Patent Application
20180010604
The present invention pertains to an eccentric screw pump and to a method for adapting the operating state of an eccentric screw pump.
The present invention pertains to an eccentric screw pump for conveying liquids and/or granular mediums.
Eccentric screw pumps are pumps for conveying a plurality of mediums, particularly thick-flowing, highly viscous and abrasive mediums such as, for example, sludges, liquid manure, mineral oil and greases. In this case, the driven helical rotor rotates within the stator. This stator consists of a housing with a helically coiled inner side. The rotor carries out an eccentric rotational motion about the stator axis with its figure axis. The outer screw, i.e. the stator, is realized in the form of a double thread whereas the rotor screw is only single-threaded. The rotor usually consists of a highly abrasion-resistant material such as steel. The stator, in contrast, consists of an elastic material such as rubber. Due to the special shapes of the rotor and the stator, sealed cavities are formed between the rotor and the stator, wherein said cavities move along axially during the rotation of the rotor and thereby convey the medium. In this case, the volume of the cavities is constant such that the medium being conveyed is not compressed. Suitably designed eccentric screw pumps are not only capable of conveying fluids, but also solids.
In order to form the transport cavities and to convey the respective medium with the least backflow possible, the rotor contacts an inner wall of the stator, which consists of an elastic material, under the influence of pressure. Certain abrasion or wear of the stator occurs due to the motion of the typically metallic rotor within the stator, which typically consists of rubber or a similar material. This wear reduces the pressure-related contact force between the rotor and the stator and, in particular, no longer makes it possible to maintain the contact between the stator and the rotor along an uninterrupted helical contact line such that the performance of the eccentric screw pump drops. This particularly applies to eccentric screw pumps that have to overcome a great suction height or a high counterpressure. The stator therefore has to be exchanged and replaced within regular intervals.
The time of the stator exchange is determined, for example, by using sensors that detect the wear of the stator based on physical parameters. DE 10157143 A1 describes a device for displaying maintenance intervals or remaining operating periods of eccentric screw pumps. The sensors detect wear-related operating parameters that are acquired by a control unit. Based on these parameters, the control unit determines an expected value for the operating period or operating cycles before the next service has to be performed or certain components have to be exchanged.
DE 202005008989 discloses an eccentric screw pump, in which the operatability and the wear of the stator are monitored, wherein the stator is provided with at least one measuring transducer that makes it possible to measure compressions and/or motions of the stator or the elastic material during the course of the rotation of the rotor.
Other options for the sensor-based monitoring of the stator condition are described, for example, in documents JP 2011112041 A, JP 2010281280 A, JP 2009235976 A and JP 20101104 A.
In addition, adjustable stators have been disclosed in order to achieve a prolonged service life of the stator. DE 3433269 A1 describes a stator casing with tensioning devices in the form of tension bolts that are distributed over the entire axial length of the stator casing. This results in a significant weight increase of the stator-rotor system. In addition, all tensioning devices have to be retightened individually for the readjustment.
EP 0292594 A1 discloses a stator casing for eccentric screw pumps that is provided with a longitudinal slot and only features a tensioning device for generating pressure, as well as for readjusting the worn stator, in its pressure zone. The tension is partially distributed over the length of the stator casing by suitable reinforcing ribs.
DE 4312123 A1 describes a stator casing with multiple longitudinally extending slots that simplify the adjustment. In order to realize a better adjustment in the region of the pressure-side stator end, the slots end shortly before the end of the suction-side stator end and only extend freely on the pressure-side end.
DE 4403979 A1 discloses an adjustable stator for eccentric screw pumps with continuous longitudinal slots and longitudinal slots that end a short distance before the suction-side stator end. A continuous slot advantageously follows each longitudinal slot.
The invention is based on the objective of achieving a simple and fast adaptation of a stator-rotor system to the respective operating states.
The above-defined objective is attained with a stator-rotor system and a method for adapting the operating state of a stator-rotor system, which respectively comprise the characteristics disclosed in the present claims. Other advantageous embodiments are described in the dependent claims.
The invention concerns an eccentric screw pump with a stator-rotor system. The stator-rotor system comprises a rotor with a rotor screw and a stator. According to a preferred embodiment, the stator-rotor system comprises a rotor with a single-threaded rotor screw and a stator with an internal double thread. The stator is composed of at least two parts and comprises a support element and an elastomer part. According to an embodiment of the invention, the elastomer part of the stator is arranged in a stator casing and typically not rigidly connected to the stator casing. A fabric part or a screen structure that at least sectionally encompasses the elastomer part may also be used as support element instead of a stator casing. In other words, the support element or the stator casing and the elastomer part are typically realized in the form of separate parts. The support element or the stator casing encloses the elastomer part at least sectionally over its entire circumference. The support element or the stator casing particularly encloses the majority of the elastomer part such that only the free outer end regions of the elastomer part protrude over the support element or the stator casing and are not enclosed thereby.
The stator particularly consists of a stator system of the type described in DE 102005042559 A1. An axial deformation of the elastomer part is possible due to the lack of a rigid connection between the elastomer part and the support element or the stator casing. The volume of the stator remains constant during a deformation. Consequently, an axial deformation of the elastomer part simultaneously leads to a change in the cross section of the oblong hole of the elastomer part, in which the rotor is guided. The prestress, i.e. the contact pressure between the stator and the rotor, can thereby also be varied in order to compensate the wear of the stator such that the adjustment or readjustment of the stator can also be used for adapting the prestress between the stator and the rotor of an eccentric screw pump to different operating conditions.
The stator-rotor system of the eccentric screw pump features an adjusting mechanism for varying and readjusting the prestress of the stator. A different prestress of the stator-rotor system is required depending on the respective operating state of the eccentric screw pump. The prestress is dependent, for example, on the viscosity of the conveyed product, product mixture or the like. The operating state is determined, in particular, by means of different operating parameters such as the pressure, rotational speed, torque and/or other operating parameters. The adjusting mechanism is coupled to a control system and activated and controlled thereby. The control system particularly comprises at least one sensor for determining actual operating parameters of the stator-rotor system and/or the eccentric screw pump and a control unit for adjusting the adjusting mechanism. This means that the adjusting mechanism is coupled to at least one sensor for determining actual operating parameters of the stator-rotor system and/or the eccentric screw pump by means of a control unit. The activation of the adjusting mechanism by the control unit takes place with consideration of the actual operating parameters determined by means of at least one sensor.
The inventive control mechanism establishes a correlation between different physical parameters of the stator-rotor system and the state of wear of the stator or the prestress between the stator and the rotor, respectively. For example, a correlation between the physical parameters pressure, torque, volumetric flow rate, rotational speed and/or viscosity and the state of wear of the stator or the prestress between the stator and the rotor is respectively established. The most direct parameter that combines these correlations with one another is the state of stress in the elastomer material. This stress can either be determined directly by means of a corresponding sensor system in the elastomer material or indirectly based on the reaction force of the elastomer on other components, for example the reaction force of the elastomer on the stator wall, particularly the support element or the stator casing, the reaction force of the elastomer on one of the end faces of the elastomer part, the reaction force of the elastomer on closures that consist, for example, of two shells and hold the support element or the stator casing together, etc.
For example, a correlation between pressure, torque, volumetric flow rate, rotational speed and the existing prestress in the elastomer is established and a corresponding adjusting position for the adjustment of the adjusting mechanism, which should be suitable for adjusting the optimal operating point, is subsequently determined. After the automated adjustment of the adjusting mechanism, the physical operating parameters of the eccentric screw pump are measured anew in order to determine if the optimal operating state is reached. If the measured operating parameters do not correspond to the desired nominal parameters, an adjustment travel is calculated anew and the adjusting mechanism is correspondingly readjusted.
According to a preferred embodiment of the invention, the actual control parameter is the predominant state of stress in the elastomer, which is measured, for example, in an indirect form and delivers an adjustment travel x and/or an adjustment direction with incremental approximation to the desired nominal value in combination with other operating parameters such as, for example, the rotational speed of the eccentric screw pump or the like.
The adjustment of the calculated adjustment travel x and/or the adjusting direction preferably takes place with incremental approximation. Consequently, an incremental approximation to the optimal adjustment of the adjusting mechanism particularly takes place. The adjusting mechanism is adjusted by a defined amount if a nominal-actual deviation lies outside a defined tolerance range. The inventive control algorithm defines the direction of the adjustment based on the nominal-actual comparison and the data stored within the control algorithm, wherein the extent of the adjustment corresponds to a predefined amount. In this way, in particular, an incremental approximation to the desired nominal value takes place until the measured nominal-actual deviation lies within the defined tolerance range.
According to a preferred embodiment, the adjusting mechanism comprises two adjusting elements that are arranged on the stator-rotor system and variable with respect to their distance from one another. In a first working position, the two adjusting elements are spaced apart from one another by a first distance whereas the two adjusting elements are in a second working position spaced apart from one another by a second distance, wherein the first distance differs from the second distance. In the second working position, the cross section and the length of the elastomer part of the stator are changed in comparison with the cross section and the length of the elastomer part in the first working position.
A mechanical coupling and/or connection preferably exists between the adjusting mechanism and the stator, wherein such a coupling and/or connection particularly exists between the adjusting mechanism and the elastomer part of the stator. A change in the cross section and the length of the elastomer part of the stator is realized by changing the relative distance between the two adjusting elements of the adjusting mechanism.
It is preferred that one of the adjusting elements is arranged on the stator-rotor system stationary and the other adjusting element is arranged on the stator-rotor system positionally variable. The first adjusting element is arranged stationary, in particular, on the support element or the stator casing and the second adjusting element is arranged positionally variable on the elastomer part of the stator. According to a preferred embodiment, the first adjusting element is arranged stationary on a flange on a free end of the support element or the stator casing and the positionally variable second adjusting element is arranged on a free end of the elastomer part of the stator.
According to an embodiment of the invention, the control unit activates an actuator that causes a repositioning of the positionally variable second adjusting element and therefore a change in the relative distance between the positionally variable second adjusting element and the stationary first adjusting element. The adjustment of the relative distance between the two adjusting elements may be realized in different ways. For example, wedge elements, tapered rings, mechanisms with spindle adjustment, cylinder-assisted mechanisms, etc. may serve as actuators.
According to an embodiment of the invention, at least one first sensor may be arranged on a stationary component of the eccentric screw pump that is assigned to the stator-rotor system, wherein said sensor can detect certain physical parameters of the stator-rotor system. At least one second sensor may alternatively or additionally be arranged on the stator-rotor system, particularly on the elastomer part of the stator. Furthermore, at least one third sensor may alternatively or additionally be arranged on the adjusting mechanism.
For example, the at least one first sensor is designed for measuring the pressure, rotational speed, torque, temperature and/or volumetric flow rate of the eccentric screw pump whereas the at least one second sensor is designed for directly or indirectly measuring the prestress between the stator and the rotor of the stator-rotor system. The second sensor may consist, for example, of a piezo element, a load cell or a dielectric elastomer. The second sensor may also be designed for measuring the reaction forces of the elastomer material whereas the at least one third sensor may be designed for measuring the position of the positionally variable second adjusting element and/or for measuring the relative distance between the stationary first adjusting element and the positionally variable second adjusting element.
The invention furthermore concerns a method for adapting the operating state of an eccentric screw pump with an above-described stator-rotor system.
The actual operating state of the eccentric screw pump is initially established. In this case, at least one actual physical operating parameter concerning the eccentric screw pump and/or at least one actual physical operating parameter concerning the elastomer part of the stator-rotor system and/or at least one actual physical operating parameter of the adjusting mechanism are determined with the aid of suitable sensors. Subsequently, the actual operating parameters determined with the aid of the sensors are compared with known or desired nominal operating parameters. This comparison particularly takes place based on data stored in the control unit. If this comparison shows a deviation between the actual operating parameters and the nominal operating parameters, the adjusting mechanism is activated in order to adjust the stator. In this case, the adjustment of the new operating state is monitored by controlling at least one actual physical operating parameter.
According to a first preferred embodiment, a required adjustment of an adjustment travel of the adjusting mechanism is calculated if it is determined that the measured actual operating parameters deviate from the nominal operating parameters, wherein the adjusting mechanism is activated accordingly and the calculated adjustment travel is carried out, which in turn leads to a readjustment or adjustment of the stator, particularly to a change in the cross section and the length of the elastomer part of the stator.
According to an alternative embodiment, the operating state is adjusted by means of an incremental approximation to an ideal operating point. In this case, the control principle or the control algorithm is respectively based on the following functional principle: a volumetric flow rate is assigned to a first rotational speed of an eccentric screw pump. At a volumetric efficiency of 100%, the volumetric flow rate particularly would amount exactly to the volume, which is conveyed from the suction side to the pressure side of the eccentric screw pump by the individual transport elements (transport cavities) in accordance with the rotational speed.
The optimal adjustment of the operating point of the eccentric screw pump takes place as follows: an observation of the volumetric flow rate at a constant rotational speed over a certain adjusting range shows that this volumetric flow rate is at least largely constant over an extended range. However, the required driving torque is not constant. If the prestress is released, the torque drops due to the lower frictional losses caused by the reduced prestress. The efficiency of the eccentric screw pump increases in the range, in which the volumetric flow rate does not change because no backflow or only slight backflow occurs as yet, wherein the efficiency of the eccentric screw pump does not drop until an operating point is reached, at which backflow increasingly occurs due to the reduced prestress. The point of maximum efficiency can be concretely defined as follows: the ideal operating point of the pump lies exactly at the point, at which the prestress between the rotor and the stator is just sufficiently high such that no or only slight backflow occurs. The ideal operating point consequently is the point, at which just as much prestress as necessary for generating the required counterpressure with the least possible backflow of the medium is generated in the rotor-stator system.
This functionality is used for the control algorithm, wherein an incremental approximation particularly takes place in order to adjust the ideal operating state. According to a preferred embodiment of the invention, the control algorithm preferably utilizes the measuring principle described below: certain operating parameters of the eccentric screw pump are initially determined. For example, the pressure, rotational speed, torque (motor current) or other operating parameters are measured with the aid of suitable sensors. The volumetric flow rate can also be measured, for example, by means of a volumetric flow meter, a measuring diaphragm or the like.
The adjusting mechanism now moves into an at least largely closed position, e.g. a position, in which the two adjusting elements are positioned as close to one another as possible. In this way, the rubber of the elastomer part is compressed such that the prestress in the stator-rotor system increases and backflow is minimized.
After ensuring that the range of sufficient compression has been reached, the adjusting mechanism is once again opened slowly and in a controlled fashion. During this process, the volumetric flow rate initially remains largely constant up to a certain point. At this point, the volumetric flow rate drops because backflow in the stator-rotor system increases. The ideal operating point lies shortly before this dropping point. The ideal operating point may also refer to a certain range, in which the eccentric screw pump performs with maximum efficiency.
The adjustment of the prestress is preferably carried out autonomously within certain time intervals by the adjusting system in the rotor-stator system. In this way, an active adjustment or adaptation to varying operating conditions of the pump can be ensured.
Alternatively, the prestress of the rotor-stator system can be increased based on the measured operating parameters and the incremental adjustment procedure until the maximum volumetric flow rate is reached. Once the maximum volumetric flow rate is reached, the prestress is once again increased by a defined number of adjusting increments. It is therefore ensured that the iBP was exceeded. The iBP is subsequently determined and adjusted by incrementally releasing the prestress. This procedure is repeated within defined time intervals. In this way, a reaction of the system to changing operating states is realized.
According to a preferred embodiment, the actual operating state of the eccentric screw pump is established anew once a defined time period after the adjustment of the adjusting mechanism has elapsed and compared with the nominal operating parameters. In this way, the success of the adjustment can be verified. The adjusting mechanism is activated and adjusted anew if a deviation between the actual operating parameters and the nominal operating parameters of the eccentric screw pump still exists, particularly a deviation outside a defined tolerance range. No additional adjustment takes place if the deviation between the actual operating parameters and the nominal operating parameters could be sufficiently reduced with the adjustment of the adjusting mechanism and therefore a readjustment or adjustment of the stator. Instead, the adjusted operating state of the eccentric screw pump is checked anew after another defined time period by means of the above-described sensor measurements.
However, if no deviation between the actual operating parameters and the nominal operating parameters, particularly no deviation outside the defined tolerance range, is detected when the actual operating state of the eccentric screw pump is initially established, the actual operating state of the eccentric screw pump is established anew after a defined time period by measuring the actual operating parameters and the actual operating parameters are once again compared with the nominal operating parameters. The stator-rotor system is constantly monitored during its operation by regularly establishing the actual operating state within defined time intervals. In this way, a deviation from the desired operating state can be promptly adjusted and adapted during the operation of the eccentric screw pump.
According to an embodiment of the invention, the pressure, rotational speed, torque, temperature and/or volumetric flow rate of the eccentric screw pump is determined with the aid of suitable sensors. The prestress between the rotor and the stator and/or the reaction forces of the elastomer material of the elastomer part are alternatively or additionally measured. In addition, the position of at least one adjusting element of the adjusting mechanism and/or the relative distance between two adjusting elements of the adjusting mechanism can be determined with the aid of suitable sensors.
According to an embodiment of the invention, in which the adjusting mechanism comprises two adjusting elements, the distance between which is variable, the adjustment of the adjusting mechanism is realized in that the relative distance between the two adjusting elements is increased or decreased. The distance change between the two adjusting elements causes a change in the cross section and the length of the coupled elastomer part of the stator-rotor system. In this case, the control mechanism calculates a nominal distance between the two adjusting elements based on physical parameters of the stator-rotor system determined with the aid of suitable sensors and, in particular, calculates the adjustment travel of the positionally variable second adjusting element. Subsequently, the adjusting mechanism is activated and the calculated position of the positionally variable second adjusting element is adjusted, particularly by adjusting the calculated distance between the two adjusting elements. The physical operating parameters are determined anew after another time interval has elapsed. If the deviation from the desired actual value is reduced, this represents the new operating state of the eccentric screw pump. The new operating state of the eccentric screw pump can be additionally approximated to the desired optimal operating state by means of additional readjustments or adjustments. Another adjustment of the adjusting mechanism takes place if the deviation from the desired actual value is not reduced. The invention therefore concerns a stator-rotor system for an eccentric screw pump and a control of such a system. The invention particularly concerns an automatic control system for varying the prestress between the stator and the rotor of an eccentric screw pump, i.e. between a soft component—the elastomer part—and a harder component—the support element, e.g. a so-called stator casing. One significant advantage can be seen in that the eccentric screw pump can always be operated at the optimal operating point such that the energy efficiency of the stator-rotor system is substantially increased.
The automatic control of the prestress particularly leads to an automatic wear compensation such that a prolonged service life of the stator can be achieved. Due to the adjustment of the stator, the initial breakaway torque can be reduced with a defined procedure when the eccentric screw pump is switched on and/or off.
The automatic control system furthermore makes it possible to advantageously adapt the prestress between the stator and the rotor to the viscosity of the conveyed medium.
Alternatively or additionally to the described characteristics, the method may comprise one or more characteristics and/or features of the above-described device. Likewise, the device may alternatively or additionally comprise individual or multiple characteristics and/or features of the described method.
Exemplary embodiments of the invention and their advantages are described in greater detail below with reference to the attached figures. In these figures, the proportions of the individual elements relative to one another do not always correspond to the actual proportions because a few shapes are simplified and other shapes are enlarged in relation to other elements in order to provide a better overview.
Identical or identically acting elements of the invention are identified by identical reference symbols. In order to provide a better overview, the individual figures furthermore only show the reference symbols required for the description of the respective figure. The embodiments shown merely represent examples of the inventive device and/or the inventive method and not a conclusive restriction.
The adjusting mechanism 12 is coupled to a control system 30 and activated and controlled thereby. The control system 30 comprises a control unit 32 and at least one sensor 35 for measuring physical operating parameters of the stator-rotor system 10 or the eccentric screw pump, respectively. At least one first sensor 36 is particularly provided on the eccentric screw pump in order to measure the pump pressure, rotational speed, temperature and/or volumetric flow rate. In addition, at least one second sensor 37 may be arranged on the elastomer part 4 and designed, for example, for determining the prestress between the rotor and the stator 3 or the reaction forces of the elastomer part. Furthermore, at least one third sensor 38 may be provided on the adjusting mechanism 12 and designed for respectively detecting, for example, the position of the positionally variable adjusting element 14 or the relative distance between the stationary adjusting element 13 and the positionally variable adjusting element 14. The data acquired with the aid of the sensors is transmitted to the control unit 32, which compares this data with nominal operating parameters and activates a corresponding adjustment of the adjusting system 12 if the measured actual operating parameters deviate from the nominal operating parameters, particularly an adjustment, during which the relative distance between the stationary adjusting element 13 and the positionally variable adjusting element 14 is changed such that the elastomer is deformed and the cross section and/or the length of the elastomer part 4 of the stator 3 changes.
It is alternatively and/or additionally also possible to use parameters that can be measured on the eccentric screw pump such as the pump pressure, the rotational speed, with which the eccentric screw pump is operated, the temperature, the volumetric flow rate of the conveyed medium, etc.
A correlation, for example, between pressure, volumetric flow rate, rotational speed and the required prestress is established with the aid of the inventive control algorithm and a corresponding adjustment travel for the adjustment of the adjusting mechanism 12, which should be suitable for adjusting the optimal operating point, is subsequently determined. It is particularly conceivable to provide sensors 38 that determine the actual state of the adjusting system, particularly the position of the positionally variable adjusting element 14 or the relative distance between the stationary adjusting element 13 and the positionally variable adjusting element 14, and/or sensors 38 that monitor the adjustment of the desired nominal position when the position of the positionally variable adjusting element 14 is adjusted.
The operating parameters determined with the aid of the sensors provide information on the operating state of the eccentric screw pump. The control unit 32 (see
However, if the comparison shows a deviation between the actual operating parameters and the nominal operating parameters, the control unit 32 determines the required adjustment of the adjusting mechanism 12 based on a stored characteristic diagram or a stored table and activates the adjusting mechanism accordingly. After the automated adjustment of the adjusting mechanism 12, the physical operating parameters of the eccentric screw pump or the stator-rotor system 10 are measured anew once another time interval Δt2 has elapsed in order to once again determine whether the optimal operating state is respectively reached or maintained. If the measured operating parameters to not correspond to the desired nominal operating parameters, the control unit 32 once again calculates an adjustment travel and the adjusting mechanism 12 is readjusted accordingly. The control algorithm particularly carries out an incremental adjustment of the type described below with reference to
Even if the desired optimal operating state of the eccentric screw pump was achieved with the adjustment, permanent monitoring takes place by regularly determining the operating parameters within defined time intervals Δt3 and, if applicable, readjusting the adjusting mechanism in order to achieve the optimal deformation of the elastomer and therefore the optimal operating state of the eccentric screw pump during its operation.
The optimal adjustment of the ideal operating point iBP of the eccentric screw pump takes place as follows: an observation of the volumetric flow rate Q at a constant rotational speed over a certain adjustment travel n shows that this volumetric flow rate Q is nearly constant over an extended adjustment travel n. However, the required torque (not illustrated in the diagram in
This functionality is used for the new control algorithm, wherein an incremental approximation to the ideal operating state iBP particularly takes place. According to an embodiment of the invention, the control algorithm utilizes the following measuring principle:
The invention was described with reference to a preferred embodiment. For a person skilled in the art, however, it is conceivable that the invention can be modified or changed without thereby deviating from the scope of protection of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 101 353.3 | Jan 2015 | DE | national |
| 10 2015 112 248.0 | Jul 2015 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2016/000033 | 1/29/2016 | WO | 00 |
