JPH0219670A - Control method for nonpulsating pump - Google Patents

Abstract

PURPOSE:To make pressure pulsation reducible to the utmost by inputting the position and speed of a plunger as well as the detected value of a circuit and pressure in resultant discharge into a computer, and adding a motor driving frequency correction value to a driving pattern where the calculated speed sum of two plungers comes to be constant. CONSTITUTION:A microcomputer 24 calculates a constant showing that a speed command value is ideally realized to what degree by a difference in performance of hard itself on the basis of a speed detection signal 19 of a plunger. Next, such speed control that composite speed of both first and second plungers comes to be constant at all times is carried out by compensating a speed of the second plunger 9 mainly. In addition, a signal out of a pressure sensor 20 is converted into a correcting portion of the plunger speed, namely, a correction portion of pulse motor driving frequency in the computer 24, and then it is added to driving frequency of the plunger 9. Thus, speed control over the plunger is carried out by the computer 24 on the basis of both speed and pressure detecting signals of the plunger, whereby stable liquid conveyance with no pressure pulsation is made possible to be done.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a pulsation-free pump used in liquid chromatography, medical testing equipment, etc. Concerning a pump control method.

[Conventional technology]

Conventional pulsationless pump devices are, as described in Japanese Patent Application Laid-Open No. 57-70976, a dual series system in which two plungers are reciprocated by a single cam drive to obtain a combined discharge amount from the pumping action of each plunger. In a type reciprocating pump, a drive control circuit is connected to the motor that drives the cam, and a circuit that detects the pressure of the combined discharge amount and the position of pressure fluctuation, and a circuit that supplies force to control the speed of the drive motor. It is configured to do this. The means for recognizing the rotational position of the cam includes:
It is equipped with a pulse generator provided on the rotating shaft of the cam and a rotation speed correction setter, and the cam position pulses detected by the pulse generator are counted by a pulse counter and outputted from the rotation speed correction setter. A comparator compares the corrected signal with the corrected signal, and corrects only an arbitrary angle during one rotation of the cam.

[Problem to be solved by the invention]

The above conventional technology effectively suppresses pressure pulsations when the plunger cannot be driven according to commands from the drive control circuit due to (1) machining errors in the cam, backlash in the reducer, or other mechanical play. Cannot be reduced. (2) Since the two plungers are driven by one motor, even if drive control is performed to locally increase the speed of the motor in order to correct the discharge pressure, there is a limit to the degree of freedom of movement, and it is not possible to difficult to control. (3) Open-loop control is used instead of feedback control (closed-loop control) in which the discharge pressure is detected by a pressure detector and the detection signal directly controls the drive motor, so the value set by the rotation speed correction setting device is However, there are problems in that it is not appropriate for the fluctuation value of the discharge pressure that has decreased dynamically, and that it is difficult to accurately reduce the pulsation in a short period of time.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks and provide a control system for a dual reciprocating pump with small pressure pulsations.

[Means to solve the problem]

The control system of the pulsationless pump according to the present invention includes a plunger that reciprocates in a pump chamber formed in a cylinder head that has check valves in the suction passage and discharge passage, and a drive device for reciprocating the plunger. In a dual reciprocating non-pulsating pump, a detector and circuit detect the position and speed of the plunger, a detector detect the pressure of the combined discharge amount, and an A/D conversion circuit that converts the detected value from A/D. These output signals are input to a microcomputer to calculate a drive pattern in which the sum of the speeds of the two plungers is constant, and a motor drive frequency correction value corresponding to the pressure fluctuation is added to this drive pattern at any time. It is characterized by performing plunger speed control that is corrected by addition.

[Effect]

Pulsationless pumps used for liquid chromatography, etc.
It is desirable to be able to discharge continuously without pulsation, and since it is necessary to discharge high-pressure liquid, for example, as shown in Figure 3, check valves are installed on the suction and discharge sides of one reciprocating pump. A two-stage reciprocating pump is used in which the outlet of the discharge valve is connected to another reciprocating pump.

As shown in FIG. 3, the mechanism for driving the two plungers of this reciprocating pump is such that each plunger is driven by a separate motor via a rotary-linear motion conversion mechanism such as a ball screw.

For example, the speed pattern of the two plungers is the fourth one.
There is something like the one shown in the figure, and when the effect of the check valve is included, it becomes 2.
The sum of the speeds of the two plungers is always constant. By doing this, in principle, the pump becomes pulsation-free. However, in reality, the plunger does not operate in accordance with the speed command value output from the microcomputer due to backlash in the reducer, machining errors in the cam, and other mechanical backlashes, resulting in pressure pulsations.

Therefore, it is necessary to control the speed of the plunger so that the combined speed of the two plungers is always constant.

In order to control the speed of the plunger, for example, a detector such as a linear encoder is attached to the plunger, and the detected value from the detector is input to the microcomputer through the plunger position and speed detection circuit, and the speed of the plunger is corrected from time to time. do it like this.

For example, when a pulse motor is applied to the motor, the plunger speed dX,/dt is d Xp/d t = where a is a constant and f is the drive frequency of the pulse motor.
a f ...(1). That is, if it is desired to control the speed of the plunger, the drive frequency of the motor that drives the plunger may be controlled. The control method will be explained below.

Let the combined velocity of the plunger be ftot(θ, t), the velocity of the first plunger be f, Cθ, t), and the velocity of the second plunger be ft, (θ, t). θ and t represent the rotation angle and time of the motor, respectively, and the drive frequency f is a function of the rotation angle of the motor or time.

The first plunger is called a master plunger, and the second plunger is called a slave plunger. Since the combined speed of the two plungers is constant, each driving frequency is given by the following equation.

The second speed command value is corrected by taking into account the gains al and Gt obtained in the first measurement.A simple model of this control method is shown in FIG.

Where fs is the speed command value, fR is the ideal speed (frequency), and fK is the measured value, the ratio of the command value to each measured value of the first and second plungers (hereinafter referred to as gain) is G a , Gb. Furthermore, the subscripts indicate the order in which they are output after the unit time has elapsed.

The speed command value and gain of each plunger after one unit of time has elapsed since the pump started moving are given by the following equation. Here, the rotation angles θ and t are omitted. ) The third time is Therefore, the nth time is .

Further, the discharge pressure is detected by a pressure detector, A/D converted by an A/D converter, and inputted to a microcomputer. In the microcomputer, based on the pressure detection signal, a motor drive frequency correction amount ΔflI for reducing pressure pulsation is calculated from time to time, and the second plunger (= (slave plunger) and output. Therefore, since the above correction is also performed, the n-th speed command value is finally as follows.

By doing so, the plunger can be reliably driven at all times with an appropriate speed command value, and pressure pulsation can be effectively reduced.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. Third
The figure shows an example of a dual reciprocating non-pulsating pump used in the present invention, in which the rotational motion of two separate pulse motors 1 is controlled by a planetary gear reducer 14° thrust bearing 15. The pistons 5 and 6 are connected via a drive transmission system consisting of a ball screw 16.
By converting the piston 5 into a linear reciprocating motion, the piston 5
．． A first plunger 8 and a second plunger 9 connected to the tip of the plunger 6 are driven by separate pulse motors 1, 1. 10 is a seal, and 18a and 18b are check valves.

An embodiment of the present invention using the above pump will be described with reference to FIG. The flow rate setting signal set by the flow rate setting device 26 (or external flow rate controller) is converted into a binary code by a binary coded decimal-binary code conversion circuit 27 and input to the microcomputer 24. When this signal and the start signal from the start/stop button 28 are input to the microcomputer 24 via the pulse generation circuit 29, the microcomputer 24 calculates the pulse motor drive frequency, etc. and outputs it from the output port of the microcomputer 24. A signal for determining the rotation direction of the pulse train 9 that creates the plunger speed drive pattern shown in FIG. 4, a current control signal, etc. is output to the pulse motor driver 25. These signals are distributed by a pulse motor driver 25 to drive two pulse motors 1. In this case, the two motors are driven at different frequencies. When the pulse motor 1 rotates, it is decelerated by the planetary gear reducer 14, and the thrust bearing 15. Rotary motion is converted into linear reciprocating motion through a drive transmission system consisting of a ball screw 16, and the plunger is reciprocated to discharge the liquid at high pressure in the liquid feeding method explained using FIG. 3. do. In this case, the plunger does not operate in accordance with the speed command value from the microcomputer 24 due to mechanical backlash such as the cam machining error and the backlash of the reducer as described above, and pulsation occurs. In order to prevent this, two detectors 19 are provided to detect the position of each plunger.
The signal from the position speed detection circuit 23 connected to it is
It is input to the microcomputer 24 through.

In addition, pulsation may occur due to factors other than plunger operation, such as a delay in the response of a check valve or a difference in bulk modulus depending on the liquid used when increasing the pressure from low pressure to high pressure. A pressure sensor 2o is provided to detect line pressure and pressure fluctuations, and its detection signal is passed through an amplifier and a filter 21 for removing noise to the A/
It is converted into a digital signal by the D converter 22 and input to the microcomputer 24.

Based on the aforementioned plunger speed detection signal, the microcomputer 24 calculates a constant (gain) indicating how ideally the speed command value is realized due to differences in the performance of the hardware itself. The speed control so that the combined speed of the first and second plungers is always constant is mainly performed by the second plunger.
This is done by correcting the speed of the plunger 9.

Further, the signal from the pressure sensor is converted within the microcomputer 24 into a correction amount for the plunger speed, that is, a correction amount for the pulse motor drive frequency, and is added to the drive frequency of the second plunger.

In this way, by controlling the plunger speed using the microcomputer 24 based on the plunger speed detection signal and pressure detection signal, stable liquid feeding without pressure pulsation is possible.

Here, as means for detecting the speed of the plunger, a device such as a near encoder or the like that detects the speed of the plunger itself is used, but if the speed of the plunger is detected repeatedly, an encoder attached to a motor may also be used.

In addition, in this embodiment, a ball screw was used as a mechanism for converting the rotational motion of the motors into linear motion and driving the piston, but the present invention can also be achieved by replacing this with two cams connected to each motor. is possible.

FIG. 2 is an explanatory diagram showing a second embodiment of the present invention. In FIG. 1 and FIG. 2, the same reference numerals indicate the same or corresponding parts.

In the second embodiment, the plunger speed detection signal that was fed back to the microcomputer 24 in the first embodiment is fed back to the pulse motor driver 25 through the position and speed detection circuit 23. The pulse motor driver 25 controls the speed of the plunger using the control method described above based on the plunger speed detection signal, and adjusts the combined speed of the plunger to always be constant.

In addition, the signal from the pressure sensor is transmitted to the microcomputer 2.
4, it is converted into a correction for the Brandin speed, that is, a correction for the pulse motor drive frequency, and is added to the drive frequency of the second plunger.

In this way, by controlling the speed of the plunger based on the plunger speed detection signal and the pressure detection signal using the pulse motor driver 25 and the microcomputer 24, stable liquid feeding without pressure pulsation is possible.

〔Effect of the invention〕

According to the present invention, the speed of the plunger can be ideally driven according to the speed command value, and the plunger speed can be corrected to an appropriate size to eliminate fluctuations in pressure pulsation. This has the effect of making it extremely small.

[Brief explanation of the drawing]

1 and 2 are control circuit system diagrams showing an embodiment of the present invention, FIG. 3 is a diagram showing a dual reciprocating type non-pulsating pump to which the present invention is applied, and FIG. (a) and (b) are diagrams showing basic speed patterns of the present invention, and FIG. 5 is an explanatory diagram in which a controlled object is modeled to explain the control method of the present invention. 1... Pulse motor, 5... First piston, 6...
- Second piston, 8... First plunger, 9... Second plunger, 10... Seal, 11... Cylinder head, 14... Planetary gear reducer, 15... Thrust bearing, 16... Ball screw, 18a, 18b...
Check valve, 19...Plunger position and speed detector, 20.
・・Pressure sensor, 21 ・・Low pass filter, 22・
・・A/D converter, 23 ・・Position speed detection circuit, 24
...Microcomputer, 25..Pulse motor driver, 26..Flow rate setting device, 27..Code conversion circuit, 28..Start/stop button, 29..
・・Pulse generation area//(6 people mowo 5, dojidaiton 3, q)゛runshi〈 /4 Incorrect entry/O stagnation screw゛/2 backstop blue 661

Claims (1)

[Claims] 1. A dual reciprocating mechanism consisting of a plunger that reciprocates in a pump chamber formed in a cylinder head having check valves in the suction passage and discharge passage, and a drive device for reciprocating the plunger. In the control method for a type pulsationless pump, the position and speed of the plunger and the combined discharge pressure are detected, and these detected signals are input to calculate a drive pattern in which the sum of the speeds of the two plungers is constant. Mainly the second
A method for controlling a pulsationless pump, characterized in that the speed of the plunger is controlled by making the speed of the plunger follow the speed of the first plunger in real time. 2. Control of the pulsationless pump according to claim 1, in which the speed of the second plunger is continuously controlled based on the speed feedback signal to keep the sum of the speeds of the two plungers constant during the discharge stroke. Method.