Patent Document

RELATED U.S. PATENT APPLICATION 
       [0001]    This application claims the benefit and priority to co-pending, commonly-owned U.S. patent application Ser. No. 13/363,713, filed on Feb. 1, 2012, by Leuthold et al., and entitled “Electric Field Measurement Apparatus,” assigned to the same assignee, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    In magnetic recording media, as used in hard disk storage devices, information is written to and read from magnetic elements that represent digital bits. In order to increase the amount of information that can be stored within a given area, the size and distance between these magnetic elements may be reduced so that they may be more densely positioned. At the same time, in order to increase production volume and decrease production cost, the speed at which disks are written to and read from when preparing the disks for use by an end-user may be increased. Thus, accurate location information as a function of time of the spin axis of the disks is useful. 
         [0003]    One way to increase disk production volume and decrease production cost is by increasing the speed at which the disks rotate. Accordingly, more magnetic elements may be accessed within a certain amount of time, thereby yielding more completed disks within the same amount of time. Another way to increase disk production volume and decrease production cost is by performing the same operations on more disks simultaneously, thereby requiring less manufacturing equipment. 
       SUMMARY 
       [0004]    An apparatus includes a circuit, a code modulator, and an actuator. The circuit may be operable to detect displacements of a rotating object while in motion. The circuit may further be operable to detect a position of the displacements. According to one embodiment, the circuit is further operable to generate a signal associated with the position and the displacements. The code modulator may be operable to generate a modulated signal based on the position and the displacements. The actuator may be operable to apply a force to the rotating object. The force may be based on the modulated signal. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0005]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements. 
           [0006]      FIG. 1  shows an apparatus for adjusting displacement motion of a rotating object in accordance with one embodiment. 
           [0007]      FIG. 2  shows a circuit for determining the displacement of a rotating object based on information provided by displacement sensors in accordance with one embodiment. 
           [0008]      FIG. 3  shows an exemplary code modulator in accordance with one embodiment. 
           [0009]      FIG. 4  shows an actuator in accordance with one embodiment. 
           [0010]      FIG. 5  shows a more detailed actuator in accordance with one embodiment. 
           [0011]      FIG. 6  shows an exemplary diagram of the displacement force and the adjustment force in accordance with one embodiment. 
           [0012]      FIG. 7  shows a system in accordance with one embodiment. 
           [0013]      FIG. 8  shows an exemplary flow diagram in accordance with one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. While the embodiments will be described in conjunction with the drawings, it will be understood that they are not intended to limit the embodiments. On the contrary, the embodiments are intended to cover alternatives, modifications and equivalents. Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding. However, it will be recognized by one of ordinary skill in the art that the embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the embodiments. 
         [0015]    For expository purposes, the terms “axially” or “axial direction” refer to a direction along a centerline axis length of a shaft and “radially” or “radial direction” refer to a direction perpendicular to the centerline axis. The term “horizontal” as used herein refers to a plane parallel to the plane or surface of an object, regardless of its orientation. The term “vertical” refers to a direction perpendicular to the horizontal as just defined. Terms such as “above,” “below,” “bottom,” “top,” “side,” “higher,” “lower,” “upper,” “over,” and “under” are referred to with respect to the horizontal plane. 
         [0016]    In general, increasing the speed at which the disks rotate or performing the same operations on more disks simultaneously require more energy, which in turn increases the noise and vibration in the disks&#39; environment. The interferences caused by rapid disk rotation and other interferences may cause random radial displacement or eccentricity of the rotating disk, resulting in non-repetitive run-out. As a result, in combination with the increasingly small size and proximate positions of the magnetic elements, the non-repetitive run-out may interfere with the accurate writing and reading of information stored on the disks, during their various manufacturing phases. In order to improve performance, amplitude of error motions, e.g., non-repetitive run-out, should be reduced. 
         [0017]    Rotating spindles may have a number of different resonance modes, e.g., 8 modes. A resonance mode may be defined as a response of a rotating object, e.g., spindle motor, characterized as a shape of a motion, e.g., pivoting side ways, up/down motions, precession motion, etc., at a given frequency. Resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system&#39;s resonant frequencies. At these frequencies, even small periodic driving forces can produce large amplitude oscillations, because the system stores vibrational energy. However, various physical conditions may change the number and the characteristics of the resonance modes. For example, adding a disk stack may add at least two additional modes. 
         [0018]    In order to improve performance, the biggest modes (e.g., the dominant modes), that store the majority of vibrational energy of the system that contribute to non-repetitive run-out, e.g., the spectrum of the path traveled by the cantilevered end of the spin axis, may be attenuated by increasing the dampening force. Damper burns the energy from motion and applies the force at the right moment in order to compensate for displacement, thereby reducing the vibrational energy stored in the system over time. Moreover, increasing dampening attenuates the amplitude and widens the phase change of the response as opposed to an active bearing element. 
         [0019]    In various embodiments, non-repetitive run-out may have two dominant modes. It is appreciated that suppressing the two dominant modes, as described by embodiments herein, is exemplary and not intended to limit the scope of the present invention. For example, one, three, four, five, or more dominant modes may be suppressed, if desired. 
         [0020]    Force may be expressed as: 
         [0000]        F={umlaut over (W)}.m+{umlaut over (W)}.C+W.k   Eqn.(1)
 
         [0000]    where the first term is related to the force related to mass, the second term is related to the dampening force, and the third term is related to the bearing force. Thus, in various embodiments, the performance of a system may be improved by altering various terms of the force equation (1) above. However, in some embodiments described herein, system performance may be improved by removing vibrational energy from the system by increasing the dampening force (e.g., {umlaut over (W)}.C in equation (1)). The two biggest modes contributing to non-repetitive run-out in X and Y direction with or without angular motion may be expressed as: 
         [0000]        W ( t )= x ( t )+ jy ( t )  Eqn. (2).
 
         [0000]    Angular motion may be defined in an analogous way as rotation about the X and/or Y axis. In order to determine the dampening force, the velocity at which displacement occurs is determined, e.g., {umlaut over (W)}. Accordingly, reducing or minimizing the area defined by Eqn. (2) attenuates the two biggest modes contained in that area, in X and Y direction, that contribute to non-repetitive run-outs. In order to identify where the two biggest modes occur, one may identify the frequencies at which they occur, e.g., two frequencies corresponding to the two biggest modes. Once the frequencies are identified, the area as defined by Eqn. (2) may be reduced to attenuate the biggest modes contributing to non-repetitive run-outs. Taking a Fourier transform of Eqn. (2) may be expressed as: 
         [0000]      Fourier( x ( t )+ jy ( t ))→ W ( f )  Eqn. (3)
 
         [0000]    and frequencies of W(f) that the two biggest mode occur as defined by Eqn. (3) may be determined. 
         [0021]    Referring now to  FIG. 1 , an apparatus for adjusting displacement motion of a rotating object in accordance with one embodiment is shown. According to one embodiment, the rotating object is a spindle, however various embodiments may include any rotating object. The apparatus  100  may include a sensor board  110 , a converter  120 , a filter  130 , and an actuator  140 . It is appreciated that the description of a spindle in the embodiments herein is merely exemplary and not intended to limit the scope of the present invention. For example, the embodiments described herein are equally applicable to other rotating objects such as a rotor, motor, gyroscope, etc. 
         [0022]    In one embodiment, the sensor board  110  detects displacement of the spindle. For example, the sensor board  110  may detect displacement of the spindle in the X-Y direction when the spindle is in motion. The sensor board  110  outputs this information as bit stream. The sensor board  110  may also determine the position of the spin axis of the spindle. It is appreciated that the sensor board  110  may utilize pressure and flow such as a microphone, it may utilize a magnetic field for sensing such as a Hall sensor, it may utilize an electric field such as charge coupling, or it may utilize optics such as optonics or laser, to name a few. However, in the described embodiments, a rotating electrical field is used to determine the position of the spin axis of the spindle. 
         [0023]    The converter  120  may receive the information associated with the displacement of the spindle and the rotational position of the electrical field, as determined by the sensor board  110 . Furthermore, the converter  120  may receive information regarding the spindle, e.g., rotational position of the spindle. Accordingly, the converter  120  generates a feedback signal that contains information regarding the shape of the electrical field and the shape of the spindle, which is stationary. As a result, the sensor board  110  may utilize the feedback signal to filter out stationary information, thereby outputting a bit stream containing only the changing portion of the signal. The bit stream generated contains the displacement of the spindle. The operation of the sensor board  110  and the converter  120  is described in greater detail in  FIG. 2 . 
         [0024]    The filter  130  may receive information associated with the displacement and the position of the rotating electrical field. The filter  130  may determine the instantaneous velocity of a non-repetitive run-out of the spindle. The filter  130  may transmit information related to the instantaneous velocity. For example, the filter  130  may send a force pulse code modulation signal. The force pulse code modulation may include information regarding the location where a force is to be applied to the spindle, the magnitude of the force, which winding coils of the actuator  140  to activate, whether an even or odd winding is to be used by the actuator, etc. Alternatively, the force pulse code modulation may include information regarding the location where a force is applied to the spindle that generates the two dominant modes, the magnitude of the force, etc. 
         [0025]    The actuator  140  generates a force in accordance with the force pulse code modulation and further based on the winding information, e.g., whether odd or even windings are to be used, in order to increase dampening force and reduce the system vibration. As such, the actuator  140  applies a force at a particular position of the actuator  140  to the spindle in order to compensate for the displacement of the spindle, thereby applying the appropriate dampening force. In this embodiment, the actuator  140  utilizes a magnetic field such as electromagnetic force. However, in other embodiments, the actuator  140  may utilize pressure and flow such as air jets, or it may utilize an electric field such as piezo element, to name a few. 
         [0026]      FIG. 2  is a schematic diagram of a circuit  200  that may be used to determine the displacement of a rotating disk based on information provided by displacement sensors, according to an embodiment of the present invention. Circuit  200  includes electrical ground nodes  204  and switches  201 ,  202 , and  203 . Circuit  200  further includes electrodes  205 - 207 , capacitors  208  and  210 , a sigma delta converter  214 , integrator  212 , a controller  211  and a  1 /rev block  216 . 
         [0027]    When a clock signal, e.g., φ 1 , φ 2 , φ 3 , or φ 4 , goes high, the switch corresponding to that clock signal may close, i.e., thereby shorting the connection. Conversely, when a clock signal goes low, the switch corresponding to that clock signal may open. 
         [0028]    Electrodes  205  may include biasing electrodes  205  and electrodes  206  may include sampling electrodes  206 . The sampling electrodes  206  may correspond to or may be coupled with a first sensing ring and a second sensing ring (not shown). Electrodes  207  may include floating electrodes  207  that may correspond to or may be coupled with a floating ring (not shown). Accordingly, the capacitor  209  may correspond to the capacitor assembly formed between the first sensing ring, the second sensing ring, the biasing electrodes  205 , and the floating electrodes  207 . Additional capacitive components between each of the first sensing ring, the second sensing ring, the biasing electrodes  205 , and the floating electrodes  207  are not shown for clarify of the figure. 
         [0029]    Switches  203  open when the signal φ 3  goes low. As a result, biasing electrodes  205  are caused to float. Approximately at the same time, signal φ 4  goes low in preparation for its next rising edge. Once signal φ 2  goes low, the switches  202  may open. Consequently, the capacitors  208  and  210  are caused to float, allowing the capacitors  208  and  210  to sample the next electric field charge created by the biasing electrodes  205  and altered by the displacement of an object within the electric field. The controller  211  may control the rotational position of the electrical field associated with control electrodes used to sample an electrical charge, and the 1/rev block  216  generates a stationary signal associated with electrical field reflecting the shape of the spindle, and a controller  211 . 
         [0030]    Once signal φ 1  goes high, switches  201  may close. As a result, biasing electrodes  205  and sensing electrodes  206  are shorted to the ground nodes  204 . At the same time, the bias is set, which results in a charge transfer across the floating capacitors  209 , which is sampled by the capacitors  208  and  210 . 
         [0031]    Once signal φ 4  goes high, a sigma-delta converter  214  may acquire the sign of the resulting charge on an integrator  212  for further processing. In various embodiments, the integrator  212  may be an operational transconductance amplifier with input and output terminals linked by capacitors  208  and  210 . The integrator  212  may integrate a previously stored value in the sigma-delta converter  214  with a currently measured value and store the integrated value in the sigma-delta converter  214 . Signal φ 2  may go high and cause the switches  202  to close. Accordingly, the charge levels on the sample and hold capacitors  208  and  210  are reset as a result of the short. 
         [0032]    Once signal φ 1  goes low the switches  201  may open, and once the signal φ 3  goes high the switches  203  may close. As a result, the biasing potentials on the biasing electrodes  205  and sensing electrodes  206  are set. At this time, the biasing electrodes  205  may be biased to rotate the electric field to the next electric field rotation. The controller  211  may control the rotational position of the electrical field associated with biasing electrodes  205 , and the 1/rev block  216  generates a stationary signal associated with electrical field reflecting the shape of the spindle, which is fed back with sensing electrodes  206 . 
         [0033]    When signal φ 3  goes low once again, the switches  203  are caused to open. Accordingly, the biasing electrodes  205  float once again, which ends the previous clock cycle  230  and initiates the next clock cycle. 
         [0034]    In another embodiment, when signal φ 2  goes low, the switches  202  may open. Consequently, the capacitors  208  and  210  are caused to float, allowing the capacitors  208  and  210  to sample the next electric field charge created by the biasing electrodes  205  and altered by the displacement of an object within the electric field. Once signal φ 3  goes low, switches  203  may open. As a result, biasing electrodes  205  and sensing electrodes  206  are caused to float. Approximately at the same time, signal φ 4  goes low in preparation for its next rising edge. 
         [0035]    According to one embodiment, once signal φ 1  goes high, switches  201  may close. As a result, biasing electrodes  205  and sensing electrodes  206  are shorted to the ground nodes  204 . This shorting to ground changes the potential of the biasing electrodes  205  and sensing electrodes  206 , which results in a charge transfer across the floating capacitors  209 , which is sampled by the capacitors  208  and  210 . 
         [0036]    In one embodiment, when signal φ 4  goes high, a sigma-delta converter  214  may acquire the sign of the resulting charge on an integrator  212  for further processing. In various embodiments, the integrator  212  may be an operational transconductance amplifier with input and output terminals linked by capacitors  208  and  210 . The integrator  212  may integrate a previously stored value in the sigma-delta converter  214  with a currently measured value and store the integrated value in the sigma-delta converter  214 . Once signal φ 2  goes high, the switches  202  may close. Accordingly, the charge levels on the sample and hold capacitors  208  and  210  are reset as a result of the short. 
         [0037]    It is appreciated that once signal φ 1  goes low, the switches  201  may open, and once signal φ 3  goes high, switches  203  may close. As a result, the biasing potentials on the biasing electrodes  205  and sensing electrodes  206  are set. At this time, the biasing electrodes  205  may be biased to rotate the electric field to the next electric field rotation. 
         [0038]    When signal φ 2  goes low once again in the next clock cycle, the switches  202  are caused to open. Accordingly, the capacitors  208  and  210  are caused to float once again, ending the previous clock cycle and initiating the next clock cycle. 
         [0039]    It is appreciated that 32 biasing electrodes  205  may be used to create 32 electric field positions. For each electric field position, the circuit may complete one clock cycle. As a result, an electric field may be created for each of the 32 positions and the electric field may be sampled for each of the 32 positions. 
         [0040]    In some embodiments, the sigma-delta converter  214  may include multiple registers to store a value corresponding to each position of the electric field. For example, if there are 32 electric field positions, the sigma-delta converter  214  may include 32 registers to store an electric field strength value that corresponds to each position. In various embodiments, when the electric field has completed one full revolution and begins a next revolution, the values in the sigma-delta converter may be overwritten by the average value of the previously stored measurement and the current measurement. As a result, the measurements of each position of an object may be oversampled. 
         [0041]    Accordingly, the sensors along with the converter may determine whether displacement of spindle has occurred. Moreover, the sensors and the converter may determine the position of the displacements and their magnitude. The determined information may be transmitted to the filter, e.g., filter  130 . According to one embodiment, the filter  130  may be a code modulator as described with respect to  FIG. 3 . 
         [0042]    Referring now to  FIG. 3 , an exemplary code modulator in accordance with one embodiment is shown. According to one embodiment, a decimation filter  302  of the code modulator  300  receives a bit stream associated with the amount of displacement and it further receives a position of the electrical field associated with the position of the displacement. The decimation filter  302  reduces the number of samples and filters out the noise. The instantaneous velocities in X and Y directions are calculated using the cosine and sine respectively. The code modulator  300  outputs two signals in this instance, e.g., signal F 1  and signal F 2 , each associated with a dominant mode. Accordingly, it is appreciated that if one desires to remove three dominant modes, the code modulator  300  outputs three signals. In various embodiments, the code modulator  300  may output any number of signals corresponding to any number of desired modes. In further embodiments, the desired modes may include modes other than dominant modes, e.g., minor modes. The output of the code modulator  300  is transmitted to the actuator  140 . 
         [0043]    Referring now to  FIG. 4 , an actuator  400  in accordance with one embodiment is shown. The actuator  400  may include a plurality of stator teeth  406 . The gap between the teeth  406  and the rotor may range between 0.1 mm to 1.0 mm, according to one embodiment. 
         [0044]    Windings  402  and  404  may be wrapped around each tooth to form a respective coil each. It is appreciated that in this embodiment, coil  402  is even and coil  404  is odd. Even and odd are referred to as the direction of the magnetic field or magnetic flux created by a current flowing in the winding of each respective coil. Other coils associated with other teeth may also be either odd or even and the number of windings for each may be equal to either coil  402  or  404  respectively. However, it is appreciated that it is not necessary for all even coils to have the same number of windings and it is further appreciated that it is not necessary for all odd coils to have the same number of windings. For example, one even coil may have 10 windings whereas another even coil may have 12 windings. As such, the number of even or odd coils, and the number of windings for each as described herein are exemplary and not intended to limit the scope of the present invention. 
         [0045]    In this embodiment, the actuator  400  is a 2×5 phase coils where 2 indicates odd/even coils. In this embodiment, the even coils are wound clockwise whereas the odd coils are wound counterclockwise. It is appreciated that the direction of winding described herein is exemplary and not intended to limit the scope of the present invention. Signals F 1  and F 2  depict the two signal forces applied by the actuator to the spindle in order to compensate and adjust the measured displacement and to dampen the force. 
         [0046]    It is appreciated that signal force F 1  and F 2  are snapshots in time and that they change over time as displacement changes and as the spindle spins. For example, possible future signals F 1  and F 2  are depicted as dashed arrows. It is appreciated that the signals F 1  and F 2  shown are exemplary and depending on the measured displacement, etc., the position and magnitude of the signals F 1  and F 2  may change. It is appreciated that signals F 1  and F 2  may be pulse width modulation signals. 
         [0047]    Referring now to  FIG. 5 , a more detailed actuator  500  in accordance with one embodiment is shown. The actuator  500  may include a plurality of teeth, two of which are shown  510  and  512 . Each tooth may have a corresponding coil winding associated with it, e.g., winding  506  associated with tooth  512  and winding  508  associated with tooth  510 . It is appreciated that the windings shown may be odd or even. However, for illustration purposes it is presumed that coil winding  506  is even and wound in clockwise direction and coil winding  508  is odd and wound in a counterclockwise direction. One side of each coil winding may be coupled to a switch. For example, coil winding  506  may be coupled to switch  502  and coil winding  508  may be coupled to switch  504 . The other side of the coil winding may be coupled to a voltage signal source, e.g., V M . 
         [0048]    It is appreciated that even though the same voltage signal source is shown being coupled to these coil windings, different voltage signal source may be coupled, e.g., V M  for one and −V M  for another one. It is also appreciated that the winding, e.g., clockwise or counterclockwise direction and odd or even coil windings, are merely exemplary and not intended to limit the scope of the present invention. 
         [0049]    It is appreciated that the gate of each switch, e.g., gate of switches  502  and  504 , may be coupled to the signal, e.g., signal F 1  and signal F 2 , received from the modulator. It is appreciated that the received signals may be pulse width modulation signals and as such the coils of the actuator perform coil to coil pulse width modulation micro stepping. In response to receiving the signals F 1  and F 2  exceeding a given threshold, switches  502  and  504  close causing V M  to be coupled, thereby causing the current to flow through the coil windings. Flow of current causes an electrical field and therefore a force that is applied to the spindle. The applied force compensates and adjusts for the measured displacements and dampens, which reduces non-repetitive run-outs. 
         [0050]    Referring now to  FIG. 6 , an exemplary top view diagram of the displacement force and the adjustment force in accordance with one embodiment is shown. In this example, two dominant forces contributing to non-repetitive run-outs are shown as nrro 1   610  and nrro 2   620 . In one embodiment, the forces  630  and  640  to be applied to the spindle in order to compensate and adjust for displacements and non-repetitive run-outs are perpendicular to the nrro 1  and nrro 2 . However, it is appreciated that in various embodiments the forces  630  and  640  may not necessarily be perpendicular to the non-repetitive run-outs (as shown). The cancellation forces  630  and  640  may be used to dampen the two dominant modes, in this instance. It is appreciated that the number of cancelation forces varies if the number of dominant modes to be dampened is varied. For example, if three dominant modes are to be dampened then the number of forces applied may be also be three. 
         [0051]    Referring now to  FIG. 7 , a system  700  in accordance with one embodiment is shown. System  700  includes a motor and resolver  710 , journal bearing  720 , thrust bearing  730 , sensor board  740 , optional sensor boards  750 - 760 , and an actuator assembly  770 . According to one embodiment, rotor/payload disk-stack may be coupled to the spindle. The motor and resolver  710  rotates, thereby rotating the spindle. As a result, the payload or the disk stack may experience windage excitation. The journal bearing  720  and the thrust bearing  730  may be used to reduce windage excitation and non-repetitive run-outs. The sensor board  740  is similar to the sensor board  110 ,  200  described above. The sensor board  740  may include the sigma delta component, as described above. 
         [0052]    System  700  may include a filter board (not shown). The filter board may be integrated within the sensor board  740  in one embodiment or it may be integrated within the actuator assembly  770  in another embodiment. According to one embodiment, the filter board is a separate board and not integrated within either of the sensor board  740  or the actuator assembly  770 . The filter board operates similar to that of the filter  130  or the code modulator  300 . 
         [0053]    The actuator assembly  770  operates similar to that of actuator  140 ,  400 , or  500 , as described above. The actuator assembly  770  uses the information from the sensor board  740  and the filter board and applies an appropriate force at an appropriate position to compensate for the measured displacements. As such, non-repetitive run-outs are reduced and dampening is increased. 
         [0054]    It is appreciated that in this exemplary embodiment, additional sensor boards  750  and  760  may also be used to measure displacements, etc., for various sections of the rotating body and for more accurate measurement. However, it is appreciated that the use of the additional sensor boards  750  and  760  is optional. The additional sensor boards  750  and  760  may operate similar to that of sensor board  740 . 
         [0055]    Referring now to  FIG. 8 , an exemplary flow diagram  800  in accordance with one embodiment is shown. At step  810 , displacements of a rotating object, e.g., spindle, is determined. For example, a sensor board as described above may be used. At step  820 , position at which the detected displacements occur is determined. According to one embodiment, a sigma delta circuitry may be used. 
         [0056]    At step  830 , the instantaneous velocity associated with the position of the displacements is determined. According to one embodiment, a filter board or a code modulator, as described above, may be used. At step  840 , a signal based on the instantaneous velocity may be generated. The signal may be generated by the filter board or a code modulator, as described above. The signal may be a pulse width modulation signal. 
         [0057]    At step  850 , an actuator device receives the generated signal. The generated signal is used to turn on/off the switches associated with the actuator device. Turning the switches on/off causes the current to flow through the appropriate tooth(s) of the actuator, e.g., appropriate winding coil. At step  860 , the current that flows through the appropriate tooth of the actuator generates an electrical field and a force resulting thereof. The generated force is applied to the rotating object, e.g., spindle, thereby compensating for the measured displacements and dampening the system. 
         [0058]    The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings.

Technology Category: 3