JP4550978B2 - Liquid level detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid level detection device, and more particularly to liquid level detection in a dispensing device that dispenses liquid with a nozzle.
[0002]
[Prior art]
In the dispensing device, a liquid such as a sample and a reagent is sucked by a nozzle and dispensed into a discharge destination container. If the nozzle tip reaches a position deeper than the liquid level when sucking the liquid, the amount of liquid adhering to the outer surface of the nozzle cannot be ignored. Occurs. Therefore, in order to make the nozzle penetration depth below the liquid level as small as possible, the liquid level of the liquid is automatically detected, and the nozzle lowering stop height is determined based on the height position. The liquid level detection method is disclosed in, for example, Japanese Patent Publication No. 6-3395. In such a conventional apparatus, a change in capacitance when a conductive probe or nozzle comes into contact with the liquid surface is detected, and the detection is realized by analog processing.
[0003]
[Problems to be solved by the invention]
However, when detecting a change in capacitance by analog processing as described above, many circuits such as a transmission circuit or a voltage comparator are required, which complicates the circuit and increases the circuit scale. is there. There is also a problem that the adjustment becomes more complicated as the number of circuits increases. Furthermore, there is a concern that when static electricity is charged in the liquid level detection using the change in capacitance, it may cause a large erroneous determination. However, in the past, sufficient measures have not been taken.
[0004]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to accurately detect the liquid level with a simple circuit configuration.
[0005]
Another object of the present invention is to take measures against static electricity.
[0006]
[Means for Solving the Problems]
(1) In order to achieve the above object, the present invention provides a liquid level detection apparatus that performs liquid level detection using a conductive member that descends with respect to the liquid level. A capacitive circuit having a signal transfer characteristic corresponding to the length, a reference signal generating circuit that outputs a reference pulse signal having a predetermined pulse width to the capacitive circuit , the reference pulse signal, and the capacitive circuit A capacity index generation circuit that generates a capacity index signal that represents the magnitude of the capacitance based on a comparison with an output pulse signal that is an output signal and has a pulse width corresponding to the collapse of the waveform of the pulse signal ; on the basis of the pulse width of the capacity measure signal, characterized in that it comprises a determining liquid level charging judgment circuit charging the liquid surface and static electricity, a.
[0007]
According to the above configuration, when the lower end of the conductive member comes into contact with the liquid surface, the signal transmission characteristic of the capacitive circuit changes, and the output signal (output pulse signal) and the reference signal (reference pulse signal) of the capacitive circuit change. The difference is reflected in the pulse width of the capacity index signal. Therefore, the liquid level can be determined by observing the pulse width of the volume index signal. In addition, since the charge determination can be performed, an erroneous determination of the liquid level can be prevented. The capacitance index signal is a pulse signal whose pulse width changes in accordance with the capacitance, and the pulse width can be easily detected by counting a reference clock or the like.
[0008]
Preferably, the conductive member is a nozzle that dispenses liquid. Alternatively, in the dispensing apparatus, a probe (conductive member) for detecting a liquid level may be provided separately from the nozzle, and the conductive member may be placed along the nozzle.
[0010]
(2) Preferably, in the liquid level detection device in which the liquid level detection device performs liquid level detection using a conductive member that descends with respect to the liquid level, according to the magnitude of the capacitance by the conductive member. A capacitive circuit having a signal transfer characteristic; a reference signal generation circuit that outputs a reference signal to the capacitive circuit; and a comparison between the reference signal and an output signal from the capacitive circuit. A capacity index generation circuit that generates a capacity index signal representing a magnitude, a liquid level determination circuit that determines a liquid level based on the capacity index signal, and a charge determination circuit that determines electrostatic charge based on the capacity index signal and, the including.
[0011]
According to the above configuration, even if a member related to the formation of capacitance such as a conductive member or a liquid container is charged, it can be determined based on the pulse width, and erroneous determination of the liquid level can be prevented.
[0012]
Preferably, a control unit that performs a discharge process when the electrostatic charge is determined is included. Preferably, in the discharging process, a discharging operation is performed in which the conductive member is brought into contact with a predetermined member. Preferably, the predetermined member is a container containing a liquid as a liquid level detection target.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
[0014]
FIG. 1 shows a preferred embodiment of a liquid level detection device according to the present invention, and FIG. 1 is a block diagram showing the overall configuration thereof. This liquid level detection device is incorporated in an automatic dispensing device.
[0015]
In the embodiment shown in FIG. 1, the nozzle 10 as a probe is made of a conductive metal material. Instead of the nozzle 10 as described above, a conductive member may be used as a probe for detecting the liquid level, or a conductive member placed along the side surface of the nozzle may be used.
[0016]
The container 12 is made of a material such as glass or plastic, and a sample 14 as a reagent or sample is accommodated therein. The nozzle 10 sucks the sample 14 and dispenses the sample 14. The container 12 is hold | maintained at the rack 16 comprised, for example with the electroconductive member.
[0017]
A dispensing pump 18 is connected to the nozzle 10. In the present embodiment, the dispensing pump 18 includes a syringe and a piston that moves inside the syringe. The dispensing pump 18 generates a discharge force and a suction force by the nozzle 10. The transport mechanism 22 is controlled by the control unit 24 and performs transport in the three-dimensional direction including the vertical movement of the nozzle 10. In addition to the transport mechanism 22, the control unit 24 controls the operation of the entire apparatus including the dispensing pump 18. In particular, as will be described later, when a liquid level detection signal is output from the monitor circuit 100, the control unit 24 performs control such as stopping the lowering of the nozzle 10 in accordance with the liquid level detection signal.
[0018]
Next, the liquid level detection circuit will be described. The oscillator 26 is a circuit that generates a reference clock as shown in FIG. The reference clock is input to the frequency divider 28. The frequency divider 28 divides the reference clock to generate a reference pulse as shown in FIG. This reference pulse is input to the inverter 30 with hysteresis, and the reference pulse is inverted by the action of the inverter 30. The inverted reference pulse is input to the capacitive circuit 33. Here, the capacitive circuit 33 is configured by a resistor 32 having a predetermined resistance value and a capacitance formed between the nozzle 10 and the container 12. Due to the action of the capacitive circuit 33, the waveform of the reference pulse inverted by the inverter 30 changes and changes, and as a result, a signal as shown in FIG. 2C is obtained. That is, a signal in which the rising edge of the pulse is lost is obtained. Here, the degree of deformation of the pulse depends on the magnitude of the capacitance.
[0019]
The signal output from the capacitive circuit 38 is input to the inverter 34 with hysteresis, and after being inverted there, it is input to one input terminal of the exclusive OR circuit 36. The reference pulse is input to the other input terminal of the exclusive OR circuit 36.
[0020]
An output signal (capacity index signal) of the exclusive OR circuit 36 is shown in FIG. This output signal pulse width depends on the magnitude of the electrostatic capacity. Therefore, when the tip of the nozzle 10 comes into contact with the sample 14 in the container 12, the electrostatic capacity changes, and specifically, the electrostatic capacity. As a result, the waveform difference between the reference pulse and the output signal of the inverter 34 increases. That is, the magnitude of the waveform difference appears as the pulse width of the output pulse of the exclusive OR circuit 36. The output signal of the exclusive OR circuit 36 is input to the monitor circuit 100. In the monitor circuit 100, the pulse signal output from the exclusive OR circuit 36 is inverted by the inverter 38 and then input to one input terminal of the AND gate 40. A reference pulse is input to the other input terminal of the AND gate 40. The AND gate 40 is a circuit that outputs a signal when both of the two input signals are high. Capacitance information is acquired only within the range of the reference pulse by the AND gate 40.
[0021]
The pulse width detector 42 is a circuit for counting the width of a pulse output from the AND gate 40 using a reference clock. The count result is input to the determination unit 44. The determination unit 44 compares the pulse width detected by the pulse width detector 42 with predetermined set values α and β (where α <β), and the pulse width is larger than the set value α and smaller than the set value β. Next, the liquid level is determined (as described above, because the capacitance increases due to the nozzle contact with the liquid level and the pulse width increases). Further, in the present embodiment, when the detected pulse width is larger than the set value β, the determination unit 44 determines that the electrostatic charge is generated in the capacitive circuit 33 (the charge is performed as shown in FIG. 3 later). This is because the pulse width is further increased as compared with the case of liquid level contact ). The determination signal of the determination unit 44, that is, the liquid level determination signal and the charging determination signal are output to the control unit 24.
[0022]
When the liquid level detection signal is obtained, the control unit 24 sets the descending amount of the nozzle 10 with reference to the height of the liquid level. When the charging is determined, the control unit 24 sets the nozzle 10. Is stopped and the tip thereof is brought into contact with the wall of the container 12 or other charged member, thereby eliminating the charged electric charge. Thereafter, the liquid level is detected again. That is, by performing such a discharge operation, there is an advantage that the liquid level can be detected with high accuracy. Incidentally, since the AND gate 40 is provided in FIG. 1, the liquid level determination is performed only within the pulse range of the reference pulse, which has the advantage that erroneous determination due to noise can be reduced.
[0023]
FIG. 3C shows the waveform of the input signal to the inverter 34 when charging occurs. As apparent from the comparison between FIG. 2 and FIG. 3, the degree of rounding of the signal is large due to charging, and the pulse width of the output signal of the exclusive OR circuit 36 is correspondingly increased as shown in FIG. Yes. In the present embodiment, it is possible to determine the charge for such a large pulse width by the determiner 44 (that is, the charge that generates a roundness of the signal waveform larger than the roundness of the signal waveform at the time of liquid surface contact. it is possible to determine the state), resulting in an advantage of being able to improve the liquid level detection accuracy.
[0024]
【The invention's effect】
As described above, according to the present invention, there is an advantage that liquid level detection can be performed with high accuracy and the liquid level detection can be realized with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration of a liquid level detection apparatus according to the present invention.
FIG. 2 is a diagram for explaining the operation of each circuit shown in FIG. 1;
FIG. 3 is a diagram for explaining the operation of each circuit shown in FIG. 1 when charging occurs.
[Explanation of symbols]
10 nozzles, 12 containers, 14 samples, 16 container racks, 18 dispensing pumps, 22 transport mechanism, 24 control unit, 26 oscillator, 28 frequency divider, 33 capacitive circuit, 36 exclusive OR circuit, 42 pulse width detection Device, 44 judgment device, 100 monitor circuit.

Claims (5)

In a liquid level detection device that performs liquid level detection using a conductive member that descends relative to the liquid level,
A capacitive circuit having a signal transmission characteristic according to the capacitance of the conductive member;
A reference signal generation circuit that outputs a reference pulse signal having a predetermined pulse width to the capacitive circuit;
The magnitude of the capacitance is expressed based on a comparison between the reference pulse signal and an output pulse signal that is an output signal from the capacitive circuit and has a pulse width corresponding to the collapse of the waveform of the pulse signal. A capacity index generation circuit for generating a capacity index signal;
A liquid surface charge determination circuit for determining charge of the liquid surface and static electricity based on the pulse width of the capacity index signal;
Only including,
The liquid surface charge determination circuit determines the liquid surface when the pulse width of the capacity index signal is larger than a set value α and smaller than a set value β when the conductive member is lowered (where α <β). The liquid level detecting device , wherein charging is determined when a pulse width of the capacity index signal is larger than a set value β . The apparatus of claim 1.
The liquid level detecting device according to claim 1, wherein the conductive member is a nozzle for dispensing a liquid. The apparatus of claim 1.
A liquid level detection apparatus comprising: a controller that performs a discharge process when the electrostatic charge is determined. The apparatus of claim 3 .
The liquid level detection apparatus according to claim 1, wherein a discharge operation for bringing the conductive member into contact with a predetermined member is performed in the discharge process. The apparatus of claim 4 .
The liquid level detection apparatus according to claim 1, wherein the predetermined member is a container containing a liquid as a liquid level detection target.

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