EP1172560B1 - Dosing pump with current controlled motor - Google Patents

Description

The invention relates to a metering pump according to the preamble of Claim 1 specified characteristics.

In metering pumps of the type mentioned drives an electric motor via a downstream gear an oscillating displacer pump on. Transmission in the context of the invention is any implementation of rotatory rotor movement in the translational motion of Displacement pump.

In metering pumps of this type with current-controlled motor, the motor usually during the entire working stroke as well as itself subsequent return stroke - this requires at least one motor rotation, often still provided a reduction gear is, so that a large number of engine rotations are required - with one usually applied constant current, which is chosen so high is that the engine is also at the time of maximum load during the working hub is always sufficiently supplied. As the engine, however only a part of the power stroke requires such a high current and for example during the return stroke a much lower Requires electricity for safe operation, such a current application leads to a poor efficiency of the device and also to a high warming of the engine, which in particular at compact engines can pose a problem. This problem For example, in the known from DE 196 23 537 A1 Metering pump occur.

Starting from the known from DE 196 23 537 A1 prior art the invention has the object, a generic Dosing pump form so that it works with higher efficiency, in particular generates lower heat loss on the motor side.

This object is achieved according to the invention by those specified in claim 1 Characteristics solved. Advantageous embodiments are in the Subclaims and in the following description.

The basic idea of the present invention is, by means of the electronic Control the current supplied to the motor according to the expected engine load depending on the stroke position of Limit working machine.

The present invention can basically be applied to all engine controls for dosing pumps find application in which the rotational movement the motor shaft converted into a translational movement is and the engine load on the stroke of the pump systemic is subject to greater fluctuations. A preferred and typical Application is with a metering pump, which by means of a servo or Stepper motor is driven and the pump through a membrane or piston pump is formed. In such dosing pumps takes place in Transmission often still has a reduction ratio, so that according to the Stroke position of the pump provided current limit particularly effective is because the engine over possibly several turns with a low current can be controlled, as for example is appropriate for the return.

In dosing pumps, the pumping is produced under pressure in the working stroke, whereas the return stroke is used for suction. Since the Pressure stroke demands more power from the engine than the suction stroke, It is advisable to use the engine during the intake stroke with a smaller one To control electricity as during the print stroke.

Even if a positive mechanical coupling between the motor shaft and the push rod of the pump is given or in particular in such cases where such is not given, for example if a belt drive is interposed, it is expedient the stroke position of the pump or a comparable position of Gear and rotor (if a positive connection is given in the work string) capture. In this way, from the controller, the push rod position the pump accurately detected at least once per Abeitszyklus and then the default curve for current limiting be temporally positioned according to the detected position. When positive locking in the drive train between the motor shaft and Push rod of the pump consists, it is sufficient, a position sensor in Area of the pump, for example, to detect an end position of Push rod provided. Here we are the position transmitter expediently arranged so that it has a signal in the central region of the working stroke. This is especially true when using a Diaphragm pump appropriate, since then reliably ensured can be that the pump immediately after receiving this signal is shut down when it is switched off, since then namely the Diaphragm of the pump is not biased, reducing the life is increased.

The engine load is on the one hand dependent on the stroke position, since For example, in an eccentric drive the moment load of Motors with changing rotational position changes, even if the applied force to the push rod remains the same, on the other hand but also from the lifting speed. This is in the end positions the pump zero and about half of the stroke on the drive biggest. Incidentally, with dosing pumps during the return stroke with higher speed than during the compression stroke. This is expediently in the current limit of the motor with too be aware of why the current limit is also in Dependence of the expected lifting speed should take place. Such a fixed current limit curve will then expediently still depending on the speed with which the pump delivers varies as the motor current at constant Engine torque load with increasing speed increases. This increase or decrease is in the determination of the Current limit curve expediently taken into account.

Furthermore, the current limitation will be done conveniently so that it depends on the pressure to be applied by the pump done so that when the pump is applying a high pressure has enough power and in phases Lower pressure of the current is lowered accordingly. To this Pressure, it is expedient to provide a corresponding sensor, which is expediently arranged in the region of the pump becomes. For this purpose, a force measuring device in the region of provided oscillating drive means, for example in the field of Push rod.

Instead of a sensory pressure detection can this at a given Speed can also be determined via the motor current since the motor current at least in the central region of the working stroke at a given Engine speed is the moment applied by the engine and thus determines the pressure applied by the pump. Conversely, through the engine control by limiting the maximum current also the maximum applied by the pump Be limited to impermissibly high loads. or to prevent the system.

To the current limit curve as close as possible to the actual To adjust the power requirements of the engine, it is convenient to the engine supplied current or a predetermined current limit curve Gradually lower as long as the engine in its speed falls below a setpoint, d. H. the engine supplied Power is no longer sufficient to deliver the required power.

When this point is reached, then the current or the current limit curve on the previously made current limit, ie the previously raised stage raised again to be sure that the engine in all stroke positions of the pump provides the required performance. The gradual reduction or increase is preferably carried out at intervals, which a working stroke including return stroke of the pump correspond.

To ensure that the engine due to the gradual lowering of the current or the current limiting curve, if the motor speed is below a set point, does not stop, it is appropriate, the engine in the following interval with the full Current (ie without the current limiting invention) to control and only in the next subsequent interval on the previously determined Stage at which such a speed reduction of the engine straight not yet done, lower. Instead of monitoring the speed of the engine, which is relatively expensive, such a also done by means of the already existing position encoder. If namely the motor the position in which the position sensor emits a signal, has not reached in a predetermined time, then this is so long energized with the full current until the position is reached then lowered to the previously determined level again.

Advantageously, the current limiting curve in its shape and position so dimensioned that not only increases the efficiency of the device but also cavitations during the suction stroke effectively prevented.

Fig. 1

die Belastung des Motors über einen Rückhub und nachfolgend einen Arbeitshub einer Membranpumpe,

Fig. 2

die Abhängigkeit des Motorstroms von dem aufzubringenden Moment in Abhängigkeit der Drehzahl anhand von zwei Stromkurven,

Fig. 3

zwei Strombegrenzungskurven eines Motors in Darstellung nach Fig. 1 für hohen und für niedrigen Druck der Arbeitsmaschine und

Fig. 4

drei Strombegrenzungskurven eines Motors in Darstellung nach Fig. 1 für unterschiedliche Geschwindigkeiten des Motors bei gleicher Momentenbelastung.

The invention is explained below by way of example with reference to three figures. Show it:

Fig. 1

the load on the motor over a return stroke and subsequently a working stroke of a diaphragm pump,

Fig. 2

the dependence of the motor current on the torque to be applied as a function of the rotational speed on the basis of two current curves,

Fig. 3

two current limiting curves of an engine in representation of FIG. 1 for high and low pressure of the working machine and

Fig. 4

three current limiting curves of an engine in representation of FIG. 1 for different speeds of the engine at the same torque load.

The curves shown in particular in FIGS. 1, 3 and 4 are at one Metering pump was added similar to that of DE 196 23 537 A1 known type. A current-controlled stepper motor drives a reduction gear on the output side an eccentric or cam drive having, which the rotational movement in a translational movement converts and drives a push rod oscillating, which is a diaphragm pump applied. The load of the engine depends on the Push rod position and the direction of movement.

As the solid line in Fig. 1 shows 1, which is the burden of Motors depending on the push rod position during a work cycle shows, the load increases from zero starting at 90 °, so on the half of the return or suction stroke reaches its maximum and falls then at 180 ° again to zero. The zero, 180 ° and 360 ° positions mark the end positions of the working machine, ie 180 ° the end of the Return stroke or start of the working stroke and 360 ° the end of the working stroke and the beginning of the return stroke (0 °).

After reaching the reversal point 180 °, the load on the engine negative, because due to the inertia of the system in rotation staggered components still need to reduce their kinetic energy potential. After this is done, so the low point of the curve 1 is reached, increases the curve to zero and then comparatively steeply, if namely the converted kinetic energy and required to generate the pressure Forces must be applied.

At 270 °, ie at half of the working stroke, these forces have their maximum reached. They then turn off continuously, with a short before End of the print stroke, these forces rise again briefly, if namely the engine accelerates already for the expected return stroke soon becomes.

This according to curve 1 during a suction or return stroke and below a working or pressure stroke applied by the engine torque according to curve 1 is composed of a static component according to Curve 2, resulting from the (constant) pressure conditions at the pump as well as the mechanical conditions of the eccentric drive results and a dynamic component (curve 3), which is due to accelerations resulting engine load represents. So it becomes clear that in the area immediately after completion of the return stroke (after 180 °) first of all acceleration forces (as braking torque) become free, namely, if the system of the higher Rückhubgeschwindigkeit on the lower working stroke speed is slowed down. Vice versa results at the end of the working stroke, ie before the 360 ° position, a share of acceleration forces that result from the engine already is accelerated before the completion of the print stroke, after completion of the Pressure or working strokes perform the return stroke at an increased speed to be able to.

The engine load shown with reference to FIG. 1, that is, in the respective Position of the working machine at a given speed of Engine applied torque, corresponds in the waveform substantially the power required by the engine.

The relationship between motor current and motor torque is shown in FIG. 2 illustrated by two curves, the curve 4 a high motor current and the curve 5 a lower, respectively constant motor current represent. About the ordinate is the engine torque M and the abscissa the engine speed n is plotted. As from the curves 4 and 5 becomes clear, the engine torque is strong at low speeds depending on the current, whereas at higher speeds towards this Difference increasingly fades, until finally the moment approaches zero drops.

The torque curve shown with reference to FIG. 2 is typical of a such stepper motor as used to drive a metering pump becomes.

In Fig. 3 are corresponding to the above-described position of the working machine shown in FIG. 1, two current limiting curves 6 and 7. The current limiting curve 6 is included in the operation of the metering pump low pressure and the current limiting curve 7 for the operation of the Pump designed at high pressure, each with the same engine speed in the working stroke or in the return stroke. Like a comparison of the two Shows curves, these are in the range of the return stroke or suction stroke (0 ° to 180 °) coincidentally, whereas in the pressure stroke or working stroke (180 ° to 360 °) the curve 7 is clearly above the curve 6. So the work machine can apply the increased pressure, is higher from the engine Moment, which is generated by a larger motor current. Accordingly, the current limiting curve in this area is higher than at lower pressure. On the return stroke, on the other hand, this difference is practically not given, since the engine load in essence is equal to.

As FIG. 3 makes clear, it is therefore expedient to use the current limiting curves 6, 7 to make pressure dependent, since the load on the engine itself does not change over the entire work cycle evenly, but only in the Range of the working stroke and there also differentiated. In that sense it is appropriate, adapted for individual pressure ranges corresponding current limiting curves be appropriate, with the appropriate Curves then gradually, as described in the introduction, so long after can be moved down until the speed of the motor one specified value falls below the current limit curve as close as possible to the actual load.

The current limiting curves 6 and 7 shown in FIG. 3 are intended for engine controls, in the return stroke of the working machine have a higher speed than in the working stroke. In such a Arrangement can use the current limit at the same time be used to avoid cavitation in the return or suction stroke. If such a speed change is not provided, then also the current limiting curves substantially the shape of in Fig. 1st have on the basis of curve 2 shown load curve.

In Fig. 4, three current limiting curves 8, 9 and 10 are shown, which are at constant pressure load during the working stroke, but at different flow rate, d. H. different speed of the Motors revealed. The current limit curves 8 to 10 are different only in the area of the working stroke (180 ° C to 360 °), and there essentially in the middle range and also only in moderation. 4 clarifies that with increasing engine speed, so with increasing Flow rate, the current required to operate the motor increases. This is also apparent from the physical contexts, because because of the higher speed and the power of the engine and thus the delivery rate of the pump increases.

Claims (13)

1. A dosing pump with a current-controlled motor with a rotor, with a gearing connected after this for converting the rotary rotor movement into a translatory stroke movement, with an oscillating positive-displacement pump driven by this, and with an electronic control, characterised in that the current supplied to the motor is limited according to the expected motor loading in dependence on the stroke position of the positive-displacement pump.
2. A dosing pump according to claim 1, characterised in that the motor is a servo-motor or a stepper-motor.
3. A dosing pump according to one of the preceding claims, characterised in that a smaller current is supplied to the motor during the intake stroke than during the pressure stroke of the pump.
4. A dosing pump according to one of the preceding claims, characterised in that a position sensor is provided which detects the stroke position of the pump or a comparable position of the gearing and rotor, and that the current limitation is effected according to a defined curve (8, 9) proceeding from a defined, detected position.
5. A dosing pump according to one of the preceding claims, characterised in that the position sensor emits a signal only once per working cycle, preferably in the middle region of a working stroke.
6. A dosing pump according to one of the preceding claims, characterised in that the current limitation of the motor is effected also in dependence of the expected stroke speed.
7. A dosing pump according to one of the preceding claims, characterised in that the current limitation is also effected in dependence on the pressure to be mustered by the pump.
8. A dosing pump according to one of the preceding claims, characterised in that means for detecting the pressure mustered by the pump are provided, or that the maximum pressure to be mustered by the pump is defined.
9. A dosing pump according to one of the preceding claims, characterised in that a force measurement means is provided in the region of the oscillating drive means.
10. A dosing pump according to one of the preceding claims, characterised in that for determining the current limitation curve (8, 9), the current supplied to the motor is reduced in steps until the motor in its speed falls below its nominal value, and the previously effected current limitation limits the current limitation curve to the top at least at this point.
11. A dosing pump according to one of the preceding claims, characterised in that by way of the current limitation curve, the working pressure of the pump is detected whilst taking into account the speed.
12. A dosing pump according to one of the preceding claims, characterised in that the stepwise reduction of the current limitation curve is effected in intervals to which in each case a working stroke and a return stroke of the working machine corresponds, and that when on account of the current reduction it is ascertained that the motor has not reached its expected position, the motor is activated with the full current until it has reached the expected position, whereupon the previously evaluated step of the current limitation curve (8, 9) is activated.
13. A dosing pump according to one of the preceding claims, characterised in that the current limitation curve is selected such that no cavitation occurs with the intake stroke of the pump.

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