Control method of a gear pump

Abstract

Control method of a gear pump (1), with: Controlling the speed of the gear pump (1) which is provided on the outflow side of a kneading system (2), wherein the gear pump (1) feeds a material kneaded in the kneading system (2) to the outflow side: Determine whether the gear pump (1) is operating at idle or not by using a pressure differential between the inlet side and the outlet side of the gear pump (1), using the following steps: Measuring a pressure P in on the inlet side of the gear pump (1) and a pressure P out on the outflow side; and when the measured pressure P in on the inlet side and the measured pressure P out on the outflow side satisfy a relationship of the following expression, Determine that the gear pump (1) is operated at idle: P in × k > P out where k denotes 1 or more; and Changing the speed of the gear pump (1) according to a determination result, wherein in a case where a determination result is obtained that an idle operation of the gear pump (1) is caused, a control to reduce the speed of the gear pump (1) is carried out.

Description

BACKGROUND OF THE INVENTION (AREA OF THE INVENTION)

[0001] The present invention relates to a control method for a gear pump provided in a kneading system. (DESCRIPTION OF THE STATE OF THE ART)

[0002] Generally, a kneading machine, such as a screw kneader or extruder, comprises a tubular housing designed to extend horizontally and a kneading rotor located within this housing to knead the material. In such a kneading machine, the material fed into the housing is kneaded by the kneading rotor and ejected from a discharge section located at the downstream end of the machine. The material ejected from the discharge section is fed to a screen changer, where foreign matter is removed.

[0003] This screen changer has a structure in which fine meshes are stacked on top of each other, and foreign matter is removed by passing molten resin through the meshes. To allow the molten resin to pass through the meshes, it is necessary to increase the pressure of the molten resin. Therefore, in the kneading systems shown in JP H02-6 118 A and JP 2013-180 560 A, a gear pump that increases the pressure of the molten resin is arranged on the inlet side and upstream side, respectively, of a screen changer.

[0004] It should be noted that this gear pump not only has a function of increasing the pressure of the material to allow it to pass through the screen changer, but also a function of retaining the material to adjust the degree of kneading.

[0005] This means that the degree of kneading downstream of the kneader is influenced by how much molten resin is retained on the downstream or outflow side of the kneader. For example, the higher the material fill rate on the outflow side of the kneader, the greater the degree of kneading. Conversely, the higher the pressure on the upstream side or inlet side of the gear pump, the greater this material fill rate on the outflow side of the kneader. In other words, the degree of kneading is changed by the speed of the gear pump.

[0006] Therefore, in a conventional kneading system, the pressure is measured on the upstream (inlet) side of the gear pump, and the speed of the gear pump is adjusted using a PID controller or similar device so that the measured pressure corresponds to the desired degree of kneading. For example, if the measured pressure on the inlet side of the gear pump is higher than a setpoint, it is assumed that this is because the material feed rate on the inlet side is too high. Therefore, the speed of the gear pump is increased, and the amount of resin supplied to the downstream (outlet) side of the gear pump is increased. This reduces the material feed rate upstream of the gear pump, thus lowering the pressure on the inlet side.In this way, in a conventional kneading system, the pressure on the inlet side of the gear pump is adjusted by changing the speed of the gear pump in order to achieve the desired pressure.

[0007] In the gear pumps JP H02-6 118 A and JP 2013-180 560 A, if the pressure on the inlet side of the gear pump is higher than a preset value, an operation to increase the speed of the gear pump is performed. However, there may be a case in which the pressure cannot be reduced, even by performing such an operation.

[0008] For example, sometimes even when the speed of the gear pump is increased, the output volume on the discharge side actually decreases. In such a case, no matter how much the speed is increased, the output volume on the discharge side never rises, and the material is not moved from the inlet side of the gear pump to the discharge side at all. Meanwhile, because the material is continuously fed from the kneading unit, the pressure on the inlet side of the gear pump continues to increase. This creates a vicious cycle, triggering a control mechanism to further increase the speed of the gear pump. Ultimately, this causes a control error, and the gear pump stops.

[0009] Further state of the art is known from publications US 5 122 315 A and JP H02-120 023 A. SUMMARY OF THE INVENTION

[0010] The present invention was made in view of the above problem, and it is an object of this invention to provide a control method for a gear pump which is suitable for detecting an idle operation of the gear pump and for operating the gear pump stably.

[0011] To solve the above problem, a control method for a gear pump according to the present invention comprises the following technical means.

[0012] This means that the control method of the gear pump according to the present invention comprises: controlling the speed of the gear pump, which is provided on the downstream or outflow side of a kneading system, wherein the gear pump feeds material kneaded in the kneading system to the outflow side; determining whether the gear pump is operating at idle or not, by using a pressure differential between the inlet and outlet sides of the gear pump, with the steps of: measuring a pressure P in on the inlet side of the gear pump and a pressure P out on the outflow side; and, if the measured pressure P in on the inlet side and the measured pressure P out On the outflow side, satisfy a relationship of the following expression, determining that the gear pump is operated at idle: Pink > Pout where k denotes 1 or more, and includes changing the speed of the gear pump according to a determination result, wherein in a case where a determination result is obtained that an idle operation of the gear pump is caused, a control to reduce the speed of the gear pump is carried out.

[0013] Preferably, the control method can also include measuring a pressure P. in on the upstream side or inlet side of the gear pump, and can in a case where the measured pressure P in The pressure on the inlet side of the gear pump is higher than a target pressure value P0, determining whether the gear pump is operated in idle mode or not.

[0014] Preferably, the control method may further include, in a case where a determination result is obtained that no idling operation of the gear pump is caused, performing a control to increase the speed of the gear pump.

[0015] An alternative control method for the gear pump according to the present invention comprises controlling the speed of the gear pump, which is provided on the downstream or outflow side of a kneading system, wherein the gear pump feeds material kneaded in the kneading system to the outflow side: Determining whether the gear pump is operated at idle or not, by using a load applied to an electric motor driving the gear pump, comprising the steps of: measuring the load of an electric motor driving the gear pump, and in a case where the measured load of the electric motor is a predetermined value or less, it is determined that the gear pump is operated at idle.

[0016] Preferably, the control method can further include measuring the load of an electric motor driving the gear pump, and in a case where the measured load of the electric motor is greater than a predetermined value, it is determined that the gear pump is not operated at idle.

[0017] According to the control method of the gear pump of the present invention, an idle operation of the gear pump can be detected, and the gear pump can be operated stably. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a view showing a kneading system in which a control method of a gear pump of the present invention is carried out. Fig. 2A is a view showing a pressure distribution in the normally rotating gear pump in operation, with a division by two different colors (black and dotted) based on a threshold of 0 MPa. Fig. 2B is a view showing a pressure distribution in the normally rotating gear pump in operation, with a division by two different colors (black and dotted) based on a threshold of 1 MPa. Fig. 2C is a view showing a pressure distribution in the normally rotating gear pump in operation, with a division by two different colors (black and dotted) based on a threshold of 10 MPa. Fig. 2D is a view showing a pressure distribution in the normally rotating gear pump during operation, with a division by two different colors (black and dotted) based on a threshold of 11 MPa. Fig. 3A is a view showing a pressure distribution in the gear pump, where an idle operation is caused during operation, while a division is made by two different colors (black and dotted) based on a limit of 0 MPa. Fig. 3B is a view showing a pressure distribution in the gear pump, where the idle operation is caused during operation, while a division is made by two different colors (black and dotted) based on a limit of 1 MPa. Fig. Figure 4A shows a kneading system with a gear pump controlled by a control method of a first embodiment. Fig. 4B is a view showing a sequence of signals to be inputted to and output from a controller in the control method in the first embodiment. Fig. Figure 5 is a flowchart showing the control procedure of the first embodiment. Fig. Figure 6A is a view showing a kneading system with a gear pump controlled by a control method of a second embodiment. Fig. Figure 6B is a view showing a sequence of signals to be inputted to and output from a controller in the control method of the second embodiment. Fig. Figure 7 is a flowchart showing the control procedure of the second embodiment. Fig. Figure 8 is a view showing a relationship between an electric motor load when the gear pump is operating normally and an electric motor load setpoint. Fig. Figure 9 is a flowchart showing a conventional control procedure. DESCRIPTION OF PREFERRED EXECUTION EXAMPLES [First Execution Example]

[0018] An embodiment of a control method for a gear pump 1 of the present invention is described in detail below based on the drawings.

[0019] First, before the control method is described, a kneading system 2, in which the control method of this first embodiment is carried out, is described.

[0020] Fig. Figure 1 schematically shows the kneading system 2 with the gear pump 1 of the first embodiment. This kneading system 2 is used for kneading a thermoplastic resin material, such as rubber and polyolefin-based resin. In reality, a system such as a continuous kneader or co-kneader, or an extruder, is used. The kneading system 2 can have a single shaft or multiple shafts (twin shafts), and the operating type of the kneading system can be continuous or batch. In the present embodiment, a system with a double continuous kneader of the oppositely rotating type is used as an example of the kneading system 2.

[0021] As in the upper part of Fig. As shown in Figure 1, the kneading system 2 (continuous kneader) of the present embodiment has a hollow cylinder 3 and a pair of kneading rotors 4, 4 which project into the interior of the cylinder 3 along the axial direction. In the continuous kneader, the pair of kneading rotors 4, 4 are rotated in opposite directions to each other in an engaged state, and the material is fed to a section between the pair of kneading rotors 4, 4, and the material (resin) is kneaded.

[0022] The material ejected from an ejection section 8 of this kneading system 2 outside the cylinder 3 is fed to the gear pump 1. The gear pump 1 has a pair of upper and lower gears 5U, 5D, whose axes are orthogonal to the horizontal direction along which the material flows. These gears 5U, 5D are meshed with each other and rotate in opposite directions. In particular, in the example of Fig. 1, the upper gear 5U is rotated clockwise around the axis and the lower gear 5D is rotated counterclockwise around the axis.

[0023] These gears 5U, 5D are housed in a housing section 7 formed within a housing 6, such that cylindrical bodies are stacked. The housing section 7 has an inner diameter slightly larger than a rotating outer diameter of the gear 5 (hereinafter, the gears 5U, 5D are sometimes referred to collectively as the gear 5). Material entering a gap between recessed portions of the teeth of the gear 5 (recessed sections 5a) and an inner wall surface 7a of the housing section 7 is fed from the upstream side to the downstream side by a rotation of the gear 5, thus conveying the material. Therefore, in the example of Fig. 1. In the clockwise rotating upper gear 5U, the material directed to the section between this upper gear 5U and the housing section 7 is fed from the upstream side to the downstream side via the further upper side of the upper gear 5U. In the counterclockwise rotating lower gear 5D, the material directed to the section between this lower gear 5D and the housing section 7 is fed from the upstream side to the downstream side via the further lower side of the lower gear 5D.

[0024] In this way, the material ejected from the discharge section 8 in the gear pump 1 is fed from the upstream side (inlet side) to the downstream side (outlet side) and pressurized before being fed to a screen changer 9. The material, from which foreign matter is removed in this screen changer 9, is fed to a pelletizer 10. Pellets or granules of the resin (material) are produced in the pelletizer 10.

[0025] The pressure of the material on the downstream side of the kneading unit 2, in other words on the upstream side or inlet side of the gear pump 1, influences the degree of kneading of the kneading unit 2. The pressure (P in , described later) on the inlet side of the gear pump 1 can be adjusted by changing the speed of the gear pump 1.

[0026] Therefore, the rotational speed of a gear pump 1 is conventionally determined in the Fig. The sequence shown in 9 is controlled in such a way that a pressure P in ' a desired upstream pressure setpoint value P0' is set on the inlet side of the gear pump 1.

[0027] In particular, a pressure sensor 12 is provided on the upstream side of the gear pump 1 (on the downstream side of a kneader), and the pressure P in The pressure on the upstream side is measured by this pressure sensor 12 for a defined time period (S31). The pressure P in The pressure measured on the upstream side is sent to a controller. The permissible upstream pressure value, i.e., the upstream pressure setpoint P0' with an upper and lower limit, is pre-programmed into the controller. The controller then regulates the speed of gear pump 1 based on the measured pressure value P. in'on the upstream side and the upstream pressure setpoint P0'. This means that the controller performs a comparison to determine whether the measured pressure value P is correct. in 'on the upstream side within a range of the upstream pressure setpoint P0' or not (S32). As a result of the comparison, in a case where the measured value of the pressure P in If the pressure on the upstream side is within the range of the upstream pressure setpoint value P0, the speed of gear pump 1 is not changed (S33). However, in a case where the measured value of the pressure P in 'on the upstream side is not within the range of the upstream pressure setpoint value P0', next determines 'whether the measured value of the pressure P in'is higher on the upstream side than the upstream pressure setpoint P0' or not" (S34). In a case where it is not determined that the "measured value of the pressure P in ' on the upstream side is higher than the upstream pressure setpoint P0'", a control is carried out to reduce the speed of the gear pump 1 (S35).

[0028] In this way, when the rotational speed of gear pump 1 is reduced, the amount of material supplied from the upstream side of gear pump 1 to the downstream side is reduced, and the material is slightly retained on the upstream side of gear pump 1, so that the pressure P in ' is amplified on the upstream side.

[0029] In a case where it is determined that the "measured value of the pressure P" in'If the pressure on the upstream side is higher than the upstream pressure setpoint P0'", a control is performed to increase the speed of gear pump 1 (S36). In this way, when the speed of gear pump 1 is increased, the amount of material fed from the upstream side of gear pump 1 to the downstream side is increased, and the material is not easily retained on the upstream side of gear pump 1, so that the pressure P in ' can be reduced on the upstream side.

[0030] In this way, in the conventional kneading system, the speed of the gear pump 1 is controlled in such a way that the pressure P in ' is maintained on the upstream side of gear pump 1 to remain at the preset value (upstream pressure preset value P0') that was previously set.

[0031] In a conventional gear pump 1, if the pressure on the upstream side of the gear pump 1 is higher than the setpoint, an operation to increase the speed of the gear pump 1 is performed. However, even if such an operation is performed, there may be a case where the pressure is not reduced.

[0032] No matter how much the rotational speed is increased, the output quantity on the downstream side never increases, and the material does not move from the upstream side of gear pump 1 to the downstream side. However, because the material is continuously fed from the kneading unit, the pressure on the upstream side of gear pump 1 continues to increase. As a consequence, due to the increased rotational speed, the pressure on the upstream side increases further, creating a vicious cycle in which the pump's speed is further increased. Ultimately, a control divergence occurs, and the gear pump stops.

[0033] To determine the cause of the problem—where, regardless of how much the rotational speed is increased, the material is not moved from the upstream (inlet) side of the gear pump 1 to the downstream (outlet) side—the inventors conducted an investigation. One result they found was that the reason the material is not moving within the gear pump is that the gear pump is running idle.

[0034] Next, this "idle operation of the gear pump" will be described in detail. It should be noted that the Fig. Figures 2A to 2D show a situation in which normal operation is carried out in the gear pump (no idling operation), and the Fig. 3A and Fig. Figure 3B shows a situation in which the gear pump is idling. It should be noted that in the Fig. 2A to 2D, 3A and 3B: the printing of the material is divided and depicted in two different colors (into a darkened part and a dotted part) based on a limit value. This means that the Fig. 2A and Fig. Figure 3A shows the pressure distribution of the material using the two colors based on the threshold of 0 MPa, such that the part of the pressure that is at or above the threshold is darkened, and the part of the pressure that is below the threshold is dotted. Fig. 2B and Fig. Figure 3B shows a distribution of pressure with both colors based on the limit of 1 MPa. Fig. 2C and Fig. 2D images show a pressure distribution of the material with the two colors based on the limit value of 10 MPa and the limit value of 11 MPa, respectively.

[0035] As from the Fig. As can be seen in Figures 2A to 2D, 3A and 3B, "the idle operation of gear pump 1" indicates a state before the material sufficiently enters the recessed sections 5a of the gears, which are located on the upstream or inlet side of gear pump 1, gear 5 rotates, and the recessed sections 5a of the gear reach the downstream or outlet side, so that the material is not completely conveyed, and only gear 5 rotates in idle mode. In other words, in gear pump 1, the Fig. 2A to 2D, where no idling operation occurs, the material fits tightly into the recessed sections 5a of the gear on the upstream side of the gear pump 1, and there is almost no empty space in the recessed sections 5a rotated towards the downstream side of the gear pump 1, but rather they are filled with material. However, some material remains in the recessed sections 5a of the gear pump 1. Fig. 3A and Fig. 3B has some empty spaces, and there is some room for the material to enter.

[0036] In particular, the average charging rate of the recess sections 5a of the gear (average recess section charging rate) in the Fig. 2A to 2D 75%, and a deepening section charging rate in the Fig. 3A to 3B is 50%. Based on this, a case in which the loading rate of the material with the average well section loading rate is 50% or lower, preferably 40% or lower, can be described as "the gear pump is operating at idle".

[0037] The loading rate of the material in the in-depth sections 5a of the section on "point D" in Fig. 2 rotated gears (point-D charging rate) is 90%, and a point-D charging rate in Fig. 3 is 75%. Based on this, a case in which the loading rate of the material in the recess sections 5a, which rotates to the “point D” in the figures, is 75% or lower, preferably 70% or lower, can be described as “the gear pump 1 is operating at idle”.

[0038] In other words, the “idle operation of gear pump 1” refers to a state in which the actual feed rate of the material conveyed by the rotation of gear 5 is lower than the feed rate of the material required at the downstream side of gear pump 1, and indicates a state in which a material discharge section 16 at the downstream side of gear pump 1 (located midway along a route from gear pump 1 to screen changer 9) is “not filled with the material without any void space.” Therefore, the “idle operation of gear pump” can also be expressed by using the rate of change of the material in the material discharge section 16.

[0039] In particular, in the gear pump 1 of Fig. 2A to 2D, in which no idling operation is effected, but the gear pump rotates normally (rotates in a non-idling operating state), in the material discharge section 16 of the gear pump, which is shown as a "point B", the rate of a volume where the material is present with respect to an internal volume of the material discharge section 16 on the downstream side of the gear pump 1 (discharge section change rate) is 90% (that is, not 100%, because an actual containment of fine air bubbles is taken into account). Therefore, there are almost no voids in the material discharge section 16. However, in one case of the gear pump 1, Fig. 3, where the gear pump rotates while the idle operation is effected, by comparing at "point B", which is the same as in Fig. 2, the rate of change of volume where the material is present (output section change rate) is 80%. Therefore, a case in which the change rate of the material in the material output section is 80% or lower, preferably 75% or lower, can also be described as "the gear pump 1 is in idle operation".

[0040] It should be noted that the idling operation of the gear pump 1 refers to a phenomenon that occurs within the gear pump 1 described above. However, whether the gear pump 1 is idling or not can be determined by using a pressure differential between the upstream or inlet side of the gear pump 1 and the downstream or outlet side, or by applying a load to an electric motor 11 that drives the gear pump 1.

[0041] Therefore, in the control method of the gear pump 1 of the present invention, a normal control of the gear pump 1 is carried out, or a control of the gear pump 1, while an idle operating state of the gear pump 1 is carried out by using the pressure difference between the upstream side of the gear pump 1 and the downstream side, or the load applied to the electric motor 11 that drives the gear pump 1.

[0042] Below, an example is described in which, based on the pressure difference between the upstream side of the gear pump 1 and the upstream side, it is determined whether the gear pump 1 is in idle operation or not, as the first embodiment of the control method of the gear pump 1.

[0043] First, a control mechanism 17 of the gear pump 1, which is used in the control method of the first embodiment, is described.

[0044] Fig. 4A is a block diagram showing the control mechanism 17 of the in Fig. Gear pump 1 is shown. As in Fig. As shown in Figure 4A, in the gear pump 1 of the first embodiment, the control mechanism 17 of the gear pump 1 comprises an upstream or inlet-side pressure sensor 12, which is provided on the upstream or inlet side of the gear pump 1 (in a material introduction section 18 (at a “point A” in the Fig. 2A to 2D, 3A and 3B, and 4A)), a downstream or outflow pressure sensor 13, which is provided on the downstream or outflow side of the gear pump 1 (in the material discharge section 16 (at the “point B” in the Fig. 2A to 2D, 3A and 3B, and 4A)), the electric motor 11, which drives the gear pump 1, and a controller 14, which controls the electric motor 11. A pressure P inon the upstream side or inlet side of the gear pump 1, which is measured by the inlet-side pressure sensor 12, and a pressure P out At the downstream side or outflow side of the gear pump 1, which is measured by the outflow side pressure sensor 13, both are sent to the control unit 14.

[0045] Fig. Figure 4B is a block diagram showing the inputs and outputs of signals to and from the controller 14 described above. This controller 14 is actually a device such as a personal computer and a PLC. As in Fig. 4B shows, in addition to the pressure measurement P in on the inlet side and the pressure reading P outOn the downstream side, an upstream or inlet pressure setpoint value P0 is previously entered into the controller 14. The controller 14 outputs a gear pump operating signal, in other words a signal to control the speed of the electric motor 11, to the gear pump 1.

[0046] In this controller 14, signal processing is performed in a sequence as described in Fig. 5 shown by using these values ​​P in , P out , P0 and the gear pump operating parameter signal.

[0047] As in Fig. As shown in section 5, the pressure P is initially applied. in The pressure P is measured on the inlet side of the gear pump 1 by the inlet-side pressure sensor 12. out The pressure is measured on the outflow side of the gear pump 1 by the outflow-side pressure sensor 13 (S11). The measured pressure values ​​P in and the pressure P out are sent to control unit 14.

[0048] In control unit 14, the entered pressure P is first displayed. in The inlet side is compared with the inlet-side pressure setpoint value P0, which has an upper limit or a lower limit that is entered beforehand, and it is determined whether the "pressure P in on the inlet side is within a range of the inlet-side pressure setpoint value P0" or not; in other words, it is determined whether the pressure P in on the inlet side within a range of numerical values ​​that are set as the inlet-side pressure setpoint value P0, or not (S12).

[0049] As a result of the determination, in a case where the “pressure P inIf the pressure on the inlet side is within the range of the inlet-side pressure setpoint value P0, in other words, if "YES" is determined, it is assumed that the operating state of gear pump 1 is normal, and the operating state of gear pump 1 is maintained. This means that the speed of gear pump 1 is not changed (S13).

[0050] However, as a result of the determination, in a case where the “pressure P in If the pressure on the inlet side is not within the range of the inlet-side pressure setpoint value P0, in other words "NO", the process continues to the next step, and it is determined whether the "pressure P in is higher on the inlet side than the inlet-side pressure setpoint value P0” or not (S14).

[0051] As a result of the determination, in a case where the “pressure P in on the inlet side is not higher than the upstream pressure setpoint P0 (the pressure P) inIf the pressure on the inlet side is lower than the inlet-side pressure setpoint P0), in other words “NO”, the pressure on the inlet side of gear pump 1 is reduced. Therefore, the speed of gear pump 1 is reduced (S15).

[0052] However, as a result of the determination, in a case where the “pressure P in If the pressure on the inlet side is higher than the inlet-side pressure setpoint value P0, in other words "YES", the pressure on the inlet side of gear pump 1 is increased. Therefore, the process continues to the next step, and it is determined whether gear pump 1 is operating in idle mode or not.

[0053] This means that in the next step, by using the entered pressure P in on the inlet side and the entered pressure P out on the outflow side it is determined whether the "pressure P in The pressure on the inlet side is lower than the pressure P outon the outflow side” or not (S16).

[0054] Whether or not "idle operation is effected in gear pump 1" is determined based on whether the pressure of the material on the outflow side, which is pressurized when the gear pump is operating normally, is lower than the pressure of the material on the inlet side, which should be higher than on the inlet side. That is, if either condition of expression (1) is satisfied, it is determined that "idle operation is effected in gear pump 1". If either condition of expression (1') is satisfied, it is determined that "idle operation is not effected in gear pump 1". [Expression 3] Pin>Pout [Expression 4] Pin≤Pout

[0055] As a result of the determination, in a case where “pressure P in on the inlet side < the pressure P outIf “on the outflow side” is determined, in other words “YES”, it is determined that the gear pump 1 is not operated at idle, and the speed of the gear pump 1 is increased (S17). In a case where the “pressure P in on the inlet side ≥ the pressure P out If “on the outflow side” is determined, in other words “NO”, it is determined that the gear pump 1 is operated at idle and the speed of the gear pump is reduced (S18).

[0056] When the control method of the gear pump 1 of the first embodiment described above is used, a control to reduce the speed of the gear pump 1 is implemented in a case where idling operation occurs in the gear pump 1, thus preventing idling operation. Therefore, the speed is not controlled while the gear pump 1 is operating at idle, and a problem of control divergence is not easily caused, allowing for more precise control of the speed of the gear pump 1. [Modified example of the first embodiment]

[0057] In the control method of the gear pump 1 of the first embodiment described above, as shown in expression (1) and expression (1'), the pressure P in on the inlet side, which is measured by the inlet-side pressure sensor 12, with the pressure P outon the downstream side, which is measured by the downstream pressure sensor 13, is compared. In a case where the pressure P in The pressure on the inlet side is lower than the pressure P out On the outflow side, it is determined that the "gear pump 1 is operated in idle mode".

[0058] However, to determine whether gear pump 1 is idling or not, it is not always necessary to wait for the pressure P to reach a certain level. in The pressure on the inlet side is lower than the pressure P out on the outflow side. For example, in the gear pump 1 rotating without any idling operation, the pressure P is... in on the inlet side approximately 0.5 MPa and the pressure P outThe pressure on the outflow side is approximately 30 MPa. Compared to the inlet side of gear pump 1, the outflow side is often pressurized, so the pressure is approximately 60 times higher. However, when gear pump 1 is operated at idle, the pressure on the outflow side is less than 60 times higher than the inlet side. For example, if the pressure on the outflow side of gear pump 1 is reduced to approximately 10 times higher than the inlet side, it can be sufficiently determined that gear pump 1 is operating at idle.

[0059] Therefore, if a relationship of the following expression (2) is used instead of the relationship of expression (1) described above, and a relationship of the following expression (2') is used instead of the relationship of expression (1') described above, the result of determining that "gear pump 1 is operating at idle" can be obtained more quickly than if expression (1) and expression (1') are used. Therefore, the idle operation of gear pump 1 can be stopped immediately, and the speed of gear pump 1 can be controlled more precisely. [Expression 5] Pink > Pout where k denotes 1 or more. [Expression 6] Pink ≤ Pout where k denotes 1 or more.

[0060] For example, a pressure value is set at "point A" between Fig. 2A, where the print value is divided by colors based on the limit of 0 MPa, and Fig. 2B, where the print value is divided by colors based on the threshold of 1 MPa, is compared. The print value at "point A" is in a region of 0 MPa or higher in Fig. 2A, however, is located in a region lower than 1 MPa in Fig. 2B. Therefore, it becomes apparent that the pressure value at “point A” lies within a range of 0 to 1 MPa.

[0061] Meanwhile, a pressure value is measured at "point B" between Fig. 2C, where the print value is divided by colors based on the limit of 10 MPa, and Fig. 2D, where the pressure value is divided by color based on the threshold of 11 MPa, is compared. The pressure value at "point B" is in a region of 10 MPa or higher in Fig. 2C, but is located in a region lower than 11 MPa in Fig. 2D. Therefore, it becomes apparent that the pressure value at "point B" lies within a range of 10 to 11 MPa.

[0062] It can be seen that in the normally rotating gear pump 1 there is a pressure difference of approximately ten times between "point A", where the pressure value is 0 to 1 MPa, and "point B", where the pressure value is 10 to 11 MPa, and if the pressure on the outflow side of the gear pump 1 is reduced to be approximately 10 times higher than the inflow side, it can be determined that the "gear pump 1 is operating at idle". [Second embodiment]

[0063] It should be noted that in the control method of the first embodiment described above, whether or not the gear pump 1 is in idle mode is determined based on the pressure difference between the inlet side and the outlet side of the gear pump. However, it can also be determined whether the gear pump 1 is in idle mode or not based on the load (torque) of the electric motor 11 that drives the gear pump 1.

[0064] A control method for a gear pump 1 of a second embodiment is to estimate the load applied to an electric motor 11 that drives the gear pump 1 and to determine that the gear pump 1 operates in no-load mode when the estimated load on the electric motor 11 is a predetermined value or lower. This means that in an no-load operating state, no material enters the recesses 5a of the gear in the gear pump 1, and the gear pump 1 rotates with virtually no load applied. Therefore, a very small load is also applied to the electric motor 11 that drives the gear pump 1.

[0065] In the control method of the second embodiment, the load (torque of the electric motor 11) is estimated based on the value of an electric current flowing through the electric motor 11 or the like. If the estimated load falls below the predetermined value, the system determines that the gear pump 1 is idling. It should be noted that a load measuring device 15 (torque meter) may be provided in the electric motor 11, and the load (torque of the electric motor 11) may be measured by this load measuring device 15.

[0066] Next, the control method of the gear pump 1 of the second embodiment will be described.

[0067] First, a control mechanism 17 of the gear pump 1, which is to be used in the control method of the second embodiment, is described.

[0068] Fig. Figure 6A is a block diagram showing a kneading machine 2, in which the control method of the second embodiment is carried out, and the control mechanism 17. As in Fig. As shown in Figure 6A, the control mechanism 17 of the gear pump 1 of the second embodiment includes an inlet-side pressure sensor 12 in a material inlet section 18, as in the first embodiment. However, no outlet-side pressure sensor 13 is provided on the outlet side or downstream side (material discharge section 16) of the gear pump 1. The torque of the electric motor 11, which is estimated from the value of the electric current or measured by the load measuring device 15, is also output to a controller 14. Further configurations of the control mechanism 17 are the same as in the first embodiment.

[0069] Fig. Figure 6B is a block diagram showing the inputs and outputs of signals to and from the controller 14 of the second embodiment.

[0070] As in Fig. As shown in 6B, in addition to a pressure measurement P in An electric motor load T (gear torque signal T) is entered into the control unit 14 of the second embodiment on the upstream or inlet side, and no pressure measurement value P is obtained. out Input is made on the downstream or outflow side. In addition to an inlet-side pressure setpoint value P0, an electric motor load setpoint value T0, which is a setting for the load of the electric motor 11, is previously entered into the control unit 14 of the second embodiment.

[0071] This means that in the control unit 14 of the second embodiment, signal processing takes place in a sequence as in Fig. 7 shown by using a gear pump operating parameter signal in addition to these values ​​P in, P0, the gear torque signal T and the electric motor load setpoint value T0 is carried out.

[0072] Fig. Figure 7 shows a signal processing method in the control unit 14 of the second embodiment, in other words the control method of the gear pump 1 of the second embodiment.

[0073] Because the actions of S21 to S25 in the control method of the gear pump 1 of the second embodiment are the same as the actions of S11 to S15 of the first embodiment, a description of these is omitted.

[0074] In S24, in a case where it is determined that the “pressure P inIf the pressure on the inlet side is higher than the inlet-side pressure setpoint P0, it is determined whether or not the gear pump 1 is idling, as in the first embodiment. Whether or not the gear pump 1 is idling is determined based on whether the electric motor load T (gear torque signal T) applied to the gear pump 1 is lower than the predetermined electric motor load setpoint T0, which is entered beforehand. That is, if a condition of the following expression (3) is met, it is determined that the gear pump 1 is idling. If a condition of the following expression (3') is met, it is determined that the gear pump 1 is not idling. [Expression 7] T <T0 [Expression 8] T≥T0

[0075] As a result of the comparison, in a case where the gear torque signal T is lower than the electric motor load setpoint T0 and expression (3) is satisfied, in other words in a case where “YES” is determined, it is determined that the gear pump 1 is operated at idle and the speed of the gear pump 1 is reduced (S28).

[0076] However, as a result of the comparison, in a case where the gear torque signal T is the electric motor load setpoint value T0 or higher and expression (3') is satisfied, in other words, in a case where "NO" is determined, it is determined that the gear pump 1 is not operated at idle, and an operation to increase the speed of the gear pump 1 is performed (S27).

[0077] It should be noted that the electric motor load setpoint T0 described above is preferably determined taking into account a change in the load of the electric motor 11, as in Fig.Figure 8 is shown. For example, with regard to a mean gear torque obtained when the gear pump 1 is operated, if the electric motor load setpoint T0 is set to substantially the same value as this mean value, an incorrect determination of "no-load operation" is frequently caused by measurement fluctuations. Therefore, with regard to this mean value, a value that is sufficiently smaller than the width of the measurement fluctuation than the electric motor load setpoint T0 is preferably set. This ensures that the determination of "no-load operation" is only correctly provided when the load of the electric motor 11 is significantly lower than the setpoint T0.

[0078] By using the control method of the gear pump 1 from the second embodiment described above, in a case where idling operation is caused in the gear pump 1, a control is implemented to reduce the speed of the gear pump 1, thus preventing idling operation. Therefore, the speed is not controlled while the gear pump 1 is operating at idle, and a problem of control divergence is not easily caused, allowing for more precise control of the speed of the gear pump 1.

[0079] This control method of the gear pump 1 of the second embodiment is effective in a situation where there is no space to install a sensor on the downstream or outflow side of the gear pump 1 or the like.

[0080] It should be noted that the embodiments disclosed herein are intended to provide an example rather than a limitation in any respect. In particular, with regard to items not explicitly disclosed in the embodiments disclosed herein, such as operating conditions, production conditions, various parameters, the size of components, weight and volume, values ​​that do not deviate from a range that a person skilled in the art would generally implement, the values ​​that a person skilled in the art would generally adopt, are hereby adopted.

[0081] The present invention serves to detect idling operation of a gear pump and to operate the gear pump stably. A control method for a gear pump according to the present invention is characterized by, after controlling the speed of the gear pump, which is provided at the outflow side of a kneading system, wherein the gear pump feeds material kneaded in the kneading system to the outflow side, determining whether the gear pump is operating idling or not, and changing the speed of the gear pump according to the result of this determination. Preferably, the control method can further include measuring a pressure at the inlet side of the gear pump and, in a case where the measured pressure at the inlet side of the gear pump is higher than a setpoint pressure, determining whether the gear pump is operating idling or not.

Claims

[1] Control method of a gear pump (1), with: Controlling the speed of the gear pump (1) which is provided on the outflow side of a kneading system (2), wherein the gear pump (1) feeds a material kneaded in the kneading system (2) to the outflow side: Determine whether the gear pump (1) is operating at idle or not by using a pressure differential between the inlet side and the outlet side of the gear pump (1), using the following steps: Measuring a pressure P in on the inlet side of the gear pump (1) and a pressure P out on the outflow side; and when the measured pressure P in on the inlet side and the measured pressure P out on the outflow side satisfy a relationship of the following expression, Determine that the gear pump (1) is operated at idle: Pink > Pout where k denotes 1 or more; and Changing the speed of the gear pump (1) according to a determination result, wherein in a case where a determination result is obtained that an idle operation of the gear pump (1) is caused, a control to reduce the speed of the gear pump (1) is carried out. [2] Control method of the gear pump (1) according to claim 1, further comprising: Measuring a pressure P in on the inlet side of the gear pump (1); and in a case where the measured pressure P in Determine whether the gear pump (1) is operated in idle mode or not when the pressure on the inlet side of the gear pump (1) is higher than a target pressure value P0. [3] Control method of the gear pump (1) according to claim 1 or 2, further comprising: In a case where a determination result is obtained that no idling operation of the gear pump (1) is caused, a control is carried out to increase the speed of the gear pump (1). [4] Control method of a gear pump (1), with: when controlling the speed of the gear pump (1) which is provided on the outflow side of a kneading system (2), wherein the gear pump (1) feeds a material kneaded in the kneading system (2) to the outflow side: Determine whether the gear pump (1) is operating at idle or not by using a load applied to an electric motor (11) that drives the gear pump (1), by the following steps: Measuring the load of the electric motor (11) that drives the gear pump (1); and In a case where the measured load of the electric motor (11) is a predetermined value or lower, determine that the gear pump (1) is operated at idle. [5] Control method of the gear pump (1) according to claim 4, further comprising: Measuring the load of the electric motor (11) that drives the gear pump (1); and In a case where the measured load of the electric motor (11) is higher than a predetermined value, determine that the gear pump (1) is not operated at idle.

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