Patent Publication Number: US-2017347721-A1

Title: Conductive thread stitched stretch sensor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional application Ser. No. 62/343,899 entitled Conductive Thread Stitched Stretch Sensor filed on Jun. 1, 2016, the contents of which are incorporated fully herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     This invention was made with government support under contract number NIH 1R21HD076092-01A1 (PI: Lobo) awarded by the National Institutes of Health. The government has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     Measuring human movement for biomechanical analysis is currently measured using motion capture laboratory equipment. This equipment is the recognized standard within the health sciences, but has inherent limitations for practical application for some users including cost, specialized knowledge, and patient burden. Alternative methods, systems, and apparatus for measuring movement, especially in humans, that address these inherent limitations are desirable. Aspect of the invention address one or more of these needs among others. 
     SUMMARY OF THE INVENTION 
     Aspects of the invention are embodied in conductive thread stitched stretch sensors. The conductive thread stitched stretch sensors include a textile configured to stretch in at least one dimension and a conductive thread having a resistance between a first point and a second point stitched to the textile in a stitch geometry, the stitch geometry configured to stretch the conductive thread as the textile is stretched in the at least one dimension such that the resistance of the conductive thread increases between the first point and the second point due to elongation of the conductive thread as the textile is stretched. 
     Aspects of the invention are also embodied in garments including conductive thread stitched stretch sensors and methods for making such sensors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is best understood from the following detailed description when read in connection with the accompanying drawings, with like elements having the same reference numerals. When a plurality of similar elements are present, a single reference numeral may be assigned to the plurality of similar elements with a letter designation referring to specific elements. When referring to the elements collectively or to a non-specific one or more of the elements, the letter designation may be dropped. This emphasizes that according to common practice, the various features of the drawings are not drawn to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures: 
         FIG. 1A  is a photograph of a representative conductive thread stitched stretch sensor in a relaxed state in accordance with aspects of the invention; 
         FIG. 1B  is a photograph of the representative conductive thread stitched stretch sensor of  FIG. 1A  in a stretched state; 
         FIG. 2A  is an conceptual illustration of a conductive thread for using in the conductive thread stitched stretch sensor of  FIG. 1A ; 
         FIG. 2B  is a cross-sectional conceptual illustration of a conductive thread for using in the conductive thread stitched stretch sensor of  FIG. 1A ; 
         FIG. 3  is a computer generated image of a hypothetical user illustrating rotation/translation for measuring kinematics of the hypothetical user; 
         FIG. 4  is an illustration of a conductive thread in a relaxed state (top) and a stretched state (bottom) in accordance with aspects of the invention; 
         FIG. 5  is an illustration of a cross section of a conductive thread in a relaxed state (top) and a stretched state (bottom) in accordance with aspects of the invention; 
         FIG. 6  is an illustration of nine different stitches using the conductive thread in accordance with aspects of the invention; and 
         FIG. 7  is a flow chart illustrating a method for making a conductive thread stitched stretch sensor in accordance with aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A and 1B  depicts a representative conductive thread stitched stretch sensor  100 A/ 100 B in an unstretched state  100 A and a stretched state  100 B in accordance with aspects of the invention. The sensor  100  includes a textile  102  and a conductive thread  104  stitched into the textile  102  in accordance with a stitch pattern. 
     The textile  102  is configured to stretch in at least one direction. A suitable textile for use at textile  102  is a knit material such as a synthetic knit material or a natural knit material. Other suitable textiles will be understood by one of skill in the art from the description herein. The textile  102  may be incorporated into a garment such as a shirt, a pair of pants, a compression sleeve, etc. or can be the garment itself. In an embodiment, the textile/garment is configured to stretch in a plurality of directions so as not to inhibit the movement of the wearer. 
     The conductive thread  104  is stitched into the textile  102  and is configured to change resistance as the textile is 102 and, in turn, the conductive thread  104  is stretched. The conductive thread is configured to exhibit an increase in resistance between a first point  106  and a second point  108  as it is stretched and a decrease in resistance as it contracts. A suitable conductive thread  104  is a Shieldex® Conductive Twisted Yarn Silver Plated Nulon 6 Yarn 22/1 dtex+113/32 dtex PET sold under part no. 261151022113 by VTT/Shieldex Trading USA of Palymyra, N.Y. Other suitable conductive threads will be understood by one of skill in the art from the description herein. 
       FIG. 2A  conceptually depicts a conductive thread  104  in accordance with an aspect of the invention. The conductive thread  104  illustrated in  FIG. 2A  includes strands of polyethylene terephthalate (PET)  200  encircled by a strand of silver coated nylon  202 .  FIG. 2B  conceptually depicts a cross section of the conductive thread  104  of  FIG. 2A  in accordance with an aspect of the invention. The conductive thread illustrated in  FIG. 2B  includes multiple strands of PET  200  and a single strand of silver coated nylon  202 . The silver coated nylon includes a nylon core  204  coated with silver  206 . 
       FIG. 3  depicts a hypothetical user  302  that would wear a garment/textile in accordance with aspects of the invention. Also depicted is rotation/translation  304  of a joint (shoulder in  FIG. 3 ) that may be measured using conductive thread stitched stretch sensors in accordance with aspects of the invention. In an embodiment, a separate stitched stretch sensor is utilized for each translation and each rotation of each joint of interest. 
       FIG. 4  depicts a stitch pattern for the conductive thread  104  in an un-stretched state (top) and stretched stated (bottom). The depicted stitch pattern is a saw tooth stitch pattern including multiple teeth. Each tooth of the pattern has a positive slope portion  402  and a negative slope portion  404  with respect to an axis  400 . As the textile and, in turn, the conductive thread  104  is stretched, the positive slope portion  402  and, the negative slope portion  404  decrease in magnitude as illustrated in the bottom half of  FIG. 4 . In an embodiment, the saw tooth pattern is an American Society for Testing and Materials (ASTM) class  300  or  304  stitch (also known as a “zig-zag stitch”). As illustrated, contact between the teeth does not change from the unstretched state to the stretched state. Rather changes in resistance are due to a change in the resistance of the thread itself. 
     Although each tooth in the illustrated geometries are symmetrical, it is contemplated that one or more of the teeth may be asymmetrical with the positive slope portion having a different magnitude than the negative slope portion. For example, the positive slope portion may be essentially perpendicular and the negative slope portion may be 30 degrees or vice versa. Additionally, the slopes of the respective portions may change from tooth to tooth. 
       FIG. 5  depicts a cross section of the strand of silver coated nylon  202  of  FIG. 2A  in a un-stretched state (top) and stretched state (bottom). As the thread and, in turn, the silver coated nylon  202  is stretched, the cross sectional area of the silver coated  206  is reduced. The reduction is cross section area results in an increase in resistance between points on the conductive thread. 
       FIG. 6  depicts nine different stitched thread geometries in a related state in accordance with aspects of the invention. The particular geometry for a conductive thread stitched stretch sensor may be selected based on the particular joint and the particular rotation/translation to be measured using that sensor. For example, if the goal is to measure large change in resistance over a short elongation distance (˜2 inches, e.g., 1 inch or ¼ inch), a narrow width, long configuration geometry (upper right) would be the most appropriate. On the other hand, if the goal is to measure a change in resistance over a long elongation distance (˜6 inches and greater, e.g., 12 inches or 3 feet), then a wide width, short configuration geometry (lower left) could be used. In an embodiment, by way of non-limiting example, the tooth width is between 0.04 and 0.14 inches and the tooth length is between 0.06 and 0.24 inches. It will be understood that smaller/greater tooth widths and tooth lengths may be selected based on the joint being measured and its associated degree of rotation/translation. 
       FIG. 7  depicts a method  700  for making a conductive thread stitched stretch sensor in accordance with aspects of the invention. It will be understood by one of skill in the art that one or more of the steps may be performed in an order other that depicted in  FIG. 7 . 
     As step  702 , a textile is selected. The textile may be selected based on comfort for the wearer, elasticity, and durability. 
     At, step  704 , a conductive thread is selected. The conductive thread may, be selected based on durability and resistance change rate when stretched. 
     At step  705 , a sensor length is selected. The length of the sensor may be based on the joint being measured and the associated degree of rotation/translation as the length of the sensor will change as the joint is moved. 
     At step  706 , a stitch geometry is selected based on the sensor length. The stitch geometry may be selected to provide the greatest change in resistance based on the particular joint, the associated rotation/translation being measured, and the sensor length taking into consideration that the stick geometry will change as the sensor stretches. For each joint there will be multiple rotations and/or translations and the magnitude of the rotations/translations may be different from one joint to the next. Thus, multiple geometries may be selected with each conductive thread stitched stretch sensor having a corresponding geometry unique to the rotation/translation it will be measuring. 
     At step  708 , the conductive thread is stitched to the textile using the selected geometry. In an embodiment, the conductive thread is stitched to the textile using a sewing machine such as an industrial lockstitch machine, an industrial zigzag machine, or a domestic sewing machine. Other suitable methods for stitching the thread to the textile will be understood by one of skill in the art from the description herein. 
     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.