JPH0755819A - Method and apparatus for detecting liquid level - Google Patents

Abstract

PURPOSE:To allow detection of liquid level even in an enclosed system without generating bubbles by providing a nozzle tip for sucking and delivering a liquid sample, a sensor for detecting the pressure in an air hose, etc. CONSTITUTION:When the air is sucked or delivered into or from a tip 36 by means of a cylinder 46, a resistance is generated in an air hose 44 and the tip 36 when the air passes through them. The resistance is detected by a pressure sensor 54 in the form of a variation of inner pressure within the air hose 54. The tip 36 is then lowered while sucking and delivering the air and the like and the liquid level is detected when the inner pressure varies significantly. When the inner pressure varies abruptly down to a negative level, the tip 36 is blocked at the end thereof and then a control section 84 makes a decision that the liquid level is reached and stops suction/delivery and lowering of the tip 36. This constitution allows to finish detection of liquid level prior to generation of bubbles on the liquid level while eliminating the need of sampling the inner pressure of the air hose 44 or the comparison of the inner pressure with a reference value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detection method and apparatus, and more particularly to improvement of liquid level detection using a nozzle tip.

[0002]

2. Description of the Related Art A dispensing device for dispensing a sample is known, and is used, for example, as a device for distributing blood collected from a human body into a plurality of containers.

As a liquid level detecting method used in a conventional dispensing apparatus, for example, Japanese Patent Laid-Open No. 2-196964 can be cited. This liquid level detection method uses a suction pump connected to the nozzle tip via a pipe to discharge about 100 to 150 μl / sec of air from the nozzle tip, and to detect the liquid level from the pressure change of the internal pressure of the pipe system. It was a way to detect. In particular, the reference value of the internal pressure of the piping system that was measured in advance before the liquid level detection was compared with the internal pressure of the piping system during air discharge, and the tip of the nozzle tip contacted the liquid surface and was blocked. It was a method of detecting the liquid surface by the pressure change due to the above.

[0004]

However, in the above liquid level detection method, the sampling response time of the internal pressure of the pipe system is compared with the sampled internal pressure of the pipe system and the reference value before the liquid level is detected. Since it takes a time to detect the pressure change and a response time to control the air discharge of the nozzle tip according to the pressure change, 1-2 times on the liquid surface in the meantime.
There was a risk that individual bubbles would be generated (see FIG. 7).

Each such bubble has a size of about 10 μl, and if it has a perfect spherical shape, a part of the liquid surface is 3
The height is increased by about mm. Therefore, there is a problem in that the liquid level is detected higher due to the bubbles, or the bubbles are sucked from the bubbles during suction. In this case, there are drawbacks that the dispensing amount becomes insufficient, and the work of the operator increases due to the warning by air suction (see FIG. 8).

Further, at present, a closed test tube (so-called vacuum blood collection tube) is used to prevent infection during blood collection. In such a vacuum blood collection tube, if air is ejected and inserted from the nozzle tip as in the conventional case without removing the cap of the test tube opening, the inside of the test tube will be in a pressurized state. For this reason, there is a problem that a pressure change occurs only by inserting the nozzle tip, and the liquid level is determined at this point (see FIG. 9).

Therefore, conventionally, the cap of the opening portion of the test tube is removed, and the liquid level is detected by using an open system like a normal test tube. However, there are cases where it is desired not to mix air into the test tube depending on the sample, and in such a case, liquid level detection could not be performed using the above liquid level detection method.

The present invention has been made in view of the above conventional problems, and an object thereof is a liquid level detection method capable of detecting a liquid level even in a closed system without generating bubbles at the time of detecting the liquid level. To provide a device.

[0009]

In order to achieve the above object, in the liquid level detecting method according to the present invention, a nozzle tip for sucking and discharging a liquid sample is connected to the nozzle tip via an air hose. In an automatic dispensing device including a suction / discharge pump and a pressure sensor for detecting the pressure in the air hose, while driving the pump while driving the nozzle tip into the container containing the sample, the nozzle A step of discharging and sucking a small amount of air or an inert gas from the tip and repeating this discharging and suction operation alternately; a step of monitoring the pressure change of the air hose internal pressure while lowering the nozzle tip; Detecting a sudden change in the internal pressure of the air hose due to the tip contacting the liquid surface and becoming blocked, the tip of the nozzle tip reaches the liquid surface. Characterized in that it comprises a, and determining the things.

Further, in the above liquid level detecting method, the discharging / sucking operation is performed at a cycle such that the liquid sample is not sucked into the nozzle tip when the liquid surface comes into contact.

Further, the liquid level detecting device according to the present invention includes a nozzle tip for sucking and discharging a liquid sample, a suction / discharge pump connected to the nozzle tip via an air hose, and In an automatic dispensing apparatus including a pressure sensor for detecting pressure, a means for lowering the nozzle tip into a container containing a sample, and driving the pump to discharge a small amount of air or an inert gas from the nozzle tip. Means for sucking and alternately repeating this discharge / sucking operation, means for monitoring the pressure change of the internal pressure of the air hose, and the fact that the tip of the nozzle tip comes into contact with the liquid surface and becomes blocked Means for detecting a rapid change in the internal pressure of the air hose and determining that the tip of the nozzle tip has reached the liquid surface.

Further, in the above liquid level detecting device,
It is characterized in that it includes means for causing the discharge / suction operation to be performed at a cycle such that the liquid sample is not sucked into the nozzle tip when the liquid surface comes into contact.

[0013]

According to the above construction, since the liquid level is detected by discharging / suctioning a small amount of air while lowering the nozzle tip and determining the magnitude of the pressure change of the air hose internal pressure at that time, the air hose internal pressure is sampled. The liquid level detection can be ended before bubbles are generated on the liquid surface of the liquid sample, without the need to perform the above operation or to compare the sampled air hose internal pressure with the reference value.

Further, since the time when the tip of the nozzle tip comes into contact with the liquid surface and is in the closed state is determined as the liquid surface, the accuracy of the liquid surface detection is high.

Further, since the suction / discharge operation is performed in a cycle such that the liquid sample is not sucked into the nozzle tip at the time of contact with the liquid surface, the suction amount error at the time of suction can be avoided.

Further, since the liquid level is detected by discharging and sucking a small amount of air while lowering the nozzle tip, even in a closed test tube, the inside of the test tube is not pressurized and the liquid level is detected accurately. Can be done.

Further, by discharging and sucking the inert gas, the liquid level can be satisfactorily detected even in the case of a liquid sample which is not desired to be brought into contact with air.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the appearance of a dispensing device 30 to which the liquid level detecting method according to the present invention is applied, and FIG. 1 is a perspective view thereof.

A nozzle portion 32 for sucking a liquid sample, which is shown in the center of the drawing, is held by an XYZ robot 34, and the nozzle portion 32 is movable three-dimensionally.

FIG. 2 shows a sectional view of the main part of the nozzle part 32. The nozzle part 32 is composed of a nozzle base 35 and a disposable chip (hereinafter referred to as a chip) 36 which constitutes a nozzle chip. . That is, in the dispensing device of the present embodiment, disposable nozzle tips are used. In addition, this chip 36
The tip portion of the nozzle base 35 is press-inserted into the upper opening of the nozzle 36. By fitting the tip portion of the nozzle base 35 into the upper opening of the tip 36 in this manner, the tip 36 is securely fixed to the nozzle base 35. To be done. A small hole 36a is formed at the lower tip of the tip 36, and the liquid sample is sucked or discharged from the small hole 36a.
The tip 36 is made of, for example, hard plastic, and the nozzle base 35 is made of metal.

In FIG. 1, the XYZ robot 34 is used.
X drive unit 34x, Y drive unit 34y, and Z drive unit 3
4z, and an elevator section 38 having a nozzle section 32 is connected to the Z drive section 34z so as to be vertically movable.
The elevator section 38 has a limit switch 40 that functions as a jamming sensor or the like, and this limit switch 40 detects an upward external action force applied to the nozzle section 32. One end of an air hose 44 is connected to the nozzle portion 32, and the other end of the air hose 44 is sucked and sucked.
It is connected to a cylinder 46 that functions as a discharge pump. A pressure sensor 54 for measuring the internal pressure in the air hose 44 is connected between the cylinder 46 and the nozzle portion 32. The signal from the limit switch 40 is sent to the apparatus main body via the signal cable 56.

Two types of test tube racks 60 are mounted on the dispensing table 58, and a plurality of test tubes 62 containing liquid samples (hereinafter referred to as sample-containing test tubes 62) are held upright on one of the test tube racks 60. The other test tube rack 60 holds a plurality of discharge test tubes 66, which are the discharge destinations, upright.

In the dispensing device 30 of this embodiment, since the nozzle tip is disposable, that is, disposable,
A plurality of new chips are prepared for the chip stand 72, and are sequentially replaced with new chips. The used chips are discarded in the chip disposal tray 74.

Therefore, according to the above-mentioned dispensing device 30, the tip 36 of the nozzle portion 32 sucks the plasma component (upper layer portion) or the red blood cell component (lower layer portion) after centrifuging the blood sample, for example. Can be freely transferred to another container. Of course, this dispensing device can be used for other than dispensing of blood samples, and various applications are possible.

FIG. 3 shows a schematic diagram for explaining the schematic structure of the dispensing apparatus of this embodiment. Further, FIG. 4 shows a block diagram of a schematic configuration of the dispensing device of the present embodiment.

The pump is composed of a piston 76 and a cylinder 46. By moving the piston 76 forward and backward, the internal volume of the cylinder 46 is changed. And the liquid sample is sucked and discharged.
The internal pressure of the air hose 44 is detected by the pressure sensor 54, the sensor signal is amplified by the DC amplifier 78, and then sent to the A / D converter 82 via the limiter circuit 80. Here, the limiter circuit 80 is a protection circuit that suppresses excessive input. The A / D converter 82 converts the sensor signal into a digital signal and sends it to the control unit 84. The controller 84 is composed of, for example, a computer and controls the internal volume of the cylinder 46 and the XYZ robot 34. Then, in the present embodiment, the control unit 84 particularly monitors the magnitude of the pressure change of the pressure sensor 54 and controls the lowering of the tip 36 and the discharge / suction of air or the like according to the pressure change.

Next, the liquid level detection method adopted in the above dispensing device 30 will be described in detail.

In the dispensing device 30, when air or the like is sucked and discharged from the tip 36 using the cylinder 46, resistance is generated in the air hose 44 and the tip 36 when the air or the like passes. This resistance is detected by the pressure sensor 54 as a change in the internal pressure of the air hose 44. Utilizing this, the tip 36 is lowered while ejecting / sucking air or the like, and the liquid level is detected when the change in the internal pressure becomes large.

FIG. 5 is an explanatory view showing a liquid level detecting step of the liquid level detecting method according to the present invention. Further, FIG. 6 is a graph showing a change in internal pressure output from the pressure sensor in the liquid level detecting method according to the present invention. Here, a negative pressure is applied when air or the like is sucked, while a pressure is applied when air is discharged. In the following, water was used as the liquid sample.

As shown in FIG. 5, the tip 36 descends toward the liquid sample while repeatedly ejecting and sucking a small amount (for example, 5 to 10 μl) of air or the like (step 1).
01, corresponding to S101 in the figure). In step 101,
The air above the liquid surface in the test tube 62 is sucked and discharged. The internal pressure of the air hose 44 at that time has a small pressure fluctuation as shown in the left half surface of the graph of FIG.

When the tip 36 is further lowered, the tip of the tip 36 comes into contact with the liquid surface, and the liquid sample is sucked and discharged.

However, in the case of this embodiment, since the pressure sensor 54 is provided in the vicinity of the cylinder 46, when suction is performed from the tip 36, the resistance of air in the thin tube of the tip 36 and the air hose 44 is added, and the pressure is reduced. Sensor 5
In 4, a large negative pressure change is detected. Therefore, actually, the negative pressure is not so much at the tip of the tip 36, and the liquid sample is not sucked into the tip 36 as the internal pressure changes.

Furthermore, since liquid has a higher viscosity than air,
Even if the tip 36 performs a suction operation at the time of contact with the liquid surface and the internal pressure of the air hose 44 largely changes to a negative pressure (a in FIG. 6).
Point), a time delay occurs from the pressure change to the suction of the liquid sample, and only the liquid sample of, for example, 1 to 2 mm is sucked into the chip 36 (step 102).

In the case of this embodiment, the conventional discharge amount (1
A small amount (for example, 5 to 1) compared to 0 to 150 μl / sec.
0 μl / sec) air etc. in a short cycle (for example, about 6 Hz)
Since the liquid sample is discharged and sucked in, even if a small amount of the liquid sample is sucked, the discharge operation is started during the time delay and the liquid sample at the tip of the chip 36 is removed. Therefore,
The inflow and outflow of the liquid sample in the tip 36 is offset (step 103). At this time, the internal pressure of the air hose 44 is largely turned to pressurization in order to push the liquid surface (b in FIG. 6).
point).

The control unit 84 closes the tip of the tip 36 and changes the internal pressure of the air hose 44 significantly (see FIG. 6).
The point a) is determined to be the liquid surface, and the discharge / suction and the descending of the tip 36 are stopped (step 104).

Although the liquid level detection using the open type test tube has been described above, the liquid level can be detected by the same operation even in the closed type test tube. That is, the tip 36 is discharged while a small amount of air or the like is discharged / sucked in a short cycle.
The pressure in the test tube of the closed system hardly changes even if the test tube is small. Therefore, the liquid level can be detected with high accuracy as in the open system.

Furthermore, in the case of this embodiment, liquid level detection can be satisfactorily performed in open and closed test tubes before bubbles are generated on the liquid surface of the liquid sample.

In this embodiment, the ejection / suction amount and the cycle of the tip 36 when water is used are shown. However, when the samples having different viscosities are used, the ejection / suction amount and the cycle thereof are changed. It is preferable to carry out.

[0040]

As described above, according to the present invention,
Air is discharged and sucked while lowering the nozzle tip, and the liquid level is detected by determining the magnitude of the pressure change in the air hose internal pressure at that time.Therefore, it is necessary to sample the air hose internal pressure and The liquid level detection can be terminated before bubbles are generated on the liquid surface of the liquid sample without the need to compare with the reference value. Therefore, it is possible to prevent a liquid level detection error and bubble suction due to bubbles.

Further, since the time when the tip of the nozzle tip comes into contact with the liquid surface and is in the closed state is judged as the liquid surface, the liquid surface can be detected with high accuracy.

Further, since the suction / discharge operation is performed in a cycle such that the liquid sample is not sucked into the nozzle tip when the liquid surface comes into contact, it is possible to prevent a suction amount error during suction. Also, air is discharged while lowering the nozzle tip.
Since suction is performed and liquid level detection is performed, liquid level detection can be performed accurately even in a closed test tube without causing a pressure inside the test tube.

Further, since the inert gas can be discharged and sucked, the liquid level can be satisfactorily detected even in the case of a liquid sample which is not desired to be brought into contact with air.

[Brief description of drawings]

FIG. 1 is an external view showing an embodiment of a dispensing device to which a liquid level detecting method according to the present invention is applied.

FIG. 2 is a cross-sectional view showing a cross section of a main part of a nozzle portion 32.

FIG. 3 is a schematic diagram illustrating a schematic configuration of the dispensing device shown in FIG.

FIG. 4 is a block diagram showing a schematic configuration of the dispensing device shown in FIG.

5 is an explanatory diagram showing a liquid level detecting step of the dispensing device shown in FIG. 1. FIG.

FIG. 6 is a graph showing changes in internal pressure output from the pressure sensor of the dispensing device shown in FIG.

FIG. 7 is a diagram illustrating a problem of liquid level detection in a conventional dispensing device.

FIG. 8 is a diagram illustrating a problem of liquid level detection in a conventional dispensing device.

FIG. 9 is a diagram illustrating a problem of liquid level detection in a conventional dispensing device.

[Explanation of symbols]

 30 Dispensing device 32 Nozzle part 34 XYZ robot 35 Nozzle base 36 Disposable tip 54 Pressure sensor 46 Cylinder 62 Test tube 76 Piston 84 Control part

Claims (4)

[Claims] 1. A nozzle tip for suctioning and discharging a liquid sample, a suction / discharge pump connected to the nozzle tip via an air hose, and a pressure sensor for detecting the pressure in the air hose. In the automatic dispensing device, while lowering the nozzle tip into the container containing the sample,
A step of driving the pump to discharge and suck a small amount of air or an inert gas from the nozzle tip, and repeating this discharging and suction operation alternately; and a pressure change of the air hose internal pressure while lowering the nozzle tip. And a step of monitoring the tip of the nozzle tip contacting the liquid surface and detecting a rapid change in the internal pressure of the air hose due to the closed state, it is determined that the tip of the nozzle tip has reached the liquid surface. A liquid level detection method comprising: 2. The liquid level detection method according to claim 1, wherein the discharging / suctioning operation is performed at a cycle such that the liquid sample is not sucked into the nozzle tip when the liquid surface is in contact. Detection method. 3. A nozzle tip for sucking and discharging a liquid sample, a suction / discharge pump connected to the nozzle tip via an air hose, and a pressure sensor for detecting the pressure in the air hose. In the automatic dispensing apparatus, a means for lowering the nozzle tip into a container containing a sample, and driving the pump to discharge / suck a small amount of air or an inert gas from the nozzle tip, and
A means for alternately repeating the suction operation, a means for monitoring a pressure change in the air hose internal pressure, and a rapid change in the air hose internal pressure due to the nozzle tip tip contacting the liquid surface and becoming blocked. And a means for determining that the tip of the nozzle tip has reached the liquid level, the liquid level detecting apparatus. 4. The liquid level detection device according to claim 3, further comprising means for causing the discharge / suction operation to be performed at a cycle such that a liquid sample is not sucked into the nozzle tip when the liquid surface is in contact. Characteristic liquid level detection device.