Patent Application
20210355613
Several groups have begun conducting research on the production of soft flexible touch sensors. Google's Project Jaquard developed a method of using industry standard jacquard machinery to produce textiles with integrated sensors for use in bespoke smart garments. Georgia Tech's Healthcare Robotics Lab developed silicone sensors with “taxels”—tactile pixels—used to characterize force applied to a robotic arm. Other methods have also been investigated such as use of conductive rubber, layering of piezo-resistive and conductive textiles, combinations of conductive knit or woven textiles and threads, screen printing, splicing of optical sensors into individual fibers and knitting of structures containing silver coated nylon, stainless steel, and carbon or polymeric conductive yarns. Sensors knit with carbon fiber filament show may improve the sensitivity of wearable devices. The knitting process helps with consistency of the design, while the carbon fiber has been shown to function well in a wider range of conditions.
While progress has been made, many of these solutions still face a number of challenges with respect to manufacturability and robustness. Hard and fragile embedded electronic components and the need for bundles of wire leads often diminish the feasibility of some solutions. Human factors can change the efficacy of these devices, for instance, the need to recalibrate antenna components that can function at different frequencies on the human body than in free space. Particularly in the case of sewn sensors, the production process is lengthy, complex, and cannot easily conform to exact measurements. Additionally, the need to wash and clean these garments or medical devices with sensors will arise, adding complexity to the design and production.
Previous fabric-based touch sensing has required a large number of sensing electrodes (wires) to form a discrete sensing mesh or has used a dense weaving of conductive yarn in an XY grid pattern to sense human touch using self-capacitance or mutual capacitance. Covering a surface with discrete electrodes is impractical for scalability of the sensor as it increases the number of required connections to a sensing integrated circuit.
Further, knitted fabrics are known to offer hybrid characteristics of conformity by having multi-stretch possibilities vs. woven fabrics. There are two main types of knitted fabrics. Weft knit formed through a single cone (end) of yarn via independent needles. The type of stitch used in weft knitting affects both the appearance and properties of the knitted fabric. The basic stitches are plain, or jersey; rib; and purl. In the plain stitch, each loop is drawn through others to the same side of the fabric. In the rib stitch, loops of the same course are drawn to both sides of the fabric. The web is formed by two sets of needles, arranged opposite to each other and fed by the same thread, with each needle in one circle taking up a position between its counterparts in the other. In a 2:2 rib, two needles on one set alternate with two of the other. The interlock structure is a variant of the rib form in which two threads are alternately knitted by the opposite needles so that interlocking occurs. In the purl stitch, loops are drawn to opposite sides of the fabric, which, on both sides, has the appearance of the back of a plain stitch fabric. Jacquard mechanisms can be attached to knitting machines, so that individual needles can be controlled for each course or for every two, and complicated patterns can be knitted. To form a tuck stitch, a completed loop is not discharged from some of the needles in each course, and loops accumulating on these needles are later discharged together. The plaited stitch is made by feeding two threads into the same hook, so that one thread shows on the one side of the fabric and the other on the opposite side. A float stitch is produced by missing interlooping over a series of needles so that the thread floats over a few loops in each course.
Warp knitting may be advantageous for some applications, and in particular, warp knitting may increase speed of production and thus may be advantageous in functional textiles.
A warp-knitted capacitive touch sensor system includes conductive and non-conductive yarns using interlooped stitches that are interlaced, intertwined, and/or spliced into a single conductive pathway having only two connection points to the electronic interface device, across a desired width or length of the textile material.
Warp Knitting
Warp knitting is the sequential formation and interlinking of loops in an axial direction on a lateral array of needles with at least one separate thread being supplied to each needle via a warp beam. The loops may be joined together in a width-wise direction by moving the threads back and forth between adjacent needles. Warp knitting machines may have 1-8 warp beams that deliver yarn to the needle bed systems. Guide bars can shift from right to left called shog. Typical shog movements can be from 1 to 3 needle positions (overlap), however may be up to eleven for bars not forming loops (underlap).
Warp knitting represents the fastest method of producing fabric from yarns. Warp knitting differs from weft knitting in that unlike weft knitting, each warp knitting needle loops its own thread. The warp-knitting machine needles produce parallel rows of loops simultaneously that are interlocked in a zigzag pattern. The fabric is produced in sheet or flat form using one or more sets of warp yarns. The yarns are fed from warp beams to a row of needles extending across the width of the machine.
All the yarns may be knitted in course simultaneously and for the purpose of shifting yarn, a guide may be used.
Warp knitting yarns are supplied to the knitting zone parallel to the selvedge of the fabric, i.e. in the direction of the wales. As stated earlier, a knitting needle often draws the new yarn loop through the knitted loop formed by another end of the yarn in the previous knitting cycle.
Warp-knitting may have several advantages over weft knitting: (1) Due to the simultaneous knit, production rate may be much higher than the weft knitting, (2) The yarn may be in crisscross form to the adjacent wale line, so that dimensional stability will be much higher; (3) The elongation of the fabric may be less.
Warp Knit Structure
A warp-knitted structure may be made up of two parts. The first is the stitch itself, which is formed by wrapping the yarn around the needle and drawing it through the previously knitted loop. This wrapping of the yarn is called an overlap.
The second part of stitch formation is the length of yarn linking together the stitches and this is termed the underlap, which is formed by the lateral movement of the yarns across the needles.
The length of the under lap is defined in terms of needle spaces. The longer the underlap, the more it lies at right angles to the fabric length axis. The longer the underlap for a given warp the greater the increase in lateral fabric stability, conversely a shorter under lap reduces the width-wise stability and strength and increases the lengthways stability of the fabric.
The length of the underlap also influences the fabric weight. When knitting with a longer underlap, more yarn has to be supplied to the knitting needles. The underlap crosses and covers more wales on its way, with the result that the fabric becomes heavier, thicker and denser. Since the underlap is connected to the root of the stitch, it causes a lateral displacement in the root of the stitch due to the warp tension. The reciprocating movements of the yarn, therefore, cause the stitch of each knitted course to incline in the same direction, alternately to the left and to the right.
In order to control both the lateral and longitudinal properties, as well as to produce an improved fabric appearance with erect loops, the second set of yarns is usually employed. The second set is usually moved in the opposite direction to the first in order to help balance the lateral forces on the needles. The length of the underlap need not necessarily be the same for both sets of yarns.
Spacer Warp Knit Structure
As shown in
Both fabric faces may be equal or different, of dense structure, plain or patterned with small design or with a napped surface on one side.
Both faces or one can be of open structure, even with different mesh size on each side. By the choice of stitch construction, spacer fabric can be almost stable but also of controlled stretch used elastic yarn.
For connection of both face fabric generally mono filament yarn is used, however a multi filament can also be used. The thickness of the spacer yarn depends amongst other criteria on distance between the fabric space and whether the space is knitted with one guide bar or with two guide bars each one knitting in opposition to each other.
Types of Warp Knitting Machines
As shown generally in
Two common types of warp knitting machines are the Tricot and Raschel machines, as well as spacer double needle bar Raschel type. Raschel machines are useful because they can process all yarn types in all forms (filament, staple, combed, carded, etc.). Warp knitting can also be used to make pile fabrics often used for upholstery.
—Tricot Warp Knitting Machine Features:
Initially only bearded needles were used.
Fine filaments are knitted.
Machine gauge up to 24 to 40 (here gauge is number of needles per inch)
Fabric is pulled at right angle to needle.
Sinker controlled fabric throughout the knitting cycle.
Low fabric take-down tension.
Number of guide bars usually not more than five.
Machine speed is high (up to 3500 courses per min)
Machines are wider and comparatively simple structures are produced.
Warp beams are positioned at the back side of the machine.
—Raschel Warp Knitting Machine Features:
Capacitive touch sensors may be made using multi bar raschel knitting machine, which may be a non-electronic mechanical type of knitting machine. These raschel machines can create intricate patterns that are run by patterning chains and spot beams of various type of yarn types and combinations including conductive yarns. Pattern changes may be much more difficult and not as easily done as they are on electronic knitting machines. A primary advantage with raschel machines is that yarn can lay-in over more needles than do the electronic jacquard machines.
Multi-bar warp knitting offers design flexibility and/or intricate, possibly larger patterns that provide the ability to create a graphic button type and custom shapes using a single end of carbon yarn.
Initially latch needles are used.
Versatile—number of guide bars up to 16.
Suitable for outer wear and furnishing.
Any type of yarn can be used.
Fabric controlled by high take down tension.
Sinkers hold fabric only when the needles raise.
Fabric pulled at about 160 degree to needle, machines are made in coarser gauges 24 to 64 (here gauge is defined as number of needles per two inch)
Machines are narrower and comparatively lower speed (up to 2000 courses per min)
Warp beams are positioned at the top of the machine.
—Spacer Double Needle Bar Raschel Type Machine
During recent years, spacer fabrics have become a new generation among textile fabrics. From the technology point of view, they are not quite new, they practically have existed for 15 years, however they have gained commercial importance recently.
Spacer fabrics may be knitted on warp knitting raschel machines with two needle bars. Depending of the product and its requirement, a minimum of four guide bars normally, however three to eight guide bars are possible. The distance between the needle bars is adjustable in certain ranges and is different for the various machine types for knitting spacer fabrics from 1 mm-55 mm.
Technical Example of Spacer Warp Knit Functional Textile Device
The overlap and underlap of this specific example has a repeat of 405 courses to accommodate the desired design parameters of the conductive pathway; length and width. This creates a wide band of non-conductive yarns along with a narrow band of conductive yarns. The conductive bands move needle positions at intervals that creates sequential underlap and overlap stitches across the width direction. The conductive yarn stitch formation for the conductive yarn warp yarns shift in left and right directions from the main chain stitch conductive yarn placement. These vertical chain stitches can have various exposed and unexposed lengths depending on the user interface programing and dimensions of the end product.
A continuous conductive pathway is achieved by the exaggerated left and right (lateral and/or oblique) underlap motions are called shog (shifting), of the conductive yarn bars #3 and #4. “The underlap of bar 3# intertwines with the previous loop of bar #4 splicing the non-conductive yarns together on one course line. The normal limit for loop forming guide bars in tricot machines is four needle spaces, but they may be as long as eleven needle spaces for bars not forming loops.”
The 640-denier conductive yarn used in this example is a nylon 6,6 40 filament twisted core with approximately one micron of carbon suffused onto the surface. Carbon, Silver, stainless steel and graphene type yarns are ideal for capacitive touch user interface, where low power is required.
In this example, bars #2, #5, and #6 are texturized polyester 167/48 denier was used.
An outcome of the warp knit spacer functional fabric may include the following:
Connectorization
There may be connections made similar to what is shown in WO 2017/095861 (PCT/US2016/064108), incorporated by reference as if fully set forth herein. One thing that should be appreciated about the capacitive sensors formed by the conductive yarns in warp-knitting is that the sensor created with overlapping/crossing yarns creates an electrical connection. And thus, the combination of all of those connections creates a shaped circuit that would only require two electrical connectors to connect the sensor to another device or circuit.
At the moment, some of the electrical connectors in conductive textiles are not ideal so minimizing the number of these connections using warp knitting in a capacitive touch sensor may present improvements in manufacturing and assembly, as well as in aesthetics (fewer “clumsy” connectors in a fabric) and in durability (fewer connection points means fewer potential failure points).
Said another way, the warp-knitting lateral loop overlaps and underlapping of the conductive yarn beams may create a serpentine or other pattern that forms a continuous conductive pathway with only one input and one output connector required.
Applications
There may be several applications uses for warp-knitted capacitive fabric described herein, without limitation as follows.
As shown in
While the invention has been described with reference to the embodiments above, a person of ordinary skill in the art would understand that various changes or modifications may be made thereto without departing from the scope of the claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US19/56315 | 10/15/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62745643 | Oct 2018 | US |
