JP2503804B2 - Liquid pump - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid pump used for sending a mobile phase in a liquid chromatograph, and more particularly to a liquid pump of a type in which a piston reciprocates.

[0002]

2. Description of the Related Art In order to feed a liquid with a liquid pump in which a piston reciprocates while reducing fluctuations in discharge pressure, high-speed suction and high-speed discharge are performed after constant-speed discharge.
After that, the speed of the piston is returned to the normal speed. Due to the high-speed discharge after the high-speed suction, the pressure dropped during the suction quickly returns to its original value, and the pressure fluctuation is reduced. In order to return from high-speed discharge after suction to constant-speed discharge, the discharge pressure from the pressure detector provided in the discharge side flow path of the pump is monitored, and when the discharge pressure returns to a predetermined level A signal indicating the end of high-speed suction / high-speed discharge is generated, and the discharge speed is returned from high speed to a constant speed based on the signal.

[0003]

In order to generate a high-speed suction / high-speed discharge end signal, the discharge pressure is monitored and compared with the level at the time of suction start, and detection is performed to generate a high-speed suction / high-speed discharge end signal. This requires a device, which increases the cost of the pump. It is an object of the present invention to provide a liquid pump that controls a pump head so as to reduce pressure fluctuation as in the conventional case without using a detection device that generates a signal for terminating high-speed suction / high-speed discharge.

[0004]

The present invention is shown in FIG. 2 is a pump head in which a piston reciprocates in a chamber having an inlet valve and an outlet valve, 4 is a drive device for reciprocating the piston of the pump head 2, and a pressure detector 6 provided in a pump outlet side flow path. The pressure detection circuit 8 for detecting the pressure from the signal constitutes the pressure detection means. 1
Reference numeral 0 is a detection means for detecting the start time point of the suction stroke of the pump head 2, and 12 is a control unit for controlling the speed of the piston in the suction stroke and the discharge stroke via the drive device 4 based on the signal from the detection means 10. When the control unit 12 obtains the suction start signal from the detecting means 10 after the discharge stroke at the constant piston speed, the rotation speed f of the piston motor determined by the discharge flow rate at the discharge stroke at the constant piston speed. , the following equation for a variable compression ratio alpha of the discharge pressure P and the solvent discharge stroke at a constant piston _{speed, W = a (f 0 -f} ) 2 + (α + B) P + C ...... defined time (1) W Only after increasing the piston speed to perform suction and discharge, control is performed to return to the discharge stroke of the original constant speed again. Here, f ₀ is the rotational speed of the piston motor during high-speed suction, and A, B, and C are experimentally determined coefficients that minimize pressure fluctuations.

[0005]

[Operation] There is almost no difference in the behavior during high-speed suction and high-speed discharge. Therefore, even if the high-speed suction / high-speed discharge is finished by the time W determined by the above-mentioned function (1), the discharge pressure is monitored as in the conventional case and the high-speed suction / high-speed discharge is detected by the pressure feedback method by the detection device. It has the same effect as determining the end point.

FIG. 2 shows the operation. (A) goes out the piston
It shows the relationship between the rotation angle and the rotation speed of the motor to be returned.Was
(B) shows the variation of discharge pressure with time.
I gave it away. As shown in (A), the discharge stroke
, The motor is driven at a constant speed corresponding to the set flow rate.
And is driven at high speed in the suction stroke and the compression stroke. compression
The stroke is a high-speed discharge stroke. When the suction process starts, the motor
Is gradually accelerated, and then driven at a constant speed and high speed.
Be done. The time W during which suction and compression are performed at a constant high speed is
In the equation (1), the coefficient is experimentally determined so that the pressure fluctuation is minimized.
The formula is determined and the variables f, α, and P are added to the formula.
It is the time determined by substitution.This acceleration section W is next
It was led like this. Piston reciprocating type
In the pump, at the beginning of the discharge process, the compressibility of the solvent
As a result, the solvent inside the pump chamber is compressed and
Is not discharged until the pressure reaches a high pressure.
Occurs, which causes pressure fluctuations. This pressure fluctuation
In order to suppress, the motor speed is usually set at the beginning of the discharge section.
Increase the pressure to compress the solvent at high speed, and
Data speed has been restored. At the end of this compression section
The decision was traditionally to monitor the signal from the pressure sensor
Therefore, the width of the compression section does not differ much between aircraft.
Since it does not exist, it is recommended to decide it by a predetermined approximation formula.
Can be. As shown in FIG. 2, suction the acceleration section W
Section W ₁ And compression section W ₂ Can be divided into W = W ₁ + W ₂ (2) W ₁ Is the suction section of the cam (constant, C ₁ From)
Since the section of rising edge a of the data is subtracted,
Can be expressed as W ₁ = C ₁ -C ₂ (f ₀ -F) ² (3) C ₂ Is a constant. W ₂ Is experimentally determined by the solvent pressure P and pressure.
It was found that the reduction ratio α can be approximated as follows. W ₂ = (Α + C ₃ ) P + C _Four (4) C ₃ , C _Four Is a constant. From (2), (3), (4) W = -C ₂ (f ₀ -F) ² + (Α + C ₃ ) P + (C ₁ + C _Four ) And then -C ₂ → A, C ₃ → B, (C ₁ + C _Four ) → C
If W = A (f ₀ -F) ² + (Α + B) P + C Thus, the equation (1) is derived.

The operation after the high speed operation time W is determined is performed as shown in FIG. That is, after the discharge operation at a constant speed, when the suction start point is reached, the suction stroke at a high speed is started, and then high-speed discharge is performed until the calculated high-speed drive time W elapses, and then discharge at a constant speed is performed again. Return to operation. This operation is continued until the stop signal is input.

[0008]

EXAMPLE FIG. 4 shows an example of a single piston reciprocating drive type pump. The pump head 2 has an inlet valve 20 and an outlet valve 22, and a piston 24 moves in a reciprocating direction inside the chamber. The base end of the piston 24 is in contact with the cam 26. The cam 26 is rotated by a motor 28. 30
Is a motor drive circuit. The cam 26, the motor 28, and the motor drive circuit 30 correspond to the drive device 4 in FIG.
An optical sensor 32 is provided to detect the origin of rotation of the cam 26, and the rotation angle detection circuit 34 detects the rotation angle from the detection output of the optical sensor 32. The optical sensor 32 and the rotation angle detection circuit 34 correspond to the detection means 10 in FIG.
The discharge side flow path of the pump head 2 is led to the analysis flow path of the liquid chromatograph, and a pressure detector 6 is provided in the discharge side flow path of the pump head, and a detection signal of the pressure detector 6 detects the pressure. The discharge pressure is guided to the circuit 8 and the discharge pressure is detected. The control unit 12 takes in the rotation angle signal from the rotation angle detection circuit 34 and the discharge pressure from the pressure detection circuit 8, determines the time W in the suction stroke and the compression stroke, and determines the discharge and suction operations in the motor drive circuit 30. Control through.

As described above, by performing high-speed suction / high-speed discharge for an optimum time depending on the discharge flow rate (or the rotation speed of the piston motor determined by the discharge flow rate), the discharge pressure and the compression rate of the liquid, the pressure dropped by suction It is possible to quickly return to the level before suction and perform the liquid feeding operation with little pressure fluctuation.

[0010]

According to the present invention, the time of high-speed suction / high-speed discharge for reducing the fluctuation of the discharge pressure is calculated, and the drive of the pump head is controlled by the calculated value.
A similar structure is realized with a simpler structure than the conventional one that uses a detection device that monitors the discharge pressure and generates a signal for high-speed suction / high-speed discharge completion in comparison with the pressure at the start of suction. It is possible to contribute to cost reduction.

[Brief description of drawings]

FIG. 1 is a block diagram showing the present invention.

2A and 2B are diagrams showing an operation of the present invention, FIG. 2A is a diagram showing a relationship between a rotation angle and a rotation speed of a motor, and FIG. 2B is a diagram showing pressure in a discharge side flow path.

FIG. 3 is a flowchart illustrating an operation.

FIG. 4 is a block diagram showing an example.

[Explanation of symbols]

 2 pump head 4 drive device 6 pressure detector 8 pressure detection circuit 10 detection means 12 control unit

Claims (1)

(57) [Claims] 1. A pressure detector including a pump head in which a piston reciprocates in a chamber having an inlet valve and an outlet valve, a drive device for reciprocating the piston, and a pressure detector provided in a pump outlet side flow path. Means, detection means for detecting the start time of the suction stroke of the pump head, and control for controlling the speed of the piston in the suction stroke and the discharge stroke via the drive device based on the signal from the detection means. When a signal for starting suction is obtained from the detection means after the discharge stroke at a constant piston speed, the control section includes a rotation section of the motor of the piston determined by the discharge flow rate at the discharge stroke at the constant piston speed. A number f, the discharge pressure P in the discharge stroke at a constant piston speed, and the following equation that uses the solvent compression rate α as variables: W = A (f ₀ −f) ² + (α + B) P + C A liquid pump that controls to return to the original discharge process at a constant speed after suctioning and discharging at a high speed. here,
f ₀ is the rotation speed of the piston motor during high-speed suction,
A, B, and C are coefficients determined experimentally so that the pressure fluctuation is minimized.