JP2585615B2 - Control method of pulseless pump - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling a pulsation-free pump, and more particularly to a method of controlling a pulsation-free pump in which pressure pulsation is suppressed by performing phase control of a piston. .

[Conventional technology]

In general, as a pump device used for a liquid chromatography / medical test device or the like, a pump device having small pressure pulsation and capable of continuously discharging a high-pressure liquid is desirable.

As such a pump device, a double reciprocating pump has been conventionally known. This double reciprocating pump has two pumps connected in series (the suction side is referred to as a first pump and the discharge side is referred to as a second pump), and a check valve is provided before and after the second pump. By separately reciprocating the first piston and the second piston respectively provided in the first pump and the second pump by the two motors, the respective pumps alternately repeat the suction stroke and the discharge stroke. Is to be obtained. The first piston and the second piston are connected to a motor via a cam mechanism or a ball screw mechanism, and when the motor rotates, both pistons reciprocate.

The speed command patterns of the first piston and the second piston are set as shown in FIG. 5 (a) when a cam mechanism is used, and are shown in FIG. 5 (b) when a ball screw mechanism is used. ). As shown in the figures, when the effect of the check valve is considered, the sum of the speeds of the first piston and the second piston is always constant, and in principle, pulsation does not occur in the composite discharge pressure. .

However, in order to continuously discharge a high-pressure fluid, the movement direction and speed of both plungers must be periodically switched. At this time, the response of the check valve is delayed, the drive system rattles, and the pressure changes from low to high. There is a drawback that pressure is reduced and a pressure ripple is likely to occur due to a shift in timing for compression or the like.

Therefore, as a method for suppressing the occurrence of pressure pulsation such as pressure ripple, the following two methods have been proposed by JP-A-61-178582. One of them is to detect the combined discharge pressure at the time of switching the piston speed, and if the fluctuation of the detection signal is to the right, the moving distance of the first piston on the first pump side is appropriately increased. Is transmitted from the control device to the motor so as to appropriately reduce. The other is that the flow rate to the first pump is slightly increased in advance, and a constant pressure release valve for releasing the excess is provided on a pipe connecting the first pump and the second pump. In this method, the operating pressure is controlled by a control device.

[Problems to be solved by the invention]

However, in the method of controlling the moving distance of the piston based on the inclination of the detection signal, there is no index for setting an appropriate moving distance, so the setting must be performed through trial and error many times, and it takes time until the setting is performed. There was a problem that was too long.

Further, in the method of providing the constant-pressure relief valve, when reducing the flow rate, it is necessary to use a highly accurate relief valve, and there is a problem that the relief valve becomes very expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of controlling a non-pulsation pump in which a state in which pressure pulsation is small can be set in a short time without providing a relief valve.

[Means for Solving the Problems] In order to achieve the above object, a method of controlling a non-pulsation pump according to the present invention comprises connecting two piston reciprocating pumps in series, and The method of controlling a non-pulsation pump in which one pump is set to a suction stroke and the other pump is set to a discharge stroke so as to control a combined discharge pressure of both pumps to be constant by switching the speeds to be opposite to each other. The pressure is detected, the peak time of the pressure pulsation is obtained from the detection signal, and the time from the start of switching the piston speed to the peak time is measured by a timer in a microcomputer. To calculate the correction time, and based on the piston speed switching time for the transition from the suction stroke to the discharge stroke, An operation of delaying the switching of the piston speed for shifting to the in-stroke by the correction time when the combined discharge pressure is decreasing, and advancing by the correction time when the combined discharge pressure is increasing. In order to reduce pressure pulsation.

[Action]

Where the pressure is reduced due to the delay in the response of the check valve, the play in the drive system, or the shift in the timing for compressing from low pressure to high pressure, the pressure drop is equivalent to that caused by the piston being stopped. . For example, in a speed command pattern of a ball screw mechanism as shown in FIG.
When the second piston shifts from the discharge stroke to the suction stroke, that is, when the first piston shifts from the suction stroke to the discharge stroke, the time required to compress from low pressure to high pressure and the reverse rotation of the motor cause backlash. Since the time required for absorption is required, the first piston can be regarded as having stopped at this time.

Therefore, for the speed change of the first piston,
If the speed switching timing of the second piston is slightly delayed, the sum of the actual piston speeds becomes constant,
Pressure drop can be prevented. From the experimental results, it has been confirmed that the pressure fluctuation at the time of switching the piston speed can be reduced by performing the phase control on the speed command pattern as shown in FIG. 6 (a) as shown in FIG. 6 (b). .

The algorithm for determining the phase difference is as follows. As shown in FIG. 7 (a), when the pressure decreases,
Until the pressure starts to decrease and starts to increase again, it indicates that the sum of the actual piston speeds has decreased due to the response delay of the check valve, mechanical backlash, etc. This indicates that the sum of the piston speeds has returned to the set value. Also, as shown in FIG. 7 (b),
When the pressure increases, the sum of the piston speeds indicates that the sum of the piston speeds is excessive until the pressure starts to increase and then starts decreasing again, and when the pressure decreases again, the sum of the piston speeds has returned to the set value. Is shown. Therefore, the times from the start of the switching of the piston speed to the peak position of the pressure are respectively set to t ₁ and t ₂ as shown in FIGS. 7 (a) and 7 (b), and these are measured using a timer in the microcomputer. Initially the pressure is falling, so that time t ₁
Is added as a phase difference. That is, in the case of FIG. 7 (a), the current transition switching time of the controlled piston (second piston) is set to 0, and the switching of the backlashed piston (first piston) and the pulsation occur. peak point time difference between the (pressure drop) and t _1. The first correction amount
At ₁ , the transition switching time of the controlled side is delayed by at ₁ . As a result, if the time difference between the switching of the second piston and the pulsation peak point (pressure drop) becomes t ', the correction amount becomes at', and the current switching switching of the second piston changes from 0 to a (t ₁ + t '). This control is repeated until the pressure pulsation disappears.

On the other hand, in the case of FIG. 7 (b), the state is in the excessive control state, and the pressure pulsation is increasing. The piston on the controlled side (second
The time current migration switching piston) and 0 to the switching time of the pulse peak point of a backlash of the side piston (first piston) time difference between the (pressure increase) and t _2.
Assuming that the first correction amount is at ₂ , the shift switching time of the controlled side is advanced by at ₂ . As a result, if the time difference between the switching of the second piston and the pulsation peak point (pressure rise) becomes t ″, the correction amount becomes at ″, and the current switching switching of the second piston changes from 0 to −a ( t ₂ + t ″).
This control is repeated until the pressure pulsation disappears.

In this manner, the phase is shifted while detecting the pressure fluctuation, and the feedback is applied so that the time of switching the transition of the second piston is appropriate.

By doing so, appropriate phase correction can be performed for the pressure pulsation.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a control circuit diagram showing an example of the present invention.
FIGS. 2 and 3 are detailed views of the double reciprocating pumps 30, 31 to which the present invention is applied, and show a cam mechanism and a ball screw mechanism. In FIG. 2, cams 2, 2 arranged on the same axis as the pulse motors 1, 1 are connected by belts 3, 3, respectively. Cam followers 4, 5 are in contact with the cams 2, 2, and the cam followers 4, 5 are fixed to the first piston 6 and the second piston 7, respectively. A spring 8 is provided on the first piston 6 and a spring 9 is provided on the second piston 7, and the cam followers 4, 5 are biased by the springs 8, 9 in a direction approaching the cams 2, 2. A first plunger 10 and a second plunger 11 made of a material having wear resistance and chemical resistance (for example, ruby) are attached to the tips of the first and second pistons 6 and 7,
The first and second plungers 10 and 11 are reciprocally inserted into pump chambers 13 and 14 formed in the cylinder bed 12. 1
Reference numerals 5 and 16 denote seals for sealing the pump chambers 13 and 14, and reference numerals 17 and 18 denote check valves arranged before and after the first piston 6.

The cam surfaces of the cams 2, 2 are formed so that the sum of the combined speeds of the first plunger 10 and the second plunger 11 is constant as shown in FIG. Also, the first plunger 10 moves at twice the speed of the second plunger 11,
The first pump discharges the liquid to the second pump while making up for the liquid. When the first pump is in the suction stroke, the check valve operates so that the liquid can be sent only by the second pump.

FIG. 3 shows a double-unit system in which ball screws 20, 20 are provided in place of the cams 2, 2, and the rotary motion of the pulse motor 1, 1 is converted into a linear reciprocating motion by the ball screws 20, 20. The other configuration is the same as that of the above-described double reciprocating pump 30. In the figure, 21 and 21 are planetary gear reducers, and 22 and 22 are ball screws 20, 20 and planetary gear reducers 21 and 21.
This is a thrust bearing that supports. Note that ball screws 20, 2
0 indicates that the first and second plungers 10, 11 are in FIG. 5 (b).
, And the synthesis speed is constant.

A method for suppressing the pressure pulsation when the above-described double reciprocating pump 31 is used will be described with reference to FIG.
As shown in the figure, a flow setting device (or an external flow controller) 32 is connected to a microcomputer 34 via a code conversion circuit 33. Start / stop button
35 is a microcomputer 34 via a pulse generation circuit 36
It is connected to the. On the other hand, the microcomputer 34 is connected to the pulse motors 1, 1 of the double reciprocating pump 31 via a pulse motor driver 37. A liquid chromatography or the like (not shown) is connected to the discharge side of the double reciprocating pump 31, and a pressure sensor 38 is provided on the way. The pressure sensor 38 is connected to the microcomputer 34 via the A / D converter 39.

 Next, the operation of this embodiment will be described.

First, the flow rate setting signal set by the flow rate setting device 32 is converted from a binary-coded decimal code to a binary code by a code conversion circuit 33, and then input to the microcomputer. When a start signal is input from the start / stop button to the microcomputer 34 via the pulse generating circuit 36, the microcomputer 34 calculates a pulse motor driving frequency and the like, and outputs the pulse motor driver 37 to the pulse motor driver 37 from its output port. A pulse train for generating the plunger speed drive pattern shown in (b), a signal for determining the rotation direction, a current control signal, and the like are output. These signals are distributed by the pulse motor driver 37 to drive the two pulse motors 1,1. When the pulse motors 1, 1 rotate, the planetary gear reducers 21,
21, the thrust bearings 22, 22, the ball screw 20,
Rotational motion is converted to linear reciprocating motion via a drive transmission system consisting of 20 and plungers 10 and 11 are reciprocated to transfer the liquid in the manner described with reference to FIG. 5 (b). Discharge at high pressure. In this case, the previously described check valve
In addition to the response delay of 17,18, pulsation occurs due to a shift in timing due to, for example, a difference in the bulk elastic modulus when the liquid is changed from low pressure to high pressure depending on the liquid used. The pressure sensor 38 detects the line pressure and the pressure fluctuation, and the detection signal is converted into a digital signal by the A / D converter 39 through an amplifier (not shown) and a filter for removing noise and enters the microcomputer 34. .

This signal is processed by the microcomputer 34, and the time until the peak value of the pressure change is measured by a timer in the computer with reference to the piston speed switching time for shifting from the suction stroke to the discharge stroke. The phase of the piston speed switching time for shifting from the discharge stroke to the suction stroke is corrected by the algorithm described above. This makes it possible to correct the plunger speed with an appropriate phase.

The flowchart of the phase control in the present embodiment is as shown in FIG.

In this embodiment, the case where the pulse motors 1, 1 are used as the driving sources of the first plunger 10 and the second plunger 11 has been described. However, instead of the pulse motors 1, 1, shown in FIG. Such linear motors 1A, 1A may be used. The use of linear motors 1A, 1A eliminates the need for a device such as a cam mechanism or a ball screw mechanism that converts rotary motion into linear motion, and reduces mechanical backlash, which is effective in suppressing pressure pulsation. is there.

〔The invention's effect〕

As described above, according to the present invention, since the piston speed can be corrected with the optimum phase difference, the pressure pulsation can be extremely reduced.

[Brief description of the drawings]

FIG. 1 is a control circuit system diagram of one embodiment of the present invention, FIG. 2 is a sectional view of a main part of a double reciprocating pump using a cam mechanism, and FIG.
The figure is a cross-sectional view of the main part of a double reciprocating pump using a ball screw mechanism, FIG. 4 is a cross-sectional view of the main part of a double reciprocating pump using a linear motor as a drive source, and FIG. 5 is a basic piston. FIG. 6 is an explanatory diagram showing the effect of the phase control, FIG. 7 is an explanatory diagram showing the behavior of pressure pulsation, FIG.
The figure is a flowchart showing the phase control method. 1 ... Pulse motor, 1A ... Linear motor, 2 ... Cam, 3 ... Belt, 6,7 ... First and second pistons, 10,11
…… First and second plungers, 12 …… Cylinder head, 1
5,16 …… Seal, 17,18 …… Check valve, 20 …… Ball screw, 21… Planetary gear reducer, 30,31 …… Dual reciprocating pump, 32 …… Flow setting device, 33… … Code conversion circuit, 34 ……
Microcomputer, 35 start / stop button, 36 pulse generator circuit, 37 pulse motor driver, 38 pressure sensor, 39 A / D converter.

Claims (1)

(57) [Claims] 1. Two pumps of a piston reciprocating type are connected in series, and the piston speeds of the two pumps are switched to be opposite to each other so that when one pump is in a suction stroke, the other pump is in a discharge stroke. In the control method of the non-pulsation pump for controlling the combined discharge pressure of both the pumps to be constant, the combined discharge pressure is detected, a peak time of the pressure pulsation is obtained from the detection signal, and the switching of the piston speed is started. The time until the peak point is measured by a timer in the microcomputer, the measured time is multiplied by a constant specific to the pump to calculate a correction time, and the piston speed switching time for shifting from the suction stroke to the discharge stroke is calculated. As a reference, when the piston speed is switched from the discharge stroke to the suction stroke, when the combined discharge pressure is low, A method of controlling a non-pulsation pump, wherein the pressure pulsation is reduced by delaying the correction discharge time and, when the combined discharge pressure is increasing, sequentially performing an operation of advancing the correction discharge time.