EP1172560A2 - Pump system with current controlled motor - Google Patents

Abstract

The feed device has a current-controlled electric motor, e.g. a servo or stepping motor and a conversion gearing, converting the motor rotation into a linear reciprocation for driving the feed device. The current for the motor is limited by the expected motor loading dependent on the stroke position of the feed device.

Description

The invention relates to a conveyor device according to the preamble of claim 1 specified features.

Conveyors of this type are typically metering pumps but also compressors or other devices in which a Electric motor via a downstream gearbox an oscillating machine drives. Gearbox in the sense of the invention is any implementation the rotary motor movement into the translatory movement the working machine.

In conveyor devices of this type with a current-controlled motor, the Engine usually during the entire working stroke as well as the then return strokes - this requires at least one engine turn, in the case of metering pumps, for example, often a reduction gear is provided so that a variety of engine rotations are required, - supplied with a usually constant current, which is selected so high that the engine is also at the time of the maximum load during the work stroke is always adequately supplied is. However, since the engine only has such a part of the working stroke high current and, for example, during the return stroke requires significantly lower current for safe operation, such leads Current application to poor device efficiency and also to a high heating of the engine, which is particularly the case with compact motors can be a problem. This is a problem can for example in the dosing pump known from DE 196 23 537 A1 occur.

Based on this prior art, the object of the invention to form a generic conveyor device so that it works with higher efficiency, especially low heat loss generated on the motor side.

This object is achieved according to the invention by those specified in claim 1 Features resolved. Advantageous embodiments are in the Subclaims and in the description below.

The basic idea of the present invention is to use the electronic Control the current supplied to the motor according to the expected engine load depending on the stroke position of the driven machine to limit.

The present invention can basically be used with all motor controls Find application where the rotational movement of the motor shaft in a translational movement is implemented and the engine load larger fluctuations due to the system's stroke is subjected, such as in compressors. A preferred one and typical application is in a metering pump, which is by means of a Servo or stepper motor is driven and its working machine by a positive displacement pump, in particular a diaphragm or piston pump, is formed. With such metering pumps takes place in the transmission often a reduction, so that according to the stroke position the current limitation provided by the pump is particularly effective since the Motor driven for several revolutions with a low current if necessary can be, as appropriate for the return stroke, for example is.

With metering pumps, the delivery is generated under pressure in the working stroke, whereas the return stroke is used for suction. Because the pressure stroke the engine requires more power than the suction stroke, it is advisable the motor with a smaller current than during the suction stroke to be controlled during the pressure stroke.

Even if there is a positive mechanical coupling between the motor shaft and the push rod of the machine is given or in particular in cases where such is not the case, For example, if a belt drive is interposed, it is advisable the stroke position of the working machine, in particular the pump, or a comparable position of gear or rotor (if a Form fit in the drive train). In this way can control the pushrod position of the working machine be recorded exactly at least once per work cycle and then the predefined curve for current limitation in accordance with the detected Position can be positioned in time. If positive locking in the drive train there is between the motor shaft and the push rod of the driven machine, it is sufficient to provide a position encoder on the motor side. For the rest preferably a position transmitter in the area of the working machine, for example provided for detecting an end position of the push rod. there the position transmitter is expediently arranged so that it is a Signal in the middle of the working stroke. This is particularly the case with Use of a diaphragm pump is advisable because it is then reliable can be ensured that the pump immediately after receipt of this Signal is stopped when it is switched off, because then the The pump diaphragm is not preloaded, which increases the service life is increased.

The motor load depends on the one hand on the stroke position, because For example, in the case of an eccentric drive, the torque load on the motor with changing rotational position, even if the one to be applied Force on the push rod remains the same, but on the other hand also from the Lifting speed. This is zero in the end positions of the machine and the largest due to the drive at about half the stroke. Furthermore becomes higher with dosing pumps during the return stroke Speed worked as during the print stroke. This will be convenient to be taken into account when limiting the current of the motor be, which is why the current limitation also depends on the expected Lifting speed should take place. A current limit curve set in this way is then expediently still depending on the The speed at which the pump delivers varies because the motor current at constant engine torque load with increasing speed increases. This increase or decrease is when the current limiting curve is determined expedient to take into account.

Furthermore, the current limitation is expediently carried out in such a way that it takes place depending on the pressure to be applied by the pump, so that when the pump has to apply high pressure, the Motor is adequately powered and in phases lower Pressure the current is reduced accordingly. To this pressure too detect, it is advisable to provide a corresponding sensor that is expediently arranged in the area of the working machine. For this purpose, a force measuring device in the area of the oscillating one is preferred Drive means are provided, for example in the area of the push rod.

Instead of a sensory pressure detection, this can be done with a predetermined one Speed can also be determined via the motor current, since the Motor current at least in the middle range of the working stroke at a given one Engine speed the moment applied by the engine and to determine the pressure applied by the pump. Vice versa can be controlled via the motor control by limiting the maximum Current also limits the maximum pressure to be applied by the pump to avoid impermissibly high loads on the device or system side to prevent.

To keep the current limiting curve as close as possible to the actual one It is advisable to adapt the motor's power requirements to the motor supplied current or a predetermined current limiting curve gradually lower until the engine is at speed falls below a setpoint, d. H. the current supplied to the motor is not more is enough to deliver the required performance. If this Point is reached, then the current or the current limiting curve is on the previous current limitation, i.e. the previously driven level again raised to be sure that the engine is in all stroke positions Machine provides the required performance. The gradual lowering or increase preferably takes place in intervals which one Correspond to the working stroke including the return stroke of the working machine.

To ensure that the engine due to the gradual lowering of the current or the current limiting curve when the motor speed falls below a setpoint, does not stop, it is advisable the motor in the following interval with the full current (i.e. without the current limitation according to the invention) and only in again following interval to the previously determined level at which such a speed reduction of the engine just not yet takes place to lower. Instead of monitoring the speed of the Motors, which is relatively expensive, can also be done by means of the anyway existing position transmitter. Because if the engine Position in which the position transmitter emits a signal in a predetermined one Time has not reached, then this will be with the full current for so long controlled until the position is reached, then to the previously determined Level to be lowered again.

The shape and position of the current limiting curve is advantageous in this way dimensioned so that not only the efficiency of the device is increased, but that cavitations are also effective during the suction stroke be 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 engine via 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 speed based on two current curves,

Fig. 3

two current limiting curves of a motor in Fig. 1 for high and for low pressure of the machine and

Fig. 4

three current limiting curves of a motor shown in FIG. 1 for different speeds of the motor with the same moment load.

The curves shown in particular in FIGS. 1, 3 and 4 are on one Dosing pump has been added similar to that from DE 196 23 537 A1 known design. A current controlled stepper motor drives a reduction gear an eccentric or cam drive on the output side which has the rotational movement in a translatory movement implements and drives a push rod oscillating, which a diaphragm pump applied. The load on the motor depends on the Push rod position and the direction of movement.

As the solid curve 1 in FIG. 1 shows, which shows the load on the Motor depending on the push rod position during a work cycle shows, the load increases from zero, has at 90 °, so reaches its maximum on half of the return or suction stroke then at 180 ° again to zero. The zero, 180 ° and 360 ° positions mark the end positions of the working machine, i.e. 180 ° the end of the Return stroke or start of the work stroke and 360 ° the end of the work stroke and the beginning of the return stroke (0 °).

After reaching the reversal point 180 °, the load on the motor negative because of the inertia of the system which is in rotation displaced components still have to reduce their kinetic energy potential. After this has taken place, ie the low point of curve 1 has been reached, increases the curve to zero and then comparatively steep, namely when the kinetic energy converted and the necessary to generate the pressure Forces must be applied.

At 270 °, i.e. half of the working stroke, these forces have their maximum reached. They then fall again continuously, just before At the end of the pressure stroke, these forces briefly increase again, if namely the engine accelerates for the return stroke to be expected shortly becomes.

This according to curve 1 during a suction or return stroke and subsequently a working or pressure stroke from the engine according to curve 1 is composed of a static part according to Curve 2, which results from the (constant) pressure conditions at the pump and the mechanical conditions of the eccentric drive results as well a dynamic part (curve 3), which is due to accelerations resulting engine load. So it becomes clear that in the area immediately after completing the return stroke (after 180 °) first of all, acceleration forces (as braking torque) are released, namely when the system from the higher return stroke speed up the lower working stroke speed is braked. Vice versa there is a portion at the end of the working stroke, i.e. before the 360 ° position of acceleration forces that result from the engine already is accelerated before the completion of the pressure stroke to after the completion of the Pressure or work strokes carry out the return stroke at 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 from The torque to be applied to the motor essentially corresponds to the curve shape the current required by the motor.

The relationship between motor current and motor torque is shown in Fig. 2 illustrated by means of two curves, curve 4 showing a high motor current and curve 5 a lower, constant motor current represent. The engine torque is M on the ordinate and on the abscissa the engine speed n plotted. As from curves 4 and 5 it becomes clear that the engine torque is strong at low engine speeds depending on the current, whereas at higher speeds this Difference gradually disappears until finally the moment approaches zero drops.

The torque curve shown in FIG. 2 is typical for one such stepper motor as used to drive a metering pump becomes.

In Fig. 3 are corresponding to the position of the machine described above 1 shows two current limiting curves 6 and 7. The current limiting curve 6 is for the operation of the metering pump low pressure and the current limiting curve 7 for the operation of the Pump designed for high pressure, always at the same motor speed in the working stroke or in the return stroke. Like a comparison of the two Shows curves, these are in the area of the return stroke or suction stroke (0 ° to 180 °), whereas in the pressure stroke or working stroke (180 ° up to 360 °) curve 7 is clearly above curve 6. So that the working machine can apply the increased pressure, the engine is a higher one Applying moment what is generated by a larger motor current. Accordingly, the current limiting curve must be designed higher in this area than at lower pressure. On the other hand, this is the difference with the return stroke practically not given, since the engine load essentially is equal to.

As illustrated in FIG. 3, it is therefore expedient to use the current limiting curves 6, 7 to be pressure-dependent, since the load on the engine increases does not change evenly over the entire working cycle, but only in Area of the working stroke and also differentiated there. So far it is Expediently adapted current limiting curves for individual pressure ranges to be provided, the respectively in question Then continue to curve in stages, as described in the introduction can be moved down until the speed of the motor one falls below the specified setpoint by the current limiting curve as close as possible to the actual load.

The current limiting curves 6 and 7 shown with reference to FIG. 3 are provided for engine controls in the return stroke of the working machine have a higher speed than in the working stroke. With one The current limiting arrangement can be used simultaneously for this purpose to avoid cavitation in the return or suction stroke. If such a change in speed is not provided, then also the current limiting curves essentially the shape of the one in FIG. 1 have load curve shown by curve 2.

In Fig. 4, three current limiting curves 8, 9 and 10 are shown, which are with constant pressure load during the working stroke, however at different output, d. H. different speed of the Engine result. The current limitation curves 8 to 10 differ only in the area of the working stroke (180 ° to 360 °), essentially there in the middle range and only in terms of amount. 4 thus illustrates that with increasing engine speed, i.e. with increasing Flow rate, the current required to operate the motor increases. This also results from the physical relationships, because because of the higher speed, the performance of the engine and thus the delivery capacity of the pump increases.

Claims (13)

Conveyor device with a current-controlled motor, with a transmission connected downstream for converting the rotary rotor movement into a translatory lifting movement, with an oscillating work machine driven by it and with an electronic control, characterized in that the current supplied to the motor in dependence on the expected motor load Stroke position of the working machine is limited. Conveying device according to claim 1 in the form of a metering pump, characterized in that the motor is a servo or stepper motor and the working machine is formed by a displacement pump. Conveying device according to one of the preceding claims, characterized in that a smaller current is supplied to the motor during the suction stroke than during the pressure stroke of the pump. Conveying device according to one of the preceding claims, characterized in that a position transmitter is provided which detects the stroke position of the working machine, in particular the pump, or a comparable position of the gearbox or rotor and that the current limitation according to a predetermined curve (8, 9) a predetermined detected position. Conveying device according to one of the preceding claims, characterized in that the position transmitter emits a signal only once per working cycle, preferably in the central region of a working stroke. Conveying device according to one of the preceding claims, characterized in that the current limitation of the motor also takes place as a function of the expected lifting speed. Conveying device according to one of the preceding claims, characterized in that the current limitation also takes place as a function of the pressure to be applied by the pump. Conveying device according to one of the preceding claims, characterized in that means are provided for detecting the pressure applied by the pump or that the maximum pressure to be provided by the pump is predetermined. Conveying device according to one of the preceding claims, characterized in that a force measuring device is provided in the region of the oscillating drive means. Conveying device according to one of the preceding claims, characterized in that, in order to determine the current limiting curve (8, 9), the current supplied to the motor is gradually reduced until the speed of the motor drops below its setpoint and the current limitation which has occurred before the current limiting curve at least in this Point limited upwards. Conveying device according to one of the preceding claims, characterized in that the working pressure of the pump is detected on the basis of the current limiting curve, taking into account the speed. Conveying device according to one of the preceding claims, characterized in that the step-by-step lowering of the current limiting curve takes place at intervals which in each case correspond to a working stroke and return stroke of the working machine, and that if it is determined on the basis of the lowering of the current that the motor does not reach its expected position the motor is driven at full current until it has reached the expected position, after which the previously determined stage of the current limiting curve (8, 9) is activated. Conveying device according to one of the preceding claims, characterized in that the current limiting curve is selected so that no cavitation occurs during the suction stroke of the pump.

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