Abstract:
The present invention comprises a mechanical timer that operates by using the ambient temperature differences during daytime and nighttime periods in order to count desired intervals of days, months, etc. Embodiments of the invention employ the timer to render safe land mines or other ordnance devices after a specified period of time. Because the present invention uses ambient temperature differences in order to operate, no outside power source is required.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to mechanical timer devices that depend upon ambient temperature fluctuations to count down, more particularly to such devices that provide actuation after a certain period of time, and most particularly to such devices used to render safe a mine or other ordnance device after a certain period of time. 
     2. Description of the Related Art 
     The need for mines or other ordnance devices placed or buried upon land to be rendered safe or self-destruct after a certain period of time is of great importance to the military. After specific military missions or actions have been completed, it is often important to neutralize or deactivate such mines in order to ensure that civilian personnel or one&#39;s own military personnel are not harmed by mines that have not been activated by enemy forces. Because it is inherently unsafe to attempt to neutralize or deactivate such mines, efforts have been made to develop a method whereby the mines would self-destruct or deactivate after a certain period of time has elapsed. However, there are problems associated with placing a standard timer and actuator system within the mines. Most importantly, any standard timer would require power to operate. This could be potentially unsafe and allow such mines to be more easily detected. Therefore, the development of a timer and actuator system requiring no external power is necessary to accomplish this goal. 
     Many actuators using bimetallic materials have been developed. Many of them apply snap-action, bimetallic disks in order to provide actuation after a certain temperature threshold has been reached. Examples of such actuators include U.S. Pat. Nos. 4,507,642; 5,043,690; and 6,039,262. These patents are hereby incorporated by reference. These actuators were developed to provide one discreet actuation, for example opening or closing an electrical circuit, when a certain temperature has been reached. Several applications of this technology have been developed wherein the properties inherent in the bimetallic materials are used to provide actuation when a certain threshold temperature has been reached and to provide deactuation when the temperature falls below this threshold. Examples of such applications include U.S. Pat. Nos. 4,303,195; 4,679,943; and 5,148,826. In these patents, the bimetallic disk technology was used to open and close valves or deliver water or scented oil after certain threshold temperatures had been reached. However, none of the these disclosures attempt to use the bimetallic material technology in order to provide a timer that can be adjusted to monitor specific time frames based upon changes in ambient temperature. 
     Therefore, it is desired to produce a mechanical timer, that uses no external power source, based upon changes in ambient temperature in order to deactivate mines or other ordnance devices after a specified period of time. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a mechanical timer that operates by using the ambient temperature differences during daytime and nighttime periods in order to count desired intervals of days, months, etc. Embodiments of the invention employ the timer to render safe land mines or other ordnance devices after a specified period of time. Because the present invention uses ambient temperature differences in order to operate, no outside power source is required. 
     Accordingly, it is an object of this invention to provide a mechanical timer that requires no external power source. 
     It is a further object of this invention to provide a mechanical timer that operates using ambient temperature differentials. 
     It is yet a further object of this invention to provide a mechanical timer that renders safe land mines or other ordnance devices after a specified time period. 
     This invention accomplishes these objectives and other needs related to mechanical timers that operate using changes in ambient temperature by providing a mechanical, temperature activated timer, comprising a housing with at least one member. The member is moveably attached to the housing. The member also has a plurality of serrations arranged unidirectionally along one or more sides of the member. First and second pawls that are attached to the housing cooperate with the serrations of the member to allow movement of the member in relationship to the housing in one direction only. At least one bimetallic material is placed within the housing. The bimetallic material has a first shape below its transition temperature and a second shape above its transition temperature. When the bimetallic material changes its shape due to reaching its transition temperature, the second pawl will transverse a serration on the member and move closer to the first pawl. The pawls are placed unidirectionally to cooperate with one another so that bringing the bimetallic material back to its original shape results in motion of the member. Therefore, if one uses temperature data for a specific location, a bimetallic material may be selected that has a transition temperature within the normal range between daytime and nighttime temperatures. Using this data, one can use the present invention in order to count days through the movement of the member wherein each serration comprises one transition cycle of the bimetallic material, or one day. 
     One specific preferred embodiment of this invention is used in order to render safe land mines by moving a safety pin or other blocking device between the trigger and firing pin of the mine through the movement of the member of the timer as described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and, together with the description, serve to explain the principles of the invention. 
     FIG. 1 is an embodiment of the invention with one bimetallic member. 
     FIG. 2 is an embodiment of the invention with three bimetallic members. 
     FIG. 2 a  is an enlarged section of the view of the ratchet mechanism shown within circle  2  of FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention, as embodied herein, comprises a mechanical timer that uses changes in the ambient temperature to count specific time intervals. In general, the invention comprises a housing with at least one member. The member is moveably attached to the housing. The member also has a plurality of serrations arranged unidirectionally along one or more sides of the member. At least one bimetallic material is placed within the housing. The bimetallic material has a first shape below its transition temperature and a second shape above its transition temperature. First and second pawls are attached to the housing and cooperate with one another to move across the serrations along the member. When the bimetallic material changes its shape due to reaching its transition temperature, the second pawl will transverse one serration of the member. The pawls are placed unidirectionally so that bringing the bimetallic material back to its original shape does not cause the member to return to its original position, but instead forces the member to physically change position. Therefore, when the bimetallic material returns to its original shape, the member will complete its movement of one serration. 
     The present invention can be tailored to operate in different locations dependent upon the climates of the locations. Weather data can be obtained to determine the normal temperature differentials during particular times of the year between daytime and nighttime and this data can be used to select an appropriate bimetallic material. The present invention operates particularly well in climates such as deserts due to the large variation in temperature between the daytime and the nighttime. 
     One preferred use for the mechanical timer of the present invention is coupling it within a land mine or other ordnance device in order to render the mine safe after a specified interval of time. Depending upon the climate wherein the mine will be deployed, one could select a preferred bimetallic material and place the timer within the mine so that the member itself or something attached to the member moves into the space between the trigger and the firing pin within the mine. In operation, the member would move one serration during each cycle of the bimetallic material between its temperature dependent shapes. The timer can be designed with any number of serrations so that it will move the requisite distance over the selected number of days in order to move the member into position to render the mine safe. 
     Referring to FIG. 1, the mechanical, temperature activated timer comprises a housing  100 , having a cylindrical rod member  102  moveably attached to the housing  100 . The member  102  has unidirectional serrations  103  arranged uniformly along its periphery. The serrations  103  can be arranged along one or multiple sides along the periphery of the member  102 . First and second pawls  104 ,  104   a  are attached the housing  100  to traverse member  102  in one direction only with respect to the member  102 . The first pawl  104  is attached to cylindrical insert  105  that is contained within cylindrical insert  105   a . The second pawl  104   a  is attached to the bimetallic material  106  that is placed within the housing. The bimetallic material  106  maintains a first shape  106   a  below its transition temperature and a second shape (see  106   b  in FIG. 2) above its A transition temperature. The bimetallic material  106  is placed so that the change from the first shape  106   a  to the second shape  106   b  causes the attached second pawl  104   a  to transverse one serration  103  of member  102 . Because the pawls  104  are unidirectional, the change from the second shape  106   b  back to the first shape  106   a  does not force the member  102  back in the opposite direction. Therefore, because of the ratcheting action of each pawl,  104 ,  104   a , the subsequent movement by the member represents one transition cycle between daytime and nighttime temperatures, one can count the number of days by the number of serrations  104  that have been traversed. 
     The mechanical timer of the present invention can also be designed to provide actuation after a certain time period has elapsed. One preferred embodiment of the invention comprises rendering safe a land mine or other ordnance device. Referring again to FIG. 1, the invention may also comprise an actuation member  108 , attached to an end of the member  102 , so the actuation member  108  provides actuation after the member  102  moves a specified distance. This actuation member  108  can be used in order to render safe a land mine as depicted in FIG.  1 . The trigger  110  can be released so that a release spring  112  initiates the firing pin  114  to activate the mine. The present invention uses the actuation member  108  as a safety pin by moving it into the space  116  between the trigger  110  and the firing pin  114  so that the mine is rendered safe. 
     In the embodiment of the invention in FIG. 1, the bimetallic material  106 , and attached second pawl  104   a , is in contact with the member  102  through an aperture  118 . The area of the aperture  118  is such that the portion of the member  102  with the serrations  103  may slide through the aperture  118  due to the downward transitioning temperature motion of the bimetallic material  106 . This would only occur when force caused by the transition in shapes of the bimetallic material  106  occur. The first pawl  104  will prevent motion of member  102  during the ratcheting of the second pawl  104   a  due to the locked ratchet position of the first pawl  104 . When the bimetallic material  106  returns to its original shape, the second pawl  104   a  is in the locked ratchet position and moves the member  102  upward with the first pawl  104  now ratcheting and allowing member  102  to pass. 
     Regarding the housing  100  and the member  102 , almost any material may be used for their construction and may be selected by one skilled in the art. The exact shape of and distance between the pawls  104  may be selected by one skilled in the art depending upon the number and type of bimetallic material  106  used. One example of a member  102  with serrations  103  that could be employed in the present invention would be plastic wire ties used to harness items in the building and electronics industry. The bimetallic material  106  itself may be selected by one skilled in the art. Bimetallic materials are fabricated from two layers of metal such as Invar (an alloy of iron, nickel, carbon, manganese, and silicon that has a low coefficient of expansion) and steel having different coefficients of expansion. However, the bimetallic, snap-action disks may be fabricated from other materials having different temperature coefficients, whether metallic or non-metallic, and the term bimetallic is intended to encompass any structure utilizing materials of different temperature coefficient as a thermal actuator. One preferred bimetallic material are bimetallic, snap-action disks disclosed in the prior art referenced above. 
     A general embodiment of the invention being discussed above, FIG. 2 depicts a second embodiment of the invention that may be fabricated using only parts that are readily available from commercial sources. Referring to FIG. 2, a plurality of bimetallic, snap-action disks  106  are used. Each bimetallic, snap-action disk  106  rests on a washer  220  that is centrally disposed about the center line of the device and held in position by a sliding member  221 ,  222 . For each snap-action disk  106 , cylindrical cap  224  and attached cylindrical guide  225  fit atop washer  220  and are held centrally disposed about the center line of the device by the sliding member  221 ,  222  into which it is press fit. The cap  224  keeps the bimetallic, snap-action disk  106  centrally disposed therein. Cap  224  and guide  225  has a cylindrical aperture  226  centrally disposed on its upper side to allow a post  228  from the lower side of sliding member  222  to slide freely therein. 
     Sliding members  221 ,  222 ,  223  are contained within housing  100  and between end-caps  230 ,  232 . The housing  100  may be connected to the end-caps  230 ,  232  by many means known to those skilled in the art with a preferred means being trepans  109 ,  110 . A cylindrical central aperture  234  in the bottom end-cap  232  holds the bottom sliding member  221  in position. The cylindrical post  228  of the bottom sliding member  221  is press fit into the aperture  234 . Spring  236  is held in the compressed state between the upper tube end-cap  230  and upper most sliding member  223 . Bottom disk  238  has a centrally disposed cylindrical aperture  240  therein to allow the bottom post  228  of the bottom sliding member  221  to freely slide. Two threaded fasteners (not shown), 180° diametrically opposed, pass through holes  242 ,  244 , and  246  to ensure that the end caps  230 ,  232  are secure and compress bottom disk  238  against end cap  232 . This compression holds the bottom of the member  102  with first pawl  104 . FIG. 2 a  shows an enlarged depiction of circle  2  that more clearly shows the ratcheting mechanism described above. 
     Referring again to FIG. 2, an upper centrally disposed post  248  of the upper sliding member  223  passes freely through centrally disposed aperture  250  in end cap  230  and is press fit into centrally disposed cylindrical aperture  256  of first upper disk  254 . Second upper disk  262  is concentrically placed on top of first upper disk  254 . Two threaded fasteners (not shown), 180° diametrically opposed, pass through holes  258 ,  260  to compress first upper disk  254  against second upper disk  262 . This compression holds the upper portion of member  102  with pawl  104   a.    
     When the temperature of the above assembly exceeds the transition temperature of the bimetallic, snap-action disks  106 , the snap-action disks  106  change shape from  106   a  to  106   b  and allow the posts  228  extending through the apertures  226  in caps  224  to extend toward the sliding member  221 ,  222 ,  223  directly beneath the post  228 . This allows the spring  236  to uncompress and move the upper and lower set of pawls  104  closer together. When the temperature of the above assembly subsequently cools down to below the transition temperature of the bimetallic, snap-action disks  106 , the snap-action disks  106  revert back into their original shape  106   a . Thus, spring  236  is compressed and moves the upper and lower set of pawls  104  further apart. However, because the first and second pawls  104 ,  104   a  are unidirectional with respect to member  102 , member  102  is moved rather than returning to its original position. This repetitive action, the moving of the pawls  104 ,  104   a  closer and further apart from each other, will result in the above-described assembly moving up the serrations  103  of the member  102 . 
     Finally, the invention comprises a method for rendering safe land mines using the present invention described above by placing the invention within the land mine so that movement of the member prevents the land mine from firing. 
     What is described are specific examples of many possible variations on the same invention and are not intended in a limiting sense. The claimed invention can be practiced using other variations not specifically described above.