JP3822362B2 - Liquid pressurizer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid pressurizing device using a reciprocating pump such as a plunger pump, and more particularly to pressure control of high-pressure liquid discharged from the pump.
[0002]
[Prior art]
The discharge pressure of the high-pressure liquid discharged from the electric reciprocating plunger pump using a servo motor or the like as a drive source is generally controlled by controlling the feed rate of the plunger that reciprocates in the cylinder. . The first method of controlling the pressure of such a high-pressure liquid is to feed back the actual discharge pressure value detected by the pressure sensor attached to the plunger pump and take the deviation from the pressure set value as the target value. Is converted into a speed signal, and the actual discharge pressure value is converged to the target value by adjusting the rotation speed of the servo motor, that is, the feed speed of the reciprocating movement of the plunger by proportional integral control (PID control) based on the deviation. The method is generally known.
[0003]
The second method is performed by ON-OFF control in which the actual discharge pressure value is fed back and converged to the pressure setting value by changing the feed rate of the reciprocating movement of the plunger while repeating the start and stop of the servo motor. .
[0004]
[Problems to be solved by the invention]
However, such a conventional pressure control method has the following problems. When pressure control is performed by PID control, due to the nature of PID control, it reacts sensitively to disturbances, so the acceleration and deceleration of the reciprocating motion of the plunger becomes intense. Particularly, since the plunger pump has a short stroke length, there is a problem that it takes time until the actual discharge pressure value reaches a stable state even if acceleration / deceleration is frequently performed. Further, since it is easily affected by disturbance, there is a problem that even after the actual discharge pressure value is stabilized, it is likely to fluctuate and it is difficult to maintain a constant pressure value.
[0005]
On the other hand, the pressure control method based on ON-OFF control has a problem that the pressure value cannot be kept constant even after the pressure value is stabilized because the reversal of the stroke of the plunger due to the start and stop of the servo motor is complicatedly repeated. Further, there is a problem that the mechanical load on the drive system such as a belt and a pulley is large due to complicated start and stop of the servo motor, and the life of the apparatus is shortened.
[0006]
By the way, in a reciprocating pump such as a plunger pump, the discharge pressure of the high-pressure liquid is uniquely determined by the reciprocating plunger feed rate if the nozzle diameter is constant. For this reason, if the feed rate of the plunger can be kept constant, the discharge pressure value can be kept stable.
[0007]
The present invention has been made in view of such problems, and provides a liquid pressurizing apparatus capable of converging a discharge pressure value to a target pressure value in a short time and accurately with a stable operation. The main purpose. Another object of the present invention is to provide a liquid pressurizing apparatus capable of maintaining the discharge pressure in a stable state at a target pressure value. Still another object of the present invention is to provide a liquid pressurizing apparatus that can reduce the mechanical burden on the apparatus.
[0008]
[Means for Solving the Problems]
To achieve the above object, the invention according to claim 1 is a reciprocating pump that pressurizes and discharges sucked liquid by reciprocating movement of a plunger, and pressure measuring means that measures an actual discharge pressure value of the high-pressure liquid. And pressure control means for controlling the actual discharge pressure value measured by the pressure measuring means to converge to a pressure set value as a target value by adjusting the reciprocating feed speed of the plunger. In the liquid pressurizing apparatus, the pressure control means moves the plunger to reach the actual discharge pressure value to a predetermined threshold value, and controls the actual discharge pressure value after the actual discharge pressure value reaches the threshold value. To determine the optimum feed speed, and thereafter, the optimum feed speed is maintained constant.
[0009]
In the present invention, the discharge pressure threshold value is determined in advance, and the actual discharge pressure value is first reached by the pressure control means, and the actual discharge pressure value is controlled after reaching the threshold value.
[0010]
Here, the predetermined threshold is a value in the vicinity of the pressure set value as the target value. That is, in the present invention, the actual discharge pressure value can be converged to the target value by performing feedback control of the actual discharge pressure value near the target value after reaching the threshold value close to the target value at once. The discharge pressure value can reach the target value in a short time compared to a device that repeats acceleration and deceleration of the plunger and stroke reversal by control and ON-OFF control.
[0011]
The feed rate of the plunger movement until reaching the threshold is not particularly limited, but the maximum feed rate of the plunger is improved in order to improve the responsiveness of pressure control and converge the discharge pressure value to the target value in a shorter time. Preferably it is speed.
[0012]
The threshold value only needs to be a pressure value in the vicinity of the target value, and can be arbitrarily set according to conditions such as the feed rate of the plunger and the stroke length. In addition to the lower limit value, an upper limit value is set as the threshold value. In this case, the plunger that is gradually decelerated tries to move even if it reaches the pressure setting value as the target value. Therefore, when the actual discharge pressure value reaches the pressure setting value as the target value, the plunger moves. Is advantageous in that it can be prevented from stopping.
[0013]
In the present invention, the actual discharge pressure value is controlled by the pressure control means after the actual discharge pressure value reaches the threshold value to determine the optimum feed speed, and thereafter the optimum feed speed is kept constant.
[0014]
Here, the optimum feed speed is a feed speed of the plunger that substantially corresponds to the pressure setting value, which is the target value, and can be corrected later to completely match the target value. That is, in the present invention, the discharge pressure of the high-pressure liquid of the reciprocating pump is determined by the feed rate of the plunger if the nozzle diameter is constant, and the actual discharge is performed by pressure control after reaching the threshold value. The feed speed at which the pressure is converged to the target value or a pressure value near the target value is determined as the optimum feed speed, and the optimum feed speed is maintained constant. For this reason, the actual discharge pressure value is maintained at a constant value in a state where it has almost converged to the target value, and unlike the conventional device that performs pressure control by PID control, the acceleration / deceleration of the plunger due to the influence of disturbance is not required. In addition, there is no need to redetermine the optimum feed rate. Accordingly, the actual discharge pressure value can be accurately and smoothly reached the target value. In addition, the actual discharge pressure value can be easily maintained at the target value, and the stability can be improved.
[0015]
According to a second aspect of the present invention, in the liquid pressurizing apparatus according to the first aspect, the pressure control means includes a proportional element, and after the actual discharge pressure value reaches the threshold value, the plunger is first advanced. The actual discharge pressure value is proportionally controlled before reaching the end.
[0016]
In the present invention, since the pressure control of the plunger after the actual discharge pressure value reaches the threshold value and until the plunger first reaches the advance end is performed by proportional control with little response to disturbance, the stroke length is short. Even in the case of the plunger, the pressure value can be converged to the vicinity of the target value in a shorter time.
[0017]
According to a third aspect of the present invention, in the liquid pressurizing apparatus according to the first or second aspect, the pressure control means is configured to change an actual discharge pressure value when switching the reciprocating motion of the plunger after the determination of the optimum feed speed. The feed rate is corrected based on the deviation from the pressure set value.
[0018]
In the present invention, after the optimum feed rate is determined, the plunger feed rate is corrected based on the deviation between the actual discharge pressure value and the pressure set value when switching between reciprocating motions. Even when the feed speed is not compatible with the above, the feed speed can be gradually converged. That is, by repeating the correction of the feed rate near the target value, the actual discharge pressure value can be converged to the target value in a shorter time. Further, since the feed speed before and after correction is maintained constant, stable operation can be performed, and the mechanical burden on the apparatus is reduced. Furthermore, even if the feed rate fluctuates due to switching between reciprocating movements and the actual discharge pressure value of the high-pressure liquid fluctuates, it can be returned to the optimum feed rate by correction, and the steady characteristics of the actual discharge pressure can be further improved. Can do.
[0019]
The configuration of the feed rate correction in the pressure control means of the present invention is not particularly limited as long as it is performed when switching between reciprocating motions. For example, based on the deviation between the pressure set value and the actual pressure set value, the correction value calculated by a predetermined calculation formula is corrected by adding / subtracting / dividing to / from the feed rate, and the correction value fixed to the deviation amount is You may comprise so that it may adjust to feed speed.
[0020]
Further, the correction may be performed separately at the time of switching at each stroke end as well as at the time of switching at one stroke end. In this case, it is possible to eliminate a feed speed error due to mechanical misalignment of the left and right plungers and maintain good steady state characteristics.
[0021]
According to a fourth aspect of the present invention, in the liquid pressurizing apparatus according to any one of the first to third aspects, the pressure control unit is configured to switch the reciprocating motion of the plunger after the determination of the optimum feed speed. The feed rate is temporarily set to a speed equal to or higher than the optimum feed rate.
[0022]
In the present invention, when the reciprocating movement of the plunger is switched by the pressure control means after the determination of the optimum feeding speed, the feeding speed is temporarily set to a speed higher than the optimum feeding speed. It is possible to prevent the pressure value from being lowered, improve the damping property, and maintain the stability. As such a set speed, for example, the maximum feed speed can be set in order to improve the attenuation.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a liquid pressurizing apparatus according to the present embodiment. In the liquid pressurizing apparatus according to this embodiment, a nozzle device for cutting a material by high-pressure liquid injection is shown. However, food in a pressure container for a food pressurizing process with a constant volume to which the high-pressure liquid is supplied is added. An apparatus for pressure treatment may be used.
[0024]
FIG. 1 is a hydraulic circuit diagram, and the liquid pressurizing apparatus includes a liquid supply unit 8, a plunger pump 1 as a reciprocating pump, a control unit 25 as pressure control means, and an injection unit 17.
[0025]
The liquid supply unit 8 is for supplying a liquid to the plunger pump 1, and includes a pressure medium tank 11 and a water supply pump 9.
[0026]
The liquid in the pressure medium tank 11 is sent to the plunger pump 1, pressurized, and then ejected from the ejection unit 17 to the outside. Accordingly, the type of the liquid can be appropriately selected according to the case where it is used for cutting a material or the case where it is used for pressurizing food.
[0027]
The feed water pump 9 is for sending this liquid to the plunger pump 1 at a predetermined pressure, and any pump that can continuously supply either a rotary pump or a reciprocating pump may be used. It is also possible to cause the plunger pump 1 to self-suck the liquid in the pressure medium tank 11 without providing the water supply pump 9.
[0028]
The plunger pump 1 has a servo motor 7 and plungers 5 </ b> A and 5 </ b> B driven by the servo motor 7. Both plungers 5A and 5B are reciprocally linked and reciprocated integrally with each other with the same stroke length, whereby in the left and right pump chambers 3A and 3B of the plunger pump 1, when one is in the suction stroke, the other is A so-called push-pull operation is performed so as to perform the discharge stroke. In other words, the plunger 5B moves in the direction of the arrow A shown in the drawing to suck the liquid into the pump chamber 3B (intake stroke), and conversely moves in the direction of the arrow B to pressurize the liquid sucked in the suction stroke. Discharge (discharge process). In the plunger 5A, the strokes in the directions of arrows A and B are opposite to those in the plunger 5B.
[0029]
Here, in this embodiment, since the plunger pump 1 and the servo motor 7 are employed, the control becomes easy.
[0030]
The pressure sensor measures the actual discharge pressure of the high-pressure liquid discharged from the plunger pump 1, and the measurement result is input to the control unit 25 as an electrical signal. In this embodiment, the pressure sensor constitutes a pressure measuring means.
[0031]
The plunger pump 1 discharges the high-pressure liquid to the injection unit 17, and the discharge pressure of the high-pressure liquid is determined by the reciprocating feed speed in the intake stroke and the discharge stroke of the plungers 5A and 5B. This feed speed is performed by feedback control based on a signal input from the pressure sensor to the control unit 25 by the control unit 25 that controls the rotation speed of the servo motor 7.
[0032]
FIG. 2 shows a control block diagram of the pressure control system of the liquid pressurizing apparatus of this embodiment. The control unit 25 inputs the pressure set value Ps as the target value and the actual discharge pressure value P fed back from the pressure sensor 23. Then, based on the deviation between the pressure set value Ps and the actual discharge pressure value P, the required speed of the plungers 5A and 5B is calculated by a control method described later, a speed command is output to the servo motor 7, and the servo motor 7 It rotates at the rotation speed according to the speed command. For this reason, the control part 25 controls the feed speed of the plungers 5A and 5B based on the actual discharge pressure value, and as a result, the discharge pressure of the high-pressure liquid is controlled.
[0033]
Check valves 13a and 13b are provided on the liquid supply part 8 side (upstream part) of the flow path connected to the plunger pump 1, and check valves 15a and 15b are provided on the injection part 17 side (downstream part). Is provided. The check valves 13a and 13b allow only liquid to flow from the liquid supply unit 8 to the plunger pump 1, and the check valves 15a and 15b allow only liquid to flow from the plunger pump 1 to the injection unit 17. Both are arranged in a direction to prevent the reverse flow from the downstream side to the upstream side.
[0034]
The high-pressure liquid from the plunger pump 1 is sent to the injection unit 17 through the check valves 15a and 15b. The injection unit 17 includes an accumulator 19 and a nozzle 21.
[0035]
The accumulator 19 is connected to the nozzle 21 and alleviates instantaneous fluctuations in the discharge amount and discharge pressure of the high-pressure liquid from the nozzle 21.
[0036]
Next, the pressure control of the high-pressure liquid by the control unit 25 of the liquid pressurization apparatus configured as described above will be described. FIG. 5 shows a flowchart of pressure control in the present embodiment.
[0037]
First, the pressure set value Ps and threshold values α and β are determined and input to the control unit 25 as target values in advance. Here, the threshold value α is used as the upper limit value (Ps + α) of the pressure value, and the threshold value β is used as the lower limit value (Ps−β) of the pressure value. Note that only the lower limit value may be set as the threshold value. Further, the threshold values α and β are values in the vicinity of the pressure setting value Ps as target values, and in this embodiment, α is set to 5 MPa and β is set to 20 MPa. Note that the values of the threshold values α and β are not limited to this, and can be arbitrarily determined depending on conditions such as the stroke length of the plungers 5A and 5B, the pressure setting value, and the like.
[0038]
Then, the servo motor 7 is driven to reciprocate the plungers 5A and 5B. The feed speed V of the plungers 5A and 5B is determined by the equation (1).
[0039]
[Expression 1]
V = Vmax (when P <Ps−β)
V = Vmax (Ps + α−P) / (α + β) (when Ps−β ≦ P <Ps + α)
V = 0 (when Ps + α ≦ P)
[0040]
Here, Vmax is the maximum feed speed of the plungers 5A and 5B.
[0041]
Therefore, the actual discharge pressure value P is detected by the pressure sensor 23 every predetermined time, and it is checked whether or not the actual discharge pressure value P has reached Ps−β (step 501). If the actual discharge pressure value P does not reach Ps−β, a speed command signal for sending the plungers 5A and 5B to Vmax is sent to the servo motor 7 (step 510).
[0042]
When the actual discharge pressure value P reaches Ps−β, it is checked whether or not the plungers 5A and 5B are positioned at the stroke end (step 503). A speed command signal having a value calculated by the equation is sent out (step 511). Then, while the plungers 5A and 5B first reach the stroke end, the control unit 25 performs proportional control of the actual discharge pressure value P (step 502). That is, the actual discharge pressure converges to the target value because proportional control is performed near the pressure set value Ps (target value). FIG. 3 is a diagram showing the fluctuation state of the actual discharge pressure value and the feed speed of the plungers 5A and 5B by the pressure control by the control unit 25. FIG. 3 (a) shows the fluctuation of the time and the actual discharge pressure value. FIG. 3B is a state diagram showing fluctuations in the feed rates of the plungers 5A and 5B.
[0043]
Next, when the plunger 5A, 5B are moved to the first stroke end, detects the feed speed in the direction switching plungers 5A, 5B, the speed of the optimum feed speed V _0, sets the feed speed V to V ₀ (Step 504). At this time, the optimum feed speed V ₀ is very close to the feed speed corresponding to the target pressure setting value Ps.
[0044]
Once the optimum feed speed _{V 0} is determined to stop the proportional control (step 505), to maintain the plunger 5A, the feed speed V of the 5B constant at _{V 0.} However, when switching the reciprocating motion at the stroke ends of the plungers 5A and 5B, the feed speed of the plungers 5A and 5B is temporarily set to the maximum feed speed Vmax. This is to prevent a decrease in the actual discharge pressure value P due to pulsation at the time of switching the directions of the plungers 5A and 5B, to improve the damping of the control system and to improve the stability.
[0045]
Specifically, when the direction is changed at the left and right stroke ends of the plungers 5A and 5B, the actual discharge pressure value P from the pressure sensor 23 and the pressure set value (target value) Ps are compared to obtain a deviation (step 506). 508). Then, a speed command signal at which the feed speed V becomes the maximum feed speed Vmax is sent to the servo motor until the actual discharge pressure value P is outside the range from the pressure set value Ps to the pressure set value Ps-2 MPa. To control the feed rate. Then, after the pressure sensor 23 detects that the actual discharge pressure value P has returned within the range from the pressure set value Ps to the pressure set value Ps-2 MPa, the feed rate is returned to the optimum feed rate V _0. Control. The range of the actual discharge pressure value to be set to the maximum feed speed is not limited to the range from the pressure set value Ps to the pressure set value Ps-2 MPa, but the stroke length of the plungers 5A and 5B, the pressure It can be arbitrarily determined according to conditions such as a set value.
[0046]
In each stroke end of the left and right plungers 5A, 5B, rotation of the servo motor 7 sends the speed command signal to the servo motor 7 to sum the feed rate the value of 1/100 of the optimum feed rate V ₀ The speed is changed to correct the feed speed of the plungers 5A and 5B (steps 507 and 509).
[0047]
The reason that the feed speed is separately corrected at the left and right stroke ends of the plungers 5A and 5B in this way is to eliminate errors in the feed speed due to mechanical displacement of the plungers 5A and 5B at the time of direction switching. Because.
[0048]
FIG. 4 is a diagram showing a change state of the feed speed at the stroke end of the plungers 5A and 5B. As can be seen from FIG. 4, the feed speed V is the maximum speed Vmax for a fixed time from the time of direction switching, and a value A obtained by correcting the optimum feed speed V ₀ after the time has elapsed until the next direction switching. ₀ , A ₁ , B ₀ , B ₁ .
[0049]
The control unit 25 holds the feed speed at a constant value. Even in this case, if the actual discharge pressure value P becomes equal to or higher than the pressure set value Ps + α for some reason, the plungers 5A and 5B are stopped. On the other hand, when the pressure falls below the set pressure value Ps-β or below the set pressure value Ps-2β, the proportional feed control is performed again to determine the optimum feed speed V ₀ . For this reason, even when the actual discharge pressure value P fluctuates greatly, it is possible to immediately return to the steady state.
[0050]
FIG. 6 shows the measurement results of the plunger feed speed V and the actual discharge pressure value V converted to the motor rotation speed when pressure control is performed with a nozzle diameter of 0.2 cm and a pressure set value (target value) of 300 MPa. As can be seen from FIG. 6, according to the liquid pressurizing apparatus according to the present embodiment, the steady characteristic, attenuation and stability of the actual discharge pressure value are all improved.
[0051]
【The invention's effect】
As described above, according to the present invention, the pressure control means moves the plunger to reach the actual discharge pressure value to a predetermined threshold value, and controls the actual discharge pressure value after the actual discharge pressure value reaches the threshold value. Since the optimum feed speed is determined, the discharge pressure value can be converged to the target pressure value in a short time and with high accuracy by a stable operation.
[0052]
Further, in the present invention, after the pressure control means determines the optimum feed speed, the optimum feed speed is maintained constant, so that the discharge pressure is stable at the target pressure value without being affected by external factors such as disturbance. There is an effect that can be maintained.
[0053]
Further, the present invention maintains the optimum feed rate after the pressure control means determines the optimum feed rate, so that it is not necessary to repeatedly start and stop the plunger, thereby reducing the mechanical burden on the device and reducing the life of the device. There is an effect that can be lengthened.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a liquid pressurizing apparatus according to the present embodiment.
FIG. 2 is a control block diagram of the liquid pressurizing apparatus according to the present embodiment.
FIG. 3 is a state diagram of fluctuations in an actual discharge pressure value and a feed rate by a control unit according to the present embodiment. FIG. 3A is a state diagram of actual discharge pressure values, and FIG. 3B is a state diagram of plunger feed rates.
FIG. 4 is a state diagram showing fluctuations in the feed rate at each stroke end of the liquid pressurizing apparatus according to the present embodiment.
FIG. 5 is a flowchart of pressure control of the liquid pressurizing apparatus according to the present embodiment.
FIG. 6 is a state diagram showing measurement results of a liquid pressurizing device plunger feed speed V and an actual discharge pressure value V according to the present embodiment.
[Explanation of symbols]
1: Plunger pump 3: Pump chamber 5: Plunger 7: Servo motor 8: Liquid supply unit 9: Water supply pump 11: Pressure medium tanks 13a, 13b, 15a, 15b: Check valve 17: Injection unit 19: Accumulator 21: Nozzle 23 : Pressure sensor 25: Control unit

Claims (4)

By adjusting the reciprocating pump that pressurizes and discharges the sucked liquid by the reciprocating movement of the plunger, the pressure measuring unit that measures the actual discharge pressure value of the high-pressure liquid, and the feed rate of the reciprocating movement of the plunger, In a liquid pressurization apparatus comprising: a pressure control means for controlling the actual discharge pressure value measured by the pressure measurement means to converge to a pressure set value as a target value,
The pressure control means moves a plunger to cause the actual discharge pressure value to reach a predetermined threshold value, and controls the actual discharge pressure value after the actual discharge pressure value has reached the threshold value to achieve an optimum feed speed. The liquid pressurizing apparatus is characterized in that, after that, the optimum feed speed is kept constant. The pressure control means has a proportional element, and proportionally controls the actual discharge pressure value until the actual discharge pressure value first reaches the forward end of the plunger after reaching the threshold value. The liquid pressurizing apparatus according to claim 1. The pressure control means corrects the feed rate based on a deviation between an actual discharge pressure value and a pressure set value when switching the reciprocating motion of the plunger after the optimum feed rate is determined. The liquid pressurizing apparatus according to claim 1 or 2. 2. The pressure control means for temporarily setting the feed speed to a speed equal to or higher than the optimum feed speed when switching the reciprocating motion of the plunger after the optimum feed speed is determined. The liquid pressurizing apparatus according to any one of?

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