Abstract:
A system and method for remotely determining a liquid level condition within a tank includes a liquid level gauge connectable to the tank, a dial assembly associated with the liquid level gauge and an optical transceiver for determining a reflectivity of the dial assembly. The dial assembly includes a reflective layer, a blocking layer positioned over the reflective layer for blocking at least a portion of the reflective layer, and a disk that is magnetically coupled to the liquid level gauge. One of the reflective and blocking layers is associated with the disk for rotation therewith. The optical transceiver is positioned for projecting radiant energy toward the reflective layer and detecting the presence or absence of reflected radiant energy and for generating a signal indicative of a low liquid level condition within the tank when at least a substantial portion of the reflective layer is covered by the blocking layer or when a failure occurs in the system to thereby provide a fail-safe mode of operation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to indicating devices for displaying liquid level condition within a tank or other container, and more particularly to a system and method for optically determining and remotely signaling a low liquid level condition within a tank. 
         [0002]    Conventional forklifts typically include a vehicle frame, a mast attached to the front end of the vehicle frame, a fork carriage adapted for elevational movement along the mast to raise and lower loads, and a counterweight located at the rear end of the vehicle frame for retaining balance of the forklift as heavyweight loads are lifted. An engine is typically mounted at the center of the vehicle frame and usually is covered with a hood. A driver&#39;s seat is typically fixedly secured to the hood and surrounded by an overhead guard which defines a cabin. Many such forklifts are powered by liquid propane and therefore include a liquid propane tank that is removably mounted for the purpose of refueling on a support structure of the counterweight. In order to prevent forklift down time or the chance of fuel outage at a location remote from the replacement tank, the propane tank is often replaced before it is completely empty. Since some tanks do not have a fuel gauge, a significant amount of cost can be incurred since useful amounts of propane may be left in the tank upon replacement. Even if a fuel sight gauge is provided, the dial indicator is not readily viewable by an operator. 
         [0003]    In order to overcome this disadvantage, remote ready gauges have been provided. Such gauges employ a magnetically driven dial for physically viewing the liquid level as well as a magnetic flux field sensor mounted on the dial for monitoring a position of the dial and generating an electric signal indicative of liquid level within the tank. Such a device is disclosed in U.S. Pat. No. 6,564,632 issued to Herbert G. Ross, Jr. on May 20, 2003. Although this device can provide the operator a means for remotely viewing the liquid level condition within the tank without leaving the operating position, it can become damaged if precautions are not observed. For example, if the magnetic flux field sensor is not removed from the gauge head before the tank is exchanged, the sensor, transmission cable and/or dial can become damaged and thus prevent transmission of the liquid level condition to the remote position. 
         [0004]    Moreover, although it is convenient for an operator to view the liquid level condition of the tank from the operating position, the operator is preoccupied with the task at hand which often requires precise maneuvering of heavy overhead loads between narrowly spaced rows of stacked inventory items. Consequently, little attention may be paid to the remote indicator until the forklift runs out of fuel, resulting in undesired downtime for replacing the tank from an inconvenient location. 
         [0005]    It would therefore be desirous to eliminate problems associated with prior art remote indicating devices while providing a signal to the operator when the tank reaches a predetermined low level condition. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    According to one aspect of the invention, a system for remotely determining a liquid level condition within a tank includes a liquid level gauge connectable to the tank, a dial assembly associated with the liquid level gauge and an optical transceiver for determining a reflectivity of the dial assembly. The gauge includes a float, a shaft operably connected to the float with the shaft being rotatable upon movement of the float in response to a change in liquid level within the tank, and a driving magnet connected to the shaft for rotation therewith. The dial assembly includes a reflective layer, a blocking layer positioned over the reflective layer for blocking at least a portion of the reflective layer, and a disk having a driven magnet that is magnetically coupled to the driving magnet such that rotation of the shaft causes rotation of the disk. One of the reflective and blocking layers is associated with the disk for rotation therewith. The optical transceiver is positioned for projecting radiant energy toward the reflective layer and detecting the presence or absence of reflected radiant energy and for generating a signal indicative of low liquid level within the tank when at least a substantial portion of the reflective layer is covered by the blocking layer. 
         [0007]    According to a further aspect of the invention, a dial assembly for use with a liquid level gauge having a gauge head for connection to a tank includes a base adapted for connection to the gauge head, a lens connected to the base, a disk rotatably connected to at least one of the base and lens for rotation with respect thereto, a reflective layer connected to one of the base and disk; and a blocking layer positioned over the reflective layer for blocking at least a portion of the reflective layer upon rotation of the disk. 
         [0008]    According to yet another aspect of the invention, a method of determining a low liquid level condition within a tank includes providing a liquid level gauge with an indicator dial, determining a reflectivity of the dial, and generating a low level warning signal when at least one of the following conditions occurs: a) the reflectivity is below a predetermined level, and b) a malfunction occurs during the determining step. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The foregoing summary as well as the following detailed description of the preferred embodiments of the present invention will be best understood when considered in conjunction with the accompanying drawings, wherein like designations denote like elements throughout the drawings, and wherein: 
           [0010]      FIG. 1  is an isometric view of a system for remotely determining a liquid level condition within a tank associated with a forklift or other vehicle; 
           [0011]      FIG. 2  is a sectional view of the system taken along line  2 - 2  of  FIG. 1 ; 
           [0012]      FIG. 3  is a top isometric view of a dial assembly in accordance with the present invention connected to a gauge head; 
           [0013]      FIG. 4  is an enlarged sectional view of the dial assembly taken along line  4 - 4  of  FIG. 3 ; 
           [0014]      FIG. 5  is a top isometric exploded view of the dial assembly and gauge head; 
           [0015]      FIG. 6  is a bottom isometric exploded view of the dial assembly; 
           [0016]      FIG. 7  is a top plan view of the dial assembly with a dial in a first position indicative of an empty tank condition; 
           [0017]      FIG. 8  is a top plan view of the dial assembly with the dial in a second position denoting a near-empty tank condition; 
           [0018]      FIG. 9  is a top plan view of the dial assembly with the dial in a third position denoting a half-full tank condition; 
           [0019]      FIG. 10  is a top plan view of the dial assembly with the dial in a fourth position indicative of a full tank condition; and 
           [0020]      FIG. 11  is a top isometric view of a dial assembly in accordance with a further embodiment of the invention. 
       
    
    
       [0021]    It is noted that the drawings are intended to depict only typical embodiments of the invention and therefore should not be considered as limiting the scope thereof. It is further noted that the drawings are not necessarily to scale. The invention will now be described in greater detail with reference to the accompanying drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Referring to the drawings, and to  FIG. 1  in particular, a system  10  for remotely determining a liquid level condition within a container  12  in accordance with a preferred embodiment of the invention is illustrated. In accordance with one adaptation of the preferred embodiment, the container  12  represents a propane tank or LP gas cylinder removably connected to a vehicle  14 , such as a gas-powered forklift or the like. 
         [0023]    The gas-powered forklift  14  is of conventional construction and accordingly is only partially shown in  FIG. 1 . The forklift  14  includes a counterweight  18  located at the rear end of a vehicle frame  20  for retaining balance of the forklift as heavyweight loads are lifted. An engine (not shown) is typically mounted at the center of the vehicle frame and usually is covered with a hood  22 . A driver&#39;s seat  24  is typically fixedly secured to the hood  22  and is surrounded by an overhead guard (not shown) supported by rear upright members or columns  26  and front upright members (not shown) to define a protective cabin for the operator. The forklift  14  is powered by liquid propane and therefore includes the tank  12  which is removably mounted on support structure  30  ( FIG. 2 ) of the counterweight and held in place by a pair of securing straps  31 . 
         [0024]    With additional reference to  FIG. 2 , the tank  12  is also of conventional construction and includes a pressure cylinder  32  for holding a quantity of propane, an annular base  34  located at one end of the cylinder  32  for orienting the cylinder in an upright position during storage, and an annular wall or valve guard  36  located at the opposite end of the cylinder  32 . Although not shown, the tank  12  may include other components typically associated with a propane cylinder, such as a fill/supply valve, over-pressure safety valve, and so on. An alignment pin  35  extends from the counterweight  18  of the forklift and through an alignment slot or opening  37  to properly orient the tank on the forklift. 
         [0025]    As will be appreciated, the present invention is not only applicable to propane tanks and forklifts, but may apply to other vehicles and/or stationary equipment as well as other containers where it is desirous to remotely determine a liquid level condition. 
         [0026]    The system  10  of the present invention preferably includes a liquid level gauge  38  mounted to and extending through an end wall  40  of the tank  12  in a well-known manner, a dial assembly  58  connected to the gauge  38 , an optical transceiver  42  connected to the forklift  14  for sensing a condition of the dial assembly  58 , and an indicator  44  operably associated with the optical transceiver  42  for remotely indicating the gauge condition to an operator. As shown, the optical transceiver  42  is preferably connected to one of the rear columns  26  via a bracket  36  or other connecting means, such as adhesives, mechanical fasteners, hook and loop material, and so on. If needed, a pivoting or articulated arm (not shown) can be associated with the bracket for aligning the transceiver  42  with the end of the gauge  38 . In accordance with one embodiment of the invention, the liquid level gauge  16  and optical transceiver  18  preferably work in conjunction to detect a predetermined low liquid level condition inside the tank  12 , as will be described in greater detail below. 
         [0027]    The indicator  44  can include any well-known means for visually and/or audibly alerting a person to the tank condition, including but not limited to speakers, warning lights, LED&#39;s, LCD or Oled displays, buzzers, chimes, and so on. 
         [0028]    Preferably, the liquid level gauge  38  has a float  46  connected to a pivot arm  48  which is in turn connected to a gear  50  rotatably mounted on a hollow support tube  52  of the liquid level gauge  38 . A spur gear  54  meshes with the gear  50  and causes rotation of a shaft  55  (shown in hidden line) extending through the support tube  52 . The shaft in turn rotates a driving magnet  57  (shown in hidden line) within a mounting head  56  of the liquid level gauge  38 . The dial assembly  58  is preferably attached to the mounting head  56  and is magnetically driven by the rotating driving magnet  57  to thereby indicate liquid level, as will be described in greater detail below. The mounting head  56  is in turn screwed into the end wall  40  of the tank  12  in a conventional manner. Further details of the liquid level gauge  38  can be found in U.S. Pat. No. 6,041,650 issued on Mar. 28, 2000 to Swinder et al., the disclosure of which is hereby incorporated by reference. It will be understood that other types of liquid level gauges can be used without departing from the spirit and scope of the present invention. 
         [0029]    Referring now to  FIGS. 3-6 , the dial assembly  58 , in accordance with a preferred embodiment of the invention, includes a base  60 , a disk  62  mounted on the base for rotation with respect thereto, a lens or cap  64  connected to the base, and a blocking layer  66  connected to the lens  64 . 
         [0030]    The base  60  is preferably circular in construction and includes a bottom wall  68 , a continuous side wall  70  extending upwardly from the bottom wall, locking fingers  72  extending downwardly from the bottom wall  68 , and a conically-shaped pin  74  located at an axial center of the bottom wall and extending upwardly therefrom. Preferably, the locking fingers  72  each include an inwardly extending projection  76  that engages a corresponding slot  78  formed in the mounting head  56  so that the base  60  can be installed on the mounting head  56  in a snap-fit engagement. However, it will be understood that other embodiments can use alternative fastening means known in the art such as screws or other fasteners, without departing from the spirit and scope of the invention. 
         [0031]    The disk  62  is preferably in the form of a circular-shaped body  80  with an upper surface  82  and a lower surface  84 . A pair of spaced bosses  86  extend downwardly from the lower surface  84  and a driven magnet  88  is located in each boss. A center pivot  90  extends downwardly from the lower surface  84  between the bosses  86  and engages the pin  74  of the base  60  so that the disk  62  rotates in both clockwise and counter-clockwise directions about a central axis  92  of the dial assembly  58  with respect to the base. It will be understood that other well-known means for rotatably connecting the disk  62  to the base  60  can be used. The driven magnets  88  are magnetically coupled to the driving magnet  57  associated with the shaft  55  of the liquid level gauge  38  and thus serve to cause corresponding rotation of the disk  62  when the float  46  is moved in response to a change in liquid level within the tank  12 . Although the disk has been shown as rotatably connected to the base, the disk can alternatively or additionally be rotatably connected to the lens or other structure without departing from the spirit and scope of the invention. 
         [0032]    A reflective layer  94  is located on the upper surface  82  of the disk  62  and preferably includes a first reflective segment  96  with a first radius  106  and a second reflective segment  100  with a second radius  102 . Preferably, the second radius is greater than the first radius such that the second reflective segment  100  extends from a center of the disk  62  to an edge  104  thereof and the first reflective segment  96  extends to a position spaced from the edge. The first reflective segment  96  preferably terminates at a first leading edge  98  and extends peripherally around the disk and terminates at a second leading edge  108  associated with the second reflective segment  100 . Preferably, the first and second leading edges extend at an obtuse angle. The second reflective segment  96  also preferably terminates at the second leading edge  108  and extends peripherally around the disk and terminates at a first trailing edge  110  of the second reflective segment  100 . The significance of the reflective segments will be described in greater detail below with respect to  FIGS. 7-10 . 
         [0033]    The reflective layer  94 , including the first and second reflective segments, is preferably die-cut from a single piece of retro-reflective adhesive tape and applied to the upper surface  82  of the disk  62 . A suitable retro-reflective tape, such as Scotchlite™ reflective tape by 3M, can include thousands of highly-efficient micro prisms that reflect radiant energy back toward the light source. It will be understood that the reflective layer can be formed from other reflective materials such as reflective glass, plastic or metallic materials or coatings, as well as paints or inks that are sprayed, screened or printed onto the disk  62 , without departing from the spirit and scope of the present invention. 
         [0034]    A pointer  112  is also preferably located on the upper surface  82  of the disk  62  and is preferably in alignment with or closely adjacent to the first leading edge  98  of the first reflective segment  96  for visually indicating a liquid level condition in conjunction with blocking layer  66 . Although shown as triangular in shape, it will be understood that the pointer  112  can be of any suitable shape for indicating a liquid level condition. In accordance with a further embodiment of the invention, the pointer  112  can be eliminated and the first leading edge  98  of the first reflective segment  96  can serve as the pointer. 
         [0035]    The lens  64  preferably includes an upper wall  114  and a continuous side wall  116  extending downwardly from the upper wall. The lens  64  can be constructed of any suitable transparent or translucent material which allows the observer to view the disk  62  and the blocking layer  66  through the upper wall  114 . The side wall  116  preferably engages the side wall  70  of the base  60  when assembled and can be connected together through any well-known means such as adhesive bonding, heat welding, mechanical fastening, mutually engageable threads, friction fit, and so on. 
         [0036]    The blocking layer  66  is preferably printed, screened or otherwise applied onto a lower surface  118  of the upper wall  114  and is therefore fixed against movement with the lens  64 . However, it will be understood that the blocking layer  66  can be formed as a separate element and connected to the lens  64  through any well-known connecting means. The blocking layer  66  preferably includes an opaque region  120  with a first transparent section or window  122  and a second transparent section or window  124  located diametrically opposite the first window. When directly printed onto the lens  64 , the first and second windows are preferably formed as cut-outs in the blocking layer. Preferably, the first window  122  is larger than the second window  124  and includes a scale  126  that denotes the liquid level condition within the tank  12 , such as empty, ¼ tank, ½ tank, full, and so on. When the blocking layer  66  is formed as a separate element, the windows  122  and  124  are preferably formed as transparent sections of the blocking layer  66 . 
         [0037]    It will be understood that the term “transparent” as used herein does not necessarily refer to completely transparent but rather denotes sufficient transparency to allow an observer to visually determine a position of the underlying disk  62  with respect to the opaque region  120  and allow at least some radiant energy from the optical transceiver to traverse the windows. Likewise, it will be understood that the term “opaque” as used herein does not necessarily mean completely opaque but rather denotes a condition where transmission of radiant energy from the optical transceiver is sufficiently impaired to prevent a sufficient quantity or intensity of radiant energy to be reflected back to the transceiver. 
         [0038]    The first window  122  is bordered by a first edge  128  and a second edge  130  of the opaque region  120  that respectively coincide with “empty” and “full” conditions of the tank  12 . An angle A ( FIG. 7 ) between the first and second edges  128 ,  130  is preferably sufficiently large to create a sufficiently long arc length to expose the pointer  112  and at least a portion of the first reflective segment  96  between the empty and full tank conditions ( FIGS. 7-10 ) as denoted by the scale  126  when the disk  62  is rotated in response to movement of the float  46  ( FIG. 2 ). Likewise, the second window  124  is bordered by a third edge  132  and a fourth edge  134  of the opaque region  120  that extend at an angle B to create a sufficiently long arc length so that at least a portion of the second reflective segment  100  is exposed during rotation of the disk  62  between the empty and full tank conditions. 
         [0039]    In accordance with an exemplary embodiment of the invention, the angle A is approximately 100 degrees while the angle B is approximately 24 degrees for a particular liquid level gauge having a predefined angular rotation of the driving magnet  57  ( FIG. 2 ) of approximately 100 degrees when the float  46  is moved in response to a change in liquid level within the tank  12  between empty and full tank positions. 
         [0040]    It will be understood that the angles for the window edges, the arc lengths of the reflective segments and the amount of angular rotation of the disk  62 , as well as the arc length and contents of the scale  126  can greatly vary and will depend at least in part on the particular liquid level gauge used and/or the type and amount of information related to liquid level to be displayed for visual observation and/or electronic detection. 
         [0041]    Referring again to  FIGS. 1 and 2 , the optical transceiver  42  preferably includes a transmitter  136  that emits radiant energy in the electromagnetic spectrum and a receiver  138  that detects the emitted radiant energy. Preferably, the transmitter  136  comprises a LED that emits radiant energy in the near-infrared region of the electromagnetic spectrum and the receiver comprises a photosensor, such as a photodiode or phototransistor, that detects radiant energy in the near-infrared region. However, it will be understood that the transmitter and/or receiver can alternatively emit and receive radiant energy in the ultraviolet, visible and/or infrared light spectrums without departing from the spirit and scope of the present invention. The transmitter  136  and receiver  138  are preferably located within a housing  140  which is in turn connected to the mounting bracket  46 . The housing may also include circuitry (not shown) for detecting when a predetermined condition has occurred and transmitting a signal via an electrical cable  142  to the indicator  44  to inform an operator of the predetermined condition. Preferably, the predetermined condition is a low liquid level condition of the tank  12  based on a predetermined reflected value detected by the receiver. The electrical cable  142  can also supply electrical power to the optical transceiver  42  from the forklift  14  or other power source. In accordance with a further embodiment of the invention, the optical transceiver  42  can be battery-powered and a signal can be sent to the indicator  44  via a wireless signal in a well-known manner. 
         [0042]    As shown in  FIG. 2 , the transmitter  136  emits light toward the dial assembly  58 , as represented by phantom lines  144 . The emitted light is then reflected toward the emitter  138 , as shown by dashed lines  146 , when at least a portion of one or more of the reflective regions  96 ,  100  ( FIG. 5 ) is exposed through the blocking layer  66 . Suitable and well-known techniques for reducing ambient noise can be employed, including but not limited to polarizing the light output, providing one or more light filters, generating a predetermined pattern of light pulses that is recognized by the receiver and related circuitry, and so on. 
         [0043]    Referring now to  FIGS. 7-10 , operation of the system  10  for remotely determining a liquid level condition within the tank  12  will now be described. As shown in  FIG. 7 , the pointer  112  of the disk  62  is in alignment with the “E” on the scale  126  of the blocking layer  66 , thereby informing an observer that the tank  12  is empty or near empty. In this position, the first and second reflective segments  96 ,  100  are covered by the opaque region  120  so that no radiant energy (or an insignificant amount) from the transmitter  136  ( FIG. 2 ) is reflected back to the receiver  138 . In this position, a switch signal is preferably generated and sent to the indicator  44  to alert an operator of the low level or “empty” tank condition. Preferably, the reflective segments and opaque region are arranged to indicate a low level condition with sufficient contents in the tank to allow the forklift (or other vehicle) to return to the refueling station. In the event that the optical transceiver  42  malfunctions, the signal will still be sent to the indicator  44 . A visual inspection of the dial assembly  58  will immediately inform an operator that a system malfunction has occurred when the pointer  112  is not aligned with an empty or near-empty condition, i.e. when the contents of the tank are sufficient to preclude a low level warning. This fail-safe mode of operation ensures, with a high level of confidence, that the system  10  is operating correctly when the indicator  44  does not receive a signal. At a particular low level condition, the low level signal may be sporadic due to fuel sloshing. Accordingly, well-known damping or delay techniques can be used for mechanically and/or electronically stabilizing the signal. 
         [0044]    When the disk  62  rotates to a level condition greater than a predetermined low level condition, as shown in  FIG. 8 , a portion of the first reflective segment  96  and second reflective segment  100  will be exposed through the first window  122  and second window  124 , respectively, of the blocking layer  66 . In this position, a critical area of the reflective segments is exposed so that radiant energy from the transmitter  136  is reflected back to the receiver  138  with sufficient intensity to stop generation of the low level warning signal. Further rotation of the disk  62  toward the half-full and full tank positions, as shown in  FIGS. 9 and 10 , respectively, expose even more of the first and second reflective segments through their respective windows. Accordingly, a low level signal will be sent to the indicator  44  only when the exposed reflective area is insufficient to reflect a significant amount of radiant energy from the transmitter  136  or when the system  10  experiences a malfunction. 
         [0045]    It will be understood that one of the windows can be eliminated where sufficient reflection is generated with a single window. It will be further understood that one or more of the windows can be enlarged or reduced in size to reveal more or less of the reflective area. In addition, more windows and/or reflective segments can be provided without departing from the spirit and scope of the present invention. 
         [0046]    Referring now to  FIG. 11 , a dial assembly  150  in accordance with a further embodiment of the invention is illustrated. The dial assembly  150  is similar in construction to the dial assembly  58  previously described, with the exception that the reflective layer  94  is preferably located on an upper surface  152  of the bottom wall  68  of the base  60  and the blocking layer  66  is located on the disk  62 A. In accordance with one embodiment of the invention, the disk  62 A is formed of a transparent material and the blocking layer  66  is an opaque layer on the transparent material to form transparent windows  122 A and  124 A. In accordance with a further embodiment of the invention, the disk  62 A is formed of an opaque material and the windows  122 A and  122 B are formed as cut-outs in the material. 
         [0047]    With this arrangement, the reflective layer is fixedly connected to the base  60  and the blocking layer is fixedly connected to the magnetically-coupled disk  62 A for rotation therewith in response to float movement. The scale  126  can either be associated with the disk  62 A or with the base  60  in this embodiment and the pointer (not shown) is associated with the other of the disk and base. In accordance with yet a further embodiment of the invention, with the scale located on the disk  62 A, the pointer can be eliminated and the leading edge  98  of the first reflective section  96  can function as the pointer for visually observing the liquid level condition within the tank. In accordance with yet another embodiment of the invention, with the scale located on the base  60 , the leading edge  128  of the blocking layer  66  can serve as the pointer. 
         [0048]    With the above-described embodiments, there is no need to remove sensor components from the tank prior to replacement, as in prior art magnetic flux field sensors. In addition, the operator need not be preoccupied with the liquid level condition of the tank until the low level warning signal is generated. Accordingly, the operator is better able to focus on the task at hand. 
         [0049]    It will be understood that the term “preferably” as used throughout the specification refers to one or more exemplary embodiments of the invention and therefore is not to be interpreted in any limiting sense. It will be further understood that the term “connect” and its various derivatives as may be used throughout the specification refer to components that may be joined together either directly or through one or more intermediate members. In addition, terms of orientation and/or position as may be used throughout the specification relate to relative rather than absolute orientations and/or positions. 
         [0050]    It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It will be understood, therefore, that this invention is not limited to the particular embodiments disclosed, but is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.