JPS6343591B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an improvement in a non-pulsation metering pump using a reciprocating plunger pump, and particularly to an improvement in a control mechanism for stabilizing the non-pulsation characteristic. It is something.

[Conventional technology]

Generally, in a single plunger type reciprocating pump, the discharge amount becomes zero during the suction stroke, so the discharge fluid generates large pulsations. In order to prevent such pulsation of the discharged fluid, two plungers with the same diameter are provided, and the phase of the reciprocating motion of each plunger is shifted by 1/2 cycle so that the total moving volume of each plunger is always constant. Pumps that control the flow rate have been proposed and implemented. This type of pump uses one or two cams with a special curve to operate so that the total moving volume of each plunger is always constant, as described above, and the combined discharge from the pumping operation of the two plungers is The amount can theoretically be made pulsating-free. That is, a specific example of this type of pulsationless reciprocating plunger pump is shown in FIG. The pump shown in FIG. 1 is a reciprocating pump configured to reciprocate two plungers 10, 10 by cam drive to obtain a composite discharge amount by the pump operation of each plunger. A single rotary cam 12 having a cam surface formed on one end surface of a cylindrical body is engaged with these plungers, and the combined discharge by the pumping action of each of the plungers is applied to the cam surface along the circumferential direction. It is constructed into a curved surface where the amount is always constant. In FIG. 1, reference numeral 14 is a crosshead for transmitting the displacement of the rotary cam 12 to the respective plungers 10, 10, and these crossheads 14, 14 have cam followers 16, 16, 14, 14, 14, 22, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 40, 40, 40, 40, 50, 40, 40, 50, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40 cam followers, respectively, crossheads 14, 14, and 14, respectively. 16, and springs 18, 18 are disposed surrounding the outer peripheries of the crossheads 14, 14 so that the cam followers 16, 16 are always in contact with the cam surfaces. Further, the rotating cam 12 has a rotating shaft 20 centered on the end surface opposite to the cam surface.
is fixed to form a cantilevered structure. Further, the plungers 10, 10 are provided with pump chambers 22, 22, respectively.
The discharge piping 2 is inserted through the gland seals 24, 24 and led out from each pump chamber 22, 22.
6 and 26 are configured to merge at a merging point A.

[Problem to be solved by the invention]

In this manner, the pump shown in FIG. 1 can obtain a pulsation-free characteristic as shown in FIG. 2a from a structural standpoint, and can make the combined discharge amount pulsation-free. However, in reality, it is difficult to completely avoid pulsations in the combined discharge amount for the following reasons.

The inflection point of the cam must be rounded during machining.

A change in the speed characteristics of the cam or plunger due to cam machining errors.

Accurately and precisely process or arrange the cam to shift the phase difference between the two plungers by 180 degrees.

Producing a small amount of backflow from the check valve connected to the pump piping system.

Each fluid handled by the pump has its own compressibility.

Air bubbles and particles may be included in the liquid being handled.

Conventionally, the following two methods have been proposed as means for correcting terms that vary relatively regularly due to the above reasons.

[] A method of compensating for the reduction in discharge amount due to compression or backflow of the handled liquid by designing a cam speed curve that increases the plunger speed only in a certain range at the beginning of the plunger discharge stroke.

[] A method of finding the average value of the discharge pressure of several strokes of the plunger and bringing the discharge pressure of subsequent strokes closer to that average value.

However, in the above method, since there is little compression or backflow of liquid in a region where the discharge pressure is relatively low, pulsation increases or the pulsation reduction effect due to correction decreases as the cam correction curve design pressure and operating pressure deviate. There are disadvantages such as a decrease in Further, in the above method, since the average pressure of several strokes is always determined and an attempt is made to maintain a discharge pressure close to this average pressure, there is a drawback that it cannot follow actual fluctuations in discharge pressure. Furthermore, both of the above methods cannot be used to quickly respond to pulsations that occur irregularly, and are ultimately dependent on the characteristics of the cam, which is unsatisfactory.

In order to overcome all the problems of the conventional non-pulsating metering pump mentioned above, the inventor of the present invention conducted various studies and made prototypes, and as a result, connected a drive motor to the cam that drives the two plungers, and connected the drive motor to the cam that drives the two plungers. A rotation speed control circuit is connected to the rotation speed control circuit, and a pressure detector is provided to detect the pressure of the combined discharge amount, and a pressure fluctuation signal detected by this pressure detector is supplied to the rotation speed control circuit as a correction signal. It has been found that by doing so, the above problems can be solved all at once.

Therefore, an object of the present invention is to provide a pulsation-free metering pump that has a simple configuration and can stably maintain pulsation-free metering performance.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a reciprocating pump configured to reciprocate two plungers by cam drive to obtain a composite discharge amount by the pumping operation of each plunger, in which the two plungers are driven. A drive motor is connected to the cam, and a rotation speed control circuit consisting of a rotation speed setting circuit, a main amplifier, and a tachogenerator that feeds back the output of the drive motor to the main amplifier is connected to the drive motor, and a composite discharge amount can be obtained. It consists of a pressure detector connected to the piping, a circuit that removes the DC component from the output signal of the pressure detector, and an amplifier circuit, and the signal obtained by the amplifier circuit is inverted and converted into a signal output from the rotation speed setting circuit. Additionally, a circuit for correcting the control signal of the rotation speed control circuit is provided.

In this case, it is most preferable to use a direct current motor with a mechanical time constant of 12 msec or less as the drive motor.

〔Example〕

Next, embodiments of the pulsationless metering pump according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 3 shows a control system diagram of the pump of the present invention, and reference numeral 30 indicates a reciprocating plunger pump having two plungers having the configuration shown in FIG. 1, for example. This plunger pump 30
A pressure detector 34 is provided in a part of the pipe 32 where the discharge pipes led out from the two pump chambers join together, and the signal detected by the pressure detector 34 is sent to a DC component removal circuit 36 and an amplification circuit 38. The configuration is configured to detect fluctuations in discharge pressure via the discharge pressure. On the other hand, a drive motor 40 is provided to drive the rotating cam of the plunger pump 30, and the rotational output of the drive motor 40 is appropriately transmitted to the cam rotating shaft via a speed reducer 42. And the drive motor 40
is configured to perform rotation speed control via a main amplifier 46 while correcting the rotation speed preset by a rotation speed setting circuit 44 based on a signal obtained from the pressure detector 34. A tachometer generator 48 is connected to the drive motor 40 and its output is fed back to the main amplifier 46.

Next, the operation of the pump of the present invention constructed as described above will be explained together with the operating characteristics shown in FIG.

First, when some pulsation occurs in the operating characteristics of the plunger pump 30, the pressure detector 34 obtains an output signal as shown in FIG. 4a, for example. In this case, the problem with the obtained output signal is not its absolute value but only the fluctuation component, that is, the ripple component. Therefore, if the DC component is removed by the DC component removal circuit 36 and appropriately amplified by the amplifier circuit 38, as shown in FIG. A characteristic curve as shown in b is obtained. The signals obtained in this way are reversed in phase [see Figure 4c], and
If the signal is supplied to the main amplifier 46 in addition to the signal from the rotation speed setting circuit 44, the output of the main amplifier 46 becomes as shown in FIG. The rotation speed of the drive motor 40 can be reduced, and the rotation speed of the drive motor 40 can be increased when the pressure detected by the pressure detector 34 has decreased. In this way, according to the present invention, the discharge pressure can be detected and the rotational speed of the pump drive motor can be controlled by negative feedback, thereby making it possible to extremely minimize fluctuations in the pump discharge pressure.

In order to drive and control the pump of the present invention most effectively, it is necessary to minimize the inertia of each mechanical part, and the response characteristics of the drive motor 40 are particularly important. For this reason, as a result of various experiments, we found that by using a DC motor with a mechanical time constant of 12 msec or less for the drive motor alone, pulsation can be easily reduced to less than a fraction of that of a method that relies only on cam characteristics. We confirmed that it can be made smaller. Therefore, it has been found that when using a motor with a mechanical time constant of 15 msec or more, it is difficult to perform sufficient follow-up control to fluctuations in discharge pressure, and pulse reduction cannot be expected.

〔Effect of the invention〕

As is clear from the embodiments described above, according to the pump of the present invention, the pulsation of the fluid discharged from the pump is corrected and controlled by electrical means. This has the excellent advantage that the magnitude of the pulsation can be arbitrarily adjusted within a predetermined range, as shown in FIG. 2c, for example, without replacing the cam.

Therefore, the pump of the present invention can be effectively applied to the reciprocating plunger pump having the configuration shown in FIG. 1, but it can of course also be widely applied to various other non-pulsation metering pump configurations. It is.

Although the preferred embodiments of the present invention have been described above, it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of the pump structure of a pulsation-free metering pump, FIGS. 2 a to c are pulsation-free characteristic curve diagrams of the pump shown in FIG. 1, and FIG. 3 is a pulsation-free metering pump according to the present invention. System diagram of the control system, Figure 4 a to d
is an operating characteristic diagram of the control system of the pump shown in FIG. 3; DESCRIPTION OF SYMBOLS 10...Plunger, 12...Rotating cam, 14...Crosshead, 16...Cam follower, 18...Spring, 20...Camshaft, 22...Pump chamber, 24...Gland seal, 26...Discharge piping, 30...Reciprocating plunger pump, 32 ...merging pipe, 34...pressure detector, 36...DC component removal circuit, 38...amplifier circuit, 40...drive motor, 42...reducer, 44...rotation speed setting circuit, 46...main amplifier, 48...tachogenerator.

Claims (1)

[Scope of Claims] 1. A reciprocating pump configured to reciprocate two plungers by cam drive to obtain a combined discharge amount by the pumping operation of each plunger,
A drive motor is connected to the cam that drives the main plunger, and a rotation speed control circuit consisting of a rotation speed setting circuit, a main amplifier, and a tachometer generator that feeds back the output of the drive motor to the main amplifier is connected to this drive motor, and further synthesis is performed. It consists of a pressure detector connected to piping from which the discharge amount can be obtained, a circuit that removes the DC component from the output signal of the pressure detector, and an amplifier circuit, and the signal obtained by the amplifier circuit is inverted and output from the rotation speed setting circuit. A non-pulsating metering pump characterized by being provided with a circuit for correcting a control signal of a rotation speed control circuit in addition to an output signal. 2 The drive motor has a mechanical time constant of the motor alone.
A pulsation-free metering pump according to claim 1, which comprises a DC motor of 12 msec or less.