EP2362100B1 - Metering pump aggregate and method for controlling same - Google Patents

Description

The invention relates to a Dosierpumpenaggregat according to the preamble of claim 1 and a method for controlling such Dosierpumpenaggregates.

Known metering pump units have a metering space, which is bounded on one side by a displacement body, for example in the form of a membrane. The displacer can change the volume of the metering chamber, whereby a pumping action is achieved. To drive the displacer a suitable linear drive is provided. For example, this is a rotationally driving drive motor in the form of a stepping motor, which displaces a connecting rod in linear oscillating motion via an eccentric. On the input and output side of the metering check valves are arranged, which prevent the suction medium to be conveyed from the pressure line back into the dosing and prevent the pressure stroke that the medium is pressed into the suction line instead of the pressure line.

WO 03 / 054392A1 discloses a metering pump, which has an electric motor drive, which is variably controllable in its speed and direction of rotation. By this control, it is possible to perform the suction stroke faster than the pressure stroke.

DE 20 2005 013 090 U1 discloses a motor metering pump whose drive is controlled so that the suction slows down to avoid cavitation.

EP 1 278 961 B1 discloses a pump for conveying liquid, which is designed as a piston pump, wherein the piston can be moved so that during the pressure stroke, the speed increases towards the center of the pressure stroke and then reduced again at the end of the pressure stroke. US 4,131,393 discloses a fluid pump system in which the suction stroke is started at a slower rate to avoid cavitation.

When dosing very small volumes or flow rates, for example, of a few milliliters per hour, very slow stroke speeds are required, for example, a pressure stroke may take several minutes, even more than a quarter of an hour. With these very slow lifting and conveying speeds, it is not possible to ensure a fast closing of the valves due to the lack of dynamics. which leads to leakage and thus to a poor dosing accuracy.

In view of this problem, it is also an object of the invention to provide a Dosierpumpenaggregat, which ensures a high dosing accuracy even at very low volumes to be dosed.

This object is achieved by a Dosierpumpenaggregat with the features specified in claim 1 and by a method for controlling a Dosierpumpenaggregates with the features specified in claim 10. Preferred embodiments will become apparent from the appended subclaims, the following description and the attached figures.

The metering pump unit according to the invention has, in a known manner, a metering space on which a displacer body is arranged adjacent. The displacer thus forms a wall of the dosing and can change the volume of the dosing by its movement. During a suction stroke, the volume of the metering chamber increases and during a pressure stroke, the displacer is moved so that the volume of the metering chamber is reduced. For the movement of the displacement body, a displacement drive is provided which can be controlled or regulated by a control device. In particular, the speed, operating time and direction of movement of the displacer drive can be predetermined via the control device in order to set or regulate the volume to be metered via the actuation of the displacer drive.

The positive displacement drive is preferably an electric drive motor, in particular a stepping motor, which can be controlled very precisely by stroke length and / or stroke speed of the displacement body to set specifically to comply with the amount to be dosed and the dosing according to predetermined values.

The drive motor may be a linear motor or a rotationally driving electric motor, wherein the rotational movement is then converted into a linear movement of the displacement body via suitable transmission means, for example a crank drive, a cam drive, an eccentric or a spindle. As drive motor can be used in addition to a stepper motor, for example, an EC motor, a servo motor or other suitable electric drive motor use.

According to the invention, the control device and the displacement drive are designed such that the travel speed of the displacement body can also be changed during a pressure stroke. This is done by changing the speed of the positive displacement drive, z. B. the speed or rotational speed of the drive motor. In this case, the control device is further designed such that it selects a specific driving or drive characteristic of the positive displacement for certain of the metering pump to be generated target flow rates and controls the displacement accordingly. According to the invention, such a special drive characteristic is configured such that the pressure stroke of the displacement body is started at a first increased lifting speed and then continued at a second lower lifting speed. Due to the fact that the pressure stroke is started with an increased stroke speed, a stronger impulse or rapid increase in pressure is exerted on the medium or fluid to be delivered at the beginning of the pressure stroke, which causes a rapid closing of the non-return valve. Subsequently, the lifting speed is then reduced by appropriate control of the positive displacement drive and the rest of the pressure stroke is with less lifting or traversing speed of the Displacer completed. This ensures that despite the increased lifting speed at the beginning of the pressure stroke in the total stroke only a small volume per unit time is promoted. This special drive characteristic is thus particularly suitable for the promotion of very low volume flows, in which there is the above-mentioned problem of not reliable immediate closure of the check valves.

The control device is designed such that it at least for certain of the metering pump to be generated flow rates the positive displacement drive, for. B. drives a drive motor such that a pressure stroke of the displacer is started with a first increased stroke speed and then continued at the second lower stroke speed. This ensures that the check valve is closed to the suction channel in a pressure stroke for particularly low flow rates quickly and reliably, so that there no or only small leakage occurs and thus a high dosing accuracy is achieved even at low flow rates. After the initial pulse due to the increased lift speed, the controller then increases the lift speed by reducing the speed of the displacer drive, i. H. z. B. reduces the speed of the drive motor, so that a total of the pressure stroke only a smaller flow rate is achieved.

Although, according to a preferred embodiment, the control device is designed such that it executes the above-described and subsequently described specific drive characteristic in the pressure stroke, it is to be understood that the control device may also be configured to additionally include the specific drive strategy described above or below in the suction stroke. The control device is thus preferably designed such that it controls the displacement drive for flow rates below a predetermined limit value in such a way that a pressure stroke of the displacement body is started at a first increased lifting speed and then continued at a second lower lifting speed. The exact limit may depend on the structural design of the metering and in particular the check valves used. In such low flow rates, in which otherwise a reliable closing of the valves is no longer achieved, the described special driving characteristics of the displacer is to be used, according to which started with an increased lifting speed and the pressure stroke is then continued with a reduced lifting speed compared to this increased , The correspondingly specific limit values are predefined for the control device or are stored in a memory of the control device.

The change in the lifting speed of the displacer drive, as described, by appropriate control by means of the control device, so that the displacer drive according to specification of the control device with different speeds or speeds is operable. In the case of using a stepping motor, the motor can execute a predetermined number of individual steps in a certain time interval. The number of individual steps per time interval can be variably set by the control device in order to change the rotational speed of the drive motor.

More preferably, the control device is designed such that the first increased lifting speed is set faster than required for a desired flow rate. This ensures that compared to the initial rapid increase in pressure, which occur at the otherwise required for the desired flow rate lifting speed would, a faster initial pressure increase is exerted on the medium to be conveyed, which leads to a reliable closing of the valves, in particular of the valve in the suction channel. To achieve this, at the beginning of the print stroke, the stroke speed must be selected for a actually higher flow rate. Due to the later reduction in the lifting speed, this is then compensated again in order to achieve a total of a smaller volume flow over the total stroke than is achieved at the beginning of the pressure stroke with the higher stroke speed.

It is further preferred that the control device is designed such that the second lower stroke speed is set slower than required for a desired flow rate. As a result, together with the stroke speed selected at the beginning of the pressure stroke, which is higher than required for the desired delivery flow, the nominal delivery flow can be achieved on average over the entire pressure stroke. Particularly preferably, the control device is configured such that it selects or calculates the first increased lifting speed and the second reduced lifting speed and the duration of the partial stroke with the first lifting speed as a function of a predetermined desired flow so that an average flow rate is achieved over the entire pressure stroke is, which corresponds to the desired target flow rate. The duration with which the pressure stroke is increased with increased lifting speed and the absolute values for the higher and the reduced lifting speed can be stored in the control device for certain nominal flow rates in a memory or currently for a selected target flow rate according to predetermined algorithms be calculated. Also, during the pressure stroke monitoring of the flow rate by suitable sensors possible, so that the lifting speed during the pressure stroke of the controller could be adjusted to a specific setpoint.

According to a preferred embodiment, 2% or more of the total pressure stroke is performed at the first increased lift speed. More preferably, less than 20% of the total pressure stroke is performed at the first increased lift speed. The hub does not have to be the maximum possible hub, it could just be a shortened hub. This is thus only a small part of the total stroke, so that the constant metering of the medium to be metered is only slightly impaired by the increased stroke speed at the beginning of the pressure stroke. However, since without the increased lifting speed at the beginning of the pressure stroke due to the poor closing quality of the valves otherwise undesired leakage and thus deterioration of the dosing accuracy would occur at low flow rate, a higher dosing accuracy is achieved by the increased stroke speed at the beginning of the print stroke.

The change in the lifting speed from the first increased lifting speed to the second lower lifting speed can be sudden or else in the form of a ramp. Also, a change in several steps or stages or a ramp with changing slope is possible. The first increased lift speed is more preferably equal to or greater than six strokes per minute, while the second lower lift speed is preferably less than six strokes per minute. The first increased lifting speed may more preferably substantially correspond to the lifting speed in the suction stroke. Conveniently, the first increased lifting speed is many times greater than the second lower lifting speed, preferably, the first increased lifting speed is three times, according to another preferred embodiment five times or seven times or more of the second lower stroke speed.

The invention further relates to a method for controlling a metering pump unit, wherein the method provides that the pressure stroke of a displacement body is carried out such that the pressure stroke is started at a first increased lifting speed and then continued at a second lower lifting speed. This method is preferably used at nominal flow rates below a predetermined threshold. Incidentally, the method is preferably designed as it results from the preceding description of the operation of the metering pump according to the invention.

Fig. 1

in einer Schnittansicht ein erfindungsgemäßes Dosierpumpenaggregat, und

Fig. 2

in einem Diagramm, in welchem die Motordrehzahl über die Hublänge aufgetragen ist, die erfindungsgemäße Antriebscharakteristik für geringe Förderströme.

The invention will now be described by way of example with reference to the accompanying drawings. In these shows:

Fig. 1

in a sectional view of a metering pump according to the invention, and

Fig. 2

in a diagram in which the engine speed is plotted over the stroke length, the drive characteristic according to the invention for low flow rates.

The metering pump unit according to the invention has a drive housing 2 with a pump head 4 arranged on the end side thereof. In the drive housing 2, a displacement drive in the form of an electric drive motor 6 is arranged, which is preferably designed as a stepper motor. The drive motor 6 drives via a gear 8 to an eccentric 10. By the eccentric 10, the rotating drive movement of the drive motor 6 is converted into a linear movement of a connecting rod 12. The connecting rod 12 causes a lifting movement of the membrane 14 in the direction of the lifting axis X. The membrane 14 defines one side of the metering chamber 16 and forms therein a displacer, through which the volume of the metering chamber 16 for pumping or metering is variable. The metering chamber 16 is in communication with a suction port 18 and a pressure port 20. In the flow path for the suction port 18 in the metering chamber 16 two check valves 22 are arranged in series in the suction channel. Accordingly, in the flow path from the metering chamber 16 to the pressure port 20 in the pressure channel in series two check valves 24 are arranged. Here, two check valves 22 and 24 are provided in each case. It should be understood, however, that only one check valve 22 and one check valve 24 could be used.

In the motor housing 2, a control device or control electronics 26 is also arranged, which is connected to an operating and display device 28, via which parameters, such as the flow adjustable and information that outputs the control electronics 26, are readable. A certain flow, which is adjusted for example via the control and display device 28 is converted by the control electronics 26 in a corresponding control or regulation of the drive motor 6, so that it is operated at a corresponding speed, so that the membrane 14 with a corresponding stroke speed is moved in the direction of the lifting axis X. The stroke length is controllable by the control electronics 26 via the rotation angle of the drive motor 6, which is preferably designed as a stepper motor.

If very low flow rates are selected, there is the problem that at the beginning of the compression stroke, the check valves 22 in the suction channel may not close completely immediately, so that there may be leakage, which affect the dosing accuracy. In order to avoid this, the electronic control unit 26 is designed or programmed in such a way that it uses a special drive characteristic for flow rates which are below a certain limit value stored in the control electronics 26 in order to cause the valves 22, 24 to close. The corresponding limit value may depend on the characteristic, size and special design of the pump head 4 and in particular of the check valves 22 and 24. Although it is preferred that this particular drive characteristic described below can be used for low flow rates below a certain limit, it is possible Understand that this drive characteristic could also be used for other flow rates.

The said drive characteristic is described in more detail with reference to Fig. 2 described. This shows a diagram in which the engine speed n of the drive motor 6 is shown over the stroke length H of the compression stroke. The point 30 in the diagram indicates the beginning of a pressure stroke, while the point 32 in the diagram indicates the end of the pressure stroke at which the full stroke length H of the diaphragm 14 in the direction of the lifting axis X is reached. According to the specific drive characteristic, the pressure stroke is started at an increased rotational speed n _{1 of} the drive motor 6. The control electronics 26 controls the drive motor 6 accordingly, so that it runs at this speed. Due to the transmission 8 and the eccentric 10, this causes a corresponding, proportional first increased lifting speed of the diaphragm 14 in the compression stroke. The increased stroke speed due to the increased speed n ₁ causes at the beginning of the stroke a pulse or rapid increase in pressure on the fluid in the metering chamber 16, ie an increased pressure, which causes a dense, reliable closing of the suction-side check valve 22. The increased speed n ₁ is maintained for a predetermined time, which corresponds to a corresponding stroke length to the point 34 of the pressure stroke. Subsequently the pressure stroke is continued at a reduced speed n _{2 of} the drive motor 6. This reduced speed n ₂ thus corresponds to a reduced lifting speed of the diaphragm 14 caused by the transmission 8 and the eccentric 10. This reduced speed n ₂ or reduced lifting speed is maintained until the end of the pressure stroke 32. This reduced speed n ₂ , which is proportional to a reduced lifting speed of the diaphragm 14, is predetermined by appropriate control of the drive motor 6 of the control electronics 26.

The control electronics 26 selects the speeds n ₁ and n ₂ in dependence on a predetermined target speed n _s . This setpoint speed n _s is proportional to a setpoint lifting speed, which in turn is proportional to a desired delivery flow, which is predetermined, for example, by input to the operating and display device 28. In the control electronics 26, the proportional setpoint rotational speeds with which the drive motor 6 must be driven, be stored or calculated by the control electronics 26 in a memory for corresponding desired flow rates. For the particular drive characteristic shown here can also be selected for certain target flow rates to be selected increased speed n ₁ , which is proportional to an increased first stroke speed, and the correspondingly reduced drive speed n ₂ , which is proportional to a second lower lifting speed of the membrane 14th is, as well as the duration of the partial stroke with the increased speed n ₁ stored. Alternatively, these speeds n ₁ and n ₂ can also be calculated on the basis of algorithms stored in the control electronics 26.

The stroke length 34 or duration in which the diaphragm 14 is operated at the first increased lifting speed or the drive motor 6 at the first increased rotational speed n ₁ , the height of the first rotational speed n ₁ and the height of the second rotational speed n ₂ , which correspond to a first increased lifting speed and a second lower lifting speed of the diaphragm 14, are adjusted by the control electronics 26 so that over the entire stroke length 32 on average the desired nominal flow rate to which the desired Speed n _{s of} the motor 6 corresponds, is reached. Thus, that is metered by the increased initial speed n _1, on average over the entire pressure stroke 32 no increased amount is ensured. The amount remains constant with respect to a dosage with a constant stroke speed proportional to the target speed n _s . Also, the stroke length 34, which takes place at the increased stroke speed, ie at the increased rotational speed n ₁ , preferably small or short in comparison with the length of the total stroke 32, so that only a very short time at the beginning of the stroke, an increased flow occurs, However, what is negligible on the total flow over the total stroke length and due to the improved closing quality of the check valves 22 and 24 nevertheless leads to an increased dosing accuracy. The point 34 preferably corresponds to between 2 and 20% of the total pressure stroke 32.

In the example shown here only two speeds n ₁ and n ₂ are used in the course of the pressure stroke, wherein the speed changes abruptly at point 34. However, it would also be possible to change the speed in several steps or slowly decreasing. Even when using several different speeds over the entire pressure stroke these are the height and the time period in which these speeds and thus the proportional Hubgeschwindigkeiten used, preferably adjusted so that a desired target flow rate is achieved on average over the entire stroke ,

LIST OF REFERENCE NUMBERS

2 - drive housing 4 - pump head 6 - drive motor 8th - transmission 10 - eccentric 12 - pleuel 14 - membrane 16 - metering 18 - suction 20 - pressure connection 22, 24 - check valves 26 - Control electronics, control device 28 - Operating and display device 30 - Beginning of a printing stroke 32 - End of the print stroke 34 - Point of the pressure stroke, end of the partial stroke with increased speed X - lifting axis n - Engine speed n ₁ , n ₂ - speeds n _s - Target speed H - stroke

Claims (11)

1. A metering pump assembly with a metering chamber (16), a displacement body (14) adjacent thereto that can be moved through a displacement drive (6), as well as a controller (26) for actuating the displacement drive (6),
   characterized in that,
   at least for certain desired flow rates to be generated by the metering pump, the controller (26) is designed so as to actuate the displacement drive (6) in such a way that a pressure stroke of the displacement body (14) begins with a first, elevated lifting speed (n₁), and is then continued with a second, lower lifting speed (n₂).
2. The metering pump assembly according to claim 1, characterized in that, for flow rates below a predetermined limit, the controller (26) is designed so as to actuate the displacement drive (6) in such a way that a pressure stroke of the displacement body (14) begins with a first, elevated lifting speed (n₁), and is then continued with a second, lower lifting speed (n₂).
3. The metering pump assembly according to one of the preceding claims, characterized in that, in order to change the lifting speed, the displacement drive (6) can be operated at different speeds (n) or different velocities by correspondingly actuating the controller (26).
4. The metering pump assembly according to one of the preceding claims, characterized in that the displacement drive (6) is a multiphase motor.
5. The metering pump assembly according to one of the preceding claims, characterized in that the controller (26) is designed in such a way that the set first, elevated lifting speed (n₁) is faster than required for a desired flow rate.
6. The metering pump assembly according to one of the preceding claims, characterized in that the controller (26) is designed in such a way that the set second, lower lifting speed (n₂) is slower than required for a desired flow rate.
7. The metering pump assembly according to one of the preceding claims, characterized in that the controller (26) is designed in such a way that the first (n₁) and second (n₂) lifting speed along with the duration (34) of the partial stroke having the first lifting speed (n₁) are set by the controller (26) so as to achieve an average flow rate over the entire pressure stroke (32) corresponding to a desired flow rate.
8. The metering pump assembly according to one of the preceding claims, characterized in that 2% or more of the entire stroke is performed at the first, elevated lifting rate (n₁).
9. The metering pump assembly according to one of the preceding claims, characterized in that less than 20% of the entire stroke is performed at the first, elevated lifting rate (n₁).
10. A method for controlling a metering pump assembly, characterized in that the pressure stroke of a displacement body (14) is performed in such a way that the pressure stroke begins with a first, elevated lifting speed (n₁), and is then continued with a second, lower lifting speed (n₂).
11. The method according to claim 10, characterized in that the method is used at desired flow rates below a predetermined limit.

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