EP1301710B2 - Dosing pump with an electric motor - Google Patents

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, ie the flow rate per 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 slotted guide, wherein the rotational movement of the motor is usually still stockier, 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 adapt the flow to be delivered by the metering pump to another flow rate (main flow rate) in order to ensure a predetermined mixing ratio between these flows, it is usual to provide a pulse control ( DE 33 13 993 A1 ). For this purpose, metering pumps of both designs 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 this per pulse delivered flow rate is usually entered by the mechanical stroke adjustment, this is possible with electric motor driven metering exclusively 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 ( DE 33 13 993 A1 ), which is operated with a non-variable speed drive and the displacement is not changeable, with simple means in such a way that an external control by means of pulse signal is possible, in particular to ensure that the promotion carried out by the metering pump or mixing by no means the exceeds given values 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 the Pump is.

In order to further increase the accuracy of the dosage is equipped according to the invention, 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.

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 Einhelt the flow rate), 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 is technically feasible 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 fully completed, a full pump stroke will be carried out regardless of the position of the motor / pump at the beginning of the cycle, at least approaching the amount that the pump delivers during a full stroke. If it is what is usual in such pumps, for example, is a diaphragm pump, which is in the unloaded center position when the controller starts the engine, then first half a working stroke then driven a full return stroke and then turn the other half of a power stroke , so that the total delivery 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 an electronic switch is sufficient for the motor control to apply a predetermined alternating voltage, preferably the mains voltage, to the motor or to separate it from this. Since the synchronous motor runs at a constant speed at a given mains frequency, it is only necessary to turn it on for a predetermined time in order to achieve a constant speed to go through the 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 not to control this after a fixed time, but after a predetermined number of mains periods of the supply voltage This can ensure that even with frequency fluctuations in the network high dosing accuracy without position recognition. Incidentally, the motor can be operated without any control-side changes with 50 Hz or 60 Hz mains frequency.

The invention will be described by way of example for a better understanding, a metering pump whose basic structure, for example DE 196 23 537 A1 is known, 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 fluid 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 stroke) thus corresponds to one through the. Mechanics predetermined number of motor rotations The synchronous motor, which can be operated with either 50, 60 or any other network frequency, has a control, which on the basis of the mains periods which have been supplied to the motor (ie in which the motor was line connected to the supply network) determines a duty cycle of the pump. Each network period is associated with a defined rotation 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 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 dosage 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 is 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 it is not the case that the dosing quantity 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 volume is 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 (4)

1. A metering pump with an electric motor, with a gearing downstream of this for converting the rotational rotor movement into a translatory stroke movement, with an oscillating pump driven by this and with an electronic control activating the motor in dependence on an external pulse generator, wherein a predefined metering quantity is assigned to each pulse, and 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 pulses which correspond to a metering quantity equal or larger than the delivery quantity which the pump delivers in the predefined part of the operating cycle, characterised in that the control evaluates a metering quantity according to the received pulses, 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, and the delivery quantity of the pump can be calibrated by way of the quantity delivered by the pump per operating cycle or part cycle being determined and stored in the control.
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 pulses which correspond to a metering quantity 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 motor is a synchronous motor.
4. A metering pump according to one of the preceding claims, characterised in that an operating cycle is determined by way of the mains periods of the supply voltage of the motor.