DE102015212960A1 - Method of operating a pump - Google Patents

Abstract

A method and a regulation for operating a pump (32) are presented. In the method, a delivery rate of the pump (32) is controlled using a pump model that takes into account as a parameter of the pump (32) a temperature in the pump (32), wherein in the regulation a nominal output of the pump (32) is such it is taken into account that a change in the parameter temperature in the pump (32) in the pump model is taken into account in the context of the control.

Description

The invention relates to a method for operating a pump, in particular for operating an induction pump for a soldering method, and a control for carrying out the method. The invention further relates to a computer program for carrying out the method and to a machine-readable storage medium having such a computer program.

State of the art

As pumps work machines are referred to with which liquids, especially incompressible liquids are promoted. Pumps serve to convert a drive work into the kinetic energy of a medium.

The method presented here is used in particular for pumping or conveying a solder in a soldering process or method. Soldering is understood to mean a thermal process for materially joining materials in which a liquid phase is formed by melting the solder.

In particular, the method is used in the context of wave soldering or selective soldering. This is a soldering process with which electronic assemblies are soldered semi or fully automatically after assembly.

Disclosure of the invention

Against this background, a method with the features of claim 1 and a scheme according to claim 7 are presented. Furthermore, a computer program according to claim 10 for carrying out the method and a machine-readable storage medium according to claim 11 are presented. The computer program can be executed on a computing unit, in particular on a computing unit in a control of the kind presented. Embodiments emerge from the dependent claims and from the description.

Thus, a method is presented that enables stable and effective soldering.

For this purpose, it is necessary to first create a model of the pump, for which the performance and the properties of the pump must first be analyzed. Based on the model then the performance of the pump can be optimized.

• – Definieren des Pumpenmodells
• – Analyse des Modells
• – Ursachenanalyse der Änderung der Effizienz der Pumpe
• – Durchführen von Messungen zur Überprüfung des Modells
• – Implementieren der Korrekturen

The individual steps are:

• - Defining the pump model
• - Analysis of the model
• - Root cause analysis of the change in the efficiency of the pump
• - Perform measurements to verify the model
• - Implement the corrections

It turns out that operating conditions affect the performance of the pump. The main change is in the temperature of the system affecting parameters of the pump, such as temperature resistance, reactance, etc.

Previously used controls are not suitable to ensure a constant performance or conductivity of the pump. It can be seen that the concept of pump control has to be changed from a simple control of the output power to a regulation of the effective output line, the nominal power of the pump.

In one embodiment, a liquid solder is provided in a solder pot of the soldering machine, wherein the soldering machine is equipped with a solder pump, in this case with an induction pump. This is intended to pump the solder into the soldering tool or the soldering nozzle. To ensure that the right amount of solder reaches the solder joint, a stable and repeatable pump delivery is required.

The pump parameters are automatically set from time to time for soldering tools, solder levels, etc. according to the user's machine settings. It is a problem that the efficiency of the pump depends on the working conditions. A main component of the induction pump is a coil which generates a magnetic field, but also acts as a heating element. The performance of the pump depends on its temperature, which constantly changes during operation. So far, only the input power of the pump or coil is controlled. The actual efficiency of the coil is not considered. However, automatic adjustment can compensate for this effect. This can take time, therefore the product cycle time is increased.

It can be seen that with the presented method, sufficient power can be effectively fed into the control loop in terms of voltage, frequency and phase angle. This prevents an effect of the temperature changes from the coil. All necessary parameters are available in the frequency converter, which represents the control device of the induction pump.

The presented method can be used in different soldering machines.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

Brief description of the drawings

1 shows a graph of the performance of a pump in a graph.

2 shows in a graph a curve of the power of a pump according to 1 ,

3 shows a schematic representation of a wave height measuring system.

4 shows in a graph the effect of the coil temperature.

5 shows in a graph the change in pump performance due to cooling.

6 shows the functional principle of a soldering pump.

7 shows a cross section through a soldering pump.

8th shows the functional principle of an induction pump.

9 shows resistance curves of the liquid solder.

10 shows an electrical model of a pump and a coil.

11 shows voltage and impedance vectors.

Embodiments of the invention

The invention is schematically illustrated by means of embodiments in the drawings and will be described in detail below with reference to the drawings.

1 shows in a graph on which an abscissa 10 the wave height in% and at an ordinate 12 the effective pump power, the rated power of the pump, is plotted in steps, a curve 14 , which shows the wave height in% of pump power and thus the course of the pump power. Furthermore, there is an offset 16 and a gradient 18 displayed.

The following applies: Pump power [steps] = offset [steps] + gradient [steps /%] · set value [%] (1)

The gradient 18 is set by the user when the tool is first set up. The wave height in% is set by the user during the soldering process. The offset 16 gets automatically set by the wave height test system. The illustration serves to clarify the setting of a working point, the reference numeral 17 is designated.

To ensure a stable or repeatable process, a stable wave height is required. Once the optimum solder wave height is defined, it must be repeatedly inserted through the machine. Effects of the solder level change, which, for example, lead to an increase in the pressure difference, maintenance, tool change, etc. must be compensated. Therefore, an automatic wave height measuring system has been developed to compensate for the effects of small changes.

2 shows a representation accordingly 1 , where additionally a test point 20 is registered. This illustration serves to illustrate the principle of operation of the automatic wave height test system.

• 1. Der Gradient wird von dem Benutzer fixiert.
• 2. Der Einstellwert wird für den Test in der Software fixiert, bspw. bei 10 %.
• 3. Die Pumpenleistung wird erhöht, bis der Vorgabewert bzw. Sollwert erreicht ist.
• 4. Der Offset wird berechnet.

The goal is to get the test point 20 on the bend 14 to find. The procedure is as follows:

• 1. The gradient is fixed by the user.
• 2. The set value is fixed in the software for the test, for example at 10%.
• 3. The pump power is increased until the preset value or setpoint is reached.
• 4. The offset is calculated.

To identify the test point, a physical limit is generated.

3 shows in a schematic representation of a wave height measuring system, the total with the reference numeral 30 is designated. The illustration shows a pump 32 , a needle 34 , a test nozzle 36 , a test point 38 , a test height 40 with two double arrows and a tool 42 , An arrow 44 indicates that at the test level 40 no overflowing takes place.

An automatic wave height test is performed when the system 30 is switched in an automatic production mode. It has been observed that the wave height changes rapidly in the first 5 to 10 minutes after a start, producing soldering errors. After a wave height test was performed again, the offset value changed. This change can be up to + -10%. After 15 to 30 minutes the system is stable, there are only slight changes in the offset after the test.

4 illustrates in a graph the effect of the coil temperature on the pump performance. Here is an abscissa 60 the wave height in% and at an ordinate 62 the effective pump power in steps. A first turn 64 shows the course of the pump power after a first setting, a second curve 66 the course after a change in the effective power and a third curve 68 the course after a second setting. Furthermore, the illustration shows a first point 70 and a second point 72 ,

The change in temperature takes place, for example, after a maintenance or a tool change, when the pump for a long time, eg. 30 minutes, does not work. The coil is then "cold" during the first test, which is indicated by the first curve 64 is clarified. The efficiency of the pump changes over time. This decreases as the coil temperature becomes higher, as seen through the second curve 66 is clarified. After the next solder wave check, the pump is readjusted, through the third curve 68 is clarified.

The pump performance does not match that after the first setting after the second setting. Only at the setpoint, the same performance, for example, at 10%, be. In the event that the solder wave with a cold pump, first point 70 at 30% of the first turn 64 , is set, the actual solder wave in mass production will be lower, namely second point 72 at 30% on the third turn 68 ,

5 shows the change in pump performance due to cooling. It is on an abscissa 100 the wave height in% and at an ordinate 102 the effective pump power in steps. A first turn 104 shows the course of the pump power after a first setting, a second curve 106 the course after a change in the effective power and a third curve 108 the course after a second setting. Furthermore, the illustration shows a first point 110 and a second point 112 ,

The change takes place after, for example, a long interruption when the pump has been working for a longer time, for example 30 minutes. The standby power is usually set at 100%, allowing the pump at a higher power during an interruption works, for example, during the lunch break. The coil is "hot" during the first setting, as through the first turn 104 is clarified. The efficiency of the pump changes over time. This increases as the coil temperature decreases, as through the second curve 106 is clarified. After the next solder wave check, the pump is readjusted, as by the third curve 108 is clarified. The pump performance becomes after the second adjustment, third curve 108 , not those after the first setting according to the first curve 104 correspond.

Only at the setpoint will the performance, for example at 10%, be the same. In the event that the solder wave is set with hot pump, first point 110 at 30% on the first corner 104 , the actual solder wave in series production will be higher, second point 112 at 30% on the third turn 108 ,

The soldering machine studied in this test is an annular linear induction pump. In this case, the pump channel has no moving parts and no direct electrical connections to the components containing liquid metal. The pressure is developed by the interaction of the magnetic field generated by the three-phase coils and the current flowing as a result of the voltage induced in the pump channel containing the liquid metal.

6 shows the principle of operation of such a soldering pump, the total with the reference numeral 120 is designated. The illustration shows a flow direction 122 , a direction 124 the force on the fluid as well as an induced current 126 and a magnetic field 128 ,

The following equation indicates the pressure applied by the soldering pump 120 provided:

Δp:

Druckdifferenz

Q:

Flussrate

R₂:

Widerstand des flüssigen Metalls

Xm:

Magnetisierungsreaktanz

S:

Schlupffaktor (1 – U_Flüssigkeit/U_Welle)

I:

Strom

Where:

Ap:

pressure difference

Q:

flow rate

R ₂ :

Resistance of the liquid metal

Xm:

magnetizing

S:

Slip factor (1 - U _fluid / U _shaft )

I:

electricity

The special feature of the soldering pump 120 is that the inlet and outlet are on the same side of the channel. To enable this, an inner tube is placed in the channel. The flow direction is determined by the surface ratio of the channels or passages. The efficiency of the soldering pump 120 is reduced by this arrangement.

7 shows a cross section through a soldering pump, the whole with the reference numeral 150 is designated. The illustration shows a coil 152 , an inner tube 154 and a housing 156 , As a diameter are given here only by way of example:
58.1 mm at reference numeral 160
57 mm at reference numeral 162
47 mm at reference number 164
40 mm at reference numeral 166
30 mm at reference number 168

Outflow A _out is 707 mm ² at reference numeral 170 , An inflow A _a is 478 mm ² at reference numeral 172 ,

8th shows the principle of operation of an induction pump, in total with the reference numeral 180 is designated. The illustration shows a tool 182 , a container 184 and a three-phase coil 186 , A first arrow 188 clarifies the effective direction of the force, an induced current is with arrows 190 displayed, arrows 192 show the flow direction of the solder, a magnetic field B is denoted by reference numeral 194 displayed.

The following are equations describing the performance of the pump: F = Δp · A (3) ΣF = Ap (A _out - A _a) (4) Output: P _volumetric = Q · Δp (5) Input: P _input = 3P _phase = 3U _phase · I _phase · cos (θ) (6) η = P _volumetric / P _input (7)

For Δp, equation (2) can be used as for the pump:

Δp:

Druckdifferenz

Q:

Flussrate

R₂:

Widerstand des flüssigen Metalls

Xm:

Magnetisierungsreaktanz

S:

Schlupffaktor (1 – U_Flüssigkeit/U_Welle)

I:

Strom

• – Eine Änderung von Q beeinflusst den Luftreibungswiderstand, was anhand der Pumpeneigenschaften erkannt werden kann. Durch Viskosität hat dies eine begrenzte Auswirkung auf die Änderung der Pumpenleistungsfähigkeit aufgrund von Änderungen der Bedingungen bzw. Umstände. Dieser Faktor selbst ist mit hoher Wahrscheinlichkeit nicht die Grundursache für die problematische Änderung.
• – R₂ ±5°C Legierungstemperaturänderung kann zu einer ±0,3 % Δp Änderung führen, was eine näherungsweise gleiche Änderung in der Leistungsfähigkeit bedeutet. Die tatsächliche Temperaturabweichung in dem Lotbehältnis beträgt weniger als ±3°C. Dieser Faktor selbst ist mit hoher Wahrscheinlichkeit nicht die Grundursache der problematischen Änderung.
• – X_m
• – Eine Änderung von s bewirkt keine Änderung in der Gesamtcharakteristik der Pumpe.
• – I = f(R₂) bewirkt keine signifikante Änderung der Pumpeneigenschaft.

The following applies:

Ap:

pressure difference

Q:

flow rate

R ₂ :

Resistance of the liquid metal

Xm:

magnetizing

S:

Slip factor (1 - U _fluid / U _shaft )

I:

electricity

• - Changing Q affects the air friction resistance, which can be detected by the pump characteristics. Viscosity has a limited effect on the change in pump performance due to changes in conditions. This factor itself is unlikely to be the root cause of the problematic change.
• - R ₂ ± 5 ° C alloy temperature change can lead to a ± 0.3% Δp change, which means an approximately equal change in performance. The actual temperature deviation in the plumb bob is less than ± 3 ° C. This factor itself is unlikely to be the root cause of the problematic change.
• - X _m
• - Changing s does not change the overall characteristics of the pump.
• - I = f (R ₂ ) does not cause a significant change in pump property.

9 shows courses of resistance of liquid solder alloys. It is on an abscissa 250 the temperature in ° C and at an ordinate 252 the electrical resistance is plotted in μO / cm. The change in the electrical resistance of lead-free solder between 290 ° C and 300 ° C is approximately 1%. The temperature tolerance during operation is not more than +/- 3 ° C. This change does not explain the 10% change in offset. It is also difficult to measure and control sizes of the liquid solder.

10 shows an electrical model of the pump and the coil, the reference numeral 300 is designated. The illustration shows effective resistances R ₁ 302 and R ₂ 304 and reactances X _l 306 and X _m 308 , A double arrow 310 indicates the drop in voltage U, a first arrow 312 illustrates the current I and a second arrow 314 the current I *.

The inductance of a coil is: L = μ ₀ μ _r A / l N ² (8) where N denotes the number of windings, I the length of the coil, A the cross-sectional area, μ ₀ the magnetic constant, μ _r the relative permeability.

The inductive reactance is: X _L = 2π · f · L (9) where f denotes the frequency.

The impedance of the coil is: Z ₁ = R ₁ + jX _L = R ₁ + j 2π * f * L [Ω] (10)

The phase angle is:

The input power for a three-phase coil is: P _in = 3P _phase = 3U _phase I _phase cosθ (12)

11 shows the voltage and impedance vectors. A first arrow indicates this 350 a voltage U, a second arrow 352 a voltage U _L , a third arrow 354 a voltage U _R , a fourth arrow 356 a current I, a fifth arrow 358 a resistance R, a sixth arrow 360 a reactance X _L and a seventh arrow 362 an impedance Z. With reference numeral 364 and 366 unknown angles are displayed.

As is known, the resistance is temperature-dependent as well as the inductive reactance.

By means of a frequency converter, the soldering device can be controlled. This frequency converter measures the phase angle, so it makes sense to check how it changes after a long break or maintenance. Time [sec] ? rated capacity Wave height% offset gradient cos? ? x 0.705 1.05 100 2600 111 0.761612 0 0.915 0,125 5 2600 111 0.609791 100.00% 120 0.915 0,125 5 2600 111 0.609791 100.00% 240 0.9 0.13 5 2600 111 0.62161 101.94% 300 0.895 0.13 5 2600 111 0.625519 102.58% 420 0.895 0.13 5 2600 111 0.625519 102.58% 0 0.8 0.39 35 2600 111 0.696707 100.00% 60 0.8 0.39 35 2600 111 0.696707 100.00% 180 0.8 0.39 35 2600 111 0.696707 100.00% 300 0.8 0.39 35 2600 111 0.696707 100.00% 480 0,795 0.395 35 2600 111 0.700285 100.51% 2600 111 0 0,695 1,095 100 2600 111 0.768054 100.00% 120 0.7 1,085 100 2600 111 0.764842 99.58% 180 0.705 1.08 100 2600 111 0.761612 99.16% 480 0.705 1,075 100 2600 111 0.761612 99.16% 600 0.705 1,075 100 2600 111 0.761612 99.16% 900 0.705 1,075 100 2600 111 0.761612 99.16% 1200 0.71 1.05 100 2600 111 0.758362 98.74% Table 1: Result of a multiple wave measurement

At first, the pump worked at high power, then the power was reduced, which is called the cooling phase. As can be seen in Table 2, θ was reduced and the active power increased during this period. The measurement was continued with an increase in power, which is called the warm-up phase. At this time, θ was increased and the active power was reduced during this period. The measurement shows that θ is a value that depends on the temperature of the coil. The sequence was repeated on another machine that has a small soldering pump but works as well. Due to the difference in size, the changes are much faster. Time P _measured ? f U I P named _phase P _{eff calculated} sec / min kW wheel Hz V A 0 0.22 0.955 120 0.22 0.96 300 0.21 0.96 420 0.2 0.96 660 0.2 0.965 25 min 0.2 0.965 26 min 0.2 0.97 29 min 0.2 0.97 29.3 135 0.9 68.68389 206.0517 Switch off the pump 1 min 0.2 0.96 35 2600 111 0.696707 100.00% 15 minutes 0.22 0.96 35 2600 111 0.696707 100.00% 40 min 0.22 to 1 0.96 35 2600 111 0.700285 100.51% Table 2 - Measurement with a smaller pump

The results are the same as those of the multiple shaft pump shown in Table 1. A difference of 10% in pump performance was measured with the same settings.

It is therefore proposed to implement a software function which monitors the active power or rated power of the pump and integrates this in the control loop.

In the case of a change in the rated power of, for example, more than 2-5%, which can be specified, a check of the wave height is performed automatically.

Claims (11)

Method for operating a pump ( 32 ), in which a delivery rate of the pump ( 32 ), using a pump model that is used as a parameter of the pump ( 32 ) a temperature in the pump ( 32 ), whereby in the regulation a rated output of the pump ( 32 ) is taken into account such that a change in the parameter temperature in the pump ( 32 ) is taken into account in the pump model in the context of the scheme. Method according to Claim 1, in which, as a pump ( 32 ) an induction pump ( 180 ) is used. Method according to claim 2, wherein a temperature of a coil ( 152 ) of the induction pump ( 180 ) is taken into account.  Method according to one of Claims 1 to 3, in which a frequency converter in which required parameters are available is used. Method according to claim 1 or 2, which is in a pump ( 32 ) is used to pump solder in a soldering process. Method according to claim 5, which is in a pump ( 32 ) is used to pump solder in a selective soldering process. Control of a pump ( 32 ), which serves to increase the delivery rate of the pump ( 32 ), in particular for carrying out a method according to one of claims 1 to 6, wherein the control is provided with a pump model which is used as a parameter of the pump ( 32 ) a temperature in the pump ( 32 ), wherein the arrangement is set up in such a way that during regulation a rated output of the pump ( 32 ) such that a change in the parameter temperature in the pump ( 32 ) is to be considered in the pump model in the context of the scheme.  Control according to claim 7, comprising a PI controller. Control according to claim 7 or 8, for controlling an induction pump ( 180 ) is set up for a soldering process.  Computer program with program code means which is set up to carry out a method according to one of Claims 1 to 6, when the computer program is executed on a computer, in particular a computer in a system according to one of Claims 7 to 9.  A machine-readable storage medium having a computer program stored thereon according to claim 10.

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