JP6605096B1 - Optical liquid level measuring device - Google Patents

Abstract

[PROBLEMS] In the field of an optical liquid level measuring device for measuring a liquid level, it has been expected to realize a device that is less affected by the state of the liquid surface during measurement, consumes less power, and is less expensive. . A boundary surface of a semiconductor laser, a collimating optical system that collimates a laser beam output from the semiconductor laser in a liquid level change direction, and a laser beam incident through the collimating optical system If the medium in contact with air is totally reflected, but the medium in contact with the boundary surface is liquid, the prismatic prism having a liquid level detection surface that transmits to the liquid side and the amount of laser light totally reflected by the liquid level detection surface An optical liquid level measuring device comprising: a photosensor for measuring the liquid level. [Selection] Figure 1

Description

  The present invention relates to an apparatus for measuring a liquid level using a laser light source and a light receiving element, and more particularly to an optical liquid level measuring apparatus capable of measuring a liquid level with low power consumption.

  In recent years, the level of liquid level has been measured in various places such as rivers, lakes, reservoirs, irrigation channels, paddy fields, pools, aquaculture ponds, harbors, closed spaces such as tanks, etc. There are a variety of fields such as hydropower generation and agricultural use.

  As a device for measuring the level of the liquid level, an optical measuring device is known in addition to the float type, electrode type, pressure type, etc., but the optical measuring device is compared with other methods. There are advantages such as no need for moving parts and no need for electrical contact with the liquid, and the usable range is wide.

  For example, Patent Document 1 discloses a method in which an infrared laser is emitted to irradiate a water surface, reflected light from the water surface is received by a light receiving device, and a distance to the water surface is obtained based on the time from light emission to light reception. ing.

  Patent Document 2 discloses an apparatus in which a plurality of light emitting units and a plurality of light receiving units corresponding to the respective light emitting units are arranged along the longitudinal direction of the prism. When the inclined surface of the prism is in contact with air, the light is reflected by the inclined surface and is incident on the light receiving element. However, when the inclined surface of the prism is in contact with water, the light is not reflected. It does not enter. It is measured to what level air (water) exists depending on which light receiving element is detected (not) from among the plurality of light receiving elements.

JP 2006-258579 A JP 2014-10055 A

  In the apparatus described in Patent Document 1, distance measurement is performed using reflected light from the water surface, but errors are likely to occur due to the influence of the surface state of the water such as the presence of waves and suspended solids, and the measurement accuracy is increased. Requires complicated data processing such as determining the validity of data.

  Moreover, in the apparatus described in Patent Document 2, in order to increase the depth at which the water level can be measured and increase the measurement resolution, it is necessary to install a large number of pairs of light emitting units and light receiving units along the longitudinal direction of the prism. In addition, the power consumption increased and the device became expensive. In addition, the apex angle of the prism was easily damaged.

  Therefore, it has been expected to realize an optical liquid level measuring device that is not easily affected by the state of the liquid surface during measurement, consumes less power, and is inexpensive.

The present invention relates to a semiconductor laser, a collimating optical system that collimates the laser light output from the semiconductor laser in a liquid level change direction, and the laser light that is incident via the collimating optical system. When the medium in contact with the boundary surface is air, it is totally reflected, but when the medium in contact with the boundary surface is the liquid, a prismatic prism having a liquid level detection surface that transmits to the liquid side and total reflection at the liquid level detection surface the amount of the laser beam have a, a photo sensor for measuring the said semiconductor direction parallel to the PN junction plane of the laser, the semiconductor laser so as to be parallel with the liquid level changing direction is disposed, that An optical liquid level measuring device characterized by the following.

  According to the present invention, it is possible to provide an optical liquid level measuring device that is not easily affected by the state of the liquid surface during measurement, consumes less power, and is inexpensive.

FIG. 3 is a schematic top view showing the configuration of the optical liquid level measuring apparatus according to the first embodiment. (A) The typical side view which shows the incident optical path to the prism 4 surface prism of Embodiment 1. FIG. (B) The typical side view which shows the incident optical path to the photosensor of Embodiment 1. FIG. FIG. 3 is a diagram illustrating a shape of a prismatic quadrilateral prism according to the first embodiment. (A) The figure which shows the desirable installation direction of a semiconductor laser. (B) The figure which shows the installation direction of a semiconductor laser. (A) The figure which shows the far field pattern of the output light of a semiconductor laser. (B) A graph showing the relationship between the liquid level and the amount of light received by the photosensor. (A) The top view which installed the optical liquid level measuring apparatus of embodiment in the water storage facility. (B) The side view which installed the optical liquid level measuring apparatus of embodiment in the water storage facility. The block diagram which shows typically the functional block of the electric system of the optical liquid level measuring apparatus of embodiment. The figure which shows the shape of the modification of a prismatic quadrilateral prism. FIG. 4 is a schematic side view showing an incident optical path to a prismatic quadrilateral prism of Embodiment 2. (A) The typical top view which shows the structure of the optical liquid level measuring apparatus of Embodiment 3. FIG. (B) The typical side view which shows the structure of the optical liquid level measuring apparatus of Embodiment 3. FIG. FIG. 6 is a schematic side view showing a configuration of an optical liquid level measurement device according to a fourth embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
[Embodiment 1]
FIG. 1 is a schematic top view for explaining the configuration of the optical liquid level measuring apparatus according to the first embodiment. A semiconductor laser 11 that functions as a light source unit and a photosensor 21 that functions as a light receiving unit are mounted on a substrate 31. These constitute the light projecting / receiving unit 32 as an integral unit. Reference numeral 51 denotes a prismatic quadrilateral prism which is a prismatic prism having four optical surfaces, 51A is a laser light incident / exit surface, 51B and 51C are total reflection surfaces, and 51D is a liquid level detection surface.

FIG. 2A is a schematic side view for explaining an optical path when the laser light emitted from the semiconductor laser 11 reaches the prismatic quadrilateral prism 51 and is totally reflected or transmitted by the liquid level detection surface 51D. is there.
FIG. 2B is a schematic side view for explaining an optical path in which the laser light reflected by the liquid level detection surface 51D of the prismatic quadrilateral prism 51 enters the photosensor 21.
In FIG. 1, FIG. 2 (a), FIG. 2 (b), the same number is attached | subjected to the same component, The liquid level change direction from which the height of the liquid used as a detection object changes is shown in a figure. It is the Y-axis direction.

  The laser light emitted from the semiconductor laser 11 passes through a cylindrical lens 41 having a curvature only in the X-axis direction, and is collimated in parallel with the Z-axis direction as viewed from above as shown in FIG.

  The laser beam that has passed through the cylindrical lens 41 passes through the cylindrical lens 42 having a curvature only in the Y-axis direction, and is condensed at the focal point f when viewed from the side as shown in FIG. The optical system is arranged so that the luminous flux becomes wider in the Y-axis direction as it goes from the focal point f, but this makes it possible to irradiate a wide range in the liquid level change direction with the laser beam, thereby increasing the liquid level measurement range. It is to do.

  The laser beam expanded widely in the Y-axis direction is collimated parallel to the Z-axis direction by passing through a wide cylindrical lens 45 having a curvature only in the Y-axis direction. As is clear from FIGS. 1 and 2A, the laser light that has passed through the wide cylindrical lens 45 becomes a light beam that is substantially parallel to the Z axis in both the XZ plane and the YZ plane, and enters and exits the prism 4 prism 51. Incident on the surface 51A.

  As described above, the cylindrical lens 41, the cylindrical lens 42, and the wide cylindrical lens 45 constitute a collimating optical system that collimates the laser light output from the semiconductor laser in the liquid level change direction.

  Since the incident / exit surface 51A of the prismatic quadrilateral prism 51 is arranged in parallel with the XY plane, the laser light is incident on the incident / exit surface 51A perpendicularly and travels in the prism toward the total reflection surface 51B.

Here, the total reflection surface 51B will be described. As is well known, when light enters a material with a high refractive index from a material with a low refractive index, total reflection occurs when the incident angle is larger than a certain angle. This angle is called a critical angle. If the critical angle is I and the refractive indexes of both substances are n1 and n2, the following relationship is established. (However, n1> n2.)
[Equation 1]
I = arc · sin (n2 / n1)

For example, when glass having a refractive index n1 of 1.52 is used as the material of the prismatic quadrilateral prism 51, if the medium in contact with the boundary surface is air (refractive index n2 _air = 1.00), the critical angle I _air Is 41.14 degrees. If the liquid whose liquid level is to be measured is water (refractive index n2 _water = 1.33), the critical angle I _water is 61.05 degrees.

  Therefore, in the case of the present embodiment, the target for measuring the liquid level is water, and the laser beam is totally reflected regardless of whether the medium in contact with the total reflection surface 51B is air or water. Set the angle. Specifically, as shown in FIG. 1, the prismatic quadrilateral prism 51 is designed so that the incident angle of the laser beam on the total reflection surface 51B is 65 degrees. Of course, this is only an example, and even if the liquid level measurement target is water, it does not necessarily have to be 65 degrees. If the liquid to be measured changes, the angle may be appropriately changed according to the critical angle. .

  The laser light reflected by the total reflection surface 51B travels in the prism toward the liquid level detection surface 51D. The liquid level detection surface 51D is a surface that totally reflects the laser light if the medium in contact is air, and transmits the laser light to the liquid side if the liquid is a liquid level measurement target. The liquid level detection surface 51D is arranged so as to be parallel to the XY plane, and the laser light reflected by the total reflection surface 51B is incident on the liquid level detection surface 51D.

As described above, when the medium is air, the critical angle I _air is 41.14 degrees, and when the medium is water, the critical angle I _water is 61.05 degrees, but the liquid level detection surface 51D has an incident angle. It is designed to be 50 degrees as shown in FIG. Since the incident angle is designed in the vicinity of the intermediate value between the critical angle I _air and the critical angle I _water , the liquid level is detected even if a slight error occurs in the shape and arrangement of the prismatic prism 51 with respect to the design value. Depending on whether the medium in contact with the surface 51D is air or water, the laser beam can be reliably totally reflected or transmitted. As indicated by the dotted line in the figure, in the region of the liquid level detection surface 51D that is in contact with water, the laser light is transmitted through the liquid level detection surface 51D. Conversely, in the region in contact with air, the laser light is totally reflected by the liquid level detection surface 51D and travels through the prism toward the total reflection surface 51C as indicated by the solid line in the figure. Therefore, the lower the liquid level, the more laser light is totally reflected by the liquid level detection surface 51D, and the higher the liquid level, the less laser light is totally reflected.

  Since the total reflection surface 51C is symmetrical with the total reflection surface 51B with respect to the Z-axis direction, the laser light totally reflected by the liquid level detection surface 51D enters the total reflection surface 51C with an incident angle of 65 degrees. For this reason, on the total reflection surface 51C, the laser light is totally reflected regardless of whether the medium in contact with the boundary surface is air or water.

  In addition, although the case where the object whose liquid level is measured is water having a refractive index of 1.33 has been described here, the object to be measured by the liquid level measuring apparatus of the present invention is not limited to water. When measuring the liquid level of a liquid having a refractive index different from that of water, the angle between the total reflection surface 51B and the total reflection surface 51C may be adjusted according to the refractive index of the liquid. That is, the angle is adjusted so that the laser beam is totally reflected between the total reflection surface 51B and the total reflection surface 51C regardless of whether the boundary surface is in contact with air or the liquid. In addition, the angle may be adjusted so that the incident angle of the laser light when entering the liquid level detection surface 51D is between the critical angle of air and the critical angle of the liquid, preferably near the center of both.

  Further, the prism 4 prism 51 does not have to use glass having a refractive index n1 of 1.52, but various glasses such as blue plate glass and optical glass BK7 (nd = 1.51 to 1.52). Alternatively, plastic (nd = 1.47 to 1.50) that can be easily molded can be used. Of course, when different materials are used, the angle of each surface may be set with reference to the critical angle in the combination of the material and air or liquid.

  In designing the prismatic quadrilateral prism, as shown in FIG. 3, when the optical path of the collimated laser beam is set to the Z-axis direction, it is necessary to determine an angle θ that the total reflection surface 51B makes with the Z-axis direction.

Since the incident angle IB of the laser beam with respect to the total reflection surface 51B is IB = 90 ° −θ, the critical angle of the medium and the air of the prismatic _tetrahedral prism is I _air , and the critical angle of the medium and the liquid of the prismatic tetrahedral prism is If it is I _liquid , it is necessary to satisfy the following relationship.
[Equation 2]
90 ° -θ> I _air
[Equation 3]
90 ° -θ> I _liquid

Further, since the incident angle ID at which the laser beam reflected by the total reflection surface 51B enters the liquid level detection surface 51D is ID = 2 × θ, it is necessary to satisfy the following relationship.
[Equation 4]
I _liquid > 2 × θ> I _air

  In the prismatic quadrilateral prism, the part off the optical path is a structural material part that does not act optically. Therefore, as long as there is no problem in strength, lightening and saving of material are performed by removing the thickness and chamfering. Can be achieved. FIG. 8 shows an example of such a prism. A concave portion 51E and a chamfered portion 51F are provided in a portion that does not interfere with the optical path. In the case of this form, 51Ain is the entrance surface and 51Aout is the exit surface.

  Returning to FIG. 1 and FIG. 2B, the laser light totally reflected by the total reflection surface 51 </ b> C is perpendicularly incident on and transmitted through the incident / exit surface 51 </ b> A and enters the wide cylindrical lens 45. As shown in the figure, the laser beam is condensed toward the focal point f in the YZ plane by the wide cylindrical lens 45, but as shown in FIG. 1, the laser beam is parallel to the Z-axis direction in the XZ plane. Maintaining sex.

  The cylindrical lens 47 and the cylindrical lens 46 are lenses having a condensing characteristic having the same function as the cylindrical lens 41 and the cylindrical lens 42, respectively. Due to the action of these cylindrical lenses, the laser light totally reflected by the liquid level detection surface 51D is condensed on the light receiving portion of the photosensor 21, as shown in FIGS. 1 and 2B. Note that the cylindrical lens 47 and the cylindrical lens 46 are not limited to the same power as the cylindrical lens 41 and the cylindrical lens 42 as long as they can collect light on the light receiving portion of the photosensor 21.

  The intensity of the laser beam received by the photosensor 21 decreases as the liquid level to be measured increases, and increases as the liquid level decreases. If the relationship between the liquid level and the photosensor output is calibrated in advance and stored in the control unit, the liquid level can be measured in real time based on the output of the photosensor 21.

  The intensity of the laser beam received by the photosensor 21 changes according to the height of the liquid level. A configuration for improving the linearity of the change in the amount of received light with respect to the change in the liquid level will be described next.

  In the present embodiment, a semiconductor laser is used for the light source unit. The reason is that a non-coherent light source other than a laser such as an LED has a large area of the light emitting unit. This is because it is difficult to obtain a wide and uniform light beam with a high degree of light. Of the laser light sources, the semiconductor laser is particularly suitable for use in the embodiment of the present invention because it has a small light emitting area and has a compact device and low power consumption.

By the way, it is known that the output light of the semiconductor laser has different angle characteristics depending on the emission direction. In general, the apparent focal position differs in a direction parallel to the direction orthogonal to the PN junction surface of the semiconductor laser, and the distance between the two focal points may be referred to as an astigmatic difference.
FIG. 5A illustrates the far field pattern of the output light from the semiconductor laser. It can be seen that the parallel direction is a pattern in which a beam having a uniform intensity distribution is emitted within a narrow angle range. On the other hand, in the orthogonal direction, it can be seen that the light is emitted in a pattern in which the intensity distribution is a mountain shape over a wide angle range.

  In the liquid level measurement device of this embodiment, as shown in FIGS. 1, 2A, and 2B, it is necessary to collimate the measurement light incident on the quadrangular prism 51 along the Z-axis direction. There is. The light beam collimated along the Z-axis direction does not need to be widened in the X-axis direction, but is widened to ensure a wide measurement range in the Y-axis direction, which is the liquid level change direction. There is a need.

  Therefore, a cylindrical lens having a curvature only in the X-axis direction and a cylindrical lens having a curvature only in the Y-axis direction are used in combination. As a method for installing the semiconductor laser 11, as shown in FIG. An arrangement in which the parallel direction is parallel to the Y-axis direction and an arrangement in which the parallel direction is parallel to the X-axis direction as shown in FIG. 4B can be considered.

  In the case of the arrangement shown in FIG. 4 (a), as can be seen from the angular characteristics in the parallel direction shown in FIG. 5 (a), if the luminous flux is spread in the Y-axis direction, which is the liquid level change direction, A light beam having a uniform intensity and a small distribution can be formed over the entire region. For this reason, as shown in the graph 100 of FIG. 5B, the linearity of the change in the amount of received light (intensity) of the laser light received by the photosensor 21 with respect to the change in the liquid level (liquid level) is high. Therefore, it is easy to calculate the liquid level based on the output signal of the photosensor 21, and the error is small at any height in the liquid level fluctuation range.

  On the other hand, in the case of the arrangement of FIG. 4 (b), as can be seen from the angular characteristics in the orthogonal direction shown in FIG. Distribution occurs in the light intensity along the Y-axis direction, which is the direction, and in particular, the intensity of light that irradiates the low and high liquid level positions becomes weak. For this reason, as shown in the graph 101 of FIG. 5B, the linearity of the change in the amount of received light (intensity) of the laser light received by the photosensor 21 with respect to the change in the liquid level (liquid level). Low. For example, when the liquid level is at a low position or at a high position, the sensitivity to changes in the liquid level is less than that when the liquid level is near the center. In order to improve the non-uniformity of sensitivity, it is possible to cut out the light at the base of the mountain of the graph in the orthogonal direction in FIG. Since the cut light is not used effectively, the energy utilization efficiency is reduced.

  Therefore, as a preferred embodiment, in the apparatus shown in FIGS. 1, 2A, and 2B, the semiconductor laser 11 is arranged in the direction shown in FIG. That is, the semiconductor laser 11 is arranged so that the direction parallel to the PN junction surface is parallel to the liquid level change direction. Since the output light of the semiconductor laser 11 has a large spread angle in the X-axis direction, which is an orthogonal direction, the cylindrical lens 41 having a curvature only in the X-axis direction is more semiconductor than the cylindrical lens 42 having a curvature only in the Y-axis direction. It is arranged on the side close to the laser 11. By arranging the cylindrical lenses in this order, these cylindrical lenses (device size) can be made compact.

  The cylindrical lenses 41, 42, 45, 46, and 47 may be formed of a plastic material in addition to a glass material, and may have an aspherical cross section. Since precise imaging characteristics such as imaging aberration are not a problem in many cases, a plate-shaped Fresnel lens may be used in place of the cylindrical lens to make the apparatus compact. Further, the cylindrical lens 41 and the cylindrical lens 47, and the cylindrical lens 42 and the cylindrical lens 46 may be formed on the same plate.

  Next, in the plan view of FIG. 6 (a) and the side view of FIG. 6 (b), the optical liquid level measuring device of the present embodiment is installed in a water storage facility such as a reservoir, paddy field, pool, aquaculture pond or the like. It is the figure which showed the example typically. Although details are omitted for the sake of schematic illustration, water 104 is stored in the water storage tank 103, and the optical liquid level measurement device 102 of this embodiment is installed on the outer edge of the tank. The quadrangular prism 51 has a sufficient length in the Y-axis direction so that the water level in a range that can be stored in the water storage tank 103 can be measured. Electrical components mounted on the apparatus, including the semiconductor laser 11, the photosensor 21, and the substrate 31, are protected by a waterproof structure (not shown).

  FIG. 7 is a block diagram schematically showing functional blocks of an electric system of the optical liquid level measuring device according to the embodiment. The optical liquid level measuring device of the present invention is capable of measuring continuous liquid level changes with low power consumption and high accuracy, and has no moving parts such as a float. It can be used for various purposes regardless of the outdoors. Moreover, in recent years, in various fields such as agriculture, aquaculture, power generation, and disaster prevention, there is a strong demand for measuring the liquid level at a remote place with a telemeter and transmitting the current data to a management center.

  Therefore, as shown in FIG. 7, the apparatus according to the present embodiment includes a functional block for enabling battery driving and communication. In the figure, 105 is a control unit, 106 is a solar panel, 107 is a storage battery, 108 is a communication unit, and 109 is a temperature sensor.

  The solar panel 106 is a main or spare power source. Although it is desirable to use a solar power generation type power supply in order to reduce the environmental load, wind power generation, a fuel cell, other power generation system power supply, or a normal power supply line may be provided depending on the installation location and application. Since the electricity generated by the power source is stored by the storage battery 107, the apparatus of this embodiment can continuously and stably observe the liquid level.

  The communication unit 108 is a communication device for transmitting and receiving data and commands to and from the management center, and can be connected to the Internet by wireless communication or wired communication.

  The control unit 105 is a computer for controlling various operations of the optical liquid level measuring device, and includes a CPU, a ROM, a RAM, an I / O port, and the like. The ROM stores a basic operation program of the optical liquid level measuring device. A program for executing various operations other than the basic operation may be stored in the ROM as with the basic operation program, but may be loaded into the RAM from the outside via the communication unit 108. Alternatively, the program may be loaded into the RAM via a computer-readable recording medium that records the program.

  The I / O port is connected to an external device or a network via the communication unit 108. For example, the liquid level measurement data is continuously transmitted to the management center computer, or a measurement request is received from the management center computer. can do.

  The control unit 105 measures the temperature of the semiconductor laser 11 or the photosensor 21 using the temperature sensor 109, and corrects the liquid level measurement result based on the temperature characteristics of the semiconductor laser 11 or the photosensor 21 to increase the measurement accuracy. be able to. Moreover, the control part 105 can also measure the temperature of the liquid and air | atmosphere to be measured using the temperature sensor 109, and can also transmit to a computer of a management center with liquid level measurement data. The control unit 105 can not only transmit these measurement data to the computer of the management center but also record them in its own memory or an external memory.

  According to the optical liquid level measuring apparatus of the present embodiment described above, since a single semiconductor laser and a single light receiving element are used, a low cost and low power consumption apparatus can be provided. In addition, despite the use of a single semiconductor laser and a single light receiving element, it is possible to measure the liquid level continuously with high linearity rather than discretely. In addition, unlike the apparatus of Patent Document 1, it is not a method of irradiating the liquid surface with laser light, so that measurement can be performed without being affected by the state of the liquid surface.

[Embodiment 2]
With reference to FIG. 9, the optical liquid level measurement apparatus of Embodiment 2 is demonstrated. FIG. 9 is a schematic side view corresponding to FIG. 2A used in the description of the first embodiment. Elements common to the first embodiment are denoted by the same reference numerals. In the description of the second embodiment, the description common to the first embodiment is omitted.

  The second embodiment is different from the first embodiment in that an optical axis rotating mirror 61 is disposed between the light projecting / receiving unit 32 and the prismatic quadrilateral prism 51. More specifically, an optical axis rotating mirror 61 is provided between the focal point f and the wide cylindrical lens 45. By adopting such an optical system, the length in the Z-axis direction of the apparatus can be shortened to make it compact, so that the space utilization efficiency when the apparatus is mounted on the edge of the tank or tank is improved. Further, since the light projecting / receiving unit 32 can be disposed above the quadrangular prism or the highest liquid level of the liquid, the semiconductor laser 11 and the photosensor 21 can be connected even if the liquid enters the apparatus due to an unexpected situation. The possibility that the mounted substrate 31 contacts the liquid can be reduced.

  Also in this embodiment, the cylindrical lens 41, the cylindrical lens 42, and the wide cylindrical lens 45 constitute a collimating optical system that collimates the laser beam output from the semiconductor laser in the liquid level change direction. .

  According to the optical liquid level measuring apparatus of this embodiment, since a single semiconductor laser and a single light receiving element are used, a low-cost and low-power-consumption apparatus can be provided. In addition, despite the use of a single semiconductor laser and a single light receiving element, it is possible to measure the liquid level continuously with high linearity rather than discretely. In addition, unlike the apparatus of Patent Document 1, it is not a method of irradiating the liquid surface with laser light, so that measurement can be performed without being affected by the state of the liquid surface.

[Embodiment 3]
With reference to FIG. 10 (a) and FIG.10 (b), the optical liquid level measuring apparatus of Embodiment 3 is demonstrated. FIG. 10A is a schematic top view corresponding to FIG. 1 used in the description of the first embodiment, and FIG. 10B is a schematic side view. Elements common to the first embodiment are denoted by the same reference numerals. In the description of the third embodiment, description of matters common to the first embodiment is omitted.

  The present embodiment employs a configuration in which an optical path is separated by a polarization beam splitter (PBS) using the fact that the output light of the semiconductor laser 11 is a linear wave having a vibration direction in a parallel direction. The length in the direction is shorter than that in the first embodiment.

  As shown in FIG. 10A and FIG. 10B, in this embodiment, the laser light emitted from the semiconductor laser 11 is converted into the Z axis by the cylindrical lens 41 and the cylindrical lens 42 in the XZ plane and the YZ plane. A PBS 64 which is a polarization beam splitter is disposed at a position collimated to be parallel. At this time, the light from the light source is set in a vibration direction parallel to the separation direction surface of the PBS 64. That is, the collimated laser beam is configured to enter the PBS 64 as a P wave. The PBS 64 transmits the P wave of the output wavelength of the semiconductor laser and reflects the S wave. In the figure, a prism type is shown as the polarization beam splitter, but it may be a plate type.

  The light transmitted through the PBS 64 passes through the quarter-wave plate 63 and is collected at the focal point f by the cylindrical lens 43 having a curvature only in the Y-axis direction. Since the Y-axis direction is the direction in which the liquid level fluctuates, it is necessary to produce a wide luminous flux. Therefore, as in the first embodiment, the curvature is only given in the Y-axis direction for collimating the light spreading from the focal point f in the vicinity of the quadrangular prism. A wide cylindrical lens 45 is disposed. However, the width in the X-axis direction of the wide cylindrical lens 45 of the present embodiment may be about half that of the first embodiment as is apparent from comparison with FIG. With this configuration, the light emitted from the wide cylindrical lens 45 becomes substantially parallel to the Z axis in both the XZ plane and the YZ plane.

  Also in this embodiment, the cylindrical lens 41, the cylindrical lens 42, and the wide cylindrical lens 45 constitute a collimating optical system that collimates the laser beam output from the semiconductor laser in the liquid level change direction. .

  The laser light emitted from the wide cylindrical lens 45 enters the incident / exit surface 52A of the prismatic quadrilateral prism 52 substantially perpendicularly. When viewed from the top surface (Y-axis direction), the prismatic quadrilateral prism 52 of the present embodiment has a shape that is cut in half along the YZ plane of the prismatic quadrilateral prism 51 of the first embodiment. A surface corresponding to the cut surface when cut in half is covered with a reflective material to form a reflective surface 52C.

The light incident on the incident / exit surface 52A of the quadrangular prism 52 is totally reflected by the total reflection surface 52B. Similar to the total reflection surface 51B in the first embodiment, the total reflection surface 52B is set to an angle at which the medium in contact with the boundary surface is totally reflected regardless of whether it is air or liquid. The light totally reflected by the total reflection surface 52B is directly incident on the liquid level detection surface 52D, or is incident on the liquid level detection surface 52D after passing through the reflection surface 52C. Regardless of which path is used, the incident angle is larger than the critical angle I _{air and} smaller than the critical angle I _water. Therefore, if the medium in contact with the liquid level detection surface 52D is air, the laser beam is totally reflected and contacted. If the medium is a liquid, the laser beam is transmitted toward the liquid.

  The light totally reflected by the liquid level detection surface 52D is directly incident on the total reflection surface 52B, or enters the total reflection surface 52B after passing through the reflection surface 52C. The light reflected by the total reflection surface 52B passes through the incident / exit surface 52A and enters the wide cylindrical lens 45 as return light traveling in the negative direction of the Z axis.

  The return light is collected by the wide cylindrical lens 45 so as to go to the focal point f in the YZ plane, and after passing through the focal point f, is collimated by the cylindrical lens 43 in parallel with the Z axis in the YZ plane. A slit 62 for cutting harmful light that becomes noise may be provided in the vicinity of the focal point f. The collimated light is converted into an S wave by the quarter wavelength plate 63, reflected by the PBS 64, and the optical path is changed in the negative direction of the Y axis. That is, the optical path of the return light is separated from the forward optical path from the semiconductor laser 11 toward the prismatic quadrilateral prism 52.

  The separated light is reflected by the mirror 65 toward the light projecting / receiving unit 32, and is collected by the condenser lens 48 having a condensing function in both the X-axis direction and the Y-axis direction, and then enters the photosensor 21. To do.

  According to the optical liquid level measuring apparatus of this embodiment, since a single semiconductor laser and a single light receiving element are used, a low-cost and low-power-consumption apparatus can be provided. In addition, despite the use of a single semiconductor laser and a single light receiving element, it is possible to measure the liquid level continuously with high linearity rather than discretely. In addition, unlike the apparatus of Patent Document 1, it is not a method of irradiating the liquid surface with laser light, so that measurement can be performed without being affected by the state of the liquid surface.

[Embodiment 4]
With reference to FIG. 11, the optical liquid level measurement apparatus of Embodiment 4 is demonstrated. FIG. 11 is a schematic side view corresponding to FIG. 10B used in the description of the third embodiment. Elements common to the third embodiment are denoted by the same reference numerals. In the description of the fourth embodiment, the description common to the third embodiment is omitted.

  The fourth embodiment is different from the third embodiment in that an optical axis rotating mirror 61 is disposed between the light projecting / receiving unit 32 and the prismatic quadrilateral prism 52. More specifically, an optical axis rotating mirror 61 is provided between the focal point f and the wide cylindrical lens 45. By adopting such an optical system, the length in the Z-axis direction of the apparatus can be shortened to make it compact, so that the space utilization efficiency when the apparatus is mounted on the edge of the tank or tank is improved. Further, since the light projecting / receiving unit 32 and the control block 33 can be arranged above the liquid or the prismatic prism 52, the semiconductor laser 11 and the photosensor 21 even if the liquid enters the apparatus due to an unexpected situation. It is possible to reduce the possibility that the substrate 31 or the control block mounted with the liquid will come into contact with the liquid.

  Also in this embodiment, the cylindrical lens 41, the cylindrical lens 42, and the wide cylindrical lens 45 constitute a collimating optical system that collimates the laser beam output from the semiconductor laser in the liquid level change direction. .

  According to the optical liquid level measuring apparatus of this embodiment, since a single semiconductor laser and a single light receiving element are used, a low-cost and low-power-consumption apparatus can be provided. In addition, despite the use of a single semiconductor laser and a single light receiving element, it is possible to measure the liquid level continuously with high linearity rather than discretely. In addition, unlike the apparatus of Patent Document 1, it is not a method of irradiating the liquid surface with laser light, so that measurement can be performed without being affected by the state of the liquid surface.

[Other Embodiments]
Embodiments of the present invention are not limited to Embodiments 1 to 4 described above, and many modifications are possible within the technical idea of the present invention.
For example, since the laser light source and the light receiving unit can be arranged close to each other, in the above-described embodiment, both are mounted on a single substrate, but the present invention is not limited to this.
In addition, the installation of the optical liquid level measuring device is not limited to the method of installing on the outer edge of the tank as illustrated in FIG. 6, and various installation forms are possible. However, it may be installed suspended from above.

  DESCRIPTION OF SYMBOLS 11 ... Semiconductor laser / 21 ... Photo sensor / 31 ... Substrate / 32 ... Projecting / receiving part / 33 ... Control block / 41 ... Cylindrical lens / 42 ... Cylindrical lens / 43 ... Cylindrical lens / 45 ... Wide cylindrical lens / 46 ... Cylindrical lens / 47 ... Cylindrical lens / 48 ... Condensing lens / 51 ... Square prismatic prism / 51A ... On Outgoing surface / 51Ain ... Incident surface / 51Aout ... Outgoing surface / 51B ... Total reflection surface / 51C ... Total reflection surface / 51D ... Liquid level detection surface / 51E ... Recess / 51F .... Chamfered part / 52 ... prismatic quadrilateral prism / 52A ... incident / exit surface / 52B ... total reflection surface / 52C ... reflection surface / 52D ... liquid level detection surface / 61 ... Optical axis rotation Mirror / 62... Slit / 63... (1/4 wavelength plate) / 64... PBS / 65... Mirror / 100... Graph of received light amount in the arrangement of FIG. ... graph of received light quantity in the arrangement of Fig. 4 (b) / 102 ... optical liquid level measuring device / 103 ... water storage tank / 104 ... water / 105 ... control unit / 106 ···・ Solar panel / 107 ... Storage battery / 108 ... Communication unit / 109 ... Temperature sensor

Claims (8)

A semiconductor laser;
A collimating optical system for collimating the laser beam output from the semiconductor laser by expanding in the liquid level change direction;
Of the laser light incident via the collimating optical system, the total reflection is performed when the medium in contact with the boundary surface is air, but the liquid level detection is transmitted to the liquid side when the medium in contact with the boundary surface is the liquid. A prismatic prism having a surface;
Have a, a photo sensor for measuring the amount of laser light totally reflected at the liquid level detecting surface,
The semiconductor laser is arranged such that a direction parallel to the PN junction surface of the semiconductor laser is parallel to the liquid level change direction,
An optical liquid level measuring device. The prism prism is
An incident surface on which the laser beam collimated by the collimating optical system is incident;
A total reflection surface that totally reflects the laser light incident from the incident surface regardless of whether the medium in contact with the boundary surface is air or the liquid;
The liquid level detection surface on which the laser beam reflected by the total reflection surface is incident;
An emission surface for emitting laser light totally reflected by the liquid level detection surface,
The optical liquid level measuring device according to claim 1. The angle between the optical axis of the laser beam collimated by the collimating optical system and the total reflection surface is θ,
Let I _air be the critical angle when the laser beam is incident on the air from the prism prism,
When the critical angle when the laser light is incident on the liquid from the prismatic prism is I _liquid ,
90 ° −θ> I _air , 90 ° −θ> I _liquid , and I _liquid > 2 × θ> I _air ,
The optical liquid level measuring device according to claim 2. The collimating optical system is
A cylindrical lens having a power for condensing laser light output from the semiconductor laser in the liquid level change direction;
A wide cylindrical lens that collimates the laser light that has passed through the focal point of the cylindrical lens and spread in the liquid level change direction in a direction perpendicular to the liquid level change direction,
The optical liquid level measuring device according to any one of claims 1 to 3 , wherein Having a lens for condensing the laser light totally reflected by the liquid level detection surface on the photosensor;
The optical liquid level measuring device according to any one of claims 1 to 4 , wherein The collimating optical system is
A polarization beam splitter that separates an optical path of laser light from the semiconductor laser toward the prism prism and an optical path of laser light from the prism prism toward the photosensor;
The optical liquid level measuring device according to any one of claims 1 to 5 , wherein Between the semiconductor laser and the photosensor, and the prism prism, a mirror that changes the optical path of the laser light,
The semiconductor laser and the photosensor are arranged above the prism prism in the liquid level change direction.
The optical liquid level measuring apparatus according to any one of claims 1 to 6 , wherein Furthermore, it has a communication part that communicates the measurement result of the liquid level,
The optical liquid level measuring device according to any one of claims 1 to 7 , wherein

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