JPS63105284A - Minute quantity liquid feed pump - Google Patents

Abstract

PURPOSE:To eliminate the delay in control by correcting the rotation of a pulse motor for driving a pump by the OR action between the forced compression signal and pressure reduction signal of said pump. CONSTITUTION:A pump 3 consists of a cam 3A, a piston 3B, a cylinder 3C, and check valves 3D, 3E, and is driven by a pulse motor 14. The OR action between the forced compression signal and pressure reduction signal of the pump 3 is carried out by AND gates 18, 18' and a one-shot circuit 19, to double the speed of the rotation of the pulse motor 14 while continuing compression. Thereby, pulsation can be eliminated without causing delay in control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a micro-volume liquid delivery pump, and particularly to a micro-volume liquid delivery pump with little pulsation that is suitable for use in liquid chromatographs.

[Conventional technology]

In conventional liquid pumps, a pressure detection element detects a decrease in pressure after the pump moves from the suction stroke to the discharge stroke, and then the pulse motor is rotated at double speed to correct the decrease.

However, control in which a mechanical system is present in a feedback loop has the disadvantage that there is a time delay and a poor response causes pulsating flow.

First, a first known example disclosed in Japanese Patent Publication No. 54-42446 will be described. This is designed to open the switching valve after pressurizing the liquid in the liquid feeding pump on the supply side to the pressure applied to the liquid in the liquid feeding pump on the load side. This is effective when the pressure is constant.

However, in amino acid analysis, for example, in one analysis, a separation column separates more than a dozen types of amino acids, so several types of eluents are used for separation, and the temperature of the separation column is also changed in several stages. To separate. Therefore, the viscosity changes depending on the type of eluent, so the pressure changes, and
Since the pressure also changes depending on the column temperature, - the pressure during analysis is not constant and changes in many steps.

As mentioned above, - No consideration is given to the case where the pressure changes in many steps during the analysis.

Next, a second known example, which is disclosed in Time Publication No. 55-128678, will be explained. This detects the pressure drop start point and pressure rise start point in the plunger pump internal chamber, increases the rotation speed of the motor that drives the cam by a certain number from the drop start point, and returns to the original value when the pressure rise start point is reached. The motor rotation speed is returned to normal, and the pressure is used as a feedback signal to double the rotation speed of the motor. It is difficult to control the motor at high speeds like electrical control, and there is a time delay from when the pressure drop is detected until the motor reaches double speed. This results in insufficient flow, resulting in pulsating flow.

As described above, no consideration is given to the fact that the time delay between detecting a pressure drop and increasing the motor's speed to double speed causes pulsation.

Next, as a third known example, the one shown in Time Publication No. 56-98582 will be explained. This predicts the time it will take for fluctuations in the volume of discharged liquid that occur when the Terranja changes direction to return to the equipment flow rate, and during this time the rotational speed of the pulse motor is changed to eliminate fluctuations in the volume of discharged liquid. It is now possible to do so.

This does not take into account the following two points. First, as mentioned in the first known example above, when multiple types of eluents are used, the compressibility of each eluate is different, so simply pressure difference cannot be used for different eluents. It is not possible to compensate optimally, so that for some eluents there is no pulsation, while for others there is pulsation.

Second, as a result of predicting the time it will take to return to the R constant flow rate, if there is an excess or deficiency in the pressure, the cam will continue to rotate and the correction will be made again the next time, so the pulsating flow It is to produce. Furthermore, the opening/closing speed of the check valve varies depending on the viscosity and specific gravity of multiple types of liquids, causing pulsating flow, but no consideration is given to the above two points.

FIG. 4 is a diagram showing the principle of a conventional liquid pump. The voltage of the current setter 10 is divided by a resistor R and applied to the switch element 11.
is applied to the VF converter 12 and converted into a frequency proportional to the voltage. The output pulses of the VF converter 12 are given to a pulse motor drive circuit 13, and the pulse motor drive circuit 13 drives a pulse motor 14. The pulse motor 14 includes cams 3A, 5A; chopper 6A.
are connected.

The pump 3 includes a cam 3A, a piston 3B, and a cylinder 3G.
, a discharge side check valve 3D, and a suction side check valve 3E, and the piston 3B reciprocates following the cam 3A.

The damper 5 includes a cam 5A, a piston 5B, and a cylinder 5.
The piston 5B reciprocates following the cam 5A.

The eluent 1 and the suction side check valve 3E communicate with each other through a solenoid valve 2, and the discharge side check valve 3D and the cylinder 5C communicate with each other through a communication pipe 4.

The discharge side of the cylinder 5'c communicates with a separation column 8 and a pressure detection element 9 through a connecting pipe 7. The outlet of the separation column 8 is connected to a primary absorbance measurement system.

The separation column 8 has an inner diameter of about 6 mm and a length of about 100 mm.
It is filled with ion exchange resin with a particle size of approximately 3 μm, and 0.5 m of 0.2 N citrate buffer is added to the separation column 8.
Approximately 200 kg/cm when pumping at a flow rate of Q/win
2 pressure.

The chopper device 6 includes a chopper 6A, a light source 6B, and a light receiving element 6C, and outputs a chopper signal when light passes through it.

The output signal of the pressure sensing element 9 is transmitted through the resistor R1, the switch element 15. Hold amplifier 16. A pressure signal hold circuit consisting of a capacitor C and a comparator 1 via a resistor R2.
Connected to 7.

The comparator 17 compares the pressure hold signal and the instantaneous value signal, and outputs a pressure drop signal when the instantaneous value is smaller.

The AND gate 18 ANDs the pressure reduction signal and the chopper signal, and when the output is "HII", it drives the switch element 11, connects it to the side opposite to that shown, and sets the voltage twice that of the flow rate setting device 10. It is added to the VF converter 12.

Next, cams 3A and 5Aρ will be explained. One rotation of the cam is 3
The first section of 173 rotations shown in the figure is designated as the first section, followed by the second section and the third section. Also, if the radius of the cam increases and the piston is in the discharge stroke as +9, the opposite as it is in the suction stroke as -, and the amount of change in volume per unit angle is Q, then the first section is the cam 3A 16Q
, cam 5A is +2Q, and in the second section, cam 3A is +IQ
.

Cam 5A is +IQ, cam 3A is +5Q in the third section,
Cam 5A is 13Q.

In the first section, the pump 3 suctions -6Q, and the damper 5 discharges +2Q, so the total discharge amount is +2
It is Q. In the second section, the pump 3 discharges +1Q, and the damper 5 also discharges +IQ, so the total discharge amount is +2Q.

In the third section, the pump 3 discharges +5Q, and the damper 5 suctions -3Q, so the total discharge amount is +2
It is Q.

FIG. 5 is a diagram showing the above-mentioned suction and discharge patterns. In FIG. 5, the first cycle of T-work shows a case where the load pressure is zero, the compressibility of the liquid is also zero, and the check valves 3D and 3E operate ideally. Fifth, Figures (a) and (b)
5 shows the suction and discharge patterns of the pump 3 and the damper 5, FIGS. 5(c) and 5(cl) show one combined discharge pattern, and FIG. shows.

Next, the decrease in pressure will be explained. In Figure 5,
The second period T2 is an explanatory diagram of pulsating flow. In reality, it is impossible for the load pressure to be zero and the compressibility of the liquid to be zero.

At the final end of the first section, the radius of the cam 3A becomes the minimum and the internal volume 3F of the cylinder 3C becomes the maximum.2 This state means that liquid at atmospheric pressure has been sucked in. Even if the cam 3A moves to a +IQ discharge stroke and presses the internal liquid 3F of the piston 3B, it is not immediately discharged. Liquid in internal volume 3F (hereinafter referred to as internal liquid 3F)
The internal liquid 3 is discharged against the discharge side check valve 3D.
This is after the pressure on F becomes the same as the pressure on the damper side. Therefore, when the pulse motor 14 rotates at a constant speed, no discharge occurs during the period Δt when compression is completed as shown in FIG. 5(a), and the discharge amount of only the damper 5 as shown in FIG. 5(c). It becomes like a pulsating stream.

Next, correction of pressure drop will be explained. ? In the section 52, the comparator 17 compares the pressure signal of the instantaneous value of the load with the hold signal that holds the pressure in the first section, and outputs a low pressure signal.

The AND gate 18 performs an AND with the chopper signal, and drives the switch element 11 if the AND is successful. When the switch element 11 is switched to the opposite side as shown, twice the voltage is applied to the VF converter 12. VF converter 12
Since twice the voltage is inputted to the motor, it outputs twice the frequency and the pulse motor 14 also rotates at twice the speed. In other words,
The second section rotates at double speed if there is a low pressure signal.

The discharge of the damper 5 in the second section is normally +IQ, but if the pulse motor 14 rotates at double speed, it becomes equivalent to +2Q. The double speed time is theoretically half of Δt. The double speed continues, the pressure becomes normal, and the low pressure signal becomes “L”
When it reaches 2x speed, it will stop running at double speed and return to normal rotation. Logically, this should also be as shown in FIG. 5(d).

However, in reality, the pulsating flow does not become zero as shown in FIG. 5(e) for the following reasons.

Moving from the first section to the second section, the pressure decreases.

This is detected as an electrical signal via the pressure sensing element 9, but a delay in the response of the pressure sensing cord 9 or a response due to the high compression rate of the liquid causes a delay in pressure detection. Therefore, the timing of shifting to 1x speed rotation is delayed. this is,
This is because the entire feedback loop is not electrically connected to the pressure sensing element 9. This is because mechanical parts such as liquid and the pulse motor 14 are present in the feedback loop.

In trace analysis, the performance of the pump may affect the performance of the analyzer. For example, in amino acid analysis,
For example, a pump that sends a liquid to a separation column and a coloring liquid that is mixed with an eluate from a separation column are sent using separate pumps. At this time, each pump has a pulsating flow,
Naturally, if the mixing ratio changes, the absorbance will also change. if,
If there is no pulsating flow in each pump and the mixing ratio is constant, y
In theory, detection sensitivity can be increased to the limit of a photometer.

However, in reality, due to the pulsating flow, the mixing ratio is not constant, so measurements are made in the low sensitivity range of the photometer.

In general, photometers used in liquid chromatographs have a photometric range that has increased from o, oozsAuFs (absorbance full scale) to 0.001AUFS, but in reality, photometers used in amino acid analyzers have a photometry range of 0.001AUFS. IAUFS
It is enough. This is because even if the sensitivity of the photometer is increased, the change in absorbance (noise) caused by changing the mixing ratio is too large and is meaningless.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology has the problem of slow response due to the presence of mechanical systems such as pressure sensing elements and pulse motors in the feedback loop, and the pulse motor does not rotate as expected, resulting in pulsating current. .

An object of the present invention is to provide a micro-liquid pump that can avoid delays in control.

[Means for solving problems]

The above purpose is that when the pump completes the suction stroke and moves on to the next discharge stroke, if the load pressure is known, it can be determined from the compressibility of the liquid how much volume will be compressed.
In addition, since the position where the pressure will decrease can be known in advance from the shape of the cam, when the pressure reaches the position where the pressure decreases, the correction is made by the theoretical amount of compression without waiting for the detection of the pressure decrease, and the theoretical correction is forced. If there is still a slight pressure drop even after doing so, at this point we enter control to eliminate the pressure drop using conventional pressure feedback control to achieve a completely pulseless liquid pump.

[Effect]

From the moment the piston enters the discharge stroke, the motor is forcibly rotated at double speed by an angle proportional to the pressure, and the liquid in the cylinder enters the compression stage, and even after the forced compression stroke has finished, the pressure has not yet fully returned. when.

Since double speed rotation is continued and compression is continued until the pressure is restored, pulsation can be eliminated by the OR output of the forced compression signal and the pressure drop signal.

〔Example〕

The present invention will be explained in detail below using the embodiments shown in FIGS. 1 to 3.

FIG. 1 is a principle diagram showing two embodiments of the micro-liquid pump of the present invention, and the same parts as in FIG. 4 are indicated by the same symbols.

In FIG. 1, chopper 6A' passes light before entering the second section, and the chopper signal is connected to AND gate 18 and one-shot circuit 19. The one-shot circuit 19 generates a negative pulse in response to the rise of the chopper signal. The S terminal of the flip-flop 20 is once “L”.
”, the output becomes “H” and remains at “H” until a negative pulse is input to the R terminal.

When one terminal of the AND gate 18' becomes "HII",
The pulse of the VF converter 12 is input to the clock terminal GK of the down counter 21. The down counter 21 has a preset digital value, and outputs a negative pulse when a preset number of clock pulses are input from the CK terminal. The negative output pulse of the down counter 21 clears the down counter 21 and the flip-flop 20
input to the R terminal of the flip-flop 2o, and the output of the flip-flop 2o
"L" and closes the AND gate 18'. At the same time, the input is input to the S terminal of the flip-flop 20', and the output of the flip-flop 20' is set to "H". This moment is the beginning of the second section.

On the other hand, the negative output pulse of the one-shot circuit 19 is A-
It also serves as an A-D conversion start signal for the D converter 22. A-
The D converter 22 converts the pressure signal of the first section into a digital quantity. The A-D converter 22 converts it into a binary number and holds the binary number until a primary A-D conversion start signal is input.

The output of flip-flop 20' is input to AND gate 18 and AND gate 18'. The output of the AND gate 18 becomes "H'", the switch element 11 is switched to the opposite side as shown in the figure, and the output frequency of the VF converter 12 is doubled. On the other hand, AND gate 18# is open,
The output pulse of the VF converter 12 is sent to the down counter 23
input to the clock terminal. The down counter 23 is A
The output of the -D converter 22 is preset, and when the preset number of clock pulses are input from the GK terminal, a negative pulse is output. The negative output pulse of the down counter 23 clears the down counter 23, is input to the R terminal of the flip-flop 20', and sets the output of the flip-flop 20' to xtL'' at the AND gate 18.
Close 18'. That is, while the output of the flip-flop 20' is "H", the pulse motor 14 rotates at double speed. The time it takes to rotate at double speed is Δ in Figure 5(d).
Corresponds to t/2.

Next, the amount of correction of Δt will be explained. In FIG. 5(C), the time Δt can also be converted into the number of pulses. The shortfall in the discharge amount corresponding to Δt is the same as the amount by which the liquid is compressed by pressure. The internal volume 3F in the cylinder 3C reaches its maximum at the end of the first section. If the volume of the internal volume 3F at this time is V, the pressure is P, and the compressibility of the liquid is k, the compression amount ΔV is.

Δv=vxkxp−(1). Therefore, by applying a volume change of ΔV with the piston 3B, the internal liquid 3F in the cylinder 3C reaches the pressure P.

In other words, the correction is completed.

The above volume change of ΔV can be converted into the number of pulses as follows. The number of pulses per revolution of the pulse motor 14 is N,
If the volume change of the piston 3B at this time is Vl, and the number of pulses corresponding to ΔV is n, then Vl is obtained, and from equation (2), V I V s is obtained. Equation (3) indicates that the number of correction pulses is proportional to the pressure. Therefore, the A-D converter 22 only needs to perform an A-D conversion such that when the pressure is p, the pressure becomes n.

The above is a forced correction without waiting for the pressure drop signal after entering the second period. therefore.

This is the same as eliminating the delay in the feedback loop, and can prevent pulsating flow.

FIG. 2 is a principle diagram corresponding to FIG. 1 showing another embodiment of the present invention, and the same parts are indicated by the same reference numerals. The first difference from FIG. 1 is that an ○R gate 24 is added.

The second section is corrected by ORing the low pressure signal and the compression signal. In other words, even if compression is forcibly corrected using the compression signal, if the low pressure signal is "IIH" due to differences in compressibility between eluents, etc., this indicates that the correction was insufficient.In this case, the OR signal Therefore, the double speed continues without delay, and when the pressure signal becomes "L", the double speed is stopped and the pulse motor 14 returns to normal rotation.

The second reason is that the preset of the down counter 21 is made variable.6Normally, the input side of the down counter 21 is preset so that the output signal is output at the end of the first period, but even with this, the output signal of the down counter 21 is Pulsating currents may occur for these reasons. In other words, if the viscosity of the solution is high, the check valve may open and close slowly. Moreover, if the specific gravity of the solution is large, it is equivalent to the movable valve (all) of the check valve becoming relatively lighter. In such a case, the response of the suction side check valve 3E will be slow even when the second section is entered and the discharge process is started, and the liquid in the cylinder 3C will be kept on the suction side until the suction side check valve 3E is completely closed. The check valve 3E prevents backflow through the electromagnetic valve 2. In such a case, by reducing the preset amount of the down counter 21, the valve operation can be started earlier than the normal cam position.

Another purpose is to facilitate the alignment of the cam 6A'.

It is very difficult to set the cam 6A' in an accurate position. The cam 6A' is connected to the shaft 3 as shown in FIG.
0 with screws 31. When adjusting the position of the cam 6A', loosen the screw 31, change the angle of the cam 6A', and tighten the screw 31 again. At this time, for example, cam 6A
' When trying to reset the clockwise direction, screw 31
, then turn the cam 6A' clockwise, but if you think you have turned it too much at this time, turn it back counterclockwise. In this case, there is a drawback that it becomes impossible to tell whether the rotation has turned clockwise or counterclockwise from the initial position. Of course, the angle is 20-30
You don't have to worry about that if you want to change the angle.For example, if one step or two steps of the pulse motor 14 is converted into an angle, it is an amount of 0.2' or 0.4°. By electrically setting this digitally using the down counter 23 and varying the angle from the chopper signal to the forced double speed, it is possible to digitally create advance or delay timing. This is an extremely easy adjustment method.

〔Effect of the invention〕

As explained above, according to the present invention, since the rotation of the pulse motor that drives the liquid pump is corrected by the OR operation of the forced compression signal and the low pressure signal, a constant flow rate that does not cause pulsation can be achieved. For example, it has the effect of enabling highly sensitive amino acid analysis.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram showing one embodiment of the micro-liquid pump of the present invention, FIG. 2 is a principle diagram corresponding to FIG. 1 showing another embodiment of the present invention, and FIG. 3 is the principle diagram shown in FIG. FIG. 2 is an explanatory diagram for explaining a method of fixing a cam of a chopper, FIG. 4 is a principle diagram of a conventional liquid feeding pump, and FIG. 5 is a diagram of suction and discharge patterns of the pump. 3... Pump, 5... Damper, 6... Chopper device, 9... Pressure detection element, 10... Flow rate setting device, 11° 15... Switch element, 12... VF converter , 13... pulse motor drive circuit, 14...
Pulse motor, 16...Hold amplifier, 17...
Comparator, 18.18', 18'...AND gate, 19...One-shot circuit, 20.20'.
...Flip-flop, 21.23...Down counter, 22...A-DizrEJ M'-11 axis-v/1-30-Axis 3/-'Vjiatsu4riJ $5 Figure (e)" ”=]] “rL σ

Claims (1)

[Claims] 1. A pump section consisting of a first piston, a first cylinder, and check valves respectively attached to the suction side and the discharge side of the first cylinder; , second
a damper section, the suction side of the second cylinder communicating with the discharge side check valve and the discharge side communicating with the pressure sensing element and the separation column, the first piston and the second piston. a driving section consisting of a first cam and a second cam connected to a pulse motor that reciprocates the pump; In a second section, the pump section and damper section perform a discharge stroke of the same amount, and in a third section, the pump section performs a discharge stroke and the damper section performs a suction step. characterized in that means is provided for forcibly driving the pulse motor at double speed from the beginning of the second section by an angle proportional to the pressure measured in the first section without receiving a pressure drop signal. Micro-liquid pump. 2. The angle proportional to the pressure is obtained by A-D converting the pressure signal in the first section, and counting this digital amount by giving a clock pulse to a down counter, and converting the time during this counting into the double speed section. 2. The micro-liquid pump according to claim 1, wherein the liquid is obtained by converting it into a signal. 3. The minute liquid transfer pump according to claim 1 or 2, wherein the clock pulse of the down counter is used as a pulse signal for rotating the pulse motor. 4. Compare the held value of the pressure signal in the first section with the instantaneous value of the pressure signal in the second section, and use the signal when the pressure has not reached it as a drop signal, and set the signal in the double speed section as a decrease signal. Claims 1, 2, or 3, wherein the pulse motor is driven at double speed in the second section using a signal that is a logical sum of the compression signal and the pressure signal.
The micro-liquid pump described in section. 5. Claims 1 or 2, wherein the timing of the compressed signal in the second section is output ahead or behind the theoretical value, and is digitally varied so that the correction start point can be varied. Or the micro-liquid pump according to item 3 or 4.