JPH0141220B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pump used in liquid chromatography and the like.

Liquid chromatography requires a pump device to deliver precisely metered amounts of solvent.
In the pump device, it is necessary to accurately control the flow rate of the solvent regardless of the load pressure. Liquid chromatography, especially devices that perform gradient elution analysis, require a high degree of accuracy even at extremely low flow rates. For example, microbore chromatography requires a flow rate resolution of about 1 μl/min.

In most conventional pump devices, the compressibility of the fluid and the mechanical compliance of the pump are interrelated, resulting in a significant drop in flow rate as the load pressure increases. This phenomenon is generally called roll-off. A two-pump system uses a high-pressure slave pump and a low-pressure metering pump, and compensates for roll-off by injecting a controlled amount of solvent from the low-pressure metering pump to the high-pressure slave pump. The metering pump is synchronized with the slave pump such that at low pressure during the slave pump's operating cycle, the metering pump pumps a regulated amount of liquid. Roll-off does not affect the accuracy of the metering pump since it always operates under low pressure loads (see US Pat. No. 4,003,679).

The patent also describes an apparatus for mechanically coupling a metering pump and slave pump pair to circulate at the same fixed rate. The flow rate is controlled by mechanically adjusting the displacement of the metering pump. However, due to the mechanical compliance and fluid compliance of the metering pump,
Each cycle of the metering pump introduces some error. This error tends to increase with increasing speed of the metering pump cycle. As the displacement of the metering pump becomes smaller, the error flow rate included in the amount of fluid pumped due to the above-mentioned errors and errors inherent in metering becomes a large proportion. Said error is reproduced every cycle of the metering pump and slave pump pair. Therefore, the accuracy of the flow rate is extremely low, especially at low flow rates, and the range of flow rates that a given metering pump can deliver is limited.

Furthermore, in a pump that adjusts the flow rate by adjusting the amount of water discharged, there is a problem that self-starting is difficult when the flow rate is small. This is because a pump with a large displacement is more likely to self-start than a pump with a small displacement.

The pump of the present invention is designed to eliminate the roll-off problem associated with the pump system described in the aforementioned US patent.

Additionally, more precise operation is achieved by using a servo-driven syringe-type liquid metering pump to deliver the diaphragm-dependent pumping solvent. The cylinder capacity of the syringe-type metering pump is designed to be several times the cylinder capacity of the slave pump, and the slave pump circulates several times during one cycle of the metering pump. The tolerance of syringe-type metering pumps is extremely low compared to the volume of solvent pumped in a single metering pump cycle. Since this metering pump is driven by a servo motor at a much lower cycle speed than the slave pumps, small errors occurring in the metering pump are distributed over a large number of slave pump cycles. The accuracy of the flow rate is therefore independent of the amount of fluid pumped.
In this way, the pump device of the present invention can control extremely low flow rates of the order of 1 μl/min. The servo motor may be synchronized to drive the metering pump only during the low pressure of the slave pump cycle. Also, a compliance may be inserted between the metering pump and the slave pump so that the metering pump operates independently from the slave pump. By using the metering pump and slave pump pair as described above, the flow rate can be accurately controlled over a relatively wide range.
Also, self-starting capability is improved.

The present invention will be explained in detail below using one embodiment.

FIG. 1 shows an embodiment of a pump according to the present invention.

In FIG. 1, a servo motor 10 drives a pair of syringe-type metering pumps 12 and 14 that are connected in a push-pull manner. Metering pump 1
The piston 30 of No. 2 is raised and lowered relative to the cylinder 32 by the engagement of the lead screw 34 with the inner threaded portion of the piston carrier 36. Similarly, the piston 38 of the metering pump 14 is raised and lowered within the cylinder 40 by the engagement of the lead screw 42 with the inner threaded portion of the piston carrier 44 . pumps 12 and 14
always move equally in opposite directions in a push-pull manner. This means that the gear 18 attached to the lead screw 34 of the pump 12 drives the gear 20 attached to the lead screw 42 of the pump 14, and the gear 18 and gear 20, the lead screw 34 and the internal thread of the piston carrier 36, This is because the screw 42 and the internal screw of the piston carrier 44 are engaged with each other. Therefore gear 16
When the servo motor 10 connected to the servo motor 10 is actuated, the gears 18 and 20 are equally driven in opposite directions.
This in turn moves pistons 30 and 38 an equal distance in opposite directions.

Selection of which metering pump 12 or 14 to deliver liquid is made by rotating a four-way rotary valve 22, operated by a servo motor 24, 90 degrees. The operation of the servo motor 24 is synchronized with the reversal of the rotational direction of the servo motor 10.
The switching sequence is controlled by a microprocessor 26 such as an Intel 8085,
One of the metering pumps 12 or 14 is controlled to deliver solvent and the other to replenish the solvent from within the container 28.

The pump which is to carry out the delivery of the solvent, for example the pump 14 shown in FIG. , pump motor 5
2 pulls up the piston 54, drawing oil from the container 56 and pumping it through the ball valve 58 into the cylinder 60. The diaphragm pump chamber 48 is the metering pump 1
2 or 14 is separated from cylinder 60 by a flexible diaphragm 49 so that the solvent from pump 2 or 14 does not mix with the oil from slave pump 50. The flexible diaphragm 49 transmits pressure between the oil in the cylinder 60 and the solvent in the diaphragm pump chamber 48. pump motor 5
When the piston 54 is driven downward by 2,
The ball valve 58 closes. When the pressure within the cylinder 50 becomes greater than the load pressure, the ball valve 62 opens. Spring loaded ball valve 64, which along with compliance 66 and ball valve 68 act as a back pressure regulator, functions as a high pressure hydraulic assist device and is regulated to open at pressures above the maximum load pressure. As piston 54 continues to move downward, oil pressure increases within cylinder 60. Said pressure is transmitted through a flexible diaphragm 49 to the solvent in the diaphragm pump chamber 48 . If ball valve 46 is not already closed, ball valve 46 is closed by the increased pressure in diaphragm pump chamber 48. When the pressure in the diaphragm pump chamber 48 reaches the load pressure, the ball valve 62
opens to release a loaded pressure of solvent from the loading tube 70. All solvents are diaphragm pump chamber 4
After being pushed out from the piston 8, the piston 54 still moves downward, so the oil pressure in the cylinder 60 rises again and opens the ball valve 68. In this manner, slave pump 50 delivers the same volume of fluid (solvent and oil) in each cycle. Diaphragm pump chamber 4 by metering pump 12 or 14
If the amount of solvent sent to 8 becomes excessive, oil is pumped through ball valve 68 to compliance 66. This compliance 66 is maintained at a pressure above the maximum load pressure by adjusting the ball valve 64. When the pressure in the cylinder 60 becomes low,
The pressure held within compliance 66 causes ball valve 68 to close. However, the adjusted opening pressure of the ball valve 64 is the compliance 66.
It remains open as long as the pressure is lower than the inside pressure. In this way, the high-pressure hydraulic auxiliary device can gradually release the excess pressure that is being held.

The ball valve 46 cannot be opened solely by the suction pressure generated by the upward movement of the piston 54. Therefore, the metering pump 12
Only solvent that is actively pumped by or 14 can enter the diaphragm pump chamber 48. The motor 52 continuously drives the slave pump 50 while the servo motor 10 drives the metering pump 12,1.
The volume of four cylinders 32 or 40 is incrementally partitioned as an auxiliary volume and this auxiliary volume is fed into each slave pump cycle. In this way, metering pump 1
2 and 14 are slowly circulated by the subordinate pumps. The flow rate is controlled by adjusting the size of the auxiliary volume.

For example, in the pair of metering pump and slave pump of this embodiment, the motor 52 operates at a constant speed to drive the slave pump 5.
0 to cause 600 pump cycles per minute, and the cylinders 32 of the metering pumps 12 and 14.
and 40 have a combined capacity of 1/5 ml, and lead screws 34 and 42 are required to feed the 1/5 ml capacity.
Assume that it requires 8 rotations (4 rotations clockwise and 4 rotations counterclockwise), a total of 2880 degrees.
At a first flow rate of 12 ml per minute, metering pump pair 12 and 14 must then deliver 1/5 ml per second. To accomplish this, servo motor 10 must rotate gears 18 and 20 through 600 equal incremental revolutions of 4.8 degrees each minute. In contrast, a second flow rate of 1 μl per minute (ie, one metering pump cycle every 200 minutes) requires gears 18 and 20 to rotate 600 times each minute by 0.0004°. In reality, a flow rate of 12 ml is divided into 1/5 ml of the combined volume of the cylinders 32 and 40 of the metering pumps 12 and 14 into 10 auxiliary volumes each having an average of 20 μl. 1/5ml each at 1μl flow rate
The volume is divided into 120,000 auxiliary volumes, each with an average of 0.001667 μl. Errors in one auxiliary capacitance are compensated for by the accumulation of multiple auxiliary capacitances over time.

Microprocessor 26 is programmed to synchronize servo motor 10 with pump motor 52 so that metering pump 12 or 14 can pump solvent out of ball valve 46 only when piston 54 is moving upwardly. This ensures that the metering pump 12 or 14 is always subject to minimal roll-off. The servo motor 10 can also be operated independently of the pump motor 52 by accumulating solvent in the compliance 72 during high pressure cycles of the slave pump 50. Another way to coordinate the operation of slave pump 50 with the amount of solvent delivered to metering pump 12 or 14 is to combine compliance 72 with a variable speed or displacement slave pump 50. In this manner, the amount of solvent delivered by metering pumps 12, 14 is communicated to microprocessor 26 by compliance 72, which causes slave pump 50 to vary the flow rate in each cycle.

Additionally, in liquid chromatography systems using gradient elution analysis, the delivery solvents from multiple metering pump pairs can be mixed and delivered to a single subordinate pump.

FIG. 2 shows the relationship between piston speed and time for three types of flow rates. The broken line 74 indicates the slave pump 50
This represents the harmonic motion of the piston 54 in one cycle of . The three curves 76a, 76b and 76c represent the filling profile of the slave pump 50 filled by the metering pumps 12 and 14, respectively. (0-50ms). If the flow rate is small, curve 7
As shown in 6a and 76b, it is a Gaussian curve, and
When the flow rate is large, it is a trapezoid like 76c. Curves 78a, b, c are the filling profile 76
3 shows the delivery profiles of slave pumps 50 corresponding to a, b, c; Pump over the amount of solvent 5
0 excess volume is dissipated by pumping oil by slave pump 50. The difference between the dashed line 74 and the curve 76c and the area 80 represent the amount of oil filled into the cylinder 60. Also, the curve 74
There is a sudden rise around 0ms, but this is due to the pressure deformation of the oil and the collapse in the ball valve.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a pump that is an embodiment of the present invention. FIG. 2 is an explanatory diagram of the operation of the pump shown in FIG. 1. 10: Servo motor, 12, 14: Metering pump, 16, 18, 20: Gear, 30, 38, 5
4: Piston, 32, 40, 60: Cylinder, 4
6, 58, 62, 64, 68: Gyokuben.

Claims (1)

[Claims] 1. A pump for supplying fluid to a column of a chromatograph, comprising: a high-pressure pump means for supplying a desired amount of fluid to the column; a first piston having a first fluid port; a second piston having a second fluid port; a mechanical drive means connected to the first and second pistons for driving the first and second pistons in a push-pull manner; a container for holding the fluid to be supplied to the first and second pistons; and a container for holding the fluid to be supplied to the first and second pistons;
and a second piston, during a first stroke, connect the first piston with the container, and connect the second piston with the high pressure pump means, and during a second stroke, connect the first piston with the high pressure pump means. and a low pressure pump means including a fluid switching means connected to the pump means and connecting the second piston to the container, and characterized in that the high pressure pump means and the low pressure pump means are mechanically driven independently. pump.