Electric heating – Heating devices – Combined with pressure application means
Reexamination Certificate
1999-08-27
2001-01-09
Jeffery, John A. (Department: 3742)
Electric heating
Heating devices
Combined with pressure application means
C219S245000, C156S579000, C038S095000, C038S082000
Reexamination Certificate
active
06172335
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to electric heating irons used for melting hot-melt seaming tape during installation of wall-to-wall carpeting, and more particularly to the method of temperature control for such seaming irons.
2. Description of the Related Art
During the installation of wall-to-wall carpeting, often the area to be carpeted is wider than the carpet as produced by the carpet mill. Therefore, two or more pieces of carpet must be joined along a seam. Wall-to-wall carpet is usually seamed using hot-melt carpet seaming tape. Carpet seaming tapes typically include a layer of thermoplastic (hot-melt) resin adhesive for bonding to the adjoining pieces of carpet. To form a seam using the face-seaming process, the two pieces of carpet to be seamed are placed with the tufts facing up and edges abutting over a length of seaming tape. The seaming tape is centered under the two abutting edges with the layer of adhesive facing the carpet backing. A hot carpet seaming iron, or other suitable implement, is used to melt the thermoplastic adhesive and the carpet backing is pushed into the molten thermoplastic adhesive. The adhesive quickly sets, forming a permanent seam. This method is disclosed by, e.g., U.S. Pat. Nos. 3,972,768, 4,097,445 and 4,536,244.
Various carpet seaming irons are commercially available from several sources. All employ similar design elements: a relatively thin, thermally insulated heating platen, an electrically powered heating element, a handle, and an electric circuit incorporating a thermostat for temperature control. Such irons are disclosed by, e.g., U.S. Pat. No. 4,536,244. The iron platen must be thin to allow the platen to fit readily underneath the two piece of carpeting. The electric power must also be relatively high (typically, irons consume about 800 Watts of power) so that the iron heats up quickly and maintains its temperature. Otherwise, the iron will not melt the carpet seaming tape quickly enough for the typical operator.
The combination of a thin platen, high power, and thermostatic control has several disadvantages. Thermostats are prone to react too slowly to temperature changes. A high-powered, low mass iron heats up so quickly that the thermostat will not shut off the power to the heater in time. That is, the iron “overshoots” the desired temperature. The platen will become hotter than desired, which can damage the carpet or seaming tape, and shorten the life of the iron. Excessive smoke can be produced when the seaming tape adhesive is overheated. After the thermostat shuts off power, the thin platen cools rapidly. Again, the thermostat reacts too slowly. The iron becomes too cool for the operator to work rapidly. The thermostat then activates the electric heater, and the iron begins heating again, repeating the cycle. The iron cycles repeatedly between a temperature that is too hot and a temperature that is too cool. The thermostat is unable to maintain a steady iron temperature.
A further disadvantage of thermostatic control is that the full power of the heater is switched through the contacts of the thermostat. After many cycles, the contacts can fuse in a permanently closed position. The iron heater will remain permanently on and can overheat dangerously.
A still further disadvantage of thermostatic control is that many commonly available thermostats do not consistently control within the same range of temperature. For example, a given thermostat may control in a range between 350° F. and 420° F. Another thermostat from the same manufacturing lot may control in a range between 370° F. and 440° F. Consequently, the seaming irons do not perform consistently. One may run relatively cool, while another runs relatively hot.
SUMMARY OF THE PRESENT INVENTION
My invention utilizes an solid-state electronic control circuit with a proportional control loop to control the temperature of a seaming iron. The resulting temperature control is more stable, consistent, and reliable than a thermostat can provide. Proportional (P) control loops, proportional-integral (PI) loops, and proportional-integral-derivative (PID) loops are well known means of temperature control. Many examples of electronic circuits implementing P, PI, and PID control are known in the art and in heating appliances generally. My electronic control circuit uses no thermostats or other mechanical control devices for temperature control, thereby avoiding the disadvantages of such devices.
However, no one has included any electronic circuit with P, PI, or PID control into the handle of a carpet seaming iron. It is too hot inside the handle of prior art carpet seaming irons for many electronic components, such as integrated circuits. Furthermore, the platen (also called the baseplate or soleplate) of industrial irons such as carpet seaming irons is hotter than mass-produced heating irons for home use. Therefore, the carpet seaming irons could not make use of the same solid state temperature sensors as the consumer products. Special high-temperature components are too expensive to be commercially feasible in the price-sensitive market for seaming irons. Some prior art irons, such as disclosed by U.S. Pat. No. 4,322,900 (Hacker, et al, 1982) and U.S. Pat. No. 4,827,104 (Foster, Jr., 1989), put portions of the electronic control circuit outside of the handle, in a separate enclosure. These irons are relatively bulky and inconvenient to use.
My invention makes it possible to put low-cost electronic components providing P, PI, or PID control inside the handle of a carpet seaming iron, and makes use of newly available, low-cost solid state temperature sensors mounted directly to the iron platen. The result is that carpet installers can now benefit from the advantages of electronic control conveniently and inexpensively.
OBJECTS AND ADVANTAGES
The object of my invention is to provide a carpet seaming iron that heats to the desired temperature setpoint quickly. This will enable a carpet installer to begin using the iron more quickly, without waiting for it to heat up.
A further object is for the iron to maintain its temperature at the setpoint during use, without temperature fluctuations. Maintaining a steady temperature will provide consistent operation of the iron at all times during the installation process. Unlike with a thermostatically controlled iron, the carpet installer will not have to adjust his pace of work as the iron heats up and cools down.
A further object of my invention is to provide solid state switching for the electric heater. This will eliminate wear that occurs with the physical contacts of a thermostatically controlled iron, leading to a longer life. In addition, the possibility that the switch will become stuck in the “closed” (heating) position is much less likely, making my iron safer than thermostatically controlled irons.
A still further object of my invention is to provide an iron with inherently more consistent and repeatable temperature control means by eliminating mechanical devices and using only solid state devices for temperature sensing, power switching, and control. Irons made with my invention are more likely to perform within the same range of temperatures from unit to unit. Operators switching from one unit to another are less likely to notice any difference in performance of my irons.
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pa
Jeffery John A.
O'Melveny & Myers LLP
Orcon Corporation
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