresponding input of the corresponding metering device, the controller being configured to actuate the or each control valve to disconnect the or each metering device from the respective source of liquid under pressure and being configured to monitor any subsequent pressure fall sensed by the or each sensor, and wherein the controller is programmed to determine if any pressure rise or any pressure fall sensed by the pressure sensors is within predetermined limits and to reactivate the or each metering device or to prohibit operation of the dispensing unit in dependence upon the determination.

14. A method of testing a dispensing unit which includes at least one metering device, for metering liquid under pressure, the outlet of the metering device being connected to a dispenser, the method comprising the steps of operating at least one valve to isolate the outlet of the or each metering device from the dispenser, and subsequently monitoring pressure at the outlet of the or each metering device to determine if the pressure at the or each outlet rises in a predetermined manner, wherein the method is a method of testing a dispensing unit which includes two said metering devices, for metering liquid under pressure, the outlets of the metering devices being connected to a mixer, the method comprising the step of operating valves to isolate the outlets of the metering devices from the mixer, and subsequently monitoring pressure at the outlets of the metering devices to determine if the pressure at the outlets rises in a predetermined manner, the further steps of operating the or each metering device to increase the pressure in the outlets of the device, terminating operation at the device and then monitoring pressure at the outlet of the or each device to determine if the pressure falls in a predetermined manner, the method further including the step of including re-commencing ordinary operation of the dispensing unit or prohibiting operation of the unit until the unit has been serviced in response to the determination.