Patent Application
20230265846
The invention relates to an eccentric screw pump, having a pump housing having a pump inlet opening and a pump outlet opening, a stator disposed in the pump housing, a rotor disposed in the stator, a drive unit comprising a drive motor and a driveshaft which for transmitting a torque connects the drive motor to the rotor, wherein the rotor for a rotating movement about a rotating axle is guided in the stator, and a state sensor for detecting a state variable of the eccentric screw pump.
Eccentric screw pumps are used for conveying various media in a multiplicity of applications. Eccentric screw pumps operate according to the principal of a volumetric displacement pump and to this end have a rotor which is driven so as to rotate about its own rotor longitudinal axis in a stator, wherein this rotor longitudinal axis in turn is rotated about a stator longitudinal axis which is spaced apart from said rotor longitudinal axis and typically runs parallel to the latter, such that a rotation of the rotor about the stator longitudinal axis and a rotation of the rotor about the rotor longitudinal axis, as a complementary eccentric rotation, results in a superimposed movement of the rotor in the stator. Eccentric screw pumps can be used for conveying volume in a defined and projectable manner in that a specific number of revolutions are carried out, the latter being proportional to the desired conveying volume. Eccentric screw pumps are often used in the field of plant engineering and often serve for supplying liquid charged with foreign matter. In particular, in the application field of plant engineering, but also generally, any failure of the eccentric screw pump often equates to a prolonged downtime of the entire plant, this being associated with significant disadvantages for the user.
A failure of an eccentric screw pump may be traced back to many causes. A frequent cause of failure is excessive wear on the stator, the latter in many construction modes of eccentric screw pumps being made as a shell construction from a rubber material or another elastomer and in which a rotor made of metal is situated such that wear arising between the rotor and that the stator often has a substantial effect on the stator. However, the wobbling mode of movement caused by the movement of the eccentric also requires a corresponding mounting and on the drive a corresponding transfer of torque by way of a wobble shaft which is often embodied with two universal joints. In many construction modes of eccentric screw pumps, these universal joints are moreover situated in the inlet region of the stator and as a result are surrounded by the wash of the conveyed medium such that the stress on these universal joints, and potentially arising leakages of the seal of the universal joints, can also lead to wear on the joints or to damage to bearings, which can likewise have the consequence of the failure of the eccentric screw pump.
Various solutions have already been proposed in order to address these problems. In the case of eccentric screw pumps with minor eccentricity, the embodiment of the wobble shaft is thus embodied as a flexing torsion bar, for example, as a result of which the two universal joints in the drivetrain can be dispensed with and one cause of wear and failure can be avoided as a result. However, this construction mode is not suitable for pumps with a high throughput volume because comparatively great eccentricities are advantageous to this end, and this construction mode is therefore limited to comparatively small types of pump constructions.
Known from EP 2 944 819 B1 is a construction mode of an eccentric screw pump which enables a highly curtailed repair time for the replacement of a rotor or stator of the eccentric screw pump. This is achieved by a specific design of the stator flange which enables the stator conjointly with the rotor disposed therein to be pivoted outward without further pipelines that are connected to the eccentric screw pump having to be disassembled for this purpose, or without other disassembly steps being required. The release of the rotor from the wobble shaft, which is required for disassembling the rotor, here can take place by way of a cavity in the rotor per se such that access to the inlet chamber for disassembling a flange disposed therein is also not required. A significant advantage in the case of maintenance is indeed achieved by way of this maintenance-friendly eccentric screw pump construction. However, it is moreover desirable to forecast the requirement of maintenance, in order to be better able to plan such maintenance procedures in the regular operation of the plant.
For this purpose, various approaches have been pursued for some time in order to identify on eccentric screw pumps an operating state which requires maintenance.
The monitoring of specific operating parameters of an eccentric screw pump is thus provided in DE 100 63 953 A1 in that pressure transducers, temperature sensors, and vibration sensors are disposed in the region of the joints or of the mounting or in the region of the rotor or stator. This measuring principle follows an approach, which for other types of pump constructions, specifically for example from JP 60-150491 A or DE 19 649 766 A, is an already known principle of obtaining a statement pertaining to the state of wear of the pump through monitoring the state by evaluating temperature or vibration values. However, this approach is such that, by virtue of the specific vibration state caused by the eccentric movement in eccentric screw pumps, an arrangement of a plurality of different sensors is provided so as to be sufficiently able to reliably detect an operating state that indicates wear as opposed to the normal operating state of the eccentric screw pump. In the case of this approach, this however leads to a disadvantageous arrangement of many different sensors in order to achieve a detection of the state of wear. Apart from the disadvantage that, as a result, the assembly and disassembly of the eccentric screw pump is additionally significantly impeded, and the costs of the eccentric screw pump are increased, it has moreover been demonstrated that, even by way of this complexity of a plurality of different sensors, a state of wear which actually requires maintenance cannot be reliably identified, or be identified only once significant damage has occurred. In particular, it is not possible to identify operating states which lead to increased wear in a reliable and preventive manner.
From DE 2005 019 063 B3 it is known for a single vibration sensor to be placed externally on the eccentric screw pump and to evaluate the measured results of said vibration sensor in order to therefrom draw conclusions in terms of specific operating states or states of wear, respectively. This does indeed address the disadvantage of impeded disassembly and increased costs by virtue of the multiplicity of sensors, but reliable detection of states of wear and operating states which lead to increased wear can also not be achieved by way of this prior art.
A renewed, more recent approach is known from DE 10 2018 113 347 A1, in which an operating parameter in the form of the operating pressure or of the torque of the pump is to be monitored on an eccentric screw pump by means of detecting pressure in the exit of the eccentric screw pump. In this monitoring of the operating pressure/torque, a statement pertaining to the specific operating parameters is to be made by an evaluation of signals by means of a Fourier transform. In principle, it is likewise achieved by way of the sensor assembly in the pump exit that easier assembly and disassembly is able to be achieved in comparison to previously known solutions. However, the disposal of the sensor has the disadvantage that a statement pertaining to the operating pressure of the pump, and indirectly derived therefrom a statement pertaining to the torque, is to be made by means of a specific evaluation mode and by comparing calibrated comparison values, said statement to a significant degree being a function of the pumped medium and of influences in the line network at the pump exit. States of wear, in particular, such that require maintenance or require maintenance to a projectable point in time in the future, cannot be reliably detected by this detection and evaluation of measured values.
The approaches to date target in particular the detection of a state that directly necessitates maintenance. According to the concept of the inventors, however, it would in principle also be advantageous if it were possible to control an eccentric screw pump in such a manner that operating states which particularly trigger wear can be preventively avoided. To this end, however, it is necessary to not only detect the state of wear that already requires maintenance but also operating states which lead to increased wear, on the one hand, and can be avoided by changing the actuation of the eccentric screw pump, on the other hand, such that the effect of wear is minimized. According to the concept of the inventors, this can manifest itself, for example, in the start-up behavior of pumps in that a low-wear ramping up of the pump is achieved by way of a specific increase in the rotating speed, for example, this potentially differing according to the medium conveyed. Furthermore, dry running states can be avoided in that the absence of conveyed medium is identified in real time, and the pump thereupon is stopped or operated at a highly reduced rotating speed.
Moreover known from WO 2018/130718 A1 is an eccentric screw pump having a conical design of the rotor and stator, which provides an axial adjustment possibility between the rotor and the stator and as a result enables the gap between the rotor and the stator to be adjusted. In this construction mode of the eccentric screw pump, the ramping up and ramping down behavior of the pump can be designed by controlling the axial actuation by an axial actuation of the rotor and the stator in relation to one another, and should knowledge pertaining to the states of wear and the operating states of the pump be available, a wear-intensive operating state, should the latter be detected, could be avoided by very rapid control, in real time, so to speak, in a targeted manner the form of a control behavior or of a feedback-control loop, by such an axial adjustment between the rotor and the stator.
Furthermore, a method and a device for monitoring eccentric screw pumps with regard to the measurement data that can be recorded from the rotor, stator, joint(s), bearing, pump inlet and pump outlet is known from WO 01/88379 A1. DE 10 2015 112 248 A1 discloses an eccentric screw pump and a method for adjusting an operating state of an eccentric screw pump. DE 101 57 143 A 1 describes a maintenance interval display for pumps.
There is, therefore, a requirement for monitoring the state on eccentric screw pumps, by way of which the disadvantages of the previously known detection modes of operating parameters of the eccentric screw pump are overcome and which permits a more spontaneous and more accurate control of an eccentric screw pump in order to avoid states of wear.
This object is achieved according to the invention by an eccentric screw pump of the construction mode described above, in which the state sensor, for detecting a state variable on the rotor or on the driveshaft, is disposed on the rotor or the driveshaft, or by means of a signal line is connected to the rotor or the driveshaft, and is disposed so as to be spaced apart from the rotor or the driveshaft.
According to the invention, a state variable is detected directly on the rotor or on the driveshaft. A state variable here is to be understood to mean a physical variable which is detected by means of a sensor installation. This physical variable can be, for example, a temperature, a fluid pressure, an elongation, a material stress, an alignment in relation to the direction of gravity, a speed in terms of absolute value and/or direction, or an exhilaration in terms of absolute value and/or direction. This state variable is detected according to the invention either by a state sensor which, according to a first alternative, is disposed on the rotor or the driveshaft. In this first alternative, the state sensor is thus fastened directly to the rotor or the driveshaft. For example, the state sensor can be fastened to the external surface of the rotor or the driveshaft, embedded in said external surface, or be disposed in an internal cavity of the rotor or of the driveshaft and be fastened, in particular in such a manner that, proceeding from a cavity of a configured rotor or a hollow shaft as the driveshaft, the state sensor is disposed on an inner surface of this cavity, or proceeding from this cavity is disposed in a duct which extends to the external surface of the rotor or the driveshaft and optionally may also penetrate this external surface.
As an alternative thereto, the state variable can be detected according to the invention by a state sensor which by means of a signal line is connected to the rotor or the driveshaft and per se is spaced apart from the rotor and the driveshaft. In this alternative case, the state sensor is disposed so as to be spaced apart from the rotor or the driveshaft, and is connected to the rotor or the driveshaft by means of a signal line. In the case of this alternative, a physically embodied signal line, thus no data transmission per radio waves or the like, is embodied in order to relay a physical state variable by way of the signal line, from a detection point on the rotor or on the driveshaft, away to the state sensor. In this way, a pressure which is detected directly on the surface of the rotor or the driveshaft, by means of a hollow line such as a duct, a hose line, a pipeline, a bore, or the like, for example, can be directed away from the detection location and be detected by the state sensor at another location. The signal line here extends from the state sensor to a terminal point which is disposed directly on the rotor or on the driveshaft, as has been explained above in the context of the state sensor disposed directly on the rotor or on the driveshaft.
As a result of the detection of the state variable on the rotor or on the driveshaft by means of the aforementioned disposal of the state sensor, or of the signal line, respectively, a direct measured variable is detected on the eccentric screw pump, said measured variable enabling a direct conclusion pertaining to a measured value relevant to the operating state of the eccentric screw pump. As a result of this direct detection it is possible, on the one hand, to detect directly in real time physical variables which have a direct correlation with the rotation of the rotor or the driveshaft, for example, pressure ratios, accelerations, or vibration values, such as an amplitude or a frequency of the pressure, or an acceleration caused by the rotation. As a result of this detection directly on the rotor, or on the driveshaft, respectively, a temperature and the potential increase of the latter is furthermore detectable in real time at a position where a temperature peak typically arises within the entire eccentric screw pump.
In vibration measurements by means of a sensor, which is disposed on the external wall of the housing, for example, the transport and the propagation of the vibration waves from the source to the sensor always have to be taken into account when evaluating the vibration signal. The material properties and dynamic structural properties such as, for example, the stiffness of the overall construction and the resulting inherent frequencies, play a decisive role here. Furthermore, the damping properties of the conveyed median and of the stator are a decisive disadvantage here. As a result of the many influential factors, a complex structural analysis of the system and a modal analysis of the measurement signal are often necessary. In this way, signal components which are adjusted for some influential factors can indeed be extracted from the overall vibration spectrum, but there is the risk, by virtue of the intensive signal processing, that signal errors systematically enter the evaluated signal, or specific state signals are systematically filtered from the signal.
In the direct and immediate measurement according to the invention on or in the component relevant for the monitoring, thus the rotor or the wobble shaft, the evaluation is significantly easier and at the same time more reliable because the influences described above are significantly reduced, and simpler methods can be applied such as, for example, a bandpass filter.
As a result of the disposal of the state sensor on the rotor or the driveshaft, the state sensor rotates conjointly with the rotor or the driveshaft, respectively, and can thus detect a 360° profile, as a result of which a cross-sectional measurement of the state is achieved. The validity of such a measurement is significantly better and more precise than any measurement by way of a state sensor disposed stationary on the eccentric screw pump can ever be.
The invention is based inter alia on the concept that an indirect detection of physical variables, and a calculation derived therefrom of critical operating parameters that can be derived therefrom has the disadvantage, on the one hand, that monitoring in real time by virtue of the necessary comparative calculations, the necessary mathematical steps per se and the necessity of comparing integral time periods herein, is not reliable and sufficiently effective to enable that an operating state which would lead to increased wear is already identified and can be avoided by corresponding control measures. On the other hand, this is based on the concept that the disposal of the state sensor on the rotor or on the driveshaft, respectively, or the offtake of the physical measured variable from the rotor or the driveshaft, respectively, by way of a signal line, enables a detection of the state variable at that location that typically makes it possible to detect the most direct state variation with the largest value of the state variation and a minor dependence on conveying parameters such as temperature or viscosity of the conveyed medium.
Therefore, according to the invention, reverse calculation, using a state variable with inaccurate assumptions detected in a damped manner at another location, back to the actual variation of the state variable at the critical location does not have to be carried out. For example, when detecting the temperature or the pressure on the rotor or the driveshaft, dry running can be detected immediately at the beginning of the dry run, and consequential wear effects can be immediately avoided by corresponding control. Likewise, excessive stress on mountings, which lead to increased wear on the mounting, can be detected by way of a corresponding characteristic vibration behavior of the rotor or of the driveshaft at that moment at which said excessive stress initially arises, and can be accordingly also effectively avoided rapidly by a corresponding reduction of the output or the rotating speed or other control variables, before wear arises as a result. Finally, the real time detection of the state variable on the rotor or the driveshaft, respectively, is also suitable for actuating therefrom control variables of a conically embodied rotor/stator assembly such that predetermined operating states of the eccentric screw pump can be approached in a targeted manner, or predetermined operating state profiles of the eccentric screw pump can be performed in a feedback-control loop, by an axial adjustment between the rotor and the stator, or by an adjustment of the eccentricity.
According to a first preferred embodiment it is provided that the state sensor is disposed within the rotor or within the drive shaft, or the signal line terminates within the rotor or within the driveshaft. According to this preferred embodiment, the state variable is detected within the rotor or the driveshaft, respectively. This enables, on the one hand, a direct detection of the state variable on the eccentrically rotating component and, on the other hand, a disposal of the state sensor, and of an optionally required sensor line or energy supply of the sensor, or the signal line, respectively, so as to be protected in relation to the influence of the conveyed medium. For this purpose, the rotor or the driveshaft, respectively, can be embodied with an internal cavity, for example be configured as a roller-type rotor or as a hollow shaft, and the state sensor, or the end of the signal line, respectively, in this instance can be disposed and fastened in this cavity.
It is furthermore preferable for the state sensor to be connected so as to be wired to an electronic evaluation unit by way of a sensor cable, and for the sensor cable or the signal line to run within a portion of the driveshaft and optionally within a portion of the rotor. According to this embodiment, a sensor signal cable which conducts the sensor signal electrically, or as an optic fiber, or in any other way, runs from the state sensor fastened to the driveshaft or to the rotor to an electronic evaluation unit, or the signal line, in the case of a state sensor disposed so as to be spaced apart from the driveshaft or the rotor, runs through a portion of the driveshaft and optionally within a portion of the rotor. This routing enables a protected placement of the sensor signal cable, or of the signal line, respectively.
In particular, the sensor cable, or the signal line, respectively, can extend along the entire driveshaft and along the entire drivetrain to the terminal point, or the fastening point, respectively, of the state sensor on the rotor or on the driveshaft, respectively, and herein in portions runs through the driveshaft or the rotor, or both. This enables an overall protected routing of the sensor cable or of the signal line, respectively, and enables the sensor signal to be routed from the rotating shaft of the drivetrain to a stationary transmission unit by means of corresponding transmission elements.
It is particularly preferable here for the driveshaft to be a wobble shaft which at the end thereof that points to the drive motor, for a rotation about a drive axle, is connected to the drive motor, and at the end thereof that points towards the rotor, for rotation about a rotor axle and for a superimposed rotation about a stator axle spaced apart from the rotor axle, is connected to the rotor.
According to this embodiment, the eccentric rotating movement of the rotor is transmitted by means of a wobble shaft as the driveshaft. This wobble shaft on the side connected to the drive motor is mounted in a rotating manner, and on the side connected to the rotor is connected to the rotor and at this location performs the eccentric rotating movement of the rotor and the rotating movement of the rotor about the longitudinal axis of the latter.
This wobble shaft can in principle be embodied as a flexing bar so as to transmit a rotation about small eccentricities. However, it is particularly preferable for the wobble shaft to have a wobble shaft central portion, a first universal joint and a second universal joint, and for the first universal joint to be inserted between the wobble shaft central portion and the drive motor, and for the second universal joint to be inserted between the wobble shaft central portion and the rotor. A wobble shaft which is also suitable for great eccentricities and high torques is provided by such a design embodiment in that two spaced apart universal joints are provided. A universal joint in this context is to be understood to be any joint which can transmit a rotation by way of an angled routing of the shaft, for example, also a pin joint, or other construction modes.
In one design embodiment of the wobble shaft having such universal joints here it is particularly preferable for the sensor cable or the signal line to be routed into the first and/or the second universal joint, or to be routed through the first and optionally through the second universal joint, or to be routed about the first and/or the second universal joint. Such inward routing, or through-routing, into or through the first and/or the second universal joint is advantageous in terms of a protected installation of the sensor cable and the signal line, this can, in particular, also be combined with routing the sensor cable or the signal line, respectively, through the central portion of the wobble shaft. Wobble shafts having universal joints are often sealed in relation to the pumped medium by means of a sealing protective tube which is in each case disposed about each universal joint and seals the latter, or a protective tube which extends across both universal joints and the central portion of the wobble shaft is sealed in relation to the pumped medium. In such a case, the sensor cable or the signal line can also be installed between this protective tube and the wobble shaft, and as a result is likewise installed so as to be protected in relation to the pumped medium. In particular, the sensor cable or the signal line can also be incorporated in such a protective tube, or be placed between two protective tubes disposed as a double casing, or the like, in order to protect the sensor cable also in relation to mechanical stress by the wobble shaft.
It is particularly preferable here for the first universal joint to be enclosed by a first sealing boot, and for the second universal joint to be enclosed by a second sealing boot, or for the first and the second universal joint and the wobble shaft to be enclosed by a sealing sleeve, and for a pressure sensor to be disposed in the first and/or the second sealing boot or in the sealing sleeve, or for a pressure line to be routed in to the first and/or the second sealing boot or into the sealing sleeve, and for a pressure sensor to be fluidically connected to the pressure line in order to detect the pressure in the first and/or second sealing boot or in the sealing sleeve, and, for signaling, for the pressure sensor to be connected to an evaluation unit which by means of the pressure sensor is configured for detecting the pressure within the first and/or the second sealing boot or within the sealing sleeve, wherein the pressure sensor preferably detects the pressure of a pressurized medium which is supplied by way of a pressure line routed into the first and/or the second sealing boot, or into the sealing sleeve, or by way of the pressure line.
According to this refinement, a pressure sensor is disposed within one of the sealing boots or the sealing sleeve, or one pressure sensor is in each case disposed in each of the sealing boots, or a pressure line which accordingly is routed into a first or a second sealing boot about the first or the second universal joint, respectively, or into a common sealing sleeve of the first or the second universal joint and detects a pressure within these sealing boots, or the sealing sleeve, respectively, is used as the signal line. In particular, a first pressure sensor which is disposed within the first sealing boot or is connected to a pressure line which opens into the first sealing boot, and a second pressure sensor which is disposed within the second sealing boot or is connected to a pressure line which opens into the second sealing boot, can also be provided here. By way of the construction of a pressure detection within the sealing boots or the sealing sleeve, respectively, a decrease or increase in pressure within this sealing boot, which indicates a leakage of the sealing boot/sealing sleeve, can be reliably and directly detected. Such a leakage, which will ultimately rapidly result in access of the pumped medium to the universal joints, is an event which will directly result in high wear. The detection of this leak is, therefore, important in order to avoid such undesirable and high wear. In this case, the invention enables the sealing sleeve to be sealed or replaced before such wear arises, such wear thereafter requiring a complex repair including the replacement of one or both universal joints and optionally further mounting elements. It is particularly advantageous here for a pressurized medium to be supplied into the sealing boot or sealing sleeve, respectively, by way of a pressure line. This to the extent that a pressure line is provided as the signal line, can also take place by way of the signal line. As a result, it is possible for a pressure to be built up and maintained within the sealing boot. This permits, on the one hand, generation of a spacing between the sealing boot or the sealing sleeve, respectively, and the universal joints, as a result of which mechanical damage to the sealing boot or the sealing sleeve, respectively, by the universal joint can be avoided. On the other hand, a defined pressure within the sealing boot or the sealing sleeve, respectively, can be generated such that a pressure loss can be reliably established and be distinguished from pressure influences that are generated by the conveyed medium per se.
According to a further embodiment it is provided that the state sensor the state sensor for signal transmission is connected to an electronic evaluation unit and the electronic evaluation unit is configured for determining a variance of an actual state detected by the state sensor by means of the state sensor data from a predetermined target state, for comparing this determined variance with a predetermined permissible variance and, when the determined variance exceeds the permissible variance, for emitting an alarm signal.
It can, in particular, be provided here, when the electronic evaluation unit is configured for receiving a state sensor signal as the actual state, that the state sensor signal is compared with a stored normal state sensor signal as the target state, and the determined variance is calculated as a difference between the state sensor signal from the normal state sensor signal, and to utilize a predetermined permissible variance value as the predetermined permissible variance, and to emit a value alarm signal as the alarm signal. According to these refinements, the detection of a sensor signal of the state sensor, which signals an unfavorable operating state, thus an operating state that causes or will cause increased wear, is based on a comparison of target data and actual data. The target data here is present in an electronically stored form, for example, as a data value, a data value profile, an algorithmic description of a data value profile, or as a comparison table having a plurality of target values for different operating states of the eccentric screw pump. The target data can be predetermined and previously stored, thus be included in the eccentric screw pump ex works, so to speak, such that said target data contains characteristic values which are characteristic and constant in terms of the construction mode of the eccentric screw pump.
The target data can be defined by the pump-inherent constructive characteristics, such as the constant state values caused by the eccentricity, stress values defined by the drive train. However, the target data can also be determined as a reference or calibration value when pumping a specific medium, so as to be stored thereafter. This reference or calibration value can be determined by the user when initially pumping a specific medium, or when initially commissioning the pump in a specific installation situation, for example, and then be utilized for comparison in the further monitoring, thus during subsequent measurements of an actual value, such that critical changes in comparison to the original reference or calibration value can be immediately identified. In principle, any variance of the actual data from the nominal data can be emitted as an alarm. However, it is often practical for a tolerance range to be defined within which the actual value may vary about the nominal value without a critical operating state of the eccentric screw pump being defined as a result.
According to a further preferred embodiment it is provided that the electronic evaluation unit is configured for receiving state sensor signals, determining from at least two temporally sequential state sensor signals a state variation value as the actual state, comparing the state variation value with a stored normal state variation value as the target state, calculating the determined variance as the difference between the state variation value and the normal state variation value, utilizing a predetermined permissible variance variation value as the predetermined permissible variance, and emitting a variation alarm signal as the alarm signal.
It is furthermore preferable for the electronic evaluation unit to be configured for receiving state sensor signals, determining from at least three temporally sequential state sensor signals a state variation speed as the actual state, and comparing the state variation speed with a stored normal state variation speed as the target state, calculating the determined variance as the difference between the state variation speed and the normal state variation speed, utilizing a predetermined permissible speed variance as the predetermined permissible variance, and emitting a variation speed alarm signal as the alarm signal.
According to these refinements, a state variation signal which characterizes the variation of two temporally sequential actual values is determined. This state variation signal can be understood to be the first temporal derivation of the state signal, and often results in an evaluation basis for a critical operating state that has arisen or is developing that is better than the absolute value of a state signal. Likewise, a state variation speed can be determined from temporally sequential state sensor signals, this to be understood to be the second temporal derivation of the state signal. By calculating and utilizing this state variation value or the state variation speed, the speed on the one hand, and the acceleration by way of which the state signal changes, on the other hand, are determined. These two values are better suited for many physical variables which are detected on the rotor or on the driveshaft than the state signal alone in order to detect a critical operating state of the eccentric screw pump that has arisen or is developing. When the state signal alone is detected, only one limit value that is considered critical can often be defined. However, in order to permit the normal operation without interruptions and alarms, this limit value has to be defined so as to be actually close to the critical limit. In contrast, when detecting the variation rate of the state signal or the speed by way of which this variation rate changes, it can be identified already in a range which is still permissible in terms of the absolute value of the state signal whether the eccentric screw pump is moving toward a critical operating state. For example, a sizeable increase of the pressure in the eccentric screw pump, or a very rapid variation of the increase or decrease of the pressure, can indicate a state of wear on the pressure side of the pump or a state of wear on the suction side of the pump, and can be identified at an early stage so as to establish an actuation of the eccentric screw pump as a result. Likewise, a sizeable increase in temperature or a sizeable variation rate of the temperature increase, thus an accelerated increase in temperature, can already signal dry running even when the absolute temperature has not yet reached a critical state value. Here too, a real-time response of the control of the eccentric screw pump as a result of the direct state detection on the rotor, or on the driveshaft, respectively, and the consideration of differences after the first temporal derivation or the second temporal derivation enabled as a result, can be achieved by monitoring the state, said real-time response being able to pre-empt the occurrence of damage and wear.
It is overall furthermore preferable here for the electronic evaluation unit to be configured for comparing a plurality of temporally sequential actual states with a plurality of temporally sequential target states, and calculating from the comparison a variance characteristic value as the determined variance, and utilizing a predetermined permissible variance characteristic value as the predetermined permissible variance. According to this embodiment, a predetermined variance for the determined variations of the state variables, or variations of the variation speeds of the state variables is utilized in order to enable an operation within a tolerance window considered to be non-critical and to trigger a corresponding alarm when this tolerance window is exceeded.
It is furthermore preferable that the eccentric screw pump has a rotor having a conical envelope and a conically tapering stator interior, and the rotor and the stator are adjustable relative to one another in the axial direction by means of an axial actuating drive, the electronic evaluation unit for signal transmission is connected to the axial actuating drive and configured for actuating the actuating drive so as to carry out an axial adjustment between the rotor and the stator, and detecting a plurality of temporally sequential state sensor signals of the state sensor during the axial adjustment process. According to this embodiment, an adjustability of the radial gap between the rotor and the stator by means of a conically tapered rotor and stator is enabled in that an axial adjustment movement takes place between the rotor and the stator. To this end, the stator can be embodied so as to be stationary, and the rotor can be axially adjustable. The axial adjustment installation can, in particular, be embodied in such a manner that an axial adjustment of the rotor can take place in the ongoing operation, for example, in that the rotor conjointly with the wobble shaft and the drive motor can be axially adjusted. To this end, an actuatable actuator can be used for example, which preferably can set a predetermined axial position by way of a path sensor. The drive motor or other parts of the drivetrain can also be configured so as to be axially stationary and to be connected to the rotor by means of a torque-transmitting axial thrust connection. The axial adjustment movement of the rotor typically influences the state signal and can be utilized for achieving a state signal variation. According to the invention, to this end, at least one state signal is detected during the adjustment procedure, preferably a plurality of sequential state signals. The axial adjustment movement can take place as a function of the state signals. This can thus take place by a control of the axial adjustment or a feedback-control loop in that the state signal serves as an input or command variable, and the axial adjustment movement serves as an output or control variable. The axial adjustment between the rotor and the stator permits a spontaneous correction of the operating state of the eccentric screw pump. Said axial adjustment can be used for optimizing a start-up procedure of the pump, for example in order to achieve a power-saving ramping up with a larger gap, and for thereafter reducing the gap upon reaching the desired rotating speed or during the ramping up. Furthermore, the axial adjustment by means of monitoring a state signal such as the drive output, the torque or the temperature can take place until an ideal gap in terms of pump efficiency and wear is obtained between the rotor and the stator.
It is furthermore preferable for the state sensor to be disposed on the driveshaft or the rotor and to be furthermore connected with a state sensor data transmission module for wirelessly transmitting state data to a data receiver outside the eccentric screw pump, wherein the state sensor and the state sensor data transmission module for receiving electric energy are connected to an energy converter which is disposed on the rotor or on the driveshaft and is configured for converting kinetic or thermal energy acting on said energy converter into electric energy. According to this embodiment, the state sensor is disposed as an autonomous module on the rotor or the driveshaft and wirelessly transmits the state data to a receiver spaced apart from said state sensor. The energy required for detecting and transmitting the state data here is provided by way of an energy converter which is likewise disposed on the rotor or the driveshaft and is connected directly to the state sensor for transmitting energy, or is embodied as a common module with said state sensor. For example, the energy converter can be embodied such that said energy converter generates electric energy by way of induction from the rotation movement, from a resultant acceleration or vibration. Other types of converters can also be used, for example thermal converters which generate electric energy from a temperature of the pumped medium.
It is particularly preferable for the energy converter to be selected from:
It is furthermore preferable for two state sensors, which are disposed on two mutually spaced apart positions, to be disposed on the rotor, and for the positions to have a phase shift of the measured state variable, wherein the phase shift is preferably achieved by an axial spacing of the state sensors that is larger or smaller than an integral multiple of the pitch of the rotor, or by an angular spacing of the two state sensors that is unequal to an integral multiple of 360° divided by the number of pitch courses of the rotor. A simultaneous, phase-shifted measurement of two state variables is achieved by this embodiment. A phase shift here is understood to mean a detection of the two state variables within a periodic profile, this taking place at two points of the periodic profile that are not mutually spaced apart by exactly an integral multiple of the wavelength of the periodic profile. In the case of the detection of these two state variables by means of two state sensors on a triple-turn eccentric screw rotor this can take place by different ways of positioning. The phase shift can thus be achieved, for example, in that the two state sensors in the axial direction are indeed not mutually spaced apart, thus lie in the cross-sectional plane of the rotor, but in this cross-sectional plane have a mutual angular offset which differs from the quotient 360°/n, where n is the number of thread courses of the rotor. Accordingly, a phase-shifted measurement in the case of a triple-turn rotor can be carried out when the state sensors are mutually offset by an angle which is not equal to 120° or equal to 240°, thus when said state sensors are mutually offset by 90° or by 180°, for example. In the case of a dual-turn rotor, the angular offset would have to be unequal to 180° in order to achieve a phase-shifted measurement; in a quadruple-turn rotor said angular offset would have to be unequal to 90°, 180°, and 270°. It is to be taken into account here that the number of thread courses of the stator in the case of eccentric screw pumps for reasons of principle always exceeds the number of thread courses of the rotor by 1.
However, a phase-shifted measurement can also be achieved when the state sensors have an angular offset which corresponds to the quotient 360°/n, in that the state sensors are axially spaced apart by a distance which is unequal to a multiple of the pitch of the thread of the rotor. The pitch here is understood to be the axial spacing of two adjacent crests of thread, and in the case of a single-turn thread corresponds to the lead, in a multi-turn thread corresponds to the quotient of lead/number of thread turns (n). A phase shift can, in particular, be set in that the state sensors are mutually spaced apart by an axial distance which corresponds to half the pitch such that a phase shift by half the wavelength is achieved.
Particularly favorable monitoring of specific indicators of wear is achieved by the measurement using a phase shift. In this way, by subtracting the sensor signals of the two state sensors, a measured variable which is adjusted in terms of effects which arise only in one phase can be obtained, this measured variable permitting a statement to consequences of wear that arise locally in an angular range. Moreover, a relative statement pertaining to state variations can be obtained by comparing sensor signals that have been obtained so as to be temporally offset by the phase shift.
Alternatively or additionally it is also advantageous in specific applications when two state sensors are disposed on the rotor, which are disposed on two phase-equal positions mutually spaced apart, wherein the phase equality is preferably achieved by an axial spacing of the state sensors that corresponds to a multiple of the pitch of the rotor, or by an angular spacing of the two state sensors by an angle which is an integral multiple of 360° divided by the number of thread turns. Achieved by this embodiment is a simultaneous, phase-synchronous measurement of two state variables. This measurement mode permits a comparison of two state values detected simultaneously at different positions, and can, therefore, enable a direct conclusion pertaining to locally caused operating state variations.
It can, in particular, also be preferable for three or more state sensors to be provided, of which two state sensors are mutually disposed by a phase shift and two state sensors are disposed in equal phases, so as to combine the advantages explained above and to achieve a comprehensive statement pertaining to the operating state.
It is furthermore preferable for the state sensor to be a temperature sensor, a pressure sensor, a vibration sensor, or an acceleration sensor.
An evaluation by means of a comparison with a previously stored and/or calibrated master curve here can offer information pertaining to a developing temperature equilibrium. Detailed analysis of the curved profile while taking into account the gradient and the curvature permit additional evaluation possibilities. In this way, the relaxation time constant correlates with the dynamic properties of the elastomer jacket of the stator, for example. A comparison of the surface integrals describes the damping performance during the running-in phase.
In principle, a pressure differential which can be used for calculating a volumetric flow, for example, can be determined by a measurement by means of two or more pressure sensors that are spaced apart axially along the rotor axle.
For example, it is possible to monitor the natural frequency of the rotor-stator system as a result of the continual excitation in the pumping operation by way of a measurement of the vibration generated in the rotor performed by way of an acceleration sensor or a vibration sensor. Conclusions pertaining to the material and structural properties of the rotor can then be made by changing significant signal proportions, and the occurrence or the propagation of cracks or deformations of the stator can thus be identified, for example. Furthermore, it is possible to detect the impact of comparatively massive foreign matter which is entrained in the conveyed medium, such as stones or screws, for example. When such an operating state is detected, the user of the pump can then be warned about damage by this foreign matter and thus verify his/her pumping process so as to pre-empt damage to the pump, or a control measure which is directly derived from the state sensor signal can be carried out, for example, an emergency stop of the pump or a reduction of the rotating speed.
Preferred embodiments of the invention will be explained by means of the appended figures, in which:
Shown in
The stator interior and the rotor can taper in the axial direction, i.e., in the pumping direction (not illustrated), such that the end of the rotor and of the stator interior that points toward an inlet opening 1 has a larger cross-sectional area than the end pointing toward the outlet opening 2. In such tapered rotors and stators (typically having a conical envelope, or being equipped with a conically tapered interior, respectively), the rotor and the stator in this instance are disposed so as to be axially mutually displaceable (axial movement Ax). An axial actuation in this instance is preferably possible during the rotating movement Ro of the rotor. As a result, play due to wear, or insufficient pre-tensioning of the rotor, in the stator, respectively, can be compensated for, on the one hand, in that the rotor is driven further into the stator. Moreover, a start-up behavior of the pump can be optimized by the axle adjustment, for example in that axial adjustment is performed by means of the state variables as a function of the pumping behavior. For example, a response to different viscosities of the conveyed medium is possible.
The rotor 20 by a wobble shaft 30 is set in rotation about the rotor longitudinal axis B of said rotor 20. The wobble shaft 30 here is inserted between the rotor and a drive input shaft which by way of a belt drive 41 is driven by a drive motor 40, said wobble shaft 30 transmitting a rotating movement of the drive motor 40 to the rotor 20. The wobble shaft 30 here extends from a drive input end 30a, which in the rotating manner is mounted in an inlet housing 50, to a drive output end 30b which is connected to the rotor. The wobble shaft 30 at the drive output end 30b performs a combined movement which is composed of a rotation about the rotor longitudinal axis B and of a rotation of the rotor longitudinal axis B about the stator longitudinal axis A. At this drive output end, the wobble shaft can be guided by means of an eccentric mounting, which is embodied by two rotary bearings having eccentrically offset axes, or said wobble shaft may be without guidance so that the movement of the drive output end of the wobble shaft is defined by the guidance of the rotor in the stator.
The wobble shaft 30 on the drive input end 30a has an input universal joint 31, and on the drive output end has an output universal joint 32. A shaft portion 33, which connects the two universal joints 31, 32, extends between the two universal joints 31, 32. The input universal joint 31 is connected to the drive input shaft, and by way of the belt drive connected to the output shaft of the drive motor 40. The output universal joint 32 is connected to the rotor.
The entire wobble shaft 30 is disposed in an inlet housing 50 and is surrounded by the wash of a medium to be pumped, which by way of an inlet opening 51 flows into the inlet housing 50. This represents the suction side of the pump. Therefore, the wobble shaft is entirely surrounded by a protective casing 36 which extends across the input universal joint 31, the shaft portion 33, and the output universal joint 32.
The rotor 20 and the stator 10 extend from an inlet end 10a, which is fastened to the inlet housing, to an outlet housing 60, which is fastened to an outlet end 20a. An outlet opening 61 is disposed on the outlet housing 60, the conveyed medium from the pump flowing through said outlet opening 61, the latter representing the pressure side of the pump.
In the embodiment according to
In this case, the signal line also runs through corresponding transverse bores in the pins of the two universal joints. It is to be understood here that the ducts in which the signal line runs, in terms of the dimensions thereof are embodied in a corresponding size such that the signal line remains free of shear effects and thus free of damage even in the wobbling movement arising during operation and during the bending of the universal joints.
The drive input shaft in
Different variants of the disposal of the sensor on the rotor are illustrated in
In general, a disposal of the sensor in the external surface of the rotor is advantageous because this position enables a revolving signal detection, on the one hand, and thus a signal detection across an angle of rotation of 160° about the rotor longitudinal axis or stator longitudinal axis, respectively, and thus enables a type of cross-sectional detection of the signal. The disposal of the sensor on the rotor is furthermore advantageous, in particular when the sensor is disposed in the region of the external surface of the rotor, because there is the possibility of carrying out by way of the sensor a signal detection of a characteristic value on the stator as well as a characteristic value on the rotor as well as a characteristic value of the conveyed medium during the ongoing operation. This signal detection can take place, in particular, during a revolution of the rotor across 360°. This is made possible in that, in the case of this sensor position on or close to the surface of the rotor, the sensor during the operation of an eccentric screw pump comes in direct contact with the stator, on the one hand, and during the further rotation also comes to be spaced apart from the stator, on the other hand, and as a result comes in contact with the conveyed medium, as a result of which it is in each case possible for the stator and the conveyed medium to be periodically detected. Moreover, the disposal in the rotor per se also makes measuring toward the rotor possible. This can, in particular, be a temperature measurement in which, depending on the angle of rotation of the rotor about the rotor longitudinal axis, the temperature of the stator is measured at specific angles, angular ranges, or across the entire circumference in relation to the stator longitudinal axis, and the temperature of the conveyed medium is moreover measured. Furthermore, for example in that the sensor is embodied with a plurality of probes, the temperature of the rotor can also be detected by the sensor. It is to be fundamentally understood that the sensor can also be embodied as a sensor unit and can detect a plurality of measurement functions for identical or dissimilar physical variables.
The sensor position shown in
Shown in
In both the embodiments according to
Plotted in
The effects behind these curved profiles depend on various factors, and the curved profile can, therefore, not be explained in terms of a general cause. On the one hand, the initial fit between the rotor and the stator plays a role; an initially tight fit can here lead to an initially high import of frictional energy, the latter then decreasing. On the other hand, the dynamic stiffness of the elastomer (of the stator) also plays a role, for example, said dynamic stiffness describing the ability for propagating vibrations and thus the transport of energy/temperature. Said dynamic stiffness changes during the running-in and starting-up phase 3011 and, when said dynamic stiffness drops, can lead to an increase in temperature which has to be directed through the elastomer.
The temperature curve T2 here represents a curve with the comparatively steepest increase whereas the curve T1 has indeed a lesser gradient but climbs to a higher temperature level than T2 by a difference ΔT12. This more steeply increasing temperature curve T2 correlates, for example, with a more heavily decreasing dynamic stiffness or other properties of the elastomer of the stator. The comparison of the stationary temperatures ΔT12 can signal a pumping situation involving a medium with better lubricating properties and a lower temperature, for example. In contrast, a temperature curve T3 having a flatter profile and in relation thereto a settled constant temperature which is lower by ΔT13 can arise in the case of an identical conveyed medium at a lower rotating speed of the pump, for example.
It can be seen here that the positions which in the Z-direction and the Y-direction have a mutual phase shift of 90° have a similar profile in both figures, whereas the position in the X-direction in the normal operating state has an almost stationary value which is subject to certain minor fluctuations only by pulsed pressure influences and axial play in the bearings.
In contrast,
The operating state of the pump, as a result of the measurement of the trajectory shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 111 386.2 | Apr 2020 | DE | national |
The present application claims the benefit under 35 U.S.C. §§ 119(b), 119(e), 120, and/or 365(c) of PCT/EP2021/060932 filed Apr. 27, 2021, which claims priority to German Application No. 10 2020 111 386.2 filed Apr. 27, 2020.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/060932 | 4/27/2021 | WO |
