In particular it relates to a safety device for electric or gas stoves.

Background to the Invention Presently used electrical stoves have no means of eliminating fire hazards if left turned on and unattended for long periods of time. In currently used electrical stoves, only ovens associated with such stoves have user programmable timers which can shut off the oven after a certain period of time elapses.

However, those devices are designed to prevent overcooking rather than eliminating possibility of fires. In Toronto, Ontario in 1992 there were over 2400 house fires registered by the Fire Marshal's Office which were attributed to cooking on top burners of cooking stoves. In addition, there were 11 fatalities related to some of these fires. There are similar statistics for the past few years.

The present invention is designed to minimize fire hazards caused by leaving an operating stove unattended for long periods of time. The device can be used with an electric or gas cooking stove. In the case that an electrical stove is turned ON and left unattended for some period of time, the present device will shut OFF the power supplied to the heating elements after a preprogrammed period of time in order to substantially eliminate the fire hazard.

Summary of the Invention The present invention provides a safety device for a stove which has at least one heating element, said device comprising: a) a sensor for detecting the presence of a person in the vicinity of the stove; b) a heating element controller for controlling whether the heating element is on or off; c) a timer-controller, connected to the sensor and the heating element controller, which i) when a person

is in the vicinity of the stove as determined by the sensor, allows the heating element to be on, and ii) when a person is not in the vicinity of the stove as determined by the sensor, turns the heating element off after a predetermined time delay.

In one embodiment, the heating element is selected from the group consisting of a gas burner and an electric element.

In another embodiment, the sensor is selected from the group consisting of a motion sensor, a body heat sensor, a laser beam, a photoelectric sensor, an electromagnetic wave sensor and a floor pressure pad.

In yet another embodiment, the stove has from one to four heating elements on top of the stove.

In a further embodiment, the stove has from one to four heating elements on top of the stove and each heating element has a separate safety device.

In another embodiment, the stove has from one to four heating elements on top of the stove and at least two heating elements are simultaneously controlled by a single safety device.

In a further embodiment, the timer-controller has a timing relay.

In yet another embodiment, the sensor is attached to the stove.

In another embodiment, the sensor is separate from the stove and the timer-controller has means for receiving a signal from the sensor to indicate the presence or otherwise of a person in the vicinity of the stove.

The invention also provides a method for installing the present device as a separate, stand alone unit connected with the stove's electric circuitry.

In another embodiment, the device protects from fire hazards every single heating element (burner) of the electric stove with separate circuitry, relays and a separate timing relay (off relay) for each heating

element (burner) protected, in which case time-delay period can be specified individually for every heating element (burner).

In a further embodiment the device protects from fire hazards any pair of stove heating elements (burners) simultaneously with separate circuitry, relays and a separate timing relay (off relay) for each pair of heating elements (burners) protected, in which case the time-delay period can be specified individually for every pair of heating elements (burners).

In yet another embodiment, the device protects from fire hazards all heating elements (burners) of the stove simultaneously with a single timing relay (off delay) and a set of relays for all heating elements (burners) protected, in which case time-delay period can only be set to the same value for every heating element (burner).

In another embodiment, the device protects from fire hazards the oven of the electric stove by the use of a different timing relay which would not allow the heating element to be turned back ON once the pre- programmed period of time on the timing relay has elapsed, causing the oven to be turned OFF, in order to turn the oven back ON the user must turn it ON manually.

Brief Description of the Drawinqs Figure 1 is an electric schematic diagram of one embodiment of the present invention.

Figure 2 is a front view of a stove with a motion sensor installed on the stove.

Figure 3 is a top view of the stove shown in Figure 2.

Figure 4 is a side view of the stove shown in Figure 2.

Detailed Description of Preferred Embodiments The present invention is described with particular reference to the embodiment shown in the drawings.

Figure 1 shows an electric schematic diagram suitable

for operating a safety device of the present invention, in relation to an electrically operated stove with electric elements.

When an electric stove is in use the sensor used in the present invention monitors surroundings of the stove for human activity. If there is no human presence detected for a preprogrammed period of time, the heating elements of the stove will be automatically turned off.

The present device may turn the heating elements back on immediately upon detecting any human presence, e.g.

motion, in the stove area.

In another embodiment, there is a further safety feature in that the safety device prevents the heating elements from coming on, even after the preprogrammed period of time, and the heating elements can only be turned back on manually.

A preferred sensor is a motion sensor. It may be permanently attached or built in to the stove.

Alternatively, the sensor may be a separate from the stove and may be connected to the stove by connector wires. The sensor, when separate from the stove may be "connected" to the timer-controller by means of radio or other electromagnetic waves.

Other sensors may be utilized instead of motion sensors. For example, human presence may be detected by judicious placement of photoelectric sensors, infra-red sensors, laser beams, or similar sensors. An advantage of such sensors is that they may be adjusted with respect to the height from the ground that detection is made, in order to avoid being triggered by small children or pets. Other sensors, such as floor pressure pads, may be used.

A suitable motion sensor is an electronic device which monitors a certain area in front of the stove for human motion. If such motion is detected, the sensor generates an electric impulse. Preferably, the motion sensor is designed to detect human activity within an

arc of about 120 degrees horizontally and about 20 degrees vertically. The typical distance for detection is up to about 5 metres. This operational range allows it to be used in most kitchens. Preferably, the motion sensor's design specifications allow it to be adjusted at any angle in relation to the floor surface upon which the stove stands. This would permit the sensor to detect motion at and above a specific height from the floor surface, thus avoiding detection of the motion of pets, and children not old enough to operate the stove safely.

The sensor, e.g. motion sensor, can be situated on the top of the stove as shown in the drawings or could be situated at any convenient location on the front or side of the stove. Alternatively the sensor may be remote from the stove. In the event that the sensor is remote from the stove, it is clear that the sensor must be able to communicate with the timer-controller. This may be done with an electrical connection, transmittal of a signal through house wiring, through the air, e.g.

at radio or other frequency, or other known methods.

The timer-controller may comprise a timing relay (off delay), which is an electronic device which operates similarly to a regular relay, except that a built-in timing device delays switching off the relay for a preset period of time. In one embodiment, an electric impulse sent to this timing relay (off delay), when the timing device counts down the time-delay period, causes the timing device to reset itself again to the preset period of time and countdown restarts.

The time-delay period can be easily set to the desired value by individual stove users according to their needs. In some embodiments it may be wise to ensure that the user-settable time does not exceed a maximum value preset according to safety considerations, for example a maximum of about 30 minutes. The timing relay (off delay) is responsible for measuring time elapsed

since the motion sensor last registered human activity and for controlling relays connected directly to the heating elements of the stove. If no signal, e.g.

electric impulse, is received from the motion sensor during a preset time-delay period, the timing relay (off delay) disconnects electric power from other relays causing them to turn off the stove's heating elements.

Relays may be present, which are responsible for making or breaking a connection in order to supply or cut off electrical power in the device's electric circuitry.

An optional transformer may be needed to supply the appropriate voltage to the sensor, e.g. motion sensor, if it operates on a voltage other than normally available for the stove, e.g. a voltage other than a mains voltage of 115 volts.

Figure 2 shows the front of a stove 31 which has an oven 32, a drawer for pans 33, a stove top 34 with heating elements 35, and a control panel 36. Control panel 36 has control knobs 37 for controlling the amount of power supplied to heating elements 35. Control panel 36 also has oven control devices 38 for the oven 32.

There may be a clock 39. The stove of the present invention has a motion sensor 40 and a timing relay 41.

There may be lights, e.g. LED lights, (not shown) to indicate the mode of operation and status of the safety device of the present invention.

Figure 3 is a top view of the stove of Figure 2 and shows the stove top 34 with heating elements 35a, 35b, 35c and 35d. The front of the stove has a handle 42 for the door to oven 32. Control panel 36 has control knobs 37, oven control devices 38, clock 39, motion sensor 40 and timing relay 41, as in Figure 2. The arc over which motion sensor 40 will sense motion is shown by lines A-A-A. Typically, the angle between the lines is up to about 120 degrees.

Figure 4 is a side view of the stove of Figure 2.

The components are labelled as in Figures 2 and 3. The line of sight for the lower level of detection for motion sensor 40 is shown by line B-B. The motion sensor may be adjustable to alter the height of the line of sight B-B.

Figure 1 is a schematic representation of the electrical circuitry for one embodiment of the present invention. For an electrically operated stove, with electric elements, the present invention operates in the following manner. When the stove's heating element is activated by turning the power knob to the ON position, the power is supplied to connection 4 and 8 of relay 51 (Figure 1) which causes a coil to connect connectors 4 and 6 (Figure 1) together which in turn transfers electric current to connector 11 of the timing relay (off delay) 54. At same time, constantly powered connector 3 of relay 51 is connected with connector 5 of relay 51 and then electric power is transferred to transformer 56 and connector 10 of the timing relay (off delay) 54. Power supplied to connector 10 of the timing relay (off delay) 54 causes coil to disconnect connectors 8 and 11 of the timing relay (off delay) 54 which in turn disconnects electric current from relay 53. If no power is supplied to relay 53 the connectors 2 and 6 of this relay are connected and conduct electricity from the fuses to the heating elements allowing for normal stove operation.

When the power is initially supplied to the timing relay (off delay) 54 timer device gets set for a preprogrammed time period and countdown begins. Two possible events may occur: 1. If the motion sensor 40 does not detect any human motion (in its operating range) no impulse is sent to the connectors 5 and 7 of timing relay (off delay) 54, and after the preprogrammed period of time elapses connectors 8 and 11 in the timing relay (off delay) 54 get connected and power is supplied to connector 7 on

the relay 53. This disconnects connectors 2 and 6 which result in the cutting off supply of electric current to the heating element. The stove's heating elements stop producing any heat.

2. In the case when motion sensor 40 detects any human motion (in its operating range) the impulse from motion sensor 40 is sent to connectors 5 and 7 of the timing relay (off delay) 54 which causes the timing device to reset itself to the originally preprogrammed time period and countdown restarts. If the power at this time was not supplied to relay 53 (because previous countdown has not elapsed yet) nothing changes in the system, otherwise power supplied to the relay 53 is immediately cut off and the relay 53 connects its own connectors 2 and 6 which in turn supplies power to the heating elements. The stove's heating elements begin to produce heat again.

When the stove's heating element is deactivated by turning the power knob to the OFF position, the supply of electric current is withdrawn from the entire device and stove's heating elements stop to produce heat.

The present invention may operate automatically as described hereinabove. Optionally, the installation of the device on a stove may allow the user other modes of operation. For example, the timer-controller may turn the heating elements off after the predetermined period of time has elapsed but not turn the heating elements on again when the sensor detects human activity, unless the timer-controller is reset manually. This is basically a fail-safe mechanism and avoids false signals from turning the heating elements on prematurely. The installation may also have an over-ride to disable the safety device and allow the heating elements to be used without interruption by the safety device. This may be desirable in the event that low heat is required over a very long time.

For gas stoves, the flow of gas to individual burners may be controlled by means of a solenoid valve or similar. Accordingly, the sensor and timer- controller can be used to open or close the solenoid valve in a manner similar to the shutting off or turning on of the electric heating elements in an electric stove.