Abstract:
The present invention pertains to vibration devices that do not require a rotating mass. In accordance with aspects of the invention, a coil causes a plunger to move linearly. A spring device is coupled to one end of the plunger. Activation of the coil causes the plunger to move in a first direction relative to a body and coil deactivation enables the spring device to move the plunger in an opposite direction relative to the body. Activating the coil at a predetermined frequency causes vibration of the plunger. Vibratory forces are transferred via the spring device and coil onto the body at predetermined locations. Opposing spring devices may be affixed to either end of the plunger. Spring devices may be linear or non-linear. Such spring devices may be used in conjunction with magnetic spring devices. A controller and a driver circuit may be used to control system operation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/641,317 filed Jan. 4, 2005 and entitled “VIBRATION DEVICE,” the entire disclosure of which is hereby expressly incorporated by reference herein. 

   BACKGROUND OF THE INVENTION 
   The present invention relates generally to vibration devices and more particularly to non-rotary vibration devices. 
   Vibration devices are used to provide tactile feel in devices such as pagers and telephones. Vibration devices can also be used to provide tactile feedback for computer interfaces and game controllers. Vibration devices can also be used to transfer energy and for vibratory feeders. 
   Some existing vibration devices are rotary actuators with an eccentric mass. In these devices, the vibration force is proportional to the velocity squared of the rotating mass. A disadvantage of such vibrating devices is that the frequency of vibration is coupled to the vibration amplitude; thus, the vibration amplitude cannot be modulated independently from the vibration frequency. Another limitation of rotary vibration devices is that the vibration force is in a radial direction relative to the axis of rotation of the motor. 
   Due to the disadvantages and above limitations mentioned above, it may be desired to build a vibration device where the vibration force is not generated from a rotation. 
   SUMMARY OF THE INVENTION 
   The present invention overcomes the disadvantages and limitations of known vibration devices by providing means of generating vibration that do not use a rotating mass to generate the vibration force. Numerous embodiments and alternatives are provided below. 
   In accordance with an embodiment of the present invention, a vibration device is provided. The vibration device comprises a coil for generating an electromagnetic field, a moveable a moveable mass of magnetic material at least partly encircled by the coil, and a spring device. The coil is affixed at a first end to a body. The spring device is coupled at a first end thereof to the moveable mass and affixed at a second end thereof to the body. The moveable mass is operable to move linearly relative to the body upon generation of the electromagnetic field by the coil and to transfer a vibratory force to the body as the mass moves. 
   In one example, the vibration device further comprises a magnetic end piece coupled to the first end of the coil and to the body adjacent to the first end of the coil. Here, the magnetic end piece is preferably operable to increase magnetic efficiency of the coil and to limit vibration amplitude of the moveable mass. In another example, the spring device comprises first and second spring devices. In this case, the first spring device is coupled at the first end thereof to a first end of the moveable mass and affixed at the second end thereof to a first portion of the body. The second spring device is coupled at the first end thereof to a second end of the moveable mass and affixed at the second end thereof to a second portion of the body. The first and second spring devices are compression fit with the first and second ends of the moveable mass. In this case, the moveable mass may have a length greater or lesser than the length of the coil. 
   In another example, the spring device is a nonlinear spring device. In this case, the nonlinear spring device may be selected so that a resonant frequency of the vibration device varies according to an amplitude of vibration. Preferably the resonant frequency varies according to the amplitude of vibration so as to simulate a vibratory force of a rotating vibration device. In an alternative, the nonlinear spring device is a hardening spring device. In another alternative, an angle of alignment of the spring device relative to the moveable mass varies based on positioning of the moveable mass. 
   In a further example, the spring device comprises a pair of nonlinear spring devices. A first one of the nonlinear spring devices is coupled at the first end thereof to a first end of the moveable mass and at the second end thereof to a first location on the body. The second spring device is coupled at the first end thereof to the first end of the moveable mass and at the second end thereof to a second location on the body. In this case, the vibration device may further comprise an aligned spring device. Here, a first end of the aligned spring device is coupled to a second end of the moveable mass opposite the first end thereof, and a second end of the aligned spring device is coupled to a third location on the body. 
   In yet another example, the spring device is an aligned spring device positioned along a plane of movement of the moveable mass and coupled to a first end of the moveable mass. In this case the vibration device further comprises a magnetic spring device in operative communication with a second end of the moveable mass opposite the first end thereof. 
   In accordance with another embodiment of the present invention a vibratory system is provided. The vibratory system comprises a coil for generating an electromagnetic field, a moveable mass of magnetic material at least partly encircled by the coil, a spring device and a driving circuit. The coil is affixed at a first end to a body. The spring device is coupled at a first end thereof to the moveable mass and affixed at a second end thereof to the body. The driving circuit is coupled to the coil and is operable to generate a modulation signal for directing operation of the coil. The moveable mass is operable to move linearly relative to the body upon generation of the electromagnetic field by the coil based upon the modulation signal and to transfer a vibratory force to the body as the mass moves. 
   In one example, the vibratory system further comprises a controller operatively connected to the driving circuit. The controller is operable to specify at least one of an amplitude of vibration and a frequency of vibration of the vibratory system. The controller preferably issues signals to the driving circuit based upon a state in a computer simulation. 
   In another example the vibratory system further comprises a resonance circuit coupled to the driver circuit for increasing resonance of the vibratory system. In a further example the spring device is a nonlinear spring device. In this case the nonlinear spring device is desirably selected so that a resonant frequency of the vibratory system varies according to an amplitude of vibration. 
   In accordance with a further embodiment of the present invention, a method of controlling a vibration device is provided. Here, the vibration device may include a coil for generating an electromagnetic field and affixed to a body, a moveable mass of magnetic material at least partly encircled by the coil, a spring device coupled at a first end thereof to the moveable mass and affixed at a second end thereof to the body, and a driving circuit coupled to the coil and operable to generate a modulation signal for directing operation of the coil. The method comprises selecting an activation frequency of the coil to approximate a natural frequency of the moveable mass; generating a control signal; supplying the control signal to the driving circuit; and varying current in the coil with the driving circuit to modulate the activation frequency. In one example, the natural frequency varies based on an amplitude of vibration. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A-B  illustrate a vibration device in accordance with aspects of the present invention. 
       FIG. 2  illustrates a vibration device having an end piece in accordance with aspects of the present invention. 
       FIG. 3  illustrates a vibration device having opposing spring devices in accordance with aspects of the present invention. 
       FIG. 4  illustrates a variation of the vibration device of  FIG. 3  in accordance with aspects of the present invention. 
       FIG. 5  is a chart plotting frequency versus amplitude for vibration devices in accordance with the present invention. 
       FIG. 6  illustrates a vibration device employing a non-linear spring device in accordance with aspects of the present invention. 
       FIG. 7  illustrates another vibration device employing non-linear spring devices in accordance with aspects of the present invention. 
       FIGS. 8A-C  illustrate actuation of the vibration device of  FIG. 7 . 
       FIGS. 9A-B  illustrate aspects of non-linear spring device actuation devices in accordance with the present invention. 
       FIG. 10  illustrates a vibration device employing non-linear spring devices and an aligned spring device in accordance with aspects of the present invention. 
       FIG. 11  illustrates a vibration device employing a magnetic coil in accordance with aspects of the present invention. 
       FIG. 12  illustrates another vibration device employing a magnetic coil in accordance with aspects of the present invention. 
       FIG. 13  illustrates a driver circuit in accordance with aspects of the present invention. 
       FIG. 14  illustrates a driver circuit and a controller in accordance with aspects of the present invention. 
       FIG. 15  illustrates an RLC circuit in accordance with aspects of the present invention. 
   

   DETAILED DESCRIPTION 
   An embodiment of the invention is show in  FIGS. 1A-B . As seen in the side view of  FIG. 1A , vibration device  100  includes a moveable mass such as plunger  102  surrounded by a coil  104 . Preferably, the plunger  102  is substantially or completely encircled by the coil  104 . The plunger  102  is attached at one end to a spring device  106 , and the spring device  106  is fixed relative to a body (not shown) onto which a vibration force is being applied. The coil  104  is also fixed relative to the body onto which a vibration force is being applied. 
   The coil  104  and plunger  102  typically have a round cross section, as seen in  FIG. 1B . The coil  104  is an electromagnetic coil and can generate an electromagnetic field when current runs through it. The plunger  102  can be made of ferromagnetic material, permanent magnet material, a combination of permanent magnetic and ferromagnetic materials, and/or materials capable of responding to exert a force in response to exposure of the material to a current, voltage, control signal, electromagnetic field, combination thereof or the like. 
   An alternative embodiment of vibration device  120  is illustrated in  FIG. 2 . As with the vibration device  100 , the vibration device  120  includes a plunger  122 , a coil  124  and a spring device  126 . End piece  128  can be placed at one end of the coil  124  as shown in the figure. When the end piece  128  is ferromagnetic or magnetic it can increase the magnetic efficiency of the coil  124 . The configuration without the end piece in  FIG. 1  has an advantage that the plunger  102  will not contact an end piece, and thus not limit vibration amplitude. Thus both configurations with an end piece and without an end piece have advantages. 
   If the plunger  102  or  122  is ferromagnetic it will be attracted to a magnetic field. Thus when the coil  104  or  124  is activated the plunger will be pulled into the coil, and when the coil is deactivated the spring device will pull the plunger back. In this fashion it is possible to create a vibration of the plunger  102  or  122  by activating and deactivating the coil at a desired frequency. Vibration forces are transferred via the spring device  106  or  126  and the coil  104  or  124  onto a body at the locations where they are fixed to the body. 
   When the plunger  102  or  122  has a permanent magnet material, or a combination of permanent magnet and ferromagnetic material, it can be magnetized along its axis so that one end is magnetic North and the other end is magnetic South. In this configuration the plunger will be attracted into the coil when the current in the coil is operated in one direction. When the current in the coil is operated in another direction, then the plunger will be repelled out outwards from the coil. In this fashion the magnetic forces can apply both an attractive and repulsive force on the plunger, thereby increasing the energy transfer to the plunger. Vibration of the plunger can be generated by controlling the current in the coil. Vibrations can be induced by activating the current in the coil in one direction and then reversing the direction of the current at the desired frequency. 
   Another embodiment of a device in accordance with the present invention is shown in  FIG. 3 . Specifically, a side view of vibration device  140  is illustrated. As with the aforementioned embodiments, a plunger  142  is preferably substantially or completely encircled by coil  144 . Here spring devices  146   a  and  146   b  are disposed on both sides of the plunger  142 . An advantage of this configuration is that the spring devices  146   a,b  can apply compression forces onto the plunger  142 . Therefore, the attachment between the plunger  142  and the spring devices  146   a,b  is simply a compression fit. There is no need for a hole in the plunger  142 , which is a common method for attaching extension spring devices. 
   The plunger can be longer or shorter than the coil.  FIG. 3  illustrates the vibration device  140  with the plunger  142  longer than the coil  144 .  FIG. 4  shows a configuration of the vibration device  140  where plunger  142 ′ is shorter than the coil  144 . 
   A vibrating device which has a mass with a spring device applying a restoring force to the mass can have resonance. When such a system is driven by an exciting force at or close to the resonant frequency large amplitude vibrations can be built up, since the energy from one vibration is transferred to the following vibration. Driving a mass-spring device system at resonance can be used to create large vibration forces from small actuation forces. 
   Many existing mass-spring device vibration systems have spring devices that provide linear or approximately linear restoring forces. In a mass spring device system with a linear spring device, the resonant frequency of the system is a constant for all amplitude vibrations. Accordingly, vibration systems with linear spring device restoring forces have a narrow frequency range over which resonance can be used to increase the force output of the vibrations. However, it may be desired to operate the vibration device at multiple frequencies. 
   To overcome the disadvantage of known linear mass-spring device vibrators and take advantage of resonance, one can use a nonlinear spring device in system of the present invention so that the natural frequency will vary as a function of amplitude. In one embodiment, a nonlinear spring device is preferably used to provide a varying resonant frequency of the vibration device, as a function of vibration amplitude. A hardening spring device is one where the restoring force of a spring device increases faster than a linear spring device (corresponding to a in  FIG. 5 ). As shown in  FIG. 5 , the natural frequency of a mass spring device system with a hardening spring device will increase with increasing amplitudes of vibration. 
   A nonlinear hardening spring device can be used to provide vibration effects that are similar to those of a rotating vibration device. With a rotating vibration device, the amplitude of vibration force increases as the frequency of rotating increases, due to an increasing centrifugal force. In a similar fashion, a mass spring device system that has a hardening nonlinear spring device will have a lower natural frequency when it is excited at lower amplitudes of vibration, and higher natural frequency at higher amplitudes of vibration. Thus, the mass spring device system could be operated at or close to resonance for different amplitude levels and different frequencies. By operating at or close to resonance, a higher level vibration force can be achieved with low power input. 
   Vibration device  200  is shown in  FIG. 6 . Here, plunger  202  may be substantially or completely encircled or otherwise encompassed by coil  204 . A nonlinear spring device  206  is attached to plunger  202 . The coil  204  attracts the plunger  202  when it is activated and the nonlinear spring device  206  opposes the plunger force. The spring device  206  and the coil  204  are preferably fixed at either end to the object onto which the vibration force is imparted. A ferromagnetic end piece  208  may be used to improve the magnetic efficiency of the coil  204 . 
   An alternative embodiment of vibration device  200  that utilizes a nonlinear spring device resorting force is shown in  FIG. 7 . As seen in this figure, vibration device  220  includes a plunger  224  and a coil  224 . An end piece  228  may be disposed at one end of the coil  224 . At least one spring device  226  is attached to the plunger  222  at an angle relative to the axis of motion of the plunger  222 . Here, a pair of spring devices  226   a  and  226   b  is shown. As the plunger  222  moves, the angle between the spring device  226  (e.g.,  226   a  or  226   b ) and the plunger  222  varies, thereby creating a nonlinear restoring force, even if the spring device  226  itself is linear. Thus, an effective nonlinear spring device can be created with nonlinear spring device elements or with linear spring device elements that are configured such that the restoring force on the moving mass is nonlinear. 
   The nonlinearity of the restoring force due to the change in spring device angle is depicted in  FIGS. 8A-C . In position A shown in  FIG. 8A , the spring devices  226   a,b  are perpendicular to the axis of motion of the plunger  222 , and the net spring device restoring force is zero. In position B shown in  FIG. 8B , the plunger  222  is slightly retracted into the coil  224  causing a small angle in the spring devices  226   a,b , and resulting in a net small spring device restoring force. In position C shown in  FIG. 8C , the plunger  222  is retracted even more into the coil  224 , resulting in a larger angle of the spring devices  226   a,b  and a larger net restoring spring device force. As best seen in  FIG. 8C , the net restoring force of the spring devices  226   a,b  is equal to the vector sum of the spring device forces from each spring device. In the configuration shown in  FIG. 8C , this vector sum is twice the magnitude of the force from one spring device multiplied by cos(β), where β is the angle between the force vector applied by the spring device and the axis of plunger motion. Thus, the net restoring spring device force increases more rapidly than with a linear spring device, due to the effect of the varying angle. Of course, it should be understood that a nonlinear spring device can also be use with embodiments that do not have an end piece. 
   A nonlinear spring device can be attached to a moving mass in any vibration device in accordance with the present invention to increase the range over which resonance can be used to increase the amplitude of vibration.  FIGS. 9A and 9B  depict a spring device system  240  showing how an elastic element can be attached to a moving mass  242  to create a desired nonlinear spring device effect. In this embodiment an elastic element such as spring device  246  is attached to the moving mass  242  such that the angle between the moving mass  242  and the spring device  246  changes as the mass moves. The spring device  246  may be implemented as one or more spring devices. Even if the elastic element/spring device  246  itself has a mostly linear relationship between its length and internal force, the net force on the moving mass  242  will be nonlinear. As shown in Position A of  FIG. 9A , the spring device  246  is vertical and perpendicular to the axis of motion of the moving mass  242 . In Position B of  FIG. 9B , the mass  242  has moved, which creates an angle θ between the direction of force of the spring device(s)  246  and the axis perpendicular to the direction of motion of the moving mass  242 . As the angle θ increases, the effective stiffness of the spring devices  246 , as applied onto the moving mass  242 , increases. This creates the effect that at low vibration amplitudes the effective stiffness will be low and the resonant frequency will be low. At higher amplitude vibrations the effective stiffness will increase and the resonant frequency of the system will increase. 
   One can select the desired nonlinearity of the spring device system  240  by choosing the width W between endpoints of the spring devices, and the amplitude of vibration, A, as best shown in  FIG. 9B . A small value for W will result in a larger change in angle θ for a given amplitude of vibration, A, and thus increase the nonlinearity. 
   A nonlinear spring device attached to a moving mass of a vibrating device that uses a mass and spring device to generate vibrations can be used to simulate the vibration achieved with a rotating vibrating device. With a rotating vibration device the amplitude of force increase with increased frequency of rotation. With a nonlinear spring device, low frequency resonance will occur at low amplitude vibrations, which corresponds to the low amplitude forces of the rotating vibrator at low frequencies. With a nonlinear spring device, higher frequency resonance will occur at higher amplitude vibrations, which corresponds to the higher amplitude forces of the rotating vibrator at higher frequencies. 
   In the configuration shown in  FIGS. 9A-B , both the top and bottom spring device  246  can be made of a single element. The top and bottom spring devices  246  cancel out forces that are not in the direction of motion of the moving mass  242 , which is the vertical direction in  FIGS. 9A-B . However, an alternative configuration could use only a single spring device element  246 . The bearing guide (not shown) for the moving mass  242  will provide the necessary reaction forces that keep the moving mass  242  within the bearing guide. 
   In the present invention, a nonlinear spring device can also be use where the plunger or moving mass is ferromagnetic or a permanent magnet. When the plunger is a permanent magnet, the coil can create magnetic forces that attract the plunger, and by reversing the direction of current in the coil, it can create repulsive magnetic forces. 
   A nonlinear spring device can also be use in combination with a linear spring device, as shown in  FIG. 10 . In this figure, vibration device  260  is presented having plunger  262  and coil  264 . Here, spring device  268  is aligned with the axis of motion of the plunger  262 , and could be a linear spring device. Angled spring devices  266   a  and  266   b  are attached to the plunger  262  such that their angle varies as the plunger  262  moves, thereby creating a nonlinear restoring force. The combined effect of the linear spring device  268  and nonlinear spring devices  268   a,b  is a nonlinear restoring force that can be used to generate varying natural frequencies of the system  260 . 
   The angled spring devices shown in the various embodiments herein can be implemented with a single spring device piece, whereby the spring device element passes through a hole or slot in the plunger. The spring devices could be made of metal or elastic (such as a rubber band). The nonlinear spring device(s) could also be formed of a cable in series with a spring device. The cable could easily be attached to the moving mass/plunger. 
   Techniques may also be used to couple programmable devices varying natural frequency into the vibration device or otherwise change the natural frequency by electronic or external control. By integrating actively controlled shape memory alloys (“SMA”), bipoles, strain gauges such as resistive strain gauges, piezoelectrics, devices such as Nanomuscle-brand actuators, or other suitable materials or devices that are capable of producing a movement when exposed to electric current into the springs, one can adjust the restoring force of the springs dynamically. Modulation schemes to programmably control natural frequency can be optimized for any particular angle of the spring device to the plunger motion. 
   It is also possible to generate a magnetic spring device. Several patents assigned to Coactive Drive Corporation describe magnetic spring devices using repulsive forces. Such patents include U.S. Pat. Nos. 6,002,184, 6,147,422 and 6,307,285, the entire disclosures of which are incorporated fully by reference herein. It is possible to modulate the stiffness of such magnetic spring devices by modulating the current in the spring device-coils. As shown in the aforementioned Coactive Drive Corporation patents, these spring devices can be configured though opposing repulsive magnetic forces, or through a single repulsive magnetic force opposed by a mechanical spring device. In either case the stiffness of the spring device can be modulated. The magnetic spring device can be configured in series or parallel with mechanical spring devices. 
   In an embodiment of the invention, a magnetic spring device is employed to achieve the restoring force of the spring device shown in  FIGS. 1A-B . In this case, the stiffness of the magnetic spring device can be modulated to change the resonant frequency of the vibration device. The modulation of frequency can used to provide high amplitude vibration forces over a wide range of frequencies. 
   An embodiment with a magnetic coil is shown in  FIG. 11 . Vibration device  300  is illustrated having a plunger  302  and a coil  304  about the plunger  302 . Here, by way of example only, the plunger end is magnetized such that it has a North pole as indicated by the N at its right side. The plunger  302  may contain permanent magnet material which has been magnetized in this orientation. Alternately the plunger  302  may have ferromagnetic material, and the coil  304  creates the magnetization in the plunger  302 . The plunger  302  is attached on the left hand side of the figure with a mechanical spring device  306 . On the right hand side of the figure is a magnetic spring device  308 . The magnetic spring device preferably contains a permanent magnet  310  which has, for instance, a North pole at its left end as indicated by the N in the figure. The magnetic force between the plunger  302  and the permanent magnet  310  in the configuration shown is repulsive. A secondary coil  312  is desirably close to the permanent magnet  310  of the magnetic spring device  308 . When the secondary coil  312  is activated it can increase or decrease the stiffness of the magnetic spring device  308  depending on the direction of current in the secondary coil  312 . The stiffness of the magnetic spring device  308  can be modified to create the desired resonant frequency of the system. 
   In  FIG. 11  the secondary coil  312  is behind the permanent magnet  310  of the magnetic spring device  308 . An alternative configuration of the vibration device  300 , namely vibration device  320 , is shown in  FIG. 12 . As with the embodiment of  FIG. 11 , the vibration device  320  includes a plunger  322 , a coil  324 , a mechanical spring device  326  and a magnetic spring device  328 . In this embodiment, secondary coil  332  preferably surrounds permanent magnet  330  of the magnetic spring device  328 . 
   The vibrating devices according to the embodiments of the invention herein may include a driver circuit for actuating the coil(s).  FIG. 13  is a block diagram of system  400  illustrating a driver circuit  402  connected to coil  404 . Information such as the operating status of the coil  404  may be fed back to the driver circuit  402 , either directly or indirectly, as shown with dashed line  406 . The driver circuit  402  provides current to the coil  404 . The driver circuit  402  modulates the current in the coil  404  at the desired frequency of vibration. The modulation can be in the form of a sine wave, square wave, rectangle wave, triangle wave, or other shape. For example the driver circuit  402  could use a CMOS 555 timer chip, which generates a rectangle wave. 
   The driver circuit for the vibrator described herein may receive a signal from a controller, such as in system  420  shown in  FIG. 14 . Here, driver circuit  422  is connected to coil  424  as well as to controller  425 . The signal from the controller  425  may specify the desired amplitude and frequency of vibration. The signal from the controller  425  may indicate a desired vibration sensation. The signal from the controller  425  may correspond to a state in a computer simulation such as in a game. For example a specified vibration frequency may correspond to a simulated vehicle driving over a rough road in a computer game. Information such as the operating status of the coil  424  may be fed back to the driver circuit  422  or the controller  425 . As shown by dashed line  426  in  FIG. 14 , coil information is preferably passed (either directly or indirectly) from the coil  424  to the controller  425 . The controller  425  may be, e.g., a general purpose processor, a microprocessor, a digital signal processor, an ASIC, or logic circuits configured to manage operation of the driver circuit  422  and/or the coil  424 . 
   The control signal from a controller, such as the controller  425 , may be a digital signal or an analog signal. There may be one signal or multiple signals. In one embodiment the signal from the controller is an analog signal, where a low voltage corresponds to a desired low frequency of vibration and a desired higher voltage correspond to a higher frequency of vibration. A driver circuit for such an embodiment can include a voltage to frequency converter that will drive the coil at the desired frequencies according to the signal from the controller. 
   Driving a vibrating device according to the present invention at or close to resonance can generate relatively large vibration forces from small actuators and with use of low amounts of electrical power. In one alternative, the driver circuit for the coil desirably includes electrical resonance to increase the overall resonance effect in the system. 
   When current to the coil is shut off, there is remaining energy in the electromagnetic field. As the field collapses this energy can be transferred into a capacitor, which is then returned to the coil in a following coil activation. This embodiment can be in the form of an LC (inductor-capacitor) or LCR (inductor-capacitor-resistor) circuit. The coil provides both inductance and resistance. Accordingly, a capacitor can be added to the circuit with a chosen value so that the electrical resonance will be at or close to the desired driving resonance of the vibration device. An embodiment of an LCR (also referred to as an RLC) circuit is shown in  FIG. 15 . In this figure, V(t) indicates the varying driving frequency, which can be in the form of a sine wave, square wave, rectangle wave, triangle wave, or other form. 
   Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. For example, the plunger and/or springs may be comprised of various materials. They may be integrated with active materials such as shaped memory alloys, bipoles, Nanomuscle-brand devices, strain gauges, piezoelectrics, etc. The actuation force to compel movement of the plunger may be caused in whole or in part by active material in the plunger and/or springs. The actuation force may also be a combination of modulation of the active material and the electromagnetic field. The natural frequency of the system may be modified by control of the active material in or around the plunger and/or springs. Active material may also be used to sharpen, dampen or contribute to the actuation, effect, dampening, linearity or manipulation of the device and haptic experience gained thereby.