CA1181509A

CA1181509A - Pulsation-free volumetric pump

Info

Publication number: CA1181509A
Application number: CA000387924A
Authority: CA
Inventors: Takashi Akiba
Original assignee: Nikkiso Co Ltd
Current assignee: Nikkiso Co Ltd
Priority date: 1980-10-18
Filing date: 1981-10-14
Publication date: 1985-01-22
Also published as: JPS6343591B2; EP0050296A1; DE3170869D1; JPS5770975A; MX154463A; EP0050296B1

Abstract

ABSTRACT OF THE DISCLOSURE

An improved pulsation-free reciprocating volumetric pump is disclosed, which comprises two reciprocating plungers, a cam for driving said plungers, a driving motor connected to said cam, a circuit connected to said driving motor for cont-rolling rotational rate, and another circuit for detecting a pressure of combined volume discharged by the two plungers and for correcting a control signal of said rotation controlling circuit through the detected signal.

Description

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FIELD OF l'~lE INVENTION
This invention relates to an improvement in a pulsation-free volumetric pump utiliz~ng a reciprocating plunger-type pump, and more particularly, to an improvemen~ in a controlling mechanism for stabilizing the pulsation-free property of the pump.
BACKGROU~ OF TH~ IN~NTION
In. general, the reciprocating pump of single plunger type generates a greater pulsation of discharged fluid because of its discharge volume of zero upon suction stroke. In order to avoid such pulsation o-f the discharged ~luid, a pump for controlling the total discharge volume to a constant volume has been proposed, in which two plungers of the same diameter are arranged in such a manner that the reciprocating phase of each plunger is shifted by 1/2 cycle from each other. In such type of the pump, one or two cams having a special curved face are used for providing a constant total volume discharged by the plungers, as described hereinbefore, whereby the combined volume discharged by pumping action of the two plungers may be theoretically free of pulsation.
BRIEF DES~IPTI.ON'OF THE DRAWINGS
-Figure 1 is a schematic illustration showing one embodiment of the pump structure in the pulsation-free volumetric pump accord-ing to the invention, Figures 2(a) to ~c) show pulsation-free characteristic curves obtained by the pump of Fi.gu.re 1, Figure 3 is a diagram showing a controlling system for the pulsation-free volumetric pump according to the invention, Figures ~(a) to ~c) show working characteristic curves obtained by the controlling system of Figure 3.
An embodiment of the type of the puIsation-free reciproca-ting plun:ger pump is illustra:ted in Fi'gure 1, wherein the two plungers ~ , ~, - 2a ~

0, 10 are reciprocated by means of the cam driving for providing a combined volume discharged through pumping action of these plungers.
The pair of plungers 10, 10 are arranged in parallelg with which is engaged a single rotary cam 12 having a cam sur~ace at its one end. The cam surface is machined so as to provide a curved surface for keeplng the constant combined volume discharged by the pumping action of the two plungers, which move along the periphery of the cam surface. In Figure 1, each cross-head 14, 14 for transmitting a displacement of the rotary cam 12 to each plunger 10, 10 is provided with each of cam followers 16, 16 which is pressed against the cam surface by each spring 18, 18 arranged around the cross-head 14, lll. Further, the rotary cam 12 is provided at its center of opposite surface with a rotary shaft 20 to form a cantilever structure. The plungers 10, 10 are inserted through g~and seals 24, 24 into respective pump chambers 22, 22, from which are derived discharge pipings 26, 26 which in turn are ~oined together at a point A.
Thus, the pump as illustrated in Fig.l may obtain, from its constructional view points, the pulsation-free property as shawn in Fig.2 (a) and provide the pulsation-free combined dis-charge volume. However, it is difficult to completely avoid the pulsation of the combined discharge volume due to the following factors:
(1) A rounded portion must be provided at an inflexion point of the cam upon machining.
(2) Velocity characteristics of the cam or the plunger can be varied due to the machining error of the cam.

(3) Accurate and strick machining and arrangement of the cam must be effected for shifting the phase of two plungers in 180 from each other.
(~) A slight back-flow occurs through a check valve connected to a line leading to the pump.
(5) A pumping liquid has its intrlnsic compression.
(6) A pumping liquid contains air bubbles and particles.

As a measure for correcting the ~actors (4) and (5) listed hereinabove, which vary rather regularly, the following two methods have been proposed:
[I] A method in which a velocity curve of cam is designed so as to increase a velocity of plunger only in a given range of a beginning delivery stroke of the plunger, thereby to correct the reduction of discharge volume due to the compression of liquid and the back-flow through the valve.
~II] A method in which discharging pressures are determined for several strokes of the plunger to obtain an average valve, to which is approached a discharging pressure of subsequent stroke.

However, the former method has such the disadvantages that the pulsation nevertheless increases in a zone having a relative low discharging pressure because of less compression or less back-flow of the liquid~ and that the effect of reducing the pulsation through correction decreases as the pressure applied by a corrected curve of the ca~ is deviated from the pressure actually employed. On the other hand, the latter method has such 5 ~ L5~

the disadvantage that the average discharging pressure determined for the several strokes ~an not be followed up by the variation in the actual discharging pressure. Furthermore, the methods I
and II have a common disadvantage in that an irregular pulsation incapable of being responded appears so that the variation in the actual discharge volume depends largely on the cam characte-ristics.
Now it has been found out that the problems and dis-advantages described hereinbefore may be solved all at once by the arrangement in that a cam for driving two plungers is connected to a driving motor, to which is in turn connected a rotation cont-rolling circuit, while a pressure detector is provided f'or detecting a pressure of combined discharge volume and that a variable pressure signal in the pressure detector is fed to the rotation controlling circuit as a corrected signal.

SUMMARY OF THE INVENTION

Accordingly, a general ob~ect of the invention is to provide a pulsation-free volumetric pump which is simple in construction and may allow the stable and pulsation-free volumetric pumping.
A principal ob~ect of the invention is to provide a pul-sat,ion-free reciprocating volumetric pump in which two plungers are reciprocated by means o~ cam driving so as to provide a com-blned discharge volume through pumping action of the plungers, which is characteri~ed in that the volumetrie pump comprises t~10 plungers, a cam for driving said plungers, a driving motor connected to said cam, a eircuit connected to said driving motor for eontrolling a rotational rate, and another circuit for detecting a pressure of said combined discharge volume and for correcting a control signal of said rotation eontrolling cireuit through the detected signal.

PREFERRED ~MBODIMENT OF THE INVENTION

In a preferred embodiment of the invention, the eircuit for controlling the rotational rate may prefera~ly eomprises a circuit for setting the rotational rate, a main amplifler and a tachogenerator for feeding baek an output of the driving motor to the main amplifier.
In a further preferred embodiment of the invention, the eireuit for eorreeting the eontrol signal of the rotation eont-rolling eireuit may eomprises a pressure deteetor eonneeted to a piping whieh provides the eombined diseharge volume through pumping aetion of the two plungers, a eireuit for eliminating a direet eurrent (DC) portion from an output signal of the pressure deteetor, and an amplifying eireuit wherein a signal from the amplifying eireuit being eonverted to a reverse phase and added to a signal from the rotation setting eireuit for eorreetion.

Most preferably~ the driving motor eomprises a DC motor having a meehanieal time eonstant below 12 msee.

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Now the invention will be described in more detail herein--after with reference to the drawings which illustra:te the preferable embodiments.
DETAILED DESCRIPTION OF THE EMBODIMENT
Figure 3 illustrates a diagram of a controlling system for the pump according to the inventiong wherein the reference 30 shows a reciprocating plunger-type pump having two plungers as shown~ for example, in Figure 1. From two pumping chambers of the plunger-type pump 30 are derived respective discharge pipints which are joined together to form a piping 32, to which is connected a pressure detector 34. A signal generated from the pressure detector 34 is fed back through ~ circuit 36 for eliminating a DC

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component and an ~mplifying circuit 38 in order to control variation in a discharging pressure. On the other hand, there is provided a driving motor 40 for driving a rotary cam of the plunger-type pump 30, an output of which motor 40 is transmitted to the rotary cam shaft optionally through a convenient gear 4 2 .
The driving motor 40 is controlled for its rotational rate through a main amplifier 4~, while the rotational rate provided by the rotation setting circuit 44 is corrected by the signal from the pressure detector 34. Further, to the driving motor 40 is connected a tachogenerator 48, an output of which is fed back to the main amplifier 46.
The working of the pump according to the invention will be described hereinbelow with reference to the working characte-ristics, as shown in Figure 4.
When a somewhat pulsation appears in the ~orking characte-ristics of the plunger-type pump 30, an output signal as shown in Fig. 4(a) is obtained in the pressure detector 34. In this case, the resulting output signal is freed from a DC component by a circuit 36 for eliminating the latter, because only a variable or ripple portion is to be treated, but not an absolute value.
Then the signal after elimination of the DC component is amplified by the amplifying circuit 38 to give a characteristic curve, as shown in Fig. 4(b). The signal thus obtained is converted to a reverse phase, as shown in Fig. 4(c) and added to a signal from the rotation setting circuit 44, thereafter fed to the main amplifier 46 for obtaining an output, as shown in Fig. 4(d). Thus, lf the pressure detected by the detector 34 increases, then the rotational - 9~

rate of the driving motor 40 may be decreased. On the contrary, if the pressure detected by the detector 34 decreases~ then the rotational rate of the driving motor 40 may be increased. In this way, in accordance with the invention, the variation in the dis~
charging pressure of the pump may be kept extremely low through detection of the discharging pressure and thereby negative feed-back control of the rotational rate of the driving motor.
In order to control the pump according to the invention most effectively, the inertia of each component should be ~ept as low as possible, and especially a response characteristic of the driving motor 40 is most important. For this purpose, various experiments have been carried out to find out that the pulsation may be readily reduced to much lower level, for example one fifth or lower, in comparison with the conventional system only based on the cam property, by use of a DC motor having a mechanical time constant below 12 msec. When the mechanical time constant is higher than 15 msec., it has been found out that the variation of the discharging pressure is difficult to be sufficiently followed up and controlled, so that the reduction of pulsat~on could not be expected.
It will be appreciated from the embodiment described hereinbefore that the pump according to the invention has such the advantages that the pulsation of the discharged fluid from the pump may be corrected and controlled by means of the electrical means, thereby allowing the electrical correction of the ripple in the discharging pressure without replacing the cam, and that the magnitude of pulsation may be suitably controlled within the desired range, as shown in Fig. 2(c).

Although the invention has been described hereinabove with the reciprocating plunger-type pump as shown in Fig. 1, it will be appreciated that the invention may be applied widely and effectively to many other types of pulsation free volumetric pumps.
The foregoing is descriptive of an embodiment of the pulsation-free volumetric pump, and rnany changes and modifications may be made without departing from the scope and spiri.t of the invention.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A pulsation-free reciprocating volumetric pump compri-sing a pump housing having two plungers providing a combined discharge volume, a cam for driving said plungers, a direct current driving motor connected to said cam, a rotation setting means operatively connected to said driving motor for supplying thereto a predetermined direct current voltage for driving the motor at a predetermined rota-tional rate, a main amplifier operatively connected to said rotation setting means for supply thereto as a first input the direct current voltage from the rotation setting means, said main amplifier having an output supplied to said drive motor, a tachogenerator operatively connected to said drive motor for drive thereby and supplying its output voltage as a second input to said main amplifier, and means for compensating for pressure pulsations produced during pumping, said last-named means comprising a pressure detector for detecting the pressure of said combined discharge volume and providing an out-put signal having a direct current component and an alternating current component representative of said pressure pulsations, means eliminating the direct current component of the pressure detector output signal and passing only the alternating current component, an amplifier circuit for amplifying the alternating current component, and adding means supplied with the direct current voltage from the rotation setting means and with the amplified alternating current component from the amplifier circuit for adding said alternating current component, after phase reversal, to the direct current voltage from the rotation setting means for modifying said first input voltage to said main amplifier in a sense to modify the rotation rate of the drive motor to compensate for said pressure pulsations.