WO1997028427A1

WO1997028427A1 - Method and apparatus for measuring dispensed doses of flowable material

Info

Publication number: WO1997028427A1
Application number: PCT/GB1997/000242
Authority: WO
Inventors: Clive Douglas Hatcher; John Numa Worth
Original assignee: W.R. Grace & Co.-Conn.
Priority date: 1996-02-02
Filing date: 1997-01-28
Publication date: 1997-08-07
Also published as: ZA97625B; GB9602160D0; AR005572A1; GB2309684A; AU1551197A; CO4650241A1; ID15859A

Abstract

Apparatus for measuring the dose of flowable material, preferably liquid, being dispensed comprises a reservoir pot (7) supplied with liquid via feed line (19) and having the surface level of the liquid sensed by two liquid level detectors (27) and (31) which define upper and lower limits of the level of liquid in the pot (7) at the start and finish of a given sequence of dosing operations. A dosing gun (1) is operated to dispense the material (29) by way of a supply line (5) and the number of dispensing doses is counted in order to enable the average dose magnitude to be determined by dividing (i) the quantity defined between the upper and lower liquid levels in the pot (7) by (ii) the counted number of cycles of the gun (1) for dispensing the material (29). The material (29) may for example be liquid compound for lining can ends. A load cell may be used to weigh the reservoir pot and contents, for establishing the magnitude of the batch of dispensed liquid by weight.

Description

METHOD AND APPARATUS FOR MEASURING DISPENSED DOSES

OF FLOWABLE MATERIAL

The present invention relates to a method of and apparatus for measuring the quantity of flowable material applied to workpieces during a continuous dosing operation on a stream of workpieces passing a dispensing station. The particular field to which the invention is principally applied is the application of liquid sealant to workpieces where a small quantity of sealant is required for each workpiece and it is desirable to know and control the quantity dispensed per workpiece. The invention also provides a method of controlling the quantity dispensed, by varying the dispensed dose in response to the measurement of the dose dispensed.

Particularly in the field of applying a liquid composition for can end lining, any system for measuring doses of lining compound must cater for the fact that the composition being dispensed is very viscous and may include an abrasive component. This therefore rules out mechanical flow meters to measure the rate of flow of compound during the dispensing sequence.

Likewise, the rates of flow of can end lining compound to a dispensing gun are in practice so low that it would not be possible to rely on a magnetic, electric or electronic flow meter. Nevertheless the effects of any abrasive constituent giving rise to nozzle wear, and the variation of viscosity of the dispensed compound in response to changes in temperature, cause the quantity dispensed to vary with time.

In the past in the application of a liquid sealant to metal workpieces such as can ends during long term production of lined can ends, it has been the practice to monitor the magnitude of dose dispensed, and to verify its uniformity with time, at regular intervals (for example hourly but sometimes only daily), by taking a pre- weighed batch of can ends (for example 10 in number) and feeding it through the lining apparatus and then re- weighing the same batch of can ends to determine the total increase in weight of that batch as a result of the lining applied. This value can be used to give the average weight of lining compound per can end.

The above described process has been found to be inadequate from the point of view of short term observation of the quality control of lined can ends, and also it requires considerable manual intervention.

It is an object of the present invention to provide a method and apparatus which enable the measurement of dispensed doses to be effected without manual intervention, and without interruption of the continuous process, during long term production of workpieces such as lined can ends.

Accordingly, a first aspect of the present invention provides a method of controlling dosing of flowable material administered in a plurality of doses, by calculating the average magnitude of dose based on the number of doses in a batch and the total quantity of material dispensed to that batch; and adjusting the magnitude of each dose to a desired value; characterized in that the doses are dispensed to a stream of workpieces passing a dosing station (23); in that the magnitude of the quantity of material to be dispensed to said batch is defined and the number of doses achieved from that defined quantity is measured, and then the average dose is derived by dividing the predefined quantity by the measured number of doses achieved therefrom; and in that the dosing to subsequent workpieces is adjusted in response to the thus determined average dose.

A further possibility is to observe a parameter of each dispensing cycle to determine local variations from one cycle to the next, or over a limited number of cycles, and to re-calibrate the cycle monitoring equipment using the averaged dose measurement of the longer term dose measuring system of the first aspect of the present invention. The parameter in question may, for example, be the feed pressure of the material being dispensed.

A further aspect of the present invention provides apparatus for controlling the magnitude of doses of flowable material being dispensed by dispensing means:- including means for delivering a quantity of material to said dosing means; means for triggering the start and finish of a sequence of dosing operations using said quantity of material; and means for adjusting the magnitude of doses of the material in response to a dose evaluation based on the number of dosing operations in said sequence and the magnitude of said quantity of material; characterized in that the means for delivering a quantity of material to be dosed include means for defining a predetermined quantity to be dosed; in that the means for counting the number of doses are responsive to the start and finish of delivery of said predefined quantity of material; and in that the dispensing means is a dispensing nozzle past which passes a stream of workpieces to be imparted a said dose of the flowable material before onward movement from the nozzle, whereby the adjustment of dose magnitude is effected on the doses dispensed to workpieces passing said dispensing means after said batch of workpieces has passed.

Preferably the apparatus is combined with means for adjusting the dose magnitude. More preferably the dispensing apparatus may further include means for monitoring on a cycle-by-cycle basis to observe a parameter, for example pressure, which varies during the cycle and whose excursion can therefore indicate the regularity or non-regularity of successive doses, and means for re-calibrating the cycle- by-cycle monitoring equipment in response to the output of said averaging means. In order that the present invention may more readily be understood the following non-limiting description is given, merely by way of example, with reference to the accompanying drawings in which:-

FIGURE 1 is a schematic view of a first embodiment of apparatus for dispensing regular doses of liquid can end lining compound to a succession of can ends passing through a lining machine, and equipped with means for measuring the dose on an averaging basis;

FIGURE 2 is a view of a modified form of the equipment illustrated in Figure 1;

FIGURE 3 is a schematic view of a logic control system in the equipment illustrated in Figures 1 and 2; and

FIGURE 4 is a trace of variations of pressure in the feed line for lining compound to the dispensing gun of Figures 1 and 2, for the purposes of observing the regularity of dispensing shots on a cycle-by-cycle basis.

In Figure 1 there is shown a dispensing gun 1 for lining compound to line a succession of can ends (not shown) passing under the nozzle 3 of the gun.

The supply line 5 of lining compound to the gun 1 runs between on the one hand an entry pipe, in this case a dip tube 6, in a reservoir pot 7 inside a preferably pressurized sealed enclosure 9 and, on the other hand, the gun 1. The entry pipe may, if desired, enter through the floor of the reservoir pot 7.

An air supply 11 applies air pressure to the interior of the sealed enclosure 9 by way of a pressurised air line 13 in which the pressure can be regulated by means of the pressurization valve 15a of a control valve 15. The analogue input 15b of the valve 15 is directly controlled by an output 15c from a logic control unit 17.

Lining compound is introduced into the bottom of the pot 7 by way of a compound feed line 19 passing in a sealed manner through the floor of the pressurized enclosure 9. In this embodiment the supply of compound to the compound feed line 19 is controlled by a spring-loaded valve 21 having a compound shut-off valve 21a driven by a pneumatic pilot valve 21b which is supplied with driving air from the pneumatic shut-off valve 23a of a solenoid valve 23 whose solenoid 23b is driven by a further output 23c of the logic control unit 17. There are other possible ways of controlling compound feed, as will readily occur to the expert in the art.

In Figure 1 the same reference numeral 11 is used to denote the fact that a common air supply 11 feeds both the pressurization air valve 15a and the air supply to the driving air valve 23a of solenoid valve 23. However, if desired, different air supplies at different supply pressures could, if desired, be used. The control inputs to the logic control unit 17 comprise firstly a line 25a carrying a "gun shot counter" or "can end counter" signal (in the former case preferably from the solenoid coil forming part of the lining compound gun 1), secondly a "high compound level" signal line 27a from a high compound level detector 27 extending into the pressurized enclosure 9 and dipping into the reservoir of compound 29 in the pot 7, and thirdly a "low compound level" signal line 31a connected to a low compound level detector 31 again extending into the pressuriza¬ tion enclosure 9 and dipping into the compound 29 in the pot 7 at a level lower than that to which the detector 27 is immersed.

The liquid level deteαors 27 and 31 in Figure 1 may be of any suitable type but are preferably conduttive level detectors which respond to the level of the interface between the compound 29 and the pressurizing atmosphere. In use of the apparatus of Figure 1, when the low compound level detector 31 indicates that the level in the pot 7 has fallen to the predetermined low level at which replenishment is required, this "low compound level" signal on the line 31a results in the logic control unit 17 generating an output on the line 23c which activates the solenoid 23b to open the driving air valve 23a of solenoid valve 23 to open the compound supply valve 21a of the servo valve 21b, against the spring effort closing the compound supply valve 21a, to allow feed of compound to the reservoir quantity 29 by way of the compound feed line 19. This continues until a "high compound level" signal is generated by the high compound level detector 27, applying a "high compound level" signal on the line 27a to alert the logic control unit 17 to the fact that replenishment has been completed and that the compound supply valve 21a must be closed (by activating the solenoid 23b to close the driving air valve 23a) preferably allowing driving air between the valve 23a and the pilot valve 21b of the servo valve 21 to be vented to atmosphere to allow rapid closing of the compound feed valve 21a.

This same "high compound level" signal on the line 31a can be used for triggering the logic control unit 17 to start counting the succession of "gun shot counter" or "can end counter" signals on the line 25a. In practice, in order to avoid inaccuracy due to valve delay resulting in overfilling to some extent of the reservoir pot 7, the logic control unit starts the counting as it senses the end of the high level of the binary signal. Counting continues until the level of compound 29 in the pot 7 has fallen to the above-mentioned low compound level detected by the low compound level detector 31, at which point a fresh "low compound level" signal is applied to the logic control unit, ceasing the count of dispensing gun shots or can ends and initiating replenishment.

The logic control unit divides (i) the total volume change of compound 29 in the pot 7 during this dispensing sequence between successive replenishments by (ii) the number of gun shots or can ends counted during that sequence between successive replenishments, in order to provide an average volume dispensed per gun shot or can end signal which can if necessary be used to correct the dispensed quantity to a predetermined value, for example by opening the pressurization air valve 15a to increase the pressurization of the enclosure 9 in order to increase the dispensed dose, or by maintaining the pressurization valve 15a closed (by appropriate control of the valve 15 thanks to the output line 15c from the logic control unit 17) to allow the pressure within the enclosure 9 to drop as the air space increases due to dropping of the level of the compound/air interface at the top of the mass 29 of compound in the pot 7. Thus the actual quantity dispensed can be controlled to a desired value thanks to the averaging compound dose measurement.

Preferably the horizontal cross-section of the pot 7 is constant throughout its height so that the drop in level of the compound/air interface is directly proportional to the change in volume between those levels, in order to provide easy measurement of the volume of compound dispensed. For example, the pot 7 may be cylindrical to achieve this result. This allows variation of the total volume of doses dispensed between replenishments by adjusting the positions of at least one of the detectors 27 and 31 relative to the pot 7. However, if the two levels defined by the detectors 27 and 31 are fixed then it will not be so important to provide this constant surface area of the interface, because the volume dispensed between the end of the "high level" signal on line 27a and the "low compound level" signal (on line 31a) can be measured to calibrate the apparatus.

An alternative form of the measurement apparatus is shown in Figure 2 where this time the pot 107 is supported in the pressurized enclosure 9 on a load cell 151 used to weigh the compound in the pot 107 (the weight of the pot itself being known and in any case able to be eliminated by subtracting the "low compound level" weight signal from the "high compound level" weight signal of the load cell). In this embodiment those components which are identical to components of Figure 1 are denoted by the same reference numerals and those which are different from but analogous to components of Figure 1 have their reference numerals increased by 100.

The Figure 2 embodiment includes a pressurization line 13 from the pressurization valve 15a of the control valve 15 controlled by the logic control unit.

However, in this embodiment the compound feed line 119 communicates with an inlet 120 sealed into the pot 109 and discharging the compound near the bottom of the body 29 of compound in the pot 107. The servo valve 21 in Figure 2 is directly equivalent to that of Figure 1 but is repositioned; the solenoid valve 23 applying driving air to the valve 21 is in the same position as the valve 23 of Figure 1.

Pressurization air to the enclosure 9 is applied by way of the overhead pressurization line 113 between the control valve 15 and the ceiling of the enclosure 9.

Again the compound supply line 5 extends between, on the one hand, the take-off tube 6 dipping into the body 29 of compound in the pot 107 and, on the other hand, the gun 3. This embodiment also has a "gun shot or can end counter" signal line 25a equivalent to that of Figure 1.

In this case the "compound weight" signal on the line 153 extends between an output of the load cell 151 and an input of the logic control unit 117. The sequence of operation in this case is as follows:- When the "compound weight" signal on line 153 reaches a predetermined lower value indicating the need for replenishment of the body 29 of compound in the pot 107, the logic control unit 117 operates the solenoid 23b to open the driving air valve 23a, and hence to pressurize the pilot valve 21b, to open the compound feed valve 21a to introduce compound into the pot 107. During this introduction of compound the "compound weight" signal on the line 153 is monitored between a lower weight set point at which replenishment starts and a predetermined upper weight set point at which replenishment ceases and the count of the "gun shot counter" or "can end counter" signal on the line 25a begins. Suitable provision may be necessary in the logic control system to allow for possible overfilling of the reservoir due to valve time delays. The count should not start if the compound feed valve is open but only when the upper weight set point is reached after the compound supply has been shut off i.e. the weight has decreased to the upper set point.

In this case the weight of compound being dispensed throughout the sequence between successive replenishments is known and, as in the case of Figure 1 embodiment, the average weight applied per can end is determined by the logic control unit simply by dividing the "compound weight" signal by the "can end counter" or "gunshot counter" signal. As a result the necessary correction of dose magnitude can be effetted by an appropriate signal on the output line 15c to control the valve 15 either to increase the pressure within the enclosure 9 or to maintain the mass of air in the enclosure 9 unaltered, in which case the air volume will gradually increase during the dispensing operation.

It will of course be understood that, for the device of Figure 2 to operate accurately, the load cell 151 must support only the pot 107 and that that the quantity 29 of compound therein, and hence the two dip tubes for compound supply 120 on the one hand and for compound extraction 6 on the other hand, are secured to the pressurized enclosure 9 and dip freely into the lower pan of the pot 107.

Throughout the above description it has been mentioned that the correction for an excessively large dose is effetted by simply avoiding replenishment of pressurization air in the enclosure 9. In the event that air is constantly consumed by use of the apparatus it may instead be the case that the quantity of pressurization air is replenished, but by a quantity which is less than that which would be introduced after a "low average dose" magnitude signal. On the other hand, it may even be the case that a venting action is provided by virtue of the pressurization valve 15a, hence allowing some of the pressurization air to be vented off to reduce the internal pressure in the enclosure 9. In general the apparatus illustrated in Figures 1 and 2 can be used for any flowable material and not simply liquid as described herein.

Figure 3 shows in more detail the logic control system. The logic control unit 17 includes a first input 55 indicative of either compound weight or volume, and a second input 57 indicative of the number of dispensing shots during the sequence between successive replenishments.

When the compound weight is the signal which is determined at the input 55 then this will be the difference between two separate signals from the load cell 151 of Figure 2 with different (start-of-batch and end-of-batch) quantities of compound in the pot, so that subtraction will both eliminate the weight of the pot 107 and simply give a value for the weight of a batch of compound dispensed during the dispensing sequence (between successive replenishments) where the signal really serves to define the start and the finish of the "window" during which the gun shots or can ends are counted. The signals from inputs 55 and 57 pass to a divider 59 whose output is applied at one input 61 of a comparator 63.

In the case of the Figure 1 embodiment it is again the start and finish times of the "window" which are defined by the unit 55 but this time the signals on 55 correspond to the "high liquid level" signal on line 31a and the "low liquid level" signal on line 27a, respectively.

A first function of the logic control unit 17 is to control the replenishment operation of the compound feed valve 21 in either of the Figure 1 and Figure 2 embodiments. Consequently the compound control valve unit here referenced 65 (representative of the assembly of the output line 23c, the solenoid valve 23 and the servo valve 21 of Figures 1 and 2) is controlled by an output 67 of the logic control unit 17 which simply defines the start and finish of a replenishment cycle. The means for achieving this control will be well known to the expert in the art and do not require any further description here.

A secondary function of the logic control unit 17 is to provide for attainment and maintenance of a target dose magnitude value. To achieve this it relies on an input from an "ideal setting" unit 69 which is effectively an input generator which provides an input signal to the input 71 of the comparator 63 which can be compared in the comparator with the signal at input 61 from the divider 59 in order to generate an error signal in error signal unit 73. This error signal is used to control the air pressure regulator unit 75 in an appropriate manner so as to eliminate the error signal by restoring the output of the divider 59 to be equal to the output of the "ideal setting" unit 69. As described above, it achieves this by appropriate maintenance of pressurization or by venting of some of the pressurization air or boosting the pressurization pressure, within the pressurized enclosure 9 in order to decrease or increase the pressure-induced flow of compound through the delivery line 5 to the gun 1.

The operator manual input is thus greatly reduced in that now all that is required, assuming that some change in the target dose magnitude is necessary, is for the "ideal setting" unit to be adjusted to output a signal equivalent to the new target dose magnitude and then the logic control unit 17 will carry out the necessary measurement and adjustment to attain that new target magnitude.

A variant of the apparatus of Figures 1 to 3 is one which has an air pressure sensor 33 in the compound input line 5 to the gun 1 as shown in dotted lines in Figure 1. This pressure sensor enables a trace 61 (Figure 4) of compound pressure to be derived continuously on a cycle-by-cycle basis.

As a result any failure of the gun 1 to operate when a particular can end is present (for example due to the valve of the dispensing gun 1 sticking) will immediately be detected and that particular workpiece (can end) can be rejected as unlined. Equally, the trace of the pressure variation on a cycle-by-cycle basis can be analysed in order to determine that the full duration of the dosed dispensing (i.e. dispensing of a full dose) has been achieved, and that the rate of outflow of compound during each dispensing cycle is correct.

This pressure sensor 33 may be associated with a compound pressure analyser unit (not shown) in order to effect the above-mentioned signalling of a reject (unlined) can end, or of any other can ends for which the compound pressure pulse during that dispensing cycle is different from normal (signifying a can end which has an incorrect dose of lining compound thereon). To the extent that the actual quantities dispensed may vary with time and yet the pressure trace of the sensor 33 may not reflect such variations (for example due to wear in the sealing faces of the dispensing valve), it is possible for the logic control system of Figure 3 to be used to output, either in parallel with or instead of the air pressure regulator 75 shown in Figure 3, a correction signal which re-calibrates the cycle-by-cycle pressure analyser unit (not shown) associated with the pressure sensor 33. In this way it is possible to ensure that the pressure-responsive cycle-by-cycle control of the machine is still corrett over prolonged periods of time, due to the ability to measure the weight of the dose of lining compound (in the case of Figure 2) or the volume of lining compound (in the case of Figure 1 where there will then be a direct portionality between the weight and the volume) during long term operation of the apparatus. We have indicated above that it is traditional for the monitoring to be effected at regular intervals of for example 1 hour or even only at daily intervals, by throughputting of a batch of pre-weighed can ends. By contrast, and as an example of the improvement offered by the apparatus of Figures 1 and 2, given that the quantity of compound dispensed between successive replenishments is expected to be sufficient to apply linings to a number of can ends of the order of 100, and given typical cycle speeds of 400 to 500 can ends per minute, the measurement frequency now increases greatly above the best previous rate of 1 per hour which is typical with the operator-controlled process used conventionally.

As a convenient way of implementing the apparatus of Figures 1 and 2, it is possible for the pressurized enclosure 9 with the pot 7 or 107 therein to be used together with the rotary union described in WO-A-96/31290.

The apparatus described above can either be built into a can end lining apparatus during manufacture, or be sold separately as an accessory or as a retro fit item.

Claims

C L A I M S

1. A method of controlling dosing of flowable material administered in a plurality of doses, by calculating the average magnitude of dose based on the number of doses in a batch and the total quantity of material dispensed to that batch; and adjusting the magnitude of each dose to a desired value; characterized in that the doses are dispensed to a stream of workpieces passing a dosing station (23); in that the magnitude of the quantity of material to be dispensed to said batch is defined and the number of doses achieved from that defined quantity is measured, and then the average dose is derived by dividing the predefined quantity by the measured number of doses achieved therefrom; and in that the dosing to subsequent workpieces is adjusted in response to the thus determined average dose.

2. A method according to claim 1, comprising loading a reservoir (6) to a predetermined high level (27b), with flowable material to be dispensed; dispensing a sequence of doses therefrom, down to a predetermined low level (31b) at which loading is to resume; counting the number of doses between departure from said high level and arrival at said low level; and calculating the magnitude of the dose using the batch volume between said predetermined low level and high level states of the flowable material in the reservoir.

3. A method according to claim 1, comprising :- loading a reservoir

(107) with material to be dispensed; weighing the reservoir after loading, to derive a first weight value; monitoring the change of weight during dispensing of a sequence of doses therefrom; defining a second, lower weight of the reservoir corresponding to the reduced weight after dispensing a known weight of material dosed; and counting the number of doses between departure from said first weight value and arrival at said second weight value.

4. A method according to claim 1, and including the step of monitoring a parameter indicative of the dosing operation cycle-by-cycle, in order to determine any malfunctions during individual dose cycles by use of a control unit (75) responsive to said parameter, and calibrating said control unit in response to the averaging division operation of the dose measuring method.

5. A method according to claim 4, wherein said parameter indicative of the dosing operation is the pressure in the supply line of material being dosed.

6. A method according to claim 4 or 5 and including the step of generating a "reject workpiece" signal in respect of a workpiece for which a malfunction of the dosing cycle has been determined.

7. A method according to any one of claims 1 to 5, when applied to the application of liquid lining composition to can ends being lined.

8. Apparatus for controlling the magnitude of doses of flowable material being dispensed by dispensing means (23):- including means for delivering a quantity of material to said dosing means (23); means for triggering the start and finish of a sequence of dosing operations using said quantity of material; and means for adjusting the magnitude of doses of the material in response to a dose evaluation based on the number of dosing operations in said sequence and the magnitude of said quantity of material; characterized in that the means for delivering a quantity of material to be dosed include means (7, 27, 31; 107, 151) for defining a predetermined quantity to be dosed; in that the means (55) for counting the number of doses are responsive to the start and finish of delivery of said predefined quantity of material; and in that the dispensing means (23) is a dispensing nozzle past which passes a stream of workpieces to be imparted a said dose of the flowable material before onward movement from the nozzle, whereby the adjustment of dose magnitude is effetted on the doses dispensed to subsequent workpieces passing said dispensing means after said batch of workpieces has passed.

9. Apparatus according to claim 8, wherein said means for defining a quantity of material to be dosed comprises a reservoir vessel (107) to hold liquid material to be dosed, and a load cell (151) operable to measure the combined weight of the reservoir vessel and liquid therein; and wherein said quantity of material being dispensed during a sequence of doses comprises the weight of compound between a pre-defined higher weight output signal of said load cell and a pre-defined lower weight output signal of said load cell.

10. Apparatus according to claim 8, wherein said means for defining a quantity of material to be dispensed comprises a reservoir vessel for material to be dispensed, means (27, 31) for sensing an upper level (27b) and a lower level (31b) of liquid in said reservoir vessel.

11. Apparatus according to claim 10, wherein said means defining upper and lower levels of material in said reservoir vessel comprise conductive liquid level detectors.

12. Apparatus according to any one of claims 8 to 11, wherein said means (75) for adjusting the magnitude of each dose comprises means for adjusting the magnitude of pressurization which expels liquid from the reservoir vessel to a dispensing unit.

13. Apparatus according to any one of claims 8 to 11, and further including a sensor (33) for sensing the pressure in the or a supply line extending from the means for defining a quantity of material to be dispensed to a dispensing unit (23) for dispensing said material, and means responsive to the pressure sensor in said supply line for indicating either a partial dose or zero dose at any individual dosing cycle, and wherein said control means are also responsive to the output of a control unit which determines the average dosing magnitude by dividing the pre-defined quantity of liquid material being dispensed by the number of doses dispensed.

14. A method of measuring doses of flowable material being dispensed, substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.

15. A method according to claim 14 when modified substantially as hereinbefore described with reference to Figure 1 or to Figure 4 of the accompanying drawings.

16. Apparatus for measuring the dose of flowable material being dispensed, construtted and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in Figures 2 and 3 of the accompanying drawings.

17. Apparatus according to claim 16, when modified substantially as hereinbefore described with reference to Figure 1.