EP1301710B1 - Dosing pump with an electric motor - Google Patents

Abstract

The invention relates to a dosing pump with a synchronous motor with a mechanical gear for reducing the motor drive and converting the rotation movement of the motor into a reciprocating movement to drive a membrane pump. An electronic controller is arranged on the motor, which controls the pumped amount by means of external impulses. The controller works in such a fashion that a full working cycle of the pump is continually carried out, when the required pumped amount, based on the received impulses is as large or larger than amount which the pump can deliver in one working cycle.

Description

The invention relates to a metering pump according to the features specified in the preamble of claim 1.

With dosing pumps, a distinction is made between two types, the electromagnetically driven and the electromotively driven. In the former type, the control of the flow rate over the frequency at which the solenoid is driven, in addition, the stroke volume is usually changed by means of a mechanical screw, d. H. the flow rate per work cycle. In the electromotive-driven metering pumps of the generic type, however, such a mechanical stroke adjustment is not regularly provided, they would be technically relatively complex. In these pumps, the oscillating movement of the pump is generated by a gear mechanism in the manner of a crank mechanism or a corresponding sliding guide, wherein the rotational movement of the motor is usually still under-staged to allow a finer control of the pump. The flow rate control is done by changing the motor speed. When using stepper motors, the interval between the motor steps is varied accordingly. However, the latter type is relatively expensive due to the engine and also requires a complex electronic control.

In order to adjust the current to be supplied by the dosing pump in time and in quantity to another flow (main flow) to To ensure a predetermined mixing ratio between these currents, it is common to provide pulse control. For this purpose, dosing pumps of both types regularly have an input for an external pulse signal. In this case, each pulse of the external pulse generator, which emits pulses corresponding to the flow rate of the main flow at intervals over time, associated with a previously set metering, that is, a specific volume to be conveyed by the metering pump. While in the above-mentioned metering pumps with electromagnetic drive these per pulse delivered flow rate is usually entered by the mechanical stroke adjustment, this is only possible by electric motor driven metering by changing the stroke speed, so the speed of the drive motor.

Stepper or servo motors with the necessary controls and electric motors with controllable speed are relatively expensive. For metering pumps with electric motor drive without speed variance, so such metering pumps simple design, therefore dispensed with the possibility of an external pulse control.

Against this background, the invention has the object, a generic metering pump, which is operated with a non-variable speed drive and the displacement is not variable, with simple means in such a way that external control by means of pulse signal is possible, in particular to ensure that the promotion or admixture carried out by the metering pump by no means exceeds the values predetermined by the external control (impulse control).

This object is achieved according to the invention by the features specified in claim 1. Advantageous embodiments of the invention are specified in the subclaims and the following description.

The basic idea of the present invention is that only when a predetermined flow rate is delivered by the pump when at least as many pulses have been registered by the controller, that the resulting dosing (desired flow) equal to or greater than the preselected minimum flow of Pump is.

If the metering pump is equipped with a position detection, which allows an assignment of the motor position to the stroke position of the pump, a predetermined part of a duty cycle can be selected, since then the amount funded by the pump in this part of the duty cycle is defined. Preferably, however, the motor is not only driven to pass through a part of the working cycle (as the smallest unit of the delivery), but in each case at least to go through a full cycle. Then the flow rate is determined by the stroke volume of the pump. Such a control has the advantage that it can be technically realized with little effort, since with a suitable choice of the components used to a position determination of the motor and / or pump can be completely dispensed with. Once the working cycle has been completed completely, a full pump stroke will be carried out regardless of the position of the motor / pump at the beginning of the cycle and thus at least approximately the amount that the pump delivers during a complete working stroke. If it is what is common in such pumps, for example, is a diaphragm pump, which is in the unloaded center position when the controller starts the engine, so first half a working stroke is driven, then a full return stroke and then turn the other half of Working hubs, so that overall the flow rate of a whole working stroke is promoted.

The dosing pump according to the invention can in principle be operated with electric motors of different design, for example with a DC motor or with an asynchronous motor. Advantageously, a synchronous motor is used as the electric motor, since then for the motor control an electronic switch is sufficient to apply a predetermined AC voltage, preferably the mains voltage, to the motor or to be separated from this. Since the synchronous motor runs at a constant speed for a given mains frequency, it must only be switched on for a predetermined time in order to drive through a full working stroke. Since the gear between electric motor and pump usually also includes a reduction, even in the pure time control, a relatively high accuracy of the metering is achieved, even if no position detection is provided.

Since the rotation of the motor is determined by the frequency of the supply voltage, it is particularly advantageous to control it not after a fixed timing, but after a predetermined number of mains periods of the supply voltage. This ensures that even with frequency fluctuations in the network, a high dosing accuracy takes place without position detection. Incidentally, the motor can be operated without any control-side changes with 50 Hz or 60 Hz mains frequency.

In order to further increase the accuracy of the dosage, it is expedient to equip the pump calibrated. In this case, the amount actually pumped by the pump in one work cycle or possibly also part cycle is determined and stored in the controller.

In the control of each external pulse, a predetermined and preferably control side predetermined dosage amount (target flow rate) is assigned. Within the controller, the incoming pulses and the respective metering quantities resulting therefrom are added until the sum of the metered quantities has reached a value which is equal to or greater than the delivery rate of the pump in one working cycle. Then the pump is promoted promotional. The control then takes into account the amount that has been delivered by the pump in this work cycle and subtracts it accordingly from the total dosing quantity.

In this way, remaining remnants of the metered amount are not lost, but are taken into account quantitatively. Conversely, in the control is also taken into account when the flow rate of the pump remains due to the limited by the power frequency motor speed below the impulse dosing dose, then, when the time intervals of the pulses are larger again, this shortage still promote.

The invention will be described by way of example for a better understanding. A metering pump, whose basic structure is known for example from DE 196 23 537 A1, is driven by a drive motor in the form of a synchronous motor. The motor drives a reduction gear, which also converts the rotary motion into a lifting movement, which in turn drives a diaphragm pump. The diaphragm pump delivers 1 ml during a full pump stroke. A duty cycle of the pump consists of a return stroke in which the diaphragm pump draws liquid into the pump chamber and a working stroke in which the liquid in the pump chamber is discharged under pressure. Since the gearbox is a mechanically form-fitting, each motor rotation is assigned a defined partial stroke. A duty cycle of the pump (return stroke and power stroke) thus corresponds to a predetermined number of engine rotations by the mechanics. The synchronous motor, which can be operated at either 50, 60 or any other mains frequency, has a control which, based on the network periods, which have been supplied to the motor (ie, in which the motor was connected to the mains supply line), a duty cycle of Pump determined. Each network period is associated with a defined rotational angle of the engine and thus, based on the engine data and the known mechanical gear ratio, it can be readily determined how many grid periods are required for the pump to go through a full duty cycle. So there is no position detection for the pump or the engine is required because when driving through the full duty cycle always a quantity of 1 ml is promoted. This amount is previously determined by calibration and entered in the controller.

If now this dosing pump to mix in a variable main flow, so a synchronization of the flow rates is required. For this purpose, a pulse generator is usually provided in the external main flow, which emits a pulse whenever the external main flow has reached a predetermined amount, so that the metering pump promotes a corresponding Dosiermenge, d. H. this main flow admixed. In the present example, the metered amount to be dispensed per pulse should be 0.3 ml.

So if at the beginning of the promotion, the controller receives the first external impulse, first a dosing amount (target flow rate) of 0.3 ml stored in the engine control. It is then checked if the contents of the reservoir are equal to or greater than the amount of 1 ml delivered by the pump in one cycle. If this is not the case, as in the above example, then the dosing quantity remains in the memory as the desired delivery rate.

Upon receipt of the next pulse, first the metered amount in the reservoir is increased by 0.3 ml, after which it is again compared whether the resulting metered dose of 0.6 ml is greater than or equal to the amount of 1 ml delivered by the pump in one working cycle , This is not the case so that the dosage remains in the memory. The same happens after receiving the third pulse.

When the fourth pulse is received, the dosing amount in the reservoir has risen to 1.2 ml. Since this amount is greater than the amount of 1 ml delivered by the pump in one working cycle, the control now drives the electric motor for the number of mains periods corresponding to a full duty cycle of the pump. Then, the storage contents are reduced by the delivered amount of 1 ml, so that a Dosage of 0.2 ml remains, which in turn is taken into account when receiving the following pulses.

In this way, even with a simply constructed metering pump (with synchronous motor and little complex motor control), a comparatively accurate metering, in particular adaptation to an external delivery flow, can take place.

Claims (6)

1. A metering pump with an electric motor, with a gearing downstream of this for converting the rotatory rotor movement into a translatory stroke movement, with an oscillating pump driven by this and with an electronic control, characterised in that the control activates the motor in dependence on an external impulse generator, wherein a predefined metering quantity is allocated to each impulse, and that the control activates the motor such that the motor, for passing through a predefined part of an operating cycle of the pump, is only activated when the control has received a number of impulses which corresponds to a metering quantity which is equal or larger than the delivery quantity which the pump delivers in the predefined part of the operating cycle.
2. A metering pump according to claim 1, characterised in that the control activates the motor for passing through a complete operating cycle of the pump when it has obtained a number of impulses which corresponds to a metering quantity which is equal or larger than the quantity delivered by the pump in one operating cycle.
3. A metering pump according to one of the preceding claims, characterised in that the control evaluates a metering quantity according to the received impulses, and subtracts the already delivered quantity from this in order to determine the quantity yet to be delivered, and where appropriate to activate the motor in delivery.
4. A metering pump according to one of the preceding claims, characterised in that the motor is a synchronous motor.
5. A metering pump according to one of the preceding claims, characterised in that one determines an operating cycle by way of the mains periods of the supply voltage of the motor.
6. A metering pump according to one of the preceding claims, characterised in that the delivery quantity of the pump may be calibrated in that the quantity delivered by the pump per operating cycle or part cycle is evaluated and stored in the control.