BACKGROUND OF THE INVENTION 
     This invention relates to a ventilation hood with a safety system for use with a cooktop. More particularly, the invention relates to a ventilation hood with a safety system designed to substantially reduce the possibility of a fire occurring in the ventilation hood and ductwork thereof, as well as reducing humidity resulting from steam generated by the operation of the cooktop. The invention further relates to a combination of a ventilation hood and cooktop system, as well as a method of operation of a ventilation hood and a cooktop. 
     A number of ventilation hood control units are known for reducing the spread of smoke resulting from cooking operations on cooktops, as well as for removing humidity caused by steam resulting from cooking on the cooktop. 
     One known system provides a control or regulating device for a stove which activates, deactivates, controls and regulates the heat energy of cooking zones of the stove in dependence upon the resulting cooking steam. The control device and corresponding sensor of such a system is installed in the ventilation hood associated with the stove. Such a system is primarily focused on controlling the level of steam detected, to control operation of the cooking zones and not the ventilation fan. The makers of the system list as one of its advantages achieving a substantial savings of energy. 
     Another prior art system proposes a smart circuit device for a smoke exhauster for cooking. The circuit device includes a sensing circuit for sensing temperature and smoke. The motor of the fan and the exhauster is controlled to operate at a rotation speed conducive to reducing noise and save energy. The fan speed is varied in response to the quantity of smoke and is controlled by a fuzzy logic controller. 
     Yet still another system for a commercial or institutional kitchen provides that the volume rate of a cooking exhaust may be increased to improve the general comfort, health and safety conditions in the kitchen and the rest of the facility. More particularly, such a system senses a parameter in the ambient air environment such as temperature and/or gas level. Depending on the activity of the cooking units, the air control system causes the exhaust system to increase the volume rate to a higher volume rate to exhaust more air from the ambient air environment, thereby reducing the temperature in the facility to improve comfort and reduce load on an high volume air conditioning (HVAC) system. 
     While all of these systems provide advantages in reducing ambient smoke and/or steam for the purpose of providing a comfortable environment for persons using a cooktop, these conventional systems still fall short in providing an optimized arrangement designed to minimize fires occurring in ventilation hoods and cooktops. 
     More particularly, the use of cooktops in an incorrect manner contrary to a manufacturer&#39;s instructions can cause a fire. Many current gas cooktops have burners which can operate at energy levels of greater than 15,000 BTUs. Such cooktops include four to six burners and the simultaneous operation of multiple ones of these burners for a long period of time can overheat ventilation elements exhaust ducts. 
     The overheating of ventilation elements exhaust ducts is particularly of concern in circumstances in which such ventilation hoods and elements in ducts have accumulated oils and fat in the duct tubes thereof as such oils and fats are entrained with gases and/or vapors being drawn through the ventilation hood duct during cooking operations. If the heat conditions above the cooktop exceeds certain parameters such as may occur, for example, as a result of a flame, or through use of many of the high BTU burners at one time, a substantial portion of the heat generated may be drawn into the duct system and cause a fire as a result of, among other reasons, the ignition of the oils or fat accumulated in the duct tubes. 
     In accordance with the invention, there is provided a ventilation hood with a safety system, a combination of a ventilation hood with a cooktop and a method of controlling operation of a ventilation hood and cooktop, which avoids the problems of the previously discussed conventional systems, and which substantially reduces or eliminates the danger of fire occurring in the duct work of the ventilation hood as a result of operation of the cooktop. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, there is provided a ventilation hood with a safety system for use with a cooktop. The hood includes a duct structure for having air flow through the duct structure. A variable speed fan is associated with the duct structure for forcing air to flow from above the cooktop through the duct structure. A temperature sensor serves to sense the temperature above the cooktop and an alarming unit serves to provide at least one type of alarming indication. A controller unit is associated with the aforementioned elements for controlling operation of the fan and the alarming unit. The controller unit is configured for increasing the speed of the fan when in operation, and for activating the alarming unit to provide a first alarm indication upon the temperature above the cooktop reaching a first predetermined level, and for causing the alarming unit to provide a second alarm indication upon the temperature above the cooktop reaching a second (higher) predetermined temperature. 
     In accordance with one aspect of the present invention, the controller unit is also connected to a cooktop for controlling operation thereof. The controller unit is further programmed for causing the alarming unit to provide a third alarm indication upon the temperature above the cooktop reaching a third predetermined temperature and for shutting down the fan and the cooktop. 
     A method of operating a ventilation hood used with a cooktop includes providing a ventilation hood having a duct structure for having airflow therethrough. A temperature sensor is provided and serves to sense temperature above the cooktop. An alarming unit is also provided and serves to provide at least one type of alarm indication. A controller unit is provided which serves to control operation of the fan and alarming unit. The method involves sensing the temperature above the cooktop, increasing the speed of the fan and providing a first alarm indication upon the sensed temperature reaching a first predetermined level. A second alarm indication is provided upon the sensed temperature reaching a second predetermined (higher) level. 
     In accordance with a further aspect of the present invention, the controller unit is connected to a cooktop associated with the hood. The method further involves shutting off the cooktop and fan and providing a third alarm indication upon the sensed temperature reaching a third predetermined (even higher) level. 
     In accordance with yet another aspect of the present invention, the invention involves a combination of a ventilation hood and a cooktop including the features of the previously described ventilation hood as connected to the cooktop for controlling operation of the cooktop and the ventilation hood. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a front elevational view in partial section of a ventilation hood safety system connected to a freestanding range that comprises a cooktop, and showing the various elements of the present invention; and 
         FIG. 2  is a temperature status table illustrating the various operating states of the system of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the present invention, there is provided a ventilation hood  11  that includes a duct structure  13  and a variable speed fan  15  with a variable speed motor  17  and a plurality of associated fan blades  19 . The hood  11  also includes a temperature or heat sensor  21  and a steam or humidity sensor  23 , both connected to a controller unit  25 . Associated with the ventilation hood  11  is a free standing range  27  including an oven  29 , cooktop  31  including a plurality of burners  33 , and controls  35  for controlling operation of the oven  29  and the burners  33 . Also associated with the freestanding range  27  is an alarming unit including an alarm indicator  36  and an automatic control module  37 , which, along with the temperature sensor  21  and the humidity sensor  23 , is connected to the controller unit  25 . 
     The operation of the ventilation hood  11  and the cooktop  31  will hereinafter be described with reference to the temperature status table set forth in  FIG. 2  in accordance with which the system, including the controller unit  25  and the module  37 , is programmed. Although the system of the present invention is described as being implemented via software programming, the same function can be provided by the appropriate hardware, as will be readily apparent to those of ordinary skill in the art. Such programming may be done in numerous ways through firmware, downloadable software, and other means as also will be readily apparent to those of skill in the art. 
     When at least one of the burners  33  of the cooktop  31  is turned on through the use of the controls  35 , the automatic control module  37  provides feedback to the controller unit  25 , whereupon the controller unit  25  activates the fan motor  17  to cause blades  19  of the fan  15  to rotate at a first normal operating speed. If the temperature above the cooktop  31  reaches a first predetermined level, as detected by the temperature sensor  21 , the controller unit  25  causes the fan  15  to increase its speed and issues an alarm signal through the module  37 . For example, if the first predetermined level of the temperature is deemed, purely for exemplary purposes, to be a temperature of between 100 degrees Fahrenheit (=one temperature unit) to 150 degrees Fahrenheit (=one and one-half temperature units), then the controller unit  25  may be controlled to cause the fan  15  to increase its speed when a temperature at the first predetermined level of the temperature is detected. 
     In a typical embodiment, the alarm signal can be activation of a signal lamp in the alarm indicator  36  of the module  37 , which serves as a warning of high temperature in or in proximity to the ventilation hood  11 . 
     If the temperature above the cooktop  31  continues to rise to a second temperature level, as detected by the temperature sensor  21 , then the controller unit  25  causes the module  37  to issue a second alarm signal, for example, through a sound generator in the alarm indicator  36  as an audible signal. For example, if the second predetermined level of the temperature is deemed, purely for exemplary purposes, to be a temperature of between 150 degrees Fahrenheit (=one and one-half temperature units) to 200 degrees Fahrenheit (=two temperature units), then the controller unit  25  may be controlled to cause the module  37  to issue a second alarm signal when a temperature at the second predetermined level of the temperature is detected. 
     In an alternative aspect, the module  37  could have a visual display in the alarm indicator  36  or separately therefrom, capable of displaying text messages, and instead of an audible signal, a text message can be provided, both of which serve as a warning of an increased danger of catching fire which then allows the operator of the cooktop  31  to make decisions about continuing cooking operations. 
     If the temperature continues to rise to a third predetermined temperature level, as detected by the temperature sensor  21 , then the controller unit  25  issues a signal to the fan motor  17  and to the module  37  which immediately shuts down the fan motor to avoid additional heat being drawn into the duct structure  13 , and also causes the module  37  to shut down the burners  33  on the cooktop  31 . A text message is then issued on the display of the module  11  indicating that the fan  15  and the burners  33  were shut down to avoid a fire. For example, if the third predetermined level of the temperature is deemed, purely for exemplary purposes, to be a temperature of between 200 degrees Fahrenheit (=two temperature units) to 250 degrees Fahrenheit (=two and one-half temperature units), then the controller unit  25  may be controlled to issue a signal to the fan motor  17  and to the module  37  which immediately shuts down the fan motor. 
     In a yet still further aspect, the ventilation hood  11  also includes a humidity or steam sensor  23 , which is connected to the controller unit  25  and serves to detect steam or humidity generated from operation of the cooktop  31 . Independent of the operation of the inventive safety system with respect to temperature, if the humidity or amount of steam rises to certain levels, the controller unit is also programmed to increase the speed of the variable speed motor  17  in a predetermined relationship to the amount of steam being generated as a result of operation of the cooktop  31 . Additionally, it can be provided in this humidity reaction approach that the temperature driven controls will always take priority and will override steam/humidity driven control. 
     While the various elements including the temperature sensor  21 , the humidity/steam sensor  23 , the module  37 , the fan motor  17  and the controller unit  25  are shown in a hardwired configuration, it will be readily apparent to those of ordinary skill in the art that these units need not be hardwired and can operate in communication with each other through various other alternative technologies, for example, such as through infrared signals, radio signals, etc. 
     Yet still further, while in one specific aspect the system is shown as providing an alarm with a signal lamp for warning of reaching the first temperature level, an audible signal also can be provided. Also both audio and visual alarms can be provide at each preset warning level, which can be different in intensity or tone, as will be readily apparent to those of ordinary skill in the art. Alternatively, visible display issuing text message can be employed to provide clear information to the user of the cooktop. 
     Thus, the present invention provides a ventilator hood safety system having a controller unit connected to a cooktop for controlling the operation thereof, and the controller unit is further programmed for causing an alarm unit to provide a third alarm indication and for shutting down the cooktop and the fan upon the temperature above the cooktop reaching a third predetermined temperature. 
     The present invention additionally provides a ventilator hood safety system having a humidity sensor for sensing the humidity resulting from steam in proximity to the hood, and associated with the controller unit for having the controller unit increase the speed of the fan in response to increasing humidity. Also, the safety system includes an alarming unit including a signal lamp, and arranged for operation the controller unit for providing the first alarm indication as activation of the signal lamp. The alarming unit may include a sound generator and is arranged for operation with the controller unit for providing the second alarm indication as an audible signal generated by the sound generator. Also, the alarming unit may include a signal lamp and a visual display which are arranged for operation with the controller unit for providing the first alarm indication as activation of the signal lamp, and the second alarm indication may display a text message on the visual display warning of the danger of fire. 
     Having thus generally described the invention, the same will become better understood from the independent claims as set forth in a non-limiting manner.
A ventilating hood and cooktop system includes safety components to reduce or eliminate the possibility of a fire in the ventilating hood. The system provides elements for sensing the temperature over the cooktop. When the temperature reaches a first predetermined level, the ventilation fan speed is increased. The system includes alarm warning elements which issue different signals depending on the temperature above the cooktop. If a maximum temperature is reached, the system shuts off the fan of the ventilating hood and shuts down the cooktop.