PATENT DOCUMENT

Publication Number: US-11817755-B2
Application Number: US-202117336074-A
Country: US
Kind Code: B2

Title: Axisymmetric linear resonant actuators

Abstract:
A linear resonant actuator includes a ferritic tube, a movable mass, first and second flexures, and a set of one or more flexures. The ferritic tube has an axis extending from a first end of the ferritic tube to a second end of the ferritic tube. The movable mass has a set of magnet sections disposed along the axis. First and second flexures mechanically couple first and second ends of the movable mass to the ferritic tube. The flexures suspend the movable mass within the ferritic tube and allow movement of the movable mass along the axis. The electric coil(s) are attached to the ferritic tube and extend around the movable mass, between the ferritic tube and the movable mass. Each magnet section has magnetic poles disposed at different positions along the axis, and like magnetic poles of adjacent magnetic sections face each other.

Claims:
What is claimed is: 
     
       1. A linear resonant actuator, comprising:
 a ferritic tube having an axis extending from a first end of the ferritic tube to a second end of the ferritic tube; 
 a movable mass having a set of magnet sections disposed along the axis; 
 a first flexure mechanically coupling a first end of the movable mass to the ferritic tube; 
 a second flexure mechanically coupling a second end of the movable mass to the ferritic tube; 
 a set of one or more electric coils attached to the ferritic tube and extending around the movable mass, between the ferritic tube and the movable mass; wherein, 
 each magnet section in the set of magnet sections has magnetic poles disposed at different positions along the axis; 
 like magnetic poles of adjacent magnetic sections face each other; and 
 the first flexure and the second flexure suspend the movable mass within the ferritic tube and allow movement of the movable mass along the axis. 
 
     
     
       2. The linear resonant actuator of  claim 1 , wherein the movable mass is axisymmetric. 
     
     
       3. The linear resonant actuator of  claim 1 , further comprising:
 a set of one or more spacers; wherein, 
 each spacer is disposed between a pair of adjacent magnet sections. 
 
     
     
       4. The linear resonant actuator of  claim 3 , wherein:
 the movable mass further includes,
 a first disc; and 
 a second disc; 
 
 the set of magnet sections is disposed between the first disc and the second disc; and 
 each of the first disc and the second disc has a first diameter, perpendicular to the axis, greater than a second diameter of any magnet section in the set of magnet sections. 
 
     
     
       5. The linear resonant actuator of  claim 1 , further comprising:
 a core; wherein, 
 each magnet section surrounds the core. 
 
     
     
       6. The linear resonant actuator of  claim 5 , wherein the core is non-ferritic or mildly ferritic. 
     
     
       7. The linear resonant actuator of  claim 1 , further comprising:
 a first endcap attached to the first end of the ferritic tube; and 
 a second endcap attached to the second end of the ferritic tube; wherein, 
 the first endcap is non-ferritic or mildly ferritic; and 
 the second endcap is non-ferritic or mildly ferritic. 
 
     
     
       8. The linear resonant actuator of  claim 7 , wherein:
 the first flexure has a portion extending between the first endcap and the ferritic tube. 
 
     
     
       9. A linear resonant actuator, comprising:
 a frame; 
 an axisymmetric movable mass mounted to the frame and movable along an axis, the axisymmetric movable mass including,
 a core; and 
 a set of magnet sections, each magnet section disposed at a different position along the axis and encircling the core, and each magnet section having opposite magnetic poles disposed at different positions along the axis, with like magnetic poles of adjacent magnet sections facing each other; 
 
 a set of flexures attaching the axisymmetric movable mass to the frame and constraining movement of the axisymmetric movable mass to movement along the axis, the set of flexures suspending the movable mass within the frame; and 
 at least one electric coil encircling the axisymmetric movable mass and fixed to the frame. 
 
     
     
       10. The linear resonant actuator of  claim 9 , wherein the set of flexures comprises a flexure having a planar rest state perpendicular to the axis. 
     
     
       11. The linear resonant actuator of  claim 9 , wherein the set of flexures comprises a flexure having an expanded three-dimensional rest state perpendicular to the axis. 
     
     
       12. The linear resonant actuator of  claim 9 , wherein the set of flexures comprises a flexure having a set of arms, each arm in the set of arms having a trajectory that spirals around the axis. 
     
     
       13. The linear resonant actuator of  claim 12 , wherein:
 at least one arm in the set of arms has,
 a distal end; 
 a proximal end; and 
 a middle portion between the distal end and the proximal end; wherein, 
 
 the middle portion has a smaller width than a width of the distal end or the proximal end. 
 
     
     
       14. The linear resonant actuator of  claim 9 , wherein the set of magnet sections is part of a monolithic material. 
     
     
       15. A haptic actuator, comprising:
 an enclosure having,
 a cylindrical body portion; 
 a first end cap disposed at a first end of the cylindrical body portion; and 
 a second end cap disposed at a second end of the cylindrical body portion; 
 
 a movable mass housed within the enclosure and movable along an axis extending between the first end cap and the second end cap, the movable mass including a set of magnet sections disposed along the axis; 
 a first flexure having a first inward portion attached to a first end of the movable mass and a first outward portion attached to the enclosure between the cylindrical body portion and the first end cap; 
 a second flexure having a second inward portion attached to a second end of the movable mass and a second outward portion attached to the enclosure between the cylindrical body portion and the second end cap, the first and second flexures cooperate to suspend the movable mass with respect to the enclosure; and 
 a set of one or more electric coils wrapped around the axis of the movable mass, between the cylindrical body portion of the enclosure and the movable mass. 
 
     
     
       16. The haptic actuator of  claim 15 , wherein:
 the movable mass comprises at least one mass-increasing disc disposed along the axis; and 
 the at least one mass-increasing disc is one of non-ferritic or mildly ferritic. 
 
     
     
       17. The haptic actuator of  claim 15 , further comprising:
 a dielectric ring around which an electric coil in the set of one or more electric coils is wound; wherein, 
 the movable mass extends through the dielectric ring. 
 
     
     
       18. The haptic actuator of  claim 17 , further comprising:
 a ferrofluid disposed between the dielectric ring and the movable mass. 
 
     
     
       19. The haptic actuator of  claim 15 , further comprising:
 a dielectric cushion attached to the first end cap, between the first end cap and the movable mass. 
 
     
     
       20. The haptic actuator of  claim 15 , further comprising:
 a flexible circuit, electrically connected to an electric coil in the set of one or more electric coils, and conformed to a portion of an outer surface of the cylindrical body portion of the enclosure.

Description:
FIELD 
     The described embodiments generally relate to the construction of linear resonant actuators (LRAs) and, more particularly, to LRAs that can be used as haptic actuators in electronic devices. 
     BACKGROUND 
     Many of today&#39;s devices include a haptic actuator. Some of the devices that may include a haptic actuator, or even multiple haptic actuators, include mobile phones, computers (e.g., tablet computers or laptop computers), wearable devices (e.g., electronic watches or health or fitness tracking devices), hand-held or worn navigation devices, gaming devices (whether worn or held), augmented or virtual reality devices, styluses, and so on. 
     SUMMARY 
     Embodiments of the systems, devices, methods, and apparatus described in the present disclosure are directed to the construction, configuration, or operation of LRAs. 
     In a first aspect, an LRA is described. The LRA may include a ferritic tube having an axis extending from a first end of the ferritic tube to a second end of the ferritic tube. The LRA may also include a movable mass having a set of magnet sections disposed along the axis. A first flexure may mechanically couple a first end of the movable mass to the ferritic tube, and a second flexure may mechanically couple a second end of the movable mass to the ferritic tube. A set of one or more electric coils may be attached to the ferritic tube and extend around the movable mass, between the ferritic tube and the movable mass. Each magnet section in the set of magnet sections may have magnetic poles disposed at different positions along the axis. Like magnetic poles of adjacent magnetic sections may face each other. The first flexure and the second flexure may suspend the movable mass within the ferritic tube and allow movement of the movable mass along the axis. 
     In a second aspect, another LRA is described. The LRA may include a frame, and an axisymmetric movable mass mounted to the frame and movable along an axis. The axisymmetric movable mass may include a core and a set of magnet sections. Each magnet section may be disposed at a different position along the axis and encircle the core. Each magnet section may have opposite magnetic poles disposed at different positions along the axis, with like magnetic poles of adjacent magnet sections facing each other. A set of flexures may attach the axisymmetric movable mass to the frame and constrain movement of the asymmetric movable mass to movement along the axis. At least one electric coil may encircle the axisymmetric movable mass and be fixed to the frame. 
     In a third aspect, a haptic actuator is described. The haptic actuator may include an enclosure having a cylindrical body portion, a first end cap disposed at a first end of the cylindrical body portion, and a second end cap disposed at a second end of the cylindrical body portion. A movable mass may be housed within the enclosure and may be movable along an axis extending between the first end cap and the second end cap. The movable mass may include a set of magnet sections disposed along the axis. A first flexure may have a first inward portion attached to a first end of the movable mass and a first outward portion attached to the enclosure between the cylindrical body portion and the first end cap. A second flexure may have a second inward portion attached to a second end of the movable mass and a second outward portion attached to the enclosure between the cylindrical body portion and the second end cap. A set of one or more electric coils may wrap around the axis of the movable mass, between the housing and the movable mass. 
     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following description. 
    
    
     
       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: 
       The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures. 
         FIGS.  1 A and  1 B  show a first example of an LRA; 
         FIG.  2    shows a cross-section of a second example of an LRA; 
         FIG.  3    shows an alternative embodiment of the LRA described with reference to  FIG.  2   ; 
         FIG.  4    shows another alternative embodiment of the LRA described with reference to  FIG.  2   ; 
         FIG.  5    shows a cross-section of a third example of an LRA; 
         FIG.  6 A  shows an example of a flexure having a planar rest state; 
         FIG.  6 B  illustrates an example movement of the movable mass shown in  FIG.  5   , when flexures that attach the movable mass to a ferritic tube are configured as shown in  FIG.  6 A , and when a current having a first polarity is driven through an electric coil of the LRA; 
         FIG.  7    shows another example of a flexure having a planar rest state; 
         FIG.  8 A  shows a cross-section of a fourth example of an LRA; 
         FIG.  8 B  illustrates an example movement of the movable mass shown in  FIG.  8 A , when a current having a first polarity is driven through an electric coil of the LRA; 
         FIG.  9    shows an exterior isometric view of a frame, cylindrical body portion of an enclosure, or ferritic tube, as might be used to house any of the LRAs described with reference to  FIG.  1 A- 5  or  8 A- 8 B ; 
         FIG.  10    shows an exterior isometric view of another frame, cylindrical body portion of an enclosure, or ferritic tube, as might be used to house any of the LRAs described with reference to  FIG.  1 A- 5  or  8 A- 8 B ; 
         FIG.  11    shows an example of a stylus, electronic pencil, or the like; and 
         FIG.  12    shows an example block diagram of an electronic device. 
     
    
    
     Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto. 
     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. 
     When selecting or designing a haptic actuator for an electronic device, the physical and electrical aspects of the haptic actuator may depend on, and may need to be weighed against or traded off against, the physical and electrical aspects of other modules that are incorporated into the device. For example, the physical and electrical aspects of a haptic actuator may need to be traded off against the physical and electrical aspects of a battery. In some cases, this may lead to a desire (or even a need) for a haptic actuator that fits into a small space and is electrically efficient. Although various parameters of a haptic actuator can be adjusted to make the haptic actuator smaller, making a haptic actuator that is both small and electrically efficient while also preserving the magnitude of the actuator&#39;s haptic output is challenging. Additional constraints may be placed on haptic actuator design when a haptic actuator is placed into a relatively small device, such as a stylus, earbud, or wearable device (e.g., an electronic watch or health or fitness tracking device). 
     The LRAs disclosed herein each incorporate one or more features that enable them to be manufactured small, or to operate in an electrically efficient way, or to be scaled/configured/adapted to different space constraints and/or haptic output requirements, and so on. Some of the features incorporated into various ones of the LRA embodiments described herein include: an axisymmetric movable mass and/or other components; a movable mass having magnets (or magnet sections) polarized in a generally axial direction of travel; a non-ferritic or mildly ferritic core that avoids stealing (or steals less) magnetic flux and/or enhances the movable mass of an LRA; ferritic spacers between magnets (or magnet sections) that channel magnetic flux and enhance the movable mass; space-efficient flexures that suspend the movable mass in all degrees of freedom and provide centering forces (restorative forces) for linear resonant movement; a ferritic tube that channels magnetic flux to improve operating efficiency and contain stray magnetic flux; easy scalability by varying the diameters, lengths, and number of magnets (or magnet sections) and electric coils of an LRA. 
     Incorporating some or all of the above features into an LRA can make the LRA more efficient in terms of acceleration and so on. 
     For purposes of this description, a “mildly ferritic” material is defined to be a material having a relative magnetic permeability less than about 1.10, plus or minus 10% (e.g., 301 type stainless steel (SUS301), tungsten, and so on). 
     These and other systems, devices, methods, and apparatus are described with reference to  FIGS.  1 A- 12   . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
     Directional terminology, such as “top”, “bottom”, “upper”, “lower”, “front”, “back”, “over”, “under”, “above”, “below”, “left”, “right”, etc. is used with reference to the orientation of some of the components in some of the figures described below. Because components in various embodiments can be positioned in a number of different orientations, directional terminology is used for purposes of illustration and is not always limiting. Directional terminology is intended to be construed broadly, and therefore should not be interpreted to preclude components being oriented in different ways. Also, as used herein, the phrase “at least one of” preceding a series of items, with the term “and” or “or” to separate any of the items, modifies the list as a whole, rather than each member of the list. The phrase “at least one of” does not require selection of at least one of each item listed; rather, the phrase allows a meaning that includes at a minimum one of any of the items, and/or at a minimum one of any combination of the items, and/or at a minimum one of each of the items. By way of example, the phrases “at least one of A, B, and C” or “at least one of A, B, or C” each refer to only A, only B, or only C; any combination of A, B, and C; and/or one or more of each of A, B, and C. Similarly, it may be appreciated that an order of elements presented for a conjunctive or disjunctive list provided herein should not be construed as limiting the disclosure to only that order provided. 
       FIGS.  1 A and  1 B  show an example LRA  100 .  FIG.  1 A  shows an isometric view of the LRA  100 , and  FIG.  1 B  shows a cross-section of the LRA  100  along cutline IB-IB. The LRA  100  includes a movable mass  102  suspended from or within a frame  104 . In some embodiments, the movable mass  102  may be housed by or enclosed within the frame  104  (e.g., as shown). 
     In some embodiments, the frame  104  may have a tubular main body section  120  that is ferritic. The frame  104  may also include an optional first end cap  122  attached to a first end  124  of the main body section  120 , and an optional second end cap  126  attached to a second end  128  of the main body section  120 . The first and second end caps  122 ,  126  may be non-ferritic or mildly ferritic, to avoid attracting the movable mass  102 . By way of example, the main body section  120  may have a stepped profile near each of the first and second ends  124 ,  128 , such that a ring-shaped shelf ( 130  or  132 ) is defined at each of the first and second ends  124 ,  128  of the main body section  120 . Each of the first and second end caps  122 ,  126  may have an outer diameter that is the same as, or slightly smaller than, the larger inner diameter of the main body section  120 , such that the first end cap  122  may slide into the first end  124  of the main body section  120 , and the second end cap  126  may slide into the second end  128  of the main body section  120 . The ring-shaped shelves  130 ,  132  provide stops that prevent the first and second end caps  122 ,  126  from sliding farther into the main body section  120  than desired. In some cases, the first and second end caps  122 ,  126  may be held in place by welds, adhesive, clips, or friction (e.g., the first and second end caps  122 ,  126  may be press-fit into the first and second ends  124 ,  128  of the main body section  120 ), or other means. In various embodiments, the first and second end caps  122 ,  126  may be differently shaped, may be solid or have holes therein, or may attach to the main body section  120  in different ways. 
     The movable mass  102  may be attached to the frame  104 , and suspended from or within the frame  104 , by a set of flexures  106 ,  108  (e.g., non-ferritic or mildly ferritic flexures). A first flexure  106  may mechanically couple a first end  110  of the movable mass  102  to the frame  104 . A second flexure  108  may mechanically couple a second end  112  of the movable mass  102  to the frame  104 . Each flexure  106 ,  108  may be attached to the movable mass  102  by one or more of a weld, adhesive, clip, fastener (e.g., bolt and spacer  134  or  136 ), and so on. In embodiments in which the frame  104  includes the main body section  120  and first and second end caps  122 ,  126 , the first flexure  106  may have one or more portions (e.g., tabs or an entire outer perimeter) that extend between the main body section  120  and the first end cap  122  and seat against the ring-shaped shelf  130 . Similarly, the second flexure  108  may have one or more portions (e.g., tabs or an entire perimeter) that extend between the main body section  120  and the second end cap  126  and seat against the ring-shaped shelf  132 . 
     The set of flexures  106 ,  108  allow movement of the movable mass  102  along an axis  114  extending through the first and second ends  110 ,  112  of the movable mass  102 , and provide restorative forces that bias the movable mass  102  to a rest position. In some cases, the flexures  106 ,  108  may constrain movement of the movable mass  102  to movement along the axis  114  (though the movement along the axis  114  may be subject to deviation due to real world tolerances (e.g., manufacturing variation and so on)). 
     In some embodiments, the movable mass  102  may be axisymmetric about the axis  114 . The flexures  106 ,  108  may also be axisymmetric about the axis  114 , and may be coupled to the movable mass  102  in an axisymmetric manner (e.g., coupled to the movable mass  102  along the axis  114 , or to attachment points on the movable mass  102  that are symmetrically distributed about the axis  114 . In some cases, additional components of the LRA  100 , or all of the LRA  100 , may be configured or coupled in an axisymmetric manner. 
     The movable mass  102  may include a set of magnet sections  116 . The magnet sections  116  may take the form of individual magnets (e.g., magnet sections  116  having donut-shaped or round cross-sections perpendicular to the axis  114 ), or magnetized portions of a monolithic material (e.g., a cylindrical-shaped material). By way of example, the movable mass  102  has two magnet sections  116 . Each magnet section  116  may be disposed at a different position along the axis  114 . Each magnet section  116  may have a pair of opposite magnetic poles (e.g., a north (N) pole and a south (S) pole). The opposite magnetic poles of a magnet section  116  may be disposed at different positions along the axis  114 . Like magnetic poles of adjacent magnet sections  116  may face each other. 
     The LRA  100  may further include a set of one or more electric coils  118 . Each electric coil  118  may be fixed with respect to the frame  104  and/or attached to the frame  104 . Each electric coil  118  may extend around the movable mass  102 . Each electric coil  118  may be positioned between the frame and the movable mass  102 . 
     When a current is driven through the electric coil  118 , magnetic flux  138  may flow in a generally axial direction through the magnet sections  116 , and into or out of the electric coil  118 , and then be recycled through the tubular main body section  120  of the frame  104  before returning to the magnet sections  116 . The magnetic flux  138  may change direction responsive to a change in the direction of current flow through the electric coil  118 . The ferritic tubular main body section  120  helps shorten the magnetic flux path and improve magnetic flux recycling (e.g., compared to magnetic flux traveling through air). 
       FIG.  2    shows a cross-section of an example LRA  200 . The LRA  200  is an example of the LRA described with reference to  FIGS.  1 A and  1 B . The LRA  200  includes a movable mass  202  suspended from or within a ferritic tube  204 . The ferritic tube  204  is an example of the frame described with reference to  FIGS.  1 A and  1 B . In some embodiments, the movable mass  202  may be housed by or enclosed within the ferritic tube  204  (e.g., as shown). 
     In some embodiments, the ferritic tube  204  may have a first end  216  that receives an optional first end cap  230 , and a second end  218  that receives an optional second end cap  234 . The first and second end caps  230 ,  234  may be non-ferritic or mildly ferritic, to avoid attracting the movable mass  202 . By way of example, each of the first and second end caps  230 ,  234  may have a stepped profile around its perimeter, such that a ring-shaped shelf ( 236  or  238 ) is defined by each of the first and second end caps  230 ,  234 . An exterior wall  240 ,  242  of each end cap  230 ,  234 , which exterior wall  240 ,  242  intersects the end cap&#39;s ring-shaped shelf  236 ,  238 , may have a diameter that is the same as, or slightly smaller than, the inner diameter of the ferritic tube  204 , such that the first end cap  230  may slide into the first end  216  of the ferritic tube  204 , and the second end cap  234  may slide into the second end  218  of the ferritic tube  204 . The ring-shaped shelves  236 ,  238  provide stops that prevent the first and second end caps  230 ,  234  from sliding farther into the ferritic tube  204  than desired. In some cases, the first and second end caps  230 ,  234  may be held in place by welds, adhesive, clips, or friction (e.g., the first and second end caps  230 ,  234  may be press-fit into the first and second ends  216 ,  218  of the ferritic tube  204 ), or other means. In various embodiments, the first and second end caps  230 ,  234  may be differently shaped, may be solid or have holes therein, or may attach to the ferritic tube  204  in different ways. 
     The movable mass  202  may be attached to the ferritic tube  204 , and suspended from or within the ferritic tube  204 , by a set of flexures  206 ,  208  (e.g., non-ferritic or mildly ferritic flexures). A first flexure  206  may mechanically couple a first end  210  of the movable mass  202  to the ferritic tube  204 . A second flexure  208  may mechanically couple a second end  212  of the movable mass  202  to the ferritic tube  204 . Each flexure  206 ,  208  may be attached to the movable mass  202  by one or more of a weld, adhesive, clip, fastener (e.g., bolt  228  or  232 ), and so on. The first flexure  206  may have one or more portions (e.g., tabs or an entire outer perimeter) that are welded or otherwise bonded to the first end cap  230 . Similarly, the second flexure  208  may have one or more portions (e.g., tabs or an entire perimeter) that are welded or otherwise bonded to the second end cap  234 . By way of example, the first and second flexures  206 ,  208  are shown to have planar rest states perpendicular to the axis  214 . In other embodiments, the first and second flexures  206 ,  208  may have expanded three-dimensional rest states perpendicular to the axis  214 . 
     The set of flexures  206 ,  208  allow movement of the movable mass  202  along an axis  214  extending from a first end  216  of the ferritic tube  204  to a second end  218  of the ferritic tube  204 , through the first and second ends  210 ,  212  of the movable mass  202 . In some cases, the flexures  206 ,  208  may constrain movement of the movable mass  202  to movement along the axis  214  (though the movement along the axis  214  may be subject to deviation due to real world tolerances (e.g., manufacturing variation and so on)). 
     In some embodiments, the movable mass  202  may be axisymmetric about the axis  214 . The flexures  206 ,  208  may also be axisymmetric about the axis  214 , and may be coupled to the movable mass  202  in an axisymmetric manner (e.g., coupled to the movable mass  202  along the axis  214 , or to attachment points on the movable mass  202  that are symmetrically distributed about the axis  214 . in some cases, additional components of the LRA  200 , or all of the LRA  200 , may be configured or coupled in an axisymmetric manner. 
     The movable mass  202  may include a set of magnet sections  220 . The magnet sections  220  may take the form of individual magnets (e.g., magnet sections  220  having donut-shaped or ring-like cross-sections perpendicular to the axis  214 ), or magnetized portions of a monolithic material (e.g., a cylindrical-shaped material). By way of example, the movable mass  202  is shown to have two magnet sections  220 , each of which is a separate magnet having a donut shape. A core  222  (e.g., a cylindrical-shaped core) is inserted through the hole in each magnet section  220 , and through a hole in a spacer  224  disposed between the magnet sections  220 . In some cases, each magnet section  220  and spacer  224  may surround or encircle the core  222 . Although each magnet section  220  and the spacer  224  is shown to be solid, but for its central hole, some or all of the one or more magnet sections  220  and/or spacer  224  may have perforations or channels, in addition to a central hole for receiving the core  222 , in some embodiments. The spacer  224  may be axisymmetric or donut-shaped, and in some cases may have a cross-section perpendicular to the axis  214  that is the same or similar to the cross-sections of the magnet sections  220 . The core  222  and spacer  224  may be ferritic, non-ferritic, or mildly ferritic. In some embodiments, the core  222  may be non-ferritic or mildly ferritic (e.g., formed of steel,  301  type stainless steel, or tungsten), which can enable higher frequency operation of the LRA  200 , and the spacer  224  may be ferritic (e.g., formed of iron). The magnet sections  220  and spacer  224  may be attached to the core  222  by welds, adhesive, clips, or friction (e.g., the magnet sections  220  and spacer  224  may be press-fit onto the core  222 ), or other means. 
     Each magnet section  220  may be disposed at a different position along the axis  214 . Each magnet section  220  may have a pair of opposite magnetic poles (e.g., a north (N) pole and a south (S) pole). The opposite magnetic poles of a magnet section  220  may be disposed at different positions along the axis  214 . Like magnetic poles of adjacent magnet sections  220  may face each other. 
     By way of example, the first and second flexures  206 ,  208  are shown attached to the movable mass  202  by means of bolts  240 ,  242  that thread into the core  222  and sandwich one or more portions (e.g., tabs or an entire inner perimeter) between a head of a respective bolt  240  or  242  and a respective end of the core  222 . 
     The LRA  200  may further include a set of one or more electric coils  226 . Each electric coil  226  may be fixed with respect to the ferritic tube  204  and/or attached to the ferritic tube  204 . Each electric coil  226  may extend around the movable mass  202 . Each electric coil  226  may be positioned between the ferritic tube  204  and the movable mass  202 . By way of example, the set of electric coils  226  is shown to include one electric coil  226 , which electric coil  226  may be positioned over and/or centered with respect to the spacer  224 . 
     When a current is driven through the electric coil  226 , magnetic flux  244  may flow in a generally axial direction through the magnet sections  220 , and into or out of the electric coil  226 , and may be recycled through the ferritic tube  204  before being returned to the magnet sections  220 . The magnetic flux  244  may change direction responsive to a change in the direction of current flow through the electric coil  226 . The ferritic tube  204  helps shorten the magnetic flux path and improve magnetic flux recycling (e.g., compared to magnetic flux traveling through air). The ferritic spacer  224  may help improve the channeling of magnetic flux  244  between the magnet sections  220 , and direct magnetic flux  244  into or out of the electric coil  226 . The non-ferritic or mildly ferritic core  222  helps prevent loss of magnetic flux  244  in the core  222  and increases magnetic flux  244  through the electric coil  226 . 
       FIG.  3    shows an alternative embodiment of the LRA  200 . In the alternative embodiment, the movable mass  202  further includes a first disc  300  and a second disc  302 . The first and second discs  300 ,  302  may be axisymmetric about the axis  214 , and may have holes through which the core  222  extends. A first magnet section  220  may be positioned between the first disc  300  and the spacer  224 , and a second magnet section  220  may be positioned between the second disc  302  and the spacer  224 . The first and second discs  300 ,  302  may be ferritic, non-ferritic, or mildly ferritic. In some cases, the first and second discs  300 ,  302  may be ferritic, to help channel the magnetic flux  244 . The first and second discs  300 ,  302  may be attached to the core  222  by welds, adhesive, clips, friction (e.g., the first and second discs  300 ,  302  may be press-fit onto the core  222 ), or other means. The first and second discs  300 ,  302  may have diameters that are the same as or larger than the diameter of the spacer  224 . 
     In some embodiments, the diameters of the first and second discs  300 ,  302 , perpendicular to the axis  214 , may be greater than a diameter of any magnet section  220  in the set of magnet sections  220 . In some cases, the diameters of the first and second discs  300 ,  302  may each be the same as, or about the same as, the inner diameter of the ferritic tube  204 . In these latter embodiments, the first and second discs  300 ,  302  may help stabilize the movable mass  202  within the ferritic tube  204 . When the diameters of the first and second discs  300 ,  302  are smaller than the inner diameter of the ferritic tube  204  (and even when the diameters are the same as, or about the same as, the inner diameter of the ferritic tube  204 ), the first and second discs  300 ,  302  may provide extra mass to the movable mass  202 . The extra mass may increase the magnitude of the haptic effect produced by the LRA  200 . In some embodiments, the discs  300 ,  302  may be formed of, or include, tungsten. 
     In some cases, the discs  300 ,  302  may be incorporated into the LRA described with reference to  FIGS.  1 A and  1 B . 
       FIG.  4    shows another alternative embodiment of the LRA  200 , in which the movable mass  202  includes a second spacer  400  and a third magnet section  402 . The third magnet section  402  may be separated from one of the magnet sections  220  by the spacer  400 . The magnet sections  220  and  402  may be constructed the same or similarly, and the spacers  224  and  400  may be constructed the same or similarly. A second electric coil  404  in the set of electric coils  226  may be fixed with respect to the ferritic tube  204  and/or attached to the ferritic tube  204 , and may extend around the movable mass  202 . The second electric coil  404  may be positioned between the ferritic tube  204  and the movable mass  202 , and may be positioned over and/or centered with respect to the second spacer  400 . 
     Applying the principles described with reference to  FIG.  4   , a set of magnet sections  220 ,  402  included in a movable mass  202  may include any number of two or more magnet sections. A set of spacers  224 ,  400  included in a movable mass  202  may include any number of one or more spacers, with each spacer being disposed between a pair of adjacent magnet sections. A set of electric coils  226 ,  404  included in a LRA, which LRA includes a movable mass, may be any number of one or more electric coils, with each electric coil being positioned over and/or centered with respect to a respective spacer. 
       FIG.  5    shows a cross-section of an example LRA  500 . The LRA  500  is an example of the LRAs described with reference to  FIGS.  1 A,  1 B,  2 , and  3   . The LRA  500  includes a movable mass  502  suspended from or within a ferritic tube  504 . The ferritic tube  504  is an example of the frame described with reference to  FIGS.  1 A and  1 B . In some embodiments, the movable mass  502  may be housed by or enclosed within the ferritic tube  504  (e.g., as shown). 
     In some embodiments, the ferritic tube  504  may have a first end  516  to which an optional first end cap  530  is attached, and a second end  518  to which an optional second end cap  534  is attached. By way of example, each of the first and second end caps  530 ,  534  is shown to have a two-part construction, with a ring ( 536  or  538 ) attached to a plate ( 540  or  542 ). Each plate  540 ,  542  may or may not have an outer wall or lip extending therefrom. In various embodiments, the first and second end caps  530 ,  534  may only include the rings  536 ,  538 , or a respective ring  536 ,  538  and plate  540 ,  542 , and may be formed as a monolithic structure or attached to each other prior to their attachment to the ferritic tube  504 . Each ring  536 ,  538  may have a diameter that is the same as, or slightly larger than, the diameter of the ferritic tube  504 , such that the first ring  536  may abut the first end  516  of the ferritic tube  504 , and the second ring  538  may abut the second end  518  of the ferritic tube  504 . Each of the first and second rings  536 ,  538  and first and second plates  540 ,  542  may be non-ferritic or mildly ferritic, to avoid attracting the movable mass  502 . In various embodiments, the first and second end caps  530 ,  534  may be differently shaped, may be solid, or may have holes therein. 
     The movable mass  502  may be attached to the ferritic tube  504 , and suspended from or within the ferritic tube  504 , by a set of flexures  506 ,  508  (e.g., non-ferritic or mildly ferritic flexures). A first flexure  506  may mechanically couple a first end  510  of the movable mass  502  to the ferritic tube  504 . A second flexure  508  may mechanically couple a second end  512  of the movable mass  502  to the ferritic tube  504 . Each flexure  506 ,  508  may be attached to the movable mass  502  by one or more of a weld, adhesive, clip, fastener, and so on. The first flexure  506  may have one or more portions (e.g., tabs or an entire outer perimeter) that extend between the ferritic tube  504  and the first end cap  530  and are sandwiched between the ferritic tube  504  and the first end cap  530 . Similarly, the second flexure  508  may have one or more portions (e.g., tabs or an entire perimeter) that extend between the ferritic tube  504  and the second end cap  534  and are sandwiched between the ferritic tube  504  and the second end cap  534 . By way of example, the first and second flexures  506 ,  508  are shown to have planar rest states perpendicular to the axis  514 . In other embodiments, the first and second flexures  506 ,  508  may have expanded three-dimensional rest states perpendicular to the axis  514 . 
     Respective ones of the first and second rings  536 ,  538  and first and second flexures  506 ,  508  may be attached to the ferritic tube  504  by welds, adhesive, clips, or other means. 
     The set of flexures  506 ,  508  allow movement of the movable mass  502  along an axis  514  extending from a first end  516  of the ferritic tube  504  to a second end  518  of the ferritic tube  504 , through the first and second ends  510 ,  512  of the movable mass  502 . In some cases, the flexures  506 ,  508  may constrain movement of the movable mass  502  to movement along the axis  514  (though the movement along the axis  514  may be subject to deviation due to real world tolerances (e.g., manufacturing variation and so on)). 
     In some embodiments, the movable mass  502  may be axisymmetric about the axis  514 . The flexures  506 ,  508  may also be axisymmetric about the axis  514 , and may be coupled to the movable mass  502  in an axisymmetric manner (e.g., coupled to the movable mass  502  along the axis  514 , or to attachment points on the movable mass  502  that are symmetrically distributed about the axis  514 . In some cases, additional components of the LRA  500 , or all of the LRA  500 , may be configured or coupled in an axisymmetric manner. 
     The movable mass  502  may include a set of magnet sections  520 . The magnet sections  520  may take the form of individual magnets (e.g., magnet sections  520  having donut-shaped or ring-like cross-sections perpendicular to the axis  514 ), or magnetized portions of a monolithic material (e.g., a cylindrical-shaped material). By way of example, the movable mass  502  is shown to have two magnet sections  520 , each of which is a separate magnet having a donut shape. A core  522  (e.g., a cylindrical-shaped core) is inserted through the hole in each magnet section  520 , and through a hole in a spacer  524  disposed between the magnet sections  520 . In some cases, each magnet section  520  and spacer  524  may surround or encircle the core  522 . Although each magnet section  520  and the spacer  524  is shown to be solid, but for its central hole, some or all of the one or more magnet sections  520  and/or spacer  524  may have perforations or channels, in addition to a central hole for receiving the core  522 , in some embodiments. The spacer  524  may be axisymmetric or donut-shaped, and in some cases may have a cross-section perpendicular to the axis  514  that is the same or similar to the cross-sections of the magnet sections  520 . The core  522  and spacer  524  may be ferritic, non-ferritic, or mildly ferritic. In some embodiments, the core  522  may be non-ferritic or mildly ferritic (e.g., formed of steel,  301  type stainless steel, or tungsten), which can enable higher frequency operation of the LRA  500 , and the spacer  524  may be ferritic (e.g., formed of iron). The magnet sections  520  and spacer  524  may be attached to the core  522  by welds, adhesive, clips, or friction (e.g., the magnet sections  520  and spacer  524  may be press-fit onto the core  522 ), or other means. 
     Each magnet section  520  may be disposed at a different position along the axis  514 . Each magnet section  520  may have a pair of opposite magnetic poles (e.g., a north (N) pole and a south (S) pole). The opposite magnetic poles of a magnet section  520  may be disposed at different positions along the axis  514 . Like magnetic poles of adjacent magnet sections  520  may face each other. 
     The movable mass  502  may also include a first disc  544  and a second disc  546 . The first and second discs  544 ,  546  may be axisymmetric about the axis  514 , and may have holes through which the core  522  extends. A first magnet section  520  may be positioned between the first disc  544  and the spacer  524 , and a second magnet section  520  may be positioned between the second disc  546  and the spacer  524 . The first and second discs  544 ,  546  may be ferritic, non-ferritic, or mildly ferritic. In some cases, the first and second discs  544 ,  546  may be ferritic, to help channel magnetic flux  560 . The first and second discs  544 ,  546  may be attached to the core  522  by welds, adhesive, clips, friction (e.g., the first and second discs  544 ,  546  may be press-fit onto the core  522 ), or other means. The first and second discs  544 ,  546  may provide extra mass to the movable mass  502 , and may therefore be referred to as mass-increasing discs. The extra mass may increase the magnitude of the haptic effect produced by the LRA  500 . In some embodiments, the discs  544 ,  546  may be formed of, or include, tungsten. 
     By way of example, the first and second flexures  506 ,  508  are shown attached to the movable mass  502  by means of welds  548 ,  550  to the core  522 . 
     The LRA  500  may further include a set of one or more electric coils  526 . Each electric coil  526  may be fixed with respect to the ferritic tube  504  and/or attached to the ferritic tube  504 . Each electric coil  526  may extend around the movable mass  502 . Each electric coil  526  may be positioned between the ferritic tube  504  and the movable mass  502 . By way of example, the set of electric coils  526  is shown to include one electric coil  526 , which electric coil  526  may be positioned over and/or centered with respect to the spacer  524 . 
     In some cases, the electric coil  526  may be wound around a dielectric ring  552  (e.g., a plastic ring). The dielectric ring  552  may serve as a carrier for the electric coil  526  and attached to the interior of the ferritic tube  504 . The movable mass  502  may extend through the dielectric ring  552 . The dielectric ring  552  may serve as a carrier for the electric coil  526 . The dielectric ring  552  may also protect the electric coil  526  from potential abrasion by the movable mass  502 . 
     In some cases, a ferrofluid  554  may be dispensed between the electric coil  526  and the movable mass  502 , or between the dielectric ring  552  and the movable mass  502 . The ferrofluid  554  may prevent the movable mass  502  from crashing into the dielectric ring  552  (or cushion the movable mass  502 ) in the event of a drop event or other shock to the LRA  500 . 
     When a current is driven through the electric coil  526 , magnetic flux  560  may flow in a generally axial direction through the magnet sections  520 , and into or out of the electric coil  526 , and may be recycled through the ferritic tube  504  before being returned to the magnet sections  520 . The magnetic flux  560  may change direction responsive to a change in the direction of current flow through the electric coil  526 . The ferritic tube  504  helps shorten the magnetic flux path and improve magnetic flux recycling (e.g., compared to magnetic flux traveling through air). The ferritic spacer  524  may help improve the channeling of magnetic flux  560  between the magnet sections  520 , and direct magnetic flux  560  into or out of the electric coil  526 . The non-ferritic or mildly ferritic core  522  helps prevent loss of magnetic flux  560  in the core  522  and increases magnetic flux  560  through the electric coil  526 . 
     In some embodiments, a crash stop or cushion  556 ,  558  may be attached (e.g., glued) to the interior of each plate  540 ,  542  (i.e., between the plate  540  (or end cap  530 ) and the movable mass  502 , or between the plate  542  (or end cap  534 ) and the movable mass  502 ). The cushions  556 ,  558  may mechanically and electrically protect the movable mass  502  and first and second plates  540 ,  542  in the event of a drop, overcurrent applied to the electric coil  526 , or the like, by preventing metal-to-metal contact between the movable mass and first or second plate  540 ,  542 . In some cases, the cushions  556 ,  558  may be formed of plastic. 
       FIGS.  6 A and  7    show plan views of example flexures. In some cases, the flexures may be the flexures described with reference to  FIG.  1 A,  1 B,  2 ,  3 ,  4   , or  5 . 
     As shown in  FIG.  6 A , the flexure  600  may have a set of arms  602 ,  604 ,  606 , each arm of which has a trajectory that spirals around a central hole  608  and axis  610 . Each of the arms  602 ,  604 ,  606  may have an outward portion (or distal end) near the outer perimeter of the flexure  600 , and an inward portion (or proximal end) near the inner perimeter of the flexure  600 . The arms  602 ,  604 ,  606  may be connected to each other at their outward portions or distal ends and, separately, at their inward portions or proximal ends. Each arm  602 ,  604 ,  606  may have a wider distal end and proximal end, and a middle portion having a width that is smaller than those of the distal and proximal ends. 
       FIG.  6 B  illustrates an example movement of the movable mass  502  shown in  FIG.  5    when the flexures  506 ,  508  are configured as shown in  FIG.  6 A  and a current having a first polarity is driven through the electric coil  526 . As shown, the movable mass  502  may move to the left and the flexures  506 ,  508  may flex to allow the movement. When the polarity of the current through the electric coil  526  alternates or is switched to a second polarity, the movable mass  502  may move to the right. When no current is driven through the electric coil  526 , the flexures  506 ,  508  may assume planar rest states, as shown in  FIG.  5   . 
     When the flexures  506 ,  508  are configured as shown in  FIG.  6 A , each flexure  506 ,  508  may be attached to the movable mass  502  with its arms  602 ,  604 ,  606  spiraling in the same direction. This helps constrain the movable mass  502  to a rifling movement about the axis  514  and helps stabilize the movable mass  502  (e.g., prevent wobble, which can cause performance to deteriorate and increase wear). 
       FIG.  7    shows another example of a flexure  700  having a planar rest state. The flexure  700  also has a set of arms  702 ,  704 ,  706 , each arm of which has a trajectory that spirals around an axis  708 . Each of the arms  702 ,  704 ,  706  may have an outward portion (or distal end) near the outer perimeter of the flexure  700 , and an inward portion (or proximal end) near the inner perimeter of the flexure  700 . The arms  702 ,  704 ,  706  may be connected to each other at their outward portions or distal ends and, separately, at their inward portions or proximal ends. Each arm  702 ,  704 ,  706  may have a wider distal end and proximal end, and a middle portion having a width that is smaller than those of the distal and proximal ends. However, the widths of the distal end, proximal end, and middle portion of each arm  702 ,  704 ,  706  may be more or less the same, and in some cases may be the same. In comparison to the arms of the flexure described with reference to  FIG.  6 A , each of the arms  702 ,  704 ,  706  has a longer length, which can increase the extension of the flexure  700 . 
       FIG.  8 A  shows a cross-section of an example LRA  800 . The LRA  800  is an example of the LRAs described with reference to  FIGS.  1 A,  1 B,  2 , and  3   . The LRA  800  includes a movable mass  802  suspended from or within a ferritic tube  804 . The ferritic tube  804  is an example of the frame described with reference to  FIGS.  1 A and  1 B . In some embodiments, the movable mass  802  may be housed by or enclosed within the ferritic tube  804  (e.g., as shown). 
     In some embodiments, the ferritic tube  804  may have a first end  816  to which an optional first end cap  830  is attached, and a second end  818  to which an optional second end cap  834  is attached. Each of the first and second end caps  830 ,  834  may take the form of a plate, but could alternately take the form of any of the end caps described herein (or other forms). Each end cap  830 ,  834  may have a diameter that is the same as, or slightly larger than, the diameter of the ferritic tube  804 , such that the first end cap  830  may abut the first end  816  of the ferritic tube  804 , and the second end cap  834  may abut the second end  818  of the ferritic tube  804 . Each of the first and second end caps  830 ,  834  may be non-ferritic or mildly ferritic, to avoid attracting the movable mass  802 . In various embodiments, the first and second end caps  830 ,  834  may be differently shaped, may be solid, or may have holes therein. 
     The movable mass  802  may be attached to the ferritic tube  804 , and suspended from or within the ferritic tube  804 , by a set of flexures  806 ,  808  (e.g., non-ferritic or mildly ferritic flexures). A first flexure  806  may mechanically couple a first end  810  of the movable mass  802  to the ferritic tube  804 . A second flexure  808  may mechanically couple a second end  812  of the movable mass  802  to the ferritic tube  804 . Each flexure  806 ,  808  may be attached to the movable mass  802  by one or more of a weld, adhesive, clip, fastener, and so on. The first flexure  806  may have one or more portions (e.g., tabs or an entire outer perimeter) that extend between the ferritic tube  804  and the first end cap  830  and are sandwiched between the ferritic tube  804  and the first end cap  830 . Similarly, the second flexure  808  may have one or more portions (e.g., tabs or an entire perimeter) that extend between the ferritic tube  804  and the second end cap  834  and are sandwiched between the ferritic tube  804  and the second end cap  834 . By way of example, the first and second flexures  806 ,  808  are shown to have expanded three-dimensional rest states perpendicular to the axis  814 . In some embodiments, each of the flexures  806 ,  808  may be formed similarly to the flexure described with reference to  FIG.  7    (or  FIG.  6   ), but may be forced into a three-dimensional state before or after its attachment to the movable mass  802  and the ferritic tube  804 . For example, each of the flexures  806 ,  808  may be pre-deformed into a three-dimensional rest state prior to installation, or each of the flexures  806 ,  808  may be deformed into a three-dimensional rest state during installation (in which case each flexure  806 ,  808  may be under tension when the movable mass  802  is at rest). The use of flexures  806 ,  808  having three-dimensional rest states can enable a shortening of the LRA  800  in comparison to the LRA described with reference to  FIG.  5   , and in some cases can reduce the number of assembly steps for the LRA  800  (e.g., since rings need not be included in the end caps  830 ,  834 . 
     Respective ones of the first and second end caps  830 ,  834  and first and second flexures  806 ,  808  may be attached to the ferritic tube  804  by welds, adhesive, clips, or other means. 
     The set of flexures  806 ,  808  allow movement of the movable mass  802  along an axis  814  extending from a first end  816  of the ferritic tube  804  to a second end  818  of the ferritic tube  804 , through the first and second ends  810 ,  812  of the movable mass  802 . In some cases, the flexures  806 ,  808  may constrain movement of the movable mass  802  to movement along the axis  814  (though the movement along the axis  814  may be subject to deviation due to real world tolerances (e.g., manufacturing variation and so on)). 
     In some embodiments, the movable mass  802  may be axisymmetric about the axis  814 . The flexures  806 ,  808  may also be axisymmetric about the axis  814 , and may be coupled to the movable mass  802  in an axisymmetric manner (e.g., coupled to the movable mass  802  along the axis  814 , or to attachment points on the movable mass  802  that are symmetrically distributed about the axis  814 . in some cases, additional components of the LRA  800 , or all of the LRA  800 , may be configured or coupled in an axisymmetric manner. 
     The movable mass  802  may include a set of magnet sections  820 . The magnet sections  820  may take the form of individual magnets (e.g., magnet sections  820  having donut-shaped or ring-like cross-sections perpendicular to the axis  814 ), or magnetized portions of a monolithic material (e.g., a cylindrical-shaped material). By way of example, the movable mass  802  is shown to have two magnet sections  820  formed in a monolithic material (e.g., by selectively magnetizing different portions of the monolithic material). A core  822  (e.g., a cylindrical-shaped core) is inserted through the hole in the monolithic material. Although the monolithic material in which the magnet sections  820  are formed is shown to be solid, but for its central hole, the monolithic material may in some cases have perforations or channels, in addition to a central hole for receiving the core  822 . The core  822  may be ferritic, non-ferritic, or mildly ferritic. In some embodiments, the core  822  may be non-ferritic or mildly ferritic (e.g., formed of steel,  301  type stainless steel, or tungsten), which can enable higher frequency operation of the LRA  800 , and the spacer  824  may be ferritic (e.g., formed of iron). The monolithic material defining the magnet sections  820  may be attached to the core  822  by welds, adhesive, clips, or friction (e.g., the monolithic material may be press-fit onto the core  822 ), or other means. 
     Each magnet section  820  may be disposed at a different position along the axis  814 . Each magnet section  820  may have a pair of opposite magnetic poles (e.g., a north (N) pole and a south (S) pole). The opposite magnetic poles of a magnet section  820  may be disposed at different positions along the axis  814 . Like magnetic poles of adjacent magnet sections  820  may face each other. 
     By way of example, the first and second flexures  806 ,  808  are shown attached to the movable mass  802  by means of welds  848 ,  850  to the core  822 . 
     The LRA  800  may further include a set of one or more electric coils  826 . Each electric coil  826  may be fixed with respect to the ferritic tube  804  and/or attached to the ferritic tube  804 . Each electric coil  826  may extend around the movable mass  802 . Each electric coil  826  may be positioned between the ferritic tube  804  and the movable mass  802 . By way of example, the set of electric coils  826  is shown to include one electric coil  826 , which electric coil  826  may be positioned over and/or centered with respect to the spacer  824 . 
     In some cases, the electric coil  826  may be wound around a dielectric ring  852  (e.g., a plastic ring). The dielectric ring  852  may serve as a carrier for the electric coil  826  and attached to the interior of the ferritic tube  804 . The movable mass  802  may extend through the dielectric ring  852 . The dielectric ring  852  may serve as a carrier for the electric coil  826 . The dielectric ring  852  may also protect the electric coil  826  from potential abrasion by the moving mass  802 . 
     In some cases, a ferrofluid  854  may be dispensed between the electric coil  826  and the movable mass  802 , or between the dielectric ring  852  and the movable mass  802 . The ferrofluid  854  may help channel magnetic flux  856 . 
     When a current is driven through the electric coil(s)  826 , magnetic flux  856  may flow in a generally axial direction through the magnet sections  820 , and into or out of the electric coil  826 , and may be recycled through the ferritic tube  804  before being returned to the magnet sections  820 . The magnetic flux  856  may change direction responsive to a change in the direction of current flow through the electric coil  826 . The ferritic tube  804  helps shorten the magnetic flux path and improve magnetic flux recycling (e.g., compared to magnetic flux traveling through air). The ferritic spacer  824  may help channel magnetic flux  856  between the magnet sections  820 , and direct magnetic flux into or out of the electric coil  826 . The non-ferritic or mildly ferritic core  822  helps prevent loss of magnetic flux  856  in the core  822  and increases magnetic flux  856  through the electric coil  826 . 
       FIG.  8 B  illustrates an example movement of the movable mass  802  shown in  FIG.  8 A  when a current having a first polarity is driven through the electric coil  826 . As shown, the movable mass  802  may move to the left and the flexures  806 ,  808  may flex to allow the movement. When the polarity of the current through the electric coil  826  alternates or is switched to a second polarity, the movable mass  802  may move to the right. 
     When the flexures  806 ,  808  are configured as shown in  FIG.  7   , each flexure  806 ,  808  may be attached to the movable mass  802  with its arms spiraling in the same direction. This helps constrain the movable mass  802  to a rifling movement about the axis  814  and helps stabilize the movable mass  802  (e.g., prevent wobble, which can cause performance to deteriorate and increase wear). 
       FIG.  9    shows an exterior isometric view of a frame and a cylindrical body portion of an enclosure having a cylindrical body portion or ferritic tube  900 , as might be used to house any of the LRAs described with reference to  FIG.  1 A- 5  or  8 A- 8 B . As shown, the ends of the wire  902  that form an electric coil internal to the ferritic tube  900  may extend through a hole  904  in the ferritic tube  900  and electrically connect to a flexible circuit  906  that is conformed to a portion of an outer surface of the ferritic tube  900 . In some cases, a portion of the flexible circuit  906  may also be folded and attached (or abutted) to an end cap  908  attached to one end of the ferritic tube  900 . 
       FIG.  10    shows an exterior isometric view of a frame and a cylindrical body portion of an enclosure having a cylindrical body portion or ferritic tube  1000 , as might be used to house any of the LRAs described with reference to  FIG.  1 A- 5  or  8 A- 8 B . As shown, the ends of the wire  1002  that form an electric coil internal to the ferritic tube  1000  may extend through a hole  1004  formed in an end cap  1006  attached to the ferritic tube  1000 . Alternatively, the hole  1004  may be formed partially or fully in the ferritic tube  1000 , near the end cap  1006 . The ends of the wire  1002  may be electrically connected to a flexible circuit  1008  that is attached (or abutted) to the end cap  1006 . 
       FIG.  11    shows an example of a stylus  1100 , electronic pencil, or the like. The stylus  1100  may be held and manipulated by a user  1102  to provide input to an electronic device. In some cases, the position or movement of the stylus&#39; tip  1104  may be sensed by an electronic device on which the tip  1104  is rested and moved. In some cases, the position or movement of the stylus&#39; tip  1104  may be sensed by electronics  1106  (e.g., one or more sensors (e.g., an accelerometer, inertial sensor, optical sensor, and so on) and a processor) within the stylus  1100 , and the sensed position or movement, or information derived from the sensed position or movement (e.g., characters drawn, object drawn, patterns traced, inputs selected, and so on), may be transmitted to a remote electronic device and/or indicated to the user via the stylus  1100 . 
     The stylus  1100  may include an LRA  1108 , including any of the LRAs described herein. The LRA  1108  may be actuated by the electronics  1106  (e.g., by a processor) to provide haptic feedback to the user  1102 . A single type of haptic feedback may be provided, or different types of haptic feedback may be provided to indicate different things to the user  1102 . Different types of haptic feedback may be provided, for example, by varying the frequency of actuation or actuating the LRA  1108  in accord with different haptic actuation waveforms. Different haptic actuation waveforms may have a series of actuations of the same or different length, at the same or different frequencies, separated by the same or different length pauses. 
     Haptic feedback may be provided to signal, for example, whether stylus input has been received; whether a letter or gesture traced by the stylus  1100  has been recognized; whether the stylus  1100  has triggered a button press or been moved to a particular position within a user interface; whether the user  1102  has moved the stylus  1100  outside of a bounded area; whether the user  1102  has moved the stylus  1100  over an actual or virtual surface having a particular texture; and so on. 
     The tubular and/or axisymmetric configurations of the LRAs described herein make them especially suitable for incorporation into the body of a stylus  1100 , although the LRAs can be incorporated into any type of electronic device, such as mobile phones, computers, earbuds, watches, health and fitness monitors, touch screens, and so on. 
     As described with reference to  FIG.  4   , additional magnet sections and electric coils can be added to any of the LRAs described herein. Furthermore, the diameters of the magnet sections, widths of the magnet sections and spacers, resistance of the flexures, and various other parameters may be changed to tune the response of an LRA for a particular application. 
       FIG.  12    shows an example block diagram of an electronic device  1200 , which in some cases may be the electronic device described with reference to  FIG.  11   , or another type of electronic device that includes one or more of the LRAs described herein. The electronic device  1200  may include an electronic display  1202  (e.g., a light-emitting display), a processor  1204 , a power source  1206 , a memory  1208  or storage device, a sensor system  1210 , and/or an input/output (I/O) mechanism  1212  (e.g., an input/output device, input/output port, or haptic input/output interface). The processor  1204  may control some or all of the operations of the electronic device  1200 . The processor  1204  may communicate, either directly or indirectly, with some or all of the other components of the electronic device  1200 . For example, a system bus or other communication mechanism  1214  can provide communication between the electronic display  1202 , the processor  1204 , the power source  1206 , the memory  1208 , the sensor system  1210 , and the I/O mechanism  1212 . 
     The processor  1204  may be implemented as any electronic device capable of processing, receiving, or transmitting data or instructions, whether such data or instructions is in the form of software or firmware or otherwise encoded. For example, the processor  1204  may include a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC), a digital signal processor (DSP), a controller, or a combination of such devices. As described herein, the term “processor” is meant to encompass a single processor or processing unit, multiple processors, multiple processing units, or other suitably configured computing element or elements. In some cases, the processor  1204  may provide part or all of the processing system or processor described herein. 
     It should be noted that the components of the electronic device  1200  can be controlled by multiple processors. For example, select components of the electronic device  1200  (e.g., the sensor system  1210 ) may be controlled by a first processor and other components of the electronic device  1200  (e.g., the electronic display  1202 ) may be controlled by a second processor, where the first and second processors may or may not be in communication with each other. 
     The power source  1206  can be implemented with any device capable of providing energy to the electronic device  1200 . For example, the power source  1206  may include one or more batteries or rechargeable batteries. Additionally or alternatively, the power source  1206  may include a power connector or power cord that connects the electronic device  1200  to another power source, such as a wall outlet. 
     The memory  1208  may store electronic data that can be used by the electronic device  1200 . For example, the memory  1208  may store electrical data or content such as, for example, timing signals, control signals, instructions, and/or data structures or databases. The memory  1208  may include any type of memory. By way of example only, the memory  1208  may include random access memory, read-only memory, Flash memory, removable memory, other types of storage elements, or combinations of such memory types. 
     The electronic device  1200  may also include one or more sensor systems  1210  positioned almost anywhere on the electronic device  1200 . The sensor system(s)  1210  may be configured to sense one or more types of parameters, such as but not limited to, vibration; light; touch; force; heat; movement; relative motion; biometric data (e.g., biological parameters) of a user; air quality; proximity; position; connectedness; surface quality; and so on. By way of example, the sensor system(s)  1210  may include an SMI sensor, a heat sensor, a position sensor, a light or optical sensor, an image sensor (e.g., one or more of the image sensors or cameras described herein), an accelerometer, a pressure transducer, a gyroscope, a magnetometer, a health monitoring sensor, or an air quality sensor, and so on. Additionally, the one or more sensor systems  1210  may utilize any suitable sensing technology, including, but not limited to, interferometric, magnetic, capacitive, ultrasonic, resistive, optical, acoustic, piezoelectric, or thermal technologies. 
     The I/O mechanism  1212  may transmit or receive data from a user or another electronic device. The I/O mechanism  1212  may include the electronic display  1202 , a touch sensing input surface, a crown, one or more buttons (e.g., a graphical user interface “home” button), one or more microphones or speakers, one or more ports such as a microphone port, and/or a keyboard. Additionally or alternatively, the I/O mechanism  1212  may transmit electronic signals via a communications interface, such as a wireless, wired, and/or optical communications interface. Examples of wireless and wired communications interfaces include, but are not limited to, cellular and Wi-Fi communications interfaces. The I/O mechanism  1212  may also include a haptic output device, such as one of the LRAs described herein. 
     The foregoing description, for purposes of explanation, uses specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art, after reading this description, 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, after reading this description, that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20210601
Publication Date: 20231114
Grant Date: 20231114
Priority Date: 20210601
Inventors: DEGNER, BRETT W.
BAUGH, BRENTON A.
YONEOKA, SHINGO
ZHOU, SONGSHENG
Assignee: APPLE INC
CPC Classifications: [{"code": "H02K33/18", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02K1/34", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/016", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02K7/025", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02K33/18", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02K5/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02K11/20", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/016", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02K33/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/016", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02K1/34", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 84193422