JP3123895B2 - Ultrasonic sensor and dispensing device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor used for distance measurement and a dispensing apparatus for dispensing or diluting a reagent, a specimen, or the like.

[0002]

2. Description of the Related Art Generally, as shown in FIG.
A dispensing head (15) is attached to an output portion of a three-axis drive table mechanism (18) controlled by a controller (19). The dispensing head (15) has a pipette ( 16) is projected downward.

When a reagent is dispensed into each recess (21) of a plate (20) placed on a dispensing table (17), a dispensing head (15) is operated by a three-axis drive table mechanism (18). ) Is moved so that the tip of the pipette (16) approaches the recess (21) of the plate (20), and the reagent in the pipette (16) is discharged into the recess (21). When diluting or mixing reagents, place other reagents in the recesses (21).
The reagent (22) has already been injected, and the reagent dropped from the pipette (16) is brought into contact with the liquid surface of the reagent (22) in the recess (21) to release the surface tension, thereby discharging the reagent. . At this time, when the pipette (16) itself comes into contact with the reagent (22) in the concave portion (21), the reagent attached to the pipette (16) is mixed with another reagent in the next dispensing step, so that the pipette (16) It is necessary to discharge the reagent at a position where the front end surface of the sample floats slightly above the liquid surface of the reagent (22).

[0004] When the reagent is diluted or mixed as described above, the dispensing head (1) is controlled by the controller (19).
5) Lower the pipette (16) into the recess (2) of the plate (20).
Although the liquid level of the reagent (22) in 1) is brought as close as possible, the liquid level of the reagent (22) varies depending on the concave portion (21), so each time the reagent (22) Measure the liquid level of
It is necessary to adjust the height position of the pipette (16). At this time, the measurement of the liquid level of the reagent (22) requires an accuracy of about 0.1 mm.

In terms of accuracy of distance measurement, it is advantageous to use a laser measuring device. However, in this case, a laser beam is applied to the reagent, so that a transparent reagent or a reagent causing a photochemical reaction is used. Is not applicable.

Therefore, conventionally, a dispensing head as shown in FIG.
Attach the ultrasonic sensor (1) to the side of (15) and add the reagent (22)
The distance to the liquid level is measured, and the measured value is
Feedback is performed to the control of the three-axis drive table mechanism (18) according to 9).

In the distance measurement by the ultrasonic sensor (1), as shown in FIG.
The transmission wave is emitted toward the, and the reception wave reflected and returned by the measurement target (24) is received by the ultrasonic sensor (1), and based on the time measurement from the transmission of the transmission wave to the reception of the reception wave. Measure the distance to the object to be measured. Here, the transmission wave has a waveform whose amplitude gradually increases and then gradually decreases as shown in FIG. 7 due to the mechanical impedance of the vibrator. Along with this, the received wave also has a similar waveform.
Note that the transmission wave and the reception wave have the same frequency, and the peak values of a plurality of waves included in the reception wave each have a constant attenuation rate with respect to the peak value of the corresponding transmission wave. Will be.

[0008]

The measurement of the time from the transmission of a transmission wave to the reception of a reception wave is accurately measured for the period from the rise of the first wave of the transmission wave to the rise of the first wave of the reception wave. However, in order to avoid erroneous detection due to noise, the rising of the first wave of the received wave is defined as the rising time of the first wave when the amplitude value of the waveform exceeds a certain threshold level. As a result, an error corresponding to several wavelengths of the ultrasonic wave occurs in the measurement value of the conventional ultrasonic sensor. In order to minimize this error, the frequency of the vibrator may be increased, but this significantly reduces the amplitude during the propagation of the ultrasonic wave and lowers the measurement sensitivity.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ultrasonic sensor capable of performing high-precision measurement even with ultrasonic waves having a relatively low frequency, and a dispensing apparatus equipped with the ultrasonic sensor.

[0010]

A first ultrasonic sensor according to the present invention includes a first ultrasonic sensor for detecting a rising point of a first wave of a transmission wave.
Detecting means, a plurality of peak points appearing in the waveform of the received wave, a second detecting means for detecting a zero crossing point at which a virtual envelope connecting these peak points crosses a zero level of the waveform, Measuring means for measuring the elapsed time from the rising point of one wave to the zero-cross point of the received wave; and adding a predetermined offset time to the time measured by the measuring means,
Calculating means for calculating the distance to the measurement object based on the addition result.

A second ultrasonic sensor according to the present invention detects a plurality of peak points appearing in a waveform of a transmission wave, and detects a zero cross point at which a virtual envelope connecting these peak points crosses a zero level of the waveform. A first detecting means for detecting a plurality of peak points appearing in the waveform of the received wave, a second detecting means for detecting a zero crossing point at which a virtual envelope connecting these peak points crosses a zero level of the waveform, and a transmitting means. Measuring means for measuring the elapsed time from the zero-cross point of the wave to the zero-cross point of the received wave, based on the time measurement by the measuring means,
Calculating means for calculating the distance to the object to be measured.

In the first or second ultrasonic sensor, the virtual envelope is specifically represented by a straight line, a quadratic curve, or an exponential curve.

Further, the dispensing apparatus according to the present invention comprises a dispensing head
The first ultrasonic sensor or the second ultrasonic sensor according to the present invention is attached to the side of (15) downward.

In the specific configuration of the dispensing apparatus, the object to be measured is the liquid surface of the liquid injected into the concave portion (21) of the plate (20), and the ultrasonic emission portion of the ultrasonic sensor (1) A cylindrical piece (23) provided with an ultrasonic path in the center is attached downward, and the ultrasonic path of the cylindrical piece (23) has the same or substantially the same cross-section as the opening shape of the concave portion (21). It is formed in a shape.

[0015]

According to the ultrasonic sensor of the present invention, as shown in FIG. 7, the elapsed time t from the rise of the first wave of the transmitted wave to the rise of the first wave of the received wave is indirectly measured, thereby obtaining the conventional ultrasonic sensor. This method eliminates measurement errors that were inevitable in the method.

That is, in the first ultrasonic sensor,
As for the transmission wave, the rising time of the first wave can be detected based on the start time of the supply of the driving pulse to the vibrator. On the other hand, the rising point of the first wave of the received wave is, as shown in FIG. 3, a point in time at which a predetermined offset time has elapsed from a zero crossing point where a virtual envelope connecting a plurality of peak points appearing in the waveform crosses a zero level. , The rising point of the first wave. Here, since all waves included in the waveform are attenuated at the same attenuation rate, a virtual envelope connecting a plurality of peak points is indicated by a broken line in FIGS. 4A and 4B from the geometric relationship. Thus, they pass through the same zero cross point regardless of the magnitude of attenuation. That is, the time (offset time) from the zero-cross point to the rising point of the first wave is constant regardless of the distance to the measurement target. Therefore, this offset time is
It can be obtained experimentally in advance as a value unique to the sensor.

Therefore, according to the first ultrasonic sensor, the elapsed time from the time when the first wave of the transmission wave rises to the time when the first wave of the reception wave rises is measured, and the distance without error in principle is measured. Measurement is possible.

Further, in the second ultrasonic sensor,
A zero-cross point is detected for both the transmission wave and the reception wave, and the elapsed time from the zero-cross point of the transmission wave to the zero-cross point of the reception wave, from the rising of the first wave of the transmission wave to the rising of the first wave of the reception wave. The elapsed time. in this case,
The time (offset time) from the zero-cross point for the transmitted wave to the rising time of the first wave and the time from the zero-cross point to the rising time of the first wave (offset time) for the received wave are geometrically obvious. Thus, they are identical to each other. Therefore, the elapsed time from the zero cross point of the transmission wave to the zero cross point of the reception wave coincides with the elapsed time from the rise of the first wave of the transmission wave to the rise of the first wave of the reception wave.

Therefore, the second ultrasonic sensor also provides
The elapsed time from the rise time of the first wave of the transmission wave to the rise time of the first wave of the reception wave is measured, and distance measurement without an error is possible in principle.

Although it is theoretically desirable that the virtual envelope connecting a plurality of peak points appearing in the waveform of the transmission wave or the reception wave is formed by an exponential curve, sufficient accuracy can be obtained by a straight line or a quadratic curve. Achieved.

In the dispensing apparatus having the first or second ultrasonic sensor, the object to be measured by the ultrasonic sensor is a liquid surface of the liquid injected into the concave portion (21) of the plate (20). The reciprocating time of the ultrasonic wave from the ultrasonic sensor (1) is measured, and the distance to the liquid surface is calculated.

The ultrasonic sensor (1) has a cylindrical piece (2
In the specific configuration of the dispensing device to which 3) is attached, the ultrasonic wave emitted from the ultrasonic sensor (1) is guided into the ultrasonic passage of the cylindrical piece (23), and is not diffused. 20)
(21). In a conventional dispensing apparatus in which the ultrasonic sensor (1) does not include the tube piece (23), as shown in FIG. 11, the ultrasonic wave emitted from the ultrasonic sensor (1) is diffused, and a part of the ultrasonic wave is dispersed. Is irradiated to the opening edge of the concave portion (21) of the plate (20), and the received wave due to the reflection at the opening edge
There was a problem that an accurate measured value H could not be obtained as detected in (1).

On the other hand, in the dispensing device of the present invention, the ultrasonic passage of the tube piece (23) is formed to have the same or substantially the same cross-sectional shape as the opening shape of the concave portion (21) of the plate (20). As shown in FIG. 9, the opening of the cylindrical piece (23) is
The distance measurement is performed with the concave portion (21) of (0) as close as possible. Therefore, some waves emitted from the ultrasonic sensor (1) do not irradiate the opening edge of the concave portion (21), and all the waves are guided into the concave portion (21), and ) Will be reflected at the liquid level of the liquid inside. As a result, an accurate measurement value H is obtained.

[0024]

The ultrasonic sensor according to the present invention employs a measurement method in which the measurement accuracy does not depend on the wavelength of the ultrasonic wave and has no error in principle. High-precision measurement is possible. Further, in the dispensing apparatus using the ultrasonic sensor according to the present invention, the positioning of the dispensing head can be performed with high accuracy by the highly accurate length measurement by the ultrasonic sensor.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. The ultrasonic sensor (1) of the present invention shown in FIG.
Switch (3) for changing the operation mode of the vibrator (2)
In the transmission mode, a clock of 400 kHz is supplied from the clock generator (4) to the drive pulse generator (5) to generate a drive pulse of 400 kHz. The drive pulse is amplified by an amplifier (6) and supplied to a vibrator (2) via a changeover switch (3). Here, the driving pulse is shown in FIG.
Are a few pulses with a constant peak value like
The vibrator (2) depends on the mechanical impedance of the vibrator (2)
2 has a waveform whose amplitude gradually increases and then gradually decreases as shown in FIG. 2B.

The output of the amplifier (6) is a sampling circuit.
The digital signal is supplied to the microcomputer (12), and the sampled signal is converted into digital data by the A / D converter (13) and supplied to the microcomputer (25) via the bus line (14).

The microcomputer (25) has a timer that operates based on a reference clock from the clock generator (10).
(7), comprising a CPU (8) and a memory (9), and a timer ON / OFF signal from a drive pulse generator (5) is supplied to a timer (7)
, The timer (7) starts counting time. The data transmitted from the A / D converter (13) via the bus line (14) is processed by the CPU (8) to detect the rising point of the first wave of the transmission wave or the zero-cross point. , And the result is stored in the memory (9).

On the other hand, in the reception mode, a received wave is detected by the vibrator (2) shown in FIG. 1, and the detection signal is supplied to the sampling circuit (12) via the amplifier (11).
The sampling circuit (12) samples the amplitude value of the waveform at a constant frequency (10 MHz), and the result is A
The data is converted into digital data by the / D converter (13) and supplied to the microcomputer (25). The microcomputer (25) stores the change of the waveform in the memory (9) as two-dimensional coordinate data in which the sampled time is the x coordinate and the sampled amplitude value is the y coordinate.

It should be noted that data having a negative y coordinate value is ignored in this embodiment. Also, to remove noise,
When sampling the waveform of the received wave, a threshold level having an appropriate size is provided, and data having a y-coordinate value equal to or smaller than the threshold level is excluded.

Thereafter, the microcomputer (25) detects the zero-cross point of the received wave according to the procedure shown in FIG. That is, in step S1, necessary counter variables n and m are initialized, and in step S2, the memory
The n-th data is extracted from (9).

Next, at step S3, the n-th, n-1st, and n-2th data are compared with each other to obtain n-1
If the data is not the maximum, n is counted up and the process returns to step S2. In step S3, n-1
When it is determined that the th data is the largest,
The process proceeds to step S4, where the (n-1) th data is set as the mth peak value.

Subsequently, in step S5, the m-th peak value is compared with the (m-1) -th peak value, and when the (m-1) -th peak value is smaller, n and m are counted. And returns to step S2.

If it is determined in step S5 that the (m-1) -th peak value is larger, the process proceeds to step S6, where the least square method is applied to the data of each peak point, and each peak point is determined. The connected virtual envelope is approximated by a straight line: V = at + b. Then, in step S7, time t when V = 0
Is calculated. The coordinate data (t, 0) at time t thus obtained is the zero cross point.

Finally, the microcomputer shown in FIG.
(25) calculates the distance L to the measurement target from the following equation 1 based on the elapsed time Tm from the rising point of the first wave of the transmission wave to the zero cross point of the reception wave.

[0035]

L = c × (Tm + To) / 2 where c is a sound speed, and To is a predetermined offset time.

The offset time To is determined by an ultrasonic sensor.
This value is specific to (1) and is obtained experimentally in advance. However, it is preferable that the value be corrected periodically in consideration of the aging of the vibrator. The calculation result of the distance L to the measurement target is
It is output by a printer or displayed on a display as needed.

In the above measurement method, the offset time To is added to the elapsed time Tm from the rising point of the first wave of the transmission wave to the zero-cross point of the reception wave, so that the reception wave from the rising point of the first wave of the transmission wave is added. Although the elapsed time t from the rise of the first wave is calculated, the same result can be obtained by calculating the elapsed time from the zero cross point of the transmission wave to the zero cross point of the reception wave.

In this case, the microcomputer (2
5) In the transmission mode, the same arithmetic processing as in FIG. 5 is performed on the sampling data of the transmission wave supplied from the A / D converter (13), and the zero-cross point of the transmission wave is detected.
Then, based on the elapsed time T (= t) from the zero cross point of the transmission wave to the zero cross point of the reception wave, the distance L to the measurement target is calculated from the following equation (2).

[0039]

L = c × T / 2

According to the ultrasonic sensor (1), it is possible to measure the length with high accuracy and high sensitivity even with an ultrasonic wave having a relatively low frequency.

FIG. 8 shows the ultrasonic sensor (1) in the dispensing apparatus.
The ultrasonic sensor (1) is attached to the output part of the three-axis drive table mechanism (18) together with the dispensing head (15) in a downward direction. Further, a cylindrical piece (23) having a circular cross section is vertically attached to the ultrasonic wave emitting portion of the ultrasonic sensor (1). The inner diameter of the tube piece (23) is the concave portion of the plate (20).
It is formed the same as the inner diameter (about 7 mm) of (21). The length of the tube piece (23) is 50 mm.

When dispensing the plate (20) on the dispensing table (17), the reagent already injected into the recess (21) of the plate (20) by the ultrasonic sensor (1) is first used. Measure the liquid level in (22). In this case, as shown in FIG. 9, the opening of the cylindrical piece (23) is made as close as possible to the opening of the recess (21) of the plate (20), and the openings are opposed to each other on the same axis. In this state, when an ultrasonic wave is emitted from the ultrasonic sensor (1), the ultrasonic wave is guided to the inner peripheral surface of the tubular piece (23), and is not diffused.
It is led to the recess (21) of the plate (20). And the reagent (22)
The ultrasonic wave reflected by the liquid surface is guided again to the inner peripheral surface of the cylindrical piece (23), and returns to the ultrasonic sensor (1).

Accordingly, unlike the conventional example shown in FIG. 11, a part of the transmission wave is not reflected at the opening edge of the concave portion (21), and the length can be measured with high accuracy. The measurement result by the ultrasonic sensor (1) is sent to the controller (19) shown in FIG. 8 and is used for positioning control of the dispensing head (15).

That is, the triaxial drive table mechanism (18) is operated based on the measurement result by the ultrasonic sensor (1), and the tip end face of the pipette (16) of the dispensing head (15) is moved to the plate (20). It is positioned at a height of 0.2 to 0.6 mm from the liquid level of the reagent (22) in the recess (21). Thereafter, the operation of the plunger device (not shown) connected to the pipette (16) causes the pipette (16) to operate.
Discharge the reagent inside. At this time, the reagent discharged from the pipette (16) is in the form of drops, comes into contact with the liquid surface of the reagent (22) in the concave portion (21) of the plate (20), and the surface tension is released, It will drop onto the plate (20).

In the above dispensing apparatus, the ultrasonic sensor
Since the liquid level is measured with high accuracy according to (1), the dispensing head (15) is accurately positioned at the time of reagent ejection, and there is a possibility that an unnecessary reagent may adhere to the tip surface of the pipette (16). There is no. Incidentally, even when the inner diameter of the cylindrical piece (23) is smaller than the inner diameter of the concave portion (21), reflection at the opening edge of the concave portion is similarly prevented,
Since the received wave may be weakened and the S / N ratio may be deteriorated, in this case, a measure for improving the S / N ratio is required.

The description of the above embodiments is for the purpose of illustrating the present invention and should not be construed as limiting the invention described in the appended claims or reducing the scope thereof. Further, the configuration of each part of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made within the technical scope described in the claims. For example, in the above embodiment, the ultrasonic sensor
Of the y coordinate values obtained by the measurement according to (1), only positive data is used. However, instead of using positive data, or using negative data together with positive data, transmission waves or reception waves are used. Can be obtained. or,
It is also possible to approximate the virtual envelope with a quadratic curve or an exponential curve.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an ultrasonic sensor according to the present invention.

FIG. 2 is a waveform diagram of a driving pulse and a vibration generated in a vibrator.

FIG. 3 is a diagram illustrating a zero cross point.

FIG. 4 is a diagram illustrating that a zero-cross point does not change depending on an amplitude attenuation rate.

FIG. 5 is a flowchart illustrating a procedure for obtaining a zero cross point.

FIG. 6 is a diagram illustrating the measurement principle of the ultrasonic sensor.

FIG. 7 is a diagram illustrating the occurrence of a measurement error in the conventional method.

FIG. 8 is a partially cutaway front view of the dispensing apparatus according to the present invention.

FIG. 9 is an enlarged sectional view showing a main part of the dispensing device.

FIG. 10 is a partially cutaway front view of a conventional dispensing apparatus.

FIG. 11 is an enlarged sectional view of the conventional device corresponding to FIG.

[Explanation of symbols]

 (1) Ultrasonic sensor (2) Transducer (3) Changeover switch (5) Drive pulse generator (25) Microcomputer (18) Three-axis drive table mechanism (23) Tube piece (20) Plate (21) Recess

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mikio Hojo 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Yoshio Ozawa 2-chome, Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Attorney Ogawa 2-5-5, Keihanhondori, Moriguchi-shi, Osaka Prefecture No. 5 Sanyo Electric Co., Ltd. No. 5 Sanyo Electric Co., Ltd. (56) References JP-A-5-248924 (JP, A) JP-A-4-72590 (JP, A) JP-A-60-138422 (JP, A) JP-A-1 -284786 (JP, A) Japanese Utility Model Showa 60-174971 (JP, U) Japanese Utility Model Showa 63-168882 (JP, U) Japanese Utility Model Application Hei 6-58327 (JP, U) (58) Fields surveyed (Int.Cl) . ^7, DB name) G01F 23/28

Claims (6)

(57) [Claims] 1. A transmission wave is emitted toward a measurement target, and a reception wave reflected and returned by the measurement target is received, and measurement is performed based on a time measurement from transmission of the transmission wave to reception of the reception wave. In an ultrasonic sensor for measuring a distance to a target, a first detecting means for detecting a rising point of a first wave of a transmission wave, a plurality of peak points appearing in a waveform of a reception wave, and connecting these peak points Second detecting means for detecting a zero-cross point at which the virtual envelope crosses the zero level of the waveform; measuring means for measuring an elapsed time from the rising point of the first wave of the transmission wave to the zero-cross point of the receiving wave; And a calculating means for adding a predetermined offset time to the time measurement value obtained by the method and calculating a distance to the object to be measured based on the addition result. 2. A transmission wave is emitted toward a measurement target, and a reception wave reflected and returned by the measurement target is received, and measurement is performed based on a time measurement from transmission of the transmission wave to reception of the reception wave. In an ultrasonic sensor for measuring a distance to a target, a plurality of peak points appearing in a waveform of a transmission wave are detected, and a first cross point where a virtual envelope connecting these peak points crosses a zero level of the waveform is detected. Detection means; second detection means for detecting a plurality of peak points appearing in the waveform of the received wave, and detecting a zero-cross point where a virtual envelope connecting these peak points crosses a zero level of the waveform; Measuring means for measuring the elapsed time from the point to the zero-cross point of the received wave, and calculating means for calculating the distance to the object to be measured based on the time measured by the measuring means. Ultrasonic sensor to. 3. The ultrasonic sensor according to claim 1, wherein the virtual envelope is represented by a straight line, a quadratic curve, or an exponential curve. 4. A dispensing apparatus in which a dispensing head (15) having a pipette (16) for sucking and discharging a liquid protruding downward is attached to an output portion of a head driving mechanism. On the side of), a transmission wave is emitted toward the measurement target, and a reception wave reflected and returned by the measurement target is received, and based on a time measurement from transmission of the transmission wave to reception of the reception wave. In a dispensing apparatus in which an ultrasonic sensor for measuring a distance to a measurement target is attached downward, the ultrasonic sensor includes: a first detection unit that detects a rising point of a first wave of a transmission wave; A second detecting means for detecting a plurality of peak points appearing in the waveform of the above, and detecting a zero cross point where a virtual envelope connecting these peak points crosses a zero level of the waveform; and Elapsed time to zero cross point of received wave And a calculating means for adding a predetermined offset time to the time measured by the measuring means and calculating a distance to the object to be measured based on the result of the addition. Dispensing device. 5. A dispensing apparatus in which a dispensing head (15) having a pipette (16) for sucking and discharging a liquid protruding downward is attached to an output portion of a head driving mechanism. On the side of), a transmission wave is emitted toward the measurement target, and a reception wave reflected and returned by the measurement target is received, and based on a time measurement from transmission of the transmission wave to reception of the reception wave. In a dispensing device in which an ultrasonic sensor for measuring a distance to a measurement target is attached downward, the ultrasonic sensor detects a plurality of peak points appearing in the waveform of a transmission wave and connects these peak points. First detecting means for detecting a zero crossing point at which the virtual envelope crosses the zero level of the waveform; detecting a plurality of peak points appearing in the waveform of the received wave; and forming a virtual envelope connecting these peak points at the zero level of the waveform. Zero crossing with Detecting means for detecting the time, a measuring means for measuring an elapsed time from a zero-cross point of a transmission wave to a zero-cross point of a receiving wave, and an operation for calculating a distance to a measurement object based on a time measurement value by the measuring means. Means for dispensing. 6. An object to be measured is a liquid surface of the liquid injected into the concave portion (21) of the plate (20). Tube piece (23) provided with
Is mounted downward, the ultrasonic path of the tubular piece (23),
The dispensing device according to claim 4 or 5, wherein the dispensing device is formed to have the same or substantially the same cross-sectional shape as the opening shape of the concave portion (21).