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TECHNICAL FIELD 
     The present disclosure relates to asphalt paving and particularly to an alert system for notifying when a paving compactor or other equipment is stopped on hot asphalt. 
     BACKGROUND 
     Asphalt paving involves depositing a mat of paving material such as hot asphalt on a bed and then compacting the asphalt to a uniform thickness and consistency. Compactors use different configurations for the compacting process. Some compactors use a steel drum with vibrators. Other compactors use separate wheels, while others use a combination of separate wheels and drums. When a compactor sits idle on an area of recently placed hot asphalt, the drum or wheels may sink into the asphalt and over-compact those areas under the drum or wheels. Once over-compacted, the dip formed in those areas is virtually unrepairable and the deformation compared to the remaining uniform asphalt mat will remain indefinitely. 
     U.S. Pat. No. 5,942,679 (the &#39;679 patent) discloses a system for monitoring environmental and machine conditions to create an index related to the state of compaction of an area where asphalt has been deposited. The index is displayed to an operator and represents a total amount of compaction that has been made on each area of the work site. The &#39;679 patent fails to disclose an alert system that notifies an operator when a compactor is stopped on an area of asphalt that is still hot enough to result in over-compaction of that area. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect of the current disclosure, an alert system for use in a compactor for an asphalt paving operation includes a speed sensor, a pavement temperature sensor, and an operator alert device. The operator alert device is configured to activate an alert to an operator when a command is received. The alert system may also include a controller determines, via the speed sensor, that the compactor is stopped, and also determines, via the pavement temperature sensor, that a pavement temperature proximate the compactor is above a threshold temperature. When both conditions are true, the controller issues the command to activate the operator alert device. The alert device signals the operator that the compactor may need to be moved to avoid over-compacting the area where the machine is resting. 
     In another aspect of the current disclosure, a method of setting an alert in equipment used in a paving application includes determining that the equipment has come to a full stop, determining that a surface proximate to the equipment is above a threshold temperature and starting a timer. When the timer reaches a preset time and the equipment has remained at the full stop for the entire preset time, the alert is activated, notifying the operator that the equipment should be moved. 
     In yet another aspect of the current disclosure, a system for activating an alarm in paving equipment includes a timer and a temperature sensor that conveys a temperature of a surface proximate to the paving equipment. The alarm may be configured to alert an operator of the paving equipment of a condition responsive to a signal from a controller. The controller may be coupled to the timer, the temperature sensor, and the alarm, and configured receive a signal indicating the paving equipment is stopped and to start the timer when both the paving equipment is stopped and a temperature of surface proximate to the paving equipment is above a threshold temperature. The controller may be further configured so that when the timer reaches a preset time, the controller activates the alarm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a compactor; 
         FIG. 2  is a block diagram of an exemplary controller for use in the compactor of  FIG. 1 ; and 
         FIG. 3  is a flowchart of an exemplary method of setting an alert in equipment used in a paving environment. 
     
    
    
     DETAILED DESCRIPTION 
     A compactor is a machine that compresses hot asphalt into a dense mat intended for use in applications from roadways to bicycle paths. Some compactors use steel drums with vibrators while others use rows of pneumatic tires, while yet others both a drum and a row of pneumatic wheels. Compactors can weigh over 10 tons and because of the relatively small contact area of, for example, two steel drums a compactor can provide very high pound per square inch pressures. 
     When left motionless for even a few minutes on a hot asphalt surface, a compactor can over-compact the area on which it is sitting and cause virtually irreparably damage in the form of a dip in an otherwise uniform surface. 
       FIG. 1  illustrates an exemplary compactor  100 . The compactor  100  may include a cab  102  or sunshade and drums  104 . Further details of an exemplary compactor  100 , such as vibrators, steering mechanisms, propulsion units, rollover protection systems, etc. are not disclosed herein but are known in the industry. 
     The compactor  100  also includes a temperature sensor  106 , such as an infrared temperature sensor that is capable of remotely reading a temperature of a surface  105  proximate to the compactor  100  at which the temperature sensor  106  is directed. In an exemplary embodiment, the temperature sensor  106  may be directed to a location between the drums  104 . In other embodiments, one or more temperature sensors may be directed in front of or behind the drums  104  and may be instead of or in addition to the illustrated temperature sensor  106  directed between the drums  104 . 
     Compactor  100  may also include a speed sensor  108  that measures and reports speed of the compactor in either direction. In some embodiments the speed sensor  108  may measure rotation of a drum  104  or may be coupled to a transmission (not depicted) that calculates compactor speed from an engine RPM and transmission gear ratio. In other embodiments, speed may be provided by a Global Positioning System (GPS) device (not depicted). In some embodiments, the speed sensor  108  may not be exclusively dedicated to providing speed for use in alerting an operator when stopping on hot asphalt. For example, the speed sensor  108  may be primarily used simply to indicate a speed of the machine to an operator in a conventional manner. 
     In another embodiment, speed may not be measured directly but may be derived from a control lever  115  used by an operator to select speed and direction. In this embodiment, the control lever  115  is pushed forward or backward to select direction and the distance that the control lever  115  is moved from a center position determines the speed. When the control lever is in the neutral position, no power is applied to drive the compactor  100 . An assumption can be made that when the control lever  115  is in the neutral position that the compactor  100  is stopped or soon will be. Evaluation of the control lever position can be used to derive when the compactor  100  is stopped. 
     The compactor  100  may optionally include an occupancy sensor  114  that may be used to determine that an operator is present in the cab  102 . The use of the optional occupancy sensor  114  is discussed in more detail below. 
     The temperature sensor  106 , speed sensor  108  or control lever position sensor and occupancy sensor  114  may be coupled to a controller  110 . The controller  110  is discussed in more detail below with respect to  FIG. 2 . The compactor  100  may also include an operator alert device  112  which may be directly or indirectly activated by the controller  110  responsive to certain conditions also discussed in more detail below. The operator alert device  112  may include a speaker, siren, indicator light, or other device used separately or in combination so that when activated there is a very high likelihood that an operator will notice that the alert device  112  has been activated. In other embodiments, the operator alert device  112  may be part of a console display or other user interface already present in the compactor  100 . The operator alert device  112  may also include a sign or an icon indicating that an undesirable condition may be present and/or simply that the compactor  100  should be moved. 
     The temperature sensor  106 , the speed sensor  108 , the operator alert device  112 , optionally, the occupancy sensor  114 , and at least those functions of the controller  110  associated with analyzing conditions and determining when to activate the operator alert device  112  may form an alert system  116  for use in the compactor  100 . 
       FIG. 2  is a block diagram of an exemplary embodiment of a controller  110 . The controller  110  may include a processor  120  and a memory  122  coupled by a data bus  124 . The controller  110  may also include or be connected to a user interface  126  that may include a display, a touchscreen, a keyboard, a pointing device, or a speaker. 
     Controller  110  may also include an input  130  that interfaces with the temperature sensor  106  and an input  132  that interfaces with the speed sensor  108 . Optionally, an occupancy sensor input  133  may be used in conjunction with other cab electronics to allow determination if an operator is in the cab  102 . A remote alert interface  131  may be optionally used to relay the alert signal related to stopping on a hot surface to a remote monitoring point  300 , such as a supervisor, a remote management facility, or a paving machine operating near the compactor  100 . The remote alert interface  131  may be a wireless interface that supports one or more local or wide area communication types, such as IEEE 802.11x (WiFi) or a cellular network protocol such as 3G, or other data communication path. 
     The memory  122  may include an operating system  134  and utilities  136  that provide, for example, diagnostics and error recovery routines, as well as low-level communication and interface support functions. An alert routine  138  may include modules that support various functions associated with providing the alert to an operator. These modules may include sensor interfaces  140  that communicate with the temperature, speed, and occupancy sensors via their respective inputs  130 ,  132 ,  133  and provide values for those parameters to a control logic module  144 . As discussed above, the speed sensor input  132  may either receive a signal from a device such as speed sensor  108  that measures actual speed or may receive a signal from a device such as a control lever  115  that controls speed. 
     The alert routine  138  may also include a module that implements a timer  142  and the control logic module  144  that evaluates data received from the temperature sensor  106 , speed sensor  108 , and occupancy sensor  114  and determines when to activate the operator alert device  112 . A settings module  146  may store various information that can be altered according to local conditions including ambient temperature, a threshold temperature of the asphalt, or a period of time counted by the timer  142 . An additional setting may be a type of asphalt, that is, a formulation of chemicals and aggregate being compacted. This setting may be used to adjust either the threshold temperature of the asphalt or the period of time for the timer  142  based on characteristics of the mix. For example, a stiffer mix being used on a cool day may tolerate a longer standing time before damage to the asphalt occurs, therefore, the time period of the timer  142  may be increased over a nominal value. While the settings module  146  may allow direct input of the time period of the timer  142 , there may be a maximum allowable time, such as 8-10 seconds, so that an operator does not disable the system by setting a very long standing time. 
     The settings module  146  may also store prompts for the operator or site manager that guide him or her through the process of selecting asphalt types and temperature settings by prompting for the various selections from a drop-down list. When information is not known, the settings module  146  may be programmed to select default values. In some instances, information may be relayed from the paving machine (not depicted), such as asphalt temperatures. The settings module  146  may also contain an algorithm or look-up table that evaluates the various inputs and selects an adjustment to the time period of the timer  142 . For example, each known pavement type may have a plus or minus adjustment factor. Similarly, temperatures above and below a pre-determined nominal temperature may also have a plus or minus adjustment factor. 
     INDUSTRIAL APPLICABILITY 
     An alert system  116  for compactors, or other vehicles that may park on hot asphalt, benefits both the contractors constructing the surface and the customers taking delivery of the finished job. Permanent dips in an asphalt surface can collect rain and cause premature eroding of the binder allowing cracks to form. Dips in the surface of roadways may cause vehicle wheels to bounce and cause instability. By alerting an operator when the conditions are present for unintended over-compacting, unintentional creation of such dips of this nature can be avoided. 
       FIG. 3  is a flowchart of a method  200  of setting an alert in equipment used in a paving application. At a block  202 , information used to determine characteristics for setting the operator alert device  112  may be received via a user interface  126 . The information may include a threshold temperature of the asphalt, a timer period, a type of asphalt, a thickness of the asphalt mat, vehicle weight, etc. 
     In some embodiments, default values may be installed at the time of manufacture or initial installation of the controller  110  into the compactor  100 . Each of the settings may affect corresponding characteristics of the evaluation process, as discussed more below. 
     At block  204 , a speed of the compactor  100  is evaluated to determine if the speed is zero or so low so that for all purposes the compactor is stopped. As discussed above, the speed of the compactor  100  may be directly measured via a speed sensor  108  or GPS, or the speed may be derived by monitoring the position of a speed/direction control lever. For some formulations of asphalt that are particularly soft, and/or when the ambient temperature is very high, a minimum speed threshold may be set to be the equivalent of stopped, for example, speeds less than 0.5 mile per hour. When the speed is at zero or below a threshold speed, the ‘yes’ branch may be taken from block  204  to block  206 . When the speed is above zero or above the threshold speed, the ‘no’ branch is taken and the loop continues at the entry to block  204 . 
     At block  206 , a temperature of the asphalt may be compared to a threshold temperature. In an embodiment, a nominal threshold temperature may be in a temperature in a range of 150° F. to 170° Fahrenheit (° F.). In another embodiment, the range may be from 158° F. to 162° F. Variations from the nominal threshold temperature and these ranges may be made based on asphalt formulation and ambient temperature. For example, a softer formulation may use a lower threshold temperature. In another example, when the asphalt layer is thicker, it may be more susceptible to over-compacting because of higher temperatures below the surface, so the threshold temperature may be lowered compared to the nominal threshold temperature. When the temperature of the asphalt is above the threshold temperature, the ‘yes’ branch may be taken from block  206  to block  208 . When the temperature of the asphalt is below the threshold temperature, the ‘no’ branch may be taken and the loop continued at the entry point to block  204 . 
     While the illustrated embodiment checks speed first, the checking of temperature and speed may be performed in the opposite sequence, that is, temperature first and then speed. Because both temperature and speed are, or can be, monitored continuously, an alternate implementation may simply use flags that are set when either condition is true and an interrupt can be activated when both flags are set. Other variations of determining when both conditions are true are also possible. 
     At block  208 , a timer  142  may be started. A timer  142  may be used because an operator may change direction from forward to reverse many times during the compacting process. During that direction change, the speed will necessarily be at or near zero for some period of time. Also during a direction change, an operator may shift in his or her seat to be better able to see in the new direction of movement, which may prolong the time during which the compactor  100  is stopped. If an alert device  112  is set during these intentional transition periods, operators would quickly learn to ignore the alert. Therefore, the timer  142  may delay issuing the command to activate the alert for a time period, for example, in a preset time range of from 3 seconds to 5 seconds in most embodiments. Ambient temperature and asphalt formulation may also affect the actual value of the timer setting. For example, a high ambient temperature may make a newly laid asphalt surface more susceptible to over-compacting, therefore, the threshold temperature may be reduced, the timer setting may be reduced, or both. Similarly, a thick asphalt layer may be more susceptible to over-compacting, so the timer period may be adjusted lower so that the timer  142  times out more quickly. 
     At block  210 , while the timer is running, the speed of the compactor  100  may be monitored. If the compactor  100  begins moving, the ‘no’ branch from block  210  may be taken to block  216 . At block  216 , the timer  142  may be reset and the method returns to block  204 . 
     If the compactor  100  remains at rest, a loop with block  210  and block  212  may be entered that lasts until the timer  142  expires. When the timer  142  expires while the speed is still at zero or below a threshold speed, the ‘yes’ branch may be taken to block  214 . As is known, the timer  142  may either count down from the time setting and expire when it reaches zero or may count up from zero to the time period. In other embodiments, the timer  142  may be a real time clock that expires when the real time clock reaches a calculated future time. 
     In some embodiments, block  212  may also include monitoring for the presence of an operator using an occupancy sensor  114  because if the operator leaves the cab  102  or operator station, waiting until the timer  142  expires may be cause the alert device  112  to be set after the operator is out of range and may not hear or see the signal. Therefore, sensing that an operator is no longer in the compactor  100  may override the timer aspect of block  212  and cause immediate execution at block  214 . The occupancy sensor  114  may be or include a seat switch, a camera, a foot plate switch or other mechanism. Similarly, if the ignition is turned off, an assumption can be made that the operator is leaving the compactor  100  and execution immediately continued at block  214 . 
     At block  214 , the alert device  112  may be activated. The alert device  112  may be an audible horn or siren, an audible signal from a speaker mounted near an operator, a visual lamp or flasher, a visual signal on a dashboard or operator console, or a combination of any of these. 
     The value of alerting an operator that a machine is stopping on soft asphalt, denoted by a high surface temperature, is not limited to compactors but may also be useful for other worksite equipment that may encroach a newly paved area, such as dump trucks, pickup trucks, or supervisor vehicles, among others. 
     The system is not limited to alerting the operator. Information related to standing on hot pavement may also be communicated to a site supervisor, master location, or other remote monitoring point for either the site or the equipment operations company. The information may be useful for monitoring the jobsite and for developing operator training. In an embodiment, a signal may be relayed to the paving machine that the compactor  100  is stopped on hot asphalt.

Summary:
An alert system in equipment used in an asphalt paving environment, such as a compactor, signals an operator when the equipment is stopped on hot asphalt, potentially over-compacting the area where the equipment is located. The alert system includes a surface temperature sensor so that the alert is only activated when there is a risk of over-compaction because the asphalt is still above a threshold temperature. The alert system may also include a timer so that the operator is not signaled during routine stopping associated with changing direction during compacting operations.