US20150159646A1

US20150159646A1 - Sensorless disturbance detection in metering pumps with stepping motor

Info

Publication number: US20150159646A1
Application number: US14/557,634
Authority: US
Inventors: Gregor Stiehl; Jens Kaibel
Original assignee: Prominent GmbH
Current assignee: Prominent GmbH
Priority date: 2013-12-05
Filing date: 2014-12-02
Publication date: 2015-06-11
Also published as: EP2881584A1; CN104763622A; DE102013113576A1; EP2881584B1

Abstract

The present invention concerns a method of sensorless detection of functional disturbances of a positive displacement pump (1), wherein the positive displacement pump (1) has a moveable positive displacement element (5) having a boundary surface (A_G) which delimits a metering chamber (3), wherein the metering chamber (3) is connected to a suction and a pressure line (6, 7) by way of valves (8, 9) so that fluid (F) to be conveyed can alternately be sucked into the metering chamber (3) by way of the suction line (6) and pressed out of the metering chamber (3) by way of the pressure line (7) by an oscillating movement of the positive displacement element (5) and wherein there is provided a stepping motor (13) as a drive for the oscillating movement of the positive displacement element (5). To provide a method of detecting functional disturbances of a positive displacement pump without additional sensors being required according to the invention it is proposed that a motor moment (M_M) provided by the stepping motor (13) is ascertained and a warning signal is delivered when the ascertained motor moment (M_M) fulfils a first predetermined criterion.

Description

This application claims the benefit of German Patent Application 102013113576.5 filed Dec. 5, 2013.
The present invention concerns a method of sensorless detection of functional disturbances of a positive displacement pump, wherein the positive displacement pump has a moveable positive displacement element having a boundary surface which delimits a metering chamber, wherein the metering chamber is connected to a suction and a pressure line by way of valves so that fluid to be conveyed can alternately be sucked into the metering chamber by way of the suction line and pressed out of the metering chamber by way of the pressure line by an oscillating movement of the positive displacement element and wherein there is provided a stepping motor as a drive for the oscillating movement of the positive displacement element.
Positive displacement pumps are known in different design configurations. In one configuration a surface of a moveable positive displacement element acting as a boundary surface delimits a metering chamber. The positive displacement element and therewith the boundary surface of the metering chamber can be reciprocated between two extreme positions. The volume of the metering chamber is increased and reduced as a result. The respective position of the boundary surface thus determines the currently prevailing volume of the metering chamber. In the first extreme position of the boundary surface the volume of the metering chamber is at a minimum while it is at a maximum in the second extreme position. When therefore the boundary surface is moved from its first extreme position into the second, the volume of the metering chamber is thereby increased or the pressure in the metering chamber falls. The resulting reduced pressure results in closure of the valve between the metering chamber and the pressure line and opening of the valve between the metering chamber and the suction line so that the fluid to be conveyed is sucked into the metering chamber by way of the suction line. In the return movement of the boundary surface from the second extreme position into the first extreme position the volume of the metering chamber is reduced again or the pressure in the metering chamber rises. Due to that increased pressure the valve between the metering chamber and the suction line is closed while the valve between the metering chamber and the pressure line is opened. The increased pressure in the metering chamber conveys the fluid to be conveyed out of the metering chamber into the pressure line. Accordingly fluid to be conveyed is alternately sucked into the metering chamber from the suction line and then conveyed into the pressure line from the metering chamber by virtue of the oscillating movement of the positive displacement element and the boundary surface between the two extreme positions.
The drive for such a positive displacement pump can be based on different physical drive principles. For example hydraulically or electromagnetically driven pumps are known. Thus in particular a stepping motor can serve as the drive for the oscillating movement of a positive displacement element. Such a stepping motor generally has a rotor, that is to say a rotatable part of the motor, with a shaft. The rotor can be rotated through a minimum angle or a step or a multiplicity thereof by a controlled, stepwise-rotating electromagnetic field of a plurality of stator coils, that is to say a plurality of coils arranged on a non-rotatable part of the motor. That rotary movement is converted by means of a thrust rod or connecting rod or the like into a translatory movement for the alternating reciprocating movement of the positive displacement element. In addition stepping motors are also known in the form of linear motors in which a stepwise translatory movement of a moveable part of the motor between two extreme positions is produced directly by means of electromagnetic force generation, which translatory movement can be transmitted directly to a positive displacement element. In that case therefore the two extreme positions of the positive displacement element generally correspond to the two extreme positions of the moveable part of the motor.
Stepping motors are distinguished in particular by a high level of robustness and a long service life. As stepping motors move in individual steps or through a plurality thereof it is possible in principle for the electronic motor system or control system to also count the steps and on the basis thereof to determine a current rotor position. It will be noted however that a mechanical loading on the motor leads to the production of a so-called load angle, that is to say a deviation between the rotation of the electromagnetic field of the stator and the mechanical rotation of the rotor. In that respect a distinction can be drawn between a static load angle and a dynamic load angle. The static load angle is the angle through which the rotor of a stepping motor is rotated relative to the electromagnetic lock-in position, that is to say the main direction of the electromagnetic field generated by the stator coils, under a statically acting rotary moment. In comparison the dynamic load angle is the angle through which the rotating rotor is moved away at a given moment in time from the electromagnetic lock-in position which is predetermined by the last pulse of the stepping cycle. Those definitions also apply in corresponding form to linear stepping motors.
The movement of the rotor in the electromagnetic field of the stator coils causes in those coils a counter-induced voltage, the so-called counter-EMF. The counter-EMF is superimposed with the voltage applied to the coils, thereby generating a phase shift between rotor and stator rotary field, corresponding to the level of the counter-EMF. The rotor trails the electromagnetic rotary field of the stator, the phase shift being proportional to the applied load. If the load moment occurring exceeds a critical value then the stepping motor falls out of step, that is to say it drops out. In the extreme case the motor comes to a stop.
In stepping motor drives therefore position detection is typically implemented by means of a reference signal, for example by means of a Hall sensor. In that case for example a small permanent magnet is fixed to the output shaft of the drive. A stationary Hall sensor produces a signal in the passage of the magnet in a given rotary angle position of the shaft. Therefore an absolute position is detected for each revolution, which can be compared to a positioning assumed in the control system. When using the stepping motor as a drive for a positive displacement pump however that can lead to problems with the metering accuracy in the case of partial stroke movements or partial cycles. If the stepping motor comes to a stop because of excessively high loads that has the result that the conveyor function fails in spite of actuation of the drive unit.
The stroke period duration which is identical to the rotational duration of the rotor can be determined by means of a measured reference signal. It is possible to infer a disturbance-free implementation of the metering process from that stroke period duration. In the event of delays or indeed blockage of the metering stroke because of over-pressure situations the signal of the Hall sensor does not appear or is delayed. That non-appearance or delay can be used as the basis for the production of a disturbance message and for implementing further reactions. It will be noted however that this information is always present only after the expiry of a monitoring interval, that is to say generally a rotational duration of the rotor or a pump cycle. To avoid that time delay the state of the art uses an additional position sensor which at any moment in time in the metering stroke determines the speed or position of the positive displacement element in relation to the actuation of the motor and can detect a blockage practically without any delay. It will be appreciated however that such an additional position sensor complicates the structure of the pump system whereby it becomes more susceptible to faults and more expensive.
DE 10 2011 000 569 A1 describes an alternative method and a circuit arrangement with which in the case of a stepping motor a load angle of the motor can be detected in sensorless fashion in order to determine therefrom the level of a mechanical load at the motor shaft.
If a stepping motor is used to drive a positive displacement pump then the load on the drive is given essentially by the counter-pressure of the fluid to be conveyed in the metering chamber, which acts in opposition to the positive displacement element. To monitor the pump operation that counteracting pressure in accordance with the state of the art is measured by means of additional sensors, for example by means of a pressure sensor arranged in the metering head.
Such an additional sensor however again complicates the structure of the pump system and by virtue of its necessary arrangement in the metering head leads in particular to additional sealing problems and increased costs.
Taking the described state of the art as the basic starting point therefore the object of the present invention is to provide a method of detecting functional disturbances in a positive displacement pump without additional sensors being required.
According to the invention that object is attained in that a motor moment provided by the stepping motor is ascertained and a warning signal is delivered when the ascertained motor moment M_Mfulfils a first predetermined criterion.
If the ascertained motor moment of the stepping motor rises as a consequence of the load on the positive displacement pump beyond a given motor-specific value it is possible to infer that there is an overload condition. Consequently it can be assumed that at least some steps of the stepping motor could be lost or indeed have already been lost. The extreme case may involve a motor stoppage. Accordingly the positive displacement pump no longer enjoys metering accuracy. If therefore the motor moment fulfils a first predetermined criterion which is related to a parameter characterising the transition from the normal state of the motor to an overload state, that is to say a corresponding motor-specific value, it is then possible on the basis of the warning signal produced to detect such an overload state. Further consequential measures can be initiated based thereon.
The first predetermined criterion can be both directly related to the motor moment involved, that is to say it can be a given value for the motor moment, and also an indirect criterion, that is to say further parameters are derived from an ascertained value for the motor moment, to which parameters the criterion is to be related.
Sensorless detection in accordance with the present invention means that a corresponding sensor is not provided either within the metering head of the positive displacement pump or within the stepping motor, that is to say in the region of its moving components.
According to the invention therefore the stepping motor can be designed both with and also without a transmission.
In an embodiment the first predetermined criterion takes account of at least one of the following parameters: the proportion of the motor moment M_Mapplied by the stepping motor to the positive displacement element as the gross drive force F_b, the proportion of the gross drive force F_bapplied to the fluid to be conveyed by the positive displacement element as the net drive force F_n, and the conveyor pressure p_Facting on the fluid to be conveyed in accordance with the relation p_F=F_n/A_G.
From an ascertained motor moment it is possible to determine the gross drive force applied to the positive displacement element for a known positive displacement pump on the basis of a suitable model of the drive kinematics in normal operation. Generally the rotary movement of the stepping motor is converted into a translatory movement by means of a thrust rod. The rod force or translatory force applied to the positive displacement element is less in principle than the motor moment provided by the motor, because of losses. That rod force represents the gross drive force for the positive displacement element in the translatory direction.
However the net drive force F_ntransmitted in fact to the fluid to be conveyed by the translatory movements of the positive displacement element between a first and a second extreme position differs generally again from the provided gross drive force F_b. At least the transmitted net drive force F_nis less. The reason for this is the additional force requirement for further components of the positive displacement pump, which are also involved in the mechanics. The influence of those components however can usually be presumed to be known so that the net drive force remaining for the conveyor process can be ascertained, taking those losses into account.
The net drive force F_ntransmitted to the fluid to be conveyed, in accordance with the present invention, includes both a pressure force applied to the fluid to be conveyed when producing an increased pressure and also a pulling force when a reduced pressure is produced.
On the basis of the net drive force F_nit is possible to determine the conveyor pressure p_Facting on the fluid to be conveyed in accordance with the relation p_F=F_n/A_G. In that case the boundary surface A_Grepresents the operative surface of the positive displacement element, acting on the medium to be conveyed. The magnitude of the boundary surface A_Gis known as being governed by the structure involved. It will be appreciated that, in the case of an elastically deformable positive displacement element, temporary changes in the boundary surface A_G, that is to say an effective boundary surface, instead of the structurally predetermined static boundary surface, are possibly to be taken into consideration. However the need for such additional corrections depends crucially on the accuracy of the measurements, that is to be achieved. If an approximate maximum or minimum value for the currently prevailing conveyor pressure is sufficient the recommendation is that only the maximum or minimum value possible within a conveyor period in respect of the effective boundary surface for A_Gis to be used, without taking account of the actual currently prevailing value.
The above-mentioned parameters can be taken into consideration for example by the predetermined criterion insofar as the criterion is based on the gross drive force F_b, the net drive force F_nor the conveyor pressure P_Fand can be calculated back from the respective value to a suitable threshold value for the motor moment. That calculated threshold value for the motor moment can be used as the predetermined criterion. The criterion is deemed to be met when the calculated threshold value is reached or exceeded as the upper threshold value or however the value reaches or falls below same as a lower threshold value. As an alternative thereto it is possible to calculate from the ascertained motor moment M_M, in particular if further parameters are of interest, a gross drive force F_b, a net drive force F_nor a conveyor pressure p_Ffor that motor moment, and a given value can be used as the threshold value for the calculated parameter, as the first predetermined criterion. If the calculated parameter meets that criterion, that is to say if it reaches or exceeds or falls below that threshold value, then a warning signal is produced. That second alternative is advantageous in particular when one or more of those additional parameters are also to be adopted for further analysis of the behavior of the positive displacement pump.
In an embodiment in addition at least the gross drive force F_b, the net drive force F_nor in accordance with the relation p_F=F_n/A_Gthe conveyor pressure p_Fis determined.
By determining those parameters it is possible for the operative condition or functional condition of the positive displacement pump to be more accurately characterised and monitored. Thus, besides possible functional disturbances in the stepping motor it is also possible to detect disturbances with further components of the pump system. For example functional disturbances in sensitive component parts are conceivable, by virtue of an excessively high pressure which however is still not so high that it causes functional disturbances with the stepping motor. If the conveyor pressure is determined, it is possible to establish whether such problems threaten or indeed are already present. In addition it is possible for example to infer a leak from a drop in the conveyor pressure.
In an embodiment a warning signal is delivered when the gross drive force F_b, the net drive force F_nor the conveyor pressure p_Ffulfils the first predetermined criterion.
As already described hereinbefore the provided motor moment M_Mcan also meet a first predetermined criterion by the gross drive force F_b, the net drive force F_nor in accordance with the relation p_F=F_n/A_Gthe conveyor pressure p_Fbeing determined on the basis of the motor moment and by an output signal being produced when that gross drive force, that net drive force or that conveyor pressure fulfils the first predetermined criterion.
In an embodiment the respective criterion is so selected that a warning signal is delivered when the corresponding parameter from the group consisting of the motor moment M_M, the gross drive force F_b, the net drive force F_nand the conveyor pressure p_Freaches or exceeds a first predetermined threshold value or the corresponding parameter reaches or falls below a second predetermined threshold value.
By predetermining a first and a second threshold value it is possible to define a range for the parameters to be monitored, which represents the desired operating range of the positive displacement pump in normal operation. If there is a departure from that predetermined range then it is possible to infer therefrom that there are malfunctions in the system, either in respect of the stepping motor or the positive displacement pump. Exceeding the first threshold value generally points to an overload situation whereas if the parameter falls below the second threshold value that points for example to a pressure drop as a consequence of a leak or a functional disturbance in the stepping motor itself. In the last-mentioned case a sufficient torque is no longer produced by the motor, which indicates a functional disturbance independent of the load situation.
In an embodiment the first criterion is so selected that the warning signal is delivered when a weighted sum of the relative deviations of the motor moment M_Mand at least one further parameter from the group consisting of the gross drive force F_b, the net drive force F_nand the conveyor pressure p_Ffrom a respective threshold value reaches or exceeds a predetermined value.
In that case the respectively relative deviation from a threshold value is detected for at least two parameters. Those at least two deviations are summed in weighted relationship. If the weighted sum reaches or exceeds a predetermined value then the criterion is deemed to be met and a warning signal is delivered. Thus, in particular non-linear relationships between the individual monitoring parameters can be taken into account in the detection of functional disturbances with the positive displacement pump.
In an embodiment the motor moment M_Mof the stepping motor is detected by ascertaining the phase shift of the motor voltage U_Mrelative to the motor current I_M, which is caused by a voltage U_indcounter-induced by virtue of the load angle δ_Lof the stepping motor.
The rotation of the rotor in the electromagnetic field generated by the stator leads to a counter-induced voltage, that is to say counter-EMF, in the stator coils. The counter-EMF causes a phase displacement in respect of the effective motor voltage relative to the motor or coil current. The corresponding currents trail the voltages in that case by a given phase angle. Upon a change in the loading on the motor the load angle changes, more precisely the dynamic load angle, and consequently the counter-EMF. In other words, the phase angle between the motor current and the motor voltage also changes, in which case the phase shift between current and voltage generally decreases with increasing load. The phase shift between motor voltage and motor current is therefore correlated with the load angle and makes it possible to determine same. By taking off the motor current and the motor voltage or ascertaining the phase shift between those parameters, it is easily possible to determine the motor moment M_Mproduced. That can be implemented without complicated and expensive structural modifications on the stepping motor, in particular without additional complicated and expensive sensor arrangements, by means of the stepping motor electronic system which is already present or which is slightly adapted. On the basis of the ascertained torque it is possible to determine further parameters which are characteristic of operation of the positive displacement pump like gross drive force F_b, net drive force F_nor conveyor pressure P_F.
Taking off the motor current and motor voltage in that way by means of the electronic motor system which thus additionally serves as a suitable ascertainment device represents sensorless detection in accordance with the present invention.
In an embodiment the gross drive force F_bapplied to the positive displacement element by the stepping motor is determined on the basis of a model of the drive kinematics of the stepping motor and the positive displacement element.
In the known structure of the pump system comprising the stepping motor and the positive displacement element the use of a suitable model of the drive kinematics is a suitable way of determining the gross drive force. Such a model describes in particular the conversion of the rotary movement of the stepping motor into the translatory movement which is transmitted to the positive displacement element. In the case of a stepping motor in the form of a linear motor that model is naturally simplified to afford a simple direct relationship which depends substantially on possible friction losses.
In an embodiment the positive displacement pump is a metering pump, preferably a diaphragm pump having a positive displacement element in the form of a metering diaphragm.
A metering pump is a positive displacement pump which supplies defined volumes per stroke or per time independently of the pressure conditions at the inlet and outlet of the metering pump. A metering pump in the form of a diaphragm pump is distinguished in particular by its insensitivity in relation to continuous loading and impurities in the fluid to be conveyed. The drive is shielded from impurities in the fluid to be conveyed by the positive displacement element in the form of a diaphragm and thus one of the serious disadvantages of conventional piston pumps, namely the problem of sealing off the piston, is resolved. Accordingly the method described here for sensorless detection of functional disturbances is appropriate in particular in the case of a diaphragm pump. As already discussed in the opening part of the this specification additional sensors generally lead to problems with sealing. Accordingly when using suitable sensors in a diaphragm pump there is the risk that the desired sealing advantage of the diaphragm pump is negated again by use of the sensors.
It is precisely in relation to metering pumps with which volumes which are measured off as precisely as possible are to be conveyed that detection of functional disturbances is essential. It is only in that way that it is possible to ensure that a given necessary metering accuracy can be maintained. If such faults in metering accuracy, which are based on functional disturbances in the stepping motor or the further pump system, are not detected, there is the risk that corresponding consequential faults occur in further use of the fluid being conveyed.
In an embodiment the net drive force F_napplied to the fluid to be conveyed is determined from the gross drive force F_bby subtraction of force components not applied directly to the fluid to be conveyed, in particular by subtraction of the deformation force F_Vnecessary for deformation of the metering diaphragm and/or a force F_Fnecessary for stressing a spring element, by means of which the metering diaphragm can be stressed in the direction of the pressure position or in the opposite direction.
To determine the net drive force F_napplied to the fluid to be conveyed, at least to a suitable approximation, the force requirement for such components of the pump which are involved in the mechanism for the transmission of force to the fluid to be conveyed is to be taken into consideration. In the case of a diaphragm pump with metering diaphragm that is in particular the deformation force F_Vwhich is necessary for deformation of the diaphragm and which is not transmitted to the fluid to be conveyed. If in addition there is provided a spring element, that is to say for example a return spring or a stroke assistance spring, for stressing the positive displacement element or the metering diaphragm, the force F_Fnecessary for that purpose is also to be taken into account when stressing the spring element or, in the case of a spring element which is already prestressed, the additionally assisting stressing force.
The spring element can generally be both in the form of a return spring and also in the form of a stroke assistance spring. In the case of the spring being in the form of a return spring the spring element is also stressed when a pressing force is applied to the fluid to be conveyed by the stepping motor. In that case a part of the gross drive force F_bafforded by the stepping motor is used for prestressing the return spring and thus the metering diaphragm in the direction of the pressure position. If then the direction of movement of the positive displacement element or the metering diaphragm is reversed so that the volume of the metering chamber is increased again then the prestressed return spring is relieved of stress. In that case the pulling force applied to the fluid to be conveyed is increased by delivery of the stored stress energy. When the spring is in the form of a stroke assistance spring the stroke assistance spring is also stressed when the stepping motor applies a pulling force to the fluid to be conveyed. In that case a part of the gross drive force F_bprovided by the stepping motor is used for prestressing the stroke assistance spring. Compared to a return spring therefore the prestressing takes place in the opposite direction. If then the direction of movement of the positive displacement element is reversed so that the volume of the metering chamber is reduced the prestressed stroke assistance spring is relieved of stress. In that case the stress energy which is now transmitted from the stroke assistance spring increases the pressure force applied to the fluid being conveyed. Thus the stored stress energy in the case of a return spring is delivered as an additional pulling force, while in the case of a stroke assistance spring it is delivered as an additional pressure force.
In regard to subtraction of the force F_Fnecessary for stressing a spring element the following is generally to be considered: if the net drive force F_napplied to the fluid to be conveyed is to be ascertained only as an average force averaged over a full pump cycle then in the subtraction process essentially only the energy losses due to friction are to be taken into consideration as the energy received by a spring element in half a cycle is delivered again in the next half cycle except for corresponding frictional losses. In that respect a pump cycle means the period of time that the positive displacement element requires to pass from an extreme position back into the same position again. In that respect a first extreme position of the positive displacement element is a position in which the volume of the metering chamber is at a minimum while a second extreme position is a position in which the volume is at a maximum.
If a net drive force F_napplied in point form to the fluid to be conveyed is to be ascertained then two cases are to be distinguished in dependence on the configuration of the spring element and the stage of movement of the pump: if a part of the gross drive force F_bcurrently provided by the stepping motor is used precisely for stressing the spring element then that proportion of force is to be subtracted from the gross drive force F_bfor ascertaining the currently prevailing net drive force F_n. If however it is precisely a part of the stress energy stored in the spring element that is delivered by the spring element to support the gross drive force F_bthen that additional force component is to be added to the gross drive force F_bto ascertain the current prevailing net drive force F_n.
In an embodiment a plurality of criteria are predetermined and when a criterion is fulfilled a warning signal characteristic of the respective criterion is delivered.
A plurality of criteria make it possible on the one hand to be able to set respective specific criteria for the various parameters, that is to say the motor moment M_M, the gross drive force F_b, the net drive force F_nand the conveyor pressure p_F. That can be effected for example by presetting suitable individual threshold values for the individual parameters. On the other hand a plurality of criteria can be provided for one and the same parameter. Thus for example a first criterion can serve only as an indicator for a given operating condition of the positive displacement pump without a functional disturbance already being implied thereby. If a further criterion is met that can indicate a shift in the operating condition for example from normal operation to the overload range. A third criterion can point to operation outside the normal condition and thus possible functional disturbances. Finally a fourth criterion can characterise a severe functional disturbance which requires immediate action.
In an embodiment a fault event is associated with each criterion and when a criterion is fulfilled an associated fault event is diagnosed, in particular an overload and/or a stoppage of the stepping motor.
As already indicated above the criteria can stand for different operating conditions or operational disturbances of graduated severity and identify same, in which case an overload or indeed a stoppage of the stepping motor generally represent the most severe disturbances. Equally however the fact that the value falls below one or more threshold values can also indicate a functional disturbance in the stepping motor itself or for example a drop in pressure because of a leak.
In an embodiment a delivered warning signal is sent to an automatic shut-down means which shuts down the pump in response to the receipt of the warning signal.
Such an automatic shut-down is advantageous in particular when the warning signal is produced on the basis of a criterion which stands for a severe functional disturbance of the pump, for example an overload or a stoppage of the stepping motor. The criterion can be a predetermined conveyor pressure, in which case the pump is shut down when that threshold value is exceeded by the ascertained conveyor pressure. Such overload protection in the form of monitoring for when threshold values are exceeded serves to protect the positive displacement pump and also further components of the installations in which such positive displacement pumps are usually employed. In that case the threshold value can be the maximum pressure which is structurally permissible for the positive displacement pump or a value just above the maximum pressure, that is to say for example between 10% and 20% above. In that case the maximum pressure is the maximum pressure at which the stepping motor can be operated without the risk of stepping losses. Likewise however the threshold value can also lie within the permissible operating range of the positive displacement pump in order for example to protect other parts of the installation which are more sensitive to pressure and which are already endangered at lower pressures than the maximum pressure which is permissible for the stepping motor. Shut-down however can also be implemented because of a considerable drop in pressure as a consequence of a leak.
Finally in an embodiment a delivered warning signal is sent to an output device which outputs an acoustic and/or visual warning indication characteristic of the warning signal in response to the receipt of the warning signal.
Such a warning indication can generally serve to display the currently prevailing operating condition to the exterior. On the other hand as an acute warning indication it can attract the attention of a person responsible for operation of the installation and in particular the pump to an acute functional disturbance and can cause implementation of further measures. Such indications can be for example signal lamps which are arranged in the region of the pump and which indicate the operating condition or a disturbance to the pump upon checking on site. If there are provided different lamps for different operating conditions, the lamps can advantageously be of differing colors. Thus a normal operating condition, a condition deviating from the normal operating condition and a disturbed or critical operating condition can be displayed by means of different colors, for example green, orange and red. In the case of more complex installations however the indication can also be effected by way of a central display unit, for example a monitor. Particularly in the case of severe functional disturbances which require immediate or direct action without a great waste of time, an acoustic warning indication is advantageous. That is not dependent on the direction of view of the person for whom the indication is intended and whose attention is to be attracted.

Further advantages, features and possible uses of the present invention will now be clearly apparent from the following description of a preferred embodiment and the accompanying FIGURE in which:

FIG. 1 shows a diagrammatic view of a metering pump with metering diaphragm whose functional condition is monitored by means of the method according to the invention.

The FIGURE shows a positive displacement pump 1 in the form of a metering pump in the form of a diaphragm pump, having a metering head 2. A metering chamber 3 is arranged in the metering head 2. The metering chamber 3 is delimited by internal side walls 4 of the metering head 2 and a boundary surface A_Gof the positive displacement element 5 in the form of a metering diaphragm. The metering chamber 3 is connected to a suction and a pressure line 6 and 7 respectively by way of valves 8, 9.
The metering diaphragm 3 is connected moveably to a thrust rod (not shown) by way of a connecting element 10. The thrust rod fits to the rotor (not shown) of a stepping motor 13, with or without transmission. That thrust rod converts the rotary movement of the rotor into a translatory movement of the connecting element 10 and the diaphragm 5 between two extreme positions E₁, E₂. Arranged between the metering head 2 and the thrust rod around the connecting element 10 is a spring element 12, more precisely a return spring or a stroke assistance spring.
When the metering diaphragm 5 is moved from a first right-hand extreme position E₁(indicated as a broken line) into a second left-hand extreme position E₂(shown with continuous lines) the metering chamber 5 increases whereby a reduced pressure is produced. As a consequence of that reduced pressure the valve 9 on the pressure line 7 closes and the valve 8 on the suction line 6 opens. As a result the fluid F to be conveyed is sucked out of the suction line 6 into the metering chamber 3 and at the same time, due to the movement of the connecting element 10, the spring element 12 in the case of a configuration in the form of stroke assistance spring is prestressed. When then the diaphragm 5 is moved back out of the second extreme position E₂into the first extreme position E₁again that movement is assisted by delivery of the stress energy stored in the stroke assistance spring 12. Equally the spring element 12 can be in the form of a return spring, in which case the return spring 12 is prestressed in a movement of the connecting element 10 from the second extreme position E₂into the first extreme position E₁. In that situation the return spring 12, with the spring force F_Estored therein in the form of stress energy assists with a return movement from the first extreme position E₁into the second extreme position E₂. A movement of the diaphragm 5 into the first extreme position E₁leads to a reduction in the volume of the metering chamber 3 whereby an increased pressure is produced. As a consequence of that increased pressure the valve 8 on the suction line 6 closes and the valve 9 on the pressure line 7 opens. As a result the fluid F present in the metering chamber 3 is pressed into the pressure line 6.
As long as the stepping motor 13 having a rotor and a stator (not shown) is functioning faultlessly and in particular is not overloaded the rotor, following the electromagnetic stator rotary field, passes stepwise at a constant speed through a plurality of provided discrete lock-in positions. Accordingly the metering diaphragm 5 is moved with an alternating reciprocating movement stepwise between the two extreme positions E₁, E₂, which leads to constant conveyance of the fluid F with a predetermined metering accuracy. By virtue of the torque M_Mprovided by the stepping motor 13 both the gross drive force F_bapplied to the positive displacement element 5 and also the net drive force F_napplied to the fluid F as well as the conveyor pressure p_Fcan be ascertained. The operation of ascertaining those conveyor parameters, in particular ascertaining the motor moment M_M, is effected by means of an ascertaining device 14 as a component part of the electronic motor system.
If the stepping motor 13 goes with its provided motor moment M_Mto its power limit there is the risk of functional disturbances as far as stoppage of the stepping motor 13. That endangers in particular the metering accuracy of the pump 1. It will be appreciated however that high torques M_Mwhich are still within the permissible operating range of the stepping motor 13 can already result in conveyor pressures p_Fwhich are possibly problematical for further components of the installation in which the pump 1 is arranged. To prevent damage to or functional disturbances of such components it is also possible to appropriately provide as a criterion a conveyor pressure p_Fat which the stepping motor 13 is still operating in disturbance-free fashion. For that purpose a target value S for the motor moment M_Mis advantageously preset. The electronic motor system 14 actuates the stepping motor 13 in such a way that the motor moment M_Mactually produced corresponds to the preset value. In that case the motor moment M_Mproduced can be ascertained by means of the device 14 and compared to the target value S. That comparison between the target value S and the ascertained motor moment M_Mcan serve as a basis for detection and signaling of a functional disturbance in accordance with a predetermined criterion. It is equally generally conceivable that such a comparison is used to regulate the motor moment M_Mby means of the electronic motor system 14 in such a way that it corresponds to the target value S or lies within a predetermined range around the target value S.
If now a predetermined criterion is fulfilled and a warning signal is produced then for example a visual warning indication can be output on the basis of that warning signal, the warning indication reproducing the operating condition of the metering pump 1, that is characterised by that criterion, so that it can be recognized outwardly. The operating condition to be indicated can be for example the normal operation of the pump 1 if the criterion is the torque intended for the pump 1 as the target value S in normal operation. It can however also be operation in the elevated load range if the criterion is for example a threshold value in the form of a torque which is at the upper end of the range that is permissible for the pump. Finally it can also be a critical condition if the criterion is a torque value above the maximum value which is permissible for the stepping motor 13. Besides that the criterion as well as the operating condition linked thereto can also be dependent on further components of pump 1 or the installation in which the pump 1 is arranged. If attention is directed to such further components then in particular a criterion is recommended, which takes account of the conveyor pressure p_Fproduced by the generated motor moment M_M. In that case for example a stricter criterion than the maximum value can be provided for the motor moment M_M. It is equally conceivable that a respective independent criterion is applied to the motor moment M_Mand also to the conveyor pressure p_Findependently of each other. Finally however it is also possible to form a weighted sum of the deviation of both values, that is to say the motor moment M_Mand the conveyor pressure p_Ffrom a respective threshold value. Advantageously an automatic shut-down system shuts down the pump 1 in response to receiving a corresponding warning indication in order to avoid damage to the installation and consequential problems as a result of defective metering operations.
The operation of determining the produced motor moment M_Mis effected by means of an ascertaining device 14 of the electronic motor system on the basis of a counter-EMF measurement at the stepping motor 13, in which the phase shift δ_UIbetween motor voltage U_Mand motor current I_Mis evaluated. Such evaluation on the basis of electrical measurement parameters of the electronic motor system 14 of the stepping motor 13 affords the advantage that no additional sensors are needed. Particularly when determining the conveyor pressure p_Fthat means that there is no risk of adversely affecting the sealing integrity of the pump 1. In addition measurement is advantageously effected at interval steps corresponding to the step size of the stepping motor 13 whereby precise monitoring of the metering accuracy is possible even in relation to partial stroke movements or partial cycles. Such recourse to the electronic motor system 14 means that in particular there is no need for further mechanical parts which lead to additional maintenance and repair expenditure. Finally the method proposed, as it is restricted to measurement of electrical characteristic parameters of the stepping motor 13, is independent of the specific design configuration of the positive displacement pump 1. Thus it can be implemented in a simple fashion in a large number of different positive displacement pumps 1. In that respect it is only knowledge about the structure of the pump that is necessary, but that is generally already established in the course of construction and is thus readily available.
For the purposes of the original disclosure it is pointed out that all features as can be seen by a man skilled in the art from the present description, the drawings and the appendant claims, even if they are described in specific terms only in connection with certain other features, can be combined both individually and also in any combination with others of the features or groups of features disclosed here insofar as that has not been expressly excluded or technical aspects makes such combinations impossible or meaningless. A comprehensive explicit representation of all conceivable combinations of features and emphasis of the independence of the individual features from each other is dispensed with here only for the sake of brevity and readability of the description.

LIST OF REFERENCES

1 positive displacement pump
2 metering head
3 metering chamber
4 side walls of the metering chamber
5 positive displacement element/metering diaphragm
6 suction line
7 pressure line
8 valve of the suction line
9 valve of the pressure line
10 connecting element
12 spring element (return spring or stroke assistance spring)
13 stepping motor (with/without transmission)
14 electronic motor system/ascertaining device
E₁first extreme position
E₂second extreme position
F fluid to be conveyed
A_Gboundary surface
M_Mmotor moment
F_bgross drive force
F_nnet drive force
p_Fconveyor pressure
U_Mmotor voltage
I_Mmotor current
U_indcounter-induced voltage
δ_Lload angle
δ_UIphase shift between U_Mand I_M
F_Vdeformation force
F_Fspring force of the spring element
S target value

Claims

1. A method of sensorless detection of functional disturbances of a positive displacement pump (1), wherein the positive displacement pump (1) has a moveable positive displacement element (5) having a boundary surface (A_G) which delimits a metering chamber (3), wherein the metering chamber (3) is connected to a suction and a pressure line (6, 7) by way of valves (8, 9) so that fluid (F) to be conveyed can alternately be sucked into the metering chamber (3) by way of the suction line (6) and pressed out of the metering chamber (3) by way of the pressure line (7) by an oscillating movement of the positive displacement element (5) and wherein there is provided a stepping motor (13) as a drive for the oscillating movement of the positive displacement element (5), characterised in that a motor moment (M_M) provided by the stepping motor (13) is ascertained and a warning signal is delivered when the ascertained motor moment (M_M) fulfils a first predetermined criterion.

2. A method as set forth in claim 1 characterised in that the first predetermined criterion takes account of at least one of the following parameters:

the proportion of the motor moment (M_M) applied by the stepping motor (13) to the positive displacement element (5) as the gross drive force (F_b),

the proportion of the gross drive force (F_b) applied to the fluid (F) to be conveyed by the positive displacement element (5) as the net drive force (F_n), and

the conveyor pressure (p_F) acting on the fluid (F) to be conveyed in accordance with the relation p_F=F_n/A_G.

3. A method as set forth in claim 1 characterised in that in addition at least the gross drive force (F_b), the net drive force (F_n) or in accordance with the relation p_F=F_n/A_Gthe conveyor pressure (p_F) is determined.

4. A method as set forth in claim 3 characterised in that a warning signal is delivered when the gross drive force (F_b), the net drive force (F_n) or the conveyor pressure (p_F) fulfils the first predetermined criterion.

5. A method as set forth in claim 1 characterised in that the respective criterion is so selected that a warning signal is delivered when the corresponding parameter from the group consisting of the motor moment (M_M), the gross drive force (F_b), the net drive force (F_n) and the conveyor pressure (p_F) reaches or exceeds a first predetermined threshold value or the corresponding parameter reaches or falls below a second predetermined threshold value.

6. A method as set forth in claim 1 characterised in that the first criterion is so selected that the warning signal is delivered when a weighted sum of the relative deviations of the motor moment (M_M) and at least one further parameter from the group consisting of the gross drive force (F_b), the net drive force (F_n) and the conveyor pressure (p_F) from a respective threshold value reaches or exceeds a predetermined value.

7. A method as set forth in claim 1 characterised in that the motor moment (M_M) of the stepping motor (13) is detected by ascertaining the phase shift (δ_UI) of the motor voltage (U_M) relative to the motor current (I_M), which is caused by a voltage (U_ind) counter-induced by virtue of the load angle (δ_L) of the stepping motor (13).

8. A method as set forth in claim 2 characterised in that the gross drive force (F_b) applied to the positive displacement element (5) by the stepping motor (13) is determined on the basis of a model of the drive kinematics of the stepping motor (13) and the positive displacement element (5).

9. A method as set forth in claim 1 characterised in that the positive displacement pump (1), is a metering pump, preferably a diaphragm pump having a positive displacement element (5) in the form of a metering diaphragm.

10. A method as set forth in claim 9 characterised in that the net drive force (F_n) applied to the fluid (F) to be conveyed is determined from the gross drive force (F_b) by subtraction of force components not applied directly to the fluid (F) to be conveyed, in particular by subtraction of the deformation force (F_V) necessary for deformation of the metering diaphragm (5) and/or the force (F_F) necessary for stressing a spring element (12), by means of which the metering diaphragm (5) can be stressed in the direction of the pressure position or in the opposite direction.

11. A method as set forth in claim 1 characterised in that a plurality of criteria are predetermined and when a criterion is fulfilled a warning signal characteristic of the respective criterion is delivered.

12. A method as set forth in claim 11 characterised in that a fault event is associated with each criterion and when a criterion is fulfilled an associated fault event is diagnosed, in particular an overload and/or a stoppage of the stepping motor (13).

13. A method as set forth in claim 1 characterised in that a delivered warning signal is sent to an automatic shut-down means which shuts down the pump (1) in response to the receipt of the warning signal.

14. A method as set forth in claim 1 characterised in that a delivered warning signal is sent to an output device which outputs an acoustic and/or visual warning indication characteristic of the warning signal in response to the receipt of the warning signal.

15. A method as set forth in claim 2 characterised in that in addition at least the gross drive force (F_b), the net drive force (F_n) or in accordance with the relation p_F=F_n/A_Gthe conveyor pressure (p_F) is determined.

16. A method as set forth in claim 4 characterised in that the respective criterion is so selected that a warning signal is delivered when the corresponding parameter from the group consisting of the motor moment (M_M), the gross drive force (F_b), the net drive force (F_n) and the conveyor pressure (p_F) reaches or exceeds a first predetermined threshold value or the corresponding parameter reaches or falls below a second predetermined threshold value.

17. A method as set forth in claim 5 characterised in that the first criterion is so selected that the warning signal is delivered when a weighted sum of the relative deviations of the motor moment (M_M) and at least one further parameter from the group consisting of the gross drive force (F_b), the net drive force (F_n) and the conveyor pressure (p_F) from a respective threshold value reaches or exceeds a predetermined value.

18. A method as set forth in claim 6 characterised in that the motor moment (M_M) of the stepping motor (13) is detected by ascertaining the phase shift (δ_UI) of the motor voltage (U_M) relative to the motor current (I_M), which is caused by a voltage (U_ind) counter-induced by virtue of the load angle (δ_L) of the stepping motor (13).

19. A method as set forth in claim 7 characterised in that the gross drive force (F_b) applied to the positive displacement element (5) by the stepping motor (13) is determined on the basis of a model of the drive kinematics of the stepping motor (13) and the positive displacement element (5).

20. A method as set forth in claim 8 characterised in that the positive displacement pump (1), is a metering pump, preferably a diaphragm pump having a positive displacement element (5) in the form of a metering diaphragm.