US20110318985A1 - Touch Sensor Fabric - Google Patents

Abstract

A method and apparatus are provided for a touch sensor made from fibers with conductive and non-conductive regions. The fibers are woven into a fabric and connected to control electronics. The fibers are grouped and the ends of the fibers in a group are connected together prior to connection to the control electronics in order to reduce the number of connections required between the sensor fabric and control electronics. The control electronics drive signals to the sensor fabric and measure signals from the sensor fabric to determine touch locations and touch contact areas.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• This application is related to U.S. patent application Ser. No. 12/107,244, filed Apr. 22, 2008 and entitled “METHOD AND APPARATUS FOR DETERMINING COORDINATES OF SIMULTANEOUS TOUCHES ON A TOUCH SENSOR PAD”, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• This invention relates to a unique fiber design that can be woven into a fabric that functions as a touch sensor. This invention further relates to a method for connecting control electronics to the fabric that are able to measure the location and determine the contact area of multiple, simultaneous touch events on the fabric.
• 2. Statement of the Problem
• Touch input sensors and controllers are becoming common as user input devices to control computers and other electronic equipment such as cell phones. When a touch sensor is transparent and placed in front of a display, the sensor-display assembly is a touch-screen. A touch sensor without a display can be opaque and is a touch-pad.
• Different technologies exploit various parameters of layered materials to make sensors. Resistive sensors are constructed to hold two linearly resistive layers apart at rest that allowed to come into contact upon a touch event. The resistor dividers resulting from the touch are read by control electronics and a location is calculated. Capacitive sensors are constructed from conductive layers that are driven by signals to generate an electric field. When the base capacitance is altered by another electric field (i.e. someone's finger) the differences are measured by control electronics and a location is calculated. Inductive sensors are driven by signals to generate a magnetic field. When the magnetic field is altered by another magnetic field (i.e. a stylus with a coil) the differences are measured by control electronics and a location is calculated. Surface Acoustic Wave sensors use transducers to initiate mechanical waves in a sensor, and process the reflected wave pattern to look for changes caused by touch points reflecting and/or absorbing the wave energy. IR sensors shine a grid of beams across the sensor surface that is monitored on opposing sides. A touch breaks the beam and the control electronics determine a location.
• Of these sensor technologies, resistive has distinct advantages. Resistive sensors are like mechanical switches so respond to touches from all actuators such as fingers (even when gloved) and common implements (e.g. pencils, pens). A touch is not ambiguous because the same pressure that informs the electronics of a touch informs the user of a touch. Resistive also has a high signal to noise ratio allowing for the possibility of high resolution.
• Major problems of resistive are optical clarity when used as a touch-screen in front of a display and robust function in the field for either touch-screen or touch-pad applications. This invention focuses on touch-pad applications for the technology so optical clarity is not important, though those skilled in the art can apply this invention to touch-screens. The problem with the robustness of traditional resistive sensors is due to the need to maintain an air gap between the layers of the sensor at rest, but allow the layers to come into contact with one another upon a touch event.
• Maintaining an air gap is particularly difficult when the sensor is large. For example, when the sensor is used as a large screen for a projected display in an interactive white board application. Maintaining a thin air gap is also a problem when the sensor needs to conform to a non-planer surface such as when draped on a user's leg or applied to a contoured surface in an automobile.
SUMMARY OF THE SOLUTION
• The present invention solves the above and other problems by the making a sensor by weaving fibers with a specific cross section made up of conductive and non-conductive regions into a fabric. The ends of the fibers are then grouped and connected to control electronics.
• Aspects
• An aspect of the invention is how a fiber is made up of conductive and non-conductive regions where the non-conductive regions of two crossing fibers keep the conductive regions of the fibers apart when no force is applied, but allow the conductive region to come into contact when an external compressive force is applied.
• Preferably, the fiber can be woven into a fabric such that the overlapping fibers form an array of switches in each location where horizontal fibers overlap vertical fibers.
• Preferably, the cross section of the fiber is longer in one direction than in the other so the orientation of the fiber remains constant throughout the fabric.
• Preferably, the middle of the fiber is conductive while the sides are non-conductive.
• Another aspect of the invention is how the fiber ends are grouped where the fibers in a group are electrically connected to one-another before being connected to the control electronics in order to reduce the number of connections between the sensor fabric and the control electronics.
• Preferably, the same fibers that are grouped at one end are grouped at the other end.
• Preferably, all the fiber groups contain the same number of fibers.
• Another aspect of the invention is the method for detecting all crossing groups experiencing a touch comprising the steps of: drive all groups in a first orientation to a positive voltage and tie one end of the groups in a second orientation to ground; read the voltages at the other end to determine which groups in a second orientation are experiencing a touch; in turn, drive groups in a second orientation that experienced a touch to a positive voltage and tie one end of the groups in a first orientation to ground; read the voltages at the other end to determine which groups in a first orientation are contacting the currently driven group in the second orientation.
• Preferably, the means for detecting which fiber in a first group is contacting a fiber in a second crossing group is to set up a voltage gradient down the second group and read the voltage of the first group. If the voltages of the edge fibers in the first group are known through a prior calibration process, the position of the contacting fiber in the first group can be calculated through interpolation.
• Another aspect of the invention is how the contact area of a touch is determined by measuring a resistance change due to fibers being shorted together at the touch point.
• Preferably, the ends of a first group of fibers are driven with a constant current source while the ends of a second group of crossing fibers are connected to ground. As the contact area between the two fiber groups gets larger, more fibers of the first group contact fibers in the second group, adding parallel current paths thereby reducing the total resistance of the path resulting in a lower voltage at the current source connection.
DESCRIPTION OF THE DRAWINGS
• The above and other advantages and features of the invention may be better understood from a reading of the detailed description taken in conjunction with the drawings. The same reference number represents the same element on all drawings.
• FIG. 1 is an isometric view of a fiber used in the touch sensor fabric.
• FIG. 2 is a top isometric view of the fibers woven into a fabric.
• FIG. 3 is a cross section view of the fibers woven into a fabric showing the conductive regions of crossing fibers being held apart when the fabric is at rest.
• FIG. 4 is a cross section view of the fibers woven into a fabric showing the conductive regions of crossing fibers coming into contract upon a touch event.
• FIG. 5 is a top isometric view of the fibers at the edge of the fabric being connected to a perimeter flex circuit.
• FIG. 6 is a bottom isometric view of the fibers at the edge of the fabric being connected to a perimeter flex circuit.
• FIG. 7 is a schematic view of the sensor connections to the control electronics.
• FIG. 8 is a flow chart of a method for conducting a search of a plurality of fiber groups to identify fiber groups experiencing touch points.
• FIG. 9 shows two overlapping fiber groups where the vertical group is driven by a voltage gradient picked up by the horizontal group at a point of touch.
• FIG. 10 is a schematic representation of two overlapping fiber groups showing the fiber resistances.
DETAILED DESCRIPTION OF THE INVENTION
• FIGS. 1-10 and the following description depict specific exemplary embodiments of the invention to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects of the invention have been simplified or omitted. Those skilled in the art will appreciate variations from these embodiments that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described below, but only by the claims and their equivalents.
• FIG. 1 shows a short piece of asynthetic fiber100 that is to be woven into a sensor fabric. The fiber is drawn with three regions: electrically insulativeouter regions101 and102, and electricallyconductive region103. The conductivity ofregion103 is controlled to establish a desired resistance per unit length. In a preferred embodiment, the fiber is made from a polymer (e.g. nylon-66) and thecenter region103 is made conductive by mixing in carbon black. To achieve high resolution from the woven sensor, cross section offiber100 may be made very small. In a preferred embodiment,fiber100 is 0.16 mm wide and 0.05 mm thick.
• FIG. 2 shows a small piece of asensor fabric200 woven from multiple fibers. The figure shows a 9×9 fiber section of a sensor. This much enlarged view represents only a small piece of a sensor as even a relatively small 64 mm×32 mm sensor would require 320 by 160 fibers.
• The outernon-conductive regions101 and102 offiber100 are slightly thicker than centerconductive region103. This keeps the conductive regions of overlappingfibers100 infabric200 from coming into contact with one another while the fabric is at rest.FIG. 3 shows a cross section offabric200.Conductive region301 of the fiber running across the page does not contactconductive region302 of the fibers running perpendicular to the page.
• InFIG. 4, touch implement404 contacts and compressesfabric200. The compressive pressure from the touch implement causes theconductive regions401,402, and403 of the fibers under the touch implement to come into contact withconductive region301.
• To detect the contact event, the ends offibers100 offabric200 are connected to control electronics. In a preferred embodiment, the fibers connect to a flex circuit that runs around the perimeter of the fabric. In turn, the flex circuit runs circuit traces from the fiber contacts to control electronics.
• In a preferred embodiment, multiple fibers are connected to a single flex circuit contact and are thereby connected together. This is necessary to reduce the high number of contacts that would otherwise be required of the control electronics. In a preferred embodiment, 32 fibers are connected together into a fiber group. Thus, in the 320 by 160 fiber sensor discussed above, 320/32+320/32+160/32+160/32=30 connections would be required to connect both ends of all fibers to the control electronics.
• FIG. 5 showsfabric200 connected to flex501. Fiber groups alternate between connecting to the top and bottom offlex501.FIG. 5 shows a top isometric view with 2 3-fiber groups connected tocontacts502 and503.FIG. 6 is a bottom isometric view of the same assembly showing the intervening 3-fiber group connected to contact602. By alternating groups between top and bottom flex connections, the contact pads can be oversized without shorting together. This simplifies assembly as it relaxes alignment requirements betweenfabric200 andflex501.
• FIG. 7 shows a schematic view of how the fabri-flex assembly500 is connected to controlelectronics706. The fibers ofgroup701 are connected together viaflex contact702 at one end and703 at the other end. Circuit traces704 and705connect flex contacts702 and703 respectively to controlelectronics706. In a like manner, all flex contact pads are individually connected to controlelectronics706.
• The control electronics sends driving voltages and currents to the sensor contact pads and measures signals coming from the sensor contact pads. The driving and measuring allows the control electronics to detect and locate touches to the sensor. The touch information is then communicated to a host computer viaconnection707. In a preferred embodiment,connection707 is a USB connection.
• Parallel searching is an efficient technique for identifying fiber groups in a first orientation that are contacting fiber groups in a second orientation due to touches.FIG. 8 illustrates a flow chart of method800 for conducting a parallel search of a plurality of fiber groups to identify all fiber group intersections that are experiencing a touch.
• Instep802control electronics706 raises the voltage of all fiber groups in a first orientation offabric200. Instep804,control electronics706 detect the fiber groups is a second orientation that experience a voltage increase. Instep806control electronics706 clears the voltages on all fiber groups. Instep808,control electronics706 raises the voltage of one of the fiber groups identified instep804. Instep810control electronics706 detects fiber groups in the first orientation experiencing a voltage increase to identify the intersecting fiber groups experiencing a touch point. Instep812, if there are additional fiber groups identified in804 that have not been processed, then controlelectronics706 loops to step806. Otherwise, processing by method800 ends having identified all fiber group intersections experiencing a touch.
• FIG. 9 helps to explain the method for determining which fibers within crossing fiber groups are contacting one-another. The control electronics drivecontact702 to a voltage V+ and connect703 to ground to set up a voltage gradient in linearlyresistive fiber group701. A fiber ingroup701 is contacting a fiber ingroup901 due to a touch atlocation904. The voltage Vi of the fiber ingroup701 at the touch point can be read atcontract903. If, through a prior calibration process, the value of the voltage ingroup701 where it intersects the top fiber ingroup901 is known to be Vn and where it intersect the bottom fiber ingroup901 is known to be V0, then the number i of the fiber ingroup901 is equal to N*(Vi−V0)/(Vn−V0) where N is the number of fibers ingroup901.
• The contacting fiber withingroup701 can be determined by drivinggroup901 and measuringgroup701 in a similar manor.
• A single touch may cause more than just two crossing fibers to come into contact. In fact, the more fibers that come into contact, the larger the contact area. Knowing the contact area can be useful in determining what is touching the sensor, or, in the case of soft touch implements such as fingers, determine the pressure of a touch.
• FIG. 10 helps to explain the method for determining how many crossing fibers are in contact due to a touch. It shows an approximation of the fiber resistances for crossingfiber groups701 and901. Ifcontacts702 and703 are connected together and driven with a constant current source “I”, whilecontact902 and903 are tied to ground, the voltage “V” atcontacts702 and703 is proportional to the circuit resistance according to V=IR.Touch904 causes one vertical fiber to come into contact with one horizontal fiber so the circuit resistance is equal to (R1*R2/(R1+R2))+(R3*R4/(R3+R4)).Touch1004 causes two vertical fibers to come into contract with two horizontal fibers so the circuit resistance will be one half of the value in the904 touch case. Thus the voltage read atcontracts702 and703 fortouch1004 will be one half of the value read fortouch904.
• Although specific embodiments were described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents therein.

Claims (9)

1. A fiber with conductive and non-conductive regions where the non-conductive regions of two crossing fibers keep the conductive regions apart when at rest, but allow the conductive regions to come into contact upon application of an external compressive force over the overlap region.

2. The fiber ofclaim 1, where multiple fibers are woven into a fabric.

3. The fiber ofclaim 1, where the cross section of the fibers is wider in one direction than the other so the orientation of the fiber stays consistent when it is woven into a fabric.

4. The fiber ofclaim 1 where the conductive region is in the middle of the fiber and the non-conductive regions are on the side of the fiber.

5. The fabric ofclaim 2, where the fibers are grouped, and then fibers within each group are connected together at their ends and then connected to control electronics.

6. The groups ofclaim 5, where all the groups have the same number of fibers.

7. The assembly ofclaim 5, wherein identifying the intersecting fiber groups experiencing a touch comprises conducting a parallel search of the fiber groups.

8. The assembly ofclaim 5, wherein identifying the fibers within a fiber group experiencing a touch comprises:

apply a voltage gradient along a fiber group in a first orientation;

read the voltage at the terminal of a fiber group in a second orientation;

determine the fiber in contact by calculating where the read voltage falls between the known voltages for the first and last fibers of the fiber group in a second orientation.

8. The assembly ofclaim 5 where the contact area of a touch on two intersecting fiber groups is determined by measuring the resistance of a path from the terminals of the fiber group in a first orientation to the terminals of the fiber group in the second orientation.

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