US 7351938 B2
An electric blanket has a woven web of warp and weft fibers. At least a portion of the warp fibers are electrically conductive. At least a portion of the weft fibers are electrically conductive and interweave with the electrically conductive warp fibers at a first area of the web. A power source in electrical communication with the web applies a voltage to the web that produces a wide area electrical distribution at the first area.
1. An electric blanket, said blanket comprising:
a woven web comprised of warp and weft fibers,
wherein at least a portion of the warp fibers are electrically conductive, and
wherein at least a portion of the weft fibers are electrically conductive and interweave in electrical contact with the electrically conductive warp fibers at a first area of the web;
a power source in electrical communication with the web so that the power source applies a voltage to the web that produces a wide area electrical distribution at the first area.
2. An electric blanket, said blanket comprising:
a woven web comprised of warp and weft fibers,
wherein a first group of said warp fibers are electrically non-conductive and a second group of said warp fibers are electrically conductive,
wherein a first group of said weft fibers are electrically non-conductive and a second group of said weft fibers are electrically conductive, and
wherein said second group of warp fibers and said second group of weft fibers interweave in electrical contact with each other at a central area of the web;
a pair of electrically conductive wires separate from each other and in electrical contact with the second group of warp fibers and the second group of weft fibers;
a power source in electrical contact with the pair of conductive wires so that the power source applies a voltage across the conductive wires that produces a wide area electrical distribution at the central area.
3. The electric blanket as in
4. The electric blanket as in
5. The electric blanket as in
This is a continuation of U.S. application Ser. No. 10/910,102, filed Aug. 2, 2004 (now U.S. Pat. No. 7,115,842), which is a division of U.S. application Ser. No. 09/942,517, filed Aug. 29, 2001 (now U.S. Pat. No. 6,770,854), the entire disclosure of each of which is incorporated by reference herein.
The present invention relates generally to electric blankets.
Electric blankets typically include a heating element that extends through the blanket and through which electric current passes to generate heat. The heating element is disposed within passageways formed in the weaving process.
While not used in electric blankets, scrim laminate blankets tend to be very comfortable.
The present invention recognizes and addresses disadvantages of prior art constructions and methods.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended Figures, in which:
Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention.
Reference is made in detail to presently preferred embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can by made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
Several preferred embodiments of electric blanket construction described herein include a heating element disposed in a laminated scrim blanket. The process of making a conventional scrim laminate blanket as shown in
In one preferred embodiment of the present invention, a heating element is disposed on one side of the scrim layer prior to it's lamination to the foam layer on that side. Referring to
The lamination process forms passageways 20 (
The blanket material is cut into sections, and a rod feeds the heating element through successive passageways in each blanket section. Any suitable tool or machine, for example as described below, may be used to run the heating element through the passageways. Bindings (not shown) sewn to the blanket ends cover the exposed heating element at the passageway openings. An electrical plug (not shown) connects the ends of the heating element to a power cord and a control circuit as described below.
While the above examples include a scrim/foam construction, it should be understood that the present invention may include other suitable arrangements. For example, a wired scrim layer may be sandwiched between woven layers bonded to the scrim by adhesive or acrylic.
The loom outputs weft fibers in three parallel transverse sections 30, 32 and 34. Sections 30 and 32 are non-conductive and may be formed from any suitable non-conductive fiber, such as used in warp sections 22 and 26. Conductive fibers, such as the fibers in section 24, form middle weft section 34. Respective sections 32 bound each middle section 34.
The loom outputs a continuous sheet having blanket segments separated by fringe layers 30 that contain little or no weft fibers and at which adjacent blanket segments are cut from each other. The dimensions of any of the warp or weft sections described above may be varied as desired for a given desired blanket size. It should therefore be understood that the illustration in
Due to the conductive and non-conductive weave described above, the interwoven conductive warp and weft fibers form a center weave section 36 composed entirely of conductive fibers. Side sections 38 and top and bottom sections 40 include conductive fibers in only one direction, while corner sections 42 include only non-conductive fibers. Accordingly, a voltage drop applied across wires 28 produces a wide area electrical distribution that heats center section 36, while sections 38 and 40, at which minimal current flow occurs, remain relatively unheated.
As should be understood in this art, the plug is typically a custom made injection-molded device. The ends of wires 28 are stripped, and a crimping tool crimps a pair of wire attachments in a jig to the stripped wire ends. An injection molding machine molds a plastic casing about the male ends of the wire attachments so that the resulting plug can receive the power cord's female end.
The blanket-forming procedure described above utilizes a predetermined blanket size. Referring to
To create a “zoned” blanket, in which different parts of the blanket may be independently controlled to desired heating levels, the blanket may include two sets of power plug/lead wires. For example, where a blanket is cut from conductive blanket layer 12 across the layer outward of wires 28 a and 28 b, a first power plug applied across wires 28 a and 28 c forms a first heating zone, and a second power plug applied across wires 28 b and 28 c defines a second heating zone. Thus, the left and right edges of the blanket sheet as shown in
Referring now to
Such power plug/control circuit/lead wire arrangements may also be used with the earlier-described blankets in which a wire heating element is disposed on or in an otherwise non-conductive scrim layer. Referring to
As described above, the feeder may deposit wire 50 onto the scrim layer before or after lamination of the foam layers onto the scrim. The scrim and foam layers are then laminated together, securing the wire in place between the two layers. In another embodiment, however, foam layers are laminated to respective scrim layers before application of the heating element. A wire feeder disposed at the output of the lamination machine deposits the element on one of the two scrim layers, which is then adhered to the other scrim/foam pair so that the heating element is sandwiched between the two scrim layers. In either embodiment, the blanket, which may also include flocked layers of oriented fibers as discussed above, may be formed in a continuous roll and cut into individual sections. In each section, a hem receives the power plug and lead lines. More specifically, the wire loops are cut, power plugs are attached across the cut element ends by lead wires as discussed above, and the plug/lead wires are hemmed into the blanket edges. A hole is cut in the hem to provide access to the plug, and the hole edges are stitched to prevent fraying.
Wired scrim layers as described with respect to
The heating element, on a scrim or other substrate or as part of a conductive weave, is inserted on top of the batting. Alternatively, an unattached heating element wire may be pushed into the quilt by a tool having one or more elongated fingers that push the heating element into the quilt bag, leaving the heating element in successive loops on the batting when the tool is removed. The batting and scrim are both preferably non-flammable or self-extinguishing. Lead wires 46 are attached to the heating element through open edge 62, and wires 46 and power plug 44 are folded or sewn into the quilt by a selvage section 64 as open edge 62 is closed. The bag is then flipped over, so that the heating element is below the batting, and a quilt pattern 61 is sewn through the quilt. A mechanical or electrical attachment skips the sewing head over the heating element in the quilt.
A quilt may also be formed by sewing a non-heated blanket layer, made from a weave, a scrim-based blanket or any desired blanket material, to a heated blanket along three of the blankets layers' edges, thereby forming a bag with an open edge. Referring to
A 120 volt AC voltage source 70 powers the heating element through a full-wave bridge rectifier 72, a sampling resistor 78 and a triac switch 80. As should be understood by those skilled in this art, a triac switch conducts AC current between inputs 82 and 84 in both directions as long as an activating signal is present on a control lead 86. If the activating signal is discontinued, the triac conducts current until the input signal's next zero crossing.
The activating signal is provided by an optically isolated triac driver 88 that acts as a switch passing current from node 84 to the control lead 90. Thus, when driver 88 is activated by its control lead 90, the signal from source 70 drives triac 80. During this signal's positive cycle portion, current travels through triac 80 in the direction indicated by arrow 92. During its negative cycle position, current travels through the triac in direction 94.
A control circuit 96 controls driver 88. Control circuit 96, for example comprising a single integrated circuit (IC), may include a microprocessor and an A/D converter. Through the converter, the IC receives voltage measurements from nodes 98 and 100. The measurement from node 100 is the voltage across sampling resistor 78. Thus, the controller may determine the current through heating element 76 by dividing the voltage measured at 100 by the known resistance of sampling resistor 78. The voltage applied to the system is measured at 98. Thus, the system's total resistance is equal to the voltage measured at 98 divided by the current measured at 100. The resistance of heating element 76 may therefore be determined by backing out the known resistances of the components upstream from the heating element.
As discussed above, the temperature of heating element 76 is related to its resistance. Wire manufacturers typically rate wire resistance with respect to a predetermined temperature, generally around 75° Fahrenheit. The manufacturer also typically provides the wire's temperature coefficient. Thus, given a known length L of heating element 76 having a temperature coefficient TC and a rated resistance X (in ohms per unit length) at Y° Fahrenheit, and given a measured resistance Z (in ohms) between nodes 98 and 100 as discussed above, heating element temperature T=Y+(1/XL) (Z−XL)/TC.
The variables Y, TC, X and L are known and may be stored in memory associated with control circuit 96. Therefore, upon determining the measured resistance Z., the control circuit may determine the heating element's temperature T by the equation above. Alternatively, temperature T may be calculated over a range of resistances Z to create a table relating temperature to measured resistance. The table may then be stored in the control circuit's memory so that the control circuit, upon determining an actual measured resistance between nodes 98 and 100, may determine temperature T by reference to the table.
The control circuit 96 may be disposed in a suitable housing attached to or within blanket 74, for example in-line with a power cord between the power source and the heating element in the examples discussed above with respect to
Control circuit 96 manages the heating element temperature by various methods. Generally, however, the heating element's heat output varies predictably with current. Since triac 26 controls the amount of current passing through the heating element, the element's heat output may be determined by controlling the ratio of the triac's on-time to its off-time based on some predetermined scale. Various control methods are described in Applicant's U.S. Pat. No. 6,222,162, the entire disclosure of which is incorporated by reference herein.
In normal operation, control circuit 96, driven by its microprocessor, may manage blanket temperature to a target temperature in a direct relationship to the heating element's measured resistance. Since a rise in measured resistance, and a drop in measured current, reflects a rise in temperature, the control circuit generally reduces current flow to the blanket responsively to a resistance increase, or current decrease, reflecting that the blanket's temperature is rising beyond the target temperature. Similarly, the control circuit reduces current flow to the heating element responsively to a measured resistance decrease, or current increase, reflecting that the blanket's temperature is falling beyond the target temperature.
The control circuit also responds, however, to conditions in which the normal relationships of current and resistance to temperature don't hold, such as opens, drastic shorts and partial shorts in the heating element. For example, while shorts may result in temperature increases, they also exhibit resistance decreases and current increases. A “drastic” short is a short circuit over a major portion of the heating element that causes a current increase significantly beyond a safe operating range. Accordingly, the control circuit stores a threshold resistance value that reflects the occurrence of a drastic short, and the control circuit disconnects the blanket's power when the measured resistance falls below this threshold. The particular threshold value depends on the heating element's characteristics, as should be understood by those skilled in the art. In a blanket having a typical heating element resistance of 100Ω, however, the control circuit disconnects power upon detecting a resistance of 80Ω or less.
Similarly, in another preferred embodiment, the control circuit disconnects the blanket's power when the current measured at 100 rises above a predetermined level. In a blanket having a typical current level of 1.1 amps, for example, control circuit disconnects power upon detecting a current level of 1.25 amps or more.
Heating elements are relatively long, and they may therefore be subject to “partial” shorts—short circuits across a limited portion of the element that produce a current increase relatively smaller than that of a drastic short. In particular, partial shorts may increase current to within a range experienced normally when the blanket is cold. The control circuit detects partial shorts, and differentiates them from a normal cold condition, based on the rate of change in the element's resistance or current. When the element's resistance or current changes due to acceptable temperature fluctuation, the change takes a relatively long time. For example, wire made from 34 gauge cadmium copper alloy takes thirty seconds or longer to change from 45° C. to 49° C., corresponding to a resistance change from 176.2Ω to 178.8Ω and a current change of 0.624 amps to 0.615 amps. Thus, assuming that this temperature change is acceptable, the control circuit should not interpret a 2.6Ω or a 0.007 amp change over a thirty second period to indicate a partial short. The circuit does recognize a partial short, however, if such a resistance or current change occurs within a period less than that acceptable for normal temperature fluctuations. The definition of this time period depends on operational factors such as the heating element's materials and dimensions. In one embodiment, for example, where a heating element is a 34 gauge cadmium copper alloy wire, the control circuit disconnects power to the heating element if there is a 0.5Ω resistance decrease or 0.002 amp current increase, or greater, from one current cycle to the next. Of course, other arrangements may be suitable under different circumstances. PTC wire, for example, has a relatively high temperature coefficient, and it's resistance may change relatively quickly without being subject to a short. In this instance, the control circuit may be configured to disconnect heating element power if the processor detects a cycle-to-cycle resistance change of 2Ω or more or a current change of 0.025 amps or more.
The control circuit also disconnects heating element power if it detects an open in the heating element. In a preferred embodiment, the control circuit disconnects power if it senses that the heating element's resistance is at or above, or if the current level is at or below, a threshold level that is sufficient to indicate an open has occurred. The particular threshold value for a particular heating element will depend on the element's characteristics. In one example, however, in which the heating element normally exhibits a 100Ω resistance and 1.1 amp current, the control circuit disconnects heating element power upon detecting a resistance of 200Ω or greater or a current of 0.55 amps or lower.
Accordingly, a measured resistance or current outside ranges that would be expected during normal operation may indicate an open or a partial or drastic short, and the control circuitry disconnects electricity flow to the heating element. Abrupt up or down resistance or current changes may also indicate these conditions, and the control circuitry therefore also disconnects power responsively to the rate at which these parameters change.
For purposes of clarity in illustrating the blanket loading procedure,
Carriage 144 includes a base plate 144 a having a pair of slots that receive the guide rails. A platform 148 has a first end pivotally attached to the base plate and a second end attached to support 130. A pneumatic piston is attached between platform 148 and the base plate. A lever (not shown) attached to platform 148 allows a user to pivot the platform and tubes between the positions shown in
Frame 122 is generally box-like and has a plurality of vertically extending posts 122 b, supports 122 a and a plurality of horizontally extending braces 122 c that combine to form the frame from which the various elements of the machine 120 are supported. A guide wall 124 at the upper front portion of frame 122 includes a rear guide wall 124 a and a pivotally supported closure wall 124 b. Hinges 125 pivotally connect the upper edge of closure wall 124 b to rear guide wall 124 a. Springs on hinges 125 urge closure of closure wall 124 b to the position as seen in
In front of frame 120, guide tubes 128 are positioned between guide wall 124 and support 130 in a generally vertical position and are adapted to be tilted forwardly from the vertical position as shown in
Tubes 228 have interior slots 230 that allow release of the heating element once it has threaded through the blanket. Each side manifold has a split construction with a pair of pivotally connected manifold halves 234. Once the heating element is looped through all the tubes and the manifold passageways connecting adjacent tubes, the manifold halves open, and one or both side manifold(s) is/are pulled away from the other. Released from the manifold loop by the open manifold halves, the heating element slides through interior slots 230 as the tubes are pulled from the blanket passageways.
Returning to the embodiment shown in
A shuttle 153 (
As explained above, hinges 125 pivotally connect front closure wall 124 b with rear wall 124 a. In operating the machine, wall 124 b is in the position shown in
To summarize the operation of blanket wire insertion machine 120, and referring first to
In another preferred embodiment, the heating element is inserted into a blanket shell having parallel passageways by a frame having a series of parallel fingers disposed correspondingly to the passageways in a manner similar to tubes 128 on support 130 (
As the shell moves over the fingers, the fingers push the heating element wire up into each passageway in a double strand. It will be understood that the heating element slides across the ends of the fingers as the fingers move up into the passageways, and grooves may be provided at the fingers' ends to retain the heating element in position. The operator then cuts the material transversely above the finger tips or, if the shell is already cut, rumples the shell down over the fingers so that the finger tips and wire loops extend through the open ends of the passageways on the shell's other side. The operator inserts hooks or pins into the heating element loops at the finger tips and across the passageway openings to prevent the wire from sliding back into the passageways and pulls the blanket and fingers away from each other so that the fingers exit the passageways.
After the fingers' removal, the blanket is stitched along lines 324 to prevent contact between sides of the individual wire loops in the passageways that might cause a partial short. In one preferred embodiment, sew tabs 322 may be attached at loop ends 320. The tabs are stitched into the blanket selvages along the dashed lines shown at sides 316 and 318 to additionally secure the heating element. A plug 312 electrically attaches to the ends of the heating element, directly or through lead wires, and is folded into the blanket hem.
In another preferred embodiment, the heating element may be inserted into a blanket shell having parallel passageways on a foundation material, such as a scrim layer. Referring to
In another preferred embodiment, however, the sew tabs are omitted, and the foundation scrim layer extends some distance, e.g. six inches, beyond the ends of the wire loops on either side. This selvage material thus extends outward of the passageway openings on either side of the blanket segment. Preferably, the blanket segment's selvage extends from the top and/or bottom of blanket segment, and the scrim extensions are then sewn into the blanket's hem on both sides, thereby securing the scrim foundation and heating element wire in the blanket.
For power efficiency, a metallized MYLAR sheet may be laminated to the side of scrim layer 326 opposite the side to which the heating element is attached, or the scrim layer may include woven metallized fibers. Moreover, it should be understood that a heat reflective sheet, or the use of woven metallized fibers, may be employed with other blanket embodiments as discussed above.
While one or more preferred embodiments of the invention have been described above, it should be understood that any and all equivalent realizations of the present invention are included within the scope and spirit thereof. Thus, the embodiments depicted are presented by way of example only and are not intended as limitations upon the present invention, and it should be understood by those of ordinary skill in this art that the present invention is not limited to these embodiments since modifications can be made. Therefore, it is contemplated that any and all such embodiments are included in the present invention as may fall within the literal or equivalent scope of the appended claims.