Patent Application
20060181973
The present invention relates to the focusing of optical media players, and in particular to differing the focus of an optical media player between dimensions.
Optical media players and recorders, such as current compact disc (CD) and digital video disc (DVD) systems operate generally by directing an optical beam from a source, causing the beam to contact a specific location on an optical medium where data is stored, and receiving the data via the reflection of the beam back to receiving devices. To make this happen, current systems are required, at least, to perform two necessary functions, which are tracking and focusing.
Current focusing involves fine-tuning the manner in which the optical beam impinges upon the optical medium. Current tracking involves placing the beam (and consequently the source of the beam) in a specific location so it will impinge upon the optical medium in the appropriate place. Thus, in a current optical media player and/or recorder, the optical media typically is rotated and an optical beam is continually both focused onto the media and moved (using tracking functionality) to the appropriate place on the media, so that the data can be reflected back to a receiving device and output, for instance to a speaker and/or a television.
Therefore, a current optical media player operates generally as shown in
Currently any phenomenon that caused focus to differ between axial and radial dimensions would force a compromise between two optimum focal planes in the focusing function 200, one for each of the two dimensions. This results in a spot 250 on the medium 260 that is not as small and bright as would be possible if focusing function 200 was performed in a manner that more closely resembled a theoretically optimal focus.
Moreover, when using modern optical devices, such as those described with respect to a co-pending patent application entitled “Low Seek Time Optical Disc Tracking System”, filed on Dec. 22, 2004, and having application Ser. No. 10/905,231, (the disclosure of which is herein incorporated by reference) there is an improvement to the invention when each dimension of focus is independently adjustable, (even if resolved by interdependent means).
The present invention obtains a more optimal focus in at least two dimensions (such as axial and radial dimensions) by setting or keeping a focus in at least a first dimension (such as both axial and radial dimensions) and detecting and adjusting the focus in a second dimension (such as radial dimension) so that it can be brought to the same focal plane as the focus for the at least first dimension (such as both axial and radial dimension). The terms radial dimension and axial dimension are used herein to refer to two dimensions that may or may not pertain to a disc shaped media. Therefore, the at least two dimension names may or may not be arbitrary rather than descriptive. Furthermore, references to two dimensions should be understood to pertain to a certain two dimensions of a tracking and focus system of at least two dimensions rather than only two dimensions.
An actuator lens assembly is used to continually adjust the focus in the radial dimension using a feedback loop. In one embodiment of the present invention, certain photocell(s), such as photocells E and F (normally used for tracking) are compared to certain photocell(s), such as photocells A and B and C and D, in order to derive a Radial Focus Error (RFE) signal, by observing radial spot size.
In the operation of one embodiment of the present invention, focus is adjusted by focus drive (FD) actuators, which move an objective lens of an optical head in a third, “Z” dimension. An additional actuator driven lens called the radial focus lens (RFD lens) is added to the optical head assembly, wherein a beam from a light source proceeds on a path from the objective lens and then through the RFD lens. The RFD lens is more cylindrical in shape (or equivalent) so that the focus of beam is modified primarily in the radial direction, leaving the axial dimension of beam focus either less significantly modified or effectively unmodified as the beam passes through.
A feedback loop is used wherein the reflectivity of certain photocell(s), such as of E and F is considered in conjunction with the reflectivity of certain photocell(s), such as A, B, C, and D in order to detect and adjust the radial spot size. Having more optimally focused in the first dimension, in this case radial, the focus is finished by adjusting in a second (axial) dimension, where the spot size is adjusted in the conventional manner of averaging between the two optimal focal planes. When the measurements and or adjustments in the first and second dimensions are combined, a spot on a medium is improved in shape, quality, and precision by the essentially independent adjustment in each dimension of focus obtained through the resolution of related focus equations or functions thereof, solving for either of or each of the dimensions of focus, or a combination thereof.
In order to facilitate a fuller understanding of the present invention, reference is now made to the appended drawings. These drawings should not be construed as limiting the present invention, but are intended to be exemplary only.
The present invention obtains a more optimal focus in both dimensions by detecting and adjusting the focus in the radial dimension so that it can be brought to the same focal plane as the focus for the axial dimension. An actuator lens assembly is used to continually adjust the focus in the radial dimension using a feedback loop. The term lens, as used herein, should be understood by one skilled in the art to represent an optical functionality comprising one or more optical elements (such as lenses or reflectors for instance), which is capable of adjusting focus.
A feedback loop is used wherein the reflectivity of certain photocell(s), such as of E and F is considered in conjunction with the reflectivity of certain photocell(s), such as A, B, C, and D in order to detect and adjust the radial spot size. Having more optimally focused in the first dimension, in this case radial, the focus is finished by adjusting in a second (axial) dimension, where the spot size is adjusted in the conventional manner of averaging between the two optimal focal planes. When the measurements and or adjustments in the first and second dimensions are combined, a spot on a medium is improved in shape, quality, and precision by the essentially independent adjustment in each dimension of focus obtained through the resolution of related focus equations or functions thereof, solving for either of or each of the dimensions of focus, or a combination thereof.
Currently focus is detected by photocells A through D in a conventional three beam tracking configuration where photocells A+C are compared to photocells B+D to obtain the Focus Error signal (FE) as shown in
The manner in which E and F are compared to photocells A, B, C, and D may vary depending on the embodiment of the present invention. One solution is via an algorithm using the logical AND operation. In such a case (E AND F) are compared to (A AND B AND C AND D). The comparison operation may also vary depending on the embodiment, but one example uses the division operation to finally produce the formula [RFE=(E AND F) DIV (A AND B AND C AND D)], another embodiment of the RFE is expressed as [RFE=(E+F)/(A+B+C+D)].
An embodiment of the present invention that uses the RFE signal is shown in
In operation of this embodiment, focus is adjusted by focus drive (FD) actuators 450 and 451, which move an objective lens 455 in the “Z” dimension 460. The additional actuator driven lens (RFD lens) 425 is added, wherein the beam path proceeds from the objective lens 455 and passes through the RFD lens 425. The RFD lens is adjusted by actuators 471 and 472 in the “Z” dimension as well.
Thus, the focusing operation of this embodiment of the present invention involves a two-step process wherein an additional stage includes an adjustment of RFD lens 425 to modify the beam mostly in the radial dimension. In one embodiment, “FE” is in a feedback loop with “FD” to resolve main focus, while “RFE” is in a feedback loop with “RFD” to resolve radial focus. This requires the use of a monitor circuit that compares the polarity of “RFE” and “RFD” to make sure that radial focus has not gone too far in the wrong direction by introducing a correcting signal to place radial focus once again within the domain where “RFE” and “RFD” are in phase.
A feedback loop is used wherein the reflectivity of certain photocell(s), such as E and F is considered in conjunction with the reflectivity of certain photocell(s), such as A, B, C, and D in order to detect and adjust the radial spot size.
Spot 521 represents the spot that will be reflected back to photocells A, B, C, and D. Spots 520 and 522 represent spots that will be reflected back to photocells E and F respectively. The nature of spots 520-522 determines the nature of the readings in the respective photocells A-F. The more a spot is above upper portion 531 of track 500 or below lower portion 532 of track 500, the weaker the reading will be in its respective photocell, since less light will be properly reflected back and received by the photocell.
Hence, the output voltages 540-545 of photocells A-F change depending on the nature of the spot. As such, there is an inherent relationship between output voltages 544 and 545 from the E and F detectors and output voltages 540-543 from the A, B, C, and D detectors. In this embodiment of the present invention, either the full photocell outputs or processed photocells may be used wherever the output of such photocells is mentioned. Such photocell output processing may include differentiation and/or peak (or peak to peak) detection.
Similarly, if they are slightly offset (as shown), slightly more than half of the luminescence should reflect back to E and F. Thus, the predetermined luminescence from the ideal relationship between A-D and E and F is used to create a RFE signal. The feedback loop continually makes its adjustment based on examining the amplitude of these detectors. In one embodiment, there is a “focus wobble”, a slight modulating, repeating wave (sine for instance) impressed upon the radial focus loop that is recovered through a (optimally high Q bandpass) filter and compared for phase, in order to determine that the radial focus loop is not out of phase. The two loops can be resolved at differing bandwidth. The two loops can be resolved with each loop alternately taking a turn at predominance.
In this embodiment's operation, light source 740 sends beam 741 through reflector 745 and then to the surface of medium 700 by passing through optical elements 750, 755, and optionally 775. Beam 741 is returned via the same path but caused by reflector 745 to be diverted at an essentially 90 degree angle to reach detector array 760, which includes for instance, detectors A, B, C, D, E, and F. The voltages are output by detector array 760 reflecting the amount of light received by array 760 which has a relationship to the beam's focus (convergence upon medium 700) and tracking (the placement of the beam 741). The output voltages of detector array 760 are shown by lines 780-783. Lines 780-783 operate in conjunction with computing block 760, which may be, for instance an analog or digital computer, having associated software and/or hardware to implement mathematical and or logical operations to represent the needed functions to maintain focus and tracking in such a system.
The processed output of the signals input to block 765 is represented by lines 790 and 791 which are coupled to drivers 770 and 771 respectively. Line 790 is associated with focus drive element 750 and line 791 is associated with radial focus drive element 755. The signals along lines 790 and 791 are used to move first and second optical elements 795 and 796 respectively, using actuators associated with those elements. Thus, as a beam 741 continues to pass through the adjusted optical elements 795 and 796 the reflection of the beam from medium 700 changes, which in turn changes the readings at detector array 760, which in turn modifies the output signals along lines 795 and 796 as conditioned by computing block 760. These signals on lines 790 and 791 reach optical elements 795 and 796 and they are adjusted again. This process repeats over time and thus a feedback loop is maintained.
In a certain embodiment, “FE” and “RFE” are both passed through an analog computer circuit at block 760 that resolves a combined solution, which outputs momentary values for both “FD” and “RFD” actuators. “FE” and “RFE” might also both be converted to digital values and passed through a digital algorithm or lookup table that resolves a combined solution, which outputs momentary values for both “FD” and “RFD” coils. Thus, there are various manners in which one skilled in the art can implement computing block 760. Such analog or digital computations (or lookups) may also be directed by other parameters, including but not limited to: the overall beam power (for instance, as recognized by (((A+B+C+D)*X)+((E+F)*Y))), tracking, and the momentary values voltage and/or current present on any or all of the detectors and driven devices, including lasers and actuators.
In another embodiment, computing block 760 includes a combined analog or digital computation (or lookup) that takes in the momentary values on photocells, such as A through F, and performs analog or digital calculations (or their equivalent) that include filters and/or polynomial expressions, whose result is obtained by observing the radial beam focus as associated with radial beam width (through comparing photocell(s), such as E&F to photocell(s) such as A&B&C&D) and observing the main (combined) beam focus as associated with diagonal beam aspect ratio (through comparing photocell(s), such as A&C to photocell(s), such as B&D).
The radial focus lens, whose task is to create a difference in focus between one dimension and another, may be any optical element that focuses more in one dimension than another, including an astigmatic reflector or lens or any two dimensional curve extended in a third dimension. Other optical detectors may be added to take the place of or augment the use of detectors E & F for comparing to detectors A, B, C & D, or to take the place of A, B, C & D for comparing to E & F or other detectors. The beam, alternatively may be split off to impinge upon radial focus detectors whose output is compared to each other or other detectors in order to derive a value for radial focus. Dedicated radial focus detectors may be oriented coaxially (or the equivalent in at least one dimension), such that the beam shall significantly fill the inner detector and only to a less extent fill the outer detector during a significant portion of the focus range. Additional concentric (or equivalent in at least one dimension) radial focus detectors could be used, such that the innermost ones provide fine radial focus error, and the larger outer ones provide gross focus error, for purposes of acquiring focus, as well as maintaining or reacquiring focus during disturbances.
Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of this invention should be determined by the appended claims and their legal equivalents.
