Operation control device for limiting the amount a positive displacement pump over or undershoots a target operating parameter value, pump system and method for operating such

Abstract

An operational control device is disclosed for a positive-displacement pump having a motor, means for actuating the motor, state sensor means for detecting an actual operating parameter (e.g., pressure) of the pump, and operating mode means for controlling an operating mode of the pump. A first actuating mode of the operating mode means is set by the actuating means below a first operating-parameter threshold value (P1). This mode brings about a constantly rising pump pressure in the direction of an operating-parameter setpoint value (Pset) in a variable manner, which is dependent on a detected change in the operating parameter over a predefined time interval. A second actuating mode is set as normal operation to the operating-parameter setpoint value by the actuating means above the first operating-parameter threshold value. P1 is fixed or is calculated as a fraction of the operating-parameter setpoint value and/or a pump parameter correlated therewith.

Claims

1. A system for operating a positive displacement pump having a pump motor, the system comprising: a control unit for receiving threshold values of an operating parameter; and a frequency converter connected between the control unit and the pump, the frequency converter for receiving the operating parameter for actuating the pump; wherein the control unit is configured to control operating the pump motor in a first actuating mode when the operating parameter of the positive displacement pump is between a lower threshold value (P2) and an upper threshold value (P1), wherein the lower threshold value (P2) is in range of 15%-25% of a target operating parameter value (Pset), and wherein the upper threshold value is in a range of 90%-98% of the target operating parameter value (Pset), the first actuating mode providing a pump pressure that constantly increases toward the target operating parameter value (Pset) and that, in its rising behavior in relation to pump pressure, is dependent on a detected change in the operating parameter over a predetermined time interval; and wherein the control unit is configured to control operating the pump motor in a second actuating mode that is different from the first actuating mode when the operating parameter is above the upper threshold value (P1) for more controlled operation toward the target operating parameter value (Pset) relative to the first actuating mode.

2. The system according to claim 1, wherein a change in the operating parameter is detected more than once, and in each case influences the respective first actuating mode.

3. The system according to claim 1, wherein the pump motor is operated at a maximum actuation power when the operating parameter is below the lower threshold value (P2).

4. The system according to claim 1, wherein a control amplification associated with operating the pump motor is greater in the first actuating mode than in the second actuating mode, and wherein the controlled operation comprises a PI control behavior.

5. The system according to claim 1, wherein the operating parameter is an actual operating pressure (Pact) of the positive displacement pump.

6. The system according to claim 1, wherein the operating parameter is derived from at least one parameter selected from a list consisting of a motor voltage, a motor current, a motor rotational speed, a rotational acceleration, and a pump constant of the positive displacement pump.

7. The system according to claim 1, wherein the operating parameter is a current delivery of the positive displacement pump.

8. The system according to claim 1, wherein a pre-specified violation of the target operating parameter value (Pset) is detected and, in response to such violation sets an actuating mode, the pump motor is operated in an actuating mode that is different from the second actuating mode.

9. The system according to claim 1, wherein at least one of a cooling fluid and a lubricating fluid is supplied to a machine tool using the positive displacement pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic illustration of a pump system including an operation control device according to an exemplary embodiment of the invention;

(2) FIG. 2 is a pressure/time diagram illustrating exemplary operating behavior of the pump system of FIG. 1;

(3) FIG. 3 is a flow chart illustrating an exemplary operating sequence according to the invention; and

(4) FIG. 4 is a pressure/time diagram analogous to FIG. 2, illustrating exemplary operating behaviour of conventional devices having varied operating requirements, such as delivery requirements, for different tools serviced by the pump system of FIG. 1.

DETAILED DESCRIPTION

(5) FIG. 1 is a schematic block diagram of the operation control device according to a preferred embodiment of the invention, which comprises a pump system. In particular, FIG. 1 shows, as indicated by the dashed border line 10, an operation control device having actuating means 12, which in one embodiment is a frequency converter, for setting speed and for actuating a screw pump 14. The screw pump 14 is connected downstream from, and interacts with, a schematically shown machine tool 16. Such machine tools may include drilling or milling machines having changeable tool inserts and correspondingly changeable coolant delivery requirements. As arranged, the screw pump 14 may deliver coolant to the machine tool 16.

(6) In the context of the preferred exemplary embodiment, operating mode means 18, in the form of a control unit, is connected upstream of the actuating means 12. The operating mode means 18 may be embodied in hardware or software components, and may take as input calculated and/or predefined threshold values 24 of an operating parameter (for example, pump pressure P) to actuate the actuating means 12. The operating mode means 18 may also take into account a respective unit-specific setpoint value 22 of the operating parameter, which in the illustrated embodiment is setpoint pressure (Pset). In the manner shown in FIG. 1, these influencing variables, namely at least one threshold value 24 and the setpoint value 22 (Pset), are provided to the operating mode means 18 in a suitable manner (as represented by functional unit blocks 22, 24). Alternatively, they may be calculated, as will be described in greater detail later.

(7) Also illustrated is a state sensor unit 20, which in the exemplary embodiment is a pressure sensor, for detecting an actual pressure “Pact” on the output side of the screw pump 14 and providing it to the operating mode means 18 to utilize in further actuation operations.

(8) The operation of the device according to FIG. 1 will now be described in relation to the pressure/time diagram of FIG. 2 and the flow chart of FIG. 3.

(9) It is assumed by way of example that a screw pump of type EMTEC 20 R38 manufactured by the applicant Allweiler A G, Radolfzell, with a rating of 7.5 kW, interacts with a single-screw machine tool 16, which is configured as a drilling machine and is operated with three different drilling tools. Each of these three drilling tools requires a different delivery of coolant/lubricant fluid to be delivered by the pump 14, it being assumed that this delivery lies between 5 liters/minute (1/min) and 351/min. An assumed operating pressure at the pump output and unit input side is 80 bar in each case.

(10) FIG. 3 illustrates, at step S10, an idle state before activating the arrangement. At step S12, initial start-up (Go) then follows by manual or automated actuation.

(11) As a comparison of FIGS. 2 and 3 shows, the present invention allows the pump motor to be operated in a plurality of operating phases which are clearly separated or delimited from each other by suitable actuation or setting by the operating mode means 18. It is, therefore, initially provided according to the exemplary embodiment of FIGS. 1 to 3 for actuation of the screw pump to take place at maximum electrical actuating power by means of the frequency converter 12, after initial start-up (step S12) at time t.sub.0. This results directly from the decision step E1 in FIG. 3, in which the differential pressure Pdiff (which is the difference between the setpoint pressure “Pset” and the detected actual pressure “Pact”, in relation to the setpoint pressure, which in the described embodiment is 80 bar) is determined to be more than 80% below the setpoint operating parameter value (Pset). Quantitatively, this means the realization of a lower threshold value, in the exemplary embodiment at the 80% threshold (in relation to 80 bar Pset, that is P2=16 bar). Accordingly, the branch in FIG. 3 leads to the operating state of step S14 “Start,” corresponding with an initial start-up mode, in this case at full electrical power.

(12) As can be seen in FIG. 2, the pump actual pressure “Pact” (shown as the solid line) reaches the lower threshold P2 value at 16 bar at time t.sub.1. In the illustrated embodiment, t.sub.1 is about 80 msec. This ends the first mode of operation, at which point the operating mode means applies another actuating mode to the pump motor or the inverter connected upstream. The following then occurs, as shown in FIG. 3. When the lower threshold value P2 of 16 bar (corresponding to a pressure difference of less than 80% in relation to the setpoint pressure value) is exceeded, a branch is made to the right in decision step E2. According to the preferred embodiment, at step S16, a parametrization of a control mode in the second operating phase takes place between times t.sub.1 and t.sub.2 (see FIG. 2—corresponding to a pressure range of 16 bar as the lower threshold value and 76 bar as the upper threshold value, correspondingly 95% of Pset). A PI control operation is thus carried out, in which a pressure difference is initially determined per unit time interval by the operating mode means 18 after time t.sub.1, as a gradient in the pressure curve (FIG. 2). Depending on this gradient, the system defines and specifies an amplification value and an integration time for the PI control behavior in the time region between t.sub.1 and t.sub.2. The system is then operated (at step S18) with this parameterization, as described by a PI control function. As can also be seen from the feedback of the loop shown in FIG. 3, a continuous parameterization (S16) takes place in the time range between t.sub.1 and t.sub.2. That is, repeated measurements are made of a current increase in the pressure curve, and thereupon P and I values of the closed-loop control are set. In the exemplary embodiment of FIG. 2, the curve profile shown with a parameterization (S16) after time t.sub.1 would lead to a typical amplification V=8 with an integration time I=5 msec (for instance, compared to the maximum actuation in the phase t.sub.0 to t.sub.1, where actuation took place with an amplification V=1 and an integration time I=2 msec).

(13) The pressure rise over time then takes place in the manner shown in FIG. 2 until an upper threshold value P1 at 76 bar is reached. In one embodiment, this threshold value is 95% of Pset. This threshold value is reached at time t.sub.2, in the illustrated embodiment, at approximately 300 msec after t.sub.0. At this time, the operating open-loop and closed-loop control behavior of the operating mode means 18 also changes, whereby, in accordance with decision step E3 (FIG. 3), the system executes a final closed-loop operation. In one embodiment, this is a closed-loop operation which has a reduced amplification and/or extended integration time for the PI parametrisation compared to closed-loop operation in the preceding operating phase. In other words, as can be seen starting from the upper threshold value P1, the operation shows a markedly flatter rising behavior in the direction towards the setpoint value Pset. Advantageously, this leads to a slowed approach to the setpoint value Pset (at 80 bar), which takes place in the time interval between t.sub.2 and t.sub.3 reducing or eliminating the chance for disadvantageous overshoot. Thus, this final closed-loop control operation, carried out at step S20, constitutes an operating state in which the setpoint value can be reached in an optimised time from t.sub.2. Stationary pump operation is then carried out in further stationary operation, even with these stationary pump operation closed-loop control parameters (typically amplification V=3, integration time I=10 msec).

(14) In the event that an unexpected loading of the system occurs, for example, due to the switching off or failure of the connected machine tool, operating states can occur in which pump pressure exceeds the setpoint value. In principle, it would be possible by means of the final closed-loop control operation (step S20) to compensate for this (upwards) deviation. This may, however, require an undesirably long time. Accordingly, as shown in FIG. 3, following the decision step E3 in which the pressure setpoint value is exceeded by more than 5% (i.e. actual pressure>105% of P), the system turns to the steep parameterization operation from step S16 or S18 (i.e., in accordance with the steep behaviour between the time sections t.sub.1 and t.sub.2). As soon as the tolerance threshold (here: 5%) for the final closed-loop control operation (step S20) is reached, operation continues accordingly.

(15) The flow chart of FIG. 3 additionally shows the introduction of an alarm routine (step S22 or S24) if a predetermined alarm condition is detected at decision E3. The alarm condition can be a predetermined pressure condition, but it can also be based on other input variables, such as exceeding a critical temperature.

(16) Various actuating modes and operating phases of the pump motor, generated in the run-up and start-up state, are shown in the curve profiles of FIG. 4. FIG. 4 shows the operating behavior of an operation control device having the same pump configuration, and which in one example is a PI controller, for use with various tools and various system loads connected therewith. Curve 40, for example, relates to a first drilling tool, in which a low required delivery (5 l/min) leads to a marked overshooting of the system. Curve 42, relates to a large tool having a comparatively high delivery requirement (delivery rate 35 l/min) which brings about a very long initial period and clearly exceeds the required 500 msec limit. Only the middle tool, represented by curve 44, and having a delivery rate of 15 l/min, approximately achieves the curve profile of FIG. 2. As can be seen, curve 44 illustrates only slight overshoot when reaching Pset, thus approximating the short curve profile of FIG. 2. Such operation is obtained independently of the respective delivery requirement, and is adaptively set for all required tools, namely by means of appropriate adaptive parametrisation in the range of operating phases below the upper threshold value, and particularly in the middle rise region (i.e., step S18 between t.sub.1 and t.sub.2).

(17) It will be appreciated that the present invention is not limited to the provision of two threshold values P2, P1, which, in the exemplary embodiment are 20% and 95% of the setpoint value, respectively. Rather, one or both of these threshold values can be set at different values from those explicitly described in relation to the preferred embodiments. In addition, it is contemplated that only a single threshold value may be used. In one embodiment, the single threshold value may be the upper threshold value P1. Alternatively, any desired number of threshold values may be used, as long as such values are appropriately described in a consistent functional context. In addition, setting or adapting the operation of the system can be in accordance with a single or repeated gradient measurement on the pressure profile. This may be done in relation to at least the upper threshold value.

(18) It is also contemplated that operating parameters other than pressure may be used in the inventive system and method. For example, the operating parameter may be the rotational speed of the pump motor, with analogous upper and, if appropriate, lower threshold values set, determined or ascertained in some manner as respective fractions.

(19) As a result, the present invention makes it possible in a surprisingly effective manner to obtain fast and dynamic run-up behaviour of a screw pump, while at the same time minimizing the required outlay in terms of equipment and hardware. According to one preferred embodiment, the system of FIG. 1 operates without a pressure regulating valve, and thus, operation of the system occurs in an energy efficient manner.