Abstract:
A portable safety device for attracting visual attention, comprises an array of flashing light sources, comprising high intensity light-emitting diodes having a light output of at least 500 mcandela. The light sources are connected in series with a solid state flashing circuit and a power supply. The power supply comprises a high energy battery and current limiting means in series therewith. The current limiting means prevents the current supplied by the battery externally of the power supply from exceeding a predetermined safe value. The solid state flashing circuit is periodically switchable between a low resistance state characterized in that the voltage across the series arrangement of high intensity light-emitting diodes exceeds a threshold voltage thereof, and a high resistance state characterized in that the voltage across the series arrangement of high intensity light-emitting diodes falls below the threshold voltage. The high intensity light-emitting diodes flash brightly to provide a low current attention-attracting device visible at lone range.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This invention is a continuation-in-part of my copending application Ser. No. 468,364, filed Jan. 22, 1990 U.S. Pat. No. 4,999,753. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a portable device for attracting visual attention, especially suited for use in potentially explosive environments, such as underground mines, but also useful for cyclists, joggers, pedestrians, children and the like. 
     BACKGROUND OF THE INVENTION 
     There are many situations where it is desirable to provide an object with a high degree of visibility. For example, pedestrians, cyclists and children are particularly vulnerable to vehicle accidents at night, especially on roads with no sidewalk. It is common practice for such persons to wear reflective clothing or arm bands, but these can only be seen when the person is sufficiently close to the oncoming vehicle for enough light to be reflected. 
     Sometimes people will carry a conventional flashlight, but this can often only be seen in one direction and generally portable flashlights have a short lifetime, which means that they soon start to fade and become less visible. 
     Problems also arise in industrial environments where visibility is obscured due to dust or darkness, such as in underground mines, open pit mines, construction sites and the like. In such environments, there is often a danger of personnel being run over or caught by moving machinery, and it is vitally important to make the machinery as visible as possible so as to give the personnel sufficient time to move out of its way. 
     In all these situations, the warning time for the person in danger or operator of the vehicle is of the essence. For example, in the case of a fast-moving vehicle, a fraction of a second can make the difference between life and death. A vehicle moving at 60 miles an hour covers about 30 meters in one second. 
     Strobe lights, such as are found near road works, are known. These generally require substantial amounts of power and are therefore not conveniently portable and cannot be left unattended for prolonged periods. They are also not suitable for attachment to personnel, largely as a result of their bulk and weight. 
     Devices with flashing lights are known. For example, one such device is described in U.S. Pat. Nos. 3,944,803 and 3,134,548. These devices are unsatisfactory because the incandescent bulbs they employ consume a large amount of power and they therefore have a short lifetime. When incandescent bulbs are periodically switched on and off their lifetime is considerably shortened. 
     A problem with all such devices is how to find a safe, longlasting, high energy power pack. Lithium batteries provide a convenient source of high energy power, but can be extremely dangerous if allowed to discharge too rapidly. Their high energy density can cause them to explode if shorted either directly or as a result of the ingress of moisture. 
     An object of the present invention is to alleviate the aforementioned problems and provide a portable safety device with high visibility and longevity. 
     SUMMARY THE INVENTION 
     According to the present invention there is provided a portable power pack comprising a pair of terminals supplying DC power, at least one high energy battery, and current limiting means in series with said terminals, said current limiting means preventing the current supplied by said terminals from exceeding a predetermined safe value, and said at least one battery and said current limiting means being completely encapsulated in solidified flowable material with only said terminals exposed, whereby shorting of said exposed terminals will not result in the passage of a current exceeding a safe limit. 
     The high energy battery is preferably a lithium battery, and desirably four batteries connected is series are employed. The solidified flowable material is preferably epoxy resin. 
     The power pack can be connected to a flashing circuit consisting of a low intensity light-emitting diode with an integrated circuit driver incorporated therein. The change in resistance of the low intensity light-emitting diode as it switches on and off, and therefore the change in voltage across its terminals, causes the high intensity diodes to switch in synchronism with it. This is a convenient low cost way of causing the high intensity light-emitting diodes to flash. 
     The current limiting means preferably comprises a pair of resistors arranged in parallel. Ideally the current should be limited to a maximum of half an amp, which for a nine volt battery means that the combined resistance of the resistors has to be 18 ohms. The advantage of using two resistors in parallel, each having a higher resistance such that the parallel combination has a resistance of 18 ohms, is that if one resistor fails the other resistor is still able to provide current at a reduced level. In case of a short circuit, a half amp fuse is connected in series with the battery, which cuts off the power completely. 
     The power pack can be provided with an end cap, which after the power pack has come to the end of its useful life can be used to short out the terminals and safely discharge any residual current remaining in the power pack. 
     To make the device safe for use in explosive environments, the complete device can be mounted in a rigid container with a window, which may be in the form of a lens, through which the light-emitting diodes are visible. The latter are preferably arranged in a line. It has been found that three such light sources arranged about half an inch apart are most effective at attracting attention. 
     Ideally the light output of the high intensity light-emitting diodes should be at least 2000 mcandela. 
     When carried by pedestrians, the safety device can be seen at a distance of approximately 1600 to 4000 feet, depending on the brightness of the light-emitting diodes and the environmental conditions. The minimum legal requirement for such devices is that a person be seen at 500 feet, which gives enough time for reaction and braking. The safety device can therefore exceed the minimum requirement by a factor of three to eight depending on the conditions. In tests, a device powered by one lithium battery has flashed continuously for over three weeks, and with normal intermittent use can last for six months or more. 
     The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a safety device in accordance with the invention; 
     FIG. 2 is a illustration of a trip lamp for use in mines and similar environments; 
     FIG. 3 is an illustration of a safety band incorporating a safety device in accordance with the invention; and 
     FIG. 4 is an illustration of a hazard warning triangle incorporating a safety device in accordance with the invention; 
     FIG. 5 shows an omni-directional safety light; 
     FIG. 6 shows in more detail a practical embodiment of a one-directional safety light for use in mines; and 
     FIG. 7 shows the safety light with the front cover pivoted open; 
     FIG. 8 is a diagrammatic illustration of a four-lithium battery power pack; and 
     FIG. 9 is a diagrammatic illustration of a further embodiment of a lithium battery power pack. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows three high intensity, super bright light-emitting diodes (LEDs) 1 with a 2000 mcandela light output, having a rating of 1.85 volts at 20 m amps. 
     The LEDs 1 are connected in series with a standard low intensity, blinking light-emitting diode 2 incorporating a MOS integrated circuit driver and a red LED within a T-5 mm 13/4 inch plastic LED housing. 
     The LEDs 1 are supplied by the Tandy Corporation under product designation 276-087™ and the LED 2 under product designation 276-036C™. 
     The LEDs 1, 2 are connected in series through a switch 3 with a power supply consisting of a battery 5, comprising four 9 volt lithium batteries in parallel, a parallel pair of resistors 6, each having a 39 ohm resistance and 0.5 watt rating, and a 0.5 amp fuse 4. Three or four lithium batteries are preferred, although any suitable number can be combined in parallel. 
     The circuit is activated by closing switch 3. The internal integrated circuit causes the standard low intensity LED 2 to start flashing, and as it does so it changes from low to high resistance, and hence low to high voltage, causing the main voltage drop to be applied across the series arrangement of high intensity LEDs 1, which in turn are caused to turn on. The high intensity LEDs 1 therefore flash in synchronism with the low intensity LED 2, even though the LEDs 1 do not incorporate internal drivers. 
     In the event of one of the resistors 6 becoming an open circuit, the remaining resistor limits the current to approximately half its previous value. While the intensity of light output falls, the safety device nonetheless continues to operate at an effective level. To ensure complete safety in the event of one or both of the resistors 6 becoming short circuited, the 0.5 amp fuse 4 is present. 
     The battery 5, consisting of four lithium batteries in parallel, parallel arrangement of resistors 6, and fuse 4 together make up the power supply. This is provided within a rigid metal or plastic box 12, completely sealed with epoxy resin such that the battery 5, resistors 6, and fuse 4 are fully encapsulated. 
     Turning now to FIG. 2, the miner&#39;s trip lamp has a hermetically sealed steel or plastic casing 7 with a removable lid 8 bolted to the casing 7 by bolts 10 and sealed by means of a rubber seal 13. 
     The casing 7 contains the battery container 12 and a further steel or plastic box 11 in which is encapsulated the flasher unit consisting of the LED 2. The box 11 is mounted such that the high intensity LEDs 1 protrude therefrom and are mounted just below a plastic lens 9 sealed in the lid 8 of the casing 7. The three LEDs 1 are arranged in a line and spaced about half an inch apart. 
     The trip lamp shown in FIG. 2 is particularly adapted for use in explosive environments, such as underground mines and the like. The casing 7 is completely hermetically sealed and the flasher unit 2 is hermetically sealed inside the box 11, mounted within the casing 7, as is the battery pack mounted within the container 12. Since the flashing circuit is entirely solid state, there is no risk of spark generation, even though any such sparks generated would be sealed both within the containers 11 and 12 and the casing 7. 
     The safety device is therefore useful for placement in mine shafts and, for instance, on the front of underground vehicles. 
     FIG. 3 shows schematically an arm band or the like for use by pedestrians. The three light-emitting diodes 1 are mounted on the arm band and are connected by wires (not shown) to a lightweight battery pack (not shown) carried by the wearer. Since there is no risk of explosion, the battery power supply can be made very small and light. Although described as a lithium battery, other suitable batteries, such as alkaline or carbon-zinc batteries can be employed. 
     FIG. 4 shows a hazard warning triangle 17 with three rows of LEDs 1, one for each side of the triangle. Such a warning triangle is considerably more effective than the passive type, yet the safety device adds little to the overall weight and is reliable even after long periods of inactivity. 
     Such safety devices, when incorporated into articles of clothing, such as belts as shown in FIG. 3, or other types of articles such as protective vests and the like, can be of very great value in enhancing safety of personnel. The extremely high visibility is an obvious benefit, but also the ability to continue flashing for long periods with a light and portable power source is also of great significance. 
     There are many examples of situations where such a device can be usefully employed. Some have been already mentioned, but others are joggers, walkers, cyclists, hunters, fishermen, motorcyclists, snowmobilers, A.T.V.s, adventurers, climbers, skiers, and explorers. 
     In a professional environment, the devices can be used at traffic check points, for ambulance attendants, firemen, tow truck attendants, search and rescue personnel, forest and game rangers, E.M.O., police, sailors, oil rig personnel, freight and cargo handlers, linesmen, military personnel, utility works, miners, railway yard and terminal operators, trip lamps, airport traffic directors (commercial, private), military, parking lot attendants, offshore life-saving capsules, marine survival suits, hazardous and disabled vehicles. 
     The device can also be applied to children&#39;s Halloween costumes to significantly enhance safety on Halloween. 
     The following is a comparative table of features of reflective devices, incandescent type devices and devices in accordance with the present invention. 
     
                       TABLE 1______________________________________PRODUCT FEATURE COMPARISONS          REFLEC-          TIVE      BULB      LEDFEATURES       DEVICES   TYPE      TYPE______________________________________DEVICE TYPE    PASSIVE   ACTIVE    ACTIVEDAYTIME VISIBILITY          GOOD      N/A       N/ANIGHTTIME VISIBIL-          POOR      GOOD      EXCITYADVERSE ENVIRON-          POOR      GOOD      EXCMENTSWATERPROOF     N/A       POOR      EXCVIBRATION RESIST-          N/A       POOR      EXCANCEIMPACT RESISTANCE          N/A       POOR      EXCVISIBILITY DISTANCE          500 Ft.   1/2 mi    1/2-3/4 mi        (DAY)   (APPROXIMATELY)POWER SOURCE SIZE          N/A       LARGE     SMALLPOWER SOURCE   N/A       HEAVY     NEGLIGI-WEIGHT                             BLEPRODUCT/LONGEV-          N/A       8 HOURS   10 WEEKSITY/(CONT.)BULKINESS      CUMBER-   BULKY     NEGLIGI-          SOME                BLEPRODUCT WEIGHT NEGLIGI-  HEAVY     NEGLIGI-          BLE                 BLE______________________________________ Abbreviation Legend: N/A = Not Applicable EXC = Excellent Ft. = Feet mi. = Miles FREQ. = Frequently CONT. = Continuously ON 
    
     The safety device in accordance with the invention can be made completely waterproof, dustproof, shockproof and impact resistant very easily in view of the fact that there a a minimum number of parts and the integrated circuit is not susceptible to shock, especially when encapsulated in the stout container. 
     In the case of devices intended for attachment to articles of clothing, many methods of attachment can be employed, such as clips, tape, bolts, glue etc., and the device can be attached to almost any article of clothing, such as jackets, pockets, or helmets, or other equipment such as bicycles, or parked or stationary machinery. 
     One of the important features of the product is its ability to operate with very low power consumption at high intensity for long periods. The high intensity LEDs employed, while having a light output some 2000 times the output of a conventional low power LED, draw about the same current. In many cases, when the device is switched off while not in use, it can last many years before requiring a change of battery. 
     The number of components required for the device described is extremely low, and this low component count translates into extremely good reliability. In the preferred embodiment, the three light sources are arranged in a straight line about half an inch apart and flash in synchronism. This combination has been found to be most effective at attracting attention. 
     The described safety device has good penetration of rainy, snowy, foggy, smokey and dusty environments. The light is reflected off the microscopic particles in the air, producing a glow from the surrounding particles. This phenomenon is especially useful for firemen in a burning building, for example, where visual contact may be very short and only enhancement of lighting conditions is extremely useful. 
     High intensity light-emitting diodes have significant advantages over conventional bulbs. Incandescent bulbs are intolerant to flashing and can consume up to ten times the rate of current in the turn on phase. By contrast, LEDs consume very low current and when switched on consume even less. They are extremely tolerant of flashing, can have a life span of over 100,000 hours and be virtually shockproof and impact proof. 
     When applied to warning triangles on motor vehicles, LEDs have a significant advantage over flares, which deteriorate over time. Flares are susceptible to environmental conditions, such as wind, rain and snow, and they are not always dependable. Also, they can be dangerous, especially if someone inadvertently trips over one. 
     A particular application for the safety device is as a trip lamp for use in underground mines. A trip lamp is attached to the front of a train or vehicle that takes coal, material or personnel throughout the mine. The trip lamp gives notice to personnel that the vehicle is approaching. Conventional trip lamps with lead acid batteries last for only eight to ten hours, and in many cases replacement is so time-consuming that lamps have not been replaced due to the nuisance aspect, leading to unfortunate accidents. 
     A further important application of the device is for use on life rafts and the like. 
     The device shown in FIG. 5 is similar to the device shown in FIG. 2, but comprises an array of LEDs on each of its five faces, except for the lower face. This provides an omni-directional device that is suitable, for instance, to be mounted on the top of an emergency life raft, such as might be carried by boats or aeroplanes. 
     A smaller version of the device can be used on personal life vests. In this regard, it should be mentioned that commercial life vests generally employ a glass encapsulated light source supplied by a lithium battery. If the glass breaks and the battery becomes exposed to sea water, the energy density in the battery is such that it will actually explode, presenting a serious danger to the wearer. The light source of the present invention will avoid this difficulty due to the fact that the lithium battery and current limiting means are encapsulated such that the lithium battery per se cannot be exposed directly to the water. 
     The invention as described represents an important advance generally in safety technology. Lithium batteries have generally come into widespread use for powering portable electronic devices because of high energy density, high voltage, high ampere capacity, very wide operating temperature range, long shelf life and flat discharge curve. 
     While the high energy density is useful for giving a long shelf life, one of the problems is that the high energy density is also capable of supplying a very high current. If the battery becomes shorted or even exposed to water or moisture, it can explode and be very dangerous. In one instance, a lithium battery employed in a cellular telephone exploded due to moisture causing injury to the user. 
     The present invention makes use of the fact that the high energy density is generally required only to supply a moderate current for a long period, rather than a high current for a short period. Furthermore, lithium does not need an air vent, and by encapsulating the battery with a current limiting device, absolute safety is ensured because only the terminals of the composite power supply are exposed. If the exposed terminals are directly shorted by moisture or even wire, the composite power supply will not supply a current sufficient to cause a dangerous explosion, or even a spark. 
     The combination of a fuse in association with the current limiting device within the epoxy is particularly desirable. If a fuse alone were used, since the fuse has to be completely encapsulate with the battery, if the fuse blew the power pack would become useless. The presence of the current limiting resistance within the epoxy and in series with the battery and fuse ensures that even if the battery is immersed in water or the leads shorted for a short period, the battery pack would not be damaged and could be reused. The resistance should be set at a value such that even in the event of a direct short no explosion will occur. The resistors should have a wattage such that a short circuit can be handled without damage. The described safety power supply thus has application in other safety areas, such as cellular telephones and the like. 
     The safety light is shown in more detail in FIGS. 6 and 7. The casing 7 is of corrosion resistance stainless steel with a front cover 7 1  attached to it by means of a piano hinge 7 11 . The lens 9 is a 44.5 mm diameter Lexan™ window. The casing is held shut by means of glass 20 on all three sides fixed to the casing by means of tamperproof screws 21. The rear of the casing 7 provided a mounting plate 22. 
     FIG. 8 is a portable power pack for use with the described safety light and for other portable applications, such as cellular telephones. 
     Four lithium batteries 30 are tightly packed and connected in parallel by wires 31, 32, which are connected respectively to exposed terminal plates 33, 35. Wire 31 interconnecting the positive terminals of the batteries is connected to terminal plate 33 through housing 34 containing the parallel combination of current-limiting resistors 6, and the fuse 4. 
     The entire package, apart from the exposed terminal plates 33, 35 is encapsulated in a two-part epoxy resin, which is allowed to set to from a completely sealed unit. As a result of this arrangement, a direct short across the exposed terminals will not give rise to a dangerous current liable to cause an explosion. Since the battery terminals are never exposed, they do not give rise to any danger. 
     The advantage of this arrangement is use is made of the desirable properties of lithium batteries, namely their ability to produce a steady moderate current for long periods without the concomitant disadvantage that the high energy density causes, namely the risk of explosion to a sudden release of stored energy. 
     Another problem with lithium batteries is environmental. Their safe disposal causes a problem because after discharge a significant amount of stored energy often remains in the battery. This has caused batteries to explode at dump sites, or it can cause an explosion hazard in the presence of flammable gases due to the risk of sparking. In accordance with a further feature of the invention, a metallic end cap 35 is provided, which is inserted over the power pack terminal after the battery has come to the end of its useful life. This allows a gradual discharge of the residual current in the battery to occur in a safe manner since the current limiting means prevents a rapid discharge from occurring. 
     In FIG. 8, the metallic end cap fits over opposite ends of the power pack to short terminals 33, 34. In FIG. 9, which has positive and negative terminals located at the same end of the power pack, the end cap fits over the top end of the power pack. 
     It has been found that power packs can also be conveniently made with three 3.6 volt lithium batteries in series and two 47 ohm, 5 watt resistors in parallel and a 0.5 amp fuse, all encapsulated in epoxy resin. Alternatively, three volt lithium batteries can be employed. 
     It has been found that in the case where such a power pack is used to power the flashing light unit, two extra LED&#39;s can be added for each 3.6 volt lithium battery. The resistance has to be increased commensurately, but the life of the power pack remains essentially the same.