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CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of co-pending and now-allowed application Ser. No. 10/774,736, filed Feb. 9, 2004, which claims the benefit of U.S. Provisional Application Ser. No. 60/446,214, filed Feb. 10, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates generally to ladders that incorporate safety features, and more particularly to ladders that provide warnings to a user that the ladder is about to tip.  
         [0003]     Conventional household ladders (including step ladders and extension ladders) have enjoyed near universal acceptance by combining their ability to facilitate reaching remote areas with portable, human-carryable packaging. Nevertheless, conventional household ladders tip over when the combined center of gravity of a user (i.e., climber) and the ladder moves to a point beyond the foot of the ladder. In such a case a moment is produced, and while the frictional force of the wall tends to counter the torque caused by the moment, often it is not enough to prevent the ladder from tipping. Unbalance leading to ladder tipping typically occurs in one of two ways. In the first, the climber leans over too far to one side such that the center of gravity is beyond the ladder footprint. In the second, the ladder is placed leaning to one side, such as due to being placed on an uneven surface. In this latter case, the vertical line from the center of gravity of the ladder may not initially be beyond a foot of the ladder; however, as the climber moves higher up the ladder, the combined center of gravity of the ladder and the climber moves outside the ladder feet. Even though the imbalance leading to tipping of a ladder develops only gradually in this second instance, the climber remains unaware of the hazard until it is too late and the ladder tips over.  
         [0004]     Accordingly, there exists a need for improvements in ladder design to enhance ladder safety, especially as it relates to ladder tipping. Moreover, there exists a need for notorious warnings that can alert a ladder user that a dangerous operating condition is imminent. Furthermore, there exists a need for a ladder that can deploy additional stabilizing members in response to dangerous ladder operating conditions. In addition, there exists a need for such a ladder that provides the above while being inexpensive and without sacrificing its human-carryable attributes.  
       SUMMARY OF THE INVENTION  
       [0005]     These needs are met by the present invention. According to a first aspect of the present invention, a ladder configured to be carried by at least one human user is disclosed. The ladder includes a plurality of legs and rungs and a tip warning system, the latter of which includes one or more weight sensors coupled to the legs or rungs, a controller signally coupled to the one or more sensors, one or more alarms, and a transmitter and receiver cooperative with one another such that wireless communication is established between the alarm(s) and the rest of the tip warning system.  
         [0006]     Optionally, the ladder is configured such that the weight sensors are disposed adjacent the first end. Furthermore, the weight sensors are disposed beneath the first end such that when the first end is placed upon a ladder-supporting surface, the sensors can measure a weight imposed by the ladder (when no one is standing on it) or by the combined weight of the ladder and a user standing on the ladder. In one form, the predetermined signal threshold can be a sensed weight that falls below a predetermined minimum. For example, if the signal threshold is set such that a sensed weight reading of close to zero (or some other predetermined number) registers with the controller (which would indicate that the weight sensor in question is detecting a significantly reduced load corresponding to the predetermined number), then the tip warning system would activate to alert the user of the unstable condition. In another form, the weight sensors can be deployed on the ladder so that the predetermined signal threshold could either be the predetermined minimum weight reading as discussed above, or another parameter such as the difference or ratio between the plurality of weight sensors, where the difference exceeds a predetermined maximum. In this configuration, it is a weight differential (either in the form of a simple difference or a ratio of readings from the disparate sensors) that is the triggering signal rather than the absolute value of the single weight sensor configuration above. This is especially beneficial in determining the onset of a side-to-side imbalance prior to such an imbalance becoming dangerous. The controller can be analog-based, utilizing comparator integrated circuits, or digital-based, using analog to digital (A/D) converters and a microprocessor.  
         [0007]     In another option, the ladder is preferably a household ladder, such as a step ladder or an extension ladder. As mentioned above, the visual alarm may be made up of one or more lights, where in the case of a plurality of lights, each of the plurality of lights corresponds to particular ladder safety category, such as a first safety category, a second safety category and a third safety category, or to a system operational status (for example, indicating whether the system is on or off). The visual display could also be configured to show a continuous display of the imbalance in the form of a percent readout. In one particular form, the display could be in the form of a liquid crystal display (LCD) or light-emitting diode (LED), or as numeric quantity or as bars. In this way, the degree of imbalance, which could be a simple ratio of measured weight sums and differences, such as (W 1 −W 2 )/(W 1 +W 2 ), could be displayed as a percentage on an LCD or LED display or by a series of bars that light up progressively with increasing imbalance, or by a numerical output. Similarly, the audio alarm can be one or more buzzers, a prerecorded verbal warning or the like. In the case of a buzzer, the alarm can be configured to emit tones of progressively higher frequency or volume as the ladder gets closer to an unstable, imbalanced position.  
         [0008]     In yet another option, the wireless nature of the alarm(s) is such that it could be wearable on a user&#39;s belt, clothing, or around the neck, in a manner similar to that of a beeping pager, cell phone or the like. Thus, an operational condition of the ladder (including a sensed imbalance condition) can be transmitted wirelessly to the wearable alarm, where the wireless receiver is tuned to the frequency of the transmitter. An operational status light (for example, a green lighted condition) can be included to verify that the system is functioning, while unstable operating conditions can be shown by the yellow and red lighted conditions. In another embodiment, the transmitter may be configured to transmit only the raw readings, such as the voltage across each sensor, to the receiver of the alarm(s). In this configuration, the box used as housing for the alarm may contain the electronics needed to calculate the imbalance and to trigger the alarm(s), thereby simplifying the electronics associated with the controller, sensors or both. It will be appreciated by those skilled in the art that a power source, such as a battery, solar cell or the like can be used to energize the one or more alarms.  
         [0009]     According to still another aspect of the invention, a method of using a ladder is disclosed. The method includes configuring a ladder to include a tip warning system, placing the tip warning system in an operational condition, placing the ladder against a ladder engaging surface, and climbing the ladder such that indicia is provided to a climber thereof to indicate at least one of an operational status or a ladder safety category. Optionally, the ladder safety category comprises at least two first ladder safety categories, where the first is indicative of no imminent tipping, while a second is indicative of a possible tipping condition. As with the previous aspect, one or more of the alarms are configured to wirelessly receive imbalance or related measured signals from a transmitter that is in turn signally coupled to one or more weight sensors, controller or both. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0010]     The following detailed description of specific embodiments of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:  
         [0011]      FIG. 1  illustrates a ladder according to an embodiment of the present invention;  
         [0012]      FIG. 2  illustrates a Wheatstone bridge circuit incorporating weight sensors R 1  and R 2 ;  
         [0013]      FIG. 3A  illustrates one form of visual display used to indicate the level of imbalance;  
         [0014]      FIG. 3B  illustrates another form of visual display used to project a warning sign;  
         [0015]      FIG. 3C  illustrates another form of visual display used to project a percent of imbalance;  
         [0016]      FIG. 4  illustrates a modified Wheatstone bridge circuit incorporating the weight sensors R 1  and R 2 ;  
         [0017]      FIG. 5  illustrates the circuit of  FIG. 4  integrated with a quad comparator to sense ladder imbalance;  
         [0018]      FIG. 6  illustrates MOSFET logic using input from the comparator of  FIG. 5  to control a plurality of colored lights and buzzers;  
         [0019]      FIG. 7  illustrates an optional counterbalance weight attached to the ladder of  FIG. 1 ; and  
         [0020]      FIG. 8  illustrates an alternate embodiment of the ladder, where one or more wireless alarms can be worn by a user rather than mounted on the ladder. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     Referring initially to  FIGS. 1 and 3 A through  3 C, a ladder  10  according to an embodiment of the present invention is shown placed on a ladder-engaging surface  5  (such as a floor, the ground or the like). Ladder  10  includes a pair of legs  12  each defined by a first end  12 A positioned on ladder-engaging surface  5 , and second end  12 B opposite first end  12 A, and a plurality of rungs  14  that connect the legs  12  together. It will be appreciated by those skilled in the art that while the embodiment depicted in the figure is a fixed household ladder, the present invention is equally suitable to extension ladders, step ladders, folding ladders or the like. In the present context, the phrase “household ladder” is not meant to limit applicability to ladders used in private, residential settings. As such, the phrase is understood to include commercial and non-residential variants, so long as the ladder is portable by being human-carryable, such as those which can be carried by an individual. Ladders that generally do not qualify as “household” or “human-carryable” are those that form an integral part of a larger structure, such as a ladder that is permanently or semi-permanently secured to a fire-engine or related safety vehicle.  
         [0022]     Ladder  10  includes weight sensors  20 , controller  30  and one or more audio alarms  40  and visual alarms  50 , where visual alarm  50  is shown in one form as a series of lights  50 A,  50 B,  50 C. Visual alarm  50  can be made up of a series of lights, where the lights are color-coded. For example, a green light  50 A can indicate a first ladder safety category, while a yellow light  50 B can indicate a second ladder safety category (possibly coinciding with a condition requiring caution), and a red light  50 C to indicate a third ladder safety category (possibly coinciding with a dangerous operating condition with a significant amount of imbalance). Together, weight sensors  20 , controller  30  and alarms  40  and  50  make up tip warning system  60 , where tip warning system  60  can give the ladder “smart” features such that it can sense and convey to the user indicia of an impending dangerous operating condition faster than the user can.  
         [0023]     Referring with particularity to  FIGS. 3A through 3C , three variations on an alternate embodiment of the visual alarm is shown. In the first and third variations of  FIGS. 3A and 3C , meters  100  and  300  register respectively the degree and percentage of imbalance, while in a second variation of  FIG. 3B , a warning display  200  responds to controller  30  by highlighting various words dependent upon the ladder safety category (also known as the imbalance status), where the aforementioned first ladder safety condition is accompanied by a green color display  200 A of the word SAFE, a moderate amount of imbalance (commensurate with the aforementioned second ladder safety condition) is indicated by a yellow display  200 B of the word CAUTION, and a hazardous condition (equivalent to the aforementioned third ladder safety condition) indicated by a red display  200 C of the exclamation DANGER! as shown. Also as previously discussed, the hazardous condition could also be accompanied by an audible warning from audio alarm  40 . It will be appreciated that other forms of display, such as LED or LCD numeric value or a series of status bars, could be used as well to convey visual warnings, operational status or both.  
         [0024]     Referring with particularity to  FIG. 1 , weight sensors  20  are placed at the bottom of each leg  12 . In a preferable form, the weight sensors  20  are of lightweight construction such that they do not appreciably add to the overall weight of ladder  10 . In one form, the sensors  20  are of the laminated thin-film variety, where the electrical conductance is substantially proportional to the applied force or weight upon them. In the present context, the term “substantially” is utilized to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. As such, it refers to an arrangement of elements or features that, while in theory would be expected to exhibit exact correspondence or behavior, may in practice embody something slightly less than exact. The term also represents the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. Although shown with two weight sensors  20 , it is also within the scope of the present invention to configure the ladder  10  with a single weight sensor  20 , mounted at or near the first end  12 A of one of the legs  12 . As previously discussed, the sensors  20  can either be coupled so that they send a difference or ratio signal to controller  30 , or they can be independent, where each can respond to a predetermined weight threshold stored in the memory of controller  30 . For example, the stored threshold may be an equivalent to an absolute force value, such as something at or near zero pounds force, zero being the condition prerequisite on one of its legs  12  for ladder  10  tipping. By using weight sensors  20  rather than a conventional pendulum-based indicator, the present invention allows a more accurate reading to be taken, as the weight sensor (or sensors)  20  can account for user-generated moments that a pendulum-based or switch-based device would not be sensitive to. This additional sensitivity is possible because the tip warning system  60  of the present invention can discriminate against user weight on the lower rungs  14 A, as such condition is not as likely to produce a tipping condition as that when the user is on the middle or upper rungs  14 B,  14 C. By contrast, a pendulum-based or switch-based device is responsive only to the angle the switch or pendulum registers relative to a predetermined axis.  
         [0025]     Referring next to  FIG. 2 , a Wheatstone (or resistance) bridge type electrical circuit  36  was formed incorporating two weight sensors  20  that demonstrate variable resistance R 1  and R 2  and two fixed resistors  22  that demonstrate substantially fixed resistance R 0 , where the imbalance between the sensor voltages provided a measure of the weight imbalance at the legs  12 . As mentioned in the previous paragraph, weights measured by the sensors  20  can be used to send a weight difference or a weight ratio to the controller  30 . For example, the measure of imbalance between the two weight sensors  20  can be given by the simple ratio of (W 1 −W 2 )/(W 1 +W 2 ), where W 1  and W 2  represent the measured weight at each of the sensors  20 , respectively. In such circumstance, it will be readily appreciated that the range of imbalance is normalized between −1 and 1, thereby removing the need for calculating actual weight values and making the range of imbalance applicable for climbers of various weights. A zero reading means an exact balance (W 1 =W 2 ) between the two sensors  20 , and an imbalance measure of ±1 means instability resulting from either of the two sensors  20  registering a weight value that approaches zero. Thresholds for the aforementioned heightened alert displays  200 B and  200 C can be set by a choice of the values for the imbalance measure.  
         [0026]     Battery  32  (for example, a conventional nine-volt battery) provides power to controller  30 , although it will be appreciated that other power sources could be employed, including, for example, solar cells or related photovoltaic devices. When equal weight is applied to both sensors  20 , R 1  will equal R 2  and the corresponding output voltages V 1  and V 2  will be equal. Contrarily, a weight imbalance on ladder  10  shows up as a difference between V 1  and V 2 . In the simplest system, output voltages V 1  and V 2  could be wired directly to meter  100 , as shown in  FIG. 3A . In a preferred (but by no means necessary) system, the output voltages V 1  and V 2  will be further processed by either digital or analog electronics in controller  30  to provide a more reliable warning system. In one preferred embodiment, voltages V 1  and V 2  will be read by controller  30  that would include an analog-to-digital (A/D) converter and a microprocessor (not shown). The microprocessor will control the tip warning system  60  according to a program stored into its memory where, as previously discussed, the tip warning system  60  may include one or more of the aforementioned alarms, such as the lights  50 , meter  100 , display  200 , audio system  40  or some combination thereof. The measured values from the weight sensors  20  are then used to calculate the imbalance according to an algorithm and compared to a predetermined threshold. If controller  30  detects imbalance beyond the predetermined threshold, at least one of the audio and visual alarms  40 ,  50  are activated to alert the user. Tip warning system  60  can be programmed such that the companion audio alarm  40  responds either progressively (with, for example, a loudness or frequency level that increases concomitant to the aforementioned ladder safety category) or selectively (for example, not until a predetermined threshold). The indicia enabled by audio alarm  40  is beneficial in that a ladder user need not constantly maintain line-of-sight contact with a visual alarm to be apprised of a potentially dangerous ladder  10  operating condition. The two separate forms of indicia made possible by combining audio and video alarms  40 ,  50  further improves the chances that a user will be alerted that a potentially dangerous ladder operating condition has been, or is about to be, reached. Operational status of tip warning system  60  could be ensured by including a confirmation signal, such as a simple, slow-period (i.e., low frequency) beep from the audio alarm  40  or a slow-period flash of light from the visual alarm  50 .  
         [0027]     Referring next to  FIGS. 4 through 6 , an approach to sensing and alerting a user as to the presence of an ladder imbalance the is shown. Referring with particularity to  FIG. 4 , a modified Wheatstone bridge  80  incorporating the weight sensing resistors  20  (again capable of registering variable resistance R 1  and R 2 ) is shown.  FIG. 5  shows how the various connections a, b, C, d, e, f and g of the Wheatstone bridge  80  of  FIG. 4  are integrated with a quad comparator  90  to provide the imbalance triggers that are then fed into the controller  30  logic circuit shown in  FIG. 6 . While one way to operate the tip warning system  60  is to monitor in real time the weight on each leg  12  such that one or both of the alarms  40 ,  50  are activated whenever the sensed weight on either leg  12  falls below preset limits, it is more reliable and more independent of the user&#39;s weight to implement tip warning system  60  in the manner described next.  
         [0028]     The construction of modified Wheatstone bridge  80  is such that two voltage divider chains  82 ,  84  comprise three resistors each. The first chain  82  includes resistors R 3 , R 4  and R 5  while the second  84  includes resistors R 6 , R 7  and R 8 . In one implementation, the resistors R 3 , R 5 , R 6  and R 8  are 10 kilo-ohms each, while resistors R 4  and R 7  are each a 22 kilo-ohms adjustable potentiometers. The resistor junctions d, e, f and g provide convenient reference voltages for comparator  90  to analyze the voltage appearing at the junction b between the weight sensors  20  (with the aforementioned variable resistances R 1  and R 2 , respectively). As shown in  FIG. 5 , the four comparator circuits  92 ,  94 ,  96  and  98  within comparator  90  were set up to compare the voltage appearing at junction b with that at junctions d, e, f and g, respectively. Circuit  91  is arranged with two pairs of comparators that are wired such that switch signals occur at points A and B at certain levels of ladder imbalance as the values measured by weight sensors  20  vary. The variable resistors R 4  and R 7  can be adjusted to select the levels of imbalance between weight sensors  20  at which A and B switch to a low voltage reading. By choosing resistor R 7  to be greater than resistor R 4 , point A is ensured to switch from a high voltage to a low voltage before point B does. Initially, with weight sensors  20  being comparable in value, the output voltage at points A and B are both high. Analysis shows that point A stays high as long as (R 3 /(R 4 +R 5 ))&lt;(R 1 /R 2 )&lt;((R 4 +R 3 )/R 5 ) and switch to the low state outside this range (where R 1  corresponds to the weight sensor  20  located between points b and c in  FIG. 4  and R 2  corresponds to the weight sensor  20  located between points a and b). With resistor R 3  chosen equal to resistor R 5  for symmetric switching, the magnitude of resistor R 4  determines the point at which point A would switch. The larger the value of resistor R 4 , the greater the imbalance between R 1  and R 2  required for the switch to occur. As an example, if R 3 =R 5 =R 6 =R 8  and R 4  is twice the value of R 3 , and R 7  is three times the value of R 3 , then point A would stay high for a ratio of R 1  to R 2  (or R 2  to R 1 , depending on which of the weight sensors  20  registers the larger load) less than three, and would switch to low when the ratio becomes greater than three. Similarly, point B will switch from high to low when the ratio of R 1  to R 2  (or R 2  to R 1  for the reason mentioned above) is greater than four. The switching of points A and B can be exploited to activate the audio alarm  40  and the lights  50 A,  50 B,  50 C or displays  100 ,  200 , shown and described previously when a state of imbalance is approached or achieved.  
         [0029]     Referring with particularity to  FIG. 6 , specific implementation of the embodiment of tip warning system  60  employing the series of lights  50 A,  50 B,  50 C is shown. The simplest logic implementation was achieved using four MOSFETs  52 ,  54 ,  56  and  58  as shown. The output from point A is connected to the gate of MOSFET  52  while point B is connected to the gate of MOSFET  56 . With points A and B registering high voltages, only the green light  50 A is turned on. When point A switched to a low voltage, the yellow light  50 B comes on while green light  50 A is turned off. With point B also switching to a low voltage (while point A stays low), the red light  50 C is turned on while yellow light  50 B is turned off. Audio alarm  40  connected in parallel with the lights  50 A,  50 B,  50 C can provide audio warnings. As previously mentioned, different sounds (or even different audio alarms  40 ) can be used to give a user a distinguishable audible warning depending on the severity of the imbalance, where variations in tone, volume or any other easily-perceivable quantity can be utilized. In the case of tone variation, the audio alarm  40  can emit a slow beep or, alternatively, a low frequency signal for a first ladder safety condition, with progressively higher frequency signals for the second and third ladder safety conditions.  
         [0030]     The attributes of tip warning system  60  hitherto described are of a passive nature; while the system  60  senses force values and reports possible ladder imbalance conditions, it does nothing to correct a potentially dangerous situation. Referring next to  FIG. 7 , ladder  10  may incorporate active tip-prevention features that utilize the imbalance information generated in the tip warning system  60  by deploying one or more members that are attached to the ladder  10 . In one form, the tip-prevention member is made up of one or more deployable counterbalancing weights  15 . These weights  15  can be released upon appropriate signal from controller  30  to motor  18  that drives a screw  17  that turns gear  16  to which weight  15  is attached. When user  1  leans too far to one lateral side of ladder  10 , sensors  20  detect the weight shift, causing controller  30  to activate motor  18 , screw  17 , gear  16 , which in turn causes deployment of counterbalancing weight  15  to the opposing lateral side of ladder  10 . In other configurations, the weight  15  could be spring-loaded or even manually adjustable.  
         [0031]     Referring next to  FIG. 8 , an alternate embodiment of the ladder and tip warning system is shown. Ladder  110  includes weight sensors  120  and controller  130 , the latter of which is shown transmitting wireless signals  135  that can be received by an alarm housing  145  that can be worn by a ladder user  1  on a belt and contain audio and visual alarms  140 ,  150 . It will be appreciated that other alarm housing  145  mounting schemes could be used, including clipping it directly to the user&#39;s clothing. In one form, the housing  145  can be the approximate size and shape of a pager, cell phone or related portable electronic device. As before, the visual alarm  150  can be made up of a series of color-coded lights, an LCD or LED readout showing numeric values or (as presently shown) a series of bars to indicate operational status, hazardous operating conditions, or both. Similarly, the audio alarm  140  can be a buzzer, beeper, synthesized voice or other form of warning as known in the art. A receiver (not shown) can be included in housing  145  to accept the wireless signals  135  emanating from a transmitter (not shown) that is coupled to the controller  130  or the weight sensors  120 . The receiver is electrically (including signally) coupled to the alarms  140 ,  150  so that operational status (including the onset of hazardous operating conditions) can be delivered to user  1  in real-time. The receiver and transmitter may include an antenna and the electronic circuitry necessary to convert the sensed signals from the weight sensors  120  or controller  130  into a form suitable for wireless transmission as is known in the art. A battery, solar cell or related device can be included in housing  145  to provide the power necessary to operate the alarms  140 ,  150 . Moreover, in one form, the controller  130  is made up of that electronic circuitry necessary to convert the sensed weight values from the weight sensors  120  into a suitable signal for transmitting to the alarms  140 ,  150 . Comparitor circuitry and microprocessor-based devices are well-known examples of such circuitry.  
         [0032]     Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.

Summary:
A ladder with a tip warning system. The ladder is configured to be carried by at least one human user, and includes a plurality of legs with rungs disposed between the legs, and a tip warning system. The tip warning system includes weight sensors, a controller cooperative with measurements taken by the weight sensors, and a warning alarm made up of one or both of audio and visual components. The alarm components may be either hardwire connected to the rest of the system or wirelessly using a transmitter and a receiver for conveying a signal corresponding to an operational status of the ladder. Imbalance conditions, such as due to the weight of a climber approaching beyond the footprint of the ladder, generate an imbalance signal that activates the tip warning system to provide notorious indicia of such condition to the user.