EP1195518A2 - Method and device for dosed pumping - Google Patents

Abstract

The moving piston (12) is controlled by a piezoelectric actuator. to Independent claim is included for the corresponding dosing method.

Description

The present invention relates to a device for Dosing of material with a fixed piston, a movable one Piston and a movable housing with a lockable with one of the pistons by moving the housing Material supply and one with one of the pistons material discharge that can be closed by moving the housing, the axis of the fixed piston with the axis of the movable piston is aligned and between fixed piston and the movable piston at least then there is a distance in the area of the material feed if the material supply is open. The invention further relates to a method of dosing material in which (A) Material by a material supply to a filling area Housing is fed during a material export the housing of a fixed piston or a movable Piston is closed, the filling area at least is partially formed by a distance which between the fixed piston and the movable piston is present, the axis of the fixed piston with the The axis of the movable piston is aligned, (B) the housing is moved in a first direction so that the material feed from the fixed piston or the movable one Piston is closed and the material discharge opened , (C) the movable piston is fed so that the distance between the fixed piston and the movable one Pistons decreased and material from material export emerges, (D) the movable piston is returned is so that the distance between the fixed Piston and the movable piston enlarged, and (E) that Housing is moved in a second direction, which the first direction is opposite.

State of the art

Conventional dosing systems mainly work according to the Principle of the piston pump, in which a piston liquid displaced from a cylinder. The liquid occurs in the Generally from a dosing tip. The leaked one However, drops only detach from the dosing tip, if it is from the dosing tip due to the surface tension the holding forces applied to the liquid, for example due to the effect of gravity. The adhesive forces result from the interfacial tension between the liquid, the dosing tip material and the air. The dosed volume is determined from the balance between gravity, which pulls the drop down, and the adhesive forces, that hold the drop on the dosing tip. Only when the weight force acting on the drop predominates, the drop falls off.

Often you want to dose the smallest possible volume. To achieve this, it is useful to minimize the adhesive forces. This can be achieved by reducing the dosing tip. But these measures are also subject to a physical limit, since when the drop radius r is reduced, the weight, which is proportional to r ³ , decreases faster than the adhesive force, which is directly proportional to the radius r.

These laws lead to being extremely fine Nozzles are needed. These are naturally very sensitive, and they tend to clog up.

For this reason, you often work for another Procedure in which the dosing tip is placed with the object, which should absorb the liquid brings. As a result, the drop no longer has to be alone tear off the dosing tip by gravity. Rather, the liquid adheres to the surface which one to apply, and by removing the dosing tip tears the volume apart.

In this way it is possible to use even smaller amounts of material to transfer, resulting in new problems, however result. For one thing, the dosing tip has to be in one exact distance to the object, to the other the piston stroke must also be monitored very closely become. This makes high-precision mechanical designs required; monitoring the piston stroke is particularly important due to the relationship between static and sliding friction very difficult. Therefore have particularly good systems for example a piston, which is about its longitudinal axis rotates to avoid the occurrence of static friction. However, this solution with a rotating piston is again complex and therefore expensive. Further if the distance between the dosing tip and the Surface to which the liquid is to be applied Problems. So thread formation occur and more non-uniform Material order on. Consequently, undefined quantities can material remaining at the dosing tip as a residual amount, thereby the repeatability with regard to the dosing quantity fluctuates.

A fundamental problem when applying adhesives is their compressibility. Because with dispensing needles with a small diameter a high back pressure is due to the compressibility of the adhesives no point order possible; this is especially true for small ones Piston strokes, which are used to provide small dosing quantities required are.

The dynamic pressure of the adhesives can be adjusted via the metering speed regulate. Fast dosing leads to one high back pressure; slow dosing has a low one Pressure. It should also be emphasized that the choice of one perfect length of stay is an important requirement for repeatable dosing. This applies to both for the length of stay before as well as for the length of stay after dosing. By choosing the appropriate length of stay you give the glue the time it takes to finish Relieve back pressure, so that the repeatability is optimized.

A difficult problem of the procedures of the State of the art is that the flow behavior the liquid due to the wetting properties of the substrate to which the liquid is applied should be very different. By different Wetting properties can cause major inaccuracies result.

In order to dispense small quantities with high accuracy you have to escape the problem areas described. In particular, one has to be aware of the adhesive forces of the liquid on the dosing tip and the wetting properties of the substrate become independent.

The individual problems in terms of dosage and the advantages and disadvantages of the possible solutions described below.

The surface tension in terms of different involved materials (dispensing needle, adhesive, component) is one of the biggest problems with regard to the exact Dosage. To work around this problem, an appropriate one Pretreatment to be taken. These pretreatments however, are very time consuming and expensive. The Surface tension affects slow drop formation the most on the needle. From a slow one Drop formation results in poor material removal. at the surface tension affects the formation of drops very quickly hardly or not at all between the dispensing needle and the adhesive not from. You shoot the drop according to the inkjet printer principle out of the needle.

The dynamic pressure in the dispensing needle influences to a great extent the repeatability of the point order. This in particular for the reason that it's discretionary which values set the dwell times during dosing become. Depending on the setting, the desired volume can be reached a residual ingredient is added, or the volume becomes only delivered incomplete. Also with regard to the Back pressure offers rapid drop formation advantages, because the dynamic pressure can be reduced many times over. You have to keep the process time low so that the Reduce the dynamic pressure in a flash via the metering needle bore got to.

The needle distance to the component is also very important, to counteract the surface tension. The setting correct needle spacing is extremely complex, especially due to the required precision of the mechanical components. This problem too can be circumvented using the inkjet printer principle, that is, by shooting the adhesive at the component becomes. Because of this, the needle distance to the component adjustable to a certain extent. This is a crucial advantage for series production, especially with a view to saving costs, since there is no need for a Z-stroke query.

Advantages of the invention

The invention builds on the prior art according to the Preamble of claim 1 characterized in that the movable Piston can be controlled by a piezo actuator. By the use of a piezo actuator makes it possible to use a piston pump to provide which the material according to the inkjet printer principle from a reservoir shoots out. Piezo actuators can be highly accurate with very little Strokes work so that extremely small volumes are dosed. Piezo actuators are also able to To feed pistons an enormous acceleration, so that the material is unaffected by the problems described of the prior art emerge from a metering needle can. In particular, the problems are considered on the surface tension, the dynamic pressure and the setting of the needle distance to the component is eliminated.

The fixed piston is preferably in a precision bushing held, the movable piston is from the precision bush out, and the precision bush is in the Housing arranged. The precision in terms of arrangement and the guidance of the pistons is an important requirement for setting exact volumes and for good reproducibility of the dosing processes.

It is preferred that the amount of material to be dosed of that in the case of open material supply Distance between the fixed piston and the movable one Piston depends in the area of the material feed. By positioning the movable piston relatively the volume to be metered can thus be added to the fixed piston to adjust.

This is useful in the case of open material feed present distance between the fixed piston and the movable piston adjustable by an adjusting screw. With appropriate design of this adjusting screw volumes can be preselected with high precision become.

It is also advantageous that the piezo actuator by an adjusting screw can be positioned. In this way the system can be adjusted, the one exact setting of the respective components relative to each other.

It is particularly advantageous if the adjusting screw for setting the in the case of open material supply existing distance between the fixed piston and the movable piston and the adjusting screw for positioning of the piezo actuator are identical. So you have one Adjustment screw with two functions, what with regard a simple construction of the piston pump is useful.

The piezo actuator is preferably of the order of magnitude for a stroke of 100 µm. With such strokes extremely small volumes can be precisely dosed.

It is particularly useful if the piezo actuator for a Acceleration in the order of 100000 g suitable is. In this way, the movable piston and thus the material to be dosed also has a high acceleration fed so that the material is unaffected from the surface tension and the dynamic pressure the metering opening is shot out.

It is useful when moving a pneumatic cylinder of the movable housing is provided. That’s it Housing can be positioned reliably and precisely.

With regard to the exact dosing of a volume of material it is particularly advantageous if the material export has a dispensing needle.

The device preferably has a control. On in this way a dosing process can be automated and execute with a high number of cycles.

The method according to the invention is based on the prior art Technology according to the preamble of claim 12 thereby that the movable piston is controlled by a piezo actuator becomes. As a result, the inventive Advantages of the device are implemented procedurally.

In terms of the process flow, it can be advantageous be when returning the moving piston and moving the housing in the second direction one after the other respectively. So you get clearly distinguishable Process steps, making the process special can be monitored well.

But it can also be useful if the return of the movable piston and moving the housing in the second direction at least partially at the same time respectively. This allows in particular the speed increase the procedure so that the number of cycles can be increased in series production.

Preferably the distance between the fixed piston and the movable piston for determining the dosing Volume set. You got through this way a simple setting measure the preselection of the to be dosed Volume in hand.

The method is particularly advantageous when using this Adhesive is dosed. Especially when it comes to glue are extreme precise dosages desired. It also switches Process the problem with regard to compressibility and the dynamic pressure of the adhesive; this in particular due to the high speed of ejection of the material.

The piezo actuator is preferably provided with a stroke in the Order of magnitude of 100 µm. Strokes of this size allow highly precise dosing of small amounts of material.

The piezo actuator is preferred with an acceleration in on the order of 100,000 g. With this acceleration is an explosive discharge of the adhesive possible, so the disadvantages in terms of Surface tension and back pressure can be avoided.

The housing is preferably provided by a pneumatic cylinder emotional. This is a highly precise and quick positioning of the housing during the course of the procedure possible.

The method is preferably controlled by a controller. Thus, the process is automatic Manufacturing process can be used at high speed.

The invention is based on the surprising finding that the use of a piezo actuator in a piston pump eliminates numerous problems which are evident in the metering of very small quantities of material. Due to the rapid formation of drops, the surface tension between the metering opening and the material to be dispensed has little or no effect. The back pressure in the dispensing needle is reduced many times over. The dispensing needle distance to the component is variable. If you compare the piezoelectric actuator with conventional actuator concepts, you will get an evaluation according to the following table (symbols: +: good, high; 0: medium; -: bad, low). The piezoelectric concept wins in particular with regard to the actuating time and also with regard to the consistently good evaluation with the various evaluation parameters. Steep link concept resolution Travel Range force Operating time Power density Temp range piezoelectric + - + + + 0 electromagnetic - + - - - + Pneumatic - + - - - + hydraulic - + + - + -

For the sake of completeness, the advantages and disadvantages of piezo actuators can be listed. The advantages show the particular suitability of the piezo actuators with regard to the object of the present invention. benefits disadvantage large mechanical actuating forces (up to a few kN) high control voltages necessary high natural frequency (up to some 10 kHz) small travel ranges (max. 100 ... 200 µm) Path resolution in the nanometer range Characteristic hysteresis and creep effects very short response time (a few µs) saturation phenomena high mechanical rigidity Depolarisationsgefahr different directions of action free of play and wear

drawings

The invention will now be described with reference to the accompanying Exemplary drawings based on preferred embodiments described.

Show it:

Figure 1

a partially sectioned illustration of a Piston pump;

Figure 2

a partially sectioned illustration of a Piston pump with piezo actuator.

Description of the embodiments

In Figure 1 is a piston pump for dosing material shown partially cut. The device contains a fixed piston 10 and a movable piston 12. The fixed piston 10 and the movable piston 12 are axially aligned so that they are aligned. The device further includes a movable housing 14. Inside the housing is a precision socket 16, of which of the fixed pistons 10 is held and in which the movable piston 12 is guided. The housing 14 and the precision bushing 16 have lateral holes, from one as material supply 18 and the other for material export 20 serves. Inside the precision bush 16 a filling chamber 22 is formed by the ends of the fixed piston 10 and the movable piston 12 one Have distance from each other, which due to the Mobility of the movable piston 12 is changeable. In the present illustration, the fixed piston 10 ends approximately in the middle between the material feed 18 and the Material removal 20, which can be seen from a vertical line is. The movable piston 12 ends in the present Representation at the position at which the dash-dot line ends. This dash-dot line defines one Middle position of the movable housing 14. By the Double arrow above the housing 14 indicates that the housing 14 moves through a pneumatic cylinder 24 leaves. The precision bush 16 is through seals 26 sealed to the outside. The housing 14 is through Screws 28 held together.

The housing 14 is in the illustrated state in a position in which the material feed 18 is open and opens into the free space 22. The material removal 20 is however, closed by the fixed piston 10. In this Condition can thus material get into the filling chamber 22. The amount of material to be dosed can be checked the size of the filling chamber 22 and thus by the distance between the fixed piston 10 and the movable piston Set 12. If the filling chamber 22 is filled, it will Housing 14. Moved to the left by the pneumatic cylinder 24. As a result, the material feed 18 is by the movable piston 12 closed during the material removal 20 is opened. By moving the piston 12 is delivered so that the distance between the fixed piston 10 and the movable piston 12 reduced, material becomes through the open material discharge 20 pushed out. Subsequently, the housing 14 moves under Action of the pneumatic cylinder 24 again in the illustrated Home position, and the movable piston 12th also goes back to its starting position shown. The execution is for the inclusion of a further dose of material prepared.

Figure 2 details the construction of a part a piston pump with a piezo actuator 30. This construction includes a main plate 32 on which the other components directly or indirectly are attached. The piezo actuator 30 is via a holder 34 and disks 36, 38 fixed with respect to the main plate 32. Furthermore, the piezo actuator 30 is held by a holder 40 held, which is screwed directly to the main plate 32 is. To adjust the piezo actuator 30 is one Adjustment screw 42 is provided, which in the holder 34th sitting. The adjusting screw 42 can also be the distance between the movable piston 12 and that in FIG. 2 Adjust the fixed piston, not shown, whereby the volume to be dosed can be selected.

The preceding description of the exemplary embodiments according to the present invention is for illustrative purposes only Purposes and not for the purpose of limiting the invention. Various changes are within the scope of the invention and modifications possible without the scope of Invention as well as leaving its equivalents.

Claims (20)

Device for dosing material with a fixed piston (10), a movable piston (12) and a movable housing (14) with one with one of the pistons (10, 12) closable by moving the housing (14) material supply (18) and one with one of the pistons (10, 12) closable by moving the housing (14) material outlet (20), the axis of the fixed piston (10) being aligned with the axis of the movable piston (12) and a distance between the fixed piston (10) and the movable piston (12) at least in the area of the material feed (18) when the material feed is open, characterized in that the movable piston (12) can be controlled by a piezo actuator (30). Device according to claim 1,
characterized, that the fixed piston (10) is held in a precision bush (16), that the movable piston (12) is guided by the precision bushing (16) and that the precision bushing (16) is arranged in the housing (14). Device according to claim 1 or 2, characterized in that the amount of the material to be dosed from the distance between the fixed piston (10) and the movable piston (12) in the case of the open material supply (18) in the region of the material supply (18) depends. Device according to one of the preceding claims, characterized in that the distance between the fixed piston (10) and the movable piston (12) in the case of the open material supply (18) is adjustable by means of an adjusting screw (42). Device according to one of the preceding claims, characterized in that the piezo actuator (30) can be positioned by an adjusting screw (42). Device according to one of the preceding claims, characterized in that the adjusting screw (42) for adjusting the distance between the fixed piston (10) and the movable piston (12) in the case of open material supply (18) and the adjusting screw (42) for Positioning the piezo actuator (30) are identical. Device according to one of the preceding claims, characterized in that the piezo actuator (30) is suitable for a stroke in the order of 100 µm. Device according to one of the preceding claims, characterized in that the piezo actuator (30) is suitable for an acceleration of the order of 100,000 g. Device according to one of the preceding claims, characterized in that a pneumatic cylinder (24) is provided for moving the movable housing (14). Device according to one of the preceding claims, characterized in that the material outlet (20) has a metering needle. Device according to one of the preceding claims, characterized in that the device has a controller. Process for dosing material in which Material is fed through a material feed (18) to a filling area (22) of a housing (14), while a material outlet (20) of the housing is closed by a fixed piston (10) or a movable piston (12), wherein the filling area (22) is at least partially formed by a distance which is present between the fixed piston (10) and the movable piston (12), and the axis of the fixed piston (10) being aligned with the axis of the movable piston (12), the housing is displaced in a first direction, so that the material feed (18) is closed by the fixed piston (10) or the movable piston (12) and the material discharge (20) is opened, the movable piston (12) is fed so that the distance between the fixed piston (10) and the movable piston (12) is reduced and material emerges from the material outlet (20), the movable piston (12) is returned so that the distance between the fixed piston (10) and the movable piston (12) increases, and the housing (14) is displaced in a second direction, which is opposite to the first direction, characterized in that the movable piston (12) is controlled by a piezo actuator (30). A method according to claim 12, characterized in that the return of the movable piston (12) and the displacement of the housing (14) in the second direction take place in succession. A method according to claim 12 or 13, characterized in that the return of the movable piston (12) and the displacement of the housing (14) in the second direction take place at least partially simultaneously. Method according to one of claims 12 to 14, characterized in that the distance between the fixed piston (10) and the movable piston (12) is set to determine the volume to be metered. Method according to one of claims 12 to 15, characterized in that adhesive is metered. Method according to one of claims 12 to 16, characterized in that the piezo actuator (30) is moved with a stroke in the order of 100 µm. Method according to one of claims 12 to 17, characterized in that the piezo actuator (30) is moved with an acceleration in the order of 100,000 g. Method according to one of claims 12 to 18, characterized in that the housing (14) is moved by a pneumatic cylinder (24). Method according to one of claims 12 to 19, characterized in that the method is controlled by a controller.

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