Liquid suction device

Abstract

To provide a liquid suction device capable of gas-liquid mixed cleaning with a simple configuration.SOLUTION: A liquid suction device 1 for sucking liquid in a container B, includes: a suction nozzle 10 having a suction port 10a at an end 10b and having the end 10b inserted into the container B; a drive unit 20 for moving the suction nozzle 10 up and down; a pump 30 for sucking liquid through the suction nozzle 10; and a control unit 40 for controlling the drive unit 20 so that the suction nozzle 10 goes down, after the suction port 10a of the suction nozzle 10 is brought close to a liquid level S of the liquid in the container B, with an average speed equal to or lower than a speed at which the liquid level S goes down in the container B due to the suction of the liquid by the pump 30.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a liquid suction device for suctioning liquid from a container, and a liquid suction method. [Background technology]

[0002] Some automatic samplers that supply liquid samples, liquid reagents, etc. (hereinafter referred to as "liquid samples") to measuring devices such as vibration-type density meters and refractometers have a liquid suction device that suctions liquid samples contained in containers such as vials through a suction nozzle.

[0003] Liquid suction devices are used not only to suction liquid samples during measurement, but also to suction cleaning liquid for cleaning the internal piping of measurement devices, automatic samplers, etc. When cleaning such piping, the cleaning effect can be improved by introducing air through a route separate from the cleaning liquid, mixing the air with the cleaning liquid, and flowing it through the piping (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-15553 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when measuring the density, refractive index, etc. of a liquid sample, errors will occur if air bubbles are mixed in the liquid sample introduced into the measurement device. Therefore, in order to apply the gas-liquid mixed cleaning method of Patent Document 1 to a liquid suction device for an automatic sampler, a valve mechanism such as an electromagnetic valve is required to enable mixing of air introduced via a separate route with the cleaning liquid sucked through the suction nozzle during cleaning, while reliably preventing air from mixing into the liquid sample sucked through the suction nozzle during measurement, which results in the problem of increased device costs.

[0006] The present invention has been made in consideration of the above problems, and has an object to provide a liquid suction device and a liquid suction method that are capable of gas-liquid mixed cleaning with a simple configuration. [Means for solving the problem]

[0007] The liquid suction device according to the present invention, which solves the above problems, has the following characteristic configuration: A liquid suction device for suctioning liquid in a container, a suction nozzle having a suction port at an end, the end being inserted into the container; a drive unit that moves the suction nozzle up and down; a pump that sucks the liquid through the suction nozzle; a control unit that controls the drive unit so that, after the suction port of the suction nozzle is brought close to the liquid surface of the liquid in the container, the suction nozzle descends at an average speed that is equal to or less than the speed at which the liquid surface descends in the container due to the suction of the liquid by the pump; The purpose is to provide the following.

[0008] This liquid suction device, which aspirates liquid from a container, includes a suction nozzle having a suction port at its end, the suction port being inserted into the container, a drive unit for moving the suction nozzle up and down, and a pump for aspirating the liquid through the suction nozzle. The control unit controls the drive unit to bring the suction port of the suction nozzle close to the liquid surface in the container and then lower the suction nozzle at an average speed less than the rate at which the liquid surface descends in the container due to the pump's suction. Here, "close to the liquid surface" refers to a state in which the suction port of the suction nozzle is in contact with the liquid surface or at least a portion of the suction port is positioned above the liquid surface, allowing the pump to drive the pump to raise the liquid surface and draw the liquid into the suction nozzle. In this state, air is drawn into the suction port during the suction. In other words, air is drawn into the suction port simultaneously with the liquid in the container. Furthermore, the suction port is constantly maintained close to the liquid surface as the suction nozzle descends at an average speed less than the rate at which the liquid surface descends in the container due to the suction. As a result, the sucked liquid and gas can be kept mixed and flowing through the piping, thereby achieving gas-liquid mixed cleaning with a simple configuration.

[0009] In the liquid suction device according to the present invention, It is preferable that the control unit controls the drive unit so that the suction nozzle descends at a constant speed.

[0010] With this liquid suction device, the control unit controls the drive unit so that the suction nozzle descends at a constant speed. This ensures that the relative positions of the suction port and the liquid level remain constant regardless of the descending liquid level, provided the pump suction speed is constant. This ensures that the ratio of liquid to air drawn through the suction port remains constant, making it easy to predict the amount of liquid and time required to clean the pipes, enabling appropriate control of pipe cleaning.

[0011] In the liquid suction device according to the present invention, It is preferable that the control unit controls the drive unit so that the suction nozzle intermittently moves down by a predetermined distance.

[0012] According to the liquid suction device of this configuration, the control unit controls the drive unit so that the suction nozzle intermittently descends by a predetermined distance, thereby enabling gas-liquid mixed cleaning with a simple control pattern.

[0013] In the liquid suction device according to the present invention, It is preferable that the control unit controls the drive unit so that the suction nozzle descends at a predetermined cycle.

[0014] With this liquid suction device, the control unit controls the drive unit so that the suction nozzle descends at a predetermined cycle, and as long as the pump suction speed is constant, the positional relationship between the suction port and the liquid surface fluctuates at the predetermined cycle. As a result, the ratio of liquid to air sucked through the suction port also fluctuates at the predetermined cycle, making it easy to predict the amount of liquid and time required to clean the pipe, and enabling appropriate control of pipe cleaning.

[0015] In the liquid suction device according to the present invention, The apparatus further includes a pipe connected to the suction nozzle and two sensors for detecting the passage of a liquid surface at different positions in the pipe, It is preferable that the control unit lowers the suction nozzle until the suction port of the suction nozzle is positioned below the liquid surface of the liquid in the container, and then calculates the speed at which the liquid surface descends in the container based on the time it takes for the liquid surface to move between the two sensors as the pump suctions the liquid, and controls the drive unit so that the suction nozzle descends at an average speed below that speed.

[0016] According to the liquid suction device of this configuration, the device further includes a pipe connected to the suction nozzle and two sensors that detect the passage of the liquid surface at different positions in the pipe.The control unit lowers the suction nozzle until the suction port of the suction nozzle is positioned below the liquid surface in the container, and then calculates the speed at which the liquid surface descends in the container based on the time it takes for the liquid surface to move between the two sensors as the pump suctions the liquid.By controlling the drive unit so that the suction nozzle descends at an average speed below this speed, even if the suction speed of the pump is affected by characteristics such as the viscosity of the liquid sample, it is possible to identify the descending speed of the liquid surface according to those characteristics and to adjust the descending speed of the suction nozzle to an appropriate value.

[0017] The liquid suction method according to the present invention for solving the above problems is characterized by the following features: A liquid suction method for suctioning a liquid in a container, comprising: a first step of inserting a suction nozzle having a suction port at an end thereof and movable up and down into a container containing a liquid and bringing the suction port of the suction nozzle close to the liquid surface in the container; a second step of driving a pump connected to the suction nozzle; a third step of lowering the suction nozzle at an average speed equal to or less than a speed at which the liquid level in the container descends while the pump is operating; The purpose is to encompass the above.

[0018] This liquid suction method includes a first step of inserting a vertically movable suction nozzle having a suction port at its end into a container containing liquid and bringing the suction port of the suction nozzle close to the liquid surface in the container, a second step of driving a pump connected to the suction nozzle, and a third step of lowering the suction nozzle at an average speed equal to or less than the speed at which the liquid surface descends in the container while the pump is running. This allows the suction port to always be close to the liquid surface, and air can be sucked into the container simultaneously through the suction port. As a result, the sucked liquid and gas can be kept mixed and flowing through the piping. Therefore, gas-liquid mixed cleaning can be performed using a simple liquid suction device. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram of a liquid suction device according to the present invention. [Figure 2] FIG. 2 is a diagram illustrating a state in which liquid is sucked by a suction nozzle having a suction port cut obliquely with respect to the suction direction. [Figure 3] FIG. 3 is a diagram illustrating a state in which liquid is sucked by a suction nozzle having a suction port cut perpendicular to the suction direction. [Figure 4] FIG. 4 is a flowchart of the liquid suction method according to the present invention. [Figure 5] FIG. 5 is a graph showing the difference between the density values ​​measured by the vibration type densitometer and the reference density in the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0020] The liquid suction device and the liquid suction method of the present invention will be described below, but the present invention is not intended to be limited to the embodiments described below or the configurations shown in the drawings.

[0021] <Liquid suction device> FIG. 1 is a schematic diagram of a liquid aspirating device 1 according to the present invention. The liquid aspirating device 1 is implemented as a mechanism for aspirating a liquid sample from a container B in an automatic sampler or the like. It supplies a liquid sample for measurement by a measuring device (not shown) and cleans the measuring device and the piping inside the liquid aspirating device 1 before and after measurement. This specification describes components related to the cleaning operation, which is a characteristic of the liquid aspirating device 1 according to the present invention. The liquid contained in the container B for cleaning may be a cleaning liquid that dissolves substances remaining in the measuring device and the piping inside the liquid aspirating device 1, or the liquid sample used for measurement in the measuring device. Cleaning using a cleaning liquid requires drying the measuring device and the piping inside the liquid aspirating device 1 by flowing air after aspirating the cleaning liquid, which increases the cleaning time, but provides a high cleaning effect. Cleaning using the liquid sample used for measurement, i.e., co-washing, eliminates the need to dry the piping, but the cleaning power may be insufficient. Therefore, whether to perform cleaning with a cleaning liquid or co-washing may be appropriately selected depending on the type of liquid sample used, the structure of the liquid aspirating device 1, and the like.

[0022] The liquid suction device 1 comprises a suction nozzle 10, a drive unit 20, a pump 30, and a control unit 40, and further comprises, as an optional configuration, a pipe 50 connected to the suction nozzle 10 and sensors 61 and 62 provided on the pipe 50.

[0023] The suction nozzle 10 is a hollow needle made of a corrosion-resistant metal material such as stainless steel, and has a suction port 10a at its end 10b, which is inserted into the container B. In the automatic sampler, a vial is used as the container B, and the suction nozzle 10 is pierced through the seal of the vial to collect a liquid sample. In this embodiment, the end 10b of the suction nozzle 10 is cut at an angle relative to the suction direction of the suction nozzle 10 so that the seal can be easily pierced. A pipe 50, such as a resin tube, is connected to the suction nozzle 10, and the liquid suctioned through the suction nozzle 10 is supplied to a measuring device.

[0024] The driving unit 20 has a motor or the like, and moves the suction nozzle 10 in the up and down direction. The end 10b of the suction nozzle 10 is inserted into the container B by the driving unit 20, and its position is adjusted.

[0025] The pump 30 is provided on the piping 50. When the pump 30 is driven, the liquid in the container B can be sucked through the suction nozzle 10. It is preferable that the pump 30 be capable of suction at a constant suction speed. If the suction speed of the pump 30 is constant, the speed at which the liquid level S of the liquid in the container B descends due to suction by the pump 30 will be constant, making it easier for the control unit 40, described below, to control the positional relationship between the suction port 10a of the suction nozzle 10 and the liquid level S of the liquid in the container B. It is preferable that the pump 30 be a peristaltic pump or the like, which can adjust the suction amount with high precision, in order to accurately suck even small amounts of liquid.

[0026] The sensors 61, 62 each comprise a light-emitting unit and a light-receiving unit disposed on either side of the pipe 50. For example, an LED can be used for the light-emitting unit. For example, a light-receiving element can be used for the light-receiving unit. The intensity of the light emitted from the light-emitting unit and transmitted through the pipe 50 decreases when the state of the pipe 50 changes from a state in which gas flows through it to a state in which liquid flows through it. Therefore, the passage of liquid (liquid level) at the arrangement positions of the sensors 61, 62 can be detected by the change in the intensity of the light received by the light-receiving unit.

[0027] The control unit 40 can be configured as a computer having a CPU, memory, storage, etc., where the CPU reads and executes a program recorded in memory, thereby realizing the function of controlling the operation of the liquid aspirating device 1. Alternatively, the control unit 40 can be configured as an integrated circuit that executes some or all of the functions. The control of the liquid aspirating device 1 by the control unit 40 includes control of the operation of supplying a liquid sample for measurement by the measuring device, and control of the operation of cleaning the measuring device and the internal piping of the liquid aspirating device 1 before and after measurement. Here, we will explain the control of the cleaning operation, which is a feature of the liquid aspirating device 1 according to the present invention.

[0028] The cleaning operation of the liquid suction device 1 according to the present invention involves suctioning the liquid in the container B and circulating the liquid through the suction nozzle 10, the piping 50, and the interior of the measuring device to clean them. During this cleaning operation, the control unit 40 controls the drive unit 20 in accordance with the control procedure of the liquid suction method according to the present invention, which will be described later, to maintain the suction port 10a of the suction nozzle 10 close to the liquid level S in the container B while the liquid is being suctioned. Here, "close to the liquid level S" means that the pump 30 is driven to suck up the liquid level S while the suction port 10a is in contact with the liquid level S or while at least a portion of the suction port 10a is positioned above the liquid level S, and the liquid can be sucked through the suction port 10a.

[0029] 2 is a diagram illustrating the state in which liquid is sucked by suction nozzle 10, which has suction port 10a cut at an angle relative to the suction direction. As shown in Fig. 2, at end 10b of suction nozzle 10, lower end X of suction port 10a is located below liquid level S, but upper end Y is located above liquid level S. Therefore, when pump 30 is driven with suction port 10a close to liquid level S, liquid flows in from the lower end X side of suction port 10a, and air flows in from the upper end Y side of suction port 10a.

[0030] 3 is a diagram illustrating the state in which a liquid is sucked by suction nozzle 10 having suction port 10a cut perpendicular to the suction direction. As shown in Fig. 3, suction port 10a is located above liquid level S at end 10b of suction nozzle 10, but because the height h from liquid level S to suction port 10a is sufficiently small, when pump 30 is driven, liquid level S is intermittently sucked up into suction port 10a, and liquid and air alternately flow into suction port 10a.

[0031] 2 or 3, by maintaining the suction port 10a close to the liquid level S in the container B during suction of the liquid, liquid layers L and air layers A are alternately formed in the piping within the suction nozzle 10, and these layers are sucked, thereby achieving gas-liquid mixed cleaning of the suction nozzle 10, the piping 50, and the interior of the measuring device. When the suction port 10a of the suction nozzle 10 is positioned above the liquid level S, it is preferable that the height h from the liquid level S to the suction port 10a be within 1 mm. If the height h from the liquid level S to the suction port 10a is within 1 mm, the liquid and air can be reliably alternately introduced through the suction port 10a by driving the pump 30. If the height h exceeds 1 mm, there is a risk that the liquid will not be able to be sucked through the suction port 10a.

[0032] <Liquid suction method> The steps of the liquid suction method executed by the control unit 40 during the cleaning operation of the liquid suction device 1 will be described. Figure 4 is a flowchart of the liquid suction method according to the present invention. The liquid suction method sequentially executes the following steps: a first step (step S1) of bringing the suction port 10a of the suction nozzle 10 close to the liquid level S of the liquid in the container B; a second step (step S2) of driving the pump 30; and a third step (steps S3 to S6) of descending the suction nozzle 10 at an average speed equal to or lower than the speed at which the liquid level S descends within the container B while the pump 30 is driving. However, as optional steps, a descending speed setting step (step S11) can be executed before the first step, and a sampling step (step S12) can be executed after the third step.

[0033] The descending speed setting step (step S11) is a step for determining the average speed v2 (mm / sec) at which the suction nozzle 10 descends in the subsequent third step (steps S3 to S5). The speed v1 (mm / sec) at which the liquid level S descends in the container B while the pump 30 is operating may be significantly affected by the physical properties of the liquid, such as viscosity. Therefore, it is preferable to perform the descending speed setting step when the viscosity of the liquid used for cleaning is high. If the viscosity of the liquid used for cleaning is low and the speed v1 (mm / sec) at which the liquid level S descends in the container B while the pump 30 is operating is known, the average speed v2 (mm / sec) at which the suction nozzle 10 descends in the third step (steps S3 to S5) may be set to a default value without performing the descending speed setting step.

[0034] In the descending speed setting step (step S11), the control unit 40 first causes the drive unit 20 to descend the suction nozzle 10 until the suction port 10a of the suction nozzle 10 is positioned below the liquid surface. In this state, the pump 30 is driven to measure the time t1 required from when the liquid surface passes the position of the first sensor 61 until when the liquid surface passes the position of the second sensor 62. The control unit 40 further determines the cross-sectional area SA (mm 2 ), the mounting distance between the sensor 61 and the sensor 62 is D (mm), the cross-sectional area of ​​the vial is SB (mm 2 ) and the following equation (1): v1 = (SA × D) / (SB × t1) ···(1) The speed v1 (mm / sec) at which the liquid level S drops while the pump 30 is running is calculated using the above formula, and the average speed v2 (mm / sec) is set to be equal to or less than the speed v1 (mm / sec). Then, the pump 30 is stopped once.

[0035] After executing the descending speed setting step (step S11), the control unit 40 executes a first step (step S1) of bringing the suction port 10a of the suction nozzle 10 close to the liquid surface S of the liquid in the container B, using the drive unit 20, and a second step (step S2) of driving the pump 30 with the suction port 10a close to the liquid surface S. As a result, air is sucked in through the suction port 10a simultaneously with the liquid in the container B.

[0036] While driving the pump 30, the control unit 40 executes the third step (steps S3 to S6). In the third step, first, it determines whether a predetermined time (e.g., 1 second) has elapsed (step S3) and continues driving the pump 30 until the predetermined time has elapsed (step S3: NO). If the predetermined time has elapsed (step S3: YES), the control unit 40 drives the drive unit 20 to lower the suction nozzle 10 by a predetermined distance (step S4). For example, if the predetermined time (wait time) in step S3 is 1 second, the suction nozzle 10 is lowered by a distance v2 (mm) in step S4, thereby lowering the suction nozzle 10 at an average speed v2 (mm / sec). As a result, if the suction speed of the pump 30 is constant during the third step, the suction port 10a is always kept close to the liquid surface S, and the liquid and gas sucked through the suction port 10a are mixed and can be maintained flowing through the suction nozzle 10, the piping 50, and the interior of the measuring device. The suction nozzle 10 is lowered a predetermined number of times, and if the predetermined number of times has not been reached (step S5: No), steps S3 and S4 are repeated. The number of times the suction nozzle 10 is lowered (step S4) may be any number of times that allows the amount of liquid required for cleaning to be sucked in. When the number of times the suction nozzle 10 has been lowered reaches the predetermined number of times (step S5: Yes), the pump 30 is stopped (step S6).

[0037] In steps S3 to S5 described above, the suction nozzle 10 is lowered intermittently by a predetermined distance each time, but the third step can also be performed in a different sequence from steps S3 to S5 shown in Figure 4. For example, the drive unit 20 can be controlled to vary the amount of descent each time so that the average speed at which the suction nozzle 10 descends is v2 (mm / sec). Alternatively, rather than lowering the suction nozzle 10 intermittently, the drive unit 20 can be controlled so that the suction nozzle 10 descends at a constant speed v2 (mm / sec).

[0038] In the third step, if the liquid aspirated from container B is a liquid sample to be used for measurement, after the third step is performed, in a sampling step (step S12), pump 30 is driven to supply the liquid sample for measurement by the measurement device.

[0039] As described above, the liquid aspirating device 1 according to the present invention brings the aspirating nozzle 10's suction port 10a close to the liquid level S in the container B. Then, by driving the pump 30, the aspirating nozzle 10 is lowered at an average speed v2 equal to or less than the speed v1 at which the liquid level S descends in the container B, thereby maintaining the aspirating port 10a always close to the liquid level S. As a result, the aspirated liquid and gas are mixed and flowing through the piping 50. Therefore, compared to conventional co-washing methods, the effectiveness of replacing and cleaning unknown substances in piping, etc., is improved, and cleaning can be performed in a short time using a small amount of sample. Furthermore, even when a cleaning solution is used, the liquid aspirating device 1 can achieve gas-liquid mixed cleaning with a simple configuration, thereby reducing the amount of cleaning solution used and the total amount of wastewater. [Example]

[0040] A liquid sample was supplied to a oscillating density meter using an automatic sampler having a liquid suction device according to the present invention, and the measured value was confirmed when the sample was washed using the co-washing cleaning method for each measurement (Example 1).For comparison, a liquid sample was supplied to a oscillating density meter using an automatic sampler having a conventional liquid suction device that does not use gas-liquid mixed cleaning, and the measured value of the density was confirmed when the sample was washed using the co-washing cleaning method for each measurement (Comparative Example 1).

[0041] [Test method] In Example 1 and Comparative Example 1, the first and third measurements were performed using a 50% by mass sucrose solution (reference density: 1.239304 g / cm 3 ) was used as the measurement sample, and in the second and fourth measurements, water (standard density: 0.998232 g / cm 3) was used as the measurement sample, and each measurement was performed consecutively. In Example 1, in each measurement, a vial containing 20 mL of the measurement sample was set, and the measurement sample was aspirated from the vial using the liquid aspirating method of the present invention, thereby performing a gas-liquid mixed co-washing cleaning using the measurement sample (replacement with the measurement sample). Next, the aspirating nozzle was lowered to near the bottom of the vial so that the aspirating nozzle's aspirating port was positioned below the liquid surface of the measurement sample in the vial, and sampling of the remaining measurement sample was performed. In Comparative Example 1, in each measurement, a vial containing 20 mL of the measurement sample was set, and the aspirating nozzle was lowered to near the bottom of the vial, and the measurement sample was then continuously aspirated from the vial, thereby performing a normal co-washing cleaning using the measurement sample and sampling of the measurement sample. In Comparative Example 1, the aspirating port of the aspirating nozzle was always positioned below the liquid surface of the measurement sample in the vial during aspirating of the measurement sample, and no air was aspirated from the aspirating port. In Example 1 and Comparative Example 1, the amount of the measurement sample remaining in the vial after each measurement was 1 mL. Therefore, in Example 1 and Comparative Example 1, the amount of the measurement sample used for each cleaning and measurement was 19 mL.

[0042] 5 is a graph showing the difference between the density values ​​measured by a vibration type densitometer and the standard density in Examples and Comparative Examples. In Example 1, the difference from the standard density was 0.0005 g / cm in all measurements. 3 In contrast, in Comparative Example 1, the difference from the standard density in all measurements was within 0.0005 g / cm 3 The density values ​​exceeded 100%, and the difference from the standard density was particularly large in the measurement of the 50% by mass sucrose solution. In Comparative Example 1, the difference from the standard density was particularly large in the density measurement of the 50% by mass sucrose solution, which is thought to be due to the high viscosity of the 50% by mass sucrose solution and the insufficient amount of liquid used for washing.

[0043] From the above, it was confirmed that the liquid suction device of the present invention can achieve a higher cleaning effect when co-washing with either 50% sucrose solution or water is used than when co-washing with the same amount of liquid is used with a conventional liquid suction device. [Industrial Applicability]

[0044] The liquid suction device of the present invention can be used to suction liquid for cleaning pipes, etc. in a sampler that supplies liquid samples, liquid reagents, etc. to measuring devices such as vibration type densitometers and refractometers. [Explanation of symbols]

[0045] 1 Liquid suction device 10 suction nozzle 10a Suction port 10b end 20 Drive unit 30 Pump 40 Control Unit 50 Piping 61, 62 Sensor B container S liquid level X Bottom end of suction port Y Top of suction port A Air layer L liquid layer

Claims

1. A liquid suction device for suctioning liquid in a container, a suction nozzle having a suction port at an end thereof, the suction port being cut obliquely with respect to the suction direction, the end being inserted into the container; a drive unit that moves the suction nozzle up and down; a pump that sucks the liquid through the suction nozzle; a control unit that controls the drive unit so that, after the suction port of the suction nozzle is brought close to the liquid level in the container, the suction nozzle descends at an average speed that is equal to or less than the speed at which the liquid level descends in the container due to the suction of the liquid by the pump; A pipe connected to the suction nozzle; two sensors for detecting the passage of a liquid level at different positions in the piping; Equipped with the speed at which the liquid level in the container descends due to the suction of the liquid by the pump is a speed calculated based on the time it takes for the liquid level to move between the two sensors due to the suction of the liquid by the pump after the suction nozzle is lowered until the suction port of the suction nozzle is positioned below the liquid level in the container; The liquid suction device is configured such that the liquid suctioned through the suction nozzle is used to measure the liquid and to clean piping before and after the measurement.

2. The liquid suction device according to claim 1 , wherein the control unit controls the drive unit so that the suction nozzle descends at a constant speed.

3. The liquid suction device according to claim 1 , wherein the control unit controls the drive unit so that the suction nozzle intermittently descends by a predetermined distance.

4. The liquid suction device according to claim 3 , wherein the control unit controls the drive unit so that the suction nozzle descends at a predetermined cycle.

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