JP5589248B2 - Laser level gauge - Google Patents

Description

Detailed Description of the Invention

Industrial application fields

  A laser-type liquid level gauge is known as a known technique by projecting laser light onto a float floated on a measurement liquid surface and measuring the distance to the float with a laser distance meter. Laser type liquid level gauges with this method have little sensor deterioration over time due to the contacted method, and can be widely applied to water level measurement in chemical plant liquid level gauges, rivers, irrigation canals, and reservoirs. However, a laser rangefinder suitable for liquid level measurement is expensive. Since the method for calibrating the measurement distance and accurately projecting the laser beam on the float in the quenching tube has not been established, the spread has been delayed. Laser rangefinders are becoming cheaper for distance measurement for construction sites. The present invention provides a laser-type water level meter that facilitates calibration of the measurement liquid level and adjustment of the projection angle with respect to the float for wide industrial use.

The following exists as literature on a water level meter or a liquid level meter using a laser distance meter.
Japanese Patent Laid-Open No. 10-281854 JP 09-203652 A JP 01-123115 A JP 2006-258579 A JP 2010-249790 A A laser-type liquid level gauge using a laser distance meter that projects laser light onto a float in a quenching tube and obtains the distance to the water surface by reflected laser light is disclosed in the above-mentioned document as a known technique. However, with respect to these documents, a calibration method for the measurement distance and a method for aligning the optical axis of the projection laser beam to the float are not shown.
The calibration method of the measurement distance is generally simple and difficult to perform easily including other types of liquid level gauges. In a breaker tube having a small diameter and a long distance, it is important to facilitate the optical axis alignment of the laser light projected onto the float. The present invention provides a method for calibrating a measurement distance and a method for aligning the optical axis of a laser beam projected onto a float.

Level gauges are widely used in the fields of chemical plant tanks, water treatment storage tanks such as waterworks and sewers, rivers, and agricultural waterways. The problems to be solved are common in these fields, but the following are the problems focused on water level gauges such as rivers and agricultural canals.
Conventionally, as a representative water level gauge, a float type has been used as a mechanical method for water level gauges such as rivers, irrigation canals, dams, and reservoirs. This method converts the water level from the rotation angle of the reel that winds the wire attached to the float that moves up and down as the water level rises and descends. It can obtain a water level measurement accuracy of about ± 1 cm, but requires a large water measuring tube as a civil engineering structure. And For this reason, dams, large rivers, etc. have not been used much recently. However, since the float type does not cause an error other than mechanical factors such as expansion and contraction of the wire attached to the float, the accuracy can be maintained even if the calibration frequency is reduced.
As a typical contact-type water level meter that measures a water level by contacting a sensor portion with a measurement water surface, a hydraulic water level meter is often used. This method measures the water pressure proportional to the water depth with a pressure-sensitive element, and requires an air release tube to measure it compared to the atmospheric pressure. If the part is buried in sediments such as rivers, it causes measurement errors. For this reason, stability, which is a common problem for contact sensors, has become an issue.
As a non-contact water level meter, a radio wave type water level meter has recently been used in place of the ultrasonic water level meter.
Radio wave level gauges can measure stably over time because the sensor unit does not touch the water surface.
However, if there are floating objects on the water surface, it will cause errors. In addition, the radiation angle increases depending on the distance from the sensor, and there is a problem that it cannot be used if there are obstacles that block radio waves within the radiation angle.
Since both the water pressure level gauge and radio wave type water level gauge do not have a self-calibration function, the water level gauge cannot be calibrated by itself. For this purpose, as a calibration method, a water meter is provided in the vicinity of the water level gauge, and the scale of the water meter is visually observed and compared with the measured value.
The scale of the quantity water mark is at least 1 cm. However, due to the effects of waves, a calibration error of about ± 5 cm is often caused in practice.
The laser-type water level meter of the present invention does not require a large-scale water measuring tube unlike the float type, and the measurement accuracy deterioration inherent in the contact-type sensor due to the submerged sensor like the water pressure type water level meter This is a water level meter that has a self-calibration function that eliminates the disadvantages of having no self-calibration function, common to water pressure level meters and radio wave type water level meters, and that can be calibrated at water levels other than the actual water level.

The measurement principle of the laser-type water level meter is the same as that shown in [Patent Document 5] Japanese Patent Application Laid-Open No. 2010-249790. In this measurement principle, a wave-dissipating tube with a cavity inside is installed under the surface of the measurement water. A laser rangefinder is installed on the top of the quencher tube so that the projection optical axis position of the laser rangefinder is aligned with the center axis of the quencher tube, and the projection laser beam is sent from the laser rangefinder into the quencher tube.
Float floats on the water surface inside the wave-dissipating tube. The float moves up and down by the same distance as the water surface. The projected laser light floats, and the diffuse reflected light is received by a laser distance meter to determine the distance to the float.
Since the distance (L) between the upper end of the float and the water surface is always kept constant by the buoyancy of the float, the distance L between the upper end of the float and the water surface is added to the distance measured by the laser rangefinder. The distance of the water surface can be obtained accurately.
The wave-dissipating tube has a function to hold the float up and down due to water waves, a function to keep the float moving in the wave-dissipating tube, and a function to prevent an obstacle from entering between the laser distance meter and the float.
Also, the wave-dissipating tube is provided with a plurality of small holes or mesh-shaped holes for ingress and discharge of water and discharge of dust.

Description of the configuration and principle of the present invention is shown in FIG. 1, FIG. 2, and FIG. FIG. 1 shows a state at the time of calibration of the measurement distance and an optical axis alignment of the laser beam. FIG. 2 shows a state where the 13-hole perforated plate is released from the 14 flange, the 12 pulling wire is extended, and hangs down toward the 2 float for distance calibration and laser beam optical axis alignment. FIG. 3 shows a normal measurement state. In a normal measurement state, 4 projection laser beams are projected toward 2 floats from 11 measurement reference planes of a 6 laser rangefinder. The 4-projection laser light is diffusely reflected on the surface of the 15-float magnet or magnetic part, and the 5-reflection laser light returns to the 6-laser distance meter to measure the distance to the float.
Since the actual position of one measurement water surface is lower than the reflection surface of the float by a certain height L due to the buoyancy of the float, the water level is calculated by adding L to the value measured by the laser distance meter.
L is the height at which the float floats from the water surface due to buoyancy, and is a value unique to the float.
There is a 13-hole perforated plate between the laser distance meter and the float, but the laser beam can pass through the 21-hole perforated portion so that it does not hinder the passage. The 13-hole perforated plate is a magnet on both the upper and lower sides. In a normal measurement state, it is adsorbed and fixed by a magnetic force to a 14 flange made of a magnetic material.
FIG. 2 shows a preparation process for distance calibration and laser beam optical axis alignment. First, it is necessary to open the 13-hole perforated plate from the 14 flange that is attracted by magnetic force. As an example of the opening method, a thin rod is inserted into a 19-hole perforated plate opening hole penetrating up and down 14 flanges, and the 13-hole perforated plate is released from the thrust from above. After opening, the 12 pulling wire is extended, and the 13-hole perforated plate is extended until it reaches the float floating on the surface of 1 measurement water, and the magnet or magnetic part of 15 float is adsorbed. In the suction state, the 12 pulling wire is wound up by a 20 wire winding machine.
As for the winding position, the length of the 12 pulling wire is confirmed on the 11 measurement reference plane, and the winding is stopped at an arbitrary position where the measurement distance calibration or the optical axis alignment of the laser beam is performed. The length of the 12 pull-up wire on the 11 measurement reference plane can be easily measured by a method of marking the length of the wire, the rotation angle of the winding reel of the 20-wire hoisting machine, or the like.
In FIG. 1, the calibration method of the measurement distance is the calibration position, and the length of the 12 pulling wire on the 11 measurement reference plane is read. The value obtained by adding the height (h) of the 13-hole perforated plate and a certain height (H) protruding above the water surface due to buoyancy to this reading value is taken as the calibration value.
Next, read the measured water level of the laser rangefinder at this position, and add the value of the height H where the float floats from the water surface due to buoyancy, and compare it with the calibration value obtained from the wire length. Perform calibration.
The measured value of the laser rangefinder after calibration is converted into a water level signal and output from the laser rangefinder.
Laser beam optical axis alignment can also be performed by adsorbing a float to a 13-hole plate and lifting the float to an arbitrary distance.
The optical axis of the laser distance meter is arranged at the center of the cross section of the quenching tube, but the center of the optical axis of the laser distance meter is slightly shifted due to the arrangement accuracy. In order to correct this deviation, a 7-laser distance meter fine rotation mechanism that adjusts the optical axis of the laser distance meter to the left and right and the front and rear angles is provided. This rotating mechanism is fixed to a 14 flange, and the optical axis of the laser rangefinder can be swung left and right and back and forth with respect to the central axis of the quenching tube. The center of rotation of the swing angle is set to 11 measurement reference planes of the cross-sectional center of the wave-dissipating tube.
As shown in FIG. 4, a laser hole non-reflective band, a reflective band, and a non-reflective band are provided on the 13-hole perforated plate at equidistant positions in the coaxial direction. At the non-reflective band position, the projection laser light is absorbed and the reflection does not return to the laser rangefinder, making it impossible to measure the distance.
The optical axis of the projected laser beam is swung to the left and right by a fine rotation mechanism. As the swing angle increases to the left or to the right, the projected light leaves the float and is absorbed by the 32 inner non-reflective band due to the black band of the 13-hole plate. If the swing angle is further increased, the laser beam is reflected by the 33 reflection band by the white band.
The reflected light from the 22 left-handed reflection point or 23 right-handed reflection point returns to the laser rangefinder and the distance can be read. If further shaken, it is projected again on the 34 outer non-reflective band by the black band, and the reflected light does not return.
The water level measurement value of the laser-type water level meter in the reflection band is read by the readable white band, which is the changing point from the non-reflection band to the reflection band and from the reflection band to the non-reflection band. The difference between the water level measurements in the left and right reflection bands indicates the inclination of the perforated plate from the horizontal. For this reason, the level of the 13-hole perforated plate is confirmed from the magnitude of this difference. When the level is within the allowable value, the deflection angle of the fine movement rotating mechanism is read.
The deflection angles of the 22 left-handed reflection point and the 23 right-handed reflection point of the 13-hole plate are read, and the optical axis is aligned with the angle of the middle point of the 24 left-right reflection point being the center of the left and right quenching tubes. Similarly, the optical axis is swung back and forth, and the midpoint angle of the front and rear reflection points of the front and rear reflection points of the perforated plate is the front and rear reflection points of the front and rear reflection points of the front and rear reflection points. Align the optical axis as the center of the wave tube. After aligning the left, right, front, and rear optical axes, the 2 float and 13-hole plate are pulled up to the 14 flange position by the 12 pull-up wire in the suction state, and the 13-hole plate is pulled into the 14 flange by the magnetic force. In this state, it is necessary to release the 2 float from the 13-hole plate. An example of the opening method is to insert a thin rod into a 16 hole perforated plate vertically passing through 14 flanges and a separation hole of the float, and release from the thrust from the upper part. As a result of the opening, the float falls in the wave-dissipating tube to the water surface, and the normal measurement state shown in FIG.

The following effects can be obtained by solving the problems of the conventional water level gauge.
First, recently, water pressure gauges and radio wave level gauges are frequently used as water level gauges for rivers, irrigation canals, adjustment ponds, and the like. The water pressure type has a drawback that accuracy cannot be maintained unless it is frequently calibrated although the sensor part is a contact type depending on the use environment. Since the radio wave type is a non-contact type, the calibration frequency is less than that of the water pressure type, but has the disadvantage of causing an error due to the floating surface. The problem with both types is that the water level gauge alone cannot be calibrated. In either case, it is necessary to calibrate the measured value by installing a scale plate corresponding to the quantitative water mark at the time of calibration or contrast with the scale of the quantitative water mark installed in the vicinity. The laser-type liquid level gauge of the present invention can be calibrated with a single liquid level gauge, improving accuracy maintenance and facilitating maintenance.
Secondly, it incorporates an optical axis alignment function for accurately projecting the projection laser light in the quenching tube onto the float, facilitating adjustment at the installation site.

When the cross-sectional shape of the wave-dissipating tube in FIG. 3 is circular, in FIG. 5, when the radius r1 of the holed portion of the three-holed plate, the radius R2 of the float, and the inner diameter 2R1 of the wave-dissipating tube, The conditions for projecting to the 2 float through the perforated part of the 13 perforated plate are that the projection laser passes through the perforated part of the perforated plate regardless of the movement of the float in the wave breaker. Light needs to be able to project to the float. This condition is 2R2> r1 + R1
In addition, the float is in a condition that fits in the wave-dissipating tube. R2 <R1
It becomes.
Actually, considering the dimensional error of the wave-dissipating tube, float, and perforated plate, and the fact that the float and perforated plate can move freely in the wave-dissipating tube, it is necessary to allow the above-mentioned dimensions to have a margin. There is.
For example, when a wave breaker having a diameter 2R1 = 150 mm is used, if the float diameter 2R2 = 120 mm is set, r1 + R1 is 120 mm or less, and R1 is 75 mm, so r1 is 45 mm or less. R1 is set to 40 mm with a margin. Further, the outer shape 2r2 of the perforated magnet plate is set to 120 mm in accordance with the outer shape of the float. In this case, the difference between the inner and outer shapes of the perforated plate is 40 mm.

In FIG. 1, as a method of configuring a 7 laser rangefinder fine rotation mechanism, a goniometer stage that freely tilts the XY plane with respect to a vertical Z axis used for camera fine adjustment head, device attitude adjustment, sample tilt rotation, etc. The adoption of a so-called rotation mechanism can be considered. Here, an example is shown in which a gonio stage capable of rotating with a small size and high accuracy is applied. In general, the gonio stage is often used with a device or the like fixed on the stage. Here, the gonio stage is turned upside down, and the laser distance meter is fixed to the downward stage and rotated. FIG. 6 shows the deflection angle of the laser light projected on the lower 13-hole plate with respect to the 11 measurement reference plane. As an example, the diameter of the 13-hole plate is 120 mm as shown in [0007]. When the distance to the perforated plate is 10 m, the deflection angle of the fine rotation mechanism relative to this is θ1 = 0.69 degrees.
As an example of a commercially available goniometer stage, there is a product called an αβ-axis goniometer stage, which has a plane that is up to ± 15 degrees in the X-axis (left-right direction) and Y-axis (front-rear) direction and about a few minutes with respect to the vertical axis. Can be shaken with accuracy. Incidentally, the αβ-axis gonio stage can swing an angle of 2 to 3 degrees per rotation by operating the rotary knob independently of the X-axis (left-right direction) and Y-axis (front-back direction).
Assuming that the distance to the perforated magnet plate is 1 m, the swing angle of the fine rotation mechanism relative to this is θ2 = 6.9 degrees. In this case, if the rotation knob swinging 6.9 degrees is set to 2 degrees per rotation, it will be rotated three or more times, and the optical axis can be aligned with high accuracy by obtaining the midpoint. Thus, the midpoint of the projection laser beam has an advantage that it can be easily combined with high accuracy by shortening the measurement distance.

The float is subjected to white processing to diffusely reflect the projected light. For better reflection, optimal reflection can be achieved by placing a directional reflective material on the float upper surface. The directional reflective material has a reflection characteristic in which reflected light returns in the same direction as the projection direction.
A directional reflective material is disposed on the float to reflect 5 reflected laser light in the direction of 4 projected laser light. The five-reflection laser light reflected from the directional reflection material is reflected at a narrow reflection angle with respect to the same direction as the four projection light, and can be efficiently received by the laser distance meter. As the directional reflecting material, a sheet in which a large number of small prisms are arranged has been put into practical use. In addition, steel pipes, vinyl chloride pipes, etc. are used as the three extinguishing tubes, but if the optical reflectivity of the inner surface of the tube is large, distance measurement becomes an obstacle when large irregularly reflected light enters the laser receiver. In order to reduce the amount of the irregularly reflected light entering the laser receiver, a black coating process is performed to absorb the irregularly reflected light.

In the present invention, the 13-hole plate is adsorbed by a magnetic force to a 14 flange and 15 float magnet or magnetic part. In this case, the combination of the coupling methods includes a permanent magnet and an electromagnet in the case where one is a magnet and the other magnet is a magnetic body or a magnet. These combinations are selected depending on the physical shape and the way of releasing the magnetic force. In the section [Means for Solving the Problems], as a method of releasing the adsorption by the magnetic force between the 13-hole perforated plate and the 2-float, the 13-hole perforated plate and the 2-float are separated by using a thin rod in the hole provided on the 14 flange. Although the method of inserting and pushing down has been described as an example, by using electromagnetic force, the float can be lowered to the water surface by extending the wire to lower the float to near the water surface and releasing the electromagnetic force. In this case, the 13-holed plate needs to have an electromagnet. The power supply in this case supplies electricity to the electromagnet using 12 pulling wires as electric wires. In addition, the shape of the magnet and the magnetic material applied to the float, the perforated plate, and the flange can be selected in various ways in consideration of adsorption and separation by magnetic force. Note that the flange and the perforated plate have an option to hold the central perforated plate in a pulled state with a pulling wire regardless of the magnetic force.

It shows the state of calibration of the measurement distance and the alignment of the optical axis of the laser beam. The preparation process of measurement distance calibration and laser beam optical axis alignment is shown. A normal distance measurement state is shown. Explanatory drawing of the optical axis alignment method by the laser beam projected to a perforated board. Explanatory drawing of the inside diameter of a wave-dissipating tube, the float outer diameter, the outer diameter of a perforated board, and the constraint conditions of a hole diameter. Explanatory drawing of the difficulty by the distance of the optical axis alignment of a projection laser beam.

Claims (2)

A hollow tube with a hollow inside,
A float that floats on the surface of the measurement liquid inside the cavity;
A laser distance meter disposed at the top of the quencher tube and measuring the distance to the float;
A perforated plate disposed above the float inside the cavity, suspended from the top by a pulling wire, and provided with a hole through which a laser beam projected to the float by the laser distance meter is provided;
Comprising a wire hoisting machine for moving said perforated plate up and down by the hoisting of the pulling wire,
When the perforated plate is lowered until it reaches the float and then wound by the wire winder, the float is wound up in a state of being attracted to the perforated plate by a magnetic force,
Ri can der to measure the length of the measurement reference surface of the pulling wire rolled up by the wire wind-up machine,
When the perforated plate with the float adsorbed is wound up to the calibration position by the wire hoisting machine, the length reading value on the measurement reference plane of the pulling wire and the laser distance meter reading value Based on this, a laser level gauge capable of calibrating the measurement distance by the laser distance meter. A hollow tube with a hollow inside,
A float that floats on the surface of the measurement liquid inside the cavity;
A laser distance meter disposed at the top of the quencher tube and measuring the distance to the float;
A perforated plate disposed above the float inside the cavity, suspended from the top by a pulling wire, and provided with a hole through which a laser beam projected to the float by the laser distance meter is provided;
A wire hoisting machine that moves the perforated plate up and down by winding the hoisting wire;
When the perforated plate is lowered until it reaches the float and then wound by the wire winder, the float is wound up in a state of being attracted to the perforated plate by a magnetic force,
It is possible to measure the length at the measurement reference plane of the lifting wire wound up by the wire winding machine,
Furthermore, with the center axis of the quenching tube as a reference, it comprises a laser distance meter fine rotation mechanism that can adjust the angle of the optical axis of the laser distance meter to the left and right and back and forth,
The perforated plate is a band that is equidistant from the center of the hole and absorbs the laser light, and a band that is equidistant from the center of the hole outside the inner nonreflective band. A laser-type liquid level gauge provided with a reflection band that reflects laser light and an outer non-reflection band that is equidistant from the center of the hole outside the reflection band and absorbs the laser light.

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