Abstract:
A warning circuit for use on ladders includes a first sensor responsive to the placement of a first of a user&#39;s feet thereon and a second sensor responsive to the placement of a second of the user&#39;s feet thereon. The second sensor is electrically connected in series to the first sensor, and a relay is electrically connected in series to one of the first and second sensors. A power source has a power output terminal electrically connected in series to the other of the sensors connected in series. A sound device is electrically connected to a load output of the relay and to the power source. The load output of the relay is energized only when the first sensor is activated prior to activation of the second sensor whereupon the load output then energizes the sound device.

Description:
FIELD OF THE INVENTION 
     The present disclosure generally relates to apparatuses and methods for ladder safety. More particularly, the present disclosure relates to a warning apparatus on a ladder for warning a climber when climbing to the top steps or descending to the bottom steps of the ladder. 
     BACKGROUND OF THE INVENTION 
     Ladders have become a useful tool to almost every individual in society and permit individuals to climb to heights unreachable by the unaided. Individual ladders can range from small stepladders having 2-3 rungs allowing an individual to access that one item just out of reach to large extension ladders that can extend to 40 feet and more for scaling large walls, trees, and buildings. One or more ladders can be found in almost every household and are utilized by professional tradesmen of all types. 
     Unfortunately, the design and usage of a ladder also contributes to its inherent instability and danger. A ladder is typically constructed of two spaced apart vertical stiles with a plurality of regularly spaced rungs extending between the stiles. The bottom end of each stile also functions as the support foot for the ladder at its base. While the base of some ladders may be wider than the ladder top, the overall width of the ladder is relatively narrow when compared to its height. As the width to height ratio decreases (with increasing ladder height) the lateral stability of the ladder also decreases such that a minor lateral shift in the combined center of gravity of the ladder, including the user who is climbing the ladder, can result in an unwanted lateral shift of the ladder. As the user climbs the ladder the combined center of gravity also translates up the ladder, and consequently the danger from a minor lateral shift in the center of gravity increases proportionately as the center of gravity rises. In extreme cases, the unwanted lateral shift can and often does result in the ladder falling to the ground with the user suffering serious injuries as a result thereof. The U.S. Consumer Product Safety Commission (CPSC) reports that each year there are in excess of 150,000 emergency room-treated injuries in the U.S. relating to ladders. A significant portion of which are attributable to ladder falls. 
     These instabilities require the total concentration of the individual climbing or descending the ladder. Probably the greatest danger to a climber is when he is approaching the topmost or bottommost rungs. He is often unable to look down to determine on which rung he is standing. Consequently, while ascending, he may think he has more rungs on which he can step at the top of the ladder thereby resulting in the ladder tipping or losing a stable foothold resulting in the ladder tipping while at a significant height. Also, when descending, he may believe he is on the bottom rung and prepare his next step for dismounting from the ladder. If however, he has misjudged the rung, he may end up attempting to dismount from a rung higher on the ladder and then fall the remainder of the way to the ground. 
     The inability to determine the exact rung on which he is standing at the top while climbing or at the bottom when descending will very likely result in injury to the climber unless he is able to determine when he has reached a specific top or bottom rung. Therefore, there is a need for a warning system on the ladder to automatically indicate to the climber when he has reached the top or the bottom to prevent injury to the climber. 
     SUMMARY OF THE INVENTION 
     The present disclosure is generally directed to an electronic warning circuit for installation on a ladder of the type having a plurality of spaced apart rungs for warning a user of approaching an end of the ladder in a single direction. The warning circuit includes a first sensor responsive to the placement of a first of a user&#39;s feet thereon and a second sensor responsive to the placement of a second of the user&#39;s feet thereon. The second sensor is electrically connected in series to the first sensor. A relay is electrically connected in series to one of the first and second sensors, and a power source has a power output terminal electrically connected in series to the other of the sensors connected in series. A sound device is electrically connected to a load output of the relay and to the power source. The load output of the relay is energized only when the first sensor is activated prior to activation of the second sensor whereupon the load output then energizes the sound device. 
     In another aspect, the relay is a single shot latching relay. 
     In still another aspect, the load output, when energized, is energized for a predetermined period of time and is then de-energized. 
     In yet another aspect, the first sensor is a normally open push-to-make switch and the second sensor is a normally open momentary push-to-make switch. 
     In a still further aspect, the single shot latching relay includes a start switch terminal, a common terminal, a power input terminal, and a load output terminal. The start switch terminal is electrically connected to one of these sensors such that the power terminal of the power source, the first sensor, the second sensor, and the start switch terminal are electrically connected in series. The common terminal is electrically connected to a common terminal of the power source and the power input terminal is electrically connected to the power terminal of the power source. The load output terminal is electrically connected to the sound device, and the sound device is further connected to the common terminal of the power source. 
     In another aspect, the power source is a battery, wherein the power output terminal of the power source is a positive terminal of the battery and the common terminal of the power source is a negative terminal of the battery. 
     In another aspect, the sound device is a piezo sound generator. 
     In a still further aspect, a safety ladder incorporating a warning circuit indicating when a user approaches an end of the safety ladder includes a ladder having two stiles laterally spaced one from the other and a plurality of rungs substantially regularly spaced therealong. The rungs are affixed to and laterally extend between the stiles. An electronic warning circuit sensing a user approaching an end of the ladder and issuing an audible warning in response thereto includes a first sensor affixed to a first of two adjacent rungs and is responsive to the placement of a first of a user&#39;s feet thereon. A second sensor is affixed to a second of the two adjacent rungs and is responsive to the placement of a second of the user&#39;s feet thereon, wherein the second sensor is electrically connected in series to the first sensor. A relay is electrically connected in series to one of the first and the second sensors. A power source has a power output terminal electrically connected in series to the other of the sensors in series therewith, and a sound device is electrically connected to a load output of the relay and to the power source. The load output of the relay is energized only when the first sensor is activated prior to activation of the second sensor, the load output then energizes the sound device. 
     In yet another aspect, the relay is a single shot latching relay. 
     In another aspect, the load output, when energized, is energized for a predetermined period of time and is then de-energized. 
     In still another aspect, the first sensor is a normally open push-to-make switch and the second sensor is a normally open momentary push-to-make switch. 
     In yet another aspect, the single shot latching relay includes a start switch terminal, a common terminal, a power input terminal, and a load output terminal. The start switch terminal is electrically connected to one of the sensors such that the power terminal of the power source, the first sensor, the second sensor, and the start switch terminal are electrically connected in series. The common terminal is electrically connected to a common terminal of the power source and the power input terminal is electrically connected to the power terminal of the power source. The load output terminal is electrically connected to the sound device and the sound device is further connected to the common terminal of the power source. 
     In another aspect, the power source is a battery, wherein the power terminal is a positive terminal of the battery and the common terminal is a negative terminal of the battery. 
     In still another aspect, the sound device is a piezo sound generator. 
     In yet another aspect, the two adjacent rungs are proximate to a top of the ladder wherein the first rung is a lower one of the two adjacent rungs and the second rung is an upper one of the two adjacent rungs. 
     In a still further aspect, the two adjacent rungs are a lowermost two rungs of the ladder wherein the first rung is an upper one of the two adjacent rungs and the second rung is a lowermost rung of the two adjacent rungs. 
     In another aspect, a safety ladder incorporating a warning circuit indicating when a user approaches a top or a bottom of the safety ladder comprises a ladder having two stiles laterally spaced one from the other and a plurality of rungs substantially regularly spaced therealong. The rungs are affixed to and laterally extending between the stiles. An upper electronic warning circuit is incorporated with two adjacent rungs proximate to a top of the ladder and senses a user ascending the ladder. The upper electronic warning circuit issues an audible warning in response thereto wherein the upper electronic warning circuit includes a first sensor affixed to a lower one of the two upper adjacent rungs and is responsive to the placement of a first of a user&#39;s feet thereon. A second sensor is affixed to an upper one of the two upper adjacent rungs and is responsive to the placement of a second of the user&#39;s feet thereon wherein the second sensor is electrically connected in series to the first sensor. A single shot latching relay is electrically connected in series to one of the first or the second sensors, and a power source having a power output terminal that is electrically connected in series to the other of the sensors in series. A sound device is electrically connected to a load output of the single shot latching relay and to the power source. The load output of the relay is energized only when the first sensor is activated prior to activation of the second sensor, the load output then energizes the sound device. A lower electronic warning circuit is incorporated with two adjacent lowermost rungs of the ladder and senses the user descending the ladder. The lower electronic warning circuit issues an audible warning in response thereto wherein the lower electronic warning circuit includes a first sensor affixed to an upper one of the two lowermost adjacent rungs and is responsive to the placement of a first of a user&#39;s feet thereon. A second sensor is affixed to a lower one of the two lowermost adjacent rungs and is responsive to the placement of a second of the user&#39;s feet thereon wherein the second sensor is electrically connected in series to the first sensor. A single shot latching relay is electrically connected in series to one of the first and second sensors. A power source has a power output terminal electrically connected in series to the other of the sensors in series. A sound device is electrically connected to a load output of the single shot latching relay and to the power source. The load output of the relay is energized only when the first sensor is activated prior to activation of the second sensor wherein the load output then energizes the sound device. 
     In another aspect, the first sensor is a normally open push-to-make switch and the second sensor is a normally open momentary push-to-make switch. 
     In a still further aspect, the single shot latching relay includes a start switch terminal, a common terminal, a power input terminal, and a load output terminal. The start switch terminal is electrically connected to one of the sensors such that the power terminal of the power source, the first sensor, the second sensor, and the start switch terminal are electrically connected in series. The common terminal is electrically connected to a common terminal of the power source and the power input terminal is electrically connected to the power terminal of the power source. The load output terminal is electrically connected to the sound device and the sound device is further connected to the common terminal of the power source. 
     In yet another aspect, the upper electronic warning circuit and the lower electronic warning circuit are powered by a single battery. 
     These and other features, aspects, and advantages of the invention will be further understood and appreciated by those skilled in the art by reference to the following written specification, claims and appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described, by way of example, with reference to the accompanying drawings, where like numerals denote like elements and in which: 
         FIG. 1  presents a right front perspective view of a ladder embodying the present invention, wherein top and bottom rungs incorporate sensors to activate an alarm; 
         FIG. 2  presents a left front perspective view of the ladder of  FIG. 1 ; 
         FIG. 3  presents a front elevation view of the ladder; 
         FIG. 4  presents a right side elevation view illustrating a user descending at the bottom rungs and a user ascending at the top rungs; 
         FIG. 5  presents a circuit diagram of a representative ladder incorporating alarms at a top and bottom of the ladder; and 
         FIG. 6  presents a circuit diagram for a single alarm circuit for use on a ladder. 
     
    
    
     Like reference numerals refer to like parts throughout the various views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the described embodiments or the application and uses of the described embodiments. As used herein, the word “exemplary” or “illustrative” means “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other implementations. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art to make or use the embodiments of the disclosure and are not intended to limit the scope of the disclosure, which is defined by the claims. For purposes of description herein, the terms “upper”, “lower”, “left”, “rear”, “right”, “front”, “vertical”, “horizontal”, and derivatives thereof shall relate to the invention as oriented in  FIG. 1 . Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. 
     In one exemplary implementation of the invention, a safety ladder  100  is shown in  FIGS. 1-3  illustrating its various components where a ladder  102  is generally comprised of a left vertical stile  104  and a right vertical stile  106  laterally separated one from the other with a plurality of substantially regularly placed rungs  110  affixed to stiles  104  and  106  and extending therebetween. The rungs  110  can also include treads  112  thereon to prevent a user from slipping. A foot  108  at the bottom of each stile  104 ,  106  can help to stabilize the ladder  102 . The safety ladder  100  includes a single warning circuit  140  or a dual warning circuit  130  which substantially combines a lower warning circuit  140  with an upper warning circuit  160  ( FIG. 5 ) to provide a user with an audible warning that the user has reached either the top or the bottom of the ladder. 
     Referring now to  FIGS. 1-3, and 5-6 , the dual warning circuit  130  is powered by a battery  132  having a power output terminal  134  (positive terminal) and a common terminal  136  (negative terminal). The lower warning circuit  140  functions to warn a user when he has reached a lower pair of rungs  114 ,  116  of the safety ladder  100  when descending therefrom. A first sensor  142  is affixed to a first lower rung  114  (as shown the rung  114  is the second rung from the bottom) and as configured the first sensor  142  is a normally open push-to-make switch. A second sensor  144  is affixed to a second lower rung  116  below first lower rung  114 , and as configured the second sensor  144  is a normally open momentary push-to-make switch. The first sensor  142  and the second sensor  144  are electrically connected one to the other in series. The first sensor  142  is also connected to the positive terminal  134  of the battery  132 . The second sensor  144  is further connected to a start switch terminal  152  of a relay  150  here configured as a single shot latching relay. The relay  150  also includes a common terminal  154  which is connected to the negative terminal  136  of the battery  132 . A power input terminal  156  is connected to the positive terminal  134  of the battery  132 . The relay  150  further includes a load output terminal  158  which is connected to a sound device  146  such as a piezo sound generator. The sound device  146  is also connected to the negative terminal  136  of the battery  132  to complete the circuit. While the lower pair of rungs  114 ,  116  is illustrated as the bottommost two rungs a different pair of lower rungs may be chosen for incorporation of the lower warning circuit  140 . 
     The upper warning circuit  160  functions to warn a user when he has reached an upper pair of rungs  118 ,  120  of the safety ladder  102 . A first sensor  162  is affixed to a first upper rung  118  and as configured the first sensor  162  is a normally open push-to-make switch. A second sensor  164  is affixed to a second upper rung  120  above first upper rung  118 , and as configured the second sensor  164  is a normally open momentary push-to-make switch. The first sensor  162  and the second sensor  164  are electrically connected one to the other in series. The first sensor  162  is also connected to the positive terminal  134  of the battery  132 . The second sensor  164  is also connected to a start switch terminal  152  of a relay  150  here configured as a single shot latching relay. The relay  150  also includes a common terminal  154  which is connected to the negative terminal  136  of the battery  132 . A power input terminal  156  is connected to the positive terminal  134  of the battery  132 . The relay  150  further includes a load output terminal  158  which is connected to a sound device  166  such as a piezo sound generator. The sound device  166  is also connected to the negative terminal  136  of the battery  132  to complete the circuit. The upper pair of rungs  118 ,  120  is typically not the uppermost pair of rungs  110 , but the rung pair is typically represent the uppermost rungs to which a user may safely climb. 
     The functionality of the single shot latching relay  150  is illustrated in  FIG. 6  wherein step curve  182  illustrates the power input over time to the power input terminal  156  of the relay  150 . The step curve  184  illustrates the momentary power pulse to activate the load output of the relay  150 , and the step curve  186  illustrates the timed power output to the sound devices  146 ,  166 . 
     In use, as illustrated in  FIG. 4  and also in reference to  FIG. 5 , a user climbs the safety ladder  102 . When approaching a top of the safety ladder  100 , the user&#39;s first, foot  192  steps on the first upper rung  118  which closes the normally open switch  162 . As the user continues to climb his weight is supported by the first foot  192  while his second foot  194  is raised to the second upper rung  120 . As he begins to shift his weight from his first foot  192  to his second foot  194 , the normally open momentary switch  164  closes and the normally open switch  162  remains closed. The normally open momentary switch  164  only closes momentarily and then resets to an open state even though the user&#39;s second foot  194  continues to put pressure on the switch  164 . The momentary closing of the normally open momentary switch  164  is sufficient to complete the current path from the positive terminal  134  of the battery  132  to the start switch terminal  152  of the relay  150  thereby generating the step curve  184  to activate the load output of the relay  150 . The single shot latching relay  150  then generates the load output represented by the step curve  186  at load output terminal  158  which continues for a predetermined time duration that is longer than the time duration of the momentary triggering pulse  184 . The output load  186  drives the sound device  166  to provide an audible warning for the time duration of the output load represented by the step curve  186  thereby indicating that the user has reached the uppermost safety limit of the safety ladder  100 . 
     Similarly, when the user has completed his task at the top of the safety ladder  100  he begins to descend. When approaching a bottom of the safety ladder  100 , the user&#39;s first foot  192  steps on the first lower rung  114  which closes the normally open switch  142 . As the user continues to descend, his weight is supported by the first foot  192  while his second foot  194  is lowered to the second lower rung  116 . As he begins to shift his weight from his first foot  192  to his second foot  194 , the normally open momentary switch  144  closes and the normally open switch  142  remains closed. The normally open momentary switch  144  only closes momentarily and then resets to an open state even though the user&#39;s second foot  194  continues to put pressure on the switch  144 . The momentary closing of the normally open momentary switch  144  is sufficient to complete the current path from the positive terminal  134  of the battery  132  to the start switch terminal  152  of the relay  150  thereby generating the step curve  184  to activate the load output of the relay  150 . The single shot latching relay  150  then generates the load output represented by the step curve  186  at the load output terminal  158  which continues for a predetermined time duration that is longer than the time duration of the momentary triggering pulse  184 . The output load  186  drives the sound device  146  to provide an audible warning for the time duration of the load output represented by the step curve  186  thereby indicating that the user has reached the bottom of the safety ladder  100 . 
     Since many modifications, variations, and changes in detail can be made to the described preferred embodiments of the invention, it is intended that all matters in the foregoing description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents.