Patent Publication Number: US-2009219791-A1

Title: Optical disc apparatus and tracking control method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-048416, filed Feb. 28, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     One embodiment of the present invention relates to an optical disc apparatus and a tracking control method. 
     2. Description of the Related Art 
     Read-only optical discs or recordable optical discs, such as CDs (Compact Discs), DVDs (Digital Versatile Discs) and HD DVDs (High Definition Digital Versatile Discs), have been used as recording media which are capable of storing digital video. 
     When tracking control is executed to record/reproduce data on/from the optical disc, there are known an optical disc apparatus and a tracking control method, wherein a track error signal is generated by a push-pull method. 
     In this optical disc apparatus, a laser beam, which is emitted from a laser light source, is radiated on an information recording surface of the optical disc through an objective lens. Further, return light is received by a light-receiving element. In the optical disc apparatus, low-frequency components of signals, which are output from the channels of the light-receiving element, are extracted, and subtraction is performed between these low-frequency components, thereby producing a track error signal. On the basis of the track error signal, tracking control is executed. 
     There has been proposed a conventional optical disc apparatus and a tracking control method, wherein a side beam is so set as to scan a position with an offset in the radial direction of the optical disc  22  by an about (¼+n)P or (¾+n)P, relative to a main beam from a laser light source, and a difference signal is generated from push-pull signals PPs 1  and PPs 2  of return light of the side beam, thereby generating a track cross signal TCS (see Patent Document 1). 
     Even if the above-described track control is executed, however, when a servo is executed on a non-recorded track, whose neighboring track is a recorded track, or on a recorded track, whose neighboring track is a non-recorded track, the return light from the optical disc is influenced by the neighboring track, and there may arise such a case that a non-negligible offset occurs in a track error signal. In such a case, track servo stability is deteriorated, and a problem such as track slip may occur. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention. 
         FIG. 1  schematically shows an example of an optical disc apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a view for explaining an example of the structure of a track error signal generating unit of the optical disc apparatus shown in  FIG. 1 ; 
         FIG. 3A  shows an example of a signal waveform which is used in tracking control according to the first embodiment of the invention; 
         FIG. 3B  shows an example of a signal waveform which is used in tracking control according to the first embodiment of the invention; 
         FIG. 3C  shows an example of a signal waveform which is used in tracking control according to the first embodiment of the invention; 
         FIG. 3D  shows an example of a signal waveform which is used in tracking control according to the first embodiment of the invention; 
         FIG. 3E  shows an example of a signal waveform which is used in tracking control according to the first embodiment of the invention; 
         FIG. 3F  shows an example of a signal waveform which is used in tracking control according to the first embodiment of the invention; 
         FIG. 4  is a flow chart for describing an example of a tracking control method according to the first embodiment of the invention; 
         FIG. 5  schematically shows an example of an optical disc apparatus according to a second embodiment of the invention; 
         FIG. 6A  shows an example of a signal waveform which is used in a tracking control method according to the second embodiment of the invention; 
         FIG. 6B  shows an example of a signal waveform which is used in the tracking control method according to the second embodiment of the invention; 
         FIG. 6C  shows an example of a signal waveform which is used in the tracking control method according to the second embodiment of the invention; and 
         FIG. 6D  shows an example of a signal waveform which is used in the tracking control method according to the second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, there is provided an optical disc apparatus comprising a light source device which radiates light on a recording medium; light detection means for detecting return light from the recording medium; track error signal generation means for generating, on the basis of a detection result by the light detection means, a second track error signal which is used for tracking control; and control means for executing tracking control on the basis of the second track error signal, wherein the track error signal generation means includes: means for extracting a plurality of low-frequency components of signals which are detected by a plurality of light-receiving units of the light detection means, and performing a subtraction between the plurality of low-frequency components, thereby generating a first track error signal; extraction means for extracting high-frequency components of the signals which are detected by the plurality of light-receiving units of the light detection means; detection means for detecting envelope signals of the high-frequency components which are obtained by the extraction means; means for generating a compensation signal by performing an addition of the envelope signals obtained by the detection means or a subtraction between the envelope signals; and compensation means for compensating the first track error signal by using the compensation signal, thereby generating the second track error signal. 
     An optical disc apparatus and a tracking control method according to a first embodiment of the present invention will now be described with reference to the accompanying drawings. 
       FIG. 1  is a block diagram showing an optical disc apparatus  1  according to the first embodiment of the invention. An optical disc  2  is a read-only optical disc or a recordable optical disc, such as a CD, a DVD or an HD DVD. Examples of the DVD include read-only DVDs, such as a DVD-Video and a DVD-ROM (Read-Only Memory), and recordable DVDs, such as a DVD-R (Recordable), a DVD-RW (Rewritable) and a DVD-RAM (Random Access Memory). 
     The optical disc  2  in this optical disc apparatus  1  according to the present embodiment is formed of an LtoH-type recording material in which the degree of light absorption decreases after recording, compared to that before recording. 
     The optical disc  2  is rotated by a disc motor  3 . The disc motor  3  is controlled by a disc motor control circuit  4 . Recording/reproduction of information on/from the optical disc  2  is performed by an optical pickup  5 . An objective lens  6  is provided in the optical pickup  5 . The objective lens  6  is movable in a focusing direction (i.e. the optical axis direction of the lens) by the driving of a focusing actuator  7 , and is movable in a tracking direction (i.e. the radial direction of the optical disc, which is perpendicular to the optical axis direction of the lens) by the driving of a tracking actuator  8 . 
     A recording data generating circuit  9  adds an error correction code to data which is supplied from a host apparatus  25  via an interface circuit  24  at a time of information recording, and adds a sync code, etc. to the data, thereby altering the data to data in a recording format. Further, the recording data generating circuit  9  modulates the data in the recording format, and delivers the modulated data to a laser control circuit  10 . At a time of information recording (at a time of mark formation), on the basis of the data delivered from the recording data generating circuit  9 , the laser control circuit  10  supplies a write signal to a laser diode  11  in the optical pickup  5 . 
     The laser diode  11  is selected from among a laser diode for CDs with a wavelength of about 780 nm (nanometer), a laser diode for DVDs with a wavelength of about 650 nm, and a laser diode for HD DVDs with a wavelength of about 405 nm. One of these laser diodes is selectively used in accordance with the kind of the optical disc  2  which is loaded in the optical disc apparatus  1 . One of the laser diodes is selected in accordance with a signal that is supplied from the laser control circuit  10 , and emits a laser beam. 
     The laser beam, which is emitted from the laser diode  11 , is radiated on the optical disc  2  via an optical unit  12  and the objective lens  6 . Reflective light of the laser beam, which is emitted from the laser diode  11  and reflected by the optical disc  2 , is led to a photodetector  13  via the objective lens  6  and optical unit  12 . As shown in  FIG. 2 , the photodetector  13  according to the present embodiment includes, for example, two light-receiving units  13 A and  13 B. These two light-receiving units  13 A and  13 B are arranged symmetric with respect to a point corresponding to the center of the track on the optical disc  2 , so as to receive the light which is reflected and diffracted from the track on the optical disc  2 . Output signals from the photodetector  13  are supplied to an RF amplifier  14 . 
     The RF amplifier  14  processes the detection signals from the photodetector  13 , generates a focus error signal (FE signal) indicative of an error from a just focus in the axial direction between the signal recording surface and the beam spot, a track error signal (TE signal) indicative of an error in the disc radial direction between the center of the beam spot of the laser beam and the center of the track, and a reproduction signal (RF signal), and delivers the generated FE signal, TE signal and RF signal to an A/D converter  15 . 
     At the time of processing the detection signals from the photodetector  13 , the RF amplifier  14  generates the above-described signals by properly setting the parameter values at the time of generating the signals in accordance with the kind of the laser diode  11  that is used. 
     The RF amplifier  14  of the optical disc apparatus  1  according to the present embodiment includes a track error signal generating unit  14 A. As shown in  FIG. 2 , the track error signal generating unit  14 A includes a low-pass filter LPF 1 , to which an output signal S 2  from the light-receiving section  13 B is supplied, and a low-pass filter LPF 2 , to which an output signal S 1  from the light-receiving section  13 A is supplied. 
     Output signals from the low-pass filter LPF 1  and low-pass filter LPF 2  are supplied to a subtracter C 1 , and the output signal from the low-pass filter LPF 2  is subtracted from the output signal from the low-pass filter LPF 1 . An output signal from the subtracter C 1  is delivered to a subtracter C 3  as a first track error signal S 3 . 
     As shown in  FIG. 2 , the track error signal generating unit  14 A includes a high-pass filter HPF 1 , to which the output signal S 2  from the light-receiving section  13 B is supplied, and a high-pass filter HPF 2 , to which the output signal S 1  from the light-receiving section  13 A is supplied. 
     An output signal from the high-pass filter HPF 1  is supplied to an envelope detector DET 1 . An output signal from the high-pass filter HPF 2  is supplied to an envelope detector DET 2 . The envelope detector DET 1  and envelope detector DET 2  detect envelopes of the high-frequency signals S 1  and S 2 . Specifically, the envelope detector DET 1  and envelope detector DET 2  extract amplitude levels of the high-frequency signals S 1  and S 2 . 
     Output signals S 4  and S 5  from the envelope detector DET 1  and envelope detector DET 2  are supplied to a subtracter C 2 , and the output signal S 5  from the envelope detector DET 2  is subtracted from the output signal S 4  from the envelope detector DET 1 . An output signal from the subtracter C 2  is delivered to the subtracter C 3  as a high-frequency push-pull signal S 6 . 
     In the subtracter C 3 , the high-frequency push-pull signal S 6  is subtracted from the first track error signal S 3  that is supplied from the subtracter C 1 , and the first track error signal S 3  is compensated. A second track error signal S 7 , which is obtained after the compensation, is output from the subtracter C 3 . In the optical disc apparatus  1  according to the present embodiment, the output signal S 7 , which is output from the subtracter C 3 , is supplied to the A/D converter circuit  15  as a TE signal. 
     The signal from the A/D converter  15  is supplied to a CPU (Central Processing Unit)  21 , etc. via a bus  20 . 
     A focus/tracking control circuit  16  generates a focus control signal and a tracking control signal in accordance with the FE signal and TE signal that are supplied from the A/D converter  15 , and outputs the focus control signal and tracking control signal to the focusing actuator  7  and tracking actuator  8 , thus driving the objective lens  6 . Thereby, a focusing servo, which constantly effects just focusing of the laser beam on the information recording surface of the optical disc  2 , and a tracking servo, with which the laser beam constantly traces the track formed on the optical disc  2 , are executed. 
     The RF signal is converted to a digital signal by the A/D converter  15 , and the digital signal is supplied to a PLL circuit  17  as channel-bit data. The PLL circuit  17  generates, from the data supplied from the A/D converter  15 , a reproduction clock, which is synchronized with the data, and channel-bit-unit reproduction data, and outputs them to a data reproduction circuit  18 . The data reproduction circuit  18  decodes the format, demodulates the reproduction data and reproduces byte data. The reproduced data is output to an error correction circuit  19 . 
     The error correction circuit  19  executes error correction by using an error correction code which is assigned to the reproduction data, and the error-corrected data is output to the host apparatus  25  via the interface circuit  24 . 
     The disc motor control circuit  4 , recording data generating circuit  9 , laser control circuit  10 , A/D converter circuit  15 , focus/tracking control circuit  16 , PLL circuit  17 , data reproduction circuit  18  and error correction circuit  19  are controlled by the CPU (Central Processing Unit)  21  via the bus  20 . 
     The CPU  21  executes an overall control of the optical disc apparatus  1  in accordance with an operation command which is supplied from the host apparatus  25  via the interface circuit  24 . The CPU  21  uses a RAM (Random Access Memory)  22  as a work area of, e.g. a buffer memory at the time of recording/reproduction, and executes a predetermined control according to the a program stored in a ROM (Read-Only Memory)  23 . 
     Next, a tracking control method inn the above-described optical disc apparatus  1  is described with reference to the accompanying drawings. The description below is directed to the case in which waveforms shown in  FIG. 3A  to  FIG. 3F  are used as examples of waveforms for use in the tracking control, and a track error signal is generated from return light from the optical disc  2  when a laser beam is radiated on a region where a recorded track and a non-recorded track neighbor on the optical disc  2 . 
     If return light from the optical disc  2  is detected by the light-receiving units  13 A and  13 B of the photodetector  13  (block ST 1 ), an output signal S 1 , which is output from the light-receiving unit  13 A, is supplied to the low-pass filter LPF 2 , and an output signal S 2 , which is output from the light-receiving unit  13 B, is supplied to the low-pass filter LPF 1 . 
     The low-pass filter LPF 1  extracts a low-frequency component of the supplied signal S 2 , and outputs the low-frequency component to the subtracter C 1 . The low-pass filter LPF 2  extracts a low-frequency component of the supplied signal S 1 , and outputs the low-frequency component to the subtracter C 1 . The subtracter C 1  subtracts the signal, which is supplied from the low-pass filter LPF 2 , from the signal that is supplied from the low-pass filter LPF 1 , and outputs a subtraction result as a first track error signal S 3 . 
     At this time, in the case where the signals, which are detected by the light-receiving units  13 A and  13 B, have signal waveforms, as shown in  FIG. 3A  and  FIG. 3B , the first track error signal S 3  has a waveform having an offset, as shown in  FIG. 3C . The first track error signal S 3  is supplied to the subtracter C 3 . 
     If attention is paid to the part where the offset occurs in the first track error signal S 3 , the timing of a transition region, where an amplitude level of the high-frequency component, in which a recording signal is superimposed from the non-recorded state, increases, differs between the output signal S 1  from the light-receiving unit  13 A and the output signal S 2  from the light-receiving unit  13 B. The reason for this is that there is a time difference in timing at which the return light of the laser beam that is radiated on the boundary between the recorded track and the non-recorded track of the optical disc  2  is detected by the light-receiving units  13 A and  13 B. 
     The initial tracking error signal S 3  is a signal which is representative of a difference between low-frequency components (i.e. mean values) which are extracted from the signals that are output from the light-receiving units  13 A and  13 B. Thus, the offset occurs in the first track error signal S 3  due to the timing difference at the transition region. 
     In the tracking control method according to the present embodiment, the offset, which occurs at the transition period as described above, is compensated in the following manner. 
     Specifically, if return light from the optical disc  2  is detected by the light-receiving units  13 A and  13 B (block ST 1 ), the output signal S 1 , which is output from the light-receiving unit  13 A, is supplied to the high-pass filter HPF 2 , and the output signal S 2 , which is output from the light-receiving unit  13 B, is supplied to the high-pass filter HPF 1 . 
     The high-pass filter HPF 1  extracts a high-frequency component of the supplied signal S 2  (block ST 2 ) and delivers the high-frequency component to the envelope detector DET 1 . The high-pass filter HPF 2  extracts a high-frequency component of the supplied signal S 1  (block ST 2 ) and delivers the high-frequency component to the envelope detector DET 2 . The reason why the high-frequency components of the signals S 1  and S 2  are extracted is that the levels of the high-frequency components included in the signals S 1  and S 2  are scarcely affected by the track error and have such properties as to maintain substantially constant amplitude levels. 
     The envelope detector DET 1  detects an envelope signal of the high-frequency signal which is supplied from the high-pass filter HPF 1  (block ST 3 ). The envelope detector DET 2  detects an envelope signal of the high-frequency signal which is supplied from the high-pass filter HPF 2  (block ST 3 ). The envelope signals S 4  and SS, which are detected by the envelope detectors DET 1  and DET 2 , are supplied to the subtracter C 2 .  FIG. 3D  shows examples of the envelope signals S 4  and S 5  which are detected by the envelope detectors DET 1  and DET 2 . 
     The subtracter C 2  subtracts the envelope signal S 5  from the envelope signal S 4  and generates a high-frequency push-pull signal S 6  (block ST 4 ). For example, in the case where envelope signals S 4  and S 5 , as shown in  FIG. 3D , are obtained by the envelope detectors DET 1  and DET 2 , the high-frequency push-pull signal S 6  has a waveform as shown in  FIG. 3E . As shown in  FIG. 3E , the high-frequency push-pull signal S 6  has a feature which is extracted with respect to the transition region of the output signals S 1  and S 2  from the light-receiving units  13 A and  13 B. The high-frequency push-pull signal S 6 , which is output from the subtracter C 2 , is supplied to the subtracter C 3 . 
     The subtracter C 3  subtracts the high-frequency push-pull signal S 6  from the first track error signal S 3  that is supplied, and compensates the first track error signal S 3  (block ST 5 ). The subtracter C 3  performs an arithmetic operation on the basis of the first track error signal S 3  and the high-frequency push-pull signal S 6 , and outputs the arithmetic result as a second track error signal S 7 . As shown in  FIG. 3F , in the compensated second track error signal S 7 , the offset in the transition region, which occurs in the first track error signal S 3  shown in  FIG. 3C , is compensated. 
     As described above, the second track error signal S 7 , in which the offset is compensated, is supplied to the A/D converter circuit  15  as the TE signal that is output from the RF amplifier  14 . The signal that is output from the A/D converter  15  is supplied to the CPU (Central Processing Unit)  21 , etc. via the bus  20 . 
     The focus/tracking control circuit  16  generates the tracking control signal in accordance with the TE signal that is supplied from the A/D converter  15 , and outputs the tracking control signal to the tracking actuator  8 , thereby driving the objective lens  6 . Thus, a tracking servo, with which the laser beam constantly traces the track formed on the optical disc  2 , is executed. 
     As has been described above, the first track error signal S 3  is compensated by using the high-frequency push-pull signal S 6 . Thereby, even in the case where a servo is executed on a non-recorded track whose neighboring track is a recorded track, or on a recorded track whose neighboring track is a non-recorded track, the occurrence of an offset in the track error signal can be suppressed, and the tracking control can be executed without the track servo stability being deteriorated. 
     Therefore, the present embodiment can provide the optical disc device  1  and tracking control method, which can improve the track servo stability, and can suppress the occurrence of a problem such as track slip. 
     Next, an optical disc apparatus and a track control method according to a second embodiment of the present invention will now be described with reference to the accompanying drawings. In the description below, the same structural parts as in the optical disc apparatus  1  and tracking control method according to the above-described first embodiment are denoted by like reference numerals, and a description thereof is omitted. 
     The description below is directed to the case in which waveforms shown in  FIG. 6A to 6D  are used as examples of waveforms for use in the tracking control, and a track error signal is generated from return light from the optical disc  2  when a laser beam is radiated on a region where a recorded track and a non-recorded track neighbor on the optical disc  2 . 
     The optical disc  2  in the optical disc apparatus  1  according to the present embodiment is formed of an HtoL-type recording material in which the degree of light absorption increases after recording, compared to that before recording. The optical disc apparatus  1  according to the present embodiment includes an adder C 4  to which the first track error signal S 3 , which is output from the subtracter C 1 , and the high-frequency push-pull signal S 6 , which is output from the subtracter C 2 , are supplied. 
     Specifically, the adder C 4  adds the first track error signal S 3  and the high-frequency push-pull signal S 6 , and compensates the first track error signal S 3  by the high-frequency push-pull signal S 6 . The adder C 4  outputs a second track error signal S 7  after compensation. In the other respects, the optical disc apparatus  1  according to the first embodiment is the same as the optical disc apparatus  1  according to the above-described first embodiment. 
     In the tracking control method in the optical disc apparatus  1  according to the present embodiment, if return light from the optical disc  2  is detected by the photodetector  13  (block ST 1 ), output signals S 1 , S 2  (not shown), which are output from the light-receiving units  13 A and  13 B of the photodetector  13 , are supplied to the low-pass filters LPF 1 , LPF 2 . 
     The low-pass filter LPF 1  extracts a low-frequency component of the supplied signal S 2 , and outputs the low-frequency component to the subtracter C 1 . The low-pass filter LPF 2  extracts a low-frequency component of the supplied signal S 1 , and outputs the low-frequency component to the subtracter C 1 . The subtracter C 1  subtracts the signal, which is supplied from the low-pass filter LPF 2 , from the signal that is supplied from the low-pass filter LPF 1 , and outputs a subtraction result as a first track error signal S 3  to the adder C 4 .  FIG. 6A  shows an example of the waveform of the first track error signal S 3  in the present embodiment. 
     On the other hand, the output signals S 1 , S 2  from the light-receiving units  13 A,  13 B are supplied to the high-pass filters HPF 1 , HPF 2 . The high-pass filter HPF 1 , HPF 2  extracts a high-frequency component of the supplied signal S 1 , S 2  (block ST 2 ), and supplies the extracted high-frequency signal to the envelope detector DET 1 , DET 2 . 
     The envelope detectors DET 1  and DET 2  detect envelopes of the supplied high-frequency signals, and supply the detected envelope signals S 4  and S 5  to the subtracter C 2 . As shown in  FIG. 6B , the envelope signals S 4  and S 5  in this embodiment have a phase relationship which is opposite to that in the above-described first embodiment. 
     The subtracter C 2  subtracts the envelope signal S 5  from the envelope signal S 4  that is supplied and generates a high-frequency push-pull signal S 6  (block ST 3 ). The high-frequency push-pull signal S 6  is supplied to the adder C 4 . As shown in  FIG. 6C , for example, the high-frequency push-pull signal S 6  in this embodiment has a feature which is extracted with respect to the transition region of the output signals S 1  and S 2  from the light-receiving units  13 A and  13 B. 
     The adder C 4  compensates the first track error signal S 3  by using the high-frequency push-pull signal S 6 . Specifically, the adder C 4  adds the high-frequency push-pull signal S 6  to the first track error signal S 3 , and outputs a compensated second track error signal S 7 . As shown in  FIG. 6D , in the compensated second track error signal S 7 , the offset in the transition region is compensated. 
     As described above, the second track error signal S 7 , in which the offset is compensated, is supplied to the A/D converter circuit  15  as the TE signal. The signal that is output from the A/D converter  15  is supplied to the CPU (Central Processing Unit)  21 , etc. via the bus  20 . 
     The focus/tracking control circuit  16  generates the tracking control signal in accordance with the TE signal that is supplied from the A/D converter  15 , and outputs the tracking control signal to the tracking actuator  8 , thereby driving the objective lens  6 . Thus, a tracking servo, with which the laser beam constantly traces the track formed on the optical disc  2 , is executed. 
     As has been described above, the first track error signal S 3  is compensated by using the high-frequency push-pull signal S 6 . Thereby, like the above-described optical disc apparatus  1  and tracking control method according to the first embodiment, even in the case where a servo is executed on a non-recorded track whose neighboring track is a recorded track, or on a recorded track whose neighboring track is a non-recorded track, the occurrence of an offset in the track error signal can be suppressed, and the tracking control can be executed without the track servo stability being deteriorated. 
     Therefore, the present embodiment can provide the optical disc device  1  and tracking control method, which can improve the track servo stability, and can suppress the occurrence of a problem such as track slip. 
     The present invention is not limited directly to the above-described embodiments. In practice, the structural elements can be modified and embodied without departing from the spirit of the invention. For example, the optical disc apparatus  1  according to the above-described second embodiment includes the adder C 4 , it may include polarity inversion means, such as an inverter, for inverting the polarity of the output signal from the subtracter C 2 . 
     In the first embodiment, the description is given of the case in which the LtoH type optical disc  2  is used. In the second embodiment, the description is given of the case in which the HtoL type optical disc  2  is used. Alternatively, the LtoH type optical disc  2  and HtoL type optical disc  2  may be used in combination so that the polarity inversion of the high-frequency push-pull signal may be switched by switching means, such as a selector, in accordance with the optical disc that is used. In this case, too, the same advantageous effects can be obtained as in the case of the optical disc apparatus  1  and tracking control method according to the first embodiment and the second embodiment. 
     Various inventions can be made by properly combining the structural elements disclosed in the embodiments. For example, some structural elements may be omitted from all the structural elements disclosed in the embodiments. Furthermore, structural elements in different embodiments may properly be combined. 
     While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 
     The various modules of the systems described herein can be implemented as software applications, hardware and/or software modules, or components on one more computers, such as servers. While the various modules are illustrated separately, they may share some or all of the same underlying logic or code.