MONITORING METHOD FOR MONITORING THE OPERATION OF A DOSING PUMP AND DOSING PUMP SYSTEM

Abstract

A monitoring method and dosing pump system monitor operation of a dosing pump including a dosing chamber (2), a displacement element (4) and an electric drive (12). A position (S) of the displacement element and a pressure (P) inside the dosing chamber are continuously recorded as a curve in a pressure-stroke diagram. The method includes monitoring at least one characteristic portion (36, 38, 40, 42, B, C) of the curve in the pressure-stroke diagram by detecting a possible shift (A) of the characteristic portion over several strokes. The method further includes one or both of: adjusting a control of the electric drive based on the detected shift; and determining a trend of the shift over several strokes of the displacement element and determining based on the trend whether and/or when the shift will reach a predefined limit. A dosing pump system with the dosing pump execute the method.

Claims

1. A monitoring method for monitoring the operation of a dosing pump comprising a dosing chamber with at least one displacement element and an electric drive, the method comprising the steps of: detecting and recording a position of the displacement element and a pressure inside the dosing chamber or a pressure related indicator as a curve in a pressure-stroke diagram; monitoring at least one characteristic portion of said curve in said pressure-stroke diagram and detecting a possible shift of the at least one characteristic portion over several strokes of the displacement element; and taking one or both of the following steps based on said detected shift: adjusting a control of the electric drive based on the detected shift of the at least one characteristic portion; and determining a trend of the shift of the of the at least one characteristic portion over several strokes of the displacement element and determining based on the determined trend whether the shift of the least one characteristic portion will reach a predefined limit in the future or when the shift of the at least one characteristic portion will reach a predefined limit in the future or both whether and when the at least one characteristic portion will reach a predefined limit in the future.

2. A monitoring method according to claim 1, wherein based on when the shift of the at least one characteristic portion will reach a predefined limit a time period is calculated as a predicted time period until failure and/or a warning based on the calculated time period and is output to a communication device, a display device and/or a control device.

3. A monitoring method according to claim 1, wherein the trend is determined based on the average speed of the shift of the at least one characteristic portion.

4. A monitoring method according to claim 1, wherein a time period, based on when the shift of the at least one characteristic portion will reach a predefined limit, is calculated by an extrapolation based on the trend.

5. A monitoring method according to claim 1, wherein a time period, based on when the shift of the at least one characteristic portion will reach a predefined limit, is calculated based on a remaining interval between a last recorded value of the at least one characteristic portion or an average of last recorded values of the at least one characteristic portion and said predefined limit.

6. A monitoring method according to claim 1, wherein said at least one characteristic portion is defined by at least one characteristic point of the curve.

7. A monitoring method according to claim 1, wherein said at least one characteristic portion is one or more of: a section of the curve; a turning point or turning portion of the curve; an inflexion point or inflexion portion of the curve; and a saddle point or saddle portion of the curve.

8. A monitoring method according to claim 1, wherein the at least one characteristic portion is one or more of: an indicator for cavitation; an indicator of air inside a pumping cavity; an indicator of overpressure; an indicator of leakage; an indicator of valve leakage; an indicator of clogging of a flow path; an indicator of malfunction of a pulsation damper; and an indicator of a line burst.

9. A monitoring method according to claim 1, wherein the at least one characteristic portion of the curve is one or more of: in a section of the curve representing a suction stroke of the displacement element; in a section of the curve representing a pressure stroke of the displacement element; in a section of the curve presenting an expansion phase; in a section of the curve representing a phase of pressure buildup; and in at least one transition section between said sections of the curve.

10. A monitoring method according to claim 1, wherein a calculation of the time period, based on when the shift of the at least one characteristic portion will reach a predefined limit, is continuously or periodically updated.

11. A monitoring method according to claim 1, wherein the control of the electric drive is adjusted by changing a stroke pattern to compensate a malfunction causing the detected shift of the at least one characteristic portion, to reduce the detected shift at least partly or to decelerate a future shift.

12. A dosing pump system comprising: a dosing pump comprising: a dosing chamber; at least one movable displacement element associated with the dosing chamber; and a drive connected to said displacement element for moving the displacement element; and a control device configured to: continuously record a position of the displacement element and at least one of a pressure inside the dosing chamber and a pressure related indicator as a curve in a pressure-stroke diagram; monitor at least one characteristic portion of said curve in said pressure-stroke diagram; detect a possible shift of the at least one characteristic portion over several strokes of said displacement element; and one or more of: adjust a control of the electric drive based on the detected shift of the at least one characteristic portion; and determine a trend of the shift of the at least one characteristic portion and based on the determined trend determine whether the shift of the least one characteristic portion will reach a predefined limit in the future or when the shift of the at least one characteristic portion will reach a predefined limit in the future or both whether and when the at least one characteristic portion will reach a predefined limit in the future.

13. A dosing pump system according to claim 12, further comprising at least one of a display device connected to the control device and a communication device forming a part of the control device or connected to the control device, wherein the control device is configured to: calculate a time period based on when the shift of the at least one characteristic portion will reach a predefined limit; and output the calculated time period via at least one of the display device and the communication device.

14. A dosing pump system according to claim 12, wherein the control device and the dosing pump are integrated into a dosing pump unit or the control device is arranged at a distance to the dosing pump and connected to the dosing pump via a data connection.

15. A dosing pump system according to claim 12, wherein: the dosing pump further comprises at least one of a force sensor and a pressure sensor connected to the control device such that the control device receives one or more of force values and pressure values representing pressure inside the dosing chamber from said at least one of a force sensor and a pressure sensor; or the control device is connected to the electric drive motor to receive data representing pressure inside the dosing chamber from said drive motor.

16. A dosing pump system according to claim 12, wherein the control device is configured such that a stroke pattern of the displacement element is changed to compensate a malfunction causing the detected shift of the at least one characteristic portion and to reduce the shift at least partly.

17. A dosing pump system according to claim 12, wherein the control device is configured to carry out a monitoring method comprising the steps of: detecting and recording the position of the displacement element and the pressure inside the dosing chamber or the pressure related indicator as a curve in a pressure-stroke diagram; monitoring at least one characteristic portion of said curve in said pressure-stroke diagram and detecting a possible shift of the at least one characteristic portion over several strokes of the displacement element; and taking one or both of the following steps based on said detected shift: adjusting a control of the electric drive based on the detected shift of the at least one characteristic portion; and determining a trend of the shift of the of the at least one characteristic portion over several strokes of the displacement element and determining based on the determined trend whether the shift of the least one characteristic portion will reach a predefined limit in the future or when the shift of the at least one characteristic portion will reach a predefined limit in the future or both whether and when the at least one characteristic portion will reach a predefined limit in the future.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In the drawings:

[0033] FIG. 1 is a schematic view of a dosing pump according to the invention;

[0034] FIG. 2 is a pressure-stroke diagram;

[0035] FIG. 3 is a pressure-stroke diagram in case of a leakage;

[0036] FIG. 4 is a pressure-stroke diagram in case of different diameters or resistance of a pressure line;

[0037] FIG. 5 is a pressure-stroke diagram in case of a malfunction of the pressure loading valve;

[0038] FIG. 6 is a pressure-stroke diagram in case of pressure peaks;

[0039] FIG. 7 is a pressure-stroke diagram in case of occurring cavitation; and

[0040] FIG. 8 is a pressure-stroke diagram for the case of gas bubbles in the dosing chamber.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0041] Referring to the drawings, FIG. 1 as an example of a dosing or metering pump shows a membrane pump. It has to be understood that the invention may be carried out in similar manner with other type of dosing pumps, for example metering or dosing pump using a piston instead of a membrane as a displacement element. The pump as shown in FIG. 1 has a pump or dosing chamber 2, a side wall of which is formed by a membrane 4. This membrane 4 is the displacement element. By displacement of the membrane 4 the volume inside the dosing chamber 2 can be increased for filling the dosing chamber 2 and decreased for discharging the liquid from the dosing chamber 2. At the lower side of the dosing chamber 2 there is arranged a suction valve 6 whereas on the opposite side there is arranged a pressure valve 8. Both valves are designed as check valves. In this case where the ball shaped valve elements are closing the valve by gravity. However, additionally a biasing element as a spring can be provided. During operation liquid is sucked from a liquid container 3 via a suction line 5 through the suction valve 6 into the dosing chamber 2 and discharged out of the dosing chamber 2 through the pressure valve 8. From the pressure valve 8 the liquid is discharged via a pressure line 9 and a pressure loading valve 7 for example into a pipe 11 of a facility. The pressure loading valve 7 in the pressure line 9 defines the pressure in the pressure line 9, i.e. maintains the pressure on the outlet side of the pressure valve 8 at a predefined pressure. This pressure is set by the pressure loading valve 7. Connected to the supply line 9 is a pulsation damper 13 for equalizing a pressure pulsation occurring in the outlet or pressure line 9.

[0042] The membrane 4 is moved in a reciprocating manner via the connection rod 10. For driving the connection rod 10 in the reciprocating manner there is provided an electric drive in the form of an electric drive motor 12, for example a stepper motor. The rotating drive motor 12 moves the connection rod 10 via an eccentric drive 14 transferring the rotational movement into a linear reciprocating movement. The eccentric drive 14 is coupled to the electric drive motor 12 via a gear drive 16. The connection rod 10 is connected to the eccentric drive 14 at a connection point 18 which is distanced (spaced a distance) from the rotational axis x of the eccentric drive 14 by the eccentricity e. This causes the linear movement of the connection rod 10 into direction S if the eccentric drive 14 is rotated in the rotational direction R. In this example, furthermore, a spring 20 is arranged in the drive. The spring 20 is a compression spring connected to the connection rod 10 such that the spring 20 is compressed when the connection rod 10 is moved backwards into direction S1 moving the membrane 4 in the retracted position. The spring 20 can accumulate energy during the suction stroke. This energy is released during the pressure stroke when the connection rod 10 together with the membrane 4 is moved in the forward, i.e. advanced position in the direction S2. By this the spring 20 smoothes the torque to be applied by the electric drive motor 12 during the entire stroke. It has to be understood that it is also possible to arrange a spring that is compressed during the pressure stroke and acts as a return spring. Furthermore, the invention may also be realized without a spring 20.

[0043] The dosing pump has a control device 22 controlling the electric drive motor 12. The control device 22 comprises a monitoring module 24 for monitoring the operation of the dosing pump. The control device 22 may comprise usual electronic components like in particular a CPU, a storage device and software applications for control of the dosing pump. The monitoring module 24 may preferably be realized as a software module. In this example the monitoring module 24 is integrated into a control device 22. However, it would be possible to transfer information to an external computing or monitoring device, in particular a cloud device acting as a monitoring module 24. For this the control device 22 may comprise a communication interface 26.

[0044] The monitoring module 24 is configured to continuously record a pressure P inside the dosing chamber 2 and the position of the displacement element. The pressure inside the dosing chamber 2 and the position of the displacement element, i.e. the membrane 4 are recorded as a curve in the pressure-stroke diagram. For detecting the position of the membrane 4 along the direction S in this example an encoder 28 detecting the angular position of the rotor of the drive motor 12 is used. Furthermore, it is possible to detect certain positions of the drive or the displacement element, for example by a single sensor and to calculate the further positions on the basis of the known velocity of the displacement element and the time past. Furthermore, instead of a special encoder a stepper motor may be used. With knowledge of the transmission ratio of the gear drive 16 and the geometrical design of the eccentric drive 14 based on the angular position, the position in direction S can be calculated. The pressure P inside the dosing chamber 2 may either be detected by a pressure sensor 30 or may be indirectly detected by detecting the torque of the drive motor 12 or a force acting in the drive (pressure related indicators) and calculating the pressure P on the basis of the force F acting onto membrane 4. In this example a pressure sensor 30 is arranged at the dosing chamber 2 and connected to the control device 22. In case that a force or torque is detected, it would be possible to continuously record this torque or pressure over the position of the displacement element instead of recording the pressure. In view of this pressure and the proportional force or torque can be regarded as being equivalent (the pressure related indicators).

[0045] FIG. 2 shows the pressure-stroke diagram as detected by the monitoring module 24 in general. The abscissa shows the stroke lengths S in percent, i.e. the linear movement of the membrane 4 between its position representing the minimum volume of the dosing chamber 2 and the position defining the maximum volume of the dosing chamber 2. The ordinate shows the pressure P as detected by the pressure sensor 30. A stroke of zero percent corresponds to the lower dead center 32 and the stroke length of hundred percent corresponds to the upper dead center 34. The curve in the diagram comprises four main portions, forming characteristic portions, representing the four essential phases of the membrane movement. The lower portion of the curve represents the suction phase 36, the portion with rapidly increasing pressure on the left side represents the compression phase 38, the upper portion represents the discharge phase 40 and the right portion with rapidly decreasing pressure represents an expansion phase 42. The expansion phase 42 together with the suction phase 36 corresponds to a movement of the membrane 4 in the direction S1, whereas the compression phase 38 and the discharge phase 40 form the pressure stroke in direction S2.

[0046] The monitoring module 24 of the control device 22 continuously records or monitors the pressure-stroke diagram so that changes in the pressure-stroke diagram over time or over several strokes can be detected by the monitoring device. Different problems or malfunctions which may occur in the dosing pump have different effects on the course of the curve in the pressure-stroke diagram. Those effects are discussed in more detail with reference to FIGS. 3 to 8.

[0047] In FIG. 3 there is shown an abnormal curve 44 which will occur in case that the suction valve 6 or dosing chamber 2 has a leakage. In this case there is less or no pressure buildup, since the liquid flows back into a suction line or out of dosing chamber 2. In case of a suddenly occurring leakage, the curve may directly change to a course of the curve 44 as shown in FIG. 3. However, in most cases the leakage will increase slowly so that the curve will shift over time from the course 38 and 40 towards the course 44. This is indicated by the curve 46 in broken line which shows an intermediate condition. The shift A of the characteristic portion 38 is detected by the monitoring module 24 over time so that a trend, i.e. the speed of the shift A can be calculated. The dotted line represents a limit curve 48. This is a predefined acceptable limit 48 for the shift A. When this limit is reached the dosing pump has to be repaired and the production has to be stopped, for example. On the basis of the trend of the shift A it is possible to make a prediction whether this time limit will be reached in the future and when this limit will be reached. In knowledge of the distance D remaining between the present position 46 of the characteristic portion 38 and the limit curve 48 the time when the limit 48 will be reached can be calculated. This can be output by the control device 22 for example on a display 50 or output to an external control device connected via the communication interface 26.

[0048] As an alternative or in addition to this prediction the control device 22 may initiate a compensation at least partly eliminating the shift A of the curve or reduce the speed of the shift A to prolonge the time until the limit 48 will be reached. This can be done by changing the control of the electric drive motor 12 such that a different stroke pattern is realized. For example, the speed may be increased to compensate a loss of liquid to be delivered due to the leakage.

[0049] FIG. 4 shows a further possible malfunction which may be detected. FIG. 4 shows the course of the characteristic portion 40 of the curve in case that the pressure line 9 connected to the pressure valve 8 has a reduced crosssection, for example due to clogging. In this case the shift A is in a direction to higher pressure, i.e. the pressure in the discharge phase 40 will increase over time. By detecting the trend, i.e. the speed of the shift A over several strokes it is possible to make an extrapolation to predict the time for the remaining shift A until the limit value 48a will be reached.

[0050] FIG. 5 shows the course of the curve in the case that the pressure loading valve 7 is not closing completely, for example due to dirt or wear. In this case the characteristic point B being the transition point between the compression phase 38 and discharge phase 40 will move in the direction of shift A towards lower pressure and the maximum pressure P will be reached earlier in the stroke. The point B thus, moves substantially along the curve representing the compression phase 38 towards lower pressure. This occurs since the maximum pressure P cannot be reached anymore. However, in a difference compared to the curve shown in FIG. 3 there is still a pressure buildup with substantially unchanged inclination, since the suction valve 6 still securely closes. Also, in this case the trend of the shift A can be detected to make a prediction how long it will take in the future until a limit value 48b will be reached.

[0051] FIG. 6 shows the curve with pressure peaks or spikes 52 in the discharge phase 40 in consideration to the stroke frequency. Those pressure peaks or spikes 52 may occur in case that the pulsation damper or damping element has a failure or is not installed in a correct way. In case of a slowly occurring failure these spikes or peaks 52 will increase over time. Thus, also in this case a shift A can be detected, and a trend of this shift A can be calculated to make an extrapolation or prediction until a certain limit value 48c will be reached. Furthermore, also in this case the control device 22 preferably makes a compensation control action to reduce or avoid these pressure peaks 52. This can for example be done by reducing the speed of the drive motor 12 at the beginning of the discharge phase 40.

[0052] FIG. 7 shows the curve in case of occurring cavitation. In this case there will be a shift A of the characteristic portion of the curve representing the suction phase 36. With increasing cavitation in the suction stroke 36, pressure equalization will be reached later. Thus, there is a shift A of the characteristic portion 36 of the curve towards lower pressure. At the same time the characteristic portion 38 has a shift A to the right side in the diagram according to FIG. 4, i.e. the pressure buildup will occur later during the pressure stroke, since first the pressure equalization must be reached. Also, in this case a slowly occurring or increasing cavitation over several strokes can be recorded and a trend of the shift A can be calculated and used for an extrapolation to predict when a limit 48d will be reached.

[0053] FIG. 8 shows a curve in case that air bubbles occur inside the liquid in the dosing chamber 2 or the dosing chamber 2 is filled with air only. Due to the compression of the air in this case the pressure buildup requires a greater stroke length, i.e. takes longer with the effect of a reduced discharge. Also, in this case there is a shift A of the characteristic portion 38 representing the compression phase towards a greater stroke length, i.e. to the right side in FIG. 8. However, compared to occurring cavitation there is a further difference. The characteristic portion 38 is increasingly curved and there is no shift of the characteristic portion 36 of the curve and in particular not of the characteristic point C representing the transition point between suction phase and compression phase. If there is an increasing amount of air inside the system over several strokes, also in this case a trend of the shift A can be taken to make a prediction when a predefined limit will be reached.

[0054] It has to be understood that the problems explained with reference to FIGS. 3 to 8 are examples, only. There are further occurring problems or malfunctions which can be detected by monitoring the curve in the pressure-stroke diagram. In all cases the shift A of a characteristic portion or point in the curve or several characteristic portions and/or points are detected by the monitoring module 24. Furthermore, it is possible to calculate a trend, i.e. a speed of the shift over time or over several strokes and to make a prediction for the future when a predefined limit will be reached in the future with the detected trend or speed of the shift. Thereby the remaining distance of the detected position of the characteristic point(s) or portion(s) and the limit is regarded. For the current point or position an average over a certain number of strokes may be regarded.

[0055] Furthermore, the control device 22 may change the drive pattern by changing the control of the drive motor 12 to compensate certain problems to eliminate the shift A or to prolonge the time until a limit will be reached.

[0056] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

LIST OF REFERENCE CHARACTERS

[0057] 2 dosing chamber, pumping cavity
3 liquid container
4 membrane, displacement element
5 suction line
6 suction valve
7 pressure loading valve
8 pressure valve
9 pressure line
10 connection rod
11 pipe
12 electric drive motor
13 pulsation damper
14 eccentric drive
16 gear drive
18 connection point
20 spring
22 control device
24 monitoring module
26 communication interface
28 encoder
30 pressure sensor
32 lower dead center
34 upper dead center
36 suction phase
38 compression phase
40 discharge phase
42 expansion phase
44, 46 curves
48, 48a, 48b, 48c, 48d limit
50 display
52 peaks
R rotational direction
S, S1, S2 linear direction
e eccentricity
x rotational axis
A shift
P pressure
D distance
B, C characteristic points