EP1754891B1 - Dosing pump - Google Patents

Description

The invention relates to a motor metering pump according to the preamble of claim 1.

Such motor metering pumps are well known and are adapted by additional equipment to the respective requirements. They work according to the volumetric principle, in which the metering process consists of transporting a sealed chamber volume through a displacement element. The dosing volume per stroke corresponds to the volume difference during the movement of the displacement element.

In such a motor metering pump, the generally continuous rotational movement of a drive motor is converted by a gear unit into an oscillating linear movement of the displacement element. The speed and torque of the engine is reduced in a gearbox and adapted to the speed and the power requirement of the displacement element. The output shaft of the transmission drives a device for converting the rotational movement into a lateral displacement, i. at right angles to the axis of rotation, at, e.g. a spring / cam or an eccentric drive. The lateral deflection movement actuates a push rod, which is guided axially displaceably in the direction of the deflection movement in bearings. This transmits the movement and the force to the displacement member, which leads in a arranged in the longitudinal axis of the push rod dosing in cooperation with an outlet and inlet valve in an alternating sequence to a pumping stroke (pressure stroke) and a suction stroke and thus to a promotion of the metering.

Differences between different embodiments are on the one hand in the nature of the engine; Common are asynchronous motors, synchronous motors and stepper motors, which are mounted outside or inside the actual pump housing. Furthermore, individual metering pump types differ in the design of the transmission, which may be a worm gear, a spur gear or a belt drive. The drive of the push rod by the deflection device can be forcibly guided or even on one side form-fitting only when the deflection device is preceded. The push rod is driven in the pressure stroke by the deflection device, for suction, however, it is driven in the latter case by a return spring, which applies it to the returning deflection free of play. The return spring is compressed in the pressure stroke and is dimensioned in its dimensioning to the power requirement during the intake process. Another distinguishing feature various pump types, the force is coupled from the push rod to a membrane as a displacement element either by a rigid connection or by a hydraulic DC link. Since the hydraulic fluid, usually oil, is not compressible, a hydraulic coupling acts like a rigid connection. In addition to the system described here with a dosing head, pump constructions are also known which operate with two or more dosing heads operated on a common drive. On the one hand can be arranged as an embodiment on both sides of an eccentric two opposing push rods in a common longitudinal axis, which are operated in opposite directions and each drive a dosing with its own displacement member. On the other hand, another known principle works with Mehrfachdosierköpfen with an elongated eccentric shaft carrying a plurality of jointly driven eccentric, which in turn each drives an associated unit of transverse to the eccentric axis arranged push rod and in the direction of the push rod axis lying dosing with displacement member.

All moving parts are stored in a simple case in a common pump housing by ball or plain bearings, in other embodiments, individual functional groups in other housing or mounting parts, which are also partially filled with oil, combined into functional groups and assembled as modules. An example of this would be a mounted outside the pump housing unit of the engine and reduction gearbox with mounting flange and already stocked output shaft.

In the simple case, the drive motor for a continuous metering is switched on continuously or for carrying out individual metering strokes for a certain time. Other designs control the drive motor via a frequency converter according to a predetermined time profile, whereby the engine speed and thus the metering performance better reproducible and independent of electrical parameters such. the frequency or the current level of mains voltage.

The engine speed is dictated by the electrical frequency of the motor drive and, together with the gear ratio and the transmission characteristic which is sinusoidal in an eccentric gear, determines the duration of each stroke. With continuous control, the duration per stroke results from the effective engine speed in the load condition and the gear reduction. In the so-called on / off operation, in which individual strokes or Hubpakete are processed, between which the engine is defined, for example, in Ansaugotpunkt stopped, start-up and braking times are added and extend the time per stroke accordingly. The stroke frequency is in continuous operation by the duration per stroke or in on / off operation given by the repetition frequency of the engine starts, which of course can not be done more often than it dictates the time required to execute a stroke.

The stroke length can be adjusted by limiting the lateral deflection. This can be done by adjusting an eccentricity, e.g. by using so-called wobble cylinders, which work on the basis of two mutually rotatable slate planes. On the other hand, as a further possibility, an adjustable stop is common, which can be used in non-positively guided deflection systems. This stop in the form of a mechanically adjustable spindle limited with appropriate adjustment the backward movement of the push rod when sucking on an adjustable position before reaching the rear dead center of the deflection device. By the stop the starting point of the lifting movement is specified; the end position results from a fully executed deflection movement. One possible embodiment is to screw a Hubverstellbolzen accessible from the device operating side knob and scale in a thread of the pump housing, which represents the stop for the push rod during suction. In hydraulic systems the stroke adjustment is e.g. realized by a sliding sleeve whose position is adjustable by an accessible from the device operating side knob with scale, which is screwed into a thread of the pump housing. The sleeve covers a bypass bore in the push rod which releases a shunt of the oil circuit after traversing a certain path and thus releases the power coupling from the push rod to the diaphragm.

The sequence of movement of the displacement member results from the interaction of the gear and other mechanical components. During forward movement, the drive operates against the force acting on the push rod by the displacer and the (occasionally present) return spring. During the backward movement, the push rod is also retracted by the drive when positively guided deflection system, in one-sided operation, the return spring pushes back the push rod and brings the force for the suction of the metering medium. The movement of the push rod follows the characteristic of the deflection device; in the case of an eccentric, this is, for example, a sinusoidal profile, which lies at full stroke length between the two dead centers of the eccentric stroke. In reduced stroke length operation, eccentricity movement continues to be purely sinusoidal with reduced amplitude, in rigidly coupled variable butt systems and by-pass hydraulic systems, the original motion and amplitude of the deflector remains intact, but is no longer completed; Rather, the push rod movement is cut off depending on the set stroke length and coupling system in the beginning or in the end (phase control). The forward movement for the execution of the pressure stroke takes place depending on the control of the engine in a time range well below one second (eg in the range 200ms), the suction stroke also takes place after a predetermined by the deflection device course within a similar time as the pressure stroke. This results in both Hubphasen relatively high instantaneous speeds of the metering medium; in an eccentric drive, the maximum is approximately halfway along the movement.

In embodiments in which several units consisting of push rod and dosing, are driven by a common, working with multiple eccentric eccentric, these eccentric can be arranged out of phase on the shaft to the respective peak power requirement of the individual dosing heads in time to a full rotation of the eccentric shaft to distribute and so optimally exploit the available engine power.

Certain designs, so-called diaphragm metering pumps, have a partially flexible membrane as the displacement element. This is not rigid, but deforms elastically in the Walk range by a certain amount when the pressure of the metering medium acts on them. The amount of this deformation, which is built up in a first, unused for the dosage portion of the lifting movement, is lost to the effectively executed lifting movement and causes the Dosiermenge decreases with increasing working pressure. This falling characteristic is much more pronounced in normal applications than the required dosing accuracy would permit. Motor metering pumps therefore usually can not be operated in a general setting over a wide range of working pressure with the desired accuracy; rather, the occurring error is detected by a calibration measurement and included in the further calculations. However, this calibration measurement must be carried out under actual working conditions in the specific application and is, especially in connection with aggressive chemicals, a work step which entails considerable expense.

Although currently common motor metering pumps are powerful and have for many processes favorable metering properties, but still have disadvantages in terms of the hydraulic properties of the dosing over the desirable ideal condition. As an example, the relatively strong dependence of the metered amount of the working pressure of the metering and disadvantages such as flow noise or pressure losses are called by high instantaneous flow rates of the metering.

Such a metering pump is in EP 0 798 558 A2 described. To achieve the dosing accuracies, the dead points, ie the points of inflection, of the movement of the displacement element are determined using a position detector and a second detector. With the help of the time difference that the Verdrängurigsorgan needed to get from one dead center to the other dead center, the average dosing speed can be determined. A disadvantage is that the average dosing speed can help to increase the average dosing accuracy, however, a statement about the dosage within a pressure or suction stroke is not possible.

The object of the present invention is in particular to eliminate the known disadvantages with respect to the hydraulic properties of the dosing process and thereby to achieve a variable, wider range of application of the motor metering pumps, without negatively affecting their production costs. Furthermore, the movement process of the push rod and the associated displacement member should be adapted to the target information that both the dosing itself is adjustable, as well as by manufacturing technology or adverse properties of components (eg the elastic membrane, if any) resulting errors by the electronic control are considered and recoverable. These measures are intended to ensure the exact metering of a given volume of a metering medium in a metering process by avoiding or detecting faulty operating conditions, and that manufacturing and / or inaccuracies occurring in use can be compensated for by the electronics used.

The solution to this problem is that the signal (x _I ) for the position of the push rod read out of the position sensor influences the speed of the drive motor and, as a consequence, the linear movement of the push rod and thus of the displacement member via a closed-loop control system it follows a predetermined setpoint profile.

With the help of the position sensor, the movement of the push rod is detected and evaluated by the electronic control. For this purpose, the controller examines the sequence of motions on characteristic features in each case on the basis of the basic conditions and responds by influencing the motor control in such a way that the dosage follows the specification as well as possible and which is otherwise e.g. be eliminated by the properties of the membrane resulting inaccuracies.

If the position sensor operates according to a non-contact principle, a wear-free operation of the sensor is ensured, which is advantageous and ultimately necessary in view of the high number of strokes during the life of a metering pump.

If the position element connected to the push rod is arranged outside the dosing head, greater flexibility is achieved with respect to the mounting space for the position sensor.

If the reference element influences the beam path of a light source and if the position sensor cooperating with it, which is fixedly arranged in the pump housing or on another stationary part, works according to a photosensitive receiver principle, wear-free operation is ensured on the one hand, as is the case in view of the high number of strokes during The life of a metering pump is essential, and the moving parts are abgetasweiterer more contact The advantage of this arrangement is that such a design of a position sensor is in principle insensitive to stray magnetic fields.

If the reference element is a shadow body or a shadowing contour and the position sensor interacting with it, which is fixedly arranged in the pump housing or at another stationary part, consists of a series of photosensitive charge-coupled receiver cells (so-called CCD cells) such an optical-based arrangement has important properties that the position sensor must meet. On the one hand, the arrangement works wear-free due to the optical principle of operation and is insensitive to stray magnetic fields, on the other hand, such a trained sensor has virtually no linearity error.

If the position sensor continues to be arranged on its own sensor carrier, which is fixedly connected to the pump housing or other stationary part, such an arrangement can be pre-assembled and tested as a unit, thus facilitating the assembly. If the sensor carrier is designed as part of non-conductive plastic, this additionally simplifies the electrical insulation of the sensor components against metallic parts of the housing or of the transmission.

If the light source, the shadow body or the shadowing contour and the receiver represent a light barrier-like arrangement and the measured values are fed continuously or intermittently to the electronic controller, such an arrangement provides the electronic data to the electronic controller with a speed that is appropriate to the requirements.

If the optical receiver of the position sensor consists of a number of linearly arranged receivers (pixels), preferably 128 pixels, such an arrangement can easily determine the position by counting the shadow boundary between illuminated and unlit cells and already achieves a resolution with this simple method the distance of the cells of the receiver module used.

If the light source is a light-emitting diode (LED), which is arranged opposite the optical receiver of the position sensor, that its light beam on the direct path to the receiver is not hindered by the push rod, this has the advantage that the inexpensive LED has an approximately punctiform spot which is indispensable for a high optical resolution, and practically has an almost infinite lifetime. The arrangement opposite the position sensor past the push rod results in a large distance between light source and receiver, which makes the projection angle of the relevant light beam relatively independent of the mounting position of the elements.

If the output value of the position sensor is formed by interpolation of the brightness values of a plurality of pixels lying in the shadow transition region, a finer resolution is achieved for the output signal of the position sensor than predetermined by the mechanical grid of the cells of the CCD receiver.

If filter measures are used during the processing of the signals of the position sensor, then the interference immunity of the position sensor is improved.

The sensitivity of the position sensor to assembly deviations and mechanical displacements during operation, e.g. due to heating or bearing wear is reduced if zero position errors of the position sensor are eliminated by means of a reference memory or scaling error of the position sensor by approaching one or more reference positions.

If exposure fluctuations of the position sensor are compensated for by control of the light source based on the obtained brightness values of the pixels, this reduces the sensitivity of the position sensor to variations in component parameters.

Compensating for brightness variations between individual pixels of the optical receiver by incorporating a reference memory for the sensitivity of each pixel reduces the effects of contamination of the optical receiver.

If the detection to which value the Hubverstellorgan is set, by measuring during dosing directly on the position sensor, the otherwise additional necessary sensor for the mechanical position of the associated adjusting elements can be omitted.

If the electronic control recognizes a blockage of the displacement element or an incompletely executed stroke by evaluating the position sensor signal, this increases the reliability of the metering. In metering pumps of conventional design without position sensor sensors are often used to deliver a feedback pulse to monitor the dosing, for example when passing a reference mark per stroke to the electronic control, from which measured the Hubperiodendauer and a trouble-free flow of dosing can be derived. Compared with such sensors, the described use of a position sensor has the advantage that the desired information is present at each time of the metering stroke, and not only when passing the reference mark, so that such additional sensors can be omitted without detriment.

The drive motor operates on a slip-prone principle by e.g. an asynchronous motor is used, and determines the electronic control of the set by the control target speed of the drive motor and the known transmission characteristics a Sollhubfrequenz or Sollhubperiode for the displacement member and detects them additionally by evaluating the position sensor signal, the actual stroke frequency or the actual stroke period of the displacement element in which it calculates the slip of the drive motor by comparing the actual stroke frequency with the Sollhubfrequenz or the actual stroke period with the Sollhubperiode the displacement member and its target speed changed so that the displacement member ultimately moves with the desired stroke frequency, this improves the accuracy of the dosage Eliminate the error in the stroke frequency that would be caused by the slip of the drive motor. With metering pumps of conventional design without position sensor, sensors are often used which are used to monitor the metering movement, e.g. when passing a reference mark per stroke deliver a feedback pulse to the electronic control, from which also the Hubperiodendauer can be measured and corrected; Such additional sensors may be omitted when using a position sensor.

The drive motor operates according to a slip-prone principle, for example by using an asynchronous motor, and determines the electronic control of the predetermined by the control target speed of the drive motor and the known transmission characteristics Sollhubfrequenz or Sollhubperiode for the displacement member and additionally detects by evaluating the position sensor signal the actual stroke frequency or the actual stroke period of the displacement member, wherein it calculates the slip of the drive motor by comparing the actual stroke frequency with the Sollhubfrequenz or the actual stroke period with the Sollhubperiode the displacement member and further determines the electronic control of the thus determined slip of the drive motor and the known transmission characteristic acting on the displacer force and thus makes a conclusion on the working pressure of the metering before, can practice with this information Monitoring and compensation functions are implemented, which improve the reliability and accuracy of the dosage. Determines the electronic control of the predetermined by the control target speed of the drive motor and the known transmission characteristics for each moment of the dosing a target speed for the displacement member and detects them in addition by evaluating the position sensor signal, the actual speed of the displacement member, wherein they by comparison the actual instantaneous speed with the target speed of the displacement member calculates the current slip of the drive motor and from it, in turn in connection with the known transmission characteristics on the momentary force curve on the displacement member closes, so is the desired information about the force at any time of the dosing and the desired Monitoring and compensation functions can be time differentiated, which further improves the reliability and accuracy of the dosage.

If the electronic control from the observed force curve on the displacement member before a conclusion on the working pressure of the metering before so known adverse effects of the working pressure can be counteracted to the dosing.

If the electronic control recognizes an operation outside the specified pressure range from the determined working pressure of the metering medium and adjusts the metering when a maximum permissible pressure specified by the specification of the metering pump or by a user input is exceeded or if a predetermined minimum pressure is undershot, erroneous results occur Operating conditions such as overpressure situations or pressure loss detected by a defective piping and it can safety measures such as Adjusting the dosage be taken, which improves the reliability of the dosage. The otherwise necessary additional resources such as e.g. Overpressure limiters can be saved as long as the dosing pump is the only pressure-increasing unit in the process. The ability to control the working pressure to values within the specified pressure range of the metering pump extends the possibilities of pressure monitoring to situations in which the monitoring system of conventional metering pumps, which responds only when the metering pump is blocked, can not be used.

If the displacement member is a partially elastic membrane and determines the electronic control of the measured working pressure of the metering and the known dependence of the metering of the working pressure, which is caused by the elastic deformation of the membrane, an expected metering error, and it affects the speed of the drive motor and so that the stroke frequency so that this expected dosing error is counteracted, this improves the accuracy of the dosage.

The signal read out from the position sensor (x _I ) for the position of the push rod via a control loop within its control accuracy influences the speed of the drive motor and as a result, the linear movement of the push rod and thus of the displacement member so that they This set influencing the movement of the displacement member to achieve or improve advantageous hydraulic properties of the dosage, eg in the slow dosing and / or the dosing accuracy in Teilhubbereich be exploited.

If the metering pump has a control device in addition to the position sensor and influences this alternatively the position (referred to below as x _I ), the speed (hereinafter referred to as v _I ) or the acceleration of the displacer via a control device influenced by changing the speed of the drive motor, can suitably For the requirements of a specific dosing task, the advantages of the respectively more suitable control method are specifically used. Control of the speed allows a direct control of the actual flow rate of the dosing medium, which is required, for example, for the slower suction to avoid cavitation. On the other hand, regulation of the position makes it possible to control situations near standstill, in which the speed information which is formed by differentiating the path signal becomes very small and can no longer be usefully processed by the control device. The control of the position avoids this difficulty and is advantageous to apply for example in the electronic stroke length limitation or slow dosing. The regulation of the acceleration is advantageous for easy controllability of the control, since the acceleration of the moving masses for fast processes is a direct reflection of engine power.

Has the metering pump in addition to the position sensor a control unit and converts them v _l of the displacement body in the intake phase and / or in the pressure phase selectively reduced, so thus is pressure losses caused by flow resistance, or to counteract the occurrence of cavitation. When dosing highly viscous media, eg lecithin, high pressure losses occur at bottlenecks, such as in the valves, when the flow velocity is too high. These pressure losses must be applied in the form of an additional force by the drive and can be kept low when using the control of v _{I of} the displacer. In addition, flow noise is effectively reduced at reduced flow rate. During the metering of slightly outgassing media, for example of sodium hypochlorite, cavitation occurs, in particular during the suction at excessively high flow velocity due to falling below the vapor pressure of the metering medium, which results in increased mechanical wear. In a control of v _{l of} the displacement member in the intake and / or in the pressure phase, this is advantageously avoided.

Does the metering pump in addition to the position sensor, a control device and the desired stroke length communicated by an operator specification of the control device and electronically limited by the control device, the movement of the displacement member to the stroke length to be executed by the controller stops the drive motor after executing the desired stroke length, in the reversing switches over and then performs a suction stroke and then stops the engine or performs the subsequent pressure stroke, in principle, the associated mechanical adjustment can be omitted.

If the metering pump has a regulating device in addition to the position sensor, the regulating device distributes the forward movement of the displacing member during the printing phase by activating the drive motor to the time predetermined by the repetition frequency of the metering strokes so that the metering medium is applied as evenly as possible, even very slowly Dosierhüben of eg a few minutes, concentration fluctuations of the dosing medium can be largely avoided.

The dosing accuracy is improved when the displacer is a partially elastic membrane and the electronic control recognizes the opening of the outlet valve from the instantaneous force flow across the membrane and uses this observation to measure the dead zone resulting from the elastic deformation of the membrane and the one actually carried out Stroke influenced by targeted termination of the stroke depending on the determined membrane deformation so that the dependence of the dosing amount is significantly reduced by the back pressure. This improvement is achieved by eliminating the error caused by the elastic deformation of the membrane under the effect of the working pressure, that the amount of this deformation does not contribute to the dosage. Due to the reduced dependence of the dosage amount on the working pressure, recalibrations that would otherwise occur if there is a significant change in operating parameters such as e.g. The working pressure required, omitted. The derivation of the membrane deformation from an observation of the force curve is particularly advantageous in evaluating the engine slip, because this represents a good reflection of the actual power requirement and thus requires no additional metrological effort.

The metering accuracy is improved if the metering pump has a control device in addition to the position sensor, the displacement member is a partially elastic membrane and the actually executed stroke is influenced depending on the determined membrane deformation by the control device, the drive motor after executing the desired stroke length from the opening of the Stops discharge valve, switches to reversing mode and then performs a suction stroke and then stops the engine or performs the subsequent pressure stroke, such that the error contribution (related to the stroke or the metered volume) caused by the membrane deformation, which arises because the amount of this deformation does not contribute to the metering, is eliminated. Due to the reduced dependence of the dosing of the working pressure recalibrations, which are otherwise required for significant change in operating parameters such as the working pressure, omitted, and the linearity of the ratio between the set stroke length and the actually metered amount of the dosing medium improves. The derivation of the membrane deformation from an observation of the force curve is particularly advantageous in evaluating the engine slip, because this represents a good reflection of the actual power requirement and thus requires no additional metrological effort.

If the displacer is a partially elastic membrane and the metering pump has a control device in addition to the position sensor, and the actually executed stroke frequency is influenced as a function of the determined membrane deformation by the control device applying a correction value for the error contribution caused by the membrane deformation (related to the stroke or stroke) The measured volume is determined and the setpoint speed of the drive motor is changed by means of this correction value so that the error contribution caused by the membrane deformation is eliminated, the dependence of the dosing amount on the working pressure is reduced.

Fig. 1:

Längsschnitt durch eine Motordosierpumpe mit Positionssensor

Fig. 2:

Explosionsdarstellung des Positionssensors (Vergrößerung des Ausschnitts X aus Fig. 1

Fig. 3:

Komponenten des Positionsregelkreises

Fig. 4:

Komponenten des Geschwindigkeitsregelkreises

Fig. 5:

Draufsicht auf den Positionssensor in Achsrichtung

Fig. 6:

Seitenansicht des Positionssensors quer zur Achse

Fig. 7:

Darstellung des Schattenbereichs des Positionssensors

Fig. 8:

Darstellung der Helligkeitswerte der Pixels, wie sie dem tatsächlichen Schattenverlauf entsprechen

Fig. 9:

Darstellung des Abbildungsmaßstabs des Positionssensors aufgrund geometrischer Anordnung

Fig. 10:

Interpolation der Positionsauflösung

Fig. 11:

Darstellung der Berechnungsgrundlage für die Interpolation der Positionsauflösung

Fig. 12:

Darstellung der Dosierleistung in Abhängigkeit von der mechanischen Hublänge und vom Arbeitsdruck

Below is described as an embodiment of the invention, a motor driven Diaphragm metering with eccentric with their various applications described in more detail. It shows:

Fig. 1:

Longitudinal section through a motor metering pump with position sensor

Fig. 2:

Exploded view of the position sensor (enlargement of section X off Fig. 1

3:

Components of the position control loop

4:

Components of the speed control loop

Fig. 5:

Top view of the position sensor in the axial direction

Fig. 6:

Side view of the position sensor across the axis

Fig. 7:

Representation of the shadow area of the position sensor

Fig. 8:

Display of the brightness values of the pixels as they correspond to the actual shadow

Fig. 9:

Representation of the image scale of the position sensor due to geometric arrangement

Fig. 10:

Interpolation of position resolution

Fig. 11:

Presentation of the calculation basis for the interpolation of the position resolution

Fig. 12:

Representation of the dosing rate as a function of the mechanical stroke length and the working pressure

Fig. 1 shows the construction of a motor metering pump (partially cut). The motor metering pump consists, as is generally known, essentially of three groups of components, namely the drive motor 2 with gear unit, the eccentric drive in the eccentric housing 1 and the electronics housing 28 with the electronic control contained therein and the electronic assemblies and components used therein. The electronics housing 28 has on the bottom of a bottom plate 4 with mounting holes, the eccentric housing 1, which is mounted on the electronics housing 28 and fixedly connected to this carries the drive motor 2 with gear unit, which is connected for example via screws with the eccentric housing.

In the so-called housing, which is formed by the eccentric housing 1 and the electronics housing 28, in its upper part, the eccentric housing 1, the components of the eccentric drive are attached. The components of the eccentric drive are mounted in an eccentric carrier 22, which ensures the positional alignment of the individual parts to one another and is fastened in the eccentric housing 1. A three-phase asynchronous motor 2 is flanged together with a reduction gear 11, which is designed as an angle gear, as a unit from the outside of the eccentric housing 1 and connected with screws. The output shaft of the geared motor forms a right angle to the shaft axis of the motor and either directly forms the drive shaft of the eccentric drive or, as in the described embodiment, is connected to the same axis via a clutch. The drive shaft of the eccentric drive, the eccentric shaft 17 is rotatably mounted in the eccentric carrier 22 and carries as an integral part with her an eccentric. The eccentric shaft penetrates with the eccentric a suitably cut push bar 20. The eccentric shaft 17 is rotated by the motor / gear unit on the shaft coupling with driven motor 2 in rotation and further drives the push bar 20 on an inner surface of its section, namely the contact surface, with the outer surface of the eccentric. The push bar 20 drives a fixedly connected to him, in the example injected, push rod 19 at. The unit of push bar 20 and push rod 19 is mounted longitudinally displaceable in two slide bushes. The axis of the eccentric shaft 17 and the longitudinal axis 18 of the push bar 20 and the push rod 19 are each in the horizontal plane and form a right angle to each other. One of the two sliding bushes 26 for the push rod 19 is seated in a bearing plate 24 which is attached to the eccentric carrier 22 on the printhead side; A stub bushing 27, which receives the side facing away from the Dosierkopfseite pins of the push bar 20, sitting in Hubverstellbolzen 8. Achsgleich to the longitudinal axis 18 of the push rod 19 is a manually operated adjusting 7 for the adjustment of the Hubverstellbolzens 8 screwed into a thread of the Exzenterträgers 22 that limits the axial movement of the push bar 20 during suction and thus the stroke of the metering pump.

The housing further contains in its lower part in a closed space, the electronics housing 28, the electronic control. The housing is splash-proof and protects the eccentric drive and the electronic control against moisture or corrosion, as dosing pumps are often used in conjunction with chemically aggressive media. The electronic control consists of a horizontal control electronics 34 with the power switching stages for the motor driver 29, which are designed as an integrated frequency converter, and arranged in a housing cover 5 electronics 6, which contains the necessary for the operation of the metering input and display elements. The controls are protected by a cover 9. Below the cover 9 connections are provided for the control lines 10 and for the power supply.

On the side opposite the control lines 10 or the power supply connection, a dosing head 12 is arranged coaxially with the longitudinal axis 18 of the push rod, in which a dosing head 12 is provided as the displacement element. made of plastic membrane 13 works, which is firmly clamped at its periphery. The dosing head 12 also carries an inlet valve 14 and an outlet valve 15 in order to press the dosing medium sucked in via the inlet valve 14 between the diaphragm 13 and the dosing head 12 into the dosing line via the outlet valve 15. The motor metering pump operates on the volumetric principle, i. a predetermined volume should be sucked in each stroke on the one hand and on the other hand discharged via the exhaust valve 15. The diaphragm 13 is set in an oscillating motion by means of the eccentric drive which reciprocates the push rod 19 in the longitudinal axis. To the side of Hubverstellbolzens 8 towards the unit of push bar 20 and push rod 19 cooperates with the adjusting member 7 as manually adjustable Hubverstellvorrichtung. At the opposite end of the metering head 12 facing part of the push rod 19 is fixedly connected to the core 30 of the membrane 13 and puts them in an oscillating motion.

Between the push bar 20 and a collar 25 of the bearing plate 24, a compression spring 23, for example, a coil spring is arranged, which engages the push bar 20 at any time form-fitting manner on the eccentric. In the preceding phase of the eccentric movement, ie the movement of the push rod towards the dosing head, the push bar is moved with the push rod towards the compression spring, at the same time the membrane 13 is pressed into the dosing chamber 16, with the result that an overpressure arises in the dosing space, the outlet valve 15, eg a spring-loaded ball valve, opens and the metering medium is forced into the metering line. In the returning phase of the eccentric movement, ie the movement of the push rod away from the dosing, the push bar 20 is moved by the compressed compression spring 23, which may be formed, for example, as a spiral spring following the eccentric movement in the opposite direction to Hubverstellbolzen 8, which As a result, the connecting rod 19 connected to the diaphragm 13 entrains the membrane in its movement, whereby a negative pressure is created in the dosing chamber 16, which opens the inlet valve 14, so that once again dosing medium can be sucked into the dosing chamber. Due to the alternating, oscillating movement of the diaphragm 13 by means of the eccentric drive, the delivery flow of the metering medium is formed in the metering line. Due to the eccentric drive creates a sinusoidal movement of the unit from push bar 20, push rod 19 and diaphragm 13 in the course of a Dosierhubs. If a reduced stroke length is set by means of the Hubverstellbolzens 8, the movement is prematurely decelerated in the intake before reaching the dead center by the adjustable stop of the Hubverstellbolzens 8, whereby the sine wave of the movement is cut off and a phase angle of the stroke occurs.

The position of the unit consisting of push bar 20, push rod 19 and diaphragm 13 is scanned by the position sensor 36, the measurement signal is in a defined relationship to this position; this relationship may be considered as possible execution e.g. be strictly proportional. The measurement signal of the position sensor 36 always refers to the position of the part of the movable unit, where it acts. This point of attack is formed by the reference element, which in this context is to be understood in an abstract sense. Depending on the requirements of the position sensor, it may be designed as a concrete component to be mounted in addition, but also only from a characteristic embodiment, e.g. an edge or surface on any of the components required anyway, e.g. on the push bar 20, exist.

In the exemplary embodiment, a sensor carrier 31 is fastened in the eccentric carrier 22 (see also the schematic representation in FIG Fig. 6 ), the one hand in the longitudinal direction of light-sensitive CCD cells 32 (CCD = charged coupled device; charge-coupled optical receiver module) and opposite a light source 33, for example, a light-emitting diode (LED), carries.

The sensor carrier 31 connected to the eccentric carrier and the components mounted thereon form a light barrier whose beam path is partially interrupted by the push bar. The reference element is formed by a shadow edge 35 of the push bar 20 in the region of the light barrier arrangement. During the oscillating movement of the push rod 19, therefore, the shadow edge 35 passes over the light-sensitive cells 32 in a non-contact manner Fig. 5 is shown schematically, which shows a plan view in the axial direction, the light source 33 must be arranged so that the light beam is not covered on its way to the photosensitive cells 32 by the push rod 19; ie, that the light source 33 and the line of the photosensitive CCD cells 32 are arranged above or below the push rod 19. How now in particular in Fig. 7 is shown schematically, by the light source 33 by means of the shadow edge 35 cast a shadow on the photosensitive cells 32, dividing the cells in principle into light (h) and non-illuminated (d) cells. Since the series of light-sensitive cells arranged parallel to the longitudinal axis 18, for example 128 pixels which cover a total distance of approximately 8 mm, is only partially exposed or shaded in the border region, the in Fig. 8 illustrated transitional situation of the shadow profile SV. The amount of in Fig. 8 In this case, the illustrated rectangular areas represents the illuminance of the respective pixels. By a special method, which will be described later in detail and based on the Fig. 10 is explained, this limit situation is used to accurately determine the respective position of the shadow edge and thus the position of the push rod or the membrane. This measuring device, consisting of thrust-arm-side shadow edge and sensor carrier side light-sensitive CCD cells with opposite light source, serves to measure the actual position or the speed of the oscillating push rod and to use this information for the realization of the described functions.

The push rod, which causes the diaphragm to oscillate, travels a distance each stroke equaling the mechanical stroke length. To take into account mounting tolerances, the longitudinal extent of the photosensitive CCD cells must be slightly larger. In principle, this also applies to any other conceivable position sensor used.

x_S:

Sollwert der Position des Verdrängungsorgans

x_I:

Istwert der Position des Verdrängungsorgans

x_SI:

Regelabweichung der Position des Verdrängungsorgans

v_S:

Sollwert der Geschwindigkeit des Verdrängungsorgans

v_I:

Istwert der Geschwindigkeit des Verdrängungsorgans

v_SI:

Regelabweichung der Geschwindigkeit des Verdrängungsorgans

SG:

Stellgröße

KSG:

Korrigierte Stellgröße

MA(U,f):

Motoransteuerung (Spannung bzw. Frequenz)

If, by means of the position sensor signal, a regulation of the diaphragm or generally of the displacement movement is to be realized, as is particularly apparent in US Pat Fig. 3 respectively. Fig. 4 schematically explained, the following mechanical and electronic components required. The short names contained in the two diagrams mean:

x _S:

Setpoint of the position of the displacer

x _I :

Actual value of the position of the displacement element

x _SI :

Control deviation of the position of the displacement element

v _S :

Setpoint of the speed of the displacement element

v _I :

Actual value of the velocity of the displacer

v _SI :

Control deviation of the speed of the displacement element

SG:

manipulated variable

KSG:

Corrected manipulated variable

MA (U, f):

Motor control (voltage or frequency)

The movable part of the drive, whose movement is to be controlled, consists of the push bar 20 with the push rod 19, with the diaphragm 30 is firmly connected. The return spring 23 retrieves the push bar after a successful stroke and thus causes the suction. The outer ring of the membrane 13 is fixedly mounted in the dosing head 12, the metal membrane core 30 injected into the membrane moves the central surface of the membrane as a displacement element in the dosing head. The inlet valve 14 closes on the suction side, the outlet valve 15 on the pressure side of the dosing and offers each a connection option for the outer casing. With the push rod 19 or with a related component, here with the push bar 20, is e.g. connected at the end facing away from the dosing head a reference element whose position is scanned by a non-contact in the present case position sensor 36. In the exemplary embodiment, the reference element is a shadow edge 35 of the push bar 20 and the position sensor is a light barrier-like arrangement consisting of the previously described light source 33 in cooperation with the row of photosensitive cells 32, which detects the position of the shadow edge 35 optically and thus without contact by the shadowing. Since the push rod 19 ensures the actual connection and adhesion to the membrane 13 and push bar and push rod are firmly connected in the present example, the following description always refers to the movement of the push rod 19, although in fact the shadow edge 35 of the push bar 20 is measured ,

The position sensor 36 outputs an actual signal x _I which is proportional to the position of the reference element 35. In the case of the speed controller, this is derived in the exemplary embodiment by a differentiator 37 in time (dx _I / dt) and thus additionally a speed-proportional actual signal v _I formed. For the control, of course, other methods are suitable, which provide a proportional to the membrane velocity signal. Depending on the type of regulation and requirements of the dosage, a time profile for the desired value 38 of the position x _S or the speed v _{S is} specified. By means of a desired-actual comparison 39, the control deviation is determined as position deviation x _SI = (x _S -x _I ) or speed deviation v _SI = (v _S -v _I ), and the result is applied to a PID controller 40 (FIG. PID controller = controller with proportional, integral and differential components). Its output, the manipulated variable SG, corresponds to a request value for the drive power. To improve the controller stability, the manipulated variable SG is further processed by a position correction 41. The Lägekorrektur 41 takes into account the fact that the speed of the motor depending on the angular position of the eccentric (derived from the push rod position) is converted according to the sinusoidal characteristics of the eccentric in a speed on the push rod. The position correction 41 calculates the output signal of the PID controller 40 via the inverse characteristic of the eccentric gear in a corrected manipulated variable KSG, which represents based on the input of the reduction gear 11, the necessary motor control, which is required to at the output of Exzentergetriebes to obtain a movement of the push rod 19 corresponding to the desired manipulated variable SG. An amplifier 42, which is designed as a frequency converter, includes the power switching stages and controls the motor according to the requested speed with the associated voltage and frequency. The amount of the position-dependent position correction, the conversion of the corrected manipulated variable KSG in a specific speed specification for the frequency converter and possibly the derivative constant for the formation of the speed signal v _l are determined by the three proportionality factors k1, k2, k3. The factor for the position-dependent position correction k1 is to be selected according to the characteristic of the eccentric gear, the two factors k2 for the power amplifier and k3 for the derivative of the speed signal can be selected based on practical considerations, such as working with as good manageable value ranges of the associated variables ,

In the Fig. 3 is the control loop for a position controller, in Fig. 4 the control circuit is shown schematically when used as a speed controller. The described control circuit sets the predetermined time profile for the desired value of the position x _S or the speed v _S , of course within the scope of its possible control accuracy.

The specification of the specific profile for the position, the speed or the acceleration and the switching between these modes is done on the basis of the requirements arising from the functions described below, for example, taking into account the functional limits of the controller such as control speed, achievable accuracy, etc.

With such a control, it is possible with a motor metering pump to specify a desired speed of the diaphragm 13, in general of the displacement member, and thus to control the effective flow rate of the metering medium.

Likewise, the membrane position can be controlled directly. This function makes it possible to selectively approach specific positions in selected dosing phases and, if necessary, to maintain them at standstill.

By regulating the movement sequence by means of a position sensor, in contrast to an unregulated operation, it is possible to react to changes in operating variables which occur over time or are caused by environmental conditions or specimen scatters, ie statistical deviations within the production series, and whose harmful influence is minimized , Examples which may be mentioned are the membrane rigidity or the viscosity of the metering medium. Both require a proportion of motive force that must be applied in addition to the force created by the application of working pressure to the membrane surface. These disturbances can be compensated by detecting their effect and readjusting the motor control. In an unregulated metering pump with a predetermined engine speed, even if this is kept stable even by means of control, such disturbances are ignored. In such an unregulated metering pump is beyond the exact prediction of the instantaneous speed of the displacement member without knowledge of the push rod position, ie the rotation angle of the eccentric, not possible due to the sinusoidal characteristics of the eccentric.

In addition, it is possible by the regulation of the movement sequence by means of a position sensor, in contrast to the spontaneously occurring dosing to react to unregulated operation on internal and external factors, which are described below, and to ensure operating conditions, with their help selected hydraulic properties of the dosage can be specifically caused or avoided. As an example, reference is made to the function described below of the protection against cavitation during suction.

In the following, for example, individual applications of a motor metering pump of the previously described type will be explained, which has a position sensor and draws conclusions about the operating state of the dosing by means of an evaluation of the position signal or influenced by a control and modification of the motor control the movement of the membrane.

Recognition of the position of the stroke length adjustment controller

Dosing pumps according to the prior art often provide a mode in which the dosing strokes carried out over the set volume of the displacement chamber (stroke length) are converted directly into a metered total volume and this example. is displayed as volume flow in the unit I / h. For such functions, knowledge of the stroke length set by the operator is required since this depends on the volume metered per stroke. The position of the Hubverstelleinrichtung must be converted for this purpose in metering pumps of previous design by a separate sensor into an electrical signal and read into the controller. An example of a practical realization would be a linear potentiometer on Hubverstellorgan 7, which scans its setting via a plunger.

A metering pump that can detect the actually worn membrane path during the stroke using integrated position sensor 36 does not require an additional sensor. By subtraction of the two position values in the end positions, each after reaching the mechanical Can be measured stop, as soon as the movement has come to a halt, the stroke length can be calculated directly and is available for further processing.

Detection of a blockage or an incompletely executed hub

In prior art metering pumps without a position sensor, sensors are often used which emit a feedback pulse to the electronic controller for monitoring the metering movement per stroke. A known embodiment is e.g. a small permanent magnet, which is attached to the output shaft of the transmission, so on the eccentric shaft 17 outside the axis and rotates with this, in conjunction with a fixed Hall sensor that generates a signal when passing the magnet in a certain angular position of the eccentric shaft. Based on this signal, the electronic control measures the stroke period, which is identical to the cycle time of the eccentric shaft, and deduces from this a trouble-free sequence of the dosing process. In the event of a blockage in the course of the metering stroke due to an overpressure situation, e.g. in the event of an accidentally closed shut-off device in the dosing line, the signal of the Hall sensor remains off and, after a monitoring period has elapsed, leads to a fault message and further reactions, e.g. Shutting down the dosing pump. In such a conventional system, the desired information is available only after the expiry of the monitoring time.

When using a position sensor 36, the speed of the push rod 19 can be set in relation to the drive of the motor 2 at any time of Dosierhubs, and a blockage can be detected virtually instantaneously.

slip compensation

Is used as drive motor 2 e.g. an asynchronous motor is used, the effective mechanical speed at the motor output shaft under load is always slightly smaller than specified by the frequency of the electrical control. The difference between the two speeds, the so-called slip, is dependent on parameters of the motor and within a reasonable load range approximately proportional to the load torque. The slip can be measured by various methods described below. From it, a correction value can be calculated, which can be included in the use of a frequency converter in the predetermined engine speed in the form of a frequency increase and thus compensated.

The slip can be determined, for example, by comparing the measured stroke period with the predetermined by the electrical control. This method is also used in metering pumps according to the prior art by measuring the time interval between two Hall sensor pulses applied. In the case of a metering pump with position sensor, a characteristic point along the stroke, for example at halfway, is defined for period duration measurement, and the time at which this point is traversed is recorded for successive metering operations; the time difference between two such times is the period of the search.

In the case of motor metering pumps with position sensor 36, a more direct method for slip detection works with the observation of the instantaneous speed of push rod 19. From the motor speed predetermined by the electric drive, an ideal push rod speed can be calculated at any time via the known transmission and eccentric characteristics. By comparing the ideal and the measured speed, the slip can be determined at any time during the eccentric revolution and corrected by readjusting the frequency of the motor control.

pressure detection

If e.g. If an asynchronous motor is used, the force acting on the displacement element can be determined with the help of the slip determined according to one of the previously described methods, thus making it possible to draw conclusions about the working pressure of the metering medium. It should be noted, however, that the eccentric transmits the force acting on the push rod 19 according to its sinusoidal characteristic depending on the instantaneous angular position via the gear 11 to the motor 2. In the two dead centers, ie the turning points of the lifting movement, the motor is decoupled from the push rod force, i. load-free, in the two points exactly in between the eccentric transmits the load torque maximum to the engine. Accordingly, assuming a constant push rod force, the torque to be applied to the motor output shaft and thus also the slip will approximate to a sine function. The fluctuation range is an image of the push rod force.

If, as described above, the deviation of the stroke period from the ideal value is determined, this represents the slip averaged over the sinusoidal curve of the eccentric, which in turn represents a measure of the average stroke rod force, ie the working pressure. If the slip continuously determined from the comparison of the predetermined by the electrical control motor speed with the push rod speed, using the known eccentric and the knowledge of the instantaneous angle of rotation of the eccentric, which follows from the push rod position, the temporal force curve at the push rod 19 can be calculated. From the force curve at the push rod, in turn, the working pressure can be derived.

If the deflection mechanism is realized by a solution other than an eccentric, its characteristic is to be applied mutatis mutandis to what has been said.

Pressure limitation, detection of pressure loss

If the working pressure is determined by one of the methods described, it can be monitored for compliance with certain limits, and if the monitoring is activated, fault messages and further reactions, such Shutting down the dosing pump to be triggered. Over-limit monitoring may be used to protect the pump or other equipment; Occasionally, a factory preset limit of e.g. However, the monitoring limit may also be within the specified operating range of the metering pump when, for example, 130% of the maximum pressure of the metering pump is exceeded. more sensitive parts of the system are to be protected, and in this case must be specified by the operator. It is also possible to monitor for maintenance of given operating conditions; In this case, a fault message, e.g. triggered when a prevailing working pressure (for example indicated by an operator) as reference changes by a percentage up or down. If the working pressure is set to maintain a minimum pressure of e.g. 1 bar monitored, it is thus possible to detect a leak caused by damage in the piping.

pressure compensation

Depending on the version, the exact dosing capacity of motor metering pumps is influenced differently by the working pressure. On the one hand, the drive motor 2, if it is designed, for example, as an asynchronous motor, with increasing working pressure with increasing slip, which has a speed drop and an associated reduced stroke frequency. On the other hand, a membrane 13 used as a displacement element undergoes an elastic deformation under the influence of the working pressure during the metering stroke. At the beginning of the Dosierhubs the internal pressure is continuously increased in the metering chamber 16 with the exhaust valve 15 still closed by the diaphragm core 30 is moved by the push rod 19 under pressure in the metering chamber 16 and the elastic Walk region of the membrane 13 to the same extent yielding to the pressure recedes in opposite directions to the movement of the diaphragm core 30. The membrane 13 deforms in itself, but in total there is virtually no change in volume, which is due to the fact that the metering medium is virtually incompressible and at this time both valves are closed. At the end of this deformation phase, the chamber pressure corresponds to the external working pressure. The distance traveled so far of the push rod 19 corresponds to the amount of membrane deformation, ie the dead zone at the beginning of the dosage, and practically does not contribute to the dosage. The deformation or the dead zone typically moves in a range of approx. 0.1-0.5mm depending on diaphragm size, working pressure, etc. At the point of pressure balance opens the pressure-side outlet valve 15. Now, the pressure acting on the diaphragm 13 is virtually identical to the external working pressure and remains, as the diaphragm deformation, for the rest Part of the dosing stroke approximately constant. The point of pressure equilibrium at which the pressure-side outlet valve opens marks the actual beginning of the metering so that the amount of membrane deformation is lost to the metering stroke, ie the effective stroke length is calculated from the mechanically predetermined minus the membrane deformation. Since the membrane deformation itself increases more or less proportionally with the working pressure, the typical dependency is a falling metering performance curve with increasing working pressure. The resulting negative deviation becomes more pronounced the smaller the set stroke length.

In a motor metering pump according to the prior art, the dosing is not only pressure-dependent, but also in Teilhubbetrieb not strictly proportional to the set mechanical stroke length. Rather, the effective metering on the stroke only begins after an initial dead zone from the point of complete membrane deformation with the opening of the exhaust valve 15. Applying a characteristic curve that shows the metering power as a function of the set mechanical stroke length results in a linearly rising curve. which only has a real metering capacity from a minimum stroke length corresponding to the dead zone of x _T1 , x _T2 , x _T3 ... x _Tn (see FIG. Fig. 12 ). Since this minimum stroke length corresponds to the membrane deformation, it is also dependent on the working pressure p ₁ , p ₂ , p ₃ ... P _n .

This characteristic shift x _T1 , x _T2 , x _T3 ... x _Tn requires prior art recalibration under real working conditions as soon as the previously set stroke length is significantly changed, since the new dosing with sufficient accuracy via a proportional conversion from the previous and the newly set stroke length can be determined.

If the working pressure is determined according to one of the previously described methods, it is possible, based on the described dependencies, which can be determined quantitatively in preliminary tests for one type of device, to predetermine and compensate for the error-producing influence of the working pressure on the metering performance. For this purpose, based on the determined working pressure and the set stroke length, which, as described above, can also be measured using the position sensor, calculated from the known error dependence, a correction value, which is added to the set stroke frequency. It should be noted that under practical and economic aspects only the systematic part of the influence can be eliminated. The pressure-dependent metering performance error is mainly determined by the material properties and dimensions of the components involved, which change to some extent due to aging may or may be subject to specimen discrepancies in the production series. These variations are not taken into account by the method described here, to correct the errors caused by the membrane deformation using predefined values derived from component parameters or determined in measurement series; rather, the concrete conditions would have to be re-measured at regular intervals or at each stroke on the present device specimen.

If the error-generating influence of the membrane deformation is compensated as described above by determining the working pressure according to one of the previously described methods and adjusting the set stroke frequency by a correction value, then the proportional error in the partial stroke operation is also eliminated so that the dosing pump is practically over the full usable setting range the stroke length of eg 20% -100% can be operated without having to perform the previously necessary recalibrations, which in a conventional metering pump with an adjustment of the stroke length by more than e.g. 10% are necessary to ensure the specified metering accuracy.

Avoidance of flow losses in highly viscous media

The function of controlling the velocity of the displacer, here the membrane 13, can be used in particular for highly viscous media (for example lecithin) to limit flow losses in valves and other bottlenecks. High flow rates have a negative influence on the dosing accuracy in such media by additional pressure losses due to flow resistance. In addition, it is advantageous here if the limited speed allows more time for the defined opening and closing of the valves. Overall, both effects improve the dosing accuracy of highly viscous media. To achieve this, the membrane velocity is kept limited to a selectable maximum value during the entire dosing process. This maximum speed depends i.a. from the viscosity of the concrete to be metered medium and is e.g. to be selected by the operator in the form of several pre-defined values adapted to common use cases or specified directly. By means of the position sensor and the above-described control of the speed of the displacer, the desired limitation of the membrane velocity can be ensured.

cavitation

In slightly outgassing media (such as sodium hypochlorite) can be particularly at the intake, but also in the metering at too high flow velocity at bottlenecks by local undershooting of the vapor pressure, including the chemical composition of the metering As well as its temperature depends, cavitation occur, which has increased wear. Cavitation can be avoided by the speed is limited by control or even by simple speed specification to values well below a critical flow rate both in the pressure stroke and during the suction, ie the return of the diaphragm 13. The speed specification for the control loop or, in the simple case, the engine speed is set for this purpose so that the membrane velocity corresponding to the medium velocity is limited to, for example, 1 mm / 50 ms.

In particular, the suction is prone to the formation of cavitation, since the static pressure is particularly low and therefore the safety range to below the vapor pressure is very low. For a refinement of the method, it is therefore useful to limit the membrane velocity in the intake to lower values than in the pressure stroke. Sensible values are for example 1mm / 50ms in the pressure stroke or 1mm / 100ms during suction, but of course different values are possible. Essential for such an individual treatment of the metering phases is that with the help of the position sensor, the exact position of the membrane is known at all times and thus the beginning of the (particularly critical) suction phase can be reliably detected.

Electronic stroke length adjustment

The invention makes it possible to save the mechanical device for adjusting the stroke length (adjusting member 7 and Hubverstellbolzen 8). For this purpose, the control device, the desired stroke length electronically, eg by an operator input, communicated. If the desired stroke length has been carried out, the reached position of the diaphragm 13 is held by braking the motor 2 and these are then returned to the intake in the reversed direction of rotation of the motor. The following stroke can be carried out by further rotation of the engine beyond the suction-side dead center with a reversed direction of rotation (printing phase in reverse operation, suction in normal operation) or in the same order as the previous stroke; in the former case, deceleration and starting operations of the engine between the strokes and the associated time and energy requirements can be saved. It should be noted that the permanent change of direction makes it impossible for a passive fan fixedly mounted on the motor shaft to fulfill its function sufficiently, so that the use of an externally driven fan is indispensable for the motor if it requires cooling measures.

Slow dosing to avoid concentration fluctuations

For applications in which good mixing with a process medium stream is important, the most uniform possible introduction of the dosing medium into the process is required. In addition, certain applications require the possibility of metering very small amounts as evenly as possible over a very long period of time, with the aim of achieving quasi-continuous metering. For these cases, prior art motor metering pumps are used, e.g. work with a stepper motor and a self-locking gearbox. A total stroke is performed reduced speed at these metering pumps or divided into several sub-steps with intermediate rest periods, at the end of the total stroke a complete (fast) suction phase is performed, and then the Dosiervorgäng continued in the manner described.

In the case of a motion-controlled motor metering pump, the available time, which results from the repetition frequency of the metering strokes, can be divided so that the portion remaining after deduction of the suction duration is utilized to a maximum for the forward movement, except for a short rest phase. The speed to be controlled is calculated from the distance to be traveled (set stroke length) and the available time. In contrast to a motor metering pump according to the prior art, when using a position sensor 36 and a control device from the known at any time position of the push rod 19, the instantaneous angular position of the Exzentergetriebes be reckoned and included in the engine speed so that the characteristic of the deflection device, which is sinusoidal when using an eccentric, balanced and the metering can be performed as exactly linear movement with a correspondingly constant application of the metering. The speed can be in a very wide range of e.g. 1 mm / min to 1mm / s and beyond.

The previously described applications of the position sensor z.T. together with a regulation show that by using a position sensor e.g. on the push rod during the entire lifting and suction, the exact position of the displacement member can be detected and monitored. The position determination and monitoring means that situation-related control specifications, which lead to the described advantages, are exactly maintained by means of the actual value measurement.

position sensor

As already stated, serves as reference element for the position sensor in the described embodiment, the shadow edge 35 on the push bar 20 for the scanning of the position whose Shadow on the line from CCD cells 32 (CCD = charge coupled device) is mapped. The active sensor elements described in more detail in this embodiment, which detect the position, are arranged on the side of the push arm 20 directed to the dosing head. As the light source 33 is an LED, the optical receiver is an electronic module with a CCD line 32, which are mounted here together on an intermediate part, the sensor carrier 31. The mounting on the sensor carrier 31 makes it possible to treat the position sensor 36 in the production process as an independent module and, for example, separately pre-assemble and check its function outside the final installation site. In addition, the described photocell-like arrangement is a touch and thus wear-free working sensor.

For the basic operation of the mounting location of the sensor in the moving unit from push bar 20 and push rod 19 is of no importance, the relevant definition can be made according to structural considerations such as space, assembly order, etc. Moreover, the parts described here as fixedly mounted (light source 33, receiver 32) and those moving together with the push rod (shadow edge 35) can also replace their function.

In the exemplary embodiment, the CCD module 32 is driven by an evaluation unit which contains a microprocessor and generates the required control signals. Instead of a microprocessor, the evaluation unit can also be realized by a DSP (Digital Signal Processor) or in discrete technology.

As a light source 33, in principle, each component is suitable, which has a sufficiently narrow confined spot. Together with the in Fig. 7 this imaging geometry determines the width of the shadow area SV, s. also Fig. 8 ,

It is also possible to use a plurality of elements or a line emitter as the light source 33, with the aid of which the shadow profile SV can be specifically designed according to particular aspects. As an example, the achievement of a higher brightness, without affecting the image sharpness in the direction of movement.

The CCD line 32 is a linear array of M optical receivers (hereinafter called pixels) arranged in a regular raster R of several μm. In the example, these are 128 pixels in the grid of about 64μm on a total length of about 8mm, ie M = 128 and R = 64μm.

The control signals which are generated by the evaluation unit, determine the exposure time, during which the individual pixels of the CCD line 32 integrate the incident light in each case in a separate amplifier within the CCD chip and cache for later evaluation. This integration occurs not only over the exposure time, but also across the photosensitive area of each pixel. After the exposure, the brightness values belonging to the pixels are successively read out of the CCD module by further control signals as analog values and detected by the evaluation unit.

Exposure and readout of the brightness values take place alternately in the simple case. Depending on the design, some commercially available CCD line components also offer options for simultaneous execution of both processes, by temporarily buffering the integrated measured values after exposure and enabling the integrators immediately for a subsequent measurement. By simultaneously reading out the results of a measurement run during the exposure phase for the subsequent passage, the measurement speed can be increased.

Im in Fig. 8 2, the integrated brightness values H are shown corresponding to the actual shadow progression in the area of the addressed pixels in the specific exemplary embodiment. The shadow area SV extends over the pixels # 60 to # 63 in this example.

As a simple evaluation method, a decision threshold H _v (in Fig. 8 shown as a dashed line) arbitrarily set at, for example, half of the maximum brightness and that pixel is sought whose brightness value H at the shadow transition first, the threshold H _v below; in the example this would be Pixel # 62.

In other embodiments, the brightness profile may be in opposite directions from unlit to illuminated CCD cells with increasing pixel number; On the one hand, this depends on the arrangement of the elements light source 33, CCD module 32 and shadow body 35 and on the other hand on the internal organization of the CCD 32 used. In this case, the pixel whose brightness value at the shadow transition first exceeds the threshold is searched for. After the three phases of exposure, readout and processing, a position value is available. The total time requirement of the three phases determines the repetition rate at which position values are obtained. The measurement resolution is equal to the pixel pitch R of the CCD line, corrected by the imaging ratio A, which results from the mounting distance with the individual components.

• Hierbei ist s = Tatsächliche Bewegung der Schattenkante
• s' = Projizierte Bewegung der Schattenkante in der Ebene des CCD
• x₂ = Abstand zwischen optisch wirksamer Schattenkante und Lichtquelle
• x₃ = Abstand zwischen CCD-Ebene und Lichtquelle

For the imaging ratio A (cf. Fig. 9 ): $$\mathrm{A}={\mathrm{s}}^{\text{'}}/\mathrm{s}={\mathrm{x}}_{\mathrm{3}}/{\mathrm{<figure-callout\; id="2"\; label="x"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">x</figure-callout>}}_{\mathrm{2}}$$

• Where s = actual movement of the shadow edge
• s' = Projected movement of the shadow edge in the plane of the CCD
• x ₂ = distance between optically effective shadow edge and light source
• x ₃ = distance between CCD plane and light source

This method determines the position by counting pixels, so it is to be regarded as a digital method. Deviations and displacements of linear parameters such as component sensitivities have practically no effect on the result compared to analogous methods. If you determine the imaging ratio. A for practical values, assembly tolerances also have only a small influence. In a practical embodiment with x ₃ = 21 mm and x ₂ = 20 mm results in a nominal value for the imaging ratio A of 1.05; ie a movement of the shadow edge 35 by a certain distance results in a 1.05-fold shift of the shadow area SV in the plane of the CCD cells 32. Let us now assume a mounting tolerance for x ₃ , ie a possible variation of the spacing of the CCD cells 32 from the light source 33, by ± 0.3mm, and a concrete mounting case at the top of this tolerance, with x ₃ = 21.3mm and x ₂ = 20mm. In this case, the imaging ratio A is calculated to be 1.065. The imaging ratio changes by 1.065 / 1.05 = 1.014 or + 1.4% in this example. This deviation can easily be eliminated by a one-time calibration, eg during production. The linearity is determined almost exclusively by the accuracy of the pixel grid within the chip geometry, deviations are thus negligible.

Although the previously described method for determining the position of the shadow edge 35 and thus the position of the diaphragm 13 already yields very precise and linear position values, an even more accurate position resolution can be achieved by interpolation. In this extended embodiment, a position resolution is achieved by evaluating the pixel brightnesses H, eg between pixels 61 and 62 (cf. Fig. 10 ), which is finer than the pixel raster R, by interpolating the brightness values of the pixels in the region of the decision threshold. The aim is to determine the point at which the brightness curve intersects the decision threshold H _v and this point of intersection assign a value on a virtual location scale whose x values in the middle of each pixel correspond exactly to the pixel number.

$${\mathrm{\Delta H}}_{\mathrm{r}}={\mathrm{H}}_{\mathrm{r}}-{\mathrm{H}}_{\mathrm{V}}$$

For this purpose, the two pixels to the left and to the right of the decision threshold H _{v are} searched for and the distances ΔH of the associated brightness values are evaluated from this threshold. As in Fig. 10 or in Fig. 11 represented, applies: $${\mathrm{AH}}_{\mathrm{l}}={\mathrm{H}}_{\mathrm{l}}-{\mathrm{H}}_{\mathrm{V}}$$

$${\mathrm{AH}}_{\mathrm{r}}={\mathrm{H}}_{\mathrm{r}}-{\mathrm{H}}_{\mathrm{V}}$$

The distances .DELTA.x calculated from the respective center axis of each of the two adjacent pixels, in this example pixels # 61 and # 62, in multiples of the pixel width to the intersection form the following relationship with the brightness distances .DELTA.H relative to the pixel # 61 to the left of the searched intersection (left-side neighboring pixel): $${\mathrm{Ax}}_{\mathrm{l}}/\left({\mathrm{Ax}}_{\mathrm{l}}+{\mathrm{Ax}}_{\mathrm{r}}\right)={\mathrm{AH}}_{\mathrm{l}}/\left({\mathrm{AH}}_{\mathrm{l}}+{\mathrm{AH}}_{\mathrm{r}}\right)$$

With (Δx _l + Δx _r ) = 1 (1 pixel width) the result is: $${\mathrm{Ax}}_{\mathrm{l}}={\mathrm{AH}}_{\mathrm{l}}/\left({\mathrm{AH}}_{\mathrm{l}}+{\mathrm{AH}}_{\mathrm{r}}\right)$$

Relative to the pixel # 62 (right-hand neighboring pixel) on the right of the desired intersection, the relationship applies: $${\mathrm{Ax}}_{\mathrm{r}}/\left({\mathrm{Ax}}_{\mathrm{l}}+{\mathrm{Ax}}_{\mathrm{r}}\right)={\mathrm{AH}}_{\mathrm{r}}/\left({\mathrm{AH}}_{\mathrm{l}}+{\mathrm{AH}}_{\mathrm{r}}\right)$$

With (Δx _l + Δx _r ) = 1 (1 pixel width) the result is: $${\mathrm{Ax}}_{\mathrm{r}}={\mathrm{AH}}_{\mathrm{r}}/\left({\mathrm{AH}}_{\mathrm{l}}+{\mathrm{AH}}_{\mathrm{r}}\right)$$

In this example, the intersection is 61.7. If the brightness progression in the interpolation range follows an ideal straight line, then both calculation paths lead to the same result, so it is basically sufficient to carry out one of the two calculations. However, with this property, error contributions can be minimized by a not exactly straight brightness curve in the considered transition range or by always expected measurement inaccuracies, for example by performing both calculations and averaging their results.

In other embodiments, depending on the brightness curve, the conditions on both sides of the point of intersection with respect to unlit and illuminated CCD cells can be reversed; in this case If necessary, the directions on the left and right change their function and the interpolation equations must be adjusted accordingly.

In addition, other embodiments are possible in which the brightness values of more than two pixels are used for the calculation. The position can then be determined by redundant multiple calculation and e.g. Averaging several results are formed. As a further possibility, a different linear interpolation than shown here or an interpolation with the data other than the direct neighbor pixels can be used.

Deviations and displacements of linear parameters, e.g. Component sensitivities affect the result only within the interpolation range. The steepness of the brightness gradient in the shadow transition, resulting from the sharpness of the image of the shadow edge on the CCD plane, is of subordinate importance since it does not affect the interpolation within wide limits; only the linearity of the brightness curve is decisive for the accuracy of the interpolation.

Independently of the previously described interpolation method, further methods for improving the sensor properties can be used based on the described basic principle. These methods are described below:

• Improvement of interference immunity by filtering

The interference immunity of the sensor can be improved by filtering measures. Filtering can be applied to both the brightness values of the pixels and the result of the position determination itself. In the first case, the method works with brightness values that have been averaged over several pixels or over several passes, in the second case several initially determined position results are combined to form a derived position value with which the further processing is then carried out.

• Compensation of mounting deviations

In a defined phase, for example in the resting phase before the end of the actual metering stroke, the position value for this phase can be determined and stored in a reference memory. During the active movement phase, the position values are then processed relative to the previously determined reference value. By this method, it is possible to automatically compensate for manufacturing-related assembly deviations of the rest position and shifts during operation, for example by thermal expansion and thus to improve the accuracy.

• Compensation of scaling errors

In an extended alternative, the scaling of the position sensor can be adjusted by approaching two or more known positions, here called reference positions. This can happen once in the course of the production or test procedure or also recurrently in operation.

In the first case, the reference positions may be determined by external means, e.g. Rest positions or external measuring devices, are specified. From the position values measured in these reference positions, together with the knowledge of the actual position of the reference positions, a correction value for the scaling of the position sensor can be derived and stored for further processing.

In the second case of recurrent scaling matching, known positions, e.g. mechanical stops or reference signals from other existing devices for position detection necessary. If the diaphragm is in such a known position during operation, a correction value for the scaling of the position sensor can also be derived from the position value measured at this point and stored for further processing.

• Compensation of the optical sensitivity parameters

In an extended embodiment, the brightness values of the fully illuminated pixels can be used to determine a representative value for the illuminance. For this purpose, for example, the mean value of the brightness can be formed from a suitable group of pixels. Based on the determined illuminance, the exposure can be controlled so that the available value ranges are optimally utilized; For example, the light source in its brightness or their duty cycle can be controlled so that the illuminance of the fully illuminated pixels is slightly below the overdrive limit of the CCD chip. For each measurement pass, the illumination intensity is then corrected on the basis of the conditions of the preceding pass, such that a sliding adaptation of the exposure parameters to possible changes in component properties, e.g. due to aging.

• Compensation of soiling and pixel deviations

In an expanded embodiment, the mechanical structure of the sensor can be designed so that in a defined phase, for example, in the resting phase before the end of the actual metering, the Complete used for the work path pixel area or a section of interest can be exposed. One possible embodiment is, for example, to use a shadow edge 35 facing the diaphragm for the evaluation, whereby the shadow edge sweeps over the sensor in the course of the lifting movement and darkens a region of the CCD cells which was illuminated in the previous resting state. In this phase, the brightness values of all relevant pixels can be determined and stored individually in a reference memory. Deviations of the measured values of individual pixels from the ideal value can, for example, be stored in the form of correction values. During the active movement phase, the brightness values of each pixel are then first corrected with the aid of the previously determined reference values for each measurement and only then further processed. By this method, it is possible to compensate for production-related sensitivity deviations of individual pixels and contamination in a certain scope and thus to improve the accuracy and to increase the reliability.

Of course, two- or more-row arrangements are also possible for the CCD receiver line to provide increased redundancy safety against failures, e.g. by pollution, or by averaging to increase the accuracy of measurement. For extra long stroke lengths, two or more CCD lines can be combined to extend the measurement range beyond the functional limits of a single line.

The motor metering pump described in detail in the exemplary embodiment may deviate from other design variants in individual areas and arrangements of components such as the engine, the transmission, the eccentric drive and other design details. It is essential, however, that the oscillating movement, which is generated by a drive, is scanned by means of a position sensor, wherein the position sensor outputs an actual signal which is in a fixed relationship to the position of the reference element and thus also to that of the displacement member, so that with help This value knowledge about the movement of the repressive organ is obtained.

LIST OF REFERENCE NUMBERS

1

eccentric housing

2

Motor (asynchronous motor)

3

housing ribs

4

baseplate

5

housing cover

6

Electronics in the housing cover

7

adjusting

8th

Hubverstellbolzen

9

cover

10

control lines

11

Gearbox (reduction gearbox)

12

dosing

13

membrane

14

intake valve

15

outlet valve

16

metering

17

eccentric shaft

18

longitudinal axis

19

pushrod

20

push handle

21

Contact surface for eccentric

22

excenter

23

Compression spring (return spring)

24

bearing disk

25

Collar for compression spring

26

Bush in bearing disc

27

Bushing in Hubverstellbolzen

28

electronics housing

29

Power switching stages for the motor control

30

diaphragm core

31

sensor support

32

Receiver, CCD module

33

light source

34

control electronics

35

Shadow edge as reference element

36

position sensor

37

differentiator

38

Setpoint

39

Target-performance comparison

40

PID controller

41

Position correction

42

amplifier

SV

shadow History

H

bright area

d

dark area

# 58 ... # 65

Cells (pixels) of the CCD

H

Brightness values of the pixels

H _v

Brightness value of the comparison threshold (VS)

H _l

Brightness value of the pixel to the left of the intersection with the VS (left-sided neighbor pixel)

ΔH _l

Brightness distance of the left-side neighboring pixel to the brightness value of the comparison threshold

H _r

Brightness value of the pixel to the right of the intersection with the VS (right-hand neighbor pixel)

ΔH _r

Brightness distance of the right-hand neighboring pixel to the brightness value of the comparison threshold

Δx _l

Position distance of the center line of the left-side neighboring pixel to the intersection with the VS

Δx _r

Position distance of the center line of the right-hand neighbor pixel to the intersection with the VS

x ₁

Distance between shadow edge and CCD plane

x ₂

Distance between shadow edge and light source

x ₃

Distance between CCD plane and light source

p ₁

Working pressure p ₁

p ₂

Working pressure p ₂

p ₃

Working pressure p ₃

p ₄

Working pressure p ₄

x _T1

Dead zone at working pressure p ₁

x _T2

Dead zone at working pressure p ₂

x _T3

Dead zone at working pressure p ₃

x _T4

Dead zone at working pressure p ₄

s

Actual movement of the shadow edge

s'

Projected movement of the shadow edge

D

Dosing capacity

HL

Mechanical stroke length

SG

manipulated variable

KSG

Corrected manipulated variable

MA (U, f)

Motor control (voltage, frequency)

k1

Factor for the position-dependent position correction

k2

Factor for the power amplifier

k3

Factor for the derivation of the speed signal

x _S

Setpoint of the position of the displacer

x _I

Actual value of the position of the displacement element

x _SI

Control deviation of the position of the displacement element

v _p

Setpoint of the speed of the displacement element

v _I

Actual value of the velocity of the displacer

v _SI

Control deviation of the speed of the displacement element

Claims (30)

1. A metering pump with a rotary drive motor and an oscillating piston, wherein the rotary motion of a drive motor (2) is transformed into an oscillatory motion of a connecting rod (19) by means of a gear arrangement, so that a displacement means actuated thereby executes an oscillating linear motion on continuous rotation of the drive motor (2), which results in transfer of a medium to be metered in a metering head (12) arranged in the longitudinal axis of the connecting rod (19) cooperating alternately with an outlet and an inlet valve to produce a pump stroke (pressure stroke) and a priming stroke, and thereby leads to conveying of the metering medium, wherein a reference element (35) is associated with the connecting rod (19), the position of which is detected by a positional sensor (36), wherein the positional sensor provides an actual signal (x_I) which is in a fixed relationship to the position of the reference element and thus to that of the displacement means and which provides information regarding the motion executed by the displacement means, so that the electronic control system of the metering pump can react to the operating conditions of the metering circuit and pump, characterized in that the signal (x_I) for the position of the connecting rod (19) read from the positional sensor (36) is fed to a control circuit and influences the rotary speed of the drive motor (2) and thus the linear motion of the connecting rod and thus of the displacement means in the context of its control accuracy so that it follows a predetermined nominal profile (38).
2. A metering pump according to claim 1, characterized in that the positional sensor (36) detects the position of the reference element (35) in accordance with a touch free principle.
3. A metering pump according to claim 1, characterized in that the reference element (35) associated with the connecting rod (19) and the positional sensor (36) are outside the metering head.
4. A metering pump according to one or more of the preceding claims, characterized in that the reference element (35) influences the path of a light source (33) and the positional sensor cooperating therewith (36), which is fixed in the pump housing or another stationary part, operates in a light-sensitive manner.
5. A metering pump according to one or more of the preceding claims, characterized in that the reference element (35) is a shadow-producing body or a shadow producing contour and the positional sensor (36) cooperating therewith which is fixed in the pump housing or another stationary part, consists of an optical receiver (32) in the form of a series of light sensitive charged coupled devices (CCD).
6. A metering pump according to one or more of the preceding claims, characterized in that the positional sensor (36) is arranged on its own sensor carrier (31) which is fixed to the pump housing or another stationary part.
7. A metering pump according to one or more of the preceding claims, characterized in that the light source (33), the shadow-producing body or shadow-producing contour (35) and the receiver (32) constitute a light box-like arrangement and the measured values are continuously or intermittently fed to the electronic control system.
8. A metering pump according to one or more of the preceding claims, characterized in that the optical receiver (32) of the positional sensor (36) consists of a number of linearly arranged receivers (pixels), preferably 128 pixels.
9. A metering pump according to one or more of the preceding claims, characterized in that the light source (33) is a light emitting diode (LED) which is arranged with respect to the optical receiver (32) of the positional sensor (36) so that its light beam directed at the receiver is not interrupted by the connecting rod (19) on the direct way to the receiver.
10. A metering pump according to one or more of the preceding claims, characterized in that the start value of the positional sensor (36) is produced by interpolating the brightness values of a plurality of pixels in the shadow transition region.
11. A metering pump according to one or more of the preceding claims, characterized in that when processing the signals for the positional sensor (36), filtering is employed.
12. A metering pump according to one or more of the preceding claims, characterized in that zero position errors of the positional sensor (36) are eliminated by means of a reference memory.
13. A metering pump according to one or more of the preceding claims, characterized in that scaling errors of the positional sensor (36) are eliminated by using one or more reference positions.
14. A metering pump according to one or more of the preceding claims, characterized in that variations in the illumination of the positional sensor (36) are compensated for by controlling or regulating the light source (33) using the pixel brightness values obtained.
15. A metering pump according to one or more of the preceding claims, characterized in that variations in brightness between individual pixels of the optical receiver (32) are compensated for by using a reference memory for the sensitivity of each pixel.
16. A metering pump according to one or more of the preceding claims, characterized in that determination of the value to which the stroke adjustment means (7) should be adjusted is obtained directly by means of the positional sensor (36) by measurement during metering.
17. A metering pump according to one or more of the preceding claims, characterized in that the electronic control system recognizes a blockage in the displacement means or an incompletely executed stroke by evaluating the signal for the positional sensor (36).
18. A metering pump according to one or more of the preceding claims, characterized in that the drive motor (2) operates with slippage, in which an asynchronous motor is employed, for example, and the electronic control system defines a nominal stroke frequency or a nominal stroke period for the displacement means from the nominal rotary speed of the drive motor and the known gear characteristics and additionally determines the actual stroke frequency or the actual stroke period of the displacement means by evaluating the positional sensor signal (36), wherein by comparing the actual stroke frequency with the nominal stroke frequency or the actual stroke period with the nominal stroke period of the displacement means, the slippage of the drive motor can be calculated and the nominal rotary speed can be changed so that finally, the displacement means moves at the desired stroke frequency.
19. A metering pump according to one or more of the preceding claims, characterized in that the drive motor (2) operates with slippage, in which an asynchronous motor is employed, for example, and the electronic control system provides a nominal stroke frequency or a nominal stroke period for the displacement means from the nominal rotary speed of the drive motor and the known gear characteristic and additionally defines the actual stroke frequency or the actual stroke period of the displacement means by evaluating the positional sensor signal (36), wherein by comparing the actual stroke frequency with the nominal stroke frequency or the actual stroke period with the nominal stroke period of the displacement means, the slippage of the drive motor can be calculated and further, the electronic control system can determine the force on the displacement means from the determined slippage of the drive motor and the known gear characteristic and thus reduce the operating pressure of the metering medium.
20. A metering pump according to one or more of the preceding claims, characterized in that the drive motor (2) operates with slippage, in which an asynchronous motor is employed, for example, and the electronic control system determines a nominal speed for the displacement means from the nominal rotary speed of the drive motor and the known gear characteristic for every instant of the metering procedure and additionally, determines the actual speed of the displacement means by evaluating the positional sensor signal (36), wherein by comparing the actual instantaneous speed with the nominal speed of the displacement means, the instantaneous slippage of the drive motor can be calculated and, again in connection with the known gear characteristics, the instantaneous force in the displacement means can be deduced therefrom.
21. A metering pump according to claim 20, characterized in that the electronic control system reduces the operating pressure of the metering medium using the observed force profile on the displacement means.
22. A metering pump according to claim 19 or claim 21, characterized in that the electronic control system recognizes operation beyond the specified pressure range from the determined metering medium operating pressure and adjusts metering when a maximum permissible pressure as dictated by the specification for the metering pump or as provided by the operator is exceeded, or when a predetermined minimum pressure is not reached.
23. A metering pump according to claim 19 or claim 21, characterized in that the displacement means is a partially elastic diaphragm (13), wherein the electronic control system determines an expected metering error from the determined operating pressure of the metering medium and the known dependency of the metering performance on the operating pressure and influences the rotary speed of the drive motor (2) and thus the stroke frequency to work against the expected metering error.
24. A metering pump according to claim 1, characterized in that the control device alternately influences the position (hereinafter denoted x_I), speed (hereinafter denoted v_I) or the acceleration of the displacement means by changing the rotary speed of the drive motor (2).
25. A metering pump according to claim 1, characterized in that the control device can deliberately decrease v_I for the displacement means during the priming phase and/or in the pressure phase, in order to counteract pressure drops which are caused by resistance to flow, or the occurring of cavitations.
26. A metering pump according to claim 1, characterized in that the desired stroke length is communicated to the control device by an operator and the control device is used to electronically limit the motion of the displacement means to the stroke length to be executed, wherein the control device stops the drive motor (2) after executing the desired stroke length, switches it into reverse and then carries out the priming stroke and the motor then stops or carries out the next pressure stroke.
27. A metering pump according to claim 1, characterized in that the control device distributes the forward motion of the displacement means during the pressure phase by driving the drive motor (2) for the time determined by the repetition rate of the metering strokes, so that the metering medium is dispensed as evenly as possible, even in the case of metering strokes which are very slow, for example of several minutes.
28. A metering pump according to claim 20, characterized in that the displacement means is partially in the form of an elastic diaphragm (13) and the electronic control system detects the opening of the outlet valve (15) from the instantaneous force on the diaphragm (13) and with the aid of said observation measures the dead region which arises because of the elastic deformation of the diaphragm (13).
29. A metering pump according to claim 28, characterized in that the actual stroke is influenced depending on the deduced diaphragm deformation, wherein the control device stops the drive motor (2) after reaching the desired stroke length from opening of the outlet valve (15), switches it into reverse and then executes the priming stroke and then stops the motor or executes the subsequent pressure stroke, so that the error caused by the diaphragm deformation (with respect to the stroke or the metered volume) is eliminated and the dependency of the metered quantity on back pressure is substantially reduced.
30. A metering pump according to claim 28, characterized in that the actual hub frequency is influenced depending on the deduced diaphragm deformation, wherein the control device determines a correction value for the error caused by the diaphragm deformation (with respect to the stroke or the metered volume) and changes the nominal rotary speed of the drive motor (2) with the aid of said correction value so that the error caused by the diaphragm deformation is eliminated.

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