Patent Application
20100126978
The present invention relates to an improved heating pad adapted for personal use under a desk to warm feet. It has an improved ground thermal insulation system and incorporates an automatic electronic shutoff system, thereby making it both safe and practical for use at the workplace or in a home office.
The problem of office employees having cold feet while working has been resolved in a plethora of methods. There is a multitude of various space heaters and space heater designs that have been used. The vast majority of these tend to heat the space under the desk and draw moderate electrical loads. It is commonplace to see employees using miniaturized ceramic space heaters that use 800 to 1500 W of electricity.
These methods of warming feet are dangerous for many reasons. The elements can burn the skin if contacted. Most must be switched on and off manually and offer no protection against units that are knocked over. They can be placed too close to combustible materials. The heat losses to the proximate space are huge and much of the heat does not reach the worker's feet unless they position their feet temporarily in front of the device. They can easily be forgotten and left on, particularly when the worker leaves their desk momentarily then is sidetracked away from their desk for an extended period of time. The electrical draw of several of these can overload the building electrical circuits including cubical power distribution. They require constant attention to the settings. Insufficient air circulation under the desk can cause the thermal switch to regularly activate switching off the unit for a temporary period of time to protect the elements. Lastly, many of these are not used so as to meet fire prevention regulations. In fact, many transmit heat to the abutting flooring materials in excess of what fire codes allow.
The present invention is a planar, pad heater that incorporates a sensing device to turn off the unit when there is no movement of the user's lower body for an extended period of time. The pad has a two layer lower heat system comprising an insulated lower layer and a reflective bottom layer that accomplishes three tasks; it keeps the outer bottom surface of the pad cool, it acts as a thermal mass to allow the pad to radiate residual heat after shut off, and it helps reflect and drive the pad's heat toward the upper surface.
The advantages of this device are that it can run with a lower power consumption than a space heater while making the most efficient use of it's heat and minimizing the fire hazard potential. Such a device eliminates the pitfalls of the prior art and would be a welcome safe alternative to what the market now offers.
The general purpose of the present invention, which will be described subsequently in greater detail, is to provide an economical, safe, energy efficient device to heat one's feet.
It has many of the advantages mentioned heretofore and many novel features that result in a new under desk foot warmer which is not anticipated, rendered obvious, suggested, or even implied by any of the prior art, either alone or in any combination thereof.
In accordance with the invention, an object of the present invention is to provide an improved under desk safety foot warmer that is simple in design, construction and operation.
It is another object of this invention to provide an improved under desk safety foot warmer that minimizes the potential for fire hazards both due to the transmission of a high temperature to abutting flooring, and due to inadvertent prolonged exposure of elevated temperatures to abutting flooring.
It is a further object of this invention to provide an improved under desk safety foot warmer that will automatically turn off when the user has not been present for a preset period of time.
It is still a further object of this invention to provide for a improved under desk safety foot warmer that is able to radiate residual stored heat for a short period after it has been turned off.
It is yet a further object of this invention to provide a improved under desk safety foot warmer that will only transmit heat in one direction thereby meeting all existing building codes for contact heater devices.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.
Other objects, features and aspects of the present invention are discussed in greater detail below.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings.
The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of descriptions and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
The present invention relates to an under desk electric foot warmer having an improved safety shut off system and superior insulating capabilities.
Referring to
In operation, the user places the pad, 4 foil side down, beneath their desk in the vicinity of their feet. Master control unit 6 is mechanically mounted under the desk and connected to a standard electrical outlet. When on/off switch 16 is switched to on electric current flows through conductor 22, (one selected that has a relatively high temperature coefficient of resistance). This generates heat, which is transmitted by conduction to the thermal mass of the heating pad 4 which in turn is radiated to the pad's contact surfaces and surrounding materials. Electric resistance heating converts nearly 100% of the energy in the electricity to heat. Resistance heating is a heat transfer technology which is ideal for such applications because it offers versatility, controllability and quick heat-up qualities. Generally, for this heating pad 4 application, the conductor 22 is a metal alloy ribbon, wire or strip heating element. Since the conductor 22 is imbedded and spatially arranged in the resilient yet flexible waterproof substrate first layer 20 as the conductor 22 heats up the surrounding mass of the first layer is evenly heated and radiates heat. Since the second layer 24 is an insulator little or no heat is transferred to the floor, and what little is transferred is reflected by the reflective foil third layer 26 back to the second layer 24 which also acts as a thermal mass. With the insulated design as described above, the warmer's power consumption will be under 800 watts with the most likely range of electrical power consumption in the 90-135 W range.
The motion detector 18 that can be used in the preferred embodiment may be selected from the group of motion detectors including but not limited to infrared, ultrasonic, microwave, acoustic proximity (radar), or capacitive proximity sensors. The use and application of each of these would be well know by one skilled in the art.
The motion detector 18 selected and most economical for use in the preferred embodiment is well known in the industry as a PIR (passive infrared) detector or pyroelectric sensor coupled to a commercially common appropriately sized (ampere rated) switching device. For this particular application the motion detector is configured to be sensitive to the temperature of a human body (having a skin temperature of about 93 degrees F., and radiating infrared energy with a wavelength between 9 and 10 micrometers) rather than the standard sensor, typically sensitive in the range of 8 to 12 micrometers. The motion detector 18 detects and monitors a change in heat as found from a warm human body. Once the temperature drops due to the absence of a user, the infrared detector 18 turns off the current to the pad 4. The motion detector 18 and/or master control unit 30, are mounted under the desk and angled so as to not “see” any thermal effect from the pad 4.
The temperature control can be accomplished in two ways. The preferred embodiment heating pad 4 uses a self-regulating heating conductor 22 that ambiently senses the pad 4 temperature and self-regulates the temperature. This acts as a safety feature and eliminates the need for a manual heat control 28.
Self-regulating conductors have a conductive polymer-heating element, such as a carbon matrix-heating element with variable resistance where the resistance exhibits a PTC (positive temperature coefficient) resistance characteristic and subsequently power output decreases with increasing temperature. As the temperature increases the conductor power output approaches zero. At this temperature the conductor effectively “shuts off”.
For larger models, the conductor will employ parallel resistance heating conductors that include a continuous series of short, independent heating circuits. In this way, localized damage will only result in partial loss of heating. In a parallel construction, the self-regulating heating conductor can adjust its power output for local condition along its length.
If a high temperature model is required the preferred embodiment pad 4 may utilize power limiting conductors, that is parallel resistance heating conductors that will reduce their power output as temperatures rise but do not have the high in-rush currents associated with self-regulating heating conductors. These conductors are capable of delivering high watt per foot heat outputs but as temperature increases do reach a “shut-off” temperature.
The second method of heat control utilizes manual heat control 28 which is incorporated into the optional master control unit 30. The preferred embodiment with optional heat control 28 maintains a tight, temperature control (one that does not wander or vary much from a specific set temperature value). It utilizes a temperature sensing device 32 and signal wire 34 which are imbedded into temperature controllable pad 36.
The manual heat control (thermostat) used to adjust the pad 4 temperature is a low-voltage thermostat which is well known to one skilled in the art. This type of device uses a relay to turn the foot warmer current on and off. The heat control 28 receives a temperature signal from a thermocouple or equivalent temperature sensing device 28. Such devices are well know in the industry.
It is well known that a line-voltage thermostat (the thermostat directly controls the power supplied to the heating device by the passage of current through a variable resistor) may also be used as an equivalent to the heat control 28. This type of temperature control is again incorporated into the master control unit but has no temperature sensing input. Rather it governs temperature by the amount of current flowing to the pad 4. The drawback therein is it they do not sense and thus control the pad temperature accurately.
The above description will enable any person skilled in the art to make and use this invention. It also sets forth the best modes for carrying out this invention. There are numerous variations and modifications thereof that will also remain readily apparent to others skilled in the art, now that the general principles of the present invention have been disclosed.
