PATENT DOCUMENT

Publication Number: US-9983696-B2
Application Number: US-201514867522-A
Country: US
Kind Code: B2

Title: Force-sensing stylus for use with electronic devices

Abstract:
Embodiments disclosed herein relate generally to a stylus for use with a portable electronic device. The stylus includes a force sensing device to measure three dimensional force components exerted by the stylus on the portable electronic device. The output of the portable electronic device is adjusted based upon the force components.

Claims:
We claim: 
     
       1. A stylus, comprising:
 a housing; 
 a tip portion at an end of the housing; and 
 a force sensing device electrically connected with the tip portion to sense forces exerted on the tip portion in axial and radial directions, the force sensing device comprising:
 a first membrane extending radially from the housing to the tip portion; and 
 a second membrane, axially separated from the first membrane and extending radially from the housing to the tip portion; 
 
 wherein the force sensing device comprises a set of strain gauges on the first membrane, each of the set of strain gauges sensitive to axial and radial forces. 
 
     
     
       2. The stylus of  claim 1 , further including a controller electrically associated with the force sensing adjust output of a touch-sensitive surface associated with the stylus. 
     
     
       3. The stylus of  claim 2  further including a transmitting device for sending an input to said controller. 
     
     
       4. The stylus according to  claim 1  wherein the first membrane and the second membrane are each fixed to the housing. 
     
     
       5. The stylus of  claim 1  wherein the second membrane includes cut out portions that extend axially through the second membrane. 
     
     
       6. A system comprising:
 a portable electronic device; 
 a display screen associated with the portable electronic device; 
 a stylus electrically connected to the portable electronic device, the stylus including:
 a tip portion associated with the stylus; 
 a force sensing device associated with the tip portion, and comprising at least one set of strain gauges operative to sense three dimensional components of force exerted on the display screen by the tip portion, the force sensing device comprising:
 a first membrane radially connected to the tip portion with a first connection; and 
 a second membrane radially connected to the tip portion with a second connection, wherein the first connection and the second connection are separated by an axial gap; 
 
 a controller associated with the portable electronic device; 
 a transmitting device electrically connected to the force sensing device for providing the three dimensional force components to the controller; and 
 the controller providing signals to the display screen; 
 whereby the controller adjusts an output of the screen in response to the three dimensional force components. 
 
 
     
     
       7. The system of  claim 6  wherein said force sensing device includes a strain gauge adjacent said stylus. 
     
     
       8. The system according to  claim 6  wherein said first membrane includes the strain gauges. 
     
     
       9. The system according to  claim 6  wherein said second membrane includes cut out portions. 
     
     
       10. A method for displaying an image on an electronic device comprising the steps of:
 moving a stylus over the electronic device; 
 measuring, using at least one strain gauge sensitive to both axial and radial forces acting on a tip of the stylus, three dimensional force components exerted by the stylus on the electronic device, the forces being transmitted from the tip to first and second membranes that are axially separated and extending radially from a housing of the stylus to the tip, one of the membranes supporting the at least one strain gauge; 
 transmitting the measured force components to the electronic device; and 
 adjusting the image based upon the measured force components. 
 
     
     
       11. The method of  claim 10  wherein said step of adjusting includes turning said electronic device on or off. 
     
     
       12. The method of  claim 10  wherein said step of adjusting includes varying a visual characteristic of said image.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a nonprovisional patent application of and claims the benefit to U.S. Provisional Patent Application No. 62/057,988, filed Sep. 30, 2014 and titled “Force Sensing Stylus,” the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD 
     Embodiments disclosed herein relate generally to a stylus for providing input to a computing device, and more particularly to a stylus capable of sensing and measuring force exerted by the stylus on a surface. 
     BACKGROUND 
     Many people use a stylus when interacting with touch-sensitive computing devices. Styli permit data entry and inputs into touch-sensitive computing devices; certain users prefer using a stylus to using their fingers. 
     Typical styli, however, are limited in the type and accuracy of input they can provide. Generic styli lack any sensing capability and instead rely on the touch sensing capability of the electronic device with which they interact. Some styli can sense a force exerted by a user on the tip of the stylus, but most are limited to single-axis force sensing. That is, such styli can sense only a magnitude of force exerted along an axis parallel to the axis of the stylus. 
     Generally, single-component force sensing may not provide especially useful input when the stylus is held at an angle other than perpendicularly to the input surface. Any non-right angle between stylus and input surface may cause the measurement of force applied to the input surface to be inaccurate. Further, single-force styli are inherently limited in the number and variety of inputs that may be provided to an electronic device. 
     Accordingly, there may be a need for a force-sensing stylus that can sense force along multiple axes. 
     SUMMARY 
     A stylus is disclosed which includes an apparatus and system for detecting the amount of force exerted by a user on a touch-sensitive surface or other surface and, in particular, with respect to a portable electronic device. The stylus may include a force sensor contained within or attached to the stylus which senses the force exerted by a user in three dimensions on a surface over which the stylus is moved. The sensor may be contained within the stylus or may otherwise be associated with the stylus. 
     One embodiment utilizes a strain gauge in a stylus to sense force exerted by a user using a stylus in both axial and radial vectors. By sensing the force vectors, the amount of force sensed by the touch-sensitive surface in a portable electronic device may be adjusted such that the quality of a line made by the user with the stylus may be adjusted to be uniform. That is, the force sensor may compensate for uneven force vectors so as to make the touch-sensitive surface sensors generate a uniform line image on the touch-sensitive surface. The determination of the force vectors may also be useful in other functions of the stylus. For example, the force exerted against a touch-sensitive surface may be used to turn the touch-sensitive surface on and off. Accurate determination of the axial force vector against the touch-sensitive surface results in more accurate determination of the intent of the user as to turning the device on or off. 
     In another embodiment of the device, the sensed force may be stored in the portable electronic device. The data storage device could be contained within the stylus or in a laptop computer or electronic tablet or other suitable device which may store the sensed data. The sensed data may be communicated to the data storage device wirelessly or through a direct connection to the stylus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a illustrates a portable electronic device held by a user; 
         FIG. 2  illustrates a stylus contacting a portable electronic device; 
         FIG. 3  depicts a stylus contacting a surface and showing force vectors exerted by the stylus on the surface; 
         FIG. 4  illustrates one embodiment of a stylus; 
         FIG. 5  illustrates a tip portion of a stylus; 
         FIG. 6  illustrates a second view of the tip portion of a stylus; 
         FIG. 7  illustrates a force sensor assembly; 
         FIG. 8  is a cross-sectional view of the force sensor taken through line  8 - 8  in  FIG. 7 ; 
         FIG. 9  illustrates a strain gauge assembly of the force sensor assembly; 
         FIG. 10  illustrates one sample layout of individual strain gauges of the strain gauge assembly; 
         FIG. 11 . illustrates an alternate strain gauge layout; 
         FIG. 12  illustrates a strain gauge assembly when axial force is exerted by the stylus; 
         FIG. 13  illustrates a strain gauge assembly when radial force is exerted by the stylus; and 
         FIG. 14  illustrates use of a sample stylus with a touch- and/or force-sensitive surface. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. Those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. Like reference numerals denote like structure throughout each of the various figures. 
     Referring to the figures,  FIG. 1  is a perspective view of an electronic device  11  held by a user  12 . Electronic device  11  is illustrated as a tablet computing device, but it should be appreciated that any suitable electronic device may be used in or with various embodiments, including a mobile phone, a wearable computing device (such as a watch, glasses, jewelry, a band and so on), a laptop or other portable computer, a display, a touch-sensitive surface, and so forth. 
       FIG. 2  is a perspective view of electronic device  11 , showing a stylus  14  contacting touch-sensitive surface  13 . Stylus  14  may be used to provide input to electronic device  11 , for example, through interaction with touch-sensitive surface  13 . Touch-sensitive surface may sense the touch of the stylus, which in turn may be interpreted as an input to the electronic device  11 . 
     The usefulness of stylus  14  in various applications may be affected by the force exerted on touch-sensitive surface by stylus  14 . For example, the width of a line generated on screen  13  may be dependent upon the force which is sensed by touch-sensitive surface  13  and exerted by user  12  in creating that line. In such an example, more force exerted by the stylus  14  may result in a wider line while less force may result in a narrower line. Many touch-sensitive surfaces  13  do not sense any force exerted thereon. However, it may be useful for the stylus  14  itself to be able to sense multi-axial forces it is applying to the touch-sensitive surface or other input surface. 
     The orientation of stylus  14  with respect to input surface  13  may play a role in determining exerted force. If stylus  14  is held near perpendicular to screen  13  virtually all the force exerted by user  12  is transferred to stylus  14  through tip  16 . By contrast, when stylus  14  is held at an angle to screen  13  (as shown in  FIG. 2 ), only one component of the force exerted by user  12  on stylus  14  would be sensed by any single-axis force-sensing stylus, namely the force vector extending through tip  16 . Since the other vectors of the exerted force extend in directions parallel to screen surface  13 , single-axis force-sensing styli cannot sense these vectors. Likewise, even if input surface  13  is force-sensitive, it may not sense these vectors. 
     Referring to  FIG. 3 , a simplified stylus  14  is shown in contact with touch-sensitive surface  13 . Stylus  14  is positioned at an angle θ from axis  15 , which is perpendicular to surface  13 . In certain embodiments, the stylus  14  may detect a force (Fn) exerted axially with respect to tip  16  (e.g., along vector Fn), parallel to the axis of the stylus  14 . However, as can be seen from  FIG. 3 , there are additional force components (Ft and Fs) exerted on tip  16  and that can be measured by the current stylus  14 . By measuring additional force components, Ft and Fs, three-dimensional force vectors can be determined with respect to tip  16 . A rotational angle component ø can be measured given known values for the three-dimensional force vectors Fn, Ft, and Fs. 
     Further, by measuring three-dimensional force components, uniform force sensitivity over all tilt angles θ is enhanced. In addition, force measurement errors due to tilt θ and rotation ø angles are reduced. Measuring force in three may reduce or minimize certain limitations experienced by single-axis force sensing styli. 
     Thus, sensitivity and accuracy of force measurement by the stylus  14  may be enhanced through the use of multi-axial force sensors. Sensitivity and accuracy may be particularly enhanced when the stylus is positioned at a large tilt angle θ with respect to the input surface  13 , as the measured force for a one-axis sensor may be skewed by frictional force. Generally, frictional force between the stylus  14  and input surface  13  may increase as the tilt angle θ increases. 
     While inclusion of a three axis force sensor in a stylus may provide useful qualities, such inclusion may also present certain design challenges. Oftentimes, a stylus is relatively thin and long to mimic the look and feel of a typical writing instrument, such as a pen or pencil, and also to provide a comfortable gripping surface for a user. However, the longer the length and narrower the diameter of the stylus  14 , the more flexible it is along its length. Generally, flexibility of the stylus may complicate or interfere with force measurement, because the force may not be exerted axially on the tip  16 . Thus, in some embodiments there may be a trade-off between the mechanical strength of stylus  14  and sensitivity of the force sensor. 
       FIG. 4  generally shows a stylus  14  having a long, narrow body coupled to a tip  16 .  FIG. 5  is a simplified representation of region  17  of the stylus  14  of  FIG. 4 , and specifically depicts a simplified mechanical model of the tip  16 . 
     The relatively long distance  18  between tip  16  and force sensor  19  (which, in one embodiment, is about 20-30 mm) may make tip  16  sensitive to radial forces (Fs, Ft) representing radial force moments  21 . A moment of force may be created when user  12  moves tip  16  along an input surface; the frictional resistance of tip  16  with respect to the surface  13  may cause rotation or displacement with respect to the longitudinal axis of stylus  14 . Accordingly, it may be useful to either stiffen the tip structure  16  or to account for the bending of the tip when determining or measuring multi-axial force. 
       FIG. 6  shows a side view of tip portion  16 . Stylus tip  16  is connected to force sensor structure  22 , shown in more detail in  FIGS. 7 and 8 . The force sensor structure  22  may generally measure the multi-axial forces exerted on tip  16  when it is in contact with an input surface. 
     Referring to  FIG. 7 , force sensor structure  22  is shown in a close-up view. A strain gauge assembly  23  is shown surrounding hollow core portion  24 . In one embodiment, strain gauge assembly  23  may have a diameter from about 5 mm to about 20 mm. An exterior surface  25  of strain gauge assembly  23  is affixed to the interior housing surface of stylus  14 . Hollow core portion  24  allows electrical connections to be made from tip  16  to strain gauge assembly  23  and, in some embodiments, to a transmitter or other components of portable electronic device  11 . 
     Force sensor structure  22  may be constructed from membranes, tubes, or other surfaces by laser welding, thermal compression bonding, or diffusion bonding. Structure  22  could also be made by three dimensional printing technologies. The various components of structure  22  could be made from aluminum, stainless steel, titanium, beryllium, copper, a copper/titanium alloy or a combination of these or other metallic or other materials. 
     Referring to  FIG. 8 , a side sectional view of strain gauge structure  22  taken along line  8 - 8  of  FIG. 7  is shown. Strain gauge assembly  23  includes a top membrane  26  and a bottom membrane  27 . Top membrane  26  and bottom membrane  27  are separated by a predetermined distance  28  of a sidewall; this distance may, in one embodiment, be from 1-25 mm. 
     Bottom membrane  27  may increase the radial stiffness of force sensing structure  22 . Bottom membrane  27  may be constructed from a flat plate, a beam, a corrugated material and so forth. Portions  29  of bottom membrane  27  may be removed to make membrane  27  somewhat flexible and reduce the overall stiffness of stylus  14 . In some embodiments, top membrane  26  may also have cutouts (not shown) to improve sensitivity of the force measurement. Membranes  27  and  28  are compliant axially (z axis) but more rigid laterally (x-y axes) by this design. In alternate embodiments, lower membrane  27  could be an elastomeric material which is also more rigid in the x-y plane but more compliant along the z axis. 
     In some embodiments, tip  16  may include an electrode or other electrically active structure or material that may electrically and/or capacitively couple to touch-sensing structures in an input surface  13 . Alternatively, the tip  16  may be doped or otherwise impregnated with a capacitive material so that a capacitive touch-sensing structure of the input surface  13  may detect a touch from the tip  16 . In still other embodiments, the tip may be electrically inert and a resistive sensor may detect a touch from the stylus tip  16 . 
     Referring to  FIG. 9 , force sensor structure  22  is shown in a detailed perspective view. Strain gauge assembly  23  is shown mounted on hollow core portion  24 . Strain gauge assembly includes a strain gauge  31  mounted on top membrane  26 . Pin grid array  32  of the strain gauge  31  may provide electrical connections from strain gauge to internal components of stylus  14  or electronic device  11 . Referring to  FIG. 10 , strain gauge  31  is shown in greater detail with pin grid array  32  and six individual strain gauges  33 . Each strain gauge  33  is electrically connected to a corresponding pin connection  34  on pin grid array  32 . 
     Strain gauge  31 , as shown in  FIG. 10 , includes six individual strain gauges  33  in one embodiment. It should be expressly understood that any number of strain gauges  33  may be included. Using six strain gauges reduces the number of connections and the complexity of the design of strain gauge  31 . 
     The variation in temperature and resistance at pin grid array  32  may be compensated for with electrical design parameters known to one skilled in the art. Similarly, the Seebeck effect of electrical induction due to use of different materials may be compensated for by differential signal lines as known to one skilled in the art. Power savings may be achieved using higher resistive strain gauges  33 . 
     Because strain gauge  31  provides a more linear signal than, for example a capacitive sensor, it improves the signal to noise ratio thereby requiring less digital signal processing which in turn reduces power requirements of the force sensor and overall apparatus. Strain gauge  31  is preferred in some embodiments because it provides a more accurate linear signal which is more sensitive than other force sensors. However, it should be expressly understood that other types of force sensors may be utilized in various embodiments. For example, a capacitive strain gauge could be used with top membrane  26  and bottom membrane  27  separated by resilient members such as springs or a gel material. The distance  28  between membranes  26  and  27  is known and any change in that distance can be measured by a change in capacitance measured between membranes  26  and  27 . 
     Referring to  FIG. 11 , in an alternate embodiment, a strain gauge design  31  may include  12  individual strain gauges  33 . The design and layout of individual strain gauges  33  on strain gauge  31  may be made so as to make strain gauge  31  sensitive to forces (Ft, Fs) in the radial direction and force Fn in the axial direction while minimizing sensitivity to rotational force (torque) along the rotation angle ø. 
     Referring to  FIG. 12 , a top view of strain gauge  31  shows the effect of axial force on strain gauge  31 . That is, the portion  35  of strain gauge  31  adjacent to hollow core portion  24  senses evenly distributed force in the area immediately surrounding hollow core portion  24  as sensed by strain gauges  33 . This is due to the force Fn exerted by user  12  in the downward axial direction along stylus  14  as he or she moves tip  16  across screen  13  on portable electronic device  11 . An area  36  on the periphery of strain gauge  31  may sense less force in this example because stylus  14  is held more perpendicular to screen  13  (tilt angle θ is small). 
     In one embodiment, the tilting of stylus  14  on the z axis may be measured as differences in the resistance of various strain gauges  33 . As certain of strain gauges  33  are deformed in the x-y directions by a force exerted on stylus tip  16  (for example, stemming from the tip impacting an input surface), their resistances change. By contrast, other strain gauges  33  which are not so deformed may maintain a relatively constant resistance. 
     Generally, certain of the strain gauges may be compressed or expanded in the x-y direction, and thereby generate a change in resistance. From the measured change in electrical resistance of various strain gauges  33  in the array, the amount of applied stress may be determined using a Wheatstone Bridge. Strain gauges  33  located closer to hollow core portion  24  may sense more z axis (axial force) than radial force in the x-y direction. 
     Referring to  FIG. 13 , a top view of strain gauge  31  shows the effect of radial force sensed by strain gauge  31 . In this view, the portion  35  of strain gauge  31  adjacent to hollow core portion  24  receives uneven force due to the tilting of stylus  14  (tilt angle θ is larger than in  FIG. 12 ) by user  12  as he or she moves tip  16  across screen  13  on portable electronic device  11 . Depending upon the direction and degree θ of tilt of stylus  14 , an area generally indicated by reference numeral  37  may sense positive strain or tension while an area generally indicated by reference numeral  38  on the opposite side of hollow core portion  24  may sense negative strain or compression as sensed by strain gauges  33  due to the tilting of stylus  14  by user  12  as he or she moves tip  16  across screen  13 . By sensing the positive or negative strain, the tilting angle θ can be measured from axis  15  and the output of stylus  14  in terms of line quality can be adjusted depending upon this measurement. 
     It should be appreciated that certain functions can be enabled by the amount of sensed force exceeding an input threshold. For example, if an amount of force F is required to activate portable electronic device  11  but user  12  is holding stylus at an angle θ from the z axis  15 , the amount of force exerted by user  12  on stylus  14  will be divided into force components along each of the x, y, and z axes. By determining the total amount of force that user  12  exerts in the x, y and z directions combined, a more accurate input can be provided. 
     Referring to  FIG. 14 , the effects of uneven force exerted by a user due to the tilting of stylus  14  by user  12  as he or she moves tip  16  across screen  13  on portable electronic device  11  may be seen. In this embodiment, user  12  may be trying to draw a series of connected circles  40  on screen  13 . Because of the tilting of stylus  14  by user  12  and because of uneven force exerted by user, the quality of a line  39  may vary from one area to another. For example, generally, user  12  exerts more force pushing stylus away from his or her person in the direction indicated by arrow  41  than he or she does moving stylus toward his or her person in the direction indicated by arrow  42 . In the lateral directions indicated by arrows  43 , user  12  may exert even less force on stylus  14  against screen  13 . 
     The effect of this uneven force is that the quality of line  39  varies from one portion of screen  13  to another. Portions  44  on the left side of circles  40  may be lighter because user  12  has exerted less force on stylus  14  when drawing stylus  14  toward him or her while portions  45  on the right side of circles  40  may be darker because user  12  has exerted more force pushing stylus  14  away from him or her. In some situations, the force exerted on screen  13  may be such that no line  39  is visible on certain portions of screen  13 . This effect on handwriting or mechanical or artistic drawing can be significant and result in unsatisfactory performance of portable electronic device  11  as perceived by user  12 . By allowing force sensor  31  to compensate for variations in the amount of force exerted by user  12  on screen  13 , in one embodiment, the quality of line  39  on screen  13  may be adjusted so as to be more uniform. The electrical signals received by controller  10  in portable electronic device  11  may be adjusted in accordance with signals received from force sensor  31  in stylus  14  so as to compensate for uneven applied force which would otherwise vary the visual characteristic of line  39 . A more uniform image on screen  13  may thus be generated. 
     While the disclosure has described various embodiments, it should be expressly understood to those of ordinary skill in the art that certain modifications may be made without departing from the spirit or scope of this disclosure. For example, while various configurations have been disclosed for a stylus to enable various applications for texture capture, additional capabilities may be employed without departing from the spirit or scope of the disclosure. Accordingly, the proper scope of this disclosure is set forth in the following claims.

Metadata:
Filing Date: 20150928
Publication Date: 20180529
Grant Date: 20180529
Priority Date: 20140930
Inventors: YONEOKA, SHINGO
BAUGH, BRENTON A.
ZIMMERMAN, AIDAN N.
HARLEY, JONAH A.
HOEN, STORRS T.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/0416", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0383", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0414", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0383", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0383", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 56164098