PATENT DOCUMENT

Publication Number: US-10566888-B2
Application Number: US-201615260047-A
Country: US
Kind Code: B2

Title: Linear actuators for use in electronic devices

Abstract:
Embodiments described herein may take the form of an electromagnetic actuator that produces a haptic output during operation. Generally, an electromagnetic coil is wrapped around a central magnet array. A shaft passes through the central magnet array, such that the central array may move along the shaft when the proper force is applied. When a current passes through the electromagnetic coil, the coil generates a magnetic field. The coil is stationary with respect to a housing of the actuator, while the central magnet array may move along the shaft within the housing. Thus, excitation of the coil exerts a force on the central magnet array, which moves in response to that force. The direction of the current through the coil determines the direction of the magnetic field and thus the motion of the central magnet array.

Claims:
What is claimed is: 
     
       1. An actuator for an electronic device, comprising:
 a housing; 
 a frame disposed within the housing; 
 multiple magnets positioned within the frame; 
 a set of spacers positioned within the frame, each of the spacers in the set separating two magnets of the multiple magnets; 
 a group of coils surrounding a portion of the multiple magnets and positioned within the frame; 
 a main mass affixed to a first magnet of the multiple magnets; 
 an end mass affixed to a second magnet of the multiple magnets; 
 a first shaft end of a shaft received within, and extending from, the main mass; 
 a second shaft end of the shaft received within, and extending from, the end mass; 
 a first bearing encircling the first shaft end; 
 a second bearing encircling the second shaft end; 
 a first end cap affixed to the housing and defining a first aperture; 
 a second end cap affixed to the housing and defining a second aperture; 
 a first spring around the first shaft end outside the frame and constrained by the first end cap and the main mass; 
 a second spring around the second shaft end outside the frame and constrained by the second end cap and the end mass; and 
 guide rails configured to constrain a motion of the multiple magnets, the main mass, and the end mass; wherein 
 the multiple magnets, the main mass, the frame, and the end mass are configured to move along the guide rails. 
 
     
     
       2. The actuator of  claim 1 , wherein:
 the first shaft end extends into a first void defined by the first end cap; and 
 the second shaft end extends into a second void defined by the second end cap. 
 
     
     
       3. The actuator of  claim 1 , wherein:
 the guide rails encompass exterior edges of the multiple magnets; and 
 the guide rails pass through the main mass. 
 
     
     
       4. The actuator of  claim 3 , wherein the guide rails are C-shaped. 
     
     
       5. The actuator of  claim 1 , further comprising a set of stabilization magnets adjacent opposing sidewalls of the housing. 
     
     
       6. The actuator of  claim 1 , wherein the first and second springs are wound oppositely from one another. 
     
     
       7. The actuator of  claim 6 , wherein the first spring is configured to counter torque from the second spring, and vice versa. 
     
     
       8. A method for providing haptic feedback, comprising:
 energizing multiple coils of an actuator that includes:
 a housing; 
 a frame disposed within the housing, the multiple coils positioned within the frame; 
 multiple magnets positioned within the frame, the multiple coils surrounding a portion of the multiple magnets; 
 a set of spacers positioned within the frame, each of the spacers in the set separating two magnets of the multiple magnets; 
 a main mass affixed to a first magnet of the multiple magnets; 
 an end mass affixed to a second magnet of the multiple magnets; 
 a first shaft received within, and extending from, the main mass; 
 a second shaft received within, and extending from, the end mass; 
 a first bearing encircling the first shaft; 
 a second bearing encircling the second shaft; 
 a first end cap affixed to the housing and defining a first aperture; 
 a second end cap affixed to the housing and defining a second aperture; 
 a first spring around the first shaft outside the frame and constrained by the first end cap and the main mass; 
 a second spring around the second shaft outside the frame and constrained by the second end cap and the end mass; and 
 guide rails configured to constrain a motion of the multiple magnets, the main mass, and the end mass; 
 
 moving the multiple magnets and the frame in a first direction in response to energizing the multiple coils, thereby compressing the first spring; 
 moving the first shaft in the first direction; 
 de-energizing the multiple coils; 
 expanding the first spring, thereby returning the multiple magnets to an initial magnet position and the first shaft to an initial shaft position; 
 moving the multiple magnets and the frame in a second direction, thereby compressing the second spring; 
 moving the second shaft in the second direction; and 
 expanding the second spring, thereby returning the multiple magnets to the initial magnet position and the second shaft to a second initial shaft position. 
 
     
     
       9. The method of  claim 8 , wherein the first shaft, the second shaft, the first bearing, and the second bearing cooperate to constrain the multiple magnets to a linear motion. 
     
     
       10. The method of  claim 8 , further comprising maintaining the first bearing and the second bearing stationary with respect to the housing while the multiple magnets move in the first direction and the second direction. 
     
     
       11. The method of  claim 8 , wherein: the operation of moving the multiple magnets in the first direction comprises moving the multiple magnets along the guide rails. 
     
     
       12. The method of  claim 8 , wherein the guide rails cooperate with the first shaft and the second shaft to constrain the multiple magnets to a linear motion. 
     
     
       13. An actuator for an electronic device, comprising:
 a housing; 
 an array cap disposed within the housing; 
 multiple magnets positioned at least partially within the array cap; 
 a set of spacers positioned at least partially within the array cap, each of the spacers in the set separating two magnets of the multiple magnets; 
 a group of coils surrounding a portion of the multiple magnets and positioned at least partially within the array cap; 
 a main mass affixed to a first magnet of the multiple magnets; 
 an end mass affixed to a second magnet of the multiple magnets; 
 a first shaft received within, and extending from, the main mass; 
 a second shaft received within, and extending from, the end mass; 
 a first bearing encircling the first shaft; 
 a second bearing encircling the second shaft; 
 a first end cap affixed to the housing and defining a first aperture; 
 a second end cap affixed to the housing and defining a second aperture; 
 a first spring around the first shaft outside the array cap and constrained by the first end cap and the main mass; 
 a second spring around the second shaft outside the array cap and constrained by the second end cap and the end mass; and 
 guide rails configured to constrain a motion of the multiple magnets, the main mass, and the end mass; wherein 
 the multiple magnets, the main mass, the array cap, and the end mass are configured to move along the guide rails. 
 
     
     
       14. The actuator of  claim 13 , wherein:
 the first shaft extends into a first void defined by the first end cap; and 
 the second shaft extends into a second void defined by the second end cap. 
 
     
     
       15. The actuator of  claim 13 , wherein:
 the guide rails encompass exterior edges of the multiple magnets; and 
 the guide rails pass through the main mass. 
 
     
     
       16. The actuator of  claim 15 , wherein the guide rails are C-shaped. 
     
     
       17. The actuator of  claim 13 , further comprising a set of stabilization magnets adjacent opposing sidewalls of the housing. 
     
     
       18. The actuator of  claim 13 , wherein the first and second springs are wound oppositely from one another. 
     
     
       19. The actuator of  claim 18 , wherein the first spring is configured to counter torque from the second spring. 
     
     
       20. The actuator of  claim 13 , wherein the first shaft and the second shaft are positioned outside the multiple magnets.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/215,686, filed on Sep. 8, 2015, and entitled “Linear Actuators for Use in Electronic Devices,” the contents of which are incorporated by reference as if fully disclosed herein. 
    
    
     FIELD 
     Embodiments described herein generally relate to actuators for producing a haptic force, and more particularly to a resonant linear actuator that moves bidirectionally in response to electromagnetic motive forces. 
     BACKGROUND 
     Many modern portable electronic devices include actuators to provide alerts and notifications. As one common example, many mobile phones include a rotary vibration motor with an eccentric weight that spins rapidly in order to produce a vibration. This vibration may alert a user to an incoming telephone call when the phone is muted, for example. The vibration takes the place of the standard audio alert and may be felt by the user if he or she is touching the phone. However, the vibration may still be noisy in certain environments and this may be undesirable. 
     Further, many rotary mass actuators not only create an audible buzz, but also an undesirable feel. Because rotary mass actuators spin up to an operating state and then wind down to a rest state, they constantly shake the enclosure of the electronic device. This feels “buzzy” to a user and there is little, if any, control over the haptic output of such a device other than to control the amplitude of the output or to provide discrete outputs with an unacceptably long time between the outputs. 
     Certain linear actuators are used instead of rotary mass actuators in some electronic devices. Linear actuators may deliver a more crisp haptic output and are quieter in certain cases. However, many such linear actuators are relatively large and some may move a mass only in a single direction. 
     Accordingly, an improved linear actuator may be useful. 
     SUMMARY 
     Embodiments described herein may take the form of a linear actuator capable of moving bidirectionally. Embodiments may provide a substantial haptic output resulting from relatively small motion of a mass within the actuator. 
     One embodiment may take the form of a haptic feedback system for an electronic device, comprising: a magnet assembly; a first shaft operably connected to the magnet assembly; a second shaft operably connected to the magnet assembly; a first spring surrounding the first shaft; a second spring surrounding the second shaft; and an electromagnetic structure operative to exert a motive force on the magnet assembly, whereby the magnet assembly, first shaft, and second shaft may translate in response to the motive force; wherein the electromagnetic structure encircles at least a portion of the magnet assembly when the magnet assembly is in a rest state. 
     Another embodiment may take the form of a method for providing haptic feedback, comprising: energizing multiple coils surrounding a set of magnets; moving the set of magnets in a first direction in response to energizing the multiple coils, thereby compressing a first spring; moving a first shaft in the first direction; de-energizing multiple coils; expanding the spring, thereby returning the set of magnets to an initial magnet position and the first shaft to an initial shaft position; moving the set of magnets in a second direction, thereby compressing a second spring; moving a second shaft in the second direction; and expanding the spring, thereby returning the set of magnets to the initial magnet position and the second shaft to a second initial shaft position. 
     Still another embodiment may take the form of an actuator for an electronic device, comprising: a housing; multiple magnets; a set of spacers, each of the spacers in the set separating two magnets of the multiple magnets; a group of coils surrounding a portion of the multiple magnets; a main mass affixed to a first magnet of the multiple magnets; an end mass affixed to a second magnet of the multiple magnets; a first shaft received within, and extending from, the main mass; a second shaft received within, and extending from, the end mass; a first bearing encircling the first shaft; a second bearing encircling the second shaft; a first end cap affixed to the housing and defining a first aperture; a second end cap affixed to the housing and defining a second aperture; a first spring around the first shaft and constrained by the first end cap and the main mass; a second spring around the second shaft and constrained by the second end cap and the second mass; and guide rails configured to constrain a motion of the multiple magnets, main mass, and end mass; wherein the multiple magnets, main mass, and end mass are configured to move along the guide rails. 
     These and other embodiments, as well as the operations and uses thereof, will be apparent upon reading the specification in its entirety. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  depicts a sample electronic device that may incorporate a linear actuator, as described herein. 
         FIG. 2  depicts a sample linear actuator, in accordance with embodiments described herein. 
         FIG. 3  depicts the sample linear actuator of  FIG. 2  with a portion of a housing removed therefrom. 
         FIG. 4  depicts a cross-section of the sample linear actuator of  FIG. 2 , taken along line  4 - 4  of  FIG. 3 , with the flex removed for clarity. 
         FIG. 5  depicts a cross-section of the sample linear actuator of  FIG. 2 , taken along line  5 - 5  of  FIG. 3 . 
         FIG. 6  depicts a cross-section of the sample linear actuator of  FIG. 2 , taken along line  6 - 6  of  FIG. 2 . 
         FIG. 7  depicts an exploded view of another sample linear actuator. 
         FIG. 8  depicts the linear actuator of  FIG. 7  in an assembled state, with the housing shown in phantom. 
         FIG. 9  shows a first cross-section of the linear actuator of  FIGS. 7 and 8 . 
         FIG. 10  shows a second cross-section of the linear actuator of  FIGS. 7 and 8 . 
         FIG. 11  shows a third cross-section of the linear actuator of  FIGS. 7 and 8 , taken along line  11 - 11  of  FIG. 10 . 
         FIG. 12  shows a fourth cross-section of the linear actuator of  FIGS. 7 and 8 , taken along line  12 - 12  of  FIG. 10 . 
         FIG. 13  shows a fifth cross-section of the linear actuator of  FIGS. 7 and 8 , taken along line  13 - 13  of  FIG. 10 . 
         FIG. 14  shows a sixth cross-section of the linear actuator of  FIGS. 7 and 8 , taken along line  14 - 14  of  FIG. 10 . 
         FIG. 15  shows a seventh cross-section of the linear actuator of  FIGS. 7 and 8 , taken along line  15 - 15  of  FIG. 10 . 
         FIG. 16  shows an eighth cross-section of the linear actuator of  FIGS. 7 and 8 , taken along line  16 - 16  of  FIG. 10 . 
     
    
    
     The use of the same or similar reference numerals in different figures indicates similar, related, or identical items. 
     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 figure. 
     DETAILED DESCRIPTION 
     Embodiments described herein may take the form of an electromagnetic actuator that produces a haptic output during operation. Generally, an electromagnetic coil is wrapped around a central magnet array. A shaft passes through the central magnet array, such that the central array may move along the shaft when the proper force is applied. 
     When a current passes through the electromagnetic coil, the coil generates a magnetic field. The coil is stationary with respect to a housing of the actuator, while the central magnet array and an associated frame may move along the shaft within the housing. (The frame and array together form a mass assembly.) Thus, excitation of the coil exerts a force on the central magnet array, which moves in response to that force. The direction of the current through the coil determines the direction of the magnetic field and thus the motion of the central magnet array. It should be appreciated, however, that alternative embodiments may generate a motive force through other means, such as purely through the injection of flux into the coil by operation of injector magnets as described elsewhere herein. 
     Generally, the central magnet array may slide along the shaft in response to the magnetic field generated by the coil. The central magnet array may be placed within, coupled to, or otherwise associated with a weight, such as a frame, that also moves with the array. The frame adds mass to the central magnet array and so may provide a greater haptic output in response to motion than would the array alone. 
     One or more bearings, such as jewel bearings, may form the interface between the central magnet array and the shaft. The bearings may be shaped to reduce contact between the bearing interiors and the shaft, thereby reducing friction and permitting greater, and/or higher velocity, motion along the shaft by the central magnet array. Further, the shape of the bore through the bearings reduces the likelihood that the bearings and/or shaft are constrained, thereby avoiding binding and/or friction due to misalignment of portions of the actuator. 
     The shaft may be affixed to the housing of the actuator at both ends. A separate spring, such as a beehive (or double beehive) spring, may encircle each end of the shaft and abut both the interior of the housing and the frame. The springs may allow the coil and array (e.g., the mass assembly) to increase an amplitude of the array&#39;s motion with each excursion from a rest state and, also may prevent the frame from hitting or crashing into the housing. Further, the springs may return the mass assembly to its rest position at or near the center of the housing. In some embodiments, the springs may cooperate with the coil&#39;s magnetic field to return the central magnet array/mass assembly to its rest position. 
     In another embodiment, a first shaft extends into a magnet assembly on a first side while a second shaft extends into the magnet array from a second side. The shafts may be coupled to the magnet assembly on one end while their opposing ends are free. The magnet assembly may incorporate a first mass on one side and be coupled to a second mass on another side. That is, this second embodiment of a linear actuator may employ a split mass to provide haptic output. 
     A coil spring (as opposed to the aforementioned beehive spring) may encircle each shaft. One coil spring may abut a first end cap and the magnet assembly, and in particular the first mass. The second coil spring may abut a second end cap and the second mass. Both shafts may pass through bearings; one bearing may be positioned in each end cap. 
     Multiple coils may be wrapped around the magnet assembly. When the coils are energized, the magnet assembly, shafts, and mass(es) (collectively, “moving portion”) may translate within a housing of the actuator. Such translation may compress the spring on the side of the actuator toward which the moving portion moves. The shafts may slide within their respective bearings to permit such translation. This motion may in turn be conveyed to the housing or frame of the actuator. 
     In the various embodiments described herein, the frame&#39;s motion, and changes in direction of motion, is transmitted to the housing of the actuator as a force. Accordingly, as the frame moves and/or changes direction, the housing experiences forces that cause it to move. This motion may be felt or otherwise sensed by a person holding or otherwise in contact with the actuator; the motion may thus provide a haptic output sensed by the user/wearer. Typically, the greater the momentum of the central magnet array and frame, the greater the force exerted on the housing in a short period of time and the greater the magnitude of the haptic output. 
     Certain embodiments may employ a set of injector magnets positioned on opposing sides or faces of the frame. The injector magnets may be adjacent or otherwise near stabilization rails, which may likewise be magnetic (or, in some embodiments, may be ferritic). Magnetic attraction between the injector magnets and the stabilization rails may prevent the frame from rotating during its lateral motion along the shaft. Further, because the injector magnets and stabilization rails need not touch one another, they may not generate friction that would otherwise oppose the lateral motion of the frame along the shaft. This lack of friction may permit the frame to reach higher velocities in the same amount of travel, thereby generating a greater haptic output than if friction-inducing stabilizing structures were employed. 
     Generally, and as described below, the injector magnets, stabilization rails, and at least portions of the housing may create magnetic return paths that control and/or focus the magnetic flux of the central magnet array and/or the coil. These magnetic return paths may reduce the amount of flux that extends beyond the housing and thereby enhance the magnetic field within the housing that, in turn, may enhance the velocity that the central magnet array may reach within a given period of time or given distance of travel. The injector magnets (described below) may likewise exert an electromotive force on the central magnet array, enhancing or adding to that generated by the coil and thus enhancing the overall operation of the actuator. 
       FIG. 1  generally depicts a sample electronic device  100  that may incorporate a linear actuator, as described herein. The sample electronic device  100  is depicted as a smart phone. It should be appreciated that the sample electronic device  100  is provided as only one example of a device that may incorporate a linear actuator as discussed herein. Other sample devices include tablet computing devices, laptop or other portable computers, input peripherals (such as keyboards, mice, joysticks, track pads and the like), wearable electronic devices, including glasses, watches, health monitoring devices, and so on. 
     Typically, although not necessarily, the sample electronic device  100  may include a number of different components within the exterior housing  110 . Sample components include one or more processing units (which may be multithreaded or multicore), memory and/or other data storage, one or more batteries, physical support structures, sensors (including position, acceleration, gyroscopic, ambient light, motion, audio, and so on), cameras, speakers, microphones, and the like. These components are not illustrated in  FIG. 1  for purposes of simplicity and clarity. 
     Likewise, a user, wearer or other entity may access from one or more input mechanisms from outside the housing  110 . For example, an input button  120  is shown in  FIG. 1 . Touch-sensitive surfaces, such as display  130 , may also function to provide user input. These input mechanisms may be used to provide input to the electronic device  100 . As one example, an input mechanism may be used to acknowledge an alert or other haptic output provided by embodiments of an actuator as described herein. 
       FIGS. 2-6  depict one embodiment of a linear actuator  200 . It should be appreciated that the embodiment shown in  FIGS. 2-6  is one sample embodiment with a sample configuration; alternative embodiments may have different shapes, structures, configurations, components and the like. Accordingly, the figures and associated discussion should be understood as examples, rather than limiting. 
     Turning now to  FIG. 2 , the linear actuator  200  may have a body  210  encompassed by a case  220 . The case  220  may extend to form a bracket  230 , which may connect to a housing  110  of the electronic device  100 . Motion of the moving mass assembly (discussed with respect to  FIGS. 3-6 ) may be transferred to the case  220 , as described below, and through the bracket  230  to the housing  110 . In this manner the moving mass assembly&#39;s motion may create a user-perceptible motion of the housing. Such motion may be selective, affecting only a portion of the housing or concentrated in a portion of the housing  110 , or may broadly affect the housing as a whole. In either event, the linear actuator  200  may thus produce a haptic output that may be used as an alert or notification to a user. 
     The linear actuator  200  may be relatively compact, making it particularly suitable for use in small electronic devices. In one embodiment, the volume of the actuator (e.g., the volume of the case and all space inside the case) is no more than 568 cubic millimeters. 
     A stiffener  240  may be affixed or otherwise placed on the bracket  230 . The stiffener  240  may be adhered, welded, mechanically fastened, or otherwise connected to the bracket  230 . The stiffener  240  may strengthen the bracket  230 . By stiffening the bracket  230 , the stiffener  240  may permit more motion of the moving mass assembly and associated frame to be transmitted to the housing  110  to which the bracket  230  is affixed. 
     A flex  250  may extend through the case  220  to provide electrical connections for components within the case  220 . Some embodiments may omit the flex  250  and may instead provide electrical contacts on the exterior of the case  220 , or may use a rigid connector in place of the flex  250 . 
     The case  220  may be formed from multiple sidewalls that are attached or affixed to one another or may be formed as an integral unit that is bent or otherwise formed into the shape of the case  220 . As shown in  FIG. 2 , protrusions  270  formed on certain sidewalls of the case may clip or snap, be laser-welded or otherwise positioned/affixed into apertures formed on adjacent sidewalls of the case, thereby maintaining structural integrity during operation. These protrusions  270  mechanically interlock the sidewalls of the case, thereby assisting in constraining the sidewalls with respect to the housing. As also shown in  FIG. 2 , the bracket  230  may be unitarily formed with at least one sidewall of the case  220 , although in alternative embodiments the bracket  230  may be separately formed and affixed to the case. 
       FIG. 3  is a three-quarters perspective view of the linear actuator  200 , with a top, front and left sidewall of the case  220  removed to expose internal components. As shown in  FIG. 3  and also in  FIG. 6 , a coil  300  encircles a central magnet array  310 , which may form a moving mass assembly in conjunction with a frame  330 . The coil  300  may be energized by transmitting a current along the length of the wire forming the coil; the direction of the current flow determines the direction of the magnetic flux emanating from the coil in response to the current. As discussed later, passing a current through the coil may cause the central magnet array  310  (and thus the assembly) to move along a shaft  320 . In order to prevent the central magnet array  310  from being attracted to the shaft  320 , which could increase friction between the two and thereby increase the force necessary to move the central magnet array  310  and frame  330 , the shaft  320  may be formed from a non-ferritic material such as tungsten, titanium, stainless steel, or the like. 
     As depicted in  FIGS. 3 and 4 , the coil  300  is positioned within a frame  330  that holds the central magnet array  310 , but is not affixed to the coil. Rather, an air gap separates the coil  300  from the central magnet array  310  and the frame  330  is free to move with respect to the coil  300 , which is generally stationary. Further, the frame  330  generally moves with the central magnet array as part of the moving mass assembly. As illustrated in  FIGS. 3 and 4 , the frame may have an aperture formed therein of sufficient size to contain the coil  300 . Even when the frame and central magnet array are maximally displaced within the case  220  (e.g., to one end or the other of the shaft  320 ), the coil  300  does not abut any portion of the frame  330 . It should be appreciated that the coil  300  remains stationary in the case  220  while the frame  330  and central magnet array move, although in other embodiments the coil  300  may move instead of, or in addition to, the frame and/or central magnet array. By keeping the coil stationary, it may be easier to provide interconnections for the coil, such as between the coil and the flex, and therefore reduce the complexity of manufacture. 
     As shown to best effect in  FIGS. 4 and 5 , the central magnet array  310  may be formed from at least two magnets  400 ,  410  of opposing polarities. A center interface  420  may be formed from a ferritic or non-ferritic material, depending on the embodiment. A ferritic material for the center interface  420  may enhance the overall magnetic field generated by the central magnet array  310 , provide at least a portion of a return path for magnetic flux and thus assist in localizing the flux within the case  220 . In many embodiments, the magnets  400 ,  410  are neodymium while the frame is tungsten. This combination may provide a strong magnetic field and a dense mass, thereby yielding a high weight per volume structure that may be used as the moving part of the linear actuator  200 . 
     As shown to best effect in  FIGS. 5 and 6 , the magnets  400 ,  410 , frame  330 , and center interface  420  may have a hole formed therethrough to receive the shaft  320 . As also illustrated in  FIGS. 5 and 6 , the shaft generally does not touch the magnets  400 ,  410 , frame  330  or shaft  320 , all of which are supported on the shaft by the jewel bearings  430  in order to reduce friction. 
     Generally, when the coil  300  is energized, it creates a magnetic field. The opposing polarities of the magnets  400 ,  410  generate a radial magnetic field (as illustrated by the radial magnetic field  500  in  FIG. 5 ) that interacts with the magnetic field of the coil. The Lorentz force resulting from the interaction of the magnetic fields with the current through the coil moves the central magnet array  310  and frame  330  along the shaft  320 , insofar as the coil is fixed with respect to the case of the actuator. Reversing current flow through the coil  300  reverses the Lorentz force, and thus the force on the central magnet array and frame. Thus, the array and frame may move in both directions along the shaft, depending on the direction of current flow through the coil. Further, the injector magnets may also create a flux through the coil, thereby resulting in, or enhancing, a Lorentz force. 
     Accordingly, when the coil is energized, the central magnet array  310  will slide along the shaft  320  in one direction or its opposite, depending on the polarity of the field. If the current through the coil  300  is sufficiently high, the central magnet array and associated frame  330  will move rapidly and reach a high velocity. If the coil is de-energized before the central magnet array moves too far (for example, before the central magnet array no longer underlies the coil), then the Lorentz force exerted on the central magnet array is reduced to zero and the frame/magnet array may continue to move. 
     In some embodiments, after a target velocity or displacement is reached the coil may be energized in a direction opposite its energization. This may cause the generated magnetic field to exert a force in a direction opposite the initial motion of the central magnet array and/or frame, thereby slowing down or braking the moving mass assembly. This may be useful to control or limit oscillation, especially at or near a resonance frequency of the linear actuator  200 , or to maintain such a resonance frequency. Accordingly, the coil  300  can not only “pull” but can also “push” the moving mass assembly, hereby imparting motive force in two opposing directions through selective application of the coil&#39;s magnetic field. This may permit fine control over motion and/or velocity of the frame  330  and central magnet array  310 , both in multiple directions and when compared to other linear actuators. 
     Turning now to  FIG. 4 , the jewel bearings  430  encircle the shaft  320  and are affixed to the frame  330 , thereby forming an interface between the shaft and frame. As shown in  FIG. 4 , the jewel bearings  430  have a generally convex inner surface to minimize contact with the shaft  320 . This, in turn, may reduce or minimize friction between the jewel bearings  430  and shaft  320 , such that a higher peak velocity may be reached in a set time by the frame  330  and central magnet array  310  than might be achieved if the bearings had greater surface contact with the shaft. The jewel bearings  430  are affixed to the frame  330  and move with the frame along the shaft  320 . 
     It should be appreciated that the jewel bearings  430  may have other surface configurations designed to reduce contact and/or friction between the bearings and the shaft and to reduce the likelihood of binding and/or friction resulting from misaligned components. For example, the inner surface of the bearings may be angled, elliptical, or the like. In addition, bearings other than jewel bearings  430  may be used in different embodiments. 
     The shaft  320  has been generally discussed with respect to the motion of the central magnet array  310  and frame  330 . The shaft  320  may be affixed to opposing sidewalls of the case  220 , as generally shown in  FIG. 5 . As also shown in  FIG. 5 , in some embodiments the shaft  320  may extend through one or more sidewalls of the case  220 . In other embodiments, the shaft  320  may be fully contained within the case. 
     Generally, the shaft passes through the central magnet array  310 , including the center interface  420  and both magnets  400 ,  410 . The shaft  320  likewise passes through the frame  330 , which is affixed to the central magnet array (and, in some embodiments, more particularly to the magnets  400 ,  410 ). The shaft extends through a spring  510  at either of the shaft&#39;s ends before passing through the case  220 , or otherwise being affixed to the case  220 . 
     Typically, although not necessarily, the shaft  320  defines a central axis along one direction of the linear actuator  200 . As illustrated in  FIG. 5 , the shaft  320  is centrally positioned within the linear actuator  200  and runs parallel to a longitudinal axis of the linear actuator  200  (e.g., left to right in the position shown in  FIG. 5 ). The shaft need not be coincident with a center axis of the linear actuator  200 , but in some embodiments such coincidence facilitates even distribution of mass about the shaft in order to maximize a haptic output of the linear actuator  200 . 
     As previously mentioned and as also illustrated in  FIG. 5 , each end of the shaft  320  passes through a spring  510 . In the embodiment shown in  FIGS. 2-6 , each spring  510  is a double beehive spring. In many embodiments, the double beehive spring shape serves multiple purposes, including: providing a large working travel range while collapsing to a small size, thereby enhancing overall possible displacement of the moving mass assembly; distributing stresses, thereby enabling the springs themselves to be smaller than may otherwise be the case; and/or centering the spring ends on both an end plate and the bearing, thus avoiding or reducing friction resulting from coils rubbing on the shaft or housing. 
     The double beehive springs  510  typically abut or are affixed to both an inner surface of the case  220  and a side of the frame  330 . Thus, as the frame  330  and central magnet array  310  move along the shaft in response to a Lorentz force generated through the interaction of the magnetic flux of the central magnet array and the current through the coil, one double beehive spring  510  structure expands and one compresses from its nominal rest state. When fully compressed, the windings of the double beehive spring  510  lie flat within a plane. The pitch between the windings of the spring may vary in order to accommodate the windings in a flat, coplanar position upon compression. Further, by sizing both springs to always be in compression, the springs act in tandem to double the spring rate. Additionally, the compression springs may not require attachment or affixing to a sidewall or other part of the actuator, thereby avoiding possible complexities, variability and stresses caused by such attachment. 
     Accordingly, the double beehive spring  510  may be space-efficient and designed to occupy a minimum volume when fully compressed. By reducing the volume or the springs when in a compressed state, or at least their thickness along a dimension parallel to the shaft  320 , the distance the moving mass assembly may move along the shaft, the size of the central magnet array  310 , and/or the amount of mass may be increased when compared to a spring that does not collapse to place its windings within a plane. 
     The springs  510  may prevent the frame  330  from impacting a sidewall of the case  220  when the frame  330  moves at a high velocity or enjoys a large displacement. Further, the coil  300  may be energized in order to move the frame  330  and central magnet array  310  along the shaft  320 , thereby further compressing one of the springs  510 . (It should be appreciated that the springs  510  are always in compression in the depicted embodiment). Current may be maintained through the coil  300  to bias the central magnet array  310  and frame  330  into a displaced position, thereby further compressing a spring  510  and storing energy in the spring. When current to the coil is terminated, the external force exerted on the central magnet array  310  may likewise terminate. In response the spring  510  may expand, propelling the moving mass assembly away from the spring  510  and along the shaft  320 . Current may flow through the coil  300  at the appropriate time to impart more motive force to the moving mass assembly, thereby increasing the velocity of the assembly and enhancing the haptic output generated by this moving element. Accordingly, the springs  510  may be used to convert kinetic energy to potential energy, thereby enabling the actuator to achieve a greater amplitude of momentum across multiple cycles of operation, and so create an enhanced or increased haptic sensation for a user or wearer when compared to the haptic sensation that may be (at least initially) experienced if the moving mass assembly is in the neutral, or rest, position as illustrated in  FIG. 5 . 
     Embodiments of a linear actuator  200 , as described herein, may include one or more injector magnets  600 , as shown in  FIGS. 2-6  generally and specifically discussed with respect to  FIG. 6 . Each injector magnet  600  may be affixed to a side of the frame  330 , and may be positioned such that a back side of the injector magnet is near an outer surface of the coil  300 , but separated therefrom by a gap (which may be an air gap). An outer surface of each injector magnet  600  may be curved or otherwise arcuate, or may be angled, taper to a point, elliptical, or the like; the injector magnets may likewise be shaped to increase or decrease the stabilization provided by the injector magnets, as generally discussed below. 
     A pair of rails  610  may be affixed to an interior of the case  220  and positioned such that each rail  610  is generally near an injector magnet  600 . The rails  610  may be magnetic, in which case their polarities match the polarities of the nearby injector magnets (e.g., magnetic attraction exists between each rail  610  and the nearby injector magnet). Alternatively, the rails  610  may be made of a ferritic material but may not be magnets themselves, such that the injector magnets  600  are attracted to the rails  610 . In alternative embodiments, the rails  610  may be magnetic and the injector magnets may be replaced with ferritic masses. The arrows shown on the injector magnets and rails in  FIG. 5  indicate the direction of magnetic flux through the magnets and rails, respectively. 
     The injector magnets  600  serve three purposes, namely to stabilize the moving mass assembly during motion along the shaft, such that the assembly does not rotate substantially about the shaft, to provide additional flux through the coil  300  (and so increase the motive force acting on the moving mass assembly) and also to provide a magnetic flux path for the magnetic fields generated by the coil and central magnet array. The first purpose will be initially discussed. It should be appreciated that the double-headed arrow shown in  FIG. 6  illustrates potential rotational motion of the central magnet array and frame about the shaft; this is the rotational motion that is resisted by the injector magnets and rails  610 . 
     The convex shape of the injector magnet  600  helps ensure that the outermost part of the injector magnet  600  (e.g., the part closest to the rail  610 ) is attracted to the rail  610 . Further, if the frame  330  assembly rotates or spins about the shaft  320  during movement such that it is angularly misaligned, the convex shape of the exterior portion of the inject magnet reduces the likelihood that the injector magnet will be attracted to any ferritic or magnetic portion of the case  220 , as compared to an injector magnet having a rectangular or square cross-section. Rather, the attraction between the injector magnet  600  and rail  610  tends to maintain the injector magnet&#39;s alignment with respect to the rail  610  in such a manner that the injector magnet remains substantially parallel to the rail  610 , in the position shown in  FIG. 6 . Thus, even if the frame and injector magnets become rotationally misaligned about the shaft, the injector magnets  600  operate to realign the frame, central magnet assembly and themselves with respect to the rails  610  and thus with respect to the shaft. The injector magnets essentially provide roll stability for the moving parts of the actuator and may permit implementation of non-axially-symmetric actuator sections that are stable without requiring addition mechanical constraints, which generally may occupy volume within the actuator and/or may add friction to the system. 
     This self-realigning action may prevent the frame  330  from binding on the shaft  320  and may maintain the frame and central magnet array  310  in a position with respect to the shaft that is configured for low-friction and/or lower-power motion of the frame along the shaft. Further, because the injector magnets  600  do not physically contact the rails  610 , there is no friction between the two, thereby reducing the overall friction of the system while maintaining the roll stability and self-aligning features of the moving parts of the actuator (e.g., injector magnets  600 , frame  330 , and central magnet array  310 ). 
     Because the strength of a magnetic field varies non-linearly with the distance between two magnets, or a magnet and a ferritic material, the stabilization provided by the injector magnets  600  and rails  610  is non-linear. That is, the closer the injector magnets  600  are to their stable position (e.g., the position illustrated in  FIG. 6 ), the stronger the force maintaining them in that stable position. Accordingly, even if the moving parts of the actuator become misaligned, any oscillation or motion that brings the injector magnets  600  near the rails  610  will cause the injector magnets  600 , and thus the frame and so on, to quickly return to the stabilization position. 
     It should be appreciated that alternative embodiments may use a repulsive magnetic force, rather than an attractive magnetic force, to center the moving parts of the linear actuator  200  and prevent roll around the shaft  320 . For example, magnetic rails  610  of polarities that oppose the polarities of the injector magnets  600  may be placed at the top and bottom of the case, substantially in vertical alignment with the injector magnets or along the joinder of the top of the case to a sidewall. Such magnetic rails  610  may repulse the injector magnets and cooperate to maintain the injector magnets in a stable position, so long as the strength of the magnetic fields is appropriately configured. Accordingly, embodiments are not limited to employing an attractive magnetic force to provide centering and stabilization. 
     The case  220  may be formed entirely from non-ferritic materials in certain embodiments, while in other embodiments the case  220  may be formed from a combination of ferritic and non-ferritic material. As one example and returning to  FIG. 2 , the case  220  may have a segment  280  that is ferritic in order to provide a return path through the case  220  for magnetic flux. The segment  280  may take the form of a cross as illustrated in  FIG. 2 . Further, the segment  280  may extend downwardly along sidewalls of the case  220  to enhance the flux return pathways. As another example, the segment  280  may be a stripe running substantially parallel to the shaft and may extend downwardly to the points at which the case  220  is affixed to the shaft. 
     The flux return path serves to contain the magnetic flux and prevent leakage substantially beyond the case  220  of the linear actuator  200 . For example, the radial magnetic field  500 , shown in  FIG. 5 , may extend through and be bound by the ferritic portions of the case  220  to complete a loop to the outer edges of the magnets  400 ,  410 . Another sample flux return path may be formed through the injector magnets  600 , the rails  610 , and along the ferritic parts of the case  220 . Generally, then, the case  220  may be configured to facilitate the formation of magnetic circuits that define flux return paths. These flux paths may also facilitate efficient transfer of energy to the moving mass, thereby increasing its velocity and haptic output during operation. 
     In some embodiments, the frame  330  is formed from a ferritic tungsten alloy to create another flux return path and also maintain a volume-to-mass efficiency (e.g., high mass per unit volume). 
       FIGS. 7-16  depict various views of another embodiment of a linear actuator  700 . Generally the linear actuator  700  shown in  FIGS. 7-10  operates to provide a haptic output in a fashion similar to that previously described with respect to  FIGS. 1-6 . That is, an electromotive force acts to move a mass linearly within a housing; the motion of the mass may be perceived by a user as a tap or other haptic output. The electromotive force may be generated by one or more coils and one or more magnets, as described above. 
     Here, however, the structure and certain specifics of operation may differ from previously described implementations. Particular details of the linear actuator  700  will now be given with respect to  FIGS. 7-16 , and initially with respect to  FIGS. 7-10 . 
       FIG. 7  depicts an exploded view of a linear actuator  700  and  FIG. 8  depicts an assembled view of the linear actuator.  FIG. 9  illustrates a first cross-sectional view of the linear actuator  700 , while  FIG. 10  illustrates a second cross-sectional view. The overall structure and configuration of the linear actuator  700  is initially discussed with respect to these figures. 
     A housing  702  forms an exterior of the linear actuator  700  and protects internal components. The housing  702  includes a first housing section  704  and a second housing section  706 . Generally, the second housing section  706  forms five of the six housing walls while the first housing section  704  forms the sixth housing wall, although this is not required or necessary and may vary between embodiments. Housing connectors  708   a ,  708   b  may be attached to opposing ends of the housing and may affix the housing to an electronic device incorporating the linear actuator  700 . The housing connectors  708   a ,  708   b  may be welded, chemically bonded, mechanically fastened, or otherwise affixed to the housing  702  (and typically the second housing section  706 ). The housing  702  and its attendant sections  702 ,  704  may be formed from any suitable material, and are often formed from a metal. 
     A magnet assembly  710  includes a series of three magnets  712 A,  712 B,  712 C, spacers  714 , and an end mass  719  (and, in some embodiments, a main mass  726 ). Adjacent magnets are separated from one another by spacers  714 . That is, first magnet  712 A is separated from second (or center) magnet  712 B by a first spacer, which in turn is separated from third magnet  712 C by another spacer  714 . In some embodiments the spacers may be ferromagnetic and/or may have relatively high magnetic permeability. In other embodiments the spacers may have low magnetic permeability. Further, the spacers may serve to redirect a lateral magnetic field (e.g., a field parallel to the center axes of the shafts  723 A,  723 B) or flux generated by the magnets  712 A,  712 B,  712 C as a radial field or flux (e.g., a field transverse to the longitudinal cylindrical axes of the shafts  732 A,  732 B, as discussed below). Thus, the spacers may act as field return elements, although this again is not required or necessary. Each adjacent pair of the magnets  712 A,  712 B,  712 C may have opposing polarities. 
     A pair of rails  716  receives the series of magnets  712 A,  712 B,  712 C and spacers  714  between them. The rails  716  may be C-shaped in some embodiments and as illustrated in  FIGS. 7 and 8 ; the legs of the C-shaped rails fit about outer edges of the magnets and spacers. The spacers and magnets may be angled, stepped, or otherwise dimensioned so that their outer edges fit within the rails. Generally, the rails  716  hold the magnets and spacers in alignment and abutting one another. 
     The rails  716  may also surround an end mass  719  that abuts the first magnet  712 A. The end mass may increase the force of a haptic response (and thus its perceptibility) provided by the linear actuator  700 , presuming that acceleration of the moving portion of the linear actuator is equal when the end mass  719  is present and when it is not. The motion of the moving portion is described in more detail, below. 
     Coils  720 A,  720 B may encompass portions of the series of magnets  712 A,  712 B,  712 C and the spacers  714 . The coils  720 A,  720 B may further encircle the rails  716 , or portions thereof. Typically, the coils are positioned with respect to the magnet assembly  710  such that a center of each coil is substantially aligned with a spacer  714  when the linear actuator  700  is at rest (e.g., the magnet assembly  710  is in a default position). In such an alignment, magnetic flux or fields generated by the coils are not countered, enhanced, diminished or otherwise affected by an offset between either coil and the amount of each magnet overlapped o encircled by the coil. That is, because each coil encircles substantially the same amount of each of two adjacent magnets, there is no positional bias between coils and magnets that would impact the generated electromotive force, either positively or negatively. 
     It should be noted that the magnets may be off-center (e.g., not evenly spaced between) the end mass  719  and the main mass  726 . Accordingly, the magnets and coils  720 A,  720 B are not centered about a midpoint of the housing. Further, in some embodiments the end mass and the main mass may be formed from different materials, such that they have approximately the same weight and/or mass as one another, despite being different sizes. In other embodiments, the main and end masses may be formed from the same material, such as tungsten. 
     A flexible circuit  722  routes electrical signals (power, control, and/or data) to the coils from a processing unit or similar element of an electronic device. The processing unit is typically positioned outside the linear actuator  700 . As discussed in more detail below, electrical end contacts  738 A,  738 B may route such signals to the flexible circuit from an exterior of the linear actuator  700 . It should be appreciated that a processing unit or like element may be housed within the linear actuator in some embodiments, and thus provide localized control. 
     An array cap  724  slides over and end of the magnet assembly  710 , and more particularly over part of the rails  716  and end mass  719 . In some embodiments the array cap  724  may be longer, such that it covers at least a portion of one or more magnets and/or spacers. The array cap  724  typically has end walls, as shown in  FIG. 7 , that abut ends of the spacers  714  and/or the end mass  719  when the array cap  724  is fitted to the magnet assembly  710 . Accordingly, the array cap  724  may prevent the components of the magnet assembly from sliding apart and/or out of the rails, at least at one end of the assembly. 
     A main mass  726  couples to an end of the magnet assembly  710  opposing the end over which the array cap  724  fits. The main mass  726  accepts ends of the rails  716  through C-shaped (or rail-shaped) apertures  727  formed in the mass. These apertures are shown to best effect in  FIG. 7 . The rails slide into the apertures in the main mass  726  until the main mass contacts the third magnet  712 C. Accordingly, the main mass may prevent the series of magnets  712 A,  712 B,  712 C and spacers  714  from shifting or decoupling, much as does the array cap  724  at the opposite end of the magnet assembly  710 . 
     Injector magnets  728 A,  728 B are affixed to opposing sides of the main mass  726 . As with the injector magnets  600  of the prior embodiment, these injector magnets  728 A,  728 B serve three purposes. They: 1) stabilize the moving portion assembly during motion along the shaft, such that the assembly does not rotate substantially about the shaft; 2) provide additional flux through the coils  720 A,  720 B (and so increase the motive force acting on the moving portion); and 3) and facilitate a magnetic flux path for the magnetic fields generated by the coil and central magnet array. Insofar as the injector magnets  728 A,  728 B operate in fashions similar to already-described injector magnets  600 , they are not described in more detail herein. 
     First and second shafts  732 A,  732 A may extend into the magnet assembly  710  and the main mass  726 , respectively. More particularly, a first shaft  732 A extends through the array cap  724  and into the magnet assembly  710 , typically being received by the end mass  719 . Likewise, the second shaft  732 B may extend into the main mass  726  but generally does not pass completely through the main mass (although it may, in alternative embodiments). The shafts may not extend into any of the magnets in the magnet assembly  710 , as that would require forming a recess in the magnets. Such recesses may be difficult to form without cracking any of the series of magnets  712 A,  712 B,  712 C. Further, hollowing or partially hollowing the magnets in this fashion may reduce the magnetic field of the magnets and thus impact the electromotive force that moves the magnet assembly  710  and masses  724 ,  726  when the linear actuator  700  operates. This, in turn, may reduce the force and haptic output of the linear actuator. 
     Ends of the shafts  732 A,  732 B that do not extend into the magnet assembly  710  or main mass  726  pass through bearings  734 A,  734 B and are received in end caps  736 A,  736 B. The end caps  736 A,  736 B each define an interior void space in which the ends of the shafts rest and may be affixed to the housing, or otherwise may be held immobile with respect to the housing. The interior void spaces are sufficiently large that the ends of the shafts do not touch walls of the void spaces. Accordingly, the shafts may translate along their major (e.g., longitudinal cylindrical) axes during operation of the linear actuator  700 , as described below. In certain embodiments and as depicted herein, the void space(s) may extend through an entirety of the end cap. 
     A shaft spring  730 A,  730 B surrounds each respective shaft  732 A,  732 B. The first shaft spring  730 A surrounds first shaft  732 A; one end of the first shaft spring  732 A is received within an aperture in the first end cap  736 A. This same aperture houses the first bearing  734 , discussed below. Likewise, the first shaft  732 A passes through the aperture and into the interior void space of the first end cap  736 A. Similarly, the second shaft spring  730 B encircles the second shaft  732 B and is received in an aperture of the second end cap  736 B that leads to that end cap&#39;s interior void space. The second bearing  734 B is received within the second aperture. The first and second shaft springs may be constrained at one end by a mass (e.g., either the end mass or main mass) and at another end by an end cap and/or a respective bearing. Thus, as the masses and series of magnets move (and the shafts move), the springs are compressed between an end cap and a mass. 
     The shaft springs  730 A,  730 B are configured such that their start and end points (e.g., the ends of the springs) align with one another. That is, the start and end points of each spring have a substantially zero degree angular offset from one another when viewed from either end of the spring. This may reduce torque generated by the shaft spring as the spring compresses, and consequently reduce torque on the moving portion of the linear actuator  700 . Certain embodiments may utilize springs that do not have ends aligned in this manner. In some embodiments the shaft springs may be leaf springs rather than coiled springs, as shown. The shaft springs (including if leaf springs) may be welded or otherwise affixed to the end caps  736 A,  736 B in certain embodiments, although they may not be so affixed in others. Likewise, the shaft springs may be affixed on their other ends to adjacent structures. 
     Additionally, the direction in which the first shaft spring  730 A is wound opposes the direction of the second shaft spring&#39;s  730 B winding. By using springs having opposing windings, any torque generated by one shaft spring and exerted on the moving portion of the linear actuator (e.g., the shafts  730 A,  730 B, the array cap  724 , the magnet assembly  710 , and/or the main mass  726 ) may be substantially or completely countered by the torque generated and exerted by the other shaft spring. Accordingly, spring torque (if any) in the system of the linear actuator  700  may be reduced or offset. 
     The end caps  736 A,  736 B have been previously mentioned. Each end cap  736 A,  736 B defines an aperture leading to an interior void space. A bearing  734 A,  734 B is disposed within each such aperture. As previously discussed, the interior void space is sized to accept an end of a spring without the spring end contacting a wall of the interior void space while the linear actuator  700  is at rest. 
     The end caps  736 A,  736 B may be affixed to sidewalls of the housing  702 . In some embodiments, the end caps are welded, mechanically coupled, chemically bonded, or otherwise so affixed. In other embodiments, the end caps may be friction-fitted within the housing. In still other embodiments, the end caps may abut sidewalls of the housing but are not affixed thereto. 
     End contacts  738 A,  738 B pass through bores formed in the first end cap  736 A and through a hole in the base of the housing  702 . The end contacts  738 A,  738 B may abut a contact patch formed on a substrate beneath the housing base. The end contacts  738 A,  738 B may thus route power, control signals, and/or data signals in and out of the linear actuator  700 , and particularly through the flexible circuit  722  to the coils  720 A,  720 B. In some embodiments the end contacts  738 A,  738 B may be springs while in others they may be pogo pins or the like. Such compliant end contacts may absorb some tolerance or offset between the actuator  700  and the contact patch on the substrate, thereby increasing reliability of the associated electrical signals. 
     Stabilization rail magnets  744 A,  744 B may be affixed to the housing  702 , and particularly to the sidewalls of the second housing section  706 . The stabilization rail magnets  744 A,  744 B may be affixed in the same position on opposing sidewalls. Generally, the stabilization rail magnets  744 A,  744 B act as do the stabilization rails  610 , which were previously discussed with respect to other configurations of a linear actuator. 
     A coil shim  740  may be placed within the housing  702  and affixed to the housing. The coil shim  740  generally maintains proper spacing of the coils  720 A,  720 B, particularly with respect to the magnets  712 A,  712 B,  712 C and/or housing  702 . The coil shim  740  may ensure that the coils do not physically touch either the housing or the magnets, for example. In certain embodiments, the coil shim  740  may be electrically nonconductive. 
     A support pad  742  may be placed between the base of the housing  702  and a substrate supporting the housing (for example, an internal structural component of an electronic device, or a housing of an electronic device). The support pad may absorb residual or unwanted motion of the linear actuator  700  with respect to the housing, thereby preventing or reducing rattles or other undesirable noise. The support pad  742  may also act as a shim for the linear actuator  700  with respect to the substrate. 
       FIG. 11  is a cross-sectional view taken along line  11 - 11  of  FIG. 10  and through the end contacts  738 A,  738 B and the end cap  736 A. As shown, the end contacts  738 A,  738 B may extend through the end cap  736 A and an aperture in the housing  702  to contact an electrical contact pad, as previously discussed.  FIG. 11  also illustrates an end of the first shaft  732 A received in the interior void space  1000 . As can be appreciated from the figure, the diameter of the shaft  732 A is less than the diameter of the interior void space  1000 . 
       FIG. 12  is a cross-sectional view taken along line  12 - 12  of  FIG. 10 , through the assembly cap  724 , magnet assembly  710  and first shaft  732 A. The assembly cap encircles the rails  716 , which in turn hold the end mass  719 . The first shaft  732 A extends into the assembly cap and the end mass. As shown, the end mass  719  has reduced thicknesses at its sidewalls so that the sidewalls can fit within the interior of, and be held by, the rails  716 . 
       FIG. 13  is a cross-sectional view taken along line  13 - 13  of  FIG. 10 , through a coil  720 A and the magnet assembly  710 . This view illustrates how the coil encircles the rails  716  and the magnet  712 C. The flex  722  is shown above and contacting the coil. As with the end mass  719  shown in  FIG. 12 , the magnet  712 C (and all magnets in the magnet assembly) have reduced thicknesses at its sidewalls in order to fit within the rails  716 . 
       FIG. 14  is a cross-sectional view taken through the main mass  726  and along line  14 - 14  of  FIG. 10 . This cross-section illustrates the rails  716  received within the main mass  726 . 
       FIG. 15  is a cross-sectional view taken through the main mass  726  and second shaft  732 B, along line  15 - 15  of  FIG. 10 . This cross-sectional view illustrates the relative positions of the injector magnets  728 A,  728 B and stabilization rail magnets  744 A,  744 B relative to the shaft. Essentially, the injector magnets  728 A,  728 B and stabilization rail magnets  744 A,  744 B are aligned with one another and the shaft. 
       FIG. 16  is a cross-section view of the second shaft  732 B received within the second bearing  734 B and the second end cap  736 B, taken along line  16 - 16  of  FIG. 10 . The second bearing  734 B permits the second shaft  732 B to move along the long axis of the actuator  700  while constraining motion in any other direction. The size of the interior void space defined within the second end cap  736 B also permits such motion. The same is true of motion of the first shaft  732 A with respect to the first bearing  734 A and first end cap  736 A. 
     Now that the overall structure of the linear actuator  700  has been described, its operation will be discussed. 
     Generally, the magnet assembly  710 , end mass  726 , and first and second shafts  732 A,  732 B form the moving portion of the linear actuator  700 . That is, these elements may translate toward either end cap  736 A,  736 B when the haptic actuator  700  operates. Typically, the various parts of the moving portion move together and without separating or changing distances from one another (e.g., they move as a unitary piece). 
     Similar to previously-discussed embodiments, coils  720 A,  720 B generate a magnetic field and flux that may drive magnets  712 A,  712 B,  712 C toward one of the two end caps  736 A,  736 B of the linear actuator  700 . (Likewise, flux return paths for the linear actuator  700  may be generally similar to those discussed with respect to  FIGS. 1-6 , above, bearing in mind differences in the coil and magnet numbers and structures.) The direction of motion varies with the direction of current through the coils and it should be appreciated that current may flow in the same direction through the coils or in opposing directions. The magnets  712 A,  712 B,  712 C move accordingly, thereby forcing the rest of the moving portion to move. Insofar as the shafts  732 A,  732 B are constrained by the bearings  734 A,  734 B, the moving portion moves only laterally along the length of the linear actuator  700 . That is, the moving portion moves in a direction of the longitudinal cylindrical axis of the shafts  732 A,  732 B. The coils, taken collectively, are one example of an electromagnetic structure. 
     As the moving portion moves, one of the two springs  730 A,  730 B compresses. For example, as the moving portion moves toward the first end cap  736 A, the first spring  730 A translates further into the first end cap&#39;s interior void space  1000  and the array cap  724  translates closer to the first end cap  736 A. This compresses the first spring  730 A between the first end cap and the array cap. Similarly, motion of the moving portion towards the second end cap  736 B compresses the second spring  730 B between the second end cap and the main mass  726 . 
     When current ceases flowing through the coils  720 A,  720 B (or other electromagnetic structure), the electromotive force ceases acting on the magnet assembly  710 . Accordingly, there is no force driving the moving portion towards either end cap  736 A,  736 B. Thus, the compressed shaft spring will decompress, pushing the moving portion back towards its initial, rest location. For example, shaft spring  730 A may expand (presuming the moving portion moved toward the first end cap  736 A), pushing on array cap  724  to drive the moving portion back towards a center of the linear actuator  700 . The second shaft spring  730 B may prevent over-travel of the moving portion. Thus, the two shaft springs  730 A,  730 B cooperate to center (or re-center) the moving portion within the linear actuator  700 . The springs may similarly cooperate to re-center the moving portion when the moving portion travels toward the second end cap  736 B. 
     By repeatedly and rapidly energizing and de-energizing the coils  720 A,  720 B, the moving portion of the linear accelerator (such as magnet assembly  710 ) may be pushed toward one of the end caps and then returned to center. Further, the end cap towards which the moving portion is driven may alternate, thereby forcing the moving portion to oscillate laterally. This lateral oscillation may be perceived by the user as a haptic output. Further, the coils may be energized separately or simultaneously, depending on the number of different actuation stages desired. For example, both coils may be initially energized to begin motion of the moving portion. Once the moving portion moves to a certain degree, only one coil may be energized, or both coils may be again energized. 
     Typically, the motion of the moving portion is not so great that the shafts  732 A,  732 B impact any part of the end caps or housing. The shaft springs  730 A,  730 B may be sized and configured to fully or substantially fully compress before the shafts can travel far enough to impact any surface, for example. In other embodiments the shafts may be prevented from impacting a surface by appropriately controlling current through the coils  720 A,  720 B. 
     Although embodiments have been described herein as having two coils and three magnets, it should be appreciated that more or fewer magnets and/or coils may be used. That is, a linear actuator may have a different number of activation (and actuation) stages than described herein. Likewise, some embodiments may have a single shaft extending between end caps. As yet another option, cross-sections of the shafts (or just one shaft, or the single shaft in a single-shaft embodiment) may vary. As yet another option, some embodiments may use pogo pins in lieu of one or more springs. 
     Although embodiments have been described herein with respect to particular structures, circuits and operations, it should be appreciated that alternative embodiments may vary any or all of the foregoing. For example, more than two magnets may be used to form the central magnet array. Likewise, multiple coils may be used to enhance electromotive force operating on the central magnet array. The width and/or shape of either or both of the central magnet array and the coil may be varied to adjust or change a force vs. distance profile of the actuator. In still other embodiments, additional magnets may be placed at either end of the case, such that the central magnet array and/or frame pass between these additional magnets while moving. The additional magnets may be polarized to provide a restoring force that assists in moving the frame and/or array back to its rest position. In still other embodiments, the coil may be flat (e.g., planar), rather than wound around the central magnet array. 
     Accordingly, the proper scope of protection is defined by the appended claims and is not limited to any particular example set forth herein.

Metadata:
Filing Date: 20160908
Publication Date: 20200218
Grant Date: 20200218
Priority Date: 20150908
Inventors: DEGNER, BRETT W.
NARAJOWSKI, DAVID H.
HARLEY, JONAH A.
GARVER, ALYSSA J.
Assignee: APPLE INC
CPC Classifications: [{"code": "H02K33/16", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02K1/34", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02K33/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02K33/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02K7/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02K35/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02K7/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02K33/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02K35/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02K33/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02K33/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02K1/34", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02K7/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02K33/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02K35/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02K35/02", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 57104175