Abstract:
A safety shut-off system controls power supply to an appliance to prevent accidental fires and the like. The shut-off system includes a shut-off switch for connection in series with the power supply of the appliance. A controller opens the switch in response to detection by the detector of a prescribed fire condition. Failsafe means are provided on the controller for opening the shut-off switch in response to a malfunction of the detector to, ensure that the appliance is only permitted to operator under safe conditions when the detector is properly operating. In order to avoid false alarms the detector may take various forms including the detection of sound or other conditions which may be indicative of a potential fire. There are also incorporated switching capabilities to control additional a/c outlets, gas, propane and other appliances which work in unison with this system.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a safety shut-off system for controlling power supply to an appliance, for example a cooking range to discontinue power being supplied in the event of a prescribed fire condition. 
   BACKGROUND 
   A known occurrence when using a cooking appliance is for fires to develop when the appliance is left unattended. If forgotten for an elapsed period of time, the appliance being left on can cause the fire to continue for a greater duration or to worsen causing greater damage then had the appliance been turned off. 
   U.S. Pat. Nos. 6,130,412, 5,945,017 and 5,742,464 disclose devices which address similar problems. U.S. Pat. No. 4,659,909 to Knutson in particular discloses a kitchen range safety shutoff in which an appliance is arranged to be turned off in response to detection by a smoke detector of a possible fire. Reliance upon a smoke detector can be misleading however and can cause many false alarms. Furthermore arrangement of the shutoff disclosed in Knutson would permit the appliance to continue to operate in the event of a power loss or failure of some form to the detector. 
   SUMMARY 
   According to one aspect of the present invention there is provided a safety shut-off system, for controlling power supply to an appliance, the shut-off system comprising: 
   a shut-off switch for connection in series with the power supply of the appliance; 
   a detector for detecting a prescribed fire condition; and 
   a controller for opening the switch in response to detection by the detector of the prescribed fire condition; 
   the controller including failsafe means for opening the shut-off switch in response to a malfunction of the detector. 
   The use of a safety shutoff system including failsafe means ensures that the appliance is only permitted to operate under safe conditions when the detector is properly operating. In order to avoid false alarms the detector may take various forms including the detection of sound or other conditions which may be indicative of a potential fire. 
   The prescribed fire condition may include elevated temperatures, ionization of air, smoke which blocks the light transmission through air, sounds indicative of a fire about to start or any combination thereof. 
   The prescribed fire condition preferably comprises noises which are recorded by the detector which are indicative of the noises made by a cooking fire just before ignition thereof. 
   Loss of power to the detector is preferably interpreted as a malfunction for opening the switch. 
   There may be provided a relay to prevent opening of the switch until the prescribed fire condition is detected over an elapsed period of time. 
   The detector preferably activates a first indicator immediately in response to detecting a prescribed fire condition and the controller preferably activates a second indicator in response to the shutoff switch being opened. 
   The controller may include a reset switch located remotely therefrom. 
   Working components of the system may be integrally located within a common housing in a first embodiment of the system. Alternatively, working components of the system may be located remotely from one another within respective housings for hardwiring within a building structure. 
   There may be provided a receptacle receiving power from the power supply which is interrupted by the shutoff switch. 
   There may be provided a main control station monitoring a plurality of controllers in association with respective appliances. 
   The main control station preferably includes a memory for recording detections of prescribed fire conditions and resetting means for remotely closing the shut-off switch. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, which illustrate exemplary embodiments of the present invention: 
       FIG. 1  is a schematic view of the components of the safety shutoff system. 
       FIG. 2  is a flow chart illustrating the steps of operation of the system. 
       FIGS. 3 and 4  are perspective views of two different embodiments of the safety shutoff system. 
   

   DETAILED DESCRIPTION 
   Referring to the accompanying drawings, there is illustrated a safety shutoff system generally indicated by reference numeral  10 . The system  10  is particularly useful for shutting off appliances, for example an electrical cooking range  12 , in the event of a prescribed fire condition. 
   While various embodiments are possible and illustrated herein, the common features of each as schematically illustrated in  FIG. 1  will first be described herein. The system includes a controller  14  which interrupts the normal power supply  16  to which the cooking range  12  plugs into. The controller  14  branches the power supply  16  into a steady power branch  18  which remains unaffected by the shutoff of the system and a regulated power branch  20  which is shutoff and interrupted in response to the prescribed fire condition. The regulated power branch is interrupted by a shutoff switch  22  formed integrally within the controller  14  to interrupt power when the switch is open. The regulated power branch includes a socket  24  at a line voltage of 220 volts, or other suitable voltage where available, for plugging in a conventional electric cooking range therein. An electrical outlet is also provided having a receptacle  26  formed therein which is associated with each one of the regulated and steady power branches  18  and  22  at a lesser line voltage of 110 volts. 
   The controller also provides power to a relay  28  which relays an alarm signal from a detector  30  of the system. The detector  30  may comprise a conventional smoke detector for producing an alarm signal in response to heat, ionisation, smoke or any combination thereof. The detector  30  may also comprise a sound detector which is able to record sounds and compare them to known sounds indicative of a prescribed fire condition. An example of a sound which may be indicative of a fire is the sound produced by grease cooking just prior to ignition thereof to produce a grease fire on a cooking range. 
   The detector  30  typically receives power from the relay  28 , however in alternative embodiments the detector may be provided with a battery  32  for wireless and remote operation thereof. In this instance a transformer  34  is provided on the detector for communication with a receiver  36  on the relay  28 . 
   The relay  28  receives the alarm signal from the detector in the event that a prescribed fire condition is detected and the normal indicators of the detector itself are immediately activated in the form of lights or noise to alert an operator. The relay includes an integral time delay to record the alarm signal and in turn relay a shutoff signal to the controller only if the alarm signal is detected from the detector for an elapsed period of time. 
   The relay is arranged to receive a steady power signal from the detector under normal conditions and accordingly the alarm signal from the detector to the relay takes the form of an interrupted signal or absence of signal for an elapsed period of time. Accordingly if the detector either detects a prescribed fire condition or loses power or occurs any other failure, the absence of a signal from the detector to the relay in the form of the alarm signal will cause the relay to send a shutoff signal to the controller upon expiration of the elapsed period of time prescribed by the relay. Once the shutoff signal has been sent, the relay  28  is reset by a reset signal activated from the controller. Resetting typically takes place by means of a manual reset switch  38 . 
   Receipt of the shut-off signal from the relay by the controller cause the indicator  39  of the controller to be activated. This indicator may also be any conventional type of indicator including lights or noises and the like similar to the integral indicators of the detector. 
   Once the controller has been notified by a shutoff signal from the relay the shutoff switch  22  is opened to interrupt the regulated power branch  20  of the power supply which effectively cuts off power to the appliance. Activation by the manual reset switch  38  or other reset means causes power to be resumed and causes the relay and detector to be reset to start over the cycle of checking for prescribed fire conditions by the detector. 
   A main control station  40  may be provided which is particularly useful when a plurality of controllers are provided, each associate with a respective appliance, for example in an apartment complex where each apartment is provided with its own appliance regulated by power from a respective controller. The controller and the relay are suitably arranged for reporting alarm signals from the detector and shutoff signals from the relay so that these reported incidents can be kept in a memory log of the control station in which each incident is associated with an identification of the appliance in question affected by the detection of a prescribed fire condition. Resetting in this instance can be accomplished by a reset signal sent remotely from the main controller  40  directly to the controller  14  of a respective one of the appliances of the system. 
   In the embodiment of  FIG. 3 , the components of the system are shown supported integrally within a single housing  50  in which a male connector  52  and a female power connector  54  are provided for connection in series with the conventional plug in of an appliance to a receptacle in the wall. The indicator  39  of the system is provided in a visible location on the housing  50  as is the manual reset switch  38 . The detector  30  remains positioned remotely from the housing  50  in an optimum location for detecting the prescribed fire condition in the cooking area over the appliance. In the embodiment of  FIG. 3 , antennas relating to the transmitter  34  and receiver  36  are illustrated in solid line while a direct wired communication is shown in dotted line. 
   Turning now to  FIG. 4  a further embodiment of the system is illustrated in which the components are hardwired into a building. In this instance the reset switch  38 , the indicator  39 , the receptacles  26 , the socket  24 , the detector  30  and the controller  14  each include their own respective housing with wiring being mainly hidden from view within the walls of the building. 
   As illustrated in  FIG. 2 , operation begins with the detector first checking if a prescribed fire condition exists. This includes ensuring that the detector receives suitable power, that all connections are properly made and that any sensors of the detector have not detected any alarming conditions including heat, fire or smoke, and more particularly including sounds which may be indicative of a fire about to start, especially cooking fires for example grease fires. If a problem is detected and power is interrupted to the relay, an alarm signal is interpreted by the relay and this alarm signal is then reported to the main control station  40 . If the alarm signal persists for the prescribed elapsed period of time, a prescribed fire condition is determined and a shutoff signal is sent to the controller to open the shutoff switch and accordingly interrupt power in the regulated power branch which interrupts the power supply to the appliance. Though any indicators of the detector itself are already actuated at this point, further indication that the appliance is being shut off then takes place and the shutoff signal is further reported to the main control station  40 . The system remains in the shutoff condition until the circuit is reset by manual activation using the reset switch or by a remote reset signal from the main control station  40 . Once this reset signal is received, the shutoff switch is closed to resume normal power to the regulated power branch and the relay and detector are reset to their starting positions. The detector then resumes checking for prescribed fire conditions. In the event that the elapsed period of time is not met by the relay, the shutoff signal is not generated but instead the detector is reset and then is permitted to continue checking for prescribed fire conditions. 
   The system according to the present invention relates to a cooking appliance and method of controlling its safe operation, while cooking. 
   A hazard control unit is added to an existing kitchen range or other appliance (electric, gas or other power source) with a fail safe detection circuit to allow intervention. The hazard control unit includes a switch for controlling all heating stove and oven elements, of the cooking appliance, wherein the entire appliance power supply can be switched off in the case of a predetermined unsafe condition, which is before stove fires can develop. The hazard control unit itself has a feature which indicates its on position. When the device is in off position the stove power supply is also off. The safety system is for electric stoves and ovens and uses a sensor to determine when the stove is heating beyond a certain rate which could constitute a safety hazard and for detecting the excessive presence of heat, smoke and/or flame, or other types of hazard indicators as in specific types of sounds. When a predetermined tolerance is exceeded, the power supply of the electric stove is shut down. Other sources of power supply such as natural gas, propane, heating fuel or others can also be controlled and shut down. Based upon the principle that when there is heat, smoke, and accumulations of various types of sounds, a fire will follow, the system intervenes upon certain accumulations of such harmful environmental factors. The user of the appliance is notified by means of audible sound, flashing warning lights, vibrating mechanisms or other means. When the user does not respond within a predetermined time, the system takes over and shuts down all cooking operations. 
   Typical fire detectors note abnormal environmental conditions such as the presence of smoke or an increase in temperature, light intensity or total radiation. Detectors for this purpose operate on principles involving thermal expansion, thermoelectric sensitivity, thermo conductivity, or photosensitivity. Of special interest in the present invention is that a specific sound is associated with cooking grease fires, therefore, a sound detector is incorporated into the system. The sound detection assists in eliminating false alarms as a result of non-threatening and minor occurrences (from a toaster for example) to the environment as mentioned. 
   While various embodiments of the present invention have been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention. The invention is to be considered limited solely by the scope of the appended claims.