METHOD AND DEVICE FOR DETECTING LIQUID LEVEL

Abstract: A method for detecting a liquid level liquid level is monitored at mutually opposing sides of a liquid containing bottle. For monitoring the liquid level at each side of the bottle, a diffused light beam is irradiated toward the liquid surface from the level below the liquid surface. The light reflected at the liquid surface and the light refracted at the liquid surface are deteted by a photo-receiving camera which is focused at a standard liquid level. An average value of the monitored liquid levels at both sides is taken as a liquid level indicative value. By employing the aforemention method, acurate detection of the liquid level becomes possible even when the liquid level is unstable.

Description: The present invention relates generally to a method and device for detecting a liquid level. More specifically, the invention relates to means for detection of the level of a liquid contained in a transparent or semi-transparent container, such as bottle. In general, in bottling of alcohols, drinks, sauces, liquid spices, it has been required to adjust the bottling amount within a predetermined range of amount. Usually, the bottling amount is controlled by controlling the liquid level in the bottle. Therefore, liquid level in the bottle has to be detected for enabling control of the bottling amount. In one of the conventional methods a light source is provided at one side of a bottle at a level approximately corresponding to the desired liquid level, and a photo-receiver camera is provided at the opposite side of the bottle at the corresponding level to the light source. The light beam is horizontally projected from the light source toward the photo-receiver camera. The photo-receiver camera receives the light beam through the bottle. The intensity of the received light beam is converted into an electric voltage by means of a photoelectric transducer. This method is based on the difference of the light transmission factor between the bottle section containing the liquid and the empty bottle section. However, the border between the liquid containing section and the empty section to be detected, may become rather vague. Therefore, with such conventional device, precise detection of the liquid level cannot be performed. In order to eliminate or reduce this drawback in the conventional process, a method and device for detecting the liquid level has been proposed, in the Japanese Patent First publication (Tokkai) Showa 60-200126, published on October 9, 1985. The disclosed device has a light source provided at the level below the liquid level. The light source is designed to project a diffused light beam toward the liquid surface. The photo-receiver camera is placed at a level corresponding to the standard liquid level. The photo-receiver camera is focused at the bottle surface approximately corresponding to the standard liquid level. The light beams passing through the liquid and bottle is received by the photo-receiver camera. The intensity of the light beam received by the photo-receiver camera becomes high at the position of liquid level because of the presence of a light beam component reflected at the rising circumferential section of the liquid surface. Therefore, the output of the photoelectric transducer becomes higher at the liquid level than remaining sections. In the prior proposed system, a difficulty has arisen when the liquid is oscillating or waving. This possibly occurs during transportation through a conveying system in an automatic bottling processes. If the liquid is oscillating or waving, the liquid surface becomes unstable and can lead to mis-detection of the liquid level. Therefore, it is a principle object of the present invention to provide an improved method and device for detecting the liquid level, which does not require precision of adjustment of the light source angle as required in the previously proposed method and device set forth above. Another object of the invention is to provide an improved method and device for detecting the liquid level in a bottle, which detects a light beam twice refracted at the liquid surface. In order to accomplish the aforementioned and other objects, the present invention provides a method in accordance with claim 1 and a device as set forth in claim 8. Thus a diffused light beam is irradiated toward the liquid surface from a level below the liquid surface. The light reflected at the liquid surface and the light refracted at the liquid surface are detected by a photo-receiving camera which is focused at a standard liquid level. An average value of the monitored liquid levels at both sides is taken as a liquid level indicative value. By employing the aforementioned method, accurate detection of the liquid level becomes possible even when the liquid level is unstable. Attention should be drawn at this stage to US-A-3 452 208 which is concerned with the automatic detection of liquid levels in manometer tubes using reflection from the meniscus. For this purpose a detecting device is designed to have a carrier on a manometer tube located always at the meniscus. A bridge circuit is balanced by matching two photoelectric cells, imbalance in the circuit operates to move the carrier up or down until it reaches meniscus level. A current is set up in the bridge circuit to operate a motor to move the carrier up or down depending on which photoelectric cell is in dominance. The at rest position or balanced condition in the circuit is brought about by a diminished beam involving both refraction of a beam and reflection of a portion of it from the under surface of the meniscus at liquid level. The need to move the carrier for the detecting device makes this apparatus unsuitable for use in detecting liquid levels in automatic bottling processes. The device of claim 8 for implementing the aforementioned liquid level detecting method preferably comprises two pairs of light sources and photo-receiving cameras focused at a standard liquid level. One of the light sources is placed at a first side of the liquid containing bottle and the associated photo-receiving camera is placed at a second side opposite to the first side. On the other hand, the other camera is placed at the second side and the other photo-receiving camera is placed at the first side. The light sources are so designed as to irradiate diffused light beam toward the liquid surface at their respective opposite sides. The light beam irradiated from the light source is reflected at the rising circumferential section of the liquid surface and refracted at the liquid surface. The photo-receiving cameras receive both the reflected light and refracted light. Based on the output from the photo-receiving cameras, light level at each side is derived. Then an average value of the derived liquid level is derived as a light level indicative value. Further preferred embodiments of the method and apparatus of the invention are set forth in the subordinate claims 2 to 7 and 9 to 14. The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiment of the invention, which, however, should not be taken to limit the invention to the specific embodiment but are for explanation and understanding only. In the drawings: Fig. 1 is a fragmentary illustration of the preferred embodiment of a liquid level detecting system according to the present invention; Fig. 2 is an enlarged section showing a part of a bottle, about which the liquid level is detected by means of the preferred embodiment of the liquid level detecting system of Fig. 1; Fig. 3 is an enlarged section of a part of a bottle, about which the liquid level is detected by means of the the preferred embodiment of the liquid level detecting system of Fig. 1, in which the condition of the liquid surface is unstable; Fig. 4 is an explanatory illustration showing an image picked up by the photodetectors in the modified embodiment of the liquid level detecting system of Fig. 1, in the condition of Fig. 3; Fig. 5 and 6 are hystograms of the result of liquid level detection performed in the conventional system; and Fig. 7 is a hystogram of the result of liquid level detection performed by the modified embodiment of the liquid level detecting system of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, particularly to Fig. 1 and 2, the preferred embodiment of a liquid level detecting system, according to the present invention, generally comprises light source assemblies 10a and 10b, and photo-receiving camera assemblies 20a and 20b. The light source assembly 10a and the photo-receiving camera assembly 20a are arranged opposite sides of a conveying path (not shown) through which liquid containing bottles 30 are fed. The light source assembly 10b is arranged on the opposite side from the light source assembly 10a and also on the opposite side from the photo-receiving camera assembly 20b. As will be seen from Fig. 1, the light source assemblies 10a and 10b are arranged at lower level than a liquid level 32 of a liquid 34 contained in the bottle 30. The light source assemblies 10a and 10b are so designed as to emit diffused light beams 12a and 12b toward the possible liquid surface 32 adjacent respectively peripheral bottle wall 30a of opposite sides. Therefore, the diffused light beams 12a and 12b emitted from the light source assemblies 10a and 10b are irradiated onto the liquid surface at an oblique angle to thereto. The angle of each of the light source assemblies 10a and 10b is selected so that a first component 12A of each of the light beams 12a and 12b pass through the liquid 34 and is refracted at the liquid surface. The refracted light beam 12A is again refracted by the surface of the circumferential rising portion 36 of the liquid to be horizontally projected through the bottle 30. The angle of each of the light source assemblies 10a and 10b is further determined so that a second component, light beam 12B, is reflected at the adjoining section 38 between the central general surface and the circumferential rising portion 36. The second component 12B of the light beam 12 is horizontally projected through the bottle 30. Each of the light source assemblies 10a and 10b comprises a light source 14 and a diffusion plate 16. The light source 14 comprises a high-power halogen lamp, high-frequency fluorescent light lamp or laser. When a halogen lamp or fluorescent light lamp is used as the light source 14, diffused light is emitted from the light source. In which case, the diffusion plate 16 is selected to deflect the diffused light from the light source and to direct the light beam 12a and 12b toward the liquid surface 32 adjacent the peripheral bottle wall 30a on the opposite side of the bottle. On the other hand, when the laser is used as the light source 14, the diffusion plate 16 may serve as a diffusion medium for forming the diffused light beam directed to the liquid surface 32. Though the shown embodiment employs the diffusion plate for forming the diffused light beam, the diffusion plate is not always necessary for forming the diffused light beam. Especially, when diffused light source, such as halogen lamp, fluorescent light lamp and so forth, is employed as the light source, the diffusion plate is practically unnecessary. Though the light source assemblies 10a and 10b are provided at a lower level than the liquid level in the bottle, it would be possible to form the diffused light beams 12a and 12b irradiated from the under-side of the liquid surface in formed various ways. For instance, the light source assemblies 10a and 10b may be placed at any vertical level irrespective of the liquid level. In which case, reflectors may be placed below the liquid level to reflect the light beams 12a and 12b from the light source assembly toward the liquid surface. The photo-receiving camera assemblies 20a and 20b may comprise a photo-receiving camera or any other light image pick-up device. The photo-receiving camera assemblies 20a and 20b are placed at a level corresponding to a predetermined standard liquid level. The photo-receiving camera assemblies 20a and 20b are respectively focused at points around the liquid containing bottle surface approximately corresponding to the standard liquid level for providing a given image pick-up range covering the possible projecting regions of the aforementioned first and second compoments 12A and 12B of the light beam. The photo-receiving camera assemblies 20a and 20b produce sensor signals Sa and Sb respectively having values indicative of the intensity of the light beam received at each elevation, as shown in Fig. 3. As will be appreciated from Fig. 3, the sensor signal value increases in an elevation range where the first and second components 12A and 12B of the light beams 12a and 12b are received. Therefore, the HIGH level range of the sensor signals Sa and Sb generally represents the range of the rising portion 36 of the circumferential section of the liquid surface. Namely, the rising edge 12C of the HIGH level sensor signals Sa and Sb essentially represent the upper end of the rising portion 36 and the rising edge 12D of the sensor signals Sa and Sb essentially represents the liquid surface level 32 at the general portion. The sensor signals Sa and Sb are fed to a signal processor 40 which processes the sensor signals to detect the positions of the rising edges 12C and 12D of the sensor signals to detect the elevation range where the first and second components 12A and 12B are received. In the signal processing, the sensor signals Sa and Sb may be compared with a predetermined threshold value S ref to avoid environmental noise component to be superimposed on the sensor signals Sa and Sb. The signal processor 40 has per se well known construction for processing the sensor signals. The signal processor 40 derives a liquid level indicative signal indicative of the elevation of the rising edges 12C and 12D of the sensor signals Sa and Sb. An average value of the liquid level indicative signal values at the rising edges 12C and 12D derived with respect to each of the sensor signals Sa and Sb is obtained. Fig. 4 shows the elevations of the rising edges 12C and 12D of respective sensor signals Sa and Sb. Assuming respective heights of the rising edges 12C and 12D of the sensor signals Sa and Sb, from the lower frame level of the view-field of the photo-reciving cameras 20a and 20b, are H₁, H₂, H₃ and H₄, the average value may be derived in the following manner. When the waving or oscillation of the liquid is relatively small and thus the liquid surface is rather stable, the average value H ave may be obtained by averaging the H₁ and H₃ values respectively representative of the elevation of the lower rising edges 12D of the sensor signals Sa and Sb. Alternatively, the average value of the H₂ and H₄ values respectively representative of elevations of the higher rising edge 12C of the sensor signals Sa and Sb may be used for indicating the liquid level. On the other hand, when the waving or oscillation of the liquid in the bottle is substantial the high intensity range becomes wider than that obtained in the stable liquid surface condition, as shown in Fig. 3. Therefore, the liquid level elevation is assumed as the intermediate position between the H₁ and H2 and H₃ and H₄. Therefore, the average value H ave may be derived from the following equation: H ave = (H₁ + H₂ + H₃ + H₄)/4 Experimental measurements have been performed for confirming accuracy of detection of the liquid level in various liquid waving conditions. In order to perform the experimentation, a liquid is disposed in a bottle up to the height of 45.3 mm. At stable condition, measured heights H₁, H₂, H₃ and H₄ are respectively 43.8, 46.3, 44.3 and 46.6. Consequently, the average value H ave becomes 45.3. An experimental measurement has been conducted with respect to samples No. 1 through No. 29. The result is shown in the following table. As will be appreciated from the foregoing result of experimentation, the resultant average values H ave is satisfactorily close to that obtained while the liquid is stable. This result has been shown in a histogram in Fig. 7. This hystogram can be compared with a histograms in Figs. 5 and 6, which shows results of experimetations conducted by means of the conventional device as described in the aforementioned Japanese Patent First Publication No. 60-200216. Figs. 5 through 7, X indicate overall average values of overall samples. As will be appreciated from these hystograms, substantially higher precision level in detecting level provided by the shown embodiment can be confirmed. In the bottling process in a factory, this average value is taken as a liquid level indicative value. The derived average value is compared with a predetermined reference values representative of the standard liquid level. When the average value is out of a predetermined standard liquid level range, the signal processor 40 produces an error signal or an alarm. Preferably, the signal processor 40 may be connected to a display 42 for graphically or neumerically displaying the detected liquid level data. In the alternative, the signal processor 40 may be connected to a controller for a bottling system for removing the bottles containing the liquid in amount out of the predetermined standard amount range from the transporting conveyer. While the present invention has been disclosed in terms of the preferred embodiment in order to facilitate better understanding of the invention, it should be appreciated that the invention can be embodied in various ways without departing from the scope of the invention as claimed. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments which can be embodied without departing from the scope of the invention set out in the appended claims.

Claims: A method for determing the level (32) of a liquid (34) in a bottle (30) comprising the steps of: irradiating a first light beam (12a) towards an area of liquid surface (32) adjacent the side wall of said bottle (30) at a first side of the bottle from a position below said liquid surface and located at a second side of the bottle opposite to said first side; irradiating a second light beam (12b) toward an area of liquid surface (32) adjacent the side wall of said bottle at said second side of the bottle from a position below said liquid surface and located at said first side of the bottle; detecting a first horizontally directed component (12B) of said first light beam reflected at the liquid surface and a second horizontally directec component (12A) of said first light beam refracted through said liquid, at said first side to produce a first detection signal representative of the spread of elevations at which light in said first and second horizontally directed components of said first light beam is detected; detecting a third horizontally directed component (12B) of said second light beam reflected at the liquid surface and a fourth horizontally directed component (12A) of said second light beam refracted through said liquid, at said second side, to produce a second detection signal representative of the spread of elevations at which light in said third and fourth horizontally directed components of said second light beam is detected; processing said first and second detection signals to derive an average value of said liquid level (32). A method as set forth in claim 1, which further comprises the steps of: positioning a first camera (20a) at an elevation corresponding to a predetermined standard liquid level at said first side of said bottle for detecting said first and second horizontally directed components (12B, 12A) of said first light beam (12a) and for producing said first detection signal; positioning a second camera (20b) at an elevation corresponding to a predetermined standard liquid level at said second side of said bottle for receiving said third and fourth horizontally directed components (12B, 12A) of said second light beam (12b) and for producing said second detection signal; and focusing said first and second cameras (20a, 20b) on the inside wall of said bottle at positions corresponding to said predetermined liquid level. A method as set forth in claim 2, wherein said first and third horizontally directed components (12B) of said first and second light beams (12a, 12b) are reflected in horizontal direction from the underside of the liquid surface at the outer portion thereof where it extends up the side wall of the bottle (30). A method as set forth in claim 2, wherein said second and fourth horizontally directed components (12A) of said first and second light beams (12a, 12b) are twice refracted first at the central portion of the surface of said liquid and subsequently at the outer portion thereof where it extends up the side wall of the bottle to finally emerge horizontally from the side of the bottle. A method as set forth in claim 2, wherein said average liquid level (32) is derived by obtaining the average of signals representative of the elevations of said first and third horizontally directed components (12B) of said first and second light beams (12a, 12b). A method as set forth in claim 2, wherein said average liquid level (32) is derived by obtaining the average of signals representative of the elevations of said second and fourth horizontally directed components (12A) of said first and second light beams (12a, 12b). A method as set forth in claim 2, wherein said average liquid level (32) is derived by obtaining the average of signals representative of the elevations of said first, second, third and fourth horizontally directed components (12B, 12A) of said first and second light beams (12a, 12b). A device for determining the level (32) of a liquid (34) in a bottle (30) comprising: first means (14, 16) arranged to irradiate a first light beam (12a) towards an area of liquid surface adjacent the side wall of said bottle at a first side of the bottle from a position below said liquid surface and located at a second side of the bottle opposite to said first side; second means (14, 16) arranged to irradiate a second light beam (12b) towards an area of liquid surface adjacent the side wall of said bottle at said second side of the bottle from a position below said liquid surface and located at said first side of the bottle; third means (20a) arranged to detect a first horizontally directed component (12B) of said first light beam (12a) reflected at the liquid surface and a second horizontally directed component (12A) of said first light beam (12a) refracted through said liquid (34), at said first side, to produce a first detection signal representative of the spread of elevations at which light in said first and second horizontally directed components (12B, 12A) of said first light beam (12a) is detected; fourth means (20b) arranged to detect a third horizontally directed component (12B) of said second light beam (12b) reflected at the liquid surface and a fourth horizontally directed component (12A) of said second light beam (12b) refracted through said liquid, at said second side to produce a second detection signal represesntative of the spread of elevations at which light in said third and fourth horizontally directed components (12B, 12A) of said second light beam (12b) is detected; and fifth means (40) arranged to process said first and second intensity indicative signals to derive an average value of said liquid level. A device as set forth in claim 8, in which said third means comprises a first camera (20a) positioned at a elevation corresponding to a predetermined standard liquid level at said first side of said bottle (30) and arranged to detect said first and second horizontally directed components (12A, 12B) of said first light beam and produce said first detection signal, said fourth means comprises a second camera (20b) positioned at a elevation corresponding to a predetermined standard liquid level at said second side of said bottle (30) and arranged to detect said third and fourth horizontally directed components (12A, 12B) of said second light beam (12b) and produce said second detection signal, and means for focusing said first and second cameras (20a, 20b) at positions on the inside wall of the bottle at positions corresponding to said predetermined liquid level. A device as set forth in claim 9, wherein said first and third horizontally directed components (12B) of said first and second light beams (12a, 12b) are reflected in horizontal direction from the underside of the liquid surface at the outer portion thereof where it extends up the side wall of the bottle (30). A device as set forth in claim 9, wherein said second and fourth horizontally directed components (12A) of said first and second light beams (12a, 12b) are twice refracted first at the central portion of the surface of said liquid and subsequently at the outer portion (36) thereof where it extends up the side wall of the bottle (30) to finally emerge horizontally from the side of the bottle. A device as set forth in claim 9, wherein said fifth means (40) derives said average liquid level by obtaining the average of signals (H₂ + H₃) representative of the elevations of said first and third horizontally directed components (12B) of said first and second light beams (12a, 12b). A device as set forth in claim 9, wherein said fifth means (40) derives said average liquid level by obtaining the average of signals (H₁, H₄) representative of the elevations of said second and fourth horizontally directed components (12A) of said first and second light beams (12a, 12b). A device as set forth in claim 9, wherein said fifth means derives said average liquid level by obtaining the average of signals (H₁, H₂, H₃, H₄) representative of the elevations of said first, second, third and fourth horizontally directed components (12A, 12B) of said first and second light beams (12a, 12b).

Inventors: DOI, YUJI, KURAHASHI, MICHITO, TOMIKAWA, HISAO
Applicants: SUNTORY LIMITED
Application year: 1986
Main classification: G01F23
IPC codes: G01F23, B67C3