PATENT DOCUMENT

Publication Number: US-10437359-B1
Application Number: US-201715445383-A
Country: US
Kind Code: B1

Title: Stylus with external magnetic influence

Abstract:
An interface system may include an electronic device defining an input surface, a stylus comprising a magnetic component and configured to provide input to the electronic device via the input surface, and a magnetic field generator coupled to the electronic device and configured to produce a magnetic field to impart a force on the magnetic component of the stylus.

Claims:
What is claimed is: 
     
       1. An interface system comprising:
 an electronic device comprising:
 a housing; and 
 a cover coupled to the housing and defining an input surface; 
 
 a stylus comprising a magnetic component and configured to provide input to the electronic device via the input surface; and 
 a dock configured to be removably coupled to the electronic device and comprising:
 a conductive coil configured to produce a magnetic field to impart a force on the magnetic component of the stylus; and 
 a magnetic shunt positioned under the conductive coil. 
 
 
     
     
       2. The interface system of  claim 1 , wherein:
 the electronic device comprises a display within the housing; 
 the dock further comprises circuitry configured to energize the conductive coil to produce the magnetic field; 
 the magnetic field extends through the housing, through the display, and through the input surface; and 
 the magnetic component is configured to interact with the magnetic field. 
 
     
     
       3. The interface system of  claim 1 , wherein:
 the dock comprises a group of conductive coils; and 
 the conductive coil is one of the group of conductive coils. 
 
     
     
       4. The interface system of  claim 3 , wherein the conductive coils of the group of conductive coils are positioned in an overlapping arrangement. 
     
     
       5. A system for magnetically influencing an input device, comprising:
 a computing device comprising:
 an enclosure; 
 a touchscreen within the enclosure and configured to:
 detect an input device at a first location on an exterior surface of the touchscreen; and 
 detect the input device at a second location on the exterior surface of the touchscreen, the second location different from the first location; and 
 
 an electromagnetic coil within the enclosure; wherein 
 
 the computing device is configured to:
 produce a magnetic field above the exterior surface of the touchscreen, using the electromagnetic coil, in response to detecting the input device at the first location, thereby producing a tactile output via the input device; and 
 in response to detecting the input device at the second location, ceasing to produce the magnetic field. 
 
 
     
     
       6. The system of  claim 5 , wherein:
 the input device comprises:
 a body; and 
 a magnetic component within the body; and 
 
 the electromagnetic coil is configured to produce the magnetic field around the magnetic component of the input device. 
 
     
     
       7. The system of  claim 6 , wherein:
 the electromagnetic coil is a first electromagnetic coil; 
 the magnetic field is a first magnetic field; 
 the magnetic component is a second electromagnetic coil; and 
 the input device further comprises:
 a power source; and 
 circuitry configured to power the second electromagnetic coil to produce a second magnetic field. 
 
 
     
     
       8. The system of  claim 6 , wherein the computing device further comprises control circuitry configured to control the electromagnetic coil in order to produce an alternating magnetic field. 
     
     
       9. The system of  claim 6 , wherein the magnetic component is a permanent magnet. 
     
     
       10. The system of  claim 6 , wherein the input device further comprises a spring movably supporting the magnetic component to the body. 
     
     
       11. The system of  claim 10 , wherein the movably supported magnetic component has a resonant frequency between about 150 Hz and about 250 Hz. 
     
     
       12. A method, comprising:
 detecting, at an electronic device with a touch sensor and a magnetic field source, a touch input from an input device having a magnetic component, the detecting comprising detecting the input device at a first location on an input surface of the electronic device; 
 in response to detecting the input device at the first location, producing a magnetic field with the magnetic field source, thereby imparting a force on the magnetic component of the input device; 
 detecting the input device at a second location on the input surface, the second location different from the first location; and 
 in response to detecting the input device at the second location, ceasing to produce the magnetic field. 
 
     
     
       13. The method of  claim 12 , wherein:
 detecting the input device at the first location on the input surface of the electronic device comprises detecting the input device outside of an input path along the input surface; and 
 detecting the input device at the second location on the input surface comprises detecting the input device within the input path. 
 
     
     
       14. The method of  claim 13 , wherein:
 the method further comprises determining a predicted input path based on at least one of a location and a direction of the touch input; and 
 the input path corresponds to the predicted input path. 
 
     
     
       15. The method of  claim 12  wherein:
 the method further comprises determining a target location of the input device on the input surface of the electronic device; and 
 producing the magnetic field comprises producing the magnetic field such that the force imparted on the magnetic component is in a direction of the target location. 
 
     
     
       16. The method of  claim 15 , wherein:
 the magnetic field source comprises a plurality of coils; and 
 producing the magnetic field comprises:
 determining a combination of coils that will produce the magnetic field such that the force imparted on the magnetic component is in the direction of the target location; and 
 actuating the determined combination of coils. 
 
 
     
     
       17. The method of  claim 12 , wherein:
 detecting the input device at the first location on the input surface of the electronic device comprises detecting the input device within a threshold distance from a graphical object displayed by the electronic device; and 
 detecting the input device at the second location on the input surface comprises detecting the input device beyond the threshold distance from the graphical object displayed by the electronic device. 
 
     
     
       18. An interface system comprising:
 an electronic device comprising:
 a housing; and 
 a cover coupled to the housing and defining an input surface; 
 
 a stylus comprising a magnetic component and configured to provide input to the electronic device via the input surface; and 
 a dock configured to be removably coupled to the electronic device and comprising:
 a frame defining a recess; and 
 a coil positioned in the frame and configured to produce a magnetic field to impart a force on the magnetic component of the stylus, wherein 
 
 the electronic device is configured to be received in the recess and at least partially surrounded by the frame. 
 
     
     
       19. The interface system of  claim 18 , wherein:
 the coil is a first coil; and 
 the dock further comprises a plurality of additional coils positioned in the frame. 
 
     
     
       20. The interface system of  claim 18 , wherein:
 the coil defines a plurality of turns wrapped about a coil axis; and 
 the coil axis is perpendicular to the input surface of the electronic device when the electronic device is received in the recess. 
 
     
     
       21. The interface system of  claim 18 , wherein the force imparted on the magnetic component of the stylus vibrates the stylus.

Description:
FIELD 
     The described embodiments relate generally to electronic devices, and more particularly, to an interface system that produces force and/or motion-based outputs on a stylus using external magnetic influence. 
     BACKGROUND 
     Styluses can be used to provide inputs to electronic devices with touch-sensitive input devices, such as touchscreens, drawing tablets, and the like. For example, styluses may be used to draw images, input text, and manipulate user interface objects. Styluses may improve the accuracy and/or precision of touch inputs. As such, they may enable or facilitate more or different types of inputs than are feasible with a finger, keyboard, or mouse. Styluses are primarily input devices and do not provide output or feedback to a user. 
     SUMMARY 
     Some example embodiments are directed to interface systems in which a stylus is subjected to an external magnetic influence to produce various types of motion and/or forces. An interface system may include an electronic device defining an input surface, a stylus comprising a magnetic component and configured to provide input to the electronic device via the input surface, and a magnetic field generator associated with the electronic device and configured to produce a magnetic field to impart a force on the magnetic component of the stylus. 
     The electronic device may include a housing and a display within the housing, and the input surface may be a surface of the display. The magnetic field generator may include a conductive coil within the housing and circuitry configured to energize the conductive coil to produce the magnetic field. The conductive coil may be coupled to a substrate that is positioned under the input surface. The electronic device may include a magnetic shunt positioned under the substrate. The magnetic field may extend from within the housing, through the display, and through the input surface, and the magnetic component may be configured to interact with the magnetic field. 
     The magnetic field generator may include a group of conductive coils coupled to the substrate. The group of conductive coils may be positioned in an overlapping arrangement on the substrate. 
     The interface system may include a dock configured to receive the electronic device and the magnetic field generator may be within the dock. 
     A system for magnetically influencing an input device may include a computing device comprising an enclosure and a touchscreen within the housing and configured to detect a location of an input device on an exterior surface of the touchscreen. The electronic device may also include an electromagnetic coil within the housing and configured to produce a magnetic field above the exterior surface of the touchscreen in response to detecting the location of the input device on the exterior surface, thereby producing a tactile output via the input device. The computing device may include control circuitry configured to control the electromagnetic coil in order to produce an alternating magnetic field. 
     The input device may include a body and a magnetic element within the body. The electromagnetic coil may be configured to produce the magnetic field around the magnetic element of the input device. The magnetic element may be a permanent magnet or an electromagnetic coil. 
     The electromagnetic coil may be a first electromagnetic coil, the magnetic field may be a first magnetic field, and the magnetic element may be a second electromagnetic coil. The input device may include a power source and circuitry configured to power the second electromagnetic coil to produce a second magnetic field. 
     The input device may include a spring movably supporting the magnetic element to the body. The movably supported magnetic element may have a resonant frequency between about 150 Hz and about 250 Hz. 
     A method may include detecting, at an electronic device with a touch sensor and a magnetic field generator, a touch input from an input device having a magnetic component, and in response to detecting the touch input, producing a magnetic field with the magnetic field source, thereby imparting a force on the magnetic component of the input device. 
     Detecting the touch input may include detecting the input device at a first location on an input surface of the electronic device, and the method may further include detecting the input device at a second location on the input surface, the second location different from the first location, and in response to detecting the input device at the second location, ceasing to produce the magnetic field. The first location may be outside of an input path along the input surface, and the second location may be within the input path. 
     The method may include determining a predicted input path based on at least one of a location and a direction of the touch input, and the input path may correspond to the predicted input path. 
     The method may include determining a target location of the input device on an input surface of the electronic device, and producing the magnetic field may include producing the magnetic field such that the force imparted on the magnetic component is in a direction of the target location. The magnetic field source may include a plurality of coils, and producing the magnetic field may include determining a combination of coils that will produce the magnetic field such that the force imparted on the magnetic component is in the direction of the target location, and actuating the determined combination of coils. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIGS. 1A-1B  depict an electronic device and stylus of an interface system. 
         FIGS. 2A-2B  depict partial views of the interface system of  FIGS. 1A-1B . 
         FIG. 3A  depicts an example electronic device with conductive coils. 
         FIG. 3B  depicts a partial cross-sectional view of the electronic device of  FIG. 3A , viewed along line A-A in  FIG. 3A . 
         FIG. 3C  depicts another example electronic device with conductive coils. 
         FIG. 4A  depicts another example electronic device with conductive coils. 
         FIG. 4B  depicts a partial cross-sectional view of the electronic device of  FIG. 4A , viewed along line B-B in  FIG. 4A . 
         FIG. 5  depicts an example electronic device with conductive traces. 
         FIGS. 6A-6B  depict an example interface system with conductive coils in a dock accessory. 
         FIG. 6C  depicts a partial cross-sectional view of the interface system of  FIGS. 6A-6B , viewed along line C-C in  FIG. 6B . 
         FIG. 7A  depicts another example interface system with conductive coils in a dock accessory. 
         FIG. 7B  depicts a partial cross-sectional view of the interface system of  FIG. 7A , viewed along line D-D in  FIG. 7A . 
         FIGS. 8A-8B  depict another example interface system with conductive coils in a dock accessory. 
         FIG. 8C  depicts a partial cross-sectional view of the interface system of  FIGS. 8A-8B , viewed along line E-E in  FIG. 8B . 
         FIGS. 9A-9B  depict partial cutaway views of example styluses. 
         FIGS. 10A-10C  depict additional example styluses. 
         FIG. 11  depicts an example stylus with a driven rolling-ball mechanism. 
         FIG. 12  depicts an example stylus with a variable friction rolling-ball mechanism. 
         FIGS. 13A-13D  depict an interface system in example use scenarios. 
         FIG. 14  depicts example components of an electronic device. 
         FIG. 15  depicts example components of a stylus. 
         FIG. 16  depicts an example process for producing motion or force outputs in an interface system. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following description is 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. 
     The embodiments herein are generally directed to an interface system in which force and/or motion outputs are provided to a user through an input device, such as a stylus. Styluses may be used to provide inputs to devices with touch-sensitive input surfaces, such as drawing tablets, tablet computers with touchscreens, and the like. However, being primarily input devices, many styluses do not provide any force or haptic outputs to the user. Accordingly, systems are described herein in which a stylus can produce force and/or motion-based outputs, such as forces (e.g., directional forces), vibrations, oscillations, or the like. Such outputs may provide users with useful feedback or information relating to the input being provided by the stylus, or related to any other aspect of the device or the stylus. For example, force and/or motion-based outputs may indicate when a stylus is deviating from an intended or predicted path (e.g., while drawing or writing), or they may be used to help differentiate or delimit different regions of an input surface (e.g., to indicate the location or boundary of an icon or other affordance). These and other uses may also improve device accessibility for visually or hearing impaired users. 
     An interface system, as described herein, may include an input device, such as a stylus, and an electronic device with a touch-sensitive input surface, such as a touchscreen. The input device may include a magnetic component or element, such as a ferromagnetic material, a permanent magnet, or an electromagnetic coil. The electronic device may include or be associated with magnetic field sources or generators, such as electromagnetic coils, that produce magnetic fields. The magnetic fields interact with the magnetic component in the input device (e.g., the stylus) to produce forces and/or motions (e.g., directional forces, vibrations, or the like) on the input device. For example, an electronic device, such as a tablet computer, may include coils within its housing or enclosure. The coils may be energized to produce a magnetic field above the input surface of the electronic device. When the input device is within the magnetic field, such as when the input device is being used to provide input to the electronic device, the magnetic component in the input device may be subjected to forces due to the interaction with the magnetic field. Such forces may produce vibrations, oscillations, linear or directional forces, or other haptic effects that may be felt and/or heard by the holder of the input device. Various combinations of magnetic field sources or generators and magnetic components or magnetic elements can be used in an input device and an electronic device to produce force and/or motion-based outputs. For example, an electronic device may include electromagnetic coils and the input device may include a permanent magnet. Alternatively, the electronic device may include permanent magnets while the input device may include an electromagnetic coil. Other combinations are also possible, as described herein. 
     Depending on the particular configuration of the electronic device and the input device (e.g., stylus), various different types of forces may be produced. For example, the interface system (which may include the electronic device and input device, among other possible components) may be configured to oscillate or vibrate the input device. As another example, the interface system may be configured to repel or attract the input device in a direction normal to the input surface. As yet another example, the interface system may be configured to apply a directional force that is substantially parallel to the input surface (or has a component that is parallel to the input surface). 
     These or other types of outputs and forces may be used alone or in various combinations to provide feedback to a user. Such feedback may be used to indicate a preferred path for the input device. For example, an electronic device may be used to train a user how to write letters. A traceable letter outline may be displayed on the electronic device for a user to trace with the input device. The electronic device may determine, using a touch-sensitive input device, whether the user is accurately tracing the letter. When the user deviates from the displayed letter, the electronic device may cause the input device to vibrate to indicate that the user has deviated. Alternatively or additionally, the electronic device may cause the input device to be forced in a direction that will lead the user back to the displayed letter. The input device may be also or instead be magnetically attracted to the electronic device to increase the amount of force required to slide the input device across the input surface until the input device returns to the displayed letter. Such functions, as well as systems and components for producing such forces, are described herein. 
       FIG. 1A  depicts an interface system  100  including an electronic device  102  (e.g., a computing device) and a stylus  104  (e.g., an input device). The electronic device  102  may include an enclosure (e.g., the housing  103 ), a display  109  within and/or coupled to the enclosure, and a cover  108  above the display  109 . The cover  108  may define an input surface, which may be an exterior surface of the device  102 , on which touch inputs are provided to the device  102  (e.g., from a finger or the stylus  104  or any other suitable object). 
     The display  109  may be adhered to, laminated with, or positioned to contact a bottom surface of the cover  108 . The display  109  may include a stack of multiple elements that facilitate the rendering of images including, for example, a transparent circuit layer, a color filter layer, a polarizer layer, and other elements or layers. The display  109  may be implemented with any suitable display technology including, but not limited to, liquid-crystal display (LCD) technology, light-emitting diode (LED) technology, organic light-emitting diode (OLED) technology, electroluminescent technology, and the like. The display  109  may also include other layers for improving its structural or optical performance, including, for example, glass sheets, polymer sheets, polarizer sheets, color masks, rigid or resilient frames, and the like. 
     In some cases, the electronic device  102  may not include a display. For example, the electronic device  102  is shown in the figures as a tablet computing device as an example only; other electronic and/or computing devices (with or without displays positioned below the cover  108 ) are envisioned. For example, the electronic device  102  of the interface system  100  can be implemented as a peripheral input device, a trackpad, a drawing tablet, or the like. 
     The electronic device  102  may also include a touch-sensitive input device positioned below, or integrated with, the cover  108  and/or the display  109  of the electronic device  102 . The electronic device  102  utilizes the touch-sensitive input device (or touch sensor) to, among other purposes, detect the presence and/or location of the stylus  104  on the exterior input surface. 
     The stylus  104  may take various forms to facilitate use and manipulation by the user  106 . In the illustrated example, the stylus  104  has the general form of a writing instrument such as a pen or a pencil. In the illustrated embodiment, the stylus  104  includes a cylindrical body or barrel with two ends; however, other shapes and configurations are also possible. The user  106  may slide the tapered tip of the stylus  104  across the cover  108  to input information to the electronic device  102 . The electronic device  102  can interpret the user&#39;s manipulation of the stylus  104  in any implementation-specific and suitable manner. The stylus  104  is an input device, and may also facilitate or produce force and/or motion-based outputs, as described herein. 
       FIG. 1B  shows the interface system  100  in an active state, with the input device (e.g., the stylus  104 ), and in particular a magnetic component  112  of the stylus  104 , being subjected to a magnetic field  110 . The magnetic component  112  may be any suitable material or component that responds to or interacts with a magnetic field. For example, the magnetic component  112  may be a permanent magnet (e.g., neodymium iron boron, samarium cobalt, alnico, ceramic, or ferrite magnets), an electromagnetic coil (e.g., a conductive coil with a power source such as a battery, capacitor, etc.), an electromagnet, or a magnetic material such as steel, iron, or the like. 
     As shown in  FIG. 1B , the magnetic field  110  is emanating from the electronic device  102 , though this is merely one example of a source of a magnetic field. In other examples, the magnetic field  110  may emanate from or be generated by a different component, such as an accessory, dock, or case associated with the electronic device  102 . 
     The presence of the magnetic component  112  or any other suitable magnetic element in the magnetic field  110  results in a force being imparted on the magnetic component  112  due to electromagnetic interaction between the magnetic component  112  and the magnetic field  110 . In particular, when a magnetic component (e.g., a permanent magnet, electromagnetic coil, electromagnet, magnetic material, or other magnetic element) is in or near a magnetic field, a resulting physical force is experienced by the magnetic component. The physical force may have any of various directions depending on factors such as the polarity of the magnetic component, the direction of the magnetic field, the orientation of the magnetic component, and the like. 
     As shown, the magnetic field  110  is an alternating magnetic field, which results in alternating forces being imparted on the magnetic component  112 , thus vibrating or oscillating the stylus  104 . An alternating magnetic field may be produced by energizing a coil with an alternating current. In other cases, the magnetic field  110  may be a pulsed magnetic field. For example, a coil may be cyclically or repeatedly energized and de-energized with direct current (e.g., a square wave or other periodic, non-sinusoidal signal). This may produce a pulsed force acting in a single direction, which may also be perceived as a vibration or oscillation. In yet other cases, the magnetic field  110  may be a constant magnetic field or otherwise configured to produce a non-oscillating force on the magnetic component  112 , such as a force acting in a particular direction to help force or guide the stylus  104  in a particular direction. Such forces may be produced by energizing a coil with a continuous direct current signal. Haptic feedback like that shown in  FIG. 1B  may be produced in response to various inputs, operational states of the device  102 , notifications, or the like, as described herein. 
       FIG. 2A  shows a side view of the interface system  100 , showing the stylus  104  and a portion of the electronic device  102 . As noted above, the stylus  104  may include a magnetic element, such as a magnetic component  112 . The magnetic component  112  may be positioned anywhere along a body (e.g., the barrel  206 ) of the stylus  104 . For example, the magnetic component  112  may be located at or near a point or tip  210  of the stylus  104 , or at or near a top  208  of the stylus  104 . The location of the magnetic component  112  in the stylus  104  may be selected or optimized based on one or more properties of the magnetic field to which the stylus  104  is subjected. For example, the strength of a magnetic field decreases with the cube of the distance from the magnetic field source. Accordingly, where a magnetic field generator or source (e.g., a coil) is located within the electronic device  102 , as described herein, the magnetic field is stronger near the cover  108  of the electronic device  102 . Accordingly, positioning the magnetic component  112  nearer to the tip  210  of the stylus  104  may result in greater forces than if the magnetic component  112  were positioned nearer the top  208  of the stylus  104 , because the magnetic component  112  will be subjected to a stronger magnetic field. 
     However, positioning the magnetic component  112  nearer the top  208  of the stylus  104  may produce a greater torque on the stylus  104  when it is being held by a user. More particularly, the increased distance between a user&#39;s hand (which may generally grip the stylus  104  near the point or tip  210 ) and the magnetic component  112  may result in a more noticeable or perceptible tactile output for a given force. Accordingly, in some cases, the magnetic component  112  is positioned nearer the tip  210  of the stylus  104  in order to take advantage of the increased strength of the magnetic field near the cover  108 , while in other cases the magnetic component  112  is positioned nearer the top  208  of the stylus  104  to take advantage of the increased amplitude of the tactile output. 
     Other positions and configurations of the magnetic component  112  or other magnetic element are also possible. For example, the magnetic component  112  may be substantially aligned with a center of mass of the stylus  104 , or it may be offset from the center of mass. As another example, the magnetic component  112  may be substantially aligned with an expected or predicted grip location of the stylus  104 , or it may be offset from the predicted grip location. As yet another example, all or a portion of the barrel  206  may be a magnet or a magnetic material (e.g., steel). In such cases, the magnetic component  112  may be integral with the barrel  206  or otherwise form a portion of the barrel  206 . 
     The magnetic element (e.g., the magnetic component  112 ) may be coupled to the stylus  104  in any suitable way. For example, the magnetic component  112  may be rigidly coupled to the barrel  206  of the stylus  104 . In such cases, electromagnetic forces acting on the magnetic component  112  due to the application of a magnetic field (e.g., the field  200 ) may be transferred directly to the barrel  206 . As another example, the magnetic component  112  may be coupled to the barrel  206  of the stylus  104  via a compliant coupling, such as with springs, elastomeric materials, or other compliant members or materials. This configuration allows the magnetic component  112  to move relative to the barrel  206  while still imparting forces to the barrel  206  through the compliant coupling. In some cases, a compliant coupling for the magnetic component  112  acts as a resonant actuator that amplifies the haptic output experienced by a user for a given magnetic field. Examples of compliant couplings are described herein with respect to  FIGS. 9A-9B . 
       FIG. 2A  shows the interface system  100  in a configuration in which the stylus  104  is subjected to a magnetic field  200  that produces forces that are substantially parallel to the cover  108  of the electronic device  102  (or at least forces having a component that is parallel to the cover  108 ). For example, the magnetic field  200  may be substantially parallel to the cover  108 , at least in the proximity of the stylus  104  and/or the magnetic component  112 . Further, the magnetic component  112  may be configured and/or oriented such that a parallel magnetic field imparts a force that is substantially parallel to the cover  108 , such as forces  202 ,  204 . For example, the magnetic component  112  may be oriented within the body of the stylus  104  so that the polar alignment of the magnetic component  112  results in the parallel forces shown in  FIG. 1B . As described herein, the magnetic field  200  may be produced by the electronic device  102 , or by a magnetic field generator or other magnetic field source that is separate from the electronic device  102 . 
     Forces that are parallel to a cover (or forces that have a parallel component), such as forces  202 ,  204 , may be used to produce vibrating haptic outputs or directional forces. For example, where the magnetic field  200  is an oscillating or alternating magnetic field, the direction of the forces on the magnetic component  112  may alternate to produce a vibration. On the other hand, where the magnetic field  200  is a constant (or non-oscillating) field, the resulting force applied to the magnetic component  112  may tend to push or move the magnetic component  112  in a particular direction. Where directional forces are produced, the stylus  104  and/or the electronic device  102  may use positional feedback to determine parameters of the magnetic field being generated and how or whether to change the magnetic field. For example, as the stylus  104  moves relative to the cover  108 , the properties of the magnetic field may need to be changed to maintain the directional force in the same direction. Similarly, if the directional force is intended to guide the stylus  104  along a non-linear path, the magnetic field (e.g., the direction, amplitude, etc.) may need to be changed as the stylus  104  moves along the cover  108 . 
     Positional feedback may be provided by any suitable device, component, or technique. For example, the stylus  104  may include position and/or orientation sensors, accelerometers, gyroscopes, inertial position sensors, optical sensors, or the like. The stylus  104  may determine absolute or relative positional information and communicate that information to a device with a magnetic field source (e.g., the device  102  or any other suitable computing device). Additionally or alternatively, an electronic or computing device may include positional sensors, such as a touch and/or force sensor. As one example, where the electronic device  102  has a touch sensitive input surface, such as a touchscreen, the touch sensor may determine the position of the stylus  104  and use that positional information (optionally along with other information such as a target location or position) to determine the parameters of the magnetic field and/or how to vary the magnetic field to produce the desired forces. 
       FIG. 2B  shows a side view of the interface system  100  where the stylus  104  (or any other suitable input device) is subjected to a magnetic field  212  that produces forces that are substantially normal to the cover  108  (or otherwise have a component normal to the cover  108  that tends to attract the stylus  104  to or repel it from the cover  108 ). In contrast to the magnetic field  200 , the magnetic field  212  is substantially perpendicular to the cover  108 , and the magnetic component  112  is oriented so that when subjected to the magnetic field  212 , a force tending to attract the magnetic component  112  to or repel it from the cover  108  is produced, such as forces  214 ,  216 . Such forces may be used to change the perceived friction or texture of the cover  108 . For example, by applying an attractive force (e.g., force  216 ), the force required to slide the stylus  104  across the cover  108  may be increased, while applying a repulsive force (e.g., force  214 ) may reduce the required force. Similarly, producing an oscillating force (e.g., cycling between an attractive force and a repulsive force or even no force) may reduce the force required to slide the stylus  104 . This may result in a perception of a lower friction surface as compared to sliding the stylus  104  with the oscillating force. Such effects may be used in similar ways as other force-based or haptic outputs, such as to differentiate between input regions or icons, indicate when the stylus has deviated from a predicted or target path, to simulate different surface textures, or the like. 
     The magnetic fields  200 ,  212  and the magnetic component  112  in  FIGS. 2A-2B  may produce oscillating or continuous forces. For example, if the magnetic fields are alternating or oscillating, the resulting force on the magnetic component  112  may be an oscillating or vibrating force, resulting in a vibratory haptic output to the stylus  104 . Where the magnetic fields are constant (or otherwise do not change in a cyclic, oscillating manner), the resulting force may be in a particular direction only, producing a force that may move or guide the stylus  104 . As noted above, such haptic outputs may be used to provide information to a user, such as to indicate when a user has deviated from a suggested or predicted path, or to indicate the boundaries of input regions or icons or the like. 
     The magnetic component  112  or other magnetic element and the magnetic field source(s) associated with the interface system  100  may be configured to produce forces along only one plane or axis. For example, magnetic field generators may be configured to generate only magnetic fields that are substantially perpendicular to the cover  108 , and the magnetic component  112  may be a permanent magnet with a polarity that produces forces on the stylus  104  that are substantially perpendicular to the cover  108  when subjected to the magnetic field. In this configuration, the interface system  100  may substantially only produce forces in one plane (though the force may be oscillating or constant, as described above). 
     On the other hand, the interface system  100  may be configured to produce forces along multiple planes or directions. For example, the magnetic field generators associated with the interface system  100  may be configured to produce magnetic fields with different orientations relative to the stylus  104 . In this way, forces having different directions (e.g., parallel to the cover  108 , perpendicular to the cover  108 , or other suitable directions) may be produced. Alternatively or additionally, the magnetic component  112  may be manipulated or configured in real-time to produce forces in different directions. For example, the magnetic component  112  may be one or more electromagnets or coils that can be selectively activated to produce different forces (in magnitude or direction) for a given magnetic field, or it may be a movable permanent magnet, coil, or electromagnet that can be moved to produce different forces. As another example, the magnetic component  112  may be one or more programmable magnets such that the polarity of the programmable magnet(s) can be changed by subjecting the magnetic component  112  to a particular current or a magnetic field. Other magnetic components or elements are also possible. Where the magnetic component  112  includes an electromagnetic coil, such as when the magnetic component  112  is an electromagnet, the magnetic component  112  may produce secondary magnetic fields that interact with the magnetic fields produced by the magnetic field generators associated with the electronic device  102  to produce forces on the stylus  104 . 
       FIGS. 3A-8C  show various example configurations of magnetic field generators that may be used in an interface system that produces forces on an input device (e.g., a stylus) via external magnetic influence, such as the interface system  100 . While some examples are shown incorporated directly into an electronic or computing device such as a tablet computer, and others are shown incorporated into accessories or external components, it will be understood that configurations other than those shown are also possible. For example, a magnetic field generator that shown incorporated directly into an electronic device may instead or additionally be incorporated into an accessory or other external component or peripheral. 
       FIG. 3A  shows an electronic device  302 , which may be an embodiment of the electronic device  102  of  FIG. 1A . The electronic device  302  includes conductive coils  300  within a housing  303  (e.g., similar to the housing  103 ,  FIG. 1A ) and under the input surface defined by the cover  308  (e.g., similar to the cover  108 ,  FIG. 1A ). As shown, there are nine coils  300 , though more or fewer coils may be used. Moreover, the coils  300  are shown arranged in a regular pattern or grid arrangement in which the coils are separated from each other (e.g., they do not overlap). Other arrangements are also contemplated. For example, in some cases, all or some of the coils may overlap other coils.  FIG. 3C  shows an example in which the coils  300  are arranged in an overlapping configuration. By eliminating the gap between adjacent coils, the overlapping configuration shown in  FIG. 3C  may reduce or eliminate areas of no or weak magnetic fields, thus facilitating more uniform force and/or motion-based output from the stylus  104  over the input surface. To illustrate an example overlapping coil configuration, a first coil  300 - 1  is shown in a first dashed line, and a second coil  300 - 2  is shown in a second dashed line. The other coils  300  shown in  FIG. 3C  may overlap in a similar manner. Other overlapping configurations are also contemplated. For example, in some cases, coils only overlap in one direction (e.g., from left-to-right or from top-to-bottom). 
       FIG. 3B  is a cross-sectional view of an example configuration of the device  302 . The device  302  includes the cover  308 , which may be formed from or include any suitable material, such as glass, plastic, polycarbonate, sapphire, or the like. As noted above, the cover  308  may define an exterior surface (e.g., an input surface) of the device  302 . 
     Below the cover  308  is a touch sensor  310 . The touch sensor  310  may use any suitable type of touch-sensing technology or techniques, such as capacitive touch sensing, resistive touch sensing, optical touch sensing, or the like. While the touch sensor  310  is shown as a single layer, the touch sensor  310  may include multiple layers, such as one or more electrode layers (e.g., sense and/or drive layers) to sense touch inputs applied to the cover  308 . The touch sensor  310  may be integrated with, or applied on, the cover  308 . For example, a first electrode layer of the touch sensor  310  may be applied to a bottom surface of the cover  308 , and a second electrode layer of the touch sensor  310  may be applied to a bottom surface of the first electrode layer. Where the cover  308  is a laminate structure, electrode layers of the touch sensor  310  may be interleaved with layers of the cover  308 . 
     Touch inputs that are sensed by the touch sensor  310  may include taps, clicks, swipes, gestures, or other inputs provided by fingers, a stylus (e.g., the stylus  104 ), or other objects, implements, or input devices. In some cases, such as where the electronic device  302  includes a display, the touch sensor  310  is substantially transparent or otherwise optically transmissive. In some cases, the touch sensor  310  is or includes a force sensor or force sensing capabilities to determine an amount of force of a touch input. 
     The electronic device  302  may also include a display  311 . The display  311  may use any suitable display technology, as described above, and may include various layers or components. For example, the display  311  may include polarizing sheets, light guide sheets, thin-film transistor layers, OLED layers, LCD layers, or the like. These sheets are not shown separately in  FIG. 3B , but are represented by the display  311 . Together, the display  311  and the touch sensor  310  may form a touchscreen display, with the cover  308  defining an input surface of the touchscreen display (which may be an exterior surface of the electronic device  302 ). 
     The electronic device  302  also includes a substrate  312  on which the coils  300  may be positioned. The substrate  312  may be any suitable substrate, such as a circuit board, flexible circuit material, Mylar, or the like. The conductive coils  300  may be coupled to or otherwise incorporated with the substrate  312  in any suitable way. For example, the coils  300  may be wires (e.g., copper, silver, gold, or other metal wires) that are adhered to or encapsulated in the substrate  312 . As another example, the coils  300  may be traces of conductive material that are deposited on or otherwise incorporated with the substrate  312 . For example, the coils  300  may be indium tin oxide (ITO), metal nanowire, or another conductive material that is formed onto the substrate  312 . The coils  300  may have any suitable dimensions, conductor sizes and shapes, and number of turns to produce a desired magnetic field. 
     As shown in  FIG. 3C , the coils  300  are positioned below display  311 . Accordingly, the coils  300  and the substrate  312  do not need to be transparent, as light and images do not need to pass through the coils  300  and substrate  312 . In such configurations, the coils  300  may be formed from opaque materials, such solid metal (e.g., copper, aluminum) wires. Moreover, where the coils  300  are below the display  311 , the thinness of the coils  300  may be less critical, as the height of the coils  300  will not affect the distance between the display  311  and the cover  308 . Thus, larger (e.g., thicker) coils  300  having more wire turns may be used when the coils  300  are positioned below the display. Such configurations may result in or enable stronger magnetic fields than may be possible with coils formed of transparent conductors disposed above the display  311 . 
     In other examples, the coils  300  and the substrate  312  may be formed from transparent or optically transmissive materials, and may be positioned above the display  311 . This configuration positions the coils closer to the cover  308 , which may result in stronger magnetic fields above the cover  308 . Moreover, where the display  311  is between the coils  300  and the cover  308 , the display may shield, weaken, or change the shape of magnetic fields produced by the coils  300 . Accordingly, positioning the coils above the display  311  (so that the display  311  is not between the coils  300  and the cover  308 ) may reduce or eliminate negative effects of the display  311  on the magnetic fields produced by the coils  300 . 
     The electronic device  302  may also include a magnetic shunt  314  positioned under the coils  300 . The magnetic shunt  314  may guide or direct part of a magnetic field  318  produced by the coils  300  through the shunt  314 . This may help prevent leakage of the magnetic field  318  through a back of the device  302  (e.g., a back surface of the housing  303  or another enclosure), and may also increase the strength of the magnetic field  318  above the cover  308  (as compared to an embodiment without the shunt  314 ). The magnetic shunt  314  may be formed from or include any suitable material, such as a ferritic or magnetic metal (e.g., steel, iron, etc.). (The magnetic field  318  shown in  FIG. 3B  is merely for illustration, and is not necessarily indicative or representative of an actual magnetic field produced by the coils  300 .) 
     Layer  316  may correspond to a back housing of the device  302  (e.g., a back member of the housing  303  or another enclosure). In some cases, the layer  316 , may be formed from or include a ferritic material. In such cases, the layer  316  (e.g., a portion of the housing  303  that defines an exterior surface of the housing  303 ) may act as a magnetic shunt, and the separate magnetic shunt  314  may be omitted. In some cases, no magnetic shunt is included. 
     Other components may also be present in the electronic device  302  shown in  FIG. 3B . For example, processors, batteries, housing components, support structures, force sensors, and the like all may be included in the device  302 . Such components may be incorporated into any suitable position in the stack shown in  FIG. 3B . Moreover, some of the components shown in  FIG. 3B  may be omitted from an electronic device that is used in an interface system as described herein. For example, where the interface system is part of a trackpad or drawing tablet, the display  311  may be omitted. 
       FIG. 4A  shows an electronic device  402 , which may be an embodiment of the electronic device  102  of  FIG. 1A . The electronic device  402  includes conductive coils  400  within a housing  403  (e.g., similar to the housing  103 ,  FIG. 1A ) and under the input surface defined by the cover  408  (e.g., similar to the cover  108 ,  FIG. 1A ). More or fewer coils  400  than those shown may be used. Moreover, the coils  400  are shown arranged in a regular pattern or grid arrangement, though other arrangements are also contemplated. For example, in some cases, all or some of the coils may overlap other coils (similar to the arrangement shown in  FIG. 3C ). By reducing the size of each coil  400  and including more coils (as compared to the configuration shown in  FIG. 3A ), greater control may be exerted over the forces imparted to the magnetic component  112  in the stylus  104 . For example, by selectively activating multiple coils  400 , different magnetic field configurations may be produced. Moreover, forces that tend to move or guide the stylus (e.g., forces parallel to the cover  108 , such as those in  FIG. 2A ) may be more accurately produced than with larger or more sparsely placed coils. 
       FIG. 4B  is a cross-sectional view of an example configuration of the device  402 . The device  402  may include a cover  408 , a touch sensor  410 , a display  411 , a substrate  412  on which the coils  400  may be positioned, a magnetic shunt  414  positioned under the coils  400 , and a layer  416  corresponding to a back of the housing  403 . These components may have the same structure, function, materials, etc., as the corresponding components described above with respect to  FIG. 3B .  FIG. 4B  also shows example magnetic fields  418  that may be produced by the coils  400 . 
     In some cases, instead of conductive coils  400  (e.g., conductive traces or wires in a coil configuration), the device  402  may include selectively magnetizable materials or components (e.g., programmable magnets). For example, the device  402  may include materials that can be selectively magnetized and/or demagnetized in real-time, as well as circuitry and components to perform the selective magnetization and/or demagnetization. Accordingly, the device  402  can change the magnetic fields above the cover  408  by changing the polarity, direction/orientation, or strength of the magnetizable materials (including possibly completely removing the magnetic field of any particular magnetizable element). 
       FIG. 5  shows an electronic device  502 , which may be an embodiment of the electronic device  102  of  FIG. 1A . The electronic device  502  may include a housing  503  (e.g., similar to the housing  103 ,  FIG. 1A ) and a cover  508  (e.g., similar to the cover  108 ,  FIG. 1A ) defining an input surface. 
     Instead of discrete conducive coils under the cover  508 , as shown in  FIGS. 3A-4B , the device  502  includes conductive traces  500  arranged in a grid pattern (though other patterns are also contemplated). Each conductive trace  500  (and/or the junctions between overlapping conductive traces  500 ) may be individually coupled to switching circuitry so that portions of the traces  500  may be selectively operated as coils. For example, as shown in  FIG. 5 , certain traces  500  may be selectively joined and powered to operate a particular cell  504  as a coil. For example, a current  510  may be passed through the conductive traces  500  that define the cell  504  to produce a magnetic field. When the cell  504  is being operated as a coil, it may act substantially the same as or similar to the conductive coils  300 ,  400  described above (e.g., it may produce magnetic fields the same or similar to those shown above). In addition, while the cell  504  is made up of the smallest grid square formed by the conductive traces  500 , larger cells, such as the cell  506 , may also be activated to produce a magnetic field. Thus, a current  512  may be passed through the conductive traces  500  that define the cell  506  to produce a magnetic field. Cells of different shapes may also be produced, such as the square cell  504  or the rectangular cell  506 . Moreover, multiple cells may be active simultaneously, thus allowing the production of a wide range of overlapping and interacting magnetic fields. 
     The conductive traces  500  may include any suitable material and may be formed in any suitable way. For example, the conductive traces  500  may be layers of ITO, metal nanowire, or other conductive materials patterned or otherwise formed on a substrate (e.g., a flexible circuit substrate material, a cover such as the cover  108 , or any other suitable substrate). Where the conductive traces  500  are formed of ITO, nanowire, or another light transmissive conductor, the conductive traces  500  may be patterned on a light transmissive substrate and may be positioned above a display (e.g., above the displays  311 ,  411  in  FIGS. 3B, 4B ). This may place the coils closer to the cover of the electronic device, which may result in stronger magnetic fields above the cover. Moreover, placing the coils above a display may reduce or eliminate 
     As another example, where conductive traces  500  are not light transmissive or transparent, such as when they are continuous metal traces, they may be positioned below a display (as described with respect to  FIGS. 3B and 4B ). Further, if the conductive traces  500  are positioned below a display, they may be larger than and/or may include more material than if they are above a display. For example, the traces  500  may be thicker, may have more material, or there may be more traces than would be practical if the traces  500  were above a display. 
       FIGS. 6A-6C  show an electronic device  602 , which may be an embodiment of the electronic device  102  of  FIG. 1A , along with an accessory case or dock  610  that may be part of an interface system that produces forces, motions, and/or haptic outputs, as described herein.  FIG. 6A  shows the electronic device  602  separate from the dock  610 , and  FIG. 6B  shows the electronic device  602  coupled to (e.g., docked with) the dock  610 . 
     The electronic device includes a housing  603  and a display  609 , which may be the same or similar to the housing  103  and display  109  of  FIG. 1A . The dock  610  may define a recess  614  that may receive the electronic device  602  therein. The electronic device  602  and the dock  610  may communicate with each other via any suitable wired or wireless communication technique, including physical connectors, Bluetooth, Wi-Fi, or the like. 
     The dock  610  may include a magnetic field source in the form of a coil  612 . The coil  612  may be positioned in a frame  613  of the dock  610  that surrounds or frames the electronic device  602 . The coil  612  may be used to generate magnetic fields above or near the display  609  in order to produce force outputs via an input device (e.g., a stylus). The dock  610  may also include other components, such as power sources (e.g., batteries, capacitors, external power adapters), processors, communication circuitry, and the like, for powering the coil  612  and communicating with the electronic device  602 . For example, the electronic device  602  may determine when a force or haptic output is to be provided, as well as parameters of the force or haptic output (e.g., whether the output should be a vibration or a directional force, the duration of the output, the location of the input device, etc.), and provide that information to the dock  610 . In response to receiving the information, the dock  610  may energize the coil  612  to produce a magnetic field that will produce the requested output. 
       FIG. 6C  is a cross-sectional view of the electronic device  602  and the dock  610 , viewed along line C-C in  FIG. 6B . The electronic device  602  is represented as a single component, though it will be understood that the electronic device  602  may include numerous components that are omitted from  FIG. 6C  for clarity. Such components may include, for example, processors, batteries, displays, touch sensors, force sensors, memory, and the like. 
     As shown in  FIG. 6C , the coil  612  may be incorporated into the frame  613  of the dock  610 . The coil  612  may have more or fewer turns than shown in  FIG. 6C . Moreover, while the coil  612  is depicted as a number of wire turns, the coil may be other materials or have other configurations, such as conductive traces applied to a substrate. 
     The coil  612  may be encapsulated in the material of the frame  613 , or it may be incorporated in any other manner. The frame  613  and the coil  612  may extend at least partially beyond (e.g., above) the input surface of the electronic device  602 , as illustrated in  FIG. 6C . This may help position a magnetic field  616  produced by the coil  612  in a more advantageous position relative to an input device (e.g., a stylus). More particularly, by placing the coil  612  further towards and/or above the input surface, the center of the coil  612 , where the magnetic field may be the strongest or the most concentrated, may be nearer the magnetic component  112  of the stylus  104 . In other cases, the frame  613  is substantially flush with or recessed with respect to the input surface of the electronic device  602 . (In some cases, the coil  612  may be incorporated into the electronic device  602  directly, rather than a separate dock  610 .) 
       FIGS. 7A-7B  show another example electronic device  702  and dock  710 .  FIG. 7A  shows the electronic device  702  coupled to (e.g., docked in) the dock  710 , and  FIG. 7B  is a cross-sectional view of the device  702  and dock  710  viewed along line D-D in  FIG. 7A . The electronic device  702  may be an embodiment of the electronic device  102  in  FIG. 1A . 
     The dock  710  may be similar to the dock  610  in  FIGS. 6A-6C , but with a different coil configuration. In particular, instead of a continuous coil that surrounds or frames the electronic device  702 , the dock  710  includes a plurality of coils  712  arranged around and/or defining a frame  713  of the dock  710 . The coils  712  may be helical coils, as shown, or they may have any other suitable shape or configuration, such as flat coils. 
     As shown in  FIG. 7B , the coils  712  may be oriented so that the longitudinal axes of the coils  712  are substantially parallel with an input surface of the electronic device  702 . This may produce magnetic fields having a different orientation relative to the input surface than the coil  612  in  FIGS. 6A-6C . For example, while the magnetic field  616  produced by the coil  612  may be substantially perpendicular to the input surface (at least in a central portion of the display of the device  602 ), the magnetic fields  716  produced by the coils  712  may be substantially parallel to the input surface of the device  702 . In some cases, the coils  712  may be oriented so that the longitudinal axes are not parallel with the input surface of the device  702 . Moreover, the coils  712  in a particular dock  710  need not have a uniform orientation. For example, some coils  712  may be parallel to the input surface while others may be perpendicular to the input surface, while others may be oriented at other angles. By combining differently oriented coils, different forces, motions, or haptic outputs may be produced by the dock  710 . For example, some coils may be used to produce vibratory outputs, while others may be used to produce directional forces. 
     In some cases, a dock may include both an array of coils, as shown in  FIGS. 7A-7B , as well as an encircling coil, as shown in  FIGS. 6A-6C . This arrangement may also enable a dock to produce various different force and/or motion-based outputs. For example, an encircling coil (e.g., the coil  612 ) may be used to produce vibratory outputs, while the coils of a coil array (e.g., the coils  712 ) may be used to produce directional forces. 
     Returning to  FIGS. 7A-7B , the coils  712  may provide power savings relative to a larger single coil such as the coil  612 . For example, the coils  712  may provide smaller, more localized magnetic fields. If the location of the stylus is known, for example by a touch sensor of the device, the dock  710  can energize only the coil (or coils) that are closest to the stylus at that time. Accordingly, a force output may be produced using less power than a single large coil. 
       FIGS. 8A-8C  show another example electronic device  802  and dock  810 .  FIG. 8A  shows the electronic device  802  separate from the dock  810 , and  FIG. 8B  shows the electronic device  802  coupled to (e.g., docked in) the dock  810 .  FIG. 8C  is a cross-sectional view of the device  802  and dock  810  viewed along line E-E in  FIG. 8B . The electronic device  802  may be an embodiment of the electronic device  102  in  FIG. 1A . 
     The dock  810  may include an array of coils  812  embedded in or otherwise incorporated in a back wall  814  of the dock  810 . The coils  812  may be similar to the coils  400  in  FIGS. 4A-4B . For example, the coils  812  may be electromagnetic coils that are individually controllable to produce magnetic fields above or proximate an input surface of the device  802  when the device  802  is docked. 
     The coils  812  may be oriented in any suitable way to produce desired magnetic fields. For example, the coils  812  may be oriented so that the magnetic field lines are substantially perpendicular to the input surface, as illustrated in  FIG. 8C  by the coil  812 - 1  and the associated magnetic field  816 . As another example, the coils  812  may be oriented so that the magnetic fields are substantially parallel to the input surface, as illustrated in  FIG. 8C  by the coil  812 - 2  and the associated magnetic field  818 . As noted above, the coils  812  may all be oriented in the same direction, or they may have different directions (e.g., some may be parallel and some may be perpendicular). Other coil orientations (e.g., oblique angles) and combinations of differently oriented coils are also contemplated. 
     The dock  810  may include a magnetic shunt (e.g., a steel or ferritic layer) below the coils  812 . The magnetic shunt may have the same effect as the shunt  314  discussed above. Also, where a dock positions magnetic field sources (e.g., coils  812 ) below the electronic device  802 , the device  802  may be substantially transparent to magnetic fields, such that the magnetic fields extend through the device  802  to reach a stylus being used on an input surface of the device  802 . 
       FIGS. 9A-9B  show example input devices that include spring-mounted magnetic components or elements. The spring-mounted magnetic components may enhance the effect of electromagnetic forces that are imparted to the magnetic component by acting as externally driven resonant actuators. More particularly, when a spring-mounted magnetic component is subjected to a magnetic field, the magnetic component may move relative to the barrel of the input device. The springs and the magnetic component may be tuned to have a resonant or harmonic frequency that amplifies the motion of the magnetic component when subjected to a magnetic field. The magnetic components shown in  FIGS. 9A-9B  may be used to produce oscillating or vibratory outputs as well as other force and/or motion-based outputs such as directional forces, attractive or repulsive forces, or the like. 
       FIG. 9A  shows a partial cut-away view of a stylus  900 . The stylus  900  includes a barrel  902  and a magnetic component  904  within the barrel  902 . As shown in  FIG. 9A , a portion of the barrel  902  is cut away to show the magnetic component  904 . The magnetic component  904  may be a permanent magnet, a magnetic material (e.g., steel), an electromagnetic coil, or an electromagnet. The magnetic component  904  may be coupled to the stylus  900  via one or more springs  906  that movably support the magnetic component  904  relative to the barrel  902 . The springs  906  may be any suitable type of spring or material that acts as a spring, such as coil springs, leaf springs, flat springs, elastomeric materials, or the like. The particular arrangement of springs  906  shown in  FIG. 9A  is merely one example configuration. In some cases, more or fewer springs may be used, and they may be coupled to the stylus  900  and/or the magnetic component  904  differently. 
     The magnetic component  904  is coupled to the stylus  900  via the springs  906  such that a primary direction of motion of the magnetic component  904  is aligned with (e.g., parallel to or coaxial with) a longitudinal axis of the stylus  900 . In some cases, the magnetic component  904  may be constrained in other directions so that it only moves substantially parallel to the longitudinal axis of the stylus  900 . In other cases, it is allowed to move parallel to the longitudinal axis as well as oblique or perpendicular to the longitudinal axis. 
       FIG. 9B  shows a partial cut-away view of a stylus  910 . The stylus  910  includes a barrel  912  and a magnetic component  914  within the barrel  912 . As shown in  FIG. 9B , a portion of the barrel  912  is cut away to show the magnetic component  914 . The magnetic component  914  may be a permanent magnet, a magnetic material (e.g., steel), a conductive coil, or an electromagnet. The magnetic component  914  may be coupled to the stylus  910  via one or more springs  916  that movably support the magnetic component  914  relative to the barrel  912 . The springs  916  may be any suitable type of spring or material (e.g., coil springs, leaf springs, flat springs, elastomeric materials, or the like). In contrast to the stylus  900 , the magnetic component  914  in the stylus  910  has a primary direction of motion that is perpendicular to the longitudinal axis of the stylus  910 . This may produce a different physical response than the configuration in  FIG. 9A . For example, motion that is perpendicular to the longitudinal axis of a barrel ( FIG. 9B ) may produce more noticeable vibratory output to the hand of a user, while motion that is parallel to the longitudinal axis ( FIG. 9A ) may be more effective at simulating different surface textures on a cover of an electronic device. 
     Either of configurations shown in  FIGS. 9A-9B  may be tuned to have a resonant frequency within a particular frequency range. For example, certain vibration or oscillation frequencies may be particularly noticeable to a human hand. Accordingly, the parameters of the springs  906 ,  916  (e.g., spring rate, size, length, etc.) and the magnetic components  904 ,  914  (e.g., weight, size, shape, spring mounting locations, etc.) may be selected so that the magnetic components have a resonant frequency within the desired range. In some cases, the resonant frequency is between about 150 Hz and about 250 Hz. Other resonant frequencies are also contemplated. 
     In some cases, a stylus may include multiple spring-mounted magnetic components or elements, or a mixture of spring-mounted and rigidly mounted magnetic components or elements. As one example, a stylus may have two spring-mounted magnetic components, each having a different primary direction of motion. The magnetic components may be tuned to the same or different resonant frequencies. Also, the magnetic components may be configured to respond to different magnetic fields. For example, one of the magnetic components may be configured to produce an oscillating motion in response to the application of a first type of magnetic field, and the other magnetic component may be configured to produce a directional force in response to the application of a second type of magnetic field (or in response to the first type of magnetic field). 
       FIG. 10A  shows an example stylus  1000  with two rigidly mounted magnetic components  1004 ,  1006 . In particular, the stylus  1000  includes a body (e.g., a barrel  1002 ), and a first magnetic component  1004  and a second magnetic component  1006  mounted to or within the barrel  1002 . The first and second magnetic components  1004 ,  1006  may be permanent magnets, magnetic materials, conductive coils, electromagnets, or the like. 
     The first and second magnetic components  1004 ,  1006  may be mounted to opposite sides of the barrel  1002 . As shown, the polarities of the first and second magnetic components  1004 ,  1006  are aligned (e.g., with North magnetic poles directed towards a top of the stylus  1000 ). However, the polarities of one or both of the magnetic components may be reversed, as shown in  FIG. 10B , where the South magnetic pole of the second magnetic component  1006  is directed towards the top of the stylus  1000 . 
     Including two (or more) separate magnetic components in a stylus may produce different or improved force or haptic responses. For example, having two magnetic components may be used to amplify or to cancel torques when the stylus is subjected to certain magnetic fields (e.g., torques tending to twist the barrel along its axis or torques tending to turn the barrel perpendicular to its axis). The particular polar alignment, number of magnetic components, and placement and/or orientation of the magnetic components may be selected to produce or optimize desired physical responses. 
       FIG. 10C  shows another example stylus  1010  with multiple magnetic components  1014 ,  1016 , and  1018  within or otherwise incorporated with a barrel  1012 . The magnetic components  1014 ,  1016 ,  1018  may be permanent magnets or magnetic materials, or they may be coils that can be selectively activated to act as magnets (or any other suitable magnetic component). Including multiple permanent magnets or magnetic materials along the barrel  1012  as shown may improve the physical response of the stylus  1010 , for example, by increasing the amount of force acting upon the stylus  1010 , thus increasing the magnitude or the detectability of the physical output for a given magnetic field. 
     Where the magnetic components  1014 ,  1016 ,  1018  are coils or other selectively activated magnetic components, different types of physical outputs may be produced by activating various combinations of the magnetic components (or individual magnetic components). For example, due to the different positions relative to a magnetic field, each of the magnetic components  1014 ,  1016 ,  1018  may produce a different magnitude of force when activated. Also, the magnetic components  1014 ,  1016 ,  1018  may have configurations so that selecting one magnetic component (e.g.,  1014 ) produces a force in a first direction (e.g., parallel to the cover) while selecting another magnetic component (e.g.,  1016 ) produces a force in a second direction (e.g., perpendicular to the cover). The magnetic components  1014 ,  1016 ,  1018  may also be used to convey different information to a user. For example, a force output (e.g., a vibration) from one magnetic component (e.g.,  1014 ) may convey that the user should move the stylus  1010  faster, while a force output (e.g., a vibration) from a different magnetic component (e.g.,  1018 ) may convey that the user should move the stylus  1010  slower. 
     The foregoing figures and description describe electronic devices and styluses that produce physical outputs via the stylus. Physical outputs may include, for example, directional forces, motions, oscillations, vibrations, or other physical or haptic outputs. As noted, such physical outputs may be used to help guide a user&#39;s hand when providing inputs to an electronic device with the stylus. For example, the stylus may vibrate to indicate when the stylus has deviated from a predicted path, or a directional force may be applied to force the user&#39;s hand towards a target location. These effects are produced via magnetic and/or electromagnetic interaction between the stylus and a magnetic field. Similar effects and functions may also be achieved with rolling-point styluses that have directional, frictional, or other types of physical control over a rolling tip. 
     For example,  FIG. 11  shows a rolling-point stylus  1100  that includes a barrel  1102  and a rolling ball  1104  retained to the barrel  1102 . The rolling ball  1104  may be capable of rotating in substantially any direction, similar to the ball of a ballpoint pen. The stylus  1100  also includes actuators  1106  that are configured to drive the rolling ball  1104 . The actuators  1106  may be any suitable actuator, such as rotational motors with friction wheels, piezoelectric actuators or motors, or the like. 
     The actuators  1106  may be controllable by the stylus  1100  and/or an associated electronic device to impart directional forces on the stylus  1100  when the rolling ball  1104  is in contact with an input surface of the electronic device. For example, the actuators may impart forces on the ball  1104  that tend to move the stylus  1100  in a desired direction, such as towards a target location or along a target input path. In some cases, the actuators  1106  may have sufficient power to move the stylus  1100  when the stylus is being held in a user&#39;s hand. In other cases, the actuators  1106  may not be able to overcome the force and/or inertia of a user&#39;s hand, but may nevertheless produce noticeable forces that can help guide the stylus  1100  in a particular direction. 
     The stylus  1100  may include onboard power sources (e.g., batteries, capacitors), processors, memory, communications circuitry, position and/or orientation sensors, accelerometers, and the like, to facilitate control and operation of the actuators  1106 . The stylus  1100  may communicate with an electronic device (e.g., the electronic device  102 ,  FIG. 1A ) to receive information and commands relating to operation of the actuators  1106 . For example, the electronic device may convey information such as a current location and a target location, and the stylus  1100  may process such information to determine how to operate the actuators  1106  to produce a force towards the target location. 
     The rolling-point stylus  1100  may be used in addition to or instead of the magnetic and systems described herein. In some cases, for example, an interface system may include a driven rolling-ball mechanism to produce directional forces, and a magnetic field source and a stylus-mounted magnetic element to produce vibrating outputs. 
       FIG. 12  shows an example of a rolling-point stylus  1200  that uses a fluid to vary the rolling resistance of the ball. In particular, the stylus  1200  includes a barrel  1202  and a rolling ball  1204  retained to the barrel  1202 . The rolling ball  1204  may be capable of rotating in substantially any direction, similar to a ballpoint pen. The stylus  1200  also includes a controllable fluid  1206  (e.g., a magnetorheological fluid) or other actuator that can selectively control the rolling resistance of the ball  1204  by changing a property of the fluid  1206 . The stylus  1200  may control the properties of the fluid  1206  in any suitable way, such as by applying or removing an electrical current or a magnetic field to the fluid  1206 . The fluid  1206  may directly contact the ball  1204 , or it may be used to force a friction pad or other member against the ball  1204 . Also, in some cases, an actuator may not use fluid, but instead may impart a force to vary the rolling resistance using other techniques. For example, the stylus may use an electrical (e.g., a solenoid) actuator. 
     By varying the rolling resistance of the ball  1204 , the stylus  1200  may provide physical and/or tactile information to a user. For example, the rolling resistance of the ball  1204  may be increased when a user moves the stylus  1200  off a suggested path or away from a target location, which may help guide the user back to the suggested path or towards the target location. In some cases, the rolling resistance increases in proportion to the distance away from a suggested path or target location. For example, small deviations may result in only small increases in resistance, while larger deviations result in large increases in resistance. This may help provide directional feedback to a user, as they will be able to determine by feel whether they are moving the stylus in a target direction. 
     The stylus  1200  may include onboard power sources (e.g., batteries), processors, memory, communications circuitry, position and/or orientation sensors, magnetic field sources, accelerometers, and the like, to facilitate control and operation of the controllable fluid  1206  (or other actuator). The stylus  1200  may communicate with an electronic device (e.g., the electronic device  102 ,  FIG. 1A ) to receive information and commands relating to operation of the controllable fluid  1206 . For example, the electronic device may convey information such as a current location and a target location, and the stylus  1200  may process such information to determine whether and how much to increase (or decrease) the rolling resistance of the ball  1204 . As noted, instead of a controllable fluid, similar outputs may be achieved by a friction pad and an actuator that can vary the force of the friction pad against the ball  1204 . 
       FIGS. 13A-13D  illustrate several example uses cases of an interface system in accordance with the present description, in which force and/or motion-based outputs (e.g., directional forces, haptic outputs) are used to provide various user experiences.  FIG. 13A  shows an interface system  1300  that includes an electronic device  1302  and a stylus  1304 . The electronic device  1302  and the stylus  1304  may include any of the components described herein for producing force-based outputs, such as magnetic field sources (e.g., conductive coils, power sources, magnets, or other magnetic field generators), magnetic components (e.g., permanent magnets, electromagnets, electromagnetic coils, resonant actuators, and the like), touch and/or force sensors, rolling-point mechanisms, or the like. 
     The electronic device  1302  is depicted as a tablet computer with a display  1309  that defines a touch-sensitive input surface. In some cases, the electronic device  1302  may be a drawing tablet or other input device without a screen incorporated with the touch-sensitive input surface. In such cases, the electronic device  1302  may be communicatively coupled to a display, such as when a drawing tablet is being used as a peripheral input device to a notebook, tablet, or desktop computer. 
       FIG. 13A  shows an example of a haptic output being produced during a writing training exercise. For example, the electronic device  1302  is displaying an outline of a letter  1306  that is intended for the user to trace. This may be part of an educational application for individuals learning to write or learning a new language or alphabet. 
     As the user traces the outline or path of the letter  1306 , the electronic device  1302  detects the location of the stylus  1304  on the input surface. As long as the stylus  1304  is within a certain threshold distance of the path corresponding to the outline of the letter  1306 , the stylus  1304  may not produce any haptic outputs. If the electronic device  1302  determines that the stylus  1304  has deviated from the outline of the letter  1306  (e.g., path  1308 ), the stylus  1304  may produce a haptic output, such as a vibration (as shown). When a deviation is detected, the stylus  1304  may also or instead produce force-based outputs such as directional forces (as shown in  FIG. 13B ), increased frictional forces (e.g., by electromagnetically attracting the stylus  1304  to the electronic device  1302  or using a driven or variable-resistance rolling-ball mechanism. 
     Instead of producing a tactile output in response to detecting a deviation from the input path of the letter, the stylus  1304  may produce a tactile output while it is within range of the input path, and may cease to produce the output when it deviates. For example, the stylus  1304  may vibrate while the pen is sufficiently close to the outline of the letter  1306 , and then cease vibrating when a deviation of sufficient magnitude is detected (e.g., path  1308 ). 
     Also, a property of the tactile output may change as the deviation from the input path (e.g., the outline of the letter  1306 ) increases. For example, a magnitude or frequency of a vibration may increase with increased deviation from the path. As another example, the magnitude of a frictional or directional force may increase with increased deviation from the path. In the case where tactile outputs (e.g., vibrations or directional forces) are present only while the stylus  1304  is on or near the input path, the magnitude or frequency of the output may be decreased with increased deviation from the path. 
       FIG. 13B  shows another example tactile output in response to detecting a deviation from a predicted or intended path, such as an outline of a letter  1312 . Whereas  FIG. 13A  showed a vibration or oscillating output,  FIG. 13B  shows a directional force  1314  acting on the stylus  1304 . In particular, as the electronic device  1302  detects a sufficient or threshold deviation between the letter  1312  and the location of the stylus  1304 , a magnetic field generator associated with the electronic device  1302  may produce a magnetic field that results in the directional force  1314  on the stylus  1304 . Alternatively or additionally, a driven or variable-resistance rolling-ball mechanism may produce the directional force. Feedback devices, such as a touch sensor of the electronic device  1302 , or accelerometers, optical sensors, gyroscopes, and the like, in the stylus  1304  may be used to provide positional feedback to control the magnetic fields and/or the rolling-ball mechanisms to produce the desired directional forces. 
     The directional force  1314  may act in a direction that tends to bring the stylus  1304  nearer to the displayed letter  1312 . This may guide a user towards or onto the letter  1312 , such as along a path  1316 . To help guide the user and to provide dynamic and useful feedback, the force  1314  may increase with increased deviation from the displayed letter  1312 . 
     Instead of or in addition to the directional force  1314  in response to deviations from a predicted or intended path, the interface system  1300  may produce directional forces that lead the stylus  1304  along the path (e.g., along the letter  1312 ). This may provide continuous force-assisted feedback that guides the user along an intended path instead of merely providing feedback when the user deviates from the path. 
       FIGS. 13A-13B  show tactile outputs (e.g., directional forces, vibrations) being provided in conjunction with drawing or tracing letters. The same or similar process may be implemented with other characters, images, shapes, alphabets, gestures, and the like. 
       FIG. 13C  shows another example use case for the interface system  1300 . In particular,  FIG. 13C  shows a tactile output being provided to assist or suggest a graphical user interface manipulation. For example,  FIG. 13C  shows an object  1320  (which may be an application icon, a cursor, an image, or any other user interface or display object) and a target location  1321  (shown as a trash or recycle bin, which is merely an example of a target location). The stylus  1304  may be used to select the object  1320  and drag the object along a path  1322  to the target location  1321 . 
     In order to guide the user to the target location  1321 , the interface system  1300  may produce a directional force  1328  on the stylus  1304  that acts in the direction of the target location  1321  and/or along the path  1322 . Should the stylus  1304  deviate from the path  1322  (such as by entering regions  1324 ,  1326 ), the directional force  1328  may change in magnitude and/or direction to continue to guide the user towards the target location  1321  or back to the path  1322 . The directional force  1328  may be produced by electromagnetic components or by driven or variable-resistance rolling-ball mechanisms. 
     In addition to or instead of the directional force  1328 , the interface system  1300  may produce other tactile or physical outputs when deviations from the path  1322  are detected. For example, if the electronic device  1302  or the stylus  1304  detects that the stylus is in region  1324  or  1326  of the display  1309 , the stylus  1304  may vibrate (or a rolling resistance may be increased) to indicate that the user has deviated from the path  1322 . 
       FIG. 13D  shows another example use case for the interface system  1300 . In particular,  FIG. 13D  combines predictive input determination with stylus-based physical outputs to help guide a stylus along a predicted path.  FIG. 13D  shows three example predictive inputs in display regions  1330 ,  1336 , and  1342 . It will be understood that these regions are not necessarily displayed at the same time, but rather are differentiated to illustrate several example uses cases of a predictive input feature. 
       FIG. 13D , and in particular region  1330 , shows tactile outputs being used in conjunction with predictive text input. In particular, the electronic device  1302  and/or the stylus  1304  may determine a predicted input letter or word (e.g., word  1334 ) based on one or more previously entered letters or words (e.g., word  1332 ). Any suitable text or word prediction technique may be used to predict input words, such as natural language processing algorithms. 
     Once the predicted input word  1334  is determined, tactile or physically detectable outputs are used to help guide the stylus  1304  along the path of the predicted word  1334 . The tactile outputs may include directional forces (e.g., forces that tend to move the stylus  1304  along a path corresponding to the predicted letters), vibrations (e.g., indicating that the user is on or has deviated from the path), or the like. Such outputs may be produced in any suitable way, such as those described herein. Also, the predicted path may be displayed on the display  1309 , or it may not be displayed. 
     The region  1336  shows another example predictive input, where the electronic device  1302  and/or the stylus  1304  predicts that the user is intending to draw a circle. This prediction may be based on detecting a portion of the shape  1338  that was input without external assistance (e.g., without physical influence on the stylus). Once it is determined that the user may be intending to input a circle, a tactile output is provided to guide the user along or towards the predicted path  1340  (or to indicate deviation from or adherence to the predicted path  1340 ). The region  1342  shows another example predictive input, but instead of a circle  1338 , the initial input  1344  is determined to be a beginning of a straight line. Accordingly, the predicted path  1346  continues the straight line in the direction of travel. 
       FIG. 14  depicts example components of an electronic device in accordance with the embodiments described herein. The schematic representation depicted in  FIG. 14  may correspond to components of the electronic devices depicted in the foregoing figures, such as the electronic devices  102 ,  302 ,  402 ,  502 ,  602 ,  702 ,  802 , or  1302 . 
     As shown in  FIG. 14 , a device  1400  includes a processing unit  1402  operatively connected to computer memory  1404  and/or computer-readable media  1406 . The processing unit  1402  may be operatively connected to the memory  1404  and computer-readable media  1406  components via an electronic bus or bridge. The processing unit  1402  may include one or more computer processors or microcontrollers that are configured to perform operations in response to computer-readable instructions. The processing unit  1402  may include the central processing unit (CPU) of the device. Additionally or alternatively, the processing unit  1402  may include other processors within the device including application specific integrated chips (ASIC) and other microcontroller devices. 
     The memory  1404  may include a variety of types of non-transitory computer-readable storage media, including, for example, read access memory (RAM), read-only memory (ROM), erasable programmable memory (e.g., EPROM and EEPROM), or flash memory. The memory  1404  is configured to store computer-readable instructions, sensor values, and other persistent software elements. Computer-readable media  1406  also includes a variety of types of non-transitory computer-readable storage media including, for example, a hard-drive storage device, a solid-state storage device, a portable magnetic storage device, or other similar device. The computer-readable media  1406  may also be configured to store computer-readable instructions, sensor values, and other persistent software elements. 
     In this example, the processing unit  1402  is operable to read computer-readable instructions stored on the memory  1404  and/or computer-readable media  1406 . The computer-readable instructions may adapt the processing unit  1402  to perform the operations or functions described above with respect to  FIGS. 1A-13B  or below with respect to the example process  1600  in  FIG. 16 . In particular, the processing unit  1402 , the memory  1404 , and/or the computer-readable media  1406  may be configured to cooperate with the touch sensor  1420 , magnetic field generators  1426 , and/or positional feedback devices  1430  to produce magnetic fields resulting in electromagnetic forces on a magnetic component of a stylus. The computer-readable instructions may be provided as a computer-program product, software application, or the like. 
     As shown in  FIG. 14 , the device  1400  also includes a display  1408 . The display  1408  may include a liquid-crystal display (LCD), organic light emitting diode (OLED) display, LED display, or the like. If the display  1408  is an LCD, the display  1408  may also include a backlight component that can be controlled to provide variable levels of display brightness. If the display  1408  is an OLED or LED type display, the brightness of the display  1408  may be controlled by modifying the electrical signals that are provided to display elements. The display  1408  may correspond to the any of the displays shown or described herein. 
     The device  1400  may also include a battery  1409  that is configured to provide electrical power to the components of the device  1400 . The battery  1409  may include one or more power storage cells that are linked together to provide an internal supply of electrical power. The battery  1409  may be operatively coupled to power management circuitry that is configured to provide appropriate voltage and power levels for individual components or groups of components within the device  1400 . The battery  1409 , via power management circuitry, may be configured to receive power from an external source, such as an AC power outlet. The battery  1409  may store received power so that the device  1400  may operate without connection to an external power source for an extended period of time, which may range from several hours to several days. 
     In some embodiments, the device  1400  includes one or more input devices  1410 . The input device  1410  is a device that is configured to receive user input. The input device  1410  may include, for example, a push button, a touch-activated button, a keyboard, a key pad, or the like. In some embodiments, the input device  1410  may provide a dedicated or primary function, including, for example, a power button, volume buttons, home buttons, scroll wheels, and camera buttons. Generally, a touch sensor (e.g., a touchscreen) or a force sensor may also be classified as an input device. However, for purposes of this illustrative example, the touch sensor  1420  and the force sensor  1422  are depicted as distinct components within the device  1400 . 
     The device  1400  may also include a touch sensor  1420  (e.g., the touch sensor  410 ,  FIG. 4B ) that is configured to determine a location of a touch over a touch-sensitive surface of the device  1400 . The touch sensor  1420  may include a capacitive array of electrodes or nodes that operate in accordance with a mutual-capacitance or self-capacitance scheme. As described herein, the touch sensor  1420  may be integrated with one or more layers of a display stack to provide the touch-sensing functionality of a touchscreen. 
     The device  1400  may also include a force sensor  1422  that is configured to receive and/or detect force inputs applied to a user input surface of the device  1400 . The force sensor  1422  may include or be coupled to capacitive sensing elements that facilitate the detection of changes in relative positions of the components of the force sensor (e.g., deflections caused by a force input). 
     The device  1400  may also include one or more sensors  1424  that may be used to detect an environmental condition, orientation, position, or some other aspect of the device  1400 . Example sensors  1424  that may be included in the device  1400  include, without limitation, one or more accelerometers, gyrometers, inclinometers, goniometers, or magnetometers. The sensors  1424  may also include one or more proximity sensors, such as a magnetic hall-effect sensor, inductive sensor, capacitive sensor, continuity sensor, and the like. 
     The sensors  1424  may also be broadly defined to include wireless positioning devices including, without limitation, global positioning system (GPS) circuitry, Wi-Fi circuitry, cellular communication circuitry, and the like. The device  1400  may also include one or more optical sensors including, without limitation, photodetectors, photosensors, image sensors, infrared sensors, and the like. 
     The device  1400  may also include a communication port  1428  that is configured to transmit and/or receive signals or electrical communication from an external or separate device. The communication port  1428  may be configured to couple to an external device via a cable, adaptor, or other type of electrical connector. In some embodiments, the communication port  1428  may be used to couple the device  1400  to an accessory, such as a dock or case (e.g., the dock  610 ,  710 ,  810  described above), a stylus or other input device, smart cover, smart stand, keyboard, or other device configured to send and/or receive electrical signals. 
       FIG. 15  depicts example components of a stylus in accordance with the embodiments described herein. The schematic representation depicted in  FIG. 15  may correspond to components of the styluses depicted in the foregoing figures, such as the stylus  104 ,  900 ,  910 ,  1000 ,  1100 ,  1200 , or  1304 . 
     As shown in  FIG. 15 , a stylus  1500  includes a processing unit  1502  operatively connected to computer memory  1504  and/or computer-readable media  1506 . The processing unit  1502  may be operatively connected to the memory  1504  and computer-readable media  1506  components via an electronic bus or bridge. The processing unit  1502  may include one or more computer processors or microcontrollers that are configured to perform operations in response to computer-readable instructions. The processing unit  1502  may include the central processing unit (CPU) of the device. Additionally or alternatively, the processing unit  1502  may include other processors within the device including application specific integrated chips (ASIC) and other microcontroller devices. 
     The memory  1504  may include a variety of types of non-transitory computer-readable storage media, including, for example, read access memory (RAM), read-only memory (ROM), erasable programmable memory (e.g., EPROM and EEPROM), or flash memory. The memory  1504  is configured to store computer-readable instructions, sensor values, and other persistent software elements. Computer-readable media  1506  also includes a variety of types of non-transitory computer-readable storage media including, for example, a hard-drive storage device, a solid-state storage device, a portable magnetic storage device, or other similar device. The computer-readable media  1506  may also be configured to store computer-readable instructions, sensor values, and other persistent software elements. 
     In this example, the processing unit  1502  is operable to read computer-readable instructions stored on the memory  1504  and/or computer-readable media  1506 . The computer-readable instructions may adapt the processing unit  1502  to perform the operations or functions described above with respect to  FIGS. 1A-13B  or below with respect to the example process  1600  in  FIG. 16 . In particular, the processing unit  1502 , the memory  1504 , and/or the computer-readable media  1506  may be configured to cooperate with magnetic component  1510 , positional feedback devices (e.g., sensors  1524 ), and/or actuators  1512  to produce tactile outputs via the stylus  1500 . The computer-readable instructions may be provided as a computer-program product, software application, or the like. 
     The stylus  1500  may also include a battery  1509  that is configured to provide electrical power to the components of the stylus  1500 . The battery  1509  may include one or more power storage cells that are linked together to provide an internal supply of electrical power. The battery  1509  may be operatively coupled to power management circuitry that is configured to provide appropriate voltage and power levels for individual components or groups of components within the stylus  1500 . The battery  1509 , via power management circuitry, may be configured to receive power from an external source, such as an AC power outlet. The battery  1509  may store received power so that the stylus  1500  may operate without connection to an external power source for an extended period of time, which may range from several hours to several days. 
     In some embodiments, the stylus  1500  includes one or more magnetic components  1510 . The magnetic components  1510  may be passive magnetic components (e.g., ferritic materials or permanent magnets) or active magnetic components (e.g., programmable magnets, electromagnets, conductive coils, or the like). The magnetic components  1510  may be controlled by the processing unit  1502 , the memory  1504 , and/or computer-readable media  1506  to produce desired tactile outputs. 
     The stylus  1500  may also include one or more sensors  1524  that may be used to detect an environmental condition, orientation, position, or some other aspect of the stylus  1500 . Example sensors  1524  that may be included in the stylus  1500  include, without limitation, one or more accelerometers, gyrometers, inclinometers, goniometers, optical sensors, inertial positioning sensors, or magnetometers. The sensors  1524  may also include one or more proximity sensors, such as a magnetic hall-effect sensor, inductive sensor, capacitive sensor, continuity sensor, and the like. 
     The sensors  1524  may also be broadly defined to include wireless positioning devices including, without limitation, global positioning system (GPS) circuitry, Wi-Fi circuitry, cellular communication circuitry, and the like. The stylus  1500  may also include one or more optical sensors including, without limitation, photodetectors, photosensors, image sensors, infrared sensors, and the like. 
     The stylus  1500  may also include a communication port  1528  that is configured to transmit and/or receive signals or electrical communication from an external or separate device. The communication port  1528  may be configured to couple to an external device via a cable, adaptor, or other type of electrical connector. In some embodiments, the communication port  1528  may be used to couple the stylus  1500  to an electronic device (e.g., the electronic device  1400  or any other electronic device described herein), an accessory such as a dock or case (e.g., the dock  610 ,  710 ,  810  described above), or any other device configured to send and/or receive electrical signals. 
     The stylus  1500  may also include one or more actuators  1512 . The actuators may include rotational motors with friction wheels, piezoelectric actuators, magnetorheological fluid actuators, or the like. The actuators  1512  may be controlled by the processing unit  1502 , the memory  1504 , and/or computer-readable media  1506  to produce desired tactile outputs, to impart a directional force on the stylus  1500 , increase a perceived surface friction when moving the stylus  1500  across an input surface, or produce any other suitable tactile or physical output. 
       FIG. 16  depicts an example process  1600  for producing tactile or physical outputs via a stylus in an interface system. The process  1600  may be used, for example, to guide a user of a stylus along a particular input path, provide tactile feedback to a user of a stylus about user interface objects, regions, or gestures, or any other suitable function. The process  1600  may be implemented using, for example, the processing unit and other hardware elements described with respect to  FIGS. 14-15  (or elsewhere in the instant application). The process  1600  may be implemented as processor-executable instructions that are stored within the memory of an electronic device and/or a stylus. 
     In operation  1602 , a touch input from a stylus having a magnetic component is detected. The touch input may be detected by a touch sensor of an electronic device (such as the touch sensor  1420 ), or by any other suitable device, module, or sensor of an electronic device, dock, stylus, or the like. 
     The touch input detected at operation  1602  may be a tap or press at a single location on an electronic device, or a gesture-type input where a stylus is slid, dragged, or otherwise moved across an input surface. In the latter case, detecting the touch input may include detecting a stylus at a first location on an input surface of an electronic device, and detecting the stylus at a second location on the input surface, where the second location is different from the first location. 
     In operation  1604 , in response to detecting the touch input, a magnetic field is produced with a magnetic field generator. The magnetic field imparts a force on the magnetic component of the stylus via the magnetic field, thereby producing a tactile output. The magnetic field may be an alternating magnetic field (which may produce a vibratory output), or a steady (though dynamic and/or changing) magnetic field that is configured to produce a directional force. In some cases, such as where the magnetic field is intended to produce a directional force, producing the magnetic field includes determining a combination of electromagnetic coils that will produce the magnetic field such that the force imparted on the magnetic component is in a particular direction (e.g., towards a target location), and actuating the determined combination of electromagnetic coils. 
     In some cases, the magnetic field is initiated when the stylus is detected at the first location (e.g., outside a target location or an input path), and is terminated or ceased when the stylus is detected at the second location (e.g., on or within a threshold distance of an input path or target location). For example, a vibration or directional force may be induced in the stylus when the stylus deviates from an input path corresponding to a displayed letter or character (or from a predicted input path), and may be ceased when the stylus returns to or is otherwise detected on the input path. Other example tactile and/or physical outputs and use cases are described herein. 
     The process may further comprise determining a predicted input path based on at least one of a location and a direction of the touch input.  FIGS. 13A-13C  show examples in which input paths are predicted for characters, words, shapes, and the like. Accordingly, a tactile or physically detectable output may be induced when the stylus deviates from the predicted input path, and may be ceased when the stylus returns to or is otherwise detected on the predicted input path (or within a threshold distance of the predicted input path). 
     In some cases, the process further comprises determining a target location of the stylus on an input surface of the electronic device. The target location may correspond to a single, static location on the input surface (e.g., a region of a user interface or an icon displayed on a display), or it may correspond to a next position along an input path. After determining the target location, the magnetic field may be produced such that the force imparted on the magnetic component of the stylus is in the direction of the target location. Instead of or in addition to producing a force toward the target location using magnetic fields, the force may be produced by a driven rolling-ball actuator, such as described above with respect to  FIG. 11 . 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not targeted to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings. Also, when used herein to refer to positions of components, the terms above and below, or their synonyms, do not necessarily refer to an absolute position relative to an external reference, but instead refer to the relative position of components with reference to the figures.

Metadata:
Filing Date: 20170228
Publication Date: 20191008
Grant Date: 20191008
Priority Date: 20170228
Inventors: WANG, PAUL X.
RUSCHER, JOEL N.
MAHALATI, REZA NASIRI
LEONG, Craig C.
CHRISTENSEN, DAVID L.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F1/1632", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1643", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1626", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/046", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/04162", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0383", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/038", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/041", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0383", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0488", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0383", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/041", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0488", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 68101781