Patent Application
20130101439
The present invention concerns a method of controlling and/or regulating a metering pump. A metering pump generally has a drive motor with a shaft driven by the motor, and a displacement member disposed in a metering head. In that case the rotary movement of the shaft is converted into an oscillating movement of the displacement member so that the displacement member, interacting with an outlet and inlet valve in alternate succession, leads to a pump stroke (pressure stroke) and an intake stroke (suction stroke) and thus delivery of a medium to be metered.
Those metering pumps operate on the basis of the volumetric principle, that is to say the metering operation is implemented by displacement of a closed chamber volume by means of a displacement member. The metering volume in each stroke is determined by the product of the stroke and the effective surface area of the displacement member.
In such a metering pump the generally continuous rotary movement of the drive motor is converted into an oscillating movement of the displacement member by a transmission unit. The drive of the displacement member can be positively controlled or can also be effected at one side in positively locking relationship only in the pressure stroke. In the latter case measures must be provided for moving the displacement member back again. That can be effected for example by a suitable return spring.
The conventional metering pumps are generally powerful and have metering properties adequate for most applications.
In the simplest case the drive motor is switched on continuously for ongoing metering or is switched on for a given time for performing individual metering strokes. The motor speed is predetermined by the electric frequency of the mains voltage or the motor actuation system and therefore defines the duration of each stroke together with the corresponding transmission step-down ratio and the transmission characteristic which for example is sinusoidal in the case of an eccentric transmission. In continuous operation the duration for each stroke is calculated from the effective motor speed in the load condition and the transmission step-down ratio. When the drive motor is switched on or off to perform individual strokes or partial strokes, corresponding start-up and braking times must be taken into consideration, which correspondingly prolong the duration per stroke. The stroke length can be adjusted for example by adjusting the eccentricity of an eccentric transmission or by using an adjustable abutment, the abutment can for example limit the movement of the displacement member in the suction stroke before reaching the rear dead point of the eccentric transmission. That predetermines the starting point of the stroke movement while the end point derives from the completely implemented deflection movement of the displacement member.
The movements of the displacement member result from the interaction of the mechanical components such as for example the transmission. During the forward movement (pressure stroke) the drive operates against the force acting on the push rod by the displacement member (and the possibly present return spring).
There are embodiments, so-called diaphragm metering pumps, which use an at least partially flexible diaphragm as the displacement member. That diaphragm can be deformed during the pressure and suction strokes. The amount of that deformation which is built up in a first part of the stroke movement, which part is not used for the metering process, is lost to the effectively performed stroke movement and has the result that the metering amount decreases with increasing working pressure. With those pumps it is therefore necessary to perform suitable calibration measurement. After calibration has been effected however the pump can only be reliably used in a given working pressure range. If the working pressure should change re-calibration has to be effected. If calibration is not done, for example because the fluctuation in working pressure is not observed, that gives a metering error.
For better adjustment of the metering process and for increasing the metering accuracy it is already proposed in EP 1 754 891 that the displacement member is connected to a reference element whose position is sensed by a position sensor, the position sensor delivering an actual signal which is fixedly related to the position of the reference element and therewith the displacement member and by means of which knowledge about the movements of the displacement member is acquired so that the electronic control of the metering pump can react to operating conditions of the metering circuit and the pump.
With that background of the described state of the art therefore the object of the present invention is to provide a method of controlling and/or regulating a metering pump, which in principle manages without a position sensor on the thrust rod and can establish the metering behaviour of the pump with a high level of precision.
According to the invention that object is attained by a method of controlling and/or regulating a metering pump comprising a drive motor having a shaft driven by the motor and a displacement member arranged in a metering head, in which the rotary movement of the shaft is converted into an oscillating movement of the displacement member, wherein the displacement member, interacting with an outlet and inlet valve in alternate sequence, leads to a pump stroke (pressure stroke) and an intake stroke (suction stroke) and thus to delivery of a medium to be metered, in which at least one motor operating parameter, preferably a motor voltage U or a motor current I, is measured, at least one regulating parameter is calculated from the at least one measured motor operating parameter and optionally further known motor characteristics, the at least one regulating parameter is compared to a predetermined guide parameter, and a comparison signal dependent on the result of the comparison is outputted, and can be used as a status, actuating and/or regulating signal.
It is for example possible to calculate the actual torque MACTUAL and optionally the magnetic actual flux φACTUAL of the motor, preferably an asynchronous motor, as the regulating parameter, and to compare it to a predetermined reference guide parameter, that is to say the reference torque and the reference flux of the motor. A comparison signal can be outputted in dependence on the result of the comparison. The comparison signal can be used for example as a status signal, that is to say the signal indicates whether a given condition is or is not met. The status signal can then serve for example as a warning signal or as a triggering means for given measures.
It is also possible to use the comparison signal as an actuating signal, that is to say to control a parameter, for example a motor operating parameter, with that signal. Alternatively the signal can also be used as a regulating signal.
Depending on the respective regulating parameter, not only motor operating parameters such as for example motor voltage and motor current are necessary for calculation purposes, but further properties characteristic of the motor or the transmission such as for example the step-up or step-down transmission ratio.
In a further preferred embodiment it is preferred that as the regulating parameter the actual motor speed is measured preferably a plurality of times, particularly preferably at least five times, during a motor revolution, or is calculated from the motor operating parameters preferably from the actual torque MACTUAL and the magnetic actual flux φACTUAL of the motor, and the difference between the actual motor speed and a predetermined reference motor speed is outputted as the comparison signal and the comparison signal is used as a regulating signal for adaptation of motor current I and/or motor voltage U to adapt the actual motor speed to the reference motor speed.
In the simplest case measurement of the actual motor speed is effected by means of a rotary angle sensor. It is however also possible for the actual motor speed to be calculated from the motor operating parameters in completely contactless fashion.
In dependence on the transmission configuration the motor load varies in dependence on the current eccentric position. The motor must therefore be designed with its power output in such a way that it can apply the desired rotary speed, even in the most disadvantageous eccentric position. If the power of the motor is too low, the result is that the desired speed is not reached in many eccentric positions, that is to say the stroke duration is prolonged. The power of the motor can be better utilised by the specified measure as the rotary speed is slightly reduced in the region of maximum eccentric deflection, in which force transmission is at its most disadvantageous, while the resulting prolongation in the stroke duration is compensated by the rotary speed being increased in a region involving advantageous force transmission.
In a further preferred embodiment it is provided that as the regulating parameter the actual motor magnetisation is calculated, preferably a plurality of times, particularly preferably at least five times during a motor revolution, from the actual torque MACTUAL and optionally further known motor characteristics, and a predetermined reference motor magnetisation is selected as the guide parameter and the difference between the regulating parameter and the guide parameter is outputted as the comparison signal and the comparison signal is used as the regulating signal for the adaptation of motor current I and/or motor voltage U to adapt the actual motor magnetisation to the reference motor magnetisation, wherein preferably the reference motor magnetisation is a periodic function with a period duration corresponding to the period duration of the displacement member.
Preferably there is provided a pressure element which presses the contact surface in the direction of the eccentric so that upon rotation of the shaft the pressure element can hold the contact surface in contact with the eccentric at least portion-wise and an intake stroke can be performed. The pressure element can be for example a spring.
In a further preferred embodiment the actual torque MACTUAL and optionally the magnetic actual flux φACTUAL of the motor, preferably an asynchronous motor, is calculated as the regulating signal and the actual torque MACTUAL and optionally the magnetic actual flux φACTUAL of the motor is substantially continuously determined over at least one period duration and the time-dependent actual torque MACTUAL calculated in that way and optionally the time-dependent magnetic actual flux φACTUAL of the motor is compared to at least one pre-determined pattern function as the guide parameter. The comparison signal represents the degree of similarity between the regulating parameter and the guide parameter and if the degree of similarity exceeds a predetermined value the comparison signal is used as the status signal. For example an overload protection function, for example in the form of an excess pressure shut-down, can be called up in reaction to the status signal.
Usually a metering pump presents wear phenomena in the course of time. That can involve for example bearing damage, warped gears or a damaged eccentric. Such wear phenomena mean that the force to be applied by the motor changes. According to the invention it is therefore provided that characteristic trouble patterns or a pattern function are associated with given wear phenomena. If for example a gear is missing a tooth then the missing tooth will be manifested in a periodic disturbance in the force implementation. If now the actual torque is calculated substantially continuously and the signal calculated in that way is compared to the pattern functions, for example by forming a correspond cross-correlation function, it is possible at a very early stage to recognise that the metering pump is presenting wear phenomena and it is optionally possible solely on the basis of the forces involved to determine which component is exhibiting wear phenomena and then has to be specifically replaced.
It can further happen that air passes into the metering head, which can cause the entire metering operation to fail although the mechanical movement of the displacement member is still occurring. In this case also the compression process, that is to say the rise in force, can be evaluated by evaluation of the actual torque and, if the compression variation points to aeration of the metering head, for example a corresponding message can be produced or counter-measure can be automatically initiated such as for example automated venting of the metering head.
In a further preferred embodiment it is provided that the metering pump has a displacement member with an at least partially elastic diaphragm, wherein the metering amount is calculated as the regulating parameter from the actual torque MACTUAL and optionally the magnetic actual flux φACTUAL of the motor having regard to further motor characteristics, wherein the influence to be expected by virtue of flexing of the elastic diaphragm on the metering amount is taken into consideration and the difference between the actual metering amount and a predetermined reference metering amount is outputted as the comparison signal and used as the regulating signal for the adaptation of motor current I and/or motor voltage U to adapt the actual metering amount to the reference metering amount.
By virtue of that measure the metering pump can be used over a wide range of different working pressures without involving any metering error worth mentioning. If more specifically there is an unexpected change in the working pressure the method according to the invention, by way of the calculation of the actual torque, allows reliable recognition and correction of the metering error by virtue of the flexing of the diaphragm of the displacement member.
Furthermore in a preferred embodiment it is provided that an actual stroke length of the displacement member is calculated as the regulating parameter from the actual torque MACTUAL and optionally the magnetic actual flux φACTUAL and the difference between the actual stroke length and a predetermined reference stroke length is outputted as the comparison signal. The comparison signal can either be used as a status signal to possibly stop the pump or it can be used as the regulating signal for the adaptation of motor current I and/or motor voltage U to adapt the actual stroke length to the reference stroke length. By virtue of that measure the stroke length can be adapted to ongoing operation if that is necessary for the area of use.
The present invention also concerns a metering pump having a control and/or regulating device for carrying out the described method. The described method means that the metering pump can also be used in a pendulum stroke mode, that is to say the direction of rotation of the motor is inverted after at most one pump and one intake stroke.
Further advantages, features and possible uses will be apparent from the description hereinafter of a preferred embodiment and the related Figures in which:
a shows a diagrammatic view of the torque of the motor and the displacer movement during a revolution for a full stroke,
b shows a diagrammatic view of the torque of the motor and the displacer movement during a revolution for a partial stroke,
a shows a diagrammatic view of the torque of the motor and the displacer movement during a revolution for a full stroke with incomplete suction stroke,
b shows a diagrammatic view of the torque of the motor and the displacer movement during a revolution for a partial stroke with incomplete suction stroke,
The components of the eccentric drive are fixed on the housing formed by the eccentric housing 1 and the electronic housing 29, in the upper part. The components of the eccentric drive are mounted in an eccentric carrier 22 which ensures positional matching of the individual parts to each other and is fixed in the eccentric housing 3. A three-phase asynchronous motor 2 is flange-mounted together with a step-down transmission 11 which is in the form of an angle transmission as a structural unit to the eccentric housing 1 from the outside, and connected with screws. The output shaft of the transmission motor forms a right angle with the axis of the shaft of the motor and either forms the drive shaft of the eccentric drive directly or, as in the illustrated embodiment, is connected thereto in co-axial relationship by way of a coupling. The drive shaft of the eccentric drive, the eccentric shaft 17, is mounted rotatably in the eccentric carrier 22 and carries an eccentric in the form of a part fixedly connected thereto. The eccentric shaft passes with the eccentric through a corresponding cut-out thrust ring 20. The eccentric shaft 17 is driven in rotation by the motor/transmission unit by way of the shaft coupling when the motor 2 is actuated and further drives the thrust ring 20 in an inside surface of its cut-out opening, namely the running contact surface with the outside surface of the eccentric. The thrust ring 20 drives a thrust rod 19 which is fixedly connected thereto, for example being injection-moulded there. The unit consisting of the thrust ring 20 and the thrust rod 19 is supported longitudinally slideably in two sliding bushes. The axis of the eccentric shaft 17 and the longitudinal axis 18 of the thrust ring 20 and the thrust rod 19 are respectively disposed in the horizontal plane and form a right angle to each other. One of the two bushes 26 for the thrust rod 19 is supported in a bearing disk 24 which at the pressure head end is fixed to the eccentric carrier 22. A further bush 27 which accommodates the trunnion, that is remote from the metering head side, of the thrust ring 20 is fitted in the stroke adjusting pin 8. An adjusting member 7 which is to be actuated by hand for adjustment of the stroke adjusting pin 8 is screwed into a thread of the eccentric carrier 22 on the same axis as the longitudinal axis 18 of the thrust rod 19; the thread limits the axial movement of the thrust ring 20 in the suction phase and thus in the stroke of the metering pump.
In addition the housing contains the electronic control system in its lower part in a closed-off space, the electronic housing 29.
Arranged on the same axis as the longitudinal axis 18 of the thrust rod, on the side opposite the control lines 10, is a metering head 12 in which a diaphragm 13 made for example from plastic material operates as the displacement member, the diaphragm being fixedly clamped at its periphery. The metering head 12 further carries an inlet valve 14 and an outlet valve 15 to press the medium to be sucked in by way of the inlet vale 14 between the diaphragm 13 and the metering head 12 in the metering chamber 16 into the metering line by way of the outlet valve 15. The metering pump operates in accordance with the volumetric principle, that is to say in each stroke a predetermined volume is to be sucked in on the one hand and expelled by way of the outlet valve 15 on the other hand. The diaphragm 13 is displaced in an oscillating movement by means of the eccentric drive which reciprocates the thrust rod 19 on the longitudinal axis. Arranged between the thrust ring 20 and a shoulder of the disk 24 is a compression spring 23, for example a coil spring, which causes the thrust ring 20 to bear against the eccentric in positively locking relationship at any moment in time. In the forward phase of the eccentric movement, that is to say in the movement of the thrust rod towards the metering head, the thrust ring with the thrust rod is moved towards the compression spring, at the same time the diaphragm 13 is pressed into the metering chamber 16, with the consequence that an increased pressure is produced in the metering chamber, the outlet valve 15 opens and the medium to be metered is pressed into the metering line. In the return phase of the eccentric movement, that is to say in the movement of the thrust rod away from the metering head, the thrust ring 20 is moved in the opposite direction in relation to the stroke adjusting pin 8 by the compressed compression spring 23 which for example can be in the form of a coil spring, to follow the eccentric movement, with the result that the thrust rod 19 connected to the diaphragm 13 entrains the diaphragm in its movement, whereby in the metering chamber 16 there is a reduced pressure which opens the inlet valve 14 so that medium to be metered can be sucked a further time into the metering chamber.
a diagrammatically shows the variation in time of the torque (above) and the movement of the displacer element (below) over a stroke period.
The movement of the displacer element is substantially sinusoidal. During a pressure stroke hD the displacer moves from the minimum deflection SMIN to the maximum deflection SMAX. During the subsequent suction stroke the displacer is moved from the maximum deflection SMAX back to the minimum deflection SMIN. The total stroke period H is composed of the pressure stroke hD and the suction stroke hS. If the torque shown above in
The variation in the torque during the pressure stroke hD is here also substantially sinusoidal and depends on the transmission characteristic. At the beginning and the end of the pressure stroke hD the force to be applied is very low by virtue of the transmission step-up ratio. Therebetween it rises to the maximum value M1.
b diagrammatically shows the variation in time of the torque (above) and the movement of the displacer element (below) over a stroke period, wherein the situation is shown here in which only a partial stroke is performed.
If the displacement element can no longer be moved back to the minimum deflection SMIN, either because an adjustable abutment limits the stroke length or because the stroke length is limited for other unpredictable reasons, only a partial stroke is performed. It will be seen from the diagrammatic view of the displacer movement, shown at the bottom in
It will also be seen at the top in
Blockade detection is also possible. While in the known embodiments a position sensor would have to detect the position of the displacement member, and then a blockade which under some circumstances has occurred could be deduced therefrom, the embodiment according to the invention provides that the pump is switched off if the torque to be applied by the motor exceed a predetermined limit value. Blockade shut-down according to the invention can therefore under some circumstances prevent damage to the motor.
It will be appreciated that blockade detection can also be such that a blockade situation is assumed to apply when the predetermined limit value is exceeded at a given moment in time or over a period longer than a predetermined period. It is also possible for the predetermined limit value to be deduced from the eccentric position, that is to say it is possible for the predetermined limit value to be adapted to be variable in time.
An incomplete suction stroke can be determined in this same manner.
b shows the same situation in the case of a partial stroke. From the time shift tV it can be deduced that an incomplete suction stroke has occurred and suitable measures can optionally be taken in order nonetheless to maintain the metering effect or a corresponding error signal can be outputted.
The method according to the invention further permits slippage detection within the stroke travel and optionally immediate stabilisation control also within a stroke period. While the rotary speed is usually determined by way of measurement of the stroke and the rotary speed is optionally adapted for the entire stroke, in the preferred embodiment it is provided that the torque is adapted with increasing slippage within a pressure and suction stroke.
For illustration purposes
That measure provides that the length of the pressure stroke is reduced and also the length of the stroke period is adjusted to its ideal value while the length of the pressure stroke and the stroke period would increase in length due to the reduction in speed.
The method according to the invention therefore makes it possible to keep the metering output constant, even at a high load which would otherwise lead to a reduction in rotary speed.
The method according to the invention therefore makes it possible to deduce the hydraulic pressure, that is to say the working pressure, from the torque. Thus it is possible for example to determine the torque generated by the motor and to compare it to a reference torque and, upon a deviation between actual torque and reference torque of for example more than 30%, to stop the pump to prevent an overload and thus to protect the drive from self-destruction.
As already stated the pressure and suction stroke involves flexing of the displacement diaphragm so that the metering volume depends on the working pressure.
If the method according to the invention allows the working pressure to be determined from the motor core parameters, the metering error can be corrected in dependence on the ascertained working pressure. A further advantage of the method according to the invention is that in principle any motion curve of the displacement member can be set. Thus for example metering and suction intake can be effected at a constant reduced speed, by the variation in speed being compensated on the basis of the deflection angle of the eccentric, whereby uniform metering occurs and the necessary peak power output of the motor is reduced. In addition it is possible to implement an electronic suction intake assistance upon first filling of the suction intake line and the metering head (start-up of operation) if for example the motor is operated in the pendulum stroke mode and the full stroke length is performed in the suction intake situation.
In addition it is possible to actuate the motor in need-oriented relationship at any moment in time by predictive adaptation of the motor actuating parameters along the stroke travel as the rise in torque is known by virtue of the eccentric. In that way the motor can be operated in more energy-saving fashion.
It is known that cavitation can occur, leading to incomplete suction intake and increased material wear, for example in the valves. The described evaluation of the variation in force and/or the movements involved make it possible to detect the cavitation in the suction stroke and it is possible to immediately take counter-measure such as for example throttling the intake suction speed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2010 003 218.2 | Mar 2010 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/054264 | 3/21/2011 | WO | 00 | 12/6/2012 |
