EP0731939A1

EP0731939A1 - Device for the controlled dosing of a fluid

Info

Publication number: EP0731939A1
Application number: EP95902826A
Authority: EP
Inventors: Yves Lecoffre
Original assignee: HELISPIRE
Current assignee: HELISPIRE
Priority date: 1993-12-03
Filing date: 1994-12-02
Publication date: 1996-09-18
Also published as: WO1995015520A1; FR2713362A1; AU1193395A; FR2713362B1

Abstract

The present invention relates to a device providing for the metering of a small flow rate of a fluid (1) by using a second drive fluid (2), the pressure of which is regulated, the flow rate of one or the other of said fluids being measured by determining head losses for long channels operating in laminar flow (14, 15, 16, 36) and arranged on their paths. It is thus possible to produce quasi universal dosers whose range of flows may reach typically 1000. It is also possible to dose dangerous fluids or fluids whose rheological properties are complex by measuring the flow rates of the drive fluid separately from the fluid to be metered, both fluids being separated by a wall or free surface. The laminar head losses may be obtained by means of spirals engraved in insets in contact with planar walls.

Description

DEVICE FOR DOSING A FLUID IN A CONTROLLED WAY

The present invention relates to a device for dosing fluids from a tank or from pressurized pipes. More specifically, it involves injecting small amounts of fluid in a controlled manner.

In many situations, it is necessary to inject small quantities of fluids, for example to make deposits, to administer liquid or gaseous drugs or to make mixtures. The classic applications include the deposition of adhesives and sealants in the automotive industry, the controlled deposit of ink in the engraving or printing industries, the controlled injection of reagents into an online chemical reactor. It sometimes happens that the products to be injected are chemically aggressive, have a degree of purity such that they cannot withstand any contact with mechanisms comprising seals or having complex rheological properties.

When, in addition, the flow rates to be delivered are very low, there is no measurement method available that can be used in real-time control. This makes precise dosing of such fluids very difficult.

Existing systems are often manual. Until recently, this was the case with the application of adhesives in the automotive industry. They are sometimes coupled to a robot, but the installation is adjusted on the basis of regular measurements, carried out manually by an operator, which give only an indication of the volume injected during a pass.

In this type of application, it would be necessary not only to control the average flow rate but also to adapt it to an external control and therefore to carry out a real control-command of the flow rates injected in almost real time.

Such an operation requires on the one hand a means of measuring the flow rates and on the other hand a means of action on said flow rates. The present invention avoids most of the drawbacks of current systems. According to the invention, the fluid to be injected is, in general, contained in a pressurized tank and flows from said tank through a pressure drop. Pressurization can be carried out by the fluid to be metered itself if it is forced into the tank by a compressor, a pump or a high pressure tank or by a second fluid which is easier to handle or can be stored under a level of significant pressure. In the latter case, the fluid can be a liquid or a gas.

The present invention essentially consists in placing at one point located on the circuit consisting of the fluid or of all of the fluids one or more laminar pressure drops provided with a differential pressure sensor which makes it possible to measure the volume flow in real time and to give the information necessary for adjusting an actuator intended to vary the pressure in the reservoir of the fluid to be metered.

More precisely, according to the invention, the flow control device is characterized in that it comprises: a reservoir containing the fluid to be dosed and a working fluid which compensates for the loss of liquid and makes it possible to pressurize said reservoir, a means for pressurizing the working fluid, a means for regulating the pressure of the working fluid as a function of the needs for the fluid to be metered, laminar pressure drop means mounted on the line in which one or the other of the fluids circulates for determining the flow rate of fluid passing through the line, and control means of the regulating means for modifying the pressure in the reservoir as a function of the value of the flow rate to be dosed and of the physical characteristics of the fluid passing through the laminar pressure drop means .

By using several pressure drops of different characteristics placed in parallel at a given point on the circuit and opened successively as required, a very large range of flow rates can be obtained. The device is then an almost universal dispenser for very low flow rates.

According to a first embodiment, the flow rate of the fluid to be delivered is directly measured and the flow rate of the working fluid is acted upon to regulate the flow rate delivered. According to a second embodiment, the flow of working fluid is measured and controlled, which makes it possible to control the flow of fluid which will ultimately be delivered. This second mode of implementation is particularly well suited to the case where the fluid to be delivered is a very viscous liquid.

Other characteristics and advantages of the present invention will be better understood during the detailed description of exemplary embodiments which follows, illustrated by the appended drawings in which: - Figure 1 is a view in longitudinal section showing the essential parts d 'a first particular embodiment of an apparatus for generating a low regulated flow rate in which the fluid to be injected is a liquid, the propellant fluid being a gas;

- Figure 2 is a longitudinal sectional view of a variant of the first particular embodiment of an apparatus according to the invention in which the pressure drop elements and the control valves are integrated into the tank cover;

- Figure 3 gives an embodiment of the laminar pressure drop element; - Figure 4 is a longitudinal sectional view of a second embodiment of an apparatus according to the invention, in which the fluid to be injected is contained in a deformable reservoir itself contained in the pressurized reservoir; and

- Figure 5 illustrates in detail a preferred form of implementation of the second embodiment of the invention.

Figure 1 illustrates an embodiment of an apparatus for creating a controlled flow of low flow fluid. The liquid 1 for which the flow is to be controlled is contained in a reservoir 3. It is pressurized by means of a gas 2 initially contained in a high pressure reservoir 4, then expanded through a regulator 5 and a laminar pressure drop 7. The pipes 8 and 9 are connected to the reservoir 3 and make it possible to admit or evacuate the gas by opening the all-or-nothing valves 6 and 11. In order to reduce the gas flow during these operations , each of these pipes is provided with a pressure drop 7 and 10 operating in laminar mode. The opening or closing of one or other of the valves 6 and 11 is controlled by the automaton 22 to starting from the knowledge of the flow rate of the liquid to be dosed, the pressure and the temperature of the fluid measured by the pressure 20 and temperature sensors 21. The liquid to be dosed is, for its part, extracted from the reservoir 3 through the piping 12 which supplies three laminar pressure drops 14, 15, 16, arranged in parallel with known characteristics. The fluid lines on which these pressure drops are placed are provided with all-or-nothing valves 17, 18, 19. The fluid is then directed to use through the piping 13.

The operation of the device is as follows: a flow order is given to the controller 22 by an operator or a computer. The automaton measures the temperature of the liquid using the temperature probe 21. It calculates the viscosity of the fluid from this temperature measurement. It deduces therefrom by calculation the pressure drop 14, 15 or 16 to be used and the pressure difference to be created between the tank 3 and the piping 13. If the pressure difference measured by means of the sensor 20 between 3 and 13 is less than this set value, the valve 6 is open, the valve 11 being closed, which has the effect of introducing gas into the tank 3 and therefore increasing the pressure. Otherwise, corresponding to a too large pressure difference, the valve 6 is closed and the valve 11 is opened. The gas then escapes from the tank 3 and the pressure drops. The pressure control is therefore done by intermittent closing and opening of all-or-nothing valves on the gas circuit. A variant of the process not shown in the drawings consists in using a traditional pressure regulation system, but the gas consumption is then much greater.

FIG. 2 gives an embodiment of a metering device based on the principle described in the previous figure in which the laminar pressure drops are integrated into the cover of the device. We find the elements described above, the reservoir 3, the fluids 1 and 2 and the pressurized gas reservoir 4, the gas lines 8 and 9 provided with laminar pressure drops 7 and 10 and all-or-nothing valves 6 and 11. The pressure and temperature sensors 20 and 21 are connected to the automaton 22 which, on the basis of the flow rate setpoint and the properties of the fluid to be metered, chooses one of the lines for discharging the liquid flow rate. through one or the other of the laminar pressure drops 14, 15 or 16 by opening one or the other of the solenoid valves 17, 18 or 19. On the other On the other hand, said automaton 22 controls the pressure in the reservoir 3 by opening or closing the all-or-nothing valves 6 and 11 of the gas lines.

In this embodiment, the pressure drops consist of shallow spirals engraved in pellets in the form of wafers, an example of which is given in FIG. 3. These engravings, brought into contact with a cylindrical counterbore, constitute a passage of small section through which the fluid passes. It therefore constitutes a long and small diameter element capable of constituting a laminar pressure drop. In the example of Figure 2, these wafers are inserted between plates 23, which allows for a compact assembly. The pressure drops 14, 15 and 16 are on a first level of the stack. The pressure drops 7 and 10 on the gas are at a second level. The upper and lower elements of FIG. 2 are respectively a section at the level of the pellets 14, 15 and 16 and a top view showing the arrangement of the on / off valves.

By way of example, we give some figures concerning figure 2. The tank 3 has a height of 150 mm and a diameter of 100 mm. It is filled with 1 liter of liquid to be dosed. The pressure drop elements 14, 15 and 16 have hydraulic diameters D of 60, 100 and 170 microns and a length of L of 1 meter. The pressure in the tank is regulated by means of pressure drops 7 and 10 and all-or-nothing valves 6 and 11 in a range between 1 and 10 bar. The nominal dynamic viscosity μ of the liquid to be dosed is 10-3 p _a .s. The liquid flow rate is given by the following expression:

ΔpD * ^{υ ~} 40 L

The range of flow rates therefore goes from 3.2 10 ^-11 m ³ / s (2.8 cm ³ / d) for the couple (1 bar, 60μ) to 2 10 ^-8 m ³ / s (72 cm ³ / h) for the couple (10 bar, 170μ). The flow dynamics are therefore around 1000.

It will be understood that it suffices to change the pellets 14, 15 and 16 to modify the range of flow rates or adapt it to a fluid of different viscosity. Figure 3 gives a representation in longitudinal section and top view of the spiral laminar pressure drop 7, 10, 14, 15, 16 or 35. In order to facilitate understanding, the parts 37 and 38 are shown diagrammatically by two cylindrical pellets. The fluid penetrates at 39 through the part 37, feeds the spiral 40 of which only a limited number of turns has been shown, then leaves the groove through the orifice 41.

French patent application No. 90 13553 of 10/31/1990 describes in more detail the production of such a capillary channel. Patent application PCT / FR 92/01075 describes another embodiment of a channel with a very small passage section by association of a cylinder and a helical spring wound on said cylindrical. Such a very low flow device could be substituted for that shown in FIG. 3. FIG. 4 shows a representation of another embodiment of the invention. In this case, the fluid 1 to be dosed is contained in a deformable reservoir 28, itself placed in the reservoir 3. The working fluid 2 is sucked by a pump 24, passes into the reservoir 35 provided with a membrane 26 'allowing to isolate the liquid contained in compartment 27 and the gas contained in compartment 26. This small reservoir makes it possible to filter any pressure pulsations from pump 24. The pressure in this reservoir is regulated by means of valve 25, controlled by the automaton 22. The operation of the system is as follows: the reservoir 3 is pressurized to a predetermined level by calculation, so that the flow rate flowing to the nozzle 33 is suitable for starting the dosing operation. The operator or the robot opens the shutter 32 which allows the fluid 2 to flow through the injection nozzle 33 at the desired flow rate. The two fluids 2 and 1 being incompressible, the flow rate of fluid 2 flowing at the nozzle 33 is the same as that of liquid 1 flowing in the laminar pressure drop 36. It is therefore sufficient to measure, by means of the sensor differential pressure 20, the pressure difference across this pressure drop element to deduce the flow of fluid 1 passing through the circuit, equal to the flow of fluid 2 injected. This measurement must be supplemented by a viscosity measurement deduced from the temperature measurement 21. Knowing the desired flow rate, the actual flow rate, the pressure difference and temperature, it is possible to control the valve 25 which acts on the pressure in the tank 3 and therefore on the flow rate at the nozzle. This method makes it possible to carry out a measurement of flow using a fluid 2 different from the fluid to be metered 1, said fluid 2 having, moreover, a power transmission function.

Referring now to Figure 5, we will describe in more detail the device of Figure 4 applied to the delivery of a controlled flow of glue, especially glues used in the automotive field. These adhesives are products with complex and very viscous rheology. Their dynamic viscosity is of the order of a thousand Pa.s.

In this installation, the working fluid is oil for substantially incompressible hydraulic circuits.

The installation comprises a regulated source A of oil, a set B for measuring the oil flow, a set C for storing and delivering the adhesive and an automaton D for controlling the various sets of the installation.

The assembly A comprises an oil storage tank 50 connected to a bladder accumulator 52 by a high pressure oil pump 54 which supplies the accumulator with an almost constant flow rate. A regulating valve 56 constituted by a variable pressure drop makes it possible to modify the pressure in the oil circuit. The output 58 of the accumulator 52 is connected to the flow measurement assembly B. The assembly B essentially consists of two laminar pressure drops 60 and 62 mounted in parallel of the type described above. The pressure drop values are different to allow adaptation to different measurement ranges. Each pressure drop is associated with a valve 64 and 66. A differential pressure sensor 68 measures the pressure across the pressure drops to deduce the flow. The valve 70 makes it possible to decompress the pressure drops. The outlet 72 for pressure drops is connected to the inside of a rigid-walled tank 74, capable of withstanding high pressure. Inside the reservoir 74, there is a capacity 76 with a tight deformable wall which is initially filled with glue by the pipe 80 and the valve 82. The glue is delivered by the outlet pipe 84 provided with the valve 86. In addition, the accumulator 52 and the reservoir 74 are provided with a temperature sensor 88 and 90 for measuring the temperatures of the oil in these two chambers.

As shown in Figure 5, the entire installation is controlled by a PLC D. Depending on the desired adhesive flow rate and the temperature, the PLC selects one of the two pressure drops 60 and 62 and controls the pump. 54 and the regulating valve 56 as a function of the measurement of the flow calculated by the automaton from the measurement supplied by the differential pressure sensor 68.

The table below gives the parameters of a preferred embodiment of the installation.

Parameter Value Unit

Glue flow 0.3 to 3 ml / s

Deformable tank volume 76 1 1

Pressure in the metering device l at 50 bar

Pressure difference across circuit 60 or 62 0.1 to 1 bar

Oil circuit pressure l to 50 bar

High pressure pump flow 1 1 / min

Pressure loss 60

Flow rate 0.3 ml / s

Oil viscosity at 70 ^* C 1.3.10-2 Pa.s

Pressure loss 104 Pa

Coil length 0.2 m

Coil depth 1.7 mm

Pressure loss 62

Flow 3 ml / s

Oil viscosity at 30 ^* C 6,6.10-2 Pa.s

Pressure loss 105 Pa

Coil length 0.2 m

Coil depth 2.5 mm These examples are not limiting of the method which applies to any pressure line comprising a working fluid and a metering fluid, on which is placed a laminar pressure drop provided with a differential pressure sensor making it possible to measure the passing flow in said line.

Claims

1. Device for metering very low fluid flow rates, characterized in that it comprises: a reservoir (3) containing the fluid (1) to be metered and a working fluid (2) which compensates for the loss of liquid (1) and used to pressurize said reservoir, a means (24, 4) for pressurizing the working fluid (2), a means (6, 7, 11, 10, 25) for regulating the pressure of the working fluid (2) as required in metering fluid (1), laminar pressure drop means (14, 15, 16, 36) mounted on the line in which one or the other of the fluids circulates to determine the flow rate of fluid passing through the line , and means (6, 11, 25) for controlling the regulating means for modifying the pressure in the reservoir (3) as a function of the value of the flow rate to be dosed and of the physical characteristics of the fluid passing through the pressure drop means laminar.

2. Device according to claim 1, characterized in that the fluid to be dosed (1) is a liquid, in that the working fluid (2) is a gas and in that the laminar pressure drop means are mounted on a outlet pipe for the liquid to be dosed connected to said reservoir and in that it further comprises means for measuring the pressure difference of the liquid on either side of the laminar pressure drop means, said control means corresponding to said differential pressure measurement.

3. Device according to claim 2, characterized in that said laminar pressure drop means comprise a plurality of laminar pressure drops mounted in parallel on said pipe, each pressure drop having a different value and means for selectively connecting one of said pressure losses at said pipe.

4. Device according to claims 1 and 2, characterized in that said working gas is air and in that the air supply (8) and the air outlet (7) are provided by circuits comprising a laminar pressure drop and an all-or-nothing valve, the opening frequency of one or other of these all-or-nothing valves being adjusted to reach the desired pressure level in the tank (3).

5. Device according to claim 1, characterized in that the fluid (1) is contained in a deformable tank (28) included in the pressurized tank (3), and that the working fluid (2) is almost incompressible, said means of laminar pressure drop being mounted on the supply line to the reservoir (3) with said motor liquid.

6. Device according to claim 5, characterized in that a measurement of the flow rate of the working fluid is done by means of said laminar pressure drop (36) provided with a differential pressure sensor (20).

7. Device according to claim 6, characterized in that it further comprises means (21) for measuring the temperature of the working fluid.

8. Device according to one of claims 1 to 7, characterized in that the laminar pressure losses consist of a channel (37) resulting from the cooperation between a spiral groove (38) hollowed out in a pellet (39) and a second flat patch (40).

9. Device according to claim 7, characterized in that the system is provided with a computer (22) to which the flow setpoint is given and which, from the measurement of pressure difference (20) and of temperature ( 21) determines the actual flow rate and calculates the regulatory action to be carried out by the specialized bodies (6, 11, 25) to modify the pressure in the tank (3).

10. Device according to claim 5, characterized in that said working fluid is oil and in that the fluid to be dosed is glue.