Liquid delivery pump and method

Abstract

The present application provides a technology for reducing the volume of a liquid delivery pump and enabling liquid delivery with small pulsation. The liquid delivery pump of the present application includes a first plunger pump having a first plunger, a second plunger pump having a second plunger and connected in series with the first plunger pump, a pressure sensor disposed downstream of the second plunger pump, and a control unit that receives input of the discharge pressure of a liquid measured by the pressure sensor and controls the driving of the first plunger and the driving of the second plunger. The control unit calculates the rate of change of the pressure of the liquid based on the past compression distance of the first plunger when the liquid is compressed by the first plunger pump and the pressure at the completion of compression. The control unit predicts the compression distance of the first plunger based on the rate of change of the pressure and the current discharge pressure. The control unit determines the timing for completing the compression by the first plunger based on the predicted compression distance.

Description

Technical Field

[0001] This invention relates to a liquid delivery pump and a liquid delivery method. Background Technology

[0002] In liquid chromatography analyses, the solvent used varies depending on the type of sample being analyzed, requiring solvent replacement in the delivery pump before each analysis. Therefore, to perform a large number of analyses on various types of samples within a constant time, solvent replacement needs to be performed quickly. Reducing the pump volume is effective in enabling this rapid solvent replacement.

[0003] Typically, the delivery pump used in liquid chromatography has a configuration consisting of two plunger pumps connected in series. The upstream plunger pump (first plunger pump) draws in, compresses, and discharges the solvent. Since a constant flow rate cannot be achieved using only the first plunger pump, another plunger pump (second plunger pump) is connected downstream. The second plunger pump, by counteracting the pulsating flow of the first plunger pump (discharging the solvent while the first plunger pump draws in and compresses it), can act as the delivery pump to deliver a constant flow rate.

[0004] The compression of the solvent in the operation of the first plunger pump is a process of increasing the pressure of the attracted solvent from atmospheric pressure to the pressure discharged by the second plunger pump (discharge pressure). Here, the compression operation needs to end once the solvent pressure reaches approximately the same as the discharge pressure. If the compression operation continues beyond the discharge pressure (overcompression), both the first and second plunger pumps discharge during this period, increasing the flow rate as delivery pumps, and correspondingly raising the discharge pressure. Conversely, if the compression operation ends before reaching the discharge pressure (undercompression), a moment occurs in subsequent processes when neither the first nor second plunger pump discharges, resulting in a decrease in discharge pressure. When the flow rate fluctuates, not only does the analytical accuracy of the liquid chromatograph deteriorate, but the accompanying pressure pulsations also load the separation column and accelerate wear.

[0005] As a technology to prevent over-compression or under-compression, Patent Document 1 discloses a liquid delivery pump, which is equipped with a pressure sensor to measure the pressure of the solvent in the first plunger pump and a pressure sensor to measure the pressure of the solvent discharged by the second plunger pump. During the compression process, the values ​​measured by each pressure sensor are compared to control the operation of the first plunger pump.

[0006] Patent document 2 discloses a liquid delivery pump having a structure in which a first plunger pump and a second plunger pump are connected in series and a pressure sensor is provided only downstream of the second plunger pump.

[0007] Patent document 3 discloses a liquid delivery pump that corrects and controls the flow rate based on the history of the compression volume during the compression process and the pressure (compression pressure) at the end of compression.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent No. 5624825

[0011] Patent Document 2: Japanese Patent Application Publication No. 2008-291848

[0012] Patent Document 3: International Publication No. 2019 / 082243 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] However, in the liquid delivery pump of Patent Document 1, pressure sensors are provided on both the first and second plunger pumps, thus increasing the pump volume. To reduce the pump volume and facilitate solvent replacement in a short time, it would be preferable to omit the pressure sensor on the first plunger pump side and reduce the corresponding volume. However, in this case, there is a challenge in controlling the operation of the first plunger pump using only the pressure sensor for the second plunger pump, thus achieving liquid delivery with minimal flow and pressure pulsations.

[0015] In the delivery pump of Patent Document 2, as described above, a pressure sensor is only provided on the second plunger pump side, thus suppressing the increase in pump volume. However, Patent Document 2 makes no mention of achieving delivery with minimal flow and pressure pulsation.

[0016] Furthermore, in the liquid delivery pump of Patent Document 3, there is no record of achieving liquid delivery with small pulsations in flow rate and pressure.

[0017] Therefore, the present invention provides a technology that can reduce the volume of the liquid delivery pump and enable liquid delivery with small pulsations.

[0018] Solution for solving the problem

[0019] To address the aforementioned issues, the liquid delivery pump of the present invention comprises: a first plunger pump having a first plunger; a second plunger pump having a second plunger and connected in series with the first plunger pump; a pressure sensor disposed downstream of the second plunger pump; and a control unit that receives an input of the liquid discharge pressure measured by the pressure sensor and controls the driving of the first plunger and the second plunger. The control unit calculates the pressure change rate of the liquid based on the past compression distance of the first plunger when compressing the liquid using the first plunger pump and the pressure at which compression is completed. Based on the pressure change rate and the current discharge pressure, the control unit predicts the compression distance of the first plunger. Based on the predicted compression distance, the control unit determines the timing for completing the compression performed by the first plunger.

[0020] Further features associated with this invention will become clear from the description and accompanying drawings. Furthermore, the solutions of this invention are achieved and implemented through elements and combinations of multiple elements, as well as the detailed description and appended technical solutions thereafter. The descriptions in this specification are merely typical examples and are not intended to limit the technical solutions or applications of this invention in any way.

[0021] Invention Effects

[0022] The pump according to the present invention has a small volume and is capable of delivering liquid with minimal pulsation. Other issues, structures, and effects beyond those described above will become clear from the following description of embodiments. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a liquid chromatograph equipped with the liquid delivery pump of the first embodiment.

[0024] Figure 2 It is a graph showing the displacement of each plunger, the discharge flow rate of the solvent, and the discharge pressure during normal solvent delivery.

[0025] Figure 3 It is a diagram used to illustrate the control method for the speed of the first plunger and the speed of the second plunger.

[0026] Figure 4 This is a diagram used to illustrate the control method of the first plunger in the first embodiment.

[0027] Figure 5 It is a graph showing the relationship between the displacement of the first plunger and the pressure when compression is complete.

[0028] Figure 6A This is a diagram used to illustrate the control method of the first plunger in the first embodiment.

[0029] Figure 6BThis is a diagram used to illustrate the control method of the first plunger in the first embodiment.

[0030] Figure 7 This is a diagram illustrating the control method of the first plunger in a variation of the first embodiment.

[0031] Figure 8 This is a diagram used to illustrate the control method of the first plunger in the second embodiment.

[0032] Figure 9 This is a schematic diagram showing the structure of a liquid chromatograph equipped with the liquid delivery pump of the third embodiment.

[0033] Figure 10 This is a graph used to illustrate the flow rate changes in the liquid delivery pump of the third embodiment.

[0034] Figure 11 This is a diagram used to illustrate the control method of the first plunger in the third embodiment. Detailed Implementation

[0035] [First Implementation Method]

[0036] <Structure example of a liquid pump and liquid chromatograph>

[0037] Figure 1 This is a schematic diagram showing the structure of a liquid chromatograph 100 equipped with the liquid delivery pump 1 of the first embodiment. (See attached diagram.) Figure 1 As shown, the liquid chromatograph 100 includes a pump 1, an ejector 2 for introducing a sample into the liquid chromatograph 100, a separation column 3, a detector 4, and a waste container 5. Regarding the ejector 2, separation column 3, detector 4, and waste container 5, ejectors, separation columns, detectors, and waste containers commonly used in liquid chromatographs can be used; therefore, their detailed structures are not specifically described in this embodiment.

[0038] The liquid delivery pump 1 includes a controller 10 (control unit), a pressure sensor 110, a first plunger pump 101, a second plunger pump 102, a connecting flow path 103, a first solenoid valve 81, a second solenoid valve 82, a motor driver 210, a discharge valve driver 310, a discharge valve 311, a waste liquid tank 312, and a solenoid valve driver 410. The first plunger pump 101 and the second plunger pump 102 are connected in series, with the first plunger pump 101 located on the upstream side and the second plunger pump 102 located on the downstream side.

[0039] Pressure sensor 110 is located downstream of the second plunger pump 102. Pressure sensor 110 measures the pressure (discharge pressure) of the solvent (liquid) discharged from the second plunger pump 102 and outputs the pressure value to controller 10.

[0040] The controller 10 assigns command values ​​to the motor driver 210 and the solenoid valve driver 410 based on the discharge pressure measured by the pressure sensor 110 and a predetermined action sequence, thereby causing them to operate. Details are described later. In addition, the controller 10 assigns command values ​​to the discharge valve driver 310 based on a predetermined action sequence, thereby causing it to operate.

[0041] The first plunger pump 101 has a first pump head 111 comprising a first pressurization chamber 11, a first plunger 21, a first suction passage 31, a first discharge passage 41, a first check valve 51, a second check valve 52, a first seal 61, and a bearing 71. The first check valve 51 is disposed in the flow path of the first suction passage 31, and the second check valve 52 is disposed in the flow path of the first discharge passage 41, thereby restricting the flow direction of the solvent. The first plunger 21 (pressurization member) is held by the bearing 71 to be able to slide within the first plunger pump 101. The first seal 61 prevents leakage from the first pressurization chamber 11.

[0042] The second plunger pump 102 has a second pump head 112 formed with a second pressurization chamber 12, a second plunger 22, a second suction passage 32, a second discharge passage 42, a second seal 62, and a bearing 72. A second check valve 52 is connected to the second suction passage 32 via a flow path 103. That is, the first plunger pump 101 and the second plunger pump 102 are configured in series, with the first plunger pump 101 located on the upstream side. The second plunger 22 (pressurization member) is held by the bearing 72 to allow sliding within the second plunger pump 102. The second seal 62 prevents leakage from the second pressurization chamber 12.

[0043] In this specification, "lower limit point" refers to the position where the plunger's movement within the pressurization chamber is at its maximum descent. Conversely, "upper limit point" refers to the position where the plunger's movement within the pressurization chamber is at its maximum descent. Furthermore, "plunger rise" refers to the direction of movement of the solvent within the pressurization chamber, either compressing or ejecting it. Figure 1 The "movement to the right" of the plunger indicates a movement in the direction that draws solvent into the pressurized chamber. Figure 1 (Move to the left in the middle).

[0044] The reciprocating motion of the first plunger 21 is controlled by the first electric motor 211, the reduction gear 221, and the direct motion device 231. More specifically, the motor driver 210 provides driving power to the first electric motor 211 based on the command value of the controller 10, causing it to rotate. The rotation of the first electric motor 211 is slowed down by the reduction gear 221 and converted into linear motion by the direct motion device 231, thereby causing the first plunger 21 to reciprocate.

[0045] Similarly, the reciprocating motion of the second plunger 22 is controlled by the second electric motor 212, the reduction gear 222, and the direct motion device 232. More specifically, the motor driver 210 provides drive power to the second electric motor 212 based on the command value of the controller 10, causing it to rotate. The rotation of the second electric motor 212 is slowed down by the reduction gear 222 and converted into linear motion by the direct motion device 232, thereby causing the second plunger 22 to reciprocate.

[0046] Since the speed reduction device 221 and the direct drive device 231 amplify and convert the rotational power of the first electric motor 211 into linear motion force by combining them, they can be broadly referred to as power transmission mechanism devices. The same applies to the speed reduction device 222 and the direct drive device 232.

[0047] Specific examples of reduction gears 221 and 222 include spur gears, pulleys, planetary gears, and worm gears. The main reason for providing reduction gears 221 and 222 is to increase the torque of the first and second electric motors 211 and 212. If the first and second electric motors 211 and 212 already have the capacity to generate sufficient torque, then reduction gears 221 and 222 are not necessary. Specific examples of direct-acting devices 231 and 232 include ball screws, cams, and rack and pinion gears.

[0048] The discharge valve actuator 310 provides drive power to the discharge valve 311 based on the command value of the controller 10. The discharge valve 311 is connected downstream of the second plunger pump 102. The discharge valve 311 switches the direction of solvent flow from the liquid delivery pump 1 to either the injector 2 side or the waste liquid tank 312 side.

[0049] The solenoid valve actuator 410 provides driving power to the first solenoid valve 81 and the second solenoid valve 82 based on the command value of the controller 10. A solvent container for containing the first solvent 511 and a solvent container for containing the second solvent 512 are provided outside the liquid delivery pump 1. By opening and closing the first solenoid valve 81 and the second solenoid valve 82, and driving the first plunger pump 101 and the second plunger pump 102 (first plunger 21 and second plunger 22), the first solvent 511 or the second solvent 512 can be delivered to the liquid delivery pump 1.

[0050] When the first plunger pump 101 draws solvent, either the first solenoid valve 81 or the second solenoid valve 82 is open and the other is closed, thus drawing either the first solvent 511 or the second solvent 512. The drawn solvent is then drawn into the first pressurization chamber 11 through the confluence 90, the first check valve 51, and the first suction passage 31. The solvent drawn into the first pressurization chamber 11 is compressed as the first plunger 21 rises.

[0051] When the pressure inside the first pressurization chamber 11 becomes greater than the pressure inside the second pressurization chamber 12 due to the compression of the solvent, the solvent flows into the second pressurization chamber 12 through the first discharge passage 41, the second check valve 52, the connecting flow path 103 and the second suction passage 32, and is discharged from the second discharge passage 42.

[0052] The sample to be analyzed is injected into the solvent discharged from the delivery pump 1 using injector 2. The solvent containing the sample is then introduced into the separation column 3 and separated according to composition. Subsequently, the absorbance, fluorescence intensity, refractive index, etc., corresponding to the sample components are detected using detector 4. The separation column 3 is filled with microparticles. Due to the fluid resistance of the solvent flowing through the gaps between the microparticles, the delivery pump 1 generates a load pressure of tens to over hundreds of megapascals. The magnitude of this load pressure varies depending on the diameter of the separation column 3 and the flow rate.

[0053] When switching from analysis using the first solvent 511 to analysis using the second solvent 512, before using the second solvent 512, the first solenoid valve 81 is switched from the open state to the closed state, and then the second solenoid valve 82 is switched from the closed state to the open state. As a result, the interior of the delivery pump 1 (first check valve 51, first suction passage 31, first pressurization chamber 11, first discharge passage 41, second check valve 52, connecting flow path 103, second suction passage 32, second pressurization chamber 12, second discharge passage 42, pressure sensor 110, discharge valve 311, and the piping connecting them) and the interior of the ejector 2, separation column 3, detector 4, and the piping connecting them are replaced with the second solvent 512 from the first solvent 511. By shortening the time required for solvent replacement, the number of analyses that can be performed within a constant time period can be increased.

[0054] <Method of delivering liquid>

[0055] A summary of the solvent delivery method when using the delivery pump 1 of this embodiment to normally deliver solvent will be described. Here, "normal delivery" refers to the method in which the solvent discharged from the delivery pump 1 flows to the ejector 2, the separation column 3, and the detector 4 to analyze the sample. It should be noted that the same operation is performed when the sample is not analyzed (when the solvent is delivered to the waste liquid tank 312), so the description is omitted.

[0056] Figure 2 It is a graph showing the displacement of each plunger, the discharge flow rate of the solvent, and the discharge pressure when the solvent is normally delivered using the liquid delivery pump 1. Figure 2The four charts shown all use a horizontal axis representing time, and a vertical axis representing, from top to bottom, the displacement of the first plunger 21, the displacement of the second plunger 22, the solvent discharge flow rate, and the solvent discharge pressure. Here, the discharge flow rate is the flow rate discharged from the liquid delivery pump 1, and the discharge pressure is the pressure detected by the pressure sensor 110. The displacements of the first plunger 21 and the second plunger 22 will be in the upward direction (…). Figure 1 Set the right direction as positive, and set the descent direction ( Figure 1 The left direction is set to negative. Output flow is set to positive, and attraction flow is set to negative.

[0057] During normal liquid delivery, both the first plunger 21 and the second plunger 22 operate based on the lower limit point.

[0058] During normal liquid delivery, both the first plunger pump 101 and the second plunger pump 102 operate periodically. Figure 2 The diagram shows the quantities for four cycles. In one delivery cycle, during the interval a where the first plunger 21 descends to draw in solvent and during the interval b where the first plunger 21 ascends to compress the solvent, solvent is not discharged from the first pressurization chamber 11; therefore, the second plunger 22 ascends to discharge solvent. In interval b, there is a section b1 where the first plunger 21 ascends and then a section b2 where it stops, as detailed later. After interval b, in interval c where the second plunger 22 descends to draw in solvent, the first plunger 21 ascends to discharge the amount of solvent drawn in by the second plunger 22 and the amount discharged downstream of the pump. Then, in interval d, the first plunger 21 ascends to discharge solvent, and the second plunger 22 stops. Through this operation, the discharge flow rate from the delivery pump 1 can be kept almost constant, and the discharge pressure can also be kept almost constant. However, at the completion of interval b1, while the first plunger 21 continues its compression action, the solvent pressure in the first pressurized chamber 11 exceeds the discharge pressure (overcompression), causing a sudden increase in discharge flow rate, accompanied by a sudden increase in discharge pressure. At the completion of interval b1, if the compression distance of the first plunger 21 (the distance the first plunger 21 moves in the compression process (interval b)) is insufficient and the solvent pressure in the first pressurized chamber 11 does not reach the discharge pressure (undercompression), the discharge flow rate decreases suddenly at the beginning of interval c, accompanied by a sudden decrease in discharge pressure. Due to these overcompressions or undercompressions, fluctuations occur in the discharge pressure. Figure 2 The image shows pressure pulsations that resulted in overcompression.

[0059] <Control methods for the speeds of the first and second plungers>

[0060] Next, the method for controlling the speed of the first plunger 21 and the speed of the second plunger 22 to reduce the pulsation of the discharge pressure caused by the over-compression of the first plunger 21 will be explained in detail. In practice, the controller 10 outputs a command value to the motor driver 210, and the first electric motor 211 and the second electric motor 212, etc., are driven according to the output value, thereby controlling the speed of the first plunger 21 and the speed of the second plunger 22. However, for the sake of simplicity, it will sometimes be described that the controller 10 directly controls the operation of the first plunger 21 and the second plunger 22.

[0061] Figure 3 This is a diagram illustrating the control method for the speeds of the first plunger 21 and the second plunger 22 during normal conveying. Figure 3 The text only shows the action of a quantity within one cycle. Figure 3 The five charts shown all use a horizontal axis representing time, and a vertical axis representing, from top to bottom, the displacement of the first plunger 21, the displacement of the second plunger 22, the velocity of the first plunger 21, the velocity of the second plunger 22, and the pressure. The velocities of the first plunger 21 and the second plunger 22 are set positive when the plunger is rising and negative when it is falling. For pressure, the solid line represents the discharge pressure measured by the pressure sensor 110, and the dashed line represents the solvent pressure P11 in the first pressurization chamber 11. Here, the discharge pressure can be measured using the pressure sensor 110, but there is no mechanism to measure the solvent pressure P11 in the first pressurization chamber 11.

[0062] In interval a, controller 10 causes the first plunger 21 to descend to the lower limit point at a negative velocity (refer to...). Figure 2 The controller 10 causes the second plunger 22 to rise from the lower limit point at a constant positive speed. When the position of the first plunger 21 reaches the lower limit point, the controller 10 sets the first plunger 21 to a temporary stop (speed 0). The discharge pressure in interval a is constant. The pressure P11 of the solvent in the first pressurization chamber 11 becomes constant after decreasing to less than atmospheric pressure, and becomes atmospheric pressure when the first plunger 21 stops.

[0063] In interval b1, controller 10 causes the first plunger 21 to rise. Initially, the first plunger 21 is raised while simultaneously increasing its speed, then the speed is set to a constant value. Simultaneously, controller 10 causes the second plunger 22 to rise continuously at the same constant positive speed as in interval a. The discharge pressure in interval b1 remains constant. As the first plunger 21 rises, the solvent is compressed, and the pressure P11 of the solvent in the first pressurization chamber 11 increases.

[0064] When the solvent pressure P11 in the first pressurization chamber 11 is greater than the discharge pressure, pulsation occurs in the discharge pressure due to overcompression. The controller 10 determines that the solvent compression is complete based on the pulsation of the discharge pressure. Specifically, the controller 10 sets the discharge pressure at the beginning of interval b1 (at the start of compression) as Pb1. When the output of the pressure sensor 110 is greater than the discharge pressure Pb1 by a predetermined threshold ΔP, it determines that the solvent compression is complete, starts the deceleration of the first plunger 21, and temporarily stops (decelerates to speed 0). That is, when the increase in discharge pressure obtained by comparing it with the discharge pressure at the start of compression is greater than or equal to the predetermined threshold ΔP, it determines that the solvent compression is complete. After that, it transitions to interval c.

[0065] In interval c, controller 10 causes the first plunger 21 to rise at a constant speed and the second plunger 22 to fall at a constant speed. When the second plunger 22 reaches its lower limit, the system transitions to interval d.

[0066] In interval d, controller 10 causes the first plunger 21 to rise at a constant rate lower than that in interval c. Additionally, controller 10 stops the second plunger 22 in interval d. In interval d, the overcompression pulsations almost converge, and the discharge pressure remains approximately constant.

[0067] It should be noted that, in Figure 3 In the example, the overall expiratory pressure (except for pulsations) is roughly constant, but sometimes the expiratory pressure increases (rises) over time.

[0068] <Methods for determining when compression is complete>

[0069] Figure 4 This diagram illustrates a situation where compression is mistakenly determined to be complete. Figure 4 The upper graph shows the discharge pressure (solid line) and the solvent pressure in the first pressurization chamber 11 (dotted line), and the lower graph shows the displacement of the first plunger 21 and the displacement of the second plunger 22. In the method for determining the completion of compression in interval b described above, compression completion is sometimes incorrectly determined. As mentioned above, when a pulsation accompanied by overcompression is detected in interval b, compression is determined to be complete, and the first plunger 21 is stopped. However, if, before compression is complete (the first plunger 21 rises and the pressure in the first pressurization chamber 11 becomes equal to the discharge pressure), a pulsation that interferes with the delivery pump 1 occurs, such as a pressure pulsation caused by the switching of the ejector 2 during sample injection (so-called injection shock), then even though the solvent pressure P11 in the first pressurization chamber 11 has not become sufficiently high, the first plunger 21 also stops (a misjudgment of compression completion). Subsequently, at the beginning of interval c, if the first plunger 21 rises and the second plunger 22 falls, the discharge pressure drops to the pressure in the first pressurization chamber 11, resulting in a large pressure drop.

[0070] It should be noted that, in Figure 4 In the examples, the expiratory pressure generally increases (except for pulsations), but the expiratory pressure sometimes becomes roughly constant and sometimes decreases (declines).

[0071] Therefore, in this embodiment, to prevent false determination of compression completion, compression determination is not performed until the estimated pressure in the first pressurization chamber 11 becomes ΔPA lower than the discharge pressure Pb1 before compression begins (at the start of compression). Compression determination begins after this pressure is exceeded. The specific method is described below.

[0072] Figure 5 This is a graph showing the relationship between the displacement and pressure of the first plunger 21 at the completion of multiple compression cycles. Figure 5 In the chart, the discharge pressure (compression pressure Pc) when compression is completed in interval b2 of each cycle is set as the vertical axis, and the moving distance of the first plunger 21 when compression is completed (compression distance xc) is set as the horizontal axis.

[0073] First, the controller 10 sets the current cycle as the nth cycle, and calculates the rate of change of solvent pressure k(n) during compression in the current cycle using the following formula (1) based on the compression distance xc(n-1) and compression pressure Pc(n-1) of the previous cycle (n-1 cycle).

[0074] k(n)=Pc(n-1) / (xc(n-1)-xc0) (1)

[0075] Equation (1) is based on Figure 5 The following equation (2) shows the relationship between the compression distance xc and the compression pressure Pc.

[0076] Pc=k(xc-xc0) (2)

[0077] Here, xc0 is the distance corresponding to the delay of the rise in discharge pressure caused by leakage from the seal, etc., relative to the movement distance of the first plunger 21. In equation (1), in order to easily calculate the rate of change k, the rate of change k is calculated based on the compression distance xc(n-1) of the previous cycle and the compression pressure Pc(n-1). The value of xc0 is predetermined and stored in the controller 10. As a result, control becomes simple and can be implemented using a low-cost controller.

[0078] In addition, in order to find Figure 5The relationship between the compression distance xc and the compression pressure Pc shown can also be calculated by storing the history of delivery at various pressures prior to the current cycle in the controller 10, and then linearly approximating the relationship between the compression distance xc and the compression pressure Pc based on these points. This allows for a more accurate calculation of the rate of change k. Furthermore, xc0 is automatically calculated during the linear approximation, allowing for time-varying changes that follow the delay in the pressure rise that causes xc0.

[0079] When the pressure of the solvent in the first pressurized chamber 11 at the time of compression is estimated to be the pressure Pb1 at the start of compression (the current discharge pressure), the displacement xA of the first plunger 21 at a pressure ΔPA lower than that pressure can be expressed by the following equation (3).

[0080] xA(n)=(Pb1(n)-ΔPA) / k(n)+xc0 (3)

[0081] The displacement xA of the first plunger 21 can be defined as a displacement that is a predetermined distance shorter than the predicted displacement of the first plunger 21 when compression is complete. The controller 10 uses the displacement xA of the first plunger 21 calculated according to equation (3) as a boundary to determine the interval where compression completion is not determined (non-determination interval) and the interval where a determination is made (determination interval). Therefore, the controller 10 does not determine whether compression is complete regardless of the presence or absence of pulsation until the displacement of the first plunger 21 reaches xA. After the displacement of the first plunger 21 exceeds xA, the determination of whether compression is complete begins.

[0082] Figure 6A This is a diagram used to illustrate the method for determining the completion of compression in the first embodiment. Figure 6A The upper graph shows the discharge pressure (solid line) and the solvent pressure in the first pressurization chamber 11 (dotted line), while the lower graph shows the displacement of the first plunger 21 and the displacement of the second plunger 22. Figure 6A As shown, the controller 10 is divided into a non-determination interval bN (where compression completion is not determined) and a determination interval bD (where compression completion is determined) by the displacement xA of the first plunger 21 calculated according to equation (3). Even if pulsations caused by pressure disturbances occur in the non-determination interval bN, compression continues, thus preventing false determinations of compression completion.

[0083] Figure 6B This is a diagram used to illustrate the method for determining compression completion in the first embodiment, and it shows a case where pulsations caused by interference occur in the determination interval bD. Figure 6B As shown, when a pressure pulsation caused by disturbance occurs in the judgment interval bD, the pressure drop at the beginning of interval c is at most the sum of ΔPA and the change in discharge pressure, thus preventing a pressure drop larger than that.

[0084] In equation (3), the pressure at the end of compression is set as the discharge pressure Pb1 at the start of compression. However, if instead of this, it is set as the pressure before the start of compression (interval a), i.e., the pressure when the controller 10 is not monitoring the pulsation of the discharge pressure, then the control process can be simplified, thus enabling control with a lower-cost controller. Alternatively, the pressure at the end of compression can be predicted by considering the change in discharge pressure Pb1. In this case, the displacement xA can be calculated more accurately. Furthermore, instead of discharge pressure Pb1, equation (3) can be always calculated for the current pressure, and the displacement xA can be updated at any time. In this case, the displacement xA can be calculated even more accurately.

[0085] The above describes an example of applying the liquid delivery pump 1 of this embodiment to a liquid chromatograph 100, but it is not limited thereto. For example, the liquid delivery pump 1 of this embodiment can also be applied to other devices that use liquid delivery pumps, such as liquid chromatograph mass analysis apparatus (LC / MS).

[0086] <Modifications of the First Embodiment>

[0087] Figure 7 This is a diagram illustrating the control method of the first plunger 21 in a variation of the first embodiment. In the first embodiment, it is shown that the first plunger 21 is stopped in interval b2 after compression is completed. In contrast, in this variation, as... Figure 7 As shown in the diagram below, the first plunger 21 is slightly raised in interval b2. In other words, the controller 10 reduces the speed of the first plunger 21 after compression is complete, thus continuing compression. Therefore, as... Figure 7 As shown in the chart above, this can reduce the initial pressure drop (pulsation) in interval c. It should be noted that the method of this variation can also be applied to the following implementation methods.

[0088] <Summary of the First Implementation>

[0089] As described above, in the solvent compression process (interval b) performed by the first plunger 21, the liquid delivery pump 1 of this embodiment calculates the rate of change of solvent pressure k based on the compression pressure Pc at the completion of compression in past cycles and the compression distance xc of the first plunger 21. Based on the rate of change of pressure k and the discharge pressure Pb1 at the start of compression (the current discharge pressure), it calculates the displacement xA of the first plunger 21 (a predetermined distance shorter than the predicted compression distance) when the solvent pressure in the first pressurization chamber 11 is ΔPA lower than the discharge pressure Pb1. Based on the displacement xA, it determines the period for determining the completion of compression (the timing of completing the compression performed by the first plunger 21). Furthermore, if the displacement of the first plunger 21 exceeds xA, causing the first plunger 21 to rise, and after the output of the pressure sensor 110 is greater than the discharge pressure Pb1 by a predetermined threshold ΔP, it determines that the solvent compression is complete and temporarily stops the first plunger 21. As a result, the probability of falsely determining the completion of compression is reduced, and even in the case of false determination, the resulting pressure pulsation is reduced.

[0090] By delivering liquid with minimal pressure pulsation, the noise generated by the detector is reduced, enabling highly sensitive analysis. Furthermore, the reduced pressure pulsation decreases the load on the separation column, extending its lifespan.

[0091] Furthermore, in this embodiment, the liquid delivery pump 1 estimates the pressure of the solvent in the first pressure chamber 11 of the first plunger pump 101 using (Equation 1), thus requiring only one pressure sensor 110 (located only downstream of the second plunger pump 102). This results in a smaller pump volume compared to using two pressure sensors, thereby accelerating solvent replacement. Additionally, since only one pressure sensor is used, the cost of the apparatus is reduced compared to using two. Moreover, because only one pressure sensor is used, there is no need for adjusting the solid difference of the pressure sensor, improving production efficiency.

[0092] [Second Implementation]

[0093] In the first embodiment, it was described that compression by the first plunger 21 was stopped upon detecting pressure pulsations caused by overcompression. Therefore, in the second embodiment, a method was proposed to reduce pressure pulsations accompanying compression determination by completing compression using a predicted value of the compression distance of the first plunger 21.

[0094] The structure of the liquid delivery pump in this embodiment can be adopted with... Figure 1 The pump 1 of the first embodiment shown has the same structure.

[0095] <Methods for determining when compression is complete>

[0096] Figure 8This is a diagram used to illustrate the method for determining the completion of compression in the second embodiment. The controller 10 calculates the rate of change of solvent pressure k(n) in equation (1), estimates the compression pressure as the discharge pressure Pb1 at the start of compression, and calculates the displacement xc' (predicted value of compression distance) of the first plunger 21 that stops compression using the following equation (4).

[0097] xc'(n)=Pb1(n) / k(n)+xc0 (4)

[0098] The first embodiment determines compression completion based on the premise that pulsation occurs during compression. However, in the second embodiment, compression completion is determined even when there is no pulsation until the displacement of the first plunger 21 reaches xc'. This further reduces pulsation at compression completion. It should be noted that, in the event of pulsation in the discharge pressure during the period from the start of compression until the displacement of the first plunger 21 reaches xc', the controller 10 can determine compression completion in the same way as in the first embodiment.

[0099] In equation (4), the pressure at the end of compression is set as the discharge pressure Pb1 at the start of compression. However, if instead of this, it is set as the pressure before the start of compression (interval a), i.e., the pressure when the controller 10 is not monitoring the pulsation of the discharge pressure, then the control process can be simplified, and thus control can be achieved using a lower-cost controller. Alternatively, the pressure at the end of compression can be predicted by considering the change in discharge pressure Pb1. In this case, the displacement xc' can be calculated more accurately. Furthermore, instead of discharge pressure Pb1, equation (4) can be always calculated for the current pressure, and the displacement xc' can be updated at any time. In this case, the displacement xc' can be calculated even more accurately, resulting in a reduction in pulsation.

[0100] <Summary of the Second Implementation>

[0101] As described above, in the solvent compression process (interval b) performed by the first plunger 21, the liquid delivery pump 1 of this embodiment calculates the rate of change of pressure k based on the compression pressure Pc at the completion of compression in past cycles and the compression distance xc of the first plunger 21. Based on the rate of change of pressure k and the discharge pressure Pb1 at the start of compression (the current discharge pressure), it predicts the displacement xc' (compression distance) of the first plunger 21 at the completion of compression. When the displacement of the first plunger 21 reaches xc' (the predicted compression distance), it determines that the solvent compression is complete and stops compression (the timing for completing the compression performed by the first plunger 21 is determined based on the displacement xc'). This reduces pressure pulsation. Furthermore, the misjudgment of compression completion caused by interference, as described in the first embodiment, is eliminated.

[0102] [Third Implementation Method]

[0103] In the first embodiment, it is described that compression by the first plunger 21 is stopped when pressure pulsation caused by overcompression is detected during the determination period of compression completion. In the second embodiment, it is described that compression by the first plunger 21 is stopped when the predicted compression distance is reached. In the third embodiment, as another method to reduce pressure pulsation accompanying the compression determination, a technique is proposed to stop compression immediately before the predicted compression distance when the flow rate of the delivery pump is 0.

[0104] <Structure example of a liquid chromatograph>

[0105] Figure 9 This is a schematic diagram showing the structure of a liquid chromatograph 200 equipped with the liquid delivery pumps 1001 and 1002 of the third embodiment. Figure 9 As shown, the liquid chromatograph 200 includes pumps 1001 and 1002, an ejector 2 for introducing a sample into the liquid chromatograph 200, a separation column 3, a detector 4, and a waste container 5. The specific structures of pumps 1001 and 1002 are the same as those of pump 1 in the first embodiment. Regarding the ejector 2, separation column 3, detector 4, and waste container 5, ejectors, separation columns, detectors, and waste containers commonly used in liquid chromatographs can be used.

[0106] The liquid chromatograph 200 of this embodiment has a so-called high-pressure gradient structure with two sets of delivery pumps connected in parallel. Delivery pumps 1001 and 1002 deliver different solvents (delivery pump 1001 delivers solvents 511 and 512, and delivery pump 1002 delivers solvents 513 and 514), which are mixed downstream of the confluence point 6 and delivered to the separation column 3. The flow rates of delivery pumps 1001 and 1002 are appropriately set according to the analytical requirements.

[0107] <Methods for determining when compression is complete>

[0108] Figure 10 This is a graph used to illustrate the flow rate changes in delivery pumps 1001 and 1002. For example... Figure 10 As shown, in the presence of one of the liquid delivery pumps (in Figure 10When the flow rate of the liquid delivery pump 1001 is zero during the interval (times B to C), the pressure of the solvent inside the pump becomes atmospheric pressure when it completely stops during this interval. Thus, when liquid delivery resumes (time C), solvent cannot be delivered until the solvent pressure rises from atmospheric pressure to the discharge pressure, causing a backflow from the liquid delivery pump 1002 side towards the liquid delivery pump 1001 side, resulting in pressure pulsations. To prevent these pulsations, the liquid delivery pump 1001 needs to compress without discharging (delivering) solvent during the zero flow rate interval (times B to C). However, in this embodiment, compression is stopped just before the liquid delivery pump 1001 completes its compression, thereby preventing pulsations.

[0109] Figure 11 This is a diagram illustrating the control method of the first plunger 21 of the liquid delivery pump 1001 in this embodiment. Similar to the first embodiment, the controller 10 calculates the rate of change of solvent pressure k (m) according to equation (1). It should be noted that the period for calculating the rate of change k is set to the interval where the flow rate is 0 ( Figure 10 The m-th period before time B to C (e.g., including until time m). Figure 10 (The period of the timing up to time A). In addition, the controller 10 estimates the compression pressure as the discharge pressure Pb1 at the start of compression, and calculates the displacement xD of the first plunger 21 that stops compression using the following equation (5).

[0110] xD(n)=(Pb1(n)-ΔPD) / k(m)+xc0 (5)

[0111] Here, ΔPD is the difference between the estimated compression pressure and the pressure at which compression stops. ΔPD can be determined through prior experiments, for example, by setting it to 5% to 10% of the discharge pressure Pb1. The closer the value of Pb1-ΔPD is to the discharge pressure Pb1, the more the pulsation of the timing (time C) at which liquid delivery resumes can be reduced.

[0112] In equation (5), the pressure at the end of compression is set as the discharge pressure Pb1 at the start of compression. However, if instead of this, it is set as the pressure before the start of compression (interval a), i.e., the pressure when the controller 10 is not monitoring the pulsation of the discharge pressure, then the control process can be simplified, and thus control can be achieved using a lower-cost controller. Alternatively, the pressure at the end of compression can be predicted by considering the change in discharge pressure Pb1. In this case, the displacement xD can be calculated more accurately. Furthermore, instead of discharge pressure Pb1, equation (5) can be always calculated for the current pressure, and the displacement xD can be updated at any time. In this case, the displacement xD can be calculated even more accurately, and as a result, the pulsation can be reduced.

[0113] <Summary of the Third Implementation>

[0114] As described above, in this embodiment, when the flow rate is 0, the liquid delivery pump 1001 calculates the pressure change rate k based on the compression pressure Pc at the completion of compression in a past cycle before the flow rate became 0 and the compression distance xc of the first plunger 21. Based on the pressure change rate k and the discharge pressure Pb1 at the start of compression (the current discharge pressure), it calculates the displacement xD of the first plunger 21 (a predetermined distance shorter than the predicted compression distance) when the pressure of the solvent in the first pressurization chamber 11 is ΔPD lower than the discharge pressure Pb1. When the displacement of the first plunger 21 reaches xD, the compression of the solvent is completed (stopped) (the timing of completing the compression performed by the first plunger 21 is determined based on the displacement xD). This reduces the pulsation of the timing of restarting liquid delivery.

[0115] [Variation Example]

[0116] This invention is not limited to the embodiments described above, but includes various modifications. For example, the embodiments described above have been explained in detail for ease of understanding of the invention, and it is not necessary to possess all the structures described. Furthermore, a portion of one embodiment can be replaced with the structure of another embodiment. Additionally, the structure of another embodiment can be added to the structure of one embodiment. Furthermore, regarding a portion of the structure of each embodiment, a portion of the structure of another embodiment can be added, deleted, or replaced.

[0117] Explanation of reference numerals in the attached figures

[0118] 1 liquid delivery pump

[0119] 2 injectors

[0120] 3 Separation Columns

[0121] 4 detectors

[0122] 5 Waste Liquid Containers

[0123] 10 controllers

[0124] 11 First pressurization chamber

[0125] 12 Second pressurization chamber

[0126] 21 First plunger

[0127] 22 Second plunger

[0128] 31 First Attraction Pathway

[0129] 32 Second Attraction Pathway

[0130] 41 First Ejection Pathway

[0131] 42 Second ejection pathway

[0132] 51 First check valve

[0133] 52 Second check valve

[0134] 100 Liquid Chromatograph

[0135] 101 First Piston Pump

[0136] 102 Second plunger pump

[0137] 103 Connecting Flow Paths

[0138] 110 pressure sensor

[0139] 210 motor driver

[0140] 310 Discharge Valve Actuator

[0141] 410 Solenoid Valve Actuator.

Claims

1. A liquid delivery pump, characterized in that, The liquid delivery pump includes: A first plunger pump, which has a first plunger; A second plunger pump has a second plunger and is connected in series with the first plunger pump; A pressure sensor is located downstream of the second plunger pump; as well as The control unit receives the input of the liquid discharge pressure measured by the pressure sensor and controls the driving of the first plunger and the second plunger. The control unit calculates the pressure change rate of the liquid based on the past compression distance of the first plunger when the liquid is compressed using the first plunger pump and the pressure at the end of compression. The control unit predicts the compression distance of the first plunger based on the pressure change rate and the current discharge pressure. The control unit determines the timing for completing the compression performed by the first plunger based on the predicted compression distance.

2. The liquid delivery pump according to claim 1, characterized in that, The control unit defines the period during which the displacement of the first plunger exceeds a predetermined distance shorter than the predicted compression distance as the period for determining that the compression is complete.

3. The liquid delivery pump according to claim 2, characterized in that, During the period when the control unit determines that the compression is complete, it stops the compression if a pulsation of the discharge pressure is generated.

4. The liquid delivery pump according to claim 1, characterized in that, The control unit stops the compression when the displacement of the first plunger reaches the predicted compression distance.

5. The liquid delivery pump according to claim 1, characterized in that, When the flow rate is 0, the control unit stops the compression if the displacement of the first plunger is a predetermined distance shorter than the predicted compression distance.

6. The liquid delivery pump according to claim 5, characterized in that, The control unit calculates the pressure change rate based on the compression distance of the first plunger before the flow rate becomes zero and the pressure when the compression is completed.

7. The liquid delivery pump according to claim 1, characterized in that, The control unit estimates the current discharge pressure as the pressure of the liquid in the first plunger pump when the compression is completed, and predicts the compression distance.

8. The liquid delivery pump according to claim 1, characterized in that, The control unit sets the discharge pressure at the start of compression to the current discharge pressure.

9. The liquid delivery pump according to claim 1, characterized in that, The control unit sets the discharge pressure before the compression begins as the current discharge pressure.

10. The liquid delivery pump according to claim 1, characterized in that, The control unit updates the predicted compression distance whenever the current discharge pressure is measured.

11. The liquid delivery pump according to claim 1, characterized in that, After determining that the compression is complete, the control unit stops the first plunger for a specified time.

12. The liquid delivery pump according to claim 1, characterized in that, After determining that the compression is complete, the control unit reduces the speed of the first plunger and continues the compression.

13. A liquid delivery method, executed by a control unit that controls the liquid delivery of a liquid delivery pump, characterized in that, The liquid delivery pump has: A first plunger pump, which has a first plunger; A second plunger pump, having a second plunger, is connected in series with the first plunger pump; and A pressure sensor, positioned downstream of the second plunger pump, measures the discharge pressure of the liquid from the second plunger pump. The liquid delivery method includes the following processing: The control unit calculates the pressure change rate of the liquid based on the past compression distance of the first plunger when the liquid is compressed using the first plunger pump and the pressure when compression is completed. The control unit predicts the compression distance of the first plunger based on the pressure change rate and the current discharge pressure. as well as The control unit determines the timing for completing the compression performed by the first plunger based on the predicted compression distance.

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