WO2019204865A1

WO2019204865A1 - On-demand mixing apparatus and method

Info

Publication number: WO2019204865A1
Application number: PCT/AU2019/050357
Authority: WO
Inventors: Grant Sidney MITCHELL; Stig Michael HOLMSTROM
Original assignee: Quik Corp Pty Ltd
Priority date: 2018-04-23
Filing date: 2019-04-23
Publication date: 2019-10-31
Also published as: AU2019258586A1

Abstract

According to an embodiment, and apparatus for on-demand mixing to produce a solution and deliver the solution through an output is disclosed, the apparatus comprising a solvent pump and a solute pump controlled in dependence on a set concentration. The solution output may be operator-controlled nozzle able to produce a variable spray. In certain embodiments a Venturi inductor is used for mixing the solute and solvent.

Description

On-Demand Mixing Apparatus and Method

Technical field

This disclosure relates generally to on-demand mixing apparatus and a related method. Background

On-demand mixing may involve creating a solution comprising a minor component (the solute) mixed with a major component (the solvent) at a location where, or time when, the solution is to be deployed. For example, when considering the spraying of pesticides, the solute is the pesticide concentrate and the solvent is water.

On-demand mixing is preferable to pre-mixed solutions since it may significantly reduce waste and allow for the safe storage, transport and disposal of the often toxic concentrate (the solute).

On-demand mixing is known where the flow rate is constant (the use of boom sprayers, for example). However, it has previously not been practical to

accommodate variable spray which may occur, for example, when a user applies the pesticide using a spray gun which has a variable spray pattern. Under these conditions, the rate of flow of the pesticide will vary as the user activates the gun as well as varying with the spray pattern selected. Often, more than one user may be operating corresponding spray guns from the same source, further increasing the variability of the flow of the pesticide.

Maintaining the correct concentration may be important, particularly when dealing with toxic substances such as pesticides. It has not previously been possible to maintain the concentration within acceptable parameters under these conditions of variable flow.

It has been found that using a process where the flow rate of the solvent is measured, and the flow rate of the solute is adjusted by setting a speed of a pump motor to match the flow rate of the solvent for a given concentration only works when the changes in flow rate of the solution are small and gradual. US2003127534A1 discloses a device for mixing a cleaning solution with water and applying that as a spray in a car wash. The apparatus is not able to vary the flow rate of both the solvent and the solution to deliver different concentrations at variable spray patterns.

US5,810,254 and US5,388,761 A relate to devices for applying polyurethane with a spray gun which atomises the solution using compressed air. To vary the spray pattern the rate of compressed air is altered; this does not change the flow rate of the solution.

Summary

According to an embodiment, an apparatus for on-demand mixing to produce a solution and deliver the solution through an output is disclosed, the apparatus comprising:

a solute conduit connectable to a source of solute;

a solute pump through which the solute conduit passes and which is adapted to control a flow-rate of the solute;

a solvent conduit connectable to a source of solvent;

a solvent pump through which the solvent passes and which is adapted to control a flow-rate of the solvent;

a solvent flow rate meter to determine a rate of flow of the solvent;

a solute flow rate meter to determine a rate of flow of the solute;

a processor for adjusting the solute pump to vary a flow rate of the solute in dependence on a determined solvent flow rate and a determined solute flow rate; and

a mixing chamber connected to the solute conduit and the solvent conduit for receiving the solute and the solvent, and for producing a solution, wherein a pressure of the solvent delivered by the solvent pump is variable and wherein a solution flow rate of the output is variable.

Embodiments therefore adjust the amount of solute in dependence on a determined solvent flow rate and the determined solute flow rate. This helps to ensure that the user-selected concentration may be maintained as the flow rate of solution varies. Furthermore, without being constrained by theory, it has been hypothesised that this helps to account for the hysteresis in the system and variations due to back-pressures.

Further, embodiments allow for variation in both the pressure of the solvent is variable, as is the flow rate of the solution delivered by the output of the apparatus. This allows the user to select both the concentration of the solute such as pesticide and the delivery rate of the solution whilst still ensuring that the concentration will remain constant as the delivery rate varies. This is particularly important where consistent concentration is needed such as in pesticide and fire fighting applications. Furthermore, since the output may be manually controlled, the pressure of the solvent (and corresponding pressure of the solute) have minimum requirements so that the solution may reach a sufficiently wide area for manual application to be practical.

The solute pump may include a motor and the solute flow rate meter may comprise a meter for determining a speed of the solute pump.

The apparatus may further comprise a manually adjustable nozzle for delivering the solution.

The nozzle may be able to adjust one or more of: a flow rate of the solution and a spray pattern of the solution.

The processor may adjust the solute pump to vary a flow rate of the solute to maintain a user-specified concentration of the solution.

The apparatus may further comprise a PID controller wherein the processor accesses the PID controller to vary the flow rate of the solute to maintain the user- specified concentration of the solution.

The apparatus may further comprise an alarm.

The alarm may be connected to the processor and the processor may be adapted to sound the alarm on the occurrence of one or more of: an underflow and an overflow.

The mixing chamber may be a Venturi inductor. The Venturi inductor may have a 1 .8 mm through hole. The size of the through hole may be selected based on a maximum pressure of the solvent pump and a desired maximum solution flow rate. The pressure produced by the solution pump may be 500 psi or less. The pressure produced by the solute pump may be 200 psi or less. A pressure produced by the solute pump may be lower than a pressure produced by the solvent pump.

The solvent may be water and the solute may be herbicide. In a further embodiment the solute may be a fire retardant.

A further embodiment relates to a method of on-demand mixing comprising: mixing a solvent and a solute in a mixing chamber to produce a solution; delivering the solvent to the mixing chamber at a selected rate;

setting a desired concentration for the solution;

obtaining a solvent rate measurement indicative of a flow rate of the solvent; obtaining a solute rate measurement indicative of a flow rate of the solute; calculating a value for a parameter related to the flow rate of the solute in dependence on the solute rate measurement, the solvent rate measurement and the desired concentration for the solution; and

setting the parameter to the value to thereby set the flow rate of the solute.

The solute may be delivered to the mixing chamber by a solute pump having a motor and the step of making a solute rate measurement comprises detecting a speed of the solute pump motor.

The method may further comprise adjusting one or more of: a flow rate of the solution and a spray pattern of the solution.

The method may further comprise sounding an alarm on the occurrence of one or more of: an underflow and an overflow.

The method may further comprise determining a relationship between the solvent flow rate and the solute flow rate over a range of operating values and wherein the step of calculating a value for a parameter related to the flow rate of the solute comprises utilising said relationship.

The method may further comprise altering the solute flow rate in dependence on a determination of the solute flow rate.

The method may further comprise determining a rate of rotation of the solute pump, and setting a voltage of the solute pump motor in accordance with the determined rate of rotation. The voltage of the solute pump motor may be set according a predetermined relationship between the determined rate of rotation of the solute pump and the voltage of the solute pump motor.

The relationship may comprise a PID algorithm. In this case, the solute flow rate may be altered with reference to both, or only one of, the line fit relationship and the PID algorithm.

The voltage of the solute pump may be set by a PID controller with reference to the PID algorithm.

To compensate for rapid changes in the flow rate of the solution, the flow rate of the solute is adjusted in dependence on a function of the measured flow rate of the solution. In one embodiment, the function is a line fit.

To further improve the accuracy of the system, a PID controller may be engaged for fine tuning. In an embodiment, the PID controller is engaged if the calculated flow rate of the solute (speed of the pump motor) is outside set margins.

There may also be an alarm to signal an under- or over-flow.

The method may further comprise the step of setting a pressure produced by the solute pump is lower than a pressure produced by the solvent pump.

The method may comprise mixing the solute and the solvent with a Venturi inductor. Brief description of Figures

Embodiments will now be described by way of example only with reference to the accompanying non-limiting Figures.

Figure 1 is a schematic illustration of an apparatus according to an

embodiment of the disclosure;

Figure 2 is a schematic illustration of an apparatus according to a further embodiment of the disclosure;

Figure 3 is a process diagram of operating the apparatus of Figure 1 or Figure 2; and

Figure 4 is a process diagram of operating the apparatus of Figure 1 or Figure 2 according to a further embodiment. Detailed description of embodiments

Figure 1 illustrates a mixing apparatus 10 according to an embodiment of the invention. Figure 1 is schematic and although the connections between various components is shown, it is to be realised that these connections will depend on the components involved. The connections may be mechanical, electrical or fluidic.

The mixing apparatus 10 comprises a water tank 12 which acts as a water reservoir. The water tank 12 is connected via a water conduit 48 to a diaphragm pump 14. The diaphragm pump 14 is connected via the conduit 48 to adjustable pressure controller 16. The adjustable pressure controller 16 is connected, via bypass 18, back to the water tank 12 and via water conduit 48 to check valve 20. The water conduit 48 then connects the check valve 20 to a flow meter 22 which, in turn, is connected via the conduit 48 to a mixing chamber 24. In this embodiment, the mixing chamber 24 is a T-piece. In this embodiment, the flow meter 22 is a paddle wheel flow meter, but it is to be realised that other flow meters could also be used.

Water passes through the water conduit 48 into the mixing chamber 24.

The apparatus 10 further comprises a herbicide tank 28 which is connected to a piston pump 30 by means of herbicide conduit 46. The herbicide conduit 46 then connects the piston pump 32 to a check valve 26 which, in turn, is connected to the mixing chamber 24.

In use, the diaphragm pump 14 controls the flow of water through the water conduit 48 and the piston pump 30 controls the flow of herbicide through the herbicide conduit 46. The herbicide and water are mixed in the mixing chamber 24 to produce a solution which exits the mixing chamber 24 through solution conduit 50, which is connected to spray nozzle 44.

As further illustrated in Figure 1 , the piston pump 30 is mechanically connected to a DC motor 32 which drives the piston pump 30. The DC motor 32 is connected to an RPM meter 34. The RPM meter 34 determines the speed at which the DC motor 32 operates to drive the piston pump 30. The DC motor 32 is controlled by a DC motor controller 36 and is connected thereto.

In the apparatus 10 herein described, the water conduit 48 which connects the water tank 12, diaphragm pump 14, adjustable pressure controller 16, check valve 20, flowmeter 22 and mixing chamber 24 has been described as a single conduit. It is to be realised however that the connecting portions of this conduit are not necessarily in fluid communication with one another and, in fact, such fluid communication would negate the function of certain of the components such as the check valve 20. It is to be realised therefore that the various components are connected by conduits as functionally required. Similar considerations apply to the herbicide conduit 46.

The flow meter 22 and the DC motor controller 36 are connected to a controller 38 which is further connected to an alarm 42 and to a display 40. The controller 38 is thereby able to control the piston pump 30 by controlling the DC motor controller 36 which controls DC motor 32 to vary the rate at which the piston pump 30 operates. The RPM meter 34 is connected to the controller 38 so that readings from this meter may be utilised by the controller 38 in the manner described below.

During use, a user operates the nozzle 44 to start and stop the flow, and to vary the flow pattern and flow rate. In an alternate embodiment, the nozzle is operable to vary only the flow pattern or only the flow rate. Generally however, most nozzles are able to start and stop the flow.

Operation of the apparatus 10 depends on setting the rate at which herbicide is delivered to the mixing tank 24 to maintain a user-specified concentration as the water flow rate varies with changes to the delivery through the nozzle 44. In order to do so, the relationship between the rate of flow of the water and the herbicide is established. In this embodiment, a straight line function has been implemented.

During a calibration phase, a straight line relationship is calculated using the least-squares fit:

DC Motor Voltage = K ^* Water Flow Rate

Where, DC Motor Voltage is the voltage applied to the DC motor 32. The

Water Flow Rate is the rate of flow of water in the water conduit 48 as determined by the flow meter 22. K is the constant to correct for the right DC voltage at a measured water flow rate. The table below outlines one of the test datasets that was used to calculate the line constant K for the embodiment of Figure 1. It is to be realised that an analogous process applies to the embodiment of Figure 2 (see below), although different readings would apply due to the different setup involved. Water flow Measured litres per minute from flow-meter

rate: sensor 22

Motor RPM: Measured motor RPM from RPM meter 34

Voltage: Measured voltage at the DC motor is

determined by the controller 38

Voltage/RPM: Calculated variable (see below)

Water flow Motor RPM Voltage Voltage/RPM

rate 4.3 0.56 0.130

0.79623 8.1 1.00 0.123

I.5728 16 I.50 0.094

2.949 30 2.55 0.085

3.932 40 3.40 0.085

4.915 50 4.00 0.080

5.898 60 5.08 0.085

6.881 70 5.9 0.084

7.864 80 6.7 0.084

9.83 100 8.4 0.084

10.813 110 9 0.082

II.796 120 9.95 0.083

12.779 130 10.7 0.082

13.6637 139 II.5 0.083

Line equation: Y (Motor Voltage) = m (K) ^* X (Water Flow Rate) Where m (K) is calculated by:

From this calculation we get the line-constant K, for this embodiment, to be 0.847 for the user-selectable concentration. This constant is then used in combination with the selected concentration to change the DC motor 32 speed as follows:

Motor Voltage = K * Water Flow Rate * Concentration

Figure 2 illustrates a mixing apparatus 70 according to a further embodiment of the invention. The mixing apparatus 70 is similar to the mixing apparatus 10 of Figure 1 and the same reference numbers are used to denote the same features. The mixing apparatus 70 of Figure 2 differs from the apparatus 10 of Figure 1 in that the mixing chamber 24 has been replaced by a Venturi inductor 60 connected to the water conduit 48 and the herbicide conduit 46. Furthermore, the pump which pumps the herbicide is a gear pump 62.

The check valve 26 may be provided as integral to the Venturi inductor.

A Venturi inductor has the advantage that it may allow for the pressure of the herbicide to be less that that of the water. In the embodiment of Figure 1 , the pressure of the herbicide must be greater than that of the water to allow mixing. As a result, the gear pump operates under reduced load, which may result in increased longevity for this pump as well as more reliable and consistent results. It is to be realised that similar advantages may be realised for other types of pumps too.

In this embodiment a Venturi inductor with a 1 8mm through hole has been selected. This limits the amount of water able to flow through the spray hose to the spray gun. In the embodiment of Figure 1 the controller 38 is pre-set to stop flow and sound the alarm 42 if the water flow exceeded 10 litres/min.

In the embodiment of Figure 2, using this 1 8mm through hole Venturi inductor, the maximum water flow permitted through this hole and into the spray hose to the spray nozzle 44 is limited to less than 10 litres/min at maximum water pump pressure (here 500 psi) - thereby alleviating the need for the Controller/Alarm limiting function to correct for system-induced excess flow. Flowever, the alarm is retained in the embodiment of Figure 2 to warn the operator when their actions cause an excess flow which could damage the components involved.

Pressure Solution Gear Flow

Control Conduit Pump Meter

(16) (psi) (50) (62) (22)

(psi) (psi) (L/min)

100 60 40 4.1

200 120 80 5.8

300^. 180^. 120^.7.2^. 400 240 160 8.3

500 300 200 9.5

A maximum gear pump 62 pressure of only 200 psi is required to inject herbicide into the solution conduit 50 at the maximum pressure of the pressure controller 16 of 500 psi (in this embodiment). Without the Venturi injector 60 the gear pump pressure would have to exceed the pressure produced by the diaphragm pump 14.

Furthermore, as can be seen from above tabulated results, the maximum flow at maximum pressure is 9.5 l/min - which is below the 10 l/min pre-set alarm/turn-off at the controller 38 for the embodiment of Figure 1.

The operation of the apparatuses 10 and 70 (both apparatuses are operated in the same way) will now be described with reference to the process of Figure 3.

The process begins at step 158 where the water flow rate is determined by the controller 38 with output from the flowmeter 22.

At the following step, step 160, a determination is made regarding upper and lower bounds of the flow rate.

These upper and lower bounds are set during initialisation and, in this embodiment, a lower bound of 3 litres per minute and an upper bound of 10 litres per minute have been set. If it is determined at step 160 that the flow rate is less than the lower bound or greater than the upper bound, the process proceeds to step 162 where the alarm 42 is sounded. The process will then proceed to step 164 where the DC motor 32 is stopped and the process will return to the beginning at step 152.

By stopping the DC motor 32 when the flow rate is outside of the

predetermined bounds, a dangerous over concentration can be avoided. Similarly, where the flow rate is too high, unnecessary wastage of the herbicide can be avoided.

If it is determined at step 160 that the water flow is within the upper and lower bounds, the process proceeds to step 166 where the output of the RPM meter 34 are determined by the controller 38. At the following step, step 168, user-specified settings, in particular the desired herbicide concentration, are determined. At the following step, step 170, the DC motor voltage is calculated with reference to the user-selected concentration. In this embodiment, this is done as follows:

DC motor voltage = user-selected concentration (as a percentage) ^* measured water flow (from step 158).

At the following step, step 172, it is determined whether or not the calculated DC motor voltage is outside preset margins. It is to be realised that the margins may be set according to the specific application of embodiments. In this embodiment, the margins are set at +/- 5% of the determined motor speed using the RPM sensor

If it is determined at step 172 that the calculated DC motor voltage lies outside of the margins, the process proceeds to step 174 where the PID controller is engaged for fine-tuning. In this embodiment, the feedback to the PID controller is the measured RPM of the DC motor and the output is the DC voltage (pulse width modulated) to the DC motor. The set point is the desired RPM value of the DC motor, based on the set mixing ratio and the current water-flow (flow meter sensor) at set out for step 170, above. The particular values selected for the PID controller will depend on a number of variables related to the precise layout and equipment used.

At step 176, the voltage of the DC motor is set according to the value calculated by the PID controller. At the following step, step 178, the display 40 is updated, and the process returns to the beginning at step 152.

If, at step 172 it is determined that the calculated DC motor speed lies within the acceptable margins, the process continues to step 180 where the speed of the DC motor 32 is controlled by setting its voltage according to the calculations set out above.

Lastly, the display 40 is updated with the values at step 182 and the process then returns to step 152.

In the embodiment illustrated, the PID controller is only engaged (at step 172) if the calculated value of the DC motor voltage are outside certain margins.

Therefore, the PID controller in this embodiment acts to fine tune the determined voltage.

Figure 4 illustrates a process diagram of operating the apparatus of Figure 1 according to a further embodiment. The same numerals have been used to denote similar steps to the process of Figure 3. The process of Figure 4 differs from that of Figure 3 in that the operation of the PID controller is not optional. Therefore in the process 200 depicted in Figure 4, after step 170, the PID controller will be engaged at step 174, following which, at step 176, the voltage of the DC motor is set according to the value calculated by the PID controller. Thereafter at step 178, the display 40 is updated, and the process returns to the beginning at step 152.

In further embodiments, the straight-line calculations may act to fine-tune the settings as determined by the PID controller for some, or all of, a range of motor voltages.

Although embodiments have been described with reference to herbicide, it is to be realised that any other liquid solute may be used. Similarly, use has been described with water but any other liquid solvent may be used instead.

The inventors have tested the ability of embodiments to maintain the user- selected concentration under varying spray patterns and what pressures. In general, it has been found that the user-selected concentration may be maintained with variances of less than 5%.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word“comprise” or variations such as“comprises” or“comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments.

Claims

1 . Apparatus for on-demand mixing to produce a solution and deliver the solution through an output, the apparatus comprising:

a solute conduit connectable to a source of solute;

a solvent conduit connectable to a source of solvent;

a solvent flow rate meter to determine a rate of flow of the solvent; a solute flow rate meter to determine a rate of flow of the solute;

2. The apparatus according to claim 1 wherein the solute pump includes a motor and the solute flow rate meter comprises a meter for determining a speed of the pump.

3. The apparatus according to claim 1 or claim 2 further comprising a manually adjustable nozzle for delivering the solution.

4. The apparatus according to claim 3 wherein the nozzle is able to adjust one or more of: a flow rate of the solution and a spray pattern of the solution.

5. The apparatus according to any preceding claim wherein the processor adjusts the solute pump to vary a flow rate of the solute to maintain a user-specified concentration of the solution.

6. The apparatus according to claim 5 further comprising a PID controller wherein the processor accesses the PID controller to vary the flow rate of the solute to maintain the user-specified concentration of the solution.

7. The apparatus according to any preceding claim further comprising an alarm.

8. The apparatus according to claim 7 wherein the alarm is connected to the processor and the processor is adapted to sound the alarm on the occurrence of one or more of: an underflow and an overflow.

9. The apparatus according to any preceding claim wherein a pressure produced by the solute pump is lower than a pressure produced by the solvent pump.

10. The apparatus according to any preceding claim wherein the mixing chamber is a Venturi inductor.

1 1 . A method of on-demand mixing comprising:

mixing a solvent and a solute in a mixing chamber to produce a solution;

delivering the solvent to the mixing chamber at a selected rate;

setting a desired concentration for the solution;

obtaining a solvent rate measurement indicative of a flow rate of the solvent;

obtaining a solute rate measurement indicative of a flow rate of the solute;

calculating a value for a parameter related to the flow rate of the solute in dependence on the solute rate measurement, the solvent rate measurement and the desired concentration for the solution; and

setting the parameter to the value to thereby set the flow rate of the solute and thereby alter the flow rate of the solute.

12. The method according to claim 1 1 wherein the solute is delivered to the mixing chamber by a solute pump having a motor and the step of making a solute rate measurement comprises detecting a speed of the solute pump motor.

13. The method according to claim 1 1 or claim 12 further comprising adjusting one or more of: a flow rate of the solution and a spray pattern of the solution.

14. The method according to any of claims 1 1 to 13 further comprising sounding an alarm on the occurrence of one or more of: an underflow and an overflow.

15. The method according to any of claims 1 1 to 14 further comprising determining a relationship between the solvent flow rate and the solute flow rate over a range of operating values and wherein the step of calculating a value for a parameter related to the flow rate of the solute comprises utilising said relationship.

16. The method according to claim 15 further comprising using a line fit relationship.

17. The method according to claim 15 or claim 16 wherein said relationship comprises a PID algorithm.

18. The method according to any of claims 1 1 to 17 further comprising altering the solute flow rate in dependence on a determination of the solute flow rate.

19. The method according to claim 18, when dependent on claim 12, further comprising determining a rate of rotation of the solute pump, and setting a voltage of the solute pump motor in accordance with the determined rate of rotation.

20. The method according to any of claims 1 1 to 19 comprising the step of setting a pressure produced by the solute pump is lower than a pressure produced by the solvent pump.

21 . The method according to any of claimsl 1 to 20 comprising mixing the solute and the solvent with a Venturi inductor.