Abstract:
A linear resonant actuator includes: (a) an electromechanical polymer (EMP) actuator; (b) a substrate having a first surface and a second surface, the EMP actuator being mounted on the first surface of the substrate; (c) clamping structure provided on two sides of the substrate so as to allow the substrate to vibrate freely between the two sides of the substrate, in response to an electrical stimulation of the EMP actuator; and (d) an inertial mass element having a contact surface for attaching to the substrate at the second surface of the substrate. The inertial mass element may include contact structures provided to attach to the substrate along thin parallel lines. In one embodiment, the inertial mass element may have a “T” shape, or any suitable shape for stability.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The patent invention is related to electro-active polymer (EAP) or electromechanical polymer (EMP) 1  actuators. In particular, the present invention is related to EAP- or EMP-based linear resonant actuators that provide a haptic response, suitable for use in handheld or mobile devices.  1  Electromechanical polymers (EMPs) refer to polymers that provide a mechanical response in response to a electrical stimulus and vice versa. EMPs are members of a broader class of polymers known as “electroactive (EAP) polymers,” which responses to electrical stimuli are not necessarily limited just to mechanical responses. 
         [0003]    2. Discussion of the Related Art 
         [0004]    Actuators that are light and miniaturized are highly desirable in many mobile applications. A class of actuators, known as linear resonant actuators (“LRAs”), use magnetic fields, electrical currents or both to control an actuator, so as to create a force that imparts motion to an attached mass. The mass may also be attached to a spring, which helps it return to a central quiescent position. Driving the mass in reciprocal motion about the central quiescent position causes a vibration. However, these actuators typically have a very narrow bandwidth, consume significant power and are limited in their applications because of their size. Resonance tuning of such actuators are also relatively difficult to provide. 
       SUMMARY 
       [0005]    According to one embodiment of the present invention, a linear resonant actuator includes: (a) an electromechanical polymer (EMP) actuator; (b) a substrate having a first surface and a second surface, the EMP actuator being mounted on the first surface of the substrate; (c) clamping structure provided on two sides of EMP actuator so as to allow the substrate to vibrate with the EMP actuator, in response to an electrical stimulation of the EMP actuator; and (d) an inertial mass element having a contact surface for attaching to the substrate at the second surface of the substrate. The inertial mass element may include contact structures provided to attach to the substrate along thin parallel lines. In one embodiment, the inertial mass element may have a “T” shape, or any suitable shape for stability. 
         [0006]    According to a second embodiment of the present invention, the linear resonant actuator may further include (a) a second EMP actuator; (b) a second substrate having a first surface and a second surface, the second EMP actuator being mounted on the first surface of the second substrate; and (c) second clamping structure provided on two sides of the second EMP actuator, so as to allow the second substrate to vibrate with the second EMP actuator, in response to an electrical stimulation of the second EMP actuator. In this second embodiment, the inertial mass element includes a second contact surface for attaching to the second substrate at the second surface of the second substrate. Preferably, the first EMP actuator and the second EMP actuator are actuated by control signals that are 180° of each other. 
         [0007]    The present invention is better understood upon consideration of the detailed description below in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows, in cross section, generalized linear resonant actuator  100 , in accordance with one embodiment of the present invention. 
           [0009]      FIG. 2  shows, in cross section, generalized linear resonant actuator  100 , in which inertial mass  103  is provided a different shape that is shown in  FIG. 1 , in accordance with one embodiment of the present invention. 
           [0010]      FIG. 3  shows, in cross section, an alternative implementation of LRA  100 , in which inertial mass  103  is provided reduced contact surface areas  107   a  and  107   b  that are collectively smaller than contact surface area  107  of the implementation of LRA  100  shown in  FIG. 1 , in accordance with one embodiment of the present invention. 
           [0011]      FIG. 4  shows, in cross section, an alternative implementation of LRA  100 , in which inertial mass  103  is provided reduced contact surface areas  107   a  and  107   b  that are collectively smaller than contact surface area  107  of the implementation of LRA  100  shown in  FIG. 2 , in accordance with one embodiment of the present invention. 
           [0012]      FIG. 5  shows an alternative implementation of LRA  100 , in which clamping structure  104  includes screw  105  to secure substrate  102 , according to one embodiment of the present invention. 
           [0013]      FIG. 6  shows EMP-based LRA  200 , according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    The present invention provides electromechanical polymer-based (EMP-based) linear resonant actuators (LRA). EMP-based LRAs are disclosed, for example, in copending U.S. patent application (“Copending Patent Application I”), Ser. No. 13/917,501, entitled “Ultra-thin Inertial Actuator,” filed on Jun. 13, 2013. The disclosure of Copending Patent Application I is hereby incorporated by reference in its entirety. 
         [0015]      FIG. 1  shows generalized linear resonant actuator (LRA)  100 , in accordance with one embodiment of the present invention. As shown in  FIG. 1 , LRA  100  includes electromechanical polymer (EMP) actuator  101 , which is mounted on flexible substrate  102 . Description of suitable EMP actuators for this application may be found, for example, in copending U.S. patent application (“Copending Patent Application II”), Ser. No. 13/683,963, entitled “Localized Multimodal Electromechanical Polymer Transducers,” filed on Nov. 21, 2012. The disclosure of the Copending Patent Application II is hereby incorporated by reference in its entirety. In this embodiment, substrate  102  may be a stainless steel metal strip (e.g., stainless steel strip) or a plastic strip. Although shown in  FIG. 1  to be much thinner than EMP actuator  101 , substrate  102  may actually be thicker or comparable to EMP actuator  101 , which may be, for example, 0.1 mm thick. Substrate  102  may be held in position by clamping structures  104  on both sides of EMP actuator  101  and is allowed to vibrate freely between the clamping structures. In  FIG. 1 , inertia mass  103  is attached on the side of substrate  102  that is opposite to the side on which EMP actuator  101  is mounted. 
         [0016]    Inertia mass  103  can be provided in any of numerous shapes. As shown in  FIG. 1 , inertial mass  103  has a “T” shape in cross section. Alternatively, inertial mass  103  may also have the trapezoidal shape in cross section, as illustrated in  FIG. 2 . As shown in  FIG. 2 , as in the “T” shape illustrated in  FIG. 1 , inertial mass  103  includes relatively small flat contact surface  107  that contacts substrate  102 . Significantly, inertial mass  103  is attached to substrate  102  in such a manner that, while designed to affect the resonant amplitude and frequency in the vibration of substrate  102 , inertial mass  103  does not otherwise limit the motion of substrate  102 . To achieve even better vibrations, the contact surface of inertial mass  103  is preferably diminished. Inertial mass  103  may include metal, or other suitable materials (e.g., polymers or dielectrics). For example, inertial mass  103  may have a mass between 0.5 g-10 g, such as 1 g-5 g. 
         [0017]      FIGS. 3 and 4  show, respectively, alternative implementations of LRA  100 , in which inertial mass  103  is provided contact surface areas  107   a  and  107   b  that are even smaller than surface areas  107  of the implementations of LRA  100  shown in  FIGS. 1 and 2 . Ideally, inertial mass  103  of  FIGS. 3 and 4  contact substrate  102  along parallel narrow lines or strips  107   a  and  107   b,  each running perpendicular to the cross section. Alternatively, contact surface areas  107   a  and  107   b  may be provided by semi-cylindrical projections from inertial mass  103 . The smaller contact areas reduce the constraints on the vibration, but at the same time maintain stability to inertial mass  103 . In some embodiments, when LRA  100  is used in an electronic device, rather than expressly providing an inertial mass, EMP  101  actuator may be attached to a movable component of the electronic device (e.g., a button or a display component), which serves the function of inertial mass  103 . 
         [0018]      FIG. 5  shows an alternative implementation of LRA  100 , in which clamping structures  104  includes screws  105  to secure substrate  102 , according to one embodiment of the present invention. Clamping structure  104  may include anchor element  108  on each side of substrate  102 . Each combination of anchor element  108  and screw  105  in clamping structure  104  allows tension to be applied to substrate  102 . For example, as shown in  FIG. 5 , anchor elements  108  each provide a contact surface to substrate  102 . As each of screws  105  is turned, substrate  102  is pulled at the corresponding contact surface of substrate  102 , thereby resulting in a corresponding tension along the surface of substrate  102 . The weight of inertial mass  103  and the tension in substrate  102  are parameters that determine the resonant frequency of LRA  100 . 
         [0019]      FIG. 6  shows EMP-based LRA  200 , according to one embodiment of the present invention. Unlike LRA  100  of  FIGS. 1-5 , LRA  200  includes EMP actuators  101   a  and  101   b  mounted on substrates  102   a  and  102   b,  respectively. (Substrates  102   a  and  102   b  may be provided from a single sheet of flexible material, such as shown in  FIG. 6 ). As shown in  FIG. 6 , inertial mass  103  has two surfaces  109   a  and  109   b  which are respectively attached to substrates  102   a  and  102   b.  Preferably, EMP actuators  101   a  and  101   b  are actuated or driven by control signals that are 180° out of phase, so as to create a maximally reinforcing vibration. In  FIG. 6 , clamping structure  104  includes single screw  105  on anchor element  108   b  and stationary anchor element  108   a  on the other side, so that tension adjustments in substrates  102   a  and  102   b  may be made simultaneously. Each of anchor elements  108   a  and  108   b  provides contact surfaces on both substrates  102   a  and  102   b.  As screw  105  is turned, substrates  102   a  and  102   b  are both pulled in the direction away from anchor  108   a,  thereby increasing the tensions in both substrates  102   a  and  102   b.  As shown in  FIG. 6 , inertial mass  103  has, in cross section, the shape of two trapezoids placed on top of each other in mirrored orientations. Alternatively, inertial mass  103  may have a shape (in cross section) of two “Ts” placed in mirrored orientations on top of each other. 
         [0020]    In conventional dielectric elastomers, a high voltage (e.g., in kilovolts) is required to create an appreciable vibration. Such a high voltage is hazardous and typically requires expensive special circuit isolation not readily available to handheld consumer electronic devices. In comparison, much lower voltages, such as voltages below 200V, may be used with an inertial actuator of the present invention. 
         [0021]    An EMP layer in an EMP actuator of the present invention, in film form, may be selected from any of: P(VDF x -TrFE y -CFEI- x - y ), P(VDF x -TrFE y -CTFEi —x   —y ), poly(vinylidene fluoride-trifluoroethylenevinylidede chloride) (P(VDF-TrFE-VC)), poly(vinylidene fluoride-tetrafluoroethylenechlorotrifluoroethylene) (P(VDF-TFE-CTFE)), poly(vinylidene fluoride-trifluoroethylenehexafluoropropylene), poly(vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene), poly(vinylidene fluoride-trifluoroethylene-tetrafluoroethylene), poly(vinylidene fluoridetetrafluoroethylene-tetrafluoroethylene), poly(vinylidene fluoride-tri fluoroethylene-vinyl fluoride), poly(vinylidene fluoride-tetrafluoroethylene-vinyl fluoride), poly(vinylidene fluoridetrifluoroethylene-perfluoro(methyl vinyl ether)), poly(vinylidene fluoride-tetrafluoroethylene-perfluoro(methyl vinyl ether)), poly(vinylidene fluoride-trifluoro ethylene-bromotrifluoroethylene, polyvinylidene), poly(vinylidene fluoride-tetrafluoroethylenechlorofluoroethylene), poly(vinylidene fluoride-trifluoroethylene-vinylidene chloride), and poly(vinylidene fluoride-tetrafluoroethylene vinylidene chloride), or in a general form of P(VDF x -2nd monomer y -3rd monomer 1-x-y ), where x may range from 0.5 to 0.75, and y may range from 0.45 to 0.2. Suitable polymers are also described in U.S. Pat. No. 6,787,238. 
         [0022]    A suitable EMP layer can also be selected from high energy electron irradiated P(VDF x -TrFE 1-x ) copolymers, where x varies from 0.5 to 0.75 (See, e.g., U.S. Pat. Nos. 6,423,412 and 6,605,246 for representative copolymers and compositions). A suitable EMP can be selected from the copolymer of P(VDF 1-x -CTFE x ) or P(VDF 1-x -HFP x ) where x ranges from 0.03 to 0.15 in moles. A suitable EMP can be a blend of one or more terpolymers with one or more other polymers. The EMP film can be uniaxially stretched and in fabricating the EMP actuator, the uniaxial stretching direction may be along the displacement direction of the actuator. The EMP films can be in a non-stretched form or biaxially stretched. 
         [0023]    An EMP layer for an EMP actuator of the present invention may include semi-crystalline electromechanical polymer-based actuator materials (e.g., modified P(VDF-TrFE)), which provide remarkably improved performance for high definition haptics in handheld consumer devices. The EMP actuators of the present invention are shock-tolerant, require modest voltages consistent with requirements in OEM products, and are capable of high definition responses. Such an electro-active material can exhibit significant electrostriction (e.g., an electric field-induced strain 7%, a 70 times increase over the conventional piezo-ceramics and piezo-polymers). Furthermore, this class of polymers also possesses a high force capability, as measured by the high elastic energy density of 1 J/cm3. Suitable EMPs in this class include high energy density irradiated poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE), as described in U.S. Pat. Nos. 6,423,412 and 6,605,246), P(VDFTrFE)-based terpolymers , such as poly(VDF-TrFE-chlorotrifluoroethylene), (P(VDF-TrFECTFE)), poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene), (P(VDF-TrFE-CFE)), and the like. U.S. Pat. No. 6,787,238). The disclosures in patent applications referred to in this application are incorporated herein by reference. The EMP layer may also be a relaxor ferroelectric polymer. A relaxor ferroelectric polymer may be a polymer, copolymer, or terpolymer of vinylidene fluoride. Examples include P(VDF-TrFE-CFE) or P(VDF-TrFE-CTFE) terpolymer, a high energy irradiated P(VDF x -TrFE1-x) copolymer, where x is between 0.5 and 0.75 inclusive, P(VDF1-x-CTFEx) or P(VDF1-x-HFPx) where x is in the range from 0.03 to 0.15 molar, polymer blends such as blends of P(VDF-CTFE) with P(VDF-TrFE-CFE) or P(VDF-TrFE-CTFE), where the content of P(VDF-CTFE) is between 1% and 10% by weight. 
         [0024]    The detailed description above is provided to illustrate specific embodiments of the present invention and is not intended to limiting. Numerous modifications and variations within the scope of the present invention are possible. The present invention is set forth in the accompanying claims.