Calibration of lens position in an optical disc drive

Disclosed are various systems, methods, and programs embodied in a computer readable medium for calibration of a lens position in an optical disc drive. In one embodiment, a method is provided that comprises manipulating a lens focus actuator to relocate the lens from a first position to a second position. The lens substantially focuses a laser onto the surface of the optical disc when in the second position. The method also comprises determining a first input setting delta to the lens focus actuator that corresponds to a predefined position offset of the lens. The first input setting delta is determined based upon a second input setting delta corresponding to a distance between the first position and the second position.

BACKGROUND

Focus actuators in optical disc drives are driven to control the position of a lens relative to an optical disc. Accurate positioning of the lens above the surface of an optical disc ensures that digital data and optically visible labeling marks made on the disc are properly produced. Unfortunately, in optical disc drives, the gain of a typical focus actuator may vary as much as plus or minus 90%, and the resulting lens positioning error can prevent the data and labeling marks from being properly recorded.

DETAILED DESCRIPTION

With reference toFIG. 1, shown is an optical disc drive100according to an embodiment of the present invention. The optical disc drive100is in data communication with a host103. In this respect, the host103may be, for example, a computer system, server, or other similar device. For the purposes of the following discussion, first the structural aspects of the optical disc drive100are discussed. Thereafter, the operation of the optical disc drive100is discussed with respect to the focusing of a lens associated with a laser of the optical disc drive100according to the various embodiments of the present invention.

In one embodiment, the optical disc drive100includes a processor circuit106. The processor circuit comprises a processor113and a memory116, both of which are coupled to a local interface119. In this respect, the local interface119may be, for example, a data bus with an accompanying control/address bus as can be appreciated by those with ordinary skill in the art. The optical disc drive100further includes an optical pickup unit123, an actuator126, a spindle129, and a positional sensor133. When in use, an optical disc136is placed on the spindle129as shown. The optical pickup unit123, actuator126, spindle129, and positional sensor133are all operatively or electrically coupled to the processor circuit106. In particular, these components are coupled to the processor circuit106by way of an electrical connection through which electrical signals may be received from or transmitted by the processor circuit106in orchestrating the operation of the optical disc drive100as will be described. In one implementation, the optical pickup unit123, actuator126, spindle129, and the positional sensor133are coupled to the local interface119through appropriate interface circuitry (not shown) as can be appreciated.

The actuator126may comprise, for example, a stepper motor or other such device. The actuator is operatively coupled to the optical pickup unit123, for example, using a screw shaft139. In this respect, the actuator126may be manipulated by the processor circuit106in order to move the optical pickup unit123back and forth along the length of the screw shaft139during the normal operation of the optical disc drive100as will be described. In this respect, the actuator126positions the optical pickup unit123relative to the optical disc136during the normal course of operation of the optical disc drive100. Alternatively, other approaches may be employed to move the optical pickup unit123as desired other than a screw shaft139.

The optical pickup unit123includes a laser140and a sensor143that may be employed to read data from the optical disc136. In this respect, the laser140is controlled to generate laser light146that is directed to the optical disc136. The laser140may operate at any one of a number of frequencies as can be appreciated by those with ordinary skill in the art. At least a portion of the laser light146may reflect off the optical disc136as reflected laser light149. Data structures are embodied in the optical disc136that reflect the laser light146as can be appreciated by those with ordinary skill in the art.

The optical pickup unit123further comprises a lens focus actuator153that controls the focus of a lens156. In this respect, the lens focus actuator153adjusts the position of the lens156in relation to the optical disc136in response to a position signal, value, or other input setting as will be described. The lens focus actuator153is operatively coupled to the processor circuit106that provides the positioning signal or data to the lens focus actuator153.

The sensor143detects reflected laser light149during a read operation and generates a voltage signal that is applied to the processor circuit106. The magnitude of the voltage signal generated by the sensor143is generally proportional to the magnitude of the incident reflected laser light149that falls upon the sensing surface area of the sensor143. Alternatively, a current signal may be generated by the sensor143. The sensor143may be a single sensor or multiple sensors operating cooperatively. Where multiple sensors are employed as the sensor143, the voltage signal may be a sum of all of the voltage signals from each of the multiple sensors. Such a signal may be referred to as a “sum signal”.

The optical pickup unit123may be manipulated to write data to the optical disc136by controlling the laser140in the optical pickup unit123so as to form the data structures in the optical disc136. The writing capabilities of the optical disc drive100may also be employed to write a label on a label surface of the optical disc136. Specifically, in one embodiment the label surface of the optical disc136is chemically treated so as to change an optical property such as darkness, reflectivity, or color upon being irradiated with laser light from the optical pickup unit123. Such treatment includes, for example, a coating of thermo-chromic material that has been screen-printed on the label surface such that this material changes from light to dark color when activated by laser light146from the laser140. The thermo-chromic material may comprise, for example, a mixture of color-forming dye, activator, and infrared antenna contained in a polymer matrix. The infrared antenna absorbs the laser energy and converts it to heat. The heat causes the activator, dye, and the polymer matrix to melt, thereby allowing the activator to interact with the dye. The interaction results in a chemical change to the dye that causes a change in color. The label material may vary slightly from manufacturer to manufacturer or from one disc to another disc, or even from one region on a disc to another region on the same disc. As a consequence, the appearance of the generated label may vary accordingly.

Also, as contemplated herein, the term “label” refers to an entire label or any portion thereof written to the surface of the optical disc136.

The spindle129comprises a motor or other such device that spins the optical disc136. This motor may be, for example, a stepper motor or other type of motor. In this respect, the optical disc136is placed in a seating position relative to the spindle129. Thereafter, the optical disc136may be spun relative to the optical pickup unit123and the positional sensor133. The positional sensor133obtains positional data159from the optical disc136as it rotates on the spindle129. By virtue of the positional data159and the stepper motor control, the precise location of the optical pickup unit123relative to the optical disc136can be tracked during the operation of the optical disc drive100.

The optical disc drive100further comprises a number of components stored in the memory116and executable by the processor113in order to control the operation of the various components of the optical disc drive100. These components comprise, for example, an operating system163and a disc drive controller166. The disc drive controller166is executed by the processor113to control the various operations of the optical disc drive100. In this respect, the disc drive controller166orchestrates the general operation of the optical disc drive100in writing data to and reading data from optical discs136. The disc drive controller166also orchestrates the operation of the optical disc drive100in writing a label on a surface of an optical disc136.

A component of the disc drive controller166is lens focus actuator control169. The disc drive controller166includes other components executed to control the operation of the optical disc drive100as can be appreciated. The lens focus actuator control169is executed as a portion of the disc drive controller166to control a positioning of the lens156to focus the laser140as desired. In one embodiment, the optical pickup unit123is coupled to the local interface119with an interface circuit that includes a register that holds a digital value that controls the positioning of the lens156by the focus actuator153. In one embodiment, the digital value is converted to an analog voltage that drives the focus actuator153and determines the actual displacement of the lens156relative to the optical disc136. In this respect, the value written to the register in such an interface circuit represents a laser focus setting.

In one embodiment, the focus actuator153responds to the voltage signal to displace the lens156from a rest position. The displacement of the lens156may be approximately proportional to the voltage applied to the focus actuator153. Alternatively, the focus actuator153may be controlled in some other manner as can be appreciated.

Where embodied in the form of software or firmware, the disc drive controller166and the lens focus actuator control169may be implemented using any one of a number of programming languages such as, for example, C, C++, Assembly, or other programming languages. The disc drive controller166as may be implemented, for example, in an object oriented design or in some other programming architecture. Where any portion of the disc drive controller166and/or the lens focus actuator control169is represented in a flow chart herein, assuming that the functionality depicted is implemented in an object oriented design, for example, then each block of such flow charts may represent functionality that is implemented in one or more methods that are encapsulated in one or more objects, etc.

The memory116may comprise, for example, random access memory (RAM), such as, for example, static random access memory (SRAM), dynamic random access memory (DRAM), or magnetic random access memory (MRAM) and other such devices. In addition, the memory116may also include, for example, read-only memory (ROM) such as a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), or other like memory device.

In addition, the processor113may represent multiple processors and the memory116may represent multiple memories that operate in parallel. In such a case, the local interface119may be an appropriate network that facilitates communication between any two of the multiple processors, between any processor and any one of the memories, or between any two of the memories etc. The processor113may be of electrical, optical, or molecular construction, or of some other construction as can be appreciated by those with ordinary skill in the art.

The operating system163is executed to control the allocation and usage of hardware resources such as the memory, processing time and peripheral devices in the optical disc drive100. In this manner, the operating system163serves as the foundation on which applications depend as is generally known by those with ordinary skill in the art.

Next, the general operation of the optical disc drive100in writing a label to an optical disc136is described according to an embodiment of the present invention. The disc drive controller166controls the operation of the various components of the optical disc drive100in order to write a label onto the surface of the optical disc136. The disc drive controller166also controls the operation of the various components of the optical disc drive100when writing data to and reading data from the optical disc136.

To the extent that the disc drive controller166orchestrates the operation of the various components of the optical disc drive100in order to write a label onto the surface of the optical disc136, it controls the movement of the optical pickup unit123by manipulating the actuator126to cause the optical pickup unit123to move along the screw shaft139as needed to select a radial position for the laser beam impinging on the optical disc136. In addition, the disc drive controller166controls the rotation of the optical disc136by controlling the speed of the spindle129. Also, the disc drive controller166can control the read and write functions of the optical disc drive100by manipulating the optical pickup unit123to transmit laser light146to the optical disc136. When the optical pickup unit123reads data from the optical disc136, then the reflected laser light149is sensed by the sensor143and a corresponding signal is generated that is applied to the processor circuit106through an appropriate interface circuit.

The disc drive controller166also tracks the angular position of the optical disc136based upon inputs from the positional sensor133. In one embodiment, the positional sensor133senses the passing of positional data159in the form of spokes disposed on the optical disc136near, for example, the center, although the spokes may be located at some other location on the optical disc136. Each time a spoke passes the positional sensor133, the positional sensor133generates a pulse that is received by the disc drive controller166by way of the local interface119. In this respect, each pulse may be viewed as a signal or an interrupt that informs the disc drive controller166of a certain amount of rotation of the optical disc136. To track the actual location of the optical disc136based upon the pulses, the disc drive controller166may include a counter that counts the pulses up to a total number of pulses in a single rotation to determine the actual position of the optical disc136at a given time.

Thus, the angular location of the laser beam146generated by the optical pickup unit123relative to the optical disc136may be determined at any given time by virtue of the positional data tracked by the disc drive controller166based upon the data generated by the positional sensor133. In particular, the location of the optical pickup unit123relative to a predefined position on the optical disc136of each pixel or segment of a label that is to be written to the optical disc136may be calculated based upon the relative positions of each of the spokes159sensed by the positional sensor133. For example, in one embodiment, the disc drive controller166tracks the passing of each of the spokes159as the optical disc136rotates, thereby tracking the angular rotation of the optical disc136.

By virtue of the above-mentioned components, the disc label controller163orchestrates the writing of a label on a writable surface of the optical disc136. In this respect, the label to be written to the circular optical disc136may be embodied in the form of radial data that comprises a number of concentric and adjacent circular tracks, or that comprises a spiral.

For the optimum writing of labels to the optical disc136, it has been discovered that the lens156should not focus the laser light146directly onto the writing surface of the optical disc136, as is the case when writing digital data to the disc136. Rather, label writing is more effective if the lens is positioned at a predefined offset distance from the focal position with respect to the surface of the optical disc136. Specifically, when the lens156is located at the approximate focal position with respect to the surface of the optical disc136, the distance from the center of the lens156to the surface is approximately equal to the focal length of the lens156.

Thus, it may be said that the most desirable position for the lens156in order for the most effective writing of a label is such that the lens156is slightly out of focus with respect to the optical disc136. Given that the optimal positioning of the lens156is when the lens is slightly out of focus with respect to the optical disc136, then it is necessary to adjust the position of the lens156by the predefined offset so that it is optimally placed for writing the label to the optical disc136during the label writing process. The actual offset from the focal position that should be applied may be determined by appropriate experimentation as can be appreciated.

Unfortunately, several factors may prevent an accurate positioning of the lens156. Specifically, the lens focus actuator153has a particular gain that can be determined based on the reflected laser light149that is detected by the respective sensor143or sensors143as described above. This gain may change over time given the change in various relevant physical conditions and manufacturing process variation as can be appreciated. Consequently, recalibration of the position of the lens156by the lens focus actuator153is performed periodically during the writing of a label to the surface of the optical disc136.

In particular, in order to position the lens156, in one embodiment the lens focus actuator153responds to a value placed in an appropriate register or other memory location that dictates the ultimate position of the lens156. In this respect, the value that is placed in such a register or other memory location may vary from a low value to a high value. Such a range may include any number of discrete values such as, for example, from 0 to 255, etc. More or less discrete points may be employed depending on the desired resolution of the focusing of the lens156as can be appreciated. The value placed in the respective register or memory location is defined herein as an “input setting”.

Thus, various input settings may be placed into the respective register to control the positioning of the lens156by the lens focus actuator153. In one embodiment, the input setting is a digital value that is converted into an analog voltage or current by a digital-to-analog converter. The analog voltage or current may be applied to the lens focus actuator153. The lens focus actuator153is configured to respond to the analog value by positioning the lens156. In one embodiment, the lens156is in a rest position when the digital value placed into the respective register is an end value such as, for example, “0” or “255” as mentioned above.

Referring then toFIG. 2, shown is a drawing of a view of the laser140, the lens focus actuator153, the lens156, and the optical disc136to illustrate the positioning of the lens156by the lens focus actuator153according to an embodiment of the present invention. As shown, the lens156may be positioned along an axis that generally parallels the direction of the laser light146toward the optical disc136. In order to focus the laser light146onto the surface of the optical disc136, the lens156is positioned accordingly.

For example, the lens156may be moved from a first position P1to a second position P2. The second position P2may be, for example, a distance between the lens156and the surface of the optical disc136that is equal to the focus distance DFof the lens156. Consequently, at the second position P2the lens156focuses the laser light146onto the surface of the optical disc136.

However, such a position is not optimal for the writing of a label onto the surface of the optical disc136. In particular, it is desirable to position the lens156by the predefined offset O, relative to the second position P2, where the distance of the lens156from the optical disc136at the second position P2is approximately equal to the focus distance DFof the lens156.

Thus, in order to position the lens156, for example, from the first position P1to the second position P2, the input setting applied to the lens focus actuator153that directs the position of the lens156is changed from a first value to a second value. The difference between these two values is defined herein as an “input setting delta” which refers to the change in the input setting itself. Because the gain of the lens focus actuator153may vary over time, the lens156may move a different distance at different times for a given input setting delta.

For example, for a given input setting delta, the lens156may be moved from the first position P1to the second position P2. Assuming that the first position P1is the rest position of the lens156, the ultimate location of the second position P2for the given input setting delta may vary significantly depending on the variation in the gain of the lens focus actuator153. Assuming that the input setting delta remained static while the gain varies over time, if the input setting delta were applied to move the lens156from the first position P1to the second position P2, the second position P2may diverge from the focus distance DF.

Consequently, it is desirable to be able to position of the lens156in a manner such that the variation over time in gain of the lens focus actuator153does not result in a variation of the actual distance that the lens156is moved for a given input setting delta. This is particularly the case, for example, when the lens156is moved by the predefined offset O relative to the second position P2, where the distance of the second position P2from the optical disc136is equal to the focus distance DFof the lens156. This is because the positioning of the lens156at the second position P2may be determined based upon the maximization of the optical feedback from the optical disc136. However, the optical feedback from the optical disc136when the lens156is positioned by the predefined offset O relative to the second position P2may not accurately reflect the positioning of the lens156in a similar manner. Ultimately, the desired offset O is a predefined distance that, once applied relative to the second position P2, the laser light146is directed toward the optical disc136in a manner that results in optimum label writing on the surface.

In order to ensure that the predefined offset O is not affected by the variation in gain of the lens focus actuator153, according to the various embodiments of the present invention, the lens focus actuator153is manipulated to locate the lens156from the first position P1to the second position P2. At the second position P2, the lens156substantially focuses the laser light146of the laser140onto the surface of the optical disc136. In one embodiment, the first position P1may be a rest position of the lens focus actuator153.

In order to position the lens156at the second position P2such that the laser light146is substantially focused onto the surface of the optical disc136, the lens focus actuator control169is configured to locate the second position P2by identifying the position of the lens156in which the amount of reflected laser light149(FIG. 1) is substantially maximized, because the reflected laser light149is maximized when the laser light146is focused on the surface of the optical disc136. Alternatively, astigmatic lenses may be employed to condition the reflected light that is received by the sensor143and provide a focus error signal that indicates whether the lens is in focus or is out of focus by a positive or negative amount. In this manner, the positioning of the lens156at the second position P2is detectable.

When the reflected laser light149detected by the sensor143(FIG. 1) is substantially maximized, the laser light146from the laser140is focused on to the optical disc146. In one embodiment, this process may be performed by impinging the laser light146on a location on the optical disc136that has not been written to previously as to reflect a greater amount of the light since the unwritten background is of a lighter shade than the labeling marks. Various methods or approaches may then be employed to determine the position of the lens156at which the reflected laser light149is maximized as can be appreciated by those with ordinary skill in the art. For example, one may employ an iterative approach by “walking” the lens156through a number of discrete positions until the maximum reflection is detected. Another approach might involve the integration of reflectivity above and below a given position, and then comparing the values, where the maximum reflectivity is reached when the values are substantially equal. Given that such approaches and methods are known by those with ordinary skill in the art, specific approaches employed are not discussed herein in greater detail.

Once the lens156has been moved from the first position P1, such as a rest position to the second position P2such that the laser light146is substantially focused onto the surface of the optical disc136, then the input setting delta that was necessary to move the lens156from the first position P1to the second position P2is known. In addition, other details are known about the positioning of the lens156. For example, the approximate distance between the first position P1and the optical disc136may be known by virtue of design parameters and by experimental measurements taken from a number of optical disc drives100. In this respect, given that the surface of the optical disc136may be slightly warped, the distance may vary. Consequently, in one embodiment an approximate average may be determined from measurements taken at different angular and/or radial positions of the optical disc136.

Alternatively, the first position P1may be other than the rest position of the lens156, if the distance between the first position P1and the surface of the optical disc136may be known or determined empirically or via some other method. For example, the surface of the optical disc136may vary depending upon which side is facing the laser140. In one embodiment, the label side is at the surface of the optical disc136, whereas the reflective surface within which the digital data is recorded is within (i.e. below the surface of) the optical disc136. The positions P1or P2may correspond to a focal distance to the external label surface or the internal data surface of the optical disc136.

Similarly, the focus distance DFof the lens156is known, typically from the design parameters of the optical disc drive100. To the extent that process variation results in variation of the focus distance DF(i.e. the approximate distance from the second position P2to the optical disc136), average values may be determined empirically. The focus distance DF is therefore equal to the distance from the second position P2to the label surface of the optical disc136at which the reflected laser light is a maximum.

Therefore, once the focus distance DFof the lens156and the approximate distance from the first position P1to the surface of the optical disc136are known, the approximate distance between the second position P2and the first position P1may be calculated. Knowing the input setting delta employed to move the lens from the first position P1to the second position P2, the distance or displacement of the lens156based upon the given input setting delta may be determined. In this respect, one may discover the actual gain of the lens focus actuator153.

Thereafter, according to various embodiments of the invention, an input setting delta is determined that corresponds to the predefined offset O of the lens156. To write a label, the lens156is positioned by the predefined offset O relative to the second position P2of the lens156, where the second position P2is the focal position of the optical lens156as described above. The input setting delta that corresponds to the predefined offset O of the lens156is determined based upon the input setting delta that corresponds to the distance between the first and second positions P1and P2. In particular, the input setting delta that corresponds to the offset O of the lens156may be calculated as follows:

It should be noted that variation in the gain of the lens focus actuator153does not adversely affect the result of the calculation described above. Once the input setting delta ΔIP1,P2is known, the actual gain of the lens focus actuator153under the present operating conditions may be calculated. Once the input setting delta ΔIOffsetthat corresponds to the position offset O of the lens156is known, the lens156may be positioned at the predefined position offset with respect to the second position P2, by placing a value in the register associated with the lens focus actuator153that is equal to the value that places the lens156at the second position P2plus the input setting delta associated with the predefined offset O.

By doing so, the lens156may be positioned by the predefined offset O relative to the second position P2in order to write a label onto the surface of the optical disc136. In this respect, in one embodiment, the writing of the label onto the surface of the optical disc136occurs after the lens156is positioned at the offset O with respect to the second position P2.

Referring next toFIG. 3, shown is a flow chart that provides one example of the operation of the lens focus actuator control169according to an embodiment of the present invention. Alternatively, the flow chart ofFIG. 3may be viewed as depicting steps of an example of a method implemented in the optical disc drive100(FIG. 1) to calibrate the position of the lens156for writing a label to the optical disc136(FIG. 1). The functionality of the lens focus actuator control169as depicted by the example flow chart ofFIG. 3may be implemented, for example, in an object oriented design or in some other programming architecture. Assuming the functionality is implemented in an object oriented design, then each block represents functionality that may be implemented in one or more methods that are encapsulated in one or more objects. The lens focus actuator control169may be implemented using any one of a number of programming languages such as, for example, C, C++, or other programming languages.

The lens focus actuator control169determines whether it is to calibrate the position of the lens156according to the various embodiments of the present invention. In one example, the lens focus actuator controller169is configured to execute the calibration of the lens position periodically during the writing of a label to the surface of the optical disc136. Alternatively, the lens focus actuator control169may be configured to execute the calibration of the lens position at predefined track intervals during the writing of the label to the surface of the optical disc136. For example, the lens position may be periodically calibrated between the writing of a predefined number of tracks to the optical disc136. Alternatively, the calibration may occur after the writing of a predefined number of pixels that partially make up the label as written to the surface of the disc136. Also, other approaches may be employed to define when it is appropriate to calibrate the position of the lens156.

The lens focus actuator control169may be programmed to make the determination as to when calibration is to take place, or the functionality that makes such a decision may be executed as some other portion of the disc drive controller166(FIG. 1). Assuming that the position of the lens156is to be calibrated as determined in box203, then in box206, a lens focus actuator control169relocates the lens156by manipulating the lens focus actuator153from a first position P1(FIG. 2) to a second position P2(FIG. 2). In one embodiment, this manipulation is performed by applying the corresponding input setting delta to the focus actuator153. According to various embodiments of the present invention, the second position P2is one in which the lens substantially focuses laser light146(FIG. 1) from the laser140(FIG. 1) onto the surface of the optical disc136. According to another embodiment of the present invention, the first position P1may be the rest position of the lens156. In this respect, the approximate or average distance between the first position P1and the surface of the optical disc136is known or may be determined empirically or via some other method as described above.

In relocating the lens to the second position in which the lens substantially focuses the laser light146onto the optical disc136, the lens focus actuator controller169may execute logic that locates the second position P2of the lens156relative to the optical disc136by adjusting the input setting delta to identify the position of the lens156at which an amount of reflected laser light149(FIG. 1) detected from the optical disc136using the sensors143(FIG. 1) is substantially maximized as described above. The distance between the first position P1and the second position P2is calculated based upon known distances and the focus distance (FIG. 2) of the lens156as described above.

Next in box213, the lens focus actuator control169determines an input setting delta that corresponds to the predefined offset to be applied for writing a label onto the surface of the optical disc136. According to one embodiment of the present invention the input setting delta corresponding to the predefined offset is determined based upon the input setting delta corresponding to the distance between the first and second positions P1and P2. Thereafter, in box216, the lens focus actuator control169positions the lens156at the predefined offset O (FIG. 2) with respect to the second position P2. In order to do so, the lens focus actuator control169adds the input setting delta corresponding to the predefined offset to the input setting that corresponds to the second position P2. Thereafter, in box219, the writing of the label to the surface of the optical disc136is initiated. Then, the lens focus actuator control169ends as shown.

Although the lens focus actuator control169is embodied in software or code executed by general purpose hardware as discussed above, as an alternative the same may also be embodied in dedicated hardware or a combination of software/general purpose hardware and dedicated hardware. If embodied in dedicated hardware, the lens focus actuator control169can be implemented as a circuit or state machine that employs any one of or a combination of a number of technologies. These technologies may include, but are not limited to, discrete logic circuits having logic gates for implementing various logic functions upon an application of one or more data signals, application specific integrated circuits having appropriate logic gates, programmable gate arrays (PGA), field programmable gate arrays (FPGA), or other components, etc. Such technologies are generally well known by those skilled in the art and, consequently, are not described in detail herein.