PATENT DOCUMENT

Publication Number: US-9928950-B2
Application Number: US-201315025254-A
Country: US
Kind Code: B2

Title: Polarized magnetic actuators for haptic response

Abstract:
A polarized electromagnetic actuator includes a movable armature, a stator, and at least one coil wrapped around the stator. At least one permanent magnet is disposed over the stator. When a current is applied to the at least one coil, the at least one coil is configured to reduce a magnetic flux of at least one permanent magnet in one direction and increase a magnetic flux of at least one permanent magnet in another direction. The movable armature moves in the direction of the increased magnetic flux.

Claims:
What is claimed is: 
     
       1. A polarized electromagnetic actuator, comprising:
 a stator including two tines extending out from the stator; 
 a movable armature disposed over the two tines of the stator; 
 a first stabilizing element connecting the movable armature and the stator; 
 a second stabilizing element connecting the movable armature and the stator; 
 a first coil positioned around one tine; 
 a second coil positioned around the other tine; 
 a first permanent magnet disposed over the stator between the two tines, wherein a magnetic flux of the first and the second coils increases a magnetic flux of the first permanent magnet in one direction to produce motion in the movable armature; and 
 a second permanent magnet disposed over the stator between the two tines; 
 wherein 
 the first stabilizing element is disposed around a first end of the stator and a first end of the moveable armature; and 
 the second stabilizing element is disposed around a second end of the stator and a second end of the moveable armature. 
 
     
     
       2. The polarized electromagnetic actuator as in  claim 1 , further comprising a pivot disposed between the permanent magnet and the movable armature. 
     
     
       3. The polarized electromagnetic actuator as in  claim 1 , further comprising a pivot disposed between the movable armature and the stator and between the first and second permanent magnets. 
     
     
       4. The polarized electromagnetic actuator of  claim 1 , wherein the first and second stabilizing elements cause the polarized electromagnetic actuator to be stable at zero displacement of the armature. 
     
     
       5. A polarized electromagnetic actuator, comprising:
 a stator including two tines extending out from the stator; 
 a movable armature positioned between the two tines of the stator; 
 a first coil positioned around one tine; 
 a second coil positioned around the other tine; and 
 a permanent magnet disposed under the movable armature and over the stator between the two tines, wherein a magnetic flux of the first and second coils increases a magnetic flux of the permanent magnet in one direction to produce motion in the movable armature. 
 
     
     
       6. The polarizing electromagnetic actuator as in  claim 5 , further comprising one or more stabilizing elements disposed between the permanent magnet and the movable armature. 
     
     
       7. The polarizing electromagnetic actuator as in  claim 5 , further comprising one or more stabilizing elements disposed between the movable armature and at least one tine of the stator. 
     
     
       8. The polarizing electromagnetic actuator as in  claim 5 , further comprising one or more bending flexures disposed between the stator and the movable armature. 
     
     
       9. A polarized electromagnetic actuator, comprising:
 a movable armature including two tines extending out from the armature; 
 a stator disposed over the two tines of the movable armature; 
 a permanent magnet disposed under the stator and over the movable armature between the two tines; 
 a first coil positioned around the stator between one tine of the armature and the permanent magnet; and 
 a second coil positioned around the stator between the other tine and the permanent magnet. 
 
     
     
       10. A polarized electromagnetic actuator, comprising:
 a stator including two tines extending out from the stator; 
 a coil positioned around the stator between the two tines; 
 a first permanent magnet disposed over one tine of the stator; 
 a second permanent magnet disposed over the other tine of the stator; and 
 a movable armature including a first arm disposed over the first permanent magnet and a second arm disposed over the second permanent magnet and a body disposed between the two tines, wherein a magnetic flux of the coil increases a magnetic flux of one permanent magnet to produce motion in the movable armature in a direction of the increased magnetic flux. 
 
     
     
       11. The polarized electromagnetic actuator as in  claim 10 , further comprising at least one stabilizing element disposed between the body of the movable armature and at least one tine of the stator. 
     
     
       12. The polarized electromagnetic actuator as in  claim 10 , further comprising at least one stabilizing element disposed between at least one permanent magnet and a respective arm of the movable armature. 
     
     
       13. A polarized electromagnetic actuator, comprising:
 a stator including two tines extending out from the stator; 
 a coil positioned around the stator between the two tines; 
 a movable armature including:
 a first arm disposed over one tine of the stator; 
 a second arm disposed over the other tine of the stator; and 
 a body disposed between the two tines; 
 
 a first permanent magnet attached to the first arm of the movable armature and disposed over one tine of the stator; and 
 a second permanent magnet attached to the second arm of the movable armature and disposed over the other tine of the stator, 
 wherein a magnetic flux of the coil increases a magnetic flux of one permanent magnet to produce motion in the movable armature in a direction of the increased magnetic flux. 
 
     
     
       14. The polarized electromagnetic actuator as in  claim 13 , further comprising at least one stabilizing element attached to an outer end of a respective arm of the armature and the stator. 
     
     
       15. A method for providing a polarized electromagnetic actuator comprising:
 providing a stator that includes two tines extending out from the stator; 
 providing a movable armature between the two tines of the stator; 
 providing a first coil positioned around a first tine of the stator and a second coil positioned around a second tine of the stator; 
 providing at least one permanent magnet under the movable armature and over the stator between the two tines; and 
 configuring the at least one coil to increase a magnetic flux of the at least one permanent magnet in one direction when a current is applied to the at least one coil, wherein the movable armature moves in the direction of the increased magnetic flux. 
 
     
     
       16. The method as in  claim 15 , further comprising providing one or more stabilizing elements to ends of the movable armature to stabilize the movable armature when a current is not applied to the at least one coil. 
     
     
       17. A polarized electromagnetic actuator, comprising:
 a stator including two tines extending out from the stator; a coil positioned around the stator between the two tines; 
 a movable armature including a first arm disposed over one tine of the stator, a second arm disposed under the other tine of the stator, and a body disposed between the two tines; 
 a first permanent magnet attached to one tine of the stator; and 
 a second permanent magnet attached to the other tine of the stator, wherein the coil produces a first magnetic flux when a current is applied to the coil and the magnetic flux of the coil increases a magnetic flux of one permanent magnet to produce motion in the movable armature in a direction of the increased magnetic flux. 
 
     
     
       18. The method as in  claim 15 , further comprising providing one or more stabilizing elements to the permanent magnet to stabilize the movable armature when a current is not applied to the at least one coil. 
     
     
       19. The method as in  claim 15 , further comprising providing one or more stabilizing elements connecting the stator to the movable armature to stabilize the movable armature when a current is not applied to the at least one coil. 
     
     
       20. The method as in  claim 15 , wherein the one or more stabilizing elements provided to ends of the movable armature are connected to the stator. 
     
     
       21. A method for providing a polarized electromagnetic actuator comprising:
 providing a stator that includes two tines extending out from the stator; 
 providing a movable armature spaced having an arm disposed over each tine of the stator and body disposed between the two tines of the stator; 
 providing at least one coil positioned around the stator between the two tines; 
 providing a first permanent magnet between a first arm of the movable armature and a first tine of the stator that the arm is disposed over; 
 providing a second permanent magnet between a second arm of the movable armature and a second tine of the stator that the arm is disposed over; and 
 configuring the at least one coil to increase a magnetic flux of at least one permanent magnet in one direction when a current is applied to the at least one coil, wherein the movable armature moves in the direction of the increased magnetic flux. 
 
     
     
       22. The method of  claim 21 , wherein the first permanent magnetic is attached to the first arm of the movable armature and the second permanent magnet is attached to the second arm of the movable armature. 
     
     
       23. The method of  claim 21 , wherein the first permanent magnetic is attached to the first tine of the stator and the second permanent magnet is attached to the second tine of the stator. 
     
     
       24. The method of  claim 21 , further comprising providing one or more stabilizing elements to the body of the movable armature to stabilize the movable armature when a current is not applied to the at least one coil.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a 35 U.S.C. § 371 application of PCT/US2013/062449, filed on Sep. 27, 2013, and entitled “Polarized Magnetic Actuators for Haptic Response,” which is incorporated by reference as if fully disclosed herein. 
     TECHNICAL FIELD 
     The present invention relates to actuators, and more particularly to electromagnetic actuators that include one or more permanent magnets. 
     BACKGROUND 
     An actuator is a device that converts one form of energy into some type of motion. There are several different types of actuators, including pneumatic, hydraulic, electrical, mechanical, and electromagnetic. An electromagnetic actuator provides mechanical motion in response to an electrical stimulus. The electromagnetic actuator typically includes a coil and a movable armature made of a ferromagnetic material. A magnetic field is produced around the coil when current flows through the coil. The magnetic field applies a force to the armature to move the armature in the direction of the magnetic field. 
     Some electromagnetic actuators are limited in the type of force that can be applied to an armature. For example, an armature can be pushed but not pulled. Additionally, some electromagnetic actuators may produce a negligible amount of force when a small amount of current is applied to the coil. And in some devices or components, such as in portable electronic devices or components used in portable electronic devices, it can be challenging to construct an electromagnetic actuator that has both a reduced size and an ability to generate a desired amount of force. 
     SUMMARY 
     In one aspect, a polarized electromagnetic actuator can include a movable armature and a stator, a first coil and a second coil wrapped around the stator, and a permanent magnet disposed over the stator. The moveable armature is spaced apart from the stator. The first and second coils produce a first magnetic flux in a first direction when a current is applied to the first and second coils. The first magnetic flux reduces a second magnetic flux of the permanent magnet in a first direction and increases the second magnetic flux in a second direction to produce motion in the movable armature in the second direction. The amount of force applied to the movable armature can be controlled by controlling the amount of current flowing through the first and second coils. Additionally, the direction of the force applied to the movable armature is dependent upon the direction of the current passing through the first and second coils. 
     In another aspect, a polarized electromagnetic actuator can include a movable armature and a stator having two tines extending out from the stator. The movable armature is spaced apart from the two tines of the stator. A first coil is wrapped around one tine and a second coil is wrapped around the other tine. At least one permanent magnet is disposed over the stator between the two tines. The first and second coils produce a first magnetic flux in a first direction when a current is applied to the first and second coils. The first magnetic flux reduces a second magnetic flux of the permanent magnet in a first direction and increases the second magnetic flux in a second direction to produce motion in the movable armature in the second direction. The amount of force applied to the movable armature can be controlled by controlling the amount of current flowing through the first and second coils. Additionally, the direction of the force applied to the movable armature is dependent upon the direction of the current passing through the first and second coils. 
     In yet another aspect, a polarized electromagnetic actuator can include a stator including two tines extending out from the stator and a coil wrapped around the stator between the two tines. A movable armature can include a first arm disposed over one tine of the stator, a second arm disposed over the other tine of the stator, and a body disposed between the two tines. A first permanent magnet can be positioned between the first arm of the armature and one tine of the stator, and a second permanent magnet can be positioned between the second arm of the armature and the other tine of the stator. For example, in one embodiment, the first permanent magnet is attached to the first arm of the armature and disposed over one tine of the stator and the second permanent magnet is attached to the second arm of the armature and disposed over the other tine of the stator. In another embodiment, the first permanent magnet is attached to one tine of the stator and the second permanent magnet is attached to the other tine of the stator. The coil produces a first magnetic flux when a current is applied to the coil and the magnetic flux of the coil can increase a magnetic flux of one permanent magnet to produce motion in the movable armature in a direction of the increased magnetic flux. 
     In another aspect, a polarized electromagnetic actuator can include a stator including two tines extending out from the stator and a coil wrapped around the stator between the two tines. A movable armature can include a first arm disposed over one tine and of the stator, a second arm disposed under the other tine of the stator, and a body disposed between the two tines. A first permanent magnet can be attached to one tine of the stator and a second permanent magnet can be attached to the other tine of the stator. The coil produces a first magnetic flux when a current is applied to the coil and the magnetic flux of the coil can increase a magnetic flux of one permanent magnet to produce motion in the movable armature in a direction of the increased magnetic flux. 
     In another aspect, a method for providing a polarized electromagnetic actuator includes providing a movable armature and a stator, providing at least one coil wrapped around the stator, and providing at least one permanent magnet over the stator. The at least one coil is configured to reduce a magnetic flux of at least one permanent magnet in one direction and increase a magnetic flux of at least one permanent magnet in another direction when a current is applied to the at least one coil to move the movable armature in the direction of the increased magnetic flux. 
     And in yet another aspect, a polarized electromagnetic actuator includes a movable armature, a stator, at least one coil wrapped around the stator, and at least one permanent magnet disposed over the stator. A method for operating the polarized electromagnetic actuator includes applying a current to the at least one coil to produce a first magnetic flux that reduces a second magnetic flux of at least one permanent magnet in a first direction and increases the second magnetic flux of at least one permanent magnet in a second direction to move the movable armature in the second direction. The current to the at least one coil can be controllably varied to adjust a force applied to the movable armature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments are better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other. Identical reference numerals have been used, where possible, to designate identical features that are common to the figures. 
         FIG. 1  is a simplified illustration of one example of a prior art electromagnetic actuator; 
         FIG. 2  is a simplified illustration of another example of a prior art electromagnetic actuator; 
         FIG. 3  is a simplified illustration of a first example of a polarized electromagnetic actuator; 
         FIG. 4  depicts an example graph of the magnetic fields B 1  and B 2  versus an applied current for the polarized electromagnetic actuator shown in  FIG. 3 ; 
         FIG. 5  illustrates an example graph of the forces varying with an applied current for the polarized electromagnetic actuator shown in  FIG. 3 ; 
         FIG. 6  depicts an example graph of the forces versus armature position for the polarized electromagnetic actuator shown in  FIG. 3 ; 
         FIG. 7  is a simplified illustration of a second example of a polarized electromagnetic actuator; 
         FIG. 8  illustrates one method for providing a restoring force to the polarized electromagnetic actuator shown in  FIG. 7 ; 
         FIG. 9  depicts an example graph of the armature displacement in the actuator  200  shown in  FIG. 3 ; 
         FIG. 10  illustrates an example graph of the armature displacement in the actuator  600  shown in  FIG. 8 ; 
         FIG. 11  is a simplified illustration of a third example of a polarized electromagnetic actuator; 
         FIG. 12  depicts a first method for providing a restoring force to the polarized electromagnetic actuator shown in  FIG. 11 ; 
         FIG. 13  illustrates a second method for providing a restoring force to the polarized electromagnetic actuator shown in  FIG. 11 ; 
         FIG. 14  is a simplified illustration of a fourth example of a polarized electromagnetic actuator; 
         FIG. 15  is a simplified illustration of a fifth example of a polarized electromagnetic actuator; 
         FIG. 16  depicts one method for providing a restoring force to the polarized electromagnetic actuator shown in  FIG. 15 ; 
         FIG. 17  is a simplified illustration of a sixth example of a polarized electromagnetic actuator; 
         FIG. 18  is a simplified illustration of a seventh example of a polarized electromagnetic actuator; 
         FIG. 19  is a flowchart of one example method of providing a polarized electromagnetic actuator; 
         FIG. 20  is a flowchart of one example method of operating a polarized electromagnetic actuator; 
         FIG. 21  is a front perspective view of an electronic device that can include one or more polarized electromagnetic actuators; and 
         FIG. 22  is a front perspective view of another electronic device that can include one or more polarized electromagnetic actuators. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments described herein provide a polarized electromagnetic actuator that includes a movable armature spaced apart from a stator. One or more permanent magnets can be disposed over the stator, and one or more coils can be wrapped around the stator. The polarized electromagnetic actuator can generate a greater amount of force by increasing a magnetic flux of a permanent magnet using a magnetic flux produced by one or more coils. For example, in one embodiment, a permanent magnet provides a background magnetic field and flux that are distributed evenly through an armature and a stator. Two coils wrapped around either the stator or the armature produces a magnetic field and flux in a given direction when a current is applied to the coil. The direction of the coil magnetic flux is dependent upon the direction of the current flowing through the coils. The magnetic flux of the coil reduces or cancels the magnetic flux of the permanent magnet in one direction and increases the magnetic flux of the permanent magnet in another direction. The increased magnetic flux of the permanent magnet applies a force to the armature to move the armature in a direction of the increased magnetic flux. 
     The amount of force applied to the armature can be controlled by controlling the current flowing through the coil or coils. The applied force can be increased by increasing the current, or the amount of force can be decreased by decreasing the current. In some embodiments, the magnetic flux of the coil or coils completely cancels a magnetic flux of a permanent magnet in a first direction. In some embodiments, the amount of force applied to the armature can increase or decrease linearly by varying the current applied to the coil(s). 
     In some embodiments, the magnetic forces can cause a destabilizing force on the armature similar to a negative spring. This destabilizing force causes the armature to be attracted to one of the tines. One or more stabilizing elements can be included with the polarized electromagnetic actuators to stabilize the armature when a current is not applied to the coil or coils. The stabilizing element or elements can compensate for the destabilizing force. Examples of stabilizing elements include, but are not limited to, springs, flexible structures, or gel packs or disks that can be positioned between the armature and the stator to assist in stabilizing the armature. 
     Embodiments of polarized electromagnetic actuators can be included in any type of device. For example, acoustical systems such as headphones and speakers, computing systems, haptic systems, and robotic devices can include one or more polarized electromagnetic actuators. Haptic systems can be included in computing devices, digital media players, input devices such as buttons, trackpads, and scroll wheels, smart telephones, and other portable electronic devices to provide tactile feedback to a user. For example, the tactile feedback can take the form of an applied force, a vibration, or a motion. One or more polarized electromagnetic actuators can be included in a haptic system to enable the tactile feedback (e.g., motion) that is applied to the user. 
     For example, the top surface of a trackpad can be disposed over the top surface of a movable armature of a polarized electromagnetic actuator, or the top surface of the trackpad can be the top surface of the movable armature. The actuator can be included under the top surface of the trackpad. One or more polarized electromagnetic actuators can be included in the trackpad. The polarized electromagnetic actuators can be positioned in the same direction or in different directions. For example, one polarized electromagnetic actuator can provide motion along an x-axis while a second polarized electromagnetic actuator provides motion along a y-axis. 
     Other embodiments switch the roles of the armature and the stator so that a polarized electromagnetic actuator includes an armature spaced apart from a movable stator. One or more permanent magnets can be disposed over the armature, and one or more coils can be wrapped around the armature. A magnetic field and flux are produced in a given direction when a current is applied to one or more coils. The direction of the coil magnetic flux is dependent upon the direction of the current flowing through the coils. The magnetic flux of the coil reduces or cancels the magnetic flux of the permanent magnet in one direction and increases the magnetic flux of the permanent magnet in another direction. Similarly, one or more stabilizing elements can be included with the polarized electromagnetic actuators to stabilize the armature when a current is not applied to the coil or coils. 
     Referring now to  FIG. 1 , there is shown a simplified illustration of one example of a prior art electromagnetic actuator. The actuator  100  includes a stator  102  having two tines  104 ,  106  that extend out from the stator  102  to form a “U” shaped region. A solenoid or helical coil  108 ,  110  is wrapped around each tine  104 ,  106 . A movable armature  112  is arranged in a spaced-apart relationship to the tines  104 ,  106  of the stator  102 . The stator  102  and the movable armature  112  can be made of any suitable ferromagnetic material, compound, or alloy, such as steel, iron, and nickel. 
     Each respective coil and tine forms an electromagnet. An electromagnet is a type of magnet in which a magnetic field is produced by a flow of electric current. The magnetic field disappears when the current is turned off. In the embodiment shown in  FIG. 1 , a magnetic field B and a magnetic flux ϕ are produced when current flows through the coils  108 ,  110 . In  FIG. 1 , the magnetic field B is represented by one magnetic field arrow and the magnetic flux ϕ is represented by one flux line. 
     The force produced by the magnetic field B can be controlled by controlling the amount of electric current (I) flowing through the coils  108 ,  110  in that the force varies according to the equation I 2 . The force is attractive and causes the armature  112  to be pulled downwards towards both tines  104 ,  106  (movement represented by arrow  114 ). Assuming the core is not saturated and does not contribute significantly to the overall reluctance, and assuming no significant fringing fields in the air gap g, the force (F) exerted by the electromagnets (i.e., tine  104  and coil  108 ; tine  106  and coil  110 ) can be determined by the following equation, 
                   F   =         μ   0     ⁢     π   2     ⁢     V   2     ⁢     D   4     ⁢     w   c     ⁢     t   c         256   ⁢           ⁢     ρ   2     ⁢         g   2     ⁡     (       w   c     +     t   m     -     2   ⁢           ⁢     t   e         )       2                 Equation   ⁢           ⁢   1               
where μ 0  is the permeability of free space or air, V is the applied voltage, D is the wire diameter (total), w c  is the core width of the coil (see  FIG. 1 ), t c  is the core thickness of the coil, ρ is the effective resistivity of the coil, g is the gap between the armature  112  and the tines  104 ,  106 , t m  is the maximum allowable thickness of the coil, and t e  is the encapsulation thickness of the coil.
 
     The force (F) divided by the power (P) for the electromagnets can be calculated by 
                     F   P     =         μ   0     ⁢   π   ⁢           ⁢     L   c     ⁢     w   c     ⁢     t   c     ⁢     t   a         16   ⁢           ⁢   ρ   ⁢           ⁢       g   2     ⁡     (       w   c     +     t   m     -     2   ⁢           ⁢     t   e         )                   Equation   ⁢           ⁢   2               
where μ 0  is the permeability of free space or air, L c  is the length of the coil, w c  is the core width of the coil, t c  is the core thickness of the coil, t a  is the thickness of the wire coil, ρ is the effective resistivity of the coil, g is the gap between the armature  112  and the tines  104 ,  106 , t m  is the maximum allowable thickness of the coil, and t e  is the encapsulation thickness of the coil.
 
     One limitation to the actuator  100  is that the force can produce motion in only one direction, such that the armature  112  can only be pulled down toward the tines  104 ,  106 . Additionally, the overall efficiency for the actuator  100  can be low. For example, in some embodiments, the overall efficiency of the actuator can be 1.3%. One reason for the reduced efficient is saturation, but the non-linear effects of the gap g can somewhat offset the reduced efficiency in some embodiments. 
     Referring now to  FIG. 2 , there is shown a simplified illustration of another example of a prior art electromagnetic actuator. The actuator  200  includes a movable armature  202  and a stator  204  held in a spaced-apart relationship to the armature  202 . The stator  204  includes two tines  206 ,  208  extending out such that the stator  204  is formed into a “U” shape. A helical coil  210  is wrapped around the stator  204  between the tines  206 ,  208 . When a current flows through the coil  210 , a magnetic flux ϕC is created that travels through the movable armature  202  and around the stator  204  through the tines  206 ,  208 . The direction of travel of the coil magnetic flux ϕC depends on the direction of the current passing through the coil  210 . 
     A magnet  212  is disposed between the two tines  206 ,  208  below the armature  202 . The magnet  212  typically has a relatively small width W. The magnet  212  is polarized with two north poles on the outer edges of the magnet and a single south pole in the center. The flux from the south pole traverses a small air gap to the armature  202  and then propagates through the armature to the upper corner of the stator  204  and back through the magnet  212 . The flux from the coil  210  interacts with the flux from the magnet  212  to produce a net torque on the armature. Relay contact arms (not shown) act as flexures that stabilize the negative spring constant of the magnetic field of the magnet  212 . 
     The double pole magnet  212  can be difficult to produce. Additionally, the illustrated actuator typically works well for a relay, but the force produced by the actuator is limited by the width W of the magnet  212 . It can be desirable to use an actuator that can produce larger forces in other types of applications and/or devices. By way of example only, other embodiments can use an actuator that creates a more powerful force that is able to produce a haptic response in a device, such as in a trackpad or other similar device. 
     Embodiments described herein provide a polarized electromagnetic actuator that is more efficient, can produce a greater amount of force for the same applied current, and can produce a controllable motion in two directions (e.g., push and pull).  FIG. 3  is a simplified illustration of a first example of a polarized electromagnetic actuator. The actuator  300  includes a stator  302  with two tines  304 ,  306  extending out to form a “U” shaped region of the stator  302 . A helical coil  308 ,  310  is wrapped around each tine  304 ,  306  and a permanent magnet  312  is positioned between the tines  304 ,  306 . A movable armature  314  is arranged in a spaced-apart relationship to the tines of the stator  302  and disposed over a pivot  316 . 
     In the illustrated embodiment, the stator  302  and the movable armature  314  can be made of any suitable ferromagnetic material, compound, or alloy, such as steel, iron, and nickel. The permanent magnet  312  can be any suitable type of permanent magnet, including, but not limited to, a neodymium (NdFeB) magnet. A ferromagnetic material is a material that can be magnetized. Unlike a ferromagnetic material, a permanent magnet is made of a magnetized material that produces a persistent magnetic field. In  FIG. 3 , the permanent magnet  312  produces a magnetic field B that is distributed evenly through each stator tine  304 ,  306  when the gaps g 1  and g 2  are equal. The magnetic flux ϕ M1 , ϕ M2  associated with the permanent magnet  312  provides a background magnetic flux traveling through the movable armature  314  and the stator  302  (including the tines  304 ,  306 ). When a current flows through the coils  308 ,  310 , a magnetic flux ϕ C  is created that travels through the movable armature  314  and around the stator  302  through the tines  304 ,  306 , but substantially not through the permanent magnet  312 . The direction of travel of the coil magnetic flux ϕ C  depends on the direction of the current passing through the coils  308 ,  310 . 
     The magnetic flux ϕ C  produced by the coils  308 ,  310  interacts with the magnetic flux ϕ M1 , ϕ M2  of the permanent magnet to reduce or cancel the magnetic flux in one direction (ϕ M1  or ϕ M2 ) and increase the magnetic flux in the other direction. Motion is produced in the movable armature  314  in the direction of the increased magnetic flux (ϕ M1  or ϕ M2 ). For example, in the illustrated embodiment, the coil magnetic flux ϕ C  is traveling in a direction that opposes the direction of the magnetic flux ϕ M1 , thereby reducing or canceling the magnetic flux ϕ M1 . Concurrently, the coil magnetic flux ϕ C  is traveling in the same direction as the direction of the magnetic flux ϕ M2 , thereby increasing the magnetic flux ϕ M2 . The armature  314  moves up and down like a teeter-totter based on the force applied to the armature (movement represented by arrow  318 ). The movable armature  314  can be pulled toward a respective tine or pushed away from a respective tine depending on the direction of the current through the coils  308 ,  310 . Additionally, the amount of force applied to the armature can be controlled by controlling the amount of current applied to the coils  308 ,  310 . 
     Ampere&#39;s Law ∇×H=J and Maxwell&#39;s Equation ∇·B=0 can be used to analyze the illustrated actuator  300 . Note that the following analysis assumes the core does not saturate and that no fringing fields are present in the gaps g 1  and g 2 .
 
∇× H=J: H   1   g   1   −H   m   L   m   =NI   1 ; and  Equation 3
 
 H   m   L   m   −H   2   g   2   =NI   2   Equation 4
 
∇· B= 0:  B   1   A   1   +B   m   A   m   +B   2   A   2 =0  Equation 5
 
where L m  is the length of the permanent magnet  312 , N is the number of turns in each coil  308 ,  310 , and H 1 , H 2 , and H m  are the H fields (magnetic strength) associated with the magnetic fields B 1 , B 2 , and B m , respectively. Another equation included in the analysis is the relationship between the magnetic field B and the H field in the permanent magnet, also known as the demagnetization curve. Magnet suppliers typically provide a demagnetization curve for each of the materials used in the permanent magnets. Typically, the relationship between B and H is linear and can be approximated as follows,
 
 B   m   =B   r +μ 0   H   m   Equation 6
 
where B r  is the remanent magnetization of the permanent magnet (e.g., ˜1.2 T). Solving equations 3 through 6, the magnetic force B 1  and B 2  can be determined by
 
     
       
         
           
             
               
                 
                   
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                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   7 
                 
               
             
             
               
                 
                   
                       
                   
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                       B 
                       2 
                     
                     = 
                     
                       
                         ( 
                         
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                       ⁢ 
                       
                         ( 
                         
                           
                             
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                               1 
                             
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                               g 
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                               0 
                             
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                         ) 
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   8 
                 
               
             
           
         
       
     
     As described earlier, the magnetic flux ϕ C  produced by the coils  308 ,  310  interacts with the magnetic flux ϕ M1 , ϕ M2  of the permanent magnet to reduce or cancel one magnetic flux (ϕ M1  or ϕ M2 ) and increase the other magnetic flux. When the magnetic flux ϕ C  cancels a magnetic flux in one direction (ϕ M1  or ϕ M2 ) completely, the magnetic field of the coil B coil  equals the magnetic field in the permanent magnet B magnet , and the force is increased. By way of example only, in the illustrated embodiment, when the magnetic field of the coil B coil  equals the magnetic field in the permanent magnet B magnet , the force produced by the left-hand side  320  of the actuator  300  can be determined by 
                     F   320     =         1     2   ⁢           ⁢     μ   0         ⁢       (       B   coil     -     B   magnet       )     2     ⁢     A   core       =   0             Equation   ⁢           ⁢   9               
Also, when the magnetic field of the coil B coil  equals the magnetic field in the permanent magnet B magnet , the force produced by the right-hand side  322  of the actuator  300  can be calculated by
 
                     F   322     =         1     2   ⁢           ⁢     μ   0         ⁢       (       B   coil     +     B   magnet       )     2     ⁢     A   core       =       4     2   ⁢           ⁢     μ   0         ⁢       (     B   coil     )     2     ⁢     A   core                 Equation   ⁢           ⁢   10               
In comparison, the amount of force generated by the left-hand side  120  and right-hand side  122  of the actuator  100  shown in  FIG. 1  can be defined by
 
     
       
         
           
             
               
                 
                   
                     F 
                     TOTAL 
                   
                   = 
                   
                     
                       
                         F 
                         120 
                       
                       + 
                       
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                         122 
                       
                     
                     = 
                     
                       
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                           2 
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                             μ 
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                           ( 
                           
                             B 
                             coil 
                           
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                         2 
                       
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                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   11 
                 
               
             
           
         
       
     
     Thus, the actuator  300  in  FIG. 3  can generate more force than the actuator  100  in  FIG. 1 . The actuator  300  in  FIG. 3  can produce a magnetic force B magnet &gt;B coil , which means a smaller B coil  can be produced to obtain the same amount of force as the actuator  100  in  FIG. 1 . In the event that the coil produces the same size field as the permanent magnet (B coil =B magnet ), then equations 10 and 11 above demonstrate that the polarized actuator produces twice the force of a conventional actuator. In some situations, the field produced by the coil is less than the field produced by the permanent magnet, in which case the polarized actuator produces more than twice the force of a conventional actuator. 
       FIG. 4  is an example graph of the magnetic fields B 1  and B 2  versus an applied current for the polarized electromagnetic actuator shown in  FIG. 3 . Plot  400  represents the applied current to the coils  308 ,  310  as it changes between approximately −2 amps and +2 amps. In the illustrated embodiment, the magnetic field B 1  increases linearly (plot  402 ) and the magnetic field B 2  decreases linearly (plot  404 ) as the current applied to the coils  308 ,  310  increases from −2 amps to +2 amps. 
     Similarly, the total force produced by the magnetic fields varies linearly with the applied current.  FIG. 5  illustrates an example graph of the forces varying with an applied current for the polarized electromagnetic actuator shown in  FIG. 3 . In the illustrated embodiment, the force F 1  produced by the magnetic field B 1  (plot  500 ) increases with the current applied to the coils while the force F 2  produced by the magnetic field B 2  (plot  502 ) decreases with the applied current. The resulting total force F 1 -F 2  increases linearly as the current applied to the coils  308 ,  310  increases from −2 amps to +2 amps, as shown in plot  504 . 
     The resulting total force F 1 -F 2  can also vary linearly with armature position. As shown in  FIG. 6 , as the gap g 2  increases, the force F 2  produced by the magnetic field B 2  decreases. Since the armature  314  pivots around a point central to the two tines  304  and  306 , increasing gap g 2  causes gap g 1  to decrease. As g 1  decreases the force F 1  produced by the magnetic field B 1  increases. The net force F 1 -F 2  thus increases with increasing gap g 2 . Detailed modeling of the magnetic fields B 1  and B 2  demonstrate that this increase in net force is approximately linear with g 2 . 
     The polarized electromagnetic actuator  300  can have a higher overall efficiency than the actuator  100  of  FIG. 1 . As described above, the actuator  300  can generate more force at the same current compared to the actuator  100  in  FIG. 1 . Moreover, the total force varies linearly with the applied current for the actuator  300 , so the actuator  300  provides linear control of the total force. In comparison, the total force of actuator  100  ( FIG. 1 ) is approximately equal to the square of the current. 
     Additionally, including the permanent magnet  312  in the actuator  300  can reduce power consumption of the actuator  300 . The force is driven by the magnetic field from the permanent magnet  312 . So a fairly substantial force can be generated by the actuator  300  even when the amount of current flowing through the coils  308 ,  310  is relatively small. With the prior art actuator  100  shown in  FIG. 1 , a small or negligible amount of force is generated when a small amount of current is flowing through the coils  108 ,  110 . 
     The permanent magnet  312  can be easier to manufacture compared to the magnet  212  shown in  FIG. 2  because the permanent magnet  312  has a single set of north and south poles compared to the magnet  212  that has a single south pole and two north poles. Additionally, the permanent magnet  312  can be relatively shorter and wider than the relatively thinner and longer magnet  212 . The shorter and wider permanent magnet  312  may provide improved volume efficiency compared to the magnet  212 . 
     Referring now to  FIG. 7 , there is shown a simplified illustration of a second example of a polarized electromagnetic actuator. The actuator  700  includes many of the same elements shown in  FIG. 3 , and as such these elements will not be described in more detail herein. A first permanent magnet  702  is positioned between the tine  304  and a pivot  704 . A second permanent magnet  706  is disposed between the pivot  704  and the tine  306 . The pivot  704  can provide a restoring force to the armature  314  so the armature naturally re-centers itself when the current in the coils  308 ,  310  is turned off. 
     Like the embodiment shown in  FIG. 3 , the magnetic flux ϕ C  produced by the coils  308 ,  310  interacts with the magnetic flux ϕ M1 , ϕ M2  of the permanent magnets to reduce or cancel one magnetic flux in one direction ϕ M1  or ϕ M2 ) and increase the magnetic flux in the other direction. Motion is produced in the direction of the increased magnetic flux. 
     For example, in the illustrated embodiment, the coil magnetic flux ϕ C  is traveling in a direction that opposes the direction of the magnetic flux ϕ M2 , thereby reducing or canceling the magnetic flux ϕ M2 . Concurrently, the coil magnetic flux ϕ C  is traveling in the same direction as the direction of the magnetic flux ϕ M1 , thereby increasing the magnetic flux ϕ M1 . The armature  314  moves up and down (e.g., like a teeter-totter) based on the force applied to the movable armature. The movable armature  314  can be pulled toward a respective tine or pushed away from a respective tine depending on the direction of the current through the coils  308 ,  310 . Additionally, the amount of applied force can be controlled by controlling the amount of current flowing through the coils  308 ,  310 . 
     In some embodiments, the movable armature can be in an unstable equilibrium when a current is not applied to the coils. In such embodiments, one or more stabilizing elements can stabilize the armature using a restoring force to prevent the armature from moving to one of the two contacts. In  FIG. 7 , the pivot  704  can provide a restoring force that stabilizes the movable armature  314 . With the actuator  300  shown in  FIG. 3 , the armature  314  can be stabilized with one or more springs or gel disks placed between the armature  314  and the stator  302 . Other embodiments can design the armature  314  to saturate at large fields and limit the growth of the force, or the armature can be designed to move in only one direction in the absence of a current through the coils, and a stop can be provided in the one direction of movement. Alternatively, the stator can be designed to include an additional non-force generating flux path. 
     With respect to the actuators shown in  FIGS. 3 and 7 , one method for providing a restoring force to the actuators  300 ,  700  is illustrated in  FIG. 8 . Stabilizing elements  800 , such as C-springs, are provided around the ends of the movable armature  314  and the protrusions  802  of the stator  302  to restrict or limit the movement of the armature  314 . By way of example only, the space between the armature  314  and the tines  304 ,  306  can be 300 microns. The movable armature  314  can therefore only move 300 microns in any one direction when the stabilizing elements  800  are placed over the ends of the actuator  700 . 
     Although the  FIG. 7  actuator  700  is used to depict the stabilizing elements  800 , those skilled in the art will recognize that the stabilizing elements  800  can be used with the actuator  300  shown in  FIG. 3 . 
       FIG. 9  illustrates an example graph of the applied force as a function of armature displacement for the actuator  300  shown in  FIG. 3 , while  FIG. 10  depicts an example graph of the applied force as a function of armature displacement for the actuator  700  shown in  FIG. 8 . In  FIG. 9 , plot  900  represents the applied force as a function of armature displacement when 100 Ampere-turns (Aturns) is applied to each coil  308 ,  310 . Plot  902  represents the applied force as a function of armature displacement when 0 Aturns is applied to each coil  308 ,  310 . When a current is not applied to the coils  308 ,  310 , the applied force ranges between approximately −6 N and +6 N as the armature is displaced between −150 and +150 microns. Since plot  902  has a positive slope, the armature is in unstable equilibrium at zero displacement. Once the armature is displaced incrementally away from the origin in either direction, it will accelerate in that direction until it reaches the end of travel. 
     In contrast, the stabilizing elements  800  can limit the applied force within the same armature displacement. When a current is not applied to the coils  308 ,  310 , plot  1002  of  FIG. 10  represents the applied force as a function of armature displacement when 0 Aturns is applied to each coil  308 ,  310 . As shown, with the stabilizing elements  800 , the applied force ranges between approximately −1 N and +1 N as the armature  314  is displaced between −150 and +150 microns. The addition of the stabilizing elements  800  causes the force to have a negative slope as it passes through the origin. Therefore, the actuator is stable at zero displacement. And the applied force ranges approximately between +9 and +7 when 100 Aturns is applied to each coil  308 ,  310  (see plot  1000 ). 
     Referring now to  FIG. 11 , there is shown a simplified illustration of a third example of a polarized electromagnetic actuator. The actuator  1100  includes a stator  1102  with two tines  1104 ,  1106  extending out to form into a “U” shaped region of the stator  1102 . A helical coil  1108 ,  1110  is wrapped around each tine  1104 ,  1106  and a permanent magnet  1112  is positioned in a spaced-apart relationship to the stator  1102  and the permanent magnet  1112 . In the illustrated embodiment, the movable armature  1114  is disposed over the permanent magnet  1112  and within the “U” shaped region between the tines  1104 ,  1106 . 
     The permanent magnet  1112  can produce a magnetic field B that is distributed evenly through each stator tine  1104 ,  1106 . The magnetic flux ϕ M1 , ϕ M2  associated with the permanent magnet  1112  provides a background magnetic flux traveling from the permanent magnet  1112  through the armature  1114 , the stator  1102  (including the tines  1104 ,  1106 ), and back to the permanent magnet  1112 . A magnetic flux ϕ C  is produced when a current is applied to the coils  1108 ,  1110 . The coil magnetic flux ϕ C  travels through the armature  1114  and around the stator  1102  through the tines  1104 ,  1106 , but largely not through the permanent magnet  1112 . The direction of travel of the coil magnetic flux ϕ C  depends on the direction of the current passing through the coils  1108 ,  1110 . 
     The magnetic flux produced by the coils  1108 ,  1110  reduces or cancels the magnetic flux in a first direction and increases the magnetic flux in a second direction of the permanent magnet. Motion is produced in the armature in the direction of the increased magnetic flux. The armature  1114  moves left and right based on the force applied to the armature (movement represented by arrow  1116 ). The movable armature  1114  can be pulled toward a respective tine or pushed away from a respective tine depending on the direction of the current through the coils  1108 ,  1110 . Additionally, the amount of force applied to the movable armature  1114  can be controlled by controlling the amount of current applied to the coils  1108 ,  1110 . 
       FIG. 12  depicts a first method for providing a restoring force to the polarized electromagnetic actuator shown in  FIG. 11 . The actuator  1200  includes many of the same elements shown in  FIG. 11 , and as such these elements will not be described in more detail in the description of  FIG. 12 . As described earlier, when a current flows through the coils  1108 ,  1110 , the magnetic field from the coils interacts with the magnetic field from the permanent magnet  1112  and increases the field on one side of the armature  1114  and decreases the field on the other side of the armature. When a current is not applied to the coils  1108 ,  1110 , there can be equal and opposite forces on the left and right sides of the armature  1114  across the gap  1202 . There can also be a force attraction between the permanent magnet  1112  and the armature  1114 . Bending flexures  1204  act as stabilizing elements by counteracting the attraction between the permanent magnet  1112  and the armature  1114 . The spring constants of the bending flexures  1204  can stabilize the armature  1114  in the center of its travel. Other embodiments can include a fewer or greater number of stabilizing elements. 
       FIG. 13  illustrates a second method for providing a restoring force to the polarized electromagnetic actuator shown in  FIG. 11 . Like the embodiment shown in  FIG. 12 , there can be equal and opposite forces on the left and right sides of the armature  1114  across the gap  1202  when a current is not applied to the coils  1108 ,  1110 . There is also a force attraction between the permanent magnet  1112  and the armature  1114 . The gel disks or pads  1302  act as stabilizing elements by stabilizing the armature  1114  in the spaces between the stator  1102  and the permanent magnet  1112 . Other embodiments can include a fewer or greater number of stabilizing elements. 
     Referring now to  FIG. 14 , there is shown a simplified illustration of a fourth example of a polarized electromagnetic actuator. The actuator  1400  includes a rectangular-shaped stator  1402  and a movable armature  1404  held in a spaced-apart relationship to the stator  1402 . The movable armature  1404  includes two tines  1406 ,  1408  extending out to form a “U” shaped region of the armature  1404 . A first helical coil  1410  is wrapped around one end of the stator  1402  between the tines  1406 ,  1408  and a second helical coil  1412  is wrapped around the other end of the stator  1402  between the tines  1406 ,  1408 . A permanent magnet  1414  is positioned over the stator  1402  between the two coils  1410 ,  1412 . 
     The permanent magnet  1414  produces a magnetic flux ϕ M1 , ϕ M2  that provides a background magnetic flux traveling through the stator  1402  and the movable armature  1404  (including the tines  1406 ,  1408 ). A magnetic flux ϕ C  is produced by the first and second coils  1410 ,  1412  when a current is applied to the coils  1410 ,  1412 . The coil magnetic flux ϕ C  travels through the armature  1404  (including the tines  1406 ,  1408 ) and around the stator  1402  (but largely not through the permanent magnet  1414 ). The direction of travel of the coil magnetic flux ϕ C  depends on the direction of the current passing through the coils  1410 ,  1412 . 
     The coil magnetic flux ϕ C  interacts with a respective magnetic flux ϕ M1  or ϕ M2 ) of the permanent magnet to reduce or cancel the magnetic flux in one direction and increase the magnetic flux in the other direction. For example, in the illustrated embodiment, the coil magnetic flux ϕ C  is traveling in a direction that opposes the direction of the magnetic flux ϕ M1 , thereby reducing or canceling the magnetic flux ϕ M1 . Concurrently, the coil magnetic flux ϕ C  is traveling in the same direction as the direction of the magnetic flux ϕ M2 , thereby increasing the magnetic flux ϕ M2 . The increase in the magnetic flux ϕ M2  by the magnetic flux ϕ C2  increases the force. The armature  1404  moves in the direction of the increased magnetic flux ϕ M2  based on the force applied to the movable armature. 
     In the embodiments of  FIGS. 3, 7, 8, and 11-14 , the coil magnetic flux largely does not pass through the permanent magnet or magnets. This is due to the fact that the permanent magnet(s) appear or act like an air gap when the coil(s) produces a magnetic flux. Since the thickness of the permanent magnets can be much larger than the thicknesses of the air gaps g 1  and g 2 , the path through the magnet is relatively high reluctance and a very small fraction of the coil flux traverses the magnet. In a fifth example of a polarized electromagnetic actuator shown in  FIG. 15 , the coil magnetic flux does not pass through the permanent magnets and the magnetic fluxes of the permanent magnets does not travel through the coil. 
     The actuator  1500  includes a stator  1502  with tines  1504 ,  1506  extending out to form a “U” shaped region of the stator. A helical coil  1508  is wrapped around the stator  1502  between the two tines  1504 ,  1506 . A first permanent magnet  1510  is positioned over the tine  1504  and a second permanent magnet  1512  is disposed over the tine  1506 . A movable armature  1514  can be formed in a “T” shape with the arms  1516 ,  1518  of the T-shaped armature  1514  disposed over the permanent magnet  1510 ,  1512 , respectively. The body of the T-shaped armature  1514  is positioned over the coil  1508  within the “U” shaped region between the tines  1504 ,  1506 . The movable armature  1514  is held in a spaced-apart relationship to the stator  1502  and the permanent magnets  1510 ,  1512 . 
     The permanent magnet  1510  produces a magnetic flux ϕ M1  and the permanent magnet  1512  produces a magnetic flux ϕ M2 . The magnetic fluxes ϕ M1 , ϕ M2  provide a background magnetic flux around respective permanent magnets  1510 ,  1512  and through the movable armature  1514  (but not through the coil  1508 ). Additionally, a magnetic flux ϕ C  is produced when a current is applied to the coil  1508 . The coil magnetic flux ϕ C  travels through the body of the T-shaped armature  1514  and around the stator  1502  and tines  1504 ,  1506 , but not (or largely not) through the permanent magnets  1510 ,  1512 . As with the other embodiments, the direction of travel of the coil magnetic flux ϕ C  depends on the direction of the current passing through the coil  1508 . 
     The magnetic flux ϕ C  produced by the coil  1508  interacts with the magnetic flux ϕ M1 , ϕ M2  of the permanent magnets  1510 ,  1512  to reduce or cancel one magnetic flux (ϕ M1 , or ϕ M2 ) and increase the other magnetic flux. Motion is produced in the movable armature  1514  in the direction of the increased magnetic flux. The armature  1514  moves in a left direction or in a right direction based on the direction of the increased magnetic flux (movement depicted by arrow  1520 ). For example, in the illustrated embodiment, the coil magnetic flux ϕ C  is traveling in a direction that opposes the direction of the magnetic flux ϕ M1 , thereby reducing or canceling the magnetic flux ϕ M1 . Concurrently, the coil magnetic flux ϕ C  is traveling in the same direction as the direction of the magnetic flux ϕ M2 , thereby increasing the magnetic flux ϕ M2 . The increase in the magnetic flux ϕ M2  by the magnetic flux ϕ C  increases the amount of force applied to the movable armature  1514 . 
     As previously described, the armature  1514  moves left or right based on the force applied to the armature (movement represented by arrow  1520 ). The movable armature  1514  can be pulled toward a respective tine or pushed away from a respective tine depending on the direction of the current through the coil  1508 . Additionally, the amount of force applied to the movable armature  1514  can be controlled by controlling the amount of current applied to the coil  1508 . Since force is approximately equal to the square of the magnetic field (F˜B 2 ), the increase in the magnetic flux ϕ M2  by the coil magnetic flux ϕ C  increases the force. With the actuator  1500 . F˜B 2  can become F=4B m B c . Thus, the force is linear in applied current. 
     A polarized electromagnetic actuator can be thinner in height (z direction) than other electromagnetic actuators when the magnetic flux from a coil does not pass through a permanent magnet and the magnetic flux from the permanent magnet(s) does not travel through the coil. The material in which a coil surrounds can be thinned to account for the diameter of the coil. And in some embodiments, it is desirable to have the field going through the coil be as small as possible. So to avoid saturation, the actuator is designed so the magnetic flux from the permanent magnet does not pass through the coil since there may not be a sufficient amount of material in the coil to carry the magnetic flux from both the coil and the permanent magnet(s). 
       FIG. 16  depicts one method for providing a restoring force to the polarized electromagnetic actuator shown in  FIG. 15 . The actuator  1600  can include stabilizing elements  1602 ,  1604 , which can be implemented as gel disks or pads. The gel disks  1602  can be positioned between the arms of the T-shaped armature  1514  and the permanent magnets  1510 ,  1512 . The gel disks  1604  can be located between the body of the T-shaped armature  1514  and the tines  1504 ,  1506 . Alternatively or additionally, the gel disks  1604  can be positioned between the body of the T-shaped armature  1514  and the permanent magnets  1510 ,  1512 , or between the body of the T-shaped armature  1514  and both the permanent magnets  1510 ,  1512  and the tines  1504 ,  1506 . The gel disks or pads  1602 ,  1604  stabilize the armature  1514  in the spaces between the stator  1502  and the permanent magnets  1510 ,  1512  when a current is not applied to the coil  1508 . Other embodiments can include a fewer or greater number of stabilizing elements. 
     Referring now to  FIG. 17 , there is shown a simplified illustration of a sixth example of a polarized electromagnetic actuator. Like the embodiment shown in  FIG. 15 , the coil magnetic flux does not pass through the permanent magnets and the magnetic fluxes of the permanent magnets does not travel through the coil. 
     The actuator  1700  includes a stator  1702  with two tines  1704 ,  1706  extending out from the stator  1702  to form a “U” shaped region of the stator  1702 . A helical coil  1708  is wrapped around the stator  1702  between the two tines  1704 ,  1706 . A movable armature  1710  can be formed in a “T” shape with the arms  1712 ,  1714  of the T-shaped armature  1710  disposed over the tines  1704 ,  1706 , respectively. The body of the T-shaped armature  1710  is positioned over the coil  1708  within the “U” shaped region between the tines  1704 ,  1706 . A first permanent magnet  1716  is attached to one arm  1714  and positioned over the tine  1704  and a second permanent magnet  1718  is attached to the other arm  1716  and disposed over the tine  1706 . The movable armature  1710  and the permanent magnets  1716 ,  1718  are held in a spaced-apart relationship to the stator  1702 . 
     The permanent magnet  1716  produces a magnetic flux ϕ M1  and the permanent magnet  1718  produces a magnetic flux ϕ M2 . The magnetic fluxes ϕ M1 , ϕ M2  provide a background magnetic flux around respective permanent magnets  1716 ,  1718 , through the movable armature  1710 , and through the tines  1704 ,  1706  (but not through the coil  1708 ). Additionally, a magnetic flux ϕ C  is produced when a current is applied to the coil  1708 . The coil magnetic flux ϕ C  travels through the body of the T-shaped armature  1710  and around the stator  1702  and tines  1704 ,  1706 , but not (or largely not) through the permanent magnets  1716 ,  1718 . As with the other embodiments, the direction of travel of the coil magnetic flux ϕ C  depends on the direction of the current passing through the coil  1708 . 
     The magnetic flux ϕ C  produced by the coil  1708  interacts with the magnetic flux ϕ M1 , ϕ M2  of the permanent magnets  1716 ,  1718  to reduce or cancel one magnetic flux (ϕ M1  or ϕ M2 ) and increase the other magnetic flux. Motion is produced in the movable armature  1710  in the direction of the increased magnetic flux (motion represented by arrow  1720 ). The armature  1710  moves in a left direction or in a right direction based on the direction of the increased magnetic flux. For example, in the illustrated embodiment, the coil magnetic flux ϕ C  is traveling in a direction that opposes the direction of the magnetic flux ϕ M2 , thereby reducing or canceling the magnetic flux ϕ M2 . Concurrently, the coil magnetic flux ϕ C  is traveling in the same direction as the direction of the magnetic flux ϕ M1 , thereby increasing the magnetic flux ϕ M1 . The increase in the magnetic flux ϕ M1  by the magnetic flux ϕ C  increases the amount of force applied to the movable armature  1710 . 
     As previously described, the armature  1710  moves left or right based on the force applied to the armature. The movable armature  1710  can be pulled toward a respective tine or pushed away from a respective tine depending on the direction of the current through the coil  1708 . In the illustrated embodiment, a first bending flexure  1722  is attached to the outer ends of the arm  1712  and the protrusion  1724  of the stator  1702 . A second bending flexure  1726  is attached to the outer ends of the arm  1714  and the protrusion  1728  of the stator  1702 . The bending flexures  1722 ,  1726  can limit the movement of the armature  1710 . The bending flexures  1722 ,  1726  can act as stabilizing elements by counteracting the attraction between the permanent magnets  1716 ,  1718  and the stator  1702 . The spring constants of the bending flexures  1722 ,  1726  can stabilize the armature  1710  in the center of its travel. Other embodiments can include a fewer or greater number of stabilizing elements. 
       FIG. 18  is a simplified illustration of a seventh example of a polarized electromagnetic actuator. The actuator  1800  includes a stator  1802  with two tines  1804 ,  1806  extending out from the stator  1802 . The first tine  1804  can be perpendicular to the stator  1802  while the other tine  1806  can extend out from the stator and have an upside down reversed “L” shape. In other words, the tine  1806  can extend out from the stator  1802  and can include an overhang  1808  that extends out perpendicularly from the tine  1806  towards the tine  1804 . A helical coil  1810  is wrapped around the stator  1802  between the two tines  1804 ,  1806 . 
     A movable armature  1812  can include an arm  1814  that is positioned over the tine  1804  and another arm  1816  that is positioned under the overhang  1808  of the second tine  1806 . The body of the armature  1812  is positioned over the coil  1810  between the tines  1804 ,  1806 . A first permanent magnet  1818  is attached to the tine  1804  between the tine  1804  and armature  1812 . A second permanent magnet  1820  is attached to the outer end of the overhang  1808  between the overhang  1808  and the armature  1812 . The movable armature  1812  is held in a spaced-apart relationship to the stator  1802  and the permanent magnets  1818 ,  1820 . 
     The permanent magnet  1818  produces a magnetic flux ϕ M1  and the permanent magnet  1820  produces a magnetic flux ϕ M2 . The magnetic fluxes ϕ M1 , ϕ M2  provide a background magnetic flux around respective permanent magnets  1818 ,  1820  through the movable armature  1812 , through the tine  1804 , and through the overhang  1808  (but not through the coil  1810 ). Additionally, a magnetic flux ϕ C  is produced when a current is applied to the coil  1810 . The coil magnetic flux ϕ C  travels through the armature  1812  and around the stator  1802  and tines  1804 ,  1806 , but not (or largely not) through the permanent magnets  1818 ,  1820 . As with the other embodiments, the direction of travel of the coil magnetic flux ϕ C  depends on the direction of the current passing through the coil  1810 . 
     The magnetic flux ϕ C  produced by the coil  1810  interacts with the magnetic flux ϕ M1 , ϕ M2  of the permanent magnets  1818 ,  1820  to reduce or cancel one magnetic flux (ϕ M1  or ϕ M2 ) and increase the other magnetic flux. Motion is produced in the movable armature  1812  in the direction of the increased magnetic flux (motion represented by arrow  1822 ). 
       FIG. 19  is a flowchart of one example method of providing a polarized electromagnetic actuator. Initially a movable armature, a stator, a coil, and a permanent magnet of the actuator are provided, as shown in block  1900 . Although only one coil and only one permanent magnet are described, those skilled in the art will recognize that a polarized electromagnetic actuator can include one or more coils and/or one or more permanent magnets. 
     The movable armature and stator can have a desired shape and thickness based on the amount of force to be generated by the actuator. The movable armature, stator, coil, and permanent magnet of the actuator are then configured at block  1902  such that the field produced by the coil does not pass through the permanent magnet. The movable armature, stator, coil, and permanent magnet of the actuator can also be configured such that the field produced by the permanent magnet does not pass through the coil (block  1904 ). Block  1904  can be omitted in some embodiments. 
     The movable armature, stator, coil, and permanent magnet of the actuator are configured so that the magnetic flux of the coil ϕ c  increases the magnetic flux of the permanent magnet in one direction to produce motion in the direction of the increased magnetic flux (block  1906 ). Next, as shown in block  1908 , one or more stabilizing elements are provided to stabilize the movable armature when a current is not applied to the coil. 
     Referring now to  FIG. 20 , there is shown a flowchart of one example method of operating a polarized electromagnetic actuator. Initially, at block  2000  a current is applied to each coil in the actuator. The current flows through each coil in a given direction to produce a magnetic flux in a first direction. The magnetic flux of the coil can increase a magnetic flux of at least one permanent magnet included in the actuator in the first direction to produce a force in the first direction. The force can produce motion in the at least the first direction. 
     The amount of current flowing through the coil can be controlled to controllably vary the amount of force applied to a movable armature and to produce motion in the direction of the increased magnetic flux associated with the at least one permanent magnet (block  2002 ). The amount of current passing through the coil can be increased or decreased depending on the desired amount of force and the desired direction of movement. 
     Next, as shown in block  2004 , a haptic response can be produced based on the force produced by the polarized electromagnetic actuator. The haptic response can be in one direction and/or in multiple directions based on the direction of the current passing through each coil. Additionally or alternatively, the magnitude of the haptic response can be controlled based on the amount of current passing through each coil. 
     Other embodiments can perform the method shown in  FIG. 20  differently. For example, in one embodiment, block  2002  can be omitted. In other embodiments, block  2004  can be performed before block  2002 . 
     Embodiments of polarized electromagnetic actuators can be included in any type of device. For example, acoustical systems such as headphones and speakers, computing systems, haptic systems, and robotic devices can include one or more polarized electromagnetic actuators. Haptic systems can be included in computing devices, digital media players, input devices such as buttons, trackpads, and scroll wheels, smart telephones, and other portable user electronic devices to provide tactile feedback to a user. For example, the tactile feedback can take the form of an applied force, a vibration, or a motion. One or more polarized electromagnetic actuators can be included in a haptic system to enable the tactile feedback (e.g., motion) that is applied to the user. 
       FIG. 21  is a front perspective view of an electronic device that can include one or more polarized electromagnetic actuators. The polarized electromagnetic actuators can be used, for example, to provide haptic feedback to a user. As shown in  FIG. 21 , the electronic device  2100  can be a laptop or netbook computer that includes a display  2102 , a keyboard  2104 , and a touch device  2106 , shown in the illustrated embodiment as a trackpad. An enclosure  2108  can form an outer surface or partial outer surface and protective case for the internal components of the electronic device  2100 , and may at least partially surround the display  2102 , the keyboard  2104 , and the trackpad  2106 . The enclosure  2108  can be formed of one or more components operably connected together, such as a front piece and a back piece. 
     The display  2102  is configured to display a visual output for the electronic device  2100 . The display  2102  can be implemented with any suitable display, including, but not limited to, a liquid crystal display (LCD), an organic light-emitting display (OLED), or organic electro-luminescence (OEL) display. 
     The keyboard  2104  includes multiple keys that can be used to enter data into an application or program, or to interact with one or more viewable objects on the display  2102 . The keyboard  2104  can include alphanumeric or character keys, navigation keys, function keys, and command keys. For example, the keyboard can be configured as a QWERTY keyboard with additional keys such as a numerical keypad, function keys, directional arrow keys, and other command keys such as control, escape, insert, page up, page down, and delete. 
     The trackpad  2106  can be used to interact with one or more viewable objects on the display  2102 . For example, the trackpad  2106  can be used to move a cursor or to select a file or program (represented by an icon) shown on the display. The trackpad  2106  can use any type of sensing technology to detect an object, such as a finger or a conductive stylus, near or on the surface of the trackpad  2106 . For example, the trackpad  2106  can include a capacitive sensing system that detects touch through capacitive changes at capacitive sensors. 
     The trackpad  2106  can include one or more polarized electromagnetic actuators to provide haptic feedback to a user. For example, a cross-section view of the trackpad  2106  along line  17 - 17  can include the cross-section view of the polarized electromagnetic actuator shown in  FIG. 17 . The top surface of the trackpad  2106  can be the top surface of the movable armature  1710 , and the actuator can be included under the top surface of the trackpad  2106 . In other embodiments, one or more polarized electromagnetic actuators included in the trackpad  2106  can be implemented as one or more actuators shown in  FIGS. 3, 7, 8, 11-16 , and  FIG. 18 . The polarized electromagnetic actuators can be positioned in the same direction or in different directions. For example, one polarized electromagnetic actuator can provide motion along an x-axis while a second polarized electromagnetic actuator provides motion along a y-axis. 
     Additionally or alternatively, one or more keys in the keyboard  2104  can include a polarized electromagnetic actuator or actuators. The top surface of a key in the keyboard can be the top surface of the movable armature, and the actuator can be included under the top surface of the key. 
     Referring now to  FIG. 22 , there is shown a front perspective view of another electronic device that can include one or more polarized electromagnetic actuators. In the illustrated embodiment, the electronic device  2200  is a smart telephone that includes an enclosure  2202  surrounding a display  2204  and one or more buttons  2206  or input devices. The enclosure  2202  can be similar to the enclosure described in conjunction with  FIG. 21 , but may vary in form factor and function. 
     The display  2204  can be implemented with any suitable display, including, but not limited to, a multi-touch touchscreen display that uses liquid crystal display (LCD) technology, organic light-emitting display (OLED) technology, or organic electro luminescence (OEL) technology. The multi-touch touchscreen display can include any suitable type of touch sensing technology, including, but not limited to, capacitive touch technology, ultrasound touch technology, and resistive touch technology. 
     The button  2206  can take the form of a home button, which may be a mechanical button, a soft button (e.g., a button that does not physically move but still accepts inputs), an icon or image on a display, and so on. Further, in some embodiments, the button  2206  can be integrated as part of a cover glass of the electronic device. 
     In some embodiments, the button  2206  can include one or more polarized electromagnetic actuators to provide haptic feedback to the user. A cross-section view of the button  2206  along line  17 - 17  can include the cross-section view of the polarized electromagnetic actuator shown in  FIG. 17 . The top surface of the button can be the top surface of the movable armature  1710 , and the actuator can be included under the top surface of the button  2206 . In other embodiments, one or more polarized electromagnetic actuators included in the button  2206  can be implemented as one or more actuators shown in  FIGS. 3, 7, 8, 11-16 , and  FIG. 18 . The polarized electromagnetic actuators can be positioned in the same direction or in different directions. For example, one polarized electromagnetic actuator can provide motion along an x-axis while a second polarized electromagnetic actuator provides motion along a y-axis. 
     Additionally or alternatively, a portion of the enclosure  2202  and/or the display  2204  can include one or more polarized electromagnetic actuators to provide haptic feedback to the user. The exterior surface of the enclosure and/or the display can be the top surface of the movable armature with the actuator included under the top surface of the enclosure and/or display. As with the button  2206 , the polarized electromagnetic actuators can be positioned in the same direction or in different directions. 
     Various embodiments have been described in detail with particular reference to certain features thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the disclosure. And even though specific embodiments have been described herein, it should be noted that the application is not limited to these embodiments. In particular, any features described with respect to one embodiment may also be used in other embodiments, where compatible. Likewise, the features of the different embodiments may be exchanged, where compatible.

Metadata:
Filing Date: 20130927
Publication Date: 20180327
Grant Date: 20180327
Priority Date: 20130927
Inventors: LUBINSKI NICHOLAUS IAN
WRIGHT JAMES E.
HARLEY JONAH A.
BROCK JOHN M.
HENDREN KEITH J.
HOEN STORRS T.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01F7/122", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F7/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F7/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F41/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F7/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F2007/1661", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F7/1646", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F7/1646", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F7/122", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F41/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F7/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F7/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F2007/1661", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F7/16", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 49382586